Comparison of theories of ion-induced nucleation

A theory of nucleation on ions and a theory of nucleation in the presence of ions are presented. The calculated data obtained within these theories are compared to the experimental data for the nucleation of vapors of different compounds. It is shown that the theory of nucleation in the presence of ions is in better agreement with the experimental data than the theory of nucleation on ions. It is assumed within the theory of nucleation in the presence of ions that each ion in the vapor phase forms a stable ion associate with vapor molecules.     

Tomographic reconstruction of the OH*-chemiluminescence distribution in premixed and diffusion flames

A fast tomographic reconstruction device has been developed to detect the two-dimensional distribution of the chemiluminescence of OH^* in the reaction zones of flames. In the set-up, special emphasis was placed on the applicability of the technique to turbulent flames. A spatial resolution of the system, <1–2 mm, and an exposure time of 100–200 μs are required to resolve the chemiluminescence signal of OH^* originating from the folded flame front of a turbulent flame.     

Graphitization of a Polycrystalline Diamond under High-Fluence Irradiation with Noble Gas and Nitrogen Ions

To analyze the process of the ion-induced graphitization of a polycrystalline diamond, the surfacelayer conductivity and microstructure are studied experimentally after high-fluence irradiation with Ne⁺, Ar⁺, N⁺, and ions with energies of 20–30 keV at irradiation and heat-treatment temperatures ranging from 30 to 720°R in vacuum. After irradiation with argon ions at room temperature and subsequent heat treatment, the resistivity ? of a modified layer decreases exponentially with increasing treatment temperature T _ht and reaches the graphite value ? at Tht = 700°R. Such a temperature T _ht is insufficient for surface-layer graphitization by nitrogen ions. The increase in the diamond temperature under irradiation leads to a decrease in the ion-induced thermal graphitization temperature T _g by several hundred degrees. It is found that the temperature T _g is almost coincident with the corresponding temperature T_a of the dynamic annealing of radiation-induced damage in graphite. Analysis of the irradiated layer using Raman spectroscopy reveals the heterogeneous structure of the modified layer containing graphite and amorphous phases, the ratio between which correlates with the layer resistivity. Under argon-ion irradiation at diamond temperatures of 500°R or more, an increase in ? of the irradiated layer is observed, which is related to the formation of nanocrystalline graphite. This effect is not observed under nitrogen-ion irradiation.     

Kinetics and thermochemistry of the unusual [2π + 2σ + 2σ]‐cycloaddition of quadricyclane with some dienophiles

Kinetic parameters of the unusual [2π + 2σ + 2σ]‐cycloaddition reactions of quadricyclane ( 1 ) with tetracyanoethylene ( 2 ), 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione ( 3 ), N‐phenylmaleimide ( 4 ), and diethyl azodicarboxylate ( 5 ) are determined experimentally. Additionally, the enthalpies of 1  +  2 reaction in 1,4‐dioxane solution (?236.6 ± 1.0 kJ mol^?1) and 1  +  3 reaction in toluene (?255.0 ± 2.8 kJ mol^?1) are determined calorimetrically and shown to be the largest in absolute magnitude among all known cycloaddition reactions involving these dienophiles. Solvent effect on the rate of 1 + 3 reaction in 11 solvents is studied and found to be moderate and similar to that of the conventional Diels‐Alder and ene reactions. The difference in the reaction rate constants of 1 with different dienophiles can be up to 9 orders of magnitude and is mainly caused by the difference in activation enthalpies. This difference is not correlated with the standard enthalpies of reactions and is likely the result of high sensitivity of the [2π + 2σ + 2σ] reaction rates to the energy of donor‐acceptor interactions between the reactants.     

On exotic hybrid meson production in γ*γ collisions

We present a theoretical study of exotic hybrid meson (J^PC=1^- +) production in photon-photon collisions where one of the photons is deeply virtual, including twist two and twist three contributions. We calculate the cross section of this process, which turns out to be large enough to imply sizeable counting rates in the present high luminosity electron–positron colliders. We emphasize the importance of the πη decay channel for the detection of the hybrid meson candidate π₁(1400) and calculate the cross section and the angular distribution for π η pair production in the unpolarized case. This angular distribution is a useful tool for disentangling the hybrid meson signal from the background. Finally, we calculate the single spin asymmetry associated with one initial longitudinally polarized lepton.     

Simple Asymptotics for a Generalized Wave Equation with Degenerating Velocity and Their Applications in the Linear Long Wave Run-Up Problem

Asymptotic solutions of the wave equation degenerating on the boundary of the domain (where the wave propagation velocity vanishes as the square root of the distance from the boundary) can be represented with the use of a modified canonical operator on a Lagrangian submanifold, invariant with respect to theHamiltonian vector field, of the nonstandard phase space constructed by the authors in earlier papers. The present paper provides simple expressions in a neighborhood of the boundary for functions represented by such a canonical operator and, in particular, for the solution of the Cauchy problem for the degenerate wave equation with initial data localized in a neighborhood of an interior point of the domain.     

Promising Neutron Detector with Anticoincidence Protection

Physics of Particles and Nuclei Letters - The method of remote neutron and gamma spectrometry of bodies in the solar system (the Moon, Mars, and Mercury) has been used for several decades to...     

Local Algorithms for Minimizing the Force Field for 3D Representation of Macromolecules

Computational Mathematics and Mathematical Physics - The majority of problems in structural computational biology require minimization of the energy function (force field) defined on the molecule...     

Quantum Birkhoff normal forms

We consider quantum analogues of several theorems on Birkhoff normal forms and prove a quantum analogue of the theorem on reducing a Hamiltonian to the normal form and the analogue of the theorem on reducing a Hamiltonian to the real normal form. We obtain the normal form explicitly in the nonresonant case. We consider the uniqueness problems of the normal form and of the normalizing transformation in the nonresonant and resonant cases.