title: Vacuum Cherenkov radiation and bremsstrahlung from disformal couplings

abstract:
  The simplest way to modify gravity is to extend the gravitational sector to
include an additional scalar degree of freedom. The most general metric that
can be built in such a theory includes disformal terms, so that standard model
fields move on a metric which is the sum of the space time metric and a tensor
constructed from first derivatives of the scalar. In such a theory
gravitational waves and photons can propagate at different speeds, and these
can in turn be different from the maximum speed limit for matter particles. In
this work we show that disformal couplings can cause charged particles to emit
Cherenkov radiation and bremsstrahlung apparently in vacuum, depending on the
background evolution of the scalar field. We discuss the implications of this
for observations of cosmic rays, and the constraints that arise for models of
dark energy with disformal couplings.


title: Noncommutative Ergodic Theorems for Connected Amenable Groups

abstract:
  This paper is devoted to the study of noncommutative ergodic theorems for
connected amenable locally compact groups. For a dynamical system
$(\mathcal{M},\tau,G,\sigma)$, where $(\mathcal{M},\tau)$ is a von Neumann
algebra with a normal faithful finite trace and $(G,\sigma)$ is a connected
amenable locally compact group with a well defined representation on
$\mathcal{M}$, we try to find the largest noncommutative function spaces
constructed from $\mathcal{M}$ on which the individual ergodic theorems hold.
By using the Emerson-Greenleaf's structure theorem, we transfer the key
question to proving the ergodic theorems for $\mathbb{R}^d$ group actions.
Splitting the $\mathbb{R}^d$ actions problem in two cases according to
different multi-parameter convergence types---cube convergence and unrestricted
convergence, we can give maximal ergodic inequalities on $L_1(\mathcal{M})$ and
on noncommutative Orlicz space $L_1\log^{2(d-1)}L(\mathcal{M})$, each of which
is deduced from the result already known in discrete case. Finally we give the
individual ergodic theorems for $G$ acting on $L_1(\mathcal{M})$ and on
$L_1\log^{2(d-1)}L(\mathcal{M})$, where the ergodic averages are taken along
certain sequences of measurable subsets of $G$.


title:
The structure and topology of rooted weighted trees modeling layered
  cyber-security systems

abstract:
  In this paper we consider a layered-security model in which the containers
and their nestings are given in the form of a rooted tree $T$. A {\em
cyber-security model\/} is an ordered three-tuple $M = (T, C, P)$ where $C$ and
$P$ are multisets of {\em penetration costs\/} for the containers and {\em
target-acquisition values\/} for the prizes that are located within the
containers, respectively, both of the same cardinality as the set of the
non-root vertices of $T$. The problem that we study is to assign the
penetration costs to the edges and the target-acquisition values to the
vertices of the tree $T$ in such a way that minimizes the total prize that an
attacker can acquire given a limited {\em budget}. For a given assignment of
costs and target values we obtain a {\em security system}, and we discuss three
types of them: {\em improved}, {\em good}, and {\em optimal}. We show that in
general it is not possible to develop an optimal security system for a given
cyber-security model $M$. We define P- and C-models where the penetration costs
and prizes, respectively, all have unit value. We show that if $T$ is a rooted
tree such that any P- or C-model $M = (T,C,P)$ has an optimal security system,
then $T$ is one of the following types: (i) a rooted path, (ii) a rooted star,
(iii) a rooted 3-caterpillar, or (iv) a rooted 4-spider. Conversely, if $T$ is
one of these four types of trees, then we show that any P- or C-model $M =
(T,C,P)$ does have an optimal security system\@. Finally, we study a duality
between P- and C-models that allows us to translate results for P-models into
corresponding results for C-models and vice versa. The results obtained give us
some mathematical insights into how layered-security defenses should be
organized.


title:
A Study on Moving Mesh Finite Element Solution of the Porous Medium
  Equation

abstract:
  An adaptive moving mesh finite element method is studied for the numerical
solution of the porous medium equation with and without variable exponents and
absorption. The method is based on the so-called moving mesh partial
differential equation approach and employs its newly developed implementation.
Three types of mesh are considered, uniform and arclength-based and
Hessian-based adaptive meshes. The method shows a first order convergence for
uniform and arclength-based adaptive meshes and a second-order convergence for
Hessian-based adaptive meshes. It is also shown that the method can be used for
situations with complex free boundaries, emerging and splitting of free
boundaries, and the porous medium equation with variable exponents and
absorption. Two dimensional numerical results are presented.


title: Variable stars identification in digitized photographic data

abstract:
  We identify 339 known and 316 new variable stars of various types among
250000 lightcurves obtained by digitizing 167 30x30cm photographic plates of
the Moscow collection. We use these data to conduct a comprehensive test of 18
statistical characteristics (variability indices) in search for the best
general-purpose variability detection statistic. We find that the highest peak
on the DFT periodogram, interquartile range, median absolute deviation, and
Stetson's L index are the most efficient in recovering variable objects from
the set of photographic lightcurves used in our test.


title:
A Novel High-Order, Entropy Stable, 3D AMR MHD Solver with Guaranteed
  Positive Pressure

abstract:
  We describe a high-order numerical magnetohydrodynamics (MHD) solver built
upon a novel non-linear entropy stable numerical flux function that supports
eight travelling wave solutions. By construction the solver conserves mass,
momentum, and energy and is entropy stable. The method is designed to treat the
divergence-free constraint on the magnetic field in a similar fashion to a
hyperbolic divergence cleaning technique. The solver described herein is
especially well-suited for flows involving strong discontinuities. Furthermore,
we present a new formulation to guarantee positivity of the pressure. We
present the underlying theory and implementation of the new solver into the
multi-physics, multi-scale adaptive mesh refinement (AMR) simulation code
$\texttt{FLASH}$ (http://flash.uchicago.edu). The accuracy, robustness and
computational efficiency is demonstrated with a number of tests, including
comparisons to available MHD implementations in $\texttt{FLASH}$.


title:
An achromatic break in the afterglow of the short GRB 140903A: evidence
  for a narrow jet

abstract:
  We report the results of our observing campaign on GRB140903A, a nearby
(z=0.351) short duration (T90~0.3 s) gamma-ray burst discovered by Swift. We
monitored the X-ray afterglow with Chandra up to 21 days after the burst, and
detected a steeper decay of the X-ray flux after approximately 1 day. Continued
monitoring at optical and radio wavelengths showed a similar decay in flux at
nearly the same time, and we interpret it as evidence of a narrowly collimated
jet. By using the standard fireball model to describe the afterglow evolution,
we derive a jet opening angle of 5 deg and a collimation-corrected total energy
release of 2E50 erg. We further discuss the nature of the GRB progenitor
system. Three main lines disfavor a massive star progenitor: the properties of
the prompt gamma-ray emission, the age and low star-formation rate of the host
galaxy, and the lack of a bright supernova. We conclude that this event was
likely originated by a compact binary merger.


title: Identifying true satellites of the Magellanic Clouds

abstract:
  The hierarchical nature of LCDM suggests that the Magellanic Clouds must have
been surrounded by a number of satellites before their infall into the Milky
Way. Many of those satellites should still be in close proximity to the Clouds,
but some could have dispersed ahead/behind the Clouds along their Galactic
orbit. Either way, prior association with the Clouds results in strong
restrictions on the present-day positions and velocities of candidate
Magellanic satellites: they must lie close to the nearly-polar orbital plane of
the Magellanic stream, and their distances and radial velocities must follow
the latitude dependence expected for a tidal stream with the Clouds at
pericenter. We use a cosmological numerical simulation of the disruption of a
massive subhalo in a Milky Way-sized LCDM halo to test whether any of the 20
dwarfs recently-discovered in the DES, SMASH, Pan-STARRS, and ATLAS surveys are
truly associated with the Clouds. Of the 6 systems with kinematic data, only
Hydra II and Hor 1 have distances and radial velocities consistent with a
Magellanic origin. Of the remaining dwarfs, six (Hor 2, Eri 3, Ret 3, Tuc 4,
Tuc 5, and Phx 2) have positions and distances consistent with a Magellanic
origin, but kinematic data are needed to substantiate that possibility.
Conclusive evidence for association would require proper motions to constrain
the orbital angular momentum direction, which, for true Magellanic satellites,
must coincide with that of the Clouds. We use this result to predict radial
velocities and proper motions for all new dwarfs. Our results are relatively
insensitive to the assumption of first or second pericenter for the Clouds.


title:
The imprint of radial migration on the vertical structure of galaxy
  disks

abstract:
  We use numerical simulations to examine the effects of radial migration on
the vertical structure of galaxy disks. The simulations follow three
exponential disks of different mass but similar circular velocity, radial
scalelength, and (constant) scale height. The disks develop different
non-axisymmetric patterns, ranging from feeble, long-lived multiple arms to
strong, rapidly-evolving few-armed spirals. These fluctuations induce radial
migration through secular changes in the angular momentum of disk particles,
mixing the disk radially and blurring pre-existing gradients. Migration affects
primarily stars with small vertical excursions, regardless of spiral pattern.
This "provenance bias" largely determines the vertical structure of migrating
stars: inward migrators thin down as they move in, whereas outward migrators do
not thicken up but rather preserve the disk scale height at destination.
Migrators of equal birth radius thus develop a strong scale-height gradient,
not by flaring out as commonly assumed, but by thinning down as they spread
inward. Similar gradients have been observed for low-[$\alpha$/Fe]
mono-abundance populations (MAPs) in the Galaxy but our results argue against
interpreting them as a consequence of radial migration. This is because outward
migration does not lead to thickening, implying that the maximum scale height
of any population should reflect its value at birth. In contrast, Galactic MAPs
have scale heights that increase monotonically outwards, reaching values that
greatly exceed those at their presumed birth radii. Given the strong vertical
bias affecting migration, a proper assessment of the importance of radial
migration in the Galaxy should take carefully into account the strong radial
dependence of the scale heights of the various stellar populations.


title: The moving mesh code Shadowfax

abstract:
  We introduce the moving mesh code Shadowfax, which can be used to evolve a
mixture of gas, subject to the laws of hydrodynamics and gravity, and any
collisionless fluid only subject to gravity, such as cold dark matter or stars.
The code is written in C++ and its source code is made available to the
scientific community under the GNU Affero General Public License. We outline
the algorithm and the design of our implementation, and demonstrate its
validity through the results of a set of basic test problems, which are also
part of the public version. We also compare Shadowfax with a number of other
publicly available codes using different hydrodynamical integration schemes,
illustrating the advantages and disadvantages of the moving mesh technique.


title:
DISCO: A 3D Moving-Mesh Magnetohydrodynamics Code Designed for the Study
  of Astrophysical Disks

abstract:
  This work presents the publicly available moving-mesh magnetohydrodynamics
code DISCO. DISCO is efficient and accurate at evolving orbital fluid motion in
two and three dimensions, especially at high Mach number. DISCO employs a
moving-mesh approach utilizing a dynamic cylindrical mesh that can shear
azimuthally to follow the orbital motion of the gas. The moving mesh removes
diffusive advection errors and allows for longer timesteps than a static grid.
Magnetohydrodynamics is implemented in DISCO using an HLLD Riemann solver and a
novel constrained transport scheme which is compatible with the mesh motion.
DISCO is tested against a wide variety of problems, which are designed to test
its stability, accuracy and scalability. In addition, several
magnetohydrodynamics tests are performed which demonstrate the accuracy and
stability of the new constrained transport approach, including two tests of the
magneto-rotational instability (MRI); one testing the linear growth rate and
the other following the instability into the fully turbulent regime.

categories: physics.comp-ph astro-ph.EP astro-ph.GA astro-ph.HE


title:
Binary star detectability in $Kepler$ data from phase modulation of
  different types of oscillations

abstract:
  Detecting binary stars in photometric time series is traditionally done by
measuring eclipses. This requires the orbital plane to be aligned with the
observer. A new method without that requirement uses stellar oscillations to
measure delays in the light arrival time and has been successfully applied to
$\delta$ Scuti stars. However, application to other types of stars has not been
explored. To investigate this we simulated light curves with a range of input
parameters. We find a correlation between the signal-to-noise of the pulsation
modes and the time delay required to detect binary motion. The detectability of
the binarity in the simulations and in real $Kepler$ data shows strong
agreement, hence, we describe the factors that have prevented this method from
discovering binary companions to stars belonging to various classes of
pulsating stars.


title:
The novel metallic states of the cuprates: Fermi liquids with
  topological order, and strange metals

abstract:
  This article is based on a talk by S.S. at the Nambu Memorial Symposium at
the University of Chicago. We review ideas on the nature of the metallic states
of the hole-doped cuprate high temperature superconductors, with an emphasis on
the connections between the Luttinger theorem for the size of the Fermi
surface, topological quantum field theories (TQFTs), and critical theories
involving changes in the size of the Fermi surface. We begin with the
derivation of the Luttinger theorem for a Fermi liquid, using momentum balance
during a process of flux-insertion in a lattice electronic model with toroidal
boundary conditions. We then review the TQFT of the Z2 spin liquid, and
demonstrate its compatibility with the toroidal momentum balance argument. This
discussion leads naturally to a simple construction of `topological' Fermi
liquid states: the fractionalized Fermi liquid (FL*) and the algebraic charge
liquid (ACL). We present arguments for a description of the pseudogap metal of
the cuprates using Z2-FL* or Z2-ACL states with Ising-nematic order. These
pseudogap metal states are also described as Higgs phases of a SU(2) gauge
theory. The Higgs field represents local antiferromagnetism, but the
Higgs-condensed phase does not have long-range antiferromagnetic order: the
magnitude of the Higgs field determines the pseudogap, the reconstruction of
the Fermi surface, and the Ising-nematic order. Finally, we discuss the route
to the large Fermi surface Fermi liquid via the critical point where the Higgs
condensate and Ising nematic order vanish, and the application of Higgs
criticality to the strange metal.


title:
Searching for intermediate-mass black holes in globular clusters with
  gravitational microlensing

abstract:
  We discuss the potential of the gravitational microlensing method as a unique
tool to detect unambiguous signals caused by intermediate-mass black holes in
globular clusters. We select clusters near the line of sight to the Galactic
Bulge and the Small Magellanic Cloud, estimate the density of background stars
for each of them, and carry out simulations in order to estimate the
probabilities of detecting the astrometric signatures caused by black hole
lensing. We find that for several clusters, the probability of detecting such
an event is significant with available archival data from the Hubble Space
Telescope. Specifically, we find that M 22 is the cluster with the best chances
of yielding an IMBH detection via astrometric microlensing. If M 22 hosts an
IMBH of mass $10^5M_\odot$, then the probability that at least one star will
yield a detectable signal over an observational baseline of 20 years is $\sim
86\%$, while the probability of a null result is around $14\%$. For an IMBH of
mass $10^6M_\odot$, the detection probability rises to $>99\%$. Future
observing facilities will also extend the available time baseline, improving
the chance of detections for the clusters we consider.


title: Bottom-Up Discrete Symmetries for Cabibbo Mixing

abstract:
  We perform a bottom-up search for discrete non-Abelian symmetries capable of
quantizing the Cabibbo angle that parameterizes CKM mixing. Given a particular
Abelian symmetry structure in the up and down sectors, we construct
representations of the associated residual generators which explicitly depend
on the degrees of freedom present in our effective mixing matrix. We then
discretize those degrees of freedom and utilize the Groups, Algorithms,
Programming (GAP) package to close the associated finite groups. This short
study is performed in the context of recent results indicating that, without
resorting to special model-dependent corrections, no small-order finite group
can simultaneously predict all four parameters of the three-generation CKM
matrix and that only groups of $\mathcal{O}(10^{2})$ can predict the analogous
parameters of the leptonic PMNS matrix, regardless of whether neutrinos are
Dirac or Majorana particles. Therefore a natural model of flavour might instead
incorporate small(er) finite groups whose predictions for fermionic mixing are
corrected via other mechanisms.


title: Bosonic Analogue of Dirac Composite Fermi Liquid

abstract:
  We introduce a particle-hole-symmetric metallic state of bosons in a magnetic
field at odd-integer filling. This state hosts composite fermions whose energy
dispersion features a quadratic band touching and corresponding $2\pi$ Berry
flux protected by particle-hole and discrete rotation symmetries. We also
construct an alternative particle-hole symmetric state---distinct in the
presence of inversion symmetry---without Berry flux. As in the Dirac composite
Fermi liquid introduced by Son, breaking particle-hole symmetry recovers the
familiar Chern-Simons theory. We discuss realizations of this phase both in 2D
and on bosonic topological insulator surfaces, as well as signatures in
experiments and simulations.


title:
Cygnus OB2 DANCe: A high precision proper motion study of the Cygnus OB2
  association

abstract:
  We present a high-precision proper motion study of 873 X-ray and
spectroscopically selected stars in the massive OB association Cygnus OB2 as
part of the DANCe project. These were calculated from images spanning a 15 year
baseline and have typical precisions < 1 mas/yr. We calculate the velocity
dispersion in the two axes to be $\sigma_\alpha(c) = 13.0^{+0.8}_{-0.7}$ and
$\sigma_\delta(c) = 9.1^{+0.5}_{-0.5}$ km/s, using a 2-component, 2-dimensional
model that takes into account the uncertainties on the measurements. This gives
a 3-dimensional velocity dispersion of $\sigma_{3D} = 17.8 \pm 0.6$ km/s
implying a virial mass significantly larger than the observed stellar mass,
confirming that the association is gravitationally unbound. The association
appears to be dynamically unevolved, as evidenced by considerable kinematic
substructure, non-isotropic velocity dispersions and a lack of energy
equipartition. The proper motions show no evidence for a global expansion
pattern, with approximately the same amount of kinetic energy in expansion as
there is in contraction, which argues against the association being an expanded
star cluster disrupted by process such as residual gas expulsion or tidal
heating. The kinematic substructures, which appear to be close to virial
equilibrium and have typical masses of 40-400 M$_\odot$, also do not appear to
have been affected by the expulsion of the residual gas. We conclude that Cyg
OB2 was most likely born highly substructured and globally unbound, with the
individual subgroups born in (or close to) virial equilibrium, and that the OB
association has not experienced significant dynamical evolution since then.


title:
Robo-AO Kepler Planetary Candidate Survey III: Adaptive Optics Imaging
  of 1629 Kepler Exoplanet Candidate Host Stars

abstract:
  The Robo-AO \textit{Kepler} Planetary Candidate Survey is observing every
\textit{Kepler} planet candidate host star with laser adaptive optics imaging
to search for blended nearby stars, which may be physically associated
companions and/or responsible for transit false positives. We present in this
paper the results of our search for stars nearby 1629 \textit{Kepler} planet
candidate hosts. With survey sensitivity to objects as close as $\sim$0.15" and
magnitude differences $\Delta$m$\le$6, we find 223 stars in the vicinity of 206
target KOIs; 209 of these nearby stars have not previously been imaged in high
resolution. We measure an overall nearby-star probability for \textit{Kepler}
planet candidates of 12.6\%$\pm$0.9\% at separations between 0.15" and 4.0".
Particularly interesting KOI systems are discussed, including 23 stars with
detected companions which host rocky, habitable zone candidates, and five new
candidate planet-hosting quadruple star systems. We explore the broad
correlations between planetary systems and stellar binarity using the combined
dataset of Baranec et al. (2016) and this paper. Our previous 2$\sigma$ result
of a low binary fraction of KOIs hosting close-in giant planets is less
apparent in this larger dataset. We also find a significant correlation between
binary fraction and KOI number, suggesting possible variation between early and
late \textit{Kepler} data releases.


title: 750 GeV Diphotons: Implications for Supersymmetric Unification II

abstract:
  Perturbative supersymmetric gauge coupling unification is possible in six
theories where complete SU(5) TeV-scale multiplets of vector matter account for
the size of the reported $750~{\rm GeV}$ diphoton resonance, interpreted as a
singlet multiplet $S = (s+ia)/\sqrt{2}$. One of these has a full generation of
vector matter and a unified gauge coupling $\alpha_G \sim 1$. The diphoton
signal rate is enhanced by loops of vector squarks and sleptons, especially
when the trilinear $A$ couplings are large. If the $SH_u H_d$ coupling is
absent, both $s$ and $a$ can contribute to the resonance, which may then have a
large apparent width if the mass splitting from $s$ and $a$ arises from loops
of vector matter. The width depends sensitively on $A$ parameters and phases of
the vector squark and slepton masses. Vector quarks and/or squarks are expected
to be in reach of the LHC. If the $SH_uH_d$ coupling is present, $a$ leads to a
narrow diphoton resonance, while a second resonance with decays $s \rightarrow
hh, W^+ W^-,ZZ$ is likely to be discovered at future LHC runs. In some of the
theories a non-standard origin or running of the soft parameters is required,
for example involving conformal hidden sector interactions.


title: Hide-and-Seek with the Fundamental Metallicity Relation

abstract:
  We use $\sim$83,000 star-forming galaxies at $0.04<z<0.3$ from the Sloan
Digital Sky Survey to study the so-called fundamental metallicity relation
(FMR) and report on the disappearance of its anti-correlation between
metallicity and star formation rate (SFR) when using the new metallicity
indicator recently proposed by Dopita et al. In this calibration, metallicity
is primarily sensitive to the emission line ratio [NII]$\lambda$6584 /
[SII]$\lambda\lambda$6717, 6731 that is insensitive to dilution by pristine
infalling gas that may drive the FMR anti-correlation with SFR. Therefore, we
conclude that the apparent disappearance of the FMR (using this new metallicity
indicator) does not rule out its existence.


title: Deep Herschel PACS point spread functions

abstract:
  The knowledge of the point spread function (PSF) of imaging instruments
represents a fundamental requirement for astronomical observations. The
Herschel PACS PSFs delivered by the instrument control centre are obtained from
observations of the Vesta asteroid, providing a characterisation of the central
part therefore excluding fainter features. However, in many cases information
on both the core and the wings of the PSFs is needed. With this aim, we combine
Vesta and Mars dedicated observations and obtain PACS PSFs with an
unprecedented dynamic range $(\sim 10^6)$, at slow and fast scan speeds and for
the three photometric bands.


title: Polarization of prompt and afterglow emission of Gamma-Ray Bursts

abstract:
  Gamma-ray bursts and their afterglows are thought to be produced by an
ultra-relativistic jet. One of the most important open questions is the outflow
composition: the energy may be carried out from the central source either as
kinetic energy (of baryons and/or pairs), or in electromagnetic form (Poynting
flux). While the total observable flux may be indistinguishable in both cases,
its polarization properties are expected to differ markedly. The prompt
emission and afterglow polarization are also a powerful diagnostic of the jet
geometry. Again, with subtle and hardly detectable differences in the output
flux, we have distinct polarization predictions. In this review we briefly
describe the theoretical scenarios that have been developed following the
observations, and the now large observational datasets that for the prompt and
the afterglow phases are available. Possible implications of polarimetric
measurements for quantum gravity theory testing are discussed, and future
perspectives for the field briefly mentioned.


title: Comparing Simulations of AGN Feedback

abstract:
  We perform adaptive mesh refinement (AMR) and smoothed particle hydrodynamics
(SPH) cosmological zoom simulations of a region around a forming galaxy
cluster, comparing the ability of the methods to handle successively more
complex baryonic physics. In the simplest, non-radiative case, the two methods
are in good agreement with each other, but the SPH simulations generate central
cores with slightly lower entropies and virial shocks at slightly larger radii,
consistent with what has been seen in previous studies. The inclusion of
radiative cooling, star formation, and stellar feedback leads to much larger
differences between the two methods. Most dramatically, at z=5, rapid cooling
in the AMR case moves the accretion shock well within the virial radius, while
this shock remains near the virial radius in the SPH case, due to excess
heating, coupled with poorer capturing of the shock width. On the other hand,
the addition of feedback from active galactic nuclei (AGN) to the simulations
results in much better agreement between the methods. In this case both
simulations display halo gas entropies of 100 keV cm^2, similar decrements in
the star-formation rate, and a drop in the halo baryon content of roughly 30%.
This is consistent with AGN growth being self-regulated, regardless of the
numerical method. However, the simulations with AGN feedback continue to differ
in aspects that are not self-regulated, such that in SPH a larger volume of gas
is impacted by feedback, and the cluster still has a lower entropy central
core.


title: Elucidating Reaction Mechanisms on Quantum Computers

abstract:
  We show how a quantum computer can be employed to elucidate reaction
mechanisms in complex chemical systems, using the open problem of biological
nitrogen fixation in nitrogenase as an example. We discuss how quantum
computers can augment classical-computer simulations for such problems, to
significantly increase their accuracy and enable hitherto intractable
simulations. Detailed resource estimates show that, even when taking into
account the substantial overhead of quantum error correction, and the need to
compile into discrete gate sets, the necessary computations can be performed in
reasonable time on small quantum computers. This demonstrates that quantum
computers will realistically be able to tackle important problems in chemistry
that are both scientifically and economically significant.


title:
From Neutron Star Observables to the Equation of State. I. An Optimal
  Parametrization

abstract:
  The increasing number and precision of measurements of neutron star masses,
radii, and, in the near future, moments of inertia offer the possibility of
precisely determining the neutron star equation of state. One way to facilitate
the mapping of observables to the equation of state is through a
parametrization of the latter. We present here a generic method for optimizing
the parametrization of any physically allowed EoS. We use mock equations of
state that incorporate physically diverse and extreme behavior to test how well
our parametrization reproduces the global properties of the stars, by
minimizing the errors in the observables mass, radius, and the moment of
inertia. We find that using piecewise polytropes and sampling the EoS with five
fiducial densities between ~1-8 times the nuclear saturation density results in
optimal errors for the smallest number of parameters. Specifically, it
recreates the radii of the assumed EoS to within less than 0.5 km for the
extreme mock equations of state and to within less than 0.12 km for 95% of a
sample of 42 proposed, physically-motivated equations of state. Such a
parametrization is also able to reproduce the maximum mass to within 0.04 M_sun
and the moment of inertia of a 1.338 M_sun neutron star to within less than 10%
for 95% of the proposed sample of equations of state.


title: Single crystal growth by the traveling solvent technique: A review

abstract:
  A description is given of the traveling solvent technique, which has been
used for the crystal growth of both congruently and incongruently melting
materials of many classes of intermetallic, chalcogenide, semiconductor and
oxide materials. The use of a solvent, growth at lower temperatures and the
zoning process, that are inherent ingredients of the method, can help to grow
large, high structural quality, high purity crystals. In order to optimize this
process, careful control of the various growth variables is imperative;
however, this can be difficult to achieve due to the large number of
independent experimental parameters that can be grouped under the broad
headings growth conditions, characteristics of the material being grown, and
experimental configuration, setup and design.This review attempts to describe
the principles behind the traveling solvent technique and the various
experimental variables. Guidelines are detailed to provide the information
necessary to allow closer control of the crystal growth process through a
systematic approach. Comparison is made between the traveling solvent technique
and other crystal growth methods, in particular the more conventional
stationary flux method. The use of optical heating is described in detail and
successful traveling solvent growth by optical heating is reported for the
first time for crystals of $Tl_5Te_3$, $Cd_3As_2$, and $FeSc_2S_4$ (using Te,
Cd and FeS fluxes, respectively).


title:
The Normalization of Co-authorship Networks in the Bibliometric
  Evaluation: The Government Stimulation Programs of China and Korea

abstract:
  Using co-authored publications between China and Korea in Web of Science
(WoS) during the one-year period of 2014, we evaluate the government
stimulation program for collaboration between China and Korea. In particular,
we apply dual approaches, full integer vs. fractional counting, to
collaborative publications in order to better examine both the patterns and
contents of Sino-Korean collaboration networks in terms of individual countries
and institutions. We first conduct a semi-automatic network analysis of
Sino-Korean publications based on the full-integer counting method, and then
compare our categorization with contextual rankings using the fractional
technique; routines for fractional counting of WoS data are made available at
http://www.leydesdorff.net/software/fraction . Increasing international
collaboration leads paradoxically to lower numbers of publications and
citations using fractional counting for performance measurement. However,
integer counting is not an appropriate measure for the evaluation of the
stimulation of collaborations. Both integer and fractional analytics can be
used to identify important countries and institutions, but with other research
questions.


title:
Variability of structural and electronic properties of bulk and
  monolayer Si2Te3

abstract:
  Since the emergence of monolayer graphene as a promising two-dimensional
material, many other monolayer and few-layer materials have been investigated
extensively. An experimental study of few-layer Si2Te3 was recently reported,
showing that the material has diverse properties for potential applications in
Si-based devices ranging from fully integrated thermoelectrics to
optoelectronics to chemical sensors. This material has a unique layered
structure: it has a hexagonal closed-packed Te sublattice, with Si dimers
occupying octahedral intercalation sites. Here we report a theoretical study of
this material in both bulk and monolayer form, unveiling a fascinating array of
diverse properties arising from reorientations of the silicon dimers between
planes of Te atoms. The lattice constant varies up to 5% and the band gap
varies up to 40% depending on dimer orientations. The monolayer band gap is 0.4
eV larger than the bulk-phase value for the lowest-energy configuration of Si
dimers. These properties are, in principle, controllable by temperature and
strain, making Si2T3 a promising candidate material for nanoscale mechanical,
optical, and memristive devices.


title:
Identifying the "true" radius of the hot sub-Neptune CoRoT-24b by mass
  loss modelling

abstract:
  For the hot exoplanets CoRoT-24b and CoRoT-24c, observations have provided
transit radii R$_{\rm T}$ of 3.7$\pm$0.4 R$_{\oplus}$ and 4.9$\pm$0.5
R$_{\oplus}$, and masses of $\le$5.7 M$_{\oplus}$ and 28$\pm$11 M$_{\oplus}$,
respectively. We study their upper atmosphere structure and escape applying an
hydrodynamic model. Assuming R$_{\rm T} \approx$ R$_{\rm PL}$, where R$_{\rm
PL}$ is the planetary radius at the pressure of 100 mbar, we obtained for
CoRoT-24b unrealistically high thermally-driven hydrodynamic escape rates. This
is due to the planet's high temperature and low gravity, independent of the
stellar EUV flux. Such high escape rates could last only for $<$100 Myr, while
R$_{\rm PL}$ shrinks till the escape rate becomes less than or equal to the
maximum possible EUV-driven escape rate. For CoRoT-24b, R$_{\rm PL}$ must be
therefore located at $\approx 1.9-2.2$ R$_{\oplus}$ and high altitude
hazes/clouds possibly extinct the light at R$_{\rm T}$. Our analysis
constraints also the planet's mass to be 5$-$5.7 M$_{\oplus}$. For CoRoT-24c,
R$_{\rm PL}$ and R$_{\rm T}$ lie too close together to be distinguished in the
same way. Similar differences between R$_{\rm PL}$ and R$_{\rm T}$ may be
present also for other hot, low-density sub-Neptunes.


title:
Holding all the ASes: Identifying and Circumventing the Pitfalls of
  AS-aware Tor Client Design

abstract:
  Traffic correlation attacks to de-anonymize Tor users are possible when an
adversary is in a position to observe traffic entering and exiting the Tor
network. Recent work has brought attention to the threat of these attacks by
network-level adversaries (e.g., Autonomous Systems). We perform a historical
analysis to understand how the threat from AS-level traffic correlation attacks
has evolved over the past five years. We find that despite a large number of
new relays added to the Tor network, the threat has grown. This points to the
importance of increasing AS-level diversity in addition to capacity of the Tor
network.
  We identify and elaborate on common pitfalls of AS-aware Tor client design
and construction. We find that succumbing to these pitfalls can negatively
impact three major aspects of an AS-aware Tor client -- (1) security against
AS-level adversaries, (2) security against relay-level adversaries, and (3)
performance. Finally, we propose and evaluate a Tor client -- Cipollino --
which avoids these pitfalls using state-of-the-art in network-measurement. Our
evaluation shows that Cipollino is able to achieve better security against
network-level adversaries while maintaining security against relay-level
adversaries and


title:
Doublon-holon binding as origin of Mott transition and fractionalized
  spin liquid -- Asymptotic solution of the Hubbard model in the limit of large
  coordination

abstract:
  An analytical solution of the Mott transition is obtained for the Hubbard
model on the Bethe lattice in the large coordination number ($z$) limit. The
excitonic binding of doublons (doubly occupied sites) and holons (empty sites)
is shown to be the origin of a continuous Mott transition between a metal and
an emergent quantum spin liquid insulator. The doublon-holon binding theory
enables a different large-$z$ limit and a different phase structure than the
dynamical meanfield theory by allowing intersite spinon correlations to lift
the $2^N$-fold degeneracy of the local moments in the insulating phase. We show
that the spinons are coupled to doublons/holons by a dissipative compact U(1)
gauge field that is in the deconfined phase, stabilizing the spin-charge
separated gapless spin liquid Mott insulator.


title: Giant Lyman-Alpha Nebulae in the Illustris Simulation

abstract:
  Several `giant' Lyman-$\alpha$ (Ly$\alpha$) nebulae with extent $\gtrsim
300\,$kpc and observed Ly$\alpha$ luminosity of $\gtrsim 10^{44}\,{\rm
erg}\,{\rm s}^{-1}\,{\rm cm}^{-2}\,{\rm arcsec}^{-2}$ have recently been
detected, and it has been speculated that their presence hints at a substantial
cold gas reservoir in small cool clumps not resolved in modern hydro-dynamical
simulations. We use the Illustris simulation to predict the Ly$\alpha$ emission
emerging from large halos ($M > 10^{11.5}M_{\odot}$) at $z\sim 2$ and thus test
this model. We consider both AGN and star driven ionization, and compare the
simulated surface brightness maps, profiles and Ly$\alpha$ spectra to a model
where most gas is clumped below the simulation resolution scale. We find that
with Illustris no additional clumping is necessary to explain the extents,
luminosities and surface brightness profiles of the `giant Ly$\alpha$ nebulae'
observed. Furthermore, the maximal extents of the objects show a wide spread
for a given luminosity and do not correlate significantly with any halo
properties. We also show how the detected size depends strongly on the employed
surface brightness cutoff, and predict that further such objects will be found
in the near future.


title: Optical flux behaviour of a sample of Fermi blazars

abstract:
  Aims: We aim at investigating the time-behaviour of a sample of gamma-ray
blazars. We present the results from a 13 month-long optical photometry
monitoring campaign of the blazars PKS 0048-097, PKS 0754+100, HB89 0827+243,
PKS 0851+202, PKS 1253-055, PKS1510-089, PKS 1749+096, PKS 2230+114 and PKS
2251+158. Methods: We analyse the variability of each object, focusing on
different time-scales (long term, short term, and microvariability), in an
attempt to achieve a statistical comparison of the results. Results: After
applying a geometric model to explain the variability results, we found that it
is possible that a slight change in the direction of the jet generates the
variations detected in some objects during this campaign.


title: The bimodal initial mass function in the Orion Nebula Cloud

abstract:
  Due to its youth, proximity and richness the Orion Nebula Cloud (ONC) is an
ideal testbed to obtain a comprehensive view on the Initial Mass Function (IMF)
down to the planetary mass regime. Using the HAWK-I camera at the VLT, we have
obtained an unprecedented deep and wide near-infrared JHK mosaic of the ONC
(90% completeness at K~19.0mag, 22'x28). Applying the most recent isochrones
and accounting for the contamination of background stars and galaxies, we find
that ONC's IMF is bimodal with distinct peaks at about 0.25 and 0.025 M_sun
separated by a pronounced dip at the hydrogen burning limit (0.08 M_sun), with
a depth of about a factor 2-3 below the log-normal distribution. Apart from
~920 low-mass stars (M < 1.4 M_sun) the IMF contains ~760 brown dwarf (BD)
candidates and ~160 isolated planetary mass object (IPMO) candidates with M >
0.005 M_sun, hence about ten times more substellar candidates than known
before. The substellar IMF peak at 0.025 M_sun could be caused by BDs and IPMOs
which have been ejected from multiple systems during the early star-formation
process or from circumstellar disks.


title: Symmetry constraints on many-body localization

abstract:
  We derive general constraints on the existence of many-body localized (MBL)
phases in the presence of global symmetries, and show that MBL is not possible
with symmetry groups that protect multiplets (e.g. all non-Abelian symmetry
groups). Based on simple representation theoretic considerations, we derive
general Mermin-Wagner-type principles governing the possible alternative fates
of non-equilibrium dynamics in isolated, strongly disordered quantum systems.
Our results rule out the existence of MBL symmetry protected topological phases
with non-Abelian symmetry groups, as well as time-reversal symmetry protected
electronic topological insulators, and in fact all fermion topological
insulators and superconductors in the 10-fold way classification. Moreover,
extending our arguments to systems with intrinsic topological order, we rule
out MBL phases with non-Abelian anyons as well as certain classes of symmetry
enriched topological orders.


title: Geometry of the Scalar Sector

abstract:
  The $S$-matrix of a quantum field theory is unchanged by field redefinitions,
and so only depends on geometric quantities such as the curvature of field
space. Whether the Higgs multiplet transforms linearly or non-linearly under
electroweak symmetry is a subtle question since one can make a coordinate
change to convert a field that transforms linearly into one that transforms
non-linearly. Renormalizability of the Standard Model (SM) does not depend on
the choice of scalar fields or whether the scalar fields transform linearly or
non-linearly under the gauge group, but only on the geometric requirement that
the scalar field manifold ${\mathcal M}$ is flat. We explicitly compute the
one-loop correction to scalar scattering in the SM written in non-linear
Callan-Coleman-Wess-Zumino (CCWZ) form, where it has an infinite series of
higher dimensional operators, and show that the $S$-matrix is finite. Standard
Model Effective Field Theory (SMEFT) and Higgs Effective Field Theory (HEFT)
have curved ${\mathcal M}$, since they parametrize deviations from the flat SM
case. We show that the HEFT Lagrangian can be written in SMEFT form if and only
if ${\cal M}$ has a $SU(2)_L \times U(1)_Y$ invariant fixed point. Experimental
observables in HEFT depend on local geometric invariants of ${\mathcal M}$ such
as sectional curvatures, which are of order $1/\Lambda^2$, where $\Lambda$ is
the EFT scale. We give explicit expressions for these quantities in terms of
the structure constants for a general $\mathcal G \to \mathcal H$ symmetry
breaking pattern. (Full abstract in pdf)


title: Traces on Topological Graph Algebras

abstract:
  Given a topological graph $E$, we give a complete description of tracial
states on the C*-algebra $\mathrm{C}^*(E)$ which are invariant under the gauge
action; there is an affine homeomorphism between the space of gauge invariant
tracial states on $\mathrm{C}^*(E)$ and Radon probability measures on the
vertex space $E^0$ which are, in a suitable sense, invariant under the action
of the edge space $E^1$. It is shown that if $E$ has no cycles, then every
tracial state on $\mathrm{C}^*(E)$ is gauge invariant. When $E^0$ is totally
disconnected, the gauge invariant tracial states on $\mathrm{C}^*(E)$ are in
bijection with the states on $\mathrm{K}_0(\mathrm{C}^*(E))$.


title: Errors and pseudo-thresholds for incoherent and coherent noise

abstract:
  We compare the effect of single qubit incoherent and coherent errors on the
logical error rate of the Steane [[7,1,3]] quantum error correction code by
performing an exact full-density-matrix simulation of an error correction step.
We find that the effective 1-qubit process matrix at the logical level reveals
the key differences between the error models and provides insight into why the
Pauli twirling approximation is a good approximation for incoherent errors and
a poor approximation for coherent ones. Approximate channels composed of
Clifford operations and Pauli measurement operators that are pessimistic at the
physical level result in pessimistic error rates at the logical level. In
addition, we observe that the pseudo-threshold can differ by a factor of five
depending on whether the error is calculated using the fidelity or the
distance.


title: Generalized Spatial Talbot Effect based on All-dielectric Metasurfaces

abstract:
  A generalized spatial Talbot effect is proposed where the period of the input
aperture is scaled by a non-integer real value, as opposed to the integer-only
factor in a conventional Talbot effect. This is achieved by allowing and
engineering the phase discontinuity distributions in space using metasurfaces,
in conjunction with free-space propagation. The introduction of such abrupt
phase discontinuities thereby enables non-integer scalings of the aperture
periodicities. Specific implementations using Huygens' metasurfaces are
proposed and their operation to achieve non-integer scaling of the input
aperture period is demonstrated using numerical results based on Fourier
propagation.


title: Lighting up stars in chemical evolution models: the CMD of Sculptor

abstract:
  We present a novel approach to draw the synthetic color-magnitude diagram of
galaxies, which can provide - in principle - a deeper insight in the
interpretation and understanding of current observations. In particular, we
`light up' the stars of chemical evolution models, according to their initial
mass, metallicity and age, to eventually understand how the assumed underlying
galaxy formation and evolution scenario affects the final configuration of the
synthetic CMD. In this way, we obtain a new set of observational constraints
for chemical evolution models beyond the usual photospheric chemical
abundances. The strength of our method resides in the very fine grid of
metallicities and ages of the assumed database of stellar isochrones. In this
work, we apply our photo-chemical model to reproduce the observed CMD of the
Sculptor dSph and find that we can reproduce the main features of the observed
CMD. The main discrepancies are found at fainter magnitudes in the main
sequence turn-off and sub-giant branch, where the observed CMD extends towards
bluer colors than the synthetic one; we suggest that this is a signature of
metal-poor stellar populations in the data, which cannot be captured by our
assumed one-zone chemical evolution model.


title: Practical engineering of hard spin-glass instances

abstract:
  Recent technological developments in the field of experimental quantum
annealing have made prototypical annealing optimizers with hundreds of qubits
commercially available. The experimental demonstration of a quantum speedup for
optimization problems has since then become a coveted, albeit elusive goal.
Recent studies have shown that the so far inconclusive results, regarding a
quantum enhancement, may have been partly due to the benchmark problems used
being unsuitable. In particular, these problems had inherently too simple a
structure, allowing for both traditional resources and quantum annealers to
solve them with no special efforts. The need therefore has arisen for the
generation of harder benchmarks which would hopefully possess the
discriminative power to separate classical scaling of performance with size,
from quantum. We introduce here a practical technique for the engineering of
extremely hard spin glass Ising-type problem instances that does not require
`cherry picking' from large ensembles of randomly generated instances. We
accomplish this by treating the generation of hard optimization problems itself
as an optimization problem, for which we offer a heuristic algorithm that
solves it. We demonstrate the genuine thermal hardness of our generated
instances by examining them thermodynamically and analyzing their energy
landscapes, as well as by testing the performance of various state-of-the art
algorithms on them. We argue that a proper characterization of the generated
instances offers a practical, efficient way to properly benchmark experimental
quantum annealers, as well as any other optimization algorithm.


title: On the center of distances

abstract:
  In this paper we introduce the notion of the center of distances of a metric
space, which is required for a generalization of the theorem by J. von Neumann
about permutations of two sequences with the same set of cluster points in a
compact metric space. Also, the introduced notion is used to study sets of
subsums of some sequences of positive reals, as well for some impossibility
proofs. We compute the center of distances of the Cantorval, which is the set
of subsums of the sequence $\frac34, \frac12, \frac3{16}, \frac18, \ldots ,
\frac3{4^n}, \frac2{4^n}, \ldots$, and also for some related subsets of the
reals.


title: On the ultimate uncertainty of the top quark pole mass

abstract:
  We combine the known asymptotic behaviour of the QCD perturbation series
expansion, which relates the pole mass of a heavy quark to the MSbar mass, with
the exact series coefficients up to the four-loop order to determine the
ultimate uncertainty of the top-quark pole mass due to the renormalon
divergence. We perform extensive tests of our procedure by varying the number
of colours and flavours, as well as the scale of the strong coupling and the
MSbar mass. Including an estimate of the internal bottom and charm quark mass
effect, we conclude that this uncertainty is around 110 MeV. We further
estimate the additional contribution to the mass relation from the five-loop
correction and beyond to be around 300 MeV.


title: Imperfect Mirrors of the Standard Model

abstract:
  Inspired by the Standard Model of particle physics, we discuss a mechanism
for constructing chiral, anomaly-free gauge theories. The gauge symmetries and
particle content of such theories are identified using subgroups and complex
representations of simple anomaly-free Lie groups, such as $SO(10)$ or $E_6$.
We explore, using mostly $SO(10)$ and the $\mathbf{16}$ representation, several
of these "imperfect copies" of the Standard Model, including $U(1)^N$ theories,
$SU(5)\otimes U(1)$ theories, $SU(4)\otimes U(1)^2$ theories with 4-plets and
6-plets, and chiral $SU(3)\otimes SU(2)\otimes U(1)$. A few general properties
of such theories are discussed, as well as how they might shed light on nonzero
neutrino masses, the dark matter puzzle, and other phenomenologically relevant
questions.


title: Optimal diabatic dynamics of Majorana-based quantum gates

abstract:
  In topological quantum computing, unitary operations on qubits are performed
by adiabatic braiding of non-Abelian quasiparticles, such as Majorana zero
modes, and are protected from local environmental perturbations. In the
adiabatic regime, with timescales set by the inverse gap of the system, the
errors can be made arbitrarily small by performing the process more slowly. To
enhance the performance of quantum information processing with Majorana zero
modes, we apply the theory of optimal control to the diabatic dynamics of
Majorana-based qubits. While we sacrifice complete topological protection, we
impose constraints on the optimal protocol to take advantage of the nonlocal
nature of topological information and increase the robustness of our gates. By
using the Pontryagin's maximum principle, we show that robust equivalent gates
to perfect adiabatic braiding can be implemented in finite times through
optimal pulses. In our implementation, modifications to the device Hamiltonian
are avoided. Focusing on thermally isolated systems, we study the effects of
calibration errors and external white and $1/f$ (pink) noise on Majorana-based
gates. While a noise-induced antiadiabatic behavior, where a slower process
creates more diabatic excitations, prohibits indefinite enhancement of the
robustness of the adiabatic scheme, our fast optimal protocols exhibit
remarkable stability to noise and have the potential to significantly enhance
the practical performance of Majorana-based information processing.


title: Asymptotics of Ramsey numbers of double stars

abstract:
  A double star $S(n,m)$ is the graph obtained by joining the center of a star
with $n$ leaves to a center of a star with $m$ leaves by an edge. Let
$r(S(n,m))$ denote the Ramsey number of the double star $S(n,m)$.
  In 1979 Grossman, Harary and Klawe have shown that $$r(S(n,m)) =
\max\{n+2m+2,2n+2\}$$ for $3 \leq m \leq n\leq \sqrt{2}m$ and $3m \leq n$. They
conjectured that equality holds for all $m,n \geq 3$. Using a flag algebra
computation, we extend their result showing that $r(S(n,m))\leq n+ 2m + 2$ for
$m \leq n \leq 1.699m$. On the other hand, we show that the conjecture fails
for $\frac{7}{4}m +o(m)\leq n \leq \frac{105}{41}m-o(m)$. Our examples
additionally give a negative answer to a question of Erd\H{o}s, Faudree,
Rousseau and Schelp from 1982.


title: On the Lattice Distortion Problem

abstract:
  We introduce and study the \emph{Lattice Distortion Problem} (LDP). LDP asks
how "similar" two lattices are. I.e., what is the minimal distortion of a
linear bijection between the two lattices? LDP generalizes the Lattice
Isomorphism Problem (the lattice analogue of Graph Isomorphism), which simply
asks whether the minimal distortion is one.
  As our first contribution, we show that the distortion between any two
lattices is approximated up to a $n^{O(\log n)}$ factor by a simple function of
their successive minima. Our methods are constructive, allowing us to compute
low-distortion mappings that are within a $2^{O(n \log \log n/\log n)}$ factor
of optimal in polynomial time and within a $n^{O(\log n)}$ factor of optimal in
singly exponential time. Our algorithms rely on a notion of basis reduction
introduced by Seysen (Combinatorica 1993), which we show is intimately related
to lattice distortion. Lastly, we show that LDP is NP-hard to approximate to
within any constant factor (under randomized reductions), by a reduction from
the Shortest Vector Problem.


title:
Spectral boundary value problems for Laplace--Beltrami operator: moduli
  of continuity of eigenvalues under domain deformation

abstract:
  The paper is pertaining to the spectral theory of operators and boundary
value problems for differential equations on manifolds. Eigenvalues of such
problems are studied as functionals on the space of domains. Resolvent
continuity of the corresponding operators is established under domain
deformation and estimates of continuity moduli of their eigenvalues $\slash$
eigenfunctions are obtained provided the boundary of nonperturbed domain is
locally represented as a graph of some continuous function and domain
deformation is measured with respect to the Hausdorff--Pompeiu metric.


title: Bass-SIR model for diffusion of new products

abstract:
  We consider the diffusion of new products in social networks, where consumers
who adopt the product can later "recover" and stop influencing others to adopt
the product. We show that the diffusion is not described by the SIR model, but
rather by a novel model, the Bass-SIR model, which combines the Bass model for
diffusion of new products with the SIR model for epidemics. The phase
transition of consumers from non-adopters to adopters is described by a
non-standard Kolmogorov-Johnson-Mehl-Avrami model, in which clusters growth is
limited by adopters' recovery. Therefore, diffusion in the Bass-SIR model only
depends on the local structure of the social network, but not on the average
distance between consumers. Consequently, unlike the SIR model, a small-worlds
structure has a negligible effect on the diffusion. Surprisingly, diffusion on
scale-free networks is nearly identical to that on Cartesian ones.


title: Interpolative Butterfly Factorization

abstract:
  This paper introduces the interpolative butterfly factorization for nearly
optimal implementation of several transforms in harmonic analysis, when their
explicit formulas satisfy certain analytic properties and the matrix
representations of these transforms satisfy a complementary low-rank property.
A preliminary interpolative butterfly factorization is constructed based on
interpolative low-rank approximations of the complementary low-rank matrix. A
novel sweeping matrix compression technique further compresses the preliminary
interpolative butterfly factorization via a sequence of structure-preserving
low-rank approximations. The sweeping procedure propagates the low-rank
property among neighboring matrix factors to compress dense submatrices in the
preliminary butterfly factorization to obtain an optimal one in the butterfly
scheme. For an $N\times N$ matrix, it takes $O(N\log N)$ operations and
complexity to construct the factorization as a product of $O(\log N)$ sparse
matrices, each with $O(N)$ nonzero entries. Hence, it can be applied rapidly in
$O(N\log N)$ operations. Numerical results are provided to demonstrate the
effectiveness of this algorithm.


title:
Monte Carlo radiation transfer simulations of photospheric emission in
  long-duration Gamma-Ray Bursts

abstract:
  We present MCRaT, a Monte Carlo Radiation Transfer code for self-consistently
computing the light curves and spectra of the photospheric emission from
relativistic, unmagnetized jets. We apply MCRaT to a relativistic hydrodynamic
simulation of a long duration gamma-ray burst jet, and present the resulting
light-curves and time-dependent spectra for observers at various angles from
the jet axis. We compare our results to observational results and find that
photospheric emission is a viable model to explain the prompt phase of
long-duration gamma-ray bursts at the peak frequency and above, but faces
challenges in reproducing the flat spectrum below the peak frequency. We
finally discuss possible limitations of these results both in terms of the
hydrodynamics and the radiation transfer and how these limitations could affect
the conclusions that we present.


title:
Viscous extended holographic Ricci dark energy in the framework of
  standard Eckart theory

abstract:
  In the present work we report a study on the viscous extended holographic
Ricci dark energy (EHRDE) model under the assumption of existence of bulk
viscosity in the linear barotropic fluid and the EHRDE in the framework of
standard Eckart theory of relativistic irreversible thermodynamics and it has
been observed that the non-equilibrium bulk viscous pressure is significantly
smaller than the local equilibrium pressure. We have studied the equation of
state (EoS) parameter and observed that the EoS behaves like "quintom" and is
consistent with the constraints set by observational data sets from SNLS3, BAO
and Planck + WMAP9 + WiggleZ measurements in the reference S. Kumar and L. Xu,
\emph{Phys. Lett. B},\textbf{737}, 244 (2014). Analysis of statefinder
parameters has shown the possibility of attainment of $\Lambda$CDM phase under
current model and at the same time it has been pointed out that the for $z=0$
i.e. current universe, the statefinder pair is different from that of
$\Lambda$CDM and the $\Lambda$CDM can be attained in a later stage of the
universe. An analysis of stability has shown that although the viscous EHRDE
along with viscous barotropic is classically unstable in the present epoch, it
can lead to a stable universe in very late stage. Considering an universe
enveloped by event horizon we have observed validity of generalized second law
of thermodynamics.


title:
Rigidity of geodesic completeness in the Brinkmann class of
  gravitational wave spacetimes

abstract:
  We consider restrictions placed by geodesic completeness on spacetimes
possessing a null parallel vector field, the so-called Brinkmann spacetimes.
This class of spacetimes includes important idealized gravitational wave models
in General Relativity, namely the plane-fronted waves with parallel rays, or
pp-waves, which in turn have been intensely and fruitfully studied in the
mathematical and physical literatures for over half a century. More concretely,
we prove a restricted version of a conjectural analogue for Brinkmann
spacetimes of a rigidity result obtained by M.T. Anderson for stationary
spacetimes. We also highlight its relation with a long-standing 1962 conjecture
by Ehlers and Kundt. Indeed, it turns out that the subclass of Brinkmann
spacetimes we consider in our main theorem is enough to settle an important
special case of the Ehlers-Kundt conjecture in terms of the well known class of
Cahen-Wallach spaces.


title: Coarrays, MUSIC, and the Cram\'er Rao Bound

abstract:
  Sparse linear arrays, such as co-prime arrays and nested arrays, have the
attractive capability of providing enhanced degrees of freedom. By exploiting
the coarray structure, an augmented sample covariance matrix can be constructed
and MUSIC (MUtiple SIgnal Classification) can be applied to identify more
sources than the number of sensors. While such a MUSIC algorithm works quite
well, its performance has not been theoretically analyzed. In this paper, we
derive a simplified asymptotic mean square error (MSE) expression for the MUSIC
algorithm applied to the coarray model, which is applicable even if the source
number exceeds the sensor number. We show that the directly augmented sample
covariance matrix and the spatial smoothed sample covariance matrix yield the
same asymptotic MSE for MUSIC. We also show that when there are more sources
than the number of sensors, the MSE converges to a positive value instead of
zero when the signal-to-noise ratio (SNR) goes to infinity. This finding
explains the "saturation" behavior of the coarray-based MUSIC algorithms in the
high SNR region observed in previous studies. Finally, we derive the
Cram\'er-Rao bound (CRB) for sparse linear arrays, and conduct a numerical
study of the statistical efficiency of the coarray-based estimator.
Experimental results verify theoretical derivations and reveal the complex
efficiency pattern of coarray-based MUSIC algorithms.


title:
ASP Vision: Optically Computing the First Layer of Convolutional Neural
  Networks using Angle Sensitive Pixels

abstract:
  Deep learning using convolutional neural networks (CNNs) is quickly becoming
the state-of-the-art for challenging computer vision applications. However,
deep learning's power consumption and bandwidth requirements currently limit
its application in embedded and mobile systems with tight energy budgets. In
this paper, we explore the energy savings of optically computing the first
layer of CNNs. To do so, we utilize bio-inspired Angle Sensitive Pixels (ASPs),
custom CMOS diffractive image sensors which act similar to Gabor filter banks
in the V1 layer of the human visual cortex. ASPs replace both image sensing and
the first layer of a conventional CNN by directly performing optical edge
filtering, saving sensing energy, data bandwidth, and CNN FLOPS to compute. Our
experimental results (both on synthetic data and a hardware prototype) for a
variety of vision tasks such as digit recognition, object recognition, and face
identification demonstrate using ASPs while achieving similar performance
compared to traditional deep learning pipelines.


title: Bringing the Cloud to Rural and Remote Areas - Cloudlet by Cloudlet

abstract:
  Instead of relying on huge and expensive data centers for rolling out
cloud-based services to rural and remote areas, we propose a hardware platform
based on small single-board computers. The role of these micro-data centers is
twofold. On the one hand, they act as intermediaries between cloud services and
clients, improving availability in the case of network or power outages. On the
other hand, they run community-based services on local infrastructure. We
illustrate how to build such a system without incurring high costs, high power
consumption, or single points of failure. Additionally, we opt for a system
that is extendable and scalable as well as easy to deploy, relying on an open
design.


title:
Diffusivity and derivatives for interstitial solutes: Activation energy,
  volume, and elastodiffusion tensors

abstract:
  Computational atomic-scale methods continue to provide new information about
geometry, energetics, and transition states for interstitial elements in
crystalline lattices. This data can be used to determine the diffusivity of
interstitials by finding steady-state solutions to the master equation. In
addition, atomic-scale computations can provide not just the site energy, but
also the stress in the cell due to the introduction of the defect to compute
the elastic dipole. We derive a general expression for the fully anistropic
diffusivity tensor from site and transition state energies, and three
derivatives of the diffusivity: the elastodiffusion tensor (derivative of
diffusivity with respect to strain), the activation barrier tensor (logarithmic
derivative of diffusivity with respect to inverse temperature) and activation
volume tensor (logarithmic derivative of diffusivity with respect to pressure).
Computation of these quantities takes advantage of crystalline symmetry, and we
provide an open-source implementation of the algorithm. We provide analytic
results for octahedral-tetrahedral networks in face-centered cubic,
body-centered cubic, and hexagonal closed-packed lattices, and conclude with
numerical results for C in Fe.


title:
Blind image separation based on exponentiated transmuted Weibull
  distribution

abstract:
  In recent years the processing of blind image separation has been
investigated. As a result, a number of feature extraction algorithms for direct
application of such image structures have been developed. For example,
separation of mixed fingerprints found in any crime scene, in which a mixture
of two or more fingerprints may be obtained, for identification, we have to
separate them. In this paper, we have proposed a new technique for separating a
multiple mixed images based on exponentiated transmuted Weibull distribution.
To adaptively estimate the parameters of such score functions, an efficient
method based on maximum likelihood and genetic algorithm will be used. We also
calculate the accuracy of this proposed distribution and compare the
algorithmic performance using the efficient approach with other previous
generalized distributions. We find from the numerical results that the proposed
distribution has flexibility and an efficient result


title:
Light Sterile Neutrinos, Lepton Number Violating Interactions and the
  LSND Anomaly

abstract:
  We develop the consequences of introducing a purely leptonic, lepton number
violating non-standard interaction (NSI) and standard model neutrino mixing
with a fourth, sterile neutrino in the analysis of short-baseline, neutrino
experiments. We focus on the muon decay at rest (DAR) result from the Liquid
Scintillation Neutrino Experiment (LSND) and the Karlsruhe and Rutherford
Medium Energy Neutrino Experiment (KARMEN). We make a comprehensive analysis of
lepton number violating, NSI effective operators and find nine that affect muon
decay relevant to LSND results. Two of these preserve the standard model (SM)
value 3/4 for the Michel rho and delta parameters and, overall, show favorable
agreement with precision data and the electron anti-neutrino signal from LSND
data. We display theoretical models that lead to these two effective operators.
In the model we choose to apply to DAR data, both electron anti-neutrino
appearance from muon anti-neutrino oscillation and electron anti-neutrino
survival after production from NSI decay of the positive muon contribute to the
expected signal. This is a unique feature of our scheme. We find a range of
parameters where both experiments can be accommodated consistently with recent
global, sterile neutrino fits to short baseline data. We comment on
implications of the models for new physics searches at colliders and comment on
further implications of the lepton number violating interactions plus sterile
neutrino-standard model neutrino mixing.


title: Predictability and hierarchy in Drosophila behavior

abstract:
  Even the simplest of animals exhibit behavioral sequences with complex
temporal dynamics. Prominent amongst the proposed organizing principles for
these dynamics has been the idea of a hierarchy, wherein the movements an
animal makes can be understood as a set of nested sub-clusters. Although this
type of organization holds potential advantages in terms of motion control and
neural circuitry, measurements demonstrating this for an animal's entire
behavioral repertoire have been limited in scope and temporal complexity. Here,
we use a recently developed unsupervised technique to discover and track the
occurrence of all stereotyped behaviors performed by fruit flies moving in a
shallow arena. Calculating the optimally predictive representation of the fly's
future behaviors, we show that fly behavior exhibits multiple time scales and
is organized into a hierarchical structure that is indicative of its underlying
behavioral programs and its changing internal states.

categories: physics.bio-ph cs.IT math.IT q-bio.NC stat.AP


title: Consistent Approximations to Impulsive Optimal Control Problems

abstract:
  We analyse the theory of consistent approximations given by Polak and we use
it in an impulsive optimal control problem. We reparametrize the original
system and build consistent approximations for this new reparametrized problem.
So, we prove that if a sequence of solution of the consistent approximations is
converging, it will converge to a solution of the reparametrized problem, and,
finally, we show that from a solution of the reparametrized problem we can find
a solution of the original one.


title: Performance Bounds with Curvature for Batched Greedy Optimization

abstract:
  The batched greedy strategy is an approximation algorithm to maximize a set
function subject to a matroid constraint. Starting with the empty set, the
batched greedy strategy iteratively adds to the current solution set a batch of
elements that results in the largest gain in the objective function while
satisfying the matroid constraints. In this paper, we develop bounds on the
performance of the batched greedy strategy relative to the optimal strategy in
terms of a parameter called the total batched curvature. We show that when the
objective function is a polymatroid set function, the batched greedy strategy
satisfies a harmonic bound for a general matroid constraint and an exponential
bound for a uniform matroid constraint, both in terms of the total batched
curvature. We also study the behavior of the bounds as functions of the batch
size. Specifically, we prove that the harmonic bound for a general matroid is
nondecreasing in the batch size and the exponential bound for a uniform matroid
is nondecreasing in the batch size under the condition that the batch size
divides the rank of the uniform matroid. Finally, we illustrate our results by
considering a task scheduling problem and an adaptive sensing problem.


title: Anatomy of Fermionic Entanglement and Criticality in Kitaev Spin Liquids

abstract:
  We analyse in detail the effect of non-trivial band topology on the area law
behaviour of the entanglement entropy in Kitaev's honeycomb model. By mapping
the translationally invariant 2D spin model into 1D fermionic subsystems, we
identify those subsystems responsible for universal entanglement contributions
in the gapped phases and those responsible for critical entanglement scaling in
the gapless phases. For the gapped phases we analytically show how the
topological edge states contribute to the entanglement entropy and provide a
universal lower bound for it. For the gapless semi-metallic phases and
topological phase transitions the identification of the critical subsystems
shows that they fall always into the Ising or the XY universality classes. As
our study concerns the fermionic degrees of freedom in the honeycomb model,
qualitatively similar results are expected to apply also to generic topological
insulators and superconductors.


title: Periods and Superstring Amplitudes

abstract:
  Scattering amplitudes which describe the interaction of physical states play
an important role in determining physical observables. In string theory the
physical states are given by vibrations of open and closed strings and their
interactions are described (at the leading order in perturbation theory) by a
world-sheet given by the topology of a disk or sphere, respectively.
  Formally, for scattering of N strings this leads to N-3-dimensional iterated
real integrals along the compactified real axis or N-3-dimensional complex
sphere integrals, respectively. As a consequence the physical observables are
described by periods on M_{0,N} - the moduli space of Riemann spheres of N
ordered marked points.
  The mathematical structure of these string amplitudes share many recent
advances in arithmetic algebraic geometry and number theory like multiple zeta
values, single-valued multiple zeta values, Drinfeld, Deligne associators, Hopf
algebra and Lie algebra structures related to Grothendiecks Galois theory. We
review these results, with emphasis on a beautiful link between generalized
hypergeometric functions describing the real iterated integrals on M_{0,N}(R)
and the decomposition of motivic multiple zeta values. Furthermore, a relation
expressing complex integrals on M_{0,N}(C) as single-valued projection of
iterated real integrals on M_{0,N}(R) is exhibited.


title:
EEF: Exponentially Embedded Families with Class-Specific Features for
  Classification

abstract:
  In this letter, we present a novel exponentially embedded families (EEF)
based classification method, in which the probability density function (PDF) on
raw data is estimated from the PDF on features. With the PDF construction, we
show that class-specific features can be used in the proposed classification
method, instead of a common feature subset for all classes as used in
conventional approaches. We apply the proposed EEF classifier for text
categorization as a case study and derive an optimal Bayesian classification
rule with class-specific feature selection based on the Information Gain (IG)
score. The promising performance on real-life data sets demonstrates the
effectiveness of the proposed approach and indicates its wide potential
applications.


title: Quasi-matter bounce and inflation in the light of the CSL model

abstract:
  The Continuous Spontaneous Localization (CSL) model has been proposed as a
possible solution to the quantum measurement problem by modifying the
Schr\"{o}dinger equation. In this work, we apply the CSL model to two
cosmological models of the early Universe: the matter bounce scenario and slow
roll inflation. In particular, we focus on the generation of the classical
primordial inhomogeneities and anisotropies that arise from the dynamical
evolution, provided by the CSL mechanism, of the quantum state associated to
the quantum fields. In each case, we obtained a prediction for the shape and
the parameters characterizing the primordial spectra (scalar and tensor), i.e.
the amplitude, the spectral index and the tensor-to-scalar ratio. We found that
there exist CSL parameter values, allowed by other non-cosmological
experiments, for which our predictions for the angular power spectrum of the
CMB temperature anisotropy are consistent with the best fit canonical model to
the latest data released by the Planck Collaboration.


title:
Robustness of topologically protected edge states in quantum walk
  experiments with neutral atoms

abstract:
  Discrete-time quantum walks allow Floquet topological insulator materials to
be explored using controllable systems such as ultracold atoms in optical
lattices. By numerical simulations, we study the robustness of topologically
protected edge states in the presence of decoherence in one- and
two-dimensional discrete-time quantum walks. We also develop a simple
analytical model quantifying the robustness of these edge states against either
spin or spatial dephasing, predicting an exponential decay of the population of
topologically protected edge states. Moreover, we present an experimental
proposal based on neutral atoms in spin-dependent optical lattices to realize
spatial boundaries between distinct topological phases. Our proposal relies on
a new scheme to implement spin-dependent discrete shift operations in a
two-dimensional optical lattice. We analyze under realistic decoherence
conditions the experimental feasibility of observing unidirectional,
dissipationless transport of matter waves along boundaries separating distinct
topological domains.


title:
The abundance discrepancy factor and t^2 in nebulae: are non-thermal
  electrons the culprits?

abstract:
  Photoionization produces supra-thermal electrons, electrons with much more
energy than is found in a thermalized gas at electron temperatures
characteristic of nebulae. The presence of these high energy electrons may
solve the long-standing t^2/ADF puzzle, the observations that abundances
obtained from recombination and collisionally excited lines do not agree, and
that different temperature indicators give different results, if they survive
long enough to affect diagnostic emission lines. The presence of these
non-Maxwellian distribution electrons is usually designated by the term kappa.
Here we use well-established methods to show that the distance over which
heating rates change are much longer than the distance supra thermal electrons
can travel, and that the timescale to thermalize these electrons are much
shorter than the heating or cooling timescales. These estimates establish that
supra thermal electrons will have disappeared into the Maxwellian velocity
distribution long before they affect the collisionally excited forbidden and
recombination lines that are used for deriving abundances relative to hydrogen.
The electron velocity distribution in nebulae should be closely thermal.


title: On the Capacity of Joint Fading and Two-path Shadowing Channels

abstract:
  The ergodic and outage channel capacity of different optimal and suboptimal
combinations of transmit power and modulation rate adaptation strategies over a
joint fading and two-path shadowing (JFTS) fading/shadowing channel is studied
in this paper. Analytically tractable expressions for channel capacity are
obtained, assuming perfect channel side information (CSI) at the receiver
and/or the transmitter with negligible feedback delay. Furthermore, the impacts
of the JFTS parameters on the channel capacity achieved by these adaptive
transmission techniques are determined.


title: Tighter Loop Bound Analysis (Technical report)

abstract:
  We present a new algorithm for computing upper bounds on the number of
executions of each program instruction during any single program run. The upper
bounds are expressed as functions of program input values. The algorithm is
primarily designed to produce bounds that are relatively tight, i.e. not
unnecessarily blown up. The upper bounds for instructions allow us to infer
loop bounds, i.e.~upper bounds on the number of loop iterations. Experimental
results show that the algorithm implemented in a prototype tool Looperman often
produces tighter bounds than current tools for loop bound analysis.


title: Eigensystem Bootstrap Multiscale Analysis for the Anderson Model

abstract:
  We use a bootstrap argument to enhance the eigensystem multiscale analysis,
introduced by Elgart and Klein for proving localization for the Anderson model
at high disorder. The eigensystem multiscale analysis studies finite volume
eigensystems, not finite volume Green's functions. It yields pure point
spectrum with exponentially decaying eigenfunctions and dynamical localization.
The starting hypothesis for the eigensystem bootstrap multiscale analysis only
requires the verification of polynomial decay of the finite volume
eigenfunctions, at some sufficiently large scale, with some minimal probability
independent of the scale. It yields exponential localization of finite volume
eigenfunctions in boxes of side $L$, with the eigenvalues and eigenfunctions
labeled by the sites of the box, with probability higher than
$1-\mathrm{e}^{-L^\xi}$, for any desired $0<\xi<1$.


title: Nonvanishing of geodesic periods over compact hyperbolic manifolds

abstract:
  Let $X$ be a compact hyperbolic manifold with dimension $d\geqslant3$. In
this paper we show that there are infinitely many nonvanishing geodesic periods
defined over any compact $n$-dimensional ($n\geqslant2$) geodesic cycle of $X$.


title: Facial Expression Recognition from World Wild Web

abstract:
  Recognizing facial expression in a wild setting has remained a challenging
task in computer vision. The World Wide Web is a good source of facial images
which most of them are captured in uncontrolled conditions. In fact, the
Internet is a Word Wild Web of facial images with expressions. This paper
presents the results of a new study on collecting, annotating, and analyzing
wild facial expressions from the web. Three search engines were queried using
1250 emotion related keywords in six different languages and the retrieved
images were mapped by two annotators to six basic expressions and neutral. Deep
neural networks and noise modeling were used in three different training
scenarios to find how accurately facial expressions can be recognized when
trained on noisy images collected from the web using query terms (e.g. happy
face, laughing man, etc)? The results of our experiments show that deep neural
networks can recognize wild facial expressions with an accuracy of 82.12%.


title:
Probing Radiative Neutrino Mass Models Using Trilepton Channel at the
  LHC

abstract:
  In this work, we probe a class of neutrino mass models through the lepton
flavor violating interactions of a singlet charged scalar, $S^{\pm}$ at the LHC
proton-proton collisions with 8 TeV and 14 TeV energies. This scalar couples to
the leptons and induces many processes such as
$pp\rightarrow\ell^{\pm}\ell^{\pm}\ell^{\mp}+\slashed{E}_{T}$. In our analysis
we discuss the opposite sign same flavor leptons signal, as well as the
background free channel with the tau contribution which can enhance the
signal/background ratio for center of mass energies $\sqrt{s}$= 8 TeV and
$\sqrt{s}$ = 14 TeV.


title:
Hard X-ray Emission from Sh2-104: A NuSTAR search for Gamma-ray
  Counterparts

abstract:
  We present NuSTAR hard X-ray observations of Sh 2-104, a compact HII region
containing several young massive stellar clusters (YMSCs). We have detected
distinct hard X-ray sources coincident with localized VERITAS TeV emission
recently resolved from the giant gamma-ray complex MGRO J2019+37 in the Cygnus
region. Faint, diffuse X-ray emission coincident with the eastern YMSC in
Sh2-104 is likely the result of colliding winds of component stars. Just
outside the radio shell of Sh 2-104 lies 3XMM J201744.7+365045 and a nearby
nebula NuSTAR J201744.3+364812, whose properties are most consistent with
extragalactic objects. The combined XMM-Newton and NuSTAR spectrum of 3XMM
J201744.7+365045 is well-fit to an absorbed power-law model with NH = (3.1 +/-
1.0)E22 cm^-2 and photon index Gamma = 2.1 +/- 0.1. Based on possible long-term
flux variation and the lack of detected pulsations (< 43% modulation), this
object is likely a background AGN rather than a Galactic pulsar. The spectrum
of the NuSTAR nebula shows evidence of an emission line at E = 5.6 keV
suggesting an optically obscured galaxy cluster at z = 0.19 +/- 0.02 (d = 800
Mpc) and Lx = 1.2E44 erg/s. Follow-up Chandra observations of Sh 2-104 will
help identify the nature of the X-ray sources and their relation to MGRO
J2019+37. We also show that the putative VERITAS gamma-ray excess south of Sh
2-104 is most likely associated with the newly discovered Fermi pulsar PSR
J2017+3625 and not the HII region.


title:
Self-coherent phase reference sharing for continuous-variable quantum
  key distribution

abstract:
  Generating "locally" the local oscillator is a fundamental requirement for
continous-variable quantum key distribution (CV-QKD), both for performance and
security reasons. As a consequence, next-generation CV- QKD systems will have
to be implemented with a local local oscillator (LLO). This issue has been
explicitly tackled in recent works, where the proposed and implemented
approach, that we call LLO-sequential, consists in sequentially (temporally)
multiplexing quantum signal optical pulses with phase reference pilot tones
optical pulses. We develop a comprehensive analysis of the noise model and the
hardware requirements in order to perform LLO CV-QKD. This analysis allows to
quantitatively understand one of the limits of CV-QKD implemented with the
LLO-sequential approach: such systems, unless operated at very high speed, have
very strong requirements in terms of tolerable laser phase noise.
LLO-sequential CV-QKD can thus in practice only be implemented with expensive,
low phase noise lasers, such as ECL lasers. The main contribution of this work
is to introduce designs for LLO CV-QKD based on self-coherence phase sharing,
in which the phase reference information and the quantum information are
coherently obtained from a single optical wavefront. We propose in particular a
design, called LLO-displacement, where the phase reference information is
encoded in the displacement of the standard CV-QKD Gaussian modulated coherent
state (GMCS) protocol. We analyze the performance and the hardware requirements
of the LLO-displacement design and our results indicate that it can be used to
perform CV-QKD over distances up to 100 km with realistic and affordable
hardware, in particular with standard telecom equipment and low cost DFB
lasers. This opens a practical path towards the development of coherent quantum
communications systems compatible with next-generation networks requirements.


title:
Parallel Equivalence Class Sorting: Algorithms, Lower Bounds, and
  Distribution-Based Analysis

abstract:
  We study parallel comparison-based algorithms for finding all equivalence
classes of a set of $n$ elements, where sorting according to some total order
is not possible. Such scenarios arise, for example, in applications, such as in
distributed computer security, where each of $n$ agents are working to identify
the private group to which they belong, with the only operation available to
them being a zero-knowledge pairwise-comparison (which is sometimes called a
"secret handshake") that reveals only whether two agents are in the same group
or in different groups. We provide new parallel algorithms for this problem, as
well as new lower bounds and distribution-based analysis.


title: How to Build Your Network? A Structural Analysis

abstract:
  Creating new ties in a social network facilitates knowledge exchange and
affects positional advantage. In this paper, we study the process, which we
call network building, of establishing ties between two existing social
networks in order to reach certain structural goals. We focus on the case when
one of the two networks consists only of a single member and motivate this case
from two perspectives. The first perspective is socialization: we ask how a
newcomer can forge relationships with an existing network to place herself at
the center. We prove that obtaining optimal solutions to this problem is
NP-complete, and present several efficient algorithms to solve this problem and
compare them with each other. The second perspective is network expansion: we
investigate how a network may preserve or reduce its diameter through linking
with a new node, hence ensuring small distance between its members. We give two
algorithms for this problem. For both perspectives the experiment demonstrates
that a small number of new links is usually sufficient to reach the respective
goal.


title: Mean curvature flows in manifolds of special holonomy

abstract:
  We study the uniqueness of minimal submanifolds and the stability of the mean
curvature flow in several well-known model spaces of manifolds of special
holonomy. These include the Stenzel metric on the cotangent bundle of spheres,
the Calabi metric on the cotangent bundle of complex projective spaces, and the
Bryant--Salamon metrics on vector bundles over certain Einstein manifolds. In
particular, we show that the zero sections, as calibrated submanifolds with
respect to their respective ambient metrics, are unique among compact minimal
submanifolds and are dynamically stable under the mean curvature flow. The
proof relies on intricate interconnections of the Ricci flatness of the ambient
space and the extrinsic geometry of the calibrated submanifolds.


title:
Monte Carlo population synthesis of post-common-envelope white dwarf
  binaries and type Ia supernova rate

abstract:
  Binary population synthesis (BPS) study provides a comprehensive way to
understand evolutions of binaries and their end products. Close white dwarf
(WD) binaries have crucial characteristics in examining in uence of
yetunresolved physical parameters on the binary evolution. In this paper, we
perform Monte Carlo BPS simulations, investigating the population of WD/main
sequence (WD/MS) binaries and double WD binaries, with a publicly available
binary star evolution code under 37 different assumptions on key physical
processes and binary initial conditions. We considered different combinations
of the binding energy parameter (lambda_g:considering gravitational energy
only, lambda_b: considering both gravitational energy and internal energy, and
lambda_e:considering gravitational energy, internal energy, and entropy of the
envelope, the values of them derived with the MESA code), CE effciency,
critical mass ratio, initial primary mass function and metallicity. We find
that a larger number of post-CE WD/MS binaries in tight orbits are formed when
the binding energy parameters is set by lambda_e than the cases adopting the
other prescriptions. We also find effects of the other input parameters on
orbital period and mass distributions of post-CE WD/MS binaries as well.
Containing at least one CO WD, the double WD system evolved from WD/MS binaries
may explode as type Ia supernovae (SNe Ia) by merging. In this work, we also
investigate a frequency of two WD mergers and compare it to the SNe Ia rate.


title:
Robust Consensus Analysis and Design under Relative State Constraints or
  Uncertainties

abstract:
  This paper proposes a new approach to analyze and design distributed robust
consensus control protocols for general linear leaderless multi-agent systems
(MASs) in presence of relative-state constraints or uncertainties. First, we
show that the MAS robust consensus under relative-state constraints or
uncertainties is equivalent to the robust stability under state constraints or
uncertainties of a transformed MAS. Next, the transformed MAS under state
constraints or uncertainties is reformulated as a network of Lur'e systems. By
employing S-procedure, Lyapunov theory, and Lasalle's invariance principle, a
sufficient condition for robust consensus and the design of robust consensus
controller gain are derived from solutions of a distributed LMI convex problem.
Finally, numerical examples are introduced to illustrate the effectiveness of
the proposed theoretical approach.


title:
Robust Consensus of Linear Multi-Agent Systems under Input Constraints
  or Uncertainties

abstract:
  This paper proposes a new approach to analyze and synthesize robust consensus
control laws for general linear leaderless multi-agent systems (MASs) subjected
to input constraints or uncertainties. First, the MAS under input constraints
or uncertainties is reformulated as a network of Lur'e systems. Next, two
scenarios of communication topology are considered, namely undirected and
directed cyclic structures. In each case, a sufficient condition for consensus
and the design of consensus controller gain are derived from solutions of a
distributed LMI convex problem. Finally, a numerical example is introduced to
illustrate the effectiveness of the proposed theoretical approach.


title: Resonance Beyond Frequency-Matching

abstract:
  Resonance, defined as the oscillation of a system when the temporal frequency
of an external stimulus matches a natural frequency of the system, is important
in both fundamental physics and applied disciplines. However, the spatial
character of oscillation is not considered in the definition of resonance. In
this work, we reveal the creation of spatial resonance when the stimulus
matches the space pattern of a normal mode in an oscillating system. The
complete resonance, which we call multidimensional resonance, is a combination
of both the spatial and the conventionally defined (temporal) resonance and can
be several orders of magnitude stronger than the temporal resonance alone. We
further elucidate that the spin wave produced by multidimensional resonance
drives considerably faster reversal of the vortex core in a magnetic nanodisk.
Our findings provide insight into the nature of wave dynamics and open the door
to novel applications.


title:
Uniform ergodicities and perturbation bounds of Markov chains on ordered
  Banach spaces

abstract:
  It is known that Dobrushin's ergodicity coefficient is one of the effective
tools in the investigations of limiting behavior of Markov processes. Several
interesting properties of the ergodicity coefficient of a positive mapping
defined on ordered Banach space with a base have been studied. In this paper,
we consider uniformly mean ergodic and asymptotically stable Markov operators
on ordered Banach spaces. In terms of the ergodicity coefficient, we prove
uniform mean ergodicity criterion in terms of the ergodicity coefficient.
Moreover, we develop the perturbation theory for uniformly asymptotically
stable Markov chains on ordered Banach spaces. In particularly, main results
open new perspectives in the perturbation theory for quantum Markov processes
defined on von Neumann algebras. Moreover, by varying the Banach spaces one can
obtain several interesting results in both classical and quantum settings as
well.


title:
Minimum-Rank Dynamic Output Consensus Design for Heterogeneous Nonlinear
  Multi-Agent Systems

abstract:
  In this paper, we propose a new and systematic design framework for output
consensus in heterogeneous Multi-Input Multi-Output (MIMO) general nonlinear
Multi-Agent Systems (MASs) subjected to directed communication topology. First,
the input-output feedback linearization method is utilized assuming that the
internal dynamics is Input-to-State Stable (ISS) to obtain linearized
subsystems of agents. Consequently, we propose local dynamic controllers for
agents such that the linearized subsystems have an identical closed-loop
dynamics which has a single pole at the origin whereas other poles are on the
open left half complex plane. This allows us to deal with distinct agents
having arbitrarily vector relative degrees and to derive rank-$1$ cooperative
control inputs for those homogeneous linearized dynamics which results in a
minimum rank distributed dynamic consensus controller for the initial nonlinear
MAS. Moreover, we prove that the coupling strength in the consensus protocol
can be arbitrarily small but positive and hence our consensus design is
non-conservative. Next, our design approach is further strengthened by tackling
the problem of randomly switching communication topologies among agents where
we relax the assumption on the balance of each switched graph and derive a
distributed rank-$1$ dynamic consensus controller. Lastly, a numerical example
is introduced to illustrate the effectiveness of our proposed framework.


title: Likelihood Analysis of Power Spectra and Generalized Moment Problems

abstract:
  We develop an approach to spectral estimation that has been advocated by
Ferrante, Masiero and Pavon and, in the context of the scalar-valued covariance
extension problem, by Enqvist and Karlsson. The aim is to determine the power
spectrum that is consistent with given moments and minimizes the relative
entropy between the probability law of the underlying Gaussian stochastic
process to that of a prior. The approach is analogous to the framework of
earlier work by Byrnes, Georgiou and Lindquist and can also be viewed as a
generalization of the classical work by Burg and Jaynes on the maximum entropy
method. In the present paper we present a new fast algorithm in the general
case (i.e., for general Gaussian priors) and show that for priors with a
specific structure the solution can be given in closed form.