Temperature and its control of isotope fractionation by a sulfate-reducing bacterium

A synthesis of previous results, which we dub the “standard model,” provides a prediction as to how isotope fractionation during sulfate reduction should respond to physiological variables such as specific rate of sulfate reduction and environmental variables such as substrate availability and temperature. The standard model suggests that isotope fractionation should decrease with increasing specific rates of sulfate reduction (rate per cell). Furthermore, the standard model predicts that low fractionations should be found at both high and low temperatures whereas the highest fractionations should be found in the intermediate temperature range. These fractionation trends are controlled, as a function of temperature, by the balance between the transfer rates of sulfate into and out of the cell and the exchange between the sulfur pools internal to the organism. We test this standard model by conducting experiments on the growth physiology and isotope fractionation, as a function of temperature, by the sulfate-reducing bacterium Desulfovibrio desulfuricans (DSMZ 642). Our results contrast with the “standard model” by showing a positive correlation between specific rates of sulfate reduction and fractionation. Also by contrast with the standard model, we found the highest fractionations at low and high temperatures and the lowest fractionations in the intermediate temperature range. We develop a fractionation model which can be used to explain both our results as well as the results of the “standard model.” Differences in fractionation with temperature relate to differences in the specific temperature response of internal enzyme kinetics as well as the exchange rates of sulfate in and out of the cell. It is expected that the kinetics of these processes will show strain-specific differences.     

Structure of the crust and upper mantle beneath the central european rift system

The crustal structure of the central European rift system has been investigated by seismic methods with varying success. Only a few investigations deal with the upper-mantle structure. Beneath the Rhinegraben the Moho is elevated, with a minimum depth of 25 km. Below the flanks it is a first-order discontinuity, while within the graben it is replaced by a transition zone with the strongest velocity gradient at 20–22 km depth. An anomalously high velocity of up to 8.6 km/s seems to exist within the underlying upper mantle at 40–50 km depth. A similar structure is also found beneath the Limagnegraben and the young volcanic zones within the Massif Central of France, but the velocity within the upper mantle at 40–50 km depth seems to be slightly lower. Here, the total crustal thickness reaches only 25 km. The crystalline crust becomes extremely thin beneath the southern Rhônegraben, where the sediments reach a thickness of about 10 km while the Moho is found at 24 km depth. The pronounced crustal thinning does not continue along the entire graben system. North of the Rhinegraben in particular the typical graben structure is interrupted by the Rhenohercynian zone with a “normal” West-European crust of 30 km thickness evident beneath the north-trending Hessische Senke. A single-ended profile again indicates a graben-like crustal structure west of the Leinegraben north of the Rhenohercynian zone. No details are available for the North German Plain where the central European rift system disappears beneath a sedimentary sequence of more than 10 km thickness.     

The Middle Miocene to Recent Davis Strait Drift Complex: implications for Arctic�CAtlantic water exchange

A large-scale contourite drift complex has been recognised on multi-channel 2D reflection seismic data acquired in the south-eastern Davis Strait and adjacent Labrador Sea slope offshore West Greenland between 63°?C66°N. Based on well-tie data, the drift complex developed from the Middle Miocene to the Recent. It has been mapped in a wide variety of water depths ranging from about 700?m, at a NNW-ESE-elongated crest located above structural highs in the Davis Strait, to more than 2,000?m beyond the slope to the Labrador Sea. The overall drift geometry has been described by subdivision into two first-order seismic units, enabling the generation of time-isochore maps. The reflection patterns demonstrating current-related deposition are illustrated by seismic examples. The time-isochores of the two first-order seismic units show lateral changes in their depocentres: the lower unit is absent in a zone slightly displaced south-westwards of the present-day crest, indicating changes in the prevailing deepwater current system during the Early Pliocene. The observations can be explained by two alternative palaeoceanographic scenarios: (1) either the present-day oceanographic setting with Arctic?CAtlantic water exchange across the Davis Strait was largely established by the mid-Miocene, with only minor adjustments during the Early Pliocene caused by tectonic movements, or (2) it became established during the Early Pliocene as a consequence of enhanced northward flow across the Davis Strait due to lowering of the sill depth.     

小型激光天文动力学空间计划概念

小型激光天文动力学空间计划是 :使用在太阳轨道上无拖曳航天器和地面站以激光干涉和脉冲测距的方法 ,精确地探讨天文动力学 ,检测相对论与时空基本定律 ,改进探测引力波的灵敏度以及更准确地测定太阳、行星和小行星的参数。 1 969年开始的月球激光 (反射 )测距 ,对地球物理、参考坐标的选定、相对论的检验均有重要的贡献。 3 0年来 ,激光技术的长足进步 ,使现在正是适合于开始进行研究空间有源 (主动 )测距和光波空间通讯的时候。激光天文动力学的兴起是必然的趋势 ,其精确度将比现在提高 3到 6个数量级 ,将是天文动力学革命性的发展。小型激光天文动力学空间计划可以起到带头作用。它的关键技术有三 ,即 :弱光锁相、极精确无拖曳航天和高衰减日冕仪。弱光锁相已有长足的进步。对高衰减日冕仪的研究 ,也有了初步的方案。LISA空间计划将于 2 0 0 6年 8月发射SMART -2 ,研究测试极精确无拖曳航天。小型激光天文动力学空间计划的关键技术已日趋成熟。在第一届国际激光天文动力学研讨会 ( 2 0 0 1 ,9.1 3 -2 3 )中介绍了各相关学科背景及前沿研究 ,讨论了激光天文动力学空间计划科学目标及相关技术 ,并召开了两次小型激光天文动力学空间计划预研究筹备会 ,建立了和欧洲的合作关系。会后着手进行此项对基础     

The motion of a lunar satellite

Presented in this theory is a semianalytical solution for the problem of the motion of a satellite in orbit around the moon. The principal perturbations on such a body are due to the nonspherical gravity field of the moon, the attraction of the earth, and, to a lesser degree, the attraction of the sun. The major part of the problem is solved by means of the celebrated von Zeipel Method, first successfully applied to the motion of an artificial earth satellite by Brouwer in 1959. After eliminating from the Hamiltonian all terms with the period of the satellite and those with the period of the moon, it is suggested to solve the remaining problem with the aid of numerical integration of the modified equations of motion.This theory was written in 1964 and presented as a dissertation to Yale University in 1965. Since then a great deal has been learned about the gravity field of the moon. It seems that quite a number of recently determined gravity coefficients would qualify as small quantities of order two. Hence, according to the truncation criteria employed, they should be considered in the present theory. However, the author has not endeavored to update the work accordingly. The final results, therefore, are incomplete in the lunar gravitational perturbations. Nevertheless, the theory does give the largest such variations and it does present the methods by which perturbations may be derived for any gravity terms not actually developed.     

The 1s 2s states of negative hydrogen

Term values for the 1s 2s states of H^– are calculated with the use of simple eigenfunction approximations constructed on the basis of available Hartree-type functions for the 1s ² and 2s ² states of the ion. The results seem to support a tentative identification of the interstellar diffuse absorption bands at 4890 and 6180 as due to negative hydrogen.     

Seeing Conditions at Sutherland. Results of the 1992/93 seeing campaign

In order to decide whether the seeing conditions at SAAO/Sutherland justify the erection of a 3.5 m telescope and also to compare Sutherland with the Gamsberg/Namibia site, a seeing campaign covering 15 months has been carried out. For direct comparison with the results of the seeing campaign at Gamsberg twenty years before the same QUESTAR telescope was employed. The seeing is determined by the scattering of the star-trail exposed on a film in the focal plane of the telescope. The campaign commenced in February 1992. Up to May 1993, data for 204 nights, that is 47.3% of the total number of nights, were collected. Due to wind speeds above 30 km h^-1, 25 out of the 204 nights were not considered in the final reduction. The useful 179 nights are evenly distributed over the campaign period. The median seeing value for the whole period is = 0.52. There are differences during the year: the best season gives = 0.42, the worst = 0.67. Each night was divided into three intervals, although data for each of the three intervals were not always available. Generally, there is an improvement in the seeing during the course of a night. The results are compared to the seeing values of Gamsberg/Namibia and ESO/La Silla.     

Role of time variant and invariant terms on soil moisture spatio-temporal variability in a subhumid coastal wetland

The knowledge of soil moisture spatio-temporal variability is highly relevant for water resources management. This paper reports an analysis of the spatial–temporal variability of soil moisture data for a small to medium-scale soil-sensors network in a coastal wetland of southwestern Spain. Measurements were taken from five sites located in the Doñana National Park over the time-period of one hydrological year from September 2017 to September 2018. The total area of the soil-sensors network shows an extension about 25 × 3 km. Soil moisture data was separated into time invariant (the temporal mean of the whole period at each site) and time-variant terms (the deviations of soil moisture from the mean, or anomalies). The time-invariant component was generally the main contributor to the total spatial variance of soil moisture and it was mostly controlled by the groundwater levels in the area. Nevertheless, the time variant terms have a huge effect on soil moisture variability in very dry states. Characteristic convex time-dependent patterns for this field site were found between spatially averaged soil moisture and its variability. This information could be used for the up and downscaling of soil moisture from satellite data. Those patterns of relation between spatial mean and variability of soil moisture were only affected by heavy rainfalls giving rise to hysteretic behaviour. This study shows that even though groundwater level is a time-variant variable, it significantly affects soil moisture's time-variant but also time-invariant terms due to the different average groundwater level depths at the different sites.