Wavelength-scalable hollow optical fibres with large photonic bandgaps for CO2 laser transmission

Conventional solid-core optical fibres require highly transparent materials. Such materials have been difficult to identify owing to the fundamental limitations associated with the propagation of light through solids, such as absorption, scattering and nonlinear effects. Hollow optical fibres offer the potential to minimize the dependence of light transmission on fibre material transparency. Here we report on the design and drawing of a hollow optical fibre lined with an interior omnidirectional dielectric mirror. Confinement of light in the hollow core is provided by the large photonic bandgaps established by the multiple alternating submicrometre-thick layers of a high-refractive-index glass and a low-refractive-index polymer. The fundamental and high-order transmission windows are determined by the layer dimensions and can be scaled from 0.75 to 10.6 micro m in wavelength. Tens of metres of hollow photonic bandgap fibres for transmission of carbon dioxide laser light at 10.6 micro m wavelength were drawn. The transmission losses are found to be less than 1.0 dB m(-1), orders of magnitude lower than those of the intrinsic fibre material, thus demonstrating that low attenuation can be achieved through structural design rather than high-transparency material selection.     

Remains of Homo erectus from Bouri, Middle Awash, Ethiopia

The genesis, evolution and fate of Homo erectus have been explored palaeontologically since the taxon's recognition in the late nineteenth century. Current debate is focused on whether early representatives from Kenya and Georgia should be classified as a separate ancestral species ('H. ergaster'), and whether H. erectus was an exclusively Asian species lineage that went extinct. Lack of resolution of these issues has obscured the place of H. erectus in human evolution. A hominid calvaria and postcranial remains recently recovered from the Dakanihylo Member of the Bouri Formation, Middle Awash, Ethiopia, bear directly on these issues. These approximately 1.0-million-year (Myr)-old Pleistocene sediments contain abundant early Acheulean stone tools and a diverse vertebrate fauna that indicates a predominantly savannah environment. Here we report that the 'Daka' calvaria's metric and morphological attributes centre it firmly within H. erectus. Daka's resemblance to Asian counterparts indicates that the early African and Eurasian fossil hominids represent demes of a widespread palaeospecies. Daka's anatomical intermediacy between earlier and later African fossils provides evidence of evolutionary change. Its temporal and geographic position indicates that African H. erectus was the ancestor of Homo sapiens.     

回归式双齿轮导杆间歇机构综合

本文从间歇区速度分析着手进行回归式双齿轮导杆间歇机构综合,使这一复杂问题变得十分简单。这种方法也可应用到其它类型的齿轮连杆间歇机构综合中去。     

多功能机械传动试验台电气控制：系统分析

本文对试验台方案的选择、双电机组的等效处理、试验台的控制和加载方式,进行了分析讨论。概要地介绍了控制系统框图的特点,给出了试验波形图。最后,指出了尚待深入研究的问题。     

分布式共享存储器型多处理机的研究

文章提出了一台分层结构的分布式共享存储器的型多处理机ＤＳＭＡｒｃ的系统结构，该系统采用总线监听和目录式相结合的ｃａｃｈｅ一致性协议，来保持分布式局部ｃａｃｈｅ与共享主存内容一致，为压缩目录所需存储空间，文章提出了一种新的目录存储结构－目录ｃａｃｈｅ在ＳｕｎＳｐａｒｃ工作站上对ＤＳＭＡｒｃ原型进行了模拟，根据模拟结果对ＤＳＭＡｒｃ的性能作了初步分析。     

A quantum scattering interferometer

The collision of two ultracold atoms results in a quantum mechanical superposition of the two possible outcomes: each atom continues without scattering, and each atom scatters as an outgoing spherical wave with an s-wave phase shift. The magnitude of the s-wave phase shift depends very sensitively on the interaction between the atoms. Quantum scattering and the underlying phase shifts are vitally important in many areas of contemporary atomic physics, including Bose-Einstein condensates, degenerate Fermi gases, frequency shifts in atomic clocks and magnetically tuned Feshbach resonances. Precise experimental measurements of quantum scattering phase shifts have not been possible because the number of scattered atoms depends on the s-wave phase shifts as well as the atomic density, which cannot be measured precisely. Here we demonstrate a scattering experiment in which the quantum scattering phase shifts of individual atoms are detected using a novel atom interferometer. By performing an atomic clock measurement using only the scattered part of each atom's wavefunction, we precisely measure the difference of the s-wave phase shifts for the two clock states in a density-independent manner. Our method will enable direct and precise measurements of ultracold atom-atom interactions, and may be used to place stringent limits on the time variations of fundamental constants.     

等离子诱变选育柠檬酸高产菌

黑曲霉TN09是1株柠檬酸生产菌株.为了进一步提高柠檬酸的生产水平,利用等离子对柠檬酸生产菌黑曲霉TN09进行了诱变.诱变后的孢子悬液涂布玉米液化液平板,35,℃培养至72,h测量透明圈直径,以酸解透明圈直径大于2.2,cm、菌落直径大于0.5,cm、其比值大于4.8的菌落作为初筛柠檬酸菌株,然后进行摇瓶复筛获得了1株遗传性能稳定的高产菌,与出发菌株(产酸12.46,g/dL)相比产酸增幅达到8.67%.     

利用应用程序特征识别降低网格监控负载的研究

针对网络监控负载随着监控任务的增加而增加,从而影响集群有效管理、利用及监控系统性能的问题,展开了利用应用程序特征识别降低网格监控负载的研究.采用主成分分析法分析程序执行过程中的监测数据,得到应用程序的主成分因子,再经由4种密集型基准程序构造的比对特征集合匹配,识别应用程序的主要特性,以此达到降低监控负载的目的.在原型系统上的应用程序特征识别及监控负载评估实验表明,对于混合类型应用程序或某种密集型应用程序,监控负载可以减少20%～60%,对于巨大的采集数据,可以做到有效精炼.     

分簇无线传感器网络可靠高效的数据传输方案

根据当前传感器节点的通信能力,提出了一种面向大规模无线传感器网络的数据传输方案(REDD).在方案中,节点间通过周期性的动态竞争产生簇首,形成分簇网络结构.簇内通信采用时分多路访问调度方式,成员节点在簇首分配的时隙内经由独立的簇内通信信道将监测数据发送至簇首.簇间通信采用载渡侦听多路访问竞争方式,簇首间形成的连通覆盖网络通过多跳转发方式将聚合后的数据发送至网关.实验结果表明,较之已有的研究,REDD方案能够以更少的消耗达到更优的分簇性能,并且在保证可靠传输的同时有效降低传榆时延.     

可分级视频编码覆盖网非一致性随机成员构建算法

为了解决采用一致性随机成员算法进行节点管理而导致覆盖网(overlay)系统不具备QoS感知能力的问题,设计并实现了一种应用非一致性随机成员算法的overlay构建协议.在协议框架中,构成overlay的节点选择某一节点为邻居节点的概率与该节点的输出带宽成正比,这样在传输可伸缩编码视频(SVC)数据时,可避免出现上游节点丢弃部分媒体数据而降低下游节点接收质量的情况.测试结果表明,与一致性随机成员算法及多树算法相比,所提协议构建的overlay可以更加有效地支持SVC数据的传输.