一种考虑静水压力和偏应力共同作用的相变临界准则

同时考虑静水压力和偏应力的影响,分别建立了“应力诱发”和“形变诱发”相变的临界准则．准则在主应力空间中给出的相变临界曲面呈现明显的拉压不对称性．在弹性阶段,偏应力对相变总是起促进作用．塑性屈服后,偏应力通过塑性功产生的温升影响相变临界面,从而对高温相到低温相转变起阻碍作用,反之起促进作用．静水压力对相变可能起促进作用,也可能起阻碍作用,取决于相变时材料的体积是膨胀还是收缩．建立的相变临界准则对准静态加载条件下的Fe-20％Ni-0．5％合金和Fe-30％Ni合金和一维应变冲击条件下的Fe-32％Ni-0．035％。C合金中的γ-α相变进行了拟合和预测,预测与实验结果有较好的吻合。在主应力空间中柱形屈服面可能与锥形相变临界面相交,从而在一定条件下将发生“形变诱发”相变和“应力诱发”相变间的转变,这一推论有待实验的验证。     

响应曲面法优化超高压杀灭金黄色葡萄球菌条件的研究

 因子试验研究结果表明,显著影响超高压杀灭金黄色葡萄球菌效果的外界因子是温度、压力和保压时间。在此基础上,采用响应曲面法（Response Surface Methodology,RSM）建立了超高压杀灭金黄色葡萄球菌的二次多项数学模型,验证了模型的有效性,并探讨了上述3个因子的交互作用及其最佳水平范围,优化出杀灭6个数量级金黄色葡萄球菌ATCC6538的外界条件为：温度34.35 ℃,压力329.84 MPa,时间15.53 min。     

THE ZONAL DISINTEGRATION MECHANISM OF SURROUNDING ROCK AROUND DEEP SPHERICAL TUNNELS UNDER HYDROSTATIC PRESSURE CONDITION: A NON-EUCLIDEAN CONTINUUM DAMAGE MODEL

A new non-Euclidean continuum damage model is proposed to investigate the zonal disintegration phenomenon of the surrounding rocks around deep spherical tunnels under hydrostatic pressure condition as well as the total elastic stress field distributions.The elastic stress fields of the surrounding rocks around deep spherical tunnels under hydrostatic pressure condition are obtained.If the elastic stresses of the surrounding rocks satisfy the strength criterion of the deep rock masses,the number,size and location of fractured and nonfractured zones are determined.The efect of physico-mechanical parameters of the surrounding rocks on the zonal disintegration phenomenon is studied and numerical computation is carried out.It is found from numerical results that the number,size and location of fractured and non-fractured zones are sensitive to the physico-mechanical parameters of the surrounding rocks.     

Inflation analyses of a circular elastomeric membrane with hydrostatic pressure

Composite diaphragm inflation (CDI) experiment is a useful methodology for exploring the mechanics relation of cell-cell junctions within a living epithelial sheet. In this paper, a new methodology of CDI experiment has been put forward. The finite deformation of a circular polydimezhylsiloxane elastomeric membrane, which is used as the substrate for the culture of epithelial cells, under hydrostatic pressure is explored by the theory of non-linear continuum mechanics. The simplified governing equations with minimum amount of differential equations and boundary conditions are obtained and solved by multiple shooting method. The influences on the membrane by hydrostatic pressure have been discussed.     

X射线衍射法研究不同类型淀粉高静压处理后晶体结构的变化

对300, 450和600 MPa不同高静压力下导致的淀粉结晶结构变化进行研究。选择不同类型、不同链/支比的三种淀粉为研究对象,进行高静压处理,利用X射线衍射法分析高静压对不同类型,不同链/支比淀粉晶体结构的影响。结果表明：由于X射线衍射峰加强及相对结晶度增大,糯玉米淀粉在300 MPa表现为韧化作用,在450 MPa结晶结构完全解体,600 MPa时发生重结晶;HylonⅦ淀粉在600 MPa以下的高静压处理只表现出韧化效果,结晶度增加但不明显;木薯淀粉在300 MPa具有韧化作用,600 MPa结晶结构完全消失,表现为韧化-颗粒结晶解体两个过程。因此,本文提出淀粉颗粒在高静压处理过程中经历压缩韧化-晶体结构解体-重结晶三个发展阶段。     

铈γ→α相变的室温动态特性

通过试样组件尺寸匹配设计的被动围压SHPB实验,获得了99.8%纯铈在1.7GPa静水压内的、包含γ?α相变和逆相变过渡区的室温动态静水压-体应变连续曲线。研究显示:室温铈γ→α相变是具有明显滞后现象的一级相变,而非以往研究认为的体积跃变的一级相变;相变过渡区的静水压范围是0.8~1.3GPa。逆相变过渡区的静水压范围是0.6~1.1GPa;逆相变过渡区的静水压-体应变曲线滞后于相变过渡区的静水压-体应变曲线0.15GPa静水压;在相变和逆相变过渡区内,静水压-体应变曲线按照约4.2GPa体积模量的线性关系演化;演化机制为γ和α两相均匀混合、静水压驱动两相组份转化。基于该演化机制,构建了描述相变前后和相变过程的静水压-体应变响应的三段线性模型。     

Bioaccessibility of Antioxidants in Prickly Pear Fruits Treated with High Hydrostatic Pressure: An Application for Healthier Foods

High hydrostatic pressure (HHP) is a commercial processing technology which can enhance the health potential of foods by improving the bioaccessibility of their bioactive compounds. Our aim was to study the bioaccessibility and digestive stability of phenolic compounds and betalains in prickly pear fruits (Opuntia ficus-indica L. Mill. var. Pelota and Sanguinos) treated with HHP (100, 350, and 600 MPa; come-up time and 5 min). The effects of HHP on pulps (edible fraction) and peels (sources of potential healthy ingredients) were assessed. In pulps, betanin bioaccessibility increased (+47% to +64%) when treated at 350 MPa/5 min. In HHP-treated pulps, increases in the bioaccessibility of piscidic acid (+67% to +176%) and 4-hydroxybenzoic acid glycoside (+126% to 136%) were also observed. Isorhamnetin glycosides in peels treated at 600 MPa/CUT had higher bioaccessibility (+17% to +126%) than their controls. The effects of HHP on the bioaccessibility of health-promoting compounds are not exclusively governed by extractability increases of antioxidants in the food matrix (direct effects). In this work we found evidence that indirect effects (effects on the food matrix) could also play a role in the increased bioaccessibility of antioxidants in fruits treated with HHP.     

Combined of ultrasound irradiation with high hydrostatic pressure (US/HHP) as a new method to improve immobilization of dextranase onto alginate gel

In this research work, dextranase was immobilized onto calcium alginate beads by the combination of ultrasonic irradiation and high hydrostatic pressure (US/HHP) treatments. Effects of US/HHP treatments on loading efficiency and immobilization yield of dextranase enzyme onto calcium alginate beads were investigated. Furthermore, the activities of immobilized enzymes prepared with and without US/HHP treatments and that prepared with ultrasonic irradiation (US) and high hydrostatic pressure (HHP), as a function of pH, temperature, recyclability and enzyme kinetic parameters, were compared with that for free enzyme. The maximum loading efficiency and the immobilization yield were observed when the immobilized dextranase was prepared with US (40 W at 25 kHz for 15 min) combined with HHP (400 MPa for 15 min), under which the loading efficiency and the immobilization yield increased by 88.92% and 80.86%, respectively, compared to immobilized enzymes prepared without US/HHP treatment. On the other hand, immobilized enzyme prepared with US/HHP treatment showed V_max, K_M, catalytic and specificity constants values higher than that for the immobilized enzyme prepared with HHP treatment, indicated that, this new US/HHP method improved the catalytic kinetics activity of immobilized dextranase at all the reaction conditions studied. Compared to immobilized enzyme prepared either with US or HHP, the immobilized enzymes prepared with US/HHP method exhibited a higher: pH optimum, optimal reaction temperature, thermal stability and recyclability, and lower activation energy, which, illustrating the effectiveness of the US/HHP method. These results indicated that, the combination of US and HHP treatments could be an effective method for improving the immobilization of enzymes in polymers.     

静水高压处理对水稻植株生理特性的影响

 以75 MPa静水高压处理萌动的水稻种子12 h，成苗后移栽至大田，研究高压处理后植株剑叶光合特性的变化。结果显示，静水高压处理后，粤香占和粤丰占种子的发芽率分别降低了14.4% 和16.6%，成苗率分别降至对照的24.6%和21.9%，生长明显受抑制，幼苗的株高在35天左右才能追赶上对照。高压处理的粤香占剑叶在生育过程中的净光合速率（P_n）和表观量子效率（AQY）的总平均值分别比未处理的对照增加了9.2%和12.4%，而粤丰占则分别增加5.7%和17.4%。高压处理后两个品种的植株叶片不同生长时期的平均光合色素含量均高于未处理的对照，在生长后期的衰老过程中高压处理植株剑叶的色素含量和PSⅡ光化学效率F_v/F_m下降速率较各自的未处理对照缓慢。高压处理后两个水稻品种的生物量和单株产量分别比对照提高了8%~27%及7%~14%。提出高压处理可能作为一种新的选育品种的方法。     

Quantitative evaluation of the microjet velocity and cavitation erosion on a copper plate produced by a spherical cavity focused transducer at the high hydrostatic pressure

Cavitation erosion at the high hydrostatic pressure causes the equipment to operate abnormally for the huge economic losses. Few methods can quantitatively evaluate the cavitation erosion intensity. In order to solve this problem, the cavitation erosion on a copper plate was carried out in a spherical cavity focused transducer system at the hydrostatic pressure of 3, 6, and 10 MPa. Meanwhile, the corresponding cavitation threshold, the initial bubble radius, and the microjet velocity in the ultrasonic field are theoretically analyzed to determine the dimension and velocity of microjet based on the following hypotheses: (1) the influence of the coalescence on the bubble collapse is ignored; (2) the dimension of the microjet is equal to the largest bubble size without the influence of gravity and buoyancy. Using the Westervelt equation for the nonlinear wave propagation and the Johnson-Cook material constitutive model for the high strain rate, a microjet impact model of the multi-bubble cavitation was constructed. In addition, through the analogy with the indentation test, an inversion model was proposed to calculate the microjet velocity and the cavitation erosion intensity. The microjet geometric model was constructed from the dimension and velocity of the microjet. The continuous microjet impact was proposed according to the equivalent impact momentum and solved by the finite element method. The relative errors of the pit depth are 4.02%, 3.34%, and 1.84% at the hydrostatic pressure of 3, 6, and 10 MPa, respectively, and the relative error in the evolution of pit morphology is 7.33% at 10 MPa, which verified the reliability of the proposed models. Experimental and simulation results show that the higher the hydrostatic pressure, the greater the pit depth, pit diameter, the pit-to-microjet diameter ratio, and the cavitation erosion intensity, but the smaller the pit diameter-to-depth ratio. The cavitation erosion intensity becomes significant with the ongoing ultrasonic exposure. In addition, a comparison of the cavitation pit morphology in the microjet pulsed and continuous impact modes shows that the continuous impact mode is effective without the elastic deformation caused by the residual stress. Using the cavitation pit morphology at the different hydrostatic pressures, the microjet velocity can be estimated successfully and accurately in a certain range, whose corresponding errors at the lower and upper limit are 5.98% and 0.11% at 3 MPa, 6.62% and 9.14% at 6 MPa, 6.54% and 5.42% at 10 MPa, respectively. Our proposed models are valid only when the cavitation pit diameter-to-depth ratio is close to 1. Altogether, the cavitation erosion induced by multi-bubble collapses in the focal region of a focused transducer could be evaluated both experimentally and numerically. Using the cavitation pit morphology and the inversion model, the microjet velocity in a certain range could be estimated successfully with satisfactory accuracy.