Simulating transuranium isotope yields upon explosive nucleosynthesis with allowance for elements of process dynamics

A two-group model of transuranium isotope production under the conditions of explosive nucleosynthesis is studied. The slow neutron effect on the yields of transuranium isotopes is considered. The static model of multiple neutron capture is supplemented with features of dynamics with allowance for the adiabatic expansion of matter at t ?? 10^?6 s. The results from calculations in the two-group model for mass numbers A = 246?C257 are compared to those of the Par experiment.     

Superconductivity in transuranium elements and compounds

We present here an overview of the properties of transuranium superconductors, but also of the (non-superconducting) transuranium analogues of uranium superconductors. We briefly review superconductivity in actinide elements and uranium compounds and focus in particular on the ${\text{PuTX}}_5$ ($T=\text{Co},\text{Rh}$; $\text{X}=\text{Ga},\text{In}$) series, the largest superconducting system in actinides and ${\text{NpPd}}_5{\text{Al}}_2$, the so far unique neptunium superconductor. The effects of chemical substitution, ageing and pressure on the properties of transuranium superconductors are also discussed.     

Calculation of transuranium element synthesis in intensive neutron fluxes under adiabatic conditions

The creation of transuranium isotopes based on intense pulsed nucleosynthesis is considered. The model of multiple neutron captures takes into account the variation of the (n, γ)-cross section resulting from adiabatic expansion of the explosive nucleosynthesis area. The calculated yields of transuranium isotopes obtained under conditions close to a “Par” nuclear explosion, enable us to improve the agreement between the model results and the experimental data within the wide range of atomic mass number A = 248–257, provided the adiabatic conditions are taken into account.     

Supernova neutrino nucleosynthesis of light elements with neutrino oscillations

Light element synthesis in supernovae through neutrino-nucleus interactions, i.e., the v process, is affected by neutrino oscillations in the supernova environment. There is a resonance of 13-mixing in the O/C layer, which increases the rates of charged-current -process reactions in the outer He-rich layer. The yields of 7Li and 11B increase by about a factor of 1.9 and 1.3, respectively, for a normal mass hierarchy and an adiabatic 13-mixing resonance, compared to those without neutrino oscillations. In the case of an inverted mass hierarchy and a nonadiabatic 13-mixing resonance, the increase in the 7Li and 11B yields is much smaller. Observations of the 7Li/11B ratio in stars showing signs of supernova enrichment could thus provide a unique test of neutrino oscillations and constrain their parameters and the mass hierarchy.     

Evaluating the yield of transuranium nuclides with masses of up to A = 270 via pulsed nucleosynthesis

A model of the creation of transuranium isotopes of up to A = 270 under conditions of pulse nucleosynthesis in a neutron flux with densities of up to ??10²⁵ neutron cm^?2 is considered. The pulse process allows us to divide it in time into two stages: the process of multiple neutron captures (t < 10^?6 s) and the subsequent ??-decay of neutron-excess nuclei. The modeling of the transuranium yields takes into account the adiabatic character of the process, the probability of delayed fission, and the emission of delayed neutrons. A target with a binary composition of ²³⁸U and ²³⁹Pu, ²⁴⁸Cm, and ²⁵¹Cf isotopes is used to predict the yields of heavy and superheavy isotopes.     

Neutron excess number and nucleosynthesis of heavy elements in a type Ia supernova explosion

Type Ia supernovae produce very powerful burst of light, which can be observed to high redshift. This fact is very attractive for cosmological applications. For supernova light curve modeling, it is very important to know the amount of Fe and Ni, formed during the explosion. In this paper, we explore both the chemical composition of the ejected supernova shells and the possibility of weak r-process under increased neutron excess number based on a set of trajectories of tracer particles, calculated in a hydrodynamic model of SNIa explosion. It is shown that no r-process elements are synthesized in the considered supernova model, even for an increased neutron excess number (Y_e ～ 0.4) because of the slow evolution of temperature and density along chosen trajectories. The results of explosive nucleosynthesis are discussed.     

Theoretical estimates for the production of transuranium elements in heavy-ion collisions

A thick target experiment of the U+U reaction at 7.5 MeV/u is analyzed within the diffusion model for dissipative heavy-ion collisions. Cross sections for the production of superheavy elements as well as probability distributions of excitation energies and spins as function of fragment charge are estimated. The influence from changes of incident energy and projectile-target combination is studied.     

Ultrashort pulse propagation under manipulated resonance conditions

The propagation of a polarized ultrashort laser pulse is analyzed by the inverse scattering method under initial conditions including a spatial pulse profile, a state of the medium, and a “switched-on” resonant atom-field interaction. Magnetic degeneracy of atomic levels is taken into account. The Maxwell-Bloch equations are rewritten in Hamiltonian form without redefining the spatial and temporal variables. The inverse scattering method is based on an analysis of a new spectral problem. Gelfand-Levitan-Marchenko-type equations are derived, a soliton solution is obtained, and the changes in parameters of two solitons after their collision are calculated. A possible experimental setup for implementing the system under analysis is discussed.     

多层陶瓷电容器在脉冲条件下寿命特性的研究

 主要研究了高储能密度多层陶瓷电容器（MLC）在不同充放电频率、充电电压、充放电占空比和放电反峰系数等条件下的寿命特性,并对其失效机理进行分析。实验发现,正常情况下MLC试品的击穿需要经过局部放电通道不断发展,绝缘逐渐被破坏的过程,寿命较长,发热和试品内部的交变应力是推动局部放电通道不断发展的根本因素。充放电频率的升高使试品发热加剧,寿命缩短;充电电压和放电反峰系数的增大使发热和介质内应力加剧,可以使寿命缩短90％以上。改善散热可以有效提高试品寿命,如当充放电频率为136 Hz时,采用油浸散热比空气自然换流散热寿命延长300％。     

Phenomenological model of the inhomogeneous state of a material under a pulse effect

A model is proposed that takes account of features of the material state under a pulse effect. The characteristic inhomogeneous states for an unstable medium are analyzed. Their correspondence with experimentally detected effects is noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 50–55, June, 1990.     

Solution to Big-Bang nucleosynthesis in hybrid axion dark matter model

Following a recent suggestion of axion cooling of photons between the nucleosynthesis and recombination epochs in the Early Universe, we investigate a hybrid model with both axions and relic supersymmetric particles. In this model we demonstrate that the ⁷Li abundance can be consistent with observations without destroying the important concordance of deuterium abundance.     

A model of solidification under microgravity conditions

The influence of the microgravity environment on solidification processes is discussed. A simple model of the solidification of a binary-alloy is presented with the chemical diffusion influenced by the gravitational field. Using the results of Mullins and Sekerka, we employ the linear theory of hydrodynamic stability to investigate the interfacial instability driving the pattern-forming processes in solidification. As a result, we estimate the characteristic size of the elements of the emerging pattern. We show that, in spite of good agreement of our result with the size of cellulae observed in experiments, the model cannot explain the changes in the patterns occurring in space environment. In conclusion we shortly discuss the possibility of adding realism to our simple model by including the effect of convection.     

Photoabsorption cross sections of the alkaline-earth-metal elements under strong interaction conditions

The strong interatomic interaction effects on photoabsorption cross sections of a private atom have been interpreted by the contribution of both the real and imaginary parts of atomic polarizability in the present work. Some unresolved differences between the photoabsorption cross sections of isolated atoms and those of condensed atoms, especially near thresholds and resonances, probably could be interpreted by the competition between the imaginary and real parts of atomic frequency-dependent polarizabilities.     

Self-induced transparency and electromagnetic pulse compression in a plasma or an electron beam under cyclotron resonance conditions

Based on analogy to the well-known process of the self-induced transparency of an optical pulse propagating through a passive two-level medium we describe similar effects for a microwave pulse interacting with a cold plasma or rectilinear electron beam under cyclotron resonance condition. It is shown that with increasing amplitude and duration of an incident pulse the linear cyclotron absorption is replaced by the self-induced transparency when the pulse propagates without damping. In fact, the initial pulse decomposes to one or several solitons with amplitude and duration defined by its velocity. In a certain parameter range, the single soliton formation is accompanied by significant compression of the initial electromagnetic pulse. We suggest using the effect of self-compression for producing multigigawatt picosecond microwave pulses.