title: On Advice Complexity of the k-server Problem under Sparse Metrics

abstract:
  We consider the k-server problem under the advice model of computation when
the underlying metric space is sparse. On one side, we show that an advice of
size {\Omega}(n) is required to obtain a 1-competitive algorithm for sequences
of size n, even for the 2-server problem on a path metric of size N >= 5.
Through another lower bound argument, we show that at least (n/2)(log {\alpha}
- 1.22) bits of advice is required to obtain an optimal solution for metric
spaces of treewidth {\alpha}, where 4 <= {\alpha} < 2k. On the other side, we
introduce {\Theta}(1)-competitive algorithms for a wide range of sparse graphs,
which require advice of (almost) linear size. Namely, we show that for graphs
of size N and treewidth {\alpha}, there is an online algorithm which receives
$O(n (log {\alpha} + log log N))$ bits of advice and optimally serves a
sequence of length n. With a different argument, we show that if a graph admits
a system of {\mu} collective tree (q,r)-spanners, then there is a
(q+r)-competitive algorithm which receives O(n (log {\mu} + log log N)) bits of
advice. Among other results, this gives a 3-competitive algorithm for planar
graphs, provided with O(n log log N) bits of advice.


title:
Stationary growth and unique invariant harmonic measure of cylindrical
  DLA

abstract:
  We prove that the harmonic measure is stationary, unique and invariant on the
interface of DLA growing on a cylinder surface. We provide a detailed
theoretical analysis puzzling together multiscaling, multifractality and
conformal invariance, supported by extensive numerical simulations of clusters
built using conformal mappings and on lattice. The growth properties of the
active and frozen zones are clearly elucidated. We show that the unique scaling
exponent characterizing the stationary growth is the DLA fractal dimension.


title: Harmonic and Wave Maps Coupled with Einstein's gravitation

abstract:
  In this paper we discuss the coupled dynamics, following from a suitable
Lagrangian, of a harmonic or wave map $\phi$ and Einstein's gravitation
described by a metric $g$. The main results concern energy conditions for wave
maps, harmonic maps from warped product manifolds, and wave maps from wave-like
Lorentzian manifolds.


title:
Electrostatic gating of metallic and insulating phases in SmNiO3
  ultrathin films

abstract:
  The correlated electron system SmNiO3 exhibits a metal-insulator phase
transition at 130 {\deg}C. Using an ionic liquid as an electric double layer
(EDL) gate on three-terminal ultrathin SmNiO3 devices, we investigate gate
control of the channel resistance and transition temperature. Resistance
reduction is observed across both insulating and metallic phases with ~25%
modulation at room temperature. We show that resistance modulation is
predominantly due to electrostatic charge accumulation and not electrochemical
doping by control experiments in inert and air en-vironments. We model the
resistance behavior and estimate the accumulated sheet density (~1-2 x 10^14
cm^-2) and EDL capacitance (~12 {\mu}F/cm^2).


title:
Intercept Probability Analysis of Cooperative Wireless Networks with
  Best Relay Selection in the Presence of Eavesdropping Attack

abstract:
  Due to the broadcast nature of wireless medium, wireless communication is
extremely vulnerable to eavesdropping attack. Physical-layer security is
emerging as a new paradigm to prevent the eavesdropper from interception by
exploiting the physical characteristics of wireless channels, which has
recently attracted a lot of research attentions. In this paper, we consider the
physical-layer security in cooperative wireless networks with multiple
decode-and-forward (DF) relays and investigate the best relay selection in the
presence of eavesdropping attack. For the comparison purpose, we also examine
the conventional direct transmission without relay and traditional max-min
relay selection. We derive closed-form intercept probability expressions of the
direct transmission, traditional max-min relay selection, and proposed best
relay selection schemes in Rayleigh fading channels. Numerical results show
that the proposed best relay selection scheme strictly outperforms the
traditional direct transmission and max-min relay selection schemes in terms of
intercept probability. In addition, as the number of relays increases, the
intercept probabilities of both traditional max-min relay selection and
proposed best relay selection schemes decrease significantly, showing the
advantage of exploiting multiple relays against eavesdropping attack.


title:
Generalized Elastic Model: Fractional Langevin Description, Fluctuation
  Relation, and Linear Response

abstract:
  The Generalized Elastic Model is a linear stochastic model which accounts for
the behaviour of many physical systems in nature, ranging from polymeric chains
to single-file systems. If an external perturbation is exerted \emph{only} on a
single point $\vec{x}^\star$ (\emph{tagged probe}), it propagates throughout
the entire system. Within the fractional Langevin equation framework, we study
the effect of such a perturbation, in cases of a constant force applied. We
report most of the results arising from our previous analysis and, in the
present work, we show that the Fox $H$-functions formalism provides a compact,
elegant and useful tool for the study of the scaling properties of any
observable. In particular we show how the generalized Kubo fluctuation
relations can be expressed in terms of $H$-functions.


title:
Comment on "Irregularity in gamma ray source spectra as a signature of
  axion-like particles"

abstract:
  D. Wouters and P. Brun in Phys. Rev. D 86, 043005 (2012) claim that an
observable effect in the spectra of distant very-high-energy blazars arises as
a consequence of oscillations of photons into axion-like particles (ALPs) in
the presence of turbulent extra-galactic magnetic fields. The main objective of
this comment is to demonstrate that such a result is physically incorrect. We
also show that a physically correct treatment of the same issue leads to a much
less relevant conclusion, which makes the effect pointed out by WB likely
unobservable with the present capabilities.


title: Classes of almost clean rings

abstract:
  A ring is clean (almost clean) if each of its elements is the sum of a unit
(regular element) and an idempotent. A module is clean (almost clean) if its
endomorphism ring is clean (almost clean). We show that every quasi-continuous
and nonsingular module is almost clean and that every right CS and right
nonsingular ring is almost clean. As a corollary, all right strongly
semihereditary rings, including finite $AW^*$-algebras and noetherian Leavitt
path algebras in particular, are almost clean.
  We say that a ring $R$ is special clean (special almost clean) if each
element $a$ can be decomposed as the sum of a unit (regular element) $u$ and an
idempotent $e$ with $aR\cap eR=0.$ The Camillo-Khurana Theorem characterizes
unit-regular rings as special clean rings. We prove an analogous theorem for
abelian Rickart rings: an abelian ring is Rickart if and only if it is special
almost clean. As a corollary, we show that a right quasi-continuous and right
nonsingular ring is left and right Rickart.
  If a special (almost) clean decomposition is unique, we say that the ring is
uniquely special (almost) clean. We show that (1) an abelian ring is
unit-regular (equiv. special clean) if and only if it is uniquely special
clean, and that (2) an abelian and right quasi-continuous ring is Rickart
(equiv. special almost clean) if and only if it is uniquely special almost
clean.
  Finally, we adapt some of our results to rings with involution: a *-ring is
*-clean (almost *-clean) if each of its elements is the sum of a unit (regular
element) and a projection (self-adjoint idempotent). A special (almost) *-clean
ring is similarly defined by replacing ``idempotent'' with ``projection'' in
the appropriate definition. We show that an abelian *-ring is a Rickart *-ring
if and only if it is special almost *-clean, and that an abelian *-ring is
*-regular if and only if it is special *-clean.


title: Proof of the Andrews-Dyson-Rhoades Conjecture on the spt-Crank

abstract:
  The notion of the spt-crank of a vector partition, or an $S$-partition, was
introduced by Andrews, Garvan and Liang. Let $N_S(m,n)$ denote the number of
$S$-partitions of $n$ with spt-crank $m$. Andrews, Dyson and Rhoades
conjectured that $\{N_S(m,n)\}_m$ is unimodal for any $n$, and they showed that
this conjecture is equivalent to an inequality between the rank and the crank
of ordinary partitions. They obtained an asymptotic formula for the difference
between the rank and the crank of ordinary partitions, which implies
$N_S(m,n)\geq N_S(m+1,n)$ for sufficiently large $n$ and fixed $m$. In this
paper, we introduce a representation of an ordinary partition, called the
$m$-Durfee rectangle symbol, which is a rectangular generalization of the
Durfee symbol introduced by Andrews. We give a proof of the conjecture of
Andrews, Dyson and Rhoades by considering two cases. For $m\geq 1$, we
construct an injection from the set of ordinary partitions of $n$ such that $m$
appears in the rank-set to the set of ordinary partitions of $n$ with rank not
less than $-m$. The case for $m=0$ requires five more injections. We also show
that this conjecture implies an inequality between the positive rank and crank
moments obtained by Andrews, Chan and Kim.


title:
Dark Matter Astrometry: Accuracy of sub-halo positions for the
  measurement of self-interaction cross sections

abstract:
  Direct evidence for the existence of dark matter and measurements of its
interaction cross-section have been provided by the physical offset between
dark matter and intra- cluster gas in merging systems like the Bullet Cluster.
Although a smaller signal, this effect is more abundant in minor mergers where
infalling substructure dark matter and gas are segregated. In such low-mass
systems the gravitational lensing signal comes primarily from weak lensing. A
fundamental step in determining such an offset in sub- structure is the ability
to accurately measure the positions of dark matter sub-peaks. Using simulated
Hubble Space Telescope observations, we make a first assessment of the
precision and accuracy with which we can measure infalling groups using weak
gravitational lensing. We demonstrate that using an existing and well-used mass
re- construction algorithm can measure the positions of 1.5x1013 M
substructures that have parent halos ten times more massive with a bias of less
than 0.3 . In this regime, our analysis suggests the precision is sufficient to
detect (at 3 {\sigma} statistical significance) the expected mean offset
between dark matter and baryonic gas in infalling groups from a sample of 50
massive clusters.


title: Complete bounded embedded complex curves in C^2

abstract:
  We prove that any convex domain of C^2 carries properly embedded complete
complex curves. In particular, we exhibit the first examples of complete
bounded embedded complex curves in C^2


title:
Gluon Transport Equation in the Small Angle Approximation and the Onset
  of Bose-Einstein Condensation

abstract:
  In this paper, we study the evolution of a dense system of gluons, such as
those produced in the early stages of ultra-relativistic heavy ion collisions.
We describe the approach to thermal equilibrium using the small angle
approximation for gluon scattering in a Boltzmann equation that includes the
effects of Bose statistics. In the present study we ignore the effect of the
longitudinal expansion, i.e., we restrict ourselves to spatially uniform
systems, with spherically symmetric momentum distributions. Furthermore we take
into account only elastic scattering, i.e., we neglect inelastic, number
changing, processes. We solve the transport equation for various initial
conditions that correspond to small or large initial gluon phase-space
densities. For a small initial phase-space density, the system evolves towards
thermal equilibrium, as expected. For a large enough initial phase-space
density the equilibrium state contains a Bose condensate. We present numerical
evidence that such over-populated systems reach the onset of Bose-Einstein
condensation in a finite time. The approach to condensation is characterized by
a scaling behavior that we briefly analyze.

categories: hep-ph cond-mat.quant-gas hep-th nucl-th


title: The parity hierarchy and new invariants of knots in thickened surfaces

abstract:
  In the present paper, we construct an invariant for virtual knots in the
thickened sphere with g handles; this invariant is a Laurent polynomial in 2g+3
variables. To this end, we use a modification of the Wirtinger presentation of
the knot group and the concept of parity introduced by V.O.Manturov. The
section 4 of the paper is devoted to an enhancement of the invariant
(construction of the invariant module) by using the parity hierarchy concept
suggested by V.O.Manturov. Namely, we discriminate between odd crossings and
two types of even crossings; the latter two types depend on whether an even
crossing remains even/odd after all odd crossings of the diagram are removed.
The construction of the invariant also works for virtual knots.


title:
Statistical Mechanics of Competitive Resource Allocation using
  Agent-based Models

abstract:
  Demand outstrips available resources in most situations, which gives rise to
competition, interaction and learning. In this article, we review a broad
spectrum of multi-agent models of competition (El Farol Bar problem, Minority
Game, Kolkata Paise Restaurant problem, Stable marriage problem, Parking space
problem and others) and the methods used to understand them analytically. We
emphasize the power of concepts and tools from statistical mechanics to
understand and explain fully collective phenomena such as phase transitions and
long memory, and the mapping between agent heterogeneity and physical disorder.
As these methods can be applied to any large-scale model of competitive
resource allocation made up of heterogeneous adaptive agent with non-linear
interaction, they provide a prospective unifying paradigm for many scientific
disciplines.


title: Precise lower bound on Monster brane boundary entropy

abstract:
  In this paper we develop further the linear functional method of deriving
lower bounds on the boundary entropy of conformal boundary conditions in 1+1
dimensional conformal field theories (CFTs). We show here how to use detailed
knowledge of the bulk CFT spectrum. Applying the method to the Monster CFT with
c=\bar c=24 we derive a lower bound s > - 3.02 x 10^{-19} on the boundary
entropy s=ln g, and find compelling evidence that the optimal bound is s>= 0.
We show that all g=1 branes must have the same low-lying boundary spectrum,
which matches the spectrum of the known g=1 branes, suggesting that the known
examples comprise all possible g=1 branes, and also suggesting that the bound
s>= 0 holds not just for critical boundary conditions but for all boundary
conditions in the Monster CFT. The same analysis applied to a second bulk CFT
-- a certain c=2 Gaussian model -- yields a less strict bound, suggesting that
the precise linear functional bound on s for the Monster CFT is exceptional.


title:
Physical-Layer Multicasting by Stochastic Transmit Beamforming and
  Alamouti Space-Time Coding

abstract:
  Consider transceiver designs in a multiuser multi-input single-output (MISO)
downlink channel, where the users are to receive the same data stream
simultaneously. This problem, known as physical-layer multicasting, has drawn
much interest. Presently, a popularized approach is transmit beamforming, in
which the beamforming optimization is handled by a rank-one approximation
method called semidefinite relaxation (SDR). SDR-based beamforming has been
shown to be promising for a small or moderate number of users. This paper
describes two new transceiver strategies for physical-layer multicasting. The
first strategy, called stochastic beamforming (SBF), randomizes the beamformer
in a per-symbol time-varying manner, so that the rank-one approximation in SDR
can be bypassed. We propose several efficiently realizable SBF schemes, and
prove that their multicast achievable rate gaps with respect to the MISO
multicast capacity must be no worse than 0.8314 bits/s/Hz, irrespective of any
other factors such as the number of users. The use of channel coding and the
assumption of sufficiently long code lengths play a crucial role in achieving
the above result. The second strategy combines transmit beamforming and the
Alamouti space-time code. The result is a rank-two generalization of SDR-based
beamforming. We show by analysis that this SDR-based beamformed Alamouti scheme
has a better worst-case effective signal-to-noise ratio (SNR) scaling, and
hence a better multicast rate scaling, than SDR-based beamforming. We further
the work by combining SBF and the beamformed Alamouti scheme, wherein an
improved constant rate gap of 0.39 bits/s/Hz is proven. Simulation results show
that under a channel-coded, many-user setting, the proposed multicast
transceiver schemes yield significant SNR gains over SDR-based beamforming at
the same bit error rate level.


title:
Reliability of Monte Carlo event generators for gamma ray dark matter
  searches

abstract:
  We study the differences in the gamma ray spectra simulated by four Monte
Carlo event generator packages developed in particle physics. Two different
versions of PYTHIA and two of HERWIG are analyzed, namely PYTHIA 6.418 and
HERWIG 6.5.10 in Fortran and PYTHIA 8.165 and HERWIG 2.6.1 in C++. For all the
studied channels, the intrinsic differences between them are shown to be
significative and may play an important role in misunderstanding dark matter
signals.


title:
Examples of infinitesimal non-trivial accumulation of secants in
  dimension three

abstract:
  We present non-trivial examples of accumulation of secants for orbits (of
real analytic three dimensional vector fields) having the origin as only
$\omega$-limit point. These non-trivial sets have the structure of a proper
algebraic variety of $\mathbb{S}^2$ intersected with a cone.


title: The singular and the 2:1 anisotropic Dunkl oscillators in the plane

abstract:
  Two Dunkl oscillator models are considered: one singular and the other with a
2:1 frequency ratio. These models are defined by Hamiltonians which include the
reflection operators in the two variables x and y. The singular or caged Dunkl
oscillator is second-order superintegrable and admits separation of variables
in both Cartesian and polar coordinates. The spectrum of the Hamiltonian is
obtained algebraically and the separated wavefunctions are given in the terms
of Jacobi, Laguerre and generalized Hermite polynomials. The symmetry
generators are constructed from the su(1,1) dynamical operators of the
one-dimensional model and generate a cubic symmetry algebra. In terms of the
symmetries responsible for the separation of variables, the symmetry algebra of
the singular Dunkl oscillator is quadratic and can be identified with a special
case of the Askey-Wilson algebra AW(3) with central involutions. The 2:1
anisotropic Dunkl oscillator model is also second-order superintegrable. The
energies of the system are obtained algebraically, the symmetry generators are
constructed using the dynamical operators and the resulting symmetry algebra is
quadratic. The general system appears to admit separation of variables only in
Cartesian coordinates. Special cases where separation occurs in both Cartesian
and parabolic coordinates are considered. In the latter case the wavefunctions
satisfy the biconfluent Heun equation and depend on a transcendental separation
constant.


title:
Differentiation of Complex Vapor Mixtures Using Versatile DNA-Carbon
  Nanotube Chemical Sensor Arrays

abstract:
  Vapor sensors based on functionalized carbon nanotubes (NTs) have shown great
promise, with high sensitivity conferred by the reduced dimensionality and
exceptional electronic properties of the NT. Critical challenges in the
development of NT-based sensor arrays for chemical detection include the
demonstration of reproducible fabrication methods and functionalization schemes
that provide high chemical diversity to the resulting sensors. Here, we outline
a scalable approach to fabricating arrays of vapor sensors consisting of NT
field effect transistors functionalized with single-stranded DNA (DNA-NT).
DNA-NT sensors were highly reproducible, with responses that could be described
through equilibrium thermodynamics. Target analytes were detected even in large
backgrounds of volatile interferents. DNA-NT sensors were able to discriminate
between highly similar molecules, including structural isomers and enantiomers.
The sensors were also able to detect subtle variations in complex vapors,
including mixtures of structural isomers and mixtures of many volatile organic
compounds characteristic of humans.


title:
Swift Discovery of a New Soft Gamma Repeater, SGR J1745-29, near
  Sagittarius A*

abstract:
  Starting in 2013 February, Swift has been performing short daily monitoring
observations of the G2 gas cloud near Sgr A* with the X-Ray Telescope to
determine whether the cloud interaction leads to an increase in the flux from
the Galactic center. On 2013 April 24 Swift detected an order of magnitude rise
in the X-ray flux from the region near Sgr A*. Initially thought to be a flare
from Sgr A*, detection of a short hard X-ray burst from the same region by the
Burst Alert Telescope suggested that the flare was from an unresolved new Soft
Gamma Repeater, SGR J1745-29. Here we present the discovery of SGR J1745-29 by
Swift, including analysis of data before, during, and after the burst. We find
that the spectrum in the 0.3-10 keV range is well fit by an absorbed blackbody
model with kTBB ~ 1 keV and absorption consistent with previously measured
values from the quiescent emission from Sgr A*, strongly suggesting that this
source is at a similar distance. Only one SGR burst has been detected so far
from the new source, and the persistent light curve shows little evidence of
decay in approximately 2 weeks of monitoring after outburst. We discuss this
light curve trend and compare it with those of other well covered SGR
outbursts. We suggest that SGR J1745-29 belongs to an emerging subclass of
magnetars characterized by low burst rates and prolonged steady X-ray emission
1-2 weeks after outburst onset.


title:
Estimation of high-resolution dust column density maps. Comparison of
  modified black-body fits and radiative transfer modelling

abstract:
  Sub-millimetre dust emission is often used to derive the column density N of
dense interstellar clouds. The observations consist of data at several
wavelengths but of variable resolution. We examine two procedures that been
proposed for the estimation of high resolution N maps. Method A uses a
low-resolution temperature map combined with higher resolution intensity data
while Method B combines N estimates from different wavelength ranges. Our aim
is to determine the accuracy of the methods relative to the true column
densities and the estimates obtainable with radiative transfer modelling. We
use magnetohydrodynamical (MHD) simulations and radiative transfer calculations
to simulate sub-millimetre observations at the wavelengths of the Herschel
Space Observatory. The observations are analysed with the methods and the
results compared to the true values and to the results from radiative transfer
modelling of observations. Both methods A and B give relatively reliable column
density estimates at the resolution of 250um data while also making use of the
longer wavelengths. For high signal-to-noise data, the results of Method B are
better correlated with the true column density, while Method A is less
sensitive to noise. When the cloud has internal heating, results of Method B
are consistent with those that would be obtained with high-resolution data.
Because of line-of-sight temperature variations, these underestimate the true
column density and, because of a favourable cancellation of errors, Method A
can sometimes give more correct values. Radiative transfer modelling, even with
very simple 3D cloud models, can provide better results. However, the
complexity of the models required for improvements increases rapidly with the
complexity and opacity of the clouds.


title:
The degeneracy between dust colour temperature and spectral index.
  Comparison of methods for estimating the beta(T) relation

abstract:
  Sub-millimetre dust emission provides information on the physics of
interstellar clouds and dust. Noise can produce anticorrelation between the
colour temperature T_C and the spectral index beta. This must be separated from
the intrinsic beta(T) relation of dust. We compare methods for the analysis of
the beta(T) relation. We examine sub-millimetre observations simulated as
simple modified black body emission or using 3D radiative transfer modelling.
In addition to chi^2 fitting, we examine the results of the SIMEX method, basic
Bayesian model, hierarchical models, and one method that explicitly assumes a
functional form for beta(T). All methods exhibit some bias. Bayesian method
shows significantly lower bias than direct chi^2 fits. The same is true for
hierarchical models that also result in a smaller scatter in the temperature
and spectral index values. However, significant bias was observed in cases with
high noise levels. Beta and T estimates of the hierarchical model are biased
towards the relation determined by the data with the highest S/N ratio. This
can alter the recovered beta(T) function. With the method where we explicitly
assume a functional form for the beta(T) relation, the bias is similar to the
Bayesian method. In the case of an actual Herschel field, all methods agree,
showing some degree of anticorrelation between T and beta.
  The Bayesian method and the hierarchical models can both reduce the
noise-induced parameter correlations. However, all methods can exhibit
non-negligible bias. This is particularly true for hierarchical models and
observations of varying signal-to-noise ratios and must be taken into account
when interpreting the results.


title:
High-energy, shock-front assisted resonant radiation in the normal
  dispersion regime

abstract:
  We present a simple yet effective theory that predicts the existence of
resonant radiation bands in the deep normal group velocity dispersion region of
a medium, even in absence of a zero-group velocity dispersion point. This
radiation is evident when the medium is pumped with high-energy ultrashort
pulses, and it is driven by the interplay between the Kerr and the shock terms
in the NLSE. Accurate experiments performed in bulk silica fully support the
theoretical phase-matching condition found by our theory.


title:
Role of HIV RNA structure in recombination and speciation: romping in
  purine A, keeps HTLV away

abstract:
  Extreme enrichment of the human immunodeficiency virus (HIV-1) RNA genome for
the purine A parallels the mild purine-loading of the RNAs of most organisms.
This should militate against loop-loop "kissing" interactions between the
structured viral genome and structured host RNAs, which can generate segments
of double-stranded RNA sufficient to trigger intracellular alarms. However,
human T cell leukaemia virus (HTLV-1), with the potential to invade the same
host cell, shows extreme enrichment for the pyrimidine C. Assuming the low GC%
HIV and the high GC% HTLV-1 to share a common ancestor, it was postulated that
differences in GC% arose to prevent homologous recombination between these
emerging lentiviral species. Sympatrically isolated by this intracellular
reproductive barrier, prototypic HIV-1 seized the AU-rich (low GC%) high ground
(thus committing to purine A rather than purine G). Prototypic HTLV-1 forwent
this advantage and evolved an independent evolutionary strategy. Evidence
supporting this hypothesis since its elaboration in the 1990s is growing. The
conflict between the needs to encode accurately both a protein, and nucleic
acid structure, is often resolved in favour of the nucleic acid because, apart
from regulatory roles, structure is critical for recombination. However, above
a sequence difference threshold, structure (and hence recombination) is
impaired. New species can then arise.


title: Geodesic Structure of Lifshitz Black Holes in 2+1 Dimensions

abstract:
  We present a study of the geodesic equations of a black hole space-time which
is a solution of the three-dimensional NMG theory and is asymptotically
Lifshitz with $z=3$ and $d=1$ as found in [Ayon-Beato E., Garbarz A., Giribet
G. and Hassaine M., Phys. Rev. {\bf D} 80, 104029 (2009)]. By means of the
corresponding effective potentials for massive particles and photons we find
the allowed motions by the energy levels. Exact solutions for radial and
non-radial geodesics are given in terms of the Weierstrass elliptic $\wp$,
$\sigma$, and $\zeta$ functions.


title: Unoccupied topological surface state in Bi$_{2}$Te$_{2}$Se

abstract:
  Bias voltage dependent scattering of the topological surface state is studied
by scanning tunneling microscopy/spectroscopy for a clean surface of the
topological insulator Bi$_2$Te$_2$Se. A strong warping of constant energy
contours in the unoccupied part of the spectrum is found to lead to a
spin-selective scattering. The topological surface state persists to higher
energies in the unoccupied range far beyond the Dirac point, where it coexists
with the bulk conduction band. This finding sheds light on the spin and charge
dynamics over the wide energy range and opens a way to designing
opto-spintronic devices.


title: Almost-commuting matrices are almost jointly diagonalizable

abstract:
  We study the relation between approximate joint diagonalization of
self-adjoint matrices and the norm of their commutator, and show that almost
commuting self-adjoint matrices are almost jointly diagonalizable by a unitary
matrix.


title: MAP-REDUCE Runtime Enforcement of Information Flow Policies

abstract:
  We propose a flexible framework that can be easily customized to enforce a
large variety of information flow properties. Our framework combines the ideas
of secure multi-execution and map-reduce computations. The information flow
property of choice can be obtained by simply changes to a map (or reduce)
program that control parallel executions.
  We present the architecture of the enforcement mechanism and its
customizations for non-interference (NI) (from Devriese and Piessens) and some
properties proposed by Mantel, such as removal of inputs (RI) and deletion of
inputs (DI), and demonstrate formally soundness and precision of enforcement
for these properties.


title: On the torsion function with Robin or Dirichlet boundary conditions

abstract:
  For $p\in (1,+\infty)$ and $b \in (0, +\infty]$ the $p$-torsion function with
Robin boundary conditions associated to an arbitrary open set $\Om \subset
\R^m$ satisfies formally the equation $-\Delta_p =1$ in $\Om$ and $|\nabla
u|^{p-2} \frac{\partial u}{\partial n} + b|u|^{p-2} u =0$ on $\partial \Om$. We
obtain bounds of the $L^\infty$ norm of $u$ {\it only} in terms of the bottom
of the spectrum (of the Robin $p$-Laplacian), $b$ and the dimension of the
space in the following two extremal cases: the linear framework (corresponding
to $p=2$) and arbitrary $b>0$, and the non-linear framework (corresponding to
arbitrary $p>1$) and Dirichlet boundary conditions ($b=+\infty$). In the
general case, $p\not=2, p \in (1, +\infty)$ and $b>0$ our bounds involve also
the Lebesgue measure of $\Om$.


title:
Disentangling Hadronic and Leptonic Cascade Scenarios from the
  Very-High-Energy Gamma-Ray Emission of Distant Hard-Spectrum Blazars

abstract:
  Recent data from the \emph{Fermi} Large Area Telescope have revealed about a
dozen distant hard-spectrum blazars that have very-high-energy (VHE; $\gtrsim
100$ GeV) photons associated with them, but most of them have not yet been
detected by imaging atmospheric Cherenkov telescopes. Most of these high-energy
gamma-ray spectra, like those of other extreme high-frequency peaked BL Lac
objects, can be well explained either by gamma rays emitted at the source or by
cascades induced by ultra-high-energy cosmic rays, as we show specifically for
KUV 00311$-$1938. We consider the prospects for detection of the VHE sources by
the planned Cherenkov Telescope Array (CTA) and show how it can distinguish the
two scenarios by measuring the integrated flux above $\sim 500$ GeV (depending
on source redshift) for several luminous sources with $z \lesssim 1$ in the
sample. Strong evidence for the origin of ultra-high-energy cosmic rays could
be obtained from VHE observations with CTA. Depending on redshift, if the often
quoted redshift of KUV 00311-1938 ($z = 0.61$) is believed, preliminary
H.E.S.S. data favor cascades induced by ultra-high-energy cosmic rays. Accurate
redshift measurements of hard-spectrum blazars are essential for this study.


title:
Higgs phenomenology in the supersymmetric grand unified theory with the
  Hosotani mechanism

abstract:
  The supersymmetric grand unified theory with the Hosotani mechanism predicts
the existence of adjoint chiral supermultiplets at the SUSY breaking scale. In
particular, the SU(2) triplet and the singlet chiral superfields affect the
Higgs sector. We investigate the contributions from these adjoint chiral
multiplets to the masses of the Higgs sector particles and their couplings to
the standard model particles. We show that the predicted values of the Higgs
sector parameters deviate from the standard model and the minimal
supersymmetric standard model by O(1)% - O(10)%.


title:
3D-HST Data Release v3.0: Extremely Deep Spectra in the UDF and WFC3
  Mosaics in the 3D-HST/CANDELS Fields

abstract:
  3D-HST is a 248-orbit Treasury program to provide WFC3 and ACS grism
spectroscopy over four extra-galactic fields (AEGIS, COSMOS, GOODS-South, and
UDS), augmented with previously obtained data in GOODS-North. We present a new
data release of the 3D-HST survey, version v3.0. This release follows the
initial v0.5 release that accompanied the survey description paper (Brammer et
al. 2012). The new v3.0 release includes the deepest near-IR HST grism spectra
currently in existence, extracted from the 8-17 orbit depth observations in the
Hubble Ultra Deep Field. Contamination-corrected 2D and 1D spectra, as well as
derived redshifts, are made available for >250 objects in this 2'x2'field. The
spectra are of extraordinary quality, and show emission features in many
galaxies as faint as F140W=26-27, absorption features in quiescent galaxies at
z~2, and several active galactic nuclei. In addition to these extremely deep
grism data we provide reduced WFC3 F125W, F140W, and F160W image mosaics of all
five 3D-HST/CANDELS fields.


title: On the minimum size of restricted sumsets in cyclic groups

abstract:
  For positive integers $n$, $m$, and $h$, we let $\rho \hat{\;}(\mathbb{Z}_n,
m, h)$ denote the minimum size of the $h$-fold restricted sumset among all
$m$-subsets of the cyclic group of order $n$. The value of $\rho
\hat{\;}(\mathbb{Z}_n, m, h)$ was conjectured for prime values of $n$ and $h=2$
by Erd\H{o}s and Heilbronn in the 1960s; Dias da Silva and Hamidoune proved the
conjecture in 1994 and generalized it for an arbitrary $h$, but little is known
about the case when $n$ is composite. Here we exhibit an explicit upper bound
for all $n$, $m$, and $h$; our bound is tight for all known cases (including
all $n$, $m$, and $h$ with $n \leq 40$). We also provide counterexamples for
conjectures made by Plagne and by Hamidoune, Llad\'o, and Serra.


title: Double and Triple Givental's J-functions for Stable Quotients Invariants

abstract:
  We use mirror formulas for the stable quotients analogue of Givental's
J-function for twisted projective invariants obtained in a previous paper to
obtain mirror formulas for the analogues of the double and triple Givental's
J-functions (with descendants at all marked points) in this setting. We then
observe that the genus 0 stable quotients invariants need not satisfy the
divisor, string, or dilaton relations of the Gromov-Witten theory, but they do
possess the integrality properties of the genus 0 three-point Gromov-Witten
invariants of Calabi-Yau manifolds. We also relate the stable quotients
invariants to the BPS counts arising in Gromov-Witten theory and obtain mirror
formulas for certain twisted Hurwitz numbers.


title: The Mahler measure of a Calabi-Yau threefold and special L-values

abstract:
  The aim of this paper is to prove a Mahler measure formula of a four-variable
Laurent polynomial whose zero locus defines a Calabi-Yau threefold. We show
that its Mahler measure is a rational linear combination of a special L-value
of the normalized newform in S_4(Gamma_0(8)) and a Riemann zeta value. This is
equivalent to a new formula for a 6F5-hypergeometric series evaluated at 1.


title:
Morphology dependence of radial elasticity in multiwalled boron nitride
  nanotubes

abstract:
  We report on the measurement of the effective radial modulus of multiwalled
Boron Nitride nanotubes with external radii in the range 3.7 to 36 nm and
number of layers in between 5 and 48. These Boron Nitride nanotubes are
radially much stiffer than previously reported thinner and smaller Boron
Nitride nanotubes. Here, we show the key role of the morphology of the
nanotubes in determining their radial rigidity, in particular we find that the
external and internal radii, R_ext and R_int, have a stronger influence on the
radial modulus than the NT's thickness, t. We find that the effective radial
modulus decreases nonlinearly with 1/R_ext until reaching, for a large number
of layers and a large radius, the transverse elastic modulus of bulk
hexagonal-Boron Nitride.


title:
Optimal control for a tuberculosis model with reinfection and
  post-exposure interventions

abstract:
  We apply optimal control theory to a tuberculosis model given by a system of
ordinary differential equations. Optimal control strategies are proposed to
minimize the cost of interventions, considering reinfection and post-exposure
interventions. They depend on the parameters of the model and reduce
effectively the number of active infectious and persistent latent individuals.
The time that the optimal controls are at the upper bound increase with the
transmission coefficient. A general explicit expression for the basic
reproduction number is obtained and its sensitivity with respect to the model
parameters is discussed. Numerical results show the usefulness of the
optimization strategies.


title: Generalised Binomial coefficients and Jarden's Theorem

abstract:
  We prove a stronger version of Jarden's Theorem for recurrence of powers of
recursive functions


title:
When the largest eigenvalue of the modularity and normalized modularity
  matrix is zero

abstract:
  In July 2012, at the Conference on Applications of Graph Spectra in Computer
Science, Barcelona, D. Stevanovic posed the following open problem: which
graphs have the zero as the largest eigenvalue of their modularity matrix? The
conjecture was that only the complete and complete multipartite graphs. They
indeed have this property, but are they the only ones? In this paper, we will
give an affirmative answer to this question and prove a bit more: both the
modularity and the normalized modularity matrix of a graph is negative
semidefinite if and only if the graph is complete or complete multipartite.


title: Record-Breaking Avalanches in Driven Threshold Systems

abstract:
  Record-breaking avalanches generated by the dynamics of several driven
nonlinear threshold models are studied. Such systems are characterized by
intermittent behavior, where slow buildup of energy is punctuated by an abrupt
release of energy through avalanche events which usually follow scale invariant
statistics. From the simulations of these systems it is possible to extract
sequences of record-breaking avalanches, where each subsequent record-breaking
event is larger in magnitude than all previous events. In the present work,
several cellular automata are analyzed among them the sandpile model, Manna
model, Olami-Feder-Christensen (OFC) model, and the forest-fire model to
investigate the record-breaking statistics of model avalanches which exhibit
temporal and spatial correlations. Several statistical measures of
record-breaking events are derived analytically and confirmed through numerical
simulations. The statistics of record-breaking avalanches for the four models
are compared to that of record-breaking events extracted from the sequences of
independent identically distributed (\emph{i.i.d.}) random variables. It is
found that the statistics of record-breaking avalanches for the above cellular
automata exhibit behavior different from that observed for \emph{i.i.d.} random
variables which in turn can be used to characterize complex spatio-temporal
dynamics. The most pronounced deviations are observed in the case of the OFC
model with a strong dependence on the conservation parameter of the model. This
indicates that avalanches in the OFC model are not independent and exhibit
spatio-temporal correlations.


title: Muscle contraction and the elasticity-mediated crosstalk effect

abstract:
  Cooperative action of molecular motors is essential for many cellular
processes. One possible regulator of motor coordination is the
elasticity-mediated crosstalk (EMC) coupling between myosin II motors whose
origin is the tensile stress that they collectively generate in actin
filaments. Here, we use a statistical mechanical analysis to investigate the
influence of the EMC effect on the sarcomere - the basic contractile unit of
skeletal muscles. We demonstrate that the EMC effect leads to an increase in
the attachment probability of motors located near the end of the sarcomere
while, simultaneously, decreasing the attachment probability of the motors in
the central part. Such a polarized attachment probability would impair the
motors ability to cooperate efficiently. Interestingly, this undesired
phenomenon becomes significant only when the system size exceeds that of the
sarcomere in skeletal muscles, which provides an explanation for the remarkable
lack of sarcomere variability in vertebrates. Another phenomenon that we
investigate is the recently observed increase in the duty ratio of the motors
with the tension in muscle. We reveal that the celebrated Hill's equation for
muscle contraction is very closely related to this observation.


title: Recurrence for powers of recursive sequence II

abstract:
  Let x(n) be a recurrence relation. The main purpose of this article is to
determine a recurrence for powers of x(n).


title: A comparison of techniques for dynamic multivariate risk measures

abstract:
  This paper contains an overview of results for dynamic multivariate risk
measures. We provide the main results of four different approaches. We will
prove under which assumptions results within these approaches coincide, and how
properties like primal and dual representation and time consistency in the
different approaches compare to each other.


title:
Competing superfluid orders in spin-orbit coupled fermionic cold atom
  optical lattices

abstract:
  The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, a superconducting state
with non-zero total momentum Cooper pairs in a large magnetic field, was first
predicted about 50 years ago, and since then became an important concept in
many branches of physics. Despite intensive search in various materials,
unambiguous experimental evidence for the FFLO phase is still lacking in
experiments. In this paper, we show that both FF (uniform order parameter with
plane-wave phase) and LO phase (spatially varying order parameter amplitude)
can be observed using fermionic cold atoms in spin-orbit coupled optical
lattices. The increasing spin-orbit coupling enhances the FF phase over the LO
phase. The coexistence of superfluid and magnetic orders is also found in the
normal BCS phase. The pairing mechanism for different phases is understood by
visualizing superfluid pairing densities in different spin-orbit bands. The
possibility of observing similar physics using spin-orbit coupled
superconducting ultra-thin films is also discussed.


title: Lecture Notes on Random Matrix Theory

abstract:
  Brief lecture notes for a course about random matrices given at the
University of Cambridge.


title: The complexity of generalized domino tilings

abstract:
  Tiling planar regions with dominoes is a classical problem in which the
decision and counting problems are polynomial. We prove a variety of hardness
results (both NP- and #P-completeness) for different generalizations of
dominoes in three and higher dimensions.


title: On reducts of Hrushovski's construction - the non-collapsed case

abstract:
  We show that the rank {\omega} structure obtained by the non-collapsed
version of Hrushovski's amalgamation construction has a proper reduct. We show
that this reduct is the Fra\"iss\'e-Hrushovski limit of its own age with
respect to a pre-dimension function generalising Hrushovski's pre-dimension
function. It follows that this reduct has a unique regular type of rank
{\omega}, and we prove that its geometry is isomorphic to the geometry of the
generic type in the original structure. We ask whether our reduct is
bi-interpretable with the original structure and whether it, too, has proper
reducts with the same geometry.


title: Playing simple loony dots and boxes endgames optimally

abstract:
  We explain a highly efficient algorithm for playing the simplest type of dots
and boxes endgame optimally (by which we mean "in such a way so as to maximise
the number of boxes that you take"). The algorithm is sufficiently simple that
it can be learnt and used in over-the-board games by humans. The types of
endgames we solve come up commonly in practice in well-played games on a 5x5
board and were in fact developed by the authors in order to improve their
over-the-board play.


title:
Relativistic AGN jets I. The delicate interplay between jet structure,
  cocoon morphology and jet-head propagation

abstract:
  Current observations have shown that astrophysical jets reveal strong signs
of radial structure. They suggest that the inner region of the jet, the jet
spine, consists of a low-density, fast-moving gas, while the outer region of
the jet consists of a more dense and slower moving gas, called the jet sheath.
Moreover, if jets carry angular momentum, the resultant centrifugal forces lead
to a radial stratification. Current observations are not able to fully resolve
the radial structure, so little is known about its actual profile. We present
three AGN jet models in $2.5D$ of which two have been given a radial structure.
The first model is a homogeneous jet, the only model that doesn't carry angular
momentum; the second model is a spine-sheath jet with an isothermal equation of
state; and the third jet model is a (piecewise) isochoric spine-sheath jet,
with constant but different densities for jet spine and jet sheath. In this
paper, we look at the effects of radial stratification on jet integrity, mixing
between the different jet components and global morphology of the jet-head and
surrounding cocoon.


title: Origin of the springs of Costa Verde beach in Lima Peru

abstract:
  This paper tries to determine the origin of springs on the Costa Verde beach,
located in the district of Barranco, Miraflores and Magdalena, province of
Lima, Peru. These springs emerge near the shoreline, from the lower layers of a
80 meter high cliff. They have survived the process of urbanization of
agricultural land, started in the early 70, which decreased the water table
aquifer of Lima, and wiped the water leaks from the cliffs. To identify the
source of the springs, isotopic, physical, chemical and bacteriological
analysis was carried out for samples from five springs. The isotopic
concentrations in waters from Costa Verde springs are depleted compared to
those obtained for Lima aquifer waters, which is recharged by infiltration of
the Rimac River. The measured values of those concentrations suggest that water
from the Costa Verde springs should come from a direct recharge in the upper
and middle basin, due to infiltration of rainfall or the river at an altitude
of about 3600 m. Conductivity and temperature, measured in situ, are similar to
those obtained on Lima aquifers. The laboratory analysis showed no significant
levels of total or fecal coliform, discarding possible leakage from Lima
sewerage.


title: Flux emergence in a magnetized convection zone

abstract:
  We study the influence of a dynamo magnetic field on the buoyant rise and
emergence of twisted magnetic flux-ropes, and their influence on the global
external magnetic field. We ran 3D MHD numerical simulations using the ASH code
and analysed the dynamical evolution of such buoyant flux-ropes from the bottom
of the convection zone until the post-emergence phases. The global nature of
this model represents very crudely and inaccurately the local dynamics of the
buoyant rise, but allows to study the influence of global effects such as
self-consistently generated differential rotation, meridional circulation and
Coriolis forces. Although motivated by the solar context, this model cannot be
thought of as a realistic model of the rise of magnetic structures and their
emergence in the Sun where the local dynamics are completely different. The
properties of initial phases of the buoyant rise in good agreement with
previous studies. However, the effects of the interaction of the background
dynamo field become increase as the flux-ropes evolve. During the buoyant rise
across the CZ, the flux-rope's magnetic field strength and scales as $rho^a$,
with $a\lesssim 1$. An increase of velocity, density and current precedes flux
emergence at all longitudes. The geometry, latitude and relative orientation of
the flux-ropes with respect to the background magnetic field influences the
rise speeds, zonal flow amplitudes (which develop within the flux-ropes) and
the corresponding surface signatures. This influences the morphology, duration
and amplitude of the associated surface shearing and Poynting flux. The emerged
flux influences the system's global polarity, leading in some cases to a
polarity reversal while inhibiting background dynamo from doing so in some
others. The emerged magnetic flux is slowly advected poleward, while being
diffused and assimilated by the background dynamo field.


title:
Exploring the Variable Sky with LINEAR. II. Halo Structure and
  Substructure Traced by RR Lyrae Stars to 30 kpc

abstract:
  We present a sample of ~5,000 RR Lyrae stars selected from the recalibrated
LINEAR dataset and detected at heliocentric distances between 5 kpc and 30 kpc
over ~8,000 deg^2 of sky. The coordinates and light curve properties, such as
period and Oosterhoff type, are made publicly available. We find evidence for
the Oosterhoff dichotomy among field RR Lyrae stars, with the ratio of the type
II and I subsamples of about 1:4. The number density distribution of halo RRab
stars as a function of galactocentric distance can be described as an oblate
ellipsoid with the axis ratio q=0.63 and with either a single or a double power
law with a power-law index in the range -2 to -3. Using a group-finding
algorithm EnLink, we detected seven candidate halo groups, only one of which is
statistically spurious. Three of these groups are near globular clusters
(M53/NGC 5053, M3, M13), and one is near a known halo substructure (Virgo
Stellar Stream); the remaining three groups do not seem to be near any known
halo substructures or globular clusters, and seem to have a higher ratio of
Oosterhoff type II to Oosterhoff type I RRab stars than what is found in the
halo. The extended morphology and the position (outside the tidal radius) of
some of the groups near globular clusters is suggestive of tidal streams
possibly originating from globular clusters. Spectroscopic followup of detected
halo groups is encouraged.


title:
On the analytic computation of massless propagators in dimensional
  regularization

abstract:
  We comment on the algorithm to compute periods using hyperlogarithms, applied
to massless Feynman integrals in the parametric representation. Explicitly, we
give results for all three-loop propagators with arbitrary insertions including
order $\varepsilon^4$ and show examples at four and more loops.
  Further we prove that all coefficients of the $\varepsilon$-expansion of
these integrals are rational linear combinations of multiple zeta values and in
some cases possibly also alternating Euler sums.


title:
Detection of the cosmic \gamma-ray horizon from multiwavelength
  observations of blazars

abstract:
  The first statistically significant detection of the cosmic \gamma-ray
horizon (CGRH) that is independent of any extragalactic background light (EBL)
model is presented. The CGRH is a fundamental quantity in cosmology. It gives
an estimate of the opacity of the Universe to very high energy (VHE) \gamma-ray
photons due to photon-photon pair production with the EBL. The only estimations
of the CGRH to date are predictions from EBL models and lower limits from
\gamma-ray observations of cosmological blazars and \gamma-ray bursts. Here, we
present homogeneous synchrotron/synchrotron self-Compton (SSC) models of the
spectral energy distributions of 15 blazars based on (almost) simultaneous
observations from radio up to the highest energy \gamma-rays taken with the
Fermi satellite. These synchrotron/SSC models predict the unattenuated VHE
fluxes, which are compared with the observations by imaging atmospheric
Cherenkov telescopes. This comparison provides an estimate of the optical depth
of the EBL, which allows a derivation of the CGRH through a maximum likelihood
analysis that is EBL-model independent. We find that the observed CGRH is
compatible with the current knowledge of the EBL.


title:
Measurement of the expansion rate of the Universe from \gamma-ray
  attenuation

abstract:
  A measurement of the expansion rate of the Universe (that is the Hubble
constant, H0) is derived here using the gamma-ray attenuation observed in the
spectra of gamma-ray sources produced by the interaction of extragalactic
gamma-ray photons with the photons of the extragalactic background light (EBL).
The Hubble constant that is determined with our technique, for a Lambda CDM
cosmology, is H0=71.8_{-5.6}^{+4.6}(stat)_{-13.8}^{+7.2}(syst) km s^{-1}
Mpc^{-1}. This value is compatible with present-day measurements using well
established methods such as local distance ladders and cosmological probes. The
recent detection of the cosmic gamma-ray horizon (CGRH) from multiwavelength
observation of blazars, together with the advances in the knowledge of the EBL,
allow us to measure the expansion rate of the Universe. This estimate of the
Hubble constant shows that gamma-ray astronomy has reached a mature enough
state to provide cosmological measurements, which may become more competitive
in the future with the construction of the Cherenkov Telescope Array. We find
that the maximum dependence of the CGRH on the Hubble constant is approximately
between redshifts 0.04 and 0.1, thus this is a smoking gun for planning future
observational efforts. Other cosmological parameters, such as the total dark
matter density Omega_m and the dark energy equation of state w, are explored as
well.


title:
Protein structure validation and refinement using amide proton chemical
  shifts derived from quantum mechanics

abstract:
  We present the ProCS method for the rapid and accurate prediction of protein
backbone amide proton chemical shifts - sensitive probes of the geometry of key
hydrogen bonds that determine protein structure. ProCS is parameterized against
quantum mechanical (QM) calculations and reproduces high level QM results
obtained for a small protein with an RMSD of 0.25 ppm (r = 0.94). ProCS is
interfaced with the PHAISTOS protein simulation program and is used to infer
statistical protein ensembles that reflect experimentally measured amide proton
chemical shift values. Such chemical shift-based structural refinements,
starting from high-resolution X-ray structures of Protein G, ubiquitin, and SMN
Tudor Domain, result in average chemical shifts, hydrogen bond geometries, and
trans-hydrogen bond (h3JNC') spin-spin coupling constants that are in excellent
agreement with experiment. We show that the structural sensitivity of the
QM-based amide proton chemical shift predictions is needed to refine protein
structures to this agreement. The ProCS method thus offers a powerful new tool
for refining the structures of hydrogen bonding networks to high accuracy with
many potential applications such as protein flexibility in ligand binding.


title:
Temporal mode selectivity by frequency conversion in second-order
  nonlinear optical waveguides

abstract:
  We explore theoretically the feasibility of using frequency conversion by
sum- or difference-frequency generation, enabled by three- wave-mixing, for
selectively multiplexing orthogonal input waveforms that overlap in time and
frequency. Such a process would enable a drop device for use in a transparent
optical network using temporally orthogonal waveforms to encode different
channels. We model the process using coupled-mode equations appropriate for
wave mixing in a uniform second- order nonlinear optical medium pumped by a
strong laser pulse. We find Green functions describing the process, and employ
Schmidt (singular- value) decompositions thereof to quantify its viability in
functioning as a coherent waveform discriminator. We define a selectivity
figure of merit in terms of the Schmidt coefficients, and use it to compare and
contrast various parameter regimes via extensive numerical computations. We
identify the most favorable regime (at least in the case of no pump chirp) and
derive the complete analytical solution for the same. We bound the maximum
achievable selectivity in this parameter space. We show that including a
frequency chirp in the pump does not improve selectivity in this optimal
regime. We also find an operating regime in which high-efficiency frequency
conversion without temporal-shape selectivity can be achieved while preserving
the shapes of a wide class of input pulses. The results are applicable to both
classical and quantum frequency conversion.


title:
Spatial dependence of the Star Formation History in the Central Regions
  of the Fornax Dwarf Spheroidal Galaxy

abstract:
  We present the Star Formation History (SFH) and the age-metallicity relation
(AMR) in three fields of the Fornax dwarf spheroidal galaxy. They sample a
region spanning from the centre of the galaxy to beyond one core radius, which
allows studying galactocentric gradients. In all the cases, we found stars as
old as 12 Gyr, together with intermediate-age and young stellar populations.
The last star formation events, as young as 1 Gyr old, are mainly located in
the central region, which may indicate that the gas reservoir in the outer
parts of the galaxy would have been exhausted earlier than in the centre or
removed by tidal interactions. The AMR is smoothly increasing in the three
analyzed regions and similar to each other, indicating that no significant
metallicity gradient is apparent within and around the core radius of Fornax.
No significant traces of global UV-reionization or local SNe feedback are
appreciated in the early SFH of Fornax.
  Our study is based on FORS1@VLT photometry as deep as I~24.5 and the
IAC-star/IAC-pop/MinnIAC suite of codes for the determination of the SFH in
resolved stellar populations.


title: The nonlinear heat equation on W-random graphs

abstract:
  For systems of coupled differential equations on a sequence of W-random
graphs, we derive the continuum limit in the form of an evolution integral
equation. We prove that solutions of the initial value problems (IVPs) for the
discrete model converge to the solution of the IVP for its continuum limit.
These results combined with the analysis of nonlocally coupled deterministic
networks in [9] justify the continuum (thermodynamic) limit for a large class
of coupled dynamical systems on convergent families of graphs.


title:
Differential branching fraction and angular analysis of the decay
  $B_s^0\to\phi\mu^{+}\mu^{-}$

abstract:
  The determination of the differential branching fraction and the first
angular analysis of the decay $B_s^0\to\phi\mu^{+}\mu^{-}$ are presented using
data, corresponding to an integrated luminosity of $1.0\,{\rm fb}^{-1}$,
collected by the LHCb experiment at $\sqrt{s}=7\,{\rm TeV}$. The differential
branching fraction is determined in bins of $q^{2}$, the invariant dimuon mass
squared. Integration over the full $q^{2}$ range yields a total branching
fraction of ${\cal B}(B_s^0\to\phi\mu^{+}\mu^{-}) = (7.07\,^{+0.64}_{-0.59}\pm
0.17 \pm 0.71)\times 10^{-7}$, where the first uncertainty is statistical, the
second systematic, and the third originates from the branching fraction of the
normalisation channel. An angular analysis is performed to determine the
angular observables $F_{\rm L}$, $S_3$, $A_6$, and $A_9$. The observables are
consistent with Standard Model expectations.


title:
Robust Hydraulic Fracture Monitoring (HFM) of Multiple Time Overlapping
  Events Using a Generalized Discrete Radon Transform

abstract:
  In this work we propose a novel algorithm for multiple-event localization for
Hydraulic Fracture Monitoring (HFM) through the exploitation of the sparsity of
the observed seismic signal when represented in a basis consisting of space
time propagators. We provide explicit construction of these propagators using a
forward model for wave propagation which depends non-linearly on the problem
parameters - the unknown source location and mechanism of fracture, time and
extent of event, and the locations of the receivers. Under fairly general
assumptions and an appropriate discretization of these parameters we first
build an over-complete dictionary of generalized Radon propagators and assume
that the data is well represented as a linear superposition of these
propagators. Exploiting this structure we propose sparsity penalized algorithms
and workflow for super-resolution extraction of time overlapping multiple
seismic events from single well data.


title:
Exploiting Structural Complexity for Robust and Rapid Hyperspectral
  Imaging

abstract:
  This paper presents several strategies for spectral de-noising of
hyperspectral images and hypercube reconstruction from a limited number of
tomographic measurements. In particular we show that the non-noisy spectral
data, when stacked across the spectral dimension, exhibits low-rank. On the
other hand, under the same representation, the spectral noise exhibits a banded
structure. Motivated by this we show that the de-noised spectral data and the
unknown spectral noise and the respective bands can be simultaneously estimated
through the use of a low-rank and simultaneous sparse minimization operation
without prior knowledge of the noisy bands. This result is novel for for
hyperspectral imaging applications. In addition, we show that imaging for the
Computed Tomography Imaging Systems (CTIS) can be improved under limited angle
tomography by using low-rank penalization. For both of these cases we exploit
the recent results in the theory of low-rank matrix completion using nuclear
norm minimization.


title: Integrable QFT and Longo-Witten endomorphisms

abstract:
  Our previous constructions of Borchers triples are extended to massless
scattering with nontrivial left and right components. A massless Borchers
triple is constructed from a set of left-left, right-right and left-right
scattering functions. We find a correspondence between massless left-right
scattering S-matrices and massive block diagonal S-matrices. We point out a
simple class of S-matrices with examples.
  We study also the restriction of two-dimensional models to the lightray.
Several arguments for constructing strictly local two-dimensional nets are
presented and possible scenarios are discussed.


title: Bounds to the Higgs Sector Masses in Minimal Supersymmetry from LHC Data

abstract:
  We update our analysis of the Higgs sector masses in Minimal Supersymmetry
and in the Two-Higgs Doublet Model to the final ATLAS and CMS data from the
2011-2012 LHC run.


title:
Optimality of Orthogonal Access for One-dimensional Convex Cellular
  Networks

abstract:
  It is shown that a greedy orthogonal access scheme achieves the sum degrees
of freedom of all one-dimensional (all nodes placed along a straight line)
convex cellular networks (where cells are convex regions) when no channel
knowledge is available at the transmitters except the knowledge of the network
topology. In general, optimality of orthogonal access holds neither for
two-dimensional convex cellular networks nor for one-dimensional non-convex
cellular networks, thus revealing a fundamental limitation that exists only
when both one-dimensional and convex properties are simultaneously enforced, as
is common in canonical information theoretic models for studying cellular
networks. The result also establishes the capacity of the corresponding class
of index coding problems.


title: A gamma function in two variables

abstract:
  We introduce a gamma function $\Ga(x,z)$ in two complex variables which
extends the classical gamma function $\Ga(z)$ in the sense that $\lim_{x\to
1}\Ga(x,z)=\Ga(z)$. We will show that many properties which $\Ga(z)$ enjoys
extend in a natural way to the function $\Ga(x,z)$. Among other things we shall
provide functional equations, a multiplication formula, and analogues of the
Stirling formula with asymptotic estimates as consequences.


title: Transversely affine foliations on projective manifolds

abstract:
  We describe the structure of singular transversely affine foliations of
codimension one on projective manifolds X with zero first Betti number. Our
result can be rephrased as a theorem on rank two reducible flat meromorphic
connections.


title: Elementary excitations in gapped quantum spin systems

abstract:
  For quantum lattice systems with local interactions, the Lieb-Robinson bound
acts as an alternative for the strict causality of relativistic systems and
allows to prove many interesting results, in particular when the energy
spectrum exhibits an energy gap. In this Letter, we show that for translation
invariant systems, simultaneous eigenstates of energy and momentum with an
eigenvalue that is separated from the rest of the spectrum in that momentum
sector, can be arbitrarily well approximated by building a momentum
superposition of a local operator acting on the ground state. The error
decreases in the size of the support of the local operator, with a rate that is
set by the gap below and above the targeted eigenvalue. We show this explicitly
for the AKLT model and discuss generalizations and applications of our result.

categories: quant-ph cond-mat.str-el math-ph math.MP


title: Conformal and projection diagrams in LaTeX

abstract:
  In general relativity, the causal structure of space-time may sometimes be
depicted by conformal Carter-Penrose diagrams or a recent extension of these -
the projection diagrams. The introduction of conformal diagrams in the sixties
was one of the progenitors of the golden age of relativity. They are the key
ingredient of many scientific papers. Unfortunately, drawing them in the form
suitable for LaTeX documents is time-consuming and not easy. We present below a
library that allows one to draw an arbitrary conformal diagram in a few simple
steps.


title:
Pseudo-Exponential-Type Solutions of Wave Equations Depending on Several
  Variables

abstract:
  Using matrix identities, we construct explicit pseudo-exponential-type
solutions of linear Dirac, Loewner and Schr\"odinger equations depending on two
variables and of nonlinear wave equations depending on three variables.


title: Shot-noise-limited spin measurements in a pulsed molecular beam

abstract:
  Heavy diatomic molecules have been identified as good candidates for use in
electron electric dipole moment (eEDM) searches. Suitable molecular species can
be produced in pulsed beams, but with a total flux and/or temporal evolution
that varies significantly from pulse to pulse. These variations can degrade the
experimental sensitivity to changes in spin precession phase of an electri-
cally polarized state, which is the observable of interest for an eEDM
measurement. We present two methods for measurement of the phase that provide
immunity to beam temporal variations, and make it possible to reach
shot-noise-limited sensitivity. Each method employs rapid projection of the
spin state onto both components of an orthonormal basis. We demonstrate both
methods using the eEDM-sensitive H state of thorium monoxide (ThO), and use one
of them to measure the magnetic moment of this state with increased accuracy
relative to previous determinations.


title: Suspended Graphene Ballistic Josephson Weak Links

abstract:
  The interplay of graphene and superconductivity has attracted great interest
for understanding the two-dimensional Dirac Fermion physics and for
superconducting device applications. In previous work, graphene-superconductor
junctions fabricated on standard SiO2 substrates were highly disordered. Due to
charge carrier scattering and potential fluctuations, the expected intrinsic
properties of graphene combined with superconductors remained elusive to
experimental observations. We propose suspended graphene-superconductor
junctions as an effective solution to the problem. Here, we show the
fabrication and characterization of the high-quality suspended monolayer
graphene-NbN Josephson junctions that have device mobility greater than 150,000
cm2/Vs, with minimum carrier density below 1e10 cm-2 and a formation of
supercurrent at temperature above 2 K.The devices have exhibited a ballistic
Josephson current that depend linearly on the Fermi energy of graphene, a
manifestation of the ultra-relativistic band structure of Dirac electrons. This
work paves the way for future studies of the intrinsic Dirac Fermion
superconducting proximity effect and new graphene-superconductor hybrid
junctions.


title:
Quasar Outflows and AGN Feedback in the Far UV: HST/COS Observations of
  QSO HE0238-1904

abstract:
  Spectroscopic observations of quasar outflows at rest-frame 500-1000 Angstrom
have immense diagnostic power. We present analyses of such data, where
absorption troughs from three important ions are measured: first, O IV and O
IV* that allow us to obtain the distance of high ionization outflows from the
AGN; second, Ne VIII and Mg X that are sensitive to the very high ionization
phase of the outflow. Their inferred column densities, combined with those of
troughs from O VI, N IV, and H I, yield two important results: 1) The outflow
shows two ionization phases, where the high ionization phase carries the bulk
of the material. This is similar to the situation seen in x-ray warm absorber
studies. Furthermore, the low ionization phase is inferred to have a volume
filling factor of 10^(-5)-10^(-6). 2) From the O IV to O IV* column density
ratio, and the knowledge of the ionization parameter, we determine a distance
of 3000 pc. from the outflow to the central source. Since this is a typical
high ionization outflow, we can determine robust values for the mass flux and
kinetic luminosity of the outflow: 40 solar masses per year and 10^45 ergs/s,
respectively, where the latter is roughly equal to 1% of the bolometric
luminosity. Such a large kinetic luminosity and mass flow rate measured in a
typical high ionization wind suggests that quasar outflows are a major
contributor to AGN feedback mechanisms.


title:
Fermilab experience of post-annealing losses in SRF niobium cavities due
  to furnace contamination and the ways to its mitigation: a pathway to
  processing simplification and quality factor improvement

abstract:
  We investigate the effect of high temperature treatments followed by only
high-pressure water rinse (HPR) of superconducting radio frequency (SRF)
niobium cavities. The objective is to provide a cost effective alternative to
the typical cavity processing sequence, by eliminating the material removal
step post furnace treatment while preserving or improving the RF performance.
The studies have been conducted in the temperature range 800-1000C for
different conditions of the starting substrate: large grain and fine grain,
electro-polished (EP) and centrifugal barrel polished (CBP) to mirror finish.
An interesting effect of the grain size on the performances is found. Cavity
results and samples characterization show that furnace contaminants cause poor
cavity performance, and a practical solution is found to prevent surface
contamination. Extraordinary values of residual resistances ~ 1 nOhm and below
are then consistently achieved for the contamination-free cavities. These
results lead to a more cost-effective processing and improved RF performance,
and, in conjunction with CBP, open a potential pathway to acid-free processing.


title: Sutured Khovanov homology distinguishes braids from other tangles

abstract:
  We show that the sutured Khovanov homology of a balanced tangle in the
product sutured manifold D x I has rank 1 if and only if the tangle is isotopic
to a braid.


title:
Modeling the horizon-absorbed gravitational flux for equatorial-circular
  orbits in Kerr spacetime

abstract:
  We propose an improved analytical model for the horizon-absorbed
gravitational-wave energy flux of a small body in circular orbit in the
equatorial plane of a Kerr black hole. Post-Newtonian (PN) theory provides an
analytical description of the multipolar components of the absorption flux
through Taylor expansions in the orbital frequency. Building on previous work,
we construct a mode-by-mode factorization of the absorbed flux whose Taylor
expansion agrees with current PN results. This factorized form significantly
improves the agreement with numerical results obtained with a frequency-domain
Teukolsky code, which evolves through a sequence of circular orbits up to the
photon orbit. We perform the comparison between model and numerical data for
dimensionless Kerr spins $-0.99 \leq q \leq 0.99$ and for frequencies up to the
light ring of the Kerr black hole. Our proposed model enforces the presence of
a zero in the flux at an orbital frequency equal to the frequency of the
horizon, as predicted by perturbation theory. It also reproduces the expected
divergence of the flux close to the light ring. Neither of these features are
captured by the Taylor-expanded PN flux. Our proposed absorption flux can also
help improve models for the inspiral, merger, ringdown of small mass-ratio
binary systems.


title:
Homogenization of Degenerate Porous Medium Type Equations in Ergodic
  Algebras

abstract:
  We consider the homogenization problem for general porous medium type
equations of the form $u_t=\D f(x,\frac{x}{\ve}, u)$. The pressure function
$f(x,y,\cdot)$ may be of two different types. In the type~1 case,
$f(x,y,\cdot)$ is a general strictly increasing function; this is a mildly
degenerate case. In the type~2 case, $f(x,y,\cdot)$ has the form
$h(x,y)F(u)+S(x,y)$, where $F(u)$ is just a nondecreasing function; this is a
strongly degenerate case. We address the initial-boundary value problem for a
general, bounded or unbounded, domain $\Om$, with null (or, more generally,
steady) pressure condition on the boundary. The homogenization is carried out
in the general context of ergodic algebras. As far as the authors know,
homogenization of such degenerate quasilinear parabolic equations is addressed
here for the first time. We also review the existence and stability theory for
such equations and establish new results needed for the homogenization
analysis. Further, we include some new results on algebras with mean value,
specially a new criterion establishing the null measure of level sets of
elements of the algebra, which is useful in connection with the homogenization
of porous medium type equations in the type~2 case.


title: Quantum interference as a resource for quantum speedup

abstract:
  Quantum states can in a sense be thought of as generalizations of classical
probability distributions, but are more powerful than probability distributions
when used for computation or communication. Quantum speedup therefore requires
some feature of quantum states that classical probability distributions lack.
One such feature is interference. We quantify interference and show that there
can be no quantum speedup due to a small number of operations incapable of
generating large amounts of interference (although large numbers of such
operations can in fact lead to quantum speedup). Low-interference operations
include sparse unitaries, Grover reflections, short time/low energy Hamiltonian
evolutions, and the Haar wavelet transform. Circuits built from such operations
can be classically simulated via a Monte Carlo technique making use of a convex
combination of two Markov chains. Applications to query complexity,
communication complexity, and the Wigner representation are discussed.


title: The density of surface states as the total time delay

abstract:
  For a scattering problem of tight-binding Bloch electrons by a weak random
surface potential, a generalized Levinson theorem is put forward showing the
equality of the total density of surface states and the density of the total
time delay. The proof uses explicit formulas for the wave operators in the new
rescaled energy and interaction (REI) representation, as well as an index
theorem for adequate associated operator algebras.


title:
Photo-Met: a non-parametric method for estimating stellar metallicity
  from photometric observations

abstract:
  Getting spectra at good signal-to-noise ratios takes orders of magnitudes
more time than photometric observations. Building on the technique developed
for photometric redshift estimation of galaxies, we develop and demonstrate a
non-parametric photometric method for estimating the chemical composition of
galactic stars. We investigate the efficiency of our method using
spectroscopically determined stellar metallicities from SDSS DR7. The technique
is generic in the sense that it is not restricted to certain stellar types or
stellar parameter ranges and makes it possible to obtain metallicities and
error estimates for a much larger sample than spectroscopic surveys would
allow. We find that our method performs well, especially for brighter stars and
higher metallicities and, in contrast to many other techniques, we are able to
reliably estimate the error of the predicted metallicities.


title:
Time Dependent Quantum Thermodynamics of a Coupled Quantum Oscillator
  System in a Small Thermal Environment

abstract:
  Simulations are performed of a small quantum system interacting with a
quantum environment. The system consists of various initial states of two
harmonic oscillators coupled to give normal modes. The environment is
"designed" by its level pattern to have a thermodynamic temperature. A random
coupling causes the system and environment to become entangled in the course of
time evolution. The approach to a Boltzmann distribution is observed, and
effective fitted temperatures close to the designed temperature are obtained.
All initial pure states of the system are driven to equilibrium at very similar
rates, with quick loss of memory of the initial state. The time evolution of
the von Neumann entropy is calculated as a measure of equilibration and of
quantum coherence. It is argued, contrary to common understanding, that quantum
interference and coherence are eliminated only with maximal entropy, which
corresponds thermally to infinite temperature. Implications of our results for
the notion of "classicalizing" behavior in the approach to thermal equilibrium
are briefly considered.


title:
Scalable Routing Easy as PIE: a Practical Isometric Embedding Protocol
  (Technical Report)

abstract:
  We present PIE, a scalable routing scheme that achieves 100% packet delivery
and low path stretch. It is easy to implement in a distributed fashion and
works well when costs are associated to links. Scalability is achieved by using
virtual coordinates in a space of concise dimensionality, which enables greedy
routing based only on local knowledge. PIE is a general routing scheme, meaning
that it works on any graph. We focus however on the Internet, where routing
scalability is an urgent concern. We show analytically and by using simulation
that the scheme scales extremely well on Internet-like graphs. In addition, its
geometric nature allows it to react efficiently to topological changes or
failures by finding new paths in the network at no cost, yielding better
delivery ratios than standard algorithms. The proposed routing scheme needs an
amount of memory polylogarithmic in the size of the network and requires only
local communication between the nodes. Although each node constructs its
coordinates and routes packets locally, the path stretch remains extremely low,
even lower than for centralized or less scalable state-of-the-art algorithms:
PIE always finds short paths and often enough finds the shortest paths.


title:
On WD-WD Mergers in Triple Systems: The Role of Kozai Resonance with
  Tidal Friction

abstract:
  White dwarf-white dwarf (WD-WD) mergers may lead to type Ia supernovae
events. Thompson (2011) suggested that many such binaries are produced in
hierarchical triple systems. The tertiary induces eccentricity oscillations in
the inner binary via the Kozai-Lidov mechanism, driving the binary to high
eccentricities, and significantly reducing the gravitational wave merger
timescale (T_GW) over a broad range of parameter space. Here, we investigate
the role of tidal forces in these systems. We show that tidal effects are
important in the regime of moderately high initial relative inclination between
the inner binary and the outer tertiary. For 85 < i_0 < 90 degrees (prograde)
and 97 < i_0 < 102 degrees (retrograde), tides combine with GW radiation to
dramatically decrease T_GW. In the regime of high inclinations between 91 < i_0
< 96 degrees, the inner binary likely suffers a direct collision, as in the
work of Katz & Dong (2012) and tidal effects do not play an important role.


title:
Does gravity induce wavefunction collapse? An examination of Penrose's
  conjecture

abstract:
  According to Penrose, the fundamental conflict between the superposition
principle of quantum mechanics and the principle of general covariance of
general relativity entails the existence of wavefunction collapse, e.g. a
quantum superposition of two different space-time geometries will collapse to
one of them due to the ill-definedness of the time-translation operator for the
superposition. In this paper, we argue that Penrose's conjecture on gravity's
role in wavefunction collapse is debatable. First of all, it is still a
controversial issue what the exact nature of the conflict is and how to resolve
it. Secondly, Penrose's argument by analogy is too weak to establish a
necessary connection between wavefunction collapse and the conflict as
understood by him. Thirdly, the conflict does not necessarily lead to
wavefunction collapse. For the conflict or the problem of ill-definedness for a
superposition of different space-time geometries also needs to be solved before
the collapse of the superposition finishes, and once the conflict has been
resolved, the wavefunction collapse will lose its physical basis relating to
the conflict. In addition, we argue that Penrose's suggestions for the collapse
time formula and the preferred basis are also problematic.


title: Correlated quantum phenomena in the strong spin-orbit regime

abstract:
  We discuss phenomena arising from the combined influence of electron
correlation and spin-orbit coupling, with an emphasis on emergent quantum
phases and transitions in heavy transition metal compounds with 4d and 5d
elements. A common theme is the influence of spin-orbital entanglement produced
by spin-orbit coupling, which influences the electronic and magnetic structure.
In the weak-to-intermediate correlation regime, we show how non-trivial
band-like topology leads to a plethora of phases related to topological
insulators. We expound these ideas using the example of pyrochlore iridates,
showing how many novel phases such as the Weyl semi-metal, axion insulator,
topological Mott insulator, and topological insulators may arise in this
context. In the strong correlation regime, we argue that spin-orbital
entanglement fully or partially removes orbital degeneracy, reducing or
avoiding the normally ubiquitous Jahn-Teller effect. As we illustrate for the
honeycomb lattice iridates and double perovskites, this leads to enhanced
quantum fluctuations of the spin-orbital entangled states and the chance to
promote exotic quantum spin liquid and multipolar ordered ground states.
Connections to experiments, materials, and future directions are discussed.

categories: cond-mat.str-el cond-mat.mes-hall cond-mat.mtrl-sci cond-mat.supr-con


title: Galileon forces in the Solar System

abstract:
  We consider the challenging problem of obtaining an analytic understanding of
realistic astrophysical dynamics in the presence of a Vainshtein screened fifth
force arising from infrared modifications of General Relativity. In particular,
we attempt to solve -- within the most general flat spacetime galileon model --
the scalar force law between well separated bodies located well within the
Vainshtein radius of the Sun. To this end, we derive the exact static Green's
function of the galileon wave equation linearized about the background field
generated by the Sun, for the minimal cubic and maximally quartic galileon
theories, and then introduce a method to compute the general leading order
force law perturbatively away from these limits. We also show that the same
nonlinearities which produce the Vainshtein screening effect present obstacles
to an analytic calculation of the galileon forces between closely bound systems
within the solar system, such as that of the Earth and Moon. Within the test
mass approximation, we deduce that a large enough quartic galileon interaction
would suppress the effect on planetary perihelion precession below the level
detectable by even the next-generation experiments.


title: Following the flow: tracer particles in astrophysical fluid simulations

abstract:
  We present two numerical schemes for passive tracer particles in the
hydrodynamical moving-mesh code AREPO, and compare their performance for
various problems, from simple setups to cosmological simulations. The purpose
of tracer particles is to allow the flow to be followed in a Lagrangian way,
tracing the evolution of the fluid with time, and allowing the thermodynamical
history of individual fluid parcels to be recorded. We find that the
commonly-used `velocity field tracers', which are advected using the fluid
velocity field, do not in general follow the mass flow correctly, and explain
why this is the case. This method can result in orders-of-magnitude biases in
simulations of driven turbulence and in cosmological simulations, rendering the
velocity field tracers inappropriate for following these flows. We then discuss
a novel implementation of `Monte Carlo tracers', which are moved along with
fluid cells, and are exchanged probabilistically between them following the
mass flux. This method reproduces the mass distribution of the fluid correctly.
The main limitation of this approach is that it is more diffusive than the
fluid itself. Nonetheless, we show that this novel approach is more reliable
than what has been employed previously and demonstrate that it is appropriate
for following hydrodynamical flows in mesh-based codes. The Monte Carlo tracers
can also naturally be transferred between fluid cells and other types of
particles, such as stellar particles, so that the mass flow in cosmological
simulations can be followed in its entirety.


title: Magnetic Correlations in Short and Narrow Graphene Armchair Nanoribbons

abstract:
  Electronic states at the ends of a narrow armchair nanoribbon give rise to a
pair of non-locally entangled spins. We propose two experiments to probe these
magnetic states, based on magnetometry and tunneling spectroscopy, in which
correlation effects lead to a striking, nonlinear response to external magnetic
fields. On the basis of low-energy theories that we derive here, it is
remarkably simple to assess these nonlinear signatures for magnetic edge
states. The effective theories are especially suitable in parameter regimes
where other methods such as quantum Monte-Carlo simulations are exceedingly
difficult due to exponentially small energy scales. The armchair ribbon setup
discussed here provides a promisingly well-controlled (both experimentally and
theoretically) environment for studying the principles behind edge magnetism in
graphene-based nano-structures.


title:
The reliability of approximate radiation transport methods for
  irradiated disk studies

abstract:
  Context: Dynamical studies of irradiated circumstellar disks require an
accurate treatment of radiation transport to, for example, properly determine
cooling and fragmentation properties. The radiation transport algorithm should
be as fast as the (magneto-) hydrodynamics to allow for an efficient usage of
computing resources.
  Methods: We use a setup of a central star and a slightly flared circumstellar
disk. We perform simulations for a wide range of optical depths of the disk's
midplane from tau(550nm) = 0.1 up to tau(810nm) = 1 million. We check the
accuracy of the gray flux-limited diffusion (FLD) approximation and a gray and
frequency-dependent ray-tracing plus FLD approximation.
  Results:
  1. For moderate optical depths, a gray approximation of the stellar
irradiation yields a slightly hotter inner rim and a slightly cooler midplane
of the disk at larger radii, but is otherwise in agreement with the
frequency-dependent treatment.
  2. The gray FLD approximation fails to compute an appropriate temperature
profile in all regimes of optical depth; the maximum deviations to the
comparison runs are 50 percent in the optically thin and up to 280 percent in
the optically thick limit. For low optical depth, the isotropic assumption
within the FLD method yields a too steep decrease of the radial temperature
slope. For higher optical depths, the FLD approximation does not reproduce the
shadow behind the optically thick inner rim of the circumstellar disk, yielding
artificial heating at larger disk radii.
  3. The frequency-dependent RT + gray FLD approximation yields remarkable
accuracy for the whole range of optical depths.
  Conclusions: The high accuracy of the frequency-dependent hybrid radiation
transport algorithm makes this method ideally suited for (magneto-)
hydrodynamical studies of irradiated circumstellar disks.


title: Oscillations and stability of polytropic filaments

abstract:
  We study the oscillations and stability of self-gravitating cylindrically
symmetric fluid systems and collisionless systems. This is done by studying
small perturbations to the equilibrium system and finding the normal modes,
using methods similar to those used in astroseismology. We find that there is a
single sequence of purely radial modes that become unstable if the adiabatic
exponent is less than 1. Nonradial modes can be divided into p modes, which are
stable and pressure-driven, and g modes, which are are gravity driven. The g
modes become unstable if the adiabatic exponent is greater than the polytrope
index. These modes are analogous to the modes of a spherical star, but their
behavior is somewhat different because a cylindrical geometry has less symmetry
than a spherical geometry. This implies that perturbations are classified by a
radial quantum number, an azimuthal quantum number, and wavelength in the z
direction, which can become arbitrarily large. We find that decreasing this
wavelength increases the frequency of stable modes and increases the growth
rate of unstable modes. We use use variational arguments to demonstrate that
filaments of collisionless matter with ergodic distribution functions are
stable to purely radial perturbations, and that filaments with ergodic
power-law distribution functions are stable to all perturbations.


title:
The most luminous quasars do not live in the most massive dark matter
  haloes at any redshift

abstract:
  Quasars represent the brightest Active Galactic Nuclei (AGN) in the Universe
and are thought to indicate the location of prodigiously growing Black Holes
(BHs), with luminosities as high as 10^48 erg/sec. It is often expected though
that such an extremely energetic process will take place in the most massive
bound structures in the dark matter (DM) distribution. We show that in contrast
to this expectation, in a galaxy formation model which includes AGN feedback,
quasars are predicted to live in average DM halo environments with typical
masses of a few times 10^12 Msun. This fundamental prediction arises from the
fact that quasar activity (i.e., BH accretion with luminosity greater than
10^46 erg/sec) is inhibited in DM haloes where AGN feedback operates. The
galaxy hosts of quasars in our simulations are identified with over massive (in
gas and stars) spheroidal galaxies, in which BH accretion is triggered via a
galaxy merger or secular processes. We further show that the z=0 descendants of
high redshift (z~6) QSOs span a wide range of morphologies, galaxy and halo
masses. The z~6 BHs typically grow only by a modest factor by the present day.
Remarkably, high redshift QSOs never inhabit the largest DM haloes at that time
and their descendants are very seldom found in the most massive haloes at z=0.
We also show that observationally it is very likely to find an enhancement in
the abundance of galaxies around quasars at z~5. However, these enhancements
are considerably weaker compared to the overdensities expected at the extreme
peaks of the DM distribution. Thus, it is very unlikely that a quasar detected
in the $z\gtrsim5$ Universe pinpoints the location of the progenitors of
superclusters in the local Universe.


title:
Constraints on black hole fuelling modes from the clustering of X-ray
  AGN

abstract:
  We present a clustering analysis of X-ray selected AGN by compiling X-ray
samples from the literature and re-estimating the dark matter (DM) halo masses
of AGN in a uniform manner. We find that moderate luminosity AGN (Lx(2-10
keV)=10^42-10^44 erg/sec) in the z=0-1.3 Universe are typically found in DM
haloes with masses of ~10^13 Msun. We then compare our findings to the
theoretical predictions of the coupled galaxy and black hole formation model
GALFORM. We find good agreement when our calculation includes the hot-halo mode
of accretion onto the central black hole. This type of accretion, which is
additional to the common cold accretion during disk instabilities and galaxy
mergers, is tightly coupled to the AGN feedback in the model. The hot-halo mode
becomes prominent in DM haloes with masses greater than ~10^12.5 Msun, where
AGN feedback typically operates, giving rise to a distinct class of moderate
luminosity AGN that inhabit rich clusters and superclusters. Cold gas fuelling
of the black hole cannot produce the observationally inferred DM halo masses of
X-ray AGN. Switching off AGN feedback in the model results in a large
population of luminous quasars (Lx(2-10 keV) > 10^44 erg/sec) in DM haloes with
masses up to ~10^14 Msun, which is inconsistent with the observed clustering of
quasars. The abundance of hot-halo AGN decreases significantly in the z~3-4
universe. At such high redshifts, the cold accretion mode is solely responsible
for shaping the environment of moderate luminosity AGN. Our analysis supports
two accretion modes (cold and hot) for the fuelling of supermassive black holes
and strongly underlines the importance of AGN feedback in cosmological models
both of galaxy formation and black hole growth.


title:
Plasma Jets and Eruptions in Solar Coronal Holes: a 3D flux emergence
  experiment

abstract:
  A three-dimensional numerical experiment of the launching of a hot and fast
coronal jet followed by several violent eruptions is analyzed in detail. These
events are initiated through the emergence of a magnetic flux rope from the
solar interior into a coronal hole. We explore the evolution of the emerging
magnetically-dominated plasma dome surmounted by a current sheet and the
ensuing pattern of reconnection. A hot and fast coronal jet with inverted-Y
shape is produced that shows properties comparable to those frequently observed
with EUV and X-Ray detectors. We analyze its 3D shape, its inhomogeneous
internal structure, and its rise and decay phases, lasting for some 15-20 min
each. Particular attention is devoted to the field-line connectivities and the
reconnection pattern. We also study the cool and high-density volume that
appears encircling the emerged dome. The decay of the jet is followed by a
violent phase with a total of five eruptions. The first of them seems to follow
the general pattern of tether-cutting reconnection in a sheared arcade,
although modified by the field topology created by the preceding reconnection
evolution. The two following eruptions take place near and above the strong
field-concentrations at the surface. They show a twisted, \Omega-loop like rope
expanding in height, with twist being turned into writhe, thus hinting at a
kink instability (perhaps combined with a torus-instability) as the cause of
the eruption. The succession of a main jet ejection and a number of violent
eruptions that resemble mini-CME's and their physical properties suggest that
this experiment may provide a model for the blowout jets recently proposed in
the literature.