title:
Evolution of emotions on networks leads to the evolution of cooperation
  in social dilemmas

abstract:
  We show that the resolution of social dilemmas on random graphs and
scale-free networks is facilitated by imitating not the strategy of better
performing players but rather their emotions. We assume sympathy and envy as
the two emotions that determine the strategy of each player by any given
interaction, and we define them as probabilities to cooperate with players
having a lower and higher payoff, respectively. Starting with a population
where all possible combinations of the two emotions are available, the
evolutionary process leads to a spontaneous fixation to a single emotional
profile that is eventually adopted by all players. However, this emotional
profile depends not only on the payoffs but also on the heterogeneity of the
interaction network. Homogeneous networks, such as lattices and regular random
graphs, lead to fixations that are characterized by high sympathy and high
envy, while heterogeneous networks lead to low or modest sympathy but also low
envy. Our results thus suggest that public emotions and the propensity to
cooperate at large depend, and are in fact determined by the properties of the
interaction network.

categories: physics.soc-ph cond-mat.stat-mech cs.SI q-bio.PE


title:
Detecting Overlapping Temporal Community Structure in Time-Evolving
  Networks

abstract:
  We present a principled approach for detecting overlapping temporal community
structure in dynamic networks. Our method is based on the following framework:
find the overlapping temporal community structure that maximizes a quality
function associated with each snapshot of the network subject to a temporal
smoothness constraint. A novel quality function and a smoothness constraint are
proposed to handle overlaps, and a new convex relaxation is used to solve the
resulting combinatorial optimization problem. We provide theoretical guarantees
as well as experimental results that reveal community structure in real and
synthetic networks. Our main insight is that certain structures can be
identified only when temporal correlation is considered and when communities
are allowed to overlap. In general, discovering such overlapping temporal
community structure can enhance our understanding of real-world complex
networks by revealing the underlying stability behind their seemingly chaotic
evolution.


title: New results on equilibria of fuzzy abstract economies

abstract:
  We obtain new equilibrium theorems for fuzzy abstract economies with
correspondences being w-upper semicontinuous or having e-USS-property.


title:
How well can we really estimate the stellar masses of galaxies from
  broadband photometry?

abstract:
  The estimated stellar masses of galaxies are widely used to characterize how
the galaxy population evolves over cosmic time. If stellar masses can be
estimated in a robust manner, free from any bias, global diagnostics such as
the stellar mass function can be used to constrain the physics of galaxy
formation. We explore how galaxy stellar masses, estimated by fitting
broad-band spectral energy distributions (SEDs) with stellar population models,
can be biased as a result of commonly adopted assumptions for the
star-formation and chemical enrichment histories, recycled fractions and dust
attenuation curves of galaxies. We apply the observational technique of
broad-band SED fitting to model galaxy SEDs calculated by the theoretical
galaxy formation model GALFORM, isolating the effect of each of these
assumptions. We find that, averaged over the entire galaxy population, the
common assumption of exponentially declining star-formation histories does not
adversely affect stellar mass estimation. We show that fixing the metallicity
in SED fitting or using sparsely sampled metallicity grids can introduce mass
dependent systematics into stellar mass estimates. We find that the common
assumption of a star-dust geometry corresponding to a uniform foreground dust
screen can cause the stellar masses of dusty model galaxies to be significantly
underestimated. Finally, we show that stellar mass functions recovered by
applying SED fitting to model galaxies at high redshift can differ
significantly in both shape and normalization from the intrinsic mass functions
predicted by a given model. Given these differences, our methodology of using
stellar masses estimated from model galaxy SEDs offers a new, self-consistent
way to compare model predictions with observations.


title: Quantum electrodynamics in a laser and the electron laser collision

abstract:
  Quantum electrodynamics in a laser is formulated, in which the electron-laser
interaction is exactly considered, while the interaction of an electron and a
single photon is considered by perturbation. The formulation is applied to the
electron-laser collisions. The effect of coherence between photons in the laser
is therefore fully considered in these collisions. The possibility of
$\gamma-$ray laser generation by use of this kind of collision is discussed.


title: Precursors of order in aggregates of patchy particles

abstract:
  We study computationally the local structure of aggregated systems of patchy
particles. By calculating the probability distribution functions of various
rotational invariants we can identify the precursors of orientation order in
amorphous phase. Surprisingly, the strongest signature of local order is
observed for 4-patch particles with tetrahedral symmetry, not for 6-patch
particles with the cubic one. This trend is exactly opposite to their known
ability to crystallize. We relate this anomaly to the observation that a
generic aggregate of patchy systems has coordination number close to 4. Our
results also suggest a significant correlation between rotational order in the
studied liquids with the corresponding crystalline phases, making this approach
potentially useful for a broader range of patchy systems.


title:
Galaxy evolution near groups and clusters: ejected satellites and the
  spatial extent of environmental quenching

abstract:
  Galaxies that are several virial radii beyond groups/clusters show
preferentially quiescent star formation rates. Using a galaxy group/cluster
catalog from the Sloan Digital Sky Survey, together with a cosmological N-body
simulation, we examine the origin of this environmental quenching beyond the
virial radius. Accounting for the clustering of groups/clusters, we show that
central galaxies show enhanced SFR quenching out to 2.5 virial radii beyond
groups/clusters, and we demonstrate that this extended environmental
enhancement can be explained simply by 'ejected' satellite galaxies that orbit
beyond their host halo's virial radius. We show that ejected satellites
typically orbit for several Gyr beyond the virial radius before falling back
in, and thus they compose up to 40% of all central galaxies near
groups/clusters. We show that a model in which ejected satellites experience
the same SFR quenching as satellites within a host halo can explain essentially
all environmental dependence of galaxy quenching. Furthermore, ejected
satellites (continue to) lose significant halo mass, an effect that is
potentially observable via gravitational lensing. The SFRs/colors and
stellar-to-halo masses of ejected satellites highlight the importance of
environmental history and present challenges to models of galaxy occupation
that ignore such history.


title: White Dwarfs constrain Dark Forces

abstract:
  The white dwarf luminosity function, which provides information about their
cooling, has been measured with high precision in the past few years.
Simulations that include well known Standard Model physics give a good fit to
the data. This leaves little room for new physics and makes these astrophysical
objects a good laboratory for testing models beyond the Standard Model. It has
already been suggested that white dwarfs might provide some evidence for the
existence of axions. In this work we study the constraints that the white dwarf
luminosity function puts on physics beyond the Standard Model involving new
light particles (fermions or bosons) that can be pair-produced in a white dwarf
and then escape to contribute to its cooling. We show, in particular, that we
can severely constrain the parameter space of models with dark forces and light
hidden sectors (lighter than a few tens of keV). The bounds we find are often
more competitive than those from current lab searches and those expected from
most future searches.


title:
Stability Analysis for Cosmic-Ray Heating of Cool Cores in Galaxy
  Clusters

abstract:
  We study the heating of the cool cores in galaxy clusters by cosmic-rays
(CRs) accelerated by the central active galactic nuclei (AGNs). We especially
focus on the stability of the heating. The CRs stream with Alfv\'en waves in
the intracluster medium (ICM) and heat the ICM. First, assuming that the
heating and radiative cooling is balanced, we search steady state solutions for
the ICM and CR profiles of clusters by solving a boundary value problem. The
boundary conditions are set so that the solutions are consistent with
observations of clusters. We find steady state solutions if the magnetic fields
are strong enough and the association between the magnetic fields and the ICM
is relatively weak. Then, we analyse the stability of the solutions via a
Lagrangian perturbation analysis and find that the solutions are globally
stable. We confirm the results by numerical simulations. Using the steady state
solutions as the initial conditions, we follow the evolution of the profiles
for 100 Gyr. We find that the profiles do not evolve on time scales much larger
than cluster lifetimes. These results, as well as consistency with observations
of radio mini-halos, suggest that the CR heating is a promising mechanism to
solve the so-called "cooling flow problem".


title:
Late-Time Spectral Observations of the Strongly Interacting Type Ia
  Supernova PTF11kx

abstract:
  PTF11kx was a Type Ia supernova (SN Ia) that showed time-variable absorption
features, including saturated Ca II H&K lines that weakened and eventually went
into emission. The strength of the emission component of H{\alpha} increased,
implying that the SN was undergoing significant interaction with its
circumstellar medium (CSM). These features were blueshifted slightly and showed
a P-Cygni profile, likely indicating that the CSM was directly related to, and
probably previously ejected by, the progenitor system itself. These and other
observations led Dilday et al. (2012) to conclude that PTF11kx came from a
symbiotic nova progenitor like RS Oph. In this work we extend the spectral
coverage of PTF11kx to 124-680 rest-frame days past maximum brightness. These
spectra of PTF11kx are dominated by H{\alpha} emission (with widths of ~2000
km/s), strong Ca II emission features (~10,000 km/s wide), and a blue
"quasi-continuum" due to many overlapping narrow lines of Fe II. Emission from
oxygen, He I, and Balmer lines higher than H{\alpha} is weak or completely
absent at all epochs, leading to large observed H{\alpha}/H{\beta} intensity
ratios. The broader (~2000 km/s) H{\alpha} emission appears to increase in
strength with time for ~1 yr, but it subsequently decreases significantly along
with the Ca II emission. Our latest spectrum also indicates the possibility of
newly formed dust in the system as evidenced by a slight decrease in the red
wing of H{\alpha}. During the same epochs, multiple narrow emission features
from the CSM temporally vary in strength. The weakening of the H{\alpha} and Ca
II emission at late times is possible evidence that the SN ejecta have
overtaken the majority of the CSM and agrees with models of other strongly
interacting SNe Ia. The varying narrow emission features, on the other hand,
may indicate that the CSM is clumpy or consists of multiple thin shells.


title:
Optical conductivity of visons in Z2 spin liquids close to a VBS
  transition on the kagome lattice

abstract:
  We consider Z2 spin liquids on the kagome lattice on the verge of a valence
bond solid (VBS) transition, where vortex excitations carrying Z2 magnetic flux
- so-called visons - condense. We show that these vison excitations can couple
directly to the external electromagnetic field, even though they carry neither
spin nor charge. This is possible via a magneto-elastic coupling mechanism
recently identified by Potter et al and Hao. For the case of transitions to a
36-site unit cell VBS state the corresponding finite ac-conductivity has a
specific power law frequency dependence, which is related to the crossover
exponent of the quantum critical point. The visons' contribution to the optical
conductivity at transitions to VBS states with a 12-site unit cell vanishes,
however.


title:
Unbiased determination of polarized parton distributions and their
  uncertainties

abstract:
  We present a determination of a set of polarized parton distributions (PDFs)
of the nucleon, at next-to-leading order, from a global set of longitudinally
polarized deep-inelastic scattering data: NNPDFpol1.0. The determination is
based on the NNPDF methodology: a Monte Carlo approach, with neural networks
used as unbiased interpolants, previously applied to the determination of
unpolarized parton distributions, and designed to provide a faithful and
statistically sound representation of PDF uncertainties. We present our
dataset, its statistical features, and its Monte Carlo representation. We
summarize the technique used to solve the polarized evolution equations and its
benchmarking, and the method used to compute physical observables. We review
the NNPDF methodology for parametrization and fitting of neural networks, the
algorithm used to determine the optimal fit, and its adaptation to the
polarized case. We finally present our set of polarized parton distributions.
We discuss its statistical properties, test for its stability upon various
modifications of the fitting procedure, and compare it to other recent
polarized parton sets, and in particular obtain predictions for polarized first
moments of PDFs based on it. We find that the uncertainties on the gluon, and
to a lesser extent the strange PDF, were substantially underestimated in
previous determinations.


title:
Crucial aspects of the initial mass function (I): The statistical
  correlation between the total mass of an ensemble of stars and its most
  massive star

abstract:
  Our understanding of stellar systems depends on the adopted interpretation of
the IMF, phi(m). Unfortunately, there is not a common interpretation of the
IMF, which leads to different methodologies and diverging analysis of
observational data.We study the correlation between the most massive star that
a cluster would host, mmax, and its total mass into stars, M, as an example
where different views of the IMF lead to different results. We assume that the
IMF is a probability distribution function and analyze the mmax-M correlation
within this context. We also examine the meaning of the equation used to derive
a theoretical M-char_mmax relationship, N x int[Char_mmax-mup] phi(m) dm = 1
with N the total number of stars in the system, according to different
interpretations of the IMF. We find that only a probabilistic interpretation of
the IMF, where stellar masses are identically independent distributed random
variables, provides a self-consistent result. Neither M nor N, can be used as
IMF scaling factors. In addition, Char_mmax is a characteristic maximum stellar
mass in the cluster, but not the actual maximum stellar mass. A <M>-Char_mmax
correlation is a natural result of a probabilistic interpretation of the IMF;
however, the distribution of observational data in the N (or M)-cmmax plane
includes a dependence on the distribution of the total number of stars, N (and
M), in the system, Phi(N), which is not usually taken into consideration. We
conclude that a random sampling IMF is not in contradiction to a possible
mmax-M physical law. However, such a law cannot be obtained from IMF algebraic
manipulation or included analytically in the IMF functional form. The possible
physical information that would be obtained from the N (or M)-mmax correlation
is closely linked with the Phi(M) and Phi(N) distributions; hence it depends on
the star formation process and the assumed.


title:
Crucial aspects of the initial mass function (II): The inference of
  total quantities from partial information on a cluster

abstract:
  In a probabilistic framework of the interpretation of the initial mass
function (IMF), the IMF cannot be arbitrarily normalized to the total mass, M,
or number of stars, N, of the system. Hence, the inference of M and N when
partial information about the studied system is available must be revised.
(i.e., the contribution to the total quantity cannot be obtained by simple
algebraic manipulations of the IMF). We study how to include constraints in the
IMF to make inferences about different quantities characterizing stellar
systems. It is expected that including any particular piece of information
about a system would constrain the range of possible solutions. However,
different pieces of information might be irrelevant depending on the quantity
to be inferred. In this work we want to characterize the relevance of the
priors in the possible inferences. Assuming that the IMF is a probability
distribution function, we derive the sampling distributions of M and N of the
system constrained to different types of information available. We show that
the value of M that would be inferred must be described as a probability
distribution Phi[M; m_a, N_a, Phi(N)] that depends on the completeness limit of
the data, m_a, the number of stars observed down to this limit, N_a, and the
prior hypothesis made on the distribution of the total number of stars in
clusters, Phi(N).


title: The Fundamental Plane of Damped Lyman Alpha Systems

abstract:
  Using a sample of 100 H I - selected damped Lyman alpha (DLA) systems,
observed with the High Resolution Echelle Spectrometer on the Keck I telescope,
we present evidence that the scatter in the well-studied correlation between
the redshift and metallicity of a DLA is largely due to the existence of a
mass-metallicity relationship at each redshift. To describe the fundamental
relations that exist between redshift, metallicity and mass, we use a
fundamental plane description, which is described by the following equation:
[M/H]=(-1.9+-0.5)+(0.74+-0.21)logdv_90-(0.32+-0.06)z. Here, we assert that the
velocity width, dv_90, which is defined as the velocity interval containing 90%
of the integrated optical depth, traces the mass of the underlying dark matter
halo. This description provides two significant improvements over the
individual descriptions of the mass-metallicity correlation and
metallicity-redshift correlation. Firstly, the fundamental equation reduces the
scatter around both relationships by about 20%, providing a more stringent
constraint on numerical simulations modeling DLAs. Secondly, it confirms that
the dark matter halos that host DLAs satisfy a mass-metallicity relationship at
each redshift between redshifts 2 through 5.


title:
Non-monotonic residual entropy in diluted spin ice: a comparison between
  Monte Carlo simulations of diluted dipolar spin ice models and experimental
  results

abstract:
  Spin ice materials, such as Dy2Ti2O7 and Ho2Ti2O7, have been the subject of
much interest for over the past fifteen years. Their low temperature strongly
correlated state can be mapped onto the proton disordered state of common water
ice and, consequently, spin ices display the same low temperature residual
Pauling entropy as water ice. Interestingly, it was found in a previous study
[X. Ke {\it et. al.} Phys. Rev. Lett. {\bf 99}, 137203 (2007)] that, upon
dilution of the magnetic rare-earth ions (Dy^{3+} and Ho^{3+}) by non-magnetic
Yttrium (Y^{3+}) ions, the residual entropy depends {\it non-monotonically} on
the concentration of Y^{3+} ions. In the present work, we report results from
Monte Carlo simulations of site-diluted microscopic dipolar spin ice models
(DSIM) that account quantitatively for the experimental specific heat
measurements, and thus also for the residual entropy, as a function of
dilution, for both Dy2Ti2O7 and Ho2Ti2O7. The main features of the dilution
physics displayed by the magnetic specific heat data are quantitatively
captured by the diluted DSIM up to, and including, 85% of the magnetic ions
diluted (x=1.7). The previously reported departures in the residual entropy
between Dy2Ti2O7 versus Ho2Ti2O7, as well as with a site-dilution variant of
Pauling's approximation, are thus rationalized through the site-diluted DSIM.
For 90% (x=1.8) and 95% (x=1.9) of the magnetic ions diluted, we find a
significant discrepancy between the experimental and Monte Carlo specific heat
results. We discuss some possible reasons for this disagreement.


title:
Superfluidity breakdown of periodic matter waves in quasi
  one-dimensional annular traps via resonant scattering with moving defects

abstract:
  We investigate, both analytically and numerically, the quasi-superfluidity
properties of periodic Bose-Einstein condensates (BECs) in a
quasi-one-dimensional (1D) ring with optical lattices (OL) of different kinds
(linear and nonlinear) and with a moving defect of an infinite mass inside. To
study the dynamics of the condensate we used a mean-field approximation
describing the condensate by use of the Gross-Pitaevskii equation for the order
parameter. We show that the resonant scattering of sound Bloch waves with the
defect profoundly affect BEC superfluidity. In particular, a moving defect
always leads to the breakdown of superfluidity independently of the value of
its velocity. For weak periodic potentials the superfluidity breakdown may
occur on a very long time scale (quasisuperfluidity) but the breakdown process
can be accelerated by increasing the strength of the OL. Quite remarkably, we
find that when the length of the ring is small enough to imply the discreteness
of the reciprocal space, it becomes possible to avoid the resonant scattering
and to restore quasi-superfluidity.


title: Projectivity in Algebraic Cobordism

abstract:
  The algebraic cobordism group of a scheme is generated by cycles that are
proper morphisms from smooth quasiprojective varieties. We prove that over a
field of characteristic zero the quasiprojectivity assumption can be omitted to
get the same theory.


title: The size of Julia sets of quasiregular maps

abstract:
  Sun Daochun and Yang Lo have shown that many results of the Fatou-Julia
iteration theory of rational functions extend to quasiregular self-maps of the
Riemann sphere for which the degree exceeds the dilatation. We show that in
this context, in contrast to the case of rational functions, the Julia set may
have Hausdorff dimension zero. On the other hand, we exhibit a gauge function
depending on the degree and the dilatation such that the Hausdorff measure with
respect to this gauge function is always positive, but may be finite.


title: A modified naturalness principle and its experimental tests

abstract:
  Motivated by LHC results, we modify the usual criterion for naturalness by
ignoring the uncomputable power divergences. The Standard Model satisfies the
modified criterion ('finite naturalness') for the measured values of its
parameters. Extensions of the SM motivated by observations (Dark Matter,
neutrino masses, the strong CP problem, vacuum instability, inflation) satisfy
finite naturalness in special ranges of their parameter spaces which often
imply new particles below a few TeV. Finite naturalness bounds are weaker than
usual naturalness bounds because any new particle with SM gauge interactions
gives a finite contribution to the Higgs mass at two loop order.


title: A characterization of normal forms for control systems

abstract:
  The study of the behavior of solutions of ODEs often benefits from deciding
on a convenient choice of coordinates. This choice of coordinates may be used
to "simplify" the functional expressions that appear in the vector field in
order that the essential features of the flow of the ODE near a critical point
become more evident. In the case of the analysis of an ordinary differential
equation in the neighborhood of an equilibrium point, this naturally leads to
the consideration of the possibility to remove the maximum number of terms in
the Taylor expansion of the vector field up to a given order. This idea was
introduced by H. Poincar\'e and the "simplified" system is called normal form.
  On another side, even though in many textbook treatments the emphasis is on
the reduction of the number of monomials in the Taylor expansion, one of the
main reasons for the success of normal forms lies in the fact that it allows to
analyze a dynamical system based on a simpler form and a simpler form doesn't
necessarily mean to remove the maximum number of terms in the Taylor series
expansion. This observation, led to introduce the so-called "inner-product
normal forms". They are based on properly choosing an inner product that allows
to simplify the computations. This inner-product will characterize the space
overwhich one performs the Taylor series expansion. The elements in this space
are the ones that characterize the normal form. Our goal in this paper is to
generalize such an approach to control systems.


title:
Towards a Classification of pseudo-Riemannian Geometries Admitting
  Twistor Spinors

abstract:
  We show that given a conformal structure whose holonomy representation fixes
a totally lightlike subspace of arbitrary dimension, there is always a local
metric in the conformal class off a singular set which is Ricci-isotropic and
gives rise to a parallel, totally lightlike distribution on the tangent bundle.
This naturally applies to parallel spin tractors resp. twistor spinors on
conformal spin manifolds and clarifies which twistor spinors are locally
equivalent to parallel spinors. Moreover, we study the zero set of a twistor
spinor using the curved orbit decomposition for parabolic geometries. We can
completely describe its local structure, construct a natural projective
structure on it, and show that locally every twistor spinor with zero is
equivalent to a parallel spinor off the zero set. An application of these
results in low-dimensional split-signatures leads to a complete geometric
description of local geometries admitting non-generic twistor spinors in
signatures (3,2) and (3,3) which complements the well-known description of the
generic case.


title:
The Log-Exponential Smoothing Technique and Nesterov's Accelerated
  Gradient Method for Generalized Sylvester Problems

abstract:
  The Sylvester smallest enclosing circle problem involves finding the smallest
circle that encloses a finite number of points in the plane. We consider
generalized versions of the Sylvester problem in which the points are replaced
by sets. Based on the log-exponential smoothing technique and Nesterov's
accelerated gradient method, we present an effective numerical algorithm for
solving these problems.


title:
Synchronization of Weakly Coupled Oscillators: Coupling, Delay and
  Topology

abstract:
  There are three key factors of a system of coupled oscillators that
characterize the interaction among them: coupling (how to affect), delay (when
to affect) and topology (whom to affect). For each of them, the existing work
has mainly focused on special cases. With new angles and tools, this paper
makes progress in relaxing some assumptions of these factors. There are three
main results in this paper. First, by using results from algebraic graph
theory, a sufficient condition is obtained which can be used to check
equilibrium stability. This condition works for arbitrary topology. It
generalizes existing results and also leads to a sufficient condition on the
coupling function with which the system is guaranteed to reach synchronization.
Second, it is known that identical oscillators with sin() coupling functions
are guaranteed to synchronize in phase on a complete graph. Using our results,
we demonstrate that for many cases certain structures instead of exact shape of
the coupling function such as symmetry and concavity are the keys for global
synchronization. Finally, the effect of heterogenous delays is investigated. We
develop a new framework by constructing a non-delayed phase model that
approximates the original one in the continuum limit. We further derive how its
stability properties depend on the delay distribution. In particular, we show
that heterogeneity, i.e. wider delay distribution, can help reach in-phase
synchronization.


title: Multiple scattering of light in cold atomic clouds with a magnetic field

abstract:
  Starting from a microscopic theory for atomic scatterers, we describe the
scattering of light by a single atom and study the coherent propagation of
light in a cold atomic cloud in the presence of a magnetic field B in the
mesoscopic regime. Non-pertubative expressions in B are given for the
magneto-optical effects and optical anisotropy. We then consider the multiple
scattering regime and address the fate of the coherent backscattering (CBS)
effect. We show that, for atoms with nonzero spin in their ground state, the
CBS interference contrast can be increased compared to its value when B=0, a
result at variance with classical samples. We validate our theoretical results
by a quantitative comparison with experimental data.


title:
Non-magnetic impurities to induce magnetism in $\alpha$-PbO crystal
  structure

abstract:
  A new route to $d^0$ magnetism is established with help of the first
principles methods. Non-magnetic interstitial impurities from group 14 in the
periodic table are found to induce $p$-orbital magnetism in polycrystalline
PbO-type structures. The half-filled $p$-orbitals occupied by two electrons is
generated on the impurity site for which the ferromagnetic state of high
stability is guaranteed by the first Hund's rule. Since the impurity is
embedded between layers of the host, its atomic radius is a key to tune not
only its solubility but also the magnetic behavior: the on-site stability of
the spin polarized state grows with reduction of the atomic radius while losing
in the long-rang order interactions. However, for impurities of smaller radius
the weaker inter-site magnetic coupling can be compensated by their
concentration as the impurity solubility limit is shifted to higher magnitudes.


title:
Magnetic neutral points and electric lines of force in strong gravity of
  a rotating black hole

abstract:
  Magnetic field can be amplified and twisted near a supermassive black hole
residing in a galactic nucleus. At the same time magnetic null points develop
near the horizon. We examine a large-scale oblique magnetic field near a
rotating (Kerr) black hole as an origin of magnetic layers, where the field
direction changes abruptly in the ergosphere region. In consequence of this,
magnetic null points can develop by purely geometrical effects of the strong
gravitational field and the frame-dragging mechanism. We identify magnetic
nulls as possible sites of magnetic reconnection and suggest that particles may
be accelerated efficiently by the electric component. The situation we discuss
is relevant for starving nuclei of some galaxies which exhibit episodic
accretion events, namely, Sagittarius A* black hole in our Galaxy.


title: Operators, Correlators and Free Fermions for SO(N) and Sp(N)

abstract:
  Using the recently constructed basis for local operators in free SO(N) gauge
theory we derive an exact formula for the correlation functions of multi trace
operators. This formula is used to obtain a simpler form and a simple product
rule for the operators in the SO(N) basis. The coefficients of the product rule
are the Littlewood-Richardson numbers which determine the corresponding product
rule in free U(N) gauge theory. SO(N) gauge theory is dual to a non-oriented
string theory on the AdS_5xRP^5 geometry. To explore the physics of this string
theory we consider the limit of the gauge theory that, for the U(N) gauge
theory, is dual to the pp-wave limit of AdS_5xS^5. Non-planar unoriented ribbon
diagrams do not survive this limit. We give arguments that the number of
operators in our basis matches counting using the exact free field partition
function of free SO(N) gauge theory. We connect the basis we have constructed
to free fermions, which has a natural interpretation in terms of a class of
1/2-BPS bubbling geometries, which arise as orientifolds of type IIB string
theory. Finally, we obtain a complete generalization of these results to Sp(N)
gauge theory by proving that the finite N physics of SO(N) and Sp(N) gauge
theory are related by exchanging symmetrizations and antisymmetrizations and
replacing N by -N.


title: High-Resolution Structure of Viruses from Random Snapshots

abstract:
  The advent of the X-ray Free Electron Laser (XFEL) has made it possible to
record snapshots of biological entities injected into the X-ray beam before the
onset of radiation damage. Algorithmic means must then be used to determine the
snapshot orientations and reconstruct the three-dimensional structure of the
object. Existing approaches are limited in reconstruction resolution to at best
1/30th of the object diameter, with the computational expense increasing as the
eighth power of the ratio of diameter to resolution. We present an approach
capable of exploiting object symmetries to recover three-dimensional structure
to 1/100th of the object diameter, and thus reconstruct the structure of the
satellite tobacco necrosis virus to atomic resolution. Combined with the
previously demonstrated capability to operate at ultralow signal, our approach
offers the highest reconstruction resolution for XFEL snapshots to date, and
provides a potentially powerful alternative route for analysis of data from
crystalline and nanocrystalline objects.


title: Emergent D5-brane Background from D-strings

abstract:
  We solve the worldsheet theory describing the near-horizon dynamics of a
D-string in the presence of a very large number N of D5-branes. The model is
pre-geometric in the sense that the near-horizon worldsheet Lagrangian does not
have dynamical fields associated with the dimensions transverse to the
D5-branes. The solution at large N is shown to be given by a classical action
for the D-string moving in a curved ten-dimensional spacetime. The four
dimensions transverse to the D5-branes emerge from the quantum loops of the
original strongly coupled quantum worldsheet field theory. By comparing with
the Dirac-Born-Infeld plus Chern-Simons action for a D-string in a general type
IIB background, we identify the string-frame metric, dilaton and Ramond-Ramond
three-form field-strength and find a match with the near-horizon geometry of a
stack of D5-branes.


title:
Optimal transportation of processes with infinite Kantorovich distance.
  Independence and symmetry

abstract:
  We consider probability measures on $\mathbb{R}^{\infty}$ and study optimal
transportation mappings for the case of infinite Kantorovich distance. Our
examples include 1) quasi-product measures, 2) measures with certain symmetric
properties, in particular, exchangeable and stationary measures. We show in the
latter case that existence problem for optimal transportation is closely
related to ergodicity of the target measure. In particular, we prove existence
of the symmetric optimal transportation for a certain class of stationary Gibbs
measures.


title:
Beta functions of $U(1)^d$ gauge invariant just renormalizable tensor
  models

abstract:
  This manuscript reports the first order $\beta$-functions of recently proved
just renormalizable random tensor models endowed with a $U(1)^d$ gauge
invariance [arXiv:1211. 2618]. The models that we consider are polynomial
Abelian $\vp^4_6$ and $\vp^6_5$ models. We show in this work that both models
are asymptotically free in the UV.


title: A sub-ensemble theory of ideal quantum measurement processes

abstract:
  To elucidate ideal measurements, one must explain how individual events
emerge from quantum theory which deals with statistical ensembles, and how
different may end up with different final states. This so-called "measurement
problem" is tackled with two guidelines. On the one hand, the dynamics of the
macroscopic apparatus A coupled to the tested system S is described
mathematically within a standard quantum formalism, where "q-probablities"
remain devoid of interpretation. On the other hand, interpretative principles
are introduced to account for the expected features of ideal measurements. Most
of the five principles, which relate the quantum formalism to physical reality,
are straightforward and refer to macroscopic variables. The process can be
identified with a relaxation of S+A to thermodynamic equilibrium, not only for
a large ensemble $\scriptE$ of runs but even for its sub-ensembles. The
different mechanisms of quantum statistical dynamics that ensure the relaxation
are exhibited. The additional information provided by the sub-ensembles remove
Schr\"odinger's quantum ambiguity of the final density operator for $\scriptE$
which hinders its direct interpretation, and bring out a commutative behaviour
of the pointer observable at the final time. The latter property supports the
introduction of a last principle, needed to switch from the statistical
ensembles and sub-ensembles described by quantum theory to individual
experimental events. It amounts to identify some formal "q-probabilities" with
ordinary frequencies, but only those which refer to the final pointer
indications. The desired properties of ideal measurements, in particular the
uniqueness of the result for each individual run and von Neumann's reduction,
are thereby recovered with economic interpretations. The status of Born's rule
involving both A and S is re-evaluated, and contextuality is made obvious.


title: CMB and Random Flights: temperature and polarization in position space

abstract:
  The fluctuations in the temperature and polarization of the cosmic microwave
background are described by a hierarchy of Boltzmann equations. In its integral
form, this Boltzmann hierarchy can be converted from the usual Fourier-space
base into a position-space and causal description. We show that probability
densities for random flights play a key role in this description. The integral
system can be treated as a perturbative series in the number of steps of the
random flights, and the properties of random flight probabilities impose
constraints on the domains of dependence. We show that, as a result of these
domains, a Fourier-Bessel decomposition can be employed in order to calculate
the random flight probability densities. We also illustrate how the H-theorem
applies to the cosmic microwave background: by using analytical formulae for
the asymptotic limits of these probability densities, we show that, as the
photon distribution approaches a state of equilibrium, both the temperature
anisotropies and the net polarization must vanish.

categories: astro-ph.CO cond-mat.stat-mech math-ph math.MP


title:
Bonding Charge Density and Ultimate Strength of Monolayer Transition
  Metal Dichalcogenides

abstract:
  Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs)
can withstand a large deformation without fracture or inelastic relaxation,
making them attractive for application in novel strain-engineered and flexible
electronic and optoelectronic devices. In this study, we characterize the
mechanical response of monolayer group VI TMDs to large elastic deformation
using first-principles density functional theory calculations. We find that the
ultimate strength and the overall stress response of these 2D materials is
strongly influenced by their chemical composition and loading direction. We
demonstrate that differences in the observed mechanical behavior can be
attributed to the spatial redistribution of the occupied hybridized electronic
states in the region between the transition metal atom and the chalcogens. In
spite of the strong covalent bonding between the transition metal and the
chalcogens, we find that a simple linear relationship can be established to
describe the dependence of the mechanical strength on the charge transfer from
the transition metal atom to the chalcogens.


title:
Measurement of beam energy dependent nuclear modification factors at
  STAR

abstract:
  The nuclear modification factors R_{AA} and R_{CP} have been used to measure
medium-induced suppression in heavy-ion collisions at sqrt{s_{NN}} = 200GeV
which was among the earliest evidence for the existence of a strongly
interacting medium called a quark-gluon plasma (QGP). Nuclear modification
factors for asymmetric collisions (R_{dA}) have measured the Cronin Effect, an
enhancement of high transverse momentum particle yields in deuteron-gold
collisions relative to proton-proton collisions. A similar enhancement is
observed in data presented in these proceedings and competes with the quenching
caused by partonic energy loss in the QGP. In these proceedings we will present
charged-hadron R_{CP} at mid-rapidity for sqrt{s_{NN}} = 7.7 - 62.4GeV as well
as identified pi^{+}, K^{+}, and proton R_{CP}. Comparisons to HIJING motivate
possible methods for disentangling competing modifications to nuclear
transverse momentum spectra.


title:
The excitation of rogue waves in a variable medium: an experimental
  study on the interaction of water waves and currents

abstract:
  We show experimentally that a stable wave propagating into a region
characterized by an opposite current may become modulationaly unstable.
Experiments have been performed in two independent wave tank facilities; both
of them are equipped with a wavemaker and a pump for generating a current
propagating in the opposite direction with respect to the waves. The
experimental results support a recent conjecture based on a current-modified
Nonlinear Schr\"odinger equation which establishes that rogue waves can be
triggered by non-homogeneous current characterized by a negative horizontal
velocity gradient.


title: Pareidolic Dark Matter (PaDaM)

abstract: A pareidolic conjecture for the Fermi Large Area Telescope.


title: Pion-mass dispersion relation in the baryon sector

abstract:
  By looking at the complex plane of the pion-mass squared we establish a
dispersion relation which the static quantities, such as baryon masses,
magnetic moments, polarizabilities, should obey. This dispersion relation
yields insight into the differences between the heavy-baryon and relativistic
calculations in the baryon sector of chiral perturbation theory.


title: Scalable Text and Link Analysis with Mixed-Topic Link Models

abstract:
  Many data sets contain rich information about objects, as well as pairwise
relations between them. For instance, in networks of websites, scientific
papers, and other documents, each node has content consisting of a collection
of words, as well as hyperlinks or citations to other nodes. In order to
perform inference on such data sets, and make predictions and recommendations,
it is useful to have models that are able to capture the processes which
generate the text at each node and the links between them. In this paper, we
combine classic ideas in topic modeling with a variant of the mixed-membership
block model recently developed in the statistical physics community. The
resulting model has the advantage that its parameters, including the mixture of
topics of each document and the resulting overlapping communities, can be
inferred with a simple and scalable expectation-maximization algorithm. We test
our model on three data sets, performing unsupervised topic classification and
link prediction. For both tasks, our model outperforms several existing
state-of-the-art methods, achieving higher accuracy with significantly less
computation, analyzing a data set with 1.3 million words and 44 thousand links
in a few minutes.

categories: cs.LG cs.IR cs.SI physics.data-an stat.ML


title:
Microscopic and Spectroscopic Evidence for a Slater Metal-Insulator
  Transition in Sr2IrO4

abstract:
  Layered 5d transition metal oxides (TMOs) have attracted significant interest
in recent years because of the rich physical properties induced by the
interplay between spin-orbit coupling, bandwidth and on-site Coulomb repulsion.
In Sr2IrO4, this interplay opens a gap near the Fermi energy and stabilizes a
Jeff=1/2 spin-orbital entangled insulating state at low temperatures. Whether
this metal-insulating transition (MIT) is Mott-type (electronic-correlation
driven) or Slater-type (magnetic-order driven) has been under intense debate.
We address this issue via spatially resolved imaging and spectroscopic studies
of the Sr2IrO4 surface using scanning tunneling microscopy/spectroscopy
(STM/S). The STS results clearly illustrate the opening of the (~150-250 meV)
insulating gap at low temperatures, in qualitative agreement with our
density-functional theory (DFT) calculations. More importantly, the measured
temperature dependence of the gap width coupled with our DFT+dynamical mean
field theory (DMFT) results strongly support the Slater-type MIT scenario in
Sr2IrO4. The STS data further reveal a pseudogap structure above the Neel
temperature, presumably related to the presence of antiferromagnetic
fluctuations.


title:
Reactive Desorption and Radiative Association as Possible Drivers of
  Complex Molecule Formation in the Cold Interstellar Medium

abstract:
  The recent discovery of terrestrial-type organic species such as methyl
formate and dimethyl ether in the cold interstellar gas has proved that the
formation of organic matter in the Galaxy begins at a much earlier stage of
star formation than was thought before. This discovery represents a challenge
for astrochemical modelers. The abundances of these molecules cannot be
explained by the previously developed "warm-up" scenario, in which organic
molecules are formed via diffusive chemistry on surfaces of interstellar grains
starting at 30 K, and then released to the gas at higher temperatures during
later stages of star formation. In this article, we investigate an alternative
scenario in which complex organic species are formed via a sequence of
gas-phase reactions between precursor species formed on grain surfaces and then
ejected into the gas via efficient reactive desorption, a process in which
non-thermal desorption occurs as a result of conversion of the exothermicity of
chemical reactions into the ejection of products from the surface. The proposed
scenario leads to reasonable if somewhat mixed results at temperatures as low
as 10 K and may be considered as a step towards the explanation of abundances
of terrestrial-like organic species observed during the earliest stages of star
formation.


title:
Connecting The Non-Singular Origin of the Universe, The Vacuum Structure
  and The Cosmological Constant Problem

abstract:
  We consider a non-singular origin for the Universe starting from an Einstein
static Universe, the so called "emergent universe" scenario, in the framework
of a theory which uses two volume elements $\sqrt{-{g}}d^{4}x$ and $\Phi
d^{4}x$, where $\Phi $ is a metric independent density, used as an additional
measure of integration. Also curvature, curvature square terms and for scale
invariance a dilaton field $\phi$ are considered in the action. The first order
formalism is applied. The integration of the equations of motion associated
with the new measure gives rise to the spontaneous symmetry breaking (S.S.B) of
scale invariance (S.I.). After S.S.B. of S.I., it is found that a non trivial
potential for the dilaton is generated. In the Einstein frame we also add a
cosmological term that parametrizes the zero point fluctuations. The resulting
effective potential for the dilaton contains two flat regions, for $\phi
\rightarrow \infty$ relevant for the non singular origin of the Universe,
followed by an inflationary phase and $\phi \rightarrow -\infty$, describing
our present Universe. The dynamics of the scalar field becomes non linear and
these non linearities produce a non trivial vacuum structure for the theory and
are responsible for the stability of some of the emergent universe solutions,
which exists for a parameter range of values of the vacuum energy in $\phi
\rightarrow -\infty$, which must be positive but not very big, avoiding the
extreme fine tuning required to keep the vacuum energy density of the present
universe small. The non trivial vacuum structure is crucial to ensure the
smooth transition from the emerging phase, to an inflationary phase and finally
to the slowly accelerated universe now. Zero vacuum energy density for the
present universe defines the threshold for the creation of the universe.


title:
Pohozaev-type inequalities and nonexistence results for non $C^2$
  solutions of $p(x)$-laplacian equations

abstract:
  In this paper a Pohozaev type inequality is stated for variable exponent
Sobolev spaces in order to prove non existence of nontrivial weak solutions for
a Dirichlet problem with non-standard growth. The obtained results generalize a
previous work of M. \^{O}tani.


title:
TPZ : Photometric redshift PDFs and ancillary information by using
  prediction trees and random forests

abstract:
  With the growth of large photometric surveys, accurately estimating
photometric redshifts, preferably as a probability density function (PDF), and
fully understanding the implicit systematic uncertainties in this process has
become increasingly important. In this paper, we present a new, publicly
available, parallel, machine learning algorithm that generates photometric
redshift PDFs by using prediction trees and random forest techniques, which we
have named TPZ. This new algorithm incorporates measurement errors into the
calculation while also dealing efficiently with missing values in the data. In
addition, our implementation of this algorithm provides supplementary
information regarding the data being analyzed, including unbiased estimates of
the accuracy of the technique without resorting to a validation data set,
identification of poor photometric redshift areas within the parameter space
occupied by the spectroscopic training data, a quantification of the relative
importance of the variables used to construct the PDF, and a robust
identification of outliers. This extra information can be used to optimally
target new spectroscopic observations and to improve the overall efficacy of
the redshift estimation. We have tested TPZ on galaxy samples drawn from the
SDSS main galaxy sample and from the DEEP2 survey, obtaining excellent results
in each case. We also have tested our implementation by participating in the
PHAT1 project, which is a blind photometric redshift contest, finding that TPZ
performs comparable to if not better than other empirical photometric redshift
algorithms. Finally, we discuss the various parameters that control the
operation of TPZ, the specific limitations of this approach and an application
of photometric redshift PDFs.


title: Data-Intensive Workload Consolidation on Hadoop Distributed File System

abstract:
  Workload consolidation, sharing physical resources among multiple workloads,
is a promising technique to save cost and energy in cluster computing systems.
This paper highlights a few challenges of workload consolidation for Hadoop as
one of the current state-of-the-art data-intensive cluster computing system.
Through a systematic step-by-step procedure, we investigate challenges for
efficient server consolidation in Hadoop environments. To this end, we first
investigate the inter-relationship between last level cache (LLC) contention
and throughput degradation for consolidated workloads on a single physical
server employing Hadoop distributed file system (HDFS). We then investigate the
general case of consolidation on multiple physical servers so that their
throughput never falls below a desired/predefined utilization level. We use our
empirical results to model consolidation as a classic two-dimensional bin
packing problem and then design a computationally efficient greedy algorithm to
achieve minimum throughput degradation on multiple servers. Results are very
promising and show that our greedy approach is able to achieve near optimal
solution in all experimented cases.


title: Efficient tools for quantum metrology with uncorrelated noise

abstract:
  Quantum metrology offers an enhanced performance in experiments such as
gravitational wave-detection, magnetometry or atomic clocks frequency
calibration. The enhancement, however, requires a delicate tuning of relevant
quantum features such as entanglement or squeezing. For any practical
application the inevitable impact of decoherence needs to be taken into account
in order to correctly quantify the ultimate attainable gain in precision. We
compare the applicability and the effectiveness of various methods of
calculating the ultimate precision bounds resulting from the presence of
decoherence. This allows us to put a number of seemingly unrelated concepts
into a common framework and arrive at an explicit hierarchy of quantum
metrological methods in terms of the tightness of the bounds they provide. In
particular, we show a way to extend the techniques originally proposed in
Demkowicz-Dobrzanski et al 2012 Nat. Commun. 3 1063, so that they can be
efficiently applied not only in the asymptotic but also in the finite-number of
particles regime. As a result, we obtain a simple and direct method, yielding
bounds that interpolate between the quantum enhanced scaling characteristic for
small number of particles and the asymptotic regime, where quantum enhancement
amounts to a constant factor improvement. Methods are applied to numerous
models including noisy phase and frequency estimation, as well as the
estimation of the decoherence strength itself.


title: Absence of Bose condensation on lattices with moat bands

abstract:
  We study hard-core bosons on a class of frustrated lattices with the lowest
Bloch band having a degenerate minimum along a closed contour, the moat, in the
reciprocal space. We show that at small density the ground state of the system
is given by a noncondensed state, which may be viewed as a state of fermions
subject to Chern-Simons gauge field. At fixed density of bosons, such a state
exhibits domains of incompressible liquids. Their fixed densities are given by
fractions of the reciprocal-space area enclosed by the moat.


title: Weak approximation for cubic hypersurfaces

abstract:
  We prove weak approximation for smooth cubic hypersurfaces of dimension at
least 2 defined over the function field of a complex curve.


title: Reputation and Impact in Academic Careers

abstract:
  Reputation is an important social construct in science, which enables
informed quality assessments of both publications and careers of scientists in
the absence of complete systemic information. However, the relation between
reputation and career growth of an individual remains poorly understood,
despite recent proliferation of quantitative research evaluation methods. Here
we develop an original framework for measuring how a publication's citation
rate $\Delta c$ depends on the reputation of its central author $i$, in
addition to its net citation count $c$. To estimate the strength of the
reputation effect, we perform a longitudinal analysis on the careers of 450
highly-cited scientists, using the total citations $C_{i}$ of each scientist as
his/her reputation measure. We find a citation crossover $c_{\times}$ which
distinguishes the strength of the reputation effect. For publications with $c <
c_{\times}$, the author's reputation is found to dominate the annual citation
rate. Hence, a new publication may gain a significant early advantage
corresponding to roughly a 66% increase in the citation rate for each tenfold
increase in $C_{i}$. However, the reputation effect becomes negligible for
highly cited publications meaning that for $c\geq c_{\times}$ the citation rate
measures scientific impact more transparently. In addition we have developed a
stochastic reputation model, which is found to reproduce numerous statistical
observations for real careers, thus providing insight into the microscopic
mechanisms underlying cumulative advantage in science.


title: Tunnel number degeneration under the connected sum of prime knots

abstract:
  We study 2-string free tangle decompositions of knots with tunnel number two.
As an application, we construct infinitely many counter-examples to a
conjecture in the literature stating that the tunnel number of the connected
sum of prime knots doesn't degenerate by more than one.


title:
The effect of limb kinematics on the speed of a legged robot on granular
  media

abstract:
  Achieving effective locomotion on diverse terrestrial substrates can require
subtle changes of limb kinematics. Biologically inspired legged robots
(physical models of organisms) have shown impressive mobility on hard ground
but suffer performance loss on unconsolidated granular materials like sand.
Because comprehensive limb-ground interaction models are lacking, optimal gaits
on complex yielding terrain have been determined empirically. To develop
predictive models for legged devices and to provide hypotheses for biological
locomotors, we systematically study the performance of SandBot, a small legged
robot, on granular media as a function of gait parameters. High performance
occurs only in a small region of parameter space. A previously introduced
kinematic model of the robot combined with a new anisotropic granular
penetration force law predicts the speed. Performance on granular media is
maximized when gait parameters minimize body acceleration and limb
interference, and utilize solidification features of granular media.

categories: physics.bio-ph cond-mat.soft physics.flu-dyn q-bio.QM


title:
Multiple Side-Band Generation for Two-Frequency Components Injected into
  a Tapered Amplifier

abstract:
  We have experimentally studied the multiple side-band generation for
two-frequency components injected into a tapered amplifier and demonstrated its
effects on atomic laser cooling. A heterodyne frequency-beat measurement and a
Fabry Perot interferometer have been applied to analyze the side-band
generation with different experimental parameters, such as frequency
difference, injection laser power and tapered amplifier current. In laser
cooling potassium40 and potassium41 with hyperfine splitting of 1.3GHz and
254MHz, respectively, the side-band generation with a small frequency
difference has a significant effect on the number of trapped atoms.


title: Black Hole Formation at the Correspondence Point

abstract:
  We study the process of bound state formation in a D-brane collision. We
consider two mechanisms for bound state formation. The first, operative at weak
coupling in the worldvolume gauge theory, is pair creation of W-bosons. The
second, operative at strong coupling, corresponds to formation of a large black
hole in the dual supergravity. These two processes agree qualitatively at
intermediate coupling, in accord with the correspondence principle of Horowitz
and Polchinski. We show that the size of the bound state and timescale for
formation of a bound state agree at the correspondence point. The timescale
involves matching a parametric resonance in the gauge theory to a quasinormal
mode in supergravity.


title: On a conjecture of Karrass and Solitar

abstract:
  We settle an old conjecture of Karrass and Solitar by proving that a finitely
generated subgroup of a non-trivial free product $G = A\ast B$ has finite index
if and only if it intersects non-trivially each non-trivial normal subgroup of
$G$. This holds, more generally, for subgroups of finite Kurosh rank.


title:
Heat kernel for the elliptic system of linear elasticity with boundary
  conditions

abstract:
  We consider the elliptic system of linear elasticity with bounded measurable
coefficients in a domain where the second Korn inequality holds. We construct
heat kernel of the system subject to Dirichlet, Neumann, or mixed boundary
condition under the assumption that weak solutions of the elliptic system are
H\"older continuous in the interior. Moreover, we show that if weak solutions
of the mixed problem are H\"older continuous up to the boundary, then the
corresponding heat kernel has a Gaussian bound. In particular, if the domain is
a two dimensional Lipschitz domain satisfying a corkscrew or non-tangential
accessibility condition on the set where we specify Dirichlet boundary
condition, then we show that the heat kernel has a Gaussian bound. As an
application, we construct Green's function for elliptic mixed problem in such a
domain.


title: Hysteretic superconducting resistive transition in Ba0.07K0.93Fe2As2

abstract:
  We have observed hysteresis in superconducting resistive transition curves of
Ba$_{0.07}$K$_{0.93}$Fe$_2$As$_2$ ($T_c\sim$8 K) below about 1 K for in-plane
fields. The hysteresis is not observed as the field is tilted away from the
$ab$ plane by 20$^{\circ}$ or more. The temperature and angle dependences of
the upper critical field indicate a strong paramagnetic effect for in-plane
fields. We suggest that the hysteresis can be attributed to a first-order
superconducting transition due to the paramagnetic effect. Magnetic torque data
are also shown.


title:
Giant magnetocaloric effect in isostructural MnNiGe-CoNiGe system by
  establishing a Curie-temperature window

abstract:
  An effective scheme of isostructural alloying was applied to establish a
Curie-temperature window in isostructural MnNiGe-CoNiGe system. With the
simultaneous accomplishment of decreasing structural-transition temperature and
converting antiferromagnetic martensite to ferromagnetic state, a 200 K
Curie-temperature window was established between Curie temperatures of
austenite and martensite phases. In the window, a first-order magnetostructural
transition between paramagnetic austenite and ferromagnetic martensite occurs
with a sharp jump in magnetization, showing a magnetic entropy change as large
as -40 J kg-1 K-1 in a 50 kOe field change. This giant magnetocaloric effect
enables Mn1-xCoxNiGe to become a potential magnetic refrigerant.


title:
Resolved Near-Infrared Spectroscopy of WISE J104915.57-531906.1AB: A
  Flux-Reversal Binary at the L dwarf/T dwarf Transition

abstract:
  We report resolved near-infrared spectroscopy and photometry of the recently
identified brown dwarf binary WISE J104915.57-531906.1AB, located 2.02+/-0.15
pc from the Sun. Low-resolution spectral data from Magellan/FIRE and IRTF/SpeX
reveal strong H2O and CO absorption features in the spectra of both components,
with the secondary also exhibiting weak CH4 absorption at 1.6 micron and 2.2
micron. Spectral indices and comparison to low-resolution spectral standards
indicate component types of L7.5 and T0.5, the former consistent with the
optical classification of the primary. Relative photometry reveals a flux
reversal between the J- and K-bands, with the T dwarf component being brighter
in the 0.95--1.3 micron range. As with other L/T transition binaries, this
reversal likely reflects significant depletion of condensate opacity across the
transition, a behavior that may be enhanced in WISE J1049-5319AB if the unusual
red color of its L dwarf component is indicative of thick clouds. On the other
hand, differing cloud properties may have modified the evolutionary paths of
these two components, and we propose a scenario in which the cooler secondary
could be the more massive of the two components. Fortunately, the proximity,
brightness and small separation (3.12+/-0.25 AU) of this system make it
amenable to astrometric and radial velocity orbit measurement during its
estimated 25 yr orbit, providing a rare opportunity for the direct
determination of individual brown dwarf masses and a unique benchmark for
studying cloud evolution across the L dwarf/T dwarf transition.


title: Wave-wave interactions and deep ocean acoustics

abstract:
  Deep ocean acoustics, in the absence of shipping and wildlife, is driven by
surface processes. Best understood is the signal generated by non-linear
surface wave interactions, the Longuet-Higgins mechanism, which dominates from
0.1 to 10 Hz, and may be significant for another octave. For this source, the
spectral matrix of pressure and vector velocity is derived for points near the
bottom of a deep ocean resting on an elastic half-space. In the absence of a
bottom, the ratios of matrix elements are universal constants. Bottom effects
vitiate the usual "standing wave approximation," but a weaker form of the
approximation is shown to hold, and this is used for numerical calculations. In
the weak standing wave approximation, the ratios of matrix elements are
independent of the surface wave spectrum, but depend on frequency and the
propagation environment. Data from the Hawaii-2 Observatory are in excellent
accord with the theory for frequencies between 0.1 and 1 Hz, less so at higher
frequencies. Insensitivity of the spectral ratios to wind, and presumably
waves, is indeed observed in the data.


title:
Docking positrophilic electrons into molecular attractive potential of
  fluorinated methanes

abstract:
  The present study shows that the positrophilic electrons of a molecule dock
into the positron attractive potential region in the annihilation process under
the plane-wave approximation. The positron-electron annihilation processes of
both polar and non-polar fluorinated methanes (CH4-nFn, n=0, 1,..., 4) are
studied under this role. The predicted gamma-ray spectra of these fluorinated
methanes agree well with the experiments. It further indicates that the
positrophilic electrons of a molecule docking at the negative end of a bond
dipole are independent from the molecular dipole moment in the annihilation
process.


title: On the symmetrical Kullback-Leibler Jeffreys centroids

abstract:
  Due to the success of the bag-of-word modeling paradigm, clustering
histograms has become an important ingredient of modern information processing.
Clustering histograms can be performed using the celebrated $k$-means
centroid-based algorithm. From the viewpoint of applications, it is usually
required to deal with symmetric distances. In this letter, we consider the
Jeffreys divergence that symmetrizes the Kullback-Leibler divergence, and
investigate the computation of Jeffreys centroids. We first prove that the
Jeffreys centroid can be expressed analytically using the Lambert $W$ function
for positive histograms. We then show how to obtain a fast guaranteed
approximation when dealing with frequency histograms. Finally, we conclude with
some remarks on the $k$-means histogram clustering.


title:
A rigorous geometry-probability equivalence in characterization of
  $\ell_1$-optimization

abstract:
  In this paper we consider under-determined systems of linear equations that
have sparse solutions. This subject attracted enormous amount of interest in
recent years primarily due to influential works \cite{CRT,DonohoPol}. In a
statistical context it was rigorously established for the first time in
\cite{CRT,DonohoPol} that if the number of equations is smaller than but still
linearly proportional to the number of unknowns then a sparse vector of
sparsity also linearly proportional to the number of unknowns can be recovered
through a polynomial $\ell_1$-optimization algorithm (of course, this assuming
that such a sparse solution vector exists). Moreover, the geometric approach of
\cite{DonohoPol} produced the exact values for the proportionalities in
question. In our recent work \cite{StojnicCSetam09} we introduced an
alternative statistical approach that produced attainable values of the
proportionalities. Those happened to be in an excellent numerical agreement
with the ones of \cite{DonohoPol}. In this paper we give a rigorous analytical
confirmation that the results of \cite{StojnicCSetam09} indeed match those from
\cite{DonohoPol}.


title:
A Full-Diversity Beamforming Scheme in Two-Way Amplified-and-Forward
  Relay Systems

abstract:
  Consider a simple two-way relaying channel where two single-antenna sources
exchange information via a multiple-antenna relay. To such a scenario, all the
existing works which can achieve full diversity order are based on the
antenna/relay selection, where the difficulty to design the beamforming lies in
the fact that a single beamformer needs to serve two destinations. In this
paper, we propose a new full-diversity beamforming scheme which ensures that
the relay signals are coherently combined at both destinations. Both analytical
and numerical results are provided to demonstrate that this proposed scheme can
outperform the existing one based on the antenna selection.


title: Upper-bounding $\ell_1$-optimization weak thresholds

abstract:
  In our recent work \cite{StojnicCSetam09} we considered solving
under-determined systems of linear equations with sparse solutions. In a large
dimensional and statistical context we proved that if the number of equations
in the system is proportional to the length of the unknown vector then there is
a sparsity (number of non-zero elements of the unknown vector) also
proportional to the length of the unknown vector such that a polynomial
$\ell_1$-optimization technique succeeds in solving the system. We provided
lower bounds on the proportionality constants that are in a solid numerical
agreement with what one can observe through numerical experiments. Here we
create a mechanism that can be used to derive the upper bounds on the
proportionality constants. Moreover, the upper bounds obtained through such a
mechanism match the lower bounds from \cite{StojnicCSetam09} and ultimately
make the latter ones optimal.


title:
Second-order Dirac equation of graphene electrons in an electromagnetic
  field and their novel spin

abstract:
  The second-order Dirac equation (DE) and its velocity operator of graphene
electrons in an electromagnetic field are obtained according to tight-binding
k.p method. With extra terms included, they demonstrate the motion of graphene
electrons more completely through a more complete Ehrenfest theorem and present
finer properties of graphene electrons. Eigen-energy given by the second-order
DE for field-free graphene indicates that extra terms may affect the trembling
motion of graphene electrons. For graphene in a magnetic field, eigen-energy
given by the second-order DE suggests that graphene electrons have a new kind
of spin of a boson other than true electronic spin and pseudo-spin of Dirac
particles, which will modify graphene properties such as the optical spectra.


title: A framework to characterize performance of LASSO algorithms

abstract:
  In this paper we consider solving \emph{noisy} under-determined systems of
linear equations with sparse solutions. A noiseless equivalent attracted
enormous attention in recent years, above all, due to work of
\cite{CRT,CanRomTao06,DonohoPol} where it was shown in a statistical and large
dimensional context that a sparse unknown vector (of sparsity proportional to
the length of the vector) can be recovered from an under-determined system via
a simple polynomial $\ell_1$-optimization algorithm. \cite{CanRomTao06} further
established that even when the equations are \emph{noisy}, one can, through an
SOCP noisy equivalent of $\ell_1$, obtain an approximate solution that is (in
an $\ell_2$-norm sense) no further than a constant times the noise from the
sparse unknown vector. In our recent works
\cite{StojnicCSetam09,StojnicUpper10}, we created a powerful mechanism that
helped us characterize exactly the performance of $\ell_1$ optimization in the
noiseless case (as shown in \cite{StojnicEquiv10} and as it must be if the
axioms of mathematics are well set, the results of
\cite{StojnicCSetam09,StojnicUpper10} are in an absolute agreement with the
corresponding exact ones from \cite{DonohoPol}). In this paper we design a
mechanism, as powerful as those from \cite{StojnicCSetam09,StojnicUpper10},
that can handle the analysis of a LASSO type of algorithm (and many others)
that can be (or typically are) used for "solving" noisy under-determined
systems. Using the mechanism we then, in a statistical context, compute the
exact worst-case $\ell_2$ norm distance between the unknown sparse vector and
the approximate one obtained through such a LASSO. The obtained results match
the corresponding exact ones obtained in \cite{BayMon10,DonMalMon10}. Moreover,
as a by-product of our analysis framework we recognize existence of an SOCP
type of algorithm that achieves the same performance.

categories: cs.IT math.IT math.OC math.PR math.ST stat.TH


title:
Multi-functional foot use during running in the zebra-tailed lizard
  (Callisaurus draconoides)

abstract:
  A diversity of animals that run on solid, level, flat, non-slip surfaces
appear to bounce on their legs; elastic elements in the limbs can store and
return energy during each step. The mechanics and energetics of running in
natural terrain, particularly on surfaces that can yield and flow under stress,
is less understood. The zebra-tailed lizard (Callisaurus draconoides), a small
desert generalist with a large, elongate, tendinous hind foot, runs rapidly
across a variety of natural substrates. We use high speed video to obtain
detailed three-dimensional running kinematics on solid and granular surfaces to
reveal how leg, foot, and substrate mechanics contribute to its high locomotor
performance. Running at ~10 body length/s (~1 m/s), the center of mass
oscillates like a spring-mass system on both substrates, with only 15%
reduction in stride length on the granular surface. On the solid surface, a
strut-spring model of the hind limb reveals that the hind foot saves about 40%
of the mechanical work needed per step, significant for the lizard's small
size. On the granular surface, a penetration force model and hypothesized
subsurface foot rotation indicates that the hind foot paddles through fluidized
granular medium, and that the energy lost per step during irreversible
deformation of the substrate does not differ from the reduction in the
mechanical energy of the center of mass. The upper hind leg muscles must
perform three times as much mechanical work on the granular surface as on the
solid surface to compensate for the greater energy lost within the foot and to
the substrate.


title:
Some properties of generalized local cohomology modules with respect to
  a pair of ideals

abstract:
  We introduce a notion of generalized local cohomology modules with respect to
a pair of ideals $(I,J)$ which is a generalization of the concept of local
cohomology modules with respect to $(I,J).$
  We show that generalized local cohomology modules $H^i_{I,J}(M,N)$ can be
computed by the \v{C}ech cohomology modules. We also study the artinianness of
generalized local cohomology modules $H^i_{I,J}(M,N).$


title: Indirect Detection of Self-Interacting Asymmetric Dark Matter

abstract:
  Self-interacting dark matter resolves the issue of cuspy profiles that appear
in non-interacting cold dark matter simluations; it may additionally resolve
the so-called "too big to fail" problem in structure formation. Asymmetric dark
matter provides a natural explanation of the comparable densities of baryonic
matter and dark matter. In this paper, we discuss unique indirect detection
signals produced by a minimal model of self-interacting asymmetric scalar dark
matter. Through the formation of dark matter bound states, a dark force
mediator particle may be emitted; the decay of this particle may produce an
observable signal. We estimate the produced signal and explicitly demonstrate
parameters for which the signal exceeds current observations.


title: Regularly random duality

abstract:
  In this paper we look at a class of random optimization problems. We discuss
ways that can help determine typical behavior of their solutions. When the
dimensions of the optimization problems are large such an information often can
be obtained without actually solving the original problems. Moreover, we also
discover that fairly often one can actually determine many quantities of
interest (such as, for example, the typical optimal values of the objective
functions) completely analytically. We present a few general ideas and
emphasize that the range of applications is enormous.


title: On Constellations for Physical Layer Network Coded Two-Way Relaying

abstract:
  Modulation schemes for two-way bidirectional relay network employing two
phases: Multiple access (MA) phase and Broadcast (BC) phase and using physical
layer network coding are currently studied intensively. Recently, adaptive
modulation schemes using Latin Squares to obtain network coding maps with the
denoise and forward protocol have been reported with good end-to-end
performance. These schemes work based on avoiding the detrimental effects of
distance shortening in the effective receive constellation at the end of the MA
phase at the relay. The channel fade states that create such distance
shortening called singular fade states, are effectively removed using
appropriate Latin squares. This scheme as well as all other known schemes
studied so far use conventional regular PSK or QAM signal sets for the end
users which lead to the relay using different sized constellations for the BC
phase depending upon the fade state. In this work, we propose a 4-point signal
set that would always require a 4-ary constellation for the BC phase for all
the channel fade conditions. We also propose an 8-point constellation that
gives better SER performance (gain of 1 dB) than 8-PSK while still using 8-ary
constellation for BC phase like the case with 8-PSK. This is in spite of the
fact that the proposed 8-point signal set has more number of singular fade
states than for 8-PSK.


title:
Infinitely imbalanced binomial regression and deformed exponential
  families

abstract:
  The logistic regression model is known to converge to a Poisson point process
model if the binary response tends to infinitely imbalanced. In this paper, it
is shown that this phenomenon is universal in a wide class of link functions on
binomial regression. The proof relies on the extreme value theory. For the
logit, probit and complementary log-log link functions, the intensity measure
of the point process becomes an exponential family. For some other link
functions, deformed exponential families appear. A penalized maximum likelihood
estimator for the Poisson point process model is suggested.


title: Generalized ideal transforms

abstract:
  We study basic properties of the generalized ideal transforms $D_I(M, N)$ and
the set of associated primes of the modules $R^iD_I(M,N).$


title: Notes on reductions of superstring theory to bosonic string theory

abstract:
  It is in general very subtle to integrate over the odd moduli of super
Riemann surfaces in perturbative superstring computations. We study how these
subtleties go away in favorable cases, including the embedding of N=0 string to
N=1 string by Berkovits and Vafa, and the relation of the graviphoton amplitude
and the topological string amplitude by Antoniadis, Gava, Narain and Taylor and
Bershadsky, Cecotti, Ooguri and Vafa. The Poincar\'e dual of the moduli space
of Riemann surfaces in the moduli space of super Riemann surfaces plays an
important role.


title:
Queuing Methodology Based Power Efficient Routing Protocol for Reliable
  Data Communications in Manets

abstract:
  A mobile ad hoc network (MANET) is a wireless network that uses multi-hop
peer-to- peer routing instead of static network infrastructure to provide
network connectivity. MANETs have applications in rapidly deployed and dynamic
military and civilian systems. The network topology in a MANET usually changes
with time. Therefore, there are new challenges for routing protocols in MANETs
since traditional routing protocols may not be suitable for MANETs. In recent
years, a variety of new routing protocols targeted specifically at this
environment have been developed, but little performance information on each
protocol and no realistic performance comparison between them is available.
This paper presents the results of a detailed packet-level simulation comparing
three multi-hop wireless ad hoc network routing protocols that cover a range of
design choices: DSR, NFPQR, and clustered NFPQR. By applying queuing
methodology to the introduced routing protocol the reliability and throughput
of the network is increased.


title: On the ubiquity of molecular anions in the dense interstellar medium

abstract:
  Results are presented from a survey for molecular anions in seven nearby
Galactic star-forming cores and molecular clouds. The hydrocarbon anion C6H- is
detected in all seven target sources, including four sources where no anions
have been previously detected: L1172, L1389, L1495B and TMC-1C. The C6H-/C6H
column density ratio is greater than about 1.0% in every source, with a mean
value of 3.0% (and standard deviation 0.92%). Combined with previous
detections, our results show that anions are ubiquitous in dense clouds
wherever C6H is present. The C6H-/C6H ratio is found to show a positive
correlation with molecular hydrogen number density, and with the apparent age
of the cloud. We also report the first detection of C4H- in TMC-1 (at 4.8-sigma
confidence), and derive an anion-to-neutral ratio C4H-/C4H = (1.2 +- 0.4) x
10^-5 (= 0.0012 +- 0.0004%). Such a low value compared with C6H- highlights the
need for a revised radiative electron attachment rate for C4H. Chemical model
calculations show that the observed C4H- could be produced as a result of
reactions of oxygen atoms with C5H- and C6H-.


title:
Seeing the orbital ordering in Iron-based superconductors with magnetic
  anisotropy

abstract:
  The orbital fluctuation of the conduction electrons in the Iron-based
superconductors is found to contribute significantly to the magnetic response
of the system. With the use of a realistic five-band model and group
theoretical analysis, we have determined the orbital magnetic susceptibility in
such a multi-orbital system. At $n=6.1$, the in-plane orbital magnetic
susceptibility is predicted to be about 10$\mu_{\mathrm{B}}^{2}/\mathrm{eV}$,
which is more than 2/3 of the observed total susceptibility around 200 K in 122
systems(of about 14$\mu_{\mathrm{B}}^{2}/\mathrm{eV}$ or
$4.5\times10^{-4}\mathrm{erg}/\mathrm{G}^{2}\mathrm{mol}_{\mathrm{AS}}$\cite{Klingeler}).
We find the in-plane orbital magnetic response is sensitive to the breaking of
the tetragonal symmetry in the orbital space. In particular, when the observed
band splitting(between the $3d_{xz}$ and the $3d_{yz}$-dominated band) is used
to estimate the strength of the symmetry breaking perturbation\cite{Shen}, a
4.5% modulation in the in-plane orbital magnetic susceptibility can be
produced, making the latter a useful probe of the orbital ordering in such a
multi-orbital system. As a by product, the theory also explains the large
anisotropy between the in-plane and the out-of-plane magnetic response observed
universally in susceptibility and NMR measurements.


title: A New Kind of Beauty Out of the Underlying Scaling of Geographic Space

abstract:
  Geographic space demonstrates scaling or hierarchy, implying that there are
far more small things than large ones. The scaling pattern of geographic space,
if visualized properly (i.e., based on head/tail breaks), can evoke a sense of
beauty. This is our central argument. This beauty is a new type of aesthetic at
a deeper structural level, and differs in essence from an intuitive sense of
harmony, perceived in terms of color, shape, texture, and ratio. This new kind
of beauty was initially defined and discovered by Christopher Alexander, and
promoted in his master work The Nature of Order. To paraphrase Mandelbrot, this
is the beauty for the sake of science rather than for art's sake or for the
sake of commerce. Throughout the paper, we attempt to argue and illustrate that
the scaling of geographic space possesses this new kind of beauty, which has a
positive impact on human well-being. The paper further draws upon the previous
work of Nikos Salingaros and Richard Taylor on the beauty in architecture and
arts to support our argument.
  Keywords: Aesthetics, heavy-tailed distributions, head/tail breaks, Zipf's
law, and fractals


title:
Modeling the quantum interference signatures of the Ba II D2 4554 A line
  in the second solar spectrum

abstract:
  Quantum interference effects play a vital role in shaping the linear
polarization profiles of solar spectral lines. The Ba II D2 line at 4554 A is a
prominent example, where the F-state interference effects due to the odd
isotopes produce polarization profiles, which are very different from those of
the even isotopes that have no F-state interference. It is therefore necessary
to account for the contributions from the different isotopes to understand the
observed linear polarization profiles of this line. Here we do radiative
transfer modeling with partial frequency redistribution (PRD) of such
observations while accounting for the interference effects and isotope
composition. The Ba II D2 polarization profile is found to be strongly governed
by the PRD mechanism. We show how a full PRD treatment succeeds in reproducing
the observations, while complete frequency redistribution (CRD) alone fails to
produce polarization profiles that have any resemblance with the observed ones.
However, we also find that the line center polarization is sensitive to the
temperature structure of the model atmosphere. To obtain a good fit to the line
center peak of the observed Stokes Q/I profile, a small modification of the
FALX model atmosphere is needed, by lowering the temperature in the
line-forming layers. Because of the pronounced temperature sensitivity of the
Ba II D2 line it may not be a suitable tool for Hanle magnetic-field
diagnostics of the solar chromosphere, because there is currently no
straightforward way to separate the temperature and magnetic-field effects from
each other.


title: Hausdorff dimension of wiggly metric spaces

abstract:
  For a compact connected set $X\subseteq \ell^{\infty}$, we define a quantity
$\beta'(x,r)$ that measures how close $X$ may be approximated in a ball
$B(x,r)$ by a geodesic curve. We then show there is $c>0$ so that if
$\beta'(x,r)>\beta>0$ for all $x\in X$ and $r<r_{0}$, then $\dim
X>1+c\beta^{2}$. This generalizes a theorem of Bishop and Jones and answers a
question posed by Bishop and Tyson.


title:
Effect of bulk charged impurities on the bulk and surface transport in
  three-dimensional topological insulators

abstract:
  In the three-dimensional topological insulator (TI), the physics of doped
semiconductors exists literally side-by-side with the physics of
ultra-relativistic Dirac fermions. This unusual pairing creates a novel
playground for studying the interplay between disorder and electronic
transport. In this mini-review we focus on the disorder caused by the
three-dimensionally distributed charged impurities that are ubiquitous in TIs,
and we outline the effects it has on both the bulk and surface transport in
TIs. We present self-consistent theories for Coulomb screening both in the bulk
and at the surface, discuss the magnitude of the disorder potential in each
case, and present results for the conductivity. In the bulk, where the band gap
leads to thermally activated transport, we show how disorder leads to a
smaller-than-expected activation energy that gives way to VRH at low
temperatures. We confirm this enhanced conductivity with numerical simulations
that also allow us to explore different degrees of impurity compensation. For
the surface, where the TI has gapless Dirac modes, we present a theory of
disorder and screening of deep impurities, and we calculate the corresponding
zero-temperature conductivity. We also comment on the growth of the disorder
potential as one moves from the surface of the TI into the bulk. Finally, we
discuss how the presence of a gap at the Dirac point, introduced by some source
of time-reversal symmetry breaking, affects the disorder potential at the
surface and the mid-gap density of states.


title: Love story under the H-bomb shadow

abstract:
  The physics is created by human beings with all weaknesses of human nature.
This story caught our attention since it demonstrates how fragile the human
destiny is and even genius cannot find freedom and preserve human dignity in
the face of the totalitarian state.


title: A simple sufficient condition for the coexistence of quantum effects

abstract:
  Two quantum effects are considered coexistent if they can be measured
together. It is known that commutativity and comparability are sufficient but
not necessary for the coexistence of two effects. We unify those two conditions
to a simple but more widely applicable sufficient condition.


title:
Some identities arising from Sheffer sequences for the powers of Sheffer
  pairs under umbral composition

abstract:
  In this paper, we study some properties of Sheffer sequences for the powers
of Sheffer pairs under umbral composition. From our properties we derive new
and interesting identities of Sheffer sequences of special polynomials for the
powers of Sheffer pairs under umbral composition.


title:
Exploring the Role of Logically Related Non-Question Phrases for
  Answering Why-Questions

abstract:
  In this paper, we show that certain phrases although not present in a given
question/query, play a very important role in answering the question. Exploring
the role of such phrases in answering questions not only reduces the dependency
on matching question phrases for extracting answers, but also improves the
quality of the extracted answers. Here matching question phrases means phrases
which co-occur in given question and candidate answers. To achieve the above
discussed goal, we introduce a bigram-based word graph model populated with
semantic and topical relatedness of terms in the given document. Next, we apply
an improved version of ranking with a prior-based approach, which ranks all
words in the candidate document with respect to a set of root words (i.e.
non-stopwords present in the question and in the candidate document). As a
result, terms logically related to the root words are scored higher than terms
that are not related to the root words. Experimental results show that our
devised system performs better than state-of-the-art for the task of answering
Why-questions.


title:
The F-method and a branching problem for generalized Verma modules
  associated to $({\LieGtwo},{so(7)})$

abstract:
  The branching problem for a couple of non-compatible Lie algebras and their
parabolic subalgebras applied to generalized Verma modules was recently
discussed in \cite{ms}. In the present article, we employ the recently
developed F-method, \cite{KOSS1}, \cite{KOSS2} to the couple of non-compatible
Lie algebras $({\LieGtwo},{so(7)})$, and generalized conformal ${so(7)}$-Verma
modules of scalar type. As a result, we classify the $\LieGtwo \cap
\gop'$-singular vectors for this class of $so(7)$-modules.


title:
Varieties of minimal rational tangents on double covers of projective
  space

abstract:
  Let $\phi: X \to \mathbb P^n$ be a double cover branched along a smooth
hypersurface of degree $2m, 2 \leq m \leq n-1$. We study the varieties of
minimal rational tangents $\mathcal C_x \subset \mathbb P T_x(X)$ at a general
point $x$ of $X$. We describe the homogeneous ideal of $\mathcal C_x$ and show
that the projective isomorphism type of $\mathcal C_x$ varies in a maximal way
as $x$ varies over general points of $X$. Our description of the ideal of
$\mathbb C_x$ implies a certain rigidity property of the covering morphism
$\phi$. As an application of this rigidity, we show that any finite morphism
between such double covers with $m=n-1$ must be an isomorphism. We also prove
that Liouville-type extension property holds with respect to minimal rational
curves on $X$.


title: The Shape of Random Pattern-Avoiding Permutations

abstract:
  We initiate the study of limit shapes for random permutations avoiding a
given pattern. Specifically, for patterns of length 3, we obtain delicate
results on the asymptotics of distributions of positions of numbers in the
permutations. We view the permutations as 0-1 matrices to describe the
resulting asymptotics geometrically. We then apply our results to obtain a
number of results on distributions of permutation statistics.


title: Cosmic rays and climate change over the past 1000 million years

abstract:
  The Galactic cosmic ray (GCR) intensity has been postulated by others to vary
cyclically with a peak to valley ratio of ~3:1, as the Solar System moves from
the Spiral Arm to the Inter-Arm regions of the Galaxy. These intensities have
been correlated with global temperatures and used to support the hypothesis of
GCR induced climate change. In this paper we show that the model used to deduce
such a large ratio of Arm to Interarm GCR intensity requires unlikely values of
some of the GCR parameters, particularly the diffusion length in the
interstellar medium, if as seems likely to be the case, the diffusion is
homogeneous. Comparison is made with the existing gamma ray astronomy data and
this also indicates that the ratio is not large. The variation in the intensity
is probably of order 10-20% and should be no more than 30% as the Solar System
moves between these two regions, unless the conventional parameters of the GCR
are incorrect. In addition we show that the variation of the GCR intensity, as
the trajectory of the Solar System oscillates about the Galactic Plane, is too
small to account for the extinctions of species as has been postulated unless,
again, conventional assumptions about the GCR parameters are not correct.


title: Polynomial Chaotic Inflation in the Planck Era

abstract:
  We propose a chaotic inflation model in supergravity based on polynomial
interactions of the inflaton. Specifically we study the chaotic inflation model
with quadratic, cubic and quartic couplings in the scalar potential and show
that the predicted scalar spectral index and tensor-to-scalar ratio can lie
within the 1 sigma region allowed by the Planck results.


title:
An operational window for radiation-resistant materials based on
  sequentially healing grain interiors and boundaries

abstract:
  Design of nuclear materials with high radiation-tolerance has great
significance1, especially for the next generation of nuclear energy systems2,3.
Response of nano- and poly-crystals to irradiation depends on the radiation
temperature, dose-rate and grain size4-13. However the dependencies had been
studied and interpreted individually, and thus severely lacking is the ability
to predict radiation performance of materials in extreme environments. Here we
propose an operational window for radiation-resistant materials, which is based
on a perspective of interactions among irradiation-induced interstitials,
vacancies, and grain boundaries. Using atomic simulations, we find that healing
grain boundaries needs much longer time than healing grain interiors. Not been
noticed before, this finding suggests priority should be thereafter given to
recovery of the grain boundary itself. This large disparity in healing time is
reflected in the spectra of defects-recombination energy barriers by the
presence of one high-barrier peak in addition to the peak of low barriers. The
insight gained from the study instigates new avenues for examining the role of
grain boundaries in healing the material. In particular, we sketch out the
radiation-endurance window in the parameter space of temperature, dose-rate and
grain size. The window helps evaluate material performance and develop
resistant materials against radiation damage.


title: Nonequilibrium Green's function method for quantum thermal transport

abstract:
  This review deals with the nonequilibrium Green's function (NEGF) method
applied to the problems of energy transport due to atomic vibrations (phonons),
primarily for small junction systems. We present a pedagogical introduction to
the subject, deriving some of the well-known results such as the Laudauer-like
formula for heat current in ballistic systems. The main aim of the review is to
build the machinery of the method so that it can be applied to other
situations, which are not directly treated here. In addition to the above, we
consider a number of applications of NEGF, not in routine model system
calculations, but in a few new aspects showing the power and usefulness of the
formalism. In particular, we discuss the problems of multiple leads, coupled
left-right-lead system, and system without a center. We also apply the method
to the problem of full counting statistics. In the case of nonlinear systems,
we make general comments on the thermal expansion effect, phonon relaxation
time, and a certain class of mean-field approximations. Lastly, we examine the
relationship between NEGF, reduced density matrix, and master equation
approaches to thermal transport.


title:
Approximate Inference for Observation Driven Time Series Models with
  Intractable Likelihoods

abstract:
  In the following article we consider approximate Bayesian parameter inference
for observation driven time series models. Such statistical models appear in a
wide variety of applications, including econometrics and applied mathematics.
This article considers the scenario where the likelihood function cannot be
evaluated point-wise; in such cases, one cannot perform exact statistical
inference, including parameter estimation, which often requires advanced
computational algorithms, such as Markov chain Monte Carlo (MCMC). We introduce
a new approximation based upon approximate Bayesian computation (ABC). Under
some conditions, we show that as $n\rightarrow\infty$, with $n$ the length of
the time series, the ABC posterior has, almost surely, a maximum \emph{a
posteriori} (MAP) estimator of the parameters which is different from the true
parameter. However, a noisy ABC MAP, which perturbs the original data,
asymptotically converges to the true parameter, almost surely. In order to draw
statistical inference, for the ABC approximation adopted, standard MCMC
algorithms can have acceptance probabilities that fall at an exponential rate
in $n$ and slightly more advanced algorithms can mix poorly. We develop a new
and improved MCMC kernel, which is based upon an exact approximation of a
marginal algorithm, whose cost per-iteration is random but the expected cost,
for good performance, is shown to be $\mathcal{O}(n^2)$ per-iteration.