Predominant time scales in fission processes in reactions of S, Ti and Ni with W: zeptosecond versus attosecond

The inhibition of fusion by quasifission is crucial in limiting the formation of superheavy elements in collisions of heavy nuclei. Time scales of ～10(-18) s inferred for fissionlike events from recent crystal blocking measurements were interpreted to show either that quasifission itself is slower than previously believed, or that the fraction of slow fusion-fission is higher than expected. New measurements of mass-angle distributions for (48)Ti and (64)Ni bombarding W targets show that in these reactions quasifission is the dominant process, typically occurring before the system formed after contact has made a single rotation, corresponding to time scales of ≤10(-20) s.     

Effect of interference on field electron emission

Carbon nanotubes are studied with the help of an electron projector and dispersion field-emitted energy analyzer. Probe current-voltage characteristics of two samples exhibited wave-like modulation caused by periodic variations in field-emitted electron energy spectra observed with increasing emission voltage. Deviations of the current from the average Fowler-Nordheim line were up to ±35% within one period. The explanation relies on the model of Young’s interference from two coherent sources.     

Vortex twins and anti-twins supported by multiring gain landscapes

We address the properties of multivortex soliton complexes supported by multiring gain landscapes in focusing Kerr nonlinear media with strong two-photon absorption. Stable complexes incorporating two, three, or four vortices featuring opposite or identical topological charges are shown to exist. In the simplest geometries with two amplifying rings vortex twins with equal topological charges exhibit asymmetric intensity distributions, while vortex anti-twins may be symmetric or asymmetric, depending on the gain level and separation between rings.     

Rotating vortex solitons supported by localized gain

We show that ringlike localized gain landscapes imprinted in focusing cubic (Kerr) nonlinear media with strong two-photon absorption support new types of stable higher-order vortex solitons containing multiple phase singularities nested inside a single core. The phase singularities are found to rotate around the center of the gain landscape, with the rotation period being determined by the strength of the gain and the nonlinear absorption.     

Stable radially symmetric and azimuthally modulated vortex solitons supported by localized gain

We discover that a spatially localized gain supports stable vortex solitons in media with cubic nonlinearity and two-photon absorption. The interplay between nonlinear losses and gain in amplifying rings results in the suppression of otherwise ubiquitous azimuthal modulation instabilities of radially symmetric vortex solitons. We find that the topology of the gain profile imposes restrictions on the maximal possible charge of vortex solitons. Symmetry breaking occurs at high gain levels, resulting in the formation of necklace vortex solitons composed of asymmetric bright spots.     

Role of the conformations of tetraoxides in the mechanism of the recombination of peroxide radicals

The MINDO/3 method was used to calculate the equilibrium three-dimensional structure of the simplest representatives of the series of tetraoxides (TO) — H₂O₄ and CH₃O₄H. In the harmonic approximation their force field, and the frequencies and forms of the normal vibrations were calculated. Satisfactory agreement between the theoretically calculated and experimentally measured frequencies was obtained for a peroxide condensate. It was shown that the recombination of tertiary peroxide radicals proceeds through a transoid configuration of the TO, while recombination of primary and secondary peroxide radicals is associated with the formation of a cisoid configuration.Translated from Teoreticheskaya i ksperimental'naya Khimiya, Vol. 22, No. 3, pp. 363–366, May–June, 1986.     

Synthesis of 1,2-azaphospholanes containing an amino acid fragment

2-Oxo-1,2-azaphospholanes and 1,2-azaphospholanium salts containing an amino acid fragment were synthesized by intramolecular P-alkylation of N-3-chloropropyl-substituted tricoordinate phosphorus amides. Hydrolysis of 2-oxo-1,2-azaphospholanes at the P-N bond gives rise to γ-aminopropylphosphonic acid derivatives. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2557–2562, November, 2005.     

Optimization method in problems of acoustic cloaking of material bodies

Optimization problems for a three-dimensional model of acoustic scattering are formulated and studied. These problems arise in designing tools for cloaking material bodies by applying the wave flow method. The cloaking effect is achieved due to an optimal choice of variable parameters of the inhomogeneous isotropic medium occupying the sought shell. The solvability of direct and optimization problems for the acoustic scattering model is proved, and sufficient conditions ensuring the uniqueness and stability of optimal solutions are established.     

Synthesis and study of ammonium hexamolybdobismuthate(III)

Ammonium hexamolybdobismuthate(III) of composition (NH₄)₃[BiMo₆O₁₈(OH)₆] · 7H₂O (I) was synthesized and studied by mass spectrometry, X-ray diffraction, IR spectroscopy, and thermogravimetry. The compound is monoclinic: a = 10.438 Å, b = 7.909 Å, c = 18.127 Å, β = 96.59°, V = 1486.76 ų, ρ_calc = 3.32 g/cm³, Z = 2.