Spectroscopic Studies of Nanopowder and Nanoceramics La2Hf2O7:Pr Scintillator

Sintered nanoceramics of Pr‐doped lanthanum hafnate, La₂Hf₂O₇:Pr, were prepared by means of a high‐pressure sintering technique using nanopowders made by Pechini method. Structure, morphology, and spectroscopic properties of the ceramics compared to the starting powder are presented and discussed. Emission and excitation spectra recorded at room temperature as well as at 7 K using synchrotron radiation are presented together with results of luminescence kinetics measurements. In ceramics, at 7 K, the Pr³⁺ luminescence from ³P₀ (blue‐green, green, and red region) and ¹D₂ (red) levels is accompanied by a broad‐band emission located in the 380–530 nm range of wavelengths, whereas powders gives only the Pr³⁺‐related luminescence. Depending on the excitation wavelength, the broad‐band emission maximum moves between 430 and 470 nm indicating superposition of at least two components. In sintered nanoceramics, the lifetimes of Pr³⁺ emissions from ³P₀ and ¹D₂ levels were by 10%–20% shorter compared to the powder. The existence of different luminescence centers was proved by the selective emission decays examination. The fast 5d → 4f luminescence of Pr³⁺ was not observed from either of the two types of La₂Hf₂O₇:Pr materials.     

Structure and mechanical properties of NiAl and Ni3Al-based alloys

The investigation of Ni–Al–Fe–Ti–B alloys was carried out to determine the influence of iron and small titanium and boron additions on the phase composition, microstructure and mechanical characteristic, particularly with respect to high-temperature deformation conditions. These alloys, containing Al 35.8 at% and Fe 3.6–8.6–17.6 at% were prepared from high-purity components and Al master alloy containing Ti₂B particles. The influence of alloying additions of chromium and iron on the mechanical properties of directionally solidified Ni–Al–Cr–Fe alloy was investigated. Additions of both Cr 8 at% and Fe 2 at% result in higher strength than exhibited by unalloyed Ni₃Al. However, the ductility is reduced by the formation of the β′ phase. The typical, lamellar structure of Ni–20Al–8Cr–2Fe alloy undergoes coagulation during a high-temperature deformation process. The sequence of structural changes of NiAl and Ni₃Al-based alloys has been correlated with mechanical characteristics of high-temperature deformation process, determined in uni-axial compression tests. Two ranges of work hardening have been identified on the stress–strain curves of these alloys. It has been found that the first range of the deformation of Ni–Al–Fe–Ti–B alloys corresponds to the intergranular slip system operating within individual grains, while the second one is connected with transgranular slip. In the directionally solidified Ni–20Al–8Cr–2Fe alloy similar work hardening curves were observed in relation to the microstructural evolution from the lamellae shape, through elliptical shape into circular shape.     

Synthesis of dicarboxylic and complex esters by transesterification

A new method of manufacturing simple dicarboxylic esters and complex esters has been developed. This method is based on a transesterification reaction in the presence of powdered calcium oxide which acts as a catalyst. Commonly accessible raw materials, namely, dimethyl adipate, 2‐ethylhexanol, neopenthyl glycol, and trimethylolpropane were used for the synthesis of the esters. The methanol formed in the transesterification reaction was continuously removed by azeotropic distillation with isooctane. The possibility of producing complex esters with different viscosities and polarities by modification of their chemical structure was studied.     

Method of abrasive wear testing in comminution processes

The abrasive wear properties of materials in sliding contact with solid mineral particles during a comminution process have been studied. The equipment used can simulate tribo-conditions inside coal pulverisers. Using the experimental apparatus, a number of different materials have been tested and classified according to their resistance to abrasive wear in rubbing contact with particulate coal. The method and principles of three new rigs have been described in the previous paper (see p. 235).     

ARS: an integrated package for shared-variable and message-passing computations in object-based systems

This paper describes the ARS library package, which supports two implementation versions of an object-based system: a shared-variable and a message-passing version. The two versions have the same object structure and synchronisation but differ in their process structure and inter-process communication models. Thus, the mechanisms related to the uniform features are common for the two versions, but the process multiplexing mechanisms differ. As a consequence, the performance characteristics of the two versions of a system related to uniform features are similar, while those related to the process multiplexing differ significantly. We present an overview of the computational model supported by the ARS package, the internal structure of the package and compare overheads in two versions of an object-based system supported by the package. © 1998 John Wiley & Sons, Ltd.     

圆筒实验数据研究高能炸药的爆轰特性（英）

根据圆筒实验数据,采用新方法计算了HMX、RDX、PETN、TNT等炸药的爆轰能,研究了爆轰产物的加速能力,并与CHEETAH的计算结果进行了对比。通过爆轰波在柱壳水介质中传播的圆筒实验方法,预估了炸药的爆压。利用实验和热化学计算的结果推导了JWL状态方程的待定常数,并依据JWL等熵线计算了做功能力。