title: Singular Ricci solitons and their stability under the Ricci flow

abstract:
  We introduce certain spherically symmetric singular Ricci solitons and study
their stability under the Ricci flow from a dynamical PDE point of view. The
solitons in question exist for all dimensions $n+1\ge 3$, and all have a point
singularity where the curvature blows up; their evolution under the Ricci flow
is in sharp contrast to the evolution of their smooth counterparts. In
particular, the family of diffeomorphisms associated with the Ricci flow
"pushes away" from the singularity causing the evolving soliton to open up
immediately becoming an incomplete (but non-singular) metric. In the second
part of this paper we study the local-in time stability of this dynamical
evolution, under spherically symmetric perturbations of the initial soliton
metric. We prove a local well-posedness result for the Ricci flow near the
singular initial data, which in particular implies that the "opening up" of the
singularity persists for the perturbations also.


title: On independence domination

abstract:
  Let G be a graph. The independence-domination number is the maximum over all
independent sets I in G of the minimal number of vertices needed to dominate I.
In this paper we investigate the computational complexity of independence
domination for graphs in several graph classes related to cographs. We present
an exact exponential algorithm. We also present a PTAS for planar graphs.


title: Representability of matroids with a large projective geometry minor

abstract:
  We prove that for each prime power $q$ there is an integer $n$ such that if
$M$ is a $3$-connected, representable matroid with a PG$(n-1,q)$-minor and no
$U_{2,q^2+1}$-minor, then $M$ is representable over GF$(q)$. We also show that
for $\ell >= 2$, if $M$ is a $3$-connected, representable matroid of
sufficiently high rank with no $U_{2,\ell+2}$-minor and $|E(M)| \geq
(4\ell)^{r(M)/2}$, then $M$ is representable over a field of order at most
$\ell$.


title:
Long-range spin current driven by superconducting phase difference in a
  Josephson junction with double layer ferromagnets

abstract:
  We theoretically study spin current through ferromagnet (F) in a Josephson
junction composed of s-wave superconductors and two layers of ferromagnets.
Using quasiclassical theory, we show that the long-range spin current can be
driven by the superconducting phase difference without voltage drop. The origin
of this spin current is due to spin-triplet Cooper pairs (STCs) formed by
electrons of equal-spin, which are induced by proximity effect inside the F. We
find that the spin current carried by the STCs exhibits long-range propagation
in the F even where the Josephson charge current is practically zero. We also
show that this spin current persists over a remarkably longer distance than the
ordinary spin current carried by spin polarized conduction electrons in the F.
Our results thus indicate the promising potential of Josephson junctions based
on multilayer ferromagnets for spintronics applications with long-range
propagating spin current.


title: On fundamental groups with the quotient topology

abstract:
  The quasitopological fundamental group $\pi_{1}^{qtop}(X,x_0)$ is the
fundamental group endowed with the natural quotient topology inherited from the
space of based loops and is typically non-discrete when $X$ does not admit a
traditional universal cover. This topologized fundamental group is an invariant
of homotopy type which has the ability to distinguish weakly homotopy
equivalent and shape equivalent spaces. In this paper, we clarify various
relationships among topological properties of the group $\pi_{1}^{qtop}(X,x_0)$
and properties of the underlying space $X$ such as `$\pi_{1}$-shape
injectivity' and `homotopically path-Hausdorff.'
  A space $X$ is $\pi_1$-shape injective if the fundamental group canonically
embeds in the first shape group so that the elements of $\pi_1(X,x_0)$ can be
represented as sequences in an inverse limit. We show a locally path connected
metric space $X$ is $\pi_1$-shape injective if and only if
$\pi_{1}^{qtop}(X,x_0)$ is invariantly separated in the sense that the
intersection of all open invariant (i.e. normal) subgroups is the trivial
subgroup. In the case that $X$ is not $\pi_1$-shape injective, the
homotopically path-Hausdorff property is useful for distinguishing homotopy
classes of loops and guarantees the existence of certain generalized covering
maps. We show that a locally path connected space $X$ is homotopically
path-Hausdorff if and only if $\pi_{1}^{qtop}(X,x_0)$ satisfies the $T_1$
separation axiom.


title:
Well-posedness and ill-posedness results for the regularized
  Benjamin-Ono equation in weighted Sobolev spaces

abstract:
  We consider the initial value problem associated to the regularized
Benjamin-Ono equation, rBO. Our aim is to establish local and global
well-posedness results in weighted Sobolev spaces via contraction principle. We
also prove a unique continuation property that implies that arbitrary
polinomial type decay is not preserved yielding sharp results regarding
well-posedness of the initial value problem in most weighted Sobolev spaces.


title: Antiferromagnetic crystalline topological insulators

abstract:
  The gapless surface Dirac cone of time reversal invariant topological
insulators is protected by time reversal symmetry due to the Kramers' theorem.
Spin degree of freedom is usually required since Kramers' theorem only
guarantees double degeneracy for spinful fermions, but not for spinless
fermions. In this paper, we present an antiferromagnetic spinless model, which
breaks time reversal symmetry. Similar to time reversal invariant topological
insulators, this model possesses a topologically non-trivial phase with a
single surface Dirac cone, which is protected by the combination of time
reversal and translation operation. Our results show that in magnetic crystals,
a single Dirac cone can exist on the surface even without any spin degree of
freedom and spin-orbit coupling.


title: Insights into capacity constrained optimal transport

abstract:
  A variant of the classical optimal transportation problem is: among all joint
measures with fixed marginals and which are dominated by a given density, find
the optimal one. Existence and uniqueness of solutions to this variant were
established in \cite{KM11}. In the present manuscript, we expose an unexpected
symmetry leading to the first explicit examples in two and more dimensions.
These are inspired in part by simulations in one dimension which display
singularities and topology and in part by two further developments: the
identification of all extreme points in the feasible set, and a new approach to
uniqueness based on constructing feasible perturbations.


title:
An Optimal and Model-Independent Measurement of the Intracluster
  Pressure Profile I: Methodology and First Applications

abstract:
  We present a statistically-optimal and model-independent method to extract
the pressure profile of hot gas in the intracluster medium (ICM). Using the
thermal Sunyaev-Zeldovich effect, we constrain the mean pressure profile of the
ICM by appropriately considering all primary cosmic microwave background (CMB)
and instrumental noise correlations, while using the maximum resolution and
sensitivity of all frequency channels. As a first application, we analyze CMB
maps of WMAP 9-year data through a study of the Meta-Catalogue of X-ray
detected Clusters of galaxies (MCXC). We constrain the universal pressure
profile out to 4R_500 with 15-sigma confidence, though our measurements are
only significant out to R_200. Using a temperature profile constrained from
X-ray observations, we measure the mean gas mass fraction out to R_200. Within
statistical and systematic uncertainties, our constraints are compatible with
the cosmic baryon fraction and the expected gas fraction in halos. While Planck
multi-frequency CMB data are expected to reduce statistical uncertainties by a
factor of 20, we argue that systematic errors in determining mass of clusters
dominate the uncertainty in gas mass fraction measurements at the level of 20
percent.


title: The Spin-2 Equation on Minkowski Background

abstract:
  The linearised general conformal field equations in their first and second
order form are used to study the behaviour of the spin-2 zero-rest-mass
equation on Minkowski background in the vicinity of space-like infinity.


title:
Measuring Transport Difficulty of Data Dissemination in Large-Scale
  Online Social Networks: An Interest-Driven Case

abstract:
  In this paper, we aim to model the formation of data dissemination in online
social networks (OSNs), and measure the transport difficulty of generated data
traffic. We focus on a usual type of interest-driven social sessions in OSNs,
called \emph{Social-InterestCast}, under which a user will autonomously
determine whether to view the content from his followees depending on his
interest. It is challenging to figure out the formation mechanism of such a
Social-InterestCast, since it involves multiple interrelated factors such as
users' social relationships, users' interests, and content semantics. We
propose a four-layered system model, consisting of physical layer, social
layer, content layer, and session layer. By this model we successfully obtain
the geographical distribution of Social-InterestCast sessions, serving as the
precondition for quantifying data transport difficulty. We define the
fundamental limit of \emph{transport load} as a new metric, called
\emph{transport complexity}, i.e., the \emph{minimum required} transport load
for an OSN over a given carrier network. Specifically, we derive the transport
complexity for Social-InterestCast sessions in a large-scale OSN over the
carrier network with optimal communication architecture. The results can act as
the common lower bounds on transport load for Social-InterestCast over any
carrier networks. To the best of our knowledge, this is the first work to
measure the transport difficulty for data dissemination in OSNs by modeling
session patterns with the interest-driven characteristics.


title: Are elite journals declining?

abstract:
  Previous work indicates that over the past 20 years, the highest quality work
have been published in an increasingly diverse and larger group of journals. In
this paper we examine whether this diversification has also affected the
handful of elite journals that are traditionally considered to be the best. We
examine citation patterns over the past 40 years of 7 long-standing
traditionally elite journals and 6 journals that have been increasing in
importance over the past 20 years. To be among the top 5% or 1% cited papers,
papers now need about twice as many citations as they did 40 years ago. Since
the late 1980s and early 1990s elite journals have been publishing a decreasing
proportion of these top cited papers. This also applies to the two journals
that are typically considered as the top venues and often used as bibliometric
indicators of "excellence", Science and Nature. On the other hand, several new
and established journals are publishing an increasing proportion of most cited
papers. These changes bring new challenges and opportunities for all parties.
Journals can enact policies to increase or maintain their relative position in
the journal hierarchy. Researchers now have the option to publish in more
diverse venues knowing that their work can still reach the same audiences.
Finally, evaluators and administrators need to know that although there will
always be a certain prestige associated with publishing in "elite" journals,
journal hierarchies are in constant flux so inclusion of journals into this
group is not permanent.


title:
Local convergence analysis of a proximal Gauss-Newton method under a
  majorant condition

abstract:
  In this paper, the proximal Gauss-Newton method for solving penalized
nonlinear least squares problems is studied. A local convergence analysis is
obtained under the assumption that the derivative of the function associated
with the penalized least square problem satisfies a majorant condition. Our
analysis provides a clear relationship between the majorant function and the
function associated with the penalized least squares problem. The convergence
for two important special cases is also derived.


title:
Entanglement-based quantum key distribution with biased basis choice via
  free space

abstract:
  We report a free-space entanglement-based quantum key distribution
experiment, implementing the biased basis protocol between two sites which are
15.3 km apart. Photon pairs from a polarization-entangled source are
distributed through two 7.8-km free-space optical links. An optimal bias 20:80
between the X and Z basis is used. A post-processing scheme with finite-key
analysis is applied to extract the final secure key. After three-hour
continuous operation at night, a 4293-bit secure key is obtained, with a final
key rate of 0.124 bit per raw key bit which increases the final key rate by
14.8% comparing to the standard BB84 case. Our results experimentally
demonstrate that the efficient BB84 protocol, which increases key generation
efficiency by biasing Alice and Bob's basis choices, is potentially useful for
the ground-satellite quantum communication.


title: The Stubborn Roots of Metabolic Cycles

abstract:
  Efforts to catalogue the structure of metabolic networks have generated
highly detailed, genome-scale atlases of biochemical reactions in the cell.
Unfortunately, these atlases fall short of capturing the kinetic details of
metabolic reactions, instead offering only \textit{topological} information
from which to make predictions. As a result, studies frequently consider the
extent to which the topological structure of a metabolic network determines its
dynamic behavior, irrespective of kinetic details. Here, we study a class of
metabolic networks known as non-autocatalytic metabolic cycles, and
analytically prove an open conjecture regarding the stability of their
steady-states. Importantly, our results are invariant to the choice of kinetic
parameters, rate laws, equilibrium fluxes, and metabolite concentrations.
Unexpectedly, our proof exposes an elementary but apparently open problem of
locating the roots of a sum of two polynomials S = P+Q, when the roots of the
summand polynomials P and Q are known. We derive two new results named the
Stubborn Roots Theorems, which provide sufficient conditions under which the
roots of S remain qualitatively identical to the roots of P. Our work
illustrates how complementary feedback, from classical fields like dynamical
systems to biology and vice versa, can expose fundamental and potentially
overlooked questions.


title:
Thermodynamic Observation of a Vortex Melting Transition in the Fe-based
  Superconductor Ba0.5K0.5Fe2As2

abstract:
  In cuprate high-temperature superconductors the small coherence lengths and
high transition termperatures result in strong thermal fluctuations, which
render the superconducting transition in applied magnetic fields into a wide
continuous crossover. A state with zero resistance is found only below the
vortex melting transition, which occurs well below the onset of superconducting
correlations. Here we investigate the vortex phase diagram of the novel
Fe-based superconductor in form of a high-quality single crystal of
Ba0.5K0.5Fe2As2, using three different experimental probes (specific heat,
thermal expansion and magnetization). We find clear thermodynamic signatures of
a vortex melting transition, which shows that the thermal fluctuations in
applied magnetic fields also have a considerable impact on the superconducting
properties of iron-based superconductors.


title: New skew Laplacian energy of a simple digraph

abstract:
  For a simple digraph $G$ of order $n$ with vertex set $\{v_1,v_2,\ldots,
v_n\}$, let $d_i^+$ and $d_i^-$ denote the out-degree and in-degree of a vertex
$v_i$ in $G$, respectively. Let $D^+(G)=diag(d_1^+,d_2^+,\ldots,d_n^+)$ and
$D^-(G)=diag(d_1^-,d_2^-,\ldots,d_n^-)$. In this paper we introduce
$\widetilde{SL}(G)=\widetilde{D}(G)-S(G)$ to be a new kind of skew Laplacian
matrix of $G$, where $\widetilde{D}(G)=D^+(G)-D^-(G)$ and $S(G)$ is the
skew-adjacency matrix of $G$, and from which we define the skew Laplacian
energy $SLE(G)$ of $G$ as the sum of the norms of all the eigenvalues of
$\widetilde{SL}(G)$. Some lower and upper bounds of the new skew Laplacian
energy are derived and the digraphs attaining these bounds are also determined.


title: Planar Ramsey Numbers of Four Cycles Versus Wheels

abstract:
  For two given graphs $G$ and $H$ the planar Ramsey number $PR(G,H)$ is the
smallest integer $n$ such that every planar graph $F$ on $n$ vertices either
contains a copy of $G$, or its complement contains a copy of $H$. In this
paper, we first characterize some structural properties of $C_4$-free planar
graphs, and then we determine all planar Ramsey numbers $PR(C_4, W_n)$, for
$n\ge 3$.


title: LP=>: Extending LP with a strong conditional operator

abstract:
  We augment LP with a strong conditional operator, to yield a logic we call
"strong LP," or LP=>. The resulting logic can speak of consistency in more
discriminating ways, but introduces new possibilities for trivializing
paradoxes.


title:
Adaptive Switched Lattice Reduction-Aided Linear Detection Techniques
  for MIMO Systems

abstract:
  Lattice reduction (LR) aided multiple-input-multiple-out (MIMO) linear
detection can achieve the maximum receive diversity of the maximum likelihood
detection (MLD). By emloying the most commonly used Lenstra, Lenstra, and L.
Lovasz (LLL) algorithm, an equivalent channel matrix which is shorter and
nearly orthogonal is obtained. And thus the noise enhancement is greatly
reduced by employing the LR-aided detection. One problem is that the LLL
algorithm can not guarantee to find the optimal basis. The optimal lattice
basis can be found by the Korkin and Zolotarev (KZ) reduction. However, the KZ
reduction is infeasible in practice due to its high complexity. In this paper,
a simple algorithm is proposed based on the complex LLL (CLLL) algorithm to
approach the optimal performance while maintaining a reasonable complexity.


title:
Fermi surface in KFe2As2 determined via de Haas-van Alphen oscillation
  measurements

abstract:
  We have completely determined the Fermi surface in KFe$_2$As$_2$ via de
Haas-van Alphen (dHvA) measurements. Fundamental frequencies $\epsilon$,
$\alpha$, $\zeta$, and $\beta$ are observed in KFe$_2$As$_2$. The first one is
attributed to a hole cylinder near the X point of the Brillouin zone, while the
others to hole cylinders at the $\Gamma$ point. We also observe magnetic
breakdown frequencies between $\alpha$ and $\zeta$ and suggest a plausible
explanation for them. The experimental frequencies show deviations from
frequencies predicted by band structure calculations. Large effective masses up
to 19 $m_e$ for $B \parallel c$ have been found, $m_e$ being the free electron
mass. The carrier number and Sommerfeld coefficient of the specific heat are
estimated to be 1.01 -- 1.03 holes per formula unit and 82 -- 94
mJmol$^{-1}$K$^{-2}$, respectively, which are consistent with the chemical
stoichiometry and a direct measure of 93 mJmol$^{-1}$K$^{-2}$ [H. Fukazawa
\textit{et al}., J. Phys. Soc. Jpn. \textbf{80SA}, SA118 (2011)]. The
Sommerfeld coefficient is about 9 times enhanced over a band value, suggesting
the importance of low-energy spin and/or orbital fluctuations, and places
KFe$_2$As$_2$ among strongly correlated metals. We have also performed dHvA
measurements on Ba$_{0.07}$K$_{0.93}$Fe$_2$As$_2$ and have observed the
$\alpha$ and $\beta$ frequencies.


title:
Low-Complexity Lattice Reduction-Aided Channel Inversion Methods for
  Large-Dimensional Multi-User MIMO Systems

abstract:
  Low-complexity precoding {algorithms} are proposed in this work to reduce the
computational complexity and improve the performance of regularized block
diagonalization (RBD) {based} precoding {schemes} for large multi-user {MIMO}
(MU-MIMO) systems. The proposed algorithms are based on a channel inversion
technique, QR decompositions{,} and lattice reductions to decouple the MU-MIMO
channel into equivalent SU-MIMO channels. Simulation results show that the
proposed precoding algorithms can achieve almost the same sum-rate performance
as RBD precoding, substantial bit error rate (BER) performance gains{,} and a
simplified receiver structure, while requiring a lower complexity.


title: Viscous decretion discs around rapidly rotating stars

abstract:
  We discuss steady viscous Keplerian decretion discs around rapidly rotating
stars. We assume that low frequency modes, which may be excited by the opacity
bump mechanism, convective motion in the core, or tidal force if the star is in
a binary system, can transport an enough amount of angular momentum to the
region close to the stellar surface. Under this assumption, we construct a
star-disc system, in which there forms a viscous decretion disc around a
rapidly rotating star because of the angular momentum supply. We find a series
of solutions of steady viscous decretion discs around a rapidly rotating star
that extend to $R_{\rm disc}\gtsim~10R_*$ with $R_*$ being the equatorial
radius of the star, depending on the amount of angular momentum supply.


title: Water-Trapped Worlds

abstract:
  Although tidally-locked habitable planets orbiting nearby M-dwarf stars are
among the best astronomical targets to search for extrasolar life, they may
also be deficient in volatiles and water. Climate models for this class of
planets show atmospheric transport of water from the dayside to the nightside,
where it is precipitated as snow and trapped as ice. Since ice only slowly
flows back to the dayside upon accumulation, the resulting hydrological cycle
can trap a large amount of water in the form of nightside ice. Using ice sheet
dynamical and thermodynamical constraints, I illustrate how planets with less
than about a quarter the Earth's oceans could trap most of their surface water
on the nightside. This would leave their dayside, where habitable conditions
are met, potentially dry. The amount and distribution of residual liquid water
on the dayside depend on a variety of geophysical factors, including the
efficiency of rock weathering at regulating atmospheric CO2 as dayside ocean
basins dry-up. Water-trapped worlds with dry daysides may offer similar
advantages as land planets for habitability, by contrast with worlds where more
abundant water freely flows around the globe.


title:
Technical report: Linking the scientific and clinical data with
  KI2NA-LHC

abstract:
  We introduce a use case and propose a system for data and knowledge
integration in life sciences. In particular, we focus on linking clinical
resources (electronic patient records) with scientific documents and data
(research articles, biomedical ontologies and databases). Our motivation is
two-fold. Firstly, we aim to instantly provide scientific context of particular
patient cases for clinicians in order for them to propose treatments in a more
informed way. Secondly, we want to build a technical infrastructure for
researchers that will allow them to semi-automatically formulate and evaluate
their hypothesis against longitudinal patient data. This paper describes the
proposed system and its typical usage in a broader context of KI2NA, an ongoing
collaboration between the DERI research institute and Fujitsu Laboratories. We
introduce an architecture of the proposed framework called KI2NA-LHC (for
Linked Health Care) and outline the details of its implementation. We also
describe typical usage scenarios and propose a methodology for evaluation of
the whole framework. The main goal of this paper is to introduce our ongoing
work to a broader expert audience. By doing so, we aim to establish an
early-adopter community for our work and elicit feedback we could reflect in
the development of the prototype so that it is better tailored to the
requirements of target users.


title: No-bomb theorem for charged Reissner-Nordstrom black holes

abstract:
  The fundamental role played by black holes in many areas of physics makes it
highly important to explore the nature of their stability. The stability of
charged Reissner-Nordstr\"om black holes to {\it neutral} (gravitational and
electromagnetic) perturbations was established almost four decades ago.
However, the stability of these charged black holes under {\it charged}
perturbations has remained an open question due to the complexity introduced by
the well-known phenomena of superradiant scattering: A charged scalar field
impinging on a charged Reissner-Nordstr\"om black hole can be {\it amplified}
as it scatters off the hole. If the incident field has a non-zero rest mass,
then the mass term effectively works as a mirror, preventing the energy
extracted from the hole from escaping to infinity. One may suspect that the
superradiant amplification of charged fields by the charged black hole may lead
to an instability of the Reissner-Nordstr\"om spacetime (in as much the same
way that rotating Kerr black holes are unstable under rotating scalar
perturbations). However, in this Letter we show that, for charged
Reissner-Nordstr\"om black holes in the regime ${(Q/M)}^2\leq 8/9$, the two
conditions which are required in order to trigger a possible superradiant
instability [namely: (1) the existence of a trapping potential well outside the
black hole, and (2) superradiant amplification of the trapped modes] cannot be
satisfied simultaneously. Our results thus support the stability of charged
Reissner-Nordstr\"om black holes under charged scalar perturbations in the
regime ${(Q/M)}^2\leq 8/9$.


title:
Revisiting Asynchronous Linear Solvers: Provable Convergence Rate
  Through Randomization

abstract:
  Asynchronous methods for solving systems of linear equations have been
researched since Chazan and Miranker's pioneering 1969 paper on chaotic
relaxation. The underlying idea of asynchronous methods is to avoid processor
idle time by allowing the processors to continue to make progress even if not
all progress made by other processors has been communicated to them.
  Historically, the applicability of asynchronous methods for solving linear
equations was limited to certain restricted classes of matrices, such as
diagonally dominant matrices. Furthermore, analysis of these methods focused on
proving convergence in the limit. Comparison of the asynchronous convergence
rate with its synchronous counterpart and its scaling with the number of
processors were seldom studied, and are still not well understood.
  In this paper, we propose a randomized shared-memory asynchronous method for
general symmetric positive definite matrices. We rigorously analyze the
convergence rate and prove that it is linear, and is close to that of the
method's synchronous counterpart if the processor count is not excessive
relative to the size and sparsity of the matrix. We also present an algorithm
for unsymmetric systems and overdetermined least-squares. Our work presents a
significant improvement in the applicability of asynchronous linear solvers as
well as in their convergence analysis, and suggests randomization as a key
paradigm to serve as a foundation for asynchronous methods.


title: Remote Homology Detection in Proteins Using Graphical Models

abstract:
  Given the amino acid sequence of a protein, researchers often infer its
structure and function by finding homologous, or evolutionarily-related,
proteins of known structure and function. Since structure is typically more
conserved than sequence over long evolutionary distances, recognizing remote
protein homologs from their sequence poses a challenge.
  We first consider all proteins of known three-dimensional structure, and
explore how they cluster according to different levels of homology. An
automatic computational method reasonably approximates a human-curated
hierarchical organization of proteins according to their degree of homology.
  Next, we return to homology prediction, based only on the one-dimensional
amino acid sequence of a protein. Menke, Berger, and Cowen proposed a Markov
random field model to predict remote homology for beta-structural proteins, but
their formulation was computationally intractable on many beta-strand
topologies.
  We show two different approaches to approximate this random field, both of
which make it computationally tractable, for the first time, on all protein
folds. One method simplifies the random field itself, while the other retains
the full random field, but approximates the solution through stochastic search.
Both methods achieve improvements over the state of the art in remote homology
detection for beta-structural protein folds.


title: Specular Andreev Reflection in Inversion-symmetric Weyl-semimetals

abstract:
  The electron-hole conversion at the normal-metal superconductor interface in
inversion-symmetric Weyl semimetals is investigated with an effective two-band
model. We find that the specular Andreev reflection of Weyl fermions has two
unusual features. The Andreev conductance for s-wave BCS pairing states is
anisotropic, depending on the angle between the line connecting a pair of Weyl
points and the normal of the junction, due to opposite chirality carried by the
paired electrons. For the Fulde-Ferrell-Larkin-Ovchinnikov pairing states, the
Andreev reflection spectrum is isotropic and is independent of the finite
momentum of the Cooper pairs.


title: The K-modes algorithm for clustering

abstract:
  Many clustering algorithms exist that estimate a cluster centroid, such as
K-means, K-medoids or mean-shift, but no algorithm seems to exist that clusters
data by returning exactly K meaningful modes. We propose a natural definition
of a K-modes objective function by combining the notions of density and cluster
assignment. The algorithm becomes K-means and K-medoids in the limit of very
large and very small scales. Computationally, it is slightly slower than
K-means but much faster than mean-shift or K-medoids. Unlike K-means, it is
able to find centroids that are valid patterns, truly representative of a
cluster, even with nonconvex clusters, and appears robust to outliers and
misspecification of the scale and number of clusters.


title:
Physics design for the C-ADS main linac basing on two different injector
  design schemes

abstract:
  The China ADS (C-ADS) project is proposed to build a 1000 MW Accelerator
Driven sub-critical System around 2032. The accelerator will work in CW mode
with 10 mA in beam current and 1.5 GeV in final beam energy. The linac is
composed of two major sections: the injector section and the main linac
section. There are two different schemes for the injector section. The
Injector-I scheme is based on a 325-MHz RFQ and superconducting spoke cavities
of same RF frequency and the Injector-II scheme is based on a 162.5-MHz RFQ and
superconducting HWR cavities of same frequency. The main linac design will be
different for different injector choice. The two different designs for the main
linac have been studied according to the beam characteristics from the
different injector schemes.


title: A Theoretical Analysis of NDCG Type Ranking Measures

abstract:
  A central problem in ranking is to design a ranking measure for evaluation of
ranking functions. In this paper we study, from a theoretical perspective, the
widely used Normalized Discounted Cumulative Gain (NDCG)-type ranking measures.
Although there are extensive empirical studies of NDCG, little is known about
its theoretical properties. We first show that, whatever the ranking function
is, the standard NDCG which adopts a logarithmic discount, converges to 1 as
the number of items to rank goes to infinity. On the first sight, this result
is very surprising. It seems to imply that NDCG cannot differentiate good and
bad ranking functions, contradicting to the empirical success of NDCG in many
applications. In order to have a deeper understanding of ranking measures in
general, we propose a notion referred to as consistent distinguishability. This
notion captures the intuition that a ranking measure should have such a
property: For every pair of substantially different ranking functions, the
ranking measure can decide which one is better in a consistent manner on almost
all datasets. We show that NDCG with logarithmic discount has consistent
distinguishability although it converges to the same limit for all ranking
functions. We next characterize the set of all feasible discount functions for
NDCG according to the concept of consistent distinguishability. Specifically we
show that whether NDCG has consistent distinguishability depends on how fast
the discount decays, and 1/r is a critical point. We then turn to the cut-off
version of NDCG, i.e., NDCG@k. We analyze the distinguishability of NDCG@k for
various choices of k and the discount functions. Experimental results on real
Web search datasets agree well with the theory.


title: A Weak Galerkin Finite Element Method with Polynomial Reduction

abstract:
  The novel idea of weak Galerkin (WG) finite element methods is on the use of
weak functions and their weak derivatives defined as distributions. Weak
functions and weak derivatives can be approximated by polynomials with various
degrees. Different combination of polynomial spaces leads to different weak
Galerkin finite element methods, which makes WG methods highly flexible and
efficient in practical computation. This paper explores the possibility of
optimal combination of polynomial spaces that minimize the number of unknowns
in the numerical scheme, yet without compromising the accuracy of the numerical
approximation. For illustrative purpose, the authors use second order elliptic
problems to demonstrate the basic idea of polynomial reduction. A new weak
Galerkin finite element method is proposed and analyzed. This new finite
element scheme features piecewise polynomials of degree $k\ge 1$ on each
element plus piecewise polynomials of degree $k-1\ge 0$ on the edge or face of
each element. Error estimates of optimal order are established for the
corresponding WG approximations in both a discrete $H^1$ norm and the standard
$L^2$ norm. In addition, the paper presents a great deal of numerical
experiments to demonstrate the power of the WG method in dealing with finite
element partitions consisting of arbitrary polygons in two dimensional spaces
or polyhedra in three dimensional spaces. The numerical examples include
various finite element partitions such as triangular mesh, quadrilateral mesh,
honey comb mesh in 2d and mesh with deformed cubes in 3d. The numerical results
show a great promise of the robustness, reliability, flexibility and accuracy
of the WG method.


title:
Improved Static Analysis of Parameterised Boolean Equation Systems using
  Control Flow Reconstruction

abstract:
  We present a sound static analysis technique for fighting the combinatorial
explosion of parameterised Boolean equation systems (PBESs). These essentially
are systems of mutually recursive fixed point equations ranging over
first-order logic formulae. Our method detects parameters that are not live by
analysing a control flow graph of a PBES, and it subsequently eliminates such
parameters. We show that a naive approach to constructing a control flow graph,
needed for the analysis, may suffer from an exponential blow-up, and we define
an approximate analysis that avoids this problem. The effectiveness of our
techniques is evaluated using a number of case studies.


title: An Apologia for Firewalls

abstract:
  We address proposed alternatives to the black hole firewall. We show that
embedding the interior Hilbert space of an old black hole into the Hilbert
space of the early radiation is inconsistent, as is embedding the
semi-classical interior of an AdS black hole into any dual CFT Hilbert space.
We develop the use of large AdS black holes as a system to sharpen the firewall
argument. We also reiterate arguments that unitary non-local theories can avoid
firewalls only if the non-localities are suitably dramatic.


title:
Aspects of Electrodynamics Modified by Some Dimension-five Lorentz
  Violating Interactions

abstract:
  Assuming Lorentz symmetry is broken by some fixed vector background, we study
the spinor electrodynamics modified by two dimension-five Lorentz-violating
interactions between fermions and photons. The effective polarization and
magnetization are identified from the modified Maxwell equations, and the
theoretical consequences are investigated. We also compute the corrections to
the relativistic energy levels of hydrogen atom induced by these
Lorentz-violating operators in the absence and presence of uniform external
fields in first-order perturbation theory. We find that the hydrogen spectrum
is insensitive to the breakdown of Lorentz boost symmetry.


title: Secure On-Off Transmission Design with Channel Estimation Errors

abstract:
  Physical layer security has recently been regarded as an emerging technique
to complement and improve the communication security in future wireless
networks. The current research and development in physical layer security is
often based on the ideal assumption of perfect channel knowledge or the
capability of variable-rate transmissions. In this work, we study the secure
transmission design in more practical scenarios by considering channel
estimation errors at the receiver and investigating both fixed-rate and
variable-rate transmissions. Assuming quasi-static fading channels, we design
secure on-off transmission schemes to maximize the throughput subject to a
constraint on secrecy outage probability. For systems with given and fixed
encoding rates, we show how the optimal on-off transmission thresholds and the
achievable throughput vary with the amount of knowledge on the eavesdropper's
channel. In particular, our design covers the interesting case where the
eavesdropper also uses the pilots sent from the transmitter to obtain imperfect
channel estimation. An interesting observation is that using too much pilot
power can harm the throughput of secure transmission if both the legitimate
receiver and the eavesdropper have channel estimation errors, while the secure
transmission always benefits from increasing pilot power when only the
legitimate receiver has channel estimation errors but not the eavesdropper.
When the encoding rates are controllable parameters to design, we further
derive both a non-adaptive and an adaptive rate transmission schemes by jointly
optimizing the encoding rates and the on-off transmission thresholds to
maximize the throughput of secure transmissions.


title:
Optimizing Cost, Delay, Packet Loss and Network Load in AODV Routing
  Protocol

abstract:
  AODV is Ad-hoc On-Demand Distance Vector.A mobile ad-hoc network is a
self-configuring network of mobile devices connected by wireless. MANET does
not have any fixed infrastructure. The device in a MANET is free to move in any
direction and will form the connection as per the requirement of the network.
Due to changing topology maintenance of factors like Packet loss, End to End
Delay, Number of hops, delivery ratio and controlling the network load is of
great challenge. This paper mainly concentrates on reducing the factors such as
cost, End-to-End Delay, Network Load and Packet loss in AODV routing protocol.
The NS-2 is used for the simulation purpose.


title: Locally linear representation for image clustering

abstract:
  It is a key to construct a similarity graph in graph-oriented subspace
learning and clustering. In a similarity graph, each vertex denotes a data
point and the edge weight represents the similarity between two points. There
are two popular schemes to construct a similarity graph, i.e., pairwise
distance based scheme and linear representation based scheme. Most existing
works have only involved one of the above schemes and suffered from some
limitations. Specifically, pairwise distance based methods are sensitive to the
noises and outliers compared with linear representation based methods. On the
other hand, there is the possibility that linear representation based
algorithms wrongly select inter-subspaces points to represent a point, which
will degrade the performance. In this paper, we propose an algorithm, called
Locally Linear Representation (LLR), which integrates pairwise distance with
linear representation together to address the problems. The proposed algorithm
can automatically encode each data point over a set of points that not only
could denote the objective point with less residual error, but also are close
to the point in Euclidean space. The experimental results show that our
approach is promising in subspace learning and subspace clustering.


title: Intertwining connectivities in representable matroids

abstract:
  Let $M$ be a representable matroid, and $Q, R, S, T$ subsets of the ground
set. We prove that, if $M$ is sufficiently large, then there is an element $e$
such that deleting or contracting $e$ preserves both the $Q$-$R$ and the
$S$-$T$ connectivities. For matroids representable over a finite field we prove
a stronger result: we show that we can remove $e$ such that both a connectivity
and a minor of $M$ are preserved.


title: Can P2P Networks be Super-Scalable?

abstract:
  We propose a new model for peer-to-peer networking which takes the network
bottlenecks into account beyond the access. This model can cope with key
features of P2P networking like degree or locality constraints together with
the fact that distant peers often have a smaller rate than nearby peers. Using
a network model based on rate functions, we give a closed form expression of
peers download performance in the system's fluid limit, as well as
approximations for the other cases. Our results show the existence of realistic
settings for which the average download time is a decreasing function of the
load, a phenomenon that we call super-scalability.


title: Density distributions of outflow driven turbulence

abstract:
  Protostellar jets and outflows are signatures of star formation and promising
mechanisms for driving supersonic turbulence in molecular clouds. We quantify
outflow-driven turbulence through three-dimensional numerical simulations using
an isothermal version of the robust total variation diminishing code. We drive
turbulence in real-space using a simplified spherical outflow model, analyse
the data through density probability distribution functions (PDF), and
investigate the Core Formation Rate per free-fall time (CFR_ff). The real-space
turbulence driving method produces a negatively skewed density PDF possessing
an enhanced tail on the low-density side. It deviates from the log-normal
distributions typically obtained from Fourier-space turbulence driving at low
densities, but can provide a good fit at high-densities, particularly in terms
of mass weighted rather than volume weighted density PDF. Due to this fact, we
suggest that the CFR_ff determined from a Fourier-driven turbulence model could
be comparable to that of our particular real-space driving model, which has a
ratio of solenoidal to compressional components from the resulting turbulence
velocity fields of ~0.6.


title:
Virtual Machine Trading in a Federation of Clouds: Individual Profit and
  Social Welfare Maximization

abstract:
  By sharing resources among different cloud providers, the paradigm of
federated clouds exploits temporal availability of resources and geographical
diversity of operational costs for efficient job service. While
interoperability issues across different cloud platforms in a cloud federation
have been extensively studied, fundamental questions on cloud economics remain:
When and how should a cloud trade resources (e.g., virtual machines) with
others, such that its net profit is maximized over the long run, while a
close-to-optimal social welfare in the entire federation can also be
guaranteed? To answer this question, a number of important, inter-related
decisions, including job scheduling, server provisioning and resource pricing,
should be dynamically and jointly made, while the long-term profit optimality
is pursued. In this work, we design efficient algorithms for inter-cloud
virtual machine (VM) trading and scheduling in a cloud federation. For VM
transactions among clouds, we design a double-auction based mechanism that is
strategyproof, individual rational, ex-post budget balanced, and efficient to
execute over time. Closely combined with the auction mechanism is a dynamic VM
trading and scheduling algorithm, which carefully decides the true valuations
of VMs in the auction, optimally schedules stochastic job arrivals with
different SLAs onto the VMs, and judiciously turns on and off servers based on
the current electricity prices. Through rigorous analysis, we show that each
individual cloud, by carrying out the dynamic algorithm in the online double
auction, can achieve a time-averaged profit arbitrarily close to the offline
optimum. Asymptotic optimality in social welfare is also achieved under
homogeneous cloud settings. We carry out trace-driven simulations to examine
the effectiveness of our algorithms and the achievable social welfare under
heterogeneous cloud settings.


title:
Kinematic quantum states for the Teleparallel Equivalent of General
  Relativity

abstract:
  A space of kinematic quantum states for the Teleparallel Equivalent of
General Relativity is constructed by means of projective techniques. The states
are kinematic in this sense that their construction bases merely on the
structure of the phase space of the theory and does not take into account
constraints on it. The space of quantum states is meant to serve as an element
of a canonical quantization of the theory.


title:
Millimeter-scale and large-angle self-collimation in a photonic crystal
  composed of silicon nanorods

abstract:
  We report the observation of a large-angle self-collimation phenomenon
occurring in photonic crystals composed of nanorods. Electromagnetic waves
incident onto such photonic crystals from directions covering a wide-range of
incident angles become highly localized along a single array of rods, which
results in narrow-beam propagation without divergence. A propagation length of
0.4 mm is experimentally observed over the wavelength range of 1540 nm to 1570
nm, even in the large incident angle case, which is a very considerable length
scale for on-chip optical interconnection.


title: Route-Based Detection of Conflicting ATC Clearances on Airports

abstract:
  Runway incursions are among the most serious safety concerns in air traffic
control. Traditional A-SMGCS level 2 safety systems detect runway incursions
with the help of surveillance information only. In the context of SESAR,
complementary safety systems are emerging that also use other information in
addition to surveillance, and that aim at warning about potential runway
incursions at earlier points in time. One such system is "conflicting ATC
clearances", which processes the clearances entered by the air traffic
controller into an electronic flight strips system and cross-checks them for
potentially dangerous inconsistencies. The cross-checking logic may be
implemented directly based on the clearances and on surveillance data, but this
is cumbersome. We present an approach that instead uses ground routes as an
intermediate layer, thereby simplifying the core safety logic.


title:
Proposal for carrier-envelope-phase stable single-cycle pulse generation
  in the mid-infrared - extreme-ultraviolet range

abstract:
  A robust method for producing half-cycle - few-cycle pulses in mid-infrared
to extreme ultraviolet spectral ranges is proposed. It is based on coherent
undulator radiation of relativistic ultrathin electron layers, which are
produced by microbunching of ultrashort electron bunches by a TW power laser in
a modulator undulator. According to our numerical calculations it is possible
to generate as short as 10 nm long electron layers in a single-period modulator
undulator having an undulator parameter of only K=0.25 and which is
significantly shorter than the resonant period length. By using these electron
layers the production of carrier-envelope-phase stable pulses with up to a few
nJ energy and down to 30 nm wavelength and 70 as duration is predicted.


title:
Transmission Sequence Design and Allocation for Wide Area Ad Hoc
  Networks

abstract:
  In this paper we examine the problem of designing and allocating transmission
sequences to users in a mobile ad hoc network that has no spatial boundary. A
basic tenet of the transmission sequence approach for addressing media access
control is that under normal operating conditions, there is no feedback
triggered re-transmission. This obviously is a major departure from the
Slotted-ALOHA or CSMA type approaches. While these solutions enjoy excellent
throughput performance, a fundamental drawback is that they are based on
feedback information. For systems without naturally defined central controller
that can play the role of a base station, the task of providing feedback
information could easily become unmanageable. This highlights the advantage of
the feedback-free approach. A second advantage is the ability to handle
unlimited spatial coverage. We propose in this paper a concept for media access
control that is akin to frequency reuse. However, instead of reusing frequency,
the new approach allows transmission sequences be reused. A study of the
transmission sequence approach against other approaches is conducted by
comparing the minimal frame lengths that can guarantee the existence of
conflict-free transmissions.


title: Statistical Study of 2XMMi-DR3/SDSS-DR8 Cross-correlation Sample

abstract:
  Cross-correlating the XMM-Newton 2XMMi-DR3 catalog with the Sloan Digital Sky
Survey (SDSS) Data Release 8, we obtain one of the largest X-ray/optical
catalogs and explore the distribution of various classes of X-ray emitters in
the multidimensional photometric parameter space. Quasars and galaxies occupy
different zones while stars scatter in them. However, X-ray active stars have a
certain distributing rule according to spectral types. The earlier the type of
stars, the stronger X-ray emitting. X-ray active stars have a similar
distribution to most of stars in the g-r versus r-i diagram. Based on the
identified samples with SDSS spectral classification, a random forest algorithm
for automatic classification is performed. The result shows that the
classification accuracy of quasars and galaxies adds up to more than 93.0%
while that of X-ray emitting stars only amounts to 45.3%. In other words, it is
easy to separate quasars and galaxies, but it is difficult to discriminate
X-ray active stars from quasars and galaxies. If we want to improve the
accuracy of automatic classification, it is necessary to increase the number of
X-ray emitting stars, since the majority of X-ray emitting sources are quasars
and galaxies. The results obtained here will be used for the optical spectral
survey performed by the Large sky Area Multi-Object fiber Spectroscopic
Telescope (LAMOST, also named the Guo Shou Jing Telescope), which is a Chinese
national scientific research facility operated by the National Astronomical
Observatories, Chinese Academy of Sciences.


title: Apricot - An Object-Oriented Modeling Language for Hybrid Systems

abstract:
  We propose Apricot as an object-oriented language for modeling hybrid
systems. The language combines the features in domain specific language and
object-oriented language, that fills the gap between design and implementation,
as a result, we put forward the modeling language with simple and distinct
syntax, structure and semantics. In addition, we introduce the concept of
design by convention into Apricot.As the characteristic of object-oriented and
the component architecture in Apricot, we conclude that it is competent for
modeling hybrid systems without losing scalability.


title: Logging safely in public spaces using color PINs

abstract:
  Nowadays, we are increasingly logging on many different Internet sites to
access private data like emails or photos remotely stored in the clouds. This
makes us all the more concerned with digital identity theft and passwords being
stolen either by key loggers or shoulder-surfing attacks. Quite surprisingly,
the current bottleneck of computer security when logging for authentication is
the User Interface (UI): How can we enter safely secret passwords when
concealed spy cameras or key loggers may be recording the login session?
Logging safely requires to design a secure Human Computer Interface (HCI)
robust to those attacks. We describe a novel method and system based on
entering secret ID passwords by means of associative secret UI passwords that
provides zero-knowledge to observers. We demonstrate the principles using a
color Personal Identification Numbers (PINs) login system and describes its
various extensions.


title:
Comparative study of monotonically convergent optimization algorithms
  for the control of molecular rotation

abstract:
  We apply two different monotonically convergent optimization algorithms to
the control of molecular rotational dynamics by laser pulses. This example
represents a quantum control problem where the interaction of the system with
the external field is non-linear. We test the validity and accuracy of the two
methods on the key control targets of producing molecular orientation and
planar delocalization at zero temperature, and maximizing permanent alignment
at non-zero temperature.


title: Occupational Fraud Detection Through Visualization

abstract:
  Occupational fraud affects many companies worldwide causing them economic
loss and liability issues towards their customers and other involved entities.
Detecting internal fraud in a company requires significant effort and,
unfortunately cannot be entirely prevented. The internal auditors have to
process a huge amount of data produced by diverse systems, which are in most
cases in textual form, with little automated support. In this paper, we exploit
the advantages of information visualization and present a system that aims to
detect occupational fraud in systems which involve a pair of entities (e.g., an
employee and a client) and periodic activity. The main visualization is based
on a spiral system on which the events are drawn appropriately according to
their time-stamp. Suspicious events are considered those which appear along the
same radius or on close radii of the spiral. Before producing the
visualization, the system ranks both involved entities according to the
specifications of the internal auditor and generates a video file of the
activity such that events with strong evidence of fraud appear first in the
video. The system is also equipped with several different visualizations and
mechanisms in order to meet the requirements of an internal fraud detection
system.


title: Fluctuation theorems in inhomogenious media under coarse graining

abstract:
  We compare the fluctuation relations for work and entropy in underdamped and
overdamped systems, when the friction coefficient of the medium is
space-dependent. We find that these relations remain unaffected in both cases.
However, for the overdamped system, the analysis is more involved, and a blind
application of normal rules of calculus would lead to inconsistent results.


title: Links and submersions to the plane on an open 3-manifold

abstract:
  We study the realization problem which asks if a given oriented link in an
open 3-manifold can be realized as a fiber of a submersion to the Euclidean
plane. We correct the results obtained before by the author which contains an
error and certain imperfection, and investigate a necessary and sufficient
condition for the realization in the words of well-known invariants. We obtain
the condition expressed by the first homology group with mod 2 coefficient.


title: An $L^p$ theory for stationary radiative transfer

abstract:
  We present a self-contained analysis of the stationary radiative transfer
equation in weighted $L^p$ spaces. The use of weighted spaces allows us to
derive uniform a-priori estimates for $1 \le p \le \infty$ under minimal
assumptions on the parameters. By constructing an explicit example, we show
that our estimates are sharp and cannot be improved in general. Better
estimates are however derived under additional assumptions on the parameters.
We also present estimates for derivatives and traces of the solution and
formulate a natural energy space, for which the data-to-solution map becomes an
isomorphism. As a side result, we are able to prove uniform convergence of the
source iteration for all $1 \le p \le \infty$ without the assumption of
positive absorption that is frequently used in the literature.


title: Software Design Principles of a DFS Tower A-CWP Prototype

abstract:
  SESAR is supposed to boost the development of new operational procedures
together with the supporting systems in order to modernize the pan-European air
traffic management (ATM). One consequence of this development is that more and
more information is presented to - and has to be processed by - air traffic
control officers (ATCOs). Thus, there is a strong need for a software design
concept that fosters the development of an advanced (tower) controller working
position (A-CWP) that comprehensively integrates the still counting amount of
information while reducing the data management workload of ATCOs. We report on
our first hands-on experiences obtained during the development of an A-CWP
prototype that was used in two SESAR validation sessions.


title:
Toward Recovering Complete SRS for Softbody Simulation System and a
  Sample Application - a Team 4 SOEN6481-W13 Project Report

abstract:
  This document gathers high-level users requirements and describes the system
features. It provides a detailed explanation of the main functionalities of the
system with a more emphasis on the stakeholders needs and wants. Indeed, the
document goes through design constraints that may restrict various aspects of
the design and implementation.


title: Surface acoustic waves in rotating orthorhombic crystals

abstract:
  The propagation of surface (Rayleigh) waves over a rotating orthorhombic
crystal is studied. The crystal possesses three crystallographic axes, normal
to the symmetry planes: the half-space is cut along a plane normal to one of
these axes, the wave travels in the direction of another, and the rotation
occurs at a uniform rate about any of the three axes. The secular equation for
the surface wave speed is found explicitly; in contrast to the non-rotating
case, it is dispersive (frequency-dependent). Both Coriolis and centrifugal
accelerations appear in the equations of motion: none can be neglected in favor
of the other, even at small rotation rates.


title:
Theoretical analysis of Sinc-collocation methods and Sinc-Nystr\"{o}m
  methods for initial value problems

abstract:
  A Sinc-collocation method has been proposed by Stenger, and he also gave
theoretical analysis of the method in the case of a `scalar' equation. This
paper extends the theoretical results to the case of a `system' of equations.
Furthermore, this paper proposes more efficient method by replacing the
variable transformation employed in Stenger's method. The efficiency is
confirmed by both of theoretical analysis and numerical experiments. In
addition to the existing and newly-proposed Sinc-collocation methods, this
paper also gives similar theoretical results for Sinc-Nystr\"{o}m methods
proposed by Nurmuhammad et al. From a viewpoint of the computational cost, it
turns out that the newly-proposed Sinc-collocation method is the most efficient
among those methods.


title:
Field-angle Resolved Flux-flow Resistivity as a Phase-sensitive Probe of
  Unconventional Cooper Pairing

abstract:
  We theoretically investigate the applied magnetic field-angle dependence of
the flux-flow resistivity $\rho_{\rm f}(\alpha_{\rm M})$ for an uniaxially
anisotropic Fermi surface. $\rho_{\rm f}$ is related to the quasiparticle
scattering rate $\varGamma$ inside a vortex core, which reflects the sign
change in the superconducting pair potential. We find that $\rho_{\rm
f}(\alpha_{\rm M})$ is sensitive to the sign-change in the pair potential and
has its maximum when the magnetic field is parallel to the gap-node direction.
We propose the measurement of the field-angle dependent oscillation of
$\rho_{\rm f}(\alpha_{\rm M})$ as a phase-sensitive field-angle resolved
experiment.


title: A Note on Hadwiger's Conjecture

abstract:
  Hadwiger's Conjecture states that every $K_{t+1}$-minor-free graph is
$t$-colourable. It is widely considered to be one of the most important
conjectures in graph theory. If every $K_{t+1}$-minor-free graph has minimum
degree at most $\delta$, then every $K_{t+1}$-minor-free graph is
$(\delta+1)$-colourable by a minimum-degree-greedy algorithm. The purpose of
this note is to prove a slightly better upper bound.


title:
Connectivities of Potts Fortuin-Kasteleyn clusters and time-like
  Liouville correlator

abstract:
  Recently, two of us argued that the probability that an FK cluster in the
Q-state Potts model connects three given points is related to the time-like
Liouville three-point correlation function. Moreover, they predicted that the
FK three-point connectivity has a prefactor which unveils the effects of a
discrete symmetry, reminiscent of the S_Q permutation symmetry of the Q=2,3,4
Potts model. Their theoretical prediction has been checked for the case of
percolation, corresponding to Q=1. We revisit the derivation of the time-like
Liouville correlator given by Al. Zamolodchikov and show that this is the the
only consistent analytic continuation of the minimal model structure constants.
We then present strong numerical tests of the relation between the time-like
Liouville correlator and percolative properties of the FK clusters for real
values of Q.


title:
Low temperature ferromagnetism, surface paramagnetism and exchange bias
  effect in nano-grained alpha-Fe1.4Ga0.6O3 oxide

abstract:
  The compound alpha-Fe1.4Ga0.6O3 has been prepared by mechanical alloying of
alpha-Fe2O3 and Ga2O3 and subsequent heating of the mechanical alloyed samples
in vacuum condition. Magnetic ordering of alpha-Fe2O3 has been modified by
substitution of non-magnetic Ga atoms. The ferromagnetism in alpha-Fe1.4Ga0.6O3
is more soft and enhanced in comparison to alpha-Fe2O3. M\"ossbauer
spectroscopy also confirmed enhanced ferromagnetic order in alpha-Fe1.4Ga0.6O3.
The room temperature soft ferromagnetism by Ga substitution is interesting for
designing alpha-Fe2O3 based unconventional ferromagnet, which is a great
challenge to the materials scientists. The alpha-Fe1.4Ga0.6O3 samples also
exhibited features of exchange bias, low temperature surface paramagnetism, and
suppression of Morin transition. These features have been affected up to
certain extent by the nano-sized grains of the samples.


title:
Numerical study of shock formation in the dispersionless
  Kadomtsev-Petviashvili equation and dispersive regularizations

abstract:
  The formation of singularities in solutions to the dispersionless
Kadomtsev-Petviashvili (dKP) equation is studied numerically for different
classes of initial data. The asymptotic behavior of the Fourier coefficients is
used to quantitatively identify the critical time and location and the type of
the singularity. The approach is first tested in detail in 1+1 dimensions for
the known case of the Hopf equation, where it is shown that the break-up of the
solution can be identified with prescribed accuracy. For dissipative
regularizations of this shock formation as the Burgers' equation and for
dispersive regularizations as the Korteweg-de Vries equation, the Fourier
coefficients indicate as expected global regularity of the solutions. The
Kadomtsev-Petviashvili (KP) equation can be seen as a dispersive regularization
of the dKP equation. The behavior of KP solutions for small dispersion
parameter $\epsilon\ll 1$ near a break-up of corresponding dKP solutions is
studied. It is found that the difference between KP and dKP solutions for the
same initial data at the critical point scales roughly as $\epsilon^{2/7}$ as
for the Korteweg-de Vries equation.


title: A minimal communication approach to parallel time integration

abstract:
  We explore an approach due to Nievergelt of decomposing a time-evolution
equation along the time dimension and solving it in parallel with as little
communication as possible between the processors. This method computes a map
from initial conditions to final conditions locally on slices of the time
domain, and then patches these operators together into a global solution using
a single communication step. A basic error analysis is given, and some
comparisons are made with other parallel in time methods. Based on the
assumption that parallel computation is cheap but communication is very
expensive, it is shown that this method can be competitive for some problems.
We present numerical simulations on graphics chips and on traditional parallel
clusters using hundreds of processors for a variety of problems to show the
practicality and scalability of the proposed method.


title:
Spin Resolution and Evidence for Superexchange on NiO(001) observed by
  Force Microscopy

abstract:
  The spin order of the nickel oxide (001) surface is resolved, employing
non-contact atomic force microscopy at 4.4 K using bulk Fe- and SmCo-tips
mounted on a qPlus sensor that oscillates at sub-50 pm amplitudes. The
spin-dependent signal is hardly detectable with Fe-tips. In contrast, SmCo-tips
yield a height contrast of 1.35 pm for Ni ions with opposite spins. SmCo tips
even show a small height contrast on the O atoms of 0.5 pm within the 2x1 spin
unit cell, pointing to the observation of superexchange. We attribute this to
the increased magnetocrystalline anisotropy energy of SmCo, which stabilizes
the magnetic moment at the apex. Atomic force spectroscopy on the Ni up, Ni
down and O lattice site reveals a magnitude of the exchange energy of merely 1
meV at the closest accessible distance with an exponential decay length of
\lambda_exc = 18 pm.


title: Charge form factors of two-neutron halo nuclei in halo EFT

abstract:
  We set up a formalism to calculate the charge form factors of two-neutron
halo nuclei with S-wave neutron-core interactions in the framework of the halo
effective field theory. The method is applied to some known and suspected halo
nuclei. In particular, we calculate the form factors and charge radii relative
to the core to leading order in the halo EFT and compare to experiments where
they are available. Moreover, we investigate the general dependence of the
charge radius on the core mass and the one- and two-neutron separation
energies.


title:
Statistics of Conductances and Subleading Corrections to Scaling near
  the Integer Quantum Hall Plateau Transition

abstract:
  We study the critical behavior near the integer quantum Hall plateau
transition by focusing on the multifractal (MF) exponents $X_q$ describing the
scaling of the disorder-average moments of the point contact conductance $T$
between two points of the sample, within the Chalker-Coddington network model.
Past analytical work has related the exponents $X_q$ to the MF exponents
$\Delta_q$ of the local density of states (LDOS). To verify this relation, we
numerically determine the exponents $X_q$ with high accuracy. We thereby
provide, at the same time, independent numerical results for the MF exponents
$\Delta_q$ for the LDOS. The presence of subleading corrections to scaling
makes such determination directly from scaling of the moments of $T$ virtually
impossible. We overcome this difficulty by using two recent advances. First, we
construct pure scaling operators for the moments of $T$ which have precisely
the same leading scaling behavior, but no subleading contributions. Secondly,
we take into account corrections to scaling from irrelevant (in the
renormalization group sense) scaling fields by employing a numerical technique
("stability map") recently developed by us. We thereby numerically confirm the
relation between the two sets of exponents, $X_q$ (point contact conductances)
and $\Delta_q$ (LDOS), and also determine the leading irrelevant (corrections
to scaling) exponent $y$ as well as other subleading exponents. Our results
suggest a way to access multifractality in an experimental setting.


title: (Sigma-Delta) Codes

abstract:
  In this paper we introduce the notion of cyclic ($f(t),\sigma,\delta$)-codes
for $f(t)\in \Ore$. These codes generalize the $\theta$-codes as introduced by
D. Boucher, F. Ulmer, W. Geiselmann \cite{BGU}. We construct generic and
control matrices for these codes. As a particular case the ($\si,\de$)-$W$-code
associated to a Wedderburn polynomial are defined and we show that their
control matrices are given by generalized Vandermonde matrices. All the
Wedderburn polynomials of $\mathbb F_q[t;\theta]$ are described and their
control matrices are presented. A key role will be played by the pseudo-linear
transformations.


title:
On extreme field limits in high power laser matter interactions:
  radiation dominant regimes in high intensity electromagnetic wave interaction
  with electrons

abstract:
  We discuss the key important regimes of electromagnetic field interaction
with charged particles. Main attention is paid to the nonlinear Thomson/Compton
scattering regime with the radiation friction and quantum electrodynamics
effects taken into account. This process opens a channel of high efficiency
electromagnetic energy conversion into hard electromagnetic radiation in the
form of ultra short high power gamma ray flashes.


title:
The Mysterious Sickle Object in the Carina Nebula: A stellar wind
  induced bow shock grazing a clump?

abstract:
  Optical and near-infrared images of the Carina Nebula show a peculiar
arc-shaped feature, which we call the "Sickle", next to the B-type star
Trumpler 14 MJ 218. We use multi-wavelength observations to explore and
constrain the nature and origin of the nebulosity. Using sub-mm data from
APEX/LABOCA as well as Herschel far-infrared maps, we discovered a dense,
compact clump with a mass of ~ 40 Msun located close to the apex of the Sickle.
We investigate how the B-star MJ 218, the Sickle, and the clump are related.
Our numerical simulations show that, in principle, a B-type star located near
the edge of a clump can produce a crescent-shaped wind shock front, similar to
the observed morphology. However, the observed proper motion of MJ 218 suggest
that the star moves with high velocity (~ 100 km/s) through the ambient
interstellar gas. We argue that the star is just about to graze along the
surface of the clump, and the Sickle is a bow shock induced by the stellar
wind, as the object moves supersonically through the density gradient in the
envelope of the clump.


title: Letter Change Bias and Local Uniqueness in Optimal Sequence Alignments

abstract:
  Considering two optimally aligned random sequences, we investigate the effect
on the alignment score caused by changing a random letter in one of the two
sequences. Using this idea in conjunction with large deviations theory, we show
that in alignments with a low proportion of gaps the optimal alignment is
locally unique in most places with high probability. This has implications in
the design of recently pioneered alignment methods that use the local
uniqueness as a homology indicator.


title:
Joint reconstruction of galaxy clusters from gravitational lensing and
  thermal gas. II. Inversion of the thermal Sunyaev-Zel'dovich effect

abstract:
  This paper continues a series in which we intend to show how all observables
of galaxy clusters can be combined to recover the two-dimensional, projected
gravitational potential of individual clusters. Our goal is to develop a
non-parametric algorithm for joint cluster reconstruction taking all cluster
observables into account. In this paper, we begin with the relation between the
Compton-y parameter and the Newtonian gravitational potential, assuming
hydrostatic equilibrium and a polytropic stratification of the intracluster
gas. We show how Richardson-Lucy deconvolution can be used to convert the
intensity change of the CMB due to the thermal Sunyaev-Zel'dovich effect into
an estimate for the two-dimensional gravitational potential. Synthetic data
simulated with characteristics of the ALMA telescope show that the
two-dimensional potential of a cluster with mass 5*10^14 M_sun/h at redshift
0.2 is possible with an error of < 5% between the cluster centre and a radius r
< 0.9 Mpc/h.


title:
Parametric study of non-relativistic electrostatic shocks and the
  structure of their transition layer

abstract:
  Nonrelativistic electrostatic unmagnetized shocks are frequently observed in
laboratory plasmas and they are likely to exist in astrophysical plasmas. Their
maximum speed, expressed in units of the ion acoustic speed far upstream of the
shock, depends only on the electron-to-ion temperature ratio if binary
collisions are absent. The formation and evolution of such shocks is examined
here for a wide range of shock speeds with particle-in-cell (PIC) simulations.
The initial temperatures of the electrons and the 400 times heavier ions are
equal. Shocks form on electron time scales at Mach numbers between 1.7 and 2.2.
Shocks with Mach numbers up to 2.5 form after tens of inverse ion plasma
frequencies. The density of the shock-reflected ion beam increases and the
number of ions crossing the shock thus decreases with an increasing Mach
number, causing a slower expansion of the downstream region in its rest frame.
The interval occupied by this ion beam is on a positive potential relative to
the far upstream. This potential pre-heats the electrons ahead of the shock
even in the absence of beam instabilities and decouples the electron
temperature in the foreshock ahead of the shock from the one in the far
upstream plasma. The effective Mach number of the shock is reduced by this
electron heating. This effect can potentially stabilize nonrelativistic
electrostatic shocks moving as fast as supernova remnant (SNR) shocks.


title: Time-resolved characterization of the formation of a collisionless shock

abstract:
  We report on the temporally and spatially resolved detection of the
precursory stages that lead to the formation of an unmagnetized, supercritical
collision-less shock in a laser-driven laboratory experiment. The measured
evolution of the electrostatic potential associated with the shock unveils the
transition from a current free double layer into a symmetric shock structure,
stabilized by ion reflection at the shock front. Supported by a matching
Particle-In-Cell simulation and theoretical considerations, we suggest that
this process is analogeous to ion reflection at supercritical collisionless
shocks in supernova remnants.


title:
Observation of an inter-sublattice exchange magnon in CoCr$_2$O$_4$ and
  analysis of magnetic ordering

abstract:
  We report on an investigation of optical properties of multiferroic
CoCr$_{2}$O$_{4}$ at terahertz frequencies in magnetic fields up to 30 T. Below
the ferrimagnetic transition (94 K), the terahertz response of
CoCr$_{2}$O$_{4}$ is dominated by a magnon mode, which shows a steep
magnetic-field dependence. We ascribe this mode to an exchange resonance
between two magnetic sublattices with different $g$-factors. In the framework
of a simple two-sublattice model (the sublattices are formed by Co$^{2+}$ and
Cr$^{3+}$ ions), we find the inter-sublattice coupling constant, $\lambda = -
(18 \pm 1)$ K, and trace the magnetization for each sublattice as a function of
field. We show that the Curie temperature of the Cr$^{3+}$ sublattice,
$\Theta_{2}$ = $(49 \pm 2)$ K, coincides with the temperature range, where
anomalies of the dielectric and magnetic properties of CoCr$_{2}$O$_{4}$ have
been reported in literature.


title:
A new proof of the uniqueness of the flow for ordinary differential
  equations with BV vector fields

abstract:
  We provide in this article a new proof of the uniqueness of the flow solution
to ordinary differential equations with $BV$ vector-fields that have divergence
in $L^\infty$ (or in $L^1$) and that are nearly incompressible (see the text
for the definition of this term). The novelty of the proof lies in the fact it
does not use the associated transport equation.


title:
Obtaining the CMB anomalies with a bounce from the contracting phase to
  inflation

abstract:
  Recent Planck data show the anomalies of CMB fluctuations on large angular
scales, which confirms the early observations by WMAP. We continue studying an
inflationary model, in which before the slow roll inflation the universe is in
a contracting phase, and fit the model with the Planck data. It is showed that
this model may generate not only the power deficit at low-l, but also a large
hemispherical power asymmetry in CMB. We also discuss the implication of the
result to the eternal inflation scenario.


title:
Nonanticipative Rate Distortion Function for General Source-Channel
  Matching

abstract:
  In this paper we invoke a nonanticipative information Rate Distortion
Function (RDF) for sources with memory, and we analyze its importance in
probabilistic matching of the source to the channel so that transmission of a
symbol-by-symbol code with memory without anticipation is optimal, with respect
to an average distortion and excess distortion probability. We show
achievability of the symbol-by-symbol code with memory without anticipation,
and we evaluate the probabilistic performance of the code for a Markov source.


title:
Existence of Anosov diffeomorphisms on infra-nilmanifolds modeled on
  free nilpotent Lie groups

abstract:
  An infra-nilmanifold is a manifold which is constructed as a quotient space
$\Gamma\backslash G$ of a simply connected nilpotent Lie group $G$, where
$\Gamma$ is a discrete group acting properly discontinuously and cocompactly on
$G$ via so called affine maps. The manifold $\Gamma\backslash G$ is said to be
modeled on the Lie group $G$. This class of manifolds is conjectured to be the
only class of closed manifolds allowing an Anosov diffeomorphism. However, it
is far from obvious which of these infra--nilmanifolds actually do admit an
Anosov diffeomorphism. In this paper we completely solve this question for
infra-nilmanifolds modeled on a free $c$--step nilpotent Lie group.


title: Parabolic Strip Telescope

abstract:
  We present a proposal of a new type of telescopes using a rotating parabolic
strip as the primary mirror. It is the most principal modification of the
design of telescopes from the times of Galileo and Newton. In order to
demonstrate the basic idea, the image of an artificial constellation observed
by this kind of telescope was reconstructed using the techniques described in
this article. As a working model of this new telescope, we have used an
assembly of the primary mirror---a strip of acrylic glass parabolic mirror 40
cm long and 10 cm wid shaped as a parabolic cylinder of focal length 1 m---and
an artificial constellation, a set of 5 apertures in a distance of 5 m
illuminated from behind. In order to reconstruct the image, we made a series of
snaps, each after a rotation of the constellation by 15 degrees. Using Matlab
we reconstructed the image of the artificial constellation.


title:
Control limitations from distributed sensing: theory and Extremely Large
  Telescope application

abstract:
  We investigate performance bounds for feedback control of distributed plants
where the controller can be centralized (i.e. it has access to measurements
from the whole plant), but sensors only measure differences between neighboring
subsystem outputs. Such "distributed sensing" can be a technological necessity
in applications where system size exceeds accuracy requirements by many orders
of magnitude. We formulate how distributed sensing generally limits feedback
performance robust to measurement noise and to model uncertainty, without
assuming any controller restrictions (among others, no "distributed control"
restriction). A major practical consequence is the necessity to cut down
integral action on some modes. We particularize the results to spatially
invariant systems and finally illustrate implications of our developments for
stabilizing the segmented primary mirror of the European Extremely Large
Telescope.


title: Absolute geometry and the Habiro topology

abstract:
  Lecture notes of a course on A. Smirnov's approach to the ABC-conjecture via
F1-geometry and an attempt to relate this to Jim Borger's F1-geometry based on
lambda-rings.


title: Locally exact modifications of discrete gradient schemes

abstract:
  Locally exact integrators preserve linearization of the original system at
every point. We construct energy-preserving locally exact discrete gradient
schemes for arbitrary multidimensional canonical Hamiltonian systems by
modifying classical discrete gradient schemes. Modifications of this kind are
found for any discrete gradient.


title: Origin of Cosmic Magnetic Fields

abstract:
  We calculate, in the free Maxwell theory, the renormalized quantum vacuum
expectation value of the two-point magnetic correlation function in de Sitter
inflation. We find that quantum magnetic fluctuations remain constant during
inflation instead of being washed out adiabatically, as usually assumed in the
literature. The quantum-to-classical transition of super-Hubble magnetic modes
during inflation, allow us to treat the magnetic field classically after
reheating, when it is coupled to the primeval plasma. The actual magnetic field
is scale independent and has an intensity of few \times 10^(-12) G if the
energy scale of inflation is few \times 10^(16) GeV. Such a field accounts for
galactic and galaxy cluster magnetic fields.


title:
The influence of the meteorological forcing data on the reconstructions
  of historical storms in the Black Sea

abstract:
  The present article is a study of the applicability of different sources of
meteorological forcing for the coastal wave and storm surge models, which
provide the operational marine forecasts for the coastal early warning systems
(EWS) and are used for reconstructions of historical storms. The reconstruction
of historical storms is one of the approaches to the natural coastal hazard
vulnerability assessment. We evaluate the importance of the input
meteorological information for the mentioned types of coastal models. For two
well documented historical storms, that caused significant damages along the
Bulgarian coast we simulate the significant wave heights and sea level change,
using SWAN wave model and a storm surge model. The wind and mean sea level
pressure fields, which are used in the present study, are extracted from the
ERA Interim reanalysis of the European Center for Medium range Forecasts
(ECMWF) and from the output of the high resolution limited area numerical
weather prediction model ALADIN. The overall conclusion is that for the
successful historical storms reconstructions ERA Interim and ERA40 reanalysis
are valuable source of meteorological forcing, but due to their limitations in
terms of spatial and temporal resolution, it is recommended to produce a higher
spatial and temporal resolution meteorological fields, using dynamical
downscaling of the reanalyzed data.


title:
Consistent non-parametric Bayesian estimation for a time-inhomogeneous
  Brownian motion

abstract:
  We establish posterior consistency for non-parametric Bayesian estimation of
the dispersion coefficient of a time-inhomogeneous Brownian motion.


title:
M theory Branes : U duality properties and a class of new Static
  Solutions

abstract:
  We obtain the most general static intersecting brane solutions by directly
solving the relevant equations of motion analytically and in complete
generality. These solutions reduce to the known ones in special cases, and
contain further a class of new static solutions which are horizonless. We
describe their properties and discuss their physical relevance. Along the way,
we also describe the features of the brane energy momentum tensors, the
equations of motion, and their solutions which arise as consequences of the
intersection rules and the U duality symmetries of M theory.


title:
On some noncommutative symmetric functions analogous to Hall-Littlewood
  and Macdonald polynomials

abstract:
  We investigate the connections between various noncommutative analogues of
Hall-Littlewood and Macdonald polynomials, and define some new families of
noncommutative symmetric functions depending on two sequences of parameters.


title: IIB horizons

abstract:
  We solve the Killing spinor equations for all near-horizon IIB geometries
which preserve at least one supersymmetry. We show that generic horizon
sections are 8-dimensional almost Hermitian spin${}_c$ manifolds. Special cases
include horizon sections with a $Spin(7)$ structure and those for which the
Killing spinor is pure. We also explain how the common sector horizons and the
horizons with only 5-form flux are included in our general analysis. We
investigate several special cases mainly focusing on the horizons with constant
scalars admitting a pure Killing spinor and find that some of these exhibit a
generalization of the 2-SCYT condition that arises in the horizons with 5-form
fluxes only. We use this to construct new examples of near-horizon geometries
with both 3-form and 5-form fluxes.


title: Crossed products for actions of crossed modules on C*-algebras

abstract:
  We decompose the crossed product functor for actions of crossed modules of
locally compact groups on C*-algebras into more elementary constructions:
taking crossed products by group actions and fibres in C*-algebras over
topological spaces. For this, we extend the theory of partial crossed products
from groups to crossed modules; extend Takesaki-Takai duality to Abelian
crossed modules; show that equivalent crossed modules have equivalent
categories of actions on C*-algebras; and show that certain crossed modules are
automatically equivalent to Abelian crossed modules.


title: Firm Frobenius monads and firm Frobenius algebras

abstract:
  Firm Frobenius algebras are firm algebras and counital coalgebras such that
the comultiplication is a bimodule map. They are investigated by categorical
methods based on a study of adjunctions and lifted functors. Their categories
of comodules and of firm modules are shown to be isomorphic if and only if a
canonical comparison functor from the category of comodules to the category of
non-unital modules factorizes through the category of firm modules. This
happens for example if the underlying algebra possesses local units, e.g. the
firm Frobenius algebra arises from a co-Frobenius coalgebra over a base field;
or if the comultiplication splits the multiplication (hence the underlying
coalgebra is coseparable).


title: Domain wall in $f(R)$ gravity

abstract:
  The gravitational impact inside and outside of a domain wall is studied in
the context of $f(R)$ gravity theory. The function $f(R)$ is found which
satisfies the stability conditions. Our results imply that the domain wall may
cause topological inflation.


title: Supramolecular Spin Valves

abstract:
  Magnetic molecules possess a high potential as building blocks for the design
of spintronic devices. Moreover, the use of molecular materials opens the way
for the controlled use of bottom-up, e.g. supramolecular, processing techniques
combining massively parallel self-fabrication with conventional top-down
nanostructuring techniques. The development of solid state spintronic devices
based on the giant magnetoresistance (GMR), tunnel magnetoresistance (TMR), and
spin valve effects has revolutionized the field of magnetic memory
applications. Recently, organic semiconductors were inserted into nanometer
sized tunnel junctions allowing enhancement of spin reversal, giant
magneto-resistance behaviour was observed in single non-magnetic molecules
coupled to magnetic electrodes, and the use of the quantum tunnelling
properties of single-molecule magnets (SMMs) in hybrid devices was proposed.
Herein, we present an original device in which a non-magnetic molecular quantum
dot, made of a single-wall carbon nanotube (SWCNT) contacted with non-magnetic
electrodes, is laterally coupled via supramolecular interactions to a TbPc2-SMM
(Pc = phthalocyanine), which provides a localized magnetic moment. The
conductance through the SWCNT is modulated by sweeping the magnetic field,
exhibiting magnetoresistance ratios up to 300% between fully polarized and
non-polarized SMMs below 1 K. We thus demonstrate the functionality of a
supramolecular spin valve without magnetic leads. Our results open up prospects
of circuit-integration and implementation of new device capabilities.


title: The probability measure corresponding to 2-plane trees

abstract:
  We study the probability measure $\mu_{0}$ for which the moment sequence is
$\binom{3n}{n}\frac{1}{n+1}$. We prove that $\mu_{0}$ is absolutely continuous,
find the density function and prove that $\mu_{0}$ is infinitely divisible with
respect to the additive free convolution.


title: Variational formulations of sound-proof models

abstract:
  We derive a family of ideal (nondissipative) 3D sound-proof fluid models that
includes both the Lipps-Hemler anelastic approximation (AA) and the Durran
pseudo-incompressible approximation (PIA). This family of models arises in the
Euler-Poincar\'{e} framework involving a constrained Hamilton's principle
expressed in the Eulerian fluid description. The derivation in this framework
establishes the following properties of each member of the entire family: the
Kelvin-Noether circulation theorem, conservation of potential vorticity on
fluid parcels, a Lie-Poisson Hamiltonian formulation possessing conserved
Casimirs, a conserved domain integrated energy and an associated variational
principle satisfied by the equilibrium solutions. \smallskip
  Having set the stage with the derivations of 3D models using the constrained
Hamilton's principle, we then derive the corresponding 2D vertical slice models
for these sound-proof theories.


title:
A highly resistive layer within the crust of X-ray pulsars limits their
  spin periods

abstract:
  The lack of X-ray pulsars with spin periods > 12 s raises the question of
where the population of evolved high magnetic field neutron stars has gone.
Unlike canonical radio pulsars, X-ray pulsars are not subject to physical
limits to the emission mechanism nor observational biases against the detection
of sources with longer periods. Here we show that a highly resistive layer in
the innermost part of the crust of neutron stars naturally limits the spin
period to a maximum value of about 10-20 s. This highly resistive layer is
expected if the inner crust is amorphous and heterogeneous in nuclear charge,
possibly due to the existence of a nuclear pasta phase. Our findings suggest
that the maximum period of isolated X-ray pulsars can be the first
observational evidence of an amorphous inner crust, which properties can be
further constrained by future X-ray timing missions combined with more detailed
models.


title: Quark Spectral Function and Deconfinement at Nonzero Temperature

abstract:
  The maximum entropy method is used to compute the quark spectral function at
nonzero temperature. We solve the gap equation of quantum chromodynamics (QCD)
self-consistently, employing a rainbow kernel which phenomenologically models
results from Dyson-Schwinger equations (DSE) and lattice QCD. We use the
criterion of positivity restoration of the spectral function as a signal for
deconfinement. Our calculation indicates that the critical temperature of
deconfinement $T_d$ is slightly smaller than the one of chiral symmetry
restoration $T_c$: $T_d\sim 94% T_c$ in the chiral limit, and $T_d\sim 96% T_c$
with physical light quark masses. Since these deviations are within the
systematic error of our approach, it is reasonable to conclude that chiral
symmetry restoration and deconfinement coincide at zero chemical potential.


title: Faraday Rotation in a Disordered Medium

abstract:
  The Faraday rotation angle is calculated in a diffusive regime in a three
dimensional disordered slab. It is shown that it is an oscillating function of
the magnetic field or the mediums internal properties, and is proportional to
the ratio of the inelastic mean free path to the mean free path, that is to the
average number of photon scatterings. The maximum rotation is achieved at
frequencies when the photons elastic mean free path is minimal. We have
obtained the rotation angle of polar backscattered light taking into account
the maximally crossed diagrams. The latter leads to an ellipticity in the
backscattered wave that can serve as precursor of weak localization.


title:
General Phase-Field Model with Stability Requirements on Interfaces in
  $N$-Dimensional Phase-Field Space

abstract:
  In this paper a general multi-phase-field model is presented which is an
extension and modification of the model proposed by Folch and Plapp for three
phase fields [R. Folch and M. Plapp, Phys. Rev. E 72 011602 (2005)] to the
arbitrary number of phases. In the model a physical constraint requiring that
the sum of all phase fields in the system is equal to one is resolved by the
method of Lagrange multipliers. Namely, the thermodynamic driving force is
reduced to its projection on the plane of the constraint. The general model
functions in a $N$-dimensional phase field space were derived which justify the
requirements for the stability of the total free energy functional on dual
interfaces and hence the absence of "ghost" phases. Furthermore, the case of
the different interface energies and mobility parameters on the individual
interfaces is resolved in a comprehensive manner. It is shown that the static
equilibrium for three or four phases fulfils Young's law for contact angles
with high accuracy. Also the model is verified by the quantitative simulation
of the solidification in an Al-Cu-Ni alloy in the case of the four-phase
transformation reaction. We found the way to control the character of new phase
nucleation using additional terms in free energy functional.


title:
Global Embedding of the Reissner-Nordstr\"om Metric in the Flat Ambient
  Space

abstract:
  We study isometric embeddings of non-extremal Reissner-Nordstr\"om metric
describing a charged black hole. We obtain three new embeddings in the flat
ambient space with minimal possible dimension. These embeddings are global,
i.e. corresponding surfaces are smooth at all values of radius, including
horizons. Each of the given embeddings covers one instance of the regions
outside the horizon, one instance between the horizons and one instance inside
the internal horizon. The lines of time for these embeddings turn out to be
more complicated than circles or hyperbolas. The obtained embeddings are also
smooth at all values of radius for extremal and hyperextremal black holes.


title: Decision-Theoretic Troubleshooting: Hardness of Approximation

abstract:
  Decision-theoretic troubleshooting is one of the areas to which Bayesian
networks can be applied. Given a probabilistic model of a malfunctioning
man-made device, the task is to construct a repair strategy with minimal
expected cost. The problem has received considerable attention over the past
two decades. Efficient solution algorithms have been found for simple cases,
whereas other variants have been proven NP-complete. We study several variants
of the problem found in literature, and prove that computing approximate
troubleshooting strategies is NP-hard. In the proofs, we exploit a close
connection to set-covering problems.


title: Numerical semigroups problem list

abstract: We propose a list of open problems in numerical semigroups.


title: The Ginzburg temperature of ionic fluids revisited

abstract:
  Using the collective variables method we revisit the estimates of the
Ginzburg temperature for the Coulomb-dominated models of ionic fluids. We
consider the charge-asymmetric primitive model supplemented by short-range
attractive interactions in the vicinity of the gas-liquid critical point. For
this model, we derive the effective Ising-like $\phi^{4}$-model Hamiltonian
expressed in terms of the collective variables describing the fluctuation modes
of the total number density. We obtain the explicit expressions for all the
Hamiltonian coefficients within the framework of the same approximation,
namely, the one-loop approximation which produces the mean-field critical
parameters. Based on this Hamiltonian, we consistently calculate the reduced
Ginzburg temperature $t_{G}$ for both the pure Coulombic model (a restricted
primitive model) and the pure solvophobic model (a hard-sphere square-well
model) as well as for the model parameters ranging between these two limiting
cases. Contrary to the previous theoretical estimates, we obtain the reduced
Ginzburg temperature for the pure Coulombic model to be about 20 times smaller
than for the pure solvophobic model. For the full model including the
short-range attractive and long-range Coulomb interactions, we show that
$t_{G}$ approaches the value found for the pure Coulombic model when the
strength of the Coulomb interactions becomes large enough. Our results suggest
a key role of the Coulomb interactions in the crossover behaviour observed
experimentally in ionic fluids as well as confirm the Ising-like criticality in
the Coulomb-dominated ionic systems.


title:
Identifying Communities and Key Vertices by Reconstructing Networks from
  Samples

abstract:
  Sampling techniques such as Respondent-Driven Sampling (RDS) are widely used
in epidemiology to sample "hidden" populations, such that properties of the
network can be deduced from the sample. We consider how similar techniques can
be designed that allow the discovery of the structure, especially the community
structure, of networks. Our method involves collecting samples of a network by
random walks and reconstructing the network by probabilistically coalescing
vertices, using vertex attributes to determine the probabilities. Even though
our method can only approximately reconstruct a part of the original network,
it can recover its community structure relatively well. Moreover, it can find
the key vertices which, when immunized, can effectively reduce the spread of an
infection through the original network.