title: Nitrogen and oxygen abundances in the Local Universe

abstract:
  We present chemical evolution models aimed at reproducing the observed (N/O)
vs. (O/H) abundance pattern of star forming galaxies in the Local Universe. We
derive gas-phase abundances from SDSS spectroscopy and a complementary sample
of low-metallicity dwarf galaxies, making use of a consistent set of abundance
calibrations. This collection of data clearly confirms the existence of a
plateau in the (N/O) ratio at very low metallicity, followed by an increase of
this ratio up to high values as the metallicity increases. This trend can be
interpreted as due to two main sources of nitrogen in galaxies: i) massive
stars, which produce small amounts of pure primary nitrogen and are responsible
for the (N/O) ratio in the low metallicity plateau; ii) low- and
intermediate-mass stars, which produce both secondary and primary nitrogen and
enrich the interstellar medium with a time delay relative to massive stars, and
cause the increase of the (N/O) ratio. We find that the length of the
low-metallicity plateau is almost solely determined by the star formation
efficiency, which regulates the rate of oxygen production by massive stars. We
show that, to reproduce the high observed (N/O) ratios at high (O/H), as well
as the right slope of the (N/O) vs. (O/H) curve, a differential galactic wind -
where oxygen is assumed to be lost more easily than nitrogen - is necessary. No
existing set of stellar yields can reproduce the observed trend without
assuming differential galactic winds. Finally, considering the current best set
of stellar yields, a bottom-heavy initial mass function is favoured to
reproduce the data.


title:
A Remarkably Luminous Galaxy at z=11.1 Measured with Hubble Space
  Telescope Grism Spectroscopy

abstract:
  We present Hubble WFC3/IR slitless grism spectra of a remarkably bright
$z\gtrsim10$ galaxy candidate, GN-z11, identified initially from
CANDELS/GOODS-N imaging data. A significant spectroscopic continuum break is
detected at $\lambda=1.47\pm0.01~\mu$m. The new grism data, combined with the
photometric data, rule out all plausible lower redshift solutions for this
source. The only viable solution is that this continuum break is the Ly$\alpha$
break redshifted to ${z_\mathrm{grism}=11.09^{+0.08}_{-0.12}}$, just $\sim$400
Myr after the Big Bang. This observation extends the current spectroscopic
frontier by 150 Myr to well before the Planck (instantaneous) cosmic
reionization peak at z~8.8, demonstrating that galaxy build-up was well
underway early in the reionization epoch at z>10. GN-z11 is remarkably and
unexpectedly luminous for a galaxy at such an early time: its UV luminosity is
3x larger than L* measured at z~6-8. The Spitzer IRAC detections up to 4.5
$\mu$m of this galaxy are consistent with a stellar mass of
${\sim10^{9}~M_\odot}$. This spectroscopic redshift measurement suggests that
the James Webb Space Telescope (JWST) will be able to similarly and easily
confirm such sources at z>10 and characterize their physical properties through
detailed spectroscopy. Furthermore, WFIRST, with its wide-field near-IR
imaging, would find large numbers of similar galaxies and contribute greatly to
JWST's spectroscopy, if it is launched early enough to overlap with JWST.


title:
The nature of H-alpha star-forming galaxies at z~0.4 in and around Cl
  0939+4713: the environment matters

abstract:
  Cluster star-forming galaxies are found to have an excess of Far-Infrared
emission relative to H-alpha (Ha), when compared to those in the field, which
could be caused by intense AGN activity, dust and/or declining star formation
histories. Here we present spectroscopic observations of Ha emitters in the Cl
0939+4713 (Abell 851) super-cluster at z=0.41, using AF2+WYFFOS on the WHT. We
measure [OII], Hbeta (Hb), [OIII], Ha and [NII] for a sample of 119 Ha emitters
in and around the cluster. We find that 17+-5% of the Ha emitters are AGN,
irrespective of environment. For star-forming galaxies, we obtain Balmer
decrements, metallicities and ionisation parameters with different methods,
individually and by stacking. We find a strong mass-metallicity relation at all
environments, with no significant dependence on environment. The ionisation
parameter declines with increasing stellar mass for low-mass galaxies. Ha
emitters residing in intermediate environments show the highest ionisation
parameters (along with high [OIII]/Ha and high [OIII]/[OII] line ratios,
typically twice as large as in the highest and lowest densities), which decline
with increasing environmental density. Dust extinction (A$_{H\alpha}$)
correlates strongly with stellar mass, but also with environmental density.
Star-forming galaxies in the densest environments are found to be significantly
dustier (A$_{H\alpha}$~1.5-1.6) than those residing in the lowest density
environments (A$_{H\alpha}$~0.6), deviating significantly from what would be
predicted given their stellar masses.


title:
Ultra-diffuse galaxies: the high-spin tail of the abundant dwarf galaxy
  population

abstract:
  Recent observations have revealed the existence of an abundant population of
faint, low surface brightness (SB) galaxies, which appear to be numerous and
ubiquitous in nearby galaxy clusters, including the Virgo, Coma and Fornax
clusters. With median stellar masses of dwarf galaxies, these ultra-diffuse
galaxies (UDGs) have unexpectedly large sizes, corresponding to a mean SB of
$24\lesssim\langle\mu_e\rangle_r\ {\rm mag}^{-1} {\rm arcsec}^2\lesssim27$
within the effective radius. We show that the UDG population represents the
tail of galaxies formed in dwarf-sized haloes with higher-than-average angular
momentum. By adopting the standard model of disk formation -- in which the size
of galaxies is set by the spin of the halo -- we recover both the abundance of
UDGs as a function of the host cluster mass and the distribution of sizes
within the UDG population. According to this model, UDGs are not failed $L_*$
galaxies, but genuine dwarfs, and their low SB is not uniquely connected to the
harsh cluster environment. We therefore expect a correspondingly abundant
population of UDGs in the field, with likely different morphologies and
colours.


title: Did LIGO detect dark matter?

abstract:
  We consider the possibility that the black-hole (BH) binary detected by LIGO
may be a signature of dark matter. Interestingly enough, there remains a window
for masses $20\,M_\odot \lesssim M_{\rm bh} \lesssim 100\, M_\odot$ where
primordial black holes (PBHs) may constitute the dark matter. If two BHs in a
galactic halo pass sufficiently close, they radiate enough energy in
gravitational waves to become gravitationally bound. The bound BHs will rapidly
spiral inward due to emission of gravitational radiation and ultimately merge.
Uncertainties in the rate for such events arise from our imprecise knowledge of
the phase-space structure of galactic halos on the smallest scales. Still,
reasonable estimates span a range that overlaps the $2-53$ Gpc$^{-3}$ yr$^{-1}$
rate estimated from GW150914, thus raising the possibility that LIGO has
detected PBH dark matter. PBH mergers are likely to be distributed spatially
more like dark matter than luminous matter and have no optical nor neutrino
counterparts. They may be distinguished from mergers of BHs from more
traditional astrophysical sources through the observed mass spectrum, their
high ellipticities, or their stochastic gravitational wave background. Next
generation experiments will be invaluable in performing these tests.


title:
A New Method for Wide-Field Near-IR Imaging with the Hubble Space
  Telescope

abstract:
  We present a new technique for wide and shallow observations using the
near-infrared channel of Wide Field Camera 3 (WFC3) on the Hubble Space
Telescope (HST). Wide-field near-IR surveys with HST are generally inefficient,
as guide star acquisitions make it impractical to observe more than one
pointing per orbit. This limitation can be circumvented by guiding with gyros
alone, which is possible as long as the telescope has three functional gyros.
The method presented here allows us to observe mosaics of eight independent
WFC3-IR pointings in a single orbit by utilizing the fact that HST drifts by
only a very small amount in the 25 seconds between non-destructive reads of
unguided exposures. By shifting the reads and treating them as independent
exposures the full resolution of WFC3 can be restored. We use this "drift and
shift" (DASH) method in the Cycle 23 COSMOS-DASH program, which will obtain 456
WFC3 $H_{160}$ pointings in 57 orbits, covering an area of 0.6 degree$^2$ in
the COSMOS field down to $H_{160} = 25$. When completed, the program will more
than triple the area of extra-galactic survey fields covered by near-IR imaging
at HST resolution. We demonstrate the viability of the method with the first
four orbits (32 pointings) of this program. We show that the resolution of the
WFC3 camera is preserved, and that structural parameters of galaxies are
consistent with those measured in guided observations.

categories: astro-ph.GA astro-ph.CO astro-ph.IM astro-ph.SR


title:
On the maximum magnetic field amplification by the magnetorotational
  instability in core-collapse supernovae

abstract:
  Whether the magnetorotational instability (MRI) can amplify initially weak
magnetic fields to dynamically relevant strengths in core collapse supernovae
is still a matter of active scientific debate. Recent numerical studies have
shown that the first phase of MRI growth dominated by channel flows is
terminated by parasitic instabilities of the Kelvin-Helmholtz type that disrupt
MRI channel flows and quench further magnetic field growth. However, it remains
to be prop- erly assessed by what factor the initial magnetic field can be
amplified and how it depends on the initial field strength and the amplitude of
the perturbations. Different termination criteria leading to different
estimates of the amplification factor were proposed within the parasitic model.
To determine the amplification factor and test which criterion is a better
predictor of the MRI termination, we perform three-dimensional shearing-disc
and shearing-box simula- tions of a region close to the surface of a
differentially rotating proto-neutron star in non-ideal MHD with two different
numerical codes. We find that independently of the initial magnetic field
strength, the MRI channel modes can amplify the magnetic field by, at most, a
factor of 100. Under the conditions found in proto-neutron stars a more
realistic value for the mag- netic field amplification is of the order of 10.
This severely limits the role of the MRI channel modes as an agent amplifying
the magnetic field in proto-neutron stars starting from small seed fields. A
further amplification should therefore rely on other physical processes, such
as for example an MRI-driven turbulent dynamo.


title:
The unreasonable weakness of r-process cosmic rays in the
  neutron-star-merger nucleosynthesis scenario

abstract:
  We reach the robust conclusion that, by combining the observed cosmic rays of
r-process elements with the fact that the velocity of the neutron-star-merger
ejecta is much higher than that of the supernova ejecta, either (1) the reverse
shock in the neutron-star-merger ejecta is a very inefficient accelerator that
converts less than 0.003% of the ejecta kinetic energy to the cosmic-ray energy
or (2) the neutron star merger is not the origin of the Galactic r-process
elements. We also find that the acceleration efficiency should be less than
0.1% for the reverse shock of the supernova ejecta with the observed cosmic
rays lighter than the iron.


title:
Sizes, Colour gradients and Resolved Stellar Mass Distributions for the
  Massive Cluster Galaxies in XMMUJ2235-2557 at z = 1.39

abstract:
  We analyse the sizes, colour gradients, and resolved stellar mass
distributions for 36 massive and passive galaxies in the cluster XMMUJ2235-2557
at z=1.39 using optical and near-infrared Hubble Space Telescope imaging. We
derive light-weighted S\'ersic fits in five HST bands
($i_{775},z_{850},Y_{105},J_{125},H_{160}$), and find that the size decreases
by ~20% going from $i_{775}$ to $H_{160}$ band, consistent with recent studies.
We then generate spatially resolved stellar mass maps using an empirical
relationship between $M_{*}/L_{H_{160}}$ and $(z_{850}-H_{160})$ and use these
to derive mass-weighted S\'ersic fits: the mass-weighted sizes are ~41% smaller
than their rest-frame $r$-band counterparts compared with an average of ~12% at
z~0. We attribute this evolution to the evolution in the $M_{*}/L_{H_{160}}$
and colour gradient. Indeed, as expected, the ratio of mass-weighted to
light-weighted size is correlated with the $M_{*}/L$ gradient, but is also
mildly correlated with the mass surface density and mass-weighted size. The
colour gradients $(\nabla_{z-H})$ are mostly negative, with a median value of
$\sim0.45$ mag dex$^{-1}$, twice the local value. The evolution is caused by an
evolution in age gradients along the semi-major axis ($a$), with $\nabla_{age}
= d \log(age) / d \log(a)$ $\sim-0.33$, while the survival of weaker colour
gradients in old, local galaxies implies that metallicity gradients are also
required, with $\nabla_{Z} = d \log(Z) / d \log(a)$ $\sim-0.2$. This is
consistent with recent observational evidence for the inside-out growth of
passive galaxies at high redshift, and favours a gradual mass growth mechanism,
such as minor mergers.


title: Generic model for hyperkagome iridate in the local moment regime

abstract:
  Hyperkagome iridate, Na$_4$Ir$_3$O$_8$, has been regarded as a promising
candidate material for a three-dimensional quantum spin liquid. Here the
three-dimensional network of corner-sharing triangles forms the hyperkagome
lattice of Ir$^{4+}$ ions. Due to strong spin-orbit coupling, the local moments
of Ir$^{4+}$ ions are described by the pseudospin $j_{\rm eff} = 1/2$ Kramers
doublet. The Heisenberg model on this lattice is highly frustrated and
quantum/classical versions have been studied in earlier literature. In this
work, we derive a generic local-moment model beyond the Heisenberg limit for
the hyperkagome iridate by considering multi-orbital interactions for all the
$t_{2g}$ orbitals and spin-orbit coupling. The lifting of massive classical
degeneracy in the Heisenberg model by various spin-anisotropy terms is
investigated at the classical level and the resulting phase diagram is
presented. We find that different anisotropy terms prefer distinct classes of
magnetically ordered phases, often with various discrete degeneracy. The
implications of our results for recent $\mu$SR and NMR experiments on this
material and possible quantum spin liquid phases are discussed.


title:
The G\"ottingen Solar Radial Velocity Project: Sub-m/s Doppler precision
  from FTS observations of the Sun as a star

abstract:
  Radial velocity observations of stars are entering the sub-m/s domain
revealing fundamental barriers for Doppler precision experiments. Observations
of the Sun as a star can easily overcome the m/s photon limit but face other
obstacles. We introduce the G\"ottingen Solar Radial Velocity Project with the
goal to obtain high precision (cm/s) radial velocity measurements of the Sun as
a star with a Fourier Transform Spectrograph. In this first paper, we present
the project and first results. The photon limit of our 2 min observations is at
the 2 cm/s level but currently limited by strong instrumental systematics. A
drift of a few m/s per h is visible in all observing days probably caused by
vignetting of the solar disk in our fiber coupled setup, and imperfections of
our guiding system adds further offsets in our data. Binning the data into 30
min groups shows m/s stability after correcting for a daily and linear
instrumental trend. Our results show the potential of Sun-as-a-star radial
velocity measurements that can possibly be achieved after a substantial upgrade
of our spectrograph coupling strategy. Sun-as-a-star observations can provide
crucial empirical information about the radial velocity signal of convective
motion and stellar activity, and on the wavelength dependence of radial
velocity signals caused by stellar line profile variations.


title: An Ultramassive 1.28 M$_\odot$ White Dwarf in NGC 2099

abstract:
  With the Keck I Low-Resolution Imaging Spectrometer we have observed nine
white dwarf candidates in the very rich open cluster NGC 2099 (M37). The
spectroscopy shows seven to be DA white dwarfs, one to be a DB white dwarf, and
one to be a DZ white dwarf. Three of these DA white dwarfs are consistent with
singly evolved cluster membership: an ultramassive (1.28$^{+0.05}_{-0.08}$
M$_\odot$) and two intermediate-mass (0.70 and 0.75 M$_\odot$) white dwarfs.
Analysis of their cooling ages allows us to calculate their progenitor masses
and establish new constraints on the initial-final mass relation. The
intermediate-mass white dwarfs are in strong agreement with previous work over
this mass regime. The ultramassive white dwarf has $V$ = 24.5, $\sim$2 mag
fainter than the other two remnants. The spectrum of this star has lower
quality, so the derived stellar properties (e.g., T$_{\rm eff}$, log g) have
uncertainties that are several times higher than the brighter counterparts. We
measure these uncertainties and establish the star's final mass as the
highest-mass white dwarf discovered thus far in a cluster, but we are unable to
calculate its progenitor mass because at this high mass and cooler T$_{\rm
eff}$ its inferred cooling age is highly sensitive to its mass. At the highest
temperatures, however, this sensitivity of cooling age to an ultramassive white
dwarf's mass is only moderate. This demonstrates that future investigations of
the upper-mass end of the initial-final mass relation must identify massive,
newly formed white dwarfs (i.e., in young clusters with ages 50-150 Myr).


title:
Super-additivity in communication of classical information through
  quantum channels from a quantum parameter estimation perspective

abstract:
  We point out a contrasting role the entanglement plays in communication and
estimation scenarios. In the first case it brings noticeable benefits at the
measurement stage (output super-additivity), whereas in the latter it is the
entanglement of the input probes that enables significant performance
enhancement (input super-additivity). We identify a weak estimation regime
where a strong connection between concepts crucial to the two fields is
demonstrated; the accessible information and the Holevo quantity on one side
and the quantum Fisher information related quantities on the other. This allows
us to shed new light on the problem of super-additivity in communication using
the concepts of quantum estimation theory.


title:
Multi-band morpho-Spectral Component Analysis Deblending Tool
  (MuSCADeT): Deblending colourful objects

abstract:
  We introduce a new algorithm for colour separation and deblending of
multi-band astronomical images called MuSCADeT which is based on
Morpho-spectral Component Analysis of multi-band images. The MuSCADeT algorithm
takes advantage of the sparsity of astronomical objects in morphological
dictionaries such as wavelets and their differences in spectral energy
distribution (SED) across multi-band observations. This allows us to devise a
model independent and automated approach to separate objects with different
colours. We show with simulations that we are able to separate highly blended
objects and that our algorithm is robust against SED variations of objects
across the field of view. To confront our algorithm with real data, we use HST
images of the strong lensing galaxy cluster MACS J1149+2223 and we show that
MuSCADeT performs better than traditional profile-fitting techniques in
deblending the foreground lensing galaxies from background lensed galaxies.
Although the main driver for our work is the deblending of strong gravitational
lenses, our method is fit to be used for any purpose related to deblending of
objects in astronomical images. An example of such an application is the
separation of the red and blue stellar populations of a spiral galaxy in the
galaxy cluster Abell 2744. We provide a python package along with all
simulations and routines used in this paper to contribute to reproducible
research efforts. Codes can be found at http://lastro.epfl.ch/page-126973.html.


title: CCD UBV photometry of the open cluster NGC 6819

abstract:
  We present the results of CCD UBV observations of the open cluster NGC 6819.
We calculated the stellar density profile in the cluster's field to determine
the structural parameters of NGC 6819. Using the existing astrometric data, we
calculated the probabilities of the stars being physical members of the
cluster, and used these objects in the determination of the astrophysical
parameters of NGC 6819. We inferred the reddening and metallicity of the
cluster as $E(B-V)=0.130\pm0.035$ mag and $[Fe/H]=+0.051\pm 0.020$ dex,
respectively, using the U-B vs B-V two-colour diagram and UV excesses of the
F-G type main-sequence stars. We fit the colour-magnitude diagrams of NGC6819
with the PARSEC isochrones and derived the distance modula, distance and age of
the cluster as $\mu_{V}=12.22\pm 0.10$ mag, $d=2309\pm106$ pc and $t=2.4\pm0.2$
Gyr, respectively. The parameters of the galactic orbit estimated for NGC 6819
indicate that the cluster is orbiting in a slightly eccentric orbit of $e=0.06$
with a period of $P_{orb}=142$ Myr. The slope of the mass function estimated
for the cluster is close to the one found for the stars in the solar
neighbourhood.


title: Super-Eddington growth of the first black holes

abstract:
  The assembly of the first super massive black holes (SMBHs) at $z \gtrsim 6$
is still a subject of intense debate. If black holes (BHs) grow at their
Eddington rate, they must start from $\gtrsim 10^4 \, M_\odot$ seeds formed by
the direct collapse of gas. Here we explore the alternative scenario where
$\sim 100 \, M_\odot$ BH remnants of the first stars grow at super-Eddington
rate via radiatively inefficient slim accretion disks. We use an improved
version of the cosmological, data-constrained semi-analytic model
GAMETE/QSOdust, where we follow the evolution of nuclear BHs and gas cooling,
disk and bulge formation of their host galaxies. Adopting SDSS J1148+5251
(J1148) at $z = 6.4$ as a prototype of luminous $z \gtrsim 6$ quasars, we find
that $\sim$ 80% of its SMBH mass is grown by super-Eddington accretion, which
can be sustained down to $z \sim 10$ in dense, gas-rich environments. The
average BH mass at $z \sim 20$ is $M_{\rm BH} \gtrsim 10^4 \,M_\odot$,
comparable to that of direct collapse BHs. At $z = 6.4$ the AGN-driven mass
outflow rate is consistent with the observations and the BH-to-bulge mass ratio
is compatible with the local scaling relation. However, the stellar mass in the
central 2.5 kpc is closer to the value inferred from CO observations. Finally,
$\sim 20 %$ of J1148 progenitors at $z=7.1$ have BH luminosities and masses
comparable to ULAS J1120+0641, suggesting that this quasar may be one of the
progenitors of J1148.


title: FastPM: a new scheme for fast simulations of dark matter and halos

abstract:
  We introduce FastPM, a highly-scalable approximated particle mesh N-body
solver, which implements the particle mesh (PM) scheme enforcing correct linear
displacement (1LPT) evolution via modified kick and drift factors. Employing a
2-dimensional domain decomposing scheme, FastPM scales extremely well with a
very large number of CPUs. In contrast to COmoving-LAgrangian (COLA) approach,
we do not require to split the force or track separately the 2LPT solution,
reducing the code complexity and memory requirements. We compare FastPM with
different number of steps ($N_s$) and force resolution factor ($B$) against 3
benchmarks: halo mass function from Friends of Friends halo finder, halo and
dark matter power spectrum, and cross correlation coefficient (or
stochasticity), relative to a high resolution TreePM simulation. We show that
the modified time stepping scheme reduces the halo stochasticity when compared
to COLA with the same number of steps and force resolution. While increasing
$N_s$ and $B$ improves the transfer function and cross correlation coefficient,
for many applications FastPM achieves sufficient accuracy at low $N_s$ and $B$.
For example, $N_s=10$ and $B=2$ simulation provides a substantial saving (a
factor of 10) of computing time relative to $N_s=40$, $B=3$ simulation, yet the
halo benchmarks are very similar at $z=0$. We find that for abundance matched
halos the stochasticity remains low even for $N_s=5$. FastPM compares well
against less expensive schemes, being only 7 (4) times more expensive than 2LPT
initial condition generator for $N_s=10$ ($N_s=5$). Some of the applications
where FastPM can be useful are generating a large number of mocks, producing
non-linear statistics where one varies a large number of nuisance or
cosmological parameters, or serving as part of an initial conditions solver.


title: Detection of protonated formaldehyde in the prestellar core L1689B

abstract:
  Complex organic molecules (COMs) are detected in many regions of the
interstellar medium, including prestellar cores. However, their formation
mechanisms in cold (~10 K) cores remain to this date poorly understood. The
formyl radical HCO is an important candidate precursor for several O-bearing
terrestrial COMs in cores, as an abundant building block of many of these
molecules. Several chemical routes have been proposed to account for its
formation, both on grain surfaces, as an incompletely hydrogenated product of H
addition to frozen-out CO molecules, or in the gas phase, either the product of
the reaction between H2CO and a radical, or as a product of dissociative
recombination of protonated formaldehyde H2COH+. The detection and abundance
determination of H2COH+, if present, could provide clues as to whether this
latter scenario might apply. We searched for protonated formaldehyde H2COH+ in
the prestellar core L1689B using the IRAM 30m telescope. The H2COH+ ion is
unambiguously detected, for the first time in a cold (~10 K) source. The
derived abundance agrees with a scenario in which the formation of H2COH+
results from the protonation of formaldehyde. We use this abundance value to
constrain the branching ratio of the dissociative recombination of H2COH+
towards the HCO channel to ~10-30%. This value could however be smaller if HCO
can be efficiently formed from gas-phase neutral-neutral reactions, and we
stress the need for laboratory measurements of the rate constants of these
reactions at 10 K. Given the experimental difficulties in measuring branching
ratios experimentally, observations can bring valuable constraints on these
values, and provide a useful input for chemical networks.


title:
The interplay of the sign problem and the infinite volume limit: gauge
  theories with a theta term

abstract:
  QCD and related gauge theories have a sign problem when a $\theta$-term is
included; this complicates the extraction of physical information from
Euclidean space calculations as one would do in lattice studies. The sign
problem arises in this system because the partition function for configurations
with fixed topological charge $Q$, $\mathcal{Z}_Q$, are summed weighted by
$\exp(i Q \theta)$ to obtain the partition function for fixed $\theta$, $
\mathcal{Z}(\theta)$. The sign problem gets exponentially worse numerically as
the space-time volume is increased. Here it is shown that apart from the
practical numerical issues associated with large volumes, there are some
interesting issues of principle. A key quantity is the energy density as a
function of $\theta$, $\varepsilon(\theta) = -\log \left( \mathcal{Z}(\theta)
\right )/V$. This is expected to be well defined in the large 4-volume limit.
Similarly, one expects the energy density for a fixed topological density
$\tilde{\varepsilon}(Q/V) = -\log \left(\mathcal{Z}_Q \right )/V$ to be well
defined in the limit of large 4-volumes. Intuitively, one might expect that if
one had the infinite volume expression for $\tilde{\varepsilon}(Q/V)$ to
arbitrary accuracy, that one could reconstruct $\varepsilon(\theta)$ by
directly summing over the topological sectors of the partition function. We
show here that there are circumstances where this is not the case. In
particular, this occurs in regions where the curvature of $\varepsilon(\theta)$
is negative.


title: Time-Reversal-Breaking Weyl Fermions in Magnetic Heusler Alloys

abstract:
  Weyl fermions have recently been observed in several time-reversal-invariant
semimetals and photonics materials with broken inversion symmetry. These
systems are expected to have exotic transport properties such as the chiral
anomaly. However, most discovered Weyl materials possess a substantial number
of Weyl nodes close to the Fermi level that give rise to complicated transport
properties. Here we predict, for the first time, a new family of Weyl systems
defined by broken time-reversal symmetry, namely, Co-based magnetic Heusler
materials XCo2Z (X = IVB or VB; Z = IVA or IIIA). To search for Weyl fermions
in the centrosymmetric magnetic systems, we recall an easy and practical
inversion invariant, which has been calculated to be -1, guaranteeing the
existence of an odd number of pairs of Weyl fermions. These materials exhibit,
when alloyed, only two Weyl nodes at the Fermi level - the minimum number
possible in a condensed matter system. The Weyl nodes are protected by the
rotational symmetry along the magnetic axis and separated by a large distance
(of order 2$\pi$) in the Brillouin zone. The corresponding Fermi arcs have been
calculated as well. This discovery provides a realistic and promising platform
for manipulating and studying the magnetic Weyl physics in experiments.


title:
Abundance analysis of SDSS J134338.67+484426.6; an extremely metal-poor
  star from the MARVELS pre-survey

abstract:
  We present an elemental-abundance analysis of an extremely metal-poor (EMP;
[Fe/H] < -3.0) star, SDSS J134338.67+484426.6, identified during the course of
the MARVELS spectroscopic pre-survey of some 20000 stars to identify suitable
candidates for exoplanet searches. This star, with an apparent magnitude V =
12.14, is the lowest metallicity star found in the pre-survey, and is one of
only ~20 known EMP stars that are this bright or brighter. Our high-resolution
spectroscopic analysis shows that this star is a subgiant with [Fe/H] = -3.42,
having "normal" carbon and no enhancement of neutron-capture abundances.
Strontium is under-abundant, [Sr/Fe] =-0.47, but the derived lower limit on
[Sr/Ba] indicates that Sr is likely enhanced relative to Ba. This star belongs
to the sparsely populated class of alpha-poor EMP stars that exhibit low ratios
of [Mg/Fe], [Si/Fe], and [Ca/Fe] compared to typical halo stars at similar
metallicity. The observed variations in radial velocity from several epochs of
(low- and high-resolution) spectroscopic follow-up indicate that SDSS
J134338.67+484426.6 is a possible long-period binary. We also discuss the
abundance trends in EMP stars for r-process elements, and compare with other
magnesium-poor stars.


title:
Shadows cast on the transition disk of HD 135344B. Multiwavelength
  VLT/SPHERE polarimetric differential imaging

abstract:
  The protoplanetary disk around the F-type star HD 135344B (SAO 206462) is in
a transition stage and shows many intriguing structures both in scattered light
and thermal (sub-)millimeter emission which are possibly related to planet
formation processes. We study the morphology and surface brightness of the disk
in scattered light to gain insight into the innermost disk regions, the
formation of protoplanets, planet-disk interactions traced in the surface and
midplane layers, and the dust grain properties of the disk surface. We have
carried out high-contrast polarimetric differential imaging (PDI) observations
with VLT/SPHERE and obtained polarized scattered light images with ZIMPOL in R-
and I-band and with IRDIS in Y- and J-band. The scattered light images reveal
with unprecedented angular resolution and sensitivity the spiral arms as well
as the 25 au cavity of the disk. Multiple shadow features are discovered on the
outer disk with one shadow only being present during the second observation
epoch. A positive surface brightness gradient is observed in the stellar
irradiation corrected images in southwest direction possibly due to an
azimuthally asymmetric perturbation of the temperature and/or surface density
by the passing spiral arms. The disk integrated polarized flux, normalized to
the stellar flux, shows a positive trend towards longer wavelengths which we
attribute to large aggregate dust grains in the disk surface. Part of the the
non-azimuthal polarization signal in the Uphi image of the J-band observation
could be the result of multiple scattering in the disk. The detected shadow
features and their possible variability have the potential to provide insight
into the structure of and processes occurring in the innermost disk regions.


title: Seeking large-scale magnetic fields in a pure-disk dwarf galaxy NGC 2976

abstract:
  It is still unknown how magnetic field-generation mechanisms could operate in
low-mass dwarf galaxies. Here, we present a detailed study of a nearby
pure-disk dwarf galaxy NGC 2976. Unlike previously observed dwarf objects, this
galaxy possesses a clearly defined disk. For the purpose of our studies, we
performed deep multi-frequency polarimetric observations of NGC 2976 with the
VLA and Effelsberg radio telescopes. Additionally, we supplement them with
re-imaged data from the WSRT-SINGS survey. The magnetic field morphology
discovered in NGC 2976 consists of a southern polarized ridge. This structure
does not seem to be due to just a pure large-scale dynamo process (possibly
cosmic-ray driven) at work in this object, as indicated by the RM data and
dynamo number calculations. Instead, the field of NGC 2976 is modified by past
gravitational interactions and possibly also by ram pressure inside the M 81
galaxy group environment. The estimates of total (7 muG) and ordered (3 muG)
magnetic field strengths, as well as degree of field order (0.46), which is
similar to those observed in spirals, suggest that tidally generated magnetized
gas flows can further enhance dynamo action in the object. NGC 2976 is
apparently a good candidate for the efficient magnetization of its
neighbourhood. It is able to provide an ordered (perhaps also regular) magnetic
field into the intergalactic space up to a distance of about 5 kpc. Tidal
interactions (and possibly also ram pressure) can lead to the formation of
unusual magnetic field morphologies (like polarized ridges) in galaxies out of
the star-forming disks, which do not follow any observed component of the
interstellar medium (ISM), as observed in NGC 2976. These galaxies are able to
provide ordered magnetic fields far out of their main disks.


title:
Local phonon mode in thermoelectric Bi2Te2Se from charge neutral
  antisites

abstract:
  Local modes caused by defects play a significant role in the thermal
transport properties of thermoelectrics. Of particular interest are
charge-neutral defects that suppress thermal conductivity, without
significantly reducing electrical transport. Here we report a temperature
dependent Raman study, that identifies such a mode in a standard thermoelectric
material, Bi2Te2Se. One of the modes observed, whose origin has been debated
for decades, was shown mostly likely to be an antisite defect induced local
mode. The anomalous temperature independent broadening of the local mode is
ascribed to the random arrangement of Se atoms. The temperature renormalization
of all modes are well explained by an anharmonic model-Klemens's model.


title: Towards a Global Evolutionary Model of Protoplanetary Disks

abstract:
  A global evolution picture of protoplanetary disks (PPDs) is key to
understanding almost every aspect of planet formation, where standard
alpha-disk models have been constantly employed for its simplicity. In the mean
time, disk mass loss has been conventionally attributed to photoevaporation,
which controls disk dispersal. However, a paradigm shift towards accretion
driven by magnetized disk winds has been realized in the recent years, thanks
to studies of non-ideal magneto-hydrodynamic effects in PPDs. I present a
framework of global PPD evolution aiming to incorporate these advances,
highlighting the role of wind-driven accretion and wind mass loss. Disk
evolution is found to be largely dominated by wind-driven processes, and
viscous spreading is suppressed. The timescale of disk evolution is controlled
primarily by the amount of external magnetic flux threading the disks, and how
rapidly the disk loses the flux. Rapid disk dispersal can be achieved if the
disk is able to hold most of its magnetic flux during the evolution. In
addition, because wind launching requires sufficient level of ionization at
disk surface (mainly via external far-UV radiation), wind kinematics is also
affected by far-UV penetration depth and disk geometry. For typical disk
lifetime of a few Myrs, the disk loses approximately the same amount of mass
through the wind as through accretion onto the protostar, and most of the wind
mass loss proceeds from the outer disk via a slow wind. Fractional wind mass
loss increases with increasing disk lifetime. Significant wind mass loss likely
substantially enhances the dust to gas mass ratio, and promotes planet
formation.


title:
Tuning a Strain-Induced Orbital Selective Mott Transition in Epitaxial
  VO$_2$

abstract:
  We present evidence of strain-induced modulation of electron correlation
effects and increased orbital anisotropy in the rutile phase of epitaxial
VO$_2$/TiO$_2$ films from hard x-ray photoelectron spectroscopy and soft V
L-edge x-ray absorption spectroscopy, respectively. By using the U(1) slave
spin formalism, we further argue that the observed anisotropic correlation
effects can be understood by a model of orbital selective Mott transition at a
filling that is non-integer, but close to the half-filling. Because the
overlaps of wave functions between $d$ orbitals are modified by the strain,
orbitally-dependent renormalizations of the bandwidths and the crystal fields
occur with the application of strain. These renormalizations generally result
in different occupation numbers in different orbitals. We find that if the
system has a non-integer filling number near the half-filling such as for
VO$_2$, certain orbitals could reach an occupation number closer to
half-filling under the strain, resulting in a strong reduction in the
quasiparticle weight $Z_{\alpha}$ of that orbital. Moreover, an orbital
selective Mott transition, defined as the case with $Z_{\alpha} = 0$ in some,
but not all orbitals, could be accessed by epitaxial strain-engineering of
correlated electron systems.


title: Iron-based superconductors: Foreword

abstract:
  We introduce the thematic (open access) issue published in Comptes Rendus
Physique. This issue is focused on the so-called Fe-based superconductors that,
since the discovery of superconductivity in F-doped LaFeAsO by Hosono group in
2008, have become one of the latest hot topics in the field of condensed
matter. The idea is to give an up-to-date overview of the fundamental
properties of this novel family of high-Tc superconductors. First we briefly
recall the scientific context of superconductivity and its relationship to
magnetism in metallic compounds, and then we detail the specific aspects of
Fe-based superconductors addressed in the issue.


title:
Stellar Activity and Exclusion of the Outer Planet in the HD 99492
  System

abstract:
  A historical problem for indirect exoplanet detection has been contending
with the intrinsic variability of the host star. If the variability is
periodic, it can easily mimic various exoplanet signatures, such as radial
velocity variations that originate with the stellar surface rather than the
presence of a planet. Here we present an update for the HD~99492 planetary
system, using new radial velocity and photometric measurements from the Transit
Ephemeris Refinement and Monitoring Survey (TERMS). Our extended time series
and subsequent analyses of the Ca II H\&K emission lines show that the host
star has an activity cycle of $\sim$13 years. The activity cycle correlates
with the purported orbital period of the outer planet, the signature of which
is thus likely due to the host star activity. We further include a revised
Keplerian orbital solution for the remaining planet, along with a new transit
ephemeris. Our transit-search observations were inconclusive.


title:
No evidence for large-scale outflows in the extended ionised halo of
  ULIRG Mrk273

abstract:
  We present deep new GTC/OSIRIS narrow-band images and optical WHT/ISIS
long-slit spectroscopy of the merging system Mrk273 that show a spectacular
extended halo of warm ionised gas out to a radius of $\sim45$ kpc from the
system nucleus. Outside of the immediate nuclear regions (r > 6 kpc), there is
no evidence for kinematic disturbance in the ionised gas: in the extended
regions covered by our spectroscopic slits the emission lines are relatively
narrow (FWHM $\lesssim$ 350 km$\rm s^{-1}$) and velocity shifts small
(|$\Delta$V| $\lesssim{} $250 km$\rm s^{-1}$). This is despite the presence of
powerful near-nuclear outflows (FWHM > 1000 km$\rm s^{-1}$; |$\Delta$V| > 400
km$\rm s^{-1}$; r < 6 kpc). Diagnostic ratio plots are fully consistent with
Seyfert 2 photo-ionisation to the NE of the nuclear region, however to the SW
the plots are more consistent with low-velocity radiative shock models. The
kinematics of the ionised gas, combined with the fact that the main structures
are aligned with low-surface-brightness tidal continuum features, are
consistent with the idea that the ionised halo represents tidal debris left
over from a possible triple-merger event, rather than a reservoir of outflowing
gas.


title: Weakly Supervised Localization using Deep Feature Maps

abstract:
  Object localization is an important computer vision problem with a variety of
applications. The lack of large scale object-level annotations and the relative
abundance of image-level labels makes a compelling case for weak supervision in
the object localization task. Deep Convolutional Neural Networks are a class of
state-of-the-art methods for the related problem of object recognition. In this
paper, we describe a novel object localization algorithm which uses
classification networks trained on only image labels. This weakly supervised
method leverages local spatial and semantic patterns captured in the
convolutional layers of classification networks. We propose an efficient beam
search based approach to detect and localize multiple objects in images. The
proposed method significantly outperforms the state-of-the-art in standard
object localization data-sets with a 8 point increase in mAP scores.


title:
Environment-dependent swimming strategy of Magnetococcus marinus under
  magnetic field

abstract:
  Magnetotactic bacteria (MTB) are fascinating micro-organisms which possess
embodied biomineralized nanomagnets providing them the ability to orient with
the Earth's magnetic field. This property is presumably related to an
evolutionary advantage in finding the oxic-anoxic interface along the up and
down direction in aquatic environments. So far the magnetic field response by
MTB, called magnetotaxis, has been well described by a paramagnetic model where
bacteria orient passively along the field lines according to a purely physical
mechanism where magnetic torque and orientational Brownian noise compete. Here
we demonstrate using Magnetococcus marinus strain MC-1 as MTB model that
magnetotaxis shows more complex behaviors, which are affected by environmental
conditions of different types. Indeed while MC-1 swimmers are found to
essentially obey the paramagnetic paradigm when swimming in their growth
medium, they exhibit a run-and-tumble dynamics in a medium devoid of energy
source. Tumbling events are found to provide isotropic reorientation
capabilities causing the cells to escape from their prescribed field direction.
This behavior has a major influence on the capabilities of the cells to explore
their environment across field lines and represents an alternative search
strategy to the back-and-forth motion along field-imposed tracks. Moreover, we
show that aside chemical conditions, steric/geometrical constraints are also
able to trigger tumbling events through obstacle encountering. Overall,
physico-chemical environmental conditions appear to be important parameters
involved in the swimming properties of MTB. Depending on environmental
conditions, the run-and-tumble mobility may provide advantages in the search
for nutrient or ecological niche, in complement to classical magnetotaxis.


title: Wanted: Floating-Point Add Round-off Error instruction

abstract:
  We propose a new instruction (FPADDRE) that computes the round-off error in
floating-point addition. We explain how this instruction benefits
high-precision arithmetic operations in applications where double precision is
not sufficient. Performance estimates on Intel Haswell, Intel Skylake, and AMD
Steamroller processors, as well as Intel Knights Corner co-processor,
demonstrate that such an instruction would improve the latency of double-double
addition by up to 55% and increase double-double addition throughput by up to
103%, with smaller, but non-negligible benefits for double-double
multiplication. The new instruction delivers up to 2x speedups on three
benchmarks that use high-precision floating-point arithmetic: double-double
matrix-matrix multiplication, compensated dot product, and polynomial
evaluation via the compensated Horner scheme.


title: Unveiling the parent population of beamed narrow-line Seyfert 1s

abstract:
  Narrow-line Seyfert 1 galaxies (NLS1s) are active galactic nuclei (AGN)
recently identified as a new class of $\gamma$-ray sources. The high energy
emission is explained by the presence of a relativistic jet observed at small
angles, just like in the case of blazars. When the latter are observed at
larger angles they appear as radio-galaxies, but an analogue parent population
for beamed NLS1s has not yet been determined. In this work we analyze this
problem by studying the physical properties of three different samples of
parent sources candidates: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s,
and disk-hosted radio-galaxies, along with compact steep-spectrum sources. In
our approach, we first derived black hole mass and Eddington ratio from the
optical spectra, then we investigated the interaction between the jet and the
narrow-line region from the [O III] $\lambda\lambda$4959,5007 lines. Finally,
the radio luminosity function allowed us to compare their jet luminosity and
hence determine the relations between the samples.


title:
Enhanced Bandwidth and Diversity in Real-Time Analog Signal Processing
  (R-ASP) using Nonuniform C-section Phasers

abstract:
  We show that a continuously nonuniform coupled line C-section phaser, as the
limiting case of the step discontinuous coupled-line multisection commensurate
and non-commensurate phasers, provides enhanced bandwidth and diversity in
real-time analog signal processing (R-ASP). The phenomenology of the component
is explained in comparison with the step-discontinuous using
multiple-reflection theory and a simple synthesis procedure is provided. The
bandwidth enhancement results from the suppression of spurious group delay
harmonics or quasi-harmonics, while the diversity enhancement results from the
greater level of freedom provided by the continuous nature of the nonuniform
profile of the phaser. These statements are supported by theoretical and
experimental results.


title:
An averaging principle for fast diffusions in domains separated by
  semi-permeable membranes

abstract:
  We prove an averaging principle which asserts convergence of diffusion
processes on domains separated by semi-permeable membranes, when diffusion
coefficients tend to infinity while the flux through the membranes remains
constant. In the limit, points in each domain are lumped into a single state of
a limit Markov chain. The limit chain's intensities are proportional to the
membranes' permeability and inversely proportional to the domains' sizes.
Analytically, the limit is an example of a singular perturbation in which
boundary and transmission conditions play a crucial role. This averaging
principle is strongly motivated by recent signaling pathways models of
mathematical biology, which are discussed towards the end of the paper.


title:
Young star clusters in the outer disks of LITTLE THINGS dwarf irregular
  galaxies

abstract:
  We examine FUV images of the LITTLE THINGS sample of nearby dwarf irregular
(dIrr) and Blue Compact Dwarf (BCD) galaxies to identify distinct young regions
in their far outer disks. We use these data, obtained with the Galaxy Evolution
Explorer satellite, to determine the furthest radius at which in situ star
formation can currently be identified. The FUV knots are found at distances
from the center of the galaxies of 1 to 8 disk scale lengths and have ages of
<20 Myrs and masses of 20 to 1E5 Msolar. The presence of young clusters and OB
associations in the outer disks of dwarf galaxies shows that dIrrs do have star
formation taking place there in spite of the extreme nature of the environment.
Most regions are found where the HI surface density is ~1 Msolar per pc2,
although both the HI and dispersed old stars go out much further. This limiting
density suggests a cutoff in the ability to form distinct OB associations and
perhaps even stars. We compare the star formation rates in the FUV regions to
the average rates expected at their radii and beyond from the observed gas,
using the conventional correlation for gas-rich regions. The localized rates
are typically 10% of the expected average rates for the outer disks. Either
star formation in dIrrs at surface densities <1 Msolar per pc2 occurs without
forming distinct associations, or the Kennicutt-Schmidt relation over-predicts
the rate beyond this point. In the latter case, the stellar disks in the
far-outer parts of dIrrs result from scattering of stars from the inner disk.


title:
Homogenization of metasurfaces formed by random resonant particles in
  periodical lattices

abstract:
  In this paper we suggest a simple analytical method for description of
electromagnetic properties of a geometrically regular two-dimensional
subwavelength arrays (metasurfaces) formed by particles with randomly
fluctuating polarizabilities. Such metasurfaces are of topical importance due
to development of mass-scale bottom-up fabrication methods, for which
fluctuations of the particles sizes, shapes, and/or composition are inevitable.
Understanding and prediction of electromagnetic properties of such random
metasurfaces is a challenge. We propose an analytical homogenization method
applicable for normal wave incidence on particles arrays with dominating
electric dipole responses and validate it with numerical point-dipole modeling
using the supercell approach. We demonstrate that fluctuations of particles
polarizabilities lead to increased diffuse scattering despite the subwavelength
lattice constant of the array. The proposed method can be readily extended to
oblique incidence and particles with both electric and magnetic dipole
resonances.


title: On the Hausdorff dimension of CAT($\kappa$) surfaces

abstract:
  We prove that a closed surface with a CAT($\kappa$) metric has Hausdorff
dimension = 2, and that there are uniform upper and lower bounds on the
two-dimensional Hausdorff measure of small metric balls. We also discuss a
connection between this uniformity condition and some results on the dynamics
of the geodesic flow for such surfaces. Finally, we give a short proof of
topological entropy rigidity for geodesic flow on certain CAT(-1) manifolds.


title:
Transport of Dirac electrons in a random magnetic field in topological
  heterostructures

abstract:
  We consider the proximity effect between Dirac states at the surface of a
topological insulator and a ferromagnet with easy plane anisotropy, which is
described by the \emph{XY}-model and undergoes a
Berezinskii-Kosterlitz-Thouless (BKT) phase transition. The surface states of
the topological insulator interacting with classical magnetic fluctuations of
the ferromagnet can be mapped onto the problem of Dirac fermions in a random
magnetic field. However, this analogy is only partial in the presence of
electron-hole asymmetry or warping of the Dirac dispersion, which results in
screening of magnetic fluctuations. Scattering at magnetic fluctuations
influences the behavior of the surface resistivity as a function of
temperature. Near the BKT phase transition temperature we find that the
resistivity of surface states scales linearly with temperature and has a clear
maximum which becomes more pronounced as the Fermi energy decreases.
Additionally at low temperatures we find linear resistivity, usually associated
with non-Fermi liquid behavior, however here it appears entirely within the
Fermi liquid picture.


title:
A Computational Method to Calculate the Exact Solution for Acoustic
  Scattering by Fluid Spheroids

abstract:
  The problem of scattering of harmonic plane acoustic waves by fluid spheroids
(prolate and oblate) is addressed from an analytical approach. Mathematically,
it consists in solving the Helmholtz equation in an unbounded domain with
Sommerfeld radiation condition at infinity. The domain where propagation takes
place is characterised by density and sound speed values $\rho_0$ and $c_0$,
respectively, while $\rho_1$ and $c_1$ are the corresponding density and sound
speed values of an immersed object that is responsible of the scattered field.
Since Helmholtz equation is separable in prolate/oblate spheroidal coordinates,
its exact solution for the scattered field can be expressed as an expansion on
prolate/oblate spheroidal functions multiplied by coefficients whose values
depend upon the boundary conditions verified at the medium-immersed fluid
obstacle interface. The general case ($c_0 \neq c_1$) is cumbersome because it
requires to solve successive matrix systems that are ill-conditioned when
$c_1/c_0$ is far from unity. In this paper, a numerical implementation of the
general exact solution that is valid for any range of eccentricity values and
for $c_0 \neq c_1$, is provided. The high level solver code has been written in
the Julia programming language while a software package recently released in
the literature has been used to compute the spheroidal functions. Several limit
cases (Dirichlet and Neumann boundary conditions, spheroid tending to sphere)
have been satisfactorily verified using the implemented code. The corresponding
example scripts can be downloaded from the authors' web (GitHub) site.
Additionally, the new code has been used to extend results reported in the
literature.


title:
BluePyOpt: Leveraging open source software and cloud infrastructure to
  optimise model parameters in neuroscience

abstract:
  At many scales in neuroscience, appropriate mathematical models take the form
of complex dynamical systems. Parametrising such models to conform to the
multitude of available experimental constraints is a global nonlinear
optimisation problem with a complex fitness landscape, requiring numerical
techniques to find suitable approximate solutions. Stochastic optimisation
approaches, such as evolutionary algorithms, have been shown to be effective,
but often the setting up of such optimisations and the choice of a specific
search algorithm and its parameters is non-trivial, requiring domain-specific
expertise. Here we describe BluePyOpt, a Python package targeted at the broad
neuroscience community to simplify this task. BluePyOpt is an extensible
framework for data-driven model parameter optimisation that wraps and
standardises several existing open-source tools. It simplifies the task of
creating and sharing these optimisations, and the associated techniques and
knowledge. This is achieved by abstracting the optimisation and evaluation
tasks into various reusable and flexible discrete elements according to
established best-practices. Further, BluePyOpt provides methods for setting up
both small- and large-scale optimisations on a variety of platforms, ranging
from laptops to Linux clusters and cloud-based compute infrastructures. The
versatility of the BluePyOpt framework is demonstrated by working through three
representative neuroscience specific use cases.


title: Unequal mass binary neutron star mergers and multimessenger signals

abstract:
  We study the merger of binary neutron stars with different mass ratios
adopting three different realistic, microphysical nuclear equations of state,
as well as incorporating neutrino cooling effects. In particular, we
concentrate on the influence of the equation of state on the gravitational wave
signature and also on its role, in combination with neutrino cooling, in
determining the properties of the resulting hypermassive neutron star, of the
neutrinos produced, and of the ejected material. The ejecta we find are
consistent with other recent studies that find that small mass ratios produce
more ejecta than equal mass cases (up to some limit) and this ejecta is more
neutron rich. This trend indicates the importance with future kilonovae
observations of measuring the individual masses of an associated binary neutron
star system, presumably from concurrent gravitational wave observations, in
order to be able to extract information about the nuclear equation of state


title:
Keypoint Density-based Region Proposal for Fine-Grained Object Detection
  and Classification using Regions with Convolutional Neural Network Features

abstract:
  Although recent advances in regional Convolutional Neural Networks (CNNs)
enable them to outperform conventional techniques on standard object detection
and classification tasks, their response time is still slow for real-time
performance. To address this issue, we propose a method for region proposal as
an alternative to selective search, which is used in current state-of-the art
object detection algorithms. We evaluate our Keypoint Density-based Region
Proposal (KDRP) approach and show that it speeds up detection and
classification on fine-grained tasks by 100% versus the existing selective
search region proposal technique without compromising classification accuracy.
KDRP makes the application of CNNs to real-time detection and classification
feasible.


title: Veech groups of infinite genus surfaces

abstract:
  We show that every countable subgroup $G<\rm GL_+(2,\mathbb{R})$ without
contracting elements is the Veech group of a tame translation surface $S$ of
infinite genus, for infinitely many different topological types of $S$.
Moreover, we prove that as long as every end has genus, there are no
restrictions on the topological type of $S$ to realise all possible uncountable
Veech groups.


title: Correlation functions of the integrable spin-s chain

abstract:
  We study the correlation functions of su(2) invariant spin-s chains in the
thermodynamic limit. We derive non-linear integral equations for an auxiliary
correlation function $\omega$ for any spin s and finite temperature T. For the
spin-3/2 chain for arbitrary temperature and zero magnetic field we obtain
algebraic expressions for the reduced density matrix of two-sites. In the zero
temperature limit, the density matrix elements are evaluated analytically and
appear to be given in terms of Riemann's zeta function values of even and odd
arguments.

categories: cond-mat.stat-mech math-ph math.MP nlin.SI


title:
The Grism Lens-Amplified Survey from Space (GLASS). VI. Comparing the
  Mass and Light in MACSJ0416.1-2403 using Frontier Field imaging and GLASS
  spectroscopy

abstract:
  We present a strong and weak gravitational lens model of the galaxy cluster
MACSJ0416.1-2403, constrained using spectroscopy from the Grism Lens-Amplified
Survey from Space (GLASS) and Hubble Frontier Fields (HFF) imaging data. We
search for emission lines in known multiply imaged sources in the GLASS
spectra, obtaining secure spectroscopic redshifts of 31 multiple images
belonging to 16 distinct source galaxies. The GLASS spectra provide the first
spectroscopic measurements for 6 of the source galaxies. The weak lensing
signal is acquired from 884 galaxies in the F606W HFF image. By combining the
weak lensing constraints with 15 multiple image systems with spectroscopic
redshifts and 9 multiple image systems with photometric redshifts, we
reconstruct the gravitational potential of the cluster on an adaptive grid. The
resulting total mass density map is compared with a stellar mass density map
obtained from the deep Spitzer Frontier Fields imaging data to study the
relative distribution of stellar and total mass in the cluster. We find that
the projected stellar mass to total mass ratio, $f_{\star}$, varies
considerably with the stellar surface mass density. The mean projected stellar
mass to total mass ratio is $\langle f_{\star} \rangle= 0.009 \pm 0.003 $
(stat.), but with a systematic error as large as $0.004-0.005$, dominated by
the choice of the IMF. We find agreement with several recent measurements of
$f_{\star}$ in massive cluster environments. The lensing maps of convergence,
shear, and magnification are made available to the broader community in the
standard HFF format.


title:
Asymptotic formulas for determinants of a special class of Toeplitz +
  Hankel matrices

abstract:
  We compute the asymptotics of the determinants of certain $n\times n$
Toeplitz + Hankel matrices $T_n(a)+H_n(b)$ as $n\to\infty$ with symbols of
Fisher-Hartwig type. More specifically we consider the case where $a$ has zeros
and poles and where $b$ is related to $a$ in specific ways. Previous results of
Deift, Its and Krasovsky dealt with the case where $a$ is even. We are
generalizing this in a mild way to certain non-even symbols.


title: Homology and orientation reversing periodic maps on surfaces

abstract:
  In this paper, we give a classification of orientation reversing periodic
maps on closed surfaces which generalizes the theory of Nielsen for the
orientation preserving periodic maps.
  On one hand, we give a group of data for each orientation reversing periodic
map such that two periodic maps with the same data must be conjugate to each
other. On the other hand, we give the criterion to judge when two different
groups of data correspond to the same conjugacy class.
  As an application of the results of this paper, we shall show that a given
orientation reversing periodic map on $\Sigma_g$ with period larger than or
equal to $3g$ must be conjugate to the power of a list of particular types of
periodic maps.


title: The cycline subalgebra of a Kumjian-Pask algebra

abstract:
  Let $\Lambda$ be a row-finite higher-rank graph with no sources. We identify
a maximal commutative subalgebra $\mathcal{M}$ inside the Kumjian-Pask algebra
${\rm KP}_R(\Lambda)$. We also prove a generalized Cuntz-Krieger uniqueness
theorem for Kumjian-Pask algebras which says that a representation of ${\rm
KP}_R(\Lambda)$ is injective if and only if it is injective on $\mathcal{M}$.


title:
A Game-Theoretic Approach for Detection of Overlapping Communities in
  Dynamic Complex Networks

abstract:
  Complex networks tend to display communities which are groups of nodes
cohesively connected among themselves in one group and sparsely connected to
the remainder of the network. Detecting such communities is an important
computational problem, since it provides an insight into the functionality of
networks. Further, investigating community structure in a dynamic network,
where the network is subject to change, is even more challenging. This paper
presents a game-theoretical technique for detecting community structures in
dynamic as well as static complex networks. In our method, each node takes the
role of a player that attempts to gain a higher payoff by joining one or more
communities or switching between them. The goal of the game is to reveal
community structure formed by these players by finding a Nash-equilibrium point
among them. To the best of our knowledge, this is the first game-theoretic
algorithm which is able to extract overlapping communities from either static
or dynamic networks. We present the experimental results illustrating the
effectiveness of the proposed method on both synthetic and real-world networks.


title: On Pl\"ucker Equations Characterizing Grassmann Cones

abstract:
  Polynomial solutions to the KP hierarchy are known to be parametrized by a
cone over an infinite-dimensional Grassmann variety. Using the notion of
Schubert derivation on a Grassmann algebra, we encode the classical Pl\"ucker
equations of Grassmannians of r-dimensional subspaces in a formula whose limit
for $r\rightarrow\infty$ coincides with the KP hierarchy phrased in terms of
vertex operators.


title: The Progenitor of GW 150914

abstract:
  The spectacular detection of gravitational waves (GWs) from GW 150914 and its
reported association with a gamma-ray burst (GRB) offer new insights into the
evolution of massive stars. Here it is shown that no single star of any mass
and credible metallicity is likely to produce the observed GW signal. Stars
with helium cores in the mass range 35 to 133 solar masses encounter the pair
instability and either explode or pulse until the core mass is less than 40
solar masses, smaller than the combined mass of the observed black holes. The
rotation of more massive helium cores is either braked by interaction with a
slowly rotating hydrogen envelope, if one is present, or by mass loss, if one
is not. The very short interval between the GW signal and the observed onset of
the putative GRB in GW 150914 is also too short to have come from a single
star. A more probable model for making the gravitational radiation is the
delayed merger of two black holes made by 70 and 90 solar mass stars in a
binary system. The more massive component was a pulsational-pair instability
supernova before making the first black hole.


title:
More-Realistic Band Gaps from Meta-Generalized Gradient Approximations:
  Only in a Generalized Kohn-Sham Scheme

abstract:
  Unlike the local density approximation (LDA) and the generalized gradient
approximation (GGA), calculations with meta-generalized gradient approximations
(meta-GGA) are usually done according to the generalized Kohn-Sham (gKS)
formalism. The exchange-correlation potential of the gKS equation is
non-multiplicative, which prevents systematic comparison of meta-GGA
bandstructures to those of the LDA and the GGA. We implement the optimized
effective potential (OEP) of the meta-GGA for periodic systems, which allows us
to carry out meta-GGA calculations in the same KS manner as for the LDA and the
GGA. We apply the OEP to several meta-GGAs, including the new SCAN functional
[Phys. Rev. Lett. 115, 036402 (2015)]. We find that the KS gaps and KS band
structures of meta-GGAs are close to those of GGAs. They are smaller than the
more realistic gKS gaps of meta-GGAs, but probably close to the less-realistic
gaps in the band structure of the exact KS potential, as can be seen by
comparing with the gaps of the EXX+RPA OEP potential. The well-known grid
sensitivity of meta-GGAs is much more severe in OEP calculations.


title:
Dynamical Buildup of a Quantized Hall Response from Non-Topological
  States

abstract:
  We consider a two-dimensional system initialized in a topologically trivial
state before its Hamiltonian is ramped through a phase transition into a Chern
insulator regime. This scenario is motivated by current experiments with
ultracold atomic gases aimed at realizing time-dependent dynamics in
topological insulators. Our main findings are twofold. First, considering
coherent dynamics, the non-equilibrium Hall response is found to approach a
topologically quantized time averaged value in the limit of slow but
non-adiabatic parameter ramps, even though the Chern number of the state
remains trivial. Second, adding dephasing, the destruction of quantum coherence
is found to stabilize this Hall response, while the Chern number generically
becomes undefined. We provide a geometric picture of this phenomenology in
terms of the time-dependent Berry curvature.


title: Superconductivity in HfTe5 Induced via Pressures

abstract:
  Recently, ZrTe5 and HfTe5 are theoretically studied to be the most promising
layered topological insulators since they are both interlayer weakly bonded
materials and also with a large bulk gap in the single layer. It paves a new
way for the study of novel topological quantum phenomenon tuned via external
parameters. Here, we report the discovery of superconductivity and properties
evolution in HfTe5 single crystal induced via pressures. Our experiments
indicated that anomaly resistance peak moves to low temperature first before
reverses to high temperature followed by disappearance which is opposite to the
low pressure effect on ZrTe5. HfTe5 became superconductive above ~5.5 GPa up to
at least 35 GPa in the measured range. The highest superconducting transition
temperature (Tc) around 5 K was achieved at 20 GPa. High pressure Raman
revealed that new modes appeared around pressure where superconductivity
occurs. Crystal structure studies shown that the superconductivity is related
to the phase transition from Cmcm structure to monoclinic C2/m structure. The
second phase transition from C2/m to P-1 structure occurs at 12 GPa. The
combination of transport, structure measurement and theoretical calculations
enable a completely phase diagram of HfTe5 at high pressures.


title: The exact form of the Bohm criterion for a collisional plasma

abstract:
  A long-standing debate in the literature about the kinetic form of the Bohm
criterion is resolved for plasmas with single positive ion species when
transport is dominated by charge exchange collisions. The solution of the
Boltzmann equation for the ions gives the exact form free of any divergence and
contains an additional term that is not included in the classical result. This
term includes collisional and geometric effects and leads to a noticeable
correction. Further, the question is addressed whether the space charge
argument at the bottom of the Bohm criterion can actually lead to a meaningful
definition of the transition point between bulk and sheath. The analysis is
supported by a numerical model and experiments, showing excellent agreement
throughout. As a novelty in diagnostics, the theoretical results allow from the
ion velocity distribution function (IVDF), measured at the wall, a
reconstruction of the IVDF and the electric field at any point in the plasma.
This property is used to reconstruct non-intrusively also the ion density, flow
velocity, mean energy and effective temperature and the electron density and
temperature as functions of the spatial coordinate and potential. Finally, the
fluid equation for ion momentum balance is verified.


title:
Secondary Analysis of Teaching Methods in Introductory Physics: a
  50k-Student Study

abstract:
  Physics education researchers have developed many evidence-based
instructional strategies to enhance physics students' conceptual learning.
These strategies have historically been tested using assessments such as the
Force Concept Inventory (FCI) and Force and Motion Conceptual Evaluation
(FMCE). We have performed a review and analysis of FCI and FMCE data published
between 1995 and 2014. We confirm previous findings that interactive engagement
teaching techniques are significantly more likely to produce high student
learning gains than traditional lecture-based instruction. We also establish
that interactive engagement instruction works in many settings, including for
students with a high and low level of prior knowledge, for liberal arts and
research universities, and for small and large class sizes.


title: Ramsey properties of random graphs and Folkman numbers

abstract:
  For two graphs, $G$ and $F$, and an integer $r\ge2$ we write $G\rightarrow
(F)_r$ if every $r$-coloring of the edges of $G$ results in a monochromatic
copy of $F$. In 1995, the first two authors established a threshold edge
probability for the Ramsey property $G(n,p)\to (F)_r$, where $G(n,p)$ is a
random graph obtained by including each edge of the complete graph on $n$
vertices, independently, with probability $p$. The original proof was based on
the regularity lemma of Szemer\'edi and this led to tower-type dependencies
between the involved parameters. Here, for $r=2$, we provide a self-contained
proof of a quantitative version of the Ramsey threshold theorem with only
double exponential dependencies between the constants. As a corollary we obtain
a double exponential upper bound on the 2-color Folkman numbers. By a different
proof technique, a similar result was obtained independently by Conlon and
Gowers.


title:
AFM study of hydrodynamics in boundary layers around micro- and
  nanofibers

abstract:
  The description of hydrodynamic interactions between a particle and the
surrounding liquid, down to the nanometer scale, is of primary importance since
confined liquids are ubiquitous in many natural and technological situations.
In this paper, we combine three non-conventional atomic force microscopes to
study hydrodynamics around micro- and nano-cylinders. These complementary
methods allow the independent measurement of the added mass and friction terms
over a large range of probe sizes, fluid viscosities and solicitation
conditions. A theoretical model based on an analytical description of the
velocity field around the probe shows that the friction force depends on a
unique parameter, the ratio of the probe radius to the thickness of the viscous
boundary layer. We demonstrate that the whole range of experimental data can be
gathered in a master curve which is well reproduced by the model. This
validates the use of these AFM modes for a quantitative study of
nano-hydrodynamics, and opens the way to the investigation of other sources of
dissipation in simple and complex fluids down to the nanometer scale.


title:
Effective Transparency in the XUV: A Pump-Probe Test of Atomistic
  Laser-Cluster Models

abstract:
  The effective transparency of rare-gas clusters, post-interaction with an
extreme ultraviolet (XUV) pump pulse, is predicted by using an atomistic hybrid
quantum-classical molecular dynamics model. We find there is an intensity range
for which an XUV probe pulse has no lasting effect on the average charge state
of a cluster after being saturated by an XUV pump pulse: the cluster is
effectively transparent to the probe pulse. The intensity range for which this
phenomena occurs increases with cluster size, and thus is amenable to
experimental verification. We present predictions for clusters at the peak of
the laser pulse profile, as well as the expected experimental time-of-flight
signal integrated over the laser profile. Since our model uses only atomic
photoionization rates, significant experimental deviations from our predictions
would provide evidence for modified ionization potentials due to plasma
effects.


title: The Yang-Mills flow for cylindrical end 4-manifolds

abstract:
  We establish various existence and uniqueness results for the Yang-Mills flow
on cylindrical end 4-manifolds. We also show long-time existence and
infinite-time convergence under certain hypotheses on the underlying data.


title: An exponential-type upper bound for Folkman numbers

abstract:
  For given integers $k$ and $r$, the Folkman number $f(k;r)$ is the smallest
number of vertices in a graph $G$ which contains no clique on $k+1$ vertices,
yet for every partition of its edges into $r$ parts, some part contains a
clique of order $k$. The existence (finiteness) of Folkman numbers was
established by Folkman (1970) for $r=2$ and by Ne\v{s}et\v{r}il and R\"odl
(1976) for arbitrary $r$, but these proofs led to very weak upper bounds on
$f(k;r)$.
  Recently, Conlon and Gowers and independently the authors obtained a doubly
exponential bound on $f(k;2)$. Here, we establish a further improvement by
showing an upper bound on $f(k;r)$ which is exponential in a polynomial
function of $k$ and $r$. This is comparable to the known lower bound
$2^{\Omega(rk)}$.
  Our proof relies on a recent result of Saxton and Thomason (2015) (or,
alternatively, on a recent result of Balogh, Morris, and Samotij (2015)) from
which we deduce a quantitative version of Ramsey's theorem in random graphs.


title:
Solving Combinatorial Games using Products, Projections and
  Lexicographically Optimal Bases

abstract:
  In order to find Nash-equilibria for two-player zero-sum games where each
player plays combinatorial objects like spanning trees, matchings etc, we
consider two online learning algorithms: the online mirror descent (OMD)
algorithm and the multiplicative weights update (MWU) algorithm. The OMD
algorithm requires the computation of a certain Bregman projection, that has
closed form solutions for simple convex sets like the Euclidean ball or the
simplex. However, for general polyhedra one often needs to exploit the general
machinery of convex optimization. We give a novel primal-style algorithm for
computing Bregman projections on the base polytopes of polymatroids. Next, in
the case of the MWU algorithm, although it scales logarithmically in the number
of pure strategies or experts $N$ in terms of regret, the algorithm takes time
polynomial in $N$; this especially becomes a problem when learning
combinatorial objects. We give a general recipe to simulate the multiplicative
weights update algorithm in time polynomial in their natural dimension. This is
useful whenever there exists a polynomial time generalized counting oracle
(even if approximate) over these objects. Finally, using the combinatorial
structure of symmetric Nash-equilibria (SNE) when both players play bases of
matroids, we show that these can be found with a single projection or convex
minimization (without using online learning).


title:
Spin orientations of the spin-half Ir4+ ions in Sr3NiIrO6, Sr2IrO4 and
  Na2IrO3: Density functional, perturbation theory and Madelung potential
  analyses

abstract:
  The spins of the low-spin Ir4+ (S = 1/2, d5) ions at the octahedral sites of
the oxides Sr3NiIrO6, Sr2IrO4 and Na2IrO3 exhibit preferred orientations with
respect to their IrO6 octahedra. We evaluated the magnetic anisotropies of
these S = 1/2 ions on the basis of DFT calculations including spin-orbit
coupling (SOC), and probed their origin by performing perturbation theory
analyses with SOC as perturbation within the LS coupling scheme. The observed
spin orientations of Sr3NiIrO6 and Sr2IrO4 are correctly predicted by DFT
calculations, and are accounted for by the perturbation theory analysis. As for
the spin orientation of Na2IrO3, both experimental studies and DFT calculations
have not been unequivocal. Our analysis reveals that the Ir4+ spin orientation
of Na2IrO3 should have nonzero components along the c- and a-axes directions.
The spin orientations determined by DFT calculations are sensitive to the
accuracy of the crystal structures employed, which is explained by perturbation
theory analyses when interactions between adjacent Ir4+ ions are taken into
consideration. There are indications implying that the 5d electrons of Na2IrO3
are less strongly localized compared with those of Sr3NiIrO6 and Sr2IrO4. This
implication was confirmed by showing that the Madelung potentials of the Ir4+
ions are less negative in Na2IrO3 than in Sr3NiIrO6, Sr2IrO4. Most
transition-metal S = 1/2 ions do have magnetic anisotropies because the SOC
induces interactions among their crystal-field split d-states, and the
associated mixing of the states modifies only the orbital parts of the states.
This finding cannot be mimicked by a spin Hamiltonian because this model
Hamiltonian lacks the orbital degree of freedom, thereby leading to the
spin-half syndrome. The spin-orbital entanglement for the 5d spin-half ions
Ir4+ is not as strong as has been assumed lately.


title: Suppression of thermal conduction in a mirror-unstable plasma

abstract:
  The ICM plasma is subject to firehose and mirror instabilities at scales of
order the ion Larmor radius. The mirror instability generates fluctuations of
magnetic-field strength $\delta B / B \sim 1$. These fluctuations act as
magnetic traps for the heat-conducting electrons, suppressing their transport.
We calculate the effective parallel thermal conductivity in the ICM in the
presence of the mirror fluctuations for different stages of the evolution of
the instability. The mirror fluctuations are limited in amplitude by the
maximum and minimum values of the field strength, with no large deviations from
the mean value. This key property leads to a finite suppression of thermal
conduction at large scales. We find suppression down to $\approx 0.2$ of the
Spitzer value for the secular phase of the perturbations' growth, and $\approx
0.3$ for their saturated phase. The effect operates in addition to other
suppression mechanisms and independently of them. Globally, fluctuations
$\delta B / B \sim 1$ can be present on much larger scales, of the order of the
scale of turbulent motions. However, we do not expect large suppression of
thermal conduction by these, because their scale is considerably larger than
the collisional mean free path of the ICM electrons. The obtained suppression
of thermal conduction by a factor of $\sim 5$ appears to be characteristic and
potentially universal for a weakly collisional mirror-unstable plasma.


title:
Permutations of the integers induce only the trivial automorphism of the
  Turing degrees

abstract:
  Let $\pi$ be an automorphism of the Turing degrees induces by a homeomorphism
$\varphi$ of the Cantor space $2^\omega$ such that $\varphi$ preserves all
Bernoulli measures. It is proved that $\pi$ must be trivial. In particular, a
permutation of $\omega$ can only induce the trivial automorphism of the Turing
degrees.


title: From cusps to cores: a stochastic model

abstract:
  The cold dark matter model of structure formation faces apparent problems on
galactic scales. Several threads point to excessive halo concentration,
including central densities that rise too steeply with decreasing radius. Yet,
random fluctuations in the gaseous component can 'heat' the centres of haloes,
decreasing their densities. We present a theoretical model deriving this effect
from first principles: stochastic variations in the gas density are converted
into potential fluctuations that act on the dark matter; the associated force
correlation function is calculated and the corresponding stochastic equation
solved. Assuming a power law spectrum of fluctuations with maximal and minimal
cutoff scales, we derive the velocity dispersion imparted to the halo particles
and the relevant relaxation time. We further perform numerical simulations,
with fluctuations realised as a Gaussian random field, which confirm the
formation of a core within a timescale comparable to that derived analytically.
Non-radial collective modes enhance the energy transport process that erases
the cusp, though the parametrisations of the analytical model persist.
  In our model, the dominant contribution to the dynamical coupling driving the
cusp-core transformation comes from the largest scale fluctuations. Yet, the
efficiency of the transformation is independent of the value of the largest
scale and depends weakly (linearly) on the power law exponent; it effectively
depends on two parameters: the gas mass fraction and the normalisation of the
power spectrum. This suggests that cusp-core transformations observed in
hydrodynamic simulations of galaxy formation may be understood and parametrised
in simple terms, the physical and numerical complexities of the various
implementations notwithstanding.


title: Affine multiple yield curve models

abstract:
  We provide a general and tractable framework under which all multiple yield
curve modeling approaches based on affine processes, be it short rate, Libor
market, or HJM modeling, can be consolidated. We model a numeraire process and
multiplicative spreads between Libor rates and simply compounded OIS rates as
functions of an underlying affine process. Besides allowing for ordered spreads
and an exact fit to the initially observed term structures, this general
framework leads to tractable valuation formulas for caplets and swaptions and
embeds all existing multi-curve affine models. The proposed approach also gives
rise to new developments, such as a short rate type model driven by a Wishart
process, for which we derive a closed-form pricing formula for caplets. The
empirical performance of two specifications of our framework is illustrated by
calibration to market data.


title:
Major Substructure in the M31 Outer Halo: Distances and Metallicities
  along the Giant Stellar Stream

abstract:
  We present a renewed look at M31's Giant Stellar Stream along with the nearby
structures Stream C and Stream D, exploiting a new algorithm capable of fitting
to the red giant branch (RGB) of a structure in both colour and magnitude
space. Using this algorithm, we are able to generate probability distributions
in distance, metallicity and RGB width for a series of subfields spanning these
structures. Specifically, we confirm a distance gradient of approximately 20
kpc per degree along a 6 degree extension of the Giant Stellar Stream, with the
farthest subfields from M31 lying ~ 120 kpc more distant than the inner-most
subfields. Further, we find a metallicity that steadily increases from
-0.7^{+0.1}_{-0.1} dex to -0.2^{+0.2}_{-0.1} dex along the inner half of the
stream before steadily dropping to a value of -1.0^{+0.2}_{-0.2} dex at the
farthest reaches of our coverage. The RGB width is found to increase rapidly
from 0.4^{+0.1}_{-0.1} dex to 1.1^{+0.2}_{-0.1} dex in the inner portion of the
stream before plateauing and decreasing marginally in the outer subfields of
the stream. In addition, we estimate Stream C to lie at a distance between 794
and 862 kpc and Stream D between 758 kpc and 868 kpc. We estimate the median
metallicity of Stream C to lie in the range -0.7 to -1.6 dex and a metallicity
of -1.1^{+0.3}_{-0.2} dex for Stream D. RGB widths for the two structures are
estimated to lie in the range 0.4 to 1.2 dex and 0.3 to 0.7 dex respectively.
In total, measurements are obtained for 19 subfields along the Giant Stellar
Stream, 4 along Stream C, 5 along Stream D and 3 general M31 spheroid fields
for comparison. We thus provide a higher resolution coverage of the structures
in these parameters than has previously been available in the literature.


title: Open Heavy Flavor in QCD Matter and in Nuclear Collisions

abstract:
  We review the experimental and theoretical status of open heavy-flavor (HF)
production in high-energy nuclear collisions at RHIC and LHC. We first overview
the theoretical concepts and pertinent calculations of HF transport in QCD
matter, including perturbative and non-perturbative approaches in the
quark-gluon plasma, effective models in hadronic matter, as well as
implementations of heavy-quark (HQ) hadronization. This is followed by a brief
discussion of bulk evolution models for heavy-ion collisions and initial
conditions for the HQ distributions which are needed to calculate HF spectra in
comparison to observables. We then turn to a discussion of experimental data
that have been collected to date at RHIC and LHC, specifically for the nuclear
suppression factor and elliptic flow of semileptonic HF decays, D mesons,
non-prompt $J/\psi$ from B-meson decays, and b-jets. Model comparisons to HF
data are conducted with regards to extracting the magnitude, temperature and
momentum-dependence of HF transport coefficients from experiment.


title: Maximal Hypersurfaces in Spacetimes with Translational Symmetry

abstract:
  We consider four-dimensional vacuum spacetimes which admit a nonvanishing
spacelike Killing field. The quotient with respect to the Killing action is a
three-dimensional quotient spacetime $(M,g)$. We establish several results
regarding maximal hypersurfaces (spacelike hypersurfaces of zero mean
curvature) in such quotient spacetimes. First, we show that a complete
noncompact maximal hypersurface must either be a cylinder $S^1 \times
\mathbb{R}$ with flat metric or else conformal to the Euclidean plane
$\mathbb{R}^2$. Second, we establish positivity of mass for certain maximal
hypersurfaces, referring to a analogue of ADM mass adapted for the quotient
setting. Finally, while lapse functions corresponding to the maximal
hypersurface gauge are necessarily bounded in the four-dimensional
asymptotically Euclidean setting, we show that nontrivial quotient spacetimes
admit the maximal hypersurface gauge only with unbounded lapse.


title: LOFS: Library of Online Streaming Feature Selection

abstract:
  As an emerging research direction, online streaming feature selection deals
with sequentially added dimensions in a feature space while the number of data
instances is fixed. Online streaming feature selection provides a new,
complementary algorithmic methodology to enrich online feature selection,
especially targets to high dimensionality in big data analytics. This paper
introduces the first comprehensive open-source library for use in MATLAB that
implements the state-of-the-art algorithms of online streaming feature
selection. The library is designed to facilitate the development of new
algorithms in this exciting research direction and make comparisons between the
new methods and existing ones available.


title: Jimbo: A Collaborative IDE with Live Preview

abstract:
  Team collaboration plays a key role in the success of any multi-user
activity. Software engineering is a highly collaborative activity, where
multiple developers and designers work together to solve a common problem.
Meaningful and effective designer-developer collaboration improves the user
experience, which can improve the chances of success for the project. Learning
to program is another activity that can be implemented in a more collaborative
way, students can learn in an active style by working with others. The growth
of online classes, from small structured seminars to massive open online
courses (MOOCs), and the isolation and impoverished learning experience some
students report in these, points to an urgent need for tools that support
remote pair programming in a distributed educational setting. In this paper, we
describe Jimbo, a collaborative integrated development environment (IDE) that
we believe is beneficial and effective in both aforementioned activities. Jimbo
integrates many features that support better collaboration and communication
between designers and developers, to bridge communication gaps and develop
mutual understanding. These novel features can improve today's CS education by
bringing students closer to each other and their instructors as well as
training them to collaborate which is consistent with current practices in
software engineering.


title:
Efficient recycling strategies for preparing large Fock states from
  single-photon sources --- Applications to quantum metrology

abstract:
  Fock states are a fundamental resource for many quantum technologies such as
quantum metrology. While much progress has been made in single-photon source
technologies, preparing Fock states with large photon number remains
challenging. We present and analyze a bootstrapped approach for
non-deterministically preparing large photon-number Fock states by iteratively
fusing smaller Fock states on a beamsplitter. We show that by employing state
recycling we are able to exponentially improve the preparation rate over
conventional schemes, allowing the efficient preparation of large Fock states.
The scheme requires single-photon sources, beamsplitters, number-resolved
photo-detectors, fast-feedforward, and an optical quantum memory.


title:
Modular periodicity of exponential sums of symmetric Boolean functions
  and some of its consequences

abstract:
  This work brings techniques from the theory of recurrent integer sequences to
the problem of balancedness of symmetric Boolean functions. In particular, the
periodicity modulo $p$ ($p$ odd prime) of exponential sums of symmetric Boolean
functions is considered. Periods modulo $p$, bounds for periods and relations
between them are obtained for these exponential sums. The concept of avoiding
primes is also introduced. This concept and the bounds presented in this work
are used to show that some classes of symmetric Boolean functions are not
balanced. In particular, every elementary symmetric Boolean function of degree
not a power of 2 and less than 2048 is not balanced. For instance, the
elementary symmetric Boolean function in $n$ variables of degree $1292$ is not
balanced because the prime $p = 176129$ does not divide its exponential sum for
any positive integer $n$. It is showed that for some symmetric Boolean
functions, the set of primes avoided by the sequence of exponential sums
contains a subset that has positive density within the set of primes. Finally,
in the last section, a brief study for the set of primes that divide some term
of the sequence of exponential sums is presented.


title: Maxwell boundary conditions imply non-Lindblad master equation

abstract:
  From the Hamiltonian connecting the inside and outside of an Fabry-Perot
cavity, which is derived from the Maxwell boundary conditions at a mirror of
the cavity, a master equation of a non-Lindblad form is derived when the cavity
embeds matters, although we can transform it to the Lindblad form by performing
the rotating-wave approximation to the connecting Hamiltonian. We calculate
absorption spectra by these Lindblad and non-Lindblad master equations and also
by the Maxwell boundary conditions in the framework of the classical
electrodynamics, which we consider the most reliable approach. We found that,
compared to the Lindblad master equation, the absorption spectra by the
non-Lindblad one agree better with those by the Maxwell boundary conditions.
Although the discrepancy is highlighted only in the ultra-strong light-matter
interaction regime with a relatively large broadening, the master equation of
the non-Lindblad form is preferable rather than of the Lindblad one for
pursuing the consistency with the classical electrodynamics.


title:
Proceedings of the Eleventh International Workshop on Developments in
  Computational Models

abstract:
  This volume contains the proceedings of DCM 2015, the 11th International
Workshop on Developments in Computational Models held on October 28, 2015 in
Cali, Colombia. DCM 2015 was organized as a one-day satellite event of the 12th
International Colloquium on Theoretical Aspects of Computing (ICTAC 2015).
  Several new models of computation have emerged in the last few years, and
many developments of traditional computational models have been proposed with
the aim of taking into account the new demands of computer systems users and
the new capabilities of computation engines. A new computational model, or a
new feature in a traditional one, usually is reflected in a new family of
programming languages, and new paradigms of software development.
  The aim of the DCM workshop series is to bring together researchers who are
currently developing new computational models or new features for traditional
computational models, in order to foster their interaction, to provide a forum
for presenting new ideas and work in progress, and to enable newcomers to learn
about current activities in this area. Topics of interest include all abstract
models of computation and their applications to the development of programming
languages and systems.


title:
The Synthesis, Structure and Electronic Properties of a Lead-Free Hybrid
  Inorganic-Organic Double Perovskite (MA)2KBiCl6 (MA = methylammonium)

abstract:
  In a search for Lead-free materials that could be used as alternatives to the
hybrid perovskites,(MA)PbX3, in photovoltaic applications, we have discovered a
hybrid double perovskite, (MA)2KBiCl6, which shows striking similarities to the
lead analogues. Spectroscopic measurements and nanoindentation studies are
combined with density functional calculations to reveal the properties of this
interesting system.


title:
Numerical tests of the gauge/gravity duality conjecture for D0-branes at
  finite temperature and finite N

abstract:
  According to the gauge/gravity duality conjecture, the thermodynamics of
gauge theory describing D-branes corresponds to that of black branes in
superstring theory. We test this conjecture directly in the case of D0-branes
by applying Monte Carlo methods to the corresponding gauge theory, which takes
the form of the BFSS matrix quantum mechanics. In particular, we take the
continuum limit by extrapolating the UV cutoff to infinity. First we perform
simulations at large N so that string loop corrections can be neglected on the
gravity side. Our results for the internal energy exhibit the temperature
dependence consistent with the prediction including the \alpha ' corrections.
Next we perform simulations at small N but at lower temperature so that the
\alpha ' corrections can be neglected on the gravity side. Our results are
consistent with the prediction including the leading string loop correction,
which suggests that the conjecture holds even at finite N.


title:
Orographic Effects on Supercell: Development and Structure, Intensity
  and Tracking

abstract:
  Terrain effects on thunderstorms, which are conducive to tornado formation,
are investigated.


title: A gradient flow approach to the Boltzmann equation

abstract:
  We show that the spatially homogeneous Boltzmann equation evolves as the
gradient flow of the entropy with respect to a suitable geometry on the space
of probability measures which takes the collision process into account. This
gradient flow structure allows to give a new proof for the convergence of Kac's
random walk to the homogeneous Boltzmann equation, exploiting the stability of
gradient flows.


title:
Surprises from the resummation of ladders in the ABJ(M) cusp anomalous
  dimension

abstract:
  We study the cusp anomalous dimension in N=6 ABJ(M) theory, identifying a
scaling limit in which the ladder diagrams dominate. The resummation is encoded
into a Bethe-Salpeter equation that is mapped to a Schroedinger problem,
exactly solvable due to the surprising supersymmetry of the effective
Hamiltonian. In the ABJ case the solution implies the diagonalization of the
U(N) and U(M) building blocks, suggesting the existence of two independent cusp
anomalous dimensions and an unexpected exponentiation structure for the related
Wilson loops. While consistent with previous perturbative analysis, the strong
coupling limit of our result does not agree with the string theory computation,
emphasizing a difference with the analogous resummation in the N=4 case.