雨滴击溅与薄层水流混合侵蚀的输沙机理

【目的】针对雨滴击溅与薄层水流混合侵蚀过程输沙机理研究中存在的问题,研究雨滴击溅对坡面径流输沙的影响。【方法】采用室内人工模拟降雨试验,以土娄土、黄绵土和黑垆土为供试土壤,在不同雨滴直径(直径2.22,2.68和3.04mm)、不同坡度(0°,2°和4°)和薄层水流厚度(0,2,4和6mm)条件下,分析单雨滴击溅时,泥沙溅蚀量与水层厚度的关系;多雨滴击溅时,泥沙溅蚀量与薄层水流厚度的关系,分别对二者关系进行拟合;同时,对于多雨滴击溅时,不同薄层水流厚度下黄绵土泥沙溅蚀量和雨滴动能的关系进行了分析。【结果】单雨滴击溅时,泥沙溅蚀量随水层厚度的增加而减少,且雨滴直径越大其扰动水层厚度越大,当雨滴直径由2.22mm增加到3.04mm时,平均扰动水层厚度由10mm增加到14.67mm。多雨滴击溅时,在相同的坡度(0°~4°),不同土壤和雨滴直径下,随薄层水流厚度的增加,泥沙溅蚀量呈先升后降趋势;当薄层水流厚度相同时,随雨滴直径的增加,泥沙溅蚀量呈增大趋势。当雨滴动能不变时,泥沙溅蚀量随着薄层水流厚度的增加而增大;当薄层水流厚度一定时,泥沙溅蚀量随雨滴动能的增加而增大。【结论】建立了单雨滴击溅和多雨滴击溅条件下扰动水层厚度关与泥沙溅蚀量的关系式。     

Seismic potential revealed by surface folding: 1983 coalinga, california, earthquake

The 2 May 1983 Coalinga, California, earthquake (magnitude 6.5) failed to rupture through surface deposits and, instead, elastically folded the top few kilometers of the crust. The subsurface rate of fault slip and the earthquake repeat time are estimated from seismic, geodetic, and geologic data. Three larger earthquakes (up to magnitude 7.5) during the past 20 years are also shown to have struck on reverse faults concealed beneath active folds.     

The onshore transport of an oil spill by internal waves

Internal waves generated by tidal currents concentrated and transported an oil spill (liquid asphalt) onshore. Plankton net samples were collected in front of and behind a set of internal waves as well as in the convergence and divergence zones over the waves. Tar "balls" were most abundant (greater than 30-fold) in the samples from the convergence zone. Comparison of the abundance of tar balls in front of and behind the set of waves suggests that the internal waves "caught" about 68% of the asphalt encountered and concentrated and swept shoreward tar balls from almost 8 kilometers of ocean.     

Apollo 11 drive-tube core samples: an initial physical analysis of lunar surface sediment

Two drive-tube core samples were obtained at Tranquillity Base. Fines include much glass, are unweathered, medium gray, loose, nonstructured, very weakly coherent, and demonstrate both accumulation and mixing in a waterless vacuum environment. In contrast to chemical weathering characteristic on the earth, lunar alteration processes are primarily mechanical. We infer that environmental processes of the lunar surface may be expressed as follows: R (regolith) = f(cl, p, r, t, b, a, . . .), in which climate (cl) is constant and the time (t)-de-pendent processes of bombardment (b) and accumulation (a) assume significance unparalleled on the earth because of their effects on parent material (p) and relief (r).     

Observation of charge transport by negatively charged excitons

We report transport of electron-hole complexes in semiconductor quantum wells under applied electric fields. Negatively charged excitons (X-), created by laser excitation of a high electron mobility transistor, are observed to drift upon applying a voltage between the source and drain. In contrast, neutral excitons do not drift under similar conditions. The X- mobility is found to be as high as 6.5 x 10(4) cm2 V-1 s-1. The results demonstrate that X- exists as a free particle in the best-quality samples and suggest that light emission from opto-electronic devices can be manipulated through exciton drift under applied electric fields.     

四川省江安县某硫铁矿区周边农田土壤重金属来源解析及污染评价

目的确定在云南兰坪铅锌矿周边污染农田种植万寿菊的最佳密度。方法种植万寿菊F1品种,研究不同种植密度(27 800、33 300、41 700 和55 600 株/hm²) 对万寿菊生长和镉铅累积特征的影响。结果 (1) 万寿菊生物量以茎部最大;镉含量在盛花期表现为茎>根>叶≈花,在成熟期表现为根≈茎>叶>花;铅含量在盛花期和成熟期表现为根≈叶>茎>花;镉铅主要累积在茎部。(2) 4个种植密度下,万寿菊单株生物量、单株镉铅含量以27 800和33 300 株/hm²种植密度最大,单位面积镉铅累积量以55 600 株/hm²最大。(3)土壤镉的化学形态以可氧化态和弱酸提取态为主;土壤铅的化学形态以可氧化态、可还原态和残渣态为主;万寿菊镉铅含量与土壤镉铅化学形态间的相关性不显著(P>0.05)。结论万寿菊可用于云南高原铅锌矿区污染农田的替代种植,为矿区污染农田的农业安全利用提供新方法。     

Structure of a eukaryotic CLC transporter defines an intermediate state in the transport cycle

CLC proteins transport chloride (Cl(-)) ions across cell membranes to control the electrical potential of muscle cells, transfer electrolytes across epithelia, and control the pH and electrolyte composition of intracellular organelles. Some members of this protein family are Cl(-) ion channels, whereas others are secondary active transporters that exchange Cl(-) ions and protons (H(+)) with a 2:1 stoichiometry. We have determined the structure of a eukaryotic CLC transporter at 3.5 angstrom resolution. Cytoplasmic cystathionine beta-synthase (CBS) domains are strategically positioned to regulate the ion-transport pathway, and many disease-causing mutations in human CLCs reside on the CBS-transmembrane interface. Comparison with prokaryotic CLC shows that a gating glutamate residue changes conformation and suggests a basis for 2:1 Cl(-)/H(+) exchange and a simple mechanistic connection between CLC channels and transporters.     

Chelation of calcium by lactose: its role in transport mechanisms

Lactose, like other sugars and polyols, prevents or delays the precipitation of calcium ion in the presence of bicarbonate buffer. That an uncharged calcium-lactose complex is formed was demonstrated by the use of paper electrophoresis and of calcium-45 as a label for the complex. Enhancement of the intestinal absorption of calcium ion by sugars could result from a complex of low molecular weight.     

Estrus-inducing pheromone of male mice: transport by movement of air

The proportion of female SJL/J mice exhibiting estrus whet 2 meters downwind (6 meters per minute) from a group of 15 hybrid mi not significantly less than that of females placed directly under the males posed to their urine. The proportion of mice showing estrus when placed 2 upwind was significantly less than that of mice downwind or of mice beloii but not different from that of females remote from males. These findings sh the pheromone from male mice is volatile and further support the concep, acts through olfactory receptors.     

Rapid and precise down regulation of fast axonal transport of transmitter in an identified neuron

Within 1 day after the removal of one branch of the bifurcated axon of an identified neuron in Aplysia, the cell body reduced its output of transmitter storage vesicles to adjust precisely for the decreased need. This adjustment terminated the initial consequence of the removal, the transport of an inappropriately large number of vesicles to the remaining synapses. The most likely cause of the reduction of transport of transmitter is the loss of information normally provided by the disconnected axon or synapses.     

Familial hypophosphatemic rickets: defective transport of inorganic phosphate by intestinal mucosa

Uptake of inorganic phosphate is impared in intestinal mucosa from hemizygous males and heterozygous females with X-linked familial hypophosphatemic rickets. Considerable intrafamilial and interfamilial variation in uptake of inorganic phosphate is observed in affected patients. Uptake by normal mucosa is concentrative and energy-dependent, and is mediated by at least two systems with widely different affinities. These results lend direct support to the thesis that the primary metabolic disturbance in this disease results from impaired transport of inorganic phosphate in kidney and gut.     

Predictable upwelling and the shoreward transport of planktonic larvae by internal tidal bores

Internal tidal bores have a crucial role in the transport of drifting larvae to marine nearshore populations, a key factor in structuring benthic communities. Shoreward transport of larvae and abrupt surface temperature drops lasting days can be explained by invoking the advection of subsurface cold water to the shore by internal tidal bores. This process is predictable within the lunar cycle and brings deep water to the surface (upwelling) in a direction perpendicular to the coastline.     

旱地、一水地玉米覆膜制种技术与推广前景分析

赤峰地区旱地、一水地面积占耕地总面积的60％以上，主要集中在山区贫困村，种植的作物也都是低产、低效的杂粮、杂豆作物。产量在70～150kg／667m^2。2000年开始推广旱地、一水地覆膜繁制玉米杂交种的技术。到2002年推广面积达2620hm^2，平均产量320．1kg／667m^2，与种植杂粮、杂豆相比，增加产值690．11元／667m^2．纯增加收入517．22元／667m^2。旱地、     

Distribution of mating types and genetic diversity induced by sexual recombination in Setosphaeria turcica in northern China

Mature ascocarps and ascospores in the heterothallic ascomycete fungus, Setosphaeria turcica, were successfully produced in Sach’s medium with barley culm as the mating stimulator after four weeks’ coincubation of two opposite mating type isolates at 25°C in darkness. A single isolate could not produce ascospores or ascocarps. The ascocarps were produced on the exposed surface and embedded parts of barley culm or in the upper layer of the medium. The asci linked themselves to ascocarp with their short handles and assembled at the bottom of the ascocarp. Many asci had four to six colorless mature ascospores with one to six septa. But asci with eight ascospores were also found. Using isolate 9914 and isolate 9961 as standard testers for mating types (MAT1 and MAT2), respectively, 94 isolates of S. turcica collected from northern China in 1999, 2003, and 2004 were grouped into three mating types: MAT1 (53 isolates), MAT2 (31 isolates) and MAT12 (10 isolates). The MAT12 isolates, which were first found in China, were compatible with not only MAT1 isolates but also MAT2 isolates. No MAT12 isolates were found in 1999, but 2 MAT12 isolates and 8 MAT12 isolates were found in 2001 and 2003, respectively. The geographic distribution of different mating types was unequal among locations. Generally the frequency of MAT1 was significantly higher than that of MAT2 and MAT12. The unequal distribution of mating types suggested a low frequency of genetic recombination. The pathogenicity of different mating type isolates was tested on the susceptible corn inbred B37 and the results revealed that the disease latency period, disease incidence, lesion area and conidia production were not significantly different among the three mating type groups. However, the pathogenicity of the progeny isolates of isolate 99-12 (MAT2, race 1) and isolate 99-15 (MAT1, race 0) was significantly different from the parent isolates, isolate 99-12 and isolate 99-15, suggesting that sexual recombination could cause significantly virulence variation in S. turcica. Random amplification of polymorphic DNA (RAPD) analysis also revealed high genotype diversity among the progeny isolates, indicating that the sexual recombination could also produce significant genetic variation in the fungal pathogen.     

Binding of alkali metal ions by cyclic polyethers: significance in ion transport processes

Values for the formation constant (log K), the change in enthalpy (triangle upH degrees ), and the change in entropy (triangle upS degrees ) have been determined for the interaction of lithium, sodium, potassium, rubidium, and cesium ions with the two isomers of the cyclic polyether, 2,5,8,15,18,21-hexaoxatricyclo[20.4.0.0(9,14)] hexacosane. The stability order of these metal ions with either isomer is identical to the permeability order for these same metal ions with the structurally related antibiotics, valinomycin and monactin.     

Transformation by v-sis occurs by an internal autoactivation mechanism

Transformation by the v-sis oncogene appears to require an interaction of its protein product, p28v-sis, with the receptor for the platelet-derived growth factor (PDGF). However, this interaction may not occur at the cell surface as predicted by the autocrine hypothesis because phenotypic transformation was not reversed by incubation of SSV-NRK cells with antisera to PDGF and because morphological transformation did not occur when nontransformed NRK cells were cultured continuously with p28v-sis. A mutant of the wild-type v-sis gene was constructed that encodes a v-sis protein targeted for retention within the endoplasmic reticulum and Golgi. NRK cells expressing the mutant v-sis gene did not secrete any detectable v-sis protein but were as fully transformed as wild-type v-sis transfectants. The results support a mechanism of transformation by v-sis in which internal activation of the PDGF receptor occurs before expression of either p28v-sis or the PDGF receptor at the cell surface.     

ES细胞囊胚注射后脱透明带移植对小鼠产仔率和嵌合率的影响

[目的]提高ES细胞囊胚注射的移植出生率。[方法]对照组采用正常囊胚ES细胞注射,试验组注射后的囊胚经酸性台氏’液消化透明带后直接移植,研究Es细胞囊胚注射后脱透明带移植对小鼠产仔率和嵌合率的影响。[结果]对照组产仔率为15．96％,嵌合率为57．89％。试验组小鼠产仔率为17．95％,嵌合率为57．14％,出生率提高2％。[结论]嵌合率无显著差异,酸性台氏液消化透明带的方法可简化操作流程。     

黄土高原植物根系增强土体抗剪强度的模型与试验研究

为研究黄土高原植物根系固土力学机制,通过Wu & Waldron(WWM)模型和Fiber Bundle(FBM)模型, 确定了黄土高原地区主要造林树种油松、刺槐、荆条和丁香4种植物根系对土体抗剪强度的增强作用,并用原位直剪试验对其进行了验证。应用ABAQUS有限元软件构建造林边坡稳定性分析模型,通过数值模拟的方法从边坡尺度上量化4种不同植物根系固土作用。结果表明:通过原位直剪试验的验证,发现评价植物根系对土体抗剪强度增强作用的WWM、FBM模型均存在一定的误差,因而建议进一步完善该理论模型。同时,基于原位直剪试验测定的根系对土体抗剪强度的增强作用,进行边坡稳定性分析,发现4种植物造林边坡稳定性均高于裸坡,边坡安全系数平均提高4.38%,最大等效塑性应变平均减小50.08%,最大水平位移平均减小40.83%,最大竖向位移平均减小14.84%;4种植物措施中,荆条造林措施对浅表层土体的固土效果最佳。研究结论为评价造林边坡的稳定性,揭示根系固土的力学机理提供理论基础和科学依据。