Application of the phase extension method in virus crystallography

The procedure for phase extension (PX) involves gradually extending the initial phases from low resolution (e.g. ～8?Å) to the high-resolution limit of a diffraction data set. Structural redundancy present in the viral capsids that display icosahedral symmetry results in a high degree of non-crystallographic symmetry (NCS), which in turn translates into higher phasing power and is critical for improving and extending phases to higher resolution. Greater completeness of the diffraction data and determination of a molecular replacement solution, which entails accurately identifying the virus particle orientation(s) and position(s), are important for the smooth progression of the PX procedure. In addition, proper definition of a molecular mask (envelope) around the NCS-asymmetric unit has been found to be important for the success of density modification procedures, such as density averaging and solvent flattening. Regardless of the degree of NCS, the PX method appears to work well in all space groups, provided an accurate molecular mask is used along with reasonable initial phases. However, in the cases with space group P1, in addition to requiring a molecular mask, starting the PX at a higher resolution (e.g. 6?Å) overcame the previously reported problems due to Babinet phases and phase flipping errors.     

Research progress of rare earth Ce on improvement of microstructure and homogeneity of as- cast steel

The thermodynamic behavior of Ce and its compounds in molten steel was summarized, and the types of stable compounds after Ce added to molten steel and its variation were predicted. The mechanisms and rules of Ce compounds and dissolves Ce refining solidification structure of as- cast steel were summarized respectively. The improvement of homogenous by Ce was analyzed and the reason of decrease of element segregation was summarized. At last, some problems were pointed out which had not been solved in the research of rare earth Ce to improve the microstructure and homogeneity of steel, and put forward the main directions of the future research in this field.     

Effect of electromagnetic stirring methods on solidification structures of Sn-11% Sb binary alloy

In this paper,a spiral magnetic field electromagnetic stirrer,which can separately induce two different magnetic fields,is introduced. The corresponding central magnetic flux curves of the stirrer were measured by two different probes of the Tesla meter. Meanwhile,the mentioned spiral magnetic field electromagnetic stirrer was used,the effect of the two different magnetic fields on solidification of Sn-11% Sb binary alloy was studied,and the segregations and metallographic structures of the ingot samples were analyzed. The research results show that,with the same electromagnetic stirring parameters,the spiral magnetic field electromagnetic stirring is more effective in reducing the composition difference between the upper and lower parts of the ingot. The microstructure photos show that the grain size was more refined.     

Investigation of crystallisation kinetics of Bi0·5Se99·5-xZnx glasses by differential scanning calorimetry

Abstract

The kinetics of crystallisation in Bi_0·5Se_99·5-xZn_x (x=0, 0·1, 0·2, 0·5, 1·0) glasses are studied by non-isothermal method using differential scanning calorimetry. Differential thermal analysis was performed at different heating rates of 5, 10, 15, and 20 K min^-1. The values of glass transition and crystallisation temperatures are found to be composition and heating rate dependent. From the heating rate dependence of the glass transition and crystallisation temperatures, the activation energy of crystallisation ΔE _c, the order parameter n and the enthalpy released ΔH _c are calculated. The thermal stability (T _c–T _g) was found to be maximum for Bi_0·5Se_99·5 glass, which suggest that this glass can be considered as a critical composition at which the system becomes chemically ordered. The crystallisation enthalpy ΔH _c is maximum for Bi_0·5Se₉₉Zn_0·5 glass, hence it is the least stable glass in the present system.     

Characterization of polycrystalline SnO2 films deposited by DC sputtering technique with potential for technological applications

Polycrystalline SnO₂ films with different thicknesses were successfully deposited on glass substrate at room temperature using a DC sputtering technique. As-grown films showed the formation of an amorphous SnO₂ phase, whereas the thermal annealed samples showed the formation of a SnO₂ rutile-type structure. The structural study showed that the crystallinity of the annealed films was improved as a function of film thickness. Scanning electron microscopy images of the annealed films unveiled the formation of cracked surfaces along with columnar growth, irrespective of the depositon time. Raman spectroscopy measurements evidenced the presence of modes related to a surface disorder,a progressive strain reduction and a crystallinity improvement. UV–vis data analysis indicates a reduction in the band gap energy with films thickness due to presence of strain states as confirmed by theoretical calcuations. It was observed that the strained states in the films affected the sensing response to a methane gas flow with a better sensitivity for the thinner film.     

超高强度马氏体时效钢的研究与应用

介绍马氏体时效钢的种类,分析其强韧化机理,论述了典型的18Ni马氏体时效钢和无钴马氏体时效钢的化学成分和力学特性。系统阐述了循环相变热处理、形变热处理及等径弯曲通道变形(ECAP)这3种目前常用的细晶强化方法,并提出了马氏体时效钢的发展趋势及进一步深入研究强韧性和细晶强化的途径。     

Characterisation of corrosion products formed on steel rebars

Abstract

In this study, corrosion products on steel reinforcing bars (rebars) exposed in mortar contaminated with chlorides were characterised. For this purpose, scanning electron images were taken on steel surface and energy dispersive spectrometry analyses, as well X-ray diffraction was employed for quantitative characterisation using the Rietveld method. The main phases present were maghemite, goethite, lepidocrocite and akaganeite.

Dans cette étude, on a caractérisé les produits de corrosion de barres de renforcement en acier (barres d’armature) exposées dans du mortier contaminé par des chlorures. À cette fin, on a pris des images au microscope électronique à balayage, à la surface de l’acier, et l’on a employé des analyses de spectroscopie à dispersion d’énergie ainsi que la diffraction des rayons X pour la caractérisation quantitative, en utilisant la méthode de Rietveld. Les principales phases présentes consistaient en maghémite, en goéthite, en lépidocrocite et en akaganéite.     

Suspension high velocity oxy-fuel spraying of TiO2: A quantitative approach to phase composition

A range of coatings from a water based suspension of anatase has been prepared by suspension high velocity oxy-fuel spraying with the aim to study effects of heat power of the flame on phase composition, microstructure and surface topography. Three most commonly used approaches of quantitative phase analysis have been scrutinized with respect to their applicability and as some of the coatings showed presence of preferred orientation and it was argued that quantitative Rietveld refinement is the most accurate method for phase composition determination. Coatings had a layered duplex anatase/rutile microstructure with fraction of rutile increasing exponentially with heat power. Spraying at the lower heat power led to a lower surface roughness and higher power resulted in surfaces with pronounced humps, which were distributed homogeneously on the surface. The emergence of humps is related to an increase in macroscopic surface area of up to 30% with respect to the flat coating.     

Microstructural evolution in silicon alloyed γ-Ti–Al alloys after thermomechanical processing

Abstract

The microstructures of silicon alloyed γ-Ti–Al alloys containing silicide particles have been studied after thermomechanical treatments to investigate microstructural evolution. Important parameters including temperature, forging strain, and sequence of thermomechanical treatments were systematically studied. Isothermal forging below the eutectoid temperature resulted in inhomogeneous dynamic recrystallisation with fine equiaxed grains in recrystallised areas and residual α₂ + γ lamellae elsewhere. Eutectic silicides play an important role in destruction of the as cast structure by promoting dynamic recrystallisation during deformation and static recrystallisation on subsequent annealing. There is evidence that silicon, in solution, also enhances recrystallisation. The presence of fine silicides produced by precipitation in the solid state restricts the size of grains produced by both dynamic and static recrystallisation. Silicon also alters significantly the phase equilibrium between the α and γ phases.