Difference between radiative transition rates in atoms and antiatoms

We demonstrate that CP violation results in a difference of the partial decay rates of atoms and antiatoms. The magnitude of this difference is estimated.     

Structure and properties of linear polyethylene-montmorillonite nanocomposites

Nanocomposites based on PE and three types of montmorillonite are prepared by melt blending on a Brabender plastograph. The structure of hybrid materials is studied with the use of X-ray diffraction analysis and transmission electron microscopy. The type of modifier and the polarity of the polyolefin matrix affect the character of the filler structure (intercalated and exfoliated) formed during blending with the polymer. A correlation is found between the parameters of structural organization and the mechanical and barrier properties of nanocomposites. The tensile modulus of the nanocomposites containing 3?C5 wt % modified montmorillonite is 75% higher than that of the unfilled PE, whereas the time of combustion and the rate of flame propagation are 20 and 10% smaller, respectively.     

Electrooptical properties of aqueous suspensions of nickel hydrosilicate nanotubes

We present the results of our investigations of electrooptical effects that occur as a result of light scattering by an aqueous polydisperse system the disperse phase of which consists of nickel hydrosilicate nanotubes with a chrysotile structure. Multilayer nanotubes were synthesized by the hydrothermal method and had the composition Ni₃Si₂O₅. The dimensions of nanotubes were as follows: the length was 0.1–1 μm or more, the outer diameter was 10–15 nm, and the inner diameter was 3 nm. We have studied relative changes in the intensities of light transmitted and scattered by the suspension that were caused by the orientation of nanotubes in an external electric field. Experiments have been performed at different directions of the linear polarization of the incident and scattered light, different scattering angles, and different degrees of orientation of nanotubes along the field. These measurements allowed us to determine the magnitude of electrooptical effects, such as the conservative dichroism, the light scattering, and the influence of the orientation of nanotubes in the field on the intensity and degree of depolarization of light scattered by them. Curves of free relaxation of electrooptical effects and their field dependences allowed us to determine the distributions of nanotubes and their aggregates in the colloid over lengths and polarizability anisotropy values. The dependences of the degree of depolarization of the scattered radiation on the scattering angle and the relaxation dependences of electrooptical effects allowed us to characterize the aggregation stability of nanotubes in water.     

Effects of montmorillonite modification on optical properties of heterogeneous nematic liquid crystal – clay mineral nanocomposites

Investigations of montmorillonite (MMT) clay mineral modification effects on electro‐optical properties of nanocomposites, based on the nematic liquid crystal 4‐pentyl‐4′‐cyanobiphenyl (5CB) and MMT have been carried out. Only the composite with MMT modified by an organic surface‐active substance, dioctadecyldimethylammonium chloride, has been shown to manifest electro‐optical memory effect and contrast. A polar dopant (acetone), added to the mixture, significantly increases composite homogeneity. Results of IR spectroscopy measurements lead to the conclusion, that there is a mutual influence of components on each other in organoclay systems, which appears as an alignment of near‐surface layers of both the organic and inorganic components of the composite. Due to such interactions these systems show electro‐optical contrast and memory effect. A composite with organophobic Na‐MMT does not show these electro‐optical properties, due to the absence of component interactions, as shown by IR spectroscopic data.     

One-dimensional models of internal rotation in CX3NO molecules (X = H, D, F)

Various non-empirical methods for estimating the parameters of one-dimensional internal rotation potentials and energies of torsional transitions were compared for the CX₃NO molecules (X = H, D, F) in the ground (S₀) and lowest excited singlet (S₁) electronic states. The potential energy surfaces were studied by the ab initio MR-AQCC/cc-pVTZ, MR-AQCC/cc-pVTZ(-f), MP2/6-311G(2d), and MP2/6-311G(d,p) methods. The one-dimensional internal rotation problem was solved using the following models: (1) geometry optimization at a given internal rotation coordinate; (2) intrinsic reaction path; (3) gradient extremal; and (4) use of only the data on potential energy surface stationary points. Special attention was paid to the problem of calculation of kinematic coefficient. In all cases, the calculated torsional energies for CX₃NO molecules (X = H, D, F) are in agreement with experiment. The results from different methods for constructing torsional cross-sections of the potential energy surface are virtually equivalent and differ insignificantly from the results of calculations within the framework of the simplest model, hence, estimates of the barrier to internal rotation are of most importance. It was found that a change in the zero-point energy could give a correction to the internal rotation potential as large as 15% of the potential barrier. However, in the case under consideration the calculations in the harmonic approximation taking into account this correction do not improve the agreement between the calculated torsional transitions and the experimental data.     

Paramagnetic Centres in Be-Doped MgO Single Crystals

Using a variation of arc-fusion technique, Be-doped MgO single crystals were grown, in which about 0.01% of the cation sites are occupied by Be^2?. This gives rise to a variety of Be-containing paramagnetic centres, easily detectable by EPR. The models of the centres are proposed and the values of their spin-Hamiltonian parameters are determined and discussed. Two of them—V_OH-Be and H-Be centres—stem from well-known paramagnetic centres such as V_OH, and interstitial H atom. In addition, because of the non-central position of the ion, an isolated Be^2? can trap a hole forming a Be^2?O^? centre. The symmetry of the Be^2?O^? centre at T<30K is rhombic, at a higher temperature a motional averaging of the spectrum takes place. It is shown that unusually for V centres physical properties of the V_OH-Be centre (a relatively small g-factor anisotropy and high thermal stability, optical absorption energy and spin-lattice relaxation time) arc caused by the non-central position of the Be^2? ion.     

Antimatter in the universe

The models leading to a high abundance of antimatter in the universe are discussed. Special attention is payed to the model of antimatter creation in the form of compact stellar-like objects. Such objects can contribute significantly to the cosmological dark matter. Observational signatures of antimatter in the Galaxy are discussed.     

Stressed state of the electrical insulation barrier in the wall structure of a thermonuclear reactor liquid-metal blanket

A technique for analytic determination of normal and tangential stresses in the three-layer structure of a multilayer wall of a flow-through part of thermonuclear reactor liquid-metal blanket is developed. The results of computational analysis of the influence of elastic properties of materials and geometric parameters of the layers on their stressed state are considered.     

Coulomb Explosion of the Debye Layer As a Mechanism for the Formation of a High-Energy Ion Flow in the Plasma of a Micropinch Discharge

Technical Physics - Flows of ions with energies on the order of megaelectronvolts, which propagate both in the axial direction and in the direction perpendicular to the symmetry axis of the...     

Primordial black holes and the observed Galactic 511 keV line

The observed 511 keV line from the Galactic Bulge is a real challenge for theoretical astrophysics: despite a lot of suggested mechanisms, there is still no convincing explanation and the origin of the annihilated positrons remains unknown. Here we discuss the possibility that a population of slowly evaporating primordial black holes with the mass around 10¹⁶–10¹⁷ g ejects (among other particles) low-energy positrons into the Galaxy. In addition to positrons, we have also calculated the spectrum and number density of photons and neutrinos produced by such black holes and found that the photons are potentially observable in the near future, while the neutrino flux is too weak and below the terrestrial and extra-terrestrial backgrounds. Depending on their mass distribution, such black holes could make a small fraction or the whole cosmological dark matter.