不同压力下的热压加工对含Mn块体纳米晶Fe3Al组织和性能的影响

对铝热反应熔化制备的含10wt%Mn块体纳米晶Fe3Al材料在800℃和1000℃温度下,采用不同压力进行热压加工,利用XRD研究热压加工前后纳米晶粒尺寸的变化,并测试硬度变化和压缩率。结果显示,不同温度、压力下热压加工后,晶粒尺寸变化不大;热压加工后,材料的硬度有所上升,但温度和压力对硬度影响不大;热压加工中,材料表现出较好的塑性变形,并随着热压压力的增大,材料压缩率逐渐增大,但温度对材料的压缩率影响不明显。热压加工后,块体纳米晶Fe3Al材料几何尺寸得到了增大。     

Size dependence of the plane-strain response of single-crystal Al to indentation by diamond wedges

A single-crystal Al specimen was indented at room temperature with a series of prismatic diamond indenters. The indenters had triangular or wedge-shaped cross-sections and were relatively long, thus inducing a two-dimensional (2-D) plane-strain response. Different included wedge angles were used. For each wedge indenter, instrumented indentations were carried out at varying loads. Analysis of the response from each wedge indentation experiment clearly revealed the presence of a size effect, manifested in an increasing projected contact pressure as the contact dimensions decreased from micron to submicron scales. When indentation responses from 2-D wedge indenters with different included angles were compared, the data showed evidence that this indentation size effect depended on the included wedge angle. This dependence was analyzed and compared to existing models of indentation based on the concept of geometrically necessary dislocations. While the model prediction of the dependence of the characteristic length on the included wedge angle appears to be consistent with current experiments, the model estimate of the magnitude of the characteristic length significantly exceeds the value deduced from experimentation. The present results offer new experimental evidence of size-dependent indentation response in plane-strain geometries.     

Phase field crystal model of solute drag

The atomic scale interaction of solute with a migrating grain boundary has been studied using a binary phase field crystal (PFC) model. This model bridges between atomistic and continuum simulation techniques as it operates on diffusive timescales but at atomistic length scales. For this study, a two-dimensional channel containing two grains separated by a flat grain boundary has been constructed that allows for a channel length on the order of one micrometer. A new formalism has been developed to allow for the application of an external driving pressure for the growth of one grain. These simulations account for solute/grain boundary interactions, resulting in a solute drag effect on the grain boundary motion. The PFC simulations show good agreement with classical solute drag theory, though deviations due to the atomic scale nature of the interface exist.     

Elastic Properties of an Epoxy - Aluminum Interphase Measured Using an Acoustic Microscope

The interphase region in an epoxy - aluminum adhesive bond has been micromechanically characterized using a new acoustic microscope which employs a coupling fluid with a low speed of sound. A V(z) curve fitting method was used to calculate the property profiles across the interphase. The interphase region appeared to have shear and longitudinal wave speeds which were, on average, 14% and 11% larger than those of the bulk adhesive, respectively. The average interphase density was 5.5% smaller than the bulk density. The results were in conformity with a previous microscopic and nano-indentation study on the same adhesive system.     

利用开关卡尔曼滤波器的目标跟踪技术研究

为了使机器人视觉伺服控制系统的目标跟踪精度得到进一步提高,构建一种基于开关卡尔曼滤波器的视觉伺服控制系统。研究视觉伺服的目标跟踪原理,推导相关的数学模型,并分析跟踪误差产生的原因;针对图像采集和处理引入的延时问题,通过卡尔曼滤波估计得到目标运动的速度信息,以此作为前馈量输入视觉伺服控制器,补偿由于目标运动和延时造成的跟踪误差;为了解决卡尔曼滤波器由于目标运动的突然变化而降低估计性能的问题,引入运动监视器以在目标运动突然变化时发出开关信号并重置卡尔曼滤波器;最后对该算法进行实验与仿真。结果表明:基于卡尔曼滤波器的视觉伺服控制器能把跟踪误差控制在1 mm以内,而开关卡尔曼滤波器能有效地减少因目标运动状态突然变化而产生的跟踪误差。     

基于平行耦合线和开路枝节的小型带通滤波器设计

为了解决耦合线滤波器谐波抑制问题,提出了一种新的结构简单的平行耦合线带通滤波器.该滤波器由平行耦合线和开路枝节组成.首先基于耦合线带通滤波器的等效电路图,通过奇偶模理论得到设计方程,并设计了带通滤波器;分析了滤波器特性与电参数之间的关系;通过仿真优化得到了滤波器的物理尺寸;制备并测试了滤波器的S参数,仿真结果和测试结果基本一致.该滤波器具有结构简单、面积小等优点,并通过引入传输零点实现了较宽的阻带抑制和较好的选择性.     

Nutrition, metabolism, and fertility in dairy cows: 1. Dietary energy source and ovarian function

In previous studies, high plasma insulin was associated with earlier resumption of postpartum estrous cycles in dairy cows. The objective of this experiment was to quantify hormonal and ovarian responses to dietary starch and fat contents. Thirty cows were fed on a standard diet from calving until 40 d in milk (DIM) and then 6 cows were allocated to each of 5 isoenergetic diets containing 231, 183, 159, 135, and 87 g of starch and 39, 42, 43, 45, and 48 g of fat/kg of dry matter (DM) for diets 1 to 5, respectively, until 70 DIM. Estrus was synchronized at 60 DIM. Between 60 and 70 DIM, energy intake, milk yield, and energy balance were similar among diet groups. Plasma insulin-to-glucagon ratio increased with increasing dietary starch and decreasing dietary fat concentrations, reaching a break point at 159 g of starch, 43 g of fat/kg of DM (diets 1 to 5: mean 3.86, 3.78, 3.59, 2.98, 2.06 ± standard error 0.22). Growth hormone, insulin-like growth factor-I, and leptin did not vary among diets. The greatest dietary starch concentration was associated with elevated plasma urea-N (diets 1 to 5: mean 3.69, 3.01, 2.94, 2.95, 2.75, ± standard error 0.13 mmol/L, respectively) and delayed postovulatory progesterone increase (progesterone at 3 to 5 d postovulation for diets 1 to 5: mean 2.7, 5.9, 4.2, 5.6, 4.3 ± standard error 0.9 ng/mL, respectively). The number of small (<5 mm) ovarian follicles was positively related to starch intake (r = 0.381) and plasma insulin concentration (r = 0.402). It is concluded that to maintain adequate insulin-to-glucagon ratio in cows at the start of the breeding period, dietary starch concentration should be above 160 g/kg of DM and dietary fat below 44 g/kg of DM, and this should have a positive effect on ovarian function.     

Developmental consequences of embryo and cell manipulation in mice and farm animals

Advances in biotechnology in recent decades have revolutionized our understanding of early mammalian development and promise to provide ever more finely tuned and precisely targeted techniques for genetic enhancement of domestic animal species. In demonstrating what is both technically and biologically possible, not only in mice but also in larger animal species, research has provided hope that previously intractable diseases and genetic defects can be successfully combated. Crucial to this research is the ability to culture oocytes, embryos and somatic cells in vitro and to sustain their development without inducing adverse short- or long-term consequences. There is a need to refine current culture strategies in farm animal species to avoid jeopardizing their dependent technologies. A key to resolving current limitations of culture strategies is to identify, acknowledge and then address those features of in vitro culture that compromise early regulation of mammalian development. The aim of this review is to appraise critically in vitro embryo and somatic cell production strategies in the context of their impact on developmental competence and normality at embryonic, fetal and later stages. In addition, effects of physically manipulating embryos and cells, most notably via nuclear and gene transfer technologies, are considered with a view to identifying how detrimental consequences can be avoided.     

Serum hyaluronic acid in Down''s syndrome

Changes in the emission intensities of ultraweak biophoton emission during the cell proliferation of human carcinoma cell culture (TE9 cell line) were detected using a highly sensitive and low noise measurement apparatus coupled with a flow culture system. In the sampling period of 93 h, the biophoton emission intensity from the culture followed a similar course as that of the growth curve. Spectral analysis of the biophoton emission from the cell culture demonstrated a significant peak at around 530 nm. Our results suggest that the emission intensity mainly depends on the cell population and that this noninvasive technique has a potential role in cancer diagnosis.