Failure mechanism and control technology of longwall coalface in large-cutting-height mining method

The stability control of longwall coalface is the key technology of large-cutting-height mining method.Therefore,a systematic study of the factors that affect coalface stability and its control technology is required in the development of large-cutting-height mining method in China. After the practical field observation and years of study,it was found that the more than 95% of failures in coalface are shear failure. The shear failure analysis model of coalface has been established,that can perform systematic study among factors such as mining height,coal mass strength,roof load,support resistance,and face flipper protecting plate horizontal force. Meanwhile,sensitivity analysis of factors influencing coalface stability showed that improving support capacity,cohesion of coal mass and decreasing roof load of coalface are the key to improve coalface stability. Numerical simulation of the factors affecting coalface stability has been performed using UDEC software and the results are consistent with the theoretical analysis. The coalface reinforcement technology of large-cutting-height mining method using the grouting combined with coir rope is presented. Laboratory tests have been carried out to verify its reinforcement effect and practical application has been implemented in several coal mines with good results.It has now become the main technology to reduce longwall coalface failure of large-cutting-height mining method.

Advances in Application of New Catalytic Materials in Petroleum Refining and Petrochemicals Production

This article introduces the solid acid catalyst for isobutene/butylenes alkylation, the HTS Ti/Si zeolite for ammonoxidation of cyclohexanone and the noncrystalline alloy catalyst and magnetically stabi- lized bed for hydrofining of caprolactam that were developed recently by SINOPEC Research Institute of Petroleum Processing (RIPP).

Reflections on stability technology for reducing risk of system collapse due to cascading outages

This paper aims at putting forward viewpoints regarding the use of stability technology to prevent and control cascading outages by examining recent blackout events.Based on the inquiry reports of the 2011 SouthwestAmerica blackout and the 2012 India power blackouts,event evolution features are first summarized from a stability perspective.Then a comparative analysis is conducted so as to propose suggestions of effective measures,either preventive or emergency,which could have avoided the blackouts.It is shown that applications of several mature technologies can create opportunities of preventing or interrupting the cascading development.These include offline dynamic simulation,online stability analysis and preventive control,real-time situational awareness and automatic emergency control.Further R&D directions are given to address the challenges of modern power systems as well.They cover system fault identification criterion of protection and control devices,verification of adaptability of control effect to system operating conditions,real-time operational management of emergency control measures and improvement of simulation accuracy.

EXISTENCE UNIQUENESS AND ASYMPTOTIC STABILITY OF PERIODIC SOLUTIONS OF A NONLINEAR EQUATION IN PHASE LOCKED TECHNOLOGY

In [1] and [2], the authors made a deep qualitative analysis of the equationwith the character of tangent detected phase and they mathematically provided atheoretical basis of why the phase looked loop has no look--losing point. However,according to many practical experts, it is rather difficult to put such a phaselooked loop into practice, though it has fine properties. W. C. Lindsey [3] made a