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21.
《Il Nuovo Cimento C》1984,7(2):223-234
Summary New possibilities are pointed out of a more accurate identification of solar flares, responsible for Forbush decreases of
galactic cosmic rays, caused by flare-generated interplanetary shock waves, based on tracking type-II radio bursts. Nine solar
flares, observed between September 1978 and December 1979, generated shock waves which produced intensive type-II radio bursts
observed in the hectometric and kilometric wave range by the ISEE-3 satellite. All the type-II shocks were responsible for
Forbush decreases. Since the observation of type-II radio bursts enables us to follow the propagation of shock waves practically
from the place where they are generated deep in the solar corona, through interplanetary space as far as the Earth, these
observations provide the possibility of exact identification of Forbush decreases with the corresponding flares. These observations
have also supplied a further dimension for analysing interplanetary disturbances and forecasting Forbush decreases.
Riassunto Sono messe in evidenza nuove possibilità per una piú accurata identificazione dei brillamenti solari responsabili delle diminuzioni di Forbush, nell’intensità dei raggi cosmici galattici, dovute ad onde d’urto interplanetarie. Tali possibilità sono basate sull’osservazione dello sviluppo spazio-temporale delle sorgenti della radioemissione di tipo II. Durante il periodo settembre 1978-dicembre 1979, sono stati osservati nove brillamenti solari, che generavano onde d’urto producenti un’intensa radioemissione di tipo II osservata dal satellite ISEE-3 nell’intervallo di lunghezze d’onda ettometrico e chilometrico. Tutte queste onde d’urto erano responsabili delle diminuzioni di Forbush. Poiché l’osservazione della radioemissione di tipo II ci permette di seguire la propagazione delle onde d’urto praticamente dal posto dove loro sono generate, in profondità nella corona, fin nello spazio interplanetario verso la Terra, i risultati ottenuti forniscono la possibilità di una precisa identificazione della connessione tra le diminuzioni di Forbush ed i brillamenti corrispondenti. Queste osservazioni danno anche un ulteriore contributo all’analisi delle perturbazioni interplanetarie ed alla possibilità di previsione di diminuzioni di Forbush.
Резюме Указываются новые возможности, связанные с прослеживанием радиовспышек типа II, для более точной идентификации солнечных вспышек, ответственных за убывание Форбуша, которые вызывают межпланетные ударные волны. Девять солнечных вспышек, наблюдавшися между сентябрем 1978 и декабрем 1979, образовали ударные волны, которые вызвали интенсивные радио-вспышки типа II, которые наблюдались спутником ISEE-3. Все эти ударные волны типа II ответственны за убывания Форбуша. Так как навпюдения радио-вспышек типа II позволяет нам проследить распространение ударных волн практически от места их образования глубоко в солнечной короне через межпланетное пространство до Земли, то такие наблюдения обеспечивают возможность точной идентификации убываний Форбуша в зависимости от соответствующих солнечных вспышек. Эти наблюдения также позволяют анализировать межпланетные возмущения и предсказывать убывания Форбуша.相似文献
22.
Summary The problem of the missing matter in the Universe is reviewed and discussed in terms of massive neutrinos. The primordial
abundances of light elements produced during the big bang nucleosynthesis can be used to determine firm bounds on the number
of neutrino flavours and on the ratio of baryon to photon densities in the Universe. These limits imply that nonbaryonic matter
is the dominant constituent of large-scale cosmic structures, being massive neutrinos the best guess for such a matter. In
order that the Universe be closed, a value of the neutrino rest mass is derived, which agrees with the bounds obtained from
the dynamics of galaxies and clusters of galaxies. It is also shown that density perturbations can hardly grow in a nucleon-dominated
Universe, and massive neutrinos may be the seed for nucleon condensations. All these astrophysical and cosmological considerations
suggest a lower and an upper bound of the neutrino rest mass.
Paper presented at the Congress ?Galactic and Extragalactic Dark Matter?, Roma, 28 to 30 June 1983. 相似文献
23.
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
24.
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
25.
26.
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
27.
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
28.
Mustapha Ishak 《Foundations of Physics》2007,37(10):1470-1498
Associated with the cosmic acceleration are the old and new cosmological constant problems, recently put into the more general context of the dark energy problem. In broad terms, the old problem is related to an unexpected order of magnitude of this component while the new problem is related to this magnitude being of the same order of the matter energy density during the present epoch of cosmic evolution. Current plans to measure the equation of state or density parameters certainly constitute an important approach; however, as we discuss, this approach is faced with serious feasibility challenges and is limited in the type of conclusive answers it could provide. Therefore, is it really too early to seek actively for new tests and approaches to these problems? In view of the difficulty of this endeavor, we argue in this work that a good place to start is by questioning some of the assumptions underlying the formulation of these problems and finding new ways to put this questioning to the test. First, we calculate how much fine tuning the cosmic coincidence problem represents. Next, we discuss the potential of some cosmological probes such as weak gravitational lensing to identify novel tests to probe dark energy questions and assumptions and provide an example of consistency tests. Then, motivated by some theorems in General Relativity, we discuss if the full identification of the cosmological constant with vacuum energy is unquestionable. We discuss some implications of the simplest solution for the principles of General Relativity. Also, we point out the relevance of experiments at the interface of astrophysics and quantum field theory, such as the Casimir effect in gravitational and cosmological contexts. We conclude that challenging some of the assumptions underlying the cosmological constant problems and putting them to the test may prove useful and necessary to make progress on these questions. 相似文献
29.
Axially symmetric space-time is considered in the presence of cosmic string source and thick domain walls in the frame work
of a scale-covariant theory of gravitation. A relation between metric potential is assumed to get a determinate solution of
the field equations of this theory. In this particular case, it is observed that the geometric (Nambu) string p-string (Takabayasi
string) and Reddy string do not survive. It is also seen that the stiff (self-gravitating) domain walls do not exist in this
theory. 相似文献
30.
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