title:
A Finite Element Approach for the Line-to-Line Contact Interaction of
  Thin Beams with Arbitrary Orientation

abstract:
  The objective of this work is the development of a novel finite element
formulation describing the contact interaction of slender beams in complex 3D
configurations involving arbitrary beam-to-beam orientations. It is shown in a
mathematically concise manner that standard beam contact models based on a
point-wise contact force fail to describe a considerable range of
configurations, which are, however, likely to occur in practical applications.
On the contrary, the formulation proposed here models beam-to-beam contact by
means of distributed line forces, a procedure that is shown to be applicable
for arbitrary geometrical configurations. The proposed formulation is based on
a Gauss-point-to-segment type contact discretization and a penalty
regularization of the contact constraint. By means of detailed theoretical and
numerical investigations, it is shown that this approach is more suitable for
beam contact than possible alternatives based on mortar type contact
discretizations or constraint enforcement by means of Lagrange multipliers. The
proposed formulation is enhanced by a consistently linearized integration
interval segmentation avoiding numerical integration across strong
discontinuities. In combination with a smoothed contact force law and the
employed C1-continuous beam elements, this procedure drastically reduces the
numerical integration error, an essential prerequisite for optimal spatial
convergence rates. The resulting line-to-line contact algorithm is supplemented
by contact contributions of the beam endpoints, which represent boundary minima
of the underlying minimal distance problem. Finally, a series of numerical test
cases is analyzed in order to investigate the accuracy and consistency of the
proposed formulation regarding integration error, spatial convergence behavior
and resulting contact force distributions.


title:
On Deterministic Attitude Observers on the Special Orthogonal Group
  SO(3)

abstract:
  We revisit the gradient based nonlinear attitude complementary filters
(observers) on the Special Orthogonal group SO(3) and provide explicit
solutions of the norm of the attitude estimation error dynamics. One smooth and
two non-smooth attitude observers are considered. The stability and performance
properties of theses attitude observers can be easily deduced from the obtained
explicit solutions. We show that the smooth complementary attitude filter,
previously proposed in the literature, is not Input-to-State-Stable (ISS) with
respect to bounded measurement disturbances while the non-smooth versions are.
We also show that the non-smooth versions of the attitude complementary filter
exhibit better convergence rates. Some simulations are provided to illustrate
our results.


title: Exotic Hadrons with Heavy Flavors -X, Y, Z and Related States-

abstract:
  In the past decade, exotic hadrons with charm and bottom flavors have been
extensively studied both in experiments and in theories. In this review, we
provide topical discussions by selecting $X,Y,Z$ particles, to which Belle has
made important contributions. These are $X(3872)$, $Y(4260)$, $Z_c(4430)^+$,
$Z_c(3900)^+$, $Z_{b}(10610)^+$ and $Z_{b}(10650)^+$. Based on the current
experimental observations, we discuss those states with emphasis on hadronic
molecule whose dynamics is governed by chiral symmetry and heavy-quark symmetry
of QCD. We also mention briefly various interpretations and some theoretical
predictions for the yet undiscovered exotic hadrons.


title: Can $X(5568)$ be described as a $B_s\pi$, $B\bar{K}$ resonant state?

abstract:
  The D0 Collaboration has recently seen a resonant-like peak in the $B_s\pi$
invariant mass spectrum, claimed to be a new state called $X(5568)$. Using a
$B_s\pi$--$B\bar{K}$ coupled channel analysis, implementing unitarity, and with
the interaction derived from Heavy Meson Chiral Perturbation Theory, we are
able to reproduce the reported spectrum, with a pole that can be associated to
the claimed $X(5568)$ state, and with mass and width in agreement with the ones
reported in the experimental analysis. However, if the $T$-matrix
regularization is performed by means of a momentum cutoff, the value for the
latter needed to reproduce the spectrum is $\Lambda = 2.80 \pm 0.04\
\text{GeV}$, much larger than a "natural" value $\Lambda \simeq 1\ \text{GeV}$.
In view of this, it is difficult to interpret the nature of this new state.
This state would not qualify as a resonance dynamically generated by the
unitarity loops. Assuming the observed peak to correspond to a physical state,
we make predictions for partners in the $D$, $D^\ast$, and $B^\ast$ sectors.
Their observation (or lack thereof) would shed light into this issue.


title: Dual-Mixed Finite Element Methods for the Navier-Stokes Equations

abstract:
  A mixed finite element method for the Navier-Stokes equations is introduced
in which the stress is a primary variable. The variational formulation retains
the mathematical structure of the Navier-Stokes equations and the classical
theory extends naturally to this setting. Finite element spaces satisfying the
associated inf-sup conditions are developed.


title:
The Matching Process and Independent Process in Random Regular Graphs
  and Hypergraphs

abstract:
  In this note, we analyze two random greedy processes on sparse random graphs
and hypergraphs with a given degree sequence. First we analyze the matching
process, which builds a set of disjoint edges one edge at a time; then we
analyze the independent process, which builds an independent set of vertices
one vertex at a time. We use the differential equations method and apply a
general theorem of Warnke. Our main contribution is to significantly reduce the
associated systems of differential equations and simplify the expression for
the final size of the matching or independent set.


title:
Optimal Recommendation to Users that React: Online Learning for a Class
  of POMDPs

abstract:
  We describe and study a model for an Automated Online Recommendation System
(AORS) in which a user's preferences can be time-dependent and can also depend
on the history of past recommendations and play-outs. The three key features of
the model that makes it more realistic compared to existing models for
recommendation systems are (1) user preference is inherently latent, (2)
current recommendations can affect future preferences, and (3) it allows for
the development of learning algorithms with provable performance guarantees.
The problem is cast as an average-cost restless multi-armed bandit for a given
user, with an independent partially observable Markov decision process (POMDP)
for each item of content. We analyze the POMDP for a single arm, describe its
structural properties, and characterize its optimal policy. We then develop a
Thompson sampling-based online reinforcement learning algorithm to learn the
parameters of the model and optimize utility from the binary responses of the
users to continuous recommendations. We then analyze the performance of the
learning algorithm and characterize the regret. Illustrative numerical results
and directions for extension to the restless hidden Markov multi-armed bandit
problem are also presented.


title: Global Exponential Angular Velocity Observer for Rigid Body Systems

abstract:
  We present a uniformly globally exponentially stable hybrid angular velocity
observer for rigid body systems designed directly on $SO(3)\times\mathbb{R}^3$.
The global exponential stability result makes this observer a good candidate
for a controller-observer combination with a guaranteed separation property.
Simulation results are provided to demonstrate the effectiveness of the
proposed hybrid observer as a part of an attitude stabilization scheme.


title:
The Hodge theory of the Decomposition Theorem (after de Cataldo and
  Migliorini)

abstract:
  In its simplest form the Decomposition Theorem asserts that the rational
intersection cohomology of a complex projective variety occurs as a summand of
the cohomology of any resolution. This deep theorem has found important
applications in algebraic geometry, representation theory, number theory and
combinatorics. It was originally proved in 1981 by Beilinson, Bernstein,
Deligne and Gabber as a consequence of Deligne's proof of the Weil conjectures.
A different proof was given by Saito in 1988, as a consequence of his theory of
mixed Hodge modules. More recently, de Cataldo and Migliorini found a much more
elementary proof which uses only classical Hodge theory and the theory of
perverse sheaves. We present the theorem and outline the main ideas involved in
the new proof.


title: On uniform approximation to successive powers of a real number

abstract:
  We establish new inequalities involving classical exponents of Diophantine
approximation. This allows for improving on the work of Davenport, Schmidt and
Laurent concerning the maximum value of the exponent $\hat{\lambda}_{n}(\zeta)$
among all real transcendental $\zeta$. In particular we refine the estimation
$\hat{\lambda}_{n}(\zeta)\leq \lceil n/2\rceil^{-1}$ due to M. Laurent by
$\hat{\lambda}_{n}(\zeta)\leq \hat{w}_{\lceil n/2\rceil}(\zeta)^{-1}$ for all
$n\geq 1$, and for even $n$ we replace the bound $2/n$ for
$\hat{\lambda}_{n}(\zeta)$ first found by Davenport and Schmidt by roughly
$\frac{2}{n}-\frac{1}{2n^{3}}$, which provides the currently best known bounds
when $n\geq 6$.


title:
Production of extra quarks at the Large Hadron Collider beyond the
  Narrow Width Approximation

abstract:
  This paper explores the effects of both finite width and interference (with
background) in the pair production and decay of extra heavy quarks with charge
2/3 at the Large Hadron Collider (LHC). This dynamics is normally ignored in
standard experimental searches and we assess herein the regions of validity of
current approaches, also evaluating the performances of a set of current
experimental analyses at 8 and 13 TeV for the deterimination of the excluded
regions in the $(M_{\rm VLQ},\Gamma_{\rm VLQ})$ plane, $M_{\rm VLQ}$ being the
mass of the VLQ and $\Gamma_{\rm VLQ}$ its width. Further, we discuss the
configurations of masses, widths and couplings where the latter breaks down.


title: Generic analytic polyhedron with non-compact automorphism group

abstract:
  In this paper we prove the following rigidity theorem: a generic analytic
polyhedron with non-compact automorphism group is biholomorphic to the product
of a complex manifold with compact automorphism group and a polydisk. Moreover,
this complex manifold and the dimension of this polydisk can be explicitly
described in terms of the limit set of the automorphism group.


title: Sisyphus random walk

abstract:
  In this paper we consider a particular version of the random walk with
restarts: random reset events which bring suddenly the system to the starting
value. We analyze its relevant statistical properties like the transition
probability and show how an equilibrium state appears. Formulas for the
first-passage time, high-water marks and other extreme statistics are also
derived: we consider counting problems associated naturally to the system.
Finally we indicate feasible generalizations useful for interpreting different
physical effects.

categories: math-ph cond-mat.stat-mech math.MP math.PR


title:
Binary Quadratic Programing for Online Tracking of Hundreds of People in
  Extremely Crowded Scenes

abstract:
  Multi-object tracking has been studied for decades. However, when it comes to
tracking pedestrians in extremely crowded scenes, we are limited to only few
works. This is an important problem which gives rise to several challenges.
Pre-trained object detectors fail to localize targets in crowded sequences.
This consequently limits the use of data-association based multi-target
tracking methods which rely on the outcome of an object detector. Additionally,
the small apparent target size makes it challenging to extract features to
discriminate targets from their surroundings. Finally, the large number of
targets greatly increases computational complexity which in turn makes it hard
to extend existing multi-target tracking approaches to high-density crowd
scenarios. In this paper, we propose a tracker that addresses the
aforementioned problems and is capable of tracking hundreds of people
efficiently. We formulate online crowd tracking as Binary Quadratic Programing.
Our formulation employs target's individual information in the form of
appearance and motion as well as contextual cues in the form of neighborhood
motion, spatial proximity and grouping constraints, and solves detection and
data association simultaneously. In order to solve the proposed quadratic
optimization efficiently, where state-of art commercial quadratic programing
solvers fail to find the answer in a reasonable amount of time, we propose to
use the most recent version of the Modified Frank Wolfe algorithm, which takes
advantage of SWAP-steps to speed up the optimization. We show that the proposed
formulation can track hundreds of targets efficiently and improves state-of-art
results by significant margins on eleven challenging high density crowd
sequences.


title:
Computing GIT-fans with symmetry and the Mori chamber decomposition of
  $\bar{M}_{0,6}$

abstract:
  We propose an algorithm to compute the GIT-fan for torus actions on affine
varieties with symmetries. The algorithm combines computational techniques from
commutative algebra, convex geometry and group theory. We have implemented our
algorithm in the Singular library gitfan.lib. Using our implementation, we
compute the Mori chamber decomposition of the cone of movable divisors of
$\bar{M}_{0,6}$.


title: Temporal variability of the wind from the star {\tau} Bo\"otis

abstract:
  We present new wind models for {\tau} Bo\"otis ({\tau} Boo), a
hot-Jupiter-host-star whose observable magnetic cycles makes it a uniquely
useful target for our goal of monitoring the temporal variability of stellar
winds and their exoplanetary impacts. Using spectropolarimetric observations
from May 2009 to January 2015, the most extensive information of this type yet
available, to reconstruct the stellar magnetic field, we produce multiple 3D
magnetohydrodynamic stellar wind models. Our results show that characteristic
changes in the large-scale magnetic field as the star undergoes magnetic cycles
produce changes in the wind properties, both globally and locally at the
position of the orbiting planet. Whilst the mass loss rate of the star varies
by only a minimal amount ($\sim$ 4 percent), the rates of angular momentum loss
and associated spin-down timescales are seen to vary widely (up to $\sim$ 140
percent), findings consistent with and extending previous research. In
addition, we find that temporal variation in the global wind is governed mainly
by changes in total magnetic flux rather than changes in wind plasma
properties. The magnetic pressure varies with time and location and dominates
the stellar wind pressure at the planetary orbit. By assuming a Jovian
planetary magnetic field for {\tau} Boo b, we nevertheless conclude that the
planetary magnetosphere can remain stable in size for all observed stellar
cycle epochs, despite significant changes in the stellar field and the
resulting local space weather environment.


title:
Cooling the Motion of Diamond Nanocrystals in a Magneto-Gravitational
  Trap in High Vacuum

abstract:
  Levitated diamond nanocrystals with nitrogen-vacancy (NV) centres in high
vacuum have been proposed as a unique system for experiments in fundamental
quantum mechanics, including the generation of large quantum superposition
states and tests of quantum gravity. This system promises extreme isolation
from its environment while providing quantum control and sensing through the NV
centre spin. While optical trapping has been the most explored method of
levitation, recent results indicate that excessive optical heating of the
nanodiamonds under vacuum may make the method impractical with currently
available materials. Here, we study an alternative magneto-gravitational trap
for diamagnetic particles, such as diamond nanocrystals, with stable levitation
from atmospheric pressure to high vacuum. Magnetic field gradients from
permanent magnets confine the particle in two dimensions, while confinement in
the third dimension is gravitational. We demonstrate that feedback cooling of
the centre-of-mass motion of a trapped nanodiamond cluster results in cooling
of one degree of freedom to less than 1 K.


title: Euclidean Supergravity in Five Dimensions

abstract:
  We construct a 5D, N = 2 Euclidean theory of supergravity coupled to vector
multiplets. Upon reducing this theory over a circle we recover the action of
4D, N = 2 Euclidean supergravity coupled to vector multiplets.


title: Tight-binding lattices with an oscillating imaginary gauge field

abstract:
  We consider non-Hermitian dynamics of a quantum particle hopping on a
one-dimensional tight-binding lattice made of $N$ sites with asymmetric hopping
rates induced by a time-periodic oscillating imaginary gauge field. A deeply
different behavior is found depending on the lattice topology. While in a
linear chain (open boundary conditions) an oscillating field can lead to a
complex quasi energy spectrum via a multiple parametric resonance, in a ring
topology (Born-von Karman periodic boundary conditions) an entirely real quasi
energy spectrum can be found and the dynamics is pseudo-Hermitian. In the large
$N$ limit, parametric instability and pseudo-Hermitian dynamics in the two
different lattice topologies are physically explained on the basis of a simple
picture of wave packet propagation.


title:
Unsupervised Learning of Visual Representations by Solving Jigsaw
  Puzzles

abstract:
  In this paper we study the problem of image representation learning without
human annotation. By following the principles of self-supervision, we build a
convolutional neural network (CNN) that can be trained to solve Jigsaw puzzles
as a pretext task, which requires no manual labeling, and then later repurposed
to solve object classification and detection. To maintain the compatibility
across tasks we introduce the context-free network (CFN), a siamese-ennead CNN.
The CFN takes image tiles as input and explicitly limits the receptive field
(or context) of its early processing units to one tile at a time. We show that
the CFN includes fewer parameters than AlexNet while preserving the same
semantic learning capabilities. By training the CFN to solve Jigsaw puzzles, we
learn both a feature mapping of object parts as well as their correct spatial
arrangement. Our experimental evaluations show that the learned features
capture semantically relevant content. Our proposed method for learning visual
representations outperforms state of the art methods in several transfer
learning benchmarks.


title:
Statistical Quadrature Evolution by Inference for Continuous-Variable
  Quantum Key Distribution

abstract:
  We define the statistical quadrature evolution (QE) method for multicarrier
continuous-variable quantum key distribution (CVQKD). A multicarrier CVQKD
protocol uses Gaussian subcarrier quantum continuous variables (CVs) for
information transmission. The QE scheme utilizes the theory of mathematical
statistics and statistical information processing. The QE model is based on the
Gaussian quadrature inference (GQI) framework to provide a minimal error
estimate of the CV state quadratures. The QE block evaluates a unique and
stable estimation of the non-observable continuous input from the measurement
results and through the statistical inference method yielded from the GQI
framework. The QE method minimizes the overall expected error by an estimator
function and provides a viable, easily implementable, and computationally
efficient way to maximize the extractable information from the observed data.
The QE framework can be established in an arbitrary CVQKD protocol and
measurement setting and is implementable by standard low-complexity functions,
which is particularly convenient for experimental CVQKD.


title: Regular Black Holes and Noncommutative Geometry Inspired Fuzzy Sources

abstract:
  We investigated regular black holes with fuzzy sources in three and four
dimensions. The density distributions of such fuzzy sources are inspired by
noncommutative geometry and given by Gaussian or generalized Gaussian
functions. We utilized mass functions to give a physical interpretation of the
horizon formation condition for the black holes. In particular, we investigated
three-dimensional BTZ-like black holes and four-dimensional Schwarzschild-like
black holes in detail, and found that the number of horizons is related to the
spacetime dimensions, and the existence of a void in the vicinity of the center
of the spacetime is significant, rather than noncommutativity. As an
application, we considered a three-dimensional black hole with the fuzzy disc
which is a disc-shaped region known in the context of noncommutative geometry
as a source. We also analyzed a four-dimensional black hole with a source whose
density distribution is an extension of the fuzzy disc, and investigated the
horizon formation condition for it.


title:
Algebraic Bethe ansatz for the quantum group invariant open XXZ chain at
  roots of unity

abstract:
  For generic values of q, all the eigenvectors of the transfer matrix of the
U_q sl(2)-invariant open spin-1/2 XXZ chain with finite length N can be
constructed using the algebraic Bethe ansatz (ABA) formalism of Sklyanin.
However, when q is a root of unity (q=exp(i pi/p) with integer p>1), the Bethe
equations acquire continuous solutions, and the transfer matrix develops Jordan
cells. Hence, there appear eigenvectors of two new types: eigenvectors
corresponding to continuous solutions (exact complete p-strings), and
generalized eigenvectors. We propose general ABA constructions for these two
new types of eigenvectors. We present many explicit examples, and we construct
complete sets of (generalized) eigenvectors for various values of p and N.

categories: math-ph cond-mat.stat-mech hep-th math.MP math.QA math.RT


title:
Ramanujan-like formulas for Fourier coefficients of all meromorphic cusp
  forms

abstract:
  In this paper, we investigate Fourier expansions of meromorphic modular
forms. Over the years, a number of special cases of meromorphic modular forms
were shown to have Fourier expansions closely resembling the expansion of the
reciprocal of the weight $6$ Eisenstein series which was computed by Hardy and
Ramanujan. By investigating meromorphic modular forms within a larger space of
so-called polar harmonic Maass forms, we prove in this paper that all
negative-weight meromorphic modular forms (and furthermore all quasi-meromorpic
modular forms) have Fourier expansions of this type, granted that they are
bounded towards $i\infty$.


title: Flux-tube geometry and solar wind speed during an activity cycle

abstract:
  The solar wind speed at 1 AU shows variations in latitude and in time which
reflect the evolution of the global background magnetic field during the
activity cycle. It is commonly accepted that the terminal wind speed in a
magnetic flux-tube is anti-correlated with its expansion ratio, which motivated
the definition of widely-used semi-empirical scaling laws relating one to the
other. In practice, such scaling laws require ad-hoc corrections. A predictive
law based solely on physical principles is still missing. We test whether the
flux-tube expansion is the controlling factor of the wind speed at all phases
of the cycle and at all latitudes using a very large sample of wind-carrying
open magnetic flux-tubes. We furthermore search for additional physical
parameters based on the geometry of the coronal magnetic field which have an
influence on the terminal wind flow speed. We use MHD simulations of the corona
and wind coupled to a dynamo model to provide a large statistical ensemble of
open flux-tubes which we analyse conjointly in order to identify relations of
dependence between the wind speed and geometrical parameters of the flux-tubes
which are valid globally (for all latitudes and moments of the cycle). Our
study confirms that the terminal speed of the solar wind depends very strongly
on the geometry of the open magnetic flux-tubes through which it flows. The
total flux-tube expansion is more clearly anti-correlated with the wind speed
for fast rather than for slow wind flows, and effectively controls the
locations of these flows during solar minima. Overall, the actual asymptotic
wind speeds attained are also strongly dependent on field-line inclination and
magnetic field amplitude at the foot-points. We suggest ways of including these
parameters on future predictive scaling-laws for the solar wind speed.


title: Large KAM tori for perturbations of the dNLS equation

abstract:
  We prove that small, semi-linear Hamiltonian perturbations of the defocusing
nonlinear Schr\"odinger (dNLS) equation on the circle have an abundance of
invariant tori of any size and (finite) dimension which support quasi-periodic
solutions. When compared with previous results the novelty consists in
considering perturbations which do not satisfy any symmetry condition (they may
depend on $x$ in an arbitrary way) and need not be analytic. The main
difficulty is posed by pairs of almost resonant dNLS frequencies. The proof is
based on the integrability of the dNLS equation, in particular the fact that
the nonlinear part of the Birkhoff coordinates is one smoothing. We implement a
Newton-Nash-Moser iteration scheme to construct the invariant tori. The key
point is the reduction of linearized operators, coming up in the iteration
scheme, to $ 2 \times 2 $ block diagonal ones with constant coefficients
together with sharp asymptotic estimates of their eigenvalues.


title:
Relative relocation of earthquakes without a predefined velocity model:
  an example from a peculiar seismic cluster on Katla volcano's south-flank
  (Iceland)

abstract:
  Relative relocation methods are commonly used to precisely relocate
earthquake clusters consisting of similar waveforms. Repeating waveforms are
often recorded at volcanoes, where, however, the crust structure is expected to
contain strong heterogeneities and therefore the 1D velocity model assumption
that is made in most location strategies is not likely to describe reality. A
peculiar cluster of repeating low-frequency seismic events was recorded on the
south flank of Katla volcano (Iceland) from 2011. As the hypocentres are
located at the rim of the glacier, the seismicity may be due to volcanic or
glacial processes. Information on the size and shape of the cluster may help
constraining the source process. The extreme similarity of waveforms points to
a very small spatial distribution of hypocentres. In order to extract
meaningful information about size and shape of the cluster, we minimize
uncertainty by optimizing the cross-correlation measurements and
relative-relocation process. With a synthetic test we determine the best
parameters for differential-time measurements and estimate their uncertainties,
specifically for each waveform. We design a relocation strategy to work without
a predefined velocity model, by formulating and inverting the problem to seek
changes in both location and slowness, thus accounting for azimuth, take-off
angles and velocity deviations from a 1D model. We solve the inversion
explicitly in order to propagate data errors through the calculation. With this
approach we are able to resolve a source volume few tens of meters wide on
horizontal directions and around 100 meters in depth. There is no suggestion
that the hypocentres lie on a single fault plane and the depth distribution
indicates that their source is unlikely to be related to glacial processes as
the ice thickness is not expected to exceed few tens of meters in the source
area.


title: A latent-observed dissimilarity measure

abstract:
  Quantitatively assessing relationships between latent variables and observed
variables is important for understanding and developing generative models and
representation learning. In this paper, we propose latent-observed
dissimilarity (LOD) to evaluate the dissimilarity between the probabilistic
characteristics of latent and observed variables. We also define four essential
types of generative models with different independence/conditional independence
configurations. Experiments using tractable real-world data show that LOD can
effectively capture the differences between models and reflect the capability
for higher layer learning. They also show that the conditional independence of
latent variables given observed variables contributes to improving the
transmission of information and characteristics from lower layers to higher
layers.


title:
sPEGG: high throughput eco-evolutionary simulations on commodity
  graphics processors

abstract:
  Integrating population genetics into community ecology theory is a major goal
in ecology and evolution, but analyzing the resulting models is computationally
daunting. Here we describe sPEGG ($\underline{\textrm{s}}\textrm{imulating}$
$\underline{\textrm{P}}\textrm{henotypic}$
$\underline{\textrm{E}}\textrm{volution}$ on
$\underline{\textrm{G}}\textrm{eneral Purpose}$
$\underline{\textrm{G}}\textrm{raphics Processing Units}$ (GPGPUs)), an
open-source, multi-species forward-time population genetics simulator. Using a
single commodity GPGPU instead of a single central processor, we find sPEGG can
accelerate eco-evolutionary simulations by a factor of over 200, comparable to
performance on a small-to-medium sized computer cluster.


title:
Electronic structure, doping, order and disorder in cuprate
  superconductors

abstract:
  The electron-phonon and spin-phonon coupling in typical high-T_C cuprates,
like LSCO and HBCO are peaked for just a few q-vectors because of the
2-dimensional Fermi surface shape. The activation of few spin-phonon modes
compensates for the low electronic density-of-states, and the superconducting
T_C can be high. Thermal disorder of the lattice perturbs the strongly coupled
modes already at moderately high temperature. This happens because of
incoherent potential fluctuations of the Madelung term and reduced spin-phonon
coupling. This effect puts a limit on long-range superconductivity, while
fluctuations can persist on a shorter length scale at higher temperatures.
BCS-type model calculations are used to show how disorder can reduce the
superconducting gap and T_C. Ordering of dopants into stripes has been
suggested to improve superconducting properties, mainly through an increased
DOS. Such a mechanism seems to be a good way to make T_C more resistant to
thermal disorder at low doping.


title:
Characterization of hyperfine interaction between an NV electron spin
  and a first-shell 13C nuclear spin in diamond

abstract:
  The Nitrogen-Vacancy (NV) center in diamond has attractive properties for a
number of quantum technologies that rely on the spin angular momentum of the
electron and the nuclei adjacent to the center. The nucleus with the strongest
interaction is the $^{13}$C nuclear spin of the first shell. Using this degree
of freedom effectively hinges on precise data on the hyperfine interaction
between the electronic and the nuclear spin. Here, we present detailed
experimental data on this interaction, together with an analysis that yields
all parameters of the hyperfine tensor, as well as its orientation with respect
to the atomic structure of the center.


title: Distributed Learning in the Presence of Disturbances

abstract:
  We consider a problem where multiple agents must learn an action profile that
maximises the sum of their utilities in a distributed manner. The agents are
assumed to have no knowledge of either the utility functions or the actions and
payoffs of other agents. These assumptions arise when modelling the
interactions in a complex system and communicating between various components
of the system are both difficult. In [1], a distributed algorithm was proposed,
which learnt Pareto-efficient solutions in this problem setting. However, the
approach assumes that all agents can choose their actions, which precludes
disturbances. In this paper, we show that a modified version of this
distributed learning algorithm can learn Pareto-efficient solutions, even in
the presence of disturbances from a finite set. We apply our approach to the
problem of ramp coordination in traffic control for different demand profiles.


title:
N-Legendre and N-Slant Curves in the Unit Tangent Bundle of Minkowski
  Surfaces

abstract:
  Let $(\mathbb{M}_{1}^{2},g)$ be a Minkowski surface and $(T_1\mathbb{M}_1^2,
g_1)$ its unit tangent bundle endowed with the pseudo-Riemannian induced Sasaki
metric. We extend in this paper the study of the N-Legendre and N-slant curves
which the inner product of normal vector and Reeb vector is zero and nonzero
constant respectively in $\left( T_1 \mathbb{M}_1^2, g_1 \right)$, given in
\cite{hmy}, to the Minkowski context and several important characterizations of
these curves are given.\newline


title: Degrees of Freedom in Deep Neural Networks

abstract:
  In this paper, we explore degrees of freedom in deep sigmoidal neural
networks. We show that the degrees of freedom in these models is related to the
expected optimism, which is the expected difference between test error and
training error. We provide an efficient Monte-Carlo method to estimate the
degrees of freedom for multi-class classification methods. We show degrees of
freedom are lower than the parameter count in a simple XOR network. We extend
these results to neural nets trained on synthetic and real data, and
investigate impact of network's architecture and different regularization
choices. The degrees of freedom in deep networks are dramatically smaller than
the number of parameters, in some real datasets several orders of magnitude.
Further, we observe that for fixed number of parameters, deeper networks have
less degrees of freedom exhibiting a regularization-by-depth.


title:
Varieties that are not stably rational, zero-cycles and unramified
  cohomology

abstract:
  This is a survey of recent examples of varieties that are not stably
rational. We review the specialization method based on properties of the Chow
group of zero-cycles used in these examples and explain the point of view of
unramified cohomology for the construction of nontrivial stable invariants of
the special fiber. In particular, we find an explicit formula for the Brauer
group of fourfolds fibered in quadrics of dimension two over a rational
surface.


title: Stable rationality of quadric surface bundles over surfaces

abstract:
  We study rationality properties of quadric surface bundles over the
projective plane. We exhibit families of smooth projective complex fourfolds of
this type over connected bases, containing both rational and non-rational
fibers.


title: Universal Lattice Codes for MIMO Channels

abstract:
  We propose a coding scheme that achieves the capacity of the compound MIMO
channel with algebraic lattices. Our lattice construction exploits the
multiplicative structure of number fields and their group of units to absorb
ill-conditioned channel realizations. To shape the constellation, a discrete
Gaussian distribution over the lattice points is applied. These techniques,
along with algebraic properties of the proposed lattices, are then used to
construct a sub-optimal de-coupled coding schemes that achieves a gap to
compound capacity by decoding in a lattice that does not depend of the channel
realization. The gap is characterized in terms of algebraic invariants of the
codes, and shown to be significantly smaller than previous schemes in the
literature. We also exhibit alternative algebraic constructions that achieve
the capacity of ergodic fading channels.


title:
Equilibrium Instability of Chiral Mesons in External Electromagnetic
  Field via AdS/CFT

abstract:
  We study the equilibrium instability of chiral quarkonia in a plasma in the
presence of constant magnetic and electric field and at finite axial chemical
potential using AdS/CFT duality. The model in use is a supersymmetric QCD at
large 't$\,$Hooft coupling and number of colors. We show that the presence of
the magnetic field and the axial chemical potential even in the absence of the
electric field make the system unstable. In a gapped system, a stable/unstable
equilibrium state phase transition is observed and the initial transition
amplitude of the equilibrium state to the non-equilibrium state is
investigated. We demonstrate that at zero temperature and large magnetic field
the instability grows linearly by increasing the quarkonium binding energy. In
the constant electric and magnetic field, the system is in a equilibrium state
if the Ohm's law and the chiral magnetic effect cancel their effects. This
happens in a sub-space of $(E,B,T,\mu_5)$ space with constraint equation
$\sigma_B B =- \sigma E$, where $\sigma$ and $\sigma_B$ are called electric and
chiral magnetic conductivity, respectively. We analyze the decay rate of a
gapless system when this constraint is slightly violated.


title:
Moderate solutions of semilinear elliptic equations with Hardy potential
  under minimal restrictions on the potential

abstract:
  We study semilinear elliptic equations with Hardy potential $\mathrm{(E)} \;
-L_\mu u+u^q=0$ in a bounded smooth domain $\Omega\subset \mathbb R^N$. Here
$q>1$, $L_\mu=\Delta+\frac{\mu}{\delta_\Omega^2}$ and
$\delta_\Omega(x)=\mathrm{dist}(x,\partial\Omega)$. Assuming that $0\leq
\mu<C_H(\Omega)$, boundary value problems with measure data and discrete
boundary singularities for positive solutions of $\mathrm{(E)}$ have been
studied earlier. In the present paper we study these problems, in arbitrary
domains, assuming only $-\infty<\mu<1/4$, even if $C_H(\Omega)<1/4$. We recall
that $C_H(\Omega)\leq 1/4$ and, in general, strict inequality holds. The key to
our study is the fact that, if $\mu<1/4$ then in smooth domains there exist
local $L_\mu$-superharmonic functions in a neighborhood of $\partial\Omega$
(even if $C_H(\Omega)<1/4$). Using this fact we extend the notion of normalized
boundary trace to arbitrary domains, provided that $\mu<1/4$. Further we study
the b.v.p. with normalized boundary trace $\nu$ in the space of positive finite
measures on $\partial\Omega$. We show that existence depends on two critical
values of the exponent $q$ and discuss the question of uniqueness. Part of the
paper is devoted to the study of the linear operator: properties of local
$L_\mu$ subharmonic and superharmonic functions and the related notion of
moderate solutions.


title: The Fermat Functors, Part I: The theory

abstract:
  In this paper, we use some basic quasi-topos theory to study two functors:
one adding infinitesimals of Fermat reals to diffeological spaces (which
generalize smooth manifolds including singular spaces and infinite dimensional
spaces), and the other deleting infinitesimals on Fermat spaces. We study the
properties of these functors, and calculate some examples. These serve as
fundamentals for developing differential geometry on diffeological spaces using
infinitesimals in a future paper.


title: Vertex operators and character varieties

abstract:
  We prove some combinatorial conjectures extending those proposed in [13, 14].
The proof uses a vertex operator due to Nekrasov, Okounkov, and the first
author [4] to obtain a "gluing formula" for the relevant generating series,
essentially reducing the computation to the case of complex projective space
with three punctures.


title: On the chiral separation effect in a slab

abstract:
  We study the influence of boundaries on chiral effects in hot dense
relativistic spinor matter in a strong magnetic field which is transverse to
bounding planes. The most general set of boundary conditions ensuring the
confinement of matter within the bounding planes is considered. We find that,
in thermal equilibrium, the nondissipative axial current along the magnetic
field is induced, depending on chemical potential and temperature, as well as
on a choice of boundary conditions. As temperature increases from zero to large
values, a stepwise behaviour of the axial current density as a function of
chemical potential is changed to a smooth one; the choice of a boundary
condition can facilitate either amplification or diminution of the chiral
separation effect. This points at a significant role of boundaries for physical
systems with hot dense magnetized relativistic spinor matter, e.g., compact
stars, heavy-ion collisions, novel materials known as Dirac and Weyl
semimetals.


title: Morse Index of Willmore spheres in $S^3$

abstract:
  We obtain an upper bound for the Morse index of Willmore spheres
$\Sigma\subset S^3$ coming from an immersion of $S^2$. The quantization of
Willmore energy shows that there exists an integer $m$ such that
$\mathscr{W}(\Sigma)=4\pi m$. Then we show that
$\mathrm{Ind}_{\mathscr{W}}(\Sigma)\leq m$. The proof relies on an explicit
computation relating the second derivative of $\mathscr{W}$ for $\Sigma$ with
the Jacobi operator of the minimal surface in $\mathbb{R}^3$ it is the image of
by stereographic projection thanks of the fundamental classification of Robert
Bryant.


title:
Effect of Priomordial non-Gaussianities on Galaxy Clusters Scaling
  Relations

abstract:
  Galaxy clusters are a valuable source of cosmological information. Their
formation and evolution depends on the underlying cosmology and on the
statistical nature of the primordial density fluctuations. In this work we
investigate the impact of primordial non-gaussianities (PNG) on the scaling
properties of galaxy clusters. We performed a series of cosmological
hydrodynamic N-body simulations featuring adiabatic gas physics and different
levels of non-Gaussian initial conditions within the $\Lambda$CDM framework. We
focus on the T-M, S-M, Y-M and Yx-M scalings relating the total cluster mass
with temperature, entropy and SZ cluster integrated pressure that reflect the
thermodynamical state of the intra-cluster medium. Our results show that PNG
have an impact on cluster scalings laws. The mass power-law indexes of the
scalings are almost unaffected by the existence of PNG but the amplitude and
redshift evolution of their normalizations are clearly affected. The effect is
stronger for the evolution of the Y-M and Yx-M normalizations, which change by
as much as 22% and 16% when $f_{NL}$ varies from -500 to 500, respectively.
These results are consistent with the view that positive/negative $f_{NL}$
affect cluster profiles due to an increase/decrease of cluster concentrations.
At low values of $f_{NL}$, as suggested by present Planck constraints on a
scale invariant $f_{NL}$, the impact on the scalings normalizations is only a
few percent, which is small when compared with the effect of additional gas
physics and other cosmological effects such as dark energy. However if $f_{NL}$
is in fact a scale dependent parameter, PNG may have larger positive/negative
amplitudes at clusters scales and therefore our results suggest that PNG should
be taken into account when galaxy cluster data is used to infer cosmological
parameters or to asses the constraining power of future cluster surveys.


title: 40 years of the Nobel prize in physics: then and now

abstract:
  The findings for which Aage Bohr and Ben R. Mottelson became co-winners of
the 1975 Nobel prize in physics provided the basis for a comprehensive and
operative answer to the central problem in the study of the nuclear structure,
namely the identification of the appropriate concepts and degrees of freedom
that are suitable for describing the phenomena encountered. To do so they
produced a breathtaking unification of a number of well established concepts,
namely liquid drop and shell models, elementary modes of excitation,
superconductivity and quantum electrodynamics, resulting eventually in the
paradigm of broken symmetry restoration to determine the nuclear collective
variables (CV, elementary modes of excitation): violation of translation
invariance by the mean field and by scattering states (single-particle motion),
of rotational invariance in the variety of spaces, in particular in 3D- and in
gauge-space, leading to surface vibrations and to quadrupole rotations, as well
as to pairing vibrations and rotations, with associated emergent properties of
generalized rigidity in these spaces, resulting from the coupling to
single-particle degrees of freedom.


title:
Bayesian inference in hierarchical models by combining independent
  posteriors

abstract:
  Hierarchical models are versatile tools for joint modeling of data sets
arising from different, but related, sources. Fully Bayesian inference may,
however, become computationally prohibitive if the source-specific data models
are complex, or if the number of sources is very large. To facilitate
computation, we propose an approach, where inference is first made
independently for the parameters of each data set, whereupon the obtained
posterior samples are used as observed data in a substitute hierarchical model,
based on a scaled likelihood function. Compared to direct inference in a full
hierarchical model, the approach has the advantage of being able to speed up
convergence by breaking down the initial large inference problem into smaller
individual subproblems with better convergence properties. Moreover it enables
parallel processing of the possibly complex inferences of the source-specific
parameters, which may otherwise create a computational bottleneck if processed
jointly as part of a hierarchical model. The approach is illustrated with both
simulated and real data.


title: Learning with Optimal Interpolation Norms

abstract:
  We analyze a class of norms defined via an optimal interpolation problem
involving the composition of norms and a linear operator. This construction,
known as infimal postcomposition in convex analysis, is shown to encompass
various of norms which have been used as regularizers in machine learning,
signal processing, and statistics. In particular, these include the latent
group lasso, the overlapping group lasso, and certain norms used for learning
tensors. We establish basic properties of this class of norms and we provide
dual norms. The extension to more general classes of convex functions is also
discussed. A stochastic block-coordinate version of the Douglas-Rachford
algorithm is devised to solve minimization problems involving these
regularizers. A prominent feature of the algorithm is that it yields iterates
that converge to a solution in the case of non smooth losses and random block
updates. Finally, we present numerical experiments with problems employing the
latent group lasso penalty.


title: A Survey on Hardware and Software Support for Thread Level Parallelism

abstract:
  To support growing massive parallelism, functional components and also the
capabilities of current processors are changing and continue to do so. Todays
computers are built upon multiple processing cores and run applications
consisting of a large number of threads, making runtime thread management a
complex process. Further, each core can support multiple, concurrent thread
execution. Hence, hardware and software support for threads is more and more
needed to improve peak-performance capacity, overall system throughput, and has
therefore been the subject of much research. This paper surveys, many of the
proposed or currently available solutions for executing, distributing and
managing threads both in hardware and software. The nature of current
applications is diverse. To increase the system performance, all programming
models may not be suitable to harness the built-in massive parallelism of
multicore processors. Due to the heterogeneity in hardware, hybrid programming
model (which combines the features of shared and distributed model) currently
has become very promising. In this paper, first, we have given an overview of
threads, threading mechanisms and its management issues during execution. Next,
we discuss about different parallel programming models considering to their
explicit thread support. We also review the programming models with respect to
their support to shared-memory, distributed-memory and heterogeneity. Hardware
support at execution time is very crucial to the performance of the system,
thus different types of hardware support for threads also exist or have been
proposed, primarily based on widely used programming models. We also further
discuss on software support for threads, to mainly increase the deterministic
behavior during runtime. Finally, we conclude the paper by discussing some
common issues related to the thread management.


title: A note on the Howson property in inverse semigroups

abstract:
  An algebra has the Howson property if the intersection of any two finitely
generated subalgebras is finitely generated. A simple necessary and sufficient
condition is given for the Howson property to hold on an inverse semigroup with
finitely many idempotents. In addition, it is shown that any monogenic inverse
semigroup has the Howson property.


title:
Non-thermal emission from high-energy binaries through interferometric
  radio observations

abstract:
  High-mass binary systems involve extreme environments that produce
non-thermal emission from radio to gamma rays. Only three types of these
systems are known to emit persistent gamma-ray emission: colliding-wind
binaries, high-mass X-ray binaries and gamma-ray binaries. This thesis is
focused on the radio emission of high-mass binary systems through
interferometric observations, and we have explored several of these sources
with low- and high-frequency radio observations, and very high-resolution VLBI
ones. We have studied two gamma-ray binaries, LS 5039 and LS I +61 303, at low
frequencies. We have obtained their light-curves and spectra, and we have
determined the physical properties of their radio emitting regions. We have
also studied the gamma-ray binary HESS J0632+057 through VLBI observations. A
new colliding wind binary, HD 93129A, has been discovered through VLBI and
optical observations. Finally, we have conducted radio observations of two
sources that were candidates to be gamma-ray binaries.


title:
Obtaining Atomic Matrix Elements from Vector Tune-Out Wavelengths using
  Atom Interferometry

abstract:
  Accurate values for atomic dipole matrix elements are useful in many areas of
physics, and in particular for interpreting experiments such as atomic parity
violation. Obtaining accurate matrix element values is a challenge for both
experiment and theory. A new technique that can be applied to this problem is
tune-out spectroscopy, which is the measurement of light wavelengths where the
electric polarizability of an atom has a zero. Using atom interferometry
methods, tune-out wavelengths can be measured very accurately. Their values
depend on the ratios of various dipole matrix elements and are thus useful for
constraining theory and broadening the application of experimental values.
Tune-out wavelength measurements to date have focused on zeros of the scalar
polarizability, but in general the vector polarizability also contributes. We
show here that combined measurements of the vector and scalar polarizabilities
can provide more detailed information about the matrix element ratios, and in
particular can distinguish small contributions from the atomic core and the
valence tail states. These small contributions are the leading error sources in
current parity violation calculations for cesium.


title:
Trust-Aware Network Utility Optimization in Multihop Wireless Networks
  with Delay Constraints

abstract:
  Many resource allocation problems can be formulated as a constrained
maximization of a utility function. Network Utility Maximization (NUM) applies
optimization techniques to achieve decomposition by duality or the primal-dual
method. Several important problems, for example joint source rate control,
routing, and scheduling design, can be optimized by using this framework. In
this work, we introduce an important network security concept, "trust", into
the NUM formulation and we integrate nodes' trust values in the optimization
framework. These trust values are based on the interaction history between
network entities and community based monitoring. Our objective is to avoid
routing packets though paths with large percentage of malicious nodes. We also
add end-to-end delay constraints for each of the traffic flows. The delay
constraints are introduced to capture the quality of service (QoS) requirements
imposed to each traffic flow.


title:
On the Geometry of Message Passing Algorithms for Gaussian Reciprocal
  Processes

abstract:
  Reciprocal processes are acausal generalizations of Markov processes
introduced by Bernstein in 1932. In the literature, a significant amount of
attention has been focused on developing dynamical models for reciprocal
processes. Recently, probabilistic graphical models for reciprocal processes
have been provided. This opens the way to the application of efficient
inference algorithms in the machine learning literature to solve the smoothing
problem for reciprocal processes. Such algorithms are known to converge if the
underlying graph is a tree. This is not the case for a reciprocal process,
whose associated graphical model is a single loop network. The contribution of
this paper is twofold. First, we introduce belief propagation for Gaussian
reciprocal processes. Second, we establish a link between convergence analysis
of belief propagation for Gaussian reciprocal processes and stability theory
for differentially positive systems.


title: Twisted bialgebroids versus bialgebroids from a Drinfeld twist

abstract:
  Bialgebroids (resp. Hopf algebroids) are bialgebras (Hopf algebras) over
noncommutative rings. Drinfeld twist techniques are particularly useful in the
(deformation) quantization of Lie algebras as well as underlying module
algebras (=quantum spaces). Smash product construction combines these two into
the new algebra which, in fact, does not depend on the twist. However, we can
turn it into bialgebroid in the twist dependent way. Alternatively, one can use
Drinfeld twist techniques in a category of bialgebroids. We show that both
techniques indicated in the title: twisting of a bialgebroid or constructing a
bialgebroid from the twisted bialgebra give rise to the same result in the case
of normalized cocycle twist. This can be useful for better description of a
quantum deformed phase space. We argue that within this bialgebroid framework
one can justify the use of deformed coordinates (i.e. spacetime
noncommutativity) which are frequently postulated in order to explain quantum
gravity effects.


title: A Tight Bound for Minimal Connectivity

abstract:
  For minimally $k$-connected graphs on $n$ vertices, Mader proved a tight
lower bound for the number $|V_k|$ of vertices of degree $k$ in dependence on
$n$ and $k$. Oxley observed 1981 that in many cases a considerably better bound
can be given if $m := |E|$ is used as additional parameter, i.e. in dependence
on $m$, $n$ and $k$. It was left open to determine whether Oxley's bound is
best possible.
  We show that this is not the case, but propose a closely related bound that
deviates from Oxley's long-standing one only for small values of $m$. We prove
that this new bound is best possible. The bound contains Mader's bound as
special case.


title: White dwarfs in an ungravity-inspired model

abstract:
  An ungravity-inspired model is employed to examine the astrophysical
parameters of white dwarf stars (WDs) using polytropic and degenerate gas
approaches. Based on the observed properties such as mass, radius, and
luminosity of selected WDs, namely, Sirius B and $\epsilon$ Reticulum, bounds
on the characteristic length and scaling dimension of the ungravity (UG) model
are estimated. The UG effect on the Chandrasekhar limit for WDs is shown. The
UG model is examined in the study of ultra-massive WDs, e.g., EUVE J1746-706.
In the contact of UG inspired model, a new location for some WDs on the
Hertzsprung-Russell diagram is found.


title: Reliability of analog quantum simulation

abstract:
  Analog quantum simulators (AQS) will likely be the first nontrivial
application of quantum technology for predictive simulation. However, there
remain questions regarding the degree of confidence that can be placed in the
results of AQS since they do not naturally incorporate error correction.
Specifically, how do we know whether an analog simulation of a quantum model
will produce predictions that agree with the ideal model in the presence of
inevitable imperfections? At the same time, there is a widely held expectation
that certain quantum simulation questions will be robust to errors and
perturbations in the underlying hardware. Resolving these two points of view is
a critical step in making the most of this promising technology. In this work
we formalize the notion of AQS reliability by determining sensitivity of AQS
outputs to underlying parameters, and formulate conditions for robust
simulation. Our approach naturally reveals the importance of model symmetries
in dictating the robust properties. To demonstrate the approach, we
characterize the robust features of a variety of quantum many-body models.


title:
Ramification of inseparable coverings of schemes and application to
  diagonalizable group actions

abstract:
  We define the notion of inseparable coverings of schemes and we propose a
ramification formalism for them, along the lines of the classical one. Using
this formalism we prove a formula analogous to the classical Riemann-Hurwitz
formula for generic torsors under infinitesimal diagonalizable group schemes.


title: Different definitions of conic sections in hyperbolic geometry

abstract:
  In classical Euclidean geometry, there are several equivalent definitions of
conic sections. We show that in the hyperbolic plane, the analogues of these
same definitions still make sense, but are no longer equivalent, and we discuss
the relationships among them.


title: Studies on Brutal Contraction and Severe Withdrawal: Preliminary Report

abstract:
  In this paper we study the class of brutal base contractions that are based
on a bounded ensconcement and also the class of severe withdrawals which are
based on bounded epistemic entrenchment relations that are defined by means of
bounded ensconcements (using the procedure proposed by Mary-Anne Williams). We
present axiomatic characterizations for each one of those classes of functions
and investigate the interrelation among them.


title: Higher weight on GL(3), I: The Eisenstein series

abstract:
  The purpose of this paper is to collect and make explicit the results of
Langlands, Bump, Miyazaki and Manabe, Ishii and Oda for the $GL(3)$ Eisenstein
series and Whittaker functions which are non-trivial on $SO(3,\mathbb{R})$. The
final goal for the series of papers is a complete and completely explicit
spectral expansion for $L^2(SL(3,\mathbb{Z})\backslash SL(3,\mathbb{R}))$ in
the style of Duke, Friedlander and Iwaniec's paper on Artin L-functions. We
derive a number of new results on the Whittaker functions and Eisenstein
series, and give new, concrete proofs of the functional equations and spectral
expansion in place of the general constructions of Langlands.


title: Annihilator ideals of two-generated metabelian p-groups

abstract:
  For a metabelian p-group G = <x,y> with two generators x and y, the
annihilator A < Z[X,Y] of the main commutator [y,x] of G, as an ideal of
bivariate polynomials with integer coefficients, is determined by means of a
presentation for G. Furtw\"angler's isomorphism of the additive group
underlying the residue class ring Z[X,Y]/A of Z[X,Y] modulo the annihilator A
to the commutator subgroup G' of G admits the calculation of the abelian type
of G'.


title: Surreal limits

abstract:
  We note that if a sequence of real numbers converges to some limit, then the
sequence of the corresponding strings in the surreal $+,-$ sign expansion
representation converges, for a natural notion of string convergence, to the
string corresponding to the limit, modulo an infinitesimal. The corresponding
statement would be obviously false if we were considering, as strings, decimal
or binary representations, instead. The string limit of a possibly transfinite
sequence of surreal numbers is always defined and, when considering increasing
sequences of ordinals, corresponds to taking the supremum. A transfinite sum
can be defined using the string limit and this sum agrees with the
representation of a surreal number in Conway normal form.


title: LifeJacket: Verifying precise floating-point optimizations in LLVM

abstract:
  Optimizing floating-point arithmetic is vital because it is ubiquitous,
costly, and used in compute-heavy workloads. Implementing precise optimizations
correctly, however, is difficult, since developers must account for all the
esoteric properties of floating-point arithmetic to ensure that their
transformations do not alter the output of a program. Manual reasoning is error
prone and stifles incorporation of new optimizations. We present an approach to
automate reasoning about floating-point optimizations using satisfiability
modulo theories (SMT) solvers. We implement the approach in LifeJacket, a
system for automatically verifying precise floating-point optimizations for the
LLVM assembly language. We have used LifeJacket to verify 43 LLVM optimizations
and to discover eight incorrect ones, including three previously unreported
problems. LifeJacket is an open source extension of the Alive system for
optimization verification.


title: Expressivity and Complexity of MongoDB (Extended Version)

abstract:
  A significant number of novel database architectures and data models have
been proposed during the last decade. While some of these new systems have
gained in popularity, they lack a proper formalization, and a precise
understanding of the expressivity and the computational properties of the
associated query languages. In this paper, we aim at filling this gap, and we
do so by considering MongoDB, a widely adopted document database managing
complex (tree structured) values represented in a JSON-based data model,
equipped with a powerful query mechanism. We provide a formalization of the
MongoDB data model, and of a core fragment, called MQuery, of the MongoDB query
language. We study the expressivity of MQuery, showing its equivalence with
nested relational algebra. We further investigate the computational complexity
of significant fragments of it, obtaining several (tight) bounds in combined
complexity, which range from LOGSPACE to alternating exponential-time with a
polynomial number of alternations. As a consequence, we obtain also a
characterization of the combined complexity of nested relational algebra query
evaluation.


title:
The structure of the free boundary in the fully nonlinear thin obstacle
  problem

abstract:
  We study the regularity of the free boundary in the fully nonlinear thin
obstacle problem. Our main result establishes that the free boundary is $C^1$
near regular points.


title: Theory of fluid slip in charged capillary nanopores

abstract:
  Based on the capillary pore model (space-charge theory) for combined fluid
and ion flow through cylindrical nanopores or nanotubes, we derive the
continuum equations modified to include wall slip. We focus on the ionic
conductance and streaming conductance, cross-coefficients of relevance for
electrokinetic energy conversion and electro-osmotic pumping. We combine the
theory with a Langmuir-Stern 1-pK charge regulation boundary condition
resulting in a non-monotonic dependence of the cross-coefficients on salt
concentration.


title: Fermionic Modular Categories and the 16-fold Way

abstract:
  We study spin and super-modular categories systematically as inspired by
fermionic topological phases of matter, which are always fermion parity
enriched and modelled by spin TQFTs at low energy. We formulate a $16$-fold way
conjecture for the minimal modular extensions of super-modular categories to
spin modular categories, which is a categorical formulation of gauging the
fermion parity. We investigate general properties of super-modular categories
such as fermions in twisted Drinfeld doubles, Verlinde formulas for naive
quotients, and explicit extensions of $PSU(2)_{4m+2}$ with an eye towards a
classification of the low-rank cases.


title: Homology Class of a Deligne-Lusztig variety and its analogues

abstract:
  In this paper we consider Deligne-Lusztig varieties and their analogues when
the Frobenius endomorphism is replaced with conjugation by an element in a
group, especially a regular semisimple or regular unipotent one. We calculate
their classes in the Chow group of the flag variety in terms of Schubert
classes. Also we give some sufficient criteria when different elements in the
Weyl group result in the same class.


title:
Relating $\hat{q}$, $\eta/s$ and $\Delta E$ in an expanding Quark-Gluon
  Plasma

abstract:
  We use linear viscous hydrodynamics to describe the energy and momentum
deposited by a fast moving parton in a quark gluon plasma. This energy-momentum
is in turn used to compute the probability density for the production of soft
partons by means of the Cooper-Frye formula. We use this probability density to
render manifest a relation between the average transverse momentum given to the
fast moving parton from the medium $\hat{q}$, the entropy density to shear
viscosity ratio $\eta/s$ and the energy lost by the fast moving parton $\Delta
E$ in an expanding medium under similar conditions to those generated in
nucleus-nucleus collisions at the LHC. We find that $\hat{q}$ increases
linearly with $\Delta E$ for both trigger and away side partons that have been
produced throughout the medium. On the other hand, $\eta/s$ is more stable with
$\Delta E$. We also study how these transport coefficients vary with the
geometrical location of the hard scattering that produces the fast moving
partons. The behavior of $\hat{q}$, with $\Delta E$ is understood as arising
from the length of medium the parton traverses from the point where it is
produced. However, since $\eta/s$ is proportional to the ratio of the length of
medium traversed by the fast parton and the average number of scatterings it
experiences, it has a milder dependence on the energy it loses. This study
represents a tool to obtain a direct connection between transport coefficients
and the description of in-medium energy loss within a linear viscous
hydrodynamical evolution of the bulk.


title:
On Distributed Frequency Estimation in Three-Phase Power Distribution
  Networks

abstract:
  The earlier work of the author on Frequency estimation in three-phase power
systems ( that is included as the reference number 1) is expanded to the
distributed setting in order present a framework for the implementation of such
a frequency estimator in real-world power distribution networks. For rigor, the
mean and mean square performance of the distributed frequency estimator is
analysed. The performance of the developed algorithm is validated through
simulations on both synthetic data and real-world data recordings, where it is
shown to outperform standard linear and the recently introduced widely liner
frequency estimators.


title: Lieb-Robinson and the butterfly effect

abstract:
  As experiments are increasingly able to probe the quantum dynamics of systems
with many degrees of freedom, it is interesting to probe fundamental bounds on
the dynamics of quantum information. We elaborate on the relationship between
one such bound---the Lieb-Robinson bound---and the butterfly effect in
strongly-coupled quantum systems. The butterfly effect implies the ballistic
growth of local operators in time, which can be quantified with the "butterfly"
velocity $v_B$. Similarly, the Lieb-Robinson velocity places a state
independent ballistic upper bound on the size of time evolved operators in
non-relativistic lattice models. Here, we argue that $v_B$ is a state-dependent
effective Lieb-Robinson velocity. We study the butterfly velocity in a wide
variety of quantum field theories using holography and compare with free
particle computations to understand the role of strong coupling. We find that,
depending on the way length and time scale, $v_B$ acquires a temperature
dependence and decreases towards the IR. We also comment on experimental
prospects and on the relationship between the butterfly velocity and signaling.

categories: hep-th cond-mat.quant-gas cond-mat.str-el quant-ph


title:
Anti Self-Dual Yang-Mills, Modified Faddeev-Jackiw Formalism and Hidden
  BRS Invariance

abstract:
  We analyze the constraints for a system of anti self-dual Yang-Mills (ASDYM)
equations by means of the modified Faddeev-Jackiw method in K and J gauges
\`{a} la Yang. We also establish the Hamiltonian flow for ASDYM system through
the hidden BRS invariance in both the gauges. Finally, we remark on the
bi-Hamiltonian nature of ASDYM and the compatibility of the symplectic
structures therein.


title: Non-Obfuscated Unprovable Programs & Many Resultant Subtleties

abstract:
  The \emph{International Obfuscated C Code Contest} was a programming contest
for the most creatively obfuscated yet succinct C code. By \emph{contrast}, an
interest herein is in programs which are, \emph{in a sense}, \emph{easily} seen
to be correct, but which can\emph{not} be proved correct in pre-assigned,
computably axiomatized, powerful, true theories {\bf T}. A point made by our
first theorem, then, is that, then, \emph{un}verifiable programs need
\emph{not} be obfuscated!
  The first theorem and its proof is followed by a motivated, concrete example
based on a remark of Hilary Putnam.
  The first theorem has some non-constructivity in its statement and proof, and
the second theorem implies some of the non-constructivity is inherent. That
result, then, brings up the question of whether there is an acceptable
programming system (numbering) for which some non-constructivity of the first
theorem disappears. The third theorem shows this is the case, but for a subtle
reason explained in the text. This latter theorem has a number of corollaries,
regarding its acceptable programming system, and providing some surprises and
subtleties about proving its program properties (including universality, and
the presence of the composition control structure). The next two theorems
provide acceptable systems with contrasting surprises regarding proving
universality in them. Finally the next and last theorem (the most difficult to
prove in the paper) provides an acceptable system with some positive and
negative surprises regarding verification of its true program properties: the
existence of the control structure composition is provable for it, but anything
about true I/O-program equivalence for syntactically unequal programs is not
provable.


title: The second Feng-Rao number for codes coming from telescopic semigroups

abstract:
  In this manuscript we show that the second Feng-Rao number of any telescopic
numerical semigroup agrees with the multiplicity of the semigroup. To achieve
this result we first study the behavior of Ap\'ery sets under gluings of
numerical semigroups. These results provide a bound for the second Hamming
weight of one-point Algebraic Geometry codes, which improves upon other
estimates such as the Griesmer Order Bound.


title: Confidence driven TGV fusion

abstract:
  We introduce a novel model for spatially varying variational data fusion,
driven by point-wise confidence values. The proposed model allows for the joint
estimation of the data and the confidence values based on the spatial coherence
of the data. We discuss the main properties of the introduced model as well as
suitable algorithms for estimating the solution of the corresponding biconvex
minimization problem and their convergence. The performance of the proposed
model is evaluated considering the problem of depth image fusion by using both
synthetic and real data from publicly available datasets.


title: ASCR/HEP Exascale Requirements Review Report

abstract:
  This draft report summarizes and details the findings, results, and
recommendations derived from the ASCR/HEP Exascale Requirements Review meeting
held in June, 2015. The main conclusions are as follows. 1) Larger, more
capable computing and data facilities are needed to support HEP science goals
in all three frontiers: Energy, Intensity, and Cosmic. The expected scale of
the demand at the 2025 timescale is at least two orders of magnitude -- and in
some cases greater -- than that available currently. 2) The growth rate of data
produced by simulations is overwhelming the current ability, of both facilities
and researchers, to store and analyze it. Additional resources and new
techniques for data analysis are urgently needed. 3) Data rates and volumes
from HEP experimental facilities are also straining the ability to store and
analyze large and complex data volumes. Appropriately configured
leadership-class facilities can play a transformational role in enabling
scientific discovery from these datasets. 4) A close integration of HPC
simulation and data analysis will aid greatly in interpreting results from HEP
experiments. Such an integration will minimize data movement and facilitate
interdependent workflows. 5) Long-range planning between HEP and ASCR will be
required to meet HEP's research needs. To best use ASCR HPC resources the
experimental HEP program needs a) an established long-term plan for access to
ASCR computational and data resources, b) an ability to map workflows onto HPC
resources, c) the ability for ASCR facilities to accommodate workflows run by
collaborations that can have thousands of individual members, d) to transition
codes to the next-generation HPC platforms that will be available at ASCR
facilities, e) to build up and train a workforce capable of developing and
using simulations and analysis to support HEP scientific research on
next-generation systems.

categories: physics.comp-ph astro-ph.CO hep-ex hep-lat hep-ph


title: Multiple codings for self-similar sets with overlaps

abstract:
  In this paper we consider a general class $\mathcal E$ of self-similar sets
with complete overlaps. Given a self-similar iterated function system $\Phi=(E,
\{f_i\}_{i=1}^m)\in\mathcal E$ on the real line, for each point $x\in E$ we can
find a sequence $(i_k)=i_1i_2\ldots\in\{1,\ldots,m\}^\mathbb N$, called a
coding of $x$, such that $$ x=\lim_{n\to\infty}f_{i_1}\circ
f_{i_{2}}\circ\cdots\circ f_{i_n}(0). $$ For $k=1,2,\ldots, \aleph_0$ or
$2^{\aleph_0}$ we investigate the subset $\mathcal U_k(\Phi)$ which consists of
all $x\in E$ having precisely $k$ different codings. Among several equivalent
characterizations we show that $\mathcal U_1(\Phi)$ is closed if and only if
$\mathcal U_{\aleph_0}(\Phi)$ is an empty set. Furthermore, we give explicit
formulae for the Hausdorff dimension of $\mathcal U_k(\Phi)$, and show that the
corresponding Hausdorff measure of $\mathcal U_k(\Phi)$ is always infinite for
any $k\ge 2$. Finally, we explicitly calculate the local dimension of the
self-similar measure at each point in $\mathcal U_k(\Phi)$ and
${U_{\aleph_0}(\Phi)}$.


title: Z/2-equivariant and R-motivic stable stems

abstract:
  We establish an isomorphism between the stable homotopy groups of the
2-completed motivic sphere spectrum over the real numbers and the corresponding
stable homotopy groups of the 2-completed Z/2-equivariant sphere spectrum, in a
certain range of dimensions.


title: A New Method for Finding Point Sources in High-energy Neutrino Data

abstract:
  The IceCube collaboration has reported the first detection of high-energy
astrophysical neutrinos including $\sim 50$ high-energy starting events, but no
individual sources have been identified. It is therefore important to develop
the most sensitive and efficient possible algorithms to identify point sources
of these neutrinos. The most popular current method works by exploring a dense
grid of possible directions to individual sources, and identifying the single
direction with the maximum probability of having produced multiple detected
neutrinos. This method has numerous strengths, but it is computationally
intensive and, because it focuses on the single best location for a point
source, additional point sources are not included in the evidence. We propose a
new maximum likelihood method that uses the angular separations between all
pairs of neutrinos in the data. Unlike existing autocorrelation methods for
this type of analysis, which also use angular separations between neutrino
pairs, our method incorporates information about the point spread function and
can identify individual point sources. We find that if the angular resolution
is a few degrees or better, then this approach reduces both false positive and
false negative errors compared to the current method, and is also more
computationally efficient up to, potentially, hundreds of thousands of detected
neutrinos.


title: M Stars in the TW Hya Association: Stellar X-rays and Disk Dissipation

abstract:
  To investigate the potential connection between the intense X-ray emission
from young, low-mass stars and the lifetimes of their circumstellar,
planet-forming disks, we have compiled the X-ray luminosities ($L_X$) of M
stars in the $\sim$8 Myr-old TW Hya Association (TWA) for which X-ray data are
presently available. Our investigation includes analysis of archival Chandra
data for the TWA binary systems TWA 8, 9, and 13. Although our study suffers
from poor statistics for stars later than M3, we find a trend of decreasing
$L_X/L_{bol}$ with decreasing $T_{eff}$ for TWA M stars wherein the
earliest-type (M0--M2) stars cluster near $\log{(L_X/L_{bol})} \approx -3.0$
and then $\log{(L_X/L_{bol})}$ decreases, and its distribution broadens, for
types M4 and later. The fraction of TWA stars that display evidence for
residual primordial disk material also sharply increases in this same (mid-M)
spectral type regime. This apparent anticorrelation between the relative X-ray
luminosities of low-mass TWA stars and the longevities of their circumstellar
disks suggests that primordial disks orbiting early-type M stars in the TWA
have dispersed rapidly as a consequence of their persistent large X-ray fluxes.
Conversely, the disks orbiting the very lowest-mass pre-MS stars and pre-MS
brown dwarfs in the Association may have survived because their X-ray
luminosities and, hence, disk photoevaporation rates are very low to begin
with, and then further decline relatively early in their pre-MS evolution.


title: Lithium Adsorbtion on Polyacenes $\&$ Zig-zag-edge Graphene Strips

abstract:
  The effect of increased electron-density (from adsorbed Li atoms) in
polyacenes and in nano-ribbons with zig-zag edge is discussed in terms of
resonance theoretical considerations and in terms edge-localized frontier
molecular orbitals. The argumentation from simple pictures is finally using the
density functional theory (DFT) for anthracene, polyacene polymer and graphene
strips. Some discussion is made for zig-zag edge graphene.


title: Global topology of hyperbolic components I: Cantor circle case

abstract:
  The hyperbolic components in the moduli space ${M}_d$ of degree $d\geq2$
rational maps are mysterious and fundamental topological objects. For those in
the connectedness locus, they are known to be the finite quotients of the
Euclidean space $\mathbb{R}^{4d-4}$. In this paper, we study the hyperbolic
components in the disconnectedness locus and with minimal complexity: those in
the Cantor circle locus. We show that each of them is a finite quotient of the
space $\mathbb{R}^{4d-4-n}\times\mathbb{T}^{n}$, where $n$ is determined by the
dynamics. The proof relates Riemann surface theory (Abel's Theorem), dynamical
system and algebraic topology.


title: On the k-regularity of the k-adic valuation of Lucas sequences

abstract:
  For integers $k \geq 2$ and $n \neq 0$, let $v_k(n)$ denotes the greatest
nonnegative integer $e$ such that $k^e$ divides $n$. Moreover, let $u_n$ be a
nondegenerate Lucas sequence satisfying $u_0 = 0$, $u_1 = 1$, and $u_{n + 2} =
a u_{n + 1} + b u_n$, for some integers $a$ and $b$. Shu and Yao showed that
for any prime number $p$ the sequence $v_p(u_{n + 1})$ is $p$-regular, while
Medina and Rowland found the rank of $v_p(F_{n + 1})$, where $F_n$ is the
$n$-th Fibonacci number. We prove that if $k$ and $b$ are relatively prime then
$v_k(u_{n + 1})$ is a $k$-regular sequence, and for $k$ a prime number we also
determine its rank. Furthermore, as an intermediate result, we give explicit
formulas for $v_k(u_n)$, generalizing a previous theorem of Sanna concerning
$p$-adic valuations of Lucas sequences.


title:
Stochastic domain decomposition for the solution of the two-dimensional
  magnetotelluric problem

abstract:
  Stochastic domain decomposition is proposed as a novel method for solving the
two-dimensional Maxwell's equations as used in the magnetotelluric method. The
stochastic form of the exact solution of Maxwell's equations is evaluated using
Monte-Carlo methods taking into consideration that the domain may be divided
into neighboring sub-domains. These sub-domains can be naturally chosen by
splitting the sub-surface domain into regions of constant (or at least
continuous) conductivity. The solution over each sub-domain is obtained by
solving Maxwell's equations in the strong form. The sub-domain solver used for
this purpose is a meshless method resting on radial basis function based finite
differences. The method is demonstrated by solving a number of classical
magnetotelluric problems, including the quarter-space problem, the
block-in-half-space problem and the triangle-in-half-space problem.


title:
Perturbative approach in the frequency domain for the intensity
  correlation spectrum at electromagnetically induced transparency

abstract:
  Correlation spectroscopy has been proposed as a spectroscopic technique for
measuring the coherence between the ground states in electromagnetically
induced transparency (EIT). While in time domain the steep dispersion in EIT
condition accounts for the robustness of the correlation linewidth against
power broadening, such physical insight was not directly established in the
frequency domain. We propose a perturbative approach to describe the
correlation spectroscopy of two noisy lasers coupled to a $\Lambda$-transition
in cold atoms, leading to EIT. Such approach leads to an analytical expression
that maps the intensity correlation directly in terms of the absorption and
dispersion of the light fields. Low and high perturbative regimes are
investigated and demonstrate that, for coherent light sources, the first oder
term in perturbation expansion represents a sufficient description for the
correlation. Sidebands resonances are also observed, showing the richness of
the frequency domain approach.


title:
Heterogeneity of Global and Local Connectivity in Spatial Network
  Structures of World Migration

abstract:
  We examine world migration as a social-spatial network of countries connected
via movements of people. We assess how multilateral migratory relationships at
global, regional, and local scales coexist ("glocalization"), divide
("polarization"), or form an interconnected global system ("globalization"). To
do this, we decompose the world migration network (WMN) into communities---sets
of countries with denser than expected migration connections---and characterize
their pattern of local (i.e., intracommunity) and global (i.e., intercommunity)
connectivity. We distinguish community signatures---"cave", "biregional", and
"bridging"---with distinct migration patterns, spatial network structures,
temporal dynamics, and underlying antecedents. Cave communities are
tightly-knit, enduring structures that tend to channel local migration between
contiguous countries; biregional communities are likely to merge migration
between two distinct geographic regions (e.g., North Africa and Europe); and
bridging communities have hub-and-spoke structures that tend to emerge
dynamically from globe-spanning movements. We find that world migration is
neither globally interconnected nor reproduces the geographic boundaries as
drawn on a world map but involves a heterogeneous interplay of global and local
tendencies in different network regions. We discuss the implications of our
results for the understating of variability in today's transnational mobility
patterns and migration opportunities across the globe.

categories: physics.soc-ph cond-mat.dis-nn cs.SI nlin.AO


title: Fusion Enhancement for Neutron-Rich Light Nuclei

abstract:
  Measurement of the fusion cross-section for neutron-rich light nuclei is
crucial in ascertaining if fusion of these nuclei occurs in the outer crust of
a neutron star. The fusion excitation function at near-barrier energies for the
$^{19}$O + $^{12}$C system was measured and the experimental results are
compared to the fusion excitation function of $^{18}$O + $^{12}$C and $^{16}$O
+ $^{12}$C. The experiment was performed by utilizing a beam of $^{19}$O,
produced via the $^{18}$O(d,p) reaction, to bombard a $^{12}$C target at
energies near the Coulomb barrier. Evaporation residues produced in fusion of
$^{18,19}$O ions with $^{12}$C target nuclei were detected with good geometric
efficiency and identified by measuring their energy and time-of-flight. A
significant enhancement is observed in the fusion probability of $^{19}$O ions
with a $^{12}$C target as compared to $^{18}$O ions. The larger cross-sections
observed at near barrier energies is related to significant narrowing of the
fusion barrier indicating a larger tunneling probability for the fusion
process.


title: On Fujita's spectrum conjecture

abstract:
  We prove Fujita's spectrum conjecture on the discreteness of pseudo-effective
thresholds for polarized varieties.


title:
Single-Sided Contacting of Out-of-Plane Polarized Piezo Films for Fluid
  Membrane Lenses

abstract:
  We present an adaptive lens which tunes its focal length with a glass
membrane that is deformed by an integrated piezo bending actuator. A particular
challenge in the fabrication of this type of actuator is the need to contact
the electrodes on both sides of the piezo element, i.e. also on the glass
surface. Therefore, we show a novel contacting method where the top electrode
on the piezo is segmented and the backside electrode is left at a floating
potential. With this setup we achieve tuning capabilities of more than 13 dpt
and response times in the range of less than 4 ms at a usable aperture of 4.5
mm.


title: Holographic anyonization: A systematic approach

abstract:
  Anyons have garnered substantial interest theoretically as well as
experimentally. Due to the intricate nature of their interactions, however,
even basic notions such as the equation of state for any kind of anyon gas have
eluded a profound understanding so far. Using holography as a guiding
principle, we propose a general method for an alternative quantization of
electromagnetic degrees of freedom in the gravitational dual to obtain an
effective physical description of strongly correlated anyonic systems. We then
demonstrate the application of this prescription in a toy model of an anyonic
fluid at finite charge density and magnetic field, dual to a dyonic black brane
in AdS_4, and compute the equation of state and various transport coefficients
explicitly.


title:
Butterfly Magnetoresistance, Quasi-2D Dirac Fermi Surfaces, and a
  Topological Phase Transition in ZrSiS

abstract:
  Magnetoresistance (MR), the change of a material's electrical resistance in
response to an applied magnetic field, is a technologically important property
that has been the topic of intense study for more than a quarter century. Here
we report the observation of an unusual "butterfly" shaped titanic angular
magnetoresistance (AMR) in the non-magnetic, Dirac material, ZrSiS. The MR is
large and positive, reaching nearly 1.8 x 10^5 percent at 9 T and 2 K at an
angle of 45o between the applied current (along the a-axis) and the applied
field (90o is H parallel to the c-axis). Approaching 90o, a "dip" is seen in
the AMR which can be traced to an angle dependent deviation from the H^2 law.
By analyzing the SdH oscillations at different angles, we find that ZrSiS has a
combination of 2D and 3D Dirac pockets comprising its Fermi surface and that
the anomalous transport behavior coincides with a topological phase transition
whose robust signature is evident despite transport contributions from other
parts of the Fermi surface. We also find that as a function of angle, the
temperature dependent resistivity in high field displays a broad peak-like
behavior, unlike any known Dirac/Weyl material. The combination of very high
mobility carriers and multiple Fermi surfaces in ZrSiS allow for large bulk
property changes to occur as a function of angle between applied fields makes
it a promising platform to study the physics stemming from the coexistence of
2D and 3D Dirac electrons.


title:
Structure and evolution of a European Parliament via a network and
  correlation analysis

abstract:
  We present a study of the network of relationships among elected members of
the Finnish parliament, based on a quantitative analysis of initiative
co-signatures, and its evolution over 16 years. To understand the structure of
the parliament, we constructed a statistically validated network of members,
based on the similarity between the patterns of initiatives they signed. We
looked for communities within the network and characterized them in terms of
members' attributes, such as electoral district and party. To gain insight on
the nested structure of communities, we constructed a hierarchical tree of
members from the correlation matrix. Afterwards, we studied parliament dynamics
yearly, with a focus on correlations within and between parties, by also
distinguishing between government and opposition. Finally, we investigated the
role played by specific individuals, at a local level. In particular, whether
they act as proponents who gather consensus, or as signers. Our results provide
a quantitative background to current theories in political science. From a
methodological point of view, our network approach has proven able to highlight
both local and global features of a complex social system.


title:
Efficient and robust approximate nearest neighbor search using
  Hierarchical Navigable Small World graphs

abstract:
  We present a new approach for the approximate K-nearest neighbor search based
on navigable small world graphs with controllable hierarchy (Hierarchical NSW,
HNSW). The proposed solution is fully graph-based, without any need for
additional search structures, which are typically used at the coarse search
stage of the most proximity graph techniques. Hierarchical NSW incrementally
builds a multi-layer structure consisting from hierarchical set of proximity
graphs (layers) for nested subsets of the stored elements. The maximum layer in
which an element is present is selected randomly with an exponentially decaying
probability distribution. This allows producing graphs similar to the
previously studied Navigable Small World (NSW) structures while additionally
having the links separated by their characteristic distance scales. Starting
search from the upper layer together with utilizing the scale separation boosts
the performance compared to NSW and allows a logarithmic complexity scaling.
Additional employment of a heuristic for selecting proximity graph neighbors
significantly increases performance at high recall and in case of highly
clustered data. Performance evaluation has demonstrated that the proposed
general metric space search index is able to strongly outperform previous
opensource state-of-the-art vector-only approaches. Similarity of the algorithm
to the skip list structure allows straightforward balanced distributed
implementation.


title:
Coherent X-ray measurements of ion-implantation-induced lattice strains
  in nano-crystals

abstract:
  Focussed Ion Beam (FIB) milling is a mainstay of nano-scale machining. By
manipulating a tightly focussed beam of energetic ions, often gallium (Ga+),
FIB can sculpt nanostructures via localised sputtering. This ability to cut
solid matter on the nano-scale has revolutionised sample preparation across the
life-, earth- and materials sciences. For example FIB is central to microchip
prototyping, 3D material analysis, targeted electron microscopy sample
extraction and the nanotechnology behind size-dependent material properties.
Despite its widespread usage, detailed understanding of the functional
consequences of FIB-induced structural damage, intrinsic to the technique,
remains elusive. Here, we present nano-scale measurements of three-dimensional,
FIB-induced lattice strains, probed using Bragg Coherent X-ray Diffraction
Imaging (BCDI). We observe that even low gallium ion doses, typical of FIB
imaging, cause substantial lattice distortions. At higher doses, extended
self-organised defect structures appear, giving rise to stresses far in excess
of the bulk yield limit. Combined with detailed numerical calculations, these
observations provide fundamental insight into the nature of the damage created
and the structural instabilities that lead to a surprisingly inhomogeneous
morphology.


title: Raman sideband cooling of a 138Ba+ ion using a Zeeman interval

abstract:
  Motional ground state cooling and internal state preparation are important
elements for quantum logic spectroscopy (QLS), a class of quantum information
processing. Since QLS does not require the high gate fidelities usually
associated with quantum computation and quantum simulation, it is possible to
make simplifying choices in ion species and quantum protocols at the expense of
some fidelity. Here, we report sideband cooling and motional state detection
protocols for $^{138}$Ba$^+$ of sufficient fidelity for QLS without an
extremely narrowband laser or the use of a species with hyperfine structure. We
use the two S$_{1/2}$ Zeeman sublevels of $^{138}$Ba$^+$ to Raman sideband cool
a single ion to the motional ground state. Because of the small Zeeman
splitting, near-resonant Raman sideband cooling of $^{138}$Ba$^+$ requires only
the Doppler cooling lasers and two additional AOMs. Observing the near-resonant
Raman optical pumping fluorescence, we estimate a final average motional
quantum number $\bar{n}\approx0.17$. We additionally employ a second,
far-off-resonant laser driving Raman $\pi$-pulses between the two Zeeman
sublevels to provide motional state detection for QLS and to confirm the
sideband cooling efficiency, measuring a final $\bar{n} = 0.15(6)$.


title:
$T^4$ fibrations over Calabi-Yau two-folds and non-Kahler manifolds in
  string theory

abstract:
  We construct a geometric model of eight-dimensional manifolds and realize
them in the context of type II string theory. These eight-manifolds are
constructed by non-trivial $T^{4}$ fibrations over Calabi-Yau two-folds. These
give rise to eight-dimensional non-Kahler Hermitian manifolds with $SU(4)$
structure. The eight-manifold is also a circle fibration over a
seven-dimensional $G_{2}$ manifold with skew torsion. The eight-manifolds of
this type appear as internal manifolds with $SU(4)$ structure in type IIB
string theory with $F_{3}$ and $F_{7}$ fluxes. These manifolds have generalized
calibrated cycles in the presence of fluxes.


title: Parisian ruin for a refracted L\'evy process

abstract:
  In this paper, we investigate Parisian ruin for a L\'evy surplus process with
an adaptive premium rate, namely a refracted L\'evy process. More general
Parisian boundary-crossing problems with a deterministic implementation delay
are also considered. Our main contribution is a generalization of the result in
Loeffen et al. (2013) for the probability of Parisian ruin of a standard L\'evy
insurance risk process. Despite the more general setup considered here, our
main result is as compact and has a similar structure. Examples are provided.


title:
A Hybrid Method and Unified Analysis of Generalized Finite Differences
  and Lagrange Finite Elements

abstract:
  Finite differences, finite elements, and their generalizations are widely
used for solving partial differential equations, and their high-order variants
have respective advantages and disadvantages. Traditionally, these methods are
treated as different (strong vs. weak) formulations and are analyzed using
different techniques (Fourier analysis or Green's functions vs. functional
analysis), except for some special cases on regular grids. Recently, the
authors introduced a hybrid method, called Adaptive Extended Stencil FEM or
AES-FEM (Int. J. Num. Meth. Engrg., 2016, DOI:10.1002/nme.5246), which combines
features of generalized finite differences and Lagrange finite elements to
achieve second-order accuracy over unstructured meshes. However, its analysis
was incomplete due to the lack of existing mathematical theory that unifies the
formulations and analysis of these different methods. In this work, we
introduce the framework of generalized weighted residuals to unify the
formulation of finite differences, finite elements, and AES-FEM. In addition,
we propose a unified analysis of the well-posedness, convergence, and
mesh-quality dependency of these different methods. We also report numerical
results with AES-FEM to verify our analysis. We show that AES-FEM improves the
accuracy of generalized finite differences while reducing the mesh-quality
dependency and simplifying the implementation of high-order finite elements.