Estimation of detectability of a horn antenna with nonlinear junction in the case of observation by “nonlinear” radar

Electromagnetic wave scattering by a horn antenna with a nonlinear Al−Al₂O₃−Al junction is studied experimentally and theoretically at the third harmonic of the irradiating field for decimeter wavelengths. The influence of junction nonlinearity on horn antenna detectability is estimated when the latter is observed by a “nonlinear” radar. The 5th Central Research Institute of the Ministry of Defense of the Russian Federation, Voronezh, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 2, pp. 126–129, February 2000.     

Probability laws of distribution of the ionization maximum of theE s layer with allowance for the boundary conditions

We consider the boundary conditions which prohibit the appearance of values of electron density of the E_s layer below the background level and above the limiting permissible level. On the basis of the Cauchy distribution, for each boundary condition we obtain the 1D probability laws of distribution of the maximum electron density of the E_s layer. These laws are verified against experimental data. State University, Voronezh, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 4, pp. 438–445, April, 1998.     

Completing the missing data in markov symmetric stable time series

Optimal algorithms for completing the missing data in Markov symmetric stable time series are proposed. We consider the cases where the data missing is caused by either a mechanism that is independent of the series values or a random censoring from below. The completing does not distort the probability properties of the series. Voronezh State University, Voronezh, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 4, pp. 365–368, April. 2000.     

Optimal reception of a rectangular pulse with unknown appearance and disappearance times

We obtain the maximum-likelihood and optimum (Bayesian) algorithms for detecting and estimating the appearance and disappearance times of a rectangular pulse against the white-noise background. Rigorous expressions for the characteristics of the maximum-likelihood algorthms are found. The characteristics of the Bayesian algorithms are obtained using computer simulations. Voronezh State University, Voronezh, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 3, pp. 271–282, March, 2000     

Optimum reception of a pulsed optical signal with unknown time of arrival

We obtain and compare the maximum-likelihood and Bayesian algorithms for detecting a signal and measuring its arrival time. Using computer statistical simulation, we test the robustness of the synthesized algorithms and determine the validity ranges of the asymptotic formulas for their characteristics. Voronezh State University, Voronezh, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 12, pp. 1201–1212, December 1999.     

Probability characteristics of the absolute maximum of generalized rayleigh stochastic process

We obtain the limiting laws of distribution of the absolute maximum of the generalized Rayleigh random process. Using the methods of statistical modeling, we show that the asymptotic approximations are in good agreement with the actual distributions over a wide range of parameters of the random process. Voronezh State University, Voronezh, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 12, pp. 1213–1222, September 1999.     

Modeling of the scattering of electromagnetic waves by cavities of elliptic cross section

Based on the mode method, we develop a technique for calculation of the effective scattering area (ESA) of a perfectly conducting cavity of elliptic cross section with the rear wall covered by a radio-absorbing coating (RAC) of constant thickness. In the case where the incident electromagnetic wave is E-polarized, we numerically calculate the angular dependences of the monostatic ESA of an elliptic cavity with and without the RAC. The results of calculations are compared with the obtained experimental data. Voronezh State University, Voronezh, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 5, pp. 426–432, May, 2000.     

Markov symmetric stable processes

Using the method of generative processes, we construct a model of a random linear symmetric stable Markov process, which is a natural generalization of the Markov Gaussian process and preserves its main property: invariance with respect to arbitrary linear transformations. Methods for analyzing such processes are developed. In particular, it is proposed to use the information correlation function as a characteristic of the pair dependence between the process values at different times. This function is used to calculate the determination interval of the process. Voronezh State University, Voronezh, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 3, pp. 264–270, March, 2000     

Scattering of an electromagnetic wave by a radially inhomogenous plasma cylinder with electron density fluctuations

Voronezh Polytechnical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 9, pp. 1055–1059, September, 1990.     

铯47D精细能级超冷里德堡原子自由演化的动力学研究

用连续窄线宽激光器将超冷铯里德堡原子分别激发到47D_3/2, 47D_5/2精细态, 观察了处于里德堡精细态的铯原子向超冷铯等离子体自由演化的过程, 详细对比了不同精细态的铯里德堡原子预电离时间、电离速率以及等离子体的转化效率. 将里德堡原子快速转化为等离子体的过程解释为局域势阱内由预电离产生的电子与里德堡原子的快速碰撞导致的雪崩电离.     

XAFS和XRD研究高能球磨对Fe70Cu30合金结构的影响

利用XRD和XAFS方法研究机械合金化Fe₇₀Cu₃₀二元金属合金随球磨时间的结构变化.XRD结果表明，球磨2 h后，部分金属Fe与Cu生成Fe-Cu合金；球磨20h后，金属Fe与Cu已完全合金化生成Fe-Cu合金，并只在2θ=44°处出现一个宽化的弱衍射峰，认为是在球磨20h后的Fe₇₀Cu₃₀合金中共存着fcc和bcc结构的Fe-Cu合金相.XAFS结果进一步表明，在球磨的初始阶段(2h)，fcc结构的Cu颗粒的晶 关键词： XAFS XRD 70Cu₃₀合金')" href="#">Fe₇₀Cu₃₀合金 机械合金化     

Atomic and magnetic structures of Fe<Subscript>70</Subscript>Al<Subscript>5</Subscript>B<Subscript>25</Subscript> amorphous alloys

The short-range order around boron, aluminum, and iron atoms in Fe₇₅B₂₅ and Fe₇₀Al₅B₂₅ amorphous alloys has been studied by ¹¹B and ²⁷Al nuclear magnetic resonance at 4.2 K and ⁵⁷Fe Mössbauer spectroscopy at 87 and 295 K. The average magnetic moment of iron atoms μ(Fe) in these alloys has been measured by a vibrating sample magnetometer. It has been revealed that the substitution of aluminum atoms for iron atoms does not disturb μ(Fe) in the Fe₇₀Al₅B₂₅ alloy, gives rise to an additional contribution to the ¹¹B NMR spectrum in the low-frequency range, and shifts maxima of the distribution of hyperfine fields at the ⁵⁷Fe nuclei. In the Fe₇₀Al₅B₂₅ amorphous alloy, the aluminum atoms substitute for iron atoms in the nearest coordination shells of boron and iron atoms. This alloy consists of nanoclusters in which boron and iron atoms have a short-range order of the tetragonal Fe₃B phase type.     

Change in the polarization of a plane electromagnetic wave when reflected by a smooth layer of collisionless plasma

Voronezh Wood Technology Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 8, pp. 912–918, August, 1990.     

Doping effect of hydrogen on Al3 cluster

The doping effect of hydrogen atoms on geometric and electronic properties of small aluminum cluster, Al₃, where deviation from the jellium model may occur, is investigated from a first-principle method. It is found that the most favorable sites for H atoms to be bound to Al atoms depend on amount of H atoms. For each cluster, Al–H bond lengths have the smallest values when the H atoms are on the top sites and have the largest values when the H atoms are on face sites, while those corresponding to bridge-site H atoms are of medium value. The doping of H increases the binding energy of the Al₃ cluster. Al₃H₃ and Al₃H₅ are found to have much lower electron affinities, higher ionization potentials and significantly larger HOMO–LUMO gaps than their neighbors, which are typical characteristics of magic clusters. The high stabilities of the Al₃H₃ and Al₃H₅ suggest that they may have a good potential applications in cluster-assembled materials.     

Structural, elastic, and electronic properties of orthorhombic NH3BH3: An ab initio study

At the generalized gradient approximation (GGA), the elastic constants of the orthorhombic phase of NH₃BH₃ were calculated with plane-wave pseudo-potential method. Our calculation showed that the orthorhombic phase NH₃BH₃ is a loose and brittle material, as well as hard to be deformed, also we calculated the elastic anisotropies and the Debye temperatures from the elastic constants. And from the band structure and density of state (DOS), we concluded that NH₃BH₃ is a wide-gap semiconductor and the band gap is almost 6.0 eV. The bonds between N atoms and H atoms show a strong covalent characteristic, B atoms and H atoms form ironic bonds, and so as to the B-N bonds. Electrons from the B atoms are absorbed by the H atoms around the B atoms, and the H atoms display electronegativity.     

稀土对镁合金应力腐蚀影响电子理论研究

建立了镁合金纯净晶界及其析出Mg₁₇Al₁₂相的晶界原子集团，应用实空间的递归方法计算了铝、稀土元素在晶界的偏聚能，晶界处铝、稀土原子间相互作用能和不同体系的费米能级.讨论了铝、稀土在晶界的偏聚行为，铝、稀土原子间的相互作用与有序化的关系及稀土对镁合金晶间应力腐蚀影响的物理本质.研究发现：铝、稀土原子偏聚于晶界；铝原子间相互排斥，在晶界区形成有序相Mg₁₇Al₁₂，稀土原子间互相吸引，形成原子团簇；稀土原子团吸引铝原子，使铝原子渗入稀土团簇中，形成稀土化合物.因此，稀土具有抑制铝在晶界形成导致应力腐蚀的阴极相Mg₁₇Al₁₂的作用，提高镁合金的晶间应力腐蚀抗力. 关键词： 电子理论 镁合金 应力腐蚀 稀土     

Encapsulation of atomic hydrogen into silsesquioxane cages and ESR of encapsulated hydrogen atoms

Hydrogen atoms are encapsulated in octasilsesquioxane, R(SiO_1.5)₈, by irradiation with γ-rays at room temperature. In deca- and dodecasilsesquioxane, hydrogen atoms are encapsulated by irradiation at 77 K. The thermal decay of the encapsulated hydrogen is well described by a single-exponential function. The excitation energies of the decay are 110–117, 50.4, and 55.6 kJ/mol for the hydrogen atoms in Q₈M₈, Q₁₀M₁₀, and Q₁₂M₁₂, respectively. Theg-values and hyperfine splitting (hfs) constants of the hydrogen atoms in R(SiO_1.5)₈ are dependent on the substituents in the corners of the polyhedra, R. Theg-values are independent of the temperatures, while the hfs constants increase as the temperature decreases. Theg-values of the hydrogen atoms in a large encapsulating cavity decrease with increasing cavity size and approach 2.0023. The temperature dependence of the hfs constants for the hydrogen atoms in Q₁₀M₁₀ or Q₁₂M₁₂ suggests that the hydrogen atoms are localized within the encapsulating cages at low temperatures.     

The magnetic and hyperfine properties of iron in silicon carbide

The magnetic and hyperfine properties of iron impurities in 3C- and 6H- silicon-carbide are calculated using the abinitio method of full-potential linear-augmented-plane-waves. The iron atoms are introduced at substitutional carbon, Fe _C , and silicon, Fe _Si , sites as well as at the tetrahedral interstitial sites with four nearest neighbours carbon atoms, Fe _I (C), and four nearest neighbours silicon atoms, Fe _I (Si). The effect of introducing vacancies at the neighbours of these sites is also studied. Fe atoms with complete neighbors substituted at Si or C sites are found to be nonmagnetic, while Fe atoms at interstitial sites are magnetic. Introduction of a vacancy at a neighboring site reverse the picture.     

The effect of doping three Al and N atoms on the chemical shielding tensor parameters of the boron phosphide nanotubes: A DFT study

In this work, an armchair model of the (4,4) boron phosphide nanotubes (BPNTs) with a 1-nm length and consisting of 32 B and 32 P atoms is considered to study the influence of doping three atoms of aluminum in sites of boron (B_3AlPNTs) and three atoms of nitrogen in sites of phosphors (BP_3NNTs) on the electrostatic structure properties. The mouths of nanotubes are capped by hydrogen atoms in order to saturate the dangling bonds of the boundaries and to decrease the calculation time. The structures of BPNTs, B_3AlPNTs and BP_3NNTs are optimized by performing the level of density functional theory (DFT) using 6-31G^? basis set. The optimized structures are used for calculating the chemical shielding (CS) tensors and nuclear magnetic resonance parameters such as isotropic chemical shielding (CS^I) and anisotropic chemical shielding (CS^A). The results reveal that in both models of B_3AlPNTs and BP_3NNTs by doping N atoms the chemical shielding parameters of P and B atoms, which are directly connected to the Al and N atoms decreased and the other sites significantly changed.     

The influence of the composition of eight-atom Pt–Ir clusters on the magnetic properties

The energetic stability, electronic structure and magnetic properties of Pt_8–nIr_n clusters have been investigated by employing the spin-polarised generalised gradient approximation. The cubic structure is expected to be the effective building block in Ir-rich clusters after optimisation extensively. The average binding energy of all the clusters presents the linear increment trend with iridium atoms, due to the stronger interaction between Ir atoms than Pt atoms. Bader charge analysis shows how tiny charge transfers from iridium to platinum. The atomic moments of Ir are larger than that of Pt, and the Ir-rich clusters show greater moments than the Pt-rich cluster, with the exception of Ir₈ and Ir₇Pt. A unique magnetic property is found in the Pt₄Ir₄ cluster, where two Pt atoms show antiferromagnetic alignment and the other atoms are found to be aligned ferromagnetically.