title: Revisiting the evolved hypergiants in the Magellanic Clouds

abstract:
  The massive stars that survive the phase of red supergiants (RSGs) spend the
rest of their life in extremity. Their unstable atmospheres facilitate the
formation and episodic ejection of shells that alter the stellar appearance and
surroundings. In the present study, we revise the evolutionary state of eight
hypergiants in the Magellanic Clouds, four of early-A type and four of FG type,
and complement the short list of the eruptive post-RSGs termed as yellow
hypergiants (YHGs). We refine the outdated temperatures and luminosities of the
stars by means of high-resolution spectroscopy with FEROS. The A-type stars are
suggested to be in their early, post-main sequence phase, showing
spectrophotometric characteristics of redward evolving supergiants. On the
other hand, the FG-type stars manifest themselves through the enhanced
atmospheric activity that is traced by emission filling in H$\alpha$ and the
dynamical modulation of the low-excitation BaII line. Of these stars, the dusty
HD269723 is suggested to have recently departed from a cool phase. We identify
double-peaked emission in the FEROS data of HD269953 that emerges from an
orbiting disk-hosting companion. The highlight of the study is an episode of
enhanced mass loss of HD271182 that manifests as a dimming event in the
lightcurve and renders the star "modest" analogue to $\rho$ Cas. The luminosity
$\log(L/L_{\odot})= 5.6$ of HD271182 can serve as an updated threshold for the
luminosity of stars exhibiting a post-RSG evolution in the Large Magellanic
Cloud.


title:
Spinless fermions in a $\mathbb{Z}_{2}$ gauge theory on the triangular
  ladder

abstract:
  A study of spinless matter fermions coupled to a constrained $\mathbb{Z}_{2}$
lattice gauge theory on a triangular ladder is presented. The triangular unit
cell and the ladder geometry strongly modify the physics, as compared to
previous analysis on the square lattice. In the static case, the even and odd
gauge theories for the empty and filled ladder are identical. The gauge field
dynamics due to the electric coupling is drastically influenced by the absence
of periodic boundary conditions, rendering the deconfinement-confinement
process a crossover in general and a quantum phase transition (QPT) only for
decorated couplings. At finite doping and in the static case, a staggered flux
insulator at half filling and vanishing magnetic energy competes with a uniform
flux metal at elevated magnetic energy. As for the square lattice, a single QPT
into a confined fermionic dimer gas is found versus electric coupling. Dimer
resonances in the confined phase are however a second order process only,
likely reducing the the tendency to phase separate for large magnetic energy.
The results obtained employ a mapping to a pure spin model of $\mathbb{Z}_{2}$
gauge-invariant moments, adapted from the square lattice, and density matrix
renormalization group calculations thereof for numerical purposes. Global scans
of the quantum phases in the intermediate coupling regime are provided.


title:
Discovery of a damped Ly$\alpha$ absorber originating in a spectacular
  interacting dwarf galaxy pair at $z = 0.026$

abstract:
  We present the discovery of neutral gas detected in both damped Ly$\alpha$
absorption (DLA) and HI 21-cm emission outside of the stellar body of a galaxy,
the first such detection in the literature. A joint analysis between the Cosmic
Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an HI
bridge connecting two interacting dwarf galaxies
(log$(M_{\text{star}}/\text{M}_{\odot}) = 8.5 \pm 0.2$) that host a $z = 0.026$
DLA with log[$N$(HI)/cm$^{-2}$]$ = 20.60 \pm 0.05$ toward the QSO J2339-5523
($z_{\text{QSO}} = 1.35$). At impact parameters of $d = 6$ and $33$ kpc, the
dwarf galaxies have no companions more luminous than $\approx 0.05L_{*}$ within
at least $\Delta v = \pm 300$ km s$^{-1}$ and $d \approx 350$ kpc. HI 21-cm
emission is spatially coincident with the DLA at the 2-3$\sigma$ level per
spectral channel over several adjacent beams. However, HI 21-cm absorption is
not detected against the radio-bright QSO; if the background UV and radio
sources are spatially aligned, the gas is either warm or clumpy (with spin
temperature to covering factor ratio $T_{s}/f_{c} > 1880$ K). VLT-MUSE
observations demonstrate that the $\alpha$-element abundance of the ionized ISM
is consistent with the DLA ($\approx 10$% solar), suggesting that the neutral
gas envelope is perturbed ISM gas. This study showcases the impact of
dwarf-dwarf interactions on the physical and chemical state of neutral gas
outside of star-forming regions. In the SKA era, joint UV and HI 21-cm analyses
will be critical for connecting the cosmic neutral gas content to galaxy
environments.


title: Can Humans Do Less-Than-One-Shot Learning?

abstract:
  Being able to learn from small amounts of data is a key characteristic of
human intelligence, but exactly {\em how} small? In this paper, we introduce a
novel experimental paradigm that allows us to examine classification in an
extremely data-scarce setting, asking whether humans can learn more categories
than they have exemplars (i.e., can humans do "less-than-one shot" learning?).
An experiment conducted using this paradigm reveals that people are capable of
learning in such settings, and provides several insights into underlying
mechanisms. First, people can accurately infer and represent high-dimensional
feature spaces from very little data. Second, having inferred the relevant
spaces, people use a form of prototype-based categorization (as opposed to
exemplar-based) to make categorical inferences. Finally, systematic,
machine-learnable patterns in responses indicate that people may have efficient
inductive biases for dealing with this class of data-scarce problems.


title: The origin and impact of Wolf-Rayet-type mass loss

abstract:
  Classical Wolf-Rayet (WR) stars mark an important stage in the late evolution
of massive stars. As hydrogen-poor massive stars, these objects have lost their
outer layers, while still losing further mass through strong winds indicated by
their prominent emission line spectra. Wolf-Rayet stars have been detected in a
variety of different galaxies. Their strong winds are a major ingredient of
stellar evolution and population synthesis models. Yet, a coherent theoretical
picture of their strong mass-loss is only starting to emerge. In particular,
the occurrence of WR stars as a function of metallicity (Z) is still far from
being understood.
  To uncover the nature of the complex and dense winds of Wolf-Rayet stars, we
employ a new generation of model atmospheres including a consistent solution of
the wind hydrodynamics in an expanding non-LTE situation. With this technique,
we can dissect the ingredients driving the wind and predict the resulting
mass-loss for hydrogen-depleted massive stars. Our modelling efforts reveal a
complex picture with strong, non-linear dependencies on the luminosity-to-mass
ratio and Z with a steep, but not totally abrupt onset for WR-type winds in
helium stars. With our findings, we provide a theoretical motivation for a
population of helium stars at low Z, which cannot be detected via WR-type
spectral features. Our study of massive He-star atmosphere models yields the
very first mass-loss recipe derived from first principles in this regime.
Implementing our first findings in stellar evolution models, we demonstrate how
traditional approaches tend to overpredict WR-type mass loss in the young
Universe.


title:
The DUVET Survey: Resolved Maps of Star Formation Driven Outflows in a
  Compact, Starbursting Disk Galaxy

abstract:
  We study star formation driven outflows in a $z\sim0.02$ starbursting disk
galaxy, IRAS08339+6517, using spatially resolved measurements from the Keck
Cosmic Web Imager (KCWI). We develop a new method incorporating a multi-step
process to determine whether an outflow should be fit in each spaxel, and then
subsequently decompose the emission line into multiple components. We detect
outflows ranging in velocity, $v_{\rm out}$, from $100-600$ km s$^{-1}$ across
a range of star formation rate surface densities, $\Sigma_{\rm SFR}$, from
$\sim$0.01-10 M$_\odot$ yr$^{-1}$ kpc$^{-2}$ in resolution elements of a few
hundred parsec. Outflows are detected in $\sim100\%$ of all spaxels within the
half-light radius, and $\sim70\%$ within $r_{90}$, suggestive of a high
covering fraction for this starbursting disk galaxy. Around $2/3$ of the total
outflowing mass originates from the star forming ring, which corresponds to
$<10\%$ of the total area of the galaxy. We find that the relationship between
$v_{\rm out}$ and the $\Sigma_{\rm SFR}$, as well as between the mass loading
factor, $\eta$, and the $\Sigma_{\rm SFR}$, are consistent with trends expected
from energy-driven feedback models. We study the resolution effects on this
relationship and find stronger correlations above a re-binned size-scale of
$\sim500$ pc. Conversely, we do not find statistically significant consistency
with the prediction from momentum-driven winds.


title: Algebraic Bethe Circuits

abstract:
  The Algebraic Bethe Ansatz (ABA) is a highly successful analytical method
used to exactly solve several physical models in both statistical mechanics and
condensed-matter physics. Here we bring the ABA to unitary form, for its direct
implementation on a quantum computer. This is achieved by distilling the
non-unitary $R$ matrices that make up the ABA into unitaries using the QR
decomposition. Our algorithm is deterministic and works for both real and
complex roots of the Bethe equations. We illustrate our method in the
spin-$\frac{1}{2}$ XX and XXZ models. We show that using this approach one can
efficiently prepare eigenstates of the XX model on a quantum computer with
quantum resources that match previous state-of-the-art approaches. We run
numerical simulations, preparing eigenstates of the XXZ model for systems of up
to 24 qubits and 12 magnons. Furthermore, we run small-scale error-mitigated
implementations on the IBM quantum computers, including the preparation of the
ground state for the XX and XXZ models in $4$ sites. Finally, we derive a new
form of the Yang-Baxter equation using unitary matrices, and also verify it on
a quantum computer.

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


title: A tale of tails through generalized unitarity

abstract:
  We introduce a novel framework to study high-order gravitational effects on a
binary from the scattering of its emitted gravitational radiation. Here we
focus on the radiation-reaction due to the background of the binary's
gravitational potential, namely on the so-called tail effects. We start from
the effective field theory of a binary composite-particle, and through
multi-loop, and generalized-unitarity methods, we derive the causal effective
actions of the dynamical multipoles, the energy spectra, and the observable
flux due to these effects. We proceed through the third subleading such
radiation-reaction effect, at the four-loop level and seventh order in
post-Newtonian gravity, shedding new light on the higher-order effects, and
completing the state of the art.


title: Bayesian Nonparametrics for Offline Skill Discovery

abstract:
  Skills or low-level policies in reinforcement learning are temporally
extended actions that can speed up learning and enable complex behaviours.
Recent work in offline reinforcement learning and imitation learning has
proposed several techniques for skill discovery from a set of expert
trajectories. While these methods are promising, the number K of skills to
discover is always a fixed hyperparameter, which requires either prior
knowledge about the environment or an additional parameter search to tune it.
We first propose a method for offline learning of options (a particular skill
framework) exploiting advances in variational inference and continuous
relaxations. We then highlight an unexplored connection between Bayesian
nonparametrics and offline skill discovery, and show how to obtain a
nonparametric version of our model. This version is tractable thanks to a
carefully structured approximate posterior with a dynamically-changing number
of options, removing the need to specify K. We also show how our nonparametric
extension can be applied in other skill frameworks, and empirically demonstrate
that our method can outperform state-of-the-art offline skill learning
algorithms across a variety of environments. Our code is available at
https://github.com/layer6ai-labs/BNPO .


title:
Connecting Galactic and extragalactic outflows: From the Cygnus-X
  cluster to active galaxies

abstract:
  Molecular outflows are often detected originating from both protostellar and
extragalactic sources. Studies of low-mass, isolated high-mass, and
extragalactic sources reveal scaling relations connecting the force carried by
an outflow and the properties of the source that drives it. The aim of this
work is to examine the effects of clustered star formation on the protostellar
outflows and their scaling relations and to explore the possibility that
outflows varying greatly scale and energetics are consistent with being
launched by the same physical processes. High-angular resolution CO J = 3-2
observations were used of ten high-mass protostars in the Cygnus-X molecular
cloud, obtained at the SMA as part of the PILS-Cygnus survey. From these data,
the outflow force was measured. In addition, an extended sample of protostellar
and extragalactic outflow-force measurements was assembled from existing
literature to allow for a direct comparison of the scaling relations of the two
types of outflows. Molecular outflows were detected originating from all ten
sources of the PILS-Cygnus survey, and their outflow forces are found in close
agreement with measurements from the literature. The comparison of the
protostellar and extragalactic sources reveals, with 95\% confidence, that
Class 0 protostars and extragalactic sources follow the same outflow
force--bolometric luminosity correlation. The close agreement between the
Cygnus-X sources and sources of similar envelope mass and bolometric luminosity
suggests that clustered star formation has no significant effect on
protostellar outflows. We find a strong indication that protostellar and
extragalactic outflows are consistent with having a similar launch mechanism.
The existence of such a mechanism would enable the development of a single
universal outflow launch model, although more observations are required in
order to verify this connection.


title:
On the Robustness of the Constancy of the Supernova Absolute Magnitude:
  Non-parametric Reconstruction \& Bayesian approaches

abstract:
  In this work, we test the robustness of the constancy of the Supernova
absolute magnitude $M_B$ using Non-parametric Reconstruction Techniques (NRT).
We isolate the luminosity distance parameter $d_L(z)$ from the Baryon Acoustic
Oscillations (BAO) data set and cancel the expansion part from the observed
distance modulus $\mu(z)$. Consequently, the degeneracy between the absolute
magnitude with the Hubble constant $H_0$, is replaced by a degeneracy with the
sound horizon at drag epoch $r_d$. When imposing the $r_d$ value, this yields
the $M_B(z) = M_B + \delta M_B(z)$ value from NRT. We perform the respective
reconstructions using the model independent Artificial Neural Network (ANN)
technique and Gaussian processes (GP) regression. For the ANN we infer $M_B =
-19.22\pm0.20$, and for the GP we get $M_B = -19.25\pm0.39$ when using the
sound horizon from late time measurements. These estimations provide a
$1\,\sigma$ possibility of a nuisance parameter presence $\delta M_B(z)$ at
higher redshifts. We also tested different known nuisance models with the
Markov Chain Monte Carlo (MCMC) technique which showed a strong preference for
the constant model, but it was not possible not single out a best fit nuisance
model.


title: Non-Linear Spectral Dimensionality Reduction Under Uncertainty

abstract:
  In this paper, we consider the problem of non-linear dimensionality reduction
under uncertainty, both from a theoretical and algorithmic perspectives. Since
real-world data usually contain measurements with uncertainties and artifacts,
the input space in the proposed framework consists of probability distributions
to model the uncertainties associated with each sample. We propose a new
dimensionality reduction framework, called NGEU, which leverages uncertainty
information and directly extends several traditional approaches, e.g., KPCA,
MDA/KMFA, to receive as inputs the probability distributions instead of the
original data. We show that the proposed NGEU formulation exhibits a global
closed-form solution, and we analyze, based on the Rademacher complexity, how
the underlying uncertainties theoretically affect the generalization ability of
the framework. Empirical results on different datasets show the effectiveness
of the proposed framework.


title:
A degenerating convection-diffusion system modelling froth flotation
  with drainage

abstract:
  Froth flotation is a common unit operation used in mineral processing. It
serves to separate valuable mineral particles from worthless gangue particles
in finely ground ores. The valuable mineral particles are hydrophobic and
attach to bubbles of air injected into the pulp. This creates bubble-particle
aggregates that rise to the top of the flotation column where they accumulate
to a froth or foam layer that is removed through a launder for further
processing. At the same time, the hydrophilic gangue particles settle and are
removed continuously. The drainage of liquid due to capillarity is essential
for the formation of a stable froth layer. This effect is included into a
previously formulated hyperbolic system of partial differential equations that
models the volume fractions of floating aggregates and settling hydrophilic
solids [R. B\"{u}rger, S. Diehl and M.C. Mart\'i, {\it IMA J. Appl. Math.} {\bf
84} (2019) 930--973]. The construction of desired steady-state solutions with a
froth layer is detailed and feasibility conditions on the feed volume fractions
and the volumetric flows of feed, underflow and wash water are visualized in
so-called operating charts. A monotone numerical scheme is derived and employed
to simulate the dynamic behaviour of a flotation column. It is also proven
that, under a suitable Courant-Friedrichs-Lewy (CFL) condition, the approximate
volume fractions are bounded between zero and one when the initial data are.


title: A Joint Variational Multichannel Multiphase Segmentation Framework

abstract:
  In this paper, we propose a variational image segmentation framework for
multichannel multiphase image segmentation based on the Chan-Vese active
contour model. The core of our method lies in finding a variable u encoding the
segmentation, by minimizing a multichannel energy functional that combines the
information of multiple images. We create a decomposition of the input, either
by multichannel filtering, or simply by using plain natural RGB, or medical
images, which already consist of several channels. Subsequently we minimize the
proposed functional for each of the channels simultaneously. Our model meets
the necessary assumptions such that it can be solved efficiently by
optimization techniques like the Chambolle-Pock method. We prove that the
proposed energy functional has global minimizers, and show its stability and
convergence with respect to noisy inputs. Experimental results show that the
proposed method performs well in single- and multichannel segmentation tasks,
and can be employed to the segmentation of various types of images, such as
natural and texture images as well as medical images.


title: Functional calculus for dual quaternions

abstract:
  We give a formula for $f(\eta)$, where $f :\mathbb C \to \mathbb C$ is a
continuously differentiable function satisfying $f(\bar z) = \overline{f(z)}$,
and $\eta$ is a dual quaternion. Note this formula is straightforward or well
known if $\eta$ is merely a dual number or a quaternion. If one is willing to
prove the result only when $f$ is a polynomial, then the methods of this paper
are elementary.


title:
"I feel invaded, annoyed, anxious and I may protect myself":
  Individuals' Feelings about Online Tracking and their Protective Behaviour
  across Gender and Country

abstract:
  Online tracking is a primary concern for Internet users, yet previous
research has not found a clear link between the cognitive understanding of
tracking and protective actions. We postulate that protective behaviour follows
affective evaluation of tracking. We conducted an online study, with N=614
participants, across the UK, Germany and France, to investigate how users feel
about third-party tracking and what protective actions they take. We found that
most participants' feelings about tracking were negative, described as deeply
intrusive - beyond the informational sphere, including feelings of annoyance
and anxiety, that predict protective actions. We also observed indications of a
`privacy gender gap', where women feel more negatively about tracking, yet are
less likely to take protective actions, compared to men. And less UK
individuals report negative feelings and protective actions, compared to those
from Germany and France. This paper contributes insights into the affective
evaluation of privacy threats and how it predicts protective behaviour. It also
provides a discussion on the implications of these findings for various
stakeholders, make recommendations and outline avenues for future work.


title: Saturation and vanishing ideals

abstract:
  We consider an homogeneous ideal $I$ in the polynomial ring $S=K[x_1,\dots,$
$x_m]$ over a finite field $K=\mathbb{F}_q$ and the finite set of projective
rational points $\mathbb{X}$ that it defines in the projective space
$\mathbb{P}^{m-1}$. We concern ourselves with the problem of computing the
vanishing ideal $I(\mathbb{X})$. This is usually done by adding the equations
of the projective space $I(\mathbb{P}^{m-1})$ to $I$ and computing the radical.
We give an alternative and more efficient way using the saturation with respect
to the homogeneous maximal ideal.


title:
Weak line discovered by Voyager 1 in the interstellar medium:
  Quasi-thermal noise produced by very few fast electrons

abstract:
  A weak continuous line has been recently discovered onboard Voyager 1 in the
interstellar medium, whose origin raised two major questions. First, how can
this line be produced by plasma quasi-thermal noise on the Voyager short
antenna? Second, why does this line emerge at some distance from the
heliopause? We provide a simple answer to these questions, which elucidates the
origin of this line. First, a minute quantity of supra-thermal electrons, as
generally present in plasmas, whence the qualifier quasi-thermal, can produce a
small plasma frequency peak on a short antenna, of amplitude independent of the
concentration of these electrons; furthermore, the detection required long
spectral averages, alleviating the smallness of the peak compared to the
background. We therefore attribute the observed line to a minute proportion of
fast electrons that contribute negligibly to the pressure. Second, we suggest
that, up to some distance from the heliopause, the large compressive
fluctuations ubiquitous in this region prevent the line to emerge from the
statistical fluctuations of the receiver noise because it is blurred out by the
averaging required for detection,especially in the presence of short-wavelength
density fluctuations. These results open up novel perspectives for interstellar
missions, by showing that a minute proportion of fast electrons may be
sufficient to measure the density even with a relatively short antenna, because
the quietness of the medium enables a large number of spectra to be averaged.

categories: astro-ph.SR astro-ph.GA astro-ph.HE physics.plasm-ph


title:
Reconstruction of the NuSTAR point spread function using single-laser
  metrology

abstract:
  This paper describes a method by which the metrology system of the Nuclear
Spectroscopic Telescope Array (NuSTAR) X-ray space observatory, which uses two
lasers to characterize the relative motion of the optics and focal plane
benches, can be approximated should one laser fail. The two benches are
separated by a ten-meter-long rigid mast that undergoes small amounts of
thermal flexing which need to be compensated for in order to produce a
non-blurred image. We analyze the trends of mast motion by archival observation
parameters in order to discover whether the mast motion in future observations
can be predicted. We find that, by using the solar aspect angle (SAA),
observation date, and orbital phase, we can simulate the motion of one laser by
translating the track produced by the other and applying modifications to the
resulting mast aspect solution, allowing the reconstruction of a minimally
distorted point spread function in most cases. We will implement the generation
of simulated mast files alongside the usual NuSTAR data reduction pipeline for
contingency purposes. This work has implications for reducing the risk of
implementing laser metrology systems on future missions that use deployable
masts to achieve the long focal lengths required in high-energy astronomy by
mitigating the impact of a metrology laser failure in the extended phase of a
mission.


title: The Thresher: Lucky Imaging without the Waste

abstract:
  In traditional lucky imaging (TLI), many consecutive images of the same scene
are taken with a high frame-rate camera, and all but the sharpest images are
discarded before constructing the final shift-and-add image. Here we present an
alternative image analysis pipeline -- The Thresher -- for these kinds of data,
based on online multi-frame blind deconvolution. It makes use of all available
data to obtain a best estimate of the astronomical scene in the context of
reasonable computational limits; it does not require prior estimates of the
point-spread functions in the images, or knowledge of point sources in the
scene that could provide such estimates. Most importantly, the scene it aims to
return is the optimum of a justified scalar objective based on the likelihood
function. Because it uses the full set of images in the stack, The Thresher
outperforms TLI in signal-to-noise; as it accounts for the individual-frame
PSFs, it does this without loss of angular resolution. We demonstrate the
effectiveness of our algorithm on both simulated data and real
Electron-Multiplying CCD images obtained at the Danish 1.54m telescope (hosted
by ESO, La Silla). We also explore the current limitations of the algorithm,
and find that for the choice of image model presented here, non-linearities in
flux are introduced into the returned scene. Ongoing development of the
software can be viewed at https://github.com/jah1994/TheThresher.


title: Self-Adjointness of Toeplitz Operators in the Segal-Bargmann Space

abstract:
  We prove a new criterion that guarantees self-adjointness of Toeplitz
operator with unbounded operator-valued symbols. Our criterion applies, in
particular, to symbols with Lipschitz continuous derivatives, which is the
natural class of Hamiltonian functions for classical mechanics. For this we
extend the Berger-Coburn estimate to the case of vector-valued Segal-Bargmann
spaces. Finally, we apply our result to prove self-adjointness for a class of
(operator-valued) quadratic forms on the space of Schwartz functions in the
Schr\"odinger representation.


title:
The Solar Neighborhood XLIX: New Discoveries and Orbits of M Dwarf
  Multiples with Speckle Interferometry at SOAR

abstract:
  We present the first results of a multi-year program to map the orbits of M
dwarf multiples within 25 parsecs. The observations were conducted primarily
during 2019 - 2020 using speckle interferometry at the Southern Astrophysical
Research (SOAR) Telescope in Chile, using the High-Resolution Camera mounted on
the adaptive optics module (HRCam+SAM). The sample of nearby M dwarfs is drawn
from three sources: multiples from the RECONS long-term astrometric monitoring
program at the SMARTS 0.9m, known multiples for which these new observations
will enable or improve orbit fits, and candidate multiples flagged by their
astrometric fits in Gaia Data Release 2 (DR2). We surveyed 333 of our 338 M
dwarfs via 830 speckle observations, detecting companions for 63% of the stars.
Most notably, this includes new companions for 76% in the subset selected from
Gaia DR2. In all, we report the first direct detections of 97 new stellar
companions to the observed M dwarfs. Here we present the properties of those
detections, the limits of each non-detection, and five orbits with periods 0.67
- 29 yr already observed as part of this program. Companions detected have
projected separations of 0.024 - 2.0 arcsec (0.25 - 66 AU) from their primaries
and have $\Delta I \lesssim 5.0$ mag. This multi-year campaign will ultimately
map complete orbits for nearby M dwarfs with periods up to 3 yr, and provide
key epochs to stretch orbital determinations for binaries to 30 yr.


title: Single-input perturbative control of a quantum symmetric rotor

abstract:
  We consider the Schr\"odinger partial differential equation of a rotating
symmetric rigid molecule (symmetric rotor) driven by a z-linearly polarized
electric field, as prototype of degenerate infinite-dimensional bilinear
control system. By introducing an abstract perturbative criterium, we classify
its simultaneous approximate controllability; based on this insight, we
numerically perform an orientational selective transfer of rotational
population.


title: Smoothed Online Learning is as Easy as Statistical Learning

abstract:
  Much of modern learning theory has been split between two regimes: the
classical offline setting, where data arrive independently, and the online
setting, where data arrive adversarially. While the former model is often both
computationally and statistically tractable, the latter requires no
distributional assumptions. In an attempt to achieve the best of both worlds,
previous work proposed the smooth online setting where each sample is drawn
from an adversarially chosen distribution, which is smooth, i.e., it has a
bounded density with respect to a fixed dominating measure. We provide tight
bounds on the minimax regret of learning a nonparametric function class, with
nearly optimal dependence on both the horizon and smoothness parameters.
Furthermore, we provide the first oracle-efficient, no-regret algorithms in
this setting. In particular, we propose an oracle-efficient improper algorithm
whose regret achieves optimal dependence on the horizon and a proper algorithm
requiring only a single oracle call per round whose regret has the optimal
horizon dependence in the classification setting and is sublinear in general.
Both algorithms have exponentially worse dependence on the smoothness parameter
of the adversary than the minimax rate. We then prove a lower bound on the
oracle complexity of any proper learning algorithm, which matches the
oracle-efficient upper bounds up to a polynomial factor, thus demonstrating the
existence of a statistical-computational gap in smooth online learning.
Finally, we apply our results to the contextual bandit setting to show that if
a function class is learnable in the classical setting, then there is an
oracle-efficient, no-regret algorithm for contextual bandits in the case that
contexts arrive in a smooth manner.


title: Tensor force effect on the neutron shell closure in super-heavy elements

abstract:
  A systematic study of the effect of tensor force on the evolution of shell
structure in even-even super-heavy nuclei in the region of proton numbers
Z=114, 120 and 126 and in the region of neutron numbers 178 $\le$ N $\le$ 188
is presented. We use, in this investigation, the Hartree-Fock framework by
means of different types of Skyrme functionals in two cases with and without
tensor force. The Bardeen-Cooper-Schriefer (BCS) approximation has been used to
treat the pairing correlations. By investigating structural and decay
properties of nuclei under consideration, it is found that N=184 shell gap is
more enhanced by the tensor interaction which depends on the isoscalar tensor
coupling constant $C_0^J$ of the used Skyrme interactions. In the case without
tensor interaction, this gap is significant only for T22, T24, T42 and SLy5.
So, it disappears with T46, T64 and T66, and is too weak for T26, T44 and T62.
Without exception, the shell gap at N=184 becomes more pronounced when the
tensor part is taken into account.


title: Quantum-information theory of a Dirichlet ring with Aharonov-Bohm field

abstract:
  Shannon quantum information entropies $S_{\rho,\gamma}$, Fisher informations
$I_{\rho,\gamma}$, Onicescu energies $O_{\rho,\gamma}$ and R\'{e}nyi entropies
$R_{\rho,\gamma}(\alpha)$ are calculated both in the position (subscript
$\rho$) and momentum ($\gamma$) spaces as functions of the inner radius $r_0$
for the two-dimensional Dirichlet unit-width annulus threaded by the
Aharonov-Bohm (AB) flux $\phi_{AB}$. Discussion is based on the analysis of the
corresponding position and momentum waveforms. Position Shannon entropy
(Onicescu energy) grows logarithmically (decreases as $1/r_0$) with large $r_0$
tending to the same asymptote $S_\rho^{asym}=\ln(4\pi r_0)-1$
[$O_\rho^{asym}=3/(4\pi r_0)$] for all orbitals whereas their Fisher
counterpart $I_{\rho_{nm}}(\phi_{AB},r_0$) approaches in the same regime the
$m$-independent limit mimicking in this way the energy spectrum variation with
$r_0$, which for the thin structures exhibits quadratic dependence on the
principal index. Frequency of the fading oscillations of the radial parts of
the wave vector functions increases with the inner radius what results in the
identical $r_0\gg1$ asymptote for all momentum Shannon entropies
$S_{\gamma_{nm}}(\phi_{AB};r_0)$ with the alike $n$ and different $m$. The same
limit causes the Fisher momentum components $I_\gamma(\phi_{AB},r_0)$ to grow
exponentially with $r_0$. It is proved that the lower limit $\alpha_{TH}$ of
the semi-infinite range of the dimensionless coefficient $\alpha$, where the
momentum component of this one-parameter entropy exists, is \textit{not}
influenced by the radius; in particular, the change of the topology from the
simply, $r_0=0$, to the doubly, $r_0>0$, connected domain is \textit{un}able to
change $\alpha_{TH}=2/5$. AB field influence on the measures is calculated too.

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


title:
Modelling Autler-Townes splitting and acoustically induced transparency
  in a waveguide loaded with resonant channels

abstract:
  We study acoustic wave propagation in a waveguide loaded with two resonant
side-branch channels. In the low frequency regime, one-dimensional models are
derived in which the effect of the channels are reduced to jump conditions
across the junction. When the separation distance is on the scale of the
wavelength, which is the case that is usually considered, the jump conditions
involve a single channel and acoustically induced transparency (AIT) occurs due
to out-of-phase interferences between the two junctions. In contrast, when the
separation distance is subwavelength, a single junction has to be considered
and the jump conditions account for the evanescent field coupling the two
channels. Such channel pairs can scatter as a dipole resulting in perfect
transmission due to Autler - Townes splitting (ATS). We show that combining the
two mechanisms offers additional degrees of freedom to control the transmission
spectra.


title: Emergent Non-Abelian Gauge Theory in Coupled Spin-Electron Dynamics

abstract:
  A clear separation of the time scales governing the dynamics of "slow" and
"fast" degrees of freedom often serves as a prerequisite for the emergence of
an independent low-energy theory. Here, we consider (slow) classical spins
exchange coupled to a tight-binding system of (fast) conduction electrons. The
effective equations of motion are derived under the constraint that the quantum
state of the electron system at any instant of time $t$ lies in the
$n$-dimensional low-energy subspace for the corresponding spin configuration at
$t$. The effective low-energy theory unfolds itself straightforwardly and takes
the form of a non-abelian gauge theory with the gauge freedom given by the
arbitrariness of the basis spanning the instantaneous low-energy sector. The
holonomic constraint generates a gauge covariant spin-Berry curvature tensor in
the equations of motion for the classical spins. In the non-abelian theory for
$n>1$, opposed to the $n=1$ adiabatic spin dynamics theory, the spin-Berry
curvature is generically nonzero, even for time-reversal symmetric systems. Its
expectation value with the representation of the electron state is gauge
invariant and gives rise to an additional {\em geometrical} spin torque.
Besides anomalous precession, the $n\ge 2$ theory also captures the spin
nutational motion, which is usually considered as a retardation effect. This is
demonstrated by proof-of-principle numerical calculations for a minimal model
with a single classical spin. Already for $n=2$ and in parameter regimes where
the $n=1$ adiabatic theory breaks down, we find good agreement with results
obtained from the full (unconstrained) theory.


title:
The nuclear dimension of extensions of commutative C*-algebras by the
  compact operators

abstract:
  Generalizing the case of the Toeplitz algebra by Brake and Winter, we prove
that the nuclear dimension of a C*-algebra extension of C(X) by the compact
operators is equal to the dimension of X.


title: Distributed Attribute-based Private Access Control

abstract:
  In attribute-based access control, users with certain verified attributes
will gain access to some particular data. Concerning with privacy of the users'
attributes, we study the problem of distributed attribute-based private access
control (DAPAC) with multiple authorities, where each authority will learn and
verify only one of the attributes.
  To investigate its fundamental limits, we introduce an information theoretic
DAPAC framework, with $N \in \mathbb{N}$, $N\geq 2$, replicated non-colluding
servers (authorities) and some users. Each user has an attribute vector
$\mathbf{v^*}=(v_1^*, ..., v_N^*)$ of dimension $N$ and is eligible to retrieve
a message $W^{\mathbf{v}^*}$, available in all servers. Each server $n\in [N]$
is able to only observe and verify the $n$'th attribute of a user. In response,
it sends a function of its data to the user. The system must satisfy the
following conditions: (1) Correctness: the user with attribute vector
$\mathbf{v^*}$ is able to retrieve his intended message $W^{\mathbf{v}^*}$ from
the servers' response, (2) Data Secrecy: the user will not learn anything about
the other messages, (3) Attribute Privacy: each Server~$n$ learns nothing
beyond attribute $n$ of the user. The capacity of the DAPAC is defined as the
ratio of the file size and the aggregated size of the responses, maximized over
all feasible schemes. We obtain a lower bound on the capacity of this problem
by proposing an achievable algorithm with rate $\frac{1}{2K}$, where $K$ is the
size of the alphabet of each attribute.


title:
Collisional open quantum dynamics with a generally correlated
  environment: Exact solvability in tensor networks

abstract:
  Quantum collision models are receiving increasing attention as they describe
many nontrivial phenomena in dynamics of open quantum systems. In a general
scenario of both fundamental and practical interest, a quantum system
repeatedly interacts with individual particles or modes forming a correlated
and structured reservoir; however, classical and quantum environment
correlations greatly complicate the calculation and interpretation of the
system dynamics. Here we propose an exact solution to this problem based on the
tensor network formalism. We find a natural Markovian embedding for the system
dynamics, where the role of an auxiliary system is played by virtual indices of
the network. The constructed embedding is amenable to analytical treatment for
a number of timely problems like the system interaction with two-photon
wavepackets, structured photonic states, and one-dimensional spin chains. We
also derive a time-convolution master equation and relate its memory kernel
with the environment correlation function, thus revealing a clear physical
picture of memory effects in the dynamics. The results advance tensor-network
methods in the fields of quantum optics and quantum transport.


title: Hole conductivity through a defect band in $\rm ZnGa_2O_4$

abstract:
  Semiconductors with wide band gap (3.0 eV), high dielectric constant (> 10),
good thermal dissipation, and capable of $n$- and $p$-type doping are highly
desirable for high-energy power electronic devices. Recent studies indicate
that $\rm ZnGa_2O_4$ may be suitable for these applications, standing out as an
alternative to $\rm Ga_2O_3$. The simple face centered cubic spinel structure
of $\rm ZnGa_2O_4$ results in isotropic electronic and optical properties, in
contrast to the large anisotropic properties of the $\beta$-monoclinic $\rm
Ga_2O_3$. In addition, $\rm ZnGa_2O_4$ has shown, on average, better thermal
dissipation and potential for $n$- and $p$-type conductivity. Here we use
density functional theory and hybrid functional calculations to investigate the
electronic, optical, and point defect properties of $\rm ZnGa_2O_4$, focusing
on the possibility for $n$- and p-type conductivity. We find that the cation
antisite $\rm Ga_{Zn}$ is the lowest energy donor defect that can lead to
unintentional $n$-type conductivity. The stability of self-trapped holes (small
hole polarons) and the high formation energy of acceptor defects make it
difficult to achieve $p$-type conductivity. However, with excess of Zn, forming
$\rm Zn_{(1+2x)}Ga_{2(1-x)}O_4$ alloys display an intermediate valence band,
facilitating $p$-type conductivity. Due to the localized nature of this
intermediate valence band, $p$-type conductivity by polaron hopping is
expected, explaining the low mobility and low hole density observed in recent
experiments.


title:
Low energy switching of phase change materials using a 2D thermal
  boundary layer

abstract:
  The switchable optical and electrical properties of phase change materials
(PCMs) are finding new applications beyond data storage in reconfigurable
photonic devices. However, high power heat pulses are needed to melt-quench the
material from crystalline to amorphous. This is especially true in silicon
photonics, where the high thermal conductivity of the waveguide material makes
heating the PCM energy inefficient. Here, we improve the energy efficiency of
the laser-induced phase transitions by inserting a layer of two-dimensional
(2D) material, either MoS2 or WS2, between the silica or silicon and the PCM.
The 2D material reduces the required laser power by at least 40% during the
amorphization (RESET) process, depending on the substrate. Thermal simulations
confirm that both MoS2 and WS2 2D layers act as a thermal barrier, which
efficiently confines energy within the PCM layer. Remarkably, the thermal
insulation effect of the 2D layer is equivalent to a ~100 nm layer of SiO2. The
high thermal boundary resistance induced by the van der Waals (vdW)-bonded
layers limits the thermal diffusion through the layer interfaces. Hence, 2D
materials with stable vdW interfaces can be used to improve the thermal
efficiency of PCM-tuned Si photonic devices. Furthermore, our waveguide
simulations show that the 2D layer does not affect the propagating mode in the
Si waveguide, thus this simple additional thin film produces a substantial
energy efficiency improvement without degrading the optical performance of the
waveguide. Our findings pave the way for energy-efficient laser-induced
structural phase transitions in PCM-based reconfigurable photonic devices.


title:
Coexistence of antiferromagnetism and ferrimagnetism in adjacent
  honeycomb layers

abstract:
  Antiferromagnetic and ferro/ferrimagnetic orders are typically exclusive in
nature, thus, their co-existence in atomic-scale proximity is expected only in
heterostructures. Breaking this paradigm and broadening the range of
unconventional magnetic states, we report here on an atomic-scale hybrid spin
state, which is stabilized in three-dimensional crystals of the polar
antiferromagnet Co$_2$Mo$_3$O$_8$ by magnetic fields applied perpendicular to
the \emph{Co} honeycomb layers and possesses a spontaneous in-plane
ferromagnetic moment. Our microscopic spin model, capturing the observed field
dependence of the longitudinal and transverse magnetization as well as the
magnetoelectric/elastic properties, reveals that this novel spin state is
composed of an alternating stacking of antiferromagnetic and ferrimagnetic
honeycomb layers. The strong intra-layer and the weak inter-layer exchange
couplings together with competing anisotropies at octahedral and tetrahedral
\emph{Co} sites are identified as the key ingredients to stabilize
antiferromagnetic and ferrimagnetic layers in such a close proximity. We show
that the proper balance of magnetic interactions can extend the stability range
of this hybrid phase down to zero magnetic field. The possibility to realize a
layer-by-layer stacking of such distinct spin orders via suitable combinations
of microscopic interactions opens a new dimension towards the nanoscale
engineering of magnetic states.


title:
Weyl Covariance and the Energy Momentum Tensors of Higher-Derivative
  Free Conformal Field Theories

abstract:
  Energy momentum tensors of higher-derivative free scalar conformal field
theories in flat spacetime are discussed. Two algorithms for the computation of
energy momentum tensors are described, which accomplish different goals: the
first is brute-force and highlights the complexity of the energy momentum
tensors, while the second displays some features of their geometric origin as
variations of Weyl invariant curved-space actions. New compact expressions for
energy momentum tensors are given and specific obstructions to defining them as
conformal primary operators in some spacetime dimensions are highlighted. Our
discussion is also extended to higher-derivative free spinor theories, which
are based on higher-derivative generalizations of the Dirac action and provide
interesting examples of conformal field theories in dimension higher than two.


title: A Carrollian Perspective on Celestial Holography

abstract:
  We propose a holographic description of gravity in $4d$ asymptotically flat
spacetime in terms of a $3d$ sourced conformal Carrollian field theory. The
external sources encode the leaks of gravitational radiation at null infinity.
The Ward identities of this theory are shown to reproduce those of the $2d$
celestial CFT after relating Carrollian to celestial operators. This suggests a
new set of interplays between gravity in asymptotically flat spacetime, sourced
conformal Carrollian field theory and celestial CFT.


title:
Improving Content-Aware Video Streaming in Congested Networks with
  In-Network Computing

abstract:
  Network congestion and packet loss pose an ever-increasing challenge to video
streaming. Despite the research efforts toward making video encoding schemes
resilient to lossy network conditions, forwarding devices have not considered
monitoring packet content to prioritize packets and minimize the impact of
packet loss on video transmission. In this work, we advocate in favor of
in-network computing employing a packet drop algorithm and an in-network
hardware module to devise a solution for improving content-aware video
streaming in congested network. Results show that our approach can reduce
intra-predicted packet loss by over 80% at negligible resource usage and
performance costs.


title: Asymmetric Self-interacting Dark Matter via Dirac Leptogenesis

abstract:
  The nature of neutrinos, whether Dirac or Majorana, is hitherto not known.
Assuming that the neutrinos are Dirac, which needs $B-L$ to be an exact
symmetry, we make an attempt to explain the observed proportionality between
the relic densities of dark matter (DM) and baryonic matter in the present
Universe ${\it i.e.,}\,\, \Omega_{\rm DM} \approx 5\, \Omega_{\rm B}$. Assuming
the existence of heavy $SU(2)_L$ scalar doublet $(X= (X^0, X^-)^T)$ in the
early Universe, an equal and opposite $B-L$ asymmetry can be generated in left
and right-handed sectors by the CP-violating out-of-equilibrium decay $X^0 \to
\nu_L \nu_R$ since $B-L$ is an exact symmetry. We ensure that $\nu_L-\nu_R$
equilibration does not occur until below the electroweak (EW) phase transition
during which a part of the lepton asymmetry gets converted to dark matter
asymmetry through a dimension eight operator, which conserves $B-L$ symmetry
and is in thermal equilibrium. The remaining $B-L$ asymmetry then gets
converted to a net B-asymmetry through EW-sphalerons which are active at a
temperature above 100 GeV. To alleviate the small-scale anomalies of
$\Lambda$CDM, we assume the DM to be self-interacting via a light mediator,
which not only depletes the symmetric component of the DM, but also paves a way
to detect the DM at terrestrial laboratories through scalar portal mixing.


title:
Deploying Vaccine Distribution Sites for Improved Accessibility and
  Equity to Support Pandemic Response

abstract:
  In response to COVID-19, many countries have mandated social distancing and
banned large group gatherings in order to slow down the spread of SARS-CoV-2.
These social interventions along with vaccines remain the best way forward to
reduce the spread of SARS CoV-2. In order to increase vaccine accessibility,
states such as Virginia have deployed mobile vaccination centers to distribute
vaccines across the state. When choosing where to place these sites, there are
two important factors to take into account: accessibility and equity. We
formulate a combinatorial problem that captures these factors and then develop
efficient algorithms with theoretical guarantees on both of these aspects.
Furthermore, we study the inherent hardness of the problem, and demonstrate
strong impossibility results. Finally, we run computational experiments on
real-world data to show the efficacy of our methods.


title: Stable allocations in discrete economies

abstract:
  We study discrete allocation problems, as in the textbook notion of an
exchange economy, but with indivisible goods. The problem is well-known to be
difficult. The model is rich enough to encode some of the most pathological
bargaining configurations in game theory, like the roommate problem. Our
contribution is to show the existence of stable allocations (outcomes in the
weak core, or in the bargaining set) under different sets of assumptions.
Specifically, we consider dichotomous preferences, categorical economies, and
discrete TU markets. The paper uses varied techniques, from Scarf's balanced
games to a generalization of the TTC algorithm by means of Tarski fixed points.


title: Random Band and Block Matrices with Correlated Entries

abstract:
  In this paper, we derive limit laws for the empirical spectral distributions
of random band and block matrices with correlated entries. In the first part of
the paper, we study band matrices with approximately uncorrelated entries. We
strengthen previously obtained results while requiring weaker assumptions,
which is made possible by a refined application of the method of moments. In
the second part of the paper, we introduce a new two-layered correlation
structure we call SSB-HKW correlated, which enables the study of structured
random matrices with correlated entries. Our results include semicircle laws in
probability and almost surely, but we also obtain other limiting spectral
distributions depending on the conditions. Simple necessary and sufficient
conditions for the limit law to be the semicircle are provided. Our findings
strengthen and extend many results already known.


title:
Active Learning Improves Performance on Symbolic RegressionTasks in
  StackGP

abstract:
  In this paper we introduce an active learning method for symbolic regression
using StackGP. The approach begins with a small number of data points for
StackGP to model. To improve the model the system incrementally adds a data
point such that the new point maximizes prediction uncertainty as measured by
the model ensemble. Symbolic regression is re-run with the larger data set.
This cycle continues until the system satisfies a termination criterion. We use
the Feynman AI benchmark set of equations to examine the ability of our method
to find appropriate models using fewer data points. The approach was found to
successfully rediscover 72 of the 100 Feynman equations using as few data
points as possible, and without use of domain expertise or data translation.


title: Transferred Q-learning

abstract:
  We consider $Q$-learning with knowledge transfer, using samples from a target
reinforcement learning (RL) task as well as source samples from different but
related RL tasks. We propose transfer learning algorithms for both batch and
online $Q$-learning with offline source studies. The proposed transferred
$Q$-learning algorithm contains a novel re-targeting step that enables vertical
information-cascading along multiple steps in an RL task, besides the usual
horizontal information-gathering as transfer learning (TL) for supervised
learning. We establish the first theoretical justifications of TL in RL tasks
by showing a faster rate of convergence of the $Q$ function estimation in the
offline RL transfer, and a lower regret bound in the offline-to-online RL
transfer under certain similarity assumptions. Empirical evidences from both
synthetic and real datasets are presented to back up the proposed algorithm and
our theoretical results.


title: Deconfinement and Error Thresholds in Holography

abstract:
  We study the error threshold properties of holographic quantum
error-correcting codes. We demonstrate that holographic CFTs admit an algebraic
threshold, which is related to the confinement-deconfinement phase transition.
We then apply geometric intuition from holography and the Hawking-Page phase
transition to motivate the CFT result, and comment on potential extensions to
other confining theories.


title: Breaking Orion's Veil bubble with fossil outflows

abstract:
  The role of feedback in the self-regulation of star formation is a
fundamental question in astrophysics. The Orion Nebula is the nearest site of
ongoing and recent massive star formation. It is a unique laboratory for the
study of stellar feedback. Recent SOFIA [CII] 158 $\mu$m observations revealed
an expanding bubble, the Veil shell, being powered by stellar winds and
ionization feedback. We have identified a protrusion-like substructure in the
Northwest portion of the Orion Veil Shell that may indicate additional feedback
mechanisms that are highly directional. Our goal is to investigate the origin
of the protrusion by quantifying its possible driving mechanisms. We use the
[CII] 158 $\mu$m map of the Orion Nebula obtained with the upGREAT instrument
onboard SOFIA. The spectral and spatial resolution of the observations are 0.3
km/s and 16 arcsec, respectively.
  We consider three possible origins for this protrusion: Fossil outflow
cavities created by jets/outflows during the protostellar accretion phase,
pre-existing clumpiness in the OMC-1 core, and the stellar wind during the main
sequence phase. Based on the energetics and the morphology, we conclude that
the northwestern part of the pre-existing cloud was locally perturbed by
outflows ejected from massive protostars in the Trapezium cluster. This
suggests that the protrusion of the Veil is the result of mechanical rather
than radiative feedback. Furthermore, we argue that the location of the
protrusion is a suitable place to break the Orion Veil owing to the
photo-ablation from the walls of the protrusion. We conclude that the outflows
of massive protostars can influence the morphology of the future \hii\,region
and even cause breakages in the ionization front. Specifically, the interaction
of stellar winds of main-sequence stars with the molecular core pre-processed
by the protostellar jet is important.


title: Crater production on Titan and surface chronology

abstract:
  Impact crater counts on the Saturnian satellites are a key element for
estimating their surface ages and placing constraints on their impactor
population. The Cassini mission radar observations allowed crater counts to be
made on the surface of Titan, revealing an unexpected scarcity of impact
craters that show high levels of degradation. Following previous studies on
impact cratering rates on the Saturnian satellites, we modeled the cratering
process on Titan to constrain its surface chronology and to assess the role of
centaur objects as its main impactors. A theoretical model previously developed
was used to calculate the crater production on Titan, considering the centaur
objects as the main impactors and including two different slopes for the
size-frequency distribution (SFD) of the smaller members of their source
population. A simple model for the atmospheric shielding effects is considered
within the cratering process and our results are then compared with other
synthetic crater distributions and updated observational crater counts. This
comparison is then used to compute Titan's crater retention age for each crater
diameter. The cumulative crater distribution produced by the SFD with a
differential index of $s_2 = 3.5$ is found to consistently predict large
craters (D > 50 km) on the surface of Titan, while it overestimates the number
of smaller craters. As both the modeled and observed distributions flatten for
craters $D \lesssim 25 $ km due to atmospheric shielding, the difference
between them can be considered as a proxy for the scale to which erosion
processes have acted on the surface of Titan throughout the Solar System age.
Our results for the surface chronology of Titan indicate that craters with D >
50 km can prevail over the Solar System age, whereas smaller craters may be
completely obliterated due to erosion processes acting globally.


title:
PINs: Progressive Implicit Networks for Multi-Scale Neural
  Representations

abstract:
  Multi-layer perceptrons (MLP) have proven to be effective scene encoders when
combined with higher-dimensional projections of the input, commonly referred to
as \textit{positional encoding}. However, scenes with a wide frequency spectrum
remain a challenge: choosing high frequencies for positional encoding
introduces noise in low structure areas, while low frequencies result in poor
fitting of detailed regions. To address this, we propose a progressive
positional encoding, exposing a hierarchical MLP structure to incremental sets
of frequency encodings. Our model accurately reconstructs scenes with wide
frequency bands and learns a scene representation at progressive level of
detail \textit{without explicit per-level supervision}. The architecture is
modular: each level encodes a continuous implicit representation that can be
leveraged separately for its respective resolution, meaning a smaller network
for coarser reconstructions. Experiments on several 2D and 3D datasets show
improvements in reconstruction accuracy, representational capacity and training
speed compared to baselines.


title: Crossed Product Equivalence of Quantum Automorphism Groups

abstract:
  We compare algebras of the quantum automorphism group of finite-dimensional
C$^\ast$-algebra $B$ and the quantum permutation group $S_N^+$, where $N = \dim
B$. We show that matrix amplification and crossed products by trace-preserving
actions by a finite Abelian group $\Gamma$ lead to isomorphic $\ast$-algebras.
This allows us to transfer various properties such as inner unitarity, Connes
embeddability, and strong $1$-boundedness between the various algebras
associated with these quantum groups.


title: Green's functions and complex Monge-Amp\`ere equations

abstract:
  Uniform $L^1$ and lower bounds are obtained for the Green's function on
compact K\"ahler manifolds. Unlike in the classic theorem of Cheng-Li for
Riemannian manifolds, the lower bounds do not depend directly on the Ricci
curvature, but only on integral bounds for the volume form and certain of its
derivatives. In particular, a uniform lower bound for the Green's function on
K\"ahler manifolds is obtained which depends only on a lower bound for the
scalar curvature and on an $L^q$ norm for the volume form for some $q>1$. The
proof relies on auxiliary Monge-Amp\`ere equations, and is fundamentally
non-linear. The lower bounds for the Green's function imply in turn $C^1$ and
$C^2$ estimates for complex Monge-Amp\`ere equations with a sharper dependence
on the function on the right hand side.


title: Ramsey and Hypersmoothness

abstract:
  Combining canonization results of Pr\"omel-Voigt, Mathias, and Soare, we
provide a new, natural example of an $F_\sigma$ equivalence relation that is
not hypersmooth.


title:
The Central Limit Theorem for Weakly Dependent Random Variables by the
  Moment Method

abstract:
  In this paper, we derive a central limit theorem for collections of weakly
correlated random variables indexed by discrete metric spaces, where the
correlation decays in the distance of the indices. The correlation structure we
study depends solely on the separability of mixed moments. Our investigation
yields a new proof for the CLT for $\alpha$-mixing random variables, but also
non-$\alpha$-mixing random variables fit within our framework, such as
MA($\infty$) processes. In particular, our results can be applied to
ARMA($p,q$) process with independent white noise.


title: Designing Closed Human-in-the-loop Deferral Pipelines

abstract:
  In hybrid human-machine deferral frameworks, a classifier can defer uncertain
cases to human decision-makers (who are often themselves fallible). Prior work
on simultaneous training of such classifier and deferral models has typically
assumed access to an oracle during training to obtain true class labels for
training samples, but in practice there often is no such oracle. In contrast,
we consider a "closed" decision-making pipeline in which the same fallible
human decision-makers used in deferral also provide training labels. How can
imperfect and biased human expert labels be used to train a fair and accurate
deferral framework? Our key insight is that by exploiting weak prior
information, we can match experts to input examples to ensure fairness and
accuracy of the resulting deferral framework, even when imperfect and biased
experts are used in place of ground truth labels. The efficacy of our approach
is shown both by theoretical analysis and by evaluation on two tasks.


title:
A Coupled CP Decomposition for Principal Components Analysis of
  Symmetric Networks

abstract:
  In a number of application domains, one observes a sequence of network data;
for example, repeated measurements between users interactions in social media
platforms, financial correlation networks over time, or across subjects, as in
multi-subject studies of brain connectivity. One way to analyze such data is by
stacking networks into a third-order array or tensor. We propose a principal
components analysis (PCA) framework for sequence network data, based on a novel
decomposition for semi-symmetric tensors. We derive efficient algorithms for
computing our proposed "Coupled CP" decomposition and establish estimation
consistency of our approach under an analogue of the spiked covariance model
with rates the same as the matrix case up to a logarithmic term. Our framework
inherits many of the strengths of classical PCA and is suitable for a wide
range of unsupervised learning tasks, including identifying principal networks,
isolating meaningful changepoints or outliers across observations, and for
characterizing the "variability network" of the most varying edges. Finally, we
demonstrate the effectiveness of our proposal on simulated data and on examples
from political science and financial economics. The proof techniques used to
establish our main consistency results are surprisingly straight-forward and
may find use in a variety of other matrix and tensor decomposition problems.


title:
Weighted posets and the enriched monomial basis of QSym (extended
  abstract)

abstract:
  Gessel's fundamental and Stembridge's peak functions are the generating
functions for (enriched) $P$-partitions on labelled chains. They are also the
bases of two significant subalgebras of formal power series, respectively the
ring of quasisymmetric functions (QSym) and the algebra of peaks. Hsiao
introduced the monomial peak functions, a basis of the algebra of peaks indexed
by odd integer compositions whose relation to peak functions mimics the one
between the monomial and fundamental bases of QSym. We show that the extension
of monomial peaks to any composition is a new basis of QSym and generalise
Hsiao's results including the product rule. To this end we introduce a weighted
variant of posets and study their generating functions.


title:
New Projection-free Algorithms for Online Convex Optimization with
  Adaptive Regret Guarantees

abstract:
  We present new efficient \textit{projection-free} algorithms for online
convex optimization (OCO), where by projection-free we refer to algorithms that
avoid computing orthogonal projections onto the feasible set, and instead relay
on different and potentially much more efficient oracles. While most
state-of-the-art projection-free algorithms are based on the
\textit{follow-the-leader} framework, our algorithms are fundamentally
different and are based on the \textit{online gradient descent} algorithm with
a novel and efficient approach to computing so-called \textit{infeasible
projections}. As a consequence, we obtain the first projection-free algorithms
which naturally yield \textit{adaptive regret} guarantees, i.e., regret bounds
that hold w.r.t. any sub-interval of the sequence. Concretely, when assuming
the availability of a linear optimization oracle (LOO) for the feasible set, on
a sequence of length $T$, our algorithms guarantee $O(T^{3/4})$ adaptive regret
and $O(T^{3/4})$ adaptive expected regret, for the full-information and bandit
settings, respectively, using only $O(T)$ calls to the LOO. These bounds match
the current state-of-the-art regret bounds for LOO-based projection-free OCO,
which are \textit{not adaptive}. We also consider a new natural setting in
which the feasible set is accessible through a separation oracle. We present
algorithms which, using overall $O(T)$ calls to the separation oracle,
guarantee $O(\sqrt{T})$ adaptive regret and $O(T^{3/4})$ adaptive expected
regret for the full-information and bandit settings, respectively.


title:
On the stability of unevenly spaced samples for interpolation and
  quadrature

abstract:
  Unevenly spaced samples from a periodic function are common in signal
processing and can often be viewed as a perturbed equally spaced grid. In this
paper, we analyze how the uneven distribution of the samples impacts the
quality of interpolation and quadrature. Starting with equally spaced nodes on
$[-\pi,\pi)$ with grid spacing $h$, suppose the unevenly spaced nodes are
obtained by perturbing each uniform node by an arbitrary amount $\leq \alpha
h$, where $0 \leq \alpha < 1/2$ is a fixed constant. We prove a discrete
version of the Kadec-1/4 theorem, which states that the nonuniform discrete
Fourier transform associated with perturbed nodes has a bounded condition
number independent of $h$, for any $\alpha < 1/4$. We go on to show that
unevenly spaced quadrature rules converge for all continuous functions and
interpolants converge uniformly for all differentiable functions whose
derivative has bounded variation when $0 \leq \alpha < 1/4$. Though, quadrature
rules at perturbed nodes can have negative weights for any $\alpha > 0$, we
provide a bound on the absolute sum of the quadrature weights. Therefore, we
show that perturbed equally spaced grids with small $\alpha$ can be used
without numerical woes. While our proof techniques work primarily when $0 \leq
\alpha < 1/4$, we show that a small amount of oversampling extends our results
to the case when $1/4 \leq \alpha < 1/2$.


title:
Importance of source structure on complex organics emission. I.
  Observations of CH$_3$OH from low-mass to high-mass protostars

abstract:
  Complex organic molecules (COMs) are often observed toward embedded Class 0
and I protostars. However, not all Class 0 and I protostars exhibit COMs
emission. In this work, variations in methanol (CH$_3$OH) emission are studied
to test if absence of CH$_3$OH emission can be linked to source properties.
Combining both new and archival observations with ALMA and sources from the
literature, a sample of 184 low-mass and high-mass protostars is investigated.
The warm (T > 100 K) gaseous CH$_3$OH mass, $M_{\rm CH_3OH}$, is determined for
each source using primarily optically thin isotopologues. On average, Class I
protostellar systems seem to have less warm $M_{\rm CH_3OH}$ ($<10^{-10}$
M$_\odot$) than younger Class 0 sources ($\sim10^{-7}$ M$_\odot$). High-mass
sources in our sample show higher warm $M_{\rm CH_3OH}$ up to $10^{-7}-10^{-3}$
M$_\odot$. To take into account the effect of the source's overall mass on
$M_{\rm CH_3OH}$, a normalized CH$_3$OH mass is defined as $M_{\rm
CH_3OH}/M_{\rm dust,0}$, where $M_{\rm dust,0}$ is the cold + warm dust mass
within a fixed radius. Excluding upper limits, a simple power-law fit to the
normalized warm CH$_3$OH masses results in $M_{\rm CH_3OH}/M_{\rm
dust,0}\propto L_{\rm bol}^{0.70\pm0.05}$. This is in good agreement with a
simple hot core toy model which predicts that the normalized $M_{\rm CH_3OH}$
increases with $L_{\rm bol}^{0.75}$ due to the snowline moving outward. Sources
for which the size of the disk is equivalent or smaller than the estimated 100
K radius agree well with the best-fit power-law model, whereas sources with
significantly larger disks show up to two orders of magnitude lower normalized
warm CH$_3$OH masses. Based on the latter results, we suggest that source
structure such as a disk can result in colder gas and thus fewer COMs in the
gas phase. Additionally, optically thick dust can hide the emission of COMs.


title: The Landscape of Distributed Complexities on Trees and Beyond

abstract:
  We study the local complexity landscape of locally checkable labeling (LCL)
problems on constant-degree graphs with a focus on complexities below $\log^*
n$.
  Our contribution is threefold:
  Our main contribution is that we complete the classification of the
complexity landscape of LCL problems on trees in the LOCAL model, by proving
that every LCL problem with local complexity $o(\log^* n)$ has actually
complexity $O(1)$. This result improves upon the previous speedup result from
$o(\log \log^* n)$ to $O(1)$ by [Chang, Pettie, FOCS 2017].
  In the related LCA and Volume models [Alon, Rubinfeld, Vardi, Xie, SODA 2012,
Rubinfeld, Tamir, Vardi, Xie, 2011, Rosenbaum, Suomela, PODC 2020], we prove
the same speedup from $o(\log^* n)$ to $O(1)$ for all bounded degree graphs.
  Similarly, we complete the classification of the LOCAL complexity landscape
of oriented $d$-dimensional grids by proving that any LCL problem with local
complexity $o(\log^* n)$ has actually complexity $O(1)$. This improves upon the
previous speed-up from $o(\sqrt[d]{\log^* n})$ by Suomela in [Chang, Pettie,
FOCS 2017].


title: TamilEmo: Finegrained Emotion Detection Dataset for Tamil

abstract:
  Emotional Analysis from textual input has been considered both a challenging
and interesting task in Natural Language Processing. However, due to the lack
of datasets in low-resource languages (i.e. Tamil), it is difficult to conduct
research of high standard in this area. Therefore we introduce this labelled
dataset (a largest manually annotated dataset of more than 42k Tamil YouTube
comments, labelled for 31 emotions including neutral) for emotion recognition.
The goal of this dataset is to improve emotion detection in multiple downstream
tasks in Tamil. We have also created three different groupings of our emotions
(3-class, 7-class and 31-class) and evaluated the model's performance on each
category of the grouping. Our MURIL-base model has achieved a 0.60 macro
average F1-score across our 3-class group dataset. With 7-class and 31-class
groups, the Random Forest model performed well with a macro average F1-scores
of 0.42 and 0.29 respectively.


title: On the possible existence of a soft dipole mode in 8He

abstract:
  With an extreme neutron-to-proton ratio of N/Z=3, 8He provides an ideal
laboratory for the study of a variety of exotic phenomena, such as the
emergence of a soft dipole mode that is dominated by transitions into the
continuum. In this contribution, a covariant density functional theory (DFT)
framework is used to compute ground-state properties and the dipole response of
8He. Although 8He is admittedly too light for DFT to be applicable, the great
merit of the approach is that the spurious contamination associated with the
center-of-mass motion is guaranteed to decouple from the physical response.
Given that a strong mixing between the isoscalar and isovector dipole modes is
expected for a system with such a large neutron-proton asymmetry as 8He, the
narrow structures that emerged at low energies in the isovector dipole response
are attributed to the shift of the spurious strength to zero (or near zero)
excitation energy. Thus, the theoretical framework implemented here disfavors
the emergence of a soft dipole mode in 8He.


title:
Terrain parameter estimation from proprioceptive sensing of the
  suspension dynamics in offroad vehicles

abstract:
  Offroad vehicle movement has to contend with uneven and uncertain terrain
which present challenges to path planning and motion control for both manned
and unmanned ground vehicles. Knowledge of terrain properties can allow a
vehicle to adapt its control and motion planning algorithms. Terrain
properties, however, can change on time scales of days or even hours,
necessitating their online estimation. The kinematics and, in particular the
oscillations experienced by an offroad vehicle carry a signature of the terrain
properties. These terrain properties can thus be estimated from proprioceptive
sensing of the vehicle dynamics with an appropriate model and estimation
algorithm. In this paper, we show that knowledge of the vertical dynamics of a
vehicle due to its suspension can enable faster and more accurate estimation of
terrain parameters. The paper considers a five degree of freedom model that
combines the well known half-car and bicycle models. We show through simulation
that the sinkage exponent, a parameter that can significantly influence the
wheel forces from the terrain and thus greatly impact the vehicle trajectory,
can be estimated from measurements of the vehicle's linear acceleration and
rotational velocity, which can be readily obtained from an onboard IMU. We show
that modelling the vertical vehicle dynamics can lead to significant
improvement in both the estimation of terrain parameters and the prediction of
the vehicle trajectory.


title: Predicting Human Similarity Judgments Using Large Language Models

abstract:
  Similarity judgments provide a well-established method for accessing mental
representations, with applications in psychology, neuroscience and machine
learning. However, collecting similarity judgments can be prohibitively
expensive for naturalistic datasets as the number of comparisons grows
quadratically in the number of stimuli. One way to tackle this problem is to
construct approximation procedures that rely on more accessible proxies for
predicting similarity. Here we leverage recent advances in language models and
online recruitment, proposing an efficient domain-general procedure for
predicting human similarity judgments based on text descriptions. Intuitively,
similar stimuli are likely to evoke similar descriptions, allowing us to use
description similarity to predict pairwise similarity judgments. Crucially, the
number of descriptions required grows only linearly with the number of stimuli,
drastically reducing the amount of data required. We test this procedure on six
datasets of naturalistic images and show that our models outperform previous
approaches based on visual information.


title:
Fractional Differential Equations with the General Fractional
  Derivatives of Arbitrary Order in the Riemann-Liouville Sense

abstract:
  In this paper, we first deal with the general fractional derivatives of
arbitrary order defined in the Riemann-Liouville sense. In particular, we
deduce an explicit form of their null space and prove the second fundamental
theorem of Fractional Calculus that leads to a closed form formula for their
projector operator. These results allow us to formulate the natural initial
conditions for the fractional differential equations with the general
fractional derivatives of arbitrary order in the Riemann-Liouville sense. In
the second part of the paper, we develop an operational calculus of the
Mikusi\'nski type for the general fractional derivatives of arbitrary order in
the Riemann-Liouville sense and apply it for derivation of an explicit form of
solutions to the Cauchy problems for the single- and multi-term linear
fractional differential equations with these derivatives. The solutions are
provided in form of the convolution series generated by the kernels of the
corresponding general fractional integrals.


title: Cavity-Enhanced Linear Dichroism in a van der Waals Antiferromagnet

abstract:
  Optical birefringence is a fundamental optical property of crystals widely
used for filtering and beam splitting of photons. Birefringent crystals
concurrently possess the property of linear dichroism (LD) that allows
asymmetric propagation or attenuation of light with two different
polarizations. This property of LD has been widely studied from small molecules
to polymers and crystals but has rarely been engineered per will. Here, we use
the newly discovered spin-charge coupling in van der Waals antiferromagnetic
(AFM) insulator FePS3 to induce large in-plane optical anisotropy and
consequently LD. We report that the LD in this AFM insulator is tunable both
spectrally and magnitude-wise as a function of cavity coupling. We demonstrate
near-unity LD in the visible-near infrared range in cavity-coupled FePS3
crystals and derive its dispersion as a function of cavity length and FePS3
thickness. Our results hold wide implications for use of cavity tuned LD as a
diagnostic probe for strongly correlated quantum materials as well as opens new
opportunities for miniaturized, on-chip beam-splitters and tunable filters.


title: Graph Neural Network for Cell Tracking in Microscopy Videos

abstract:
  We present a novel graph neural network (GNN) approach for cell tracking in
high-throughput microscopy videos. By modeling the entire time-lapse sequence
as a direct graph where cell instances are represented by its nodes and their
associations by its edges, we extract the entire set of cell trajectories by
looking for the maximal paths in the graph. This is accomplished by several key
contributions incorporated into an end-to-end deep learning framework. We
exploit a deep metric learning algorithm to extract cell feature vectors that
distinguish between instances of different biological cells and assemble same
cell instances. We introduce a new GNN block type which enables a mutual update
of node and edge feature vectors, thus facilitating the underlying message
passing process. The message passing concept, whose extent is determined by the
number of GNN blocks, is of fundamental importance as it enables the `flow' of
information between nodes and edges much behind their neighbors in consecutive
frames. Finally, we solve an edge classification problem and use the identified
active edges to construct the cells' tracks and lineage trees. We demonstrate
the strengths of the proposed cell tracking approach by applying it to 2D and
3D datasets of different cell types, imaging setups, and experimental
conditions. We show that our framework outperforms most of the current
state-of-the-art methods.


title: Online Learning to Transport via the Minimal Selection Principle

abstract:
  Motivated by robust dynamic resource allocation in operations research, we
study the Online Learning to Transport (OLT) problem where the decision
variable is a probability measure, an infinite-dimensional object. We draw
connections between online learning, optimal transport, and partial
differential equations through an insight called the minimal selection
principle, originally studied in the Wasserstein gradient flow setting by
Ambrosio et al. (2005). This allows us to extend the standard online learning
framework to the infinite-dimensional setting seamlessly. Based on our
framework, we derive a novel method called the minimal selection or exploration
(MSoE) algorithm to solve OLT problems using mean-field approximation and
discretization techniques. In the displacement convex setting, the main
theoretical message underpinning our approach is that minimizing transport cost
over time (via the minimal selection principle) ensures optimal cumulative
regret upper bounds. On the algorithmic side, our MSoE algorithm applies beyond
the displacement convex setting, making the mathematical theory of optimal
transport practically relevant to non-convex settings common in dynamic
resource allocation.


title: Optical and Strain Stabilization of Point Defects in Silicon Carbide

abstract:
  The photoluminescence and spin properties of ensembles of color centers in
silicon carbide are enhanced by fabricating optically isolated slab waveguide
structures and carefully controlling annealing and cooling conditions. We find
that the photoluminescence signal of an ensemble of implanted defects is
enhanced in slab waveguides by an order of magnitude over identically implanted
bulk defects. The slab waveguide-enhanced photoluminescence of several defect
species is used to study recombination and diffusion in the presence of thermal
annealing with both rapid quench cooling and a longer return to ambient
conditions. The confined mechanical geometry of the thin film is exploited to
measure the spin-strain coupling of the negatively charged silicon monovacancy.
The methods in this work can be used to exercise greater control on
near-surface emitters in silicon carbide and better understand and control the
effects of strain on spin measurements of silicon carbide based color centers.


title:
Broadband wavelength-selective isotype heterojunction n+-ZnO/n-Si
  photodetector with variable polarity

abstract:
  An isotype heterojunction n+-ZnO/n-Si photodetector is developed,
demonstrating wavelength-selective or broadband operation, depending on the
applied bias voltage. Additionally, at self-powered (zero bias) operation, it
distinguishes between UV, visible, and near IR (NIR) photons by polarity
control of the photocurrent. The photodetector is developed by atomic layer
deposition (ALD) of ZnO on n-Si, followed by electric contact deposition and
annealing. Photoluminescence measurements reveal high optical quality and
improved crystallinity of annealed ZnO on silicon. Photocurrent measurements as
a function of illumination wavelength and bias voltage show small negative
values in the UV-visible spectral range at zero and positive bias voltage and
high positive values in the NIR spectral range. For these measurements, we
consider the electric contact to ZnO as the anode and the electric contact to
silicon as the cathode. At negative bias voltage, the device shows broadband
operation with high photocurrent values across the UV-vis-NIR.


title: Assessing the quality of near-term photonic quantum devices

abstract:
  For near-term quantum devices, an important challenge is to develop efficient
methods to certify that noise levels are low enough to allow potentially useful
applications to be carried out. We present such a method tailored to photonic
quantum devices consisting of single photon sources coupled to linear optical
circuits coupled to photon detectors. It uses the output statistics of
BosonSampling experiments with input size $n$ ($n$ input photons in the ideal
case). We propose a series of benchmark tests targetting two main sources of
noise, namely photon loss and distinguishability. Our method results in a
single-number metric, the Photonic Quality Factor, defined as the largest
number of input photons for which the output statistics pass all tests. We
provide strong evidence that passing all tests implies that our experiments are
not efficiently classically simulable, by showing how several existing
classical algorithms for efficiently simulating noisy BosonSampling fail the
tests. Finally we show that BosonSampling experiments with average photon loss
rate per mode scaling as $o(1)$ and average fidelity of $
(1-o(\frac{1}{n^6}))^2$ between any two single photon states is sufficient to
keep passing our tests. Unsurprisingly, our results highlight that scaling in a
manner that avoids efficient classical simulability will at some point
necessarily require error correction and mitigation.


title: Coarsening the Granularity: Towards Structurally Sparse Lottery Tickets

abstract:
  The lottery ticket hypothesis (LTH) has shown that dense models contain
highly sparse subnetworks (i.e., winning tickets) that can be trained in
isolation to match full accuracy. Despite many exciting efforts being made,
there is one "commonsense" seldomly challenged: a winning ticket is found by
iterative magnitude pruning (IMP) and hence the resultant pruned subnetworks
have only unstructured sparsity. That gap limits the appeal of winning tickets
in practice, since the highly irregular sparse patterns are challenging to
accelerate on hardware. Meanwhile, directly substituting structured pruning for
unstructured pruning in IMP damages performance more severely and is usually
unable to locate winning tickets.
  In this paper, we demonstrate the first positive result that a structurally
sparse winning ticket can be effectively found in general. The core idea is to
append "post-processing techniques" after each round of (unstructured) IMP, to
enforce the formation of structural sparsity. Specifically, we first "re-fill"
pruned elements back in some channels deemed to be important, and then
"re-group" non-zero elements to create flexible group-wise structural patterns.
Both our identified channel- and group-wise structural subnetworks win the
lottery, with substantial inference speedups readily supported by existing
hardware. Extensive experiments, conducted on diverse datasets across multiple
network backbones, consistently validate our proposal, showing that the
hardware acceleration roadblock of LTH is now removed. Specifically, the
structural winning tickets obtain up to {64.93%, 64.84%, 64.84%} running time
savings at {36% ~ 80%, 74%, 58%} sparsity on {CIFAR, Tiny-ImageNet, ImageNet},
while maintaining comparable accuracy. Codes are available in
https://github.com/VITA-Group/Structure-LTH.


title:
Telegram Monitor: Monitoring Brazilian Political Groups and Channels on
  Telegram

abstract:
  Instant messaging platforms such as Telegram became one of the main means of
communication used by people all over the world. Most of them are home of
several groups and channels that connect thousands of people focused on
political topics. However, they have suffered with misinformation campaigns
with a direct impact on electoral processes around the world. While some
platforms, such as WhatsApp, took restrictive policies and measures to
attenuate the issues arising from the abuse of their systems, others have
emerged as alternatives, presenting little or no restrictions on content
moderation or actions in combating misinformation. Telegram is one of those
systems, which has been attracting more users and gaining popularity. In this
work, we present the "Telegram Monitor", a web-based system that monitors the
political debate in this environment and enables the analysis of the most
shared content in multiple channels and public groups. Our system aims to allow
journalists, researchers, and fact-checking agencies to identify trending
conspiracy theories, misinformation campaigns, or simply to monitor the
political debate in this space along the 2022 Brazilian elections. We hope our
system can assist the combat of misinformation spreading through Telegram in
Brazil.


title: Nonadditive drag of tandem rods drafting in granular sediments

abstract:
  We examine the drag experienced by a pair of vertical rods moving in tandem
through a granular bed immersed in a fluid as a function of their separation
distance and speed. As in Newtonian fluids, the net drag experienced by the
rods initially increases with distance from the value for a single rod before
plateauing to twice the value. However, the drag acting on the two rods is
remarkably different, with the leading rod experiencing roughly similar drag
compared to a solitary rod, while the following rod experiences far less drag.
The anomalous relationship of drag and the distance between the leading and
following body is observed in both dry granular beds and while immersed in
viscous Newtonian fluids across the quasi-static and the rate-dependent
regimes. Through refractive index matching, we visualize the sediment flow past
the two rods and show that a stagnant region develops in their reference frame
between the rods for small separations. Thus, the following rod is increasingly
shielded from the granular flow with decreasing separation distance, leading to
a lower net drag. Care should be exercised in applying resistive force theory
to multi-component objects moving in granular sediments based on our result
that drag is not additive at short separation distances.


title:
A generalisation of quasi-shuffle algebras and an application to
  multiple zeta values

abstract:
  A large family of relations among multiple zeta values may be described using
the combinatorics of shuffle and quasi-shuffle algebras. While the structure of
shuffle algebras have been well understood for some time now, quasi-shuffle
algebras were only formally studied relatively recently. In particular, Hoffman
gives a thorough discussion of the algebraic structure, including a choice of
algebra basis, and applies his results to produce families of relations among
multiple zeta values and their generalisations. In a series of recent talks,
Hirose and Sato proposed a conjectural family of relations coming from a new
generalised shuffle structure, lifting a set of graded relations established by
the author to conjectural genuine relations. In this paper, we define a
commutative algebra structure on the space of non-commutative polynomials in a
countable alphabet, generalising the shuffle-like structure of Hirose and Sato.
We show that, over the rational numbers, this generalised quasi-shuffle algebra
is isomorphic to the standard shuffle algebra, allowing us to reproduce most of
Hoffman's results on quasi-shuffle algebras. We then apply these results to the
case of multiple zeta values, reproducing several known families of results and
suggesting several more which can be verified numerically, hence providing
further evidence for the conjecture of Hirose and Sato.


title:
Preservation of product structures under the Ricci flow with
  instantaneous curvature bounds

abstract:
  In this note, we prove that there exists a constant $\epsilon >0$, depending
only on the dimension, such that if a complete solution to the Ricci flow
splits as a product at time $t=0$ and has curvature bounded by
$\frac{\epsilon}{t}$, then the solution splits for all time.


title: Spectral form factor for free large $N$ gauge theory and strings

abstract:
  We investigate the spectral form factor in two different systems, free large
$N$ gauge theories and highly excited string gas. In both cases, after a rapid
decay of the spectral form factor at early time, new contributions come in,
preventing the spectral form factor from ever becoming exponentially small. We
consider $U(N)$ gauge theories with only adjoint matter and compute the
spectral form factor using a matrix integral of the thermal holonomy $U$. The
new saddles differ from the early time saddle by preserving certain subgroups
of the center symmetry. For a gas of strings, the short time decay of the
spectral form factor is governed by the continuous Hagedorn density of states,
which can be associated to the thermal winding mode with winding number $\pm
1$. We show that the rise of the spectral form factor comes from other winding
modes that also carry momentum along the time direction. We speculate on the
existence of a family of classical solutions for these string modes, similar to
the Horowitz-Polchinski solution.
  We review a similar problem for black holes. In particular, we examine the
Kontsevich-Segal criterion on complex black holes that contribute to the
spectral form factor. In the canonical ensemble quantity $Z(\beta+it)$, the
black hole becomes unallowed at $t\sim \mathcal{O}(\beta)$. A way to avoid this
is to consider the microcanonical ensemble, where the black hole stays
allowable.


title:
FedQAS: Privacy-aware machine reading comprehension with federated
  learning

abstract:
  Machine reading comprehension (MRC) of text data is one important task in
Natural Language Understanding. It is a complex NLP problem with a lot of
ongoing research fueled by the release of the Stanford Question Answering
Dataset (SQuAD) and Conversational Question Answering (CoQA). It is considered
to be an effort to teach computers how to "understand" a text, and then to be
able to answer questions about it using deep learning. However, until now
large-scale training on private text data and knowledge sharing has been
missing for this NLP task. Hence, we present FedQAS, a privacy-preserving
machine reading system capable of leveraging large-scale private data without
the need to pool those datasets in a central location. The proposed approach
combines transformer models and federated learning technologies. The system is
developed using the FEDn framework and deployed as a proof-of-concept alliance
initiative. FedQAS is flexible, language-agnostic, and allows intuitive
participation and execution of local model training. In addition, we present
the architecture and implementation of the system, as well as provide a
reference evaluation based on the SQUAD dataset, to showcase how it overcomes
data privacy issues and enables knowledge sharing between alliance members in a
Federated learning setting.


title: Auditory Feedback for Standing Balance Improvement in Virtual Reality

abstract:
  Virtual Reality (VR) users often experience postural instability, i.e.,
balance problems, which could be a major barrier to universal usability and
accessibility for all, especially for persons with balance impairments. Prior
research has confirmed the imbalance effect, but minimal research has been
conducted to reduce this effect. We recruited 42 participants (with balance
impairments: 21, without balance impairments: 21) to investigate the impact of
several auditory techniques on balance in VR, specifically spatial audio,
static rest frame audio, rhythmic audio, and audio mapped to the center of
pressure (CoP). Participants performed two types of tasks - standing visual
exploration and standing reach and grasp. Within-subject results showed that
each auditory technique improved balance in VR for both persons with and
without balance impairments. Spatial and CoP audio improved balance
significantly more than other auditory conditions. The techniques presented in
this research could be used in future virtual environments to improve standing
balance and help push VR closer to universal usability.


title:
Robust Bayesian Inference for Simulator-based Models via the MMD
  Posterior Bootstrap

abstract:
  Simulator-based models are models for which the likelihood is intractable but
simulation of synthetic data is possible. They are often used to describe
complex real-world phenomena, and as such can often be misspecified in
practice. Unfortunately, existing Bayesian approaches for simulators are known
to perform poorly in those cases. In this paper, we propose a novel algorithm
based on the posterior bootstrap and maximum mean discrepancy estimators. This
leads to a highly-parallelisable Bayesian inference algorithm with strong
robustness properties. This is demonstrated through an in-depth theoretical
study which includes generalisation bounds and proofs of frequentist
consistency and robustness of our posterior. The approach is then assessed on a
range of examples including a g-and-k distribution and a toggle-switch model.


title: A Review of Sc-containing "Scandate" Thermionic Cathodes

abstract:
  Although thermionic emission has been studied for more than 100 years, recent
interest in novel electron devices for military and civilian use has led to a
surge in demand for cathodes with enhanced emission properties (e.g. higher
current density, more uniform emission, lower operating temperatures, or
extended in-service longevity). Sc-containing "scandate" cathodes have been
widely reported to exhibit superior emission properties compared to
previous-generation thermionic cathodes, including oxide, B-, and M-type
cathodes. Despite extensive study spanning several decades, the mechanism by
which the addition of Sc enhances cathode emission remains ambiguous, and
certain limitations -- non-uniform emission, low reproducibility, inconsistent
longevity -- continue to prevent widespread commercial integration of scandate
cathodes into electron devices. This review attempts to survey the literature
to-date addressing the fabrication, structure, and properties of scandate
cathodes, with particular attention to studies addressing the role of Sc in
enhancing emission.