Image approximation to the reaction field

The reaction field for a charge at an arbitrary position in a spherical cavity in a medium of dielectric constant ε may be expressed in terms of the electrical potential of a certain image charge. For ε τ 1 the potential of the reaction field in the cavity is quite accurately the same as the electrical potential of the image charge. These observations form the basis of a rather economical and accurate way to calculate the reaction field's contribution to the interaction potential of particles with electric moments within a cavity within a dielectric. The results promise to be useful in the study of models for polar fluids and solutions by the Monte Carlo and Molecular Dynamics methods.     

Iterative solutions to the nuclear reaction problem

An iterative technique is probably the most efficient and practical way to solve the large sets of integro-differential equations resulting from a CRC analysis of the nuclear reaction problem. In this paper we present the theoretical and practical convergence properties of a new and different type of iterative technique, namely the method of moments. In order to show the power of this method we present a comparison with three other well known iterative methods: the Sasakawa method, the Austern-Sasakawa method, and the method of successive approximation. The dependence of the practical convergence on coupling strength and angular momentum is discussed for the case of inelastic scattering. The method of moments emerges as clearly superior according to both the theoretical and practical convergence criteria. Non-local potentials are shown to introduce very little additional computational difficulty when the iterative technique is used within the framework of the plane-wave expansion method. The method of moments was the only technique capable of guaranteeing convergence when non-local interactions were involved. One merely requires a Hilbert-Schmidt kernel in a finite region of space to guarantee convergence at a rate faster than that of any geometric progression.     

The thermodynamical approach to the back reaction problem

A new approach to the back reaction of Hawking radiation on a Schwarzschild black hole (SBH), based on thermodynamics, is proposed, in which the thermodynamical system composed of SBH and thermal radiation in curved space is treated as a thermodynamical system composed of SBH, thermal radiation and a two-dimensional thermodynamical membrane (i.e. event horizon) in flat space.     

Force approach to radiation reaction

The difficulty of the usual approach to deal with the radiation reaction is pointed out, and under the condition that the radiation force must be a function of the external force and is zero whenever the external force be zero, a new and straightforward approach to radiation reaction force and damping is proposed. Starting from the Larmor formula for the power radiated by an accelerated charged particle, written in terms of the applied force instead of the acceleration, an expression for the radiation force is established in general, and applied to the examples for the linear and circular motion of a charged particle. This expression is quadratic in the magnitude of the applied force, inversely proportional to the speed of the charged particle, and directed opposite to the velocity vector. This force approach may contribute to the solution of the very old problem of incorporating the radiation reaction to the motion of the charged particles, and future experiments may tell us whether or not this approach point is in the right direction.     

Development of the new approach to the diffusion-limited reaction rate theory

The new approach to the diffusion-limited reaction rate theory, recently proposed by the author, is further developed on the base of a similar approach to Brownian coagulation. The traditional diffusion approach to calculation of the reaction rate is critically analyzed. In particular, it is shown that the traditional approach is applicable only in the special case of reactions with a large reaction radius, $\bar r_A \ll R_{AB} \ll \bar r_B $ (where $\bar r_A $ and $\bar r_B $ are the mean inter-particle distances), and becomes inappropriate in calculating the reaction rate in the case of a relatively small reaction radius, $R_{AB} \ll \bar r_A ,\bar r_B $ . In the latter case, most important for chemical reactions, particle collisions occur not in the diffusion regime but mainly in the kinetic regime characterized by homogeneous (random) spatial distribution of particles on the length scale of the mean inter-particle distance. The calculated reaction rate for a small reaction radius in three dimensions formally (and fortuitously) coincides with the expression derived in the traditional approach for reactions with a large reaction radius, but notably deviates at large times from the traditional result in the planar two-dimensional geometry. In application to reactions on discrete lattice sites, new relations for the reaction rate constants are derived for both three-dimensional and two-dimensional lattices.     

Contribution to the nucleon-nucleus optical potential due to a pick-up reaction

In terms of diagrams the essential contribution to the self-energy, which is due to a pick-up reaction, comes from the particle-particle ladder. This ladder contribution is calculated in an approximative way. An absorptive part of the optical potential is obtained which acts essentially as a surface absorptive. For each partial wave of the elastic channel it is a finite sum of separable terms. A strong angular momentum dependence of the imaginary part of the potential at pick-up threshold is found. This dependence is governed by the angular momentum of the bound orbitals, from which pick-up occurs.     

Application of the Three-Component-Dual-Deck-Model to the ΛK channel inpp reaction

We have applied the Three-Component Dual-Deck-Model (TCDDM) to the (ΛK) channel inpp reaction. We conclude that our results are very satisfactory and take into account the experience. In this paper we take advantage of the fact that spin-structure is the same as (N π) channel which has been calculated in previous papers [3].     

Enhancement of the subbarrier fusion reaction due to neck formation

Subbarrier fusion reaction cross sections have been calculated based on the idea of the neck formation. Barrier heights for the no neck configuration and for the neck formed one are calculated by the Krappe-Nix-Sierk model and the transition between them are calculated by the perturbation formula. The relative motion between two nuclei is treated by the semiclassical model introducing the imaginary time. The formulation was applied to the fusion of identical nuclei and for six systems we examined we got a good reproduction of the data. Our calculation shows that transfer of about one tenth of the incident flux to the neck formed configuration is necessary and enough to explain the experimental data.     

Calculation of the indirect contribution to the heavy-ion nucleon transfer reaction amplitude

The indirect contribution to the heavy-ion nucleon transfer reaction amplitude has been evaluated using the distorted-wave Born approximation neglecting recoil effects. This contribution is usually ignored. Two different formulations of the indirect interaction were tried. One of these formulations gives a completely negligible contribution to the nucleon transfer reaction amplitude. The other gives a negligible effect for the angular dependence of the differential cross section but nevertheless produces a considerable change in the magnitude of the cross section.     

Corrosion reaction of iron exposed to the open atmosphere in the Antarctic

Within a cooperative program for the elaboration of a Latin American Map of Atmospheric Corrosion, weathering steel and mild steel samples were exposed to the Antarctic atmosphere and the corrosion products analyzed by ICEMS, XPS and XRD. Superparamagnetic -FeOOH was the main corrosion product after 24 h of exposure. Cl^– ions are found on the surface of the corroded samples by XPS.     

Contribution of the two-nucleon pion absorption-emission mechanism to the pion-nucleus double-charge-exchange reaction

The two-nucleon pion absorption-emission mechanism 1) and its contribution to the pioni-induced double-charge-exchange (DCX) reaction at energies T_π 300 MeV is studied. By combiing this new mechanism with the conventional sequential mechanism, the 0° excitation functions for the DCX reactions to the isobaric analog states on the ¹⁴C, ¹⁸O, ²⁶Mg, and ⁴²Ca are calculated and compared with the experimental data. We find that the theoretical results are much improved after considering the contribution of the new mechanism, especially at low energies.     

A formula used to subtract the effect of gamma-ray of the others to that of measured reaction in measurement of cross section of nuclear reaction and its application

Abstract According to the regulation of growing and decay of artificial radioactive nuclide, a formula used to subtract the effect of characteristic γ-ray of the others to that of measured reaction was deduced. And then the cross sections of 120Te (n, 2n)119mTe reaction induced by neutrons around 14 MeV were measured by activation relative to the 93Nb (n, 2n)92mNb. In the process of the cross sections measured to be calculated, it was subtracted that the effect of characteristic γ-ray of 126Te (n, p)126Sb to that of measured 120Te (n, 2n)119mTe reaction using the formula deduced. The experimental results were (689±37) and (750±41) mb at the neutron energies of (13.5±0.3) and (14.6±0.3) MeV, respectively. Measurements were carried out by γ-detection using a coaxial HPGe detector. As samples, spectroscopically pure tellurium powder has been used. The fast neutrons were produced by the T(d, n)4He reaction. The neutron energies in these measurements were determined by the method of cross-section ratios between 90Zr (n, 2n) 89m+gZr and 93Nb (n, 2n) 92mNb reactions.     

Classical radiation reaction off-shell corrections to the covariant Lorentz force

We show that the problem of radiation reaction may be formulated in a space of five dimensions, with five corresponding gauge fields in the framework of the classical version of a fully gauge covariant form of the Stueckelberg–Feynman–Schwinger covariant mechanics (the zero mode fields of the 0,1,2,3 components correspond to the Maxwell fields). The particles and fields are not confined to their mass shells. We show that in the mass-shell limit, the generalized Lorentz force obtained by means of the retarded Green's functions for the five-dimensional field equations provides the classical Abraham–Lorentz–Dirac radiation reaction terms (with renormalized mass and charge). We also obtain general coupled equations for the orbit and the off-shell dynamical mass during the evolution as well as an autonomous nonlinear equation of third order for the off-shell mass. The theory does not admit radiation if the particle does not move off-shell. The structure of the equations implies that the mass-shell deviation is bounded when the external field is removed.     

Sensitivity of styrene oxidation reaction to the catalyst structure of silver nanoparticles

This study shows how different morphologies of silver nanoparticles affect the selective oxidation of styrene in the gas phase using oxygen as oxidant. Silver nanoparticles (nanowires and nanopolyhedra), prepared using the polyol process, were supported on α-Al₂O₃. For comparison, a conventional catalyst obtained by wet impregnation was also prepared. Phenylacetaldehyde (Phe) and styrene oxide (SO) were the main products for nanoparticles catalysts. The promotion effect on the catalytic activity of potassium and cesium on the silver nanowires catalysts was also studied. At 573 K, the styrene conversion and selectivity to styrene oxide with the silver nanowires catalyst were 57.6 and 42.5%, respectively. Silver nanopolyhedra catalyst showed 57.5% conversion and 30.8% selectivity to styrene oxide. The promotion by cesium played an important role in improving the epoxidation of styrene. The samples were structurally characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) were applied to characterize the oxygen species detected (O_β, O_γ) on the silver surface.     

Contribution of the σ meson exchange to pionic double charge exchange reaction

The contribution of the σ meson exchange to the pionic double charge exchange (DCX) reaction is investigated. A concrete calculation on the forward excitation function of the low energy DCX reaction ¹⁴C(π⁺, π⁻)¹⁴O has been performed. It shows that the contribution of the σ meson exchange can reproduce well the resonance like excitation function of low energy DCX reaction. Received: 5 August 1998     

The application of power ultrasound to reaction crystallization

The action of power ultrasound in controlling the supersaturation, nucleation and crystal growth during the acid-base reaction crystallization of 7-amino-3-desacetoxy cephalosporanic acid (7-ACDA) has been investigated. The experimental results show that ultrasound can mix the reaction more efficiently and uniformly than conventional agitation methods. Insonation leads to the reduction of both the induction period and metastable zone width of the crystallization, so that the process of crystallization can be more efficiently controlled than without insonation. Agglomeration is also greatly reduced. Adjusting the ultrasonic parameters can modulate the crystal size and size distribution. The mechanism of the sonoprocess has been analyzed and comments are made on the potential applicability of sonication in large-scale crystallization practice.     

Energy dependence of the charge exchange reaction from muonic hydrogen to oxygen

The charge exchange reaction of negative muons from the atom to oxygen has been measured in gaseous mixtures of H₂ + O₂. The measurements were performed at three different relative oxygen concentrations ranging from 0.2% to 0.8% and total pressures 3.5–15 bar. A mean transfer rate of , describing the transfer from the ground state of thermalized atoms to oxygen, was determined. In order to investigate the energy dependence of the transfer rate, Monte Carlo simulations of the thermalization and the muon transfer were carried out. The comparison of measured and simulated time spectra yielded an epithermal transfer rate =3.9 10¹¹ s^-1 in the energy interval 0.12–0.22 eV. The analysis with the model of Two components shows that all measured time spectra can be reproduced with the same set of parameters.     

Experimental investigation of the muon transfer reaction from deuterium to helium isotopes

Muon transfer from the ground state of muonic deuterium to a helium atom proceeds mainly via the formation of a muonic molecule in an excited state. A large number of decay X rays ( 6.8 keV) from these (dµHe)^* molecules were observed for the⁴He as well as for the³He case. The time distributions of these X rays allow the determination of the ground state transfer rate. The simultaneous employment of Ge/Si-detectors and CCDs for the same target conditions allows the determination of the branching ratio of radiative to nonradiative decay for the first time.     

The SNP measurement of the electron transfer reaction from quadricyclane to tetrafluoro-p-benzoquinone

The stimulated nuclear polarization (SNP) [1] is measured in the photoinduced electron transfer reaction from quadricyclane to tetrafluoro-p-benzoquinone. We conclude that the radicalion pair in this system involves quadricyclane cation radical and that the isomerization reaction from quadricyclane cation radical to norbornadiene cation radical mainly occurs outside the cage of radical-ion pair.