共查询到20条相似文献,搜索用时 15 毫秒
1.
Asher Yahalom 《Physics letters. A》2013,377(31-33):1898-1904
It is shown that an Aharonov–Bohm (AB) effect exists in magnetohydrodynamics (MHD). This effect is best described in terms of the MHD variational variables (Kats, 2004; Yahalom and Lynden-Bell, 2008; Yahalom, 2010) [1], [10], [12]. If a MHD flow has a non-trivial topology some of the functions appearing in the MHD Lagrangian are non-single-valued. These functions have properties similar to the phases in the AB celebrated effect (Aharonov and Bohm, 1959; van Oudenaarden et al., 1998) [2], [3]. While the manifestation of the quantum AB effect is in interference fringe patterns (Tonomura et al., 1982) [4], the manifestation of the MHD Aharonov–Bohm effects are through new dynamical conservation laws. 相似文献
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Event-by-event hydrodynamics (or hydrodynamics with fluctuating initial conditions) has been developed in the past few years. Here we discuss how it may help to understand the various structures observed in two-particle correlations. 相似文献
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We investigate how thermalization of gluons depends on the initial conditions assumed in ultrarelativistic heavy-ion collisions
at RHIC. The study is based on simulations employing the pQCD inspired parton cascade solving the Boltzmann equation for gluons.
We consider independently produced minijets with p
T > p
0 = 1.3-2.0GeV and a color glass condensate as possible initial conditions for the freed gluons. It turns out that full kinetic
equilibrium is achieved slightly sooner in denser systems and its timescale tends to saturate. Compared with the kinetic equilibration
we find a stronger dependence of chemical equilibration on the initial conditions. 相似文献
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Bojowald M 《Physical review letters》2001,87(12):121301
Loop quantum cosmology is shown to provide both the dynamical law and initial conditions for the wave function of a universe by one discrete evolution equation. Accompanied by the condition that semiclassical behavior is obtained at large volume, a unique wave function is predicted. 相似文献
8.
《Physics letters. A》1987,122(5):253-256
Magnetohydrodynamics (MHD) is treated by truncating Taylor series representations in cartesian coordinates of the velocity, magnetic and pressure fields. Model systems of ordinary differential equations are constructed and found to have oscillatory solutions. This work provides fresh insight into the magnetic reconnection problem. 相似文献
9.
CMB measurements reveal an unnaturally smooth early universe. We propose a mechanism to make this smoothness natural by weakening the strength of gravity at early times, and therefore altering which initial conditions have low entropy. 相似文献
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M.-C. Heitz G. Durand F. Spiegelman C. Meier 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):181-184
The excited state dynamics of the
Na2F cluster initiated by a femtosecond
laser pulse is studied considering a thermally excited initial
sample. Within a pump-probe set-up, the time-dependent
photoelectron spectrum is calculated, which is shown to be a
sensitive tool to study intramolecular motion of the cluster.
Temperature effects are taken into account through thermal
averaging over the time-dependent spectra obtained from
different initial vibrational states of the cluster. The nuclear
motion upon laser excitation is described by full-dimensional
quantum wavepacket propagation using explicit, realistic pump
and probe pulses. The characteristic features of the
time-resolved photoelectron spectra of the
Na2F cluster, identified as due to
periodic bending motion of the cluster as well as to the
excitation of the stretching mode, are found to be robust
against increasing vibrational temperature of the cluster beam.
This finding is important for possible future experiments. 相似文献
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13.
This work uses Lorentz-signature in-in perturbation theory to analyze the late-time behavior of correlators in time-dependent
interacting massive scalar field theory in de Sitter space. We study a scenario recently considered by Krotov and Polyakov
in which the coupling g turns on smoothly at finite time, starting from g = 0 in the far past where the state is taken to be the (free) Bunch–Davies vacuum. Our main result is that the resulting
correlators (which we compute at the one-loop level) approach those of the interacting Hartle–Hawking state at late times.
We argue that similar results should hold for other physically-motivated choices of initial conditions. This behavior is to
be expected from recent quantum “no hair” theorems for interacting massive scalar field theory in de Sitter space which established
similar results to all orders in perturbation theory for a dense set of states in the Hilbert space. Our current work (1)
indicates that physically motivated initial conditions lie in this dense set, (2) provides a Lorentz-signature counter-part
to the Euclidean techniques used to prove such theorems, and (3) provides an explicit example of the relevant renormalization
techniques. 相似文献
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15.
《Physics letters. [Part B]》1988,215(4):635-641
In a higher-dimensional theory of gravity containing higher-derivative terms and a cosmological constant, a period of super-exponential inflation of the physical spacetime is possible, during which the Hubble parameter H increases with time, as discovered by Shafi and Wetterich. This means that the initial value H0 must be small H0 < 6 × 10−5mp. We discuss the meaning of this initial condition from the standpoint of quantum cosmology. 相似文献
16.
We investigate the possibility to improve the noise performance of a chaotic digital communication scheme by utilizing further dynamical information. We show that by encoding the initial information of the chaotic carrier according to the transmitting bits, extra redundance can be introduced into the segments of chaotic signals corresponding to the consecutive bits. Such redundant information can be exploited effectively at the receiver end to improve the noise performance of the system. Compared to other methods (e.g., differential chaos shift keying), straightforward application of the proposed modulation/demodulation scheme already provides significant performance gain in the low signal-to-noise ratio (SNR) region. Furthermore, maximum likelihood precleaning procedure based on the Viterbi algorithm can be applied before the demodulation step to overcome the performance degradation in the high SNR region. The study indicates that it is possible to improve the noise performance of the chaotic digital communication scheme if further dynamics information is added to the system. 相似文献
17.
V. M. Kenkre 《Journal of statistical physics》1978,19(4):333-340
The initial condition term that must be appended to the generalized master equation (GME) when the density matrix is not initially diagonal in the representation chosen is studied and explicit expressions are obtained for several cases. The term is shown to vanish for initial occupation of a Bloch state of arbitrary wave vector if the system is a crystal and the representation is that of site states, despite the violation of the initial diagonality condition. It is pointed out how one is to use the expressions for the initial term in transport calculations.This article is dedicated to Prof. Max Dresden on the occasion of his sixtieth birthday. 相似文献
18.
O.V. Bychuk B. O'Shaughnessy N.J. Turro 《The European physical journal. E, Soft matter》2001,4(3):281-291
We propose and theoretically study an experiment designed to measure short-time polymer reaction kinetics in melts or dilute
solutions. The photolysis of groups centrally located along chain backbones, one group per chain, creates pairs of spatially
highly correlated macroradicals. We calculate time-dependent rate coefficients κ(t) governing their first-order recombination kinetics, which are novel on account of the far-from-equilibrium initial conditions.
In dilute solutions (good solvents) reaction kinetics are intrinsically weak, despite the highly reactive radical groups involved.
This leads to a generalised mean-field kinetics in which the rate of radical density decay - ∼S(t), where S(t) ∼t
- (1 + g/3) is the equilibrium return probability for 2 reactive groups, given initial contact. Here g≈ 0.27 is the correlation hole exponent for self-avoiding chain ends. For times beyond the longest coil relaxation time τ,
- ∼S(t) remains true, but center of gravity coil diffusion takes over with rms displacement of reactive groups x(t) ∼t
1/2 and S(t) ∼ 1/x
3(t). At the shortest times ( t
10-6s), recombination is inhibited due to spin selection rules and we find ∼tS(t). In melts, kinetics are intrinsically diffusion-controlled, leading to entirely different rate laws. During the regime limited
by spin selection rules, the density of radicals decays linearly, n(0) - n(t) ∼t. At longer times the standard result - ∼d
3(t)/d (for randomly distributed ends) is replaced by ∼d2x
3(t)/d
2 for these correlated initial conditions. The long-time behavior, t > τ, has the same scaling form in time as for dilute solutions.
Received 18 May 2000 相似文献
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We present a generic threshold model for the co-evolution of the structure of a network and the binary state of its nodes. We focus on regular directed networks and derive equations for the evolution of the system toward its absorbing state. It is shown that the system displays a transition from a connected phase to a fragmented phase, and that this transition is driven by the initial configuration of the system, as different initial conditions may lead to drastically different final configurations. Computer simulations are performed and confirm the theoretical predictions. 相似文献