Sediment routing in a small drainage basin in the blast zone at Mount St. Helens, Washington, U.S.A.     

Richard D. Smith  Frederick J. Swanson   《Geomorphology》1987,1(1)

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Fish community ecology in an Altered River delta: Spatial patterns in species composition, life history strategies, and biomass   总被引：1，自引：0，他引：1  

Matthew L. Nobriga  Frederick Feyrer  Randall D. Baxter  Michael Chotkowski 《Estuaries and Coasts》2005,28(5):776-785

We sampled nearshore fishes in the Sacramento-San Joaquin Delta, California, United States, during 2001 and 2003 with beach seines and gill nets. We addressed three questions. How and why did fish assemblages vary, and what local habitat features best explained the variation? Did spatial variation in assemblages reflect greater success of particular life history strategies? Did fish biomass vary among years or, across habitats? Nonmetric multidimensional scaling showed that habitat variables had more influence on fish assemblages than temporal variables. Results from both gear types indicated fish assemblages varied between Sacramento and San Joaquin River sampling sites. Results from gill net sampling were less pronounced than those from beach seine sampling. The Sacramento and San Joaquin river sites differed most notably in terms of water clarity and abundance of submerged aquatic vegetation (SAV), suggesting a link between these habitat characteristics and fish relative abundance. Among-site differences in the relative abundance of periodic and equilibrium strategist species suggested a gradient in the importance of abiotic versus biotic community structuring mechanisms. Fish biomass varied among years, but was generally higher in SAV-dominated habitats than the turbid, open habitats in which we found highest abundances of striped bassMorone saxatilis and special-status native fishes such as delta smeltHypomesus transpacificus, Chinook salmonOncorhyncus tschawytscha, and splittailPogonichthys macrolepidotus. The low abundance of special-status fishes in the comparatively productive SAV-dominated habitats suggests these species would benefit more from large-scale restoration actions that result in abiotic variability that mirrors natural river-estuary habitat than from actions that emphasize local (site-specific) productivity.  相似文献   

Improving Spatial Accuracy of Roadway Networks and Geocoded Addresses     

Jun Wu  Tami H. Funk  Frederick W. Lurmann  Arthur M. Winer 《Transactions in GIS》2005,9(4):585-601

Exposure to traffic‐related pollutants is associated with both morbidity and mortality. Because vehicle‐exhaust are highly localized, within a few hundred meters of heavily traveled roadways, highly accurate spatial data are critical in studies concerned with exposure to vehicle emissions. We compared the positional accuracy of a widely used U.S. Geological Survey (USGS) roadway network containing traffic activity data versus a global positioning system (GPS)‐validated road network without traffic information; developed a geographical information system (GIS)‐based methodology for producing improved roadway data associated with traffic activities; evaluated errors from geocoding processes; and used the CALINE4 dispersion model to demonstrate potential exposure misclassifications due to inaccurate roadway data or incorrectly geocoded addresses. The GIS‐based algorithm we developed was effective in transferring vehicle activity information from the less accurate USGS roadway network to a GPS‐accurate road network, with a match rate exceeding 95%. Large discrepancies, up to hundreds of meters, were found between the two roadway networks, with the GPS‐validated network having higher spatial accuracy. In addition, identifying and correcting errors associated with geocoding resulted in improved address matching. We demonstrated that discrepancies in roadway geometry and geocoding errors, can lead to serious exposure misclassifications, up to an order of magnitude in assigned pollutant concentrations.  相似文献   

Saturn’s F ring as seen by Cassini UVIS: Kinematics and statistics     

Nicole Albers  Miodrag Sremčević  Joshua E. Colwell  Larry W. Esposito 《Icarus》2012,217(1):367-388

We present a new orbital model of Saturn’s F ring core based on 93 occultations by the Cassini Ultraviolet Imaging Spectrograph (UVIS) and the Voyager radio and stellar occultations. We demonstrate that the core, despite its intrinsic variability, is well-described as an inclined, freely precessing ellipse. We find that post-fit residuals with a root-mean-square of 24 km are genuine, representing the well-known non-Keplerian features observed in the ring. Over the nearly 4 years of UVIS observations we find the residual variance to increase, coincident with the apse anti-alignment of Prometheus and F ring core in December 2009. This increase in dynamical F ring core temperature most likely reflects the ever-stronger perturbations by Prometheus. Our results are in good agreement with Earth-based and HST observations as well as Voyager imaging.Cassini UVIS stellar occultations resolve the F ring at unprecedented resolutions of a few meters and we identify the F ring core and inner and outer strands. We infer their normal optical depth and full width at half maximum (FWHM) and show that core and strands form distinct morphological groups. Typically, a strand is about ten times wider than the core (average FWHM is ～10 km) while having a ten times smaller optical depth. Unlike in pre-Cassini occultations the F ring core displays significant optical depth with in some cases >3. In many cases we find a narrow optically thick component (～ few km and τ > 0.5) embedded in the F ring core. Entertaining the possibility that this is the actual, “true” F ring core then UVIS results suggest that this “true” core is highly non-continuous. In addition, we report the detection of a previously unknown structure – dubbed the “secondary” as it visually resembles the F ring core. Its morphology is similar to that of the core in optical depth and FWHM and it displays individual opaque features. Despite its core-like appearance, we show that its kinematics is consistent with that of strands. We conclude that it is the most prominent strand seen to date. It represents a striking example of strand creation resulting in what could be called a morphological “small-scale” version of the F ring core. This extraordinary object should be one of the prime targets of future F ring studies.  相似文献   

Reducing Drift and Bias of a Global Ocean Model by Frequency-Dependent Nudging     

Zhongjie He  Keith R. Thompson  Harold Ritchie  Youyu Lu  Frederick Dupont 《大气与海洋》2014,52(3):242-255

Frequency-dependent nudging is applied to a coarse resolution (nominal 1°) global ocean model to suppress its drift and bias, and the impact of the nudging on the skill of the model is assessed. The nudging is applied to temperature and salinity in frequency bands centred on 0 and 1 cycles per year. As expected, the nudging significantly reduces the biases in the long-term mean and annual cycle of temperature, salinity, and sea level. By comparing the simulated (i) sea surface temperature with operational analyses based on observations, (ii) vertical profiles of temperature and salinity with observations made by Argo floats, and (iii) sea level with altimeter observations, it is shown that the skill of the model in simulating variability about the annual cycle is also improved. The potential benefit of applying frequency-dependent nudging to the ocean component of a coupled atmosphere–ocean model is discussed.  相似文献   

Longitudinal Social Science Research in Natural Resource Communities: Lessons and Considerations     

Melanie Stidham  Christine Olsen  Eric Toman  Stacey Frederick  Sarah McCaffrey  Bruce Shindler 《社会与自然资源》2014,27(10):1104-1108

The majority of social science research is cross-sectional in nature, with data collected at a single point in time. However, social systems are dynamic and many of the variables of interest to social scientists may change over time. Longitudinal research methods enable data collection at two or more points in time among a population of interest to examine change in measured variables and influencing factors. Despite the opportunities it affords, longitudinal research is relatively uncommon in natural-resource-based social science research as compared to other fields (e.g., medical, criminal, education). We feel that the field of natural resource social science is ripe for a proliferation of longitudinal studies, now that a substantial body of cross-sectional data has been built. In the spirit of encouraging more of this type of research, we draw on our collective experiences in longitudinal studies to share lessons learned in research design, sampling, and data management.  相似文献   

Applications to subseabed disposal: (ISHTE)—A model experiment     

C. Mark Percival  Leroy O. Olson  Richard H. Bennett  Frederick L. Sayles  Armand J. Silva 《Marine Georesources & Geotechnology》2013,31(4):285-371

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The trigonometric parallax of the neutron star Geminga     

Jacqueline Faherty  Frederick M. Walter  Jay Anderson 《Astrophysics and Space Science》2007,308(1-4):225-230

We obtained a series of four observations of the isolated neutron star Geminga over an 18 month period using the Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) on the Hubble Space Telescope in order to determine its trigonometric parallax. We find the parallax π=4.0±1.3 mas, corresponding to a distance to Geminga of 250 _?62 ⁺¹²⁰  pc, a result 60% larger than the previously published value. The proper motion is 178.2±1.8 mas/year. In this paper, we describe the analysis techniques in detail since the amplitude of the parallactic shift is smaller than the camera’s pixel size. We fit each star in the images with an appropriate effective PSF and applied a distortion correction to generate stellar positions accurate to 0.01 pixels (～0.5 mas). The 134 stars common to all images serve to establish a reference frame for alignment of the image series. Our observations were made around the times of maximum parallactic shift. We discuss the implications of this new distance measurement for the inferred radius of Geminga, and the neutron star equation of state.  相似文献   

Waves in Cassini UVIS stellar occultations: 2. The C ring     

Kévin Baillié  Joshua E. Colwell  Larry W. Esposito 《Icarus》2011,216(1):292-308

We performed a complete wavelet analysis of Saturn’s C ring on 62 stellar occultation profiles. These profiles were obtained by Cassini’s Ultraviolet Imaging Spectrograph High Speed Photometer. We used a WWZ wavelet power transform to analyze them. With a co-adding process, we found evidence of 40 wavelike structures, 18 of which are reported here for the first time. Seventeen of these appear to be propagating waves (wavelength changing systematically with distance from Saturn). The longest new wavetrain in the C ring is a 52-km-long wave in a plateau at 86,397 km. We produced a complete map of resonances with external satellites and possible structures rotating with Saturn’s rotation period up to the eighth order, allowing us to associate a previously observed wave with the Atlas 2:1 inner Lindblad resonance (ILR) and newly detected waves with the Mimas 6:2 ILR and the Pandora 4:2 ILR. We derived surface mass densities and mass extinction coefficients, finding σ = 0.22(±0.03) g cm⁻² for the Atlas 2:1 ILR, σ = 1.31(±0.20) g cm⁻² for the Mimas 6:2 ILR, and σ = 1.42(±0.21) g cm⁻² for the Pandora 4:2 ILR. We determined a range of mass extinction coefficients (κ = τ/σ) for the waves associated with resonances with κ = 0.13 (±0.03) to 0.28(±0.06) cm² g⁻¹, where τ is the optical depth. These values are higher than the reported values for the A ring (0.01-0.02 cm² g⁻¹) and the Cassini Division (0.07-0.12 cm² g⁻¹ from Colwell et al. (Colwell, J.E., Cooney, J.H., Esposito, L.W., Srem?evi?, M. [2009]. Icarus 200, 574-580)). We also note that the mass extinction coefficient is probably not constant across the C ring (in contrast to the A ring and the Cassini Division): it is systematically higher in the plateaus than elsewhere, suggesting smaller particles in the plateaus. We present the results of our analysis of these waves in the C ring and estimate the mass of the C ring to be between3.7(±0.9) × 10¹⁶ kg and 7.9(±2.0) × 10¹⁶ kg (equivalent to an icy satellite of radius between 28.0(±2.3) km and 36.2(±3.0) km with a density of 400 kg m⁻³, close to that of Pan or Atlas). Using the ring viscosity derived from the wave damping length, we also estimate the vertical thickness of the C ring between 1.9(±0.4) m and 5.6(±1.4) m, comparable to the vertical thickness of the Cassini Division.  相似文献   

DXL: a sounding rocket mission for the study of solar wind charge exchange and local hot bubble X-ray emission     

Massimiliano Galeazzi  Meng Chiao  Michael R. Collier  Thomas Cravens  Dimitra Koutroumpa  Kip D. Kuntz  Susan Lepri  Dan McCammon  Frederick S. Porter  Krishna Prasai  Ina Robertson  Steve Snowden  Youaraj Uprety 《Experimental Astronomy》2011,32(2):83-99

The Diffuse X-rays from the Local galaxy (DXL) mission is an approved sounding rocket project with a first launch scheduled around December 2012. Its goal is to identify and separate the X-ray emission generated by solar wind charge exchange from that of the local hot bubble to improve our understanding of both. With 1,000 cm² proportional counters and grasp of about 10 cm² sr both in the 1/4 and 3/4 keV bands, DXL will achieve in a 5-min flight what cannot be achieved by current and future X-ray satellites.  相似文献