An objective method to monitor and quantify texture of salted herring during ripening in barrels at 4°C

Changes in the texture (elastic nature) of the flesh of barrel salted herring during the ripening process at 4°C have been monitored. The method employs the analysis of stress-relaxation curves after compression to half of the sample thickness on an lnstron Model 1112. The parameter 'T/P' for each sample represents the reciprocal of the gradient of a line connecting P and T0.368p. This parameter characteristic of each sample's texture was calculated as the ratio of 'T/P' where, T is the relaxation time and is defined as the time required for a stress at constant strain to decrease to 1/e of its original value, where 'e' is the base of natural logarithms (2.7183). Since 1/e=0.368, the relaxation time is the time required for the force to decay to 36.8% of its original value. P is the peak height of the curve (i.e. the force value at the maximum height). This method was adopted from the bakery industry for testing the degree of gluten development in bread dough. The 'T/P' values obtained over the course of ripening for differently treated salted-herring in barrels ranged between 1 and 12. The trends in 'T/P' value, during ripening period for the different samples, appeared to be parallel changes in texture perceived by sensory observation (subjective measurement), although the heterogeneous nature of the samples gave standard deviations, about the replicate sample mean, around 5%. The method appears promising as an objective measure for monitoring this aspect of the textural quality of barrel salted-herring through ripening if reproducibility of test results can be improved by more careful standardization of sample preparation and test protocol.

磁场对小鼠两种迷宫学习记忆的影响

据发现,磁场对生物体有一定作用,但是磁场对于人类或实验动物的学习记忆是否有影响,目前的报道结果很不一致本实验采用实验小白鼠,给予不同强度(65高斯/50Hz,35高斯/25Hz)的低频磁场照射(每天1小时,持续25天)。磁场照射后,采用旷场行为测试、Y-迷宫和Morris水迷宫,检测小鼠的活动性、空间辨别、空间学习记忆和非空间学习记忆能力。结果表明:65高斯/50Hz磁场显著增高小鼠的活动性,并损伤小鼠Y-迷宫的空间辨别能力,但对Morris水迷宫的空间、非空间学习记忆无明显影响。35高斯/25Hz磁场处理动物行为在三个指标上均接近对照组。提示:长期的磁场照射可能会给动物,甚至人类造成一些影响。

微囊藻毒素LR诱导无DNA片断化的细胞凋亡

目的研究微囊藻毒素(microcystin,MC)损伤肝细胞的毒性机制。方法以不同浓度的微囊藻毒素LR(MCLR)处理L-02肝细胞,通过光镜和电镜下的形态观察、DNA片断化分析、线粒体膜电位变化等了解MCLR对肝细胞的毒性效应。结果光镜下观察表明,50!g/mlMCLR处理可使细胞变圆、萎缩、不贴壁生长,电镜下L-02细胞呈现皱缩、膜发泡及染色质凝聚并边缘化等变化,这是典型的细胞凋亡形态特征,但电镜下没有观察到凋亡小体的形成;DNA电泳表明凋亡细胞没有出现明显的DNAladder,与电镜观察的结果一致。

HLA-DRB1等位基因多态性与食管癌遗传易感性研究

目的 :从基因水平探讨湖北地区汉族人食管癌HLA -DRB1等位基因的遗传易感性。方法 :运用序列特异性引物聚合酶链反应结合基因序列分析等技术 ,检测无亲缘关系湖北汉族健康人 136例、食管癌组 4 2例患者的HLA -DRB1等位基因。SAS统计软件数据处理。结果 :湖北地区汉族人食管癌患者与正常人比较 ,HLA -DRB1 0 90 1基因频率显著增高 (0 2 5 0 0vs 0 1397,P =0 0 2 8,OR =2 0 5 3,病因分数 =0 12 82 ) ;两者间其余HLA -DRB1等

Context-dependent decay of motor memories during skill acquisition.

Current models of motor learning posit that skill acquisition involves both the formation and decay of multiple motor memories that can be engaged in different contexts. Memory formation is assumed to be context dependent, so that errors most strongly update motor memories associated with the current context. In contrast, memory decay is assumed to be context independent, so that movement in any context leads to uniform decay across all contexts. We demonstrate that for both object manipulation and force-field adaptation, contrary to previous models, memory decay is highly context dependent. We show that the decay of memory associated with a given context is greatest for movements made in that context, with more distant contexts showing markedly reduced decay. Thus, both memory formation and decay are strongest for the current context. We propose that this apparently paradoxical organization provides a mechanism for optimizing performance. While memory decay tends to reduce force output, memory formation can correct for any errors that arise, allowing the motor system to regulate force output so as to both minimize errors and avoid unnecessary energy expenditure. The motor commands for any given context thus result from a balance between memory formation and decay, while memories for other contexts are preserved.

Optimising the dynamic performance of an all-wide-bandgap cascode switch

A SPICE simulation model of a novel cascode switch that combines a high voltage normally-on silicon carbide (SiC) junction field effect transistor (JFET) with a low voltage enhancement-mode gallium nitride field effect transistor (eGaN FET) has been developed, with the aim of optimising cascode switching performance. The effect of gate resistance on stability and switching losses is investigated and optimum values chosen. The effects of stray inductance on cascode switching performance are considered and the benefits of low inductance packaging discussed. The use of a positive JFET gate bias in a cascode switch is shown to reduce switching losses as well as reducing on-state losses. The findings of the simulation are used to produce a list of priorities for the design and layout of wide-bandgap cascode switches, relevant to both SiC and GaN high voltage devices. © 2013 IEEE.

生物小分子体系稀土和钙化学形态研究

随着稀土的广泛开发和利用，稀土日益进入环境，并且相继发现稀土具有多种生物效应。稀土与生物小分子配体多元体系中稀土化学形态的研究正是考察稀土在人体内的分布、代谢和生物效应的关键，对阐明稀土对环境和人体健康的影响及作用机理具有十分重要的意义。本论文进行了如下几方面的研究，并取得了创新性结果。1 稀土与生物小分子三元体系研究 在模拟生理条件下研究了Pr~(3+)、Gd~(3+)、Tb~(3+)、Yb~(3+)四种稀土离子和Ca~(2+)、Zn~(2+)两种生物金属离子分别与以天冬氨酸或柠檬酸为第一配体、分别以水扬酸、精氨酸、丝氨酸、异亮氨酸和苏氨酸为第二配体的三元溶液体系。经计算机程度优化得到体系中所生成的物种类型并计算得到各物种的稳定常数。在所研究的十个体系中，只是在金属离子-天冬氨酸-精氨酸、金属离子—柠檬酸-水杨酸和金属离子-柠檬酸-精氨酸三个体系中生成了两种三元配合物(1111型和1112型或1113型)，其它体系只生成了一种1112型三元配合物。重稀土配合物的稳定常数比轻稀土配合物的大。稀土配合物的稳定性明显强于钙配合物，接近或大于锌配合物的稳定常数，这表明稀土对钙有强竞争配位作用，对锌也有强竞争取代作用。以上稀土与生物小分子三元体系的研究取得了重要新结果。这些结果为考察稀土在体内的代谢、生物效应以及研究稀土对生物金属离子的拮抗、协同效应提供了重要科学依据。同时该研究也是多元体系数学模型法研究的基础。2. 金属离子生物小分子多元体系的数学模型法研究（1）对稀土与钙共存于两种生物配体（柠檬酸和精氨酸、天冬氨酸和精氨酸、柠檬酸和丝氨酸、柠檬酸和异亮氨酸、天冬氨酸和苏氨酸）的五个四元体系，经COMICS程序，利用已有二、三元配合物的稳定常数进行了计算。得到了稀土和钙的各物种随pH值变化的分布图。与三元体系相比，自由金属离子和二元配合物的含量显著增加。这表明稀土和钙之间存在着明显的竞争作用。（2）用数学模型法模拟研究了金属离子与血液中羧肽酶A的活性中心的作用。确定了Zn(II)和Tb(111)与该酶活性中心各残基的结合随pH的变化情况。当血液中稀Tb(III)的浓度较小时（与Zn(II)的浓度相近），Tb(III)对该酶活性中心的Zn(II)几乎没有影响；当Tb(III)达到较高浓度时，则能够与Zn(II)竞争活性中心各残基，从而可能影响该酶的结构和活性。（3）用数学模型法研究了人体血浆中生物小分子体系（二十种配体共存）Tb(III)和Ca(11)的分布情况及Tb(III)的存在对Ca(11)化学形态的影响。结果表明大部分铽与生物小分子配体形成多种形式的配合物，三元配合物占绝对优势。钙与铽明显不同，相当一部分的钙以自由离子形式存在，同时三元配合物也是钙的主要物种形式。模拟研究还表明当铽离子的浓度达到1E-4mol/L时，铽的存在会明显影响钙离子的物种形式及分布。以上多元体系的数学模型法研究所得创新性结果对考察稀土的分布、代谢及其生物效应和阐明稀土对钙的竞争取代作用都具有十分的重要意义。并且也进一步丰富和发展了稀土的生物无机化学。

大功率激光二极管高亮度、高功率密度光纤耦合（英文）

将条宽为100μm，有源区厚度为1μm的大功率激光二极管(LD)的输出光束高效地耦合到芯径是50μm的多模光纤中，得到了高亮度、高功率密度的光纤输出。功率密度高达3.6×10~4W/cm~2，耦合效率为70%。LD输出光束的发散角较大并且存在较大的像散，因此耦合系统中需要结构复杂、性能可靠的微透镜。采用在一个玻璃衬底上，具有两个不同曲率半径的双曲面透镜实现LD与多模光纤的耦合。

立方相GaN/GaAs（100）质量的X射线双晶衍射研究

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