Proportional versus semiproportional region in gaseous detectors: A simple method of discrimination

Pulse heights of anodic signals in proportional detectors are normalized in such a way that a straightforward method of accurate determination of the frontier between true and semiproportional modes of operation comes out without any data handling. Experimental results are presented. One interesting feature is that the frontier stands above the voltage for which the energy resolution is minimum.     

Microtexture and structure of semi-cokes and cokes

During carbonization, before the semi-coke stage, parallel local orientation of polyaromatic structures occurs (local molecular orientation or LMO). The oriented species are usually classified in decreasing order by the extent of optical isochromatic areas and are studied at molecular range by means of transmission electron microscopy. A continuous series of microtextures exist from stiff and flat lamellae to crumpled and then porous microtextures according to a decreasing curvature radius of the sheets of polyaromatic structures. This continuous degradation of coke texture, related to a continuous decrease in the local molecular orientation, brings about a decrease in carbon graphitizability. It is shown that textural and structural variations of coke depend upon the functional groups linked to polyaromatic structures, these groups having antagonistic effects of either cross-linkage (oxygen or sulphur) or saturation (hydrogen).     

Pyrolysis studies of some simple coal related aromatic methyl ethers

Pyrolysis of the coal related model compounds o-, m-, and p-hydroxy and methoxyanisoles has been studied under inert atmosphere at reaction temperatures from 598 to 673 K, and for reaction times from 1 to 600 min. The thermal decomposition of all these anisoles takes place via two main primary pathways, namely by demethylation of the methoxyl groups, and by an intramolecular ipso substitution of the methoxyl groups via a spiranic oxiran intermediate. The demethoxylation under mild reaction conditions obviously takes place as a secondary reaction via the ipso substitution pathway. The demethylation of o-hydroxyanisole (guaiacol) is partly concerted on the basis of kinetics and of e.p.r. measurements of the residual spin concentration of the pyrolysis products. There is, however, no indication of a concerted mechanism for 0-methoxyanisole (veratrole). The apparent first order activation energy of all the anisoles studied is of the order 240 ± 20 kJ mol⁻¹ corresponding to the average bond energy of the methyl CO bond in the aromatic methoxyl group.     

Exploiting hydrodynamic instabilities. Resonant heat transfer enhancement

We introduce here the concept of resonant heat transfer enhancement based on excitation of shear-layer instabilities present in internal separated flows. Exploitation of natural instabilities requires: creation of a system with separated flow; determination of the system's resonant frequency; and excitation of that frequency with appropriate modulation. The resulting large scale motions lead to significant lateral mixing and correspondingly dramatic heat transfer enhancement. The method is applicable both in laminar and turbulent flows. Results, experimental and numerical, for a subcritieal grooved channel flow and a cross flow around a cylinder are presented. For the case of grooved channel, up to three-fold enhancement of heat transfer is observed when the flow is modulated at the system's natural frequency.     

Second moment of n.m.r. line for the Wiser model of coal

The Wiser model of coal structure was tested using the Van Vleck moment of theory of n.m.r. lines the second moment of rigid and rotational structures being calculated. The results correspond to the second moment of the Gaussian component of free induction decay (FID) observed experimentally in some coals.     

Breakability analysis of the elastic rock beam based on the winkler model

Based on the Winkler model, a mechanic model was established with formulas derived concerned with the deformations before and after a roof breakage at places in front of and at the back of the working face. In accordance with the theory for rock beam breakage, the beam breaking position in front of the working face is specified. In addition, the formulas were developed for the velocity of the subsidence at observatory point A in front of the working face when the coal wall serves as the coordinate center and the advance distance at time t as the dynamic coordinate. In the application of the above-mentioned achievements to the practice of Xieqiao Mine and the mines of the Eastern Panji Company of Huainan Mining（Group） Co. Ltd., the results concerned with the velocity with which the roof stratum tends to subside before and after breakage as derived from the mechanic model are well compatible to the results based on in-situ observations and measurements.     

A vacuum ultraviolet laser with a submicrometer spot for spatially resolved photoemission spectroscopy

Vacuum ultraviolet(VUV)lasers have demonstrated great potential as the light source for various spectroscopies,which,if they can be focused into a small beam spot,will not only allow investigation of mesoscopic materials and structures but also find application in the manufacture of nano-objects with excellent precision.In this work,we report the construction of a 177 nm VUV laser that can achieve a record-small(〜0.76 μm)focal spot at a long focal length(~45 mm)by using a flat lens without spherical aberration.The size of the beam spot of this VUV laser was tested using a metal grating and exfoliated graphene flakes,and we demonstrated its application in a fluorescence spectroscopy study on pure and Tm3+-doped NaYF4 microcrystals,revealing a new emission band that cannot be observed in the traditional up-conversion process.In addition,this laser system would be an ideal light source for spatially and angleresolved photoemission spectroscopy.     

Self-quenching streamer discharge under extremely large amounts of quenching gas

The self-quenching streamer mode behaviors appear in both pure carbon dioxide and pure methane filling gas. In pure ethane and pure propane we saw the large saturated pulses, but no transition at any attainable voltage. When the carbon dioxide concentration is larger than 98% in argon-carbon dioxide mixtures, Q_trl increases with the concentration.     

Experimental study on the deformation and failure mechanism of overburden rock during coal mining using a comprehensive intelligent sensing method

Understanding the spatiotemporal evolution of overburden deformation during coal mining is still a challenge in engineering practice due to the limitation of monitoring techniques. Taking the Yangliu Coal Mine as an example, a similarity model test was designed and conducted to investigate the deformation and failure mechanism of overlying rocks in this study. Distributed fiber optic sensing(DFOS), highdensity electrical resistivity tomography(HD-ERT) and close-range photogrammetry(CRP) technolo...     

基于闭环矢量法的六足机器人关节位姿研究

设计出了一种新型的三自由度缩放式的并联机构,并把该机构作为六足步行机器人的腿机构.采用闭环矢量法求解腿机构运动位置的正运动学问题,用MATLAB软件编写函数来求解腿机构的最大腿行程和最大抬跨高度/研究表明,原动件较小的位移可以获得较大的足端运动空间.