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41.
42.
I.?A.?Pshenichnov B.?L.?Berman W.?J.?BriscoeEmail author C.?Cetina G.?Feldman P.?Heimberg A.?S.?Iljinov I.?I.?Strakovsky 《The European Physical Journal A - Hadrons and Nuclei》2005,24(1):69-84
We have calculated the fission probabilities for 237Np, 233, 235, 238U, 232Th, and natPb following the absorption of photons with energies from 68 MeV to 3.77 GeV using the RELDIS Monte Carlo code. This code implements the cascade-evaporation-fission model of intermediate-energy photonuclear reactions. It includes multiparticle production in photoreactions on intranuclear nucleons, pre-equilibrium emission, and the statistical decay of excited residual nuclei via competition of evaporation, fission, and multifragmentation processes. The calculations show that in the GeV energy region the fission process is not solely responsible for the entire total photoabsorption cross-section, even for the actinides. The fission probabilities are 80-95% for 233U, 235U, and 237Np, 70-80% for 238U, and only 55-70% for 232Th. This is because certain residual nuclei that are created by deep photospallation at GeV photon energies have relatively low fission probabilities. The results of those model calculations are in reasonable agreement (at the 10% level) with recent experimental data on relative photofission cross-sections for 237Np and 233, 235, 238U (but not for 232Th or natPb) from the Saskatchewan and Jefferson Laboratories over a very wide range in photon energy. Using our calculated fission probabilities plus the total photoabsorption cross-sections per nucleon, estimated from previous cross-section data for nuclei from C to Pb, we can infer absolute photofission cross-sections for the actinide nuclei and compare them with the SAL and JLab results. The resulting discrepancies, however, clearly demonstrate the need for direct measurement of the total photoabsorption cross-sections for the heavy actinides. 相似文献
43.
Sergio?del?CampoEmail author Mauricio?Cataldo Francisco?Pe?a 《General Relativity and Gravitation》2005,37(4):675-683
We study a model in which a closed universe with dust and quintessence matter components may look like an accelerated flat Friedmann–Robertson–Walker (FRW) universe at low redshifts. Several quantities relevant to the model are expressed in terms of observed density parameters,
M
and , and of the associated density parameter
Q
related to the quintessence scalar field Q. 相似文献
44.
F.?RahamanEmail author B.?C.?Bhui M.?Kalam 《International Journal of Theoretical Physics》2005,44(9):1413-1418
We analyze the space-time structure of local gauge string with a phenomenological energy–momentum tensor, as prescribed by
Vilenkin, in an arbitrary number of space-time dimensions with a non-zero cosmological constant Λ. A set of solutions of the
full non-linear Einstein's equations for the interior region of such a string is presented. 相似文献
45.
46.
47.
A.?A.?YambartsevEmail author A.?A.?Zamyatin 《Bulletin of the Brazilian Mathematical Society》2003,34(3):361-388
We consider a Markov chain that describes the evolution of
two interacting strings of symbols. The transitions
probalitities of this Markov chain depend only on the rightmost
symbols of both strings. The main goal of the present paper is
to prove a limit theorem (stabilization law): the distribution
of the rightmost symbols converges to some limit correlation
function.1 Partially supported by FAPESP (2002/01501-9) and
RFBR (02-01-00415)2 Partially supported by RFBR
(02-01-00415) 相似文献
48.
49.
S. J. Brodsky 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):638-644
The AdS/CFT correspondence between conformal field theory and string states in an extended space-time has provided new insights
into not only hadron spectra, but also their light-front wave functions. We show that there is an exact correspondence between
the fifth-dimensional coordinate of anti-de Sitter space z and a specific impact variable ζ which measures the separation of the constituents within the hadron in ordinary space-time. This connection allows one to
predict the form of the light-front wave functions of mesons and baryons, the fundamental entities which encode hadron properties
and scattering amplitudes. A new relativistic Schr?dinger light-front equation is found which reproduces the results obtained
using the fifth-dimensional theory. Since they are complete and orthonormal, the AdS/CFT model wave functions can be used
as an initial ansatz for a variational treatment or as a basis for the diagonalization of the light-front QCD Hamiltonian.
A number of applications of light-front wave functions are also discussed. 相似文献
50.
We construct stable bundle extensions on elliptically fibered Calabi–Yau threefolds. We show that these bundles can solve the topological anomaly constraint in heterotic string theory without the need for invoking background five-branes. 相似文献