A method for computing unsupported roof distance in roadway advancement and its in-situ application

A reasonable unsupported roof distance(URD) when advancing underground coal mine roadways can contribute greatly to safe and rapid roadway development.A mechanical model of the roof,using the relationship between the roof stress distribution and URD,obtained by the difference method,and roof stability according to the in-situ roof stress and rock mass strength was developed.We subsequently designed a proper range of URD,developed a testing method of URD with the function of mining protection,evaluated roof stability through analyzing the test data and then determined a reasonable URD.Considering the factors of the geological conditions,the immediate roof stability and the efficiency of the labor arrangement system,the URD of the advancing roadway of 9802 working face in Zhangshuanglou coal mine was determined to be 6 m using the proposed method.The results show that,when a 2 m length of roadway was reinforced by temporary support and high pre-stressed bolt support after the roadway advancement of 6 m per cycle,the speed and the security of the roadway development can be achieved and the advance rate can reach more than 400 m per month.

Social distancing and testing as optimal strategies against the spread of COVID-19 in the Rio Grande Valley of Texas

At the beginning of August 2020,the Rio Grande Valley(RGV)of Texas experienced a rapid increase of coronavirus disease 2019(abbreviated as COVID-19)cases and deaths.This study aims to determine the optimal levels of effective social distancing and testing to slow the virus spread at the outset of the pandemic.We use an age-stratified eight compartment epidemiological model to depict COVID-19 transmission in the community and within households.With a simulated 120-day outbreak period data we obtain a post 180-days period optimal control strategy solution.Our results show that easing social distancing between adults by the end of the 180-day period requires very strict testing a month later and then daily testing rates of 5%followed by isolation of positive cases.Relaxing social distancing rates in adults from 50%to 25%requires both children and seniors to maintain social distancing rates of 50%for nearly the entire period while maintaining maximum testing rates of children and seniors for 150 of the 180 days considered in this model.Children have higher contact rates which leads to transmission based on our model,emphasizing the need for caution when considering school reopenings.

Design and test of a capacitance detection circuit based on a transimpedance amplifier

This paper presents a transimpedance amplifier （TIA） capacitance detection circuit aimed at detecting micro-capacitance, which is caused by ultrasonic stimulation applied to the capacitive micro-machined ultrasonic transducer （CMUT）. In the capacitance interface, a TIA is adopted to amplify the received signal with a center frequency of 400 kHz, and finally detect ultrasound pressure. The circuit has a strong anti-stray property and this paper also studies the calculation of compensation capacity in detail. To ensure high resolution, noise analysis is conducted. After optimization, the detected minimum ultrasound pressure is 2.1 Pa, which is two orders of magni- tude higher than the former. The test results showed that the circuit was sensitive to changes in ultrasound pressure and the distance between the CMUT and stumbling block, which also successfully demonstrates the functionality of the developed TIA of the analog-front-end receiver.