title:
In-plane anisotropic magnetoresistance in antiferromagnetic
  Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ and
  Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$

abstract:
  Using the Kubo-Greenwood formalism the resistivity anisotropy for electron
doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, hole doped (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$
and isovalently doped Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ in their antiferromagnetic
state has been calculated in order to clarify the origin of this important
phenomenon. The results show good agreement with experiment for all cases
without considering impurity states extending over several unit cells or
temperature induced spin fluctuations. From this it is concluded that the
resistivity anisotropy at low temperatures is primarily caused by an in-plane
anisotropic magnetoresistance. Accounting for the band dispersion with respect
to $k_z$ is however mandatory to explain the results, showing the importance of
the three-dimensional character of the electronic structure for the iron
pnictides. Furthermore, it is shown that the counterintuitive sign of the
resistivity anisotropy is no fundamental property but just a peculiarity of the
anisotropic band structure.


title: Root numbers and parity of local Iwasawa invariants

abstract:
  Given two elliptic curves $E_1$ and $E_2$ defined over the field of rational
numbers, $\mathbb{Q}$, with good reduction at an odd prime $p$ and equivalent
mod $p$ Galois representation, we compare the $p$-Selmer rank, global and local
root numbers of $E_1$ and $E_2$ over number fields.


title:
Orthogonal polynomials on the unit circle: Verblunsky coefficients with
  some restrictions imposed on a pair of related real sequences

abstract:
  It was shown recently that associated with a pair of real sequences
$\{\{c_{n}\}_{n=1}^{\infty}, \{d_{n}\}_{n=1}^{\infty}\}$, with
$\{d_{n}\}_{n=1}^{\infty}$ a positive chain sequence, there exists a unique
nontrivial probability measure $\mu$ on the unit circle. The Verblunsky
coefficients $\{\alpha_{n}\}_{n=0}^{\infty}$ associated with the orthogonal
polynomials with respect to $\mu$ are given by the relation $$
\alpha_{n-1}=\overline{\tau}_{n-1}\left[\frac{1-2m_{n}-ic_{n}}{1-ic_{n}}\right],
\quad n \geq 1, $$ where $\tau_0 = 1$,
$\tau_{n}=\prod_{k=1}^{n}(1-ic_{k})/(1+ic_{k})$, $n \geq 1$ and
$\{m_{n}\}_{n=0}^{\infty}$ is the minimal parameter sequence of
$\{d_{n}\}_{n=1}^{\infty}$.
  In this manuscript we consider this relation and its consequences by imposing
some restrictions of sign and periodicity on the sequences
$\{c_{n}\}_{n=1}^{\infty}$ and $\{m_{n}\}_{n=1}^{\infty}$. When the sequence $
  \{c_{n}\}_{n=1}^{\infty}$ is of alternating sign, we use information about
the zeros of associated para-orthogonal polynomials to show that there is a gap
in the support of the measure in the neighbourhood of $z= -1$. Furthermore, we
show that it is possible to ge\-nerate periodic Verblunsky coefficients by
choosing periodic sequences $\{c_{n}\}_{n=1}^{\infty}$ and
$\{m_{n}\}_{n=1}^{\infty}$ with the additional restriction $c_{2n}=-c_{2n-1},
\, n\geq 1.$ We also give some results on periodic Verblunsky coefficients from
the point of view of positive chain sequences. An example is provided to
illustrate the results obtained.


title: A Multi-Urn Model for Network Search

abstract:
  We consider the problem of finding a specific target individual hiding in a
social network. We propose a method for network vertex search that looks for
the target vertex by sequentially examining the neighbors of a set of "known"
vertices to which the target vertex may have connected. The objective is to
find the target vertex as quickly as possible from amongst the neighbors of the
known vertices. We model this type of search as successively drawing marbles
from a set of urns, where each urn represents one of the known vertices and the
marbles in each urn represent the respective vertex's neighbors. Using a
dynamic programming approach, we analyze this model and show that there is
always an optimal "block" policy, in which all of the neighbors of a known
vertex are examined before moving on to another vertex. Surprisingly, this
block policy result holds for arbitrary dependencies in the connection
probabilities of the target vertex and known vertices. Furthermore, we give
precise characterizations of the optimal block policy in two specific cases:
(1) when the connections between the known vertices and the target vertex are
independent, and (2) when the target vertex is connected to at most one known
vertex. Finally, we provide some general monotonicity properties and discuss
the relevance of our findings in social media and other applications.


title:
Phase transitions to dipolar clusters and charge density waves in high
  Tc superconductors

abstract:
  We show that doping of hole charge carriers leads to formation of electric
dipolar clusters in cuprates. They are created by many-body interactions
between the dopant ion outside and holes inside the CuO planes. Because of the
two-fold degeneracy holes in the CuO plane cluster into four-particles
resonance valence bond plaquettes bound with dopant ions. Such dipoles may
order into charge-density waves (CDW) or stripes or form a disordered state
depending on doping and temperature. The lowest energy of the ordered system
corresponds to a local anti-ferroelectric ordering. The mobility of individual
disordered dipoles is very low at low temperatures and they prefer first to
bind into dipole-dipole pairs. Electromagnetic radiation interacts strongly
with electric dipoles and when the sample is subjected to it the mobility
changes significantly. This leads to a fractal growth of dipolar clusters. The
existence of electric dipoles and CDW induce two phase transitions with
increasing temperature, melting of the ordered state and disappearance of the
dipolar state. Ferroelectricity at low doping is a natural consequence of such
dipole moments. We develop a theory based on two-level systems and
dipole-dipole interaction to explain the behavior of the polarization as a
function of temperature and electric field.


title: On the Location of the Non-Trivial Zeros of the RH

abstract:
  This research paper presents the results of a study on the application of
extended analytic continuation to locate the non-trivial zeros of the Riemann
Hypothesis.


title:
Magnetically-regulated fragmentation of a massive, dense and turbulent
  clump

abstract:
  Massive stars, multiple stellar systems and clusters are born from the
gravitational collapse of massive dense gaseous clumps, and the way these
systems form strongly depends on how the parent clump fragments into cores
during collapse. Numerical simulations show that magnetic fields may be the key
ingredient in regulating fragmentation. Here we present ALMA observations at
~0.25'' resolution of the thermal dust continuum emission at ~278 GHz towards a
turbulent, dense, and massive clump, IRAS 16061-5048c1, in a very early
evolutionary stage. The ALMA image shows that the clump has fragmented into
many cores along a filamentary structure. We find that the number, the total
mass and the spatial distribution of the fragments are consistent with
fragmentation dominated by a strong magnetic field. Our observations support
the theoretical prediction that the magnetic field plays a dominant role in the
fragmentation process of massive turbulent clump.


title:
On the second derivatives of periods and braking indices in radio
  pulsars

abstract:
  The analysis of some braking mechanisms for neutron stars was carried out to
determine the sign of the second derivative of the pulsar period. This quantity
is the important parameter for calculations of the braking index n. It is shown
that this derivative can be positive and lead to decreasing of n. It is
necessary to correct the methods of calculations of n used this moment because
they are based as a rule on the suggestion on the constancy of pulsar
parameters (magnetic fields, angles between some axes and so on). The
estimations of corrections to braking indices are obtained. It is shown that
these corrections can be marked for pulsars with long periods and their small
derivatives.


title: Playing Tennis without Envy

abstract:
  A group of friends organize their tennis games by submitting each their
availability over the weekdays. They want to obtain an assignment such that:
each game must be a double tennis match, i.e. requires four people, and nobody
plays in a day he is unavailable. Can we construct assignments that will always
produce efficient, fair, and envy-free outcomes? The answer is no, and extends
to any sport that requires any group size.


title:
An analytical proof for Lehmer's totient conjecture using Mertens'
  theorems

abstract:
  We make an analytical proof for Lehmer's totient conjecture. Lehmer
conjectured that there is no solution for the congruence equation $n-1\equiv
0~(mod~\phi(n))$ with composite integers,$n$, where $\phi(n)$ denotes Euler's
totient function. He also showed that if the equation has any composite
solutions, $n$ must be odd, square-free, and divisible by at least 7 primes.
Several people have obtained conditions on values ,$n$, and number of
square-free primes constructing $n$ if the equation can have composite
solutions. Using Mertens' theorems, we show that it is impossible that the
equation can have any composite solution and implies that the conjecture should
be true for all the positively composite numbers.


title: Equisectional equivalence of triangles

abstract:
  We study equivalence relation of the set of triangles generated by similarity
and operation on a triangle to get a new one by joining division points of
three edges with the same ratio. Using the moduli space of similarity classes
of triangles introduced by Nakamura and Oguiso, we give characterization of
equivalent triangles in terms of circles of Apollonius (or hyperbolic pencil of
circles) and properties of special equivalent triangles. We also study
rationality problem and constructibility problem.


title: Bigeometric Calculus and its applications

abstract:
  Based on M. Grossman in \cite{Grossman83} and Grossman an Katz
\cite{GrossmanKatz}, in this paper we discuss about the applications of
bigeometric calculus in different branches of mathematics and economics.


title: Theory of groove-envelope phase effects in self-diffraction

abstract:
  If two laser beams cross in a medium under shallow angle, the laser-induced
grating consists of only a few grooves. In this situation, the phase between
the grooves of the grating and its envelope is a decisive parameter for
nonlinear effects. Here, models are established for reproducing the
groove-envelope phase effects that have been observed in the interference
pattern of self-diffraction. Four-wave mixing leads to interferences that are
dominant in the spatial region between the orders of diffraction and with
tilted interference fringes in the diagram of transverse coordinate vs. pulse
delay. The vertical interference fringes that are dominant directly on the
diffraction orders, experimentally observed at high intensity close to the
damage threshold, require a model beyond four-wave mixing. A model is suggested
that is based on optical transmission changes with confinement to regions in
the medium that are smaller than the groove spacing.


title:
Thermodynamics Quantities for the Klein-Gordon Equation with a Linear
  plus Inverse-linear Potential: Biconfluent Heun functions

abstract:
  We study some thermodynamics quantities for the Klein-Gordon equation with a
linear plus inverse-linear, scalar potential. We obtain the energy eigenvalues
with the help of the quantization rule coming from the biconfluent Heun's
equation. We use a method based on the Euler-MacLaurin formula to compute the
thermal functions analytically by considering only the contribution of positive
part of spectrum to the partition function.


title: Cooling of neutron stars with diffusive envelopes

abstract:
  We study the effects of heat blanketing envelopes of neutron stars on their
cooling. To this aim, we perform cooling simulations using newly constructed
models of the envelopes composed of binary ion mixtures (H--He, He--C, C--Fe)
varying the mass of lighter ions (H, He or C) in the envelope. The results are
compared with those calculated using the standard models of the envelopes which
contain the layers of lighter (accreted) elements (H, He and C) on top of the
Fe layer, varying the mass of accreted elements. The main effect is that the
chemical composition of the envelopes influences their thermal conductivity
and, hence, thermal insulation of the star. For illustration, we apply these
results to estimate the internal temperature of the Vela pulsar and to study
the cooling of neutron stars of ages of 0.1 - 1 Myr at the photon cooling
stage. The uncertainties of the cooling models associated with our poor
knowledge of chemical composition of the heat insulating envelopes strongly
complicate theoretical reconstruction of the internal structure of cooling
neutron stars from observations of their thermal surface emission.


title: Universal Lower Limit on Vortex Creep in Superconductors

abstract:
  Superconductors are excellent testbeds for studying vortices, topological
excitations that also appear in superfluids, liquid crystals, and Bose-Einstein
condensates. Vortex motion can be disruptive; it can cause phase transitions,
glitches in pulsars, and losses in superconducting microwave circuits, and it
limits the current carrying capacity of superconductors. Understanding vortex
dynamics is therefore of fundamental and technological importance, and the
competition between the effects of thermal energy and energy barriers defined
by material disorder is not completely understood. In particular, early
measurements of thermally-activated vortex motion (creep) in iron-based
superconductors unveiled fast rates (S) comparable to measurements of YBa2Cu3O7
(YBCO). This was puzzling because S is thought to somehow positively correlate
with the Ginzburg number (Gi), and Gi is orders of magnitude lower in most
iron-based superconductors than in YBCO. Here, we report very slow creep in
BaFe2(As0.67P0.33)2 films, and propose that there is a universal minimum
realizable (where Tc is the superconducting transition temperature) that has
been achieved in our films, few other materials, and violated by none. This
limitation provides new clues on how to design materials with slow creep and
helps elucidate open questions regarding the interplay between system-specific
length scales and vortex dynamics.


title:
Comment on "Direct photodetachment of F$^-$ by mid-infrared few-cycle
  femtosecond laser pulses"

abstract:
  Multiphoton detachment of F$^-$ by strong few-cycle laser pulses was studied
by Shearer and Monteith using a Keldysh-type approach [Phys. Rev. A 88, 033415
(2013)]. We believe that this work contained errors in the calculation of the
detachment amplitude and photoelectron spectra. We describe the necessary
corrections to the theory and show that the results, in particular, the
interference features of the photoelectron spectra, appear noticeably
different.


title:
A fixed-point-free map of a tree-like continuum induced by bounded
  valence maps on trees

abstract:
  Towards attaining a better working understanding of fixed points of maps of
tree-like continua, Oversteegen and Rogers constructed a tree-like continuum
with a fixed-point-free self-map, described explicitly in terms of inverse
limits. Specifically, they developed a sequence of trees $T_n$, $n \in
\mathbb{N}$ and maps $f_n$ and $g_n$ from $T_{n+1}$ to $T_n$ for each $n$, such
that the $g_n$ maps induce a fixed-point-free self-map of the inverse limit
space $\varprojlim (T_n,f_n)$.
  The complexity of the trees and the valences of the maps in their example all
grow exponentially with $n$, making it difficult to visualize and compute with
their space and map. We construct another such example, in which the maps $f_n$
and $g_n$ have uniformly bounded valence, and the trees $T_n$ have a simpler
structure.


title: Green-Kubo approach to the average swim speed in active Brownian systems

abstract:
  We develop an exact Green-Kubo formula relating nonequilibrium averages in
systems of interacting active Brownian particles to equilibrium
time-correlation functions. The method is applied to calculate the
density-dependent average swim speed, which is a key quantity entering coarse
grained theories of active matter. The average swim speed is determined by
integrating the equilibrium autocorrelation function of the interaction force
acting on a tagged particle. Analytical results are validated using Brownian
dynamics simulations.


title:
Clinical trials with rescue medication applied according to a
  deterministic rule

abstract:
  Clinical trials in specific indications require the administration of rescue
medication in case a patient does not sufficiently respond to investigational
treatment. The application of additional treatment on an as needed basis causes
problems to the analysis and interpretation of the results of these studies
since the effect of the investigational treatment can be confounded by the
additional medication. Following-up all patients until study end and capturing
all data is not fully addressing the issue. We present an analysis that takes
care of the fact that rescue is a study outcome and not a covariate when rescue
medication is administered according to a deterministic rule. This approach
allows to clearly define a biological effect. For normally distributed
longitudinal data a practically unbiased estimator of the biological effect can
be obtained. The results are compared to an ITT analysis and an analysis on all
patients not receiving rescue.


title: Water-mediated correlations in DNA-enzyme interactions

abstract:
  In this paper we consider dipole-mediated correlations between DNA and
enzymes in the context of their water environment. Such correlations emerge
from electric dipole-dipole interactions between aromatic ring structures in
DNA and in enzymes. We show that there are matching collective modes between
DNA and enzyme dipole fields, and that a dynamic time-averaged polarization
vanishes in the water dipole field only if either DNA, enzyme, or both are
absent from the sample. This persistent field may serve as the electromagnetic
image that, in popular colloquialisms about DNA biochemistry, allows enzymes to
"scan" or "read" the double helix. Topologically nontrivial configurations in
the coherent ground state requiring clamplike enzyme behavior on the DNA may
stem, ultimately, from spontaneously broken gauge symmetries.


title: Fusion procedure for cyclotomic BMW algebras

abstract:
  Inspired by the work [IMOg2], in this note, we prove that the pairwise
orthogonal primitive idempotents of generic cyclotomic Birman-Murakami-Wenzl
algebras can be constructed by consecutive evaluations of a certain rational
function. In the appendix, we prove a similar result for generic cyclotomic
Nazarov-Wenzl algebras.


title:
A fast scheme for the implementation of the quantum Rabi model with
  trapped ions

abstract:
  We show how to produce a fast quantum Rabi model with trapped ions. Its
importance resides not only in the acceleration of the phenomena that may be
achieved with these systems, from quantum gates to the generation of
nonclassical states of the vibrational motion of the ion, but also in reducing
unwanted effects such as the decay of coherences that may appear in such
systems.


title: Finding Trends in Software Research

abstract:
  This paper explores the structure of research papers in software engineering.
Using text mining, we study 35,391 software engineering (SE) papers from 34
leading SE venues over the last 25 years. These venues were divided, nearly
evenly, between conferences and journals. An important aspect of this analysis
is that it is fully automated and repeatable. To achieve that automation, we
used a stable topic modeling technique called LDADE that fully automates
parameter tuning in LDA. Using LDADE, we mine 11 topics that represent much of
the structure of contemporary SE. The 11 topics presented here should not be
"set in stone" as the only topics worthy of study in SE. Rather our goal is to
report that (a) text mining methods can detect large scale trends within our
community; (b) those topic change with time; so (c) it is important to have
automatic agents that can update our understanding of our community whenever
new data arrives.


title:
Guiding of relativistic electron beams in dense matter by longitudinally
  imposed strong magnetic fields

abstract:
  High-energy-density flows through dense matter are needed for effective
progress in the production of laser-driven intense sources of energetic
particles and radiation, in driving matter to extreme temperatures creating
state regimes relevant for planetary or stellar science as yet inaccessible at
the laboratory scale, or in achieving high-gain laser-driven thermonuclear
fusion. When interacting at the surface of dense (opaque) targets, intense
lasers accelerate relativistic electron beams which transport a significant
fraction of the laser energy into the target depth. However, the overall
laser-to-target coupling efficiency is impaired by the large divergence of the
electron beam, intrinsic to the laser-plasma interaction. By imposing a
longitudinal 600T laser-driven magnetic-field, our experimental results show
guided >10MA-current of MeV-electrons in solid matter. Due to the applied
magnetic field, the transported energy-density and the peak background electron
temperature at the 60micron-thick targets rear surface rise by factors 5,
resulting from unprecedentedly efficient guiding of relativistic electron
currents.


title:
Cavity-enhanced ultrafast two-dimensional spectroscopy using
  higher-order modes

abstract:
  We describe methods using frequency combs and optical resonators for
recording two-dimensional (2D) ultrafast spectroscopy signals with high
sensitivity. By coupling multiple frequency combs to higher-order modes of one
or more optical cavities, background-free, cavity-enhanced 2D spectroscopy
signals are naturally generated via phase cycling. As in cavity-enhanced
ultrafast transient absorption spectroscopy (CE-TAS), the signal to noise is
enhanced by a factor proportional to the cavity finesse squared, so even using
cavities of modest finesse, a very high sensitivity is expected, enabling
ultrafast 2D spectroscopy experiments in dilute molecular beams.


title: Central Exclusive Production at LHCb

abstract:
  Central Exclusive Production (CEP) is a unique process at hadron machines in
which particles are produced via colourless propagators. LHCb have measured the
cross-sections for the CEP of vector mesons,
$J/\psi,\psi(2S),\Upsilon(1S),\Upsilon(2S)$ and $\Upsilon(3S)$, which are
photo-produced. In the double pomeron exchange process, preliminary
measurements have been made of $\chi_{c0},\chi_{c1}, \chi_{c2}$ meson
production while the first observations of the CEP of pairs of charmonia,
$J/\psi J/\psi$ and $J/\psi \psi(2S)$, have been made and limits obtained on
the pair production of other charmonia.


title: Constraint matrix factorization for space variant PSFs field restoration

abstract:
  Context: in large-scale spatial surveys, the Point Spread Function (PSF)
varies across the instrument field of view (FOV). Local measurements of the
PSFs are given by the isolated stars images. Yet, these estimates may not be
directly usable for post-processings because of the observational noise and
potentially the aliasing. Aims: given a set of aliased and noisy stars images
from a telescope, we want to estimate well-resolved and noise-free PSFs at the
observed stars positions, in particular, exploiting the spatial correlation of
the PSFs across the FOV. Contributions: we introduce RCA (Resolved Components
Analysis) which is a noise-robust dimension reduction and super-resolution
method based on matrix factorization. We propose an original way of using the
PSFs spatial correlation in the restoration process through sparsity. The
introduced formalism can be applied to correlated data sets with respect to any
euclidean parametric space. Results: we tested our method on simulated
monochromatic PSFs of Euclid telescope (launch planned for 2020). The proposed
method outperforms existing PSFs restoration and dimension reduction methods.
We show that a coupled sparsity constraint on individual PSFs and their spatial
distribution yields a significant improvement on both the restored PSFs shapes
and the PSFs subspace identification, in presence of aliasing. Perspectives:
RCA can be naturally extended to account for the wavelength dependency of the
PSFs.


title: The Athena X-ray Integral Field Unit (X-IFU)

abstract:
  The X-ray Integral Field Unit (X-IFU) on board the Advanced Telescope for
High-ENergy Astrophysics (Athena) will provide spatially resolved
high-resolution X-ray spectroscopy from 0.2 to 12 keV, with 5 arc second pixels
over a field of view of 5 arc minute equivalent diameter and a spectral
resolution of 2.5 eV up to 7 keV. In this paper, we first review the core
scientific objectives of Athena, driving the main performance parameters of the
X-IFU, namely the spectral resolution, the field of view, the effective area,
the count rate capabilities, the instrumental background. We also illustrate
the breakthrough potential of the X-IFU for some observatory science goals.
Then we briefly describe the X-IFU design as defined at the time of the mission
consolidation review concluded in May 2016, and report on its predicted
performance. Finally, we discuss some options to improve the instrument
performance while not increasing its complexity and resource demands (e.g.
count rate capability, spectral resolution).
  The X-IFU will be provided by an international consortium led by France, The
Netherlands and Italy, with further ESA member state contributions from
Belgium, Finland, Germany, Poland, Spain, Switzerland and two international
partners from the United States and Japan.

categories: astro-ph.IM astro-ph.CO astro-ph.GA astro-ph.HE


title:
Monte Carlo analysis of a lateral IBIC experiment on a 4H-SiC Schottky
  diode

abstract:
  The transport properties of a 4H-SiC Schottky diode have been investigated by
the Ion Beam Induced Charge (IBIC) technique in lateral geometry through the
analysis of the charge collection efficiency (CCE) profile at a fixed applied
reverse bias voltage. The cross section of the sample orthogonal to the
electrodes was irradiated by a rarefied 4 MeV proton microbeam and the charge
pulses have been recorded as function of incident proton position with a
spatial resolution of 2 um. The CCE profile shows a broad plateau with CCE
values close to 100% occurring at the depletion layer, whereas in the neutral
region, the exponentially decreasing profile indicates the dominant role played
by the diffusion transport mechanism. Mapping of charge pulses was accomplished
by a novel computational approach, which consists in mapping the Gunn's
weighting potential by solving the electrostatic problem by finite element
method and hence evaluating the induced charge at the sensing electrode by a
Monte Carlo method. The combination of these two computational methods enabled
an exhaustive interpretation of the experimental profiles and allowed an
accurate evaluation both of the electrical characteristics of the active region
(e.g. electric field profiles) and of basic transport parameters (i. e.
diffusion length and minority carrier lifetime).


title:
Fabrication of quantum dots in undoped Si/Si$_{0.8}$Ge$_{0.2}$
  heterostructures using a single metal-gate layer

abstract:
  Enhancement-mode Si/SiGe electron quantum dots have been pursued extensively
by many groups for \revEdit{their} potential in quantum computing. Most of the
reported dot designs utilize multiple metal-gate layers and use Si/SiGe
heterostructures with Ge concentration close to 30\%. Here we report the
fabrication and low-temperature characterization of quantum dots in
Si/Si$_{0.8}$Ge$_{0.2}$ heterostructures using only one metal-gate layer. We
find that the threshold voltage of a channel narrower than 1 $\mu$m increases
as the width decreases. The higher threshold can be attributed to the
combination of quantum confinement and disorder. We also find that the lower Ge
ratio used here leads to a narrower operational gate bias range. The higher
threshold combined with the limited gate bias range constrains the device
design of lithographic quantum dots. We incorporate such considerations in our
device design and demonstrate a quantum dot that can be tuned from a single dot
to a double dot. The device uses only a single metal-gate layer, greatly
simplifying device design and fabrication.


title:
Empirical Optimization of Undulator Tapering at FLASH2 and Comparison
  with Numerical Simulations

abstract:
  In a free-electron laser equipped with variable-gap undulator modules, the
technique of undulator tapering opens up the possibility to increase the
radiation power beyond the initial saturation point, thus enhancing the
efficiency of the laser. The effectiveness of the enhancement relies on the
proper optimization of the taper profile. In this work, a multidimensional
optimization approach is implemented empirically in the x-ray free-electron
laser FLASH2. The empirical results are compared with numerical simulations.


title:
Spontaneous dimerization, critical lines, and short-range correlations
  in a frustrated spin-1 chain

abstract:
  We report on a detailed investigation of the spin-1 $J_1-J_2-J_3$ Heisenberg
model, a frustrated model with nearest-neighbor coupling $J_1$, next-nearest
neighbor coupling $J_2$, and a three site interaction $J_3\left[({\bf
S}_{i-1}\cdot {\bf S}_i)({\bf S}_i\cdot {\bf S}_{i+1})+{\mathrm H.c.}\right]$
previously studied in [Phys. Rev. B 93, 241108(R) (2016)]. Using DMRG and exact
diagonalizations, we show that the phase boundaries between the Haldane phase,
the next-nearest neighbor Haldane phase and the dimerized phase can be very
accurately determined by combining the information deduced from the
dimerization, the ground-state energy, the entanglement spectrum and the Berry
phase. By a careful investigation of the finite-size spectrum, we also show
that the transition between the next-nearest neighbor Haldane phase and the
dimerized phase is in the Ising universality class all along the critical line.
Furthermore, we justify the conformal embedding of the $SU(2)_2$
Wess-Zumino-Witten conformal field theory in terms of a boson and an Ising
field, and we explicitly derive a number of consequences of this embedding for
the spectrum along the $SU(2)_2$ transition line between the Haldane phase and
the dimerized phase. We also show that the solitons along the first-order
transition line between the Haldane phase and the dimerized phase carry a
spin-1/2, while those between different dimerization domains inside the
dimerized phase carry a spin 1. Finally, we show that short-range correlations
change character in the Haldane and dimerized phases through disorder and
Lifshitz lines, as well as through the development of short-range dimer
correlations in the Haldane phase, leading to a remarkably rich phase diagram.


title:
Lattice QCD calculation of form factors for $\Lambda_b \to \Lambda(1520)
  \ell^+ \ell^-$ decays

abstract:
  Experimental results for mesonic $b \to s \mu^+ \mu^-$ decays show a pattern
of deviations from Standard-Model predictions, which could be due to new
fundamental physics or due to an insufficient understanding of hadronic
effects. Additional information on the $b \to s \mu^+ \mu^-$ transition can be
obtained from $\Lambda_b$ decays. This was recently done using the process
$\Lambda_b \to \Lambda \mu^+ \mu^-$, where the $\Lambda$ is the lightest
strange baryon. A further interesting channel is $\Lambda_b \to p^+ K^- \mu^+
\mu^-$, where the $p^+ K^-$ final state receives contributions from multiple
higher-mass $\Lambda$ resonances. The narrowest and most prominent of these is
the $\Lambda(1520)$, which has $J^P=\frac32^-$. Here we present an ongoing
lattice QCD calculation of the relevant $\Lambda_b \to \Lambda(1520)$ form
factors. We discuss the choice of interpolating field for the $\Lambda(1520)$,
and explain our method for extracting the fourteen $\Lambda_b \to
\Lambda(1520)$ helicity form factors from correlation functions that are
computed in the $\Lambda(1520)$ rest frame. We present preliminary numerical
results at a pion mass of 340 MeV and a lattice spacing of 0.11 fm. This
calculation uses a domain-wall action for the $u$, $d$, and $s$ quarks and a
relativistic heavy-quark action for the $b$ quark, and is based on gauge-field
configurations generated by the RBC and UKQCD Collaborations.


title: Finite element analysis of ion-implanted diamond surface swelling

abstract:
  We present experimental results and numerical Finite Element analysis to
describe surface swelling due to the creation of buried graphite-like
inclusions in diamond substrates subjected to MeV ion implantation. Numerical
predictions are compared to experimental data for MeV proton and helium
implantations, performed with scanning ion microbeams. Swelling values are
measured with white light interferometric profilometry in both cases.
Simulations are based on a model which accounts for the through-the-thickness
variation of mechanical parameters in the material, as a function of ion type,
fluence and energy. Surface deformation profiles and internal stress
distributions are analyzed and numerical results are seen to adequately fit
experimental data. Results allow us to draw conclusions on structural damage
mechanisms in diamond for different MeV ion implantations.


title: Scholarly use of social media and altmetrics: a review of the literature

abstract:
  Social media has become integrated into the fabric of the scholarly
communication system in fundamental ways: principally through scholarly use of
social media platforms and the promotion of new indicators on the basis of
interactions with these platforms. Research and scholarship in this area has
accelerated since the coining and subsequent advocacy for altmetrics -- that
is, research indicators based on social media activity. This review provides an
extensive account of the state-of-the art in both scholarly use of social media
and altmetrics. The review consists of two main parts: the first examines the
use of social media in academia, examining the various functions these
platforms have in the scholarly communication process and the factors that
affect this use. The second part reviews empirical studies of altmetrics,
discussing the various interpretations of altmetrics, data collection and
methodological limitations, and differences according to platform. The review
ends with a critical discussion of the implications of this transformation in
the scholarly communication system.


title: Module tensor product of subnormal modules need not be subnormal

abstract:
  Let $\kappa : \mathbb D \times \mathbb D \to \mathbb C$ be a diagonal
positive definite kernel and let $\mathscr H_{\kappa}$ denote the associated
reproducing kernel Hilbert space of holomorphic functions on the open unit disc
$\mathbb D$. Assume that $zf \in \mathscr H$ whenever $f \in \mathscr H.$ Then
$\mathscr H$ is a Hilbert module over the polynomial ring $\mathbb C[z]$ with
module action $p \cdot f \mapsto pf$. We say that $\mathscr H_{\kappa}$ is a
subnormal Hilbert module if the operator $\mathscr M_{z}$ of multiplication by
the coordinate function $z$ on $\mathscr H_{\kappa}$ is subnormal. %If
$\kappa_1$ and $\kappa_2$ are two diagonal positive definite kernels then so is
their pointwise (tensor) product $\kappa:=\kappa_1\kappa_2$. In [Oper. Theory
Adv. Appl, 32: 219-241, 1988], N. Salinas asked whether the module tensor
product $\mathscr H_{\kappa_1} \otimes_{\mathbb C[z]} \mathscr H_{\kappa_2}$ of
subnormal Hilbert modules $\mathscr H_{\kappa_1}$ and $\mathscr H_{\kappa_2}$
is again subnormal. In this regard, we describe all subnormal module tensor
products $L^2_a(\mathbb D, w_{s_1}) \otimes_{\mathbb C[z]} L^2_a(\mathbb D,
w_{s_2})$, where $L^2_a(\mathbb D, w_s)$ denotes the weighted Bergman Hilbert
module with radial weight $$w_s(z)=\frac{1}{s \pi}|z|^{\frac{2(1-s)}{s}}~(z \in
\mathbb D, ~s > 0).$$ In particular, the module tensor product $L^2_a(\mathbb
D, w_{s}) \otimes_{\mathbb C[z]} L^2_a(\mathbb D, w_{s})$ is never subnormal
for any $s \geq 6$. Thus the answer to this question is no.


title: A survey of Gersten's conjecture

abstract:
  This article is the extended notes of my survey talk of Gersten's conjecture
given at the workshop "Bousfield classes form a set: a workshop in a memory of
Tetsusuke Ohkawa" at Nagoya University in August 2015. In the last section, I
give an explanation of my recent work of motivic Gernsten's conjecture.


title:
Direct Observation of Acoustic Phonon Confinement in Free-Standing
  Semiconductor Nanowires

abstract:
  Similar to electron waves, the phonon states in semiconductors can undergo
changes induced by external boundaries. Modification of acoustic phonon
spectrum in structures with periodically modulated elastic constant or mass
density - referred to as phononic crystals - has been proven experimentally and
utilized in practical applications. A possibility of modifying acoustic phonon
spectrum in individual nanostructures via spatial confinement would bring
tremendous benefits for controlling phonon-electron interaction and thermal
conduction at nanoscale. However, despite strong scientific and practical
importance, conclusive experimental evidence of acoustic phonon confinement in
individual free-standing nanostructures, e.g. nanowires, is still missing. The
length scale, at which phonon dispersion undergoes changes and a possibility of
the phonon group velocity reduction, are debated. Here, we utilize specially
designed high-quality GaAs nanowires (NWs) with different diameters, D, and
large inter-nanowire distances to directly demonstrate acoustic phonon
confinement. The measurements conducted with Brillouin - Mandelstam
spectroscopy reveal confined phonon polarization branches with frequencies from
4 GHz to 40 GHz in NWs with D as large as ~128 nm, i.e. at length scale, which
exceeds the "grey" phonon mean-free path in GaAs by an almost an order of
magnitude. The phonon dispersion modification and phonon energy scaling with D
in individual nanowires are in excellent agreement with theory. The obtained
results can lead to more efficient nanoscale control of acoustic phonons, with
benefits for nanoelectronics, thermoelectric energy conversion, thermal
management, and novel spintronic technologies.


title: Resumming the POPE at One Loop

abstract:
  The Pentagon Operator Product Expansion represents polygonal Wilson loops in
planar $\mathcal{N}=4$ super Yang-Mills in terms of a series of flux tube
excitations for finite coupling. We demonstrate how to re-sum this series at
the one loop level for the hexagonal Wilson loop dual to the six-point MHV
amplitude. By summing over a series of effective excitations we find
expressions which integrate to logarithms and polylogarithms, reproducing the
known one-loop result.


title:
Improved Accuracy of High-Order WENO Finite Volume Methods on Cartesian
  Grids

abstract:
  We propose a simple modification of standard WENO finite volume methods for
Cartesian grids, which retains the full spatial order of accuracy of the
one-dimensional discretization when applied to nonlinear multidimensional
systems of conservation laws.
  We derive formulas, which allow us to compute high-order accurate point
values of the conserved quantities at grid cell interfaces. Using those point
values, we can compute a high-order flux at the center of a grid cell
interface. Finally, we use those point values to compute high-order accurate
averaged fluxes at cell interfaces as needed by a finite volume method.
  The method is described in detail for the two-dimensional Euler equations of
gas dynamics. An extension to the three-dimensional case as well as to other
nonlinear systems of conservation laws in divergence form is straightforward.
Furthermore, similar ideas can be used to improve the accuracy of WENO type
methods for hyperbolic systems which are not in divergence form.
  Several test computations confirm the high-order accuracy for smooth
nonlinear problems.


title:
On the growth of a particle coalescing in a Poisson distribution of
  obstacles

abstract:
  In this paper we consider the coalescence dynamics of a tagged particle
moving in a random distribution of particles with volumes independently
distributed according to a probability distribution (CTP model). We provide a
rigorous derivation of a kinetic equation for the probability density for the
size and position of the tagged particle in the kinetic limit where the volume
fraction $\phi$ filled by the background of particles tends to zero. Moreover,
we prove that the particle system, i.e. CTP model, is well posed for a small
but positive volume fraction with probability one as long as the the
distribution of the particle sizes is compactly supported.


title: A resurgence analysis for cubic and quartic anharmonic potentials

abstract:
  In this work we explicitly show resurgence relations between perturbative and
one instanton sectors of the resonance energy levels for cubic and quartic
anharmonic potentials in one-dimensional quantum mechanics. Both systems
satisfy the Dunne-Unsal relation and hence we are able to derive one-instanton
non-perturbative contributions with the fluctuation terms to the energy merely
from the perturbative data. We confirm our results with previous results
obtained by Zinn-Justin et al.


title: Nonlinear Breit-Wheeler pair production in a tightly focused laser beam

abstract:
  The only available analytical framework for investigating QED processes in a
strong laser field systematically relies on approximating the latter as a plane
wave. However, realistic high-intensity laser beams feature much more complex
space-time structures than plane waves. Here, we show the feasibility of an
analytical framework for investigating strong-field QED processes in laser
beams of arbitrary space-time structure by determining the energy spectrum of
positrons produced via nonlinear Breit-Wheeler pair production as a function of
the background field in the realistic assumption that the energy of the
incoming photon is the largest dynamical energy in the problem. A numerical
evaluation of the angular resolved positron spectrum shows significant
quantitative differences with respect to the analogous result in a plane wave,
such that the present results will be also important for the design of upcoming
strong laser facilities aiming at measuring this process.


title: Summary of Structure Functions and PDFs Working Group

abstract:
  This summary presents personal highlights from the Structure Functions and
PDFs Working Group (WG1) at DIS 2016.


title: Universal factorization spaces and algebras

abstract:
  We introduce categories of weak factorization algebras and factorization
spaces, and prove that they are equivalent to the categories of ordinary
factorization algebras and spaces, respectively. This allows us to define the
pullback of a factorization algebra or space by an \'etale morphism of schemes,
and hence to define the notion of a universal factorization space or algebra.
This provides a generalization to higher dimensions and to non-linear settings
of the notion of a vertex algebra.


title:
Impurity effects on spin dynamics in magnetic and superconducting iron
  pnictides and chalcogenides

abstract:
  In this paper we summarize the effects of magnetic and nonmagnetic impurities
on the spin dynamics in Febased superconductors and their parent compounds. The
effects of chemical substitution, vacancies, and disorder on the suppression or
stabilization of superconductivity and spin-density-wave phases are reviewed in
the context of recent neutron-spectroscopy measurements of spin excitations. We
also present new results on the structure of magnetic fluctuations in BaFe2As2
single crystals doped with Mn local moments and discuss them in relationship to
the previously reported (pi, pi) branch of checkerboard magnetic excitations.


title:
Wide-range shell correction to the Thomas--Fermi theory and equation of
  state for electrons

abstract:
  Shell effects reflects irregularities of physical quantities caused by a
discrete energy spectrum. The theory of the shell effects by Kirzhnits and
Shpatakovskaya is valid only at relatively low densities providing for
oscillations of thermodynamic functions. Similar effects for the electronic
binding energy of a neutral atom were considered by Englert and Schwinger. In
this work we propose a method of calculation of shell effects applicable in a
wide range of density and temperature. The model is based on the
finite-temperature Thomas-Fermi theory. Shell corrections to thermodynamic
functions are obtained by special accounting of semiclassical states of bound
electrons in the Thomas-Fermi potential. The results are in good correspondence
with the precise Saha approach for the low density plasma and density
functional theory simulation at high density.


title:
Detecting 3D vegetation structure with the Galileo space probe: Can a
  distant probe detect vegetation structure on Earth?

abstract:
  Sagan et al. (1993) used the Galileo space probe data and first principles to
find evidence of life on Earth. Here we ask whether Sagan et al. (1993) could
also have detected whether life on Earth had three-dimensional structure, based
on the Galileo space probe data. We reanalyse the data from this probe to see
if structured vegetation could have been detected in regions with abundant
photosynthetic pigments through the anisotropy of reflected shortwave
radiation. We compare changing brightness of the Amazon forest (a region where
Sagan et al. (1993) noted a red edge in the reflectance spectrum, indicative of
photosynthesis) as the planet rotates to a common model of reflectance
anisotropy and found measured increase of surface reflectance of 0.019 versus a
0.007 predicted from only anisotropic effects. We hypothesize the difference
was due to minor cloud contamination. However, the Galileo dataset had only a
small change in phase angle (sun-satellite position) which reduced the observed
anisotropy signal and we demonstrate that theoretically if the probe had a
variable phase angle between 0-20, there would have been a much larger
predicted change in surface reflectance of 0.06 and under such a scenario
three-dimensional vegetation structure on Earth could possibly have been
detected. These results suggest that anisotropic effects may be useful to help
determine whether exoplanets have three-dimensional vegetation structure in the
future but that further comparisons between empirical and theoretical results
are first necessary.


title:
Simultaneous penalized M-estimation of covariance matrices using
  geodesically convex optimization

abstract:
  A common assumption when sampling $p$-dimensional observations from $K$
distinct group is the equality of the covariance matrices. In this paper, we
propose two penalized $M$-estimation approaches for the estimation of the
covariance or scatter matrices under the broader assumption that they may
simply be close to each other, and hence roughly deviate from some positive
definite "center". The first approach begins by generating a pooled
$M$-estimator of scatter based on all the data, followed by a penalised
$M$-estimator of scatter for each group, with the penalty term chosen so that
the individual scatter matrices are shrunk towards the pooled scatter matrix.
In the second approach, we minimize the sum of the individual group
$M$-estimation cost functions together with an additive joint penalty term
which enforces some similarity between the individual scatter estimators, i.e.
shrinkage towards a mutual center. In both approaches, we utilize the concept
of geodesic convexity to prove the existence and uniqueness of the penalized
solution under general conditions. We consider three specific penalty functions
based on the Euclidean, the Riemannian, and the Kullback-Leibler distances. In
the second approach, the distance based penalties are shown to lead to
estimators of the mutual center that are related to the arithmetic, the
Riemannian and the harmonic means of positive definite matrices, respectively.
A penalty based on an ellipticity measure is also considered which is
particularly useful for shape matrix estimators. Fixed point equations are
derived for each penalty function and the benefits of the estimators are
illustrated in regularized discriminant analysis problem.


title:
Realistic calculations for $c$-coefficients of the isobaric mass
  multiplet equation in $1p0f$ shell nuclei

abstract:
  We present calculations for the $c$-coefficients of the isobaric mass
multiplet equation for nuclei from $A=42$ to $A=54$ based on input from three
realistic nucleon-nucleon interactions. We demonstrate that there is a clear
dependence on the short-ranged charge-symmetry breaking (CSB) part of the
strong interaction and that there is significant disagreement in the CSB part
between the commonly used CD-Bonn, N$^3$LO, and Argonne V18 nucleon-nucleon
interactions. In addition, we show that all three interactions give a CSB
contribution to the $c$-coefficient that is too large when compared to
experiment.


title:
Temporal Activity Detection in Untrimmed Videos with Recurrent Neural
  Networks

abstract:
  This thesis explore different approaches using Convolutional and Recurrent
Neural Networks to classify and temporally localize activities on videos,
furthermore an implementation to achieve it has been proposed. As the first
step, features have been extracted from video frames using an state of the art
3D Convolutional Neural Network. This features are fed in a recurrent neural
network that solves the activity classification and temporally location tasks
in a simple and flexible way. Different architectures and configurations have
been tested in order to achieve the best performance and learning of the video
dataset provided. In addition it has been studied different kind of post
processing over the trained network's output to achieve a better results on the
temporally localization of activities on the videos. The results provided by
the neural network developed in this thesis have been submitted to the
ActivityNet Challenge 2016 of the CVPR, achieving competitive results using a
simple and flexible architecture.


title:
Laboratory spectroscopic study and astronomical detection of
  vibrationally excited n-propyl cyanide

abstract:
  We performed a spectral line survey called Exploring Molecular Complexity
with ALMA (EMoCA) toward Sagittarius~B2(N) between 84.1 and 114.4 GHz with the
Atacama Large Millimeter/submillimeter Array (ALMA) in its Cycles 0 and 1. We
determined line intensities of n-propyl cyanide in the ground vibrational
states of its gauche and anti conformers toward the hot molecular core
Sagittarius B2(N2) which suggest that we should also be able to detect
transitions pertaining to excited vibrational states. We wanted to determine
spectroscopic parameters of low-lying vibrational states of both conformers of
n-propyl cyanide to search for them in our ALMA data. We recorded laboratory
rotational spectra of n-propyl cyanide in two spectral windows between 36 and
127 GHz. We searched for emission lines produced by these states in the ALMA
spectrum of Sagittarius B2(N2). We modeled their emission and the emission of
the ground vibrational states assuming local thermodynamic equilibrium (LTE).
We have made extensive assignments of a- and b-type transitions of the four
lowest vibrational states of the gauche conformer which reach J and Ka quantum
numbers of 65 and 20, respectively. We assigned mostly a-type transitions for
the anti conformer with J and Ka quantum numbers up to 48 and 24, respectively.
Rotational and Fermi perturbations between two anti states allowed us to
determine their energy difference. The resulting spectroscopic parameters
enabled us to identify transitions of all four vibrational states of each
conformer in our ALMA data. The emission features of all states, including the
ground vibrational state, are well-reproduced with the same LTE modeling
parameters, which gives us confidence in the reliability of the
identifications, even for the states with only one clearly detected line.


title:
Scheduling Refresh Queries for Keeping Results from a SPARQL Endpoint
  Up-to-Date (Extended Version)

abstract:
  Many datasets change over time. As a consequence, long-running applications
that cache and repeatedly use query results obtained from a SPARQL endpoint may
resubmit the queries regularly to ensure up-to-dateness of the results. While
this approach may be feasible if the number of such regular refresh queries is
manageable, with an increasing number of applications adopting this approach,
the SPARQL endpoint may become overloaded with such refresh queries. A more
scalable approach would be to use a middle-ware component at which the
applications register their queries and get notified with updated query results
once the results have changed. Then, this middle-ware can schedule the repeated
execution of the refresh queries without overloading the endpoint. In this
paper, we study the problem of scheduling refresh queries for a large number of
registered queries by assuming an overload-avoiding upper bound on the length
of a regular time slot available for testing refresh queries. We investigate a
variety of scheduling strategies and compare them experimentally in terms of
time slots needed before they recognize changes and number of changes that they
miss.


title: The sigma meson from QCD sum rules for large-$N_c$ Regge spectra

abstract:
  The QCD sum rules in the large-$N_c$ limit for the light non-strange vector,
axial and scalar mesons are considered assuming a string-like linear spectrum
for the radially excited states. We propose a improved method for combined
analysis of these channels that gives a reasonable description of the observed
spectrum. In the vector-axial case, fixing the pion decay constant and the
gluon condensate we obtain more or less physical values for the masses of
ground states and the quark condensate. Thus a typical need for this method to
fix the mass of some ground state is overcome. Using in the scalar channel the
values of presumably universal slope of radial trajectories and the quark
condensate obtained in the vector-axial channel, we find that, in contrast to
some strong claims in the literature, a prediction of light scalar state with a
mass close to the mass of $f_0(500)$ seems to be natural in the considered
approach and may follow in a natural way from the Regge phenomenology.


title:
Higher Order Smallest Parts Functions and Rank-Crank Moment Inequalities
  from Bailey Pairs

abstract:
  We generalize a result of Garvan on inequalities and interpretations of the
moments of the partition rank and crank functions. In particular for nearly 30
Bailey pairs, we introduce a rank-like function, establish inequalities with
the moments of the rank-like function and an associated crank-like function,
and give an associated so called higher order smallest parts function. In some
cases we are able to deduce inequalities among the rank-like functions. We also
conjecture additional inequalities and a large number of congruences for the
higher order smallest parts functions.


title: Interlayer Configurations in Twisted Bilayers of Folded Graphene

abstract:
  The folding of monolayer graphene leads to new layered systems, termed
twisted bilayer graphene (TBG), generally displaying a certain interlayer
rotation away from crystallographic alignment. We here present an atomic force
microscopy study on folded graphene, revealing unexpectedly large twist angle
dependent modulations of ~3 angstrom in interlayer distance. At the TBG
surface, we find enhanced friction attributable to superlubricity in between
incommensurate layers. At the bended edge, the radius of curvature scales with
the folded length, congruent to earlier studies on carbon nanotubes.


title: The full Ward-Takahashi Identity for colored tensor models

abstract:
  Colored tensor models (CTM) is a random geometrical approach to quantum
gravity. We scrutinize the structure of the connected correlation functions of
general CTM-interactions and organize them by boundaries of Feynman graphs. For
rank-$D$ interactions including, but not restricted to, all melonic
$\varphi^4$-vertices---to wit, solely those quartic vertices that can lead to
dominant spherical contributions in the large-$N$ expansion---the
aforementioned boundary graphs are shown to be precisely all (possibly
disconnected) vertex-bipartite regularly edge-$D$-colored graphs. The concept
of CTM-compatible boundary-graph automorphism is introduced and an auxiliary
graph calculus is developed. With the aid of these constructs, certain $\mathrm
U(\infty)$-invariance of the path integral measure is fully exploited in order
to derive a strong Ward-Takahashi Identity for CTMs with a symmetry-breaking
kinetic term. For the rank-$3$ $\varphi^4$-theory, we get the exact
integral-like equation for the 2-point function. Similarly, exact equations for
higher multipoint functions can be readily obtained departing from this full
Ward-Takahashi identity. Our results hold for some Group Field Theories as
well. Altogether, our non-perturbative approach trades some graph theoretical
methods for analytical ones. We believe that these tools can be extended to
tensorial SYK-models.


title:
Degenerate higher order scalar-tensor theories beyond Horndeski up to
  cubic order

abstract:
  We present all scalar-tensor Lagrangians that are cubic in second derivatives
of a scalar field, and that are degenerate, hence avoiding Ostrogradsky
instabilities. Thanks to the existence of constraints, they propagate no more
than three degrees of freedom, despite having higher order equations of motion.
We also determine the viable combinations of previously identified quadratic
degenerate Lagrangians and the newly established cubic ones. Finally, we study
whether the new theories are connected to known scalar-tensor theories such as
Horndeski and beyond Horndeski, through conformal or disformal transformations.


title: Zero discord implies classicality

abstract:
  The "classical-quantum" ($\mathit{cq}$) discord of a bipartite state
$\rho^{AB}$ is the smallest difference between the mutual information
$S(\rho^{A:B})$ of $\rho$ and that of $\rho$ after a measurement channel is
applied on the $A$ system. Relating zero discord to the strong subadditivity of
the Von Neumann entropy, Datta proved that a state has zero $\mathit{cq}$
discord iff and only if it can be written in the form $\sum_i p_i\,
|i\rangle\langle i|\otimes \rho^B_i$ for $p_i$ a probability distribution,
$|i\rangle$ a basis of the $A$ system and $\rho^B_i$ states of the $B$ system.
We provide a simple proof of that same result using directly a theorem of Petz
on channels that leave unchanged the relative entropy of two given states.


title:
An a posteriori error analysis for an optimal control problem with point
  sources

abstract:
  We propose and analyze a reliable and efficient a posteriori error estimator
for a constrained linear-quadratic optimal control problem involving Dirac
measures; the control variable corresponds to the amplitude of forces modeled
as point sources. The proposed a posteriori error estimator is defined as the
sum of two contributions, which come from the state and adjoint equations. The
estimator associated with the state equation is based on Muckenhoupt weighted
Sobolev spaces, while the one associated with the adjoint is in the maximum
norm and allows for unbounded right hand sides. The analysis is valid for two
and three-dimensional domains. On the basis of the devised a posteriori error
estimator, we design a simple adaptive strategy that yields optimal rates of
convergence for the numerical examples that we perform.


title: Dust polarization and ISM turbulence

abstract:
  Perhaps the most intriguing result of Planck's dust-polarization measurements
is the observation that the power in the E-mode polarization is twice that in
the B mode, as opposed to pre-Planck expectations of roughly equal dust powers
in E and B modes. Here we show how the E- and B-mode powers depend on the
detailed properties of the fluctuations in the magnetized interstellar medium.
These fluctuations are classified into the slow, fast, and Alfv\'en
magnetohydrodynamic (MHD) waves, which are determined once the ratio of gas to
magnetic-field pressures is specified. We also parametrize models in terms of
the power amplitudes and power anisotropies for the three types of waves. We
find that the observed EE/BB ratio (and its scale invariance) and positive TE
correlation cannot be easily explained in terms of favored models for MHD
turbulence. The observed power-law index for temperature/polarization
fluctuations also disfavors MHD turbulence. We thus speculate that the 0.1--30
pc length scales probed by these dust-polarization measurements are not
described by MHD turbulence but, rather, probe the large-scale physics that
drives ISM turbulence. We develop a simple phenomenological model, based on
random displacements of the magnetized fluid, that produces EE/BB $\simeq2$ and
a positive TE cross-correlation. According to this model, the EE/BB and TE
signals are due to longitudinal, rather than transverse, modes in the
random-displacement field, providing, perhaps, some clue to the mechanism that
stirs the ISM. Future investigations involving the spatial dependence of the
EE/BB ratio, TE correlation, and local departures from statistical isotropy in
dust-polarization maps, as well as further tests of some of the assumptions in
this analysis, are outlined. This work may also aid in the improvement of
foreground-separation techniques for studies of CMB polarization.


title: Where is my Phone ? Personal Object Retrieval from Egocentric Images

abstract:
  This work presents a retrieval pipeline and evaluation scheme for the problem
of finding the last appearance of personal objects in a large dataset of images
captured from a wearable camera. Each personal object is modelled by a small
set of images that define a query for a visual search engine.The retrieved
results are reranked considering the temporal timestamps of the images to
increase the relevance of the later detections. Finally, a temporal
interleaving of the results is introduced for robustness against false
detections. The Mean Reciprocal Rank is proposed as a metric to evaluate this
problem. This application could help into developing personal assistants
capable of helping users when they do not remember where they left their
personal belongings.


title: Free loop spaces and dihedral homology

abstract:
  We prove an $O(2)$-equivariant version of the Jones isomorphism relating the
Borel $O(2)$-equivariant cohomology of the free loop space to the dihedral
homology of the cochain algebra. We discuss polynomial forms and a variation of
the de Rham isomorphism and use these to do a computation for the 2-sphere.


title: Spectrally Perron Polynomials and the Cauchy-Ostrovsky Theorem

abstract:
  In this note, we simplify the statements of theorems attributed to Cauchy and
Ostrovsky and give proofs of each theorem via combinatorial and nonnegative
matrix theory. We also show that each simple sufficient condition in each
statement is also necessary in its respective case. In addition, we introduce
the notion of a spectrally Perron polynomial and pose a problem that appeals to
a wide mathematical audience.


title:
Maximizing Data Rate for Multiway Relay Channels with Pairwise
  Transmission Strategy

abstract:
  In a multiway relay channel (MWRC), pairwise transmission strategy can be
used to reduce the computational complexity at the relay and the users without
sacrificing the data rate, significantly. The performance of such pairwise
strategies, however, is affected by the way that the users are paired to
transmit. In this paper, we study the effect of pairing on the common rate and
sum rate of an MWRC with functional-decode-forward (FDF) relaying strategy
where users experience asymmetric channel conditions. To this end, we first
develop a graphical model for an MWRC with pairwise transmission strategy.
Using this model, we then find the maximum achievable common rate and sum rate
as well as the user pairings that achieve these rates. This marks the ultimate
performance of FDF relaying in an MWRC setup. Further, we show that the rate
enhancement achieved through the optimal user pairing becomes less pronounced
at higher SNRs. Using computer simulations, the performance of the optimal
pairing is compared with those of other proposed pairings in the literature.


title: Floquet Majorana and Para-Fermions in Driven Rashba Nanowires

abstract:
  We study a periodically driven nanowire with Rashba-like conduction and
valence bands in the presence of a magnetic field. We identify topological
regimes in which the system hosts zero-energy Majorana fermions. We further
investigate the effect of strong electron-electron interactions that give rise
to parafermion zero energy modes hosted at the nanowire ends. The first setup
we consider allows for topological phases by applying only static magnetic
fields without the need of superconductivity. The second setup involves both
superconductivity and time-dependent magnetic fields and allows one to generate
topological phases without fine-tuning of the chemical potential. Promising
candidate materials are graphene nanoribbons due to their intrinsic
particle-hole symmetry.


title: Achievements in Answer Set Programming

abstract:
  This paper describes an approach to the methodology of answer set programming
(ASP) that can facilitate the design of encodings that are easy to understand
and provably correct. Under this approach, after appending a rule or a small
group of rules to the emerging program we include a comment that states what
has been "achieved" so far. This strategy allows us to set out our
understanding of the design of the program by describing the roles of small
parts of the program in a mathematically precise way.


title:
CARMENES input catalogue of M dwarfs II. High-resolution imaging with
  FastCam

abstract:
  Aims: We search for low-mass companions of M dwarfs and characterize their
multiplicity fraction with the purpose of helping in the selection of the most
appropriate targets for the CARMENES exoplanet survey. Methods: We obtained
high-resolution images in the I band with the lucky imaging instrument FastCam
at the 1.5 m Telescopio Carlos Sanchez for 490 mid- to late-M dwarfs. For all
the detected binaries, we measured angular separations, position angles, and
magnitude differences in the I band. We also calculated the masses of each
individual component and estimated orbital periods, using the available
magnitude and colour relations for M dwarfs and our own MJ-spectral type and
mass-MI relations. To avoid biases in our sample selection, we built a
volume-limited sample of M0.0-M5.0 dwarfs that is complete up to 86% within 14
pc. Results: From the 490 observed stars, we detected 80 companions in 76
systems, of which 30 are new discoveries. The multiplicity fraction in our
observed sample is 16.7+-2.0% . In our volume-limited sample it is 19.5+-2.3%
for angular separations of 0.2 to 5.0 arcsec (1.4-65.6 au), The distribution of
the projected physical separations peaks at 2.5-7.5 au. For M0.0-M3.5 V
primaries, our search is sensitive to mass ratios higher than 0.3. Binaries
with projected physical separations shorter than 50 au tend to be of equal
mass. For 26 of our systems, we estimated orbital periods shorter than 50 a, 10
of which are presented here for the first time. We measured variations in
angular separation and position angle that are due to orbital motions in 17 of
these systems. The contribution of binaries and multiples with angular
separations shorter than 0.2 arcsec, longer than 5.0 arcsec, and of
spectroscopic binaries identified from previous searches, although not
complete, may increase the multiplicity fraction of M dwarfs in our
volume-limited sample to at least 36%.


title: Noncommutative Deformations of Locally Symmetric K\"ahler manifolds

abstract:
  We derive algebraic recurrence relations to obtain a deformation quantization
with separation of variables for a locally symmetric K\"ahler manifold. This
quantization method is one of the ways to perform a deformation quantization of
K\"ahler manifolds, which is introduced by Karabegov. From the recurrence
relations, concrete expressions of star products for one-dimensional local
symmetric K\"ahler manifolds and ${\mathbb C}P^N$ are constructed. The
recurrence relations for a Grassmann manifold $G_{2,2}$ are closely studied
too.


title: Itinerant conductance in fuse-antifuse networks

abstract:
  We report on a novel dynamic phase in electrical networks, in which current
channels perpetually change in time. This occurs when the individual elements
of the network are fuse-antifuse devices, namely, become insulators within a
certain finite interval of local applied voltages. As a consequence, the
macroscopic current exhibits temporal fluctuations which increase with system
size. We determine the conditions under which this exotic situation appears by
establishing a phase diagram as a function of the applied field and the size of
the insulating window. Besides its obvious application as a versatile
electronic device, due to its rich variety of behaviors, this network model
provides a possible description for particle-laden flow through porous media
leading to dynamical clogging and reopening of the local channels in the pore
space.


title: brTPF: Bindings-Restricted Triple Pattern Fragments (Extended Preprint)

abstract:
  The Triple Pattern Fragment (TPF) interface is a recent proposal for reducing
server load in Web-based approaches to execute SPARQL queries over public RDF
datasets. The price for less overloaded servers is a higher client-side load
and a substantial increase in network load (in terms of both the number of HTTP
requests and data transfer). In this paper, we propose a slightly extended
interface that allows clients to attach intermediate results to triple pattern
requests. The response to such a request is expected to contain triples from
the underlying dataset that do not only match the given triple pattern (as in
the case of TPF), but that are guaranteed to contribute in a join with the
given intermediate result. Our hypothesis is that a distributed query execution
using this extended interface can reduce the network load (in comparison to a
pure TPF-based query execution) without reducing the overall throughput of the
client-server system significantly. Our main contribution in this paper is
twofold: we empirically verify the hypothesis and provide an extensive
experimental comparison of our proposal and TPF.


title: ORBSLAM-based Endoscope Tracking and 3D Reconstruction

abstract:
  We aim to track the endoscope location inside the surgical scene and provide
3D reconstruction, in real-time, from the sole input of the image sequence
captured by the monocular endoscope. This information offers new possibilities
for developing surgical navigation and augmented reality applications. The main
benefit of this approach is the lack of extra tracking elements which can
disturb the surgeon performance in the clinical routine. It is our first
contribution to exploit ORBSLAM, one of the best performing monocular SLAM
algorithms, to estimate both of the endoscope location, and 3D structure of the
surgical scene. However, the reconstructed 3D map poorly describe textureless
soft organ surfaces such as liver. It is our second contribution to extend
ORBSLAM to be able to reconstruct a semi-dense map of soft organs. Experimental
results on in-vivo pigs, shows a robust endoscope tracking even with organs
deformations and partial instrument occlusions. It also shows the
reconstruction density, and accuracy against ground truth surface obtained from
CT.


title: High-Energy Neutrino Emission from White Dwarf Mergers

abstract:
  The merger of two white dwarfs is expected to result in a central fast
rotating core surrounded by a debris disk, in which magnetorotational
instabilities give rise to a hot magnetized corona and a magnetized outflow.
The dissipation of magnetic energy via reconnection could lead to the
acceleration of cosmic-rays in the expanding material, which would result in
high energy neutrinos. We discuss the possibility of using these neutrino
signals as probes of the outflow dynamics, magnetic energy dissipation rate and
cosmic-ray acceleration efficiency. Importantly, the accompanying high-energy
gamma-rays are absorbed within these sources because of the large optical
depth, so these neutrino sources can be regarded as hidden cosmic-ray
accelerators that are consistent with the non-detection of gamma-rays with
Fermi-LAT. While the cosmic-ray generation rate is highly uncertain, if it
reaches $\sim10^{45}\,\rm erg\,Mpc^{-3}\,yr^{-1}$, the diffuse neutrino flux
could contribute a substantial fraction of the IceCube observations. We also
evaluate the prospect of observing individual merger events, which provides a
means for testing such sources in the future.


title: Luna-Vust invariants of Cox rings and skeletons of spherical varieties

abstract:
  Given the Luna-Vust invariants of a spherical variety, we determine the
Luna-Vust invariants of the spectrum of its Cox ring. In particular, we deduce
an explicit description of the divisor class group of the Cox ring. It follows
that every spherical variety admits iteration of Cox rings. Moreover, we obtain
a combinatorial proof of the fact that the Cox ring is determined by the
spherical skeleton, which is a known result following from the description of
the Cox ring due to Brion. Finally, we show that a conjectural combinatorial
smoothness criterion can be reduced to the case of a factorial affine spherical
variety with a fixed point.


title:
On characterization of monomial representations of discrete
  supersolvable groups

abstract:
  We prove that an abstract (possibly infinite dimensional) complex irreducible
representation of a discrete supersolvable group is monomial if and only if it
has finite weight. We also prove a general result that implies converse of
Schur's lemma holds true for certain induced representations of finitely
generated discrete groups. At last, we work out example of infinite dihedral
group and prove that it is a monomial group.


title: Spin pumping and measurement of spin currents in optical superlattices

abstract:
  We report on the experimental implementation of a spin pump with ultracold
bosonic atoms in an optical superlattice. In the limit of isolated double wells
it represents a 1D dynamical version of the quantum spin Hall effect. Starting
from an antiferromagnetically ordered spin chain, we periodically vary the
underlying spin-dependent Hamiltonian and observe a spin current without charge
transport. We demonstrate a novel detection method to measure spin currents in
optical lattices via superexchange oscillations emerging after a projection
onto static double wells. Furthermore, we directly verify spin transport
through in-situ measurements of the spins' center of mass displacement.


title:
Extracting host galaxy dispersion measure and constraining cosmological
  parameters using fast radio burst data

abstract:
  The excessive dispersion measures (DMs) and high Galactic latitudes of fast
radio bursts (FRBs) hint toward a cosmological origin of these mysterious
transients. Methods of using measured DM and redshift $z$ to study cosmology
have been proposed, but one needs to assume a certain amount of DM contribution
from the host galaxy (DM$_{\rm HG}$) in order to apply those methods. We
introduce a slope parameter $\beta(z) \equiv d \ln \left< {\rm DM}_{\rm E}
\right> / d \ln z$ (where DM$_{\rm E}$ is the observed DM subtracting the
Galactic contribution), which can be directly measured when a sample of FRBs
have $z$ measured. We show that $\left< {\rm DM_{HG}}\right>$ can be roughly
inferred from $\beta$ and the mean values, $\overline{\rm \left<DM_{\rm
E}\right>}$ and $\bar z$, of the sample. Through Monte Carlo simulations, we
show that the mean value of local host galaxy DM,
$\left<\rm{DM_{HG,loc}}\right>$, along with other cosmological parameters (mass
density $\Omega_m$ in the $\Lambda$CDM model, and the IGM portion of the baryon
energy density $\Omega_b f_{\rm IGM}$) can be independently measured through
MCMC fitting to the data.


title: On the limit closure of a sequence of elements in local rings

abstract:
  We present a systematic study for the limit closure $(\underline{x})^{\lim}$
of a sequence of elements $\underline{x}$ (eg. a system of of parameters) in a
local ring. Firstly, we answer the question which elements are always contained
in the limit closure of a system of parameters. Then we apply this result to
give a characterization of systems of parameters which is a generalization of
previous results of Dutta and Roberts in \cite{DR} and of Fouli and Huneke in
\cite{FH}. We also prove a topological characterization of unmixed local rings.
In two dimensional case, we compute explicitly the limit closure of a system of
parameters. Some interesting examples are given.


title: Counterexamples To Bertini Theorems for Test Ideals

abstract:
  In algebraic geometry, Bertini theorems are an extremely important tool. A
generalization of the classical theorem to multiplier ideals show that
multiplier ideals restrict to a general hyperplane section. In characteristic
$p > 0$, the test ideal can be seen to be the characteristic $p > 0$ analog of
the multiplier ideal. However, in this paper it is shown that the same type of
Bertini type theorem does not hold for test ideals.


title: Projecting light beams with 3D waveguide arrays

abstract:
  Free-space light beams with complex intensity patterns, or non-trivial phase
structure, are demanded in diverse fields, ranging from classical and quantum
optical communications, to manipulation and imaging of microparticles and
cells. Static or dynamic spatial light modulators, acting on phase or intensity
of an incoming light wave, are the conventional choices to produce beams with
such non-trivial characteristics. However, interfacing these devices with
optical fibers or integrated optical circuits often requires difficult
alignment or cumbersome optical setups. Here we explore theoretically and with
numerical simulations the potentialities of directly using the output of
engineered three-dimensional waveguide arrays, illuminated with linearly
polarized light, to project light beams with peculiar structures. We
investigate through a collection of illustrative configurations the far field
distribution, showing the possibility to achieve orbital angular momentum, or
to produce elaborate intensity or phase patterns with several singularity
points. We also simulate the propagation of the projected beam, showing the
possibility to concentrate light. We note that these devices should be at reach
of current technology, thus perspectives are open for the generation of complex
free-space optical beams from integrated waveguide circuits.


title: Slope Estimates for Generalized Artin-Schreier Curves

abstract:
  We provide first slope estimates of the Newton polygon of generalized
Artin-Schreier curves, which are proved using the action of Frobenius and
Verschiebung on cohomology. We provide a number of applications such as an
improved Hasse-Weil bound for this class of curves.


title: Coloring Jordan regions and curves

abstract:
  A Jordan region is a subset of the plane that is homeomorphic to a closed
disk. Consider a family $\mathcal{F}$ of Jordan regions whose interiors are
pairwise disjoint, and such that any two Jordan regions intersect in at most
one point. If any point of the plane is contained in at most $k$ elements of
$\mathcal{F}$ (with $k$ sufficiently large), then we show that the elements of
$\mathcal{F}$ can be colored with at most $k+1$ colors so that intersecting
Jordan regions are assigned distinct colors. This is best possible and answers
a question raised by Reed and Shepherd in 1996. As a simple corollary, we also
obtain a positive answer to a problem of Hlin\v{e}n\'y (1998) on the chromatic
number of contact systems of strings.
  We also investigate the chromatic number of families of touching Jordan
curves. This can be used to bound the ratio between the maximum number of
vertex-disjoint directed cycles in a planar digraph, and its fractional
counterpart.


title:
Temperature-tunable Fano resonance induced by strong coupling between
  Weyl fermions and phonons in TaAs

abstract:
  Strong coupling between discrete phonon and continuous electron-hole pair
excitations can give rise to a pronounced asymmetry in the phonon line shape,
known as the Fano resonance. This effect has been observed in a variety of
systems, such as stripe-phase nickelates, graphene and high-$T_{c}$
superconductors. Here, we reveal explicit evidence for strong coupling between
an infrared-active $A_1$ phonon and electronic transitions near the Weyl points
(Weyl fermions) through the observation of a Fano resonance in the recently
discovered Weyl semimetal TaAs. The resultant asymmetry in the phonon line
shape, conspicuous at low temperatures, diminishes continuously as the
temperature increases. This anomalous behavior originates from the suppression
of the electronic transitions near the Weyl points due to the decreasing
occupation of electronic states below the Fermi level ($E_{F}$) with increasing
temperature, as well as Pauli blocking caused by thermally excited electrons
above $E_{F}$. Our findings not only elucidate the underlying mechanism
governing the tunable Fano resonance, but also open a new route for exploring
exotic physical phenomena through the properties of phonons in Weyl semimetals.


title: The Bundled Crossing Number

abstract:
  We study the algorithmic aspect of edge bundling. A bundled crossing in a
drawing of a graph is a group of crossings between two sets of parallel edges.
The bundled crossing number is the minimum number of bundled crossings that
group all crossings in a drawing of the graph.
  We show that the bundled crossing number is closely related to the orientable
genus of the graph. If multiple crossings and self-intersections of edges are
allowed, the two values are identical; otherwise, the bundled crossing number
can be higher than the genus.
  We then investigate the problem of minimizing the number of bundled
crossings. For circular graph layouts with a fixed order of vertices, we
present a constant-factor approximation algorithm. When the circular order is
not prescribed, we get a $\frac{6c}{c-2}$ approximation for a graph with $n$
vertices having at least $cn$ edges for $c>2$. For general graph layouts, we
develop an algorithm with an approximation factor of $\frac{6c}{c-3}$ for
graphs with at least $cn$ edges for $c > 3$.


title:
Distinguishing nanobubbles from nanodroplets with AFM: the influence of
  vertical and lateral imaging forces

abstract:
  The widespread application of surface-attached nanobubbles and nanodroplets
in biomedical engineering and nanotechnology is limited by numerous
experimental challenges, in particular, the possibility of contamination in
nucleation experiments. These challenges are complicated by recent reports that
it can be difficult to distinguish between nanoscale drops and bubbles. Here we
identify clear differences in the mechanical responses of nanobubbles and
nanodroplets under various modes of AFM imaging which subject the objects to
predominantly vertical or lateral forces. This allows to distinguish between
nanodroplets, nanobubbles, and oil covered nanobubbles in water.


title: Singular Knots and Involutive Quandles

abstract:
  The aim of this paper is to define certain algebraic structures coming from
generalized Reidemeister moves of singular knot theory. We give examples, show
that the set of colorings by these algebraic structures is an invariant of
singular links. As an application we distinguish several singular knots and
links.


title:
Evidence of nodes in the order parameter of the superconducting doped
  topological insulator Nb$_x$Bi$_2$Se$_3$ via penetration depth measurements

abstract:
  The low-temperature variation of the London penetration depth $\lambda (T)$
in the candidate topological superconductor Nb$_x$Bi$_2$Se$_3$ (x = 0.25) is
reported for several crystals. The measurements were carried out by means of a
tunnel-diode oscillator (TDO) technique in both field orientations ($H_{rf}
\parallel$ $c$ and $H_{rf} \parallel$ $ab$ planes). All samples exhibited power
law behavior at low temperatures ($\Delta\lambda\sim T^2$) clearly indicating
the presence of point nodes in the superconducting order parameter. The results
presented here are consistent with a nematic odd-parity spin-triplet $E_u$
pairing state in Nb$_x$Bi$_2$Se$_3$.


title: Analysis of $X(3872)$ production via Heavy-Meson Effective Theory

abstract:
  We analyze the $X(3872)$ production in the processes $ \bar{D} D \rightarrow
\pi X $, $\bar{D}^* D \rightarrow \pi X $ and $\bar{D}^* D^* \rightarrow \pi X
$, making use of the Heavy-Meson Effective Theory, with an effective Lagrangian
built based on chiral $SU(3)_{L} \times SU(3)_{R}$ and heavy quark symmetries.
In this scenario, we consider $X$ as a bound state of $D^{*} \bar{D} + c.c.$,
including neutral and charged components, and obtain the cross sections the
mentioned reactions as function of collision energy.


title: Population Genetics with Fluctuating Population Sizes

abstract:
  Standard neutral population genetics theory with a strictly fixed population
size has important limitations. An alternative model that allows independently
fluctuating population sizes and reproduces the standard neutral evolution is
reviewed. We then study a situation such that the competing species are neutral
at the equilibrium population size but population size fluctuations
nevertheless favor fixation of one species over the other. In this case, a
separation of timescales emerges naturally and allows adiabatic elimination of
a fast population size variable to deduce the fluctuations-induced selection
dynamics near the equilibrium population size. The results highlight the
incompleteness of the standard population genetics with a strictly fixed
population size.


title:
A proposed paradigm for solar cycle dynamics mediated via turbulent
  pumping of magnetic flux in Babcock-Leighton type solar dynamos

abstract:
  At present, Babcock-Leighton flux transport solar dynamo models appear as the
most promising model for explaining diverse observational aspects of the
sunspot cycle. The success of these flux transport dynamo models is largely
dependent upon a single-cell meridional circulation with a deep equatorward
component at the base of the Sun's convection zone. However, recent
observations suggest that the meridional flow may in fact be very shallow
(confined to the top 10 % of the Sun) and more complex than previously thought.
Taken together these observations raise serious concerns on the validity of the
flux transport paradigm. By accounting for the turbulent pumping of magnetic
flux as evidenced in magnetohydrodynamic simulations of solar convection, we
demonstrate that flux transport dynamo models can generate solar-like magnetic
cycles even if the meridional flow is shallow. Solar-like periodic reversals is
recovered even when meridional circulation is altogether absent, however, in
this case the solar surface magnetic field dynamics does not extend all the way
to the polar regions. Very importantly, our results demonstrate that the
Parker-Yoshimura sign rule for dynamo wave propagation can be circumvented in
Babcock-Leighton dynamo models by the latitudinal component of turbulent
pumping -- which can generate equatorward propagating sunspot belts in the
absence of a deep, equatorward meridional flow. We also show that variations in
turbulent pumping coefficients can modulate the solar cycle amplitude and
periodicity. Our results suggest the viability of an alternate magnetic flux
transport paradigm -- mediated via turbulent pumping -- for sustaining
solar-stellar dynamo action.


title: Learning Preferences and User Engagement Using Choice and Time Data

abstract:
  Choice decisions made by users of online applications can suffer from biases
due to the users' level of engagement. For instance, low engagement users may
make random choices with no concern for the quality of items offered. This
biased choice data can corrupt estimates of user preferences for items.
However, one can correct for these biases if additional behavioral data is
utilized. To do this we construct a new choice engagement time model which
captures the impact of user engagement on choice decisions and response times
associated with these choice decisions. Response times are the behavioral data
we choose because they are easily measured by online applications and reveal
information about user engagement. To test our model we conduct online polls
with subject populations that have different levels of engagement and measure
their choice decisions and response times. We have two main empirical findings.
First, choice decisions and response times are correlated, with strong
preferences having faster response times than weak preferences. Second, low
user engagement is manifested through more random choice data and faster
response times. Both of these phenomena are captured by our choice engagement
time model and we find that this model fits the data better than traditional
choice models. Our work has direct implications for online applications. It
lets these applications remove the bias of low engagement users when estimating
preferences for items. It also allows for the segmentation of users according
to their level of engagement, which can be useful for targeted advertising or
marketing campaigns.


title: Instability in nonlinear Schr\"odinger breathers

abstract:
  We consider the \emph{focusing} nonlinear Schr\"odinger equation posed on the
one dimensional line, with nonzero background condition at spatial infinity,
given by a homogeneous plane wave. For this problem of physical interest, we
study the initial value problem for perturbations of the background wave in
Sobolev spaces. It is well-known that the associated linear dynamics for this
problem describes a phenomenon known in the literature as \emph{modulational
instability}, also recently related to the emergence of \emph{rogue waves} in
ocean dynamics. In qualitative terms, small perturbations of the background
state increase its size exponentially in time. In this paper we show that, even
if there is no time decay for the linear dynamics due to the modulationally
unstable regime, the equation is still locally well-posed in $H^s$,
$s>\frac12$. We apply this result to give a rigorous proof of the unstable
character of two well-known NLS solutions: the Peregrine and Kuznetsov-Ma
breathers.


title: The action dimension of Artin groups

abstract:
  The \emph{action dimension} of a discrete group $G$ is the minimum dimension
of a contractible manifold, which admits a proper $G$-action. In this paper, we
study the action dimension of general Artin groups. The main result is that the
action dimension of an Artin group with the nerve $L$ of dimension $n$ for $n
\ne 2$ is less than or equal to $(2n + 1)$ if the Artin group satisfies the
$K(\pi, 1)$-Conjecture and the top cohomology group of $L$ with
$\mathbb{Z}$-coefficients is trivial. For $n = 2$, we need one more condition
on $L$ to get the same inequality; that is the fundamental group of $L$ is
generated by $r$ elements where $r$ is the rank of $H_1(L, \mathbb{Z})$.


title: Tracking Completion

abstract:
  A fundamental component of modern trackers is an online learned tracking
model, which is typically modeled either globally or locally. The two kinds of
models perform differently in terms of effectiveness and robustness under
different challenging situations. This work exploits the advantages of both
models. A subspace model, from a global perspective, is learned from previously
obtained targets via rank-minimization to address the tracking, and a
pixel-level local observation is leveraged si- multaneously, from a local point
of view, to augment the subspace model. A matrix completion method is employed
to integrate the two models. Unlike previous tracking methods, which locate the
target among all fully observed target candidates, the proposed approach first
estimates an expected target via the matrix completion through partially
observed target candidates, and then, identifies the target according to the
estimation accuracy with respect to the target candidates. Specifically, the
tracking is formulated as a problem of target appearance estimation. Extensive
experiments on various challenging video sequences verify the effectiveness of
the proposed approach and demonstrate that the proposed tracker outperforms
other popular state-of-the-art trackers.


title:
Field induced spontaneous quasiparticle decay and renormalization of
  quasiparticle dispersion in a quantum antiferromagnet

abstract:
  The notion of a quasiparticle, such as a phonon, a roton, or a magnon, is
used in modern condensed matter physics to describe an elementary collective
excitation. The intrinsic zero-temperature magnon damping in quantum spin
systems can be driven by the interaction of the one-magnon states and
multi-magnon continuum. However, detailed experimental studies on this quantum
many-body effect induced by an applied magnetic field are rare. Here we present
a high-resolution neutron scattering study in high fields on an S=1/2
antiferromagnet C9H18N2CuBr4. Compared with the non-interacting linear
spin-wave theory, our results demonstrate a variety of phenomena including
field-induced renormalization of one-magnon dispersion, spontaneous magnon
decay observed via intrinsic linewidth broadening, unusual non-Lorentzian
two-peak structure in the excitation spectra, and a dramatic shift of spectral
weight from one-magnon state to the two-magnon continuum.


title:
Real-Time Visual Tracking: Promoting the Robustness of Correlation
  Filter Learning

abstract:
  Correlation filtering based tracking model has received lots of attention and
achieved great success in real-time tracking, however, the lost function in
current correlation filtering paradigm could not reliably response to the
appearance changes caused by occlusion and illumination variations. This study
intends to promote the robustness of the correlation filter learning. By
exploiting the anisotropy of the filter response, three sparsity related loss
functions are proposed to alleviate the overfitting issue of previous methods
and improve the overall tracking performance. As a result, three real-time
trackers are implemented. Extensive experiments in various challenging
situations demonstrate that the robustness of the learned correlation filter
has been greatly improved via the designed loss functions. In addition, the
study reveals, from an experimental perspective, how different loss functions
essentially influence the tracking performance. An important conclusion is that
the sensitivity of the peak values of the filter in successive frames is
consistent with the tracking performance. This is a useful reference criterion
in designing a robust correlation filter for visual tracking.


title:
Efficient parameter sensitivity computation for spatially-extended
  reaction networks

abstract:
  Reaction-diffusion models are widely used to study spatially-extended
chemical reaction systems. In order to understand how the dynamics of a
reaction-diffusion model are affected by changes in its input parameters,
efficient methods for computing parametric sensitivities are required. In this
work, we focus on stochastic models of spatially-extended chemical reaction
systems that involve partitioning the computational domain into voxels.
Parametric sensitivities are often calculated using Monte Carlo techniques that
are typically computationally expensive; however, variance reduction techniques
can decrease the number of Monte Carlo simulations required. By exploiting the
characteristic dynamics of spatially-extended reaction networks, we are able to
adapt existing finite difference schemes to robustly estimate parametric
sensitivities in a spatially-extended network. We show that algorithmic
performance depends on the dynamics of the given network and the choice of
summary statistics. We then describe a hybrid technique that dynamically
chooses the most appropriate simulation method for the network of interest. Our
method is tested for functionality and accuracy in a range of different
scenarios.


title:
Circular polarization opportunities at the SASE3 undulator line of the
  European XFEL

abstract:
  XFELs provide X-ray pulses with unprecedented peak brightness and ultrashort
duration. They are usually driven by planar undulators, meaning that the output
radiation is linearly polarized. For many experimental applications, however,
polarization control is critical: besides the ability to produce linearly
polarized radiation, one often needs the possibility of generating circularly
polarized radiation with a high, stable degree of polarization. This may be
achieved by using a first part of the XFEL undulator to produce bunching and
then, by propagating the the bunched beam through an "afterburner" - a short
undulator with tunable polarization, where only limited gain takes place. One
of the issues that one needs to consider in this case is the separation of the
circularly polarized radiation obtained in the radiator from the linearly
polarized background produced in the first part of the FEL. In this article we
review several methods to do so, including the inverse tapering technique. In
particular, we use the Genesis FEL code to simulate a case study pertaining to
the SASE3 FEL line at the European XFEL with up-to-date parameters and we
confirm that a high degree of circular polarization is expected. Moreover, we
propose to further improve the effectiveness of the inverse tapering technique
either via angular separation of the linearly polarized radiation or strongly
defocusing it at the sample position. In this way we exploit the unique
flexibility of the European XFEL from both the electron beam and the photon
beam optics side.