TECHNOLOGY OF QUANTITATIVE ANALYSIS ON VIBRATORY STRESS RELIEF BASED ON ULTRASONIC TIME-OF-ARRIVAL METHOD

The effect of vibratory stress relief （VSR） is usually evaluated with the indirect method of observing the change of amplitude frequency response characteristics of structures. A new kind of evaluating method of VSR based on the ultrasonic time-of-arrival method （UTM）, which can obtain the residual stress directly through measuring the propagation time of ultrasonic wave in the material, is presented. At first, the principle of the measuring method of residual stress based on UTM is analyzed. Then the measuring system of the method is described, which is in virtue of ultrasonic flaw detector and high-sampling-rate digital oscillograph. And a set of calibration system that contains a piece of standard specimen is also introduced. Experimental results prove the relation between the residual stress and the propagation time of ultrasonic in workpieces. Finally, the measuring and calibration systems are applied in evaluating the effect of VSR. The final test results show that the method is effective.

Large excavations and their effect on displacement of land boundaries

A study to estimate land surface movement caused by large surface excavations in sedimentary strata is presented.In stratified or jointed strata the stress relief driven movement adjacent to large excavations can be significantly larger than expected.High lateral stresses measured in Australia and other places around the world indicate that the ratio of horizontal to vertical stress has been particularly high at shallow depths.The in situ strata is in compression and during excavation,stress is relieved towards the opening causing strata movement.Large excavations such as,open cut mines or highway cuttings,can initiate an extensive horizontal slide of surface layers towards the excavation.These ground movements can be damaging to surface structures such as water storage dams and large buildings.Based on stress measurements at shallow depths in Australian coal mines the study presented here calculates and models the extent of potential ground movement along the bedding surface adjacent to large excavations and provides a new prediction tool of land movement at the excavation boundary that can benefit the geotechnical practitioners in the mining industry.

Dealing with the COVID-19 Pandemic:Economic Recovery Through Taxation in Africa

COVID-19 negatively impacted the economies of many African countries that had previously been on a positive trajectory.Both economic growth and revenue collections were severely eroded,triggered by the lockdowns implemented,stimu-lus packages offered to small and medium enterprises,financial support to vulnera-ble households,and the tax relief measures to businesses.ATAF administered three surveys on its member tax administrations to gauge the tax administration and pol-icy responses to COVID-19,assess the customs revenue losses,and evaluate the tax administrations’preparedness on business continuity and risk management.Results showed that tax administrations implemented a variety of tax relief measures which included accelerated refunds,tax deferrals,suspension of audits,suspension of duties on health products imported for fighting COVID-19 and tax amnesty programs.Some of the non-tax measures included measures meant for enhancing business cash flow,enhancing business con-tinuity,enhancing household cash-flow and supporting the informal sector and small businesses.Customs revenue was negatively impacted on,with an estimated loss of USD400 million~USD500 million from February to April 2020,for the 18 countries whose data was available.Additionally,some African tax administrations either did not have,or were not implementing Business Conti-nuity Plans(BCPs)and enterprise risk management.Sectors that benefitted from the pandemic include the health,pharmaceuticals and medical supplies,and telecommunication and informa-tion technology.The hardest hit sectors were the tourism,education,accommodation and food services and mining.Some countries realised positive revenue growth,despite the pandemic,due to increased usage of automated tax systems.To recover from negative effects of COVID-19,tax administrations should embark on reforms geared towards implementation of the following measures:taxation of digital economies through digital services taxes and a comprehensive VAT strategy for e-commerce transactions;combating transfer pricing and other forms of illicit financial flows;reducing the informal sector;and streamlining tax incentives.Tax administrations could also embrace digitalisation and leverage on big data considering the Fourth Industrial Revolution.