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271.
Diversity of faunal assemblages associated with ribbed mussel beds along the South American coast: relative roles of biogeography and bioengineering
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Benthic organisms are among the most diverse and abundant in the marine realm, and some species are a key factor in studies related to bioengineering. However, their importance has not been well noted in biogeographic studies. Macrofaunal assemblages associated with subtidal beds of the ribbed mussel (Aulacomya atra) along South America were studied to assess the relationship between their diversity patterns and the proposed biogeographic provinces in the Southeastern Pacific and Southwestern Atlantic Oceans. Samples from ribbed mussel beds were obtained from 10 sites distributed from the Peruvian coast (17°S) to the Argentinean coast (41°S). The sampling included eight beds in the Pacific and two in the Atlantic and the collections were carried out using five 0.04 m2 quadrants per site. Faunal assemblages were assessed through classification analyses using binary and log‐transformed abundance data. Variation in the size and density of mussels, and in the species richness, abundance and structure of their faunal assemblages were tested using a permutational multivariate analysis of variance. Faunal assemblages showed a north–south latitudinal gradient along both the Pacific and Atlantic coasts. Binary and abundance data showed a difference in the resulting clustering arrangement of Pacific sites between 40°S and 44°S, indicating a pattern of continuity in the species distribution associated with biological substrates. At a regional scale, the distribution of species along the South American coast matched the general provincial pattern shown by prior studies, which show two biogeographic units on the Pacific coast separated by an intermediate (probably transitional) zone and a single province on the Atlantic coast extending up to Northern Argentina. Biological substrates such as ribbed mussel beds play an important ecological role by making a similar habitat type available on a large scale for a variety of invertebrate species. Despite such habitat homogeneity, however, the associated fauna exhibit marked distribution breaks, suggesting strong constraints on dispersal. This therefore suggests that macrofaunal assemblages could possibly be used as biogeographic indicators. 相似文献
272.
Nicholas Edkins Werner Schmutz Luca Egli Roger Davies Teruo Aoki Greg Mcfarquhar 《大气科学进展》2016,33(12):1325-1328
正1.Overview The 2016 International Radiation Symposium,a joint venture between the IRC(International Radiation Commission)and IAMAS(International Association of Meteorology and Atmospheric Sciences),took place at the University of Auckland from April 16th to 22nd.The wide scope of atmospheric radiation research was apparent,with focuses rang- 相似文献
273.
Young-Chan NOH Byung-Ju SOHN Yoonjae KIM Sangwon JOO William BELL Roger SAUNDERS 《大气科学进展》2017,34(11):1265-1281
A new set of Infrared Atmospheric Sounding Interferometer(IASI) channels was re-selected from 314 EUMETSAT channels.In selecting channels,we calculated the impact of the individually added channel on the improvement in the analysis outputs from a one-dimensional variational analysis(1D-Var) for the Unified Model(UM) data assimilation system at the Met Office,using the channel score index(CSI) as a figure of merit.Then,200 channels were selected in order by counting each individual channel's CSI contribution.Compared with the operationally used 183 channels for the UM at the Met Office,the new set shares 149 channels,while the other 51 channels are new.Also examined is the selection from the entropy reduction method with the same 1D-Var approach.Results suggest that channel selection can be made in a more objective fashion using the proposed CSI method.This is because the most important channels can be selected across the whole IASI observation spectrum.In the experimental trial runs using the UM global assimilation system,the new channels had an overall neutral impact in terms of improvement in forecasts,as compared with results from the operational channels.However,upper-tropospheric moist biases shown in the control run with operational channels were significantly reduced in the experimental trial with the newly selected channels.The reduction of moist biases was mainly due to the additional water vapor channels,which are sensitive to the upper-tropospheric water vapor. 相似文献
274.
Roger M. Downs 《Geographical review》2017,107(4):660-679
Geography's existence as a school or college subject has never been a given. While geographers make cases for geography's importance, acceptance of those cases rests not on impassioned rhetoric but on the social and intellectual contexts into which disciplines fit. Contexts are contested and they change. From a seemingly secure position at the beginning of the twentieth century, geography's role in American schools has been eroded and diminished by corrosive forces. Geographers need convincing answers to the existential question lest the subject disappear entirely. Geography's enviable position was in large measure the work of William Torrey Harris. Harris made a compelling existential case for geography and his vision, its implementation, its rejection, and its fate offer a model from which geographers can learn. Understanding how to respond to a social and intellectual context is crucial to geography's future. 相似文献
275.
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
276.
Roger A. Kopp 《Solar physics》1980,68(2):307-316
In this paper we point out the existence of a special class of solutions to the nonlinear hydrodynamic equations describing the time-dependent solar wind, namely that for which the velocity profile is time-invariant but the density at each point of the corona changes exponentially with time. Theoretical velocity curves are calculated for the case of isothermal expansion and compared with the Parker model for steady-state expansion. These solutions can be used to obtain quantitative estimates for the degree of departure from the latter of a real corona undergoing evolution on a finite time scale.On leave from Los Alamos Scientific Laboratory, Los Alamos, N.M., U.S.A. 相似文献
277.
New near-infrared (0.65–2.5 μm) reflectance spectra of the Galilean satellites with 1.5% spectral resolution and ≈2% intensity precision are presented. These spectra more precisely define the water ice absorption features previously identified on Europa, Ganymede, and Callisto at 1.55 and 2.0 μm. In addition, previously unreported spectral features due to water ice are seen at 1.25, 1.06, 0.90, and 0.81 μm on Europa, and at 1.25, 1.04, and possibly 0.71 μm on Ganymede. Unreported absorption features in Callisto's spectrum occur at 1.2 μm, probably due to H2O, and a weak, broad band extending from 0.75 to 0.95 μm, due possibly to other minerals. The spectrum of Io has only weak absorption features at 1.15 μm and between 0.8 and 1.0 μm. No water absorptions are positively identified in the Io spectra, indicating an upper limit of areal water frost coverage of 2% (leading and trailing sides). It is found for Callisto, Ganymede, and Europa that the water ice absorption features are due to free water and not to water bound or absorbed onto minerals. The areal coverage of water frost is ≈ 100% on Europa (trailing side), ≈65% on Ganymede (leading side), and 20–30% on Callisto (leading side). An upper limit of ≈5% bound water (in addition to the 20–30% ice) may be present on Callisto, based on the strong 3-μm band seen by other investigators. A summary of spectra of the satellites from 0.325 to about 5 μm to aid in laboratory and interpretation studies is also presented. 相似文献
278.
279.
A review of vortex shedding research and its application 总被引:1,自引:0,他引:1
Roger King 《Ocean Engineering》1977,4(3):141-171
This paper is a review of research work with cylinders in steady currents. The emphasis is mainly on cylinders in water, particularly the research undertaken at BHRA and its general application. Comparisons are made with the work of other authors for both water and air flow and over 60 references are reviewed. The mechanisms of flow-excited oscillations are discussed for isolated vertical and inclined cylinders. The effects of length/diameter ratio, cylinder surface roughness and channel blockage are presented. Wake interactions caused by cylinder-cylinder and cylinder-splitter arrangements are detailed. The results of tests with pane and three-dimensional frames are described and quantified in terms of isolated cylinder data.The paper closes with a section describing methods of avoiding oscillations by calculation at the design stage or by the use of clamp-on devices for completed structures in water flow. 相似文献
280.
Eric N. Powell Julie D. Gauthier Elizabeth A. Wilson Alanna Nelson Roger R. Fay James M. Brooks 《Marine Ecology》1992,13(3):243-270