Short-range fundamental forces

We consider theoretical motivations to search for extra short-range fundamental forces as well as experiments constraining their parameters. The forces could be of two types: 1) spin-independent forces; 2) spin-dependent axion-like forces. Different experimental techniques are sensitive in respective ranges of characteristic distances. The techniques include measurements of gravity at short distances, searches for extra interactions on top of the Casimir force, precision atomic and neutron experiments. We focus on neutron constraints, thus the range of characteristic distances considered here corresponds to the range accessible for neutron experiments.     

Ordering of tysonite structure in an as-grown Er0.715Ca0.285F2.715 crystal and in a component of annealed two-phase crystal of the Er0.67Ca0.33F2.67 composition

The structures of the as-grown tysonite phase (TP) Er_0.715Ca_0.285F_2.715 as grown and the tysonite component in a crystal of the Er0.67Ca0.33F2.67 composition annealed at 760°C have been determined by X-ray diffraction methods from the main reflections in the sp. gr. P6₃/mmc, Z = 2. Ca²⁺ cations in the Er_0.715Ca_0.285F_2.715 structure occupy the 2c site on the 6₃ axis, thus confirming the conclusion about the symmetrizing effect of alkaline earth cation, which was made previously for the Y_0.715Ca_0.285F_2.715 compound. Er³⁺ cations are disordered over 6h sites around this axis. The Er_0.67Ca_0.33F_2.67 composition contains Er_0.67+δCa_0.33?δF_2.67+δ TP and inclusions of distorted fluorite phase rhβ-Ca₈Er₅F₃₁. The tysonite and two fluorite lattices have no “correct” relationship. Ca²⁺ cations and a half of TP Er³⁺ cations are fixed in the 2c sites, while the other Er³⁺ cations are disordered over the 6h sites. Superstructural ordering occurs in Er_0.715Ca_0.285F_2.715 crystals; however, the process is not completed, as follows from the character of the diffraction pattern. Weak satellite reflections in the diffraction pattern of the Er_0.67Ca_0.33F_2.67 composition are indicative of the development of TP ordering processes but remain unfit for structural calculations.     

Development of High-Power Long-Pulse Submillimeter-Wave Free-Electron Lasers on the Basis of the Linear Induction Accelerator Complex

Radiophysics and Quantum Electronics - The high-power long-pulse submillimeter-wave free-electron laser (FEL) is developed jointly by the Institute of Nuclear Physics and the Institute of Applied...     

Stability of a spherical cavity in a sound field

The linear theory of the stability of the spherical shape of a cavity and the stability of its radial oscillations in a sound field are discussed. An equation is derived for the amplitudes of the spherical harmonics with allowance for surface tension, viscosity, and compressibility of the surrounding liquid in the Herring-Flynn approximation. The radial pulsation stability is analyzed in the same approximation. The equations derived in the article are subjected to numerical analysis.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 109–114, November–December, 1973.     

Rinneite,K3Na[FeCl6], at 293, 84 and 9.5 K

The crystal structure of tripotassium sodium hexa­chloro­ferrate(II) has been determined by X‐ray diffraction at 293, 84 and 9.5 K. The accurate and extensive data sets collected should be suitable for charge–density analysis studies.     

Congruently melting compositions in the series of solid solutions R1 ? xSrxF3 ? x (R = La-Nd, 0 ≤ x ≤ 0.15) with tysonite structure (Refinement by directional crystallization)

Congruently melting compositions in the series of solid solutions R _{1 − x} Sr_xF_{3 − x} (R = La-Nd with a defect structure of the tysonite type (LaF₃) were found by the comparing the densities (determined by hydrostatic weighing) of the top and bottom parts of the single crystals grown using the Bridgman method. Measurement errors are analyzed. __________ Translated from Kristallografiya, Vol. 48, No. 5, 2003, pp. 940–944. Original Russian Text Copyright ? 2003 by Krivandina, Zhmurova, Glushkova, Firsova, Shtyrkova, Sobolev. Dedicated to the 60th Anniversary of the Shubnikov Institute of Crystallography of the Russian Academy of Sciences     

Influence of defects on the optical and structural properties of Ge dots embedded in an Si/Ge superlattice

In this work we studied the influence of high-energy proton irradiation on the optical and structural properties of an Si/Ge superlattice (SL) with embedded Ge quantum dots (QDs). The presence of QDs in the as-grown samples was established by transmission electron microscopy and photoluminescence (PL). The samples were irradiated with 2.0 MeV protons to fluences in the range 2×10¹²-2×10¹⁴ cm^-2. The structural characterization made by X-ray reciprocal space mapping, X-ray reflection and Rutherford backscattering/channelling has shown no changes in the as-grown heterostructure due to the irradiation. In spite of the expected high concentration of nonradiative recombination centres caused by the proton-induced damage, the PL emission from the Ge dots has been observed even for the highest irradiation fluence. The studied QD-in-SL structure has shown an extraordinarily high radiation hardness when compared with previously studied QD heterostructures.