Phase-separation kinetics of 3He-4He solid solutions at various degrees of supersaturation

The phase-separation kinetics of ³He-⁴He solid solutions at various degrees of supersaturation Δx are studied using precise pressure measurements. It is found that the characteristic phase-separation times do not depend on the degree of supersaturation but are determined by the final temperature to which the crystal is cooled. The behavior of the effective diffusion coefficient, which governs the corresponding mass transfer, cannot be described within the impuriton model of the mobility of ³He atoms in a ⁴He crystal. Fiz. Tverd. Tela (St. Petersburg) 41, 2062–2064 (November 1999)     

Polar-center phase nuclei in He+-irradiated CuO single crystals

Irradiation of various single-crystal CuO faces [ac,bc,(110)] with 4.6-MeV He⁺ ions has been found to result in reduction of CuO to Cu₂O and Cu on the irradiated and unirradiated sides, lifting of forbiddenness from optical transitions in the [CuO₄]⁷⁻ electron center in the 0.7–0.95-eV energy range, a change in dichroism near the bands corresponding to transitions in the hole centers, [CuO₄]⁵⁻, and electron centers, [CuO₄]⁷⁻, as well as in a resonant increase of absorption at 0.95–1.30 eV with an unusual polarization dependence. The results of He⁺ irradiation of CuO single crystals are discussed in terms of a model of the nucleation of the phase of polar (electron and hole) centers in copper-oxygen systems. Fiz. Tverd. Tela (St. Petersburg) 40, 419–424 (March 1998)     

X-ray microanalysis of quaternary semiconductor solid solutions and its application to the (SnTe-SnSe):In system

A reliable technique of local chemical characterization of multicomponent semiconductor solid solutions has been developed, and the possibility of its application to the SnTe-SnSe quaternary solid solutions doped with 16 at.% In verified. The behavior of the electrical resistivity of samples of these solid solutions at low temperatures, 0.4–4.2 K, has been studied. The critical temperature T _c and the second critical magnetic field H _c2 of the superconducting transition and their dependences on the solid-solution composition have been determined. The superconducting transition at T _c≈2–3 K is due to hole filling of the In-impurity resonance states, and the observed variation of the superconducting transition parameters with increasing Se content in the solid solution is related to the extrema in the valence band and the In band of resonance states shifting with respect to one another. Fiz. Tverd. Tela (St. Petersburg) 41, 612–617 (April 1999)     

Synthesis, anticancer, and anti-inflammatory activity evaluation of methanesulfonamide and amidine derivatives of 3,4-diaryl-2-imino-4-thiazolines

Condensation of 3,4-diaryl-2-imino-4-thiazoli-nes 1a–j with methanesulfonyl chloride gave methanesulfonamide derivatives 2a–j. Condensation of 2-cyanopyrazine, 4-cyanopyridine, and 2-cyanopyridine with 3,4-diaryl-2- imino-4-thiazolines 1h–m in the presence of sodium methoxide afforded amidine derivatives 3a–j. Compounds 2a–j and 3a–j were screened against various human cancer cell lines (COLO-205, HEP-2, A-549, IMR-32) and their percentage growth inhibition profile determined at 1 × 10⁻⁵M. The anti-inflammatory activity of these compounds was assessed using the carrageenan-induced paw edema model. Compound 2i exhibited 34.7% anti-inflammatory activity at 50 mg/kg p.o., which is comparable to standard care drug phenyl butazone (37% activity at 50 mg/kg p.o.)     

Determination of the neutron electric form factor from the reaction 3 He(e,e'n) at medium momentum transfer

The electric form factor of the neutron G_En has been determined in double polarized exclusive ³ He(e,e'n) scattering in quasi–elastic kinematics by measuring asymmetries A _⊥, A _∥ of the cross section with respect to helicity reversal of the electron, with the nuclear spin being oriented perpendicular to the momentum transfer q in case of A_⊥ and parallel in case of A_∥. The experiment was performed at the 855 MeV c. w. microtron MAMI at Mainz. The degree of polarization of the electron beam and of the gaseous ³ He target were each about 50%. Scattered electrons and neutrons were detected in coincidence by detector arrays covering large solid angles. Quasi–elastic scattering events were reconstructed from the measured electron scattering angles ϑ_e, φ_e and the neutron momentum vector p _n ^′ in the plane wave impulse approximation. We obtain the result <G _En>_{(0.27 < Q2c2/GeV2 < 0.5)}= 0.0334 ± 0.0033_stat± 0.0028_syst which is averaged over the indicated range of Q ², the squared momentum transfer. This G _En value is significantly smaller than measured from the D(e,e'n) reaction under similar kinematical conditions. To what extent final state interactions in ³He quench the G _En result is subject of calculations currently in progress elsewhere. Received: 29 April 1999     

Nuclear fusion in the mesic molecule d μ 3He

A new scheme is presented for the physical processes leading to the nuclear fusion reaction d(³He, ⁴He)p catalyzed by a negatively charged muon μ⁻. It is shown that the observable rate and yield of the nuclear reaction depend on a chain of ion-molecular reactions involving the participation of the dμ ³He molecule. New calculations of the nuclear fusion rates in the dμ³He molecule are presented. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 89–94 (25 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Bipolar atmospheric-pressure corona discharge in a He/H2 mixture

Results are presented from a study of the characteristics of a steady-state plasma in a He/H₂ mixture at high pressures. The plasma is formed in the outer region of a multielectrode corona discharge. It is shown that molecules of helium hydride form in such a medium, and their decomposition is accompanied by continuum emission in the 350–650 nm region. The corona discharge is distributed over the length and can be used in systems for the transverse electric circulation of the working medium of atmospheric-pressure plasma radiation sources. The reference spectra of the plasma emission and the dependence of the relative intensity of the lines and the brightness of the bands of He ₂ ^* on the value of the discharge current, pressure, and composition of the working mixture are investigated. Zh. Tekh. Fiz. 69, 33–37 (July 1999)     

Charge mobility anisotropy in hcp 4He crystals

A strong anisotropy of the positive-charge mobility is observed in hcp ⁴He crystals. The mobility activation energies in the principal directions are determined. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 90–95 (10 January 1997)     

Soft dipole mode in 8He

The low-lying spectrum of ⁸He was studied in the ³H(⁶He, p)⁸He transfer reaction for small center of mass angles. The 0⁺ ground state (g.s.) of ⁸He and excited states, 2⁺ at 3.6–3.9 MeV and (1⁺) at 5.3–5.5 MeV, were populated with cross sections of 200, 100–250, and 90–125 μb/sr. Some evidence for the excited state at about 7.5 MeV can be found in the data. The possible nature of the near-threshold anomaly above 2.14 MeV in ⁸He is related to the population of a 1⁻ continuum (soft dipole excitation) with a peak energy value at about 3 MeV. This assumption can probably resolve the problem of a large uncertainty existing in the experimental data on the ⁸He 2⁺ state energy. The article is published in the original.     

Structural, magnetic, and electrical properties of solid solutions of the chromium telluride-manganese telluride system

The conditions for synthesis of solid solutions in the quasibinary CrTe-MnTe system are analyzed. A study is made of the effect of cation substitution on the properties of the synthesized solid solutions in measurements of magnetization, magnetic susceptibility, electrical conductivity, and the Seebeck coefficient at temperatures of 80–750 K. Fiz. Tverd. Tela (St. Petersburg) 39, 320–324 (February 1997)     

Fluorescence of N,N-di(2-carboxyethyl)-<Emphasis Type="Italic">p</Emphasis>-anisidine in solution and crystalline states

The fluorescence properties of N,N-di(2-carboxyethyl)-p-anisidine (I) in solvents of various nature and in the crystalline state have been studied at room temperature (273 K) and at the boiling point of liquid nitrogen (77 K). Fluorescence in aqueous solutions of I with protonated (λ _ex /λ _fl ^max = 225/290 nm) and unprotonated (λ _ex /λ _fl ^max = 270/380 nm) amino nitrogen has been detected. On going from aqueous solutions to nonaqueous, the fluorescence band of unprotonated I experiences a blue shift and its intensity rises. The fluorescence intensity of the band in aprotic polar solvents is higher than that in protic solvents. A linear dependence of the fluorescence intensity of deprotonated I on Cu(II) concentration (ranging from 1.0 to 5.0 mg/dm³) in aqueous solution has been found. The fluorescence intensity of I in aqueous solutions at 77 K and pH 1–6 has been shown to increase in the presence of Zn(II) (1–170 mg/dm³) and Cd(II) (2–330 mg/dm³) although a similar dependence is not observed at 293 K.     

AB interface in superfluid 3He and the Casimir effect

The friction force on the moving interface between two different vacuum states of superfluid ³He is considered at low temperature. Since the dominating mechanism of the friction is the Andreev reflection of the massless “relativistic” fermions, which live on the A-phase side of the interface, the results are similar to that for a perfectly reflecting mirror moving in the quantum vacuum. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 6, 457–462 (25 March 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Alteration of the lattice constant and the composition of KCl and KBr crystals under macrogravity

In KCl and KBr crystals grown from supersaturated aqueous solutions under centrifuging (3g, 7g, and 12g) the lattice constant and the halogen content are altered significantly in comparison with original compounds, and the microhardness is increased by 1.5–2 fold. Fiz. Tverd. Tela (St. Petersburg) 39, 1792–1793 (October 1997)     

Theoretical analysis of the impurity distribution in single-crystal silicon

Results are presented for the total energies calculated for oxygen and carbon impurities in silicon at T=0 K. The equilibrium positions of these point defects are determined at low (10⁻³–10⁻² at. %) concentrations. Fiz. Tverd. Tela (St. Petersburg) 39, 1384–1385 (August 1996)     

Thermodynamic properties of the mixed elpasolites Rb2KGaxSc1−x F6 (x=0.6–1.0)

Measurements of the heat capacity of the elpasolite Rb₂KGaF₆ and the solid solutions Rb₂KGa_xSc_1−x F₆ with a gallium content in the range x=0.6–0.95 are performed. The nature of the influence of the chemical composition of the compounds and the hydrostatic pressure on the temperature and entropy of the ferroelastic phase transitions is established. Fiz. Tverd. Tela (St. Petersburg) 39, 1844–1849 (October 1997)     

A new class of inhomogeneous cosmological models with Yang-Mills fields

Exact solutions corresponding to spherically symmetric inhomogeneous nonstationary Tolman metrics are obtained for the self-consistent system of Einstein-Yang-Mills equations for the gauge group SO ₃ . Pis’ma Zh. éksp. Teor. Fiz. 64, No. 2, 65–70 (25 July 1996)     

Colossal magnetoresistance of FexMn1−xS magnetic semiconductors

The magnetic, electric, magnetoresistive, and structural properties are investigated in the sulfide solid solutions Fe_xMn_1−2x S, which are based on the antiferromagnetic semiconductor α-MnS (the fcc NaCl lattice). Colossal negative magnetoresistance (δ_H∼−83% at 160 K for x ∼ 0.29), comparable to that observed in La-Ca-Mn-O polycrystals and films (δ_H∼−90% at 100 K and 40 kOe), is observed in compounds with intermediate concentrations 0.26<x<0.4, corresponding to the region of incipient ferromagnetism. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 12, 895–899 (25 June 1999)     

Theoretical analysis of impurity distributions in crystalline silicon

Calculations of the total energy of oxygen and carbon impurities in silicon at T=0 K are presented. The equilibrium position of point defects is determined for low (10⁻³–10⁻² at. %) concentrations. Fiz. Tverd. Tela (St. Petersburg) 39, 2001–2002 (November 1997)     

Giant magnetoresistance of vanadium films with a surface magnetic superlattice

Giant (up to 68%) room-temperature magnetoresistance is observed in (110) V films on mica with a periodic system of 5–25 nm wide, thin (⩽10 nm) Co strips, separated by 1–2 nm gaps, grown on the films. The effect is observed only for samples in which the magnetization tilts out of the plane of the film. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 346–349 (10 September 1996)