A new method for selecting calf pericardium for use in cardiac bioprostheses on the basis of morphological and mechanical criteria

The durability of existing calf pericardium bioprostheses is limited by phenomena such as mechanical stress and calcification, the factors most frequently implicated in valve failure. Varying the preferred direction of the collagen fibers influences the mechanical behavior of the pericardial membrane. Given this possible variation, a strict control of the selection of the biomaterial employed in the construction of valve leaflets is essential, but a reliable method of selection has yet to be established.This study describes the development of a new system of in vitro selection involving a hydraulic simulator that reproduces the mechanical behavior of pericardial membranes subjected to the stress of continuous flow.By combining morphological criteria such as thickness and homogeneity with those of mechanical behavior, and by selecting paired samples from different parts of the pericardium, we obtained excellent mathematical fits. Linear regression analysis provided the mode of predicting the tensile strength in a given sample when this value had been determined in its twin. The upper zones of calf pericardium, corresponding to either right or left ventricle but at a distance from ligamentous structures, showed the best mean results at rupture (60 MPa) and permitted the most reliable prediction. The expected stress for an elongation of 30% was 1.12 MPa, as was previously observed, with a 95% confidence interval of between 1.11 and 1.14 MPa.These trials, together with the careful selection of the pairs, should help to establish definitive selection criteria. © 2001 Kluwer Academic Publishers     

孔隙率对Al2O3高孔隙率多孔介质EHC的影响

新型多孔介质燃烧技术主要采用泡沫陶瓷 ( Ceramic Foams)、波纹状陶瓷 ( Fabric LamellaStructure)等高孔隙率多孔介质。基于气、固相局部热平衡假设的有效导热系数 EHC( EffectiveHeat Conductivity)描述了气流与固体骨架中导热、弥散和热辐射多种传热方式的综合效果 ,是一个重要的传热特性 ,对其研究非常不足。通过实验与数值模拟确定不同孔隙率 Al2 O3 陶瓷的 EHC:基于测定的温度分布 ,给定 EHC的初值 ,采用有限体积法进行流场数值模拟 ;比较测量与计算的温度均方根差 ,通过对 EHC搜索寻优 ,间接确定泡沫陶瓷的有效导热系数。结果表明 Al2 O3 陶瓷的EHC随温度增加而增加 ,对速度不敏感 ;孔隙率高的陶瓷其 EHC较大。给出试样 EHC与温度和空管速度的拟合式 ;将颗粒床 EHC的 Z&B模型外推到 Al2 O3 高孔隙率陶瓷 ,并给出 EHC预示结果     

In vitro conditions for the study of the in vivo performance of sustained-release theophylline matrix tablets administered in fasted conditions and with a high-fat diet

Dissolution profiles of theophylline (TP) from three types of sustained-release (SR) matrix tablets (plastic [PL], lipid [LP], and hydrophilic [HP]) in different dissolution media, with and without enzymes, were established. Also investigated was the influence of a treatment of the tablets with peanut oil prior to the dissolution test. The in vivo behavior of the tablets under the fasted state and with the concomitant administration with a high-fat diet was previously evaluated; the diet produced changes in the absorption profiles for the three matrix tablets in comparison with fasted administration. Level A correlations were obtained between cumulative percentage dissolved (CPD) and cumulative percentage absorbed (CPA). For the fasted condition, better correlations were obtained with water as the dissolution medium for the HP and LP matrix; for PL matrix, the best correlation was obtained with a medium with gradual change of pH. The pretreatment with peanut oil showed better correlations for the fed state.     

实验室用的气体纯化系统

叙述了一种简单而有效的惰性气体和氮气的纯化系统，它能除掉气体中的机械杂质，氧和水，并能在高流量和高压力下工作。文中对系统的特性和吸附剂的再生方法作了说明。     

数控齿轮加工机床的自动调整

齿面加工精度基本上取决于机床的啮合参数,如刀具与工件的轴间距a_c和轴间角∑_c。这些参数确定了机床啮合线的理论正确位置,因而用来评定传动质量。通常,依螺旋副刀具产生的两个无隙啮合渐开线齿轮来研究机床的啮合。因为这种齿轮啮合基本上是变位啮合(传动中假定的齿轮啮合特性或刀具的重磨)、刀具几何参数的实际值不同于名义值,所以必须确定参数a_c和∑_c的需要值. 采用试切法,在每次调整几何尺寸参数后切削齿轮,这种生产情况增加了准备——结束时间,降低了机械加工生产率。在机床中装入数控系统,使齿轮啮合角、     

Conservation of Cervus elaphus meat in modified atmospheres

This study examines the effect of three types of modified atmospheres, each with a different gas composition (A:40% CO(2)+60% N(2); B:80% CO(2)+20% O(2); C:80% CO(2)+20% N(2)), on the development of meat quality of Cervus elaphus in order to suggest a gas composition that best preserves this type of meat. Meat quality was assessed by examining pH, colour as L(?)a(?)b(?) values, drip loss (DL), cooking loss (CL) and shear force (SF). In samples of group A, pH values tended to be higher in all storage periods than those packed with 80% CO(2) and significant differences (P<0.001) among the groups were found at 16 d of storage. Gas composition affected a(?) and b(?) parameters (P<0.001), in samples packed with O(2), the b(?) values were higher than in other groups, while the opposite was true in a(?) values. Similar values of DL and CL were observed for all treatments and both parameters increased over time. SF values decreased with ageing, with similar values observed for all treatments.     

Photothermal analysis of polymeric dye laser materials excited at different pump rates

The photothermal properties and heat diffusion of polymeric lasers, made up from solutions of Rhodamine 6G in solid matrices of poly(2-hydroxyethyl methacrylate) with different amounts of the cross-linking monomer ethylene glycol dimethacrylate and copolymers of 2-hydroxyethyl methacrylate and methyl methacrylate have been studied through photothermal deflection spectroscopy. The heat load that is due to the pumping process was quantified as a function of the pump excitation repetition frequency (0.25-10 Hz), determining the time-dependent temperature changes at different locations within the laser matrix. A theoretical model, which reproduces these changes with high accuracy, was developed on the basis of the heat-diffusion equation of optically dense fluids. The observed thermal effects became important for impairing the laser stability at pump repetition frequencies higher than 1 Hz. In addition, the irreversible optical changes produced in the laser matrices at high pump fluence values (>1 J/cm2) were also analyzed. These effects originate, most likely, from a two-step photothermal mechanism.     

Gastric response to acute copper exposure

Early effects of acute copper exposure consist mainly of nausea and altered gastric permeability. To assess copper effects on gastric response 30 apparently healthy volunteers underwent two controlled trials receiving a solution with (10 mg Cu/l) and without (<0.01 mg Cu/l) copper sulfate after overnight fasting, in random order. Ultrasonography was chosen to follow indirectly the gastric emptying pattern for 120 min. Measurements were expressed as z scores [z=(mean-Xi)/S.D.]. Results showed that nobody presented symptoms after drinking water without added copper while 9 subjects presented nausea after receiving the 10 mg Cu/l solution. The group receiving drinking water with 10 mg Cu/l presented greater antral areas during the first 60 min of observation. Individual and mean fitted curves for antral area, calculated and compared using the linear mixed-effects model fit by REML, showed a group effect of copper on antral area over time (L. Ratio=23.98, P<0.0001); the effect was due to delay in decreasing antral area in the copper treated group during the first hour after ingestion. No differences were found by gender or nausea. Results show a copper effect on gastric response suggesting that acute exposure to copper in water modify the first phase of gastric emptying.