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11.
12.
We extend a theory of first order ? corrections to Gutzwiller’s trace formula for systems with a smooth potential to systems with discrete symmetries and, as an example, apply the method to the two-dimensional hydrogen atom in a uniform magnetic field. We exploit the C4v-symmetry of the system in the calculation of the correction terms. The numerical results for the semiclassical values will be compared with values extracted from exact quantum mechanical calculations. The comparison shows an excellent agreement and demonstrates the power of the ? expansion method. 相似文献
13.
M. Naylor I. G. Main 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(1):139-146
We examine the cell scale self organising mechanisms in the Olami Feder Christensen (OFC) model that have the potential to
generate critical behaviour. In particular we demonstrate how spatial organisation and quantisation of strain distributions
occurs, why temporal strain fluctuations are minimised as the local strain conservation factor, β → 1.0, and how the strain distributions are dependent upon the lattice geometry employed. The origin of the self-organising
behaviour can be divided into two regimes; at low β where no re-rupturing of cells occurs and for higher β where the probability of re-rupturing becomes increasingly significant. The presence or absence of the re-rupturing mechanism
leads to different system optimisations, tending from spatially well ordered strain domains at intermediate β to a spatially rough strain field but a temporally stationary, memory less strain distribution at β = 1. The construction of the Markov chain demonstrates that degeneracy of the transitions is a primary control on transition
probabilities at β = 1. The stationary state occupation is controlled by transition degeneracy, local correlations and mean residence times. 相似文献
14.
Michael G Main Richard J Lorentz 《Journal of Algorithms in Cognition, Informatics and Logic》1984,5(3):422-432
Any nonempty string of the form xx is called a repetition. An O(n log n) algorithm is presented to find all repetitions in a string of lenght n. The algorithm is based on a linear algorithm to find all the new repetitions formed when two strings are concatenated. This linear algorithm is possible because new repetitions of equal length must occur in blocks with consecutive starting positions. The linear algorithm uses a variation of the Knuth-Morris-Pratt algorithm to find all partial occurrences of a pattern within a text string. It is also shown that no algorithm based on comparisons of symbols can improve O(n log n). Finally, some open problems and applications are suggested. 相似文献
15.
Mass spectra of positive and negative secondary ions from various alkali halides have been measured in the Manitoba time-of-flight mass spectrometer. The ions were produced by Cs+ and K+ bombardment at primary ion energies of 3 to 19 keV for the positive spectra, and 11 to 28 keV for the negative spectra. The ions measured were those emitted within a time interval ~ 20 ns after the primary ion impact. The secondary ion yields are strongly dependent on the sample composition and treatment; prior irradiation may change the yield by an order of magnitude or more. The secondary ion yields also depend strongly on the energy loss of the primary ion, but the ratio of yields of different cluster ions from a given target is almost independent of this parameter. The results appear to be consistent with models in which the clusters are ejected directly from the target, but do not determine whether or not they possess the original surface structure. The results may also be described by a recombination model if the recombination is essentially complete. 相似文献
16.
17.
A. Polimeni A. Patan M. Henini L. Eaves P. C. Main G. Hill 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
The optical properties of InAs/AlyGa1−yAs self-assembled quantum dots are studied as a function of temperature from 10 K to room temperature. The temperature dependence of carrier hopping between dots is discussed in terms of the depth of the dot confinement potential and the dispersion in dot size and composition. We show that carrier hopping between dots influences both the electrical and optical properties of laser devices having dots as active medium. 相似文献
18.
19.
CM Thaker S Rayaprol Krushna Mavani DS Rana MS Sahasrabudhe SI Patil DG Kuberkar 《Pramana》2002,58(5-6):1035-1039
The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO3 perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good
example of these properties is (La1−2x
Pr
x
Ca
x
)MnO3 (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T
c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using
X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for
understanding the structural, transport and magnetic properties are discussed in detail. 相似文献
20.
B. Wallbank C.E. Johnson I.G. Main 《Journal of Electron Spectroscopy and Related Phenomena》1974,4(3):263-269
Pronounced surface reduction of some 3d transition metal compounds has been observed during measurements with an AEI ES200 X-ray photoelectron spectrometer. Systematic data indicate that the degree of reduction in a given compound does not depend on temperature, vacuum pressure or X-ray flux, but is a function only of the integrated X-ray dose. Particularly strong effects were found in cupric fluoride and potassium ferricyanide. 相似文献