title: Second order perturbed Heisenberg Hamiltonian of Fe3O4 ultra-thin films

abstract:
  Due to the wide range of applications, theoretical models of Fe3O4 films are
found to be important. Ultra thin Fe3O4 films with ferrite structure have been
theoretically investigated using second order perturbed modified Heisenberg
Hamiltonian. Matrices for ultra thin films with two and three spin layers are
presented in this manuscript. Total magnetic energy was expressed in terms of
spin exchange interaction, magnetic dipole interaction, second order magnetic
anisotropy and stress induced magnetic anisotropy. Magnetic properties were
observed for films with two spin layers and variant second order magnetic
anisotropy. For the film with three spin layers, second order anisotropy
constant was fixed to avoid tedious derivations. Magnetic easy axis rotates
toward the in plane direction as the number of spin layers is increased from
two to three because the stress induced anisotropy energy dominates at higher
number of spin layers. According to some other experimental data, the magnetic
easy axis of thin films rotates toward the in plane direction as the thickness
is increased. For ferrite film with two spin layers, magnetic easy and hard
directions can be observed at 0.75 and 1.2 radians, respectively, when the
ratio of stress induced anisotropy to the long range dipole interaction
strength is 3.9. For ferrite film with three spin layers, magnetic easy and
hard directions can be observed at 2.4 and 2.3 radians, respectively, when the
ratio of stress induced anisotropy to the long range dipole interaction
strength is 4.2.


title: Forecasting Fluid Flows Using the Geometry of Turbulence

abstract:
  The existence and dynamical role of particular unstable Navier-Stokes
solutions (exact coherent structures) is revealed in laboratory studies of weak
turbulence in a thin, electromagnetically-driven fluid layer. We find that the
dynamics exhibit clear signatures of numerous unstable equilibrium solutions,
which are computed using a combination of flow measurements from the experiment
and fully-resolved numerical simulations. We demonstrate the dynamical
importance of these solutions by showing that turbulent flows visit their state
space neighborhoods repeatedly. Furthermore, we find that the unstable manifold
associated with one such unstable equilibrium predicts the evolution of
turbulent flow in both experiment and simulation for a considerable period of
time.


title:
Magnetic anisotropy dependence of the energy of oriented thick
  ferromagnetic films

abstract:
  Heisenberg Hamiltonian was employed to describe the variation of energy of
thick ferromagnetic films with second and fourth order anisotropies. At angle
of 1.36 degrees and anisotropies of 1.25, energy is minimum for thick film of
sc(001) with 1000 layers. Energy becomes minimum at angle of 1.18 degrees and
fourth order anisotropy of 1.15 for thick film of bcc(001) with the same
thickness. According to these simulations, these lattices can be easily
oriented in some certain directions under the influence of some particular
values of anisotropies. Energy varies with second and fourth order anisotropies
in similar passion for both types of lattices. The energy gradually decreases
with second and fourth order anisotropy for both types of lattices in the range
described here.


title:
Thick ferromagnetic films and their anisotropies as described by second
  order perturbed Heisenberg Hamiltonian

abstract:
  Second and fourth order anisotropy dependence of energy of thick simple cubic
ferromagnetic films with 10000 layers is explained using Heisenberg Hamiltonian
with second order perturbation in this manuscript. The second and fourth order
anisotropy constants were assumed to be constants through out the film. When
the fourth order anisotropy is given by fourth order anisotropy of 6, the
sc(001) ferromagnetic thick films with 10000 layers can be easily oriented in
0.6 radians direction for the energy parameters given this report. Under the
influence of the second order anisotropy given by second order anisotropy of
6.3, the easy direction of sc(001) film with 10000 layers is given by 0.66
radians. Although the energy varies periodically in all cases, the maximum
energy considerably decreases with fourth order anisotropy constant. According
to 3-D plots, energy under influence of second order anisotropy is larger than
energy under influence of fourth order anisotropy.


title:
Effect of stress induced anisotropy and applied magnetic field on second
  order perturbed energy of thin ferromagnetic films

abstract:
  All the simulations were carried out for sc(001) film with three (N=3)
layers. The effect of applied magnetic field and stress induced anisotropy on
energy of ultra-thin ferromagnetic films has been investigated using Heisenberg
Hamiltonian with second order perturbation. The energy becomes minimums at
certain values of angles, applied magnetic field and stress, by indicating that
film can be easily oriented in theses certain directions by applying particular
applied magnetic field or stress. For example, when applied magnetic field
perpendicular to film plane is 3.6, the film can be easily oriented along 0.97
and 2.65 radians directions. When in plane applied magnetic field is 3, energy
minimums can be detected at 1 and 2.6 radians. When applied stress is 2.7, film
can be easily oriented in 2.8 direction.


title:
Third Order Perturbed Heisenberg Hamiltonian of Thick Spinel Ferrite
  Films

abstract:
  The third order perturbed Heisenberg Hamiltonian was employed to investigate
the spinel thick nickel ferrite films. The variation of energy up to N=10000
was studied. At N=75, the energy required to rotate from easy to hard direction
is very small. For film with N=10000, the first major maximum and minimum can
be observed at 202 and 317 degrees, respectively. This curve shows some abrupt
changes after introducing third order perturbation. The maximum energy of this
curve is higher than that of spinel thick ferrite films with second order
perturbed Heisenberg Hamiltonian. At some values of stress induced anisotropy,
the maximum energy is less than that of spinel thick ferrite films with second
order perturbed Heisenberg Hamiltonian derived by us previously.


title:
Modulo $k$-Orientations and Tutte's $3$-Flow Conjecture in Graphs with
  Many Edge-Disjoint Spanning Trees

abstract:
  Let $k$ be an integer, $k\ge 3$, and let $Z_k$ be the cyclic group of order
$k$. Take $\lambda_k\in [k+2, \infty)$ to be the smallest integer such that for
every $\lambda_k$-edge-connected graph $G$ and every mapping $f:V(G)\rightarrow
Z_k$ with $|E(G)|\stackrel{k}{\equiv} \sum_{v\in V(G)}f(v)$, there exits an
orientation for $G$ such that for each vertex $v$,
$d_G^+(v)\stackrel{k}{\equiv}f(v) $, where $d_G^+(v)$ denotes the out-degree of
$v$. Lov{\'a}sz, Thomassen, Wu, and Zhang (2013) proved that $\lambda_k\le
3k-3$ when $k$ is odd and $\lambda_k\le 3k-2$ when $k$ is even. In this note,
we prove that if a graph $G$ contains $\lambda_k-2$ edge-disjoint spanning
trees, then it has an orientation such that for each vertex $v$,
$d_G^+(v)\stackrel{k}{\equiv}f(v) $, where $f:V(G)\rightarrow Z_k$ is a mapping
with $|E(G)|\stackrel{k}{\equiv} \sum_{v\in V(G)}f(v)$. This result confirms
Tutte's $3$-Flow Conjecture in graphs with $4$ edge-disjoint spanning trees.


title:
The e-ASTROGAM mission (exploring the extreme Universe with gamma rays
  in the MeV-GeV range)

abstract:
  e-ASTROGAM (`enhanced ASTROGAM') is a breakthrough Observatory mission
dedicated to the study of the non-thermal Universe in the photon energy range
from 0.3 MeV to 3 GeV. The mission is based on an advanced space-proven
detector technology, with unprecedented sensitivity, angular and energy
resolution, combined with polarimetric capability. In the largely unexplored
MeV-GeV domain, e-ASTROGAM will open a new window on the non-thermal Universe,
making pioneering observations of the most powerful Galactic and extragalactic
sources, elucidating the nature of their relativistic outflows and their
effects on Galactic ecosystems. With a line sensitivity in the MeV energy range
one to two orders of magnitude better than previous generation instruments,
will determine the origin of key isotopes fundamental for the understanding of
supernova explosion and the chemical evolution of our Galaxy. The mission will
provide unique data of significant interest to a broad astronomical community,
complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA,
ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and the promise of
eLISA.
  Keywords: High-energy gamma-ray astronomy, High-energy astrophysics, Nuclear
Astrophysics, Compton and Pair creation telescope, Gamma-ray bursts, Active
Galactic Nuclei, Jets, Outflows, Multiwavelength observations of the Universe,
Counterparts of gravitational waves, Fermi, Dark Matter, Nucleosynthesis, Early
Universe, Supernovae, Cosmic Rays, Cosmic antimatter.

categories: astro-ph.HE astro-ph.IM astro-ph.SR nucl-ex


title: A generalized inverse for graphs with absorption

abstract:
  We consider weighted, directed graphs with a notion of absorption on the
vertices, related to absorbing random walks on graphs. We define a generalized
inverse of the graph Laplacian, called the absorption inverse, that reflects
both the graph structure as well as the absorption rates on the vertices.
Properties of this generalized inverse are presented, including a matrix forest
theorem relating this generalized inverse to spanning forests of a related
graph, as well as relationships between the absorption inverse and the
fundamental matrix of the absorbing random walk. Applications of the absorption
inverse for describing the structure of graphs with absorption are presented,
including a directed distance metric, spectral partitioning algorithm, and
centrality measure.


title: Hot Particles Attract in a Cold Bath

abstract:
  Controlling interactions out of thermodynamic equilibrium is crucial for
designing addressable and functional self-organizing structures. These active
interactions also underpin collective behavior in biological systems. Here we
study a general setting of active particles in a bath of passive particles, and
demonstrate a novel mechanism for long range attraction between active
particles. The mechanism operates when the translational persistence length of
the active particle motion is smaller than the particle diameter. In this
limit, the system reduces to particles of higher diffusivity ("hot" particles)
in a bath of particles with lower diffusivity ("cold" particles). This
attractive interaction arises as a hot particle pushes cold particles away to
create a large hole around itself, and the holes interact via a depletion-like
attraction. Strikingly, the interaction range is more than an order of
magnitude larger than the particle radius, well beyond the range of
conventional depletion force. Although the mechanism occurs outside the
parameter regime of typical biological swimmers, the mechanism could be
realized in the laboratory.


title:
On relationships between symmetries depending on arbitrary functions and
  integrals of discrete equations

abstract:
  The paper is devoted to the conjecture that an equation is Darboux integrable
if and only if it possesses symmetries depending on arbitrary functions. We
note that results of previous works together prove this conjecture for scalar
partial differential equations of the form $u_{xy}=F(x,y,u,u_x,u_y)$. For
autonomous semi-discrete and discrete analogues of these equations we prove
that the sequence of Laplace invariants is terminated by zero for an equation
if this equation admits an operator mapping any function of one independent
variable into a symmetry of the equation. The vanishing of an Laplace invariant
allows us to construct a formal integral, i.e. an operator that maps symmetries
into integrals (including, generally speaking, trivial integrals). This and
results of previous works together prove a `formal' version of the
aforementioned conjecture in the semi-discrete and pure discrete cases.


title: Elaborating the phase diagram of spin-1 anyonic chains

abstract:
  We revisit the phase diagram of spin-1 $su(2)_k$ anyonic chains, originally
studied by Gils {\it et. al.} [Phys. Rev. B, {\bf 87} (23) (2013)]. These
chains possess several integrable points, which were overlooked (or only
briefly considered) so far.
  Exploiting integrability through a combination of algebraic techniques and
exact Bethe ansatz results, we establish in particular the presence of new
first order phase transitions, a new critical point described by a $Z_k$
parafermionic CFT, and of even more phases than originally conjectured. Our
results leave room for yet more progress in the understanding of spin-1 anyonic
chains.

categories: cond-mat.str-el cond-mat.stat-mech math-ph math.MP


title:
Polarisation of microwave emission from reconnecting twisted coronal
  loops

abstract:
  Magnetic reconnection and particle acceleration due to the kink instability
in twisted coronal loops can be a viable scenario for confined solar flares.
Detailed investigation of this phenomenon requires reliable methods for
observational detection of magnetic twist in solar flares, which may not be
possible solely through extreme UV and soft X-ray thermal emission.
Polarisation of microwave emission in flaring loops can be used as one of the
detection criteria. The aim of this study is to investigate the effect of
magnetic twist in flaring coronal loops on the polarisation of gyro-synchrotron
microwave (GSMW) emission, and determine whether it could provide a means for
magnetic twist detection. We use time-dependent magnetohydrodynamic and
test-particle models developed using LARE3D and GCA codes to investigate
twisted coronal loops relaxing following the kink-instability. Synthetic GSMW
emission maps (I and V Stokes components) are calculated using GX simulator. It
is found that flaring twisted coronal loops produce GSMW radiation with a
gradient of circular polarisation across the loop. However, these patterns may
be visible only for a relatively short period of time due to fast magnetic
reconfiguration after the instability. Their visibility also depends on the
orientation and position of the loop on solar disk. Typically, it would be
difficult to see these characteristic polarisation pattern in a twisted loop
seen from the top (close to the centre of the solar disk), but easier in a
twisted loop seen from the side (i.e. observed very close to the limb).


title: Equivalence of Szegedy's and Coined Quantum Walks

abstract:
  Szegedy's quantum walk is a quantization of a classical random walk or Markov
chain, where the walk occurs on the edges of the bipartite double cover of the
original graph. To search, one can simply quantize a Markov chain with
absorbing vertices. Recently, Santos proposed two alternative search algorithms
that instead utilize the sign-flip oracle in Grover's algorithm rather than
absorbing vertices. In this paper, we show that these two algorithms are
exactly equivalent to two algorithms involving coined quantum walks, which are
walks on the vertices of the original graph with an internal degree of freedom.
The first scheme is equivalent to a coined quantum walk with one walk-step per
query of Grover's oracle, and the second is equivalent to a coined quantum walk
with two walk-steps per query of Grover's oracle. These equivalences lie
outside the previously known equivalence of Szegedy's quantum walk with
absorbing vertices and the coined quantum walk with the negative identity
operator as the coin for marked vertices, whose precise relationships we also
investigate.


title:
Weyl Exceptional Rings in a Three-Dimensional Dissipative Cold Atomic
  Gas

abstract:
  Three-dimensional topological Weyl semimetals can generally support a
zero-dimensional Weyl point characterized by a quantized Chern number or a
one-dimensional Weyl nodal ring (or line) characterized by a quantized Berry
phase in the momentum space. Here, in a dissipative system with particle gain
and loss, we discover a new type of topological ring, dubbed Weyl exceptional
ring consisting of exceptional points at which two eigenstates coalesce. Such a
Weyl exceptional ring is characterized by both a quantized Chern number and a
quantized Berry phase, which are defined via the Riemann surface. We propose an
experimental scheme to realize and measure the Weyl exceptional ring in a
dissipative cold atomic gas trapped in an optical lattice.


title:
Integrable cosmological models with non-minimal coupling and bounce
  solutions

abstract:
  We remind the way to obtain integrable models with non-minimally coupled
scalar fields. We are interesting to models with bounce solutions and compare
bounce solutions in two known integrable models. We show that only one model
has a bounce solution that tends to a stable de Sitter solution.


title: Entropy-based inhomogeneity detection in porous media

abstract:
  We study a change-point problem for random fields based on a univariate
detection of outliers via the $3\sigma$-rule in order to recognize
inhomogeneities in porous media. In particular, we focus on fibre reinforced
polymers modeled by stochastic fibre processes with high fibre intensity and
search for abrupt changes in the direction of the fibres. As a measure of
change, the entropy of the directional distribution is locally estimated within
a window that scans the region to be analyzed.


title: Temperature and Humidity Dependence of Resistance in Nano-Diamond Powder

abstract:
  The electrical resistance of detonation nano-diamond powders was measured
from liquid nitrogen temperature to room temperature and in relative humidity
environments from around 10% to 100%. After sample exposures of several hours
at 100% relative humidity at room temperature (around 295 K), when the
temperature was reduced, the resistance increased to the upper measurement
limit of our apparatus (120 M{\Omega}) at around 240 K. Upon warming, the
resistance dropped back to the room temperature value, with some hysteresis.
For sample exposures after several hours at 100% relative humidity at room
temperature, as the relative humidity was reduced, the sample resistance
increased to the upper range limit of the apparatus. As the relative humidity
was then increased (all at room temperature), the resistance dropped. For
samples exposed to low (~10%) relative humidity for several hours at room
temperature, as the humidity was increased (at room temperature), the
resistance decreased, and then increased when the humidity was reduced. The
temperature behavior was markedly differ from that of powdered graphite and
multi-walled carbon nano tubes.


title:
On Riemann Solvers and Kinetic Relations for Isothermal Two-Phase Flows
  with Surface Tension

abstract:
  We consider a sharp-interface approach for the inviscid isothermal dynamics
of compressible two-phase flow, that accounts for phase transition and surface
tension effects. To fix the mass exchange and entropy dissipation rate across
the interface kinetic relations are frequently used. The complete
uni-directional dynamics can then be understood by solving generalized
two-phase Riemann problems. We present new well-posedness theorems for the
Riemann problem and corresponding computable Riemann solvers, that cover quite
general equations of state, metastable input data and curvature effects. The
new Riemann solver is used to validate different kinetic relations on
physically relevant problems including a comparison with experimental data.
Riemann solvers are building blocks for many numerical schemes that are used to
track interfaces in two-phase flow. It is shown that the new Riemann solver
enables reliable and efficient computations for physical situations that could
not be treated before.


title:
Pfaffian structures and certain solutions to BKP hierarchies II.
  Multiple integrals

abstract:
  We introduce a useful and rather simple classes of BKP tau functions which
which we shall shall call "easy tau functions". We consider the "large BKP
hiearchy" related to $O(2\infty +1)$ which was introduced in \cite{KvdLbispec}
(which is closely related to the DKP $O(2\infty) $hierarchy introduced in
\cite{JM}). Actually "easy tau functions" of the small BKP was already
considered in \cite{HLO}, here we are more interested in the large BKP and also
the mixed small-large BKP tau functions \cite{KvdLbispec}. Tau functions under
consideration are equal to sums over partitions and to multi-integrals. In this
way they may be appliciable in models of random partitions and models of random
matrices. Here in the part II we consider multi-intergals and series of $N$-ply
integrals in $N$. Relations to matrix models is explained. This paper may be
viewed as a developement of the the paper by J.van de Leur \cite{L1} related to
orthogonal and symplectic ensembles of random matrices.


title: Applications of KP Nuclear Parton Distributions

abstract:
  We review the nuclear parton distribution functions computed on the basis of
our microscopic model taking into account a number of nuclear effects including
Fermi motion and nuclear binding, nuclear meson-exchange currents, off-shell
corrections to bound nucleon distributions and nuclear shadowing. We discuss
applications to a number of different processes including lepton-nucleus deep
inelastic scattering, proton-nucleus Drell-Yan lepton pair production at
Fermilab, as well as $W^\pm$ and $Z^0$ boson production in proton-lead
collisions at the LHC.


title: Almost all Steiner triple systems have perfect matchings

abstract:
  We show that for any n divisible by 3, almost all order-n Steiner triple
systems have a perfect matching (also known as a parallel class or resolution
class). In fact, we prove a general upper bound on the number of perfect
matchings in a Steiner triple system and show that almost all Steiner triple
systems essentially attain this maximum. We accomplish this via a general
theorem comparing a uniformly random Steiner triple system to the outcome of
the triangle removal process, which we hope will be useful for other problems.
Our methods can also be adapted to other types of designs; for example, we
sketch a proof of the theorem that almost all Latin squares have transversals.


title: Q-Prop: Sample-Efficient Policy Gradient with An Off-Policy Critic

abstract:
  Model-free deep reinforcement learning (RL) methods have been successful in a
wide variety of simulated domains. However, a major obstacle facing deep RL in
the real world is their high sample complexity. Batch policy gradient methods
offer stable learning, but at the cost of high variance, which often requires
large batches. TD-style methods, such as off-policy actor-critic and
Q-learning, are more sample-efficient but biased, and often require costly
hyperparameter sweeps to stabilize. In this work, we aim to develop methods
that combine the stability of policy gradients with the efficiency of
off-policy RL. We present Q-Prop, a policy gradient method that uses a Taylor
expansion of the off-policy critic as a control variate. Q-Prop is both sample
efficient and stable, and effectively combines the benefits of on-policy and
off-policy methods. We analyze the connection between Q-Prop and existing
model-free algorithms, and use control variate theory to derive two variants of
Q-Prop with conservative and aggressive adaptation. We show that conservative
Q-Prop provides substantial gains in sample efficiency over trust region policy
optimization (TRPO) with generalized advantage estimation (GAE), and improves
stability over deep deterministic policy gradient (DDPG), the state-of-the-art
on-policy and off-policy methods, on OpenAI Gym's MuJoCo continuous control
environments.


title: Instantons in $\sigma$ model and tau functions

abstract:
  We show that a number of multiple integrals may viewed as tau functions of
various integrable hierarchies. The instanton contributions in the
two-dimensional O(3)$\ \sigma $ model is an example of such an approach.


title: Relational PK-Nets for Transformational Music Analysis

abstract:
  In the field of transformational music theory, which emphasizes the possible
transformations between musical objects, Klumpenhouwer networks (K-Nets)
constitute a useful framework with connections in both group theory and graph
theory. Recent attempts at formalizing K-Nets in their most general form have
evidenced a deeper connection with category theory. These formalizations use
diagrams in sets, i.e. functors $\mathbf{C} \to \mathbf{Sets}$ where
$\mathbf{C}$ is often a small category, providing a general framework for the
known group or monoid actions on musical objects. However, following the work
of Douthett and Cohn, transformational music theory has also relied on the use
of relations between sets of the musical elements. Thus, K-Net formalizations
have to be further extended to take this aspect into account. This work
proposes a new framework called relational PK-Nets, an extension of our
previous work on Poly-Klumpenhouwer networks (PK-Nets), in which we consider
diagrams in $\mathbf{Rel}$ rather than $\mathbf{Sets}$. We illustrate the
potential of relational PK-Nets with selected examples, by analyzing pop music
and revisiting the work of Douthett and Cohn.


title:
On the incidence of \textit{WISE} infrared excess among solar analog,
  twin and sibling stars

abstract:
  This study presents a search for IR excess in the 3.4, 4.6, 12 and 22 $\mu$m
bands in a sample of 216 targets, composed of solar sibling, twin and analog
stars observed by the \textit{WISE} mission. In general, an infrared excess
suggests the existence of warm dust around a star. We detected 12 $\mu$m and/or
22 $\mu$m excesses at the 3$\sigma$ level of confidence in five solar analog
stars, corresponding to a frequency of 4.1 $\%$ of the entire sample of solar
analogs analyzed, and in one out of 29 solar sibling candidates, confirming
previous studies. The estimation of the dust properties shows that the sources
with infrared excesses possess circumstellar material with temperatures that,
within the uncertainties, are similar to that of the material found in the
asteroid belt in our solar system. No photospheric flux excess was identified
at the W1 (3.4 $\mu$m) and W2 (4.6 $\mu$m) \textit{WISE} bands, indicating
that, in the majority of stars of the present sample, no detectable dust is
generated. Interestingly, among the sixty solar twin stars analyzed in this
work, no \textit{WISE} photospheric flux excess was detected. However, a
null-detection excess does not necessarily indicate the absence of dust around
a star because different causes, including dynamic processes and instrument
limitations, can mask its presence.


title: Spectrum of the Laplacian on the Vicsek Set "with no loose ends"

abstract:
  We study the spectral properties of a fractal VNLE obtained from the standard
Vicsek set VS by making a countable number of identifications of points so that
all the line segments in VS become circles in VNLE. We show that the standard
Laplacian on VNLE satisfies spectral decimation with the same cubic
renormalization polynomial as for VS, and thereby give a complete description
of all eigenfunctions of the Laplacian. We then study the restrictions of
eigenfunctions to the large circles in VNLE and prove that these are Lipschitz
functions.


title: Hierarchical compositional feature learning

abstract:
  We introduce the hierarchical compositional network (HCN), a directed
generative model able to discover and disentangle, without supervision, the
building blocks of a set of binary images. The building blocks are binary
features defined hierarchically as a composition of some of the features in the
layer immediately below, arranged in a particular manner. At a high level, HCN
is similar to a sigmoid belief network with pooling. Inference and learning in
HCN are very challenging and existing variational approximations do not work
satisfactorily. A main contribution of this work is to show that both can be
addressed using max-product message passing (MPMP) with a particular schedule
(no EM required). Also, using MPMP as an inference engine for HCN makes new
tasks simple: adding supervision information, classifying images, or performing
inpainting all correspond to clamping some variables of the model to their
known values and running MPMP on the rest. When used for classification, fast
inference with HCN has exactly the same functional form as a convolutional
neural network (CNN) with linear activations and binary weights. However, HCN's
features are qualitatively very different.


title:
A relativistic compact stellar model of anisotropic quark matter mixed
  with dark energy

abstract:
  The possibility of strange stars mixed with dark energy to be one of the
candidates for dark energy stars is the main issue of the present study. Our
investigation shows that quark matter acts as dark energy after a certain yet
unknown critical condition inside the quark stars. Our proposed model reveals
that strange stars mixed with dark energy feature a physically acceptable
stable model mimic characteristics of dark energy stars. The plausible
connections are shown through the mass-radius relation as well as the entropy
and temperature. We particularly note that a two-fluid distribution is a major
reason for the anisotropic nature of the spherical stellar system.


title: Pulsation versus metallicism in Am stars as revealed by LAMOST and WASP

abstract:
  We present the results of a study of a large sample of A and Am stars with
spectral types from LAMOST and light curves from WASP. We find that, unlike
normal A stars, $\delta$ Sct pulsations in Am stars are mostly confined to the
effective temperature range 6900 $<$ $T_{\rm eff}$ $<$ 7600 K. We find evidence
that the incidence of pulsations in Am stars decreases with increasing
metallicism (degree of chemical peculiarity). The maximum amplitude of the
pulsations in Am stars does not appear to vary significantly with metallicism.
The amplitude distributions of the principal pulsation frequencies for both A
and Am stars appear very similar and agree with results obtained from Kepler
photometry. We present evidence that suggests turbulent pressure is the main
driving mechanism in pulsating Am stars, rather than the $\kappa$-mechanism,
which is expected to be suppressed by gravitational settling in these stars.


title:
Quasiparticles in an interacting system of charge and monochromatic
  field

abstract:
  The spectrum of an exactly solvable non-relativistic system of a charged
particle interacting with a quantized electromagnetic mode is studied with
various polarizations. Quasiparticle dispersion relations can be derived from
the diagonalized Hamiltonian which, in the case of a linearly polarized field,
indicates a bulk plasmon excitation, whereas in the elliptically and circularly
polarized cases the dispersions exhibit a global minimum and show a singular
behavior as the wavenumber tends to zero. These new type of dispersion
relations lead to modified plasma frequencies and reflectivities, as well as to
negative group velocities. It is shown that the zero-point energy of the system
implies a repulsive force between two parallel plates, which vanishes when the
charge is set to zero.

categories: quant-ph cond-mat.other physics.optics physics.plasm-ph


title:
A Big-Data Approach to Handle Many Process Variations: Tensor Recovery
  and Applications

abstract:
  Fabrication process variations are a major source of yield degradation in the
nano-scale design of integrated circuits (IC), microelectromechanical systems
(MEMS) and photonic circuits. Stochastic spectral methods are a promising
technique to quantify the uncertainties caused by process variations. Despite
their superior efficiency over Monte Carlo for many design cases, these
algorithms suffer from the curse of dimensionality; i.e., their computational
cost grows very fast as the number of random parameters increases. In order to
solve this challenging problem, this paper presents a high-dimensional
uncertainty quantification algorithm from a big-data perspective. Specifically,
we show that the huge number of (e.g., $1.5 \times 10^{27}$) simulation samples
in standard stochastic collocation can be reduced to a very small one (e.g.,
$500$) by exploiting some hidden structures of a high-dimensional data array.
This idea is formulated as a tensor recovery problem with sparse and low-rank
constraints; and it is solved with an alternating minimization approach.
Numerical results show that our approach can simulate efficiently some ICs, as
well as MEMS and photonic problems with over 50 independent random parameters,
whereas the traditional algorithm can only handle several random parameters.


title: Multiround Private Information Retrieval: Capacity and Storage Overhead

abstract:
  The capacity has recently been characterized for the private information
retrieval (PIR) problem as well as several of its variants. In every case it is
assumed that all the queries are generated by the user simultaneously. Here we
consider multiround PIR, where the queries in each round are allowed to depend
on the answers received in previous rounds. We show that the capacity of
multiround PIR is the same as the capacity of single-round PIR (the result is
generalized to also include $T$-privacy constraints). Combined with previous
results, this shows that there is no capacity advantage from multiround over
single-round schemes, non-linear over linear schemes or from $\epsilon$-error
over zero-error schemes. However, we show through an example that there is an
advantage in terms of storage overhead. We provide an example of a multiround,
non-linear, $\epsilon$-error PIR scheme that requires a strictly smaller
storage overhead than the best possible with single-round, linear, zero-error
PIR schemes.


title: Learning Time Series Detection Models from Temporally Imprecise Labels

abstract:
  In this paper, we consider a new low-quality label learning problem: learning
time series detection models from temporally imprecise labels. In this problem,
the data consist of a set of input time series, and supervision is provided by
a sequence of noisy time stamps corresponding to the occurrence of positive
class events. Such temporally imprecise labels commonly occur in areas like
mobile health research where human annotators are tasked with labeling the
occurrence of very short duration events. We propose a general learning
framework for this problem that can accommodate different base classifiers and
noise models. We present results on real mobile health data showing that the
proposed framework significantly outperforms a number of alternatives including
assuming that the label time stamps are noise-free, transforming the problem
into the multiple instance learning framework, and learning on labels that were
manually re-aligned.


title:
Single-branch Er:fiber frequency comb for optical synthesis at the
  $10^{-18}$ level

abstract:
  Laser frequency combs based on erbium-doped fiber mode-locked lasers have
shown great potential for compact, robust and efficient optical clock
comparisons. However, to simultaneously compare multiple optical clock species,
fiber laser frequency combs typically require multiple amplifiers and fiber
optic paths that reduce the achievable frequency stability near 1 part in
$10^{16}$ at 1s. In this paper we describe an erbium-fiber laser frequency comb
that overcomes these conventional challenges and supports optical frequency
synthesis at the millihertz level, or fractionally $3 x 10^{-18}$ $tau^{-1/2}$
by ensuring that all critical fiber paths are within the servo-controlled
feedback loop. We demonstrate the application of this frequency comb as a
synthesizer for optical clocks operating across a wavelength range from 650 nm
to 2100 nm.


title:
Meat adulteration detection through digital image analysis of
  histological cuts using LBP

abstract:
  Food fraud has been an area of great concern due to its risk to public
health, reduction of food quality or nutritional value and for its economic
consequences. For this reason, it's been object of regulation in many countries
(e.g. [1], [2]). One type of food that has been frequently object of fraud
through the addition of water or an aqueous solution is bovine meat. The
traditional methods used to detect this kind of fraud are expensive,
time-consuming and depend on physicochemical analysis that require complex
laboratory techniques, specific for each added substance. In this paper, based
on digital images of histological cuts of adulterated and not-adulterated
(normal) bovine meat, we evaluate the of digital image analysis methods to
identify the aforementioned kind of fraud, with focus on the Local Binary
Pattern (LBP) algorithm.


title: Memory-augmented Attention Modelling for Videos

abstract:
  We present a method to improve video description generation by modeling
higher-order interactions between video frames and described concepts. By
storing past visual attention in the video associated to previously generated
words, the system is able to decide what to look at and describe in light of
what it has already looked at and described. This enables not only more
effective local attention, but tractable consideration of the video sequence
while generating each word. Evaluation on the challenging and popular MSVD and
Charades datasets demonstrates that the proposed architecture outperforms
previous video description approaches without requiring external temporal video
features.


title: Varied reasoning schema in students' written solutions

abstract:
  The Mathematization project investigates students' use of mathematical tools
across the undergraduate physics curriculum. As a part of this project, we look
at intermediate mechanics students' written homework solutions to understand
how they use these tools in approaching traditional mechanics problems. We use
a modified version of the ACER (Activation-Construction-Execution-Reflection)
framework to analyze students' solutions and to identify patterns of
mathematical skills used on traditional problems. We apply techniques borrowed
from network analysis and the Resources Framework to build a "fingerprint" of
students' mathematical tool use. In this paper, we present preliminary findings
on patterns that we identified in students' problem solving.


title: Covariant derivative of fermions and all that

abstract:
  We present detailed pedagogical derivation of covariant derivative of
fermions and some related expressions, including commutator of covariant
derivatives and energy-momentum tensor of a free Dirac field. The text
represents a part of the initial chapter of a one-semester course on
semiclassical gravity.


title:
Revisiting Evidence of Chaos in X-ray Light Curves: The Case of GRS
  1915+105

abstract:
  Nonlinear time series analysis has been widely used to search for signatures
of low-dimensional chaos in light curves emanating from astrophysical bodies. A
particularly popular example is the microquasar GRS 1915+105, whose irregular
but systematic X-ray variability has been well studied using data acquired by
the Rossi X-ray Timing Explorer. With a view to building simpler models of
X-ray variability, attempts have been made to classify the light curves of GRS
1915+105 as chaotic or stochastic. Contrary to some of the earlier suggestions,
after careful analysis, we find no evidence for chaos or determinism in any of
the GRS 1915+105 classes. The dearth of long and stationary data sets
representing all the different variability classes of GRS 1915+105 makes it a
poor candidate for analysis using nonlinear time series techniques. We conclude
that either very exhaustive data analysis with sufficiently long and stationary
light curves should be performed, keeping all the pitfalls of nonlinear time
series analysis in mind, or alternative schemes of classifying the light curves
should be adopted. The generic limitations of the techniques that we point out
in the context of GRS 1915+105 affect all similar investigations of light
curves from other astrophysical sources.


title:
Calibrating Column Density Tracers with Gamma-ray Observations of the
  $\rho$ Ophiuchi Molecular Cloud

abstract:
  Diffuse gamma-ray emission from interstellar clouds results largely from
cosmic ray (CR) proton collisions with ambient gas, regardless of the gas
state, temperature, or dust properties of the cloud. The interstellar medium is
predominantly transparent to both CRs and gamma-rays, so GeV emission is a
unique probe of the total gas column density. The gamma-ray emissivity of a
cloud of known column density is then a measure of the impinging CR population
and may be used to map the kpc-scale CR distribution in the Galaxy. To this
end, we test a number of commonly used column density tracers to evaluate their
effectiveness in modeling the GeV emission from the relatively quiescent,
nearby $\rho$ Ophiuchi molecular cloud. We confirm that both \hi\ and an
appropriate H$_2$ tracer are required to reproduce the total gas column
densities probed by diffuse gamma-ray emisison. We find that the optical depth
at 353 GHz $\tau_{353}$ from Planck reproduces the gamma-ray data best overall
based on the test statistic across the entire region of interest, but near
infrared stellar extinction also performs very well, with smaller spatial
residuals in the densest parts of the cloud.


title:
Gaussian Attention Model and Its Application to Knowledge Base Embedding
  and Question Answering

abstract:
  We propose the Gaussian attention model for content-based neural memory
access. With the proposed attention model, a neural network has the additional
degree of freedom to control the focus of its attention from a laser sharp
attention to a broad attention. It is applicable whenever we can assume that
the distance in the latent space reflects some notion of semantics. We use the
proposed attention model as a scoring function for the embedding of a knowledge
base into a continuous vector space and then train a model that performs
question answering about the entities in the knowledge base. The proposed
attention model can handle both the propagation of uncertainty when following a
series of relations and also the conjunction of conditions in a natural way. On
a dataset of soccer players who participated in the FIFA World Cup 2014, we
demonstrate that our model can handle both path queries and conjunctive queries
well.


title: Topoi of parametrized objects

abstract:
  We give necessary and sufficient conditions on a presentable
infinity-category C so that families of objects of C form an infinity-topos. In
particular, we prove a conjecture of Joyal that this is the case whenever C is
stable.


title: Optimal Binary Autoencoding with Pairwise Correlations

abstract:
  We formulate learning of a binary autoencoder as a biconvex optimization
problem which learns from the pairwise correlations between encoded and decoded
bits. Among all possible algorithms that use this information, ours finds the
autoencoder that reconstructs its inputs with worst-case optimal loss. The
optimal decoder is a single layer of artificial neurons, emerging entirely from
the minimax loss minimization, and with weights learned by convex optimization.
All this is reflected in competitive experimental results, demonstrating that
binary autoencoding can be done efficiently by conveying information in
pairwise correlations in an optimal fashion.


title: Emergent Gravity and the Dark Universe

abstract:
  Recent theoretical progress indicates that spacetime and gravity emerge
together from the entanglement structure of an underlying microscopic theory.
These ideas are best understood in Anti-de Sitter space, where they rely on the
area law for entanglement entropy. The extension to de Sitter space requires
taking into account the entropy and temperature associated with the
cosmological horizon. Using insights from string theory, black hole physics and
quantum information theory we argue that the positive dark energy leads to a
thermal volume law contribution to the entropy that overtakes the area law
precisely at the cosmological horizon. Due to the competition between area and
volume law entanglement the microscopic de Sitter states do not thermalise at
sub-Hubble scales: they exhibit memory effects in the form of an entropy
displacement caused by matter. The emergent laws of gravity contain an
additional `dark' gravitational force describing the `elastic' response due to
the entropy displacement. We derive an estimate of the strength of this extra
force in terms of the baryonic mass, Newton's constant and the Hubble
acceleration scale a_0 =cH_0, and provide evidence for the fact that this
additional `dark gravity~force' explains the observed phenomena in galaxies and
clusters currently attributed to dark matter.


title:
Functional Forms for Tractable Economic Models and the Cost Structure of
  International Trade

abstract:
  We present functional forms allowing a broader range of analytic solutions to
common economic equilibrium problems. These can increase the realism of
pen-and-paper solutions or speed large-scale numerical solutions as
computational subroutines. We use the latter approach to build a tractable
heterogeneous firm model of international trade accommodating economies of
scale in export and diseconomies of scale in production, providing a natural,
unified solution to several puzzles concerning trade costs. We briefly
highlight applications in a range of other fields. Our method of generating
analytic solutions is a discrete approximation to a logarithmically modified
Laplace transform of equilibrium conditions.


title: A Lax pair of the discrete Euler top in terms of quaternions

abstract:
  We proposed the discrete Euler top in 2000. In that paper, exact solutions
and conserved quantities are described. However, a Lax pair of our proposed
discrete Euler top is not contained. Moreover, the Lax pair is still unknown.
In this paper, from a generalized eigenvalue problem, we obtain the Lax pair of
the discrete Euler top. In addition, we introduce another Lax pair of the
discrete Euler top in terms of quaternions.


title: Neuromorphic Silicon Photonic Networks

abstract:
  Photonic systems for high-performance information processing have attracted
renewed interest. Neuromorphic silicon photonics has the potential to integrate
processing functions that vastly exceed the capabilities of electronics. We
report first observations of a recurrent silicon photonic neural network, in
which connections are configured by microring weight banks. A mathematical
isomorphism between the silicon photonic circuit and a continuous neural
network model is demonstrated through dynamical bifurcation analysis.
Exploiting this isomorphism, a simulated 24-node silicon photonic neural
network is programmed using "neural compiler" to solve a differential system
emulation task. A 294-fold acceleration against a conventional benchmark is
predicted. We also propose and derive power consumption analysis for
modulator-class neurons that, as opposed to laser-class neurons, are compatible
with silicon photonic platforms. At increased scale, Neuromorphic silicon
photonics could access new regimes of ultrafast information processing for
radio, control, and scientific computing.


title: Application-layer Fault-Tolerance Protocols

abstract:
  The central topic of this book is application-level fault-tolerance, that is
the methods, architectures, and tools that allow to express a fault-tolerant
system in the application software of our computers. Application-level
fault-tolerance is a sub-class of software fault-tolerance that focuses on the
problems of expressing the problems and solutions of fault-tolerance in the top
layer of the hierarchy of virtual machines that constitutes our computers. This
book shows that application-level fault-tolerance is a key ingredient to craft
truly dependable computer systems--other approaches, such as hardware
fault-tolerance, operating system fault-tolerance, or fault-tolerant
middleware, are also important ingredients to achieve resiliency, but they are
not enough. Failing to address the application layer means leaving a backdoor
open to problems such as design faults, interaction faults, or malicious
attacks, whose consequences on the quality of service could be as unfortunate
as, e.g., a physical fault affecting the system platform. In other words, in
most cases it is simply not possible to achieve complete coverage against a
given set of faults or erroneous conditions without embedding fault-tolerance
provisions also in the application layer.


title:
GPU-Based Parallel Integration of Large Numbers of Independent ODE
  Systems

abstract:
  The task of integrating a large number of independent ODE systems arises in
various scientific and engineering areas. For nonstiff systems, common explicit
integration algorithms can be used on GPUs, where individual GPU threads
concurrently integrate independent ODEs with different initial conditions or
parameters. One example is the fifth-order adaptive Runge-Kutta-Cash-Karp
(RKCK) algorithm. In the case of stiff ODEs, standard explicit algorithms
require impractically small time-step sizes for stability reasons, and implicit
algorithms are therefore commonly used instead to allow larger time steps and
reduce the computational expense. However, typical high-order implicit
algorithms based on backwards differentiation formulae (e.g., VODE, LSODE)
involve complex logical flow that causes severe thread divergence when
implemented on GPUs, limiting the performance. Therefore, alternate algorithms
are needed. A GPU-based Runge-Kutta-Chebyshev (RKC) algorithm can handle
moderate levels of stiffness and performs significantly faster than not only an
equivalent CPU version but also a CPU-based implicit algorithm (VODE) based on
results shown in the literature. In this chapter, we present the mathematical
background, implementation details, and source code for the RKCK and RKC
algorithms for use integrating large numbers of independent systems of ODEs on
GPUs. In addition, brief performance comparisons are shown for each algorithm,
demonstrating the potential benefit of moving to GPU-based ODE integrators.


title: Automated Application Offloading through Ant-inspired Decision-Making

abstract:
  -The explosive trend of smartphone usage as the most effective and convenient
communication tools of human life in recent years make developers build ever
more complex smartphone applications. Gaming, navigation, video editing,
augmented reality, and speech recognition applications require considerable
computational power and energy. Although smart- phones have a wide range of
capabilities - GPS, WiFi, cameras - their inherent limitations - frequent
disconnections, mobility - and significant constraints - size, lower weights,
longer battery life - make difficult to exploiting their full potential to run
complex applications. Several research works have proposed solutions in
application offloading domain, but few ones concerning the highly changing
properties of the environment. To address these issues, we realize an automated
application offloading middleware, ACOMMA, with dynamic and re-adaptable
decision-making engine. The decision engine of ACOMMA is based on an ant-
inspired algorithm.


title: Towards the neural code endowed in cortical microcolumns

abstract:
  This article reports on simulations that show how, starting with a form of
neural lattice structure, it is possible to reversibly generate many
alternative isomers with a lower structural symmetry, which results from
twisting two hexagons around a central bond.


title:
Clusters of calcium release channels harness the Ising phase transition
  to confine their elementary intracellular signals

abstract:
  Intracellular Ca signals represent a universal mechanism of cell function.
Messages carried by Ca are local, rapid, and powerful enough to be delivered
over the thermal noise. A higher signal to noise ratio is achieved by a
cooperative action of Ca release channels such as IP3 receptors or ryanodine
receptors arranged in clusters or release units containing a few to several
hundred release channels. The release channels synchronize their openings via
Ca-induced-Ca-release, generating high-amplitude local Ca signals known as
puffs in neurons or sparks in muscle cells. Despite the high release amplitude
and positive feedback nature of the activation, Ca signals are strictly
confined in time and space by an unexplained termination mechanism. Here we
show that the collective transition of release channels from an open to a
closed state is identical to the phase transition associated with the reversal
of magnetic field in an Ising ferromagnet. We demonstrate this mechanism using
numerical model simulations of Ca sparks over a wide range of cluster sizes
from 25 to 169 release channels. While prior studies suggested contributions of
stochastic attrition and Ca store depletion, our new simple quantitative
criterion closely predicts the depletion level required for spark termination
for each cluster size. We further formulate exact requirements for a cluster of
release channels to follow the Ising model in any cell type. Thus we describe
deterministically the behaviour of a system on a coarser scale (release unit)
which is random on a finer scale (release channels), bridging the gap between
scales. Our results provide the first exact mapping of a nanoscale biological
signalling model to an interacting particle system in statistical physics,
making the extensive mathematical apparatus available to quantitative biology.


title:
The nova-like nebular optical spectrum of V404 Cygni at the beginning of
  the 2015 outburst decay

abstract:
  We report on FORS2 optical spectroscopy of the black hole X-ray binary V404
Cygni, performed at the very beginning of its 2015 outburst decay, complemented
by quasi-simultaneous $Swift$ X-ray and ultra-violet as well as REM
near-infrared observations. Its peculiar spectrum is dominated by a wealth of
emission signatures of HI, HeI, and higher ionisation species, in particular
FeII. The spectral features are divided between broad red-shifted and narrow
stationary varieties, the latter being emitted in the outer regions. Continuum
and line variability at short time scale is high and we find Baldwin
effect-like anti-correlations between the full-widths at half-maximum and
equivalent widths of the broad lines with their local continua. The Balmer
decrement H{\alpha}/H{\beta} is also abnormally large at $4.61\pm0.62$. We
argue that these properties hint at the broad lines being optically thick and
arising within a circumbinary component in which shocks between faster
optically thick and slower optically thin regions may occur. We associate it to
a nova-like nebula formed by the cooling remnant of strong accretion disc winds
that turned off when the mass-accretion rate dropped following the last major
flare. The FeII lines likely arise from the overlap region between this nebula
and the companion star winds, whereas we favour the shocks within the nebula as
responsible for the optical continuum via self-absorbed optically thin
bremsstrahlung. The presence of a near-infrared excess also points towards the
contribution of a strongly variable compact jet or a dusty component.


title: SOHO Comets: 20-Years and 3,000 Objects Later

abstract:
  We present a summary of the more than 3,000 sungrazing and near-Sun comets
discovered in coronagraph images returned by the Solar and Heliospheric
Observatory (SOHO), since its launch in December 1995. We address each of the
four main populations of objects observed by SOHO: Kreutz (sungrazing) group,
Meyer group, Marsden and Kracht (96P-Family) group, and non-group comets.
Discussions for each group include basic properties, discovery statistics, and
morphological appearance. In addition to updating the community on the status
of the discoveries by SOHO, we also show that the rate of discovery of Kreutz
sungrazers has likely remained static since approximately 2003, and report on
the first likely fragmentation pair observed within the Meyer group.


title:
The intermediate r-process in core-collapse supernovae driven by the
  magneto-rotational instability

abstract:
  We investigated r-process nucleosynthesis in magneto-rotational supernovae,
based on a new explosion mechanism induced by the magneto-rotational
instability. A series of axisymmetric magneto-hydrodynamical simulations with
detailed microphysics including neutrino heating is performed, numerically
resolving the magneto-rotational instability. Neutrino-heating dominated
explosions, enhanced by magnetic fields, showed mildly neutron-rich ejecta
producing nuclei up to $A \sim 130$ (i.e. the weak r-process), while explosion
models with stronger magnetic fields reproduce a solar-like r-process pattern.
More commonly seen abundance patterns in our models are in between the weak and
regular r-process, producing lighter and intermediate mass nuclei. These {\it
intermediate r-processes} exhibit a variety of abundance distributions,
compatible with several abundance patterns in r-process-enhanced metal-poor
stars. The amount of Eu ejecta $\sim 10^{-5} M_\odot$ in magnetically-driven
jets agrees with predicted values in the chemical evolution of early galaxies.
In contrast, neutrino-heating dominated explosions have a significant amount of
Fe ($^{56}{\rm Ni}$) and Zn, comparable to regular supernovae and hypernovae,
respectively. These results indicate magneto-rotational supernovae can produce
a wide range of heavy nuclei from iron-group to r-process elements, depending
on the explosion dynamics.


title: FIRE in the Field: Simulating the Threshold of Galaxy Formation

abstract:
  We present a suite of 15 cosmological zoom-in simulations of isolated dark
matter halos, all with masses of $M_{\rm halo} \approx 10^{10}\,{\rm M}_\odot$
at $z=0$, in order to understand the relationship between halo assembly, galaxy
formation, and feedback's effects on the central density structure in dwarf
galaxies. These simulations are part of the Feedback in Realistic Environments
(FIRE) project and are performed at extremely high resolution. The resultant
galaxies have stellar masses that are consistent with rough abundance matching
estimates, coinciding with the faintest galaxies that can be seen beyond the
virial radius of the Milky Way ($M_\star/{\rm M}_\odot\approx 10^5-10^7$). This
non-negligible spread in stellar mass at $z=0$ in halos within a narrow range
of virial masses is strongly correlated with central halo density or maximum
circular velocity $V_{\rm max}$. Much of this dependence of $M_\star$ on a
second parameter (beyond $M_{\rm halo}$) is a direct consequence of the $M_{\rm
halo}\sim10^{10}\,{\rm M}_\odot$ mass scale coinciding with the threshold for
strong reionization suppression: the densest, earliest-forming halos remain
above the UV-suppression scale throughout their histories while late-forming
systems fall below the UV-suppression scale over longer periods and form fewer
stars as a result. In fact, the latest-forming, lowest-concentration halo in
our suite fails to form any stars. Halos that form galaxies with
$M_\star\gtrsim2\times10^{6}\,{\rm M}_\odot$ have reduced central densities
relative to dark-matter-only simulations, and the radial extent of the density
modifications is well-approximated by the galaxy half-mass radius $r_{1/2}$.
This apparent stellar mass threshold of $M_\star \approx 2\times 10^{6} \approx
2\times 10^{-4} \,M_{\rm halo}$ is broadly consistent with previous work and
provides a testable prediction of FIRE feedback models in LCDM.


title:
Hubble Space Telescope Proper Motions of Individual Stars in Stellar
  Streams: Orphan, Sagittarius, Lethe, and the New "Parallel" Stream

abstract:
  We present a multi-epoch Hubble Space Telescope (HST) study of stellar proper
motions (PMs) for four fields along the Orphan Stream. We determine absolute
PMs of several individual stars per target field using established techniques
that utilize distant background galaxies to define a stationary reference
frame. Five Orphan Stream stars are identified in one of the four fields based
on combined color-magnitude and PM information. The average PM is consistent
with the existing model of the Orphan stream by Newberg et al. In addition to
the Orphan stream stars, we detect stars that likely belong to other stellar
streams. To identify which stellar streams these stars belong to, we examine
the 2-d bulk motion of each group of stars on the sky by subtracting the PM
contribution of the solar motion (which is a function of position on the sky
and distance) from the observed PMs, and comparing the vector of net motion
with the spatial extent of known stellar streams. By doing this, we identify
candidate stars in the Sagittarius and Lethe streams, and a newly-found stellar
stream at a distance of ~17 kpc, which we tentatively name the "Parallel
stream". Together with our Sagittarius stream study (Sohn et al., 2015, ApJ,
803, 56), this work demonstrates that even in the Gaia era, HST will continue
to be advantageous in measuring PMs of old stellar populations on a
star-by-star basis, especially for distances beyond ~10 kpc.


title:
Non-equilibrium effective field theory for absorbing state phase
  transitions in driven open quantum spin systems

abstract:
  Phase transitions to absorbing states are among the simplest examples of
critical phenomena out of equilibrium. The characteristic feature of these
models is the presence of a fluctuationless configuration which the dynamics
cannot leave, which has proved a rather stringent requirement in experiments.
Recently, a proposal to seek such transitions in highly tuneable systems of
cold atomic gases offers to probe this physics and, at the same time, to
investigate the robustness of these transitions to quantum coherent effects.
Here we specifically focus on the interplay between classical and quantum
fluctuations in a simple driven open quantum model which, in the classical
limit, reproduces a contact process, which is known to undergo a continuous
transition in the "directed percolation" universality class. We derive an
effective long-wavelength field theory for the present class of open spin
systems and show that, due to quantum fluctuations, the nature of the
transition changes from second to first order, passing through a bicritical
point which appears to belong instead to the "tricritical directed percolation"
class.


title: Emergent equilibrium in many-body optical bistability

abstract:
  Many-body systems constructed of quantum-optical building blocks can now be
realized in experimental platforms ranging from exciton-polariton fluids to
ultracold gases of Rydberg atoms, establishing a fascinating interface between
traditional many-body physics and the driven-dissipative, non-equilibrium
setting of cavity-QED. At this interface, the standard techniques and
intuitions of both fields are called into question, obscuring issues as
fundamental as the role of fluctuations, dimensionality, and symmetry on the
nature of collective behavior and phase transitions. Here, we study the
driven-dissipative Bose-Hubbard model, a minimal description of numerous
atomic, optical, and solid-state systems in which particle loss is countered by
coherent driving. Despite being a lattice version of optical bistability---a
foundational and patently non-equilibrium model of cavity-QED---the steady
state possesses an emergent equilibrium description in terms of a classical
Ising model. We establish this picture by identifying a limit in which the
quantum dynamics is asymptotically equivalent to non-equilibrium Langevin
equations, which support a phase transition described by model A of the
Hohenberg-Halperin classification. Numerical simulations of the Langevin
equations corroborate this picture, producing results consistent with the
behavior of a finite-temperature Ising model.


title:
Initial mass function of planetesimals formed by the streaming
  instability

abstract:
  The streaming instability is a mechanism to concentrate solid particles into
overdense filaments that undergo gravitational collapse and form planetesimals.
However, it remains unclear how the initial mass function of these
planetesimals depends on the box dimensions of numerical simulations. To
resolve this, we perform simulations of planetesimal formation with the largest
box dimensions to date, allowing planetesimals to form simultaneously in
multiple filaments that can only emerge within such large simulation boxes. In
our simulations, planetesimals with sizes between 80 km and several hundred
kilometers form. We find that a power law with a rather shallow exponential
cutoff at the high-mass end represents the cumulative birth mass function
better than an integrated power law. The steepness of the exponential cutoff is
largely independent of box dimensions and resolution, while the exponent of the
power law is not constrained at the resolutions we employ. Moreover, we find
that the characteristic mass scale of the exponential cutoff correlates with
the mass budget in each filament. Together with previous studies of
high-resolution simulations with small box domains, our results therefore imply
that the cumulative birth mass function of planetesimals is consistent with an
exponentially tapered power law with a power-law exponent of approximately -1.6
and a steepness of the exponential cutoff in the range of 0.3-0.4.


title:
Galaxy formation in the Planck cosmology - IV. Mass and environmental
  quenching, conformity and clustering

abstract:
  We study the quenching of star formation as a function of redshift,
environment and stellar mass in the galaxy formation simulations of Henriques
et al. (2015), which implement an updated version of the Munich semi-analytic
model (L-GALAXIES) on the two Millennium Simulations after scaling to a Planck
cosmology. In this model massive galaxies are quenched by AGN feedback
depending on both black hole and hot gas mass, and hence indirectly on stellar
mass. In addition, satellite galaxies of any mass can be quenched by
ram-pressure or tidal stripping of gas and through the suppression of gaseous
infall. This combination of processes produces quenching efficiencies which
depend on stellar mass, host halo mass, environment density, distance to group
centre and group central galaxy properties in ways which agree qualitatively
with observation. Some discrepancies remain in dense regions and close to group
centres, where quenching still seems too efficient. In addition, although the
mean stellar age of massive galaxies agrees with observation, the assumed AGN
feedback model allows too much ongoing star formation at late times. The fact
that both AGN feedback and environmental effects are stronger in higher density
environments leads to a correlation between the quenching of central and
satellite galaxies which roughly reproduces observed conformity trends inside
haloes.


title: A map of the non-thermal WIMP

abstract:
  We study the effect of the elastic scattering on the non-thermal WIMP, which
is produced by direct decay of heavy particles at the end of reheating. The
non-thermal WIMP becomes important when the reheating temperature is well below
the freeze-out temperature. Usually, two limiting cases have been considered.
One is that the produced high energetic dark matter particles are quickly
thermalized due to the elastic scattering with background radiations. The
corresponding relic abundance is determined by the thermally averaged
annihilation cross-section at the reheating temperature. The other one is that
the initial abundance is too small for the dark matter to annihilate so that
the final relic is determined by the initial amount itself. We study the
regions between these two limits, and show that the relic density depends not
only on the annihilation rate, but also on the elastic scattering rate.
Especially, the relic abundance of the p-wave annihilating dark matter
crucially relies on the elastic scattering rate because the annihilation
cross-section is sensitive to the dark matter velocity. We categorize the
parameter space into several regions where each region has distinctive
mechanism for determining the relic abundance of the dark matter at the present
Universe. The consequence on the (in)direct detection is also studied.


title: Realizing Haldane Model in Fe-based Honeycomb Ferromagnetic Insulators

abstract:
  The topological Haldane model (THM) on a honeycomb lattice is a prototype of
systems hosting topological phases of matter without external fields. It is the
simplest model exhibiting the quantum Hall effect without Landau levels, which
motivated theoretical and experimental explorations of topological insulators
and superconductors. Despite its simplicity, its realization in condensed
matter systems has been elusive due to a seemingly difficult condition of
spinless fermions with sublattice-dependent magnetic flux terms. While there
have been theoretical proposals including elaborate atomic-scale engineering,
identifying candidate THM materials has not been successful, and the first
experimental realization was recently made in ultracold atoms. Here we suggest
that a series of Fe-based honeycomb ferromagnetic insulators, AFe2(PO4)2
(A=Ba,Cs,K,La) possess Chern bands described by the THM. How to detect the
quantum anomalous Hall effect is also discussed.


title:
Identifying four $INTEGRAL$ sources in the Galactic Plane via
  VLT/optical and $XMM$-$Newton$/X-ray spectroscopy

abstract:
  We report on FORS2 spectroscopy aiming at the identification of four Galactic
Plane sources discovered by $INTEGRAL$, IGR J18088-2741, IGR J18381-0924, IGR
J17164-3803, and IGR J19173+0747, complemented by $XMM$-$Newton$ spectroscopy
for IGR J18381-0924. The presence of broad emission lines of neutral H and He
and a flat Balmer decrement H{\alpha}/H{\beta} show that IGR J18088-2741 is a
cataclysmic variable located beyond 8 kpc. For IGR J18381-0924, the detection
of red-shifted H{\alpha} and neutral O emission signatures and the absence of
narrow forbidden emission lines point towards a low-luminosity Seyfert 1.9
nature at $z=0.031\pm0.002$. Its $XMM$-$Newton$ spectrum, best-fit by an
absorbed ${\Gamma}=1.19\pm0.07$ power law combined with a
$z=0.026_{-0.016}^{+0.008}$ red-shifted iron emission feature, is in agreement
with this classification. The likely IGR J17164-3803 optical counterpart is an
M2 III star at 3 to 4 kpc which, based on the X-ray spectrum of the source, is
the companion of a white dwarf in an X-ray faint symbiotic system. Finally, we
challenge the accepted identification of IGR J19173+0747 as an high mass X-ray
binary. Indeed, the USNO optical counterpart is actually a blend of two objects
located at the most likely 3 kpc distance, both lying within the error circle
of the Swift position. The first is a cataclysmic variable, which we argue is
the real nature of IGR J19173+0747. However, we cannot rule out the second one
that we identify as an F3 V star that, if associated to IGR J19173+0747, likely
belongs to a quiescent X-ray binary.


title:
Constraining the epoch of reionization from the observed properties of
  the high-z Universe

abstract:
  We combine observational data on a dozen independent cosmic properties at
high-$z$ with the information on reionization drawn from the spectra of distant
luminous sources and the cosmic microwave background (CMB) to constrain the
interconnected evolution of galaxies and the intergalactic medium since the
dark ages. The only acceptable solutions are concentrated in two narrow sets.
In one of them reionization proceeds in two phases: a first one driven by
Population III stars, completed at $z\sim 10$, and after a short recombination
period a second one driven by normal galaxies, completed at $z\sim 6$. In the
other set both kinds of sources work in parallel until full reionization at
$z\sim 6$. The best solution with double reionization gives excellent fits to
all the observed cosmic histories, but the CMB optical depth is 3-$\sigma$
larger than the recent estimate from the Planck data. Alternatively, the best
solution with single reionization gives less good fits to the observed star
formation rate density and cold gas mass density histories, but the CMB optical
depth is consistent with that estimate. We make several predictions, testable
with future observations, that should discriminate between the two reionization
scenarios. As a byproduct our models provide a natural explanation to some
characteristic features of the cosmic properties at high-$z$, as well as to the
origin of globular clusters.


title:
New physical insights about Tidal Disruption Events from a comprehensive
  observational inventory at X-ray wavelengths

abstract:
  We perform a comprehensive study of the X-ray emission from 70 transient
sources which have been classified as a tidal disruption event (TDE) in the
literature. We explore the properties of these candidates using nearly three
decades of X-ray observations to quantify the properties and characteristics of
X-ray TDEs observationally. We find that the emission from X-ray TDEs increase
by two to four orders of magnitude compared to pre-flare constraints, which
evolves significantly with time and decays with powerlaw indices that are
typically shallower than the canonical $t^{-5/3}$ decay law, implying that
X-ray TDEs are viscously delayed. These events exhibit enhanced column
densities relative to Galactic and are quite soft in nature, with no strong
correlation between the amount of detected soft and hard emission. At peak,
jetted events have an X-ray to optical ratio $\gg$1, while non-jetted events
have a ratio $\sim$1, which suggests that these events undergo reprocessing at
different rates. X-ray TDEs have long $T_{90}$ values consistent with that
expected from a viscously-driven accretion disk formed by the disruption of a
main-sequence star by a black hole with a mass $<$$10^{7}M_{\odot}$. The
isotropic luminosities of X-ray TDEs is bimodal such that jetted and non-jetted
events are separated by a "reprocessing valley" which we suggest is naturally
populated by optical/UV TDEs that most likely produce X-rays, but due to
reprocessing this emission is "veiled" from observations. Our results suggest
that non-jetted X-ray TDEs likely originate from partial disruptions and/or
disruptions of low mass stars.


title: On higher Dirac structures

abstract:
  We study higher-order analogues of Dirac structures, extending the
multisymplectic structures that arise in field theory. We define higher Dirac
structures as involutive subbundles of $TM+\wedge^k TM^*$ satisfying a weak
version of the usual lagrangian condition (which agrees with it only when
$k=1$). Higher Dirac structures transversal to $TM$ recover the higher Poisson
structures introduced in [8] as the infinitesimal counterparts of
multisymplectic groupoids. We describe the leafwise geometry underlying an
involutive isotropic subbundle in terms of a distinguished 1-cocycle in a
natural differential complex, generalizing the presymplectic foliation of a
Dirac structure. We also identify the global objects integrating higher Dirac
structures.


title: Asymmetric Dark Matter and Baryogenesis from Pseudoscalar Inflation

abstract:
  We show that both the baryon asymmetry of the Universe and the dark matter
abundance can be explained within a single framework that makes use of
maximally helical hypermagnetic fields produced during pseudoscalar inflation
and the chiral anomaly in the Standard Model. We consider a minimal asymmetric
dark matter model free from anomalies and constraints. We find that the
observed baryon and the dark matter abundances are achieved for a wide range of
inflationary parameters, and the dark matter mass ranges between 7-15 GeV. The
novelty of our mechanism stems from the fact that the same source of CP
violation occurring during inflation explains both baryonic and dark matter in
the Universe with two inflationary parameters, hence addressing all the initial
condition problems in an economical way.


title: Active demultiplexing of single-photons from a solid-state source

abstract:
  A scheme for active temporal-to-spatial demultiplexing of single-photons
generated by a solid-state source is introduced. The scheme scales
quasi-polynomially with photon number, providing a viable technological path
for routing n photons in the one temporal stream from a single emitter to n
different spatial modes. The active demultiplexing is demonstrated using a
state-of-the-art photon source---a quantum-dot deterministically coupled to a
micropillar cavity---and a custom-built demultiplexer---a network of
electro-optically reconfigurable waveguides monolithically integrated in a
lithium niobate chip. The measured demultiplexer performance can enable a
six-photon rate three orders of magnitude higher than the equivalent heralded
SPDC source, providing a platform for intermediate quantum computation
protocols.


title:
KPZ equation with short-range correlated noise: emergent symmetries and
  non-universal observables

abstract:
  We investigate the stationary-state fluctuations of a growing one-dimensional
interface described by the KPZ dynamics with a noise featuring smooth spatial
correlations of characteristic range $\xi$. We employ Non-perturbative
Functional Renormalization Group methods in order to resolve the properties of
the system at all scales. We show that the physics of the standard
(uncorrelated) KPZ equation emerges on large scales independently of $\xi$.
Moreover, the Renormalization Group flow is followed from the initial condition
to the fixed point, that is from the microscopic dynamics to the large-distance
properties. This provides access to the small-scale features (and their
dependence on the details of the noise correlations) as well as to the
universal large-scale physics. In particular, we compute the kinetic energy
spectrum of the stationary state as well as its non-universal amplitude. The
latter is experimentally accessible by measurements at large scales and retains
a signature of the microscopic noise correlations. Our results are compared to
previous analytical and numerical results from independent approaches. They are
in agreement with direct numerical simulations for the kinetic energy spectrum
as well as with the prediction, obtained with the replica trick by Gaussian
variational method, of a crossover in $\xi$ of the non-universal amplitude of
this spectrum.


title: Clustering of non-ergodic eigenstates in quantum spin glasses

abstract:
  The two primary categories for eigenstate phases of matter at finite
temperature are many-body localization (MBL) and the eigenstate thermalization
hypothesis (ETH). We show that in the paradigmatic quantum $p$-spin models of
spin-glass theory, eigenstates violate ETH yet are not MBL either. A mobility
edge, which we locate to leading order in $1/p$ using the forward-scattering
approximation and replica techniques, separates the non-ergodic phase at small
transverse field from an ergodic phase at large transverse field. The
non-ergodic phase is also bounded from above in temperature, by a transition in
configuration-space statistics reminiscent of the clustering transition in
spin-glass theory. We show that the non-ergodic eigenstates are organized in
clusters which exhibit distinct magnetization patterns, as characterized by an
eigenstate variant of the Edwards-Anderson order parameter.


title:
Dynamical modeling validation of parent bodies associated with newly
  discovered CMN meteor showers

abstract:
  Context: Results from previous searches for new meteor showers in the
combined Croatian Meteor Network and SonotaCo meteor databases suggested
possible parent bodies for several newly identified showers. Aims: We aim to
perform an analysis to validate the connection between the identified showers
and candidate parent bodies. Methods: Simulated particles were ejected from
candidate parent bodies, a dynamical modeling was performed and the results
were compared to the real meteor shower observations. Results: From the 13
analysed cases, three were found to be connected with comets, four with
asteroids which are possibly dormant comets, four were inconclusive or
negative, and two need more observational data before any conclusions can be
drawn.


title: Synchronizing noisy nonidentical oscillators by transient uncoupling

abstract:
  Synchronization is the process of achieving identical dynamics among coupled
identical units. If the units are different from each other, their dynamics
cannot become identical; yet, after transients, there may emerge a functional
relationship between them -- a phenomenon termed "generalized synchronization."
Here, we show that the concept of transient uncoupling, recently introduced for
synchronizing identical units, also supports generalized synchronization among
nonidentical chaotic units. Generalized synchronization can be achieved by
transient uncoupling even when it is impossible by regular coupling. We
furthermore demonstrate that transient uncoupling stabilizes synchronization in
the presence of common noise. Transient uncoupling works best if the units stay
uncoupled whenever the driven orbit visits regions that are locally diverging
in its phase space. Thus, to select a favorable uncoupling region, we propose
an intuitive method that measures the local divergence at the phase points of
the driven unit's trajectory by linearizing the flow and subsequently
suppresses the divergence by uncoupling.


title:
Measuring the Magnetic Flux Density with Flux Loops and Hall Probes in
  the CMS Magnet Flux Return Yoke

abstract:
  The Compact Muon Solenoid (CMS) is a general purpose detector, designed to
run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its
distinctive features include a 4 T superconducting solenoid with 6-m-diameter
by 12.5-m-length free bore, enclosed inside a 10,000-ton return yoke made of
construction steel. The flux return yoke consists of five dodecagonal
three-layered barrel wheels and four end-cap disks at each end comprised of
steel blocks up to 620 mm thick, which serve as the absorber plates of the muon
detection system. To measure the field in and around the steel, a system of 22
flux loops and 82 3-D Hall sensors is installed on the return yoke blocks. A
TOSCA 3-D model of the CMS magnet is developed to describe the magnetic field
everywhere outside the tracking volume that was measured with the field-mapping
machine. The voltages induced in the flux loops by the magnetic flux changing
during the CMS magnet standard ramps down are measured with six 16-bit DAQ
modules. The off-line integration of the induced voltages reconstructs the
magnetic flux density in the yoke steel blocks at the operational magnet
current of 18.164 kA. The results of the flux loop measurements during three
magnet ramps down are presented and discussed.


title:
Nanostructured LnBaCo2O6-d (Ln = Sm, Gd) with layered structure for
  Intermediate Temperature SOFC cathodes

abstract:
  We evaluated for the first time the use of nanostructured layered perovskites
of formulae LnBaCo2O6-d with Ln = Sm and Gd (SBCO and GBCO, respetively) as
SOFC cathodes, finding promising electrochemical properties in the intermediate
temperature range (~700{\deg}C). The synthesis of these nanomaterials, not
reported before, was achieved by using porous templates to confine the chemical
reagents in regions of about 200 nm and 800 nm. The performance of
nanostructured SBCO and GBCO cathodes for the oxygen reduction reaction was
analyzed in symmetrical cells using Gd2O3-doped CeO2 (GDC) as electrolyte. For
this purpose, nanostructured SBCO and GBCO cathodes were deposited on both
sides of the electrolyte by a simple thick-film procedure and evaluated by
Electrochemical Impedance Spectroscopy technique under different operating
conditions. We found that cathodes synthesized using smaller template pores
exhibited better performance. Besides, SBCO cathodes displayed lower
area-specific resistance than GBCO ones.


title: Antiproton identification below threshold with AMS-02 RICH detector

abstract:
  The Alpha Magnetic Spectrometer (AMS-02) was installed on the International
Space Station (ISS) and it has been collecting data successfully since May
2011. The main goals of AMS-02 are the search for cosmic anti-matter, dark
matter and the precise measurement of the relative abundance of elements and
isotopes in galactic cosmic rays. In order to identify particle properties,
AMS-02 includes several specialized sub-detectors. Among them, the AMS-02 Ring
Imaging Cherenkov detector (RICH) is designed to provide a very precise
measurement of the velocity and electric charge of particles. We describe a
method to reject the dominant electron background in antiproton identification
with the use of the AMS-02 RICH detector as a veto for rigidities below 3 GV.
Ray tracing integration method is used to maximize the statistics of $\bar{p}$
with the lowest possible $e^{-}$ background, providing 4 times rejection power
gain for $e^{-}$ background with respect to only 3\% of $\bar{p}$ signal
efficiency loss. By using the collected cosmic-rays data, $e^{-}$ contamination
can be well suppressed within 3\% with $\beta \approx 1$, while keeping 76\%
efficiency for $\bar{p}$ below the threshold.


title:
Quantum spectral analysis: frequency in time, with applications to
  signal and image processing

abstract:
  A quantum time-dependent spectrum analysis, or simply, quantum spectral
analysis (QSA) is presented in this work, and it is based on Schrodinger
equation, which is a partial differential equation that describes how the
quantum state of a non-relativistic physical system changes with time. In
classic world is named frequency in time (FIT), which is presented here in
opposition and as a complement of traditional spectral analysis
frequency-dependent based on Fourier theory. Besides, FIT is a metric, which
assesses the impact of the flanks of a signal on its frequency spectrum, which
is not taken into account by Fourier theory and even less in real time. Even
more, and unlike all derived tools from Fourier Theory (i.e., continuous,
discrete, fast, short-time, fractional and quantum Fourier Transform, as well
as, Gabor) FIT has the following advantages: a) compact support with excellent
energy output treatment, b) low computational cost, O(N) for signals and O(N2)
for images, c) it does not have phase uncertainties (indeterminate phase for
magnitude = 0) as Discrete and Fast Fourier Transform (DFT, FFT, respectively),
d) among others. In fact, FIT constitutes one side of a triangle (which from
now on is closed) and it consists of the original signal in time, spectral
analysis based on Fourier Theory and FIT. Thus a toolbox is completed, which it
is essential for all applications of Digital Signal Processing (DSP) and
Digital Image Processing (DIP); and, even, in the latter, FIT allows edge
detection (which is called flank detection in case of signals), denoising,
despeckling, compression, and superresolution of still images. Such
applications include signals intelligence and imagery intelligence. On the
other hand, we will present other DIP tools, which are also derived from the
Schrodinger equation.


title: Large widely-connected spaces

abstract:
  We show that there are widely-connected spaces of arbitrarily large
cardinality, answering a question by David Bellamy.


title: Normalizing Flows on Riemannian Manifolds

abstract:
  We consider the problem of density estimation on Riemannian manifolds.
Density estimation on manifolds has many applications in fluid-mechanics,
optics and plasma physics and it appears often when dealing with angular
variables (such as used in protein folding, robot limbs, gene-expression) and
in general directional statistics. In spite of the multitude of algorithms
available for density estimation in the Euclidean spaces $\mathbf{R}^n$ that
scale to large n (e.g. normalizing flows, kernel methods and variational
approximations), most of these methods are not immediately suitable for density
estimation in more general Riemannian manifolds. We revisit techniques related
to homeomorphisms from differential geometry for projecting densities to
sub-manifolds and use it to generalize the idea of normalizing flows to more
general Riemannian manifolds. The resulting algorithm is scalable, simple to
implement and suitable for use with automatic differentiation. We demonstrate
concrete examples of this method on the n-sphere $\mathbf{S}^n$.


title: Learning Influence Functions from Incomplete Observations

abstract:
  We study the problem of learning influence functions under incomplete
observations of node activations. Incomplete observations are a major concern
as most (online and real-world) social networks are not fully observable. We
establish both proper and improper PAC learnability of influence functions
under randomly missing observations. Proper PAC learnability under the
Discrete-Time Linear Threshold (DLT) and Discrete-Time Independent Cascade
(DIC) models is established by reducing incomplete observations to complete
observations in a modified graph. Our improper PAC learnability result applies
for the DLT and DIC models as well as the Continuous-Time Independent Cascade
(CIC) model. It is based on a parametrization in terms of reachability
features, and also gives rise to an efficient and practical heuristic.
Experiments on synthetic and real-world datasets demonstrate the ability of our
method to compensate even for a fairly large fraction of missing observations.


title: Coronal properties of the luminous radio-quiet quasar QSO B2202$-$209

abstract:
  We present an analysis of the joint $XMM$-$Newton$ and $NuSTAR$ observations
of the radio-quiet quasar QSO B2202$-$209. Using an optical observation from
the Hale Telescope at the Palomar Observatory, we revise the redshift of the
source from the previously reported $z=1.77$ to $z=0.532$, and we estimate the
mass of the central black hole, $\log (M_{\rm BH}/M_{\odot}) = 9.08 \pm 0.18$.
The X-ray spectrum of this source can be well described by a power-law of
photon index $\Gamma = 1.82 \pm 0.05$ with $E_{\rm cut} =
152_{-54}^{+103}\,{\rm keV}$, in the rest frame of the source. Assuming a
Comptonisation model, we estimate the coronal temperature to be $kT_{\rm
e}=42\pm 3 \,{\rm keV}$ and $kT_{\rm e}= 56 \pm 3\,{\rm keV}$ for a spherical
and a slab geometry, respectively. The coronal properties are comparable to the
ones derived for local AGN, despite a difference of around one order of
magnitude in black hole mass and X-ray luminosity ($L_{2-10} = 1.93\times
10^{45}\,{\rm erg\,s^{-1}}$). The quasar is X-ray loud, with an unusually flat
observed optical-to-X-ray spectral slope $\alpha_{\rm OX} = 1.00 \pm 0.02$, and
has an exceptionally strong optical [O III] line. Assuming that both the X-ray
emission and the [O III] line are isotropic, these two extreme properties can
be explained by a nearly edge-on disk, leading to a reduction in the observed
UV continuum light.


title: Structural characterizations of water-metal interfaces

abstract:
  We analyze and compare the structural, dynamical, and electronic properties
of liquid water next to prototypical metals including Pt, graphite, and
graphene. Our results are built on Born-Oppenheimer molecular dynamics (BOMD)
generated using density functional theory (DFT) which explicitly include van
der Waals (vdW) interactions within a first principles approach. All
calculations reported use large simulation cells, allowing for an accurate
treatment of the water-electrode interfaces. We have included vdW interactions
through the use of the optB86b-vdW exchange correlation functional. Comparisons
with the Perdew-Burke-Ernzerhof (PBE) exchange correlation functional are also
shown. We find an initial peak, due to chemisorption, in the density profile of
the liquid water-Pt interface not seen in the liquid water-graphite interface,
liquid water-graphene interface, nor interfaces studied previously. To further
investigate this chemisorption peak, we also report differences in the
electronic structure of single water molecules on both Pt and graphite
surfaces. We find that a covalent bond forms between the single water molecule
and the Pt surface, but not between the single water molecule and the graphite
surface. We also discuss the effects that defects and dopants in the graphite
and graphene surfaces have on the structure and dynamics of liquid water.


title:
Nested algorithms for optimal reservoir operation and their embedding in
  a decision support platform

abstract:
  This is a PhD thesis of Blagoj Delipetrev explaining nested dynamic
programming, nested stochastic dynamic programming and nested reinforcement
learning algorithms that are applied in reservoir optimization problem.
Additionally there are also multi-objective version of these algorithms.


title: Flows and Instabilities of Ferrofluids at the Microscale

abstract:
  In the present work we report on the behavior of ferrofluid microdrops in an
immiscible nonmagnetic carrier fluid and vice versa subjected to the action of
magnetic fields. Our experiments evidence previously unexplored instability and
flow patterns. We investigated the instabilities initiated by constant magnetic
field and by combined action of constant and rotating magnetic fields. The
observed instabilities lead to the formation of various microdrop
configurations such as star-like and comb-like shapes, bending deformation,
ridges and crests, spiral arms and rings, etc. The reviled peculiarities of the
microscopic drops behavior can be of interest in applications to the
ferrofluid-based microfluidics.


title: Phase separation for the long range one--dimensional ising model

abstract:
  We consider the phase separation problem for the one--dimensional
ferromagnetic Ising model with long--range two--body interaction,
$J(n)=n^{-2+\a}$ where $n\in \N$ denotes the distance of the two spins and $
\alpha \in ]0,\a_+[$ with $\a_+=(\log 3)/(\log 2) -1$. We prove that given
$m\in ]-1,+1[$, if the temperature is small enough, then typical configuration
for the $\mu^{+}$ Gibbs measure conditionally to have a empirical magnetization
of the order $m$ are made of a single interval that occupy almost a proportion
$\frac{1}{2}(1-\frac{m}{m_\b})$ of the volume with the minus phase inside and
the rest of the volume is the plus phase, here $m_\b>0 $ is the spontaneous
magnetization.


title: Jamming of semiflexible polymers

abstract:
  We study jamming in model freely rotating polymers as a function of chain
length $N$ and bond angle $\theta_0$. The volume fraction at jamming,
$\phi_J(\theta_0)$, is minimal for rigid-rod-like chains ($\theta_0 = 0$), and
increases monotonically with increasing $\theta_0 \leq \pi/2$. In contrast to
flexible polymers, marginally jammed states of freely rotating polymers are
highly hypostatic, even when bond and angle constraints are accounted for.
Large aspect ratio (small $\theta_0$) chains behave comparably to stiff fibers:
resistance to large-scale bending plays a major role in their jamming
phenomenology. Low aspect ratio (large $\theta_0$) chains behave more like
flexible polymers, but still jam at much lower densities due to the presence of
frozen-in 3-body correlations corresponding to the fixed bond angles.
Long-chain systems jam at lower $\phi$ and are more hypostatic at jamming than
short-chain systems. Implications of these findings for polymer solidification
are discussed.


title: Complex Langevin for Lattice QCD at $T=0$ and $\mu \ge 0$

abstract:
  QCD at finite quark-/baryon-number density, which describes nuclear matter,
has a sign problem which prevents direct application of standard simulation
methods based on importance sampling. When such finite density is implemented
by the introduction of a quark-number chemical potential $\mu$, this manifests
itself as a complex fermion determinant. We apply simulations using the Complex
Langevin Equation (CLE) which can be applied in such cases. However, this is
not guaranteed to give correct results, so that extensive tests are required.
In addition, gauge cooling is required to prevent runaway behaviour. We test
these methods on 2-flavour lattice QCD at zero temperature on a small ($12^4$)
lattice at an intermediate coupling $\beta=6/g^2=5.6$ and relatively small
quark mass $m=0.025$, over a range of $\mu$ values from $0$ to saturation.
While this appears to show the correct phase structure with a phase transition
at $\mu \approx m_N/3$ and a saturation density of $3$ at large $\mu$, the
observables show departures from known values at small $\mu$. We are now
running on a larger lattice ($16^4$) at weaker coupling $\beta=5.7$. At $\mu=0$
this significantly improves agreement between measured observables and known
values, and there is some indication that this continues to small $\mu$s. This
leads one to hope that the CLE might produce correct results in the
weak-coupling -- continuum -- limit.


title:
Approximative characteristics of classes of functions
  $S^{\Omega}_{p,\theta}B(\mathbb{R}^d)$ with a given majorant of mixed modulus
  of smoothness

abstract:
  We obtain order estimates of approximation of functions from the classes
$S^{\Omega}_{p,\theta}B (\mathbb{R}^d)$ in the space $L_q(\mathbb{R}^d)$,
$1<p<q<\infty$, by entire functions of exponential type with supports of their
Fourier transforms in sets generated by the level surfaces of a function
$\Omega$.