title:
Arrival time differences between gravitational waves and electromagnetic
  signals due to gravitational lensing

abstract:
  In this study, we demonstrate that general relativity predicts arrival time
differences between gravitational wave (GW) and electromagnetic (EM) signals
caused by the wave effects in gravitational lensing. The GW signals can arrive
$earlier$ than the EM signals in some cases if the GW/EM signals have passed
through a lens, even if both signals were emitted simultaneously by a source.
GW wavelengths are much larger than EM wavelengths; therefore, the propagation
of the GWs does not follow the laws of geometrical optics, including the
Shapiro time delay, if the lens mass is less than approximately $10^5 {\rm
M}_\odot (f/{\rm Hz})^{-1}$, where $f$ is the GW frequency. The arrival time
difference can reach $\sim 0.1 \, {\rm s} \, (f/{\rm Hz})^{-1}$ if the signals
have passed by a lens of mass $\sim 8000{\rm M}_\odot (f/{\rm Hz})^{-1}$ with
the impact parameter smaller than the Einstein radius; therefore, it is more
prominent for lower GW frequencies. For example, when a distant super massive
black hole binary (SMBHB) in a galactic center is lensed by an intervening
galaxy, the time lag becomes of the order of $10$ days. Future pulsar timing
arrays including SKA (the Square Kilometre Array) and X-ray detectors may
detect several time lags by measuring the orbital phase differences between the
GW/EM signals in the SMBHBs. Gravitational lensing imprints a characteristic
modulation on a chirp waveform; therefore, we can deduce whether a measured
arrival time lag arises from intrinsic source properties or gravitational
lensing. Determination of arrival time differences would be extremely useful in
multimessenger observations and tests of general relativity.


title: Rolling axions during inflation: perturbativity and signatures

abstract:
  The motion of a pseudo-scalar field $X$ during inflation naturally induces a
significant amplification of the gauge fields to which it is coupled. The
amplified gauge fields can source characteristic scalar and tensor primordial
perturbations. Several phenomenological implications have been discussed in the
cases in which (i) $X$ is the inflation, and (ii) $X$ is a field different from
the inflation, that experiences a temporary speed up during inflation. In this
second case, visible sourced gravitational waves (GW) can be produced at the
CMB scales without affecting the scalar perturbations, even if the scale of
inflation is several orders of magnitude below what is required to produce a
visible vacuum GW signal. Perturbativity considerations can be used to limit
the regime in which these results are under perturbative control. We revised
limits recently claimed for the case (i), and we extend these considerations to
the case (ii). We show that, in both cases, these limits are satisfied by the
applications that generate signals at CMB scales. Applications that generate
gravitational waves and primordial black holes at much smaller scales are at
the limit of the validity of this perturbativity analysis, so we expect those
results to be valid up to possibly order one corrections.


title:
Electronic topological transitions in Nb$_3$X (X = Al, Ga, In, Ge and
  Sn) under compression investigated by first principles calculations

abstract:
  First principles electronic structure calculations of A-15 type Nb$_3$X (X =
Al, Ga, In, Ge and Sn) compounds are performed at ambient and high pressures.
Mechanical stability is confirmed in all the compounds both at ambient as well
as under compression from the calculated elastic constants. We have observed
four holes and two electron Fermi surfaces (FS) for all the compounds studied
and FS nesting feature is observed at M and along X - $\Gamma$ in all the
compounds. A continuous change in the FS topology is observed under pressure in
all the compounds which is also reflected in the calculated elastic constants
and density of states under pressure indicating the Electronic topological
transitions (ETT). The ETT observed at around 21.5 GPa, 17.5 GPa in Nb$_3$Al
and Nb$_3$Ga are in good agreement with the anomalies observed by the
experiments.


title: Maass form twisted Shintani $\mathscr{L}$-functions

abstract:
  The Maass-form twisted Shintani $\mathscr{L}$-functions are introduced, and
some of their analytic properties are studied. These functions contain data
regarding the distribution of shapes of cubic rings.


title:
Analysis of applications suitable for mobile learning of preschool
  children

abstract:
  This article considers the use of mobile learning in Bulgarian education by
young children. The most used mobile operating systems are analyzed. Also some
of the most used existing applications suitable for mobile learning of
preschool children are presented and classified. Keywords: Mobile applications
for preschool children, mobile learning.


title:
Mathematical Modeling of Perifusion Cell Culture Experiments on GnRH
  Signaling

abstract:
  The effects of pulsatile GnRH stimulation on anterior pituitary cells are
studied using perifusion cell cultures, where constantly moving medium over the
immo- bilized cells allows intermittent GnRH delivery. The LH content of the
outgoing medium serves as a readout of the GnRH signaling pathway activation in
the cells. The challenge lies in relating the LH content of the medium leaving
the chamber to the cellular processes producing LH secretion. To investigate
this relation we developed and analyzed a mathematical model consisting of
coupled partial differential equations describing LH secretion in a perifusion
cell culture. We match the mathematical model to three different data sets and
give cellular mechanisms that explain the data. Our model illustrates the
importance of the negative feedback in the signaling pathway and receptor
desensitization. We demonstrate that different LH outcomes in oxytocin and GnRH
stimulations might originate from different receptor dynamics and
concentration. We ana- lyze the model to understand the influence of
parameters, like the velocity of the medium flow or the fraction collection
time, on the LH outcomes. We show that slow velocities lead to high LH
outcomes. Also, we show that fraction collection times, which do not divide the
GnRH pulse period evenly, lead to irregularities in the data. We examine the
influence of the rate of binding and dissociation of GnRH on the GnRH movement
down the chamber. Our model serves as an important tool that can help in the
design of perifusion experiments and the interpretation of results.


title: Rectangular Statistical Cartograms in R: The recmap Package

abstract:
  Cartogram drawing is a technique for showing geography-related statistical
information, such as demographic and epidemiological data. The idea is to
distort a map by resizing its regions according to a statistical parameter by
keeping the map recognizable. This article describes an R package implementing
an algorithm called RecMap which approximates every map region by a rectangle
where the area corresponds to the given statistical value (maintain zero
cartographic error). The package implements the computationally intensive tasks
in C++. This paper's contribution is that it demonstrates on real and synthetic
maps how recmap can be used, how it is implemented and used with other
statistical packages.


title: Complete permutation polynomials from exceptional polynomials

abstract:
  We classify complete permutation polynomials of type
$aX^{\frac{q^n-1}{q-1}+1}$ over the finite field with $q^n$ elements, for $n+1$
a prime and $n^4 < q$. For the case $n+1$ a power of the characteristic we
study some known families. We also classify indecomposable exceptional
polynomials of degree $8$ and $9$.


title:
A statistical model of three-dimensional anisotropy and intermittency in
  strong Alfv\'enic turbulence

abstract:
  We propose a simple statistical model of three-dimensionally anisotropic,
intermittent, strong Alfv\'enic turbulence, incorporating both critical balance
and dynamic alignment. Our model is based on log-Poisson statistics for
Elsasser-field increments along the magnetic field. We predict the scalings of
Elsasser-field conditional two-point structure functions with point separations
in all three directions in a coordinate system locally aligned with the
direction of the magnetic field and of the fluctuating fields and obtain good
agreement with numerical simulations. We also derive a scaling of the parallel
coherence scale of the fluctuations, $l_\parallel \propto \lambda^{1/2}$, where
$\lambda$ is the perpendicular scale. This is indeed observed for the bulk of
the fluctuations in numerical simulations.


title:
Attack resilient architecture to replace embedded Flash with STTRAM in
  homogeneous IoTs

abstract:
  Spin-Transfer Torque RAM (STTRAM) is an emerging Non-Volatile Memory (NVM)
technology that provides better endurance, write energy and performance than
traditional NVM technologies such as Flash. In embedded application such as
microcontroller SoC of Internet of Things (IoT), embedded Flash (eFlash) is
widely employed. However, eFlash is also associated with cost. Therefore,
replacing eFlash with STTRAM is desirable in IoTs for power-efficiency.
Although promising, STTRAM brings several new security and privacy challenges
that pose a significant threat to sensitive data in memory. This is inevitable
due to the underlying dependency of this memory technology on environmental
parameters such as temperature and magnetic fields that can be exploited by an
adversary to tamper with the program and data. In this paper, we investigate
these attacks and propose a novel memory architecture for attack resilient IoT
network. The information redundancy present in a homogeneous peer-to-peer
connected IoT network is exploited to restore the corrupted memory of any IoT
node when under attack. We are able to build a failsafe IoT system with STTRAM
based program memory which allows guaranteed execution of all the IoT nodes
without complete shutdown of any node under attack. Experimental results using
commercial IoT boards demonstrate the latency and energy overhead of the attack
recovery process.


title:
Multi-Nucleon Short-Range Correlation Model for Nuclear Spectral
  Functions: I. Theoretical Framework

abstract:
  We develop a theoretical approach for nuclear spectral functions at high
missing momenta and removal energies based on the multi-nucleon short-range
correlation~(SRC) model. The approach is based on the effective Feynman
diagrammatic method which allows to account for the relativistic effects
important in the SRC domain. In addition to two-nucleon SRC with center of mass
motion we derive also the contribution of three-nucleon SRCs to the nuclear
spectral functions. The latter is modeled based on the assumption that 3N SRCs
are a product of two sequential short range NN interactions. This approach
allowed us to express the 3N SRC part of the nuclear spectral function as a
convolution of two NN SRCs. Thus the knowledge of 2N SRCs allows us to model
both two- and three-nucleon SRC contributions to the spectral function. The
derivations of the spectral functions are based on the two theoretical
frameworks in evaluating covariant Feynman diagrams: In the first, referred as
virtual nucleon approximation, we reduce Feynman diagrams to the time ordered
noncovariant diagrams by evaluating nucleon spectators in the SRC at their
positive energy poles, neglecting explicitly the contribution from vacuum
diagrams. In the second approach, referred as light-front approximation, we
formulate the boost invariant nuclear spectral function in the light-front
reference frame in which case the vacuum diagrams are generally suppressed and
the bound nucleon is described by its light-cone variables such as momentum
fraction, transverse momentum and invariant mass.


title:
The Evolution Of The Faint End Of The UV Luminosity Function During The
  Peak Epoch Of Star Formation (1<z<3)

abstract:
  [Abridged] We present a robust measurement of the rest-frame UV luminosity
function (LF) and its evolution during the peak epoch of cosmic star formation
at 1<z<3. We use our deep near ultraviolet imaging from WFC3/UVIS on the Hubble
Space Telescope (HST) and existing ACS/WFC and WFC3/IR imaging of three lensing
galaxy clusters, Abell 2744 and MACSJ0717 from the Hubble Frontier Field survey
and Abell 1689. We use photometric redshifts to identify 780 ultra-faint
galaxies with $M_{UV}$<-12.5 AB mag at 1<z<3. From these samples, we identified
5 new, faint, multiply imaged systems in A1689. We compute the rest-frame UV LF
and find the best-fit faint-end slopes of $\alpha=-1.56\pm0.04$,
$\alpha=-1.72\pm0.04$ and $\alpha=-1.94\pm0.06$ at 1.0<z<1.6, 1.6<z<2.2 and
2.2<z<3.0, respectively. Our results demonstrate that the UV LF becomes steeper
from z\sim1.3 to z\sim2.6 with no sign of a turnover down to $M_{UV}=-14$ AB
mag. We further derive the UV LFs using the Lyman break "dropout" selection and
confirm the robustness of our conclusions against different selection
methodologies. Because the sample sizes are so large, and extend to such faint
luminosities, the statistical uncertainties are quite small, and systematic
uncertainties (due to the assumed size distribution, for example), likely
dominate. If we restrict our analysis to galaxies and volumes above > 50%
completeness in order to minimize these systematics, we still find that the
faint-end slope is steep and getting steeper with redshift, though with
slightly shallower (less negative) values ($\alpha=-1.55\pm0.06$,
$-1.69\pm0.07$ and $-1.79\pm0.08$ for $z\sim1.3$, 1.9 and 2.6, respectively).
Finally, we conclude that the faint star-forming galaxies with UV magnitudes of
$-18.5<M_{UV}<-12.5$ covered in this study, produce the majority (55%-60%) of
the unobscured UV luminosity density at 1<z<3.


title: Multi-Bit Read and Write Methodologies for Diode-STTRAM Crossbar Array

abstract:
  Crossbar arrays using emerging non-volatile memory technologies such as
Resistive RAM (ReRAM) offer high density, fast access speed and low-power.
However the bandwidth of the crossbar is limited to single-bit read/write per
access to avoid selection of undesirable bits. We propose a technique to
perform multi-bit read and write in a diode-STTRAM (Spin Transfer Torque RAM)
crossbar array. Simulation shows that the biasing voltage of half-selected
cells can be adjusted to improve the sense margin during read and thus reduce
the sneak path through the half-selected cells. In write operation, the
half-selected cells are biased with a pulse voltage source which increases the
write latency of these cells and enables to write 2-bits while keeping the
half-selected bits undisturbed. Simulation results indicate biasing the
half-selected cells by 700mV can enable reading as much as 512-bits while
sustaining 512x512 crossbar with 2.04 years retention. The 2-bit writing
requires pulsing by 50mV to optimize energy.


title:
Graphene-plasmon polaritons: From fundamental properties to potential
  applications

abstract:
  With the unique possibilities for controlling light in nanoscale devices,
graphene plasmonics has opened new perspectives to the nanophotonics community
with potential applications in metamaterials, modulators, photodetectors, and
sensors. This paper briefly reviews the recent exciting progress in graphene
plasmonics. We begin with a general description for optical properties of
graphene, particularly focusing on the dispersion of graphene-plasmon
polaritons. The dispersion relation of graphene-plasmon polaritons of spatially
extended graphene is expressed in terms of the local response limit with
intraband contribution. With this theoretical foundation of graphene-plasmon
polaritons, we then discuss recent exciting progress, paying specific attention
to the following topics: excitation of graphene plasmon polaritons,
electron-phonon interactions in graphene on polar substrates, and tunable
graphene plasmonics with applications in modulators and sensors. Finally, we
seek to address some of the apparent challenges and promising perspectives of
graphene plasmonics.


title: A Note on the Justification of the Eddy Current Model in Electrodynamics

abstract:
  The issue of justifying the eddy current approximation of Maxwell's equations
is re-considered in the time-dependent setting. Convergence of the solution
operators is shown in the sense of strong operator limits.


title: Anomalous refraction based on acoustic metasurfaces with membranes

abstract:
  The investigation of metasurface, which is of great current interest, has
opened up new degrees of freedom to research metamaterials. In this paper, we
propose an ultrathin acoustic metasurface consisting of a series of
structurally simple drum-like subunit cells. Eight units with different sizes
aer selected to realize discrete transmisson phase shifts ranging from 0 to 360
degrees ar 3.5 KHz. The designed metasurface is capable of manipulating sound
waves at will, including anomalous refraction and conversion of propagating
waves into surface waves, which can be predicted precisely by the generalized
Snell's law. It id worth noting that the total thickness of such planar
metasurface is approximately 1/5 of working wavelength, which may be beneficial
to the miniaturization and integration of acoustic equipment.


title:
A 3D Face Modelling Approach for Pose-Invariant Face Recognition in a
  Human-Robot Environment

abstract:
  Face analysis techniques have become a crucial component of human-machine
interaction in the fields of assistive and humanoid robotics. However, the
variations in head-pose that arise naturally in these environments are still a
great challenge. In this paper, we present a real-time capable 3D face
modelling framework for 2D in-the-wild images that is applicable for robotics.
The fitting of the 3D Morphable Model is based exclusively on automatically
detected landmarks. After fitting, the face can be corrected in pose and
transformed back to a frontal 2D representation that is more suitable for face
recognition. We conduct face recognition experiments with non-frontal images
from the MUCT database and uncontrolled, in the wild images from the PaSC
database, the most challenging face recognition database to date, showing an
improved performance. Finally, we present our SCITOS G5 robot system, which
incorporates our framework as a means of image pre-processing for face
analysis.


title:
Permutation-based cluster size correction for voxel-based lesion-symptom
  mapping

abstract:
  Voxel-based lesion-symptom mapping (VLSM) is a major method for studying
brain-behavior relationships that leverages modern neuroimaging analysis
techniques to build on the classic approach of examining the relationship
between location of brain damage and cognitive deficits. Testing an association
between deficit severity and lesion status in each voxel involves very many
individual tests and requires statistical correction for multiple comparisons.
Several strategies have been adapted from analysis of functional neuroimaging
data, though VLSM faces a more difficult trade-off between avoiding false
positives and statistical power (missing true effects). One such strategy is
using permutation to non-parametrically determine a null distribution of
cluster sizes, which is then used to establish a minimum cluster size
threshold. This strategy is intuitively appealing because it respects the
necessary spatial contiguity of stroke lesions and connects with the typical
cluster-based interpretation of VLSM results. We evaluated this strategy for
detecting true lesion-symptom relations using simulated deficit scores based on
percent damage to defined brain regions (BA 45 and BA 39) in a sample of 124
individuals with left hemisphere stroke. Even under the most conservative
settings tested here, the region identified by VLSM with cluster size
correction systematically extended well beyond the true region. As a result,
this strategy appears to be effective for ruling out situations with no true
lesion-symptom relations, but the spatial contiguity of stroke lesions may
cause identified lesion-symptom relations to extend beyond their true regions.


title: Non-Linear Compton Scattering in a Strong Rotating Electric Field

abstract:
  The non-linear Compton scattering rate in a rotating electric field is
explicitly calculated for the first time. For this purpose, a novel solution to
the Klein-Gordon equation in the presence of a rotating electric field is
applied. An analytical expression for the emission rate is obtained, as well as
a simplified approximation adequate for emplementation in kinetic codes. The
spectrum is numerically calculated for nowadays optical and X-ray laser
parameters. The results are compared to the standard Volkov-Ritus rate for a
particle in a plane wave, which is commonly assumed to be valid for a rotating
electric field under certain conditions. Subsequent deviations between the two
models, both in the radiated power and the spectral shape, are demonstrated.
First, the typical number of photons participating in the scattering process is
much smaller compared to the Volkov-Ritus rate, resulting in up to an order of
magnitude lower emitted power. Furthermore, our model predicts a discrete
harmonics spectrum for electrons with low asymptotic momentum compared to the
field amplitude. This discrete structure is a clear imprint of the electric
field frequency, as opposed to the Volkov-Ritus rate which reduces to the
constant crossed field rate for the physical conditions under consideration.
Our model predictions can be tested with present-days laser facilities.


title:
Demonstration of the enhanced Purcell factor in all-dielectric
  structures

abstract:
  The Purcell effect is usually described as a modification of the spontaneous
decay rate in the presence of a resonator. In plasmonics, this effect is
commonly associated with a large local-field enhancement in "hot spots" due to
the excitation of surface plasmons. However, high-index dielectric
nanostructures, which become the basis of all-dielectric nanophotonics, can not
provide high values of the local-field enhancement due to larger radiation
losses. Here, we demonstrate how to achieve a strong Purcell effect in
all-dielectric nanostructures, and show theoretically that the Purcell factor
can be increased by two orders of magnitude in a finite chain of silicon
nanoparticles. Using the eigenmode analysis for an infinite chain, we
demonstrate that the high Purcell factor regime is associated with a Van Hove
singularity. We perform a proof-of-concept experiment for microwave frequencies
and observe the 65-fold enhancement of the Purcell factor in a chain of 10
dielectric particles.


title:
Uplink and Downlink Rate Analysis of a Full-Duplex C-RAN with Radio
  Remote Head Association

abstract:
  We characterize the uplink (UL) and downlink (DL) rates of a full-duplex
cloud radio access network (C-RAN) with all participate and single best remote
radio head (RRH) association schemes. Specifically, multi-antenna equipped RRHs
distributed according to a Poisson point process is assumed. The UL and DL sum
rate of the single best RRH association scheme is maximized using receive and
transmit beamformer designs at the UL and DL RRHs, respectively. In the case of
the single best strategy, we study both optimum and sub-optimum schemes based
on maximum ratio combining/maximal ratio transmission (MRC/MRT) and
zero-forcing/MRT (ZF/MRT) processing. Numerical results show that significant
performance improvements can be achieved by using the full-duplex mode as
compared to the half-duplex mode. Moreover, the choice of the beamforming
design and the RRH association scheme have a major influence on the achievable
full-duplex gains.


title: Every genus one algebraically slice knot is 1-solvable

abstract:
  Cochran, Orr, and Teichner developed a filtration of the knot concordance
group indexed by half integers called the solvable filtration. Its terms are
denoted by $\mathcal{F}_n$. It has been shown that
$\mathcal{F}_n/\mathcal{F}_{n.5}$ is a very large group for $n\ge 0$. For a
generalization to the setting of links the third author showed that
$\mathcal{F}_{n.5}/\mathcal{F}_{n+1}$ is non-trivial. In this paper we provide
evidence that for knots $\mathcal{F}_{0.5}=\mathcal{F}_1$. In particular we
prove that every genus 1 algebraically slice knot is 1-solvable.


title: A Formal Graph Model for RDF and Its Implementation

abstract:
  Formalizing an RDF abstract graph model to be compatible with the RDF formal
semantics has remained one of the foundational problems in the Semantic Web. In
this paper, we propose a new formal graph model for RDF datasets. This model
allows us to express the current model-theoretic semantics in the form of a
graph. We also propose the concepts of resource path and triple path as well as
an algorithm for traversing the new graph. We demonstrate the feasibility of
this graph model through two implementations: one is a new graph engine called
GraphKE, and the other is extended from RDF-3X to show that existing systems
can also benefit from this model. In order to evaluate the empirical aspect of
our graph model, we choose the shortest path algorithm and implement it in the
GraphKE and the RDF-3X. Our experiments on both engines for finding the
shortest paths in the YAGO2S-SP dataset give decent performance in terms of
execution time. The empirical results show that our graph model with
well-defined semantics can be effectively implemented.


title: Splittings of link concordance groups

abstract:
  We establish several results about two short exact sequences involving lower
terms of the $n$-solvable filtration, $\{\mathcal{F}^m_n\}$ of the string link
concordance group $\mathcal{C}^m$. We utilize the Thom-Pontryagin construction
to show that the Sato-Levine invariants $\bar{\mu}_{(iijj)}$ must vanish for
0.5-solvable links. Using this result, we show that the short exact sequence
$0\rightarrow \mathcal{F}^m_0/\mathcal{F}^m_{0.5} \rightarrow
\mathcal{F}^m_{-0.5}/\mathcal{F}^m_{0.5} \rightarrow
\mathcal{F}^m_{-0.5}/\mathcal{F}^m_0 \rightarrow 0$ does not split for links of
two or more components, in contrast to the fact that it splits for knots.
Considering lower terms of the filtration $\{\mathcal{F}^m_n\}$ in the short
exact sequence $0\rightarrow \mathcal{F}^m_{-0.5}/\mathcal{F}^m_{0} \rightarrow
\mathcal{C}^m/\mathcal{F}^m_{0} \rightarrow \mathcal{C}^m/\mathcal{F}^m_{-0.5}
\rightarrow 0$, we show that while the sequence does not split for $m\ge 3$, it
does indeed split for $m=2$. We conclude that the quotient
$\mathcal{C}^2/\mathcal{F}^2_0 \cong \mathbb{Z}_2\oplus
\mathbb{Z}_2\oplus\mathbb{Z}_2 \oplus \mathbb{Z}$.


title: Witt vector rings and quotients of monoid algebras

abstract:
  In a previous paper Cuntz and Deninger introduced the ring $C(R)$ for a
perfect $\mathbb{F}_p$-algebra $R$. The ring $C(R)$ is canonically isomorphic
to the $p$-typical Witt ring $W(R)$. In fact there exist canonical isomorphisms
$\alpha_n \colon \mathbb{Z}R/I^n \xrightarrow{\sim} W_n(R)$. In this paper we
give explicit descriptions of the isomorphisms $\alpha_n$ for $n\geq 2$ if
$p\geq n$.


title: Millimeter Wave Absorber for Secure Identification

abstract:
  We demonstrate thin, flexible, metamaterial films with a strong, narrowband,
polarization- and angle-insensitive absorption designed for wavelengths near
one millimeter. These structures, fabricated by photolithography on a
commercially available, copper-backed polyimide substrate, are nearly
indistinguishable to the unaided human eye but can be easily observed by
imaging at the resonance frequency of the film. We demonstrate that these
patterns can be used to mark or barcode objects for secure identification with
a terahertz imaging system.


title: Fast Deterministic Selection

abstract:
  The Median of Medians (also known as BFPRT) algorithm, although a landmark
theoretical achievement, is seldom used in practice because it and its variants
are slower than simple approaches based on sampling. The main contribution of
this paper is a fast linear-time deterministic selection algorithm
QuickselectAdaptive based on a refined definition of MedianOfMedians. The
algorithm's performance brings deterministic selection---along with its
desirable properties of reproducible runs, predictable run times, and immunity
to pathological inputs---in the range of practicality. We demonstrate results
on independent and identically distributed random inputs and on
normally-distributed inputs. Measurements show that QuickselectAdaptive is
faster than state-of-the-art baselines.


title: Trends in Nuclear Astrophysics

abstract:
  Nuclear Astrophysics is a vibrant field at the intersection of nuclear
physics and astrophysics that encompasses research in nuclear physics,
astrophysics, astronomy, and computational science. This paper is not a review.
It is intended to provide an incomplete personal perspective on current trends
in nuclear astrophysics and the specific role of nuclear physics in this field.


title: Planar Legendrian $\Theta$-graphs

abstract:
  We classify topologically trivial Legendrian $\Theta$-graphs and identify the
complete family of nondestabilizeable Legendrian realizations in this
topological class. In contrast to all known results for Legendrian knots, this
is an infinite family of graphs. We also show that any planar graph that
contains a subdivision of a $\Theta$-graph or $S^1 \vee S^1$ as a subgraph will
have an infinite number of distinct, topologically trivial nondestabilizeable
Legendrian embeddings. Additionally, we introduce two moves, vertex
stabilization and vertex twist, that change the Legendrian type within a smooth
isotopy class.


title: Recurrent Fully Convolutional Networks for Video Segmentation

abstract:
  Image segmentation is an important step in most visual tasks. While
convolutional neural networks have shown to perform well on single image
segmentation, to our knowledge, no study has been been done on leveraging
recurrent gated architectures for video segmentation. Accordingly, we propose a
novel method for online segmentation of video sequences that incorporates
temporal data. The network is built from fully convolutional element and
recurrent unit that works on a sliding window over the temporal data. We also
introduce a novel convolutional gated recurrent unit that preserves the spatial
information and reduces the parameters learned. Our method has the advantage
that it can work in an online fashion instead of operating over the whole input
batch of video frames. The network is tested on the change detection dataset,
and proved to have 5.5\% improvement in F-measure over a plain fully
convolutional network for per frame segmentation. It was also shown to have
improvement of 1.4\% for the F-measure compared to our baseline network that we
call FCN 12s.


title: Phonons and Thermal Transport in Graphene and Graphene-Based Materials

abstract:
  A discovery of the unusual thermal properties of graphene stimulated
experimental, theoretical and computational research directed at understanding
phonon transport and thermal conduction in two-dimensional material systems. We
provide a critical review of recent results in the graphene thermal field
focusing on phonon dispersion, specific heat, thermal conductivity, and
comparison of different models and computational approaches. The correlation
between the phonon spectrum in graphene-based materials and the heat conduction
properties is analyzed in details. The effects of the atomic plane rotations in
bilayer graphene, isotope engineering, and relative contributions of different
phonon dispersion branches are discussed. For readers' convenience, the
summaries of main experimental and theoretical results on thermal conductivity
as well as phonon mode contributions to thermal transport are provided in the
form of comprehensive annotated tables.


title:
Equilibrium properties of blackbody radiation with an ultraviolet energy
  cut-off

abstract:
  We study various equilibrium thermodynamic properties of blackbody radiation
(i.e. a photon gas) with an ultraviolet energy cut-off. We find that the energy
density, specific heat etc. follow usual acoustic phonon dynamics as have been
well studied by Debye. Other thermodynamic quantities like pressure, entropy
etc. have also been calculated. The usual Stefan-Boltzmann law gets modified.
We observe that the values of the thermodynamic quantities with the energy
cut-off is lower than the corresponding values in the theory without any such
scale. The phase-space measure is also expected to get modified for an exotic
spacetime appearing at Planck scale, which in turn leads to the modification of
Planck energy density distribution and the Wien's displacement law. We found
that the non-perturbative nature of the thermodynamic quantities in the SR
limit (for both the case with ultravilolet cut-off and the modified measure
case), due to nonanalyticity of the leading term, is a general feature of the
theory accompanied with an ultraviolet energy cut-off. We have also discussed
the possible modification in the case of Big Bang and the Stellar objects and
have suggested a table top experiment for verification in effective low energy
case.


title:
Isoperimetry with upper mean curvature bounds and sharp stability
  estimates

abstract:
  It was proved by Almgren that among boundaries whose mean curvature is
bounded from above, perimeter is uniquely minimized by balls. We obtain sharp
stability estimates for Almgren's isoperimetric principle and, as an
application, we deduce a sharp description of boundaries with almost constant
mean curvature under a total perimeter bound which prevents bubbling.


title:
Computing the generators of the truncated real radical ideal by moment
  matrices and SDP facial reduction

abstract:
  Recent breakthroughs have been made in the use of semidefinite programming
and its application to real polynomial solving. For example, the real radical
of a zero dimensional ideal, can be determined by such approaches as shown by
Lasserre and collaborators. Some progress has been made on the determination of
the real radical in positive dimension by Ma, Wang and Zhi. Such work involves
the determination of maximal rank semidefinite moment matrices. Existing
methods are computationally expensive and have poorer accuracy on larger
examples.
  This paper is motivated by problems in the numerical computation of the real
radical ideal in the general positive case.
  In this paper we give a method to compute the generators of the real radical
for any given degree $d$. We combine the use of moment matrices and techniques
from SDP optimization: facial reduction first developed by Borwein and
Wolkowicz. In use of the semidefinite moment matrices to compute the real
radical, the maximum rank property is very key, and with facial reduction, it
can be guaranteed with very high accuracy. Our algorithm can be used to test
the real radical membership of a given polynomial. In a special situation, we
can determine the real radical ideal in the positive dimensional case.


title: On the orthogonality of the Chebyshev-Frolov lattice and applications

abstract:
  We deal with lattices that are generated by the Vandermonde matrices
associated to the roots of Chebyshev-polynomials. If the dimension $d$ of the
lattice is a power of two, i.e. $d=2^m, m \in \mathbb{N}$, the resulting
lattice is an admissible lattice in the sense of Skriganov. Those are related
to the Frolov cubature formulas, which recently drew attention due to their
optimal convergence rates in a broad range of function spaces with mixed
smoothness. We prove that the resulting lattices are orthogonal and possess a
lattice representation matrix with entries not larger than $2$ (in modulus).
This allows for an efficient enumeration of the Frolov cubature nodes in the
$d$-cube $[-1/2,1/2]^d$ up to dimension $d=16$.


title: Minimal positive design for self-assembly of the Archimedean tilings

abstract:
  A challenge of molecular self-assembly is to understand how to design
particles that self-assemble into a desired structure and not any of a
potentially large number of undesired structures. Here we use simulation to
show that a strategy of minimal positive design allows the self-assembly of
networks equivalent to the 8 semiregular Archimedean tilings of the plane,
structures not previously realized in simulation. This strategy consists of
identifying the fewest distinct types of interparticle interaction that appear
in the desired structure, and does not require enumeration of the many possible
undesired structures. The resulting particles, which self-assemble into the
desired networks, possess DNA-like selectivity of their interactions. Assembly
of certain molecular networks may therefore require such selectivity.


title:
The average singular value of a complex random matrix decreases with
  dimension

abstract:
  We obtain a recurrence relation in $d$ for the average singular value $%
\alpha (d)$ of a complex valued $d\times d$\ matrix $\frac{1}{\sqrt{d}}X$ with
random i.i.d., N( 0,1) entries, and use it to show that $\alpha (d)$ decreases
monotonically with $d$ to the limit given by the Marchenko-Pastur
distribution.\ The monotonicity of $\alpha (d)$ has been recently conjectured
by Bandeira, Kennedy and Singer in their study of the Little Grothendieck
problem over the unitary group $\mathcal{U}_{d}$ \cite{BKS}, a combinatorial
optimization problem. The result implies sharp global estimates for $\alpha
(d)$, new bounds for the expected minimum and maximum singular values, and a
lower bound for the ratio of the expected maximum and the expected minimum
singular value. The proof is based on a connection with the theory of Tur\'{a}n
determinants of orthogonal polynomials. We also discuss some applications to
the problem that originally motivated the conjecture.


title:
Modelling cross-reactivity and memory in the cellular adaptive immune
  response to influenza infection in the host

abstract:
  The cellular adaptive immune response plays a key role in resolving influenza
infection. Experiments where individuals are successively infected with
different strains within a short timeframe provide insight into the underlying
viral dynamics and the role of a cross-reactive immune response in resolving an
acute infection. We construct a mathematical model of within-host influenza
viral dynamics including three possible factors which determine the strength of
the cross-reactive cellular adaptive immune response: the initial naive T cell
number, the avidity of the interaction between T cells and the epitopes
presented by infected cells, and the epitope abundance per infected cell. Our
model explains the experimentally observed shortening of a second infection
when cross-reactivity is present, and shows that memory in the cellular
adaptive immune response is necessary to protect against a second infection.


title:
On the equivalence between Kolmogorov-Smirnov and ROC curve metrics for
  binary classification

abstract:
  Binary decisions are very common in artificial intelligence. Applying a
threshold on the continuous score gives the human decider the power to control
the operating point to separate the two classes. The classifier,s
discriminating power is measured along the continuous range of the score by the
Area Under the ROC curve (AUC_ROC) in most application fields. Only finances
uses the poor single point metric maximum Kolmogorov-Smirnov (KS) distance.
This paper proposes the Area Under the KS curve (AUC_KS) for performance
assessment and proves AUC_ROC = 0.5 + AUC_KS, as a simpler way to calculate the
AUC_ROC. That is even more important for ROC averaging in ensembles of
classifiers or n fold cross-validation. The proof is geometrically inspired on
rotating all KS curve to make it lie on the top of the ROC chance diagonal. On
the practical side, the independent variable on the abscissa on the KS curve
simplifies the calculation of the AUC_ROC. On the theoretical side, this
research gives insights on probabilistic interpretations of classifiers
assessment and integrates the existing body of knowledge of the information
theoretical ROC approach with the proposed statistical approach based on the
thoroughly known KS distribution.


title: The Jackknife Estimation Method

abstract:
  Statistical resampling methods have become feasible for parametric
estimation, hypothesis testing, and model validation now that the computer is a
ubiquitous tool for statisticians. This essay focuses on the resampling
technique for parametric estimation known as the Jackknife procedure. To
outline the usefulness of the method and its place in the general class of
statistical resampling techniques, I will quickly delineate two similar
resampling methods: the bootstrap and the permutation test. I then outline the
Jackknife method and show an example of its use.


title:
A Comprehensive Linear Speedup Analysis for Asynchronous Stochastic
  Parallel Optimization from Zeroth-Order to First-Order

abstract:
  Asynchronous parallel optimization received substantial successes and
extensive attention recently. One of core theoretical questions is how much
speedup (or benefit) the asynchronous parallelization can bring us. This paper
provides a comprehensive and generic analysis to study the speedup property for
a broad range of asynchronous parallel stochastic algorithms from the zeroth
order to the first order methods. Our result recovers or improves existing
analysis on special cases, provides more insights for understanding the
asynchronous parallel behaviors, and suggests a novel asynchronous parallel
zeroth order method for the first time. Our experiments provide novel
applications including model blending problems using the proposed asynchronous
parallel zeroth order method.


title: Generalizing and Hybridizing Count-based and Neural Language Models

abstract:
  Language models (LMs) are statistical models that calculate probabilities
over sequences of words or other discrete symbols. Currently two major
paradigms for language modeling exist: count-based n-gram models, which have
advantages of scalability and test-time speed, and neural LMs, which often
achieve superior modeling performance. We demonstrate how both varieties of
models can be unified in a single modeling framework that defines a set of
probability distributions over the vocabulary of words, and then dynamically
calculates mixture weights over these distributions. This formulation allows us
to create novel hybrid models that combine the desirable features of
count-based and neural LMs, and experiments demonstrate the advantages of these
approaches.


title:
Variation of transition temperatures and residual resistivity ratio in
  vapor-grown FeSe

abstract:
  The study of the iron-based superconductor FeSe has blossomed with the
availability of high quality single crystals, obtained through
flux/vapor-transport growth techniques below the structural transformation
temperature of its tetragonal phase, T~450 C. Here, we report on the variation
of sample morphology and properties due to small modifications in the growth
conditions. A considerable variation of the superconducting transition
temperature Tc, from 8.8 K to 3 K, which cannot be correlated with the sample
composition, is observed. Instead, we point out a clear correlation between Tc
and disorder, as measured by the residual resistivity ratio. Notably, the
tetragonal-to-orthorhombic structural transition is also found to be quite
strongly disorder dependent (Ts =72 - 90 K), and linearly correlated with Tc.


title:
Effect of nonmagnetic impurities on $s_\pm$ superconductivity in the
  presence of incipient bands

abstract:
  Several Fe chalcogenide superconductors without hole pockets at the Fermi
level display high temperature superconductivity, in apparent contradiction to
naive spin fluctuation pairing arguments. Recently, scanning tunneling
microscopy measurements have measured the influence of impurities on some of
these materials, and claimed that non-magnetic impurities do not create in-gap
states, leading to the conclusion that the gap must be $s_{++}$, i.e.
conventional $s$ wave with no gap sign change. Here we critique this argument,
and give various ways sign-changing gaps can be consistent with the absence of
such bound states. In particular, we calculate the bound states for an $s_\pm$
system with a hole pocket below the Fermi level, and show that the nonmagnetic
impurity bound state energy generically tracks the gap edge $E_{min}$ in the
system, thereby rendering it unobservable. A failure to observe a bound state
in the case of a nonmagnetic impurity can therefore not be used as an argument
to exclude sign-changing pairing states.


title: Program Repair by Stepwise Correctness Enhancement

abstract:
  Relative correctness is the property of a program to be more-correct than
another with respect to a given specification. Whereas the traditional
definition of (absolute) correctness divides candidate program into two classes
(correct, and incorrect), relative correctness arranges candidate programs on
the richer structure of a partial ordering. In other venues we discuss the
impact of relative correctness on program derivation, and on program
verification. In this paper, we discuss the impact of relative correctness on
program testing; specifically, we argue that when we remove a fault from a
program, we ought to test the new program for relative correctness over the old
program, rather than for absolute correctness. We present analytical arguments
to support our position, as well as an empirical argument in the form of a
small program whose faults are removed in a stepwise manner as its relative
correctness rises with each fault removal until we obtain a correct program.


title:
Model-based Testing of Mobile Systems -- An Empirical Study on QuizUp
  Android App

abstract:
  We present an empirical study in which model-based testing (MBT) was applied
to a mobile system: the Android client of QuizUp, the largest mobile trivia
game in the world. The study shows that traditional MBT approaches based on
extended finite-state machines can be used to test a mobile app in an effective
and efficient way. Non-trivial defects were detected on a deployed system that
has millions of users and was already well tested. The duration of the overall
testing effort was of three months, including the construction of the models.
Maintaining a single behavioral model for the app was key in order to test it
in an efficient way.


title:
Using Multi-Viewpoint Contracts for Negotiation of Embedded Software
  Updates

abstract:
  In this paper we address the issue of change after deployment in
safety-critical embedded system applications. Our goal is to substitute
lab-based verification with in-field formal analysis to determine whether an
update may be safely applied. This is challenging because it requires an
automated process able to handle multiple viewpoints such as functional
correctness, timing, etc. For this purpose, we propose an original methodology
for contract-based negotiation of software updates. The use of contracts allows
us to cleanly split the verification effort between the lab and the field. In
addition, we show how to rely on existing viewpoint-specific methods for update
negotiation. We illustrate our approach on a concrete example inspired by the
automotive domain.


title: Monitoring Assumptions in Assume-Guarantee Contracts

abstract:
  Pre-deployment verification of software components with respect to behavioral
specifications in the assume-guarantee form does not, in general, guarantee
absence of errors at run time. This is because assumptions about the
environment cannot be discharged until the environment is fixed. An intuitive
approach is to complement pre-deployment verification of guarantees, up to the
assumptions, with post-deployment monitoring of environment behavior to check
that the assumptions are satisfied at run time. Such a monitor is typically
implemented by instrumenting the application code of the component. An
additional challenge for the monitoring step is that environment behaviors are
typically obtained through an I/O library, which may alter the component's view
of the input format. This transformation requires us to introduce a second
pre-deployment verification step to ensure that alarms raised by the monitor
would indeed correspond to violations of the environment assumptions. In this
paper, we describe an approach for constructing monitors and verifying them
against the component assumption. We also discuss limitations of
instrumentation-based monitoring and potential ways to overcome it.


title: Preliminary Results Towards Contract Monitorability

abstract:
  This paper discusses preliminary investigations on the monitorability of
contracts for web service descriptions. There are settings where servers do not
guarantee statically whether they satisfy some specified contract, which forces
the client (i.e., the entity interacting with the server) to perform dynamic
checks. This scenario may be viewed as an instance of Runtime Verification,
where a pertinent question is whether contracts can be monitored for adequately
at runtime, otherwise stated as the monitorability of contracts. We consider a
simple language of finitary contracts describing both clients and servers, and
develop a formal framework that describes server contract monitoring. We define
monitor properties that potentially contribute towards a comprehensive notion
of contract monitorability and show that our simple contract language satisfies
these properties.


title:
The Gorenstein property for projective coordinate rings of the moduli of
  parabolic $\mathrm{SL}_2$-principal bundles on a smooth curve

abstract:
  Using combinatorial methods, we determine that a projective coordinate ring
of the moduli of parabolic principal $\mathrm{SL}_2$-bundles on a marked
projective curve is not Gorenstein when the genus and number of marked points
are greater than $1$.


title: Open string multi-branched and Kahler potentials

abstract:
  We consider type II string compactifications on Calabi-Yau orientifolds with
fluxes and D-branes, and analyse the F-term scalar potential that
simultaneously involves closed and open string modes. In type IIA models with
D6-branes such potential can be directly computed by integrating out Minkowski
three-forms. The result shows a multi-branched structure along the space of
lifted open string moduli, in which discrete shifts in special Lagrangian and
Wilson line deformations are compensated by changes in the RR flux quanta. The
same sort of discrete shift symmetries are present in the superpotential and
constrain the Kahler potential. As for the latter, inclusion of open string
moduli breaks the factorisation between complex structure and Kahler moduli
spaces. Nevertheless, the 4d Kahler metrics display a set of interesting
relations that allow to rederive the scalar potential analytically. Similar
results hold for type IIB flux compactifications with D7-brane Wilson lines.


title: High Current Density 2D/3D Esaki Tunnel Diodes

abstract:
  The integration of two-dimensional materials such as transition metal
dichalcogenides with bulk semiconductors offer interesting opportunities for
2D/3D heterojunction-based novel device structures without any constraints of
lattice matching. By exploiting the favorable band alignment at the GaN/MoS2
heterojunction, an Esaki interband tunnel diode is demonstrated by transferring
large area, Nb-doped, p-type MoS2 onto heavily n-doped GaN. A peak current
density of 446 A/cm2 with repeatable room temperature negative differential
resistance, peak to valley current ratio of 1.2, and minimal hysteresis was
measured in the MoS2/GaN non-epitaxial tunnel diode. A high current density of
1 kA/cm2 was measured in the Zener mode (reverse bias) at -1 V bias. The
GaN/MoS2 tunnel junction was also modeled by treating MoS2 as a bulk
semiconductor, and the electrostatics at the 2D/3D interface was found to be
crucial in explaining the experimentally observed device characteristics.


title:
Full extremal process, cluster law and freezing for the two-dimensional
  discrete Gaussian Free Field

abstract:
  We study the local structure of the extremal process associated with the
Discrete Gaussian Free Field (DGFF) in scaled-up (square-)lattice versions of
bounded open planar domains subject to mild regularity conditions on the
boundary. We prove that, in the scaling limit, this process tends to a Cox
process decorated by independent, correlated clusters whose distribution is
completely characterized. As an application, we control the scaling limit of
the discrete supercritical Liouville measure, extract a Poisson-Dirichlet
statistics for the limit of the Gibbs measure associated with the DGFF and
establish the "freezing phenomenon" conjectured to occur in the "glassy" phase.
In addition, we prove a local limit theorem for the position and value of the
absolute maximum. The proofs are based on a concentric, finite-range
decomposition of the DGFF and entropic-repulsion arguments for an associated
random walk. Although we naturally build on our earlier work on this problem,
the methods developed here are largely independent.


title: Distributed Hessian-Free Optimization for Deep Neural Network

abstract:
  Training deep neural network is a high dimensional and a highly non-convex
optimization problem. Stochastic gradient descent (SGD) algorithm and it's
variations are the current state-of-the-art solvers for this task. However, due
to non-covexity nature of the problem, it was observed that SGD slows down near
saddle point. Recent empirical work claim that by detecting and escaping saddle
point efficiently, it's more likely to improve training performance. With this
objective, we revisit Hessian-free optimization method for deep networks. We
also develop its distributed variant and demonstrate superior scaling potential
to SGD, which allows more efficiently utilizing larger computing resources thus
enabling large models and faster time to obtain desired solution. Furthermore,
unlike truncated Newton method (Marten's HF) that ignores negative curvature
information by using na\"ive conjugate gradient method and Gauss-Newton Hessian
approximation information - we propose a novel algorithm to explore negative
curvature direction by solving the sub-problem with stabilized bi-conjugate
method involving possible indefinite stochastic Hessian information. We show
that these techniques accelerate the training process for both the standard
MNIST dataset and also the TIMIT speech recognition problem, demonstrating
robust performance with upto an order of magnitude larger batch sizes. This
increased scaling potential is illustrated with near linear speed-up on upto 16
CPU nodes for a simple 4-layer network.


title:
Generalized gradient expansion for inhomogeneous dynamical mean-field
  theory: Application to ultracold atoms in a harmonic trap

abstract:
  We develop a generalized gradient expansion of the inhomogeneous dynamical
mean-field theory method for determining properties of ultracold atoms in a
trap. This approach goes beyond the well-known local density approximation and
at higher temperatures, in the normal phase, it shows why the local density
approximation works so well, since the local density and generalized gradient
approximations are essentially indistinguishable from each other (and from the
exact solution within full inhomogeneous dynamical mean-field theory). But
because the generalized gradient expansion only involves nearest-neighbor
corrections, it does not work as well at low temperatures, when the systems
enter into ordered phases. This is primarily due to the problem that ordered
phases often satisfy some global constraints which determine the spatial
ordering pattern, and the local density and generalized gradient approximations
are not able to impose those kinds of constraints; they also overestimate the
tendency to order. The theory is applied to phase separation of different mass
fermionic mixtures represented by the Falicov-Kimball model and to determining
the entropy per particle of a fermionic system represented by the Hubbard
model. The generalized gradient approximation is a useful diagnostic for the
accuracy of the local density approximation---when both methods agree, they are
likely accurate, when they disagree, neither is likely to be correct.


title: Productive Interactions: heavy particles and non-Gaussianity

abstract:
  We analyze the shape and amplitude of oscillatory features in the primordial
power spectrum and non-Gaussianity induced by periodic production of heavy
degrees of freedom coupled to the inflaton $\phi$. We find that non-adiabatic
production of particles can contribute effects which are detectable or
constrainable using cosmological data even if their time-dependent masses are
always heavier than the scale $\dot \phi^{1/2}$, much larger than the Hubble
scale. This provides a new role for UV completion, consistent with the criteria
from effective field theory for when heavy fields cannot be integrated out.
This analysis is motivated in part by the structure of axion monodromy, and
leads to an additional oscillatory signature in a subset of its parameter
space. At the level of a quantum field theory model that we analyze in detail,
the effect arises consistently with radiative stability for an interesting
window of couplings up to of order $\lesssim 1$. The amplitude of the
bispectrum and higher-point functions can be larger than that for Resonant
Non-Gaussianity, and its signal/noise may be comparable to that of the
corresponding oscillations in the power spectrum (and even somewhat larger
within a controlled regime of parameters). Its shape is distinct from
previously analyzed templates, but was partly motivated by the oscillatory
equilateral searches performed recently by the {\it Planck} collaboration. We
also make some general comments about the challenges involved in making a
systematic study of primordial non-Gaussianity.


title:
High-harmonic and terahertz wave spectroscopy (HATS) for aligned
  molecules

abstract:
  We present the experimental and theoretical details of our recent published
letter [Phys. Rev. Lett. 115. 123002] on synchronized high-harmonic and
terahertz-wave spectroscopy (HATS) from nonadiabatically aligned nitrogen
molecules in dual-color laser fields. Associating the alignment-angle dependent
terahertz wave generation with the synchronizing high-harmonic signal, the
angular differential photoionization cross section (PICS) for molecules can be
reconstructed, and the minima of the angle on PICS show great convergence
between the theoretical predictions and the experimental deduced results. We
also show the optimal relative phase between the dual-color laser fields for
terahertz wave generation dose not change with the alignment angle at a
precision of $50$ attoseconds. This all-optical method provides an alternative
for investigating molecular structures and dynamics.


title:
PEXSI-$\Sigma$: A Green's function embedding method for Kohn-Sham
  density functional theory

abstract:
  In this paper, we propose a new Green's function embedding method called
PEXSI-$\Sigma$ for describing complex systems within the Kohn-Sham density
functional theory (KSDFT) framework, after revisiting the physics literature of
Green's function embedding methods from a numerical linear algebra perspective.
The PEXSI-$\Sigma$ method approximates the density matrix using a set of nearly
optimally chosen Green's functions evaluated at complex frequencies. For each
Green's function, the complex boundary conditions are described by a self
energy matrix $\Sigma$ constructed from a physical reference Green's function,
which can be computed relatively easily. In the linear regime, such treatment
of the boundary condition can be numerically exact. The support of the $\Sigma$
matrix is restricted to degrees of freedom near the boundary of computational
domain, and can be interpreted as a frequency dependent surface potential. This
makes it possible to perform KSDFT calculations with $\mathcal{O}(N^2)$
computational complexity, where $N$ is the number of atoms within the
computational domain. Green's function embedding methods are also naturally
compatible with atomistic Green's function methods for relaxing the atomic
configuration outside the computational domain. As a proof of concept, we
demonstrate the accuracy of the PEXSI-$\Sigma$ method for graphene with
divacancy and dislocation dipole type of defects using the DFTB+ software
package.


title:
Effect of rotational-state-dependent molecular alignment on the optical
  dipole force

abstract:
  The properties of molecule-optical elements such as lenses or prisms based on
the interaction of molecules with optical fields depend in a crucial way on the
molecular quantum state and its alignment created by the optical field.
However, in previous experimental studies, the effects of state-dependent
alignment have never been included in estimates of the optical dipole force
acting on the molecules while previous theoretical investigations took the
state-dependent molecular alignment into account only implicitly. Herein, we
consider the effects of molecular alignment explicitly and, to this end,
introduce an effective polarizability which takes proper account of molecular
alignment and is directly related to the alignment-dependent optical dipole
force. We illustrate the significance of including molecular alignment in the
optical dipole force by a trajectory study that compares previously used
approximations with the present approach. The trajectory simulations were
carried out for an ensemble of linear molecules subject to either propagating
or standing-wave optical fields for a range of temperatures and laser
intensities. The results demonstrate that the alignment-dependent effective
polarizability can serve to provide correct estimates of the optical dipole
force, on which a state-selection method applicable to nonpolar molecules could
be based. We note that an analogous analysis of the forces acting on polar
molecules subject to an inhomogeneous static electric field reveals a similarly
strong dependence on molecular orientation.


title:
Wormholes versus black holes: quasinormal ringing at early and late
  times

abstract:
  Recently it has been argued that the phantom thin-shell wormholes matched
with the Schwarzschild space-time near the Schwarzschild radius ring like
Schwarzschild black holes at early times, but differently at late times
(arXiv:1602.07309). Here we consider perturbations of the wormhole which was
constructed without thin-shells: the Bronnikov-Ellis wormhole supported by the
phantom matter and electromagnetic field. This wormhole solution is known to be
stable under specific equation of state of the phantom matter. We show that if
one does not use the above thin-shell matching, the wormhole, depending on the
values of its parameters, either rings as the black hole at all times or rings
differently also at all times. The wormhole's spectrum, investigated here,
posses a number of distinctive features.
  In the final part we have considered general properties of scattering around
arbitrary rotating traversable wormholes. We have found that symmetric and
non-symmetric (with respect to the throat) wormholes are qualitatively
different in this respect: First, superradiance is allowed only if for those
non-symmetric wormholes for which the asymptotic values of the rotation
parameters are different on both sides from the throat. Second, the symmetric
wormholes cannot mimic effectively the ringing of a black hole at a few various
dominant multipoles at the same time, so that the future observations of
various events should easily tell the symmetric wormhole from a black hole.


title:
The challenge of engaging all students via self-paced interactive
  e-learning tutorials for introductory physics

abstract:
  As research-based self-paced e-learning tools become increasingly available,
a critical issue educators encounter is implementing strategies to ensure that
all students engage with them as intended. Here, we discuss the effectiveness
of research-based e-learning tutorials as self-paced learning tools in large
enrollment brick and mortar introductory physics courses. These interactive
tutorials were developed via research in physics education and were found to be
effective for a diverse group of introductory physics students in one-on-one
implementation. Instructors encouraged the use of these self-paced tools in a
self-paced learning environment by telling students that they would be helpful
for solving the assigned homework problems and that the underlying physics
principles in the tutorial problems would be similar to those in the in-class
quizzes (which we call paired problems). We find that many students, who
struggled in the courses in which these adaptive e-learning tutorials were
assigned as a self-study tool, performed poorly on the paired problems. In
contrast, a majority of student volunteers in one-on-one implementation greatly
benefited from the tutorials and performed well on the paired problems. This
suggests that many students enrolled in introductory physics courses did not
effectively engage with the self-paced tutorials outside of class and may have
only used them superficially. The findings suggest that many students in need
of out-of-class remediation via self-paced learning tools may have difficulty
motivating themselves and may lack the self-regulation and time-management
skills to engage effectively with tools specially designed to help them learn
at their own pace. We conclude by proposing a theoretical framework to help
students with diverse prior preparations engage effectively with self-study
tools.


title: Massively-Parallel Lossless Data Decompression

abstract:
  Today's exponentially increasing data volumes and the high cost of storage
make compression essential for the Big Data industry. Although research has
concentrated on efficient compression, fast decompression is critical for
analytics queries that repeatedly read compressed data. While decompression can
be parallelized somewhat by assigning each data block to a different process,
break-through speed-ups require exploiting the massive parallelism of modern
multi-core processors and GPUs for data decompression within a block. We
propose two new techniques to increase the degree of parallelism during
decompression. The first technique exploits the massive parallelism of GPU and
SIMD architectures. The second sacrifices some compression efficiency to
eliminate data dependencies that limit parallelism during decompression. We
evaluate these techniques on the decompressor of the DEFLATE scheme, called
Inflate, which is based on LZ77 compression and Huffman encoding. We achieve a
2X speed-up in a head-to-head comparison with several multi-core CPU-based
libraries, while achieving a 17% energy saving with comparable compression
ratios.


title: K-theory and perturbations of absolutely continuous spectra

abstract:
  We study the K_0 group of the commutant modulo a normed ideal of an n-tuple
of commuting Hermitian operators in some of the simplest cases. In case n=1,
the results, under some technical conditions are rather complete and show the
key role of the absolutely continuous part when the ideal is the trace-class.
For a commuting n-tuple, n>2 and the Lorentz (n, 1) ideal, we show under an
absolute continuity assumption that the commutant determines a canonical direct
summand in K_0. Also, certain properties involving the compact ideal,
established assuming quasicentral approximate units mod the normed ideal, have
weaker versions which hold assuming only finiteness of the obstruction to
quasicentral approximate units.


title:
Initial and Eventual Software Quality Relating to Continuous Integration
  in GitHub

abstract:
  The constant demand for new features and bug fixes are forcing software
projects to shorten cycles and deliver updates ever faster, while sustaining
software quality. The availability of inexpensive, virtualized, cloud-computing
has helped shorten schedules, by enabling continuous integration (CI) on
demand. Platforms like GitHub support CI in-the-cloud. In projects using CI, a
user submitting a pull request triggers a CI step. Besides speeding up build
and test, this fortuitously creates voluminous archives of build and test
successes and failures. CI is a relatively new phenomenon, and these archives
allow a detailed study of CI. How many problems are exposed? Where do they
occur? What factors affect CI failures? Does the "initial quality" as
ascertained by CI predict how many bugs will later appear ("eventual quality")
in the code? In this paper, we undertake a large-scale, fine resolution study
of these records, to better understand CI processes, the nature, and predictors
of CI failures, and the relationship of CI failures to the eventual quality of
the code. We find that: a) CI failures appear to be concentrated in a few
files, just like normal bugs; b) CI failures are not very highly correlated
with eventual failures; c) The use of CI in a pull request doesn't necessarily
mean the code in that request is of good quality.


title:
Emergent Electric Polarization by Kondo Effect in a Triangular Triple
  Quantum Dot

abstract:
  A triangular triple quantum dot gives various Kondo effects, such as the
emergence of an electric polarization accompanied by a complete compensation of
spin degrees of freedom. The interplay of spin and charge of electrons in
quantum dots is investigated using an Anderson model with an equilateral
triangular spin cluster, in which a single electron state at one site is
hybridized with a conduction band in a lead. The numerical renormalization
group analysis shows how a nonzero electric polarization develops with local
electrons traveling in the loop and how it depends on the hybridization
strength as an experimentally controllable parameter in the Kondo effect.


title:
Photon-induced Background for Dilepton Searches and Measurements in pp
  Collisions at 13 TeV

abstract:
  The production of high invariant mass opposite sign lepton pairs in
proton-proton collisions at the LHC is dominated by the Drell-Yan process. In
addition to this photon or Z exchange mediated mechanism, gamma-gamma
collisions, where photons radiated by the incoming protons collide, can produce
lepton pairs. This is an important additional source of background for high
mass resonant (like Z') or non-resonant (like contact interactions) searches.
In this paper detailed calculations of the Drell-Yan and photon-induced cross
sections in the typical acceptance of a multi-purpose LHC detector at center of
mass energy 13 TeV are presented. The hint for a diphoton excess at a mass
around 750 GeV, reported by the ATLAS and CMS experiments from the analysis of
the 2015 data at 13 TeV, raises the possibility that such an excess could be
produced through gamma-gamma collisions. A good theoretical understanding and
measurements in the dilepton channels at these energies can help to elucidate
this production hypothesis.


title: Revisiting Lepton Flavour Universality in B Decays

abstract:
  Lepton flavour universality (LFU) in B-decays is revisited by considering a
class of semileptonic operators defined at a scale Lambda above the electroweak
scale v. The importance of quantum effects, so far neglected in the literature,
is emphasised. We construct the low-energy effective Lagrangian taking into
account the running effects from Lambda down to v through the one-loop
renormalization group equations (RGE) in the limit of exact electroweak
symmetry and QED RGEs from v down to the 1 GeV scale. The most important
quantum effects turn out to be the modification of the leptonic couplings of
the vector boson Z and the generation of a purely leptonic effective
Lagrangian. Large LFU breaking effects in Z and tau decays and visible lepton
flavour violating (LFV) effects in the processes tau -> mu ll, tau -> mu rho,
tau -> mu pi and tau -> mu eta^(') are induced.


title: Pfaffian Schur processes and last passage percolation in a half-quadrant

abstract:
  We study last passage percolation in a half-quadrant, which we analyze within
the framework of Pfaffian Schur processes. For the model with exponential
weights, we prove that the fluctuations of the last passage time to a point on
the diagonal are either GSE Tracy-Widom distributed, GOE Tracy-Widom
distributed, or Gaussian, depending on the size of weights along the diagonal.
Away from the diagonal, the fluctuations of passage times follow the GUE
Tracy-Widom distribution. We also obtain a two-dimensional crossover between
the GUE, GOE and GSE distribution by studying the multipoint distribution of
last passage times close to the diagonal when the size of the diagonal weights
is simultaneously scaled close to the critical point. We expect that this
crossover arises universally in KPZ growth models in half-space. Along the way,
we introduce a method to deal with diverging correlation kernels of point
processes where points collide in the scaling limit.

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


title:
Dynamical structure of magnetized dissipative accretion flow around
  black holes

abstract:
  We study the global structure of optically thin, advection dominated,
magnetized accretion flow around black holes. We consider the magnetic field to
be turbulent in nature and dominated by the toroidal component. With this, we
obtain the complete set of accretion solutions for dissipative flows where
bremsstrahlung process is regarded as the dominant cooling mechanism. We show
that rotating magnetized accretion flow experiences virtual barrier around
black hole due to centrifugal repulsion that can trigger the discontinuous
transition of the flow variables in the form of shock waves. We examine the
properties of the shock waves and find that the dynamics of the post-shock
corona (PSC) is controlled by the flow parameters, namely viscosity, cooling
rate and strength of the magnetic field, respectively. We separate the
effective region of the parameter space for standing shock and observe that
shock can form for wide range of flow parameters. We obtain the critical
viscosity parameter that allows global accretion solutions including shocks. We
estimate the energy dissipation at the PSC from where a part of the accreting
matter can deflect as outflows and jets. We compare the maximum energy that
could be extracted from the PSC and the observed radio luminosity values for
several super-massive black hole sources and the observational implications of
our present analysis are discussed.


title: On the work of Rodriguez Hertz on rigidity in dynamics

abstract:
  This paper is a survey about recent progress in measure rigidity and global
rigidity of Anosov actions, and celebrates the profound contributions by
Federico Rodriguez Hertz to rigidity in dynamical systems.


title:
ZFIRE: The Kinematics of Star-Forming Galaxies as a Function of
  Environment at z~2

abstract:
  We perform a kinematic analysis of galaxies at $z\sim2$ in the COSMOS legacy
field using near-infrared (NIR) spectroscopy from Keck/MOSFIRE as part of the
ZFIRE survey. Our sample consists of 75 Ks-band selected star-forming galaxies
from the ZFOURGE survey with stellar masses ranging from
log(M$_{\star}$/M$_{\odot}$)$=9.0-11.0$, 28 of which are members of a known
overdensity at $z=2.095$. We measure H$\alpha$ emission-line integrated
velocity dispersions ($\sigma_{\rm int}$) from 50$-$230 km s$^{-1}$, consistent
with other emission-line studies of $z\sim2$ field galaxies. From these data we
estimate virial, stellar, and gas masses and derive correlations between these
properties for cluster and field galaxies at $z\sim2$. We find evidence that
baryons dominate within the central effective radius. However, we find no
statistically significant differences between the cluster and the field, and
conclude that the kinematics of star-forming galaxies at $z\sim2$ are not
significantly different between the cluster and field environments.


title:
The selection rules of high harmonic generation: the symmetries of
  molecules and laser fields

abstract:
  The selection rules of high harmonic generation (HHG) are investigated using
three-dimensional time-dependent density functional theory (TDDFT). From the
harmonic spectra obtained with various real molecules and different forms of
laser fields, several factors that contribute to selection rules are revealed.
Extending the targets to stereoscopic molecules, it is shown that the allowed
harmonics are dependent on the symmetries of the projections of molecules. For
laser fields, the symmetries contributing to the selection rules are discussed
according to Lissajous figures and their dynamical directivities. All the
phenomena are explained by the symmetry of the full time-dependent Hamiltonian
under a combined transformation. We present a systematic study on the selection
rules and propose an intuitive method for the judgment of allowed harmonic
orders, which can be extended to more complex molecules and various forms of
laser pulses.


title: On American VIX options under the generalized 3/2 and 1/2 models

abstract:
  In this paper, we extend the 3/2-model for VIX studied by Goard and Mazur
(2013) and introduce the generalized 3/2 and 1/2 classes of volatility
processes. Under these models, we study the pricing of European and American
VIX options and, for the latter, we obtain an early exercise premium
representation using a free-boundary approach and local time-space calculus.
The optimal exercise boundary for the volatility is obtained as the unique
solution to an integral equation of Volterra type.
  We also consider a model mixing these two classes and formulate the
corresponding optimal stopping problem in terms of the observed factor process.
The price of an American VIX call is then represented by an early exercise
premium formula. We show the existence of a pair of optimal exercise boundaries
for the factor process and characterize them as the unique solution to a system
of integral equations.


title: Fast and Robust Compressive Phase Retrieval with Sparse-Graph Codes

abstract:
  In this paper, we tackle the compressive phase retrieval problem in the
presence of noise. The noisy compressive phase retrieval problem is to recover
a $K$-sparse complex signal $s \in \mathbb{C}^n$, from a set of $m$ noisy
quadratic measurements: $ y_i=| a_i^H s |^2+w_i$, where $a_i^H\in\mathbb{C}^n$
is the $i$th row of the measurement matrix $A\in\mathbb{C}^{m\times n}$, and
$w_i$ is the additive noise to the $i$th measurement. We consider the regime
where $K=\beta n^\delta$, with constants $\beta>0$ and $\delta\in(0,1)$. We use
the architecture of PhaseCode algorithm, and robustify it using two schemes:
the almost-linear scheme and the sublinear scheme. We prove that with high
probability, the almost-linear scheme recovers $s$ with sample complexity
$\Theta(K \log(n))$ and computational complexity $\Theta(n \log(n))$, and the
sublinear scheme recovers $s$ with sample complexity $\Theta(K\log^3(n))$ and
computational complexity $\Theta(K\log^3(n))$. To the best of our knowledge,
this is the first scheme that achieves sublinear computational complexity for
compressive phase retrieval problem. Finally, we provide simulation results
that support our theoretical contributions.


title: Effect of Energy Polydispersity on the Nature of Lennard-Jones Liquids

abstract:
  In the companion paper [T. S. Ingebrigtsen and H. Tanaka, J. Phys. Chem. B
119, 11052 (2015)] the effect of size polydispersity on the nature of
Lennard-Jones (LJ) liquids, which represent most molecular liquids without
hydrogen bonds, was studied. More specifically, it was shown that even highly
size polydisperse LJ liquids are Roskilde-simple (RS) liquids. RS liquids are
liquids with strong correlation between constant volume equilibrium
fluctuations of virial and potential energy and are simpler than other types of
liquids. Moreover, it was shown that size polydisperse LJ liquids have
isomorphs to a good approximation. Isomorphs are curves in the phase diagram of
RS liquids along which structure, dynamics, and some thermodynamic quantities
are invariant in dimensionless (reduced) units. In this paper, we study the
effect of energy polydispersity on the nature of LJ liquids. We show that
energy polydisperse LJ liquids are RS liquids. However, a tendency of particle
segregation which increases with the degree of polydispersity leads to a loss
of strong virial-potential energy correlation, but is mitigated with increasing
temperature and/or density. Isomorphs are a good approximation also for energy
polydisperse LJ liquids, although particle-resolved quantities display a
somewhat poorer scaling compared to the mean quantities along the isomorph.


title:
Hierarchy, dimension, attractor and self-organization -- dynamics of
  mode-locked fiber lasers

abstract:
  Mode-locked fiber lasers are one of the most important sources of ultra-short
pulses. However, A unified description for the rich variety of states and the
driving forces behind the complex and diverse nonlinear behavior of mode-locked
fiber lasers have yet to be developed. Here we present a comprehensive
theoretical framework based upon complexity science, thereby offering a
fundamentally new way of thinking about the behavior of mode-locked fiber
lasers. This hierarchically structured frame work provide a model with and
changeable variable dimensionality resulting in a simple and elegant view, with
which numerous complex states can be described systematically. The existence of
a set of new mode-locked fiber laser states is proposed for the first time.
Moreover, research into the attractors' basins reveals the origin of
stochasticity, hysteresis and multistability in these systems. These findings
pave the way for dynamics analysis and new system designs of mode-locked fiber
lasers. The paradigm will have a wide range of potential applications in
diverse research fields.


title: Dynamic Control of Interference Limited Underlay D2D Network

abstract:
  Device-to-Device (D2D) communication appears as a key communication paradigm
to realizing the vision of Internet of Things (IoT) into reality by supporting
heterogeneous objects interconnection in a large scale network. These devices
may be many types of objects with embedded intelligence and communication
capabilities, e.g., smart phones, cars, or home appliances. The issue in in
this type of communication is the interference to cellular communication caused
by D2D communication. Thus, proper power control and resource allocation should
be coordinated in D2D network to prevent excessive interference and drastic
decrease in the throughput of the cellular system. In this paper, we consider
the problem of cross-layer resource allocation in time-varying cellular
wireless networks with D2D communication and incorporate average interference
to cellular system as a quality-of-service constraint. Specifically, each D2D
pair in the network injects packets to its queue, at rates chosen in order to
maximize a global utility function, subject to network stability and
interference constraints. The interference constraint enforces an arbitrarily
low interference to the cellular system caused by D2D communication. We first
obtain the stability region for the multiuser systems assuming that the nodes
have full channel state information (CSI) of their neighbors. Then, we provide
a joint flow control and scheduling scheme, which is proven to achieve a
utility arbitrarily close to the maximum achievable utility. Finally, we
address the consequences of practical implementation issue such as distributed
scheduling by a designing algorithm, which is capable of taking advantage of
diversity gain introduced by fading channels. We demonstrate the efficacy of
our policies by numerical studies under various network conditions.


title:
Conditions for cell size homeostasis: A stochastic hybrid systems
  approach

abstract:
  A ubiquitous feature of living cells is their growth over time followed by
division into daughter cells. How isogenic cell populations maintain size
homeostasis, i.e., a narrow distribution of cell size, is an intriguing
fundamental problem. We model cell size using a stochastic hybrid system, where
a cell grows exponentially in size (volume) over time and probabilistic
division events are triggered at discrete time intervals. Moreover, whenever
division events occur, size is randomly partitioned among daughter cells. We
first consider a scenario, where a timer (i.e., cell-cycle clock) that measures
the time since the last division event regulates both the cellular growth and
division rates. Analysis reveals that such a timer-controlled system cannot
achieve size homeostasis, in the sense that, the cell-to-cell size variation
grows unboundedly with time. To explore biologically meaningful mechanisms for
controlling size we consider two classes of regulation: a size-dependent growth
rate and a size-dependent division rate. Our results show that these strategies
can provide bounded intercellular variation in cell size, and exact
mathematical conditions on the form of regulation needed for size homeostasis
are derived. Different known forms of size control strategies, such as, the
adder and the sizer are shown to be consistent with these results.
Interestingly, for timer-based division mechanisms, the mean cell size depends
on the noise in the cell-cycle duration but independent of errors incurred in
partitioning of volume among daughter cells. In contrast, the mean cell size
decreases with increasing partitioning errors for size-based division
mechanisms. Finally, we discuss how organisms ranging from bacteria to
mammalian cells have adopted different control approaches for maintaining size
homeostasis.


title: On injective dimension of F-finite F-modules and holonomic D-modules

abstract:
  We investigate injective dimension of $F$-finite $F$-modules in
characteristic $p$ and holonomic $D$-modules in characteristic 0. One of our
main results is the following. If, either $R$ is a regular ring of finite type
over an infinite field of characteristic $p>0$ and $M$ is an $F_R$-finite
$F_R$-module, or $R=k[x_1,\dots,x_n]$ where $k$ is a field of characteristic 0
and $M$ is a holonomic $D(R,k)$-module, then the injective dimension of $M$ is
the same as the dimension of its support.


title:
Study for (anti)hypertriton and light (anti)nuclei productions in high
  energy collisions at 200 GeV

abstract:
  We use the parton and hadron cascade (PACIAE) model and the dynamically
constrained phase-space coalescence (DCPC) model to investigate the productions
of (anti)hypertriton and light (anti)nuclei generated by 0-10% centrality
$^{12}$C+$^{12}$C, $^{24}$Mg+$^{24}$Mg, $^{40}$Ca+$^{40}$Ca, and
$^{64}$Cu+$^{64}$Cu collisions at $\sqrt{S_{NN}}$ = 200 GeV with $|y|$ $<$ 1.5
and $p_{T}$ $<$ 5. We study the yield ratios of the antiparticle to particle
and the rapidity distributions of the different (anti)nuclei. We find that the
amounts of antimatter produced are significantly lower than that of the
corresponding particles, the results of theoretical models are well consistent
with the PHOBOS data. The yield ratios of the particle to antiparticle in
different transverse momentum regions are also given, and we find that the
ratios are raise with the increase of the transverse momentum.


title: Dictionary Learning for Robotic Grasp Recognition and Detection

abstract:
  The ability to grasp ordinary and potentially never-seen objects is an
important feature in both domestic and industrial robotics. For a system to
accomplish this, it must autonomously identify grasping locations by using
information from various sensors, such as Microsoft Kinect 3D camera. Despite
numerous progress, significant work still remains to be done in this field. To
this effect, we propose a dictionary learning and sparse representation (DLSR)
framework for representing RGBD images from 3D sensors in the context of
determining such good grasping locations. In contrast to previously proposed
approaches that relied on sophisticated regularization or very large datasets,
the derived perception system has a fast training phase and can work with small
datasets. It is also theoretically founded for dealing with masked-out entries,
which are common with 3D sensors. We contribute by presenting a comparative
study of several DLSR approach combinations for recognizing and detecting grasp
candidates on the standard Cornell dataset. Importantly, experimental results
show a performance improvement of 1.69% in detection and 3.16% in recognition
over current state-of-the-art convolutional neural network (CNN). Even though
nowadays most popular vision-based approach is CNN, this suggests that DLSR is
also a viable alternative with interesting advantages that CNN has not.


title: Geometric embedding properties of Bestvina-Brady subgroups

abstract:
  We compute the relative divergence and the subgroup distortion of
Bestvina-Brady subgroups. We also show that for each integer $n\geq 3$, there
is a free subgroup of rank $n$ of some right-angled Artin group whose inclusion
is not a quasi-isometric embedding. This result answers the question of Carr
about the minimum rank $n$ such that some right-angled Artin group has a free
subgroup of rank $n$ whose inclusion is not a quasi-isometric embedding. It is
well-known that a right-angled Artin group $A_\Gamma$ is the fundamental group
of a graph manifold whenever the defining graph $\Gamma$ is a tree. We show
that the Bestvina-Brady subgroup $H_\Gamma$ in this case is a horizontal
surface subgroup.


title: Multi-pretrained Deep Neural Network

abstract:
  Pretraining is widely used in deep neutral network and one of the most famous
pretraining models is Deep Belief Network (DBN). The optimization formulas are
different during the pretraining process for different pretraining models. In
this paper, we pretrained deep neutral network by different pretraining models
and hence investigated the difference between DBN and Stacked Denoising
Autoencoder (SDA) when used as pretraining model. The experimental results show
that DBN get a better initial model. However the model converges to a
relatively worse model after the finetuning process. Yet after pretrained by
SDA for the second time the model converges to a better model if finetuned.


title: Parallel Triangular Solvers on GPU

abstract:
  In this paper, we investigate GPU based parallel triangular solvers
systematically. The parallel triangular solvers are fundamental to incomplete
LU factorization family preconditioners and algebraic multigrid solvers. We
develop a new matrix format suitable for GPU devices. Parallel lower triangular
solvers and upper triangular solvers are developed for this new data structure.
With these solvers, ILU preconditioners and domain decomposition
preconditioners are developed. Numerical results show that we can speed
triangular solvers around seven times faster.


title: Homomorphisms from Specht Modules to Signed Young Permutation Modules

abstract:
  We construct a class $\Theta_{\mathscr{R}}$ of homomorphisms from a Specht
module $S_{\mathbb{Z}}^{\lambda}$ to a signed permutation module
$M_{\mathbb{Z}}(\alpha|\beta)$ which generalises James's construction of
homomorphisms whose codomain is a Young permutation module. We show that any
$\phi \in
\operatorname{Hom}_{{\mathbb{Z}}\mathfrak{S}_{n}}\big(S_{\mathbb{Z}}^\lambda,
M_{\mathbb{Z}}(\alpha|\beta)\big)$ lies in the $\mathbb{Q}$-span of
$\Theta_{\text{sstd}}$, a subset of $\Theta_{\mathscr{R}}$ corresponding to
semistandard $\lambda$-tableaux of type $(\alpha|\beta)$. We also study the
conditions for which $\Theta^{\mathbb{F}}_{\mathrm{sstd}}$ - a subset of
$\operatorname{Hom}_{\mathbb{F}\mathfrak{S}_{n}}\big(S_{\mathbb{F}}^\lambda,M_{\mathbb{F}}(\alpha|\beta)\big)$
induced by $\Theta_{\mathrm{sstd}}$ - is linearly independent, and show that it
is a basis for
$\operatorname{Hom}_{\mathbb{F}\mathfrak{S}_{n}}\big(S_{\mathbb{F}}^\lambda,M_{\mathbb{F}}(\alpha|\beta)\big)$
when $\mathbb{F}\mathfrak{S}_{n}$ is semisimple.


title: On stationary solutions to the vacuum Einstein field equations

abstract:
  We prove that any 4-dimensional geodesically complete spacetime with a
timelike Killing field satisfying the vacuum Einstein field equation
$Ric(g_{M})=\lambda g_{M}$ with nonnegative cosmological constant $\lambda\geq
0$ is flat. When dim $\geq 5$, if the spacetime is assumed to be static
additionally, we prove that its universal cover splits isometrically as a
product of a Ricci flat Riemannian manifold and a real line.


title:
Distribution of residence times as a marker to distinguish different
  pathways for quantum transport

abstract:
  Electron transport through a nanoscale system is an inherently stochastic
quantum mechanical process. Electric current is a time series of electron
tunnelling events separated by random intervals. Thermal and quantum noise are
two sources of this randomness. In this paper, we used the quantum master
equation to consider the following questions: (i) Given that an electron has
tunnelled into the electronically unoccupied system from the source electrode
at some particular time, how long is it until an electron tunnels out to the
drain electrode to leave the system electronically unoccupied, where there were
no intermediate tunnelling events ("the" tunnelling path)? (ii) Given that an
electron has tunnelled into the unoccupied system from the source electrode at
some particular time, how long is it until an electron tunnels out to the drain
electrode to leave the system electronically unoccupied, where there were no
intermediate tunnelling events ("an" tunnelling path)? (iii) What are the
distributions of these times? We show that electron correlations suppress the
difference between "the" and "an" electron tunnelling paths.


title:
Development of Krylov and AMG linear solvers for large-scale sparse
  matrices on GPUs

abstract:
  This research introduce our work on developing Krylov subspace and AMG
solvers on NVIDIA GPUs. As SpMV is a crucial part for these iterative methods,
SpMV algorithms for single GPU and multiple GPUs are implemented. A HEC matrix
format and a communication mechanism are established. And also, a set of
specific algorithms for solving preconditioned systems in parallel environments
are designed, including ILU(k), RAS and parallel triangular solvers. Based on
these work, several Krylov solvers and AMG solvers are developed. According to
numerical experiments, favorable acceleration performance is acquired from our
Krylov solver and AMG solver under various parameter conditions.


title:
Forecasting wind power - Modeling periodic and non-linear effects under
  conditional heteroscedasticity

abstract:
  In this article we present an approach that enables joint wind speed and wind
power forecasts for a wind park. We combine a multivariate seasonal time
varying threshold autoregressive moving average (TVARMA) model with a power
threshold generalized autoregressive conditional heteroscedastic (power-TGARCH)
model. The modeling framework incorporates diurnal and annual periodicity
modeling by periodic B-splines, conditional heteroscedasticity and a complex
autoregressive structure with non-linear impacts. In contrast to usually
time-consuming estimation approaches as likelihood estimation, we apply a
high-dimensional shrinkage technique. We utilize an iteratively re-weighted
least absolute shrinkage and selection operator (lasso) technique. It allows
for conditional heteroscedasticity, provides fast computing times and
guarantees a parsimonious and regularized specification, even though the
parameter space may be vast. We are able to show that our approach provides
accurate forecasts of wind power at a turbine-specific level for forecasting
horizons of up to 48 h (short- to medium-term forecasts).


title:
Modelling discrete valued cross sectional time series with observation
  driven models

abstract:
  This paper develops computationally feasible methods for estimating random
effects models in the context of regression modelling of multiple independent
time series of discrete valued counts in which there is serial dependence.
Given covariates, random effects and process history, the observed responses at
each time in each series are independent and have an exponential family
distribution. We develop maximum likelihood estimation of the mixed effects
model using an observation driven generalized linear autoregressive moving
average specification for the serial dependence in each series. The paper
presents an easily implementable approach which uses existing single time
series methods to handle the serial dependence structure in combination with
adaptive Gaussian quadrature to approximate the integrals over the regression
random effects required for the likelihood and its derivatives. The models and
methods presented allow extension of existing mixed model procedures for count
data by incorporating serial dependence which can differ in form and strength
across the individual series. The structure of the model has some similarities
to longitudinal data transition models with random effects. However, in
contrast to that setting, where there are many cases and few to moderate
observations per case, the time series setting has many observations per series
and a few to moderate number of cross sectional time series. The method is
illustrated on time series of binary responses to musical features obtained
from a panel of listeners.


title: Large-scale Reservoir Simulations on IBM Blue Gene/Q

abstract:
  This paper presents our work on simulation of large-scale reservoir models on
IBM Blue Gene/Q and studying the scalability of our parallel reservoir
simulators. An in-house black oil simulator has been implemented. It uses MPI
for communication and is capable of simulating reservoir models with hundreds
of millions of grid cells. Benchmarks show that our parallel simulator are
thousands of times faster than sequential simulators that designed for
workstations and personal computers, and the simulator has excellent
scalability.


title: Smoothing of semistable Fano varieties

abstract:
  Given any field $k$ (not necessarily perfect), we study the smoothing of a
semistable Fano variety over $k$. In characteristic 0, the reduced semistable
Fano degenerate fibers of Mori fibrations are classified. In positive
characteristic, under a suitable $W_2$ lifting assumption, we prove that a
semistable Fano variety always appears as a degenerate fiber in a semistable
family if it has a global log structure (in the sense of Fontaine-Illusie-Kato)
of semistable type. A similar smoothing result over a mixed characteristic base
is also obtained.