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281.
José Natário 《General Relativity and Gravitation》2006,38(3):475-484
We find a class of warp drive spacetimes possessing Newtonian limits, which we then determine. The same method is used to
compute Newtonian limits of the Schwarzschild solution and spatially flat Friedmann-Robertson-Walker cosmological models.
This work was partially supported by FCT/POCTI/FEDER. 相似文献
282.
A. Hotzel P. Thirolf Ch. Ender D. Schwalm M. Mutterer P. Singer M. Klemens J. P. Theobald M. Hesse F. Gönnenwein H. v. d. Ploeg 《Zeitschrift für Physik A Hadrons and Nuclei》1987,356(3):299-308
The γ-ray spectrum of 252Cf(sf) was measured in the Darmstadt-Heidelberg Crystal Ball spectrometer, with a double ionization chamber mounted inside to detect the fission fragments. The measurement was aimed at a better understanding of an unusual component found in the high-energy region between 3 and 8 MeV, with fragment mass splits near symmetry. This component was proved to be predominantly emitted by the heavier fragment, to reach its highest intensity at a fragment mass split of 132:120, and to have an almost isotropic angular distribution. Calculations with the statistical code CASCADE could reproduce the main features. 相似文献
283.
T. González-Lezana G. Delgado-Barrio P. Villarreal F.X. Gadéa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):227-232
The stabilization method is applied to the case of interacting resonances in the photo-dissociation of van der Waals clusters
composed by a rare gas atom bound to a dihalogen molecule. The study of an illustrative two-dimensional model consisting in
a T-shaped NeI2 molecule shows the adequacy of the method whenever the projection of the stabilization wave functions on the assumed prepared
initial state is accounted for. The agreement of the fragmentation cross-sections with some previous results using the effective
resolvent method and accurate close-coupling calculations is excellent. The method reveals its utility as a complementary
tool since allows, through the analysis of the stabilization wave function in terms of zero-order levels, a precise characterization
of the resonant states involved.
Received 5 April 2002 / Received in final form 24 May 2002 Published online 19 July 2002 相似文献
284.
A new and rather trivial model is suggested with mechanism that implies simultaneous violation of the zeroth and the second
laws of thermodynamics. Mathematically rigorous quantum theory reduces to a trivial application of the Golden rule formula.
It yields exciton on-energy-shell diffusion caused by bath-nonassisted excitation hopping between tails of different exciton
site levels ε1 < ε2 broadened by bath-assisted finite life-time effects. The elastic character of the hopping implies 1 ↔ 2-symmetric transfer
rate W. Thus the net diffusion exciton flow W(P
1 - P
2) and also, as argued, the net energy flow are possible due to different near-to-equilibrium exciton populations P
1 > P
2. As the sites are provided with two different baths, the population imbalance and the flows survive even for slightly different
local bath temperatures T
1 < T
2 < T
1ε2/ε1. Thus spontaneous exciton and also energy flows against temperature step become possible, in contradiction with the Clausius
form of the second law. Violations of both the laws disappear in the high-temperature, i.e. classical limit
Received 16 May 2001 and Received in final form 20 September 2001 相似文献
285.
286.
Márton Balázs Firas Rassoul-Agha Timo Seppäläinen 《Communications in Mathematical Physics》2006,266(2):499-545
We study space-time fluctuations around a characteristic line for a one-dimensional interacting system known as the random average process. The state of this system is a real-valued function on the integers. New values of the function are created by averaging previous values with random weights. The fluctuations analyzed occur on the scale n 1/4, where n is the ratio of macroscopic and microscopic scales in the system. The limits of the fluctuations are described by a family of Gaussian processes. In cases of known product-form invariant distributions, this limit is a two-parameter process whose time marginals are fractional Brownian motions with Hurst parameter 1/4. Along the way we study the limits of quenched mean processes for a random walk in a space-time random environment. These limits also happen at scale n 1/4 and are described by certain Gaussian processes that we identify. In particular, when we look at a backward quenched mean process, the limit process is the solution of a stochastic heat equation. 相似文献
287.
Jan Andres Karel Pastor Pavla Šnyrychová 《Journal of Fixed Point Theory and Applications》2007,2(1):153-170
A multivalued version of Sharkovskiĭ’s theorem is formulated for M-maps on linear continua and, more generally, for triangular M-maps on a Cartesian product of linear continua. This improves the main result of [AP1] in the sense that our multivalued
analogue holds with at most two exceptions. A further specification requires some additional restrictions. For instance, 3-
orbits of m-maps imply the existence of k-orbits for all
k ? \mathbbNk \in {\mathbb{N}}
, except possibly for
k ?k \in
{4, 6}. It is also shown that, on every connected linearly ordered topological space, an M-map with orbits of all periods can always be constructed. This demonstrates that Baldwin’s classification of linear continua
in terms of admissible periods [Ba] is useless for multivalued maps. 相似文献
288.
Lubomír Kubáček 《Mathematica Slovaca》2007,57(1):59-82
In some situations estimates of unknown parameters must be corrected by additional measurements. It is in principle no problem
to calculate the corrected estimates, however, it is of more interest to find formulae for correction itself. The formulae
enable us to design an additional experiment and to judge its usefulness.
The aim of the paper is to find such formulae for several situations.
Supported by the grant of the Council of Czech Government MSM 6 198 959 214. 相似文献
289.
There is a general interest in ranking schemes applied to complex entities described by multiple attributes. Published rankings
for universities are in great demand but are also highly controversial. We compare two classification and ranking schemes
involving universities; one from a published report, ‘Top American Research Universities’ by the University of Florida's TheCenter and the other using DEA. Both approaches use the same data and model. We compare the two methods and discover important equivalences.
We conclude that the critical aspect in classification and ranking is the model. This suggests that DEA is a suitable tool
for these types of studies. 相似文献
290.
Influence of boric acid on the electrochemical deposition of Ni 总被引:1,自引:0,他引:1
M. Šupicová R. Rozik L. Trnková R. Oriňáková M. Gálová 《Journal of Solid State Electrochemistry》2006,10(2):61-68
The electrolytic deposition of Ni onto a paraffin-impregnated graphite electrode from supporting chloride electrolyte (0.5 mol dm−3 NaCl) adjusted to the required pH using dilute HCl is investigated. The effect of electrolyte composition on the Ni electrodeposition
is studied using linear sweep voltammetry in the cathodic region. An elimination voltammetry procedure was applied to evaluate
the polarization curves. The aim of this work was to deduce the mechanism of Ni reduction in the chloride bath as well as
the influence of boric acid on this. Positively-charged NiCl+ ions were found to be the electroactive particles in the Ni reduction mechanism. The strong competition between the NiCl+, Cl− and H+ ions for active sites at the electrode is discussed. Kinetically-controlled adsorption/desorption processes of various species
were also confirmed using elimination voltammetry with a linear scan. The evolution of gaseous hydrogen, catalyzed by the
freshly-deposited Ni, accompanies the electrodeposition process. The presence of boric acid at a sufficiently high concentration
inhibits the deposition of Ni and, at the same time, improves the morphology and brightness, as well as the adhesion of the
deposited Ni.
Elimination voltammetry with a linear scan is an efficient way to evaluate current–potential curves that reflect the electrodeposition
of one-component Ni coatings. By eliminating selected currents, additional interesting and useful information can be obtained
from voltammetric data. 相似文献