title:
$B^0_{(s)}$-mixing matrix elements from lattice QCD for the Standard
  Model and beyond

abstract:
  We calculate---for the first time in three-flavor lattice QCD---the hadronic
matrix elements of all five local operators that contribute to neutral $B^0$-
and $B_s$-meson mixing in and beyond the Standard Model. We present a complete
error budget for each matrix element and also provide the full set of
correlations among the matrix elements. We also present the corresponding bag
parameters and their correlations, as well as specific combinations of the
mixing matrix elements that enter the expression for the neutral $B$-meson
width difference. We obtain the most precise determination to date of the
SU(3)-breaking ratio $\xi = 1.206(18)(6)$, where the second error stems from
the omission of charm sea quarks, while the first encompasses all other
uncertainties. The threefold reduction in total uncertainty, relative to the
2013 Flavor Lattice Averaging Group results, tightens the constraint from $B$
mixing on the Cabibbo-Kobayashi-Maskawa (CKM) unitarity triangle. Our
calculation employs gauge-field ensembles generated by the MILC Collaboration
with four lattice spacings and pion masses close to the physical value. We use
the asqtad-improved staggered action for the light valence quarks, and the
Fermilab method for the bottom quark. We use heavy-light meson chiral
perturbation theory modified to include lattice-spacing effects to extrapolate
the five matrix elements to the physical point. We combine our results with
experimental measurements of the neutral $B$-meson oscillation frequencies to
determine the CKM matrix elements $|V_{td}| = 8.00(34)(8) \times 10^{-3}$,
$|V_{ts}| = 39.0(1.2)(0.4) \times 10^{-3}$, and $|V_{td}/V_{ts}| =
0.2052(31)(10)$, which differ from CKM-unitarity expectations by about
2$\sigma$. These results and others from flavor-changing-neutral currents point
towards an emerging tension between weak processes that are mediated at the
loop and tree levels.


title:
Electric double layer of anisotropic dielectric colloids under electric
  fields

abstract:
  Anisotropic colloidal particles constitute an important class of building
blocks for self-assembly directed by electrical fields. The aggregation of
these building blocks is driven by induced dipole moments, which arise from an
interplay between dielectric effects and the electric double layer. For
particles that are anisotropic in shape, charge distribution, and dielectric
properties, calculation of the electric double layer requires coupling of the
ionic dynamics to a Poisson solver. We apply recently proposed methods to solve
this problem for experimentally employed colloids in static and time-dependent
electric fields. This allows us to predict the effects of field strength and
frequency on the colloidal properties.


title:
The large-scale correlations of multi-cell densities and profiles,
  implications for cosmic variance estimates

abstract:
  In order to quantify the error budget in the measured probability
distribution functions of cell densities, the two-point statistics of cosmic
densities in concentric spheres is investigated. Bias functions are introduced
as the ratio of their two-point correlation function to the two-point
correlation of the underlying dark matter distribution. They describe how cell
densities are spatially correlated. They are computed here via the so-called
large deviation principle in the quasi-linear regime. Their large-separation
limit is presented and successfully compared to simulations for density and
density slopes: this regime is shown to be rapidly reached allowing to get
sub-percent precision for a wide range of densities and variances. The
corresponding asymptotic limit provides an estimate of the cosmic variance of
standard concentric cell statistics applied to finite surveys. More generally,
no assumption on the separation is required for some specific moments of the
two-point statistics, for instance when predicting the generating function of
cumulants containing any powers of concentric densities in one location and one
power of density at some arbitrary distance from the rest. This exact "one
external leg" cumulant generating function is used in particular to probe the
rate of convergence of the large-separation approximation.


title: QoS Evaluation of Heterogeneous Networks: Application-based Approach

abstract:
  In this paper, an application-based QoS evaluation approach for heterogeneous
networks is proposed.It is possible to expand the network capacity and coverage
in a dynamic fashion by applying heterogeneous wireless network architecture.
However, the Quality of Service (QoS) evaluation of this type of network
architecture is very challenging due to the presence of different communication
technologies. Different communication technologies have different
characteristics and the applications that utilize them have unique QoS
requirements. Although, the communication technologies have different
performance measurement parameters, the applications using these radio access
networks have the same QoS requirements. As a result, it would be easier to
evaluate the QoS of the access networks and the overall network configuration
based on the performance of applications running on them. Using such
application-based QoS evaluation approach, the heterogeneous nature of the
underlying networks and the diversity of their traffic can be adequately taken
into account. Through simulation studies, we show that the application
performance based assessment approach facilitates better QoS management and
monitoring of heterogeneous network configurations.


title: A quantum Leray-Hirsch theorem for banded gerbes

abstract:
  For a gerbe $\Y$ over a smooth proper Deligne-Mumford stack $\B$ banded by a
finite group $G$, we prove a structure result on the Gromov-Witten theory of
$\Y$, expressing Gromov-Witten invariants of $\Y$ in terms of Gromov-Witten
invariants of $\B$ twisted by various flat $U(1)$-gerbes on $\B$. This is
interpreted as a Leray-Hirsch type of result for Gromov-Witten theory of
gerbes.


title: Light-Front Quark Model Analysis of Meson-Photon Transition Form Factor

abstract:
  We discuss $(\pi^0,\eta,\eta')\to\gamma^*\gamma$ transition form factors
using the light-front quark model.
  Our discussion includes the analysis of the mixing angles for $\eta-\eta'$.
Our results for $Q^2 F_{(\pi^0,\eta,\eta')\to\gamma^*\gamma}(Q^2)$ show scaling
behavior for high $Q^2$ consistent with pQCD predictions.


title: Inversion-symmetry-breaking-activated shear Raman bands in $T'$-MoTe$_2$

abstract:
  Type-II Weyl fermion nodes, located at the touching points between electron
and hole pockets, have been recently predicted to occur in distorted octahedral
($T'$) transition metal dichalcogenide semimetals, contingent upon the
condition that the layered crystal has the noncentrosymmetric orthorhombic
($T'_{or}$) stacking. Here, we report on the emergence of two shear Raman bands
activated by inversion symmetry breaking in $T'$-MoTe$_2$ due to sample
cooling. Polarization and crystal orientation resolved measurements further
point to a phase transition from the monoclinic ($T'_{mo}$) structure to the
desired $T'_{or}$ lattice. These results provide spectroscopic evidence that
low-temperature $T'$-MoTe$_2$ is suitable for probing type-II Weyl physics.


title:
Rate of convergence: the packing and centered Hausdoff measures of
  totally disconnected self-similar sets

abstract:
  In this paper we obtain the rates of convergence of the algorithms given in
[13] and [14] for an automatic computation of the centered Hausdorff and
packing measures of a totally disconnected self-similar set. We evaluate these
rates empirically through the numerical analysis of three standard classes of
self-similar sets, namely, the families of Cantor type sets in the real line
and the plane and the class of Sierpinski gaskets. For these three classes and
for small contraction ratios, sharp bounds for the exact values of the
corresponding measures are obtained and it is shown how these bounds
automatically yield estimates of the corresponding measures, accurate in some
cases to as many as 14 decimal places. In particular, the algorithms accurately
recover the exact values of the measures in all cases in which these values are
known by geometrical arguments. Positive results, which confirm some
conjectural values given in [13] and [14] for the measures, are also obtained
for an intermediate range of larger contraction ratios. We give an argument
showing that, for this range of contraction ratios, the problem is inherently
computational in the sense that any theoretical proof, such as those mentioned
above, might be impossible, so that in these cases, our method is the only
available approach. For contraction ratios close to those of the connected case
our computational method becomes intractably time consuming, so the computation
of the exact values of the packing and centered Hausdorff measures in the
general case, with the open set condition, remains a challenging problem.


title:
Imaging Spin Dynamics in Monolayer WS2 by Time-Resolved Kerr Rotation
  Microscopy

abstract:
  Monolayer transition metal dichalcogenides (TMD) have immense potential for
future spintronic and valleytronic applications due to their two-dimensional
nature and long spin/valley lifetimes. We investigate the origin of these
long-lived states in n-type WS2 using time-resolved Kerr rotation microscopy
and photoluminescence microscopy with ~1 micron spatial resolution. Comparing
the spatial dependence of the Kerr rotation signal and the photoluminescence
reveals a correlation with neutral exciton emission, which is likely due to the
transfer of angular momentum to resident conduction electrons with long
spin/valley lifetimes. In addition, we observe an unexpected anticorrelation
between the Kerr rotation and trion emission, which provides evidence for the
presence of long-lived spin/valley-polarized dark trions. We also find that the
spin/valley polarization in WS2 is robust to magnetic fields up to 700 mT,
indicative of spins and valleys that are stabilized with strong spin-orbit
fields.


title:
The independence number of non-uniform uncrowded hypergraphs and an
  anti-Ramsey type result

abstract:
  We prove the following: Fix an integer $k\geq 2$, and let $T$ be a real
number with $T\geq 1.5$. Let $\cH=(V,\cE_2\cup \cE_3\cup\dots\cup\cE_k)$ be a
non-uniform hypergraph with the vertex set $V$ and the set $\cE_i$ of edges of
size $i=2,\ldots , k$. Suppose that $\cH$ has no $2$-cycles (regardless of
sizes of edges), and neither contains $3$-cycles nor $4$-cycles consisting of
$2$-element edges. If the average degrees $t_i^{i-1} := i |\cE_i|/ |V|$ satisfy
that $t_i^{i-1} \leq T^{i-1} (\ln T)^{\frac{k-i}{k-1}}$ for $i= 2, \dots , k$,
then there exists a constant $C_k > 0$, depending only on $k$, such that
$\alpha(\cH)\geq C_k \frac{|V|}{T} (\ln T)^{\frac{1}{k-1}}$, where
$\alpha(\cH)$ denotes the independence number of $\cH$. This extends results of
Ajtai, Koml\'os, Pintz, Spencer and Szemer\'edi and Duke, R\"odl and the second
author for uniform hypergraphs.
  As an application, we consider an anti-Ramsey type problem on non-uniform
hypergraphs. Let $\cH=\cH(n;2,\ldots,\ell)$ be the hypergraph on the $n$-vertex
set $V$ in which, for $s=2,\ldots,\ell$, each $s$-subset of $V$ is a hyperedge
of $\cH$. Let $\Delta$ be an edge-coloring of $\cH$ satisfying the following:
(a) two hyperedges sharing a vertex have different colors; (b) two hyperedges
with distinct size have different colors; (c) a color used for a hyperedge of
size $s$ appears at most $u_s$ times. For such a coloring $\Delta$, let
$f_{\Delta}(n;u_2,\ldots,u_{\ell})$ be the maximum size of a subset $U$ of $V$
such that each hyperedge of $\cH[U]$ has a distinct color, and let
$f(n;u_2,\ldots,u_{\ell}):=\min_{\Delta} f_{\Delta}(n;u_2,\ldots,u_{\ell}).$ We
determine $f(n;u_2,\ldots,u_{\ell})$ up to a multiplicative logarithm factor.


title: Optimized Kernel-based Projection Space of Riemannian Manifolds

abstract:
  It is proven that encoding images and videos through Symmetric Positive
Definite (SPD) matrices, and considering the Riemannian geometry of the
resulting space, can lead to increased classification performance. Taking into
account manifold geometry is typically done via embedding the manifolds in
tangent spaces, or Reproducing Kernel Hilbert Spaces (RKHS). Recently, it was
shown that embedding such manifolds into a Random Projection Spaces (RPS),
rather than RKHS or tangent space, leads to higher classification and
clustering performance. However, based on structure and dimensionality of the
randomly generated hyperplanes, the classification performance over RPS may
vary significantly. In addition, fine-tuning RPS is data expensive (as it
requires validation-data), time consuming, and resource demanding. In this
paper, we introduce an approach to learn an optimized kernel-based projection
(with fixed dimensionality), by employing the concept of subspace clustering.
As such, we encode the association of data points to the underlying subspace of
each point, to generate meaningful hyperplanes. Further, we adopt the concept
of dictionary learning and sparse coding, and discriminative analysis, for the
optimized kernel-based projection space (OPS) on SPD manifolds. We validate our
algorithm on several classification tasks. The experiment results also
demonstrate that the proposed method outperforms state-of-the-art methods on
such manifolds.


title:
High Dimensional Inference with Random Maximum A-Posteriori
  Perturbations

abstract:
  This paper presents a new approach, called perturb-max, for high-dimensional
statistical inference that is based on applying random perturbations followed
by optimization. This framework injects randomness to maximum a-posteriori
(MAP) predictors by randomly perturbing the potential function for the input. A
classic result from extreme value statistics asserts that perturb-max
operations generate unbiased samples from the Gibbs distribution using
high-dimensional perturbations. Unfortunately, the computational cost of
generating so many high-dimensional random variables can be prohibitive.
However, when the perturbations are of low dimension, sampling the perturb-max
prediction is as efficient as MAP optimization. This paper shows that the
expected value of perturb-max inference with low dimensional perturbations can
be used sequentially to generate unbiased samples from the Gibbs distribution.
Furthermore the expected value of the maximal perturbations is a natural bound
on the entropy of such perturb-max models. A measure concentration result for
perturb-max values shows that the deviation of their sampled average from its
expectation decays exponentially in the number of samples, allowing effective
approximation of the expectation.


title:
Effective Sample Size for Importance Sampling based on discrepancy
  measures

abstract:
  The Effective Sample Size (ESS) is an important measure of efficiency of
Monte Carlo methods such as Markov Chain Monte Carlo (MCMC) and Importance
Sampling (IS) techniques. In the IS context, an approximation $\widehat{ESS}$
of the theoretical ESS definition is widely applied, involving the inverse of
the sum of the squares of the normalized importance weights. This formula,
$\widehat{ESS}$, has become an essential piece within Sequential Monte Carlo
(SMC) methods, to assess the convenience of a resampling step. From another
perspective, the expression $\widehat{ESS}$ is related to the Euclidean
distance between the probability mass described by the normalized weights and
the discrete uniform probability mass function (pmf). In this work, we derive
other possible ESS functions based on different discrepancy measures between
these two pmfs. Several examples are provided involving, for instance, the
geometric mean of the weights, the discrete entropy (including theperplexity
measure, already proposed in literature) and the Gini coefficient among others.
We list five theoretical requirements which a generic ESS function should
satisfy, allowing us to classify different ESS measures. We also compare the
most promising ones by means of numerical simulations.


title:
Space CoBot: a collaborative aerial robot for indoor microgravity
  environments

abstract:
  This paper presents a first contribution to the design of a small aerial
robot for inhabited microgravity environments, such as orbiting space stations.
In particular, we target a fleet of robots for collaborative tasks with humans,
such as telepresence and cooperative mobile manipulation. We explore a
propeller based propulsion system, arranged in such a way that the
translational and the rotational components can be decoupled, resulting in an
holonomic hexarotor. Since propellers have limited thrust, we employ an
optimization approach to select the geometric configuration given a criteria of
uniform maximum thrust across all directions in the body reference frame. We
also tackle the problem of motion control: due to the decoupling of
translational and rotational modes we use separate converging controllers for
each one of these modes. In addition, we present preliminary simulation results
in a realistic simulator, in closed loop with the proposed controller, thus
providing a first validation of the followed methodology.


title: A knockoff filter for high-dimensional selective inference

abstract:
  This paper develops a framework for testing for associations in a possibly
high-dimensional linear model where the number of features/variables may far
exceed the number of observational units. In this framework, the observations
are split into two groups, where the first group is used to screen for a set of
potentially relevant variables, whereas the second is used for inference over
this reduced set of variables; we also develop strategies for leveraging
information from the first part of the data at the inference step for greater
power. In our work, the inferential step is carried out by applying the
recently introduced knockoff filter, which creates a knockoff copy-a fake
variable serving as a control-for each screened variable. We prove that this
procedure controls the directional false discovery rate (FDR) in the reduced
model controlling for all screened variables; this says that our
high-dimensional knockoff procedure 'discovers' important variables as well as
the directions (signs) of their effects, in such a way that the expected
proportion of wrongly chosen signs is below the user-specified level (thereby
controlling a notion of Type S error averaged over the selected set). This
result is non-asymptotic, and holds for any distribution of the original
features and any values of the unknown regression coefficients, so that
inference is not calibrated under hypothesized values of the effect sizes. We
demonstrate the performance of our general and flexible approach through
numerical studies, showing more power than existing alternatives. Finally, we
apply our method to a genome-wide association study to find locations on the
genome that are possibly associated with a continuous phenotype.


title: Automorphism Groups of Trees: Generalities and Prescribed Local Actions

abstract:
  This article is an expanded version of the talks given by the authors at the
Arbeitsgemeinschaft "Totally Disconnected Groups", held at Oberwolfach in
October 2014. We recall the basic theory of automorphisms of trees and Tits'
simplicity theorem, and present two constructions of tree groups via local
actions with their basic properties: the universal group associated to a finite
permutation group by M. Burger and S. Mozes, and the $k$-closures of a given
group by C. Banks, M. Elder and G. Willis.


title:
Electronic Evidence of Temperature-Induced Lifshitz Transition and
  Topological Nature in ZrTe5

abstract:
  The topological materials have attracted much attention recently. While
three-dimensional topological insulators are becoming abundant, two-dimensional
topological insulators remain rare, particularly in natural materials. ZrTe5
has host a long-standing puzzle on its anomalous transport properties; its
underlying origin remains elusive. Lately, ZrTe5 has ignited renewed interest
because it is predicted that single-layer ZrTe5 is a two-dimensional
topological insulator and there is possibly a topological phase transition in
bulk ZrTe5. However, the topological nature of ZrTe5 is under debate as some
experiments point to its being a three-dimensional or quasi-two-dimensional
Dirac semimetal. Here we report high-resolution laser-based angle-resolved
photoemission measurements on ZrTe5. The electronic property of ZrTe5 is
dominated by two branches of nearly-linear-dispersion bands at the Brillouin
zone center. These two bands are separated by an energy gap that decreases with
decreasing temperature but persists down to the lowest temperature we measured
(~2 K). The overall electronic structure exhibits a dramatic temperature
dependence; it evolves from a p-type semimetal with a hole-like Fermi pocket at
high temperature, to a semiconductor around ~135 K where its resistivity
exhibits a peak, to an n-type semimetal with an electron-like Fermi pocket at
low temperature. These results indicate a clear electronic evidence of the
temperature-induced Lifshitz transition in ZrTe5. They provide a natural
understanding on the underlying origin of the resistivity anomaly at ~135 K and
its associated reversal of the charge carrier type. Our observations also
provide key information on deciphering the topological nature of ZrTe5 and
possible temperature-induced topological phase transition.


title:
Probing defects and correlations in the hydrogen-bond network of ab
  initio water

abstract:
  The hydrogen-bond network of water is characterized by the presence of
coordination defects relative to the ideal tetrahedral network of ice, whose
fluctuations determine the static and time-dependent properties of the liquid.
Because of topological constraints, such defects do not come alone, but are
highly correlated coming in a plethora of different pairs. Here we discuss in
detail such correlations in the case of ab initio water models and show that
they have interesting similarities to regular and defective solid phases of
water. Although defect correlations involve deviations from idealized
tetrahedrality, they can still be regarded as weaker hydrogen bonds that retain
a high degree of directionality. We also investigate how the structure and
population of coordination defects is affected by approximations to the
inter-atomic potential, finding that in most cases, the qualitative features of
the hydrogen bond network are remarkably robust.


title: Distinguished-root formulas for generalized Calabi-Yau hypersurfaces

abstract:
  By a "generalized Calabi-Yau hypersurface" we mean a hypersurface in
${\mathbb P}^n$ of degree $d$ dividing $n+1$. The zeta function of a generic
such hypersurface has a reciprocal root distinguished by minimal
$p$-divisibility. We study the $p$-adic variation of that distinguished root in
a family and show that it equals the product of an appropriate power of $p$
times a product of special values of a certain $p$-adic analytic function
${\mathcal F}$. That function ${\mathcal F}$ is the $p$-adic analytic
continuation of the ratio $F(\Lambda)/F(\Lambda^p)$, where $F(\Lambda)$ is a
solution of the $A$-hypergeometric system of differential equations
corresponding to the Picard-Fuchs equation of the family.


title: New Invariants of Knotoids

abstract:
  In this paper we construct new invariants of knotoids including the odd
writhe, the parity bracket polynomial, the affine index polynomial and the
arrow polynomial, and give an introduction to the theory of virtual knotoids.
The invariants in this paper are defined for classical knotoids in analogy to
corresponding invariants of virtual knots. The affine index polynomial and the
arrow polynomial provide bounds on the height (minimum crossing distance
between endpoints) of a classical knotoid. We show that classical knotoids have
symmetric affine index polynomials.


title:
Fermat's Last Theorem and Catalan's Conjecture in Weak Exponential
  Arithmetics

abstract:
  We study Fermat's Last Theorem and Catalan's conjecture in the context of
weak arithmetics with exponentiation. We deal with expansions (B,e) of models
of arithmetical theories (in the language L=(0,1,+,x,<)) by a binary (partial
or total) function e intended as an exponential. We provide a general
construction of such expansions and prove that it is universal for the class of
all exponentials e which satisfy a certain natural set of axioms Exp. We
construct a model (B,e) of Th(N) + Exp and a substructure (A,e) with e total
and A model of Pr (Presburger arithmetic) such that in both (B,e) and (A,e)
Fermat's Last Theorem for e is violated by cofinally many exponents n and (in
all coordinates) cofinally many pairwise linearly independent triples a,b,c. On
the other hand, under the assumption of ABC conjecture (in the standard model),
we show that Catalan's conjecture for e is provable in Th(N)+Exp (even in a
weaker theory) and thus holds in (B,e) and (A,e). Finally, we also show that
Fermat's Last Theorem for e is provable (again, under the assumption of ABC in
N) in Th(N)+Exp+"coprimality for e".


title:
Efficient methods for time-dependence in semiclassical Schr\"odinger
  equations

abstract:
  We build an efficient and unitary (hence stable) method for the solution of
the semi-classical Schr\"odinger equation subject with explicitly
time-dependent potentials. The method is based on a combination of the
Zassenhaus decomposition (Bader, Iserles, Kropielnicka & Singh 2014) with the
Magnus expansion of the time-dependent Hamiltonian. We conclude with numerical
experiments.


title:
Torsion groups of elliptic curves over quadratic cyclotomic fields in
  elementary abelian 2-extensions

abstract:
  Let K denote the quadratic field $\mathbb{Q}(\sqrt{d})$ where d=$-1$ or $-3$.
Let E be an elliptic curve defined over K. In this paper, we analyze the
torsion subgroups of E in the maximal elementary abelian $2$-extension of $K$.


title: Divisor problem in arithmetic progressions modulo a prime power

abstract:
  We obtain an asymptotic formula for the average value of the divisor function
over the integers $n \le x$ in an arithmetic progression $n \equiv a \pmod q$,
where $q=p^k$ for a prime $p\ge 3$ and a sufficiently large integer $k$. In
particular, we break the classical barrier $q \le x^{2/3}$ for such formulas,
and generalise a recent result of R.~Khan (2015), making it uniform in $k$.


title: Generalised hyperbolicity in spacetimes with string-like singularities

abstract:
  In this paper we present well-posedness results of the wave equation in
$H^{1}$ for spacetimes that contain string-like singularities. These results
extend a framework able to characterise gravitational singularities as
obstruction to the dynamics of test fields rather than point particles. In
particular, we discuss spacetimes with cosmic strings and the relation of our
results to the Strong Cosmic Censorship Conjecture.


title: Generating Discriminative Object Proposals via Submodular Ranking

abstract:
  A multi-scale greedy-based object proposal generation approach is presented.
Based on the multi-scale nature of objects in images, our approach is built on
top of a hierarchical segmentation. We first identify the representative and
diverse exemplar clusters within each scale by using a diversity ranking
algorithm. Object proposals are obtained by selecting a subset from the
multi-scale segment pool via maximizing a submodular objective function, which
consists of a weighted coverage term, a single-scale diversity term and a
multi-scale reward term. The weighted coverage term forces the selected set of
object proposals to be representative and compact; the single-scale diversity
term encourages choosing segments from different exemplar clusters so that they
will cover as many object patterns as possible; the multi-scale reward term
encourages the selected proposals to be discriminative and selected from
multiple layers generated by the hierarchical image segmentation. The
experimental results on the Berkeley Segmentation Dataset and PASCAL VOC2012
segmentation dataset demonstrate the accuracy and efficiency of our object
proposal model. Additionally, we validate our object proposals in simultaneous
segmentation and detection and outperform the state-of-art performance.


title: Guessing Numbers of Odd Cycles

abstract:
  For a given number of colours, $s$, the guessing number of a graph is the
base $s$ logarithm of the size of the largest family of colourings of the
vertex set of the graph such that the colour of each vertex can be determined
from the colours of the vertices in its neighbourhood. An upper bound for the
guessing number of the $n$-vertex cycle graph $C_n$ is $n/2$. It is known that
the guessing number equals $n/2$ whenever $n$ is even or $s$ is a perfect
square \cite{Christofides2011guessing}. We show that, for any given integer
$s\geq 2$, if $a$ is the largest factor of $s$ less than or equal to
$\sqrt{s}$, for sufficiently large odd $n$, the guessing number of $C_n$ with
$s$ colours is $(n-1)/2 + \log_s(a)$. This answers a question posed by
Christofides and Markstr\"{o}m in 2011 \cite{Christofides2011guessing}. We also
present an explicit protocol which achieves this bound for every $n$. Linking
this to index coding with side information, we deduce that the information
defect of $C_n$ with $s$ colours is $(n+1)/2 - \log_s(a)$ for sufficiently
large odd $n$. Our results are a generalisation of the $s=2$ case which was
proven in \cite{bar2011index}.


title: Low Bending Loss Nodeless Hollow-core Anti-Resonant Fiber

abstract:
  We report a high performance nodeless hollow-core anti-resonant fiber with a
broadband guidance from 1050 nm to >1900 nm, a transmission attenuation of 200
dB/km, and a low bending loss of 0.25 dB/m for a 5 cm radius at wavelength of
1550 nm.


title: Blowing Up Finitely Supported Complete Ideals in a Regular Local Ring

abstract:
  Let I be a finitely supported complete m-primary ideal of a regular local
ring (R, m). We consider singularities of the normalization of the blow-up Proj
R[It] of I. A theorem of Lipman implies that the ideal I has a unique
factorization as a star-product of special star-simple complete ideals with
possibly negative exponents for some of the factors. If the normalization of
the projective model Proj R[It] is regular, we prove that it is the regular
model obtained by blowing up the finite set of base points of I. Extending work
of Lipman and Huneke-Sally in dimension 2, we prove that every local ring S on
the normalization of Proj R[It] that is a unique factorization domain is
regular. Moreover, if dim S is at least 2 and S dominates R, then S is an
infinitely near point to R, that is, S is obtained from R by a finite sequence
of local quadratic transforms.


title:
The knockoff filter for FDR control in group-sparse and multitask
  regression

abstract:
  We propose the group knockoff filter, a method for false discovery rate
control in a linear regression setting where the features are grouped, and we
would like to select a set of relevant groups which have a nonzero effect on
the response. By considering the set of true and false discoveries at the group
level, this method gains power relative to sparse regression methods. We also
apply our method to the multitask regression problem where multiple response
variables share similar sparsity patterns across the set of possible features.
Empirically, the group knockoff filter successfully controls false discoveries
at the group level in both settings, with substantially more discoveries made
by leveraging the group structure.


title: Spectral characterization of matchings in graphs

abstract:
  A spectral characterization of the matching number (the size of a maximum
matching) of a graph is given. More precisely, it is shown that the graphs G of
order n whose matching number is k are precisely those graphs with the maximum
skew rank 2k such that for any given set of k distinct nonzero purely imaginary
numbers there is a real skew-symmetric matrix A with graph G whose spectrum
consists of the given k numbers, their conjugate pairs, and n-2k zeros.


title: Using session types as an effect system

abstract:
  Side effects are a core part of practical programming. However, they are
often hard to reason about, particularly in a concurrent setting. We propose a
foundation for reasoning about concurrent side effects using sessions.
Primarily, we show that session types are expressive enough to encode an effect
system for stateful processes. This is formalised via an effect-preserving
encoding of a simple imperative language with an effect system into the
pi-calculus with session primitives and session types (into which we encode
effect specifications). This result goes towards showing a connection between
the expressivity of session types and effect systems. We briefly discuss how
the encoding could be extended and applied to reason about and control
concurrent side effects.


title: Broadcast and aggregation in BBC

abstract:
  In distributed systems, where multi-party communication is essential, two
communication paradigms are ever present: (1) one-to-many, commonly denoted as
broadcast; and (2) many-to-one denoted as aggregation or collection.
  In this paper we present the BBC process calculus, which inherently models
the broadcast and aggregation communication modes. We then apply this process
calculus to reason on hierarchical network structure and provide examples on
its expressive power.


title: Precise subtyping for synchronous multiparty sessions

abstract:
  The notion of subtyping has gained an important role both in theoretical and
applicative domains: in lambda and concurrent calculi as well as in programming
languages. The soundness and the completeness, together referred to as the
preciseness of subtyping, can be considered from two different points of view:
operational and denotational. The former preciseness has been recently
developed with respect to type safety, i.e. the safe replacement of a term of a
smaller type when a term of a bigger type is expected. The latter preciseness
is based on the denotation of a type which is a mathematical object that
describes the meaning of the type in accordance with the denotations of other
expressions from the language. The result of this paper is the operational and
denotational preciseness of the subtyping for a synchronous multiparty session
calculus. The novelty of this paper is the introduction of characteristic
global types to prove the operational completeness.


title: Reversible Communicating Processes

abstract:
  Reversible distributed programs have the ability to abort unproductive
computation paths and backtrack, while unwinding communication that occurred in
the aborted paths. While it is natural to assume that reversibility implies
full state recovery (as with traditional roll-back recovery protocols), an
interesting alternative is to separate backtracking from local state recovery.
For example, such a model could be used to create complex transactions out of
nested compensable transactions where a programmer-supplied compensation
defines the work required to "unwind" a transaction.
  Reversible distributed computing has received considerable theoretical
attention, but little reduction to practice; the few published implementations
of languages supporting reversibility depend upon a high degree of central
control. The objective of this paper is to demonstrate that a practical
reversible distributed language can be efficiently implemented in a fully
distributed manner.
  We discuss such a language, supporting CSP-style synchronous communication,
embedded in Scala. While this language provided the motivation for the work
described in this paper, our focus is upon the distributed implementation. In
particular, we demonstrate that a "high-level" semantic model can be
implemented using a simple point-to-point protocol.


title: Retractable Contracts

abstract:
  In calculi for modelling communication protocols, internal and external
choices play dual roles. Two external choices can be viewed naturally as dual
too, as they represent an agreement between the communicating parties. If the
interaction fails, the past agreements are good candidates as points where to
roll back, in order to take a different agreement. We propose a variant of
contracts with synchronous rollbacks to agreement points in case of deadlock.
The new calculus is equipped with a compliance relation which is shown to be
decidable.


title: A Typed Model for Dynamic Authorizations

abstract:
  Security requirements in distributed software systems are inherently dynamic.
In the case of authorization policies, resources are meant to be accessed only
by authorized parties, but the authorization to access a resource may be
dynamically granted/yielded. We describe ongoing work on a model for specifying
communication and dynamic authorization handling. We build upon the pi-calculus
so as to enrich communication-based systems with authorization specification
and delegation; here authorizations regard channel usage and delegation refers
to the act of yielding an authorization to another party. Our model includes:
(i) a novel scoping construct for authorization, which allows to specify
authorization boundaries, and (ii) communication primitives for authorizations,
which allow to pass around authorizations to act on a given channel. An
authorization error may consist in, e.g., performing an action along a name
which is not under an appropriate authorization scope. We introduce a typing
discipline that ensures that processes never reduce to authorization errors,
even when authorizations are dynamically delegated.


title: Communicating machines as a dynamic binding mechanism of services

abstract:
  Distributed software is becoming more and more dynamic to support
applications able to respond and adapt to the changes of their execution
environment. For instance, service-oriented computing (SOC) envisages
applications as services running over globally available computational
resources where discovery and binding between them is transparently performed
by a middleware. Asynchronous Relational Networks (ARNs) is a well-known formal
orchestration model, based on hypergraphs, for the description of
service-oriented software artefacts. Choreography and orchestration are the two
main design principles for the development of distributed software. In this
work, we propose Communicating Relational Networks (CRNs), which is a variant
of ARNs, but relies on choreographies for the characterisation of the
communicational aspects of a software artefact, and for making their automated
analysis more efficient.


title: Distributed Programming via Safe Closure Passing

abstract:
  Programming systems incorporating aspects of functional programming, e.g.,
higher-order functions, are becoming increasingly popular for large-scale
distributed programming. New frameworks such as Apache Spark leverage
functional techniques to provide high-level, declarative APIs for in-memory
data analytics, often outperforming traditional "big data" frameworks like
Hadoop MapReduce. However, widely-used programming models remain rather ad-hoc;
aspects such as implementation trade-offs, static typing, and semantics are not
yet well-understood. We present a new asynchronous programming model that has
at its core several principles facilitating functional processing of
distributed data. The emphasis of our model is on simplicity, performance, and
expressiveness. The primary means of communication is by passing functions
(closures) to distributed, immutable data. To ensure safe and efficient
distribution of closures, our model leverages both syntactic and type-based
restrictions. We report on a prototype implementation in Scala. Finally, we
present preliminary experimental results evaluating the performance impact of a
static, type-based optimization of serialization.


title: Behavioural types for non-uniform memory accesses

abstract:
  Concurrent programs executing on NUMA architectures consist of concurrent
entities (e.g. threads, actors) and data placed on different nodes. Execution
of these concurrent entities often reads or updates states from remote nodes.
The performance of such systems depends on the extent to which the concurrent
entities can be executing in parallel, and on the amount of the remote reads
and writes.
  We consider an actor-based object oriented language, and propose a type
system which expresses the topology of the program (the placement of the actors
and data on the nodes), and an effect system which characterises remote reads
and writes (in terms of which node reads/writes from which other nodes). We use
a variant of ownership types for the topology, and a combination of behavioural
and ownership types for the effect system.


title: Data-Driven Online Decision Making with Costly Information Acquisition

abstract:
  In most real-world settings such as recommender systems, finance, and
healthcare, collecting useful information is costly and requires an active
choice on the part of the decision maker. The decision-maker needs to learn
simultaneously what observations to make and what actions to take. This paper
incorporates the information acquisition decision into an online learning
framework. We propose two different algorithms for this dual learning problem:
Sim-OOS and Seq-OOS where observations are made simultaneously and
sequentially, respectively. We prove that both algorithms achieve a regret that
is sublinear in time. The developed framework and algorithms can be used in
many applications including medical informatics, recommender systems and
actionable intelligence in transportation, finance, cyber-security etc., in
which collecting information prior to making decisions is costly. We validate
our algorithms in a breast cancer example setting in which we show substantial
performance gains for our proposed algorithms.


title: Korn inequalities for shells with zero Gaussian curvature

abstract:
  We consider shells with zero Gaussian curvature, namely shells with one
principal curvature zero and the other one having a constant sign. Our
particular interests are shells that are diffeomorphic to a circular
cylindrical shell with zero principal longitudinal curvature and positive
circumferential curvature, including, for example, cylindrical and conical
shells with arbitrary convex cross sections. We prove that the best constant in
the first Korn inequality scales like thickness to the power 3/2 for a wide
range of boundary conditions at the thin edges of the shell. Our methodology is
to prove, for each of the three mutually orthogonal two-dimensional
cross-sections of the shell, a "first-and-a-half Korn inequality" - a hybrid
between the classical first and second Korn inequalities. These three
two-dimensional inequalities assemble into a three-dimensional one, which, in
turn, implies the asymptotically sharp first Korn inequality for the shell.
This work is a part of mathematically rigorous analysis of extreme sensitivity
of the buckling load of axially compressed cylindrical shells to shape
imperfections.


title:
Wireless Communications with Unmanned Aerial Vehicles: Opportunities and
  Challenges

abstract:
  Wireless communication systems that include unmanned aerial vehicles (UAVs)
promise to provide cost-effective wireless connectivity for devices without
infrastructure coverage. Compared to terrestrial communications or those based
on high-altitude platforms (HAPs), on-demand wireless systems with low-altitude
UAVs are in general faster to deploy, more flexibly re-configured, and are
likely to have better communication channels due to the presence of short-range
line-of-sight (LoS) links. However, the utilization of highly mobile and
energy-constrained UAVs for wireless communications also introduces many new
challenges. In this article, we provide an overview of UAV-aided wireless
communications, by introducing the basic networking architecture and main
channel characteristics, highlighting the key design considerations as well as
the new opportunities to be exploited.


title: High frequency homogenization for travelling waves in periodic media

abstract:
  We consider high frequency homogenization in periodic media for travelling
waves of several different equations: the wave equation for scalar-valued waves
such as acoustics; the wave equation for vector-valued waves such as
electromagnetism and elasticity; and a system that encompasses the
Schr{\"o}dinger equation. This homogenization applies when the wavelength is of
the order of the size of the medium periodicity cell. The travelling wave is
assumed to be the sum of two waves: a modulated Bloch carrier wave having
crystal wave vector $\Bk$ and frequency $\omega_1$ plus a modulated Bloch
carrier wave having crystal wave vector $\Bm$ and frequency $\omega_2$. We
derive effective equations for the modulating functions, and then prove that
there is no coupling in the effective equations between the two different waves
both in the scalar and the system cases. To be precise, we prove that there is
no coupling unless $\omega_1=\omega_2$ and $(\Bk-\Bm)\odot\Lambda \in 2\pi
\mathbb Z^d,$ where $\Lambda=(\lambda_1\lambda_2\dots\lambda_d)$ is the
periodicity cell of the medium and for any two vectors $a=(a_1,a_2,\dots,a_d),
b=(b_1,b_2,\dots,b_d)\in\mathbb R^d,$ the product $a\odot b$ is defined to be
the vector $(a_1b_1,a_2b_2,\dots,a_db_d).$ This last condition forces the
carrier waves to be equivalent Bloch waves meaning that the coupling constants
in the system of effective equations vanish.
  We use two-scale analysis and some new weak-convergence type lemmas. The
analysis is not at the same level of rigor as that of Allaire and coworkers who
use two-scale convergence theory to treat the problem, but has the advantage of
simplicity which will allow it to be easily extended to the case where there is
degeneracy of the Bloch eigenvalue.


title: Diphotons, New Vacuum Angles, and Strong CP

abstract:
  The Standard Model contains a well-understood, natural, spin-0 diphoton
resonance: the $\pi^0$. Numerous studies have pointed out that the hint of a
new diphoton resonance at 750 GeV could be a pion analog, identified with the
pseudo-Nambu-Goldstone boson of a chiral symmetry spontaneously broken by new
strong dynamics at the TeV scale. These "hypercolor" models are generically
expected to violate parity through a topological angle $\tilde\theta$. We
discuss the physics of $\tilde\theta$ and its impact on the phenomenology of
the new sector. We also describe some of the theoretical implications of a
nonzero $\tilde\theta$. In particular, $\tilde\theta$ can generate an ${\cal
O}(1)$ threshold correction to the QCD vacuum angle $\theta$ near the TeV
scale, sharply constraining ultraviolet solutions to the strong CP problem.
Alternatively, finding that $\tilde\theta$ is small may be interpreted as
evidence in favor of UV solutions to strong CP, particularly those based on
spontaneously broken P or CP symmetries.


title:
Nonlinear internal wave penetration via parametric subharmonic
  instability

abstract:
  We present the results of a laboratory experimental study of an internal wave
field generated by harmonic, spatially-periodic boundary forcing from above of
a density stratification comprising a strongly-stratified, thin upper layer
sitting atop a weakly-stratified, deep lower layer. In linear regimes, the
energy flux associated with relatively high frequency internal waves excited in
the upper layer is prevented from entering the lower layer by virtue of
evanescent decay of the wave field. In the experiments, however, we find that
the development of parametric subharmonic instability (PSI) in the upper layer
transfers energy from the forced primary wave into a pair of subharmonic
daughter waves, each capable of penetrating the weakly-stratified lower layer.
We find that around $10\%$ of the primary wave energy flux penetrates into the
lower layer via this nonlinear wave-wave interaction for the regime we study.


title:
Variations of the Similarity Function of TextRank for Automated
  Summarization

abstract:
  This article presents new alternatives to the similarity function for the
TextRank algorithm for automatic summarization of texts. We describe the
generalities of the algorithm and the different functions we propose. Some of
these variants achieve a significative improvement using the same metrics and
dataset as the original publication.


title:
Radiative Seesaw-type Mechanism of Fermion Masses and Non-trivial Quark
  Mixing

abstract:
  We propose a predictive inert 2 Higgs doublet model, where the Standard Model
(SM) symmetry is extended by $S_{3}\otimes Z_{2}\otimes Z_{12}$ and the field
content is enlarged by extra scalar fields, charged exotic fermions and two
heavy right-handed Majorana neutrinos. The charged exotic fermions generate a
nontrivial quark mixing and provide one-loop-level masses for the first- and
second-generation charged fermions. The masses of the light active neutrinos
are generated from a one loop-level radiative seesaw mechanism. Our model
successfully explains the observed SM fermion mass and mixing pattern.


title: Weak Localization in Few-Layer Black Phosphorus

abstract:
  We have conducted a comprehensive investigation into the magneto-transport
properties of few-layer black phosphorus in terms of phase coherence length,
phase coherence time, and mobility via weak localization measurement and
Hall-effect measurement. We present magnetoresistance data showing the weak
localization effect in bare p-type few-layer black phosphorus and reveal its
strong dependence on temperature and carrier concentration. The measured weak
localization agrees well with the Hikami-Larkin-Nagaoka model and the extracted
phase coherence length of 104 nm at 350 mK, decreasing as ~T^-0.51+-0.05 with
increased temperature. Weak localization measurement allows us to qualitatively
probe the temperature-dependent phase coherence time {\tau}, which is in
agreement with the theory of carrier interaction in the diffusive regime. We
also observe the universal conductance fluctuation phenomenon in few-layer
black phosphorus within moderate magnetic field and low temperature regime.


title: Attentive Pooling Networks

abstract:
  In this work, we propose Attentive Pooling (AP), a two-way attention
mechanism for discriminative model training. In the context of pair-wise
ranking or classification with neural networks, AP enables the pooling layer to
be aware of the current input pair, in a way that information from the two
input items can directly influence the computation of each other's
representations. Along with such representations of the paired inputs, AP
jointly learns a similarity measure over projected segments (e.g. trigrams) of
the pair, and subsequently, derives the corresponding attention vector for each
input to guide the pooling. Our two-way attention mechanism is a general
framework independent of the underlying representation learning, and it has
been applied to both convolutional neural networks (CNNs) and recurrent neural
networks (RNNs) in our studies. The empirical results, from three very
different benchmark tasks of question answering/answer selection, demonstrate
that our proposed models outperform a variety of strong baselines and achieve
state-of-the-art performance in all the benchmarks.


title: Upper bounds on the first eigenvalue for the $p$-Laplacian

abstract:
  In this paper, we establish gradient estimates for positive solutions to the
following equation with respect to the $p$-Laplacian $$\Delta_{p}u=-\lambda
|u|^{p-2}u$$ with $p>1$ on a given complete Riemannian manifold. Consequently,
we derive upper bound estimates of the first nontrivial eigenvalue of the
$p$-Laplacian.


title: Asymptotics of the number of involutions in finite classical groups

abstract:
  Answering a question of Geoff Robinson, we compute the large n limiting
proportion of i(n,q)/q^[n^2/2], where i(n,q) denotes the number of involutions
in GL(n,q). We give similar results for the finite unitary, symplectic, and
orthogonal groups, in both odd and even characteristic. At the heart of this
work are certain new "sum=product" identities. Our self-contained treatment of
the enumeration of involutions in even characteristic symplectic and orthogonal
groups may also be of interest.


title:
Singular solutions for divergence-form elliptic equations involving
  regular variation theory: Existence and classification

abstract:
  We generalise and sharpen several recent results in the literature regarding
the existence and complete classification of the isolated singularities for a
broad class of nonlinear elliptic equations of the form \begin{equation} -{\rm
div}\,(\mathcal A(|x|) \,|\nabla u|^{p-2} \nabla u)+b(x)\,h(u)=0\quad \text{in
} B_1\setminus\{0\}, \end{equation} where $B_r$ denotes the open ball with
radius $r>0$ centred at zero in $\mathbb{R}^N$ $(N\geq 2)$. We assume that
$\mathcal{A} \in C^1(0,1]$, $b\in C(\bar{B_1}\setminus\{0\})$ and $h\in
C[0,\infty)$ are positive functions associated with regularly varying functions
of index $\vartheta$, $\sigma$ and $q$ at $0$, $0$ and $\infty$ respectively,
satisfying $q>p-1>0$ and $\vartheta-\sigma<p<N+\vartheta$. We prove that the
condition $b(x) \,h(\Phi)\not \in L^1(B_{1/2})$ is sharp for the removability
of all singularities at zero for the positive solutions of our problem, where
$\Phi$ denotes the "fundamental solution" of $-{\rm div}\,(\mathcal A(|x|)\,
|\nabla u|^{p-2} \nabla u)=\delta_0$ (the Dirac mass at zero) in $B_1$, subject
to $\Phi|_{\partial B_1}=0$. If $b(x) \,h(\Phi)\in L^1(B_{1/2})$, we show that
any non-removable singularity at zero for a positive solution to our equation
is either weak (i.e., $\lim_{|x|\to 0} u(x)/\Phi(|x|)\in (0,\infty)$) or strong
($ \lim_{|x|\to 0} u(x)/\Phi(|x|)=\infty$). The main difficulty and novelty of
this paper, for which we develop new techniques, come from the explicit
asymptotic behaviour of the strong singularity solutions in the critical case,
which had previously remained open even for $\mathcal{A}=1$. We also study the
existence and uniqueness of the positive solution to our problem with a
prescribed admissible behaviour at zero and a Dirichlet condition on $\partial
B_1$.


title:
Renormalization Group Study of a Fragile Fermi liquid in $1+\epsilon$
  dimensions

abstract:
  We present a calculation of the low energy Greens function in $1+\epsilon$
dimensions using the method of extended poor man's scaling, developed here. We
compute the wave function renormalization $Z(\omega)$ and also the decay rate
near the Fermi energy. Despite the lack of $\omega^2$ damping characteristic of
3-dimensional Fermi liquids, we show that quasiparticles do exist in
$1+\epsilon$ dimensions, in the sense that the quasiparticle weight $Z$ is
finite and that the damping rate is smaller than the energy. We explicitly
compute the crossover from this behavior to a 1-dimensional type
Tomonaga-Luttinger liquid behavior at higher energies.


title: The free-boundary Brakke flow

abstract:
  We develop the notion of Brakke flow with free-boundary in a barrier surface.
Unlike the classical free-boundary mean curvature flow, the free-boundary
Brakke flow must "pop" upon tangential contact with the barrier. We prove a
compactness theorem for free-boundary Brakke flows, define a Gaussian
monotonicity formula valid at all points, and use this to adapt the local
regularity theorem of White to the free-boundary setting. We use Ilmanen's
elliptic regularization procedure to prove existence of free-boundary Brakke
flows.


title: The Bergman analytic content of planar domains

abstract:
  Given a planar domain $\Omega$, the Bergman analytic content measures the
$L^{2}(\Omega)$-distance between $\bar{z}$ and the Bergman space
$A^{2}(\Omega)$. We compute the Bergman analytic content of simply-connected
quadrature domains with quadrature formula supported at one point, and we also
determine the function $f \in A^2(\Omega)$ that best approximates $\bar{z}$. We
show that, for simply-connected domains, the square of Bergman analytic content
is equivalent to torsional rigidity from classical elasticity theory, while for
multiply-connected domains these two domain constants are not equivalent in
general.


title:
Multifaceted Feature Visualization: Uncovering the Different Types of
  Features Learned By Each Neuron in Deep Neural Networks

abstract:
  We can better understand deep neural networks by identifying which features
each of their neurons have learned to detect. To do so, researchers have
created Deep Visualization techniques including activation maximization, which
synthetically generates inputs (e.g. images) that maximally activate each
neuron. A limitation of current techniques is that they assume each neuron
detects only one type of feature, but we know that neurons can be multifaceted,
in that they fire in response to many different types of features: for example,
a grocery store class neuron must activate either for rows of produce or for a
storefront. Previous activation maximization techniques constructed images
without regard for the multiple different facets of a neuron, creating
inappropriate mixes of colors, parts of objects, scales, orientations, etc.
Here, we introduce an algorithm that explicitly uncovers the multiple facets of
each neuron by producing a synthetic visualization of each of the types of
images that activate a neuron. We also introduce regularization methods that
produce state-of-the-art results in terms of the interpretability of images
obtained by activation maximization. By separately synthesizing each type of
image a neuron fires in response to, the visualizations have more appropriate
colors and coherent global structure. Multifaceted feature visualization thus
provides a clearer and more comprehensive description of the role of each
neuron.


title: Two-hop Power-Relaying for Linear Wireless Sensor Networks

abstract:
  This paper presents two-hop relay gain-scheduling control in a Wireless
Sensor Network to estimate a static target prior characterized by Gaussian
probability distribution. The target is observed by a network of linear
sensors, whose observations are transmitted to a fusion center for carrying out
final estimation via a amplify-and-forward relay node. We are concerned with
the joint transmission power allocation for sensors and relay to optimize the
minimum mean square error (MMSE) estimator, which is deployed at the fusion
center. Particularly, such highly nonlinear optimization problems are solved by
an iterative procedure of very low computational complexity. Simulations are
provided to support the efficiency of our proposed power allocation.


title: Characterising Probability Distributions via Entropies

abstract:
  Characterising the capacity region for a network can be extremely difficult,
especially when the sources are dependent. Most existing computable outer
bounds are relaxations of the Linear Programming bound. One main challenge to
extend linear program bounds to the case of correlated sources is the
difficulty (or impossibility) of characterising arbitrary dependencies via
entropy functions. This paper tackles the problem by addressing how to use
entropy functions to characterise correlation among sources.


title: Optimal Inference in Crowdsourced Classification via Belief Propagation

abstract:
  Crowdsourcing systems are popular for solving large-scale labelling tasks
with low-paid workers. We study the problem of recovering the true labels from
the possibly erroneous crowdsourced labels under the popular Dawid-Skene model.
To address this inference problem, several algorithms have recently been
proposed, but the best known guarantee is still significantly larger than the
fundamental limit. We close this gap by introducing a tighter lower bound on
the fundamental limit and proving that Belief Propagation (BP) exactly matches
this lower bound. The guaranteed optimality of BP is the strongest in the sense
that it is information-theoretically impossible for any other algorithm to
correctly label a larger fraction of the tasks. Experimental results suggest
that BP is close to optimal for all regimes considered and improves upon
competing state-of-the-art algorithms.


title:
Borophane: Stable Two-dimensional Anisotropic Dirac Material with
  Ultrahigh Fermi Velocity

abstract:
  Recent synthesis of monolayer borophene (triangle boron monolayer) on the
substrate opens the era of boron nanosheet (Science, 350, 1513,
$\mathbf{2015}$), but the structural stability and novel physical properties
are still open issues. Here we demonstrated borophene can be stabilized with
fully surface hydrogenation, called as borophane, from first-principles
calculations. Most interesting, it shows that borophane has direction-dependent
Dirac cones, which are mainly contributed by in-plane \emph{p$_{x}$} and
\emph{p$_{y}$} orbitals of boron atoms. The Dirac fermions possess an ultrahigh
Fermi velocity up to 3.0$\times$10$^{6}$ m/s, 4 times higher than that of
graphene. The Young's modules are calculated to be 129 and 200 GPa$\cdot$nm
along two different directions, which is comparable with steel. The ultrahigh
Fermi velocity and high mechanical feature render borophane ideal for
nanoelectronics applications.


title: Towards thermal noise free optomechanics

abstract:
  Thermal noise generally greatly exceeds quantum noise in optomechanical
devices unless the mechanical frequency is very high or the thermodynamic
temperature is very low. This paper addresses the design concept for a novel
optomechanical device capable of ultrahigh quality factors in the audio
frequency band with negligible thermal noise. The proposed system consists of a
minimally supported millimeter scale pendulum mounted in a Double End-Mirror
Sloshing (DEMS) cavity that is topologically equivalent to a
Membrane-in-the-Middle (MIM) cavity. The radiation pressure inside the
high-finesse cavity allows for high optical stiffness, cancellation of terms
which lead to unwanted negative damping and suppression of quantum radiation
pressure noise. We solve for the optical spring dynamics of the system using
the Hamiltonian, find the noise spectral density and show that stable optical
trapping is possible. We also assess various loss mechanisms, one of the most
important being the acceleration loss due to the optical spring. We show that
practical devices, starting from a centre-of-mass pendulum frequency of 0.1 Hz,
could achieve a maximum quality factor of $10^{14}$ with optical spring
stiffened frequency 1-10 kHz. Small resonators of mass 1 $\mu$g or less could
achieve a Q-factor of $10^{11}$ at a frequency of 100 kHz. Applications for
such devices include white light cavities for improvement of gravitational wave
detectors, or sensors able to operate near the quantum limit.


title:
Gravitational wave tests of quantum modifications to black hole
  structure -- with post-GW150914 update

abstract:
  A preliminary discussion is given of the prospects that gravitational-wave
observations of binary inspiral of black holes could reveal or constrain
quantum modifications to black hole dynamics, such as are required to preserve
postulates of quantum mechanics. Different proposals for such modifications are
characterized by different scales, and the size of these scales relative to
those probed by observation of inspiral signals is important in determining the
feasibility of finding experimental signatures. Certain scenarios with strong
quantum modifications in a region extending well outside the horizon are
expected to modify classical evolution, and distort the near-peak gravitational
wave signal, suggesting a search for departures from waveforms predicted by
general relativity. The near agreement of the GW150914 signal with such
waveforms is discussed, and indicates constraints on some such scenarios.
Important strategies for more precise future tests are 1) to develop more
precise predictions from scenarios proposing quantum modifications, and 2)
searching for observed deviations from numerical relativity predictions via
analysis of gravity wave data, particularly focussing on the signal region
corresponding to plunge and merger.


title: Dynamic Group Behaviors for Interactive Crowd Simulation

abstract:
  We present a new algorithm to simulate dynamic group behaviors for
interactive multi-agent crowd simulation. Our approach is general and makes no
assumption about the environment, shape, or size of the groups. We use the
least effort principle to perform coherent group navigation and present
efficient inter-group and intra-group maintenance techniques. We extend the
reciprocal collision avoidance scheme to perform agent-group and group-group
collision avoidance that can generate collision-free as well as coherent and
trajectories. The additional overhead of dynamic group simulation is relatively
small. We highlight its interactive performance on complex scenarios with
hundreds of agents and compare the trajectory behaviors with real-world videos.


title:
On the validity of power functionals for the homogeneous electron gas in
  reduced.density-matrix-functional theory

abstract:
  Physically valid and numerically efficient approximations for the exchange
and correlation energy are critical for reduced density-matrix functional
theory to become a widely used method in electronic structure calculations.
Here we examine the physical limits of power functionals of the form
$f(n,n')=(n n')^\alpha$ for the scaling function in the exchange-correlation
energy. To this end we obtain numerically the minimizing momentum distributions
for the three- and two-dimensional homogeneous electron gas, respectively. In
particular, we examine the limiting values for the power $\alpha$ to yield
physically sound solutions that satisfy the Lieb-Oxford lower bound for the
exchange-correlation energy and exclude pinned states with the condition
$n({\mathbf k})<1$ for all wave vectors ${\mathbf k}$. The results refine the
constraints previously obtained from trial momentum distributions. We also
compute the values for $\alpha$ that yield the exact correlation energy and its
kinetic part for both the three- and two-dimensional electron gas. In both
systems, narrow regimes of validity and accuracy are found at $\alpha\gtrsim
0.6$ and at $r_s\gtrsim 10$ for the density parameter, corresponding to
relatively low densities.


title:
Molecular shape and the energetics of chemisorption: From simple to
  complex energy landscapes

abstract:
  We enumerate all local minima of the energy landscape for model rigid
adsorbates characterized by three or four equivalent binding sites (e.g., thiol
groups) on a close-packed (111) surface of a face-centered-cubic crystal. We
show that the number of energy minima increases linearly with molecular size
with a rate of increase that depends on the degree of registry between the
molecule shape and the surface structure. The sparseness of energy minima and
the large variations in the center-of-mass positions of these minima vs
molecular size for molecules that are incommensurate with the surface suggests
a strong coupling in these molecules between surface mobility and shape or size
fluctuations resulting from molecular vibrations. We also find that the
variation in the binding energy with respect to molecular size decreases more
rapidly with molecular size for molecules with a higher degree of registry with
the surface. This indicates that surface adsorption should be better able to
distinguish molecules by size if the molecules are incommensurate with the
surface.


title: Hyperbolic inverse problem with data on disjoint sets

abstract:
  We consider a restricted Dirichlet-to-Neumann map associated to a wave type
operator on a Riemannian manifold with boundary. The restriction corresponds to
the case where the Dirichlet traces are supported on one subset of the boundary
and the Neumann traces are restricted on another subset. We show that the
restricted Dirichlet-to-Neumann map determines the lower order terms in the
wave equation, up the natural gauge invariances, along a convex foliation of
the manifold. We allow the lower order terms to be non-self-adjoint, and in
particular, the corresponding physical system may have dissipation of energy.


title:
Pomeron pole plus grey disk model: real parts, inelastic cross sections
  and LHC data

abstract:
  I propose a two component analytic formula $F(s,t)=F^{(1)}(s,t)+F^{(2)}(s,t)$
for $(ab\rightarrow ab) +(a\bar{b}\rightarrow a\bar{b})$ scattering at energies
$\ge 100 GeV$ ,where $s,t$ denote squares of c.m. energy and momentum
transfer.It saturates the Froissart-Martin bound and obeys
Auberson-Kinoshita-Martin (AKM) \cite{AKM1971} scaling. I choose $Im
F^{(1)}(s,0)+Im F^{(2)}(s,0)$ as given by Particle Data Group (PDG) fits to
total cross sections. The PDG formula is extended to non-zero momentum
transfers using partial waves of $Im F^{(1)}$ and $Im F^{(2)}$ motivated by
Pomeron pole and 'grey disk' amplitudes . $Re F(s,t)$ is deduced from real
analyticity: I prove that $Re F(s,t)/ImF(s,0) \rightarrow (\pi/\ln{s}) d/d\tau
(\tau Im F(s,t)/ImF(s,0) )$ for $s\rightarrow \infty$ with $\tau=t (ln s)^2$
fixed, and apply it to $F^{(2)}$.Using also the forward slope fit by
Schegelsky-Ryskin , the model gives real parts,differential cross sections for
$(-t)<.3 GeV^2$, and inelastic cross sections in good agreement with data at
$546 GeV, 1.8 TeV,7 TeV$ and $ 8 TeV $. It predicts for inelastic cross
sections for $pp$ or $\bar{p} p$, $\sigma_{inel}=72.7\pm 1.0 mb$ at $7TeV$ and
$74.2 \pm 1.0mb$ at $8 TeV$ in agreement with $pp$ Totem experimental values
$73.1\pm 1.3 mb $ and $74.7\pm 1.7 mb$ respectively, and with Atlas values
$71.3\pm 0.9 mb$ and $71.7\pm 0.7mb$ respectively. The predictions at $546 GeV$
and $1800 GeV$ also agree with $\bar{p} p$ experimental results of Abe et al
\cite{Abe} at $546 GeV$ and $1800 GeV$.
  The model yields for $\sqrt{s}> 0.5 TeV$, with PDG2013 total cross sections ,
and Schegelsky-Ryskin slopes as input, $\sigma_{inel} (s) =22.6 + .034 ln s +
.158 (ln s)^2 mb , and \sigma_{inel} / \sigma_{tot} \rightarrow 0.56,
s\rightarrow \infty ,$ where $s$ is in $GeV^2$


title:
Nonlinear reflection process of linearly-polarized, broadband Alfv\'en
  waves in the fast solar wind

abstract:
  Using one-dimensional numerical simulations, we study the elementary process
of Alfv\'{e}n wave reflection in a uniform medium, including nonlinear effects.
In the linear regime, Alfv\'{e}n wave reflection is triggered only by the
inhomogeneity of the medium, whereas in the nonlinear regime, it can occur via
nonlinear wave-wave interactions. Such nonlinear reflection (backscattering) is
typified by decay instability. In most studies of decay instabilities, the
initial condition has been a circularly polarized Alfv\'{e}n wave. In this
study we consider a linearly polarized Alfv\'en wave, which drives density
fluctuations by its magnetic pressure force. For generality, we also assume a
broadband wave with a red-noise spectrum. In the data analysis, we decompose
the fluctuations into characteristic variables using local eigenvectors, thus
revealing the behaviors of the individual modes. Different from
circular-polarization case, we find that the wave steepening produces a new
energy channel from the parent Alfv\'en wave to the backscattered one. Such
nonlinear reflection explains the observed increasing energy ratio of the
sunward to the anti-sunward Alfv\'{e}nic fluctuations in the solar wind with
distance against the dynamical alignment effect.


title:
TeV gamma-ray emission initiated by the population or individual
  millisecond pulsars within globular clusters

abstract:
  Two energetic millisecond pulsars (MSPs) within globular clusters (GC),
J1823-3021A in NGC 6624 and PSR B1821-24 in M28, have been recently discovered
to emit pulsed GeV gamma-rays. These MSPs are expected to eject energetic
leptons. Therefore, GCs have been proposed to produce GeV-TeV gamma-rays as a
result of the comptonization process of the background radiation within a GC.
We develop this general scenario by taking into account not only the diffusion
process of leptons within a GC but also their advection with the wind from the
GC. Moreover, we consider distribution of MSP within a GC and the effects
related to the non-central location of the dominating, energetic MSP. Such more
complete scenario is considered for the modelling of the GeV-TeV gamma-ray
emission from the core collapsed GC M15 and also for GCs which contain recently
discovered energetic MSPs within NGC 6624 and M28. The confrontation of the
modelling of the gamma-ray emission with the observations with the present
Cherenkov telescopes and the future Cherenkov Telescope Array (CTA) allows to
constrain more reliably the efficiency of lepton production within the inner
magnetosphere of the MSPs and re-accelerated in their vicinity. We discuss the
expected limits on this parameter in the context of expectations from the
pulsar models. we conclude that deep observations of GCs, even with the present
sensitivity of Cherenkov telescopes (H.E.S.S., MAGIC, VERITAS), should start to
constrain the models for the acceleration and radiation processes of leptons
within the inner pulsar magnetosphere and its surrounding.


title:
Simultaneous Multi-frequency Topological Edge Modes between
  One-dimensional Photonic Crystals

abstract:
  We show theoretically that, in the limit of weak dispersion, one-dimensional
(1D) binary centrosymmetric photonic crystals can support topological edge
modes in all photonic band gaps. By analyzing their bulk band topology, these
"harmonic" topological edge modes can be designed in a way that they exist at
all photonic band gaps opened at the center of the Brillouin Zone, or at all
gaps opened at the zone boundaries, or both. The results may suggest a new
approach to achieve robust multi-frequency coupled modes for applications in
nonlinear photonics, such as frequency up-conversion.


title:
Dynamics of interaction of radially symmetric topological solitons in
  two-dimensional nonlinear sigma model

abstract:
  By methods of numerical simulations the dynamics of interaction of radially
symmetric Bellavin-Polyakov type topological vortex in (2+1)-dimensional O(3)
nonlinear sigma model is investigated. Obtained numerically the model of
topological vortex decay for different values of radius of ring-shaped
structure of their energy density onto the localized perturbations, where the
sum of Hopf index is preserved. It is shown that the stability of topological
solitons, in particularly, depends on the values of radius of ring-shaped
structure of their energy density.


title: Strain effect on power factor in monolayer $\mathrm{MoS_2}$

abstract:
  Biaxial strain dependence of electronic structures and thermoelectric
properties of monolayer $\mathrm{MoS_2}$, including compressive and tensile
strain, are investigated by using local-density approximation (LDA) plus
spin-orbit coupling (SOC). Both LDA and LDA+SOC results show that
$\mathrm{MoS_2}$ is a direct gap semiconductor with optimized lattice
constants. It is found that SOC has important effect on power factor, which can
enhance one in n-type doping, but has a obvious detrimental influence for
p-type. Both compressive and tensile strain can induce direct-indirect gap
transition, which produce remarkable influence on power factor. Calculated
results show that strain can induce significantly enhanced power factor in
n-type doping by compressive strain and in p-type doping by tensile strain at
the critical strain of direct-indirect gap transition. These can be explained
by strain-induced accidental degeneracies, which leads to improved Seebeck
coefficient. Calculated results show that n-type doping can provide better
power factor than p-type doping. These results make us believe that
thermoelectric properties of monolayer $\mathrm{MoS_2}$ can be improved in
n-type doping by compressive strain.


title:
Singular behavior of the leading Lyapunov exponent of a product of
  random $2 \times 2$ matrices

abstract:
  We consider a certain infinite product of random $2 \times 2$ matrices
appearing in the solution of some $1$ and $1+1$ dimensional disordered models
in statistical mechanics, which depends on a parameter $\varepsilon>0$ and on a
real random variable with distribution $\mu$. For a large class of $\mu$, we
prove the prediction by B. Derrida and H. J. Hilhorst (J. Phys. A 16:2641,
1983) that the Lyapunov exponent behaves like $C \varepsilon^{2 \alpha}$ in the
limit $\varepsilon \searrow 0$, where $\alpha \in (0,1)$ and $C>0$ are
determined by $\mu$. Derrida and Hilhorst performed a two-scale analysis of the
integral equation for the invariant distribution of the Markov chain associated
to the matrix product and obtained a probability measure that is expected to be
close to the invariant one for small $\varepsilon$. We introduce suitable norms
and exploit contractivity properties to show that such a probability measure is
indeed close to the invariant one in a sense which implies a suitable control
of the Lyapunov exponent.


title:
Directed searches for broadband extended gravitational-wave emission in
  nearby energetic core-collapse supernovae

abstract:
  Core-collapse supernovae are factories of neutron stars and stellar mass
black holes. Type Ib/c supernovae stand out as potentially originating in
relatively compact stellar binaries and their branching ratio of about 1\% into
long gamma-ray bursts. The most energetic events probably derive from central
engines harboring rapidly rotating black holes, wherein accretion of fall-back
matter down to the Inner Most Stable Circular Orbit (ISCO) offers a window to
{\em broadband extended gravitational-wave emission} (BEGE). To search for
BEGE, we introduce a butterfly filter in time-frequency space by Time Sliced
Matched Filtering. To analyze long epochs of data, we propose using coarse
grained searches followed by high resolution searches on events of interest. We
illustrate our proposed coarse grained search on two weeks of LIGO S6 data
prior to SN 2010br $(z=0.002339)$ using a bank of up to 64 thousand templates
of one second duration covering a broad range in chirp frequencies and
bandwidth. Correlating events with signal-to-noise ratios $>6$ from the LIGO L1
and H1 detectors each reduces to a few events of interest. Lacking any further
properties reflecting a common excitation by broadband gravitational radiation,
we disregarded these as spurious. This new pipeline may be used to
systematically search for long duration chirps in nearby core-collapse
supernovae from robotic optical transient surveys using embarrassingly parallel
computing.


title: Optimization of Caching Devices with Geometric Constraints

abstract:
  It has been recently advocated that in large communication systems it is
beneficial both for the users and for the network as a whole to store content
closer to users. One particular implementation of such an approach is to
co-locate caches with wireless base stations. In this paper we study
geographically distributed caching of a fixed collection of files. We model
cache placement with the help of stochastic geometry and optimize the
allocation of storage capacity among files in order to minimize the cache miss
probability. We consider both per cache capacity constraints as well as an
average capacity constraint over all caches. The case of per cache capacity
constraints can be efficiently solved using dynamic programming, whereas the
case of the average constraint leads to a convex optimization problem. We
demonstrate that the average constraint leads to significantly smaller cache
miss probability. Finally, we suggest a simple LRU-based policy for
geographically distributed caching and show that its performance is close to
the optimal.


title: Link prediction in Foursquare network

abstract:
  Foursquare is an online social network and can be represented with a
bipartite network of users and venues. A user-venue pair is connected if a user
has checked-in at that venue. In the case of Foursquare, network analysis
techniques can be used to enhance the user experience. One such technique is
link prediction, which can be used to build a personalized recommendation
system of venues. Recommendation systems in bipartite networks are very often
designed using the global ranking method and collaborative filtering. A less
known method- network based inference is also a feasible choice for link
prediction in bipartite networks and sometimes performs better than the
previous two. In this paper we test these techniques on the Foursquare network.
The best technique proves to be the network based inference. We also show that
taking into account the available metadata can be beneficial.


title:
Asymptotic normalization coefficients for ${\rm {^7Be}}+p\to{\rm{^8B}}$
  from the peripheral ${\rm{^7Be}}$($d$,$n$)${\rm{^8B}}$ reaction and their
  astrophysical application

abstract:
  The proton transfer ${\rm{^7Be}}$($d$,$n$)${\rm{^8B}}$ reaction at the energy
of 4.5 MeV (c.m.) has been analysed within the modified DWBA. New estimates and
their uncertainties are obtained for values of the asymptotic normalization
coefficients for $p + {\rm{^7Be}} \to {\rm{^8B}}$, the astrophysical
$S_{17}(0)$ factor and the s-wave $p + {\rm{^7Be}}$ scattering lengths.


title:
High performance Python for direct numerical simulations of turbulent
  flows

abstract:
  Direct Numerical Simulations (DNS) of the Navier Stokes equations is an
invaluable research tool in fluid dynamics. Still, there are few publicly
available research codes and, due to the heavy number crunching implied,
available codes are usually written in low-level languages such as C/C++ or
Fortran. In this paper we describe a pure scientific Python pseudo-spectral DNS
code that nearly matches the performance of C++ for thousands of processors and
billions of unknowns. We also describe a version optimized through Cython, that
is found to match the speed of C++. The solvers are written from scratch in
Python, both the mesh, the MPI domain decomposition, and the temporal
integrators. The solvers have been verified and benchmarked on the Shaheen
supercomputer at the KAUST supercomputing laboratory, and we are able to show
very good scaling up to several thousand cores.
  A very important part of the implementation is the mesh decomposition (we
implement both slab and pencil decompositions) and 3D parallel Fast Fourier
Transforms (FFT). The mesh decomposition and FFT routines have been implemented
in Python using serial FFT routines (either NumPy, pyFFTW or any other serial
FFT module), NumPy array manipulations and with MPI communications handled by
MPI for Python (mpi4py). We show how we are able to execute a 3D parallel FFT
in Python for a slab mesh decomposition using 4 lines of compact Python code,
for which the parallel performance on Shaheen is found to be slightly better
than similar routines provided through the FFTW library. For a pencil mesh
decomposition 7 lines of code is required to execute a transform.


title:
Free subgroups in almost subnormal subgroups of general skew linear
  groups

abstract:
  Let $D$ be a weakly locally finite division ring and $n$ a positive integer.
In this paper, we investigate the problem on the existence of non-cyclic free
subgroups in non-central almost subnormal subgroups of the general linear group
${\rm GL}_n(D)$. Further, some applications of this fact are also investigated.
In particular, all infinite finitely generated almost subnormal subgroups of
${\rm GL}_n(D)$ are described.


title: The International Pulsar Timing Array: First Data Release

abstract:
  The highly stable spin of neutron stars can be exploited for a variety of
(astro-)physical investigations. In particular arrays of pulsars with
rotational periods of the order of milliseconds can be used to detect
correlated signals such as those caused by gravitational waves. Three such
"Pulsar Timing Arrays" (PTAs) have been set up around the world over the past
decades and collectively form the "International" PTA (IPTA). In this paper, we
describe the first joint analysis of the data from the three regional PTAs,
i.e. of the first IPTA data set. We describe the available PTA data, the
approach presently followed for its combination and suggest improvements for
future PTA research. Particular attention is paid to subtle details (such as
underestimation of measurement uncertainty and long-period noise) that have
often been ignored but which become important in this unprecedentedly large and
inhomogeneous data set. We identify and describe in detail several factors that
complicate IPTA research and provide recommendations for future pulsar timing
efforts. The first IPTA data release presented here (and available online) is
used to demonstrate the IPTA's potential of improving upon gravitational-wave
limits placed by individual PTAs by a factor of ~2 and provides a 2-sigma limit
on the dimensionless amplitude of a stochastic GWB of 1.7x10^{-15} at a
frequency of 1 yr^{-1}. This is 1.7 times less constraining than the limit
placed by (Shannon et al. 2015), due mostly to the more recent, high-quality
data they used.


title:
Parallel Vertex Approximate Gradient discretization of hybrid
  dimensional Darcy flow and transport in discrete fracture networks

abstract:
  This paper proposes a parallel numerical algorithm to simulate the flow and
the transport in a discrete fracture network taking into account the mass
exchanges with the surrounding matrix. The discretization of the Darcy fluxes
is based on the Vertex Approximate Gradient finite volume scheme adapted to
polyhedral meshes and to heterogeneous anisotropic media, and the transport
equation is discretized by a first order upwind scheme combined with an Euler
explicit integration in time. The parallelization is based on the SPMD (Single
Program, Multiple Data) paradigm and relies on a distribution of the mesh on
the processes with one layer of ghost cells in order to allow for a local
assembly of the discrete systems. The linear system for the Darcy flow is
solved using different linear solvers and preconditioners implemented in the
PETSc and Trilinos libraries. The convergence of the scheme is validated on two
original analytical solutions with one and four intersecting fractures. Then,
the parallel efficiency of the algorithm is assessed on up to 512 processes
with different types of meshes, different matrix fracture permeability ratios,
and different levels of complexity of the fracture network.


title: Access Control Encryption: Enforcing Information Flow with Cryptography

abstract:
  We initiate the study of Access Control Encryption (ACE), a novel
cryptographic primitive that allows fine-grained access control, by giving
different rights to different users not only in terms of which messages they
are allowed to receive, but also which messages they are allowed to send.
  Classical examples of security policies for information flow are the well
known Bell-Lapadula [BL73] or Biba [Bib75] model: in a nutshell, the
Bell-Lapadula model assigns roles to every user in the system (e.g., public,
secret and top-secret). A users' role specifies which messages the user is
allowed to receive (i.e., the no read-up rule, meaning that users with public
clearance should not be able to read messages marked as secret or top-secret)
but also which messages the user is allowed to send (i.e., the no write-down
rule, meaning that a user with top-secret clearance should not be able to write
messages marked as secret or public).
  To the best of our knowledge, no existing cryptographic primitive allows for
even this simple form of access control, since no existing cryptographic
primitive enforces any restriction on what kind of messages one should be able
to encrypt.
  Our contributions are: - Introducing and formally defining access control
encryption (ACE); - A construction of ACE with complexity linear in the number
of the roles based on classic number theoretic assumptions (DDH, Paillier); - A
construction of ACE with complexity polylogarithmic in the number of roles
based on recent results on cryptographic obfuscation;


title: Oasis: a high-level/high-performance open source Navier-Stokes solver

abstract:
  Oasis is a high-level/high-performance finite element Navier-Stokes solver
written from scratch in Python using building blocks from the FEniCS project
(fenicsproject.org). The solver is unstructured and targets large-scale
applications in complex geometries on massively parallel clusters. Oasis
utilizes MPI and interfaces, through FEniCS, to the linear algebra backend
PETSc. Oasis advocates a high-level, programmable user interface through the
creation of highly flexible Python modules for new problems. Through the
high-level Python interface the user is placed in complete control of every
aspect of the solver. A version of the solver, that is using piecewise linear
elements for both velocity and pressure, is shown reproduce very well the
classical, spectral, turbulent channel simulations of Moser, Kim and Mansour at
$Re_{\tau}=180$ [Phys. Fluids, vol 11(4), p. 964]. The computational speed is
strongly dominated by the iterative solvers provided by the linear algebra
backend, which is arguably the best performance any similar implicit solver
using PETSc may hope for. Higher order accuracy is also demonstrated and new
solvers may be easily added within the same framework.


title:
Impact of LOS/NLOS Propagation and Path Loss in Ultra-Dense Cellular
  Networks

abstract:
  Most prior work on performance analysis of ultra-dense cellular networks
(UDNs) has considered standard power-law path loss models and non-line-of-sight
(NLOS) propagation modeled by Rayleigh fading. The effect of line-of-sight
(LOS) on coverage and throughput and its implication on network densification
are still not fully understood. In this paper, we investigate the performance
of UDNs when the signal propagation includes both LOS and NLOS components.
Using a stochastic geometry based cellular network model, we derive expressions
for the coverage probability, as well as tight approximations and upper bounds
for both closest and strongest base station (BS) association. Our results show
that under standard singular path loss model, LOS propagation increases the
coverage, especially with nearest BS association. On the contrary, using dual
slope path loss, LOS propagation is beneficial with closest BS association and
detrimental for strongest BS association.


title:
Incompatibility between Carnot efficiency and finite power in Markovian
  dynamics

abstract:
  In Markovian dynamics with the local detailed balance condition, we decompose
the total entropy production rate into microscopic transitions. By applying
this decomposition to the heat to work conversion process, we rigorously show
that the Carnot efficiency implies zero power for any heat engine, even with
broken time-reversal symmetry beyond the linear response regime. Moreover, we
propose a trade-off relationship between the entropy production rate and the
heat flow between the system and bath.


title: Bleb Nucleation through Membrane Peeling

abstract:
  We study the nucleation of blebs, i.e., protrusions arising from a local
detachment of the membrane from the cortex of a cell. Based on a simple model
of elastic linkers with force-dependent kinetics, we show that bleb nucleation
is governed by membrane peeling. By this mechanism, the growth or shrinkage of
a detached membrane patch is completely determined by the linker kinetics,
regardless of the energetic cost of the detachment. We predict the critical
nucleation radius for membrane peeling and the corresponding effective energy
barrier. These may be typically smaller than those predicted by classical
nucleation theory, implying a much faster nucleation. We also perform
simulations of a continuum stochastic model of membrane-cortex adhesion to
obtain the statistics of bleb nucleation times as a function of the stress on
the membrane. The determinant role of membrane peeling changes our
understanding of bleb nucleation and opens new directions in the study of
blebs.


title: On the Difficulty of Selecting Ising Models with Approximate Recovery

abstract:
  In this paper, we consider the problem of estimating the underlying graph
associated with an Ising model given a number of independent and identically
distributed samples. We adopt an \emph{approximate recovery} criterion that
allows for a number of missed edges or incorrectly-included edges, in contrast
with the widely-studied exact recovery problem. Our main results provide
information-theoretic lower bounds on the sample complexity for graph classes
imposing constraints on the number of edges, maximal degree, and other
properties. We identify a broad range of scenarios where, either up to constant
factors or logarithmic factors, our lower bounds match the best known lower
bounds for the exact recovery criterion, several of which are known to be tight
or near-tight. Hence, in these cases, approximate recovery has a similar
difficulty to exact recovery in the minimax sense.
  Our bounds are obtained via a modification of Fano's inequality for handling
the approximate recovery criterion, along with suitably-designed ensembles of
graphs that can broadly be classed into two categories: (i) Those containing
graphs that contain several isolated edges or cliques and are thus difficult to
distinguish from the empty graph; (ii) Those containing graphs for which
certain groups of nodes are highly correlated, thus making it difficult to
determine precisely which edges connect them. We support our theoretical
results on these ensembles with numerical experiments.


title: Joint Beamforming and Broadcasting in Massive MIMO

abstract:
  The downlink of a massive MIMO system is considered for the case in which the
base station must concurrently serve two categories of terminals: one group to
which imperfect instantaneous channel state information (CSI) is available, and
one group to which no CSI is available. Motivating applications include
broadcasting of public channels and control information in wireless networks.
  A new technique is developed and analyzed: joint beamforming and broadcasting
(JBB), by which the base station beamforms to the group of terminals to which
CSI is available, and broadcasts to the other group of terminals, to which no
CSI is available. The broadcast information does not interfere with the
beamforming as it is placed in the nullspace of the channel matrix collectively
seen by the terminals targeted by the beamforming. JBB is compared to
orthogonal access (OA), by which the base station partitions the time-frequency
resources into two disjunct parts, one for each group of terminals.
  It is shown that JBB can substantially outperform OA in terms of required
total radiated power for given rate targets.


title: Bayesian Filtering of Smooth Signals: Application to Altimetry

abstract:
  This paper presents a novel Bayesian strategy for the estimation of smooth
signals corrupted by Gaussian noise. The method assumes a smooth evolution of a
succession of continuous signals that can have a numerical or an analytical
expression with respect to some parameters. The Bayesian model proposed takes
into account the Gaussian properties of the noise and the smooth evolution of
the successive signals. In addition, a gamma Markov random field prior is
assigned to the signal energies and to the noise variances to account for their
known properties. The resulting posterior distribution is maximized using a
fast coordinate descent algorithm whose parameters are updated by analytical
expressions. The proposed algorithm is tested on satellite altimetric data
demonstrating good denoising results on both synthetic and real signals. The
proposed algorithm is also shown to improve the quality of the altimetric
parameters when combined with a parameter estimation strategy.


title: Higher order assortativity in complex networks

abstract:
  Assortativity was first introduced by Newman and has been extensively studied
and applied to many real world networked systems since then. Assortativity is a
graph metrics and describes the tendency of high degree nodes to be directly
connected to high degree nodes and low degree nodes to low degree nodes. It can
be interpreted as a first order measure of the connection between nodes, i.e.
the first autocorrelation of the degree-degree vector. Even though
assortativity has been used so extensively, to the author's knowledge, no
attempt has been made to extend it theoretically. This is the scope of our
paper. We will introduce higher order assortativity by extending the Newman
index based on a suitable choice of the matrix driving the connections. Higher
order assortativity will be defined for paths, shortest paths, random walks of
a given time length, connecting any couple of nodes. The Newman assortativity
is achieved for each of these measures when the matrix is the adjacency matrix,
or, in other words, the correlation is of order 1. Our higher order
assortativity indexes can be used for describing a variety of real networks,
help discriminating networks having the same Newman index and may reveal new
topological network features.


title:
Critical Temperature of Chiral Symmetry Restoration for Quark Matter
  with a Chiral Chemical Potential

abstract:
  In this article we study restoration of chiral symmetry at finite temperature
for quark matter with a chiral chemical potential, $\mu_5$, by means of a
quark-meson model with vacuum fluctuations included. Vacuum fluctuations give a
divergent contribution to the vacuum energy, so the latter has to be
renormalized before computing physical quantities. The vacuum term is important
for restoration of chiral symmetry at finite temperature and $\mu_5\neq0$,
therefore we present several plausible renormalization schemes for the
ultraviolet divergences at $\mu_5\neq0$. Then we compute the critical
temperature as a function of $\mu_5$. The main result of our study is that the
choice of a renormalization scheme affects the critical temperature; among the
three renormalization schemes we investigate, there exists one in which the
critical temperature increases with $\mu_5$, a result which has not been found
before by chiral model studies and which is in qualitative agreement with
recent lattice data as well as with studies based on Schwinger-Dyson equations
and universality arguments.