title: Anti-solar differential rotation on the active sub-giant HU Virginis

abstract:
  Measuring surface differential rotation (DR) on different types of stars is
important when characterizing the underlying stellar dynamo. It has been
suggested that anti-solar DR laws can occur when strong meridional flows exist.
We aim to investigate the differential surface rotation on the primary star of
the RS CVn binary HU Vir by tracking its starspot distribution as a function of
time. We also aim to recompute and update the values for several system
parameters of the triple system HU Vir (close and wide orbits). Time-series
high-resolution spectroscopy for four continuous months was obtained with the
1.2-m robotic STELLA telescope. Nine consecutive Doppler images were
reconstructed from these data, using our line-profile inversion code iMap. An
image cross-correlation method was applied to derive the surface
differential-rotation law for HU Vir. New orbital elements for the close and
the wide orbits were computed using our new STELLA radial velocities (RVs)
combined with the RV data available in the literature. Photometric observations
were performed with the Amadeus Automatic Photoelectric Telescope (APT),
providing contemporaneous Johnson-Cousins $V$ and $I$ data for approximately 20
years. This data was used to determine the stellar rotation period and the
active longitudes. We confirm anti-solar DR with a surface shear parameter
$\alpha$ of -0.029 $\pm$ 0.005 and -0.026 $\pm$ 0.009, using single-term and
double-term differential rotation laws, respectively. The best fit is achieved
assuming a solar-like double-term law with a lap time of $\approx$ 400 d. Our
orbital solutions result in a period of 10.387678 $\pm$ 0.000003 days for the
close orbit and 2726 $\pm$ 7 d ($\approx$ 7.5 yr) for the wide orbit. A
Lomb-Scarge (L-S) periodogram of the pre-whitened $V$-band data reveals a
strong single peak providing a rotation period of 10.391 $\pm$ 0.008 d.


title:
Mid-Infrared Mapping of Jupiter's Temperatures, Aerosol Opacity and
  Chemical Distributions with IRTF/TEXES

abstract:
  Global maps of Jupiter's atmospheric temperatures, gaseous composition and
aerosol opacity are derived from a programme of 5-20 $\mu$m mid-infrared
spectroscopic observations using the Texas Echelon Cross Echelle Spectrograph
(TEXES) on NASA's Infrared Telescope Facility (IRTF). Image cubes from December
2014 in eight spectral channels, with spectral resolutions of $R\sim2000-12000$
and spatial resolutions of $2-4^\circ$ latitude, are inverted to generate 3D
maps of tropospheric and stratospheric temperatures, 2D maps of upper
tropospheric aerosols, phosphine and ammonia, and 2D maps of stratospheric
ethane and acetylene. The results are compared to a re-analysis of Cassini
Composite Infrared Spectrometer (CIRS) observations acquired during Cassini's
closest approach to Jupiter in December 2000, demonstrating that this new
archive of ground-based mapping spectroscopy can match and surpass the quality
of previous investigations, and will permit future studies of Jupiter's
evolving atmosphere. We identify mid-infrared signatures of Jupiter's 5-$\mu$m
hotspots via simultaneous M, N and Q-band observations, which are interpreted
as temperature and ammonia variations in the northern Equatorial Zone and on
the edge of the North Equatorial Belt (NEB). Equatorial plumes enriched in
NH$_3$ gas are located south-east of NH$_3$-desiccated `hotspots' on the edge
of the NEB. Comparison of the hotspot locations in several channels across the
5-20 $\mu$m range indicate that these anomalous regions tilt westward with
altitude. Aerosols and PH$_3$ are both enriched at the equator but are not
co-located with the NH$_3$ plumes. We find hemispheric asymmetries in the
distribution of tropospheric PH$_3$, stratospheric hydrocarbons and the 2D wind
field. Jupiter's stratosphere is notably warmer at northern mid-latitudes than
in the south in both 2000 and 2014. [Abridged]


title:
Attack of the Flying Snakes : Formation of Isolated HI Clouds By
  Fragmentation of Long Streams

abstract:
  The existence of long (> 100 kpc) HI streams and small (< 20 kpc)
free-floating HI clouds is well-known. While the formation of the streams has
been investigated extensively, and the isolated clouds are often purported to
be interaction debris, little research has been done on the formation of
optically dark HI clouds that are not part of a larger stream. One possibility
is that such features result from the fragmentation of more extended streams,
while another idea is that they are primordial, optically dark galaxies. We
test the validity of the fragmentation scenario (via harassment) using
numerical simulations. In order to compare our numerical models with
observations, we present catalogues of both the known long HI streams (42
objects) and free-floating HI clouds suggested as dark galaxy candidates (51
objects). In particular, we investigate whether it is possible to form compact
features with high velocity widths (> 100 km/s), similar to observed clouds
which are otherwise intriguing dark galaxy candidates. We find that producing
such features is possible but extremely unlikely, occurring no more than 0.2%
of the time in our simulations. In contrast, we find that genuine dark galaxies
could be extremely stable to harassment and remain detectable even after 5 Gyr
in the cluster environment (with the important caveat that our simulations only
explore harassment and do not yet include the intracluster medium, heating and
cooling, or star formation). We also discuss the possibility that such objects
could be the progenitors of recently discovered ultra diffuse galaxies.


title:
A Short Note on the Comparison of Interpolation Widths, Entropy Numbers,
  and Kolmogorov Widths

abstract:
  We compare the Kolmogorov and entropy numbers of compact operators mapping
from a Hilbert space into a Banach space. We then apply these general findings
to embeddings between reproducing kernel Hilbert spaces and $L_\infty(\mu)$.
Here we provide a sufficient condition for a gap of the order $n^{1/2}$ between
the associated interpolation and Kolmogorov $n$-widths. Finally, we show that
in the multi-dimensional Sobolev case, this gap actually occurs between the
Kolmogorov and approximation widths.


title:
The secular evolution of discrete quasi-Keplerian systems. I. Kinetic
  theory of stellar clusters near black holes

abstract:
  We derive the kinetic equation that describes the secular evolution of a
large set of particles orbiting a dominant massive object, such as stars bound
to a supermassive black hole or a proto-planetary debris disc encircling a
star. Because the particles move in a quasi-Keplerian potential, their orbits
can be approximated by ellipses whose orientations remain fixed over many
dynamical times. The kinetic equation is obtained by simply averaging the BBGKY
equations over the fast angle that describes motion along these ellipses. This
so-called Balescu-Lenard equation describes self-consistently the long-term
evolution of the distribution of quasi-Keplerian orbits around the central
object: it models the diffusion and drift of their actions, induced through
their mutual resonant interaction. Hence, it is the master equation that
describes the secular effects of resonant relaxation. We show how it captures
the phenonema of mass segregation and of the relativistic Schwarzschild barrier
recently discovered in $N$-body simulations.


title: Stark units in positive characteristic

abstract:
  We show that the module of Stark units associated to a sign-normalized rank
one Drinfeld module can be obtained from Anderson's equivariant $A$-harmonic
series. We apply this to obtain a class formula \`a la Taelman and to prove a
several variable log-algebraicity theorem, generalizing Anderson's
log-algebraicity theorem. We also give another proof of Anderson's
log-algebraicity theorem using shtukas and obtain various results concerning
the module of Stark units for Drinfeld modules of arbitrary rank.


title:
Two-photon vibrational excitation of air by long-wave infrared laser
  pulses

abstract:
  Ultrashort long-wave infrared (LWIR) laser pulses can resonantly excite
vibrations in N2 and O2 through a two-photon transition. The absorptive,
vibrational component of the ultrafast optical nonlinearity grows in time,
starting smaller than, but quickly surpassing, the electronic, rotational, and
vibrational refractive components. The growth of the vibrational component
results in a novel mechanism of 3rd harmonic generation, providing an
additional two-photon excitation channel, fundamental + 3rd harmonic. The
original and emergent two-photon excitations drive the resonance exactly out of
phase, causing spatial decay of the absorptive, vibrational nonlinearity. This
nearly eliminates two-photon vibrational absorption. Here we present
simulations and analytical calculations demonstrating how these processes
modify the ultrafast optical nonlinearity in air. The results reveal nonlinear
optical phenomena unique to the LWIR regime of ultrashort pulse propagation in
atmosphere.


title: The column density distribution of hard X-ray radio galaxies

abstract:
  In order to investigate the role of absorption in AGN with jets, we have
studied the column density distribution of a hard X-ray selected sample of
radio galaxies, derived from the INTEGRAL/IBIS and Swift/BAT AGN catalogues
(~7-10% of the total AGN population). The 64 radio galaxies have a typical FRII
radio morphology and are characterized by high 20-100 keV luminosities (from
10^42 to 10^46 erg/s) and high Eddington ratios (Log L_{Bol}/L_{Edd} typically
larger than ~0.01). The observed fraction of absorbed AGN (N_{H} > 10^{22}
cm^{-2}) is around 40% among the total sample, and ~75% among type 2 AGN. The
majority of obscured AGN are narrow line objects, while unobscured AGN are
broad line objects, obeying to the zeroth-order predictions of unified models.
A significant anti-correlation between the radio core dominance parameter and
the X-ray column density is found. The observed fraction of Compton thick AGN
is ~2-3%, in comparison with the 5-7% found in radio-quiet hard X-ray selected
AGN. We have estimated the absorption and Compton thick fractions in a hard
X-ray sample containing both radio galaxies and non-radio galaxies and
therefore affected by the same selection biases. No statistical significant
difference was found in the absorption properties of radio galaxies and non
radio galaxies sample. In particular, the Compton thick objects are likely
missing in both samples and the fraction of obscured radio galaxies appears to
decrease with luminosity as observed in hard X-ray non-radio galaxies.


title: Multilevel tensor approximation of PDEs with random data

abstract:
  In this paper, we introduce and analyze a new low-rank multilevel strategy
for the solution of random diffusion problems. Using a standard stochastic
collocation scheme, we first approximate the infinite dimensional random
problem by a deterministic parameter-dependent problem on a high-dimensional
parameter domain. Given a hierarchy of finite element discretizations for the
spatial approximation, we make use of a multilevel framework in which we
consider the differences of the solution on two consecutive finite element
levels in the collocation points. We then address the approximation of these
high-dimensional differences by adaptive low-rank tensor techniques. This
allows to equilibrate the error on all levels by exploiting analytic and
algebraic properties of the solution at the same time. We arrive at an explicit
representation in a low-rank tensor format of the approximate solution on the
entire parameter domain, which can be used for, e.g., the direct and cheap
computation of statistics. Numerical results are provided in order to
illustrate the approach.


title: Learning Abstract Classes using Deep Learning

abstract:
  Humans are generally good at learning abstract concepts about objects and
scenes (e.g.\ spatial orientation, relative sizes, etc.). Over the last years
convolutional neural networks have achieved almost human performance in
recognizing concrete classes (i.e.\ specific object categories). This paper
tests the performance of a current CNN (GoogLeNet) on the task of
differentiating between abstract classes which are trivially differentiable for
humans. We trained and tested the CNN on the two abstract classes of horizontal
and vertical orientation and determined how well the network is able to
transfer the learned classes to other, previously unseen objects.


title: Coloring Graphs with Forbidden Minors

abstract:
  Hadwiger's conjecture from 1943 states that for every integer $t\ge1$, every
graph either can be $t$-colored or has a subgraph that can be contracted to the
complete graph on $t+1$ vertices. As pointed out by Paul Seymour in his recent
survey on Hadwiger's conjecture, proving that graphs with no $K_7$ minor are
$6$-colorable is the first case of Hadwiger's conjecture that is still open. It
is not known yet whether graphs with no $K_7$ minor are $7$-colorable. Using a
Kempe-chain argument along with the fact that an induced path on three vertices
is dominating in a graph with independence number two, we first give a very
short and computer-free proof of a recent result of Albar and Gon\c{c}alves and
generalize it to the next step by showing that every graph with no $K_t$ minor
is $(2t-6)$-colorable, where $t\in\{7,8,9\}$. We then prove that graphs with no
$K_8^-$ minor are $9$-colorable and graphs with no $K_8^=$ minor are
$8$-colorable. Finally we prove that if Mader's bound for the extremal function
for $K_p$ minors is true, then every graph with no $K_p$ minor is
$(2t-6)$-colorable for all $p\ge5$. This implies our first result. We believe
that the Kempe-chain method we have developed in this paper is of independent
interest.


title:
A class of asymmetric gapped Hamiltonians on quantum spin chains and its
  characterization III

abstract:
  In this paper, we consider classification problem of asymmetric gapped
Hamiltonians, which are given as the non-degenerate part of the Hamiltonians
introduced in [O1]. We consider the $C^1$-classification, which takes into
account the effect of boundaries. We show that the left and right degeneracies
of edge ground states are the complete invariant. As a corollary, we consider
the bulk-classification problem. We study Hamiltonians that1.are given by
translation invariant finite range interactions, 2.are gapped in the bulk,
3.are frustration-free, 4.have uniformly bounded ground state degeneracy on
finite intervals, and 5.have a unique bulk ground state. We show that for the
bulk-classification, any such Hamiltonians are equivalent.

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


title: Physical and Geometrical Parameters of CVBS XI: COU1511 (HIP12552)

abstract:
  Model atmospheres of the close visual binary star COU1511 (HIP12552) are
constructed using grids of Kuruz's blanketed models to build the individual
synthetic SEDs for both components. These synthetic SED's are combined together
for the entire system and compared with the observational one following
Al-Wardat's complex method for analyzing close visual binary stars. The entire
observational spectral energy distribution (SED) of the system is used as a
reference for comparison between synthetic SED and the observed one. The
parameters of both components are derived as: $T_{\rm eff}^{a} =6180\pm50 $\,K,
$T_{\rm eff}^{b} =5865\pm70$\,K, log $g_{a}=4.35\pm0.12$, log
$g_{b}=4.45\pm0.14$, $R_{a}=1.262\pm0.08R_\odot$, $R_{b}=1.006\pm0.07R_\odot$,
$L_a=2.09\pm0.10 L_\odot$, $L_b=1.08\pm0.12L_\odot$, with spectral types F8 and
G1 for both components (a,b) respectively, and age of $3.0\pm 0.9$ Gy. A
modified orbit of the system is built and the masses of the two components are
calculated as $M_a=1.17\pm0.11M_\odot$, $M_b=1.06\pm0.10M_\odot$.


title:
Finite-density phase diagram of a (1+1)-d non-abelian lattice gauge
  theory with tensor networks

abstract:
  We investigate the finite-density phase diagram of a non-abelian SU(2)
lattice gauge theory in (1+1)-dimensions using tensor network methods. We
numerically characterise the phase diagram as a function of the matter filling
and of the matter-field coupling, identifying different phases, some of them
appearing only at finite densities. For weak matter-field coupling we find a
meson BCS liquid phase, which is confirmed by second-order analytical
perturbation theory. At unit filling and for strong coupling, the system
undergoes a phase transition to a charge density wave of single-site (spin-0)
mesons via spontaneous chiral symmetry breaking. At finite densities, the
chiral symmetry is restored almost everywhere, and the meson BCS liquid becomes
a simple liquid at strong couplings, with the exception of filling two-thirds,
where a charge density wave of mesons spreading over neighbouring sites
appears. Finally, we identify two tri-critical points between the chiral and
the two liquid phases which are compatible with a $SU(2)_2$
Wess-Zumino-Novikov-Witten model. Here we do not perform the continuum limit
but we explicitly address the global $U(1)$ charge conservation symmetry.


title:
Two-photon luminescence of single colloidal gold nanorods: revealing the
  origin of plasmon relaxation in small nanocrystals

abstract:
  The two-photon luminescence (TPL) of small 10 nm x 40 nm colloidal gold
nanorods (GNR) is investigated at the single object level, combining
polarization resolved TPL and simultaneously acquired topography. A very high
dependence of the TPL signal with both the nanorods longitudinal axis and the
incident wavelength is observed confirming the plasmonic origin of the signal
and pointing the limit of the analogy between GNRs and molecules. The spectral
analysis of the TPL evidences two emission bands peaks: in the visible (in
direct connection with the gold band structure), and in the infrared. Both
bands are observed to vary quadradically with the incident excitation beam but
exhibit different polarization properties. The maximum two-photon brightness of
a single GNR is measured to be a few millions higher than the two-photon
brightness of fluorescein molecules. We show that the important TPL observed in
these small gold nanorods results from resonance effects both at the excitation
and emission level : local field enhancement at the longitudinal surface
plasmon resonances (LSPR) first results in an increase of the electron-hole
generation. Further relaxation of electron-hole pairs then mostly leads to the
excitation of the GNR transverse plasmon mode and its subsequent radiative
relaxation.


title:
Critical exponent and Hausdorff dimension in pseudo-Riemannian
  hyperbolic geometry

abstract:
  The aim of this article is to understand the geometry of limit sets in
pseudo-Riemannian hyperbolic geometry. We focus on a class of subgroups of
$\mathrm{PO}(p,q+1)$ introduced by Danciger, Gu\'eritaud and Kassel, called
$\mathbb{H}^{p,q}$-convex cocompact. We define a pseudo-Riemannian analogue of
critical exponent and Hausdorff dimension of the limit set. We show that they
are equal and bounded from above by the usual Hausdorff dimension of the limit
set. We also prove a rigidity result in $\mathbb{H}^{2,1}=\mathrm{ADS}^3$ which
can be understood as a Lorentzian version of a famous Theorem of R. Bowen in
$3$-dimensional hyperbolic geometry.


title: Uncoupled dark states can inherit polaritonic properties

abstract:
  When a collection of quantum emitters interacts with an electromagnetic
field, the whole system can enter into the collective strong coupling regime in
which hybrid light-matter states, i.e., polaritons can be created. Only a small
portion of excitations in the emitters are coupled to the light field, and
there are many dark states that, in principle, retain their pure excitonic
nature. Here we theoretically demonstrate that these dark states can have a
delocalized character, which is inherent to polaritons, despite the fact that
they do not have a photonic component. This unexpected behavior only appears
when the electromagnetic field displays a discrete spectrum. In this case, when
the main loss mechanism in the hybrid system stems from the radiative losses of
the light field, dark states are even more efficient than polaritons in
transferring excitations across the structure.


title: Sampling and Distortion Tradeoffs for Indirect Source Retrieval

abstract:
  Consider a continuous signal that cannot be observed directly. Instead, one
has access to multiple corrupted versions of the signal. The available
corrupted signals are correlated because they carry information about the
common remote signal. The goal is to reconstruct the original signal from the
data collected from its corrupted versions. The information theoretic
formulation of the remote reconstruction problem assumes that the corrupted
signals are uniformly sampled and the focus is on optimal compression of the
samples. In this paper we revisit this problem from a sampling perspective. We
look at the problem of finding the best sampling locations for each signal to
minimize the total reconstruction distortion of the remote signal. In finding
the sampling locations, one can take advantage of the correlation among the
corrupted signals. Our main contribution is a fundamental lower bound on the
reconstruction distortion for any arbitrary nonuniform sampling strategy. This
lower bound is valid for any sampling rate. Furthermore, it is tight and
matches the optimal reconstruction distortion in low and high sampling rates.
Moreover, it is shown that in the low sampling rate region, it is optimal to
use a certain nonuniform sampling scheme on all the signals. On the other hand,
in the high sampling rate region, it is optimal to uniformly sample all the
signals. We also consider the problem of finding the optimal sampling locations
to recover the set of corrupted signals, rather than the remote signal. Unlike
the information theoretic formulation of the problem in which these two
problems were equivalent, we show that they are not equivalent in our setting.


title:
Mass bounds for compact spherically symmetric objects in generalized
  gravity theories

abstract:
  We derive upper and lower bounds on the mass-radius ratio of stable compact
objects in extended gravity theories, in which modifications of the
gravitational dynamics via-{\' a}-vis standard general relativity are described
by an effective contribution to the matter energy-momentum tensor. Our results
include the possibility of a variable coupling between the matter sector and
the gravitational field and are valid for a large class of generalized gravity
models. The generalized continuity and Tolman-Oppenheimer-Volkoff equations are
expressed in terms of the effective mass, density and pressure, given by the
bare values plus additional contributions from the total energy-momentum
tensor, and general theoretical limits for the maximum and minimum mass-radius
ratios are explicitly obtained. As an applications of the formalism developed
herein, we consider compact bosonic objects, described by scalar-tensor
gravitational theories with self-interacting scalar field potentials, and
charged compact objects, respectively. For Higgs type models, we find that
these bounds can be expressed in terms of the value of the potential at the
surface of the compact object. Minimizing the energy with respect to the
radius, we obtain explicit upper and lower bounds on the mass, which admits a
Chandrasekhar type representation. For charged compact objects, we consider the
effects of the Poincar\'{e} stresses on the equilibrium structure and obtain
bounds on the radial and tangential stresses. As a possible astrophysical test
of our results, we obtain the general bound on the gravitational redshift for
compact objects in extended gravity theories. General implications of minimum
mass bounds for the gravitational stability of fundamental particles and for
the existence of holographic duality between bulk and boundary degrees of
freedom are also considered.


title: Superlensing using hyperbolic metamaterials: the scalar case

abstract:
  This paper is devoted to superlensing using hyperbolic metamaterials: the
possibility to image an arbitrary object using hyperbolic metamaterials without
imposing any conditions on size of the object and the wave length. To this end,
two types of schemes are suggested and their analysis are given. The
superlensing devices proposed are independent of the object. It is worth noting
that the study of hyperbolic metamaterials is challenging due to the change
type of modelling equations, elliptic in some regions, hyperbolic in some
others.


title:
Crystal growth by Bridgman and Czochralski method of the ferromagnetic
  quantum critical material YbNi$_4$P$_2$

abstract:
  The tetragonal YbNi$_4$P$_2$ is one of the rare examples of compounds that
allow the investigation of a ferromagnetic quantum critical point. We report in
detail on two different methods which have been used to grow YbNi$_4$P$_2$
single crystals from a self-flux. The first, a modified Bridgman method, using
a closed crucible system yields needle-shaped single crystals oriented along
the $[001]$-direction. The second method, the Czochralski growth from a
levitating melt, yields large single crystals which can be cut in any desired
orientation. With this crucible-free method, samples without flux inclusions
and a resistivity ratio at 1.8 K of RR$_{1.8\rm K}= 17$ have been grown.


title: The BBM formula revisited

abstract:
  In this paper, we revise the BBM formula due to J. Bourgain, H. Brezis, and
P. Mironescu in [1].


title:
Open Connect Everywhere: A Glimpse at the Internet Ecosystem through the
  Lens of the Netflix CDN

abstract:
  The importance of IXPs to interconnect different networks and exchange
traffic locally has been well studied over the last few years. However, far
less is known about the role IXPs play as a platform to enable large-scale
content delivery and to reach a world-wide customer base. In this paper, we
study the infrastructure deployment of a content hypergiant, Netflix, and show
that the combined worldwide IXP substrate is the major corner stone of its
Content Delivery Network. To meet its worldwide demand for high-quality video
delivery, Netflix has built a dedicated CDN. Its scale allows us to study a
major part of the Internet ecosystem, by observing how Netflix takes advantage
of the combined capabilities of IXPs and ISPs present in different regions. We
find wide disparities in the regional Netflix deployment and traffic levels at
IXPs and ISPs across various local ecosystems. This highlights the complexity
of large-scale content delivery as well as differences in the capabilities of
IXPs in specific regions. On a global scale we find that the footprint provided
by IXPs allows Netflix to deliver most of its traffic directly from them. This
highlights the additional role that IXPs play in the Internet ecosystem, not
just in terms of interconnection, but also allowing players such as Netflix to
deliver significant amounts of traffic.


title: Complete monotonicity of some entropies

abstract:
  It is well-known that the Shannon entropies of some parameterized probability
distributions are concave functions with respect to the parameter. In this
paper we consider a family of such distributions (including the binomial,
Poisson, and negative binomial distributions) and investigate the Shannon,
R\'{e}nyi, and Tsallis entropies of them with respect to the complete
monotonicity.


title:
Higher-order Wilson coefficients for c $\to$ u transitions in the
  Standard Model

abstract:
  The standard theoretical framework to deal with weak decays of heavy mesons
is the so-called weak effective Hamiltonian. It involves the short-distance
Wilson coefficients, which depend on the renormalisation scale $\mu$. For
specific calculations one has to evolve the Wilson coefficients down from the
electroweak scale $\mu=M_W$ to the typical mass scale of the decay under
consideration. This is done by solving a renormalisation group equation for the
effective operator basis. In this paper the results of a consistent two-step
running of the $c \to u \,\ell^+\ell^-$ Wilson coefficients for dimension-6
operators are presented. This running involves the intermediate scale $\mu=m_b$
(with $M_W > m_b > m_c$) where the bottom quark is integrated out. The matching
coefficients and anomalous dimensions are taken to the required order by
generalizing and extending results from $b \to s$ or $s \to d$ transitions
available in the literature.


title:
A novel method linking neural connectivity to behavioral fluctuations:
  Behavior-Regressed Connectivity

abstract:
  Background: During an experimental session, behavioral performance
fluctuates, yet most neuroimaging analyses of functional connectivity derive a
single connectivity pattern. These conventional connectivity approaches assume
that since the underlying behavior of the task remains constant, the
connectivity pattern is also constant.
  New Method: We introduce a novel method, behavior-regressed connectivity
(BRC), to directly examine behavioral fluctuations within an experimental
session and capture their relationship to changes in functional connectivity.
This method employs the weighted phase lag index (WPLI) applied to a window of
trials with a weighting function. Using two datasets, the BRC results are
compared to conventional connectivity results during two time windows: the one
second before stimulus onset to identify predictive relationships, and the one
second after onset to capture task-dependent relationships.
  Results: In both tasks, we replicate the expected results for the
conventional connectivity analysis, and extend our understanding of the
brain-behavior relationship using the BRC analysis, demonstrating
subject-specific connectivity patterns that correspond to both positive and
negative relationships with behavior.
  Comparison with Existing Method(s): Conventional connectivity analyses assume
a consistent relationship between behaviors and functional connectivity, but
the BRC method examines performance variability within an experimental session
to understand dynamic connectivity and transient behavior.
  Conclusion: The BRC approach examines connectivity as it covaries with
behavior to complement the knowledge of underlying neural activity derived from
conventional connectivity analyses. Within this framework, BRC may be
implemented for the purpose of understanding performance variability both
within and between participants.


title: Unveiling the scattering behavior of small spheres

abstract:
  A classical way for exploring the scattering behavior of a small sphere is to
approximate Mie coefficients with a Taylor series expansion. This ansatz
delivered a plethora of insightful results, mostly for small spheres supporting
localized plasmonic resonances. However, many scattering aspects are still
uncharted, especially with regards to magnetic resonances. Here, an alternative
system ansatz is proposed based on the Pad\'e approximants for the Mie
coefficients. The result reveal the existence of a self-regulating radiative
damping mechanism for the first magnetic resonance and new general resonating
aspects for the higher order multipoles. Hence, a systematic way of exploring
the scattering behavior is introduced, sharpening our understanding about the
sphere's scattering behavior and its emergent functionalities.


title:
Illuminating Molecular Symmetries with Bicircular High-Order-Harmonic
  Generation

abstract:
  We present a complete theory of bicircular high-order-harmonic emission from
N-fold rotationally symmetric molecules. Using a rotating frame of reference we
predict the complete structure of the high-order-harmonic spectra for arbitrary
driving frequency ratios and show how molecular symmetries can be directly
identified from the harmonic signal. Our findings reveal that a characteristic
fingerprint of rotational molecular symmetries can be universally observed in
the ultrafast response of molecules to strong bicircular fields.


title: On the Zero Defect Conjecture

abstract:
  Brlek et al. conjectured in 2008 that any fixed point of a primitive morphism
with finite palindromic defect is either periodic or its palindromic defect is
zero. Bucci and Vaslet disproved this conjecture in 2012 by a counterexample
over ternary alphabet. We prove that the conjecture is valid on binary
alphabet. We also describe a class of morphisms over multiliteral alphabet for
which the conjecture still holds. The proof is based on properties of extension
graphs.


title: Compact Stars in Vector-Tensor-Horndeski Theory of Gravity

abstract:
  In this paper, we will analyse a theory of modified gravity, in which the
field content of general relativity will be increased to include a vector
field. We will use the Horndeski formalism to non-minimally couple this vector
field to the metric. As we will be using the Horndeski formalism, this theory
will not contain Ostrogradsky ghost degree of freedom. We will analyse compact
stars using this Vector-Tensor-Horndeski theory.


abstract:
  Tate objects have been studied by many authors. They allow us to deal with
infinite dimensional spaces by identifying some more structure. In this
article, we set up the theory of Tate objects in stable
$(\infty,1)$-categories, while the literature only treats with exact
categories. We will prove the main properties expected from Tate objects. This
new setting includes several useful examples: Tate objects in the category of
spectra for instance, or in the derived category of a derived algebraic object
-- which can be thought as structured infinite dimensional vector bundle in
derived setting.


title: Convexity and the Euclidean metric of space-time

abstract:
  We address the question about the reasons why the "Wick-rotated",
positive-definite, space-time metric obeys the Pythagorean theorem. An answer
is proposed based on the convexity and smoothness properties of the functional
spaces purporting to provide the kinematic framework of approaches to quantum
gravity. We employ moduli of convexity and smoothness which are eventually
extremized by Hilbert spaces. We point out the potential physical significance
that functional analytical dualities play in this framework. Following the
spirit of the variational principles employed in classical and quantum Physics,
such Hilbert spaces dominate in a generalized functional integral approach. The
metric of space-time is induced by the inner product of such Hilbert spaces.


title: Towards a unified framework for decomposability of processes

abstract:
  The concept of process is ubiquitous in science, engineering and everyday
life. Category theory, and monoidal categories in particular, provide an
abstract framework for modelling processes of many kinds. In this paper, we
concentrate on sequential and parallel decomposability of processes in the
framework of monoidal categories: We will give a precise definition, what it
means for processes to be decomposable. Moreover, through examples, we argue
that viewing parallel processes as coupled in this framework can be seen as a
category mistake or a misinterpretation. We highlight the suitability of
category theory for a structuralistic interpretation of mathematical modelling
and argue that for appliers of mathematics, such as engineers, there is a
pragmatic advantage from this.


title: FinInG: a package for Finite Incidence Geometry

abstract:
  FinInG is a package for computation in Finite Incidence Geometry. It provides
users with the basic tools to work in various areas of finite geometry from the
realms of projective spaces to the flat lands of generalised polygons. The
algebraic power of GAP is exploited, particularly in its facility with matrix
and permutation groups.


title:
Long-range charge density wave proximity effect at cuprate-manganate
  interfaces

abstract:
  The interplay between charge density waves (CDWs) and high-temperature
superconductivity is currently under intense investigation. Experimental
research on this issue is difficult because CDW formation in bulk copper-oxides
is strongly influenced by random disorder, and a long-range-ordered CDW state
in high magnetic fields is difficult to access with spectroscopic and
diffraction probes. Here we use resonant x-ray scattering in zero magnetic
field to show that interfaces with the metallic ferromagnet
La$_{2/3}$Ca$_{1/3}$MnO$_3$ greatly enhance CDW formation in the optimally
doped high-temperature superconductor YBa$_2$Cu$_3$O$_{6+\delta}$ ($\bf \delta
\sim 1$), and that this effect persists over several tens of nm. The wavevector
of the incommensurate CDW serves as an internal calibration standard of the
charge carrier concentration, which allows us to rule out any significant
influence of oxygen non-stoichiometry, and to attribute the observed phenomenon
to a genuine electronic proximity effect. Long-range proximity effects induced
by heterointerfaces thus offer a powerful method to stabilize the charge
density wave state in the cuprates, and more generally, to manipulate the
interplay between different collective phenomena in metal oxides.


title: Surpassing the Carnot Efficiency by extracting imperfect work

abstract:
  A suitable way of quantifying work for microscopic quantum systems has been
constantly debated in the field of quantum thermodynamics. One natural approach
is to measure the average increase in energy of an ancillary system, called the
battery, after a work extraction protocol. The quality of energy extracted is
usually argued to be good by quantifying higher moments of the energy
distribution, or by restricting the amount of entropy to be low. This limits
the amount of heat contribution to the energy extracted, but does not
completely prevent it. We show that the definition of "work" is crucial. If one
allows for a definition of work that tolerates a non-negligible entropy
increase in the battery, then a small scale heat engine can possibly exceed the
Carnot efficiency. This can be achieved even when one of the heat baths is
finite in size.


title: Excited Scalar Mesons and the Search for Glueballs

abstract:
  We discuss the importance of mixing between glueballs -- bound states of
gluons -- and excited $\bar{q}q$ states for the glueball search. A preliminary
study of the excited states in the Extended Linear Sigma Model (eLSM) suggests
their masses in the scalar channel to be in the vicinity of the scalar-glueball
mass found in Lattice QCD. This could have implications for future glueball
searches.


title: A Radiatively induced Elementary Goldstone Higgs in SU(4)/Sp(4)

abstract:
  Using a $SU(4)\rightarrow Sp(4)$ pattern of chiral symmetry breaking, we
investigate the pseudo-Goldstone nature of the Higgs boson in an elementary
realisation that at the same time provides an ultraviolet completion. The
renormalizability of the model together with the perturbative corrections
determine dynamically the direction of vacuum of the theory and the
corresponding Higgs chiral symmetry breaking scale $ f \sim 14~$TeV. The Higgs
boson is radiatively generated and the scalar mass spectrum, together with a
second massive Higgs boson, lie in the multi-TeV range.


title: Tensor Ring Decomposition

abstract:
  Tensor networks have in recent years emerged as the powerful tools for
solving the large-scale optimization problems. One of the most popular tensor
network is tensor train (TT) decomposition that acts as the building blocks for
the complicated tensor networks. However, the TT decomposition highly depends
on permutations of tensor dimensions, due to its strictly sequential
multilinear products over latent cores, which leads to difficulties in finding
the optimal TT representation. In this paper, we introduce a fundamental tensor
decomposition model to represent a large dimensional tensor by a circular
multilinear products over a sequence of low dimensional cores, which can be
graphically interpreted as a cyclic interconnection of 3rd-order tensors, and
thus termed as tensor ring (TR) decomposition. The key advantage of TR model is
the circular dimensional permutation invariance which is gained by employing
the trace operation and treating the latent cores equivalently. TR model can be
viewed as a linear combination of TT decompositions, thus obtaining the
powerful and generalized representation abilities. For optimization of latent
cores, we present four different algorithms based on the sequential SVDs, ALS
scheme, and block-wise ALS techniques. Furthermore, the mathematical properties
of TR model are investigated, which shows that the basic multilinear algebra
can be performed efficiently by using TR representaions and the classical
tensor decompositions can be conveniently transformed into the TR
representation. Finally, the experiments on both synthetic signals and
real-world datasets were conducted to evaluate the performance of different
algorithms.


title:
The 3XMM/SDSS Stripe 82 Galaxy Cluster Survey: Cluster catalogue and
  discovery of two merging cluster candidates

abstract:
  We present a galaxy cluster survey based on XMM-Newton observations that are
located in Stripe 82 of the Sloan Digital Sky Survey (SDSS). The survey covers
an area of 11.25 deg$^2$. The X-ray cluster candidates were selected as
serendipitously extended detected sources from the third XMM-Newton
serendipitous source catalogue (3XMM-DR5). A cross-correlation of the candidate
list that comprises 94 objects with recently published X-ray and optically
selected cluster catalogues provided optical confirmations and redshift
estimates for about half of the candidate sample. We present a catalogue of
X-ray cluster candidates previously known in X-ray and/or optical bands from
the matched catalogues or NED. The catalogue consists of 54 systems with
redshift measurements in the range of 0.05-1.19 with a median of 0.36. Of
these, 45 clusters have spectroscopic confirmations as stated in the matched
catalogues. We spectroscopically confirmed another 6 clusters from the
available spectroscopic redshifts in the SDSS-DR12. The cluster catalogue
includes 17 newly X-ray discovered clusters, while the remainder were detected
in previous XMM-Newton and/or ROSAT cluster surveys. Based on the available
redshifts and fluxes given in the 3XMM-DR5 catalogue, we estimated the X-ray
luminosities and masses for the cluster sample. We also present the list of the
remaining X-ray cluster candidates (40 objects) that have no redshift
information yet in the literature. Of these candidates, 25 sources are
considered as distant cluster candidates beyond a redshift of 0.6. We also
searched for galaxy cluster mergers in our cluster sample and found two strong
candidates for newly discovered cluster mergers at redshifts of 0.11 and 0.26.
The X-ray and optical properties of these systems are presented.


title: Three-qutrit entanglement and simple singularities

abstract:
  In this paper, we use singularity theory to study the entanglement nature of
pure three-qutrit systems. We first consider the algebraic variety $X$ of
separable three-qutrit states within the projective Hilbert space
$\mathbb{P}(\mathcal{H}) = \mathbb{P}^{26}$. Given a quantum pure state
$|\varphi\rangle\in \mathbb{P}(\mathcal{H})$ we define the
$X_\varphi$-hypersuface by cutting $X$ with a hyperplane $H_\varphi$ defined by
the linear form $\langle\varphi|$ (the $X_\varphi$-hypersurface of $X$ is
$X\cap H_\varphi \subset X$).
  We prove that when $|\varphi\rangle$ ranges over the SLOCC entanglement
classes, the "worst" possible singular $X_\varphi$-hypersuface with isolated
singularities, has a unique singular point of type $D_4$.


title: On computing the total displacement number via weighted Motzkin paths

abstract:
  Counting the number of permutations of a given total displacement is
equivalent to counting weighted Motzkin paths of a given area (Guay-Paquet and
Petersen, 2014). The former combinatorial problem is still open. In this work,
we show that this connection allows to construct efficient algorithms for
counting and for sampling such permutations. These algorithms provide a tool to
better understand the original combinatorial problem. A by-product of our
approach is a different way of counting based on certain building sequences for
Motzkin paths, which may be of independent interest.


title: Zooming in on the large-scale geometry of locally compact groups

abstract:
  The purpose of this survey is to describe how locally compact groups can be
studied as geometric objects. We will emphasize the main ideas and skip or just
sketch most proofs, often referring the reader to our much more detailed book
arXiv:1403.3796


title:
Supercloseness of the SDFEM on Shishkin triangular meshes for problems
  with exponential layers

abstract:
  In this paper, we analyze the supercloseness property of the streamline
diffusion finite element method (SDFEM) on Shishkin triangular meshes, which is
different from one in the case of rectangular meshes. The analysis depends on
integral inequalities for the part related to the diffusion in the bilinear
form. Moreover, our result allows the construction of a simple postprocessing
that yields a more accurate solution. Finally, numerical experiments support
these theoretical results.


title:
What is the theoretical time precision achievable using a dCFD algorithm
  ?

abstract:
  The time precision achievable using standard analog methods is well known.
Several expressions for timing methods using digitized signals have been
recently proposed in workshops, conferences or training courses. Most of them
are only partially exact. This paper presents a comprehensive calculation of
the timing precision for algorithms using digital treatment of digitized signal
to mimic analog discriminator-based methods. The results of these calculations
are discussed for various cases of correlation between samples.


title: Admissible subsets and Littelmann paths in affine Kazhdan-Lusztig theory

abstract:
  The center of an extended affine Hecke algebra is known to be isomorphic to
the ring of symmetric functions associated to the underlying finite Weyl group
$W\_0$. The set of Weyl characters ${\sf s}\_\la$ forms a basis of the center
and Lusztig showed in [Lus15] that these characters act as translations on the
Kazhdan-Lusztig basis element $C\_{w\_0}$ where $w\_0$ is the longest element
of $W\_0$, that is we have $C\_{w\_0}{\sf s}\_\la =C\_{w\_0t\_\la}$. As a
consequence, the coefficients that appear when
decomposing~$C\_{w\_0t\_{\la}}{\sf s}\_\tau$ in the Kazhdan-Lusztig basis are
tensor multiplicities of the Lie algebra with Weyl group $W\_0$. The aim of
this paper is to explain how admissible subsets and Littelmann paths, which are
models to compute such multiplicities, naturally appear when working out this
decomposition.


title: A (human) proof of a triple binomial sum supercongruence

abstract:
  In the recent article arXiv:1606.03351, Apagodu and Zeilberger discuss some
applications of an algorithm for finding and proving congruence identities
(modulo primes) of indefinite sums of many combinatorial sequence. At the end
they propose some supercongruences as conjectures. Here we prove one of them
and we leave some remarks for the others.


title:
Conceptual design of the BRIKEN detector: A hybrid neutron-gamma
  detection system for nuclear physics at the RIB facility of RIKEN

abstract:
  BRIKEN is a complex detection system to be installed at the RIB-facility of
the RIKEN Nishina Center. It is aimed at the detection of heavy-ion implants,
$\beta$-particles, $\gamma$-rays and $\beta$-delayed neutrons. The whole
detection setup involves the Advanced Implantation Detection Array (AIDA), two
HPGe Clover detectors and a large set of 166 counters of 3He embedded in a
high-density polyethylene matrix. This article reports on a novel methodology
developed for the conceptual design and optimisation of the 3He-tubes array,
aiming at the best possible performance in terms of neutron detection. The
algorithm is based on a geometric representation of two selected parameters of
merit, namely, average neutron detection efficiency and efficiency flatness, as
a function of a reduced number of geometric variables. The response of the
detection system itself, for each configuration, is obtained from a systematic
MC-simulation implemented realistically in Geant4. This approach has been found
to be particularly useful. On the one hand, due to the different types and
large number of 3He-tubes involved and, on the other hand, due to the
additional constraints introduced by the ancillary detectors for charged
particles and gamma-rays. Empowered by the robustness of the algorithm, we have
been able to design a versatile detection system, which can be easily
re-arranged into a compact mode in order to maximize the neutron detection
performance, at the cost of the gamma-ray sensitivity. In summary, we have
designed a system which shows, for neutron energies up to 1(5) MeV, a rather
flat and high average efficiency of 68.6%(64%) and 75.7%(71%) for the hybrid
and compact modes, respectively. The performance of the BRIKEN system has been
also quantified realistically by means of MC-simulations made with different
neutron energy distributions.


title: Universal, Unsupervised (Rule-Based), Uncovered Sentiment Analysis

abstract:
  We present a novel unsupervised approach for multilingual sentiment analysis
driven by compositional syntax-based rules. On the one hand, we exploit some of
the main advantages of unsupervised algorithms: (1) the interpretability of
their output, in contrast with most supervised models, which behave as a black
box and (2) their robustness across different corpora and domains. On the other
hand, by introducing the concept of compositional operations and exploiting
syntactic information in the form of universal dependencies, we tackle one of
their main drawbacks: their rigidity on data that are structured differently
depending on the language concerned. Experiments show an improvement both over
existing unsupervised methods, and over state-of-the-art supervised models when
evaluating outside their corpus of origin. Experiments also show how the same
compositional operations can be shared across languages. The system is
available at http://www.grupolys.org/software/UUUSA/


title: Statistical tweaks and flow scale from masses

abstract:
  We compare lattice scales determined from the vector meson mass and the
Wilson flow scale w_0 in QCD with two-flavours of rooted naive staggered
fermions over a wide range of lattice spacing and quark mass. We find that the
distributions of meson correlation functions are non-Gaussian. We modify the
statistical analysis to take care of the non-Gaussianity. Current day
improvements in the statistical quality of data on hadron correlations further
allow us to simplify certain aspects of the analysis of masses. We examine
these changes through the analysis of pions and apply them to the vector meson.
We compare the flow scale determined using the rho mass with that using
Lambda_{MSbar}.


title: Percolation in binary and ternary mixtures of patchy colloids

abstract:
  We investigate percolation in binary and ternary mixtures of patchy colloidal
particles theoretically and using Monte Carlo simulations. Each particle has
three identical patches, with distinct species having different types of patch.
Theoretically we assume tree-like clusters and calculate the bonding
probabilities using Wertheim's first-order perturbation theory for association.
For ternary mixtures we find up to eight fundamentally different percolated
states. The states differ in terms of the species and pairs of species that
have percolated. The strongest gel is a trigel or tricontinuous gel, in which
each of the three species has percolated. The weakest gel is a mixed gel in
which all of the particles have percolated, but none of the species percolates
by itself. The competition between entropy of mixing and internal energy of
bonding determines the stability of each state. Theoretical and simulation
results are in very good agreement. The only significant difference is the
temperature at the percolation threshold, which is overestimated by the theory
due to the absence of closed loops in the theoretical description.


title:
Ordering effects in 2D hexagonal systems of binary and ternary BCN
  alloys

abstract:
  We present theoretical study of ordering phenomena in binary $C_{1-x}B_{x}$,
$C_{1-x}N_{x}$ and ternary $B_{x}C_{1-x-y}N_{y}$ alloys forming
two-dimensional, graphene-like systems. For calculating energy of big systems
(20 000 atoms in the supercell with periodic boundary conditions assumed)
empirical Tersoff potential was employed. In order to find equilibrium
distribution of different species corresponding to minima of the energy, we use
Monte Carlo approach in Metropolis regime. We take into consideration wide
range of concentrations (1-50%) and temperatures (70-1500 K), to provide more
complete picture. For quantitative description of order, we determine
Warren-Cowley Short Range Order (SRO) parameters for the first coordination
shell. This procedure allows us to determine energetically favorable
compositions of all alloys, and characterize resulting types of order for both
binary and ternary systems.


title: Is the activity level of HD 80606 influenced by its eccentric planet?

abstract:
  Aims: Several studies suggest that the activity level of a planet-host star
can be influenced by the presence of a close-by orbiting planet. Moreover, the
interaction mechanisms that have been proposed, magnetic interaction and tidal
interaction, exhibit a very different dependence on orbital separation between
the star and the planet. A detection of activity enhancement and
characterization of its dependence on planetary orbital distance can, in
principle, allow us to characterize the physical mechanism behind the activity
enhancement.
  Methods: We used the HARPS-N spectrograph to measure the stellar activity
level of HD 80606 during the planetary periastron passage and compared the
activity measured to that close to apastron. Being characterized by an
eccentricity of 0.93 and an orbital period of 111 days, the system's extreme
variation in orbital separation makes it a perfect target to test our
hypothesis.
  Results: We find no evidence for a variation in the activity level of the
star as a function of planetary orbital distance, as measured by all activity
indicators employed log($R'_{HK}$), H$_\alpha$, NaI, and HeI. None of the
models employed, whether magnetic interaction or tidal interaction, provides a
good description of the data.
  Conclusions: We find no evidence for star-planet interaction in HD\,80606 at
the moment of the periastron passage of its very eccentric planet. The
straightforward explanation for the non-detection is the absence of interaction
as a result of a low magnetic field strength on either the planet or the star
and of the low level of tidal interaction between the two. However, we cannot
exclude two scenarios: i) the interaction can be instantaneous and of magnetic
origin, being concentrated on the substellar point and its surrounding area,
and ii) the interaction can lead to a delayed activity enhancement. (abridged)


title: Stochastic Characteristics of Qubits and Qubit chains on the D-Wave 2X

abstract:
  This document presents a studies of the stochastic behavior of D-Wave qubits,
qubit cells, and qubit chains. The purpose of this paper is to address the
algorithmic behavior of execution rather than the physical behavior, though
they are related. The measurements from an actual D-Wave adiabatic quantum
computer are compare with calculated measurements from a theoretical adiabatic
quantum computer running with an effective temperature of zero. In this way the
paper attempts to shed light on how the D-Wave's behavior effects how well it
minimizes its objective function and why the D-Wave performs as it does.


title: Self-adaptation of Mutation Rates in Non-elitist Populations

abstract:
  The runtime of evolutionary algorithms (EAs) depends critically on their
parameter settings, which are often problem-specific. Automated schemes for
parameter tuning have been developed to alleviate the high costs of manual
parameter tuning. Experimental results indicate that self-adaptation, where
parameter settings are encoded in the genomes of individuals, can be effective
in continuous optimisation. However, results in discrete optimisation have been
less conclusive. Furthermore, a rigorous runtime analysis that explains how
self-adaptation can lead to asymptotic speedups has been missing. This paper
provides the first such analysis for discrete, population-based EAs. We apply
level-based analysis to show how a self-adaptive EA is capable of fine-tuning
its mutation rate, leading to exponential speedups over EAs using fixed
mutation rates.


title:
Topological Defects and nano-Hz Gravitational Waves in Aligned Axion
  Models

abstract:
  We study the formation and evolution of topological defects in an aligned
axion model with multiple Peccei-Quinn scalars, where the QCD axion is realized
by a certain combination of the axions with decay constants much smaller than
the conventional Peccei-Quinn breaking scale. When the underlying U(1)
symmetries are spontaneously broken, the aligned structure in the axion field
space exhibits itself as a complicated string-wall network in the real space.
We find that the string-wall network likely survives until the QCD phase
transition if the number of the Peccei-Quinn scalars is greater than two. The
string-wall system collapses during the QCD phase transition, producing a
significant amount of gravitational waves in the nano-Hz range at present. The
typical decay constant is constrained to be below O(100) TeV by the pulsar
timing observations, and the constraint will be improved by a factor of 2 in
the future SKA observations.


title:
Effective mass of elementary excitations in Galilean-invariant
  integrable models

abstract:
  We study low-energy excitations of one-dimensional Galilean-invariant models
integrable by Bethe ansatz and characterized by nonsingular two-particle
scattering phase shifts. We prove that the curvature of the excitation spectra
is described by the recently proposed phenomenological expression for the
effective mass. Our results apply to such models as the repulsive Lieb-Liniger
model and the hyperbolic Calogero-Sutherland model.


title:
SMS Spam Filtering using Probabilistic Topic Modelling and Stacked
  Denoising Autoencoder

abstract:
  In This paper we present a novel approach to spam filtering and demonstrate
its applicability with respect to SMS messages. Our approach requires minimum
features engineering and a small set of la- belled data samples. Features are
extracted using topic modelling based on latent Dirichlet allocation, and then
a comprehensive data model is created using a Stacked Denoising Autoencoder
(SDA). Topic modelling summarises the data providing ease of use and high
interpretability by visualising the topics using word clouds. Given that the
SMS messages can be regarded as either spam (unwanted) or ham (wanted), the SDA
is able to model the messages and accurately discriminate between the two
classes without the need for a pre-labelled training set. The results are
compared against the state-of-the-art spam detection algorithms with our
proposed approach achieving over 97% accuracy which compares favourably to the
best reported algorithms presented in the literature.


title:
Necessary conditions of first-order for an optimal boundary control
  problem for viscous damage processes in 2D

abstract:
  Controlling the growth of material damage is an important engineering task
with plenty of real world applications. In this paper we approach this topic
from the mathematical point of view by investigating an optimal boundary
control problem for a damage phase-field model for viscoelastic media. We
consider non-homogeneous Neumann data for the displacement field which describe
external boundary forces and act as control variable. The underlying
hyberbolic-parabolic PDE system for the state variables exhibit highly
nonlinear terms which emerge in context with damage processes. The cost
functional is of tracking type, and constraints for the control variable are
prescribed. Based on recent results from [M. H. Farshbaf-Shaker, C. Heinemann:
A phase field approach for optimal boundary control of damage processes in
two-dimensional viscoelastic media. Math. Models Methods Appl. Sci. 25 (2015),
2749--2793], where global-in-time well-posedness of strong solutions to the
lower level problem and existence of optimal controls of the upper level
problem have been established, we show in this contribution differentiability
of the control-to-state mapping, well-posedness of the linearization and
existence of solutions of the adjoint state system. Due to the highly nonlinear
nature of the state system which has by our knowledge not been considered for
optimal control problems in the literature, we present a very weak formulation
and estimation techniques of the associated adjoint system. For mathematical
reasons the analysis is restricted here to the two-dimensional case. We
conclude our results with first-order necessary optimality conditions in terms
of a variational inequality together with PDEs for the state and adjoint state
system.


title:
A critical analysis of some popular methods for the discretisation of
  the gradient operator in finite volume methods

abstract:
  Finite volume methods (FVMs) constitute a popular class of methods for the
numerical simulation of fluid flows. Among the various components of these
methods, the discretisation of the gradient operator has received less
attention despite its fundamental importance with regards to the accuracy of
the FVM. The most popular gradient schemes are the divergence theorem (DT) (or
Green-Gauss) scheme, and the least-squares (LS) scheme. Both are widely
believed to be second-order accurate, but the present study shows that in fact
the common variant of the DT gradient is second-order accurate only on
structured meshes whereas it is zeroth-order accurate on general unstructured
meshes, and the LS gradient is second-order and first-order accurate,
respectively. This is explained through a theoretical analysis and is confirmed
by numerical tests. The schemes are then used within a FVM to solve a simple
diffusion equation on unstructured grids generated by several methods; the
results reveal that the zeroth-order accuracy of the DT gradient is inherited
by the FVM as a whole, and the discretisation error does not decrease with grid
refinement. On the other hand, use of the LS gradient leads to second-order
accurate results, as does the use of alternative, consistent, DT gradient
schemes, including a new iterative scheme that makes the common DT gradient
consistent at almost no extra cost. The numerical tests are performed using
both an in-house code and the popular public domain PDE solver OpenFOAM.


title:
Modified teleparallel theories of gravity -- Gauss-Bonnet and trace
  extensions

abstract:
  We investigate modified theories of gravity in the context of teleparallel
geometries with possible Gauss-Bonnet contributions. The possible coupling of
gravity with the trace of the energy-momentum tensor is also taken into
account. This is motivated by the various different theories formulated in the
teleparallel approach and the metric approach without discussing the exact
relationship between them. Our formulation clarifies the connections between
different well known theories. For instance, we are able to formulate the
correct teleparallel equivalent of Gauss-Bonnet modified general relativity,
amongst other results. Finally, we are able to identify modified gravity models
which have not been studied in the past. These appear naturally within our
setup and would make a interesting starting point for further studies.


title: Kinetics of spontaneous baryogenesis in non-stationary background

abstract:
  Generation of the cosmological baryon asymmetry in frameworks of spontaneous
baryogenesis is studied in detail. It is shown that the relation between
baryonic chemical potential and the time derivative of the (pseudo)Goldstone
field essentially depends upon the representation chosen for the fermionic
fields with non-zero baryonic number (quarks). Kinetic equation is modified and
numerically solved in equilibrium for the case of time dependent external
background or finite integration time to be applicable to the case when energy
conservation law is formally violated.


title: The Mu2e experiment at Fermilab

abstract:
  The Mu2e experiment searches for the neutrino-less muon to electron
conversion in the field of a nucleus, which is a charged lepton flavor
violating process. The goal of the experiment is to reach a single event
sensitivity of 2.8 x 10^{-17}, setting an upper limit on the muon conversion
rate at 6.7 x 10^{-17}. This corresponds to a four order of magnitude
improvement with respect to the existing limits.


title: Estimation of matrix trace using machine learning

abstract:
  We present a new trace estimator of the matrix whose explicit form is not
given but its matrix multiplication to a vector is available. The form of the
estimator is similar to the Hutchison stochastic trace estimator, but instead
of the random noise vectors in Hutchison estimator, we use small number of
probing vectors determined by machine learning. Evaluation of the quality of
estimates and bias correction are discussed. An unbiased estimator is proposed
for the calculation of the expectation value of a function of traces. In the
numerical experiments with random matrices, it is shown that the precision of
trace estimates with $\mathcal{O}(10)$ probing vectors determined by the
machine learning is similar to that with $\mathcal{O}(10000)$ random noise
vectors.


title:
The QCD phase diagram in the limit of heavy quarks using complex
  Langevin dynamics

abstract:
  Complex Langevin simulations allow numerical studies of theories that exhibit
a sign problem, such as QCD, and are thereby potentially suitable to determine
the QCD phase diagram from first principles. Here we study QCD in the limit of
heavy quarks for a wide range of temperatures and chemical potentials. Our
results include an analysis of the adaptive gauge cooling technique, which
prevents large excursions into the non-compact directions of the SL($3,
\mathbb{C}$) manifold. We find that such excursions may appear spontaneously
and change the statistical distribution of physical observables, which leads to
disagreement with known results. Results whose excursions are sufficiently
small are used to map the boundary line between confined and deconfined quark
phases.


title: An Orthogonal 16-point Approximate DCT for Image and Video Compression

abstract:
  A low-complexity orthogonal multiplierless approximation for the 16-point
discrete cosine transform (DCT) was introduced. The proposed method was
designed to possess a very low computational cost. A fast algorithm based on
matrix factorization was proposed requiring only 60~additions. The proposed
architecture outperforms classical and state-of-the-art algorithms when
assessed as a tool for image and video compression. Digital VLSI hardware
implementations were also proposed being physically realized in FPGA technology
and implemented in 45 nm up to synthesis and place-route levels. Additionally,
the proposed method was embedded into a high efficiency video coding (HEVC)
reference software for actual proof-of-concept. Obtained results show
negligible video degradation when compared to Chen DCT algorithm in HEVC.


title:
Computing all Space Curve Solutions of Polynomial Systems by Polyhedral
  Methods

abstract:
  A polyhedral method to solve a system of polynomial equations exploits its
sparse structure via the Newton polytopes of the polynomials. We propose a
hybrid symbolic-numeric method to compute a Puiseux series expansion for every
space curve that is a solution of a polynomial system. The focus of this paper
concerns the difficult case when the leading powers of the Puiseux series of
the space curve are contained in the relative interior of a higher dimensional
cone of the tropical prevariety. We show that this difficult case does not
occur for polynomials with generic coefficients. To resolve this case, we
propose to apply polyhedral end games to recover tropisms hidden in the
tropical prevariety.


title: Alternating Surgeries

abstract:
  This thesis is concerned with the question of when the double branched cover
of an alternating knot can arise by Dehn surgery on a knot in $S^3$. We
approach this problem using a surgery obstruction, first developed by Greene,
which combines Donaldson's Diagonalization Theorem with the $d$-invariants of
Ozsv{\'a}th and Szab{\'o}'s Heegaard Floer homology. This obstruction shows
that if the double branched cover of an alternating knot or link $L$ arises by
surgery on $S^3$, then for any alternating diagram the lattice associated to
the Goeritz matrix takes the form of a changemaker lattice. By analyzing the
structure of changemaker lattices, we show that the double branched cover of
$L$ arises by non-integer surgery on $S^3$ if and only if $L$ has an
alternating diagram which can be obtained by rational tangle replacement on an
almost-alternating diagram of the unknot. When one considers half-integer
surgery the resulting tangle replacement is simply a crossing change. This
allows us to show that an alternating knot has unknotting number one if and
only if it has an unknotting crossing in every alternating diagram.
  These techniques also produce several other interesting results: they have
applications to characterizing slopes of torus knots; they produce a new proof
for a theorem of Tsukamoto on the structure of almost-alternating diagrams of
the unknot; and they provide several bounds on surgeries producing the double
branched covers of alternating knots which are direct generalizations of
results previously known for lens space surgeries.
  The thesis begins with an exposition of the changemaker surgery obstruction,
giving an amalgamation of results due to Gibbons, Greene and the author. It
then gives background material on alternating knots and changemaker lattices.
The latter part of the thesis is then taken up with the applications of this
theory.


title: Quantum preparation uncertainty and lack of information

abstract:
  The quantum uncertainty principle famously predicts that there exist
measurements that are inherently incompatible, in the sense that their outcomes
cannot be predicted simultaneously. In contrast, no such uncertainty exists in
the classical domain, where all uncertainty results from ignorance about the
exact state of the physical system. Here, we critically examine the concept of
preparation uncertainty and ask whether similarly in the quantum regime, some
of the uncertainty that we observe can actually also be understood as a lack of
information (LOI), albeit a lack of quantum information. We answer this
question affirmatively by showing that for the well known measurements employed
in BB84 quantum key distribution, the amount of uncertainty can indeed be
related to the amount of available information about additional registers
determining the choice of the measurement. We proceed to show that also for
other measurements the amount of uncertainty is in part connected to a LOI.
Finally, we discuss the conceptual implications of our observation to the
security of cryptographic protocols that make use of BB84 states.


title: Graphene Gas Osmometers

abstract:
  Here it is shown that graphene membranes that separate 2 gases at identical
pressure are deflected by osmotic pressure. The osmotic pressure is a
consequence of differences in gas permeation rates into a graphene enclosed
cavity. The deflection of the few layer graphene membranes is detected by an
interferometric technique for measuring their tension-induced resonance
frequency. Using a calibration measurement of the relation between resonance
frequency and pressure, the time dependent osmotic pressure on the graphene is
extracted. The osmotic pressure for different combinations of gases shows large
differences that can be accounted for by a model based on the different gas
permeation rates. Thus a graphene membrane based gas osmometer with a
responsitivity of ~60 kHz/mbar and nanoscale dimensions is demonstrated.


title:
Classification of magnetic inhomogeneities and $0-\pi$ transitions in
  superconducting-magnetic hybrid structures

abstract:
  We present a comparative study of pair correlations and currents through
superconducting-magnetic hybrid systems with a particular emphasis on the
tunable Bloch domain wall of an exchange spring. This study of the Gor'kov
functions contrasts magnetic systems with domain walls that change at discrete
points in the magnetic region with those that change continuously throughout.
We present results for misaligned homogeneous magnetic multilayers, including
spin valves, for discrete domain walls, as well as exchange springs and helical
domain walls --such as Holmium-- for the continuous case. Introducing a
rotating basis to disentangle the role of singlet and triplet correlations, we
demonstrate that substantial amounts of (so-called short range) singlet
correlations are generated throughout the magnetic system in a continuous
domain wall via the cascade effect. We propose a classification of $0-\pi$
transitions of the Josephson current into three types, according to the
predominant pair correlations symmetries involved in the current. Properties of
exchange springs for an experimental study of the proposed effects are
discussed. The interplay between components of the Gor'kov function that are
parallel and perpendicular to the local magnetization lead to a novel
prediction about their role in a proximity system with a progressively twisting
helix that is experimentally measurable.


title: Noncoherent uniform algebras in $\mathbb C^n$

abstract:
  Let $\mathbf D=\bar{\mathbb D}$ be the closed unit disk in $\mathbb C$ and
$\mathbf B_n=\bar{\mathbb B_n}$ the closed unit ball in $\mathbb C^n$. For a
compact subset $K$ in $\mathbb C^n$ with nonempty interior, let $A(K)$ be the
uniform algebra of all complex-valued continuous functions on $K$ that are
holomorphic in the interior of $K$. We give short and non-technical proofs of
the known facts that $A(\bar{\mathbb D}^n)$ and $A(\mathbf B_n)$ are
noncoherent rings. Using, additionally, Earl's interpolation theorem in the
unit disk and the existence of peak-functions, we also establish with the same
method the new result that $A(K)$ is not coherent.
  As special cases we obtain Hickel's theorems on the noncoherence of
$A(\bar\Omega)$, where $\Omega$ runs through a certain class of pseudoconvex
domains in $\mathbb C^n$, results that were obtained with deep and complicated
methods. Finally, using a refinement of the interpolation theorem we show that
no uniformly closed subalgebra $A$ of $C(K)$ with $P(K)\subseteq A\subseteq
C(K)$ is coherent provided the polynomial convex hull of $K$ has no isolated
points.


title:
Entanglement of four-qubit systems: a geometric atlas with polynomial
  compass II (the tame world)

abstract:
  We propose a new approach to the geometry of the four-qubit entanglement
classes depending on parameters. More precisely, we use invariant theory and
algebraic geometry to describe various stratifications of the Hilbert space by
SLOCC invariant algebraic varieties. The normal forms of the four-qubit
classification of Verstraete {\em et al.} are interpreted as dense subsets of
components of the dual variety of the set of separable states and an algorithm
based on the invariants/covariants of the four-qubit quantum states is proposed
to identify a state with a SLOCC equivalent normal form (up to qubits
permutation).


title:
Demagnetization of a Complete Superconducting Radiofrequency Cryomodule:
  Theory and Practice

abstract:
  A significant advance in magnetic field management in a fully assembled
superconducting radiofrequency cryomodule has been achieved and is reported
here. Demagnetization of the entire cryomodule after assembly is a crucial step
toward the goal of field less than 5x10-7 Tesla. An explanation of the basic
physics of demagnetization as well as experimental results are presented.


title:
Gate-voltage response of a one-dimensional ballistic spin valve without
  spin-orbit interaction

abstract:
  We show that engineering of tunnel barriers forming at the interfaces of a
one-dimensional spin valve provides a viable path to a strong gate-voltage
tunability of the magnetoresistance effect. In particular, we investigate
theoretically a carbon nanotube (CNT) spin valve in terms of the influence of
the CNT-contact interface on the performance of the device. The focus is on the
strength and the spin selectivity of the tunnel barriers that are modelled as
Dirac-delta potentials. The scattering matrix approach is used to derive the
transmission coefficient that yields the tunneling magnetoresistance (TMR). We
find a strong non-trivial gate-voltage response of the TMR in the absence of
spin-orbit coupling when the energy of the incident electrons matches the
potential energy of the barrier. Analytic expressions for the TMR in various
limiting cases are derived. These are used to explain previous experimental
results, but also to predict parameters for device optimization with respect to
size and tunability of the TMR effect in the ballistic transport regime.


title: Learning Interpretable Musical Compositional Rules and Traces

abstract:
  Throughout music history, theorists have identified and documented
interpretable rules that capture the decisions of composers. This paper asks,
"Can a machine behave like a music theorist?" It presents MUS-ROVER, a
self-learning system for automatically discovering rules from symbolic music.
MUS-ROVER performs feature learning via $n$-gram models to extract
compositional rules --- statistical patterns over the resulting features. We
evaluate MUS-ROVER on Bach's (SATB) chorales, demonstrating that it can recover
known rules, as well as identify new, characteristic patterns for further
study. We discuss how the extracted rules can be used in both machine and human
composition.


title: Multiplicity of constant scalar curvature metrics on warped products

abstract:
  Let $(M^m,g_M)$ be a closed, connected manifold with positive scalar
curvature and $(T^k,g)$ some flat $k$-Torus of unit volume. By a result of F.
Dobarro and E. Lami Dozo, there exists a unique $f: M \rightarrow
\mathbf{R}_{>0}$ such that the warped product $M\times_f T^k$ has constant
scalar curvature and unit volume. We study the Yamabe equation on these spaces.
We use techniques from bifurcation theory, along with spectral theory for
warped products, to prove multiplicity results for the Yamabe problem.


title: An algebraic approach to a charged particle in an uniform magnetic field

abstract:
  We study the problem of a charged particle in a uniform magnetic field with
two different gauges, known as Landau and symmetric gauges. By using a
similarity transformation in terms of the displacement operator we show that,
for the Landau gauge, the eigenfunctions for this problem are the harmonic
oscillator number coherent states. In the symmetric gauge, we calculate the
$SU(1,1)$ Perelomov number coherent states for this problem in cylindrical
coordinates in a closed form. Finally, we show that these Perelomov number
coherent states are related to the harmonic oscillator number coherent states
by the contraction of the $SU(1,1)$ group to the Heisenberg-Weyl group.


title: Nevanlinna Theory of the Wilson Divided-difference Operator

abstract:
  Sitting at the top level of the Askey-scheme, Wilson polynomials are regarded
as the most general hypergeometric orthogonal polynomials. Instead of a
differential equation, they satisfy a second order Sturm-Liouville type
difference equation in terms of the Wilson divided-difference operator. This
suggests that in order to better understand the distinctive properties of
Wilson polynomials and related topics, one should use a function theory that is
more natural with respect to the Wilson operator. Inspired by the recent work
of Halburd and Korhonen, we establish a full-fledged Nevanlinna theory of the
Wilson operator for meromorphic functions of finite order. In particular, we
prove a Wilson analogue of the lemma on logarithmic derivatives, which helps us
to derive Wilson operator versions of Nevanlinna's Second Fundamental Theorem,
some defect relations and Picard's Theorem. These allow us to gain new insights
on the distributions of zeros and poles of functions related to the Wilson
operator, which is different from the classical viewpoint. We have also
obtained a relevant five-value theorem and Clunie type theorem as applications
of our theory, as well as a pointwise estimate of the logarithmic Wilson
difference, which yields new estimates to the growth of meromorphic solutions
to some Wilson difference equations and Wilson interpolation equations.


title: SensingKit: Evaluating the Sensor Power Consumption in iOS devices

abstract:
  Today's smartphones come equipped with a range of advanced sensors capable of
sensing motion, orientation, audio as well as environmental data with high
accuracy. With the existence of application distribution channels such as the
Apple App Store and the Google Play Store, researchers can distribute
applications and collect large scale data in ways that previously were not
possible. Motivated by the lack of a universal, multi-platform sensing library,
in this work we present the design and implementation of SensingKit, an
open-source continuous sensing system that supports both iOS and Android mobile
devices. One of the unique features of SensingKit is the support of the latest
beacon technologies based on Bluetooth Smart (BLE), such as iBeaconand
Eddystone. We evaluate and compare the power consumption of each supported
sensor individually, using an iPhone 5S device running on iOS 9. We believe
that this platform will be beneficial to all researchers and developers who
plan to use mobile sensing technology in large-scale experiments.


title:
Some remarks on the Lp regularity of second derivatives of solutions to
  non-divergence elliptic equations and the Dini condition

abstract:
  In this note we prove an end-point regularity result on the Lp integrability
of the second derivatives of solutions to non-divergence form uniformly
elliptic equations whose second derivatives are a priori only known to be
integrable. The main assumption on the elliptic operator is the Dini continuity
of the coefficients. We provide a counterexample showing that the Dini
condition is somehow optimal. We also give a counterexample related to the BMO
regularity of second derivatives of solutions to elliptic equations.


title: Proximity Without Consensus in Online Multi-Agent Optimization

abstract:
  We consider stochastic optimization problems in multi-agent settings, where a
network of agents aims to learn parameters which are optimal in terms of a
global objective, while giving preference to locally observed streaming
information. To do so, we depart from the canonical decentralized optimization
framework where agreement constraints are enforced, and instead formulate a
problem where each agent minimizes a global objective while enforcing network
proximity constraints. This formulation includes online consensus optimization
as a special case, but allows for the more general hypothesis that there is
data heterogeneity across the network. To solve this problem, we propose using
a stochastic saddle point algorithm inspired by Arrow and Hurwicz. This method
yields a decentralized algorithm for processing observations sequentially
received at each node of the network. Using Lagrange multipliers to penalize
the discrepancy between them, only neighboring nodes exchange model
information. We establish that under a constant step-size regime the
time-average suboptimality and constraint violation are contained in a
neighborhood whose radius vanishes with increasing number of iterations. As a
consequence, we prove that the time-average primal vectors converge to the
optimal objective while satisfying the network proximity constraints. We apply
this method to the problem of sequentially estimating a correlated random field
in a sensor network, as well as an online source localization problem, both of
which demonstrate the empirical validity of the aforementioned convergence
results.


title: Early Visual Concept Learning with Unsupervised Deep Learning

abstract:
  Automated discovery of early visual concepts from raw image data is a major
open challenge in AI research. Addressing this problem, we propose an
unsupervised approach for learning disentangled representations of the
underlying factors of variation. We draw inspiration from neuroscience, and
show how this can be achieved in an unsupervised generative model by applying
the same learning pressures as have been suggested to act in the ventral visual
stream in the brain. By enforcing redundancy reduction, encouraging statistical
independence, and exposure to data with transform continuities analogous to
those to which human infants are exposed, we obtain a variational autoencoder
(VAE) framework capable of learning disentangled factors. Our approach makes
few assumptions and works well across a wide variety of datasets. Furthermore,
our solution has useful emergent properties, such as zero-shot inference and an
intuitive understanding of "objectness".


title:
Coherence preservation of a single neutral atom qubit transferred
  between magic-intensity optical traps

abstract:
  We demonstrate that the coherence of a single mobile atomic qubit can be well
preserved during a transfer process among different optical dipole traps
(ODTs). This is a prerequisite step in realizing a large-scale neutral atom
quantum information processing platform. A qubit encoded in the hyperfine
manifold of $^{87}$Rb atom is dynamically extracted from the static quantum
register by an auxiliary moving ODT and reinserted into the static ODT.
Previous experiments were limited by decoherences induced by the differential
light shifts of qubit states. Here we apply a magic-intensity trapping
technique which mitigates the detrimental effects of light shifts and
substantially enhances the coherence time to $225 \pm 21\,\mathrm{ms}$. The
experimentally demonstrated magic trapping technique relies on the previously
neglected hyperpolarizability contribution to the light shifts, which makes the
light shift dependence on the trapping laser intensity to be parabolic. Because
of the parabolic dependence, at a certain "magic" intensity, the first order
sensitivity to trapping light intensity variations over ODT volume is
eliminated. We experimentally demonstrate the utility of this approach and
measure hyperpolarizability for the first time. Our results pave the way for
constructing a scalable quantum-computing architectures with single atoms
trapped in an array of magic ODTs.


title: 2d Fu-Kane-Mele invariant as Wess-Zumino action of the sewing matrix

abstract:
  We show that the Fu-Kane-Mele invariant of the 2d time-reversal-invariant
crystalline insulators is equal to the properly normalized Wess-Zumino action
of the so-called sewing matrix field defined on the Brillouin torus. Applied to
3d, the result permits a direct proof of the known relation between the strong
Fu-Kane-Mele invariant and the Chern-Simons action of the non-Abelian Berry
connection on the bundle of valence states.


title:
Designing exotic many-body states of atomic spin and motion in photonic
  crystals

abstract:
  Cold atoms coupled to photonic crystals constitute an exciting platform for
exploring quantum many-body physics. Here we investigate the strong coupling
between atomic internal ("spin") degrees of freedom and motion, which arises
from spin-dependent forces associated with the exchange of guided photons. We
show that this system can realize a remarkable and extreme limit of quantum
spin-orbital systems, where both the direct spin exchange between neighboring
sites and the kinetic energy of the orbital motion vanish. We find that this
previously unexplored system has a rich phase diagram of emergent orders,
including spatially dimerized spin-entangled pairs, a fluid of composite
particles comprised of joint spin-phonon excitations, phonon-induced N\'eel
ordering, and a fractional magnetization plateau associated with trimer
formation.


title: Computing maximal subsemigroups of a finite semigroup

abstract:
  A proper subsemigroup of a semigroup is maximal if it is not contained in any
other proper subsemigroup. A maximal subsemigroup of a finite semigroup has one
of a small number of forms, as described in a paper of Graham, Graham, and
Rhodes. Determining which of these forms arise in a given finite semigroup is
difficult, and no practical mechanism for doing so appears in the literature.
We present an algorithm for computing the maximal subsemigroups of a finite
semigroup given knowledge of its Green's structure, and the ability to
determine maximal subgroups of certain subgroups.
  For a finite semigroup $S$ represented by a generating set $X$, in many
examples, if it is practical to compute the Green's structure of $S$ from $X$,
then it is also practical to find the maximal subsemigroups of $S$ using the
algorithm we present. The generating set $X$ for $S$ may consist, for example,
of transformations, or partial permutations, of a finite set, or of matrices
over a semiring. In such examples, the time taken to determine the Green's
structure of $S$ is comparable to that taken to find the maximal subsemigroups.
  Certain aspects of the problem of finding maximal subsemigroups reduce to
other well-known computational problems, such as finding all maximal cliques in
a graph and computing the maximal subgroups in a group. The algorithm presented
comprises two parts. One part relates to computing the maximal subsemigroups of
a special class of semigroups, known as Rees 0-matrix semigroups. The other
part involves a careful analysis of certain graphs associated to the semigroup
$S$, which, roughly speaking, capture the essential information about the
action of $S$ on its $\mathscr{J}$-classes.


title:
Bandwidth selection for kernel density estimation with length-biased
  data

abstract:
  Length-biased data are a particular case of weighted data, which arise in
many situations: biomedicine, quality control or epidemiology among others. In
this paper we study the theoretical properties of kernel density estimation in
the context of length-biased data, proposing two consistent bootstrap methods
that we use for bandwidth selection. Apart from the bootstrap bandwidth
selectors we suggest a rule-of-thumb. These bandwidth selection proposals are
compared with a least-squares cross-validation method. A simulation study is
accomplished to understand the behaviour of the procedures in finite samples.


title: Probing Cosmic Superstrings with Gravitational Waves

abstract:
  We compute the stochastic gravitational wave background generated by cosmic
superstrings using a semi-analytical velocity-dependent model to describe their
dynamics. We show that heavier string types may leave distinctive signatures on
the stochastic gravitational wave background spectrum within the reach of
present and upcoming gravitational wave detectors. We examine the physically
motivated scenario in which the physical size of loops is determined by the
gravitational backreaction scale and use NANOGRAV data to derive a conservative
constraint of $G\mu_F<3.2 \times 10^{-9}$ on the tension of fundamental
strings. We demonstrate that approximating the gravitational wave spectrum
generated by cosmic superstring networks using the spectrum generated by
ordinary cosmic strings with reduced intercommuting probability (which is often
done in the literature) leads, in general, to weaker observational constraints
on $G\mu_F$. We show that the inclusion of heavier string types is required for
a more accurate characterization of the region of the $(g_s,G\mu_F)$ parameter
space that may be probed using direct gravitational wave detectors. In
particular, we consider the observational constraints that result from NANOGRAV
data and show that heavier strings generate a secondary exclusion region of
parameter space.


title: The Maxwell-Boltzmann approximation for ion kinetic modeling

abstract:
  This paper aims to justify the Maxwell-Boltzmann approximation for electrons,
preserving the dynamics of ions at the kinetic level. Under sufficient
regularity assumption, we provide a precise scaling where the Maxwell-Boltzmann
approximation is obtained. In addition, we prove that the reduced ions problem
is well-posed globally in time.


title:
SU(2) low energy quark effective couplings in weak external magnetic
  field

abstract:
  In this work corrections to the usual flavor SU(2) Nambu-Jona-Lasinio
coupling due to a weak external magnetic field are calculated by considering
quark polarization in a (dressed) gluon exchange mechanism for quark
interactions. The quark field is splitted into two components, one that
condenses and another one that is a background field for interacting quarks,
being the former integrated out. The resulting determinant is expanded for
relatively large quark mass and small magnetic field, $(eB_0/{M^*}^2)<1$ by
resolving magnetic field dependent low energy quark effective interactions.
Besides the corrections for the NJL and vector NJL effective couplings,
different $B_0-$dependent effective couplings that break isospin and chiral
symmetry emerge.


title:
Relativistic Interpretation of Newtonian Simulations for Cosmic
  Structure Formation

abstract:
  The standard numerical tools for studying non-linear collapse of matter are
Newtonian $N$-body simulations. Previous work has shown that these simulations
are in accordance with General Relativity (GR) up to first order in
perturbation theory, provided that the effects from radiation can be neglected.
In this paper we show that the present day matter density receives more than
1$\%$ corrections from radiation on large scales if Newtonian simulations are
initialised before $z=50$. We provide a relativistic framework in which
\emph{unmodified} Newtonian simulations are compatible with linear GR even in
the presence of radiation. Our idea is to use GR perturbation theory to keep
track of the evolution of relativistic species and the relativistic space-time
consistent with the Newtonian trajectories computed in $N$-body simulations. If
metric potentials are sufficiently small, they can be computed using a
first-order Einstein--Boltzmann code such as CLASS. We make this idea rigorous
by defining a class of GR gauges, the \emph{Newtonian motion} gauges, which are
defined such that matter particles follow Newtonian trajectories. We construct
a simple example of a relativistic space-time within which unmodified Newtonian
simulations can be interpreted.


title:
Human Attention in Visual Question Answering: Do Humans and Deep
  Networks Look at the Same Regions?

abstract:
  We conduct large-scale studies on `human attention' in Visual Question
Answering (VQA) to understand where humans choose to look to answer questions
about images. We design and test multiple game-inspired novel
attention-annotation interfaces that require the subject to sharpen regions of
a blurred image to answer a question. Thus, we introduce the VQA-HAT (Human
ATtention) dataset. We evaluate attention maps generated by state-of-the-art
VQA models against human attention both qualitatively (via visualizations) and
quantitatively (via rank-order correlation). Overall, our experiments show that
current attention models in VQA do not seem to be looking at the same regions
as humans.


title: Dark Energy and Doubly Coupled Bigravity

abstract:
  We analyse the late time cosmology and the gravitational properties of doubly
coupled bigravity in the constrained vielbein formalism (equivalent to the
metric formalism) when the mass of the massive graviton is of the order of the
present Hubble rate. We focus on one of the two branches of background
cosmology where the ratio between the scale factors of the two metrics is
algebraically determined. The Universe evolves from a matter dominated epoch to
a dark energy dominated era where the equation of state of dark energy can
always be made close to -1 now by appropriately tuning the graviton mass. We
also analyse the perturbative spectrum of the theory in the quasi static
approximation well below the strong coupling scale where no instability is
present and we show that there are five scalar degrees of freedom, two vectors
and two gravitons. In a cosmological FRW background for both metrics, four of
the five scalars are Newtonian potentials which lead to a modification of
gravity on large scales. In this scalar sector, gravity is modified with
effects on both the growth of structure and the lensing potential. In
particular, we find that the $\Sigma$ parameter governing the Poisson equation
of the weak lensing potential can differ from one in the recent past of the
Universe. Overall, the nature of the modification of gravity at low energy,
which reveals itself in the growth of structure and the lensing potential, is
intrinsically dependent on the couplings to matter and the potential term of
the vielbeins. We also find that the time variation of Newton's constant in the
Jordan frame can easily satisfy the bound from solar system tests of gravity.
Finally we show that the two gravitons present in the spectrum have a
non-trivial mass matrix whose origin follows from the potential term of
bigravity. This mixing leads to gravitational birefringence.


title: Strong light-matter coupling in the presence of lasing

abstract:
  The regime of strong light-matter coupling is typically associated with weak
excitation. With current realizations of cavity-QED systems, strong coupling
may persevere even at elevated excitation levels sufficient to cross the
threshold to lasing. In the presence of stimulated emission, the vacuum-Rabi
doublet in the emission spectrum is modified and the established criterion for
strong coupling no longer applies. We provide a generalized criterion for
strong coupling and the corresponding emission spectrum, which includes the
influence of higher Jaynes-Cummings states. The applicability is demonstrated
in a theory-experiment comparison of a few-emitter quantum-dot--micropillar
laser as a particular realization of the driven dissipative Jaynes-Cummings
model. Furthermore, we address the question if and for which parameters true
single-emitter lasing can be achieved, and provide evidence for the coexistence
of strong coupling and lasing in our system in the presence of background
emitter contributions.