title: The Tulczyjew triple in mechanics on a Lie group

abstract:
  Tulczyjew triple for physical systems with configuration manifold equipped
with Lie group structure is constructed and discussed. The case of systems
invariant with respect to group acton is considered together with appropriate
reduction of the Tulczyjew triple. The theory is applied to free rigid-body
dynamics.


title:
What We Don't Know About Spreadsheet Errors Today: The Facts, Why We
  Don't Believe Them, and What We Need to Do

abstract:
  Research on spreadsheet errors is substantial, compelling, and unanimous. It
has three simple conclusions. The first is that spreadsheet errors are rare on
a per-cell basis, but in large programs, at least one incorrect bottom-line
value is very likely to be present. The second is that errors are extremely
difficult to detect and correct. The third is that spreadsheet developers and
corporations are highly overconfident in the accuracy of their spreadsheets.
The disconnect between the first two conclusions and the third appears to be
due to the way human cognition works. Most importantly, we are aware of very
few of the errors we make. In addition, while we are proudly aware of errors
that we fix, we have no idea of how many remain, but like Little Jack Horner we
are impressed with our ability to ferret out errors. This paper reviews human
cognition processes and shows first that humans cannot be error free no matter
how hard they try, and second that our intuition about errors and how we can
reduce them is based on appallingly bad knowledge. This paper argues that we
should reject any prescription for reducing errors that has not been rigorously
proven safe and effective. This paper also argues that our biggest need, based
on empirical data, is to do massively more testing than we do now. It suggests
that the code inspection methodology developed in software development is
likely to apply very well to spreadsheet inspection.


title:
Equivalence and stable isomorphism of groupoids, and diagonal-preserving
  stable isomorphisms of graph C*-algebras and Leavitt path algebras

abstract:
  We prove that ample groupoids with sigma-compact unit spaces are equivalent
if and only if they are stably isomorphic in an appropriate sense, and relate
this to Matui's notion of Kakutani equivalence. We use this result to show that
diagonal-preserving stable isomorphisms of graph C*-algebras or Leavitt path
algebras give rise to isomorphisms of the groupoids of the associated
stabilised graphs. We deduce that the Leavitt path algebras $L_Z(E_2)$ and
$L_Z(E_{2-})$ are not stably *-isomorphic.


title: Quasi-isometric rigidity of piecewise geometric manifolds

abstract:
  Two groups are virtually isomorphic if they can be obtained one from the
other via a finite number of steps, where each step consists in taking a finite
extension or a finite index subgroup (or viceversa). Virtually isomorphic
groups are always quasi-isometric, and a group G is quasi-isometrically rigid
if every group quasi-isometric to G is virtually isomorphic to G.
  In this survey we describe quasi-isometric rigidity results for fundamental
groups of manifolds which can be decomposed into geometric pieces. After
stating by now classical results on lattices in semisimple Lie groups, we focus
on the class of fundamental groups of $3$-manifolds, and describe the behaviour
of quasi-isometries with respect to the Milnor-Kneser prime decomposition
(following Papasoglu and Whyte) and with respect to the JSJ decomposition
(following Kapovich and Leeb). We also discuss quasi-isometric rigidity results
for fundamental groups of higher dimensional graph manifolds, that were
recently defined by Lafont, Sisto and the author. Our main tools are the study
of geometric group actions and quasi-actions on Riemannian manifolds and on
trees of spaces, via the analysis of the induced actions on asymptotic cones.


title: Capture into resonance and phase space dynamics in optical centrifuge

abstract:
  The process of capture of a molecular enesemble into rotational resonance in
the optical centrifuge is investigated. The adiabaticity and phase space
incompressibility are used to find the resonant capture probability in terms of
two dimensionless parameters P1,P2 characterising the driving strength and the
nonlinearity, and related to three characteristic time scales in the problem.
The analysis is based on the transformation to action-angle variables and the
single resonance approximation, yielding reduction of the three-dimensional
rotation problem to one degree of freedom. The analytic results for capture
probability are in a good agreement with simulations. The existing experiments
satisfy the validity conditions of the theory.


title:
Statistical estimate of the proportional hazard premium of loss under
  random censoring

abstract:
  Many insurance premium principles are defined and various estimation
procedures introduced in the literature. In this paper, we focus on the
estimation of the excess-of-loss reinsurance premium when the risks are
randomly right-censored. The asymptotic normality of the proposed estimator is
established under suitable conditions and its performance evaluated through
sets of simulated data.


title:
Hidden Gibbs random fields model selection using Block Likelihood
  Information Criterion

abstract:
  Performing model selection between Gibbs random fields is a very challenging
task. Indeed, due to the Markovian dependence structure, the normalizing
constant of the fields cannot be computed using standard analytical or
numerical methods. Furthermore, such unobserved fields cannot be integrated out
and the likelihood evaluztion is a doubly intractable problem. This forms a
central issue to pick the model that best fits an observed data. We introduce a
new approximate version of the Bayesian Information Criterion. We partition the
lattice into continuous rectangular blocks and we approximate the probability
measure of the hidden Gibbs field by the product of some Gibbs distributions
over the blocks. On that basis, we estimate the likelihood and derive the Block
Likelihood Information Criterion (BLIC) that answers model choice questions
such as the selection of the dependency structure or the number of latent
states. We study the performances of BLIC for those questions. In addition, we
present a comparison with ABC algorithms to point out that the novel criterion
offers a better trade-off between time efficiency and reliable results.


title: Lusin approximation for horizontal curves in step 2 Carnot groups

abstract:
  A Carnot group $\mathbb{G}$ admits Lusin approximation for horizontal curves
if for any absolutely continuous horizontal curve $\gamma$ in $\mathbb{G}$ and
$\varepsilon>0$, there is a $C^1$ horizontal curve $\Gamma$ such that
$\Gamma=\gamma$ and $\Gamma'=\gamma'$ outside a set of measure at most
$\varepsilon$. We verify this property for free Carnot groups of step 2 and
show that it is preserved by images of Lie group homomorphisms preserving the
horizontal layer. Consequently, all step 2 Carnot groups admit Lusin
approximation for horizontal curves.


title: Tico Spines

abstract:
  Any bounding compact smooth manifold bounds a compact manifold with a spine
consisting of transversely intersecting codimension one submanifolds. This
paper provides details for a picture proof given in previous papers with S.
Akbulut.


title: Dimensions of fibers of generic continuous maps

abstract:
  In an earlier paper Buczolich, Elekes and the author described the Hausdorff
dimension of the level sets of a generic real-valued continuous function (in
the sense of Baire category) defined on a compact metric space $K$. Later on,
the author extended the theory for maps from $K$ to $\mathbb{R}^n$. The main
goal of this paper is to generalize the relevant results for topological and
packing dimensions.
  Let $K$ be a compact metric space and let us denote by $C(K,\mathbb{R}^n)$
the set of continuous maps from $K$ to $\mathbb{R}^n$ endowed with the maximum
norm. Let $\dim_{*}$ be one of the topological dimension $\dim_T$, the
Hausdorff dimension $\dim_H$, or the packing dimension $\dim_P$. Define
$$d_{*}^n(K)=\inf\{\dim_{*}(K\setminus F): F\subset K \textrm{ is
$\sigma$-compact with } \dim_T F<n\}.$$ We prove that $d^n_{*}(K)$ is the right
notion to describe the dimensions of the fibers of a generic continuous map
$f\in C(K,\mathbb{R}^n)$. In particular, we show that $\sup\{\dim_{*}f^{-1}(y):
y\in \mathbb{R}^n\} =d^n_{*}(K)$ provided that $\dim_T K\geq n$, otherwise
every fiber is finite. Proving the above theorem for packing dimension requires
entirely new ideas. Moreover, we show that the supremum is attained on the left
hand side of the above equation.
  Assume $\dim_T K\geq n$. If $K$ is sufficiently homogeneous, then we can say
much more. For example, we prove that $\dim_{*}f^{-1}(y)=d^n_{*}(K)$ for a
generic $f\in C(K,\mathbb{R}^n)$ for all $y\in \textrm{int} f(K)$ if and only
if $d^n_{*}(U)=d^n_{*}(K)$ or $\dim_T U<n$ for all open sets $U\subset K$. This
is new even if $n=1$ and $\dim_{*}=\dim_H$. It is known that for a generic
$f\in C(K,\mathbb{R}^n)$ the interior of $f(K)$ is not empty. We augment the
above characterization by showing that $\dim_T \partial f(K)=\dim_H \partial
f(K)=n-1$ for a generic $f\in C(K,\mathbb{R}^n)$.


title: Metric Dimension of Bounded Tree-length Graphs

abstract:
  The notion of resolving sets in a graph was introduced by Slater (1975) and
Harary and Melter (1976) as a way of uniquely identifying every vertex in a
graph. A set of vertices in a graph is a resolving set if for any pair of
vertices x and y there is a vertex in the set which has distinct distances to x
and y. A smallest resolving set in a graph is called a metric basis and its
size, the metric dimension of the graph. The problem of computing the metric
dimension of a graph is a well-known NP-hard problem and while it was known to
be polynomial time solvable on trees, it is only recently that efforts have
been made to understand its computational complexity on various restricted
graph classes. In recent work, Foucaud et al. (2015) showed that this problem
is NP-complete even on interval graphs. They complemented this result by also
showing that it is fixed-parameter tractable (FPT) parameterized by the metric
dimension of the graph. In this work, we show that this FPT result can in fact
be extended to all graphs of bounded tree-length. This includes well-known
classes like chordal graphs, AT-free graphs and permutation graphs. We also
show that this problem is FPT parameterized by the modular-width of the input
graph.


title:
The global nonlinear stability of Minkowski space for the massless
  Einstein--Vlasov system

abstract:
  Minkowski space is shown to be globally stable as a solution to the
Einstein--Vlasov system in the case when all particles have zero mass. The
proof proceeds by showing that the matter must be supported in the "wave zone",
and then proving a small data semi-global existence result for the
characteristic initial value problem for the massless Einstein--Vlasov system
in this region. This relies on weighted estimates for the solution which, for
the Vlasov part, are obtained by introducing the Sasaki metric on the mass
shell and estimating Jacobi fields with respect to this metric by geometric
quantities on the spacetime. The stability of Minkowski space result for the
vacuum Einstein equations is then appealed to for the remaining regions.


title: Sign-Compute-Resolve for Tree Splitting Random Access

abstract:
  We present a framework for random access that is based on three elements:
physical-layer network coding (PLNC), signature codes and tree splitting. In
presence of a collision, physical-layer network coding enables the receiver to
decode, i.e. compute, the sum of the packets that were transmitted by the
individual users. For each user, the packet consists of the user's signature,
as well as the data that the user wants to communicate. As long as no more than
K users collide, their identities can be recovered from the sum of their
signatures. This framework for creating and transmitting packets can be used as
a fundamental building block in random access algorithms, since it helps to
deal efficiently with the uncertainty of the set of contending terminals. In
this paper we show how to apply the framework in conjunction with a
tree-splitting algorithm, which is required to deal with the case that more
than K users collide. We demonstrate that our approach achieves throughput that
tends to 1 rapidly as K increases. We also present results on net data-rate of
the system, showing the impact of the overheads of the constituent elements of
the proposed protocol. We compare the performance of our scheme with an upper
bound that is obtained under the assumption that the active users are a priori
known. Also, we consider an upper bound on the net data-rate for any PLNC based
strategy in which one linear equation per slot is decoded. We show that already
at modest packet lengths, the net data-rate of our scheme becomes close to the
second upper bound, i.e. the overhead of the contention resolution algorithm
and the signature codes vanishes.


title: Most Interval Exchanges Have No Roots

abstract:
  Let $T$ be an $m$-interval exchange transformation. By the rank of $T$ we
mean the dimension of the $\mathbb{Q}$-vector space spanned by the lengths of
the exchanged intervals. We prove that if $T$ is minimal and the rank of $T$ is
greater than $1+\lfloor m/2 \rfloor$, then $T$ cannot be written as a power of
another interval exchange. We also demonstrate that this estimate on the rank
cannot be improved. In the case that $T$ is a minimal 3-interval exchange
transformation, we prove a stronger result: $T$ cannot be written as a power of
another interval exchange if and only if $T$ satisfies Keane's infinite
distinct orbit condition. In the course of proving this result, we give a
classification (up to conjugacy) of those minimal IETs whose discontinuities
all belong to a single orbit.


title: Existence of Unpredictable Solutions and Chaos

abstract:
  In paper [1] unpredictable points were introduced based on Poisson stability,
and this gives rise to the existence of chaos in the quasi-minimal set. This
time, an unpredictable function is determined as an unpredictable point in the
Bebutov dynamical system. The existence of an unpredictable solution and
consequently chaos of a quasi-linear system of ordinary differential equations
are verified. This is the first time that the description of chaos is initiated
from a single function, but not on a collection of them. The results can be
easily extended to different types of differential equations. An application of
the main theorem for Duffing equations is provided.


title: Regularity of the Szeg\"o projection on model worm domains

abstract:
  In this paper we study the regularity of the Szeg\"o projection on Lebesgue
and Sobolev spaces on the boundary of the unbounded model worm domain
$D'_\beta$.
  We consider the Hardy space $H^2(D'_\beta)$. Denoting by $bD'_\beta$ the
boundary of $D'_\beta$, it is classical that $H^2(D'_\beta)$ can be identified
with the closed subspace of $L^2(bD'_\beta,d\sigma)$, denoted by
$H^2(bD'_\beta)$, consisting of the boundary values of functions in
$H^2(D'_\beta)$, where $d\sigma$ is the induced Lebesgue measure. The
orthogonal Hilbert space projection $P: L^2(D'_\beta,d\sigma)\to
H^2(bD'_\beta)$ is called the Szeg\"o projection.
  Let $W^{s,p}(bD'_\beta)$ denote the Lebesgue--Sobolev space on $bD'_\beta$.
We prove that $P$, initially defined on the dense subspace
$W^{s,p}(bD'_\beta)\cap L^2(bD'_\beta,d\sigma)$, extends to a bounded operator
$P: W^{s,p}(bD'_\beta)\to
  W^{s,p}(bD'_\beta)$, for $1<p<\infty$ and $s\ge0$.


title:
Guarantees in Wasserstein Distance for the Langevin Monte Carlo
  Algorithm

abstract:
  We study the problem of sampling from a distribution $\target$ using the
Langevin Monte Carlo algorithm and provide rate of convergences for this
algorithm in terms of Wasserstein distance of order $2$. Our result holds as
long as the continuous diffusion process associated with the algorithm
converges exponentially fast to the target distribution along with some
technical assumptions. While such an exponential convergence holds for example
in the log-concave measure case, it also holds for the more general case of
asymptoticaly log-concave measures. Our results thus extends the known rates of
convergence in total variation and Wasserstein distances which have only been
obtained in the log-concave case. Moreover, using a sharper approximation bound
of the continuous process, we obtain better asymptotic rates than traditional
results. We also look into variations of the Langevin Monte Carlo algorithm
using other discretization schemes. In a first time, we look into the use of
the Ozaki's discretization but are unable to obtain any significative
improvement in terms of convergence rates compared to the Euler's scheme. We
then provide a (sub-optimal) way to study more general schemes, however our
approach only holds for the log-concave case.


title:
Adaptive imputation of missing values for incomplete pattern
  classification

abstract:
  In classification of incomplete pattern, the missing values can either play a
crucial role in the class determination, or have only little influence (or
eventually none) on the classification results according to the context. We
propose a credal classification method for incomplete pattern with adaptive
imputation of missing values based on belief function theory. At first, we try
to classify the object (incomplete pattern) based only on the available
attribute values. As underlying principle, we assume that the missing
information is not crucial for the classification if a specific class for the
object can be found using only the available information. In this case, the
object is committed to this particular class. However, if the object cannot be
classified without ambiguity, it means that the missing values play a main role
for achieving an accurate classification. In this case, the missing values will
be imputed based on the K-nearest neighbor (K-NN) and self-organizing map (SOM)
techniques, and the edited pattern with the imputation is then classified. The
(original or edited) pattern is respectively classified according to each
training class, and the classification results represented by basic belief
assignments are fused with proper combination rules for making the credal
classification. The object is allowed to belong with different masses of belief
to the specific classes and meta-classes (which are particular disjunctions of
several single classes). The credal classification captures well the
uncertainty and imprecision of classification, and reduces effectively the rate
of misclassifications thanks to the introduction of meta-classes. The
effectiveness of the proposed method with respect to other classical methods is
demonstrated based on several experiments using artificial and real data sets.


title:
On the use of Hahn's asymptotic formula and stabilized recurrence for a
  fast, simple, and stable Chebyshev--Jacobi transform

abstract:
  We describe a fast, simple, and stable transform of Chebyshev expansion
coefficients to Jacobi expansion coefficients and its inverse based on the
numerical evaluation of Jacobi expansions at the Chebyshev--Lobatto points.
This is achieved via a decomposition of Hahn's interior asymptotic formula into
a small sum of diagonally scaled discrete sine and cosine transforms and the
use of stable recurrence relations. It is known that the Clenshaw--Smith
algorithm is not uniformly stable on the entire interval of orthogonality.
Therefore, Reinsch's modification is extended for Jacobi polynomials and
employed near the endpoints to improve numerical stability.


title:
An analytical condition for the violation of Mermin's inequality by any
  three qubit state

abstract:
  Mermin's inequality is the generalization of the Bell-CHSH inequality for
three qubit states. The violation of the Mermin inequality guarantees the fact
that there exists quantum non-locality either between two or three qubits in a
three qubit system. In the absence of an analytical result to this effect, in
order to check for the violation of Mermin's inequality one has to perform a
numerical optimization procedure for even three qubit pure states. Here we
derive an analytical formula for the maximum value of the expectation of the
Mermin operator in terms of eigenvalues of symmetric matrices, that gives the
maximal violation of the Mermin inequality for all three qubit pure and mixed
states.


title: Scalability and Total Recall with Fast CoveringLSH

abstract:
  Locality-sensitive hashing (LSH) has emerged as the dominant algorithmic
technique for similarity search with strong performance guarantees in
high-dimensional spaces. A drawback of traditional LSH schemes is that they may
have \emph{false negatives}, i.e., the recall is less than 100\%. This limits
the applicability of LSH in settings requiring precise performance guarantees.
Building on the recent theoretical "CoveringLSH" construction that eliminates
false negatives, we propose a fast and practical covering LSH scheme for
Hamming space called \emph{Fast CoveringLSH (fcLSH)}. Inheriting the design
benefits of CoveringLSH our method avoids false negatives and always reports
all near neighbors. Compared to CoveringLSH we achieve an asymptotic
improvement to the hash function computation time from $\mathcal{O}(dL)$ to
$\mathcal{O}(d + L\log{L})$, where $d$ is the dimensionality of data and $L$ is
the number of hash tables. Our experiments on synthetic and real-world data
sets demonstrate that \emph{fcLSH} is comparable (and often superior) to
traditional hashing-based approaches for search radius up to 20 in
high-dimensional Hamming space.


title:
Tackling excess noise from bilinear and nonlinear couplings in
  gravitational-wave interferometers

abstract:
  We describe a tool we improved to detect excess noise in the gravitational
wave (GW) channel arising from its bilinear or nonlinear coupling with
fluctuations of various components of a GW interferometer and its environment.
We also describe a higher-order statistics tool we developed to characterize
these couplings, e.g., by unraveling the frequencies of the fluctuations
contributing to such noise, and demonstrate its utility by applying it to
understand nonlinear couplings in Advanced LIGO engineering data. Once such
noise is detected, it is highly desirable to remove it or correct for it. Such
action in the past has been shown to improve the sensitivity of the instrument
in searches of astrophysical signals. If this is not possible, then steps must
be taken to mitigate its influence, e.g., by characterizing its effect on
astrophysical searches. We illustrate this through a study of the effect of
transient sine-Gaussian noise artifacts on a compact binary coalescence
template bank.


title: A Review of Control Algorithms for Autonomous Quadrotors

abstract:
  The quadrotor unmanned aerial vehicle is a great platform for control systems
research as its nonlinear nature and under-actuated configuration make it ideal
to synthesize and analyze control algorithms. After a brief explanation of the
system, several algorithms have been analyzed including their advantages and
disadvantages: PID, Linear Quadratic Regulator (LQR), Sliding mode,
Backstepping, Feedback linearization, Adaptive, Robust, Optimal, L1,
H-infinity, Fuzzy logic and Artificial neutral networks. The conclusion of this
work is a proposal of hybrid systems to be considered as they combine
advantages from more than one control philosophy.


title: Delaunay hypersurfaces with constant nonlocal mean curvature

abstract:
  We study hypersurfaces of $\mathbb{R}^N$ with constant nonlocal (or
fractional) mean curvature. This is the equation associated to critical points
of the fractional perimeter functional under a volume constraint. We establish
the existence of a smooth branch of periodic cylinders in $\mathbb{R}^N$,
$N\geq 2$, all of them with the same constant nonlocal mean curvature, and
bifurcating from a straight cylinder. These are Delaunay type cylinders in the
nonlocal setting. The proof uses the Crandall-Rabinowitz theorem applied to a
quasilinear type fractional elliptic equation.


title:
Customized ion flux-energy distribution functions in capacitively
  coupled plasmas by voltage waveform tailoring

abstract:
  We propose a method to generate a single peak at a distinct energy in the ion
flux-energy distribution function (IDF) at the electrode surfaces in
capacitively coupled plasmas. The technique is based on the tailoring of the
driving voltage waveform, i.e. adjusting the phases and amplitudes of the
applied harmonics, to optimize the accumulation of ions created by charge
exchange collisions and their subsequent acceleration by the sheath electric
field. The position of the peak (i.e. the ion energy) and the flux of the ions
within the peak of the IDF can be controlled in a wide domain by tuning the
parameters of the applied RF voltage waveform, allowing optimization of various
applications where surface reactions are induced at particular ion energies.


title:
Gap opening and large spin-orbit splitting in MX2 (M=Mo,W X=S,Se,Te)
  from the interplay between crystal field and hybridizations: insights from
  ab-initio theory

abstract:
  By means of first-principles density functional calculations, we study the
maximally localized Wannier functions for the 2D transition metal
dichalcogenides MX2 (M=Mo,W X=S,Se,Te). We found a M^+4-like ionic charge and a
single occupied d-band. The center of the d-like maximally localized Wannier
function associated with this band is distributed among three M sites. Part of
the energy gap is opened by the crystal field splitting induced by the
X^-2-like atoms. We extract the hopping parameters for the Wannier functions
and provide a perspective on tight-binding model. From the analysis of the
tight binding model, we have found an inversion of the band character between
the Gamma and the K points of the Brillouin zone due to the M-M hybridization.
The consequence of this inversion is the closure of the gap. The M-X
hybridization is the only one that tends to open the gap at every k-point, the
change in the M-X and M-M hybridization is the main responsible for the
difference in the gap between the different dichalcogenide materials. The
inversion of the bands gives rise to different spin-orbit splitting at Gamma
and K point in the valence band. The different character of the gap at Gamma
and K point offers the chance to manipulate the semiconductive properties of
these compounds. For a bilayer system, the hybridizations between the out of
plane orbitals and the hybridizations between the in plane orbitals split the
valence band respectively at the Gamma and K point. The splitting in the
valence band is opened also without spin-orbit coupling and comes from the M-M
and X-X hybridization between the two monolayers.


title: Magnetization of laser-produced plasma in a chiral hollow target

abstract:
  It is demonstrated that targets with a broken rotational symmetry may
facilitate generation of a strong axial (poloidal) magnetic field. An intense
laser beam irradiating such a target creates intense electron currents carrying
vorticity and producing strong spontaneous magnetic fields. Combined with a
laser electron acceleration, such targets may be used for generation and
guiding of magnetized, collimated particle or plasma beams.


title:
Optimal and asymptotically optimal NCT reversible circuits by the gate
  types

abstract:
  We report optimal and asymptotically optimal reversible circuits composed of
NOT, CNOT, and Toffoli (NCT) gates, keeping the count by the subsets of the
gate types used. This study fine tunes the circuit complexity figures for the
realization of reversible functions via reversible NCT circuits. An important
consequence is a result on the limitation of the use of the $T$-count quantum
circuit metric popular in applications.


title: CHSH Inequality on a single probability space

abstract:
  A number of papers have suggested that it is inappropriate to combine data
from different experiments when undertaking experimental tests of Bell's
inequalities. It has been suggested that a correct analysis, using a single
probability space, leads to inequalities which are not violated by experiment.
If correct, this would be contrary to the normal interpretation of such
experimental data.
  However, in this note, a generalised Clauser-Horne-Shimony-Holt (CHSH)
inequality is derived for a system of four experiments constructed on a single
probability space which combines the data from the four experiments. It is
shown that this leads to the standard CHSH inequality which is normally used to
interpret experimental data. Thus the commonly accepted conclusion that
experimental violations of Bell's inequality imply that local realistic models
are inconsistent with the predictions of quantum mechanics has not been
challenged.


title: Improved Bounds for the Excluded Grid Theorem

abstract:
  We study the Excluded Grid Theorem of Robertson and Seymour. This is a
fundamental result in graph theory, that states that there is some function $f:
Z^+\rightarrow Z^+$, such that for all integers $g>0$, every graph of treewidth
at least $f(g)$ contains the $(g\times g)$-grid as a minor. Until recently, the
best known upper bounds on $f$ were super-exponential in $g$. A recent work of
Chekuri and Chuzhoy provided the first polynomial bound, by showing that
treewidth $f(g)=O(g^{98}\operatorname{poly}\log g)$ is sufficient to ensure the
existence of the $(g\times g)$-grid minor in any graph. In this paper we
improve this bound to $f(g)=O(g^{19}\operatorname{poly}\log g)$. We introduce a
number of new techniques, including a conceptually simple and almost entirely
self-contained proof of the theorem that achieves a polynomial bound on $f(g)$.


title:
An efficient null space inexact Newton method for hydraulic simulation
  of water distribution networks

abstract:
  Null space Newton algorithms are efficient in solving the nonlinear equations
arising in hydraulic analysis of water distribution networks. In this article,
we propose and evaluate an inexact Newton method that relies on partial updates
of the network pipes' frictional headloss computations to solve the linear
systems more efficiently and with numerical reliability. The update set
parameters are studied to propose appropriate values. Different null space
basis generation schemes are analysed to choose methods for sparse and
well-conditioned null space bases resulting in a smaller update set. The Newton
steps are computed in the null space by solving sparse, symmetric positive
definite systems with sparse Cholesky factorizations. By using the constant
structure of the null space system matrices, a single symbolic factorization in
the Cholesky decomposition is used multiple times, reducing the computational
cost of linear solves. The algorithms and analyses are validated using medium
to large-scale water network models.


title:
A study of the magnetotransport properties of the graphene (III.
  Bilayer)

abstract:
  The present paper corresponds to the third work of the author related to the
magnetotransport properties concerning on the graphene systems. In the first
one the integer quantum Hall effect in the monolayer graphene, (MG), MGIQHE,
was analysed, (Hidalgo, 2014). The subject of the second one was the
understanding of the fractional quantum Hall also in the MG, (MGFQHE),
(Hidalgo, 2015), basing us in our model on the fractional quantum Hall effect
in semiconductor quantum systems, Hidalgo (2013). The aim of the present work
is the analysis of the integer quantum Hall effect observed in bilayer
graphene, (BG), BGIQHE, as a function of both, the gate voltage and the
magnetic field. Our approach is a single electron approach, firstly developed
for the study of the integer quantum Hall (IQHE) and Shubnikov-de Haas (SdH)
effects of a two-dimensional electron gas (2DEG) in any semiconductor quantum
well (QW), (Hidalgo, 1995, 1998, 2007). The extension of this model for the BG
reproduces its main observed features for the IQHE and the SdH, and as a
function of both, the gate voltage and the magnetic field, in particular the
plateaux at the values , with n=0,1,2... Therefore, the approach integrates the
quantum Hall effects (integer and fractional) observed in both, QW and
graphene, in the same physical frame.


title: On p-adic approximation of sums of binomial coefficients

abstract:
  We propose higher-order generalizations of Jacobsthal's $p$-adic
approximation for binomial coefficients. Our results imply explicit formulae
for linear combinations of binomial coefficients $\binom{ip}{p}$
($i=1,2,\dots$) that are divisible by arbitrarily large powers of prime $p$.


title: Shelah's eventual categoricity conjecture in universal classes. Part II

abstract:
  We prove that a universal class categorical in a high-enough cardinal is
categorical on a tail of cardinals. As opposed to other results in the
literature, we work in ZFC, do not require the categoricity cardinal to be a
successor, do not assume amalgamation, and do not use large cardinals. Moreover
we give an explicit bound on the "high-enough" threshold:
  $\mathbf{Theorem}$
  Let $\psi$ be a universal $\mathbb{L}_{\omega_1, \omega}$ sentence. If $\psi$
is categorical in some $\lambda \ge \beth_{\beth_{\omega_1}}$, then $\psi$ is
categorical in all $\lambda' \ge \beth_{\beth_{\omega_1}}$.
  As a byproduct of the proof, we show that a conjecture of Grossberg holds in
universal classes:
  $\mathbf{Corollary}$
  Let $\psi$ be a universal $\mathbb{L}_{\omega_1, \omega}$ sentence that is
categorical in some $\lambda \ge \beth_{\beth_{\omega_1}}$, then the class of
models of $\psi$ has the amalgamation property for models of size at least
$\beth_{\beth_{\omega_1}}$.
  We also establish generalizations of these two results to uncountable
languages. As part of the argument, we develop machinery to transfer
model-theoretic properties between two different classes satisfying a
compatibility condition. This is used as a bridge between Shelah's milestone
study of universal classes (which we use extensively) and a categoricity
transfer theorem of the author for abstract elementary classes that have
amalgamation, are tame, and have primes over sets of the form $M \cup \{a\}$.


title: Around the Complete Intersection Theorem

abstract:
  The celebrated theorem of Ahlswede and Khachatrian determines the maximum
size of a family of $k$-element subsets of an $n$-element set where the
intersection of any two subsets has at least $r$ elements. This survey first
gives a historical introduction, then it shows some applications.


title:
Constraining Polarized Foregrounds for EoR Experiments I: 2D Power
  Spectra from the PAPER-32 Imaging Array

abstract:
  Current-generation low frequency interferometers constructed with the
objective of detecting the high-redshift 21 cm background, aim to generate
power spectra of the brightness-temperature contrast of neutral hydrogen in
primordial intergalactic medium. Two-dimensional power spectra (power in
Fourier modes parallel and perpendicular to the line of sight) formed from
interferometric visibilities have been shown to delineate a boundary between
spectrally-smooth foregrounds (known as the wedge) and spectrally-structured 21
cm background emission (the EoR-window). However, polarized foregrounds are
known to possess spectral structure due to Faraday rotation, which can leak
into the EoR window. In this work, we create and analyze 2D power spectra from
the PAPER-32 imaging array in Stokes I, Q, U and V. These allow us to observe
and diagnose systematic effects in our calibration at high signal-to-noise
within the Fourier space most relevant to EoR experiments. We observe
well-defined windows in the Stokes visibilities, with Stokes Q, U and V power
spectra sharing a similar wedge shape to that seen in Stokes I. With modest
polarization calibration, we see no evidence that polarization calibration
errors move power outside the wedge in any Stokes visibility, to the noise
levels attained. Deeper integrations will be required to confirm that this
behavior persists to the depth required for EoR detection.


title:
Excitation spectra of solitary waves in scalar field models with
  polynomial self-interaction

abstract:
  We study excitations of solitary waves -- the kinks -- in scalar models with
degree eight polynomial self-interaction in (1+1) dimensions. We perform
numerical studies of scattering of two kinks with an exponential asymptotic off
each other and analyse the occurring resonance phenomena. We connect these
phenomena to the energy exchange between the translational and the vibrational
modes of the colliding kinks. We also point out that the interaction of two
kinks with power-law asymptotic can lead to a long-range interaction between
the two kinks.


title: On cobordisms between knots, braid index, and the Upsilon-invariant

abstract:
  We use Ozsv\'ath, Stipsicz, and Szab\'o's Upsilon-invariant to provide bounds
on cobordisms between knots that `contain full-twists'. In particular, we
recover and generalize a classical consequence of the Morton-Franks-Williams
inequality for knots: positive braids that contain a positive full-twist
realize the braid index of their closure. We also establish that quasi-positive
braids that are sufficiently twisted realize the minimal braid index among all
knots that are concordant to their closure. Finally, we provide inductive
formulas for the Upsilon invariant of torus knots and compare it to the
Levine-Tristram signature profile.


title:
Response to "Comment on 'Zero and negative energy dissipation at
  information-theoretic erasure'"

abstract:
  We prove that statistical information theoretic quantities, such as
information entropy, cannot generally be interrelated with the lower limit of
energy dissipation during information erasure. We also point out that, in
deterministic and error-free computers, the information entropy of memories
does not change during erasure because its value is always zero. On the other
hand, for information-theoretic erasure - i.e., "thermalization" /
randomization of the memory - the originally zero information entropy (with
deterministic data in the memory) changes after erasure to its maximum value, 1
bit / memory bit, while the energy dissipation is still positive, even at
parameters for which the thermodynamic entropy within the memory cell does not
change. Information entropy does not convert to thermodynamic entropy and to
the related energy dissipation; they are quantities of different physical
nature. Possible specific observations (if any) indicating convertibility are
at most fortuitous and due to the disregard of additional processes that are
present.


title: Nonlinear single Compton scattering of an electron wave-packet

abstract:
  Nonlinear single Compton scattering has been thoroughly investigated in the
literature under the assumption that initially the electron has a definite
momentum. Here, we study a more general initial state, and consider the
electron as a wave-packet. In particular, we investigate the energy spectrum of
the emitted radiation and show that in typical experimental situations some
features of the spectra shown in previous works are almost completely washed
out. Moreover, we show that at comparable relative uncertainties, the one in
the momentum of the incoming electron has a larger impact on the photon spectra
at a fixed observation direction than the one on the laser frequency.


title:
Elastic pion-nucleon scattering in chiral perturbation theory: A fresh
  look

abstract:
  Elastic pion-nucleon scattering is analyzed in the framework of chiral
perturbation theory up to fourth order within the heavy-baryon expansion and a
covariant approach based on an extended on-mass-shell renormalization scheme.
We discuss in detail the renormalization of the various low-energy constants
and provide explicit expressions for the relevant $\beta$-functions and the
finite subtractions of the power-counting breaking terms within the covariant
formulation. To estimate the theoretical uncertainty from the truncation of the
chiral expansion, we employ an approach which has been successfully applied in
the most recent analysis of the nuclear forces. This allows us to reliably
extract the relevant low-energy constants from the available scattering data at
low energy. The obtained results provide a clear evidence that the breakdown
scale of the chiral expansion for this reaction is related to the
$\Delta$-resonance. The explicit inclusion of the leading contributions of the
$\Delta$-isobar is demonstrated to substantially increase the range of
applicability of the effective field theory. The resulting predictions for the
phase shifts are in an excellent agreement with the ones from the recent
Roy-Steiner-equation analysis of pion-nucleon scattering.


title: Many-body electron correlations in graphene

abstract:
  The conduction electrons in graphene promise new opportunities to access the
region of strong many-body electron-electron correlations. Extremely high
quality, atomically flat two-dimensional electron sheets and
quasi-one-dimensional electron nanoribbons with tuneable band gaps that can be
switched on by gates, should exhibit new many-body phenomena that have long
been predicted for the regions of phase space where the average Coulomb
repulsions between electrons dominate over their Fermi energies. In electron
nanoribbons a few nanometres wide etched in monolayers of graphene, the quantum
size effects and the van Hove singularities in their density of states further
act to enhance electron correlations. For graphene multilayers or nanoribbons
in a double unit electron-hole geometry, it is possible for the many-body
electron-hole correlations to be made strong enough to stabilise
high-temperature electron-hole superfluidity.


title:
Classical quasi-steady state reduction -- A mathematical
  characterization

abstract:
  We discuss parameter dependent polynomial ordinary differential equations
that model chemical reaction networks. By classical quasi-steady state (QSS)
reduction we understand the following familiar heuristic: Set the rate of
change for certain (a priori chosen) variables equal to zero and use the
resulting algebraic equations to obtain a system of smaller dimension for the
remaining variables. This procedure will generally be valid only for certain
parameter ranges. We start by showing that the reduction is accurate if and
only if the corresponding parameter is what we call a QSS parameter value, and
that the reduction is approximately accurate if and only if the corresponding
parameter is close to a QSS parameter value. These QSS parameter values can be
characterized by polynomial equations and inequations, hence parameter ranges
for which QSS reduction is valid are accessible in an algorithmic manner. A
closer investigation of QSS parameter values and the associated systems shows
the existence of certain invariant sets; here singular perturbations enter the
picture in a natural manner. We compare QSS reduction and singular perturbation
reduction, and show that, while they do not agree in general, they do, up to
lowest order in a small parameter, for a quite large and relevant class of
examples. This observation, in turn, allows the computation of QSS reductions
even in cases where an explicit resolution of the polynomial equations is not
possible.


title:
Creativity Training for Future Engineers: Preliminary Results from an
  Educative Experience

abstract:
  Due in part to the increased pace of cultural and environmental change, as
well as increased competition due to globalization, innovation is become one of
the primary concerns of the 21st century. We present an academic course
designed to develop cognitive abilities related to creativity within an
engineering education context, based on a conceptual framework rooted in
cognitive sciences. The course was held at \'Ecole Polytechnique de Montr\'eal
(\'EPM), a world renowned engineering school and a pillar in Canada's
engineering community. The course was offered twice in the 2014-2015 academic
year and more than 30 students from the graduate and undergraduate programs
participated. The course incorporated ten pedagogical strategies, including
serious games, an observation book, individual and group projects, etc., that
were expected to facilitate the development of cognitive abilities related to
creativity such as encoding, and associative analytical thinking. The CEDA
(Creative Engineering Design Assessment) test was used to measure the students'
creativity at the beginning and at the end of the course. Field notes were
taken after each of the 15 three-hour sessions to qualitatively document the
educative intervention along the semester and students gave anonymous written
feedback after completing the last session. Quantitative and qualitative
results suggest that an increase in creativity is possible to obtain with a
course designed to development cognitive abilities related to creativity. Also,
students appreciated the course, found it relevant, and made important,
meaningful learnings regarding the creative process, its cognitive mechanism
and the approaches available to increase it.


title:
Generating Images with Perceptual Similarity Metrics based on Deep
  Networks

abstract:
  Image-generating machine learning models are typically trained with loss
functions based on distance in the image space. This often leads to
over-smoothed results. We propose a class of loss functions, which we call deep
perceptual similarity metrics (DeePSiM), that mitigate this problem. Instead of
computing distances in the image space, we compute distances between image
features extracted by deep neural networks. This metric better reflects
perceptually similarity of images and thus leads to better results. We show
three applications: autoencoder training, a modification of a variational
autoencoder, and inversion of deep convolutional networks. In all cases, the
generated images look sharp and resemble natural images.


title: On the exotic Higgs decays in effective field theory

abstract:
  We discuss exotic Higgs decays in an effective field theory where the
Standard Model is extended by dimension-6 operators. We review and update the
status of 2-body lepton- and quark-flavor violating decays involving the Higgs
boson. We also comment on the possibility of observing 3-body flavor-violating
Higgs decays in this context.


title:
Fast iterative solution of the Bethe-Salpeter eigenvalue problem using
  low-rank and QTT tensor approximation

abstract:
  In this paper, we study and implement the structural iterative eigensolvers
for the large-scale eigenvalue problem in the Bethe-Salpeter equation (BSE)
based on the reduced basis approach via low-rank factorizations in generating
matrices, introduced in the previous paper. The approach reduces numerical
costs down to $\mathcal{O}(N_b^2)$ in the size of atomic orbitals basis set,
$N_b$, instead of practically intractable $\mathcal{O}(N_b^6)$ complexity
scaling for the direct diagonalization of the BSE matrix. As an alternative to
rank approximation of the static screen interaction part of the BSE matrix, we
propose to restrict it to a small active sub-block, with a size balancing the
storage for rank-structured representations of other matrix blocks. We
demonstrate that the enhanced reduced-block approximation exhibits higher
precision within the controlled numerical cost, providing as well a distinct
two-sided error estimate for the BSE eigenvalues. It is shown that further
reduction of the asymptotic computational cost is possible due to ALS-type
iteration in block tensor train (TT) format applied to the quantized-TT (QTT)
tensor representation of both long eigenvectors and rank-structured matrix
blocks. The QTT-rank of these entities possesses almost the same magnitude as
the number of occupied orbitals in the molecular systems, $N_o$, hence the
overall asymptotic complexity for solving the BSE problem can be estimated by
$\mathcal{O}(\log(N_o) N_o^{2})$. We confirm numerically a considerable
decrease in computational time for the presented iterative approach applied to
various compact and chain-type molecules, while supporting sufficient accuracy.


title: The NS limit of the 5D Superconformal Index

abstract:
  We consider the Nekrasov-Shatashvili (NS) limit of the five-dimensional
superconformal index and propose a novel prescription for selecting the finite
contributions. Applying the latter to various examples of U(1) theories, we
find that the 5D NS index can be reproduced using recent techniques of
C\'ordova and Shao, who related the 4D Schur index to the BPS spectrum of the
theory on the Coulomb branch. In this picture, the 5D instanton solitons are
interpreted as additional flavour nodes in an associated 5D BPS quiver.


title: Coding in the fork network in the framework of Kolmogorov complexity

abstract:
  Many statements from the classic information theory (the theory of Shannon's
entropy) have natural counterparts in the algorithmic information theory (in
the framework of Kolmogorov complexity). In this paper we discuss one simple
instance of the parallelism between Shannon's and Kolmogorov's theories: we
prove in the setting of Kolmogorov complexity a version of Wolf's
characterization of admissible rates for the fork network.


title:
Tight-binding theory of NMR shifts in topological insulators Bi2Se3 and
  Bi2Te3

abstract:
  Motivated by recent nuclear magnetic resonance (NMR) experiments, we present
a microscopic sp3 tight-binding model calculation of the NMR shifts in bulk
Bi2Se3, and Bi2Te3. We compute the contact, dipolar, orbital and core
polarization contributions to the carrier-density-dependent part of the NMR
shifts in Bi209, Te125 and Se77. The spin-orbit coupling and the layered
crystal structure result in a contact Knight shift with strong uniaxial
anisotropy. Likewise, because of spin-orbit coupling, dipolar interactions make
a significant contribution to the isotropic part of the NMR shift. The contact
interaction dominates the isotropic Knight shift in Bi209 NMR, even though the
electronic states at the Fermi level have a rather weak s-orbital character. In
contrast, the contribution from the contact hyperfine interaction to the NMR
shift of Se77 and Te125 is weak compared to the dipolar and orbital shifts
therein. In all cases, the orbital shift is at least comparable to the contact
and dipolar shifts, while the shift due to core polarization is subdominant
(except for Te nuclei located at the inversion centers). By artificially
varying the strength of spin-orbit coupling, we evaluate the evolution of the
NMR shift across a band inversion but find no clear signature of the
topological transition.


title: Josephson traveling-wave parametric amplifier with three-wave mixing

abstract:
  We develop a concept of the traveling-wave Josephson parametric amplifier
exploiting quadratic nonlinearity of a serial array of one-junction SQUIDs
embedded in a superconducting transmission line. The external magnetic flux
applied to the SQUIDs makes it possible to efficiently control the shape of
their current-phase relation and, hence, the balance between quadratic and
cubic (Kerr-like) nonlinearities. This property allows us to operate in the
favorable three-wave-mixing mode with minimal phase mismatch, an exponential
dependence of the power gain on number of sections $N$, a large bandwidth, a
high dynamic range, and substantially separated signal ($f_s$) and pump ($f_p$)
frequencies obeying relation $f_s+f_i = f_p$, where $f_i$ is the idler
frequency. An estimation of the amplifier characteristics with typical
experimental parameters, a pump frequency of $12$ GHz, and $N = 300$ yields a
flat gain of 20 dB in the bandwidth of 5.6 GHz.


title: Automatic Face Reenactment

abstract:
  We propose an image-based, facial reenactment system that replaces the face
of an actor in an existing target video with the face of a user from a source
video, while preserving the original target performance. Our system is fully
automatic and does not require a database of source expressions. Instead, it is
able to produce convincing reenactment results from a short source video
captured with an off-the-shelf camera, such as a webcam, where the user
performs arbitrary facial gestures. Our reenactment pipeline is conceived as
part image retrieval and part face transfer: The image retrieval is based on
temporal clustering of target frames and a novel image matching metric that
combines appearance and motion to select candidate frames from the source
video, while the face transfer uses a 2D warping strategy that preserves the
user's identity. Our system excels in simplicity as it does not rely on a 3D
face model, it is robust under head motion and does not require the source and
target performance to be similar. We show convincing reenactment results for
videos that we recorded ourselves and for low-quality footage taken from the
Internet.


title: Instabilities and Solitons in Minimal Strips

abstract:
  We show that highly twisted minimal strips can undergo a non-singular
transition, unlike the singular transitions seen in the M\"obius strip and the
catenoid. If the strip is non-orientable this transition is topologically
frustrated, and the resulting surface contains a helical defect. Through a
controlled analytic approximation the system can be mapped onto a scalar
$\phi^4$ theory on a non-orientable line bundle over the circle, where the
defect becomes a topologically protected kink soliton or domain wall, thus
establishing their existence in minimal surfaces. Experimental studies of soap
films confirm these results and demonstrate how the position of the defect can
be controlled through boundary deformation.


title: BMS in Cosmology

abstract:
  Symmetries play an interesting role in cosmology. They are useful in
characterizing the cosmological perturbations generated during inflation and
lead to consistency relations involving the soft limit of the statistical
correlators of large-scale structure dark matter and galaxies overdensities. On
the other hand, in observational cosmology the carriers of the information
about these large-scale statistical distributions are light rays traveling on
null geodesics. Motivated by this simple consideration, we study the structure
of null infinity and the associated BMS symmetry in a cosmological setting. For
decelerating Friedmann-Robertson-Walker backgrounds, for which future null
infinity exists, we find that the BMS transformations which leaves the
asymptotic metric invariant to leading order. Contrary to the asymptotic flat
case, the BMS transformations in cosmology generate Goldstone modes
corresponding to both scalar and tensor degrees of freedom which may exist at
null infinity and perturb the asymptotic data. Therefore, BMS transformations
generate physically inequivalent vacua as they populate the universe at null
infinity with these physical degrees of freedom. We also discuss the
gravitational memory effect when cosmological expansion is taken into account.
In this case, there are extra contribution to the gravitational memory due to
the tail of the retarded Green functions which are supported not only on the
light-cone, but also in its interior. The gravitational memory effect can be
understood also from an asymptotic point of view as a transition among
cosmological BMS-related vacua.


title: A remark on fullness of some group measure space von Neumann algebras

abstract:
  Recently C. Houdayer and Y. Isono have proved among other things that every
biexact group $\Gamma$ has the property that for any non-singular strongly
ergodic action $\Gamma\curvearrowright (X,\mu)$ on a standard measure space the
group measure space von Neumann algebra $\Gamma\ltimes L^\infty(X)$ is full. In
this note, we prove the same property for a wider class of groups, notably
including $\mathrm{SL}(3,{\mathbb Z})$. We also prove that for any connected
simple Lie group $G$ with finite center, any lattice $\Gamma\le G$, and any
closed non-amenable subgroup $H\le G$, the non-singular action
$\Gamma\curvearrowright G/H$ is strongly ergodic and the von Neumann factor
$\Gamma\ltimes L^\infty(G/H)$ is full.


title:
Optimisation of Simulations of Stochastic Processes by Removal of
  Opposing Reactions

abstract:
  Models invoking the chemical master equation are used in many areas of
science, and, hence, their simulation is of interest to many researchers. The
complexity of the problems at hand often requires considerable computational
power, so a large number of algorithms have been developed to speed up
simulations. However, a drawback of many of these algorithms is that their
implementation is more complicated than, for instance, the Gillespie algorithm,
which is widely used to simulate the chemical master equation, and can be
implemented with a few lines of code. Here, we present an algorithm which does
not modify the way in which the master equation is solved, but instead modifies
the transition rates, and can thus be implemented with a few lines of code. It
works for all models in which reversible reactions occur by replacing such
reversible reactions with effective net reactions. Examples of such systems
include reaction-diffusion systems, in which diffusion is modelled by a random
walk. The random movement of particles between neighbouring sites is then
replaced with a net random flux. Furthermore, as we modify the transition rates
of the model, rather than its implementation on a computer, our method can be
combined with existing algorithms that were designed to speed up simulations of
the stochastic master equation. By focusing on some specific models, we show
how our algorithm can significantly speed up model simulations while
maintaining essential features of the original model.

categories: physics.bio-ph physics.chem-ph physics.comp-ph q-bio.QM


title:
LSTM Deep Neural Networks Postfiltering for Improving the Quality of
  Synthetic Voices

abstract:
  Recent developments in speech synthesis have produced systems capable of
outcome intelligible speech, but now researchers strive to create models that
more accurately mimic human voices. One such development is the incorporation
of multiple linguistic styles in various languages and accents.
  HMM-based Speech Synthesis is of great interest to many researchers, due to
its ability to produce sophisticated features with small footprint. Despite
such progress, its quality has not yet reached the level of the predominant
unit-selection approaches that choose and concatenate recordings of real
speech. Recent efforts have been made in the direction of improving these
systems.
  In this paper we present the application of Long-Short Term Memory Deep
Neural Networks as a Postfiltering step of HMM-based speech synthesis, in order
to obtain closer spectral characteristics to those of natural speech. The
results show how HMM-voices could be improved using this approach.


title:
Floquet engineering of correlated tunneling in the Bose-Hubbard model
  with ultracold atoms

abstract:
  We report on the experimental implementation of tunable occupation-dependent
tunneling in a Bose-Hubbard system of ultracold atoms via time-periodic
modulation of the on-site interaction energy. The tunneling rate is inferred
from a time-resolved measurement of the lattice site occupation after a quantum
quench. We demonstrate coherent control of the tunneling dynamics in the
correlated many-body system, including full suppression of tunneling as
predicted within the framework of Floquet theory. We find that the tunneling
rate explicitly depends on the atom number difference in neighboring lattice
sites. Our results may open up ways to realize artificial gauge fields that
feature density dependence with ultracold atoms.


title: Graying the black box: Understanding DQNs

abstract:
  In recent years there is a growing interest in using deep representations for
reinforcement learning. In this paper, we present a methodology and tools to
analyze Deep Q-networks (DQNs) in a non-blind matter. Moreover, we propose a
new model, the Semi Aggregated Markov Decision Process (SAMDP), and an
algorithm that learns it automatically. The SAMDP model allows us to identify
spatio-temporal abstractions directly from features and may be used as a
sub-goal detector in future work. Using our tools we reveal that the features
learned by DQNs aggregate the state space in a hierarchical fashion, explaining
its success. Moreover, we are able to understand and describe the policies
learned by DQNs for three different Atari2600 games and suggest ways to
interpret, debug and optimize deep neural networks in reinforcement learning.


title: Isolated elliptic fixed points for smooth Hamiltonians

abstract:
  We construct on $\R^{2d}$, for any $d \geq 3$, smooth Hamiltonians having an
elliptic equilibrium with an arbitrary frequency, that is not accumulated by a
positive measure set of invariant tori. For $d\geq 4$, the Hamiltonians we
construct have not any invariant torus of dimension $d$. Our examples are
obtained by a version of the successive conjugation scheme {\it \`a la}
Anosov-Katok.


title: Exploiting Cyclic Symmetry in Convolutional Neural Networks

abstract:
  Many classes of images exhibit rotational symmetry. Convolutional neural
networks are sometimes trained using data augmentation to exploit this, but
they are still required to learn the rotation equivariance properties from the
data. Encoding these properties into the network architecture, as we are
already used to doing for translation equivariance by using convolutional
layers, could result in a more efficient use of the parameter budget by
relieving the model from learning them. We introduce four operations which can
be inserted into neural network models as layers, and which can be combined to
make these models partially equivariant to rotations. They also enable
parameter sharing across different orientations. We evaluate the effect of
these architectural modifications on three datasets which exhibit rotational
symmetry and demonstrate improved performance with smaller models.


title:
Spectral representations of normal operators via Intertwining
  Quaternionic Projection Valued Measures

abstract:
  The possibility of formulating quantum mechanics over quaternionic Hilbert
spaces can be traced back to von Neumann's foundational works in the thirties.
The absence of a suitable quaternionic version of spectrum prevented the full
development of the theory. The first rigorous quaternionic formulation has been
started only in 2007 with the definition of the spherical spectrum of a
quaternionic operator based on a quadratic version of resolvent operator. The
relevance of this notion is proved by the existence of a quaternionic
continuous functional calculus and a theory of quaternionic semigroups relying
upon it. A problem of quaternionic formulation is the description of composite
quantum systems in absence of a natural tensor product due to non-commutativity
of quaternions. A promising tool towards a solution is a quaternionic
projection-valued measure (PVM), making possible a tensor product of
quaternionic operators with physical relevance. A notion with this property,
called intertwining quaternionic PVM, is presented here. This foundational
paper aims to investigate the interplay of this new mathematical object and the
spherical spectral features of quaternionic generally unbounded normal
operators. We discover in particular the existence of other spectral notions
equivalent to the spherical ones, but based on a standard non-quadratic notion
of resolvent operator.

categories: math.FA hep-th math-ph math.CV math.MP math.OA


title: Planar Para Algebras, Reflection Positivity

abstract:
  We define a planar para algebra, which arises naturally from combining planar
algebras with the idea of $\mathbb{Z}_{N}$ para symmetry in physics. A
subfactor planar para algebra is a Hilbert space representation of planar
tangles with parafermionic defects, that are invariant under para isotopy. For
each $\mathbb{Z}_{N}$, we construct a family of subfactor planar para algebras
which play the role of Temperley-Lieb-Jones planar algebras. The first example
in this family is the parafermion planar para algebra (PAPPA). Based on this
example, we introduce parafermion Pauli matrices, quaternion relations, and
braided relations for parafermion algebras which one can use in the study of
quantum information. An important ingredient in planar para algebra theory is
the string Fourier transform (SFT), that we use on the matrix algebra generated
by the Pauli matrices. Two different reflections play an important role in the
theory of planar para algebras. One is the adjoint operator; the other is the
modular conjugation in Tomita-Takesaki theory. We use the latter one to define
the double algebra and to introduce reflection positivity. We give a new and
geometric proof of reflection positivity, by relating the two reflections
through the string Fourier transform.

categories: math.QA cond-mat.mes-hall hep-th math-ph math.MP math.OA


title: A stellar model with diffusion in general relativity

abstract:
  We consider a spherically symmetric stellar model in general relativity whose
interior consists of a pressureless fluid undergoing microscopic velocity
diffusion in a cosmological scalar field. We show that the diffusion dynamics
compel the interior to be spatially homogeneous, by which one can infer
immediately that within our model, and in contrast to the diffusion-free case,
no naked singularities can form in the gravitational collapse. We then study
the problem of matching an exterior Bondi type metric to the surface of the
star and find that the exterior can be chosen to be a modified Vaidya metric
with variable cosmological constant. Finally, we study in detail the causal
structure of an explicit, self-similar solution.


title:
A convolution formula for Tutte polynomials of arithmetic matroids and
  other combinatorial structures

abstract:
  In this note we generalize the convolution formula for the Tutte polynomial
of Kook-Reiner-Stanton and Etienne-Las Vergnas to a more general setting that
includes both arithmetic matroids and delta-matroids. As corollaries, we obtain
new proofs of two positivity results for pseudo-arithmetic matroids and a
combinatorial interpretation of the arithmetic Tutte polynomial at infinitely
many points in terms of arithmetic flows and colorings. We also exhibit
connections with a decomposition of Dahmen-Micchelli spaces and lattice point
counting in zonotopes.


title: The happiness paradox: your friends are happier than you

abstract:
  Most individuals in social networks experience a so-called Friendship
Paradox: they are less popular than their friends on average. This effect may
explain recent findings that widespread social network media use leads to
reduced happiness. However the relation between popularity and happiness is
poorly understood. A Friendship paradox does not necessarily imply a Happiness
paradox where most individuals are less happy than their friends. Here we
report the first direct observation of a significant Happiness Paradox in a
large-scale online social network of $39,110$ Twitter users. Our results reveal
that popular individuals are indeed happier and that a majority of individuals
experience a significant Happiness paradox. The magnitude of the latter effect
is shaped by complex interactions between individual popularity, happiness, and
the fact that users cluster assortatively by level of happiness. Our results
indicate that the topology of online social networks and the distribution of
happiness in some populations can cause widespread psycho-social effects that
affect the well-being of billions of individuals.


title: A Variational Analysis of Stochastic Gradient Algorithms

abstract:
  Stochastic Gradient Descent (SGD) is an important algorithm in machine
learning. With constant learning rates, it is a stochastic process that, after
an initial phase of convergence, generates samples from a stationary
distribution. We show that SGD with constant rates can be effectively used as
an approximate posterior inference algorithm for probabilistic modeling.
Specifically, we show how to adjust the tuning parameters of SGD such as to
match the resulting stationary distribution to the posterior. This analysis
rests on interpreting SGD as a continuous-time stochastic process and then
minimizing the Kullback-Leibler divergence between its stationary distribution
and the target posterior. (This is in the spirit of variational inference.) In
more detail, we model SGD as a multivariate Ornstein-Uhlenbeck process and then
use properties of this process to derive the optimal parameters. This
theoretical framework also connects SGD to modern scalable inference
algorithms; we analyze the recently proposed stochastic gradient Fisher scoring
under this perspective. We demonstrate that SGD with properly chosen constant
rates gives a new way to optimize hyperparameters in probabilistic models.


title:
Model and Set-Theoretic Aspects of Exotic Smoothness Structures on
  $\mathbb{R}^4$

abstract:
  Model-theoretic aspects of exotic smoothness were studied long ago uncovering
unexpected relations to noncommutative spaces and quantum theory. Some of these
relations were worked out in detail in later work. An important point in the
argumentation was the forcing construction of Cohen but without a direct
application to exotic smoothness. In this article we assign the set-theoretic
forcing on trees to Casson handles and characterize small exotic smooth $R^4$
from this point of view. Moreover, we show how models in some Grothendieck
toposes can help describing such differential structures in dimension 4. These
results can be used to obtain the deformation of the algebra of usual complex
functions to the noncommutative algebra of operators on a Hilbert space. We
also discuss the results in the context of the Epstein-Glaser renormalization
in QFT.


title:
Incommensurate crystal supercell and polarization-flop observed in the
  magnetoelectric ilmenite, MnTiO3

abstract:
  MnTiO3 has been studied for many decades, but it was only in the last few
years that its strong magnetoelectric behavior had been observed. Here, we use
neutron scattering on two separately grown single crystals and two powder
samples to show the presence of a supercell that breaks R-3 symmetry. We also
present the temperature and field dependence of the dielectric constant and
pyroelectric current, and show evidence of non-zero off-diagonal
magnetoelectric tensor elements (forbidden by R-3 symmetry) followed by a
polarization flop accompanying the spin flop transition at {\mu}0HSF = 6.5 T.
M\"ossbauer spectroscopy on MnTiO3 gently doped with 57Fe was used to help shed
light on the impact of the supercell on the observed behavior. Although the
full supercell structure could not be solved at this time due to a lack of
visible reflections, the full-scope of the results presented here suggest that
the role of local spin-lattice coupling in the magnetoelectric properties of
MnTiO3 is likely more important than previously thought.


title:
A note on the possibility of roughness enhancement of adhesion in
  Persson's theory

abstract:
  In an attempt to model the observed enhancement of adhesion in some classical
experiments in the 1970-1980's, Persson introduced in his theory of adhesion
between rough solids a term which corresponds to an area increase due to
roughness. In the old experiments, the adhesion enhancement was shown to be up
to one order of magnitude, whereas the area increase could not be defined
quantitatively because of possibly multiscale roughness. However, in more
recent studies by Guduru and collaborators, this enhancement has been further
explained with classical Linear Elastic Fracture Mechanics theory, the area
enhancement has been shown to be negligible, and therefore the problem of
adhesion of rough surfaces remains qualitatively and quantitatively unsolved by
Persson's theory.


title:
Model and Objective Separation with Conditional Lower Bounds:
  Disjunction is Harder than Conjunction

abstract:
  Given a model of a system and an objective, the model-checking question asks
whether the model satisfies the objective. We study polynomial-time problems in
two classical models, graphs and Markov Decision Processes (MDPs), with respect
to several fundamental $\omega$-regular objectives, e.g., Rabin and Streett
objectives. For many of these problems the best-known upper bounds are
quadratic or cubic, yet no super-linear lower bounds are known. In this work
our contributions are two-fold: First, we present several improved algorithms,
and second, we present the first conditional super-linear lower bounds based on
widely believed assumptions about the complexity of CNF-SAT and combinatorial
Boolean matrix multiplication. A separation result for two models with respect
to an objective means a conditional lower bound for one model that is strictly
higher than the existing upper bound for the other model, and similarly for two
objectives with respect to a model. Our results establish the following
separation results: (1) A separation of models (graphs and MDPs) for
disjunctive queries of reachability and B\"uchi objectives. (2) Two kinds of
separations of objectives, both for graphs and MDPs, namely, (2a) the
separation of dual objectives such as reachability/safety (for disjunctive
questions) and Streett/Rabin objectives, and (2b) the separation of conjunction
and disjunction of multiple objectives of the same type such as safety,
B\"uchi, and coB\"uchi. In summary, our results establish the first model and
objective separation results for graphs and MDPs for various classical
$\omega$-regular objectives. Quite strikingly, we establish conditional lower
bounds for the disjunction of objectives that are strictly higher than the
existing upper bounds for the conjunction of the same objectives.


title: Qudit Isotopy

abstract:
  We explore a general diagrammatic framework to understand qudits and their
braiding, especially in its relation to entanglement. This involves
understanding the role of isotopy in interpreting diagrams that implement
entangling gates as well as some standard quantum information protocols. We
give qudit Pauli operators $X,Y,Z$ and comment on their structure, both from an
algebraic and from a diagrammatic point of view. We explain alternative models
for diagrammatic interpretations of qudits and their transformations. We use
our diagrammatic approach to define an entanglement-relay protocol for
long-distance entanglement. Our approach rests on algebraic and topological
relations discovered in the study of planar para algebras. In summary, this
work provides bridges between the new theory of planar para algebras and
quantum information, especially in questions involving entanglement.

categories: quant-ph cond-mat.mes-hall math-ph math.MP math.OA math.QA


title:
Learning to Communicate to Solve Riddles with Deep Distributed Recurrent
  Q-Networks

abstract:
  We propose deep distributed recurrent Q-networks (DDRQN), which enable teams
of agents to learn to solve communication-based coordination tasks. In these
tasks, the agents are not given any pre-designed communication protocol.
Therefore, in order to successfully communicate, they must first automatically
develop and agree upon their own communication protocol. We present empirical
results on two multi-agent learning problems based on well-known riddles,
demonstrating that DDRQN can successfully solve such tasks and discover elegant
communication protocols to do so. To our knowledge, this is the first time deep
reinforcement learning has succeeded in learning communication protocols. In
addition, we present ablation experiments that confirm that each of the main
components of the DDRQN architecture are critical to its success.


title: On Sparsity by NUV-EM, Gaussian Message Passing, and Kalman Smoothing

abstract:
  Normal priors with unknown variance (NUV) have long been known to promote
sparsity and to blend well with parameter learning by expectation maximization
(EM). In this paper, we advocate this approach for linear state space models
for applications such as the estimation of impulsive signals, the detection of
localized events, smoothing with occasional jumps in the state space, and the
detection and removal of outliers. The actual computations boil down to
multivariate-Gaussian message passing algorithms that are closely related to
Kalman smoothing. We give improved tables of Gaussian-message computations from
which such algorithms are easily synthesized, and we point out two preferred
such algorithms.


title:
SDSS-II Supernova Survey: An Analysis of the Largest Sample of Type Ia
  Supernovae and Correlations with Host-Galaxy Spectral Properties

abstract:
  Using the largest single-survey sample of Type Ia supernovae (SNe Ia) to
date, we study the relationship between properties of SNe Ia and those of their
host galaxies, focusing primarily on correlations with Hubble residuals (HR).
Our sample consists of 345 photometrically-classified or
spectroscopically-confirmed SNeIa discovered as part of the SDSS-II Supernova
Survey (SDSS-SNS). This analysis utilizes host-galaxy spectroscopy obtained
during the SDSS-I/II spectroscopic survey and from an ancillary program on the
SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) that obtained spectra
for nearly all host galaxies of SDSS-II SN candidates. In addition, we use
photometric host-galaxy properties from the SDSS-SNS data release (Sako et al.
2014) such as host stellar mass and star-formation rate. We confirm the
well-known relation between HR and host-galaxy mass and find a 3.6{\sigma}
significance of a non-zero linear slope. We also recover correlations between
HR and host-galaxy gas-phase metallicity and specific star-formation rate as
they are reported in the literature. With our large dataset, we examine
correlations between HR and multiple host-galaxy properties simultaneously and
find no evidence of a significant correlation. We also independently analyze
our spectroscopically-confirmed and photometrically-classified SNe Ia and
comment on the significance of similar combined datasets for future surveys.


title:
Performance of 1-D and 2-D Lattice Boltzmann (LB) in Solution of the
  Shock Tube Problem

abstract:
  In this paper we presented a lattice Boltzmann with square grid for
compressible flow problems. Triple level velocity is considered for each cell.
Migration step use discrete velocity but continuous parameters are utilized to
calculate density, velocity, and energy. So, we called this semi-discrete
method. To evaluate the performance of the method the well-known shock tube
problem is solved, using 1-D and 2-D version of the lattice Boltzmann method.
The results of these versions are compared with each other and with the results
of the analytical solution.


title:
Numerical calculation of the relativistic acceleration of an electron in
  curved spacetime using the Dirac equation

abstract:
  The relativistic acceleration of an electron in a uniform gravitational field
is calculated numerically using the generalization of the Dirac equation to
curved spacetime. Equivalent results are also obtained analytically using an
iterative approach that is not based on the WKB approximation, which has been
used extensively in the past. The acceleration is found to be proportional to a
factor of $(1-3v^2/c^2)$ using Schwarzschild coordinates, which is consistent
with the classical geodesic of a particle. These techniques may be useful in
resolving the differences between commonly-used approximations.


title:
Internal energy of the classical two- and three-dimensional
  one-component-plasma

abstract:
  We summarize several semi-phenomenological approaches to estimate the
internal energy of one-component-plasma (OCP) in two (2D) and three (3D)
dimensions. Particular attention is given to a hybrid approach, which
reproduces the Debye-H$\ddot{\text{u}}$ckel asymptote in the limit of weak
coupling, the ion sphere (3D) and ion disc (2D) asymptotes in the limit of
strong coupling, and provides reasonable interpolation between these two
limits. More accurate ways to estimate the internal energy of 2D and 3D OCP are
also discussed. The accuracy of these analytic results is quantified by
comparison with existing data from numerical simulations. The relevance of the
KTHNY theory in locating melting transition in 2D OCP is briefly discussed.


title:
Additional Information on Heavy Quark Parameters from Charged Lepton
  Forward-Backward Asymmetry

abstract:
  The determination of $|V_{cb}|$ using inclusive and exclusive (semi-)leptonic
decays exhibits a long-standing tension of varying ${\cal O}(3 \sigma)$
significance. For the inclusive determination the decay rate is expanded in
$1/m_b$ using heavy quark expansion, and from moments of physical observables
the higher order heavy quark parameters are extracted from experimental data in
order to assess $|V_{cb}|$ from the normalisation. The drawbacks are high
correlations both theoretically as well as experimentally among these
observables. We will scrutinise the inclusive determination in order to add a
new and less correlated observable. This observable is related to the decay
angle of the charged lepton and can help to constrain the important heavy quark
parameters in a new way. It may validate the current seemingly stable
extraction of $|V_{cb}|$ from inclusive decays or hints to possible issues, and
even may be sensitive to New Physics operators.


title:
Hysteretic magnetoresistance and unconventional anomalous Hall effect in
  the frustrated magnet TmB_4

abstract:
  We study TmB_4, a frustrated magnet on the Archimedean Shastry-Sutherland
lattice, through magnetization and transport experiments. The lack of
anisotropy in resistivity shows that TmB_4 is an electronically
three-dimensional system. The magnetoresistance (MR) is hysteretic at
low-temperature even though a corresponding hysteresis in magnetization is
absent. The Hall resistivity shows unconventional anomalous Hall effect (AHE)
and is linear above saturation despite a large MR. We propose that complex
structures at magnetic domain walls may be responsible for the hysteretic MR
and may also lead to the AHE.


title: Numerical Solution of Cylindrically Converging Shock Waves

abstract:
  The cylindrically converging shock wave was numerically simulated by solving
the Euler equations in cylindrical coordinates with TVD scheme and MUSCL
approach, using Roe's approximate Riemann solver and super-bee nonlinear
limiter. The present study used the in house code developed for this purpose.
The behavior of the solution in the vicinity of axis is investigated and the
results of the numerical solution are compared with the computed data given by
Payne, Lapidus, Abarbanel, and Goldberg, Sod, and Leutioff et al.


title: Macdonald's solid-angle sum for real dilations of rational polygons

abstract:
  The solid-angle sum $A_{\mathcal{P}} (t)$ of a rational polytope
${\mathcal{P}} \subset \mathbb{R}^d$, with $t \in \mathbb{Z}$ was first
investigated by I.G. Macdonald. Using our Fourier-analytic methods, we are able
to establish an explicit formula for $A_{\mathcal{P}} (t)$, for any real
dilation $t$ and any rational polygon ${\mathcal{P}} \subset \mathbb{R}^2$. Our
formulation sheds additional light on previous results, for lattice-point
enumerating functions of triangles, which are usually confined to the case of
integer dilations. Our approach differs from that of Hardy and Littlewood in
1992, but offers an alternate point of view for enumerating weighted lattice
points in real dilations of real triangles.


title:
Layer-dependent anisotropic electronic structure of freestanding
  quasi-two-dimensional MoS$_2$

abstract:
  The anisotropy of the electronic transition is a well-known characteristic of
low-dimensional transition-metal dichalcogenides, but their layer-thickness
dependence has not been properly in- vestigated experimentally until now. Yet,
it not only determines the optical properties of these low-dimensional
materials, but also holds the key in revealing the underlying character of the
elec- tronic states involved. Here we used both angle-resolved electron
energy-loss spectroscopy and spectral analysis of angle-integrated spectra to
study the evolution of the anisotropic electronic transition involving the low
energy valence electrons in the freestanding MoS$_2$ layers with different
thicknesses. We are able to demonstrate that the well-known direct gap at 1.8
eV is only excited by the in-plane polarized field while the out-of-plane
polarized optical gap is 2.4$\pm$0.2 eV in monolayer MoS$_2$. This contrasts
with the much smaller anisotropic response found for the indirect gap in the
few-layer MoS$_2$ systems. In addition, we determined that the joint density of
states associated with the indirect gap transition in the multilayer systems
and the corresponding indirect transition in the monolayer case has a
characteristic three-dimensional-like character. We attribute this to the
soft-edge behavior of the confining potential and it is an important factor
when considering the dynamical screening of the electric field at the relevant
excitation energies. Our result provides a logical explanation, for the large
sensitivity of the indirect transition to thickness variation compared with
that for the direct transition, in terms of quantum confinement.


title:
Measurements of Cylindrical Ice Crystal Growth Limited by Combined
  Particle and Heat Diffusion

abstract:
  We present measurements of the growth of long columnar ice crystals from
water vapor over a broad range of temperatures and supersaturation levels in
air. Starting with thin, c-axis ice needle crystals, we observed their
subsequent growth behavior in a vapor diffusion chamber, extracting the initial
radial growth velocities of the needles under controlled conditions.
Approximating the hexagonal needle crystals as infinitely long cylinders, we
created an analytical growth model that includes effects from particle
diffusion of water molecules through the surrounding air along with the
diffusion of heat generated by solidification. With only minimal adjustment of
model parameters, we obtained excellent agreement with our experimental data.
To our knowledge, this is the first time that the combined effects from
particle and heat diffusion have been measured in ice growth from water vapor.
This analysis further provides an accurate method for calibration of the
water-vapor supersaturation levels in experimental growth chambers.


title: Leptogenesis in supersymmetry with one $L$ violating coupling

abstract:
  We have shown a new scenario of successful leptogenesis with one $L$
violating coupling and a relative Majorana phase playing the role of $CP$
violation. This is in contrast to the usual consideration of Feynman diagram
with at least two $L$ violating couplings. We have considered $R$-parity
violating Minimal Supersymmetric Standard Model (MSSM) for leptogenesis at TeV
scale. This scenario is also consistent with generating light neutrino mass if
asymmetry is generated through semileptonic $\lambda^{\prime}$ coupling.


title:
Predicting Clinical Events by Combining Static and Dynamic Information
  Using Recurrent Neural Networks

abstract:
  In clinical data sets we often find static information (e.g. patient gender,
blood type, etc.) combined with sequences of data that are recorded during
multiple hospital visits (e.g. medications prescribed, tests performed, etc.).
Recurrent Neural Networks (RNNs) have proven to be very successful for
modelling sequences of data in many areas of Machine Learning. In this work we
present an approach based on RNNs, specifically designed for the clinical
domain, that combines static and dynamic information in order to predict future
events. We work with a database collected in the Charit\'{e} Hospital in Berlin
that contains complete information concerning patients that underwent a kidney
transplantation. After the transplantation three main endpoints can occur:
rejection of the kidney, loss of the kidney and death of the patient. Our goal
is to predict, based on information recorded in the Electronic Health Record of
each patient, whether any of those endpoints will occur within the next six or
twelve months after each visit to the clinic. We compared different types of
RNNs that we developed for this work, with a model based on a Feedforward
Neural Network and a Logistic Regression model. We found that the RNN that we
developed based on Gated Recurrent Units provides the best performance for this
task. We also used the same models for a second task, i.e., next event
prediction, and found that here the model based on a Feedforward Neural Network
outperformed the other models. Our hypothesis is that long-term dependencies
are not as relevant in this task.


title:
Structure and Composition of the 200 K-Superconducting Phase of H2S
  under Ultrahigh Pressure: The Perovskite (SH-)(H3S+)

abstract:
  H2S is converted under ultrahigh pressure (> 110 GPa) to a metallic phase
that becomes superconducting with a record Tc of 200 K. It has been proposed
that the superconducting phase is body-centered cubic H3S ( Im3m , a = 3.089
{\AA}) resulting from a decomposition reaction 3H2S --> 2H3S + S. The analogy
of H2S and H2O leads us to a very different conclusion. The well-known
dissociation of water into H3O+ and OH- increases by orders of magnitude under
pressure. An equivalent behavior of H2S is anticipated under pressure with the
dissociation, 2H2S --> H3S+ + SH- forming a perovskite structure (SH-)(H3S+),
which consists of corner-sharing SH6 octahedra with SH- at each A-site (i.e.,
the center of each S8 cube). Our DFT calculations show that the perovskite
(SH-)(H3S+) is thermodynamically more stable than the Im3m structure of H3S,
and suggest that the A-site H atoms are most likely fluxional even at Tc.


title: Modified Brans-Dicke cosmology with matter-scalar field interaction

abstract:
  We discuss the cosmological implications of an extended Brans-Dicke theory
presented recently, in which there is an energy exchange between the scalar
field and ordinary matter, determined by the theory. A new mass scale is
generated in the theory which modifies the Friedmann equations with
field-dependent corrected kinetic terms. In a radiation universe the general
solutions are found and there are branches with complete removal of the initial
singularity, while at the same time a transient accelerating period can occur
within deceleration. Entropy production is also possible in the early universe.
In the dust era, late-times acceleration has been found numerically in
agreement with the correct behaviour of the density parameters and the dark
energy equation of state, while the gravitational constant has only a slight
variation over a large redshift interval in agreement with observational
bounds.


title:
A note on the $R_\infty$ property for groups $\mathrm{FAlt}(X)\leqslant
  G\leqslant \mathrm{Sym}(X)$

abstract:
  Given a set $X$, the group $\mathrm{Sym}(X)$ consists of all bijections from
$X$ to $X$, and $\mathrm{FSym}(X)$ is the subgroup of maps with finite support
i.e. those that move only finitely many points in $X$. We describe the
automorphism structure of groups $\mathrm{FSym}(X)\le G\le \mathrm{Sym}(X)$ and
use this to state some conditions on $G$ for it to have the $R_\infty$
property. Our main results are that if $G$ is infinite, torsion, and
$\mathrm{FSym}(X)\le G\le \mathrm{Sym}(X)$, then it has the $R_\infty$
property. Also, if $G$ is infinite and residually finite, then there is a set
$X$ such that $G$ acts faithfully on $X$ and, using this action, $\langle G,
\mathrm{FSym}(X)\rangle$ has the $R_\infty$ property. Finally we have a result
for the Houghton groups, which are a family of groups we denote $H_n$, where $n
\in \mathbb{N}$. We show that, given any $n\in \mathbb{N}$, any group
commensurable to $H_n$ has the $R_\infty$ property.


title:
Systematic Uncertainties in RF-Based Measurement of Superconducting
  Cavity Quality Factors

abstract:
  Q0 determinations based on RF power measurements are subject to at least
three potentially large systematic effects that have not been previously
appreciated. Instrumental factors that can systematically bias RF based
measurements of Q0 are quantified and steps that can be taken to improve the
determination of Q0 are discussed.


title:
Robust Beamforming Against Direction-of-Arrival Mismatch Using
  Subspace-Constrained Diagonal Loading

abstract:
  In this study, a new subspace-constrained diagonal loading (SSC-DL) method is
presented for robust beamforming against the issue of a mismatched direction of
arrival (DoA), based on an extension to the well known diagonal loading (DL)
technique. One important difference of the proposed SSC-DL from conventional DL
is that it imposes an additional constraint to restrict the optimal weight
vector within a subspace whose basis vectors are determined by a number of
angles neighboring to the estimated DoA. Unlike many existing methods which
resort to a beamwidth expansion, the weight vector produced by SSC-DL has a
relatively small beamwidth around the DoA of the target signal. Yet, the SSC-DL
beamformer has a great interference suppression level, thereby achieving an
improved overall SINR performance. Simulation results suggest the proposed
method has a near-to-optimal SINR performance.


title: Symmetric exclusion processes on a ring with moving defects

abstract:
  We study symmetric simple exclusion processes (SSEP) on a ring in the
presence of uniformly moving multiple defects or disorders - a generalization
of the model proposed earlier [Phys. Rev. E 89, 022138 (2014)]. The defects
move with uniform velocity and change the particle hopping rates locally. We
explore the collective effects of the defects on the spatial structure and
transport properties of the system. We also introduce an SSEP with ordered
sequential (sitewise) update and elucidate the close connection with our model.


title:
Science on YouTube: What users find when they search for climate science
  and climate manipulation

abstract:
  Online video-sharing sites such as YouTube are very popular and also used by
a lot of people to obtain knowledge and information, also on science, health
and technology. Technically they could be valuable tools for the public
communication of science and technology, but the users of YouTube are also
confronted with conspiracy theories and erroneous and misleading information
that deviates from scientific consensus views. This contribution details the
results of a study that investigates what kind of information users find when
they are searching for climate science and climate manipulation topics on
YouTube and whether this information corresponds with or challenges scientific
consensus views. An innovative methodological approach using the anonymization
network Tor is introduced for drawing randomized samples of YouTube videos.
This approach was used to select and examine a sample of 140 YouTube videos on
climate topics.


title: Active colloids in complex fluids

abstract:
  We review recent work on active colloids or swimmers, such as self-propelled
microorganisms, phoretic colloidal particles, and artificial micro-robotic
systems, moving in fluid-like environments. These environments can be
water-like and Newtonian but can frequently contain macromolecules, flexible
polymers, soft cells, or hard particles, which impart complex, nonlinear
rheological features to the fluid. While significant progress has been made on
understanding how active colloids move and interact in Newtonian fluids, little
is known on how active colloids behave in complex and non-Newtonian fluids. An
emerging literature is starting to show how fluid rheology can dramatically
change the gaits and speeds of individual swimmers. Simultaneously, a moving
swimmer induces time dependent, three dimensional fluid flows, that can modify
the medium (fluid) rheological properties. This two-way, non-linear coupling at
microscopic scales has profound implications at meso- and macro-scales: steady
state suspension properties, emergent collective behavior, and transport of
passive tracer particles. Recent exciting theoretical results and current
debate on quantifying these complex active fluids highlight the need for
conceptually simple experiments to guide our understanding.


title:
WLS-ENO: Weighted-Least-Squares Based Essentially Non-Oscillatory
  Schemes for Finite Volume Methods on Unstructured Meshes

abstract:
  ENO (Essentially Non-Oscillatory) and WENO (Weighted Essentially
Non-Oscillatory) schemes are widely used high-order schemes for solving partial
differential equations (PDEs), especially hyperbolic conservation laws with
piecewise smooth solutions. For structured meshes, these techniques can achieve
high order accuracy for smooth functions while being non-oscillatory near
discontinuities. For unstructured meshes, which are needed for complex
geometries, similar schemes are required but they are much more challenging. We
propose a new family of non-oscillatory schemes, called WLS-ENO, in the context
of solving hyperbolic conservation laws using finite-volume methods over
unstructured meshes. WLS-ENO is derived based on Taylor series expansion and
solved using a weighted least squares formulation. Unlike other non-oscillatory
schemes, the WLS-ENO does not require constructing sub-stencils, and hence it
provides more flexible framework and is less sensitive to mesh quality. We
present rigorous analysis of the accuracy and stability of WLS-ENO, and present
numerical results in 1-D, 2-D, and 3-D for a number of benchmark problems, and
also report some comparisons against WENO.