Numerical modeling of the formation of D-T mixture spherical layer in micro-targets of LTS

The article presents a two-dimensional economical computational model of the formation of D-T mixture cryogenic layer in a spherical shell. The model is based on the description of the motion of the gas phase in the Boussinesq approximation. The thermal problem is a Stefan problem with a gas-solid phase transition. The technique is based on the finite volume method, the use of a structured mobile grid, whose movement is associated with the separation of the phase front, implicit approximations and the method of splitting two-dimensional equations in directions into one-dimensional equations. It is numerically shown that, due to natural radioactivity, the target is symmetrized. A calculated estimation of the symmetrization time for one geometry of the target with different filling coefficients is carried out.

Low Temperature and High-Pressure Study of Bending L-Leucinium Hydrogen Maleate Crystals

The polymorphism of molecular crystals is a well-known phenomenon, resulting in modifications of physicochemical properties of solid phases. Low temperatures and high pressures are widely used to find phase transitions and quench new solid forms. In this study, L-Leucinium hydrogen maleate (LLHM), the first molecular crystal that preserves its anomalous plasticity at cryogenic temperatures, is studied at extreme conditions using Raman spectroscopy and optical microscopy. LLHM was cooled down to 11 K without any phase transition, while high pressure impact leads to perceptible changes in crystal structure in the interval of 0.0–1.35 GPa using pentane-isopentane media. Surprisingly, pressure transmitting media (PTM) play a significant role in the behavior of the LLHM system at extreme conditions—we did not find any phase change up to 3.05 GPa using paraffin as PTM. A phase transition of LLHM to amorphous form or solid–solid phase transition(s) that results in crystal fracture is reported at high pressures. LLHM stability at low temperatures suggests an alluring idea to prove LLHM preserves plasticity below 77 K.

Polymorphic Crystallization Design to Prevent the Degradation of the β-Lactam Structure of a Carbapenem

The cooling crystallization of carbapenem CS-023 was performed at 25 °C in an aqueous solution. Tetrahydrate crystals (form H) were obtained. Hydrate crystals are promising drugs, but there has been problems in manufacturing such crystals. During cooling crystallization, a dissolution process at a high temperature of 70 °C was utilized. The main problem in manufacturing was that the degradation rate of CS-023 at 70 °C was high, as expressed in the half-life period of 2.97 h. Poor solvent crystallization using ethanol was observed at 25 °C. Thus, a different polymorph (Form A) was obtained. Form A comprised CS-023, 5/2 ethanol, and 1/2 H2O. Form A, containing ethanol, is not suitable as a drug. Form A was then transformed to another polymorph of hydrate crystals or tetrahydrate Form H. Another hydrate polymorph, Form B, was obtained through the solid phase transformation of Form A and further transformed to the tetrahydrate Form H, at high humidity over 80% RH. This process, which proceeded at the low temperature of 25 °C, helped to prevent the degradation of CS-023, thereby avoiding wastage. Furthermore, the solid-phase transition could be controlled with vapor composition.

A Review of the Mechanical and Physical Properties of Polyethylene Fibers

Since the 1970s and 1980s, a major effort has been made to study UHMWPE (Ultra-High Molecular Weight PolyEthylene) fibers with remarkable mechanical properties, based on a basic polymer such as PE (PolyEthylene). These performances are above all associated with a very strong alignment of the molecules and the microfibrillar structures formed using various processes. However, they vary greatly depending on many parameters, and particularly on the draw ratio. Thus, these characteristics have been extensively analyzed by dynamic, static tensile, and creep tests, and are predominantly viscoelastic. The behavior appears to be associated with physical considerations and with the characteristic orthorhombic-hexagonal solid phase transition. The presence of a hexagonal phase is detrimental to the behavior because the chains slide easily relative to each other. Shifting this transition to higher temperatures is a challenge and many factors influence it and the temperature at which it takes place, such as the application of stress or annealing. The objective here is to give an overview of what has been done so far to understand the behavior of UHMWPE yarns. This is important given future numerical modeling work on the dimensioning of structural parts in which these UHMWPE yarns will be reinforcements within composites.

(S)-Alanine ethyl ester tetracyanidoborate, (C5H12NO)[B(CN)4]

The title molecular salt, C5H12NO+·C4BN4 − or (C5H12NO)[B(CN)4], was obtained as single crystals by slow evaporation of a solution of the compound in acetonitrile over several weeks. The asymmetric unit contains two (S)-alanine ethyl ester cations and two tetracyanidoborate anions, which are linked by N—H...N hydrogen bonds. The compound exhibits a relatively low melting point of 110°C and shows a solid–solid phase transition near room temperature (T s–s = 29°C) on the basis of DSC measurements.

Liquid-to-solid phase transition of oskar RNP granules is essential for their function in the Drosophila germline

SummaryAsymmetric localization of oskar RNP granules to the oocyte posterior is crucial for abdominal patterning and germline formation of the Drosophila embryo. We show that oskar RNP granules in the oocyte are condensates with solid-like physical properties. Using purified oskar RNA and scaffold proteins Bruno and Hrp48, we confirm in vitro that oskar granules undergo a liquid-to-solid phase transition. Whereas the liquid phase allows RNA incorporation, the solid phase precludes incorporation of additional RNA while allowing RNA-dependent partitioning of specific proteins. Genetic modification of scaffold granule proteins, or tethering the intrinsically disordered region of human Fused in Sarcoma to oskar mRNA, allowed modulation of granule material properties in vivo. The resulting liquid-like properties impaired oskar localization and translation with severe consequences on embryonic development. Our study reflects how physiological phase transitions shape RNA-protein condensates to regulate localization and expression of a maternal RNA that instructs germline formation.

Sound Velocities of Generalized Lennard-Jones (n − 6) Fluids Near Freezing

In a recent paper [S. Khrapak, Molecules 25, 3498 (2020)], the longitudinal and transverse sound velocities of a conventional Lennard–Jones system at the liquid–solid coexistence were calculated. It was shown that the sound velocities remain almost invariant along the liquid–solid coexistence boundary lines and that their magnitudes are comparable with those of repulsive soft-sphere and hard-sphere models at the fluid–solid phase transition. This implies that attraction does not considerably affect the magnitude of the sound velocities at the fluid–solid phase transition. This paper provides further evidence to this by examining the generalized Lennard–Jones (n − 6) fluids with n ranging from 12 to 7 and demonstrating that the steepness of the repulsive term has only a minor effect on the magnitude of the sound velocities. Nevertheless, these minor trends are identified and discussed.

Temperature Induced Diameter Variation of Silicon Nanowires via a Liquid-Solid Phase Transition in the Zn Seed

Herein, we demonstrate the ability of Zn to catalyze the growth of Si nanowires via reaction temperature determined, vapour-liquid-solid (VLS) or vapour-solid-solid (VSS) growth mechanisms. This is the first reported...