title: Atelier: Repurposing Expert Crowdsourcing Tasks as Micro-internships

abstract:
  Expert crowdsourcing marketplaces have untapped potential to empower workers'
career and skill development. Currently, many workers cannot afford to invest
the time and sacrifice the earnings required to learn a new skill, and a lack
of experience makes it difficult to get job offers even if they do. In this
paper, we seek to lower the threshold to skill development by repurposing
existing tasks on the marketplace as mentored, paid, real-world work
experiences, which we refer to as micro-internships. We instantiate this idea
in Atelier, a micro-internship platform that connects crowd interns with crowd
mentors. Atelier guides mentor-intern pairs to break down expert crowdsourcing
tasks into milestones, review intermediate output, and problem-solve together.
We conducted a field experiment comparing Atelier's mentorship model to a
non-mentored alternative on a real-world programming crowdsourcing task,
finding that Atelier helped interns maintain forward progress and absorb best
practices.


title: Clock Distributing for BaF2 Readout Electronics at CSNS-WNS

abstract:
  aF2 (Barium Fluoride) detector array is designed for the measurement of
(n,{\gamma}) cross section precisely at CSNS-WNS (white neutron source at China
Spallation Neutron Source). It is a 4{\pi}solid angle-shaped detector array
consisting of 92 BaF2 crystal elements. To discriminate signals from BaF2
detector, pulse shape discrimination methodology is used, which is supported by
waveform digitization technique. There are total 92 channels for digitizing.
The precision and synchronization of clock distribution restricts the
performance of waveform digitizing. In this paper, the clock prototype for BaF2
readout electronics at CSNS-WNS is introduced. It is based on PXIe platform and
has a twin-stage tree topology. In the first stage, clock is distributed from
the tree root to each PXIe crate synchronously through coaxial cable over long
distance, while in the second stage, clock is further distributed to each
electronic module through PXIe dedicated differential star bus. With the help
of this topology, each tree node can fan out up to 20 clocks with 3U size. Test
result shows the clock jitter is less than 20ps, which can meet the requirement
of BaF2 readout electronics. Besides, this clock system has advantages of high
density, simplicity, scalability and cost saving, which makes it can be used in
other applications of clock distributing preciously.


title: Is a hyperchaotic attractor superposition of two multifractals?

abstract:
  In the context of chaotic dynamical systems with exponential divergence of
nearby trajectories in phase space, hyperchaos is defined as a state where
there is divergence or stretching in at least two directions during the
evolution of the system. Hence the detection and characterization of a
hyperchaotic attractor is usually done using the spectrum of Lyapunov Exponents
(LEs) that measure this rate of divergence along each direction. Though
hyperchaos arise in different dynamical situations and find several practical
applications, a proper understanding of the geometric structure of a
hyperchaotic attractor still remains an unsolved problem. In this paper, we
present strong numerical evidence to suggest that the geometric structure of a
hyperchaotic attractor can be characterized using a multifractal spectrum with
two superimposed components. In other words, apart from developing an extra
positive LE, there is also a structural change as a chaotic attractor makes a
transition to the hyperchaotic phase and the attractor changes from a simple
multifractal to a dual multifractal, equivalent to two inter-mingled
multifractals. We argue that a cross-over behavior in the scaling region for
computing the correlation dimension is a manifestation of such a structure. In
order to support this claim, we present an illustrative example of a
synthetically generated set of points in the unit interval (a Cantor set with a
variable iteration scheme) displaying dual multifractal spectrum. Our results
are also used to develop a general scheme to generate both hyperchaotic as well
as high dimensional chaotic attractors by coupling two low dimensional chaotic
attractors and tuning a time scale parameter.


title: When physical intuition fails

abstract:
  We analyze the problem solving strategies of physics professors in a case
where their physical intuition fails. A non-intuitive introductory-level
problem was identified and posed to twenty physics professors. The problem
placed the professors in a situation often encountered by students, and their
response highlights the importance of intuition and experience in problem
solving. While professors had difficulty in solving the problem under the time
constraint, they initially employed a systematic approach, e.g., visualizing
the problem, considering various conservation laws, and examining limiting
cases. After finding that familiar techniques were not fruitful, they made
incorrect predictions based on one of two equally important factors. By
contrast, other more familiar problems that require the consideration of two
important principles (e.g., conservation of both energy and momentum for a
ballistic pendulum) are quickly solved by the same professors. The responses of
students who were given the same problem reflected no overarching strategies or
systematic approaches, and a much wider variety of incorrect responses were
given. This investigation highlights the importance of teaching effective
problem solving heuristics, and suggests that instructors assess the difficulty
of a problem from the perspective of beginning students.


title:
Efficient and accurate methods for solving the time-dependent spin-1
  Gross-Pitaevskii equation

abstract:
  We develop a numerical method for solving the spin-1 Gross-Pitaevskii
equation. The basis of our work is a two-way splitting of the spin-1 evolution
equation that leads to two exactly solvable flows. We use this to implement a
second-order and a fourth-order symplectic integration method. These are the
first fully symplectic methods for evolving spin-1 condensates. We develop two
non-trivial numerical tests to compare our methods against two other
approaches.


title: Laser-assisted Oxidation of Multi-layer Tungsten Diselenide Nanosheets

abstract:
  We report the structural and electrical characterization of tungsten oxides
formed by illuminating multi-layer tungsten diselenide (WSe2) nanosheets with
an intense laser beam in the ambient environment. A noninvasive microwave
impedance microscope (MIM) was used to perform electrical imaging of the
samples. The local conductivity ~100 S/m of the oxidized product, measured by
the MIM and conventional transport experiments, is much higher than that of the
pristine WSe2, suggesting the formation of sub-stoichiometric WO3-x
polycrystals with n-type carriers. With further efforts to improve the
conductivity of the oxides, the laser-assisted oxidation process may be useful
for patterning conductive features on WSe2 or forming electrical contacts to
various transition metal dichalcogenides.


title:
High-Multipole Excitations of Hydrogen-Like Atoms by Twisted Photons
  near Phase Singularity

abstract:
  We calculate transition amplitudes and cross sections for excitation of
hydrogen-like atoms by the twisted photon states, or photon states with angular
momentum projection on the direction of propagation exceeding $\hbar$. If the
target atom is located at distances of the order of atomic size near the phase
singularity in the vortex center, the transitions rates into the states with
orbital angular momentum $l_f>1$ become comparable with the rates for electric
dipole transitions. It is shown that when the transition rates are normalized
to the local photon flux, the resulting cross sections for $l_f>1$ are singular
near the optical vortex center. Relation to the "quantum core" concept
introduced by Berry and Dennis is discussed.


title: Trace and inverse trace of Steklov eigenvalues II

abstract:
  This is a continuation of our previous work arXiv:1601.05617 on trace and
inverse trace of Steklov eigenvalues. More new inequalities for the trace and
inverse trace of Steklov eigenvalues are obtained.


title: Uniformly expanding vacuum: a possible interpretation of the dark energy

abstract:
  Following the spirit of the equivalence principle, we take a step further to
recognize the free fall of the observer as a method to eliminate causes that
would lead the perceived vacuum to change its original state. Thus, it is
expected that the vacuum should be in a rigid Minkowski state or be uniformly
expanding. By carefully investigating the impact on measurement caused by the
expansion, we clarify the exact meaning of the uniformly expanding vacuum and
find that this proposal may be able to explain the current observations of an
accelerating universe.


title:
An Algebraic Topological Approach to Privacy: Numerical and Categorical
  Data

abstract:
  In this paper, we cast the classic problem of achieving k-anonymity for a
given database as a problem in algebraic topology. Using techniques from this
field of mathematics, we propose a framework for k-anonymity that brings new
insights and algorithms to anonymize a database. We begin by addressing the
simpler case when the data lies in a metric space. This case is instrumental to
introduce the main ideas and notation. Specifically, by mapping a database to
the Euclidean space and by considering the distance between datapoints, we
introduce a simplicial representation of the data and show how concepts from
algebraic topology, such as the nerve complex and persistent homology, can be
applied to efficiently obtain the entire spectrum of k-anonymity of the
database for various values of k and levels of generalization. For this
representation, we provide an analytic characterization of conditions under
which a given representation of the dataset is k-anonymous. We introduce a
weighted barcode diagram which, in this context, becomes a computational tool
to tradeoff data anonymity with data loss expressed as level of generalization.
Some simulations results are used to illustrate the main idea of the paper. We
conclude the paper with a discussion on how to extend this method to address
the general case of a mix of categorical and metric data.


title: Spin-Orbit States of Neutron Wavepackets

abstract:
  We propose a method to prepare an entangled spin-orbit state between the spin
and the orbital angular momenta of a neutron wavepacket. This spin-orbit state
is created by passing neutrons through the center of a quadrupole magnetic
field, which provides a coupling between the spin and orbital degrees of
freedom. A Ramsey fringe type measurement is suggested as a means of verifying
the spin-orbit correlations.


title: Creating Simplified 3D Models with High Quality Textures

abstract:
  This paper presents an extension to the KinectFusion algorithm which allows
creating simplified 3D models with high quality RGB textures. This is achieved
through (i) creating model textures using images from an HD RGB camera that is
calibrated with Kinect depth camera, (ii) using a modified scheme to update
model textures in an asymmetrical colour volume that contains a higher number
of voxels than that of the geometry volume, (iii) simplifying dense polygon
mesh model using quadric-based mesh decimation algorithm, and (iv) creating and
mapping 2D textures to every polygon in the output 3D model. The proposed
method is implemented in real-time by means of GPU parallel processing.
Visualization via ray casting of both geometry and colour volumes provides
users with a real-time feedback of the currently scanned 3D model. Experimental
results show that the proposed method is capable of keeping the model texture
quality even for a heavily decimated model and that, when reconstructing small
objects, photorealistic RGB textures can still be reconstructed.


title:
Constraints on $s-\bar s$ asymmetry of the proton in chiral effective
  theory

abstract:
  We compute the $s-\bar s$ asymmetry in the proton in chiral effective theory,
using phenomenological constraints based upon existing data. Unlike previous
meson cloud model calculations, which accounted for kaon loop contributions
with on-shell intermediate states alone, this work includes off-shell terms and
contact interactions, which impact the shape of the $s-\bar s$ difference. We
identify a valence-like component of $s(x)$ which is balanced by a
$\delta$-function contribution to $\bar s(x)$ at $x=0$, so that the integrals
of $s$ and $\bar s$ over the experimentally accessible region $x > 0$ are not
equal. Using a regularization procedure that preserves chiral symmetry and
Lorentz invariance, we find that existing data limit the integrated value of
the second moment of the asymmetry to the range $-0.07 \times 10^{-3} \leq
\langle x(s-\bar s) \rangle \leq 1.12 \times 10^{-3}$ at a scale of $Q^2=1
$GeV$^2$. This is too small to account for the NuTeV anomaly and of the wrong
sign to enhance it.


title: Planogram Compliance Checking Based on Detection of Recurring Patterns

abstract:
  In this paper, a novel method for automatic planogram compliance checking in
retail chains is proposed without requiring product template images for
training. Product layout is extracted from an input image by means of
unsupervised recurring pattern detection and matched via graph matching with
the expected product layout specified by a planogram to measure the level of
compliance. A divide and conquer strategy is employed to improve the speed.
Specifically, the input image is divided into several regions based on the
planogram. Recurring patterns are detected in each region respectively and then
merged together to estimate the product layout. Experimental results on real
data have verified the efficacy of the proposed method. Compared with a
template-based method, higher accuracies are achieved by the proposed method
over a wide range of products.


title:
Strategic Decompositions of Normal Form Games: Zero-sum Games and
  Potential Games

abstract:
  We study new classes of games, called zero-sum equivalent games and zero-sum
equivalent potential games, and prove decomposition theorems involving these
classes of games. We say that two games are "strategically equivalent" if, for
every player, the payoff differences between two strategies (holding other
players' strategies fixed) are identical. A zero-sum equivalent game is a game
that is strategically equivalent to a zero-sum game; a zero-sum equivalent
potential game is a zero-sum equivalent game that is strategically equivalent
to a common interest game. We also call a game "normalized" if the sum of one
player's payoffs, given the other players' strategies, is always zero. We show
that any normal form game can be uniquely decomposed into either (i) a zero-sum
equivalent game and a normalized common interest game, or (ii) a zero-sum
equivalent potential game, a normalized zero-sum game, and a normalized common
interest game, each with distinctive equilibrium properties. For example, we
show that two-player zero-sum equivalent games with finite strategy sets
generically have a unique Nash equilibrium and that two-player zero-sum
equivalent potential games with finite strategy sets generically have a
strictly dominant Nash equilibrium.


title:
On the Upper Ocean Turbulent Dissipation Rate due to Very Short Breaking
  Wind-Waves

abstract:
  Sutherland and Melville (2015a) investigated the relative contributions to
the total dissipation rate in the ocean surface wave boundary layer of
different breaking wave scales, from large-scale whitecaps to micro-breakers.
Based on their measurements of geometric/kinematic properties of breaking waves
for a wide range of wave ages, they inferred the dissipation rates from
breaking as a function of scale. These results were compared with their
complementary measurements of the total dissipation rate in the underlying wave
boundary layer. They reported that the total depth-integrated dissipation rate
in the water column agreed well with dissipation rate from breaking waves for
young to very old wind seas. They also reported high observed levels of
dissipation rate very near the sea surface. They concluded that this showed a
large fraction of the total dissipation rate was due to non-air entraining
micro-breakers and very small whitecaps. Because of its fundamental importance,
both physically and for accurate air-sea interaction modeling, we assess the
validity of these conclusions. Our analysis of their data shows that the
microbreakers and small whitecaps do not make a significant contribution to the
total turbulent dissipation rate in the wave boundary layer.


title:
Exact solutions to a Muskat problem with line distributions of sinks and
  sources

abstract:
  The evolution of a two-phase Hele-Shaw problem, a Muskat problem, under
assumption of a negligible surface tension is considered. We use the Schwarz
function approach and allow the sinks and sources to be line distributions with
disjoint supports located in the exterior and the interior domains, a two-phase
mother body. We give examples of exact solutions when the interface belongs to
a certain family of algebraic curves, defined by the initial shape of the
boundary, and the cusp formation does not occur.


title:
Consequences of an Abelian $Z'$ for neutrino oscillations and dark
  matter

abstract:
  The Standard Model's accidental and anomaly-free currents: $B-L$,
$L_e-L_\mu$, $L_e-L_\tau$, and $L_\mu-L_\tau$, could be indicative of a hidden
gauge structure beyond the Standard Model. Additionally, neutrino masses can be
generated by a dimension-5 operator that generically breaks all of these
symmetries. It is therefore important to investigate the compatibility of a
gauged $U'(1)$ and neutrino phenomenology. We consider gauging each of the
symmetries above with a minimal extended matter content. This includes the
$Z'$, an order parameter to break the $U'(1)$, and three right-handed
neutrinos. We find all but $B-L$ require additional matter content to explain
the measured neutrino oscillation parameters. We also discuss the compatibility
of the measured neutrino textures with a non-thermal dark matter production
mechanism involving the decay of the $Z'$. Finally, we present a parametric
relation that implies that a sterile neutrino dark matter candidate should not
be expected to contribute to neutrino masses beyond ten parts per million.


title: Auditory System for a Mobile Robot

abstract:
  In this thesis, we propose an artificial auditory system that gives a robot
the ability to locate and track sounds, as well as to separate simultaneous
sound sources and recognising simultaneous speech. We demonstrate that it is
possible to implement these capabilities using an array of microphones, without
trying to imitate the human auditory system. The sound source localisation and
tracking algorithm uses a steered beamformer to locate sources, which are then
tracked using a multi-source particle filter. Separation of simultaneous sound
sources is achieved using a variant of the Geometric Source Separation (GSS)
algorithm, combined with a multi-source post-filter that further reduces noise,
interference and reverberation. Speech recognition is performed on separated
sources, either directly or by using Missing Feature Theory (MFT) to estimate
the reliability of the speech features.
  The results obtained show that it is possible to track up to four
simultaneous sound sources, even in noisy and reverberant environments.
Real-time control of the robot following a sound source is also demonstrated.
The sound source separation approach we propose is able to achieve a 13.7 dB
improvement in signal-to-noise ratio compared to a single microphone when three
speakers are present. In these conditions, the system demonstrates more than
80% accuracy on digit recognition, higher than most human listeners could
obtain in our small case study when recognising only one of these sources. All
these new capabilities will allow humans to interact more naturally with a
mobile robot in real life settings.


title:
Analysis of Multiple Flows using Different High Speed TCP protocols on a
  General Network

abstract:
  We develop analytical tools for performance analysis of multiple TCP flows
(which could be using TCP CUBIC, TCP Compound, TCP New Reno) passing through a
multi-hop network. We first compute average window size for a single TCP
connection (using CUBIC or Compound TCP) under random losses. We then consider
two techniques to compute steady state throughput for different TCP flows in a
multi-hop network. In the first technique, we approximate the queues as M/G/1
queues. In the second technique, we use an optimization program whose solution
approximates the steady state throughput of the different flows. Our results
match well with ns2 simulations.


title: Structured Learning of Binary Codes with Column Generation

abstract:
  Hashing methods aim to learn a set of hash functions which map the original
features to compact binary codes with similarity preserving in the Hamming
space. Hashing has proven a valuable tool for large-scale information
retrieval. We propose a column generation based binary code learning framework
for data-dependent hash function learning. Given a set of triplets that encode
the pairwise similarity comparison information, our column generation based
method learns hash functions that preserve the relative comparison relations
within the large-margin learning framework. Our method iteratively learns the
best hash functions during the column generation procedure. Existing hashing
methods optimize over simple objectives such as the reconstruction error or
graph Laplacian related loss functions, instead of the performance evaluation
criteria of interest---multivariate performance measures such as the AUC and
NDCG. Our column generation based method can be further generalized from the
triplet loss to a general structured learning based framework that allows one
to directly optimize multivariate performance measures. For optimizing general
ranking measures, the resulting optimization problem can involve exponentially
or infinitely many variables and constraints, which is more challenging than
standard structured output learning. We use a combination of column generation
and cutting-plane techniques to solve the optimization problem. To speed-up the
training we further explore stage-wise training and propose to use a simplified
NDCG loss for efficient inference. We demonstrate the generality of our method
by applying it to ranking prediction and image retrieval, and show that it
outperforms a few state-of-the-art hashing methods.


title:
Phonon dispersion unfolding in the presence of heavy breaking of spatial
  translational symmetry

abstract:
  The phonon dispersion unfolding method is useful for obtaining hidden Bloch
symmetries and comparing theoretical results with experiment spectrums (e.g.,
inelastic neutron scattering, inelastic X-ray scattering, Raman). In this
paper, we propose a method to unfold phonon dispersions. The main advantage of
this method is the ability to handle systems with heavy breaking of spatial
translational symmetry. Its validity is tested by pure diamond, diamond with Si
substitution, and diamond with C vacancies.


title:
Measuring correlations in non-separable vector beams using projective
  measurements

abstract:
  Doubts regarding the completeness of quantum mechanics as raised by Einstein,
Podolsky and Rosen(EPR) have predominantly been resolved by resorting to a
measurement of correlations between entangled photons which clearly demonstrate
violation of Bell's inequality. This article is an attempt to reconcile
incompatibility of hidden variable theories with reality by demonstrating
experimentally a violation of Bell's inequality in locally correlated systems
whose two degrees of freedom, the spin and orbital angular momentum, are
maximally correlated. To this end we propose and demonstrate a linear,
achromatic modified Sagnac interferometer to project orbital angular momentum
states which we combine with spin projections to measure correlations.


title: Influencing Busy People in a Social Network

abstract:
  We identify influential early adopters in a social network, where individuals
are resource constrained, to maximize the spread of multiple, costly behaviors.
A solution to this problem is especially important for viral marketing. The
problem of maximizing influence in a social network is challenging since it is
computationally intractable. We make three contributions. First, propose a new
model of collective behavior that incorporates individual intent, knowledge of
neighbors actions and resource constraints. Second, we show that the multiple
behavior influence maximization is NP-hard. Furthermore, we show that the
problem is submodular, implying the existence of a greedy solution that
approximates the optimal solution to within a constant. However, since the
greedy algorithm is expensive for large networks, we propose efficient
heuristics to identify the influential individuals, including heuristics to
assign behaviors to the different early adopters. We test our approach on
synthetic and real-world topologies with excellent results. We evaluate the
effectiveness under three metrics: unique number of participants, total number
of active behaviors and network resource utilization. Our heuristics produce
15-51% increase in expected resource utilization over the naive approach.


title: Spatial adiabatic passage: a review of recent progress

abstract:
  Adiabatic techniques are known to allow for engineering quantum states with
high fidelity. This requirement is currently of large interest, as applications
in quantum information require the preparation and manipulation of quantum
states with minimal errors. Here we review recent progress on developing
techniques for the preparation of spatial states through adiabatic passage,
particularly focusing on three state systems. These techniques can be applied
to matter waves in external potentials, such as cold atoms or electrons, and to
classical waves in waveguides, such as light or sound.


title:
Non-preemptive Scheduling in a Smart Grid Model and its Implications on
  Machine Minimization

abstract:
  We study a scheduling problem arising in demand response management in smart
grid. Consumers send in power requests with a flexible feasible time interval
during which their requests can be served. The grid controller, upon receiving
power requests, schedules each request within the specified interval. The
electricity cost is measured by a convex function of the load in each timeslot.
The objective is to schedule all requests with the minimum total electricity
cost. Previous work has studied cases where jobs have unit power requirement
and unit duration. We extend the study to arbitrary power requirement and
duration, which has been shown to be NP-hard. We give the first online
algorithm for the general problem, and prove that the problem is fixed
parameter tractable. We also show that the online algorithm is asymptotically
optimal when the objective is to minimize the peak load. In addition, we
observe that the classical non-preemptive machine minimization problem is a
special case of the smart grid problem with min-peak objective, and show that
we can solve the non-preemptive machine minimization problem asymptotically
optimally.


title:
Student understanding of quantum mechanics at the beginning of graduate
  instruction

abstract:
  A survey was developed to probe student understanding of quantum mechanics at
the beginning of graduate instruction. The survey was administered to 202
physics graduate students enrolled in first-year quantum mechanics courses from
seven universities at the beginning of the first semester. We also conducted
one-on-one interviews with fifteen graduate or advanced undergraduate students
who had just completed a course in which all the content on the survey was
covered. Although students from some universities performed better on average
than others, we found that students share universal difficulties understanding
the concepts of quantum mechanics. The difficulties were often due to
over-generalizations of concepts learned in one context to other contexts where
they are not directly applicable. Difficulties in distinguishing between
closely related concepts and making sense of the formalism of quantum mechanics
were common. The results of this study can sensitize instructors of first-year
graduate quantum physics to some of the difficulties students are likely to
face.


title:
Error bounds, quadratic growth, and linear convergence of proximal
  methods

abstract:
  The proximal gradient algorithm for minimizing the sum of a smooth and a
nonsmooth convex function often converges linearly even without strong
convexity. One common reason is that a multiple of the step length at each
iteration may linearly bound the "error" -- the distance to the solution set.
We explain the observed linear convergence intuitively by proving the
equivalence of such an error bound to a natural quadratic growth condition. Our
approach generalizes to linear convergence analysis for proximal methods (of
Gauss-Newton type) for minimizing compositions of nonsmooth functions with
smooth mappings. We observe incidentally that short step-lengths in the
algorithm indicate near-stationarity, suggesting a reliable termination
criterion.


title: Recurrent Orthogonal Networks and Long-Memory Tasks

abstract:
  Although RNNs have been shown to be powerful tools for processing sequential
data, finding architectures or optimization strategies that allow them to model
very long term dependencies is still an active area of research. In this work,
we carefully analyze two synthetic datasets originally outlined in (Hochreiter
and Schmidhuber, 1997) which are used to evaluate the ability of RNNs to store
information over many time steps. We explicitly construct RNN solutions to
these problems, and using these constructions, illuminate both the problems
themselves and the way in which RNNs store different types of information in
their hidden states. These constructions furthermore explain the success of
recent methods that specify unitary initializations or constraints on the
transition matrices.


title:
Temperature effects in excitonic condensation driven by the lattice
  distortion

abstract:
  The stability of the excitonic condensation at low temperature driven by a
coupling of electrons to vibrational degrees of freedom in semimetal
two-dimensional electronic system is discussed. In the framework of the
unrestricted Hartree-Fock approximation, we derive a set of equations to
determine both the excitonic condensate order parameter and lattice
displacement self-consistently. By lowering temperature we find out a
semimetal-insulator transition in the system if the coupling is large enough.
The insulating state typifies an excitonic condensation accompanied by a finite
lattice distortion. Increasing temperature, both excitonic condensate order
parameter and the lattice distortion decrease and then disappear in the same
manner. Microscopic analysis in momentum space strongly specifies that the
excitonic condensate driven by the lattice distortion favours the BCS type.


title: A Geometric Analysis of Phase Retrieval

abstract:
  Can we recover a complex signal from its Fourier magnitudes? More generally,
given a set of $m$ measurements, $y_k = |\mathbf a_k^* \mathbf x|$ for $k = 1,
\dots, m$, is it possible to recover $\mathbf x \in \mathbb{C}^n$ (i.e.,
length-$n$ complex vector)? This **generalized phase retrieval** (GPR) problem
is a fundamental task in various disciplines, and has been the subject of much
recent investigation. Natural nonconvex heuristics often work remarkably well
for GPR in practice, but lack clear theoretical explanations. In this paper, we
take a step towards bridging this gap. We prove that when the measurement
vectors $\mathbf a_k$'s are generic (i.i.d. complex Gaussian) and the number of
measurements is large enough ($m \ge C n \log^3 n$), with high probability, a
natural least-squares formulation for GPR has the following benign geometric
structure: (1) there are no spurious local minimizers, and all global
minimizers are equal to the target signal $\mathbf x$, up to a global phase;
and (2) the objective function has a negative curvature around each saddle
point. This structure allows a number of iterative optimization methods to
efficiently find a global minimizer, without special initialization. To
corroborate the claim, we describe and analyze a second-order trust-region
algorithm.


title: How Much Bandpass Filtering is Required in Massive MIMO Basestations?

abstract:
  In this paper, we study the impact of aliased out-of-band interference
signals on the information sum-rate of the maximum ratio combining receiver in
massive multiple-input multiple-output (MIMO) uplink, with both perfect and
imperfect channel estimates, in order to determine the required out-of-band
attenuation in RF bandpass filters (BPFs). With imperfect channel estimates,
our study reveals that as the number of base-station (BS) antennas ($M$)
increases, the required attenuation at the BPFs increases as
$\mathcal{O}(\sqrt{M})$ with $M \to \infty$, provided the desired information
sum-rate (both in the presence and in the absence of AOOBIs (aliased
out-of-band interferers)) remains fixed. This implies a practical limit on the
number of BS antennas due to the increase in BPF design complexity and power
consumption with increasing $M$.


title: Helping Students Learn Quantum Mechanics for Quantum Computing

abstract:
  Quantum information science and technology is a rapidly growing
interdisciplinary field drawing researchers from science and engineering
fields. Traditional instruction in quantum mechanics is insufficient to prepare
students for research in quantum computing because there is a lack of emphasis
in the current curriculum on quantum formalism and dynamics. We are
investigating the difficulties students have with quantum mechanics and are
developing and evaluating quantum interactive learning tutorials (QuILTs) to
reduce the difficulties. Our investigation includes interviews with individual
students and the development and administration of free-response and
multiple-choice tests. We discuss the implications of our research and
development project on helping students learn quantum mechanics relevant for
quantum computing.


title:
A Motion Planning Strategy for the Active Vision-Based Mapping of
  Ground-Level Structures

abstract:
  This paper presents a strategy to guide a mobile ground robot equipped with a
camera or depth sensor, in order to autonomously map the visible part of a
bounded three-dimensional structure. We describe motion planning algorithms
that determine appropriate successive viewpoints and attempt to fill holes
automatically in a point cloud produced by the sensing and perception layer.
The emphasis is on accurately reconstructing a 3D model of a structure of
moderate size rather than mapping large open environments, with applications
for example in architecture, construction and inspection. The proposed
algorithms do not require any initialization in the form of a mesh model or a
bounding box, and the paths generated are well adapted to situations where the
vision sensor is used simultaneously for mapping and for localizing the robot,
in the absence of additional absolute positioning system. We analyze the
coverage properties of our policy, and compare its performance to the classic
frontier based exploration algorithm. We illustrate its efficacy for different
structure sizes, levels of localization accuracy and range of the depth sensor,
and validate our design on a real-world experiment.


title:
nIFTy Galaxy Cluster simulations IV: Quantifying the Influence of
  Baryons on Halo Properties

abstract:
  Building on the initial results of the nIFTy simulated galaxy cluster
comparison, we compare and contrast the impact of baryonic physics with a
single massive galaxy cluster, run with 11 state-of-the-art codes, spanning
adaptive mesh, moving mesh, classic and modern SPH approaches. For each code
represented we have a dark matter only (DM) and non-radiative (NR) version of
the cluster, as well as a full physics (FP) version for a subset of the codes.
We compare both radial mass and kinematic profiles, as well as global measures
of the cluster (e.g. concentration, spin, shape), in the NR and FP runs with
that in the DM runs. Our analysis reveals good consistency (<= 20%) between
global properties of the cluster predicted by different codes when integrated
quantities are measured within the virial radius R200. However, we see larger
differences for quantities within R2500, especially in the FP runs. The radial
profiles reveal a diversity, especially in the cluster centre, between the NR
runs, which can be understood straightforwardly from the division of codes into
classic SPH and non-classic SPH (including the modern SPH, adaptive and moving
mesh codes); and between the FP runs, which can also be understood broadly from
the division of codes into those that include AGN feedback and those that do
not. The variation with respect to the median is much larger in the FP runs
with different baryonic physics prescriptions than in the NR runs with
different hydrodynamics solvers.


title:
Bosonic excitations and electron pairing in an electron-doped cuprate
  superconductor

abstract:
  Superconductivity originates from the coupling between charge carriers and
bosonic excitations of either phononic or electronic origin. Identifying the
most relevant pairing glue is a key step towards a clear understanding of the
unconventional superconductivity. Here, by applying the ultrafast optical
spectroscopy on the electron-doped cuprates
La$_{1.9}$Ce$_{0.1}$CuO$_{4\pm\delta}$, we discern a bosonic mode of electronic
origin that has the strongest coupling with the charge carriers near $T_c$. We
argue that this mode is associated with the two-dimensional antiferromagnetic
spin fluctuations, and can fully account for the superconducting pairing. Our
work may help to establish a quantitative relation between bosonic excitations
and superconducting pairing in electron-doped cuprates, and pave the way for
systematic exploration of superconductivity and other collective phenomena in
all correlated materials.


title: Density domains of a photo-excited electron gas on liquid helium

abstract:
  The Coulombic effect on the stability range of the photo-excited electron gas
on liquid helium is shown to favor formation of domains of different densities.
Domains appear to eliminate or greatly reduce regions with negative
conductivity. An analysis of the density domain structure allows explaining
remarkable observations reported recently for the photo-excited electron gas.


title: Gas Kinematics and Star Formation in the Filamentary IRDC G34.43+0.24

abstract:
  We performed a multiwavelength study toward infrared dark cloud (IRDC)
G34.43+0.24. New maps of 13CO $J$=1-0 and C18}O J=1-0 were obtained from the
Purple Mountain Observatory (PMO) 13.7 m radio telescope. At 8 um (Spitzer -
IRAC), IRDC G34.43+0.24 appears to be a dark filament extended by 18 arcmin
along the north-south direction. Based on the association with the 870 um and
C18O J=1-0 emission, we suggest that IRDC G34.43+0.24 should not be 18 arcmin
in length, but extend by 34 arcmin. IRDC G34.43+0.24 contains some massive
protostars, UC H II regions, and infrared bubbles. The spatial extend of IRDC
G34.43+0.24 is about 37 pc assuming a distance of 3.7 kpc. IRDC G34.43+0.24 has
a linear mass density of 1.6*10^{3} M_{sun} pc^{-1}, which is roughly
consistent with its critical mass to length ratio. The turbulent motion may
help stabilizing the filament against the radial collapse. Both infrared
bubbles N61 and N62 show a ringlike structure at 8 um. Particularly, N61 has a
double-shell structure, which has expanded into IRDC G34.43+0.24. The outer
shell is traced by 8 um and 13}CO J=1-0 emission, while the inner shell is
traced by 24 um and 20 cm emission. We suggest that the outer shell (9.9*10^{5}
yr) is created by the expansion of H II region G34.172+0.175, while the inner
shell (4.1-6.3*10^{5} yr) may be produced by the energetic stellar wind of its
central massive star. From GLIMPSE I catalog, we selected some Class I sources
with an age of 10^{5} yr. These Class I sources are clustered along the
filamentary molecular cloud.


title:
Smoothed Particle Hydrodynamics Method for Two-dimensional Stefan
  Problem

abstract:
  Smoothed particle hydrodynamics (SPH) is developed for modelling of melting
and solidification. Enthalpy method is used to solve heat conduction equations
which involved moving interface between phases. At first, we study the melting
of floating ice in the water for two-dimensional system. The ice objects are
assumed as solid particles floating in fluid particles. The fluid and solid
motion are governed by Navier-Stokes equation and basic rigid dynamics
equation, respectively. We also propose a strategy to separate solid particles
due to melting and solidification. Numerical results are obtained and plotted
for several initial conditions.


title: Effects of Landau-Lifshitz-Gilbert damping on domain growth

abstract:
  Domain patterns are simulated by the Landau-Lifshitz-Gilbert (LLG) equation
with an easy-axis anisotropy. If the Gilbert damping is removed from the LLG
equation, it merely describes the precession of magnetization with a
ferromagnetic interaction. However, even without the damping, domains that look
similar to those of scalar fields are formed, and they grow with time. It is
demonstrated that the damping has no significant effects on domain growth laws
and large-scale domain structure. In contrast, small-scale domain structure is
affected by the damping. The difference in small-scale structure arises from
energy dissipation due to the damping.


title: Comparison of sheaf cohomology and singular cohomology

abstract:
  A classic result states that on any locally contractible and paracompact
topological space, singular cohomology and sheaf cohomology are isomorphic. A
result by Ramanan claims that the paracompactness assumption may be removed,
but Ramanan's proof in fact implicitly relies on the assumption of
paracompactness and does not work in the stated generality. This paper gives a
modified proof that, in fact, singular cohomology and sheaf cohomology agree on
any locally contractible topological space.


title:
Path tracking and stabilization for a reversing general 2-trailer
  configuration using a cascaded control approach

abstract:
  In this paper a cascaded approach for stabilization and path tracking of a
general 2-trailer vehicle configuration with an off-axle hitching is presented.
A low level Linear Quadratic controller is used for stabilization of the
internal angles while a pure pursuit path tracking controller is used on a
higher level to handle the path tracking. Piecewise linearity is the only
requirement on the control reference which makes the design of reference paths
very general. A Graphical User Interface is designed to make it easy for a user
to design control references for complex manoeuvres given some representation
of the surroundings. The approach is demonstrated with challenging path
following scenarios both in simulation and on a small scale test platform.


title:
Spin-orbit-coupling induced torque in ballistic domain walls:
  equivalence of charge-pumping and nonequilibrium magnetization formalisms

abstract:
  To study the effect of spin-orbit coupling (SOC) on spin-transfer torque in
magnetic materials, we have implemented two theoretical formalisms that can
accommodate SOC. Using the "charge-pumping" formalism, we find two
contributions to the out-of-plane spin-transfer torque parameter $\beta$ in
ballistic Ni domain walls (DWs). For short DWs, the nonadiabatic reflection of
conduction electrons caused by the rapid spatial variation of the exchange
potential results in an out-of-plane torque that increases rapidly with
decreasing DW length. For long DWs, the Fermi level conduction channel
anisotropy that gives rise to an intrinsic DW resistance in the presence of SOC
leads to a linear dependence of $\beta$ on the DW length. To understand this
counterintuitive divergence of $\beta$ in the long DW limit, we use the
"nonequilibrium magnetization" formalism to examine the spatially resolved
spin-transfer torque. The SOC-induced out-of-plane torque in ballistic DWs is
found to be quantitatively consistent with the values obtained using the
charge-pumping calculations indicating the equivalence of the two theoretical
methods.


title: Phase diagram of the B-B2O3 system at pressures to 24 GPa

abstract:
  The evolution of topology of the B-B2O3 phase diagram has been studied at
pressures up to 24 GPa using models of phenomenological thermodynamics with
interaction parameters derived from experimental data on phase equilibria at
high pressures and high temperatures.


title:
WeBrowse: Mining HTTP logs online for network-based content
  recommendation

abstract:
  A powerful means to help users discover new content in the overwhelming
amount of information available today is sharing in online communities such as
social networks or crowdsourced platforms. This means comes short in the case
of what we call communities of a place: people who study, live or work at the
same place. Such people often share common interests but either do not know
each other or fail to actively engage in submitting and relaying information.
To counter this effect, we propose passive crowdsourced content discovery, an
approach that leverages the passive observation of web-clicks as an indication
of users' interest in a piece of content. We design, implement, and evaluate
WeBrowse , a passive crowdsourced system which requires no active user
engagement to promote interesting content to users of a community of a place.
Instead, it extracts the URLs users visit from traffic traversing a network
link to identify popular and interesting pieces of information. We first
prototype WeBrowse and evaluate it using both ground-truths and real traces
from a large European Internet Service Provider. Then, we deploy WeBrowse in a
campus of 15,000 users, and in a neighborhood. Evaluation based on our
deployments shows the feasibility of our approach. The majority of WeBrowse's
users welcome the quality of content it promotes. Finally, our analysis of
popular topics across different communities confirms that users in the same
community of a place share common interests, compared to users from different
communities, thus confirming the promise of WeBrowse's approach.


title:
Particle-Hole Symmetry in Generalized Seniority, Microscopic Interacting
  Boson (Fermion) Model, Nucleon-Pair Approximation, and Others

abstract:
  The particle-hole symmetry (equivalence) of the full shell-model Hilbert
space is straightforward and routinely used in practical calculations. In this
work we show that this symmetry is preserved in the subspace truncated at a
certain generalized seniority, and give the explicit transformation between the
states in the two types (particle and hole) of representations. Based on the
results, we study the particle-hole symmetry in popular theories that could be
regarded as further truncations on top of the generalized seniority, including
the microscopic interacting boson (fermion) model, the nucleon-pair
approximation, and others.


title: Weak containment and Rokhlin entropy

abstract:
  We define a new notion of weak containment for joinings, and we show that
this notion implies an inequality between relative Rokhlin entropies. This
leads to new upper bounds to Rokhlin entropy. We also use this notion to study
how Pinsker algebras behave under direct products, and we study the Rokhlin
entropy of restricted actions of finite-index subgroups.


title: AST: A library for modelling and manipulating coordinate systems

abstract:
  In view of increased interest in object-oriented systems for describing
coordinate information, we present a description of the data model used by the
Starlink AST library. AST provides a comprehensive range of facilities for
attaching world co-ordinate systems to astronomical data, and for retrieving
and interpreting that information in a variety of formats, including FITS-WCS.
AST is a mature system that has been in use for more than 17 years, and may
consequently be useful as a means of informing development of similar systems
in the future.


title: Minimal Darboux transformations

abstract:
  We derive a permutability theorem for the Christoffel, Goursat and Darboux
transformations of isothermic surfaces. As a consequence we obtain a simple
proof of a relation between Darboux pairs of minimal surfaces in Euclidean
space, curved flats in the 2-sphere and flat fronts in hyperbolic space.


title: EDCC 2015 - Fast Abstracts & Student Forum Proceedings

abstract:
  Fast Abstracts are short presentations of work in progress or opinion pieces
and aim to serve as a rapid and flexible mechanism to (i) Report on current
work that may or may not be complete; (ii) Introduce new ideas to the
community; (iii) State positions on controversial issues or open problems.
  On the other hand, the goal of the Student Forum is to encourage students to
attend EDCC and present their work, exchange ideas with researchers and
practitioners, and get early feedback on their research efforts.


title:
Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck
  effect using one-dimensional spin-current conducting films

abstract:
  We demonstrated a flexible thermoelectric (TE) sheet based on the
longitudinal spin Seebeck effect (LSSE) that is especially suitable for
heat-flow sensing applications. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4
film which was formed on a flexible plastic sheet using a spray-coating method
known as ferrite plating. The experimental results suggest that the
ferrite-plated film, which has a columnar crystal structure aligned
perpendicular to the film plane, functions as a unique one-dimensional
spin-current conductor suitable for bendable LSSE-based sensors.


title:
Non-concave optimal investment and no-arbitrage: a measure theoretical
  approach

abstract:
  We consider non-concave and non-smooth random utility functions with do- main
of definition equal to the non-negative half-line. We use a dynamic pro-
gramming framework together with measurable selection arguments to establish
both the no-arbitrage condition characterization and the existence of an
optimal portfolio in a (generically incomplete) discrete-time financial market
model with finite time horizon. In contrast to the existing literature, we
propose to consider a probability space which is not necessarily complete.


title: Designing a Disaster-resilient Network with Software Defined Networking

abstract:
  With the wide deployment of network facilities and the increasing requirement
of network reliability, the disruptive event like natural disaster, power
outage or malicious attack has become a non-negligible threat to the current
communication network. Such disruptive event can simultaneously destroy all
devices in a specific geographical area and affect many network based
applications for a long time. Hence, it is essential to build
disaster-resilient network for future highly survivable communication services.
In this paper, we consider the problem of designing a highly resilient network
through the technique of SDN (Software Defined Networking). In contrast to the
conventional idea of handling all the failures on the control plane (the
controller), we focus on an integrated design to mitigate disaster risks by
adding some redundant functions on the data plane. Our design consists of a
sub-graph based proactive protection approach on the data plane and a splicing
approach at the controller for effective restoration on the control plane. Such
a systematic design is implemented in the OpenFlow framework through the
Mininet emulator and Nox controller. Numerical results show that our approach
can achieve high robustness with low control overhead.


title: An Effective and Efficient Approach for Clusterability Evaluation

abstract:
  Clustering is an essential data mining tool that aims to discover inherent
cluster structure in data. As such, the study of clusterability, which
evaluates whether data possesses such structure, is an integral part of cluster
analysis. Yet, despite their central role in the theory and application of
clustering, current notions of clusterability fall short in two crucial aspects
that render them impractical; most are computationally infeasible and others
fail to classify the structure of real datasets.
  In this paper, we propose a novel approach to clusterability evaluation that
is both computationally efficient and successfully captures the structure of
real data. Our method applies multimodality tests to the (one-dimensional) set
of pairwise distances based on the original, potentially high-dimensional data.
We present extensive analyses of our approach for both the Dip and Silverman
multimodality tests on real data as well as 17,000 simulations, demonstrating
the success of our approach as the first practical notion of clusterability.


title:
siEDM: an efficient string index and search algorithm for edit distance
  with moves

abstract:
  Although several self-indexes for highly repetitive text collections exist,
developing an index and search algorithm with editing operations remains a
challenge. Edit distance with moves (EDM) is a string-to-string distance
measure that includes substring moves in addition to ordinal editing operations
to turn one string into another. Although the problem of computing EDM is
intractable, it has a wide range of potential applications, especially in
approximate string retrieval. Despite the importance of computing EDM, there
has been no efficient method for indexing and searching large text collections
based on the EDM measure. We propose the first algorithm, named string index
for edit distance with moves (siEDM), for indexing and searching strings with
EDM. The siEDM algorithm builds an index structure by leveraging the idea
behind the edit sensitive parsing (ESP), an efficient algorithm enabling
approximately computing EDM with guarantees of upper and lower bounds for the
exact EDM. siEDM efficiently prunes the space for searching query strings by
the proposed method, which enables fast query searches with the same guarantee
as ESP. We experimentally tested the ability of siEDM to index and search
strings on benchmark datasets, and we showed siEDM's efficiency.


title:
Correlation and fluctuation in Random Average Process on an infinite
  line with a driven tracer

abstract:
  We study the effect of single biased tracer particle in a bath of other
particles performing the random average process (RAP) on an infinite line. We
focus on the large time behavior of the mean and the fluctuations of the
positions of the particles and also the correlations among them. In the large
time t limit these quantities have well-defined scaling forms and grow with
time as $\sqrt{t}$. A differential equation for the scaling function associated
with the correlation function is obtained and solved perturbatively around the
solution for a symmetric tracer. Interestingly, when the tracer is totally
asymmetric, further progress is enabled by the fact that the particles behind
of the tracer do not affect the motion of the particles in front of it, which
leads in particular to an exact expression for the variance of the position of
the tracer. Finally, the variance and correlations of the gaps between
successive particles are also studied. Numerical simulations support our
analytical results.


title:
Erasure Schemes Using Generalized Polar Codes: Zero-Undetected-Error
  Capacity and Performance Trade-offs

abstract:
  We study the performance of generalized polar (GP) codes when they are used
for coding schemes involving erasure. GP codes are a family of codes which
contains, among others, the standard polar codes of Ar{\i}kan and Reed-Muller
codes. We derive a closed formula for the zero-undetected-error capacity
$I_0^{GP}(W)$ of GP codes for a given binary memoryless symmetric (BMS) channel
$W$ under the low complexity successive cancellation decoder with erasure. We
show that for every $R<I_0^{GP}(W)$, there exists a generalized polar code of
blocklength $N$ and of rate at least $R$ where the undetected-error probability
is zero and the erasure probability is less than
$2^{-N^{\frac{1}{2}-\epsilon}}$. On the other hand, for any GP code of rate
$I_0^{GP}(W)<R<I(W)$ and blocklength $N$, the undetected error probability
cannot be made less than $2^{-N^{\frac{1}{2}+\epsilon}}$ unless the erasure
probability is close to $1$.


title:
Testing black hole neutrino-dominated accretion discs for long-duration
  gamma-ray bursts

abstract:
  Long-duration gamma-ray bursts (LGRBs) are generally considered to originate
from the massive collapsars. It is believed that the central engine of
gamma-ray bursts (GRBs) is a neutrino-dominated accretion flow (NDAF) around a
rotating stellar-mass black hole (BH). The neutrino annihilation above the NDAF
is a feasible mechanism to power GRB. In this work, we analyse the
distributions of the isotropic gamma-ray radiated energy and jet kinetic energy
of 48 LGRBs. According to the NDAF and fireball models, we estimate the mean
accreted masses of LGRBs in our sample to investigate whether the NDAFs can
power LGRBs with the reasonable BH parameters and conversion efficiency of
neutrino annihilation. The results indicate that most of the values of the
accreted masses are less than $5~M_\odot$ for the extreme Kerr BHs and high
conversion efficiency. It suggests that the NDAFs may be suitable for most of
LGRBs except for some extremely high energy sources.


title: Cage Electron-Hydroxyl Complex State as Electron Donor in Mayenite

abstract:
  It is inferred from the chemical shift of muon spin rotation ($\mu$SR)
spectra that muons implanted in pristine (fully oxidized) mayenite,
[Ca$_{12}$Al$_{14}$O$_{32}]^{2+}$[$\square_5$O$^{2-}$] (C12A7, with $\square$
referring to the vacant cage), are bound to O$^{2-}$ at the cage center to form
OMu$^-$ (where Mu represents muonium, a muonic analog of the H atom). However,
an isolated negatively charged state (Mu$^-$, an analog of H$^-$) becomes
dominant when the compound approaches the state of electride
[Ca$_{12}$Al$_{14}$O$_{32}]^{2+}$[$\square_4$2e$^{-}$] as a result of the
reduction process. Moreover, the OMu$^-$ state in the pristine specimen
exhibits depolarization of paramagnetic origin at low temperatures (below
$\sim$30~K), indicating that OMu$^-$ accompanies a loosely bound electron in
the cage that can be thermally activated. This suggests that interstitial muons
(and hence H) forming a "cage electron-hydroxyl" complex can serve as electron
donors in C12A7.


title: Preconditioning Kernel Matrices

abstract:
  The computational and storage complexity of kernel machines presents the
primary barrier to their scaling to large, modern, datasets. A common way to
tackle the scalability issue is to use the conjugate gradient algorithm, which
relieves the constraints on both storage (the kernel matrix need not be stored)
and computation (both stochastic gradients and parallelization can be used).
Even so, conjugate gradient is not without its own issues: the conditioning of
kernel matrices is often such that conjugate gradients will have poor
convergence in practice. Preconditioning is a common approach to alleviating
this issue. Here we propose preconditioned conjugate gradients for kernel
machines, and develop a broad range of preconditioners particularly useful for
kernel matrices. We describe a scalable approach to both solving kernel
machines and learning their hyperparameters. We show this approach is exact in
the limit of iterations and outperforms state-of-the-art approximations for a
given computational budget.


title:
Groups of central type, maximal Connected Gradings and Intrinsic
  Fundamental Groups of Complex Semisimple Algebras

abstract:
  Maximal connected grading classes of a finite-dimensional algebra $A$ are in
one-to-one correspondence with Galois covering classes of $A$ which admit no
proper Galois covering and therefore are key in computing the intrinsic
fundamental group $\pi_1(A)$. Our first concern here is the algebras
$A=M_n(\mathbb{C})$. Their maximal connected gradings turn out to be in
one-to-one correspondence with the Aut$(G)$-orbits of non-degenerate classes in
$H^2(G,\C^*)$, where $G$ runs over all groups of central type whose orders
divide $n^2$. We show that there exist groups of central type $G$ such that
$H^2(G,\C^*)$ admits more than one such orbit of non-degenerate classes. We
compute the family $\Lambda$ of positive integers $n$ such that there is a
unique group of central type of order $n^2$, namely $C_n\times C_n$. The family
$\Lambda$ is of square-free integers and contains all prime numbers. It is
obtained by a full description of all groups of central type whose orders are
cube-free. We establish the maximal connected gradings of all finite
dimensional semisimple complex algebras using the fact that such gradings are
determined by dimensions of complex projective representations of finite
groups. In some cases we give a description of the corresponding fundamental
groups.


title: Optimal Mode Selection in D2D-Enabled Multi-Base Station Systems

abstract:
  In this paper, we consider device-to-device (D2D) communication underlaying
uplink cellular networks with multiple base stations (BSs), where each user can
switch between traditional cellular mode (through BS) and D2D mode (by
connecting proximity user), namely mode selection. We impose load balancing
constraints on BSs to efficient resource usage. The joint problem of mode
selection and user association is formulated as a combinatorial problem and
NP-complete. We adopt a graph-based approach to solve the problem globally
optimally in polynomial time. To further reduce complexity, we also propose a
distributed algorithm based on dual method. We show that the proposed
distributed algorithm achieves nearly the same performance as the proposed
optimal graph based algorithm.


title: A note on basis dimension selection in generalized additive modelling

abstract:
  Two new approaches for checking the dimension of the basis functions when
using penalized regression smoothers are presented. The first approach is a
test for adequacy of the basis dimension based on an estimate of the residual
variance calculated by differencing residuals that are neighbours according to
the smooth covariates. The second approach is based on estimated degrees of
freedom for a smooth of the model residuals with respect to the model
covariates. In comparison with basis dimension selection algorithms based on
smoothness selection criterion (GCV, AIC, REML) the above procedures are
computationally efficient enough for routine use as part of model checking.


title: Correlation Hashing Network for Efficient Cross-Modal Retrieval

abstract:
  Hashing is widely applied to approximate nearest neighbor search for
large-scale multimodal retrieval with storage and computation efficiency.
Cross-modal hashing improves the quality of hash coding by exploiting semantic
correlations across different modalities. Existing cross-modal hashing methods
first transform data into low-dimensional feature vectors, and then generate
binary codes by another separate quantization step. However, suboptimal hash
codes may be generated since the quantization error is not explicitly minimized
and the feature representation is not jointly optimized with the binary codes.
This paper presents a Correlation Hashing Network (CHN) approach to cross-modal
hashing, which jointly learns good data representation tailored to hash coding
and formally controls the quantization error. The proposed CHN is a hybrid deep
architecture that constitutes a convolutional neural network for learning good
image representations, a multilayer perception for learning good text
representations, two hashing layers for generating compact binary codes, and a
structured max-margin loss that integrates all things together to enable
learning similarity-preserving and high-quality hash codes. Extensive empirical
study shows that CHN yields state of the art cross-modal retrieval performance
on standard benchmarks.


title:
Wireless Information and Power Transfer for Multi-Relay Assisted
  Cooperative Communication

abstract:
  In this paper, we consider simultaneous wireless information and power
transfer (SWIPT) in multi-relay assisted two-hop relay system, where multiple
relay nodes simultaneously assist the transmission from source to destination
using the concept of distributed space-time coding. Each relay applies power
splitting protocol to coordinate the received signal energy for information
decoding and energy harvesting. The optimization problems of power splitting
ratios at the relays are formulated for both decode-and-forward (DF) and
amplify-and-forward (AF) relaying protocols. Efficient algorithms are proposed
to find the optimal solutions. Simulations verify the effectiveness of the
proposed schemes.


title:
Dynamically Emergent Flavor in a Confining Theory with Unbroken Chiral
  Symmetry

abstract:
  I discuss "truncated" QCD studied recently by Glozman et al. through
numerical simulations. For two flavors it was observed that truncation restores
the full chiral U(2)\times U(2) symmetry of the Lagrangian. Moreover,
additional enhancement of the above symmetry connecting representations with
distinct Lorentz spins was observed. I argue that the chiral symmetry
restoration in a confining theory could entail emergent (extra) dynamical
flavors which would show up in the spectrum of color-singlet particles provided
their mass \neq 0. As an example, I consider truncated QCD with a single
massless Dirac quark. Assuming the validity of the above observations,I
demonstrate how a dynamical SU(2)_{fl} symmetry could emerge for massive spin-1
mesons without contradicting general principles.


title: StreamingBandit; Experimenting with Bandit Policies

abstract:
  A large number of statistical decision problems in the social sciences and
beyond can be framed as a (contextual) multi-armed bandit problem. However, it
is notoriously hard to develop and evaluate policies that tackle these types of
problem, and to use such policies in applied studies. To address this issue,
this paper introduces StreamingBandit, a Python web application for developing
and testing bandit policies in field studies. StreamingBandit can sequentially
select treatments using (online) policies in real time. Once StreamingBandit is
implemented in an applied context, different policies can be tested, altered,
nested, and compared. StreamingBandit makes it easy to apply a multitude of
bandit policies for sequential allocation in field experiments, and allows for
the quick development and re-use of novel policies. In this article, we detail
the implementation logic of StreamingBandit and provide several examples of its
use.


title: Inference Networks for Sequential Monte Carlo in Graphical Models

abstract:
  We introduce a new approach for amortizing inference in directed graphical
models by learning heuristic approximations to stochastic inverses, designed
specifically for use as proposal distributions in sequential Monte Carlo
methods. We describe a procedure for constructing and learning a structured
neural network which represents an inverse factorization of the graphical
model, resulting in a conditional density estimator that takes as input
particular values of the observed random variables, and returns an
approximation to the distribution of the latent variables. This recognition
model can be learned offline, independent from any particular dataset, prior to
performing inference. The output of these networks can be used as
automatically-learned high-quality proposal distributions to accelerate
sequential Monte Carlo across a diverse range of problem settings.


title: Superhumps and their Evolution during Superoutbursts

abstract:
  Light curves of superhumps and their evolution during superoutbursts are
analyzed by decomposing them into their Fourier components, including the
fundamental mode and the first three overtones. The amplitudes of the
fundamental mode are found to decrease significantly during superoutburst while
those of the overtones remain practically constant. The phases of maxima of the
fundamental mode {\it increase} systematically during superoutburst while those
of the overtones -- systematically {\it decrease}. The combination of the two
effects is responsible for the characteristic evolution of superhump light
curves: the appearance and growth of the secondary humps and the spurious phase
jumps in the (O-C) diagrams. Two intrepretations are possible. Either that
instead of just one superhump period $P_{sh}$ there are four periods $P_k$
which resemble -- but are significantly different from -- the fundamental mode
and the first three overtones of $P_{sh}$. Or -- more likely -- that those
time-dependent phase shifts are genuine.


title: Cognitive Architecture for Mutual Modelling

abstract:
  In social robotics, robots needs to be able to be understood by humans.
Especially in collaborative tasks where they have to share mutual knowledge.
For instance, in an educative scenario, learners share their knowledge and they
must adapt their behaviour in order to make sure they are understood by others.
Learners display behaviours in order to show their understanding and teachers
adapt in order to make sure that the learners' knowledge is the required one.
This ability requires a model of their own mental states perceived by others:
\textit{"has the human understood that I(robot) need this object for the task
or should I explain it once again ?"} In this paper, we discuss the importance
of a cognitive architecture enabling second-order Mutual Modelling for
Human-Robot Interaction in educative contexts.


title:
$S$-Functions, Spectral Functions of Hyperbolic Geometry, and Vertex
  Operators with Applications to Structure for Weyl and Orthogonal Group
  Invariants

abstract:
  In this paper we analyze the quantum homological invariants (the Poincar\'e
polynomials of the $\mathfrak{sl}_N$ link homology). In the case when the
dimensions of homologies of appropriate topological spaces are precisely known,
the procedure of the calculation of the Kovanov-Rozansky type homology, based
on the Euler-Poincar\'e formula can be appreciably simplified. We express the
formal character of the irreducible tensor representation of the classical
groups in terms of the symmetric and spectral functions of hyperbolic geometry.
On the basis of Labastida-Mari\~{n}o-Ooguri-Vafa conjecture, we derive a
representation of the Chern-Simons partition function in the form of an
infinite product in terms of the Ruelle spectral functions (the cases of a
knot, unknot, and links have been considered). We also derive an
infinite-product formula for the orthogonal Chern-Simons partition functions
and analyze the singularities and the symmetry properties of the
infinite-product structures.


title:
On the Hardness of Partially Dynamic Graph Problems and Connections to
  Diameter

abstract:
  Conditional lower bounds for dynamic graph problems has received a great deal
of attention in recent years. While many results are now known for the
fully-dynamic case and such bounds often imply worst-case bounds for the
partially dynamic setting, it seems much more difficult to prove amortized
bounds for incremental and decremental algorithms. In this paper we consider
partially dynamic versions of three classic problems in graph theory. Based on
popular conjectures we show that:
  -- No algorithm with amortized update time $O(n^{1-\varepsilon})$ exists for
incremental or decremental maximum cardinality bipartite matching. This
significantly improves on the $O(m^{1/2-\varepsilon})$ bound for sparse graphs
of Henzinger et al. [STOC'15] and $O(n^{1/3-\varepsilon})$ bound of Kopelowitz,
Pettie and Porat. Our linear bound also appears more natural. In addition, the
result we present separates the node-addition model from the edge insertion
model, as an algorithm with total update time $O(m\sqrt{n})$ exists for the
former by Bosek et al. [FOCS'14].
  -- No algorithm with amortized update time $O(m^{1-\varepsilon})$ exists for
incremental or decremental maximum flow in directed and weighted sparse graphs.
No such lower bound was known for partially dynamic maximum flow previously.
Furthermore no algorithm with amortized update time $O(n^{1-\varepsilon})$
exists for directed and unweighted graphs or undirected and weighted graphs.
  -- No algorithm with amortized update time $O(n^{1/2 - \varepsilon})$ exists
for incremental or decremental $(4/3-\varepsilon')$-approximating the diameter
of an unweighted graph. We also show a slightly stronger bound if node
additions are allowed. [...]


title: On parametric extensions over number fields

abstract:
  Given a number field $F$, a finite group $G$ and an indeterminate $T$, {\it{a
$G$-parametric extension over $F$}} is a finite Galois extension $E/F(T)$ with
Galois group $G$ and $E/F$ regular that has all the Galois extensions of $F$
with Galois group $G$ among its specializations. We are mainly interested in
producing non-$G$-parametric extensions, which relates to classical questions
in inverse Galois theory like the Beckmann-Black problem. Building on a
strategy developed in previous papers, we show that there exists at least one
non-$G$-parametric extension over $F$ for a given non-trivial finite group $G$
and a given number field $F$ under the sole necessary condition that $G$ occurs
as the Galois group of a Galois extension $E/F(T)$ with $E/F$ regular.


title: Growth of Epitaxial Graphene: Theory and Experiment

abstract:
  A detailed review of the literature for the last 5-10 years on epitaxial
growth of graphene is presented. Both experimental and theoretical aspects
related to growth on transition metals and on silicon carbide are thoroughly
reviewed. Thermodynamic and kinetic aspects of growth on all these materials,
where possible, are discussed. To make this text useful for a wider audience, a
range of important experimental techniques that have been used over the last
decade to grow (e.g. CVD, TPG and segregation) and characterize (STM, LEEM,
etc.) graphene are reviewed, and a critical survey of the most important
theoretical techniques is given. Finally, we critically discuss various
unsolved problems related to growth and its mechanism which we believe require
proper attention in future research.


title: Online Bounded Analysis

abstract:
  Though competitive analysis is often a very good tool for the analysis of
online algorithms, sometimes it does not give any insight and sometimes it
gives counter-intuitive results. Much work has gone into exploring other
performance measures, in particular targeted at what seems to be the core
problem with competitive analysis: the comparison of the performance of an
online algorithm is made to a too powerful adversary. We consider a new
approach to restricting the power of the adversary, by requiring that when
judging a given online algorithm, the optimal offline algorithm must perform as
well as the online algorithm, not just on the entire final request sequence,
but also on any prefix of that sequence. This is limiting the adversary's usual
advantage of being able to exploit that it knows the sequence is continuing
beyond the current request. Through a collection of online problems, including
machine scheduling, bin packing, dual bin packing, and seat reservation, we
investigate the significance of this particular offline advantage.


title: Distributed Deep Learning Using Synchronous Stochastic Gradient Descent

abstract:
  We design and implement a distributed multinode synchronous SGD algorithm,
without altering hyper parameters, or compressing data, or altering algorithmic
behavior. We perform a detailed analysis of scaling, and identify optimal
design points for different networks. We demonstrate scaling of CNNs on 100s of
nodes, and present what we believe to be record training throughputs. A 512
minibatch VGG-A CNN training run is scaled 90X on 128 nodes. Also 256 minibatch
VGG-A and OverFeat-FAST networks are scaled 53X and 42X respectively on a 64
node cluster. We also demonstrate the generality of our approach via
best-in-class 6.5X scaling for a 7-layer DNN on 16 nodes. Thereafter we attempt
to democratize deep-learning by training on an Ethernet based AWS cluster and
show ~14X scaling on 16 nodes.


title:
Exchange magnon induced resistance asymmetry in permalloy spin-Hall
  oscillators

abstract:
  We investigate magnetization dynamics in a spin-Hall oscillator using a
direct current measurement as well as conventional microwave spectrum analysis.
When the current applies an anti-damping spin-transfer torque, we observe a
change in resistance which we ascribe to the excitation of incoherent exchange
magnons. A simple model is developed based on the reduction of the effective
saturation magnetization, quantitatively explaining the data. The observed
phenomena highlight the importance of exchange magnons on the operation of
spin-Hall oscillators.


title: 3D Weak Lensing: Modified Theories of Gravity

abstract:
  Weak lensing (WL) promises to be a particularly sensitive probe of both the
growth of large scale structure (LSS) as well as the fundamental relation
between matter density perturbations and metric perturbations, thus providing a
powerful tool with which we may constrain modified theories of gravity (MG) on
cosmological scales. Future deep, wide-field WL surveys will provide an
unprecedented opportunity to constrain deviations from General Relativity (GR).
Employing a three-dimensional (3D) analysis based on the spherical
Fourier-Bessel (sFB) expansion, we investigate the extent to which MG theories
will be constrained by a typical 3D WL survey configuration including noise
from the intrinsic ellipticity distribution $\sigma_{\epsilon}$ of source
galaxies. Here we focus on two classes of screened theories of gravity: i)
$f(R)$ chameleon models and ii) environmentally dependent dilaton models. We
use one-loop perturbation theory combined with halo models in order to
accurately model the evolution of matter power-spectrum with redshift in these
theories. Using a Fisher information matrix based approach, we show that for an
all-sky spectroscopic survey, the parameter $f_{R_0}$ can be constrained in the
range $f_{R_0}< 5\times 10^{-6}(9\times 10^{-6})$ for $n=1(2)$ with a 3$\sigma$
confidence level. This can be achieved by using relatively low order angular
harmonics $\ell<100$. Including higher order harmonics $\ell>100$ can further
tighten the constraints, making them comparable to current solar-system
constraints. We also employ a Principal Component Analysis (PCA) in order to
study the parameter degeneracies in the MG parameters. Our results can
trivially be extended to other MG theories, such as the K-mouflage models. The
confusion from intrinsic ellipticity correlation and modification of the matter
power-spectrum at small scale due to feedback mechanisms is briefly discussed.


title: Dense granular flow rheology in turbulent bedload transport

abstract:
  The local granular rheology is investigated numerically in turbulent bedload
transport. Considering spherical particles, steady uniform configurations are
simulated using a coupled fluid-discrete-element model. The stress tensor is
computed as a function of the depth for a series of simulations varying the
Shields number, the specific density and the particle diameter. The results are
analyzed in the framework of the $\mu(I)$ rheology and exhibit a collapse of
both the shear to normal stress ratio and the solid volume fraction over a wide
range of inertial numbers. Contrary to expectations, the effect of the
interstitial fluid on the granular rheology is shown to be negligible,
supporting recent work suggesting the absence of a clear transition between the
free-fall and turbulent regime. In addition, data collapse is observed up to
unexpectedly high inertial numbers $I\sim2$, challenging the existing
conceptions and parametrization of the $\mu(I)$ rheology. Focusing upon bedload
transport modelling, the results are pragmatically analyzed in the $\mu(I)$
framework in order to propose a granular rheology for bedload transport. The
proposed rheology is tested using a 1D volume-averaged two-phase continuous
model, and is shown to accurately reproduce the dense granular flow profiles
and the sediment transport rate over a wide range of Shields numbers. The
present contribution represents a step in the upscaling process from
particle-scale simulations toward large-scale applications involving complex
flow geometry.


title:
Daughter Fragmentation is Unlikely To Occur in Self-Gravitating
  Circumstellar Discs

abstract:
  Circumstellar discs are thought to be self-gravitating at very early times.
If the disc is relatively cool, extended and accreting sufficiently rapidly, it
can fragment into bound objects of order a few Jupiter masses and upwards.
Given that the fragment's initial angular momentum is non-zero, and it will
continue to accrete angular momentum from the surrounding circumstellar disc,
we should expect that the fragment will also possess a relatively massive disc
at early times. Therefore, we can ask: is disc fragmentation a hierarchical
process? Or, can a disc fragment go on to produce its own self-gravitating
circumfragmentary disc that produces daughter fragments?
  We investigate this using a set of nested 1D self-gravitating disc models. We
calculate the radial structure of a marginally stable, self-gravitating
circumstellar disc, and compute its propensity to fragmentation. We use this
data to construct the local fragment properties at this radius. For each
circumstellar disc model that results in fragmentation, we then compute a
marginally stable self-gravitating circumfragmentary disc model.
  In general, the circumfragmentary discs are geometrically thick and truncated
inside the Hill radius, and are hence stable against daughter fragmentation.
The typical steady-state accretion rate is between 0.1 and 10 percent of the
local circumstellar disc accretion rate. The lifetime of the circumfragmentary
discs' self-gravitating phase is somewhat less than 0.1 Myr, quite comparable
with that of the circumstellar disc. We should therefore expect that disc
fragments will not produce satellites via gravitational instability, but
equally the self-gravitating phase of circumfragmentary discs is likely to
affect the properties of satellites subsequently formed via core accretion.


title: Zonal flows as statistical equilibria

abstract:
  Zonal jets are striking and beautiful examples of the propensity for
geophysical turbulent flows to spontaneously self-organize into robust, large
scale coherent structures. There exist many dynamical mechanisms for the
formation of zonal jets: statistical theories (kinetic approaches, second order
or larger oder closures), deterministic approaches (modulational instability,
$\beta$-plumes, radiating instability, zonostrophic turbulence, and so on). A
striking remark is that all these different dynamical approaches, each of them
possibly relevant in some specific regimes, lead to the same kind of final jet
structures. Is it then possible to have a more general explanation of why all
these different dynamical regimes, from fully turbulent flows to gentle
quasilinear regime, consistently lead to the same jet attractors ? Equilibrium
statistical mechanics provides an answer to this general question. Here we we
present the salient features of this theory and review applications of this
approach to the description of zonal jets. We show that equilibrium states on a
beta plane or a sphere are usually zonal or quasi-zonal, and that increasing
the energy leads to bifurcations breaking the zonal symmetry.


title: Stability result for sets with $3A\ne{\mathbb Z}_5^n$

abstract:
  As an easy corollary of Kneser's Theorem, if $A$ is a subset of the
elementary abelian group ${\mathbb Z}_5^n$ of density $5^{-n}|A|>0.4$, then
$3A={\mathbb Z}_5^n$. We establish the complementary stability result: if
$5^{-n}|A|>0.3$ and $3A\ne{\mathbb Z}_5^n$, then $A$ is contained in a union of
two cosets of an index-$5$ subgroup of ${\mathbb Z}_5^n$. Here the density
bound $0.3$ is sharp.
  Our argument combines combinatorial reasoning with a somewhat non-standard
application of the character sum technique.


title:
On the uniqueness of probability measure solutions to Liouville's
  equation of Hamiltonian PDEs

abstract:
  In this paper, we give a uniqueness result to a transport equation fulfilled
by probability measure on a infinite dimensional Hilbert space. Main arguments
are based on projective aspects and a probabilistic representation of the
solutions. It extends the work of Maniglia, which concerns the finite
dimensional case and the work of Ammari and Nier, for a wider class of velocity
field.


title:
A Method for Detecting Life-Threatening Signals in Serum Potassium Level
  after Myocardial Infarction

abstract:
  Clinical guidelines recommend maintaining serum potassium levels between 4.0
and 5.0 mEq/L in patients with acute myocardial infarction (MI). These
guidelines are based on recent studies that found significant associations
between crossing of absolute potassium limits (by in-hospital mean or by
min/max values) and mortality. This paper investigates a different approach: we
hypothesized that a change in the potassium level may be a harbinger of short
survivability, rather than crossing of absolute boundaries. Our objectives
were: (1) to examine if a "change in mean" indicator has the ability to
distinguish between survivors and non-survivors of MI hospitalization, and if
so, (2) to formulate a framework for detecting life-threatening changes in
potassium level of patients hospitalized with MI. The study included 195
patients who were hospitalized for MI from 2002 to 2014, with at least 40
potassium measurements (i.e., severely ill). In a retrospective analysis we
found evidence that the "change in mean" criterion significantly discriminated
between survivors and non-survivors. A threshold for raising an alarm was
specified by plotting an ROC curve and choosing the value that yields the best
combination of sensitivity and specificity. In this case, the method detected
~80% of the patients that eventually died, while wrongly alerting for only ~40%
of the survivors. The proposed approach is not intended for replacing the
absolute-level protocols but to add valuable knowledge to cardiologists.


title: Quantitative estimates for the flux of TASEP with dilute site disorder

abstract:
  We prove that the flux function of the totally asymmetric simple exclusion
process (TASEP) with site disorder exhibits a flat segment for sufficiently
dilute disorder. For high dilution, we obtain an accurate description of the
flux. The result is established undera decay assumption of the maximum current
in finite boxes, which is implied in particular by a sufficiently slow power
tail assumption on the disorder distribution near its minimum. To circumvent
the absence of explicit invariant measures, we use an original renormalization
procedure and some ideas inspired by homogenization.


title: On (p, q) Baskakov-Durrmeyer-Stancu Operators

abstract:
  In the present paper, we introduce the generalized form of $(p,q)$
Baskakov-Durrmeyer Operators with Stancu type parameters. We derived the local
and global approximation properties of these operators and obtained the
convergence rate and behaviour for the Lipschitz functions. Moreover, we give
comparisons and some illustrative graphics for the convergence of operators to
some function.


title: Fluctuations of large-scale jets in the stochastic 2D Euler equation

abstract:
  Two-dimensional turbulence in a rectangular domain self-organises into
large-scale unidirectional jets. While several results are present to
characterize the mean jets velocity profile, much less is known about the
fluctuations. We study jets dynamics in the stochastically forced
two-dimensional Euler equations. In the limit where the average jets velocity
profile evolves slowly with respect to turbulent fluctuations, we employ a
multi-scale (kinetic theory) approach, which relates jet dynamics to the
statistics of Reynolds stresses. We study analytically the Gaussian
fluctuations of Reynolds stresses and predict the spatial structure of the jets
velocity covariance. Our results agree qualitatively well with direct numerical
simulations, clearly showing that the jets velocity profile are enhanced away
from the stationary points of the average velocity profile. A numerical test of
our predictions at quantitative level seems out of reach at the present day.


title: Local Structure and Spin Transition in Fe2O3 Hematite at High-Pressure

abstract:
  The pressure evolution of the local structure of Fe2O3 hematite has been
determined for the first time by extended x-ray absorption fine structure up to
79 GPa. The comparison to the different high-pressure forms proposed in the
literature suggests that the orthorhombic structure with space group Aba2 is
the most probable. The crossover from Fe high-spin to low-spin states with
pressure increase has been monitored from the pre-edge region of the Fe K-edge
absorption spectra. The "simultaneous" comparison with the local structural
changes allows us to definitively conclude that it is the electronic transition
that drives the structural transition and not viceversa.


title:
Sensing Throughput Optimization in Fading Cognitive Multiple Access
  Channels With Energy Harvesting Secondary Transmitters

abstract:
  The paper investigates the problem of maximizing expected sum throughput in a
fading multiple access cognitive radio network when secondary user (SU)
transmitters have energy harvesting capability, and perform cooperative
spectrum sensing. We formulate the problem as maximization of sum-capacity of
the cognitive multiple access network over a finite time horizon subject to a
time averaged interference constraint at the primary user (PU) and almost sure
energy causality constraints at the SUs. The problem is a mixed integer
non-linear program with respect to two decision variables namely spectrum
access decision and spectrum sensing decision, and the continuous variables
sensing time and transmission power. In general, this problem is known to be NP
hard. For optimization over these two decision variables, we use an exhaustive
search policy when the length of the time horizon is small, and a heuristic
policy for longer horizons. For given values of the decision variables, the
problem simplifies into a joint optimization on SU \textit{transmission power}
and \textit{sensing time}, which is non-convex in nature. We solve the
resulting optimization problem as an alternating convex optimization problem
for both non-causal and causal channel state information and harvested energy
information patterns at the SU base station (SBS) or fusion center (FC). We
present an analytic solution for the non-causal scenario with infinite battery
capacity for a general finite horizon problem.We formulate the problem with
causal information and finite battery capacity as a stochastic control problem
and solve it using the technique of dynamic programming. Numerical results are
presented to illustrate the performance of the various algorithms.


title: Clique coloring $B_1$-EPG graphs

abstract:
  We consider the problem of clique coloring, that is, coloring the vertices of
a given graph such that no (maximal) clique of size at least two is
monocolored. It is known that interval graphs are $2$-clique colorable. In this
paper we prove that $B_1$-EPG graphs (edge intersection graphs of paths on a
grid, where each path has at most one bend) are $4$-clique colorable. Moreover,
given a $B_1$-EPG representation of a graph, we provide a linear time algorithm
that constructs a $4$-clique coloring of it.


title: Multiplicative bases and an Erd\H{o}s problem

abstract:
  In this paper we investigate how small the density of a multiplicative basis
of order $h$ can be in $\{1,2,\dots,n\}$ and in $\mathbb{Z}^+$. Furthermore, a
related problem of Erd\H os is also studied: How dense can a set of integers
be, if none of them divides the product of $h$ others?


title: Variational inference for Monte Carlo objectives

abstract:
  Recent progress in deep latent variable models has largely been driven by the
development of flexible and scalable variational inference methods. Variational
training of this type involves maximizing a lower bound on the log-likelihood,
using samples from the variational posterior to compute the required gradients.
Recently, Burda et al. (2016) have derived a tighter lower bound using a
multi-sample importance sampling estimate of the likelihood and showed that
optimizing it yields models that use more of their capacity and achieve higher
likelihoods. This development showed the importance of such multi-sample
objectives and explained the success of several related approaches.
  We extend the multi-sample approach to discrete latent variables and analyze
the difficulty encountered when estimating the gradients involved. We then
develop the first unbiased gradient estimator designed for importance-sampled
objectives and evaluate it at training generative and structured output
prediction models. The resulting estimator, which is based on low-variance
per-sample learning signals, is both simpler and more effective than the NVIL
estimator proposed for the single-sample variational objective, and is
competitive with the currently used biased estimators.


title: Fermat's Last Theorem for the Exponent 3

abstract:
  `Fermat's Last Theorem for the exponent 3 has received numerous proofs, the
most common of which being either in Euler's or in Gauss' style. This latter
works entirely in the ring of integers of the quadratic field generated by the
square root of -3. A proof in Euler's style is based on a central lemma related
to properties of the quadratic form x^2 + 3y^2, then it proceeds by descent by
considering Two main cases. In the present version, the central lemma receives
a short proof and the classical proof by descent in Two main cases boils down
to a One-case proof.


title:
Improving Trajectory Modelling for DNN-based Speech Synthesis by using
  Stacked Bottleneck Features and Minimum Generation Error Training

abstract:
  We propose two novel techniques --- stacking bottleneck features and minimum
generation error training criterion --- to improve the performance of deep
neural network (DNN)-based speech synthesis. The techniques address the related
issues of frame-by-frame independence and ignorance of the relationship between
static and dynamic features, within current typical DNN-based synthesis
frameworks. Stacking bottleneck features, which are an acoustically--informed
linguistic representation, provides an efficient way to include more detailed
linguistic context at the input. The minimum generation error training
criterion minimises overall output trajectory error across an utterance, rather
than minimising the error per frame independently, and thus takes into account
the interaction between static and dynamic features. The two techniques can be
easily combined to further improve performance. We present both objective and
subjective results that demonstrate the effectiveness of the proposed
techniques. The subjective results show that combining the two techniques leads
to significantly more natural synthetic speech than from conventional DNN or
long short-term memory (LSTM) recurrent neural network (RNN) systems.


title:
Periodic perturbations of unbounded Jacobi matrices II: Formulas for
  density

abstract:
  We give formulas for the density of the measure of orthogonality for
orthonormal polynomials with unbounded recurrence coefficients. The formulas
involve limits of appropriately scaled Tur\'an determinants or Christoffel
functions. Exact asymptotics of the polynomials and numerical examples are also
provided.


title:
Large and uniform optical emission shifts in quantum dots externally
  strained along their growth axis

abstract:
  We introduce a method which enables to directly compare the impact of elastic
strain on the optical properties of distinct quantum dots (QDs). Specifically,
the QDs are integrated in a cross-section of a semiconductor core wire which is
surrounded by an amorphous straining shell. Detailed numerical simulations show
that, thanks to the mechanical isotropy of the shell, the strain field in a
core section is homogeneous. Furthermore, we use the core material as an in
situ strain gauge, yielding reliable values for the emitter energy tuning
slope. This calibration technique is applied to self-assembled InAs QDs
submitted to incremental tensile strain along their growth axis. In contrast to
recent studies conducted on similar QDs stressed perpendicularly to their
growth axis, optical spectroscopy reveals 5-10 times larger tuning slopes, with
a moderate dispersion. These results highlight the importance of the stress
direction to optimise QD response to applied strain, with implications both in
static and dynamic regimes. As such, they are in particular relevant for the
development of wavelength-tunable single photon sources or hybrid QD
opto-mechanical systems.


title:
Examining nuclear effects in neutrino interactions with transverse
  kinematic imbalance

abstract:
  We present a Monte Carlo truth study examining nuclear effects in
charged-current neutrino interactions using observables constructed in the
transverse plane. Three distributions are introduced that show very weak
dependence on neutrino flux and its associated uncertainty. Measurements
comparing these distributions between quasi-elastic-like and single charged
pion final states will provide new constraints of nuclear effects. It is
suggested that the on-axis position in the NuMI beam provides the correct flux
to take advantage of this reduced energy dependence in measuring nuclear
effect-generated transverse imbalances.