Investigation of cold rubidium Rydberg atoms in a magneto-optical trap

This paper reports on the results of experiments with cold rubidium Rydberg atoms in a magneto-optical trap. The specific feature of the experiments is the excitation of Rydberg atoms in a small volume within a cloud of cold atoms and the sorting of measured signals and spectra according to the number of detected Rydberg atoms. The effective lifetime of the 37P Rydberg state and its polarizability in a weak electric field are measured. The results obtained are in good agreement with theoretical calculations. It is demonstrated that the localization of the excitation volume in the vicinity of the zero-magnetic-field point makes it possible to improve the spectral resolution and to obtain narrow microwave resonances in Rydberg atoms without switching off the quadrupole magnetic field of the trap. The dependence of the amplitude of dipole-dipole interaction resonances in Rydberg atoms on the number of atoms is measured. This dependence exhibits a linear behavior and agrees with the theory for a weak dipole-dipole interaction.     

Cosmology in modified <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">R</Emphasis>, <Emphasis Type="Italic">T</Emphasis>)-gravity

In the present paper we propose a further modification of f(R, T)-gravity (where T is trace of the energy-momentum tensor) by introducing higher derivatives matter fields. We discuss stability conditions in the proposed theory and find restrictions for the parameters to prevent appearance of main type of instabilities, such as ghost-like and tachyon-like instabilities. We derive cosmological equations for a few representations of the theory and discuss main differences with conventional f(R, T)-gravity without higher derivatives. It is demonstrated that in the theory presented inflationary scenarios appear quite naturally even in the dust-filled Universe without any additional matter sources. Finally, we construct an inflationary model in one of the simplest representation of the theory, calculate the main inflationary parameters and find that it may be in quite good agreement with observations.     

Temperature dependence of pressure broadening of the N = 1− fine structure oxygen line at 118.75 GHz

The absorption profile of the N = 1− fine structure line of oxygen was recorded by a resonator spectrometer at a frequency range of 110-130 GHz at atmospheric pressure and different temperatures ranging from −21 °C up to +22 °C. Analysis of the observed line shape allowed determination of the temperature dependence of the line pressure broadening. The measured value of the temperature exponent is n = 0.74(5) for self-broadening. Consistency of the measurements is supported by simultaneous measurements of the line intensity, the line mixing parameter and the line center frequency, and by comparison of obtained values with previously known data.     

A probabilistic approach to the solution of the Neumann problem for nonlinear parabolic equations

A number of new layer methods for solving the Neumann problemfor semilinear parabolic equations are constructed by usingprobabilistic representations of their solutions. The methodsexploit the ideas of weak-sense numerical integration of stochasticdifferential equations in a bounded domain. In spite of theprobabilistic nature these methods are nevertheless deterministic.Some convergence theorems are proved. Numerical tests on theBurgers equation are presented.     

Chemical Design of Magnetic Nanocomposites Based on Layered Double Hydroxides

Chemical modification of anion-substituted layered double hydroxides (LDHs) was used for the preparation of anisotropic magnetic nanocomposites. The method combines the simplicity of chemical methods and the possibility to prepare two-, one-, or zero-dimensional nanoparticles in oxide/hydroxide matrices. An LDH structure consists of positively charged hydroxide layers bonded with negatively charged anions, which occupy the interlayer space. During chemical reactions of anions in the interlayer space, reaction zone is spatially constrained by the hydroxide layers, giving rise to the conditions similar to those in two-dimensional nanoreactors, such as Langmuir–Blodgett films and self-assembling monolayers. Here we used LDH precursors for the preparation of the Fe- and Ni-based nanocomposites. The precursors were obtained by intercalation of ethylenediaminetetraacetate (edta) complexes of Fe(III) or Ni(II) into the Mg–Al LDH. Substituted LDHs were reduced by H₂ to give metal nanoparticles entrapped into the inert Mg–Al oxide matrix. Reduction of anion-substituted LDHs with different content of anionic complexes (and ratio Mg/Al in matrix) occurs at a relatively low temperature (～600°C) and results in the formation of metal nanoparticles with different morphology and sizes. The formation of anisotropic metal nanoparticles in the former case is believed to be due to the spatial constraints of the reaction zone and their formation occurs simultaneously with buckling of hydroxide layers.     

Quasimolecular KX-ray excitation by bombarding La targets with La and Xe ions

The X-ray emission from 85 to 150 MeV Xe and 115 MeV La bombardments of thick natural La targets has been measured. The spectra and yields of X-ray emission are obtained. Continuous X-ray distributions have been found to lie beyond the target and projectile characteristic X-ray energies. The high-energy parts of these continua are interpreted as K-radiation of quasi-molecules with effective atomic numbers Z = 111 and Z = 114, respectively.     

Cross-coupling of aryl iodides with paramagnetic terminal acetylenes derived from 4,4,5,5-tetramethyl-2-imidazoline-1-oxyl 3-oxide

2-(Arylylethynylphenyl)-4,4,5,5-tetramethyl-2-imidazoline-1-oxyl 3-oxides 12 and 13 were synthesized by cross-coupling of aryl iodides with 1-alkynes containing the 4,4,5,5-tetramethyl-2-imidazoline-1-oxyl 3-oxide fragment. A procedure was developed for the preparation of 3- and 4-ethynylbenzaldehydes with the use of 2-methylbut-3-yn-2-ol.     

Synthesis of glass ceramics containing finely dispersed particles of aluminum-doped M-type strontium hexaferrite

Glasses with nominal compositions SrFe₁₀Al₂O₁₉+4(SrB₂O₄+Sr₂B₂O₅) (1) and SrFe₉Al₃O₁₉+4(SrB₂O₄+Sr₂B₂O₅) (2) were prepared by rapid quenching of melts. Thermal treatment of glass samples at 600–900 °C resulted in crystallization of the magnetic phase SrFe_12−x Al_xO₁₉ (x = 1.1±0.1) and strontium borates. Platelet hexaferrite particles with average sizes from (250×60) nm² to (450×140) nm² were prepared. The coercive force of glass ceramics is 580 and 475 kA m⁻¹ for glasses 1 and 2, respectively. The coercive force of 580 kA m⁻¹ is the highest known value compared to hexaferrite particles prepared earlier by glass crystallization.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 74–77, January, 2005.