Robust prediction of chatter stability in milling based on the analytical chatter stability

A major obstacle that limits the productivity in machining operations is the presence of machine tool chatter. Machining is a dynamic process and chatter behavior depends upon a number of different aspects including spindle speeds, material properties, tool geometry, and even the location of tool respect to the rest of machine. Many of the traditional models used to predict chatter stability lobes assume that parameters such as natural frequency, stiffness, and cutting coefficients remain constant. In reality, these parameters vary and they affect the chatter stability. The uncertainty in these parameters can be taken into consideration by employing the robust stability theory into a two degree of freedom milling model. Utilizing the Edge theorem and the Zero Exclusion condition, a robust chatter stability model, based on the analytical chatter stability milling model, is developed. This improves the reliability compared to the projected pseudo single degree of freedom model. The method is verified experimentally for milling operations while considering a changing natural frequency and cutting coefficient.     

工业生态系统类型及稳定性的相关性探讨

在分析了工业生态系统及其稳定性涵义的基础上，结合实例把工业生态系统分为3种类型：星式工业生态系统、放射式工业生态系统和点式工业生态系统，从多方面探讨了各种类型工业生态系统的特征，并分析了工业生态系统类型与稳定的相关性，有针对性地提出提高各类型工业生态系统稳定性的对策。     

Causes and consequences of thermal runaway incidents—Will they ever be avoided?

A study of runaway incidents involving thermal chemical reactions in the UK over the past 25 years (1988–2013) has been carried out. The objective of this study is to determine possible causes of thermal runaway incidents. A statistical analysis of the underlying problems that led to thermal runaway incidents has been provided. A comparison of the current study on thermal runaway incidents with those identified prior to 1988 has been carried out. This study clearly shows that lessons have not been learnt from thermal runaway incidents caused by operator errors, management failures and lack of organised operating procedures. These factors have been the possible causes of about 77% of all the thermal runaway incidents analysed in this study. The number of fatalities and injuries as a result of thermal runaway incidents has increased by ∼325% and ∼279%, respectively, in the last 25 years even though the number of incidents was significantly less. On the basis of this analysis, several recommendations have been proposed that could help to minimise the risks associated with any thermal runaway incidents in the future.     

Upward movement of plutonium to surface sediments during an 11-year field study

An 11-year lysimeter study was established to monitor the movement of Pu through vadose zone sediments. Sediment Pu concentrations as a function of depth indicated that some Pu moved upward from the buried source material. Subsequent numerical modeling suggested that the upward movement was largely the result of invading grasses taking up the Pu and translocating it upward. The objective of this study was to determine if the Pu of surface sediments originated from atmosphere fallout or from the buried lysimeter source material (weapons-grade Pu), providing additional evidence that plants were involved in the upward migration of Pu. The ²⁴⁰Pu/²³⁹Pu and ²⁴²Pu/²³⁹Pu atomic fraction ratios of the lysimeter surface sediments, as determined by Thermal Ionization Mass Spectroscopy (TIMS), were 0.063 and 0.00045, respectively; consistent with the signatures of the weapons-grade Pu. Our numerical simulations indicate that because plants create a large water flux, small concentrations over multiple years may result in a measurable accumulation of Pu on the ground surface. These results may have implications on the conceptual model for calculating risk associated with long-term stewardship and monitored natural attenuation management of Pu contaminated subsurface and surface sediments.     

Adsorption,desorption, soil mobility,aqueous persistence and octanol‐water partitioning coefficients of terbufos,terbufos sulfoxide and terbufos sulfone

Abstract

Terbufos, t. sulfoxide and t. sulfone (5 μg ml^‐1) were incubated in natural, sterilized natural and distilled water, with initial pH values of 8.8, 8.8 and 6.0, respectively, at 20°C. First‐order disappearance was observed for the three compounds. Rates in natural and sterilized water were similar indicating chemical degradation predominated. Terbufos disappeared rapidly (t½>=3 days) in all systems. T. sulfoxide and t. sulfone were more persistent in the natural (t½>=18–40 days) and distilled water (t½>=280–350 days). Adsorption data for the three compounds in four soil‐water systems showed the decreasing order of adsorption to be terbufos>>t. sulfoxide=t. sulfone. Desorption from soils fortified at 5 μg g^‐1 with water was examined for 4 successive 18‐hr cycles. T. sulfoxide and t. sulfone were totally desorbed; terbufos was too unstable to study. The mobility of the compound in soil eluted with water was in the order, t. sulfoxide=t. sulfone>> terbufos, in agreement with adsorption‐desorption results. The octanol‐water partitioning coefficients for terbufos, t. sulfoxide and t. sulfone, at 23°C, were 3:30 x 10 , 164, and 302, respectively.     

温度和pH值对重组杆状病毒(AcMNPV-BmKIT-Chi)的毒力影响

研究了温度、酸碱度对重组杆状病毒(AcMNPV-BmKIT-Chi)毒力的影响.结果显示,多角体病毒在温度4~50℃,pH6.0~8.0范围内可以保持较高的毒力稳定性;不同虫龄棉铃虫幼虫对重组病毒的毒力敏感性差异显著,低虫龄对重组核型多角体病毒更为敏感;病毒对幼虫存在亚致死作用,饲毒组与对照组幼虫体重差异显著.图3表3参13     

Ground Fires as a Factor of Maintenance of Pine–Larch Forests in the Southern Urals

Russian Journal of Ecology -     

Eutectic mixture promoted CO2 sorption on MgO-TiO2 composite at elevated temperature

The development of carbon dioxide(CO_2) sorbents that can operate at elevated temperatures is significant for the advancement of pre-combustion capture technologies.Recently, promoter-based systems composed of alkali/alkaline earth metal nitrates and/or carbonates have been considered as next-generation solid sorbents due to their improved CO_2 uptake and kinetics. However, obtaining stable MgO sorbents against temperature swing regeneration still remained challenging. Herein, we report MgO-TiO_2 solid sorbents promoted by eutectic mixture(KNO_3 and LiNO_3) for elevated temperature CO_2 sorption. The developed sorbents show improved CO_2 sorption capacity, which may be attributed to the alternative CO_2 sorption pathway provided by the ionization of highly dispersed MgO in the eutectic mixture. The MgO-TiO_2 framework was also shown to assist in retaining the MgO configuration by constraining its interaction with CO_2. Furthermore, it is demonstrated that constructing composite structures is essential to improve the CO_2 sorption characteristics,mainly recyclability, at elevated temperatures. The developed promoter integrated sorbents showed exceptionally high CO_2 sorption capacity of 30 wt.% at an elevated temperature(300°C) with pronounced stability under temperature swing operation.     

Control of exhaled SARS-CoV-2-laden aerosols in the interpersonal breathing microenvironment in a ventilated room with limited space air stability

The Coronavirus Disease 2019 (COVID-19) highlights the importance of understanding and controlling the spread of the coronavirus between persons. We experimentally and numerically investigated an advanced engineering and environmental method on controlling the transmission of airborne SARS-CoV-2-laden aerosols in the breathing microenvironment between two persons during interactive breathing process by combining the limited space air stability and a ventilation method. Experiments were carried out in a full-scale ventilated room with different limited space air stability conditions, i.e., stable condition, neutral condition and unstable condition. Two real humans were involved to conducted normal breathing process in the room and the exhaled carbon dioxide was used as the surrogate of infectious airborne SARS-CoV-2-laden aerosols from respiratory activities. A correspondent numerical model was established to visualize the temperature field and contaminated field in the test room. Results show that the performance of a ventilation system on removing infectious airborne SARS-CoV-2-laden aerosols from the interpersonal breathing microenvironment is dependent on the limited space air stability conditions. Appropriate ventilation method should be implemented based on an evaluation of the air condition. It is recommended that total volume ventilation methods are suitable for unstable and neutral conditions and local ventilation methods are preferable for stable conditions. This study provides an insight into the transmission of airborne SARS-CoV-2-laden aerosols between persons in ventilated rooms with different limited space air stability conditions. Useful guidance has been provided to cope with COVID-19 in limited spaces.