AMERICAN GEOGRAPHERS AND CHINA     

Jack F. Williams 《The Professional geographer》1969,21(5):354-357

  相似文献   

Variability in the lengths of Dover sole (Solea solea) after death     

Jack Lavety 《Marine Policy》1987,11(4)

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   

Burrow morphologies in north-central Pacific sediments     

Jack Donahue 《Marine Geology》1971

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   

Possible diagenetic mobilization of barium in sapropelic sediment from the eastern Mediterranean     

Bertil J. H. van Os  Jack J. Middelburg  Gert J. de Lange 《Marine Geology》1991,100(1-4):125-136

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   

Geochemistry of eastern Mediterranean sediments: Primary sediment composition and diagenetic alterations     

Peter A. Pruysers  Gert J. de Lange  Jack J. Middelburg 《Marine Geology》1991,100(1-4):137-154

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   

Sovereign rights and responsibilities: Applying public trust principles to the management of EEZ space and resources     

Jack H. Archer 《Ocean & Coastal Management》1992,17(3-4)

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   

Investigation of unrestrained cylinders rolling in steady uniform flows     

Jack E. Davis  Billy L. Edge  Hamn-Ching Chen 《Ocean Engineering》2007,34(10):1431-1448

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   

Characterization of random fields and their impact on the mechanics of geosystems at multiple scales     

Qiushi Chen  Andrew Seifried  José E. Andrade  Jack W. Baker 《国际地质力学数值与分析法杂志》2012,36(2):140-165

  相似文献   

Models of Jupiter's growth incorporating thermal and hydrodynamic constraints     

Jack J. Lissauer  Olenka Hubickyj  Gennaro D'Angelo  Peter Bodenheimer 《Icarus》2009,199(2):338-350

We model the growth of Jupiter via core nucleated accretion, applying constraints from hydrodynamical processes that result from the disk-planet interaction. We compute the planet's internal structure using a well tested planetary formation code that is based upon a Henyey-type stellar evolution code. The planet's interactions with the protoplanetary disk are calculated using 3-D hydrodynamic simulations. Previous models of Jupiter's growth have taken the radius of the planet to be approximately one Hill sphere radius, RH. However, 3-D hydrodynamic simulations show that only gas within ∼0.25RH remains bound to the planet, with the more distant gas eventually participating in the shear flow of the protoplanetary disk. Therefore in our new simulations, the planet's outer boundary is placed at the location where gas has the thermal energy to reach the portion of the flow not bound to the planet. We find that the smaller radius increases the time required for planetary growth by ∼5%. Thermal pressure limits the rate at which a planet less than a few dozen times as massive as Earth can accumulate gas from the protoplanetary disk, whereas hydrodynamics regulates the growth rate for more massive planets. Within a moderately viscous disk, the accretion rate peaks when the planet's mass is about equal to the mass of Saturn. In a less viscous disk hydrodynamical limits to accretion are smaller, and the accretion rate peaks at lower mass. Observations suggest that the typical lifetime of massive disks around young stellar objects is ∼3 Myr. To account for the dissipation of such disks, we perform some of our simulations of Jupiter's growth within a disk whose surface gas density decreases on this timescale. In all of the cases that we simulate, the planet's effective radiating temperature rises to well above 1000 K soon after hydrodynamic limits begin to control the rate of gas accretion and the planet's distended envelope begins to contract. According to our simulations, proto-Jupiter's distended and thermally-supported envelope was too small to capture the planet's current retinue of irregular satellites as advocated by Pollack et al. [Pollack, J.B., Burns, J.A., Tauber, M.E., 1979. Icarus 37, 587-611].  相似文献   

Physical properties of (2) Pallas     

Benoît Carry  Christophe Dumas  Jérôme Berthier  Stéphane Erard  Jack D. Drummond  Marcello Fulchignoni 《Icarus》2010,205(2):460-472

Ground-based high angular-resolution images of asteroid (2) Pallas at near-infrared wavelengths have been used to determine its physical properties (shape, dimensions, spatial orientation and albedo distribution).We acquired and analyzed adaptive optics (AO) J/H/K-band observations from Keck II and the Very Large Telescope taken during four Pallas oppositions between 2003 and 2007, with spatial resolution spanning 32-88 km (image scales 13-20 km/pixel). We improve our determination of the size, shape, and pole by a novel method that combines our AO data with 51 visual light-curves spanning 34 years of observations as well as archived occultation data.The shape model of Pallas derived here reproduces well both the projected shape of Pallas on the sky (average deviation of edge profile of 0.4 pixel) and light-curve behavior (average deviation of 0.019 mag) at all the epochs considered. We resolved the pole ambiguity and found the spin-vector coordinates to be within 5° of [longitude, latitude] = [30°, −16°] in the Ecliptic J2000.0 reference frame, indicating a high obliquity of about 84°, leading to high seasonal contrast. The best triaxial-ellipsoid fit returns ellipsoidal radii of , and . From the mass of Pallas determined by gravitational perturbation on other minor bodies , [Michalak, G., 2000. Astron. Astrophys. 360, 363-374], we derive a density of significantly different from the density of C-type (1) Ceres of [Carry, B., Dumas, C., Fulchignoni, M., Merline, W.J., Berthier, J., Hestroffer, D., Fusco, T., Tamblyn, P., 2008. Astron. Astrophys. 478 (4), 235-244]. Considering the spectral similarities of Pallas and Ceres at visible and near-infrared wavelengths, this may point to fundamental differences in the interior composition or structure of these two bodies.We define a planetocentric longitude system for Pallas, following IAU guidelines. We also present the first albedo maps of Pallas covering ∼80% of the surface in K-band. These maps reveal features with diameters in the 70-180 km range and an albedo contrast of about 6% with respect to the mean surface albedo.  相似文献