title:
Swarm in situ observations of F region polar cap patches created by cusp
  precipitation

abstract:
  High-resolution in situ measurements from the three Swarm spacecraft, in a
string-of-pearls configuration, provide new insights about the combined role of
flow channel events and particle impact ionization in creating $\textit{F}$
region electron density structures in the northern Scandinavian dayside cusp.
We present a case of polar cap patch formation where a reconnection-driven
low-density relative westward flow channel is eroding the dayside solar-ionized
plasma but where particle impact ionization in the cusp dominates the initial
plasma structuring. In the cusp, density features are observed which are twice
as dense as the solar-ionized background. These features then follow the polar
cap convection and become less structured and lower in amplitude. These are the
first in situ observations tracking polar cap patch evolution from creation by
plasma transport and enhancement by cusp precipitation, through entrainment in
the polar cap flow and relaxation into smooth patches as they approach the
nightside auroral oval.


title:
Degenerate Operators and the $1/c$ Expansion: Lorentzian Resummations,
  High Order Computations, and Super-Virasoro Blocks

abstract:
  One can obtain exact information about Virasoro conformal blocks by
analytically continuing the correlators of degenerate operators. We argued in
recent work that this technique can be used to explicitly resolve information
loss problems in AdS$_3$/CFT$_2$. In this paper we use the technique to perform
calculations in the small $1/c \propto G_N$ expansion: (1) we prove the
all-orders resummation of logarithmic factors $\propto \frac{1}{c} \log z$ in
the Lorentzian regime, demonstrating that $1/c$ corrections directly shift
Lyapunov exponents associated with chaos, as claimed in prior work, (2) we
perform another all-orders resummation in the limit of large $c$ with fixed
$cz$, interpolating between the early onset of chaos and late time behavior,
(3) we explicitly compute the Virasoro vacuum block to order $1/c^2$ and
$1/c^3$, corresponding to $2$ and $3$ loop calculations in AdS$_3$, and (4) we
derive the heavy-light vacuum blocks in theories with $\mathcal{N}=1,2$
superconformal symmetry.


title: Homomorphisms into loop-threshold graphs

abstract:
  Many problems in extremal graph theory correspond to questions involving
homomorphisms into a fixed image graph. Recently, there has been interest in
maximizing the number of homomorphisms from graphs with a fixed number of
vertices and edges into small image graphs. For the image graph
$H_{\text{ind}}$, the graph on two adjacent vertices, one of which is looped,
each homomorphism from $G$ to $H_{\text{ind}}$ corresponds to an independent
set in $G$. It follows from the Kruskal-Katona theorem that the number of
homomorphisms to $H_{\text{ind}}$ is maximized by the lex graph, whose edges
form an initial segment of the lex order.
  A \emph{loop-threshold graph} is a graph built recursively from a single
vertex, which may be looped or unlooped, by successively adding either a looped
dominating vertex or an unlooped isolated vertex at each stage. Thus, the graph
$H_{\text{ind}}$ is a loop-threshold graph. We survey known results for
maximizing the number of homomorphisms into small loop-threshold image graphs.
The only extremal homomorphism problem with a loop-threshold image graph on at
most three vertices not yet solved is $H_{\text{ind}}\cup E_1$, where extremal
graphs are the union of a lex graph and an empty graph. The only question that
remains is the size of the lex component of the extremal graph. While we cannot
give an exact answer for every number of vertices and edges, we establish the
significance of and give a bound for $\ell(m)$, the number of vertices in the
lex component of the extremal graph with $m$ edges and at least $m+1$ vertices.


title:
Decoherence enhances performance of quantum walks applied to graph
  isomorphism testing

abstract:
  Computational advantages gained by quantum algorithms rely largely on the
coherence of quantum devices and are generally compromised by decoherence. As
an exception, we present a quantum algorithm for graph isomorphism testing
whose performance is optimal when operating in the partially coherent regime,
as opposed to the extremes of fully coherent or classical regimes. The
algorithm builds on continuous-time quantum stochastic walks (QSWs) on graphs
and the algorithmic performance is quantified by the distinguishing power (DIP)
between non-isomorphic graphs. The QSW explores the entire graph and acquires
information about the underlying structure, which is extracted by monitoring
stochastic jumps across an auxiliary edge. The resulting counting statistics of
stochastic jumps is used to identify the spectrum of the dynamical generator of
the QSW, serving as a novel graph invariant, based on which non-isomorphic
graphs are distinguished. We provide specific examples of non-isomorphic graphs
that are only distinguishable by QSWs in the presence of decoherence.


title:
Far-field linear optical superresolution via heterodyne detection in a
  higher-order local oscillator mode

abstract:
  The Rayleigh limit has so far applied to all microscopy techniques that rely
on linear optical interaction and detection in the far field. Here we
demonstrate that detecting the light emitted by an object in higher-order
transverse electromagnetic modes (TEMs) can help achieving sub-Rayleigh
precision for a variety of microscopy-related tasks. Using optical heterodyne
detection in TEM01, we measure the position of coherently and incoherently
emitting objects to within 0.0015 and 0.012 of the Rayleigh limit,
respectively, and determine the distance between two incoherently emitting
slits positioned within 0.28 of the Rayleigh limit with a precision of 0.019 of
the Rayleigh limit. Extending our technique to higher-order TEMs enables full
imaging with resolution significantly below the Rayleigh limit in a way that is
reminiscent of quantum tomography of optical states.


title:
Imaging the Breakdown of Molecular-Frame Dynamics through Rotational
  Uncoupling

abstract:
  We demonstrate the breakdown of molecular-frame dynamics induced by the
uncoupling of molecular rotation from electronic motion in molecular Rydberg
states. We observe this non-Born-Oppenheimer regime in the time domain through
photoelectron imaging of a coherent molecular Rydberg wave packet in
$\textrm{N}_2$. The photoelectron angular distribution shows a radically
different time evolution than that of a typical molecular-frame-fixed electron
orbital, revealing the uncoupled motion of the electron as it precesses around
the $averaged$ anisotropic potential of the rotating ion-core.


title:
Simultaneous classical communication and quantum key distribution using
  continuous variable

abstract:
  Presently, classical optical communication systems employing strong laser
pulses and quantum key distribution (QKD) systems working at single-photon
levels are very different communication modalities. Dedicated devices are
commonly required to implement QKD. In this paper, we propose a scheme which
allows classical communication and QKD to be implemented simultaneously using
the same communication infrastructure. More specially, we propose a coherent
communication scheme where both the bits for classical communication and the
Gaussian distributed random numbers for QKD are encoded on the same weak
coherent pulse, and decoded by the same coherent receiver. Simulation results
based on practical system parameters show that both deterministic classical
communication with a bit error rate of 10^{-9} and secure key distribution
could be achieved over tens of kilometers single mode fibers. It is conceivable
that in the future coherent optical communication network, QKD is operated in
the background of classical communication at a minimal cost.


title:
Angular velocity of a spheroid log rolling in a simple shear at small
  Reynolds number

abstract:
  We analyse the angular velocity of a small neutrally buoyant spheroid log
rolling in a simple shear. When the effect of fluid inertia is negligible the
angular velocity $\omega$ equals half the fluid vorticity. We compute by
singular perturbation theory how weak fluid inertia reduces the angular
velocity in an unbounded shear, and how this reduction depends upon the shape
of the spheroid (on its aspect ratio). In addition we determine the angular
velocity by direct numerical simulations. The results are in excellent
agreement with the theory at small but not too small values of the shear
Reynolds number, for all aspect ratios considered. For the special case of a
sphere we find $\omega/s = -1/2+0.0540\, \mbox{Re}_\mbox{s}^{3/2}$ where $s$ is
the shear rate, and $\mbox{Re}_\mbox{s}$ is the shear Reynolds number. This
result differs from that derived by Lin et al. [J. Fluid Mech. 44 (1970) 1] who
obtained a numerical coefficient roughly three times larger.


title: Beating Rayleigh's Curse by Imaging Using Phase Information

abstract:
  Any imaging device such as a microscope or telescope has a resolution limit,
a minimum separation it can resolve between two objects or sources; this limit
is typically defined by "Rayleigh's criterion", although in recent years there
have been a number of high-profile techniques demonstrating that Rayleigh's
limit can be surpassed under particular sets of conditions. Quantum information
and quantum metrology have given us new ways to approach measurement ; a new
proposal inspired by these ideas has now re-examined the problem of trying to
estimate the separation between two poorly resolved point sources. The "Fisher
information" provides the inverse of the Cramer-Rao bound, the lowest variance
achievable for an unbiased estimator. For a given imaging system and a fixed
number of collected photons, Tsang, Nair and Lu observed that the Fisher
information carried by the intensity of the light in the image-plane (the only
information available to traditional techniques, including previous
super-resolution approaches) falls to zero as the separation between the
sources decreases; this is known as "Rayleigh's Curse." On the other hand, when
they calculated the quantum Fisher information of the full electromagnetic
field (including amplitude and phase information), they found it remains
constant. In other words, there is infinitely more information available about
the separation of the sources in the phase of the field than in the intensity
alone. Here we implement a proof-of-principle system which makes use of the
phase information, and demonstrate a greatly improved ability to estimate the
distance between a pair of closely-separated sources, and immunity to
Rayleigh's curse.


title:
Renyi entanglement entropies of descendant states in critical systems
  with boundaries: conformal field theory and spin chains

abstract:
  We discuss the Renyi entanglement entropies of descendant states in critical
one-dimensional systems with boundaries, that map to boundary conformal field
theories in the scaling limit. We unify the previous conformal-field-theory
approaches to describe primary and descendant states in systems with both open
and closed boundaries. We provide universal expressions for the first two
descendants in the identity family. We apply our technique to critical systems
belonging to different universality classes with non-trivial boundary
conditions that preserve conformal invariance, and find excellent agreement
with numerical results obtained for finite spin chains. We also demonstrate
that entanglement entropies are a powerful tool to resolve degeneracy of higher
excited states in critical lattice models.


title:
Convergence Analysis and Error Estimates for a Second Order Accurate
  Finite Element Method for the Cahn-Hilliard-Navier-Stokes System

abstract:
  In this paper, we present a novel second order in time mixed finite element
scheme for the Cahn-Hilliard-Navier-Stokes equations with matched densities.
The scheme combines a standard second order Crank-Nicholson method for the
Navier-Stokes equations and a modification to the Crank-Nicholson method for
the Cahn-Hilliard equation. In particular, a second order Adams-Bashforth
extrapolation and a trapezoidal rule are included to help preserve the energy
stability natural to the Cahn-Hilliard equation. We show that our scheme is
unconditionally energy stable with respect to a modification of the continuous
free energy of the PDE system. Specifically, the discrete phase variable is
shown to be bounded in $\ell^\infty \left(0,T;L^\infty\right)$ and the discrete
chemical potential bounded in $\ell^\infty \left(0,T;L^2\right)$, for any time
and space step sizes, in two and three dimensions, and for any finite final
time $T$. We subsequently prove that these variables along with the fluid
velocity converge with optimal rates in the appropriate energy norms in both
two and three dimensions.


title:
Formal Semantics and Soundness of a Translation from Event-B Actions to
  SQL Statements

abstract:
  The EventB2SQL tool translates Event-B models to persistent Java applications
that store the state of the model in a relational database. Most Event-B
assignments are translated directly to SQL database modification statements,
which can then be executed against the database. In this work, we present a
formal semantics for and prove the soundness of the translation of sets of
assignment statements representing the actions of an Event-B event. This allows
the generated code to be used with confidence in its correctness.


title: On rigidity of flag varieties

abstract:
  We prove that the variety of complete flags for any semisimple algebraic
group is rigid in any smooth family of Fano manifolds.


title:
An Efficient Computation of Coherent Synchrotron Radiation in a
  Rectangular Chamber, Applied to Resistive Wall Heating

abstract:
  We study coherent synchrotron radiation (CSR) in a perfectly conducting
vacuum chamber of rectangular cross section, in a formalism allowing an
arbitrary sequence of bends and straight sections. We apply the paraxial method
in the frequency domain, with a Fourier development in the vertical coordinate
but with no other mode expansions. A line charge source is handled numerically
by a new method that rids the equations of singularities through a change of
dependent variable. The resulting algorithm is fast compared to earlier
methods, works for short bunches with complicated structure, and yields all six
field components at any space-time point. As an example we compute the
tangential magnetic field at the walls. From that one can make a perturbative
treatment of the Poynting flux to estimate the energy deposited in resistive
walls. The calculation was motivated by a design issue for LCLS-II, the
question of how much wall heating from CSR occurs in the last bend of a bunch
compressor and the following straight section. Working with a realistic
longitudinal bunch form of r.m.s. length $10.4~\mu$m and a charge of 100 pC we
conclude that the radiated power is quite small (28 W at a 1 MHz repetition
rate), and all radiated energy is absorbed in the walls within 7 m along the
straight section.


title:
Color superconductivity in the Nambu Jona-Lasinio model complemented by
  a Polyakov loop

abstract:
  The color superconductivity was studied with an adaptation of the Nambu and
Jona-Lasinio model (NJL). This one was coupled to a Polyakov loop, to form the
PNJL model. A $\mu$-dependent Polyakov loop potential was considered. An
objective of the presented works was to describe the analytical calculations
required to establish the equations to be solved, in all of the treated cases.
They concerned the normal quark phase, the 2-flavor color-superconducting and
the color-flavor-locked phases, in an SU(3)f X SU(3)c description. The
calculations were performed according to the temperature T, the chemical
potentials $\mu_{f}$ or according to the densities $\rho_{f}$, with or without
the isospin symmetry. Among the obtained results, it was found that at low T,
the restoration of the chiral symmetry, the deconfinement transition and the
transition between the normal quark and 2-flavor color-superconducting phases
occur via first order phase transitions at the same chemical potential.
Moreover, an sSC phase was identified in the $\rho_{q}$, $\rho_{s}$ plane.


title: Generalized Representation Stability and FI_d-modules

abstract:
  In this note we consider the complex representation theory of FI_d, a natural
generalization of the category FI of finite sets and injections. We prove that
finitely generated FI_d-modules exhibit behaviors in the spirit of Church-Farb
representation stability theory, generalizing a theorem of Church, Ellenberg,
and Farb which connects finite generation of FI-modules to representation
stability.


abstract:
  Standard routing protocols for Low power and Lossy Networks are typically
designed to optimize bottom-up data flows, by maintaining a cycle-free network
topology. The advantage of such topologies is low memory footprint to store
routing information (only the parent's address needs to me known by each node).
The disadvantage is that other communication patterns, like top-down and
bidirectional data flows, are not easily implemented. In this work we propose
MHCL: IPv6 Multihop Host Configuration for Low-Power Wireless Networks. MHCL
employs hierarchical address allocation that explores cycle-free network
topologies and aims to enable top-down data communication with low message
overhead and memory footprint. We evaluated the performance of MHCL both
analytically and through simulations. We implemented MHCL as a subroutine of
RPL protocol on Contiki OS and showed that it significantly improves top-down
message delivery in RPL, while using a constant amount of memory (i.e.,
independent of network size) and being efficient in terms of setup time and
number of control messages.


title: Quantum fidelity of symmetric multipartite states

abstract:
  For two symmetric quantum states one may be interested in maximizing the
overlap under local operations applied to one of them. The question arises
whether the maximal overlap can be obtained by applying the same local
operation to each party. We show that for two symmetric multiqubit states and
local unitary transformations this is the case; the maximal overlap can be
reached by applying the same unitary matrix everywhere. For local invertible
operations (stochastic local operations assisted by classical communication
equivalence), however, we present counterexamples, demonstrating that
considering the same operation everywhere is not enough.


title: Dissipative Waves in Real Gases

abstract:
  In this paper, we characterize a class of solutions to the unsteady
2-dimensional flow of a van der Waals fluid involving shock waves, and derive
an asymptotic amplitude equation exhibiting quadratic and cubic nonlinearities
including dissipation and diffraction. We exploit the theory of nonclassical
symmetry reduction to obtain some exact solutions. Because of the
nonlinearities present in the evolution equation, one expects that the wave
profile will eventually encounter distortion and steepening which in the limit
of vanishing dissipation culminates into a shock wave; and once shock is
formed, it will propagate by separating the portions of the continuous region.
Here we have shown how the real gas effects, which manifest themselves through
the van der Waals parameters $\tilde{a}$ and $\tilde{b}$ influence the wave
characteristics, namely the shape, strength, and decay behavior of shocks.


title: The role of conformal symmetry in gravity and the standard model

abstract:
  In this paper we consider conformal symmetry in the context of manifolds with
general affine connection. We extend the conformal transformation law of the
metric to a general metric compatible affine connection, and find that it is a
symmetry of both the geodesic equation and the Riemann tensor. We derive the
generalised Jacobi equation and Raychaudhuri equation and show that they are
both conformally invariant. Using the geodesic deviation~(Jacobi) equation we
analyse the behaviour of geodesics in different conformal frames.
  Since we find that our version of conformal symmetry is exact in classical
pure Einstein's gravity, we ask whether one can extend it to the standard
model. We find that it is possible to write conformal invariant lagrangians in
any dimensions for vector, fermion and scalar fields, but that such lagrangians
are only gauge invariant in four dimensions. Provided one introduces a dilaton
field, gravity can be conformally coupled to matter.


title:
Comment on arXiv:0709.3700 "Orientation dependence of the optical
  spectra in graphene at high frequencies"

abstract:
  Zhang et al. reported in [Phys. Rev. B 77, 241402(R) (2008)] a theoretical
study of the optical spectra of monolayer graphene employing the Kubo formula
within a tight-binding model. Their calculations predicted that at high
frequencies the optical conductivity of graphene becomes strongly anisotropic.
In particular, at frequencies comparable to the energy separation of the upper
and lower bands at the $\Gamma$-point, the optical conductivity is strongly
suppressed if the field polarization is along the zigzag direction while it is
significantly high for the armchair one. We find that, unfortunately, this
result is just a consequence of the incorrect determination of the current
operator in k-space. Here, we present the standard scheme to obtain this
operator correctly. As a result, we show that the optical conductivity of
monolayer graphene is indeed isotropic, which is consistent with the results of
other (both theoretical and experimental) studies in the literature.


title: Learning Power Spectrum Maps from Quantized Power Measurements

abstract:
  Power spectral density (PSD) maps providing the distribution of RF power
across space and frequency are constructed using power measurements collected
by a network of low-cost sensors. By introducing linear compression and
quantization to a small number of bits, sensor measurements can be communicated
to the fusion center with minimal bandwidth requirements. Strengths of data-
and model-driven approaches are combined to develop estimators capable of
incorporating multiple forms of spectral and propagation prior information
while fitting the rapid variations of shadow fading across space. To this end,
novel nonparametric and semiparametric formulations are investigated. It is
shown that PSD maps can be obtained using support vector machine-type solvers.
In addition to batch approaches, an online algorithm attuned to real-time
operation is developed. Numerical tests assess the performance of the novel
algorithms.


title: First Result on Arabic Neural Machine Translation

abstract:
  Neural machine translation has become a major alternative to widely used
phrase-based statistical machine translation. We notice however that much of
research on neural machine translation has focused on European languages
despite its language agnostic nature. In this paper, we apply neural machine
translation to the task of Arabic translation (Ar<->En) and compare it against
a standard phrase-based translation system. We run extensive comparison using
various configurations in preprocessing Arabic script and show that the
phrase-based and neural translation systems perform comparably to each other
and that proper preprocessing of Arabic script has a similar effect on both of
the systems. We however observe that the neural machine translation
significantly outperform the phrase-based system on an out-of-domain test set,
making it attractive for real-world deployment.


title: Algebras of cubic matrices

abstract:
  We consider algebras of $m\times m\times m$-cubic matrices (with
$m=1,2,\dots$). Since there are several kinds of multiplications of cubic
matrices, one has to specify a multiplication first and then define an algebra
of cubic matrices (ACM) with respect to this multiplication. We mainly use the
associative multiplications introduced by Maksimov. Such a multiplication
depends on an associative binary operation on the set of size $m$. We introduce
a notion of equivalent operations and show that such operations generate
isomorphic ACMs. It is shown that an ACM is not baric. An ACM is commutative
iff $m=1$. We introduce a notion of accompanying algebra (which is
$m^2$-dimensional) and show that there is a homomorphism from any ACM to the
accompanying algebra. We describe (left and right) symmetric operations and
give left and right zero divisors of the corresponding ACMs. Moreover several
subalgebras and ideals of an ACM are constructed.


title: Principal Score Methods: Assumptions and Extensions

abstract:
  Researchers addressing post-treatment complications in randomized trials
often turn to principal stratification to define relevant assumptions and
quantities of interest. One approach for estimating causal effects in this
framework is to use methods based on the "principal score," typically assuming
that stratum membership is as-good-as-randomly assigned given a set of
covariates. In this paper, we clarify the key assumption in this context, known
as Principal Ignorability, and argue that versions of this assumption are quite
strong in practice. We describe different estimation approaches and demonstrate
that weighting-based methods are generally preferable to subgroup-based
approaches that discretize the principal score. We then extend these ideas to
the case of two-sided noncompliance and propose a natural framework for
combining Principal Ignorability with exclusion restrictions and other
assumptions. Finally, we apply these ideas to the Head Start Impact Study, a
large-scale randomized evaluation of the Head Start program. Overall, we argue
that, while principal score methods are useful tools, applied researchers
should fully understand the relevant assumptions when using them in practice.


title:
On the Nature of High Field Charge Transport in Reinforced Silicone
  Dielectrics: Experiment and Simulation

abstract:
  The high field charge injection and transport properties in reinforced
silicone dielectrics were investigated by measuring the time-dependent space
charge distribution and the current under dc conditions up to the breakdown
field, and were compared with properties of other dielectric polymers. It is
argued that the energy and spatial distribution of localized electronic states
are crucial to determining these properties for polymer dielectrics. Tunneling
to localized states likely dominates the charge injection process. A transient
transport regime arises due to the relaxation of charge carriers into deep
traps at the energy band tails, and is successfully verified by a Monte Carlo
simulation using the multiple-hopping model. The charge carrier mobility is
found to be highly heterogeneous due to non-uniform trapping. The slow moving
electron packet exhibits a negative field dependent drift velocity possibly due
to the spatial disorder of traps.


title: Neutrino Oscillations With Two Sterile Neutrinos

abstract:
  This work estimates the probability of $\mu$ to $e$ neutrino oscillation with
two sterile neutrinos using a 5x5 U-matrix, an extension of the previous
estimate with one sterile neutrino and a 4x4 U-matrix. The sterile
neutrino-active neutrino mass differences and the mixing angles of the two
sterile neutrinos with the three active neutrinos are taken from recent
publications, and the oscillation probability for one sterile neutrino is
compared to the previous estimate.


title: Optimal Hamiltonian Simulation by Quantum Signal Processing

abstract:
  The physics of quantum mechanics is the inspiration for, and underlies,
quantum computation. As such, one expects physical intuition to be highly
influential in the understanding and design of many quantum algorithms,
particularly simulation of physical systems. Surprisingly, this has been
challenging, with current Hamiltonian simulation algorithms remaining abstract
and often the result of sophisticated but unintuitive constructions. We contend
that physical intuition can lead to optimal simulation methods by showing that
a focus on simple single-qubit rotations elegantly furnishes an optimal
algorithm for Hamiltonian simulation, a universal problem that encapsulates all
the power of quantum computation. Specifically, we show that the query
complexity of implementing time evolution by a $d$-sparse Hamiltonian $\hat{H}$
for time-interval $t$ with error $\epsilon$ is
$\mathcal{O}(td\|\hat{H}\|_{\text{max}}+\frac{\log{(1/\epsilon)}}{\log{\log{(1/\epsilon)}}})$,
which matches lower bounds in all parameters. This connection is made through
general three-step "quantum signal processing" methodology, comprised of (1)
transducing eigenvalues of $\hat{H}$ into a single ancilla qubit, (2)
transforming these eigenvalues through an optimal-length sequence of
single-qubit rotations, and (3) projecting this ancilla with near unity success
probability.


title:
A figure of merit for describing the performance of scaling of
  parallelization

abstract:
  With the spread of multi- and many-core processors more and more typical task
is to re-implement some source code written originally for a single processor
to run on more than one cores. Since it is a serious investment, it is
important to decide how much efforts pays off, and whether the resulting
implementation has as good performability as it could be. The Amdahl's law
provides some theoretical upper limits for the performance gain reachable
through parallelizing the code, but it needs the detailed architectural
knowledge of the program code, does not consider the housekeeping activity
needed for parallelization and cannot tell how the actual stage of
parallelization implementation performs. The present paper suggests a
quantitative measure for that goal. This figure of merit is derived
experimentally, from measured running time, and number of threads/cores. It can
be used to quantify the used parallelization technology, the connection between
the computing units, the acceleration technology under the given conditions,
communication method within SoC, or the performance of the software
team/compiler.


title:
Multi-orbital physics in lithium-molybdenum purple-bronze: going beyond
  paradigm

abstract:
  We investigate the role of inter-orbital fluctuations in the low energy
physics of a quasi-1D material - lithium molybdenum purple bronze (LMO). It is
an exceptional material that may provide us a long sought realization of a
Tomonaga-Luttinger liquid (TLL) physics, but its behaviour at temperatures of
the order of $T^*\approx 30$K remains puzzling despite numerous efforts. Here
we make a conjecture that the physics around $T^*$ is dominated by
multi-orbital excitations. Their properties can be captured using an excitonic
picture. Using this relatively simple model we compute fermionic Green's
function in the presence of excitons. We find that the spectral function is
broadened with a Gaussian and its temperature dependence acquires an extra
$T^1$ factor. Both effects are in perfect agreement with experimental findings.
We also compute the resistivity for temperatures above and below critical
temperature $T_o$. We explain an upturn of the resistivity at 28K and interpret
the suppression of this extra component of resistivity when a magnetic field is
applied along the conducting axis. Furthermore, in the framework of our model,
we qualitatively discuss and consistently explain other experimentally detected
peculiarities of purple bronze: the breaking of Wiedmann-Franz law and the
magnetochromatic behaviour.


title: Hardness of approximation for H-free edge modification problems

abstract:
  The $H$-Free Edge Deletion problem asks, for a given graph $G$ and an integer
$k$, whether it is possible to delete at most $k$ edges from $G$ to make it
$H$-free, that is, not containing $H$ as an induced subgraph. The $H$-Free Edge
Completion problem is defined similarly, but we add edges instead of deleting
them. The study of these two problem families has recently been the subject of
intensive studies from the point of view of parameterized complexity and
kernelization. In particular, it was shown that the problems do not admit
polynomial kernels (under plausible complexity assumptions) for almost all
graphs $H$, with several important exceptions occurring when the class of
$H$-free graphs exhibits some structural properties.
  In this work we complement the parameterized study of edge modification
problems to $H$-free graphs by considering their approximability. We prove that
whenever $H$ is $3$-connected and has at least two non-edges, then both
$H$-Free Edge Deletion and $H$-Free Edge Completion are very hard to
approximate: they do not admit $\mathrm{poly}(\mathsf{OPT})$-approximation in
polynomial time, unless $\mathrm{P}=\mathrm{NP}$, or even in time
subexponential in $\mathsf{OPT}$, unless the Exponential Time Hypothesis fails.
The assumption of the existence of two non-edges appears to be important: we
show that whenever $H$ is a complete graph without one edge, then $H$-Free Edge
Deletion is tightly connected to the Min Horn problem, whose approximability is
still open. Finally, in an attempt to extend our hardness results beyond
$3$-connected graphs, we consider the cases of $H$ being a path or a cycle, and
we achieve an almost complete dichotomy there.


title: Continuously Learning Neural Dialogue Management

abstract:
  We describe a two-step approach for dialogue management in task-oriented
spoken dialogue systems. A unified neural network framework is proposed to
enable the system to first learn by supervision from a set of dialogue data and
then continuously improve its behaviour via reinforcement learning, all using
gradient-based algorithms on one single model. The experiments demonstrate the
supervised model's effectiveness in the corpus-based evaluation, with user
simulation, and with paid human subjects. The use of reinforcement learning
further improves the model's performance in both interactive settings,
especially under higher-noise conditions.


title:
Integrative analysis of transcriptomic and metabolomic data via sparse
  canonical correlation analysis with incorporation of biological information

abstract:
  Integrative analyses of different high dimensional data types are becoming
increasingly popular. Similarly, incorporating prior functional relationships
among variables in data analysis has been a topic of increasing interest as it
helps elucidate underlying mechanisms among complex diseases. In this paper,
the goal is to assess association between transcriptomic and metabolomic data
from a Predictive Health Institute (PHI) study including healthy adults at high
risk of developing cardiovascular diseases. To this end, we develop statistical
methods for identifying sparse structure in canonical correlation analysis
(CCA) with incorporation of biological/structural information. Our proposed
methods use prior network structural information among genes and among
metabolites to guide selection of relevant genes and metabolites in sparse CCA,
providing insight on the molecular underpinning of cardiovascular disease. Our
simulations demonstrate that the structured sparse CCA methods outperform
several existing sparse CCA methods in selecting relevant genes and metabolites
when structural information is informative and are robust to mis-specified
structural information. Our analysis of the PHI study reveals that a number of
genes and metabolic pathways including some known to be associated with
cardiovascular diseases are enriched in the subset of genes and metabolites
selected by our proposed approach.


title: Lagrangian Flows, Maslov Index Zero and Special Lagrangians

abstract:
  We introduce a notion of vanishing Maslov index for lagrangian varifolds and
lagrangian integral cycles in a Calabi-Yau manifold. We construct
mass-decreasing flows of lagrangian varifolds and lagrangian cycles which
satisfy this condition. The flow of cycles converges, at infinite time, to a
sum of special lagrangian cycles (possibly with differing phases).
  We use the flow of cycles to obtain the fact that special lagrangian cycles
generate the part of the lagrangian homology which lies in the image of the
Hurewicz homomorphism. We also establish a weak version of a conjecture of
Thomas-Yau regarding lagrangian mean curvature flow.


title: Rapidity Correlation Structure in Nuclear Collisions

abstract:
  We show that measurements of the rapidity dependence of transverse momentum
correlations can be used to determine the characteristic time $\tau_\pi$ that
dictates the rate of isotropization of the stress energy tensor, as well as the
shear viscosity $\nu = \eta/sT$. We formulate methods for computing these
correlations using second order dissipative hydrodynamics with noise. Current
data are consistent with $\tau_\pi/\nu \sim 10$, but targeted measurements can
improve this precision.


title:
Algebraicity and Asymptotics: An explosion of BPS indices from algebraic
  generating series

abstract:
  It is an observation of Kontsevich and Soibelman that generating series that
produce certain (generalized) Donaldson Thomas invariants are secretly
algebraic functions over the rationals. From a physical perspective this
observation arises naturally for DT invariants that appear as BPS indices in
theories of class S[A]: explicit algebraic equations (that completely determine
these series) can be derived using (degenerate) spectral networks. In this
paper, we conjecture an algebraic equation associated to DT invariants for the
Kronecker 3-quiver with dimension vectors (3n,2n), n>0 in the non-trivial
region of its stability parameter space. Using a functional equation due to
Reineke, we show algebraicity of generating series for Euler characteristics of
stable moduli for the Kronecker m-quiver assuming algebraicity of generating
series for DT invariants. In the latter part of the paper we deduce very
explicit results on the asymptotics of DT invariants/Euler characteristics
under the assumption of algebraicity of their generating series; explicit large
n asymptotics are deduced for dimension vectors (3n,2n) for the Kronecker
3-quiver. The algebraic equation is derived using spectral network techniques
developed by Gaiotto-Moore-Neitzke, but the main results can be understood
without knowledge of spectral networks.


title:
Estimating the Mass of the Local Group using Machine Learning Applied to
  Numerical Simulations

abstract:
  We revisit the estimation of the combined mass of the Milky Way and Andromeda
(M31), which dominate the mass of the Local Group. We make use of an ensemble
of 30,190 halo pairs from the Small MultiDark simulation, assuming a
$\Lambda$CDM (Cosmological Constant with Cold Dark Matter) cosmology, to
investigate the relationship between the bound mass and parameters
characterising the orbit of the binary and their local environment with the aid
of machine learning methods (artificial neural networks, ANN). Results from the
ANN are most successful when information about the velocity shear is provided,
which demonstrates the flexibility of machine learning to model physical
phenomena and readily incorporate new information as it becomes available. The
resulting estimate for the Local Group mass, when shear information is
included, is $4.9 \times 10^{12} M_\odot$, with an error of $\pm0.8 \times
10^{12} M_\odot$ from the 68% uncertainty in observables, and a 68% confidence
interval of $^{+1.3}_{-1.4} \times 10^{12}M_\odot$ from the intrinsic scatter
from the differences between the model and simulation masses. We also consider
a recently reported large transverse velocity of M31 relative to the Milky Way,
and produce an alternative mass estimate of $3.6\pm0.3\pm1.4 \times
10^{12}M_\odot$. Although different methods predict similar values for the most
likely mass of the LG, application of ANN compared to the Timing Argument
reduces the scatter in the log mass by over half when tested on samples from
the simulation.


title:
Radiative contribution to the effective potential in composite Higgs
  models from lattice gauge theory

abstract:
  We develop methods to calculate the electroweak gauge boson contribution to
the effective Higgs potential in the context of composite Higgs models, using
lattice gauge theory. The calculation is analogous to that of the
electromagnetic mass splitting of the pion multiplet in QCD. We discuss
technical details of carrying out this calculation, including modeling of the
momentum and fermion-mass dependence of the underlying current-current
correlation function; direct integration of the correlation function over
momentum; and fits based on the minimal-hadron approximation. We show results
of a numerical study using valence overlap fermions, carried out in an SU(4)
gauge theory with two flavors of Dirac fermions in the two-index antisymmetric
representation.


title:
Reconsideration of the inclusive prompt photon production at LHC with
  kt-factorization

abstract:
  We reconsider the inclusive production of isolated prompt photons in $pp$
collisions at the LHC energies in the framework of $k_T$-factorization
approach. Our analysis is based on the ${\cal O}(\alpha \alpha_s)$ off-shell
(depending on the transverse momenta of initial quarks and gluons) production
amplitudes of $q^* g^* \to \gamma q$ and $q^* \bar q^* \to \gamma g$ partonic
subprocesses and transverse momentum dependent (or unintegrated) quark and
gluon densities in a proton, which are chosen in accordance with the
Kimber-Martin-Ryskin prescription. We show that the sub-leading high-order
${\cal O}(\alpha \alpha_s^2)$ contributions, not covered by the non-collinear
evolution of parton densities, are important to describe latest LHC data.


title: Comments On "A New Transient Attack On The Kish Key Distribution System"

abstract:
  A recent IEEE Access Paper by Gunn, Allison and Abbott (GAA) proposed a new
transient attack against the Kirchhoff-law-Johnson-noise (KLJN) secure key
exchange system. The attack is valid, but it is easy to build a defense for the
KLJN system. Here we note that GAA's paper contains several invalid statements
regarding security measures and the continuity of functions in classical
physics. These deficiencies are clarified in our present paper, wherein we also
emphasize that a new version of the KLJN system is immune against all existing
attacks, including the one by GAA.


title:
Three-dimensional noncompact $\kappa$-solutions that are Type I forward
  and backward

abstract:
  As indicated by the third author in [19], there is a gap in the previous
version of this paper by the first two authors [5]. We provide in this version
an argument to fix the aforementioned gap. The main proposition, whose proof
uses Perelman's techniques, is implied by Ding [9] and is covered by [19]. Our
approach, however, is different from theirs. In addition, we prove a necessary
and sufficient condition for a three-dimensional $\kappa$-solution to form a
forward singularity. We hope that this condition is helpful in the
classification of all three-dimensional $\kappa$-solutions. Up to now, the only
main progress on such a classification, as conjectured by Perelman, is by
Brendle [2].


title:
Measurement of the $t\bar{t}$ production cross-section using $e\mu$
  events with b-tagged jets in pp collisions at $\sqrt{s}$=13 TeV with the
  ATLAS detector

abstract:
  This paper describes a measurement of the inclusive top quark pair production
cross-section ($\sigma_{t\bar{t}}$) with a data sample of 3.2 fb$^{-1}$ of
proton--proton collisions at a centre-of-mass energy of $\sqrt{s}$=13 TeV,
collected in 2015 by the ATLAS detector at the LHC. This measurement uses
events with an opposite-charge electron--muon pair in the final state. Jets
containing $b$-quarks are tagged using an algorithm based on track impact
parameters and reconstructed secondary vertices. The numbers of events with
exactly one and exactly two $b$-tagged jets are counted and used to determine
simultaneously $\sigma_{t\bar{t}}$ and the efficiency to reconstruct and
$b$-tag a jet from a top quark decay, thereby minimising the associated
systematic uncertainties. The cross-section is measured to be:
$\sigma_{t\bar{t}}$= 818 $\pm$ 8 (stat) $\pm$ 27 (syst) $\pm$ 19 (lumi) $\pm$
12 (beam) pb, where the four uncertainties arise from data statistics,
experimental and theoretical systematic effects, the integrated luminosity and
the LHC beam energy, giving a total relative uncertainty of 4.4%. The result is
consistent with theoretical QCD calculations at next-to-next-to-leading order.
A fiducial measurement corresponding to the experimental acceptance of the
leptons is also presented.


title:
Distance, Borders, and Time: The Diffusion and Permeability of Political
  Violence in North and West Africa

abstract:
  This paper explores the spatial and temporal diffusion of political violence
in North and West Africa. It does so by endeavoring to represent the mental
landscape that lives in the back of a group leader's mind as he contemplates
strategic targeting. We assume that this representation is a combination of the
physical geography of the target environment, and the mental and physical cost
of following a seemingly random pattern of attacks. Focusing on the distance
and time between attacks and taking into consideration the transaction costs
that state boundaries impose, we wish to understand what constrains a group
leader to attack at a location other than the one that would seem to yield the
greatest overt payoff. By its very nature, the research problem defies the
collection of a full set of structural data. Instead, we leverage functional
data from the Armed Conflict Location and Event Data project (ACLED) dataset
that, inter alia, meticulously catalogues violent extremist incidents in North
and West Africa since 1997, to generate a network whose nodes are
administrative regions. These nodes are connected by edges of qualitatively
different types: undirected edges representing geographic distance, undirected
edges representing borders, and directed edges representing consecutive attacks
by the same group at the two endpoints. We analyze the resulting network using
novel spectral embedding techniques that are able to account fully for the
different types of edges. The result is a map of North and West Africa that
depicts the permeability to violence. A better understanding of how location,
time, and borders condition attacks enables planning, prepositioning, and
response.


title:
H-alpha Variability in PTFO8-8695 and the Possible Direct Detection of
  Emission from a 2 Million Year Old Evaporating Hot Jupiter

abstract:
  We use high time cadence, high spectral resolution optical observations to
detect excess H-alpha emission from the 2 - 3 Myr old weak lined T Tauri star
PTFO8-8695. This excess emission appears to move in velocity as expected if it
were produced by the suspected planetary companion to this young star. The
excess emission is not always present, but when it is, the predicted velocity
motion is often observed. We have considered the possibility that the observed
excess emission is produced by stellar activity (flares), accretion from a
disk, or a planetary companion; we find the planetary companion to be the most
likely explanation. If this is the case, the strength of the H-alpha line
indicates that the emission comes from an extended volume around the planet,
likely fed by mass loss from the planet which is expected to be overflowing its
Roche lobe.


title:
Efficient Smoothed Concomitant Lasso Estimation for High Dimensional
  Regression

abstract:
  In high dimensional settings, sparse structures are crucial for efficiency,
both in term of memory, computation and performance. It is customary to
consider $\ell_1$ penalty to enforce sparsity in such scenarios. Sparsity
enforcing methods, the Lasso being a canonical example, are popular candidates
to address high dimension. For efficiency, they rely on tuning a parameter
trading data fitting versus sparsity. For the Lasso theory to hold this tuning
parameter should be proportional to the noise level, yet the latter is often
unknown in practice. A possible remedy is to jointly optimize over the
regression parameter as well as over the noise level. This has been considered
under several names in the literature: Scaled-Lasso, Square-root Lasso,
Concomitant Lasso estimation for instance, and could be of interest for
confidence sets or uncertainty quantification. In this work, after illustrating
numerical difficulties for the Smoothed Concomitant Lasso formulation, we
propose a modification we coined Smoothed Concomitant Lasso, aimed at
increasing numerical stability. We propose an efficient and accurate solver
leading to a computational cost no more expansive than the one for the Lasso.
We leverage on standard ingredients behind the success of fast Lasso solvers: a
coordinate descent algorithm, combined with safe screening rules to achieve
speed efficiency, by eliminating early irrelevant features.


title: Mixing times for exclusion processes on hypergraphs

abstract:
  We introduce a natural extension of the exclusion process to hypergraphs and
prove an upper bound for its mixing time. In particular we show the existence
of a constant $C$ such that for any connected, regular hypergraph $G$ within
some natural class, the $\varepsilon$-mixing time of the exclusion process on
$G$ with any feasible number of particles can be upper-bounded by
$CT_{\text{EX}(2,G)}\log(|V|/\varepsilon)$, where $|V|$ is the number of
vertices in $G$ and $T_{\text{EX}(2,G)}$ is the 1/4-mixing time of the
corresponding exclusion process with just two particles. Moreover we show this
is optimal in the sense that there exist hypergraphs in the same class for
which $T_{\mathrm{EX}(2,G)}$ and the mixing time of just one particle are not
comparable. The proofs involve an adaptation of the chameleon process, a
technical tool invented by Morris and developed by Oliveira for studying the
exclusion process on a graph.


title:
Updated pseudoscalar contributions to the hadronic light-by-light of the
  muon (g-2)

abstract:
  In this work, we present our recent results on a new and alternative
data-driven determination for the hadronic light-by-light pseudoscalar-pole
contribution to the muon $(g-2)$. Our approach is based on Canterbury
approximants, a rational approach to describe the required transition form
factors, which provides a systematic and model-independent framework beyond
traditional large-$N_c$ approaches. As a result, we obtain a competitive
determination with errors according to future $(g-2)$ experiments including,
for the first time, a well-defined systematic uncertainty.


title:
Wars Without Beginning or End: Violent Political Organizations and
  Irregular Warfare in the Sahel-Sahara

abstract:
  This article examines the structure and spatial patterns of violent political
organizations in the Sahel-Sahara, a region characterized by growing political
instability over the last 20 years. Drawing on a public collection of
disaggregated data, the article uses network science to represent alliances and
conflicts of 179 organizations that were involved in violent events between
1997 and 2014. To this end, we combine two spectral embedding techniques that
have previously been considered separately: one for directed graphs
(relationships are asymmetric), and one for signed graphs (relationships are
positive or negative). Our result show that groups that are net attackers are
indistinguishable at the level of their individual behavior, but clearly
separate into pro- and anti-political violence based on the groups to which
they are close. The second part of the article maps a series of 389 events
related to nine Trans-Saharan Islamist groups between 2004 and 2014. Spatial
analysis suggests that cross-border movement has intensified following the
establishment of military bases by AQIM in Mali but reveals no evidence of a
border sanctuary. Owing to the transnational nature of conflict, the article
shows that national management strategies and foreign military interventions
have profoundly affected the movement of Islamist groups.


title:
Halpha imaging survey of Wolf-Rayet galaxies: morphologies and star
  formation rates

abstract:
  The Halpha and optical broadband images of 25 nearby Wolf-Rayet (WR) galaxies
are presented. The WR galaxies are known to have the presence of a recent
($\le$10 Myr) and massive star formation episode. The photometric Halpha fluxes
are estimated, and corrected for extinction and line contamination in the
filter pass-bands. The star formation rates (SFRs) are estimated using Halpha
images and from the archival data in the far-ultraviolet (FUV), far-infrared
(FIR) and 1.4 GHz radio continuum wave-bands. A comparison of SFRs estimated
from different wavebands is made after including similar data available in
literature for other WR galaxies. The Halpha based SFRs are found to be tightly
correlated with SFRs estimated from the FUV data. The correlations also exist
with SFRs estimates based on the radio and FIR data. The WR galaxies also
follow the radio-FIR correlation known for normal star forming galaxies,
although it is seen here that majority of dwarf WR galaxies have radio
deficiency. An analysis using ratio of non-thermal to thermal radio continuum
and ratio of FUV to Halpha SFR indicates that WR galaxies have lesser
non-thermal radio emission compared to normal galaxies, most likely due to lack
of supernova from the very young star formation episode in the WR galaxies. The
morphologies of 16 galaxies in our sample are highly suggestive of an ongoing
tidal interaction or a past merger in these galaxies. This survey strengthens
the conclusions obtained from previous similar studies indicating the
importance of tidal interactions in triggering star-formation in WR galaxies.


abstract:
  An oblique pulsar magnetosphere with a plasma conductivity is studied by
using a pseudo-spectral method. In the pseudo-spectral method, the
time-dependent Maxwell equations are solved, both electric and magnetic fields
are expanded in terms of the vector spherical harmonic (VSH) functions in
spherical geometry and the divergencelessness of magnetic field is analytically
enforced by a projection method. The pulsar magnetospheres in infinite (i. e.,
force-free approximation) and finite conductivities are simulated and a family
of solutions that smoothly transition from the Deutsch vacuum solution to the
force-free solution are obtained. The $\sin^2\alpha$ dependence of the
spin-down luminosity on the magnetic inclination angle $\alpha$ in which the
full electric current density are taken into account is retrieved in the
force-free regime.


title:
Correlation Analysis for Total Electron Content Anomalies on 11th March,
  2011

abstract:
  We can observe the changes of Total Electron Content, TEC, in ionosphere by
analyzing the data from GNSS satellites. There are many reports about TEC
anomalies after earthquakes, i.e. large earthquakes often disturb the
ionosphere. Up to now, preseismic TEC anomalies have been reported in several
papers. However, they are not so clear as coseismic TEC anomalies, and their
analysis methods have some problems for practical earthquake prediction. One
factor making it difficult to detect TEC anomalies is large noises in TEC data.
Non-negligible TEC disturbances are caused by many natural mechanisms. To
overcome this difficulty, we propose correlation analyses between one GNSS
station and GNSS stations surrounding it. First, we model TEC time series over
a few hours using polynomial functions of time. Second, we calculate prediction
errors as the departure of the TEC time series from the models over time scale
of a few minutes, and define it as the TEC anomaly. Third, we calculate the
correlation between anomaly of one GNSS station and those at the surrounding
stations. Although such a correlation method has long been used for radio
communications, in particular for spread spectrum communications and very long
baseline interferometry (VLBI) to increase SNR (signal to noise ratio), it has
not been widely applied for TEC analyses. As a result of our method, we
demonstrate that the correlation analysis let us detect TEC anomaly one hour
before 2011 Tohoku-oki earthquake. In this paper, we examined the 2011
Tohoku-oki case extensively.


title: How two-dimensional bending can extraordinarily stiffen thin sheets

abstract:
  Curved thin sheets are ubiquitously found in nature and manmade structures.
Within the framework of classical thin plate theory, the stiffness of thin
sheets is independent of its bending state. This assumption, however, goes
against intuition. Simple experiments with a cantilever sheet made of paper
show that the cantilever stiffness largely increases with the transversal
curvature. We here demonstrate by using simple geometric arguments that thin
sheets subject to two-dimensional bending necessarily develop internal
stresses. The coupling between the internal stresses and the bending moments
can increase the stiffness of the plate by several times. We develop a theory
that describes the stiffness of curved thin sheets with simple equations in
terms of the longitudinal and transversal curvatures. The theory perfectly fits
experimental results with a macroscopic cantilever sheet as well as numerical
simulations by the finite element method. The results shed new light on plant
and insect wing biomechanics and provide an easy route to engineer micro- and
nanomechanical structures based on ultrathin materials with extraordinary
stiffness tunability.


title: A Modified Vortex Search Algorithm for Numerical Function Optimization

abstract:
  The Vortex Search (VS) algorithm is one of the recently proposed
metaheuristic algorithms which was inspired from the vortical flow of the
stirred fluids. Although the VS algorithm is shown to be a good candidate for
the solution of certain optimization problems, it also has some drawbacks. In
the VS algorithm, candidate solutions are generated around the current best
solution by using a Gaussian distribution at each iteration pass. This provides
simplicity to the algorithm but it also leads to some problems along.
Especially, for the functions those have a number of local minimum points, to
select a single point to generate candidate solutions leads the algorithm to
being trapped into a local minimum point. Due to the adaptive step-size
adjustment scheme used in the VS algorithm, the locality of the created
candidate solutions is increased at each iteration pass. Therefore, if the
algorithm cannot escape a local point as quickly as possible, it becomes much
more difficult for the algorithm to escape from that point in the latter
iterations. In this study, a modified Vortex Search algorithm (MVS) is proposed
to overcome above mentioned drawback of the existing VS algorithm. In the MVS
algorithm, the candidate solutions are generated around a number of points at
each iteration pass. Computational results showed that with the help of this
modification the global search ability of the existing VS algorithm is improved
and the MVS algorithm outperformed the existing VS algorithm, PSO2011 and ABC
algorithms for the benchmark numerical function set.


title: ChinMotion Rapidly Enables 3D Computer Interaction after Tetraplegia

abstract:
  Individuals with severe paralysis require hands-free interfaces to control
assistive devices that can improve their quality of life. We present
ChinMotion, an interface that noninvasively harnesses preserved chin, lip and
tongue sensorimotor function after tetraplegia to convey intuitive control
commands. After two hours of practice, ChinMotion enables superior
point-and-click performance over existing interfaces and it facilitates
accurate 3D control of a virtual robotic arm.


title: On the stability of anti-de Sitter spacetime

abstract:
  We present results from a detailed study of spherically symmetric
Einstein-massless-scalar field dynamics with a negative cosmological constant
in four to nine spacetime dimensions. This study is the first to present a
detailed examination of the dynamics in AdS beyond five dimensions, including a
detailed comparison with numerical solutions of perturbative methods and their
gauge dependence. Using these perturbative methods, we provide evidence that
the oscillatory divergence of the first derivative used to argue for
instability of anti-de Sitter space by Bizon et al. is a gauge-dependent effect
in five spacetime dimensions but the divergence of the second derivative is
gauge-independent. We find that the divergence of the first derivative appears
to be gauge-independent in higher dimensions; however, understanding how this
divergence depends on the initial data is more difficult. We also find that
four dimensions is more difficult to study than higher dimensions. The results
we present show that while much progress has been made in understanding the
rich dynamics and stability of anti-de Sitter space, much work is still to be
done. The recent work of Moschidis is encouraging that it is possible to
understand the problem analytically.


title:
MESA meets MURaM: Surface effects in main-sequence solar-like
  oscillators computed using three-dimensional radiation hydrodynamics
  simulations

abstract:
  ... [C]urrent stellar models predict oscillation frequencies that are
systematically affected by simplified modelling of the near-surface layers. We
use three-dimensional radiation hydrodynamics simulations to better model the
near-surface equilibrium structure of dwarfs with spectral types F3, G2, K0 and
K5, and examine the differences between oscillation mode frequencies. ... We
precisely match stellar models to the simulations' gravities and effective
temperatures at the surface, and to the temporally- and horizontally-averaged
densities and pressures at their deepest points. We then replace the
near-surface structure with that of the averaged simulation and compute the
change in the oscillation mode frequencies. We also fit the differences using
several parametric models currently available in the literature. The surface
effect in the stars of solar-type and later is qualitatively similar and
changes steadily with decreasing effective temperature. In particular, the
point of greatest frequency difference decreases slightly as a fraction of the
acoustic cut-off frequency and the overall scale of the surface effect
decreases. The surface effect in the hot, F3-type star follows the same trend
in scale (i.e. it is larger in magnitude) but shows a different overall
variation with mode frequency. We find that the two-term fit by Ball & Gizon
(2014) is best able to reproduce the surface terms across all four spectral
types, although the scaled solar term and a modified Lorentzian function also
match the three cooler simulations reasonably well. ... Our simplified results
suggest that the surface effect is generally larger in hotter stars (and
correspondingly smaller in cooler stars) and of similar shape in stars of solar
type and cooler. However, we cannot presently predict whether this will remain
so when other components of the surface effect are included.


title: Simulating the dust content of galaxies: successes and failures

abstract:
  We present full volume cosmological simulations using the moving-mesh code
AREPO to study the coevolution of dust and galaxies. We extend the dust model
in AREPO to include thermal sputtering of grains and investigate the evolution
of the dust mass function, the cosmic distribution of dust beyond the
interstellar medium, and the dependence of dust-to-stellar mass ratio on
galactic properties. The simulated dust mass function is well-described by a
Schechter fit and lies closest to observations at $z = 0$. The radial scaling
of projected dust surface density out to distances of $10 \, \text{Mpc}$ around
galaxies with magnitudes $17 < i < 21$ is similar to that seen in Sloan Digital
Sky Survey data, albeit with a lower normalisation. At $z = 0$, the predicted
dust density of $\Omega_\text{dust} \approx 1.3 \times 10^{-6}$ lies in the
range of $\Omega_\text{dust}$ values seen in low-redshift observations. We find
that dust-to-stellar mass ratio anti-correlates with stellar mass for galaxies
living along the star formation main sequence. Moreover, we estimate the $850
\, \mu\text{m}$ number density functions for simulated galaxies and analyse the
relation between dust-to-stellar flux and mass ratios at $z = 0$. At high
redshift, our model fails to produce enough dust-rich galaxies, and this
tension is not alleviated by adopting a top-heavy initial mass function. We do
not capture a decline in $\Omega_\text{dust}$ from $z = 2$ to $z = 0$, which
suggests that dust production mechanisms more strongly dependent on star
formation may help to produce the observed number of dusty galaxies near the
peak of cosmic star formation.


title:
Gaps in globular cluster streams: giant molecular clouds can cause them
  too

abstract:
  As a result of their internal dynamical coherence, thin stellar streams
formed by disrupting globular clusters (GCs) can act as detectors of dark
matter (DM) substructure in the Galactic halo. Perturbations induced by close
flybys amplify into detectable density gaps, providing a probe both of the
abundance and of the masses of DM subhaloes. Here, we use N-body simulations to
show that the Galactic population of giant molecular clouds (GMCs) can also
produce gaps (and clumps) in GC streams, and so may confuse the detection of DM
subhaloes. We explore the cases of streams analogous to the observed Palomar 5
and GD1 systems, quantifying the expected incidence of structure caused by GMC
perturbations. Deep observations should detect such disturbances regardless of
the substructure content of the Milky Way's halo. Detailed modelling will be
needed to demonstrate that any detected gaps or clumps were produced by DM
subhaloes rather than by molecular clouds.


title: Uncovering the relation of a scalar resonance to the Higgs boson

abstract:
  We consider the associated production of a scalar resonance with the standard
model Higgs boson. We demonstrate via a realistic phenomenological analysis
that couplings of such a resonance to the Higgs boson can be constrained in a
meaningful way in future runs of the LHC, providing insights on its origin and
its relation to the electroweak symmetry breaking sector. Moreover, the final
state can provide a direct way to determine whether the new resonance is
produced predominantly in gluon fusion or quark-anti-quark annihilation. The
analysis focusses on a resonance coming from a scalar field with vanishing
vacuum expectation value and its decay to a photon pair. It can however be
straightforwardly generalised to other scenarios.


title:
Discovery of a z=0.65 Post-Starburst BAL Quasar in the DES Supernova
  Fields

abstract:
  We present the discovery of a z=0.65 low-ionization broad absorption line
(LoBAL) quasar in a post-starburst galaxy in data from the Dark Energy Survey
(DES) and spectroscopy from the Australian Dark Energy Survey (OzDES). LoBAL
quasars are a minority of all BALs, and rarer still is that this object also
exhibits broad FeII (an FeLoBAL) and Balmer absorption. This is the first BAL
quasar that has signatures of recently truncated star formation, which we
estimate ended about 40 Myr ago. The characteristic signatures of an FeLoBAL
require high column densities, which could be explained by the emergence of a
young quasar from an early, dust-enshrouded phase, or by clouds compressed by a
blast wave. The age of the starburst component is comparable to estimates of
the lifetime of quasars, so if we assume the quasar activity is related to the
truncation of the star formation, this object is better explained by the blast
wave scenario.


title: Learning Thermodynamics with Boltzmann Machines

abstract:
  A Boltzmann machine is a stochastic neural network that has been extensively
used in the layers of deep architectures for modern machine learning
applications. In this paper, we develop a Boltzmann machine that is capable of
modelling thermodynamic observables for physical systems in thermal
equilibrium. Through unsupervised learning, we train the Boltzmann machine on
data sets constructed with spin configurations importance-sampled from the
partition function of an Ising Hamiltonian at different temperatures using
Monte Carlo (MC) methods. The trained Boltzmann machine is then used to
generate spin states, for which we compare thermodynamic observables to those
computed by direct MC sampling. We demonstrate that the Boltzmann machine can
faithfully reproduce the observables of the physical system. Further, we
observe that the number of neurons required to obtain accurate results
increases as the system is brought close to criticality.


title: Cosmic reionization after Planck II: contribution from quasars

abstract:
  In the light of the recent Planck downward revision of the electron
scattering optical depth, and of the discovery of a faint AGN population at $z
> 4$, we reassess the actual contribution of quasars to cosmic reionization. To
this aim, we extend our previous MCMC-based data-constrained semi-analytic
reionization model and study the role of quasars on global reionization
history. We find that, the quasars can alone reionize the Universe only for
models with very high AGN emissivities at high redshift. These models are still
allowed by the recent CMB data and most of the observations related to HI
reionization. However, they predict an extended and early HeII reionization
ending at $z\gtrsim4$ and a much slower evolution in the mean HeII Ly-$\alpha$
forest opacity than what the actual observation suggests. Thus when we further
constrain our model against the HeII Ly-$\alpha$ forest data, this
AGN-dominated scenario is found to be clearly ruled out at 2-$\sigma$ limits.
The data seems to favour a standard two-component picture where quasar
contributions become negligible at $z\gtrsim6$ and a non-zero escape fraction
of $\sim10\%$ is needed from early-epoch galaxies. For such models, mean
neutral hydrogen fraction decreases to $\sim10^{-4}$ at $z=6.2$ from $\sim0.8$
at $z=10.0$ and helium becomes doubly ionized at much later time, $z\sim3$. We
find that, these models are as well in good agreement with the observed thermal
evolution of IGM as opposed to models with very high AGN emissivities.


title:
Current driven spin-orbit torque oscillator: ferromagnetic and
  antiferromagnetic coupling

abstract:
  We consider theoretically the impact of Rashba spin-orbit coupling on spin
torque oscillators (STOs) in synthetic ferromagnets and antiferromagnets that
have either a bulk multilayer or a thin film structure. The synthetic magnets
consist of a fixed polarizing layer and two free magnetic layers that interact
through the Ruderman-Kittel-Kasuya-Yosida interaction. We determine
analytically which collinear states along the easy axis that are stable, and
establish numerically the phase diagram for when the system is in the STO mode
and when collinear configurations are stable, respectively. It is found that
the Rashba spin-orbit coupling can induce anti-damping in the vicinity of the
collinear states, which assists the spin transfer torque in generating
self-sustained oscillations, and that it can substantially increase the STO
part of the phase diagram. Moreover, we find that the STO phase can extend deep
into the antiferromagnetic regime in the presence of spin-orbit torques.


title: Identifying Phase Space Boundaries with Voronoi Tessellations

abstract:
  Determining the masses of new physics particles appearing in decay chains is
an important and longstanding problem in high energy phenomenology. Recently it
has been shown that these mass measurements can be improved by utilizing the
boundary of the allowed region in the fully differentiable phase space in its
full dimensionality. Here we show that the practical challenge of identifying
this boundary can be solved using techniques based on the geometric properties
of the cells resulting from Voronoi tessellations of the relevant data. The
robust detection of such phase space boundaries in the data could also be used
to corroborate a new physics discovery based on a cut-and-count analysis.


title: Unitarisation of EFT Amplitudes for Dark Matter Searches at the LHC

abstract:
  We propose a new approach to the LHC dark matter search analysis within the
effective field theory (EFT) framework by utilising the K-matrix unitarisation
formalism. This approach provides a reasonable estimate of the dark matter
production cross section at high energies, and hence allows reliable bounds to
be placed on the cut-off scale of relevant operators without running into the
problem of perturbative unitarity violation. We exemplify this procedure for
the effective operator D5 in monojet dark matter searches in the collinear
approximation. We compare our bounds to those obtained using the truncation
method and identify a parameter region where the unitarisation prescription
leads to more stringent bounds.


title: Radial velocity monitoring of Kepler heartbeat stars

abstract:
  Heartbeat stars (HB stars) are a class of eccentric binary stars with close
periastron passages. The characteristic photometric HB signal evident in their
light curves is produced by a combination of tidal distortion, heating, and
Doppler boosting near orbital periastron. Many HB stars continue to oscillate
after periastron and along the entire orbit, indicative of the tidal excitation
of oscillation modes within one or both stars. These systems are among the most
eccentric binaries known, and they constitute astrophysical laboratories for
the study of tidal effects. We have undertaken a radial velocity (RV)
monitoring campaign of Kepler HB stars in order to measure their orbits. We
present our first results here, including a sample of 21 Kepler HB systems,
where for 19 of them we obtained the Keplerian orbit and for 3 other systems we
did not detect a statistically significant RV variability. Results presented
here are based on 218 spectra obtained with the Keck/HIRES spectrograph during
the 2015 Kepler observing season, and they have allowed us to obtain the
largest sample of HB stars with orbits measured using a single instrument,
which roughly doubles the number of HB stars with an RV measured orbit. The 19
systems measured here have orbital periods from 7 to 90 d and eccentricities
from 0.2 to 0.9. We show that HB stars draw the upper envelope of the
eccentricity - period distribution. Therefore, HB stars likely represent a
population of stars currently undergoing high eccentricity migration via tidal
orbital circularization, and they will allow for new tests of high eccentricity
migration theories.


title: The holographic supersymmetric Casimir energy

abstract:
  We consider a general class of asymptotically locally AdS_5 solutions of
minimal gauged supergravity, that are dual to superconformal field theories on
curved backgrounds S^1 x M_3 preserving two supercharges. We demonstrate that
standard holographic renormalization corresponds to a scheme that breaks
supersymmetry. We propose new boundary terms that restore supersymmetry, and
show that for smooth solutions with topology S^1 x R^4 the improved on-shell
action reproduces both the supersymmetric Casimir energy and the field theory
BPS relation between charges.


title: Du Val curves and the pointed Brill-Noether Theorem

abstract:
  We show that a general curve in an explicit class of what we call Du Val
pointed curves satisfies the Brill-Noether Theorem for pointed curves.
Furthermore, we prove that a generic pencil of Du Val pointed curves is
disjoint from all Brill-Noether divisors on the universal curve. This provides
explicit examples of smooth pointed curves of arbitrary genus defined over Q
which are Brill-Noether general. A similar result is proved for 2-pointed
curves as well using explicit curves on elliptic ruled surfaces.


title:
CIV Emission Line Properties and Systematic Trends in Quasar Black Hole
  Mass Estimates

abstract:
  Black-hole masses are crucial to understanding the physics of the connection
between quasars and their host galaxies and measuring cosmic black hole-growth.
At high redshift, z > 2.1, black hole masses are normally derived using the
velocity-width of the CIV broad emission line, based on the assumption that the
observed velocity-widths arise from virial-induced motions. In many quasars,
the CIV-emission line exhibits significant blue asymmetries (`blueshifts') with
the line centroid displaced by up to thousands of km/s to the blue. These
blueshifts almost certainly signal the presence of strong outflows, most likely
originating in a disc wind. We have obtained near-infrared spectra, including
the H$\alpha$ emission line, for 19 luminous ($L_{Bol}$ = 46.5-47.5 erg/s)
Sloan Digital Sky Survey quasars, at redshifts 2 < z < 2.7, with CIV emission
lines spanning the full-range of blueshifts present in the population. A strong
correlation between CIV-velocity width and blueshift is found and, at large
blueshifts, > 2000 km/s, the velocity-widths appear to be dominated by
non-virial motions. Black-hole masses, based on the full width at half maximum
of the CIV-emission line, can be overestimated by a factor of five at large
blueshifts. A larger sample of quasar spectra with both CIV and H$\beta$, or
H$\alpha$, emission lines will allow quantitative corrections to CIV-based
black-hole masses as a function of blueshift to be derived. We find that
quasars with large CIV blueshifts possess high Eddington luminosity ratios and
that the fraction of high-blueshift quasars in a flux-limited sample is
enhanced by a factor of approximately four relative to a sample limited by
black hole mass.


title:
The OGLE Collection of Variable Stars. Over 45 000 RR Lyrae Stars in the
  Magellanic System

abstract:
  We present the largest collection of RR Lyrae stars in the Magellanic System
and in its foreground. The sample consists of 45 451 RR Lyr stars, of which 39
082 were detected toward the Large Magellanic Cloud and 6369 toward the Small
Magellanic Cloud. We provide long-term time-series photometric measurements
collected during the fourth phase of the Optical Gravitational Lensing
Experiment (OGLE-IV).
  We discuss several potential astrophysical applications of our collection:
investigation of the structure of the Magellanic Clouds and the Galactic halo,
studies of the globular clusters in the Magellanic System, analysis of
double-mode RR Lyr stars, and search for RR Lyr stars in eclipsing binary
systems.


title: Criticality in Einstein-Gauss-Bonnet Gravity: Gravity without Graviton

abstract:
  General Einstein-Gauss-Bonnet gravity with a cosmological constant allows two
(A)dS spacetimes as its vacuum solutions. We find a critical point in the
parameter space where the two (A)dS spacetimes coalesce into one and the
linearized perturbations lack any bilinear kinetic terms. The vacuum
perturbations hence loose their interpretation as linear graviton modes at the
critical point. Nevertheless, the critical theory admits black hole solutions
due to the nonlinear effect. We also consider Einstein gravity extended with
general quadratic curvature invariants and obtain critical points where the
theory has no bilinear kinetic terms for either the scalar trace mode or the
transverse modes. Such critical phenomena are expected to occur frequently in
general higher derivative gravities.


title: Resolving flows around black holes: the impact of gas angular momentum

abstract:
  Cosmological simulations almost invariably estimate the accretion of gas on
to supermassive black holes using a Bondi-Hoyle-like prescription. Doing so
ignores the effects of the angular momentum of the gas, which may prevent or
significantly delay accreting material falling directly on to the black hole.
We outline a black hole accretion rate prescription using a modified
Bondi-Hoyle formulation that takes into account the angular momentum of the
surrounding gas. Meaningful implementation of this modified Bondi-Hoyle
formulation is only possible when the inner vorticity distribution is well
resolved, which we achieve through the use of a super-Lagrangian refinement
technique around black holes within our simulations. We then investigate the
effects on black hole growth by performing simulations of isolated as well as
merging disc galaxies using the moving-mesh code AREPO. We find that the gas
angular momentum barrier can play an important role in limiting the growth of
black holes, leading also to a several Gyr delay between the starburst and the
quasar phase in major merger remnants. We stress, however, that the magnitude
of this effect is highly sensitive to the thermodynamical state of the
accreting gas and to the nature of the black hole feedback present.


title:
Development of high resolution arrayed waveguide grating spectrometers
  for astronomical applications: first results

abstract:
  Astrophotonics is the next-generation approach that provides the means to
miniaturize near-infrared (NIR) spectrometers for upcoming large telescopes and
make them more robust and inexpensive. The target requirements for our
spectrograph are: a resolving power of about 3000, wide spectral range (J and H
bands), free spectral range of about 30 nm, high on-chip throughput of about
80% (-1dB) and low crosstalk (high contrast ratio) between adjacent on-chip
wavelength channels of less than 1% (-20dB). A promising photonic technology to
achieve these requirements is Arrayed Waveguide Gratings (AWGs). We have
developed our first generation of AWG devices using a silica-on-silicon
substrate with a very thin layer of silicon-nitride in the core of our
waveguides. The waveguide bending losses are minimized by optimizing the
geometry of the waveguides. Our first generation of AWG devices are designed
for H band and have a resolving power of around 1500 and free spectral range of
about 10 nm around a central wavelength of 1600 nm. The devices have a
footprint of only 12 mm x 6 mm. They are broadband (1450-1650 nm), have a peak
on-chip throughput of about 80% (-1 dB) and contrast ratio of about 1.5% (-18
dB). These results confirm the robustness of our design, fabrication and
simulation methods. Currently, the devices are designed for Transverse Electric
(TE) polarization and all the results are for TE mode. We are developing
separate J- and H-band AWGs with higher resolving power, higher throughput and
lower crosstalk over a wider free spectral range to make them better suited for
astronomical applications.


title:
Large enhancement in high-energy photoionization of Fe XVII and missing
  continuum plasma opacity

abstract:
  Aimed at solving the outstanding problem of solar opacity, and radiation
transport plasma models in general, we report substantial photoabsorption in
the high-energy regime due to atomic core photo-excitations not heretofore
considered. In extensive R-Matrix calculations of unprecedented complexity for
an important iron ion Fe xvii (Fe$^{16+}$), with a wave function expansion of
99 Fe xviii (Fe$^{17+}$) LS core states from $n \leq 4$ complexes (equivalent
to 218 fine structure levels), we find: i) up to orders of magnitude
enhancement in background photoionization cross sections, in addition to
strongly peaked photo-excitation-of-core resonances not considered in current
opacity models, and ii) demonstrate convergence with respect to successive core
excitations. The resulting increase in the monochromatic continuum, and 35% in
the Rosseland Mean Opacity, are compared with the "higher-than-predicted" iron
opacity measured at the Sandia Z-pinch fusion device at solar interior
conditions.


title:
A tetraquark or not a tetraquark: A holography inspired stringy hadron
  (HISH) perspective

abstract:
  We suggest to use the state $Y(4630)$, which decays predominantly to
$\Lambda_c\bar\Lambda_c$, as a window to the landscape of tetraquarks. We
propose a simple criterion to decide whether a state is a genuine stringy
exotic hadron - a tetraquark - or a "molecule". If it is the former it should
be on a (modified) Regge trajectory. We present the predictions of the mass and
width of the higher excited states on the $Y(4630)$ trajectory. We argue that
there should exist an analogous "$Y_b$" state that decays to
$\Lambda_b\bar\Lambda_b$ and describe its trajectory. We conjecture also a
similar trajectory for tetraquarks containing strange quarks, and the modified
Regge trajectories can in fact be predicted for any resonances found decaying
to a baryon-antibaryon pair. En route to the results regarding tetraquarks, we
also make some additional predictions on higher excited charmonium states. We
briefly discuss the zoo of exotic stringy hadrons and in particular we sketch
all the possibilities of tetraquark states.


title:
Dyonic (A)dS Black Holes in Einstein-Born-Infeld Theory in Diverse
  Dimensions

abstract:
  We study Einstein-Born-Infeld gravity and construct the dyonic (A)dS planar
black holes in general even dimensions, that carry both the electric charge and
magnetic fluxes along the planar space. In four dimensions, the solution can be
constructed with also spherical and hyperbolic topologies. We study the black
hole thermodynamics and obtain the first law. We also classify the singularity
structure.


title: Universal Quantum Emulator

abstract:
  We propose a quantum algorithm that emulates the action of an unknown unitary
transformation on a given input state, using multiple copies of some unknown
sample input states of the unitary and their corresponding output states. The
algorithm does not assume any prior information about the unitary to be
emulated, or the sample input states. To emulate the action of the unknown
unitary, the new input state is coupled to the given sample input-output pairs
in a coherent fashion. Remarkably, the runtime of the algorithm is logarithmic
in D, the dimension of the Hilbert space, and increases polynomially with d,
the dimension of the subspace spanned by the sample input states. Furthermore,
the sample complexity of the algorithm, i.e. the total number of copies of the
sample input-output pairs needed to run the algorithm, is independent of D, and
polynomial in d. In contrast, the runtime and the sample complexity of
incoherent methods, i.e. methods that use tomography, are both linear in D. The
algorithm is blind, in the sense that at the end it does not learn anything
about the given samples, or the emulated unitary. This algorithm can be used as
a subroutine in other algorithms, such as quantum phase estimation.


title:
On the Accuracy of the Noninteracting Electron Approximation for
  Vibrationally Coupled Electron Transport

abstract:
  The accuracy of the noninteracting electron approximation is examined for a
model of vibrationally coupled electron transport in single molecule junction.
In the absence of electronic-vibrational coupling, steady state transport in
this model is described exactly by Landauer theory. Including coupling, both
electronic-vibrational and vibrationally induced electron-electron correlation
effects may contribute to the real time quantum dynamics. Using the multilayer
multiconfiguration time-dependent Hartree (ML-MCTDH) theory to describe nuclear
dynamics exactly while maintaining the noninteracting electron approximation
for the electronic dynamics, the correlation effects are analyzed in different
physical regimes. It is shown that although the noninteracting electron
approximation may be reasonable for describing short time dynamics, it does not
give the correct long time limit for certain initial conditions.


title:
Physical extracurricular activities in educational child-robot
  interaction

abstract:
  In an exploratory study on educational child-robot interaction we investigate
the effect of alternating a learning activity with an additional shared
activity. Our aim is to enhance and enrich the relationship between child and
robot by introducing "physical extracurricular activities". This enriched
relationship might ultimately influence the way the child and robot interact
with the learning material. We use qualitative measurement techniques to
evaluate the effect of the additional activity on the child-robot relationship.
We also explore how these metrics can be integrated in a highly exploratory
cumulative score for the relationship between child and robot. This cumulative
score suggests a difference in the overall child-robot relationship between
children who engage in a physical extracurricular activity with the robot, and
children who only engage in the learning activity with the robot.


title:
Claws, Disorder, and Conformational Dynamics of the C-terminal Region of
  Human Desmoplakin

abstract:
  Multicellular organisms consist of cells that interact via elaborate adhesion
complexes. Desmosomes are membrane-associated adhesion complexes that
mechanically tether the cytoskeletal intermediate filaments (IFs) between two
adjacent cells, creating a network of tough connections in tissues such as skin
and heart. Desmoplakin (DP) is the key desmosomal protein that binds IFs, and
the DP-IF association poses a quandary: desmoplakin must stably and tightly
bind IFs to maintain the structural integrity of the desmosome. Yet, newly
synthesized DP must traffick along the cytoskeleton to the site of nascent
desmosome assembly without 'sticking' to the IF network, implying weak or
transient DP--IF contacts. Recent work reveals that these contacts are
modulated by post-translational modifications (PTMs) in DP's C-terminal tail.
Using molecular dynamics simulations, we have elucidated the structural basis
of these PTM-induced effects. Our simulations, nearing 2 microseconds in
aggregate, indicate that phosphorylation of S2849 induces an 'arginine claw' in
desmoplakin's C-terminal tail (DPCTT). If a key arginine, R2834, is methylated,
the DPCTT preferentially samples conformations that are geometrically
well-suited as substrates for processive phosphorylation by the cognate kinase
GSK3. We suggest that DPCTT is a molecular switch that modulates, via its
conformational dynamics, DP's efficacy as a substrate for GSK3. Finally, we
show that the fluctuating DPCTT can contact other parts of DP, suggesting a
competitive binding mechanism for the modulation of DP--IF interactions.


title:
SWIFT: Using task-based parallelism, fully asynchronous communication,
  and graph partition-based domain decomposition for strong scaling on more
  than 100,000 cores

abstract:
  We present a new open-source cosmological code, called SWIFT, designed to
solve the equations of hydrodynamics using a particle-based approach (Smooth
Particle Hydrodynamics) on hybrid shared/distributed-memory architectures.
SWIFT was designed from the bottom up to provide excellent strong scaling on
both commodity clusters (Tier-2 systems) and Top100-supercomputers (Tier-0
systems), without relying on architecture-specific features or specialized
accelerator hardware. This performance is due to three main computational
approaches: (1) Task-based parallelism for shared-memory parallelism, which
provides fine-grained load balancing and thus strong scaling on large numbers
of cores. (2) Graph-based domain decomposition, which uses the task graph to
decompose the simulation domain such that the work, as opposed to just the
data, as is the case with most partitioning schemes, is equally distributed
across all nodes. (3) Fully dynamic and asynchronous communication, in which
communication is modelled as just another task in the task-based scheme,
sending data whenever it is ready and deferring on tasks that rely on data from
other nodes until it arrives. In order to use these approaches, the code had to
be re-written from scratch, and the algorithms therein adapted to the
task-based paradigm. As a result, we can show upwards of 60% parallel
efficiency for moderate-sized problems when increasing the number of cores
512-fold, on both x86-based and Power8-based architectures.


title:
Efficient collective influence maximization in cascading processes with
  first-order transitions

abstract:
  In social networks, the collective behavior of large populations can be
shaped by a small set of influencers through a cascading process induced by
"peer pressure". For large-scale networks, efficient identification of multiple
influential spreaders with a linear algorithm in threshold models that exhibit
a first-order transition still remains a challenging task. Here we address this
issue by exploring the collective influence in general threshold models of
behavior cascading. Our analysis reveals that the importance of spreaders is
fixed by the subcritical paths along which cascades propagate: the number of
subcritical paths attached to each spreader determines its contribution to
global cascades. The concept of subcritical path allows us to introduce a
linearly scalable algorithm for massively large-scale networks. Results in both
synthetic random graphs and real networks show that the proposed method can
achieve larger collective influence given same number of seeds compared with
other linearly scalable heuristic approaches.


title:
Collective Influence of Multiple Spreaders Evaluated by Tracing Real
  Information Flow in Large-Scale Social Networks

abstract:
  Identifying the most influential spreaders that maximize information flow is
a central question in network theory. Recently, a scalable method called
"Collective Influence (CI)" has been put forward through collective influence
maximization. In contrast to heuristic methods evaluating nodes' significance
separately, CI method inspects the collective influence of multiple spreaders.
Despite that CI applies to the influence maximization problem in percolation
model, it is still important to examine its efficacy in realistic information
spreading. Here, we examine real-world information flow in various social and
scientific platforms including American Physical Society, Facebook, Twitter and
LiveJournal. Since empirical data cannot be directly mapped to ideal
multi-source spreading, we leverage the behavioral patterns of users extracted
from data to construct "virtual" information spreading processes. Our results
demonstrate that the set of spreaders selected by CI can induce larger scale of
information propagation. Moreover, local measures as the number of connections
or citations are not necessarily the deterministic factors of nodes' importance
in realistic information spreading. This result has significance for rankings
scientists in scientific networks like the APS, where the commonly used number
of citations can be a poor indicator of the collective influence of authors in
the community.


title:
Stochastic stability analysis of a reduced galactic dynamo model with
  perturbed {\alpha}-effect

abstract:
  We investigate the asymptotic behaviour of a reduced {\alpha}{\Omega}-dynamo
model of magnetic field generation in spiral galaxies where fluctuation in the
{\alpha}-effect results in a system with state-dependent stochastic
perturbations.
  By computing the upper Lyapunov exponent of the linearised model, we can
identify regions of instability and stability in probability for the
equilibrium of the nonlinear model; in this case the equilibrium solution
corresponds to a magnetic field that has undergone catastrophic quenching.
These regions are compared to regions of exponential mean-square stability and
regions of sub- and super-criticality in the unperturbed linearised model.
Prior analysis in the literature which focuses on these latter regions does not
adequately address the corresponding transition in the nonlinear stochastic
model.
  Finally we provide a visual representation of the influence of drift
non-normality and perturbation intensity on these regions.


title:
A study of symmetry breaking in a relativistic Bose gas using the
  contraction algorithm

abstract:
  A relativistic Bose gas at finite density suffers from a sign problem that
makes direct numerical simulations not feasible. One possible solution to the
sign problem is to re-express the path integral in terms of Lefschetz thimbles.
Using this approach we study the relativistic Bose gas both in the symmetric
phase (low-density) and the spontaneously broken phase (high-density). In the
high-density phase we break explicitly the symmetry and determine the
dependence of the order parameter on the breaking. We study the relative
contributions of the dominant and sub-dominant thimbles in this phase. We find
that the sub-dominant thimble only contributes substantially when the explicit
symmetry breaking is small, a regime that is dominated by finite volume
effects. In the regime relevant for the thermodynamic limit, this contribution
is negligible.


title:
A critical look at the merger scenario to explain multiple populations
  and rotation in iron-complex globular clusters

abstract:
  Merging has been proposed to explain multiple populations in globular
clusters (GCs) where there is a spread in iron abundance (hereafter,
iron-complex GCs). By means of N-body simulations, we investigate if merging is
consistent with the observations of sub-populations and rotation in
iron-complex GCs. The key parameters are the initial mass and density ratios of
the progenitors. When densities are similar, the more massive progenitor
dominates the central part of the merger remnant and the less massive
progenitor forms an extended rotating population. The low-mass progenitor can
become the majority population in the central regions of the merger remnant
only if its initial density is higher by roughly the mass ratio. To match the
radial distribution of multiple populations in two iron-complex GCs ({\omega}
Cen and NGC 1851), the less massive progenitor needs to be four times as dense
as the larger one. Our merger remnants show solid-body rotation in the inner
parts, becoming differential in the outer parts. Rotation velocity V and
ellipticity {\epsilon} are in agreement with models for oblate rotators with
isotropic dispersion. We discuss several kinematic signatures of a merger with
a denser lower mass progenitor that can be tested with future observations.