预防胃肠道疾病的经验

通过分析文献资料和已有的研究证明,在大的畜牧农场和乳牛综合管理中,新生犊牛患胃肠道疾病有增长趋势。预先就有的患病的主要因素是,母牛(特别是在怀孕停乳期)和尚未产犊的母牛的饲养的不平衡和不合质量。这就导致动物代谢过程的破坏,从反面影响到了初乳的质量和子宫内胎儿的发育(出现大量地营养不良)。     

协合学

当科学以巨人的步伐迅速发展的时候,它分成越来越多的专门学科。从表面上看来,这些学科不仅有它们自己的语言,而且是由完全不同的现象和原理支配着。协合学则是学科间交叉研究的一个新领域,它在揭示一些看上去完全不同的学科的共同本质特征方面获得了颇为惊人的成功。协合学是如何进行研究的,以及迄今为止它取得了一些什么成就,这些是本文的主题。确实,在物理学、天体物理学、化学、生物学、生态学、电气和机械工程、社会学以及其他一     

数学的不合情理的有效性

数学的不合情理的有效性,是西方数学基础研究中,受人注目的问题之一。作者首先概要地介绍了该问题的讨论的沿革,然后深入分析了数学的实质,并且在此基础上,提出了自己对该问题的看法:对数学的不合情理的有效性的探讨是有意义的,但很困难,目前离该问题的解决,为期尚远。     

美国的区域性仪器设备中心

目前,我国一些科研单位和高等院校的现代化大型仪器,如加速器、大型电子计算机、电子显微镜……等使用率不高,有的则在同一省、市打算搞两个电子计算机计算中心,这就没有必要。特别像我们这样一个发展中的社会主义国家,办任何事情都要从实际出发,以发挥现有各类仪器的效用。美国近年来发展起来的区域性仪器设备中心,这一做法很值得我们借鉴。希望我国的科学技术管理部门、教育部门的同志都来研究一下,以较少的投资,取得更大的效益。这篇文章所提供的经验值得参考。     

Controlling the dynamics of spontaneous emission from quantum dots by photonic crystals

Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from miniature lasers and light-emitting diodes, to single-photon sources for quantum information, and to solar energy harvesting. To explore such new quantum optics applications, a suitably tailored dielectric environment is required in which the vacuum fluctuations that control spontaneous emission can be manipulated. Photonic crystals provide such an environment: they strongly modify the vacuum fluctuations, causing the decay of emitted light to be accelerated or slowed down, to reveal unusual statistics, or to be completely inhibited in the ideal case of a photonic bandgap. Here we study spontaneous emission from semiconductor quantum dots embedded in inverse opal photonic crystals. We show that the spectral distribution and time-dependent decay of light emitted from excitons confined in the quantum dots are controlled by the host photonic crystal. Modified emission is observed over large frequency bandwidths of 10%, orders of magnitude larger than reported for resonant optical microcavities. Both inhibited and enhanced decay rates are observed depending on the optical emission frequency, and they are controlled by the crystals' lattice parameter. Our experimental results provide a basis for all-solid-state dynamic control of optical quantum systems.     

Ultra-remote stereocontrol by conformational communication of information along a carbon chain

Many receptors and allosteric proteins function through binding of a molecule to induce a conformational change, which then influences a remote active site. In synthetic systems, comparable intramolecular information transfer can be effected by using the shape of one part of a molecule to control the stereoselectivity of reactions occurring some distance away. However, the need for direct communication with the reaction site usually limits such remote stereocontrol to distances of not more than about five bond lengths. Cyclic structures overcome this problem by allowing the controlling centre and the reaction site to approach each other, but the information transfer spans only short absolute distances. Truly remote stereocontrol can, however, be achieved with rigid compounds containing amide groups: the conformation of the amides can be controlled by stereogenic centres and responds to that of neighbouring amide groups and in turn influences stereoselective reactions. This strategy has allowed remote stereocontrol spanning 8 (ref. 11) or 9 (ref. 12) bonds. Here we demonstrate stereocontrol over a reaction taking place more than 20 bond lengths from the controlling centre, corresponding to a linear distance of over 2.5 nm. This transmission of information, achieved by conformational changes relayed through the molecule, provides a chemical model of allostery and might serve as a molecular mechanism for communicating and processing information.     

Cadherin 23 is a component of the tip link in hair-cell stereocilia

Mechanoelectrical transduction, the conversion of mechanical force into electrochemical signals, underlies a range of sensory phenomena, including touch, hearing and balance. Hair cells of the vertebrate inner ear are specialized mechanosensors that transduce mechanical forces arising from sound waves and head movement to provide our senses of hearing and balance; however, the mechanotransduction channel of hair cells and the molecules that regulate channel activity have remained elusive. One molecule that might participate in mechanoelectrical transduction is cadherin 23 (CDH23), as mutations in its gene cause deafness and age-related hearing loss. Furthermore, CDH23 is large enough to be the tip link, the extracellular filament proposed to gate the mechanotransduction channel. Here we show that antibodies against CDH23 label the tip link, and that CDH23 has biochemical properties similar to those of the tip link. Moreover, CDH23 forms a complex with myosin-1c, the only known component of the mechanotransduction apparatus, suggesting that CDH23 and myosin-1c cooperate to regulate the activity of mechanically gated ion channels in hair cells.