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排序方式: 共有649条查询结果,搜索用时 15 毫秒
111.
The results of a 2007 survey of fishers, managers, scientists, and enforcement officials indicate that noncompliance is a significant problem in the Northeast multispecies groundfish (NEGF) fishery, as it has been for at least 20 years. The percent of total harvest taken illegally is estimated to be 12–24%, which is significantly higher than estimates of 6–14% in the 1980s. Thirty-seven percent of fishers, 61% of fishery managers and 80% of fishery enforcement staff believe that “the combined adverse impact of all violations on the health and manageability of fish resources” is significant, highly significant, or extremely significant. Many fishers believe that illegal fishing will prevent them from ever benefiting from stock rebuilding programs. 相似文献
112.
Recent studies have suggested that poikilothermic animals, such as fish, may represent a previously overlooked source of the faecal indicator bacteria (FIB) used for the assessment of water quality. However, quantitative studies of FIB in poikilotherms are scarce. We investigated the presence of FIB in the faeces of five freshwater fish species. E. coli and enterococci were detected in 71 and 76% of faecal samples, respectively. Concentrations were highly variable, with maximum concentrations (2.1?×?104 E. coli and 1.3?×?106 enterococci per gram of faecal material) up to four orders of magnitude higher than present in the water column. FIB were not detected in faecal samples from marine fish. Our findings suggest that FIB ingested from the environment may be capable of replication within the fish gut, making fish a potential source and transport mechanism for FIB in New Zealand freshwaters. This may have implications for water quality monitoring. 相似文献
113.
Jon Y. Landvik 《第四纪科学杂志》1994,9(1):81-92
A profile across the unglaciated coast of northeast Greenland at 77°N was studied with regard to the Quaternary stratigraphy and glacial history. The Germania Land peninsula is characterised by till-covered lower ground which contrasts sharply with the blockfields and extensive gelifluction deposits of its higher altitudes. Two glaciations are distinguished. The older one extended over the entire area and had its margin on the continental shelf. The younger one, of Late Weichselian age, reached the present coastline and several mountains and high plateaus on western Germania Land formed nunataks. The Late Weichselian glaciation was more extensive and occurred later on the Germania Land peninsula than on the coast further south. Radiocarbon dates suggest that the glacier margin rested to the east of the present coastline until ca. 10 000 yr BP. This correlates with the Late Weichselian Milne Land Stage, which is found as a late glacial readvance along the coast of East Greenland. A series of recessional moraines formed during the deglaciation were probably caused by glacier dynamics, as opposed to being of climatic origin. 相似文献
114.
Summary. Seismic travel times for extrema, zero-crossings, or entire body waves need to be determined precisely to one part in 103 or better in several varieties of seismic studies employing an impulsive artificial source. Examples are crosshole surveys which delineate rock crack distribution separating the holes and monitoring of crustal seismic travel times in earthquake precursor studies. A timing resolution of one part in 103 has been achieved previously using digitally recorded seismic data. These methods, however, do not use interpolation between digitized data points as a method to increase the timing resolution. We report travel-time determinations based on interpolation between digitized points which achieve a precision of two parts in 104 , a five-fold improvement over the existing methods. In addition, the effects of seismic noise on travel-time measurement have been compared for the extremum location, the unnormalized correlation, and the normalized correlation method. The following conclusions are drawn from this comparison: (1) the normalized correlation method provides an 18–55 per cent improvement in the standard deviation of the mean over the extremum location method, and (2) results as accurate as those by the normalized correlation can be obtained by the unnormalized correlation if a complete up-and-down swing of the waveform is used as the master trace and if the master trace is close to being sinusoidal. The advantage of the unnormalized correlation over the normalized correlation is speed; the unnormalized correlation is faster by a factor of 28 in computing time. 相似文献
115.
116.
James R. Vermilion Roger N. Clark Thomas F. Greene Jon F. Seamans William F. Yantis 《Icarus》1974,23(1):89-96
Analysis of three occultations of JII (Europa) by JI (Io) has resulted in a preliminary reflectivity map of JII for the hemisphere centered on longitude 324°, a measurement of 1483±20 km for the radius of JII, estimates of the event impact parameters, determination of the mid event times, and a visual geometric albedo, pν = 0.74, for JII. A fourth occultation light curve was used after derivation of the results to confirm their validity. 相似文献
117.
Marina Brozovi? Lance A.M. Benner Michael C. Nolan Christopher Magri Jon D. Giorgini Petr Pravec Julia Fang Michael W. Busch Daniel E. Reichart Joshua B. Haislip Joseph Jao Kenneth J. Lawrence 《Icarus》2011,216(1):241-256
We report radar, photometric, and spectroscopic observations of near-Earth Asteroid (136617) 1994 CC. The radar measurements were obtained at Goldstone (8560 MHz, 3.5 cm) and Arecibo (2380 MHz, 12.6 cm) on 9 days following the asteroid’s approach within 0.0168 AU on June 10, 2009. 1994 CC was also observed with the Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT) on May 21 and June 1-3. Visible-wavelength spectroscopy was obtained with the 5-m Hale telescope at Palomar on August 25. Delay-Doppler radar images reveal that 1994 CC is a triple system; along with (153591) 2001 SN263, this is only the second confirmed triple in the near-Earth population. Photometry obtained with PROMPT yields a rotation period for the primary P = 2.38860 ± 0.00009 h and a lightcurve amplitude of ∼0.1 mag suggesting a shape with low elongation. Hale telescope spectroscopy indicates that 1994 CC is an Sq-class object. Delay-Doppler radar images and shape modeling reveal that the primary has an effective diameter of 0.62 ± 0.06 km, low pole-on elongation, few obvious surface features, and a prominent equatorial ridge and sloped hemispheres that closely resemble those seen on the primary of binary near-Earth Asteroid (66391) 1999 KW4. Detailed orbit fitting reported separately by Fang et al. (Fang, J., Margot, J.-L., Brozovic, M., Nolan, M.C., Benner, L.A.M., Taylor, P.A. [2011]. Astron. J. 141, 154-168) gives a mass of the primary of 2.6 × 1011 kg that, coupled with the effective diameter, yields a bulk density of 2.1 ± 0.6 g cm−3. The images constrain the diameters of the inner and outer satellites to be 113 ± 30 m and 80 ± 30 m, respectively. The inner satellite has a semimajor axis of ∼1.7 km (∼5.5 primary radii), an orbital period of ∼30 h, and its Doppler dispersion suggests relatively slow rotation, 26 ± 12 h, consistent with spin-orbit lock. The outer satellite has an orbital period of ∼9 days and a rotation period of 14 ± 7 h, establishing that the rotation is not spin-orbit locked. Among all binary and triple systems observed by radar, at least 25% (7/28) have a satellite that rotates more rapidly than its orbital period. This suggests that asynchronous configurations with Protation < Porbital are relatively common among multiple systems in the near-Earth population. 1994 CC’s outer satellite has an observed maximum separation from the primary of ∼5.7 km (∼18.4 primary radii) that is the largest separation relative to primary radius seen to date among all 36 known binary and triple NEA systems. 1994 CC, (153591) 2001 SN263, and 1998 ST27 are the only triple and binary systems known with satellite separations >10 primary radii, suggesting either a detection bias, or that such widely-separated satellites are relatively uncommon in NEA multiple systems. 相似文献
118.
Stephanos P. Kilias Jon Naden Ioannis Cheliotis Thomas J. Shepherd Heleni Constandinidou John Crossing Ioannis Simos 《Mineralium Deposita》2001,36(1):32-44
The Profitis Ilias gold deposit, located on the western part of Milos Island, Greece, is the first epithermal gold deposit
discovered in the Pliocene–Pleistocene Aegean volcanic arc. Estimated ore reserves are 5 million tonnes grading 4.4 g/tonne
Au and 43 g/tonne Ag. The deposit is closely associated with a horst and graben structure, and occurs in a series of steep
interconnected crustiform-banded quartz veins up to 3 m wide, extending to depths of at least 300 m. The mineralisation occurs
in three stages and is hosted by 3.5–2.5 Ma old silicified and sericitised rhyolitic lapilli-tuffs and ignimbrites. It consists
of pyrite, galena, chalcopyrite, electrum and native gold. Additionally, adularia occurs with quartz mainly in veins. Homogenisation
temperatures of primary liquid-rich inclusions vary from 145 to 399 °C for the ore stage, and 112 to 263 °C for the post-ore
stage. Salinities range between 0.1 and 11.4 wt% NaCl equiv. and 0.93 to 8.5 wt% NaCl equiv. for the ore stage and the post-ore
stage, respectively. Rare vapour-rich inclusions in ore stage quartz homogenise between 368 and 399 °C and estimates of eutectic
melting (−25 to −38 °C) indicate the presence of Ca and Mg in the ore fluids. Sample elevation versus fluid inclusion Th–salinity relationships show (1) a high-salinity trend, where moderate-temperature (300–250 °C) and moderate-salinity brines
(∼3 wt% NaCl equiv.) trend to high-salinity (up to 15 wt% NaCl equiv.) fluids with lower (∼25–50 °C) homogenisation temperatures,
and (2) a high-Th trend where moderate-salinity and moderate-temperature brines (200–250 °C; 3 wt% NaCl equiv.) develop into low-salinity (<1 wt%
NaCl equiv.), high-temperature (>350 °C) fluids. These trends are best explained by extreme boiling and vapourisation phenomena
between 200 and 250 °C. The 430–450 m asl (metres above sea level) level marks the transition between a lower liquid-dominated
segment of the system where only the steep high-salinity trend is seen, and an upper vapour-dominated segment where the high-Th trend or a combination of both are seen. There is a close spatial association between mineable gold grades and the upper
segment of the system. Depth-to-boiling curves suggest that the paleo-surface was ∼200 m above the present summit of Profitis
Ilias. Comparison of the mineralisation and fluid geochemistry at Profitis Ilias with that of the nearby modern geothermal
system indicates that the processes of metal mineralisation have probably been continuous since the Late Pliocene.
Received: 24 February 2000 / Accepted: 15 July 2000 相似文献
119.
Our study investigates possible formation mechanisms of the very recent bright gully deposits (BGDs) observed on Mars in order to assess if liquid water was required. We use two models in our assessment: a one-dimensional (1D) kinematic model to model dry granular flows and a two-dimensional (2D) fluid-dynamic model, FLO-2D (O’Brien et al., 1993, FLO Engineering), to model water-rich and wet sediment-rich flows. Our modeling utilizes a high-resolution topographic model generated from a pair of images acquired by the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter. For the 1D kinematic modeling of dry granular flows, we examine a range of particle sizes, flow thicknesses, initial velocities, flow densities, and upslope initiation points to examine how these parameters affect the flow run-out distances of the center of mass of a flow. Our 1D modeling results show that multiple combinations of realistic parameters could produce dry granular flows that travel to within the observed deposits’ boundaries. We run the 2D fluid-dynamic model, FLO-2D, to model both water-rich and wet sediment-rich flows. We vary the inflow volume, inflow location, discharge rate, water-loss rate (water-rich models only), and simulation time and examine the resulting maximum flow depths and velocities. Our 2D modeling results suggest that both wet sediment-rich and water-rich flows could produce the observed bright deposits. Our modeling shows that the BGDs are not definitive evidence of recent liquid water on the surface of Mars. 相似文献
120.
Torkild Bakken Jon Anders Kongsrud Eivind Oug Sabine K.J. Cochrane Toril Loennechen Moen & Beata E.B. Solbakken 《Polar research》2010,29(1):1-21
A thorough literature review has been undertaken to establish the first complete account of polychaetes recorded from the area around the volcanic island of Jan Mayen. The annotated checklist lists 121 species-level taxa, representing an increase from the 75 species previously recorded. The checklist is based on existing records, supplemented with material sampled in 1999, from which 42 species new to the area were reported. Some previously reported species from the area have been excluded because of inadequate documentation. The polychaete fauna of Jan Mayen is comparable with that of the mainland Norwegian coast and the Svalbard area. No taxa unique to the island were found. However, knowledge of the marine invertebrate fauna in general at Jan Mayen is sparse because few surveys have been undertaken there. It is expected that future expeditions will reveal further new taxon records for the area. 相似文献