Ferromagnetic material CdGeP2:Mn for spintronics

Solid solutions Cd_1?x Mn_xGeP₂ (x=0?0.19) have been synthesized and identified. In these solutions, the unit cell parameters decrease with an increase in the manganese content. The solid solution Cd_0.81Mn_0.19GeP₂ is a ferromagnet with the Curie temperature T _C ≈ 311 K. The paramagnetic moment of Mn²⁺ ions equal to 5.8 μ_B, as well as the spontaneous magnetization constituting 76% of the total magnetization of a crystal, has been determined with the use of the Langevin function. The origin of ferromagnetism in CdGeP₂:Mn is exchange mediated by charge carriers (holes). These holes are caused by cationic defects in the structure of chalcopyrite.     

Structure–activity studies on the fungitoxicity of some triorganotin(IV) compounds

Seventeen triorganotin(IV) compounds, with the general formula R₃SnX, containing symmetrical and unsymmetrical combinations of alkyl and aryl groups on tin and with a wide variation in the non-carbon-bonded anionic (X) residues, were examined along with three formally pentacoordinated adducts of triaryltin chlorides with triphenylphosphine oxide for their antifungal activity against nine plant pathogenic and saprophytic fungi. The in vitro tests included inhibitory studies on radial growth, mycelial growth, spore germination, and germ tube elongation. A significant finding was the dependence of fungitoxicity on the nature of the X group in both the tributyltin and triaryltin series, in contrast to earlier published reports on the negligible influence of the X groups on overall toxicity relative to the R group. This suggests that the X group is significantly involved in transporting the biocide to the reactive sites, and that the X group which tends to confer increased solubility to the triorganotin compound gives rise to increased activity. In studies of R group variations, tri-iso-butyltin bromide was found to be much less fungitoxic than tri-n-butyltin compounds, a result which is reconcilable in terms of increased steric encumbrance at the tin site in the former case. The steric factor is also implicated in the reduced activities observed for tris(p-tolyl)tin and tris(p-chlorophenyl)tin compounds relative to (Ph₃SnX) towards most of the fungi screened in this study. In general, it was also noted that the triaryltins were more selective in their antifungal action than the trialkyltins, which exhibited broad spectral activity when applied at the concentration level of 10 μg cm^?3.     

Fluctuations of the energy absorption of electron-photon radiation in a model with collision-grouping elements

In the present work, the general method proposed earlier for calculating the distribution density and moments of the absorbed energy in isolated sensitive regions of absorbers irradiated by ionizing particles is developed and made specific for the electron-photon problem. Electron transfer is considered within the framework of a model using grouping of excitations and slipping ionization; the presence of electron equilibrium in the vicinity of sensitive regions is assumed. Two similar methods of calculating these characteristics are developed. Both reduce the initial problem to two independent problems: determining the electron spectrum in the sensitive region (in one of the methods, the spectrum of electron sources is also needed) and calculating the coefficients characterizing electron transfer in the sensitive region and its immediate vicinity.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 89–94, September.     

Kinetics of methylchlorosilane formation on Zn-promoted Cu3Si

The kinetics of the direct synthesis reaction (Si + 2CH₃Cl → (CH₃)₂SiCl₂) were measured on a Cu₃Si alloy containing 1.2 atom % Zn. Reaction was carried out in a differential reactor (520–595 K, 1 atm) attached to an ultrahigh vacuum (UHV) system. Auger spectroscopy was used to characterize the surface before and after reaction. Zinc does not significantly change the overall rate of reaction, but it changes selectivity to dimethyldichlorosilane (the desired product), surface composition, activation energies, and induction times. The rate of silicon diffusion to the surface is not limiting in the presence of zinc. Zinc is found to be a promoter for improved selectivity only in low concentrations, and only a fraction of the surface appears to be active for reaction. The kinetics appear relatively insensitive to the surface composition or the form of surface carbon. A Cu₃Si surface with Zn is shown to be a good model catalyst for the direct synthesis reaction.     

Dielectric spectroscopy of a smectic liquid crystal

Complex dielectric spectroscopy (frequency range 5 Hz-13 MHz) has been used to analyse the frequency, temperature and bias-field dependences of the molecular dynamics of a very high-spontaneous-polarization ferroelectric liquid crystalline material exhibiting SmA, SmC* and unknown SmX smectic phases. Different smectic phase transition temperatures have been observed from the study of the temperature dependence of the dielectric strength and the relaxation frequency. The phase transition temperatures (crystalline to isotropic phases) have also been described very accurately from the temperature-dependent symmetric and asymmetric shape parameters of the relaxation function and also the dc conductivity. In a planar aligned cell, two symmetric modes (Goldstone mode and domain mode) have been observed in both the SmX and SmC* phases. One asymmetric mode (X-mode) observed in the SmC* and SmA phases could be related to the interaction of dipoles of the ferroelectric liquid crystals being affected by the surface of the cell. The soft mode, which usually appears very close to the SmC*-SmA phase transition was not observed until the bias field was applied. The second order nature of the SmC*-SmA phase transition was revealed.     

Numerical and experimental investigation of burner device for anode gas reburning

A complex numerical and experimental investigation of burner devices for a reburning of the anode gas of aluminum production was carried out. The chosen mathematical model of the processes of aerodynamics, heat exchange, and gas burning was identified and adapted on the basis of data of real-scale measurements. Basing on computational experiments the optimization of the design of elements of the system for anode gas detoxication and transport was carried out. A new system was proposed and tested for reburning the anode gases of electrolysis production, which consists of an improved burner device and a dust-sedimenting chamber with a possibility of regulating the amount of gas suction.     

Chaotic buffering and its mathematical models

We propose a general idea of obtaining different chains of coupled oscillators with chaotic buffering. As examples, we consider chains of diffusively coupled generalized cubic Schrödinger equations and nonlinear telegraph equations. We also give examples of systems that have an infinite-dimensional chaotic attractor.