title:
Enhanced dual-beam excitation photoelectric detection of NV magnetic
  resonances in diamond

abstract:
  The core issue for the implementation of the diamond NV centre qubits
technology is the sensitive readout of NV spin state. We have recently
demonstrated the photoelectric detection of NV magnetic resonances (PDMR),
anticipated to be faster and more sensitive than optical detection (ODMR). Here
we report on a PDMR contrast of 9 % - three times enhanced compared to previous
work - on shallow N-implanted diamond. Based on ab-initio modelling, we
demonstrate a novel one-photon ionization dual-beam PDMR protocol. We predict
that this scheme is significantly less vulnerable to the influence of defects
such as substitutional nitrogen.


title:
Auger recombination of dark excitons in ${\rm WS_2}$ and ${\rm WSe_2}$
  monolayers

abstract:
  We propose a novel phonon assisted Auger process unique to the electronic
band structure of monolayer transition metal dichalcogenides (TMDCs), which
dominates the radiative recombination of ground state excitons in Tungsten
based TMDCs. Using experimental and DFT computed values for the exciton
energies, spin-orbit splittings, optical matrix element, and the Auger matrix
elements, we find that the Auger process begins to dominate at carrier
densities as low as $10^{9-10}~{\rm cm^{-2}}$, thus providing a plausible
explanation for the low quantum efficiencies reported for these materials.


title:
Optimal bandwidth selection for semi-recursive kernel regression
  estimators

abstract:
  In this paper we propose an automatic selection of the bandwidth of the
semi-recursive kernel estimators of a regression function defined by the
stochastic approximation algorithm. We showed that, using the selected
bandwidth and some special stepsizes, the proposed semi-recursive estimators
will be very competitive to the nonrecursive one in terms of estimation error
but much better in terms of computational costs. We corroborated these
theoretical results through simulation study and a real dataset.


title: A general framework for weighted sum-rate and common-rate optimization

abstract:
  In this paper, we propose a framework for solving a class of optimization
problems encountered in a range of power allocation problems in wireless relay
networks. In particular, power allocation for weighted sum-rate and common-rate
optimization problems fall in this framework. Subject to some conditions on the
region of feasible powers, the optimal solutions are analytically found. The
optimization problems are posed in a general form and their solutions are shown
to have applications in a number of practical scenarios. Numerical results
verify the optimality of the analytical approach.


title: Finite groups of units of finite characteristic rings

abstract:
  In \cite[Problem 72]{Fuchs60} Fuchs asked the following question: which
groups can be the group of units of a commutative ring? In the following years,
some partial answers have been given to this question in particular cases. The
aim of the present paper is to address Fuchs' question when $A$ is a {\it
finite characteristic ring}. The result is a pretty good description of the
groups which can occur as group of units in this case, equipped with examples
showing that there are obstacles to a "short" complete classification. As a
byproduct, we are able to classify all possible cardinalities of the group of
units of a finite characteristic ring, so to answer Ditor's question
\cite{ditor}.


title:
The jamming transition in high dimension: an analytical study of the TAP
  equations and the effective thermodynamic potential

abstract:
  We present a parallel derivation of the Thouless-Anderson-Palmer (TAP)
equations and of an effective potential for the negative perceptron and soft
sphere models in high dimension. Both models are continuous constrained
satisfaction problems with a critical jamming transition characterized by the
same exponents. Our analysis reveals that a power expansion of the potential up
to the second order represents a successful framework to approach the jamming
line from the SAT phase (the region of the phase diagram where at least one
configuration verifies all the constraints), where the ground-state energy is
zero. An interesting outcome is that close to jamming the effective
thermodynamic potential has a logarithmic contribution, which turns out to be
dominant in a proper scaling regime. Our approach is quite general and can be
directly applied to other interesting models. Finally, we study the spectrum of
small harmonic fluctuations in the SAT phase recovering the typical scaling
$D(\omega) \sim \omega^2$ below the cutoff frequency but a different behavior
characterized by a non-trivial exponent above it.


title:
Gapped Excitations in the High-Pressure Antiferromagnetic Phase of
  URu$_2$Si$_2$

abstract:
  We report a neutron scattering study of the magnetic excitation spectrum in
each of the three temperature and pressure driven phases of URu$_2$Si$_2$. We
find qualitatively similar excitations throughout the (H0L) scattering plane in
the hidden order and large moment phases, with no changes in the
$\hbar\omega$-widths of the excitations at the $\Sigma$ = (1.407,0,0) and $Z$ =
(1,0,0) points, within our experimental resolution. There is, however, an
increase in the gap at the $\Sigma$ point from 4.2(2) meV to 5.5(3) meV,
consistent with other indicators of enhanced antiferromagnetism under pressure.


title: Full waveform inversion guided by travel time tomography

abstract:
  Full waveform inversion (FWI) is a process in which seismic numerical
simulations are fit to observed data by changing the wave velocity model of the
medium under investigation. The problem is non-linear, and therefore
optimization techniques have been used to find a reasonable solution to the
problem. The main problem in fitting the data is the lack of low spatial
frequencies. This deficiency often leads to a local minimum and to
non-plausible solutions. In this work we explore how to obtain low frequency
information for FWI. Our approach involves augmenting FWI with travel time
tomography, which has low-frequency features. By jointly inverting these two
problems we enrich FWI with information that can replace low frequency data. In
addition, we use high order regularization, in a preliminary inversion stage,
to prevent high frequency features from polluting our model in the initial
stages of the reconstruction. This regularization also promotes the
non-dominant low-frequency modes that exist in the FWI sensitivity. By applying
a joint FWI and travel time inversion we are able to obtain a smooth model than
can later be used to recover a good approximation for the true model. A second
contribution of this paper involves the acceleration of the main computational
bottleneck in FWI--the solution of the Helmholtz equation. We show that the
solution time can be reduced by solving the equation for multiple right hand
sides using block multigrid preconditioned Krylov methods.


title:
Cell assemblies at multiple time scales with arbitrary lag
  constellations

abstract:
  Hebb's idea of a cell assembly as the fundamental unit of neural information
processing has dominated neuroscience like no other theoretical concept within
the past 60 years. A range of different physiological phenomena, from precisely
synchronized spiking to broadly simultaneous rate increases, has been subsumed
under this term. Yet progress in this area is hampered by the lack of
statistical tools that would enable to extract assemblies with arbitrary
constellations of time lags, and at multiple temporal scales, partly due to the
severe computational burden. Here we present such a unifying methodological and
conceptual framework which detects assembly structure at many different time
scales, levels of precision, and with arbitrary internal organization. Applying
this methodology to multiple single unit recordings from various cortical
areas, we find that there is no universal cortical coding scheme, but that
assembly structure and precision significantly depends on brain area recorded
and ongoing task demands.


title:
Sequence to Backward and Forward Sequences: A Content-Introducing
  Approach to Generative Short-Text Conversation

abstract:
  Using neural networks to generate replies in human-computer dialogue systems
is attracting increasing attention over the past few years. However, the
performance is not satisfactory: the neural network tends to generate safe,
universally relevant replies which carry little meaning. In this paper, we
propose a content-introducing approach to neural network-based generative
dialogue systems. We first use pointwise mutual information (PMI) to predict a
noun as a keyword, reflecting the main gist of the reply. We then propose
seq2BF, a "sequence to backward and forward sequences" model, which generates a
reply containing the given keyword. Experimental results show that our approach
significantly outperforms traditional sequence-to-sequence models in terms of
human evaluation and the entropy measure, and that the predicted keyword can
appear at an appropriate position in the reply.


title:
Can we unify monocular detectors for autonomous driving by using the
  pixel-wise semantic segmentation of CNNs?

abstract:
  Autonomous driving is a challenging topic that requires complex solutions in
perception tasks such as recognition of road, lanes, traffic signs or lights,
vehicles and pedestrians. Through years of research, computer vision has grown
capable of tackling these tasks with monocular detectors that can provide
remarkable detection rates with relatively low processing times. However, the
recent appearance of Convolutional Neural Networks (CNNs) has revolutionized
the computer vision field and has made possible approaches to perform full
pixel-wise semantic segmentation in times close to real time (even on hardware
that can be carried on a vehicle). In this paper, we propose to use full image
segmentation as an approach to simplify and unify most of the detection tasks
required in the perception module of an autonomous vehicle, analyzing major
concerns such as computation time and detection performance.


title: Torsion Gravity for Dirac Fields

abstract:
  In this article we will take into account the most complete back-ground with
torsion and curvature, providing the most exhaustive coupling for the Dirac
field: we will discuss the integrability of the interaction of the matter field
and the reduction of the matter field equations.


title: A fast marching algorithm for the factored eikonal equation

abstract:
  The eikonal equation is instrumental in many applications in several fields
ranging from computer vision to geoscience. This equation can be efficiently
solved using the iterative Fast Sweeping (FS) methods and the direct Fast
Marching (FM) methods. However, when used for a point source, the original
eikonal equation is known to yield inaccurate numerical solutions, because of a
singularity at the source. In this case, the factored eikonal equation is often
preferred, and is known to yield a more accurate numerical solution. One
application that requires the solution of the eikonal equation for point
sources is travel time tomography. This inverse problem may be formulated using
the eikonal equation as a forward problem. While this problem has been solved
using FS in the past, the more recent choice for applying it involves FM
methods because of the efficiency in which sensitivities can be obtained using
them. However, while several FS methods are available for solving the factored
equation, the FM method is available only for the original eikonal equation.
  In this paper we develop a Fast Marching algorithm for the factored eikonal
equation, using both first and second order finite-difference schemes. Our
algorithm follows the same lines as the original FM algorithm and requires the
same computational effort. In addition, we show how to obtain sensitivities
using this FM method and apply travel time tomography, formulated as an inverse
factored eikonal equation. Numerical results in two and three dimensions show
that our algorithm solves the factored eikonal equation efficiently, and
demonstrate the achieved accuracy for computing the travel time. We also
demonstrate a recovery of a 2D and 3D heterogeneous medium by travel time
tomography using the eikonal equation for forward modelling and inversion by
Gauss-Newton.


title: Lecture Notes on Channel Coding

abstract:
  These lecture notes on channel coding were developed for a one-semester
course for graduate students of electrical engineering. Chapter 1 reviews the
basic problem of channel coding. Chapters 2-5 are on linear block codes, cyclic
codes, Reed-Solomon codes, and BCH codes, respectively. The notes are
self-contained and were written with the intent to derive the presented results
with mathematical rigor. The notes contain in total 68 homework problems, of
which 20% require computer programming.


title:
Black hole nonmodal linear stability: odd perturbations of
  Reissner-Nordstr\"om

abstract:
  Following a program on black hole nonmodal linear stability initiated in
Phys.\ Rev.\ Lett.\ {\bf 112} (2014) 191101, we study odd linear perturbations
of the Einstein-Maxwell equations around a Reissner-Nordstr\"om (A)dS black
hole. We show that all the gauge invariant information in the metric and
Maxwell field perturbations is encoded in the spacetime scalars $\mathcal{F}
=\delta (F^*_{\alpha \beta} F^{\alpha \beta})$ and $\mathcal{Q} =\delta
(\tfrac{1}{48} C^*_{\alpha \beta \gamma \delta} C^{\alpha \beta \gamma
\delta})$, where $C_{\alpha \beta \gamma \delta}$ is the Weyl tensor,
$F_{\alpha \beta}$ the Maxwell field, a star denotes Hodge dual and $\delta$
means first order variation, and that the linearized Einstein-Maxwell equations
are equivalent to a coupled system of wave equations for $\mathcal{F}$ and
$\mathcal{Q}$. For nonnegative cosmological constant we prove that
$\mathcal{F}$ and $\mathcal{Q}$ are pointwise bounded on the outer static
region. The fields are shown to diverge as the Cauchy horizon is approached
from the inner dynamical region, providing evidence supporting strong cosmic
censorship. In the asymptotically AdS case the dynamics depends on the boundary
condition at the conformal timelike boundary and there are instabilities if
Robin boundary conditions are chosen.


title:
Modelling Context with User Embeddings for Sarcasm Detection in Social
  Media

abstract:
  We introduce a deep neural network for automated sarcasm detection. Recent
work has emphasized the need for models to capitalize on contextual features,
beyond lexical and syntactic cues present in utterances. For example, different
speakers will tend to employ sarcasm regarding different subjects and, thus,
sarcasm detection models ought to encode such speaker information. Current
methods have achieved this by way of laborious feature engineering. By
contrast, we propose to automatically learn and then exploit user embeddings,
to be used in concert with lexical signals to recognize sarcasm. Our approach
does not require elaborate feature engineering (and concomitant data scraping);
fitting user embeddings requires only the text from their previous posts. The
experimental results show that our model outperforms a state-of-the-art
approach leveraging an extensive set of carefully crafted features.


title:
On the symmetry of four particles in a one-dimensional box with harmonic
  interaction

abstract:
  We show that a system of four particles in a one-dimensional box with a
two-particle harmonic interaction can by described by means of the symmetry
point group $O_h$. Group theory proves useful for the discussion of both the
small-box and large-box regimes. We apply perturbation theory and obtain the
corrections of first order for the lowest states. We carry out a simple
Rayleigh-Ritz variational calculation with basis sets adapted to the symmetries
of the system. We also obtain alternative variational results for the first
three lowest energy levels that are more suitable for larger box sizes.


title: Tautological relations via r-spin structures

abstract:
  Relations among tautological classes on the moduli space of stable curves are
obtained via the study of Witten's r-spin theory for higher r. In order to
calculate the quantum product, a new formula relating the r-spin correlators in
genus 0 to the representation theory of sl2 is proven. The Givental-Teleman
classification of CohFTs is used at two special semisimple points of the
associated Frobenius manifold. At the first semisimple point, the R-matrix is
exactly solved in terms of hypergeometric series. As a result, an explicit
formula for Witten's r-spin class is obtained (along with tautological
relations in higher degrees). As an application, the r=4 relations are used to
bound the Betti numbers of the tautological ring of the moduli of nonsingular
curves. At the second semisimple point, the form of the R-matrix implies a
polynomiality property in r of Witten's r-spin class.
  In the Appendix (with F. Janda), a conjecture relating the r=0 limit of
Witten's r-spin class to the class of the moduli space of holomorphic
differentials is presented.


title:
Maximal operators of exotic and non-exotic Laguerre and other semigroups
  associated with classical orthogonal expansions

abstract:
  Classical settings of discrete and continuous orthogonal expansions, like
Laguerre, Bessel and Jacobi, are associated with second order differential
operators playing the role of the Laplacian. These depend on certain parameters
of type that are usually restricted to a half-line, or a product of half-lines
if higher dimensions are considered. Following earlier research done by
Hajmirzaahmad, we deal in this paper with Laplacians in the above-mentioned
contexts with no restrictions on the type parameters and bring to attention
naturally associated orthogonal systems that in fact involve the classical
ones, but are different. This reveals new frameworks related to classical
orthogonal expansions and thus new potentially rich research areas, at least
from the harmonic analysis perspective. To support the last claim we focus on
maximal operators of multi-dimensional Laguerre, Bessel and Jacobi semigroups,
with unrestricted type parameters, and prove that they satisfy weak type (1,1)
estimates with respect to the appropriate measures. Generally, these measures
are not (locally) finite, which makes a contrast with the classical situations
and generates new difficulties. An important partial result of the paper is a
new proof of the weak type (1,1) estimate for the classical multi-dimensional
Laguerre semigroup maximal operator.


title: Analogue Magnetism: An Ansatz

abstract:
  We present an ansatz for the relationship between magnetic flux density and
fluid vorticity evolution equations. We also suggest that the magnetic flux
density evolution equations be compared to the evolution equation for an
effective vorticity ($\omega_{eff}$), which bears a power law relation to the
ordinary vorticity.


title:
Almost reducibility of linear difference systems from a spectral point
  of view

abstract:
  We prove that, under some conditions, a linear nonautonomous difference
system is Bylov's almost reducible to a diagonal one whose terms are contained
in the Sacker and Sell spectrum of the original system.
  We also provide an example of the concept of diagonally significant system,
recently introduced by P\"otzche. This example plays an essential role in the
demonstration of our results.


title:
Discretization of the density matrix as a nonlinear positive map and
  entanglement

abstract:
  The discretization of the density matrix is proposed as a nonlinear positive
map for systems with continuous variables. This procedure is used to calculate
the entanglement between two modes through different criteria, such as Tsallis
entropy, von Neumann entropy and linear entropy and the logarithmic negativity.
As an example, we study the dynamics of entanglement for the two-mode squeezed
vacuum state in the parametric amplifier and show good agreement with the
analytic results. The loss of information on the system state due to the
discretization of the density matrix is also addressed.


title:
Magnetoresistance of vertical Co-graphene-NiFe junctions controlled by
  charge transfer and proximity-induced spin splitting in graphene

abstract:
  Graphene is hailed as an ideal material for spintronics due to weak intrinsic
spin-orbit interaction that facilitates lateral spin transport and tunability
of its electronic properties, including a possibility to induce magnetism in
graphene. Another promising application of graphene is related to its use as a
spacer separating ferromagnetic metals (FMs) in vertical magnetoresistive
devices, the most prominent class of spintronic devices widely used as magnetic
sensors. In particular, few-layer graphene was predicted to act as a perfect
spin filter. Here we show that the role of graphene in such devices (at least
in the absence of epitaxial alignment between graphene and the FMs) is
different and determined by proximity-induced spin splitting and charge
transfer with adjacent ferromagnetic metals, making graphene a weak FM
electrode rather than a spin filter. To this end, we report observations of
magnetoresistance (MR) in vertical Co-graphene-NiFe junctions with 1 to 4
graphene layers separating the ferromagnets, and demonstrate that the
dependence of the MR sign on the number of layers and its inversion at
relatively small bias voltages is consistent with spin transport between weakly
doped and differently spin-polarized layers of graphene. The proposed
interpretation is supported by the observation of an MR sign reversal in biased
Co-graphene-hBN-NiFe devices and by comprehensive structural characterization.
Our results suggest a new architecture for vertical devices with electrically
controlled MR.


title:
Dual Chain Perturbation theory: A new equation of state for polyatomic
  molecules

abstract:
  In the development of equations of state for polyatomic molecules,
thermodynamic perturbation theory (TPT) is widely used to calculate the change
in free energy due to chain formation. TPT is a simplification of a more
general and exact multi-density cluster expansion for associating fluids. In
TPT all contributions to the cluster expansion which contain chain - chain
interactions are neglected. That is, all inter-chain interactions are treated
at the reference fluid level. This allows for the summation of the cluster
theory in terms of reference system correlation functions only. While highly
successful, TPT has many handicaps which result from the neglect of chain -
chain interactions. The subject of this document is to move beyond the
limitations of TPT, and included chain - chain contributions to the equation of
state.


title: An Approach to Injective Acts over Monoids Based on Indecomposability

abstract:
  The main purpose of this paper is investigating classes of acts that are
injective relative to all embeddings with indecomposable domains or codomains.
We give some homological classifications of monoids in light of such kinds of
injectivity. Our approach to indecomposable property provides a new
characterization of right absolutely injective monoids as ones that all
indecomposable acts are injective.


title:
Linking Spatial Distributions of Potential and Current in Viscous
  Electronics

abstract:
  Viscous electronics is an emerging field dealing with systems in which
strongly interacting electrons behave as a fluid. Electron viscous flows are
governed by a nonlocal current-field relation which renders the spatial
patterns of current and electric field strikingly distinct. Notably, driven by
the viscous friction force from adjacent layers, current can flow against the
electric field, generating negative resistance, vorticity and vortices.
Moreover, different current flows can result in identical potential
distributions. This sets a new situation where inferring the electron flow
pattern from the measured potentials presents a nontrivial problem. Using the
inherent relation between these patterns through the complex analysis, here we
propose a method for extracting the current flows from potential distributions
measured in the presence of a magnetic field.


title:
Heavy quark symmetry and weak decays of the $b$-baryons in pentaquarks
  with a $c\bar{c}$ component

abstract:
  The discovery of the baryonic states $P_c^+(4380)$ and $P_c^+(4450)$ by the
LHCb collaboration has evoked a lot of theoretical interest. These states have
the minimal quark content $c \bar{c} u u d$. Interpreted as hidden charm
diquark-diquark-antiquark baryons, the assigned spin and angular momentum
quantum numbers are $P_c^+(4380)= \{\bar{c} [cu]_{s=1} [ud]_{s=1};
L_{\mathcal{P}}=0, J^{\rm P}=\frac{3}{2}^- \}$ and $P_c^+(4450)= \{\bar{c}
[cu]_{s=1} [ud]_{s=0}; L_{\mathcal{P}}=1, J^{\rm P}=\frac{5}{2}^+ \}$, where
$s=0,1$ are the spins of the diquarks and $L_{\mathcal{P}}=0,1$ are the orbital
angular momentum quantum numbers of the pentaquarks. We point out that heavy
quark symmetry allows only the higher mass pentaquark state $P_c^+(4450)$
having $[ud]_{s=0}$ to be produced in $\Lambda_b^0$ decays, whereas the lower
mass state $P_c^+(4380)$ having $[ud]_{s=1}$ is disfavored. Pentaquark spectrum
is rich enough to accommodate a $J^P=\frac{3}{2}^-$ state, which has the
correct light diquark spin $\{\bar{c} [cu]_{s=1} [ud]_{s=0}; L_{\mathcal{P}}=0,
J^{\rm P}=\frac{3}{2}^- \}$ to be produced in $\Lambda_b^0$ decays. Assuming
that the orbital mass difference between the charmed pentaquarks is similar to
the corresponding mass difference in the charmed baryons, we estimate the mass
of the lower pentaquark $J^P=3/2^-$ state to be about 4110 MeV and suggest to
reanalyze the LHCb data to search for this third state. We present the
spectroscopy of the $S$- and $P$-wave pentaquark states having a $c\bar{c}$
pair and three light quarks using an effective Hamiltonian approach. Some of
these pentaquarks can be produced in weak decays of the $b$-baryons. Combining
heavy quark symmetry and the $SU(3)_F$ symmetry results in strikingly simple
relations among the decay amplitudes which are presented here.


title:
Design of a quasi-2D photonic crystal optomechanical cavity with
  tunable, large $x^2$-coupling

abstract:
  We present the optical and mechanical design of a mechanically compliant
quasi-two-dimensional photonic crystal cavity formed from thin-film silicon in
which a pair of linear nanoscale slots are used to create two coupled high-$Q$
optical resonances. The optical cavity supermodes, whose frequencies are
designed to lie in the $1500$~nm wavelength band, are shown to interact
strongly with mechanical resonances of the structure whose frequencies range
from a few MHz to a few GHz. Depending upon the symmetry of the mechanical
modes and the symmetry of the slot sizes, we show that the optomechanical
coupling between the optical supermodes can be either linear or quadratic in
the mechanical displacement amplitude. Tuning of the nanoscale slot size is
also shown to adjust the magnitude and sign of the cavity supermode splitting
$2J$, enabling near-resonant motional scattering between the two optical
supermodes and greatly enhancing the $x^2$-coupling strength. Specifically, for
the fundamental flexural mode of the central nanobeam of the structure at
$10$~MHz the per-phonon linear cross-mode coupling rate is calculated to be
$\tilde{g}_{+-}/2\pi = 1$~MHz, corresponding to a per-phonon $x^2$-coupling
rate of $\tilde{g}'/2\pi=1$~kHz for a mode splitting $2J/2\pi = 1$~GHz which is
greater than the radiation-limited supermode linewidths.


title: Integral formula for codimension-one foliated $(\alpha,\beta)$-spaces

abstract:
  Integral formulae for foliated Riemannian manifolds provide obstructions for
existence of foliations or compact leaves of them with given geometric
properties. Recently, we associated a new Riemannian metric to a
codimension-one foliated Finsler space and proved integral formulae for general
and for Randers spaces. In the paper, we study this metric for a wider class of
codimension-one foliated $(\alpha,\beta)$-spaces and embody it in a set of
metrics that can be viewed as a perturbed metric associated with $\alpha$. For
such metrics we calculate the Weingarten operator of the leaves and deduce the
Reeb type integral formula, which can be used for $(\alpha,\beta)$-spaces, e.g.
Randers and Kropina spaces.


title: Precise top-quark mass from the diphoton mass spectrum

abstract:
  We calculate the $gg\to\gamma\gamma$ amplitude by including the $t\bar t$
bound-state effects near their mass threshold. In terms of the non-relativistic
expansion of the amplitude, the LO contribution is an energy-independent term
in the one-loop amplitude. We include the NLO contribution described by the
non-relativistic Green function and part of the NNLO contribution. Despite a
missing NLO piece which can be accomplished with the two-loop-level amplitude
via massive quarks, the shape of the diphoton mass spectrum is predicted with a
good accuracy. Thanks to the simple and clean nature of the observable, its
experimental measurement can be a direct method to determine the short-distance
mass of the top quark at hadron colliders.


title: Verifying Reachability in Networks with Mutable Datapaths

abstract:
  Recent work has made great progress in verifying the forwarding correctness
of networks . However, these approaches cannot be used to verify networks
containing middleboxes, such as caches and firewalls, whose forwarding behavior
depends on previously observed traffic. We explore how to verify reachability
properties for networks that include such "mutable datapath" elements. We want
our verification results to hold not just for the given network, but also in
the presence of failures. The main challenge lies in scaling the approach to
handle large and complicated networks, We address by developing and leveraging
the concept of slices, which allow network-wide verification to only require
analyzing small portions of the network. We show that with slices the time
required to verify an invariant on many production networks is independent of
the size of the network itself.


title: Generic Statistical Relational Entity Resolution in Knowledge Graphs

abstract:
  Entity resolution, the problem of identifying the underlying entity of
references found in data, has been researched for many decades in many
communities. A common theme in this research has been the importance of
incorporating relational features into the resolution process. Relational
entity resolution is particularly important in knowledge graphs (KGs), which
have a regular structure capturing entities and their interrelationships. We
identify three major problems in KG entity resolution: (1) intra-KG reference
ambiguity; (2) inter-KG reference ambiguity; and (3) ambiguity when extending
KGs with new facts. We implement a framework that generalizes across these
three settings and exploits this regular structure of KGs. Our framework has
many advantages over custom solutions widely deployed in industry, including
collective inference, scalability, and interpretability. We apply our framework
to two real-world KG entity resolution problems, ambiguity in NELL and merging
data from Freebase and MusicBrainz, demonstrating the importance of relational
features.


title: Controlling local order of athermal self-propelled particles

abstract:
  We consider a model of self-propelled dynamics for athermal active particles,
where the non-equilibrium active forces are modelled by a Ornstein-Uhlenbeck
process. In the limit of no-driving force, the model reduces to the passive,
Brownian dynamics of an atomistic glass forming fluid, the Wahnstr\"om binary
mixture. The Wahnstr\"om mixture is known to show strong correlations between
the emergence of slow dynamics and the formation of locally favoured structures
based on icosahedra. Here, we study how the non-equilibrium forces affect the
local structure of the system, and find that these strongly promote icosahedral
order. The phases rich in local icosahedral order correspond to configurations
of very low potential energy, suggesting that the non-equilibrium dynamics in
the self propelled model can be effectively exploited to explore the potential
energy surface of the binary mixture and have access to states that are
difficult to attain using passive dynamics.


title: Implications of Coupling in Quantum Thermodynamic Machines

abstract:
  We study coupled quantum systems as the working media of thermodynamic
machines. Under a suitable phase-space transformation, the coupled systems can
be expressed as a composition of independent subsystems. We find that for the
coupled systems, the figures of merit, that is the efficiency for engine and
the coefficient of performance for refrigerator, are bounded (both from above
and from below) by the corresponding figures of merit of the independent
subsystems. We also show that the optimum work extractable from a coupled
system is upper bounded by the optimum work obtained from the uncoupled system,
thereby showing that the quantum correlations do not help in optimal work
extraction. Further, we study two explicit examples, coupled spin-$1/2$ systems
and coupled quantum oscillators with analogous interactions. Interestingly, for
particular kind of interactions, the efficiency of the coupled oscillators
outperforms that of the coupled spin-$1/2$ systems when they work as heat
engines. However, for the same interaction, the coefficient of performance
behaves in a reverse manner, while the systems work as the refrigerator. Thus
the same coupling can cause opposite effects in the figures of merit of heat
engine and refrigerator.


title:
Slow quenches in XXZ spin-chains -- the role of Galilean invariance
  breaking

abstract:
  We study a XXZ spin-chain in a gapless Tomonaga-Luttinger liquid (TLL) phase
with time dependent anisotropy of spin exchange interactions. To begin we focus
on a linear ramp of $J_z$, starting at XX point and slowly increasing towards
the anti-ferromagnetic Heisenberg point. Although the problem of a linear ramp
in the TLL has been recently under intense scrutiny in a perturbative
\emph{g-ology} framework, an aspect that has been overlooked so far is the role
of the Galilean invariance breaking. We find that, although the differential
equation that needs to be solved to find time evolution of the system is
substantially more complicated, in some cases exact analytic solutions can be
given. We obtain them for the linear ramp in the limit of small $J_z$ as well
as $J_z\rightarrow 1$, and for such protocols that are tailored to keep the
Galilean invariance breaking term constant for every $J_z$. We point out the
features of dynamics during the quench that stays unaltered, and those that
need to be taken with care when Galilean invariance breaking is present. We are
able to deduce that it is the shape of the propagating front that is affected
in the most pronounced way.


title: The Phantom of the New Oscillatory Cosmological Phase

abstract:
  We study a recently proposed new cosmological phase where a scalar field
moves periodically in an expanding spatially-flat Friedmann universe. This
phase corresponds to a limiting cycle of the equations of motion and can be
considered as a cosmological realization of a "time-crystal". We show that this
phase is only possible, provided the Null Energy Condition is violated and the
so-called Phantom divide is crossed. We prove that in general k-essence models:
i) this crossing causes infinite growth of quantum perturbations on short
scales, and ii) exactly periodic solutions are only possible, provided the
limiting cycle encircles a singularity in the phase plane. The configurations
neighboring this singular curve in the phase space are linearly unstable on one
side of the curve and superluminal on the other side. Moreover, the increment
of the instability is infinitely growing for each mode by approaching the
singularity, while for the configurations on the other side, the sound speed is
growing without limit. We illustrate our general results by analytical and
numerical studies of a particular class of such k-essence models.


title:
On the average number of 2-Selmer elements of elliptic curves over
  $\mathbb{F}_q(X)$ with two marked points

abstract:
  We consider elliptic curves over global fields of positive characteristic
with two distinct marked non-trivial rational points. Restricting to a certain
subfamily of the universal one, we show that the average size of the 2-Selmer
groups of these curves exists, in a natural sense, and equals 12. Along the
way, we consider a map from these 2-Selmer groups to the moduli space of
$G$-torsors over an algebraic curve, where $G$ is isogenous to
$\mathrm{SL}_2^4$, and show that the images of 2-Selmer elements under this map
become equidistributed in the limit.


title:
The Host-Pathogen Game: an evolutionary approach to biological
  competitions

abstract:
  We introduce a model called Host-Pathogen game for studying biological
competitions. Notably, we focus on the invasive dynamics of external agents,
like bacteria, within a host organism. The former are mapped to a population of
defectors that aim to spread in the extracellular medium of the host. In turn,
the latter is composed of cells, mapped to a population of cooperators, that
aim to kill pathogens. The cooperative behavior of cells is fundamental for the
emergence of the living functions of the whole organism, since each one
contributes to a specific set of tasks. So, broadly speaking, their
contribution can be viewed as a form of energy. When bacteria are spatially
close to a cell, the latter can use a fraction of its energy to remove them. On
the other hand, when bacteria survive an attack, they absorb the received
energy, becoming stronger and more resistant to further attacks. In addition,
since bacteria play as defectors, their unique target is to increase their
wealth, without supporting their own kind. As in many living organisms, the
host temperature plays a relevant role in the host-pathogen equilibrium. For
instance, in animals like human beings, a neural mechanism triggers the
increasing of the body temperature in order to activate the immune system.
Here, cooperators succeed once bacteria are completely removed while, in the
opposite scenario, the host undergoes a deep invasive process, like a blood
poisoning. Results of numerical simulations show that the dynamics of the
proposed model allow to reach a variety of states. At a very high level of
abstraction, some of these states seem to be similar to those that can be
observed in some living systems. Therefore, to conclude, we deem that our model
might be exploited for studying further biological phenomena.


title: Random walks and branching processes in correlated Gaussian environment

abstract:
  We study persistence probabilities for random walks in correlated Gaussian
random environment first studied by Oshanin, Rosso and Schehr. From the
persistence results, we can deduce properties of critical branching processes
with offspring sizes geometrically distributed with correlated random
parameters. More precisely, we obtain estimates on the tail distribution of its
total population size, of its maximum population, and of its extinction time.

categories: math.PR cond-mat.dis-nn cond-mat.stat-mech math-ph math.MP


title: Quantisation of derived Lagrangians

abstract:
  We investigate quantisations of line bundles $\mathcal{L}$ on derived
Lagrangians $X$ over $0$-shifted symplectic derived Artin $N$-stacks $Y$. In
our derived setting, a deformation quantisation consists of a curved
$A_{\infty}$ deformation of the structure sheaf $\mathcal{O}_{Y}$, equipped
with a curved $A_{\infty}$ morphism to the ring of differential operators on
$\mathcal{L}$; for line bundles on smooth Lagrangian subvarieties of smooth
symplectic algebraic varieties, this simplifies to deforming $(\mathcal{L},
\mathcal{O}_{Y})$ to a DQ module over a DQ algebroid.
  For each choice of formality isomorphism between the $E_2$ and $P_2$ operads,
we construct a map from the space of non-degenerate quantisations to power
series with coefficients in relative cohomology groups of the respective de
Rham complexes. When $\mathcal{L}$ is a square root of the dualising line
bundle, this leads to an equivalence between even power series and certain
anti-involutive quantisations, ensuring that the deformation quantisations
always exist for such line bundles. This gives rise to a dg category of
algebraic Lagrangians, an algebraic Fukaya category of the form envisaged by
Behrend and Fantechi. We also sketch a generalisation of these quantisation
results to Lagrangians on higher $n$-shifted symplectic derived stacks.


title: Dark Matter from a Classically Scale-Invariant $SU(3)_X$

abstract:
  In this work we study a classically scale-invariant extension of the Standard
Model in which the dark matter and electroweak scales are generated through the
Coleman-Weinberg mechanism. The extra $SU(3)_X$ gauge factor gets completely
broken by the vacuum expectation values of two scalar triplets. Out of the
eight resulting massive vector bosons the three lightest are stable due to an
intrinsic $Z_2\times Z_2'$ discrete symmetry and can constitute dark matter
candidates. We analyze the phenomenological viability of the predicted
multi-Higgs sector imposing theoretical and experimental constraints. We
perform a comprehensive analysis of the dark matter predictions of the model
solving numerically the set of coupled Boltzmann equations involving all
relevant dark matter processes and explore the direct detection prospects of
the dark matter candidates.


title: Spin-orbit scattering in superconducting nanoparticles

abstract:
  We review interaction effects in chaotic metallic nanoparticles. Their
single-particle Hamiltonian is described by the proper random-matrix ensemble
while the dominant interaction terms are invariants under a change of the
single-particle basis. In the absence of spin-orbit scattering, the non-trivial
invariants consist of a pairing interaction, which leads to superconductivity
in the bulk, and a ferromagnetic exchange interaction. Spin-orbit scattering
breaks spin-rotation invariance and when it is sufficiently strong, the only
dominant nontrivial interaction is the pairing interaction. We discuss how the
magnetic response of discrete energy levels of the nanoparticle (which can be
measured in single-electron tunneling spectroscopy experiments) is affected by
such pairing correlations and how it can provide a signature of pairing
correlations. We also consider the spin susceptibility of the nanoparticle and
discuss how spin-orbit scattering changes the signatures of pairing
correlations in this observable.


title: Intersection patterns of finite sets and of convex sets

abstract:
  The main result is a common generalization of results on lower bounds for the
chromatic number of r-uniform hypergraphs and some of the major theorems in
Tverberg-type theory, which is concerned with the intersection pattern of faces
in a simplicial complex when continuously mapped to Euclidean space. As an
application we get a simple proof of a generalization of a result of Kriz for
certain parameters. This specializes to a short and simple proof of Kneser's
conjecture. Moreover, combining this result with recent work of Mabillard and
Wagner we show that the existence of certain equivariant maps yields lower
bounds for chromatic numbers. We obtain an essentially elementary proof of the
result of Schrijver on the chromatic number of stable Kneser graphs. In fact,
we show that every neighborly even-dimensional polytope yields a small induced
subgraph of the Kneser graph of the same chromatic number. We furthermore use
this geometric viewpoint to give tight lower bounds for the chromatic number of
certain small subhypergraphs of Kneser hypergraphs.


title:
On generalized hexagons of order $(3, t)$ and $(4, t)$ containing a
  subhexagon

abstract:
  We prove that there are no semi-finite generalized hexagons with $q + 1$
points on each line containing the known generalized hexagons of order $q$ as
full subgeometries when $q$ is equal to $3$ or $4$, thus contributing to the
existence problem of semi-finite generalized polygons posed by Tits. The case
when $q$ is equal to $2$ was treated by us in an earlier work, for which we
give an alternate proof. For the split Cayley hexagon of order $4$ we obtain
the stronger result that it cannot be contained as a proper full subgeometry in
any generalized hexagon.


title: CosmicFish Validation Notes V1.0

abstract:
  These notes show and comment the examples that have been used to validate the
CosmicFish code. We compare the results obtained with the code to several other
results available in literature finding an overall good level of agreement. We
will update this set of notes when relevant modifications to the CosmicFish
code will be released or other validation examples are worked out. The
CosmicFish code and the package to produce all the validation results presented
here are publicly available at http://cosmicfish.github.io. The present version
is based on CosmicFish Jun16.


title:
Watson-type 3F2-series and summation formulae involving generalized
  harmonic numbers

abstract:
  In terms of the derivative operator and Watson-type $_3F_2$-series
identities, three families of summation formulae involving generalized harmonic
numbers are established.


title: On the Union-Closed Set Conjecture

abstract:
  We provide a simple proof for the union-closed sets conjecture, a
long-standing open problem in set theory with immediate applications to graph
theory, number theory, and order-theory.


title: Cholera forecast for Dhaka, Bangladesh, with the 2016 El Ni\~no

abstract:
  A substantial body of work supports a teleconnection between the El Ni\~no
Southern Oscillation (ENSO) and cholera incidence in Bangladesh. In particular,
high positive anomalies during the winter (Dec-Feb) in Sea Surface Temperatures
(SST) in the Tropical Pacific have been shown to exacerbate the seasonal
outbreak of cholera following the monsoons from Aug to Nov, and climate studies
have indicated a role of regional precipitation over Bangladesh in mediating
this long-distance effect. Thus, the current strong El Ni\~no has the potential
to significantly increase cholera risk this year in Dhaka, Bangladesh, where
the last five years have experienced low seasons of the disease. To examine
this possibility and produce a forecast for the city, we considered two models
for the transmission dynamics of cholera: a statistical model previously
developed for the disease in this region, and a process-based model presented
here that includes the effect of SST anomalies in the force of infection and is
fitted to extensive cholera surveillance record between 1995 and 2010.
Prediction accuracy was evaluated with 'out-of-fit' data from the same
surveillance efforts, by comparing the total number of cholera cases observed
for the season to those predicted by model simulations 8 to 12 months ahead,
starting in January each year. Encouraged by accurate forecasts for the low
risk of cholera for this period, we then generated a prediction for this coming
season. An increase above the third quantile in cholera cases is expected for
the period of Aug - Dec 2016 with 92% and 87% probability respectively for the
two models. This alert warrants the preparedness of the public health system.
We discuss the possible limitations of our approach, including variations in
the impact of El Ni\~no events, and the importance of this large, warm event
for further informing an early-warning system for cholera in Dhaka


title: Direct Detection of sub-GeV Dark Matter with Scintillating Targets

abstract:
  We describe a novel search for MeV-to-GeV-mass dark matter, in which the dark
matter scatters off electrons in a scintillating target. The excitation and
subsequent de-excitation of the electron produces one or more photons, which
could be detected with an array of cryogenic low-noise photodetectors, such as
transition edge sensors (TES) or microwave kinetic inductance devices (MKID).
Scintillators may have distinct advantages over other experiments searching for
a low ionization signal from sub-GeV DM. First, the detection of one or a few
photons may be technologically easier. Second, since no electric field is
required to detect the photons, there may be far fewer dark counts mimicking a
DM signal. We discuss various target choices, but focus on calculating the
expected dark matter-electron scattering rates in three scintillating crystals,
sodium iodide (NaI), cesium iodide (CsI), and gallium arsenide (GaAs). Among
these, GaAs has the lowest band gap (1.52 eV) compared to NaI (5.9 eV) or CsI
(6.4 eV), allowing it to probe dark matter masses possibly as low as ~0.5 MeV,
compared to ~1.5 MeV with NaI or CsI. We compare these scattering rates with
those expected in silicon (Si) and germanium (Ge). The proposed experimental
concept presents an important complementary path to existing efforts, and its
potential advantages may make it the most sensitive direct-detection probe of
DM down to MeV masses.


title:
Developmental increases in white matter network controllability support
  a growing diversity of brain dynamics

abstract:
  As the human brain develops, it increasingly supports coordinated control of
neural activity. The mechanism by which white matter evolves to support this
coordination is not well understood. We use a network representation of
diffusion imaging data from 882 youth ages 8 to 22 to show that white matter
connectivity becomes increasingly optimized for a diverse range of predicted
dynamics in development. Notably, stable controllers in subcortical areas are
negatively related to cognitive performance. Investigating structural
mechanisms supporting these changes, we simulate network evolution with a set
of growth rules. We find that all brain networks are structured in a manner
highly optimized for network control, with distinct control mechanisms
predicted in child versus older youth. We demonstrate that our results cannot
be simply explained by changes in network modularity. This work reveals a
possible mechanism of human brain development that preferentially optimizes
dynamic network control over static network architecture.

categories: q-bio.NC cond-mat.dis-nn nlin.CD q-bio.QM


title:
Sub-kpc ALMA imaging of compact star-forming galaxies at z~2.5:
  revealing the formation of dense galactic cores in the progenitors of compact
  quiescent galaxies

abstract:
  We present spatially-resolved Atacama Large Millimeter/sub-millimeter Array
(ALMA) 870 $\mu$m dust continuum maps of six massive, compact, dusty
star-forming galaxies (SFGs) at $z\sim2.5$. These galaxies are selected for
their small rest-frame optical sizes ($r_{\rm e, F160W}\sim1.6$ kpc) and high
stellar-mass densities that suggest that they are direct progenitors of compact
quiescent galaxies at $z\sim2$. The deep observations yield high far-infrared
(FIR) luminosities of L$_{\rm IR}=10^{12.3-12.8}$ L$_{\odot}$ and star
formation rates (SFRs) of SFR$=200-700$ M$_{\odot}$yr$^{-1}$, consistent with
those of typical star-forming "main sequence" galaxies. The high-spatial
resolution (FWHM$\sim$0.12"-0.18") ALMA and HST photometry are combined to
construct deconvolved, mean radial profiles of their stellar mass and (UV+IR)
SFR. We find that the dusty, nuclear IR-SFR overwhelmingly dominates the
bolometric SFR up to $r\sim5$ kpc, by a factor of over 100$\times$ from the
unobscured UV-SFR. Furthermore, the effective radius of the mean SFR profile
($r_{\rm e, SFR}\sim1$ kpc) is $\sim$30% smaller than that of the stellar mass
profile. The implied structural evolution, if such nuclear starburst last for
the estimated gas depletion time of $\Delta t=\pm100$ Myr, is a 4$\times$
increase of the stellar mass density within the central 1 kpc and a 1.6$\times$
decrease of the half-mass radius. This structural evolution fully supports
dissipation-driven, formation scenarios in which strong nuclear starbursts
transform larger, star-forming progenitors into compact quiescent galaxies.


title: Anomalous thermalization in ergodic systems

abstract:
  It is commonly believed that quantum isolated systems satisfying the
eigenstate thermalization hypothesis (ETH) are diffusive. We show that this
assumption is too restrictive, since there are systems that are asymptotically
in a thermal state, yet exhibit anomalous, subdiffusive thermalization. We show
that such systems satisfy a modified version of the ETH ansatz and derive a
general connection between the scaling of the variance of the offdiagonal
matrix elements of local operators, written in the eigenbasis of the
Hamiltonian, and the dynamical exponent. We find that for subdiffusively
thermalizing systems the variance scales more slowly with system size than
expected for diffusive systems. We corroborate our findings by numerically
studying the distribution of the coefficients of the eigenfunctions and the
offdiagonal matrix elements of local operators of the random field Heisenberg
chain, which has anomalous transport in its thermal phase. Surprisingly, this
system also has non-Gaussian distributions of the eigenfunctions, thus directly
violating Berry's conjecture.


title:
Knot a Bad Idea: Testing BLISS Mapping for Spitzer Space Telescope
  Photometry

abstract:
  Much of transiting exoplanet science relies on high-precision photometry. The
current generation of instruments can exhibit sensitivity variations greater
than the astrophysical signals. For the InfraRed Array Camera (IRAC) on the
Spitzer Space Telescope, a popular way to handle this is
BiLinearly-Interpolated Subpixel Sensitivity (BLISS) mapping. As part of a
Markov Chain Monte Carlo (MCMC), BLISS mapping estimates the sensitivity at
many locations (knots) on the pixel, then interpolates to the target star's
centroids. We show that such embedded optimization schemes can misfit or bias
parameters. Thus, we construct a model of $\textit{Spitzer}$ eclipse light
curves to test the accuracy and precision of BLISS mapping. We compare standard
BLISS mapping to a variant where the knots are fit during the MCMC, as well as
to a polynomial model. Both types of BLISS mapping give similar eclipse depths,
and we find that standard knots behave like real parameters. Standard BLISS
mapping is therefore a reasonable shortcut to fitting for knots in an MCMC.
BLISS maps become inaccurate when the photon noise is low, but typically
approximate the real sensitivity well. We also find there is no perfect method
for choosing the ideal number of BLISS knots to use on given data. BLISS
mapping gives fits that are usually more accurate than precise (i.e. they are
overly conservative), and the routine is more precise than polynomial models
for significant eclipses or pixels with more varied sensitivities. BLISS
mapping has better predictive power for most of these particular synthetic
data, depending on how one treats time-correlated residuals. Overall, we
conclude that BLISS mapping can be a reasonable sensitivity model for IRAC
photometry.


title:
Integrated approach to cosmology: Combining CMB, large-scale structure
  and weak lensing

abstract:
  Recent observational progress has led to the establishment of the standard
$\Lambda$CDM model for cosmology. This development is based on different
cosmological probes that are usually combined through their likelihoods at the
latest stage in the analysis. We implement here an integrated scheme for
cosmological probes, which are combined in a common framework starting at the
map level. This treatment is necessary as the probes are generally derived from
overlapping maps and are thus not independent. It also allows for a thorough
test of the cosmological model and of systematics through the consistency of
different physical tracers. As a first application, we combine current
measurements of the Cosmic Microwave Background (CMB) from the Planck
satellite, and galaxy clustering and weak lensing from SDSS. We consider the
spherical harmonic power spectra of these probes including all six auto- and
cross-correlations along with the associated full Gaussian covariance matrix.
This provides an integrated treatment of different analyses usually performed
separately including CMB anisotropies, cosmic shear, galaxy clustering,
galaxy-galaxy lensing and the Integrated Sachs-Wolfe (ISW) effect with galaxy
and shear tracers. We derive constraints on $\Lambda$CDM parameters that are
compatible with existing constraints and highlight tensions between data sets,
which become apparent in this integrated treatment. We discuss how this
approach provides a complete and powerful integrated framework for probe
combination and how it can be extended to include other tracers in the context
of current and future wide field cosmological surveys.


title:
Thermodynamics and renormalized quasi-particles in the vicinity of the
  dilute Bose gas quantum critical point in two dimensions

abstract:
  We use the functional renormalization group (FRG) to derive analytical
expressions for thermodynamic observables (density, pressure, entropy, and
compressibility) as well as for single-particle properties (wavefunction
renormalization and effective mass) of interacting bosons in two dimensions as
a function of temperature $T$ and chemical potential $\mu$. We focus on the
quantum disordered and the quantum critical regime close to the dilute Bose gas
quantum critical point. Our approach is based on a truncated vertex expansion
of the hierarchy of FRG flow equations and the decoupling of the two-body
contact interaction in the particle-particle channel using a suitable
Hubbard-Stratonovich transformation. Our analytic FRG results extend previous
analytical renormalization group calculations for thermodynamic observables at
$\mu =0$ to finite values of $\mu$. To confirm the validity of our FRG
approach, we have also performed quantum Monte Carlo simulations to obtain the
magnetization, the susceptibility, and the correlation length of the
two-dimensional spin-$1/2$ quantum $XY$ model with coupling $J$ in a regime
where its quantum critical behavior is controlled by the dilute Bose gas
quantum critical point. We find that our analytical results describe the Monte
Carlo data for $\mu \leq 0$ rather accurately up to relatively high
temperatures $T \lesssim 0.1 J$.


title: The "forgotten" decay S -> Z+h as a CP analyzer

abstract:
  Scalar particles $S$ which are gauge singlets under the Standard Model are
generic features of many models of fundamental physics, in particular as
possible mediators to a hidden or dark sector. We show that the decay $S\to Zh$
provides a powerful probe of the CP nature of the scalar, because it is allowed
only if $S$ has CP-odd interactions. We perform a model-independent analysis of
this decay in the context of an effective Lagrangian and compute the relevant
Wilson coefficients arising from integrating out heavy fermions to one-loop
order. We illustrate our findings with the example of the 750 GeV diphoton
resonance seen by ATLAS and CMS and show that the $S\to Zh$ decay rate could
naturally be of similar magnitude or larger than the diphoton rate.


title: Face-on accretion onto a protoplanetary disc

abstract:
  Globular clusters (GCs) are known to harbor multiple stellar populations. To
explain these observations Bastian et al. suggested a scenario in which a
second population is formed by the accretion of enriched material onto the
low-mass stars in the initial GC population. The idea is that the low-mass,
pre-main sequence stars sweep up gas expelled by the massive stars of the same
generation into their protoplanetary disc as they move through the GC core. We
perform simulations with 2 different smoothed particle hydrodynamics codes to
investigate if a low-mass star surrounded by a protoplanetary disc can accrete
the amount of enriched material required in this scenario. We focus on the gas
loading rate onto the disc and star as well as on the lifetime of the disc. We
find that the gas loading rate is a factor of 2 smaller than the geometric
rate, because the effective cross section of the disc is smaller than its
surface area. The loading rate is consistent for both codes, irrespective of
resolution. The disc gains mass in the high resolution runs, but loses angular
momentum on a time scale of 10^4 yrs. Two effects determine the loss of
(specific) angular momentum in our simulations: 1) continuous ram pressure
stripping and 2) accretion of material with no azimuthal angular momentum. Our
study and previous work suggest that the former, dominant process is mainly
caused by numerical rather than physical effects, while the latter is not. The
latter process causes the disc to become more compact, increasing the surface
density profile at smaller radii. The disc size is determined in the first
place by the ram pressure when the flow first hits the disc. Further evolution
is governed by the decrease in the specific angular momentum of the disc. We
conclude that the size and lifetime of the disc are probably not sufficient to
accrete the amount of mass required in Bastian et al.'s scenario.


title:
Bounded energy waves on the black hole interior of
  Reissner-Nordstr\"om-de Sitter

abstract:
  Motivated by the Strong Cosmic Censorship Conjecture, in the presence of a
cosmological constant, we consider solutions of the scalar wave equation
$\Box_g\phi=0$ on fixed subextremal Reissner--Nordstr\"om--de Sitter
backgrounds $({\mathcal M}, g)$, without imposing symmetry assumptions on
$\phi$. We provide a sufficient condition, in terms of surface gravities and a
parameter for an exponential decaying Price law, for a local energy of the
waves to remain bounded up to the Cauchy horizon. The energy we consider
controls, in particular, regular transverse derivatives at the Cauchy horizon;
this allows us to extend the solutions with bounded energy, to the Cauchy
horizon, as functions in $C^0\cap H^1_{loc}$. Our results correspond to another
manifestation of the potential breakdown of Strong Cosmic Censorship in the
positive cosmological constant setting.


title:
Galaxy Zoo: comparing the demographics of spiral arm number and a new
  method for correcting redshift bias

abstract:
  The majority of galaxies in the local Universe exhibit spiral structure with
a variety of forms. Many galaxies possess two prominent spiral arms, some have
more, while others display a many-armed flocculent appearance. Spiral arms are
associated with enhanced gas content and star-formation in the disks of
low-redshift galaxies, so are important in the understanding of star-formation
in the local universe. As both the visual appearance of spiral structure, and
the mechanisms responsible for it vary from galaxy to galaxy, a reliable method
for defining spiral samples with different visual morphologies is required. In
this paper, we develop a new debiasing method to reliably correct for
redshift-dependent bias in Galaxy Zoo 2, and release the new set of debiased
classifications. Using these, a luminosity-limited sample of ~18,000 Sloan
Digital Sky Survey spiral galaxies is defined, which are then further
sub-categorised by spiral arm number. In order to explore how different spiral
galaxies form, the demographics of spiral galaxies with different spiral arm
numbers are compared. It is found that whilst all spiral galaxies occupy
similar ranges of stellar mass and environment, many-armed galaxies display
much bluer colours than their two-armed counterparts. We conclude that
two-armed structure is ubiquitous in star-forming disks, whereas many-armed
spiral structure appears to be a short-lived phase, associated with more
recent, stochastic star-formation activity.


title: Far-reaching Dust Distribution in Galaxy Disks

abstract:
  In most studies of dust in galaxies, dust is only detected from its emission
to approximately the optical radius of the galaxy. By combining the signal of
110 spiral galaxies observed as part of the Herschel Reference Survey, we are
able to improve our sensitivity by an order-of-magnitude over that for a single
object. Here we report the direct detection of dust from its emission that
extends out to at least twice the optical radius. We find that the distribution
of dust is consistent with an exponential at all radii with a gradient of ~-1.7
dex R$_{25}^{-1}$. Our dust temperature declines linearly from ~25 K in the
centre to 15 K at R$_{25}$ from where it remains constant out to ~2.0 R$_{25}$.
The surface-density of dust declines with radius at a similar rate to the
surface-density of stars but more slowly than the surface-density of the
star-formation rate. Studies based on dust extinction and reddening of
high-redshift quasars have concluded that there are substantial amounts of dust
in intergalactic space. By combining our results with the number counts and
angular correlation function from the SDSS, we show that with Milky Way type
dust we can explain the reddening of the quasars by the dust within galactic
disks alone. Given the uncertainties in the properties of any intergalactic
dust, we cannot rule out its existence, but our results show that statistical
investigations of the dust in galactic halos that use the reddening of
high-redshift objects must take account of the dust in galactic disks.


title: Constraining a halo model for cosmological neutral hydrogen

abstract:
  We describe a combined halo model to constrain the distribution of neutral
hydrogen (HI) in the post-reionization universe. We combine constraints from
the various probes of HI at different redshifts: the low-redshift 21-cm
emission line surveys, intensity mapping experiments at intermediate redshifts,
and the Damped Lyman-Alpha (DLA) observations at higher redshifts. We use a
Markov Chain Monte Carlo (MCMC) approach to combine the observations and place
constraints on the free parameters in the model. Our best-fit model involves a
relation between neutral hydrogen mass $M_{\rm HI}$ and halo mass $M$ with a
non-unit slope, and an upper and a lower cutoff. We find that the model fits
all the observables but leads to an underprediction of the bias parameter of
DLAs at $z \sim 2.3$. We also find indications of a possible tension between
the HI column density distribution and the mass function of HI-selected
galaxies at $z\sim 0$. We provide the central values of the parameters of the
best-fit model so derived. We also provide a fitting form for the derived
evolution of the concentration parameter of HI in dark matter haloes, and
discuss the implications for the redshift evolution of the HI-halo mass
relation.


title: Contributions of axion-like particles to lepton dipole moments

abstract:
  Contributions of a spin 0 axion-like particle (ALP) to lepton dipole moments,
g-2 and EDMs, are examined. Barr-Zee and light-by-light loop effects from a
light pseudoscalar ALP are found to be capable of resolving the long-standing
muon g-2 discrepancy at the expense of relatively large ALP-gammagamma
couplings. The compatibility of such large couplings with direct experimental
constraints and perturbative unitarity bounds is discussed. Future tests of
such a scenario are described. For CP violating ALP couplings, the electron EDM
is found to probe much smaller, theoretically more easily accommodated ALP
interactions. Future planned improvement in electron EDM searches is advocated
as a way to not only significantly constrain ALP parameters but also, to
potentially unveil a new source of CP violation which could have far reaching
ramifications.


title:
Numerical simulations challenged on the prediction of massive subhalo
  abundance in galaxy clusters: the case of Abell 2142

abstract:
  In this Letter we compare the abundance of member galaxies of a rich, nearby
($z=0.09$) galaxy cluster, Abell 2142, with that of halos of comparable virial
mass extracted from sets of state-of-the-art numerical simulations, both
collisionless at different resolutions and with the inclusion of baryonic
physics in the form of cooling, star formation, and feedback by active galactic
nuclei. We also use two semi-analytical models to account for the presence of
orphan galaxies. The photometric and spectroscopic information, taken from the
Sloan Digital Sky Survey Data Release 12 (SDSS DR12) database, allows us to
estimate the stellar velocity dispersion of member galaxies of Abell 2142. This
quantity is used as proxy for the total mass of secure cluster members and is
properly compared with that of subhalos in simulations. We find that simulated
halos have a statistically significant ($\gtrsim 7$ sigma confidence level)
smaller amount of massive (circular velocity above $200\,{\rm km\, s^{-1}}$)
subhalos, even before accounting for the possible incompleteness of
observations. These results corroborate the findings from a recent strong
lensing study of the Hubble Frontier Fields galaxy cluster MACS J0416
\citep{grillo2015} and suggest that the observed difference is already present
at the level of dark matter (DM) subhalos and is not solved by introducing
baryonic physics. A deeper understanding of this discrepancy between
observations and simulations will provide valuable insights into the impact of
the physical properties of DM particles and the effect of baryons on the
formation and evolution of cosmological structures.


title: Linear and non-linear bias: predictions vs. measurements

abstract:
  We study the linear and non-linear bias parameters which determine the
mapping between the distributions of galaxies and the full matter density
fields, comparing different measurements and predictions. Associating galaxies
with dark matter haloes in the MICE Grand Challenge N-body simulation we
directly measure the bias parameters by comparing the smoothed density
fluctuations of haloes and matter in the same region at different positions as
a function of smoothing scale. Alternatively we measure the bias parameters by
matching the probability distributions of halo and matter density fluctuations,
which can be applied to observations. These direct bias measurements are
compared to corresponding measurements from two-point and different third-order
correlations, as well as predictions from the peak-background model, which we
presented in previous articles using the same data. We find an overall
variation of the linear bias measurements and predictions of $\sim 5 \%$ with
respect to results from two-point correlations for different halo samples with
masses between $\sim 10^{12} - 10^{15}$ $h^{-1}M_\odot$ at the redshifts
$z=0.0$ and $0.5$. Variations between the second- and third-order bias
parameters from the different methods show larger variations, but with
consistent trends in mass and redshift. The various bias measurements reveal a
tight relation between the linear and the quadratic bias parameters, which is
consistent with results from the literature based on simulations with different
cosmologies. Such a universal relation might improve constraints on
cosmological models, derived from second-order clustering statistics at small
scales or higher-order clustering statistics.


title:
Observables, gravitational dressing, and obstructions to locality and
  subsystems

abstract:
  Quantum field theory - our basic framework for describing all
non-gravitational physics - conflicts with general relativity: the latter
precludes the standard definition of the former's essential principle of
locality, in terms of commuting local observables. We examine this conflict
more carefully, by investigating implications of gauge (diffeomorphism)
invariance for observables in gravity. We prove a dressing theorem, showing
that any operator with nonzero Poincare charges, and in particular any
compactly-supported operator, in flat-spacetime quantum field theory must be
gravitationally dressed once coupled to gravity, i.e. it must depend on the
metric at arbitrarily long distances, and we put lower bounds on this nonlocal
dependence. This departure from standard locality occurs in the most severe way
possible: in perturbation theory about flat spacetime, at leading order in
Newton's constant. The physical observables in a gravitational theory therefore
do not organize themselves into local commuting subalgebras: the principle of
locality must apparently be reformulated or abandoned, and in fact we lack a
clear definition of the coarser and more basic notion of a quantum subsystem of
the Universe. We discuss relational approaches to locality based on
diffeomorphism-invariant nonlocal operators, and reinforce arguments that any
such locality is state-dependent and approximate. We also find limitations to
the utility of bilocal diffeomorphism-invariant operators that are considered
in cosmological contexts. An appendix provides a concise review of the
canonical covariant formalism for gravity, instrumental in the discussion of
Poincare charges and their associated long-range fields.


title:
Beyond Kaiser bias: mildly non-linear two-point statistics of densities
  in distant spheres

abstract:
  Simple parameter-free analytic bias functions for the two-point correlation
of densities in spheres at large separation are presented. These bias functions
generalize the so-called Kaiser bias to the mildly non-linear regime for
arbitrary density contrasts. The derivation is carried out in the context of
large deviation statistics while relying on the spherical collapse model. A
logarithmic transformation provides a saddle approximation which is valid for
the whole range of densities and shown to be accurate against the 30 Gpc cube
state-of-the-art Horizon Run 4 simulation. Special configurations of two
concentric spheres that allow to identify peaks are employed to obtain the
conditional bias and a proxy to BBKS extrema correlation functions. These
analytic bias functions should be used jointly with extended perturbation
theory to predict two-point clustering statistics as they capture the
non-linear regime of structure formation at the percent level down to scales of
about 10 Mpc/h at redshift 0. Conversely, the joint statistics also provide us
with optimal dark matter two-point correlation estimates which can be applied
either universally to all spheres or to a restricted set of biased (over- or
underdense) pairs. Based on a simple fiducial survey, this estimator is shown
to perform five times better than usual two-point function estimators.
Extracting more information from correlations of different types of objects
should prove essential in the context of upcoming surveys like Euclid, DESI,
PFS or LSST.


title:
Accelerate Stochastic Subgradient Method by Leveraging Local Growth
  Condition

abstract:
  In this paper, a new theory is developed for first-order stochastic convex
optimization, showing that the global convergence rate is sufficiently
quantified by a local growth rate of the objective function in a neighborhood
of the optimal solutions. In particular, if the objective function $F(\mathbf
w)$ in the $\epsilon$-sublevel set grows as fast as $\|\mathbf w - \mathbf
w_*\|_2^{1/\theta}$, where $\mathbf w_*$ represents the closest optimal
solution to $\mathbf w$ and $\theta\in(0,1]$ quantifies the local growth rate,
the iteration complexity of first-order stochastic optimization for achieving
an $\epsilon$-optimal solution can be $\widetilde O(1/\epsilon^{2(1-\theta)})$,
which is optimal at most up to a logarithmic factor. To achieve the faster
global convergence, we develop two different accelerated stochastic subgradient
methods by iteratively solving the original problem approximately in a local
region around a historical solution with the size of the local region gradually
decreasing as the solution approaches the optimal set. Besides the theoretical
improvements, this work also includes new contributions towards making the
proposed algorithms practical: (i) we present practical variants of accelerated
stochastic subgradient methods that can run without the knowledge of
multiplicative growth constant and even the growth rate $\theta$; (ii) we
consider a broad family of problems in machine learning to demonstrate that the
proposed algorithms enjoy faster convergence than traditional stochastic
subgradient method. We also characterize the complexity of the proposed
algorithms for ensuring the gradient is small without the smoothness
assumption.


title:
NIHAO X: Reconciling the local galaxy velocity function with Cold Dark
  Matter via mock HI observations

abstract:
  We used 87 high resolution hydrodynamical cosmological simulations from the
NIHAO suite to investigate the relation between the maximum circular velocity
(Vmax) of a dark matter halo in a collisionless simulation and the velocity
width of the HI gas in the same halo in the hydrodynamical simulation. These
two quantities are normally used to compare theoretical and observational
velocity functions and have led to a possible discrepancy between observations
and predictions based on the Cold Dark Matter (CDM) model. We show that below
100 km/s, there is clear bias between HI based velocities and Vmax, that leads
to an underestimation of the actual circular velocity of the halo. When this
bias is taken into account the CDM model has no trouble in reproducing the
observed velocity function and no lack of low velocity galaxies is actually
present. Our simulations also reproduce the linewidth - stellar mass
(Tully-Fisher) relation and HI sizes, indicating that the HI gas in our
simulations is as extended as observed. The physical reason for the lower than
expected linewidths is that, in contrast to high mass galaxies, low mass
galaxies no longer have extended thin HI rotating disks, as is commonly
assumed.


title:
The neurobiology of self-generated thought from cells to systems:
  Integrating evidence from lesion studies, human intracranial
  electrophysiology, neurochemistry, and neuroendocrinology

abstract:
  Investigation of the neural basis of self-generated thought is moving beyond
a simple identification with default network activation toward a more
comprehensive view recognizing the role of the frontoparietal control network
and other areas. A major task ahead is to unravel the functional roles and
temporal dynamics of the widely distributed brain regions recruited during
self-generated thought. We argue that various other neuroscientific methods -
including lesion studies, human intracranial electrophysiology, and
manipulation of neurochemistry - have much to contribute to this project. These
diverse data have yet to be synthesized with the growing understanding of
self-generated thought gained from neuroimaging, however. Here, we highlight
several areas of ongoing inquiry and illustrate how evidence from other
methodologies corroborates, complements, and clarifies findings from functional
neuroimaging. Each methodology has particular strengths: functional
neuroimaging reveals much about the variety of brain areas and networks
reliably recruited. Lesion studies point to regions critical to generating and
consciously experiencing self-generated thought. Human intracranial
electrophysiology illuminates how and where in the brain thought is generated
and where this activity subsequently spreads. Finally, measurement and
manipulation of neurotransmitter and hormone levels can clarify what kind of
neurochemical milieu drives or facilitates self-generated cognition.
Integrating evidence from multiple complementary modalities will be a critical
step on the way to improving our understanding of the neurobiology of
functional and dysfunctional forms of self-generated thought.


title: Inflation, Universality and Attractors

abstract:
  In this PhD thesis, we investigate generic features of inflation which are
strictly related to fundamental aspects of UV-physics scenarios, such as string
theory or supergravity. After a short introduction to standard and inflationary
cosmology, we present our research findings. On the one hand, we show that
focusing on universality properties of inflation can yield surprisingly
stringent bounds on its dynamics. This approach allows us to identify the
regime where the inflationary field range is uniquely determined by both the
tensor-to-scalar ratio and the spectral index. Then, we derive a novel
field-range bound, which is two orders of magnitude stronger than the original
one derived by Lyth. On the other hand, we discuss the embedding of inflation
in supergravity and prove that non-trivial hyperbolic K\"ahler geometries
induce an attractor for the inflationary observables: the spectral tilt tends
automatically to the center of the Planck dome whereas the amount of primordial
gravitational waves is directly controlled by curvature of the internal
manifold. We identify the origin of this attractor mechanism in the so-called
$\alpha$-scale supergravity model. Finally, we show how the inclusion of a
nilpotent sector, allowing for a unified description of inflation and dark
energy, implies an enhancement of the attractor nature of the theory. The main
results of this thesis have been already published elsewhere. However, here we
pay special attention to present them in a comprehensive way and provide the
reader with the necessary background.


title:
Initial sequences and Waldschmidt constants of planar point
  configurations

abstract:
  The purpose of this work is to extend the classification of planar point
configurations with low Waldschmidt constants for all values less than $5/2$.
As a consequence we prove a conjecture of Dumnicki, Szemberg and
Tutaj-Gasi\'nska concerning initial sequences with low first differences.


title: Echo Chambers: Emotional Contagion and Group Polarization on Facebook

abstract:
  Recent findings showed that users on Facebook tend to select information that
adhere to their system of beliefs and to form polarized groups -- i.e., echo
chambers. Such a tendency dominates information cascades and might affect
public debates on social relevant issues. In this work we explore the
structural evolution of communities of interest by accounting for users
emotions and engagement. Focusing on the Facebook pages reporting on scientific
and conspiracy content, we characterize the evolution of the size of the two
communities by fitting daily resolution data with three growth models -- i.e.
the Gompertz model, the Logistic model, and the Log-logistic model. Then, we
explore the interplay between emotional state and engagement of users in the
group dynamics. Our findings show that communities' emotional behavior is
affected by the users' involvement inside the echo chamber. Indeed, to an
higher involvement corresponds a more negative approach. Moreover, we observe
that, on average, more active users show a faster shift towards the negativity
than less active ones.


title:
An Application of the EM-algorithm to Approximate Empirical
  Distributions of Financial Indices with the Gaussian Mixtures

abstract:
  In this study I briefly illustrate application of the Gaussian mixtures to
approximate empirical distributions of financial indices (DAX, Dow Jones,
Nikkei, RTSI, S&P 500). The resulting distributions illustrate very high
quality of approximation as evaluated by Kolmogorov-Smirnov test. This implies
further study of application of the Gaussian mixtures to approximate empirical
distributions of financial indices.


title:
Blockers for simple Hamiltonian paths in convex geometric graphs of even
  order

abstract:
  Let G be a complete convex geometric graph on 2m vertices, and let F be a
family of subgraphs of G. A blocker for F is a set of edges, of smallest
possible size, that meets every element of F. In [C. Keller and M. A. Perles,
On the smallest sets blocking simple perfect matchings in a convex geometric
graph, Israel J. Math. 187 (2012), pp. 465-484], we gave an explicit
description of all blockers for the family of simple perfect matchings (SPMs)
of G. In this paper we show that the family of simple Hamiltonian paths (SHPs)
in G has exactly the same blockers as the family of SPMs. Our argument is
rather short, and provides a much simpler proof of the result of [KP12].


title:
Detection of Solar-Like Oscillations, Observational Constraints, and
  Stellar Models for $\theta$ Cyg, the Brightest Star Observed by the {\it
  Kepler} Mission

abstract:
  $\theta$ Cygni is an F3 spectral-type main-sequence star with visual
magnitude V=4.48. This star was the brightest star observed by the original
Kepler spacecraft mission. Short-cadence (58.8 s) photometric data using a
custom aperture were obtained during Quarter 6 (June-September 2010) and
subsequently in Quarters 8 and 12-17. We present analyses of the solar-like
oscillations based on Q6 and Q8 data, identifying angular degree $l$ = 0, 1,
and 2 oscillations in the range 1000-2700 microHz, with a large frequency
separation of 83.9 plus/minus 0.4 microHz, and frequency with maximum amplitude
1829 plus/minus 54 microHz. We also present analyses of new ground-based
spectroscopic observations, which, when combined with angular diameter
measurements from interferometry and Hipparcos parallax, give T_eff = 6697
plus/minus 78 K, radius 1.49 plus/minus 0.03 solar radii, [Fe/H] = -0.02
plus/minus 0.06 dex, and log g = 4.23 plus/minus 0.03. We calculate stellar
models matching the constraints using several methods, including using the Yale
Rotating Evolution Code and the Asteroseismic Modeling Portal. The best-fit
models have masses 1.35-1.39 solar masses and ages 1.0-1.6 Gyr. theta Cyg's
T_eff and log g place it cooler than the red edge of the gamma Doradus
instability region established from pre-Kepler ground-based observations, but
just at the red edge derived from pulsation modeling. The pulsation models show
gamma Dor gravity-mode pulsations driven by the convective-blocking mechanism,
with frequencies of 1 to 3 cycles/day (11 to 33 microHz). However, gravity
modes were not detected in the Kepler data, one signal at 1.776 cycles/day
(20.56 microHz) may be attributable to a faint, possibly background, binary.
Asteroseismic studies of theta Cyg and other A-F stars observed by Kepler and
CoRoT, will help to improve stellar model physics and to test pulsation driving
mechanisms.


title: Bootstrap Model Aggregation for Distributed Statistical Learning

abstract:
  In distributed, or privacy-preserving learning, we are often given a set of
probabilistic models estimated from different local repositories, and asked to
combine them into a single model that gives efficient statistical estimation. A
simple method is to linearly average the parameters of the local models, which,
however, tends to be degenerate or not applicable on non-convex models, or
models with different parameter dimensions. One more practical strategy is to
generate bootstrap samples from the local models, and then learn a joint model
based on the combined bootstrap set. Unfortunately, the bootstrap procedure
introduces additional noise and can significantly deteriorate the performance.
In this work, we propose two variance reduction methods to correct the
bootstrap noise, including a weighted M-estimator that is both statistically
efficient and practically powerful. Both theoretical and empirical analysis is
provided to demonstrate our methods.


title: Gravitational waves in geometric scalar gravity

abstract:
  We investigate the gravitational waves phenomena in the geometric scalar
theory of gravity (GSG) that belongs to a class of theories such that gravity
is described by a single scalar field. The associated physical metric
describing the spacetime is constructed from a disformal transformation of
Minkowski geometry. In this theory, a weak field approximation gives rise to a
description similar to that one obtained in general relativity, although the
gravitational waves in GSG have a characteristic longitudinal polarization
mode, besides others modes that are observer dependent. We also analyze the
energy carried by the gravitational waves as well as how their emission affects
the orbital period of a binary system.


title:
Statistical theory of reversals in two-dimensional confined turbulent
  flows

abstract:
  It is shown that the Truncated Euler Equations, i.e. a finite set of ordinary
differential equations for the amplitude of the large-scale modes, can
correctly describe the complex transitional dynamics that occur within the
turbulent regime of a confined 2D Navier-Stokes flow with bottom friction and a
spatially periodic forcing. In particular, the random reversals of the large
scale circulation on the turbulent background involve bifurcations of the
probability distribution function of the large-scale circulation velocity that
are described by the related microcanonical distribution which displays
transitions from gaussian to bimodal and broken ergodicity. A minimal 13-mode
model reproduces these results.


title: Practical Tera-scale Walsh-Hadamard Transform

abstract:
  In the mid-second decade of new millennium, the development of IT has reached
unprecedented new heights. As one derivative of Moore's law, the operating
system evolves from the initial 16 bits, 32 bits, to the ultimate 64 bits. Most
modern computing platforms are in transition to the 64-bit versions. For
upcoming decades, IT industry will inevitably favor software and systems, which
can efficiently utilize the new 64-bit hardware resources. In particular, with
the advent of massive data outputs regularly, memory-efficient software and
systems would be leading the future.
  In this paper, we aim at studying practical Walsh-Hadamard Transform (WHT).
WHT is popular in a variety of applications in image and video coding, speech
processing, data compression, digital logic design, communications, just to
name a few. The power and simplicity of WHT has stimulated research efforts and
interests in (noisy) sparse WHT within interdisciplinary areas including (but
is not limited to) signal processing, cryptography. Loosely speaking, sparse
WHT refers to the case that the number of nonzero Walsh coefficients is much
smaller than the dimension; the noisy version of sparse WHT refers to the case
that the number of large Walsh coefficients is much smaller than the dimension
while there exists a large number of small nonzero Walsh coefficients. Clearly,
general Walsh-Hadamard Transform is a first solution to the noisy sparse WHT,
which can obtain all Walsh coefficients larger than a given threshold and the
index positions. In this work, we study efficient implementations of very large
dimensional general WHT. Our work is believed to shed light on noisy sparse
WHT, which remains to be a big open challenge. Meanwhile, the main idea behind
will help to study parallel data-intensive computing, which has a broad range
of applications.


title:
Facial Expression Classification Using Rotation Slepian-based Moment
  Invariants

abstract:
  Rotation moment invariants have been of great interest in image processing
and pattern recognition. This paper presents a novel kind of rotation moment
invariants based on the Slepian functions, which were originally introduced in
the method of separation of variables for Helmholtz equations. They were first
proposed for time series by Slepian and his coworkers in the 1960s. Recent
studies have shown that these functions have an good performance in local
approximation compared to other approximation basis. Motivated by the good
approximation performance, we construct the Slepian-based moments and derive
the rotation invariant. We not only theoretically prove the invariance, but
also discuss the experiments on real data. The proposed rotation invariants are
robust to noise and yield decent performance in facial expression
classification.


title: Heterodyne Hall Effect in a Two Dimensional Electron Gas

abstract:
  We study the hitherto un-addressed phenomenon of Quantum Hall Effect with a
magnetic and electric fields oscillating in time with resonant frequencies.
This phenomenon realizes an example of heterodyne device with the magnetic
field acting as a driving and is analyzed in detail in its classical and
quantum versions using Floquet theory. A bulk current flowing perpendicularly
to the applied electric field is found, with a frequency shifted by integer
multiples of the driving frequency. When the ratio of the cyclotron and driving
frequency takes special values, the electron's classical trajectory forms a
loop and the effective mass diverges, while in the quantum case we find an
analogue of the Landau quantization. Possible realization using metamaterial
plasmonics is discussed.


title: Searching for turbulence models by artificial neural network

abstract:
  Artificial neural network (ANN) is tested as a tool for finding a new subgrid
model of the subgrid-scale (SGS) stress in large-eddy simulation. ANN is used
to establish a functional relation between the grid-scale (GS) flow field and
the SGS stress without any assumption of the form of function. Data required
for training and test of ANN are provided by direct numerical simulation (DNS)
of a turbulent channel flow. It is shown that ANN can establish a model similar
to the gradient model. The correlation coefficients between the real SGS stress
and the output of ANN are comparable to or larger than similarity models, but
smaller than a two-parameter dynamic mixed model.


title:
Non-existence of exceptional collections on twisted flags and
  categorical representability via noncommutative motives

abstract:
  In this paper we prove that a finite product of Brauer--Severi varieties is
categorical representable in dimension zero if and only if it admits a
$k$-rational point if and only if it is rational over $k$. The same is true for
certain isotropic involution varieties over a field $k$ of characteristic
different from two. For finite products of generalized Brauer--Severi
varieties, categorical representability in dimension zero is equivalent to the
existence of a full exceptional collection. In this case however categorical
representability in dimension zero is not equivalent to the existence of a
rational point. We also show that non-trivial twisted flags of classical type
$A_n$ and $C_n$ cannot have full exceptional collections, enlarging in this way
the set of previous known examples. Finally, we determine the categorical
representability dimension $\mathrm{rdim}(X)$ for generalized Brauer--Severi
varieties of index $\leq 3$ and for certain twisted forms of smooth quadrics
(involution varieties).


title:
Efficient target control of complex networks based on preferential
  matching

abstract:
  Controlling a complex network towards a desire state is of great importance
in many applications. Existing works present an approximate algorithm to find
the driver nodes used to control partial nodes of the network. However, the
driver nodes obtained by this algorithm depend on the matching order of nodes
and cannot get the optimum results. Here we present a novel algorithm to find
the driver nodes for target control based on preferential matching. The
algorithm elaborately arrange the matching order of nodes in order to minimize
the size of the driver nodes set. The results on both synthetic and real
networks indicate that the performance of proposed algorithm are better than
the previous one. The algorithm may have various application in controlling
complex networks.


title:
Taking stock of SLSN and LGRB host galaxy comparison using a complete
  sample of LGRBs

abstract:
  Long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe) are both
explosive transients with very massive progenitor stars. Clues about the nature
of the progenitors can be found by investigating environments in which such
transients occur. While studies of LGRB host galaxies have a long history,
dedicated observational campaigns have only recently resulted in a high enough
number of photometrically and spectroscopically observed SLSN hosts to allow
statistically significant analysis of their properties. In this paper we make a
comparison of the host galaxies of hydrogen-poor (H-poor) SLSNe and the
Swift/BAT6 sample of LGRBs. In contrast to previous studies we use a complete
sample of LGRBs and we address a special attention to the comparison
methodology and the selection of SLSN sample whose data have been compiled from
the available literature. At intermediate redshifts (0.3 < z < 0.7) the two
classes of transients select galaxies whose properties (stellar mass,
luminosity, star-formation rate, specific star-formation rate and metallicity)
do not differ on average significantly. Moreover, the host galaxies of both
classes of objects follow the fundamental metallicity relation and the
fundamental plane of metallicity. In contrast to previous studies we show that
at intermediate redshifts the emission line equivalent widths of the two
populations are essentially the same and that the previous claims regarding the
higher fraction of SLSN hosts among the extreme emission line galaxies with
respect to LGRBs are mostly due to a larger fraction of strong-line emitters
among SLSN hosts at z < 0.3, where samples of LGRB hosts are small and poorly
defined.


title:
Walking without a Map: Optimizing Response Times of Traversal-Based
  Linked Data Queries (Extended Version)

abstract:
  The emergence of Linked Data on the WWW has spawned research interest in an
online execution of declarative queries over this data. A particularly
interesting approach is traversal-based query execution which fetches data by
traversing data links and, thus, is able to make use of up-to-date data from
initially unknown data sources. The downside of this approach is the delay
before the query engine completes a query execution. In this paper, we address
this problem by proposing an approach to return as many elements of the result
set as soon as possible. The basis of this approach is a traversal strategy
that aims to fetch result-relevant data as early as possible. The challenge for
such a strategy is that the query engine does not know a priori which of the
data sources that will be discovered during the query execution contain
result-relevant data. We introduce 16 different traversal approaches and
experimentally study their impact on response times. Our experiments show that
some of the approaches can achieve significant improvements over the baseline
of looking up URIs on a first-come, first-served basis. Additionally, we verify
the importance of these approaches by showing that typical query optimization
techniques that focus solely on the process of constructing the query result
cannot have any significant impact on the response times of traversal-based
query executions.