title:
Simultaneous Modeling of the Stellar and Dust Emission in Distant
  Galaxies: Implications for Star Formation Rate Measurements

abstract:
  We have used near-ultraviolet (NUV) to mid-infrared (MIR) composite spectral
energy distributions (SEDs) to simultaneously model the attenuated stellar and
dust emission of 0.5 < z < 2.0 galaxies. These composite SEDs were previously
constructed from the photometric catalogs of the NEWFIRM Medium-Band Survey, by
stacking the observed photometry of galaxies that have similar rest-frame
NUV-to-NIR SEDs. In this work, we include a stacked MIPS 24 micron measurement
for each SED type to extend the SEDs to rest-frame MIR wavelengths. Consistent
with previous studies, the observed MIR emission for most SED types is higher
than expected from only the attenuated stellar emission. We fit the NUV-to-MIR
composite SEDs by the Flexible Stellar Population Synthesis (SPS) models, which
include both stellar and dust emission. We compare the best-fit star formation
rates (SFRs) to the SFRs based on simple UV+IR estimators. Interestingly, the
UV and IR luminosities overestimate SFRs - compared to the model SFRs - by more
than ~ 1 dex for quiescent galaxies, while for the highest star-forming
galaxies in our sample the two SFRs are broadly consistent. The difference in
specific SFRs also shows a gradually increasing trend with declining specific
SFR, implying that quiescent galaxies have even lower specific SFRs than
previously found. Contributions from evolved stellar populations to both the UV
and the MIR SEDs most likely explain the discrepancy. Based on this work, we
conclude that SFRs should be determined from modeling the attenuated stellar
and dust emission simultaneously, instead of employing simple UV+IR-based SFR
estimators.


title: Ultra Low Surface Brightness Imaging with the Dragonfly Telephoto Array

abstract:
  We describe the Dragonfly Telephoto Array, a robotic imaging system optimized
for the detection of extended ultra low surface brightness structures. The
array consists of eight Canon 400mm f/2.8 telephoto lenses coupled to eight
science-grade commercial CCD cameras. The lenses are mounted on a common
framework and are co-aligned to image simultaneously the same position on the
sky. The system provides an imaging capability equivalent to a 0.4m aperture
f/1.0 refractor with a 2.6 deg X 1.9 deg field of view. The system has no
obstructions in the light path, optimized baffling, and internal optical
surfaces coated with a new generation of anti-reflection coatings based on
sub-wavelength nanostructures. As a result, the array's point spread function
has a factor of ~10 less scattered light at large radii than well-baffled
reflecting telescopes. The Dragonfly Telephoto Array is capable of imaging
extended structures to surface brightness levels below 30 mag/arcsec^2 in 10h
integrations (without binning or foreground star removal). This is considerably
deeper than the surface brightness limit of any existing wide-field telescope.
At present no systematic errors limiting the usefulness of much longer
integration times has been identified. With longer integrations (50-100h),
foreground star removal and modest binning the Dragonfly Telephoto Array is
capable of probing structures with surface brightnesses below 32 mag/arcsec^2.
Detection of structures at these surface brightness levels may hold the key to
solving the "missing substructure" and "missing satellite" problems of
conventional hierarchical galaxy formation models. The Dragonfly Telephoto
Array is therefore executing a fully-automated multi-year imaging survey of a
complete sample of nearby galaxies in order to undertake the first census of
ultra-faint substructures in the nearby Universe.

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


title:
The Wolf-Rayet stars in the Large Magellanic Cloud: A comprehensive
  analysis of the WN class

abstract:
  Aims: Following our comprehensive studies of the WR stars in the Milky Way,
we now present spectroscopic analyses of almost all known WN stars in the LMC.
Methods: For the quantitative analysis of the wind-dominated emission-line
spectra, we employ the Potsdam Wolf-Rayet (PoWR) model atmosphere code. By
fitting synthetic spectra to the observed spectral energy distribution and the
available spectra (ultraviolet and optical), we obtain the physical properties
of 107 stars. Results: We present the fundamental stellar and wind parameters
for an almost complete sample of WN stars in the LMC. Among those stars that
are putatively single, two different groups can be clearly distinguished. While
12% of our sample are more luminous than 10^6 Lsun and contain a significant
amount of hydrogen, 88% of the WN stars, with little or no hydrogen, populate
the luminosity range between log (L/Lsun) = 5.3...5.8. Conclusions: While the
few extremely luminous stars (log (L/Lsun) > 6), if indeed single stars,
descended directly from the main sequence at very high initial masses, the bulk
of WN stars have gone through the red-supergiant phase. According to their
luminosities in the range of log (L/Lsun) = 5.3...5.8, these stars originate
from initial masses between 20 and 40 Msun. This mass range is similar to the
one found in the Galaxy, i.e. the expected metallicity dependence of the
evolution is not seen. Current stellar evolution tracks, even when accounting
for rotationally induced mixing, still partly fail to reproduce the observed
ranges of luminosities and initial masses. Moreover, stellar radii are
generally larger and effective temperatures correspondingly lower than
predicted from stellar evolution models, probably due to subphotospheric
inflation.


title: A mechanism for hysteresis in black hole binary state transitions

abstract:
  We suggest that the hysteretic cycle of black hole state transitions arises
from two established properties of accretion disks: the increase in turbulent
stress in disks threaded by a net magnetic field and the ability of thick (but
not thin) disks to advect such a field radially. During quiescence, magnetic
field loops are generated by the magnetorotational instability at the interface
between the inner hot flow and outer thin disk. Vertical flux is advected into
and accumulates stochastically within the inner flow, where it stimulates the
turbulence so that $\alpha \sim 1$. The transition to a geometrically thin
inner disk occurs when $L \sim \alpha^2 L_{\rm Edd} \sim L_{\rm Edd}$, and the
first "thin" disk to form is itself moderately thick, strongly magnetized, and
able to advect field inward. These properties favor episodic jet production. As
the accretion rate declines magnetic flux escapes, $\alpha$ decreases to
$\alpha \sim 0.01 - 0.1$, and a hot inner flow is not re-established until $L
\ll L_{\rm Edd}$. We discuss possible observational consequences of our
scenario.


title: Variable Stars in the Globular Cluster NGC 288: [Fe/H] and Distance

abstract:
  A search for variable stars in the globular cluster NGC 288 was carried out
using a time-series of CCD images in the $V$ and $I$ filters. The photometry of
all stellar sources in the field of view of our images, down to $V\approx19$
mag, was performed using difference image analysis (DIA). For stars of
$\approx15$ mag, measurement accuracies of $\approx8$ mmag and $\approx10$ mmag
were achieved for $V$ and $I$ respectively. Three independent search strategies
were applied to the 5525 light curves but no new variables were found above the
threshold limits characteristic of our data set. The use of older data from the
literature combined with the present data allowed the refinement of the periods
of all known variables. Fourier light curve decomposition was performed for the
RRab and the RRc stars to obtain an estimate of ${\rm
[Fe/H]}_{ZW}=-1.62\pm0.02$ (statistical) $\pm0.14$ (systematic). A true
distance modulus of $14.768\pm0.003$ mag (statistical) $\pm0.042$ mag
(systematic), or a distance of $8.99\pm0.01$ kpc (statistical) $\pm0.17$ kpc
(systematic) was calculated from the RRab star. The RRc star predicts a
discrepant distance about one kiloparsec shorter but it is possibly a Blazhko
variable. An independent distance from the P--L relationship for SX Phe stars
leads to a distance of $8.9\pm0.3$ kpc. The SX Phe stars V5 and V9 are found to
be double mode pulsators.


title:
Morphologies of z~0.7 AGN Host Galaxies in CANDELS: No trend of merger
  incidence with AGN luminosity

abstract:
  The processes that trigger Active Galactic Nuclei (AGN) remain poorly
understood. While lower luminosity AGN may be triggered by minor disturbances
to the host galaxy, stronger disturbances are likely required to trigger
luminous AGN. Major wet mergers of galaxies are ideal environments for AGN
triggering since they provide large gas supplies and galaxy scale torques.
There is however little observational evidence for a strong connection between
AGN and major mergers. We analyse the morphological properties of AGN host
galaxies as a function of AGN and host galaxy luminosity and compare them to a
carefully matched sample of control galaxies. AGN are X-ray selected in the
redshift range 0.5 < z < 0.8 and have luminosities 41 < log(L_X [erg/s]) <
44.5. 'Fake AGN' are simulated in the control galaxies by adding point sources
with the magnitude of the matched AGN. We find that AGN host and control
galaxies have comparable assymetries, Sersic indices and ellipticities at
restframe ~950nm. AGN host galaxies show neither higher average asymmetries nor
higher fractions of very disturbed objects. There is no increase in the
prevalence of merger signatures with AGN luminosity. At 95% confidence we find
that major mergers are responsible for <6% of all AGN in our sample as well as
<40% of the highest luminosity AGN log(L_X [erg/s]) ~ 43.5). Major mergers
therefore either play only a very minor role in the triggering of AGN in the
luminosity range studied or time delays are too long for merger features to
remain visible.


title: The Quark Beam Function at Two Loops

abstract:
  In differential measurements at a hadron collider, collinear initial-state
radiation is described by process-independent beam functions. They are the
field-theoretic analog of initial-state parton showers. Depending on the
measured observable they are differential in the virtuality and/or transverse
momentum of the colliding partons in addition to the usual longitudinal
momentum fraction. Perturbatively, the beam functions can be calculated by
matching them onto standard quark and gluon parton distribution functions. We
calculate the inclusive virtuality-dependent quark beam function at NNLO, which
is relevant for any observables probing the virtuality of the incoming partons,
including N-jettiness and beam thrust. For such observables, our results are an
important ingredient in the resummation of large logarithms at N3LL order, and
provide all contributions enhanced by collinear t-channel singularities at NNLO
for quark-initiated processes in analytic form. We perform the calculation in
both Feynman and axial gauge and use two different methods to evaluate the
discontinuity of the two-loop Feynman diagrams, providing nontrivial checks of
the calculation. As part of our results we reproduce the known two-loop QCD
splitting functions and confirm at two loops that the virtuality-dependent beam
and final-state jet functions have the same anomalous dimension.


title:
Colour Transformations between BVRc and g'r'i' Photometric Systems for
  Giant Stars

abstract:
  The transformation equations from $BVR_c$ to $g'r'i'$ magnitudes and vice
versa for the giants were established from a sample of 80 stars collected from
Soubiran et al. (2010) with confirmed surface gravity ($2\leq \log g$
(cms$^{-2}$)$ \leq3$) at effective temperatures $4000<T_{eff} (K)<16000$. The
photometric observations, all sample stars at $g'r'i'$ and 65 of them at
$BVR_c$, were obtained at T\"UB\.ITAK National Observatory (TUG) 1m (T100)
telescope, on the Taurus Mountains in Turkey. The $M_V$ absolute magnitudes of
the giant stars were estimated from the absolute magnitude-temperature data for
the giant stars by Sung et al. (2013) using the $T_{eff}$ from the intrinsic
colours considered in this study. The transformation equations could be
considered to be valid through the ranges of the following magnitudes and
colours involved: $7.10<V_0<14.50$, $7.30<g'_0<14.85$, $-0.20<(B-V)_0<1.41$,
$-0.11<(V-R_c)_0<0.73$, $-0.42<(g'-r')_0<1.15$, and $-0.37<(r'-i')_0<0.47$ mag.
The transformations were successfully applied to the synthetic $BVR_c$ data of
427 field giants in order to obtain the $g'r'i'$ magnitudes and colours.
Comparisons of these data with the $g'r'i'$ observations of giants in this
study show that the mean residuals and standard deviations lie within [-0.010,
0.042] and [0.028, 0.068] mag, respectively.


title:
Tuning heat transport in trapped-ion chains across a structural phase
  transition

abstract:
  We explore heat transport across an ion Coulomb crystal beyond the harmonic
regime by tuning it across the structural phase transition between the linear
and zigzag configurations. This demonstrates that the control of the spatial
ion distribution by varying the trapping frequencies renders ion Coulomb
crystals an ideal test-bed to study heat transport properties in finite open
system of tunable non-linearities.


title: "Phase freezeout" in isentropically expanding matter

abstract:
  Features of isentropic expansion of warm dense matter (WDM) created by
intense energy fluxes (strong shock compression or instant isochoric heating by
laser or heavy ions) are under discussion in situation when ($i$) --
thermodynamic trajectory of such expansion crosses binodal of liquid-gas phase
transition, and ($ii$) -- expansion within the two-phase region is going along
equilibrium branch (not metastable one) of the two-phase mixture isentrope. It
is known in the plane case that because of break in the expansion isentrope at
binodal point (in $P-V$ plane) i.e. jump of sound velocity in this point, there
appears extended zone ("boiling layer") of uniformity in expanding material
with constant thermodynamic and kinematic parameters. It corresponds just to
the state on this binodal of boiling liquid. The point is that because of
self-similarity of such expansion (in plane case) this boiling layer contains
finite and fixed part of whole expanding material. This property makes it
possible (at least formally) to discuss this type of isentropic expansion of
WDM as a tool for generation (and diagnostics) of extended uniform state of
matter exactly on binodal (and even in critical point) when parameters of this
binodal (and/or thermophysical properties on it) are not known. It is natural
to use the term "phase freezeout" for this regime of expansion. It is similar
to the terms "chemical freezeout" and "kinetic freezeout", which are widely
used in interpretation of quark-hardon transformations during expansion of
quark-gluon "fireball" in ultra-high energy ionic collisions in supercolliders.
General hydrodynamic scheme of adiabatic movements for the case of ensemble of
well positioned plates or foils (stack target) under instant isochoric heating
(for example, by heavy ion beam) is considered as elaboration of simple idea of
phase freeze-out ("reverberation" regime).


title: On-Chip Cavity Optomechanical Coupling

abstract:
  On-chip cavity optomechanics, in which strong co-localization of light and
mechanical motion is engineered, relies on efficient coupling of light both
into and out of the on-chip optical resonator. Here we detail our particular
style of tapered and dimpled optical fibers, pioneered by the Painter group at
Caltech, which are a versatile and reliable solution to efficient on-chip
coupling. First, a brief overview of tapered, single mode fibers is presented,
in which the single mode cutoff diameter is highlighted. The apparatus used to
create a dimpled tapered fiber is then described, followed by a comprehensive
account of the procedure by which a dimpled tapered fiber is produced and
mounted in our system. The custom-built optical access vacuum chambers in which
our on-chip optomechanical measurements are performed are then discussed.
Finally, the process by which our optomechanical devices are fabricated and the
method by which we explore their optical and mechanical properties is
explained. It is our expectation that this manuscript will enable the novice to
develop advanced optomechanical experiments.


title:
Discovery of a Population of Bulgeless Galaxies with Extremely Red
  Mid-IR Colors: Obscured AGN Activity in the Low Mass Regime?

abstract:
  In contrast to massive, bulge hosting galaxies, very few supermassive black
holes (SMBHs) are known in either low mass, or bulgeless galaxies. Such a
population could provide clues to the origins of SMBHs and to secular pathways
for their growth. Using the all-sky Wide-Field Infrared Survey Explorer (WISE)
survey, and bulge-to-disk decompositions from the Sloan Digital Sky Survey
(SDSS) Data Release 7, we report the discovery of a population of local (z<0.3)
bulgeless disk galaxies with extremely red mid-infrared colors highly
suggestive of a dominant active galactic nucleus (AGN), despite having no
optical AGN signatures in their SDSS spectra. Using various mid-infrared
selection criteria from the literature, there are between 30 to over 300
bulgeless galaxies with possible AGNs. Other known scenarios that can heat the
dust to high temperatures do not appear to explain the observed colors of this
sample. If these galaxies are confirmed to host AGNs, this study will provide a
breakthrough in characterizing the properties of SMBHs in the low bulge mass
regime and in understanding their relation with their host galaxies.
Mid-infrared selection identifies AGNs that dominate their host galaxy's
emission and therefore reveal a different AGN population than is uncovered by
optical studies. We find that the fraction of all galaxies identified as
candidate AGNs by WISE is highest at lower stellar masses and drops
dramatically in higher mass galaxies, in striking contrast to the findings from
optical studies.


title:
Infinite horizon Stochastic Optimal Control for Volterra equations with
  completely monotone kernels

abstract:
  The aim of the paper is to study an optimal control problem on infinite
horizon for an infinite dimensional integro-differential equation with
completely monotone kernelskernels, where we assume that the noise enters the
system when we introduce a control. We start by reformulating the state
equation into a semilinear evolution equation which can be treated by semigroup
methods. The application to optimal control provide other interesting result
and require a precise descriprion of the properties of the generated semigroup.
The main tools consist in studying the differentiability of the
forward-backward system with infinite horizon corresponding with the
reformulated problem and the proof of existence and uniqueness of of mild
solutions to the corresponding HJB equation.


title: Superconductivity from weak repulsion in hexagonal lattice systems

abstract:
  We analyze the pairing instabilities for fermions on hexagonal lattices (both
honeycomb and triangular ones) in a wide range of fermionic densities. We argue
that for a generic doping in this range, superconductivity at weak coupling is
of Kohn-Luttinger type, and, due to the presence of electronic interactions
beyond on-site repulsion, is a threshold phenomenon, with superconductivity
emerging only if the attraction generated by the Kohn-Luttinger mechanism
exceeds the bare repulsion in some channel. For disconnected Fermi pockets, we
predict that Kohn-Luttinger superconductivity, if it occurs, is likely to be
$f$-wave. While the Kohn-Luttinger analysis is adequate over most of the doping
range, a more sophisticated analysis is needed near Van Hove doping. We treat
Van Hove doping using a parquet renormalization group, the equations for which
we derive and analyze. Near this doping level, superconductivity is a universal
phenomenon, arising from any choice of bare repulsive interactions. The
strongest pairing instability is into a chiral $d-$wave state ($d+id$). At a
truly weak coupling, the strongest competitor is a spin-density-wave
instability, however, $d-$wave superconductivity still wins. Moreover, the
feedback of the spin density fluctuations into the Cooper channel significantly
enhances the critical temperature over the estimates of the Kohn Luttinger
theory. We analyze renormalization group equations at stronger couplings and
find that the main competitor to $d-$wave supoerconductivity away from weak
coupling is actually ferromagnetism. We also discuss the effect of the edge
fermions and show that they are unimportant in the asymptotic weak coupling
limit, but may give rise to, e.g., a charge-density-wave order at moderate
coupling strengths.


title: General Divisibility Criteria

abstract:
  We believe we have made progress in the age-old problem of divisibility rules
for integers. Universal divisibility rule is introduced for any divisor in any
base number system. The divisibility criterion is written down explicitly as a
linear form in the digits of the test number. The universal criterion contains
only two parameters that depend on the divisor and are easily calculated. These
divisibility parameters are not unique for a given divisor but each
two-parameter set yields a unique criterion. Well-known divisibility rules for
exemplary divisors in the decimal system follow from the universal expression
as special cases.


title: The Wind of Variable C in M33

abstract:
  We discuss the spectrum of Var C in M33 obtained just before the onset of its
current brightening and recent spectra during its present "eruption" or
optically thick wind stage. These spectra illustrate the typical LBV transition
in apparent spectral type or temperature that characterizes the classical LBV
or S Dor-type variability. LBVs are known to have slow, dense winds during
their maximum phase. Interestingly, Var C had a slow wind even during its hot,
quiescent stage in comparison with the normal hot supergiants with similar
temperatures. Its outflow or wind speeds also show very little change between
these two states.


title: Light WIMPs, Equivalent Neutrinos, BBN, and the CMB

abstract:
  Recent updates to the observational determinations of the primordial
abundances of helium and deuterium are compared to the predictions of BBN to
infer the universal ratio of baryons to photons (or, the present Universe
baryon mass density parameter Omega_B h^2), as well as to constrain the
effective number of neutrinos (N_eff) and the number of equivalent neutrinos
(Delta N_nu). These BBN results are compared to those derived independently
from the Planck CMB data. In the absence of a light WIMP (chi), N_eff = 3.05(1
+ Delta N_nu/3). In this case, there is excellent agreement between BBN and the
CMB, but the joint fit finds that Delta N_nu = 0.40 +/- 0.17, disfavoring
standard big bang nucleosynthesis (SBBN: Delta N_nu = 0) at 2.4 sigma, as well
as a sterile neutrino (Delta N_nu = 1) at 3.5 sigma. In the presence of a light
WIMP, the relation between N_eff and Delta N_nu depends on the WIMP mass,
leading to degeneracies among N_eff, Delta N_nu, and m_chi. The complementary
and independent BBN and CMB data can break some of these degeneracies.
Depending on the nature of the light WIMP (Majorana or Dirac fermion, real or
complex scalar) the joint BBN + CMB analyses set a lower bound to m_chi in the
range from 0.5 to 5 MeV, and they identify best fit values for m_chi in the
range from 5 to 10 MeV. The joint BBN + CMB analyses find a best fit value for
the number of equivalent neutrinos, Delta N_nu = 0.65, nearly independent of
the nature of the WIMP. The best fit still disfavors the absence of dark
radiation (Delta N_nu = 0 at 95% confidence), while allowing for the presence
of a sterile neutrino (Delta N_nu = 1 at less than 1 sigma). For all cases
considered here, the lithium problem persists. These results, presented at the
2013 Rencontres de l'Observatoire de Paris - ESO Workshop, are based on Nollett
& Steigman 2013 (arXiv:1312.5725 [astro-ph.CO]).


title:
Systematic Problems With Using Dark Matter Simulations to Model Stellar
  Halos

abstract:
  The limits of available computing power have forced models for the structure
of stellar halos to adopt one or both of the following simplifying assumptions:
(1) stellar mass can be "painted" onto dark matter particles in progenitor
satellites; (2) pure dark matter simulations that do not form a luminous galaxy
can be used. We estimate the magnitude of the systematic errors introduced by
these assumptions using a controlled set of stellar halo models where we
independently vary whether we look at star particles or painted dark matter
particles, and whether we use a simulation in which a baryonic disk galaxy
forms or a matching pure dark matter simulation that does not form a baryonic
disk. We find that the "painting" simplification reduces the halo concentration
and internal structure, predominantly because painted dark matter particles
have different kinematics than star particles even when both are buried deep in
the potential well of the satellite. The simplification of using pure dark
matter simulations reduces the concentration further, but increases the
internal structure, and results in a more prolate stellar halo. These
differences can be a factor of 1.5-7 in concentration (as measured by the
half-mass radius) and 2-7 in internal density structure. Given this level of
systematic uncertainty, one should be wary of overinterpreting differences
between observations and the current generation of stellar halo models based on
dark matter only simulations when such differences are less than an order of
magnitude.


title:
Rest-Frame Optical Emission Lines in z~3.5 Lyman Break selected
  Galaxies: The Ubiquity of Unusually High [OIII]/Hbeta Ratios at 2 Gyr

abstract:
  We present K-band spectra of rest-frame optical emission lines for 24
star-forming galaxies at z~3.2-3.7 using MOSFIRE on the Keck 1 telescope.
Strong rest-frame optical [O III] and Hbeta emission lines were detected in 18
LBGs. The median flux ratio of [O III]5007 to Hbeta is 5.1+/-0.5, a factor of
5-10x higher than in local galaxies with similar stellar masses. The observed
Hbeta luminosities are in good agreement with expectations from the estimated
star-formation rates, and none of our sources are detected in deep X-ray
stacks, ruling out significant contamination by active galactic nuclei.
Combining our sample with a variety of LBGs from the literature, including 49
galaxies selected in a very similar manner, we find a high median ratio of
[OIII]/Hbeta = 4.8+0.8-1.7. This high ratio seems to be an ubiquitous feature
of z~3-4 LBGs, very different from typical local star-forming galaxies at
similar stellar masses. The only comparable systems at z~0 are those with
similarly high specific star-formation rates, though ~5x lower stellar masses.
High specific star-formation rates either result in a much higher ionization
parameter or other unusual conditions for the interstellar medium, which result
in a much higher [OIII]/Hbeta line ratio. This implies a strong relation
between a global property of a galaxy, the specific star-formation rate, and
the local conditions of ISM in star-forming regions.


title:
On Time Variations of Gravitational and Yang-Mills Constants in a
  Cosmological Model of Superstring Origin

abstract:
  In the framework of 10-dimensional "Friedmann-Calabi-Yau" cosmology of
superstring origin we show that the time variation of either Newton's
gravitational constant or Yang-Mills one is unavoidable in the present epoch.


title:
Alternating direction method of multipliers for penalized zero-variance
  discriminant analysis

abstract:
  We consider the task of classification in the high dimensional setting where
the number of features of the given data is significantly greater than the
number of observations. To accomplish this task, we propose a heuristic, called
sparse zero-variance discriminant analysis (SZVD), for simultaneously
performing linear discriminant analysis and feature selection on high
dimensional data. This method combines classical zero-variance discriminant
analysis, where discriminant vectors are identified in the null space of the
sample within-class covariance matrix, with penalization applied to induce
sparse structures in the resulting vectors. To approximately solve the
resulting nonconvex problem, we develop a simple algorithm based on the
alternating direction method of multipliers. Further, we show that this
algorithm is applicable to a larger class of penalized generalized eigenvalue
problems, including a particular relaxation of the sparse principal component
analysis problem. Finally, we establish theoretical guarantees for convergence
of our algorithm to stationary points of the original nonconvex problem, and
empirically demonstrate the effectiveness of our heuristic for classifying
simulated data and data drawn from applications in time-series classification.


title: A New Relativistic Orthogonal States Quantum Key Distribution Protocol

abstract:
  We introduce a new relativistic orthogonal states quantum key distribution
protocol which leverages the properties of both quantum mechanics and special
relativity to securely encode multiple bits onto the spatio-temporal modes of a
single photon. If the protocol is implemented using a single photon source, it
can have a key generation rate faster than the repetition rate of the source,
enabling faster secure communication than is possible with existing protocols.
Further, we provide a proof that the protocol is secure and give a method of
implementing the protocol using line-of-sight and fiber optic channels.


title:
Two spotted and magnetic early B-type stars in the young open cluster
  NGC2264 discovered by MOST and ESPaDOnS

abstract:
  Star clusters are known as superb tools for understanding stellar evolution.
In a quest for understanding the physical origin of magnetism and chemical
peculiarity in about 7% of the massive main-sequence stars, we analysed two of
the ten brightest members of the ~10 Myr old Galactic open cluster NGC 2264,
the early B-dwarfs HD47887 and HD47777. We find accurate rotation periods of
1.95 and 2.64 days, respectively, from MOST photometry. We obtained ESPaDOnS
spectropolarimetric observations, through which we determined stellar
parameters, detailed chemical surface abundances, projected rotational
velocities, and the inclination angles of the rotation axis. Because we found
only small (<5 km/s) radial velocity variations, most likely caused by spots,
we can rule out that HD47887 and HD47777 are close binaries. Finally, using the
least-squares deconvolution technique, we found that both stars possess a
large-scale magnetic field with an average longitudinal field strength of about
400 G. From a simultaneous fit of the stellar parameters we determine the
evolutionary masses of HD47887 and HD47777 to be 9.4+/-0.7 M0 and 7.6+/-0.5 M0.
Interestingly, HD47777 shows a remarkable helium underabundance, typical of
helium-weak chemically peculiar stars, while the abundances of HD47887 are
normal, which might imply that diffusion is operating in the lower mass star
but not in the slightly more massive one. Furthermore, we argue that the rather
slow rotation, as well as the lack of nitrogen enrichment in both stars, can be
consistent with both the fossil and the binary hypothesis for the origin of the
magnetic field. However, the presence of two magnetic and apparently single
stars near the top of the cluster mass-function may speak in favour of the
latter.


title: RG flows of Quantum Einstein Gravity on maximally symmetric spaces

abstract:
  We use the Wetterich-equation to study the renormalization group flow of
$f(R)$-gravity in a three-dimensional, conformally reduced setting. Building on
the exact heat kernel for maximally symmetric spaces, we obtain a partial
differential equation which captures the scale-dependence of $f(R)$ for
positive and, for the first time, negative scalar curvature. The effects of
different background topologies are studied in detail and it is shown that they
affect the gravitational RG flow in a way that is not visible in
finite-dimensional truncations. Thus, while featuring local background
independence, the functional renormalization group equation is sensitive to the
topological properties of the background. The detailed analytical and numerical
analysis of the partial differential equation reveals two globally well-defined
fixed functionals with at most a finite number of relevant deformations. Their
properties are remarkably similar to two of the fixed points identified within
the $R^2$-truncation of full Quantum Einstein Gravity. As a byproduct, we
obtain a nice illustration of how the functional renormalization group realizes
the "integrating out" of fluctuation modes on the three-sphere.


title:
Exploratory X-ray Monitoring of Luminous Radio-Quiet Quasars at High
  Redshift: Initial Results

abstract:
  We present initial results from an exploratory X-ray monitoring project of
two groups of comparably luminous radio-quiet quasars (RQQs). The first
consists of four sources at 4.10 <= z <= 4.35, monitored by Chandra, and the
second is a comparison sample of three sources at 1.33 <= z <= 2.74, monitored
by Swift. Together with archival X-ray data, the total rest-frame temporal
baseline spans ~2-4 yr and ~5-13 yr for the first and second group,
respectively. Six of these sources show significant X-ray variability over
rest-frame timescales of ~10^2 - 10^3 d; three of these also show significant
X-ray variability on rest-frame timescales of ~1-10 d. The X-ray variability
properties of our variable sources are similar to those exhibited by nearby and
far less luminous active galactic nuclei (AGNs). While we do not directly
detect a trend of increasing X-ray variability with redshift, we do confirm
previous reports of luminous AGNs exhibiting X-ray variability above that
expected from their luminosities, based on simplistic extrapolation from lower
luminosity sources. This result may be attributed to luminous sources at the
highest redshifts having relatively high accretion rates. Complementary
UV-optical monitoring of our sources shows that variations in their
optical-X-ray spectral energy distribution are dominated by the X-ray
variations. We confirm previous reports of X-ray spectral variations in one of
our sources, HS 1700+6416, but do not detect such variations in any of our
other sources in spite of X-ray flux variations of up to a factor of ~4. This
project is designed to provide a basic assessment of the X-ray variability
properties of RQQs at the highest accessible redshifts that will serve as a
benchmark for more systematic monitoring of such sources with future X-ray
missions.


title: Determining Factors for the Accuracy of DMRG in Chemistry

abstract:
  The Density Matrix Renormalization Group (DMRG) algorithm has been a rising
star for the accurate ab initio exploration of Born-Oppenheimer potential
energy surfaces in theoretical chemistry. However, owing to its iterative
numerical nature, pit falls, that can affect the accuracy of DMRG energies,
need to be circumvented. Here, after a brief introduction into this quantum
chemical method, we discuss criteria that determine the accuracy of DMRG
calculations.

categories: physics.chem-ph cond-mat.str-el physics.comp-ph quant-ph


title: Excursion probability of Gaussian random fields on sphere

abstract:
  Let $X=\{X(x): x\in\mathbb{S}^N\}$ be a real-valued, centered Gaussian random
field indexed on the $N$-dimensional unit sphere $\mathbb{S}^N$. Approximations
to the excursion probability ${\mathbb{P}}\{\sup_{x\in\mathbb{S}^N}X(x)\ge
u\}$, as $u\to\infty$, are obtained for two cases: (i) $X$ is locally isotropic
and its sample functions are non-smooth and; (ii) $X$ is isotropic and its
sample functions are twice differentiable. For case (i), the excursion
probability can be studied by applying the results in Piterbarg (Asymptotic
Methods in the Theory of Gaussian Processes and Fields (1996) Amer. Math.
Soc.), Mikhaleva and Piterbarg (Theory Probab. Appl. 41 (1997) 367--379) and
Chan and Lai (Ann. Probab. 34 (2006) 80--121). It is shown that the asymptotics
of ${\mathbb{P}}\{\sup_{x\in\mathbb {S}^N}X(x)\ge u\}$ is similar to Pickands'
approximation on the Euclidean space which involves Pickands' constant. For
case (ii), we apply the expected Euler characteristic method to obtain a more
precise approximation such that the error is super-exponentially small.


title: The decategorification of bordered Khovanov homology

abstract:
  In two previous papers, the author showed how to decompose the Khovanov
homology of a link $\mathcal{L}$ into the algebraic pairing of a type D
structure and a type A structure (as defined in bordered Floer homology),
whenever a diagram for $\mathcal{L}$ is decomposed into the union of two
tangles. Since Khovanov homology is the categorification of a version of the
Jones polynomial, it is natural to ask what the type A and type D structures
categorify, and how their pairing is encoded in the decategorifications. In
this paper, the author constructs the decategorifications of these two
structures, in a manner similar to Ina Petkova's decategorification of bordered
Floer homology and shows how they recover the Jones polynomial. We also give a
new proof of the mutation invariance of the Jones polynomial which uses these
decomposition techniques.


title: $C^*$-non-linear second quantization

abstract:
  Recently, we have constructed a non{linear (polynomial) extension of the
1-mode Heisenberg group and the corresponding Fock and Weyl representations.
The transition from the 1-mode case to the current algebra level, in which the
operators are indexed by elements of an appropriate test function space (second
quantization), can be done at Lie algebra level. A way to bypass the
difficulties of constructing a (non trivial) Hilbert space representation is to
try and construct directly a $C^*$-algebra rep- resentation and then to look
for its Hilbert space representations. In usual (linear) quantization, this
corresponds to the construction of the Weyl $C^*$-algebra. In this paper, we
produce such a construction for the above mentioned polynomial extension of the
Weyl $C^*$-algebra. The result of this construction is a factorizable system of
local alge- bras localized on bounded Borel subsets of $\mathbb{R}$ and
obtained as induc- tive limit of tensor products of finite sets of copies of
the one mode $C^*$-algebra. The $C^*$-embeddings of the inductive system
require some non{trivial re{scaling of the generators of the algebras involved.
These re{scalings are responsible of a $C^*$-analogue of the "no-go" theorems,
first met at the level of Fock second quantization, namely the proof that the
family of Fock states defined on the inductive family of $C^*$-algebras is
projective only in the linear case (i.e. the case of the usual Weyl algebra).
Thus the solution of the representa- tion problem at $C^*$-level does not
automatically imply its solution at Hilbert space level.


title: Planar algebras and the decategorification of bordered Khovanov homology

abstract:
  We give a simple, combinatorial construction of a unital, spherical,
non-degenerate $\ast$-planar algebra over the ring
$\mathbb{Z}[q^{1/2},q^{-1/2}]$. This planar algebra is similar in spirit to the
Temperley-Lieb planar algebra, but computations show that they are different.
The construction comes from the combinatorics of the decategorifications of the
type A and type D structures in the author's previous work on bordered Khovanov
homology. In particular, the construction illustrates how gluing of tangles
occurs in his bordered Khovanov homology and its difference from that in
Khovanov's tangle homology, without being encumbered by any extra homological
algebra. It also provides a simple framework for showing that these theories
are not related through a simple process, thereby confirming recent work of A.
Manion. Furthermore, using Khovanov's conventions and a state sum approach to
the Jones polynomial, we obtain new invariant for tangles in $\Sigma \times
[-1,1]$ where $\Sigma$ is a compact, planar surface with boundary, and the
tangle intersects each boundary cylinder in an even number of points. This
construction naturally generalizes Khovanov's approach to the Jones polynomial.


title: A Representation Theorem for Smooth Brownian Martingales - New Example

abstract:
  We show that, under certain smoothness conditions, a Brownian martingale,
when evaluated at a fixed time, can be represented via an exponential formula
at a later time. The time-dependent generator of this exponential operator only
depends on the second order Malliavin derivative operator evaluated along a
"frozen path". The exponential operator can be expanded explicitly to a series
representation, which resembles the Dyson series of quantum mechanics. Our
continuous-time martingale representation result can be proven independently by
two different methods. In the first method, one constructs a time-evolution
equation, by passage to the limit of a special case of a backward Taylor
expansion of an approximating discrete time martingale. The exponential formula
is a solution of the time-evolution equation, but we emphasize in our article
that the time-evolution equation is a separate result of independent interest.
In the second method, which we only highlight in this article, we use the
property of denseness of exponential functions. We provide several applications
of the exponential formula, and briefly highlight numerical applications of the
backward Taylor expansion.


title:
Two-color pump-probe dynamics of transitions between doubly excited
  states of Helium

abstract:
  We discuss the dynamics of the two-photon resonant ionization of helium
involving two autoionizing states in the presence of two-color laser fields.
The first source is tuned around the transition from the ground state to the
2s2p 1Po autoionizing state, and the second couples the state 2s2p 1Po to the
2p2 1S autoionizing state. The laser coupling between the doubly excited states
is shown to lead to modifications of the Beutler-Fano profile and the
appearance of an Autler-Townes doublet. This double resonance effect between
autoionizing states can be observed at moderate laser intensities easily
attainable by currently operated sources.


title:
Architectural considerations in the design of a superconducting quantum
  annealing processor

abstract:
  We have developed a quantum annealing processor, based on an array of tunably
coupled rf-SQUID flux qubits, fabricated in a superconducting integrated
circuit process [1]. Implementing this type of processor at a scale of 512
qubits and 1472 programmable inter-qubit couplers and operating at ~ 20 mK has
required attention to a number of considerations that one may ignore at the
smaller scale of a few dozen or so devices. Here we discuss some of these
considerations, and the delicate balance necessary for the construction of a
practical processor that respects the demanding physical requirements imposed
by a quantum algorithm. In particular we will review some of the design
trade-offs at play in the floor-planning of the physical layout, driven by the
desire to have an algorithmically useful set of inter-qubit couplers, and the
simultaneous need to embed programmable control circuitry into the processor
fabric. In this context we have developed a new ultra-low power embedded
superconducting digital-to-analog flux converters (DACs) used to program the
processor with zero static power dissipation, optimized to achieve maximum flux
storage density per unit area. The 512 single-stage, 3520 two-stage, and 512
three-stage flux-DACs are controlled with an XYZ addressing scheme requiring 56
wires. Our estimate of on-chip dissipated energy for worst-case reprogramming
of the whole processor is ~ 65 fJ. Several chips based on this architecture
have been fabricated and operated successfully at our facility, as well as two
outside facilities (see for example [2]).


title: Eigenpolarizations for Giant Transverse Optical Beam Shifts

abstract:
  We show how careful control of the incident polarization of a light beam
close to the Brewster angle gives a giant transverse spatial shift on
reflection. This resolves the long-standing puzzle of why such beam shifts
transverse to the incident plane [Imbert-Fedorov (IF) shifts] tend to be an
order of magnitude smaller than the related Goos-H\"anchen (GH) shifts in the
longitudinal direction, which are largest close to critical incidence. We
demonstrate that with the proper initial polarization the transverse
displacements can be equally large, which we confirm experimentally near
Brewster incidence. In contrast to the established understanding these
polarizations are elliptical and angle-dependent. We explain the magnitude of
the IF shift by an analogous change of the symmetry properties for the
reflection operators as compared to the GH shift.


title:
An attraction-repulsion point process model for respiratory syncytial
  virus infections

abstract:
  How is the progression of a virus influenced by properties intrinsic to
individual cells? We address this question by studying the susceptibility of
cells infected with two strains of the human respiratory syncytial virus (RSV-A
and RSV-B) in an in vitro experiment. Spatial patterns of infected cells give
us insight into how local conditions influence susceptibility to the virus. We
observe a complicated attraction and repulsion behavior, a tendency for
infected cells to lump together or remain apart. We develop a new spatial point
process model to describe this behavior. Inference on spatial point processes
is difficult because the likelihood functions of these models contain
intractable normalizing constants; we adapt an MCMC algorithm called double
Metropolis-Hastings to overcome this computational challenge. Our methods are
computationally efficient even for large point patterns consisting of over
10,000 points. We illustrate the application of our model and inferential
approach to simulated data examples and fit our model to various RSV
experiments. Because our model parameters are easy to interpret, we are able to
draw meaningful scientific conclusions from the fitted models.


title: Families of L-functions and their Symmetry

abstract:
  In [90] the first-named author gave a working definition of a family of
automorphic L-functions. Since then there have been a number of works [33],
[107], [67] [47], [66] and especially [98] by the second and third-named
authors which make it possible to give a conjectural answer for the symmetry
type of a family and in particular the universality class predicted in [64] for
the distribution of the zeros near s=1/2. In this note we carry this out after
introducing some basic invariants associated to a family.


title: Hilbert Space Methods for Reduced-Rank Gaussian Process Regression

abstract:
  This paper proposes a novel scheme for reduced-rank Gaussian process
regression. The method is based on an approximate series expansion of the
covariance function in terms of an eigenfunction expansion of the Laplace
operator in a compact subset of $\mathbb{R}^d$. On this approximate eigenbasis
the eigenvalues of the covariance function can be expressed as simple functions
of the spectral density of the Gaussian process, which allows the GP inference
to be solved under a computational cost scaling as $\mathcal{O}(nm^2)$
(initial) and $\mathcal{O}(m^3)$ (hyperparameter learning) with $m$ basis
functions and $n$ data points. Furthermore, the basis functions are independent
of the parameters of the covariance function, which allows for very fast
hyperparameter learning. The approach also allows for rigorous error analysis
with Hilbert space theory, and we show that the approximation becomes exact
when the size of the compact subset and the number of eigenfunctions go to
infinity. We also show that the convergence rate of the truncation error is
independent of the input dimensionality provided that the differentiability
order of the covariance function is increases appropriately, and for the
squared exponential covariance function it is always bounded by ${\sim}1/m$
regardless of the input dimensionality. The expansion generalizes to Hilbert
spaces with an inner product which is defined as an integral over a specified
input density. The method is compared to previously proposed methods
theoretically and through empirical tests with simulated and real data.


title:
Intelligent Product: Mobile Agent Architecture Integrating the End of
  Life Cycle (EOL) For minimizing the lunch phase PLM

abstract:
  To improve the increasingly demands products that are customized, all
business activities performed along the product life cycle must be coordinated
and efficiently managed along the extended enterprise. For this, enterprise had
wanted to retain control over the whole product lifecycle especially when the
product is in use/recycling (End Of Life phase). Although there have been many
previous research works about product lifecycle management in the beginning of
life (BOL) and middle of life (MOL) phases, few addressed the end of life (EOL)
phase, in particular, when the product is at the customers. In this paper,
based on product embedded device identification (PEID) and mobile agent
technologies, and with the advent of the development of the "intelligent
products", we will try to improve innovation: (a) by minimize the lunch phase,
(b) and the involvement of the customer in product lifecycle.


title:
The role of phase interface energy in martensitic transformations: a
  lattice Monte-Carlo simulation

abstract:
  To study martensitic phase transformation we use a micromechanical model
based on statistical mechanics. Employing lattice Monte-Carlo simulations and
realistic material properties for shape-memory alloys (SMA), we investigate the
combined influence of the external stress, temperature, and interface energy
between the austenitic and martensitic phase on the transformation kinetics and
the effective material compliance. The one-dimensional model predicts well many
features of the martensitic transformation that are observed experimentally.
Particularly, we study the influence of the interface energy on the
transformation width and the effective compliance. In perspective, the obtained
results might be helpful for the design of new SMAs for more sensitive smart
structures and more efficient damping systems.


title: Mass loss in main-sequence B stars

abstract:
  We calculate radiatively driven wind models of main-sequence B stars and
provide the wind mass-loss rates and terminal velocities. The main-sequence
mass-loss rate strongly depends on the stellar effective temperature. For the
hottest B stars the mass-loss rate amounts to
$10^{-9}\,\text{M}_\odot\,\text{year}^{-1}$, while for the cooler ones
themass-loss rate is lower by more than three orders of magnitude.
Main-sequence B stars with solar abundance and effective temperatures lower
than about$15\,000\,\text{K}$ (later than spectral type B5) do not have any
homogeneous line-driven wind. We predict the wind mass-loss rates for the solar
chemical composition and for the modified abundance of heavier elements to
study the winds of chemically peculiar stars. The mass-loss rate may either
increase or decrease with increasing abundance, depending on the importance of
the induced emergent flux redistribution. Stars with overabundant silicon may
have homogeneous winds even below the solar abundance wind limit at
$15\,000\,\text{K}$. The winds of main-sequence B stars lie below the static
limit, that is, a static atmosphere solution is also possible. This points to
an important problem regarding the initiation of these winds. We discuss the
implications of our models for rotational braking, filling the magnetosphere of
Bp stars, and for chemically peculiar stars.


title: 0-1 Integer Linear Programming with a Linear Number of Constraints

abstract:
  We give an exact algorithm for the 0-1 Integer Linear Programming problem
with a linear number of constraints that improves over exhaustive search by an
exponential factor. Specifically, our algorithm runs in time
$2^{(1-\text{poly}(1/c))n}$ where n is the number of variables and cn is the
number of constraints. The key idea for the algorithm is a reduction to the
Vector Domination problem and a new algorithm for that subproblem.


title: The Right Side of Einstein's Equation

abstract:
  Recent developments in observational cosmology have led to attempts to make
modifications on both sides of the Einstein equation to explain some of the
puzzling new findings. What follows is an examination of the source of gravity
that we usually find on the right hand side of Einstein's equation. The outcome
is a modified version of the stress-energy tensor that is the source of the
gravitational field. The derivation is based on the kinetic theory of a gas of
identical particles with no internal structure.
  The presentation here is in two parts. In Part I, I describe the stress
tensor that Xinzhong Chen and I have proposed for the matter tensor for a
nonrelativistic gas with input from Hongling Rao and Jean-Luc Thiffeault. Our
derivation of the equations of fluid dynamics is based on kinetic theory
without recourse to the standard Chapman-Enskog approximation.
  In Part II, I present the analogous derivation of our form for the
stress-energy tensor in the relativistic case. Then I exhibit its application
to the usual isotropic cosmological model. The result of that, in addition to
the Friedmann solution, is a second solution that arises from terms discarded
in the usual Chapman-Enskog approximation. The new solution is a temporal
analogue of a spatial shock wave.
  Just as the usual shock waves make transitions in properties within a mean
free path, the new solution can change its properties appreciably in a mean
flight time. Whereas the Friedmann solution is not dissipative, the new
solution produces entropy at a rate that may be of cosmological interest. For
the calculation of cosmic entropy production I use a formula derived in the
ultrarelativistic limit in which particle masses are negligible.
  Independently of the cosmological aspects, the fluid dynamical equations that
we derive are causal, even for the heat equation (or Fourier equation).


title: Charmless Three-body Decays of B_s Mesons

abstract:
  Branching fractions and CP-violating asymmetries of charmless $B_s\to PPP$
decays with $P=K,\pi$ are studied using a simple model based on the
factorization approach. The penguin-dominated modes $B_s\to \bar K^0 K^+\pi^-$
and $K^0K^-\pi^+$ have the largest rates among the three-body $B_s$ decays and
they are dominated by the $K_0^*(1430)$ resonances and nonresonant
contributions. The branching fraction of $B_s\to K^0K^+K^-$ is predicted to be
$1.4\times 10^{-6}$, which is close to the high end of the measured result
$(0.2-3.4)\times 10^{-6}$ obtained by LHCb. We find sizable CP violation in
$K^0\pi^+\pi^-$, $K^0\pi^0\pi^0$, $K^0K^+K^-$ and $K_SK_SK_S$ channels. Just as
the $B_u$ sector, the correlation of CP asymmetries $A_{CP}(B_s\to
K^0\pi^+\pi^-)\approx -A_{CP}(B_s\to K^0K^+K^-)$ holds in $B_s$ decays. Several
model-independent relations based on $U$-spin symmetry for CP asymmetries are
derived. Although they cannot be tested by the present available data, they can
be checked by the dynamical calculations. Since the $U$-spin symmetry which
relates various matrix elements of scalar densities, for example, $<K^0K|\bar
dq|0>$ and $<\bar K^0\pi|\bar sq|0>$, is badly broken, the derived $U$-spin
relations are generally not well respected.


title:
Generalized Langevin equations for a driven tracer in dense soft
  colloids: construction and applications

abstract:
  We describe a tracer in a bath of soft Brownian colloids by a particle
coupled to the density field of the other bath particles. From the Dean
equation, we derive an exact equation for the evolution of the whole system,
and show that the density field evolution can be linearized in the limit of a
dense bath. This linearized Dean equation with a tracer taken apart is
validated by the reproduction of previous results on the mean-field liquid
structure and transport properties. Then, the tracer is submitted to an
external force and we compute the density profile around it, its mobility and
its diffusion coefficient. Our results exhibit effects such as bias enhanced
diffusion that are very similar to those observed in the opposite limit of a
hard core lattice gas, indicating the robustness of these effects. Our
predictions are successfully tested against molecular dynamics simulations.


title: KAM theory and the 3D Euler equation

abstract:
  We prove that the dynamical system defined by the hydrodynamical Euler
equation on any closed Riemannian 3-manifold $M$ is not mixing in the $C^k$
topology ($k > 4$ and non-integer) for any prescribed value of helicity and
sufficiently large values of energy. This can be regarded as a 3D version of
Nadirashvili's and Shnirelman's theorems showing the existence of wandering
solutions for the 2D Euler equation. Moreover, we obtain an obstruction for the
mixing under the Euler flow of $C^k$-neighborhoods of divergence-free
vectorfields on $M$. On the way we construct a family of functionals on the
space of divergence-free $C^1$ vectorfields on the manifold, which are
integrals of motion of the 3D Euler equation. Given a vectorfield these
functionals measure the part of the manifold foliated by ergodic invariant tori
of fixed isotopy types. We use the KAM theory to establish some continuity
properties of these functionals in the $C^k$-topology. This allows one to get a
lower bound for the $C^k$-distance between a divergence-free vectorfield (in
particular, a steady solution) and a trajectory of the Euler flow.


title:
Gamov-Teller transitions from 14N ground to 14C ground and excited
  states

abstract:
  Gamov-Teller transitions from the $^{14}$N ground state to the $^{14}$C
ground and excited states were investigated, based on the model of
antisymmetrized molecular dynamics. The calculated strengths for the allowed
transitions to the $0^+$, $1^+$, and $2^+$ states of $^{14}$C were compared
with the experimental data measured by high-resolution charge-exchange
reactions. The calculated GT transition to the $2^+_1$ state is strong while
those to the $0^+_{2,3}$ and $2^+_{2,3}$ states having dominant $2\hbar\omega$
excited configurations are relatively weak. The present calculation can not
describe the anonymously long life time of $^{14}$C, though the strength of the
$^{14}$C ground state is somewhat suppressed because of the cluster (many-body)
correlation in the ground states of $^{14}$C and $^{14}$N.


title:
Sensitivity of helioseismic travel-times to the imposition of a Lorentz
  force limiter in computational helioseismology

abstract:
  The rapid exponential increase in the Alfv\'en wave speed with height above
the solar surface presents a serious challenge to physical modelling of the
effects of magnetic fields on solar oscillations, as it introduces a
significant CFL time-step constraint for explicit numerical codes. A common
approach adopted in computational helioseismology, where long simulations in
excess of 10 hours (hundreds of wave periods) are often required, is to cap the
Alfv\'en wave speed by artificially modifying the momentum equation when the
ratio between Lorentz and hydrodynamic forces becomes too large. However,
recent studies have demonstrated that the Alfv\'en wave speed plays a critical
role in the MHD mode conversion process, particularly in determining the
reflection height of the upward propagating helioseismic fast wave. Using
numerical simulations of helioseismic wave propagation in constant inclined
(relative to the vertical) magnetic fields we demonstrate that the imposition
of such artificial limiters significantly affects time-distance travel times
unless the Alfv\'en wave-speed cap is chosen comfortably in excess of the
horizontal phase speeds under investigation.


title:
Spectroscopic evidence for spin-polarized edge states in graphitic Si
  nanowires

abstract:
  The step edges on the Si(553)-Au surface undergo a 1 x 3 reconstruction at
low temperature which has recently been interpreted theoretically as the x3
ordering of spin-polarized silicon atoms at the edges of the graphitic Si
nanowires on this vicinal surface. This predicted magnetic ground state has a
clear spectroscopic signature - a silicon step-edge state at 0.5 eV above the
Fermi level - that arises from strong exchange splitting and hence would not
occur without spin polarization. Here we report spatially resolved scanning
tunneling spectroscopy data for these nanowires. At low temperature we find an
unoccupied state at 0.5 eV above every third step edge silicon atom, in
excellent agreement with the spin-polarized ground state predicted
theoretically. This spin-polarized state survives up to room temperature where
the position of the spins rapidly fluctuates among all Si step-edge sites.


title: Analysing the impact of anisotropy pressure on tokamak equilibria

abstract:
  Neutral beam injection or ion cyclotron resonance heating induces pressure
anisotropy. The axisymmetric plasma equilibrium code HELENA has been upgraded
to include anisotropy and toroidal flow. With both analytical and numerical
methods, we have studied the determinant factors in anisotropic equilibria and
their impact on flux surfaces, magnetic axis shift, the displacement of
pressures and density contours from flux surface. With $p_\parallel/p_\perp
\approx 1.5$, $p_\perp$ can vary 20% on $s=0.5$ flux surface, in a MAST like
equilibrium. We have also re-evaluated the widely applied approximation to
anisotropy in which $p^*=(p_\parallel + p_\perp)/2$, the average of parallel
and perpendicular pressure, is taken as the approximate isotropic pressure. We
find the reconstructions of the same MAST discharge with $p_\parallel/p_\perp
\approx 1.25$, using isotropic and anisotropic model respectively, to have a 3%
difference in toroidal field but a 66% difference in poloidal current.


title:
Harnessing synthetic gauge fields for maximally entangled state
  generation

abstract:
  We study the generation of entanglement between two species of neutral cold
atoms living on an optical ring lattice, where each group of particles can be
described by a $d$-dimensional Hilbert space (qu$d$it). Synthetic magnetic
fields are exploited to create an entangled state between the pair of qu$d$its.
Maximally entangled eigenstates are found for well defined values of the
Aharonov-Bohm phase, which are zero energy eigenstates of both the kinetic and
interacting parts of the Bose-Hubbard Hamiltonian, making them quite
exceptional and robust against certain non-perturbative fluctuations of the
Hamiltonian. We propose a protocol to reach the maximally entangled state (MES)
by starting from an initially prepared ground state. Also, an indirect method
to detect the MES by measuring the current of the particles is proposed.


title: Designing LU-QR hybrid solvers for performance and stability

abstract:
  This paper introduces hybrid LU-QR al- gorithms for solving dense linear
systems of the form Ax = b. Throughout a matrix factorization, these al-
gorithms dynamically alternate LU with local pivoting and QR elimination steps,
based upon some robustness criterion. LU elimination steps can be very
efficiently parallelized, and are twice as cheap in terms of floating- point
operations, as QR steps. However, LU steps are not necessarily stable, while QR
steps are always stable. The hybrid algorithms execute a QR step when a
robustness criterion detects some risk for instability, and they execute an LU
step otherwise. Ideally, the choice between LU and QR steps must have a small
computational overhead and must provide a satisfactory level of stability with
as few QR steps as possible. In this paper, we introduce several robustness
criteria and we establish upper bounds on the growth factor of the norm of the
updated matrix incurred by each of these criteria. In addition, we describe the
implementation of the hybrid algorithms through an exten- sion of the PaRSEC
software to allow for dynamic choices during execution. Finally, we analyze
both stability and performance results compared to state-of-the-art linear
solvers on parallel distributed multicore platforms.


title: Mid-infrared PL relations for Globular Cluster RR Lyrae

abstract:
  The period - metallicity - WISE W1- and W2-band luminosity relations are
derived for RR Lyrae stars based on WISE epoch photometry for 360 and 275 stars
in 15 and 9 Galactic globular clusters, respectively. Our final relations have
the form <MW1> = gamma(W1) - (2.381 +/- 0.097) log PF + (0.096 +/- 0.021)[Fe/H]
and <MW2> = gamma(W2)-(2.269 +/- 0.127)log PF + (0.108 +/- 0.021)[Fe/H], where
[Fe/H] values are on the scale of Carretta et al. (2009). We obtained two
appreciably discrepant estimates for the zero points gamma(W1) and gamma(W2) of
both relations: one based on a statistical-parallax analysis -- gamma(W1) =
-0.829 +/- 0.093 and gamma(W2)=-0.776 +/- 0.093 and another, significantly
brighter one, based on HST FGS trigonometric parallaxes -- gamma(W1, HST)
=-1.150 +/- 0.077 and gamma(W2, HST) =-1.105 +/- 0.077. The
period-metallicity-luminosity relations in the two bands yield highly
consistent distance moduli for the calibrator clusters and the distance moduli
computed using the W1- and W2-band relations with the HST zero points agree
well with those computed by \citet{sollima} based on their derived
period-metallicity-K-band luminosity relation whose zero point is tied to the
HST trigonometric parallax of RR Lyrae itself (Delta DM0 = +0.04 and +0.06,
respectively, with a scatter of only 0.06).


title:
Particle-in-cell simulations of laser beat-wave magnetization of dense
  plasmas

abstract:
  The interaction of two lasers with a difference frequency near that of the
ambient plasma frequency produces beat waves that can resonantly accelerate
thermal electrons. These beat waves can be used to drive electron current and
thereby embed magnetic fields into the plasma [D. R. Welch et al., Phys. Rev.
Lett. 109, 225002 (2012)]. In this paper, we present two-dimensional
particle-in-cell simulations of the beat-wave current-drive process over a wide
range of angles between the injected lasers, laser intensities, and plasma
densities. We discuss the application of this technique to the magnetization of
dense plasmas, motivated in particular by the problem of forming high-beta
plasma targets in a standoff manner for magneto-inertial fusion. The
feasibility of a near-term experiment embedding magnetic fields using lasers
with micron-scale wavelengths into a $\sim 10^{18}$-cm$^{-3}$-density plasma is
assessed.


title: The Anglo-Australian Planet Search. XXIII. Two New Jupiter Analogs

abstract:
  We report the discovery of two long-period giant planets from the
Anglo-Australian Planet Search. HD 154857c is in a multiple-planet system,
while HD 114613b appears to be solitary. HD 114613b has an orbital period
P=10.5 years, and a minimum mass m sin i of 0.48 Jupiter masses; HD 154857c has
P=9.5 years and m sin i=2.6 Jupiter masses. These new data confirm the
planetary nature of the previously unconstrained long-period object in the HD
154857 system. We have performed detailed dynamical stability simulations which
show that the HD 154857 two-planet system is stable on timescales of at least
100 million years. These results highlight the continued importance of "legacy"
surveys with long observational baselines; these ongoing campaigns are critical
for determining the population of Jupiter analogs, and hence of those planetary
systems with architectures most like our own Solar system.


title:
Emergence of a sustained current by coupling equilibrating systems:
  Making a NESS out of equilibrium

abstract:
  We show that coupling together two closed thermodynamic systems that
independently attain equilibrium may give rise to a nonequilibrium stationary
state (NESS) with a persistent, non-vanishing current. We study a simple
example that is exactly soluble, consisting of random walkers with different
biases towards a reflecting boundary, modelling, for example, Brownian
particles with different charge states in an electric field. We obtain exact
analytical expressions for the (generating functions of) concentrations and
currents in the NESS for this model, and exhibit the main features by numerical
simulation.

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


title: A photometric search for active Main Belt asteroids

abstract:
  It is well known that some Main Belt asteroids show comet-like features. A
representative example is the first known Main Belt comet 133P/(7968)
Elst-Pizarro. If the mechanisms causing this activity are too weak to develop
visually evident comae or tails, the objects stay unnoticed. We are presenting
a novel way to search for active asteroids, based on looking for objects with
deviations from their expected brightnesses in a database. Just by using the
MPCAT-OBS Observation Archive we have found five new candidate objects that
possibly show a type of comet-like activity, and the already known Main Belt
comet 133P/(7968) Elst-Pizarro. Four of the new candidates, (315) Constantia,
(1026) Ingrid, (3646) Aduatiques, and (24684) 1990 EU4, show brightness
deviations independent of the object's heliocentric distance, while (35101)
1991 PL16 shows deviations dependent on its heliocentric distance, which could
be an indication of a thermal triggered mechanism. The method could be
implemented in future sky survey programmes to detect outbursts on Main Belt
objects almost simultaneously with their occurrence.


title:
Distributed and Centralized Hybrid CSMA/CA-TDMA Schemes for Single-Hop
  Wireless Networks

abstract:
  The strength of carrier-sense multiple access with collision avoidance
(CSMA/CA) can be combined with that of time-division multiple access (TDMA) to
enhance the channel access performance in wireless networks such as the IEEE
802.15.4-based wireless personal area networks (WPANs). In particular, the
performance of legacy CSMA/CA-based medium access control (MAC) scheme in
congested networks can be enhanced through a hybrid CSMA/CA-TDMA scheme while
preserving the scalability property. In this paper, we present distributed and
centralized channel access models which follow the transmission strategies
based on Markov decision process (MDP) to access both contention period and
contention-free period in an intelligent way. The models consider the buffer
status as an indication of congestion provided that the offered traffic does
not exceed the channel capacity. We extend the models to consider the hidden
node collision problem encountered due to the signal attenuation caused by
channel fading. The simulation results show that the MDP-based distributed
channel access scheme outperforms the legacy slotted CSMA/CA scheme. This
scheme also works efficiently in a network consisting of heterogeneous nodes.
The centralized model outperforms the distributed model but requires the global
information of the network.


title:
Modeling the Optical-X-ray Accretion Lag in LMC X-3: Insights Into
  Black-Hole Accretion Physics

abstract:
  The X-ray persistence and characteristically soft spectrum of the black hole
X-ray binary LMC X-3 make this source a touchstone for penetrating studies of
accretion physics. We analyze a rich, 10-year collection of optical/infrared
(OIR) time-series data in conjunction with all available contemporaneous X-ray
data collected by the ASM and PCA detectors aboard the Rossi X-ray Timing
Explorer. A cross-correlation analysis reveals an X-ray lag of ~2 weeks.
Motivated by this result, we develop a model that reproduces the complex OIR
light curves of LMC X-3. The model is comprised of three components of
emission: stellar light; accretion luminosity from the outer disk inferred from
the time-lagged X-ray emission; and light from the X-ray-heated star and outer
disk. Using the model, we filter a strong noise component out of the
ellipsoidal light curves and derive an improved orbital period for the system.
Concerning accretion physics, we find that the local viscous timescale in the
disk increases with the local mass accretion rate; this in turn implies that
the viscosity parameter alpha decreases with increasing luminosity. Finally, we
find that X-ray heating is a strong function of X-ray luminosity below ~50% of
the Eddington limit, while above this limit X-ray heating is heavily
suppressed. We ascribe this behavior to the strong dependence of the flaring in
the disk upon X-ray luminosity, concluding that for luminosities above ~50% of
Eddington, the star lies fully in the shadow of the disk.


title:
Evolution Towards 5G Multi-tier Cellular Wireless Networks: An
  Interference Management Perspective

abstract:
  The evolving fifth generation (5G) cellular wireless networks are envisioned
to overcome the fundamental challenges of existing cellular networks, e.g.,
higher data rates, excellent end-to-end performance and user-coverage in
hot-spots and crowded areas with lower latency, energy consumption and cost per
information transfer. To address these challenges, 5G systems need to adopt a
multi-tier architecture consisting of macrocells, different types of licensed
small cells, relays, and device-to-device (D2D) networks to serve users with
different quality-of-service (QoS) requirements in a spectrum and
energy-efficient manner. Starting with the visions and requirements of 5G
multi-tier networks, this article outlines the challenges of interference
management (e.g., power control, cell association) in these networks with
shared spectrum access (i.e., when the different network tiers shares the same
licensed spectrum). It is argued that the existing interference management
schemes will not be able to address the interference management problem in
prioritized 5G multi-tier networks where users in different tiers have
different priorities for channel access. In this context, a survey and
qualitative comparison of the potential existing cell association and power
control schemes is provided to demonstrate their limitations for interference
management in 5G networks. Open challenges are highlighted and guidelines are
provided to modify the existing schemes in order to overcome these limitations
and make them suitable for the emerging 5G systems.


title:
Hadron Spectroscopy and Dynamics from Light-Front Holography and
  Conformal Symmetry

abstract:
  To a first semiclassical approximation one can reduce the multi-parton
light-front problem in QCD to an effective one-dimensional quantum field
theory, which encodes the fundamental conformal symmetry of the classical QCD
Lagrangian. This procedure leads to a relativistic light-front wave equation
for arbitrary spin which incorporates essential spectroscopic and
non-perturbative dynamical features of hadron physics. The mass scale for
confinement and higher dimensional holographic mapping to AdS space are also
emergent properties of this framework.


title:
Accurate potential energy, dipole moment curves, and lifetimes of
  vibrational states of heteronuclear alkali dimers

abstract:
  We calculate the potential energy curves, the permanent dipole moment curves,
and the lifetimes of the ground and excited vibrational states of the
heteronuclear alkali dimers XY (X, Y = Li, Na, K, Rb, Cs) in the X1{\Sigma}+
electronic state using the coupled cluster with singles doubles and triples
(CCSDT) method. All-electron quadruple-{\zeta} basis sets with additional core
functions are used for Li and Na, and small-core relativistic effective core
potentials with quadruple-{\zeta} quality basis sets are used for K, Rb and Cs.
The inclusion of the coupled cluster non-perturbative triple excitations is
shown to be crucial for obtaining the accurate potential energy curves. Large
one-electron basis set with additional core functions is needed for the
accurate prediction of permanent dipole moments. The dissociation energies are
overestimated by only 14 cm-1 for LiNa and by no more than 114 cm-1 for the
other molecules. The discrepancies between the experimental and calculated
harmonic vibrational frequencies are less than 1.7 cm-1, and the discrepancies
for the anharmonic correction are less than 0.1 cm-1. We show that correlation
between atomic electronegativity differences and permanent dipole moment of
heteronuclear alkali dimers is not perfect. To obtain the vibrational energies
and wave functions the vibrational Schr\"odinger equation is solved with the
B-spline basis set method. The transition dipole moments between all
vibrational states, the Einstein coefficients and the lifetimes of the
vibrational states are calculated. We analyze the decay rates of the
vibrational states in terms of spontaneous emission, and stimulated emission
and absorption induced by black body radiation. In all studied heteronuclear
alkali dimers the ground vibrational states have much longer lifetimes than any
excited states.


title:
Heavy-ion Collisions: Direct and indirect probes of the density and
  temperature dependence of Esym

abstract:
  Heavy-ion collisions provide a versatile terrestrial probe of the nuclear
equation of state through the formation of nuclear matter at a wide variety of
temperatures, densities, and pressures. Direct and indirect approaches for
constraining the density dependence of the symmetry energy using heavy-ion
collisions have been developed. The direct approach relies on scaling methods
which attempt to connect isotopic fragment distributions to the symmetry
energy. Using the indirect approach constraints on the equation of state are
extracted from comparison of experimental results and theoretical transport
calculations which utilize effective nucleon-nucleon interactions. Besides
exploring the density dependence of the equation of state, heavy-ion collisions
are simultaneously probing different temperature gradients of nuclear matter
allowing for the temperature dependence of the symmetry energy to be examined.
The current progress and open questions related to constraining the density and
temperature dependence of the symmetry energy with heavy-ion collisions are
discussed in the review.


title: The statistical mechanics of self-gravitating Keplerian disks

abstract:
  We describe the dynamics and thermodynamics of collisionless particle disks
orbiting a massive central body, in the case where the disk mass is small
compared to the central mass, the self-gravity of the disk dominates the
non-Keplerian force, and the spread in semi-major axes is small. We show that
with plausible approximations such disks have logarithmic two-body interactions
and a compact phase space, and therefore exhibit thermodynamics that are
simpler than most other gravitating systems, which require a confining box and
artificial softening of the potential at small scales to be thermodynamically
well-behaved. We solve for the microcanonical axisymmetric thermal equilibria
and demonstrate the existence of a symmetry-breaking bifurcation into lopsided
equilibria. We discuss the relation between thermal and dynamical instability
in these systems and draw connections to astrophysical settings, as well as to
the wider subject of the statistical mechanics of particles with logarithmic
long-range interactions, such as point vortices in two-dimensional fluids.


title:
Learning Mid-Level Features and Modeling Neuron Selectivity for Image
  Classification

abstract:
  We now know that mid-level features can greatly enhance the performance of
image learning, but how to automatically learn the image features efficiently
and in an unsupervised manner is still an open question. In this paper, we
present a very efficient mid-level feature learning approach (MidFea), which
only involves simple operations such as $k$-means clustering, convolution,
pooling, vector quantization and random projection. We explain why this simple
method generates the desired features, and argue that there is no need to spend
much time in learning low-level feature extractors. Furthermore, to boost the
performance, we propose to model the neuron selectivity (NS) principle by
building an additional layer over the mid-level features before feeding the
features into the classifier. We show that the NS-layer learns
category-specific neurons with both bottom-up inference and top-down analysis,
and thus supports fast inference for a query image. We run extensive
experiments on several public databases to demonstrate that our approach can
achieve state-of-the-art performances for face recognition, gender
classification, age estimation and object categorization. In particular, we
demonstrate that our approach is more than an order of magnitude faster than
some recently proposed sparse coding based methods.


title:
On Discrete Alphabets for the Two-user Gaussian Interference Channel
  with One Receiver Lacking Knowledge of the Interfering Codebook

abstract:
  In multi-user information theory it is often assumed that every node in the
network possesses all codebooks used in the network. This assumption is however
impractical in distributed ad-hoc and cognitive networks. This work considers
the two- user Gaussian Interference Channel with one Oblivious Receiver
(G-IC-OR), i.e., one receiver lacks knowledge of the interfering cookbook while
the other receiver knows both codebooks. We ask whether, and if so how much,
the channel capacity of the G-IC- OR is reduced compared to that of the
classical G-IC where both receivers know all codebooks. Intuitively, the
oblivious receiver should not be able to jointly decode its intended message
along with the unintended interfering message whose codebook is unavailable. We
demonstrate that in strong and very strong interference, where joint decoding
is capacity achieving for the classical G-IC, lack of codebook knowledge does
not reduce performance in terms of generalized degrees of freedom (gDoF).
Moreover, we show that the sum-capacity of the symmetric G-IC- OR is to within
O(log(log(SNR))) of that of the classical G-IC. The key novelty of the proposed
achievable scheme is the use of a discrete input alphabet for the non-oblivious
transmitter, whose cardinality is appropriately chosen as a function of SNR.


title: Polynomial Rings and Topological Strings

abstract:
  An overview is given of the construction of a differential polynomial ring of
functions on the moduli space of Calabi-Yau threefolds. These rings coincide
with the rings of quasi modular forms for geometries with duality groups for
which these are known. They provide a generalization thereof otherwise. Higher
genus topological string amplitudes can be expressed in terms of the generators
of this ring giving them a global description in the moduli space. An action of
a duality exchanging large volume and conifold loci in moduli space is
discussed. The connection to quasi modular forms is illustrated by the local
P^2 geometry and its mirror, the generalization is extended to several compact
geometries with one-dimensional moduli spaces.


title: Walker-Breaker games

abstract:
  We introduce and analyze the Walker-Breaker game, a variant of Maker-Breaker
games where Maker is constrained to choose edges of a walk or path in a given
graph G, with the goal of visiting as many vertices of the underlying graph as
possible.


title:
A Priori $hp$-estimates for Discontinuous Galerkin Approximations to
  Linear Hyperbolic Integro-Differential Equations

abstract:
  An $hp$-discontinuous Galerkin (DG) method is applied to a class of second
order linear hyperbolic integro-differential equations. Based on the analysis
of an expanded mixed type Ritz-Volterra projection, {\it a priori} $hp$-error
estimates in $L^{\infty}(L^2)$-norm of the velocity as well as of the
displacement, which are optimal in the discretizing parameter $h$ and
suboptimal in the degree of polynomial $p$ are derived. For optimal estimates
of the displacement in $L^{\infty}(L^2)$-norm with reduced regularity on the
exact solution, a variant of Baker's nonstandard energy formulation is
developed and analyzed. Results on order of convergence which are similar in
spirit to linear elliptic and parabolic problems are established for the
semidiscrete case after suitably modifying the numerical fluxes. For the
completely discrete scheme, an implicit-in-time procedure is formulated,
stability results are derived and {\it a priori} error estimates are discussed.
Finally, numerical experiments on two dimensional domains are conducted which
confirm the theoretical results.


title:
On a three level two-grid finite element method for the 2D-transient
  Navier-Stokes equations

abstract:
  In this paper, an error analysis of a three steps two level Galekin finite
element method for the two dimensional transient Navier-Stokes equations is
discussed. First of all, the problem is discretized in spatial direction by
employing finite element method on a coarse mesh $\mathcal{T} _H$ with mesh
size $H$. Then, in step two, the nonlinear system is linearized around the
coarse grid solution, say, $u_H$, which is similar to Newton's type iteration
and the resulting linear system is solved on a finer mesh $\mathcal{T}_h$ with
mesh size $h$. In step three, a correction is obtained through solving a linear
problem on the finer mesh and an updated final solution is derived. Optimal
error estimates in $L^{\infty}({\bf L}^2)$-norm, when $h=\mathcal{O}
(H^{2-\delta})$ and in $L^{\infty}(\bH^1)$-norm, when
$h=\mathcal{O}(H^{4-\delta})$ for the velocity and in $L^{\infty}(L^2)$-norm,
when $h=\mathcal{O}(H^{4-\delta})$ for the pressure are established for
arbitrarily small $\delta>0$. Further, under uniqueness assumption, these
estimates are proved to be valid uniformly in time. Then based on backward
Euler method, a completely discrete scheme is analyzed and {\it a priori} error
estimates are derived. Finally, the paper is concluded with some numerical
experiments.


title: Spontaneous Stochasticity and Anomalous Dissipation for Burgers Equation

abstract:
  We develop a Lagrangian approach to conservation-law anomalies in weak
solutions of inviscid Burgers equation, motivated by previous work on the
Kraichnan model of turbulent scalar advection. We show that the entropy
solutions of Burgers possess Markov stochastic processes of (generalized)
Lagrangian trajectories backward in time for which the Burgers velocity is a
backward martingale. This property is shown to guarantee dissipativity of
conservation-law anomalies for general convex functions of the velocity. The
backward stochastic Burgers flows with these properties are not unique,
however. We construct infinitely many such stochastic flows, both by a
geometric construction and by the zero-noise limit of the Constantin-Iyer
stochastic representation of viscous Burgers solutions. The latter proof yields
the spontaneous stochasticity of Lagrangian trajectories backward in time for
Burgers, at unit Prandtl number. It is conjectured that existence of a backward
stochastic flow with the velocity as martingale is an admissibility condition
which selects the unique entropy solution for Burgers. We also study linear
transport of passive densities and scalars by inviscid Burgers flows. We show
that shock solutions of Burgers exhibit spontaneous stochasticity backward in
time for all Prandtl numbers, implying conservation-law anomalies for linear
transport. We discuss the relation of our results for Burgers with
incompressible Navier-Stokes turbulence, especially Lagrangian admissibility
conditions for Euler solutions and the relation between turbulent cascade
directions and time-asymmetry of Lagrangian stochasticity.


title: The Ptolemy field of $3$-manifold-representations

abstract:
  The Ptolemy coordinates for boundary-unipotent SL(n,C)-representations of a
3-manifold group were introduced in Garoufalidis-Thurston-Zickert inspired by
the A-coordinates on higher Teichm\"{u}ller space due to Fock and Goncharov. In
this paper, we define the Ptolemy field of a (generic) PSL(2,\C)-representation
and prove that it coincides with the trace field of the representation. This
gives an efficient algorithm to compute the trace field of a cusped hyperbolic
manifold.


title: Lower Bounds on the Probability of a Finite Union of Events

abstract:
  In this paper, lower bounds on the probability of a finite union of events
are considered, i.e. $P\left(\bigcup_{i=1}^N A_i\right)$, in terms of the
individual event probabilities $\{P(A_i), i=1,\ldots,N\}$ and the sums of the
pairwise event probabilities, i.e., $\{\sum_{j:j\neq i} P(A_i\cap A_j),
i=1,\ldots,N\}$. The contribution of this paper includes the following: (i) in
the class of all lower bounds that are established in terms of only the
$P(A_i)$'s and $\sum_{j:j\neq i} P(A_i\cap A_j)$'s, the optimal lower bound is
given numerically by solving a linear programming (LP) problem with $N^2-N+1$
variables; (ii) a new analytical lower bound is proposed based on a relaxed LP
problem, which is at least as good as the bound due to Kuai, et al.; (iii)
numerical examples are provided to illustrate the performance of the bounds.


title:
The Generalized Point-Vortex Problem and Rotating Solutions to the
  Gross-Pitaevskii Equation on Surfaces of Revolution

abstract:
  We study the generalized point-vortex problem and the Gross-Pitaevskii
equation on surfaces of revolution. We find rotating periodic solutions to the
generalized point-vortex problem, which have two two rings of $n$ equally
spaced vortices with degrees $\pm 1$. In particular we prove the existence of
such solutions when the surface is longitudinally symmetric. Then we seek a
rotating solution to the Gross-Pitaevskii equation having vortices that follow
those of the point-vortex flow for $\varepsilon$ sufficiently small.


title:
Purcell effect with microwave drive: Suppression of qubit relaxation
  rate

abstract:
  We analyze the Purcell relaxation rate of a superconducting qubit coupled to
a resonator, which is coupled to a transmission line and pumped by an external
microwave drive. Considering the typical regime of the qubit measurement, we
focus on the case when the qubit frequency is significantly detuned from the
resonator frequency. Surprisingly, the Purcell rate decreases when the strength
of the microwave drive is increased. This suppression becomes significant in
the nonlinear regime. In the presence of the microwave drive, the loss of
photons to the transmission line also causes excitation of the qubit; however,
the excitation rate is typically much smaller than the relaxation rate. Our
analysis also applies to a more general case of a two-level quantum system
coupled to a cavity.


title: GreenMail: Reducing Email Service's Carbon Emission with Minimum Cost

abstract:
  Internet services contribute a large fraction of worldwide carbon emission
nowadays, in a context of increasing number of companies tending to provide and
more and more developers use Internet services. Noticeably, a trend is those
service providers are trying to reduce their carbon emissions by utilizing
on-site or off-site renewable energy in their datacenters in order to attract
more customers. With such efforts have been paid, there are still some users
who are aggressively calling for even cleaner Internet services. For example,
over 500,000 Facebook users petitioned the social networking site to use
renewable energy to power its datacenter. However, it seems impossible for such
demand to be satisfied merely from the inside of those production datacenters,
considering the transition cost and stability. Outside the existing Internet
services, on the other hand, may easily set up a proxy service to attract those
renewable-energy-sensitive users, by 1) using carbon neutral or even
over-offsetting cloud instances to bridge the end user and traditional Internet
services; and 2) estimating and offsetting the carbon emissions from the
traditional Internet services. In our paper, we proposed GreenMail, which is a
general IMAP proxy caching system that connects email users and traditional
email services. GreenMail runs on green web hosts to cache users' emails on
green cloud instances. Besides, it offsets the carbon emitted by traditional
backend email services. With GreenMail, users could set a carbon emission
constraint and use traditional email service without breaking any code
modification of user side and email server side.


title: A Spatio-Temporal Point Process Model for Ambulance Demand

abstract:
  Ambulance demand estimation at fine time and location scales is critical for
fleet management and dynamic deployment. We are motivated by the problem of
estimating the spatial distribution of ambulance demand in Toronto, Canada, as
it changes over discrete 2-hour intervals. This large-scale dataset is sparse
at the desired temporal resolutions and exhibits location-specific serial
dependence, daily and weekly seasonality. We address these challenges by
introducing a novel characterization of time-varying Gaussian mixture models.
We fix the mixture component distributions across all time periods to overcome
data sparsity and accurately describe Toronto's spatial structure, while
representing the complex spatio-temporal dynamics through time-varying mixture
weights. We constrain the mixture weights to capture weekly seasonality, and
apply a conditionally autoregressive prior on the mixture weights of each
component to represent location-specific short-term serial dependence and daily
seasonality. While estimation may be performed using a fixed number of mixture
components, we also extend to estimate the number of components using
birth-and-death Markov chain Monte Carlo. The proposed model is shown to give
higher statistical predictive accuracy and to reduce the error in predicting
EMS operational performance by as much as two-thirds compared to a typical
industry practice.


title: On Bayesian inference for the M/G/1 queue with efficient MCMC sampling

abstract:
  We introduce an efficient MCMC sampling scheme to perform Bayesian inference
in the M/G/1 queueing model given only observations of interdeparture times.
Our MCMC scheme uses a combination of Gibbs sampling and simple Metropolis
updates together with three novel "shift" and "scale" updates. We show that our
novel updates improve the speed of sampling considerably, by factors of about
60 to about 180 on a variety of simulated data sets.


title: On conjugate points and geodesic loops in a complete Riemannian manifold

abstract:
  A well-known Lemma in Riemannian geometry by Klingenberg says that if $x_0$
is a minimum point of the distance function $d(p,\cdot)$ to $p$ in the cut
locus $C_p$ of $p$, then either there is a minimal geodesic from $p$ to $x_0$
along which they are conjugate, or there is a geodesic loop at $p$ that
smoothly goes through $x_0$. In this paper, we prove that: for any point $q$
and any local minimum point $x_0$ of $F_q(\cdot)=d(p,\cdot)+d(q,\cdot)$ in
$C_p$, either $x_0$ is conjugate to $p$ along each minimal geodesic connecting
them, or there is a geodesic from $p$ to $q$ passing through $x_0$. In
particular, for any local minimum point $x_0$ of $d(p,\cdot)$ in $C_p$, either
$p$ and $x_0$ are conjugate along every minimal geodesic from $p$ to $x_0$, or
there is a geodesic loop at $p$ that smoothly goes through $x_0$. Earlier
results based on injective radius estimate would hold under weaker conditions.


title:
Thermal Interface Conductance between Aluminum and Silicon by Molecular
  Dynamics Simulations

abstract:
  The thermal interface conductance between Al and Si was simulated by a
non-equilibrium molecular dynamics method. In the simulations, the coupling
between electrons and phonons in Al are considered by using a stochastic force.
The results show the size dependence of the interface thermal conductance and
the effect of electron-phonon coupling on the interface thermal conductance. To
understand the mechanism of interface resistance, the vibration power spectra
are calculated. We find that the atomic level disorder near the interface is an
important aspect of interfacial phonon transport, which leads to a modification
of the phonon states near the interface. There, the vibrational spectrum near
the interface greatly differs from the bulk. This change in the vibrational
spectrum affects the results predicted by AMM and DMM theories and indicates
new physics is involved with phonon transport across interfaces. Keywords:


title: Algebraic Methods of Classifying Directed Graphical Models

abstract:
  Directed acyclic graphical models (DAGs) are often used to describe common
structural properties in a family of probability distributions. This paper
addresses the question of classifying DAGs up to an isomorphism. By considering
Gaussian densities, the question reduces to verifying equality of certain
algebraic varieties. A question of computing equations for these varieties has
been previously raised in the literature. Here it is shown that the most
natural method adds spurious components with singular principal minors, proving
a conjecture of Sullivant. This characterization is used to establish an
algebraic criterion for isomorphism, and to provide a randomized algorithm for
checking that criterion. Results are applied to produce a list of the
isomorphism classes of tree models on 4,5, and 6 nodes. Finally, some evidence
is provided to show that projectivized DAG varieties contain useful information
in the sense that their relative embedding is closely related to efficient
inference.