Supernova-Explosion Mechanism Involving Neutrinos

A major part of the energy released upon the gravitational collapse of massive-star cores is carried away by neutrinos. Neutrinos play a crucial role in collapsing supernovae (SNe). At the present time, mathematical models of core-collapse SNe are based on multidimensional gas dynamics and thermonuclear reactions, whereas the neutrino transport is frequently treated in simplified way. An accurate analysis of neutrinos in a spherically symmetric gravitational collapse is performed on the basis of Boltzmann kinetic equations including all weak-interaction reactions with exact quantum-mechanical matrix elements. The role of multidimensional effects is studied bymeans of multidimensional gas dynamics allowing for the neutrino transport via diffusion treated by employing flux limiters. The possibility of largescale convection, which is of interest both from the point of view of explaining a type II supernova (SN) and from the point of view of implementing an experiment aimed at detecting possible energetic (?10 MeV) neutrinos from an SN, is discussed. Thermonuclear burning leads to the explosion of a type I SN. A hot central region and the subsequent large-scale convection may also play an important role in the SN mechanism. If neutrinos and convection play a key role for a type II SN, then, in order to explain gamma radiation from product radioactive elements, convection is of importance in the case of SNe belonging to both types. In addition, convection may be important for bright type I SNe. Original methods are presented for multidimensional gas dynamics involving thermonuclear burning and for multitemperature gas dynamics involving radiative transfer.     

Crystal structure of manganese-rich variety of eudialyte from Suchina Hill,India, and manganese ordering in eudialyte-group minerals

The crystal structure of eudialyte of hydrothermal genesis from Sushina Hill, India, where it was found associated with potassium feldspathoid, albite, aegirine, and nepheline, has been solved by X-ray diffraction analysis. One specific feature of the chemical composition of this mineral is a low content of CaO (7–8.5 wt %) and an elevated manganese content (9–10.5 wt % MnO). When compared with eudialytes of magmatic genesis, this eudialyte is enriched in Nb, Sr, Y, and rare earth elements (REEs). It is described within the sp. gr. R3m, with the unit-cell parameters a = 14.2483(3) Å and b = 30.294(1) Å; R = 4.7%. The idealized formula (Z = 3) is (Na,□,Sr)₁₅(Ca,Mn)₆Mn₃(Si,Nb)₂Zr₃[Si₂₄O₇₂](OH,Cl,H₂O)_5.5. It is established that Mn atoms occupy three sites: two subsites in five-vertex polyhedra M2a and M2b, spaced by a distance of 0.87 Å and characterized by occupancies of 0.51 and 0.49, respectively, and the M1 site in the octahedron of six-membered ring, jointly with Ca and REE. With allowance for the established features of chemical composition and structure, the mineral under study can be considered as a strontium-rich variety of kentbrooksite.     

Electrophilically Activated Nitroalkanes in Double Annulation of [1,2,4]Triazolo[4,3-a]quinolines and 1,3,4-Oxadiazole Rings

Nitroalkanes activated with polyphosphoric acid could serve as efficient electrophiles in reactions with amines and hydrazines, enabling various cascade transformations toward heterocyclic systems. This strategy was developed for an innovative synthetic protocol employing simultaneous or sequential annulation of two different heterocyclic cores, affording [1,2,4]triazolo[4,3-a]quinolines with 1,3,4-oxadiazole substituents.     

Time-of-flight neutron spectrometer for micro sample studies under high pressure

Abstract

A new neutron spectrometer for investigations of elastic and inelastic neutron scattering on polycrystal microsamples under high pressure in diamond and sapphire anvils cells is described. The spectrometer is operating at the IBR-2 pulsed reactor at JINR. The time-of-flight method and ring-shaped multicounter detector are used to register the scattered neutrons. Parameters and methodical peculiarities of the device and the examples of experimental studies are given.     

Comparative structural characterization of the water dispersions of detonation nanodiamonds by small-angle neutron scattering

The structure of nanodiamond water dispersions prepared under different conditions was investigated by small-angle neutron scattering at the scale of 1 to 100 nm. The study of diluted dispersions was regarded as of paramount importance. Similarly to previous studies, strong clustering of particles was revealed in the solutions. The typical size of clusters (40 nm and above) depends on the modification of the dispersions. A common property can be distinguished for different systems: the fractal dimension of the clusters is in the range of 2.3?C2.4, which indicates that there is a common clustering mechanism in such systems. Using contrast variation, the existence of a nondiamond component in the colloidal particles of the dispersions was confirmed; it correlates with the presence of a graphene shell on crystallite surfaces.