Simulation of generation of ultradisperse particles upon irradiation of metals by a high-power electron beam

A model of formation of ultradisperse particles in the plasma torch emerging during evaporation of a metal target by a high-power electron beam is described. A model of heterogeneous media is proposed for describing the plasma torch dynamics taking into account heat conduction, heat transfer and friction between components, relaxation of components to equilibrium, condensation, and evaporation and coagulation of drops as a result of their collisions. Numerical simulation of the generation of ultradisperse particles in the plasma torch formed during irradiation of a metal target by a powerful electron beam is performed. The size distribution of ultradisperse particles is obtained for various regimes of irradiation and cooling.     

Topological phases for composite particles with dynamic properties

We show that, if a given electromagnetic property of a particle is allowed to vary during an evolution where the particle will accrue a topological phase, then it is both the time average and the statistical variance of this property which will affect the observable phenomena. The time average is shown to affect the topological aspect of the phase. This is in addition to a second smaller dynamical phase term, which depends upon only the variance of the changing property. The theory is illustrated in reference to the time dependence of the dipole moment in both the Aharonov-Casher and He-McKellar-Wilkens effects.     

Structure of ultradisperse diamonds

The structure of crystallites (regions of coherent scattering — RCS), which comprise the grains of ultradisperse diamond (UDD) powder, was investigated by x-ray crystallography and coordination-sphere diffractometry. It was established that the RCS have an average size $\bar L = 42 \pm 2{\AA}$ and that these regions are themselves UDD grains with the structure of a diamond lattice and a negligible content of clusters of carbon atoms distributed throughout the volume that do not form a lattice and are mainly located at interatomic distances ～1.5 Å. The clusters of carbon atoms, for which the distribution of interatomic distances is close to Gaussian, which may indicate an amorphous structure of the boundary layers, lie along grain boundaries.     

Unification of interactions in a model with composite particles

A model for the unification of interactions with composite quarks, leptons, and Higgs fields is proposed on the basis of the SU(5) group. The model explains in a natural manner the appearance of generations, mixing of cato-quarks, proton decay, and so on. A number of effects are predicted, specifically, the existence of a fourth generation of particles. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 5, 293–298 (10 September 1997)     

球形粒子复合介质非线性有效电导交流响应

利用摄动方法，研究了在外加交流电场作用下，含球形杂质的非线性复合介质有效电导的交流响应问题。在一类形如E1sinωt +E3sin3ωt的正弦电场作用下，分别导出了非线性复合介质中杂质粒子及基质所在区域的局部电势。在杂质浓度较低时，进一步得到了复合介质非线性有效电导在基频和三阶谐波下的响应，并讨论了二者之间的关系。     

Optical potential for composite particles

Optical potentials for the elastic scattering of deuterons, ³He and tritons are calculated in terms of the optical potentials of neutrons and protons forming the projectile. The angular distributions for the elastic scattering of these particles from various targets are calculated and compared with experimental results.     

Photoluminescence spectra of ultradisperse diamond

The first study of materials based on ultradisperse diamond produced by detonation is reported. A luminescence band in the visible has been observed, and some of its structural features have been interpreted by analogy with the known luminescence bands of centers in synthetic and natural diamonds. A comparison of the spectra obtained from ultradisperse diamond samples with the surface modified by different chemical treatments suggests that their pattern is governed to a considerable extent by the presence of a graphitic layer on the grain surface. Fiz. Tverd. Tela (St. Petersburg) 39, 2156–2158 (December 1997)     

Numerical investigation of the flow of ultradisperse particles of the aluminum oxide in the solid-fuel rocket engine nozzle

The work deals with the two-phase flow investigation. The computations were done for a continuous coagulation model within the framework of the phenomenological multi-fluid model of the medium. A conclusion was drawn that the diminution of the particles size leads to a reduction of two-phase losses in the nozzle unit of the solid-fuel engine.     

Two-photon-excited fluorescence in ultradisperse diamond powders

The spectra of two-photon-excited fluorescence in the near ultraviolet are studied in diamond powders prepared by detonation synthesis, with particle sizes of 20–40 Å. The spectra of ultradisperse diamond powders are compared with that of a diamond single crystal. It is shown that the proposed method can be used to detect ultradisperse diamonds in quantities as low as 10^?12 g.     

Effective dielectric function of a metal-dielectric composite with nonrandomly distributed particles

Summary The optical properties of a metal-dielectric binary composite with nonrandomly distributed particles were studied within the framework of the effective medium theory. All the particles, as usual, were assumed to be spherical and the nonrandomness of their distribution was achieved by forcing onto the system the correlation that prevents the metal particles from touching each other or the one that forces them to aggregate in pairs, either oriented at random or all alike. The drawbacks of the effective medium theory due to the assumption that the particles be very small were overcome by describing the scattering properties of the particles through their exact Mie amplitudes. Both kinds of correlation we considered turned out to have substantial effects on the onset of the percolation phenomena. The transition induced by the correlation of exclusion from a behaviour typical of the Bruggeman model to one more appropriate to the Maxwell-Garnett model was followed as a function of the exclusion radius. In the case of aggregation the onset of the percolation phenomena was found to be strongly influenced by the further introduction of an orientational order of the pairs. Based on work supported in part by the U. S. Army European Research Office through Contract DAJA45-86-C-0003 and in part by the Consiglio Nazionale delle Ricerche through the Gruppo Nazionale Struttura della Materia.     

Quantum transmittance of barriers for composite particles

The transmission of two bound particles through a repulsive barrier is studied. A simple mechanism for the appearance of barrier resonances, which results in anomalous barrier transmittance as compared with the transmission probability for structureless objects, is demonstrated. It is shown that the probabilities for two interacting particles to tunnel from a false vacuum can be much higher than previously thought.     

Finite temperature formalism for composite quantum particles

This Letter provides the missing part of the newly constructed many-body formalism for composite quantum particles: the introduction of a finite temperature. The finite T formalism we propose deeply relies on the existence of a compact closure relation for the (overcomplete) set of N-composite-particle states. As a first application, we here calculate the energy mean value of the exciton gas outside the condensation regime. We show that carrier exchanges increase its temperature dependence compared to elementary bosons, a signature of the degree-of-freedom increase resulting from the particle composite nature.     

Aharonov-Bohm effect for composite particles and collective excitations

The energies of neutral and charged excitons in quantum rings and the plasmon frequencies in nanotubes are analyzed as functions of a magnetic field.     

Nanometer gold-silica composite particles manipulated by optical tweezers

We have studied the behavior of nano or micro size composite particles submitted to optical trapping forces and a comparison was made with homogeneous particles of similar dimension. The forces were measured using the power spectrum signal analysis. Most of the results presented were obtained using a lateral effect position sensitive detector (PSD), which allowed the fluctuations of the particle position in the optical trap to be monitored. A 4-quadrant photodiode was also used for the same purpose. We bring clear experimental evidence that the trapping force was increased by a factor of about 2-3 for composite particles made of a colloidal gold core encapsulated in a silica shell, with respect to homogeneous silica or latex beads. These results were discussed in the frame of the various approaches currently used for modeling optical tweezing forces.     

Adaptive optical properties of ER fluid incorporating composite particles

Electrorheological (ER) fluid is one of the popular materials used in smart materials and structures. The material properties of ER fluid can be changed markedly while an external electric field is imposed on ER fluid domain. In this paper, the optical properties of ER suspensions consisting of composite particles dispersed in silicone oil are investigated. Both dc and ac electric fields are utilized to be imposed on ER fluid. The transmissivity of light through ER fluid under various electric fields is detected and analyzed. It is shown that the transmissivity of light increases with the increasing electric field strength and time. The change of transmissivity is caused by the formation of particle chains. The higher the particle concentration, the faster the change occurs. When an ac electric field is applied, the transmissivity can be affected by the frequency of electric field.