磁州窑观台窑址不同时期绿釉器原料来源的 PIXE 分析?

磁州窑是宋、金、元时期北方最著名的民间窑场之一,其烧制的以铅为助溶剂的氧化铜绿釉器装饰技法和装饰品种丰富多彩.为了解不同时期绿釉器的原料来源和配方,以及它们之间的关系,用质子激发X射线荧光分析(PIXE)技术无损测定磁州窑观台窑址不同时期11个样品胎、釉的化学组成,对这些数据分别进行模糊聚类分析,结果表明:多数宋金时期绿釉器胎样品的胎料来源相对比较集中;多数金代绿釉器胎样品的胎料来源相对比较分散;多数金代绿釉器样品的釉料来源相对比较集中,配方变化相对较小;多数宋金时期绿釉器样品的釉料来源相对有些分散,配方变化比较多;护胎酱釉的釉料来源和绿釉明显不同.     

Mid-depth recirculation observed in the interior Labrador and Irminger seas by direct velocity measurements

The Labrador Sea is one of the sites where convection exports surface water to the deep ocean in winter as part of the thermohaline circulation. Labrador Sea water is characteristically cold and fresh, and it can be traced at intermediate depths (500-2,000 m) across the North Atlantic Ocean, to the south and to the east of the Labrador Sea. Widespread observations of the ocean currents that lead to this distribution of Labrador Sea water have, however, been difficult and therefore scarce. We have used more than 200 subsurface floats to measure directly basin-wide horizontal velocities at various depths in the Labrador and Irminger seas. We observe unanticipated recirculations of the mid-depth (approximately 700 m) cyclonic boundary currents in both basins, leading to an anticyclonic flow in the interior of the Labrador basin. About 40% of the floats from the region of deep convection left the basin within one year and were rapidly transported in the anticyclonic flow to the Irminger basin, and also eastwards into the subpolar gyre. Surprisingly, the float tracks did not clearly depict the deep western boundary current, which is the expected main pathway of Labrador Sea water in the thermohaline circulation. Rather, the flow along the boundary near Flemish Cap is dominated by eddies that transport water offshore. Our detailed observations of the velocity structure with a high data coverage suggest that we may have to revise our picture of the formation and spreading of Labrador Sea water, and future studies with similar instrumentation will allow new insights on the intermediate depth ocean circulation.     

公路隧道内主动降噪声源布置位置仿真模拟

基于声波干涉原理对高速公路隧道内噪声的主动降噪特性进行了理论分析,采用有限元法建立了3条隧道全尺寸断面模型,计算得出隧道内声压级分布,分析了主动降噪时的隧道内声场特性.考虑噪声声源频率的差异,噪声频率越低,隧道内主动降噪效果越好;考虑主动降噪设备位置的不同,将主动声源与噪声源、降噪点的空间距离加和,再与噪声源与降噪点的空间距离作比较,若两者差值为噪声波长的整数倍,则可在降噪点附近实现3dB以上区域降噪.     

封闭空间有源噪声控制次级声源优化策略

针对封闭矩形空间,建立了基于小波迦辽金法的结构-声耦合计算模型.采用正交试验设计方法研究了次级声源位置和复强度2个因素的交互作用对有源噪声控制系统的降噪量的影响.虽然此交互作用均被以往文献所忽略,但研究表明该交互作用对于系统降噪量的影响比较显著.在此基础上,分别采用遗传算法和基于均匀设计的模式搜索方法,优化次级声源的位置和复强度.通过比较发现,考虑交互作用的优化结果较忽略交互作用的优化结果性能提高约30%,并且基于均匀设计的模式搜索算法的搜索效率虽然高于遗传算法,但容易陷入局部最优.     

Cleavage of pre-tRNAs by the splicing endonuclease requires a composite active site

Splicing is required for the removal of introns from a subset of transfer RNAs in all eukaryotic organisms. The first step of splicing, intron recognition and cleavage, is performed by the tRNA-splicing endonuclease, a tetrameric enzyme composed of the protein subunits Sen54, Sen2, Sen34 and Sen15. It has previously been demonstrated that the active sites for cleavage at the 5' and 3' splice sites of precursor tRNA are contained within Sen2 and Sen34, respectively. A recent structure of an archaeal endonuclease complexed with a bulge-helix-bulge RNA has led to the unexpected hypothesis that catalysis requires a critical 'cation-pi sandwich' composed of two arginine residues that serve to position the RNA substrate within the active site. This motif is derived from a cross-subunit interaction between the two catalytic subunits. Here we test the role of this interaction within the eukaryotic endonuclease and show that catalysis at the 5' splice site requires the conserved cation-pi sandwich derived from the Sen34 subunit in addition to the catalytic triad of Sen2. The catalysis of pre-tRNA by the eukaryotic tRNA-splicing endonuclease therefore requires a previously unrecognized composite active site.     

牙周炎维护治疗期活动性位点临床指标、X-Ray及微生物变化特征

对牙周非手术基础治疗后进入维护治疗期的22名慢性牙周炎患者进行9个月的纵向观察。每3个月给予口腔卫生宣教,龈上下洁刮治和根面平整,并在基线和每次复查时记录临床检查指标。结果表明:活动性位点的年发生率为5.75%,上下颌磨牙及上颌前磨牙为活动性破坏好发牙位。附着增加的位点数和增加的量随基线袋深增加呈增多趋势,X-Ray检查牙槽骨高度无明显变化,活动性位点螺旋体数量明显多于非活动性位点。说明非手术基础治疗配合定期维护,在较短观察期内可使大多数位点临床指标保持稳定甚至好转,但不能带来明显的骨量增加。     

Radio source counts from the Ohio survey

The Ohio survey shows a decrease in the number of faint sources relative to the number which would be expected for a uniform, Euclidean universe. This confirms the results of the Cambridge 5C2 survey at 408 MHz, but the decrease is sharper for the Ohio counts at 1415 MHz.     

Constraints on the origins of hydrocarbon gas from compositions of gases at their site of origin

It is widely accepted that natural gas is formed from thermal decomposition of both oil in reservoirs and, to a lesser extent, the organic matter in shales from which the oil was derived. But laboratory pyrolysis experiments on shales do not reproduce the methane-rich composition typical of most gas reservoirs, leading to suggestions that other mechanisms, such as transition-metal catalysis, may be important. The discrepancy might, however, instead arise because gas (and oil) deposits have migrated from their source rocks, so that the reservoir composition might not be representative of the composition in the source rocks where the hydrocarbons were generated. To address this question, we have analysed gas samples coproduced with oils directly from a source rock (the Bakken shales, North Dakota, USA) where the local geology has prevented significant hydrocarbon migration. The methane contents of these Bakken-shale gases are much lower than that of conventional gas reservoirs, but are consistent with that from pyrolysis experiments on these shales. Thus, because these Bakken gases form with (rather than from) oils, we argue that compositional differences between gases from source rocks and conventional gas deposits result from fractionation processes occurring after hydrocarbon expulsion from the source rock.     

Timing of the Last Glacial Maximum from observed sea-level minima

During the Last Glacial Maximum, ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today. But few direct estimates exist of the volume of the ice sheets, or the timing and rates of change during their advance and retreat. Here we analyse four distinct sediment facies in the shallow, tectonically stable Bonaparte Gulf, Australia--each of which is characteristic of a distinct range in sea level--to estimate the maximum volume of land-based ice during the last glaciation and the timing of the initial melting phase. We use faunal assemblages and preservation status of the sediments to distinguish open marine, shallow marine, marginal marine and brackish conditions, and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio-hydro-isostatic modelling. Our results indicate that from at least 22,000 to 19,000 (calendar) years before present, land-based ice volume was at its maximum, exceeding today's grounded ice sheets by 52.5 x 10(6) km. A rapid decrease in ice volume by about 10% within a few hundred years terminated the Last Glacial Maximum at 19,000 +/- 250 years.     

The essential light chains constitute part of the active site of smooth muscle myosin

Myosin, a major contractile protein, characteristically possesses a long coiled-coil alpha-helical tail and two heads. Each head contains both an actin binding site and an ATPase site and is formed from the NH2-terminal half of one of the two heavy chains (relative molecular mass, Mr, 200,000) and a pair of light chains; the so-called regulatory and essential light chains of approximately Mr 20,000 each. Recently we have identified Trp 130 of the myosin heavy chain from rabbit skeletal muscle as an active-site amino-acid residue after labelling with a new photoaffinity analogue of ADP, N-(4-azido-2-nitrophenyl)-2-aminoethyl diphosphate (NANDP). Nonspecific labelling was eliminated by first trapping NANDP at the active site with thiol crosslinking agents. Exclusive labelling of the heavy chains with no labelling of the light chains agreed with previous findings that the heavy chains alone contain the actin-activated Mg-ATPase activity of rabbit skeletal myosin. Here we report similar photolabelling experiments with smooth muscle myosin (chicken gizzard) in which 3H-NANDP is trapped at the active site with vanadate and which show that both the heavy chains and the essential light chains are labelled. The results indicate that both chains contribute to the ATP binding site and represent the first direct evidence for participation of the essential light chains in the active site of any type of myosin.     

大柳树坝址岩体渗漏量物理模拟

在对拟建的黄河大柳树坝址岩体地质情况及渗漏情况分析的基础上,根据相似定理及规律,选取普通烧结砖作为实验材料,确定了渗漏的物理模型,包括几何条件、物理条件、边界条件及初始条件.并通过模型试验的数据计算得出渗透量.与根据传统方式分析计算出的结果进行对比,其值较接近.     

Hemispherical variations in seismic velocity at the top of the Earth's inner core

Knowledge of the seismic velocity structure at the top of the Earth's inner core is important for deciphering the physical processes responsible for inner-core growth. Previous global seismic studies have focused on structures found 100 km or deeper within the inner core, with results for the uppermost 100 km available for only isolated regions. Here we present constraints on seismic velocity variations just beneath the inner-core boundary, determined from the difference in travel time between waves reflected at the inner-core boundary and those transmitted through the inner core. We found that these travel-time residuals-observed on both global seismograph stations and several regional seismic networks-are systematically larger, by about 0.8 s, for waves that sample the 'eastern hemisphere' of the inner core (40 degrees E to 180 degrees E) compared to those that sample the 'western hemisphere' (180 degrees W to 40 degrees E). These residuals show no correlation with the angle at which the waves traverse the inner core; this indicates that seismic anisotropy is not strong in this region and that the isotropic seismic velocity of the eastern hemisphere is about 0.8% higher than that of the western hemisphere.     

Response of water budget to recent climatic changes in the source region of the Yellow River

Discharge in the source region of the Yellow River significantly declined after 1990.China Meteorological Administration(CMA) data show that precipitation in this region was low in the 1990s but returned to above normal after 2002;in recent decades there has been rapid warming of surface air,moistening and wind speed decrease.To investigate the influences of recent climatic changes on the water budget,this study simulates the surface water budget at CMA stations within and surrounding the source region during 1960-2006,using an improved land surface model.Results indicate that the spatial pattern of precipitation change is an important factor(except for precipitation amount and intensity) in determining the response of runoff to precipitation changes.Low runoff in the 1990s was consistent with precipitation amount and intensity.The recovery of precipitation after 2002 is mainly from increased precipitation in the dry area of the source region.Evaporation was mainly limited by water availability in this dry area,and thus most of the precipitation increase was evaporated.By contrast,energy availability was a more important influence on evaporation in the wet area.There was more evaporation in the wet area because of rapid warming,although precipitation amount partly decreased and partly increased,contributing to the reduction of runoff after 2002.This control on evaporation and its response,together with the modified spatial pattern of precipitation,produced a water budget unfavorable for runoff generation in the source region during recent years.     

The architecture of active zone material at the frog's neuromuscular junction

Active zone material at the nervous system's synapses is situated next to synaptic vesicles that are docked at the presynaptic plasma membrane, and calcium channels that are anchored in the membrane. Here we use electron microscope tomography to show the arrangement and associations of structural components of this compact organelle at a model synapse, the frog's neuromuscular junction. Our findings indicate that the active zone material helps to dock the vesicles and anchor the channels, and that its architecture provides both a particular spatial relationship and a structural linkage between them. The structural linkage may include proteins that mediate the calcium-triggered exocytosis of neurotransmitter by the synaptic vesicles during synaptic transmission.     

高校源头治腐关键初探

在社会主义市场经济体系逐步形成的特殊历史条件下,腐败滋生是不可避免的社会现象,高校在源头治腐方面做了不少工作,但还存在着一些问题,应当抓住关键,研究权力之对策,要牢固确立制权思想,探索以权制权途径,建立健全以权制权等方面的规章制度,经监部门应主动担负起监督执行相关制度的责任。     

Spatiotemporal characteristics of freezing and thawing of the active layer in the source areas of the Yellow River （SAYR）

Based on the analysis of data on temperatures and moisture of soils in the active layer at four different permafrost sites in the source areas of the Yellow River(SAYR)in 2010–2012,the freeze–thaw processes of soils in the active layer were compared and contrasted for understanding the spatiotemporal variations.At the four studied sites,the thickness and mean annual temperature of permafrost are different.The temperatures at the top of permafrost(TTOP),i.e.,the maximum depth(s)of seasonal frost and/or thaw penetration,are-1.9°C at the Chalaping site(CLP),-0.9°C at the site on the southern bank of the Zhaling Lake(ZLH),-0.4°C at the Maduo Town site(MDX),and 1.1°C at the site on the northern bank of the Eling Lake(ELH).Differences in the mean annual ground temperature of permafrost and TTOPs may be responsible for the differentiations in the freeze–thaw processes of soils in the active layer.With rising TTOPs,the ground thawing started earlier:CLP in early June,ZLH in late May,MDX in early May,and ELH in mid-April,while the freezing began later:CLP in early October,ZLH in early to midOctober,MDX in mid-October,and ELH in the mid-to late October.With increasing TTOPs,the freeze-up periods for permafrost sites were shortened:202 days at CLP,130 days at ZLH,100 days at MDX,and the period of complete thaw was 89 days at ELH.At the CLP and ZLH sites,the two-directional ground freezing(downwards from ground surfaces and upwards from the permafrost table)and thawing finished in the same year,but the ground freezing at the MDX continued to the end of the nextJanuary,with very slow freezing rates in the end.At the ELH site,ground freezing kept on until early May when thawing began on the surface,and upward and downward thawing became increasingly stable in late June to early July.At each site,with rising TTOPs,the downward freezing accelerated in comparison with the upward freezing,and with an increasing proportion of downward frozen depth,and with the larger ratios of freezing to thawing duration.In summary,the patterns of thawing and freezing processes in the active layer in the SAYR differ from those in other parts of the Qinghai–Tibet Plateau to a noticeable extent.