排序方式: 共有68条查询结果,搜索用时 15 毫秒
31.
32.
Marc Dixmier 《Pramana》1994,43(6):453-465
We suggest a new answer to the problem of the solar neutrinos: a neutrino-photon interaction that would cause the neutrinos
to disappear before they leave the sun or make them lose energy towards detection thresholds. We calculate the available energy
in the system of the centre of mass, and show that the photons may be endowed with a pseudo-cross-section in the system of
the sun. Under the assumption of an absorption, made to simplify the neutrino transport calculation, the chlorine experiment
yields:σ
a
=1.8(
−1.0
+0.7
)*10−9 barn, which is close tog
β/(ℏc)=4·49*10−9 barn. The escape probability is substantially larger for the gallium neutrinos than for the chlorine neutrinos. Thermal radiation
in the core of a supernova is suppressed by electrical conductivity, therefore the neutrinos from SN1987A could escape; they
interacted with the photon piston in the outer layers of the supernova and the interaction has to be a scattering. The cosmological
implications of a neutrino-photon interaction are discussed; Hubble’s constant may have to be modified. The case of an elastic
scattering between neutrino and photon is discussed in more detail.
An erratum to this article is available at . 相似文献
33.
Background: Ribozymes catalyze an important set of chemical transformations in metabolism, and ‘engineered’ ribozymes have been made that catalyze a variety of additional reactions. The possibility that catalytic DNAs or ‘deoxyribozymes’ can be made has only recently been addressed. Specifically, it is unclear whether the absence of the 2′ hydroxyl renders DNA incapable of exhibiting efficient enzyme-like activity, making it impossible to discover natural or create artificial DNA biocatalysts.Results: We report the isolation by in vitro selection of two distinct classes of self-cleaving DNAs from a pool of random-sequence oligonucleotides. Individual catalysts from ‘class I’ require both Cu2+ and ascorbate to mediate oxidative self-cleavage. Individual catalysts from class II use Cu2+ as the sole cofactor. Further optimization of a class II individual by in vitro selection yielded new catalytic DNAs that facilitate Cu2+-dependent self-cleavage with rate enhancements exceeding 1000 000-fold relative to the uncatalyzed rate of DNA cleavage.Conclusions: Despite the absence of 2′ hydroxyls, single-stranded DNA can adopt structures that promote divalent-metal-dependent self-cleavage via an oxidative mechanism. These results suggest that an efficient DNA enzyme might be made to cleave DNA in a biological context. 相似文献
34.
35.
C. Volpe 《Progress in Particle and Nuclear Physics》2010,64(2):325-333
One of the major open issues in neutrino physics is the possible existence of CP violation in the neutrino sector. Such an observation would have an important impact in various domains of physics, from high energy physics to cosmology. Its search requires future accelerator neutrino facilities producing intense and pure neutrino beams such as “beta-beams”. Here we review the different beta-beam scenarios proposed so far and discuss the present status, with a particular emphasis on the original baseline scenario and its feasibility. Alternative strategies for the CP violation search are to be pursued as well. A possibility is to search for CP violation effects in astrophysical environments. Here we present recent analytical and numerical results obtained in the context of core-collapse supernovae. In particular, we point out the conditions under which there can be CP violating effects in dense media and show numerical results on the supernova (anti-)neutrino fluxes and on the electron fraction, relevant for the r-process nucleosynthesis. 相似文献
36.
Core-collapse supernovae produce a hot protoneutron star that cools emitting huge amounts of neutrinos of all flavors. The interaction of these neutrinos with the outer layers of the protoneutron star produces an outflow of matter whose composition is determined by the luminosities and energies of the emitted neutrinos and antineutrinos. The presence of light nuclei like deuterons and tritons can have a big impact in the average energies of the emitted antineutrinos and consequently in the neutron-richness of the ejected matter. Recent hydrodynamical models show that the ejected matter is in fact proton-rich and constitutes the site of the νp-process where antineutrino absorption reactions catalyze the nucleosynthesis of nuclei with A>64. 相似文献
37.
38.
39.
基于壳模型与Random Phase Approximation理论, 利用Shell-Model Monte Carlo方法, 研究了超新星爆发环境核素56,57,59,60Co的电子俘获与电子丰度变化率. 我们的结果与利用Aufderheide方法计算的结果进行了误差对比. 结果表明: 电子俘获率受温度和密度的影响大大增加, 甚至增加达6个数量级以上(如在ρ7=0.43, Ye=0.48核素57,59,60Co). 另一方面, 随着温度和密度的增大, 电子丰度变化率大大降低, 甚至减小达5个数量级以上(如在ρ7=5.86, Ye=0.47核素59Co). 通过对误差因子的分析表明, 在低温低密度环境二种结果误差较大; 而在高温高密度环境, 二种结果误差相对较小.
关键词:
电子俘获
超新星 相似文献
40.
In recent years,with the development of simulations about supernova explosion,we have a better understanding about the density profiles and the shock waves in supernovae than before.There might be a reverse shock wave,another sudden change of density except the forward shock wave,or even no shock wave,emerging in the supernova.Instead of using the expression of the crossing probability at the high resonance,PH,we have studied the matter effects on neutrino oscillations in different supernova models.In detail,we have calculated the survival probability of νe(P_s)and the conversion probability of ν_x(P_c) in the Schrodinger equation within a simplified two-flavor framework for a certain case,in which the neutrino transfers through the supernova matter from an initial flavor eigenstate located at the core of the supernova.Our calculations was based on the data of density in three different supernova models obtained from simulations.In our work,we do not steepen the density gradient around the border of the shock wave,which differs to what was done in most of the other simulations.It is found that the mass and the density distribution of the supernova do make a difference on the behavior of P_s and P_c.With the results of P_s and P_c,we can estimate the number of νe(and ν_x) remained in the beam after they go through the matter in the supernova. 相似文献