title:
Direct observation of chiral currents and magnetic reflection in atomic
  flux lattices

abstract:
  The prospect of studying topological matter with the precision and control of
atomic physics has driven the development of many techniques for engineering
artificial magnetic fields and spin-orbit interactions. Recently, the idea of
introducing nontrivial topology through the use of internal (or external)
atomic states as effective "synthetic dimensions" has garnered attraction for
its versatility and possible immunity from heating. Here, we directly engineer
tunable artificial gauge fields through the local control of tunneling phases
in an effectively two-dimensional manifold of discrete atomic momentum states.
We demonstrate the ability to create homogeneous gauge fields of arbitrary
value, directly imaging the site-resolved dynamics of induced chiral currents.
We furthermore engineer the first inhomogeneous artificial gauge fields for
cold atoms, observing the magnetic reflection of atoms incident upon a
step-like variation of an artificial vector potential. These results open up
new possibilities for the study of topological phases and localization
phenomena in atomic gases.


title:
Reconstructing Vechicles from a Single Image: Shape Priors for Road
  Scene Understanding

abstract:
  We present an approach for reconstructing vehicles from a single (RGB) image,
in the context of autonomous driving. Though the problem appears to be
ill-posed, we demonstrate that prior knowledge about how 3D shapes of vehicles
project to an image can be used to reason about the reverse process, i.e., how
shapes (back-)project from 2D to 3D. We encode this knowledge in \emph{shape
priors}, which are learnt over a small keypoint-annotated dataset. We then
formulate a shape-aware adjustment problem that uses the learnt shape priors to
recover the 3D pose and shape of a query object from an image. For shape
representation and inference, we leverage recent successes of Convolutional
Neural Networks (CNNs) for the task of object and keypoint localization, and
train a novel cascaded fully-convolutional architecture to localize vehicle
\emph{keypoints} in images. The shape-aware adjustment then robustly recovers
shape (3D locations of the detected keypoints) while simultaneously filling in
occluded keypoints. To tackle estimation errors incurred due to erroneously
detected keypoints, we use an Iteratively Re-weighted Least Squares (IRLS)
scheme for robust optimization, and as a by-product characterize noise models
for each predicted keypoint. We evaluate our approach on autonomous driving
benchmarks, and present superior results to existing monocular, as well as
stereo approaches.


title: Cosmic neutrinos: dispersive and non-linear

abstract:
  We present a description of cosmic neutrinos as a dispersive fluid. In this
approach, the neutrino phase space is reduced to density and velocity fields
alongside a scale-dependent sound speed. This sound speed depends on redshift,
the initial neutrino phase space density and the cold dark matter gravitational
potential. The latter is a new coupling between neutrinos and large scale
structure not described by previous fluid approaches. We compute the sound
speed in linear theory and find that it asymptotes to constants at small and
large scales regardless of the gravitational potential. By comparing with
neutrino N-body simulations, we measure the small scale sound speed and find it
to be lower than linear theory predictions. This allows for an explanation of
the discrepency between N-body and linear response predictions for the neutrino
power spectrum: neutrinos are still driven predominantly by the cold dark
matter, but the sound speed on small scales is not stable to perturbations and
decreases. Finally, we present a calibrated model for the neutrino power
spectrum that requires no additional integrations outside of standard Boltzmann
codes.


title:
Macroscopic Modeling, Calibration, and Simulation of Managed
  Lane-Freeway Networks, Part I: Topological and Phenomenological Modeling

abstract:
  To help mitigate road congestion caused by the unrelenting growth of traffic
demand, many transit authorities have implemented managed lane policies.
Managed lanes typically run parallel to a freeway's standard, general-purpose
(GP) lanes, but are restricted to certain types of vehicles. It was originally
thought that managed lanes would improve the use of existing infrastructure
through incentivization of demand-management behaviors like carpooling, but
implementations have often been characterized by unpredicted phenomena that is
often to detrimental system performance.
  This paper presents several macroscopic traffic modeling tools we have used
for study of freeways equipped with managed lanes, or "managed lane-freeway
networks." The proposed framework is based on the widely-used first-order
kinematic wave theory. In this model, the GP and the managed lanes are modeled
as parallel links connected by nodes, where certain type of traffic may switch
between GP and managed lane links. Two types of managed lane topologies are
considered: full-access, where vehicles can switch between the GP and the
managed lanes anywhere; and separated, where such switching is allowed only at
certain locations called gates.
  We also describe methods to incorporate in three phenomena into our model
that are particular to managed lane-freeway networks. The inertia effect
reflects drivers' inclination to stay in their lane as long as possible and
switch only if this would obviously improve their travel condition. The
friction effect reflects the empirically-observed driver fear of moving fast in
a managed lane while traffic in the adjacent GP lanes moves slowly due to
congestion. The smoothing effect describes how managed lanes can increase
throughput at bottlenecks by reducing lane changes. We present simple models
for each of these phenomena that fit within the general macroscopic theory.


title: Classifier comparison using precision

abstract:
  New proposed models are often compared to state-of-the-art using statistical
significance testing. Literature is scarce for classifier comparison using
metrics other than accuracy. We present a survey of statistical methods that
can be used for classifier comparison using precision, accounting for
inter-precision correlation arising from use of same dataset. Comparisons are
made using per-class precision and methods presented to test global null
hypothesis of an overall model comparison. Comparisons are extended to multiple
multi-class classifiers and to models using cross validation or its variants.
Partial Bayesian update to precision is introduced when population prevalence
of a class is known. Applications to compare deep architectures are studied.


title: Phase space methods for the spin dynamics in condensed matter systems

abstract:
  Using the phase-space formulation of quantum mechanics, we derive a
four-component Wigner equation for a system composed of spin-1/2 fermions
(typically, electrons) including the Zeeman effect and the spin-orbit coupling.
This Wigner equation is coupled to the appropriate Maxwell equations to form a
self-consistent mean-field model. A set of semiclassical Vlasov equations with
spin effects is obtained by expanding the full quantum model to first order in
the Planck constant. The corresponding hydrodynamic equations are derived by
taking velocity moments of the phase-space distribution function. A simple
closure relation is proposed to obtain a closed set of hydrodynamic equations.


title:
Adiabatic evolution generated by a one-dimensional Schr\"odinger
  operator with decreasing number of eigenvalues

abstract:
  We study a one-dimensional non-stationary Schr\"odinger equation with a
potential slowly depending on time. The corresponding stationary operator
depends on time as on a parameter. It has a finite number of negative
eigenvalues and absolutely continuous spectrum filling the positive semiaxis.
The eigenvalues move with time to the edge of the continuous spectrum and,
having reached it, disappear one after another. We study the asymptotic
behavior of a solution close at some moment to an eigenfunction of the
stationary operator, and, in particular, the phenomena occurring when the
corresponding eigenvalue approaches the absolutely continuous spectrum and
disappears.


title: Testing Lorentz and CPT invariance with neutrinos

abstract:
  Neutrino experiments can be considered sensitive tools to test Lorentz and
CPT invariance. Taking advantage of the great variety of neutrino experiments,
including neutrino oscillations, weak decays, and astrophysical neutrinos, the
generic experimental signatures of the breakdown of these fundamental
symmetries in the neutrino sector are presented.


title:
Multi-view Self-supervised Deep Learning for 6D Pose Estimation in the
  Amazon Picking Challenge

abstract:
  Robot warehouse automation has attracted significant interest in recent
years, perhaps most visibly in the Amazon Picking Challenge (APC). A fully
autonomous warehouse pick-and-place system requires robust vision that reliably
recognizes and locates objects amid cluttered environments, self-occlusions,
sensor noise, and a large variety of objects. In this paper we present an
approach that leverages multi-view RGB-D data and self-supervised, data-driven
learning to overcome those difficulties. The approach was part of the
MIT-Princeton Team system that took 3rd- and 4th- place in the stowing and
picking tasks, respectively at APC 2016. In the proposed approach, we segment
and label multiple views of a scene with a fully convolutional neural network,
and then fit pre-scanned 3D object models to the resulting segmentation to get
the 6D object pose. Training a deep neural network for segmentation typically
requires a large amount of training data. We propose a self-supervised method
to generate a large labeled dataset without tedious manual segmentation. We
demonstrate that our system can reliably estimate the 6D pose of objects under
a variety of scenarios. All code, data, and benchmarks are available at
http://apc.cs.princeton.edu/


title: Hilbert schemes of points on some classes of surface singularities

abstract:
  We study the geometry and topology of Hilbert schemes of points on the
orbifold surface [C^2/G], respectively the singular quotient surface C^2/G,
where G is a finite subgroup of SL(2,C) of type A or D. We give a decomposition
of the (equivariant) Hilbert scheme of the orbifold into affine space strata
indexed by a certain combinatorial set, the set of Young walls. The generating
series of Euler characteristics of Hilbert schemes of points of the singular
surface of type A or D is computed in terms of an explicit formula involving a
specialized character of the basic representation of the corresponding affine
Lie algebra; we conjecture that the same result holds also in type E. Our
results are consistent with known results for type A, and are new for type D.
The crystal basis theory of the fundamental representation of the affine Lie
algebra corresponding to the surface singularity (via the McKay correspondence)
plays an important role in our approach. The result gives a generalization of
G\"ottsche's formula and has interesting modular properties related to the
S-duality conjecture.
  The moduli space of torsion free sheaves on surfaces are higher rank analogs
of the Hilbert schemes. In type A our results reveal their Euler characteristic
generating function as well. Another very interesting class of normal surface
singularities is the so-called cyclic quotient singularities of type (p,1). As
an outlook we also obtain some results about the associated generating
functions.


title:
Non-perturbative determination of improvement coefficients using
  coordinate space correlators in $N_f=2+1$ lattice QCD

abstract:
  We determine quark mass dependent order $a$ improvement terms of the form
$b_J am$ for non-singlet scalar, pseudoscalar, vector and axialvector currents,
using correlators in coordinate space. We use a set of CLS ensembles comprising
non-perturbatively improved Wilson Fermions and the tree-level Luescher-Weisz
gauge action at $\beta=3.4,3.46,3.55$ and $\beta=3.7$, corresponding to lattice
spacings $a$ ranging from $0.05$ fm to $0.09$ fm. We report the values of the
$b_J$ improvement coefficients which are proportional to non-singlet quark mass
combinations and also discuss the possibility of determining the $\bar{b}_J$
coefficients which are proportional to the trace of the quark mass matrix.


title: Vibronic spectroscopy of sympathetically cooled CaH$^+$

abstract:
  We report the measurement of the 1$^{1}\Sigma\longrightarrow$ 2$^{1}\Sigma$
transition of CaH$^+$ by resonance-enhanced photodissociation of CaH$^+$ that
is co-trapped with laser-cooled Ca$^+$ . We observe four resonances that we
assign to transitions from the vibrational $v$=0 ground state to the $v'$=1-4
excited states based on theoretical predictions. A simple theoretical model
that assumes instantaneous dissociation after resonant excitation yield results
in good agreement with the observed spectral features except for the unobserved
$v'$=0 peak. The resolution of our experiment is limited by the mode-locked
excitation laser, but this survey spectroscopy enables future rotationally
resolved studies with applications in astrochemistry and precision measurement.


title:
Probing shock geometry via the charge to mass ratio dependence of heavy
  ion spectra from multiple spacecraft observations of the 2013 November 4
  event

abstract:
  In large SEP events, ions can be accelerated at CME-driven shocks to very
high energies. Spectra of heavy ions in many large SEP events show features
such as roll-overs or spectral breaks. In some events when the spectra are
plotted in energy/nucleon they can be shifted relative to each other to make
the spectral breaks align. The amount of shift is charge-to-mass ratio (Q/A)
dependent and varies from event to event. This can be understood if the spectra
of heavy ions are organized by the diffusion coefficients (Cohen et al., 2005).
In the work of Li et al. (2009), the Q/A dependences of the scaling is related
to shock geometry when the CME-driven shock is close to the Sun. For events
where multiple in-situ spacecraft observations exist, one may expect that
different spacecraft are connected to different portions of the CME-driven
shock that have different shock geometries, therefore yielding different Q/A
dependence. In this work, we examine one SEP event which occurred on 2013
November 4. We study the Q/A dependence of the energy scaling for heavy ion
spectra using Helium, oxygen, and iron ions. Observations from STEREO-A,
STEREO-B and ACE are examined. We find that the scalings are different for
different spacecraft. We suggest that this is because ACE, STEREO-A and STEREO-
B are connected to different parts of the shock that have different shock
geometries. Our analysis indicates that studying the Q/A scaling of in-situ
particle spectra can serve as a powerful tool to remotely examine the shock
geometry for large SEP events.


title:
Actions affines isom\'etriques propres des groupes hyperboliques sur des
  espaces $\ell^{p}$

abstract:
  We give a simple and relatively short proof of the following fact: any
hyperbolic group admits a proper affine isometric action on a $\ell^p$-space
for $p$ large enough. A first proof of this result was given by Guoliang Yu.


title: Fast learning rates with heavy-tailed losses

abstract:
  We study fast learning rates when the losses are not necessarily bounded and
may have a distribution with heavy tails. To enable such analyses, we introduce
two new conditions: (i) the envelope function $\sup_{f \in \mathcal{F}}|\ell
\circ f|$, where $\ell$ is the loss function and $\mathcal{F}$ is the
hypothesis class, exists and is $L^r$-integrable, and (ii) $\ell$ satisfies the
multi-scale Bernstein's condition on $\mathcal{F}$. Under these assumptions, we
prove that learning rate faster than $O(n^{-1/2})$ can be obtained and,
depending on $r$ and the multi-scale Bernstein's powers, can be arbitrarily
close to $O(n^{-1})$. We then verify these assumptions and derive fast learning
rates for the problem of vector quantization by $k$-means clustering with
heavy-tailed distributions. The analyses enable us to obtain novel learning
rates that extend and complement existing results in the literature from both
theoretical and practical viewpoints.


title: Topological Superconductivity in a Planar Josephson Junction

abstract:
  We consider a two-dimensional electron gas with strong spin-orbit coupling
contacted by two superconducting leads, forming a Josephson junction. We show
that in the presence of an in-plane Zeeman field the quasi-one-dimensional
region between the two superconductors can support a topological
superconducting phase hosting Majorana bound states at its ends. We study the
phase diagram of the system as a function of the Zeeman field and the phase
difference between the two superconductors (treated as an externally controlled
parameter). Remarkably, at a phase difference of $\pi$, the topological phase
is obtained for almost any value of the Zeeman field and chemical potential. In
a setup where the phase is not controlled externally, we find that the system
undergoes a first-order topological phase transition when the Zeeman field is
varied. At the transition, the phase difference in the ground state changes
abruptly from a value close to zero, at which the system is trivial, to a value
close to $\pi$, at which the system is topological. The critical current
through the junction exhibits a sharp minimum at the critical Zeeman field, and
is therefore a natural diagnostic of the transition. We point out that in
presence of a symmetry under a modified mirror reflection followed by time
reversal, the system belongs to a higher symmetry class and the phase diagram
as a function of the phase difference and the Zeeman field becomes richer.


title:
In-Situ Measurement of Relative Attenuation Length of Gadolinium-Loaded
  Liquid Scintillator Using Source Data at RENO Experiment

abstract:
  We present an in-situ method of measuring the relative attenuation length of
gadolinium-loaded liquid scintillator in the RENO detectors using radioactive
source calibration data without requiring any PMT performance model. We
observed the degradation of the attenuation length of the gadolinium-loaded
liquid scintillator in the RENO detectors by ~50% over a period of about 4
years.


title:
Effects of the Substitutions and Vacany Defects on the Stable monolayer
  structures of Black and Blue Arsenic Phosphorus: A First Principles Study

abstract:
  We investigate two dimensional monolayer structures of arsenic phosphorus (
AsP) by means of first principles plane wave method within density functional
theory using the generalized gradient approximation. Two structures of arsenic
phosphorus are taken into account which are called buckled (B-AsP) and puckered
(Pu-AsP). From our numerical calculations we predicted the optimized states of
a single-layer buckled and puckered honeycomb like allotropes of AsP. We
demonstrate that buckled and puckered arsenic phosphorus are semiconducting
single layers with band gap energies 1.858 eV and 0.924 eV, respectively.
Especially, we have found that the puckered monolayer has a direct band gap.
Furhermore, we examined the electronic and magnetic properties of various kind
of point defects including single and double vacancies, antisite and
substitutions on both buckled and puckered arsenic phosphorus. We conclude that
AsP monolayers can attain magnetic state with vacancies and the semiconductor
nature can turn into metal with diverse defect types. In considered system also
the band gap of B-AsP can be tuned from metal character to 1.858 eV and for
Pu-AsP from metal to 0.924 eV which these ranges are especially important for
radar and atmosferic applications.


title: Mathematical formulae on coins, parts I and II

abstract:
  In the article "The Tale of Two Queens and Two Towering Figures" published in
CNJ in 2012 (CNJ vol. 57 No. 5, pp. 304-315), we discussed the contributions of
Copernicus and Newton to coin minting and monetary reforms, as well as the
commemoration of their achievements on contemporary coins. In the current
article we will examine more explicit aspects of the relationship between
mathematical sciences and numismatics, namely the presence of mathematical
formulae on coins. We will survey examples of coins depicting mathematical
formulae, ranging from some universally recognizable ones to more advanced
symbolic expressions which are known only to specialists.


title:
Atomic Lattice Disorder in Charge Density Wave Phases of Exfoliated
  Dichalcogenides (1T-TaS2)

abstract:
  Charge density waves (CDW) and their concomitant periodic lattice distortions
(PLD) govern the electronic properties in many layered transition-metal
dichalcogenides. In particular, 1T-TaS2 undergoes a metal-to-insulator phase
transition as the PLD becomes commensurate with the crystal lattice. Here we
directly image PLDs of the nearly-commensurate (NC) and commensurate (C) phases
in thin exfoliated 1T-TaS2 using atomic resolution scanning transmission
electron microscopy at room and cryogenic temperature. At low temperatures, we
observe commensurate PLD superstructures, suggesting ordering of the CDWs both
in- and out-of-plane. In addition, we discover stacking transitions in the
atomic lattice that occur via one bond length shifts. Interestingly, the NC
PLDs exist inside both the stacking domains and their boundaries. Transitions
in stacking order are expected to create fractional shifts in the CDW between
layers and may be another route to manipulate electronic phases in layered
dichalcogenides.


title: Quantum common causes and quantum causal models

abstract:
  Reichenbach's principle asserts that if two observed variables are found to
be correlated, then there should be a causal explanation of these correlations.
Furthermore, if the explanation is in terms of a common cause, then the
conditional probability distribution over the variables given the complete
common cause should factorize. The principle is generalized by the formalism of
causal models, in which the causal relationships among variables constrain the
form of their joint probability distribution. In the quantum case, however, the
observed correlations in Bell experiments cannot be explained in the manner
Reichenbach's principle would seem to demand. Motivated by this, we introduce a
quantum counterpart to the principle. We demonstrate that under the assumption
that quantum dynamics is fundamentally unitary, if a quantum channel with input
A and outputs B and C is compatible with A being a complete common cause of B
and C, then it must factorize in a particular way. Finally, we show how to
generalize our quantum version of Reichenbach's principle to a formalism for
quantum causal models, and provide examples of how the formalism works.


title: Polish spaces of causal curves

abstract:
  We propose and study a new approach to the topologization of spaces of
(possibly not all) future-directed causal curves in a stably causal spacetime.
It relies on parametrizing the curves "in accordance" with a chosen time
function. Thus obtained topological spaces of causal curves are separable and
completely metrizable, i.e. Polish. The latter property renders them
particularly useful in the optimal transport theory. To illustrate this fact,
we explore the notion of a causal time-evolution of measures in globally
hyperbolic spacetimes and discuss its physical interpretation.


title:
Virial Black Hole Mass Estimates for 280,000 AGNs from the SDSS
  Broad-Band Photometry and Single Epoch Spectra

abstract:
  We use the Sloan Digital Sky Survey (SDSS) Quasar Data Release 12 (DR12Q),
containing nearly 300,000 AGNs, to calculate the monochromatic luminosities at
5100\AA, 3000\AA, and 1350\AA, derived from the broad-band extinction-corrected
SDSS magnitudes. After matching them to their counterparts based on spectra and
published in the SDSS Quasar Data Release 7 (DR7Q), we find perfect
correlations with minute mean offsets ($\sim$0.01 dex) and dispersions of
differences of 0.11, 0.10, 0.12 dex, respectively, across a 2.5 dex luminosity
range. We then estimate the active galactic nuclei (AGNs) black hole masses
using the broad line region radius--luminosity relations and the FWHM of the
MgII and CIV emission lines, to provide a catalog of 283,032 virial black hole
mass estimates (132,451 for MgII, 213,068 for CIV, and 62,487 for both) along
with the bolometric luminosity and the Eddington ratio estimates for
$0.1<z<5.5$ and for roughly a quarter of the sky covered by SDSS. The black
hole mass estimates from MgII turned out to be closely matched to the ones from
DR7Q with the dispersion of differences of 0.34 dex across a $\sim$2 dex BH
mass range. We uncovered a bias in the derived CIV FWHMs from DR12Q as compared
to DR7Q, that we correct empirically. The CIV BH mass estimates should be used
with caution because the CIV line is known to cause problems in the BH mass
estimation from single-epoch spectra. Finally, after the FWHM correction, the
AGN black hole mass estimates from CIV closely match the DR7Q ones (with the
dispersion of 0.28 dex), and more importantly the MgII and CIV BH masses agree
internally with the mean offset of 0.07 dex and the dispersion of 0.39 dex.


title:
Measuring the Innermost Stable Circular Orbits of Supermassive Black
  Holes

abstract:
  We present a promising new technique, the g-distribution method, for
measuring the inclination angle (i), the innermost stable circular orbit
(ISCO), and the spin of a supermassive black hole. The g-distribution method
uses measurements of the energy shifts in the relativistic iron line emitted by
the accretion disk of a supermassive black hole due to microlensing by stars in
a foreground galaxy relative to the g-distribution shifts predicted from
microlensing caustic calculations. We apply the method to the gravitationally
lensed quasars RX J1131-1231 (z_s=0.658, z_l=0.295), QJ 0158-4325 (z_s=1.294,
z_l=0.317), and SDSS 1004+4112 (z_s=1.734, z_l=0.68). For RX J1131-1231 our
initial results indicate that r_ISCO<8.5 gravitational radii (r_g) and i > 76
degrees. We detect two shifted Fe lines, in several observations, as predicted
in our numerical simulations of caustic crossings. The current
DeltaE-distribution of RX J1131-1231 is sparsely sampled but further X-ray
monitoring of RX J1131-1231 and other lensed quasars will provide improved
constraints on the inclination angles, ISCO radii and spins of the black holes
of distant quasars.


title: More about unphysical zeroes in quark mass matrices

abstract:
  We look for all weak bases that lead to texture zeroes in the quark mass
matrices and contain a minimal number of parameters in the framework of the
standard model. Since there are ten physical observables, namely, six
nonvanishing quark masses, three mixing angles and one CP phase, the maximum
number of texture zeroes in both quark sectors is altogether nine. The nine
zero entries can only be distributed between the up- and down-quark sectors in
matrix pairs with six and three texture zeroes or five and four texture zeroes.
In the weak basis where a quark mass matrix is nonsingular and has six zeroes
in one sector, we find that there are 54 matrices with three zeroes in the
other sector, obtainable through right-handed weak basis transformations. It is
also found that all pairs composed of a nonsingular matrix with five zeroes and
a nonsingular and nondecoupled matrix with four zeroes simply correspond to a
weak basis choice. Without any further assumptions, none of these pairs of up-
and down-quark mass matrices has physical content. It is shown that all
non-weak-basis pairs of quark mass matrices that contain nine zeroes are not
compatible with current experimental data. The particular case of the so-called
nearest-neighbour-interaction pattern is also discussed.


title: gPhoton: The GALEX Photon Data Archive

abstract:
  gPhoton is a new database product and software package that enables analysis
of GALEX ultraviolet data at the photon level. The project's stand-alone,
pure-Python calibration pipeline reproduces the functionality of the original
mission pipeline to reduce raw spacecraft data to lists of time-tagged,
sky-projected photons, which are then hosted in a publicly available database
by the Mikulski Archive at Space Telescope (MAST). This database contains
approximately 130 terabytes of data describing approximately 1.1 trillion
sky-projected events with a timestamp resolution of five milliseconds. A
handful of Python and command line modules serve as a front-end to interact
with the database and to generate calibrated light curves and images from the
photon-level data at user-defined temporal and spatial scales. The gPhoton
software and source code are in active development and publicly available under
a permissive license. We describe the motivation, design, and implementation of
the calibration pipeline, database, and tools, with emphasis on divergence from
prior work, as well as challenges created by the large data volume. We
summarize the astrometric and photometric performance of gPhoton relative to
the original mission pipeline. For a brief example of short time domain science
capabilities enabled by gPhoton, we show new flares from the known M dwarf
flare star CR Draconis. The gPhoton software has permanent object identifiers
with the ASCL (ascl:1603.004) and DOI (doi:10.17909/T9CC7G). This paper
describes the software as of version v1.27.2.


title:
On vector spaces of linearizations for matrix polynomials in orthogonal
  bases

abstract:
  Matrix polynomials given in an orthogonal basis are considered. Following the
ideas of Mackey et al. "Vector spaces of Linearizations for Matrix Polynomials"
(2006), the vec- tor spaces, called M1(P), M2(P) and DM(P), of potential
linearizations for P are analyzed. All pencils in M1(P) are characterized
concisely. Moreover, several easy to check criteria whether a pencil in M1(P)
is a (strong) linearization of P are given. The equivalence of some of them to
the Z-rank-condition (see Mackey et al. 2006) is pointed out. Results on the
vector space dimensions, the genericity of linearizations in and the form of
block-symmetric pencils are derived in a new way on a basic algebraic level.
Throughout the paper, structural resemblances between the matrix pencils in L1
, i.e. the results obtained in Mackey et al. 2006, and their generalized
versions are pointed out.


title: On the singular values of matrices with displacement structure

abstract:
  Matrices with displacement structure such as Pick, Vandermonde, and Hankel
matrices appear in a diverse range of applications. In this paper, we use an
extremal problem involving rational functions to derive explicit bounds on the
singular values of such matrices. For example, we show that the $k$th singular
value of a real $n\times n$ positive definite Hankel matrix, $H_n$, is bounded
by $C\rho^{-k/\log n}\|H\|_2$ with explicitly given constants $C>0$ and
$\rho>1$, where $\|H_n\|_2$ is the spectral norm. This means that a real
$n\times n$ positive definite Hankel matrix can be approximated, up to an
accuracy of $\epsilon\|H_n\|_2$ with $0<\epsilon<1$, by a rank
$\mathcal{O}(\log n\log(1/\epsilon) )$ matrix. Analogous results are obtained
for Pick, Cauchy, real Vandermonde, L\"{o}wner, and certain Krylov matrices.


title: ALMA view of the Galactic Center 50km/s molecular cloud

abstract:
  We have observed the Galactic Center 50km/s molecular cloud (50MC) with ALMA
to search for filamentary structures. In the CS J=2-1 emission line channel
maps, we succeeded in identifying 27 molecular cloud filaments using the
DisPerSE algorithm. This is the first attempt of "filament-finding" in the
Galactic Center Region. These molecular cloud filaments strongly suggest that
the molecular cloud filaments are also ubiquitous in the molecular clouds of
the Galactic Center Region.


title:
Two-body wave functions and compositeness from scattering amplitudes. I.
  General properties with schematic models

abstract:
  For a general two-body bound state in quantum mechanics, both in the stable
and decaying cases, we establish a way to extract its two-body wave function in
momentum space from the scattering amplitude of the constituent two particles.
For this purpose, we first show that the two-body wave function of the bound
state corresponds to the residue of the off-shell scattering amplitude at the
bound state pole. Then, we examine our scheme to extract the two-body wave
function from the scattering amplitude in several schematic models. As a
result, the two-body wave functions from the Lippmann--Schwinger equation
coincides with that from the Schr\"{o}dinger equation for an energy-independent
interaction. Of special interest is that the two-body wave function from the
scattering amplitude is automatically scaled; the norm of the two-body wave
function, to which we refer as the compositeness, is unity for an
energy-independent interaction, while the compositeness deviates from unity for
an energy-dependent interaction, which can be interpreted to implement missing
channel contributions. We also discuss general properties of the two-body wave
function and compositeness for bound states in the schematic models.


title: Inflation in Flatland

abstract:
  We investigate the symmetry structure of inflation in 2+1 dimensions. In
particular, we show that the asymptotic symmetries of three-dimensional de
Sitter space are in one-to-one correspondence with cosmological adiabatic modes
for the curvature perturbation. In 2+1 dimensions, the asymptotic symmetry
algebra is infinite-dimensional, given by two copies of the Virasoro algebra,
and can be traced to the conformal symmetries of the two-dimensional spatial
slices of de Sitter. We study the consequences of this infinite-dimensional
symmetry for inflationary correlation functions, finding new soft theorems that
hold only in 2+1 dimensions. Expanding the correlation functions as a power
series in the soft momentum $q$, these relations constrain the traceless part
of the tensorial coefficient at each order in $q$ in terms of a lower-point
function. As a check, we verify that the ${\cal O}(q^2)$ identity is satisfied
by inflationary correlation functions in the limit of small sound speed.


title: The role of mergers and halo spin in shaping galaxy morphology

abstract:
  Mergers and the spin of the dark matter halo are factors traditionally
believed to determine the morphology of galaxies within a $\Lambda$CDM
cosmology. We study this hypothesis by considering approximately 18,000 central
galaxies at $z=0$ with stellar masses $M_{\ast} = 10^{9}-10^{12} \, {\rm
M}_{\odot}$ selected from the Illustris cosmological hydrodynamic simulation.
The fraction of accreted stars -- which measures the importance of massive,
recent and dry mergers -- increases steeply with galaxy stellar mass, from less
than 5 per cent in dwarfs to 80 per cent in the most massive objects, and the
impact of mergers on galaxy morphology increases accordingly. For galaxies with
$M_{\ast} \gtrsim 10^{11} \, {\rm M}_{\odot}$, mergers have the expected
effect: if gas-poor they promote the formation of spheroidal galaxies, whereas
gas-rich mergers favour the formation and survivability of massive discs. This
trend, however, breaks at lower masses. For objects with $M_{\ast} \lesssim
10^{11} \, {\rm M}_{\odot}$, mergers do not seem to play any significant role
in determining the morphology, with accreted stellar fractions and mean merger
gas fractions that are indistinguishable between spheroidal and disc-dominated
galaxies. On the other hand, halo spin correlates with morphology primarily in
the least massive objects in the sample ($M_{\ast} \lesssim 10^{10} \, {\rm
M}_{\odot}$), but only weakly for galaxies above that mass. Our results support
a scenario where (1) mergers play a dominant role in shaping the morphology of
massive galaxies, (2) halo spin is important for the morphology of dwarfs, and
(3) the morphology of medium-sized galaxies -- including the Milky Way -- shows
little dependence on galaxy assembly history or halo spin, at least when these
two factors are considered individually.


title: Young and turbulent: the early life of massive galaxy progenitors

abstract:
  We present results from the "Ponos" simulation suite on the early evolution
of a massive, $M_{\rm vir}(z=0)=1.2\times 10^{13}$ M$_{\odot}$ galaxy. At
$z\gtrsim6$, before feedback from a central supermassive black hole becomes
dominant, the main galaxy has a stellar mass $\sim 2\times 10^{9}$ M$_{\odot}$
and a star formation rate $\sim 20$ M$_{\odot}$ yr$^{-1}$. The galaxy sits near
the expected main sequence of star-forming galaxies at those redshifts, and
resembles moderately star-forming systems observed at $z>5$. The high specific
star formation rate results in vigorous heating and stirring of the gas by
supernovae feedback, and the galaxy develops a thick and turbulent disc, with
gas velocity dispersion $\sim 40$ km s$^{-1}$, rotation to dispersion ratio
$\sim 2$, and with a significant amount of gas at $\sim 10^5$ K. The Toomre
parameter always exceeds the critical value for gravito-turbulence, $Q\sim
1.5-2$, mainly due to the contribution of warm/hot gas inside the disc. Without
feedback, a nearly gravito-turbulent regime establishes with similar gas
velocity dispersion and lower $Q$. We propose that the "hot and turbulent" disc
regime seen in our simulations, unlike the "cold and turbulent"
gravito-turbulent regime of massive clumpy disc galaxies at $z\sim 1-2$, is a
fundamental characterisation of main sequence galaxies at $z\gtrsim 6$, as they
can sustain star formation rates comparable to those of low-mass starbursts at
$z=0$. This results in no sustained coherent gas inflows through the disc, and
in fluctuating and anisotropic mass transport, possibly postponing the assembly
of the bulge and causing the initial feeding of the central black hole to be
highly intermittent.


title:
Re-grouping stars based on the chemical tagging technique: A case study
  of M67 and IC4651

abstract:
  The chemical tagging technique proposed by Freeman & Bland-Hawthorn (2002) is
based on the idea that stars formed from the same molecular cloud should share
the same chemical signature. Thus, using only the chemical composition of stars
we should be able to re-group the ones that once belonged to the same stellar
aggregate. In Blanco-Cuaresma et al. (2015), we tested the technique on open
cluster stars using iSpec (Blanco-Cuaresma et al. 2014a), we demonstrated their
chemical homogeneity but we found that the 14 studied elements lead to chemical
signatures too similar to reliably distinguish stars from different clusters.
This represents a challenge to the technique and a new question was open: Could
the inclusion of other elements help to better distinguish stars from different
aggregates? With an updated and improved version of iSpec, we derived
abundances for 28 elements using spectra from HARPS, UVES and NARVAL archives
for the open clusters M67 and IC4651, and we found that the chemical signatures
of both clusters are very similar.


title:
SDSSJ143244.91+301435.3 at VLBI: a compact radio galaxy in a narrow-line
  Seyfert 1

abstract:
  We present VLBI observations, carried out with the European Very Long
Baseline Interferometry Network (EVN), of SDSSJ143244.91+301435.3, a radio-loud
narrow-line Seyfert 1 (RLNLS1) characterized by a steep radio spectrum. The
source, compact at Very Large Array (VLA) resolution, is resolved on the
milliarcsec scale, showing a central region plus two extended structures. The
relatively high brightness temperature of all components (5x10^6-1.3x10^8 K)
supports the hypothesis that the radio emission is non-thermal and likely
produced by a relativistic jet and/or small radio lobes. The observed radio
morphology, the lack of a significant core and the presence of a low frequency
(230 MHz) spectral turnover are reminiscent of the Compact Steep Spectrum
sources (CSS). However, the linear size of the source (~0.5kpc) measured from
the EVN map is lower than the value predicted using the turnover/size relation
valid for CSS sources (~6kpc). This discrepancy can be explained by an
additional component not detected in our observations, accounting for about a
quarter of the total source flux density, combined to projection effects. The
low core-dominance of the source (CD<0.29) confirms that
SDSSJ143244.91+301435.3 is not a blazar, i.e. the relativistic jet is not
pointing towards the observer. This supports the idea that
SDSSJ143244.91+301435.3 may belong to the "parent population" of flat-spectrum
RLNLS1 and favours the hypothesis of a direct link between RLNLS1 and compact,
possibly young, radio galaxies.


title:
The Gamma-ray Blazar Quest: new optical spectra, state of art and future
  perspectives

abstract:
  We recently developed a procedure to recognize gamma-ray blazar candidates
within the positional uncertainty regions of the unidentified/unassociated
gamma-ray sources (UGSs). Such procedure was based on the discovery that Fermi
blazars show peculiar infrared colors. However, to confirm the real nature of
the selected candidates, optical spectroscopic data are necessary. Thus, we
performed an extensive archival search for spectra available in the literature
in parallel with an optical spectroscopic campaign aimed to reveal and confirm
the nature of the selected gamma-ray blazar candidates. Here, we first search
for optical spectra of a selected sample of gamma-ray blazar candidates that
can be potential counterparts of UGSs using the Sloan Digital Sky Survey (SDSS
DR12). This search enables us to update the archival search carried out to
date. We also describe the state-of-art and the future perspectives of our
campaign to discover previously unknown gamma-ray blazars.


title:
A Systematic Search for Periodically Varying Quasars in Pan-STARRS1: An
  Extended Baseline Test in Medium Deep Survey Field MD09

abstract:
  We present a systematic search for periodically varying quasars and
supermassive black hole binary (SMBHB) candidates in the Pan-STARRS1 (PS1)
Medium Deep Survey's MD09 field. From a color-selected sample of 670 quasars
extracted from a multi-band deep-stack catalog of point sources, we locally
select variable quasars and look for coherent periods with the Lomb-Scargle
periodogram. Three candidates from our sample demonstrate strong variability
for more than ~3 cycles, and their PS1 light curves are well fitted to
sinusoidal functions. We test the persistence of the candidates' apparent
periodic variations detected during the 4.2 years of the PS1 survey with
archival photometric data from the SDSS Stripe 82 survey or new monitoring with
the Large Monolithic Imager at the Discovery Channel Telescope. None of the
three periodic candidates (including PSO J334.2028+1.4075) remain persistent
over the extended baseline of 7 - 14 years, corresponding to a detection rate
of < 1 in 670 quasars in a search area of 5 deg^2. Even though SMBHBs should be
a common product of the hierarchal growth of galaxies, and periodic variability
in SMBHBs has been theoretically predicted, a systematic search for such
signatures in a large optical survey is strongly limited by its temporal
baseline and the "red noise" associated with normal quasar variability. We show
that follow-up long-term monitoring (>5 cycles) is crucial to our search for
these systems.


title:
Direct Probe of Topological Invariants Using Bloch Oscillating Quantum
  Walks

abstract:
  The topology of a single-particle band structure plays a fundamental role in
understanding a multitude of physical phenomena. Motivated by the connection
between quantum walks and such topological band structures, we demonstrate that
a simple time-dependent, Bloch-oscillating quantum walk enables the direct
measurement of topological invariants. We consider two classes of
one-dimensional quantum walks and connect the global phase imprinted on the
walker with its refocusing behavior. By disentangling the dynamical and
geometric contributions to this phase we describe a general strategy to measure
the topological invariant in these quantum walks. As an example, we propose an
experimental protocol in a circuit QED architecture where a superconducting
transmon qubit plays the role of the coin, while the quantum walk takes place
in the phase space of a cavity.


title: Scattered light mapping of protoplanetary disks

abstract:
  High-contrast scattered light observations have revealed the surface
morphology of several dozens of protoplanetary disks at optical and
near-infrared wavelengths. Inclined disks offer the opportunity to measure part
of the phase function of the dust grains that reside in the disk surface which
is essential for our understanding of protoplanetary dust properties and the
early stages of planet formation. We aim to construct a method which takes into
account how the flaring shape of the scattering surface of an (optically thick)
protoplanetary disk projects onto the image plane of the observer. This allows
us to map physical quantities (scattering radius and scattering angle) onto
scattered light images and retrieve stellar irradiation corrected (r^2-scaled)
images and dust phase functions. We apply the method on archival polarized
intensity images of the protoplanetary disk around HD 100546 that were obtained
with VLT/SPHERE in R'-band and VLT/NACO in H- and Ks-band. The brightest side
of the r^2-scaled R'-band polarized intensity image of HD 100546 changes from
the far to the near side of the disk when a flaring instead of a geometrically
flat disk surface is used for the r^2-scaling. The decrease in polarized
surface brightness in the scattering angle range of ~40-70 deg is likely a
result of the dust phase function and degree of polarization which peak in
different scattering angle regimes. The derived phase functions show part of a
forward scattering peak which indicates that large, aggregate dust grains
dominate the scattering opacity in the disk surface. Projection effects of a
protoplanetary disk surface need to be taken into account to correctly
interpret scattered light images. Applying the correct scaling for the
correction of stellar irradiation is crucial for the interpretation of the
images and the derivation of the dust properties in the disk surface layer.


title: Stability of a Light Sail Riding on a Laser Beam

abstract:
  The stability of a light sail riding on a laser beam is analyzed both
analytically and numerically. Conical sails on Gaussian beams, which have been
studied in the past, are shown to be unstable without active control or
additional mechanical modifications. A new architecture for a passively stable
sail-and-beam configuration is proposed. The novel spherical shell design for
the sail is capable of "beam riding" without the need for active feedback
control. Full three-dimensional ray-tracing simulations are performed to verify
our analytical results.


title: Integrable reductions of the Bogoyavlenskij-Itoh Lotka-Volterra systems

abstract:
  Given a constant skew-symmetric matrix A, it is a difficult open problem
whether the associated Lotka-Volterra system is integrable or not. We solve
this problem in the special case when A is a Toepliz matrix where all
off-diagonal entries are plus or minus one. In this case, the associated
Lotka-Volterra system turns out to be a reduction of Liouville integrable
systems, whose integrability was shown by Bogoyavlenskij and Itoh. We prove
that the reduced systems are also Liouville integrable and that they are also
non-commutative integrable by constructing a set of independent first
integrals, having the required involutive properties (with respect to the
Poisson bracket). These first integrals fall into two categories. One set
consists of polynomial functions which can be obtained by a matricial
reformulation of Itoh's combinatorial description. The other set consists of
rational functions which are obtained through a Poisson map from the first
integrals of some recently discovered superintegrable Lotka-Volterra systems.
The fact that these polynomial and rational first integrals, combined, have the
required properties for Liouville and non-commutative integrability is quite
remarkable; the quite technical proof of functional independence of the first
integrals is given in detail.


title:
Two-Stage Bulk Electron Heating in the Diffusion Region of Anti-Parallel
  Symmetric Reconnection

abstract:
  Electron bulk energization in the diffusion region during anti-parallel
symmetric reconnection entails two stages. First, the inflowing electrons are
adiabatically trapped and energized by an ambipolar parallel electric field.
Next, the electrons gain energy from the reconnection electric field as they
undergo meandering motion. These collisionless mechanisms have been decribed
previously, and they lead to highly-structured electron velocity distributions.
Nevertheless, a simplified control-volume analysis gives estimates for how the
net effective heating scales with the upstream plasma conditions in agreement
with fully kinetic simulations and spacecraft observations.


title: Brillouin Optomechanics in Coupled Silicon Microcavities

abstract:
  The simultaneous control of optical and mechanical waves has enabled a range
of fundamental and technological breakthroughs, from the demonstration of
ultra-stable frequency reference devices to the exploration of the
quantum-classical boundaries in laser-cooling experiments. More recently, such
an opto-mechanical interaction has been observed in integrated nano-waveguides
and microcavities in the Brillouin regime, where short-wavelength mechanical
modes scatters light at several GHz. Here we engineer coupled optical
microcavities spectra to enable a low threshold excitation of mechanical
travelling-wave modes through backward stimulated Brillouin scattering.
Exploring the backward scattering we propose microcavity designs supporting
super high frequency modes ($\sim25$ GHz) an large optomechanical coupling
rates ($g_0/2\pi \sim 50$ kHz).


title:
(Non-adiabatic) string creation on nice slices in Schwarzschild black
  holes

abstract:
  Nice slices have played a pivotal role in the discussion of the black hole
information paradox as they avoid regions of strong spacetime curvature and yet
smoothly cut through the infalling matter and the outgoing Hawking radiation,
thus, justifying the use of low energy field theory. To avoid information loss
it has been argued recently, however, that local effective field theory has to
break down at the horizon. To assess the extent of this breakdown in a UV
complete framework we study string-theoretic effects on nice slices in
Schwarzschild black holes. Our purpose is two-fold. First, we use nice slices
to address various open questions and caveats of arXiv:1402.1486 where it was
argued that boost-enhanced non-adiabatic string-theoretic effects at the
horizon could provide a dynamical mechanism for the firewall. Second, we
identify two non-adiabatic effects on nice slices in Schwarzschild black holes:
pair production of open strings near the horizon enhanced by the presence of
the infinite tower of highly excited string states and a late-time
non-adiabatic effect intrinsic to nice slices.


title:
A dichotomy between the hard state spectral properties of black hole and
  neutron star X-ray~binaries

abstract:
  We analyse the spectra of black hole (BH) and neutron star (NS) X-ray
binaries (XBs) in the hard state using archival RXTE observations. We find that
there is a clear dichotomy in the strength of Comptonisation between NS and BH
sources, as measured by both the Compton y-parameter and amplification factor
A, with distinct groups of BH and NS XBs separated at y~0.9 and A~3. The
electron temperature kTe can occupy a broad range in BH systems, from
kTe~30-200 keV, whereas for NSs kTe is peaked at ~15-25 keV, but can extend to
higher values. The difference between BHs and NSs in y implies that kTe is
higher at a given optical depth for BH XBs. Our results also imply that for NS
systems the accreting material loses ~1/2-2/3 of its energy through
Comptonisation in the corona. The remaining energy is released on the surface
of the neutron star, making it a powerful source of soft radiation, which
alters the properties of the Comptonising corona. Finally, we find evidence at
the 2.4 sigma confidence level that Comptonisation parameters may be correlated
with the neutron star spin, whereas no correlation with the BH spin is found.
Our results highlight a further observational distinction between BH and NS XBs
that is a consequence of NSs possessing a physical surface.


title:
Probability of Physical Association of 104 Blended Companions to
  \textit{Kepler} Objects of Interest Using Visible and Near-Infrared Adaptive
  Optics Photometry

abstract:
  We determine probabilities of physical association for stars in blended
Kepler Objects of Interest, and find that $14.5\%^{+3.8\%}_{-3.4\%}$ of
companions within $\sim4\arcsec$ are consistent with being physically
unassociated with their primary. This produces a better understanding of
potential false positives in the Kepler catalog and will guide models of planet
formation in binary systems. Physical association is determined through two
methods of calculating multi-band photometric parallax using visible and
near-infrared adaptive optics observation of 84 KOI systems with 104
contaminating companions within $\sim4\arcsec$. We find no evidence that KOI
companions with separation of less than $1\arcsec$ are more likely to be
physically associated than KOI companions generally. We also reinterpret
transit depths for 94 planet candidates, and calculate that $2.6\% \pm 0.4\%$
of transits have $R > 15R_{\earth}$, which is consistent with prior modeling
work.


title: Neutron electric dipole moment from gauge/string duality

abstract:
  We compute the electric dipole moment of nucleons in the large $N_c$ QCD
model by Witten, Sakai and Sugimoto with $N_f=2$ degenerate massive flavors.
Baryons in the model are instantonic solitons of an effective five-dimensional
action describing the whole tower of mesonic fields. We find that the dipole
electromagnetic form factor of the nucleons, induced by a finite topological
$\theta$ angle, exhibits complete vector meson dominance. We are able to
evaluate the contribution of each vector meson to the final result - a small
number of modes are relevant to obtain an accurate estimate. Extrapolating the
model parameters to real QCD data, the neutron electric dipole moment is
evaluated to be $d_n = 1.8 \cdot 10^{-16}\, \theta\;e\cdot \mathrm{cm}$. The
electric dipole moment of the proton is exactly the opposite.


title:
Non-linear partially massless symmetry in an SO(1,5) continuation of
  conformal gravity

abstract:
  We construct a non-linear theory of interacting spin-2 fields that is
invariant under the partially massless (PM) symmetry to all orders. This theory
is based on the SO(1,5) group, in analogy with the SO(2,4) formulation of
conformal gravity, but has a quadratic spectrum free of ghost instabilities.
The action contains a vector field associated to a local SO(2) symmetry which
is manifest in the vielbein formulation of the theory. We show that, in a
perturbative expansion, the SO(2) symmetry transmutes into the PM
transformations of a massive spin-2 field. In this context, the vector field is
crucial to circumvent earlier obstructions to an order-by-order construction of
PM symmetry. Although the non-linear theory lacks enough first class
constraints to remove all helicity-0 modes from the spectrum, the PM
transformations survive to all orders. The absence of ghosts and strong
coupling effects at the non-linear level are not addressed here.


title:
Gauge and global symmetries of the candidate partially massless bimetric
  gravity

abstract:
  In this paper we investigate a particular ghost-free bimetric theory that
exhibits the partially massless (PM) symmetry at quadratic order. At this order
the global SO(1,4) symmetry of the theory is enhanced to SO(1,5). We show that
this global symmetry becomes inconsistent at cubic order, in agreement with a
previous calculation. Furthermore, we find that the PM symmetry of this theory
cannot be extended beyond cubic order in the PM field. More importantly, it is
shown that the PM symmetry cannot be extended to quartic order in any theory
with one massless and one massive spin-2 fields.


title: Surface modeling for optical fabrication with linear ion source

abstract:
  We present a concept of surface decomposition extended from double Fourier
series to nonnegative sinusoidal wave surfaces, on the basis of which linear
ion sources apply to the ultra-precision fabrication of complex surfaces and
diffractive optics. It is the first time that we have a surface descriptor for
building a relationship between the fabrication process of optical surfaces and
the surface characterization based on PSD analysis, which akin to Zernike
polynomials used for mapping the relationship between surface errors and Seidel
aberrations. Also, we demonstrate that the one-dimensional scanning of linear
ion source is applicable to the removal of surface errors caused by small-tool
polishing in raster scan mode as well as the fabrication of beam sampling
grating of high diffractive uniformity without a post-processing procedure. The
simulation results show that, in theory, optical fabrication with linear ion
source is feasible and even of higher output efficiency compared with the
conventional approach.


title: Experimentally, How Dark Are Black Hole Mergers?

abstract:
  The first Advanced LIGO observing run detected two black hole merger events
with confidence and likely a third. Many groups organized to followup the
events in the optical even though the strong theoretical prior that no optical
emission should be seen. We carry through the logic of this by asking about the
experimental upper limits to the optical light from Advanced LIGO black hole
mergere events. We inventory the published optical searches for transient
events associated with the black hole mergers. We describe the factors that go
into a formal limit on the visibility of an event (sky area coverage, the
coverage factor of the camera, the fraction of sky not covered by intervening
objects), and list what is known from the literature of the followup teams
quantitative assessment of each factor. Where possible we calculate the total
probability from each group that the source was imaged. The calculation of
confidence level is reviewed for the case of no background. We find that an
experimental 95% upper limit on the magnitude of a black hole requires the sum
of the total probabilities over all events to be more than 3. In the first
Advanced LIGO observing run we were far from reaching that threshold.


title: Real-time sensing of flowing nanoparticles with electro-opto-mechanics

abstract:
  High-Q optical resonators allow label-free detection of individual
nanoparticles through perturbation of optical signatures but have practical
limitations due to reliance on random diffusion to deliver particles to the
sensing region. We have recently developed microfluidic optomechanical
resonators that allow detection of free-flowing particles in fluid media with
near perfect detection efficiency, without requiring labeling, binding, or
direct access to the optical mode. Rapid detection of single particles is
achieved through a long-range optomechanical interaction that influences the
scattered light spectra from the resonator, which can be quantified with
post-processing. Here, we present a hybrid electromechanical-optomechanical
technique for substantially increasing the bandwidth of these
optomechanofluidic sensors, enabling real-time operation. The presented system
demonstrates temporal resolution of better than 20~\us (50,000 events/second)
with particle sensing resolution down to 490 nm, operating in the air without
any stabilization or environmental control. Our technique significantly
enhances the sensing capabilities of high-Q optical resonators into the
mechanics domain, and allows extremely high-throughput analysis of large
nanoparticle populations.


title: Max-plus statistical leverage scores

abstract:
  The statistical leverage scores of a complex matrix $A\in\mathbb{C}^{n\times
d}$ record the degree of alignment between col$(A)$ and the coordinate axes in
$\mathbb{C}^n$. These score are used in random sampling algorithms for solving
certain numerical linear algebra problems. In this paper we present a max-plus
algebraic analogue for statistical leverage scores. We show that max-plus
statistical leverage scores can be used to calculate the exact asymptotic
behavior of the conventional statistical leverage scores of a generic matrices
of Puiseux series and also provide a novel way to approximate the conventional
statistical leverage scores of a fixed or complex matrix. The advantage of
approximating a complex matrices scores with max-plus scores is that the
max-plus scores can be computed very quickly. This approximation is typically
accurate to within an order or magnitude and should be useful in practical
problems where the true scores are known to vary widely.


title: Modelling Galaxy Merger Timescales and Tidal Destruction

abstract:
  We present a model for the dynamical evolution of subhaloes based on an
approach combining numerical and analytical methods. Our method is based on
tracking subhaloes in an N-body simulation up to the last point that it can be
resolved, and applying an analytic prescription for its merger timescale that
takes dynamical friction and tidal disruption into account. When applied to
cosmological N-body simulations with mass resolutions that differ by two orders
of magnitude, the technique produces halo occupation distributions that agree
to within 3%.


title: Trapping and Sympathetic Cooling of Boron Ions

abstract:
  We demonstrate the trapping and sympathetic cooling of B$^{+}$ ions in a
Coulomb crystal of laser-cooled Ca$^{+}$, We non-destructively confirm the
presence of the both B$^+$ isotopes by resonant excitation of the secular
motion. The B$^{+}$ ions are loaded by ablation of boron and the secular
excitation spectrum also reveals features consistent with ions of the form
B$_{n}^{+}$.


title:
Charged Point Normalization: An Efficient Solution to the Saddle Point
  Problem

abstract:
  Recently, the problem of local minima in very high dimensional non-convex
optimization has been challenged and the problem of saddle points has been
introduced. This paper introduces a dynamic type of normalization that forces
the system to escape saddle points. Unlike other saddle point escaping
algorithms, second order information is not utilized, and the system can be
trained with an arbitrary gradient descent learner. The system drastically
improves learning in a range of deep neural networks on various data-sets in
comparison to non-CPN neural networks.


title: Minimal lectures on two-dimensional conformal field theory

abstract:
  We provide a brief but self-contained review of two-dimensional conformal
field theory, from the basic principles to some of the simplest models. From
the representations of the Virasoro algebra on the one hand, and the
state-field correspondence on the other hand, we deduce Ward identities and
Belavin--Polyakov--Zamolodchikov equations for correlation functions. We then
explain the principles of the conformal bootstrap method, and introduce
conformal blocks. This allows us to define and solve minimal models and
Liouville theory. In particular, we study their three- and four-point
functions, and discuss their existence and uniqueness. In appendices, we
introduce the free boson theory (with an arbitrary central charge), and the
modular bootstrap in minimal models.


title: Dirac Material Graphene

abstract:
  The paper presents the author view on spin-rooted properties of graphene
supported by numerous experimental and calculation evidences. Dirac fermions of
crystalline graphene and local spins of graphene molecules are suggested to
meet a strict demand - different orbitals for different spins- which leads to a
large spectrum of effects caused by spin polarization of electronic states. The
consequent topological non-triviality, making graphene topological insulator,
and local spins, imaging graphene chemical activity, are proposed to discuss
such peculiar properties of graphene as high temperature ferromagnetism and
outstanding chemical behavior. The connection of these new findings with
difficulties met at attempting to convert semimetal graphene into semiconductor
one is discussed.


title:
Multi-dimensional signal approximation with sparse structured priors
  using split Bregman iterations

abstract:
  This paper addresses the structurally-constrained sparse decomposition of
multi-dimensional signals onto overcomplete families of vectors, called
dictionaries. The contribution of the paper is threefold. Firstly, a generic
spatio-temporal regularization term is designed and used together with the
standard $\ell_1$ regularization term to enforce a sparse decomposition
preserving the spatio-temporal structure of the signal. Secondly, an
optimization algorithm based on the split Bregman approach is proposed to
handle the associated optimization problem, and its convergence is analyzed.
Our well-founded approach yields same accuracy as the other algorithms at the
state-of-the-art, with significant gains in terms of convergence speed.
Thirdly, the empirical validation of the approach on artificial and real-world
problems demonstrates the generality and effectiveness of the method. On
artificial problems, the proposed regularization subsumes the Total Variation
minimization and recovers the expected decomposition. On the real-world problem
of electro-encephalography brainwave decomposition, the approach outperforms
similar approaches in terms of P300 evoked potentials detection, using
structured spatial priors to guide the decomposition.


title: On Ehrhart polynomials of lattice triangles

abstract:
  The Ehrhart polynomial of a lattice polygon P is completely determined by the
pair (b(P),i(P)) where b(P) equals the number of lattice points on the boundary
and i(P) equals the number of interior lattice points. All possible pairs
(b(P),i(P)) are completely described by a theorem due to Scott. In this note,
we describe the shape of the set of pairs (b(T),i(T)) for lattice triangles T
by finding infinitely many new Scott-type inequalities.


title: Non-LTE inversions of the Mg II h&k and UV triplet lines

abstract:
  The Mg II h&k lines are powerful diagnostics for studying the solar
chromosphere. They have become particularly popular with the launch of the IRIS
satellite, and a number of studies that include these lines have lead to great
progress in understanding chromospheric heating, in many cases thanks to the
support from 3D MHD simulations. In this study we utilize another approach to
analyze observations: non-LTE inversions of the Mg II h&k and UV triplet lines
including the effects of partial redistribution. Our inversion code attempts to
construct a model atmosphere that is compatible with the observed spectra. We
have assessed the capabilities and limitations of the inversions using the FALC
atmosphere and a snapshot from a 3D radiation-MHD simulation. We find that Mg
II h&k allow reconstructing a model atmosphere from the middle photosphere to
the transition region. We have also explored the capabilities of a
multi-line/multi-atom setup, including the Mg II h&k, the Ca II 854.2 nm and
the Fe I 630.25 lines to recover the full stratification of physical
parameters, including the magnetic field vector, from the photosphere to the
chromosphere. Finally, we present the first inversions of observed IRIS spectra
from quiet-Sun, plage and sunspot, with very promising results.


title: JINA-NuGrid Galactic Chemical Evolution Pipeline

abstract:
  Galactic chemical evolution is a topic that involves nuclear physics, stellar
evolution, galaxy evolution, observation, and cosmology. Continuous
communication and feedback between these fields is a key component in improving
our understanding of how galaxies form and how elements are created and
recycled in galaxies and intergalactic space. In this proceedings, we present
the current state of the JINA-NuGrid chemical evolution pipeline. It is
designed to probe the impact of nuclear astrophysics uncertainties on galactic
chemical evolution, to improve our knowledges regarding the origin of the
elements in a cosmological context, and to create the required
interdisciplinary connections.


title: Loss of information in feedforward social networks

abstract:
  We consider model social networks in which information propagates
directionally across layers of rational agents. Each agent makes a locally
optimal estimate of the state of the world, and communicates this estimate to
agents downstream. When agents receive information from the same source their
estimates are correlated. We show that the resulting redundancy can lead to the
loss of information about the state of the world across layers of the network,
even when all agents have full knowledge of the network's structure. A simple
algebraic condition identifies networks in which information loss occurs, and
we show that all such networks must contain a particular network motif. We also
study random networks asymptotically as the number of agents increases, and
find a sharp transition in the probability of information loss at the point at
which the number of agents in one layer exceeds the number in the previous
layer.


title: Fast L1-L2 minimization via a proximal operator

abstract:
  This paper aims to develop new and fast algorithms for recovering a sparse
vector from a small number of measurements, which is a fundamental problem in
the field of compressive sensing (CS). Currently, CS favors incoherent systems,
in which any two measurements are as little correlated as possible. In reality,
however, many problems are coherent, and conventional methods such as $L_1$
minimization do not work well. Recently, the difference of the $L_1$ and $L_2$
norms, denoted as $L_1$-$L_2$, is shown to have superior performance over the
classic $L_1$ method, but it is computationally expensive. We derive an
analytical solution for the proximal operator of the $L_1$-$L_2$ metric, and it
makes some fast $L_1$ solvers such as forward-backward splitting (FBS) and
alternating direction method of multipliers (ADMM) applicable for $L_1$-$L_2$.
We describe in details how to incorporate the proximal operator into FBS and
ADMM and show that the resulting algorithms are convergent under mild
conditions. Both algorithms are shown to be much more efficient than the
original implementation of $L_1$-$L_2$ based on a difference-of-convex approach
in the numerical experiments.


title: The Generalized Reed-Muller codes in a modular group algebra

abstract:
  First we study some properties of the modular group algebra
$\mathbb{F}_{p^r}[G]$ where $G$ is the additive group of a Galois ring of
characteristic $p^r$ and $\mathbb{F}_{p^r}$ is the field of $p^r$ elements.
Secondly a description of the Generalized Reed-Muller codes over
$\mathbb{F}_{p^r}$ in $\mathbb{F}_{p^r}[G]$ is presented.


title: Inferring Brain Signals Synchronicity from a Sample of EEG Readings

abstract:
  Inferring patterns of synchronous brain activity from a heterogeneous sample
of electroencephalograms (EEG) is scientifically and methodologically
challenging. While it is intuitively and statistically appealing to rely on
readings from more than one individual in order to highlight recurrent patterns
of brain activation, pooling information across subjects presents non-trivial
methodological problems. We discuss some of the scientific issues associated
with the understanding of synchronized neuronal activity and propose a
methodological framework for statistical inference from a sample of EEG
readings. Our work builds on classical contributions in time-series, clustering
and functional data analysis, in an effort to reframe a challenging inferential
problem in the context of familiar analytical techniques. Some attention is
paid to computational issues, with a proposal based on the combination of
machine learning and Bayesian techniques.


title:
Modulational instability and solitary waves in polariton topological
  insulators

abstract:
  Optical microcavities supporting exciton-polariton quasi-particles offer one
of the most powerful platforms for investigation of rapidly developing area of
topological photonics in general, and of photonic topological insulators in
particular. Energy bands of the microcavity polariton graphene are readily
controlled by magnetic field and influenced by the spin-orbit coupling effects,
a combination leading to formation of linear unidirectional edge states in
polariton topological insulators as predicted very recently. In this work we
depart from the linear limit of non-interacting polaritons and predict
instabilities of the nonlinear topological edge states resulting in formation
of the localized topological quasi-solitons, which are exceptionally robust and
immune to backscattering wavepackets propagating along the graphene lattice
edge. Our results provide a background for experimental studies of nonlinear
polariton topological insulators and can influence other subareas of photonics
and condensed matter physics, where nonlinearities and spin-orbit effects are
often important and utilized for applications.


title:
Experimental determination of the correlation properties of plasma
  turbulence using 2D BES systems

abstract:
  A procedure is presented to map from the spatial correlation parameters of a
turbulent density field (the radial and binormal correlation lengths and
wavenumbers, and the fluctuation amplitude) to correlation parameters that
would be measured by a Beam Emission Spectroscopy (BES) diagnostic. The inverse
mapping is also derived, which results in resolution criteria for recovering
correct correlation parameters, depending on the spatial response of the
instrument quantified in terms of Point-Spread Functions (PSFs). Thus, a
procedure is presented that allows for a systematic comparison between
theoretical predictions and experimental observations. This procedure is
illustrated using the MAST BES system and the validity of the underlying
assumptions is tested on fluctuating density fields generated by direct
numerical simulations using the gyrokinetic code GS2. The measurement of the
correlation time, by means of the cross-correlation time-delay (CCTD) method,
is also investigated and is shown to be sensitive to the fluctuating radial
component of velocity, as well as to small variations in the spatial properties
of the PSFs.


title: Raman study of the vibrational modes in ZnGeN2 (0001)

abstract:
  A Raman spectroscopy study was carried out for ZnGeN2 with direction of
propagation along the (0001) crystallographic direction on hexagonal single
crystal platelets obtained by reaction of gaseous ammonia with a Zn-Ge-Sn
liquid alloy at 758 degree C. The sample geometry allowed measurement of the a2
and a1 Raman modes. First-principles calculations were carried out of the
spectra. Measurements with crossed polarizers yielded spectra that agreed well
with first-principles calculations of the a2 modes. Measurements with parallel
polarizers should in principle provide the a1L modes. However, for most of the
Raman modes, the LO-TO splitting was calculated to be very small, and for the
few modes which were predicted to have larger LO-TO splittings, the LO mode was
not observed. This absence is tentatively explained in terms of overdamped
LO-plasmon coupling. LO-TO mode crossing was identified by comparing the
calculated eigenvectors and intensities of individual modes. Some features in
the experimental spectra were identified as arising from critical points in the
phonon density of states and are indicative of the degree of disorder on the
cation lattice.


title:
Prediction of superconducting iron-bismuth intermetallic compounds at
  high pressure

abstract:
  The synthesis of materials in high-pressure experiments has recently
attracted increasing attention, especially since the discovery of record
breaking superconducting temperatures in the sulfur-hydrogen and other
hydrogen-rich systems. Commonly, the initial precursor in a high pressure
experiment contains constituent elements that are known to form compounds at
ambient conditions, however the discovery of high-pressure phases in systems
immiscible under ambient conditions poses an additional materials design
challenge. We performed an extensive multi component $ab\,initio$ structural
search in the immiscible Fe--Bi system at high pressure and report on the
surprising discovery of two stable compounds at pressures above $\approx36$
GPa, FeBi$_2$ and FeBi$_3$. According to our predictions, FeBi$_2$ is a metal
at the border of magnetism with a conventional electron-phonon mediated
superconducting transition temperature of $T_{\rm c}=1.3$ K at 40 GPa. In
analogy to other iron-based materials, FeBi$_2$ is possibly a non-conventional
superconductor with a real $T_{\rm c}$ significantly exceeding the values
obtained within Bardeen-Cooper-Schrieffer (BCS) theory.

categories: cond-mat.mtrl-sci cond-mat.supr-con physics.chem-ph physics.comp-ph


title: Covert Attacks in Cyber-Physical Control Systems

abstract:
  The advantages of using communication networks to interconnect controllers
and physical plants motivate the increasing number of Networked Control
Systems, in industrial and critical infrastructure facilities. However, this
integration also exposes such control systems to new threats, typical of the
cyber domain. In this context, studies have been conduced, aiming to explore
vulnerabilities and propose security solutions for cyber-physical systems. In
this paper, it is proposed a covert attack for service degradation, which is
planned based on the intelligence gathered by another attack, herein proposed,
referred as System Identification attack. The simulation results demonstrate
that the joint operation of the two attacks is capable to affect, in a covert
and accurate way, the physical behavior of a system.


title:
Levi Subgroup Actions on Schubert Varieties, Induced Decompositions of
  their Coordinate Rings, and Sphericity Consequences

abstract:
  Let $L_w$ be the Levi part of the stabilizer $Q_w$ in $GL_N$ (for left
multiplication) of a Schubert variety $X(w)$ in the Grassmannian $G_{d,N}$. For
the natural action of $L_w$ on $\mathbb{C}[X(w)]$, the homogeneous coordinate
ring of $X(w)$ (for the Pl\"ucker embedding), we give a combinatorial
description of the decomposition of $\mathbb{C}[X(w)]$ into irreducible
$L_w$-modules; in fact, our description holds more generally for the action of
the Levi part $L$ of any parabolic subgroup $Q$ that is contained in $Q_w$.
This decomposition is then used to show that all smooth Schubert varieties, all
determinantal Schubert varieties, and all Schubert varieties in $G_{2,N}$ are
spherical $L_w$-varieties.


title:
Nonlinear Optical Observation of Coherent Acoustic Dirac Plasmons in
  Thin-Film Topological Insulators

abstract:
  Low-energy collective electronic excitations exhibiting sound-like linear
dispersion have been intensively studied both experimentally and theoretically
for a long time. However, coherent acoustic plasmon modes appearing in
time-domain measurements are rarely observed due to Landau damping by the
single-particle continua. Here we report on the observation of coherent
acoustic Dirac plasmon (CADP) modes excited in indirectly (electrostatically)
opposite-surface coupled films of the topological insulator Bi2Se3. Using
transient second harmonic generation, a technique capable of independently
monitoring the in-plane and out-of-plane electron dynamics in the films, the
GHz-range oscillations were observed without corresponding oscillations in the
transient reflectivity. These oscillations were assigned to the transverse
magnetic and transverse electric guided CADP modes induced by the evanescent
guided Lamb acoustic waves and remained Landau undamped due to fermion
tunneling between the opposite-surface Dirac states.


title: Derived McKay correspondence for GL(3,C)

abstract:
  We prove that the equivariant derived category for a finite subgroup of
GL(3,C) has a semi-orthogonal decomposition into the derived category of a
certain partial resolution, called a maximal Q-factorial terminalization, of
the corresponding quotient singularity and a relative exceptional collection.
This is a generalization of a result of Bridgeland, King and Reid.


title:
Knowledge management metrics for Public Organizations: A literature
  review-based proposal

abstract:
  Knowledge Management (KM) is a relatively new phenomenon that appears in the
field of Public Sector Organizations (PSO) bringing new paradigms of
organizational management, challenges, risks and opportunities for its
implementation, development and evaluation. KM can be seen as a systematic and
deliberate effort to coordinate people, technology, organizational structures
and its environment through knowledge reuse and innovation. This management
approach has been established in parallel with the development and use of
information and communications technologies (ICT). Nowadays more PSO are
embodying KM practices in their core processes for support them, and as an
advanced management strategy to create a new culture based on technology and
resources efficiency. In this paper, we observed that KM can support
organizational goals in PSO. The aim of this paper is to understand KM factors
and its associated components, and propose KM metrics for measure KM programs
in PSO. Through a critical literature review we analysed diverse studies
related with KM performance indicators in PSO, then based on previous works we
summarized the more convenient this purpose. We found that, in academic
literature, studies about KM measurement in PSO are uncommon and emerging. As
well, in the last section of this paper, we present a proposal of KM metrics
for PSO, and some recommendations and practical implications for KM metrics
development in PSO. This academic endeavour seeks to contribute to theoretical
debate about KM measure development for KM initiatives in PSO.


title: Peakompactons: Peaked compact nonlinear waves

abstract:
  This article is meant as an accessible introduction to/tutorial on the
analytical construction and numerical simulation of a class of non-standard
solitary waves termed \emph{peakompactons}. These peaked compactly supported
waves arise as solutions to nonlinear evolution equations from a hierarchy of
nonlinearly dispersive Korteweg--de Vries-type models. Peakompactons, like the
now-well-know compactons and unlike the soliton solutions of the Korteweg--de
Vries equation, have finite support, {\it i.e.}, they are of finite wavelength.
However, unlike compactons, peakompactons are also peaked, {\it i.e.}, a higher
spatial derivative suffers a jump discontinuity at the wave's crest. Here, we
construct such solutions exactly by reducing the governing partial differential
equation to a nonlinear ordinary differential equation and employing a
phase-plane analysis. A simple, but reliable, finite-difference scheme is also
designed and tested for the simulation of collisions of peakompactons. In
addition to the peakompacton class of solutions, the general physical features
of the so-called $K^\#(n,m)$ hierarchy of nonlinearly dispersive Korteweg--de
Vries-type models are discussed as well.


title:
Energy gap of neutral excitations implies vanishing charge
  susceptibility

abstract:
  In quantum many-body systems with a U(1) symmetry, such as the particle
number conservation and the axial spin conservation, there are two distinct
types of excitations: charge-neutral excitations and charged excitations. The
energy gaps of these excitations may be independent with each other in strongly
correlated systems. The static susceptibility of the U(1) charge vanishes when
the charged excitations are all gapped, but its relation to the neutral
excitations is not obvious. Here we show that a finite excitation gap of the
neutral excitations is, in fact, sufficient to prove that the charge
susceptibility vanishes (i.e. the system is incompressible). This result gives
a partial explanation on why the celebrated quantization condition
$n(S-m_z)\in\mathbb{Z}$ at magnetization plateaus works even in spatial
dimensions greater than one.


title: Algorithms for item categorization based on ordinal ranking data

abstract:
  We present a new method for identifying the latent categorization of items
based on their rankings. Complimenting a recent work that uses a Dirichlet
prior on preference vectors and variational inference, we show that this
problem can be effectively dealt with using existing community detection
algorithms, with the communities corresponding to item categories. In
particular we convert the bipartite ranking data to a unipartite graph of item
affinities, and apply community detection algorithms. In this context we modify
an existing algorithm - namely the label propagation algorithm to a variant
that uses the distance between the nodes for weighting the label propagation -
to identify the categories. We propose and analyze a synthetic ordinal ranking
model and show its relation to the recently much studied stochastic block
model. We test our algorithms on synthetic data and compare performance with
several popular community detection algorithms. We also test the method on real
data sets of movie categorization from the Movie Lens database. In all of the
cases our algorithm is able to identify the categories for a suitable choice of
tuning parameter.


title:
Two-stage Convolutional Part Heatmap Regression for the 1st 3D Face
  Alignment in the Wild (3DFAW) Challenge

abstract:
  This paper describes our submission to the 1st 3D Face Alignment in the Wild
(3DFAW) Challenge. Our method builds upon the idea of convolutional part
heatmap regression [1], extending it for 3D face alignment. Our method
decomposes the problem into two parts: (a) X,Y (2D) estimation and (b) Z
(depth) estimation. At the first stage, our method estimates the X,Y
coordinates of the facial landmarks by producing a set of 2D heatmaps, one for
each landmark, using convolutional part heatmap regression. Then, these
heatmaps, alongside the input RGB image, are used as input to a very deep
subnetwork trained via residual learning for regressing the Z coordinate. Our
method ranked 1st in the 3DFAW Challenge, surpassing the second best result by
more than 22%.


title: Dynamic Models of Appraisal Networks Explaining Collective Learning

abstract:
  This paper proposes models of learning process in teams of individuals who
collectively execute a sequence of tasks and whose actions are determined by
individual skill levels and networks of interpersonal appraisals and influence.
The closely-related proposed models have increasing complexity, starting with a
centralized manager-based assignment and learning model, and finishing with a
social model of interpersonal appraisal, assignments, learning, and influences.
We show how rational optimal behavior arises along the task sequence for each
model, and discuss conditions of suboptimality. Our models are grounded in
replicator dynamics from evolutionary games, influence networks from
mathematical sociology, and transactive memory systems from organization
science.


title:
Competitive Propagation: Models, Asymptotic Behavior and Multi-stage
  Games

abstract:
  In this paper we propose a class of propagation models for multiple competing
products over a social network. We consider two propagation mechanisms: social
conversion and self conversion, corresponding, respectively, to endogenous and
exogenous factors. A novel concept, the product-conversion graph, is proposed
to characterize the interplay among competing products. According to the
chronological order of social and self conversions, we develop two Markov-chain
models and, based on the independence approximation, we approximate them with
two respective difference equations systems.
  Theoretical analysis on these two approximation models reveals the dependency
of the systems' asymptotic behavior on the structures of both the
product-conversion graph and the social network, as well as the initial
condition. In addition to the theoretical work, accuracy of the independence
approximation and the asymptotic behavior of the Markov-chain model are
investigated via numerical analysis, for the case where social conversion
occurs before self conversion.
  Finally, we propose a class of multi-player and multi-stage competitive
propagation games and discuss the seeding-quality trade-off, as well as the
allocation of seeding resources among the individuals. We investigate the
unique Nash equilibrium at each stage and analyze the system's behavior when
every player is adopting the policy at the Nash equilibrium.


title:
Approximate Hierarchical Clustering via Sparsest Cut and Spreading
  Metrics

abstract:
  Dasgupta recently introduced a cost function for the hierarchical clustering
of a set of points given pairwise similarities between them. He showed that
this function is NP-hard to optimize, but a top-down recursive partitioning
heuristic based on an alpha_n-approximation algorithm for uniform sparsest cut
gives an approximation of O(alpha_n log n) (the current best algorithm has
alpha_n=O(sqrt{log n})). We show that the aforementioned sparsest cut heuristic
in fact obtains an O(alpha_n)-approximation for hierarchical clustering. The
algorithm also applies to a generalized cost function studied by Dasgupta.
Moreover, we obtain a strong inapproximability result, showing that the
hierarchical clustering objective is hard to approximate to within any constant
factor assuming the Small-Set Expansion (SSE) Hypothesis. Finally, we discuss
approximation algorithms based on convex relaxations. We present a spreading
metric SDP relaxation for the problem and show that it has integrality gap at
most O(sqrt{log n}). The advantage of the SDP relative to the sparsest cut
heuristic is that it provides an explicit lower bound on the optimal solution
and could potentially yield an even better approximation for hierarchical
clustering. In fact our analysis of this SDP served as the inspiration for our
improved analysis of the sparsest cut heuristic. We also show that a spreading
metric LP relaxation gives an O(log n)-approximation.


title:
Experimental realization of type-II Weyl state in non-centrosymmetric
  TaIrTe$_4$

abstract:
  Recent breakthrough in search for the analogs of fundamental particles in
condensed matter systems lead to experimental realizations of 3D Dirac and Weyl
semimetals. Weyl state can be hosted either by non-centrosymmetric or magnetic
materials and can be of the first or the second type. Several
non-centrosymmetric materials have been proposed to be type-II Weyl semimetals,
but in all of them the Fermi arcs between projections of multiple Weyl points
either have not been observed directly or they were hardly distinguishable from
the trivial surface states which significantly hinders the practical
application of these materials. Here we present experimental evidence for
type-II non-centrosymmetric Weyl state in TaIrTe$_4$ where it has been
predicted theoretically. We find direct correspondence between ARPES spectra
and calculated electronic structure both in the bulk and the surface and
clearly observe the exotic surface states which support the quasi-1D Fermi arcs
connecting only four Weyl points. Remarkably, these electronic states are
spin-polarized in the direction along the arcs, thus highlighting TaIrTe$_4$ as
a novel material with promising application potential.


title: Counting Hamilton decompositions of oriented graphs

abstract:
  A Hamilton cycle in a directed graph $G$ is a cycle that passes through every
vertex of $G$. A Hamiltonian decomposition of $G$ is a partition of its edge
set into disjoint Hamilton cycles. In the late $60$s Kelly conjectured that
every regular tournament has a Hamilton decomposition. This conjecture was
recently settled by K\"uhn and Osthus, who proved more generally that every
$r$-regular $n$-vertex oriented graph $G$ (without antiparallel edges) with
$r=cn$ for some fixed $c>3/8$ has a Hamiltonian decomposition, provided
$n=n(c)$ is sufficiently large. In this paper we address the natural question
of estimating the number of such decompositions of $G$ and show that this
number is $n^{(1-o(1))cn^2}$. In addition, we also obtain a new and much
simpler proof for the approximate version of Kelly's conjecture.


title: Cotangent Bundle to the Flag Variety - I

abstract:
  We show that there is a ${SL_n}$-stable closed subset of an affine Schubert
variety in the infinite dimensional Flag variety (associated to the Kac-Moody
group ${\widehat{SL_n}}$) which is a natural compactification of the cotangent
bundle to the finite-dimensional Flag variety ${{SL_n/B}}$.


title: Controlling Output Length in Neural Encoder-Decoders

abstract:
  Neural encoder-decoder models have shown great success in many sequence
generation tasks. However, previous work has not investigated situations in
which we would like to control the length of encoder-decoder outputs. This
capability is crucial for applications such as text summarization, in which we
have to generate concise summaries with a desired length. In this paper, we
propose methods for controlling the output sequence length for neural
encoder-decoder models: two decoding-based methods and two learning-based
methods. Results show that our learning-based methods have the capability to
control length without degrading summary quality in a summarization task.


title: On Weighted MSE Model for MIMO Transceiver Optimization

abstract:
  Mean-squared-error (MSE) is one of the most widely used performance metrics
for the designs and analysis of multi-input-multiple-output (MIMO)
communications. Weighted MSE minimization, a more general formulation of MSE
minimization, plays an important role in MIMO transceiver optimization. While
this topic has a long history and has been extensively studied, existing
treatments on the methods in solving the weighted MSE optimization are more or
less sporadic and non-systematic. In this paper, we firstly review the two
major methodologies, Lagrange multiplier method and majorization theory based
method, and their common procedures in solving the weighted MSE minimization.
Then some problems and limitations of the methods that were usually neglected
or glossed over in existing literature are provided. These problems are
fundamental and of critical importance for the corresponding MIMO transceiver
optimizations. In addition, a new extended matrix-field weighted MSE model is
proposed. Its solutions and applications are discussed in details. Compared
with existing models, this new model has wider applications, e.g., nonlinear
MIMO transceiver designs and capacity-maximization transceiver designs for
general MIMO networks.


title: Gaussian noise and the two-network frustrated Kuramoto model

abstract:
  We examine analytically and numerically a variant of the stochastic Kuramoto
model for phase oscillators coupled on a general network. Two populations of
phased oscillators are considered, labelled `Blue' and `Red', each with their
respective networks, internal and external couplings, natural frequencies, and
frustration parameters in the dynamical interactions of the phases. We
disentagle the different ways that additive Gaussian noise may influence the
dynamics by applying it separately on zero modes or normal modes corresponding
to a Laplacian decomposition for the sub-graphs for Blue and Red. Under the
linearisation ansatz that the oscillators of each respective network remain
relatively phase-sychronised centroids or clusters, we are able to obtain
simple closed-form expressions using the Fokker-Planck approach for the
dynamics of the average angle of the two centroids. In some cases, this leads
to subtle effects of metastability that we may analytically describe using the
theory of ratchet potentials. These considerations are extended to a regime
where one of the populations has fragmented in two. The analytic expressions we
derive largely predict the dynamics of the non-linear system seen in numerical
simulation. In particular, we find that noise acting on a more tightly coupled
population allows for improved synchronisation of the other population where
deterministically it is fragmented.


title: Study of Parameterized-Chain networks

abstract:
  In areas such as computer software and hardware, manufacturing systems, and
transportation, engineers encounter networks with arbitrarily large numbers of
isomorphic subprocesses. Parameterized systems provide a framework for modeling
such networks. The analysis of parameterized systems is a challenge as some key
properties such as nonblocking and deadlock-freedom are undecidable even for
the case of a parameterized system with ring topology. In this paper, we
introduce \textit{Parameterized-Chain Networks} (PCN) for modeling of networks
containing several linear parameterized segments. Since deadlock analysis is
undecidable, to achieve a tractable subproblem we limit the behavior of
subprocesses of the network using our previously developed mathematical notion
`weak invariant simulation.' We develop a dependency graph for analysis of PCN
and show that partial and total deadlocks of the proposed PCN are characterized
by full, consistent subgraphs of the dependency graph. We investigate deadlock
in a traffic network as an illustrative example. This document contains all the
details and proofs of the study.


title: Spin pumping into two-dimensional electron systems

abstract:
  We study the spin current injected by spin pumping into single layer graphene
and the two-dimensional electron gas (2DEG) with ferromagnetic contacts using
scattering theory. The spin currents pumped into graphene are very distinct
from that into the 2DEG since importantly affected by Klein tunneling.