Redistribution of photogenerated carriers in neutral and charged InAs quantum dot systems

Time-integrated and time-resolved photoluminescence spectra of neutral and negatively charged self-assembled InAs quantum dots (QDs) were studied. Obtained spectra have indicated that the redistribution of carriers in QDs occurs in all samples, but the temperature dependence of spectra are quite different for neutral and charged QDs. To clarify the origin of these behaviors, a model calculation based on two possible redistribution mechanisms has been carried out, and compared with experiments to show that the carrier tunneling between neighboring QDs is suppressed in charged QDs.     

Spinning combustion regimes in gasless systems containing one melting component

The propagation of a gasless combustion wave in a continuous cylindrical sample pressed from a mixture of solid reactants has been numerically simulated with allowance made for the melting of one of the components. The melting point of the component has been assumed to be equal to the reaction rate “cutoff” temperature. Symmetric and asymmetric combustion regimes can take place in the sample, depending on the sample radius. The reaction rate cutoff temperature is an additional perturbation factor in the propagation of the gasless combustion wave.     

Order parameter profiles in one component systems with a temperature gradient

Order parameter profiles are investigated under heat flow in a certain class of one-component systems in the neighborhood of a second order phase transition. A surface transition is also discussed, which occurs at a cooler boundary.     

Time fluctuations of charged and neutral cosmic-ray component fluxes as measured in the region of the brazilian magnetic anomaly

Summary Measurements of charged particles, gamma emission and neutrons were fulfilled on balloon in the region of the Brazilian magnetic anomaly on 8 November 1991. The flight lasted approximately 18 hours, including 15 hours on the ceiling at the height of 32 km just during the beginning of the recovery phase of the moderate geomagnetic storm. The main conclusion from the analysis of the obtained experimental data is the following:a) the fluxes of charged and neutral particles were measured and are in agreement with the data of previous works for the close values of geomagnetic cut-off rigidity;b) no sporadic increases of charged- and neutral-particle fluxes were recorded;c) the pulsations of charged particles, gamma-rays and neutrons with characteristic time of ≈ 30 min were found. The sporadic pulsations of charged particles and gamma-rays with shorter periods were observed too. But later pulsations were absent in the neutron flux data. This points to the magnetospheric origin of the observed phenomenon.     

中性及带电钴团簇的密度泛函理论研究

本文采用基于自旋极化的密度泛函理论系统研究了 小尺寸钴团簇的几何结构和电子结构特性。随尺寸的递增,团簇的基态几何结构由一维演变为三维的几何构型。总磁矩随尺寸的增加线性递增,并呈现奇偶交替的现象。从所研究的系统中分离一个Co原子带正电的团簇体系需要的能量相对较大。本文对体系的电子亲和能（EA）以及离化势（IP）也进行了讨论。     

Fragmentation channels of neutral and charged sodium clusters

The Density Functional Formalism (with the local density approximation for exchange and correlation) is applied to jellium-like spherical particles to obtain heats of fragmentation of Na_n; Na⁺_n and Na²⁺_n (n ⩽ 90) following different decay paths. Masses of the fragments are analyzed resulting that the energetically more favorable channels are controlled by the tendency to fragments with a magic number of electrons, mainly 2 or 8. We have also obtained that, provided we consider parent clusters with the same number of electrons and decay modes involving a neutral fragment, the fragmentations of neutral and ionized clusters are very similar.     

Channeling of fast charged and neutral particles in nanotubes

We present a theory to describe the propagation of relativistic charged particles, X-rays and thermal neutrons through straight or slightly bent nanotubes and calculated the spectra of electromagnetic radiation accompanying the channeling of charged particles.     

Evolution of zero-dispersion peaks in fluctuation spectra with temperature

Zero-dispersion peaks (ZDPs) can arise in fluctuation spectra of underdamped systems for which the dependence of the eigenfrequency on energy has an extremum. It is shown that ZDPs exist only for temperatures T higher than the critical one, T_c. The shape of the ZDP is described analytically as well as the process of the onset of this peak at T ≈ T_c. In the low-friction limit the shape of the ZDP turns out to be universal for T > T_c.     

中性和带电小钨团簇的第一性原理研究

采用基于密度泛函理论的第一性原理方法,计算了中性和带电小钨团簇W_n（n＝3—6）的构型,得到了一些能量较低的结构,它们都有可能是团簇的基态.研究发现,这些团簇大多具有较低的自旋多重度：中性小钨团簇为自旋单态或三重态;带电小钨团簇为自旋双重态或四重态.当n>3时,小钨团簇具有三维立体结构.通过拟合光电子谱、计算垂直离化能并与实验值比较,进一步讨论了带负电小钨团簇的基态结构. 关键词： 小钨团簇 构型 密度泛函理论     

Lifetime of charged and neutral B hadrons using event topology

The lifetimes of charged and neutral B hadrons have been measured using data collected by the DELPHI experiment at LEP between 1991 and 1993. B hadrons are tagged as jets with a secondary vertex and the charge of the B candidate is taken to be the sum of the charges of the particles in the secondary vertex. Approximately 1,434,000 multihadronic Z⁰ decays yielded 1817 B hadron candidates. The B purity was estimated to be around 99.1±0.3%, and 83% (70%) of the events measured as neutral (charged) came from neutral (charged) B's. The mean lifetimes of charged and neutral B hadrons were found to be 1.72±0.08 (stat.) ±0.06 (syst.) ps and 1.58±0.11 (stat.)±0.09 (syst.) ps respectively. The ratio of their lifertimes, _charged/_neutral, was 1.09 _–0.10 ^+0.11 (stat.)±0.08 (syst.). By making assumptions about the B _s ⁰ and _b ⁰ states, the B⁺ and B⁰ meson lifetimes were determined to be _B+ = 1.72 ± 0.08 (stat.) ±0.06 (syst.) ps and _B+ = 1.63 ± 0.14 (stat.)±0.13 (syst.) ps and the ratio of their lifetimes was:_B+/_B0 = 1.06 _–0.11 ^+0.13 ±0.10. The mean B lifetime was also deduced to be <> > = 1.64 ±0.06 (stat.)±0.04 (syst.) ps.     

非简并参量下转换中信号模的起伏谱

利用线性Langevin方程和谱矩阵,采用全量子方法讨论了非简并参量下转换中,腔外信号模在阈值以上和阈值以下的起伏谱,得出在这一过程中信号模与闲置模通常处于最小测不准态.     

Quantum chaos and fluctuation properties of regular and irregular spectra

Fluctuation properties of the regular and irregular energy levels for the Hénon-Heiles Hamiltonian are examined. The spacing distributions and the calculated values of the Δ₃-statistic show that there is no difference in the short range correlation properties of these spectra. Remarkably, the Δ₃ values agree with the results of random matrix theory. on leave of absence from P.R.L., Ahmedabad     

Coagulation of charged microparticles in neutral gas and charge-induced gel transitions

Coagulation of charged particles was studied using the mean-field Smoluchowski equation. The coagulation equation was generalized for the case of a conserved system of charged particles. It was shown that runaway cluster growth (gelation) solutions exist if the charge-dipole (induced) interaction of clusters is included. When clusters are in thermal equilibrium with the ambient gas, the charge-dipole interaction dramatically enhances the aggregation process and considerably increases the likelihood of a gelation transition.