title: Work Extraction and Energy Storage in the Dicke Model

abstract:
  We study work extraction from the Dicke model achieved using simple unitary
cyclic transformations keeping into account both a non optimal unitary
protocol, and the energetic cost of creating the initial state. By analyzing
the role of entanglement, we find that highly entangled states can be
inefficient for energy storage when considering the energetic cost of creating
the state. Such surprising result holds notwithstanding the fact that the
criticality of the model at hand can sensibly improve the extraction of work.
While showing the advantages of using a many-body system for work extraction,
our results demonstrate that entanglement is not necessarily advantageous for
energy storage purposes, when non optimal processes are considered. Our work
shows the importance of better understanding the complex interconnections
between non-equilibrium thermodynamics of quantum systems and correlations
among their subparts.


title: Extreme Value Laws for sequences of intermittent maps

abstract:
  We study non-stationary stochastic processes arising from sequential
dynamical systems built on maps with a neutral fixed points and prove the
existence of Extreme Value Laws for such processes. We use an approach
developed in \cite{FFV16}, where we generalised the theory of extreme values
for non-stationary stochastic processes, mostly by weakening the uniform mixing
condition that was previously used in this setting. The present work is an
extension of our previous results for concatenations of uniformly expanding
maps obtained in \cite{FFV16}.


title:
Isogeometric shape optimisation of shell structures using
  multiresolution subdivision surfaces

abstract:
  We introduce the isogeometric shape optimisation of thin shell structures
using subdivision surfaces. Both triangular Loop and quadrilateral
Catmull-Clark subdivision schemes are considered for geometry modelling and
finite element analysis. A gradient-based shape optimisation technique is
implemented to minimise compliance, i.e. to maximise stiffness. Different
control meshes describing the same surface are used for geometry
representation, optimisation and finite element analysis. The finite element
analysis is performed with subdivision basis functions corresponding to a
sufficiently refined control mesh. During iterative shape optimisation the
geometry is updated starting from the coarsest control mesh and proceeding to
increasingly finer control meshes. This multiresolution approach provides a
means for regularising the optimisation problem and prevents the appearance of
sub-optimal jagged geometries with fine-scale oscillations. The finest control
mesh for optimisation is chosen in accordance with the desired smallest feature
size in the optimised geometry. The proposed approach is applied to three
optimisation examples, namely a catenary, a roof over a rectangular domain and
a freeform architectural shell roof. The influence of the geometry description
and the used subdivision scheme on the obtained optimised curved geometries is
investigated in detail.


title:
Evolution Patterns: Designing and Reusing Architectural Evolution
  Knowledge to Introduce Architectural Styles

abstract:
  Software architectures are critical in the successful development and
evolution of software-intensive systems. While formal and automated support for
architectural descriptions has been widely addressed, their evolution is
equally crucial, but significantly less well-understood and supported. In order
to face a recurring evolution need, we introduce the concept of evolution
pattern. It formalises an architectural evolution through both a set of
concepts and a reusable evolution process. We propose it through the recurring
need of introducing an architectural style on existing software architectures.
We formally describe and analyse the feasibility of architectural evolution
patterns, and provide a practical validation by implementing them in
COSABuilder, an Eclipse plugin for the COSA architectural description language.


title: Constant Envelope Precoding for MIMO Systems

abstract:
  Constant envelope (CE) precoding is an appealing transmission technique,
which enables highly efficient power amplification, and is realizable with a
single radio frequency (RF) chain at the multi-antenna transmitter. In this
paper, we study the transceiver design for a point-to-point multiple-input
multiple-output (MIMO) system with CE precoding. Both single-stream
transmission (i.e., beamforming) and multi-stream transmission (i.e., spatial
multiplexing) are considered. For single-stream transmission, we optimize the
receive beamforming vector to minimize the symbol error rate (SER) for any
given channel realization and desired constellation at the combiner output. By
reformulating the problem as an equivalent quadratically constrained quadratic
program (QCQP), we propose an efficient semi-definite relaxation (SDR) based
algorithm to find an approximate solution. Next, for multi-stream transmission,
we propose a new scheme based on antenna grouping at the transmitter and
minimum mean squared error (MMSE) or zero-forcing (ZF) based beamforming at the
receiver. The transmit antenna grouping and receive beamforming vectors are
then jointly designed to minimize the maximum SER over all data streams.
Finally, the error-rate performance of single- versus multi-stream transmission
is compared via simulations under different setups.


title:
Dust Impact Monitor (SESAME-DIM) on board Rosetta/Philae: Millimetric
  particle flux at comet 67P/Churyumov-Gerasimenko

abstract:
  The Philae lander of the Rosetta mission, aimed at the in situ investigation
of comet 67P/C-G, was deployed to the surface of the comet nucleus on 12 Nov
2014 at 2.99 AU heliocentric distance. The Dust Impact Monitor (DIM) as part of
the Surface Electric Sounding and Acoustic Monitoring Experiment (SESAME) on
the lander employed piezoelectric detectors to detect the submillimetre- and
millimetre-sized dust and ice particles emitted from the nucleus. We determine
the upper limit of the ambient flux of particles in the measurement range of
DIM based on the measurements performed with the instrument during Philae's
descent to its nominal landing site Agilkia at distances of about 22 km, 18 km,
and 5 km from the nucleus barycentre and at the final landing site Abydos. The
geometric factor of the DIM sensor is calculated assuming an isotropic ambient
flux of the submillimetre- and millimetre-sized particles. For the measurement
intervals when no particles were detected the maximum true impact rate was
calculated by assuming Poisson distribution of the impacts, and it was given as
the detection limit at a 95% confidence level. Based on measurements performed
with DIM, the upper limit of the flux of particles in the measurement range of
the instrument was of the order of $10^{-8}-10^{-7}m^{-2}s^{-1}sr^{-1}$ during
descent and $1.6\cdot10^{-9}m^{-2}s^{-1}sr^{-1}$ at Abydos on 13 and 14 Nov
2014. Considering particle speeds below escape velocity, the upper limit for
the volume density of particles in the measurement range of DIM was constrained
to $10^{-11}m^{-3}-10^{-12}m^{-3}$. Results of the calculations performed with
the GIPSI tool on the expected particle fluxes during the descent of Philae
were compatible with the non-detection of compact particles by the DIM
instrument.


title:
Dynamical Theory of Scattering, Exact Unidirectional Invisibility, and
  Truncated $\mathfrak{z}\,e^{-2ik_0x}$ potential

abstract:
  The dynamical formulation of time-independent scattering theory that is
developed in [Ann. Phys. (NY) 341, 77-85 (2014)] offers simple formulas for the
reflection and transmission amplitudes of finite-range potentials in terms of
the solution of an initial-value differential equation. We prove a theorem that
simplifies the application of this result and use it to give a complete
characterization of the invisible configurations of the truncated
$\mathfrak{z}\,e^{-2ik_0 x}$ potential to a closed interval, $[0,L]$, with
$k_0$ being a positive integer multiple of $\pi/L$. This reveals a large class
of exact unidirectionally and bidirectionally invisible configurations of this
potential. The former arise for particular values of $\mathfrak{z}$ that are
given by certain zeros of Bessel functions. The latter occur when the
wavenumber $k$ is an integer multiple of $\pi/L$ but not of $k_0$. We discuss
the optical realizations of these configurations and explore spectral
singularities of this potential.


title:
The performance of univariate goodness-of-fit tests for normality based
  on the empirical characteristic function in large samples

abstract:
  An empirical power comparison is made between two tests based on the
empirical characteristic function and some of the best performing tests for
normality. A simple normality test based on the empirical characteristic
function calculated in a single point is shown to outperform the more
complicated Epps-Pulley test and the frequentist tests included in the study in
large samples.


title:
Regularity of Minimizers of Shape Optimization Problems involving
  Perimeter

abstract:
  We prove existence and regularity of optimal shapes for the
problem$$\min\Big\{P(\Omega)+\mathcal{G}(\Omega):\ \Omega\subset D,\
|\Omega|=m\Big\},$$where $P$ denotes the perimeter, $|\cdot|$ is the volume,
and the functional $\mathcal{G}$ is either one of the
following:\textless{}ul\textgreater{}\textless{}li\textgreater{} the Dirichlet
energy $E\_f$, with respect to a (possibly sign-changing) function $f\in
L^p$;\textless{}/li\textgreater{}\textless{}li\textgreater{}a spectral
functional of the form $F(\lambda\_{1},\dots,\lambda\_{k})$, where $\lambda\_k$
is the $k$th eigenvalue of the Dirichlet Laplacian and
$F:\mathbb{R}^k\to\mathbb{R}$ is Lipschitz continuous and increasing in each
variable.\textless{}/li\textgreater{}\textless{}/ul\textgreater{}The domain $D$
is the whole space $\mathbb{R}^d$ or a bounded domain. We also give general
assumptions on the functional $\mathcal{G}$ so that the result remains valid.


title: Generic singularities of line fields on 2D manifolds

abstract:
  Generic singularities of line fields have been studied for lines of principal
curvature of embedded surfaces. In this paper we propose an approach to
classify generic singularities of general line fields on 2D manifolds. The idea
is to identify line fields as bisectors of pairs of vector fields on the
manifold, with respect to a given conformal structure. The singularities
correspond to the zeros of the vector fields and the genericity is considered
with respect to a natural topology in the space of pairs of vector fields. Line
fields at generic singularities turn out to be topologically equivalent to the
Lemon, Star and Monstar singularities that one finds at umbilical points.


title: On the Robustness of Decision Tree Learning under Label Noise

abstract:
  In most practical problems of classifier learning, the training data suffers
from the label noise. Hence, it is important to understand how robust is a
learning algorithm to such label noise. This paper presents some theoretical
analysis to show that many popular decision tree algorithms are robust to
symmetric label noise under large sample size. We also present some sample
complexity results which provide some bounds on the sample size for the
robustness to hold with a high probability. Through extensive simulations we
illustrate this robustness.


title:
Central Limit Theorem for probability measures defined by sum-of-digits
  function in base 2

abstract:
  In this paper we prove a central limit theorem for some probability measures
defined as asymtotic densities of integer sets defined via
sum-of-digit-function. To any integer a we can associate a measure on Z called
$\mu$a such that, for any d, $\mu$a(d) is the asymptotic density of the set of
integers n such that s\_2(n + a) -- s\_2(n) = d where s\_2(n) is the number of
digits "1" in the binary expansion of n. We express this probability measure as
a product of matrices. Then we take a sequence of integers (a\_X(n)) n$\in$N
via a balanced Bernoulli process. We prove that, for almost every sequence, and
after renormalization by the typical variance, we have a central limit theorem
by computing all the moments and proving that they converge towards the moments
of the normal law N (0, 1).


title: Leptonic Precision Test of Leptophilic Two-Higgs-Doublet Model

abstract:
  The type X (lepton-specific) two-Higgs-doublet model at large $\tan\beta$
becomes leptophilic and thus allows a light pseudoscalar $A$ accommodating the
observed muon $g-2$ deviation without conflicting with various hadronic
constraints. On the other hand, it is strongly constrained by leptonic
precision observables such as lepton universality test in the neutral and
charged currents. Treating all the lepton universality data in a consistent
way, we show how the current data constrain the parameter space of $m_A$ and
$\tan\beta$ for given degenerate masses of heavy Higgs bosons $H$ and $H^\pm$.
While no overlapping region is found at $1\sigma$, a sizable region is still
viable at $2\sigma$ for $H/H^\pm$ masses at around 200$\sim$400 GeV.


title: String Moduli Stabilization at the Conifold

abstract:
  We study moduli stabilization for type IIB orientifolds compactified on
Calabi-Yau threefolds in the region close to conifold singularities in the
complex structure moduli space. The form of the periods implies new phenomena
like exponential mass hierarchies even in the regime of negligible warping.
Integrating out the heavy conic complex structure modulus leads to an effective
flux induced potential for the axio-dilaton and the remaining complex structure
moduli containing exponentially suppressed terms that imitate non-perturbative
effects. It is shown that this scenario can be naturally combined with the
large volume scenario so that all moduli are dynamically stabilized in the
dilute flux regime. As an application of this moduli stabilization scheme, a
string inspired model of aligned inflation is designed that features a
parametrically controlled hierarchy of mass scales.


title: $\eta/s$ in a strongly coupled QFT

abstract:
  We consider $O(N)$ $g\varphi^4$ theory with the coupling $g$ being large, and
calculate shear viscosity to entropy density ratio ($\eta/s$). The final result
for $\eta/s$ has a form remarkably similar to that obtained from string theory
calculations via the AdS/CFT conjecture. The method adopted can be used to
compute quantities of interest in other theories as well with some
modifications and reveals some very interesting features within the considered
theory.


title: BSDEs with mean reflection

abstract:
  In this paper, we study a new type of BSDE, where the distribution of the
Y-component of the solution is required to satisfy an additional constraint,
written in terms of the expectation of a loss function. This constraint is
imposed at any deterministic time t and is typically weaker than the classical
pointwise one associated to reflected BSDEs. Focusing on solutions (Y, Z, K)
with deterministic K, we obtain the well-posedness of such equation, in the
presence of a natural Skorokhod type condition. Such condition indeed ensures
the minimality of the enhanced solution, under an additional structural
condition on the driver. Our results extend to the more general framework where
the constraint is written in terms of a static risk measure on Y. In
particular, we provide an application to the super hedging of claims under
running risk management constraint.


title:
A notion of $\alpha\beta$-statistical convergence of order $\gamma$ in
  probability

abstract:
  A sequence of real numbers $\{x_{n}\}_{n\in \mathbb{N}}$ is said to be
$\alpha \beta$-statistically convergent of order $\gamma$ (where $0<\gamma\leq
1$) to a real number $x$ \cite{a} if for every $\delta>0,$
$$\underset{n\rightarrow \infty} {\lim} \frac{1}{(\beta_{n} - \alpha_{n} +
1)^\gamma}~ |\{k \in [\alpha_n,\beta_n] : |x_{k}-x|\geq \delta \}|=0.$$ where
$\{\alpha_{n}\}_{n\in \mathbb{N}}$ and $\{\beta_{n}\}_{n\in \mathbb{N}}$ be two
sequences of positive real numbers such that $\{\alpha_{n}\}_{n\in \mathbb{N}}$
and $\{\beta_{n}\}_{n\in \mathbb{N}}$ are both non-decreasing, $\beta_{n}\geq
\alpha_{n}$ $\forall ~n\in \mathbb{N},$ ($\beta_{n}-\alpha_{n})\rightarrow
\infty$ as $n\rightarrow \infty.$ In this paper we study a related concept of
convergences in which the value $|x_{k}-x|$ is replaced by $P(|X_{k}-X|\geq
\varepsilon)$ and $E(|X_{k}-X|^{r})$ repectively (Where $X, X_k$ are random
variables for each $k\in \mathbb{N}$, $\varepsilon>0$, $P$ denote the
probability, $E$ denote the expectation) and we call them $\alpha
\beta$-statistical convergence of order $\gamma$ in probability and
$\alpha\beta$-statistical convergence of order $\gamma$ in $r^{\mbox{th}}$
expectation respectively. The results are applied to build the probability
distribution for $\alpha\beta$-strong $p$-Ces$\grave{\mbox{a}}$ro summability
of order $\gamma$ in probability and $\alpha\beta$-statistical convergence of
order $\gamma$ in distribution. Our main objective is to interpret a relational
behavior of above mentioned four convergences.


title: Properties of {\pi}-mode vibrations in strained carbon chains

abstract:
  Nonlinear vibrations in strained monoatomic carbon chains are studied with
the aid of ab initio methods based on the density functional theory. An
unexpected phenomenon of structural transformation at the atomic level above a
certain value of the strain was revealed in cumulene chain (carbyne-{\beta}).
This phenomenon is a consequence of stability loss of the old equilibrium
atomic positions that occur at small strain, and appearance of two new stable
equilibrium positions near each of them. The aforementioned restructuring gives
rise to a softening of {\pi}-mode whose frequency tends to zero in a certain
region of amplitudes when carbon atoms begin to vibrate near new equilibrium
positions. This resembles the concept of soft mode whose "freezing" is
postulated in the theory of phase transitions in crystals to explain the
transitions of displacement type. The dynamical modeling of mass point chains
whose particles interact via Lennard-Jones potential can approximate our ab
initio results well enough. In particular, this study demonstrates an essential
role of dipole-dipole interactions between carbon atoms in formation of their
new equilibrium positions in the cumulene chain. We believe that computer
studying of Lennard-Jones chains enables to predict properties of various
dynamical objects in carbon chains (different nonlinear normal modes and their
bushes, discrete breathers etc.) which then can be verified by ab initio
methods.


title:
Local communities obstruct global consensus: Naming game on
  multi-local-world networks

abstract:
  Community structure is essential for social communications, where individuals
belonging to the same community are much more actively interacting and
communicating with each other than those in different communities within the
human society. Naming game, on the other hand, is a social communication model
that simulates the process of learning a name of an object within a community
of humans, where the individuals can generally reach global consensus
asymptotically through iterative pair-wise conversations. The underlying
network indicates the relationships among the individuals. In this paper, three
typical topologies, namely random-graph, small-world and scale-free networks,
are employed, which are embedded with the multi-local-world community
structure, to study the naming game. Simulations show that 1) the convergence
process to global consensus is getting slower as the community structure
becomes more prominent, and eventually might fail; 2) if the inter-community
connections are sufficiently dense, neither the number nor the size of the
communities affects the convergence process; and 3) for different topologies
with the same average node-degree, local clustering of individuals obstruct or
prohibit global consensus to take place. The results reveal the role of local
communities in a global naming game in social network studies.


title: Gravity from the viewpoint of theory of sources

abstract:
  I examine the $G^2$-approximation of Schwarzschild solution from the
viewpoint of theory of sources. The method suggests the following definition of
the privileged coordinate system: it is a system in which in each approximation
the gauge degrees of freedom are put to zero, i.e. the metric is formed solely
by sources. I calculate the metric in this system. In $G^2$-approximation the
exterior metric has the term which is of the form of a gauge function.
Considering it as such I have the agreement with Schwarzschild metric. But I
cannot consider it as a gauge function because it is generated by sources. It
should be observable. It is proportional to the radius of matter ball and seems
violate the Birckhoff theorem.


title:
A modification of the projective construction of quantum states for
  field theories

abstract:
  The projective construction of quantum states for field theories may be
flawed--in some cases the construction may possibly lead to spaces of quantum
states which are "too small" to be used in quantization of field theories. Here
we present a slight modification of the construction which is free from this
flaw.


title:
Translational symmetry breaking and the disintegration of the Hofstadter
  butterfly

abstract:
  We study the effect of interactions on the Hofstadter butterfly of the
honeycomb lattice. We show that the interactions induce charge ordering that
breaks the translational and rotational symmetries of the system. These phase
transitions are prolific and occur at many values of the flux and particle
density. The breaking of the translational symmetry introduces a new length
scale in the problem and this affects the energy band diagram resulting in the
disintegration of the fractal structure in the energy flux plot, the Hofstadter
butterfly. This disintegration increases with increase in the interaction
strength. Many of these phase transitions are accompanied with change in the
Hall conductivity. Consequently, the disintegration of the Hofstadter butterfly
is manifested in the Landau fan diagram also.


title:
The Bass diffusion model on networks with correlations and inhomogeneous
  advertising

abstract:
  The Bass model, which is an effective forecasting tool for innovation
diffusion based on large collections of empirical data, assumes an homogeneous
diffusion process. We introduce a network structure into this model and we
investigate numerically the dynamics in the case of networks with link density
$P(k)=c/k^\gamma$, where $k=1, \ldots , N$. The resulting curve of the total
adoptions in time is qualitatively similar to the homogeneous Bass curve
corresponding to a case with the same average number of connections. The peak
of the adoptions, however, tends to occur earlier, particularly when $\gamma$
and $N$ are large (i.e., when there are few hubs with a large maximum number of
connections). Most interestingly, the adoption curve of the hubs anticipates
the total adoption curve in a predictable way, with peak times which can be,
for instance when $N=100$, between 10% and 60% of the total adoptions peak.
This may allow to monitor the hubs for forecasting purposes. We also consider
the case of networks with assortative and disassortative correlations and a
case of inhomogeneous advertising where the publicity terms are "targeted" on
the hubs while maintaining their total cost constant.


title: First Principles Attempt to Unify some Population Growth Models

abstract:
  In this work, some phenomenological models, those that are based only on the
population information (macroscopic level), are deduced in an intuitive way.
These models, as for instance Verhulst, Gompertz and Bertalanffy models, are
posted in such a manner that all the parameters involved have physical
interpretation. A model based on the interaction (distance dependent) between
the individuals (microscopic level) is also presented. This microscopic model
reachs the phenomenological models presented as particular cases. In this
approach, the Verhulst model represents the situation in which all the
individuals interact in the same way, regardless of the distance between them.
That means Verhulst model is a kind of mean field model. The other
phenomenological models are reaching from the microscopic model according to
two quantities: i) the relation between the way that the interaction decays
with the distance; and ii) the dimension of the spatial structure formed by the
population. This microscopic model allows understanding population growth by
first principles, because it predicts that some phenomenological models can be
seen as a consequence of the same individual level kind of interaction. In this
sense, the microscopic model that will be discussed here paves the way to
finding universal patterns that are common to all types of growth, even in
systems of very different nature.


title: The quantum state-dependent gauge fields of Jacobi

abstract:
  It is commonly understood that the Yang-Mills non-Abelian gauge fields is the
natural generalization of the well known Abelian gauge group symmetry $U(1)$ in
the electrodynamics. Taking into account that the problems of the localization
and divergences in QFT are not solved in the framework of the Standard Model
(SM), I proposed a different approach to the quantum theory of the single
self-interacting electron. In connection with this theory, I would like attract
the attention to the state-dependent gauge transformations $U(1) \times U(N-1)$
associated with the Jacobi vector fields of the geodesic variations in the
complex projective Hilbert space $CP(N-1)$ of the unlocated quantum states
(UQS's).


title:
Poisson multi-Bernoulli conjugate prior for multiple extended object
  filtering

abstract:
  This paper presents a Poisson multi-Bernoulli mixture (PMBM) conjugate prior
for multiple extended object filtering. A Poisson point process is used to
describe the existence of yet undetected targets, while a multi-Bernoulli
mixture describes the distribution of the targets that have been detected. The
prediction and update equations are presented for the standard transition
density and measurement likelihood. Both the prediction and the update preserve
the PMBM form of the density, and in this sense the PMBM density is a conjugate
prior. However, the unknown data associations lead to an intractably large
number of terms in the PMBM density, and approximations are necessary for
tractability. A gamma Gaussian inverse Wishart implementation is presented,
along with methods to handle the data association problem. A simulation study
shows that the extended target PMBM filter performs well in comparison to the
extended target d-GLMB and LMB filters. An experiment with Lidar data
illustrates the benefit of tracking both detected and undetected targets.


title:
Spatially open Friedmann--Robertson--Walker Universe fueled with
  interacting sources

abstract:
  In the present paper, we are analyzing the $k=-1-$FRW Universe with two
interacting ideal fluids. The energy densities and the pressures are used to
derive the corresponding Equations of State. For a particular form of the
interaction term between the two fluids, it turns out that the Universe is
filled with a mixture of dust and radiation.


title:
Towards a unified explanation of $R_{D^{(\ast)}}$, $R_{K}$ and
  $(g-2)_{\mu}$ anomalies in a left-right model with leptoquarks

abstract:
  We present a unified explanation for the $B$-decay anomalies in
$R_{D^{(\ast)}}$ and $R_{K}$ together with the anomalous muon magnetic moment,
consistent with the constraints from the current measurements of leptonic decay
rates and $D^0-\bar{D}^0$, $B_{s}^0-\bar{B}_{s}^0$ mixings, within the
framework of a minimal left-right symmetric gauge theory motivated by one of
the low-energy subgroups of $E_{6}$ naturally accommodating leptoquarks.


title:
Scale invariant cosmology III: dynamical models and comparisons with
  observations

abstract:
  We examine the properties of the scale invariant cosmological models, also
making the specific hypothesis of the scale invariance of the empty space at
large scales. Numerical integrations of the cosmological equations for
different values of the curvature parameter k and of the density parameter
Omega_m are performed. We compare the dynamical properties of the models to the
observations at different epochs. The main numerical data and graphical
representations are given for models computed with different curvatures and
density parameters. The models with non-zero density start explosively with
first a braking phase followed by a continuously accelerating expansion. The
comparison of the models with the recent observations from supernovae SN Ia,
BAO and CMB data from Planck 2015 shows that the scale invariant model with k=0
and Omega_m=0.30 very well fits the observations in the usual Omega_m vs.
Omega_Lambda plane and consistently accounts for the accelerating expansion or
dark energy. The expansion history is compared to observations in the plot H(z)
vs. redshift z, the parameters q_0 is also examined, as well the recent data
about the redshift z_trans of the transition between braking and acceleration.
These dynamical tests are fully satisfied by the scale invariant models. The
past evolution of matter and radiation density is studied, it shows small
differences with respect to the standard case. These first comparisons are
encouraging further investigations on scale invariant cosmology with the
assumption of scale invariance of the empty space at large scales.


title: Scale invariant cosmology I: the vacuum and the cosmological constant

abstract:
  The source of the acceleration of the expansion of the Universe is still
unknown. We examine some consequences of the possible scale invariance of the
empty space at large scales. The central hypothesis of this work is that, at
macroscopic and large scales where General Relativity may be applied, the empty
space in the sense it is used in the Minkowski metric, is also scale invariant.
It is shown that if this applies, the Einstein cosmological constant and the
scale factor of the scale invariant framework are related by two differential
equations.


title: Scale invariant cosmology II: model equations and properties

abstract:
  We want to establish the basic properties of a scale invariant cosmology,
that also accounts for the hypothesis of scale invariance of the empty space at
large scales. We write the basic analytical properties of the scale invariant
cosmological models. The hypothesis of scale invariance of the empty space at
large scale brings interesting simplifications in the scale invariant equations
for cosmology. There is one new term, depending on the scale factor of the
scale invariant cosmology, that opposes to gravity and favours an accelerated
expansion. We first consider a zero-density model and find an accelerated
expansion, going like t square. In models with matter present, the
displacements due to the new term make a significant contribution Omega_l to
the energy-density of the Universe, satisfying an equation of the form Omega_m
+ Omega_k + Omega_l = 1. Unlike the Friedman's models, there is a whole family
of flat models (k=0) with different density parameters Omega_m smaller than 1.
We examine the basic relations between the density and geometrical properties,
as well as the conservation laws. The models containing matter have an
inflexion point, with first a braking phase followed by an accelerated
expansion phase. The scale invariant models have interesting properties and
deserve further investigations.


title:
Dynamics of Solitons in the One-Dimensional Nonlinear Schr\"odinger
  Equation

abstract:
  We investigate bright solitons in the one-dimensional Schr\"odinger equation
in the framework of an extended variational approach. We apply the latter to
the stationary ground state of the system as well as to coherent collisions
between two or more solitons. Using coupled Gaussian trial wave functions, we
demonstrate that the variational approach is a powerful method to calculate the
soliton dynamics. This method has the advantage that it is computationally
faster compared to numerically exact grid calculations. In addition, it goes
far beyond the capability of analytical ground state solutions, because the
variational approach provides the ability to treat excited solitons as well as
dynamical interactions between different wave packets. To demonstrate the power
of the variational approach, we calculate the stationary ground state of the
soliton and compare it with the analytical solution showing the convergence to
the exact solution. Furthermore, we extend our calculations to nonstationary
solitons by investigating the breathing oscillations of excited solitons and
the coherent collisions of several wave packets in both the low- and
high-energy regime. Comparisons of the variational approach with numerically
exact simulations on grids reveal excellent agreement in the high-energy regime
while deviations can be observed for low energies.


title:
Hybrid confinement of optical and mechanical modes in a bullseye
  optomechanical resonator

abstract:
  Optomechanical cavities have proven to be an exceptional tool to explore
fundamental and technological aspects of the interaction between mechanical and
optical waves. Such interactions strongly benefit from cavities with large
optomechanical coupling, high mechanical and optical quality factors, and
mechanical frequencies larger than the optical mode linewidth, the so called
resolved sideband limit. Here we demonstrate a novel optomechanical cavity
based on a disk with a radial mechanical bandgap. This design confines light
and mechanical waves through distinct physical mechanisms which allows for
independent control of the mechanical and optical properties. Our device design
is not limited by unique material properties and could be easily adapted to
allow large optomechanical coupling and high mechanical quality factors with
other promising materials. Finally, our demonstration is based on devices
fabricated on a commercial silicon photonics facility, demonstrating that our
approach can be easily scalable.


title:
As Cool as a Cucumber: Towards a Corpus of Contemporary Similes in
  Serbian

abstract:
  Similes are natural language expressions used to compare unlikely things,
where the comparison is not taken literally. They are often used in everyday
communication and are an important part of cultural heritage. Having an
up-to-date corpus of similes is challenging, as they are constantly coined
and/or adapted to the contemporary times. In this paper we present a
methodology for semi-automated collection of similes from the world wide web
using text mining techniques. We expanded an existing corpus of traditional
similes (containing 333 similes) by collecting 446 additional expressions. We,
also, explore how crowdsourcing can be used to extract and curate new similes.


title:
Perturbation theory for graphene integrated waveguides: cubic
  nonlinearity and third harmonic generation

abstract:
  We present perturbation theory for analysis of generic third-order nonlinear
processes in graphene integrated photonic structures. Optical response of
graphene is treated as the nonlinear boundary condition in Maxwell equations.
The derived models are applied for analysis of third harmonic generation in a
graphene coated dielectric micro-fibre. The efficiency of up to few percent is
predicted when using sub-picosecond pump pulses with energies of the order of
$0.1$nJ in a sub-millimeter long fibre, when operating near the resonance of
the graphene nonlinear conductivity $\hbar\omega=(2/3)E_F$.


title: Equitable orientations of sparse uniform hypergraphs

abstract:
  Caro, West, and Yuster studied how $r$-uniform hypergraphs can be oriented in
such a way that (generalizations of) indegree and outdegree are as close to
each other as can be hoped. They conjectured an existence result of such
orientations for sparse hypergraphs, of which we present a proof.


title: Asymptotic analysis of threshold models for social networks

abstract:
  A class of dynamic threshold models is proposed, for describing the upset of
collective actions in social networks. The agents of the network have to decide
whether to undertake a certain action or not. They make their decision by
comparing the activity level of their neighbors with a time-varying threshold,
evolving according to a time-invariant opinion dynamic model. Key features of
the model are a parameter representing the degree of self-confidence of the
agents, and the mechanism adopted by the agents to evaluate the activity level
of their neighbors. The case in which a radical agent, initially eager to
undertake the action, interacts with a group of ordinary agents, is considered.
The main contribution of the paper is the complete analytic characterization of
the asymptotic behaviors of the network, for three different graph topologies.
The asymptotic activity patterns are determined as a function of the
self-confidence parameter and of the initial threshold of the ordinary agents.


title: Generic norms and metrics on countable abelian groups

abstract:
  For a countable abelian group $G$ we investigate generic properties of the
space of all invariant metrics on $G$. We prove that for every such an
unbounded group $G$, i.e. group which has elements of arbitrarily high order,
there is a dense set of invariant metrics on $G$ which make $G$ isometric to
the rational Urysohn space, and a comeager set of invariant metrics such that
the completion is isometric to the Urysohn space. This generalizes results of
Cameron and Vershik, Niemiec, and the author.
  Then we prove that for every $G$ such that $G\cong \bigoplus_\mathbb{N} G$
there is a comeager set of invariant metrics on $G$ such that all of them give
rise to the same metric group after completion. If moreover $G$ is unbounded,
then using a result of Melleray and Tsankov we get that the completion is
extremely amenable.


title:
Probing deep photospheric layers of the quiet Sun with high magnetic
  sensitivity

abstract:
  Context. Investigations of the magnetism of the quiet Sun are hindered by
extremely weak polarization signals in Fraunhofer spectral lines. Photon noise,
straylight, and the systematically different sensitivity of the Zeeman effect
to longitudinal and transversal magnetic fields result in controversial results
in terms of the strength and angular distribution of the magnetic field vector.
  Aims. The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of spatial
straylight and photon noise into account.
  Methods. Highly sensitive full Stokes measurements of a quiet-Sun region at
disk center in the deep photospheric Fe I lines in the 1.56 {\mu}m region were
obtained with the infrared spectropolarimeter GRIS at the GREGOR telescope.
Noise statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple diagnostics
based directly on the shape and strength of the profiles were applied to the
GRIS data. We made use of the magnetic line ratio technique, which was tested
against MHD simulations.
  Results. About 80% of the GRIS spectra of a very quiet solar region show
polarimetric signals above a 3{\sigma} level. Area and amplitude asymmetries
agree well with small-scale surface dynamo MHD simulations. The magnetic line
ratio analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields.
  Conclusions. The GRIS spectropolarimetric data at a spatial resolution of
0.40" are so far unique in the combination of high spatial resolution scans and
high magnetic field sensitivity. Nevertheless, the unavoidable effect of
spatial straylight and the resulting dilution of the weak Stokes profiles means
that inversion techniques still bear a high risk of misinterpretating the data.


title: Superpixel Hierarchy

abstract:
  Superpixel segmentation is becoming ubiquitous in computer vision. In
practice, an object can either be represented by a number of segments in finer
levels of detail or included in a surrounding region at coarser levels of
detail, and thus a superpixel segmentation hierarchy is useful for applications
that require different levels of image segmentation detail depending on the
particular image objects segmented. Unfortunately, there is no method that can
generate all scales of superpixels accurately in real-time. As a result, a
simple yet effective algorithm named Super Hierarchy (SH) is proposed in this
paper. It is as accurate as the state-of-the-art but 1-2 orders of magnitude
faster. The proposed method can be directly integrated with recent efficient
edge detectors like the structured forest edges to significantly outperforms
the state-of-the-art in terms of segmentation accuracy. Quantitative and
qualitative evaluation on a number of computer vision applications was
conducted, demonstrating that the proposed method is the top performer.


title: Opinion dynamics: models, extensions and external effects

abstract:
  Recently, social phenomena have received a lot of attention not only from
social scientists, but also from physicists, mathematicians and computer
scientists, in the emerging interdisciplinary field of complex system science.
Opinion dynamics is one of the processes studied, since opinions are the
drivers of human behaviour, and play a crucial role in many global challenges
that our complex world and societies are facing: global financial crises,
global pandemics, growth of cities, urbanisation and migration patterns, and
last but not least important, climate change and environmental sustainability
and protection. Opinion formation is a complex process affected by the
interplay of different elements, including the individual predisposition, the
influence of positive and negative peer interaction (social networks playing a
crucial role in this respect), the information each individual is exposed to,
and many others. Several models inspired from those in use in physics have been
developed to encompass many of these elements, and to allow for the
identification of the mechanisms involved in the opinion formation process and
the understanding of their role, with the practical aim of simulating opinion
formation and spreading under various conditions. These modelling schemes range
from binary simple models such as the voter model, to multi-dimensional
continuous approaches. Here, we provide a review of recent methods, focusing on
models employing both peer interaction and external information, and
emphasising the role that less studied mechanisms, such as disagreement, has in
driving the opinion dynamics. [...]


title: Games from Basic Data Structures

abstract:
  In this paper, we consider combinatorial game rulesets based on data
structures normally covered in an undergraduate Computer Science Data
Structures course: arrays, stacks, queues, priority queues, sets, linked lists,
and binary trees. We describe many rulesets as well as computational and
mathematical properties about them. Two of the rulesets, Tower Nim and Myopic
Col, are new. We show polynomial-time solutions to Tower Nim and to Myopic Col
on paths.


title:
Control and Detection of Discrete Spectral Amplitudes in Nonlinear
  Fourier Spectrum

abstract:
  Nonlinear Fourier division Multiplexing (NFDM) can be realized from
modulating the discrete nonlinear spectrum of an $N$-solitary waveform. To
generate an $N$-solitary waveform from desired discrete spectrum (eigenvalue
and discrete spectral amplitudes), we use the Darboux Transform. We explain how
to the norming factors must be set in order to have the desired discrete
spectrum. To derive these norming factors, we study the evolution of nonlinear
spectrum by adding a new eigenvalue and its spectral amplitude. We further
simplify the Darboux transform algorithm.
  We propose a novel algorithm (to the best of our knowledge) to numerically
compute the nonlinear Fourier Transform (NFT) of a given pulse. The NFT
algorithm, called forward-backward method, is based on splitting the signal
into two parts and computing the nonlinear spectrum of each part from boundary
($\pm\infty$) inward. The nonlinear spectrum (discrete and continuous) derived
from efficiently combining both parts has a promising numerical precision. This
method can use any of one-step discretization NFT methods, e.g. Crank-Nicolson,
as an NFT kernel for the forward or backward part. Using trapezoid rule of
integral, we use an NFT kernel (we called here Trapezoid discretization NFT) in
forward-backward method which results discrete spectral amplitudes with a very
good numerical precision.
  These algorithms, forward-backward method and Darboux transform, are used in
[1],[2] for design and detection of phase-modulated 2-soliton pulses, and more
recently, in [3] for design and detection of more complex pulses with 7
eigenvalues and modulation of spectral phase. For those soliton pulses, the
discrete spectral amplitudes (in particular, phase) of both eigenvalues are
quite precisely estimated using the forward-backward method.


title:
Shapley Supercluster Survey: Ram-Pressure Stripping vs. Tidal
  Interactions in the Shapley Supercluster

abstract:
  We present two new examples of galaxies undergoing transformation in the
Shapley supercluster core. These low-mass (stellar mass from 0.4E10 to 1E10
Msun) galaxies are members of the two clusters SC-1329-313 (z=0.045) and
SC-1327-312 (z=0.049). Integral-field spectroscopy complemented by imaging in
ugriK bands and in Halpha narrow-band are used to disentangle the effects of
tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies,
SOS-61086 and SOS-90630, we observe one-sided extraplanar ionized gas extending
respectively 30kpc and 41kpc in projection from their disks. The galaxies'
gaseous disks are truncated and the kinematics of the stellar and gas
components are decoupled, supporting the RPS scenario. The emission of the
ionized gas extends in the direction of a possible companion for both galaxies
suggesting a TI. The overall gas velocity field of SOS-61086 is reproduced by
ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and
starting about 250Myr ago, consistent with the age of the young stellar
populations. A link between the observed gas stripping and the cluster-cluster
interaction experienced by SC-1329-313 and A3562 is suggested. Simulations of
ram pressure acting almost edge-on are able to fully reproduce the gas velocity
field of SOS-90630, but cannot at the same time reproduce the extended tail of
outflowing gas. This suggests that an additional disturbance from a TI is
required. This study adds a piece of evidence that RPS may take place in
different environments with different impacts and witnesses the possible effect
of cluster-cluster merger on RPS.


title: Varieties of $G_r$-summands in Rational $G$-modules

abstract:
  Let $G$ be a simple simply connected algebraic group over an algebraically
closed field $k$ of characteristic $p$, with $r$-th Frobenius kernel $G_r$. Let
$M$ be a $G_r$-module and $V$ a rational $G$-module. We put a variety structure
on the set of all $G_r$-summands of $V$ that are isomorphic to $M$, and study
basic properties of these varieties. We give a few applications of this work to
the representation theory of $G$, primarily in providing some sufficient
conditions for when a $G_r$-module decomposition of $V$ can be extended to a
$G$-module decomposition. In particular we are interested in connections to
Donkin's tilting module conjecture, and more generally to the problem of
finding a $G$-structure for the projective indecomposable $G_r$-modules. To
that end, we show that Donkin's conjecture is equivalent to determining the
linearizability or non-linearizability of $G$-actions on certain affine spaces.


title:
Fast reconnection in relativistic plasmas: the magnetohydrodynamics
  tearing instability revisited

abstract:
  Fast reconnection operating in magnetically dominated plasmas is often
invoked in models for magnetar giant flares, for magnetic dissipation in pulsar
winds, or to explain the gamma-ray flares observed in the Crab nebula, hence
its investigation is of paramount importance in high-energy astrophysics. Here
we study, by means of two dimensional numerical simulations, the linear phase
and the subsequent nonlinear evolution of the tearing instability within the
framework of relativistic resistive magnetohydrodynamics, as appropriate in
situations where the Alfven velocity approaches the speed of light. It is found
that the linear phase of the instability closely matches the analysis in
classical MHD, where the growth rate scales with the Lundquist number S as
S^-1/2, with the only exception of an enhanced inertial term due to the thermal
and magnetic energy contributions. In addition, when thin current sheets of
inverse aspect ratio scaling as S^-1/3 are considered, the so-called "ideal"
tearing regime is retrieved, with modes growing independently on S and
extremely fast, on only a few light crossing times of the sheet length. The
overall growth of fluctuations is seen to solely depend on the value of the
background Alfven velocity. In the fully nonlinear stage we observe an inverse
cascade towards the fundamental mode, with Petschek-type supersonic jets
propagating at the external Alfven speed from the X-point, and a fast
reconnection rate at the predicted value R~(ln S)^-1.


title:
A new approach of the Chebyshev wavelets for the variable-order time
  fractional mobile-immobile advection-dispersion model

abstract:
  This paper proposes a new numerical method based on the Chebyshev wavelets
(CWs) to solve the variable-order time fractional mobile-immobile
advection-dispersion equation. To do this, a new operational matrix of
variable-order fractional derivative in the Caputo sense for the CWs is derived
and is used to obtain an approximate solution for the problem under study.
Along the way a new family of piecewise functions is introduced and employed to
derive a general method to compute this matrix. The main advantage behind the
proposed approach is that the problem under consideration is transformed into a
linear system of algebraic equations. So, it can be solved simply to obtain an
approximate solution. The efficiency and accuracy of the proposed method are
shown for some concrete examples. These results show that the proposed method
is very efficient and accurate.


title:
Students as Partners in Curricular Design: Creation of Student-Generated
  Calculus Projects

abstract:
  For the past five years advanced students have developed projects for our
redesigned Calculus II classes to use. Our student project designers are often
mathematically early in their careers, and so this provides them with an
opportunity to create and explore new mathematics while giving us the ability
to involve students of all levels in research projects. It also gives them the
chance to present their work at conferences and local talks.
  Our course redesign affected three groups of students: ones taking the class,
ones designing projects for the course, and embedded tutors. This qualitative
study examines how the second and third groups of students benefited from their
experiences and how we can modify our program to improve it. Evidence was
gathered from interviews, surveys, and observation of student research work and
its implementation in the classroom. We found that tutors reported more
confidence in their knowledge of calculus and insights into teaching it, and
project designers experienced similar benefits to that of a traditional
research experience.


title:
The impact of JWST broad-band filter choice on photometric redshift
  estimation

abstract:
  The determination of galaxy redshifts in James Webb Space Telescope (JWST)'s
blank-field surveys will mostly rely on photometric estimates, based on the
data provided by JWST's Near-Infrared Camera (NIRCam) at 0.6-5.0 {\mu}m and Mid
Infrared Instrument (MIRI) at {\lambda}>5.0 {\mu}m. In this work we analyse the
impact of choosing different combinations of NIRCam and MIRI broad-band filters
(F070W to F770W), as well as having ancillary data at {\lambda}<0.6 {\mu}m, on
the derived photometric redshifts (zphot) of a total of 5921 real and simulated
galaxies, with known input redshifts z=0-10. We found that observations at
{\lambda}<0.6 {\mu}m are necessary to control the contamination of high-z
samples by low-z interlopers. Adding MIRI (F560W and F770W) photometry to the
NIRCam data mitigates the absence of ancillary observations at {\lambda}<0.6
{\mu}m and improves the redshift estimation. At z=7-10, accurate zphot can be
obtained with the NIRCam broad bands alone when S/N>=10, but the zphot quality
significantly degrades at S/N<=5. Adding MIRI photometry with one magnitude
brighter depth than the NIRCam depth allows for a redshift recovery of 83-99%,
depending on SED type, and its effect is particularly noteworthy for galaxies
with nebular emission. The vast majority of NIRCam galaxies with [F150W]=29 AB
mag at z=7-10 will be detected with MIRI at [F560W, F770W]<28 mag if these
sources are at least mildly evolved or have spectra with emission lines
boosting the mid-infrared fluxes.


title: Nested Defects on the Boundary of Topological Superconductors

abstract:
  Helical Majorana edge states at the 2D boundaries of 3D topological
superconductors can be gapped by a surface Zeeman field. Here we study the
effect nested defects imprinted on the Zeeman field can have on the edge
states. We demonstrate that depending on the configuration of the field we can
induce dimensional reduction of gapless Majorana modes from 2D to 1D or
quasi-0D at magnetic domain walls. We determine the nature of the Majorana
localisation on these defects as a function of the magnitude and configuration
of the Zeeman field. Finally, we observe a generalisation of the index theorem
governing the number of gapless modes at the interface between topologically
non-trivial systems with partial Chern numbers.


title:
Unsupervised Feature Extraction by Time-Contrastive Learning and
  Nonlinear ICA

abstract:
  Nonlinear independent component analysis (ICA) provides an appealing
framework for unsupervised feature learning, but the models proposed so far are
not identifiable. Here, we first propose a new intuitive principle of
unsupervised deep learning from time series which uses the nonstationary
structure of the data. Our learning principle, time-contrastive learning (TCL),
finds a representation which allows optimal discrimination of time segments
(windows). Surprisingly, we show how TCL can be related to a nonlinear ICA
model, when ICA is redefined to include temporal nonstationarities. In
particular, we show that TCL combined with linear ICA estimates the nonlinear
ICA model up to point-wise transformations of the sources, and this solution is
unique --- thus providing the first identifiability result for nonlinear ICA
which is rigorous, constructive, as well as very general.


title: Two-component Dirac equation

abstract:
  We provide an alternative approach to relativistic dynamics based on the
Feshbach projection technique. Instead of directly studying the Dirac equation,
we derive a two-component equation for the upper spinor. This approach allows
one to investigate the underlying physics in a different perspective. For
particles with small mass such as the neutrino, the leading order equation has
a Hermitian effective Hamiltonian, implying there is no leakage between the
upper and lower spinors. In the weak relativistic regime, the leading order
corresponds to a non-Hermitian correction to the Pauli equation, which takes
into account the non-zero possibility of finding the lower-spinor state and
offers a more precise description.


title:
Understanding Nanopore Window Distortions in the Reversible Molecular
  Valve Zeolite RHO

abstract:
  Molecular valves are becoming popular for potential biomedical applications.
However, little is known concerning their performance in energy and
environmental areas. Zeolite RHO shows unique pore deformations upon changes in
hydration, cation siting, cation type, or temperature-pressure conditions. By
varying the level of distortion of double eight-rings, it is possible to
control the adsorption properties, which confer a molecular valve behavior to
this material. We have employed interatomic potentials-based simulations to
obtain a detailed atomistic view of the structural distortion mechanisms of
zeolite RHO, in contrast with the averaged and space group restricted
information provided by diffraction studies. We have modeled four
aluminosilicate structures, containing Li$^+$, Na$^+$, K$^+$, Ca$^{2+}$, and
Sr$^{2+}$ cations. The distortions of the three different zeolite rings are
coupled, and the six- and eight-membered rings are largely flexible. A large
dependence on the polarizing power of the extra-framework cations and with the
loading of water has been found for the minimum aperture of the eight-membered
rings that control the nanovalve effect. The calculated energy barriers for
moving the cations across the eight-membered rings are very high, which
explains the experimentally observed slow kinetics of the phase transition as
well as the appearance of metastable phases.


title:
Simulation of Quiet-Sun Hard X-rays Related to Solar Wind Superhalo
  Electrons

abstract:
  In this paper, we propose that the accelerated electrons in the quiet Sun
could collide with the solar atmosphere to emit Hard X-rays (HXRs) via
non-thermal bremsstrahlung, while some of these electrons would move upwards
and escape into the interplanetary medium, to form a superhalo electron
population measured in the solar wind. After considering the electron energy
loss due to Coulomb collisions and the ambipolar electrostatic potential, we
find that the sources of the superhalo could only occur high in the corona (at
a heliocentric altitude $\gtrsim 1.9$ R$_\odot$ (the mean radius of the Sun)),
to remain a power-law shape of electron spectrum as observed by STEREO at 1AU
near solar minimum (Wang et al., 2012). The modeled quiet-Sun HXRs related to
the superhalo electrons fit well to a power-law spectrum, $f \sim
\varepsilon^{-\gamma}$, with an index $\gamma$ $\approx$ 2.0 - 2.3 (3.3 - 3.7)
at 10 - 100 keV, for the warm/cold thick-target (thin-target) emissions
produced by the downward-traveling (upward-traveling) accelerated electrons.
These simulated quiet-Sun spectra are significantly harder than the observed
spectra of most solar HXR flares. Assuming that the quiet-Sun sources cover 5%
of the solar surface, the modeled thin-target HXRs are more than six orders of
magnitude weaker than the RHESSI upper limit for quiet-Sun HXRs (Hannah et al.,
2010). Using the thick-target model for the downward-traveling electrons, the
RHESSI upper limit restricts the number of downward-traveling electrons to at
most $\approx$3 times the number of escaping electrons. This ratio is
fundamentally different from what is observed during solar flares associated
with escaping electrons where the fraction of downward-traveling electrons
dominates by a factor of 100 to 1000 over the escaping population.


title: Three-body resonance in meteoroid streams

abstract:
  Mean-motion resonances play an important role in the evolution of various
meteoroid streams. Previous works have studied the effects of two-body
resonances in different comets and streams. These already established two-body
resonances were mainly induced either by Jovian or Saturnian effects but not
both at the same time. Some of these resonances have led to spectacular meteor
outbursts and storms in the past. In this work, we find a new resonance
mechanism involving three bodies -- i.e. meteoroid particle, Jupiter and
Saturn, in the Perseid meteoroid stream. Long-term three-body resonances are
not very common in real small bodies in our solar system although they can
mathematically exist at many resonant sweet spots in an abstract sense in any
dynamical system. This particular resonance combination in the Perseid stream
is such that it is close to the ratio of 1:4:10 if the orbital periods of
Perseid particle, Saturn and Jupiter are considered respectively. These
resonant Perseid meteoroids stay resonant for typically about 2 kyr. Highly
compact dust trails due to this unique resonance phenomenon are present in our
simulations. Some past and future years are presented where three-body resonant
meteoroids of different sizes (or subject to different radiation pressures) are
computed to come near the Earth. This is the first theoretical example of an
active and stable three-body resonance mechanism in the realm of meteoroid
streams.


title: Quantum Tunneling of Thermal Protons Through Pristine Graphene

abstract:
  Atomically thin two-dimensional materials such as graphene and hexagonal
boron nitride have recently been found to exhibit appreciable permeability to
thermal protons, making these materials emerging candidates for separation
technologies [S. Hu et al., Nature 516, 227 (2014); M. Lozada-Hidalgo et al.,
Science 351, 68 (2016).]. These remarkable findings remain unexplained by
density-functional electronic structure calculations, which instead yield
barriers that exceed by 1.0 eV those found in experiments. Here we resolve this
puzzle by demonstrating that the proton transfer through pristine graphene is
driven by quantum nuclear effects, which substantially reduce the transport
barrier by up to 1.4 eV compared to the results of classical molecular dynamics
(MD). Our Feynman-Kac path-integral MD simulations unambiguously reveal the
quantum tunneling mechanism of strongly interacting hydrogen ions through
two-dimensional materials. In addition, we predict a strong isotope effect of 1
eV on the transport barrier for graphene in vacuum and at room temperature.
These findings not only shed light on the graphene permeability to protons and
deuterons, but also offer new insights for controlling the underlying quantum
ion transport mechanisms in nanostructured separation membranes.


title:
A semi-analytical method to estimate the slip length of spreading
  cap-shaped droplets using Cox theory

abstract:
  The Cox-Voinov law on dynamic spreading relates the difference between the
cubic values of the apparent contact angle (theta) and the equilibrium contact
angle to the instantaneous contact line speed (U). Comparing spreading results
with this law requires accurate data of theta and U during the entire process.
We consider the case when gravitational forces are negligible and transform the
general Cox law in a relationship for the temporal evolution of the spreading
radius. For cap-shaped droplets, this enables a comparison of experimental or
computational results with Cox theory without the need for instantaneous data
of theta and U. The fitting of Cox theory against measured or computed
base-radius-over-time curves allows estimating the effective slip length. This
is useful for establishing relationships between slip length and parameters in
numerical methods for moving contact lines. The procedure is illustrated by
numerical simulations for partially wetting droplets employing the coupled
level-set volume-of-fluid and phase field methods.


title:
Particle Acceleration in Collapsing Magnetic Traps with a Braking Plasma
  Jet

abstract:
  Collapsing magnetic traps (CMTs) are one proposed mechanism for generating
non-thermal particle populations in solar flares. CMTs occur if an initially
stretched magnetic field structure relaxes rapidly into a lower-energy
configuration, which is believed to happen as a by-product of magnetic
reconnection. A similar mechanism for energising particles has also been found
to operate in the Earth's magnetotail. One particular feature proposed to be of
importance for particle acceleration in the magnetotail is that of a braking
plasma jet, i.e. a localised region of strong flow encountering stronger
magnetic field which causes the jet to slow down and stop. Such a feature has
not been included in previously proposed analytical models of CMTs for solar
flares. In this work we incorporate a braking plasma jet into a well studied
CMT model for the first time. We present results of test particle calculations
in this new CMT model. We observe and characterise new types of particle
behaviour caused by the magnetic structure of the jet braking region, which
allows electrons to be trapped both in the braking jet region and the loop
legs. We compare and contrast the behaviour of particle orbits for various
parameter regimes of the underlying trap by examining particle trajectories,
energy gains and the frequency with which different types of particle orbit are
found for each parameter regime.


title: On the maximality of the triangular subgroup

abstract:
  We prove that the subgroup of triangular automorphisms of the complex affine
$n$-space is maximal among all solvable subgroups of
$\mathrm{Aut}(\mathbb{A}_{\mathbb{C}}^n)$ for every $n$. In particular, it is a
Borel subgroup of $\mathrm{Aut}(\mathbb{A}_{\mathbb{C}}^n)$, when the latter is
viewed as an ind-group. In dimension two, we prove that the triangular subgroup
is a maximal closed subgroup. Nevertheless, it is not maximal among all
subgroups of $\mathrm{Aut}(\mathbb{A}_{\mathbb{C}}^2)$. Given an automorphism
$f$ of $\mathbb{A}_{\mathbb{C}}^2$, we study the question whether the group
generated by $f$ and the triangular subgroup is equal to the whole group
$\mathrm{Aut}(\mathbb{A}_{\mathbb{C}}^2)$.


title: Generation of high harmonics from silicon

abstract:
  We generate high-order harmonics of a mid-infrared laser from a silicon
single crystal and find their origin in the recollision of coherently
accelerated electrons with their holes, analogously to the atomic and molecular
case, and to ZnO [Vampa et al., Nature 522, 462-464 (2015)], a direct bandgap
material. Therefore indirect bandgap materials are shown to sustain the
recollision process as well as direct bandgap materials. Furthermore, we find
that the generation is perturbed with electric fields as low as 30 V/$\mu$m,
equal to the DC damage threshold. Our results extend high-harmonic spectroscopy
to the most technologically relevant material, and open the possibility to
integrate high harmonics with conventional electronics.


title: Revisiting instanton corrections to the Konishi multiplet

abstract:
  We revisit the calculation of instanton effects in correlation functions in
${\cal N}=4$ SYM involving the Konishi operator and operators of twist two.
Previous studies revealed that the scaling dimensions and the OPE coefficients
of these operators do not receive instanton corrections in the semiclassical
approximation. We go beyond this approximation and demonstrate that, while
operators belonging to the same ${\cal N}=4$ supermultiplet ought to have the
same conformal data, the evaluation of quantum instanton corrections for one
operator can be mapped into a semiclassical computation for another operator in
the same supermultiplet. This observation allows us to compute explicitly the
leading instanton correction to the scaling dimension of operators in the
Konishi supermultiplet as well as to their structure constants in the OPE of
two half-BPS scalar operators. We then use these results, together with
crossing symmetry, to determine instanton corrections to scaling dimensions of
twist-four operators with large spin.


title:
Semiclassical theory of the magnetization process of the triangular
  lattice Heisenberg model

abstract:
  Motivated by the numerous examples of 1/3 magnetization plateaux in the
triangular lattice Heisenberg an- tiferromagnet with spins ranging from 1/2 to
5/2, we revisit the semiclassical calculation of the magnetization curve of
that model, with the aim of coming up with a simple method that allows one to
calculate the full mag- netization curve, and not just the critical fields of
the 1/3 plateau. We show that it is actually possible to calculate the
magnetization curve including the first quantum corrections and the appearance
of the 1/3 plateau entirely within linear spin-wave theory, with predictions
for the critical fields that agree to order 1/S with those derived a long-time
ago on the basis of arguments that required to go beyond linear spin-wave
theory. This calculation relies on the central observation that there is a kink
in the semiclassical energy at the field where the classical ground state is
the collinear up-up-down structure, and that this kink gives rise to a locally
linear behavior of the energy with the field when all semiclassical ground
states are compared to each other for all fields. The magnetization curves
calculated in this way for spin 1/2, 1 and 5/2 are shown to be in good
agreement with available experimental data.


title:
The non-locality of Markov chain approximations to two-dimensional
  diffusions

abstract:
  In this short paper, we consider discrete-time Markov chains on lattices as
approximations to continuous-time diffusion processes. The approximations can
be interpreted as finite difference schemes for the generator of the process.
We derive conditions on the diffusion coefficients which permit transition
probabilities to match locally first and second moments. We derive a novel
formula which expresses how the matching becomes more difficult for larger
(absolute) correlations and strongly anisotropic processes, such that
instantaneous moves to more distant neighbours on the lattice have to be
allowed. Roughly speaking, for non-zero correlations, the distance covered in
one timestep is proportional to the ratio of volatilities in the two
directions. We discuss the implications to Markov decision processes and the
convergence analysis of approximations to Hamilton-Jacobi-Bellman equations in
the Barles-Souganidis framework.


title:
A Multilevel Approach towards Unbiased Sampling of Random Elliptic
  Partial Differential Equations

abstract:
  Partial differential equation is a powerful tool to characterize various
physics systems. In practice, measurement errors are often present and
probability models are employed to account for such uncertainties. In this
paper, we present a Monte Carlo scheme that yields unbiased estimators for
expectations of random elliptic partial differential equations. This algorithm
combines multilevel Monte Carlo [Giles, 2008] and a randomization scheme
proposed by [Rhee and Glynn, 2012, Rhee and Glynn, 2013]. Furthermore, to
obtain an estimator with both finite variance and finite expected computational
cost, we employ higher order approximations.


title: Reheating in Gauss-Bonnet-coupled inflation

abstract:
  We investigate the feasibility of models of inflation with a large
Gauss-Bonnet coupling at late times, which have been shown to modify and
prevent the end of inflation. Despite the potential of Gauss-Bonnet models in
predicting favourable power spectra, capable of greatly lowering the
tensor-to-scalar-ratio compared to now-disfavoured models of standard chaotic
inflation, it is important to also understand in what context it is possible
for post-inflationary (p)reheating to proceed and hence recover an acceptable
late-time cosmology. We argue that in the previously-studied inverse power law
coupling case, reheating cannot happen due to a lack of oscillatory solutions
for the inflaton, and that neither instant preheating nor gravitational
particle production would avoid this problem due to the persistence of the
inflaton's energy density, even if it were to partially decay. Hence we proceed
to define a minimal generalisation of the model which can permit perturbative
reheating and study the consequences of this, including heavily modified
dynamics during reheating and predictions of the power spectra.


title: Two-loop six gluon all plus helicity amplitude

abstract:
  We present an analytic expression for the six-point all-plus helicity
amplitude in QCD at two-loops. We compute the rational terms in a compact
analytic form organised by their singularity structure.


title:
Magnetization reversal and negative volume thermal expansion in Fe doped
  Ca2RuO4

abstract:
  We report physical and structural properties of single-crystal Ca2Ru1-xFexO4
(0<x<0.20) as functions of temperature, magnetic field and pressure. Ca2RuO4 is
a structurally-driven Mott insulator with a metal-insulator (MI) transition at
TMI = 357 K, which is well separated from antiferromagnetic order at TN = 110
K. Fe substitution for Ru in Ca2RuO4 causes a pronounced magnetization reversal
and giant negative volume thermal expansion (NVTE). The magnetization reversal
is a result of a field-induced antiferromagnetic coupling between the Ru- and
Fe-magnetic sublattices that have different temperature dependence. The NVTE is
closely associated with the orthorhombic distortion, and becomes smaller as the
orthorhombicity weakens due to either Fe doping or application of pressure. The
study highlights an intriguing interplay between lattice, orbital and spin
degrees of freedom that is at the root of the novel phenomena in Ca2RuO4.


title:
Phrase-based Machine Translation is State-of-the-Art for Automatic
  Grammatical Error Correction

abstract:
  In this work, we study parameter tuning towards the M^2 metric, the standard
metric for automatic grammar error correction (GEC) tasks. After implementing
M^2 as a scorer in the Moses tuning framework, we investigate interactions of
dense and sparse features, different optimizers, and tuning strategies for the
CoNLL-2014 shared task. We notice erratic behavior when optimizing sparse
feature weights with M^2 and offer partial solutions. We find that a bare-bones
phrase-based SMT setup with task-specific parameter-tuning outperforms all
previously published results for the CoNLL-2014 test set by a large margin
(46.37% M^2 over previously 41.75%, by an SMT system with neural features)
while being trained on the same, publicly available data. Our newly introduced
dense and sparse features widen that gap, and we improve the state-of-the-art
to 49.49% M^2.


title: Dealing with Big Data

abstract:
  This book chapter attempts to counter anxieties in the humanities and social
science about the role of big data in research by focusing on approaches which,
by being firmly grounded in the traditional values of disciplines, enhance
existing methods to produce fruitful research. Big data poses many
methodological challenges, but these pressures should prompt scholars to pay
much closer attention to methodological issues than they have in the past.


title:
Quantum criticality with a twist - interplay of correlations and Kohn
  anomalies in three dimensions

abstract:
  A general understanding of quantum phase transitions in strongly correlated
materials is still lacking. By exploiting a cutting-edge quantum many-body
approach, the dynamical vertex approximation, we make an important progress,
determining the quantum critical properties of the antiferromagnetic transition
in the fundamental model for correlated electrons, the Hubbard model in three
dimensions. In particular, we demonstrate that -in contradiction to the
conventional Hertz-Millis-Moriya theory- its quantum critical behavior is
driven by the Kohn anomalies of the Fermi surface, even when electronic
correlations become strong.


title:
XMM-Newton discovery of mHz quasi-periodic oscillations in the high mass
  X-ray binary IGRJ19140+0951

abstract:
  We report on the discovery of mHz quasi-periodic oscillations (QPOs) from the
high mass X-ray binary (HMXB) IGRJ19140+0951, during a 40 ks XMM-Newton
observation performed in 201 5, which caught the source in its faintest state
ever observed. At the start of the observation, IGRJ19140+0951 was at a low
flux of 2$\times$10$^{-12}$~erg~cm$^{-2}$~s$^{-1}$ ( 2-10 keV; L$_{\rm
X}$=3$\times$10$^{33}$~erg~s$^{-1}$ at 3.6 kpc), then its emission rised
reaching a flux 10 times higher, in a flare-like activity. The investigation of
the pow er spectrum reveals the presence of QPOs, detected only in the second
part of the observation, with a strong peak at a frequency of
1.46$\pm{0.07}$~mHz, together with higher harm onics. The X-ray spectrum is
highly absorbed (N$_{\rm H}$=$10^{23}$~cm$^{-2}$), well fitted by a power-law
with a photon index in the range 1.2-1.8. The re-analysis of a Chandra archival
observation shows a modulation at 0.17+/-0.05mHz, very likely the neutron star
spin period (although a QPO cannot be excluded). We discuss the origin of the
1.46 mHz QPO in the framework of both disc-fed and wind-fed HMXBs, favouring
the quasi-spherical accretion scenario. The low flux observed by XMM-Newton
leads to about three orders of magnit ude the source dynamic range, overlapping
with the one observed from Supergiant Fast X-ray Transients (SFXTs). However,
since its duty cycle is not as low as in SFXTs, IGRJ19140 +0951 is an
intermediate system between persistent supergiant HMXBs and SFXTs, suggesting a
smooth transition between these two sub-classes.


title:
Physical origins of ruled surfaces on the reduced density matrices
  geometry

abstract:
  The reduced density matrices (RDMs) of many-body quantum states form a convex
set. The boundary of low dimensional projections of this convex set may exhibit
nontrivial geometry such as ruled surfaces. In this paper, we study the
physical origins of these ruled surfaces for bosonic systems. The emergence of
ruled surfaces was recently proposed as signatures of symmetry-breaking phase.
We show that, apart from being signatures of symmetry-breaking, ruled surfaces
can also be the consequence of gapless quantum systems by demonstrating an
explicit example in terms of a two-mode Ising model. Our analysis was largely
simplified by the quantum de Finetti's theorem---in the limit of large system
size, these RDMs are the convex set of all the symmetric separable states. To
distinguish ruled surfaces originated from gapless systems from those caused by
symmetry-breaking, we propose to use the finite size scaling method for the
corresponding geometry. This method is then applied to the two-mode XY model,
successfully identifying a ruled surface as the consequence of gapless systems.


title:
Elementary specific spin and orbital moments of ultrathin CoFeB
  amorphous films on GaAs(100)

abstract:
  Nanoscale CoFeB amorphous films have been synthesized on GaAs(100) and
studied with X-ray magnetic circular dichroism (XMCD) and transmission electron
microscopy (TEM). We have found that the ratios of the orbital to spin magnetic
moments of both the Co and Fe in the ultrathin amorphous film have been
enhanced by more than 300% compared with those of the bulk crystalline Co and
Fe, and in specifically, a large orbital moment of 0.56*10^-6 B from the Co
atoms has been observed and at the same time the spin moment of the Co atoms
remains comparable to that of the bulk hcp Co. The results indicate that the
large uniaxial magnetic anisotropy (UMA) observed in the ultrathin CoFeB film
on GaAs(100) is related to the enhanced spin-orbital coupling of the Co atoms
in the CoFeB. This work offers experimental evidences of the correlation
between the UMA and the elementary specific spin and orbital moments in the
CoFeB amorphous film on the GaAs(100) substrate, which is significant for
spintronics applications.


title: Learning to Discover Sparse Graphical Models

abstract:
  We consider structure discovery of undirected graphical models from
observational data. Inferring likely structures from few examples is a complex
task often requiring the formulation of priors and sophisticated inference
procedures. Popular methods rely on estimating a penalized maximum likelihood
of the precision matrix. However, in these approaches structure recovery is an
indirect consequence of the data-fit term, the penalty can be difficult to
adapt for domain-specific knowledge, and the inference is computationally
demanding. By contrast, it may be easier to generate training samples of data
that arise from graphs with the desired structure properties. We propose here
to leverage this latter source of information as training data to learn a
function, parametrized by a neural network that maps empirical covariance
matrices to estimated graph structures. Learning this function brings two
benefits: it implicitly models the desired structure or sparsity properties to
form suitable priors, and it can be tailored to the specific problem of edge
structure discovery, rather than maximizing data likelihood. Applying this
framework, we find our learnable graph-discovery method trained on synthetic
data generalizes well: identifying relevant edges in both synthetic and real
data, completely unknown at training time. We find that on genetics, brain
imaging, and simulation data we obtain performance generally superior to
analytical methods.


title: Eigenvalues of subgraphs of the cube

abstract:
  We consider the problem of maximising the largest eigenvalue of subgraphs of
the hypercube $Q_d$ of a given order. We believe that in most cases, Hamming
balls are maximisers, and our results support this belief. We show that the
Hamming balls of radius $o(d)$ have largest eigenvalue that is within $1 +
o(1)$ of the maximum value. We also prove that Hamming balls with fixed radius
maximise the largest eigenvalue exactly, rather than asymptotically, when $d$
is sufficiently large. Our proofs rely on the method of compressions.


title: A family of extremal hypergraphs for Ryser's conjecture

abstract:
  Ryser's Conjecture states that for any $r$-partite $r$-uniform hypergraph,
the vertex cover number is at most $r{-}1$ times the matching number. This
conjecture is only known to be true for $r\leq 3$ in general and for $r\leq 5$
if the hypergraph is intersecting. There has also been considerable effort made
for finding hypergraphs that are extremal for Ryser's Conjecture, i.e.
$r$-partite hypergraphs whose cover number is $r-1$ times its matching number.
Aside from a few sporadic examples, the set of uniformities $r$ for which
Ryser's Conjecture is known to be tight is limited to those integers for which
a projective plane of order $r-1$ exists.
  We produce a new infinite family of $r$-uniform hypergraphs extremal to
Ryser's Conjecture, which exists whenever a projective plane of order $r-2$
exists. Our construction is flexible enough to produce a large number of
non-isomorphic extremal hypergraphs. In particular, we define what we call the
{\em Ryser poset} of extremal intersecting $r$-partite $r$-uniform hypergraphs
and show that the number of maximal and minimal elements is exponential in
$\sqrt{r}$.
  This provides further evidence for the difficulty of Ryser's Conjecture.


title: Reconstruction of convex bodies from moments

abstract:
  We investigate how much information about a convex body can be retrieved from
a finite number of its geometric moments. We give a sufficient condition for a
convex body to be uniquely determined by a finite number of its geometric
moments, and we show that among all convex bodies, those which are uniquely
determined by a finite number of moments form a dense set. Further, we derive a
stability result for convex bodies based on geometric moments. It turns out
that the stability result is improved considerably by using another set of
moments, namely Legendre moments. We present a reconstruction algorithm that
approximates a convex body using a finite number of its Legendre moments. The
consistency of the algorithm is established using the stability result for
Legendre moments. When only noisy measurements of Legendre moments are
available, the consistency of the algorithm is established under certain
assumptions on the variance of the noise variables.


title: Locally finite derivations and modular coinvariants

abstract:
  We consider a finite dimensional $\kk G$-module $V$ of a $p$-group $G$ over a
field $\kk$ of characteristic $p$. We describe a generating set for the
corresponding Hilbert Ideal. In case $G$ is cyclic this yields that the algebra
$\kk[V]_G$ of coinvariants is a free module over its subalgebra generated by
$\kk G$-module generators of $V^*$. This subalgebra is a quotient of a
polynomial ring by pure powers of its variables. The coinvariant ring was known
to have this property only when $G$ was cyclic of prime order,
\cite{SezerCoinv}. In addition, we show that if $G$ is the Klein 4-group and
$V$ does not contain an indecomposable summand isomorphic to the regular
module, then the Hilbert Ideal is a complete intersection, extending a result
of the second author and R. J. Shank \cite{SezerShank}.


title: Probing inflation models with gravitational waves

abstract:
  A direct detection of primordial gravitational waves is the ultimate probe
for any inflation model. While current CMB bounds predict the generic
scale-invariant gravitational wave spectrum from slow-roll inflation to be
below the reach of upcoming gravitational wave interferometers, this prospect
may dramatically change if the inflaton is a pseudoscalar. In this case, a
coupling to any abelian gauge field leads to a tachyonic instability for the
latter and hence to a new source of gravitational waves, directly related to
the dynamics of inflation. In this contribution we discuss how this setup
enables the upcoming gravitational wave interferometers advanced LIGO/VIRGO and
eLISA to probe the microphysics of inflation, distinguishing between different
universality classes of single-field slow-roll inflation models. We find that
the prime candidate for an early detection is a Starobinsky-like model.


title:
Fokker-Planck equations for Marcus stochastic differential equations
  driven by Levy processes

abstract:
  Marcus stochastic differential equations (SDEs) often are appropriate models
for stochastic dynamical systems driven by non-Gaussian Levy processes and have
wide applications in engineering and physical sciences. The probability density
of the solution to an SDE offers complete statistical information on the
underlying stochastic process. Explicit formula for the Fokker-Planck equation,
the governing equation for the probability density, is well-known when the SDE
is driven by a Brownian motion. In this paper, we address the open question of
finding the Fokker-Plank equations for Marcus SDEs in arbitrary dimensions
driven by non-Gaussian Levy processes. The equations are given in a simple form
that facilitates theoretical analysis and numerical computation. Several
examples are presented to illustrate how the theoretical results can be applied
to obtain Fokker-Planck equations for Marcus SDEs driven by Levy processes.


title: Changes of Variables and the Renormalization Group

abstract:
  A class of exact infinitesimal renormalization group transformations is
proposed and studied. These transformations are pure changes of variables
(i.e., no integration or elimination of some degrees of freedom is required)
such that a saddle point approximation is more accurate, becoming, in some
cases asymptotically exact as the transformations are iterated. The formalism
provides a simplified and unified approach to several known renormalization
groups. It also suggests some new ways in which renormalization group methods
might successfully be applied. In particular, an exact gauge covariant
renormalization group transformation is constructed. Solutions for a scalar
field theory are obtained both as an expansion in {\epsilon}=4-d and as an
expansion in a single coupling constant.


title: Exciton absorption in narrow armchair graphene nanoribbons

abstract:
  We develop an analytical approach to the exciton optical absorption for
narrow gap armchair graphene nanoribbons (AGNR). We focus on the regime of
dominant size quantization in combination with the attractive electron-hole
interaction. An adiabatic separation of slow and fast motions leads via the
two-body Dirac equation to the isolated and coupled subband approximations.
Discrete and continuous exciton states are in general coupled and form quasi
Rydberg series of purely discrete and resonance type character. Corresponding
oscillator strengths and widths are derived. We show that the exciton peaks are
blue-shifted, become broader and increase in magnitude upon narrowing the
ribbon. At the edge of a subband the singularity related to the 1D density of
states is transformed into finite absorption via the presence of the exciton.
Our analytical results are in good agreement with those obtained by other
methods including numerical approaches. Estimates of the expected experimental
values are provided for realistic AGNRs.


title: Modeling Evolutionary Dynamics of Lurking in Social Networks

abstract:
  Lurking is a complex user-behavioral phenomenon that occurs in all
large-scale online communities and social networks. It generally refers to the
behavior characterizing users that benefit from the information produced by
others in the community without actively contributing back to the production of
social content. The amount and evolution of lurkers may strongly affect an
online social environment, therefore understanding the lurking dynamics and
identifying strategies to curb this trend are relevant problems. In this
regard, we introduce the Lurker Game, i.e., a model for analyzing the
transitions from a lurking to a non-lurking (i.e., active) user role, and vice
versa, in terms of evolutionary game theory. We evaluate the proposed Lurker
Game by arranging agents on complex networks and analyzing the system
evolution, seeking relations between the network topology and the final
equilibrium of the game. Results suggest that the Lurker Game is suitable to
model the lurking dynamics, showing how the adoption of rewarding mechanisms
combined with the modeling of hypothetical heterogeneity of users' interests
may lead users in an online community towards a cooperative behavior.


title: The Unreasonable Effectiveness of Address Clustering

abstract:
  Address clustering tries to construct the one-to-many mapping from entities
to addresses in the Bitcoin system. Simple heuristics based on the
micro-structure of transactions have proved very effective in practice. In this
paper we describe the primary reasons behind this effectiveness: address reuse,
avoidable merging, super-clusters with high centrality, and the incremental
growth of address clusters. We quantify their impact during Bitcoin's first
seven years of existence.


title:
Large Non-Gaussianity in Non-Minimally Coupled Derivative Inflation with
  Gauss-Bonnet Correction

abstract:
  We study a nonminimal derivative inflationary model in the presence of the
Gauss-Bonnet term. To have a complete treatment of the model, we consider a
general form of the nonminimal derivative function and also the Gauss-Bonnet
coupling term. By following the ADM formalism, expanding the action up to the
third order in the perturbations and using the correlation functions, we study
the perturbation and its non-Gaussian feature in details. We also study the
consistency relation that gets modified in the presence of the Gauss-Bonnet
term in the action. We compare the results of our consideration in
confrontation with Planck2015 observational data and find some constraints on
the model's parameters. Our treatment shows that this model in some ranges of
the parameters is consistent with the observational data. Also, in some ranges
of model's parameters, the model predicts blue-tilted power spectrum. Finally,
we show that nonminimal derivative model in the presence of the GB term has
capability to have large non-Gaussianity.


title: Regularized degenerate multi-solitons

abstract:
  We report complex PT-symmetric multi-soliton solutions to the Korteweg
de-Vries equation that asymptotically contain one-soliton solutions, with each
of them possessing the same amount of finite real energy. We demonstrate how
these solutions originate from degenerate energy solutions of the Schroedinger
equation. Technically this is achieved by the application of Darboux-Crum
transformations involving Jordan states with suitable regularizing shifts.
Alternatively they may be constructed from a limiting process within the
context Hirota's direct method or on a nonlinear superposition obtained from
multiple Baecklund transformations. The proposed procedure is completely
generic and also applicable to other types of nonlinear integrable systems.


title: Multi-Higgs production in gluon fusion at 100 TeV

abstract:
  We carry out a detailed study of multi-Higgs production processes in the
gluon fusion channel in the high energy regime relevant to Future Circular
hadron colliders and in the high-Higgs-multiplicity limit (> 20). Our results
are based on the computation of the leading polygons - the triangles, boxes,
pentagons and hexagons - to the scattering processes, further combined with the
subsequent branchings to reach high final state multiplicities. The factorial
growth of the number of diagrams leads to an exponential enhancement of such
large multiplicity cross-sections and, ultimately, in breaking of
perturbativity. We find that the characteristic energy and multiplicity scales
where these perturbative rates become highly enhanced and grow with increasing
energy are within the 100 TeV regime with of the order of 130 Higgses (or more)
in the final state. We also show that already for a 50 TeV hadron collider the
perturbative cross-sections for 140 bosons are at picobarn level.


title:
Symmetry for extremal functions in subcritical Caffarelli-Kohn-Nirenberg
  inequalities

abstract:
  We use the formalism of the R{\'e}nyi entropies to establish the symmetry
range of extremal functions in a family of subcriti-cal
Caffarelli-Kohn-Nirenberg inequalities. By extremal functions we mean functions
which realize the equality case in the inequalities, written with optimal
constants. The method extends recent results on critical
Caffarelli-Kohn-Nirenberg inequalities. Using heuristics given by a nonlinear
diffusion equation, we give a variational proof of a symmetry result, by
establishing a rigidity theorem: in the symmetry region, all positive critical
points have radial symmetry and are therefore equal to the unique positive,
radial critical point, up to scalings and multiplications. This result is
sharp. The condition on the parameters is indeed complementary of the condition
which determines the region in which symmetry breaking holds as a consequence
of the linear instability of radial optimal functions. Compared to the critical
case, the subcritical range requires new tools. The Fisher information has to
be replaced by R{\'e}nyi entropy powers, and since some invariances are lost,
the estimates based on the Emden-Fowler transformation have to be modified.


title: Sensitive dependence and transitivity of fuzzified dynamical systems

abstract:
  This paper proves that a set-valued dynamical system is sensitively dependent
on initial conditions (resp., $\mathscr{F}$-sensitive, multi-sensitive) if and
only if its $g$-fuzzification is sensitively dependent on initial conditions
(resp., $\mathscr{F}$-sensitive, multi-sensitive), where $\mathscr{F}$ is a
Furstenberg family. As an application, it is shown that there exists a
sensitive dynamical system whose $g$-fuzzification does not have such sensitive
dependence for any $g$ in a certain domain. Moreover, a sufficient condition
ensuring that the $g$-fuzzification of every nontrivial dynamical system is not
transitive is obtained. These give an answer to a question posed in \cite[J.
Kupka, Information Sciences, {\bf 279} (2014): 642--653]{Kupka2014}.


title: The Ancient Astronomy of Easter Island: Mars and Sweet Potatoes

abstract:
  The role of the monument Moai a Mata Mea at Easter Island in the fertility
cult has been explained. The own late statue that belonged to the ruling Miru
group can provisionally be dated back to ca. 1691 A.D. on the backbone of the
archaeoastronomical studies as well as the written sources. Some data about
watchings of the total solar eclipse of September 16, 1773 A.D. and Halley's
Comet of 1682 A.D. are presented as well. A new information on the early
settlement of Rapanui is of our interest, too.


title:
Fast $\epsilon$-free Inference of Simulation Models with Bayesian
  Conditional Density Estimation

abstract:
  Many statistical models can be simulated forwards but have intractable
likelihoods. Approximate Bayesian Computation (ABC) methods are used to infer
properties of these models from data. Traditionally these methods approximate
the posterior over parameters by conditioning on data being inside an
$\epsilon$-ball around the observed data, which is only correct in the limit
$\epsilon\!\rightarrow\!0$. Monte Carlo methods can then draw samples from the
approximate posterior to approximate predictions or error bars on parameters.
These algorithms critically slow down as $\epsilon\!\rightarrow\!0$, and in
practice draw samples from a broader distribution than the posterior. We
propose a new approach to likelihood-free inference based on Bayesian
conditional density estimation. Preliminary inferences based on limited
simulation data are used to guide later simulations. In some cases, learning an
accurate parametric representation of the entire true posterior distribution
requires fewer model simulations than Monte Carlo ABC methods need to produce a
single sample from an approximate posterior.


title:
Towards Automation of Knowledge Understanding: An Approach for
  Probabilistic Generative Classifiers

abstract:
  After data selection, pre-processing, transformation, and feature extraction,
knowledge extraction is not the final step in a data mining process. It is then
necessary to understand this knowledge in order to apply it efficiently and
effectively. Up to now, there is a lack of appropriate techniques that support
this significant step. This is partly due to the fact that the assessment of
knowledge is often highly subjective, e.g., regarding aspects such as novelty
or usefulness. These aspects depend on the specific knowledge and requirements
of the data miner. There are, however, a number of aspects that are objective
and for which it is possible to provide appropriate measures. In this article
we focus on classification problems and use probabilistic generative
classifiers based on mixture density models that are quite common in data
mining applications. We define objective measures to assess the
informativeness, uniqueness, importance, discrimination, representativity,
uncertainty, and distinguishability of rules contained in these classifiers
numerically. These measures not only support a data miner in evaluating results
of a data mining process based on such classifiers. As we will see in
illustrative case studies, they may also be used to improve the data mining
process itself or to support the later application of the extracted knowledge.