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0704.0401 | Modelling the Near-IR Spectra of Red Supergiant-dominated Populations | We report on recent progress in the modelling of the near-IR spectra of young
stellar populations, i.e. populations in which red supergiants (RSGs) are
dominant. First, we discuss the determination of fundamental parameters of RSGs
using fits to their near-IR spectra with new PHOENIX model spectra;
RSG-specific surface abundances are accounted for and effects of the
microturbulence parameter are explored. New population synthesis predictions
are then described and, as an example, it is shown that the spectra of young
star clusters in M82 can be reproduced very well from 0.5 to 2.4 micrometers.
We warn of remaining uncertainties in cluster ages.
| astro-ph |
0704.0402 | Locating the peaks of least-energy solutions to a quasilinear elliptic
Neumann problem | In this paper we study the shape of least-energy solutions to a singularly
perturbed quasilinear problem with homogeneous Neumann boundary condition. We
use an intrinsic variation method to show that at limit, the global maximum
point of least-energy solutions goes to a point on the boundary faster than the
linear rate and this point on the boundary approaches to a point where the mean
curvature of the boundary achieves its maximum. We also give a complete proof
of exponential decay of least-energy solutions.
| math.AP |
0704.0403 | Review: Semiconductor Quantum Light Sources | Lasers and LEDs display a statistical distribution in the number of photons
emitted in a given time interval. New applications exploiting the quantum
properties of light require sources for which either individual photons, or
pairs, are generated in a regulated stream. Here we review recent research on
single-photon sources based on the emission of a single semiconductor quantum
dot. In just a few years remarkable progress has been made in generating
indistinguishable single-photons and entangled photon pairs using such
structures. It suggests it may be possible to realise compact, robust, LED-like
semiconductor devices for quantum light generation.
| quant-ph |
0704.0404 | To the origin of the difference of FSI phases in $B\to\pi\pi$ and
$B\to\rho\rho$ decays | The final state interactions (FSI) model in which soft rescattering of low
mass intermediate states dominates is suggested. It explains why the strong
interaction phases are large in the $B_d\to\pi\pi$ channel and are considerably
smaller in the $B_d\to\rho\rho$ one. Direct CP asymmetries of $B_d\to\pi\pi$
decays which are determined by FSI phases are considered as well.
| hep-ph hep-ex |
0704.0405 | An invariance principle for semimartingale reflecting Brownian motions
in domains with piecewise smooth boundaries | Semimartingale reflecting Brownian motions (SRBMs) living in the closures of
domains with piecewise smooth boundaries are of interest in applied probability
because of their role as heavy traffic approximations for some stochastic
networks. In this paper, assuming certain conditions on the domains and
directions of reflection, a perturbation result, or invariance principle, for
SRBMs is proved. This provides sufficient conditions for a process that
satisfies the definition of an SRBM, except for small random perturbations in
the defining conditions, to be close in distribution to an SRBM. A crucial
ingredient in the proof of this result is an oscillation inequality for
solutions of a perturbed Skorokhod problem. We use the invariance principle to
show weak existence of SRBMs under mild conditions. We also use the invariance
principle, in conjunction with known uniqueness results for SRBMs, to give some
sufficient conditions for validating approximations involving (i) SRBMs in
convex polyhedrons with a constant reflection vector field on each face of the
polyhedron, and (ii) SRBMs in bounded domains with piecewise smooth boundaries
and possibly nonconstant reflection vector fields on the boundary surfaces.
| math.PR |
0704.0406 | Finite Drude weight for 1D low temperature conductors | We apply well established finite temperature Quantum Monte Carlo techniques
to one dimensional Bose systems with soft and hardcore constraint, as well as
to spinless fermion systems. We give clear and robust numerical evidence that,
as expected, no superfluid density for Bosons or Meissner fraction for
fermions. is possible at {\em any} non zero temperature in one dimensional
interacting Bose or fermi lattice models, whereas a finite Drude weight is
generally observed in gapless systems, in partial disagreement to previous
expectations.
| cond-mat.str-el cond-mat.supr-con |
0704.0407 | Density dependent hadronic models and the relation between neutron stars
and neutron skin thickness | In the present work we investigate the main differences in the lead neutron
skin thickness, binding energy, surface energy and density profiles obtained
with two different density dependent relativistic hadronic models, within the
Thomas-Fermi approximation. We show that the asymmetry parameter for low
momentum transfer polarized electron scattering is not sensitive to the model
parametrization differences.
| nucl-th |
0704.0408 | Photoconductance of organic single-molecule contacts | We study the dc conductance of organic single-molecule contacts in the
presence of external electromagnetic radiation (photoconductance). In agreement
with previous predictions, we find that the radiation can lead to large
enhancements of the conductance of such contacts by bringing off-resonant
levels into resonance through photoassisted processes. In our analysis we make
use of the simplifying fact that, under certain assumptions, the
photoconductance can be expressed in terms of the transmission function in the
absence of the radiation. The conductance enhancement is demonstrated for
oligophenylene molecules between gold electrodes, whose electronic structure is
calculated based on density-functional theory. It is shown that the exponential
decay of the conductance with the length of the molecule can be replaced by a
length-independent value in the presence of radiation.
| cond-mat.mes-hall |
0704.0409 | On the over-barrier reflection in quantum mechanics with multiple
degrees of freedom | We present an analytic example of two dimensional quantum mechanical system,
where the exponential suppression of the probability of over-barrier reflection
changes non-monotonically with energy. The suppression is minimal at certain
"optimal" energies where reflection occurs with exponentially larger
probability than at other energies.
| quant-ph hep-th nlin.CD physics.atom-ph physics.chem-ph |
0704.0410 | Cyclotron Resonance study of the electron and hole velocity in graphene
monolayers | We report studies of cyclotron resonance in monolayer graphene. Cyclotron
resonance is detected using the photoconductive response of the sample for
several different Landau level occupancies. The experiments measure an electron
velocity at the K- (Dirac) point of $c_{K}^{*}$ = 1.093 x 10$^{6}$ ms$^{-1}$
and in addition detect a significant asymmetry between the electron and hole
bands, leading to a difference in the electron and hole velocities of 5% by
energies of 125 meV away from the Dirac point.
| cond-mat.mes-hall |
0704.0411 | Molecular circuits based on graphene nano-ribbon junctions | Graphene nano-ribbons junctions based electronic devices are proposed in this
Letter. Non-equilibrium Green function calculations show that nano-ribbon
junctions tailored from single layer graphene with different edge shape and
width can act as metal-semiconductor junctions and quantum dots can be
implemented. In virtue of the possibilities of patterning monolayer graphene
down to atomic precision, these structures, quite different from the previously
reported two-dimensional bulk graphene or carbon nanotube devices, are expected
to be used as the building blocks of the future nano-electronics.
| cond-mat.mes-hall cond-mat.mtrl-sci |
0704.0412 | Unit groups of integral finite group rings with no noncyclic abelian
finite subgroups | It is shown that in the units of augmentation one of an integral group ring
$\mathbb{Z} G$ of a finite group $G$, a noncyclic subgroup of order $p^{2}$,
for some odd prime $p$, exists only if such a subgroup exists in $G$. The
corresponding statement for $p=2$ holds by the Brauer--Suzuki theorem, as
recently observed by W. Kimmerle.
| math.RT math.RA |
0704.0413 | Exotic Hadron in Pole-dominated QCD Sum Rules | We study pentaquark $\Theta^{+} (I=0,J=1/2)$ in the QCD sum rules emphasizing
that we can not extract any properties of the pentaquark outside of the Borel
window. To find the appropriate Borel window, we prepare a favorable set up of
the correlators and carry out the operator product expansion up to dimension 15
within factorization hypothesis. Our procedures reduce the unwanted high energy
contaminations and enhance the low energy correlation. In the Borel window,
independent analyses for the chiral-even and odd sum rules give the consistent
values of the $\Theta^+$ mass, $1.68\pm0.22$ GeV, and the residue. The parity
is found to be {\it positive}.
| hep-ph |
0704.0414 | Leaky modes of a left-handed slab | Using complex plane analysis we show that left-handed slab may support either
leaky slab waves, which are backward because of negative refraction, or leaky
surface waves, which are backward or forward depending on the propagation
direction of the surface wave itself. Moreover, there is a general connection
between the reflection coefficient of the left-handed slab and the one of the
corresponding right-handed slab (with opposite permittivity and permeability)
so that leaky slab modes are excited for the same angle of incidence of the
impinging beam for both structures. Many negative giant lateral shifts can be
explained by the excitation of these leaky modes.
| physics.optics |
0704.0415 | Coulomb blockade of field emission from nanoscale conductors | Theoretical description of the field emission of electrons from nanoscale
objects weakly coupled to the cathode is presented. It is shown that the field-
emission current increases in a step-like fashion due to single-electron
charging which leads to abrupt changes of the effective electric field
responsible for the field emission. A detailed consideration of the
current-voltage characteristics is carried out for a nanocluster modelled by a
metallic spherical particle in the close vicinity of the cathode and for a
cylindrical silicon nanowire grown on the cathode surface.
| cond-mat.mes-hall |
0704.0416 | Origamis with non congruence Veech groups | As main result we show that for each g > 1 there is some translation surface
of genus g whose Veech group is a non congruence subgroup of SL(2,Z). We use
origamis/square-tiled surfaces to produce our examples. The article is divided
into two parts: In the first part we introduce translation surfaces, origamis,
Veech groups and Teichmueller curves and show for two origamis in genus 2 that
their Veech groups are non congruence groups; in the second part we provide a
technique that produces sequences of origamis whose Veech groups are
decreasing. This is used to prove the main result.
| math.GT math.AG |
0704.0417 | Thermodynamic Stability - A note on a footnote in Ruelle's book | Thermodynamic stable interaction pair potentials which are not of the form
``positive function + real continuous function of positive type'' are presented
in dimension one. Construction of such a potential in dimension two is
sketched. These constructions use only elementary calculations. The
mathematical background is discussed separately.
| math-ph math.MP |
0704.0418 | Entanglement entropy at infinite randomness fixed points in higher
dimensions | The entanglement entropy of the two-dimensional random transverse Ising model
is studied with a numerical implementation of the strong disorder
renormalization group. The asymptotic behavior of the entropy per surface area
diverges at, and only at, the quantum phase transition that is governed by an
infinite randomness fixed point. Here we identify a double-logarithmic
multiplicative correction to the area law for the entanglement entropy. This
contrasts with the pure area law valid at the infinite randomness fixed point
in the diluted transverse Ising model in higher dimensions.
| cond-mat.dis-nn quant-ph |
0704.0419 | Ultrasound attenuation of superfluid $^{3}$He in aerogel | We have performed longitudinal ultrasound (9.5 MHz) attenuation measurements
in the B-phase of superfluid $^3$He in 98% porosity aerogel down to the zero
temperature limit for a wide range of pressures at zero magnetic field. The
absolute attenuation was determined by direct transmission of sound pulses.
Compared to the bulk fluid, our results revealed a drastically different
behavior in attenuation, which is consistent with theoretical accounts with
gapless excitations and a collision drag effect.
| cond-mat.supr-con |
0704.0420 | The Hourglass - Consequences of Pure Hamiltonian Evolution of a
Radiating System | Hourglass is the name given here to a formal isolated quantum system that can
radiate. Starting from a time when it defines the system it represents clearly
and no radiation is present, it is given straightforward Hamiltonian evolution.
The question of what significance hourglasses have is raised, and this question
is proposed to be more consequential than the measurement problem.
| quant-ph |
0704.0421 | The Sigma-D Relation for Planetary Nebulae: Preliminary Analysis | An analysis of the relation between radio surface brightness and diameter,
so-called Sigma-D relation, for planetary nebulae (PNe) is presented: i) the
theoretical Sigma-D relation for the evolution of bremsstrahlung surface
brightness is derived; ii) contrary to the results obtained earlier for the
Galactic supernova remnant (SNR) samples, our results show that the updated
sample of Galactic PNe does not severely suffer from volume selection effect -
Malmquist bias (same as for the extragalactic SNR samples) and; iii) we
conclude that the empirical Sigma-D relation for PNe derived in this paper is
not useful for valid determination of distances for all observed PNe with
unknown distances.
| astro-ph |
0704.0422 | Polarization conversion in a silica microsphere | We experimentally demonstrate controlled polarization-selective phenomena in
a whispering gallery mode resonator. We observed efficient ($\approx 75 %$)
polarization conversion of light in a silica microsphere coupled to a tapered
optical fiber with proper optimization of the polarization of the propagating
light. A simple model treating the microsphere as a ring resonator provides a
good fit to the observed behavior.
| physics.optics |
0704.0423 | Limits on WIMP-nucleon interactions with CsI(Tl) crystal detectors | The Korea Invisible Mass Search(KIMS) experiment presents new limits on
WIMP-nucleon cross section using the data from an exposure of 3409 kgd taken
with low background CsI(Tl) crystals at Yangyang underground laboratory. The
most stringent limit on the spin dependent interaction for pure proton case is
obtained. The DAMA signal region for both spin independent and spin dependent
interactions for the WIMP mass higher than 20 GeV/c^2are excluded by the single
experiment with crystal scintillators.
| astro-ph |
0704.0424 | Stopping effects in U+U collisions with a beam energy of 520 MeV/nucleon | A Relativistic Transport Model (ART1.0) is applied to simulate the stopping
effects in tip-tip and body-body U+U collisions, at a beam kinetic energy of
520 MeV/nucleon. Our simulation results have demonstrated that both central
collisions of the two extreme orientations can achieve full stopping, and also
form a bulk of hot, dense nuclear matter with a sufficiently large volume and
long duration, due to the largely deformed uranium nuclei. The nucleon sideward
flow in the tip-tip collisions is nearly 3 times larger than that in body-body
ones at normalized impact parameter $b/b_{max}<0.5$, and that the body-body
central collisions have a largest negative nucleon elliptic flow $v_{2}=-12%$
in contrast to zero in tip-tip ones. Thus the extreme circumstance and the
novel experimental observables in tip-tip and body-body collisions can provide
a good condition and sensitive probe to study the nuclear EoS, respectively.
The Cooling Storage Ring (CSR) External Target Facility (ETF) to be built at
Lanzhou, China, delivering the uranium beam up to 520 MeV/nucleon is expected
to make significant contribution to explore the nuclear equation of state
(EoS).
| nucl-ex |
0704.0425 | QED for fields obeying a square root operator equation | Instead of using local field equations - like the Dirac equation for spin-1/2
and the Klein-Gordon equation for spin-0 particles - one could try to use
non-local field equations in order to describe scattering processes. The latter
equations can be obtained by means of the relativistic energy together with the
correspondence principle, resulting in equations with a square root operator.
By coupling them to an electromagnetic field and expanding the square root (and
taking into account terms of quadratic order in the electromagnetic coupling
constant e), it is possible to calculate scattering matrix elements within the
framework of quantum electrodynamics, e.g. like those for Compton scattering or
for the scattering of two identical particles. This will be done here for the
scalar case. These results are then compared with the corresponding ones based
on the Klein-Gordon equation. A proposal of how to transfer these reflections
to the spin-1/2 case is also presented.
| hep-th |
0704.0426 | Feedback from first radiation sources: H- photodissociation | During the epoch of reionization, the formation of radiation sources is
accompanied by the growth of a H- photodissociating flux. We estimate the
impact of this flux on the formation of molecular hydrogen and cooling in the
first galaxies, assuming different types of radiation sources (e.g. Pop II and
Pop III stars, miniquasars). We find that H- photodissociation reduces the
formation of H2 molecules by a factor of ~1+1000k_s*x/(f_esc*delta), where x is
the mean ionized fraction in the IGM, f_esc is the fraction of ionizing photons
that escape from their progenitor halos, delta is the local gas overdensity and
k_s is an order unity constant which depends on the type of radiation source.
By the time a significant fraction of the universe becomes ionized, H-
photodissociation may significantly reduce the H2 abundance and, with it, the
primordial star formation rate, delaying the progress of reionization.
| astro-ph |
0704.0427 | The 3D +-J Ising model at the ferromagnetic transition line | We study the critical behavior of the three-dimensional $\pm J$ Ising model
[with a random-exchange probability $P(J_{xy}) = p \delta(J_{xy} - J) + (1-p)
\delta(J_{xy} + J)$] at the transition line between the paramagnetic and
ferromagnetic phase, which extends from $p=1$ to a multicritical (Nishimori)
point at $p=p_N\approx 0.767$. By a finite-size scaling analysis of Monte Carlo
simulations at various values of $p$ in the region $p_N<p<1$, we provide strong
numerical evidence that the critical behavior along the ferromagnetic
transition line belongs to the same universality class as the three-dimensional
randomly-dilute Ising model. We obtain the results $\nu=0.682(3)$ and
$\eta=0.036(2)$ for the critical exponents, which are consistent with the
estimates $\nu=0.683(2)$ and $\eta=0.036(1)$ at the transition of
randomly-dilute Ising models.
| cond-mat.dis-nn cond-mat.stat-mech |
0704.0428 | Star Formation in the Bok Globule CB54 | We present mid-infrared (10.4 \micron, 11.7 \micron, and 18.3 \micron)
imaging intended to locate and characterize the suspected protostellar
components within the Bok globule CB54. We detect and confirm the protostellar
status for the near-infrared source CB54YC1-II. The mid-infrared luminosity for
CB54YC1-II was found to be $L_{midir} \approx 8 L_\sun$, and we estimate a
central source mass of $M_* \approx 0.8 M_\sun$ (for a mass accretion rate of
${\dot M}=10^{-6} M_\sun yr^{-1}$). CB54 harbors another near-infrared source
(CB54YC1-I), which was not detected by our observations. The non-detection is
consistent with CB54YC1-I being a highly extinguished embedded young A or B
star or a background G or F giant. An alternative explanation for CB54YC1-I is
that the source is an embedded protostar viewed at an extremely high
inclination angle, and the near-infrared detections are not of the central
protostar, but of light scattered by the accretion disk into our line of sight.
In addition, we have discovered three new mid-infrared sources, which are
spatially coincident with the previously known dense core in CB54. The source
temperatures ($\sim100$K) and association of the mid-infrared sources with the
dense core suggests that these mid-infrared objects may be embedded class 0
protostars.
| astro-ph |
0704.0429 | Quantitative Resolution to some "Absolute Discrepancies" in Cancer
Theories: a View from Phage lambda Genetic Switch | Is it possible to understand cancer? Or more specifically, is it possible to
understand cancer from genetic side? There already many answers in literature.
The most optimistic one has claimed that it is mission-possible. Duesberg and
his colleagues reviewed the impressive amount of research results on cancer
accumulated over 100 years. It confirms the a general opinion that considering
all available experimental results and clinical observations there is no cancer
theory without major difficulties, including the prevailing gene-based cancer
theories. They have then listed 9 "absolute discrepancies" for such cancer
theory. In this letter the quantitative evidence against one of their major
reasons for dismissing mutation cancer theory, by both in vivo experiment and a
first principle computation, is explicitly pointed out.
| q-bio.SC q-bio.CB |
0704.0430 | Reduced phase space and toric variety coordinatizations of Delzant
spaces | In this note we describe the natural coordinatizations of a Delzant space
defined as a reduced phase space (symplectic geometry view-point) and give
explicit formulas for the coordinate transformations. For each fixed point of
the torus action on the Delzant polytope, we have a maximal coordinatization of
an open cell in the Delzant space which contains the fixed point. This cell is
equal to the domain of definition of one of the natural coordinatizations of
the Delzant space as a toric variety (complex algebraic geometry view-point),
and we give an explicit formula for the toric variety coordinates in terms of
the reduced phase space coordinates. We use considerations in the maximal
coordinate neighborhoods to give simple proofs of some of the basic facts about
the Delzant space, as a reduced phase space, and as a toric variety. These can
be viewed as a first application of the coordinatizations, and serve to make
the presentation more self-contained.
| math.SG math.AG |
0704.0431 | Fragmentation of general relativistic quasi-toroidal polytropes | We investigate the role of rotational instabilities in the context of black
hole formation in relativistic stars. In addition to the standard scenario - an
axially symmetric dynamical instability forming a horizon at the star's center
- the recently found low-$T/|W|$ instabilities are shown to lead to
fragmentation and off-center horizon formation in differentially rotating
stars. This process might be an alternative pathway to produce SMBHs from
supermassive stars with inefficient angular momentum transport.
| gr-qc astro-ph.HE |
0704.0432 | A Survey of Huebschmann and Stasheff's Paper: Formal Solution of the
Master Equation via HPT and Deformation Theory | These notes, based on the paper "Formal Solution of the Master Equation via
HPT and Deformation Theory" by Huebschmann and Stasheff, were prepared for a
series of talks at Illinois State University with the intention of applying
Homological Perturbation Theory to the derived bracket constructions of
Kosmann-Schwarzbach and T. Voronov, and eventually writing Part II of the paper
"Higher Derived Brackets and Deformation Theory I" by the present authors.
| math.QA |
0704.0433 | A variational formulation of electrodynamics with external sources | We present a variational formulation of electrodynamics using de Rham even
and odd differential forms. Our formulation relies on a variational principle
more complete than the Hamilton principle and thus leads to field equations
with external sources and permits the derivation of the constitutive relations.
We interpret a domain in space-time as an odd de Rham 4-current. This permits a
treatment of different types of boundary problems in an unified way. In
particular we obtain a smooth transition to the infinitesimal version by using
a current with a one point support.
| math-ph math.DG math.MP |
0704.0434 | Protein and ionic surfactants - promoters and inhibitors of contact line
pinning | We report a new effect of surfactants in pinning a drop contact line,
specifically that lysozyme promotes while lauryl sulfate inhibits pinning. We
explain the pinning disparity assuming difference in wetting: the protein-laden
drop wets a "clean" surface and the surfactant-laden drop wets an
auto-precursored surface.
| physics.chem-ph physics.flu-dyn |
0704.0435 | Type D Einstein spacetimes in higher dimensions | We show that all static spacetimes in higher dimensions are of Weyl types G,
I_i, D or O. This applies also to stationary spacetimes if additional
conditions are fulfilled, as for most known black hole/ring solutions. (The
conclusions change when the Killing generator becomes null, such as at Killing
horizons.) Next we demonstrate that the same Weyl types characterize warped
product spacetimes with a one-dimensional Lorentzian (timelike) factor, whereas
warped spacetimes with a two-dimensional Lorentzian factor are restricted to
the types D or O. By exploring the Bianchi identities, we then analyze the
simplest non-trivial case from the above classes - type D vacuum spacetimes,
possibly with a cosmological constant, dropping, however, the assumptions that
the spacetime is static, stationary or warped. It is shown that for ``generic''
type D vacuum spacetimes the corresponding principal null directions are
geodetic in any dimension (this applies also to type II spacetimes). For n>=5,
however, there may exist particular cases of type D spacetimes which admit
non-geodetic multiple principal null directions and we present such examples in
any n>=7. Further studies are restricted to five dimensions, where the type D
Weyl tensor is described by a 3x3 matrix \Phi_{ij}. In the case with
``twistfree'' (A_{ij}=0) principal null geodesics we show that in a ``generic''
case \Phi_{ij} is symmetric and eigenvectors of \Phi_{ij} coincide with those
of the expansion matrix S_{ij}, providing us with three preferred spacelike
directions of the spacetime. Similar results are also obtained when relaxing
the twistfree condition and assuming instead that \Phi_{ij} is symmetric. The
n=5 Myers-Perry black hole and Kerr-NUT-AdS metrics in arbitrary dimension are
briefly studied as specific examples of type D vacuum spacetime.
| gr-qc hep-th |
0704.0436 | Eigen Equation of the Nonlinear Spinor | How to effectively solve the eigen solutions of the nonlinear spinor field
equation coupling with some other interaction fields is important to understand
the behavior of the elementary particles. In this paper, we derive a simplified
form of the eigen equation of the nonlinear spinor, and then propose a scheme
to solve their numerical solutions. This simplified equation has elegant and
neat structure, which is more convenient for both theoretical analysis and
numerical computation.
| physics.gen-ph |
0704.0437 | Measurement of B(D_S^+ --> ell^+ nu) and the Decay Constant f_D_{S^+} | We examine e+e- --> Ds- Ds*+ and Ds*- Ds+ interactions at 4170 MeV using the
CLEO-c detector in order to measure the decay constant fDs+. We use the Ds+ -->
l+ nu channel, where the l+ designates either a mu+ or a tau+, when the tau+
--> pi+ nu. Analyzing both modes independently, we determine B(Ds+ --> mu+ nu)
= (0.594 +- 0.066 +- 0.031)%, and B(Ds+ --> tau+ nu) = (8.0 +- 1.3 +- 0.4)%. We
also analyze them simultaneously to find an effective value of B{eff}(Ds+ -->
mu+ nu) = (0.638 +- 0.059 +- 0.033)% and extract fDs = (274 +- 13 +- 7) MeV.
Combining with our previous determination of B(D+ -> mu+ nu), we also find the
ratio fDs/fD+ = 1.23 +- 0.11 +- 0.04. We compare to current theoretical
estimates. Finally, we find B(Ds+ --> e+ nu) < 1.3 x10^{-4} at 90% confidence
level.
| hep-ex hep-lat hep-ph |
0704.0438 | Broadening the Higgs Boson with Right-Handed Neutrinos and a Higher
Dimension Operator at the Electroweak Scale | The existence of certain TeV suppressed higher-dimension operators may open
up new decay channels for the Higgs boson to decay into lighter right-handed
neutrinos. These channels may dominate over all other channels if the Higgs
boson is light. For a Higgs boson mass larger than $2 m_W$ the new decays are
subdominant yet still of interest. The right-handed neutrinos have macroscopic
decay lengths and decay mostly into final states containing leptons and quarks.
A distinguishing collider signature of this scenario is a pair of displaced
vertices violating lepton number. A general operator analysis is performed
using the minimal flavor violation hypothesis to illustrate that these novel
decay processes can occur while remaining consistent with experimental
constraints on lepton number violating processes. In this context the question
of whether these new decay modes dominate is found to depend crucially on the
approximate flavor symmetries of the right-handed neutrinos.
| hep-ph |
0704.0439 | Coulomb blockade of anyons | Coulomb interaction turns anyonic quasiparticles of a primary quantum Hall
liquid with filling factor $\nu =1/(2m+1)$ into hard-core anyons. We have
developed a model of coherent transport of such quasiparticles in systems of
multiple antidots by extending the Wigner-Jordan description of 1D abelian
anyons to tunneling problems. We show that the anyonic exchange statistics
manifests itself in tunneling conductance even in the {\em absence} of
quasiparticle exchanges. In particular, it can be seen as a non-vanishing
resonant peak associated with quasiparticle tunneling through a line of three
antidots.
| cond-mat.mes-hall |
0704.0440 | Dynamics of a quantum phase transition in a ferromagnetic Bose-Einstein
condensate | We discuss dynamics of a slow quantum phase transition in a spin-1
Bose-Einstein condensate. We determine analytically the scaling properties of
the system magnetization and verify them with numerical simulations in a one
dimensional model.
| cond-mat.other hep-th quant-ph |
0704.0441 | Evidence for a planetary companion around a nearby young star | We report evidence for a planetary companion around the nearby young star HD
70573. The star is a G type dwarf located at a distance of 46 pc with age
estimation between 20 and 300 Myrs. We carried out spectroscopic observations
of this star with FEROS at the 2.2 m MPG/ESO telescope at La Silla. Our
spectroscopic analysis yields a spectral type of G1-1.5V and an age of about
100 Myrs. Variations in stellar radial velocity of HD 70573 have been monitored
since December 2003 until January 2007. The velocity accuracy of FEROS within
this period is about 10 m/s. HD 70573 shows a radial velocity variation with a
period of 852 +/- 12 days and a semi-amplitude of 149 +/- 6 m/s. The period of
this variation is significantly longer than its rotational period, which is 3.3
days. Based on the analysis of the Ca II K emission line, Halpha and Teff
variation as stellar activity indicators as well as the lack of a correlation
between the bisector velocity span and the radial velocity, we can exclude the
rotational modulation and non-radial pulsations as the source of the
long-period radial velocity variation. Thus, the presence of a low-mass
companion around the star provides the best explanation for the observed radial
velocity variation. Assuming a primary mass m1=1.0 +/- 0.1 Msun for the host
star, we calculated a minimum mass of the companion m2sini of 6.1 Mjup, which
lies in the planetary mass regime, and an orbital semi-major axis of 1.76 AU.
The orbit of the planet has an eccentricity of e=0.4. The planet discovery
around the young star HD 70573 gives an important input for the study of debris
disks around young stars and their relation to the presence of planets.
| astro-ph |
0704.0442 | Quantum electromagnetic X-waves | We show that two distinct quantum states of the electromagnetic field can be
associated to a classical vector X wave or a propagation-invariant solution of
Maxwell equations. The difference between the two states is of pure quantum
mechanical origin since they are internally entangled and disentangled,
respectively and can be generated by different linear or nonlinear processes.
Detection and generation of Schr\"odinger-cat states comprising two entangled
X-waves and their possible applications are discussed.
| physics.optics physics.gen-ph quant-ph |
0704.0443 | Neutron-neutron scattering length from the reaction gamma d --> pi^+ nn
employing chiral perturbation theory | We discuss the possibility to extract the neutron-neutron scattering length
a_{nn} from experimental spectra on the reaction gamma d --> pi^+ nn. The
transition operator is calculated to high accuracy from chiral perturbation
theory. We argue that for properly chosen kinematics, the theoretical
uncertainty of the method can be as low as 0.1 fm.
| nucl-th nucl-ex |
0704.0444 | Multiple Unfoldings of Orbifold Singularities: Engineering Geometric
Analogies to Unification | Katz and Vafa showed how charged matter can arise geometrically by the
deformation of ADE-type orbifold singularities in type IIa, M-theory, and
F-theory compactifications. In this paper we use those same basic ingredients,
used there to geometrically engineer specific matter representations, here to
deform the compactification manifold itself in a way which naturally
compliments many features of unified model building. We realize this idea
explicitly by deforming a manifold engineered to give rise to an $SU_5$ grand
unified model into a one giving rise to the Standard Model. In this framework,
the relative local positions of the singularities giving rise to Standard Model
fields are specified in terms of the values of a small number of complex
structure moduli which deform the original manifold, greatly reducing the
arbitrariness of their relative positions.
| hep-th |
0704.0445 | Geometrically Engineering the Standard Model: Locally Unfolding Three
Families out of E8 | This paper extends and builds upon the results of an earlier paper, in which
we described how to use the tools of geometrical engineering to deform
geometrically-engineered grand unified models into ones with lower symmetry.
This top-down unfolding has the advantage that the relative positions of
singularities giving rise to the many `low energy' matter fields are related by
only a few parameters which deform the geometry of the unified model. And
because the relative positions of singularities are necessary to compute the
superpotential, for example, this is a framework in which the arbitrariness of
geometrically engineered models can be greatly reduced.
In our earlier paper, this picture was made concrete for the case of
deforming the representations of an SU(5) model into their Standard Model
content. In this paper we continue that discussion to show how a geometrically
engineered 16 of SO(10) can be unfolded into the Standard Model, and how the
three families of the Standard Model uniquely emerge from the unfolding of a
single, isolated E8 singularity.
| hep-th |
0704.0446 | The classification of surfaces with p_g=q=1 isogenous to a product of
curves | A projective surface S is said to be isogenous to a product if there exist
two smooth curves C, F and a finite group G acting freely on C \times F so that
S=(C \times F)/G. In this paper we classify all surfaces with p_g=q=1 which are
isogenous to a product.
| math.AG math.GR |
0704.0447 | Manipulating the rotational properties of a two-component Bose gas | A rotating, two-component Bose-Einstein condensate is shown to exhibit
vortices of multiple quantization, which are possible due to the interatomic
interactions between the two species. Also, persistent currents are absent in
this system. Finally, the order parameter has a very simple structure for a
range of angular momenta.
| cond-mat.mes-hall |
0704.0448 | Giant Planet Migration in Viscous Power-Law Discs | Many extra-solar planets discovered over the past decade are gas giants in
tight orbits around their host stars. Due to the difficulties of forming these
`hot Jupiters' in situ, they are generally assumed to have migrated to their
present orbits through interactions with their nascent discs. In this paper, we
present a systematic study of giant planet migration in power law discs. We
find that the planetary migration rate is proportional to the disc surface
density. This is inconsistent with the assumption that the migration rate is
simply the viscous drift speed of the disc. However, this result can be
obtained by balancing the angular momentum of the planet with the viscous
torque in the disc. We have verified that this result is not affected by
adjusting the resolution of the grid, the smoothing length used, or the time at
which the planet is released to migrate.
| astro-ph |
0704.0449 | Worldsheet Instantons and Torsion Curves, Part B: Mirror Symmetry | We apply mirror symmetry to the problem of counting holomorphic rational
curves in a Calabi-Yau threefold X with Z_3 x Z_3 Wilson lines. As we found in
Part A [hep-th/0703182], the integral homology group H_2(X,Z)=Z^3 + Z_3 + Z_3
contains torsion curves. Using the B-model on the mirror of X as well as its
covering spaces, we compute the instanton numbers. We observe that X is
self-mirror even at the quantum level. Using the self-mirror property, we
derive the complete prepotential on X, going beyond the results of Part A. In
particular, this yields the first example where the instanton number depends on
the torsion part of its homology class. Another consequence is that the
threefold X provides a non-toric example for the conjectured exchange of
torsion subgroups in mirror manifolds.
| hep-th |
0704.0450 | Disorder screening near the Mott-Anderson transition | Correlation-driven screening of disorder is studied within the typical-medium
dynamical mean-field theory (TMT-DMFT) of the Mott-Anderson transition. In the
strongly correlated regime, the site energies epsilon_R^i characterizing the
effective disorder potential are strongly renormalized due to the phenomenon of
Kondo pinning. This effect produces very strong screening when the interaction
U is stronger then disorder W, but applies only to a fraction of the sites in
the opposite limit (U<W).
| cond-mat.str-el |
0704.0451 | Electromigrated nanoscale gaps for surface-enhanced Raman spectroscopy | Single-molecule detection with chemical specificity is a powerful and much
desired tool for biology, chemistry, physics, and sensing technologies.
Surface-enhanced spectroscopies enable single molecule studies, yet reliable
substrates of adequate sensitivity are in short supply. We present a simple,
scaleable substrate for surface-enhanced Raman spectroscopy (SERS)
incorporating nanometer-scale electromigrated gaps between extended electrodes.
Molecules in the nanogap active regions exhibit hallmarks of very high Raman
sensitivity, including blinking and spectral diffusion. Electrodynamic
simulations show plasmonic focusing, giving electromagnetic enhancements
approaching those needed for single-molecule SERS.
| cond-mat.mes-hall |
0704.0452 | Dramatic Variability of X-ray Absorption Lines in the Black Hole
Candidate Cygnus X-1 | We report results from a 30 ks observation of Cygnus X-1 with the High Energy
Transmission Grating Spectrometer (HETGS) on board the {\em Chandra X-ray
Observatory}. Numerous absorption lines were detected in the HETGS spectrum.
The lines are associated with highly ionized Ne, Na, Mg, Al, Si, S, and Fe,
some of which have been seen in earlier HETGS observations. Surprisingly,
however, we discovered dramatic variability of the lines over the duration of
the present observation. For instance, the flux of the Ne X line at 12.14 \AA\
was about $5 \times 10^{-3}$ photons cm$^{-2}$ s$^{-1}$ in the early part of
the observation but became subsequently undetectable, with a 99% upper limit of
$0.06 \times 10^{-3}$ photons cm$^{-2}$ s$^{-1}$ on the flux of the line. This
implies that the line weakened by nearly two orders of magnitude on a timescale
of hours. The overall X-ray flux of the source did also vary during the
observation but only by 20--30%. For Cyg X-1, the absorption lines are
generally attributed to the absorption of X-rays by ionized stellar wind in the
binary system. Therefore, they may provide valuable diagnostics on the physical
condition of the wind. We discuss the implications of the results.
| astro-ph |
0704.0453 | Antiferromagnetism-superconductivity competition in electron-doped
cuprates triggered by oxygen reduction | We have performed a systematic angle-resolved photoemission study of as-grown
and oxygen-reduced Pr$_{2-x}$Ce$_x$CuO$_4$ and Pr$_{1-x}$LaCe$_{x}$CuO$_4$
electron-doped cuprates. In contrast to the common belief, neither the band
filling nor the band parameters are significantly affected by the oxygen
reduction process. Instead, we show that the main electronic role of the
reduction process is to remove an anisotropic leading edge gap around the Fermi
surface. While the nodal leading edge gap is induced by long-range
antiferomagnetic order, the origin of the antinodal one remains unclear.
| cond-mat.supr-con cond-mat.str-el |
0704.0454 | An Extrasolar Planet Census with a Space-based Microlensing Survey | A space-based gravitational microlensing exoplanet survey will provide a
statistical census of exoplanets with masses down to 0.1 Earth-masses and
orbital separations ranging from 0.5AU to infinity. This includes analogs to
all the Solar System's planets except for Mercury, as well as most types of
planets predicted by planet formation theories. Such a survey will provide
results on the frequency of planets around all types of stars except those with
short lifetimes. Close-in planets with separations < 0.5 AU are invisible to a
space-based microlensing survey, but these can be found by Kepler. Other
methods, including ground-based microlensing, cannot approach the comprehensive
statistics on the mass and semi-major axis distribution of extrasolar planets
that a space-based microlensing survey will provide. The terrestrial planet
sensitivity of a ground-based microlensing survey is limited to the vicinity of
the Einstein radius at 2-3 AU, and space-based imaging is needed to identify
and determine the mass of the planetary host stars for the vast majority of
planets discovered by microlensing. Thus, a space-based microlensing survey is
likely to be the only way to gain a comprehensive understanding of the nature
of planetary systems, which is needed to understand planet formation and
habitability. The proposed Microlensing Planet Finder (MPF) mission is an
example of a space-based microlensing survey that can accomplish these
objectives with proven technology and a cost that fits comfortably under the
NASA Discovery Program cost cap.
| astro-ph |
0704.0455 | USco1606-1935: An Unusually Wide Low-Mass Triple System? | We present photometric, astrometric, and spectroscopic observations of
USco160611.9-193532 AB, a candidate ultrawide (~1600 AU), low-mass (M_tot~0.4
M_sun) multiple system in the nearby OB association Upper Scorpius. We conclude
that both components are young, comoving members of the association; we also
present high-resolution observations which show that the primary is itself a
close binary system. If the Aab and B components are gravitationally bound, the
system would fall into the small class of young multiple systems which have
unusually wide separations as compared to field systems of similar mass.
However, we demonstrate that physical association can not be assumed purely on
probabilistic grounds for any individual candidate system in this separation
range. Analysis of the association's two-point correlation function shows that
there is a significant probability (25%) that at least one pair of low-mass
association members will be separated in projection by <15", so analysis of the
wide binary population in Upper Sco will require a systematic search for all
wide systems; the detection of another such pair would represent an excess at
the 98% confidence level.
| astro-ph |
0704.0456 | Particle propagation in cosmological backgrounds | We study the quantum propagation of particles in cosmological backgrounds, by
considering a doublet of massive scalar fields propagating in an expanding
universe, possibly filled with radiation. We focus on the dissipative effects
related to the expansion rate. At first order, we recover the expected result
that the decay rate is determined by the local temperature. Beyond linear
order, the decay rate has an additional contribution governed by the expansion
parameter. This latter contribution is present even for stable particles in the
vacuum. Finally, we analyze the long time behaviour of the propagator and
briefly discuss applications to the trans-Planckian question.
| gr-qc |
0704.0457 | Quantum analysis of a linear DC SQUID mechanical displacement detector | We provide a quantum analysis of a DC SQUID mechanical displacement detector
within the sub-critical Josephson current regime. A segment of the SQUID loop
forms the mechanical resonator and motion of the latter is transduced
inductively through changes in the flux threading the loop. Expressions are
derived for the detector signal response and noise, which are used to evaluate
the position and force detection sensitivity. We also investigate cooling of
the mechanical resonator due to back reaction noise from the detector.
| cond-mat.supr-con cond-mat.mes-hall quant-ph |
0704.0458 | Rotation Measures of Extragalactic Sources Behind the Southern Galactic
Plane: New Insights into the Large-Scale Magnetic Field of the Inner Milky
Way | We present new Faraday rotation measures (RMs) for 148 extragalactic radio
sources behind the southern Galactic plane (253o < l < 356o, |b| < 1.5o), and
use these data in combination with published data to probe the large-scale
structure of the Milky Way's magnetic field. We show that the magnitudes of
these RMs oscillate with longitude in a manner that correlates with the
locations of the Galactic spiral arms. The observed pattern in RMs requries the
presence of at least one large-scale magnetic reversal in the fourth Galactic
quadrant, located between the Sagittarius- Carina and Scutum-Crux spiral arms.
To quantitatively compare our measurements to other recent studies, we consider
all available extragalactic and pulsar RMs in the region we have surveyed, and
jointly fit these data to simple models in which the large-scale field follows
the spiral arms. In the best-fitting model, the magnetic field in the fourth
Galactic quadrant is directed clockwise in the Sagittarius-Carina spiral arm
(as viewed from the North Galactic pole), but is oriented counter- clockwise in
the Scutum-Crux arm. This contrasts with recent analyses of pulsar RMs alone,
in which the fourth-quadrant field was presumed to be directed
counter-clockwise in the Sagittarius- Carina arm. Also in contrast to recent
pulsar RM studies, our joint modeling of pulsar and extragalactic RMs
demonstrates that large numbers of large-scale magnetic field reversals are not
required to account for observations.
| astro-ph |
0704.0459 | On iterated image size for point-symmetric relations | Let $\Gamma =(V,E)$ be a point-symmetric reflexive relation and let $v\in V$
such that
$|\Gamma (v)|$ is finite (and hence $|\Gamma (x)|$ is finite for all $x$, by
the transitive action of the group of automorphisms). Let $j\in \N$ be an
integer such that $\Gamma ^j(v)\cap \Gamma ^{-}(v)=\{v\}$. Our main result
states that
$$ |\Gamma ^{j} (v)|\ge | \Gamma ^{j-1} (v)| + |\Gamma (v)|-1.$$
As an application we have $ |\Gamma ^{j} (v)| \ge 1+(|\Gamma (v)|-1)j.$ The
last result confirms a recent conjecture of Seymour in the case of
vertex-symmetric graphs. Also it gives a short proof for the validity of the
Caccetta-H\"aggkvist conjecture for vertex-symmetric graphs and generalizes an
additive result of Shepherdson.
| math.CO |
0704.0460 | The Kilodegree Extremely Little Telescope (KELT): A Small Robotic
Telescope for Large-Area Synoptic Surveys | The Kilodegree Extremely Little Telescope (KELT) project is a survey for
planetary transits of bright stars. It consists of a small-aperture, wide-field
automated telescope located at Winer Observatory near Sonoita, Arizona. The
telescope surveys a set of 26 x 26 degree fields, together covering about 25%
of the Northern sky, targeting stars in the range of 8<V<10 mag, searching for
transits by close-in Jupiters. This paper describes the system hardware and
software and discusses the quality of the observations. We show that KELT is
able to achieve the necessary photometric precision to detect planetary
transits around solar-type main sequence stars.
| astro-ph |
0704.0461 | Entanglement increase from local interactions with
not-completely-positive maps | Simple examples are constructed that show the entanglement of two qubits
being both increased and decreased by interactions on just one of them. One of
the two qubits interacts with a third qubit, a control, that is never entangled
or correlated with either of the two entangled qubits and is never entangled,
but becomes correlated, with the system of those two qubits. The two entangled
qubits do not interact, but their state can change from maximally entangled to
separable or from separable to maximally entangled. Similar changes for the two
qubits are made with a swap operation between one of the qubits and a control;
then there are compensating changes of entanglement that involve the control.
When the entanglement increases, the map that describes the change of the state
of the two entangled qubits is not completely positive. Combination of two
independent interactions that individually give exponential decay of the
entanglement can cause the entanglement to not decay exponentially but,
instead, go to zero at a finite time.
| quant-ph |
0704.0462 | Extended solar emission - an analysis of the EGRET data | The Sun was recently predicted to be an extended source of gamma-ray
emission, produced by inverse-Compton scattering of cosmic-ray electrons with
the solar radiation. The emission was predicted to contribute to the diffuse
extragalactic background even at large angular distances from the Sun. While
this emission is expected to be readily detectable in future by GLAST, the
situation for available EGRET data is more challenging. We present a detailed
study of the EGRET database, using a time dependent analysis, accounting for
the effect of the emission from 3C 279, the moon, and other sources, which
interfere with the solar signal. The technique has been tested on the moon
signal, with results consistent with previous work. We find clear evidence for
emission from the Sun and its vicinity. The observations are compared with our
model for the extended emission.
| astro-ph |
0704.0463 | Mass and Temperature of the TWA 7 Debris Disk | We present photometric detections of dust emission at 850 and 450 micron
around the pre-main sequence M1 dwarf TWA 7 using the SCUBA camera on the James
Clerk Maxwell Telescope. These data confirm the presence of a cold dust disk
around TWA 7, a member of the TW Hydrae Association. Based on the 850 micron
flux, we estimate the mass of the disk to be 18 lunar masses (0.2 Earth masses)
assuming a mass opacity of 1.7 cm^2/g with a temperature of 45 K. This makes
the TWA 7 disk (d=55 pc) an order of magnitude more massive than the disk
reported around AU Microscopii (GL 803), the closest (9.9 pc) debris disk
detected around an M dwarf. This is consistent with TWA 7 being slightly
younger than AU Mic. We find that the mid-IR and submillimeter data require the
disk to be comprised of dust at a range of temperatures. A model in which the
dust is at a single radius from the star, with a range of temperatures
according to grain size, is as effective at fitting the emission spectrum as a
model in which the dust is of uniform size, but has a range of temperatures
according to distance. We discuss this disk in the context of known disks in
the TW Hydrae Association and around low-mass stars; a comparison of masses of
disks in the TWA reveals no trend in mass or evolutionary state (gas-rich vs.
debris) as a function of spectral type.
| astro-ph |
0704.0464 | Annealed importance sampling of dileucine peptide | Annealed importance sampling is a means to assign equilibrium weights to a
nonequilibrium sample that was generated by a simulated annealing protocol. The
weights may then be used to calculate equilibrium averages, and also serve as
an ``adiabatic signature'' of the chosen cooling schedule. In this paper we
demonstrate the method on the 50-atom dileucine peptide, showing that
equilibrium distributions are attained for manageable cooling schedules. For
this system, as naively implemented here, the method is modestly more efficient
than constant temperature simulation. However, the method is worth considering
whenever any simulated heating or cooling is performed (as is often done at the
beginning of a simulation project, or during an NMR structure calculation), as
it is simple to implement and requires minimal additional CPU expense.
Furthermore, the naive implementation presented here can be improved.
| q-bio.BM |
0704.0465 | A General Nonlinear Fokker-Planck Equation and its Associated Entropy | A recently introduced nonlinear Fokker-Planck equation, derived directly from
a master equation, comes out as a very general tool to describe
phenomenologically systems presenting complex behavior, like anomalous
diffusion, in the presence of external forces. Such an equation is
characterized by a nonlinear diffusion term that may present, in general, two
distinct powers of the probability distribution. Herein, we calculate the
stationary-state distributions of this equation in some special cases, and
introduce associated classes of generalized entropies in order to satisfy the
H-theorem. Within this approach, the parameters associated with the transition
rates of the original master-equation are related to such generalized
entropies, and are shown to obey some restrictions. Some particular cases are
discussed.
| cond-mat.stat-mech cond-mat.other |
0704.0466 | Conduction electron spin-lattice relaxation time in the MgB2
superconductor | The spin-lattice relaxation time, $T_{1}$, of conduction electrons is
measured as a function of temperature and magnetic field in MgB$_2$. The method
is based on the detection of the $z$ component of the conduction electron
magnetization under electron spin resonance conditions with amplitude modulated
microwave excitation. Measurement of $T_{1}$ below $T_c$ at 0.32 T allows to
disentangle contributions from the two Fermi surfaces of MgB$_{2}$ as this
field restores normal state on the Fermi surface part with $\pi$ symmetry only.
| cond-mat.supr-con cond-mat.str-el |
0704.0467 | Modeling Accretion Disk X-ray Continuum of Black Hole Candidates | We critically examine issues associated with determining the fundamental
properties of the black hole and the surrounding accretion disk in an X-ray
binary based on modeling the disk X-ray continuum of the source. We base our
work mainly on two XMM-Newton observations of GX 339-4, because they provided
high-quality data at low energies (below 1 keV) which are critical for reliably
modeling the spectrum of the accretion disk. A key issue examined is the
determination of the so-called "color correction factor", which is often
empirically introduced to account for the deviation of the local disk spectrum
from a blackbody (due to electron scattering). This factor cannot be
pre-determined theoretically because it may vary with, e.g., mass accretion
rate, among a number of important factors. We follow up on an earlier
suggestion to estimate the color correction observationally by modeling the
disk spectrum with saturated Compton scattering. We show that the spectra can
be fitted well and the approach yields reasonable values for the color
correction factor. For comparison, we have also attempted to fit the spectra
with other models. We show that even the high-soft-state continuum (which is
dominated by the disk emission) cannot be satisfactorily fitted by
state-of-the-art disk models. We discuss the implication of the results.
| astro-ph |
0704.0468 | Inapproximability of Maximum Weighted Edge Biclique and Its Applications | Given a bipartite graph $G = (V_1,V_2,E)$ where edges take on {\it both}
positive and negative weights from set $\mathcal{S}$, the {\it maximum weighted
edge biclique} problem, or $\mathcal{S}$-MWEB for short, asks to find a
bipartite subgraph whose sum of edge weights is maximized. This problem has
various applications in bioinformatics, machine learning and databases and its
(in)approximability remains open. In this paper, we show that for a wide range
of choices of $\mathcal{S}$, specifically when $| \frac{\min\mathcal{S}} {\max
\mathcal{S}} | \in \Omega(\eta^{\delta-1/2}) \cap O(\eta^{1/2-\delta})$ (where
$\eta = \max\{|V_1|, |V_2|\}$, and $\delta \in (0,1/2]$), no polynomial time
algorithm can approximate $\mathcal{S}$-MWEB within a factor of $n^{\epsilon}$
for some $\epsilon > 0$ unless $\mathsf{RP = NP}$. This hardness result gives
justification of the heuristic approaches adopted for various applied problems
in the aforementioned areas, and indicates that good approximation algorithms
are unlikely to exist. Specifically, we give two applications by showing that:
1) finding statistically significant biclusters in the SAMBA model, proposed in
\cite{Tan02} for the analysis of microarray data, is
$n^{\epsilon}$-inapproximable; and 2) no polynomial time algorithm exists for
the Minimum Description Length with Holes problem \cite{Bu05} unless
$\mathsf{RP=NP}$.
| cs.CC cs.DS |
0704.0469 | On line arrangements with applications to 3-nets | We show a one-to-one correspondence between arrangements of d lines in the
projective plane, and lines in P^{d-2}. We apply this correspondence to
classify (3,q)-nets over the complex numbers for all q<=6. When q=6, we have
twelve possible combinatorial cases, but we prove that only nine of them are
realizable. This new case shows several new properties for 3-nets: different
dimensions for moduli, strict realization over certain fields, etc. We also
construct a three dimensional family of (3,8)-nets corresponding to the
Quaternion group.
| math.AG math.CO |
0704.0470 | Testing turbulence model at metric scales with mid-infrared VISIR images
at the VLT | We probe turbulence structure from centimetric to metric scales by
simultaneous imagery at mid-infrared and visible wavelengths at the VLT
telescope and show that it departs significantly from the commonly used
Kolmogorov model. The data can be fitted by the von Karman model with an outer
scale of the order of 30 m and we see clear signs of the phase structure
function saturation across the 8-m VLT aperture. The image quality improves in
the infrared faster than the standard lambda^{-1/5} scaling and may be
diffraction-limited at 30-m apertures even without adaptive optics at
wavelengths longer than 8 micron.
| astro-ph |
0704.0471 | Density dependence of the symmetry energy and the nuclear equation of
state: A Dynamical and Statistical model perspective | The density dependence of the symmetry energy in the equation of state of
isospin asymmetric nuclear matter is of significant importance for studying the
structure of systems as diverse as the neutron-rich nuclei and the neutron
stars. A number of reactions using the dynamical and the statistical models of
multifragmentation, and the experimental isoscaling observable, is studied to
extract information on the density dependence of the symmetry energy. It is
observed that the dynamical and the statistical model calculations give
consistent results assuming the sequential decay effect in dynamical model to
be small. A comparison with several other independent studies is also made to
obtain important constraint on the form of the density dependence of the
symmetry energy. The comparison rules out an extremely " stiff " and " soft "
form of the density dependence of the symmetry energy with important
implications for astrophysical and nuclear physics studies.
| nucl-ex nucl-th |
0704.0472 | Competitive nucleation and the Ostwald rule in a generalized Potts model
with multiple metastable phases | We introduce a simple nearest-neighbor spin model with multiple metastable
phases, the number and decay pathways of which are explicitly controlled by the
parameters of the system. With this model we can construct, for example, a
system which evolves through an arbitrarily long succession of metastable
phases. We also construct systems in which different phases may nucleate
competitively from a single initial phase. For such a system, we present a
general method to extract from numerical simulations the individual nucleation
rates of the nucleating phases. The results show that the Ostwald rule, which
predicts which phase will nucleate, must be modified probabilistically when the
new phases are almost equally stable. Finally, we show that the nucleation rate
of a phase depends, among other things, on the number of other phases
accessible from it.
| cond-mat.stat-mech cond-mat.mtrl-sci cond-mat.soft |
0704.0473 | Contrasting Two Transformation-Based Methods for Obtaining Absolute
Extrema | In this note we contrast two transformation-based methods to deduce absolute
extrema and the corresponding extremizers. Unlike variation-based methods, the
transformation-based ones of Carlson and Leitmann and the recent one of Silva
and Torres are direct in that they permit obtaining solutions by inspection.
| math.OC |
0704.0474 | Application of Ewald summations to long-range dispersion forces | We present results illustrating the effects of using explicit summation terms
for the $r^{-6}$ dispersion term on the interfacial properties of a
Lennard-Jones fluid and SPC/E water. For the Lennard-Jones fluid, we find that
the use of long-range summations, even with a short ``crossover radius,''
yields results that are consistent with simulations using large cutoff radii.
Simulations of SPC/E water demonstrate that the long-range dispersion forces
are of secondary importance to the Coulombic forces. In both cases, we find
that the ratio of box size $L_{\parallel}$ to crossover radius $r_{\rm
c}^{\mathbf k}$ plays an important role in determining the magnitude of the
long-range dispersion correction, although its effect is secondary when
Coulombic interactions are also present.
| cond-mat.mtrl-sci cond-mat.stat-mech |
0704.0475 | Possible non-thermal nature of the soft-excess emission in the cluster
of galaxies Sersic 159-03 | We present an analysis of new Suzaku data and archival data from XMM-Newton
of the cluster of galaxies Sersic 159-03, which has a strong soft X-ray excess
emission component. The Suzaku observation confirms the presence of the soft
excess emission, but it does not confirm the presence of redshifted OVII lines
in the cluster. Radial profiles and 2D maps derived from XMM-Newton
observations show that the soft excess emission has a strong peak at the
position of the central cD galaxy and the maps do not show any significant
azimuthal variations. Although the soft excess emission can be fitted equally
well with both thermal and non-thermal models, its spatial distribution is
neither consistent with the models of intercluster warm-hot filaments, nor with
models of clumpy warm intracluster gas associated with infalling groups. Using
the data obtained by the XMM-Newton Reflection Grating Spectrometers we do not
confirm the presence of the warm gas in the cluster centre with the expected
properties assuming the soft excess is of thermal origin. The observed
properties of the soft excess emission are consistent with the non-thermal
interpretation. While the high density of relativistic electrons associated
with the peak of the soft emission in the cluster centre might have been
provided by an active galactic nucleus in the central cD galaxy, the underlying
population might have been accelerated in diffuse shocks.
| astro-ph |
0704.0476 | Geometric phase of an atom inside an adiabatic radio frequency potential | We investigate the geometric phase of an atom inside an adiabatic radio
frequency (rf) potential created from a static magnetic field (B-field) and a
time dependent rf field. The spatial motion of the atomic center of mass is
shown to give rise to a geometric phase, or Berry's phase, to the adiabatically
evolving atomic hyperfine spin along the local B-field. This phase is found to
depend on both the static B-field along the semi-classical trajectory of the
atomic center of mass and an ``effective magnetic field'' of the total B-field,
including the oscillating rf field. Specific calculations are provided for
several recent atom interferometry experiments and proposals utilizing
adiabatic rf potentials.
| quant-ph |
0704.0477 | The Transition from the First Stars to the Second Stars in the Early
Universe | We observe a sharp transition from a singular, high-mass mode of star
formation, to a low-mass dominated mode, in numerical simulations, at a
metallicity of 10^-3 Zsolar. We incorporate a new method for including the
radiative cooling from metals into adaptive mesh-refinement hydrodynamic
simulations. Our results illustrate how metals, produced by the first stars,
led to a transition from the high-mass star formation mode of Pop III stars, to
the low-mass mode that dominates today. We ran hydrodynamic simulations with
cosmological initial conditions in the standard LambdaCDM model, with
metallicities, from zero to 10^-2 Zsolar, beginnning at redshift, z = 99. The
simulations were run until a dense core forms at the center of a 5 x 10^5
Msolar dark matter halo, at z ~ 18. Analysis of the central 1 Msolar core
reveals that the two simulations with the lowest metallicities, Z = 0 and 10^-4
Zsolar, contain one clump with 99% of the mass, while the two with
metallicities, Z = 10^-3 and 10^-2 Zsolar, each contain two clumps that share
most of the mass. The Z = 10^-3 Zsolar simulation also produced two low-mass
proto-stellar objects with masses between 10^-2 and 10^-1 Msolar. Gas with Z >=
10^-3 Zsolar is able to cool to the temperature of the CMB, which sets a lower
limit to the minimum fragmentation mass. This suggests that the second
generation stars produced a spectrum of lower mass stars, but were still more
massive on average than stars formed in the local universe.
| astro-ph |
0704.0478 | Super Star Cluster Velocity Dispersions and Virial Masses in the M82
Nuclear Starburst | We use high-resolution near-infrared spectroscopy from Keck Observatory to
measure the stellar velocity dispersions of 19 super star clusters (SSCs) in
the nuclear starburst of M82. The clusters have ages on the order of 10 Myr,
which is many times longer than the crossing times implied by their velocity
dispersions and radii. We therefore apply the Virial Theorem to derive the
kinematic mass for 15 of the SSCs. The SSCs have masses of 2 x 10^5 to 4 x 10^6
solar masses, with a total population mass of 1.4 x 10^7 solar masses.
Comparison of the loci of the young M82 SSCs and old Milky Way globular
clusters in a plot of radius versus velocity dispersion suggests that the SSCs
are a population of potential globular clusters. We present the mass function
for the SSCs, and find a power law fit with an index of gamma = -1.91 +/- 0.06.
This result is nearly identical to the mass function of young SSCs in the
Antennae galaxies.
| astro-ph |
0704.0479 | The affine part of the Picard scheme | We describe the maximal torus and maximal unipotent subgroup of the Picard
variety of a proper scheme over a perfect field.
| math.AG math.KT |
0704.0480 | Enhanced quantum Zeno effect and bunching in the decay of interacting
bosons from an unstable state | paper withdrawn due to the possible error in numerical eigenfunction
calculation
| cond-mat.mes-hall |
0704.0481 | The few scales of nuclei and nuclear matter | The well-known correlations of low-energy three and four-nucleon observables
with a typical three-nucleon scale (e.g., the Tjon line) is extended to light
nuclei and nuclear matter. Evidence for the scaling between light nuclei
binding energies and the triton one are pointed out. We argue that the
saturation energy and density of nuclear matter are correlated to the triton
binding energy. The available systematic nuclear matter calculations indicate a
possible band structure representing these correlations.
| nucl-th |
0704.0482 | Implementation of holonomic quantum computation through engineering and
manipulating environment | We consider an atom-field coupled system, in which two pairs of four-level
atoms are respectively driven by laser fields and trapped in two distant
cavities that are connected by an optical fiber. First, we show that an
effective squeezing reservoir can be engineered under appropriate conditions.
Then, we show that a two-qubit geometric CPHASE gate between the atoms in the
two cavities can be implemented through adiabatically manipulating the
engineered reservoir along a closed loop. This scheme that combines engineering
environment with decoherence-free space and geometric phase quantum computation
together has the remarkable feature: a CPHASE gate with arbitrary phase shift
is implemented by simply changing the strength and relative phase of the
driving fields.
| quant-ph |
0704.0483 | Vortex state in a Fulde-Ferrell-Larkin-Ovchinnikov superconductor based
on the quasiclassical theory | We investigate the vortex state with Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)
modulations suggested for a high field phase of CeCoIn_5. On the basis of the
quasiclassical Eilenberger theory, we calculate the three dimensional structure
of pair potentials, internal magnetic fields, paramagnetic moments, and
electronic states, for the s-wave and the d-wave pairings comparatively. The
\pi-phase shift of the pair potential at the FFLO nodal plane or at the vortex
core induces sharp peak states in the local density of states, and enhances the
local paramagnetic moment. We also discuss the NMR spectrum and the neutron
scattering as methods to detect the FFLO structure.
| cond-mat.supr-con |
0704.0484 | Search for Chaotic Behavior in a Flapping Flag | We measured the correlation of the times between successive flaps of a flag
for a variety of wind speeds and found no evidence of low dimensional chaotic
behavior in the return maps of these times. We instead observed what is best
modeled as random times determined by an exponential distribution. This study
was done as an undergraduate experiment and illustrates the differences between
low dimensional chaotic and possibly higher dimensional chaotic systems.
| physics.ed-ph physics.gen-ph |
0704.0485 | Optimal Shape Design for Stokes Flow Via Minimax Differentiability | This paper is concerned with a shape sensitivity analysis of a viscous
incompressible fluid driven by Stokes equations with nonhomogeneous boundary
condition. The structure of shape gradient with respect to the shape of the
variable domain for a given cost function is established by using the
differentiability of a minimax formulation involving a Lagrangian functional
combining with function space parametrization technique or function space
embedding technique. We apply an gradient type algorithm to our problem.
Numerical examples show that our theory is useful for practical purpose and the
proposed algorithm is feasible.
| math.OC |
0704.0486 | Kinematic Decoupling of Globular Clusters with Extended
Horizontal-Branch | About 25% of the Milky Way globular clusters (GCs) exhibit unusually extended
color distribution of stars in the horizontal-branch (HB) phase. This
phenomenon is now best understood as due to the presence of helium enhanced
second generation subpopulations, which has raised a possibility that these
peculiar GCs might have a unique origin. Here we show that these GCs with
extended HB are clearly distinct from other normal GCs in kinematics and mass.
The GCs with extended HB are more massive than normal GCs, and are dominated by
random motion with no correlation between kinematics and metallicity.
Surprisingly, however, when they are excluded, most normal GCs in the inner
halo show clear signs of dissipational collapse that apparently led to the
formation of the disk. Normal GCs in the outer halo share their kinematic
properties with the extended HB GCs, which is consistent with the accretion
origin. Our result further suggests heterogeneous origins of GCs, and we
anticipate this to be a starting point for more detailed investigations of
Milky Way formation, including early mergers, collapse, and later accretion.
| astro-ph |
0704.0487 | Scalar potential model progress | Because observations of galaxies and clusters have been found inconsistent
with General Relativity (GR), the focus of effort in developing a Scalar
Potential Model (SPM) has been on the examination of galaxies and clusters. The
SPM has been found to be consistent with cluster cellular structure, the flow
of IGM from spiral galaxies to elliptical galaxies, intergalactic redshift
without an expanding universe, discrete redshift, rotation curve (RC) data
without dark matter, asymmetric RCs, galaxy central mass, galaxy central
velocity dispersion, and the Pioneer Anomaly. In addition, the SPM suggests a
model of past expansion, past contraction, and current expansion of the
universe. GR corresponds to the SPM in the limit in which the effect of the
Sources and Sinks approximate a flat scalar potential field such as between
clusters and on the solar system scale, which is small relative to the distance
to a Source.
| physics.gen-ph |
0704.0488 | Teleparallel Version of the Stationary Axisymmetric Solutions and their
Energy Contents | This work contains the teleparallel version of the stationary axisymmetric
solutions. We obtain the tetrad and the torsion fields representing these
solutions. The tensor, vector and axial-vector parts of the torsion tensor are
evaluated. It is found that the axial-vector has component only along $\rho$
and $z$ directions. The three possibilities of the axial vector depending on
the metric function $B$ are discussed. The vector related with spin has also
been evaluated and the corresponding extra Hamiltonian is furnished. Further,
we use the teleparallel version of M$\ddot{o}$ller prescription to find the
energy-momentum distribution of the solutions. It is interesting to note that
(for $\lambda=1$) energy and momentum densities in teleparallel theory are
equal to the corresponding quantities in GR plus an additional quantity in
each, which may become equal under certain conditions. Finally, we discuss the
two special cases of the stationary axisymmetric solutions.
| gr-qc |
0704.0489 | Relativistic treatment in D-dimensions to a spin-zero particle with
noncentral equal scalar and vector ring-shaped Kratzer potential | The Klein-Gordon equation in D-dimensions for a recently proposed Kratzer
potential plus ring-shaped potential is solved analytically by means of the
conventional Nikiforov-Uvarov method. The exact energy bound-states and the
corresponding wave functions of the Klein-Gordon are obtained in the presence
of the noncentral equal scalar and vector potentials. The results obtained in
this work are more general and can be reduced to the standard forms in
three-dimensions given by other works.
| quant-ph |
0704.0490 | Long Distance Signaling Using Axion-like Particles | The possible existence of axion-like particles could lead to a new type of
long distance communication. In this work, basic antenna concepts are defined
and a Friis-like equation is derived to facilitate long-distance link
calculations. An example calculation is presented showing that communication
over distances of 1000 km or more may be possible for $m_{a}< 3.5$ meV and
$g_{a\gamma \gamma} > 5 \times 10^{- 8} {\text{GeV}}^{- 1}$.
| hep-ph astro-ph hep-th |
0704.0491 | Weighted percolation on directed networks | We present an analysis of the percolation transition for general node removal
strategies valid for locally tree-like directed networks. On the basis of
heuristic arguments we predict that, if the probability of removing node $i$ is
$p_i$, the network disintegrates if $p_i$ is such that the largest eigenvalue
of the matrix with entries $A_{ij}(1-p_i)$ is less than 1, where $A$ is the
adjacency matrix of the network. The knowledge or applicability of a Markov
network model is not required by our theory, thus making it applicable to
situations not covered by previous works. We test our predicted percolation
criterion against numerical results for different networks and node removal
strategies.
| cond-mat.soft cond-mat.dis-nn |
0704.0492 | Refuting the Pseudo Attack on the REESSE1+ Cryptosystem | We illustrate through example 1 and 2 that the condition at theorem 1 in [8]
dissatisfies necessity, and the converse proposition of fact 1.1 in [8] does
not hold, namely the condition Z/M - L/Ak < 1/(2 Ak^2) is not sufficient for
f(i) + f(j) = f(k). Illuminate through an analysis and ex.3 that there is a
logic error during deduction of fact 1.2, which causes each of fact 1.2, 1.3, 4
to be invalid. Demonstrate through ex.4 and 5 that each or the combination of
qu+1 > qu * D at fact 4 and table 1 at fact 2.2 is not sufficient for f(i) +
f(j) = f(k), property 1, 2, 3, 4, 5 each are invalid, and alg.1 based on fact 4
and alg.2 based on table 1 are disordered and wrong logically. Further,
manifest through a repeated experiment and ex.5 that the data at table 2 is
falsified, and the example in [8] is woven elaborately. We explain why Cx = Ax
* W^f(x) (% M) is changed to Cx = (Ax * W^f(x))^d (% M) in REESSE1+ v2.1. To
the signature fraud, we point out that [8] misunderstands the existence of T^-1
and Q^-1 % (M-1), and forging of Q can be easily avoided through moving H.
Therefore, the conclusion of [8] that REESSE1+ is not secure at all (which
connotes that [8] can extract a related private key from any public key in
REESSE1+) is fully incorrect, and as long as the parameter Omega is fitly
selected, REESSE1+ with Cx = Ax * W^f(x) (% M) is secure.
| cs.CR |
0704.0493 | Phase structure of a surface model on dynamically triangulated spheres
with elastic skeletons | We find three distinct phases; a tubular phase, a planar phase, and the
spherical phase, in a triangulated fluid surface model. It is also found that
these phases are separated by discontinuous transitions. The fluid surface
model is investigated within the framework of the conventional curvature model
by using the canonical Monte Carlo simulations with dynamical triangulations.
The mechanical strength of the surface is given only by skeletons, and no
two-dimensional bending energy is assumed in the Hamiltonian. The skeletons are
composed of elastic linear-chains and rigid junctions and form a
compartmentalized structure on the surface, and for this reason the vertices of
triangles can diffuse freely only inside the compartments. As a consequence, an
inhomogeneous structure is introduced in the model; the surface strength inside
the compartments is different from the surface strength on the compartments.
However, the rotational symmetry is not influenced by the elastic skeletons;
there is no specific direction on the surface. In addition to the three phases
mentioned above, a collapsed phase is expected to exist in the low bending
rigidity regime that was not studied here. The inhomogeneous structure and the
fluidity of vertices are considered to be the origin of such variety of phases.
| cond-mat.stat-mech cond-mat.soft |
0704.0494 | Vortex Dynamics at the Initial Stage of Resistive Transition in
Superconductors with Fractal Cluster Structure | The effect of fractal normal-phase clusters on vortex dynamics in a
percolative superconductor is considered. The superconductor contains
percolative superconducting cluster carrying a transport current and clusters
of a normal phase, acting as pinning centers. A prototype of such a structure
is YBCO film, containing clusters of columnar defects, as well as the BSCCO/Ag
sheathed tape, which is of practical interest for wire fabrication. Transition
of the superconductor into a resistive state corresponds to the percolation
transition from a pinned vortex state to a resistive state when the vortices
are free to move. The dependencies of the free vortex density on the fractal
dimension of the cluster boundary as well as the resistance on the transport
current are obtained. It is revealed that a mixed state of the vortex glass
type is realized in the superconducting system involved. The current-voltage
characteristics of superconductors containing fractal clusters are obtained and
their features are studied.
| cond-mat.supr-con cond-mat.mtrl-sci |
0704.0495 | The Veldkamp Space of Two-Qubits | Given a remarkable representation of the generalized Pauli operators of
two-qubits in terms of the points of the generalized quadrangle of order two,
W(2), it is shown that specific subsets of these operators can also be
associated with the points and lines of the four-dimensional projective space
over the Galois field with two elements - the so-called Veldkamp space of W(2).
An intriguing novelty is the recognition of (uni- and tri-centric) triads and
specific pentads of the Pauli operators in addition to the "classical" subsets
answering to geometric hyperplanes of W(2).
| quant-ph math-ph math.MP |
0704.0496 | Fusion process studied with preequilibrium giant dipole resonance in
time dependent Hartree-Fock theory | The equilibration of macroscopic degrees of freedom during the fusion of
heavy nuclei, like the charge and the shape, are studied in the Time-Dependent
Hartree-Fock theory. The pre-equilibrium Giant Dipole Resonance (GDR) is used
to probe the fusion path. It is shown that such isovector collective state is
excited in N/Z asymmetric fusion and to a less extent in mass asymmetric
systems. The characteristics of this GDR are governed by the structure of the
fused system in its preequilibrium phase, like its deformation, rotation and
vibration. In particular, we show that a lowering of the pre-equilibrium GDR
energy is expected as compared to the statistical one. Revisiting experimental
data, we extract an evidence of this lowering for the first time. We also
quantify the fusion-evaporation enhancement due to gamma-ray emission from the
pre-equilibrium GDR. This cooling mechanism along the fusion path may be
suitable to synthesize in the future super heavy elements using radioactive
beams with strong N/Z asymmetries in the entrance channel.
| nucl-th |
0704.0497 | Penalization approach for mixed hyperbolic systems with constant
coefficients satisfying a Uniform Lopatinski Condition | In this paper, we describe a new, systematic and explicit way of
approximating solutions of mixed hyperbolic systems with constant coefficients
satisfying a Uniform Lopatinski Condition via different Penalization
approaches.
| math.AP |
0704.0498 | A unified analysis of the reactor neutrino program towards the
measurement of the theta_13 mixing angle | We present in this article a detailed quantitative discussion of the
measurement of the leptonic mixing angle theta_13 through currently scheduled
reactor neutrino oscillation experiments. We thus focus on Double Chooz (Phase
I & II), Daya Bay (Phase I & II) and RENO experiments. We perform a unified
analysis, including systematics, backgrounds and accurate experimental setup in
each case. Each identified systematic error and background impact has been
assessed on experimental setups following published data when available and
extrapolating from Double Chooz acquired knowledge otherwise. After reviewing
the experiments, we present a new analysis of their sensitivities to sin^2(2
theta_13) and study the impact of the different systematics based on the pulls
approach. Through this generic statistical analysis we discuss the advantages
and drawbacks of each experimental setup.
| hep-ex |
0704.0499 | Optimal Routing for Decode-and-Forward based Cooperation in Wireless
Networks | We investigate cooperative wireless relay networks in which the nodes can
help each other in data transmission. We study different coding strategies in
the single-source single-destination network with many relay nodes. Given the
myriad of ways in which nodes can cooperate, there is a natural routing
problem, i.e., determining an ordered set of nodes to relay the data from the
source to the destination. We find that for a given route, the
decode-and-forward strategy, which is an information theoretic cooperative
coding strategy, achieves rates significantly higher than that achievable by
the usual multi-hop coding strategy, which is a point-to-point non-cooperative
coding strategy. We construct an algorithm to find an optimal route (in terms
of rate maximizing) for the decode-and-forward strategy. Since the algorithm
runs in factorial time in the worst case, we propose a heuristic algorithm that
runs in polynomial time. The heuristic algorithm outputs an optimal route when
the nodes transmit independent codewords. We implement these coding strategies
using practical low density parity check codes to compare the performance of
the strategies on different routes.
| cs.IT math.IT |
0704.0500 | On the polynomial automorphisms of a group | We prove that if a group is nilpotent (resp. metabelian), then so is the
subgroup of its automorphism group generated by all polynomial automorphisms.
| math.GR |