968 resultados para Space Telescope Science Institute (U.S.)
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An overview on the onset of thermocapillary oscillatory convection in a floating half zone is provided, and it is a typical subject in the microgravity sciences related to the space materials science, especially the floating zone processing, and also to the microgravity fluid physics. The main interests are focused around the process for onset of oscillatory thermocapillary convection, which is known also as the bifurcation transition from quasi-steady convection to oscillatory convection. The onset of oscillation depends on a set of critical parameters, such as the Marangoni number, Prandtl number, geometrical parameters, and heat transfer parameters. Recent studies show that, there exists the bifurcation transition from steady and axial symmetric convection to the steady and axial non-symmetric convection before the onset of oscillation in cases of small Prandtl number fluids and in cases of larger Prandtl number fluids of fat liquid bridge with small aspect ratio. The transition process is a strong non-linear process because the velocity deviation has the same order of magnitude as that of an average flow after the onset of oscillation, and unsteady 3-D numerical simulation is suitable to do in depth analysis on strong non-linear process, and leads generally to a better comparison with the experimental results.
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Buildings in Port Aransas encounter drastic environmental challenges: the potential catastrophic storm surge and high winds from a hurricane, and daily conditions hostile to buildings, vehicles, and even most vegetation. Its location a few hundred feet from the Gulf of Mexico and near-tropical latitude expose buildings to continuous high humidity, winds laden with scouring sand and corrosive salt, and extremes of temperature and ultraviolet light. Building construction methods are able to address each of these, but doing so in a sustainable way creates significant challenges. The new research building at the Marine Science Institute has been designed and is being constructed to meet the demand for both survivability and sustainability. It is tracking towards formal certification as a LEED Gold structure while being robust and resistant to the harsh coastal environment. The effects of a hurricane are mitigated by elevating buildings and providing a windproof envelope. Ground-level enclosures are designed to be sacrificial and non-structural so they can wash or blow away without imposing damage on the upper portions of the building, and only non-critical functions and equipment will be supported within them. Design features that integrate survivability with sustainability include: orientation of building axis; integral shading from direct summer sunlight; light wells; photovoltaic arrays; collection of rainwater and air conditioning condensate for use in landscape irrigation; reduced impervious cover; xeriscaping and indigenous plants; recycling of waste heat from air conditioning systems; roofing system that reflects light and heat; long life, low maintenance stainless steel, high-tensile vinyl, hard-anodized aluminum and hot-dipped galvanized mountings throughout; chloride-resistant concrete; reduced visual impact; recycling of construction materials.
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本文基于华南、华北地区二叠纪—三叠纪陆生植物大化石和孢粉的数据库, 对中国二叠纪—三叠纪陆生植物的多样性变化进行了统计分析研究,并重点探讨了在二叠纪—三叠纪界线(Permian-Triassic Boundary,PTB )陆生植物是否与同期的海洋动物一样发生了同步的集群灭绝事件。 统计分析表明,华南、华北陆生植物大化石的分异度穿过PTB 均显示了较长时续(约37.8Ma)的下降和残存阶段,而孢粉化石在早三叠世的分异度则是上升的。总体上,陆生植物分异度穿过PTB 的变化较同期的海洋动物平稳缓慢。华南地区陆生植物大化石在晚二叠世末长兴期(Changhsingian)虽然伴随着最高的属灭绝率85.94% 和最低的属新生率28.12%,发生了最大的灭绝事件,但在晚二叠世早期和早三叠世的属的灭绝率也较高,分别为61.02% 和66.67% 。种的灭绝率在晚二叠世早期从早二叠世晚期的39%大幅度上升到80.36%,晚二叠世晚期达峰值97%,早三叠世稍降为93%,显然高于其它时段灭绝率范围(30—70%)。种和属的灭绝率呈现了同样的高峰阶段,从晚二叠世早期至早三叠世,时续为20.8 百万年(Ma)。基于更替率分析,华南地区陆生植物的高更替率事件分别发生在早二叠世晚期(93.75%)、早三叠世(90.92%)和晚三叠世(91.38%),但陆生植物在穿越早二叠世晚期—晚三叠世的整个过程中,更替率波动不大、比较平稳。华北地区陆生植物大化石穿越PTB 的灭绝率比华南地区低,属级高灭绝率事件集中在晚二叠世早期(67.31%)和晚二叠世晚期(63.89%), 时续为14.8Ma,种级高灭绝率事件与华南地区类似,集中在晚二叠世早期(85.67%)、晚二叠世晚期(90.86%)和早三叠世(80.28% )三个阶段,时续为20.8Ma 。显而易见,这比同期海洋动物集群灭绝的时续(3—11Ma )要长。 本文基于这些分析结果,仔细考虑了集群灭绝的4 个特点(即量值、广度、幅度和时续),认为华南、华北陆生植物在PTB 并未发生集群灭绝事件,而是发生了演化替代,即陆生植物穿过PTB 经历了大的植物群重组和新种的演化。总体上,中国二叠纪—三叠纪陆生植物中选择性灭绝非常明显,古生代占优势的种子蕨、真蕨类、木本石松类和楔叶类逐渐被早中生代比较进化的裸子植物和真蕨类植物所替代,陆生植物穿过PTB 显示了危机(灭绝)—残存—复苏—辐射的宏演化式样。
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Silicon nanowires (SiNWs) were grown directly from n-(111) single-crystal silicon (c-Si) substrate based on a solid-liquid-solid mechanism, and Au film was used as a metallic catalyst. The room temperature photoluminescence properties of SiNWs were observed by an Xe lamp with an exciting wavelength of 350 nm. The results show that the SiNWs exhibit a strongly blue luminescent band in the wavelength range 400-480 nm at an emission peak position of 420 nm. The luminescent mechanism of SiNWs indicates that the blue luminescence is attributed to the oxygen-related defects, which are in SiOx amorphous oxide shells around the crystalline core of SiNWs.
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Based on a set of microoptics the output radiation from a continuous wave (CW) linear laser diode array is coupled into a multi-mode optical fiber of 400 ptm diameter. The CW linear laser diode array is a 1 cm laser diode bar with 19 stripes with 100 fxm aperture spaced on 500 (xm centers. The coupling system contains packaged laser diode bar, fast axis collimator, slow axis collimation array, beam transformation system and focusing system. The high brightness, high power density and single fiber output of a laser diode bar is achieved. The coupling efficiency is 65% and the power density is up to 1.03 * 10~4 W/cm~2.
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论文的结构分为空间望远镜系统的设计和硅(锂)探测器研制两个部分。第一部分主要介绍了空间望远镜系统的设计,该空间望远镜系统能鉴别Z≤26、M≤56范围内的空间带电粒子,该系统的设计在国内是首例,它将使我国空间高能带电粒子的鉴别和测量上一个新的台阶;第二个部分主要介绍适合于探测空间粒子的硅(锂)探测器的研制及其性能的测试过程。该探测器的研制成功为空间高能带电粒子的探测提供了必要的准备。 我们已经提供给空间科学与应用研究中心二十多块硅(锂)探测器。我们用ThC'-C源和137Cs源对硅(锂)探测器进行了测试,我们在120V时便可得到137Cs电子谱;我们在250V常温常压得到α粒子谱,其能量分辨可好于37Kev,长期加压测试时硅(锂)探测器的反向电流变化稳定,在持续20天加压250V时,其中直径为12mm的硅(锂)探测器的电流变化可达1.10±0.50微安,信噪比可达420倍。
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Chinese Academy of Sciences [KZCX2-YW-315, KZCX2-YW-Q1-01]; National Natural Science Foundation of China [40625002, 90502009, 200905006]; Office of Science (BER), U. S. Department of Energy ; EU/FP7 [212250]
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讨论同伦算法求解并联机器人运动学正问题。通过参系数同伦法大大减少了跟踪路径的数目,从而提高了同伦算法的效率使之对求解一般非线性代数方程组更为可行。采用这一算法,求出了中科院沈阳自动化研究所机器人开放研究实验室的新型并联机器人模型的全部正解,为新模型的机构分析和实时控制提供了理论依据。
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华南下寒武统保存着国际著名的生物群(如澄江生物群),同时蕴藏着磷块岩、重晶石、稀土及Ni-Mo-PGE等丰富的矿产资源,因此,它一直为地质科学家们持续关注的热点之一。关于华南下寒武统的研究,前人在古生物学方面已经取得了卓著的成就,主要表现在国际权威期刊上(如期刊《Science》和《Nature》)已发表大量的关于澄江生物群的研究成果,对早期生命演化研究具有重要而广泛的影响。然而,华南下寒武统年代学及国际对比研究方面已明显滞后,公开发表的华南下寒武统的高精度、可靠的锆石U-Pb年龄数据至本研究论文截稿时止仍然仅有唯一的一个,即Jenkins et al. (2002)报道的国际前寒武系-寒武系界线层型候选剖面―云南晋宁梅树村剖面的朱家菁组中谊村段中部(第5层)钾质斑脱岩锆石SHRIMP U-Pb年龄(538.2 ± 1.5 Ma)。因而,华南下寒武统中的重要生物群、矿床及具全球对比意义的C同位素漂移事件缺乏地层精确年龄的约束,进而制约了早期生命演化理论、矿床成因解释及地层国际对比等方面研究的发展。 近来,发现华南下寒武统赋存独特的钾质斑脱岩层,它们在横向上广泛分布于云南东部、四川峨眉麦地坪、贵州西部(如织金和金沙岩孔)及北部(如遵义松林)、湖北宜昌泰山庙和湖南张家界等地区,在地层序列垂向上主要产出于朱家菁组中谊村段中部、石岩头组底部以及它们的相当层位。这些钾质斑脱岩既是建立地层框架等时层潜在的物质基础,亦是获取地层精确锆石U-Pb年龄的具重要意义的研究对象之一。因此,对它们进行系统研究可望改观华南下寒武统年代学及国际对比研究方面的落后现状。 同时,华南下寒武统广泛产出的磷块岩既具有重要的资源价值,另一方面,任一磷块岩层代表着一次独立的成磷事件,因而将华南地区下寒武统磷块岩进行区域上的对比研究,从而以磷块岩层作为等时层,对构建华南下寒武统地层框架具有重要的地层学意义。 此外,华南下寒武统产出的Ni-Mo多元素富集层广泛分布于扬子地台范围,西起云南东部,东部延至浙江诸暨地区,在NE-SW向延伸近1600 km,它既代 表了重要的成矿事件,亦为关键的地球化学异常层位。因此,对Ni-Mo多元素富集层进行区域上的对比研究,明确它在华南下寒武统各重要剖面的产出位置,对于构建华南下寒武统层序框架具有重要意义。 遵义松林地区的下寒武统因赋存Ni-Mo-PGE矿床及与滇东地区澄江生物群相当的遵义生物群而日益受到国内外地质学家们的广泛关注。该区牛蹄塘组底部产出磷块岩、钾质斑脱岩及Ni-Mo多元素富集层,与滇东地区梅树村剖面出露的地层具有潜在的可对比性。因此,本研究选取近年来日益受科学家们关注的遵义松林地区下寒武统作为研究对象,重点对该区牛蹄塘组底部的钾质斑脱岩开展矿物学、地球化学和年代学研究。同时,将遵义松林地区下寒武统剖面上磷块岩、钾质斑脱岩、Ni-Mo多元素富集层主要与滇东地区梅树村剖面的相应岩层进行地球化学对比研究。研究的目的在于通过对华南地区上述两条代表性的下寒武统剖面进行地层对比研究,初步构建华南下寒武统具时间、空间涵义的层序框架,从而约束华南下寒武统中的重要生物群、矿床及具全球对比意义的C同位素漂移事件的时间,进一步促进华南下寒武统的划分和全球对比。论文获得以下主要结论性认识: (1)滇东地区朱家菁组中谊村段中部钾质斑脱岩及其邻近的磷块岩可构成华南下寒武统层序框架的第一个标志层。这一标志层在贵州大部分地区(或华南地区的多数下寒武统剖面)缺失。该标志层的磷块岩稀土元素总量和Y含量高于新元古代陡山沱期磷块岩,低于遵义松林地区牛蹄塘组底部及其华南其它地区相当层位(石岩头组底部及戈仲伍组)的磷块岩。第一个标志层的钾质斑脱岩的原始岩浆为亚碱性系列的酸性岩浆,其典型特征为具有较低的Zr(变化范围144×10-6~291×10-6,平均196.4×10-6)、Nb(变化范围10×10-6~13×10-6,平均11.86×10-6)含量和较高的Zr/Nb比值(变化范围为12.63~24.24,平均值为16.55)。这一层钾质斑脱岩的锆石U-Pb年龄为538.2±1.5 Ma(Jenkins et al., 2002)。 (2)遵义松林地区牛蹄塘组底部钾质斑脱岩和磷块岩分别相当于滇东地区石岩头组底部钾质斑脱岩和磷块岩,它们构成华南下寒武统层序框架的第二个标志层。该标志层中钾质斑脱岩的原始岩浆性质为中性岩浆,其碱性程度高于朱家菁组中谊村段中部钾质斑脱岩的原始岩浆。相对于中谊村段中部钾质斑脱岩,该层位的钾质斑脱岩具有高的Zr(变化范围187.0910-6~391.5710-6,平均值318.4010-6)、Nb(49.6910-6~140.0010-6,平均值90.6810-6)含量和低的Zr/Nb(2.60~4.32,平均值3.61)比值。该钾质斑脱岩的年龄为518 ± 5 Ma。该标志层的磷块岩以极其富REE和Y为特征,其稀土元素总量平均值为636.01×10-6,Y含量平均值262.43×10-6,明显高于滇东地区中谊村段磷块岩(∑REE平均值为195.45×10-6,Y含量平均值为91.2310-6),它们代表早寒武世时期一次特殊的以极其富REE和Y为特征的成磷事件。 (3)Ni-Mo多元素富集层可以作为构建华南下寒武统层序框架中的第三个等时标志层。滇东地区梅树村剖面的Ni-Mo多元素富集层被重新校正在玉案山组底部(即13层,Ni、Mo含量分别为135×10-6和583×10-6)。Ni-Mo多元素地球化学标志层的典型特征为在剖面上具Ni、Mo等多种微量元素及贵金属元素的最高异常。该标志层的Re-Os年龄为537~542 Ma,可能代表的不是地层层序的年龄。 (4)初步建立华南下寒武统时间框架。约束了华南地区下寒武统Ni-Mo-PGE矿床的下限年龄应为518 ± 5 Ma。同时,该时间框架亦约束了滇东地区澄江生物群及最古老三叶虫的下限年龄(518 ± 5 Ma),考虑到石岩头组底部钾质斑脱岩的产出位置与玉案山组中部澄江生物群的产出层位存在相当的距离(大于80 m),因此,前人对澄江生物群的推测年龄(525~530 Ma)可能有些偏老。此外,初步约束了华南地区具全球对比意义的C同位素正漂移事件的年龄(538~518 Ma)。该时间框架是建立在两个相互支持的地层高精度锆石SHRIMP U-Pb年龄的基础之上,而国际前寒武系-寒武系界线年龄的最新研究成果为542 Ma,因此,它支持将华南地区的前寒武系-寒武系界线置于朱家菁组中谊村段中部钾质斑脱岩层(第5层)的下伏地层的方案。结合华南地区最新的地层古生物学研究成果(朱茂炎等,2001;Zhu et al., 2003),将这一界线置于朱家菁组中谊村段底界可作为一种合理的选择。
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Ellis, D.I., Broadhurst, D., Rowland, J.J. and Goodacre, R. (2005) Rapid detection method for microbial spoilage using FT-IR and machine learning. In: Rapid Methods for Food and Feed Quality Determination, (Eds) van Amerongen, A., Barug, D and Lauwaars, M., Wageningen Academic Publishers, Wageningen, Netherlands, in press.
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King, R.D., Garrett, S.M., Coghill, G.M. (2005). On the use of qualitative reasoning to simulate and identify metabolic pathways. Bioinformatics 21(9):2017-2026 RAE2008
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David P. Enot and Ross D. King (2003). Structure based drug design with inductive logic programming. The ACS National Meeting Spring 2003, New Orleans
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David P. Enot and Ross D. King (2002) The use of Inductive Logic Programming in drug design. Proceedings of the 14th EuroQSAR Symposium (EuroQSAR 2002). Blackwell Publishing, p247-250
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G. M. Coghill, S. M. Garrett and R. D. King (2002), Learning Qualitative Models in the Presence of Noise, QR'02 Workshop on Qualitative Reasoning
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Modification of GaAs Schottky diodes by thin organic interlayers, A.R. Vearey-Roberts and D.A. Evans, Appl. Phys. Lett. 86, 072105 (2005)