title: On the coloring of 3-element subsets

abstract:
  In this paper we prove that for numbers $n = 8k+1$, such that $8k-1$ is
prime, there exists the coloring of all 3-element subsets of {1, ..., n} such
that any sets $A, B: |A\cap B|=2$ have different colors.


title: Relativistic Stern-Gerlach Deflection

abstract:
  Modern advances in polarized beam control should make it possible to
accurately measure Stern-Gerlach (S-G) deflection of relativistic beams. Toward
this end a relativistically covariant S-G formalism is developed that respects
the opposite behavior under inversion of electric and magnetic fields. Not at
all radical, or even new, this introduces a distinction between electric and
magnetic fields that is not otherwise present in pure Maxwell theory.
Experimental configurations (mainly using polarized electron beams passing
through magnetic or electric quadrupoles) are described. Electron beam
preparation and experimental methods needed to detect the extremely small
deflections are discussed.


title:
HoneyFaces: Increasing the Security and Privacy of Authentication Using
  Synthetic Facial Images

abstract:
  One of the main challenges faced by Biometric-based authentication systems is
the need to offer secure authentication while maintaining the privacy of the
biometric data. Previous solutions, such as Secure Sketch and Fuzzy Extractors,
rely on assumptions that cannot be guaranteed in practice, and often affect the
authentication accuracy.
  In this paper, we introduce HoneyFaces: the concept of adding a large set of
synthetic faces (indistinguishable from real) into the biometric "password
file". This password inflation protects the privacy of users and increases the
security of the system without affecting the accuracy of the authentication. In
particular, privacy for the real users is provided by "hiding" them among a
large number of fake users (as the distributions of synthetic and real faces
are equal). In addition to maintaining the authentication accuracy, and thus
not affecting the security of the authentication process, HoneyFaces offer
several security improvements: increased exfiltration hardness, improved
leakage detection, and the ability to use a Two-server setting like in
HoneyWords. Finally, HoneyFaces can be combined with other security and privacy
mechanisms for biometric data.
  We implemented the HoneyFaces system and tested it with a password file
composed of 270 real users. The "password file" was then inflated to
accommodate up to $2^{36.5}$ users (resulting in a 56.6 TB "password file"). At
the same time, the inclusion of additional faces does not affect the true
acceptance rate or false acceptance rate which were 93.33\% and 0.01\%,
respectively.


title: Quantum cosmology in an anisotropic n-dimensional universe

abstract:
  We investigate quantum cosmological models in an n-dimensional anisotropic
universe in the presence of a massless scalar field. Our basic inspiration
comes from Chodos and Detweiler's classical model which predicts an interesting
behaviour of the extra dimension, shrinking down as time goes by. We work in
the framework of a recent geometrical scalar-tensor theory of gravity.
Classically, we obtain two distinct type of solutions. One of them has an
initial singularity while the other represents a static universe considered as
a whole. By using the canonical approach to quantum cosmology, we investigate
how quantum effects could have had an influence in the past history of these
universes.


title: Controlled opacity in a class of nonlinear dielectric media

abstract:
  Motivated by new technologies for designing and tailoring metamaterials, we
seek properties for certain classes of nonlinear optical materials that allow
room for a reversibly controlled opacity-to-transparency phase transition
through the application of external electromagnetic fields. We examine some
mathematically simple models for the dielectric parameters of the medium and
compute the relevant geometric quantities that describe the speed and
polarization of light rays.


title: Towards the Science of Security and Privacy in Machine Learning

abstract:
  Advances in machine learning (ML) in recent years have enabled a dizzying
array of applications such as data analytics, autonomous systems, and security
diagnostics. ML is now pervasive---new systems and models are being deployed in
every domain imaginable, leading to rapid and widespread deployment of software
based inference and decision making. There is growing recognition that ML
exposes new vulnerabilities in software systems, yet the technical community's
understanding of the nature and extent of these vulnerabilities remains
limited. We systematize recent findings on ML security and privacy, focusing on
attacks identified on these systems and defenses crafted to date. We articulate
a comprehensive threat model for ML, and categorize attacks and defenses within
an adversarial framework. Key insights resulting from works both in the ML and
security communities are identified and the effectiveness of approaches are
related to structural elements of ML algorithms and the data used to train
them. We conclude by formally exploring the opposing relationship between model
accuracy and resilience to adversarial manipulation. Through these
explorations, we show that there are (possibly unavoidable) tensions between
model complexity, accuracy, and resilience that must be calibrated for the
environments in which they will be used.


title:
Prompt neutrino fluxes in the atmosphere with PROSA parton distribution
  functions

abstract:
  Effects on atmospheric prompt neutrino fluxes of present uncertainties
affecting the nucleon composition are studied by using the PROSA fit to parton
distribution functions (PDFs). The PROSA fit extends the precision of the PDFs
to low x, which is the kinematic region of relevance for high-energy neutrino
production, by taking into account LHCb data on charm and bottom
hadroproduction. In the range of neutrino energies explored by present Very
Large Volume Neutrino Telescopes, it is found that PDF uncertainties are far
smaller with respect to those due to renormalization and factorization scale
variation and to assumptions on the cosmic ray composition, which at present
dominate and limit our knowledge of prompt neutrino fluxes. A discussion is
presented on how these uncertainties affect the expected number of atmospheric
prompt neutrino events in the analysis of high-energy events characterized by
interaction vertices fully contained within the instrumented volume of the
detector, performed by the IceCube collaboration.


title: Spin filtering and thermopower in star coupled quantum dot devices

abstract:
  We analyze the linear thermoelectric transport properties of devices with
three quantum dots in a star configuration. A central quantum dot is
tunnel-coupled to source and drain electrodes and to two additional quantum
dots. For a wide range of parameters, in the absence of an external magnetic
field, the system is a singular Fermi liquid with a non-analytic behavior of
the electric transport properties at low energies. The singular behavior is
associated with the development of a ferromagnetic or an underscreened Kondo
effect, depending on the parameter regime. A magnetic field drives the system
into a regular Fermi liquid regime and leads to a large peak ($\sim k_B/|e|$)
in the spin thermopower as a function of the temperature, and to a $\sim 100\%$
spin polarized current for a wide range of parameters due to interference
effects. We find a qualitatively equivalent behavior for systems with a larger
number of side coupled quantum dots, with the maximum value of the spin
thermopower decreasing as the number of side-coupled quantum dots increases.


title:
Deviation pattern approach for optimizing perturbative terms of QCD
  renormalization group invariant observables

abstract:
  We first consider the idea of renormalization group-induced estimates, in the
context of optimization procedures, for the Brodsky-Lepage-Mackenzie approach
to generate higher-order contributions to QCD perturbative series. Secondly, we
develop the deviation pattern approach (DPA) in which through a series of
comparisons between lower-order RG-induced estimates and the corresponding
analytical calculations, one could modify higher-order RG-induced estimates.
Finally, using the normal estimation procedure and DPA, we get estimates of
$\alpha_s^4$ corrections for the Bjorken sum rule of polarized deep-inelastic
scattering and for the non-singlet contribution to the Adler function.


title:
Configuration Interaction of Hydropathic Waves Enables Ubiquitin
  Functionality

abstract:
  Ubiquitin, discovered less than 50 years ago, tags thousands of diseased
proteins for destruction. It is small (only 76 amino acids), and is found
unchanged in mammals, birds, fish and even worms. Key features of its
functionality are identified here using critical point thermodynamic scaling
theory. These include Fano interference between first- and second-order
elements of globular surface shape transitions. Comparison with its closest
relative, 76 amino acid Nedd8, shows that the latter lacks these features. A
cracked elastic network model is proposed for the common target shared by many
diseased proteins.


title:
Recovery Guarantee of Non-negative Matrix Factorization via Alternating
  Updates

abstract:
  Non-negative matrix factorization is a popular tool for decomposing data into
feature and weight matrices under non-negativity constraints. It enjoys
practical success but is poorly understood theoretically. This paper proposes
an algorithm that alternates between decoding the weights and updating the
features, and shows that assuming a generative model of the data, it provably
recovers the ground-truth under fairly mild conditions. In particular, its only
essential requirement on features is linear independence. Furthermore, the
algorithm uses ReLU to exploit the non-negativity for decoding the weights, and
thus can tolerate adversarial noise that can potentially be as large as the
signal, and can tolerate unbiased noise much larger than the signal. The
analysis relies on a carefully designed coupling between two potential
functions, which we believe is of independent interest.


title:
Twist Two Operator Approach for Even Spin Glueball Masses and Pomeron
  Regge Trajectory from the Hardwall Model

abstract:
  We compute the masses of even spin glueball states $ J^{PC} $, with $ P=C=+1
$, using a twist two operator from an AdS/QCD model known as the hardwall
model, using Dirichlet and Neumann boundary conditions. Within this approach,
we found that the glueball masses are comparable with those in literature. From
these masses, we obtained the Pomeron Regge trajectories for both boundary
conditions in agreement with experimental data available and other holographic
models.


title: Radiation Fluid Stars in the Non-minimally Coupled $Y(R)F^2$ Gravity

abstract:
  We propose a non-minimally coupled gravity model in $ Y(R)F^2 $ form to
describe the radiation fluid stars which have the radiative equation of state
between the energy density $ \rho $ and the pressure $p$ as $\rho=3p $. Here
$F^2$ is the Maxwell invariant and $Y(R)$ is a function of the Ricci scalar
$R$. We give the gravitational and electromagnetic field equations in
differential form notation taking the infinitesimal variations of the model. We
look for electrically charged star solutions to the field equations under a
constraint which eliminating complexity of the higher order terms in the field
equations. We determine the non-minimally coupled function $Y(R)$ and the
corresponding model which admits new exact solutions in the interior of star
and Reissner-Nordstrom solution at the exterior region. Using vanishing
pressure condition at the boundary together with the continuity conditions of
the metric functions and the electric charge, we find the mass-radius ratio,
charge-radius ratio and gravitational surface redshift depending on the
parameter of the model for the radiation fluid star. We derive general
restrictions for the ratios and redshift of the charged compact stars. We
obtain a slightly smaller upper mass-radius ratio limit than the Buchdahl bound
$ 4/9 $ and a smaller upper redshift limit than the bound of the standard
General Relativistic stars.


title:
About the electroweak vacuum and its connection with the quark
  condensates

abstract:
  We make a change of variable in the standard model Higgs field by a fermion
operator and show that the latter is responsible for the electroweak vacuum. By
computing the vacuum expectation value of this fermion operator in the path
integral formalism we determine a relation among the quark vacuum condensates,
the quark masses and the intrinsic scale of the theory. We show that the heavy
quark vacuum condensates do not justify the hypothesis of dynamical electroweak
symmetry breaking with only standard model fermions.


title:
Extreme diagonally and antidiagonally symmetric alternating sign
  matrices of odd order

abstract:
  For each $\alpha \in \{0,1,-1 \}$, we count diagonally and antidiagonally
symmetric alternating sign matrices (DASASMs) of fixed odd order with a maximal
number of $\alpha$'s along the diagonal and the antidiagonal, as well as
DASASMs of fixed odd order with a minimal number of $0$'s along the diagonal
and the antidiagonal. In these enumerations, we encounter product formulas that
have previously appeared in plane partition or alternating sign matrix
counting, namely for the number of all alternating sign matrices, the number of
cyclically symmetric plane partitions in a given box, and the number of
vertically and horizontally symmetric ASMs. We also prove several refinements.
For instance, in the case of DASASMs with a maximal number of $-1$'s along the
diagonal and the antidiagonal, these considerations lead naturally to the
definition of alternating sign triangles. These are new objects that are
equinumerous with ASMs, and we are able to prove a two parameter refinement of
this fact, involving the number of $-1$'s and the inversion number on the ASM
side. To prove our results, we extend techniques to deal with triangular
six-vertex configurations that have recently successfully been applied to
settle Robbins' conjecture on the number of all DASASMs of odd order.
Importantly, we use a general solution of the reflection equation to prove the
symmetry of the partition function in the spectral parameters. In all of our
cases, we derive determinant or Pfaffian formulas for the partition functions,
which we then specialize in order to obtain the product formulas for the
various classes of extreme odd DASASMs under consideration.


title: Learning to Learn without Gradient Descent by Gradient Descent

abstract:
  We learn recurrent neural network optimizers trained on simple synthetic
functions by gradient descent. We show that these learned optimizers exhibit a
remarkable degree of transfer in that they can be used to efficiently optimize
a broad range of derivative-free black-box functions, including Gaussian
process bandits, simple control objectives, global optimization benchmarks and
hyper-parameter tuning tasks. Up to the training horizon, the learned
optimizers learn to trade-off exploration and exploitation, and compare
favourably with heavily engineered Bayesian optimization packages for
hyper-parameter tuning.


title:
Limits on the effective quark radius from inclusive ep scattering &
  contact interactions at HERA

abstract:
  The high-precision HERA data allow searches for up to TeV scales "Beyond the
Standard Model" contributions to electron-quark scattering. Combined H1 and
ZEUS measurements of inclusive deep inelastic cross sections in neutral and
charged current ep scattering are considered, corresponding to a luminosity of
around 1 fb$^{-1}$. A new approach to the beyond the Standard Model analysis of
the inclusive $ep$ data is presented; simultaneous fits of parton distribution
functions and contributions of "new physics" processes are performed.
Considered are possible deviations from the Standard Model due to a finite
radius of quarks, described within the quark form-factor model, and due to new
electron-quark interactions in the framework of $eeqq$ contact interactions
(CI). The resulting 95% C.L. upper limit on the effective quark radius is
$0.43\cdot 10^{-16}$ cm. The limits on the CI mass scale extend up to 10 TeV
depending on the CI scenario.


title: Bell-like examples for spin-1 hidden variable theories

abstract:
  Though John Bell had claimed that his spin-1/2 example of a hidden-variable
theory(HV) is an \emph{explicit} counterexample to von Neumann's proof of the
non-existence of hidden variable theories empirically equivalent to quantum
mechanics, such examples can be so construed only if they met all of von
Neumann's requirements. In particular, that they reproduced all the observed
predictions of quantum theory. To shed light on these aspects, we have, on the
one hand, simplified and critically examined Bell's original example and on the
other hand, constructed explicit such examples for spin-1 systems. We have
clarified the relation of our example to the Kochen-Specker and Bell's powerful
earlier results. Our spin-1 examples are manifestly non-contextual, yet
violating the K-S constraints configuration by configuration. Nevertheless,
they reproduce the correct quantum expectation values and variances for
arbitrary linear combinations of the beables in one case, and for close
approximants to the beables representing K-S constraints. In conformity with
the K-S theorem, the variance of the K-S constraint is nonzero. The
implications of this non-vanishing variance are analysed in detail. In the
other example, we show how this variance can be made arbitrarily small but not
zero.


title:
Naturalness, Vacuum Stability and Leptogenesis in the Minimal Seesaw
  Model

abstract:
  The right-handed neutrinos within the type-I seesaw mechanism can induce
large radiative corrections to the Higgs mass, and naturalness arguments can
then be used to set limits on their mass scale and Yukawa couplings. Driven by
minimality, we consider the presence of two degenerate right-handed neutrinos.
We compare the limits from naturalness with the ones from the stability of the
electroweak vacuum and from lepton flavor violation. Implications from
neutrinoless double beta decay are also discussed and renormalization effects
for the light neutrino parameters are presented. Adding small perturbations to
the degenerate heavy neutrino spectrum allows for successful leptogenesis.


title:
Spatial variation of short-range order in amorphous intergranular
  complexions

abstract:
  Amorphous materials lack long-range order but short-range order can still
persist through the recurrence of similar local packing motifs. While the
short-range order in bulk amorphous phases has been well studied and identified
as an intrinsic factor determining the material properties, these features have
not been studied in disordered intergranular complexions. In this work, the
short-range order in two types of amorphous complexions is studied with a
Voronoi tessellation method. Amorphous complexions can have three distinct
regions: amorphous-crystalline interfaces, regions deep inside the films that
have short-range order identical to a bulk amorphous phase, and transition
regions that connect the first two regions. However, thin amorphous films
contain only the amorphous-crystalline interface and the transition region,
providing further evidence of the constraints imposed by the abutting crystals.
The thickness of the transition region depends on film thickness at low
temperatures but becomes thickness-independent at high temperatures. Similarly,
the complexion short-range order is dependent on the interfacing crystal plane
at low temperatures, but this effect is lost at high temperatures. Our findings
show that amorphous complexions contain spatial gradients in short-range order,
meaning they are both structurally and chemically different from bulk metallic
glasses.


title:
Environment of $1\le z \le 2$ obscured and unobscured AGNs in the
  Extended Chandra Deep Field South

abstract:
  In unified models, different types of active galaxy nuclei correspond to a
single class of objects, where their observed differences are solely due to the
different orientations of the obscuring material around the central inner
regions. Recent studies also show that this obscuring material can even extend
at galactic scales due to debris and/or mergers. In standard unified models the
different AGN types are expected to show similar galaxy environments. We aim to
investigate properties and environment of obscured and unobscured AGNs selected
from the MUSYC survey, in order to test the unified model and evolutionary
scenarios. The sample of AGNs was selected from images obtained with the IRAC
Camera, based on their MIR colors. We selected two samples of AGNs with
redshifts in the range $1\le z \le 2$ and $M_v\leq -$21: obscured and
unobscured AGNs by means of a simple optical-MIR color cut criterion. We find
that obscured AGNs are intrinsically optically faint in the R band, suggesting
that luminous IR-selected AGNs have a significant dust extinction. From a
cross-correlation with several X-ray surveys, we find that the majority of the
AGNs have X-ray luminosities similar to those found in Seyfert-like galaxies.
Neighbouring galaxies located close to ($\sim$200 kpc) obscured AGNs tend to
have redder colors, compared to the local environment of unobscured AGNs.
Results obtained from a KS test show that the two color distributions are
different at $\sim$95% confidence level. We find that obscured AGNs are located
in denser local galaxy environments compared to the unobscured AGN sample. Our
results suggest that AGN obscuration can occur at galactic scales, possibly due
to galaxy interactions or mergers, and that the simple unified model based
solely on the local torus orientation may not be sufficient to explain all the
observations.


title: Straight Round the Twist: Frustration and Chirality in Smectics-A

abstract:
  Frustration is a powerful mechanism in condensed matter systems, driving both
order and co plexity. In smectics, the frustration between macroscopic
chirality and equally spaced layers generates textures characterised by a
proliferation of defects. In this article, we study several different ground
states of the chiral Landau-de Gennes free energy for a smectic liquid crystal.
The standard theory finds the twist grain boundary (TGB) phase to be the ground
state for chiral type II smectics. However, for very highly chiral systems, the
hierarchical helical nanofilament (HN) phase can form and is stable over the
TGB.


title:
Supersymmetric Casimir Energy and $\mathrm{SL(3,\mathbb{Z})}$
  Transformations

abstract:
  We provide a recipe to extract the supersymmetric Casimir energy of theories
defined on primary Hopf surfaces directly from the superconformal index. It
involves an $\mathrm{SL(3,\mathbb{Z})}$ transformation acting on the complex
structure moduli of the background geometry. In particular, the known relation
between Casimir energy, index and partition function emerges naturally from
this framework, allowing rewriting of the latter as a modified elliptic
hypergeometric integral. We show this explicitly for $\mathcal{N}=1$ SQCD and
$\mathcal{N}=4$ supersymmetric Yang-Mills theory for all classical gauge
groups, and conjecture that it holds more generally. We also use our method to
derive an expression for the Casimir energy of the nonlagrangian
$\mathcal{N}=2$ SCFT with $\mathrm{E_6}$ flavour symmetry. Furthermore, we
predict an expression for Casimir energy of the $\mathcal{N}=1$
$\mathrm{SP(2N)}$ theory with $\mathrm{SU(8)\times U(1)}$ flavour symmetry that
is part of a multiple duality network, and for the doubled $\mathcal{N}=1$
theory with enhanced $\mathrm{E}_7$ flavour symmetry.


title:
Generalized Phase-Type Distribution and Competing Risks for Markov
  Mixtures Process

abstract:
  Phase-type distribution has been an important probabilistic tool in the
analysis of complex stochastic system evolution. It was introduced by Neuts
\cite{Neuts1975} in 1975. The model describes the lifetime distribution of a
finite-state absorbing Markov chains, and has found many applications in wide
range of areas. It was brought to survival analysis by Aalen \cite{Aalen1995}
in 1995. However, the model has lacks of ability in modeling heterogeneity and
inclusion of past information which is due to the Markov property of the
underlying process that forms the model. We attempt to generalize the
distribution by replacing the underlying by Markov mixtures process. Markov
mixtures process was used to model jobs mobility by Blumen \cite{Blumen} et al.
in 1955. It was known as the mover-stayer model describing low-productivity
workers tendency to move out of their jobs by a Markov chains, while those with
high-productivity tend to stay in the job. Frydman \cite{Frydman2005} later
extended the model to a mixtures of finite-state Markov chains moving at
different speeds on the same state space. In general the mixtures process does
not have Markov property. We revisit the mixtures model \cite{Frydman2005} for
mixtures of multi absorbing states Markov chains, and propose generalization of
the phase-type distribution under competing risks. The new distribution has two
main appealing features: it has the ability to model heterogeneity and to
include past information of the underlying process, and it comes in a closed
form. Built upon the new distribution, we propose conditional forward intensity
which can be used to determine rate of occurrence of future events (caused by
certain type) based on available information. Numerical study suggests that the
new distribution and its forward intensity offer significant improvements over
the existing model.


title: Bulk viscosity, interaction and the viability of phantom solutions

abstract:
  We study the dynamics of a bulk viscosity model in the Eckart approach for a
spatially flat Friedmann-Robertson-Walker (FRW) universe. We have included
radiation and dark energy, assumed as perfect fluids, and dark matter treated
as an imperfect fluid having bulk viscosity. We also introduce an interaction
term between the dark matter and dark energy components. Considering that the
bulk viscosity is proportional to the dark matter energy density and imposing a
complete cosmological dynamics, we find bounds on the bulk viscosity in order
to reproduce a matter-dominated era (MDE). This constraint is independent of
the interaction term. Some late time phantom solutions are mathematically
possible. However, the constraint imposed by a MDE restricts the interaction
parameter, in the phantom solutions, to a region consistent with a null value,
eliminating the possibility of late time stable solutions with $w<-1$. From the
different cases that we study, the only possible scenario, with bulk viscosity
and interaction term, belongs to the quintessence region. In this latter case,
we find bounds on the interaction parameter compatible with latest
observational data.


title: Manufactured Turbulence with Langevin equations

abstract:
  By definition, Manufactured turbulence(MT) is purported to mimic physical
turbulence rather than model it. The MT equations are constrained to be simple
to solve and provide an inexpensive surrogate to Navier-Stokes based Direct
Numerical Simulations (DNS) for use in engineering applications or theoretical
analyses. In this article, we investigate one approach in which the linear
inviscid aspects of MT are derived from a linear approximation of the
Navier-Stokes equations while the non-linear and viscous physics are
approximated via stochastic modeling. The ensuing Langevin MT equations are
used to compute planar, quadratic turbulent flows. While much work needs to be
done, the preliminary results appear promising.


title:
A Bayesian adaptive ensemble Kalman filter for sequential state and
  parameter estimation

abstract:
  This paper proposes new methodology for sequential state and parameter
estimation within the ensemble Kalman filter. The method is fully Bayesian and
propagates the joint posterior density of states and parameters over time. In
order to implement the method we consider two representations of the marginal
posterior distribution of the parameters: a grid-based approach and a Gaussian
approximation. Contrary to existing algorithms, the new method explicitly
accounts for parameter uncertainty and provides a formal way to combine
information about the parameters from data at different time periods. The
method is illustrated and compared to existing approaches using simulated and
real data.


abstract:
  As a generalization of acyclic 2-Calabi-Yau categories, we consider
2-Calabi-Yau categories with a directed cluster-tilting subcategory; we study
their cluster-tilting subcategories and the cluster combinatorics that they
encode. We show that such categories have a cluster structure.
  Triangulated 2-Calabi-Yau categories with a directed cluster-tilting
subcategory are closely related to representations of certain semi-hereditary
categories, more specifically to representations of thread quivers. Thread
quivers are a tool to classify and study certain semi-hereditary categories
using both quivers and linearly ordered sets (threads).
  We study the case where the thread quiver consists of a single thread (so
that representations of this thread quiver correspond to representations of
some linearly ordered set), and show that, similar to the case of a Dynkin
quiver of type $A$, the cluster-tilting subcategories can be understood via
triangulations of an associated cyclically ordered set.
  In this way, we gain insight into the structure of the cluster-tilting
subcategories of 2-Calabi-Yau categories with a directed cluster-tilting
subcategory. As an application, we show that every 2-Calabi-Yau category which
admits a directed cluster-tilting subcategory with countably many isomorphism
classes of indecomposable objects has a cluster-tilting subcategory
$\mathcal{V}$ with the following property: any rigid object in the cluster
category can be reached from $\mathcal{V}$ by finitely many mutations. This
implies that there is a cluster map which is defined on all rigid objects, and
thus that there is a cluster algebra whose cluster variables are exactly given
by the rigid indecomposable objects.


title: The 2016 Al-Mishraq sulphur plant fire: source and risk area estimation

abstract:
  On October 20, 2016, Daesh (Islamic State) set fire to the sulphur production
site Al-Mishraq as the battle of Mosul in northern Iraq became more intense. An
extensive plume of toxic sulphur dioxide and hydrogen sulphide caused
comprehensive casualties. The intensity of the SO2 release was reaching levels
of minor volcanic eruptions and the plume was observed by several satellites.
By investigation of the measurement data from instruments on the MetOp-A,
MetOp-B, Aura and Soumi satellites we have estimated the time-dependent source
term to 161 kilotonnes sulphur dioxide released into the atmosphere during
seven days. A long-range dispersion model was utilized to simulate the
atmospheric transport over the Middle East. The ground level concentrations
predicted by the simulation were compared with observation from the Turkey
National Air Quality Monitoring Network. Finally, the simulation data provided,
using a probit analysis of the simulated data, an estimate of the health risk
area that was compared to reported urgent medical treatments.
  This article has been published in Atmospheric Environment, see cross link
below.


title:
Absence of superfluidity in a quasi one-dimensional parahydrogen fluid
  adsorbed inside carbon nanotubes

abstract:
  A recent claim of superfluid behaviour of parahydrogen adsorbed inside
armchair carbon nanotubes [M. Rossi and F. Ancilotto, Phys. Rev. B 94, 100502
(2016)] is disproven by means of first principle computer simulations.
Conclusive numerical evidence shows that the low temperature equilibrium
thermodynamic phase of parahydrogen adsorbed inside a (10,10) armchair nanotube
features a crystalline shell adsorbed on the inner surface of the tube, and a
well separated quasi one-dimensional central column showing no evidence of
possible fluid or superfluid behaviour. Rather, the system is quasi-crystalline
and non-superfluid; its physical character is qualitatively identical to that
observed in similar confined settings extensively studied in the past. The
incorrect prediction of superfluidity stems from the erroneous use of an
effective one-dimensional interaction potential that does not describe
parahydrogen at the center of the nanotube.


title:
Uniform definition of sets using relations and complement of Presburger
  Arithmetic

abstract:
  In 1996, Michaux and Villemaire considered integer relations $R$ which are
not definable in Presburger Arithmetic. That is, not definable in first-order
logic over integers with the addition function and the order relation
(FO[N,+,<]-definable relations). They proved that, for each such $R$, there
exists a FO[N,+,<,$R$]-formula $\nu_{R}(x)$ which defines a set of integers
which is not ultimately periodic, i.e. not FO[N,+,<]-definable.
  It is proven in this paper that the formula $\nu(x)$ can be chosen such that
it does not depend on the interpretation of $R$. It is furthermore proven that
$\nu(x)$ can be chosen such that it defines an expanding set. That is, an
infinite set of integers such that the distance between two successive elements
is not bounded.


title:
The Length of the Longest Common Subsequence of Two Independent Mallows
  Permutations

abstract:
  The Mallows measure is a probability measure on $S_n$ where the probability
of a permutation $\pi$ is proportional to $q^{l(\pi)}$ with $q > 0$ being a
parameter and $l(\pi)$ the number of inversions in $\pi$. We prove a weak law
of large numbers for the length of the longest common subsequences of two
independent permutations drawn from the Mallows measure, when $q$ is a function
of $n$ and $n(1-q)$ has limit in $\mathbb{R}$ as $n \to \infty$.


title:
Designing Security-Aware Incentives for Computation Offloading via
  Device-to-Device Communication

abstract:
  Computation offloading via device-to-device (D2D) communication, or D2D
offloading, has recently been proposed to enhance mobile computing performance
by exploiting spare computing resources of nearby user devices. The success of
D2D offloading relies on user participation in collaborative service
provisioning, which incurs extra costs to users providing the service, thus
mandating an incentive mechanism that can compensate for these costs. Although
incentive mechanism design has been intensively studied in the literature, this
paper considers a much more challenging yet less investigated problem in which
selfish users are also facing interdependent security risks, such as infectious
proximity-based attacks. Security cost is significantly different in nature
from conventional service provisioning costs such as energy consumption, since
security risks often depend on the collective behavior of all users. To this
end, we build a novel mathematical framework by leveraging the combined power
of game theory and epidemic theory to investigate the interplay between user
incentives and interdependent security risks in D2D offloading, thereby
enabling the design of security-aware incentive mechanisms. Our analysis
discovers an interesting "less is more" phenomenon: although giving users more
incentives promotes more participation, it may harm the network operator's
utility. This is because too much participation may foster persistent security
risks and as a result, the effective participation level does not improve. Our
model and analysis shed new insights on the optimization of D2D offloading
networks in the presence of interdependent security risks. Extensive
simulations are carried out to verify our analytical conclusions.


title: Strong and tunable couplings in flux-mediated optomechanics

abstract:
  We investigate superconducting interference device (SQUID) with two
asymmetric Josephson junctions coupled to a mechanical resonator embedded in
the loop of the SQUID. We quantize this system in the case when the frequency
of the mechanical resonator is much lower than the cavity frequency of the
SQUID and in the case when they are comparable. In the first case, the
radiation pressure and cross-Kerr type interactions arise and are modified by
asymmetry. Cross-Kerr type coupling is the leading term at the extremum points
where radiation pressure is zero. In the second case, the main interaction is
single-photon beam splitter, which exists only at finite asymmetry. Another
interaction in this regime is of cross-Kerr type, which exists at all
asymmetries, but generally much weaker than the beam splitter interaction.
Increasing magnetic field can substantially enhance optomechanical couplings
strength with the potential for the radiation pressure coupling to reach the
single-photon strong coupling regime, even the ultrastrong coupling regime, in
which the single-photon coupling rate exceeds the mechanical frequency.


title:
Localized four-dimensional gravity in the D-brane background with NS $B$
  field

abstract:
  We calculate small correction terms to gravitational potential near
$p$-branes embedded in a constant NS $B$ field background in the context of
M-theory or string theory. The normalizable wave functions of gravity
fluctuations around the brane describe only massive modes. We compute such wave
functions analytically. We estimate the correction to gravitational potential
for small and long distances, and show that there is an intermediate range of
distances in which we can identify $4D$ gravity on the brane below a crossover
scale given in terms of components of the $B$ field. The $4D$ gravity is
metastable and for distances much larger than the crossover scale the $5D$
gravity is recovered.


title:
Measurements of differential production cross sections for a Z boson in
  association with jets in pp collisions at sqrt(s) = 8 TeV

abstract:
  Cross sections for the production of a Z boson in association with jets in
proton-proton collisions at a centre-of-mass energy of sqrt(s) = 8 TeV are
measured using a data sample collected by the CMS experiment at the LHC
corresponding to 19.6 inverse femtobarns. Differential cross sections are
presented as functions of up to three observables that describe the jet
kinematics and the jet activity. Correlations between the azimuthal directions
and the rapidities of the jets and the Z boson are studied in detail. The
predictions of a number of multileg generators with leading or next-to-leading
order accuracy are compared with the measurements. The comparison shows the
importance of including multi-parton contributions in the matrix elements and
the improvement in the predictions when next-to-leading order terms are
included.


title: Heegaard Floer Homologies and Rational Cuspidal Curves. Lecture notes

abstract:
  This is an expanded version of the lecture course the second author gave at
Winterbraids VI in Lille in February 2016. Version 2: revision incorporating
referee remarks.


title: Search for bottom squarks in the baryon-number violating MSSM

abstract:
  We consider a scenario of Minimal Supersymmetric Standard Model (MSSM) with
$R$-parity violation, where the lightest supersymmetric particle (LSP) is the
lighter sbottom $(\tilde b_1)$. We study the production of a sbottom pair at
the LHC and their subsequent decays through the baryon number violating $(U D
D)$ operators leading to a top pair with two light quarks. Looking for both
semi-leptonic and fully hadronic (no leptons) final states, we perform
cut-based as well as multivariate analyses (MVA) to estimate the signal
significance at the 13 TeV run of the LHC. We find that a cut-based analysis
can probe sbottom mass upto $\sim 650 $ GeV which may be extended upto $\sim
750 $ GeV using MVA with $300~{\rm fb}^{-1}$ integrated luminosity. The fully
hadronic final state, however, is not as promising.


title:
Q_l-cohomology projective planes from Enriques surfaces in odd
  characteristic

abstract:
  We give a complete classification of Q_l-cohomology projective planes with
isolated ADE-singularities and numerically trivial canonical bundle in odd
characteristic. This leads to a beautiful relation with certain Enriques
surfaces which parallels the situation in characteristic zero, yet displays
intriguing subtleties.


title: Fast Radio Bursts with Extended Gamma-Ray Emission?

abstract:
  We consider some general implications of bright gamma-ray counterparts to
fast radio bursts (FRBs). We show that even if these manifest in only a
fraction of FRBs, gamma-ray detections with current satellites (including
Swift) can provide stringent constraints on cosmological FRB models. If the
energy is drawn from the magnetic energy of a compact object such as a
magnetized neutron star, the sources should be nearby and be very rare. If the
intergalactic medium is responsible for the observed dispersion measure, the
required gamma-ray energy is comparable to that of the early afterglow or
extended emission of short gamma-ray bursts. While this can be reconciled with
the rotation energy of compact objects, as expected in many merger scenarios,
the prompt outflow that yields the gamma-rays is too dense for radio waves to
escape. Highly relativistic winds launched in a precursor phase, and forming a
wind bubble, may avoid the scattering and absorption limits and could yield FRB
emission. Largely independent of source models, we show that detectable radio
afterglow emission from gamma-ray bright FRBs can reasonably be anticipated.
Gravitational wave searches can also be expected to provide useful tests.


title:
Applying the Density Matrix Expansion with Coordinate-Space Chiral
  Interactions

abstract:
  We apply the density matrix expansion (DME) at Hartree-Fock level with
long-range chiral effective field theory interactions defined in coordinate
space up to next-to-next-to-leading order. We consider chiral potentials both
with and without explicit Delta isobars. The challenging algebra associated
with applying the DME to three-nucleon forces is tamed using a new organization
scheme, which will also facilitate generalizations. We include local regulators
on the interactions to mitigate the effects of singular potentials on the DME
couplings and simplify the optimization of generalized Skyrme-like functionals.


title: Integration of generalized complex structures

abstract:
  We solve the integration problem for generalized complex manifolds, obtaining
as the natural integrating object a weakly holomorphic symplectic groupoid,
which is a real symplectic groupoid with a compatible complex structure defined
only on the associated stack, i.e., only up to Morita equivalence. We explain
how such objects differentiate to give generalized complex manifolds, and we
show that a generalized complex manifold is integrable in this sense if and
only if its underlying real Poisson structure is integrable. Crucial to our
solution are several new technical tools which are of independent interest,
namely, a reduction procedure for Lie groupoid actions on Courant algebroids,
as well as certain local-to-global extension results for multiplicative forms
on local Lie groupoids. Finally, we implement our generalized complex
integration procedure in several concrete examples.


title:
Constraining gravity with hadron physics: neutron stars, modified
  gravity and gravitational waves

abstract:
  The finding of Gravitational Waves by the aLIGO scientific and VIRGO
collaborations opens opportunities to better test and understand strong
interactions, both nuclear-hadronic and gravitational. Assuming General
Relativity holds, one can constrain hadron physics at a neutron star. But
precise knowledge of the Equation of State and transport properties in hadron
matter can also be used to constrain the theory of gravity itself.
  I review a couple of these opportunities in the context of modified f(R)
gravity, the maximum mass of neutron stars, and progress in the Equation of
State of neutron matter from the chiral effective field theory of QCD.


title:
A Connection between Generative Adversarial Networks, Inverse
  Reinforcement Learning, and Energy-Based Models

abstract:
  Generative adversarial networks (GANs) are a recently proposed class of
generative models in which a generator is trained to optimize a cost function
that is being simultaneously learned by a discriminator. While the idea of
learning cost functions is relatively new to the field of generative modeling,
learning costs has long been studied in control and reinforcement learning (RL)
domains, typically for imitation learning from demonstrations. In these fields,
learning cost function underlying observed behavior is known as inverse
reinforcement learning (IRL) or inverse optimal control. While at first the
connection between cost learning in RL and cost learning in generative modeling
may appear to be a superficial one, we show in this paper that certain IRL
methods are in fact mathematically equivalent to GANs. In particular, we
demonstrate an equivalence between a sample-based algorithm for maximum entropy
IRL and a GAN in which the generator's density can be evaluated and is provided
as an additional input to the discriminator. Interestingly, maximum entropy IRL
is a special case of an energy-based model. We discuss the interpretation of
GANs as an algorithm for training energy-based models, and relate this
interpretation to other recent work that seeks to connect GANs and EBMs. By
formally highlighting the connection between GANs, IRL, and EBMs, we hope that
researchers in all three communities can better identify and apply transferable
ideas from one domain to another, particularly for developing more stable and
scalable algorithms: a major challenge in all three domains.


title: Gravitational Waves, Gamma Ray Bursts, and Black Stars

abstract:
  Stars that are collapsing toward forming a black hole but appear frozen near
their Schwarzschild horizon are termed "black stars". The collision of two
black stars leads to gravitational radiation during the merging phase followed
by a delayed gamma ray burst during coalescence. The recent observation of
gravitational waves by LIGO, followed by a possible gamma ray counterpart by
Fermi, suggests that the source may have been a merger of two black stars with
profound implications for quantum gravity and the nature of black holes.


title: Massive MIMO-Enabled Full-Duplex Cellular Networks

abstract:
  In this paper, we provide a theoretical framework for the study of massive
multiple-input multiple-output (MIMO)-enabled full-duplex (FD) cellular
networks in which the self-interference (SI) channels follow the Rician
distribution and other channels are Rayleigh distributed. To facilitate
bi-directional wireless functionality, we adopt (i) a downlink (DL) linear
zero-forcing with self-interference-nulling (ZF-SIN) precoding scheme at the FD
base stations (BSs), and (ii) an uplink (UL) self-interference-aware (SIA)
fractional power control mechanism at the FD user equipments (UEs). Linear ZF
receivers are further utilized for signal detection in the UL. The results
indicate that the UL rate bottleneck in the baseline FD single-antenna system
can be overcome via exploiting massive MIMO. On the other hand, the findings
may be viewed as a reality-check, since we show that, under state-of-the-art
system parameters, the spectral efficiency (SE) gain of FD massive MIMO over
its half-duplex (HD) counterpart largely depends on the SI cancellation
capability of the UEs. In addition, the anticipated two-fold increase in SE is
shown to be only achievable with an infinitely large number of antennas.


title:
A Novel Compact and Selective Gas Sensing System Based on Microspherical
  Lasers

abstract:
  We propose the use of wavelength-dependent spectroscopic absorption in the
evanescent field of ultra-compact whispering gallery mode microspherical lasers
as selective gas sensors and estimate few ppm detection sensitivity using a
simple model. We also propose a sensor configuration based on integrated
multi-channel microspherical laser arrays capable of selective gas detection at
low concentration, and demonstrate that a compact 14channel device could
generate a unique and distinguishable power distribution over channel outputs
upon exposure to three different gases.


title:
Limitations of the intrinsic cut-off frequency to correctly quantify the
  speed of nanoscale transistors

abstract:
  The definition of the intrinsic cut-off frequency ($f_T$) based on the
current gain equals to one (0 dB) is critically analyzed. A condition for the
validity of the quasi-static estimation of $f_T$ is established in terms of the
temporal variations of the electric charge and electric flux on the drain,
source and gate terminals. Due to the displacement current, an electron
traversing the channel length generates a current pulse of finite temporal
width. For electron devices where the intrinsic delay time of the current after
a transient perturbation is comparable to such width, the displacement currents
cannot be neglected and the quasi-static approximation becomes inaccurate. We
provide numerical results for some ballistic transistors where the estimation
of $f_T$ under the quasi-static approximation can be one order of magnitude
larger than predictions obtained from a time-dependent numerical simulations of
the intrinsic delay time (including particle and displacement currents). In
other ballistic transistors, we show that the gate current phasor can be
smaller than the drain one at all frequencies, giving no finite value for
$f_T$.


title:
The Physics of Motorcycles and Fast Bicycles : Lean, Stability and
  Counter-steering

abstract:
  In this work I will obtain the system of nonlinear equations that correctly
describes the motion of motorcycles and fast bicycles (above 30 km/hr) for the
first time in literature. I will use it to calculate the lean angle during a
turn and prove that the motion of the vehicle is unconditionally stable at all
operating speeds under consideration. I will then employ it to give a
quantitative model of counter-steering - the phenomenon by which a turning
mobike first goes the wrong way and then starts going the right way.


title:
Few quantum mechanical models in higher dimension-framed with Elzaki
  transform

abstract:
  Very first time Elzaki transform is used in non relativistic quantum
mechanics to solve $N$-dimensional Schr\"{o}dinger equation in a closed form
for different solvable potential models. A universal transformation scheme is
introduced and a formula based approach is developed which shows how to apply
Elzaki transform to differential equation with non-constant coefficients that
generally appear in solving quantum mechanical initial value problems specially
for multidimensional Schr\"{o}dinger equation.


title: Rocky Planetesimal Formation via Fluffy Aggregates of Nanograins

abstract:
  Several pieces of evidence suggest that silicate grains in primitive
meteorites are not interstellar grains but condensates formed in the early
solar system. Moreover, the size distribution of matrix grains in chondrites
implies that these condensates might be formed as nanometer-sized grains.
Therefore, we propose a novel scenario for rocky planetesimal formation in
which nanometer-sized silicate grains are produced by evaporation and
recondensation events in early solar nebula, and rocky planetesimals are formed
via aggregation of these nanograins. We reveal that silicate nanograins can
grow into rocky planetesimals via direct aggregation without catastrophic
fragmentation and serious radial drift, and our results provide a suitable
condition for protoplanet formation in our solar system.


title: Higgs pair production in vector-boson fusion at the LHC and beyond

abstract:
  The production of pairs of Higgs bosons at hadron colliders provides unique
information on the Higgs sector and on the mechanism underlying electroweak
symmetry breaking (EWSB). Most studies have concentrated on the gluon fusion
production mode which has the largest cross section. However, despite its small
production rate, the vector-boson fusion channel can also be relevant since
even small modifications of the Higgs couplings to vector bosons induce a
striking increase of the cross section as a function of the invariant mass of
the Higgs boson pair. In this work, we exploit this unique signature to propose
a strategy to extract the $hhVV$ quartic coupling and provide model-independent
constraints on theories where EWSB is driven by new strong interactions. We
take advantage of the higher signal yield of the $b\bar b b\bar b$ final state
and make extensive use of jet substructure techniques to reconstruct signal
events with a boosted topology, characteristic of large partonic energies,
where each Higgs boson decays to a single collimated jet . Our results
demonstrate that the $hhVV$ coupling can be measured with 45% (20%) precision
at the LHC for $\mathcal{L}=$ 300 (3000) fb$^{-1}$, while a 1% precision can be
achieved at a 100 TeV collider.


title:
Prospects of Establishing the Origin of Cosmic Neutrinos using Source
  Catalogs

abstract:
  The cosmic neutrino flux recently discovered by IceCube will be instrumental
in probing the highest-energy astrophysical processes. Nevertheless, the origin
of these neutrinos is still unknown. While it would be more straightforward to
identify a transient, or galactic source class, finding a population of
distant, continuous sources is challenging. We introduce a source-type
classification technique that incorporates all available information from
catalogs of source candidates. We show that IceCube-Gen2 can statistically
establish the origin of cosmic neutrinos even for the most challenging source
populations--starburst galaxies, AGN or galaxy clusters, if neutrino track
directions can be reconstructed with a precision ~$0.3^\circ$. We further show
that source catalog out to ~100 Mpc can be sufficient for the most challenging
source types, allowing for more straightforward source surveys. We also
characterize the role of detector properties, namely angular resolution, size
and veto power in order to understand the effects of IceCube-Gen2's design
specifics.


title:
Linking the X3D pathway to integral field spectrographs: YSNR
  1E0102.2-7219 in the SMC as a case study

abstract:
  The concept of the X3D pathway was introduced by Vogt et al. (2016) as a new
approach to sharing and publishing 3-D structures interactively in online
scientific journals. The core characteristics of the X3D pathway are that: 1)
it does not rely on specific software, but rather a file format (X3D), 2) it
can be implemented using fully open-source tools, and 3) article readers can
access the interactive models using most main stream web browsers without the
need for any additional plugins. In this article, we further demonstrate the
potential of the X3D pathway to visualize datasets from optical integral field
spectrographs. We use recent observations of the oxygen-rich young supernova
remnant 1E0102.2-7219 in the Small Magellanic Cloud to implement additional
X3DOM tools & techniques and expand the range of interactions that can be
offered to article readers. In particular, we present a set of javascript
functions allowing the creation and interactive handling of clip planes,
effectively allowing users to take measurements of distances and angles
directly from the interactive model itself.


title:
Kinematics of the ionized and molecular gas in nearby luminous infrared
  interacting galaxies

abstract:
  We have observed three luminous infrared galaxy systems (LIRGS) which are
pairs of interacting galaxies, with the Galaxy H$\alpha$ Fabry-Perot system
(GH$\alpha$FaS) mounted on the 4.2m William Herschel Telescope at the Roque de
los Muchachos Observatory, and combined the observations with the Atacama Large
Millimeter Array (ALMA) observations of these systems in CO emission to compare
the physical properties of the star formation regions and the molecular gas
clouds, and specifically the internal kinematics of the star forming regions.
We identified 88 star forming regions in the H$\alpha$ emission data-cubes, and
27 molecular cloud complexes in the CO emission data-cubes. The surface
densities of the star formation rate and the molecular gas are significantly
higher in these systems than in non-interacting galaxies and the Galaxy, and
are closer to the surface densities of the star formation rate and the
molecular gas of extreme star forming galaxies at higher redshifts. The large
values of the velocity dispersion also show the enhanced gas surface density.
The HII regions are situated on the ${\rm{SFR}}-\sigma_v$ envelope, and so are
also in virial equilibrium. Since the virial parameter decreases with the
surface densities of both the star formation rate and the molecular gas, we
claim that the clouds presented here are gravitationally dominated rather than
being in equilibrium with the external pressure.


title: Revisiting Supernova 1987A Constraints on Dark Photons

abstract:
  We revisit constraints on dark photons with masses below ~ 100 MeV from the
observations of Supernova 1987A. If dark photons are produced in sufficient
quantity, they reduce the amount of energy emitted in the form of neutrinos, in
conflict with observations. For the first time, we include the effects of
finite temperature and density on the kinetic-mixing parameter, epsilon, in
this environment. This causes the constraints on epsilon to weaken with the
dark-photon mass below ~ 15 MeV. For large-enough values of epsilon, it is well
known that dark photons can be reabsorbed within the supernova. Since the rates
of reabsorption processes decrease as the dark-photon energy increases, we
point out that dark photons with energies above the Wien peak can escape
without scattering, contributing more to energy loss than is possible assuming
a blackbody spectrum. Furthermore, we estimate the systematic uncertainties on
the cooling bounds by deriving constraints assuming one analytic and four
different simulated temperature and density profiles of the proto-neutron star.
Finally, we estimate also the systematic uncertainty on the bound by varying
the distance across which dark photons must propagate from their point of
production to be able to affect the star. This work clarifies the bounds from
SN1987A on the dark-photon parameter space.


title:
LITTLE THINGS in 3D: robust determination of the circular velocity of
  dwarf irregular galaxies

abstract:
  Dwarf Irregular galaxies (dIrrs) are the smallest stellar systems with
extended HI discs. The study of the kinematics of such discs is a powerful tool
to estimate the total matter distribution at these very small scales. In this
work, we study the HI kinematics of 17 galaxies extracted from the `Local
Irregulars That Trace Luminosity Extremes, The HI Nearby Galaxy Survey' (LITTLE
THINGS). Our approach differs significantly from previous studies in that we
directly fit 3D models (two spatial dimensions plus one spectral dimension)
using the software $^\text{3D}$BAROLO, fully exploiting the information in the
HI datacubes. For each galaxy we derive the geometric parameters of the HI disc
(inclination and position angle), the radial distribution of the surface
density, the velocity-dispersion ($\sigma_v$) profile and the rotation curve.
The circular velocity (V$_{\text{c}}$), which traces directly the galactic
potential, is then obtained by correcting the rotation curve for the asymmetric
drift. As an initial application, we show that these dIrrs lie on a baryonic
Tully-Fisher relation in excellent agreement with that seen on larger scales.
The final products of this work are high-quality, ready-to-use kinematic data
($\textrm{V}_\textrm{c}$ and $\sigma_v$) that we make publicly available. These
can be used to perform dynamical studies and improve our understanding of these
low-mass galaxies.


title:
Cluster Mass Calibration at High Redshift: HST Weak Lensing Analysis of
  13 Distant Galaxy Clusters from the South Pole Telescope Sunyaev-Zel'dovich
  Survey

abstract:
  We present an HST/ACS weak gravitational lensing analysis of 13 massive
high-redshift (z_median=0.88) galaxy clusters discovered in the South Pole
Telescope (SPT) Sunyaev-Zel'dovich Survey. This study is part of a larger
campaign that aims to robustly calibrate mass-observable scaling relations over
a wide range in redshift to enable improved cosmological constraints from the
SPT cluster sample. We introduce new strategies to ensure that systematics in
the lensing analysis do not degrade constraints on cluster scaling relations
significantly. First, we efficiently remove cluster members from the source
sample by selecting very blue galaxies in V-I colour. Our estimate of the
source redshift distribution is based on CANDELS data, where we carefully mimic
the source selection criteria of the cluster fields. We apply a statistical
correction for systematic photometric redshift errors as derived from Hubble
Ultra Deep Field data and verified through spatial cross-correlations. We
account for the impact of lensing magnification on the source redshift
distribution, finding that this is particularly relevant for shallower surveys.
Finally, we account for biases in the mass modelling caused by miscentring and
uncertainties in the concentration-mass relation using simulations. In
combination with temperature estimates from Chandra we constrain the
normalisation of the mass-temperature scaling relation ln(E(z) M_500c/10^14
M_sun)=A+1.5 ln(kT/7.2keV) to A=1.81^{+0.24}_{-0.14}(stat.) +/- 0.09(sys.),
consistent with self-similar redshift evolution when compared to lower redshift
samples. Additionally, the lensing data constrain the average concentration of
the clusters to c_200c=5.6^{+3.7}_{-1.8}.


title:
Kinetic Tomography I: A Method for Mapping the Milky Way's Interstellar
  Medium in Four Dimensions

abstract:
  We have developed a method for deriving the distribution of the Milky Way's
interstellar medium as a function of longitude, latitude, distance and
line-of-sight velocity. This method takes as input maps of reddening as a
function of longitude, latitude, and distance and maps of line emission as a
function of longitude, latitude, and line-of-sight velocity. We have applied
this method to datasets covering much of the Galactic plane. The output of this
method correctly reproduces the line-of-sight velocities of high-mass star
forming regions with known distances from Reid et al. (2014) and qualitatively
agrees with results from the Milky Way kinematics literature. These maps will
be useful for measuring flows of gas around the Milky Way's spiral arms and
into and out of giant molecular clouds.


title: Origins of carbon-enhanced metal-poor stars

abstract:
  We investigate the nature of carbon-enhanced metal poor (CEMP) stars in Milky
Way (MW) analogues selected from the EAGLE cosmological hydrodynamical
simulation. The stellar evolution model in EAGLE includes the physics of
enrichment by asymptotic giant branch (AGB) stars, winds from massive stars,
and type I and type II supernovae (SNe). In the simulation, star formation in
young MW progenitors is bursty due to efficient stellar feedback, which causes
poor metal mixing leading to the formation of CEMP stars with extreme abundance
patterns. In this scenario, two classes of CEMP stars emerge: those mostly
enriched by low-metallicity type II SNe with low Fe yields that drive galactic
outflows, and those mostly enriched by AGB stars when a gas-poor progenitor
accretes pristine gas. The first class resembles CEMP-no stars with high [C/Fe]
and low [C/O], the second class resembles CEMP-s stars overabundant in
s-process elements and high values of [C/O]. This scenario explains several
trends seen in data: (i) the increase in the scatter and median of [C/O] at low
and decreasing [O/H], (ii) the trend of stars with very low [Fe/H] or [C/H] to
be of type CEMP-no, and (iii) the reduction in the scatter of [{\alpha}/Fe]
with atomic number in metal poor stars. In this interpretation CEMP-no stars
were enriched by the stars that enabled galaxies to reionise the Universe.


title:
The Nature of Massive Transition Galaxies in CANDELS, GAMA, and
  Cosmological Simulations

abstract:
  We explore observational and theoretical constraints on how galaxies might
transition between the "star-forming main sequence" (SFMS) and varying "degrees
of quiescence" out to $z=3$. Our analysis is focused on galaxies with stellar
mass $M_*>10^{10}M_{\odot}$, and is enabled by GAMA and CANDELS observations, a
semi-analytic model (SAM) of galaxy formation, and a cosmological
hydrodynamical "zoom in" simulation with momentum-driven AGN feedback. In both
the observations and the SAM, transition galaxies tend to have intermediate
S\'ersic indices, half-light radii, and surface stellar mass densities compared
to star-forming and quiescent galaxies out to $z=3$. We place an observational
upper limit on the average population transition timescale as a function of
redshift, finding that the average high-redshift galaxy is on a "fast track"
for quenching whereas the average low-redshift galaxy is on a "slow track" for
quenching. We qualitatively identify four physical origin scenarios for
transition galaxies in the SAM: oscillations on the SFMS, slow quenching, fast
quenching, and rejuvenation. Quenching timescales in both the SAM and the
hydrodynamical simulation are not fast enough to reproduce the quiescent
population that we observe at $z\sim3$. In the SAM, we do not find a clear-cut
morphological dependence of quenching timescales, but we do predict that the
mean stellar ages, cold gas fractions, SMBH masses, and halo masses of
transition galaxies tend to be intermediate relative to those of star-forming
and quiescent galaxies at $z<3$.


title:
The environmental dependence of gas accretion onto galaxies: quenching
  satellites through starvation

abstract:
  Galaxies that have fallen into massive haloes may no longer be able to
accrete gas from their surroundings, a process referred to as 'starvation' or
'strangulation' of satellites. We study the environmental dependence of gas
accretion onto galaxies using the cosmological, hydrodynamical EAGLE
simulation. We quantify the dependence of gas accretion on stellar mass,
redshift, and environment, using halo mass and galaxy overdensity as
environmental indicators. We find a strong suppression, by many orders of
magnitude, of the gas accretion rate in dense environments, primarily for
satellite galaxies. This suppression becomes stronger at lower redshift.
However, the scatter in accretion rates is very large for satellites. This is
(at least in part) due to the variation in halocentric radius, since gas
accretion is more suppressed at smaller radii. Central galaxies are influenced
less strongly by their environment and exhibit less scatter in their gas
accretion rates. The star formation rates of both centrals and satellites show
similar behaviour to their gas accretion rates. The relatively small
differences between gas accretion and star formation rates demonstrate that
galaxies generally exhaust their gas reservoir somewhat faster at higher
stellar mass, lower redshift, and in denser environments. We conclude that the
environmental suppression of gas accretion could directly result in the
quenching of star formation.


title:
Exo-Transmit: An Open-Source Code for Calculating Transmission Spectra
  for Exoplanet Atmospheres of Varied Composition

abstract:
  We present Exo-Transmit, a software package to calculate exoplanet
transmission spectra for planets of varied composition. The code is designed to
generate spectra of planets with a wide range of atmospheric composition,
temperature, surface gravity, and size, and is therefore applicable to
exoplanets ranging in mass and size from hot Jupiters down to rocky
super-Earths. Spectra can be generated with or without clouds or hazes with
options to (1) include an optically thick cloud deck at a user-specified
atmospheric pressure or (2) to augment the nominal Rayleigh scattering by a
user-specified factor. The Exo-Transmit code is written in C and is extremely
easy to use. Typically the user will only need to edit parameters in a single
user input file in order to run the code for a planet of their choosing.
Exo-Transmit is available publicly on Github with open-source licensing at
https://github.com/elizakempton/Exo_Transmit .


title:
The density of dark matter haloes of early-type galaxies in low-density
  environments

abstract:
  New photometric and long-slit spectroscopic observations are presented for
NGC 7113, PGC 1852, and PGC 67207 which are three bright galaxies residing in
low-density environments. The surface-brightness distribution is analysed from
the K_S-band images taken with adaptive optics at the Gemini North Telescope
and the ugriz-band images from the Sloan Digital Sky Survey while the
line-of-sight stellar velocity distribution and line-strength Lick indices
inside the effective radius are measured along several position angles. The
age, metallicity, and alpha-element abundance of the galaxies are estimated
from single stellar-population models. In spite of the available morphological
classification, images show that PGC 1852 is a barred spiral which we do not
further consider for mass modelling. The structural parameters of the two
early-type galaxies NGC 7113 and PGC 67207 are obtained from a two-dimensional
photometric decomposition and the mass-to-light ratio of all the (luminous and
dark) mass that follows the light is derived from orbit-based axisymmetric
dynamical modelling together with the mass density of the dark matter halo. The
dynamically derived mass that follows the light is about a factor of 2 larger
than the stellar mass derived using stellar-population models with Kroupa
initial mass function. Both galaxies have a lower content of halo dark matter
with respect to early-type galaxies in high-density environments and in
agreement with the predictions of semi-analytical models of galaxy formation.


abstract:
  Effective sparse representation of X-Ray medical images within the context of
data reduction is considered. The proposed framework is shown to render an
enormous reduction in the cardinality of the data set required to represent
this class of images at very good quality. The particularity of the approach is
that it can be implemented at very competitive processing time and low memory
requirements


title:
The contribution of Fermi-2LAC blazars to the diffuse TeV-PeV neutrino
  flux

abstract:
  The recent discovery of a diffuse cosmic neutrino flux extending up to PeV
energies raises the question of which astrophysical sources generate this
signal. One class of extragalactic sources which may produce such high-energy
neutrinos are blazars. We present a likelihood analysis searching for
cumulative neutrino emission from blazars in the 2nd Fermi-LAT AGN catalogue
(2LAC) using an IceCube neutrino dataset 2009-12 which was optimised for the
detection of individual sources. In contrast to previous searches with IceCube,
the populations investigated contain up to hundreds of sources, the largest one
being the entire blazar sample in the 2LAC catalogue. No significant excess is
observed and upper limits for the cumulative flux from these populations are
obtained. These constrain the maximum contribution of the 2LAC blazars to the
observed astrophysical neutrino flux to be $27 \%$ or less between around 10
TeV and 2 PeV, assuming equipartition of flavours at Earth and a single
power-law spectrum with a spectral index of $-2.5$. We can still exclude that
the 2LAC blazars (and sub-populations) emit more than $50 \%$ of the observed
neutrinos up to a spectral index as hard as $-2.2$ in the same energy range.
Our result takes into account that the neutrino source count distribution is
unknown, and it does not assume strict proportionality of the neutrino flux to
the measured 2LAC $\gamma$-ray signal for each source. Additionally, we
constrain recent models for neutrino emission by blazars.


title: The Hall number across a van Hove singularity

abstract:
  In the context of the relaxation time approximation to Boltzmann transport
theory, we examine the behavior of the Hall number, $n_H$, of a metal in the
neighborhood of a Lifshitz transition from a closed Fermi surface to open
sheets. We find a universal non-analytic dependence of $n_H$ on the electron
density in the high field limit, but a non-singular dependence at low fields.
The existence of an assumed nematic transition produces a doping dependent
$n_H$ similar to that observed in recent experiments in the high temperature
superconductor YBa$_2$Cu$_3$O$_{7-x}$.


title:
PTFE surface etching in the post-discharge of a RF scanning plasma
  torch: evidence of ejected fluorinated species

abstract:
  The texturization of poly(tetrafluoroethylene) (PTFE) surfaces is achieved at
atmospheric pressure by using the post-discharge of a radio-frequency plasma
torch supplied in helium and oxygen gases. The surface properties are
characterized by contact angle measurement, X-ray photoelectron spectroscopy
and atomic force microscopy. We show that the plasma treatment increases the
surface hydrophobicity (with water contact angles increasing from 115 to
155{\deg}) only by modifying the PTFE surface morphology and not the
stoichiometry. Measurements of sample mass losses correlated to the ejection of
CF$_2$ fragments from the PTFE surface evidenced an etching mechanism at
atmospheric pressure.

categories: cond-mat.other cond-mat.soft physics.ins-det physics.plasm-ph


title:
Accurate Interatomic Force Fields via Machine Learning with Covariant
  Kernels

abstract:
  We present a novel scheme to accurately predict atomic forces as vector
quantities, rather than sets of scalar components, by Gaussian Process (GP)
Regression. This is based on matrix-valued kernel functions, on which we impose
the requirements that the predicted force rotates with the target configuration
and is independent of any rotations applied to the configuration database
entries. We show that such covariant GP kernels can be obtained by integration
over the elements of the rotation group SO(d) for the relevant dimensionality
d. Remarkably, in specific cases the integration can be carried out
analytically and yields a conservative force field that can be recast into a
pair interaction form. Finally, we show that restricting the integration to a
summation over the elements of a finite point group relevant to the target
system is sufficient to recover an accurate GP. The accuracy of our kernels in
predicting quantum-mechanical forces in real materials is investigated by tests
on pure and defective Ni, Fe and Si crystalline systems.


title: New High-z Fermi BL Lacs with the Photometric Dropout Technique

abstract:
  Determining redshifts for BL Lacertae (BL Lac) objects using the traditional
spectroscopic method is challenging due to the absence of strong emission lines
in their optical spectra. We employ the photometric dropout technique to
determine redshifts for this class of blazars using the combined 13 broad-band
filters from Swift-UVOT and the multi-channel imager GROND at the MPG 2.2 m
telescope at ESO's La Silla Observatory. The wavelength range covered by these
13 filters extends from far ultraviolet to the near-Infrared. We report results
on 40 new Fermi detected BL Lacs with the photometric redshifts determinations
for 5 sources, with 3FGL J1918.2-4110 being the most distant in our sample at
z=2.16. Reliable upper limits are provided for 20 sources in this sample. Using
the highest energy photons for these Fermi-LAT sources, we evaluate the
consistency with the Gamma-ray horizon due to the extragalactic background
light.


title: Annealing Gaussian into ReLU: a New Sampling Strategy for Leaky-ReLU RBM

abstract:
  Restricted Boltzmann Machine (RBM) is a bipartite graphical model that is
used as the building block in energy-based deep generative models. Due to
numerical stability and quantifiability of the likelihood, RBM is commonly used
with Bernoulli units. Here, we consider an alternative member of exponential
family RBM with leaky rectified linear units -- called leaky RBM. We first
study the joint and marginal distributions of leaky RBM under different
leakiness, which provides us important insights by connecting the leaky RBM
model and truncated Gaussian distributions. The connection leads us to a simple
yet efficient method for sampling from this model, where the basic idea is to
anneal the leakiness rather than the energy; -- i.e., start from a fully
Gaussian/Linear unit and gradually decrease the leakiness over iterations. This
serves as an alternative to the annealing of the temperature parameter and
enables numerical estimation of the likelihood that are more efficient and more
accurate than the commonly used annealed importance sampling (AIS). We further
demonstrate that the proposed sampling algorithm enjoys faster mixing property
than contrastive divergence algorithm, which benefits the training without any
additional computational cost.


title:
Statistical properties for directional alignment and chasing of players
  in football games

abstract:
  Focusing on motion of two interacting players in football games, two velocity
vectors for the pair of one player and the nearest opponent player exhibit
strong alignment. Especially, we find that there exists a characteristic
interpersonal distance $ r\simeq 500 $ cm below which the circular variance for
their alignment decreases rapidly. By introducing the order parameter $ \phi(t)
$ in order to measure degree of alignment of players' velocity vectors, we also
find that the angle distribution between the nearest players' velocity vectors
becomes wrapped Cauchy ($ \phi \lesssim 0.7 $) and the mixture of von Mises and
wrapped Cauchy distributions ($ \phi \gtrsim 0.7 $), respectively. To
understand these findings, we construct a simple model for the motion of the
two interacting players with the following rules: chasing between the players
and the reset of the chasing. We numerically show that our model successfully
reproduce the results obtained from the actual data. Moreover, from the
numerical study, we find that there is another characteristic distance $
r\simeq 1000 $ cm below which player's chasing starts.


title:
Ranging with frequency-shifted feedback lasers: from $\mu$m-range
  accuracy to MHz-range measurement rate

abstract:
  We report results on ranging based on frequency shifted feedback (FSF) lasers
with two different implementations: (1) An Ytterbium-fiber system for
measurements in an industrial environment with accuracy of the order of 1
$\mu$m, achievable over a distance of the order of meters with potential to
reach an accuracy of better than 100 nm; (2) A semiconductor laser system for a
high rate of measurements with an accuracy of 2 mm @ 1 MHz or 75 $\mu$m @ 1 kHz
and a limit of the accuracy of $\geq $ 10 $\mu$m. In both implementations, the
distances information is derived from a frequency measurement. The method is
therefore insensitive to detrimental influence of ambient light. For the
Ytterbium-fiber system a key feature is the injection of a single frequency
laser, phase modulated at variable frequency $\Omega$, into the FSF-laser
cavity. The frequency $\Omega_{max}$ at which the detector signal is maximal
yields the distance. The semiconductor FSF laser system operates without
external injection seeding. In this case the key feature is frequency counting
that allows convenient choice of either accuracy or speed of measurements
simply by changing the duration of the interval during which the frequency is
measured by counting.


title:
Ent: A Multipartite Entanglement Measure, and Parameterization of
  Entangled States

abstract:
  A multipartite entanglement measure called the ent is presented and shown to
be an entanglement monotone, with the special property of automatic
normalization. Necessary and sufficient conditions are developed for
constructing maximally entangled states in every multipartite system such that
they are true-generalized X states (TGX) states, a generalization of the Bell
states, and are extended to general nonTGX states as well. These results are
then used to prove the existence of maximally entangled basis (MEB) sets in all
systems. A parameterization of general pure states of all ent values is given,
and proposed as a multipartite Schmidt decomposition. Finally, we develop an
ent vector and ent array to handle more general definitions of multipartite
entanglement, and the ent is extended to general mixed states, providing a
general multipartite entanglement measure.


title:
Self-Propelled Colloidal Particle Near a Planar Wall: A Brownian
  Dynamics Study

abstract:
  Miniaturized, self-propelled locomotors use chemo-mechanical transduction
mechanisms to convert fuel in the environment to autonomous motion. Recent
experimental and theoretical studies demonstrate that these autonomous engines
can passively follow the contours of solid boundaries they encounter. Boundary
guidance, however, is not necessarily stable: Mechanical disturbances can cause
the motor to hydrodynamically depart from the passively guided pathway.
Furthermore, given the scaled-down size of micromotors (typically 100 nm -10
$\mu$m), Brownian thermal fluctuation forces are necessarily important and
these stochastic forces can randomize passively-steered trajectories.
  Here we examine theoretically the stability of boundary guided motion of
micromotors along infinite planar walls to mechanical disturbances and to
Brownian forces. Our aim is to understand under what conditions this passively
guided motion is stable. We choose a locomotor design in which spherical
colloids are partially coated with a catalytic cap that reacts with solute to
produce a product. The product is repelled from the particle surface, causing
the particle to move with the inert face at the front (autonomous motion via
self-diffusiophoresis). When propelled towards a planar wall, deterministic
hydrodynamic studies demonstrate that these locomotors can exhibit, for large
enough cap sizes, steady trajectories in which the particle either skims
unidirectionally along the surface at a constant distance from the wall, or
becomes stationary. We first investigate the linear hydrodynamic stability of
these states by expanding the equations of motion about the states, and find
that linear perturbations decay exponentially in time. We then study the
effects of thermal fluctuations by formulating a Langevin equation for the
particle motion which includes the Brownian stochastic force...


title: \'Etale fundamental groups of strongly $F$-regular schemes

abstract:
  We prove that a strongly $F$-regular scheme $X$ admits a finite, generically
Galois, and \'etale-in-codimension-one cover $\widetilde X \to X$ such that the
\'etale fundamental groups of $\widetilde X$ and $\widetilde X_{reg}$ agree.
Equivalently, every finite \'etale cover of $\widetilde X_{reg}$ extends to a
finite \'etale cover of $\widetilde X$. This is analogous to a result for
complex klt varieties by Greb, Kebekus and Peternell.


title:
Influence of Collimation and Detector length on CT exposures measured in
  a 60cm long body phantom

abstract:
  Background: Data fitting approaches to modeling allow for parametric formulae
that may not reveal the physical quantities involved and their influence on the
function being studied. In this paper the author models the approach to
equilibrium function by a method that allows the physical quantities to be
defined beforehand, allows their influence to be studied, and can be used to
predict how each physical quantity affects approach to equilibrium. Methods: An
ordinary differential equation (ODE) is used to model the approach to
equilibrium function for the case where collimation is changed at fixed
detector size. A parallel model is used to study the approach to equilibrium as
a function of detector size for fixed collimation. Both models are validated by
experimental measurements in a 60cm body phantom. Influence of detector size is
simulated by using leaded sleeves of varying sizes wrapped around a 100mm
pencil chamber. This creates sleeve gaps of 10 - 60mm around the chamber. A
100mm detector size is the pencil chamber without a leaded sleeve. Results:
Model accurately describes the experimental data for the cases studied. Except
for the smallest collimation of 5mm, linear regression analysis shows good
correlation between data and model according to the R^2 values at all
collimations. Further analysis of the model reveals minimum detector size that
will integrate 98% of the signal for a given collimation is, d=4.95L.
Additional analysis shows the minimum collimation at which a given detector
will collect 98% of the signal is, L=5.49d. Conclusion: Modeling by
differential equations is an accurate method for the approach to equilibrium
function, and has advantages over curve fitting methods.


title:
The destabilizing effect of external damping: Singular flutter boundary
  for the Pfluger column with vanishing external dissipation

abstract:
  Elastic structures loaded by nonconservative positional forces are prone to
instabilities induced by dissipation: it is well-known in fact that internal
viscous damping destabilizes the marginally stable Ziegler's pendulum and
Pfluger column (of which the Beck's column is a special case), two structures
loaded by a tangential follower force. The result is the so-called
'destabilization paradox', where the critical force for flutter instability
decreases by an order of magnitude when the coefficient of internal damping
becomes infinitesimally small. Until now external damping, such as that related
to air drag, is believed to provide only a stabilizing effect, as one would
intuitively expect. Contrary to this belief, it will be shown that the effect
of external damping is qualitatively the same as the effect of internal
damping, yielding a pronounced destabilization paradox. Previous results
relative to destabilization by external damping of the Ziegler's and Pfluger's
elastic structures are corrected in a definitive way leading to a new
understanding of the destabilizating role played by viscous terms.


title:
Concurrent growth and formation of electrically contacted monolayer
  transition metal dichalcogenides on bulk metallic patterns

abstract:
  While new species and properties of two-dimensional (2D) materials are being
reported with extraordinary regularity, a significant bottleneck in the field
is the ability to controllably process material into working devices. We report
a chemical vapor deposition process to selectively grow 2D material in a
deterministic manner around lithographically defined bulk metallic patterns
which concurrently provide as-grown contacts to the material. Monolayer films,
with lateral extent of up to hundreds of microns are controllably grown on and
around patterned regions of transition metals. By using different combinations
of metallic pattern and oxide based precursor, heterostructured MoS2/WS2 growth
has been observed as well. The materials display strong luminescence, monolayer
Raman signatures, and relatively large crystal domains. In addition to
producing high optical quality monolayer material deterministically and
selectively over large regions, the metallic patterns remain conductive and
therefore have the advantage of providing as-grown metallic contacts to the
material, offering a path for simple device fabrication and large scale
production


title: Fundamental limits of symmetric low-rank matrix estimation

abstract:
  We consider the high-dimensional inference problem where the signal is a
low-rank symmetric matrix which is corrupted by an additive Gaussian noise.
Given a probabilistic model for the low-rank matrix, we compute the limit in
the large dimension setting for the mutual information between the signal and
the observations, as well as the matrix minimum mean square error, while the
rank of the signal remains constant. We also show that our model extends beyond
the particular case of additive Gaussian noise and we prove an universality
result connecting the community detection problem to our Gaussian framework. We
unify and generalize a number of recent works on PCA, sparse PCA, submatrix
localization or community detection by computing the information-theoretic
limits for these problems in the high noise regime. In addition, we show that
the posterior distribution of the signal given the observations is
characterized by a parameter of the same dimension as the square of the rank of
the signal (i.e. scalar in the case of rank one). Finally, we connect our work
with the hard but detectable conjecture in statistical physics.


title: A PTAS for Three-Edge Connectivity in Planar Graphs

abstract:
  We consider the problem of finding the minimum-weight subgraph that satisfies
given connectivity requirements. Specifically, given a requirement $r \in
\{0,1,2,3\}$ for every vertex, we seek the minimum-weight subgraph that
contains, for every pair of vertices $u$ and $v$, at least $\min\{ r(v),
r(u)\}$ edge-disjoint $u$-to-$v$ paths. We give a polynomial-time approximation
scheme (PTAS) for this problem when the input graph is planar and the subgraph
may use multiple copies of any given edge. This generalizes an earlier result
for $r \in \{0,1,2\}$. In order to achieve this PTAS, we prove some properties
of triconnected planar graphs that may be of independent interest.


title: A Theory of Taxonomy

abstract:
  A taxonomy is a standardized framework to classify and organize items into
categories. Hierarchical taxonomies are ubiquitous, ranging from the
classification of organisms to the file system on a computer. Characterizing
the typical distribution of items within taxonomic categories is an important
question with applications in many disciplines. Ecologists have long sought to
account for the patterns observed in species-abundance distributions (the
number of individuals per species found in some sample), and computer
scientists study the distribution of files per directory. Is there a universal
statistical distribution describing how many items are typically found in each
category in large taxonomies? Here, we analyze a wide array of large,
real-world datasets -- including items lost and found on the New York City
transit system, library books, and a bacterial microbiome -- and discover such
an underlying commonality. A simple, non-parametric branching model that
randomly categorizes items and takes as input only the total number of items
and the total number of categories successfully reproduces the abundance
distributions in these datasets. This result may shed light on patterns in
species-abundance distributions long observed in ecology. The model also
predicts the number of taxonomic categories that remain unrepresented in a
finite sample.

categories: physics.soc-ph cs.SI physics.data-an q-bio.QM


title:
Tractors and Twistors from conformal Cartan geometry: a gauge theoretic
  approach II. Twistors

abstract:
  Tractors and Twistors bundles both provide natural conformally covariant
calculi on $4D$-Riemannian manifolds. They have different origins but are
closely related, and usually constructed bottom-up through prolongation of
defining differential equations. We propose alternative top-down gauge
theoretic constructions, starting from the conformal Cartan bundle $\P$ and its
vectorial $E$ and spinorial $\sE$ associated bundles. Our key ingredient is the
dressing field method of gauge symmetry reduction, which allows to exhibit
tractors and twistors and their associated connections as gauge fields of a
non-standard kind as far as Weyl rescaling symmetry is concerned. By
\emph{non-standard} we mean that they implement the gauge principle of physics,
but are of a different geometric nature than the well known differential
geometric objects usually underlying gauge theories. We provide the
corresponding BRST treatment. In a companion paper we dealt with tractors, in
the present one we address the case of twistors.


title: Equations of motion for charged particles in strong laser fields

abstract:
  Starting from the Dirac equation coupled to a classical radiation field a set
of equations of motion for charged quasi-particles in the classical limit for
slowly varying radiation and matter fields is derived. The radiation reaction
term derived in the paper is the Abraham-Lorentz-Dirac term.


title:
Approximation operators for matrix-valued functions based on matrix
  decompositions

abstract:
  Given a set of matrices, modeled as samples of a matrix-valued function, we
suggest a method to approximate the underline function using a product
approximation operator. This operator extends known approximation methods by
exploiting the structure of the matrices in the samples set, and based on
decomposition theorems. We introduce our approach in detail and discuss its
advantages using a few examples. In addition, we provide basic tools for
analyzing properties of the matrix functions generated by our approximation
operators.


title: Unsupervised Learning For Effective User Engagement on Social Media

abstract:
  In this paper, we investigate the effectiveness of unsupervised feature
learning techniques in predicting user engagement on social media.
Specifically, we compare two methods to predict the number of feedbacks (i.e.,
comments) that a blog post is likely to receive. We compare Principal Component
Analysis (PCA) and sparse Autoencoder to a baseline method where the data are
only centered and scaled, on each of two models: Linear Regression and
Regression Tree. We find that unsupervised learning techniques significantly
improve the prediction accuracy on both models. For the Linear Regression
model, sparse Autoencoder achieves the best result, with an improvement in the
root mean squared error (RMSE) on the test set of 42% over the baseline method.
For the Regression Tree model, PCA achieves the best result, with an
improvement in RMSE of 15% over the baseline.


title: traIXroute: Detecting IXPs in traceroute paths

abstract:
  Internet eXchange Points (IXP) are critical components of the Internet
infrastructure that affect its performance, evolution, security and economics.
In this work, we introduce techniques to augment the well-known traceroute tool
with the capability of identifying if and where exactly IXPs are crossed in
endto- end paths. Knowing this information can help end-users have more
transparency over how their traffic flows in the Internet. Our tool, called
traIXroute, exploits data from the PeeringDB (PDB) and the Packet Clearing
House (PCH) about IXP IP addresses of BGP routers, IXP members, and IXP
prefixes. We show that the used data are both rich, i.e., we find 12,716 IP
addresses of BGP routers in 460 IXPs, and mostly accurate, i.e., our validation
shows 92-93% accuracy. In addition, 78.2% of the detected IXPs in our data are
based on multiple diverse evidence and therefore help have higher confidence on
the detected IXPs than when relying solely on IXP prefixes. To demonstrate the
utility of our tool, we use it to show that one out of five paths in our data
cross an IXP and that paths do not normally cross more than a single IXP, as it
is expected based on the valley-free model about Internet policies.
Furthermore, although the top IXPs both in terms of paths and members are
located in Europe, US IXPs attract many more paths than their number of members
indicates.


title: The Supernovae Analysis Application (SNAP)

abstract:
  The SuperNovae Analysis aPplication (SNAP) is a new tool for the analysis of
SN observations and validation of SN models. SNAP consists of an open source
relational database with (a) observational light curve, (b) theoretical light
curve, and (c) correlation table sets, statistical comparison software, and a
web interface available to the community. The theoretical models are intended
to span a gridded range of parameter space. The goal is to have users to upload
new SN models or new SN observations and run the comparison software to
determine correlations via the web site. There are looming problems on the
horizon that SNAP begins to solve. Namely, large surveys will discover
thousands of SNe annually. Frequently, the parameter space of a new SN event is
unbounded. SNAP will be a resource to constrain parameters and determine if an
event needs follow-up without spending resources to create new light curve
models from scratch. Secondly, there is not a rapidly available, systematic way
to determine degeneracies between parameters or even what physics is needed to
model a realistic SNe. The correlations made within the SNAP system begin to
solve these problems.


title: Escape rate of active particles in the effective equilibrium approach

abstract:
  The escape rate of a Brownian particle over a potential barrier is accurately
described by the Kramers theory. A quantitative theory explicitly taking the
activity of Brownian particles into account has been lacking due to the
inherently out-of-equilibrium nature of these particles. Using an effective
equilibrium approach [Farage et al., Phys. Rev. E 91, 042310 (2015)] we study
the escape rate of active particles over a potential barrier and compare our
analytical results with data from direct numerical simulation of the colored
noise Langevin equation. The effective equilibrium approach generates an
effective potential which, when used as input to Kramers rate theory, provides
results in excellent agreement with the simulation data.


title:
Low Latency Anomaly Detection and Bayesian Network Prediction of Anomaly
  Likelihood

abstract:
  We develop a supervised machine learning model that detects anomalies in
systems in real time. Our model processes unbounded streams of data into time
series which then form the basis of a low-latency anomaly detection model.
Moreover, we extend our preliminary goal of just anomaly detection to
simultaneous anomaly prediction. We approach this very challenging problem by
developing a Bayesian Network framework that captures the information about the
parameters of the lagged regressors calibrated in the first part of our
approach and use this structure to learn local conditional probability
distributions.