title:
Ultra-Broadband Super-Planckian Radiative Heat Transfer with Artificial
  Continuum Cavity States in Patterned Hyperbolic Metamaterial

abstract:
  Localized cavity resonances due to nanostructures at material surfaces can
greatly enhance radiative heat transfer (RHT) between two closely placed bodies
owing to stretching of cavity states in momentum space beyond light line. Based
on such understanding, we numerically demonstrate the possibility of
ultra-broadband super-Planckian RHT between two plates patterned with
trapezoidal-shaped hyperbolic metamaterial (HMM) arrays. The phenomenon is
rooted not only in HMM's high effective index for creating sub-wavelength
resonators, but also its extremely anisotropic isofrequency contour. The two
properties enable one to create photonic bands with a high spectral density to
populate a desired thermal radiation window. At sub-micron gap sizes between
such two plates, the artificial continuum states extend outside light cone,
tremendously increasing overall RHT. Our study reveals that structured HMM
offers unprecedented potential in achieving a controllable super-Planckian
radiative heat transfer for thermal management at nanoscale.


title:
Anomalous effect of turning off long-range mobility interactions in
  Stokesian Dynamics

abstract:
  In Stokesian Dynamics, particles are assumed to interact in two ways: through
long-range mobility interactions and through short-range lubrication
interactions. To speed up computations, in shear-driven concentrated
suspensions, often found in rheometric contexts, it is common to consider only
lubrication. We show that, although this approximation may provide acceptable
results in shear-driven, periodic suspensions, for bidisperse suspensions where
the particles are exposed to an external force, it can produce physically
unreasonable results. We suggest that this problem could be mitigated by a
careful choice of particle pairs on which lubrication interactions should be
included.


title:
Very Simple Classifier: a Concept Binary Classifier toInvestigate
  Features Based on Subsampling and Localility

abstract:
  We propose Very Simple Classifier (VSC) a novel method designed to
incorporate the concepts of subsampling and locality in the definition of
features to be used as the input of a perceptron. The rationale is that
locality theoretically guarantees a bound on the generalization error. Each
feature in VSC is a max-margin classifier built on randomly-selected pairs of
samples. The locality in VSC is achieved by multiplying the value of the
feature by a confidence measure that can be characterized in terms of the
Chebichev inequality. The output of the layer is then fed in a output layer of
neurons. The weights of the output layer are then determined by a regularized
pseudoinverse. Extensive comparison of VSC against 9 competitors in the task of
binary classification is carried out. Results on 22 benchmark datasets with
fixed parameters show that VSC is competitive with the Multi Layer Perceptron
(MLP) and outperforms the other competitors. An exploration of the parameter
space shows VSC can outperform MLP.


title: Compact maximal hypersurfaces in stably causal spacetimes

abstract:
  Several uniqueness results on compact maximal hypersurfaces in a wide class
of sta- bly causal spacetimes are given. They are obtained from the study of a
distinguished function on the maximal hypersurface, under suitable natural
first order conditions of the spacetime. As a consequence several applications
to Geometric Analysis are given.


title: Huneke's degree-computing problem

abstract:
  In this short note, we deal with a problem posted by Huneke on a numerical
invariant attached to symbolic powers of homogenous ideals.


title:
Effect of magnetic field on the photon radiation from quark-gluon plasma
  in heavy ion collisions

abstract:
  We develop a formalism for the photon emission from the quark-gluon plasma
with an external electromagnetic field. We then use it to investigate the
effect of magnetic field on the photon emission from the quark-gluon plasma
created in $AA$ collisions. We find that even for very optimistic assumption on
the magnitude of the magnetic field generated in $AA$ collisions its effect on
the photon emission rate is practically negligible. For this reason the
magnetic field cannot generate a significant azimuthal asymmetry in the photon
spectrum.


title: Transliteration in Any Language with Surrogate Languages

abstract:
  We introduce a method for transliteration generation that can produce
transliterations in every language. Where previous results are only as
multilingual as Wikipedia, we show how to use training data from Wikipedia as
surrogate training for any language. Thus, the problem becomes one of ranking
Wikipedia languages in order of suitability with respect to a target language.
We introduce several task-specific methods for ranking languages, and show that
our approach is comparable to the oracle ceiling, and even outperforms it in
some cases.


title:
Photometric Calibration of the [$\alpha$/Fe] Element: I. Calibration
  with UBV Photometry

abstract:
  We present the calibration of the [$\alpha$/Fe] element in terms of the
ultra-violet excess for 469 dwarf stars with $0.325<(B-V)_0 \leq 0.775$ mag
corresponding the spectral type range F0-K2. The star sample is separated into
nine sub-samples with equal range in $(B-V)_0$ colour, $\Delta(B-V)_0=0.05$
mag, and a third degree polynomial is fitted to each dataset. Our calibrations
provide [$\alpha$/Fe] elements in the range [0.0, 0.4]. We applied the
procedure to two sets of field stars and two sets of clusters. The mean and the
corresponding standard deviation of the residuals for 43 field stars taken from
the Hypatia catalogue are [$\alpha$/Fe]=-0.090 and $\sigma =0.102$ dex, while
for the 39 ones taken from the same catalogue of stars used in the calibration
are [$\alpha$/Fe]=-0.009 and $\sigma = 0.079$ dex, respectively. We showed that
the differences between the mean of the residuals and standard deviations for
two sets of clusters ([$\alpha$/Fe]=0.073 and $\sigma = 0.91$ dex;
[$\alpha$/Fe]=-0.012 and $\sigma = 0.053$ dex) originate from the $(B-V)_0$ and
$(U-B)_0$ colour indices of the clusters which are taken from different
sources. The differences between the original [$\alpha$/Fe] elements and the
estimated ones (the residuals) are compatible with the uncertainties in the
literature. Also, there is a good agreement between the distribution of the
synthetic alpha elements versus ultra-violet excesses and the ones obtained via
our calibrations.


title: The bumpy road towards iPhone 5c NAND mirroring

abstract:
  This paper is a short summary of a real world mirroring attack on the Apple
iPhone 5c passcode retry counter under iOS 9. This was achieved by desoldering
the NAND Flash chip of a sample phone in order to physically access its
connection to the SoC and partially reverse engineering its proprietary bus
protocol. The process does not require any expensive and sophisticated
equipment. All needed parts are low cost and were obtained from local
electronics distributors. By using the described and successful hardware
mirroring process it was possible to bypass the limit on passcode retry
attempts. This is the first public demonstration of the working prototype and
the real hardware mirroring process for iPhone 5c. Although the process can be
improved, it is still a successful proof-of-concept project. Knowledge of the
possibility of mirroring will definitely help in designing systems with better
protection. Also some reliability issues related to the NAND memory allocation
in iPhone 5c are revealed. Some future research directions are outlined in this
paper and several possible countermeasures are suggested. We show that claims
that iPhone 5c NAND mirroring was infeasible were ill-advised.


title:
First-principles multiscale modelling of charged adsorbates on doped
  graphene

abstract:
  Adsorbed atoms and molecules play an important role in controlling and tuning
the functional properties of two-dimensional (2D) materials. Understanding and
predicting this process from theory is challenging because of the need to
capture the complex interplay between the local chemistry and the long-range
screening response. To address this problem, we present a first-principles
multiscale approach that combines linear-scaling density-functional theory,
continuum screening theory and large-scale tight-binding simulations into a
seamless parameter-free theory of adsorbates on 2D materials. We apply this
method to investigate the electronic structure of doped graphene with a single
calcium (Ca) adatom and find that the Ca atom acts as a Coulomb impurity which
modifies the graphene local density of states (LDOS) within a distance of
several nanometres in its vicinity. We also observe an important doping
dependence of the graphene LDOS near the Ca atom, which gives insights into
electronic screening in graphene. Our multiscale framework opens up the
possibility of investigating complex mesoscale adsorbate configurations on 2D
materials relevant to real devices.


title:
Monteswitch: A package for evaluating solid-solid free energy
  differences via lattice-switch Monte Carlo

abstract:
  Lattice-switch Monte Carlo (LSMC) is a method for evaluating the free energy
between two given solid phases. LSMC is a general method, being applicable to a
wide range of problems and interatomic potentials. Furthermore it is extremely
efficient, ostensibly more efficient than other existing general methods. Here
we introduce a package, monteswitch, which can be used to perform LSMC
simulations. The package can be used to evaluate the free energy differences
between pairs of solid phases, including multicomponent phases, via LSMC for
atomic (i.e., non-molecular) systems in the NVT and NPT ensembles. It could
also be used to evaluate the free energy cost associated with interfaces and
defects. Regarding interatomic potentials, monteswitch currently supports
various commonly-used pair potentials, including the hard-sphere,
Lennard-Jones, and Morse potentials, as well as the embedded atom model.
However the main strength of the package is its versatility: it is designed so
that users can easily implement their own potentials.


title: Rational points of bounded height on general conic bundle surfaces

abstract:
  A conjecture of Manin predicts the asymptotic distribution of rational points
of bounded height on Fano varieties. In this paper we use conic bundles to
obtain correct lower bounds or a wide class of surfaces over number fields for
which the conjecture is still far from being proved. For example, we obtain the
conjectured lower bound of Manin's conjecture for any del Pezzo surface whose
Picard rank is sufficiently large, or for arbitrary del Pezzo surfaces after
possibly an extension of the ground field of small degree.


title:
ContextLocNet: Context-Aware Deep Network Models for Weakly Supervised
  Localization

abstract:
  We aim to localize objects in images using image-level supervision only.
Previous approaches to this problem mainly focus on discriminative object
regions and often fail to locate precise object boundaries. We address this
problem by introducing two types of context-aware guidance models, additive and
contrastive models, that leverage their surrounding context regions to improve
localization. The additive model encourages the predicted object region to be
supported by its surrounding context region. The contrastive model encourages
the predicted object region to be outstanding from its surrounding context
region. Our approach benefits from the recent success of convolutional neural
networks for object recognition and extends Fast R-CNN to weakly supervised
object localization. Extensive experimental evaluation on the PASCAL VOC 2007
and 2012 benchmarks shows hat our context-aware approach significantly improves
weakly supervised localization and detection.


title:
Properties of collapse dynamics in relativistic theory of gravitation in
  the case of smooth initial matter distributions

abstract:
  We use both numerical and analytical approaches to study the dynamics of the
gravitational collapse in the framework of the relativistic theory of
gravitation (RTG). We use various equations of state for the collapsing matter
and relatively realistic initial conditions with smooth matter distribution,
which corresponds to static solution for the given equation of state. We also
obtain results concerning the influence of the graviton mass on the properties
of static solutions. We specify several characteristics of the process of the
collapse, in particular, we determine the dependence of the turning point time
(when contraction is replaced by inflation) on the graviton mass. We also study
the influence of non-zero pressure on the dynamics of the collapse.


title: A mass-deformed BLG theory in Gribov-Zwanziger framework

abstract:
  In this paper, we extend the Gribov-Zwanziger framework accounting for the
existence of Gribov copies to the mass deformed Bagger--Lambert--Gustavsson
(BLG) theory in $\mathcal{N} =1 $ superspace. The restriction of the domain of
integration in the Euclidean functional integral to the first Gribov horizon is
implemented, by adding a non-local horizon term to the effective action.
Furthermore, the soft breaking of the BRST symmetry due to horizon term is
restored with the help of external sources. We compute the various Ward
identities for this theory relying on the Lie 3-algebras.


title:
The effect of intrinsic point defects on ferroelectric polarization
  behavior of SrTiO$_3$

abstract:
  The effect of a variety of intrinsic defects and defect clusters in bulk and
thin films of SrTiO$_3$ on ferroelectric polarization and switching mechanism
is investigated by means of density-functional-theory (DFT) based calculations
and the Berry phase approach. Our results show that both the titanium
Ti$_\mathrm{Sr}^{\bullet \bullet}$ and strontium Sr$_\mathrm{Ti}^{"}$ antisite
defects induce ferroelectric polarization in SrTiO$_3$, with the
Ti$_\mathrm{Sr}^{\bullet \bullet}$ defect causing a more pronounced spontaneous
polarization and higher activation barriers of polarization reversal than
Sr$_\mathrm{Ti}^{"}$. The presence of oxygen vacancies bound to the antisite
defects can either enhance or diminish polarization depending on the
configuration of the defect pair, but it always leads to larger activation
barriers of polarization switching as compared to the antisite defects with no
oxygen vacancies. We also show that the magnitude of spontaneous polarization
in SrTiO$_3$ can be tuned by controlling the degree of Sr/Ti nonstroichiometry.
Other intrinsic point defects such as Frenkel defect pairs and electron small
polarons also contribute to the emergence of ferroelectric polarization in
SrTiO$_{3}$.


title: Finite group schemes of $p$-rank $\leq1$

abstract:
  Let $\mathcal{G}$ be a finite group scheme over an algebraically closed field
$k$ of characteristic ${\rm char}(k)=p\geq 3$. In generalization of the
familiar notion from the modular representation theory of finite groups, we
define the $p$-rank $\mathsf{rk}_p(\mathcal{G})$ of $\mathcal{G}$ and determine
the structure of those group schemes of $p$-rank $1$, whose linearly reductive
radical is trivial. The most difficult case concerns infinitesimal groups of
height $1$, which correspond to restricted Lie algebras. Our results show that
group schemes of $p$-rank $\leq 1$ are closely related to those being of finite
or domestic representation type.


title:
On the Difference Between the Vacuum Casimir Energies for Grounded and
  Isolated Conductors

abstract:
  We study the vacuum (i.e., zero-temperature) Casimir energy for a system of
neutral conductors which are isolated, as opposed to grounded. The former is
meant to describe a situation where the total charge on each conductor, as well
as all of its fluctuations, vanishes, while the latter describes a situation
where the conductors are connected to a charge reservoir. We compute the
difference between the vacuum energies for a given system of conductors, but
subjected to the two different conditions stated above. The results can be
written in terms of a generalized, frequency-dependent capacitance matrix of
the system. Using a multipolar expansion, we show that the grounded Casimir
energy includes a monopole-monopole interaction term that is absent in the
isolated case in the large distance limit


title:
Quick and energy-efficient Bayesian computing of binocular disparity
  using stochastic digital signals

abstract:
  Reconstruction of the tridimensional geometry of a visual scene using the
binocular disparity information is an important issue in computer vision and
mobile robotics, which can be formulated as a Bayesian inference problem.
However, computation of the full disparity distribution with an advanced
Bayesian model is usually an intractable problem, and proves computationally
challenging even with a simple model. In this paper, we show how probabilistic
hardware using distributed memory and alternate representation of data as
stochastic bitstreams can solve that problem with high performance and energy
efficiency. We put forward a way to express discrete probability distributions
using stochastic data representations and perform Bayesian fusion using those
representations, and show how that approach can be applied to diparity
computation. We evaluate the system using a simulated stochastic implementation
and discuss possible hardware implementations of such architectures and their
potential for sensorimotor processing and robotics.


title: Dynamics of tax evasion through an epidemic-like model

abstract:
  In this work we study a model of tax evasion. We considered a fixed
population divided in three compartments, namely honest tax payers, tax evaders
and a third class between the mentioned two, which we call
\textit{susceptibles} to become evaders. The transitions among those
compartments are ruled by probabilities, similarly to a model of epidemic
spreading. These probabilities model social interactions among the individuals,
as well as the government's fiscalization. We simulate the model on
fully-connected graphs, as well as on scale-free and random complex networks.
For the fully-connected and random graph cases we observe that the emergence of
tax evaders in the population is associated with an active-absorbing
nonequilibrium phase transition, that is absent in scale-free networks.


title: On high-order perturbative calculations at finite density

abstract:
  We discuss the prospects of performing high-order perturbative calculations
in systems characterized by a vanishing temperature but finite density. In
particular, we show that the determination of generic Feynman integrals
containing fermionic chemical potentials can be reduced to the evaluation of
three-dimensional phase space integrals over vacuum on-shell amplitudes - a
result reminiscent of a previously proposed "naive real-time formalism" for
vacuum diagrams. Applications of these rules are discussed in the context of
the thermodynamics of cold and dense QCD, where it is argued that they
facilitate an extension of the Equation of State of cold quark matter to higher
perturbative orders.


title: PSI ({\Psi}): a Private data Sharing Interface

abstract:
  We provide an overview of PSI ("a Private data Sharing Interface"), a system
we are developing to enable researchers in the social sciences and other fields
to share and explore privacy-sensitive datasets with the strong privacy
protections of differential privacy.


title: The Satake sextic in elliptic fibrations on K3

abstract:
  We describe explicit formulas relevant to the F-theory/heterotic string
duality that reconstruct from a specific Jacobian elliptic fibration on the
Shioda-Inose surface covering a generic Kummer surface the corresponding
genus-two curve using the level-two Satake coordinate functions. We derive
explicitly the rational map on the moduli space of genus-two curves realizing
the algebraic correspondence between a sextic curve and its Satake sextic. We
will prove that it is not the original sextic defining the genus-two curve, but
its corresponding Satake sextic which is manifest in the F-theory model, dual
to the $\mathfrak{so}(32)$ heterotic string with an unbroken
$\mathfrak{so}(28)\oplus \mathfrak{su}(2)$ gauge algebra.


title: A Tighter Relation between Sensitivity and Certificate Complexity

abstract:
  The sensitivity conjecture which claims that the sensitivity complexity is
polynomially related to block sensitivity complexity, is one of the most
important and challenging problem in decision tree complexity theory. Despite
of a lot of efforts, the best known upper bound of block sensitivity, as well
as the certificate complexity, are still exponential in terms of sensitivity:
$bs(f)\leq C(f)\leq\max\{2^{s(f)-1}(s(f)-\frac{1}{3}),s(f)\}$. In this paper,
we give a better upper bound of $bs(f)\leq C(f)\leq(\frac{8}{9} +
o(1))s(f)2^{s(f) - 1}$. The proof is based on a deep investigation on the
structure of the sensitivity graph. We also provide a tighter relationship
between $C_0(f)$ and $s_0(f)$ for functions with $s_1(f)=2$.


title: Hadronic structure of the photon at small x in holographic QCD

abstract:
  We present our analysis on the photon structure functions at small Bjorken
variable x in the framework of the holographic QCD. In the kinematic region, a
photon can fluctuate into vector mesons and behaves like a hadron rather than a
pointlike particle. Assuming the Pomeron exchange dominance, the dominant
hadronic contribution to the structure functions is computed by convoluting the
probe and target photon density distributions obtained from the wave functions
of the U(1) vector field in the five-dimensional AdS space and the
Brower-Polchinski-Strassler-Tan Pomeron exchange kernel. Our calculations are
in agreement with both the experimental data from OPAL collaboration at LEP and
those calculated from the parton distribution functions of the photon proposed
by Gl\"uck, Reya, and Schienbein. The predictions presented here will be tested
at future linear colliders, such as the planned International Linear Collider.


title: Non-existence theorems on infinite order corks

abstract:
  Suppose that $X,X'$ are simply-connected closed exotic 4-manifolds. It is
well-known that $X'$ is obtained by an order 2 cork twist of $X$. We give an
infinite exotic family of 4-manifolds not generated by any infinite order cork.
This is the first example admitting such a condition. We prove a necessary
condition of 4-dimensional OS-invariants for a family to be generated by an
infinite order cork and give non-contractible relatively exotic 4-manifolds
that are never induced by any cork. Furthermore, we prove an estimate of the
number of OS-invariants of 4-manifolds generated by a cork.


title: Notes on Gompf's infinite order corks

abstract:
  For any positive integer $n$ we give a ${\mathbb Z}^n$-cork with a ${\mathbb
Z}^n$-effective embedding in a 4-manifold being homeomorphic to $E(n)$. This
means that a cork gives a subset ${\mathbb Z}^n$ in the differential structures
on $E(n)$. Further, we describe handle decompositions of the twisted doubles
(homotopy $S^4$) of Gompf's infinite order corks and show that they are Gluck
twists and log transforms of $S^4$.


title:
A New Milky Way Satellite Discovered In The Subaru/Hyper Suprime-Cam
  Survey

abstract:
  We report the discovery of a new ultra-faint dwarf satellite companion of the
Milky Way based on the early survey data from the Hyper Suprime-Cam Subaru
Strategic Program. This new satellite, Virgo I, which is located in the
constellation of Virgo, has been identified as a statistically significant (5.5
sigma) spatial overdensity of star-like objects with a well-defined main
sequence and red giant branch in their color-magnitude diagram. The
significance of this overdensity increases to 10.8 sigma when the relevant
isochrone filter is adopted for the search. Based on the distribution of the
stars around the likely main sequence turn-off at r ~ 24 mag, the distance to
Virgo I is estimated as 87 kpc, and its most likely absolute magnitude
calculated from a Monte Carlo analysis is M_V = -0.8 +/- 0.9 mag. This stellar
system has an extended spatial distribution with a half-light radius of 38
+12/-11 pc, which clearly distinguishes it from a globular cluster with
comparable luminosity. Thus, Virgo I is one of the faintest dwarf satellites
known and is located beyond the reach of the Sloan Digital Sky Survey. This
demonstrates the power of this survey program to identify very faint dwarf
satellites. This discovery of VirgoI is based only on about 100 square degrees
of data, thus a large number of faint dwarf satellites are likely to exist in
the outer halo of the Milky Way.


title: A Linear Time Parameterized Algorithm for Directed Feedback Vertex Set

abstract:
  In the Directed Feedback Vertex Set (DFVS) problem, the input is a directed
graph $D$ on $n$ vertices and $m$ edges, and an integer $k$. The objective is
to determine whether there exists a set of at most $k$ vertices intersecting
every directed cycle of $D$. Whether or not DFVS admits a fixed parameter
tractable (FPT) algorithm was considered the most important open problem in
parameterized complexity until Chen, Liu, Lu, O'Sullivan and Razgon [JACM 2008]
answered the question in the affirmative. They gave an algorithm for the
problem with running time $O(k!4^kk^4nm)$. Since then, no faster algorithm for
the problem has been found. In this paper, we give an algorithm for DFVS with
running time $O(k!4^kk^5(n+m))$. Our algorithm is the first algorithm for DFVS
with linear dependence on input size. Furthermore, the asymptotic dependence of
the running time of our algorithm on the parameter $k$ matches up to a factor
$k$ the algorithm of Chen, Liu, Lu, O'Sullivan and Razgon.
  On the way to designing our algorithm for DFVS, we give a general methodology
to shave off a factor of $n$ from iterative-compression based algorithms for a
few other well-studied covering problems in parameterized complexity. We
demonstrate the applicability of this technique by speeding up by a factor of
$n$, the current best FPT algorithms for Multicut [STOC 2011, SICOMP 2014] and
Directed Subset Feedback Vertex Set [ICALP 2012, TALG 2014].


title: Integrability of the one dimensional Schroedinger equation

abstract:
  We present a definition of integrability for the one dimensional Schroedinger
equation, which encompasses all known integrable systems, i.e. systems for
which the spectrum can be explicitly computed. For this, we introduce the class
of rigid functions, built as Liouvillian functions, but containing all
solutions of rigid differential operators in the sense of Katz, and a notion of
natural boundary conditions. We then make a complete classification of rational
integrable potentials. Many new integrable cases are found, some of them
physically interesting.


title:
Electronic structure tuning via surface modification in semimetallic
  nanowires

abstract:
  Electronic structure properties of nanowires (NW) with diameters of 1.5 nm
and 3 nm based on semimetallic $\alpha$-Sn are investigated by employing
density functional theory and perturbative $GW$ methods. We explore the
dependence of electron affinity, band structure and band gap values with
crystallographic orientation, NW cross-sectional size and surface passivants of
varying electronegativity. We consider four chemical terminations in our study:
methyl ($\rm{CH_3}$), hydrogen ($\rm{H}$), hydroxyl ($\rm{OH}$), and fluorine
($\rm{F}$). Results suggest a high degree of elasticity of Sn-Sn bonds within
the SnNWs' cores with no significant structural variations for nanowires with
different surface passivants. Direct band gaps at Brillouin zone centers are
found for most studied structures with quasi-particle corrected band gap
magnitudes ranging from 0.25 eV to 3.54 eV in 1.5 nm diameter structures
indicating an exceptional range of properties for semimetal NWs below the
semimetal-to-semiconductor transition. Band gap variations induced by changes
in surface passivants indicate the possibility of realizing
semimetal-semiconductor interfaces in NWs with constant cross-section and
crystallographic orientation allowing the design of novel dopant-free NW-based
electronic devices.


title: Time-Variant Graph Classification

abstract:
  Graphs are commonly used to represent objects, such as images and text, for
pattern classification. In a dynamic world, an object may continuously evolve
over time, and so does the graph extracted from the underlying object. These
changes in graph structure with respect to the temporal order present a new
representation of the graph, in which an object corresponds to a set of
time-variant graphs. In this paper, we formulate a novel time-variant graph
classification task and propose a new graph feature, called a graph-shapelet
pattern, for learning and classifying time-variant graphs. Graph-shapelet
patterns are compact and discriminative graph transformation subsequences. A
graph-shapelet pattern can be regarded as a graphical extension of a shapelet
-- a class of discriminative features designed for vector-based temporal data
classification. To discover graph-shapelet patterns, we propose to convert a
time-variant graph sequence into time-series data and use the discovered
shapelets to find graph transformation subsequences as graph-shapelet patterns.
By converting each graph-shapelet pattern into a unique tokenized graph
transformation sequence, we can measure the similarity between two
graph-shapelet patterns and therefore classify time-variant graphs. Experiments
on both synthetic and real-world data demonstrate the superior performance of
the proposed algorithms.


title: Revisit to Thermodynamic Relations in the AdS/CMT Models

abstract:
  Motivated by the recent unified approach to the Smarr-like relation of AdS
planar black holes in conjunction with the quasi-local formalism on conserved
charges, we revisit the quantum statistical and thermodynamic relations of
hairy AdS planar black holes. By extending the previous results, we identify
the hairy contribution in the bulk and show that the holographic computation
can be improved so that it is consistent with the bulk computation. We argue
that the first law can be retained in its universal form while the relation
between the on-shell renormalized Euclidean action and its free energy
interpretation in gravity may be deformed to contain the hairy contribution in
hairy AdS black holes.


title: Segregation effects in DEEP2 galaxy groups

abstract:
  We investigate segregation phenomena in galaxy groups in the range of
$0.2<z<1$. We study a sample of groups selected from the 4th Data Release of
the DEEP2 galaxy redshift survey. We used only groups with at least 8 members
within a radius of 4$\;$Mpc. Outliers were removed with the shifting gapper
techinque and, then, the virial properties were estimated for each group. The
sample was divided into two stacked systems: low($z\leq0.6$) and high($z>0.6$)
redshift groups. Assuming that the color index ${(U-B)_0}$ can be used as a
proxy for the galaxy type, we found that the fraction of blue (star-forming)
objects is higher in the high-z sample, with blue objects being dominant at
$M_{B}>-19.5$ for both samples, and red objects being dominant at $M_{B}<-19.5$
only for the low-z sample. Also, the radial variation of the red fraction
indicates that there are more red objects with $R<R_{200}$ in the low-z sample
than in the high-z sample. Our analysis indicates statistical evidence of
kinematic segregation, at the 99%c.l., for the low-z sample: redder and
brighter galaxies present lower velocity dispersions than bluer and fainter
ones. We also find a weaker evidence for spatial segregation between red and
blue objects, at the 70%c.l. The analysis of the high-z sample reveals a
different result: red and blue galaxies have velocity dispersion distributions
not statistically distinct, although redder objects are more concentrated than
the bluer ones at the 95%c.l. From the comparison of blue/red and bright/faint
fractions, and considering the approximate lookback timescale between the two
samples ($\sim$3 Gyr), our results are consistent with a scenario where bright
red galaxies had time to reach energy equipartition, while faint blue/red
galaxies in the outskirts infall to the inner parts of the groups, thus
reducing spatial segregation from $z\sim0.8$ to $z\sim0.4$.


title: Splitting numbers of links and the four-genus

abstract:
  The splitting number of a link is the minimum number of crossing changes
between distinct components that is required to convert the link into a split
link. We provide a bound on the splitting number in terms of the four-genus of
related knots.


title: A general family of multi-peakon equations and their properties

abstract:
  A general family of peakon equations is introduced, involving two arbitrary
functions of the wave amplitude and the wave gradient. This family contains all
of the known breaking wave equations, including the integrable ones:
Camassa-Holm equation, Degasperis-Procesi equation, Novikov equation, and
FORQ/modified Camassa-Holm equation. One main result is to show that all of the
equations in the general family possess weak solutions given by multi-peakons
which are a linear superposition of peakons with time-dependent amplitudes and
positions. In particular, neither an integrability structure nor a Hamiltonian
structure is needed to derive $N$-peakon weak solutions for arbitrary $N>1$. As
a further result, single peakon travelling-wave solutions are shown to exist
under a simple condition on one of the two arbitrary functions in the general
family of equations, and when this condition fails, generalized single peakon
solutions that have a time-dependent amplitude and a time-dependent speed are
shown to exist. Wave breaking criteria are outlined for this general family of
peakon equations. An interesting generalization of the Camassa-Holm and
FORQ/modified Camassa-Holm equations is obtained by deriving the most general
subfamily of peakon equations that possess the Hamiltonian structure shared by
the Camassa-Holm and FORQ/modified Camassa-Holm equations. Peakon
travelling-wave solutions and their features, including a variational
formulation (minimizer problem), are derived for these generalized equations. A
final main result is that $2$-peakon weak solutions are investigated and shown
to exhibit several novel kinds of behaviour, including the formation of a bound
pair consisting of a peakon and an anti-peakon that have a maximum finite
separation.


title:
Photoproduction of vector mesons: from ultraperipheral to semi-central
  heavy ion collisions

abstract:
  We discuss nuclear cross sections for $AA \to AAV$ and $AA \to AAVV$
reactions with one or two vector mesons in the final state. Our analysis is
done in the impact parameter space equivalent photon approximation. This
approach allows to consider the above processes taking into account distance
between colliding nuclei. We consider both ultraperipheral and semi-central
collisions. We are a first group which undertook a study of single $J/\psi$
photoproduction for different centrality bins. We show that one can describe
new ALICE experimental data by including geometrical effects of collisions in
the flux factor.
  Next, total and differential cross section for double-scattering mechanism in
the exclusive $AA \to AAVV$ reaction in ultrarelativistic ultraperipheral heavy
ion collisions is presented. In this context we consider double photoproduction
and photon-photon processes. Simultaneously, we get very good agreement of our
results with STAR (RHIC), CMS and ALICE (LHC) experimental data for single
$\rho^0$ and $J/\psi$ vector meson production. A comparison of our predictions
for exclusive four charged pions production is also presented.


title:
Combining Texture and Shape Cues for Object Recognition With Minimal
  Supervision

abstract:
  We present a novel approach to object classification and detection which
requires minimal supervision and which combines visual texture cues and shape
information learned from freely available unlabeled web search results. The
explosion of visual data on the web can potentially make visual examples of
almost any object easily accessible via web search. Previous unsupervised
methods have utilized either large scale sources of texture cues from the web,
or shape information from data such as crowdsourced CAD models. We propose a
two-stream deep learning framework that combines these cues, with one stream
learning visual texture cues from image search data, and the other stream
learning rich shape information from 3D CAD models. To perform classification
or detection for a novel image, the predictions of the two streams are combined
using a late fusion scheme. We present experiments and visualizations for both
tasks on the standard benchmark PASCAL VOC 2007 to demonstrate that texture and
shape provide complementary information in our model. Our method outperforms
previous web image based models, 3D CAD model based approaches, and weakly
supervised models.


title:
Global existence of weak solutions to dissipative transport equations
  with nonlocal velocity

abstract:
  We consider 1D dissipative transport equations with nonlocal velocity field:
\[ \theta_t+u\theta_x+\delta u_{x} \theta+\Lambda^{\gamma}\theta=0, \quad
u=\mathcal{N}(\theta), \] where $\mathcal{N}$ is a nonlocal operator given by a
Fourier multiplier. Especially we consider two types of nonlocal operators:
  $\mathcal{N}=\mathcal{H}$, the Hilbert transform,
  $\mathcal{N}=(1-\partial_{xx} )^{-\alpha}$.
  In this paper, we show several global existence of weak solutions depending
on the range of $\gamma$ and $\delta$. When $0<\gamma<1$, we take initial data
having finite energy, while we take initial data in weighted function spaces
(in the real variables or in the Fourier variables), which have infinite
energy, when $\gamma \in (0,2)$.


title: Studies of final state interactions via femtoscopy in ALICE

abstract:
  Femtoscopy is a technique enabling measurements of the space-time
characteristics of particle-emitting sources. However, the femtoscopic analysis
is also sensitive to the interaction cross-section. In this paper we show the
first preliminary measurements of $\rm K^0_SK^{\pm}$ correlation functions in
Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. These correlations originate
from the final-state interactions which proceed through the $a_0(980)$
resonance only and can be employed to constrain its parameters. A similar
approach can be applied to baryon pairs to extract the unknown interaction
cross-sections for some (anti-)baryon-(anti-)baryon pairs. We show
baryon--baryon and baryon--anti-baryon correlation functions of protons and
lambdas, as well as discuss shortly the fitting method.


title:
Spatial distribution of FIR rotationally excited CH+ and OH emission
  lines in the Orion Bar PDR

abstract:
  The abundance of CH+ and OH and excitation are predicted to be enhanced by
the presence of vibrationally excited H2 or hot gas (~500-1000 K) in PDRs with
high incident FUV radiation field. The excitation may also originate in dense
gas (>10^5 cm-3) followed by nonreactive collisions. Previous observations
suggest that the CH+ and OH correlate with dense and warm gas, and formation
pumping contributes to CH+ excitation. We examine the spatial distribution of
the CH+ and OH emission in the Orion Bar to establish their physical origin and
main formation and excitation mechanisms. We present spatially sampled maps of
the CH+ J=3-2 transition at 119.8 {\mu}m and the OH {\Lambda}-doublet at 84
{\mu}m in the Orion Bar over an area of 110"x110" with Herschel (PACS). We
compare the spatial distribution of these molecules with those of their
chemical precursors, C+, O and H2, and tracers of warm and dense gas. We assess
the spatial variation of CH+ J=2-1 velocity-resolved line profile observed with
Herschel (HIFI). The OH and CH+ lines correlate well with the high-J CO
emission and delineate the warm and dense molecular region. While similar, the
differences in the CH+ and OH morphologies indicate that CH+ formation and
excitation are related to the observed vibrationally excited H2. This indicates
that formation pumping contributes to the excitation of CH+. Interestingly, the
peak of the rotationally excited OH 84 {\mu}m emission coincides with a bright
young object, proplyd 244-440, which shows that OH can be an excellent tracer
of UV-irradiated dense gas. The spatial distribution of CH+ and OH revealed in
our maps is consistent with previous modeling studies. Both formation pumping
and nonreactive collisions in a UV-irradiated dense gas are important CH+ J=3-2
excitation processes. The excitation of the OH {\Lambda}-doublet at 84 {\mu}m
is mainly sensitive to the temperature and density.


title: How to Compute Modulo Prime-Power Sums

abstract:
  The problem of computing modulo prime-power sums is investigated in
distributed source coding as well as computation over Multiple-Access Channel
(MAC). We build upon group codes and present a new class of codes called Quasi
Group Codes (QGC). A QGC is a subset of a group code. These codes are not
closed under the group addition. We investigate some properties of QGC's, and
provide a packing and a covering bound. Next, we use these bounds to derived
achievable rates for distributed source coding as well as computation over MAC.
We show that strict improvements over the previously known schemes can be
obtained using QGC's.


title:
Inversion formulas and range characterizations for the attenuated
  geodesic ray transform

abstract:
  We present two range characterizations for the attenuated geodesic X-ray
transform defined on pairs of functions and one-forms on simple surfaces. Such
characterizations are based on first isolating the range over sums of functions
and one-forms, then separating each sub-range in two ways, first by implicit
conditions, second by deriving new inversion formulas for sums of functions and
one-forms.


title: Direct and Central Products of Localities

abstract:
  We develop a theory of direct and central products of partial groups and
localities.


title:
On topological approach to local theory of surfaces in Calabi-Yau
  threefolds

abstract:
  We study the web of dualities relating various enumerative invariants,
notably Gromov-Witten invariants and invariants that arise in topological gauge
theory. In particular, we study Donaldson-Thomas gauge theory and its
reductions to D=4 and D=2 which are relevant to the local theory of surfaces in
Calabi-Yau threefolds.


title: Implementation of a discrete Immersed Boundary Method in OpenFOAM

abstract:
  In this paper, the Immersed Boundary Method (IBM) proposed by Pinelli is
implemented for finite volume approximations of incompressible Navier-Stokes
equations solutions in the open source toolbox OpenFOAM version 2.2. Solid
obstacles are described using a discrete forcing approach for boundary
conditions. Unlike traditional approaches encompassing the presence of a solid
body using conformal meshes and imposing no-slip boundary conditions on the
boundary faces of the mesh, the solid body is here represented on the Eulerian
Cartesian mesh through an ad-hoc body force evaluated on a set of Lagrangian
markers. The markers can move across the Eulerian mesh, hence allowing for a
straightforward analysis of motion or deformation of the body. The IBM method
is described and implemented in PisoFOAM, whose Pressure-Implicit
Split-Operator (PISO) solver is modified accordingly. The presence of the solid
body and the divergence-free of the fluid velocity are imposed simultaneously
by sub-iterating between IBM and the pressure correction step. This scheme
allows for the use of fast optimized Poisson solvers while granting excellent
accuracy with respect to the previously mentioned constraints. Various 2D and
3D well-documented test cases of flows around fixed or moving circular
cylinders are simulated and carefully validated against existing data from the
literature. The capability of the new solver is discussed in terms of accuracy
and numerical performances.


title: Rare event simulation via importance sampling for linear SPDE's

abstract:
  The goal of this paper is to develop provably efficient importance sampling
Monte Carlo methods for the estimation of rare events within the class of
linear stochastic partial differential equations (SPDEs). We find that if a
spectral gap of appropriate size exists, then one can identify a lower
dimensional manifold where the rare event takes place. This allows one to build
importance sampling changes of measures that perform provably well even
pre-asymptotically (i.e. for small but non-zero size of the noise) without
degrading in performance due to infinite dimensionality or due to long
simulation time horizons. Simulation studies supplement and illustrate the
theoretical results.


title:
Non-interacting fermions at finite temperature in a $d$-dimensional
  trap: universal correlations

abstract:
  We study a system of $N$ non-interacting spin-less fermions trapped in a
confining potential, in arbitrary dimensions $d$ and arbitrary temperature $T$.
The presence of the trap introduces an edge where the average density of
fermions vanishes. Far from the edge, near the center of the trap (the so
called "bulk regime"), physical properties of the fermions have traditionally
been understood using the Local Density Approximation. However, this
approximation drastically fails near the edge where the density vanishes. In
this paper we show that, even near the edge, novel universal properties emerge,
independently of the details of the confining potential. We show that for large
$N$, these fermions in a confining trap, in arbitrary dimensions and at finite
temperature, form a determinantal point process. As a result, any $n$-point
correlation function can be expressed as an $n \times n$ determinant whose
entry is called the kernel. Near the edge, we derive the large $N$ scaling form
of the kernels. In $d=1$ and $T=0$, this reduces to the so called Airy kernel,
that appears in the Gaussian Unitary Ensemble (GUE) of random matrix theory. In
$d=1$ and $T>0$ we show a remarkable connection between our kernel and the one
appearing in the $1+1$-dimensional Kardar-Parisi-Zhang equation at finite time.
Consequently our result provides a finite $T$ generalization of the Tracy-Widom
distribution, that describes the fluctuations of the rightmost fermion at
$T=0$. In $d>1$ and $T \geq 0$, while the connection to GUE no longer holds,
the process is still determinantal whose analysis provides a new class of
kernels, generalizing the $1d$ Airy kernel at $T=0$ obtained in random matrix
theory. Some of our finite temperature results should be testable in
present-day cold atom experiments, most notably our detailed predictions for
the temperature dependence of the fluctuations near the edge.

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


title:
Explaining the $R_{K}$ and $R_{D^{(*)}}$ anomalies with vector
  leptoquarks

abstract:
  Recently the $B$ factories BaBar and Belle as well as the LHCb experiment
have reported several anomalies in the semileptonic $B$ meson decays such as
$R_{K}$ and $R_{D^{(*)}}$ etc. We investigate these deviations by considering
the vector leptoquarks relevant for both $b \to s l^+ l^-$ and $b \to c l \bar
\nu_l$ transitions. The leptoquark parameter space is constrained by using the
experimentally measured branching ratios of $B_s \to l^+ l^-$, $\bar B \to X_s
l^+ l^- (\nu \bar \nu)$ and $B_u^+ \to l^+ \nu_l$ processes. Using the
constrained leptoquark couplings, we compute the branching ratios,
forward-backward asymmetries, $\tau$ and $D^*$ polarization parameters in the
$\bar B \to D^{(*)} l \bar \nu_l$ processes. We find that the vector
leptoquarks can explain both $R_{D^{(*)}}$ and $R_K$ anomalies simultaneously.
Furthermore, we study the rare leptonic $B_{u, c}^* \to l \bar\nu$ decay
processes in this model.


title: On the energy landscape of the mixed even $p$-spin model

abstract:
  We investigate the energy landscape of the mixed even $p$-spin model with
Ising spin configurations. We show that for any given energy level between zero
and the maximal energy, with overwhelming probability there exist exponentially
many distinct spin configurations such that their energies stay near this
energy level. Furthermore, their magnetizations and overlaps are concentrated
around some fixed constants. In particular, at the level of maximal energy, we
prove that the Hamiltonian exhibits exponentially many orthogonal peaks. This
improves the results of Chatterjee and Ding-Eldan-Zhai, where the former
established a logarithmic size of the number of the orthogonal peaks, while the
latter proved a polynomial size. Our second main result obtains disorder chaos
at zero temperature and at any external field. As a byproduct, this implies
that the fluctuation of the maximal energy is superconcentrated when the
external field vanishes and obeys a Gaussian limit law when the external field
is present.


title:
Eta-Eta' mixing and the derivative of the topological susceptibility at
  zero momentum transfer

abstract:
  The couplings of the isosinglet axial-vector currents to the Eta and Eta'
mesons are evaluated in a stable, model independent way by use of polynomial
kernels in dispersion integrals. The corrections to the Gell-Mann-Oakes-Renner
relation in the isoscalar channel are deduced. The derivative of the
topological susceptibility at the origin is calculated taking into account
instantons and instanton screening.


title:
Analyzing signal attenuation in PFG anomalous diffusion via a
  non-Gaussian phase distribution approximation approach by fractional
  derivatives

abstract:
  Anomalous diffusion exists widely in polymer and biological systems. Pulsed
field gradient (PFG) techniques have been increasingly used to study anomalous
diffusion in NMR and MRI. However, the interpretation of PFG anomalous
diffusion is complicated. Moreover, there is not an exact signal attenuation
expression based on fractional derivatives for PFG anomalous diffusion, which
includes the finite gradient pulse width effect. In this paper, a new method, a
Mainardi-Luchko-Pagnini (MLP) phase distribution approximation, is proposed to
describe PFG fractional diffusion. MLP phase distribution is a non-Gaussian
phase distribution. From the fractional diffusion equation based on fractional
derivatives in both real space and phase space, the obtained probability
distribution function is a MLP distribution. The MLP distribution leads to a
Mittag-Leffler function based PFG signal attenuation rather than the
exponential or stretched exponential attenuation that is obtained from a
Gaussian phase distribution (GPD) under a short gradient pulse approximation.
The MLP phase distribution approximation is employed to get a complete signal
attenuation expression E{\alpha}(-Dfb*{\alpha},\b{eta}) that includes the
finite gradient pulse width effect for all three types of PFG fractional
diffusion. The results obtained in this study are in agreement with the results
from the literature. These results provide a new, convenient approximation
formalism to interpret complex PFG fractional diffusion experiments.


title: Finite LTL Synthesis is EXPTIME-complete

abstract:
  LTL synthesis -- the construction of a function to satisfy a logical
specification formulated in Linear Temporal Logic -- is a 2EXPTIME-complete
problem with relevant applications in controller synthesis and a myriad of
artificial intelligence applications. In this research note we consider De
Giacomo and Vardi's variant of the synthesis problem for LTL formulas
interpreted over finite rather than infinite traces. Rather surprisingly, given
the existing claims on complexity, we establish that LTL synthesis is
EXPTIME-complete for the finite interpretation, and not 2EXPTIME-complete as
previously reported. Our result coincides nicely with the planning perspective
where non-deterministic planning with full observability is EXPTIME-complete
and partial observability increases the complexity to 2EXPTIME-complete; a
recent related result for LTL synthesis shows that in the finite case with
partial observability, the problem is 2EXPTIME-complete.


title: QUBIC Technical Design Report

abstract:
  QUBIC is an instrument aiming at measuring the B mode polarisation
anisotropies at medium scales angular scales (30-200 multipoles). The search
for the primordial CMB B-mode polarization signal is challenging, because of
many difficulties: smallness of the expected signal, instrumental systematics
that could possibly induce polarization leakage from the large E signal into B,
brighter than anticipated polarized foregrounds (dust) reducing to zero the
initial hope of finding sky regions clean enough to have a direct primordial
B-modes observation. The QUBIC instrument is designed to address all aspects of
this challenge with a novel kind of instrument, a Bolometric Interferometer,
combining the background-limited sensitivity of Transition-Edge-Sensors and the
control of systematics allowed by the observation of interference fringe
patterns, while operating at two frequencies to disentangle polarized
foregrounds from primordial B mode polarization. Its characteristics are
described in details in this Technological Design Report.


title: Consistency of Social Sensing Signatures Across Major US Cities

abstract:
  Previous studies have shown that Twitter users have biases to tweet from
certain locations, locational bias, and during certain hours, temporal bias. We
used three years of geolocated Twitter Data to quantify these biases and test
our central hypothesis that Twitter users biases are consistent across US
cities. Our results suggest that temporal and locational bias of Twitter users
are inconsistent between three US metropolitan cities. We derive conclusions
about the role of the complexity of the underlying data producing process on
its consistency and argue for the potential research avenue for Geospatial Data
Science to test and quantify these inconsistencies in the class of organically
evolved Big Data.


title: The cross-over from tunnelling to multiphoton ionization of atoms

abstract:
  We present a theory illuminating the cross-over from strong-field tunnelling
ionization to weak-field multiphoton ionization in the interaction of a
classical laser field with a hydrogen atom. A simple formula is derived in
which the ionization amplitude appears as a product of two separate amplitudes.
The first describes the initial polarization of the atom by virtual multiphoton
absorption and the second the subsequent tunnelling out of the polarized atom.
Tunnelling directly from the ground state and multiphoton absorption without
tunnelling appear naturally as the limits of the theory.


title: A Perspective on Deep Imaging

abstract:
  The combination of tomographic imaging and deep learning, or machine learning
in general, promises to empower not only image analysis but also image
reconstruction. The latter aspect is considered in this perspective article
with an emphasis on medical imaging to develop a new generation of image
reconstruction theories and techniques. This direction might lead to
intelligent utilization of domain knowledge from big data, innovative
approaches for image reconstruction, and superior performance in clinical and
preclinical applications. To realize the full impact of machine learning on
medical imaging, major challenges must be addressed.


title:
Super-resolution community detection for layer-aggregated multilayer
  networks

abstract:
  Applied network science often involves preprocessing network data before
applying a network-analysis method, and there is typically a theoretical
disconnect between these steps. For example, it is common to aggregate
time-varying network data into windows prior to analysis, and the tradeoffs of
this preprocessing are not well understood. Focusing on the problem of
detecting small communities in multilayer networks, we study the effects of
layer aggregation by developing random-matrix theory for modularity matrices
associated with layer-aggregated networks with $N$ nodes and $L$ layers, which
are drawn from an ensemble of Erd\H{o}s-R\'enyi networks. We study phase
transitions in which eigenvectors localize onto communities (allowing their
detection) and which occur for a given community provided its size surpasses a
detectability limit $K^*$. When layers are aggregated via a summation, we
obtain $K^*\varpropto \mathcal{O}(\sqrt{NL}/T)$, where $T$ is the number of
layers across which the community persists. Interestingly, if $T$ is allowed to
vary with $L$ then summation-based layer aggregation enhances small-community
detection even if the community persists across a vanishing fraction of layers,
provided that $T/L$ decays more slowly than $ \mathcal{O}(L^{-1/2})$. Moreover,
we find that thresholding the summation can in some cases cause $K^*$ to decay
exponentially, decreasing by orders of magnitude in a phenomenon we call
super-resolution community detection. That is, layer aggregation with
thresholding is a nonlinear data filter enabling detection of communities that
are otherwise too small to detect. Importantly, different thresholds generally
enhance the detectability of communities having different properties,
illustrating that community detection can be obscured if one analyzes network
data using a single threshold.


title:
Dynamical History Of The Local Group In $\Lambda$CDM $\rm{II}$ $-$
  Including External Perturbers In 3D

abstract:
  We attempt to fit the observed radial velocities (RVs) of ${\,{\sim}\,}30$
Local Group (LG) galaxies using a 3D dynamical model of it and its immediate
environment within the context of the standard cosmological paradigm,
$\Lambda$CDM. This extends and confirms the basic results of our previous
axisymmetric investigation of the LG (MNRAS, 459, 2237). We find that there
remains a tendency for observed RVs to exceed those predicted by our
best-fitting model. The typical mismatch is slightly higher than in our 2D
model, with a root mean square value of ${\,{\sim}\,}50$ km/s. Our main finding
is that including the 3D distribution of massive perturbing dark matter halos
is unlikely to help greatly with the high velocity galaxy problem. Nonetheless,
the 2D and 3D results differ in several other ways such as which galaxies' RVs
are most problematic and the preferred values of parameters common to both
models.
  The anomalously high RVs of several LG dwarfs may be better explained if the
Milky Way (MW) and Andromeda (M31) were once moving much faster than in our
models. This would allow LG dwarfs to gain very high RVs via gravitational
slingshot encounters with a massive fast-moving galaxy. Such a scenario is
possible in some modified gravity theories, especially those which require the
MW and M31 to have previously undergone a close flyby. In a $\Lambda$CDM
context, however, this scenario is not feasible as the resulting dynamical
friction would cause a rapid merger.


title:
An improved current potential method for fast computation of stellarator
  coil shapes

abstract:
  Several fast methods for computing stellarator coil shapes are compared,
including the classical NESCOIL procedure [Merkel, Nucl. Fusion 27, 867
(1987)], its generalization using truncated singular value decomposition, and a
Tikhonov regularization approach we call REGCOIL in which the squared current
density is included in the objective function. Considering W7-X and NCSX
geometries, and for any desired level of regularization, we find the REGCOIL
approach simultaneously achieves lower surface-averaged and maximum values of
both current density (on the coil winding surface) and normal magnetic field
(on the desired plasma surface). This approach therefore can simultaneously
improve the free-boundary reconstruction of the target plasma shape while
substantially increasing the minimum distances between coils, preventing
collisions between coils while improving access for ports and maintenance. The
REGCOIL method also allows finer control over the level of regularization, it
preserves convexity to ensure the local optimum found is the global optimum,
and it eliminates two pathologies of NESCOIL: the resulting coil shapes become
independent of the arbitrary choice of angles used to parameterize the coil
surface, and the resulting coil shapes converge rather than diverge as Fourier
resolution is increased. We therefore contend that REGCOIL should be used
instead of NESCOIL for applications in which a fast and robust method for coil
calculation is needed, such as when targeting coil complexity in fixed-boundary
plasma optimization, or for scoping new stellarator geometries.


title:
Threaded-Field-Lines Model for the Low Solar Corona Powered by the
  Alfven Wave Turbulence

abstract:
  We present an updated global model of the solar corona, including the
transition region. We simulate the realistic tree-dimensional (3D) magnetic
field using the data from the photospheric magnetic field measurements and
assume the magnetohydrodynamic (MHD) Alfv\'en wave turbulence and its
non-linear dissipation to be the only source for heating the coronal plasma and
driving the solar wind. In closed field regions the dissipation efficiency in a
balanced turbulence is enhanced. In the coronal holes we account for a
reflection of the outward propagating waves, which is accompanied by generation
of weaker counter-propagating waves. The non-linear cascade rate degrades in
strongly imbalanced turbulence, thus resulting in colder coronal holes.
  The distinctive feature of the presented model is the description of the low
corona as almost-steady-state low-beta plasma motion and heat flux transfer
along the magnetic field lines. We trace the magnetic field lines through each
grid point of the lower boundary of the global corona model, chosen at some
heliocentric distance, $R=R_{b}\sim1.1\ R_\odot$ well above the transition
region. One can readily solve the plasma parameters along the magnetic field
line from 1D equations for the plasma motion and heat transport together with
the Alfv\'en wave propagation, which adequately describe physics within the
heliocentric distances range, $R_{\odot}<R<R_{b}$, in the low solar corona. By
interfacing this threaded-field-lines model with the full MHD global corona
model at $r=R_{b}$, we find the global solution and achieve a
faster-than-real-time performance of the model on $\sim200$ cores.


title:
Light scattering study of the "pseudo-layer" compression elastic
  constant in a twist-bend nematic liquid crystal

abstract:
  The nematic twist-bend (TB) phase, exhibited by certain achiral thermotropic
liquid crystalline (LC) dimers, features a nanometer-scale, heliconical
rotation of the average molecular long axis (director) with equally probable
left- and right-handed domains. On meso to macroscopic scales, the TB phase may
be considered as a stack of equivalent slabs or "pseudo-layers", each one
helical pitch in thickness. The long wavelength fluctuation modes should then
be analogous to those of a smectic-A phase, and in particular the hydrodynamic
mode combining "layer" compression and bending ought to be characterized by an
effective layer compression elastic constant $B_{eff}$ and average director
splay constant $K_1^{eff}$. The magnitude of $K_1^{eff}$ is expected to be
similar to the splay constant of an ordinary nematic LC, but due to the absence
of a true mass density wave, $B_{eff}$ could differ substantially from the
typical value of $\sim 10^6$ Pa in a conventional smectic-A. Here we report the
results of a dynamic light scattering study, which confirms the "pseudo-layer"
structure of the TB phase with $B_{eff}$ in the range $\sim 10^3-10^4$ Pa. We
show additionally that the temperature dependence of $B_{eff}$ at the TB to
nematic transition is accurately described by a coarse-grained free energy
density, which is based on a Landau-deGennes expansion in terms of a heli-polar
order parameter that characterizes the TB state and is linearly coupled to bend
distortion of the director.


title:
Layer-dependent properties of SnS2 and SnSe2 novel two-dimensional
  materials

abstract:
  The layer dependent structural, electronic and vibrational properties of SnS2
and SnSe2 are investigated using first-principles density functional theory
(DFT). The in-plane lattice constants, interlayer distances and binding
energies are found to be layer-independent. Bulk SnS2 and SnSe2 are both
indirect band gap semiconductors with Eg = 2.18 eV and 1.07 eV, respectively.
Few-layer and monolayer 2D systems also possess an indirect band gap, which is
increased to 2.41 eV and 1.69 eV for single layers of SnS2 and SnSe2. The
effective mass theory of 2D excitons, which takes into account the combined
effect of the anisotropy, non-local 2D screening and layer-dependent 3D
screening, predicts strong excitonic effects. The binding energy of indirect
excitons in monolayer samples, Ex~0.9 eV, is substantially reduced to Ex = 0.14
eV in bulk SnS2 and Ex = 0.09 eV in bulk SnSe2. The layer-dependent Raman
spectra display a strong decrease of intensities of the Raman active A1g mode
upon decreasing the number of layers down to a monolayer, by a factor of 7 in
the case of SnS2 and a factor of 20 in the case of SnSe2 which can be used to
identify number of layers in a 2D sample.


title: Warped Convolutions: Efficient Invariance to Spatial Transformations

abstract:
  Convolutional Neural Networks (CNNs) are extremely efficient, since they
exploit the inherent translation-invariance of natural images. However,
translation is just one of a myriad of useful spatial transformations. Can the
same efficiency be attained when considering other spatial invariances? Such
generalized convolutions have been considered in the past, but at a high
computational cost. We present a construction that is simple and exact, yet has
the same computational complexity that standard convolutions enjoy. It consists
of a constant image warp followed by a simple convolution, which are standard
blocks in deep learning toolboxes. With a carefully crafted warp, the resulting
architecture can be made equivariant to a wide range of two-parameter spatial
transformations. We show encouraging results in realistic scenarios, including
the estimation of vehicle poses in the Google Earth dataset (rotation and
scale), and face poses in Annotated Facial Landmarks in the Wild (3D rotations
under perspective).


title:
Probabilistic Population Projections for Countries with Generalized
  HIV/AIDS Epidemics

abstract:
  The United Nations (UN) issued official probabilistic population projections
for all countries to 2100 in July 2015. This was done by simulating future
levels of total fertility and life expectancy from Bayesian hierarchical
models, and combining the results using a standard cohort-component projection
method. The 40 countries with generalized HIV/AIDS epidemics were treated
differently from others, in that the projections used the highly multistate
Spectrum/EPP model, a complex 15-compartment model that was designed for
short-term projections of quantities relevant to policy for the epidemic. Here
we propose a simpler approach that is more compatible with the existing UN
probabilistic projection methodology for other countries. Changes in life
expectancy are projected probabilistically using a simple time series
regression model on current life expectancy, HIV prevalence and ART coverage.
These are then converted to age- and sex-specific mortality rates using a new
family of model life tables designed for countries with HIV/AIDS epidemics that
reproduces the characteristic hump in middle adult mortality. These are then
input to the standard cohort-component method, as for other countries. The
method performed well in an out-of-sample cross-validation experiment. It gives
similar population projections to Spectrum/EPP in the short run, while being
simpler and avoiding multistate modeling.


title: Electrohydrodynamic Quincke rotation of a prolate ellipsoid

abstract:
  We experimentally study the occurrence of spontaneous spinning (Quincke
rotation) of an ellipsoid in a uniform DC electric field. For an ellipsoid
suspended in an unbounded fluid, we find two stable states characterized by the
orientation of the ellipsoid long axis relative to the applied electric field :
spinless (parallel) and spinning (perpendicular). The phase diagram of
ellipsoid behavior as a function of field strength and aspect ratio is in close
agreement with the theory of Cebers et al. Phys. Rev .E 63:016301 (2000). We
also investigated the dynamics of the ellipsoidal Quincke rotor resting on a
planar surface with normal perpendicular to the field direction. We find novel
behaviors, such as swinging (long axis oscillating around the applied field
direction) and tumbling, due to the confinement.


title: Behavior of the maximum likelihood in quantum state tomography

abstract:
  Quantum state tomography on a d-dimensional system demands resources that
grow rapidly with d. They may be reduced by using model selection to tailor the
number of parameters in the model (i.e., the size of the density matrix). Most
model selection methods typically rely on a test statistic and a null theory
that describes its behavior when two models are equally good. Here, we consider
the loglikelihood ratio. Because of the positivity constraint $\rho \geq 0$,
quantum state space does not generally satisfy local asymptotic normality,
meaning the classical null theory for the loglikelihood ratio (the Wilks
theorem) should not be used. Thus, understanding and quantifying how positivity
affects the null behavior of this test statistic is necessary for its use in
model selection for state tomography. We define a new generalization of local
asymptotic normality, metric-projected local asymptotic normality, show that
quantum state space satisfies it, and derive a replacement for the Wilks
theorem. In addition to enabling reliable model selection, our results shed
more light on the qualitative effects of the positivity constraint on state
tomography.


title: Dispersive Stiffness of Dzyaloshinskii Domain Walls

abstract:
  It is well documented that subjecting perpendicular magnetic films which
exhibit the interfacial Dzyaloshinskii-Moriya interaction (DMI) to an in-plane
magnetic field results in a domain wall (DW) energy, $\sigma$, that is highly
anisotropic with respect to the orientation of the DW in the film plane,
$\Theta$. We demonstrate that this anisotropy has a profound impact on the
elastic response of the DW as characterized by the surface stiffness,
$\tilde{\sigma}(\Theta) = \sigma(\Theta) + \sigma"(\Theta)$, and evaluate its
dependence on the length scale of deformation. The influence of the stiffness
on DW mobility in the creep regime is assessed, with analytic and numerical
calculations showing trends in $\tilde{\sigma}$ that better represent
experimental measurements of domain wall velocity in magnetic thin films
compared to $\sigma$ alone. Our treatment provides experimental support for
theoretical models of the mobility of anisotropic elastic manifolds and makes
progress toward a more complete understanding of magnetic domain wall creep.


title: 3D Face Reconstruction by Learning from Synthetic Data

abstract:
  Fast and robust three-dimensional reconstruction of facial geometric
structure from a single image is a challenging task with numerous applications.
Here, we introduce a learning-based approach for reconstructing a
three-dimensional face from a single image. Recent face recovery methods rely
on accurate localization of key characteristic points. In contrast, the
proposed approach is based on a Convolutional-Neural-Network (CNN) which
extracts the face geometry directly from its image. Although such deep
architectures outperform other models in complex computer vision problems,
training them properly requires a large dataset of annotated examples. In the
case of three-dimensional faces, currently, there are no large volume data
sets, while acquiring such big-data is a tedious task. As an alternative, we
propose to generate random, yet nearly photo-realistic, facial images for which
the geometric form is known. The suggested model successfully recovers facial
shapes from real images, even for faces with extreme expressions and under
various lighting conditions.


title: Relativistic Monte Carlo

abstract:
  Hamiltonian Monte Carlo (HMC) is a popular Markov chain Monte Carlo (MCMC)
algorithm that generates proposals for a Metropolis-Hastings algorithm by
simulating the dynamics of a Hamiltonian system. However, HMC is sensitive to
large time discretizations and performs poorly if there is a mismatch between
the spatial geometry of the target distribution and the scales of the momentum
distribution. In particular the mass matrix of HMC is hard to tune well. In
order to alleviate these problems we propose relativistic Hamiltonian Monte
Carlo, a version of HMC based on relativistic dynamics that introduce a maximum
velocity on particles. We also derive stochastic gradient versions of the
algorithm and show that the resulting algorithms bear interesting relationships
to gradient clipping, RMSprop, Adagrad and Adam, popular optimisation methods
in deep learning. Based on this, we develop relativistic stochastic gradient
descent by taking the zero-temperature limit of relativistic stochastic
gradient Hamiltonian Monte Carlo. In experiments we show that the relativistic
algorithms perform better than classical Newtonian variants and Adam.


title:
Accurate, Empirical Radii and Masses of Planets and their Host Stars
  with Gaia Parallaxes

abstract:
  We present empirical measurements of the radii of 116 stars that host
transiting planets. These radii are determined using only direct
observables-the bolometric flux at Earth, the effective temperature, and the
parallax provided by the Gaia first data release-and thus are virtually model
independent, extinction being the only free parameter. We also determine each
star's mass using our newly determined radius and the stellar density, itself a
virtually model independent quantity from previously published transit
analyses. These stellar radii and masses are in turn used to redetermine the
transiting planet radii and masses, again using only direct observables. The
median uncertainties on the stellar radii and masses are ~8% and ~30%,
respectively, and the resulting uncertainties on the planet radii and masses
are ~9% and ~22%, respectively. These accuracies are generally larger than
previously published model-dependent precisions of ~5% and ~6% on the planet
radii and masses, respectively, but the newly determined values are purely
empirical. We additionally report radii for 242 stars hosting radial-velocity
(non-transiting) planets, with median achieved accuracy of ~2%. Using our
empirical stellar masses we verify that the majority of putative "retired A
stars" in the sample are indeed more massive than ~1.2 Msun. Most importantly,
the bolometric fluxes and angular radii reported here for a total of 498 planet
host stars-with median accuracies of 1.7% and 1.8%, respectively-serve as a
fundamental dataset to permit the re-determination of transiting planet radii
and masses with the Gaia second data release to ~3% and ~5% accuracy, better
than currently published precisions, and determined in an entirely empirical
fashion.


title: Nonlinear dynamics and chaos in an optomechanical beam

abstract:
  Optical non-linearities, such as thermo-optic effects and
free-carrier-dispersion, are often considered as undesired effects in
silicon-based resonators and, more specifically, optomechanical (OM) cavities,
affecting the relative detuning between an optical resonance and the excitation
laser. However, the interplay between such mechanisms could also enable
unexpected physical phenomena to be used in new applications. In the present
work, we exploit those non-linearities and their intercoupling with the
mechanical degrees of freedom of a silicon OM nanobeam to unveil a rich set of
fundamentally different complex dynamics. By smoothly changing the parameters
of the excitation laser, namely its power and wavelength, we demonstrate
accurate control for activating bi-dimensional and tetra-dimensional
limit-cycles, a period doubling route and chaos. In addition, by scanning the
laser parameters in opposite senses we demonstrate bistability and hysteresis
between bi-dimensional and tetra-dimensional limit-cycles, between different
coherent mechanical states and between tetra-dimensional limit-cycles and
chaos. As a result of implementing the Rosenstein algorithm to the experimental
time series we have extracted a Largest Lyapunov Exponent of LLE=1.3x10^5 s-1,
which is between one and two orders of magnitude lower than the typical
oscillating frequencies of the system. Most of the experimental features can be
well reproduced with a model of first-order non-linear differential equations
coupled through the number of intracavity photons. Our findings open several
routes towards exploiting silicon-based OM photonic crystals for systems with
memory and, more specifically, for chaos based applications such as secure
information transfer or sensing.


title: When is $a^{n} + 1$ the sum of two squares?

abstract:
  Using Fermat's two squares theorem and properties of cyclotomic polynomials,
we prove assertions about when numbers of the form $a^{n}+1$ can be expressed
as the sum of two integer squares. We prove that $a^n + 1$ is the sum of two
squares for all $n \in \mathbb{N}$ if and only if $a$ is a perfect square. We
also prove that for $a\equiv 0,1,2\pmod{4},$ if $a^{n} + 1$ is the sum of two
squares, then $a^{\delta} + 1$ is the sum of two squares for all $\delta | n, \
\delta>1$. Using Aurifeuillian factorization, we show that if $a$ is a prime
and $a\equiv 1 \pmod{4}$, then there are either zero or infinitely many odd $n$
such that $a^n+1$ is the sum of two squares. When $a\equiv 3\pmod{4},$ we
define $m$ to be the least positive integer such that $\frac{a+1}{m}$ is the
sum of two squares, and prove that if $a^n+1$ is the sum of two squares for any
odd integer $n,$ then $m | n$, and both $a^m+1$ and $\frac{n}{m}$ are sums of
two squares.


title:
Learning Robust Features for Gait Recognition by Maximum Margin
  Criterion

abstract:
  In the field of gait recognition from motion capture data, designing
human-interpretable gait features is a common practice of many fellow
researchers. To refrain from ad-hoc schemes and to find maximally
discriminative features we may need to explore beyond the limits of human
interpretability. This paper contributes to the state-of-the-art with a machine
learning approach for extracting robust gait features directly from raw joint
coordinates. The features are learned by a modification of Linear Discriminant
Analysis with Maximum Margin Criterion so that the identities are maximally
separated and, in combination with an appropriate classifier, used for gait
recognition. Experiments on the CMU MoCap database show that this method
outperforms eight other relevant methods in terms of the distribution of
biometric templates in respective feature spaces expressed in four class
separability coefficients. Additional experiments indicate that this method is
a leading concept for rank-based classifier systems.


title: Subalgebras of Solomon's descent algebra based on alternating runs

abstract:
  The number of alternating runs is a natural permutation statistic. We show it
can be used to define some commutative subalgebras of the symmetric group
algebra, and more precisely of the descent algebra. The Eulerian peak algebras
naturally appear as subalgebras of our run algebras. We also calculate the
orthogonal idempotents for run algebras in terms of noncommutative symmetric
functions.


title: Cardinal kinematics: I. Rotation fields of the APOGEE Survey

abstract:
  Correlations between stellar chemistry and kinematics have long been used to
gain insight into the evolution of the Milky Way Galaxy. Orbital angular
momentum is a key physical parameter and it is often estimated from
three-dimensional space motions. We here demonstrate the lower uncertainties
that can be achieved in the estimation of one component of velocity through
selection of stars in key directions and use of line-of-sight velocity alone
(i.e. without incorporation of proper motion data). In this first paper we
apply our technique to stars observed in the direction of Galactic rotation in
the APOGEE survey. We first derive the distribution of azimuthal velocities,
$v_\phi$, then from these and observed radial coordinates, estimate the stellar
guiding centre radii, $R_g$, within $6.9\leq R \leq 10$ kpc with uncertainties
smaller than (or of the order of) 1kpc. We show that there is no simple way to
select a clean stellar sample based on low errors on proper motions and
distances to obtain high-quality 3D velocities and hence one should pay
particular attention when trying to identify kinematically peculiar stars based
on velocities derived using the proper motions. Using our azimuthal velocity
estimations, we investigate the joint distribution of elemental abundances and
rotational kinematics free from the blurring effects of epicyclic motions, and
we derive the $\partial v_\phi / \partial R_g$ trends for the thin and thick
discs as a function of radius. Our analysis provides further evidence for
radial migration within the thin disc and hints against radial migration
playing a significant role in the evolution of the thick disc.


title:
First Gaia Local Group Dynamics: Magellanic Clouds Proper Motion and
  Rotation

abstract:
  We use the Gaia data release 1 (DR1) to study the proper motion (PM) fields
of the Large and Small Magellanic Clouds (LMC, SMC). This uses the Tycho-Gaia
Astrometric Solution (TGAS) PMs for 29 Hipparcos stars in the LMC and 8 in the
SMC. The LMC PM in the West and North directions is inferred to be
$(\mu_W,\mu_N) = (-1.872 \pm 0.045, 0.224 \pm 0.054)$ mas/yr, and the SMC PM
$(\mu_W,\mu_N) = (-0.874 \pm 0.066, -1.229 \pm 0.047)$ mas/yr. These results
have similar accuracy and agree to within the uncertainties with existing
Hubble Space Telescope (HST) PM measurements. Since TGAS uses different methods
with different systematics, this provides an external validation of both data
sets and their underlying approaches. Residual DR1 systematics may affect the
TGAS results, but the HST agreement implies this must be below the random
errors. Also in agreement with prior HST studies, the TGAS LMC PM field clearly
shows the clockwise rotation of the disk, even though it takes the LMC disk in
excess of $10^8$ years to complete one revolution. The implied rotation curve
amplitude for young LMC stars is consistent with that inferred from
line-of-sight (LOS) velocity measurements. Comparison of the PM and LOS
rotation curves implies a kinematic LMC distance modulus $m-M = 18.54 \pm
0.39$, consistent but not yet competitive with photometric methods. These first
results from Gaia on the topic of Local Group dynamics provide an indication of
how its future data releases will revolutionize this field.


title: Quantum Speed Limit Bounds in an Open Quantum Evolution

abstract:
  Quantum mechanics dictates bounds for the minimal evolution time between
predetermined initial and final states. Several of these Quantum Speed Limit
(QSL) bounds were derived for non-unitary dynamics using different approaches.
Here, we perform a systematic analysis of the most common QSL bounds in the
damped Jaynes-Cummings model, covering the Markovian and non-Markovian regime.
We show that only one of the analysed bounds cleaves to the essence of the QSL
theory outlined in the pioneer works of Mandelstam \& Tamm and Margolus \&
Levitin in the context of unitary evolutions. We also show that all of QSL
bounds analysed reflect the fact that in our model non-Markovian effects speed
up the quantum evolution. However, it is not possible to infer the Markovian or
non-Markovian behaviour of the dynamics only analysing the QSL bounds.


title: Soft Black Hole Absorption Rates as Conservation Laws

abstract:
  The absorption rate of low-energy, or soft, electromagnetic radiation by
spherically symmetric black holes in arbitrary dimensions is shown to be fixed
by conservation of energy and large gauge transformations. We interpret this
result as the explicit realization of the Hawking-Perry-Strominger Ward
identity for large gauge transformations in the background of a non-evaporating
black hole. Along the way we rederive and extend previous analytic results
regarding the absorption rate for the minimal scalar and the photon.


title:
Star Formation Quenching Timescale of Central Galaxies in a Hierarchical
  Universe

abstract:
  Central galaxies make up the majority of the galaxy population, including the
majority of the quiescent population at $\mathcal{M}_* >
10^{10}\mathrm{M}_\odot$. Thus, the mechanism(s) responsible for quenching
central galaxies plays a crucial role in galaxy evolution as whole. We combine
a high resolution cosmological $N$-body simulation with observed evolutionary
trends of the "star formation main sequence," quiescent fraction, and stellar
mass function at $z < 1$ to construct a model that statistically tracks the
star formation histories and quenching of central galaxies. Comparing this
model to the distribution of central galaxy star formation rates in a group
catalog of the SDSS Data Release 7, we constrain the timescales over which
physical processes cease star formation in central galaxies. Over the stellar
mass range $10^{9.5}$ to $10^{11} \mathrm{M}_\odot$ we infer quenching
e-folding times that span $1.5$ to $0.5\; \mathrm{Gyr}$ with more massive
central galaxies quenching faster. For $\mathcal{M}_* =
10^{10.5}\mathrm{M}_\odot$, this implies a total migration time of $\sim
4~\mathrm{Gyrs}$ from the star formation main sequence to quiescence. Compared
to satellites, central galaxies take $\sim 2~\mathrm{Gyrs}$ longer to quench
their star formation, suggesting that different mechanisms are responsible for
quenching centrals versus satellites. Finally, the central galaxy quenching
timescale we infer provides key constraints for proposed star formation
quenching mechanisms. Our timescale is generally consistent with gas depletion
timescales predicted by quenching through strangulation. However, the exact
physical mechanism(s) responsible for this still remain unclear.


title: Stellar clusterings around "Isolated" Massive YSOs in the LMC

abstract:
  Observations suggest that there is a significant fraction of O-stars in the
field of the Milky Way that appear to have formed in isolation or in low mass
clusters ($<$100 $M_\odot$). The existence of these high-mass stars that
apparently formed in the field challenges the generally accepted paradigm,
which requires star formation to occur in clustered environments. In order to
understand the physical conditions for the formation of these stars, it is
necessary to observe isolated high-mass stars while they are still forming.
With the $Hubble$ $Space$ $Telescope$, we observe the seven most isolated
massive ($>$8 $M_\odot$) young stellar objects (MYSOs) in the Large Magellanic
Cloud (LMC). The observations show that while these MYSOs are remote from other
MYSOs, OB associations, and even from known giant molecular clouds, they are
actually not isolated at all. Imaging reveals $\sim$100 to several hundred
pre--main-sequence (PMS) stars in the vicinity of each MYSO. These previously
undetected PMS stars form prominent compact clusters around the MYSOs, and in
most cases they are also distributed sparsely across the observed regions.
Contrary to what previous high-mass field star studies show, these observations
suggest that high-mass stars may not be able to form in clusters with masses
less than 100 $M_\odot$. If these MYSOs are indeed the best candidates for
isolated high-mass star formation, then the lack of isolation is at odds with
random sampling of the IMF. Moreover, while isolated MYSOs may not exist, we
find evidence that isolated clusters containing O-stars can exist, which in
itself is rare.


title:
Extending Semi-numeric Reionisation Models to the First Stars and
  Galaxies

abstract:
  Semi-numeric methods have made it possible to efficiently model the epoch of
reionisation (EoR). While most implementations involve a reduction to a simple
three-parameter model, we introduce a new mass-dependent ionising efficiency
parameter that folds in physical parameters that are constrained by the latest
numerical simulations. This new parameterization enables the effective modeling
of a broad range of host halo masses containing ionising sources, extending
from the smallest Population III host halos with $M \sim 10^6 M_\odot$, which
are often ignored, to the rarest cosmic peaks with $M \sim 10^{12} M_\odot$
during EoR. We compare the resulting ionising histories with a typical
three-parameter model and also compare with the latest constraints from the
Planck mission. Our model results in a optical depth due to Thomson scattering,
$\tau_{\mathrm{e}}$ = 0.057, that is consistent with Planck. The largest
difference in our model is shown in the resulting bubble size distributions
which peak at lower characteristic sizes and are broadened. We also consider
the uncertainties of the various physical parameters and comparing the
resulting ionising histories broadly disfavors a small contribution from
galaxies. As the smallest haloes cease a meaningful contribution to the
ionising photon budget after $z = 10$, implying they play a role in determining
the start of EoR and little else.


title: Spherical Harmonic Analyses of Intensity Mapping Power Spectra

abstract:
  Intensity mapping is a promising technique for surveying the large scale
structure of our Universe from $z=0$ to $z \sim 150$, using the brightness
temperature field of spectral lines to directly observe previously unexplored
portions of out cosmic timeline. Examples of targeted lines include the
$21\,\textrm{cm}$ hyperfine transition of neutral hydrogen, rotational lines of
carbon monoxide, and fine structure lines of singly ionized carbon. Recent
efforts have focused on detections of the power spectrum of spatial
fluctuations, but have been hindered by systematics such as foreground
contamination. This has motivated the decomposition of data into Fourier modes
perpendicular and parallel to the line-of-sight, which has been shown to be a
particularly powerful way to diagnose systematics. However, such a method is
well-defined only in the limit of a narrow-field, flat-sky approximation. This
limits the sensitivity of intensity mapping experiments, as it means that wide
surveys must be separately analyzed as a patchwork of smaller fields. In this
paper, we develop a framework for analyzing intensity mapping data in a
spherical Fourier-Bessel basis, which incorporates curved sky effects without
difficulty. We use our framework to generalize a number of techniques in
intensity mapping data analysis from the flat sky to the curved sky. These
include visibility-based estimators for the power spectrum, treatments of
interloper lines, and the "foreground wedge" signature of spectrally smooth
foregrounds.


title: The Most Massive Galaxies and Black Holes Allowed by $\Lambda$CDM

abstract:
  Given a galaxy's stellar mass, its host halo mass has a lower limit from the
cosmic baryon fraction and known baryonic physics. At z>4, galaxy stellar mass
functions place lower limits on halo number densities that approach expected
$\Lambda$CDM halo mass functions. High-redshift galaxy stellar mass functions
can thus place interesting limits on number densities of massive haloes, which
are otherwise very difficult to measure. Although halo mass functions at z<8
are consistent with observed galaxy stellar masses if galaxy baryonic
conversion efficiencies increase with redshift, JWST and WFIRST will more than
double the redshift range over which useful constraints are available. We
calculate maximum galaxy stellar masses as a function of redshift given
expected halo number densities from $\Lambda$CDM. We apply similar arguments to
black holes. If their virial mass estimates are accurate, number density
constraints alone suggest that the quasars SDSS J1044-0125 and SDSS
J010013.02+280225.8 likely have black hole mass -- stellar mass ratios higher
than the median z=0 relation, confirming the expectation from Lauer bias.
Finally, we present a public code to evaluate the probability of an apparently
$\Lambda$CDM-inconsistent high-mass halo being detected given the combined
effects of multiple surveys and observational errors.


title: The Long Term Evolution of ASASSN-14li

abstract:
  We present late-time optical spectroscopy taken with the Large Binocular
Telescope's Multi-Object Double Spectrograph, late-time SWIFT UVOT and XRT
observations, as well as improved ASAS-SN pre-discovery limits on the nearby
(d=90.3 Mpc, z=0.0206) tidal disruption event (TDE) ASASSN-14li. The late-time
optical spectra show H$\alpha$ emission well in excess of that seen in the SDSS
host galaxy spectrum, indicating that the processes powering the luminous
flares associated with TDEs can operate for several hundreds of days. The SWIFT
observations reveal the presence of lingering apparently thermal UV (T$_{\rm
UV} \sim 3.5\times10^4$ K) and X-ray (T$_{\rm X} \sim 7\times10^5$ K) emission.
The characteristic temperatures evolve by, at most, a factor of $\sim2$ over
the 600 day follow-up campaign. The X-ray, UV, and H$\alpha$ luminosities
evolve roughly in tandem and at a rate that is consistent with a power-law
decay at late times. This behavior is in stark contrast with the majority of
optically discovered TDEs, which are X-ray faint and evolve on shorter
timescales. Finally we address how the unique properties of ASASSN-14li can be
used to probe the relationship between the TDE rate and host galaxy properties.


title:
Geometric constraints on the space of N=2 SCFTs III: enhanced Coulomb
  branches and central charges

abstract:
  This is the third in a series of three papers on the systematic analysis of
rank 1 four dimensional $\mathcal{N}=2$ SCFTs. In the first two papers we
developed and carried out a strategy for classifying and constructing physical
planar rank-1 Coulomb branch geometries of $\mathcal{N}=2$ SCFTs. Here we
describe general features of the Higgs and mixed branch geometries of the
moduli space of these SCFTs, and use this, along with their Coulomb branch
geometry, to compute their conformal and flavor central charges. We conclude
with a summary of the state of the art for rank-1 $\mathcal{N}=2$ SCFTs.


title: Are Cosmological Gas Accretion Streams Multiphase and Turbulent?

abstract:
  Simulations of cosmological filamentary accretion reveal flows ("streams") of
warm gas, ~$10^4$ K, which are efficient in bringing gas into galaxies. We
present a phenomenological scenario where gas in such flows -- if it is shocked
as it enters the halo as we assume -- become biphasic and, as a result,
turbulent. We consider a collimated stream of warm gas that flows into a halo
from an over dense filament of the cosmic web. The post-shock streaming gas
expands because it has a higher pressure than the ambient halo gas, and
fragments as it cools. The fragmented stream forms a two phase medium: a warm
cloudy phase embedded in hot post-shock gas. We argue that the hot phase
sustains the accretion shock. A fraction of the initial kinetic energy of the
infalling gas is converted into turbulence among and within the warm clouds.
The thermodynamic evolution of the post-shock gas is largely determined by the
relative timescales of several processes -- the cooling, the expansion of the
post-shock gas, the amount of turbulence in the clouds, and the halo dynamics.
We expect the gas to become multiphase when the cooling and dynamical times are
of the same order-of-magnitude. In this framework, we show that this occurs in
the important mass range of ~$10^{11}$ to $10^{13}$ M$_\odot$ , where the bulk
of stars have formed in galaxies. Gas accreting along cosmic web filaments may
eventually lose coherence and mix with the ambient halo gas. Through both the
phase separation and "disruption" of the stream, the accretion efficiency onto
a galaxy in a halo dynamical time is lowered. De-collimating flows make the
direct interaction between galaxy feedback and accretion streams more likely,
thereby further reducing the overall accretion efficiency. Moderating the gas
accretion efficiency through these mechanisms may help to alleviate a number of
significant challenges in theoretical galaxy formation.


title: Vortices and Vermas

abstract:
  In three-dimensional gauge theories, monopole operators create and destroy
vortices. We explore this idea in the context of 3d N=4 gauge theories in the
presence of an Omega-background. In this case, monopole operators generate a
non-commutative algebra that quantizes the Coulomb-branch chiral ring. The
monopole operators act naturally on a Hilbert space, which is realized
concretely as the equivariant cohomology of a moduli space of vortices. The
action furnishes the space with the structure of a Verma module for the
Coulomb-branch algebra. This leads to a new mathematical definition of the
Coulomb-branch algebra itself, related to that of
Braverman-Finkelberg-Nakajima. By introducing additional boundary conditions,
we find a construction of vortex partition functions of 2d N=(2,2) theories as
overlaps of coherent states (Whittaker vectors) for Coulomb-branch algebras,
generalizing work of Braverman-Feigin-Finkelberg-Rybnikov on a finite version
of the AGT correspondence. In the case of 3d linear quiver gauge theories, we
use brane constructions to exhibit vortex moduli spaces as handsaw quiver
varieties, and realize monopole operators as interfaces between handsaw-quiver
quantum mechanics, generalizing work of Nakajima.