Superconductivity in the alkali metals

At ambient pressure there are 29 elemental superconductors in the periodic table, none of which is an alkali metal. The first alkali metal to become superconducting under high pressure is Cs followed years later by Li. Alkali metals are believed to be exemplary free-electron systems. The fact that an alkali metal becomes superconducting at all is surprising and is a result of the fact that under pressure it shows marked deviations from free-electron behaviour where, counterintuitively, bands narrow and gaps widen. For this reason the alkali metals are among the most interesting systems known to study in high-pressure experiments and superconductivity is one of their most fascinating properties.     

High-pressure spectroscopic studies of free and self-trapped excitons in alkali halides at low temperatures

Abstract

A brief survey of our studies of free and self-trapped excitons (FE and STE) in alkali halide crystals under hydrostatic pressure up to 12.5 kbar at 4.2–140 K is presented. Main attention is paid to the following effects observed: (1) the strong coupling of three energy levels of FE in CsI revealing itself as an exciton analog of pressure-scanned Fermi resonance; (2) emergence of a new emission band of STE in CsI under pressure; (3) a large pressure shift of the thermal quenching curve for STE emission in NaCl.     

A one step synthesis of novel 4-alkoxy-β-lactams by high pressure promoted [2 + 21 cycloadditions of enol ethers and isocyanates derived from amino acids

Abstract

Novel moni-β-lactams derived from esters of amino acids have been prepared in one step by the high pressure promoted [2 + 2] cycloaddition of enol ethers with isocyanates derived from esters of amino acids. The effect of substituents in the enol ether and in the isocyanate on the scope of the synthesis has been demonstrated.     

Controlling the generation of high frequency electromagnetic pulses with relativistic flying mirrors using an inhomogeneous plasma

A method for the controlled generation of intense high frequency electromagnetic fields by a breaking Langmuir wave (relativistic flying mirrors) in a gradually inhomogeneous plasma is proposed. The wave breaking threshold depends on the local plasma density gradient. Compression, chirping and frequency multiplication of an electromagnetic wave reflected from relativistic mirrors is demonstrated using Particle-In-Cell simulations. Adjusting the shape of the density profile enables control of the reflected light properties.     

Externally applied stress sign and film elastic properties effects on brittle film fracture

Rectangular stainless steel samples with TiN film deposited on the front lateral surface were loaded in three-point bending to the maximum normal strain of 6%. Scanning electron microscopy showed that vertical cracks appeared in the tension zone when the tensile strain exceeded 1.5%, while horizontal cracks appeared in the compression zone when the compressive strain exceeded –2.9%. Film cracks in the compressive zone originate from the tensile stress imposed by the plastically deformed substrate due to the Poisson’s expansion. Taking plastic deformation and Poisson’s expansion of the substrate in compression into account, theoretical analysis of normal stress distribution along the cracked film segment in compression is presented. Substrate strain and film elastic properties affect film cracking in the compressive zone. At larger compressive strain, some transverse cracks along with buckling cause the film spallation. The presented method is useful for studying brittle film fracture with variable strain levels in a single sample.     

Influence of chemistry and hot rolling conditions on high permeability non-grain oriented silicon steel

This paper discusses the influence of chemical composition on the final electromagnetic properties in higher permeability material. Furthermore, the effect of the hot rolling practice and the end of austenite transformation temperature range on the hot band microstructure is described. The magnetic polarization J₅₀₀₀ better than 1.7 T, using hot rolling conditions 40 mm transfer bar thickness, finish mill entry temperature 1000 °C, and finishing temperature 800–840 °C and after decarburization heat treatment and grain growth treatment, was obtained.     

Deformation and annealing behaviour of a low carbon high Mn TWIP steel microalloyed with Ti

ABSTRACT

A low carbon high Mn, Ti microalloyed dual phase TWIP steel has been processed through cold rolling and annealing. X-ray diffraction reveals the maximum austenite (≈92%) in HRACST sample whereas, the 50CD sample shows 29% ferrite. The microstructure of HRAC and HRACST samples reveal austenite grains with annealing twins and deformation induced ferrite (DIF). The higher amount of DIF along with deformation twins form during cold deformation. Annealing at 500°C shows recovery, whereas at 700°C shows partial recrystallisation and at 900°C reveals almost full recrystallisation. TEM microstructures of the 900°C for 30?min samples reveal annealing twins with TiC particle. Strong Brass {110}<112> and Goss{110}<001> texture components are observed in HRAC, HRACST and 50CD samples. Goss Twin (GT) {113}<332> and Copper Twin (Cu-T) {552}<115> components are observed in 50CD sample. Addition of Ti results in an average grain size of 20?μm. Maximum YS (1176?MPa) and UTS (1283?MPa) values with the lowest ductility of 11% have been obtained for the 50CD sample which is related to the formation of extensive deformation twin and a higher fraction of DIF. 700°C-30?min and 700°C-60?min samples show an increase in ductility (23% and 34%, respectively) with a marginal decrease in tensile strength (1054?MPa). Annealing at 900°C shows ductility restoration up to 60% with higher tensile strength compared to HRACST sample. Ductile fracture of HRAC and HRACST samples transform to brittle fracture in the 50CD sample. Annealing at 900°C for 30?min shows ductile fracture with some (Fe, Mn)S and TiC particles.     

The aging of atmospheric plasma-treated ultrahigh-modulus polyethylene fibers

The aging effects of atmospheric plasma treatments on UHMPE fibers are studied. UHMPE fibers are treated for 0.5 and 1 min with He/O₂/air gas and for 2 and 4 min with He/air gas by atmospheric pressure plasma on a capacitively coupled device at a frequency of 5 kHz. The samples are tested for fiber/epoxy interfacial shear strength at time intervals of 0, 3, 15 and 30 days after initial plasma treatment. Scanning electron microscopy shows micro-cracks on each set of treated fibers, which is not affected by aging over the 30 day study. Interfacial shear strengths (IFSS) for plasma-treated fibers are 2–3 times as high as that of the control. The IFSS for the plasma treated fibers remains constant up to 15 days and then decreases afterwards. XPS Analysis shows a slight increase in atomic concentration of oxygen and nitrogen for each plasma-treated sample. For the He/O₂/air plasma-treated samples, XPS analysis shows an observable increase in C–OH bonds, C=O bonds and COOH bonds, while for the He/air plasma-treated samples, there is a slight increase in C–OH and O=C–O bonds. After 30 days, a decrease in oxygen content for all plasma-treated samples is manifested.     

新型对开门高低温动态试验箱研制

介绍了新型对开门高低温动态试验箱的研制过程,包括系统热负荷计算、复叠制冷循环系统的热力计算等。并根据系统的热力计算,进行了冷凝器和蒸发器的结构设计以及主要部件压缩机和通风机的设计选型。