MANIFESTATION OF AN EXCITED ELECTRON IN e⁺e¯ → γγ REACTION

The differential cross section and some polarization observables have been calculated for the e⁺e¯ → γγ reaction taking into account the contribution of the excited electron. The spin correlation coefficients were calculated for the case when both beams are polarized. We consider two approaches for the excited electron contribution: the eу → γγ contact interaction and the exchange of the excited electron in t- and u-channels. Numerical estimations are given for the excited electron contribution to the differential cross section and spin correlation coefficients for vari-ous values of the electron beam energy and excited electron mass.

Theoretical Study of a Novel Infrared Nonlinear Optical Crystal of BaGa4S7

The first-principles calculation based on density functional theory, the electronic structure and optical properties of BaGa4S7 (BGS) were systematically investigated by using generalized gradient approximation (GGAPBE) and hybrid functional method (HSE06). The results showed that the theoretical results from the HSE06 method coincided well with the experimental values. Geometry optimization showed that the theoretical lattice parameters of the BGS were also in agreement with the experimental values. Furthermore, the results of the electronic structure showed that the BGS is a nonlinear optical crystal with a wide direct bandgap energy value, as the bandgap width obtained by the HSE06 method was 3.54 eV, which was in accordance with the experimental values. The band structure and density values of state calculations showed that the top of the valence band was mainly composed of S-3p orbital and Ga-4s, 4p orbital electron contribution. On the other hand, the bottom of the conduction band was mainly composed of Ga-4s, 4p, S-3p, and Ba-5d orbital electron contribution, showing that the orbital coupling between Ga and S atoms determined the optical properties of the BGS, while the contribution of Ba atoms to the optical properties was small. The optical properties obtained from the calculation results showed that the crystal material had strong absorption and reflection characteristics in the ultraviolet band, good transmittance in the infrared area, average static dielectric constant, and an average refractive index of 2.873, 1.69, respectively. Moreover, the static double refractive index was 0.07, showing that BGS crystal materials had excellent phase matching performance in a wider range of wavelengths, with a high laser damage threshold. These results proved that the BGS could be a promising material for IR nonlinear optical crystals.

The Orion Region: Evidence of enhanced cosmic-ray density in a stellar wind forward shock interaction with a high density shell

Context. In recent years, an in-depth γ-ray analysis of the Orion region has been carried out by the AGILE and Fermi/LAT (Large Area Telescope) teams with the aim of estimating the H2–CO conversion factor, XCO. The comparison of the data from both satellites with models of diffuse γ-ray Galactic emission unveiled an excess at (l, b)=[213.9, −19.5], in a region at a short angular distance from the OB star κ-Ori. Possible explanations of this excess are scattering of the so-called “dark gas”, non-linearity in the H2–CO relation, or cosmic-ray (CR) energization at the κ-Ori wind shock. Aims. Concerning this last hypothesis, we want to verify whether cosmic-ray acceleration or re-acceleration could be triggered at the κ-Ori forward shock, which we suppose to be interacting with a star-forming shell detected in several wavebands and probably triggered by high energy particles. Methods. Starting from the AGILE spectrum of the detected γ-ray excess, showed here for the first time, we developed a valid physical model for cosmic-ray energization, taking into account re-acceleration, acceleration, energy losses, and secondary electron contribution. Results. Despite the characteristic low velocity of an OB star forward shock during its “snowplow” expansion phase, we find that the Orion γ-ray excess could be explained by re-acceleration of pre-existing cosmic rays in the interaction between the forward shock of κ-Ori and the CO-detected, star-forming shell swept-up by the star expansion. According to our calculations, a possible contribution from freshly accelerated particles is sub-dominant with respect the re-acceleration contribution. However, a simple adiabatic compression of the shell could also explain the detected γ-ray emission. Futher GeV and TeV observations of this region are highly recommended in order to correctly identify the real physical scenario.

Эффекты Холла и Зеебека в тонких пленках висмута на подложке из слюды в диапазоне температур 77-300 K

The effects of film thickness and block size on the Hall and Seebeck effects in bismuth films on mica substrates are analyzed using experimental data. A preferential decrease in the electron contribution with a decrease in the film thickness and a preferential decrease in the hole contribution with a decrease in the block size are established. The Hall and Seebeck coefficients are calculated using the classical size effect with regard to carrier scattering at block boundaries and anisotropy of the properties of carriers. In the calculation, the electron and hole mobility components and their concentration in a bismuth single crystal are used and the crystallographic orientation of the film crystal are taken into account. The results of the calculation are in good agreement with the experimental data. It is concluded that the value and sign of the Hall and Seebeck coefficients in bismuth films are determined by the competition of the classical size effect and scattering at block boundaries.

PENENTUAN GEOMETRI DAN KARAKTERISTIK IKATAN SENYAWA KOMPLEKS NI(II)-DIBUTILDITIOKARBAMAT DENGAN METODE DENSITY FUNCTIONAL THEORY

AbstrakDensity Functional Theory (DFT) merupakan salah satu metode komputasi yang digunakan untuk perhitungan kimia. Metode ini dapat menyelesaian persamaan Schrödinger secara sederhana karena didasarkan pada densitas elektron. Dalam penelitian ini ditentukan geometri dan karaktersitik ikatan dari senyawa kompleks Ni(II)-dibutilditiokarbamat menggunakan metode DFT dengan fungsi B3LYP, B3PW91 dan BLYP. Basis set yang akan digunakan adalah LANL2DZ dan perangkat lunak Gaussian 03W. Hasil optimasi geometri Ni(II)-dibutilditiokarbamat menunjukkan bentuk struktur yang sama dengan Ni(II)-dietilditiokarbamat sebagai data pembanding, yaitu persegi planar. Keterisian elektron pada ikatan Ni – S adalah 1,8873 elektron, yang merupakan 20,24 % elektron dari Ni dan 79,76 % dari S. Bentuk geometri persergi planar dibuktikan dengan hasil analisis NBO yang menunjukkan hibridisasi Ni(II)-dibutilditiokarbamat adalah d1,05sp2.05. Kata kunci: DFT, dibutilditiokarbamat, geometri, karakteristik ikatan, senyawa kompleks. AbstractDensity Functional Theory (DFT) is one of computational method that used for chemical calculation. This method simplifies the complex solution of Schrödinger equation using electron density. In this study the geometry and bond characterization of Ni(II)-dibutyldithiocarbamat complex compound was determined. The computational method used was Density Functional Theory as applied in B3LYP, B3PW91 and BLYP functions. All calculations were performed at LANL2DZ level of basis set as implemented Gaussian 03W. The theoretical result on geometry showed a similar structure to square-planar Ni(II)-dietyldithiocarbamate. The electronic occupation of Ni–S molecular orbital was 1.8873 electron, which was 20.24% electron contribution from Ni and 79.76% from S. Square-planar geometry proved by NBO analysis result that the hybridization of Ni(II)-dibutyldithiocarbamate was d1,05sp2.05. Keywords: DFT, dibutyldithiocarbamate, geometry, bond characterization, complexes compound.