Analysis of obsidian from moho cay, belize: new evidence on classic maya trade routes

Trace element analysis of obsidian artifacts from Moho Cay, Belize, reveals that the obsidian derives primarily from the El Chayal outcrop in highland Guatemala and not from the Ixtepeque source. This is contrary to the widely accepted obsidian trade route model for Classic Maya civilization and suggests that Classic Maya obsidian trade was a more complex economic phenomenon than has been recognized.     

The Physcomitrella genome reveals evolutionary insights into the conquest of land by plants

We report the draft genome sequence of the model moss Physcomitrella patens and compare its features with those of flowering plants, from which it is separated by more than 400 million years, and unicellular aquatic algae. This comparison reveals genomic changes concomitant with the evolutionary movement to land, including a general increase in gene family complexity; loss of genes associated with aquatic environments (e.g., flagellar arms); acquisition of genes for tolerating terrestrial stresses (e.g., variation in temperature and water availability); and the development of the auxin and abscisic acid signaling pathways for coordinating multicellular growth and dehydration response. The Physcomitrella genome provides a resource for phylogenetic inferences about gene function and for experimental analysis of plant processes through this plant's unique facility for reverse genetics.     

Light control of growth form in colonial reef corals: computer simulation

Computer simulation with plotter output reveals the close interrelation between ambient light and the skeletal morphogenesis of the massive Caribbean reef coral Montastrea annularis. This technique illustrates a new quantitative approach to evaluating ecological growth responses of colonial organisms.     

Testing the vision of cataract patients by means of laser-generated interference fringes

In a new technique for measuring the visual acuity of cataract patients the light from a laser is used to form interference patterns of variable fineness on the patient's retina. The fineness of the interference pattern that the patient can detect gives an indication of the potential for improved vision. Comparison of this estimate of the potential with the patient's vision after cataract extraction shows that this test can indicate the condition of the fovea behind a cataract.     

Transatlantic abundance of the N2-fixing colonial cyanobacterium Trichodesmium

Colonial diazotrophic cyanobacteria of the genus Trichodesmium are thought to play a significant role in the input of new nitrogen to upper layers of the tropical and subtropical oceanic ecosystems that cover nearly half of Earth's surface. Here we describe results of a transatlantic survey in which a noninvasive underwater digital microscope (the video plankton recorder), was towed across the North Atlantic at 6 meters per second while undulating between the surface and 130 meters. Colony abundance had a basin-scale trend, a clear association with anticyclonic eddies, and was not affected by hurricane-forced mixing. Subsurface abundance was higher than previously reported, which has important implications for the global ocean nitrogen cycle.     

水稻优化群体质量调控技术的应用效果

为提高水稻群体质量指标,于１９９９年旱季在晋江市实施由福建省农业厅制订的“优控法”栽培方案。结果表明,“优控法”与习惯栽培技术对比,水稻成穗率提高１２．１个百分点,有效叶面积比率高７．２个百分点,结实率高１．６２个百分点,千粒重高０．４４ｇ,单位面积产量增幅达１７．３％。     

Homograft target cells: contact destruction in vitro by immune macrophages

Specific adherence of immune macrophages to monolayers of target cells is a passive phenomenon which represents only the first step in the mutually destructive interaction of immune macrophages and target cells. A specific hemagglutinin, responsible for specific adherence, was eluted from well-washed immune macrophages by heat treatment. The nature of the events in the interaction subsequent to adherence are unknown, but apparently demand the biosynthetic activities of the immune macrophage.     

对农业承包中不完善合同的几点思考

农业承包合同的完善与否是关系到承包合同能否顺利实施，承包主体的合法权益能否得到保障的关键，也是保护农业资源，实现农业可持续发展的重要方面，尤其是山地的承包，如果合同不完善极易出现掠夺经营、短期经营的现象，与国家退耕还林的政策相违背。然而，现实中却往往存在签订合同简单，条款不完善等问题，通过分析农业承包合同不完善带来的不利因素，提出完善合同的对策。     

有限元法在分析轴承接触问题中的应用

以一个圆柱滚子轴承为分析对象,利用有限元分析软件ANSYS求解圆柱滚子和滚道接触区的最大接触压力,通过和解析结果进行对比,总结出利用ANSYS分析轴承接触问题的一般方法。     

The mosaic of surface charge in contact electrification

When dielectric materials are brought into contact and then separated, they develop static electricity. For centuries, it has been assumed that such contact charging derives from the spatially homogeneous material properties (along the material's surface) and that within a given pair of materials, one charges uniformly positively and the other negatively. We demonstrate that this picture of contact charging is incorrect. Whereas each contact-electrified piece develops a net charge of either positive or negative polarity, each surface supports a random "mosaic" of oppositely charged regions of nanoscopic dimensions. These mosaics of surface charge have the same topological characteristics for different types of electrified dielectrics and accommodate significantly more charge per unit area than previously thought.     

Attenuation of allergic contact dermatitis through the endocannabinoid system

Allergic contact dermatitis affects about 5% of men and 11% of women in industrialized countries and is one of the leading causes for occupational diseases. In an animal model for cutaneous contact hypersensitivity, we show that mice lacking both known cannabinoid receptors display exacerbated allergic inflammation. In contrast, fatty acid amide hydrolase-deficient mice, which have increased levels of the endocannabinoid anandamide, displayed reduced allergic responses in the skin. Cannabinoid receptor antagonists exacerbated allergic inflammation, whereas receptor agonists attenuated inflammation. These results demonstrate a protective role of the endocannabinoid system in contact allergy in the skin and suggest a target for therapeutic intervention.     

马铃薯跌落碰撞时的接触应力分布特性

【目的】研究马铃薯跌落碰撞时的损伤原理。【方法】采用Prescale感压胶片和高速摄像技术测量在不同跌落高度马铃薯与5种材料碰撞时的接触应力分布特性和规律,确定马铃薯损伤和接触应力分布的关系。【结果】正交试验的响应曲面分析表明,碰撞材料、跌落高度、马铃薯质量对马铃薯碰撞的冲击压缩变形量影响显著,且影响程度由大到小为碰撞材料跌落高度马铃薯质量。研究结果发现,碰撞材料为65Mn钢、跌落高度为300 mm时,马铃薯开始出现损伤,碰撞材料为塑料ABS、土块、马铃薯和丁晴橡胶、跌落高度为400 mm时,马铃薯开始出现损伤。跌落高度200～800 mm,接触应力≤0.50 MPa占主要的接触面积,对马铃薯的损伤起主要贡献作用。马铃薯与不同材料碰撞在跌落高度400 mm (65Mn钢300 mm)时,接触应力≤0.20 MPa的区域占主要的接触面积,在跌落高度≥400 mm (65Mn钢≥300 mm)后,接触应力(0.20,0.60] MPa的区域为主要接触面积,0.20 MPa为马铃薯跌落碰撞损伤的临界应力。跌落高度与接触面积呈高度线性正相关,决定系数(R~2)均大于0.95。接触应力和接触面积的乘积(碰撞冲击力)与冲击压缩变形量呈高度线性相关,R~2大于0.96。【结论】建立的马铃薯碰撞损伤的线性回归模型能够准确预测和评估马铃薯跌落碰撞损伤。     

Fossil birds from the hawaiian islands: evidence for wholesale extinction by man before Western contact

Thousands of fossil bird bones from the Hawaiian Islands collected since 1971 include remains of at least 39 species of land birds that are not known to have survived into the historic period; this more than doubles the number of endemic species of land birds previously known from the main islands. Bones were found in deposits of late Quaternary age; most are Holocene and many are contemporaneous with Polynesian culture. The loss of species of birds appears to be due to predation and destruction of lowland habitats by humans before the arrival of Europeans. Because the historically known fauna and flora of the Hawaiian Islands represent only afraction of natural species diversity, biogeographical inferences about natural processes based only on historically known taxa may be misleading or incorrect.     

接触辉光放电等离子体降解水体中的邻氯苯酚

接触辉光放电电解是一种新型的产生等离子体的电化学方法。本文测定了催化剂、pH 值对接触辉光放电等离子体降解水体中邻氯苯酚降解效率的影响;并利用高效液相色谱检测了中间产物和邻氯苯酚降解浓度随时间的变化。实验表明:碱性条件下降解有利,Fe2+催化作用下降解效率明显提高。     

Measuring the spin polarization of a metal with a superconducting point contact

A superconducting point contact is used to determine the spin polarization at the Fermi energy of several metals. Because the process of supercurrent conversion at a superconductor-metal interface (Andreev reflection) is limited by the minority spin population near the Fermi surface, the differential conductance of the point contact can reveal the spin polarization of the metal. This technique has been applied to a variety of metals where the spin polarization ranges from 35 to 90 percent: Ni0.8Fe0.2, Ni, Co, Fe, NiMnSb, La0.7Sr0.3MnO3, and CrO2.     

试论高校图书馆有偿服务的方向——竞争情报

从开展有偿服务的必要性和现状出发,指出竞争情报服务是高校图书馆有偿服务的最主要的形式,并提出了高校图书馆如何提供竞争情报。     

月氏(Yuèzhī)乎?月氏(Ròuzhī)乎?——浅论语言的微观变化

语言变化规律常常呈现出无序—有序—无序这样的变化发展过程。语言的无序状态是绝对的,而有序则是相对的。这种无序与有序状态构成社会语言系统的“内稳态”。无序和有序是社会语言的非规范和规范的语言现象长期磨合,相互依存的变化过程。这个过程时间有长有短,其中还有地域的差别,过程的结果是语言词汇发生了变异,词汇的发音也起了变化。本文试图通过对“大月氏”词汇的微观音变的个案考察,揭示语言在社会生活中的微观变化。     

蒸汽热处理对杉木表面接触角的影响

探索热处理对杉木接触角的影响,分析接触角变化的因素.杉木经180℃热处理后,接触角变化曲线更加集中和有序,处理时间对接触角影响显著.与未处理材相比,处理4h后,接触角由51.增至124.,亲水官能团羟基的吸光度由2.08降至1.63,羰基吸光度从0.92降到0.62.粗糙度对接触角的影响并不显著.热处理使杉木表面形貌发生改变,有镂空现象产生.杉木热处理后接触角增大,可以应用在户外、桑拿等场所.