title: Is the tautochrone curve unique?

abstract:
  The answer to this question is no. In fact, in addition to the solution first
obtained by Christiaan Huygens in 1658, given by the cycloid, we show that
there is an infinite number of tautochrone curves. With this goal, we start by
briefly reviewing an the problem of finding out the possible potential energies
that lead to periodic motions of a particle whose period is a given function of
its mechanical energy. There are infinitely many solutions, called sheared
potentials. As an interesting example, we show that a P\"oschl-Teller and the
one-dimensional Morse potentials are sheared relative to one another for
negative energies, clarifying why they share the same periods of oscillations
for their bounded solutions. We then consider periodic motions of a particle
sliding without friction over a track around its minimum under the influence of
an uniform gravitational field. After a brief historical survey of the
tautochrone problem we show that, given the period of oscillations, there is an
infinity of tracks which lead to the same periods. As a bonus, we show that
there are infinitely many tautochrones.


title:
Formation of the prebiotic molecule NH$_2$CHO on astronomical amorphous
  solid water surfaces: accurate tunneling rate calculations

abstract:
  Investigating how formamide forms in the interstellar medium is a hot topic
in astrochemistry, which can contribute to our understanding of the origin of
life on Earth. We have constructed a QM/MM model to simulate the hydrogenation
of isocyanic acid on amorphous solid water surfaces to form formamide. The
binding energy of HNCO on the ASW surface varies significantly between
different binding sites, we found values between $\sim$0 and 100 kJ mol$^{-1}$.
The barrier for the hydrogenation reaction is almost independent of the binding
energy, though. We calculated tunneling rate constants of H + HNCO
$\rightarrow$ NH$_2$CO at temperatures down to 103 K combining QM/MM with
instanton theory. Tunneling dominates the reaction at such low temperatures.
The tunneling reaction is hardly accelerated by the amorphous solid water
surface compared to the gas phase for this system, even though the activation
energy of the surface reaction is lower than the one of the gas-phase reaction.
Both the height and width of the barrier affect the tunneling rate in practice.
Strong kinetic isotope effects were observed by comparing to rate constants of
D + HNCO $\rightarrow$ NHDCO. At 103 K we found a KIE of 231 on the surface and
146 in the gas phase. Furthermore, we investigated the gas-phase reaction
NH$_2$ + H$_2$CO $\rightarrow$ NH$_2$CHO + H and found it unlikely to occur at
cryogenic temperatures. The data of our tunneling rate constants are expected
to significantly influence astrochemical models.


title: Isotropic and Dominating Mixed Lizorkin - Triebel Spaces - a Comparison

abstract:
  We shall compare isotropic Lizorkin-Triebel spaces with their counterparts of
dominating mixed smoothness.


title:
A New Generation of Cool White Dwarf Atmosphere Models Using Ab Initio
  Calculations

abstract:
  Due to their high photospheric density, cool helium-rich white dwarfs
(particularly DZ, DQpec and ultracool) are often poorly described by current
atmosphere models. As part of our ongoing efforts to design atmosphere models
suitable for all cool white dwarfs, we investigate how the ionization ratio of
heavy elements and the H$_2$-He collision-induced absorption (CIA) spectrum are
altered under fluid-like densities. For the conditions encountered at the
photosphere of cool helium-rich white dwarfs, our ab initio calculations show
that the ionization of most metals is inhibited and that the H$_2$-He CIA
spectrum is significantly distorted for densities higher than 0.1 g/cm$^3$.


title:
Sources of false positives and false negatives in the STATCHECK
  algorithm: Reply to Nuijten et al. (2016)

abstract:
  STATCHECK is an R algorithm designed to scan papers automatically for
inconsistencies between test statistics and their associated p values (Nuijten
et al., 2016). The goal of this comment is to point out an important and
well-documented flaw in this busily applied algorithm: It cannot handle
corrected p values. As a result, statistical tests applying appropriate
corrections to the p value (e.g., for multiple tests, post-hoc tests,
violations of assumptions, etc.) are likely to be flagged as reporting
inconsistent statistics, whereas papers omitting necessary corrections are
certified as correct. The STATCHECK algorithm is thus valid for only a subset
of scientific papers, and conclusions about the quality or integrity of
statistical reports should never be based solely on this program.


title: Strong arithmetic mirror symmetry and toric isogenies

abstract:
  We say a mirror pair of Calabi-Yau varieties exhibits strong arithmetic
mirror symmetry if the number of points on each variety over a finite field is
equivalent, modulo the order of that field. We search for strong mirror
symmetry in pencils of toric hypersurfaces generated using polar dual pairs of
reflexive polytopes. We characterize the pencils of elliptic curves where
strong arithmetic mirror symmetry arises, and provide experimental evidence
that the phenomenon generalizes to higher dimensions. We also provide
experimental evidence that pencils of K3 surfaces with the same Picard-Fuchs
equation have related point counts.


title: Rumor propagation with heterogeneous transmission in social networks

abstract:
  Rumor models consider that information transmission occurs with the same
probability between each pair of nodes. However, this assumption is not
observed in social networks, which contain influential spreaders. To overcome
this limitation, we assume that central individuals have a higher capacity of
convincing their neighbors than peripheral subjects. By extensive numerical
simulations we find that the spreading is improved in scale-free networks when
the transmission probability is proportional to PageRank, degree, and
betweenness centrality. In addition, the results suggest that the spreading can
be controlled by adjusting the transmission probabilities of the most central
nodes. Our results provide a conceptual framework for understanding the
interplay between rumor propagation and heterogeneous transmission in social
networks.


title: Towards phase-coherent caloritronics in superconducting circuits

abstract:
  The emerging field of phase-coherent caloritronics (from the Latin word
"calor", i.e., heat) is based on the possibility to control heat currents using
the phase difference of the superconducting order parameter. The goal is to
design and implement thermal devices able to master energy transfer with a
degree of accuracy approaching the one reached for charge transport by
contemporary electronic components. This can be obtained by exploiting the
macroscopic quantum coherence intrinsic to superconducting condensates, which
manifests itself through the Josephson and the proximity effect. Here, we
review recent experimental results obtained in the realization of heat
interferometers and thermal rectifiers, and discuss a few proposals for exotic
non-linear phase-coherent caloritronic devices, such as thermal transistors,
solid-state memories, phase-coherent heat splitters, microwave refrigerators,
thermal engines and heat valves. Besides being very attractive from the
fundamental physics point of view, these systems are expected to have a vast
impact on many cryogenic microcircuits requiring energy management, and
possibly lay the first stone for the foundation of electronic thermal logic.


title: Dedicated breast CT: effect of adaptive filtration on dose distribution

abstract:
  Purpose: The purpose of the work was experimental investigations of the
breast dose distributions with adaptive filtration. Adaptive filtration reduces
detector dynamic range and improves image quality. The adaptive filter with
predetermined shape is placed at the x-ray beam such that the x-ray intensity
at the detector surface is flat. However, adaptive filter alters the mean dose
to the breast, as well as volume distribution of the dose. Methods: The dose
was measured using a 14 cm diameter cylindrical acrylic breast phantom. An
acrylic adaptive filter was fabricated to match the 14 cm diameter of the
phantom. The dose was measured using ion chamber inserted into holes
distributed along the radius of the phantom from the center to the edge. The
radial distribution of dose was measured and fitted by an analytical function
and the volume distribution and mean value of dose was calculated. The
measurements were performed at 40, 60, 90, and 120 kVp tube voltages and 6.6
mGy air kerma. Results: The adaptive filter decreased mean breast dose by a
factor of 1.6-2.2 depending on the tube voltage. To maintain image quality, the
tube output was increased by these factors when adaptive filter was used. The
adaptive filter provided uniform volume distribution of dose at 40 kVp and 60
kVp tube voltages, but the distribution was non-uniform at 90 kVp and 120 kVp
tube voltages. Conclusion: While adaptive filtration helps with detector
dynamic range, CT number uniformity, and CT noise uniformity, the volume
non-uniformity of the dose with adaptive filter depends on tube voltage. On the
other hand, at the same average breast dose, volume non-uniformity of the dose
with adaptive filter was not higher that that without adaptive filter. The
results allowed also to determine necessary dose increase factor to compensate
for x-ray absorption in the adaptive filter.


title:
Effects of bulk and interfacial anharmonicity on thermal conductance at
  solid/solid interfaces

abstract:
  We present the results of classical molecular dynamics simulations to assess
the relative contributions to interfacial thermal conductance from inelastic
phonon processes at the interface and in the adjacent bulk materials. The
simulated system is the prototypical interface between argon and "heavy argon"
crystals, which enables comparison with many past computational studies. We run
simulations interchanging the Lennard-Jones potential with its harmonic
approximation to test the effect of anharmonicity on conductance. The results
confirm that the presence of anharmonicity is correlated with increasing
thermal conductance with temperature, which supports conclusions from prior
experimental and theoretical work. However, in the model Ar/heavy-Ar system,
anharmonic effects at the interface itself contribute a surprisingly small part
of the total thermal conductance. The larger fraction of the thermal
conductance at high temperatures arises from anharmonic effects away from the
interface. These observations are supported by comparisons of the spectral
energy density, which suggest that bulk anharmonic processes increase
interfacial conductance by thermalizing energy from modes with low transmission
to modes with high transmission.


title: Modified Gravity Explains Dark Matter?

abstract:
  We explore a new horizon of modified gravity from the viewpoint of the
particle physics. As a concrete example, we take the $F(R)$ gravity to raise a
question: can a scalar particle ("scalaron") derived from the $F(R)$ gravity be
a dark matter candidate? We place the limit on the parameter in a class of
$F(R)$ gravity model from the constraint on the scalaron as a dark matter. The
role of the screening mechanism and compatibility with the dark energy problem
are addressed.


title:
Empirical parametrizations of the resonance amplitudes based on the
  Siegert's theorem

abstract:
  We present parametrizations of the $\gamma^\ast N \to N(1535)1/2^-$,
$\gamma^\ast N \to N(1520)3/2^-$ and $\gamma^\ast N \to \Delta(1232)3/2^+$
transition amplitudes that are compatible with the analytic constraints at the
pseudothreshold (Siegert's theorem). The presented parametrizations also
provide a fair description of the experimental data. For the case of the
$\gamma^\ast N \to \Delta(1232)3/2^+$ transition, we discuss how the pion cloud
parametrizations of the electric and the Coulomb quadrupole form factors can be
adjusted according to the Siegert's theorem.


title:
Simplification of the Flux Function for a Higher-order Gas-kinetic
  Evolution Model

abstract:
  The higher-order gas-kinetic scheme for solving the Navier-Stokes equations
has been studied in recent years. In addition to the use of higher-order
reconstruction techniques, many terms are used in the Taylor expansion of the
gas distribution functions. Therefore, a large number of coefficients need to
be determined in the calculation of the time evolution of the gas distribution
function at cell interfaces. As a consequence, the higher-order flux function
takes much more computational time than that of a second-order gas-kinetic
scheme. This paper aims to simplify the evolution model by two steps. Firstly,
the coefficients related to the higher-order spatial and temporal derivatives
of a distribution function are redefined to reduce the computational cost.
Secondly, based on the physical analysis, some terms can be removed without
loss of accuracy. Through the simplifications, the computational efficiency of
the higher-order scheme is increased significantly. In addition, a
self-adaptive numerical viscosity is designed to minimize the necessary
numerical dissipation. Several numerical examples are tested to demonstrate the
accuracy and robustness of the current scheme.


title:
Towards a Characterization of Constant-Factor Approximable Finite-Valued
  CSPs

abstract:
  In this paper we study the approximability of (Finite-)Valued Constraint
Satisfaction Problems (VCSPs) with a fixed finite constraint language {\Gamma}
consisting of finitary functions on a fixed finite domain. An instance of VCSP
is given by a finite set of variables and a sum of functions belonging to
{\Gamma} and depending on a subset of the variables. Each function takes values
in [0, 1] specifying costs of assignments of labels to its variables, and the
goal is to find an assignment of labels to the variables that minimizes the
sum. A recent result of Ene et al. says that, under the mild technical
condition that {\Gamma} contains the equality relation, the basic LP relaxation
is optimal for constant-factor approximation for VCSP({\Gamma}) unless the
Unique Games Conjecture fails. Using the algebraic approach to the CSP, we give
new natural algebraic conditions for the finiteness of the integrality gap for
the basic LP relaxation of VCSP({\Gamma}). We also show how these algebraic
conditions can in principle be used to round solutions of the basic LP
relaxation, and how, for several examples that cover all previously known
cases, this leads to efficient constant-factor approximation algorithms.
Finally, we show that the absence of another algebraic condition leads to
NP-hardness of constant-factor approximation.


title: A study of the gamma* - f0(980) transition form factors

abstract:
  The spin wave function of the f0(980)-meson is constructed under the
assumption that the meson is dominantly a quark-antiquark state. This wave
function is used in a calculation of the gamma* - f0 transition form factors.
In the real-photon limit the results for the transverse form factor are
compared to the large momentum transfer data measured by the BELLE
collaboration recently. It turns out that, for the momentum-transfer range
explored by BELLE, the collinear approximation does not suffer, power
corrections to it, modeled as quark transverse moment effects, seem to be
needed. Mixing of the f0 with the sigma(500) is also briefly discussed.


title:
A regularized Lagrange-mesh method based on an orthonormal
  Lagrange-Laguerre basis

abstract:
  The Lagrange-mesh method is an approximate variational approach having the
form of a mesh calculation because of the use of a Gauss quadrature. Although
this method provides accurate results in many problems with small number of
mesh points, its accuracy can be strongly reduced by the presence of
singularities in the potential term. In this paper, a new regularized
Lagrange-Laguerre mesh, based on \textit{exactly} orthonormal Lagrange
functions, is devised. It is applied to two solvable radial potentials: the
harmonic-oscillator and Coulomb potentials. In spite of the singularities of
the Coulomb and centrifugal potentials, accurate bound-state energies are
obtained for all partial waves. The analysis of these results and a comparison
with other Lagrange-mesh calculations lead to a simple rule to predict in which
cases a singularity does induce or not a significant loss of accuracy in
Lagrange-mesh calculations. In addition, the Lagrange-Laguerre-mesh approach is
applied to the evaluation of phase shifts via integral relations. Small numbers
of mesh points suffice to provide very accurate results.


title: Engineering Bright Matter-Wave Solitons of Dipolar Condensates

abstract:
  We present a comprehensive analysis of the form and interaction of dipolar
bright solitons across the full parameter space afforded by dipolar
Bose-Einstein condensates, revealing the rich behaviour introduced by the
non-local nonlinearity. Working within an effective one-dimensional
description, we map out the existence of the soliton solutions and show three
collisional regimes: free collisions, bound state formation and soliton fusion.
Finally, we examine the solitons in their full three-dimensional form through a
variational approach; along with regimes of instability to collapse and runaway
expansion, we identify regimes of stability which are accessible to current
experiments.


title: Segmentation of Coronal Holes Using Active Contours Without Edges

abstract:
  An application of active contours without edges is presented as an efficient
and effective means of extracting and characterizing coronal holes. Coronal
holes are regions of low-density plasma on the Sun with open magnetic field
lines. As the source of the fast solar wind, the detection and characterization
of these regions is important for both testing theories of their formation and
evolution and from a space weather perspective. Coronal holes are detected in
full disk extreme ultraviolet (EUV) images of the corona obtained with the
Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA). The proposed
method detects coronal boundaries without determining any fixed intensity value
in the data. Instead, the active contour segmentation employs an
energy-minimization in which coronal holes are assumed to have more homogeneous
intensities than surrounding active regions and quiet Sun. The segmented
coronal holes tend to correspond to unipolar magnetic regions, are consistent
with concurrent solar wind observations, and qualitatively match the coronal
holes segmented by other methods. The means to identify a coronal hole without
specification of a final intensity threshold may allow this algorithm to be
more robust across multiple datasets, regardless of data type, resolution, and
quality.


title:
Structure and dynamics of liquid CS2: Going from ambient to elevated
  pressure conditions

abstract:
  Molecular dynamics simulation studies were performed to investigate the
structural and dynamic properties of liquid carbon disulfide from ambient to
elevated pressure conditions. The results obtained have revealed structural
changes at high pressures, which are related to the more dense packing of the
molecules inside the first solvation shell. The calculated neutron and X-Ray
structure factors have been compared with available experimental diffraction
data, also revealing the pressure effects on the short-range structure of the
liquid. The pressure effects on the translational, reorientational and
residence dynamics are very strong, revealing a significant slowing down when
going from ambient pressure to 1.2 GPa. The translational dynamics of the
linear CS2 molecules have been found to be more anisotropic at elevated
pressures, where cage effects and librational motions are reflected on the
shape of the calculated time correlation functions and their corresponding
spectral densities.


title: Thin layered drawing media probed by THz time-domain spectroscopy

abstract:
  Dry and wet drawing materials were investigated by THz time-domain
spectroscopy in transmission mode. Carbon-based and iron-gall inks have been
studied, some prepared following ancient recipes and others using current
synthetic materials; a commercial ink was studied as well. We measured the THz
signals on thin film of liquid inks deposited on polyethylene pellicles,
comparing the results with the thick pellets of dried inks blended with
polyethylene powder. This study required the implementation of a new
experimental method and data analysis procedure able to provide a reliable
extraction of the material transmission parameters from a structured sample
composed of thin layers, down to thickness of few tens of micrometers. THz
measurements on thin ink layers enabled the determination of both the
absorption and the refractive index in an absolute scale in the 0.1 - 3 THz
range, as well as the layer thickness. THz spectroscopic features of a paper
sheet dyed by one of the iron-gall inks were also investigated. Our results
showed that THz time-domain spectroscopy enables to discriminate the various
inks on different supports, including the application on paper, together with a
proper determination of the absorption coefficients and indices of refraction.


title:
Triplet pair amplitude in a trapped $s$-wave superfluid Fermi gas with
  broken spin rotation symmetry. II. Three dimensional continuum case

abstract:
  We extend our recent work [Y. Endo et. al., Phys. Rev. 92, 023610 (2015)] for
a parity-mixing effect in a model two-dimensional lattice fermions to a
realistic three-dimensional ultracold Fermi gas. Including effects of broken
local spatial inversion symmetry by a trap potential within the framework of
the real-space Bogoliubov-de Gennes theory at $T=0$, we point out that an
odd-parity $p$-wave Cooper-pair amplitude is expected to have already been
realized in previous experiments on an (even-parity) $s$-wave superfluid Fermi
gas with spin imbalance. This indicates that, when one suddenly changes the
$s$-wave pairing interaction to an appropriate $p$-wave one by using a Feshbach
technique in this case, a non-vanishing $p$-wave superfluid order parameter is
immediately obtained, which is given by the product of the $p$-wave interaction
and the $p$-wave pair amplitude that has already been induced in the
spin-imbalanced $s$-wave superfluid Fermi gas. Thus, by definition, the system
is in the $p$-wave superfluid state, at least just after this manipulation.
Since the achievement of a $p$-wave superfluid state is one of the most
exciting challenges in cold Fermi gas physics, our results may provide an
alternative approach to this unconventional pairing state. In addition, since
the parity-mixing effect cannot be explained as far as one deals with a trap
potential in the local density approximation (LDA), it is considered as a
crucial example which requires us to go beyond LDA.


title: Vacuum alignment and radiatively induced Fermi scale

abstract:
  We extend the discussion about vacuum misalignment by quantum corrections in
models with composite pseudo-Goldstone Higgs boson to renormalisable models
with elementary scalars. As a concrete example, we propose a framework, where
the hierarchy between the unification and the Fermi scale emerges radiatively.
This scenario provides an interesting link between the unification and Fermi
scale physics.


title: Small f-vectors of 3-spheres and of 4-polytopes

abstract:
  We present a new algorithmic approach that can be used to determine whether a
given quadruple $(f_0,f_1,f_2,f_3)$ is the f-vector of any convex 4-dimensional
polytope. By implementing this approach, we classify the f-vectors of
4-polytopes in the range $f_0+f_3\le22$.
  In particular, we thus prove that there are f-vectors of cellular 3-spheres
with the intersection property that are not f-vectors of any convex
4-polytopes, thus answering a question that may be traced back to the works of
Steinitz (1906/1922). In the range $f_0+f_3\le22$, there are exactly three such
f-vectors with $f_0\le f_3$, namely $(10,32,33,11)$, $(10,33,35,12)$, and
$(11,35,35,11)$.


title: Supersymmetric versions of the Fokas-Gel'fand formula for immersion

abstract:
  In this paper, we construct and investigate two supersymmetric versions of
the Fokas-Gel'fand formula for the immersion of 2D surfaces associated with a
supersymmetric integrable system. The first version involves an infinitesimal
deformation of the zero-curvature condition and the linear spectral problem
associated with this system. This deformation leads the surfaces to be
represented in terms of a bosonic supermatrix immersed in a Lie superalgebra.
The second supersymmetric version is obtained by using a fermionic parameter
deformation to construct surfaces expressed in terms of a fermionic supermatrix
immersed in a Lie superalgebra. For both extensions, we provide a geometrical
characterization of deformed surfaces using the super Killing form as an inner
product and a super moving frame formalism. The theoretical results are applied
to the supersymmetric sine-Gordon equation in order to construct super soliton
surfaces associated with five different symmetries. We find integrated forms of
these surfaces which represent constant Gaussian curvature surfaces and
nonlinear Weingarten-type surfaces.


title:
Applications of Online Deep Learning for Crisis Response Using Social
  Media Information

abstract:
  During natural or man-made disasters, humanitarian response organizations
look for useful information to support their decision-making processes. Social
media platforms such as Twitter have been considered as a vital source of
useful information for disaster response and management. Despite advances in
natural language processing techniques, processing short and informal Twitter
messages is a challenging task. In this paper, we propose to use Deep Neural
Network (DNN) to address two types of information needs of response
organizations: 1) identifying informative tweets and 2) classifying them into
topical classes. DNNs use distributed representation of words and learn the
representation as well as higher level features automatically for the
classification task. We propose a new online algorithm based on stochastic
gradient descent to train DNNs in an online fashion during disaster situations.
We test our models using a crisis-related real-world Twitter dataset.


title: Progress towards a universal family of UV-IR extinction laws

abstract:
  We present our progress on the study of extinction laws along three diferent
lines. [a] We compare how well different families of extinction laws fit
existing photometric data for Galactic sightlines and we find that the Ma\'iz
Apell\'aniz et al. (2014) family provides better results than those of Cardelli
et al. (1989) or Fitzpatrick (1999). [b] We describe the HST/STIS
spectrophotometry in the 1700-10 200 Angstrom range that we are obtaining for
several tens of sightlines in 30 Doradus with the purpose of deriving an
improved wavelength-detailed family of extinction laws. [c] We present the
study we are conducting on the behavior of the extinction law in the infrared
by combining 2MASS and WISE photometry with Spitzer and ISO spectrophotometry.


title: On $(H,\widetilde{H})$-harmonic Maps between pseudo-Hermitian manifolds

abstract:
  In this paper, we investigate critical maps of the horizontal energy
functional $E_{H,\widetilde{H}}(f)$ for maps between two pseudo-Hermitian
manifolds $(M^{2m+1},H(M),J,\theta )$ and $(N^{2n+1},\widetilde{H}(N),
\widetilde{J},\widetilde{\theta})$. These critical maps are referred to as
$(H,\widetilde{H})$-harmonic maps. We derive a CR Bochner formula for the
horizontal energy density $|df_{H, \widetilde{H}}|^{2}$, and introduce a
Paneitz type operator acting on maps to refine the Bochner formula. As a
result, we are able to establish some Bochner type theorems for
$(H,\widetilde{H})$-harmonic maps. We also introduce
$(H,\widetilde{H})$-pluriharmonic, $(H,\widetilde{H})$-holomorphic maps between
these manifolds, which provide us examples of $(H,\widetilde{H})$-harmonic
maps. Moreover, a Lichnerowicz type result is established to show that foliated
$(H,\widetilde{ H})$-holomorphic maps are actually minimizers of
$E_{H,\widetilde{H}}(f)$ in their foliated homotopy classes. We also prove some
unique continuation results for characterizing either horizontally constant
maps or foliated $(H,\widetilde{H})$-holomorphic maps. Furthermore,
Eells-Sampson type existence results for $(H,\widetilde{H})$-harmonic maps are
established if both manifolds are compact Sasakian and the target is regular
with non-positive horizontal sectional curvature. Finally, we give a foliated
rigidity result for $(H,\widetilde{H})$-harmonic maps and Siu type strong
rigidity results for compact regular Sasakian manifolds with either strongly
negative horizontal curvature or adequately negative horizontal curvature.


title: Experimental observation of optical Weyl points

abstract:
  Weyl fermions are hypothetical two-component massless relativistic particles
in three-dimensional (3D) space, proposed by Hermann Weyl in 1929. Their
band-crossing points, called 'Weyl points,' carry a topological charge and are
therefore highly robust. There has been much excitement over recent
observations of Weyl points in microwave photonic crystals and the semimetal
TaAs. Here, we report on the first experimental observation of Weyl points of
light at optical frequencies. These are also the first observations of
'type-II' Weyl points for photons, which have strictly positive group velocity
along one spatial direction. We use a 3D structure consisting of laser-written
waveguides, and show the presence of type-II Weyl points by (1) observing
conical diffraction along one axis when the frequency is tuned to the Weyl
point; and (2) observing the associated Fermi arc surface states. The
realization of Weyl points at optical frequencies allow these novel
electromagnetic modes to be further explored in the context of linear,
nonlinear, and quantum optics.


title:
Dependence of the maximal superconducting current on resonance frequency
  in shunted Josephson junction

abstract:
  We have investigated the phase dynamics and IV-characteristics of shunted
Josephson junctions coupled to an $LC$ circuit. When the Josephson frequency
$\omega_J$ is close to the eigen frequency $\omega_{rc}$ of the coupled
resonance circuit, the IV-characteristic demonstrates an additional
$rc$-branch. We have investigated the features of the $rc$-branch and of the
superconducting current component for different values of the resonance
frequency. It has been found that the maximal value of the superconducting
current depends on the resonance frequency and that it increases when the end
point of the $rc$-branch approaches the critical current. The dependence of the
maximal superconducting current on the resonance frequency at different values
of the dissipation parameter is peculiar, for the optimized maximum appears to
be independent of the system parameters within $1\%$.


title: Koszul calculus for N-homogeneous algebras

abstract:
  We extend the Koszul calculus defined on quadratic algebras by Berger, Lambre
and Solotar, to N-homogeneous algebras. When N>2, the Koszul cup and cap
products are defined by specific expressions, and they are compatible with the
Koszul differentials, providing associative products on (co)homology classes.
The N-Koszul calculus is calculated for the truncated polynomial algebras.


title: Critical fluctuations in models with van der Waals interactions

abstract:
  Particle number fluctuations are considered within the van der Waals (VDW)
equation, which contains both attractive (mean-field) and repulsive
(eigenvolume) interactions. The VDW equation is used to calculate the scaled
variance of particle number fluctuations in generic Boltzmann VDW system and in
nuclear matter. The strongly intensive measures $\Delta[E^*,N]$ and
$\Sigma[E^*,N]$ of the particle number and excitation energy fluctuations are
also considered, and, similarly, show singular behavior near the critical
point. The $\Delta[E^*,N]$ measure is shown to attain both positive and
negative values in the vicinity of critical point. Based on universality
argument, similar behavior is expected to occur in the vicinity of the QCD
critical point.


title: Super-Activation of Quantum Steering

abstract:
  We consider Einstein-Podolsky-Rosen steering in the regime where the parties
can perform collective measurements on many copies of a given shared entangled
state. We derive a simple and efficient condition for guaranteeing that an
entangled state is $k$-copy steerable. In particular we show that any two-qubit
and qubit-qutrit entangled states is $k$-copy steerable. This allows us to
discuss the effect of super-activation of steering, whereby an entangled state
that is unsteerable (i.e., admits a local hidden state model) in the one-copy
regime becomes $k$-copy steerable. We provide examples with few copies and low
dimensions. Our results give evidence that entanglement and steering could
become equivalent in the multi-copy regime.


title:
Herschel-ATLAS: Revealing dust build-up and decline across gas, dust and
  stellar mass selected samples: I. Scaling relations

abstract:
  We present a study of the dust, stars and atomic gas (HI) in an HI-selected
sample of local galaxies (z<0.035) in the Herschel Astrophysical Terahertz
Large Area Survey (H-ATLAS) fields. This HI-selected sample reveals a
population of very high gas fraction (>80 per cent), low stellar mass sources
that appear to be in the earliest stages of their evolution. We compare this
sample with dust and stellar mass selected samples to study the dust and gas
scaling relations over a wide range of gas fraction (proxy for evolutionary
state of a galaxy). The most robust scaling relations for gas and dust are
those linked to NUV-r (SSFR) and gas fraction, these do not depend on sample
selection or environment. At the highest gas fractions, our additional sample
shows the dust content is well below expectations from extrapolating scaling
relations for more evolved sources, and dust is not a good tracer of the gas
content. The specific dust mass for local galaxies peaks at a gas fraction of
~75 per cent. The atomic gas depletion time is also longer for high gas
fraction galaxies, opposite to the trend found for molecular gas depletion
timescale. We link this trend to the changing efficiency of conversion of HI to
H2 as galaxies increase in stellar mass surface density as they evolve.
Finally, we show that galaxies start out barely obscured and increase in
obscuration as they evolve, yet there is no clear and simple link between
obscuration and global galaxy properties.


title:
Interpolatory methods for $\mathcal{H}_\infty$ model reduction of
  multi-input/multi-output systems

abstract:
  We develop here a computationally effective approach for producing
high-quality $\mathcal{H}_\infty$-approximations to large scale linear
dynamical systems having multiple inputs and multiple outputs (MIMO). We extend
an approach for $\mathcal{H}_\infty$ model reduction introduced by Flagg,
Beattie, and Gugercin for the single-input/single-output (SISO) setting, which
combined ideas originating in interpolatory $\mathcal{H}_2$-optimal model
reduction with complex Chebyshev approximation. Retaining this framework, our
approach to the MIMO problem has its principal computational cost dominated by
(sparse) linear solves, and so it can remain an effective strategy in many
large-scale settings. We are able to avoid computationally demanding
$\mathcal{H}_\infty$ norm calculations that are normally required to monitor
progress within each optimization cycle through the use of "data-driven"
rational approximations that are built upon previously computed function
samples. Numerical examples are included that illustrate our approach. We
produce high fidelity reduced models having consistently better
$\mathcal{H}_\infty$ performance than models produced via balanced truncation;
these models often are as good as (and occasionally better than) models
produced using optimal Hankel norm approximation as well. In all cases
considered, the method described here produces reduced models at far lower cost
than is possible with either balanced truncation or optimal Hankel norm
approximation.


title:
The N/D method with non-perturbative left-hand-cut discontinuity and the
  $^1S_0$ $NN$ partial wave

abstract:
  In this letter we deduce an integral equation that allows to calculate the
exact left-hand-cut discontinuity for an uncoupled $S$-wave partial-wave
amplitude in potential scattering for a given finite-range potential. The
results obtained from the $N/D$ method for the partial-wave amplitude are
rigorous, since now the discontinuities along the left-hand cut and right-hand
cut are exactly known. This solves the open question with respect to the $N/D$
method and the effect on the final result of the non-perturbative iterative
diagrams in the evaluation of $\Delta(A)$. A big advantage of the method is
that short-range physics (corresponding to integrated out degrees of freedom
within low-energy Effective Field Theory) does not contribute to $\Delta(A)$
and it manifests through the extra subtractions that are implemented within the
method. We show the equivalence of the $N/D$ method and the Lippmann-Schwinger
(LS) equation for a nonsingular $^1S_0$ $NN$ potential (Yukawa potential). The
equivalence between the $N/D$ method with one extra subtraction and the LS
equation renormalized with one counter term or with subtractive renormalization
also holds for the singular attractive higher-order ChPT potentials. The $N/D$
method also allows to evaluate partial-wave amplitudes with a higher number of
extra subtractions, that we fix in terms of shape parameters within the
effective range expansion. The result at NNLO shows that the $^1S_0$ phase
shifts might be accurately described once the electromagnetic and charge
symmetry breaking terms are included. Our present results can be extended to
higher partial waves as well as to coupled channel scattering.


title: Superconductivity and hybrid soft modes in TiSe$_2$

abstract:
  The competition between superconductivity and other ground states of solids
is one of the challenging topics in condensed matter physics. Apart from
high-temperature superconductors [1,2] this interplay also plays a central role
in the layered transition-metal dichalcogenides, where superconductivity is
stabilized by suppressing charge-density-wave order to zero temperature by
intercalation [3] or applied pressure [4-7]. 1T-TiSe$_2$ forms a prime example,
featuring superconducting domes on intercalation as well as under applied
pressure. Here, we present high energy-resolution inelastic x-ray scattering
measurements of the CDW soft phonon mode in intercalated Cu$_x$TiSe$_2$ and
pressurized 1T-TiSe$_2$ along with detailed ab-initio calculations for the
lattice dynamical properties and phonon-mediated superconductivity. We find
that the intercalation-induced superconductivity can be explained by a solely
phonon-mediated pairing mechanism, while this is not possible for the
superconducting phase under pressure. We argue that a hybridization of phonon
and exciton modes in the pairing mechanism is necessary to explain the full
observed temperature-pressure-intercalation phase diagram. These results
indicate that 1T-TiSe$_2$ under pressure is close to the elusive state of the
excitonic insulator.


title:
Experimental demonstration of phase bistability in a broad area optical
  oscillator with injected signal

abstract:
  We demonstrate experimentally that a broad area laser-like optical oscillator
(a nondegenerate photorefractive oscillator) with structured injected signal
displays two-phase patterns. The technique (G. J. de Valc\'arcel and K.
Staliunas, Phys. Rev. Lett. (105), 054101 (2010)) consists in spatially
modulating the injection, so that its phase alternates periodically between two
opposite values, i.e. differing by pi


title: Electronic quantum optics beyond the integer quantum Hall effect

abstract:
  The analog of two seminal quantum optics experiments are considered in a
condensed matter setting with single electron sources injecting electronic wave
packets on edge states coupled through a quantum point contact. When only one
electron is injected, the measurement of noise correlations at the output of
the quantum point contact corresponds to the Hanbury-Brown and Twiss setup.
When two electrons are injected on opposite edges, the equivalent of the
Hong-Ou-Mandel collision is achieved, exhibiting a dip as in the coincidence
measurements of quantum optics. The Landauer-Buttiker scattering theory is used
to first review these phenomena in the integer quantum Hall effect, next, to
focus on two more exotic systems: edge states of two dimensional topological
insulators, where new physics emerges from time reversal symmetry and three
electron collisions can be achieved; and edges states of a hybrid
Hall/superconducting device, which allow to perform electron quantum optics
experiments with Bogoliubov quasiparticles.


title: DeepAlgebra - an outline of a program

abstract:
  We outline a program in the area of formalization of mathematics to automate
theorem proving in algebra and algebraic geometry. We propose a construction of
a dictionary between automated theorem provers and (La)TeX exploiting syntactic
parsers. We describe its application to a repository of human-written facts and
definitions in algebraic geometry (The Stacks Project). We use deep learning
techniques.


title:
A Game-Theoretic Approach to Robust Fusion and Kalman Filtering Under
  Unknown Correlations

abstract:
  This work addresses the problem of fusing two random vectors with unknown
cross-correlations. We present a formulation and a numerical method for
computing the optimal estimate in the minimax sense. We extend our formulation
to linear measurement models that depend on two random vectors with unknown
cross-correlations. As an application we consider the problem of decentralized
state estimation for a group of agents. The proposed estimator takes
cross-correlations into account while being less conservative than the widely
used Covariance Intersection. We demonstrate the superiority of the proposed
method compared to Covariance Intersection with numerical examples and
simulations within the specific application of decentralized state estimation
using relative position measurements.


title:
Engineering chiral light--matter interaction in photonic crystal
  waveguides with slow light

abstract:
  We design photonic crystal waveguides with efficient chiral light--matter
interfaces that can be integrated with solid-state quantum emitters. By using
glide-plane-symmetric waveguides, we show that chiral light-matter interaction
can exist even in the presence of slow light with slow-down factors of up to
$100$ and therefore the light--matter interaction exhibits both strong Purcell
enhancement and chirality. This allows for near-unity directional
$\beta$-factors for a range of emitter positions and frequencies. Additionally,
we design an efficient mode adapter to couple light from a standard nanobeam
waveguide to the glide-plane symmetric photonic crystal waveguide. Our work
sets the stage for performing future experiments on a solid-state platform.


title:
Total Internal Reflection for Effectively Transparent Solar Cell
  Contacts

abstract:
  A new strategy for eliminating photocurrent losses due to the metal contacts
on the front of a solar cell was proposed, simulated, and tested. By placing
triangular cross-section lines of low refractive index on top of the contacts,
total-internal reflection at the interface of the low-index triangles and the
surrounding material can direct light away from the metal and into the
photoactive absorber. Simulations indicated that losses can be eliminated for
any incident angle, and that yearly energy production improvements commensurate
with the metallized area are possible. Proof of principle experiments were
carried out to eliminate the reflective losses of a commercial solar cell's
busbar contact. Spatially resolved laser beam induced current measurements
demonstrated that reflection losses due to the busbar were reduced by voids
with triangular cross-section.


title:
Optical signatures of low spin Fe3+: a new probe for the spin state of
  bridgmanite and post-perovskite

abstract:
  Iron spin transition directly affects properties of lower mantle minerals and
can thus alter geophysical and geochemical characteristics of the deep Earth.
While the spin transition in ferropericlase has been vigorously established at
P ~ 60 GPa and 300 K, experimental evidence for spin transitions in other
rock-forming minerals, such as bridgmanite and post-perovskite, remains
controversial. Multiple valence, spin, and coordination states of iron in
bridgmanite and post-perovskite are difficult to resolve with conventional
spin-probing techniques. Optical spectroscopy, on the other hand, is sensitive
to high/low spin ferrous/ferric iron at different sites; thus, it can be a
powerful probe for spin transitions. Here we establish the optical signature of
low spin Fe3+O6, a plausible low spin unit in bridgmanite and post-perovskite,
by optical absorption experiments in diamond anvil cells. We show that the
optical absorption of Fe3+O6 in NAL (new aluminous phase) is very sensitive to
the iron spin state and represents a model behavior of bridgmanite and
post-perovskite in the deep lower mantle across a spin transition.
Specifically, an absorption band centered at ~ 19000 cm-1 is characteristic of
the 2T2g to 2T1g (2A2g) transition in low spin Fe3+ in NAL at 40 GPa. This new
spectroscopic information constrains the crystal field splitting energy of low
spin Fe3+ to ~ 22200 cm-1 which we also independently confirm by our
first-principles calculations. Together with available information on the
electronic structure of Fe3+O6-compounds, we constrain the spin-pairing energy
of Fe3+ in an octahedral field to ~ 20000-23000 cm-1. This implies that
octahedrally-coordinated Fe3+ in bridgmanite is low spin at P > ~ 40 GPa.


title:
Hadamard states for a scalar field in anti-de Sitter spacetime with
  arbitrary boundary conditions

abstract:
  We consider a real, massive scalar field on ${\rm PAdS}_{d+1}$, the
Poincar\'e domain of the $(d+1)$-dimensional anti-de Sitter (AdS) spacetime. We
first determine all admissible boundary conditions that can be applied on the
conformal boundary, noting that there exist instances where "bound states"
solutions are present. Then, we address the problem of constructing the
two-point function for the ground state satisfying those boundary conditions,
finding ultimately an explicit closed form. In addition, we investigate the
singularities of the resulting two-point functions, showing that they are
consistent with the requirement of being of Hadamard form in every globally
hyperbolic subregion of ${\rm PAdS}_{d+1}$ and proposing a new definition of
Hadamard states which applies to ${\rm PAdS}_{d+1}$.


title: An Efficient High-Dimensional Sparse Fourier Transform

abstract:
  We propose RSFT, which is an extension of the one dimensional Sparse Fourier
Transform algorithm to higher dimensions in a way that it can be applied to
real, noisy data. The RSFT allows for off-grid frequencies. Furthermore, by
incorporating Neyman-Pearson detection, the frequency detection stages in RSFT
do not require knowledge of the exact sparsity of the signal and are more
robust to noise. We analyze the asymptotic performance of RSFT, and study the
computational complexity versus the worst case signal SNR tradeoff. We show
that by choosing the proper parameters, the optimal tradeoff can be achieved.
We discuss the application of RSFT on short range ubiquitous radar signal
processing, and demonstrate its feasibility via simulations.


title: Comparison results for proper multisplittings of rectangular matrices

abstract:
  The least square solution of minimum norm of a rectangular linear system of
equations can be found out iteratively by using matrix splittings. However, the
convergence of such an iteration scheme arising out of a matrix splitting is
practically very slow in many cases. Thus, works on improving the speed of the
iteration scheme have attracted great interest. In this direction, comparison
of the rate of convergence of the iteration schemes produced by two matrix
splittings is very useful. But, in the case of matrices having many matrix
splittings, this process is time-consuming. The main goal of the current
article is to provide a solution to the above issue by using proper
multisplittings. To this end, we propose a few comparison theorems for proper
weak regular splittings and proper nonnegative splittings first. We then derive
convergence and comparison theorems for proper multisplittings with the help of
the theory of proper weak regular splittings.


title:
A novel and effective scoring scheme for structure classification and
  pairwise similarity measurement

abstract:
  Protein tertiary structure defines its functions, classification and binding
sites. Similar structural characteristics between two proteins often lead to
the similar characteristics thereof. Determining structural similarity
accurately in real time is a crucial research issue. In this paper, we present
a novel and effective scoring scheme that is dependent on novel features
extracted from protein alpha carbon distance matrices. Our scoring scheme is
inspired from pattern recognition and computer vision. Our method is
significantly better than the current state of the art methods in terms of
family match of pairs of protein structures and other statistical measurements.
The effectiveness of our method is tested on standard benchmark structures. A
web service is available at http://research.buet.ac.bd:8080/Comograd/score.html
where you can get the similarity measurement score between two protein
structures based on our method.


title:
Magnetic state of Nb(1-7nm)/Cu$_{30}$Ni$_{70}$(6nm) superlattices
  revealed by Polarized Neutron Reflectometry and SQUID magnetometry

abstract:
  We report results of a magnetic characterization of
[Cu$_{30}$Ni$_{70}$(6nm)]$_{20}$ (x=1-7nm) superlattices using Polarized
Neutron Reflectometry (PNR) and SQUID magnetometry. The study has shown that
the magnetic moment of the structures growths almost linearly from H = 0 to
H$_{sat}$ = 1.3kOe which is an indirect evidence of antiferromagnetic (AF)
coupling of the magnetic moments in neighbouring layers. PNR, however, did not
detect any in-plane AF coupling. Taking into account the out-of-plane easy axis
of the Cu$_{30}$Ni$_{70}$ layers, this may mean that only the out-of-plane
component of the magnetic moments are AF coupled.


title:
SMILY: A numerical algorithm to decompose unitary representations and
  compute Clebsch-Gordan coefficients

abstract:
  A numerical algorithm that computes the decomposition of a finite-dimensional
unitary reducible representation of a compact Lie group is presented. The
algorithm, inspired by notions of quantum mechanics, generates two adapted
states and, after appropriate algebraic manipulations, returns the block matrix
structure of the representation in terms of its irreducible components. It also
provides an adapted orthonormal basis. The algorithm can be used to compute the
Clebsch--Gordan coefficients of the tensor product of irreducible
representations of a given compact Lie group. The performance of the algorithm
is tested on various examples: the decomposition of the regular representation
of finite groups and the computation of the Clebsch--Gordan coefficients of
tensor products of representations of SU(2).


title:
Homing in for New Year: impact parameters and pre-impact orbital
  evolution of meteoroid 2014 AA

abstract:
  On 2008 October 7, small asteroid 2008 TC3 turned itself into the parent body
of the first meteor ever to be predicted before entering the Earth's
atmosphere. Over five years later, the 2014 AA event became the second instance
of such an occurrence. The uncertainties associated with the pre-impact orbit
of 2008 TC3 are relatively small because thousands of observations were made
during the hours preceding the actual meteor airburst. In sharp contrast, 2014
AA was only observed seven times before impact and consequently its trajectory
is somewhat uncertain. Here, we present a recalculation of the impact
parameters -location and timing- of this meteor based on infrasound recordings.
The new values and their uncertainties together with Monte Carlo and N-body
techniques, are applied to obtain an independent determination of the
pre-impact orbit of 2014 AA. Our orbital solution is used to investigate the
possible presence of known near-Earth objects (NEOs) moving in similar orbits.
Prior to impact, 2014 AA was subjected to a web of overlapping secular
resonances and it followed a path similar to those of 2011 GJ3, 2011 JV10, 2012
DJ54, and 2013 NJ4. NEOs in this transient group have their orbits controlled
by close encounters with the Earth-Moon system at perihelion and Mars at
aphelion, perhaps constituting a dynamical family. Extensive comparison with
other studies is also presented.


title: Gaps between equations and experiments in quantum cryptography

abstract:
  Proofs of the security of quantum key distribution are propositions about
models written in the mathematical language of quantum mechanics, and the issue
is the linking of such models to actual devices in an experiment on security.
To explore this issue, we adapt Wittgenstein's method of language games to view
quantum language in its application to experimental activity involving
transmitting and receiving devices.
  We sketch concepts with which to think about models in relation to
experiments, without assuming the experiments accord with any model included is
a concept of one quantum-mechanical model enveloping another. For any model
that agrees with given experimental results and implies the security of a key,
there is an enveloping model that agrees with the same results while denying
that security. As a result there is a gap between equations and the behavior
recorded from devices in an experiment, a gap bridged only by resort to
something beyond the reach of logic and measured data, well named by the word
guesswork.
  While this recognition of guesswork encourages eavesdropping, a related
recognition of guesswork in the design of feedback loops can help a transmitter
and receiver to reduce their vulnerability to eavesdropping.


title:
The Mass Function of Unprocessed Dark Matter Halos and Merger Tree
  Branching Rates

abstract:
  A common approach in semi-analytic modeling of galaxy formation is to
construct Monte Carlo realizations of merger histories of dark matter halos
whose masses are sampled from a halo mass function. Both the mass function
itself, and the merger rates used to construct merging histories are calibrated
to N-body simulations. Typically, "backsplash" halos (those which were once
subhalos within a larger halo, but which have since moved outside of the halo)
are counted in both the halo mass function, and in the merger rates (or,
equivalently, progenitor mass functions). This leads to a double-counting of
mass in Monte Carlo merger histories which will bias results relative to N-body
results. We measure halo mass functions and merger rates with this
double-counting removed in a large, cosmological N-body simulation with
cosmological parameters consistent with current constraints. Furthermore, we
account for the inherently noisy nature of N-body halo mass estimates when
fitting functions to N-body data, and show that ignoring these errors leads to
a significant systematic bias given the precision statistics available from
state-of-the-art N-body cosmological simulations.


title: Approximation Algorithms for Stochastic k-TSP

abstract:
  We consider the stochastic $k$-TSP problem where rewards at vertices are
random and the objective is to minimize the expected length of a tour that
collects reward $k$. We present an adaptive $O(\log k)$-approximation
algorithm, and a non-adaptive $O(\log^2k)$-approximation algorithm. We also
show that the adaptivity gap of this problem is between $e$ and $O(\log^2k)$.


title: Large-Scale Tides in General Relativity

abstract:
  Density perturbations in cosmology, i.e. spherically symmetric adiabatic
perturbations of a Friedmann-Lema\^itre-Robertson-Walker (FLRW) spacetime, are
locally exactly equivalent to a different FLRW solution, as long as their
wavelength is much larger than the sound horizon of all fluid components. This
fact is known as the "separate universe" paradigm. However, no such relation is
known for anisotropic adiabatic perturbations, which correspond to an FLRW
spacetime with large-scale tidal fields. Here, we provide a closed, fully
relativistic set of evolutionary equations for the nonlinear evolution of such
modes, based on the conformal Fermi (CFC) frame. We show explicitly that the
tidal effects are encoded by the Weyl tensor, and are hence entirely different
from an anisotropic Bianchi I spacetime, where the anisotropy is sourced by the
Ricci tensor. In order to close the system, certain higher derivative terms
have to be dropped. We show that this approximation is equivalent to the local
tidal approximation of Hui and Bertschinger (1995). We also show that this very
simple set of equations matches the exact evolution of the density field at
second order, but fails at third and higher order. This provides a useful,
easy-to-use framework for computing the fully relativistic growth of structure
at second order.


title: Creating Entanglement Using Integrals of Motion

abstract:
  A quantum Galilean cannon is a 1D sequence of $N$ hard-core particles with
special mass ratios, and a hard wall; conservation laws due to the reflection
group $A_{N}$ prevent both classical stochastization and quantum diffraction.
It is realizable through specie-alternating mutually repulsive bosonic soliton
trains. We show that an initial disentangled state can evolve into one where
the heavy and light particles are entangled, and propose a sensor, containing
$N_{\text{total}}$ atoms, with a $\sqrt{N_{\text{total}}}$ times higher
sensitivity than in a one-atom sensor with $N_{\text{total}}$ repetitions.


title: On Some Multiple Character Sums

abstract:
  We improve a recent result of B. Hanson (2015) on multiplicative character
sums with expressions of the type $a + b +cd$ and variables $a,b,c,d$ from four
distinct sets of a finite field. We also consider similar sums with $a +
b(c+d)$. These bounds rely on some recent advances in additive combinatorics.


title: On more variants of the Majority Problem

abstract:
  The problem we are considering is the following. A colorblind player is given
a set $B = \{b_1,b_2,...,b_N\}$ of $N$ colored balls. He knows that each ball
is colored either red or green, and that there are less green balls (this will
be called a Red-green coloring), but he cannot distinguish the two colors. For
any two balls he can ask whether they are colored the same. His goal is to
determine the set of all green balls of $B$ (and hence the set of all red
balls). We study here the case where the Red-green coloring is such that there
are at most $p$ green balls, where $p$ is given, and denote by $Q(N,p,\le)$ the
minimum integer $k$ such that there exists a method that finds for sure, for
any Red-green coloring, the color of each ball of $B$ after at most $k$ (color)
comparisons. We extend the cases for which the exact value of $Q(N,p,\le)$ is
known and provide lower and upper bounds as well as exact values for $Q(N, p,
=)$ (defined similarly as $Q(N, p, \le)$, but for a Red-green coloring with
exactly $p$ green balls).


title: Quasiperfect numbers with the same exponent

abstract:
  We study some divisibility properties of quasiperfect numbers. We show that
if $N=(p_1 p_2 \cdots p_t)^{2a}=m^2$ is quasiperfect, then $2a+1$ is divisible
by $3$ and $N$ has at least one prime factor smaller than $\exp 716.7944$.
Moreover, we find some lower bounds concerning quasiperfect numbers of the form
$N=m^2$ with $m$ squarefree.


title:
Online wheel speed filtering for periodic disturbance reduction: a
  strategy for an advanced bicycle application

abstract:
  Due to geometrical errors and possible misalignment of the sensors, wheel
speed measurements provided by incremental encoders in road vehicles are
usually affected by significant periodic noises. This paper presents an online
wheel speed filtering procedure, based on a model of the sensor, aimed at
processing the speed measurement to make it suitable for advanced vehicle
dynamics applications. In particular, differently from low-pass and notch
filtering, this strategy is reliable for the cycling cadence estimation from
the wheel speed on bicycles. Experimental data are used to show the
effectiveness of the proposed approach.


title: Access Control in Internet of Things: A Survey

abstract:
  Cheating is a real problem in the Internet of Things. The fundamental
question that needs to be answered is how we can trust the validity of the data
being generated in the first place. The problem, however, isn't inherent in
whether or not to embrace the idea of an open platform and open-source
software, but to establish a methodology to verify the trustworthiness and
control any access. This paper focuses on building an access control model and
system based on trust computing. This is a new field of access control
techniques which includes Access Control, Trust Computing, Internet of Things,
network attacks, and cheating technologies. Nevertheless, the target access
control systems can be very complex to manage. This paper presents an overview
of the existing work on trust computing, access control models and systems in
IoT. It not only summarizes the latest research progress, but also provides an
understanding of the limitations and open issues of the existing work. It is
expected to provide useful guidelines for future research.


title:
Sparsity-based Color Image Super Resolution via Exploiting Cross Channel
  Constraints

abstract:
  Sparsity constrained single image super-resolution (SR) has been of much
recent interest. A typical approach involves sparsely representing patches in a
low-resolution (LR) input image via a dictionary of example LR patches, and
then using the coefficients of this representation to generate the
high-resolution (HR) output via an analogous HR dictionary. However, most
existing sparse representation methods for super resolution focus on the
luminance channel information and do not capture interactions between color
channels. In this work, we extend sparsity based super-resolution to multiple
color channels by taking color information into account. Edge similarities
amongst RGB color bands are exploited as cross channel correlation constraints.
These additional constraints lead to a new optimization problem which is not
easily solvable; however, a tractable solution is proposed to solve it
efficiently. Moreover, to fully exploit the complementary information among
color channels, a dictionary learning method is also proposed specifically to
learn color dictionaries that encourage edge similarities. Merits of the
proposed method over state of the art are demonstrated both visually and
quantitatively using image quality metrics.


title:
On the pronormality of subgroups of odd indices in finite simple
  symplectic groups

abstract:
  A subgroup $H$ of a group $G$ is said to be pronormal in $G$ if $H$ and $H^g$
are conjugate in $\langle H, H^g\rangle$ for every element $g \in G$. In [Sib.
Math. J. 2015. Vol. 56, no. 6] we proved that subgroups of odd indeces are
pronormal in many finite simple group. In [Proc. Steklov Inst. Math., to
appear] we proved that a group $PSp_{6n}(q)$ with $q \equiv \pm 3 \pmod 8$
contains a nonpronormal subgroup of odd index.
  In this paper we prove that if $n \not \in \{2^m, 2^m(2^{2k}+1) \mid m, k \in
\mathbb{N} \cup \{0\}\}$ then a group $PSp_{2n}(q)$ with $q \equiv \pm 3 \pmod
8$ contains a nonpronormal subgroup of odd index; if $n=2^m$ then any subgroup
of odd index is pronormal in a group $PSp_{2n}(q)$, where $q \equiv \pm 3 \pmod
8$.


title: Fast Image Classification by Boosting Fuzzy Classifiers

abstract:
  This paper presents a novel approach to visual objects classification based
on generating simple fuzzy classifiers using local image features to
distinguish between one known class and other classes. Boosting meta learning
is used to find the most representative local features. The proposed approach
is tested on a state-of-the-art image dataset and compared with the
bag-of-features image representation model combined with the Support Vector
Machine classification. The novel method gives better classification accuracy
and the time of learning and testing process is more than 30% shorter.


title: Monogamy of quantum correlations - a review

abstract:
  Monogamy is an intrinsic feature of quantum correlations that gives rise to
several interesting quantum characteristics which are not amenable to classical
explanations. The monogamy property imposes physical restrictions on
unconditional sharability of quantum correlations between the different parts
of a multipartite quantum system, and thus has a direct bearing on the
cooperative properties of states of multiparty systems, including large
many-body systems. On the contrary, a certain party can be maximally classical
correlated with an arbitrary number of parties in a multiparty system. In
recent years, the monogamy property of quantum correlations has been applied to
understand several key aspects of quantum physics, including distribution of
quantum resources, security in quantum communication, critical phenomena, and
quantum biology. In this chapter, we look at some of the salient developments
and applications in quantum physics that have been closely associated with the
monogamy of quantum discord, and "discord-like" quantum correlation measures.


title: Equivariant geometry of Banach spaces and topological groups

abstract:
  We study uniform and coarse embeddings between Banach spaces and topological
groups. A particular focus is put on equivariant embeddings, i.e., continuous
cocycles associated to continuous affine isometric actions of topological
groups on separable Banach spaces with varying geometry.


title:
Projective multiscale time-integration for electrostatic
  particle-in-cell methods

abstract:
  The simulation of problems in kinetic plasma physics are often challenging
due to strongly coupled phenomena across multiple scales. In this work, we
propose a wavelet-based coarse-grained numerical scheme, based on the framework
of Equation-Free Projective Integration, for a kinetic plasma system modeled by
the Vlasov-Poisson equations. A kinetic particle-in-cell (PIC) code is used to
simulate the meso scale dynamics for short time intervals. This allows the
extrapolation over long time-steps of the behavior of a coarse wavelet-based
discretization of the system. To validate the approach and the underlying
concepts, we perform two 1D1V numerical experiments: nonlinear propagation and
steepening of an ion wave, and the expansion of a plasma slab in vacuum. The
direct comparisons to resolved PIC simulations show good agreement. We show
that the speedup of the projective integration scheme over the full particle
scheme scales linearly with the system size, demonstrating efficiency while
taking into account fully kinetic, non-Maxwellian effects. This suggests that
the approach is potentially interesting for kinetic plasma problems with a
large separation of scales, especially in higher dimensions.


title:
Magnetomechanical coupling and ferromagnetic resonance in magnetic
  nanoparticles

abstract:
  We address the theory of the coupled lattice and magnetization dynamics of
freely suspended single-domain nanoparticles. Magnetic anisotropy generates
low-frequency satellite peaks in the microwave absorption spectrum and a
blueshift of the ferromagnetic resonance (FMR) frequency. The low-frequency
resonances are very sharp with maxima exceeding that of the FMR, because their
magnetic and mechanical precessions are locked, thereby suppressing Gilbert
damping. Magnetic nanoparticles can operate as nearly ideal motors that convert
electromagnetic into mechanical energy. The Barnett/Einstein-de Haas effect is
significant even in the absence of a net rotation.


title:
Excited and exotic charmonium, $D_s$ and $D$ meson spectra for two light
  quark masses from lattice QCD

abstract:
  We present highly-excited charmonium, $D_s$ and $D$ meson spectra from
dynamical lattice QCD calculations with light quarks corresponding to $M_{\pi}
\sim 240$ MeV and compare these to previous results with $M_{\pi} \sim 400$
MeV. Utilising the distillation framework, large bases of carefully constructed
interpolating operators and a variational procedure, we extract and reliably
identify the continuum spin of an extensive set of excited mesons. These
include states with exotic quantum numbers which, along with a number with
non-exotic quantum numbers, we identify as having excited gluonic degrees of
freedom and interpret as hybrid mesons. Comparing the spectra at the two
different $M_\pi$, we find only a mild light-quark mass dependence and no
change in the overall pattern of states.


title: Effects of a local defect on one-dimensional nonlinear surface growth

abstract:
  The slow-bond problem is a long-standing question about the minimal strength
$\epsilon_\mathrm{c}$ of a local defect with global effects on the
Kardar--Parisi--Zhang (KPZ) universality class. A consensus on the issue has
been delayed due to the discrepancy between various analytical predictions
claiming $\epsilon_\mathrm{c} = 0$ and numerical observations claiming
$\epsilon_\mathrm{c} > 0$. We revisit the problem via finite-size scaling
analyses of the slow-bond effects, which are tested for different boundary
conditions through extensive Monte Carlo simulations. Our results provide
evidence that the previously reported nonzero $\epsilon_\mathrm{c}$ is an
artifact of a crossover phenomenon, which logarithmically converges to zero as
the system size goes to infinity.


title:
Exact results for the behavior of the thermodynamic Casimir force in a
  model with a strong adsorption

abstract:
  When massless excitations are limited or modified by the presence of material
bodies one observes a force acting between them generally called Casimir force.
Such excitations are present in any fluid system close to its true bulk
critical point. We derive exact analytical results for both the temperature and
external ordering field behavior of the thermodynamic Casimir force within the
mean-field Ginzburg-Landau Ising type model of a simple fluid or binary liquid
mixture. We investigate the case when under a film geometry the boundaries of
the system exhibit strong adsorption onto one of the phases (components) of the
system. We present analytical and numerical results for the (temperature-field)
relief map of the force in both the critical region of the film close to its
finite-size or bulk critical points as well as in the capillary condensation
regime below but close to the finite-size critical point.


title: Tutorial on Answering Questions about Images with Deep Learning

abstract:
  Together with the development of more accurate methods in Computer Vision and
Natural Language Understanding, holistic architectures that answer on questions
about the content of real-world images have emerged. In this tutorial, we build
a neural-based approach to answer questions about images. We base our tutorial
on two datasets: (mostly on) DAQUAR, and (a bit on) VQA. With small tweaks the
models that we present here can achieve a competitive performance on both
datasets, in fact, they are among the best methods that use a combination of
LSTM with a global, full frame CNN representation of an image. We hope that
after reading this tutorial, the reader will be able to use Deep Learning
frameworks, such as Keras and introduced Kraino, to build various architectures
that will lead to a further performance improvement on this challenging task.


title:
Stellar variability in open clusters. II. Discovery of a new
  period-luminosity relation in a class of fast-rotating pulsating stars in NGC
  3766

abstract:
  $Context.$ Pulsating stars are windows to the physics of stars enabling us to
see glimpses of their interior. Not all stars pulsate, however. On the main
sequence, pulsating stars form an almost continuous sequence in brightness,
except for a magnitude range between $\delta$ Scuti and slowly pulsating B
stars. Against all expectations, 36 periodic variables were discovered in 2013
in this luminosity range in the open cluster NGC 3766, the origins of which was
a mystery. $Aims.$ We investigate the properties of those new variability class
candidates in relation to their stellar rotation rates and stellar
multiplicity. $Methods.$ We took multi-epoch spectra over three consecutive
nights using ESO's Very Large Telescope. $Results.$ We find that the majority
of the new variability class candidates are fast-rotating pulsators that obey a
new period-luminosity relation. We argue that the new relation discovered here
has a different physical origin to the period-luminosity relations observed for
Cepheids. $Conclusions.$ We anticipate that our discovery will boost the
relatively new field of stellar pulsation in fast-rotating stars, will open new
doors for asteroseismology, and will potentially offer a new tool to estimate
stellar ages or cosmic distances.


title: Noetherianity of some degree two twisted skew-commutative algebras

abstract:
  A major open problem in the theory of twisted commutative algebras (tca's) is
proving noetherianity of finitely generated tca's. For bounded tca's this is
easy, in the unbounded case, noetherianity is only known for
Sym(Sym^2(C^\infty)) and Sym(\wedge^2(C^\infty)). In this paper, we establish
noetherianity for the skew-commutative versions of these two algebras, namely
\wedge(Sym^2(C^\infty)) and \wedge(\wedge^2(C^\infty)). The result depends on
work of Serganova on the representation theory of the infinite periplectic Lie
superalgebra, and has found application in the work of Miller-Wilson on
"secondary representation stability" in the cohomology of configuration spaces.


title:
Electric-field noise from carbon-adatom diffusion on a Au(110) surface:
  first-principles calculations and experiments

abstract:
  The decoherence of trapped-ion quantum gates due to heating of their motional
modes is a fundamental science and engineering problem. This heating is
attributed to electric-field noise arising from the trap-electrode surfaces. In
this work, we investigate the source of this noise by focusing on the diffusion
of carbon-containing adsorbates on the surface of Au(110). We show by density
functional theory, based on detailed scanning probe microscopy, how the carbon
adatom diffusion on the gold surface changes the energy landscape, and how the
adatom dipole moment varies with the diffusive motion. A simple model for the
diffusion noise, which varies quadratically with the variation of the dipole
moment, qualitatively reproduces the measured noise spectrum, and the estimate
of the noise spectral density is in accord with measured values.


title: Pick interpolation on the polydisc: small families of sufficient kernels

abstract:
  We give a solution to Pick's interpolation problem on the unit polydisc in
$\mathbb{C}^n$, $n\geq 2$, by characterizing all interpolation data that admit
a $\mathbb{D}$-valued interpolant, in terms of a family of positive-definite
kernels parametrized by a class of polynomials. This uses a duality approach
that has been associated with Pick interpolation, together with some
approximation theory. Furthermore, we use duality methods to understand the set
of points on the $n$-torus at which the boundary values of a given solution to
an extremal interpolation problem are not unimodular.


title:
Second-Order Hydrodynamics and Universality in Non-Conformal Holographic
  Fluids

abstract:
  We study second-order hydrodynamic transport in strongly coupled
non-conformal field theories with holographic gravity duals in asymptotically
anti-de Sitter space. We first derive new Kubo formulae for five second-order
transport coefficients in non-conformal fluids in $(3+1)$ dimensions. We then
apply them to holographic RG flows induced by scalar operators of dimension
$\Delta=3$. For general background solutions of the dual bulk geometry, we find
explicit expressions for the five transport coefficients at infinite coupling
and show that a specific combination,
$\tilde{H}=2\eta\tau_\pi-2(\kappa-\kappa^*)-\lambda_2$, always vanishes. We
prove analytically that the Haack-Yarom identity
$H=2\eta\tau_\pi-4\lambda_1-\lambda_2=0$, which is known to be true for
conformal holographic fluids, also holds when taking into account leading
non-conformal corrections. The numerical results we obtain for two specific
families of RG flows suggest that $H$ vanishes regardless of conformal
symmetry. Our work provides further evidence that the Haack-Yarom identity
$H=0$ may be universally satisfied by strongly coupled fluids.


title: Observation of subluminal twisted light in vacuum: comment

abstract:
  Our analysis based on analytical and numerical calculations leads to
conclusion that the promising results obtained in [F. Bouchard, J. Harris, H.
Mand, R. W. Boyd, and E. Karimi, Optica 3, 351, 2016] are questionable in
several respects.


title: On the univalence of polyharmonic mappings

abstract:
  A 2p-times continuously differentiable complex valued function $f = u + iv$
in a simply connected domain is polyharmonic (or p-harmonic) if it satisfies
the polyharmonic equation $\Delta^pF = 0$ . Every polyharmonic mapping f can be
written as $f(z) =\sum_{k}^{p} |z|^{2(p-1)}G_{p-k+1}(z)$ where each $G_{p-k+1}$
is harmonic. In this paper we investigate the univalence of polyharmonic
mappings on linearly connected domains and the relation between univalence of
f(z) and that of $G_p(z)$. The notions of stable univalence and logpolyharminc
mappings are also considered.


title:
On the observation of field-free orientation of a symmetric top molecule
  by terahertz laser pulses at high temperature

abstract:
  We investigate experimentally and numerically the field-free orientation of
the symmetric top molecule of methyl-iodide at high temperature using a
terahertz radiation generated by a plasma induced by a two-color laser beam.
The degree of orientation is measured from the free-induction decay emitted by
the sample. The observed experimental signal is reproduced with a good accuracy
by numerical simulations.


title:
Towards the Design of Prospect-Theory based Human Decision Rules for
  Hypothesis Testing

abstract:
  Detection rules have traditionally been designed for rational agents that
minimize the Bayes risk (average decision cost). With the advent of
crowd-sensing systems, there is a need to redesign binary hypothesis testing
rules for behavioral agents, whose cognitive behavior is not captured by
traditional utility functions such as Bayes risk. In this paper, we adopt
prospect theory based models for decision makers. We consider special agent
models namely optimists and pessimists in this paper, and derive optimal
detection rules under different scenarios. Using an illustrative example, we
also show how the decision rule of a human agent deviates from the Bayesian
decision rule under various behavioral models, considered in this paper.


title:
Fast evolving pair-instability supernova models: evolution, explosion,
  light curves

abstract:
  With an increasing number of superluminous supernovae (SLSNe) discovered the
question of their origin remains open and causes heated debates in the
supernova community. Currently, there are three proposed mechanisms for SLSNe:
(1) pair-instability supernovae (PISN), (2) magnetar-driven supernovae, and (3)
models in which the supernova ejecta interacts with a circumstellar material
ejected before the explosion. Based on current observations of SLSNe, the PISN
origin has been disfavoured for a number of reasons. Many PISN models provide
overly broad light curves and too reddened spectra, because of massive ejecta
and a high amount of nickel. In the current study we re-examine PISN properties
using progenitor models computed with the GENEC code. We calculate supernova
explosions with FLASH and light curve evolution with the radiation
hydrodynamics code STELLA. We find that high-mass models (200 and 250 solar
masses) at relatively high metallicity (Z=0.001) do not retain hydrogen in the
outer layers and produce relatively fast evolving PISNe Type I and might be
suitable to explain some SLSNe. We also investigate uncertainties in light
curve modelling due to codes, opacities, the nickel-bubble effect and
progenitor structure and composition.


title: On geometrical properties of logharmonic mappings

abstract:
  In this paper, we find the radius of the disk $\Omega _{r}$ such that every
starlike logharmonic mapping $f(z)$ of order $\alpha ,$ is starlike in $%
|z|\leq r$ with respect to any point of $\Omega _{r}.$ We also establish a
relation between the set of starlike logharmonic mappings \ and the set of
starlike logharmonic mappings of order alpha. Moreover, the radius of
starlikeness and univalence for the set of close to starlike logharmonic
mappings of order $\alpha $ is determined.


title:
Temperature-dependent optical spectra of single-crystal
  (CH$_3$NH$_3$)PbBr$_3$ cleaved in ultrahigh vacuum

abstract:
  We measure temperature-dependent one-photon and two-photon induced
photoluminescence from (CH3NH3)PbBr3 single crystals cleaved in ultrahigh
vacuum. An approach is presented to extract absorption spectra from a
comparison of both measurements. Cleaved crystals exhibit broad
photoluminescence spectra. We identify the direct optical band gap of 2.31 eV.
Below 200 K the band gap increases with temperature, and it decreases at
elevated temperature, as described by the Bose-Einstein model. An excitonic
transition is found 22 meV below the band gap at temperatures <200 K. Defect
emission occurs at photon energies <2.16 eV. In addition, we observe a
transition at 2.25 eV (2.22 eV) in the orthorhombic (tetragonal and cubic)
phase. Below 200 K, the associated exciton binding energy is also 22 meV, and
the transition redshifts at higher temperature. The binding energy of the
exciton related to the direct band gap, in contrast, decreases in the cubic
phase. High-energy emission from free carriers is observed with higher
intensity than reported in earlier studies. It disappears after exposing the
crystals to air.


title: Quantum parallelism may be limited

abstract:
  We consider quantum formalism limited by the classical simulating computer
with the fixed memory. The memory is redistributed in the course of modeling by
the variation of the set of classical states and the accuracy of the
representation of amplitudes. This computational description completely
preserves the conventional formalism and does not contradicts to experiments,
but it makes impossible fast quantum algorithms. This description involves the
slow down of quantum evolutions with the growth of the dimension of the minimal
subspace containing entangled states, which arise in the evolution. This slow
down is the single difference of the proposed formalism from the standard one;
it is negligible for the systems from the usual experiments, including those in
which many entangled particle participate, but grows rapidly in the attempt to
realize the scalable quantum computations, which require the unlimited
parallelism. The experimental verification of this version of quantum formalism
is reduced to the fixation of this slow down.


title:
Cosmological Attractors and Anisotropies in Two Measure Theories,
  Effective EYMH systems, and Off--Diagonal Inflation Models

abstract:
  Applying the anholonomic frame deformation method, we construct various
classes of cosmological solutions for effective Einstein -- Yang-Mills --
Higgs, and two measure theories. The types of models considered are
Freedman-Lema\^{i}tre-Robertson-Walker, Bianchi, Kasner and models with
attractor configurations. The various regimes pertaining to plateau--type
inflation, quadratic inflation, Starobinsky type and Higgs type inflation are
presented.


title:
An efficient method for tracing high-resolution invariant manifolds of
  three-dimensional flows

abstract:
  In Hamiltonian systems subjected to periodic perturbations the stable and
unstable manifolds of the unstable periodic orbits provide the dynamical
"skeleton" that drives the mixing process and bounds the chaotic regions of the
phase space. Determining the behavior of these objects is valuable in physical
applications involving asymmetric solenoidal fields or time-dependent
Hamiltonian systems. Here we introduce a simple method to calculate an unstable
periodic orbit given an initial guess on its position. Then we present an
efficient adaptive method to build its high-resolution invariant manifolds to
arbitrary length and compare it to a random sampling method with the same
computational cost. The adaptive method gives a high-quality representation of
the manifolds and reveals fine details that become lost in the random sampling
method. Finally, we introduce an approximation to the adaptive method to build
the manifolds avoiding redundant calculations and reducing logarithmically the
number of computations needed to represent these surfaces.


title:
Detecting dimensional crossover and finite Hilbert space through
  entanglement entropies

abstract:
  The information content of the two-particle one- and two-dimensional Calogero
model is studied using the von Neumann and R\'enyi entropies. The
one-dimensional model is shown to have non-monotonic entropies with finite
values in the large interaction strength limit. On the other hand, the von
Neumann entropy of the two-dimensional model with isotropic confinement is a
monotone increasing function of the interaction strength which diverges
logarithmically. By considering an anisotropic confinement in the
two-dimensional case we show that the one-dimensional behavior is eventually
reached when the anisotropy increases. The crossover from two to one dimensions
is demonstrated using the harmonic approximation and it is shown that the von
Neumann divergence only occurs in the isotropic case. The R\'enyi entropies are
used to highlight the structure of the model spectrum. In particular, it is
shown that these entropies have a non-monotonic and non-analytical behavior in
the neighborhood of the interaction strength parameter values where the Hilbert
space and, consequently, the spectrum of the reduced density matrix are both
finite.


title: Construction of two-bubble solutions for the energy-critical NLS

abstract:
  We construct pure two-bubbles for the energy-critical focusing nonlinear
Schr\"odinger equation in space dimension $N \geq 7$. The constructed solution
is global in (at least) one time direction and approaches a superposition of
two stationary states both centered at the origin, with the ratio of their
length scales converging to $0$. One of the bubbles develops at scale $1$,
whereas the length scale of the other converges to $0$ at rate
$|t|^{-\frac{2}{N-6}}$. The phases of the two bubbles form the right angle.


title: A fluxonium-based artificial molecule with a tunable magnetic moment

abstract:
  Engineered quantum systems allow us to observe phenomena that are not easily
accessible naturally. The LEGO-like nature of superconducting circuits makes
them particularly suited for building and coupling artificial atoms. Here, we
introduce an artificial molecule, composed of two strongly coupled fluxonium
atoms, which possesses a tunable magnetic moment. Using an applied external
flux, one can tune the molecule between two regimes: one in which the
ground-excited state manifold has a magnetic dipole moment and one in which the
ground-excited state manifold has only a magnetic quadrupole moment. By varying
the applied external flux, we find the coherence of the molecule to be limited
by local flux noise. The ability to engineer and control artificial molecules
paves the way for building more complex circuits for protected qubits and
quantum simulation.


title: Interaction-induced insulating state in thick multilayer graphene

abstract:
  Close to charge neutrality, the low-energy properties of high-quality
suspended devices based on atomically thin graphene layers are determined by
electron-electron interactions. Bernal-stacked layers, in particular, have
shown a remarkable even-odd effect with mono- and tri-layers remaining gapless
conductors, and bi- and tetra-layers becoming gapped insulators. These
observations $-$at odds with the established notion that (Bernal) trilayers and
thicker multilayers are semi-metals$-$ have resulted in the proposal of a
physical scenario leading to a surprising prediction, namely that even-layered
graphene multilayers remain insulating irrespective of their thickness. Here,
we present data from two devices that conform ideally to this hypothesis,
exhibiting the behavior expected for Bernal-stacked hexa and octalayer
graphene. Despite their large thickness, these multilayers are insulating for
carrier density |n|<2-3x10$^{10}$cm$^{-2}$, possess an energy gap of
approximately 1.5 meV at charge neutrality (in virtually perfect agreement with
what is observed in bi and tetra layer graphene) and exhibit the expected
integer quantum Hall effect. These findings indicate the soundness of our basic
insights on the effect of electron interactions in Bernal graphene multilayers,
show that graphene multilayers exhibit unusual and interesting physics that
remains to be understood, and pose ever more pressing questions as to the
microscopic mechanisms behind the semimetallic behavior of bulk graphite.


title: FLOCK: Combating Astroturfing on Livestreaming Platforms

abstract:
  Livestreaming platforms have become increasingly popular in recent years as a
means of sharing and advertising creative content. Popular content streamers
who attract large viewership to their live broadcasts can earn a living by
means of ad revenue, donations and channel subscriptions. Unfortunately, this
incentivized popularity has simultaneously resulted in incentive for fraudsters
to provide services to astroturf, or artificially inflate viewership metrics by
providing fake "live" views to customers. Our work provides a number of major
contributions: (a) formulation: we are the first to introduce and characterize
the viewbot fraud problem in livestreaming platforms, (b) methodology: we
propose FLOCK, a principled and unsupervised method which efficiently and
effectively identifies botted broadcasts and their constituent botted views,
and (c) practicality: our approach achieves over 98% precision in identifying
botted broadcasts and over 90% precision/recall against sizable synthetically
generated viewbot attacks on a real-world livestreaming workload of over 16
million views and 92 thousand broadcasts. FLOCK successfully operates on larger
datasets in practice and is regularly used at a large, undisclosed
livestreaming corporation.


title:
Hourglass dispersion and resonance of magnetic excitations in the
  superconducting state of the single-layer cuprate HgBa2CuO4+{\delta} near
  optimal doping

abstract:
  We use neutron scattering to study magnetic excitations near the
antiferromagnetic wave vector in the underdoped single-layer cuprate
HgBa2CuO4+{\delta} (superconducting transition temperature Tc ~ 88 K, pseudogap
temperature T* ~ 220 K). The response is distinctly enhanced below T* and
exhibits a Y-shaped dispersion in the pseudogap state, whereas the
superconducting state features an X-shaped (hourglass) dispersion and a further
resonance-like enhancement. A large spin gap of about 40 meV is observed in
both states. This phenomenology is reminiscent of that exhibited by bilayer
cuprates. The resonance spectral weight, irrespective of doping and compound,
scales linearly with the putative binding energy of a spin-exciton described by
an itinerant-spin formalism.


title:
6-dimensional product Lie algebras admitting integrable complex
  structures

abstract:
  We classify the 6-dimensional Lie algebras of the form $g\times g$ that admit
integrable complex structure. We also endow a Lie algebra of the kind
$o(n)\oplus o(n)$ with such a complex structure. The motivation comes from
geometric structures \'a la Sasaki on $g$-manifolds.


title: Figures of merit for quantum transducers

abstract:
  Recent technical advances have sparked renewed interest in physical systems
that couple simultaneously to different parts of the electromagnetic spectrum,
thus enabling transduction of signals between vastly different frequencies at
the level of single photons. Such hybrid systems have demonstrated frequency
conversion of classical signals and have the potential of enabling quantum
state transfer, e.g., between superconducting circuits and traveling optical
signals. This article describes a simple approach for the theoretical
characterization of the performance of quantum transducers. Given that, in
practice, one cannot attain ideal one-to-one quantum conversion, we explore how
well the transducer performs in scenarios ranging from classical signal
detection to applications for quantum information processing. While the
performance of the transducer depends on the particular application in which it
enters, we show that the performance can be characterized by defining two
simple parameters: the signal transfer efficiency $\eta$ and the added noise
$N$.


title: Coulomb drag between helical Luttinger liquids

abstract:
  We theoretically study Coulomb drag between two helical edges with broken
spin-rotational symmetry, such as would occur in two capacitively coupled
quantum spin Hall insulators. For the helical edges, Coulomb drag is
particularly interesting because it specifically probes the inelastic
interactions that break the conductance quantization for a single edge. Using
the kinetic equation formalism, supplemented by bosonization, we find that the
drag resistivity $\rho_D$ exhibits a nonmonotonic dependence on the temperature
$T$. In the limit of low $T$, $\rho_D$ vanishes with decreasing $T$ as a power
law if intraedge interactions are not too strong. This is in stark contrast to
Coulomb drag in conventional quantum wires, where $\rho_D$ diverges at $T\to 0$
irrespective of the strength of repulsive interactions. Another unusual
property of Coulomb drag between the helical edges concerns higher $T$ for
which, unlike in the Luttinger liquid model, drag is mediated by plasmons. The
special type of plasmon-mediated drag can be viewed as a distinguishing feature
of the helical liquid---because it requires peculiar Umklapp scattering only
available in the presence of a Dirac point in the electron spectrum.


title:
A SMART Stochastic Algorithm for Nonconvex Optimization with
  Applications to Robust Machine Learning

abstract:
  In this paper, we show how to transform any optimization problem that arises
from fitting a machine learning model into one that (1) detects and removes
contaminated data from the training set while (2) simultaneously fitting the
trimmed model on the uncontaminated data that remains. To solve the resulting
nonconvex optimization problem, we introduce a fast stochastic
proximal-gradient algorithm that incorporates prior knowledge through nonsmooth
regularization. For datasets of size $n$, our approach requires
$O(n^{2/3}/\varepsilon)$ gradient evaluations to reach $\varepsilon$-accuracy
and, when a certain error bound holds, the complexity improves to $O(\kappa
n^{2/3}\log(1/\varepsilon))$. These rates are $n^{1/3}$ times better than those
achieved by typical, full gradient methods.


title:
Bottomonium-like states: physics case for energy scan above the
  $B\bar{B}$ threshold at Belle-II

abstract:
  The Belle-II experiment is expected to collect large data samples at the
$\Upsilon(4S)$ and $\Upsilon(5S)$ resonances to study primarily $B$ and $B_s$
mesons. We discuss what other data above the $B\bar{B}$ threshold are of
interest. We propose to perform a high-statistics energy scan from the
$B\bar{B}$ threshold up to the highest possible energy, and to collect data at
the $\Upsilon(6S)$ and at higher mass states if they are found in the scan. We
emphasize the interest in increasing the maximal energy from 11.24\,GeV to 11.5
- 12\,GeV in the future. These data are needed for investigation of bottomonium
and bottomonium-like states.


title:
Expansion of the spectrum in the weak disorder regime for random
  operators in continuum space

abstract:
  We study the spectrum of random ergodic Schroedinger-type operators in the
weak disorder regime. We give upper and lower bounds on how much the spectrum
expands at its bottom for very general perturbations. The background operator
is assumed to be a periodic elliptic differential operator on R^d, not
necessarily of second order.


title: Ion crystals in anharmonic traps

abstract:
  There is currently intensive research into creating a large-scale quantum
computer with trapped ions. It is well known that for a linear ion crystal in a
harmonic potential, the ions near the center are more closely spaced compared
to the ions near the ends. This is problematic as the number of ions increases.
Here, we consider a linear ion crystal in an anharmonic potential that is
purely quartic in position. We find that the ions are more evenly spaced
compared to the harmonic case. We develop a variational approach to calculate
the properties of the ground state. We also characterize the zigzag transition
in an anharmonic potential.


title:
Systematic Magnus-based approach for suppressing leakage and
  non-adiabatic errors in quantum dynamics

abstract:
  We present a systematic, perturbative method for correcting quantum gates to
suppress errors that take the target system out of a chosen subspace. It
addresses the generic problem of non-adiabatic errors in adiabatic evolution
and state preparation, as well as general leakage errors due to spurious
couplings to undesirable states. The method is based on the Magnus expansion:
by correcting control pulses, we modify the Magnus expansion of an
initially-given, imperfect unitary in such a way that the desired evolution is
obtained. Applications to adiabatic quantum state transfer, superconducting
qubits and generalized Landau-Zener problems are discussed.