The nature and origin of deep ocean clay crust from the Gulf of Guinea

Deep ocean sediments off the west coast of Africa exhibit a peculiar undrained strength profile in the form of a crust, albeit of exceptionally high water content, overlying normally consolidated clay. Hot-oil pipelines are installed into these crustal sediments, so their origins and characteristics are of great interest to pipeline designers. This paper provides evidence for the presence of burrowing invertebrates in crust material, and for the way sediment properties are modified through their creation of burrows, and through the deposition of faecal pellets. A variety of imaging techniques are used to make these connections, including photography, scanning electron microscopy and X-ray computer tomography. However, the essential investigative technology is simply the wet-sieving of natural cores, which reveals that up to 60% by dry mass of the crustal material can consist of smooth, highly regular, sand-sized capsules that have been identified as the faecal pellets of invertebrates such as polychaetes. Mechanical tests reveal that these pellets are quite robust under effective stresses of the order of 10 kPa, acting like sand grains within a matrix of fines. Their abundance correlates closely with the measured strength of the crust. While this can easily be accepted in the context of a pellet fraction as high as 60%, the question arises how a smaller proportion of pellets, such as 20%, is apparently able to enhance significantly the strength of a sediment that otherwise appears to be normally consolidated. A hypothesis is suggested based on the composition of the matrix of fines around the pellets. These appear to consist of agglomerates of clay platelets, which may be the result of the breakdown of pellets by other organisms. Their continued degradation at depths in excess of 1 m is taken to explain the progressive loss of crustal strength thereafter.

Study of thermal effects in bulk RE-BCO superconductors submitted to a variable magnetic field

When bulk RE-BCO superconductors are used as permanent magnets in engineering applications, they are likely to experience transient variations of the applied magnetic field. The resulting vortex motion may cause a significant temperature increase. As a consequence the initial trapped flux is reduced. In the present work, we first focus on the cause of a temperature increase. The temperature distribution within a superconducting finite cylinder subjected to an alternating magnetic field is theoretically predicted. Results are compared to experimental data obtained by two temperature sensors attached to a bulk YBCO pellet. Second, we consider curative methods for reducing the effect of heat flux on the temperature increase. Hall-probe mappings on YBCO samples maintained out of the thermal equilibrium are performed for two different morphologies : a plain single domain and a single domain with a regularly spaced hole array. The drilled single-domain displays a trapped induction which is weakly affected by the local heating while displaying a high trapped field. © 2006 IOP Publishing Ltd.

Microheterogeneous Thoria-Urania Fuels for Pressurized Water Reactors

A thorium-based fuel cycle for light water reactors will reduce the plutonium generation rate and enhance the proliferation resistance of the spent fuel. However, priming the thorium cycle with ²³⁵U is necessary, and the ²³⁵U fraction in the uranium must be limited to below 20% to minimize proliferation concerns. Thus, a once-through thorium-uranium dioxide (ThO2-UO2) fuel cycle of no less than 25% uranium becomes necessary for normal pressurized water reactor (PWR) operating cycle lengths. Spatial separation of the uranium and thorium parts of the fuel can improve the achievable burnup of the thorium-uranium fuel designs through more effective breeding of ²³³U from the ²³²Th. Focus is on microheterogeneous fuel designs for PWRs, where the spatial separation of the uranium and thorium is on the order of a few millimetres to a few centimetres, including duplex pellet, axially microheterogeneous fuel, and a checkerboard of uranium and thorium pins. A special effort was made to understand the underlying reactor physics mechanisms responsible for enhancing the achievable burnup at spatial separation of the two fuels. The neutron spectral shift was identified as the primary reason for the enhancement of burnup capabilities. Mutual resonance shielding of uranium and thorium is also a factor; however, it is small in magnitude. It is shown that the microheterogeneous fuel can achieve higher burnups, by up to 15%, than the reference all-uranium fuel. However, denaturing of the ²³³U in the thorium portion of the fuel with small amounts of uranium significantly impairs this enhancement. The denaturing is also necessary to meet conventional PWR thermal limits by improving the power share of the thorium region at the beginning of fuel irradiation. Meeting thermal-hydraulic design requirements by some of the microheterogeneous fuels while still meeting or exceeding the burnup of the all-uranium case is shown to be potentially feasible. However, the large power imbalance between the uranium and thorium regions creates several design challenges, such as higher fission gas release and cladding temperature gradients. A reduction of plutonium generation by a factor of 3 in comparison with all-uranium PWR fuel using the same initial ²³⁵U content was estimated. In contrast to homogeneously mixed U-Th fuel, microheterogeneous fuel has a potential for economic performance comparable to the all-UO2 fuel provided that the microheterogeneous fuel incremental manufacturing costs are negligibly small.

An enzyme-linked immunosorbent assay for rare minnow (Gobiocypris rarus) vitellogenin and comparison of vitellogenin responses in rare minnow and zebrafish (Danio rerio)

A competitive enzyme-linked immunosorbent assay (ELISA) was developed to determine vitellogenin (Vtg) in rare minnow (Gobiocypris rarus) based on the separation and purification of rare minnow Vtg (r-Vtg) as well as the production of polyclonal antibody against r-Vtg in rabbits. Three different ELISAs for measuring r-Vtg were then compared: (1) indirect ELISA with the antibody against carp (Cyprinus carpio) Vtg (c-Vtg) (IC-ELISA); (2) competitive ELISA with the antibody against c-Vtg, and using r-Vtg for coating the plates and preparing standard curve (CC-ELISA); (3) competitive ELISA with the antibody against r-Vtg, and using r-Vtg for coating the plates and preparing standard curve (CR-ELISA). The result showed that the homologous CR-ELISA was the most sensitive among the three assays for quantifying r-Vtg. The sensitivities to 17 alpha-ethinylestradiol (EE2) Of rare minnow and zebrafish (Danio rerio) were compared upon the establishment of homologous competitive ELISA. The lowest observed effect concentrations (LOECs) to induce Vtg were found to be 0.8 ng EE2 l(-1) for rare minnow and 4 ng EE2 l(-1) for zebrafish respectively. Afterwards, CR-ELISA was applied to measure Vtg concentration in whole body homogenate (WBH) of juvenile rare minnow fed by three diets (tubifex from wastewater treatment plant, Artemia nauplii and commercial pellet food), and the agreements between bioassay and GC-MS analysis demonstrated that rare minnow was a sensitive fish model for assessing estrogenic effects of endocrine disrupting compounds in aquatic environment. (c) 2006 Elsevier B.V. All rights reserved.

CSRm内靶实验中的轻离子束流寿命模拟研究

建立了内靶对兰州冷却储存环主环束流影响的单粒子跟踪模拟程序,对pellet小丸靶和碳靶对束流带来的负面影响进行了模拟研究,主要讨论CSRm内靶实验中的束流存活率和束流寿命状态。结果显示利用厚度为1×1016atoms.cm-2小丸内靶时,2.6 GeV质子束流寿命在100 s量级,而对于目前技术水平下的碳膜靶(厚度为5×1017atoms.cm-2),质子束流寿命为s量级;束流寿命和束流能量基本成正比关系,束流寿命和内靶厚度近似成反比关系。

兰州CSRm小丸内靶热力学和流体力学的研究

兰州CSRm内靶终端是进行强子物理实验的平台，可开展奇异介子产生和衰变的研究、重子谱的研究、多夸克态的研究及介子介质效应和手征对称破缺与恢复等多方面的研究。这些物理目标都需要内靶实验终端提供足够多的事件率，并能进行准确的径迹构建。在众多候选的内靶装置中，小丸靶具有其它内靶所欠缺的优点，如可以获得与外靶实验相比拟的实验亮度，可以配置4π立体角的探测器单元等。因此，小丸靶被确定为CSRm内靶实验终端中的主要内靶之一。小丸内靶（Pellet Internal Target）就是将氦以外的某种气体通过低温冷却而形成的固体微球。小丸内靶靶束与储存环离子束在反应室正交并发生相互作用，其反应事例被反应室周围环绕的探测器单元探测到并被记录下来。这篇论文对小丸内靶装置的结构进行了简要的介绍，并对小丸在反应室内的热力学行为进行了模拟。计算表明，靶丸速度是影响靶丸在反应区正常运行的重要因素之一。靶丸速度越大，靶丸在反应室内爆炸的可能性越小。通过对小丸的速度进行的流体动力学分析，发现即使对所有实验条件进行优化，小丸内靶的速度至多能达到100 m/s左右

CSRm内靶实验中的轻离子束流储存寿命研究

束流储存寿命对于储存环的建造和内靶实验都是一个很重要的参数。由于重离子冷却储存环工程的优化，HIRFL-CSR主环将能提供2．SGev的质子束流，这为强子物理研究提供了一个很好的平台。设计并建立一套针对强子物理的内靶系统己经列入到计划当中，与内靶相关的束流储存寿命研究也随之展开。本论文首先分析了在内靶实验中束流储存寿命的影响因素，即真空管道中的残余气体分子、冷却电子束和内靶，以及束内散射和集体效应等，并用理论解析和数值计算的方法，对各种因素的影响程度进行估算。研究表明，内靶散射影响下的束流储存寿命比其他因素导致的短2～3个数量级，内靶是影响束流寿命的决定性因素。其次，对CSRm将来实验中主要用到的Pelle七内靶和碳薄膜靶做了简要介绍，并计算了它们的有效靶厚大约为lx10、切ms／cmZ和5火1017atoms／CmZ。再者，用理论推导方法，对内靶的多次库仑散射和束流能量损失扰动对束流的影响进行了研究，推导了束流的横向和纵向发射度增长与束流每次打靶产生的小库仑散射角均方值气s和相对动量分散气了：之间的关系，并通过数值计算的方法给出了CSRm内靶实验条件的发射度增长曲线。最后，建立了内靶散射的MOnte-Carlo模拟程序，在模拟数据的基础上，总结研究束流的发射度增长规律，以及束流存储寿命与内靶厚度和束流能量的关系。计算表明，当存在Pellet靶（1、1016atoms／cm2）和c膜（5*1017 atoms／cmZ）时，2800Mev质子束的束流储存寿命分别为397秒和0．7秒，将来的内靶实验亮度大约为2 x 1033cm-2·s-1。

Native growth of vertically pattened ZnO nanowire arrays under mild conditions without templates or catalysts

Based on the implications of a pellet experiment,we have designed and implemented a low temperature(≤90℃) approach to generate native patterned,vertically aligned ZnO nanoarrys without any templates or catalysts.This simple,economic and spontaneous patterning process offers a promising avenue for overcoming several inherent limitations of the artificial manners[1].While the purity,orientation and electrical properties of the as prepared materials allow them to be applied in various fields.

Magnetic and electric properties of Bi(La)Sr(Ca)Mn2O6

Bi1-xLaxSrMn2O6 and BiSr1-xCaxMn2O6 are prepared by solid state reaction. They are n-type semiconductors with ferromagnetism at room temperture. When Bi is substituted partly by rare earth, a negative magnetoresistance effect is observed in the pellet of Bi1-xLaxSrMn2O6. There are semiconductor-metal transitions at 820 K in BiSrMn2O6. The transitions are attributed to the magnetic transition at high temperature. The substitution of Ca for Sr makes the transition temperature increase. However, when Bi is partly substituted by La, the solid solution does not change into metal. (C) 1996 Academic Press, Inc.

SUPERCONDUCTIVITY IN BI1.5PB0.4SBXSR2CA2CU2OY SYSTEM (X=0-0.32)

The effect of doping with various amount of Sb (0.06-0.32) to (Bi,Pb):Sr:Ca:Cu = 1:1:1:1 system were studied with XRD and Tc measurements. The presence of Sb promotes the conversion of low Tc phase (2212 phase) to high Tc phase (2223 phase) and at around Sb = 0.18 the 2212 phase nearly completely disappears; but at the same time a new phase of unknown structure appears even with Sb = 0.06 showing that the incorporation of Sb into the Bi-based superconducting phase is of very low concentration. Tc measurements show that the optimum concentration of Sb-doping is around 0.10 and that unknown phase has an adverse effect to the superconducting properties; a composition disproportion at the surface of pellet was observed.