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AbstractAbstract

[en] A three-dimensional parametric decay is theoretically studied of a pump Langmuir wave with a given finite wavenumber K into a longitudinal low frequency wave with an ajustable wavenumber k and another Langmuir wave. In this paper we study an extreme case; y+γ>>ωsub(e)K

^{2}lambda sub(e)sup(2) where y is the growth rate of the excited waves, γ the linear damping rate of the excited Langmuir wave and ωsub(e) the Langmuir frequency. It is shown that the pump energy well above the threshold takes a minimum at a wavenumber satisfying k>>K. However, the minimum of the pump energy just above the threshold is attained when k -- O(K) or when k>>K, according mainly to the strength and the wavenumber of the pump. In particular when k -- O(K), the maximum growth is realized when the three wave-vectors form a certain triangle, satisfying the wavevector conservation law. (auth.)Primary Subject

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Journal of the Physical Society of Japan; v. 42(2); p. 644-651

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AbstractAbstract

[en] The decay of orthopositronium to three photons can be studied using a method of covariant amplitudes previously used to calculate the Z → 3γ partial decay rate. Three independent amplitudes are needed to describe the decay. The orthopositronium decay amplitudes were calculated analytically to one-loop order using the method of Passarino and Veltman for evaluating one-loop integrals. The amplitudes are given in terms of dilogrithms, logarithms, and other elementary functions. These amplitudes were used to find new, higher precision results for the one-loop decay rate and the contribution to the two-loop decay rate coming from the squares of the one-loop amplitudes

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27. annual meeting of the Division of Atomic, Molecular and Optical Physics (DAMOP) of the American Physical Society (APS); Ann Arbor, MI (United States); 15-18 May 1996; CONF-9605105--

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AbstractAbstract

[en] The law for spontaneous transmutations, such as radioactive decay processes in atomic and nuclear physics, has been derived for the general case where the decay rates may be time dependent. The general formula for the ingrowth and decay in successive steps of radioactive decay chains, with multiple branches at each step, are given. As an example of current interest, the formalism is applied to the decay cascade of highly excited nuclei, where a time delay of the fission decay width is caused by the dynamics of the fission process. Several frequently used forms of the time dependence of the fission decay width are explored and discussed in connection with measurements of pre-scission γ- and particle emission

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1993 joint meeting of the American Physical Society and the American Association of Physics Teachers; Washington, DC (United States); 12-15 Apr 1993; CONF-9304297--

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AbstractAbstract

[en] We have studied the effects of colored multiplicative noises incorporated into the damping and the frequency term on the decay ratio (DR). It is clarified that the colored multiplicative noises can induce a long-time correlation and non-stationarity (random switching between unstable state and stable one) which give rise to the estimation errors of the DR

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S0306454997000947; Copyright (c) 1998 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: Malaysia

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Bromage, G.E.

Rutherford Appleton Lab., Chilton (UK)

Rutherford Appleton Lab., Chilton (UK)

AbstractAbstract

[en] The ill-conditioned nature of sums-of-exponentials analyses is confirmed and quantified, using synthetic noisy data. In particular, the magnification of errors is plotted for various two-exponential models, to illustrate its dependence on the ratio of decay constants, and on the ratios of amplitudes of the contributing terms. On moving from two- to three-exponential models, the condition deteriorates badly. It is also shown that the use of 'direct' Prony-type analyses (rather than general iterative nonlinear optimisation) merely aggravates the condition. (author)

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Jun 1983; 15 p; To be published in Computer Physics Communications.

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AbstractAbstract

[en] The properties of a simples quantum mechanical model for the decay of two equal mass particles are studied and related to some recent work on complex energy eigenvalues. It consists essentially in a generalization of the Lee-Friedrichs model for an unstable particle and gives a highly idealized version of the K

^{0}-anti K^{0}system, including CP violations. The model is completely solvable, thus allowing a comparison with the well known Weisskopf-Wigner formalism for the decay amplitudes. A different model, describing the same system is also briefly outlined. (Author)[pt]

As propriedades de um modelo quantico simples para o decaimento de duas particulas de massas iguais sao estudadas e relacionadas a alguns trabalhos recentes sobre autovalores complexos da energia. Consiste essencialmente em uma generalizacao do modelo de Lee-Friedrichs para uma particula instavel e da uma versao altamente idealizada do sistema K^{0}-anti K

^{0}, incluindo violacoes CP. O modelo e completamente soluvel, permitindo uma comparacao com o bem conhecido formalismo de Weisskopf-Wigner para as amplitudes de decaimento. Um modelo diferente, descrevendo o mesmo sistema, e tambem esbocado. (Autor)

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Journal Article

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Revista Brasileira de Fisica; ISSN 0374-4922; ; v. 10(3); p. 431-444

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AbstractAbstract

[en] Relativistic corrections of order α

^{2}to the decay width of orthopositronium are calculated using the local quasipotential equation. Necessary contributions coming from the amplitude of the three-photon decay of orthopositronium and from the normalization of the wave function, as well as second-order perturbative corrections, are taken into account. 20 refs., 2 figsPrimary Subject

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Translated from Yadernaya Fizika; 58: No. 8, 1454-1459(1995).

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Hussein, M.S.; Kerman, A.K.; McVoy, K.W.

Sao Paulo Univ. (Brazil). Inst. de Fisica

Sao Paulo Univ. (Brazil). Inst. de Fisica

AbstractAbstract

[en] The decay properties of overlapping compound nucleus resonances are discussed. It is argued that the correlation width of Agassi,Weidenmuller and Mantzouranis is to be identified with the average total width of Kawai, Kerman and McVoy. It is also shown that in the very strong coupling limit, the compound system behaves like a system with isolated resonances (weak absorption). (Author)

[pt]

Discutem-se as propriedades de decaimento das ressonancias de nucleos compostos sobrepostas. Argue-se que a largura de correlacao de Agassi, Weidenmuller e Mantzouranis identifica-se com a largura total media de Kawai, Kerman e McVoy. Mostra-se tambem que no limite de acoplamento muito forte, o sistema composto comporta-se como um sistema com ressonancias isoladas (absorcao fraca). (L.C.)Primary Subject

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May 1983; 11 p

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AbstractAbstract

[en] Part 3 of the paper mostly discusses the problem of justifying the approximation in which the reduced resolvent is replaced by the pole term alone. Imposing additional regularity assumptions on the function v, which specifies the interaction, it is possible to estimate the difference in the corresponding reduced propagators. The result is used to derive the estimate of the deviations from the exponential decay law which results from the pole approximation. With the exception of very small and very large times, the obtained bound is proportional to the fourth power of the coupling constant. The Fermi golden rule was proved for the model under consideration, and the present method compared to the one previously used by Demuth. (author). 7 refs

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For Part II see Czech. J. Phys. (1987) v. 37(9) p. 1028-1034.

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Adkins, G.S.

California Univ., Los Angeles (USA)

California Univ., Los Angeles (USA)

AbstractAbstract

[en] A method for calculating radiative corrections to positronium decay is presented that is direct and allows for calculations to any desired degree of accuracy. An expression for the decay amplitude in terms of the Bethe-Salpeter wave function is employed. The Bethe-Salpeter wave function is evaluated perturbatively in a scheme having a lowest order bound state equation that is exactly soluble. Various gauges are examined to see in which gauge the calculation is most straightforward. Coulomb gauge and Yennie gauge are suggested as preferred gauges. The use of other gauges for virtual photons is permitted with the addition of a correction term, which is obtained. Divergent integrals encountered in this calculation are defined by dimensional regularization. Renormalization in Coulomb gauge is discussed, and a useable form of the Coulomb gauge self-energy function is presented. A physically motivated subtraction scheme is used to define and calculate the renormalization constants Z

^{1}and A^{2}in Coulomb gauge. One-loop renormalization in Coulomb gauge, as well as in Yennie gauge, presents no difficulties. These two gauges can be renormalized in this scheme without the introduction of unphysical infrared divergences. Using this method the known analytic result for the o(α) correction to the parapositronium decay rate is obtained. The same method is applied to orthopositronium, and the existing theoretical discrepancy in the value of the o(α) correction to the decay rate is resolved. This o(α) correction is obtained with an error which corresponds to an uncertainty in the total rate much smaller than α_{2}Inα GAMMA/sub LO and α_{2}GAMMA/sub LO/ (where GAMMA/sub LO/ is the lowest order rate)Primary Subject

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1981; 139 p; University Microfilms Order No. 82-01,069; Thesis (Ph. D.).

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Thesis/Dissertation

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