title: Shell-Model Monte Carlo Simulations of Pairing in Few-Fermion Systems

abstract:
  We study a trapped system of fermions with an attractive zero-range two-body
interaction using the Shell-Model Monte Carlo method. The method provides {\em
ab initio} results in the low $N$ limit where mean-field theory is not
applicable. The energy and pairing properties are presented as functions of
interaction strength, particle number, and temperature. In the interesting
region where typical matrix elements of the two-body interaction are comparable
to the level spacing of the trap we find large odd-even effects and signatures
of shell structure. As a function of temperature, we observe the disappearance
of these effects as in a phase transition.


title:
The Origins and the Early Evolution of Quasars and Supermassive Black
  Holes

abstract:
  The relationship between galaxies and supermassive black holes (SMBH) found
in their cores plays a key role in the formation and evolution of both of these
major constituents of the universe, as well as the evolution of the
intergalactic medium. Neither can be fully understood on their own, and studies
of galaxy and SMBH co-formation and co-evolution are now among the central
topics of research in cosmology. Yet the very origins, and the early growth
phases of the SMBH are still not firmly established. We review our current
understanding of the relevant processes and their astrophysical and
cosmological context, with an emphasis on the observability of the SMBH growth
mechanisms at high redshifts, and their leftover progeny at low redshifts.


title:
Entanglement reciprocation using three level atoms in a lambda
  configuration

abstract:
  We propose a scheme in which entanglement can be transferred from atoms
(discrete variables) to entangled states of cavity fields (continuous
variables). The cavities play the role of a kind of quantum memory for
entanglement, in such a way that it is possible to retrieve it back to the
atoms. In our method, two three level atoms in a lambda configuration,
previously entangled, are set to interact with single mode cavity fields
prepared in coherent states. During the process, one e-bit of entanglement may
be deposited in the cavities in an efficient way. We also show that the stored
entanglement may be transferred back to flying atoms.


title: Exact 'antigravity-field' solutions of Einstein's equation

abstract:
  Exact time-dependent solutions of Einstein's gravitational field equation for
a spherical mass moving with arbitrarily high constant velocity are derived and
analyzed. The threshold conditions required for gravitational repulsion of
particles at rest are determined as a function of source speed and field
strength and particle position.


title: MHD simulations of disk-star interaction

abstract:
  We discuss a number of topics relevant to disk-magnetosphere interaction and
how numerical simulations illuminate them. The topics include: (1)
disk-magnetosphere interaction and the problem of disk-locking; (2) the wind
problem; (3) structure of the magnetospheric flow, hot spots at the star's
surface, and the inner disk region; (4) modeling of spectra from 3D funnel
streams; (5) accretion to a star with a complex magnetic field; (6) accretion
through 3D instabilities; (7) magnetospheric gap and survival of protoplanets.
Results of both 2D and 3D simulations are discussed.


title: Charmonium in strongly coupled quark-gluon plasma

abstract:
  The growing consensus that a strongly-coupled quark-gluon plasma (sQGP) has
been observed at the SPS and RHIC experiments suggests a different framework
for examining heavy quark dynamics. We present both semi-analytical treatment
of Fokker-Planck (FP) evolution in pedagogical examples and numerical Langevin
simulations of evolving charm quark-antiquark pairs on top of a
hydrodynamically expanding fireball. In this way, we may conclude that the
survival probability of bound charmonia states is greater than previously
estimated, as the spatial equilibration of pairs proceeds through a ``slowly
dissolving lump'' stage related to the pair interaction.


title: Non-anticommutative solitons

abstract:
  Certain supersymmetric sigma models in 2+1 dimensions feature multi-soliton
solutions, with and without scattering. We subject these systems to a
non-anticommutative deformation by replacing the Grassmann algebra of the odd
superspace coordinates with a Clifford algebra. Static CP^1 and scattering U(2)
solitons are constructed and carry an additional spin-1/2 degree of freedom due
to the deformation. Abelian BPS solutions exist as well but have infinite
action, in contrast to the Moyal case.


title: Topological superfluids with time reversal symmetry

abstract:
  It is shown that superfluids in two and three dimensions which have time
reversal invariant ground states have phases which are distinguished by a
topological invariant. Further, it is shown that the B-phase of $^3$ He is a
superfluid in the non-trivial topological class. Superfluids in the non-trivial
topological class are shown to have gapless edge states and support various
kinds of vortices with zero energy modes localized in their cores. Some of
these vortices have non-abelian statistics.


title: Two-Photon Widths of the chi_cJ States of Charmonium

abstract:
  Using a data sample of 24.5 million psi(2S) the reactions psi(2S)->gamma
chi_cJ, chi_cJ->gamma gamma have been studied for the first time to determine
the two-photon widths of the chi_cJ states of charmonium in their decay into
two photons. The measured quantities are B(psi(2S)->gamma
chi_c0)xB(chi_c0->gamma gamma)=(2.22+-0.32+-0.10)x10^-5, and B(psi(2S)->gamma
chi_c2)xB(chi_c2->gamma gamma)=(2.70+-0.28+-0.15)x10^-5. Using values for
B(psi(2S)->gamma chi_c0,c2) and \Gamma(chi_c0,c2) from the literature the
two-photon widths are derived to be \Gamma_{gamma
gamma}(chi_c0)=(2.53+-0.37+-0.26) keV, \Gamma_{gamma
gamma}(chi_c2)=(0.60+-0.06+-0.06) keV, and R=\Gamma_{gamma
gamma}(chi_c2)/\Gamma_{gamma gamma}(chi_c0)= 0.237+-0.043+-0.034. The
importance of the measurement of R is emphasized. For the forbidden transition,
chi_c1->gamma gamma, an upper limit of \Gamma_{gamma gamma}(chi_c1)<0.03 keV is
established.


title: Properties of the Nonextensive Gaussian entropy

abstract:
  The present work investigates the Lesche stability (experimental robustness),
the thermodynamic stability, the Legendre structure of thermodynamics, and
derives the Maximum Entropy distribution of the one--parametric ``nonextensive
Gaussian'' entropy. We show that this entropy definition fulfills both
stability conditions for all values of its parameter ($q\in\mathbb{R}$). The
entropy maximizer contains the Lambert $W$--function, which allows the
preservation of the Legendre transformations.


title:
Strong linewidth variation for spin-torque nano-oscillators as a
  function of in-plane magnetic field angle

abstract:
  We measure the microwave signals produced by spin-torque-driven magnetization
dynamics in patterned magnetic multilayer devices at room temperature, as a
function of the angle of a magnetic field applied in the sample plane. We find
strong variations in the frequency linewidth of the signals, with a decrease by
more than a factor of 20 as the field is rotated from the magnetic easy axis to
the in-plane hard axis. Based on micromagnetic simulations, we identify these
variations as due to a transition from spatially incoherent to coherent
precession.


title: Internal Dynamics of the Hypercompact H II Region G28.20-0.04N

abstract:
  High resolution (0.15") Very Large Array observations of 7 mm continuum and
H53a line emission toward the hypercompact H II region G28.20-0.04N reveal the
presence of large-scale ordered motions. We find a velocity gradient of 1000
km/s/pc along the minor axis of the continuum source. Lower resolution
(1.0"-2.3") radio recombination line observations indicate a systematic
increase of line width from H30alpha to H92alpha. Under the assumption that the
H30alpha line does not suffer significant pressure broadening, we have
deconvolved the contributions of statistical broadening (thermal, turbulent,
and pressure) from large-scale motions. The pressure broadening of the
H53alpha, H76alpha, and H92alpha lines implies an electron density of 6.9E+06,
8.5E+05, and 2.8E+05 cm^(-3), respectively.


title: A mass for ALF manifolds

abstract:
  We prove positive mass theorems on ALF manifolds, i.e. complete noncompact
manifolds that are asymptotic to a circle fibration over a Euclidean base, with
fibers of asymptotically constant length.


title: Minimal weight expansions in Pisot bases

abstract:
  For applications to cryptography, it is important to represent numbers with a
small number of non-zero digits (Hamming weight) or with small absolute sum of
digits. The problem of finding representations with minimal weight has been
solved for integer bases, e.g. by the non-adjacent form in base~2. In this
paper, we consider numeration systems with respect to real bases $\beta$ which
are Pisot numbers and prove that the expansions with minimal absolute sum of
digits are recognizable by finite automata. When $\beta$ is the Golden Ratio,
the Tribonacci number or the smallest Pisot number, we determine expansions
with minimal number of digits $\pm1$ and give explicitely the finite automata
recognizing all these expansions. The average weight is lower than for the
non-adjacent form.


title:
Phase Transition with Non-Thermodynamic States in Reversible
  Polymerization

abstract:
  We investigate a reversible polymerization process in which individual
polymers aggregate and fragment at a rate proportional to their molecular
weight. We find a nonequilibrium phase transition despite the fact that the
dynamics are perfectly reversible. When the strength of the fragmentation
process exceeds a critical threshold, the system reaches a thermodynamic steady
state where the total number of polymers is proportional to the system size.
The polymer length distribution has a sharp exponential tail in this case. When
the strength of the fragmentation process falls below the critical threshold,
the steady state becomes non-thermodynamic as the total number of polymers
grows sub-linearly with the system size. Moreover, the length distribution has
an algebraic tail and the characteristic exponent varies continuously with the
fragmentation rate.


title: D-Instanton Generated Dirac Neutrino Masses

abstract:
  We present a stringy mechanism to generate Dirac neutrino masses by
D-instantons in an experimentally relevant mass scale without fine-tuning.
Within Type IIA string theory with intersecting D6-branes, we spell out
specific conditions for the emergence of such couplings and provide a class of
supersymmetric local SU(5) Grand Unified models, based on the Z_2 x Z'_2
orientifold compactification, where perturbatively absent Dirac neutrino masses
can be generated by D2-brane instantons in the experimentally observed mass
regime, while Majorana masses remain absent, thus providing an intriguing
mechanism for the origin of small neutrino masses due to non-perturbative
stringy effects.


title: Shifting the Universe: Early Dark Energy and Standard Rulers

abstract:
  The presence of dark energy at high redshift influences both the cosmic sound
horizon and the distance to last scattering of the cosmic microwave background.
We demonstrate that through the degeneracy in their ratio, early dark energy
can lie hidden in the CMB temperature and polarization spectra, leading to an
unrecognized shift in the sound horizon. If the sound horizon is then used as a
standard ruler, as in baryon acoustic oscillations, then the derived
cosmological parameters can be nontrivially biased. Fitting for the absolute
ruler scale (just as supernovae must be fit for the absolute candle magnitude)
removes the bias but decreases the leverage of the BAO technique by a factor 2.


title: Proofs of two conjectures on ternary weakly regular bent functions

abstract:
  We study ternary monomial functions of the form $f(x)=\Tr_n(ax^d)$, where
$x\in \Ff_{3^n}$ and $\Tr_n: \Ff_{3^n}\to \Ff_3$ is the absolute trace
function. Using a lemma of Hou \cite{hou}, Stickelberger's theorem on Gauss
sums, and certain ternary weight inequalities, we show that certain ternary
monomial functions arising from \cite{hk1} are weakly regular bent, settling a
conjecture of Helleseth and Kholosha \cite{hk1}. We also prove that the
Coulter-Matthews bent functions are weakly regular.


title:
A Direct Measurement of the Dust Extinction Curve in an
  Intermediate-Redshift Galaxy

abstract:
  We present a proof-of-concept study that dust extinction curves can be
extracted from the infrared (IR), optical, ultraviolet (UV) and X-ray afterglow
observations of GRBs without assuming known extinction laws. We focus on GRB
050525A (z = 0.606), for which we also present IR observations from the Spitzer
Space Telescope at about 2.3 days post-burst. We construct the spectral energy
distribution (SED) of the afterglow and use it to derive the dust extinction
curve of the host galaxy in 7 optical/UV wavebands. By comparing our derived
extinction curve to known templates, we see that the Galactic or Milky Way
extinction laws are disfavored versus the Small and Large Magellanic Cloud (SMC
and LMC) ones, but that we cannot rule out the presence of a LMC-like 2175
angstrom bump in our extinction curve. The dust-to-gas ratio present within the
host galaxy of GRB 050525A is similar to that found in the LMC, while about 10
to 40% more dust is required if the SMC template is assumed. Our method is
useful to observatories that are capable of simultaneously observing GRB
afterglows in multiple wavebands from the IR to the X-ray.


title:
Resonant Spin-Transfer-Driven Switching of Magnetic Devices Assisted by
  Microwave Current Pulses

abstract:
  The torque generated by the transfer of spin angular momentum from a
spin-polarized current to a nanoscale ferromagnet can switch the orientation of
the nanomagnet much more efficiently than a current-generated magnetic field,
and is therefore in development for use in next-generation magnetic random
access memory (MRAM). Up to now, only DC currents and square-wave current
pulses have been investigated in spin-torque switching experiments. Here we
present measurements showing that spin transfer from a microwave-frequency
pulse can produce a resonant excitation of a nanomagnet and lead to improved
switching characteristics in combination with a square current pulse. With the
assistance of a microwave-frequency pulse, the switching time is reduced and
achieves a narrower distribution than when driven by a square current pulse
alone, and this can permit significant reductions in the integrated power
required for switching. Resonantly excited switching may also enable
alternative, more compact MRAM circuit architectures.


title: Kernel Granger causality and the analysis of dynamical networks

abstract:
  We propose a method of analysis of dynamical networks based on a recent
measure of Granger causality between time series, based on kernel methods. The
generalization of kernel Granger causality to the multivariate case, here
presented, shares the following features with the bivariate measures: (i) the
nonlinearity of the regression model can be controlled by choosing the kernel
function and (ii) the problem of false-causalities, arising as the complexity
of the model increases, is addressed by a selection strategy of the
eigenvectors of a reduced Gram matrix whose range represents the additional
features due to the second time series. Moreover, there is no {\it a priori}
assumption that the network must be a directed acyclic graph. We apply the
proposed approach to a network of chaotic maps and to a simulated genetic
regulatory network: it is shown that the underlying topology of the network can
be reconstructed from time series of node's dynamics, provided that a
sufficient number of samples is available. Considering a linear dynamical
network, built by preferential attachment scheme, we show that for limited data
use of bivariate Granger causality is a better choice w.r.t methods using $L1$
minimization. Finally we consider real expression data from HeLa cells, 94
genes and 48 time points. The analysis of static correlations between genes
reveals two modules corresponding to well known transcription factors; Granger
analysis puts in evidence nineteen causal relationships, all involving genes
related to tumor development.


title:
Properties of Non-Abelian Fractional Quantum Hall States at Filling
  $\nu=\frac{k}{r}$

abstract:
  We compute the physical properties of non-Abelian Fractional Quantum Hall
(FQH) states described by Jack polynomials at general filling
$\nu=\frac{k}{r}$. For $r=2$, these states are identical to the $Z_k$
Read-Rezayi parafermions, whereas for $r>2$ they represent new FQH states. The
$r=k+1$ states, multiplied by a Vandermonde determinant, are a non-Abelian
alternative construction of states at fermionic filling $2/5, 3/7, 4/9...$. We
obtain the thermal Hall coefficient, the quantum dimensions, the electron
scaling exponent, and show that the non-Abelian quasihole has a well-defined
propagator falling off with the distance. The clustering properties of the Jack
polynomials, provide a strong indication that the states with $r>2$ can be
obtained as correlators of fields of \emph{non-unitary} conformal field
theories, but the CFT-FQH connection fails when invoked to compute physical
properties such as thermal Hall coefficient or, more importantly, the quasihole
propagator. The quasihole wavefuntion, when written as a coherent state
representation of Jack polynomials, has an identical structure for \emph{all}
non-Abelian states at filling $\nu=\frac{k}{r}$.


title: Hot Dirac Fermions in Epitaxial Graphene

abstract:
  We investigate the ultrafast relaxation dynamics of hot Dirac fermionic
quasiparticles in multilayer epitaxial graphene using ultrafast optical
differential transmission spectroscopy. We observe DT spectra which are well
described by interband transitions with no electron-hole interaction. Following
the initial thermalization and emission of high-energy phonons, the electron
cooling is determined by electron-acoustic phonon scattering, found to occur on
the time scale of 1 ps for highly doped layers, and 4-11 ps in undoped layers.
The spectra also provide strong evidence for the multilayer stucture and doping
profile of thermally grown epitaxial graphene on SiC.


title:
A theoretical investigation into the trapping of noble gases by
  clathrates on Titan

abstract:
  In this paper, we use a statistical thermodynamic approach to quantify the
efficiency with which clathrates on the surface of Titan trap noble gases. We
consider different values of the Ar, Kr, Xe, CH4, C2H6 and N2 abundances in the
gas phase that may be representative of Titan's early atmosphere. We discuss
the effect of the various parameters that are chosen to represent the
interactions between the guest species and the ice cage in our calculations. We
also discuss the results of varying the size of the clathrate cages. We show
that the trapping efficiency of clathrates is high enough to significantly
decrease the atmospheric concentrations of Xe and, to a lesser extent, of Kr,
irrespective of the initial gas phase composition, provided that these
clathrates are abundant enough on the surface of Titan. In contrast, we find
that Ar is poorly trapped in clathrates and, as a consequence, that the
atmospheric abundance of argon should remain almost constant. We conclude that
the mechanism of trapping noble gases via clathration can explain the
deficiency in primordial Xe and Kr observed in Titan's atmosphere by Huygens,
but that this mechanism is not sufficient to explain the deficiency in Ar.


title:
Deep infrared observations of the puzzling central X-ray source in
  RCW103

abstract:
  1E 161348-5055 (1E 1613) is a point-like, soft X-ray source originally
identified as a radio-quiet, isolated neutron star, shining at the center of
the 2000 yr old supernova remnant RCW103. 1E 1613 features a puzzling 6.67 hour
periodicity as well as a dramatic variability over a time scale of few years.
Such a temporal behavior, coupled to the young age and to the lack of an
obvious optical counterpart, makes 1E 1613 a unique source among all compact
objects associated to SNRs. It could either be the first low-mass X-ray binary
system discovered inside a SNR, or a peculiar isolated magnetar with an
extremely slow spin period. Analysis of archival IR observations, performed in
2001 with the VLT/ISAAC instrument, and in 2002 with the NICMOS camera onboard
HST unveils a very crowded field. A few sources are positionally consistent
with the refined X-ray error region that we derived from the analysis of 13
Chandra observations. To shed light on the nature of 1E 1613, we have performed
deep IR observations of the field with the NACO instrument at the ESO/VLT,
searching for variability. We find no compelling reasons to associate any of
the candidates to 1E 1613. On one side, within the frame of the binary system
model for the X-ray source, it is very unlikely that one of the candidates be a
low-mass companion star to 1E 1613. On the other side, if the X-ray source is
an isolated magnetar surrounded by a fallback disc, we cannot exclude that the
IR counterpart be hidden among the candidates. If none of the potential
counterparts is linked to the X-ray source, 1E 1613 would remain undetected in
the IR down to Ks>22.1. Such an upper limit is consistent only with an
extremely low-mass star (an M6-M8 dwarf) at the position of 1E 1613, and makes
rather problematic the interpretation of 1E 1613 as an accreting binary system.


title: Spectra of Sparse Random Matrices

abstract:
  We compute the spectral density for ensembles of of sparse symmetric random
matrices using replica, managing to circumvent difficulties that have been
encountered in earlier approaches along the lines first suggested in a seminal
paper by Rodgers and Bray. Due attention is payed to the issue of localization.
Our approach is not restricted to matrices defined on graphs with Poissonian
degree distribution. Matrices defined on regular random graphs or on scale-free
graphs, are easily handled. We also look at matrices with row constraints such
as discrete graph Laplacians. Our approach naturally allows to unfold the total
density of states into contributions coming from vertices of different local
coordination.


title:
Derivation of Maxwell-Bloch-type equations by projection of quantum
  models

abstract:
  A simple algebraic procedure is described for deriving Maxwell-Bloch-type
equations from single-atom cavity quantum electrodynamics (cavity QED) master
equations via orthogonal projection onto a manifold of semiclassical states. In
particular the usual Maxwell-Bloch Equations are obtained--up to a
state-dependent correction factor of order unity--straightforwardly from the
unconditional Jaynes-Cummings master equation. The technique of projecting onto
a semiclassical manifold can also be applied with conditional master equations
(quantum filters), leading to stochastic simulation models that include
multiplicative noise terms associated with fluctuations of the atomic dipole.
The utility of such models is briefly explored in the context of single-atom
absorptive bistability.


title: Scintillation yield of liquid xenon at room temperature

abstract:
  The intensity of scintillation light emission from liquid xenon at room
temperature was measured. The scintillation light yield at 1 deg. was measured
to be 0.64 +/- 0.02 (stat.) +/- 0.06 (sys.) of that at -100 deg. Using the
reported light yield at -100 deg. (46 photons/keV), the measured light yield at
1 deg. corresponds to 29 photons/keV. This result shows that liquid xenon
scintillator gives high light yield even at room temperature.


title: Mapping out SU(5) GUTs with non-Abelian discrete flavor symmetries

abstract:
  We construct a class of supersymmetric SU(5) GUT models that produce nearly
tribimaximal lepton mixing, the observed quark mixing matrix, and the quark and
lepton masses, from discrete non-Abelian flavor symmetries. The SU(5) GUTs are
formulated on two five-dimensional throats in the flat limit and the neutrino
masses become small due to the type-I seesaw mechanism. The discrete
non-Abelian flavor symmetries are given by semi-direct products of cyclic
groups that are broken at the infrared branes at the tip of the throats. As a
result, we obtain SU(5) GUTs that provide a combined description of non-Abelian
flavor symmetries and quark-lepton complementarity.


title: Drag force at finite 't Hooft coupling from AdS/CFT

abstract:
  We find that the drag force for a heavy quark moving through N=4 SU(N_c)
supersymmetric Yang-Mills plasma is generally enhanced by the leading
correction due to finite 't Hooft coupling. For a bottom quark, the drag force
increases by about 50%, whereas for a charm quark it increases by about 5%. We
also discuss the drag force for the case of Gauss-Bonnet gravity.


title:
Nuclear activity in galaxy pairs: a spectroscopic analysis of 48
  UZC-BGPs

abstract:
  Galaxy pairs are ideal sites in which to investigate the role of interaction
on nuclear activity. For this reason we have undertaken a spectroscopic survey
of a large homogeneous sample of galaxy pairs (UZC-BGP) and we present the
results of the nuclear spectral classification of 48 pairs (more than half of
the whole sample). The fraction of emission line galaxies is extremely large,
especially among spirals (84 % and 95 %, for early and late spirals
respectively). SB is the most frequent type of nuclear activity encountered (30
% of galaxies) while AGNs are only 19%. The fractions raise to 45 % and 22 %
when considering only spirals. Late spirals are characterized by both an
unusual increase (35 %) of AGN activity and high luminosity (44 % have M_B
<-20.0 + 5log h). LLAGNs are only 8% of the total number of galaxies, but this
activity could be present in another 10 % of the galaxies (LLAGN candidates).
Absorption line galaxies reside mostly (61 %) in S0 galaxies and display the
lowest B luminosity in the sample, only 18 % of them have M_B < -20 + 5 log h,
but together with LLAGNs they are the most massive galaxies in the sample.
Intense-SB nuclei are found in galaxy pairs with galaxy-galaxy projected
separations up to 160 h^{-1} kpc suggesting that in bright isolated galaxy
pairs interaction may be at work and effective up to that distance. AGNs are
characterized by an advanced morphology while SB phenomenon occurs with the
same frequency in early and late spirals. LLAGNs and LLAGN candidates do not
always show similar properties, a finding which might confirm the heterogeneous
nature of this class of objects. Half LLAGNs are hosted in galaxies showing
visible signs of interaction with fainter companions, suggesting that minor
interactions might be a driving mechanism for a relevant fraction of LLAGNs.


title:
The Origin and Kinematics of Cold Gas in Galactic Winds: Insight from
  Numerical Simulations

abstract:
  We study the origin of Na I absorbing gas in ultraluminous infrared galaxies
motivated by the recent observations by Martin of extremely superthermal
linewidths in this cool gas. We model the effects of repeated supernova
explosions driving supershells in the central regions of molecular disks with
M_d=10^10 M_\sun, using cylindrically symmetric gas dynamical simulations run
with ZEUS-3D. The shocked swept-up shells quickly cool and fragment by
Rayleigh-Taylor instability as they accelerate out of the dense, stratified
disks. The numerical resolution of the cooling and compression at the shock
fronts determines the peak shell density, and so the speed of Rayleigh-Taylor
fragmentation. We identify cooled shells and shell fragments as Na I absorbing
gas and study its kinematics. We find that simulations with a numerical
resolution of \le 0.2 pc produce multiple Rayleigh-Taylor fragmented shells in
a given line of sight. We suggest that the observed wide Na I absorption lines,
<v> = 320 \pm 120 km s^-1 are produced by these multiple fragmented shells
traveling at different velocities. We also suggest that some shell fragments
can be accelerated above the observed average terminal velocity of 750 km s^-1
by the same energy-driven wind with an instantaneous starburst of \sim 10^9
M_\sun. The bulk of mass is traveling with the observed average shell velocity
330 \pm 100 km s^-1. Our results show that an energy-driven bubble causing
Rayleigh-Taylor instabilities can explain the kinematics of cool gas seen in
the Na I observations without invoking additional physics relying primarily on
momentum conservation, such as entrainment of gas by Kelvin-Helmholtz
instabilities, ram pressure driving of cold clouds by a hot wind, or radiation
pressure acting on dust. (abridged)


title: Zonal Jets as Transport Barriers in Planetary Atmospheres

abstract:
  The connection between transport barriers and potential vorticity (PV)
barriers in PV-conserving flows is investigated with a focus on zonal jets in
planetary atmospheres. A perturbed PV-staircase model is used to illustrate
important concepts. This flow consists of a sequence of narrow eastward and
broad westward zonal jets with a staircase PV structure; the PV-steps are at
the latitudes of the cores of the eastward jets. Numerically simulated
solutions to the quasigeostrophic PV conservation equation in a perturbed
PV-staircase flow are presented. These simulations reveal that both eastward
and westward zonal jets serve as robust meridional transport barriers. The
surprise is that westward jets, across which the background PV gradient
vanishes, serve as robust transport barriers. A theoretical explanation of the
underlying barrier mechanism is provided. It is argued that transport barriers
near the cores of westward zonal jets, across which the background PV gradient
is small, are found in Jupiter's midlatitude weather layer and in the Earth's
summer hemisphere subtropical stratosphere.


title: Revisiting glueball wave functions at zero and finite temperature

abstract:
  We study the sizes and thermal properties of glueballs in a three dimensional
compact Abelian gauge model on improved lattice. We predict the radii of $\sim
0.60$ and $\sim 1.12$ in the units of string tension, or $\sim 0.28$ and $\sim
0.52$ fm, for the scalar and tensor glueballs, respectively. We perform a well
controlled extrapolation of the radii to the continuum limit and observe that
our results agree with the predicted values. Using Monte Carlo simulations, we
extract the pole-mass of the lowest scalar and tensor glueballs from the
temporal correlators at finite temperature. We see a clear evidence of the
deconfined phase, and the transition appears to be similar to that of the
two-dimensional XY model as expected from universality arguments. Our results
show no significant changes in the glueball wave functions and masses in the
deconfined phase.


title:
Dynamically Solving the $\mu/B_\mu$ Problem in Gauge-mediated
  Supersymmetry Breaking

abstract:
  We provide a simple solution to the $\mu/B_\mu$ problem in the gauge-mediated
Next-to-Minimal Supersymmetric Standard Model. In this model the messenger
sector contains one pair of $3+\bar 3$ and one pair of $2+\bar 2$ messengers.
These two messenger pairs couple to different gauge singlets in the hidden
sector in which supersymmetry (SUSY) is broken. Such a gauge-mediation
structure can naturally arise in many backgrounds. Because of the two effective
SUSY breaking scales $\frac{< F_i>}{< M_i>}$ in the messenger sector, the
renormalization group evolutions of the soft SUSY breaking parameters can be
properly modified, leading to a negative enough singlet soft mass square
$m_N^2(\Lambda_{EW})$ and hence reasonable $\mu/B_\mu$ values. In most of the
perturbative (up to the GUT scale) parameter region, as a result, the
electroweak scale is stabilized and phenomenologically interesting mass spectra
of particles and superparticles are obtained. In addition, this model favors
large values of $\tan\beta$: $5 \sim 50$ and a heavy scalar spectrum. With the
relatively large $\tan\beta$, the light $U(1)_R$ pseudoscalar (mainly appearing
in the low-scale gauge-mediated SUSY breaking models) becomes extremely
singlet-like, and is no longer a problem in this model. These features apply to
all cases of low-, intermediate- and high-scale gauge-mediated SUSY breaking.


title: Global m=1 instabilities and lopsidedness in disc galaxies

abstract:
  Lopsidedness is common in spiral galaxies. Often, there is no obvious
external cause, such as an interaction with a nearby galaxy, for such features.
Alternatively, the lopsidedness may have an internal cause, such as a dynamical
instability. In order to explore this idea, we have developed a computer code
that searches for self-consistent perturbations in razor-thin disc galaxies and
performed a thorough mode-analysis of a suite of dynamical models for disc
galaxies embedded in an inert dark-matter halo with varying amounts of rotation
and radial anisotropy. Models with two equal-mass counter-rotating discs and
fully rotating models both show growing lopsided modes. For the
counter-rotating models, this is the well-known counter-rotating instability,
becoming weaker as the net rotation increases. The m=1 mode of the maximally
rotating models, on the other hand, becomes stronger with increasing net
rotation. This rotating m=1 mode is reminiscent of the eccentricity instability
in near-Keplerian discs. To unravel the physical origin of these two different
m=1 instabilities, we studied the individual stellar orbits in the perturbed
potential and found that the presence of the perturbation gives rise to a very
rich orbital behaviour. In the linear regime, both instabilities are supported
by aligned loop orbits. In the non-linear regime, other orbit families exist
that can help support the modes. In terms of density waves, the
counter-rotating m=1 mode is due to a purely growing Jeans-type instability.
The rotating m=1 mode, on the other hand, grows as a result of the swing
amplifier working inside the resonance cavity that extends from the disc center
out to the radius where non-rotating waves are stabilized by the model's
outwardly rising Q-profile.


title:
Confirmation of the binary status of Cha Halpha 2 - a very young
  low-mass binary in Chamaeleon

abstract:
  Neuhaeuser & Comeron (1998, 1999) presented direct imaging evidence, as well
as first spectra, of several young stellar and sub-stellar M6- to M8-type
objects in the Cha I dark cloud. One of these objects is Cha Halpha 2,
classified as brown dwarf candidate in several publications and suggested as
possible binary in Neuhaeuser et al. (2002). We have searched around Cha Halpha
2 for close and faint companions with adaptive optics imaging. Two epochs of
direct imaging data were taken with the Very Large Telescope (VLT) Adaptive
Optics instrument NACO in February 2006 and March 2007 in Ks-band. We retrieved
an earlier image from 2005 from the European Southern Observatory (ESO) Science
Archive Facility, increasing the available time coverage. After confirmation of
common proper motion, we deduce physical parameters of the objects by
spectroscopy, like temperature and mass. We find Cha Halpha 2 to be a very
close binary of ~0.16 arcsec separation, having a flux ratio of ~0.91, thus
having almost equal brightness and indistinguishable spectral types within the
errors. We show that the two tentative components of Cha Halpha 2 form a common
proper motion pair, and that neither component is a non-moving background
object. We even find evidence for orbital motion. A combined spectrum of both
stars spanning optical and near-infrared parts of the spectral energy
distribution yields a temperature of 3000+/-100 K, corresponding to a spectral
type of M6+/-1 and a surface gravity of log g= 4.0 +0.75-0.5, both from a
comparison with GAIA model atmospheres. We derive masses of ~0.110 Msun (>0.070
Msun) and ~0.124 Msun (>0.077 Msun) for the two components of Cha Halpha 2,
i.e., probably low-mass stars, but one component could possibly be a brown
dwarf.


title: Validation of a Model of the Domino Effect?

abstract:
  A recent paper proposing a model of the limiting speed of the domino effect
is discussed with reference to its need and the need of models in general for
validation against experimental data. It is shown that the proposed model
diverges significantly from experimentally derived speed estimates over a
significant range of domino spacing using data from the existing literature and
this author's own measurements, hence if its use had had economic importance
its use outside its range of validity could have led to loses of one sort or
another to its users.


title: Static charged fluid around a massive magnetic dipole

abstract:
  An analytical solution of Einstein-Maxwell equations with a static fluid as a
source is presented. The spacetime is represented by the axially symmetric Weyl
metric and the energy-momentum tensor describes a coupling of a fluid with an
electromagnetic field. When appropriate limits are performed we recover the
well-known solutions of Gutsunaev-Manko and Schwarzschild. Also, using Eckart's
thermodynamics, we calculated the temperature, the mechanical pressure, the
charge density and the energy density of the system. The analysis of
thermodynamic quantities suggests that the solution can be used to represent a
magnetized compact stellar object surrounded by a charged fluid.


title:
Canonical Trajectories and Critical Coupling of the Bose-Hubbard
  Hamiltonian in a Harmonic Trap

abstract:
  Quantum Monte Carlo (QMC) simulations and the Local Density Approximation
(LDA) are used to map the constant particle number (canonical) trajectories of
the Bose Hubbard Hamiltonian confined in a harmonic trap onto the $(\mu/U,t/U)$
phase diagram of the uniform system. Generically, these curves do not intercept
the tips of the Mott insulator (MI) lobes of the uniform system. This
observation necessitates a clarification of the appropriate comparison between
critical couplings obtained in experiments on trapped systems with those
obtained in QMC simulations. The density profiles and visibility are also
obtained along these trajectories. Density profiles from QMC in the confined
case are compared with LDA results.


title: Eigenvalues of the Derangement Graph

abstract:
  We consider the Cayley graph on the symmetric group Sn generated by
derangements. It is well known that the eigenvalues of this grpah are indexed
by partitions of n. We investigate how these eigenvalues are determined by the
shape of their corresponding partitions. In particular, we show that the sign
of an eigenvalue is the parity of the number of cells below the first row of
the corresponding Ferrers diagram. We also provide some lower and upper bounds
for the absolute values of these eigenvalues.


title:
Theory of quantum metal to superconductor transitions in highly
  conducting systems

abstract:
  We derive the theory of the quantum (zero temperature) superconductor to
metal transition in disordered materials when the resistance of the normal
metal near criticality is small compared to the quantum of resistivity. This
can occur most readily in situations in which ``Anderson's theorem'' does not
apply. We explicitly study the transition in superconductor-metal composites,
in an s-wave superconducting film in the presence of a magnetic field, and in a
low temperature disordered d-wave superconductor. Near the point of the
transition, the distribution of the superconducting order parameter is highly
inhomogeneous. To describe this situation we employ a procedure which is
similar to that introduced by Mott for description of the temperature
dependence of the variable range hopping conduction. As the system approaches
the point of the transition from the metal to the superconductor, the
conductivity of the system diverges, and the Wiedemann-Franz law is violated.
In the case of d-wave (or other exotic) superconductors we predict the
existence of (at least) two sequential transitions as a function of increasing
disorder: a d-wave to s-wave, and then an s-wave to metal transition.


title: Turbulence and transport in two-dimensional magnetized electron plasmas

abstract:
  Electron plasmas confined by an external magnetic field exhibit variations in
a two-dimensional plane orthogonal to the confining magnetic field. A nonlinear
fluid simulation code to investigate the properties of 2-D electron plasma wave
turbulence in a nonuniform magnetoplasma has been developed. It is found that
the presence of the density gradient convection by mean electric fields
considerably influence the characteristic nonlinear interaction processes, such
as the energy cascades and the cross-field electron transport. The initial
random turbulent state evolves towards an intermittent state where forward
cascade of vorticity coexists with an inverse cascade of electric potential
fluctuations. The latter lead to the formation of large scale entities in 2D
electron plasmas and can be alternatively understood by seeking exact nonlinear
coherent vortex solutions in the form of a dipolar-like configuration. The
energy cascades are governed typically by the Kolmogorov-like $k^{-5/3}$
spectrum. In agreement with the experimental observations, we find that the
electron transport is improved significantly by the application of an
externally imposed electric field.


title: A Distance Metric for Tree-Sibling Time Consistent Phylogenetic Networks

abstract:
  The presence of reticulate evolutionary events in phylogenies turn
phylogenetic trees into phylogenetic networks. These events imply in particular
that there may exist multiple evolutionary paths from a non-extant species to
an extant one, and this multiplicity makes the comparison of phylogenetic
networks much more difficult than the comparison of phylogenetic trees. In
fact, all attempts to define a sound distance measure on the class of all
phylogenetic networks have failed so far. Thus, the only practical solutions
have been either the use of rough estimates of similarity (based on comparison
of the trees embedded in the networks), or narrowing the class of phylogenetic
networks to a certain class where such a distance is known and can be
efficiently computed. The first approach has the problem that one may identify
two networks as equivalent, when they are not; the second one has the drawback
that there may not exist algorithms to reconstruct such networks from
biological sequences.
  We present in this paper a distance measure on the class of tree-sibling time
consistent phylogenetic networks, which generalize tree-child time consistent
phylogenetic networks, and thus also galled-trees. The practical interest of
this distance measure is twofold: it can be computed in polynomial time by
means of simple algorithms, and there also exist polynomial-time algorithms for
reconstructing networks of this class from DNA sequence data.
  The Perl package Bio::PhyloNetwork, included in the BioPerl bundle,
implements many algorithms on phylogenetic networks, including the computation
of the distance presented in this paper.


title:
Full optimization of Jastrow-Slater wave functions with application to
  the first-row atoms and homonuclear diatomic molecules

abstract:
  We pursue the development and application of the recently-introduced linear
optimization method for determining the optimal linear and nonlinear parameters
of Jastrow-Slater wave functions in a variational Monte Carlo framework. In
this approach, the optimal parameters are found iteratively by diagonalizing
the Hamiltonian matrix in the space spanned by the wave function and its
first-order derivatives, making use of a strong zero-variance principle. We
extend the method to optimize the exponents of the basis functions,
simultaneously with all the other parameters, namely the Jastrow, configuration
state function and orbital parameters. We show that the linear optimization
method can be thought of as a so-called augmented Hessian approach, which helps
explain the robustness of the method and permits us to extend it to minimize a
linear combination of the energy and the energy variance. We apply the linear
optimization method to obtain the complete ground-state potential energy curve
of the C_2 molecule up to the dissociation limit, and discuss size consistency
and broken spin-symmetry issues in quantum Monte Carlo calculations. We perform
calculations of the first-row atoms and homonuclear diatomic molecules with
fully optimized Jastrow-Slater wave functions, and we demonstrate that
molecular well depths can be obtained with near chemical accuracy quite
systematically at the diffusion Monte Carlo level for these systems.

categories: physics.comp-ph cond-mat.mtrl-sci cond-mat.other physics.chem-ph


title: Nucleon EDM and rare decays of eta mesons

abstract:
  I consider rare CP-violating decay modes $\eta(\eta')\to\pi\pi$ and note that
an interaction that leads to such decays would necessarily induce a nucleon
electric dipole moment (EDM). The experimental limits for the corresponding
branching ratios are quite soft. I relate these decay branching ratios to the
value of the induced nucleon EDM and translate the experimental limits on the
neutron EDM into much more stringent constraints on these decay rates:
$\frac{\Gamma_{\eta\to\pi\pi}}{\Gamma_\eta}\lesssim3.5\times10^{-14}$ and
$\frac{\Gamma_{\eta'\to\pi\pi}}{\Gamma_\eta'}\lesssim1.8\times10^{-17}$.


title: Excitonic States in Medium-Size Quantum Dots

abstract:
  In a quantum dot with dozens of electrons, an approximation beyond
Tamm-Dankoff is used to construct the quantum states with an additional
electron-hole pair, i.e. the "excitonic" states. The lowest states mimic the
non-interacting spectrum, but with excitation gaps renormalized by Coulomb
interactions. At higher excitation energies, the computed density of energy
levels shows an exponential increase with energy. In the interband absorption,
we found a background level in the quasicontinuum of states rising linearly
with the excitation energy. Above this background, there are distinct peaks
related to single resonances or to groups of many states with small interband
dipole moments.


title: Casimir-Lifshitz Theory and Metamaterials

abstract:
  Based on a generalization of the Lifshiftz theory we calculate Casimir forces
involving magnetodielectric and possibly anisotropic metamaterials, focusing on
the possibility of repulsive forces. It is found that Casimir repulsion
decreases with magnetic dissipation, and even a small Drude background in
metallic-based metamaterials acts to make attractive a Casimir force that would
otherwise be predicted to be repulsive. The sign of the force also depends
sensitively on the degree of optical anisotropy of the metamaterial, and on the
form of the frequency-dependency of the magnetic response.


title: New Dissipation Relaxation Phenomenon in Oscillating Solid He-4

abstract:
  We describe the first observations on the time-dependent dissipation when the
drive level of a torsional oscillator containing solid He-4 is abruptly
changed. The relaxation of dissipation in solid He-4 shows rich dynamical
behavior including exponential and logarithmic time-dependent decays,
hysteresis, and memory effects.


title: Baryonic D Decay $D_s^+\to p\bar n$ and Its Implication

abstract:
  The channel $D_s^+\to p\bar n$ is the only kinematically allowed baryonic D
decay. It proceeds solely through the W-annihilation topology. Hence, a recent
observation of this mode by CLEO will shed light on the dynamics of
W-annihilation. At the short-distance level, its branching ratio is very small,
of order $10^{-6}$, owing to chiral suppression. It receives long-distance
contributions through final-state scattering of the leading tree and
color-suppressed amplitudes. Assuming that the long-distance enhancement of
W-annihilation in the baryonic D decay is similar to that in the mesonic
$D_s^+$ decay, where the latter can be obtained from the analysis of the
diagrammatic approach, we find that $D_s^+\to p\bar n$ becomes visible. The
observation of this baryonic D decay implies the dynamical enhancement of the
W-annihilation topology in the $D_s^+$ decay.


title:
The impact of bound states on similarity renormalization group
  transformations

abstract:
  We study a simple class of unitary renormalization group transformations
governed by a parameter f in the range [0,1]. For f=0, the transformation is
one introduced by Wegner in condensed matter physics, and for f=1 it is a
simpler transformation that is being used in nuclear theory. The transformation
with f=0 diagonalizes the Hamiltonian but in the transformations with f near 1
divergent couplings arise as bound state thresholds emerge. To illustrate and
diagnose this behavior, we numerically study Hamiltonian flows in two simple
models with bound states: one with asymptotic freedom and a related one with a
limit cycle. The f=0 transformation places bound-state eigenvalues on the
diagonal at their natural scale, after which the bound states decouple from the
dynamics at much smaller momentum scales. At the other extreme, the f=1
transformation tries to move bound-state eigenvalues to the part of the
diagonal corresponding to the lowest momentum scales available and inevitably
diverges when this scale is taken to zero. We analyze the shift mechanism
analytically in a 3x3 matrix model, which displays the essense of this RG
behavior.


title: RS Ophiuchi in Quiescence: Why is it X-ray Faint?

abstract:
  The short interval between successive outbursts of RS Oph strongly suggests
that it has a high mass white dwarf accreting at a high rate. This, in turn,
suggests the possibility of prominent X-ray emission from RS Oph in quiescence.
However, archival quiescent X-ray observations of RS Oph show it to be a modest
soft X-ray source but not a strong 2-10 keV X-ray source. In this aspect, RS
Oph differs markedly from T CrB. We speculate on the possible mechanisms that
could significantly suppress the 2-10 keV X-ray emission in RS Oph.


title: Origin of holographic dark energy models

abstract:
  We investigate the origin of holographic dark energy models which were
recently proposed to explain the dark energy-dominated universe. For this
purpose, we introduce the spacetime foam uncertainty of $\delta l \ge l_{\rm
p}^{\alpha}l^{\alpha-1}$. It was argued that the case of $\alpha=2/3$ could
describe the dark energy with infinite statistics, while the case of
$\alpha=1/2$ can describe the ordinary matter with Bose-Fermi statistics.
However, two cases may lead to the holographic energy density if the latter
recovers from the geometric mean of UV and IR scales. Hence the dark energy
with infinite statistics based on the entropy bound is not an ingredient for
deriving the holographic dark energy model. Furthermore, it is shown that the
agegraphic dark energy models are the holographic dark energy model with
different IR length scales.


title:
Asymptotics of coefficients of multivariate generating functions:
  improvements for smooth points

abstract:
  Let $\sum_{\beta\in\nats^d} F_\beta x^\beta$ be a multivariate power series.
For example $\sum F_\beta x^\beta$ could be a generating function for a
combinatorial class. Assume that in a neighbourhood of the origin this series
represents a nonentire function $F=G/H^p$ where $G$ and $H$ are holomorphic and
$p$ is a positive integer. Given a direction $\alpha\in\pnats^d$ for which the
asymptotics are controlled by a smooth point of the singular variety $H = 0$,
we compute the asymptotics of $F_{n \alpha}$ as $n\to\infty$. We do this via
multivariate singularity analysis and give an explicit formula for the full
asymptotic expansion. This improves on earlier work of R. Pemantle and the
second author and allows for more accurate numerical approximation, as
demonstrated by our examples.


title: Nuclear Schiff moment and soft vibrational modes

abstract:
  The atomic electric dipole moment (EDM) currently searched by a number of
experimental groups requires that both parity and time-reversal invariance be
violated. According to current theoretical understanding, the EDM is induced by
the nuclear Schiff moment. The enhancement of the Schiff moment by the
combination of static quadrupole and octupole deformation was predicted
earlier. Here we study a further idea of the possible enhancement in the
absence of static deformation but in a nuclear system with soft collective
vibrations of two types. Both analytical approximation and numerical solution
of the simplified problem confirm the presence of the enhancement. We discuss
related aspects of nuclear structure which should be studied beyond mean-field
and random phase approximations.


title:
Persistent antimonotonic bifurcations and strange attractors for cubic
  homoclinic tangencies

abstract:
  In this paper, we study a two-parameter family of two-dimensional
diffeomorphisms such that it has a cubic homoclinic tangency unfolding
generically which is associated with a dissipative saddle point. Our first
theorem presents an open set in the parameter-plane such that, for any
parameter value in the open set, there exists a one-parameter subfamily through
this value exhibiting cubically related persistent contact-making and
contact-breaking quadratic tangencies. Moreover, the second theorem shows that
any such two-parameter family satisfies Wang-Young's conditions which guarantee
that it exhibits a cubic polynomial-like strange attractor with an SRB measure.


title: Mass Transportation on Sub-Riemannian Manifolds

abstract:
  We study the optimal transport problem in sub-Riemannian manifolds where the
cost function is given by the square of the sub-Riemannian distance. Under
appropriate assumptions, we generalize Brenier-McCann's Theorem proving
existence and uniqueness of the optimal transport map. We show the absolute
continuity property of Wassertein geodesics, and we address the regularity
issue of the optimal map. In particular, we are able to show its approximate
differentiability a.e. in the Heisenberg group (and under some weak assumptions
on the measures the differentiability a.e.), which allows to write a weak form
of the Monge-Amp\`ere equation.


title:
Time-dependent current-density functional theory for the friction of
  ions in an interacting electron gas

abstract:
  Due to the strongly nonlocal nature of $f_{xc}({\bf r},{\bf r}',\omega)$ the
{\em scalar} exchange and correlation (xc) kernel of the time-dependent
density-functional theory (TDDFT), the formula for Q the friction coefficient
of an interacting electron gas (EG) for ions tends to give a too large value of
Q for heavy ions in the medium- and low-density EG, if we adopt the
local-density approximation (LDA) to $f_{xc}({\bf r},{\bf r}',\omega)$, even
though the formula itself is formally exact. We have rectified this unfavorable
feature by reformulating the formula for Q in terms of the {\em tensorial} xc
kernel of the time dependent current-density functional theory, to which the
LDA can be applied without intrinsic difficulty. Our numerical results find
themselves in a considerably better agreement with the experimental stopping
power of Al and Au for slow ions than those previously obtained within the LDA
to the TDDFT.


title:
Distributed Relay Protocol for Probabilistic Information-Theoretic
  Security in a Randomly-Compromised Network

abstract:
  We introduce a simple, practical approach with probabilistic
information-theoretic security to mitigate one of quantum key distribution's
major limitations: the short maximum transmission distance (~200 km) possible
with present day technology. Our scheme uses classical secret sharing
techniques to allow secure transmission over long distances through a network
containing randomly-distributed compromised nodes. The protocol provides
arbitrarily high confidence in the security of the protocol, with modest
scaling of resource costs with improvement of the security parameter. Although
some types of failure are undetectable, users can take preemptive measures to
make the probability of such failures arbitrarily small.


title:
Scalable cavity-QED-based scheme of generating entanglement of atoms and
  of cavity fields

abstract:
  We propose a cavity-QED-based scheme of generating entanglement between
atoms. The scheme is scalable to an arbitrary number of atoms, and can be used
to generate a variety of multipartite entangled states such as the
Greenberger-Horne-Zeilinger, W, and cluster states. Furthermore, with a role
switching of atoms with photons, the scheme can be used to generate
entanglement between cavity fields. We also introduce a scheme that can
generate an arbitrary multipartite field graph state.


title: Inductive Algebras for Finite Heisenberg Groups

abstract:
  A characterization of the maximal abelian sub-algebras of matrix algebras
that are normalized by the canonical representation of a finite Heisenberg
group is given. Examples are constructed using a classification result for
finite Heisenberg groups.


title:
Theory of correlations between ultra-cold bosons released from an
  optical lattice

abstract:
  In this paper we develop a theoretical description of the correlations
between ultra-cold bosons after free expansion from confinement in an optical
lattice. We consider the system evolution during expansion and give criteria
for a far field regime. We develop expressions for first and second order
two-point correlations based on a variety of commonly used approximations to
the many-body state of the system including Bogoliubov, meanfield decoupling,
and particle-hole perturbative solution about the perfect Mott-insulator state.
Using these approaches we examine the effects of quantum depletion and pairing
on the system correlations. Comparison with the directly calculated correlation
functions is used to justify a Gaussian form of our theory from which we
develop a general three-dimensional formalism for inhomogeneous lattice systems
suitable for numerical calculations of realistic experimental regimes.


title:
Dynamic polarizability of rotating particles in electrorheological
  fluids

abstract:
  A rotating particle in electrorheological (ER) fluid leads to a displacement
of its polarization charges on the surface which relax towards the external
applied field ${\bf E}_0$, resulting in a steady-state polarization at an angle
with respect to ${\bf E}_0$. This dynamic effect has shown to affect the ER
fluids properties dramatically. In this paper, we develop a dynamic effective
medium theory (EMT) for a system containing rotating particles of finite volume
fraction. This is a generalization of established EMT to account for the
interactions between many rotating particles. While the theory is valid for
three dimensions, the results in a special two dimensional configuration show
that the system exhibits an off-diagonal polarization response, in addition to
a diagonal polarization response, which resembles the classic Hall effect. The
diagonal response monotonically decreases with an increasing rotational speed,
whereas the off-diagonal response exhibits a maximum at a reduced rotational
angular velocity $\omega_0$ comparing to the case of isolated rotating
particles. This implies a way of measurement on the interacting relaxation
time. The dependencies of the diagonal and off-diagonal responses on various
factors, such as $\omega_0$, the volume fraction, and the dielectric contrast,
are discussed.

categories: physics.chem-ph cond-mat.mtrl-sci cond-mat.soft physics.class-ph


title: Eigenfunctions of the Laplace-Beltrami Operator on Hyperboloids

abstract:
  Eigenfunctions of the Laplace-Beltrami operator on a hyperboloid are studied
in the spirit of the treatment of the spherical harmonics by Stein and Weiss.
As a special case, a simple self-contained proof of Laplace's integral for a
Legendre function is obtained.


title: Equivalence of Probabilistic Tournament and Polynomial Ranking Selection

abstract:
  Crucial to an Evolutionary Algorithm's performance is its selection scheme.
We mathematically investigate the relation between polynomial rank and
probabilistic tournament methods which are (respectively) generalisations of
the popular linear ranking and tournament selection schemes. We show that every
probabilistic tournament is equivalent to a unique polynomial rank scheme. In
fact, we derived explicit operators for translating between these two types of
selection. Of particular importance is that most linear and most practical
quadratic rank schemes are probabilistic tournaments.


title: Matrix universality of gauge and gravitational dynamics

abstract:
  A simple cubic matrix model is presented, which has truncations that, it is
argued, lead at the classical level to a variety of theories of gauge fields
and gravity. These include Chern-Simons theory in d=3, and BF theory and
general relativity in d=4. General relativity coupled to Yang-mills theory for
any SU(N) may also arise from quantum corrections.
  On the basis of these results we conjecture that there are large universality
classes of cut-off gauge and gravity theories, connected by transformations
that mix up local and spacetime symmetries. If our universe is described by one
of these theories then the question of the choice of the laws of physics is to
a large extent subsumed in the problem of the choice of initial conditions in
cosmology.


title:
Novel Jeff = 1/2 Mott State Induced by Relativistic Spin-Orbit Coupling
  in Sr2IrO4

abstract:
  We investigated electronic structure of 5d transition-metal oxide Sr2IrO4
using angle-resolved photoemission, optical conductivity, and x-ray absorption
measurements and first-principles band calculations. The system was found to be
well described by novel effective total angular momentum Jeff states, in which
relativistic spin-orbit (SO) coupling is fully taken into account under a large
crystal field. Despite of delocalized Ir 5d states, the Jeff-states form so
narrow bands that even a small correlation energy leads to the Jeff = 1/2 Mott
ground state with unique electronic and magnetic behaviors, suggesting a new
class of the Jeff quantum spin driven correlated-electron phenomena.


title: psi(2S) Radiative Decay Measurements

abstract:
  Using a sample of 14 million $\psip$ events collected with the BESII
detector, branching fractions or upper limits on the branching fractions of
$\psip$ decays into $\gamma\ppb$, $\gamma 2(\pip\pim)$, $\gamma \kskp$, $\gamma
\kap\kam\pip\pim$, $\gamma\kstarz\kam\pip+c.c.$, $\gamma \kstarz \kstarzb$,
$\gamma\pip\pim\ppb$, $\gamma2(\kap\kam)$, $\gamma3(\pip\pim)$ and
$\gamma2(\pip\pim)\kap\kam$ with hadron invariant mass less than 2.9$\gev/c^2$
are reported. We also report branching fractions of $\psip$ decays into
$\gamma\ppb\piz$, $\ppb\piz\piz$, $2(\pip\pim)\piz$, $\omega\pp$, $\omega
f_2(1270)$, $b_1^\pm\pi^\mp$, $\piz\kskp$, $K^\pm\rho^\mp\ks$,
$\piz2(\pip\pim)\kap\kam$ and $\gamma\piz2(\pip\pim)\kap\kam$.


title: Quasi-exactly solvable models based on special functions

abstract:
  We suggest a systematic method of extension of quasi-exactly solvable (QES)
systems. We construct finite-dimensional subspaces on the basis of special
functions (hypergeometric, Airy, Bessel ones) invariant with respect to the
action of differential operators of the second order with polynomial
coefficients. As a example of physical applications, we show that the known
two-photon Rabi Hamiltonian becomes quasi-exactly solvable at certain values of
parameters when it can be expressed in terms of corresponding QES operators
related to the hypergeometric function.


title:
Present Acceleration of Universe, Holographic Dark Energy and
  Brans-Dicke Theory

abstract:
  The present day accelerated expansion of the universe is naturally addressed
within the Brans-Dicke theory just by using holographic dark energy model with
inverse of Hubble scale as IR cutoff. It is also concluded that if the universe
continues to expand, then one day it might be completely filled with dark
energy.


title: Extensions of smoothing via taut strings

abstract:
  Suppose that we observe independent random pairs $(X_1,Y_1)$, $(X_2,Y_2)$,
>..., $(X_n,Y_n)$. Our goal is to estimate regression functions such as the
conditional mean or $\beta$--quantile of $Y$ given $X$, where $0<\beta <1$. In
order to achieve this we minimize criteria such as, for instance, $$
\sum_{i=1}^n \rho(f(X_i) - Y_i) + \lambda \cdot \mathop TV\nolimits (f) $$
among all candidate functions $f$. Here $\rho$ is some convex function
depending on the particular regression function we have in mind, $\mathop {\rm
TV}\nolimits (f)$ stands for the total variation of $f$, and $\lambda >0$ is
some tuning parameter. This framework is extended further to include binary or
Poisson regression, and to include localized total variation penalties. The
latter are needed to construct estimators adapting to inhomogeneous smoothness
of $f$. For the general framework we develop noniterative algorithms for the
solution of the minimization problems which are closely related to the taut
string algorithm (cf. Davies and Kovac, 2001). Further we establish a
connection between the present setting and monotone regression, extending
previous work by Mammen and van de Geer (1997). The algorithmic considerations
and numerical examples are complemented by two consistency results.


title: Singlet fermionic dark matter

abstract:
  We propose a renormalizable model of a fermionic dark matter by introducing a
gauge singlet Dirac fermion and a real singlet scalar. The bridges between the
singlet sector and the standard model sector are only the singlet scalar
interaction terms with the standard model Higgs field. The singlet fermion
couples to the standard model particles through the mixing between the standard
model Higgs and singlet scalar and is naturally a weakly interacting massive
particle (WIMP). The measured relic abundance can be explained by the singlet
fermionic dark matter as the WIMP within this model. Collider implication of
the singlet fermionic dark matter is also discussed. Predicted is the elastic
scattering cross section of the singlet fermion into target nuclei for a direct
detection of the dark matter. Search of the direct detection of the dark matter
provides severe constraints on the parameters of our model.


title: Critical power of collapsing vortices

abstract:
  We calculate the critical power for collapse of linearly-polarized phase
vortices, and show that this expression is more accurate than previous results.
Unlike the non-vortex case, deviations from radial symmetry do not increase the
critical power for collapse, but rather lead to disintegration into collapsing
non-vortex filaments. The cases of circular, radial and azimuthal polarizations
are also considered.


title: Stepup procedures controlling generalized FWER and generalized FDR

abstract:
  In many applications of multiple hypothesis testing where more than one false
rejection can be tolerated, procedures controlling error rates measuring at
least $k$ false rejections, instead of at least one, for some fixed $k\ge 1$
can potentially increase the ability of a procedure to detect false null
hypotheses. The $k$-FWER, a generalized version of the usual familywise error
rate (FWER), is such an error rate that has recently been introduced in the
literature and procedures controlling it have been proposed. A further
generalization of a result on the $k$-FWER is provided in this article. In
addition, an alternative and less conservative notion of error rate, the
$k$-FDR, is introduced in the same spirit as the $k$-FWER by generalizing the
usual false discovery rate (FDR). A $k$-FWER procedure is constructed given any
set of increasing constants by utilizing the $k$th order joint null
distributions of the $p$-values without assuming any specific form of
dependence among all the $p$-values. Procedures controlling the $k$-FDR are
also developed by using the $k$th order joint null distributions of the
$p$-values, first assuming that the sets of null and nonnull $p$-values are
mutually independent or they are jointly positively dependent in the sense of
being multivariate totally positive of order two (MTP$_2$) and then discarding
that assumption about the overall dependence among the $p$-values.


title: Orbital Dynamics Of A Possible Second Planet In HD 17156

abstract:
  In this letter we report the possible existence of a second planet in the
transiting extrasolar planet system HD 17156 and its interactive dynamics with
the previously known planet. The analysis is achieved through the \POFP\
optimization software which is based on a full integration of the system's
multiple-body Newtonian equations of motion. The two-planet solution yields a
significantly improved fit to the previously published radial velocities. The
two planets are strongly interacting and exchange angular momentum in a 5:1
mean motion resonance, yet remain stable as they mutually excite orbital
eccentricities and periastron advances.


title:
Exotic decay modes of the nucleon resonance $N^*(1535)$ and the
  $\theta^+$ problem

abstract:
  Baryon resonance state with strangeness $S = +1$ observed in systems $p K^0$
and $n K^+$ is interpreted as a result of the decay $N^{*+} \to p \eta$ of the
well-known resonance $N^*(1535)$ (with spin-parity $j^P = {1/2}^-$ and mass $m
\approx 1.54$ GeV) and the subsequent oscillation $\eta \rightleftarrows K^0$.
It is argued that the latter is noticeably enhanced by the neighbourhood of the
$\eta$ and $K^0$ levels and the gluon exchanges of the "penguin" form.


title:
Standoff Detection of Solid Traces by Single-Beam Nonlinear Raman
  Spectroscopy Using Shaped Femtosecond Pulses

abstract:
  We demonstrate a single-beam, standoff (>10m) coherent anti-Stokes Raman
scattering spectroscopy (CARS) of various materials, including trace amounts of
explosives and nitrate samples, under ambient light conditions. The multiplex
measurement of characteristic molecular vibrations with <20cm-1 spectral
resolution is carried out using a single broadband (>550cm-1) phase-shaped
femtosecond laser pulse. We exploit the strong nonresonant background signal
for amplification of the weak backscattered resonant CARS signal by using a
homodyne detection scheme. This facilitates a simple, highly sensitive
single-beam spectroscopic technique, with a potential for hazardous materials
standoff detection applications.


title:
Neutrino Mass Differences and Nonunitarity of Neutrino Mixing Matrix
  from Interfering Recoil Ions

abstract:
  We show that the recent observation of the time modulation of two-body weak
decays of heavy ions reveals the mass content of the electron neutrinos via
interference patterns in the recoiling ion wave function. From the modulation
period we derive the difference of the square masses $ \Delta m^2\approx
22.5\times 10^{-5}$ eV${}^2$, which is about 2.8 times larger than that derived
from a combined analysis of KamLAND and solar neutrino oscillation experiments.
It is, however, compatible with a data regime to which the KamLAND analysis
attributes a smaller probability.
  The experimental results imply that the neutrino mixing matrix violates
unitarity by about 10%.


title:
Strictly all-fiber picosecond Ytterbium fiber laser utilizing
  chirped-fiber-Bragg-gratings for dispersion control

abstract:
  A compact, strictly all-fiber, picosecond pulse source based on ytterbium
(Yb) doped fiber is described. Stable solitary mode-locking is obtained in a
fiber-oscillator utilizing a carefully designed chirped fiber-Bragg-grating
(C-FBG) for both dispersion control and spectral filtering. Self-starting is
assured through the use of a fiber-coupled
semiconductor-saturable-absorber-mirror (SESAM). The oscillator's 50MHz 3.8ps
pulse-train output at 1064nm wavelength is amplified to 1.2W average power by
an Yb doped fiber-amplifier, yielding 6.45ps parabolic pulses. Numerical
simulations of the fiber oscillator design based on the modified nonlinear
Schrodinger equation (NLSE), agree well with the experimental results.


title: Operator fidelity susceptibility: an indicator of quantum criticality

abstract:
  We introduce the operator fidelity and propose to use its susceptibility for
characterizing the sensitivity of quantum systems to perturbations. Two typical
models are addressed: one is the transverse Ising model exhibiting a quantum
phase transition, and the other is the one dimensional Heisenberg spin chain
with next-nearest-neighbor interactions, which has the degeneracy. It is
revealed that the operator fidelity susceptibility is a good indicator of
quantum criticality regardless of the system degeneracy.


title:
A non-commutative Sobolev estimate and its application to spectral
  synthesis

abstract:
  In [M. K. Vemuri, Realizations of the canonical representation], it was shown
that the spectral synthesis problem for the Alpha transform is closely related
to the problem of classifying realizations of the canonical representation (of
the Heisenberg group). In this paper, we show that discrete sets are sets of
spectral synthesis for the Alpha transform.


title: Thermal transistor: Heat flux switching and modulating

abstract:
  Thermal transistor is an efficient heat control device which can act as a
heat switch as well as a heat modulator. In this paper, we study systematically
one-dimensional and two-dimensional thermal transistors. In particular, we show
how to improve significantly the efficiency of the one-dimensional thermal
transistor. The study is also extended to the design of two-dimensional thermal
transistor by coupling different anharmonic lattices such as the
Frenkel-Kontorova and the Fermi-Pasta-Ulam lattices. Analogy between anharmonic
lattices and single-walled carbon nanotube is drawn and possible experimental
realization with multi-walled nanotube is suggested.


title:
High-energy cosmic ray fluxes in the Earth atmosphere: calculations vs
  experiments

abstract:
  A new calculation of the atmospheric fluxes of cosmic-ray hadrons and muons
in the energy range 10-10^5 GeV has been performed for the set of hadron
production models, EPOS 1.6, QGSJET II-03, SIBYLL 2.1, and others that are of
interest to cosmic ray physicists. The fluxes of secondary cosmic rays at
several levels in the atmosphere are computed using directly data of the
ATIC-2, GAMMA experiments, and the model proposed recently by Zatsepin and
Sokolskaya as well as the parameterization of the primary cosmic ray spectrum
by Gaisser and Honda. The calculated energy spectra of the hadrons and muon
flux as a function of zenith angle are compared with measurements as well as
other calculations. The effect of uncertainties both in the primary cosmic ray
flux and hadronic model predictions on the spectra of atmospheric hadrons and
muons is considered.


title: New theoretical approaches to black holes

abstract:
  Quite recently, some new mathematical approaches to black holes have appeared
in the literature. They do not rely on the classical concept of event horizon
-- which is very global, but on the local concept of hypersurfaces foliated by
trapped surfaces. After a brief introduction to these new horizons, we focus on
a viscous fluid analogy that can be developed to describe their dynamics, in a
fashion similar to the membrane paradigm introduced for event horizons in the
seventies, but with a significant change of sign of the bulk viscosity.


title: Entropy of Pairs of Dual Attractors in 6D/7D

abstract:
  We study the attractor mechanism of dual pairs of black brane bounds in N=2
supergravity in six and seven dimensions. First, we consider the effective
potentials of the 6D and 7D black branes as well as their entropies. The
contribution coming from the SO(1,1) factor of the moduli spaces M_{6D} and
M_{7D} of these theories is carefully analyzed and it is used to motivate the
study of the dual black branes bounds; which in turn allow to fix the critical
value of the dilaton at horizon. The attractor eqs of the black branes and the
bound pairs are derived by combining the criticality conditions of the
corresponding effective potentials and the Lagrange multiplier method capturing
constraints eqs on the fields moduli.


title:
Higher-dimensional charged black holes solutions with a nonlinear
  electrodynamics source

abstract:
  We obtain electrically charged black hole solutions of the Einstein equations
in arbitrary dimensions with a nonlinear electrodynamics source. The matter
source is deriving from a Lagrangian given by an arbitrary power of the Maxwell
invariant. The form of the general solution suggests a natural partition for
the different ranges of this power. For a particular range, we exhibit a class
of solutions whose behavior resemble to the standard Reissner-Nordstrom black
holes. There also exists a range for which the black hole solutions approach
asymptotically the Minkowski spacetime slower than the Schwarzschild spacetime.
We have also found a family of not asymptotically flat black hole solutions
with an asymptotic behavior growing slower than the Schwarzschild (anti) de
Sitter spacetime. In odd dimensions, there exists a critical value of the
exponent for which the metric involves a logarithmic dependence. This critical
value corresponds to the transition between the standard behavior and the
solution decaying to Minkowski slower than the Schwarzschild spacetime.


title:
Spreading of correlations and entanglement after a quench in the
  one-dimensional Bose-Hubbard model

abstract:
  We investigate the spreading of information in a one-dimensional Bose-Hubbard
system after a sudden parameter change. In particular, we study the
time-evolution of correlations and entanglement following a quench. The
investigated quantities show a light-cone like evolution, i.e. the spreading
with a finite velocity. We discuss the relation of this veloctiy to other
characteristic velocities of the system, like the sound velocity. The
entanglement is investigated using two different measures, the von-Neuman
entropy and mutual information. Whereas the von-Neumann entropy grows rapidly
with time the mutual information between two small subsystems can as well
decrease after an initial increase. Additionally we show that the static von
Neuman entropy characterises the location of the quantum phase transition.


title: Low-temperature specific heat of the superconductor Mo3Sb7

abstract:
  The low-temperature specific heat of a superconductor Mo3Sb7 with T_c = 2.25
(0.05) K has been measured in magnetic fields up to 5 T. In the normal state,
the electronic specific heat coefficient gamma_n, and the Debye temperature
Theta_D are found to be 34.5(2) mJ/molK^2 and 283(5) K, respectively. The
enhanced gamma_n value is interpreted due to a narrow Mo-4d band pinned at the
Fermi level. The electronic specific heat in the superconducting state can be
analyzed in terms a phenomenological two BCS-like gap model with the gap widths
2Delta_1/k_BT_c = 4.0 and 2Delta_2/k_BT_c = 2.5, and relative weights of the
mole electronic heat coefficients gamma_1/gamma_n = 0.7 and gamma_2/gamma_n =
0.3. Some characteristic thermodynamic parameters for the studied
superconductor, like the specific heat jump at T_c, DeltaC_p(T_c)/gamma_nT_c,
the electron-phonon coupling constant,lambda_eph, the upper H_c2 and
thermodynamic critical H_c0 fields, the penetration depth, lambda, coherence
length xi, and the Ginzburg-Landau parameter kappa are evaluated. The estimated
values of parameters like 2Delta/k_BT_c, DeltaC_p(T_c)/gamma_nT_c, N(E_F), and
lambda_eph suggest that Mo3Sb7 belongs to intermediate-coupling regime. The
electronic band structure calculations indicate that the density of states near
the Fermi level is formed mainly by the Mo-4d orbitals and there is no
overlapping between the Mo- 4d and Sb-sp orbitals.


title: Density oscillations in a model of water and other similar liquids

abstract:
  It is suggested that the dynamics of liquid water has a component consisting
of O^{-2z} (oxygen) anions and H^{+z} (hydrogen) cations, where z is a (small)
reduced effective electron charge. Such a model may apply to other similar
liquids. The eigenmodes of density oscillations are derived for such a
two-species ionic plasma, included the sound waves, and the dielectric function
is calculated. The plasmons may contribute to the elementary excitations in a
model introduced recently for the thermodynamics of liquids. It is shown that
the sound anomaly in water can be understood on the basis of this model. The
results are generalized to an asymmetric short-range interaction between the
ionic species as well as to a multi-component plasma, and the structure factor
is calculated.


title: Density oscillations in multi-component molecular mixtures

abstract:
  The excitation spectrum of the density collective oscillations is computed
for multi-component molecular mixtures both with Coulomb and (repulsive)
short-range interactions. Distinct sound-like excitations appear, governed by
the short-range interaction, which differ from the ordinary hydrodynamic sound.
The dielectric function and the structure factor are also calculated. The
"two-sounds phenomenon" can be understood by means of the predictions of this
model.


title:
Quantum spin pumping at fractionally quantized magnetization state for a
  system with competing exchange interactions

abstract:
  We study the quantum spin pumping of an antiferromagnetic spin-1/2 chain with
competing exchange interactions. We show that spatially periodic potential
modulated in space and time acts as a quantum spin pump. In our model system,
an applied electric field causes a spin gap to its critical ground state by
introducing bond-alternation exchange interactions. We study quantum spin
pumping at different quantized magnetization states and also explain physically
the presence and absence of quantum spin pumping at different fractionally
quantized magnetization states.


title:
Cancellation of simple optical anisotropies without use of a Faraday
  mirror

abstract:
  We first derive the round-trip Jones matrix for double passage through a
reciprocal optical medium by means of reflection off a plane mirror that could
be optically anisotropic. We then show that if a medium with only linear
birefringence and linear dichroism is placed between a pair of orthogonal
quarterwave plates with principal axes at 45 deg to that of the medium and the
sandwich is placed in front of an isotropic mirror it behaves, under double
passage, like an isotropic medium. We describe a simple liquid crystal device
that behaves, in reflection, as an isotropic medium whose refractive index can
be varied by application of an electric field, thus acting as a phase only
modulator for light in any polarization state.


title: Structure Constant of the Yang-Lee Edge Singularity

abstract:
  This paper studies the Yang-Lee singularity of the 2-dimensional Ising model
on the cylinder via transfer matrix and finite-size scaling techniques. These
techniques enable a measurement of the 2-point and 3-point correlations and a
comparison of a measurement of a corresponding universal amplitude with a
prediction for the amplitude from the (A4,A1) minimal conformal field theory.


title: Entanglement Monogamy of Tripartite Quantum States

abstract:
  An interesting monogamy equation with the form of Pythagorean theorem is
found for $2\otimes 2\otimes n$-dimensional pure states, which reveals the
relation among bipartite concurrence, concurrence of assistance, and genuine
tripartite entanglement. At the same time, a genuine tripartite entanglement
monotone as a generalization of 3-tangle is naturally obtained for $(2\otimes
2\otimes n)$- dimensional pure states in terms of a distinct idea. For mixed
states, the monogamy equation is reduced to a monogamy inequality. Both results
for tripartite quantum states can be employed to multipartite quantum states.


title: Locked constraint satisfaction problems

abstract:
  We introduce and study the random "locked" constraint satisfaction problems.
When increasing the density of constraints, they display a broad "clustered"
phase in which the space of solutions is divided into many isolated points.
While the phase diagram can be found easily, these problems, in their clustered
phase, are extremely hard from the algorithmic point of view: the best known
algorithms all fail to find solutions. We thus propose new benchmarks of really
hard optimization problems and provide insight into the origin of their typical
hardness.


title: A note on the determination of light quark masses

abstract:
  We provide a model-independent determination of the quantity B_0(m_d-m_u).
Our approach rests only on chiral symmetry and data from the decay of the eta
into three neutral pions. Since the low-energy prediction at next-to-leading
order fails to reproduce the experimental results, we keep the strong
interaction correction as an unknown parameter. As a first step, we relate this
parameter to the quark mass difference using data from the Dalitz plot. A
similar relation is obtained using data from the decay width. Combining both
relations we obtain B_0(m_d-m_u)=(4495+/-440) MeV^2. The preceding value,
combined with lattice determinations, leads to the values m_u(2
GeV)=(2.9+/-0.8) MeV and m_d(2 GeV)=(4.7+/-0.8) MeV.


title:
Enhanced Direct and Indirect Genetic Algorithm Approaches for a Mall
  Layout and Tenant Selection Problem

abstract:
  During our earlier research, it was recognised that in order to be successful
with an indirect genetic algorithm approach using a decoder, the decoder has to
strike a balance between being an optimiser in its own right and finding
feasible solutions. Previously this balance was achieved manually. Here we
extend this by presenting an automated approach where the genetic algorithm
itself, simultaneously to solving the problem, sets weights to balance the
components out. Subsequently we were able to solve a complex and non-linear
scheduling problem better than with a standard direct genetic algorithm
implementation.


title: Generalizations of Popoviciu's inequality

abstract:
  We establish a general criterion for the validity of inequalities of the
following form: A certain convex combination of the values of a convex function
at n points and of its value at a weighted mean of these n points is always
greater or equal to a convex combination of the values of the function at some
other weighted means of these points. Here, the left hand side contains only
one weighted mean, while the right hand side may contain as many as possible,
as long as there are finitely many. The weighted mean on the left hand side
must have positive weights, while those on the right hand side must have
nonnegative weights.
  The most prominent example of such kind of inequalities, Popoviciu's
inequality in its most general form, follows from the general criterion. As
another application, a result by Vasile Cirtoaje is sharpened.


title:
Width of the analyticity strip in space variable of viscous Burgers
  shockwaves

abstract:
  Analytic continuation of viscous shock solution for the generalized Burgers
equation with polynomial nonlinear source term is investigated. We show that a
pertubated wave recovers its analyticity in the space variable in the strip
limited by the first pair of singularities of the wave.


title:
Addendum to: A simultaneous Frobenius splitting for closures of
  conjugacy classes of nilpotent matrices, by V. B. Mehta and Wilberd van der
  Kallen

abstract:
  Prompted by an exercise in the Brion Kumar book on Frobenius splittings, we
show compatibility with a few more subvarieties of the Frobenius splitting from
our 1992 paper.


title: On the genus of a cyclic plane curve over a finite field

abstract:
  Cyclic curves, i.e. curves fixed by a cyclic collineation group, play a
central role in the investigation of cyclic arcs in Desarguesian projective
planes. In this paper, the genus of a cyclic curve arising from a cyclic k-arc
of Singer type is computed.


title:
Phenomenology of the General NMSSM with Gauge Mediated Supersymmetry
  Breaking

abstract:
  We investigate various classes of Gauge Mediated Supersymmetry Breaking
models and show that the Next-to-Minimal Supersymmetric Standard Model can
solve the mu-problem in a phenomenologically acceptable way. These models
include scenarios with singlet tadpole terms, which are phenomenologically
viable, e.g., in the presence of a small Yukawa coupling <~ 10^{-5}. Scenarios
with suppressed trilinear A-terms at the messenger scale lead naturally to
light CP-odd scalars, which play the r\^ole of pseudo R-axions. A wide range of
parameters of such models satisfies LEP constraints, with CP-even Higgs scalars
below 114 GeV decaying dominantly into a pair of CP-odd scalars.


title: Consistency of cross validation for comparing regression procedures

abstract:
  Theoretical developments on cross validation (CV) have mainly focused on
selecting one among a list of finite-dimensional models (e.g., subset or order
selection in linear regression) or selecting a smoothing parameter (e.g.,
bandwidth for kernel smoothing). However, little is known about consistency of
cross validation when applied to compare between parametric and nonparametric
methods or within nonparametric methods. We show that under some conditions,
with an appropriate choice of data splitting ratio, cross validation is
consistent in the sense of selecting the better procedure with probability
approaching 1. Our results reveal interesting behavior of cross validation.
When comparing two models (procedures) converging at the same nonparametric
rate, in contrast to the parametric case, it turns out that the proportion of
data used for evaluation in CV does not need to be dominating in size.
Furthermore, it can even be of a smaller order than the proportion for
estimation while not affecting the consistency property.


title: Multiferroicity due to charge ordering

abstract:
  In this contribution to the special issue on multiferroics we focus on
multiferroicity driven by different forms of charge ordering. We will present
the generic mechanisms by which charge ordering can induce ferroelectricity in
magnetic systems. There is a number of specific classes of materials for which
this is relevant. We will discuss in some detail $(i)$ perovskite manganites of
the type (PrCa)MnO$_3$, $(ii)$ the complex and interesting situation in
magnetite Fe$_3$O$_4$, $(iii)$ strongly ferroelectric frustrated LuFe$_2$O$_4$,
$(iv)$ an example of a quasi one-dimensional organic system. All these are
"type-I" multiferroics, in which ferroelectricity and magnetism have different
origin and occur at different temperatures. In the second part of this article
we discuss "type-II" multiferroics, in which ferroelectricity is completely
{\it due to} magnetism, but with charge ordering playing important role, such
as $(v)$ the newly-discovered multiferroic Ca$_3$CoMnO$_6$, $(vi)$ possible
ferroelectricity in rare earth perovskite nickelates of the type RNiO$_3$,
$(vii)$ multiferroic properties of manganites of the type RMn$_2$O$_5$,
$(viii)$ of perovskite manganites with magnetic E-type ordering and $(ix)$ of
bilayer manganites.


title: An Indirect Genetic Algorithm for Set Covering Problems

abstract:
  This paper presents a new type of genetic algorithm for the set covering
problem. It differs from previous evolutionary approaches first because it is
an indirect algorithm, i.e. the actual solutions are found by an external
decoder function. The genetic algorithm itself provides this decoder with
permutations of the solution variables and other parameters. Second, it will be
shown that results can be further improved by adding another indirect
optimisation layer. The decoder will not directly seek out low cost solutions
but instead aims for good exploitable solutions. These are then post optimised
by another hill-climbing algorithm. Although seemingly more complicated, we
will show that this three-stage approach has advantages in terms of solution
quality, speed and adaptability to new types of problems over more direct
approaches. Extensive computational results are presented and compared to the
latest evolutionary and other heuristic approaches to the same data instances.


title:
On the Application of Hierarchical Coevolutionary Genetic Algorithms:
  Recombination and Evaluation Partners

abstract:
  This paper examines the use of a hierarchical coevolutionary genetic
algorithm under different partnering strategies. Cascading clusters of
sub-populations are built from the bottom up, with higher-level sub-populations
optimising larger parts of the problem. Hence higher-level sub-populations
potentially search a larger search space with a lower resolution whilst
lower-level sub-populations search a smaller search space with a higher
resolution. The effects of different partner selection schemes amongst the
sub-populations on solution quality are examined for two constrained
optimisation problems. We examine a number of recombination partnering
strategies in the construction of higher-level individuals and a number of
related schemes for evaluating sub-solutions. It is shown that partnering
strategies that exploit problem-specific knowledge are superior and can counter
inappropriate (sub)fitness measurements.


title: Building Better Nurse Scheduling Algorithms

abstract:
  The aim of this research is twofold: Firstly, to model and solve a complex
nurse scheduling problem with an integer programming formulation and
evolutionary algorithms. Secondly, to detail a novel statistical method of
comparing and hence building better scheduling algorithms by identifying
successful algorithm modifications. The comparison method captures the results
of algorithms in a single figure that can then be compared using traditional
statistical techniques. Thus, the proposed method of comparing algorithms is an
objective procedure designed to assist in the process of improving an
algorithm. This is achieved even when some results are non-numeric or missing
due to infeasibility. The final algorithm outperforms all previous evolutionary
algorithms, which relied on human expertise for modification.


title:
Some features of the statistical complexity, Fisher-Shannon information,
  and Bohr-like orbits in the Quantum Isotropic Harmonic Oscillator

abstract:
  The Fisher-Shannon information and a statistical measure of complexity are
calculated in the position and momentum spaces for the wave functions of the
quantum isotropic harmonic oscillator. We show that these magnitudes are
independent of the strength of the harmonic potential. Moreover, for each level
of energy, it is found that these two indicators take their minimum values on
the orbitals that correspond to the classical (circular) orbits in the
Bohr-like quantum image, just those with the highest orbital angular momentum.


title: An Indirect Genetic Algorithm for a Nurse Scheduling Problem

abstract:
  This paper describes a Genetic Algorithms approach to a manpower-scheduling
problem arising at a major UK hospital. Although Genetic Algorithms have been
successfully used for similar problems in the past, they always had to overcome
the limitations of the classical Genetic Algorithms paradigm in handling the
conflict between objectives and constraints. The approach taken here is to use
an indirect coding based on permutations of the nurses, and a heuristic decoder
that builds schedules from these permutations. Computational experiments based
on 52 weeks of live data are used to evaluate three different decoders with
varying levels of intelligence, and four well-known crossover operators.
Results are further enhanced by introducing a hybrid crossover operator and by
making use of simple bounds to reduce the size of the solution space. The
results reveal that the proposed algorithm is able to find high quality
solutions and is both faster and more flexible than a recently published Tabu
Search approach.


title: A Recommender System based on Idiotypic Artificial Immune Networks

abstract:
  The immune system is a complex biological system with a highly distributed,
adaptive and self-organising nature. This paper presents an Artificial Immune
System (AIS) that exploits some of these characteristics and is applied to the
task of film recommendation by Collaborative Filtering (CF). Natural evolution
and in particular the immune system have not been designed for classical
optimisation. However, for this problem, we are not interested in finding a
single optimum. Rather we intend to identify a sub-set of good matches on which
recommendations can be based. It is our hypothesis that an AIS built on two
central aspects of the biological immune system will be an ideal candidate to
achieve this: Antigen-antibody interaction for matching and idiotypic
antibody-antibody interaction for diversity. Computational results are
presented in support of this conjecture and compared to those found by other CF
techniques.


title: Transport in a Dissipative Luttinger Liquid

abstract:
  We study theoretically the transport through a single impurity in a
one-channel Luttinger liquid coupled to a dissipative (ohmic) bath . For
non-zero dissipation $\eta$ the weak link is always a relevant perturbation
which suppresses transport strongly. At zero temperature the current voltage
relation of the link is $I\sim \exp(-E_0/eV)$ where $E_0\sim\eta/\kappa$ and
$\kappa$ denotes the compressibility. At non-zero temperature $T$ the linear
conductance is proportional to $\exp(-\sqrt{{\cal C}E_0/k_BT})$. The decay of
Friedel oscillation saturates for distance larger than $L_{\eta}\sim 1/\eta $
from the impurity.


title: Reaction e^+e^-\to\pi^+\pi^-\pi^+\pi^- at energies \sqrt{s}\leq 1 GeV

abstract:
  The cross section of reaction e^+e^-\to\pi^+\pi^-\pi^+\pi^- is calculated for
energies 0.65\leq \sqrt{s}\leq1 GeV in the framework of the generalized hidden
local symmetry model. The calculations are compared with the data of CMD-2 and
BaBaR. It is shown that the inclusion of heavy isovector resonances \rho(1450)
and \rho(1700) is necessary for reconciling calculations with the data. It is
found that at \sqrt{s}\approx1 GeV the contributions of above resonances are
much larger, by the factor of 30, than the \rho(770) one, and are amount to a
considerable fraction \sim0.3-0.6 of the latter at \sqrt{s}\sim m_\rho.