title:
Minimal supergravity sneutrino dark matter and inverse seesaw neutrino
  masses

abstract:
  We show that within the inverse seesaw mechanism for generating neutrino
masses minimal supergravity is more likely to have a sneutrino as the lightest
superparticle than the conventional neutralino. We also demonstrate that such
schemes naturally reconcile the small neutrino masses with the correct relic
sneutrino dark matter abundance and accessible direct detection rates in
nuclear recoil experiments.


title:
Non-magnetic simplified cylindrical cloak with suppressed zero-th order
  scattering

abstract:
  A new type of simplified cloaks with matched exterior boundaries is proposed.
The cloak uses non-magnetic material for the TM polarization and can function
with a relatively thin thickness. It is shown that the $zero^{th}$ order
scattering of such cloak is dominant among all cylindrical scattering terms. A
gap is added at the cloak's inner surface to eliminate the zero-th order
scattering, through the mechanism of scattering resonance. The reduction in
scattering is relatively smooth, indicating that the proposed scattering
reduction method has good tolerance to perturbations. Numerical simulations
also confirm that the proposed structure has very low scattering.


title:
A Non-differential Distributed Space-Time Coding for Partially-Coherent
  Cooperative Communication

abstract:
  In a distributed space-time coding scheme, based on the relay channel model,
the relay nodes co-operate to linearly process the transmitted signal from the
source and forward them to the destination such that the signal at the
destination appears as a space time block code. Recently, a code design
criteria for achieving full diversity in a partially-coherent environment have
been proposed along with codes based on differential encoding and decoding
techniques. For such a set up, in this paper, a non-differential encoding
technique and construction of distributed space time block codes from unitary
matrix groups at the source and a set of diagonal unitary matrices for the
relays are proposed. It is shown that, the performance of our scheme is
independent of the choice of unitary matrices at the relays. When the group is
cyclic, a necessary and sufficient condition on the generator of the cyclic
group to achieve full diversity and to minimize the pairwise error probability
is proved. Various choices on the generator of cyclic group to reduce the ML
decoding complexity at the destination is presented. It is also shown that, at
the source, if non-cyclic abelian unitary matrix groups are used, then
full-diversity can not be obtained. The presented scheme is also robust to
failure of any subset of relay nodes.


title: Dirac particle in gravitational field

abstract:
  Classical dynamics of spinning zero-size objects in an external gravitational
field is derived from the conservation law of the stress-energy and spin
tensors. The resulting world line equations differ from those in the existing
literature. In particular, the spin of the Dirac particle does not couple to
the background curvature. As a check of consistency, the wave packet solution
of the free Dirac equation is considered. The resulting equations are shown to
include a constraint that relates the wave packet spin to its orbital angular
momentum. In the zero-size limit, both contributions to the total angular
momentum disappear simultaneously.


title:
The lightest Higgs boson mass in effective field theory with bulk and
  brane supersymmetry breaking

abstract:
  We study the mass of the lightest Higgs boson in an effective Kaluza-Klein
theory with two sources of supersymmetry breaking. When stop mass matrices are
non-diagonal with respect to Kaluza-Klein modes and each element is not small
in unit of the inverse compactification radius, a very small eigenvalue can be
accommodated in the diagonalized basis. We show that in the model with the two
sources, the Higgs boson mass can receive suitable corrections for various
compactification radii.


title: Linear precision for toric surface patches

abstract:
  We classify the homogeneous polynomials in three variables whose toric polar
linear system defines a Cremona transformation. This classification also
includes, as a proper subset, the classification of toric surface patches from
geometric modeling which have linear precision. Besides the well-known tensor
product patches and B\'ezier triangles, we identify a family of toric patches
with trapezoidal shape, each of which has linear precision. B\'ezier triangles
and tensor product patches are special cases of trapezoidal patches.


title:
Necessary and sufficient conditions for reflectionless transformation
  media in an isotropic and homogenous background

abstract:
  It has been known that, keeping the outer boundary coordinates intact before
and after a coordinate transformation is a sufficient condition for obtaining a
reflectionless transformation medium. Here we prove that it is also a necessary
condition for reflectionless transformation media in an isotropic and
homogenous background. Our analytical results show that the outer boundary
coordinates of a reflectionless transformation medium must be the same as the
original coordinates with a combination of rotation and displacement, which is
equivalent to situation that the boundary coordinates are kept intact before
and after transformation.


title: Understanding Kinetic Energy paradox in Quantum Mechanics

abstract:
  A concept of Kinetic Energy in Quantum Mechanics is analyzed. Kinetic Energy
is not zero in many cases where there are no motion and flux. This paradox can
be understood, using expansion of the wave function in Fourier integral, that
is on the basis of virtual plane waves.


title: Shuttle-mediated proton pumping across the inner mitochondrial membrane

abstract:
  Shuttle-assisted charge transfer is pivotal for the efficient energy
transduction from the food-stuff electrons to protons in the respiratory chain
of animal cells and bacteria. The respiratory chain consists of four
metalloprotein Complexes (I-IV) embedded in the inner membrane of a
mitochondrion. Three of these complexes pump protons across the membrane,
fuelled by the energy of food-stuff electrons. Despite extensive biochemical
and biophysical studies, the physical mechanism of this proton pumping is still
not well understood. Here we present a nanoelectromechanical model of the
electron-driven proton pump related to the second loop of the respiratory
chain, where a lipid-soluble ubiquinone molecule shuttles between the Complex I
and Complex III, carrying two electrons and two protons. We show that the
energy of electrons can be converted to the transmembrane proton potential
gradient via the electrostatic interaction between electrons and protons on the
shuttle. We find that the system can operate either as a proton pump, or, in
the reverse regime, as an electron pump. For membranes with various
viscosities, we demonstrate that the uphill proton current peaks near the body
temperature $T \approx 37 ^{\circ}$C.


title:
New Stability Conditions for Linear Differential Equations with Several
  Delays

abstract:
  New explicit conditions of asymptotic and exponential stability are obtained
for the scalar nonautonomous linear delay differential equation $$
\dot{x}(t)+\sum_{k=1}^m a_k(t)x(h_k(t))=0 $$ with measurable delays and
coefficients. These results are compared to known stability tests.


title: A note on Stormer condition for decomposability of positive maps

abstract:
  We present a partial characterization of matrices in $M_n(\cA)^+$ satisfying
the St{\o}rmer condition.


title: Non-perturbative approach to random walk in markovian environment

abstract:
  We prove an averaged CLT for a random walk in a dynamical environment where
the states of the environment at different sites are independent Markov chains.


title:
The Arecibo Legacy Fast ALFA Survey: VI. Second HI Source Catalog of the
  Virgo Cluster Region

abstract:
  We present the third installment of HI sources extracted from the Arecibo
Legacy Fast ALFA extragalactic survey. This dataset continues the work of the
Virgo ALFALFA catalog. The catalogs and spectra published here consist of data
obtained during the 2005 and 2006 observing sessions of the survey. The catalog
consists of 578 HI detections within the range 11h 36m < R.A.(J2000) < 13h 52m
and +08 deg < Dec.(J2000) < +12 deg, and cz_sun < 18000 km/s. The catalog
entries are identified with optical counterparts where possible through the
examination of digitized optical images. The catalog detections can be
classified into three categories: (a) detections of high reliability with S/N >
6.5; (b) high velocity clouds in the Milky Way or its periphery; and (c)
signals of lower S/N which coincide spatially with an optical object and known
redshift. 75% of the sources are newly published HI detections. Of particular
note is a complex of HI clouds projected between M87 and M49 that do not
coincide with any optical counterparts. Candidate objects without optical
counterparts are few. The median redshift for this sample is 6500 km/s and the
cz distribution exhibits the local large scale structure consisting of Virgo
and the background void and the A1367-Coma supercluster regime at cz_sun ~7000
km/s. Position corrections for telescope pointing errors are applied to the
dataset by comparing ALFALFA continuum centroid with those cataloged in the
NRAO VLA Sky Survey. The uncorrected positional accuracy averages
  27 arcsec ~(21 arcsec ~median) for all sources with S/N > 6.5 and is of order
~21 arcsec ~(16 arcsec ~median) for signals with S/N > 12. Uncertainties in
distances toward the Virgo cluster can affect the calculated HI mass
distribution.


title:
75As NQR/NMR Studies on Oxygen-deficient Iron-based Oxypnictide
  Superconductors LaFeAsO_{1-y} (y=0,0.25,0.4) and NdFeAsO_{0.6}

abstract:
  We report 75As-NQR/NMR studies on the oxygen-deficient iron(Fe)-based
oxypnictide superconductors LaFeAsO_{0.6} (T_c=28 K) along with the results on
LaFeAsO, LaFeAsO_{0.75}(T_c=20 K) and NdFeAsO_{0.6}(T_c=53 K). Nuclear
spin-lattice relaxation rate 1/T_1 of 75As NQR at zero field on LaFeAsO_{0.6}
has revealed a T^3 dependence below T_c upon cooling without the coherence peak
just below T_c, evidencing the unconventional superconducting state with the
line-node gap. We have found an intimate relationship between the nuclear
quadrupole frequencyof 75As and T_c for four samples used in this study. It
implies microscopically that the local configuration of Fe and As atoms is
significantly related to the T_c of the Fe-oxypnictide superconductors, namely,
the T_c can be enhanced up to 50 K when the local configuration of Fe and As
atoms is optimal, in which the band structure may be also optimized through the
variation of hybridization between As 4p orbitals and Fe 3d orbitals.


title: Coherent resonant Ka-band photonic microwave receiver

abstract:
  We propose theoretically and demonstrate experimentally a coherent microwave
photonic receiver operating at 35 GHz carrier frequency. The device is based on
a lithium niobate or lithium tantalate optical whispering gallery mode
resonator coupled to a microwave strip line resonator. Microwave local
oscillator is fed into the microwave resonator along with the microwave signal.
We show that the sensitivity of this receiver significantly exceeds the
sensitivity of the incoherent quadratic receiver based on the same technology.
The coherent receiver can possess a dynamic range in excess of 100 dB in 5 MHz
band if a low noise laser is utilized.


title:
Bohmian mechanics, the quantum-classical correspondence and the
  classical limit: the case of the square billiard

abstract:
  Square billiards are quantum systems complying with the dynamical
quantum-classical correspondence. Hence an initially localized wavefunction
launched along a classical periodic orbit evolves along that orbit, the
spreading of the quantum amplitude being controlled by the spread of the
corresponding classical statistical distribution. We investigate wavepacket
dynamics and compute the corresponding de Broglie-Bohm trajectories in the
quantum square billiard. We also determine the trajectories and statistical
distribution dynamics for the equivalent classical billiard. Individual Bohmian
trajectories follow the streamlines of the probability flow and are generically
non-classical. This can also hold even for short times, when the wavepacket is
still localized along a classical trajectory. This generic feature of Bohmian
trajectories is expected to hold in the classical limit. We further argue that
in this context decoherence cannot constitute a viable solution in order to
recover classicality.


title: Magnetoelastic-magnetoelectric phase transitions in multiferroic BiFeO3

abstract:
  Our measured dielectric constant and mechanical response of multiferroic
BiFeO3 indicate four phase transitions below room temperature. Features
correlate with those reported at 50K (from a peak in the zero-field-cooled
magnetic susceptibility) and 230K (from splitting between field-cooled and
zero-field-cooled magnetic data[1], and 200K (from magnon light scattering
cross sections[2]). The primary order parameter is not the polarization in any
of the low-T transitions. Instead, the transition near 230 K shows strong
elastic coupling, while that at 50K is fundamentally magnetic, but
magnetostrictively coupled to the the lattice. The low-T phase transitions
display glassy behaviour. A further anomaly at 140K interpreted as spin
reorientation[2,3] shows only weakly in dielectric and mechanical studies,
indicating that it is predominantly magnetic with little coupling to any of the
other order parameters.


title: Metric Lie 3-algebras in Bagger-Lambert theory

abstract:
  We recast physical properties of the Bagger-Lambert theory, such as
shift-symmetry and decoupling of ghosts, the absence of scale and parity
invariance, in Lie 3-algebraic terms, thus motivating the study of metric Lie
3-algebras and their Lie algebras of derivations. We prove a structure theorem
for metric Lie 3-algebras in arbitrary signature showing that they can be
constructed out of the simple and one-dimensional Lie 3-algebras iterating two
constructions: orthogonal direct sum and a new construction called a double
extension, by analogy with the similar construction for Lie algebras. We
classify metric Lie 3-algebras of signature (2,p) and study their Lie algebras
of derivations, including those which preserve the conformal class of the inner
product. We revisit the 3-algebraic criteria spelt out at the start of the
paper and select those algebras with signature (2,p) which satisfy them, as
well as indicate the construction of more general metric Lie 3-algebras
satisfying the ghost-decoupling criterion.


title:
Analysis of Verification-based Decoding on the q-ary Symmetric Channel
  for Large q

abstract:
  We discuss and analyze a list-message-passing decoder with verification for
low-density parity-check (LDPC) codes on the q-ary symmetric channel (q-SC).
Rather than passing messages consisting of symbol probabilities, this decoder
passes lists of possible symbols and marks some lists as verified. The density
evolution (DE) equations for this decoder are derived and used to compute
decoding thresholds. If the maximum list size is unbounded, then we find that
any capacity-achieving LDPC code for the binary erasure channel can be used to
achieve capacity on the q-SC for large q. The decoding thresholds are also
computed via DE for the case where each list is truncated to satisfy a maximum
list size constraint. Simulation results are also presented to confirm the DE
results. During the simulations, we observed differences between two
verification-based decoding algorithms, introduced by Luby and Mitzenmacher,
that were implicitly assumed to be identical. In this paper, we provide an
analysis of the node-based algorithms from that paper and verify that it
matches simulation results. The probability of false verification (FV) is also
considered and techniques are discussed to mitigate the FV. Optimization of the
degree distribution is also used to improve the threshold for a fixed maximum
list size. Finally, the proposed algorithm is compared with a variety of other
algorithms using both density evolution thresholds and simulation results.


title: On the spectrum of nonrelativistic AdS/CFT

abstract:
  We develop a Hamiltonian picture for a family of models of nonrelativistic
AdS/CFT duality. The Schrodinger group is realized via the conformal quantum
mechanics of De Alfaro, Fubini and Furlan in the holographic direction. We show
that most physical requirements, including the introduction of harmonic traps,
can be realized with exact AdS metrics, but without any need for exotic matter
sectors in the bulk dynamics. This Hamiltonian picture can be used to compare
directly with many-body spectra of fermions at unitarity on harmonic traps,
thereby providing a direct physical interpretation of the holographic radial
coordinate for these systems. Finally, we add some speculations on the
dynamical generation of mass gaps in the AdS description, the resulting
quasiparticle spectra, and the analog of `deconfining' phase transitions that
may occur.


title: Rational Witt classes of pretzel knots

abstract:
  In his pioneering work from 1969, Jerry Levine introduced a complete set of
invariants of algebraic concordance of knots. The evaluation of these
invariants requires a factorization of the Alexander polynomial of the knot,
and is therefore in practice often hard to realize. We thus propose the study
of an alternative set of invariants of algebraic concordance - the rational
Witt classes of knots. Though these are rather weaker invariants than those
defined by Levine, they have the advantage of lending themselves to quite
manageable computability. We illustrate this point by computing the rational
Witt classes of all pretzel knots. We give many examples and provide
applications to obstructing sliceness for pretzel knots. We also obtain
explicit formulae for the determinants and signatures of all pretzel knots.
  This article is dedicated to Jerry Levine and his lasting mathematical
legacy; on the occasion of the conference "Fifty years since Milnor and Fox"
held at Brandeis University on June 2-5, 2008.


title: Broadcasting with side information

abstract:
  A sender holds a word x consisting of n blocks x_i, each of t bits, and
wishes to broadcast a codeword to m receivers, R_1,...,R_m. Each receiver R_i
is interested in one block, and has prior side information consisting of some
subset of the other blocks. Let \beta_t be the minimum number of bits that has
to be transmitted when each block is of length t, and let \beta be the limit
\beta = \lim_{t \to \infty} \beta_t/t. In words, \beta is the average
communication cost per bit in each block (for long blocks). Finding the coding
rate \beta, for such an informed broadcast setting, generalizes several coding
theoretic parameters related to Informed Source Coding on Demand, Index Coding
and Network Coding.
  In this work we show that usage of large data blocks may strictly improve
upon the trivial encoding which treats each bit in the block independently. To
this end, we provide general bounds on \beta_t, and prove that for any constant
C there is an explicit broadcast setting in which \beta = 2 but \beta_1 > C.
One of these examples answers a question of Lubetzky and Stav.
  In addition, we provide examples with the following counterintuitive
direct-sum phenomena. Consider a union of several mutually independent
broadcast settings. The optimal code for the combined setting may yield a
significant saving in communication over concatenating optimal encodings for
the individual settings. This result also provides new non-linear coding
schemes which improve upon the largest known gap between linear and non-linear
Network Coding, thus improving the results of Dougherty, Freiling, and Zeger.
  The proofs use ideas related to Witsenhausen's rate, OR graph products,
colorings of Cayley graphs and the chromatic numbers of Kneser graphs.


title: Top Quark Compositeness: Feasibility and Implications

abstract:
  In models of electroweak symmetry breaking in which the SM fermions get their
masses by mixing with composite states, it is natural to expect the top quark
to show properties of compositeness. We study the phenomenological viability of
having a mostly composite top. The strongest constraints are shown to mainly
come from one-loop contributions to the T-parameter. Nevertheless, the presence
of light custodial partners weakens these bounds, allowing in certain cases for
a high degree of top compositeness. We find regions in the parameter space in
which the T-parameter receives moderate positive contributions, favoring the
electroweak fit of this type of models. We also study the implications of
having a composite top at the LHC, focusing on the process pp-> t\bar t t\bar t
(b\bar b) whose cross-section is enhanced at high-energies.


title: Maximum Likelihood Drift Estimation for Multiscale Diffusions

abstract:
  We study the problem of parameter estimation using maximum likelihood for
fast/slow systems of stochastic differential equations. Our aim is to shed
light on the problem of model/data mismatch at small scales. We consider two
classes of fast/slow problems for which a closed coarse-grained equation for
the slow variables can be rigorously derived, which we refer to as averaging
and homogenization problems. We ask whether, given data from the slow variable
in the fast/slow system, we can correctly estimate parameters in the drift of
the coarse-grained equation for the slow variable, using maximum likelihood. We
show that, whereas the maximum likelihood estimator is asymptotically unbiased
for the averaging problem, for the homogenization problem maximum likelihood
fails unless we subsample the data at an appropriate rate. An explicit formula
for the asymptotic error in the log likelihood function is presented. Our
theory is applied to two simple examples from molecular dynamics.


title:
Zero-free regions for multivariate Tutte polynomials (alias Potts-model
  partition functions) of graphs and matroids

abstract:
  The chromatic polynomial P_G(q) of a loopless graph G is known to be nonzero
(with explicitly known sign) on the intervals (-\infty,0), (0,1) and (1,32/27].
Analogous theorems hold for the flow polynomial of bridgeless graphs and for
the characteristic polynomial of loopless matroids. Here we exhibit all these
results as special cases of more general theorems on real zero-free regions of
the multivariate Tutte polynomial Z_G(q,v). The proofs are quite simple, and
employ deletion-contraction together with parallel and series reduction. In
particular, they shed light on the origin of the curious number 32/27.


title: Issues of duality in Abelian Gauge Theory and in Linearized Gravity

abstract:
  We start by describing two of the main proposals for duality in Abelian gauge
theories, namely $F$(ield strength)-duality approach and the $S$% -duality
formalism. We then discuss how $F$-duality and $S$-duality can be applied to
the case of linearized gravity. By emphasizing the similarities and differences
between these two type of dualities we explore the possibility of combining
them in just one duality formalism.


title: Superconformal Indices for ${\cal N}=6$ Chern Simons Theories

abstract:
  Aharony, Bergman, Jafferis and Maldacena have recently proposed a dual
gravitational description for a family of superconformal Chern Simons theories
in three spacetime dimensions. In this note we perform the one loop computation
that determines the field theory superconformal index of this theory and
compare with the index computed over the Fock space of dual supersymmetric
gravitons. In the appropriate limit (large $N$ and large $k$) we find a perfect
match.


title: On Matrix Model Formulations of Noncommutative Yang-Mills Theories

abstract:
  We study stability of noncommutative spaces in matrix models and discuss the
continuum limit which leads to noncommutative Yang-Mills theories (NCYM). It
turns out that most of noncommutative spaces in bosonic models are unstable.
This indicates perturbative instability of fuzzy R^D pointed out by Van
Raamsdonk and Armoni et al. persists to nonperturbative level in these cases.
In this sense, these bosonic NCYM are not well-defined, or at least their
matrix model formulations studied in this paper do not work. We also show that
noncommutative backgrounds are stable in a supersymmetric matrix model deformed
by a cubic Myers term, though the deformation itself breaks supersymmetry.


title: Multiple M2-Branes and Plane Waves

abstract:
  We propose a natural generalisation of the BLG multiple M2-brane action to
membranes in curved plane wave backgrounds, and verify in two different ways
that the action correctly captures the non-trivial space-time geometry. We show
that the M2 to D2 reduction of the theory along a non-trivial direction in
field space is equivalent to the D2-brane world-volume Yang-Mills theory with a
non-trivial (null-time dependent) dilaton in the corresponding IIA background
geometry. As another consistency check of this proposal we show that the
properties of metric 3-algebras ensure the equivalence of the Rosen coordinate
version of this action (time-dependent metric on the space of 3-algebra valued
scalar fields, no mass terms) and its Brinkmann counterpart (constant couplings
but time-dependent mass terms). We also establish an analogous result for
deformed Yang-Mills theories in any dimension which, in particular,
demonstrates the equivalence of the Rosen and Brinkmann forms of the plane wave
matrix string action.


title:
Lepton Masses in a Minimal Model with Triplet Higgs Bosons and $S_3$
  Flavor Symmetry

abstract:
  Viable neutrino and charged lepton masses and mixings are obtained by
imposing a $S_3 \times Z_4 \times Z_3$ flavor symmetry in a model with a few
additional Higgs. We use two $SU(2)_L$ triplet Higgs which are arranged as a
doublet of $S_3$, and standard model singlet Higgs which are also put as
doublets of $S_3$. We break the $S_3$ symmetry in this minimal model by giving
vacuum expectation values (VEV) to the additional Higgs fields. Dictated by the
minimum condition for the scalar potential, we obtain certain VEV alignments
which allow us to maintain $\mu-\tau$ symmetry in the neutrino sector, while
breaking it maximally for the charged leptons. This helps us to simultaneously
explain the hierarchical charged lepton masses, and the neutrino masses and
mixings. In particular, we obtain maximal $\theta_{23}$ and zero $\theta_{13}$.
We allow for a mild breaking of the $\mu-\tau$ symmetry for the neutrinos and
study the phenomenology. We give predictions for $\theta_{13}$ and the CP
violating Jarlskog invariant $J_{CP}$, as a function of the $\mu-\tau$ symmetry
breaking parameter. We also discuss possible collider signatures and
phenomenology associated with lepton flavor violating processes.


title: DLCQ and Plane Wave Matrix Big Bang Models

abstract:
  We study the generalisations of the Craps-Sethi-Verlinde matrix big bang
model to curved, in particular plane wave, space-times, beginning with a
careful discussion of the DLCQ procedure. Singular homogeneous plane waves are
ideal toy-models of realistic space-time singularities since they have been
shown to arise universally as their Penrose limits, and we emphasise the role
played by the symmetries of these plane waves in implementing the flat space
Seiberg-Sen DLCQ prescription for these curved backgrounds. We then analyse
various aspects of the resulting matrix string Yang-Mills theories, such as the
relation between strong coupling space-time singularities and world-sheet
tachyonic mass terms. In order to have concrete examples at hand, in an
appendix we determine and analyse the IIA singular homogeneous plane wave -
null dilaton backgrounds.


title: Gale duality and Koszul duality

abstract:
  Given an affine hyperplane arrangement with some additional structure, we
define two finite-dimensional, noncommutative algebras, both of which are
motivated by the geometry of hypertoric varieties. We show that these algebras
are Koszul dual to each other, and that the roles of the two algebras are
reversed by Gale duality. We also study the centers and representation
categories of our algebras, which are in many ways analogous to integral blocks
of category O.


title: The Bloch-Okounkov correlation functions, a classical half-integral case

abstract:
  Bloch and Okounkov's correlation function on the infinite wedge space has
connections to Gromov-Witten theory, Hilbert schemes, symmetric groups, and
certain character functions of $\hgl_\infty$-modules of level one. Recent works
have calculated these character functions for higher levels for $\hgl_\infty$
and its Lie subalgebras of classical type. Here we obtain these functions for
the subalgebra of type $D$ of half-integral levels and as a byproduct, obtain
$q$-dimension formulas for integral modules of type $D$ at half-integral level.


title: Local Search Heuristics For The Multidimensional Assignment Problem

abstract:
  The Multidimensional Assignment Problem (MAP) (abbreviated s-AP in the case
of s dimensions) is an extension of the well-known assignment problem. The most
studied case of MAP is 3-AP, though the problems with larger values of s also
have a large number of applications. We consider several known neighborhoods,
generalize them and propose some new ones. The heuristics are evaluated both
theoretically and experimentally and dominating algorithms are selected. We
also demonstrate a combination of two neighborhoods may yield a heuristics
which is superior to both of its components.


title:
$\Upsilon(4S,5S)\to\Upsilon(1S)\eta$ transitions in the rescattering
  model and the new BaBar measurement

abstract:
  The $\eta$ transitions of $\Upsilon(4S,5S)$ into $\Upsilon(1S,2S)$ are
studied in the rescattering model by considering the final state interactions
above the $B\bar B$ threshold. The width of the $\eta$ transition of
$\Upsilon(4S)$ into $\Upsilon(1S)$ is found to be larger than that of the
dipion transition, and the ratio of $\Gamma(\Upsilon(4S)\to\Upsilon(1S)\eta)$
to $\Gamma(\Upsilon(4S)\to\Upsilon(1S)\pi^+\pi^-)$ is predicted to be
$R_4=1.8{-}4.5$, which is about two orders of magnitude larger than the
expectation of the conventional hadronic transition theory, and is supported by
the new BaBar measurement. The widths of the $\eta$ transitions of
$\Upsilon(5S)$ are found to be sensitive to the coupling constants
$g_{\Upsilon(5S)B^{(*)}B^{(*)}}$ due to a large cancelation between
contributions from the $B\bar{B}$, $B^*\bar{B}+c.c.$, and $B^*\bar{B}^*$
channels, and only a rough estimate
$\Gamma(\Upsilon(5S)\to\Upsilon(1S,2S)\eta)=10{-}200$ KeV can be given. The
widths of the $\eta'$ transitions of $\Upsilon(4S,5S)$ are also discussed, and
they could be much smaller than that of the corresponding $\eta$ transitions
mainly due to the tiny phase space.


title:
The cycle-convergence of restarted GMRES for normal matrices is
  sublinear

abstract:
  We prove that the cycle-convergence of the restarted GMRES applied to a
system of linear equations with a normal coefficient matrix is sublinear.


title: Light-pulse atom interferometry

abstract:
  The light-pulse atom interferometry method is reviewed. Applications of the
method to inertial navigation and tests of the Equivalence Principle are
discussed.


title: Envelope Algebras of Partial Actions as Groupoid C*-Algebras

abstract:
  We describe the envelope C*-algebra associated to a partial action of a
countable discrete group on a locally compact space as a groupoid C*-algebra
(more precisely as a C*-algebra from an equivalence relation) and we use our
approach to show that, for a large class of partial actions of Z on the Cantor
set, the envelope C*-algebra is an AF-algebra. We also completely characterize
partial actions of a countable discrete group on a compact space such that the
envelope action acts in a Hausdorff space.


title: Comparative statistics and origin of triple and quadruple stars

abstract:
  The statistics of catalogued quadruple stars consisting of two binaries
(hierarchy 2+2) is studied in comparison with triple stars, with respective
sample sizes of 81 and 724. Seven representative quadruple systems are
discussed in greater detail. The properties of multiple stars do not correspond
to the products of dynamical decay of small clusters, hence the N-body dynamics
is not the dominant process of their formation. On the other hand,
rotationally-driven (cascade) fragmentation possibly followed by migration of
inner and/or outer orbits to shorter periods is a promising scenario to explain
the origin of triple and quadruple stars. Our main results are: (i) Quadruple
systems of Epsilon Lyr type with similar masses and inner periods are common.
(ii) The distributions of the inner periods in triple and quadruple stars are
similar and bimodal. The inner mass ratios do not correlate with the inner
periods. (iii) The statistics of outer periods and mass ratios in triples and
quadruples are different. The median outer mass ratio in triples is 0.39
independently of the outer period, which has a smooth distribution. In
contrast, the outer periods of 25% quadruples concentrate in the narrow range
from 10yr to 100yr, the outer mass ratios of these tight quadruples are above
0.6 and their two inner periods are similar to each other. (iv) The outer and
inner mass ratios in triple and quadruple stars are not mutually correlated.
(v) The inner and outer orbital angular momenta and periods in triple and
quadruple systems with inner periods above 30d show some correlation, the ratio
of outer-to-inner periods is mostly comprised between 5 and 10^4. In the
systems with small period ratios the directions of the orbital spins are
correlated, while in the systems with large ratios they are not.


title: The Spatial String Tension and Dimensional Reduction in QCD

abstract:
  We calculate the spatial string tension in (2+1) flavor QCD with physical
strange quark mass and almost physical light quark masses using lattices with
temporal extent N_tau=4,6 and 8. We compare our results on the spatial string
tension with predictions of dimensionally reduced QCD. This suggests that also
in the presence of light dynamical quarks dimensional reduction works well down
to temperatures 1.5T_c.


title: Energy transport in jammed sphere packings

abstract:
  We calculate the normal modes of vibration in jammed sphere packings to
obtain the energy diffusivity, a spectral measure of transport. At the boson
peak frequency, we find an Ioffe-Regel crossover from a diffusivity that drops
rapidly with frequency to one that is nearly frequency-independent. This
crossover frequency shifts to zero as the system is decompressed towards the
jamming transition, providing unambiguous evidence of a regime in frequency of
nearly constant diffusivity. Such a regime, postulated to exist in glasses to
explain the temperature dependence of the thermal conductivity, therefore
appears to arise from properties of the jamming transition.


title:
Probing the Reheating Temperature at Colliders and with Primordial
  Nucleosynthesis

abstract:
  Considering gravitino dark matter scenarios with a long-lived charged
slepton, we show that collider measurements of the slepton mass and its
lifetime can probe not only the gravitino mass but also the post-inflationary
reheating temperature TR. In a model independent way, we derive upper limits on
TR and discuss them in light of the constraints from the primordial catalysis
of lithium-6 through bound-state effects. In the collider-friendly region of
slepton masses below 1 TeV, the obtained conservative estimate of the maximum
reheating temperature is about TR=3\times 10^9 GeV for the limiting case of a
small gluino-slepton mass splitting and about TR=10^8 GeV for the case that is
typical for universal soft supersymmetry breaking parameters at the scale of
grand unification. We find that a determination of the gluino-slepton mass
ratio at the Large Hadron Collider will test the possibility of TR>10^9 GeV and
thereby the viability of thermal leptogenesis with hierarchical heavy
right-handed Majorana neutrinos.


title:
Implications of Two Type Ia Supernova Populations for Cosmological
  Measurements

abstract:
  Recent work suggests that Type Ia supernovae (SNe) are composed of two
distinct populations: prompt and delayed. By explicitly incorporating
properties of host galaxies, it may be possible to target and eliminate
systematic differences between these two putative populations. However, any
resulting {\em post}-calibration shift in luminosity between the components
will cause a redshift-dependent systematic shift in the Hubble diagram.
Utilizing an existing sample of 192 SNe Ia, we find that the average luminosity
difference between prompt and delayed SNe is constrained to be $(4.5 \pm
8.9)%$. If the absolute difference between the two populations is 0.025 mag,
and this is ignored when fitting for cosmological parameters, then the dark
energy equation of state (EOS) determined from a sample of 2300 SNe Ia is
biased at $\sim1\sigma$. By incorporating the possibility of a two-population
systematic, this bias can be eliminated. However, assuming no prior on the
strength of the two-population effect, the uncertainty in the best-fit EOS is
increased by a factor of 2.5, when compared to the equivalent sample with no
underlying two-population systematic. To avoid introducing a bias in the EOS
parameters, or significantly degrading the measurement accuracy, it is
necessary to control the post-calibration luminosity difference between prompt
and delayed SN populations to better than 0.025 mag.


title: Subgrid Modeling of AGN-Driven Turbulence in Galaxy Clusters

abstract:
  Hot, underdense bubbles powered by active galactic nuclei (AGN) are likely to
play a key role in halting catastrophic cooling in the centers of cool-core
galaxy clusters. We present three-dimensional simulations that capture the
evolution of such bubbles, using an adaptive-mesh hydrodynamic code, FLASH3, to
which we have added a subgrid model of turbulence and mixing. While pure-hydro
simulations indicate that AGN bubbles are disrupted into resolution-dependent
pockets of underdense gas, proper modeling of subgrid turbulence indicates that
this a poor approximation to a turbulent cascade that continues far beyond the
resolution limit. Instead, Rayleigh-Taylor instabilities act to effectively mix
the heated region with its surroundings, while at the same time preserving it
as a coherent structure, consistent with observations. Thus bubbles are
transformed into hot clouds of mixed material as they move outwards in the
hydrostatic intracluster medium (ICM), much as large airbursts lead to a
distinctive ``mushroom cloud'' structure as they rise in the hydrostatic
atmosphere of Earth. Properly capturing the evolution of such clouds has
important implications for many ICM properties. In particular, it significantly
changes the impact of AGN on the distribution of entropy and metals in
cool-core clusters such as Perseus.


title: Lyman Alpha Galaxies: Primitive, Dusty or Evolved Galaxies?

abstract:
  We present stellar population modeling results for 10 newly discovered Lyman
alpha emitting galaxies (LAEs), as well as four previously known LAEs at z ~
4.5 in the Chandra Deep Field - South. We fit stellar population models to
these objects in order to learn specifically if there exists more than one
class of LAE. Past observational and theoretical evidence has shown that while
many LAEs appear to be young, they may be much older, with Lyman alpha EWs
enhanced due to resonant scattering of Lyman alpha photons in a clumpy
interstellar medium (ISM). Our results show a large range of stellar population
age (3 - 500 Myr), stellar mass (1.6 x 10^8 - 5.0 x 10^10 Msol) and dust
extinction (A_1200 = 0.3 - 4.5 mag), broadly consistent with previous studies.
With such a large number of individually analyzed objects, we have looked at
the distribution of stellar population ages in LAEs for the first time, and we
find a very interesting bimodality, in that our objects are either very young
(< 15 Myr) or old (> 450 Myr). This bimodality may be caused by dust, and it
could explain the Lyman alpha duty cycle which has been proposed in the
literature. We find that eight of the young objects are best fit with a clumpy
ISM. We find that dust geometry appears to play a large role in shaping the
SEDs that we observe, and that it may be a major factor in the observed Lyman
alpha equivalent width distribution in high redshift Lyman alpha galaxies,
although other factors (i.e. outflows) may be in play. We conclude that 12 out
of our 14 LAEs are dusty star-forming galaxies, with the other two LAEs being
evolved galaxies.


title:
Observational Consequences of the Recently Proposed Super-Earth Orbiting
  GJ436

abstract:
  Ribas and collaborators have recently proposed that an additional, ~5 M_earth
planet orbits the transiting planet host star GJ436. Long-term dynamical
interactions between the two planets leading to eccentricity excitation might
provide an explanation for the transiting planet's unexpectedly large orbital
eccentricity. In this paper we examine whether the existence of such a second
planet is supported by the available observational data when the short-term
interactions that would result from its presence are accounted for. We find
that the model for the system suggested by Ribas and collaborators lead to
predictions that are strongly inconsistent with the measured host star radial
velocities, transiting planet primary and secondary eclipse times, and
transiting planet orbital inclinations. A search for an alternative two planet
model that is consistent with the data yields a number of plausible solutions,
although no single one stands out as particularly unique by giving a
significantly better fit to the data than the nominal single planet model. We
conclude from this study that Ribas and collaborator's general hypothesis of an
additional short-period planet in the GJ436 system is still plausible, but that
there is not sufficient evidence to support their claim of a planet detection.


title:
First Stellar Velocity Dispersion Measurement of a Luminous Quasar Host
  with Gemini North Laser Guide Star Adaptive Optics

abstract:
  We present the first use of the Gemini North laser guide star adaptive optics
(LGS AO) system and an integral field unit (IFU) to measure the stellar
velocity dispersion of the host of a luminous quasar. The quasar PG1426+015
(z=0.086) was observed with the Near-Infrared Integral Field Spectrometer
(NIFS) on the 8m Gemini North telescope in the H-band as part of the Science
Verification phase of the new ALTAIR LGS AO system. The NIFS IFU and LGS AO are
well suited for host studies of luminous quasars because one can achieve a
large ratio of host to quasar light. We have measured the stellar velocity
dispersion of PG1426+015 from 0.1'' to 1'' (0.16 kpc to 1.6 kpc) to be 217+/-15
km/s based on high signal-to-noise ratio measurements of Si I, Mg I, and
several CO bandheads. This new measurement is a factor of four more precise
than a previous measurement obtained with long-slit spectroscopy and good,
natural seeing, yet was obtained with a shorter net integration time. We find
that PG1426+015 has a velocity dispersion that places it significantly above
the M-sigma relation of quiescent galaxies and lower-luminosity active galactic
nuclei with black hole masses estimated from reverberation mapping. We discuss
several possible explanations for this discrepancy that could be addressed with
similar observations of a larger sample of luminous quasars.


title: Exploring the magnetized cosmic web through low frequency radio emission

abstract:
  Recent improvements in the capabilities of low frequency radio telescopes
provide a unique opportunity to study thermal and non-thermal properties of the
cosmic web. We argue that the diffuse, polarized emission from giant radio
relics traces structure formation shock waves and illuminates the large-scale
magnetic field. To show this, we model the population of shock-accelerated
relativistic electrons in high-resolution cosmological simulations of galaxy
clusters and calculate the resulting radio synchrotron emission. We find that
individual shock waves correspond to localized peaks in the radio surface
brightness map which enables us to measure Mach numbers for these shocks. We
show that the luminosities and number counts of the relics strongly depend on
the magnetic field properties, the cluster mass and dynamical state. By
suitably combining different cluster data, including Faraday rotation measures,
we are able to constrain some macroscopic parameters of the plasma at the
structure formation shocks, such as models of turbulence. We also predict upper
limits for the properties of the warm-hot intergalactic medium, such as its
temperature and density. We predict that the current generation of radio
telescopes (LOFAR, GMRT, MWA, LWA) have the potential to discover a
substantially larger sample of radio relics, with multiple relics expected for
each violently merging cluster. Future experiments (SKA) should enable us to
further probe the macroscopic parameters of plasma physics in clusters.


title: On the shoulders of Giants - Quantum gravity and braneworld stability

abstract:
  The semi-classical nature of braneworld cosmological models does not account
for any quantum gravitational effects. In this letter we use the gauge/gravity
correspondence to argue that quantum string corrections cannot be ignored in
any study of braneworld stability. As an example, we find, by analysing the
quantum gravitational backreaction, that a closed universe is unstable to
radiation into the bulk.


title: Significance tests for comparing digital gene expression profiles

abstract:
  Most of the statistical tests currently used to detect differentially
expressed genes are based on asymptotic results, and perform poorly for low
expression tags. Another problem is the common use of a single canonical cutoff
for the significance level (p-value) of all the tags, without taking into
consideration the type II error and the highly variable character of the sample
size of the tags.
  This work reports the development of two significance tests for the
comparison of digital expression profiles, based on frequentist and Bayesian
points of view, respectively. Both tests are exact, and do not use any
asymptotic considerations, thus producing more correct results for low
frequency tags than the chi-square test. The frequentist test uses a
tag-customized critical level which minimizes a linear combination of type I
and type II errors. A comparison of the Bayesian and the frequentist tests
revealed that they are linked by a Beta distribution function. These tests can
be used alone or in conjunction, and represent an improvement over the
currently available methods for comparing digital profiles.


title: Water-mediated ordering of nanoparticles in electric field

abstract:
  Interfacial polar molecules feature a strongly anisotropic response to
applied electric field, favoring dipole orientations parallel to the interface.
In water, in particular, this effect combines with generic orientational
preferences induced by spatial asymmetry of water hydrogen bonding under
confined geometry, which may give rise to a Janus interface. The two effects
manifest themselves in considerable dependence of water polarization on both
the field direction relative to the interface, and the polarity (sign) of the
field. Using molecular simulations, we demonstrate strong field-induced
orientational forces acting on apolar surfaces through water mediation. At a
field strength comparable to electric fields around a DNA polyion, the torques
we predict to act on an adjacent nanoparticle are sufficient to overcome
thermal fluctuations. These torques can align a particle with surface as small
as 1 nm2. The mechanism can support electrically controlled ordering of
suspended nanoparticles as a means of tuning their properties, and can find
application in electro-nanomechanical devices.


title:
GALEX Spectroscopy of SN 2005ay suggests a UV spectral uniformity among
  type II-P supernovae

abstract:
  We present the first results from our GALEX program designed to obtain
ultraviolet (UV) spectroscopy of nearby core-collapse supernovae (SNe). Our
first target, SN 2005ay in the nearby galaxy NGC 3938, is a typical member of
the II-P SN subclass. Our spectra show remarkable similarity to those of the
prototypical type II-P event SN 1999em, and resemble also Swift observations of
the recent type II-P event SN 2005cs. Taken together, the observations of these
three events trace the UV spectral evolution of SNe II-P during the first month
after explosion, as required in order to interpret optical observations of
high-redshift SNe II-P, and to derive cross-filter K-corrections. While still
highly preliminary, the apparent UV homogeneity of SNe II-P bodes well for the
use of these events as cosmological probes at high redshift.


title: On McMillan's theorem about uniquely decipherable codes

abstract:
  Karush's proof of McMillan's theorem is recast as an argument involving
polynomials with non-commuting indeterminates certain evaluations of which
yield the Kraft sums of codes, proving a strengthened version of McMillan's
theorem.


title:
Correlations between MIR, FIR, H$\alpha$, and FUV Luminosities for SWIRE
  galaxies

abstract:
  e present and analyze the correlations between mid-infrared (MIR),
far-infrared (FIR), total-infrared (TIR), H$\alpha$, and FUV luminosities for
star-forming galaxies, composite galaxies and AGNs, based on a large sample of
galaxies selected from the $Spitzer$ SWIRE fields. The MIR luminosities of
star-forming galaxies are well correlated with their H$\alpha$, TIR and FUV
luminosities, and we re-scaled the MIR-derived SFR formulae according to the
above correlations with differences less than 15%. We confirm the recent result
by calzetti et al. (2007) that the combined observed H$\alpha$ + 24$\mu$m
luminosities L(H$\alpha$$_{\rm obs}$+ 24$\mu$m) possess very tight correlation
with the extinction-corrected H$\alpha$ luminosities L(H$\alpha$$\_$corr) for
star-forming and even for dwarf galaxies, and show that the combined
L(H$\alpha$$_{\rm obs}$+ 8$\mu$m[dust]) are also tightly correlated with
L(H$\alpha$$\_$corr) for the above sample galaxies. Among all the L(MIR)-L(FIR)
correlations for star-forming galaxies, the L(24$\mu$m) vs. L(70$\mu$m) and
L(8$\mu$m[dust]) vs. L(160$\mu$m) are the tightest and also nearly linear. The
former could be related to young massive star formation, while the latter might
be relevant to diffuse dust emissions heated by old stellar populations.
Composite galaxies and AGNs have higher MIR-to-H$\alpha$/MIR-to-FUV luminosity
ratios than star-forming galaxies, nevertheless their correlations among MIR,
FIR and TIR luminosities are completely following those of star-forming
galaxies.


title: Modeling the Milky-Way Satellite galaxies

abstract:
  We revisit the Milky Way satellite problem using a semi-analytical model of
galaxy formation and compare the predicted luminosity function to recent result
from the SDSS. With cosmic photoionization, the luminosity function can be
brought into broad agreement with the data between $-15< M_{V} <-2$. This
improvement over previous semi-analytical model results (e.g., Benson et
al.2002) is from our adoption of improved models for galaxy merger history and
galaxy merging time-scales. The very faint satellites ($M_{v} > -5$) formed in
halos with virial temperature over $10^{4}K$ (mass around $10^{9} M_{\odot}$
before accretion), but their baryon content are strongly suppressed by
photoionization. We model the mass evolution of the subhalos, and compare the
predicted mass-to-light ratio with the data. We find that the measured total
mass inside the luminous radii of satellites are about 5% of their present
total dark matter mass.


title:
Sobre o papel dos Departamentos de Matem\'atica na vida e
  desenvolvimento da comunidade

abstract:
  The objective of this article is to stimulate discussions in mathematical
society about the role of mathematical departments in the life of the
community. University community is the center of knowledge and promotes the
intellectual development. However, this is questioned today because of its
reduced participation on the global learning process as there are many other
components.


title:
Topological nonrealization results via the Goodwillie tower approach to
  iterated loopspace homology

abstract:
  We prove a strengthened version of a theorem of Lionel Schwartz that says
that certain modules over the Steenrod algebra cannot be the mod 2 cohomology
of a space.
  What is most interesting is our method, which replaces his iterated use of
the Eilenberg--Moore spectral sequence by a single use of the spectral sequence
converging to the mod 2 cohomology of Omega^nX obtained from the Goodwillie
tower for the suspension spectrum of Omega^nX. Much of the paper develops basic
properties of this spectral sequence.


title: Upsilon production at the Tevatron and the LHC

abstract:
  We update the theoretical predictions for direct Y(nS) hadroproduction in the
framework of NRQCD. We show that the next-to-leading order corrections in
alpha_s to the color-singlet transition significantly raise the differential
cross section at high pT and substantially affect the polarization of the
Upsilon. Motivated by the remaining gap between the NLO yield and the cross
section measurements at the Tevatron, we evaluate the leading part of the
alpha_s^5 contributions, namely those coming from Y(nS) associated with three
light partons. The differential color-singlet cross section at alpha_s^5 is in
substantial agreement with the data, so that there is no evidence for the need
of color-octet contributions. Furthermore, we find that the polarization of the
Y(nS) is longitudinal. We also present our predictions for Y(nS) production at
the LHC.


title:
Dynamics of a vortex domain wall in a magnetic nanostrip: an application
  of the collective coordinate approach

abstract:
  The motion of a vortex domain wall in a ferromagnetic strip of submicron
width under the influence of an external magnetic field exhibits three distinct
dynamical regimes. In a viscous regime at low fields the wall moves rigidly
with a velocity proportional to the field. Above a critical field the viscous
motion breaks down giving way to oscillations accompanied by a slow drift of
the wall. At still higher fields the drift velocity starts rising with the
field again but with a much lower mobility dv/dH than in the viscous regime. To
describe the dynamics of the wall we use the method of collective coordinates
that focuses on soft modes of the system. By retaining two soft modes,
parametrized by the coordinates of the vortex core, we obtain a simple
description of the wall dynamics at low and intermediate applied fields that
describes both the viscous and oscillatory regimes below and above the
breakdown. The calculated dynamics agrees well with micromagnetic simulations
at low and intermediate values of the driving field. In higher fields,
additional modes become soft and the two-mode approximation is no longer
sufficient. We explain some of the significant features of vortex domain wall
motion in high fields through the inclusion of additional modes associated with
the half-antivortices on the strip edge.


title: Optimal hash functions for approximate closest pairs on the n-cube

abstract:
  One way to find closest pairs in large datasets is to use hash functions. In
recent years locality-sensitive hash functions for various metrics have been
given: projecting an n-cube onto k bits is simple hash function that performs
well. In this paper we investigate alternatives to projection. For various
parameters hash functions given by complete decoding algorithms for codes work
better, and asymptotically random codes perform better than projection.


title:
Bandwidth and Fermi surface of Iron-Oxypnictides: covalency and
  sensitivity to structural changes

abstract:
  Some important aspects of the electronic structure of the iron oxypnictides
depend very sensitively on small changes in interatomic distances and bond
angles within the iron-pnictogen subunit. Using first-principles full-potential
electronic structure calculations, we investigate this sensitive dependence,
contrasting in particular LaOFeAs and LaOFeP. The width of the Fe-bands is
significantly larger for LaOFeP, indicating a better metal and weaker
electronic correlations. When calculated at their experimental crystal
structure these two materials have significantly different low-energy band
structure. The topology of the Fermi surface changes when going from LaOFeP to
LaOFeAs, with a three-dimensional hole pocket present in the former case
transforming into a tube with two-dimensional dispersion. We show that the
low-energy band structure of LaOFeAs evolves towards that of LaOFeP as the As
atom is lowered closer to the Fe plane with respect to its experimental
position. The physical origin of this sensitivity to the iron-pnictogen
distance is the covalency of the iron-pnictogen bond, leading to strong
hybridization effects. To illustrate this, we construct Wannier functions,
which are found to have a large spatial extension when the energy window is
restricted to the bands with dominant iron character. Finally, we show that the
Fe bandwidth slightly increases as one moves along the rare-earth series in
ReOFeAs and discuss the physical origin of this effect.


title: BART: Bayesian additive regression trees

abstract:
  We develop a Bayesian "sum-of-trees" model where each tree is constrained by
a regularization prior to be a weak learner, and fitting and inference are
accomplished via an iterative Bayesian backfitting MCMC algorithm that
generates samples from a posterior. Effectively, BART is a nonparametric
Bayesian regression approach which uses dimensionally adaptive random basis
elements. Motivated by ensemble methods in general, and boosting algorithms in
particular, BART is defined by a statistical model: a prior and a likelihood.
This approach enables full posterior inference including point and interval
estimates of the unknown regression function as well as the marginal effects of
potential predictors. By keeping track of predictor inclusion frequencies, BART
can also be used for model-free variable selection. BART's many features are
illustrated with a bake-off against competing methods on 42 different data
sets, with a simulation experiment and on a drug discovery classification
problem.


title: Multi-layered Spectral Formation in SNe Ia Around Maximum Light

abstract:
  We use the radiative transfer code PHOENIX to study the line formation of the
wavelength region 5000-7000 Angstroms. This is the region where the SNe Ia
defining Si II feature occurs. This region is important since the ratio of the
two nearby silicon lines has been shown to correlate with the absolute blue
magnitude. We use a grid of LTE synthetic spectral models to investigate the
formation of line features in the spectra of SNe Ia. By isolating the main
contributors to the spectral formation we show that the ions that drive the
spectral ratio are Fe III, Fe II, Si II, and S II. While the first two strongly
dominate the flux transfer, the latter two form in the same physical region
inside of the supernova. We also show that the naive blackbody that one would
derive from a fit to the observed spectrum is far different than the true
underlying continuum.


title:
Medium modifications of the bound nucleon GPDs and incoherent DVCS on
  nuclear targets

abstract:
  We study incoherent DVCS on $^4$He in the $^4{\rm He}(e,e^{\prime}\gamma p)X$
reaction, which probes medium-modifications of the bound nucleon GPDs and
elastic form factors. Assuming that the bound nucleon GPDs are modified in
proportion to the corresponding bound nucleon elastic form factors, as
predicted in the Quark-Meson Coupling model, we develop an approach to
calculate various incoherent nuclear DVCS observables. As an example, we
compute the beam-spin DVCS asymmetry, and predict the $x_B$- and $t$-dependence
of the ratio of the bound to free proton asymmetries, $A_{\rm
LU}^{p^{\ast}}(\phi)/A_{\rm LU}^{p}(\phi)$. We find that the deviation of
$A_{\rm LU}^{p^{\ast}}(\phi)/A_{\rm LU}^{p}(\phi)$ from unity is as much as
$\sim$ 6%.


title: Gravitational Lensing by Rotating Naked Singularities

abstract:
  We model massive compact objects in galactic nuclei as stationary,
axially-symmetric naked singularities in the Einstein-massless scalar field
theory and study the resulting gravitational lensing. In the weak deflection
limit we study analytically the position of the two weak field images, the
corresponding signed and absolute magnifications as well as the centroid up to
post-Newtonian order. We show that there are a static post-Newtonian
corrections to the signed magnification and their sum as well as to the
critical curves, which are function of the scalar charge. The shift of the
critical curves as a function of the lens angular momentum is found, and it is
shown that they decrease slightingly for the weakly naked and vastly for the
strongly naked singularities with the increase of the scalar charge. The
point-like caustics drift away from the optical axis and do not depend on the
scalar charge. In the strong deflection limit approximation we compute
numerically the position of the relativistic images and their separability for
weakly naked singularities. All of the lensing quantities are compared to
particular cases as Schwarzschild and Kerr black holes as well as
Janis--Newman--Winicour naked singularities.


title: The Classification of Exceptional CDQL Webs on Compact Complex Surfaces

abstract:
  Codimension one webs are configurations of finitely many codimension one
foliations in general position. Much of the classical theory evolved around the
concept of abelian relation: a functional relation among the first integrals of
the foliations defining the web reminiscent of Abel's addition theorem in
classical algebraic geometry. The abelian relations of a given web form a
finite dimensional vector space with dimension (the rank of the web) bounded by
Castelnuovo number p(n,k) where n is the dimension of the ambient space and k
is the number of foliations defining the web. A fundamental problem in web
geometry is the classification of exceptional webs, that is, webs of maximal
rank not equivalent to the dual of a projective curve. Recently, J.-M. Trepreau
proved that there are no exceptional k-webs for n>2 and k > 2n-1. In dimension
two there are examples of exceptional k-webs for arbitrary k and the
classification problem is wide open.
  In this paper, we classify the exceptional Completely Decomposable
Quasi-Linear (CDQL) webs globally defined on compact complex surfaces. By
definition, the CDQL (k+1)-webs are formed by the superposition of k linear
foliations and one non-linear foliation. For instance, we show that up to
projective transformations there are exactly four countable families and
thirteen sporadic exceptional CDQL webs on the projective plane.


title: Coherent optical control of correlation waves of spins in semiconductors

abstract:
  We calculate the dynamical fluctuation spectrum of electronic spins in a
semiconductor under a steady-state illumination by light containing
polarization squeezing correlations. Taking into account quasi-particle
lifetime and spin relaxation for this non-equilibrium situation we consider up
to fourth order optical effects which are sensitive to the squeezing phases.
  We demonstrate the possibility to control the spin fluctuations by optically
modulating these phases as a function of frequency, leading to a non-Lorentzian
spectrum which is very different from the thermal equilibrium fluctuations in
n-doped semiconductors. Specifically, in the time-domain spin-spin correlation
can exhibit time delays and sign flips originating from the phase modulations
and correlations of polarizations, respectively. For higher light intensity we
expect a regime where the squeezing correlations will dominate the spectrum.


title: Jack polynomials and the coinvariant ring of $G(r,p,n)$

abstract:
  We study the coinvariant ring of the complex reflection group $G(r,p,n)$ as a
module for the corresponding rational Cherednik algebra $\HH$ and its
generalized graded affine Hecke subalgebra $\mathcal{H}$. We construct a basis
consisting of non-symmetric Jack polynomials, and using this basis decompose
the coinvariant ring into irreducible modules for $\mathcal{H}$. The basis
consists of certain non-symmetric Jack polynomials, whose leading terms are the
``descent monomials'' for $G(r,p,n)$ recently studied by Adin, Brenti, and
Roichman and Bagno and Biagoli. The irreducible $\mathcal{H}$-submodules of the
coinvariant ring are their ``colored descent representations''.


title: A Rigorous Derivation of Gravitational Self-force

abstract:
  There is general agreement that the MiSaTaQuWa equations should describe the
motion of a "small body" in general relativity, taking into account the leading
order self-force effects. However, previous derivations of these equations have
made a number of ad hoc assumptions and/or contain a number of unsatisfactory
features. For example, all previous derivations have invoked, without proper
justification, the step of "Lorenz gauge relaxation", wherein the linearized
Einstein equation is written down in the form appropriate to the Lorenz gauge,
but the Lorenz gauge condition is then not imposed--thereby making the
resulting equations for the metric perturbation inequivalent to the linearized
Einstein equations. In this paper, we analyze the issue of "particle motion" in
general relativity in a systematic and rigorous way by considering a
one-parameter family of metrics, $g_{ab} (\lambda)$, corresponding to having a
body (or black hole) that is "scaled down" to zero size and mass in an
appropriate manner. We prove that the limiting worldline of such a
one-parameter family must be a geodesic of the background metric, $g_{ab}
(\lambda=0)$. Gravitational self-force--as well as the force due to coupling of
the spin of the body to curvature--then arises as a first-order perturbative
correction in $\lambda$ to this worldline. No assumptions are made in our
analysis apart from the smoothness and limit properties of the one-parameter
family of metrics. Our approach should provide a framework for systematically
calculating higher order corrections to gravitational self-force, including
higher multipole effects, although we do not attempt to go beyond first order
calculations here. The status of the MiSaTaQuWa equations is explained.


title:
Two-Qubit Separabilities as Piecewise Continuous Functions of Maximal
  Concurrence

abstract:
  The generic real (b=1) and complex (b=2) two-qubit states are 9-dimensional
and 15-dimensional in nature, respectively. The total volumes of the spaces
they occupy with respect to the Hilbert-Schmidt and Bures metrics are
obtainable as special cases of formulas of Zyczkowski and Sommers. We claim
that if one could determine certain metric-independent 3-dimensional
"eigenvalue-parameterized separability functions" (EPSFs), then these formulas
could be readily modified so as to yield the Hilbert-Schmidt and Bures volumes
occupied by only the separable two-qubit states (and hence associated
separability probabilities). Motivated by analogous earlier analyses of
"diagonal-entry-parameterized separability functions", we further explore the
possibility that such 3-dimensional EPSFs might, in turn, be expressible as
univariate functions of some special relevant variable--which we hypothesize to
be the maximal concurrence (0 < C <1) over spectral orbits. Extensive numerical
results we obtain are rather closely supportive of this hypothesis. Both the
real and complex estimated EPSFs exhibit clearly pronounced jumps of magnitude
roughly 50% at C=1/2, as well as a number of additional matching
discontinuities.


title: Mean representation number of integers as the sum of primes

abstract:
  Assuming the Riemann Hypothesis we obtain asymptotic estimates for the mean
value of the number of representations of an integer as a sum of two primes. By
proving a corresponding Omega-term, we prove that our result is essentially the
best possible.


title:
Signature of quantum criticality in photoemission spectroscopy at
  elevated temperature

abstract:
  A quantum phase transition (QPT) in a heavy-fermion (HF) compound may destroy
the Fermi liquid groundstate. However, the conditions for this breakdown have
remained obscure. We report the first direct investigation of heavy
quasiparticle formation and breakdown in the canonical system
CeCu$_{6-x}$Au$_x$ by ultraviolet photoemission spectroscopy at elevated
temperatures without the complications of lattice coherence. Surprisingly, the
single-ion Kondo energy scale $T_K$ exhibits an abrupt step near the quantum
critical Au concentration of $x_c=0.1$. We show theoretically that this step is
expected from a highly non-linear renormalization of the local spin coupling at
each Ce site, induced by spin fluctuations on neighboring sites. It provides a
general high-temperature indicator for HF quasiparticle breakdown at a QPT.


title:
Ground State and Resonances in the Standard Model of Non-relativistic
  QED

abstract:
  We prove existence of a ground state and resonances in the standard model of
the non-relativistic quantum electro-dynamics (QED). To this end we introduce a
new canonical transformation of QED Hamiltonians and use the spectral
renormalization group technique with a new choice of Banach spaces.


title: F-injective singularities are Du Bois

abstract:
  In this paper, we prove that singularities of $F$-injective type are Du Bois.
This extends the correspondence between singularities associated to the minimal
model program and singularities defined by the action of Frobenius in positive
characteristic.


title: On the Quintessence Scalar Field Potential

abstract:
  In this work we propose a new analytical method for determining the scalar
field potential $V(\phi)$ in FRW type cosmologies containing a mixture of
perfect fluid plus a quintessence scalar field. By assuming that the equation
of state parameters of the perfect fluid, $\gamma -1 \equiv
p_{\gamma}/\rho_{\gamma}$ and the quintessence, $\omega \equiv p/\rho$ are
constants, it is shown that the potential for the flat case is $V(\phi) =
A\rho_{\phi_{0}}\sinh^{B}(\lambda \phi)$, where $A$, $B$ and $\lambda$ are
functions of $\gamma$ and $\omega$. This general result is a pure consequence
of the Einstein field equations and the constancy of the parameters. Applying
the same method for closed and open universes, the corresponding scalar field
potentials are also explicitly obtained for a large set of values of the free
parameters $\gamma$ and $\omega$. A formula yielding the transition redshift
from a decelerating to an accelerating regime is also determined and compared
to the $\Lambda$CDM case.


title:
Nanonewton force generation and detection based on a sensitive torsion
  pendulum

abstract:
  In this paper, we introduce the experiment based on a sensitive torsion
pendulum for measuring and calibrating small forces at nanonewton scale. The
force standard for calibration is the universal gravitation between four masses
separated by known distances. It is realized by two test masses suspended as
the part of torsion pendulum and two source masses on a rotation table. Two
force generation mechanisms, optical force from radiation pressure and
electrostatic force by capacitive actuation unit, are designed and will be
calibrated by the gravitation force. We present our recent results of radiation
pressure measurements, and describe the design of capacitive displacement
sensing/actuating unit.


title: Fast computation of the median by successive binning

abstract:
  This paper describes a new median algorithm and a median approximation
algorithm. The former has O(n) average running time and the latter has O(n)
worst-case running time. These algorithms are highly competitive with the
standard algorithm when computing the median of a single data set, but are
significantly faster in updating the median when more data is added.


title:
Charge excitations associated with charge stripe order in the 214-type
  nickelate and superconducting cuprate

abstract:
  Charge excitations were studied for stipe-ordered 214 compounds,
La$_{5/3}$Sr$_{1/3}$NiO$_{4}$ and 1/8-doped La$_{2}$(Ba, Sr)$_{x}$CuO$_{4}$
using resonant inelastic x-ray scattering in hard x-ray regime. We have
observed charge excitations at the energy transfer of 1 eV with the momentum
transfer corresponding to the charge stripe spatial period both for the
diagonal (nikelate) and parallel (cuprates) stripes. These new excitations can
be interpreted as a collective stripe excitation or charge excitonic mode to a
stripe-related in-gap state.


title:
Gamma-ray spectrum of RX J1713.7-3946 in the Fermi era and future
  detection of neutrinos

abstract:
  The recently launched satellite, Fermi Gamma-ray Space Telescope, is expected
to find out if cosmic-ray (CR) protons are generated from supernova remnants
(SNRs), especially RX J1713.7-3946, by observing the GeV-to-TeV gamma-rays. The
GeV emission is thought to be bright if the TeV emission is hadronic, i.e., of
proton origin, while dim if leptonic. We reexamine the above view using a
simple theoretical model of nonlinear acceleration of particles to calculate
the gamma-ray spectrum of Galactic young SNRs. If the nonlinear effects of CR
acceleration are considered, it may be impossible to distinguish the evidence
of proton acceleration from leptonic in the gamma-ray spectrum of Galactic
young SNRs like RX J1713.7-3946. On the other hand, future km^3-class neutrino
observations will likely find a clear evidence of the proton acceleration
there.


title: Ferromagnetic spin fluctuation in LaFeAsO1-xFx

abstract:
  The F doped LaFeAsO, a recently discovered superconductor with the high Tc of
26 K, has been studied by the resistivity, magnetic susceptibility, and heat
capacity measurements in the F doping range from 0 to 0.14 (x in LaFeAsO1-xFx).
In the low temperature region, a T3lnT term in the heat capacity and a T2 term
in the magnetic susceptibility, which are derived from the spin fluctuation,
are observed. The nearly ferromagnetic nature evidenced by a large Wilson ratio
(6.5 for x = 0, and 11.2 for x = 0.025) suggests that the superconductivity in
the LaFeAsO system is mediated by ferromagnetic spin fluctuation.


title: Regarding confinement and dynamical chiral symmetry breaking in QED3

abstract:
  We establish that QED3 can possess a critical number of flavours, N_f^c,
associated with dynamical chiral symmetry breaking if, and only if, the fermion
wave function renormalisation and photon vacuum polarisation are homogeneous
functions at infrared momenta when the fermion mass function vanishes. The Ward
identity entails that the fermion-photon vertex possesses the same property and
ensures a simple relationship between the homogeneity degrees of each of these
functions. Simple models for the photon vacuum polarisation and fermion-photon
vertex are used to illustrate these observations. The existence and value of
N_f^c are contingent upon the precise form of the vertex but any discussion of
gauge dependence is moot. We introduce an order parameter for confinement.
Chiral symmetry restoration and deconfinement are coincident owing to an abrupt
change in the analytic properties of the fermion propagator when a nonzero
scalar self-energy becomes insupportable.


title:
Decoherence of two qubits in a non-Markovian reservoir without
  rotating-wave approximation

abstract:
  The decoherence of two initially entangled qubits in a non-Markovian
reservoir has been investigated exactly without Born Markovian approximation
and rotating-wave approximation(RWA). The non-perturbative quantum master
equation is derived and its exact solution is obtained. The decoherence
behaviors of two qubits, initially entangled in Bell states, has been
investigated in three different cases of parameters. The results show that the
counter-rotating wave terms have great influence on the decoherence behavior,
and there are differences between the exact solution of the Hamiltonian with
RWA and that of the exact Hamiltonian without RWA. It might be improper to take
RWA when the atom is in a non-markovian reservoir.


title: Electromagnetic Leptogenesis

abstract:
  We present a new leptogenesis scenario, where the lepton asymmetry is
generated by CP violating decays of heavy electroweak singlet neutrinos via
electromagnetic dipole moment couplings to the ordinary light neutrinos. Akin
to the usual scenario where the decays are mediated through Yukawa
interactions, we have shown, by explicit calculations, that the desired
asymmetry can be produced through the interference of the corresponding
tree-level and one-loop decay amplitudes involving the effective dipole moment
operators. We also find that the relationship of the leptogenesis scale to the
light neutrino masses is similar to that for the standard Yukawa-mediated
mechanism.


title:
Probing the nodal gap in the pressure-induced heavy fermion
  superconductor CeRhIn5

abstract:
  We report field-orientation specific heat studies of the pressure-induced
heavy fermion superconductor CeRhIn5. Theses experiments provide the
momentum-dependent superconducting gap function for the first time in any
pressure-induced superconductor. In the coexisting phase of superconductivity
and antiferromagnetism, field rotation within the Ce-In plane reveals four-fold
modulation in the density of states, which favors a d-wave order parameter and
constrains a theory of the interplay between superconductivity and magnetism.


title: Universal phase diagrams for the quantum spin Hall systems

abstract:
  We describe how the three-dimensional quantum spin Hall phase arises from the
insulator phase by changing an external parameter. In 3D systems without
inversion symmetry, a gapless phase should appear between the two phases with a
bulk gap. The gapless points are monopoles and antimonopoles (in k space),
whose topological nature is the source of this gapless phase. In general, when
the external parameter is changed from the ordinary insulator phase, two
monopole-antimonopole pairs are created and the system becomes gapless. The
gap-closing points (monopoles and antimonopoles) then move in the k space as
the parameter is changed further. They eventually annihilate in pairs, with
changing partners from the pair creations, and the system opens a gap again,
entering into the quantum spin Hall phase.


title: Semiweak Cullen-regular quaternionic functions

abstract:
  We introduce the class of semiweak Cullen-regular quaternionic functions by
interpreting Cullen-regular functions as solutions to an inhomogeneous PDE in
terms of the Fueter operator.


title:
Zariski-van Kampen method and transcendental lattices of certain
  singular K3 surfaces

abstract:
  We present a method of Zariski-van Kampen type for the calculation of the
transcendental lattice of a complex projective surface. As an application, we
calculate the transcendental lattices of complex singular K3 surfaces
associated with an arithmetic Zariski pair of maximizing sextics of type
$A_{10}+A_{9}$ that are defined over a real quadratic field and are conjugate
to each other over the field of rational numbers.


title: Novel interface-selected waves and their influences on wave competitions

abstract:
  The topic of interface effects in wave propagation has attracted great
attention due to their theoretical significance and practical importance. In
this paper we study nonlinear oscillatory systems consisting of two media
separated by an interface, and find a novel phenomenon: interface can select a
type of waves (ISWs). Under certain well defined parameter condition, these
waves propagate in two different media with same frequency and same wave
number; the interface of two media is transparent to these waves. The frequency
and wave number of these interface-selected waves (ISWs) are predicted
explicitly. Varying parameters from this parameter set, the wave numbers of two
domains become different, and the difference increases from zero continuously
as the distance between the given parameters and this parameter set increases
from zero. It is found that ISWs can play crucial roles in practical problems
of wave competitions, e.g., ISWs can suppress spirals and antispirals.


title: Viscoelastic shear banding in foam

abstract:
  Shear banding is an important feature of flow in complex fluids. Essentially,
shear bands refer to the coexistence of flowing and non-flowing regions in
driven material. Understanding the possible sources of shear banding has
important implications for a wide range of flow applications. In this regard,
quasi-two dimensional flow offers a unique opportunity to study competing
factors that result in shear bands. One proposal is the competition between
intrinsic dissipation and an external source of dissipation. In this paper, we
report on the experimental observation of the transition between different
classes of shear-bands that have been predicted to exist in cylindrical
geometry as the result of this competition [R. J. Clancy, E. Janiaud, D.
Weaire, and S. Hutzlet, Eur. J. Phys. E, {\bf 21}, 123 (2006)].


title:
Effective Resistance Mismatch and Magnetoresistance of a CPP-GMR system
  with Current-Confined-Paths

abstract:
  We theoretically study the magnetoresistance of a CPP-GMR system with current
confined paths (CCP) in the framework of Valet-Fert theory. The continuity
equations for charge and spin currents are numerically solved with the
three-dimensional CCP geometry by use of finite element method. It is confirmed
that the MR ratio is enhanced by the CCP structure, which is consistent with
the experimental results. Moreover, we find that there exists a certain contact
width which maximize the MR ratio. We show that the contact width which
maximize the MR ratio is well described by the effective resistance matching.


title: Penetration Depth of Transverse Spin Current in Ferromagnetic Metals

abstract:
  The line width of the ferromagnetic resonance (FMR) spectrum of
Cu/CoFeB/Cu/Co/Cu is studied. Analyzing the FMR spectrum by the theory of spin
pumping, we determined the penetration depth of the transverse spin current in
the Co layer. The obtained penetration depth of Co is 1.7 nm.


title: Rotating Kaluza-Klein Multi-Black Holes with Godel Parameter

abstract:
  We obtain new five-dimensional supersymmetric rotating multi-Kaluza-Klein
black hole solutions with the Godel parameter in the Einstein-Maxwell system
with a Chern-Simons term. These solutions have no closed timelike curve outside
the black hole horizons. At the infinity, the space-time is effectively
four-dimensional. Each horizon admits various lens space topologies
L(n;1)=S^3/Z_n in addition to a round S^3. The space-time can have outer
ergoregions disjointed from the black hole horizons, as well as inner
ergoregions attached to each horizon. We discuss the rich structures of
ergoregions.


title:
Differential Transmit Diversity Based on Quasi-Orthogonal Space-Time
  Block Code

abstract:
  By using joint modulation and customized constellation set, we show that
Quasi-Orthogonal Space-Time Block Code (QO-STBC) can be used to form a new
differential space-time modulation (DSTM) scheme to provide full transmit
diversity with non-coherent detection. Our new scheme can provide higher code
rate than existing DSTM schemes based on Orthogonal STBC. It also has a lower
decoding complexity than the other DSTM schemes, such as those based on Group
Codes, because it only requires a joint detection of two complex symbols. We
derive the design criteria for the customized constellation set and use them to
construct a constellation set that provides a wide range of spectral efficiency
with full diversity and maximum coding gain.


title:
A tropical analogue of Fay's trisecant identity and the ultra-discrete
  periodic Toda lattice

abstract:
  We introduce a tropical analogue of Fay's trisecant identity for a special
family of hyperelliptic tropical curves. We apply it to obtain the general
solution of the ultra-discrete Toda lattice with periodic boundary conditions
in terms of the tropical Riemann's theta function.


title: Fractionalization in dimerized graphene and graphene bilayer

abstract:
  We show that the fractional statistics of quasiparticles in dimerized
graphene, in recent proposals for charge and statistics fractionalization, can
have two realizations depending whether elementary objects can be considered as
point-like or extended objects. Therefore, there are two phases of proposed
excitations and we give their topological descriptions with their respective
statistics. We propose that a natural setting for fractionalization are certain
systems with excitonic instabilities and demonstrate this by an example of
graphene bilayer.


title: Unitary Differential Space-Time Modulation with Joint Modulation

abstract:
  We develop two new designs of unitary differential space-time modulation
(DSTM) with low decoding complexity. Their decoder can be separated into a few
parallel decoders, each of which has a decoding search space of less than
sqrt(N) if the DSTM codebook contains N codewords. Both designs are based on
the concept of joint modulation, which means that several information symbols
are jointly modulated, unlike the conventional symbol-by-symbol modulation. The
first design is based on Orthogonal Space-Time Block Code (O-STBC) with joint
constellation constructed from spherical codes. The second design is based on
Quasi-Orthogonal Space-Time Block Code (QO-STBC) with specially designed
pair-wise constellation sets. Both the proposed unitary DSTM schemes have
considerably lower decoding complexity than many prior DSTM schemes, including
those based on Group Codes and Sp(2) which generally have a decoding search
space of N for a codebook size of N codewords, and much better decoding
performance than the existing O-STBC DSTM scheme. Between two designs, the
proposed DSTM based on O-STBC generally has better decoding performance, while
the proposed DSTM based on QO-STBC has lower decoding complexity when 8
transmit antennas.


title:
Achieving Near-Capacity at Low SNR on a Multiple-Antenna Multiple-User
  Channel

abstract:
  We analyze the sensitivity of the capacity of a multi-antenna multi-user
system to the number of users being served. We show analytically that, for a
given desired sum-rate, the extra power needed to serve a subset of the users
at low SNR (signal-to-noise ratio) can be very small, and is generally much
smaller than the extra power needed to serve the same subset at high SNR. The
advantages of serving only subsets of the users are many: multi-user algorithms
have lower complexity, reduced channel-state information requirements, and,
often, better performance. We provide guidelines on how many users to serve to
get near-capacity performance with low complexity. For example, we show how in
an eight-antenna eight-user system we can serve only four users and still be
approximately 2 dB from capacity at very low SNR.


title: Power-Balanced Orthogonal Space-Time Block Code

abstract:
  In this paper, we propose two new systematic ways to construct amicable
orthogonal designs (AOD), with an aim to facilitate the construction of
power-balanced orthogonal spacetime block codes (O-STBC) with favorable
practical attributes. We also show that an AOD can be constructed from an
Amicable Family (AF), and such a construction is crucial for achieving a
power-balanced O-STBC. In addition, we develop design guidelines on how to
select the "type" parameter of an AOD so that the resultant O-STBC will have
better power-distribution and code-coefficient attributes. Among the new
O-STBCs obtained, one is shown to be optimal in terms of power distribution
attributes. In addition, one of the proposed construction methods is shown to
generalize some other construction methods proposed in the literature.


title: Na4Ir3O8 as a 3D spin liquid with fermionic spinons

abstract:
  Spin liquid states for spin-1/2 antiferromagnetic Heisenberg model on a
hyperkagome lattice are studied. We classify and study flux states according to
symmetries. Applying this model to Na4Ir3O8, we propose that the high
temperature state may be described by a spinon Fermi surface, which forms a
paired state with line nodes below 20 K. The possible mixed spin singlet and
spin triplet pairing states are discussed according to the lattice symmetry
which breaks inversion.


title:
Optimizing Quasi-Orthogonal STBC Through Group-Constrained Linear
  Transformation

abstract:
  In this paper, we first derive the generic algebraic structure of a
Quasi-Orthogonal STBC (QO-STBC). Next we propose Group-Constrained Linear
Transformation (GCLT) as a means to optimize the diversity and coding gains of
a QO-STBC with square or rectangular QAM constellations. Compared with QO-STBC
with constellation rotation (CR), we show that QO-STBC with GCLT requires only
half the number of symbols for joint detection, hence lower maximum-likelihood
decoding complexity. We also derive analytically the optimum GCLT parameters
for QO-STBC with square QAM constellation. The optimized QO-STBCs with GCLT are
able to achieve full transmit diversity, and have negligible performance loss
compared with QO-STBCs with CR at the same code rate.


title: On the Search for High-Rate Quasi-Orthogonal Space-Time Block Code

abstract:
  A Quasi-Orthogonal Space-Time Block Code (QO-STBC) is attractive because it
achieves higher code rate than Orthogonal STBC and lower decoding complexity
than nonorthogonal STBC. In this paper, we first derive the algebraic structure
of QO-STBC, then we apply it in a novel graph-based search algorithm to find
high-rate QO-STBCs with code rates greater than 1. From the four-antenna codes
found using this approach, it is found that the maximum code rate is limited to
5/4 with symbolwise diversity level of four, and 4 with symbolwise diversity
level of two. The maximum likelihood decoding of these high-rate QO-STBCs can
be performed on two separate sub-groups of symbols. The rate-5/4 codes are the
first known QO-STBCs with code rate greater 1 that has full symbolwise
diversity level.


title:
Probing microscopic origins of confined subdiffusion by first-passage
  observables

abstract:
  Subdiffusive motion of tracer particles in complex crowded environments, such
as biological cells, has been shown to be widepsread. This deviation from
brownian motion is usually characterized by a sublinear time dependence of the
mean square displacement (MSD). However, subdiffusive behavior can stem from
different microscopic scenarios, which can not be identified solely by the MSD
data. In this paper we present a theoretical framework which permits to
calculate analytically first-passage observables (mean first-passage times,
splitting probabilities and occupation times distributions) in disordered media
in any dimensions. This analysis is applied to two representative microscopic
models of subdiffusion: continuous-time random walks with heavy tailed waiting
times, and diffusion on fractals. Our results show that first-passage
observables provide tools to unambiguously discriminate between the two
possible microscopic scenarios of subdiffusion. Moreover we suggest experiments
based on first-passage observables which could help in determining the origin
of subdiffusion in complex media such as living cells, and discuss the
implications of anomalous transport to reaction kinetics in cells.

categories: cond-mat.stat-mech cond-mat.dis-nn physics.bio-ph q-bio.QM


title: The Volume of a Local Nodal Domain

abstract:
  Let M either be a closed real analytic Riemannian manifold or a closed smooth
Riemannian surface. We estimate from below the volume of a nodal domain
component in an arbitrary ball provided that this component enters the ball
deeply enough.


title:
Limited Feedback for Multi-Antenna Multi-user Communications with
  Generalized Multi-Unitary Decomposition

abstract:
  In this paper, we propose a decomposition method called Generalized
Multi-Unitary Decomposition (GMUD) which is useful in multi-user MIMO
precoding. This decomposition transforms a complex matrix H into PRQ, where R
is a special matrix whose first row contains only a non-zero user defined value
at the left-most position, P and Q are a pair of unitary matrices. The major
attraction of our proposed GMUD is we can obtain multiple solutions of P and Q
>. With GMUD, we propose a precoding method for a MIMO multi-user system that
does not require full channel state information (CSI) at the transmitter. The
proposed precoding method uses the multiple unitary matrices property to
compensate the inaccurate feedback information as the transmitter can steer the
transmission beams of individual users such that the inter-user interference is
kept minimum.


title: Beamforming Matrix Quantization with Variable Feedback Rate

abstract:
  We propose an improved beamforming matrix compression by Givens Rotation with
the use of variable feedback rate. The variable feedback rate means that the
number of bits used to represent the quantized beamforming matrix is based on
the value of the matrix. Compared with the fixed feedback rate scheme, the
proposed method has better performance without additional feedback bandwidth.


title: Open string engineering of D-brane geometry

abstract:
  One-loop scattering on a stack of D3 branes was considered in arXiv:0801.0218
[hep-th]. Divergence was found and its cancelation mechanism was proposed,
wherein it was conjectured that the D-brane geometry be introduced in the form
of counter vertex operators. Here we verify the conjecture at the first few
leading orders in an expansion method that we call large-$r_0$ expansion. We
comment on the relation with the Fischler-Susskind mechanism and discuss the
implications of our result for AdS/CFT.


title: Solar Grand Minima and random fluctuations in dynamo parameters

abstract:
  We consider to what extent the long-term dynamics of cyclic solar activity in
the form of Grand Minima can be associated with random fluctuations of the
parameters governing the solar dynamo. We consider fluctuations of the
alpha-coefficient in the conventional Parker migratory dynamo, and also in
slightly more sophisticated dynamo models, and demonstrate that they can mimic
the gross features of the phenomenon of the occurrence of Grand Minima over a
suitable parameter range. The temporal distribution of these Grand Minima
appears chaotic, with a more or less exponential waiting time distribution,
typical of Poisson processes. In contrast however, the available reconstruction
of Grand Minima statistics based on cosmogenic isotope data demonstrates
substantial deviations from this exponential law. We were unable to reproduce
the non-Poissonic tail of the waiting time distribution either in the framework
of a simple alpha-quenched Parker model, or in its straightforward
generalization, nor in simple models with feedback on the differential
rotation. We suggest that the disagreement may only be apparent and is
plausibly related to the limited observational data, and that the observations
and results of numerical modeling can be consistent and represent physically
similar dynamo regimes.


title: Compressed Sensing of Analog Signals in Shift-Invariant Spaces

abstract:
  A traditional assumption underlying most data converters is that the signal
should be sampled at a rate exceeding twice the highest frequency. This
statement is based on a worst-case scenario in which the signal occupies the
entire available bandwidth. In practice, many signals are sparse so that only
part of the bandwidth is used. In this paper, we develop methods for low-rate
sampling of continuous-time sparse signals in shift-invariant (SI) spaces,
generated by m kernels with period T. We model sparsity by treating the case in
which only k out of the m generators are active, however, we do not know which
k are chosen. We show how to sample such signals at a rate much lower than m/T,
which is the minimal sampling rate without exploiting sparsity. Our approach
combines ideas from analog sampling in a subspace with a recently developed
block diagram that converts an infinite set of sparse equations to a finite
counterpart. Using these two components we formulate our problem within the
framework of finite compressed sensing (CS) and then rely on algorithms
developed in that context. The distinguishing feature of our results is that in
contrast to standard CS, which treats finite-length vectors, we consider
sampling of analog signals for which no underlying finite-dimensional model
exists. The proposed framework allows to extend much of the recent literature
on CS to the analog domain.


title: Integral equation for gauge invariant quark Green's function

abstract:
  We consider gauge invariant quark two-point Green's functions in which the
gluonic phase factor follows a skew-polygonal line. Using a particular
representation for the quark propagator in the presence of an external gluon
field, functional relations between Green's functions with different numbers of
segments of the polygonal lines are established. An integral equation is
obtained for the Green's function having a phase factor along a single straight
line. The related kernels involve Wilson loops with skew-polygonal contours and
with functional derivatives along the sides of the contours.


title: Minimal Surfaces in the Four-Dimensional Euclidean Space

abstract:
  We prove that the Gauss curvature and the curvature of the normal connection
of any minimal surface in the four dimensional Euclidean space satisfy an
inequality, which generates two classes of minimal surfaces: minimal surfaces
of general type and minimal super-conformal surfaces. We prove a Bonnet-type
theorem for strongly regular minimal surfaces of general type in terms of their
invariants. We introduce canonical parameters on strongly regular minimal
surfaces of general type and prove that any such a surface is determined up to
a motion by two invariant functions satisfying a system of two natural partial
differential equations. On any minimal surface of the basic class of non
strongly regular minimal surfaces we define canonical parameters and prove that
any such a surface is determined up to a motion by two invariant functions of
one variable satisfying a system of two natural ordinary differential
equations. We find a geometric description of this class of non strongly
regular minimal surfaces.