title:
Impurity effects in a vortex core in a chiral p-wave superconductor
  within the t-matrix approximation

abstract:
  We study the effects of non-magnetic impurity scattering on the Andreev bound
states (ABS) in an isolated vortex in a two-dimensional chiral p-wave
superconductor numerically. We incorporate the impurity scattering effects into
the quasiclassical Eilenberger formulation through the self-consistent
$t$-matrix approximation. Within this scheme, we calculate the local density of
states (LDOS) around two types of vortices: "parallel" ("anti-parallel") vortex
where the phase winding of the pair-potential coming from vorticity and that
coming from chirality have the same (opposite) sign.
  When the scattering phase-shift $\delta_0$ of each impurity is small, we find
that impurities affect differently low energy quasiparticle spectrum around the
two types of vortex in a way similar to that in the Born limit
($\delta_0\rightarrow 0$). For a larger $\delta_0(\leq \pi/2)$ however we find
that ABS in the vortex is strongly suppressed by impurities for both types of
vortex. We found that there are some correlations between the suppression of
ABS near vortex cores and the low energy density of states due to impurity
bands in the bulk.


title:
Integral Equation Analysis of Plane Wave Scattering by Coplanar
  Graphene-Strip Gratings in the THz Range

abstract:
  The plane wave scattering and absorption by finite and infinite gratings of
free-space standing infinitely long graphene strips are studied in the THz
range. A novel numerical approach, based on graphene surface impedance,
hyper-singular integral equations, and the Nystrom method, is proposed. This
technique guarantees fast convergence and controlled accuracy of computations.
Reflectance, transmittance, and absorbance are carefully studied as a function
of graphene and grating parameters, revealing the presence of surface plasmon
resonances. Specifically, larger graphene relaxation times increases the number
of resonances in the THz range, leading to higher wave transmittance due to the
reduced losses; on the other hand an increase of graphene chemical potential
up-shifts the frequency of plasmon resonances. It is also shown that a
relatively low number of graphene strips (>10) are able to reproduce Rayleigh
anomalies. These features make graphene strips good candidates for many
applications, including tunable absorbers and frequency selective surfaces.


title: Feedback from students' tests as a tool in teaching

abstract:
  A close look at students' written work on examinations offers a wealth of
information about their performance, their knowledge of the subject, their
strengths, weaknesses and misconceptions, and their overall level of
mathematical skills and abilities. This information can be used to better
ascertain how mathematical concepts taught in class were understood by students
and to suggest various approaches that could be used to improve teaching. The
process of analyzing students' work, although time consuming, can be rewarding
and can have positive results for both students and instructors.
  My aim is fourfold: (a) To give a rationale for analysis of students' work,
especially tests (b) to give possible explanations of students' performance;
(c) to revisit aspects of teaching some mathematical constructs, such as
function and, (d) to provide possible ways of improving the teaching of
concepts considered in this paper.


title:
Fake quadrics from irreducible lattices acting on the product of upper
  half planes

abstract:
  In the present article, we provide examples of fake quadrics, that is,
minimal complex surfaces of general type with the same numerical invariants as
the smooth quadric in $\PP ^3$ which are quotients of the bidisc by an
irreducible lattice of automorphisms. Moreover, we list classes of arithmetic
lattices over a real quadratic number field which define a fake quadric and
give general results towards a classification of all such fake quadrics.


title: Positive curvature and the elliptic genus

abstract:
  We prove several results about the vanishing of the elliptic genus on
positively curved Spin manifolds with logarithmic symmetry rank. The proofs are
based on the rigidity of the elliptic genus and Kennard's improvement of the
Connectedness Lemma for transversely intersecting, totally geodesic
submanifolds.


title: Experiments in Information Sharing

abstract:
  This paper reports experimental data describing the dynamics of three key
information-sharing outcomes: quantity of information shared, falsification and
accuracy. The experimental design follows a formal model predicting that
cooperative incentives are needed to motivate subsidiaries of large
organizations to share information. Empirical reaction functions reveal how
lagged values of information-sharing outcomes influence information sharing in
the current round. Cooperative treatments pay bonuses to everyone if at least
one individual (or subsidiary) achieves accuracy. Tournament treatments pay a
single bonus to whoever achieves accuracy first. As expected, tournament
incentives tend to reduce sharing, increase falsification and impair accuracy.
Several surprises not predicted by the formal model emerge from the data.
Conditional cooperation occurs regardless of the incentive scheme, implying
that the mechanism through which incentives influence improvements in
information sharing is indirect.


title: Infrared background signatures of the first black holes

abstract:
  Angular fluctuations of the Near InfraRed Background (NIRB) intensity are
observed up to scales $\simlt 1^{\ensuremath{^{\circ}}}$. Their interpretation
is challenging as even after removing the contribution from detected sources,
the residual signal is $>10$ times higher than expected from distant galaxies
below the detection limit and first stars. We propose here a novel
interpretation in which early, intermediate mass, accreting direct collapse
black holes (DCBH), which are too faint to be detected individually in current
surveys, could explain the observed fluctuations. We find that a population of
highly obscured ($N_{\rm H}\simgt 10^{25} \rm cm^{-2}$) DCBHs formed in
metal-free halos with virial temperature $10^4$ K at $z\simgt 12$, can explain
the observed level $\approx 10^{-3}$ (nW m$^{-2}$ sr$^{-1})^2$ of the 3.6 and
4.5 $\mu$m fluctuations on scales $>100''$. The signal on smaller scales is
instead produced by undetected galaxies at low and intermediate redshifts.
Albeit Compton-thick, at scales $\theta> 100''$ DCBHs produce a CXB (0.5-2
keV)-NIRB ($4.5 \rm \mu m$) cross-correlation signal of $\simeq 10^{-11}$ erg
s$^{-1}$ cm$^{-2}$ nW m$^{-2}$ sr$^{-1}$ slightly dependent on the specific
value of the absorbing gas column ($N_{\rm H} \approx 10^{25} \rm cm^{-2}$)
adopted and in agreement with the recent measurements by
\cite{2012arXiv1210.5302C}. At smaller scales the cross-correlation is
dominated by the emission of high-mass X-ray binaries (HMXB) hosted by the same
low-$z$, undetected galaxies accounting for small scale NIRB fluctuations.
These results outline the great potential of the NIRB as a tool to investigate
the nature of the first galaxies and black holes.


title: Formation of the First Stars

abstract:
  Understanding the formation of the first stars is one of the frontier topics
in modern astrophysics and cosmology. Their emergence signaled the end of the
cosmic dark ages, a few hundred million years after the Big Bang, leading to a
fundamental transformation of the early Universe through the production of
ionizing photons and the initial enrichment with heavy chemical elements. We
here review the state of our knowledge, separating the well understood elements
of our emerging picture from those where more work is required. Primordial star
formation is unique in that its initial conditions can be directly inferred
from the Lambda Cold Dark Matter (LCDM) model of cosmological structure
formation. Combined with gas cooling that is mediated via molecular hydrogen,
one can robustly identify the regions of primordial star formation, the
so-called minihalos, having total masses of ~10^6 M_sun and collapsing at
redshifts z~20-30. Within this framework, a number of studies have defined a
preliminary standard model, with the main result that the first stars were
predominantly massive. This model has recently been modified to include a
ubiquitous mode of fragmentation in the protostellar disks, such that the
typical outcome of primordial star formation may be the formation of a binary
or small multiple stellar system. We will also discuss extensions to this
standard picture due to the presence of dynamically significant magnetic
fields, of heating from self-annihalating WIMP dark matter, or cosmic rays. We
conclude by discussing possible strategies to empirically test our theoretical
models.


title: Surface Reconstruction from Scattered Point via RBF Interpolation on GPU

abstract:
  In this paper we describe a parallel implicit method based on radial basis
functions (RBF) for surface reconstruction. The applicability of RBF methods is
hindered by its computational demand, that requires the solution of linear
systems of size equal to the number of data points. Our reconstruction
implementation relies on parallel scientific libraries and is supported for
massively multi-core architectures, namely Graphic Processor Units (GPUs). The
performance of the proposed method in terms of accuracy of the reconstruction
and computing time shows that the RBF interpolant can be very effective for
such problem.


title: On the uniqueness of higher-spin symmetries in AdS and CFT

abstract:
  We study the uniqueness of higher-spin algebras which are at the core of
higher-spin theories in AdS and of CFTs with exact higher-spin symmetry, i.e.
conserved tensors of rank greater than two. The Jacobi identity for the gauge
algebra is the simplest consistency test that appears at the quartic order for
a gauge theory. Similarly, the algebra of charges in a CFT must also obey the
Jacobi identity. These algebras are essentially the same. Solving the Jacobi
identity under some simplifying assumptions spelled out, we obtain that the
Eastwood-Vasiliev algebra is the unique solution for d=4 and d>6. In 5d there
is a one-parameter family of algebras that was known before. In particular, we
show that the introduction of a single higher-spin gauge field/current
automatically requires the infinite tower of higher-spin gauge fields/currents.
The result implies that from all the admissible non-Abelian cubic vertices in
AdS(d), that have been recently classified for totally symmetric higher-spin
gauge fields, only one vertex can pass the Jacobi consistency test. This cubic
vertex is associated with a gauge deformation that is the germ of the
Eastwood-Vasiliev's higher-spin algebra.


title: A framework for fractional Hardy inequalities

abstract:
  We provide a general framework for fractional Hardy inequalities. Our
framework covers, for instance, fractional inequalities related to the
Dirichlet forms of some L\'evy processes, and weighted fractional inequalities
on irregular open sets.


title:
Linear and nonlinear rheology of dense emulsions: Identifying the glass
  and jamming regimes

abstract:
  We discuss the linear and non-linear rheology of concentrated (sub)microscale
emulsions, amorphous disordered solids composed of repulsive and deformable
soft colloidal spheres. Based on recent results from simulation and theory, we
derive quantitative predictions for the dependences of the elastic shear
modulus and the yield stress on the droplet volume fraction. The remarkable
agreement with experiments we observe supports the scenario that the repulsive
glass and the jammed state can be clearly identified in the rheology of soft
spheres at finite temperature while crossing continuously from a liquid to a
highly compressed yet disordered solid.


title:
Dark Matter Search Backgrounds from Primordial Radionuclide Chain
  Disequilibrium

abstract:
  Dark matter direct-detection searches for weakly interacting massive
particles (WIMPs) are commonly limited in sensitivity by neutron and gamma
backgrounds from the decay of radioactive isotopes. Several common
radioisotopes in detector construction materials are found in long decay
chains, notably those headed by 238U, 235U, and 232Th. Gamma radioassay using
Ge detectors identifies decay rates of a few of the radioisotopes in each
chain, and typically assumes that the chain is in secular equilibrium. If the
chains are out of equilibrium, detector background rates can be elevated
significantly above expectation. In this work we quantify the increase in
neutron and gamma production rates from an excess of various sub-chains of the
238U decay chain. We find that the 226Ra sub-chain generates x10 higher neutron
flux per decay than the 238U early sub-chain and 210Pb sub-chain, in materials
with high (alpha,n) neutron yields. Typical gamma screening results limit
potential 238U early sub-chain activity to x20-60 higher than 226Ra sub-chain
activity. Monte Carlo simulation is used to quantify the contribution of the
sub-chains of 238U to low-energy nuclear recoil (NR) and electron recoil (ER)
backgrounds in simplified one tonne liquid Ar and liquid Xe detectors. NR and
ER rates generated by 238U sub-chains in the Ar and Xe detectors are found
after comparable fiducial and multiple-scatter cuts. The Xe detector is found
to have x12 higher signal-to-background for 100 GeV WIMPs over neutrons than
the Ar detector. ER backgrounds in both detectors are found to increase weakly
for excesses of 238U early sub-chain and 210Pb sub-chain relative to 226Ra
sub-chain. Experiments in which backgrounds are NR-dominated are sensitive to
undetected excesses of 238U early sub-chain and 210Pb sub-chain concentrations.
Experiments with ER-dominated backgrounds are relatively insensitive to these
excesses.


title: An Approach to Discrete Quantum Gravity

abstract:
  This article presents a simplified version of the author's previous work. We
first construct a causal growth process (CGP). We then form path Hilbert spaces
using paths of varying lengths in the CGP. A sequence of positive operators on
these Hilbert spaces that satisfy certain normalization and consistency
conditions is called a quantum sequential growth process (QSGP). The operators
of a QSGP are employed to define natural decoherence functionals and quantum
measures. These quantum measures are extended to a single quantum measure
defined on a suitable collection of subsets of a space of all paths. Continuing
our general formalism, we define curvature operators and a discrete analogue of
Einstein's field equations on the Hilbert space of causal sets. We next present
a method for constructing a QSGP using an amplitude process (AP). We then
consider a specific AP that employs a discrete analogue of a quantum action.
Finally, we consider the special case in which the QSGP is classical. It is
pointed out that this formalism not only gives a discrete version of general
relativity, there is also emerging a discrete analogue of quantum field theory.
We therefore have discrete versions of these two theories within one unifying
framework.


title: Power scaling of high efficiency 1.5micron cascaded Raman fiber lasers

abstract:
  High power fiber lasers operating at the 1.5micron wavelength region have
attractive features like eye-safety and atmospheric transparency, and cascaded
Raman fiber lasers offer a convenient method to obtain high power sources at
these wavelengths. A limitation to power scaling however has been the lower
conversion efficiency of these lasers. We recently introduced a high efficiency
architecture for high power cascaded Raman fiber lasers applicable for
1.5micron fiber lasers. Here we demonstrate further power scaling using this
new architecture. Using numerical simulations we identify the ideal operating
conditions for the new architecture. We demonstrate a high efficiency 1480nm
cascaded Raman fiber laser with an output power of 301 W, comparable to record
power levels achieved with rare-earth doped fiber lasers in the 1.5 micron
wavelength region.


title:
All CAT(0) Boundaries of Croke-Kleiner-Admissible Groups are
  Equivariantly CE Equivalent]

abstract:
  Question 2.6 of Bestvina's Questions in Geometric Group Theory asks whether
every pair of boundaries of a given CAT(0) group G is cell-like equivalent. The
question was posed by Bestvina shortly after the discovery, by Croke and
Kleiner, of a CAT(0) group that admits multiple boundaries. Previously, it had
been observed by Bestvina and Geoghegan that all boundaries of a torsion free
CAT(0) G would necessarily have the same shape. Since "cell-like equivalence"
is weaker than topological equivalence, but in most circumstances, stronger
(and more intuitive) than shape equivalence, this question is a natural one
when working with the pathological types of spaces that occur as group
boundaries. Furthermore, the definition of cell-like equivalence allows for a
obvious G-equivariant extension.
  In this paper we provide a positive answer to Bestvina's G-equivariant
Cell-like Equivalence Question for the class of admissible groups studied by
Croke and Kleiner in 2002. Since that collection includes the original
Croke-Kleiner group, our result provides a strong solution to Q2.6, for the
group that originally motivated the question.


title: Novel detector systems for the Positron Emission Tomography

abstract:
  In this contribution we describe a novel solution for the construction of
Positron Emission Tomograph. We present the device allowing for determination
of the impact position as well as time and deph of interaction of the
annihilation gamma quanta. The device is comprised of scintillation chamber
consisting of organic scintillators surrounding the body of the patient. We
discuss two possible solutions: (i) the tomograph built out of scintillator
strips, and (ii) the tomograph built out of the scintillator plates. The
application of the fast scintillators will enable to take advantage of the
difference between time of the registration of the annihilation quanta. The
invented method will permit to use a thick layers of detector material with the
possibility of measuring the depth of the gamma quantum interaction (DOI) and
the determination of their time of flight (TOF), and will allow for increasing
the size of the diagnostic chamber without a significant increase of costs. The
method is a subject of two patent applications which are based on the
techniques used in the particle physics experiments.


title: Gravitational Radiation Detection with Laser Interferometry

abstract:
  Gravitational-wave detection has been pursued relentlessly for over 40 years.
With the imminent operation of a new generation of laser interferometers, it is
expected that detections will become a common occurrence. The research into
more ambitious detectors promises to allow the field to move beyond detection
and into the realm of precision science using gravitational radiation. In this
article, I review the state of the art for the detectors and describe an
outlook for the coming decades.

categories: gr-qc astro-ph.IM physics.ins-det physics.optics


title:
Analysis of player's in-game performance vs rating: Case study of Heroes
  of Newerth

abstract:
  We evaluate the rating system of "Heroes of Newerth" (HoN), a multiplayer
online action role-playing game, by using statistical analysis and comparison
of a player's in-game performance metrics and the player rating assigned by the
rating system. The datasets for the analysis have been extracted from the web
sites that record the players' ratings and a number of empirical metrics.
Results suggest that the HoN's Matchmaking rating algorithm, while generally
capturing the skill level of the player well, also has weaknesses, which have
been exploited by players to achieve a higher placement on the ranking ladder
than deserved by actual skill. In addition, we also illustrate the effects of
the choice of the business model (from pay-to-play to free-to-play) on player
population.

categories: physics.soc-ph cs.SI physics.data-an physics.pop-ph


title:
Probing kinematics and fate of the Universe with linearly time-varying
  deceleration parameter

abstract:
  The parametrizations $q=q_0+q_1 z$ and $q=q_0+q_1 (1-a/a_0)$
(Chevallier-Polarski-Linder parametrization) of deceleration parameter, which
are linear in cosmic redshift $z$ and scale factor $a$, have been frequently
utilized in the literature to study kinematics of Universe. In this paper, we
follow a strategy that leads to these two well known parametrizations of
deceleration parameter as well as an additional new parametrization
$q=q_0+q_1(1-t/t_0)$, which is linear in cosmic time $t$. We study the features
of this linearly time-varying deceleration parameter in contrast with the other
two linear parametrizations. We investigate in detail the kinematics of the
Universe by confronting the three models with the latest observational data. We
further study the dynamics of the Universe by considering the linearly
time-varying deceleration parameter model in comparison with the standard
$\Lambda$CDM model. We also discuss future of the Universe in the context of
the models under consideration.


title: A small cosmological constant due to non-perturbative quantum effects

abstract:
  We propose that the expectation value of the stress energy tensor of the
Standard Model should be given by $< T_{\mu \nu} > = \rho_\vac \eta_{\mu\nu}$,
with a vacuum energy $\rho_\vac$ that differs from the usual "dimensional
analysis" result by an exponentially small factor associated with
non-perturbative effects. We substantiate our proposal by a rigorous analysis
of a toy model, namely the 2-dimensional Gross-Neveu model. In particular, we
address, within this model, the key question of the renormalization ambiguities
affecting the calculation. The stress energy operator is constructed concretely
via the operator-product-expansion. The non-perturbative factor in the vacuum
energy is seen as a consequence of the facts that a) the OPE-coefficients have
an analytic dependence on $g$, b) the vacuum correlations have a non-analytic
(=non-perturbative) dependence on $g$, which we propose to be a generic feature
of QFT. Extrapolating our result from the Gross-Neveu model to the Standard
Model, one would expect to find $\rho_\vac ~ \Lambda^4 \e^{-O(1)/g^2}$, where
$\Lambda$ is an energy scale such as $\Lambda = M_{H}$, and $g$ is a gauge
coupling such as $g^2/4\pi = \alpha_{EW}$. The exponentially small factor due
to non-perturbative effects could explain the "unnatural" smallness of this
quantity.


title: Coexistence of phase transitions and hysteresis near BEC

abstract:
  Multiple phases occurring in a Bose gas with finite-range interaction are
investigated. In the vicinity of the onset of Bose-Einstein condensation (BEC)
the chemical potential and the pressure show a van-der-Waals like behavior
indicating a first-order phase transition although there is no long-range
attraction. Furthermore the equation of state becomes multivalued near the BEC
transition. For a Hartree-Fock or Popov (Hartree-Fock-Bogoliubov) approximation
such a multivalued region can be avoided by the Maxwell construction. For
sufficiently weak interaction the multivalued region can also be removed using
a many-body \mbox{T-matrix} approximation. However, for strong interactions
there remains a multivalued region even for the \mbox{T-matrix} approximation
and after the Maxwell construction, what is interpreted as a density
hysteresis. This unified treatment of normal and condensed phases becomes
possible due to the recently found scheme to eliminate self-interaction in the
\mbox{T-matrix} approximation, which allows to calculate properties below and
above the critical temperature.


title: On a sharp estimate for Hankel operators and Putnam's inequality

abstract:
  We obtain a sharp norm estimate for Hankel operators with anti-analytic
symbol for weighted Bergman spaces. For the classical Bergman space, the
estimate improves the corresponding classical Putnam inequality for commutators
of Toeplitz operators with analytic symbol by a factor of $1/2$, answering a
recent conjecture by Bell, Ferguson and Lundberg. As an application, this
yields a new proof of the de St. Venant inequality, which relates the torsional
rigidity of a domain with its area.


title:
Extension of many-electron theory and approximate density functionals to
  fractional charges and fractional spins

abstract:
  The exact conditions for density functionals and density matrix functionals
in terms of fractional charges and fractional spins are known, and their
violation in commonly used functionals has been shown to be the root of many
major failures in practical applications. However, approximate functionals are
not normally expressed in terms of the fractional variables. Here we develop a
general framework for extending approximate density functionals and
many-electron theory to fractional-charge and fractional-spin systems. Our
development allows for the fractional extension of any approximate theory that
is a functional of $G^{0}$, the one-electron Green's function of the
non-interacting reference system. The extension to fractional charge and
fractional spin systems is based on the ensemble average of the basic variable,
$G^{0}$. We demonstrate the fractional extension for the following theories:
(1) any explicit functional of the one-electron density, such as the LDA and
GGA; (2) any explicit functional of the one-electron density matrix of the
non-interacting reference system, such as the exact exchange functional and
hybrid functionals; (3) many-body perturbation theory; and (4) random-phase
approximations. A general rule for such an extension has also been derived
through scaling the orbitals and should be useful for functionals where the
link to the Green's function is not obvious. The development thus enables the
examination of approximate theories against known exact conditions on the
fractional variables and the analysis of their failures in chemical and
physical applications in terms of violations of exact conditions of the energy
functionals. The present work should facilitate the calculation of chemical
potentials and fundamental band gaps with approximate functionals and
many-electron theories through the energy derivatives with respect to the
fractional charge.


title:
Combining particle acceleration and coronal heating via data-constrained
  calculations of nanoflares in coronal loops

abstract:
  We model nanoflare heating of extrapolated active-region coronal loops via
the acceleration of electrons and protons in Harris-type current sheets. The
kinetic energy of the accelerated particles is estimated using semi-analytical
and test-particle-tracing approaches. Vector magnetograms and photospheric
Doppler velocity maps of NOAA active region 09114, recorded by the Imaging
Vector Magnetograph (IVM), were used for this analysis. A current-free field
extrapolation of the active-region corona was first constructed. The
corresponding Poynting fluxes at the footpoints of 5000 extrapolated coronal
loops were then calculated. Assuming that reconnecting current sheets develop
along these loops, we utilized previous results to estimate the kinetic-energy
gain of the accelerated particles and we related this energy to nanoflare
heating and macroscopic loop characteristics. Kinetic energies of 0.1 to 8 keV
(for electrons) and 0.3 to 470 keV (for protons) were found to cause heating
rates ranging from $10^{-6}$ to 1 $\mathrm{erg\, s^{-1} cm^{-3}}$. Hydrodynamic
simulations show that such heating rates can sustain plasma in coronal
conditions inside the loops and generate plasma thermal distributions which are
consistent with active region observations. We concluded the analysis by
computing the form of X-ray spectra generated by the accelerated electrons
using the thick target approach that were found to be in agreement with
observed X-ray spectra, thus supporting the plausibility of our
nanoflare-heating scenario.


title: Discrete helicoidal states in chiral magnetic thin films

abstract:
  Magnetometry and magnetoresistance measurements in MnSi thin films and
rigorous analytical solutions of the micromagnetic equations show that the
field-induced unwinding of confined helicoids occurs via discrete steps. A
comparison between the magnetometry data and theoretical results shows that
finite size effects confine the wavelength and lead to a quantization of the
number of turns in the helicoid. We demonstrate a prototypical spintronic
device where the magnetic field can push or pull individual turns into a
magnetic spring that can be read by electrical means.


title:
Iron abundance correlations and an occurrence distribution discrepancy
  from ongoing planet migration

abstract:
  Whether the higher occurrence of giant planets being hosted by metal-rich
versus metal-poor stars results from formation or from "pollution" has been a
question of intense debate. We present new patterns that emerge when
planet/star systems are separated by stellar [Fe/H], and when systems with
stellar companions are separated out. These differences can best be explained
if the onset of high eccentricity planet migration is also a time when planet
are sent into merge with the star. Planet migration into the star is likely a
complementary explanation to the view that systems with higher initial iron
abundance form more planets, and that more crowded planets are more likely to
scatter into eccentric orbits. Planets of iron-rich single stars have
eccentricity distributions that are higher than planets of iron-poor single
stars (where "rich" and "poor" are stars whose [Fe/H] is above and below solar,
respectively). Stars with planets that have a stellar companion comprise a
third population of systems in which the stars are preferentially iron-rich. We
describe new patterns that are best explained by eccentric planet migration
being associated with other planets migrating into the star. Though medium
planets are more numerous than giant planets at periods greater than three
days, giant planets are more numerous than medium planets at the shortest
periods. Since giant planets migrate into the star faster, we show this as
evidence of giant planet migration. Planet migration into the star is certain
to be an important part of planetary system evolution.


title: Regularity Properties for Sparse Regression

abstract:
  Statistical and machine learning theory has developed several conditions
ensuring that popular estimators such as the Lasso or the Dantzig selector
perform well in high-dimensional sparse regression, including the restricted
eigenvalue, compatibility, and $\ell_q$ sensitivity properties. However, some
of the central aspects of these conditions are not well understood. For
instance, it is unknown if these conditions can be checked efficiently on any
given data set. This is problematic, because they are at the core of the theory
of sparse regression.
  Here we provide a rigorous proof that these conditions are NP-hard to check.
This shows that the conditions are computationally infeasible to verify, and
raises some questions about their practical applications.
  However, by taking an average-case perspective instead of the worst-case view
of NP-hardness, we show that a particular condition, $\ell_q$ sensitivity, has
certain desirable properties. This condition is weaker and more general than
the others. We show that it holds with high probability in models where the
parent population is well behaved, and that it is robust to certain data
processing steps. These results are desirable, as they provide guidance about
when the condition, and more generally the theory of sparse regression, may be
relevant in the analysis of high-dimensional correlated observational data.


title: Design, Calibration, and Performance of the MINERvA Detector

abstract:
  The MINERvA experiment is designed to perform precision studies of
neutrino-nucleus scattering using $\nu_\mu$ and ${\bar\nu}_\mu$ neutrinos
incident at 1-20 GeV in the NuMI beam at Fermilab. This article presents a
detailed description of the \minerva detector and describes the {\em ex situ}
and {\em in situ} techniques employed to characterize the detector and monitor
its performance. The detector is comprised of a finely-segmented
scintillator-based inner tracking region surrounded by electromagnetic and
hadronic sampling calorimetry. The upstream portion of the detector includes
planes of graphite, iron and lead interleaved between tracking planes to
facilitate the study of nuclear effects in neutrino interactions. Observations
concerning the detector response over sustained periods of running are
reported. The detector design and methods of operation have relevance to future
neutrino experiments in which segmented scintillator tracking is utilized.


title: The forbidden number of a knot

abstract:
  Every classical or virtual knot is equivalent to the unknot via a sequence of
extended Reidemeister moves and the so-called forbidden moves. The minimum
number of forbidden moves necessary to unknot a given knot is an invariant we
call the {\it forbidden number}. We relate the forbidden number to several
known invariants, and calculate bounds for some classes of virtual knots.


title: Action principle for continuous quantum measurement

abstract:
  We present a stochastic path integral formalism for continuous quantum
measurement that enables the analysis of rare events using action methods. By
doubling the quantum state space to a canonical phase space, we can write the
joint probability density function of measurement outcomes and quantum state
trajectories as a phase space path integral. Extremizing this action produces
the most-likely paths with boundary conditions defined by preselected and
postselected states as solutions to a set of ordinary differential equations.
As an application, we analyze continuous qubit measurement in detail and
examine the structure of a quantum jump in the Zeno measurement regime.


title: HFiTT - Higgs Factory in Tevatron Tunnel

abstract:
  This paper proposes a Higgs factory located in the Tevatron tunnel. It is
based on a photon collider by using a recirculating e- linac and fiber laser
technology. The design goal is 10,000 Higgs per year.


title: A computable framework for Loop Quantum Gravity

abstract:
  We present a non-perturbative quantization of general relativity coupled to
dust and other matter fields. The dust provides a natural time variable,
leading to a physical Hamiltonian with spatial diffeomorphism symmetry. The
methods of loop quantum gravity applied to this model lead to a physical
Hilbert space and Hamiltonian. This provides a framework for physical
calculations in the theory.


title:
Theoretical prediction and spectroscopic fingerprints of an orbital
  transition in CeCu2Si2

abstract:
  We show that the heavy-fermion compound CeCu2Si2 undergoes a transition
between two regimes dominated by different crystal-field states. At low
pressure P and low temperature T the Ce 4f electron resides in the atomic
crystal-field ground state, while at high P or T the electron occupancy and
spectral weight is transferred to an excited crystal-field level that
hybridizes more strongly with itinerant states. These findings result from
first-principles dynamical-mean-field-theory calculations. We predict
experimental signatures of this orbital transition in X-ray spectroscopy. The
corresponding fluctuations may be responsible for the second high-pressure
superconducting dome observed in this and similar materials.


title:
Research talk: On the Classification of Generalized Cartan Matrices of
  Rank 3

abstract:
  In this talk we describe very briefly how Gritsenko and Nikulin classified in
\cite{3} the generalised Cartan matrices of rank 3, of elliptic type (so they
have the generalised lattice Weyl vector), which are twisted to symmetric
generalised Cartan matrices. We then introduce a conjecture on this
classification and propose an algorithm for attacking it. The author would like
to thank prof. V.V. Nikulin for giving him the opportunity to study this
subject.


title: Two-loop virtual corrections to Higgs pair production

abstract:
  We present the two-loop virtual corrections to Standard Model Higgs boson
pair production via gluon fusion $gg\to HH$ in the heavy top quark limit. Based
on this result, we evaluate the corresponding cross section at the LHC at 14
TeV in the next-to-next-to-leading order soft-virtual approximation. We find an
inclusive K-factor of about 2.4, resulting in an increase close to 23% with
respect to the previous available calculation at next-to-leading order. As
expected, we observe a considerable reduction in the renormalization and
factorization scale dependence.


title: Quantum jump approach for work and dissipation in a two-level system

abstract:
  We apply the quantum jump approach to address the statistics of work in a
driven two-level system coupled to a heat bath. We demonstrate how this
question can be analyzed by counting photons absorbed and emitted by the
environment in repeated experiments. We find that the common non-equilibrium
fluctuation relations are satisfied identically. The usual
fluctuation-dissipation theorem for linear response applies for weak
dissipation and/or weak drive. We point out qualitative differences between the
classical and quantum regimes.


title: The Ptolemaean Inequality in H--type groups

abstract:
  We prove the Ptolemaean Inequality and the Theorem of Ptolemaeus in the
setting of $H$--type groups of Iwasawa--type.


title: A Note on the Unsolvability of the Weighted Region Shortest Path Problem

abstract:
  Let S be a subdivision of the plane into polygonal regions, where each region
has an associated positive weight. The weighted region shortest path problem is
to determine a shortest path in S between two points s, t in R^2, where the
distances are measured according to the weighted Euclidean metric-the length of
a path is defined to be the weighted sum of (Euclidean) lengths of the
sub-paths within each region. We show that this problem cannot be solved in the
Algebraic Computation Model over the Rational Numbers (ACMQ). In the ACMQ, one
can compute exactly any number that can be obtained from the rationals Q by
applying a finite number of operations from +, -, \times, \div, \sqrt[k]{}, for
any integer k >= 2. Our proof uses Galois theory and is based on Bajaj's
technique.


title: The wave-function description of the electromagnetic field

abstract:
  For an arbitrary electromagnetic field, we define a prepotential $S$, which
is a complex-valued function of spacetime. The prepotential is a modification
of the two scalar potential functions introduced by E. T. Whittaker. The
prepotential is Lorentz covariant under a spin half representation. For a
moving charge and any observer, we obtain a complex dimensionless scalar. The
prepotential is a function of this dimensionless scalar. The prepotential $S$
of an arbitrary electromagnetic field is described as an integral over the
charges generating the field. The Faraday vector at each point may be derived
from $S$ by a convolution of the differential operator with the alpha matrices
of Dirac. Some explicit examples will be calculated. We also present the
Maxwell equations for the prepotential.


title:
A note on the growth factor in Gaussian elimination for generalized
  Higham matrices

abstract:
  The Higham matrix is a complex symmetric matrix A=B+iC, where both B and C
are real, symmetric and positive definite and $\mathrm{i}=\sqrt{-1}$ is the
imaginary unit. For any Higham matrix A, Ikramov et al. showed that the growth
factor in Gaussian elimination is less than 3. In this paper, based on the
previous results, a new bound of the growth factor is obtained by using the
maximum of the condition numbers of matrixes B and C for the generalized Higham
matrix A, which strengthens this bound to 2 and proves the Higham's conjecture.


title: An investigation of Lorentz transformation

abstract:
  A new method of derivation of Lorentz Transformation (LT) is given based on
both axioms of special relativity (SR) and physical intuitions. The essence of
the transformation is established and the crucial role played by the
presumptions is presented for clarification. I consider the most general form
of transformations between two sets of events in two inertial reference frames
and use the most basic properties expected from such a transformation together
with the principle of the constancy of the velocity of light to derive LT. The
method is very simple, succinct and useful for students trying a better
understanding of the subject.


title: The strong global dimension of piecewise hereditary algebras

abstract:
  Let T be a tilting object in a triangulated category equivalent to the
bounded derived category of a hereditary abelian category with finite
dimensional homomorphism spaces and split idempotents. This text investigates
the strong global dimension, in the sense of Ringel, of the endomorphism
algebra of T. This invariant is expressed using the infimum of the lengths of
the sequences of tilting objects successively related by tilting mutations and
where the last term is T and the endomorphism algebra of the first term is
quasi-tilted. It is also expressed in terms of the hereditary abelian
generating subcategories of the triangulated category.


title:
On quantitative bounds on eigenvalues of a complex perturbation of a
  Dirac operator

abstract:
  We prove a Lieb-Thirring type inequality for a complex perturbation of a
d-dimensional massive Dirac operator $D_m, m\geq 0$ whose spectrum is $]-\infty
, -m]\cup[m , +\infty[$. The difficulty of the study is that the unperturbed
operator is not bounded from below in this case, and, to overcome it, we use
the methods of complex function theory. The methods of the article also give
similar results for complex perturbations of the Klein-Gordon operator.


title:
Bullet Retarding Forces in Ballistic Gelatin by Analysis of High Speed
  Video

abstract:
  Though three distinct wounding mechanisms (permanent cavity, temporary
cavity, and ballistic pressure wave) are described in the wound ballistics
literature, they all have their physical origin in the retarding force between
bullet and tissue as the bullet penetrates. If the bullet path is the same,
larger retarding forces produce larger wounding effects and a greater
probability of rapid incapacitation. By Newton's third law, the force of the
bullet on the tissue is equal in magnitude and opposite in direction to the
force of the tissue on the bullet. For bullets penetrating with constant mass,
the retarding force on the bullet can be determined by frame by frame analysis
of high speed video of the bullet penetrating a suitable tissue simulant such
as calibrated 10% ballistic gelatin. Here the technique is demonstrated with
9mm NATO bullets, 32 cm long blocks of gelatin, and a high speed video camera
operating at 20,000 frames per second. It is found that different 9mm NATO
bullets have a wide variety of potential for wounding and rapid incapacitation.
This technique also determines the energy transfer in the first 15 cm and/or
first 30 cm of tissue, which are important parameters in estimating the
probability of rapid incapacitation in some of the ARL/BRL models. This method
predicts that some 9mm bullets have a much higher probability of rapid
incapacitation than others and the rank ordering of bullet effectiveness is in
agreement with other studies.


title:
Wireless Device-to-Device Caching Networks: Basic Principles and System
  Performance

abstract:
  As wireless video transmission is the fastest-growing form of data traffic,
methods for spectrally efficient video on-demand wireless streaming are
essential to service providers and users alike. A key property of video
on-demand is the asynchronous content reuse, such that a few dominant videos
account for a large part of the traffic, but are viewed by users at different
times. Caching of content on devices in conjunction with D2D communications
allows to exploit this property, and provide a network throughput that is
significantly in excess of both the conventional approach of unicasting from
the base station and the traditional D2D networks for regular data traffic.
This paper presents in a semi-tutorial concise form some recent results on the
throughput scaling laws of wireless networks with caching and asynchronous
content reuse, contrasting the D2D approach with a competing approach based on
combinatorial cache design and network coded transmission from the base station
(BS) only, referred to as coded multicasting. Interestingly, the spatial reuse
gain of the former and the coded multicasting gain of the latter yield, somehow
surprisingly, the same near-optimal throughput behavior in the relevant regime
where the number of video files in the library is smaller than the number of
streaming users. Based on our recent theoretical results, we propose a holistic
D2D system design that incorporates traditional microwave (2 GHz) as well as
millimeter-wave D2D links; the direct connections to the base station can be
used to provide those rare video requests that cannot be found in local caches.
We provide extensive simulations under a variety of system settings, and
compare our scheme with other existing schemes by the BS. We show that, despite
the similar behavior of the scaling laws, the proposed D2D approach offers very
significant throughput gains with respect to the BS-only schemes.


title:
Period and index, symbol lengths, and generic splittings in Galois
  cohomology

abstract:
  We use constructions of versal cohomology classes based on a new notion of
"presentable functors," to describe a relationship between the problems of
bounding symbol length in cohomology and of finding the minimal degree of a
splitting field. The constructions involved are then also used to describe
generic splitting varieties for degree 2 cohomology with coefficients in a
commutative algebraic group of multiplicative type.


title: Giant Secondary Grain Growth in Cu Films on Sapphire

abstract:
  Single crystal metal films on insulating substrates are attractive for
microelectronics and other applications, but they are difficult to achieve on
macroscopic length scales. The conventional approach to obtaining such films is
epitaxial growth at high temperature using slow deposition in ultrahigh vacuum
conditions. Here we describe a different approach: sputter deposition at modest
temperatures followed by annealing to induce secondary grain growth. We show
that polycrystalline as-deposited Cu on \alpha-Al2O3(0001) can be transformed
into Cu(111) with centimeter-sized grains. Employing optical microscopy, x-ray
diffraction, and electron backscatter diffraction to characterize the films
before and after annealing, we find a particular as-deposited grain structure
that promotes the growth of giant grains upon annealing. To demonstrate one
potential application of such films, we grow graphene by chemical vapor
deposition on wafers of annealed Cu and obtain epitaxial graphene grains of 0.2
mm diameter.


title:
Approach to Equilibrium of a Body Colliding Specularly and Diffusely
  with a Sea of Particles

abstract:
  We consider a rigid body acted upon by two forces, a constant force and the
collective force of interaction with a continuum of particles. We assume that
some of the particles that collide with the body reflect elastically
(specularly), while others reflect probabilistically with some probablility
distribution K. We find that the rate of approach of the body to equilibrium is
O(t^{-3-p}) in three dimensions where p can take any value from 0 to 2,
depending on K.


title:
Pricing bonds with optional sinking feature using Markov Decision
  Processes

abstract:
  An efficient method to price bonds with optional sinking feature is
presented. Such instruments equip their issuer with the option (but not the
obligation) to redeem parts of the notional prior to maturity, therefore the
future cash flows are random. In a one-factor model for the issuer's default
intensity we show that the pricing algorithm can be formulated as a Markov
Decision Process, which is both accurate and quick. The method is demonstrated
using a 1.5-factor credit-equity model which defines the default intensity in a
reciprocal relationship to the issuer's stock price process, termed
jump-to-default extended model with constant elasticity of variance (JDCEV).


title:
Simulation of two-flavors symmetry-locking phases in ultracold fermionic
  mixtures

abstract:
  We describe an ultracold fermionic set-up where it is possible to synthesize
a superfluid phase with symmetry obtained by locking independent invariance
groups of the normal state. In this phase, named two-flavors symmetry-locking
phase (TFSL), non-Abelian fractional vortices with semi-integer flux and
gapless non-Abelian Goldstone modes localized on them appear. Considerations on
the possible experimental realization of the TFSL are also provided.


title:
A Game Theory Interpretation for Multiple Access in Cognitive Radio
  Networks with Random Number of Secondary Users

abstract:
  In this paper a new multiple access algorithm for cognitive radio networks
based on game theory is presented. We address the problem of a multiple access
system where the number of users and their types are unknown. In order to do
this, the framework is modelled as a non-cooperative Poisson game in which all
the players are unaware of the total number of devices participating
(population uncertainty). We propose a scheme where failed attempts to transmit
(collisions) are penalized. In terms of this, we calculate the optimum
penalization in mixed strategies. The proposed scheme conveys to a Nash
equilibrium where a maximum in the possible throughput is achieved.


title: Sensitive Chiral Analysis via Microwave Three-wave Mixing

abstract:
  We demonstrate chirality-induced three-wave mixing in the microwave regime,
using rotational transitions in cold gas-phase samples of 1,2-propanediol and
1,3-butanediol. We show that bulk three-wave mixing, which can only be realized
in a chiral environment, provides a sensitive, species selective probe of
enantiomeric excess and is applicable to a broad class of molecules. The doubly
resonant condition provides simultaneous identification of species and of
handedness, which should allow sensitive chiral analysis even within a complex
mixture.


title: Generalized Lorentz Transformations

abstract:
  Generalized Lorentz transformations with modified velocity parameter are
considered. Lorentz transformations depending on the mass of the observer are
suggested.The modified formula for the addition of velocities remarkably
preserves the constancy of the velocity of light for all observers. The Doppler
red shift is affected and can provide a test of such generalisations.


title: Chirp-wave Expansion of the Electron Wavefunctions in Atoms

abstract:
  The description of the electron wavefunctions in atoms is generalized to the
fractional Fourier series. This method introduces a continuous and infinite
number of chirp basis sets with linear variation of the frequency to expand the
wavefunctions, in which plane-waves are a special case. The chirp
characteristics of each basis set can be adjusted through a single parameter.
Thus, the basis set cutoff can be optimized variationally. The approach is
tested with the expansion of the electron wavefunctions in atoms, and it is
shown that chirp basis sets substantially improve the convergence in the
description of the electron density. We have found that the natural
oscillations of the electron core states are efficiently described in
chirp-waves.


title:
The Generation of Random Variates From a Relativistic Maxwellian
  Distribution

abstract:
  A procedure for generating random variates from a relativistic Maxwellian
distribution with arbitrary temperature and drift velocity is presented. The
algorithm is based on the rejection method and can be used to initialize
particle velocities in kinetic simulations of plasmas and gases.


title: A Ramsey-type result for geometric l-hypergraphs

abstract:
  Let n \geq l \geq 2 and q \geq 2. We consider the minimum N such that
whenever we have N points in the plane in general position and the l-subsets of
these points are colored with q colors, there is a subset S of n points all of
whose l-subsets have the same color and furthermore S is in convex position.
This combines two classical areas of intense study over the last 75 years: the
Ramsey problem for hypergraphs and the Erd\H os-Szekeres theorem on convex
configurations in the plane. For the special case l = 2, we establish a single
exponential bound on the minimum N, such that every complete $N$-vertex
geometric graph whose edges are colored with q colors, yields a monochromatic
convex geometric graph on n vertices.
  For fixed l \geq 2 and q \geq 4, our results determine the correct
exponential tower growth rate for N as a function of n, similar to the usual
hypergraph Ramsey problem, even though we require our monochromatic set to be
in convex position. Our results also apply to the case of l=3 and q=2 by using
a geometric variation of the stepping up lemma of Erd\H os and Hajnal. This is
in contrast to the fact that the upper and lower bounds for the usual 3-uniform
hypergraph Ramsey problem for two colors differ by one exponential in the
tower.


title: Stochastic Parity Games on Lossy Channel Systems

abstract:
  We give an algorithm for solving stochastic parity games with almost-sure
winning conditions on lossy channel systems, for the case where the players are
restricted to finite-memory strategies. First, we describe a general framework,
where we consider the class of 2.5-player games with almost-sure parity winning
conditions on possibly infinite game graphs, assuming that the game contains a
finite attractor. An attractor is a set of states (not necessarily absorbing)
that is almost surely re-visited regardless of the players' decisions. We
present a scheme that characterizes the set of winning states for each player.
Then, we instantiate this scheme to obtain an algorithm for stochastic game
lossy channel systems.


title: On Radial Colorings of Annuli

abstract:
  We consider the chromatic numbers of unit-distance graphs of various annuli.
In particular, we consider radial colorings, which are "nice" colorings, and
completely determine the radial chromatic numbers of various annuli.


title:
Determining biholomorphic type of a manifold using combinatorial and
  algebraic structures

abstract:
  We settle two problems of reconstructing a biholomorphic type of a manifold.
In the first problem we use graphs associated to Riemann surfaces of a
particular class. In the second one we use the semigroup structure of analytic
endomorphisms of domains in $\C^n$.


title:
A Master Equation for Gravitational Decoherence: Probing the Textures of
  Spacetime

abstract:
  We give a first principles derivation of a master equation for the evolution
of a quantum matter field in a linearly perturbed Minkowski spacetime, based
solely on quantum field theory and general relativity. We make no additional
assumptions nor introduce extra ingredients, as is often done in alternative
quantum theories. When the quantum matter field is projected to a one-particle
state, the master equation for a non-relativistic quantum particle in a weak
gravitational field predicts decoherence in the energy basis, in contrast to
most existing theories of gravitational decoherence. We point out the gauge
nature of time and space reparameterizations in matter-gravity couplings, and
warn that `intrinsic' decoherence or alternative quantum theories invoking
stochastic dynamics arising from temporal or spatial fluctuations violate this
fundamental symmetry of classical general relativity. Interestingly we find
that the decoherence rate depends on extra parameters other than the Planck
scale, an important feature of gravitational decoherence. This is similar to
the dependence of the decoherence rate of a quantum Brownian particle to the
temperature and spectral density of the environment it interacts with. The
corresponding features when gravity acts as an environment in decohering
quantum objects are what we call the `textures' of spacetime. We point out the
marked difference between the case when gravity is represented as a background
spacetime versus the case when gravity acts like a thermodynamic bath to
quantum particles. This points to the possibility of using gravitational
decoherence measurements to discern whether gravity is intrinsically elemental
or emergent.


title:
A Semiparametric Estimator for Long-Range Dependent Multivariate
  Processes

abstract:
  In this paper we propose a generalization of a class of Gaussian
Semiparametric Estimators (GSE) of the fractional differencing parameter for
long-range dependent multivariate time series. We generalize a known GSE-type
estimator by introducing some modifications at the objective function level
regarding the process' spectral density matrix estimator. We study large sample
properties of the estimator without assuming Gaussianity as well as hypothesis
testing. The class of models considered here satisfies simple conditions on the
spectral density function, restricted to a small neighborhood of the zero
frequency. This includes, but is not limited to, the class of VARFIMA models. A
simulation study to assess the finite sample properties of the proposed
estimator is presented and supports its competitiveness. We also present an
empirical application to an exchange rate data.


title: Boxicity and Cubicity of Product Graphs

abstract:
  The 'boxicity' ('cubicity') of a graph G is the minimum natural number k such
that G can be represented as an intersection graph of axis-parallel rectangular
boxes (axis-parallel unit cubes) in $R^k$. In this article, we give estimates
on the boxicity and the cubicity of Cartesian, strong and direct products of
graphs in terms of invariants of the component graphs. In particular, we study
the growth, as a function of $d$, of the boxicity and the cubicity of the
$d$-th power of a graph with respect to the three products. Among others, we
show a surprising result that the boxicity and the cubicity of the $d$-th
Cartesian power of any given finite graph is in $O(\log d / \log\log d)$ and
$\theta(d / \log d)$, respectively. On the other hand, we show that there
cannot exist any sublinear bound on the growth of the boxicity of powers of a
general graph with respect to strong and direct products.


title: Countable subgroups of Euclidean Space

abstract:
  In his PhD Thesis Konstantinos Beros proved a number of results about
compactly generated subgroups of Polish groups. Such a group is K-sigma - the
countable union of compact sets. He notes that the group of rationals under
addition with the discrete topology is an example of a Polish group which is
K-sigma (since it is countable) but not compactly generated. Beros showed that
for any Polish group G, every K-sigma subgroup of G is compactly generated iff
every countable subgroup of G is compactly generated. Beros showed that any
K-sigma subgroup of Z^omega (infinite product of the integers) is compactly
generated and more generally, for any Polish group G, if every countable
subgroup of G is finitely generated, then every countable subgroup of G^omega
is compactly generated. In unpublished work Beros asked whether finitely
generated may be replaced by compactly generated in his theorem. He conjectured
that the reals R under addition might be an example such that every countable
subgroup of R is compactly generated but not every countable subgroup of
R^omega is compactly generated. We prove that this is not true. The general
question remains open. In the course of our proof we came up with some
interesting countable subgroups. We show that there is a dense subgroup of the
plane which meets every line in a discrete set. Furthermore, for each n there
is a dense subgroup of Euclidean space R^n which meets every (n-1)-dimensional
subspace in a discrete set. Similarly there is a dense subgroup of R^omega
which meets every finite dimensional subspace of R^omega in a discrete set.


title: Lognormal Infection Times of Online Information Spread

abstract:
  The infection times of individuals in online information spread such as the
inter-arrival time of Twitter messages or the propagation time of news stories
on a social media site can be explained through a convolution of lognormally
distributed observation and reaction times of the individual participants.
Experimental measurements support the lognormal shape of the individual
contributing processes, and have resemblance to previously reported lognormal
distributions of human behavior and contagious processes.


title: Hang With Your Buddies to Resist Intersection Attacks

abstract:
  Some anonymity schemes might in principle protect users from pervasive
network surveillance - but only if all messages are independent and unlinkable.
Users in practice often need pseudonymity - sending messages intentionally
linkable to each other but not to the sender - but pseudonymity in dynamic
networks exposes users to intersection attacks. We present Buddies, the first
systematic design for intersection attack resistance in practical anonymity
systems. Buddies groups users dynamically into buddy sets, controlling message
transmission to make buddies within a set behaviorally indistinguishable under
traffic analysis. To manage the inevitable tradeoffs between anonymity
guarantees and communication responsiveness, Buddies enables users to select
independent attack mitigation policies for each pseudonym. Using trace-based
simulations and a working prototype, we find that Buddies can guarantee
non-trivial anonymity set sizes in realistic chat/microblogging scenarios, for
both short-lived and long-lived pseudonyms.


title:
Status of Higher Order Mode Beam Position Monitors in 3.9 GHz
  Superconducting Accelerating Cavities at FLASH

abstract:
  Higher order mode (HOM) beam position monitors (BPM) are being developed for
the 3.9 GHz third harmonic superconducting accelerating cavities at FLASH. The
transverse beam position in a cavity can be determined utilizing beam-excited
HOMs based on dipole components. The existing couplers used for HOM suppression
provide necessary signals. The diagnostics principle is similar to a cavity
BPM, but requires no additional vacuum instruments on the linac. The challenges
of HOM-BPM for 3.9 GHz cavities lie in the dense HOM spectrum arising from the
coupling of the majority HOMs amongst the four cavities in the cryo-module
ACC39. HOMs with particularly promising diagnostics features were evaluated
using a spectrum analyzer and custom-built test electronics with various data
analysis techniques, data reduction was focused on. After careful theoretical
and experimental assessment of the HOM spectrum, multi-cavity modes in the
region of 5 GHz were chosen to provide a global position over the complete
module with superior resolution (~20 um) while trapped modes in the 9 GHz
region provide local position in each cavity with comparable resolution (~50
um). A similar HOM-BPM system has been planned for the European XFEL 3.9 GHz
module which encompasses eight cavities. This paper reviews both the current
status and the future prospects of HOM-BPMs in 3.9 GHz cavities at FLASH.


title: Risk Measure Estimation On Fiegarch Processes

abstract:
  We consider the Fractionally Integrated Exponential Generalized
Autoregressive Conditional Heteroskedasticity process, denoted by
FIEGARCH(p,d,q), introduced by Bollerslev and Mikkelsen (1996). We present a
simulated study regarding the estimation of the risk measure $VaR_p$ on
FIEGARCH processes. We consider the distribution function of the portfolio
log-returns (univariate case) and the multivariate distribution function of the
risk-factor changes (multivariate case). We also compare the performance of the
risk measures $VaR_p$, $ES_p$ and MaxLoss for a portfolio composed by stocks of
four Brazilian companies.


title: Markov two-components processes

abstract:
  We propose Markov two-components processes (M2CP) as a probabilistic model of
asynchronous systems based on the trace semantics for concurrency. Considering
an asynchronous system distributed over two sites, we introduce concepts and
tools to manipulate random trajectories in an asynchronous framework: stopping
times, an Asynchronous Strong Markov property, recurrent and transient states
and irreducible components of asynchronous probabilistic processes. The
asynchrony assumption implies that there is no global totally ordered clock
ruling the system. Instead, time appears as partially ordered and random. We
construct and characterize M2CP through a finite family of transition matrices.
M2CP have a local independence property that guarantees that local components
are independent in the probabilistic sense, conditionally to their
synchronization constraints. A synchronization product of two Markov chains is
introduced, as a natural example of M2CP.


title: FOLE: The First-order Logical Environment

abstract:
  This paper describes the first-order logical environment FOLE. Institutions
in general, and logical environments in particular, give equivalent
heterogeneous and homogeneous representations for logical systems. As such,
they offer a rigorous and principled approach to distributed interoperable
information systems via system consequence. Since FOLE is a particular logical
environment, this provides a rigorous and principled approach to distributed
interoperable first-order information systems. The FOLE represents the
formalism and semantics of first-order logic in a classification form. By using
an interpretation form, a companion approach defines the formalism and
semantics of first-order logical/relational database systems. In a strict
sense, the two forms have transformational passages (generalized inverses)
between one another. The classification form of first-order logic in the FOLE
corresponds to ideas discussed in the Information Flow Framework (IFF). The
FOLE representation follows a conceptual structures approach, that is
completely compatible with formal concept analysis and information flow.


title: A Uniform Version of a Finiteness Conjecture for CM Elliptic Curves

abstract:
  Let A be an abelian variety defined over a number field F. For a prime number
$\ell$, we consider the field extension of F generated by the $\ell$-powered
torsion points of A. According to a conjecture made by Rasmussen and Tamagawa,
if we require these fields to be both a pro-$\ell$ extension of
$F(\mu_{\ell^{\infty}})$ and unramified away from $\ell$, examples are quite
rare. Indeed, it is expected that for a fixed dimension and field of
definition, there exists such an abelian variety for only a finite number of
primes.
  We prove a uniform version of the conjecture in the case where the abelian
varieties are elliptic curves with complex multiplication. In addition, we
provide explicit bounds in cases where the number field has degree less than or
equal to 100.


title: Quantum Logical Structures For Identical Particles

abstract:
  In this work we discuss logical structures related to indistinguishable
particles. Most of the framework used to develop these structures was presented
in [17, 28] and in [20, 14, 15, 16]. We use these structures and constructions
to discuss possible ontologies for identical parti-cles. In other words, we use
these structures in order to characterize the logical structure of quantum
systems for the case of indistinguishable particles, and draw possible
philosoph-ical implications. We also review some proposals available in the
literature which may be considered within the framework of the quantum logical
tradition regarding the problem of indistinguishability. Besides these
discussions and constructions, we advance novel technical results, namely, a
lattice theoretical structure for identical particles for the finite
dimensional case. This kind of approach was not present in the scarcely
literature of quantum logic and indistinguishable particles.


title: A Model for Neutrinos

abstract:
  Neutrinos are the weirdest of elementary particles, nearly massless and
chiral. They oscillate between flavours, furthermore. We try to find a
rationale for this maverick behaviour.


title:
A formal framework for the study of the notion of undefined particle
  number in quantum mechanics

abstract:
  It is usually stated that quantum mechanics presents problems with the
identity of particles, the most radical position -supported by E. Schrodinger-
asserting that elementary particles are not individuals. But the subject goes
deeper, and it is even possible to obtain states with an undefined particle
number. In this work we present a set theoretical framework for the description
of undefined particle number states in quantum mechanics which provides a
precise logical meaning for this notion. This construction goes in the line of
solving a problem posed by Y. Manin, namely, to incorporate quantum mechanical
notions at the foundations of mathematics. We also show that our system is
capable of representing quantum superpositions.


title:
The Recurrent Nova T Pyx: Distance and Remnant Geometry from Light
  Echoes

abstract:
  The recurrent nova T Pyxidis (T Pyx) is well known for its small binary
separation, its unusually high luminosity in quiescence, and the spectacular
Hubble Space Telescope (HST) images of its surrounding remnant. In 2011 April,
T Pyx erupted for the first time since 1966. Here we describe HST observations
in late 2011 of a transient reflection nebula around the erupting white dwarf
(WD). Our observations of this light echo in the pre-existing remnant show that
it is dominated by a clumpy ring with a radius of about 5", and an inclination
of 30 to 40 degrees, with the eastern edge tilted toward the observer. The
delay times between the direct optical light from the central source, and the
scattering of this light from dust in several clumps with the same foreground
distance as the central source, give a distance to T Pyx of 4.8 +- 0.5 kpc.
Given past evidence from two-dimensional optical spectra that the remnant
contains a shell-like component, it must actually consist of a ring embedded
within a quasi-spherical shell. The large distance of 4.8 kpc supports the
contention that T Pyx has an extraordinarily high rate of mass transfer in
quiescence, and thus that nova explosions themselves can enhance mass loss from
a donor star, and reduce the time between eruptions in a close binary.


title:
Combining Higher-Order Resummation with Multiple NLO Calculations and
  Parton Showers in the GENEVA Monte Carlo Framework

abstract:
  We discuss the GENEVA Monte Carlo framework, which combines higher-order
resummation (NNLL) of large Sudakov logarithms with multiple
next-to-leading-order (NLO) matrix-element corrections and parton showering
(using PYTHIA8) to give a complete description at the next higher perturbative
accuracy in alpha_s at both small and large jet resolution scales. Results for
e+e- -> jets compared to LEP data and for Drell-Yan production are presented.


title: Arithmetic of abelian varieties in Artin-Schreier extensions

abstract:
  We study abelian varieties defined over function fields of curves in positive
characteristic $p$, focusing on their arithmetic within the system of
Artin-Schreier extensions. First, we prove that the $L$-function of such an
abelian variety vanishes to high order at the center point of its functional
equation under a parity condition on the conductor. Second, we develop an
Artin-Schreier variant of a construction of Berger. This yields a new class of
Jacobians over function fields for which the Birch and Swinnerton-Dyer
conjecture holds. Third, we give a formula for the rank of the Mordell-Weil
groups of these Jacobians in terms of the geometry of their fibers of bad
reduction and homomorphisms between Jacobians of auxiliary Artin-Schreier
curves. We illustrate these theorems by computing the rank for explicit
examples of Jacobians of arbitrary dimension $g$, exhibiting Jacobians with
bounded rank and others with unbounded rank in the tower of Artin-Schreier
extensions. Finally, we compute the Mordell-Weil lattices of an isotrivial
elliptic curve and a family of non-isotrivial elliptic curves. The latter
exhibits an exotic phenomenon whereby the angles between lattice vectors are
related to point counts on elliptic curves over finite fields. Our methods also
yield new results about supersingular factors of Jacobians of Artin-Schreier
curves.


title: Dark Matter and MOOCs

abstract:
  To teach the topic of Dark Matter in Galaxies to undergraduate and PhD
students is not easy, one reason being that the scientific community has not
converged yet to a generally shared knowledge. We argue that the teaching of
this topic and its subsequent scientific progress may benefit by Massive Online
and Open Courses.
  The reader of this paper can express his/her opinion on this by means of a
confidence vote at:
https://moocfellowship.org/submissions/dark-matter-in-galaxies-the-last-mystery


title:
The extragalactic background light from the measurements of the
  attenuation of high-energy gamma-ray spectrum

abstract:
  The attenuation of high-energy gamma-ray spectrum due to the
electron-positron pair production against the extragalactic background light
(EBL) provides an indirect method to measure the EBL of the universe. We use
the measurements of the absorption features of the gamma-rays from blazars as
seen by Fermi Gamma-ray Space Telescope to explore the EBL flux density and
constrain the EBL spectrum, star formation rate density (SFRD) and photon
escape fraction from galaxies out to z=6. Our results are basically consistent
with the existing determinations of the quantities. We find a larger photon
escape fraction at high redshifts, especially at z=3, compared to the result
from the recent Ly-alpha measurements. Our SFRD result is consistent with the
data from both gamma-ray burst and UV observations in 1-sigma level. However,
the average SFRD we obtain at z>~3 matches the gamma-ray data better than the
UV data. Thus our SFRD result at z>~6 favors that it is sufficiently high
enough to reionize the universe.


title: N=1 dynamics with T_N theory

abstract:
  We study the dynamics of N=1 supersymmetric systems consisting of the
strongly-coupled superconformal theory T_N, SU(N) gauge groups, and fundamental
chiral multiplets. We demonstrate that such systems exhibit familiar phenomena
such as deformation of the vacuum moduli space, appearance of the dynamical
superpotential, and Coulomb branches with N=1 Seiberg-Witten curves. The
analysis requires a rather detailed knowledge of the chiral ring of the T_N
theory, which will also be discussed at length.


title: A New Probe of Naturalness

abstract:
  Any new scalar fields that perturbatively solve the hierarchy problem by
stabilizing the Higgs mass also generate new contributions to the Higgs
field-strength renormalization, irrespective of their gauge representation.
These new contributions are physical and their magnitude can be inferred from
the requirement of quadratic divergence cancellation, hence they are directly
related to the resolution of the hierarchy problem. Upon canonically
normalizing the Higgs field these new contributions lead to modifications of
Higgs couplings which are typically great enough that the hierarchy problem and
the concept of electroweak naturalness can be probed thoroughly within a
precision Higgs program. Specifically, at a Linear Collider this can be
achieved through precision measurements of the Higgs associated production
cross-section. This would lead to indirect constraints on perturbative
solutions to the hierarchy problem in the broadest sense, even if the relevant
new fields are gauge singlets.


title: Scattering Amplitudes and Toric Geometry

abstract:
  In this paper we provide a first attempt towards a toric geometric
interpretation of scattering amplitudes. In recent investigations it has indeed
been proposed that the all-loop integrand of planar N=4 SYM can be represented
in terms of well defined finite objects called on-shell diagrams drawn on
disks. Furthermore it has been shown that the physical information of on-shell
diagrams is encoded in the geometry of auxiliary algebraic varieties called the
totally non negative Grassmannians. In this new formulation the infinite
dimensional symmetry of the theory is manifest and many results, that are quite
tricky to obtain in terms of the standard Lagrangian formulation of the theory,
are instead manifest. In this paper, elaborating on previous results, we
provide another picture of the scattering amplitudes in terms of toric
geometry. In particular we describe in detail the toric varieties associated to
an on-shell diagram, how the singularities of the amplitudes are encoded in
some subspaces of the toric variety, and how this picture maps onto the
Grassmannian description. Eventually we discuss the action of cluster
transformations on the toric varieties. The hope is to provide an alternative
description of the scattering amplitudes that could contribute in the
developing of this very interesting field of research.


title:
The Influence of Outer Solar System Architecture on the Structure and
  Evolution of the Oort Cloud

abstract:
  We study the influence of outer Solar System architecture on the structural
evolution of the Oort Cloud (OC) and the flux of Earth-crossing comets. In
particular, we seek to quantify the role of the giant planets as "planetary
protectors". To do so, we have run simulations in each of four different
planetary mass configurations to understand the significance of each of the
giant planets. Because the outer planets modify the structure of the OC
throughout its formation, we integrate each simulation over the full age of the
Solar System. Over this time, we follow the evolution of cometary orbits from
their starting point in the protoplanetary disk to their injection into the OC
to their possible re-entry into the inner planetary region. We find that the
overall structure of the OC, including the location of boundaries and the
relative number of comets in the inner and outer parts, does not change
significantly between configurations; however, as planetary mass decreases, the
trapping efficiency (TE) of comets into the OC and the flux of comets into the
observable region increases. We determine that those comets that evolve onto
Earth-crossing orbits come primarily from the inner OC but show no preference
for initial protoplanetary disk location. We also find that systems that have
at least a Saturn-mass object are effective at deflecting possible
Earth-crossing comets but the difference in flux between systems with and
without such a planet is less than an order of magnitude. We conclude by
discussing the individual roles of the planets and the implications of
incorporating more realistic planetary accretion and migration scenarios into
simulations, particularly on existing discrepancies between low TE and the mass
of the protoplanetary disk and on determining the structural boundaries of the
OC.


title:
The Stellar Mass Growth of Brightest Cluster Galaxies in the IRAC
  Shallow Cluster Survey

abstract:
  The details of the stellar mass assembly of brightest cluster galaxies (BCGs)
remain an unresolved problem in galaxy formation. We have developed a novel
approach that allows us to construct a sample of clusters that form an
evolutionary sequence, and have applied it to the Spitzer IRAC Shallow Cluster
Survey (ISCS) to examine the evolution of BCGs in progenitors of present-day
clusters with mass of (2.5-4.5)x10^{14}Msun. We follow the cluster mass growth
history extracted from a high resolution cosmological simulation, and then use
an empirical method that infers the cluster mass based on the ranking of
cluster luminosity to select high-z clusters of appropriate mass from ISCS to
be progenitors of the given set of z=0 clusters. We find that, between z=1.5
and 0.5, the BCGs have grown in stellar mass by a factor of 2.3, which is
well-matched by the predictions from a state-of-the-art semi-analytic model.
Below z=0.5 we see hints of differences in behavior between the model and
observation.


title: Pure spinor equations to lift gauged supergravity

abstract:
  We rewrite the equations for ten-dimensional supersymmetry in a way formally
identical to a necessary and sufficient G-structure system in N=2 gauged
supergravity, where all four-dimensional quantities are replaced by
combinations of pure spinors and fluxes in the internal space. This provides a
way to look for lifts of BPS solutions without having to reduce or even rewrite
the ten-dimensional action. In particular this avoids the problem of consistent
truncation, and the introduction of unphysical gravitino multiplets.


title:
Non-parametric method for measuring gas inhomogeneities from X-ray
  observations of galaxy clusters

abstract:
  We present a non-parametric method to measure inhomogeneities in the
intracluster medium (ICM) from X-ray observations of galaxy clusters. Analysing
mock Chandra X-ray observations of simulated clusters, we show that our new
method enables the accurate recovery of the 3D gas density and gas clumping
factor profiles out to large radii of galaxy clusters. We then apply this
method to Chandra X-ray observations of Abell 1835 and present the first
determination of the gas clumping factor from the X-ray cluster data. We find
that the gas clumping factor in Abell 1835 increases with radius and reaches
~2-3 at r=R_{200}. This is in good agreement with the predictions of
hydrodynamical simulations, but it is significantly below the values inferred
from recent Suzaku observations. We further show that the radially increasing
gas clumping factor causes flattening of the derived entropy profile of the ICM
and affects physical interpretation of the cluster gas structure, especially at
the large cluster-centric radii. Our new technique should be useful for
improving our understanding of the cluster structure and to advance the use of
galaxy clusters as cosmological probes, by helping to exploit rich data sets
provided by Chandra and XMM-Newton X-ray space telescopes.


title: Deep LBT/LUCI Spectroscopy of a Lyman-alpha Emitter Candidate at z ~ 7.7

abstract:
  We present deep spectroscopic observations of a Lyman-alpha emitter (LAE)
candidate at z ~ 7.7 using the infrared spectrograph LUCI on the 2 x 8.4m Large
Binocular Telescope (LBT). The candidate is the brightest among the four z ~
7.7 LAE candidates found in a narrow-band imaging survey by Krug et al. 2012.
Our spectroscopic data include a total of 7.5 hours of integration with
LBT/LUCI and are deep enough to significantly (3.2-4.9 sigma) detect the
Lyman-alpha emission line of this candidate, based on its Lyman-alpha flux 1.2
x 10^{-17} erg s^{-1} cm^{-2} estimated from the narrow-band photometry.
However, we do not find any convincing signal at the expected position of its
Lyman-alpha emission line, suggesting that this source is not an LAE at z ~
7.7. The non-detection in this work, together with the previous studies of z ~
7.7 LAEs, puts a strong constraint on the bright-end Lyman-alpha luminosity
function (LF) at z ~ 7.7. We find a rapid evolution of the Lyman-alpha LF from
z ~ 6.5 to 7.7: the upper limit of the z ~ 7.7 LF is more than 5 times lower
than the z ~ 6.5 LF at the bright end (f > 1.0 x 10^{-17} erg s^{-1} cm^{-2},
or L > 6.9 x 10^{42} erg s^{-1}). This is likely caused by an increasing
neutral fraction in the IGM that substantially attenuates Lyman-alpha emission
at z ~ 7.7.


title:
Extinction and PAH intensity variations across the HII region IRAS
  12063-6259

abstract:
  The spatial variations in PAH band intensities are normally attributed to the
physical conditions of the emitting PAHs, however in recent years it has been
suggested that such variations are caused mainly by extinction. To resolve this
question, we have obtained near-infrared (NIR), mid-infrared (MIR) and radio
observations of the compact H ii region IRAS 12063-6259. We use these data to
construct multiple independent extinction maps and also to measure the main PAH
features (6.2, 7.7, 8.6 and 11.2 {\mu}m) in the MIR. Three extinction maps are
derived: the first using the NIR hydrogen lines and case B recombination
theory; the second combining the NIR data with radio data; and the third making
use of the Spitzer/IRS MIR observations to measure the 9.8 {\mu}m silicate
absorption feature using the Spoon method and PAHFIT (as the depth of this
feature can be related to overall extinction). The silicate absorption over the
bright, southern component of IRAS 12063-6259 is almost absent while the other
methods find significant extinction. While such breakdowns of the relationship
between the NIR extinction and the 9.8 {\mu}m absorption have been observed in
molecular clouds, they have never been observed for HII regions. We then
compare the PAH intensity variations in the Spitzer/IRS data after dereddening
to those found in the original data. It was found that in most cases, the PAH
band intensity variations persist even after dereddening, implying that
extinction is not the main cause of the PAH band intensity variations.


title: Two Field Matter Bounce Cosmology

abstract:
  We re-examine the non-singular Matter Bounce scenario first developed in
[arXiv:1206.2382], which starts with a matter-dominated period of contraction
and transitions into an Ekpyrotic phase of contraction. We consider both matter
fields, the first of which plays the role of regular matter, and the second of
which is responsible for the non-singular bounce. Since the dominant matter
field is massive, the induced curvature fluctuations are initially not
scale-invariant, whereas the fluctuations of the second scalar field (which are
initially entropy fluctuations) are scale-invariant. We study the transfer of
the initial entropy perturbations into curvature fluctuations in the
matter-dominated phase of contraction and show that the latter become nearly
scale invariant on large scales but are blue tilted on small scales. We study
the evolution of both curvature and entropy fluctuations through the bounce,
and show that both have a scale-invariant spectrum which is blue-tilted on
small scales. However, we find that the entropy fluctuations have an amplitude
that is much smaller than that of the curvature perturbations, due to
gravitational amplification of curvature perturbations during the bounce phase.


title: Resurrecting power law inflation in the light of Planck results

abstract:
  It is well known that a canonical scalar field with an exponential potential
can drive power law inflation (PLI). However, the tensor-to-scalar ratio in
such models turns out to be larger than the stringent limit set by recent
Planck results. We propose a new model of power law inflation for which the
scalar spectra index, the tensor-to-scalar ratio and the non-gaussianity
parameter $f_{_{\mathbf{NL}}}^{\mathrm{equil}}$ are in excellent agreement with
Planck results. Inflation, in this model, is driven by a non-canonical scalar
field with an inverse power law potential. The Lagrangian for our model is
structurally similar to that of a canonical scalar field and has a power law
form for the kinetic term. A simple extension of our model resolves the
graceful exit problem which usually afflicts models of power law inflation.


title:
Local energy decay for Maxwell fields part I: Spherically symmetric
  black-hole backgrounds

abstract:
  We prove local energy decay estimates for solutions to the inhomogeneous
Maxwell system on a generic class of spherically symmetric black holes.


title: The Mass Dependence Between Protoplanetary Disks and their Stellar Hosts

abstract:
  We present a substantial extension of the mm-wave continuum photometry
catalog for Taurus circumstellar dust disks. Combining new Submillimeter Array
data with measurements in the literature, we construct a mm-wave luminosity
distribution for Class II disks that is statistically complete for stellar
hosts with spectral types earlier than M8.5 and has a (3-sigma) depth of ~3
mJy. The resulting census eliminates a longstanding bias against disks with
late-type hosts, and thereby reveals a strong correlation between L_mm and the
host spectral type. We confirm that this corresponds to a statistically robust
relationship between the masses of dust disks and the stars that host them. A
Bayesian regression technique is used to characterize these relationships: the
results indicate a typical 1.3 mm flux density of 25 mJy for solar mass hosts
and a power-law scaling L_mm \propto M_star^1.5-2.0. We suggest that a
reasonable treatment of dust temperature in the conversion from L_mm to M_disk
favors an inherently linear M_disk \propto M_star scaling, with a typical
disk-to-star mass ratio of $\sim$0.2--0.6%. The RMS dispersion around this
regression is 0.7 dex, suggesting that the combined effects of diverse
evolutionary states, dust opacities, and temperatures in these disks imprint a
FWHM range of a factor of 40 on the inferred M_disk (or L_mm) at any given host
mass. We argue that this relationship between M_disk and M_star likely
represents the origin of the inferred correlation between giant planet
frequency and host star mass in the exoplanet population, and provides some
basic support for the core accretion model for planet formation. Moreover, we
caution that selection bias must be considered in comparative studies of disk
evolution, and illustrate that fact with statistical comparisons of L_mm
between Taurus and other clusters (abridged).


title:
Three-dimensional integral equation approach to light scattering,
  extinction cross sections, local density of states and quasinormal modes

abstract:
  We present a numerical formalism for solving the Lippmann-Schwinger equation
for the electric field in three dimensions. The formalism may be applied to
scatterers of different shapes and embedded in different background media, and
we develop it in detail for the specific case of spherical scatterers in a
homogeneous background medium. In addition, we show how several physically
important quantities may readily be calculated with the formalism. These
quantities include the extinction cross section, the total Green's tensor, the
projected local density of states and the Purcell factor as well as the
quasinormal modes of leaky resonators with the associated resonance frequencies
and quality factors. We demonstrate the calculations for the well-known
plasmonic dimer consisting of two silver nanoparticles and thus illustrate the
versatility of the formalism for use in modeling of advanced nanophotonic
devices.


title:
Negative frequencies get real: a missing puzzle piece in nonlinear
  optics

abstract:
  Motivated by recent experimental results, we demonstrate that the ubiquitous
pulse propagation equation based on a single generalized nonlinear Schroedinger
equation is incomplete and inadequate to explain the formation of the so called
negative resonant radiation emitted by optical solitons. The origin of this
deficiency is due to the absence of a peculiar nonlinear coupling between the
positive and negative frequency components of the ultrashort pulse spectrum
during propagation, a feature that the slowly-varying envelope approximation is
unable to capture. We therefore introduce a conceptually new model, based on
the envelope of the analytic signal, that takes into account the full spectral
dynamics of all frequency components, is prone to analytical treatment and
retains the simulation efficiency of the nonlinear Schroedinger equation. We
use our new equation to derive from first principles the phase-matching
condition of the negative resonant radiation observed in previous experiments.


title:
On the Offset of Barred Galaxies From the Black Hole $M_{BH}$-$\sigma$
  Relationship

abstract:
  We use collisionless $N$-body simulations to determine how the growth of a
supermassive black hole (SMBH) influences the nuclear kinematics in both barred
and unbarred galaxies. In the presence of a bar, the increase in the velocity
dispersion $\sigma$ (within the effective radius) due to the growth of an SMBH
is on average $\lesssim 10%$, whereas the increase is only $\lesssim 4%$ in an
unbarred galaxy. In a barred galaxy, the increase results from a combination of
three separate factors (a) orientation and inclination effects; (b) angular
momentum transport by the bar that results in an increase in the central mass
density; (c) an increase in the vertical and radial velocity anisotropy of
stars in the vicinity of the SMBH. In contrast the growth of the SMBH in an
unbarred galaxy causes the velocity distribution in the inner part of the
nucleus to become less radially anisotropic. The increase in $\sigma$ following
the growth of the SMBH is insensitive to a variation of a factor of 10 in the
final mass of the SMBH, showing that it is the growth process rather than the
actual SMBH mass that alters bar evolution in a way that increases $\sigma$. We
argue that using an axisymmetric stellar dynamical modeling code to measure
SMBH masses in barred galaxies could result in a slight overestimate of the
derived $M_{BH}$, especially if a constant M/L ratio is assumed. We conclude
that the growth of a black hole in the presence of a bar could result in an
increase in $\sigma$ which is roughly of $4-8%$ larger than the increase that
occurs in an axisymmetric system. While the increase in $\sigma$ due to SMBH
growth in a barred galaxy might partially account for the claimed offset of
barred galaxies and pseudo bulges from the $M_{BH}-\sigma$ relation obtained
for elliptical galaxies and classical bulges in unbarred galaxies, it is
inadequate to account for all of the offset.


title:
A linear bound on the number of scalarizations needed to solve discrete
  tricriteria optimization problems

abstract:
  General multi-objective optimization problems are often solved by a sequence
of parametric single objective problems, so-called scalarizations. If the set
of nondominated points is finite, and if an appropriate scalarization is
employed, the entire nondominated set can be generated in this way. In the
bicriteria case it is well known that this can be realized by an adaptive
approach which, given an appropriate initial search space, requires the
solution of a number of subproblems which is at most two times the number of
nondominated points. For higher dimensional problems, no linear methods were
known up to now. We present a new procedure for finding the entire nondominated
set of tricriteria optimization problems for which the number of scalarized
subproblems to be solved is at most three times the number of nondominated
points of the underlying problem. The approach includes an iterative update of
the search space that, given a (sub-)set of nondominated points, describes the
area in which additional nondominated points may be located. In particular, we
show that the number of boxes, into which the search space is decomposed,
depends linearly on the number of nondominated points.


title: Investigating Deletion in Wikipedia

abstract:
  Several hundred Wikipedia articles are deleted every day because they lack
sufficient significance to be included in the encyclopedia. We collect a
dataset of deleted articles and analyze them to determine whether or not the
deletions were justified. We find evidence to support the hypothesis that many
deletions are carried out correctly, but also find that a large number were
done very quickly. Based on our conclusions, we make some recommendations to
reduce the number of non-significant pages and simultaneously improve retention
of new editors.


title: A Spectral-Lagrangian Boltzmann Solver for a Multi-Energy Level Gas

abstract:
  In this paper a spectral-Lagrangian method for the Boltzmann equation for a
multi-energy level gas is proposed. Internal energy levels are treated as
separate species and inelastic collisions (leading to internal energy
excitation and relaxation) are accounted for. The formulation developed can
also be used for the case of a mixture of monatomic gases without internal
energy (where only elastic collisions occur). The advantage of the
spectral-Lagrangian method lies in the generality of the algorithm in use for
the evaluation of the elastic and inelastic collision operators. The
computational procedure is based on the Fourier transform of the partial
elastic and inelastic collision operators and exploits the fact that these can
be written as weighted convolutions in Fourier space with no restriction on the
cross- section model. The conservation of mass, momentum and energy during
collisions is enforced through the solution of constrained optimization
problems. Numerical solutions are obtained for both space homogeneous and space
in- homogeneous problems. Computational results are compared with those
obtained by means of the DSMC method in order to assess the accuracy of the
proposed spectral-Lagrangian method.


title: Various interplays between relation and cylindric algebras

abstract:
  Using model theoretic techniques that proved that the class of $n$ neat
reducts of $m$ dimensional cylindric algebras, $\Nr_n\CA_m$, is not elementary,
we prove the same result for $\Ra\CA_k$, $k\geq 5$, and we show that
$\Ra\CA_k\subset S_c\Ra\CA_k$ for all $k\geq 5$. Conversely, using the rainbow
construction for cylindric algebra, we show that several classes of algebras,
related to the class $\Nr_n\CA_m$, $n$ finite and $m$ arbitrary, are not
elementary. Our results apply to many cylindric-like algebras, including
Pinter's substitution algebras and Halmos' polyadic algebras with and without
equality. The techniques used are essentially those used by Hirsch and
Hodkinson, and later by Hirsch in \cite{hh} and \cite{r}. In fact, the main
result in \cite{hh} follows from our more general construction. Finally we blow
up a little the {\it blow up and blur construction} of Andr\'eka nd N\'emeti,
showing that various constructions of weakly representable atom structures that
are not strongly representable, can be formalized in our blown up, blow up and
blur construction, both for relation and cylindric algebras. Two open problems
are discussed, in some detail, proposing ideas. One is whether class of subneat
reducts are closed under completions, the other is whether there exists a
weakly representable $\omega$ dimensional atom structure, that is not strongly
representable. For the latter we propose a lifting argument, due to Monk,
applied to what we call anti-Monk algebras (the algebras, constructed by Hirsch
and Hodkinson, are atomic, and their atom structure is stongly representable.)