Variable range cotunneling and conductivity of a granular metal

The Efros-Shklovskii law for the conductivity of granular metals is interpreted as a result of a variable range cotunneling process. The cotunneling between distant resonant grains is predominantly elastic at low T << T_c, while it is inelastic (i.e., accompanied by creation of electron-hole pairs on a string of intermediate non-resonant grains) at T > T_c. The corresponding E-S temperature T_ES in the latter case is slightly (logarithmically) T-dependent. The magnetoresistance in the two cases is different: it may be relatively strong and negative at T much below T_c, while at T>T_c it is suppressed due to inelastic processes which destroy the interference.Comment: Submitted to JETP Letter

Population of isomers in decay of the giant dipole resonance

The value of an isomeric ratio (IR) in N=81 isotones ($^{137}$Ba, $^{139}$Ce, $^{141}$Nd and $^{143}$Sm) is studied by means of the ($\gamma, n)$ reaction. This quantity measures a probability to populate the isomeric state in respect to the ground state population. In ($\gamma, n)$ reactions, the giant dipole resonance (GDR) is excited and after its decay by a neutron emission, the nucleus has an excitation energy of a few MeV. The forthcoming $\gamma$ decay by direct or cascade transitions deexcites the nucleus into an isomeric or ground state. It has been observed experimentally that the IR for $^{137}$Ba and $^{139}$Ce equals about 0.13 while in two heavier isotones it is even less than half the size. To explain this effect, the structure of the excited states in the energy region up to 6.5 MeV has been calculated within the Quasiparticle Phonon Model. Many states are found connected to the ground and isomeric states by $E1$, $E2$ and $M1$ transitions. The single-particle component of the wave function is responsible for the large values of the transitions. The calculated value of the isomeric ratio is in very good agreement with the experimental data for all isotones. A slightly different value of maximum energy with which the nuclei rest after neutron decay of the GDR is responsible for the reported effect of the A-dependence of the IR.Comment: 16 pages, 4 Fig

Structural and phase characteristics of vanadium oxide films

Проведены исследования влияния параметров процесса нанесения и последующего отжига на структуру и фазовый состав пленок оксида ванадия (VOx ). Пленки VOx наносились методом импульсного реактивного магнетронного распыления V мишени в Ar/O2 смеси газов и подвергались отжигу в атмосфере O2 при давлении 10 5 Па. Температура отжига изменялась от 100 до 450 °С. Время отжига варьировалось от 10 до 120 мин. Установлено, что при отжиге начальные процессы кристаллизации наблюдаются при температурах 250–275 °С. При этом, в зависимости от концентрации кислорода в процессе распыления, формируются поликристаллические пленки кубической или смешанной моноклинной/кубической кристаллической решеткой. При увеличении температуры отжига происходит переход от промежуточного оксида V 4 O 9 к смешанной фазе VO 2 /VO x /V 2 O 5 и далее к высшему оксиду V 2 O 5 . При увеличении времени отжига формирование высшего оксида V 2 O 5 наблюдается при более низких температурах и его концентрация увеличивается. The article The influence of the parameters of the deposition and subsequent annealing on the structure and phase composition of vanadium oxide (VO x ) films has been studied. VO x films were deposited by pulsed reactive magnetron sputtering of a V target in an Ar/O 2 gas mixture and annealed in an O 2 atmosphere at a pressure of 105 Pa. The temperature of the annealing varied from 100 to 450 °C. The time of the annealing varied from 10 to 120 min. It was found that during annealing, the initial crystallization processes are observed at temperatures of 250–275 °C. In this case, depending on the oxygen concentration during sputtering, polycrystalline films of a cubic or mixed monoclinic (cubic) crystal lattice are formed. As the temperature of the annealing rises, a transition occurs from the intermediate oxide V 4 O 9 to the mixed phase VO 2 /VO x /V 2 O 5 and then to the higher oxide V 2 O 5. With an increase in the annealing time, the formation of the higher oxide V 2 O 5 is observed at lower temperatures and its concentration increases

Allyl Isothiocyanate that Induces GST and UGT Expression Confers Oxidative Stress Resistance on C. elegans, as Demonstrated by Nematode Biosensor

Electrophilic xenobiotics and endogenous products from oxidative stresses induce the glutathione S-transferases (GSTs), which form a large family within the phase II enzymes over both animal and plant kingdoms. The GSTs thus induced in turn detoxify these external as well as internal stresses. Because these stresses are often linked to ageing and damage to health, the induction of phase II enzymes without causing adverse effects would be beneficial in slowing down ageing and keeping healthy conditions. for use as a nematode biosensor. With the nematode biosensor, we found that AITC induced GST expression and conferred tolerance on the nematode against various oxidative stresses. We also present evidence that the transcription factor SKN-1 is involved in regulating the GST expression induced by AITC.We show the applicability of the nematode biosensor for discovering and evaluating functional food substances and chemicals that would provide anti-ageing or healthful benefits

Luminescence spectra and kinetics of disordered solid solutions

We have studied both theoretically and experimentally the luminescence spectra and kinetics of crystalline, disordered solid solutions after pulsed excitation. First, we present the model calculations of the steady-state luminescence band shape caused by recombination of excitons localized in the wells of random potential induced by disorder. Classification of optically active tail states of the main exciton band into two groups is proposed. The majority of the states responsible for the optical absorption corresponds to the group of extended states belonging to the percolation cluster, whereas only a relatively small group of “radiative” states forms the steady-state luminescence band. The continuum percolation theory is applied to distinguish the “radiative” localized states, which are isolated in space and have no ways for nonradiative transitions along the tail states. It is found that the analysis of the exciton-phonon interaction gives the information about the character of the localization of excitons. We have shown that the model used describes quite well the experimental cw spectra of CdS(1−c)Sec and ZnSe(1−c)Tec solid solutions. Further, the experimental results are presented for the temporal evolution of the luminescence band. It is shown that the changes of band shape with time come from the interplay of population dynamics of extended states and spatially isolated “radiative” states. Finally, the measurements of the decay of the spectrally integrated luminescence intensity at long delay times are presented. It is shown that the observed temporal behavior can be described in terms of relaxation of separated pairs followed by subsequent exciton formation and radiative recombination. Electron tunneling processes are supposed to be responsible for the luminescence in the long-time limit at excitation below the exciton mobility edge. At excitation by photons with higher energies the diffusion of electrons can account for the observed behavior of the luminescence