Nonlinear effects of the finite amplitude ultrasound wave in biological tissues

Nonlinear effects will occur during the transmission of the finite amplitude wave in biological tissues. The theoretical prediction and experimental demonstration of the nonlinear effects on the propagation of the finite amplitude wave at the range of biomedical ultrasound frequency and intensity are studied. Results show that the efficiency factor and effective propagation distance will decrease while the attenuation coefficient increases due to the existence of nonlinear effects. The experimental results coincided quite well with the theory. This shows that the effective propagation distance and efficiency factor can be used to describe quantitatively the influence of nonlinear effects on the propagation of the finite amplitude sound wave in biological tissues.     

Changes in porosity of foamed aluminum during solidification

In order to control the porosity of foamed aluminum, the changes in the porosity of foamed aluminum melt in the processes of foaming and solidification, the distribution of the porosity of foamed aluminum, and the relationship between them were studied. The results indicated that the porosity of foamed aluminum coincides well with the foaming time.     

用重折率法鉴别材料中的晶相转变类型

材料研制中经常要对材料的有关物相及其相变进行经常的、大量的检测。在这些检测中遇到的最大难题是相变类型。该文提出如何用重折率法来检测晶相的相变类型。这种方法简便。     

黄土物理性质变化规律研究

研究了黄土孔隙度和湿陷性在垂向上变化的规律和原因 .结果表明 ,孔隙度高和湿陷强的层位是风化成壤弱的黄土层 ,孔隙度低和湿陷弱的层位是红色古土壤或风化成壤强的黄土层 .第四纪冷干与温湿气候的交替和由此产生的成壤过程的变化是造成黄土地层孔隙度和湿陷性波动变化的根本原因 .黄土湿陷性是在干旱与半干旱地区弱的成壤过程中产生的 ,是草原地带灰黄色土壤具有的特征 .     

陕西渭北旱塬近43年气候暖干化研究

利用 1 95 5 - 1 997年陕西渭北地区 5个县、市的气温和降水资料 ,对近 43年来陕西渭北地区气候变化特征进行了分析 .结果表明 ,近 43年来 ,陕西渭北地区温度、降水的变化呈明显多重周期波动 ,年平均气温上升 ,降水量减少 ,变旱趋势明显 ,气候呈暖干化     

相变效应理论

研究了天体恒星、行星、卫星等宇宙星系的自转和不同步公转而产生观测周期差的主、次要原因及其组成部分,分析了Romer天文学方法测光速理论分析的错误,修正了Romer天文法测光速的光速理论计算公式,讨论了FanHoupeng相变效应理论与Romer天文学测光速理论的关系并计算出精确光速值,建立了FanHoupeng相变效应理论。     

中部槽磨损失效中的能量转化分析

从摩擦学系统的概念出发 ,分析了影响刮板输送机中部槽摩擦学系统能量平衡的各种因素 ,特别对中部槽磨损失效过程中的能量转化进行了分析和探讨 分析表明 :中部槽的摩擦能量转化成 4部分 :表层和亚表层变形能量、内能的变化、形成的热量和表面能的增加 ;根据中部槽磨损类型和井下工况条件的不同 ,摩擦物体总的摩擦能量WR 的分配系数 (α)也各不相同 图 2 ,参 5     

一种近似恒力弹簧装置的设计

为消除弹簧装置中应力随应变不断变化而产生的多余应力 ,在卷簧结构中 ,采用螺旋变径输出轮 ,用半径的变化抵消力矩的变化 ,获得近似恒定的输出力 .在精度要求不高的场合 ,采用此方式可形成简便可靠的近似恒力的弹簧装置 .     

旋转电场中的阻尼Λ-型原子

研究了旋转电场中阻尼Λ－型原子的能级分裂和寿命变化。可以看到在旋转电场中阻尼Λ－型原子将分成６个能级,其寿命也将改变。利用一定的调谐方式,并在一些近似条件下,我们得到了在强场和弱场情况下,原子能级和寿命的比较简单的表达式。     

Public perception of climate change and disaster preparedness: Evidence from the Philippines

The Philippines is highly susceptible to both geophysical and climate-related disasters. This article explores Filipinos knowledge and perception of climate change and their association with what action Filipinos take to prepare for rapid onset natural hazards such as typhoons. Data for this study were collected from a nationally representative random survey of 5,184 adults conducted between March and April of 2017. Filipinos self-report relatively low levels of knowledge of climate change and cited increased temperatures, shifts in seasons, and heavier rains as the most likely consequences. Levels of disaster preparedness in the Philippines differ widely by region. Although most Filipinos perceive that natural hazards are a risk to them, only a third of Filipinos undertake measures to prepare for disasters. Filipinos who perceive climate-related changes directly impacting their households report taking greater action to prepare for disasters. Filipinos who believe they have been directly impacted by climate-related changes are also more likely to prepare for disasters, take planning actions, and undertake material actions to prepare, such as dwelling improvements. Other factors associated with disaster preparedness include gender, membership in an association, wealth, risk perception, and prior exposure to and losses due to disasters. The findings imply that, while posing different challenges and requiring different responses, adaptation to climate change and disaster preparedness are inherently associated and potentially mutually reinforcing. Policies and programs would arguably benefit from a more unified intervention framework that links climate change adaptation and disaster preparedness.