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D-\bar D mixing and rare D decays in the Littlest Higgs model with
non-unitarity matrix | We study the $D-\bar D$ mixing and rare D decays in the Littlest Higgs model.
As the new weak singlet quark with the electric charge of 2/3 is introduced to
cancel the quadratic divergence induced by the top-quark, the standard unitary
$3\times 3$ Cabibbo-Kobayashi-Maskawa matrix is extended to a non-unitary
$4\times 3$ matrix in the quark charged currents and Z-mediated flavor changing
neutral currents are generated at tree level. In this model, we show that the
$D-\bar D$ mixing parameter can be as large as the current experimental value
and the decay branching ratio (BR) of $D\to X_u \ga$ is small but its direct CP
asymmetry could be $O(10%)$. In addition, we find that the BRs of $D\to X_u
\ell^{+} \ell^{-}$, $D\to X_u\nu \bar \nu$ and $D\to \mu^{+} \mu^{-}$ could be
enhanced to be $O(10^{-9})$, $O(10^{-8})$ and $O(10^{-9})$, respectively.
|
Alternative Large Nc Schemes and Chiral Dynamics | We compare the dependences on the number of colors of the leading pion pion
scattering amplitudes using the single index quark field and two index quark
fields. These are seen to have different relationships to the scattering
amplitudes suggested by chiral dynamics which can explain the long puzzling
pion pion s wave scattering up to about 1 GeV. This may be interesting for
getting a better understanding of the large Nc approach as well as for
application to recently proposed technicolor models.
|
The height dependence of temperature - velocity correlation in the solar
photosphere | We derive correlation coefficients between temperature and line-of-sight
velocity as a function of optical depth throughout the solar photosphere for
the non-magnetic photosphere and a small area of enhanced magnetic activity.
The maximum anticorrelation of about -0.6 between temperature and line-of-sight
velocity in the non-magnetic photosphere occurs at log tau5 = -0.4. The
magnetic field is another decorrelating factor along with 5-min oscillations
and seeing.
|
Magnetism in the high-Tc analogue Cs2AgF4 studied with muon-spin
relaxation | We present the results of a muon-spin relaxation study of the high-Tc
analogue material Cs2AgF4. We find unambiguous evidence for magnetic order,
intrinsic to the material, below T_C=13.95(3) K. The ratio of inter- to
intraplane coupling is estimated to be |J'/J|=1.9 x 10^-2, while fits of the
temperature dependence of the order parameter reveal a critical exponent
beta=0.292(3), implying an intermediate character between pure two- and three-
dimensional magnetism in the critical regime. Above T_C we observe a signal
characteristic of dipolar interactions due to linear F-mu-F bonds, allowing the
muon stopping sites in this compound to be characterized.
|
Reconciling the X(3872) with the near-threshold enhancement in the
D^0\bar{D}^{*0} final state | We investigate the enhancement in the D^0\bar{D}^0\pi^0 final state with the
mass M=3875.2\pm 0.7^{+0.3}_{-1.6}\pm 0.8 MeV found recently by the Belle
Collaboration in the B\to K D^0\bar{D}^0\pi^0 decay and test the possibility
that this is yet another manifestation of the well-established resonance
X(3872). We perform a combined Flatte analysis of the data for the
D^0\bar{D}^0\pi^0 mode, and for the \pi^+\pi^- J/\psi mode of the X(3872). Only
if the X(3872) is a virtual state in the D^0\bar{D}^{*0} channel, the data on
the new enhancement comply with those on the X(3872). In our fits, the mass
distribution in the D^0\bar{D}^{*0} mode exhibits a peak at 2-3 MeV above the
D^0\bar{D}^{*0} threshold, with a distinctive non-Breit-Wigner shape.
|
Three-dimensional effects in "atom diodes": atom-optical devices for
one-way motion | The ``atom diode'' is a laser device that lets the ground state atom pass in
one direction but not in the opposite direction. We examine three-dimensional
effects of that device for arbitrary atomic incidence angles on flat laser
sheets and set breakdown limiting angles and velocities. It is found that a
correct diodic behavior independent of the incident angle can be obtained with
blue detuned lasers.
|
Plasmon Amplification through Stimulated Emission at Terahertz
Frequencies in Graphene | We show that plasmons in two-dimensional graphene can have net gain at
terahertz frequencies. The coupling of the plasmons to interband electron-hole
transitions in population inverted graphene layers can lead to plasmon
amplification through the process of stimulated emission. We calculate plasmon
gain for different electron-hole densities and temperatures and show that the
gain values can exceed $10^{4}$ cm$^{-1}$ in the 1-10 terahertz frequency
range, for electron-hole densities in the $10^{9}$-$10^{11}$ cm$^{-2}$ range,
even when plasmon energy loss due to intraband scattering is considered.
Plasmons are found to exhibit net gain for intraband scattering times shorter
than 100 fs. Such high gain values could allow extremely compact terahertz
amplifiers and oscillators that have dimensions in the 1-10 $\mu$m range.
|
On the homology of two-dimensional elimination | We study birational maps with empty base locus defined by almost complete
intersection ideals. Birationality is shown to be expressed by the equality of
two Chern numbers. We provide a relatively effective method of their
calculation in terms of certain Hilbert coefficients. In dimension two the
structure of the irreducible ideals leads naturally to the calculation of
Sylvester determinants via a computer-assisted method. For degree at most 5 we
produce the full set of defining equations of the base ideal. The results
answer affirmatively some questions raised by D. Cox.
|
The effectiveness of quantum operations for eavesdropping on sealed
messages | A quantum protocol is described which enables a user to send sealed messages
and that allows for the detection of active eavesdroppers. We examine a class
of eavesdropping strategies, those that make use of quantum operations, and we
determine the information gain versus disturbance caused by these strategies.
We demonstrate this tradeoff with an example and we compare this protocol to
quantum key distribution, quantum direct communication, and quantum seal
protocols.
|
Shocks in nonlocal media | We investigate the formation of collisionless shocks along the spatial
profile of a gaussian laser beam propagating in nonlocal nonlinear media. For
defocusing nonlinearity the shock survives the smoothing effect of the nonlocal
response, though its dynamics is qualitatively affected by the latter, whereas
for focusing nonlinearity it dominates over filamentation. The patterns
observed in a thermal defocusing medium are interpreted in the framework of our
theory.
|
Modeling the field of laser welding melt pool by RBFNN | Efficient control of a laser welding process requires the reliable prediction
of process behavior. A statistical method of field modeling, based on
normalized RBFNN, can be successfully used to predict the spatiotemporal
dynamics of surface optical activity in the laser welding process. In this
article we demonstrate how to optimize RBFNN to maximize prediction quality.
Special attention is paid to the structure of sample vectors, which represent
the bridge between the field distributions in the past and future.
|
Solving The High Energy Evolution Equation Including Running Coupling
Corrections | We study the solution of the nonlinear BK evolution equation with the
recently calculated running coupling corrections [hep-ph/0609105,
hep-ph/0609090]. Performing a numerical solution we confirm the earlier result
of [hep-ph/0408216] that the high energy evolution with the running coupling
leads to a universal scaling behavior for the dipole scattering amplitude. The
running coupling corrections calculated recently significantly change the shape
of the scaling function as compared to the fixed coupling case leading to a
considerable increase in the anomalous dimension and to a slow-down of the
evolution with rapidity. The difference between the two recent calculations is
due to an extra contribution to the evolution kernel, referred to as the
subtraction term, which arises when running coupling corrections are included.
These subtraction terms were neglected in both recent calculations. We evaluate
numerically the subtraction terms for both calculations, and demonstrate that
when the subtraction terms are added back to the evolution kernels obtained in
the two works the resulting dipole amplitudes agree with each other! We then
use the complete running coupling kernel including the subtraction term to find
the numerical solution of the resulting full non-linear evolution equation with
the running coupling corrections. Again the scaling regime is recovered at very
large rapidity.
|
Anomalous c-axis transport in layered metals | Transport in metals with strongly anisotropic single-particle spectrum is
studied. Coherent band transport in all directions, described by the standard
Boltzmann equation, is shown to withstand both elastic and inelastic scattering
as long as $E_F\tau\gg 1$. A model of phonon-assisted tunneling via resonant
states located in between the layers is suggested to explain a non-monotonic
temperature dependence of the c-axis resistivity observed in experiments.
|
Proper holomorphic mappings of the spectral unit ball | We prove an Alexander type theorem for the spectral unit ball $\Omega_n$
showing that there are no non-trivial proper holomorphic mappings in
$\Omega_n$, $n\geq 2$.
|
Parsimony via concensus | The parsimony score of a character on a tree equals the number of state
changes required to fit that character onto the tree. We show that for
unordered, reversible characters this score equals the number of tree
rearrangements required to fit the tree onto the character. We discuss
implications of this connection for the debate over the use of consensus trees
or total evidence, and show how it provides a link between incongruence of
characters and recombination.
|
Millimeter imaging of HD 163296: probing the disk structure and
kinematics | We present new multi-wavelength millimeter interferometric observations of
the Herbig Ae star HD 163296 obtained with the IRAM/PBI, SMA and VLA arrays
both in continuum and in the 12CO, 13CO and C18O emission lines. Gas and dust
properties have been obtained comparing the observations with self-consistent
disk models for the dust and CO emission. The circumstellar disk is resolved
both in the continuum and in CO. We find strong evidence that the circumstellar
material is in Keplerian rotation around a central star of 2.6 Msun. The disk
inclination with respect to the line of sight is 46+-4 deg with a position
angle of 128+-4 deg. The slope of the dust opacity measured between 0.87 and 7
mm (beta=1) confirms the presence of mm/cm-size grains in the disk midplane.
The dust continuum emission is asymmetric and confined inside a radius of 200
AU while the CO emission extends up to 540 AU. The comparison between dust and
CO temperature indicates that CO is present only in the disk interior. Finally,
we obtain an increasing depletion of CO isotopomers from 12CO to 13CO and C18O.
We argue that these results support the idea that the disk of HD 163296 is
strongly evolved. In particular, we suggest that there is a strong depletion of
dust relative to gas outside 200 AU; this may be due to the inward migration of
large bodies that form in the outer disk or to clearing of a large gap in the
dust distribution by a low mass companion.
|
Spectropolarimetric observations of the Ca II 8498 A and 8542 A lines in
the quiet Sun | The Ca II infrared triplet is one of the few magnetically sensitive
chromospheric lines available for ground-based observations. We present
spectropolarimetric observations of the 8498 A and 8542 A lines in a quiet Sun
region near a decaying active region and compare the results with a simulation
of the lines in a high plasma-beta regime. Cluster analysis of Stokes V profile
pairs shows that the two lines, despite arguably being formed fairly close,
often do not have similar shapes. In the network, the local magnetic topology
is more important in determining the shapes of the Stokes V profiles than the
phase of the wave, contrary to what our simulations show. We also find that
Stokes V asymmetries are very common in the network, and the histograms of the
observed amplitude and area asymmetries differ significantly from the
simulation. Both the network and internetwork show oscillatory behavior in the
Ca II lines. It is stronger in the network, where shocking waves, similar to
those in the high-beta simulation, are seen and large self-reversals in the
intensity profiles are common.
|
Number of moduli of irreducible families of plane curves with nodes and
cusps | Consider the family S of irreducible plane curves of degree n with d nodes
and k cusps as singularities. Let W be an irreducible component of S. We
consider the natural rational map from W to the moduli space of curves of genus
g=(n-1)(n-2)/2-d-k. We define the "number of moduli of W" as the dimension of
the image of W with respect to this map. If W has the expected dimension equal
to 3n+g-1-k, then the number of moduli of W is at most equal to the min(3g-3,
3g-3+\rho-k), dove \rho is the Brill-Neother number of the linear series of
degree n and dimension 2 on a smooth curve of genus g. We say that W has the
expected number of moduli if the equality holds. In this paper we construct
examples of families of irreducible plane curves with nodes and cusps as
singularities having expected number of moduli and with non-positive
Brill-Noether number.
|
Search for Heavy Neutral MSSM Higgs Bosons with CMS: Reach and
Higgs-Mass Precision | The search for MSSM Higgs bosons will be an important goal at the LHC. We
analyze the search reach of the CMS experiment for the heavy neutral MSSM Higgs
bosons with an integrated luminosity of 30 or 60 fb^-1. This is done by
combining the latest results for the CMS experimental sensitivities based on
full simulation studies with state-of-the-art theoretical predictions of MSSM
Higgs-boson properties. The results are interpreted in MSSM benchmark scenarios
in terms of the parameters tan_beta and the Higgs-boson mass scale, M_A. We
study the dependence of the 5 sigma discovery contours in the M_A-tan_beta
plane on variations of the other supersymmetric parameters. The largest effects
arise from a change in the higgsino mass parameter mu, which enters both via
higher-order radiative corrections and via the kinematics of Higgs decays into
supersymmetric particles. While the variation of $\mu$ can shift the
prospective discovery reach (and correspondingly the ``LHC wedge'' region) by
about Delta tan_beta = 10, we find that the discovery reach is rather stable
with respect to the impact of other supersymmetric parameters. Within the
discovery region we analyze the accuracy with which the masses of the heavy
neutral Higgs bosons can be determined. We find that an accuracy of 1-4% should
be achievable, which could make it possible in favourable regions of the MSSM
parameter space to experimentally resolve the signals of the two heavy MSSM
Higgs bosons at the LHC.
|
White dwarf masses derived from planetary nebulae modelling | We compare the mass distribution of central stars of planetary nebulae (CSPN)
with those of their progeny, white dwarfs (WD). We use a dynamical method to
measure masses with an uncertainty of 0.02 M$_\odot$. The CSPN mass
distribution is sharply peaked at $0.61 \rm M_\odot$. The WD distribution peaks
at lower masses ($0.58 \rm M_\odot$) and shows a much broader range of masses.
Some of the difference can be explained if the early post-AGB evolution is
faster than predicted by the Bl\"ocker tracks. Between 30 and 50 per cent of WD
may avoid the PN phase because of too low mass. However, the discrepancy cannot
be fully resolved and WD mass distributions may have been broadened by
observational or model uncertainties.
|
Uniqueness theorems for Cauchy integrals | If $\mu$ is a finite complex measure in the complex plane $\C$ we denote by
$C^\mu$ its Cauchy integral defined in the sense of principal value. The
measure $\mu$ is called reflectionless if it is continuous (has no atoms) and
$C^\mu=0$ at $\mu$-almost every point. We show that if $\mu$ is reflectionless
and its Cauchy maximal function $C^\mu_*$ is summable with respect to $|\mu|$
then $\mu$ is trivial. An example of a reflectionless measure whose maximal
function belongs to the "weak" $L^1$ is also constructed, proving that the
above result is sharp in its scale. We also give a partial geometric
description of the set of reflectionless measures on the line and discuss
connections of our results with the notion of sets of finite perimeter in the
sense of De Giorgi.
|
On the number of moduli of plane sextics with six cusps | Let S be the variety of irreducible sextics with six cusps as singularities.
Let W be one of irreducible components of W. Denoting by M_4 the space of
moduli of smooth curves of genus 4, the moduli map of W is the rational map
from W to M_4 sending the general point of W, corresponding to a plane curve D,
to the point of M_4 parametrizing the normalization curve of D. The number of
moduli of W is, by definition the dimension of the image of W with respect to
the moduli map. We know that this number is at most equal to seven. In this
paper we prove that both irreducible components of S have number of moduli
exactly equal to seven.
|
Algorithm for anisotropic diffusion in hydrogen-bonded networks | In this paper I describe a specialized algorithm for anisotropic diffusion
determined by a field of transition rates. The algorithm can be used to
describe some interesting forms of diffusion that occur in the study of proton
motion in a network of hydrogen bonds. The algorithm produces data that require
a nonstandard method of spectral analysis which is also developed here.
Finally, I apply the algorithm to a simple specific example.
|
Temporal Evolution of Step-Edge Fluctuations Under Electromigration
Conditions | The temporal evolution of step-edge fluctuations under electromigration
conditions is analysed using a continuum Langevin model. If the
electromigration driving force acts in the step up/down direction, and
step-edge diffusion is the dominant mass-transport mechanism, we find that
significant deviations from the usual $t^{1/4}$ scaling of the terrace-width
correlation function occurs for a critical time $\tau$ which is dependent upon
the three energy scales in the problem: $k_{B}T$, the step stiffness, $\gamma$,
and the bias associated with adatom hopping under the influence of an
electromigration force, $\pm \Delta U$. For ($t < \tau$), the correlation
function evolves as a superposition of $t^{1/4}$ and $t^{3/4}$ power laws. For
$t \ge \tau$ a closed form expression can be derived. This behavior is
confirmed by a Monte-Carlo simulation using a discrete model of the step
dynamics. It is proposed that the magnitude of the electromigration force
acting upon an atom at a step-edge can by estimated by a careful analysis of
the statistical properties of step-edge fluctuations on the appropriate
time-scale.
|
Renormgroup origin and analysis of Split Higgsino scenario | We present a renormalization group motivation of scale hierarchies in SUSY
SU(5) model. The Split Higgsino scanrio with a high scale of the SUSY breaking
is considered in detail. Its manifestations in experiments are discussed.
|
Probing dark energy with steerable wavelets through correlation of WMAP
and NVSS local morphological measures | Using local morphological measures on the sphere defined through a steerable
wavelet analysis, we examine the three-year WMAP and the NVSS data for
correlation induced by the integrated Sachs-Wolfe (ISW) effect. The steerable
wavelet constructed from the second derivative of a Gaussian allows one to
define three local morphological measures, namely the signed-intensity,
orientation and elongation of local features. Detections of correlation between
the WMAP and NVSS data are made with each of these morphological measures. The
most significant detection is obtained in the correlation of the
signed-intensity of local features at a significance of 99.9%. By inspecting
signed-intensity sky maps, it is possible for the first time to see the
correlation between the WMAP and NVSS data by eye. Foreground contamination and
instrumental systematics in the WMAP data are ruled out as the source of all
significant detections of correlation. Our results provide new insight on the
ISW effect by probing the morphological nature of the correlation induced
between the cosmic microwave background and large scale structure of the
Universe. Given the current constraints on the flatness of the Universe, our
detection of the ISW effect again provides direct and independent evidence for
dark energy. Moreover, this new morphological analysis may be used in future to
help us to better understand the nature of dark energy.
|
Electromagnetic structure and weak decay of meson K in a light-front
QCD-inspired | The kaon electromagnetic (e.m.) form factor is reviewed considering a
light-front constituent quark model. In this approach, it is discussed the
relevance of the quark-antiquark pair terms for the full covariance of the e.m.
current. It is also verified, by considering a QCD dynamical model, that a good
agreement with experimental data can be obtained for the kaon weak decay
constant once a probability of about 80% of the valence component is taken into
account.
|
Black hole puncture initial data with realistic gravitational wave
content | We present improved post-Newtonian-inspired initial data for non-spinning
black-hole binaries, suitable for numerical evolution with punctures. We
revisit the work of Tichy et al. [W. Tichy, B. Bruegmann, M. Campanelli, and P.
Diener, Phys. Rev. D 67, 064008 (2003)], explicitly calculating the remaining
integral terms. These terms improve accuracy in the far zone and, for the first
time, include realistic gravitational waves in the initial data. We investigate
the behavior of these data both at the center of mass and in the far zone,
demonstrating agreement of the transverse-traceless parts of the new metric
with quadrupole-approximation waveforms. These data can be used for numerical
evolutions, enabling a direct connection between the merger waveforms and the
post-Newtonian inspiral waveforms.
|
Measurement of the Decay Constant $f_D{_S^+}$ using $D_S^+ --> ell^+ nu | We measure the decay constant fDs using the Ds -> l+ nu channel, where the l+
designates either a mu+ or a tau+, when the tau+ -> pi+ nu. Using both
measurements we find fDs = 274 +-13 +- 7 MeV. Combining with our previous
determination of fD+, we compute the ratio fDs/fD+ = 1.23 +- 0.11 +- 0.04. We
compare with theoretical estimates.
|
The $e^+ e^-\to K^+ K^- \pi^+\pi^-$, $K^+ K^- \pi^0\pi^0$ and $K^+ K^-
K^+ K^-$ Cross Sections Measured with Initial-State Radiation | We study the processes $e^+ e^-\to K^+ K^- \pi^+\pi^-\gamma$,
$K^+K^-\pi^0\pi^0\gamma$ and $K^+ K^- K^+ K^-\gamma$, where the photon is
radiated from the initial state. About 34600, 4400 and 2300 fully reconstructed
events, respectively, are selected from 232 \invfb of \babar data. The
invariant mass of the hadronic final state defines the effective \epem
center-of-mass energy, so that the $K^+ K^- \pi^+\pi^-\gamma$ data can be
compared with direct measurements of the $e^+ e^-\to K^+K^- \pipi$ reaction; no
direct measurements exist for the $e^+ e^-\to K^+ K^- \pi^0\pi^0$ or $\epem\to
K^+ K^- K^+ K^-$ reactions. Studying the structure of these events, we find
contributions from a number of intermediate states, and we extract their cross
sections where possible. In particular, we isolate the contribution from $e^+
e^-\to\phi(1020) f_{0}(980)$ and study its structure near threshold. In the
charmonium region, we observe the $J/\psi$ in all three final states and
several intermediate states, as well as the $\psi(2S)$ in some modes, and
measure the corresponding branching fractions. We see no signal for the Y(4260)
and obtain an upper limit of
$\BR_{Y(4260)\to\phi\pi^+\pi^-}\cdot\Gamma^{Y}_{ee}<0.4 \ev$ at 90% C.L.
|
Orthogonality criterion for banishing hydrino states from standard
quantum mechanics | Orthogonality criterion is used to shown in a very simple and general way
that anomalous bound-state solutions for the Coulomb potential (hydrino states)
do not exist as bona fide solutions of the Schr\"{o}dinger, Klein-Gordon and
Dirac equations.
|
Detecting and Characterizing Planetary Systems with Transit Timing | In the coming decades, research in extrasolar planets aims to advance two
goals: 1) detecting and characterizing low-mass planets increasingly similar to
the Earth, and 2) improving our understanding of planet formation. We present a
new planet detection method that is capable of making large advances towards
both of these objectives and describe a modest network of telescopes that is
able to make the requisite observations. In a system where a known planet
transits its host star, a second planet in that system will cause the time
between transits to vary. These transit timing variations can be used to infer
the orbital elements and mass of the perturbing planet even if it has a mass
that is smaller than the mass of the Earth. This detection technique
complements other techniques because it is most sensitive in mean-motion
resonances where, due to degeneracies, other techniques have reduced
sensitivity. Small ground-based observatories have already exceeded the
photometric precision necessary to detect sub-Earth mass planets. However, TTV
planet searches are currently limited by the relatively small number of
high-precision transit data and insufficient observing time on existing
telescopes. These issues will be compounded as the number of known transiting
planets suitable for TTV study will increase substantially in the near future.
A relatively modest investment in a ground-based network of small ($\sim 0.5
{\rm m}$ telescopes could provide the needed coverage and so dramatically
increase the effectiveness of transit timing observations.
|
d-wave superconductivity from electron-phonon interactions | I examine electron-phonon mediated superconductivity in the intermediate
coupling and phonon frequency regime of the quasi-2D Holstein model. I use an
extended Migdal-Eliashberg theory which includes vertex corrections and spatial
fluctuations. I find a d-wave superconducting state that is unique close to
half-filling. The order parameter undergoes a transition to s-wave
superconductivity on increasing filling. I explain how the inclusion of both
vertex corrections and spatial fluctuations is essential for the prediction of
a d-wave order parameter. I then discuss the effects of a large Coulomb
pseudopotential on the superconductivity (such as is found in contemporary
superconducting materials like the cuprates), which results in the destruction
of the s-wave states, while leaving the d-wave states unmodified.
|
A Finite Element framework for computation of protein normal modes and
mechanical response | A coarse-grained computational procedure based on the Finite Element Method
is proposed to calculate the normal modes and mechanical response of proteins
and their supramolecular assemblies. Motivated by the elastic network model,
proteins are modeled as homogeneous isotropic elastic solids with volume
defined by their solvent-excluded surface. The discretized Finite Element
representation is obtained using a surface simplification algorithm that
facilitates the generation of models of arbitrary prescribed spatial
resolution. The procedure is applied to compute the normal modes of a mutant of
T4 phage lysozyme and of filamentous actin, as well as the critical Euler
buckling load of the latter when subject to axial compression. Results compare
favorably with all-atom normal mode analysis, the Rotation Translation Blocks
procedure, and experiment. The proposed methodology establishes a computational
framework for the calculation of protein mechanical response that facilitates
the incorporation of specific atomic-level interactions into the model,
including aqueous-electrolyte-mediated electrostatic effects. The procedure is
equally applicable to proteins with known atomic coordinates as it is to
electron density maps of proteins, protein complexes, and supramolecular
assemblies of unknown atomic structure.
|
Reply to 'Comment on 'Heavy element production in inhomogeneous big bang
nucleosynthesis'' | This is a reply report to astro-ph/0604264. We studied heavy element
production in high baryon density region in early universe astro-ph/0507439.
However it is claimed in astro-ph/0604264 that small scale but high baryon
density region contradicts observations for the light element abundance or in
order not to contradict to observations high density region must be so small
that it cannot affect the present heavy element abundance.
In this paper we study big bang nucleosynthesis in high baryon density region
and show that in certain parameter spaces it is possible to produce enough
amount of heavy element without contradiction to CMB and light element
observations.
|
Sum-over-states vs quasiparticle pictures of coherent correlation
spectroscopy of excitons in semiconductors; femtosecond analogues of
multidimensional NMR | Two-dimensional correlation spectroscopy (2DCS) based on the nonlinear
optical response of excitons to sequences of ultrafast pulses, has the
potential to provide some unique insights into carrier dynamics in
semiconductors. The most prominent feature of 2DCS, cross peaks, can best be
understood using a sum-over-states picture involving the many-body eigenstates.
However, the optical response of semiconductors is usually calculated by
solving truncated equations of motion for dynamical variables, which result in
a quasiparticle picture. In this work we derive Green's function expressions
for the four wave mixing signals generated in various phase-matching directions
and use them to establish the connection between the two pictures. The formal
connection with Frenkel excitons (hard-core bosons) and vibrational excitons
(soft-core bosons) is pointed out.
|
Are constant loop widths an artifact of the background and the spatial
resolution? | We study the effect of the coronal background in the determination of the
diameter of EUV loops, and we analyze the suitability of the procedure followed
in a previous paper (L\'opez Fuentes, Klimchuk & D\'emoulin 2006) for
characterizing their expansion properties. For the analysis we create different
synthetic loops and we place them on real backgrounds from data obtained with
the Transition Region and Coronal Explorer (\textit{TRACE}). We apply to these
loops the same procedure followed in our previous works, and we compare the
results with real loop observations. We demonstrate that the procedure allows
us to distinguish constant width loops from loops that expand appreciably with
height, as predicted by simple force-free field models. This holds even for
loops near the resolution limit. The procedure can easily determine when loops
are below resolution limit and therefore not reliably measured. We find that
small-scale variations in the measured loop width are likely due to
imperfections in the background subtraction. The greatest errors occur in
especially narrow loops and in places where the background is especially bright
relative to the loop. We stress, however, that these effects do not impact the
ability to measure large-scale variations. The result that observed loops do
not expand systematically with height is robust.
|
Polarizations of J/psi and psi(2S) Mesons Produced in ppbar Collisions
at 1.96 TeV | We have measured the polarizations of $\jpsi$ and $\psiprime$ mesons as
functions of their transverse momentum $\pt$ when they are produced promptly in
the rapidity range $|y|<0.6$ with $\pt \geq 5 \pgev$. The analysis is performed
using a data sample with an integrated luminosity of about $800 \ipb$ collected
by the CDF II detector. For both vector mesons, we find that the polarizations
become increasingly longitudinal as $\pt$ increases from 5 to $30 \pgev$. These
results are compared to the predictions of nonrelativistic quantum
chromodynamics and other contemporary models. The effective polarizations of
$\jpsi$ and $\psiprime$ mesons from $B$-hadron decays are also reported.
|
A measure of the non-Gaussian character of a quantum state | We address the issue of quantifying the non-Gaussian character of a bosonic
quantum state and introduce a non-Gaussianity measure based on the
Hilbert-Schmidt distance between the state under examination and a reference
Gaussian state. We analyze in details the properties of the proposed measure
and exploit it to evaluate the non-Gaussianity of some relevant single- and
multi-mode quantum states. The evolution of non-Gaussianity is also analyzed
for quantum states undergoing the processes of Gaussification by loss and
de-Gaussification by photon-subtraction. The suggested measure is easily
computable for any state of a bosonic system and allows to define a
corresponding measure for the non-Gaussian character of a quantum operation.
|
Skew-Hadamard matrices of orders 188 and 388 exist | We construct several difference families on cyclic groups of orders 47 and
97, and use them to construct skew-Hadamard matrices of orders 188 and 388.
Such difference families and matrices are constructed here for the first time.
The matrices are constructed by using the Goethals-Seidel array.
|
Quantum engineering of photon states with entangled atomic ensembles | We propose and analyze a new method to produce single and entangled photons
which does not require cavities. It relies on the collective enhancement of
light emission as a consequence of the presence of entanglement in atomic
ensembles. Light emission is triggered by a laser pulse, and therefore our
scheme is deterministic. Furthermore, it allows one to produce a variety of
photonic entangled states by first preparing certain atomic states using simple
sequences of quantum gates. We analyze the feasibility of our scheme, and
particularize it to: ions in linear traps, atoms in optical lattices, and in
cells at room temperature.
|
Direct photons and dileptons via color dipoles | Drell-Yan dilepton pair production and inclusive direct photon production can
be described within a unified framework in the color dipole approach. The
inclusion of non-perturbative primordial transverse momenta and DGLAP evolution
is studied. We successfully describe data for dilepton spectra from 800-GeV pp
collisions, inclusive direct photon spectra for pp collisions at RHIC energies
$\sqrt{s}=200$ GeV, and for $p\bar{p}$ collisions at Tevatron energies
$\sqrt{s}=1.8$ TeV, in a formalism that is free from any extra parameters.
|
Mapping the Youngest Galaxies to Redshift One | We describe results of a narrow band search for ultra-strong emission line
galaxies (USELs) with EW(H beta) > 30 A. 542 candidate galaxies are found in a
half square degree survey using two ~100 Angstrom 8150 A and 9140 A filters
with Subaru/SuprimeCam. Followup spectroscopy for randomly selected objects in
the sample with KeckII/DEIMOS shows they consist of [OIII] 5007, [OII] 3727,
and H alpha selected strong-emission line galaxies at intermediate redshifts (z
< 1), and Ly alpha emitting galaxies at high-redshift (z >> 5). We determine
the H beta luminosity functions and the star formation density of the USELs,
which is 5-10% of the value found from ultraviolet continuum objects at z=0-1,
suggesting they correspond to a major epoch in galaxy formation at these
redshifts. Many USELs show the temperature-sensitive [OIII] 4363 auroral lines
and about a dozen have oxygen abundances characteristic of eXtremely Metal Poor
Galaxies (XMPGs). These XMPGs are the most distant known today. Our high yield
rate of XMPGs suggests this is a powerful method for finding such populations.
The lowest metallicity measured in our sample is 12+log(O/H) = 7.06
(6.78-7.44), close to the minimum metallicity found in local galaxies. The
luminosities, metallicities and star formation rates of USELs are consistent
with the strong emitters being start-up intermediate mass galaxies and suggest
that galaxies are still forming in relatively chemically pristine sites at z <
1.
|
On the HOMFLY and Tutte polynomials | A celebrated result of F. Jaeger states that the Tutte polynomial of a planar
graph is determined by the HOMFLY polynomial of an associated link. Here we are
interested in the converse of this result. We consider the question `to what
extent does the Tutte polynomial determine the HOMFLY polynomial of any knot?'
We show that the HOMFLY polynomial of a knot is determined by Tutte polynomials
of plane graphs associated to the knot.
|
Discovery of extreme asymmetry in the debris disk surrounding HD 15115 | We report the first scattered light detection of a dusty debris disk
surrounding the F2V star HD 15115 using the Hubble Space Telescope in the
optical, and Keck adaptive optics in the near-infrared. The most remarkable
property of the HD 15115 disk relative to other debris disks is its extreme
length asymmetry. The east side of the disk is detected to ~315 AU radius,
whereas the west side of the disk has radius >550 AU. We find a blue optical to
near-infrared scattered light color relative to the star that indicates grain
scattering properties similar to the AU Mic debris disk. The existence of a
large debris disk surrounding HD 15115 adds further evidence for membership in
the Beta Pic moving group, which was previously argued based on kinematics
alone. Here we hypothesize that the extreme disk asymmetry is due to dynamical
perturbations from HIP 12545, an M star 0.5 degrees (0.38 pc) east of HD 15115
that shares a common proper motion vector, heliocentric distance, galactic
space velocity, and age.
|
The Mathematical Universe | I explore physics implications of the External Reality Hypothesis (ERH) that
there exists an external physical reality completely independent of us humans.
I argue that with a sufficiently broad definition of mathematics, it implies
the Mathematical Universe Hypothesis (MUH) that our physical world is an
abstract mathematical structure. I discuss various implications of the ERH and
MUH, ranging from standard physics topics like symmetries, irreducible
representations, units, free parameters, randomness and initial conditions to
broader issues like consciousness, parallel universes and Godel incompleteness.
I hypothesize that only computable and decidable (in Godel's sense) structures
exist, which alleviates the cosmological measure problem and help explain why
our physical laws appear so simple. I also comment on the intimate relation
between mathematical structures, computations, simulations and physical
systems.
|
Testing String Theory with CMB | Future detection/non-detection of tensor modes from inflation in CMB
observations presents a unique way to test certain features of string theory.
Current limit on the ratio of tensor to scalar perturbations, r=T/S, is r <
0.3, future detection may take place for r > 10^{-2}-10^{-3}. At present all
known string theory inflation models predict tensor modes well below the level
of detection. Therefore a possible experimental discovery of tensor modes may
present a challenge to string cosmology.
The strongest bound on r in string inflation follows from the observation
that in most of the models based on the KKLT construction, the value of the
Hubble constant H during inflation must be smaller than the gravitino mass. For
the gravitino mass in the usual range, m_{3/2} < O(1) TeV, this leads to an
extremely strong bound r < 10^{-24}. A discovery of tensor perturbations with r
> 10^{-3} would imply that the gravitinos in this class of models are
superheavy, m_{3/2} > 10^{13} GeV. This would have important implications for
particle phenomenology based on string theory.
|
Behavioral response to strong aversive stimuli: A neurodynamical model | In this paper a theoretical model of functioning of a neural circuit during a
behavioral response has been proposed. A neural circuit can be thought of as a
directed multigraph whose each vertex is a neuron and each edge is a synapse.
It has been assumed in this paper that the behavior of such circuits is
manifested through the collective behavior of neurons belonging to that
circuit. Behavioral information of each neuron is contained in the coefficients
of the fast Fourier transform (FFT) over the output spike train. Those
coefficients form a vector in a multidimensional vector space. Behavioral
dynamics of a neuronal network in response to strong aversive stimuli has been
studied in a vector space in which a suitable pseudometric has been defined.
The neurodynamical model of network behavior has been formulated in terms of
existing memory, synaptic plasticity and feelings. The model has an analogy in
classical electrostatics, by which the notion of force and potential energy has
been introduced. Since the model takes input from each neuron in a network and
produces a behavior as the output, it would be extremely difficult or may even
be impossible to implement. But with the help of the model a possible
explanation for an hitherto unexplained neurological observation in human brain
has been offered. The model is compatible with a recent model of sequential
behavioral dynamics. The model is based on electrophysiology, but its relevance
to hemodynamics has been outlined.
|
Quivers with potentials and their representations I: Mutations | We study quivers with relations given by non-commutative analogs of Jacobian
ideals in the complete path algebra. This framework allows us to give a
representation-theoretic interpretation of quiver mutations at arbitrary
vertices. This gives a far-reaching generalization of
Bernstein-Gelfand-Ponomarev reflection functors. The motivations for this work
come from several sources: superpotentials in physics, Calabi-Yau algebras,
cluster algebras.
|
Coherent macroscopic quantum tunneling in boson-fermion mixtures | We show that the cold atom systems of simultaneously trapped Bose-Einstein
condensates (BEC's) and quantum degenerate fermionic atoms provide promising
laboratories for the study of macroscopic quantum tunneling. Our theoretical
studies reveal that the spatial extent of a small trapped BEC immersed in a
Fermi sea can tunnel and coherently oscillate between the values of the
separated and mixed configurations (the phases of the phase separation
transition of BEC-fermion systems). We evaluate the period, amplitude and
dissipation rate for $^{23}$Na and $^{40}$K-atoms and we discuss the
experimental prospects for observing this phenomenon.
|
Efficiency of thin film photocells | We propose a new concept for the design of high-efficiency photocells based
on ultra-thin (submicron) semiconductor films of controlled thickness. Using a
microscopic model of a thin dielectric layer interacting with incident
electromagnetic radiation we evaluate the efficiency of conversion of solar
radiation into the electric power. We determine the optimal range of parameters
which maximize the efficiency of such photovoltaic element.
|
Galactic Wind Signatures around High Redshift Galaxies | We carry out cosmological chemodynamical simulations with different strengths
of supernova (SN) feedback and study how galactic winds from star-forming
galaxies affect the features of hydrogen (HI) and metal (CIV and OVI)
absorption systems in the intergalactic medium at high redshift. We find that
the outflows tend to escape to low density regions, and hardly affect the dense
filaments visible in HI absorption. As a result, the strength of HI absorption
near galaxies is not reduced by galactic winds, but even slightly increases. We
also find that a lack of HI absorption for lines of sight (LOS) close to
galaxies, as found by Adelberger et al., can be created by hot gas around the
galaxies induced by accretion shock heating. In contrast to HI, metal
absorption systems are sensitive to the presence of winds. The models without
feedback can produce the strong CIV and OVI absorption lines in LOS within 50
kpc from galaxies, while strong SN feedback is capable of creating strong CIV
and OVI lines out to about twice that distance. We also analyze the mean
transmissivity of HI, CIV, and OVI within 1 h$^{-1}$ Mpc from star-forming
galaxies. The probability distribution of the transmissivity of HI is
independent of the strength of SN feedback, but strong feedback produces LOS
with lower transmissivity of metal lines. Additionally, strong feedback can
produce strong OVI lines even in cases where HI absorption is weak. We conclude
that OVI is probably the best tracer for galactic winds at high redshift.
|
`St\"uckelberg interferometry' with ultracold molecules | We report on the realization of a time-domain `St\"uckelberg interferometer',
which is based on the internal state structure of ultracold Feshbach molecules.
Two subsequent passages through a weak avoided crossing between two different
orbital angular momentum states in combination with a variable hold time lead
to high-contrast population oscillations. This allows for a precise
determination of the energy difference between the two molecular states. We
demonstrate a high degree of control over the interferometer dynamics. The
interferometric scheme provides new possibilities for precision measurements
with ultracold molecules.
|
An integral field spectroscopic survey for high redshift damped
Lyman-alpha galaxies | We search for galaxy counterparts to damped Lyman-alpha absorbers (DLAs) at
z>2 towards nine quasars, which have 14 DLAs and 8 sub-DLAs in their spectra.
We use integral field spectroscopy to search for Ly-alpha emission line objects
at the redshifts of the absorption systems. Besides recovering two previously
confirmed objects, we find six statistically significant candidate Ly-alpha
emission line objects. The candidates are identified as having wavelengths
close to the DLA line where the background quasar emission is absorbed. In
comparison with the six currently known Ly-alpha emitting DLA galaxies the
candidates have similar line fluxes and line widths, while velocity offsets
between the emission lines and systemic DLA redshifts are larger. The impact
parameters are larger than 10 kpc, and lower column density systems are found
at larger impact parameters. Assuming that a single gas cloud extends from the
QSO line of sight to the location of the candidate emission line, we find that
the average candidate DLA galaxy is surrounded by neutral gas with an
exponential scale length of ~5 kpc.
|
Exploring the Variable Sky with the Sloan Digital Sky Survey | We quantify the variability of faint unresolved optical sources using a
catalog based on multiple SDSS imaging observations. The catalog covers SDSS
Stripe 82, and contains 58 million photometric observations in the SDSS ugriz
system for 1.4 million unresolved sources. In each photometric bandpass we
compute various low-order lightcurve statistics and use them to select and
study variable sources. We find that 2% of unresolved optical sources brighter
than g=20.5 appear variable at the 0.05 mag level (rms) simultaneously in the g
and r bands. The majority (2/3) of these variable sources are low-redshift (<2)
quasars, although they represent only 2% of all sources in the adopted
flux-limited sample. We find that at least 90% of quasars are variable at the
0.03 mag level (rms) and confirm that variability is as good a method for
finding low-redshift quasars as is the UV excess color selection (at high
Galactic latitudes). We analyze the distribution of lightcurve skewness for
quasars and find that is centered on zero. We find that about 1/4 of the
variable stars are RR Lyrae stars, and that only 0.5% of stars from the main
stellar locus are variable at the 0.05 mag level. The distribution of
lightcurve skewness in the g-r vs. u-g color-color diagram on the main stellar
locus is found to be bimodal (with one mode consistent with Algol-like
behavior). Using over six hundred RR Lyrae stars, we demonstrate rich halo
substructure out to distances of 100 kpc. We extrapolate these results to
expected performance by the Large Synoptic Survey Telescope and estimate that
it will obtain well-sampled 2% accurate, multi-color lightcurves for ~2 million
low-redshift quasars, and will discover at least 50 million variable stars.
|
Necessary optimality conditions for the calculus of variations on time
scales | We study more general variational problems on time scales. Previous results
are generalized by proving necessary optimality conditions for (i) variational
problems involving delta derivatives of more than the first order, and (ii)
problems of the calculus of variations with delta-differential side conditions
(Lagrange problem of the calculus of variations on time scales).
|
The Boundary Conditions of the Heliosphere: Photoionization Models
Constrained by Interstellar and In Situ Data | The boundary conditions of the heliosphere are set by the ionization, density
and composition of inflowing interstellar matter. Constraining the properties
of the Local Interstellar Cloud (LIC) at the heliosphere requires radiative
transfer ionization models. We model the background interstellar radiation
field using observed stellar FUV and EUV emission and the diffuse soft X-ray
background. We also model the emission from the boundary between the LIC and
the hot Local Bubble (LB) plasma, assuming that the cloud is evaporating
because of thermal conduction. We create a grid of models covering a plausible
range of LIC and LB properties, and use the modeled radiation field as input to
radiative transfer/thermal equilibrium calculations using the Cloudy code. Data
from in situ observations of He^O, pickup ions and anomalous cosmic rays in the
heliosphere, and absorption line measurements towards epsilon CMa were used to
constrain the input parameters. A restricted range of assumed LIC HI column
densities and LB plasma temperatures produce models that match all the
observational constraints. The relative weakness of the constraints on N(HI)
and T_h contrast with the narrow limits predicted for the H^O and electron
density in the LIC at the Sun, n(H^0) = 0.19 - 0.20 cm^-3, and n(e) = 0.07 +/-
0.01 cm^-3. Derived abundances are mostly typical for low density gas, with
sub-solar Mg, Si and Fe, possibly subsolar O and N, and S about solar; however
C is supersolar. The interstellar gas at the Sun is warm, low density, and
partially ionized, with n(H) = 0.23 - 0.27 cm^-3, T = 6300 K, X(H^+) ~ 0.2, and
X(He^+) ~ 0.4. These results appear to be robust since acceptable models are
found for substantially different input radiation fields. Our results favor low
values for the reference solar abundances for the LIC composition.
|
Collective excitations in a magnetically doped quantized Hall
ferromagnet | A theory of collective states in a magnetically quantized two-dimensional
electron gas (2DEG) with half-filled Landau level (quantized Hall ferromagnet)
in the presence of magnetic 3d impurities is developed. The spectrum of bound
and delocalized spin-excitons as well as the renormalization of Zeeman
splitting of the impurity 3d levels due to the indirect exchange interaction
with the 2DEG are studied for the specific case of n-type GaAs doped with Mn
where the Lande` g-factors of impurity and 2DEG have opposite signs. If the
sign of the 2DEG g-factor is changed due to external influences, then impurity
related transitions to new ground state phases, presenting various spin-flip
and skyrmion-like textures, are possible. Conditions for existence of these
phases are discussed. PACS: 73.43.Lp, 73.21.Fg, 72.15.Rn
|
Long Gamma-Ray Burst Progenitors: Boundary Conditions and Binary Models | The observed association of Long Gamma-Ray Bursts (LGRBs) with peculiar Type
Ic supernovae gives support to Woosley`s collapsar/hypernova model, in which
the GRB is produced by the collapse of the rapidly rotating core of a massive
star to a black hole. The association of LGRBs with small star-forming galaxies
suggests low-metallicity to be a condition for a massive star to evolve to the
collapsar stage. Both completely-mixed single star models and binary star
models are possible. In binary models the progenitor of the GRB is a massive
helium star with a close companion. We find that tidal synchronization during
core-helium burning is reached on a short timescale (less than a few
millennia). However, the strong core-envelope coupling in the subsequent
evolutionary stages is likely to rule out helium stars with main-sequence
companions as progenitors of hypernovae/GRBs. On the other hand, helium stars
in close binaries with a neutron-star or black-hole companion can, despite the
strong core-envelope coupling in the post-helium burning phase, retain
sufficient core angular momentum to produce a hypernova/GRB.
|
Multiscale model of electronic behavior and localization in stretched
dry DNA | When the DNA double helix is subjected to external forces it can stretch
elastically to elongations reaching 100% of its natural length. These
distortions, imposed at the mesoscopic or macroscopic scales, have a dramatic
effect on electronic properties at the atomic scale and on electrical transport
along DNA. Accordingly, a multiscale approach is necessary to capture the
electronic behavior of the stretched DNA helix. To construct such a model, we
begin with accurate density-functional-theory calculations for electronic
states in DNA bases and base pairs in various relative configurations
encountered in the equilibrium and stretched forms. These results are
complemented by semi-empirical quantum mechanical calculations for the states
of a small size [18 base pair poly(CG)-poly(CG)] dry, neutral DNA sequence,
using previously published models for stretched DNA. The calculated electronic
states are then used to parametrize an effective tight-binding model that can
describe electron hopping in the presence of environmental effects, such as the
presence of stray water molecules on the backbone or structural features of the
substrate. These effects introduce disorder in the model hamiltonian which
leads to electron localization. The localization length is smaller by several
orders of magnitude in stretched DNA relative to that in the unstretched
structure.
|
Ample subvarieties and rationally connected fibrations | Under some positivity assumptions, extension properties of rationally
connected fibrations from a submanifold to its ambient variety are studied.
Given a family of rational curves on a complex projective manifold X inducing a
covering family on a submanifold Y with ample normal bundle in X, the main
results relate, under suitable conditions, the associated rational connected
fiber structures on X and on Y. Applications of these results include an
extension theorem for Mori contractions of fiber type and a classification
theorem in the case Y has a structure of projective bundle or quadric
fibration.
|
Bounds for Multiplicities of Unitary Representations of Cohomological
Type in Spaces of Cusp Forms | Let $\Goo$ be a semisimple real Lie group with unitary dual $\Ghat$. The goal
of this note is to produce new upper bounds for the multiplicities with which
representations $\pi \in \Ghat$ of cohomological type appear in certain spaces
of cusp forms on $\Goo$.
|
Decoherence of Quantum-Enhanced Timing Accuracy | Quantum enhancement of optical pulse timing accuracy is investigated in the
Heisenberg picture. Effects of optical loss, group-velocity dispersion, and
Kerr nonlinearity on the position and momentum of an optical pulse are studied
via Heisenberg equations of motion. Using the developed formalism, the impact
of decoherence by optical loss on the use of adiabatic soliton control for
beating the timing standard quantum limit [Tsang, Phys. Rev. Lett. 97, 023902
(2006)] is analyzed theoretically and numerically. The analysis shows that an
appreciable enhancement can be achieved using current technology, despite an
increase in timing jitter mainly due to the Gordon-Haus effect. The decoherence
effect of optical loss on the transmission of quantum-enhanced timing
information is also studied, in order to identify situations in which the
enhancement is able to survive.
|
Stock market return distributions: from past to present | We show that recent stock market fluctuations are characterized by the
cumulative distributions whose tails on short, minute time scales exhibit power
scaling with the scaling index alpha > 3 and this index tends to increase
quickly with decreasing sampling frequency. Our study is based on
high-frequency recordings of the S&P500, DAX and WIG20 indices over the
interval May 2004 - May 2006. Our findings suggest that dynamics of the
contemporary market may differ from the one observed in the past. This effect
indicates a constantly increasing efficiency of world markets.
|
Global well-posedness and scattering for the energy-critical, defocusing
Hartree equation for radial data | We consider the defocusing, $\dot{H}^1$-critical Hartree equation for the
radial data in all dimensions $(n\geq 5)$. We show the global well-posedness
and scattering results in the energy space. The new ingredient in this paper is
that we first take advantage of the term $\displaystyle - \int_{I}\int_{|x|\leq
A|I|^{1/2}}|u|^{2}\Delta \Big(\frac{1}{|x|}\Big)dxdt$ in the localized Morawetz
identity to rule out the possibility of energy concentration, instead of the
classical Morawetz estimate dependent of the nonlinearity.
|
String inspired explanation for the super-acceleration of our universe | We investigate the effect of the bulk content in the general Gauss-Bonnet
braneworld on the evolution of the universe. We find that the Gauss-Bonnet term
and the combination of the dark radiation and the matter content of the bulk
play a crucial role in the universe evolution. We show that our model can
describe the super-acceleration of our universe with the equation of state of
the effective dark energy in agreement with observations.
|
Topological Free Entropy Dimension of in Unital C^*-algebras | The notion of topological free entropy dimension of $n-$tuples of elements in
a unital C$^*$ algebra was introduced by Voiculescu. In the paper, we compute
topological free entropy dimension of one self-adjoint element and topological
orbit dimension of one self-adjoint element in a unital C$^*$ algebra.
Moreover, we calculate the values of topological free entropy dimensions of
families of generators of some unital C$^*$ algebras (for example: irrational
rotation C$^*$ algebras or minimal tensor product of two reduced C$^*$ algebras
of free groups).
|
J/psi Production in an Equilibrating Partonic System | Any color singlet or octet ccbar pair is created at short distances and then
expands to a full size of J/psi. Such a dynamical evolution process is included
here in calculations for the J/psi number distribution as a function of
transverse momentum and rapidity in central Au-Au collisions at both RHIC and
LHC energies. The ccbar pairs are produced in the initial collision and in the
partonic system during the prethermal and thermal stages through the partonic
channels ab to ccbar [{2S+1}L_J] and ab to ccbar [{2S+1}L_J]x, and then they
dissociate in the latter two stages. Dissociation of ccbar in the medium occurs
via two reactions: (a) color singlet ccbar plus a gluon turns to color octet
ccbar, (b) color octet ccbar plus a gluon persists as color octet. There are
modest yields of ccbar in the prethermal stage at RHIC energy and through the
reactions ab to ccbar [{2S+1}L_J] at LHC energy for partons with large average
momentum in the prethermal stage at both collider energies and in the thermal
stage at LHC energy. Production from the partonic system competes with the
suppression of the initial yield in the deconfined medium. Consequently, a
bulge within -1.5<y<1.5 has been found for the J/psi number distribution and
the ratio of J/psi number distributions for Au-Au collisions to nucleon-nucleon
collisions. This bulge is caused by the partonic system and is thus an
indicator of a deconfined partonic medium. Based on this result we suggest the
rapidity region worth measuring in future experiments at RHIC and LHC to be
-3<y<3.
|
Reduced and Extended Weak Coupling Limit | We give an extended review of recent work on the extended weak coupling
limit. Background material on completely positive semigroups and their unitary
dilations is given, as well as a particularly easy construction of `quadratic
noises'.
|
Complete Set of Polarization Transfer Observables for the $^{12}{\rm
C}(p,n)$ Reaction at 296 MeV and 0$^{\circ}$ | A complete set of polarization transfer observables has been measured for the
$^{12}{\rm C}(p,n)$ reaction at $T_p=296 {\rm MeV}$ and $\theta_{\rm
lab}=0^{\circ}$. The total spin transfer $\Sigma(0^{\circ})$ and the observable
$f_1$ deduced from the measured polarization transfer observables indicate that
the spin--dipole resonance at $E_x \simeq 7 {\rm MeV}$ has greater $2^-$
strength than $1^-$ strength, which is consistent with recent experimental and
theoretical studies. The results also indicate a predominance of the spin-flip
and unnatural-parity transition strength in the continuum. The exchange tensor
interaction at a large momentum transfer of $Q \simeq 3.6 {\rm fm}^{-1}$ is
discussed.
|
Learning from compressed observations | The problem of statistical learning is to construct a predictor of a random
variable $Y$ as a function of a related random variable $X$ on the basis of an
i.i.d. training sample from the joint distribution of $(X,Y)$. Allowable
predictors are drawn from some specified class, and the goal is to approach
asymptotically the performance (expected loss) of the best predictor in the
class. We consider the setting in which one has perfect observation of the
$X$-part of the sample, while the $Y$-part has to be communicated at some
finite bit rate. The encoding of the $Y$-values is allowed to depend on the
$X$-values. Under suitable regularity conditions on the admissible predictors,
the underlying family of probability distributions and the loss function, we
give an information-theoretic characterization of achievable predictor
performance in terms of conditional distortion-rate functions. The ideas are
illustrated on the example of nonparametric regression in Gaussian noise.
|
Hamiltonian formalism in Friedmann cosmology and its quantization | We propose a Hamiltonian formalism for a generalized
Friedmann-Roberson-Walker cosmology model in the presence of both a variable
equation of state (EOS) parameter $w(a)$ and a variable cosmological constant
$\Lambda(a)$, where $a$ is the scale factor. This Hamiltonian system containing
1 degree of freedom and without constraint, gives Friedmann equations as the
equation of motion, which describes a mechanical system with a variable mass
object moving in a potential field. After an appropriate transformation of the
scale factor, this system can be further simplified to an object with constant
mass moving in an effective potential field. In this framework, the $\Lambda$
cold dark matter model as the current standard model of cosmology corresponds
to a harmonic oscillator. We further generalize this formalism to take into
account the bulk viscosity and other cases. The Hamiltonian can be quantized
straightforwardly, but this is different from the approach of the
Wheeler-DeWitt equation in quantum cosmology.
|
Optimal stimulus and noise distributions for information transmission
via suprathreshold stochastic resonance | Suprathreshold stochastic resonance (SSR) is a form of noise enhanced signal
transmission that occurs in a parallel array of independently noisy identical
threshold nonlinearities, including model neurons. Unlike most forms of
stochastic resonance, the output response to suprathreshold random input
signals of arbitrary magnitude is improved by the presence of even small
amounts of noise. In this paper the information transmission performance of SSR
in the limit of a large array size is considered. Using a relationship between
Shannon's mutual information and Fisher information, a sufficient condition for
optimality, i.e. channel capacity, is derived. It is shown that capacity is
achieved when the signal distribution is Jeffrey's prior, as formed from the
noise distribution, or when the noise distribution depends on the signal
distribution via a cosine relationship. These results provide theoretical
verification and justification for previous work in both computational
neuroscience and electronics.
|
Three Different Types of Galaxy Alignment within Dark Matter Halos | Using a large galaxy group catalogue based on the Sloan Digital Sky Survey
Data Release 4 we measure three different types of intrinsic galaxy alignment
within groups: halo alignment between the orientation of the brightest group
galaxies (BGG) and the distribution of its satellite galaxies, radial alignment
between the orientation of a satellite galaxy and the direction towards its
BGG, and direct alignment between the orientation of the BGG and that of its
satellites. In agreement with previous studies we find that satellite galaxies
are preferentially located along the major axis. In addition, on scales r < 0.7
Rvir we find that red satellites are preferentially aligned radially with the
direction to the BGG. The orientations of blue satellites, however, are
perfectly consistent with being isotropic. Finally, on scales r < 0.1 \Rvir, we
find a weak but significant indication for direct alignment between satellites
and BGGs. We briefly discuss the implications for weak lensing measurements.
|
Proto-Neutron Star Winds, Magnetar Birth, and Gamma-Ray Bursts | We begin by reviewing the theory of thermal, neutrino-driven proto-neutron
star (PNS) winds. Including the effects of magnetic fields and rotation, we
then derive the mass and energy loss from magnetically-driven PNS winds for
both relativistic and non-relativistic outflows, including important
multi-dimensional considerations. With these simple analytic scalings we argue
that proto-magnetars born with ~ millisecond rotation periods produce
relativistic winds just a few seconds after core collapse with luminosities,
timescales, mass-loading, and internal shock efficiencies favorable for
producing long-duration gamma-ray bursts.
|
A very massive runaway star from Cygnus OB2 | Aims: We analyze the available information on the star BD+43 3654 to
investigate the possibility that it may have had its origin in the massive OB
association Cygnus OB2.
Methods: We present new spectroscopic observations allowing a reliable
spectral classification of the star, and discuss existing MSX observations of
its associated bow shock and astrometric information not previously studied.
Results: Our observations reveal that BD+43 3654 is a very early and luminous
star of spectral type O4If, with an estimated mass of (70 +/- 15) solar masses
and an age of about 1.6 Myr. The high spatial resolution of the MSX
observations allows us to determine its direction of motion in the plane of the
sky by means of the symmetry axis of the well-defined bow shock, which matches
well the orientation expected from the proper motion. Tracing back its path
across the sky we find that BD+43 3654 was located near the central, densest
region of Cygnus OB2 at a time in the past similar to its estimated age.
Conclusions: BD+43 3654 turns out to be one of the three most massive runaway
stars known, and it most likely formed in the central region of Cygnus OB2. A
runaway formation mechanism by means of dynamical ejection is consistent with
our results.
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Optical spectrum of the post-AGB star HD56126 in the region 4010-8790 AA | We studied in detail the optical spectrum of the post-AGB star HD56126
(IRAS07134+1005). We use high resolution spectra (R=25000 and 60000) obtained
with the echelle spectrographs of the 6-m telescope. About one and a half
thousand absorptions of neutral atoms and ions, absorption bands of C_2, CN,
and CH molecules, and interstellar bands (DIBs) are identified in the 4010 to
8790 AA wavelength region, and the depths and radial velocities of these
spectral features are measured. Differences are revealed between the variations
of the radial velocities measured from spectral features of different
excitation. In addition to the well-known variability of the Halpha profile, we
found variations in the profiles of a number of FeII, YII, and BaII lines. We
also produce an atlas of the spectrum of HD56126 and its comparison staralpha
Per. The full version of the atlas is available in electronic form from
Web-address: http://www.sao.ru/hq/ssl/Atlas/Atlas.html
|
Generation of Large Number-Path Entanglement Using Linear Optics and
Feed-Forward | We show how an idealised measurement procedure can condense photons from two
modes into one, and how, by feeding forward the results of the measurement, it
is possible to generate efficiently superpositions of components for which only
one mode is populated, commonly called ``N00N states''. For the basic
procedure, sources of number states leak onto a beam splitter, and the output
ports are monitored by photodetectors. We find that detecting a fixed fraction
of the input at one output port suffices to direct the remainder to the same
port with high probability, however large the initial state. When instead
photons are detected at both ports, Schr\"{o}dinger cat states are produced. We
describe a circuit for making the components of such a state orthogonal, and
another for subsequent conversion to a N00N state. Our approach scales
exponentially better than existing proposals. Important applications include
quantum imaging and metrology.
|
Finite branch solutions to Painleve VI around a fixed singular point | Every finite branch solutions to the sixth Painleve equation around a fixed
singular point is an algebraic branch solution. In particular a global solution
is an algebraic solution if and only if it is finitely many-valued globally.
The proof of this result relies on algebraic geometry of Painleve VI,
Riemann-Hilbert correspondence, geometry and dynamics on cubic surfaces,
resolutions of Kleinian singularities, and power geometry of algebraic
differential equations. In the course of the proof we are also able to classify
all finite branch solutions up to Backlund transformations.
|
An Inverse $f(R)$ Gravitation for Cosmic Speed up, and Dark Energy
Equivalent | To explain the cosmic speed up, brought to light by the recent SNIa and CMB
observations, we propose the following: a) In a spacetime endowed with a FRW
metric, we choose an empirical scale factor that best explains the
observations. b) We assume a modified gravity, generated by an unspecified
field lagrangian, $f(R)$. c) We use the adopted empirical scale factor to work
back retroactively to obtain $f(R)$, hence the term `Inverse $f(R)$'. d) Next
we consider the classic GR and a conventional FRW universe that, in addition to
its known baryonic content, possesses a hypothetical `Dark Energy' component.
We compare the two scenarios, and find the density, the pressure, and the
equation of the state of the Dark Energy required to make up for the
differences between the conventional and the modified GR models.
|
Monitoring spatially heterogeneous dynamics in a drying colloidal thin
film | We report on a new type of experiment that enables us to monitor spatially
and temporally heterogeneous dynamic properties in complex fluids. Our approach
is based on the analysis of near-field speckles produced by light diffusely
reflected from the superficial volume of a strongly scattering medium. By
periodic modulation of an incident speckle beam we obtain pixel-wise ensemble
averages of the structure function coefficient, a measure of the dynamic
activity. To illustrate the application of our approach we follow the different
stages in the drying process of a colloidal thin film. We show that we can
access ensemble averaged dynamic properties on length scales as small as ten
micrometers over the full field of view.
|
Mapping the circumstellar SiO maser emission in R Leo | The study of the innermost circumstellar layers around AGB stars is crucial
to understand how these envelopes are formed and evolve. The SiO maser emission
occurs at a few stellar radii from the central star, providing direct
information on the stellar pulsation and on the chemical and physical
properties of these regions. Our data also shed light on several aspects of the
SiO maser pumping theory that are not well understood yet. We aim to determine}
the relative spatial distribution of the 43 GHz and 86 GHz SiO maser lines in
the oxygen-rich evolved star R Leo. We have imaged with milliarcsecond
resolution, by means of Very Long Baseline Interferometry, the 43 GHz (28SiO
v=1, 2 J=1-0 and 29SiO v=0 J=1-0) and 86 GHz (28SiO v=1 J=2-1 and 29SiO v=0
J=2-1) masing regions. We confirm previous results obtained in other
oxygen-rich envelopes. In particular, when comparing the 43 GHz emitting
regions, the 28SiO v=2 transition is produced in an inner layer, closer to the
central star. On the other hand, the 86 GHz line arises in a clearly farther
shell. We have also mapped for the first time the 29SiO v=0 J=1-0 emission in R
Leo. The already reported discrepancy between the observed distributions of the
different maser lines and the theoretical predictions is also found in R Leo.
|
Partially disordered state near ferromagnetic transition in MnSi | The polarized neutron scattering in helimagnetic MnSi at low $T$ reveals
existence of a partially disordered chiral state at ambient pressure in the
magnetic field applied along $<111>$ axis below the first order transition to
the non-chiral ferromagnetic state. This unexpected phenomenon is explained by
the analysis of the spin-wave spectrum. We demonstrate that the square of the
spin-wave gap becomes negative under magnetic field applied along $<111>$ and
$<110>$ but not along the $<100>$ direction. It is a result of competition
between the spin-wave interaction and cubic anisotropy. This negative sign
means an instability of the spin wave spectrum for the helix and leads to a
destruction of the helical order, giving rise to the partially disordered state
below the first order ferromagnetic transition.
|
Fluctuations in glassy systems | We summarize a theoretical framework based on global time-reparametrization
invariance that explains the origin of dynamic fluctuations in glassy systems.
We introduce the main ideas without getting into much technical details. We
describe a number of consequences arising from this scenario that can be tested
numerically and experimentally distinguishing those that can also be explained
by other mechanisms from the ones that we believe, are special to our proposal.
We support our claims by presenting some numerical checks performed on the 3d
Edwards-Anderson spin-glass. Finally, we discuss up to which extent these ideas
apply to super-cooled liquids that have been studied in much more detail up to
present.
|
A generalization of Chebyshev polynomials and non rooted posets | In this paper we give a generalization of Chebyshev polynomials and using
this we describe the M\"obius function of the generalized subword order from a
poset {a1,...as,c |ai<c}, which contains an affirmative answer for the
conjecture by Bj\"orner, Sagan, Vatter.[5,10]
|
Statistical analysis of weighted networks | The purpose of this paper is to assess the statistical characterization of
weighted networks in terms of the generalization of the relevant parameters,
namely average path length, degree distribution and clustering coefficient.
Although the degree distribution and the average path length admit
straightforward generalizations, for the clustering coefficient several
different definitions have been proposed in the literature. We examined the
different definitions and identified the similarities and differences between
them. In order to elucidate the significance of different definitions of the
weighted clustering coefficient, we studied their dependence on the weights of
the connections. For this purpose, we introduce the relative perturbation norm
of the weights as an index to assess the weight distribution. This study
revealed new interesting statistical regularities in terms of the relative
perturbation norm useful for the statistical characterization of weighted
graphs.
|
Finite dimensionality of 2-D micropolar fluid flow with periodic
boundary conditions | This paper is devoted to describe the finite-dimensionality of a
two-dimensional micropolar fluid flow with periodic boundary conditions. We
define the notions of determining modes and nodes and estimate the number of
them, we also estimate the dimension of the global attractor. Finally we
compare our results with analogous results for Navier-Stokes equation.
|
Strong Spherical Asymptotics for Rotor-Router Aggregation and the
Divisible Sandpile | The rotor-router model is a deterministic analogue of random walk. It can be
used to define a deterministic growth model analogous to internal DLA. We prove
that the asymptotic shape of this model is a Euclidean ball, in a sense which
is stronger than our earlier work. For the shape consisting of $n=\omega_d r^d$
sites, where $\omega_d$ is the volume of the unit ball in $\R^d$, we show that
the inradius of the set of occupied sites is at least $r-O(\log r)$, while the
outradius is at most $r+O(r^\alpha)$ for any $\alpha > 1-1/d$. For a related
model, the divisible sandpile, we show that the domain of occupied sites is a
Euclidean ball with error in the radius a constant independent of the total
mass. For the classical abelian sandpile model in two dimensions, with $n=\pi
r^2$ particles, we show that the inradius is at least $r/\sqrt{3}$, and the
outradius is at most $(r+o(r))/\sqrt{2}$. This improves on bounds of Le Borgne
and Rossin. Similar bounds apply in higher dimensions.
|
Study on Correlations between the Twin Kilohertz Quasi-periodic
Oscillations in Low-mass X-ray Binaries | The recently updated data of the twin kilohertz quasi-periodic oscillations
(kHz QPOs) in the neutron star low-mass X-ray binaries are analyzed. The
power-law fitting $\nu_{1}=a(\nu_{2}/1000)^{b}$ and linear fitting
$\nu_{2}=A\nu_{1}+B$ are applied, individually, to the data points of four Z
sources (GX 17+2, GX 340+0, GX 5-1 and Sco X-1) and four Atoll sources (4U
0614+09, 4U 1608-52, 4U 1636-53 and 4U 1728-34). The $\chi^{2}$-tests show that
the power-law correlation and linear correlation both can fit data well.
Moreover, the comparisons between the data and the theoretical models for kHz
QPOs are discussed.
|
Fuzzballs with internal excitations | We construct general 2-charge D1-D5 horizon-free non-singular solutions of
IIB supergravity on T^4 and K3 describing fuzzballs with excitations in the
internal manifold; these excitations are characterized by arbitrary curves. The
solutions are obtained via dualities from F1-P solutions of heterotic and type
IIB on T^4 for the K3 and T^4 cases, respectively. We compute the holographic
data encoded in these solutions, and show that the internal excitations are
captured by vevs of chiral primaries associated with the middle cohomology of
T^4 or K3. We argue that each geometry is dual to a specific superposition of R
ground states determined in terms of the Fourier coefficients of the curves
defining the supergravity solution. We compute vevs of chiral primaries
associated with the middle cohomology and show that they indeed acquire vevs in
the superpositions corresponding to fuzzballs with internal excitations, in
accordance with the holographic results. We also address the question of
whether the fuzzball program can be implemented consistently within
supergravity.
|
Birth, survival and death of languages by Monte Carlo simulation | Simulations of physicists for the competition between adult languages since
2003 are reviewed. How many languages are spoken by how many people? How many
languages are contained in various language families? How do language
similarities decay with geographical distance, and what effects do natural
boundaries have? New simulations of bilinguality are given in an appendix.
|
Rigorous derivation of the mean field Green functions of the two-band
Hubbard model of superconductivity | The Green function (GF) equation of motion technique for solving the
effective two-band Hubbard model of high-T_c superconductivity in cuprates
[N.M. Plakida et al., Phys. Rev. B, v. 51, 16599 (1995); JETP, v. 97, 331
(2003)] rests on the Hubbard operator (HO) algebra. We show that, if we take
into account the invariance to translations and spin reversal, the HO algebra
results in invariance properties of several specific correlation functions. The
use of these properties allows rigorous derivation and simplification of the
expressions of the frequency matrix (FM) and of the generalized mean field
approximation (GMFA) Green functions (GFs) of the model.
For the normal singlet hopping and anomalous exchange pairing correlation
functions which enter the FM and GMFA-GFs, an approximation procedure based on
the identification and elimination of exponentially small quantities is
described. It secures the reduction of the correlation order to GMFA-GF
expressions.
|
Geometry Effects at Atomic-Size Aluminium Contacts | We present electronic structure calculations for aluminium nanocontacts.
Addressing the neck of the contact, we compare characteristic geometries to
investigate the effects of the local aluminium coordination on the electronic
states. We find that the Al 3pz states are very sensitive against modifications
of the orbital overlap, which has serious consequences for the transport
properties. Stretching of the contact shifts states towards the Fermi energy,
leaving the system instable against ferromagnetic ordering. By spacial
restriction, hybridization is locally suppressed at nanocontacts and the charge
neutrality is violated. We discuss the influence of mechanical stress by means
of quantitative results for the charge transfer.
|
Current - voltage characteristics of break junctions of high-$T_c$
superconductors | The current-voltage ($I$-$V$) characteristics of break junctions of
polycrystalline La$_{1.85}$Sr$_{0.15}$CuO$_4$,
Y$_{0.75}$Lu$_{0.25}$Ba$_2$Cu$_3$O$_{7-\delta}$,
Bi$_{1.8}$Pb$_{0.3}$Sr$_{1.9}$Ca$_2$Cu$_3$O$_x$ and composite
YBa$_2$Cu$_3$O$_{7-\delta}$ + Ag are investigated. The experimental $I$-$V$
curves exhibit the specific peculiarities of
superconductor/normal-metal/superconductor junctions. The relation between an
$I$-$V$ characteristic of network of weak links and $I$-$V$ dependencies of
typical weak links is suggested to describe the experimental data. The $I$-$V$
curves of typical weak links are calculated by the K\"{u}mmel - Gunsenheimer -
Nicolsky model considering the multiple Andreev reflections.
|
Photon splitting in a laser field | Photon splitting due to vacuum polarization in a laser field is considered.
Using an operator technique, we derive the amplitudes for arbitrary strength,
spectral content and polarization of the laser field. The case of a
monochromatic circularly polarized laser field is studied in detail and the
amplitudes are obtained as three-fold integrals. The asymptotic behavior of the
amplitudes for various limits of interest are investigated also in the case of
a linearly polarized laser field. Using the obtained results, the possibility
of experimental observation of the process is discussed.
|
Phonon instability and structural phase transition in Vanadium under
high pressure | Results of the first-principles calculations are presented for the group-VB
metals V, Nb and Ta up to couple of megabar pressure. An unique structural
phase transition sequence BCC-->(at 60 GPa) rhombohedral (angle=110.5
degree)-->(at ~ 160 GPa)rhombohedral(angle=108.5 degree)--> (at ~ 430 GPa) BCC
is predicted in V. We also find that BCC-V becomes mechanically and
vibrationally unstable at around 112 GPa pressure. Similar transitions are
absent in Nb and Ta.
|
CP violation due to multi Froggatt-Nielsen fields | We study how to incorporate CP violation in the Froggatt--Nielsen (FN)
mechanism. To this end, we introduce non-renormalizable interactions with a
flavor democratic structure to the fermion mass generation sector. It is found
that at least two iso-singlet scalar fields with imposed a discrete symmetry
are necessary to generate CP violation due to the appearance of the relative
phase between their vacuum expectation values.
In the simplest model, ratios of quark masses and the
Cabibbo-Kobayashi-Maskawa (CKM) matrix including the CP violating phase are
determined by the CKM element |V_{us}| and the ratio of two vacuum expectation
values R=|R|e^{i*alpha} (a magnitude and a phase). It is demonstrated how the
angles phi_i (i=1--3) of the unitarity triangle and the CKM off-diagonal
elements |V_{ub}| and |V_{cb}| are predicted as a function of |V_{us}|, |R| and
\alpha. Although the predicted value of the CP violating phase does not agree
with the experimental data within the simplest model, the basic idea of our
scenario would be promising to construct a more realistic model of flavor and
CP violation.
|
Rigorous Results for the Periodic Oscillation of an Adiabatic Piston | We study a heavy piston of mass $M$ that moves in one dimension. The piston
separates two gas chambers, each of which contains finitely many ideal, unit
mass gas particles moving in $d$ dimensions, where $ d\geq 1$. Using averaging
techniques, we prove that the actual motions of the piston converge in
probability to the predicted averaged behavior on the time scale $M^ {1/2} $
when $M$ tends to infinity while the total energy of the system is bounded and
the number of gas particles is fixed. Neishtadt and Sinai previously pointed
out that an averaging theorem due to Anosov should extend to this situation.
When $ d=1$, the gas particles move in just one dimension, and we prove that
the rate of convergence of the actual motions of the piston to its averaged
behavior is $\mathcal{O} (M^ {-1/2}) $ on the time scale $M^ {1/2} $. The
convergence is uniform over all initial conditions in a compact set. We also
investigate the piston system when the particle interactions have been
smoothed. The convergence to the averaged behavior again takes place uniformly,
both over initial conditions and over the amount of smoothing.
In addition, we prove generalizations of our results to $N$ pistons
separating $N+1$ gas chambers. We also provide a general discussion of
averaging theory and the proofs of a number of previously known averaging
results. In particular, we include a new proof of Anosov's averaging theorem
for smooth systems that is primarily due to Dolgopyat.
|
Thermal decomposition of norbornane (bicyclo[2.2.1]heptane) dissolved in
benzene. Experimental study and mechanism investigation | The thermal decomposition of norbornane (dissolved in benzene) has been
studied in a jet stirred reactor at temperatures between 873 and 973 K, at
residence times ranging from 1 to 4 s and at atmospheric pressure, leading to
conversions from 0.04 to 22.6%. 25 reaction products were identified and
quantified by gas chromatography, amongst which the main ones are hydrogen,
ethylene and 1,3-cyclopentadiene. A mechanism investigation of the thermal
decomposition of the norbornane - benzene binary mixture has been performed.
Reactions involved in the mechanism have been reviewed: unimolecular
initiations 1 by C-C bond scission of norbornane, fate of the generated
diradicals, reactions of transfer and propagation of norbornyl radicals,
reactions of benzene and cross-coupling reactions.
|
Detailed kinetic study of the ring opening of cycloalkanes by CBS-QB3
calculations | This work reports a theoretical study of the gas phase unimolecular
decomposition of cyclobutane, cyclopentane and cyclohexane by means of quantum
chemical calculations. A biradical mechanism has been envisaged for each
cycloalkane, and the main routes for the decomposition of the biradicals formed
have been investigated at the CBS-QB3 level of theory. Thermochemical data
(\delta H^0_f, S^0, C^0_p) for all the involved species have been obtained by
means of isodesmic reactions. The contribution of hindered rotors has also been
included. Activation barriers of each reaction have been analyzed to assess the
1 energetically most favorable pathways for the decomposition of biradicals.
Rate constants have been derived for all elementary reactions using transition
state theory at 1 atm and temperatures ranging from 600 to 2000 K. Global rate
constant for the decomposition of the cyclic alkanes in molecular products have
been calculated. Comparison between calculated and experimental results allowed
to validate the theoretical approach. An important result is that the
rotational barriers between the conformers, which are usually neglected, are of
importance in decomposition rate of the largest biradicals. Ring strain
energies (RSE) in transition states for ring opening have been estimated and
show that the main part of RSE contained in the cyclic reactants is removed
upon the activation process.
|