An in-situ modification method for coal roadways with heightened burst risk

It is hard to control roadways effectively with a heightened burst risk using conventional support techniques, which may cause burst fatalities in the coal mine. Thus, an in-situ modification method, which involves artificially constructing a cracked zone and a reinforced zone, was proposed to improve the stability of the roadways with heightened burst risk. This paper investigated the efficiency to non of the in-situ modification method in improving burstroadway safety by performing a physical experiment. The results of the experiment indicated that the dynamic stress was obviously reduced in the modified roadway. Accordingly, the influence factors of the in-situ modification method were explored using numerical simulation. It was found that the thickness and the degree of damage to the cracked zone were key governing factors in reducing energy and improving roadway stability. The energy dissipation value increased as the thickness and the degree of damage to the cracked zone increased but showed a slower growth trend when the thickness and the degree of damage to the cracked zone increased to a certain value. In addition, the high sensitivity to dynamic load was found in parts of the roadway side exhibiting a larger stress reduction rate even with thinner cracked zone thickness and a lower degree of damage. This research provides an effective and economical method for coal roadways with heightened burst risk

Size Effect Analysis of Scale Test Model for High-speed Railway Foundation under Dynamic Loading Condition

To determine the energy attenuation and energy reflection coefficients in layered foundation is the key factor to reveal the dynamic response characteristics of the high-speed railway foundation. Based on the foundation test model under the dynamic loading of the high-speed railway, the energy attenuation and energy reflection coefficients were introduced and the attenuation formulas of the vibration acceleration in the layered foundation were deduced. Five scale models of 1:1, 1:2, 1:5, 1:10 and 1:20 are established respectively by using Abaqus technique. The energy attenuation mechanism and interfacial energy reflection characteristics in the layered foundation were analyzed. Results show that it is appropriate to use vibration acceleration to characterize the propagation rule of the energy attenuation in the layered foundation. The size effect equations of the energy attenuation and energy reflection coefficients in the layered foundation are deduced and the size effect of the energy attenuation is revealed. Based on the nonlinear relationships among the energy attenuation coefficient, the model scale, the loading amplitude and the vibration frequency, the energy attenuation equation of the scale test model is constructed. The reliability of the theoretical and simulation results is verified by the scale test model. The conclusions obtained in this study can provide a reference for a similar engineering practice

A digital direct controller for buck converter

International audienceA novel integrated digital controller for buck converter based on the direct system-variable calculation is presented. Compared with linear compensators, the discrete-time direct controller is conceived to generate an additional control variable during each switching period that increases the convergence rate when system states change. An all-digital current estimator is adopted to eliminate the use of current sensor. Experimental results verify closed-loop operation at switching frequency up to 4MHz. The dynamic response time for a load current step-up from 0.3A to 0.45A is 23.8μs, and 21.4μs for a step-down from 0.45A to 0.3A. An efficiency of over 75% is maintained over a power range from 29.3mW to 1.12W in which the maximum efficiency of 93.2% is achieved at 1.88V output

Alteration of resting brain function by genetic variation in angiotensin converting enzyme in amnestic-type mild cognitive impairment of Chinese Han

Using a cross-sectional case–control study of amnestic-mild cognitive impairment (aMCI), we characterised the relationships among cognitive function, serum levels of angiotensin converting enzyme (ACE), brain activity, and ACE insertion or deletion (I/D) polymorphism. Forty-eight patients with aMCI and 36 well-matched normal controls were assessed by a comprehensive battery of standardized neuropsychological tests. In addition, regional homogeneity (ReHo) approaches were used to analyze blood oxygen level-dependent functional magnetic resonance imaging data on the resting state in all subjects, and genotyping of the serum ACE was measured in aMCI patients. The D carriers with aMCI patients were found to have markedly higher serum ACE levels than I homozygote carriers. Importantly, compared with the carried I homozygote group of patients with aMCI, the D carriers of aMCI patients were significantly impaired in the AVLT-delayed recall and had decreased ReHo over the bilateral precuneus, left middle occipital gyrus, right inferior parietal lobe, and right angular gyrus, whilst increased ReHo was found mainly in the left medial frontal gyrus, right paracentral lobe, and right anterior cingulate cortex. The findings indicated that ACE genotype was associated with episodic memory, serum levels of ACE, and resting-state brain activity in aMCI patients, and the findings of cognitive function and brain activity further suggests that the ACE D allele may have a specific role in semantic memory dysfunction and brain activity in aMCI

Molecular detection of vector-borne agents in dogs from ten provinces of China

Abstract Background Although many vector-borne agents are potential zoonoses and cause substantial morbidity and mortality in dogs worldwide, there are limited data on these organisms in dogs of China. Methods Quantitative PCRs for vector-borne agents were performed to investigate their prevalences in convenience whole blood samples obtained from 1114 dogs from 21 veterinary clinics and a commercial dog breeding facility in ten provinces of China. In addition, the PCRs were performed on 146 Rhipicephalus sanguineus senso lato and 37 Linognathus setosus collected from dogs in the commercial dog breeding facility. Results DNAs of Babesia gibsoni and B. vogeli (1.2 %), Ehrlichia canis (1.3 %), Hepatozoon canis (1.8 %) and Theileria orientalis (0.1 %) or a closely related organism were detected in the bloods of the dogs studied, and Babesia vogeli (3.4 %) and Ehrlichia canis (4.1 %) in R. sanguineus senso lato. The qPCRs for Anaplasma spp., Dirofilaria immitis and Leishmania spp. were negative for all blood samples, ticks and lice. At least one vector-borne agent was found in dogs from 5 of the 10 provinces investigated in this study. Overall, 4.4 % (49/1117) of the dogs studied were positive for at least one vector-borne agent with the prevalence being highest in the commercial breeding colony (24/97; 24.7 %). Conclusions Our study confirms that B. vogeli, B. gibsoni, H. canis, and E. canis occur in China. Also, we present evidence that T. orientalis or a closely related organism can infect dogs