多树种合理配置抗御光肩星天牛灾害控灾阈值的研究

为了明确多树种合理配置抗御天牛灾害措施的可行性,首次提出了控灾阈值的概念．在宁夏引黄灌区选择对不同诱饵树配置、不同树龄的样地35块进行调查,并对15株平均标准木进行树干解析,建立虫口模型及其材积损失模型,结合综合效益评价结果并根据目前市场木材收购标准,确定了光肩星天牛控灾阈值模型．结果表明:诱饵树比例应控制在［7,093%,25%］的区间内,同时可以根据对不同树种的不同要求计算出适宜的控灾阈值,体现了控灾阈值的动态性、灵活性．      

Greek marbles: determination of provenance by isotopic analysis

A study has been made of carbon-13 and oxygen-18 variations in Greek marbles from the ancient quarry localities of Naxos, Paros, Mount Hymettus, and Mount Pentelikon. Parian, Hymettian, and Pentelic marbles can be clearly distinguished by the isotopic relationships; Naxian marbles fall into two groups characterized by different oxygen-18/oxygen-16 ratios. Ten archeological samples were also analyzed; the isotopic data indicate that the "Theseion" is made of Pentelic marble and a block in the Treasury of Siphnos at Delphi is probably Parian marble.     

纳米零价铁修复Cr(Ⅵ)污染土壤的研究进展

随着铬盐生产、金属加工、电镀、皮革等工业活动以及污水灌溉和施用污泥等农业活动的进行,六价铬(Cr(Ⅵ))不断进入土壤中,严重污染土壤环境。纳米零价铁由于其比表面积大、反应活性高及还原能力强等优点,已日渐用于Cr(Ⅵ)污染土壤的修复中。本文概述了纳米零价铁修复Cr(Ⅵ)污染土壤的最新研究进展,总结了主要修复机理及影响因素,最后指出了纳米零价铁修复Cr(Ⅵ)污染土壤的发展前景及研究方向。     

Atomic-scale control of friction by actuation of nanometer-sized contacts

Stiction and wear are demanding problems in nanoelectromechanical devices, because of their large surface-to-volume ratios and the inapplicability of traditional liquid lubricants. An efficient way to switch friction on and off at the atomic scale is achieved by exciting the mechanical resonances of the sliding system perpendicular to the contact plane. The resulting variations of the interaction energy reduce friction below 10 piconewtons in a finite range of excitation and load, without any noticeable wear. Without actuation, atomic stick-slip motion, which leads to dissipation, is observed in the same range. Even if the normal oscillations require energy to actuate, our technique represents a valuable way to minimize energy dissipation in nanocontacts.     

Ultralow friction of carbonate faults caused by thermal decomposition

High-velocity weakening of faults may drive fault motion during large earthquakes. Experiments on simulated faults in Carrara marble at slip rates up to 1.3 meters per second demonstrate that thermal decomposition of calcite due to frictional heating induces pronounced fault weakening with steady-state friction coefficients as low as 0.06. Decomposition produces particles of tens of nanometers in size, and the ultralow friction appears to be associated with the flash heating on an ultrafine decomposition product. Thus, thermal decomposition may be an important process for the dynamic weakening of faults.     

Enhancement of symbioses between butterfly caterpillars and ants by vibrational communication

Butterfly caterpillars produce calls that appear to play a role in maintaining symbiotic associations with ants. A survey of butterfly species from South and Central America, North America, Europe, Thailand, and Australia suggests that the ability for caterpillars to call has evolved independently at least three times, and that calling may be ubiquitous among ant-associated species. Because ants use substrate-borne sound in their communication systems, this study points to the possibility that the calls of one insect species have evolved to attract other, unrelated species.     

Production of isotopic variability in continental basalts by cryptic crustal contamination

Regional variations in the Nd, Sr, and Pb isotopic compositions of Neogene basalts from the western United States are commonly interpreted to originate in the subcontinental mantle. In southern California, isotopic variability is restricted to lavas that lack mantle-derived xenoliths; xenolith-bearing basalts have uniform isotopic compositions similar to those of ocean-island basalts (OIBs). Combined with available geochemical data, these observations suggest that isotopic variability at these volcanoes results from subtle crustal contamination, locally by mafic crust, of primitive OIB-like magma. Recognition of such cryptic contamination may help to reconcile local discrepancies between tectonic and isotopic views of the subcontinental mantle.     

动态条件下壳聚糖稳定纳米铁去除水体中Cr（Ⅵ）的研究

以重金属Cr(Ⅵ)为目标污染物,在两种实验条件下(实验柱Ⅰ为模拟污染水样,实验柱Ⅱ为实际污染水样)考察了壳聚糖稳定纳米铁对Cr(Ⅵ)的去除能力。实验柱Ⅰ和实验柱Ⅱ分别在第160PV和127PV时发生了击穿效应。与实验柱Ⅰ相比,实验柱Ⅱ中壳聚糖稳定纳米铁对Cr(Ⅵ)的去除能力降低了25%。SEM表征显示,实验柱Ⅱ中壳聚糖稳定纳米铁的表面形成了许多葡萄状晶体,它们的存在导致实验柱Ⅱ中纳米铁的去除能力明显低于实验柱Ⅰ。XPS表征显示,由于Ca和Mg的氢氧化物替代了部分铁氢氧化物,导致实验柱Ⅱ中壳聚糖稳定纳米铁表面Fe原子的相对含量低于实验柱I。Cr元素高分辨率XPS能谱分析显示,在实验柱Ⅰ的条件下Cr(Ⅵ)被还原得更充分,而且在两种实验条件下都有部分Cr(Ⅵ)被吸附在纳米铁表面最终没有被零价铁所还原。     

纳米Fe3O4协同微生物对除草剂2,4-D的降解

 【目的】采用纳米Fe3O4协同微生物降解水溶液中2,4-D,提高2,4-D的降解效率,为有机氯农药污染环境的生物修复提供理论基础。【方法】利用纳米Fe3O4的还原作用脱去2,4-D环上的氯原子,使其毒性降低或消除;再利用微生物的共代谢作用,引入降解菌,协同降解2,4-D。通过分析纳米Fe3O4与微生物之间的相互关系,揭示纳米Fe3O4与微生物降解的协同作用机理。【结果】纳米Fe3O4对2,4-D有还原降解作用,投加纳米Fe3O4体系中2,4-D浓度降低、氯离子浓度升高,纳米Fe3O4对2,4-D的降解是一个还原脱氯过程;微生物能以2,4-D为C源,投加降解菌体系中2,4-D浓度降低、微生物生长的OD600值增大,2,4-D为微生物生长提供营养;纳米Fe3O4/微生物联合体系能明显加快2,4-D的降解,7 d时2,4-D的残留率降至35.7%,远低于纳米Fe3O4或微生物单独降解体系中2,4-D的残留率。采用微生物对中间产物2,4-DCP进行降解,反应5 d时,2,4-DCP 的残留率为50.1%,相应地,降解菌生长的OD600值为3.29。【结论】纳米Fe3O4/微生物联合体系对2,4-D的降解效率显著高于单一纳米Fe3O4或微生物体系;纳米Fe3O4能够刺激微生物的生长,2,4-D还原降解的中间产物2,4-DCP比2,4-D更易于被微生物降解。     

Origin of the sudbury complex by meteoritic impact: neodymium isotopic evidence

Samarium-neodymium isotopic data on whole rocks and minerals of the Sudbury Complex in Canada gave an igneous crystallization age of 1840 +/- 21 x 10(6) years. The initial epsilon neodymium values for 15 whole rocks are similar to those for average upper continental crust, falling on the crustal trend of neodymium isotopic evolution as defined by shales. The rare earth element concentration patterns of Sudbury rocks are also similar to upper crustal averages. These data suggest that the Sudbury Complex formed from melts generated in the upper crust and are consistent with a meteoritic impact.     

Interception of excited vibrational quantum states by O2 in atmospheric association reactions

Bimolecular reactions in Earth's atmosphere are generally assumed to proceed between reactants whose internal quantum states are fully thermally relaxed. Here, we highlight a dramatic role for vibrationally excited bimolecular reactants in the oxidation of acetylene. The reaction proceeds by preliminary adduct formation between the alkyne and OH radical, with subsequent O(2) addition. Using a detailed theoretical model, we show that the product-branching ratio is determined by the excited vibrational quantum-state distribution of the adduct at the moment it reacts with O(2). Experimentally, we found that under the simulated atmospheric conditions O(2) intercepts ~25% of the excited adducts before their vibrational quantum states have fully relaxed. Analogous interception of excited-state radicals by O(2) is likely common to a range of atmospheric reactions that proceed through peroxy complexes.     

Oxygen isotopic compositions of asteroidal materials returned from Itokawa by the Hayabusa mission

Meteorite studies suggest that each solar system object has a unique oxygen isotopic composition. Chondrites, the most primitive of meteorites, have been believed to be derived from asteroids, but oxygen isotopic compositions of asteroids themselves have not been established. We measured, using secondary ion mass spectrometry, oxygen isotopic compositions of rock particles from asteroid 25143 Itokawa returned by the Hayabusa spacecraft. Compositions of the particles are depleted in (16)O relative to terrestrial materials and indicate that Itokawa, an S-type asteroid, is one of the sources of the LL or L group of equilibrated ordinary chondrites. This is a direct oxygen-isotope link between chondrites and their parent asteroid.     

Structural dynamics of a catalytic monolayer probed by ultrafast 2D IR vibrational echoes

Ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy has proven broadly useful for studying molecular dynamics in solutions. Here, we extend the technique to probing the interfacial dynamics and structure of a silica surface-tethered transition metal carbonyl complex--tricarbonyl (1,10-phenanthroline)rhenium chloride--of interest as a photoreduction catalyst. We interpret the data using a theoretical framework devised to separate the roles of structural evolution and excitation transfer in inducing spectral diffusion. The structural dynamics, as reported on by a carbonyl stretch vibration of the surface-bound complex, have a characteristic time of ~150 picoseconds in the absence of solvent, decrease in duration by a factor of three upon addition of chloroform, and decrease another order of magnitude for the bulk solution. Conversely, solvent-complex interactions increase the lifetime of the probed vibration by 160% when solvent is applied to the monolayer.     

纳米Fe3O4/微生物联合体系对2,4-D和阿特拉津降解的研究

采用纳米Fe3O4/微生物联合体系降解溶液中2,4-D和阿特拉津,考察了不同2,4-D和阿特拉津初始浓度、微生物接种量、纳米Fe3O4投加量、溶液pH值等对降解效果的影响。结果表明,纳米Fe3O4/微生物联合体系对2,4-D和阿特拉津的降解率显著高于纳米Fe3O4和微生物单一体系;2,4-D和阿特拉津初始浓度在0～10mg·L-1、微生物接种量在0～12mg·L-1、纳米Fe3O4的投加量在0～200mg·L-1范围内,2,4-D和阿特拉津的降解率随其初始浓度、微生物接种量和纳米Fe3O4投加量的增大而增加。溶液pH3.0左右、2,4-D和阿特拉津初始浓度10mg·L-1、微生物接种量12mg·L-1、纳米Fe3O4投加量200mg·L-1,是反应的最佳条件,此实验条件下反应7d,2,4-D和阿特拉津的残留率分别降低至35.7%和54.0%。     

Diffusive isotopic contamination of mafic magma by coexisting silicic liquid in the muskox intrusion

Shifts in (87)Sr/(86)Sr and (143)Nd/(144)Nd ratios measured in cumulates from the upper levels of the Muskox mafic intrusion indicate that isotopic and bulk chemical exchange were decoupled across a mafic-silicic liquid interface during crystallization of the intrusion. Modeling of diffusive exchange between liquid layers demonstrates that isotopic compositions of silicate liquids in layered magma chambers may be strongly affected by this process on time scales of 10(3) to 10(4) years. Diffusive contamination can be used to place constraints on the physical processes and time scales of magmatic systems.     

生长压力对Bacillus subtilis磷脂脂肪酸同位素分馏的影响

已有研究表明,深海中嗜高压革兰氏阴性细菌在磷脂脂肪酸生物合成过程中稳定碳同位素分馏与细菌生长压力之间呈现出线性相关性,而表层革兰氏阳性细菌脂肪酸同位素特征与压力的关系尚不清楚。因此,本研究通过不同压力培养、脂肪酸提取以及二维单体同位素分析等工作,研究了在0. 1,10,20,30,40,50MPa压力下,革兰氏阳性细菌Bacillus subtilis磷脂脂肪酸碳、氢同位素特征。结果表明:(1)高压下(≥10MPa)支链与单不饱和脂肪酸氢同位素分馏随生长压力上升负偏趋势减弱,并与压力之间存在明显线性相关性。(2)高压下(≥10 MPa),支链与饱和脂肪酸的碳同位素分馏随压力上升而负偏趋势减弱,也与生长压力存在明显线性关系,并且,单不饱和脂肪酸δ13C保持稳定。由于压力促进了氢从NADPH向脂肪酸转化的效率,使反应更加完全,分馏效应减弱。因为碳、氢同位素分馏受压力控制,故而在研究深海有机物来源、转运、循环,尤其是深渊生物地球化学时,应充分评估:(1)稳定同位素分馏对生长压力的依赖;(2)嗜高压微生物对海底沉积物中有机物同位素组成的改造。     

Desorption of H from Si(111) by resonant excitation of the Si-H vibrational stretch mode

Past efforts to achieve selective bond scission by vibrational excitation have been thwarted by energy thermalization. Here we report resonant photodesorption of hydrogen from a Si(111) surface using tunable infrared radiation. The wavelength dependence of the desorption yield peaks at 0.26 electron volt: the energy of the Si-H vibrational stretch mode. The desorption yield is quadratic in the infrared intensity. A strong H/D isotope effect rules out thermal desorption mechanisms, and electronic effects are not applicable in this low-energy regime. A molecular mechanism accounting for the desorption event remains elusive.     

Excitation of surface waves by events in southern algeria

Surface-wave magnitudes (M(8)) of 4.1 and 3.2 are determined for two events in southern Algeria. The corresponding body-wave magnitudes (m(b)) are 5.8 and 4.9, respectively. The surface waves from these events are much smaller than would be expected from most earthquakes of comparable body-wave magnitudes, which fact suggests that these waves were generated by underground explosions.     

Imaging surface atomic structure by means of auger electrons

Measurements of the complete angular distribution of Auger electrons emitted from well-defined platinum[111] single-crystal surfaces have led to the discovery that the distributions are composed of "silhouettes" of surface atoms "back lit" by emission from atoms deeper in the solid. Theoretical simulations of Auger electron angular distributions based upon atomic point emitters and spherical atomic scatterers of uniform cross section are in close agreement with these experimental results, but opposite to previous theoretical predictions. In view of the definitive results obtained and the straightforward agreement between theory and experiment, angular distribution Auger microscopy (ADAM) is useful for direct imaging of interfacial structure and investigation of electron-solid interactions in the physical and biological sciences and engineering. Applicability of ADAM is illustrated by images obtained for monolayers of silver and iodine on platinum[111].