共查询到20条相似文献,搜索用时 31 毫秒
1.
G. P. Berman A. R. Bishop D. A. R. Dalvit G. V. Shlyapnikov N. Tarkhanov E. M. Timmermans 《International Journal of Theoretical Physics》2008,47(9):2393-2408
We rigorously analyze the stability of the “quasi-classical” dynamics of a Bose-Einstein condensate with repulsive and attractive
interactions, trapped in an effective 1D toroidal geometry. The “classical” dynamics, which corresponds to the Gross-Pitaevskii
mean field theory, is stable in the case of repulsive interaction, and unstable (under some conditions) in the case of attractive
interaction. The corresponding quantum dynamics for observables is described by using a closed system of linear partial differential
equations. In both cases of stable and unstable quasi-classical dynamics the quantum effects represent a singular perturbation
to the quasi-classical solutions, and are described by the terms in these equations which consist of a small quasi-classical
parameter which multiplies high-order “spatial” derivatives. We demonstrate that as a result of the quantum singularity for
observables a convergence of quantum solutions to the corresponding classical solutions exists only for limited times, and
estimate the characteristic time-scales of the convergence. 相似文献
2.
T.-S. Kim H. Park K. Ko G. Lim Y.-H. Cha J. Han D.-Y. Jeong 《Applied physics. B, Lasers and optics》2010,100(2):437-442
Currently, the nuclear industry needs strongly a reliable detection system to continuously monitor a coolant leak during a
normal operation of reactors for the ensurance of nuclear safety. In this work, we propose a new device for the coolant leak
detection based on tunable diode laser spectroscopy (TDLS) by using a compact diode laser. For the feasibility experiment,
we established an experimental setup consisted of a near-IR diode laser with a wavelength of about 1392 nm, a home-made multi-pass
cell and a sample injection system. The feasibility test was performed for the detection of the heavy water (D2O) leaks which can happen in a pressurized heavy water reactor (PWHR). As a result, the device based on the TDLS is shown
to be operated successfully in detecting a HDO molecule, which is generated from the leaked heavy water by an isotope exchange
reaction between D2O and H2O. Additionally, it is suggested that the performance of the new device, such as sensitivity and stability, can be improved
by adapting a cavity enhanced absorption spectroscopy and a compact DFB diode laser. We presume that this laser-based leak
detector has several advantages over the conventional techniques currently employed in the nuclear power plant, such as radiation
monitoring, humidity monitoring and FT-IR spectroscopy. 相似文献
3.
D. Nodop J. Rothhardt S. H?drich J. Limpert A. Tünnermann 《Applied physics. B, Lasers and optics》2009,94(3):399-401
We present a Q-switched microchip laser emitting 1064-nm pulses as short as 100 ps synchronized to a cavity dumped femtosecond
laser emitting 800-nm pulses as short as 80 fs. The synchronization is achieved by presaturating the saturable absorber of
the microchip laser with femtosecond pulses even though both lasers emit at widely separated wavelengths. The mean timing
jitter is 40 ps and thus considerably shorter than the pulse duration of the microchip laser. 相似文献
4.
José Ignacio Rosado 《Foundations of Physics》2011,41(7):1200-1213
The quantum state of a d-dimensional system can be represented by a probability distribution over the d
2 outcomes of a Symmetric Informationally Complete Positive Operator Valued Measure (SIC-POVM), and then this probability distribution
can be represented by a vector of
\mathbb Rd2-1\mathbb {R}^{d^{2}-1} in a (d
2−1)-dimensional simplex, we will call this set of vectors Q\mathcal{Q}. Other way of represent a d-dimensional system is by the corresponding Bloch vector also in
\mathbb Rd2-1\mathbb {R}^{d^{2}-1}, we will call this set of vectors B\mathcal{B}. In this paper it is proved that with the adequate scaling B=Q\mathcal{B}=\mathcal{Q}. Also we indicate some features of the shape of Q\mathcal{Q}. 相似文献
5.
Mohsen Daeimohamad Fardin Kheirandish Khaled Saeedi 《International Journal of Theoretical Physics》2011,50(1):171-180
The dissipative quantum dynamics of a harmonic oscillator in the presence of a deformed bath is investigated. The deformed
bath is modelled by a collection of deformed quantum harmonic oscillators as a generalization of Hopfield model. The transition
probabilities between energy levels of the oscillator are obtained perturbatively and discussed. 相似文献
6.
We study the dynamics of the thermal momentum distribution function for an interacting, homogeneous Fermi gas on ℤ3 in the presence of an external weak static random potential, where the pair interactions between the fermions are modeled
in dynamical Hartree-Fock theory. We determine the Boltzmann limits associated to different scaling regimes defined by the
size of the random potential, and the strength of the fermion interactions. 相似文献
7.
Marzio Cassandro Immacolata Merola Maria Eulalia Vares 《Journal of statistical physics》2011,142(3):487-509
We consider a one dimensional ferromagnetic Ising spin system with interactions that correspond to a 1/r
2 long range perturbation of the usual Kac model. We apply a coarse graining procedure widely used for higher-dimensional finite
range Kac potentials to describe the basic properties of the system and the relation with the mean field theory. 相似文献
8.
Erhard Scholz 《Foundations of Physics》2009,39(1):45-72
A Weyl geometric approach to cosmology is explored, with a scalar field φ of (scale) weight −1 as crucial ingredient besides classical matter. Its relation to Jordan-Brans-Dicke theory is analyzed;
overlap and differences are discussed. The energy-stress tensor of the basic state of the scalar field consists of a vacuum-like
term Λg
μ
ν
with Λ depending on the Weylian scale connection and, indirectly, on matter density. For a particularly simple class of Weyl
geometric models (called Einstein-Weyl universes) the energy-stress tensor of the φ-field can keep space-time geometries in equilibrium. A short glance at observational data, in particular supernovae Ia (Riess
et al. in Astrophys. J. 659:98ff, 2007), shows encouraging empirical properties of these models. 相似文献
9.
A completely Lorentz-invariant Bohmian model has been proposed recently for the case of a system of non-interacting spinless
particles, obeying Klein-Gordon equations. It is based on a multi-temporal formalism and on the idea of treating the squared
norm of the wave function as a space-time probability density. The particle’s configurations evolve in space-time in terms
of a parameter σ with dimensions of time. In this work this model is further analyzed and extended to the case of an interaction with an external
electromagnetic field. The physical meaning of σ is explored. Two special situations are studied in depth: (1) the classical limit, where the Einsteinian Mechanics of Special
Relativity is recovered and the parameter σ is shown to tend to the particle’s proper time; and (2) the non-relativistic limit, where it is obtained a model very similar
to the usual non-relativistic Bohmian Mechanics but with the time of the frame of reference replaced by σ as the dynamical temporal parameter. 相似文献
10.
Xian-Qiao Yu 《The European Physical Journal C - Particles and Fields》2009,64(4):529-532
We study the nucleon electromagnetic form factors in a quark–gluon core model framework, which can be viewed as an extension
of the Isgur–Karl model of baryons. Using this picture we derive nucleon electromagnetic dipole form factors at low Q
2 and the deviation from the dipole form at high Q
2, that are consistent with the existing experimental data. 相似文献
11.
R. S. Kolevatov 《The European Physical Journal C - Particles and Fields》2010,68(3-4):513-521
A fragmenting relativistic string is widely used for modeling particle production via quark–gluon strings formed in hadronic and nuclear inelastic interactions at high energies. In this note we focus on motion and fragmentation of a relativistic string with non-zero transverse separation of its ends and study this scenario as a possible mechanism for bringing anisotropy into the azimuthal angle distribution of produced particles in inelastic interactions of hadrons. 相似文献
12.
We discuss the decay of unstable states into a quasicontinuum using Hamiltonian models. We show that exponential decay and
the golden rule are exact in a suitable scaling limit, and that there is an associated renormalization group (RG) with these
properties as a fixed point. The method is inspired by a limit theorem for infinitely divisible distributions in probability
theory, where there is a RG with a Cauchy distribution, i.e. a Lorentz line shape, as a fixed point. Our method of solving
for the spectrum is well known; it does not involve a perturbation expansion in the interaction, and needs no assumption of
a weak interaction. Using random matrices for the interaction we show that the ensemble fluctuations vanish in the scaling
limit. For non-random models we can use uniformity assumptions on the density of states and the interaction matrix elements
to estimate the deviations from the decay rate defined by the golden rule. 相似文献
13.
Peter Gregorčič Rok Petkovšek Janez Možina Griša Močnik 《Applied Physics A: Materials Science & Processing》2008,93(4):901-905
We present an optodynamic measurement of a laser-induced cavitation bubble and its oscillations based on a scanning technique
using a laser beam-deflection probe. The deflection of the beam was detected with a fast quadrant photodiode which was built
into the optical probe. The applied experimental setup enabled us to carry out one- or two-dimensional scanning of the cavitation
bubble, automatic control of the experiment, data acquisition and data processing. Shadow photography was used as a comparative
method during the experiments. 相似文献
14.
Amine Asselah 《Journal of statistical physics》2010,138(4-5):619-644
We consider a randomly charged polymer. Each monomer carries a random charge, and only charges on the same site interact pairwise. We study the lower tails of the energy, when averaged over both randomness, in dimension three or more. As a corollary, we obtain the correct temperature-scale for the Gibbs measure. 相似文献
15.
A Kerr nonlinear blackbody (KNB) is a new kind of blackbody in which bare photons with opposite wave vectors and helicities
are bound into pairs and unpaired photons are transformed into nonpolaritons. In the present paper, the radiation of a KNB
is considered from the viewpoint of an observer in arbitrary uniform motion with respect to a rest frame of reference of the
radiation. It is found that the radiation laws, which include the distribution of nonpolaritons and so forth, are modified
due to the motion. Moreover, under a special condition, we notice that the only effect of the motion is to introduce an angle-dependent
directional temperature, which replaces the rest-frame temperature of the cavity. Besides, we try to extend the model of a
KNB to the whole Universe and apply the modified radiation laws to the question of 2.7 K cosmic microwave background radiation
(CMBR). 相似文献
16.
Yudi Rosandi Herbert M. Urbassek 《Applied Physics A: Materials Science & Processing》2010,101(3):509-515
The optical properties of blue-violet InGaN light-emitting diodes under normal and reversed polarizations are numerically
studied. The best light-emitting performance under normal and reversed polarization is obtained in a single quantum-well structure
and double quantum-well structure, respectively. The key factors responsible for these phenomena are presumably the carrier
concentration distribution and the amount of carriers in quantum wells. The turn-on voltage of light-emitting diodes under
reversed polarization is lower than that of light-emitting diodes under normal polarization, due mainly to lower potential
heights for electrons and holes in the active region. 相似文献
17.
Alexandre Mermillod-Blondin Euan McLeod Craig B. Arnold 《Applied Physics A: Materials Science & Processing》2008,93(1):231-234
The ability to dynamically shape the spatial intensity profile of an incident laser beam enables new ways to modify and structure
surfaces through pulsed laser processing. Here we describe a method to generate doughnut-shaped beams from an input Gaussian
source using a tunable acoustic gradient index (TAG) lens. The TAG lens is capable of modulating between focused beams and
annular rings of variable size, using sinusoidal driving frequencies. Laser micromachining is accomplished by synchronizing
the TAG lens to a 355 nm pulsed nanosecond laser. Results in polyimide demonstrate the ability to generate adjacent surface
features with different shapes and sizes. 相似文献
18.
Ekaterina Turilova 《International Journal of Theoretical Physics》2009,48(11):3083-3091
Let ℳ be a von Neumann algebra acting on a Hilbert space H and let S be a dense lineal in H that is affiliated with a von Neumann algebra ℳ. The “topological” definition of measures on the classes of orthoclosed and
splitting subspaces of S affiliated with a von Neumann algebra ℳ is given and results on the relationships of these measures to measures on orthoprojections
of the algebra ℳ are presented. 相似文献
19.
We study the divergence of the solution to a Schrödinger-type amplifier driven by the square of a Gaussian noise in presence of a random potential. We follow the same approach as Mounaix, Collet, and Lebowitz (MCL) in terms of a distributional formulation of the amplified field and the use of the Paley-Wiener theorem (Mounaix et al. in Commun. Math. Phys. 264:741–758, 2006, Erratum: ibid. 280:281–283, 2008). Our results show that the divergence is not affected by the random potential, in the sense that it occurs at exactly the same coupling constant as what was found by MCL without a potential. It follows a fortiori that the breakdown of the amplifier is not affected by the possible existence of a localized regime in the amplification free limit. 相似文献
20.
We study the problem of localizing and tracking in a confocal laser scanning microscope a single fluorescent particle diffusing
in three dimensions. The position of the particle is estimated from a collection of intensity measurements using a novel analytical
algorithm. This estimator is then combined with a tracking algorithm based on a linear quadratic Gaussian controller to steer
the detection volume of the microscope and follow the molecule. The feasibility of the approach is demonstrated through numerical
simulations. These results indicate that, in such a system, tracking in three dimensions of a particle moving with a diffusion
constant larger than 1 μm2/s is possible without the need for additional sensors or lasers. 相似文献