The infrared absorption cross-sections for eight commonly used halogenated methanes and ethanes have been measured as a function of temperature from 203 to 293 K. High resolution spectra (0.03 cm-1) have been used to derive integrated band strengths and peak cross-sections associated with the spectral features in the infrared region from 600 to 1500 cm-2. The values obtained in this study are compared to those from previous reports, and recommendations are made for uses in atmospheric sensing and radiative energy transfer models. The observed temperature dependence in the spectral features is also discussed. 相似文献
Craters in the 0.4 mm and larger size class were observed on six Apollo 12 whole rock surfaces (12017, 12021, 12038, 12047, 12051 and 12073). Craters on crystalline surfaces are characterized by a central, glass-lined cavity, a concentric zone of shock fractured, high albedo material and a concentric spallation area. The crater geometries observed are similar to craters produced on glasses and crystalline materials in the laboratory with projectile velocities exceeding 10 km/sec. The high projectile velocities required and the presence of a distinct demarcation line between cratered and uncratered surfaces on individual rocks indicate that most of the microcraters are produced by primary cosmic particles. These discrete impact events account for most of the erosion and fragmentation of lunar surface rocks. 相似文献
This report looks at how the lengths of Dover sole can vary according to handling after death and the method of measurement. The work described is part of the UK Ministry of Agriculture, fisheries and food programme. 相似文献
An examination of split core photographs from the north-central Pacific reveals the presence of three different burrow morphologies. Simple burrows occur throughout the region. Halo burrows are present in water deeper than 4,000 m (3,000 m along the equator) and removed from continental areas. Imbricate burrows are uncommon and have an irregular distribution. Organisms responsible for the burrows are interpreted as surface to near-surface feeders which do not penetrate deeply into the sediments. Thus, the zone of sediment mixing caused by burrowing ranges from 10 to 30 cm and averages 20 cm. 相似文献
In the last few years it has frequently been suggested that Ba is a useful indicator of paleoproductivity. The formation of some sapropels in the Eastern Mediterranean is considered to be related to, or to coincide with, periods of enhanced productivity. A high-resolution sampling study has been undertaken in order to investigate whether the Ba distribution in sapropels reflects a primary input signal or whether it has been altered by diagenetic processes.
On the basis of our results we suggest that three diagenetic stages determine the distribution of Ba. During deposition of the sapropel (stage 1) Ba is mobilized as anoxic conditions prograde. After deposition of the sapropel (stage 2), a progressive oxidation front develops. This front induces the formation of Mn and Fe enrichments and barite precipitation at the oxic/anoxic boundary. Barite precipitation is believed to be caused mainly by a rise in the porewater sulphate concentration after sulphides have been oxidized by the front.
Upon burial (stage 3), suboxic conditions develop as the oxygen becomes exhausted again. In contrast to Fe- and Mn-oxyhydroxides which dissolve and reprecipitate at higher levels, barite is preserved because dissolved sulphate is not depleted.
The interpretation of the Ba distribution in organic-rich sediment is not straightforward. Diagenetic reallocation of a primary Ba signal will possibly disturb the relationship between Ba and organic production. Consequently, one must be very cautious when invoking Ba as a paleoproductivity indicator. 相似文献
Two cores recovered in the eastern Mediterranean were analysed for major, minor and trace elements. The primary chemical composition of the sediment is different at each location, probably because the lithological sources and the relative biogenic contributions differ.
Carbonates are important for the concentration of Ca, Mg and Sr, whereas aluminosilicates determine the concentration of Si, Al, K, Li, Y and Be, and to a lesser extent that of Fe, Cr, Ti, Mg, Zn and Zr. In sapropels, organic carbon and sulphur seem to be closely related. Bromine, Mo, P, Fe, V, Cu, Zn, Co, Ni and Cr are closely associated with organic and sulphidic compounds. The concentration versus depth profile for organic carbon in two sapropels points to a rapid establishment of conditions that gave rise to sapropel formation, followed by a gradual transition back to “normal” conditions.
The primary composition is overprinted by diagenetic processes. Sulphate-reducing conditions occurred during and just after sapropel deposition. A progressive oxidation front mechanism, which became active after sapropel deposition, is responsible for additional major geochemical changes. This diagenetic phenomenon has strong implications for the chemistry of Fe, Mn, Ni, Co, Zn, Cu, Cr, V, U, As and Sb. 相似文献
Since the United States proclaimed its 200 nautical mile Exclusive Economic Zone in 1983, US agencies have given little attention to the need to develop effective management principles and strategies for the resources of this vast ocean area. Instead, they have relied upon existing programs and authorities to oversee the development of ocean energy and fisheries. This approach has been criticized by marine policy analysts because it perpetuates the existing, fragmented single-sector ocean regime characterized by inconsistent policies and endemic use conflicts.This paper proposes the adoption of certain principles deriving from the common law public trust doctrine in the management of EEZ resources and space. Historically, the public trust doctrine protected the public's rights and interests in nearshore resources and uses (commerce, navigation, and fishing). These traditional public rights were held by the crown or the government in trust for the people and could not be readily destroyed even though shorelands and coastal waters subject to the public trust might be conveyed into private ownership. In modern times the doctrine has been expanded in the United States to protect public rights in other uses and activities (e.g. conservation, scenic and ecological values, and preservation of open space and habitat) and extended geographically to apply to inland rivers, streams, and lakes.The public trust doctrine already applies in many states to the space, resources, and uses of the territorial sea. Because of the overlap of EEZ and territorial sea resources and uses, this paper considers the advantages of applying public trust principles and concepts to managing the EEZ. These principles include the need to preserve trust lands, waters, and resources for public use and benefit. The doctrine also provides a basis for distinguishing between, and ranking, public uses of trust resources, and imposes both substantive and procedural standards against which the conduct of the govermental trustees of trust, resources may be measured.The authors contrast the public trust doctrine with the ‘public trust’ deriving from the property clause of the US Constitution, and conclude that the broad discretion afforded federal officals under the latter is inconsistent with effective environmental management. Finally, the authors recommend a set of ‘presumptions’ derived from public trust principles that federal courts might follow to resolve serious EEZ space and resource-use conflicts. 相似文献
The goal of this study is to understand the movement of unexploded ordnance that may become unburied and forced by currents. Symmetrical, smooth, finite-length, unrestrained cylinders were studied in steady, uniform flows over a range of Reynolds numbers in a smooth-bottomed, horizontal flume. The study uses PIV tracking methods in the laboratory to identify the movement of ordnance simulated by unrestrained cylinders. The PIV is supported with a numerical analysis using a RANS flow solver. The simulations showed that at low Reynolds numbers the cylinders should roll at speeds near 70% of the free-stream flow. 相似文献