Designation of a new genus <Emphasis Type="Italic">Bathymenes</Emphasis> for the deep-sea pontoniine shrimps of the ‘<Emphasis Type="Italic">Periclimenes alcocki</Emphasis> species group’ (Decapoda,Caridea, Palaemonidae), with a checklist of the species assigned to the genus     

寇琦  李新正 《中国海洋湖沼学报》2016,34(1):170-176

A new genus of the deep-sea pontoniine shrimps, Bathymenes gen. nov., is established for the ‘Periclimenes alcocki species group’ of the genus Periclimenes Costa, 1844. The new genus is distinguished from other genera of the Pontoniinae by a combination of characters: the posteriormost dorsal rostral tooth remote from other teeth, situated in the epigastric position, cornea usually reduced, the propodus of second pereiopods covered with fine granules, the dactylus of the major second chela being generally flanged, the ambulatory pereiopods with the dactyli being biunguiculate and telson with more than two pairs of dorsolateral spines. The genus is mainly distributed in the tropical to warm-temperate Indo-West Pacific waters at depths greater than 200 m. Fifteen species previously recognized as belonging to the ‘P. a lcocki species group’ are now placed in Bathymenes gen. nov. A key for their identification and a checklist of congeneric species are provided.  相似文献   

Infrared polarimetry and imaging of ultracompact partially ionized optical sources in the orion nebula     

Bruce McCollum  Michael W. Castelaz 《Astrophysics and Space Science》1995,224(1-2):509-510

Hubble Space Telescope images of the Orion nebula taken with the Wide-Field Camera have revealed subarcsecond structure in several dozen objects which are apparently ionized externally from nearby stars. We have obtained near-IR images and IR polarimetry of the Orion region to search for correlations with the WFC objects. We find that all of the ultracompact WFC objects are associated with IR features of some sort, and that some are associated with strongly polarized IR emission. The object with strongest polarization also shows small IR lobes. In addition, we find some previously unreported sources, showing polarized IR emission, outside the field of the HST images, which we believe may be the same sorts of object. We note that the object with strongest polarization has a double-lobed appearance in the K band image.  相似文献   

Generation of Icelandic rhyolites: silicic lavas from the Torfajökull central volcano     

Bjrn Gunnarsson  Bruce D. Marsh  Hugh P. Taylor Jr. 《Journal of Volcanology and Geothermal Research》1998,83(1-2)

The Torfajökull central volcano in south-central Iceland contains the largest volume of exposed silicic extrusives in Iceland (225 km³). Within SW-Torfajökull, postglacial mildly alkalic to peralkalic silicic lavas and lava domes (67–74 wt.% SiO₂) have erupted from a family of fissures 1–2.5 km apart within or just outside a large caldera (12×18 km). The silicic lavas show a fissure-dependent variation in composition, and form five chemically distinct units. The lavas are of low crystallinity (0–7 vol.%) and contain phenocrysts in the following order of decreasing abundance: plagioclase (An_10-40), Na-rich anorthoclase (<Or₂₃), clinopyroxene (Fs_37-20), FeTi oxides (Usp_32-60; Ilm_93-88), hornblende (edenitic–ferroedenitic) and olivine (Fo_22-37), with apatite, pyrrhotite and zircon as accessory phases. The phenocryst assemblage (0.2–4.0 mm) consistently exhibits pervasive disequilibrium with the host melt (glass). Xenoliths include sparse, disaggregated, and partially fused leucocratic fragments as well as amphibole-bearing rocks of broadly intermediate composition. The values of the silicic lavas are in the range 3.6–4.4, and these are lower than the values of comagmatic, contemporaneous basaltic extrusives within SW-Torfajökull, implying that the former can not be derived from the latter by simple fractional crystallization. FeTi-oxide geothermometry reveals temperatures as low as 750–800°C. To explain the fissure-dependent chemical variations, depletions, low FeTi-oxide temperatures and pervasive crystal-melt disequilibrium, we propose the extraction and collection of small parcels of silicic melt from originally heterogeneous basaltic crustal rock through heterogeneous melting and wall rock collapse (solidification front instability, SFI). The original compositional heterogeneity of the source rock is due to (1) silicic segregations, in the form of pods and lenses characteristically formed in the upper parts of gabbroic intrusives, and (2) extreme isostatic subsidence of the earlier, less differentiated lavas of the Torfajökull central volcano. Ridge migration into older crustal terranes, coupled with establishment of concentrated volcanism at central volcanoes like Torfajökull due to propagating regional fissure swarms, supplies the heat source for this overall process. Continued magmatism in these fissures promotes extensive prograde heating of older crust and the progressive vitality and rise of the central volcano magmatic system that leads to, respectively, SFI and subsidence melting. The ensuing silicic melts (with relict crystals) are extracted, collected and extruded before reaching complete internal equilibrium. Chemically, this appears as a two-stage process of crystal fractionation. In general, the accumulation of high-temperature basaltic magmas at shallow depths beneath the Icelandic rift zones and major central volcanoes, coupled with unique tectonic conditions, allows large-scale reprocessing and recycling of the low- , hydrothermally altered Icelandic crust. The end result is a compositionally bimodal proto-continental crust.  相似文献   

Introduction     

Bruce C. Heezen 《Tectonophysics》1970,10(5-6):473

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OSO-8 observations of the impulsive phase of solar flares in the transition-zone and corona     

Bruce W. Lites  E. C. Bruner Jr.  C. J. Wolfson 《Solar physics》1981,69(2):373-389

Several solar flares have been observed from their onset in C IV 1548.2 and 1–8 Å X-rays using instruments aboard OSO-8. In addition, microwave and H flare patrol data have been obtained for this study. The impulsive brightening in C IV is frequently accompanied by redshifts, interpreted as downflows, of the order of 80 km s^-1. The maximum soft X-ray intensity usually arrives several minutes after the maximum C IV intensity. The most energetic C IV event studied shows a small blueshift just before reaching maximum intensity, and estimates of the mass flux associated with this upflow through the transition-zone are consistent with the increase of mass in the coronal loops as observed in soft X-rays. This event had no observable microwave burst, suggesting that electron beams did not play a major role in the chromospheric and transition-zone excitation. Lastly, our observations suggest that the frequent occurrence of violent dynamical processes at the onset of the flare are associated with the initial energy release mechanism.Currently at High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, Colo. 80307, U.S.A.  相似文献   

ATLAS OF ALBERTA. Government of Alberta and the University of Alberta.     

R. Bruce  Rains 《New Zealand geographer》1972,28(1):104-105

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The Effects of Spatial Scale of Climate Scenarios on Economic Assessments: An Example from U.S. Agriculture     

Richard M. Adams  Bruce A. McCarl  Linda O. Mearns 《Climatic change》2003,60(1-2):131-148

The appropriate level of spatial resolution for climate scenarios is a key uncertainty in climate impact studies and regional integrated assessments. To the extent that such uncertainty may affect the magnitude of economic estimates of climate change, it has implications for the public policy debates concerning the efficiency of CO₂ control options. In this article, we investigate the effects that different climate scenario resolutions have on economic estimates of the impacts of future climate changeon agriculture in the United States. These results are derived via a set of procedures and an analytical model that has been used previously in climate change assessments. The results demonstrate that the spatial scale of climate scenarios affects the estimates of both regional changes in crop yields and the economic impact on the agricultural sector as a whole. An assessment based on the finer scale climatological information consistently yielded a less favorable assessment of the implications of climate change. Regional indicators of economic activity were of opposite sign in some regions, based on the scenario scale. Such differences in economic magnitudes or signs are potentially important in examining whether past climate change assessments may misstate the economic consequences of such changes. The results reported here suggest that refinement of the spatial scale of scenarios should be carefully considered in future impacts research.  相似文献   

Snow Avalanche Hazard in Canada – a Review     

Chris Stethem  Bruce Jamieson  Peter Schaerer  David Liverman  Daniel Germain  Simon Walker 《Natural Hazards》2003,28(2-3):487-515

Snow avalanches affect recreation, transportation, resource industries and property. During the 1990s an average of 12.5 persons per year were killed in avalanches in Canada. The snow avalanche hazard has affected people and facilities in B.C, Alberta, Yukon, NWT, Nunavut, Ontario, Quebec and Newfoundland. Avalanche risk may be voluntary, for example skiing and snowmobiling, or involuntary, for example public transportation corridors. A worst-case avalanche scenario is most likely to occur in the Western Cordillera, resulting from a single large-scale weather pattern, where a cold period resulting in the development of a weak layer in the snowpack is followed by a series of major mid-winter storms. Emergency preparedness for avalanches is most advanced in western Canada. New education and information initiatives in Quebec and Newfoundland are aimed at improving preparedness there. Current research is focused on avalanche forecasting, weather forecasting for avalanche prediction, avalanche failure characteristics, forestry and avalanches and geomorphology and avalanches. An important area of future research is the impact of climate change on avalanches, particularly in northern Canada.  相似文献   

Erosion and Sedimentation from the 17 July, 1998 Papua New Guinea Tsunami   总被引：1，自引：0，他引：1  

Guy Gelfenbaum  Bruce Jaffe 《Pure and Applied Geophysics》2003,160(10-11):1969-1999

— This paper describes erosion and sedimentation associated with the 17 July 1998 Papua New Guinea tsunami. Observed within two months of the tsunami, distinct deposits of a layer averaging 8-cm thick of gray sand rested on a brown muddy soil. In most cases the sand is normally graded, with more coarse sand near the base and fine sand at the top. In some cases the deposit contains rip-up clasts of muddy soil and in some locations it has a mud cap. Detailed measurements of coastal topography, tsunami flow height and direction indicators, and deposit thickness were made in the field, and samples of the deposit were collected for grain-size analysis in the laboratory. Four shore-normal transects were examined in detail to assess the shore-normal and along shore distribution of the tsunami deposit. Near the shoreline, the tsunami eroded approximately 10–25 cm of sand from the beach and berm. The sandy layer deposited by the tsunami began 50–150 m inland from the shoreline and extended across the coastal plain to within about 40 m of the limit of inundation; a total distance of up to 750 m from the beach. As much as 2/3 of the sand in the deposit originated from offshore. Across most of the coastal plain the deposit thickness and mean grain size varied little. In the along-shore direction the deposit thickness varied with the tsunami wave height; both largest near the entrance to Sissano Lagoon.  相似文献   

Three‐dimensional flow structure and channel change in an asymmetrical compound meander loop,Embarras River,Illinois     

Kelly M. Frothingham  Bruce L. Rhoads 《地球表面变化过程与地形》2003,28(6):625-644

The planform dynamics of meandering rivers produce a complex array of meander forms, including elongated meander loops. Thus far, few studies have examined in detail the flow structure within meander loops and the relation of flow structure to patterns of planform change. This field‐based investigation examines relations between three‐dimensional fluid motion and channel change within an elongated, asymmetrical meander loop containing multiple pool–riffle structures. The downstream velocity field is characterized by a high‐velocity core that shifts slightly outward as flow moves through individual lobes of the loop. For some of the measured flows this core becomes submerged below the water surface downstream of the lobe apexes. Vectors of cross‐stream/vertical velocities indicate that skew‐induced helical motion develops within the pools near lobe apexes and decays over riffles where channel curvature is less pronounced. Maximum rates of bank retreat generally occur near lobe apexes where impingement of the flow on the outer channel bank is greatest. However, maximum rates and loci of bank retreat differ for upstream and downstream lobes of the loop, leading to increasing asymmetry of loop geometry over time—a finding consistent with experimental investigations of loop evolution. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献