Interplanetary dust: trace element analysis of individual particles by neutron activation

Although micrometeorites of cometary origin are thought to be the dominant component of interplanetary dust, it has never been possible to positively identify such micrometer-sized particles. Two such particles have been identified as definitely micrometeorites since their abundances of volatile and nonvolatile trace elements closely match those of primitive solar system material.     

Shock synthesis of amino acids in simulated primitive environments

A mixture of gases roughly simulating the primitive terrestrial atmosphere has been subjected to shock heating followed by a rapid thermal quench. Under strictly homogeneous conditions there is a very high efficiency of 5 x 10(10) molecules per erg of shock-injected energy for production of alpha-amino acids. Calculations suggest that rapid quenching bypasses the usual thermochemical barrier. The product of energy flux and efficiency implies the unexpected conclusion that shocks occurring on atmospheric entry of cometary meteors and micrometeorites and from thunder may have been the principal energy sources for pre-biological organic synthesis on the primitive earth.     

Discovery of nucler tracks in interplanetary dust

Nuclear tracks have been identified in interplanetary dust particles (IDP's) collected from the stratosphere. The presence of tracks unambiguously confirms the extraterrestrial nature of IDP's, and the high track densities (10(10) to 10(11) per square centimeter) suggest an exposure age of approximately 10(4) years within the inner solar system. Tracks also provide an upper temperature limit for the heating of IDP's during atmospheric entry, thereby making it possible to distinguish between pristine and thermally modified micrometeorites.     

Micrometeorite craters discovered on chondrule-like objects from kapoeta meteorite

Craters attributable to hypervelocity impacts of micrometeorites have been discovered on rare chondrule-like objects from the gas-rich meteorite Kapoeta. These chondrule-like objects, probably generated by impacts themselves, provide further evidence for the regolith origin of Kapoeta. The micrometeorite flux at the time of formation of the meteorites was probably an order of magnitude higher than the present flux, but the solar luminosity could not have been higher than 1.7 times its present value.     

Zodiacal dust and deep-sea sediments

The recent detection of radioactive Al(26) in marine sediments has led to the conclusion that it is brought into the earth's atmosphere by micrometeorites which have been exposed, in interplanetary space, to solar high-energy protons. The Al(26) method is not precise enough to yield directly a reliable value for the mass accretion rate to the earth to better than about 3 orders of magnitude, but is sufficiently accurate to allow a crucial decision between two widely differing of interplanetary dust which have been proposed to explain observations of the zodiacal light. The two models lead to Al(26) concentrations which would differ by about 5 orders of magnitude. Thus, the presence of Al(26) is consistent with the zodiacal dust model with particles of some tens of microns rather then with submicron particles. From this model a mass accretion to the earth then be calculated which is set at 1250 (upper limit, 2500; lower limit, 250) tons per day, or 2.8 x 10(-15) g/cm(2) sec, or 4.5 x 10(11) g over the earth per This value does not depend on the flux of the solar high-energy particles, which may be uncertain by an order of magnitude or more. The presence of Al(26) supports the idea that an important fraction of the dust is stony in composition material density, and thus eliminates some more exotic dust models, as such one consisting entirely of carbon grains. We may also conclude that the accreted dust particles have been in the solar system and exposed to protons from solar high-energy particles for a time interval which is greater than a significant of the Al(26) half-life (0.74 x 10(6) years).     

Carbon compounds in interplanetary dust: evidence for formation by heterogeneous catalysis

Associations of carbonaceous material with iron-nickel alloy, carbides, and oxides were identified by analytical electron microscopy in ten unmelted chondritic porous micrometeorites from the earth's stratosphere. These associations, which may be interpreted in terms of reactions between a carbon-containing gas and catalytically active dust grains, suggest that some of the carbon in the chondritic porous subset of interplanetary dust was emplaced through heterogeneous catalysis.     

Photoemission studies of high-tc superconductors: the superconducting gap

Over the last several years there have been great improvements in the energy resolution and detection efficiency of angle-resolved photoemission spectroscopy. These improvements have made it possible to discover a number of fascinating features in the electronic structure of the high transition temperature (T(c)) superconductors: apparently bandlike Fermi surfaces, flat-band saddle points, and nested Fermi surface sections. Recent work suggests that these features, previously thought explainable only by one-electron band theory, may be better understood with a many-body approach. Furthermore, other properties of the high-T(c) superconductors, which are difficult to understand with band theory, are well described using a many-body picture. Angle-resolved photoemission spectroscopy has also been used to investigate the nature of the superconducting pairing state, revealing an anisotropic gap consistent with a d-wave order parameter and fueling the current debate over s-wave versus d-wave superconductivity.     

中国芍药分类学研究进展

该文从历史和现状两个层面上概述了中国芍药的分类学研究进展.芍药科系单属科,由芍药属从毛茛科独立而来.芍药属内划分为3个组,即牡丹组、北美芍药组和芍药组,其中芍药组系属内最大的组,约含22个种,组内又有全缘羽叶亚组和多裂叶亚组之分.在中国芍药种质资源的分类史上曾先后提名过13个种,但目前已基本得到公认的却主要有8个种(5个变种),皆隶属于芍药组.中国芍药品种资源众多,其分类历史悠久,按照花型演进规律目前已形成日趋一致的花型分类方案.     

焦作地区野生园林绿化植物资源的调查与研究

焦作地区山地广阔,自然条件优越,野生园林绿化植物资源十分丰富,从2004年7月开始,对焦作地区的野生园林绿化植物进行调查研究,经初步统计,焦作地区有各类野生园林绿化植物83科、376种（含变种、变型）。然而,目前这些资源中的很多种类还未被人们充分重视和利用。保护、研究和利用好这些资源对于丰富园林植物种类,建立合理的绿化结构,提高城市绿化水平具有重要的意义,对于保护和改善焦作太行山区生态环境,促进山区经济发展也将发挥重要作用。     

Obsidian hydration dates glacial loading?

Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming. The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow.     

Experimental and theoretical differential cross sections for a four-atom reaction: HD + OH → H₂O + D

Quantum dynamical theories have progressed to the stage in which state-to-state differential cross sections can now be routinely computed with high accuracy for three-atom systems since the first such calculation was carried out more than 30 years ago for the H + H(2) system. For reactions beyond three atoms, however, highly accurate quantum dynamical calculations of differential cross sections have not been feasible. We have recently developed a quantum wave packet method to compute full-dimensional differential cross sections for four-atom reactions. Here, we report benchmark calculations carried out for the prototypical HD + OH → H(2)O + D reaction on an accurate potential energy surface that yield differential cross sections in excellent agreement with those from a high-resolution, crossed-molecular beam experiment.     

Djerfisherite, alkali copper-iron sulfide: a new mineral from enstatite chondrites

A new mineral, essentially a potassium-copper-iron sulfide, occurs in accessory amounts in the enstatite chondrites Kota Kota (a find) and St. Marks (a fall), and has been identified visually in the enstatite achondrite Pena Blanca Springs (a fall). The x-ray diffraction pattern, electron-microprobe analysis, and its appearance in polished sections all serve to identify it.     

粤西凤尾蕨属药用植物组种资源的调查

目的：调查粤西地区凤尾蕨属组种植物资源。方法：实地调查、标本采集、分类鉴定研究与查阅文献资料相结合。结果与结论：粤西地区凤尾蕨属植物共有3组13种，其中7种为已知药用植物，并列出种鉴索表。     

Global increase in quaternary explosive volcanism

The worldwide distribution of volcanic ash has been determinmined from 320 deep-sea sections drilled during the Deep Sea Drilling Project. The ash distribution in the deep-sea sections, which span the last 20 million years, indicates that there has been a much higher rate of explosive volcanism from both island arc and hot spot volcanoes during the last 2 million years. This episode, and perhaps another in the Middle Miocene cprrelates with previously reported widespread synchronism in increased volcanicity in certain oceanic islands. Increased Quaternary volcanism coincides approximately with that episode of the Cenozoic marked by major and rapidly fluctuating climatic change.     

Transvaal Stromatolite: First Evidence for the Diversification of Cells about 2.2 x 109 Years Ago

The well-preserved fossil remnants of filamentous blue-green algae have been found in petrographic thin sections of a dolomitic limestone stromatolite in the Transvaal Sequence of South Africa. Some of these filaments contain enlarged cells which are interpreted as akinetes. A new species and genus, Petraphera vivescenticula, is proposed for this microfossil, which is morphologically similar to the living cyanophyte genus Raphidiopsis. This would constitute the first known occurrence of cell diversification in the Precambrian with an age of about 2.2 x 10(9) years.     

Rapid acidification of the ocean during the Paleocene-Eocene thermal maximum

The Paleocene-Eocene thermal maximum (PETM) has been attributed to the rapid release of approximately 2000 x 10(9) metric tons of carbon in the form of methane. In theory, oxidation and ocean absorption of this carbon should have lowered deep-sea pH, thereby triggering a rapid (<10,000-year) shoaling of the calcite compensation depth (CCD), followed by gradual recovery. Here we present geochemical data from five new South Atlantic deep-sea sections that constrain the timing and extent of massive sea-floor carbonate dissolution coincident with the PETM. The sections, from between 2.7 and 4.8 kilometers water depth, are marked by a prominent clay layer, the character of which indicates that the CCD shoaled rapidly (<10,000 years) by more than 2 kilometers and recovered gradually (>100,000 years). These findings indicate that a large mass of carbon (>2000 x 10(9) metric tons of carbon) dissolved in the ocean at the Paleocene-Eocene boundary and that permanent sequestration of this carbon occurred through silicate weathering feedback.     

High-voltage transmission electron microscopy study of lunar surface material

The internal substructures of a type B sample have been examined at high magnification and compared with terrestrial rocks. Selected ultrathin sections were prepared from these multiphase materials by an ion-thinning technique and examined in a 1-Mev electron microscope, with complementary optical analyses. The structures in the ilmenite and plagioclase indicate that the lunar material has undergone plastic deformation by dislocation movement and possibly microtwinning, with subsequent recovery. The pyroxene exhibits complex lamellar structures of submicron spacing. These various observations are consistent with the optical microscopy evidence for distortion and recovery and identify the processes involved.     

江西天然气管道交流干扰检测与防护

江西省天然气有限公司所辖管道存在多处与高压输电线路或电气化铁路相邻的情况,为了全面评价管道的交流干扰风险,参照欧洲标准DDCEN—TS15280—2006及国家标准GB／T50698—2011,进行了交流干扰的初步检测和详细检测,检测参数包括交流干扰电压、交流电流密度、交直流电流密度之比及土壤电阻率。选取交流干扰严重位置,通过开展现场缓解试验和设计计算,确定了交流干扰防护方案：在干扰严重位置与管道平行铺设锌带缓解线,并在缓解线和管道之间串接去耦合器。设计方案实施后,获得了理想的防护效果,可为同类工程提供参考。（图6,表4,参10）。     

中华鲟GH蛋白二级结构和B细胞抗原表位的预测

笔者采用RT—PCR技术从中华鲟脑垂体中克隆出了生长激素（GH）基因,该文根据已获得的GH氨基酸序列一级结构,运用计算机技术和分子生物学软件对中华鲟GH蛋白二级结构和B细胞表位进行分析和预测,为中华鲟GH蛋白单克隆抗体的制备提供依据,为探讨中华鲟分子调控机理提供参考。     

Setting the optimal length to be scanned in rows of vines by using mobile terrestrial laser scanners

Mapping the leaf area index (LAI) by using mobile terrestrial laser scanners (MTLS) is of significance for viticulture. LAI is related to plant vigour and foliar development being an important parameter for many agricultural practices. Since it may present spatial variability within vineyards, it is very interesting monitoring it in an objective repeatable way. Considering the possibility of using on-the-go sensors such as MTLS within an agricultural plot, it is necessary to set a proper length of the row to be scanned at each sample point for a reliable operation of the scanner. Three different row length sections of 0.5, 1, and 2 m have been tested. Data analysis has shown that models required to estimate LAI differ significantly depending on the scanned length of the row; the model required to estimate LAI for short sections (0.5 m) is different from that required for longer sections (1 and 2 m). Of the two models obtained, we recommend using MTLS for scanning row length sections of 1 m because the practical use of the sensor in the field is simplified without compromising the results (there is little variation in the model when the row length section changes from 1 to 2 m). In addition, a sufficient number of sampling points is obtained to support a map of the LAI. Linear regression models using as explanatory variable the tree area index, obtained from the data provided by the scanner, are used to estimate the LAI.