Field electron emission from carbon nanotubes in the presence of a weak high-frequency electric field

Series of narrow peaks in the frequency range of f ≈ 50–1200 MHz have been revealed in the frequency responses of the emission current from carbon nanotubes in the presence of a weak high-frequency electric field. The analysis makes it possible to attribute these peaks to resonance of the first and second harmonics of forced mechanical vibrations of carbon nanotubes in a high-frequency electric field. The determined Q factor of nanotubes is in the range of 100–300.     

Gamma-ray bursts from evaporating primordial black holes

It is believed that the detection of gamma-ray bursts from evaporating primordial black holes is highly improbable in the near future since the expected photon flux, consisting mainly of photons with energies ? GeV, is too low. Contrary to this point of view, we show that a large fraction of the black hole power at the final stage of evaporation (the last 10³ s) can be liberated as a burst of soft γ-ray emission of duration 10^?1–10³ s and luminosity 10²⁸–10³¹ erg/s in the energy range 0.1–1 MeV. According to our calculations of the black hole evaporation rate (within the Standard Model of elementary particles), when the black hole temperature exceeds approximately 10 GeV, the charged particle outflow from a black hole forms a well-defined plasma and can be described in the hydrodynamic approximation. In this case more than half of the rest energy of a black hole can be converted into soft gamma-rays due to the presence of the magnetic field with energy density comparable to that of charged particles. We consider various mechanisms leading to such transformation and estimate their efficiency. It is shown that, at least, some of the gamma-ray bursts detected by BATSE can be associated with evaporating black holes.     

Quantum-chemical study of color reactions of the nitrite ion with <Emphasis Type="Italic">o</Emphasis>-arylenediamines

For the prediction of promising directions of the modification of o-arylenediamines as reagents for the nitrite ion, quantum-chemical studies of the corresponding color reactions were performed. It was found that the introduction of C-substituents into aromatic rings insignificantly affects the analytical characteristics of the reactions. An increase in the number of condensed aromatic rings and N-substitution are of interest in searching for a new analytical reagent. The spectrophotometric characteristics of the reaction products of reagents based on 2,3-and 1,8-naphthylenediamines are close to each other, which, possibly, will allow the replacement of 2,3-naphthylenediamine, whose synthesis is extremely complicated, with substantially more available 1,8-naphthylenediamine or its substituted derivatives. The obtained results allowed for the selection of a group of o-arylenediamines interesting as analytical reagents for the nitrite ion, which should be examined practically.     

Study of the chemical mechanism of color reactions of selenium(IV) with <Emphasis Type="Italic">o</Emphasis>-arylenediamines

o-Arylenediamines are promising for the photometric determination of selenium. The search for new reagents of this group is desirable. To obtain information necessary for this purpose, the chemical mechanism of color reactions of selenium(IV) with o-arylenediamines was studied. The optimum conditions of these reactions and the spectrophotometric characteristics of reagents and complexes were found. The ratio of components in the reaction products (piazoselenols) of 1: 1 was determined by elemental analysis, NMR spectroscopy, and the isomolar series method. The formation of the selenium-nitrogen bond was confirmed and the quasiaromatic character of piazoselenols was revealed by IR and NMR spectroscopy. Binding energies of valence orbitals, electron density distribution, and charges of nitrogen and selenium atoms were estimated by x-ray photoelectron spectroscopy. In the case of piazoselenol from 1,2-phenylenediamine, the existence of two tautomeric forms with the oxidation numbers of selenium close to +2 and +4 were found. Piazoselenol based on N-phenyl-1,2-phenylenediamine predominantly occurs as a single compound with the oxidation number of selenium close to +2. The most probable structures of the resulting piazoselenols were proposed, and the probable schemes of the reactions of selenium(IV) with 1,2-phenylenediamine and N-phenyl-1,2-phenylenediamine were justified.     

Pro duction of Exotic Nuclei in Low-Energy Multi-Nucleon Transfer Reactions

Multinucleon transfer processes in low-energy heavy ion collisions open a new field of research in nuclear physics, namely, production and studying properties of heavy neutron rich nuclei. This not-yet-explored area of the nuclear map is extremely important for understanding the astrophysical nucleosynthesis and the origin of heavy elements. Beams of very heavy U-like ions are needed to produce new long-living isotopes of transfermium and superheavy elements located very close to the island of stability.The calculated cross sections are high enough to perform the experiments at available accelerators.Beams of medium-mass ions (such as 136Xe, 192Os, 198Pt) can be used for the production of neutron rich nuclei located along the neutron closed shell N = 126 (the last waiting point) having the largest impact on the astrophysical r-process. The Low-energy multinucleon transfer reactions is a very efficient tool also for the production and spectroscopic study of light exotic nuclei. The corresponding cross sections are 2 or 3 orders of magnitude larger as compared with high energy fragmentation reactions.     

An easy access to 2-Amino-5,6-dihydro-3H-pyrimidin-4-one building blocks: The reaction under conventional and microwave conditions

Summary A new one-stage fast multicomponent synthesis of title compounds leads to products in 21–55% isolated yields under both conventional and microwave conditions. The primary amino group in the building blocks can be easily acylated by various usual electophilic agents that can be utilized in the synthesis of diverse heterocylic compounds libraries.     

α,β-Unsaturated ketones based on allobetulone

Crotonization of allobetulone with aromatic and heteroaromatic aldehydes gave a number of new α,β-unsaturated ketones of the lupane series, and their steric structure was determined by X-ray analysis of (E)-4-[(3-oxoallobetulan-2-ylidene)methyl]benzonitrile as an example.     

Model with uniquely deducible parameters for the combined analysis of two resonating vibrational states. Anharmonic resonances in molecules of asymmetric-gyroscope type

A model of an effective Hamiltonian with parameters that are uniquely deducible from the spectrum for the combined analysis of the rotational structure of two resonating vibrational states is proposed and validated. Anharmonic resonances in molecules of asymmetric-gyroscope type are considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 108–112, February, 1982.     

Reactions of 2-aryl-4-arylidene-4<Emphasis Type="Italic">H</Emphasis>-oxazol-5-ones with 3-amino-1,2,4-triazole, 5-aminotetrazole,and 2-aminobenzimidazole

The reactions of 3-amino-1,2,4-triazole, 5-aminotetrazole, and 2-aminobenzimidazole with 2-aryl-4-arylidene-4H-oxazol-5-ones (azlactones) were studied. The electron-releasing properties of the azole ring were demonstrated to influence the reaction pathway of azlactones with aminoazoles. The structures of the resulting compounds were established by ¹H and ¹³C NMR spectroscopy using spin-spin decoupling and the nuclear Overhauser effect.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2730–2733, December, 2004.