The acraman impact structure: source of ejecta in late precambrian shales, South australia

A major probable impact structure occurs in middle Proterozoic dacitic volcanics in the Gawler Ranges, central South Australia. The structure has an inner depressed area about 30 kilometers in diameter that contains the Lake Acraman salina, an intermediate depression or ring about 90 kilometers in diameter, and a possible outer ring approximately 160 kilometers in diameter. Outcrops of dacite in Lake Acraman are intensely shattered and contain shatter cones and multiple sets of shock lamellac in quartz grains. The Acraman structure is the largest probable impact structure known in Australia and is the likely source of dacitic ejecta found in late Precambrian marine shales some 300 kilometers to the east.     

Photoprotection by carotenoids during photosynthesis: motional dependence of intramolecular energy transfer

A new carotenoporphyrin has been prepared in which a synthetic carotenoid is joined to a tetraarylporphyrin through a flexible trimethylene linkage. This molecule exists primarily in an extended conformation with the carotenoid chromophore far from the porphyrin pi-electron system. In benzene solution, where large-amplitude molecular motions are rapid, the molecule can momentarily assume less stable conformations which favor triplet energy transfer, and quenching of the porphyrin triplet by the carotenoid is fast. In a polystyrene matrix or frozen glass such motions are slow, and energy transfer cannot compete with other pathways for depopulating the triplet state. These observations help establish the requirements for biological photoprotection.     

Microtektites and mass extinctions: evidence for a late devonian asteroid impact

Glass spherules, similar to microtektites, have been found near the Frasnian-Famennian boundary (F/F) (Upper Devonian) at Senzeilles, Belgium, contemporaneous with one of the largest marine mass extinctions of the Phanerozoic. These spherules exhibit a wide range of compositions and display teardrop, dumbbell, and compound morphologies analogous to microtektites. In addition, they lack crystallites, have few or no vesicles, and have a low content of volatile material. These characteristics are supportive of an impact origin. The Siljan Ring (Sweden) and Charlevoix structure (Quebec,Canada) are candidate craters of this age. The presence of microtektites near the F/F boundary supports the hypothesis that an impact caused the Upper Devonian worldwide benthic mass extinctions.     

Free energy and temperature dependence of electron transfer at the metal-electrolyte interface

The rate constant of the electron-transfer reaction between a gold electrode and an electroactive ferrocene group has been measured at a structurally well-defined metal-electrolyte interface at temperatures from 1 degrees to 47 degrees C and reaction free energies from -1.0 to +0.8 electron volts (eV). The ferrocene group was positioned a fixed distance from the gold surface by the self-assembly of a mixed thiol monolayer of (eta(5)C(5)H(5))Fe(eta(5)C(5)H(4))CO(2)(CH(2))(16)SH and CH(3)(CH(2))(15)SH. Rate constants from 1 per second (s(-1)) to 2 x 10(4) s(-1) in 1 molar HClO(4) are reasonably fit with a reorganization energy of 0.85 eV and a prefactor for electron tunneling of 7 x 10(4) s(-1) eV(-1). Such self-assembled monolayers can be used to systematically probe the dependence of electron-transfer rates on distance, medium, and spacer structure, and to provide an empirical basis for the construction of interfacial devices such as sensors and transducers that utilize macroscopically directional electron-transfer reactions.     

要素价格变动影响农业能源效率的实证研究

运用协整分析、格兰杰因果关系检验、VAR模型、脉冲响应函数以及岭回归方法,研究要素价格变动对农业能源效率的影响。实证研究结果表明:能源要素、资本要素以及劳动力要素价格与农业能源效率存在长期的均衡关系。3种要素价格都是农业能源效率的格兰杰原因,而反向的格兰杰因果关系则不存在。能源价格和劳动力价格对能源效率产生正向影响,其上涨1%分别使能源效率提高0.341%和0.364%;而资本价格对能源效率的影响却相反,资本价格下降1%会可使能源效率提高0.084%。应进一步推进要素价格的市场化改革,形成有效的价格约束机制;同时应充分利用价格手段,加快农业产业结构升级,提高农业能源效率。     

Alcohol dependence and opiate dependence: lack of relationship in mice

According to a recently proposed hypothesis, physical dependence upon alcohol is due to the formation of an endogenous opiate. We tested the hypothesis by determining whether or not ethanol-dependent mice would show typical opiate-dependent behavior (withdrawal jumping syndrome) when challenged with the opiate antagonist naloxone. Our results do not support the hypothesis.     

Genes lost and genes found: evolution of bacterial pathogenesis and symbiosis

Traditionally, evolutionary biologists have viewed mutations within individual genes as the major source of phenotypic variation leading to adaptation through natural selection, and ultimately generating diversity among species. Although such processes must contribute to the initial development of gene functions and their subsequent fine-tuning, changes in genome repertoire, occurring through gene acquisition and deletion, are the major events underlying the emergence and evolution of bacterial pathogens and symbionts. Furthermore, pathogens and symbionts depend on similar mechanisms for interacting with hosts and show parallel trends in genome evolution.     

Mineral-produced high-pressure striae and clay polish: key evidence for nonballistic transport of ejecta from ries crater

Recently discovered mineral-produced, deeply incised striae and mirror-like polish on broken surfaces of limestone fragments from the sedimentary ejecta of the Ries impact crater of southern Germany are described. The striae and polish were produced under high confining pressures during high-velocity nonballistic transport of the ejecta mass within the time span of the cratering event (measured in terms of seconds). The striae on these fragments were produced by scouring by small mineral grains embedded in the surrounding clay matrix, and the polish was formed under the same condition, by movements of relatively fragment-free clay against the fragment surfaces. The occurrence of these striae and polish is key evidence for estimating the distribution and determining the relative importance of nonballistic and ballistic transport of ejecta from the shallow Ries stony meteorite impact crater.     

Acropetal movement of auxin: dependence on temperature

The amounts of radioactive indole-3-acetic acid that moved, both basipetally and acropetally, through short sections of bean epicotyl were measured at 15 degrees and 25 degrees C in the presence and absence of 2,3,5-triiodobenzoic acid. Low temperature and this second compound each inhibited acropetal efflux of indole 3-acetic acid more than they did the influx. Results are interpreted as supporting a metabolically dependent component of the acropetal movement of auxin in bean epicotyls.     

Climate response times: dependence on climate sensitivity and ocean mixing

The factors that determine climate response times were investigated with simple models and scaling statements. The response times are particularly sensitive to (i) the amount that the climate response is amplified by feedbacks and (ii) the representation of ocean mixing. If equilibrium climate sensitivity is 3 degrees C or greater for a doubling of the carbon dioxide concentration, then most of the expected warming attributable to trace gases added to the atmosphere by man probably has not yet occurred. This yet to be realized warming calls into question a policy of "wait and see" regarding the issue of how to deal with increasing atmospheric carbon dioxide and other trace gases.     

Developmental neuroethology: changes in escape and defensive behavior during growth of the lobster

The changes in relative efficacy of two incompatible behaviors was investigated during growth of the lobster, Homarus americanus. In larval and early juvenile stages, physiological and morphological factors favor use of the escape response over defensive behavior. In large animals, defensive behavior is preferred almost exclusively to escape behavior unless the claws are lost. The interaction of escape and defensive behavior is modified by neural and morphological factors, which are dependent on the stage in the life cycle of the organism.     

锶对人骨髓间充质干细胞增殖和成骨分化的影响

\t\t\t\t\t目的\t\t\t\t\t研究稳定性同位素锶对大豆抗氧化系统的影响。\t\t\t\t\t\t\t\t\t\t\t\t\t方法\t\t\t\t\t在1/2浓度Hoagland营养液培育的大豆中,用不同浓度(0.00、1.00、5.00、10.00、20.00和40.00 mmol/L)的SrCl₂溶液处理Vc期(单叶半展开,叶片的叶缘已分离),待大豆生长至V2期(单叶以上第一片复叶充分生长),分析不同浓度处理对大豆生长以及POD、SOD和CAT酶活性及同工酶的影响。\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t结果\t\t\t\t\tSrCl₂处理显著抑制大豆的生长(P<0.05),并随浓度升高抑制作用增强。0.00~10.00 mmol/L范围内SrCl₂处理大豆中POD酶活性迅速升高;此后,随浓度升高,POD酶活性逐渐降低。SrCl₂处理使SOD和CAT酶活性显著升高(P<0.05),并且在5.00 mmol/L达到最大;此后,随浓度升高,酶活性降低。SrCl₂处理大豆的SOD/POD、SOD/CAT和SOD/(POD+CAT)比值都显著降低(P<0.05)。POD同工酶在1.00和5.00 mmol/L SrCl₂处理时出现了1条新的同工酶谱带,但5.00 mmol/L以上浓度处理时POD同工酶谱带减少。SOD和CAT在SrCl₂处理时都出现了1条新的谱带。\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t结论\t\t\t\t\t大豆能够通过增强抗氧化酶活性来缓解SrCl₂造成的胁迫,然而SOD酶活性增强较小,是造成伤害的限制因素。SrCl₂处理能够影响不同类型的抗氧化同工酶表达。\t\t\t\t\t\t\t\t\t     

Noise-induced reduction of inner-ear microphonic response: dependence on body temperature

The rate of reduction of chinchilla cochlear microphonic response with exposure to steady noise is less at lower body temperatures and greater at higher body temperatures. Before exposure to noise, this auditory response is invariant within the range of temperatures employed. The mechanism of reduction of cochlear response appears to involve processes sensitive to body temperature.     

Deep-sea carbonates: dissolution and mass wasting on ontong-java plateau

Seismic reflection profiles and the structure of sediments in box cores from Ontong-Java Plateau indicate large-scale land sliding and sediment flow processes, respectively. The topographic morphology of sliding and slumping is depth- dependent, suggesting control by dissolution processes.     

Maize leaf elongation: continuous measurements and close dependence on plant water status

A simple method was developed for measuring extensive intact leaves of monocots on a minute-by-minute basis. Growth was markedly reduced by a slight reduction in leaf water potential. When plants mildly deficient in water were irrigated, growth resumed virtually instantly. The transitional rapid growth aftr watering suggests that water deficit increased cell extensibility.     

Nondependence of frequency on mass: a differential experiment

A differential Loran C experiment, which is independent of variations in clock rates, shows that the frequency of a radio transmission is not affected by the mass of the earth.