Hardness of materials at high temperature and high pressure

The intrinsic character of the correlation between hardness and thermodynamic properties of solids has been established. The proposed thermodynamic model of hardness allows one to easily estimate hardness and bulk moduli of known or even hypothetical solids from the data on Gibbs energy of atomization of the elements or on the enthalpy at the melting point. The correctness of this approach is illustrated by an example of the recently synthesized superhard diamond-like BC₅ and orthorhombic modification of boron, γ-B₂₈. The pressure and/or temperature dependences of hardness were calculated for a number of hard and superhard phases, i.e. diamond, cBN, B₆O, B₄C, SiC, Al₂O₃, β-B₂O₃ and β-rh boron. Excellent agreement between experimental and calculated values is observed for temperature dependences of Vickers and Knoop hardness. In addition, the model predicts that some materials can become harder than diamond at pressures in the megabar range.     

Multi-element Josephson structures for implementing broadband devices

It is proposed the solution of an urgent problem of developing broadband superconducting devices via implementation of multi-element Josephson structures with an expanded dynamic range (due to the increase in the number of cells) and required high linearity of the transfer function of magnetic signal into voltage (due to the use of specially designed Josephson cells with a highly linear voltage response). Active electrically small antenna prototypes based on the proposed multi-element structures are experimentally studied.     

Synthesis and study of photochromic asymmetric bis-spiropyran

Asymmetric indoline-benzoxazine bis-spiropyran showing improved photochromic properties due to the electron-donating methoxy group has been prepared by multistage synthesis. The molecular structure of 8-methoxy-3-methyl-4-oxo-2H-1,3-benzoxazine-2-spiro-2′H,8′H-pyrano-[2,3-f]chromene-8′-spiro-2″-1″,3″,3″-trimethylindoline has been studied by X-ray diffraction. After exposure to UV light, the absorption spectra display several long-wavelength maxima, which can correspond to different merocyanine isomers of the bis-spiro compound.     

Melting of B12P2 boron subphosphide under pressure

Melting of boron subphosphide (B₁₂P₂) to 26?GPa has been studied by in situ synchrotron X-ray powder diffraction in a laser-heated diamond anvil cell, and by quenching and electrical resistance measurements in a toroid-type high pressure apparatus. B₁₂P₂ melts congruently, and the melting curve has a positive slope of 23(6)?K/GPa. No solid-state phase transition was observed up to the melting in the whole pressure range under study.     

Nucleosynthesis Without Computer

Complete analytical derivation of the time evolution and final abundances of the light elements (up to ⁷Be) formed in the big-bang nucleosynthesis is presented. This highlights an interesting physics taking place during the formation of light elements in the early universe.     

Comments on the Statistical Origin of Black Hole Entropy

This paper shows that the black hole entropy can be interpreted as emerging as a result of missing information about the exact state of the matter from which the black hole was formed.     

Structure and properties of 3,6′-dimethyl-2,3-dihydrospiro-[naphtho[1,3]oxazine-2,2′-[2<Emphasis Type="Italic">H</Emphasis>]-chromen]-4-ones

New spiropyrans of the naphthoxazinone series containing structurally different hetarene moieties were synthesized. The structures of all resulting compounds were preliminary investigated by IR and ¹H NMR spectroscopy. The structures of some of the newly synthesized spiropyrans were completely characterized by X-ray diffraction. An analysis of the structures and photochromic properties of the spiropyrans led to the conclusion about the influence of the aldehyde group on the photochromic characteristics of spiropyrans.     

Structures of spiropyrans exhibiting photochromic properties in the solid state

Russian Chemical Bulletin - Solid-state photochromic indoline spiropyrans bearing a formyl group at the 6′ and 8′ positions of the 2H-chromene moiety of the molecules were...     

Nonsingular black hole

We consider the Schwarzschild black hole and show how, in a theory with limiting curvature, the physical singularity “inside it” is removed. The resulting spacetime is geodesically complete. The internal structure of this nonsingular black hole is analogous to Russian nesting dolls. Namely, after falling into the black hole of radius \(r_{g}\), an observer, instead of being destroyed at the singularity, gets for a short time into the region with limiting curvature. After that he re-emerges in the near horizon region of a spacetime described by the Schwarzschild metric of a gravitational radius proportional to \(r_{g}^{1/3}\). In the next cycle, after passing the limiting curvature, the observer finds himself within a black hole of even smaller radius proportional to \(r_{g}^{1/9}\), and so on. Finally after a few cycles he will end up in the spacetime where he remains forever at limiting curvature.