Real part of the optical potential for composite particles

The optical potential for a composite particle is most simply approximated by the sum of the optical potentials of the constituent nucleons. Restricting ourselves to the real parts of the potentials we use this model as a first approximation in a calculation of the potentials for d, ³He, α and ¹²C. We add corrections for (i) the energy dependence of the nucleon potentials, (ii) three-body terms, (iii) the Pauli principle. All corrections can be important and that for the Pauli principle can be very large. We obtain a good explanation of the following phenomena: (a) the deuteron potential is nearly the sum of the neutron and proton potentials, (b) the potential for ³He is about 20 % less than the sum of the potentials of the nucleons in the ³He projectile, (c) the volume integral of the potential for ³He falls at both high and low energies in the energy range 20–100 MeV, (d) shallow potentials with large radii are found for low energy (30 MeV) scattering of α-particles, (e) deeper potentials are found for higher energy α-particle scattering. We predict shallow potentials for ¹²C scattering from light targets but deeper potentials for heavier targets.     

A physical interpretation of the discrete ambiguities in the optical potential for composite particles

It is shown that the appearance of discrete ambiguities in the optical potential of composite particles is caused by the existence of partly Pauli-forbidden states. The given interpretation is tested in the case ofα-⁵⁸Ni scattering atE _α=50.2 MeV where seven different optical potentials give satisfactory agreement with experiment.     

A contraction rule for composite particles

A contraction rule for an arbitrary composite particle is derived, based on results due to Nishijima, and Klein and Zemach. The relation between this contraction rule and the analogous problem in potential scattering is demonstrated by an explicit reduction to the nonrelativistic limit. Applications of these rules are briefly discussed.     

Unstable composite particles

A functional derivative formulation of relativistic three-particle equations as a framework for unstable composite particles is developed.     

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.     

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.     

Effective potential method for active particles

ABSTRACT

We investigate the steady-state properties of an active fluid modelled as an assembly of soft repulsive spheres subjected to Gaussian coloured noise. Such a noise captures one of the salient aspects of active particles, namely the persistence of their motion and determines a variety of novel features with respect to familiar passive fluids. We show that within the so-called multidimensional unified coloured noise approximation, recently introduced in the field of active matter, the model can be treated by methods similar to those employed in the study of standard molecular fluids. The system shows a tendency of the particles to aggregate even in the presence of purely repulsive forces because the combined action of coloured noise and interactions enhances the effective friction between nearby particles. We also discuss whether an effective two-body potential approach, which would allow to employ methods similar to those of density functional theory, is appropriate. The limits of such an approximation are discussed.     

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.     

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.     

Optical absorption resonances of trapped particles

We have previously shown the possibility of the existence of a one-photon resonance with homogeneous width in the center of an absorption line of trapped particles. The results of a detailed investigation of this resonance are given in the first part of the present paper. The second part is devoted to a two-photon resonance in a standing-wave field: the time of coherent interaction with the field is increased for trapped particles, which permits the elimination of transit resonance broadening.     

Optical microrheology using rotating laser-trapped particles

We demonstrate an optical system that can apply and accurately measure the torque exerted by the trapping beam on a rotating birefringent probe particle. This allows the viscosity and surface effects within liquid media to be measured quantitatively on a micron-size scale using a trapped rotating spherical probe particle. We use the system to measure the viscosity inside a prototype cellular structure.     

Optical absorption by small metallic particles

We study theoretically the dependence of absorption by small metallic particles on particle shape and wave polarization in the IR frequency range. We examine the electric and magnetic absorption by small particles. The particles may be either larger or smaller than the electron mean free path. We show that for asymmetric particles smaller than the mean free path the light-induced conductivity is a tensor. We also show that the total absorption and the electric-to-magnetic absorption ratio are strongly dependent on particle shape and wave polarization. Finally, we construct curves representing the dependence of the ratio of the electric and magnetic contributions to absorption on the degree of particle asymmetry for different wave polarizations. Similar curves are constructed for the ratio of the components of the light-induced conductivity tensor. Zh. éksp. Teor. Fiz. 112, 661–678 (August 1997)     

Optical absorption in ultrafine gold particles

Optical absorption of ultrafine, gas evaporated gold particles (diameters 3—4 nm) has been measured in the wavelength interval 0.3—2.5 μm. The data agree well with the Maxwell-Garnett theory in conjunction with optical constants for bulk Au, provided these are modified to incorporate the effect of size dependent electron scattering.     

Polymer-inorganic composite with ultradisperse gadolinium particles

The objects of investigation are polystyrene-based composites with ultradisperse particles (including nanoparticles) of metallic Gd and SiO₂. The composites prepared by milling starting materials in a barrel mill at room temperature are studied by the ferromagnetic resonance method, transmission electron microscopy (TEM), and reflection X-ray diffraction (RXD). It is found that the magnetic subsystem of the composites is formed by magnetic nanoclusters, Gd crystallites 30 ± 10 nm across, which possess volume and surface magnetic anisotropy and pass into the superparamagnetic state at 210 ± 10 K. It is also found that the Landau-Lifshitz equation with the damping term in the Landau-Lifshitz form provides the best quantitative fit to experimental data for the ferromagnetic resonance of superparamagnetic metal nanoparticles.