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921.
922.
HF ground-wave radar runs of roughly ten days duration were carded out in two tidally dominated regions off the Canadian East Coast in conjunction with oceanographic experiments. The surface current deduced from the HF radar observations are here compared with Eulerian velocities from various moored current meters and Lagrangian velocities derived from surface drifters. The agreement with the current meters is generally better than 0.05 m/s. Real current shear in the top 15 m of the water column of up to 0.1 m/s, lasting for up to 12 h, was observed on several occasions, coincident with wind reversals. The agreement between moored instruments and shallow-draft rectangular drifters was good, and with deeper draft cylindrical drifters it was excellent. 相似文献
923.
924.
Harold C. Connolly Caroline Smith Gretchen Benedix Luigi Folco Kevin Righter Jutta Zipfel Akira Yamaguchi Hasnaa Chennaoui Aoudjehane 《Meteoritics & planetary science》2007,42(9):1647-1694
Abstract— In this edition of The Meteoritical Bulletin, 1394 recognized meteorites are reported, 27 from specific locations within Africa, 133 from Northwest Africa, 1227 from Antarctica (from ANSMET, PNRA, and PRIC expeditions), and 7 from Asia. The Meteoritical Bulletin announces the approval of four new names series by the Nomenclature Committee of the Meteoritical Society, two from Africa and one from Asia, including Al Haggounia, from Al Haggounia, Morocco, which is projected to be on the order of 3 metric tons of material related to enstatite chondrites and aubrites. Approved are two falls from Africa, Bassikounou (Mauritania) and Gashua (Nigeria). Approved from areas other than Antarctica are one lunar, two Martian, 32 other achondrites, three mesosiderites, two pallasites, one CM, two CK, one CR2, two CV3, one CR2, and four R chondrites. The Nomenclature Committee of the Meteoritical Society announces 48 newly approved relict meteorites from two new name series, Österplana and Gullhögen (both from Sweden). 相似文献
925.
Colliding Blast Waves Driven by the Interaction of a Short-Pulse Laser with a Gas of Atomic Clusters
Roland A. Smith James Lazarus Matthias Hohenberger Alastair S. Moore Joseph S. Robinson Edward T. Gumbrell Mike Dunne 《Astrophysics and Space Science》2007,307(1-3):131-137
Collisions between shocks are commonly found in many astrophysical objects, however robust numerical models or laboratory
analogues of these complex systems remain challenging to implement. We report on the development of scaled laboratory experiments
which employ new techniques for launching and diagnosing colliding shocks and high Mach number blast waves, scalable to a
limited subset of astrophysically-relevant regimes. Use of an extended medium of atomic clusters enables efficient (>80%)
coupling of 700 fs, 1 J, 1054 nm laser pulses to a “cluster” gas with an average density of ≈1019 particles cm−3, producing an initial energy density >105 J cm−3, equivalent to ≈5×109 J/g. Multiple laser foci are used to tailor the spatial profile of energy deposition, or to launch pairs of counter-propagating
cylindrical shocks which then collide. By probing the collision interferometrically at multiple view angles in 5^ increments and applying an inverse Radon transform to the resulting phase projections we have been able to tomographicall
reconstruct the full three-dimensional, time-framed electron density profile of the system. 相似文献
926.
Abstract: This paper explores the impediments to optimizing the economic and environmental performance of agriculture in the North Island hill country. The work draws on a range of data sources including consolidated statistical data obtained from The New Zealand Meat and Wool Board's Economic Service (NZMWB) for all North Island hill and hard country farms for the period 1976–77 to 1996–97 and interviews in June and July 1999 with 35 farm households throughout the North Island. Despite generally low levels of profitability, there is considerable evidence that New Zealand farmers have engaged in moves to sustainability to a significant extent. 相似文献
927.
Guleid Artan Hussein Gadain Jodie L. Smith Kwabena Asante Christina J. Bandaragoda James P. Verdin 《Natural Hazards》2007,43(2):167-185
Floods are the most common and widespread climate-related hazard on Earth. Flood forecasting can reduce the death toll associated
with floods. Satellites offer effective and economical means for calculating areal rainfall estimates in sparsely gauged regions.
However, satellite-based rainfall estimates have had limited use in flood forecasting and hydrologic stream flow modeling
because the rainfall estimates were considered to be unreliable. In this study we present the calibration and validation results
from a spatially distributed hydrologic model driven by daily satellite-based estimates of rainfall for sub-basins of the
Nile and Mekong Rivers. The results demonstrate the usefulness of remotely sensed precipitation data for hydrologic modeling
when the hydrologic model is calibrated with such data. However, the remotely sensed rainfall estimates cannot be used confidently
with hydrologic models that are calibrated with rain gauge measured rainfall, unless the model is recalibrated.
G. Artan, J. L. Smith and K. Asante – work performed under USGS contract 03CRCN0001. 相似文献
928.
M. D. Roberts D. L. Reid J. A. Miller I. J. Basson M. Roberts D. Smith 《Mineralium Deposita》2007,42(3):271-292
The Merensky Reef of the Bushveld Complex occurs in its highest stratigraphic position as a heterogeneous, pegmatitic, feldspathic
melanorite bounded by two narrow chromitite stringers at the base of the Merensky Cyclic Unit (MCU). In the Swartklip Facies
of the Rustenburg Layered Suite, the occurrence of widespread thermal and mechanical erosion termed “potholing” has led to
the subdivision of the Merensky Reef into Normal Reef and Regional Pothole Reef sub-facies. The transition between the two
sub-facies occurs where the MCU transgresses the lower chromitite stringer of the Normal Merensky Reef and cuts down into
the underlying cumulate lithologies. In the Regional Pothole Reef at the Northam Platinum Mine, several economic reef types
are identified, where the Merensky Reef becomes conformable to cumulate layering, in particular, to the footwall marker (NP2
reef type) and the upper pseudoReef (P2 reef type). The Normal Merensky Reef, as well as the P2 and NP2 Reefs, contains economic
platinum group element (PGE) grades and includes the lower portion of the MCU melanorite and the Merensky Chromitite. Whole
rock geochemistry indicates that this package is compositionally identical in Normal, P2, and NP2 Reefs, suggesting that the
base of the MCU is a relatively homogeneous drape over both Normal and Regional Pothole Reef regions. However, the lower sections
of the three Reefs are variables depending on the depth of transgression of the MCU. In the Normal and P2 reef types, transgression
by the MCU was arrested within harzburgites, melanorites, and norites, resulting in coarse, pegmatitic textures in the immediate
footwall units. For the NP2 Reef, transgression by the MCU was arrested within leucocratic rocks and resulted in the formation
of troctolites below the Merensky Chromitite. These troctolites are characterised by a coupled relationship between olivine
and sulphides and by changes in major element chemistry and PGE contents relative to equivalent units in the footwall of the
Normal Reef. Along with micro-textural relationships, these features suggest that troctolization of leucocratic cumulates
in the NP2 Reef beneath the Merensky chromitite was a result of a reactive infiltration of a chromite-saturated melt and an
immiscible sulphide liquid from the overlying MCU, rather than a significant fluid flux from below. In all reef types, the
concentration of S defines symmetrical peaks centred on the Merensky Chromitite (and chromitites from pre-existing cyclic
units in Normal and P2 Reefs), whereas PGE concentrations define asymmetrical peaks with higher PGE contents in reconstituted
footwall rocks relative to the MCU melanorite. This signature is attributable to a magmatic model of PGE collection followed
by deposition towards the base of the MCU and within reconstituted footwall rocks. The continuity of the asymmetrical magmatic
PGE signature between the Normal Reef and Regional Pothole Reef sub-facies indicates that PGE mineralization inherent to the
Merensky magma occurred as a drape over a variably eroded and subsequent texturally and geochemically reworked or reconstituted
footwall. 相似文献
929.
The objective of this simulation study was to create an age-structured population model for horseshoe crabs (Limulus polyphemus) in the Delaware Bay region using best available estimates of age-specific mortality and recent harvest levels. Density dependence
was incorporated using a spatial model relating egg mortality with abundance of spawning females. Combinations of annual female
harvest (0, 50, 100, and 200 thousand), timing of female harvest (before or after spawning), and three levels of density-dependent
egg mortality were simulated. The probability of the population increasing was high (>80%) with low and medium egg mortality
and harvest less than 200 thousand females per year. Under the high egg mortality case, the probability of the population
increasing was <50% regardless of harvest. Harvest occurring after spawning increased the probability of population growth.
The number of eggs available to shorebirds was highest when egg mortality was lowest and female abundance was at its highest
levels. Although harvest and egg mortality influenced population growth and food availability to shorebirds, sensitivity and
elasticity analyses showed that early-life stage mortality, age 0 mortality in particular, was the most important parameter
for population growth. Our modeling results indicate areas where further research is needed and suggest effective management
will involve a combination of harvest management and actions to increase early juvenile survival. 相似文献
930.
James F. Humpula Hasand Gandhi Angela K. Walker James J. Smith R. George Corner 《Geochimica et cosmochimica acta》2007,71(24):5956-5967
Ancient DNA sequences offer an extraordinary opportunity to unravel the evolutionary history of ancient organisms. Protein sequences offer another reservoir of genetic information that has recently become tractable through the application of mass spectrometric techniques. The extent to which ancient protein sequences resolve phylogenetic relationships, however, has not been explored. We determined the osteocalcin amino acid sequence from the bone of an extinct Camelid (21 ka, Camelops hesternus) excavated from Isleta Cave, New Mexico and three bones of extant camelids: bactrian camel (Camelus bactrianus); dromedary camel (Camelus dromedarius) and guanaco (Llama guanacoe) for a diagenetic and phylogenetic assessment. There was no difference in sequence among the four taxa. Structural attributes observed in both modern and ancient osteocalcin include a post-translation modification, Hyp9, deamidation of Gln35 and Gln39, and oxidation of Met36. Carbamylation of the N-terminus in ancient osteocalcin may result in blockage and explain previous difficulties in sequencing ancient proteins via Edman degradation.A phylogenetic analysis using osteocalcin sequences of 25 vertebrate taxa was conducted to explore osteocalcin protein evolution and the utility of osteocalcin sequences for delineating phylogenetic relationships. The maximum likelihood tree closely reflected generally recognized taxonomic relationships. For example, maximum likelihood analysis recovered rodents, birds and, within hominins, the Homo-Pan-Gorilla trichotomy. Within Artiodactyla, character state analysis showed that a substitution of Pro4 for His4 defines the Capra-Ovis clade within Artiodactyla. Homoplasy in our analysis indicated that osteocalcin evolution is not a perfect indicator of species evolution. Limited sequence availability prevented assigning functional significance to sequence changes. Our preliminary analysis of osteocalcin evolution represents an initial step towards a complete character analysis aimed at determining the evolutionary history of this functionally significant protein. We emphasize that ancient protein sequencing and phylogenetic analyses using amino acid sequences must pay close attention to post-translational modifications, amino acid substitutions due to diagenetic alteration and the impacts of isobaric amino acids on mass shifts and sequence alignments. 相似文献