Factorization of a convolution operator and inverse problems for difference equations

Translated from Matematicheskie Zametki, Vol. 48, No. 5, pp. 97–108, November, 1990.     

Specific features of the nuclear drip line in the region of light nuclei

The problem of the drip line in the region of the even isotopes ^4–12He, ^14–44O, and ^38–80Ca with respect to the emission of one or two neutrons is studied in the Hartree-Fock approximation by using the SLy4 and Ska effective Skyrme forces. The “stability peninsula” in the vicinity of ⁴⁰O is found.     

Synthesis of carbon nanofibers by catalytic pyrolysis of ethylene in the presence of vapors of volatile components

Catalytic pyrolysis of ethylene was carried out at 700 °C in the presence of vapors of H₂O, EtOH, NH₄OH, PCl₃, (MeO)₃P, Me₂SO₄, (MeO)₃B, and HCl. The composition of solid pyrolysis products was studied using the elemental analysis, X-ray diffraction analysis, and electron microscopy. The composition of the gaseous pyrolysis products was studied using mass spectrometry. The processes in the gas phase were characterized, and the relationship between conditions of ethylene pyrolysis and the structure of formed carbon nanofibers was revealed. The introduction of gaseous additives has a substantial effect on the formation, growth, and structure of the carbon nanofibers formed.     

Synthesis,properties, and examples of the use of carbon nanomaterials

The results of a series of works on the synthesis and investigation of various carbon nanostructures and elaboration of functional materials of their basis are generalized and reviewed. Fullerenes and single-, double-, and multi-walled carbon nanotubes were prepared by the electric arc evaporation of graphite and metal—graphite rods. Diverse types of carbon nanofibers and nanotubes were grown by the catalytic pyrolysis of ethylene and methane. Graphene structures were synthesized by the chemical reduction of graphite oxide. Methods for isolation, purification, and functionalization of carbon nanostructures were elaborated. Chemical transformations in the fullerene—metal phase—hydrogen system were studied. Methods for metal cluster application on carbon nanostuctures and formation of metal hydride—carbon composites were developed. The possibilities were elucidated of using carbon nanostructures for the development of hydrogen accumulating and hydrogen generating composites, for forming carbon—polymer and carbon—ceramic composites, for preparing hardening additives to polymers and glue compositions, and for producing high-performance catalysts for hydrogenation and redox processes in fuel cells.     

Spin relaxation and magnetic shielding of 93Nb nuclei in [NbCl n Br6-n ]- anions

The temperature dependence of T ₁ and T ₂ relaxation times of ⁹³Nb nuclei in octahedral [NbCl _n Br_6-n ]^-(n = 0 to 6) complexes contained in acetonitrile solution is measured. The relaxation rate is found to be controlled by quadrupole interactions in all complexes except cis-[NbCl₃Br₃]^-. The relaxation mechanism in cis-[NbCl₃Br₃]^- anion depends on exchange processes associated with intramolecular cis?trans isomerization. Calculated values of the electric field gradient (EFG) tensor invariant g _φ ² agree qualitatively with experimental values of T _1,2 ^-1. For cis-[NbCl₃Br₃]^- g _φ ² = 0. On the basis of data for T ₁ and T ₂ the assignment of resonant signals to isomers has been established. The relative chemical shift of cis and trans isomers does not correspond to that evaluated by using a pairwise additivity model. The variations of diamagnetic Δσ^d and paramagnetic Δσ^p contributions to the shielding constant of ⁹³Nb nuclei with the composition of coordination sphere are calculated. Δσ^p contribution to the chemical shifts in the [NbCl _n Br_6-n ]^- is shown to be about 70 per cent.     

EPR Study of the Vanadium Ions in Mg2SiO4 Crystal

Vanadium-doped forsterite crystal has been studied with X-band electron paramagnetic resonance (EPR) spectroscopy. The sample was grown by the Czochralski technique in an argon atmosphere with 2 vol% of hydrogen. The EPR spectrum of the sample at T = 15 K is predominantly represented by the V⁴⁺ ion signals that possess a characteristic eight-line hyperfine structure and are observed close to g = 2. The observation of the two magnetically nonequivalent centers in the angular dependence in the (ab) crystal plane and one center in the (ac) and (bc) planes, combined with the published optical spectroscopy data, unambiguously show that the V⁴⁺ ions are located at the silicon lattice site. Principal values of the hyperfine A and g-tensor and magnetic axes orientations of the V⁴⁺ centers have been determined. The orientation disorder of the V⁴⁺ centers has been found around the crystalline c axis but not in the (ab) crystal plane. The angular variation of the hyperfine component linewidth is described best with a disorder range of ±3.0°.     

Watson representation for the amplitude of lepton-pair production in nucleus-nucleus collisions

An expression for the amplitude of lepton pair production in nucleus-nucleus collisions is obtained in terms of the amplitudes of lepton-nucleus scattering. By using this representation an approximate compact expression for this amplitude valid to terms of the order (Zα)⁵ is obtained.     

Numerical analysis and synthesis of electron-optical systems of complex structure

The problem of the numerical analysis of the electrostatic field of individual elements in complex three-dimensional electron-optical systems is considered. Zh. Tekh. Fiz. 68, 97–103 (February 1998)