32,982 research outputs found
Approximation in LQG control of a thermoelastic rod
Control and estimator gains are computed for linear-quadratic-Gaussian (LQG) optimal control of the axial vibrations of a thermoelastic rod. The computations are based on a modal approximation of the partial differential equations representing the rod, and convergence of the approximations to control and estimator gains is the main issue
Lamellar phase separation and dynamic competition in La0.23Ca0.77MnO3
We report the coexistence of lamellar charge-ordered (CO) and
charge-disordered (CD) domains, and their dynamical behavior, in
La0.23Ca0.77MnO3. Using high resolution transmission electron microscopy (TEM),
we show that below Tcd~170K a CD-monoclinic phase forms within the established
CO-orthorhombic matrix. The CD phase has a sheet-like morphology, perpendicular
to the q vector of the CO superlattice (a axis of the Pnma structure). For
temperatures between 64K and 130K, both the TEM and resistivity experiments
show a dynamic competition between the two phases: at constant T, the CD phase
slowly advances over the CO one. This slow dynamics appears to be linked to the
magnetic transitions occurring in this compound, suggesting important
magnetoelastic effects.Comment: 4 pages, 4 figure
Information on the Pion Distribution Amplitude from the Pion-Photon Transition Form Factor with the Belle and BaBar Data
The pion-photon transition form factor (TFF) provides strong constraints on
the pion distribution amplitude (DA). We perform an analysis of all existing
data (CELLO, CLEO, BaBar, Belle) on the pion-photon TFF by means of light-cone
pQCD approach in which we include the next-to-leading order correction to the
valence-quark contribution and estimate the non-valence-quark contribution by a
phenomenological model based on the TFF's limiting behavior at both
and . At present, the pion DA is not definitely determined, it is
helpful to have a pion DA model that can mimic all the suggested behaviors,
especially to agree with the constraints from the pion-photon TFF in whole
measured region within a consistent way. For the purpose, we adopt the
conventional model for pion wavefunction/DA that has been constructed in our
previous paper \cite{hw1}, whose broadness is controlled by a parameter . We
fix the DA parameters by using the CELLO, CLEO, BABAR and Belle data within the
smaller region ( GeV), where all the data are consistent
with each other. And then the pion-photon TFF is extrapolated into larger
region. We observe that the BABAR favors which has the behavior close
to the Chernyak-Zhitnitsky DA, whereas the recent Belle favors which
is close to the asymptotic DA. We need more accurate data at large region
to determine the precise value of , and the definite behavior of pion DA can
be concluded finally by the consistent data in the coming future.Comment: 6 pages, 5 figures. Slightly changed and references update
Phenomenological theory of spin excitations in La- and Y-based cuprates
Motivated by recent inelastic neutron scattering (INS) experiments on
La-based cuprates and based on the fermiology theories, we study the spin
susceptibility for La-based (e.g., LaSrCuO) and Y-based (e.g.,
YBaCuO) cuprates, respectively. The spin excitation in
YBaCuO is dominated by a sharp resonance peak at the frequency 40
meV in the superconducting state. Below and above the resonance frequency, the
incommensurate (IC) peaks develop and the intensity of the peaks decreases
dramatically. In the normal state, the resonant excitation does not occur and
the IC peaks are merged into commensurate ones. The spin excitation of
LaSrCuO is significantly different from that of Y-based ones,
namely, the resonance peak does not exist due to the decreasing of the
superconducting gap and the presence of the possible spin-stripe order. The
spectra are only enhanced at the expected resonance frequency (about 18 meV)
while it is still incommensurate. On the other hand, another frequency scale at
the frequency 55 meV is also revealed, namely the spectra are commensurate and
local maximum at this frequency. We elaborate all the results based on the
Fermi surface topology and the d-wave superconductivity, and suggest that the
spin-stripe order be also important in determining the spin excitation of
La-based cuprates. A coherent picture for the spin excitations is presented for
Y-based and La-based cuprates.Comment: 8 pages, 8 figure
Cluster size dependence of high-order harmonic generation
We investigate high-order harmonic generation (HHG) from noble gas clusters
in a supersonic gas jet. To identify the contribution of harmonic generation
from clusters versus that from gas monomers, we measure the high-order harmonic
output over a broad range of the total atomic number density in the jet (from
3*10^16 cm^{-3} to 3x10^18 cm{-3}) at two different reservoir temperatures (303
K and 363 K). For the firrst time in the evaluation of the harmonic yield in
such measurements, the variation of the liquid mass fraction, g, versus
pressure and temperature is taken into consideration, which we determine,
reliably and consistently, to be below 20% within our range of experimental
parameters. By comparing the measured harmonic yield from a thin jet with the
calculated corresponding yield from monomers alone, we find an increased
emission of the harmonics when the average cluster size is less than 3000.
Using g, under the assumption that the emission from monomers and clusters add
up coherently, we calculate the ratio of the average single-atom response of an
atom within a cluster to that of a monomer and find an enhancement of around 10
for very small average cluster size (~200). We do not find any dependence of
the cut-off frequency on the composition of the cluster jet. This implies that
HHG in clusters is based on electrons that return to their parent ions and not
to neighbouring ions in the cluster. To fully employ the enhanced average
single-atom response found for small average cluster sizes (~200), the nozzle
producing the cluster jet must provide a large liquid mass fraction at these
small cluster sizes for increasing the harmonic yield. Moreover, cluster jets
may allow for quasi-phase matching, as the higher mass of clusters allows for a
higher density contrast in spatially structuring the nonlinear medium.Comment: 16 pages, 6 figure
Kinetics of viral self-assembly: the role of ss RNA antenna
A big class of viruses self-assemble from a large number of identical capsid
proteins with long flexible N-terminal tails and ss RNA. We study the role of
the strong Coulomb interaction of positive N-terminal tails with ss RNA in the
kinetics of the in vitro virus self-assembly. Capsid proteins stick to
unassembled chain of ss RNA (which we call "antenna") and slide on it towards
the assembly site. We show that at excess of capsid proteins such
one-dimensional diffusion accelerates self-assembly more than ten times. On the
other hand at excess of ss RNA, antenna slows self-assembly down. Several
experiments are proposed to verify the role of ss RNA antenna.Comment: 4 pages, 3 figures, several experiments are proposed, a new idea of
experiment is adde
Necessity of integral formalism
To describe the physical reality, there are two ways of constructing the
dynamical equation of field, differential formalism and integral formalism. The
importance of this fact is firstly emphasized by Yang in case of gauge field
[Phys. Rev. Lett. 33 (1974) 445], where the fact has given rise to a deeper
understanding for Aharonov-Bohm phase and magnetic monopole [Phys. Rev. D. 12
(1975) 3845]. In this paper we shall point out that such a fact also holds in
general wave function of matter, it may give rise to a deeper understanding for
Berry phase. Most importantly, we shall prove a point that, for general wave
function of matter, in the adiabatic limit, there is an intrinsic difference
between its integral formalism and differential formalism. It is neglect of
this difference that leads to an inconsistency of quantum adiabatic theorem
pointed out by Marzlin and Sanders [Phys. Rev. Lett. 93 (2004) 160408]. It has
been widely accepted that there is no physical difference of using differential
operator or integral operator to construct the dynamical equation of field.
Nevertheless, our study shows that the Schrodinger differential equation (i.e.,
differential formalism for wave function) shall lead to vanishing Berry phase
and that the Schrodinger integral equation (i.e., integral formalism for wave
function), in the adiabatic limit, can satisfactorily give the Berry phase.
Therefore, we reach a conclusion: There are two ways of describing physical
reality, differential formalism and integral formalism; but the integral
formalism is a unique way of complete description.Comment: 13Page; Schrodinger differential equation shall lead to vanishing
Berry phas
Single-shot fluctuations in waveguided high-harmonic generation
For exploring the application potential of coherent soft x-ray (SXR) and
extreme ultraviolet radiation (XUV) provided by high-harmonic generation, it is
important to characterize the central output parameters. Of specific importance
are pulse-to-pulse (shot-to-shot) fluctuations of the high-harmonic output
energy, fluctuations of the direction of the emission (pointing instabilities),
and fluctuations of the beam divergence and shape that reduce the spatial
coherence. We present the first single-shot measurements of waveguided
high-harmonic generation in a waveguided (capillary-based) geometry. Using a
capillary waveguide filled with Argon gas as the nonlinear medium, we provide
the first characterization of shot-to-shot fluctuations of the pulse energy, of
the divergence and of the beam pointing. We record the strength of these
fluctuations vs. two basic input parameters, which are the drive laser pulse
energy and the gas pressure in the capillary waveguide. In correlation
measurements between single-shot drive laser beam profiles and single-shot
high-harmonic beam profiles we prove the absence of drive laser
beam-pointing-induced fluctuations in the high-harmonic output. We attribute
the main source of high-harmonic fluctuations to ionization-induced nonlinear
mode mixing during propagation of the drive laser pulse inside the capillary
waveguide
X(1835): A Natural Candidate of 's Second Radial Excitation
Recently BES collaboration observed one interesting resonance X(1835). We
point out that its mass, total width, production rate and decay pattern favor
its assignment as the second radial excitation of meson very
naturally
Small ball probability, Inverse theorems, and applications
Let be a real random variable with mean zero and variance one and
be a multi-set in . The random sum
where are iid copies of
is of fundamental importance in probability and its applications.
We discuss the small ball problem, the aim of which is to estimate the
maximum probability that belongs to a ball with given small radius,
following the discovery made by Littlewood-Offord and Erdos almost 70 years
ago. We will mainly focus on recent developments that characterize the
structure of those sets where the small ball probability is relatively
large. Applications of these results include full solutions or significant
progresses of many open problems in different areas.Comment: 47 page
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