On the equivalence between the effective cosmology and excursion set treatments of environment     

Matthew C. Martino  Ravi K. Sheth 《Monthly notices of the Royal Astronomical Society》2009,394(4):2109-2112

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A close look at Saturn's rings with Cassini VIMS     

Philip D. Nicholson  Matthew M. Hedman  Mark R. Showalter  Jeffrey N. Cuzzi  Fabrizio Capaccioni  Gary B. Hansen  Pierre Drossart  Bonnie J. Buratti  Angioletta Coradini 《Icarus》2008,193(1):182-212

Soon after the Cassini-Huygens spacecraft entered orbit about Saturn on 1 July 2004, its Visual and Infrared Mapping Spectrometer obtained two continuous spectral scans across the rings, covering the wavelength range 0.35-5.1 μm, at a spatial resolution of 15-25 km. The first scan covers the outer C and inner B rings, while the second covers the Cassini Division and the entire A ring. Comparisons of the VIMS radial reflectance profile at 1.08 μm with similar profiles at a wavelength of 0.45 μm assembled from Voyager images show very little change in ring structure over the intervening 24 years, with the exception of a few features already known to be noncircular. A model for single-scattering by a classical, many-particle-thick slab of material with normal optical depths derived from the Voyager photopolarimeter stellar occultation is found to provide an excellent fit to the observed VIMS reflectance profiles for the C ring and Cassini Division, and an acceptable fit for the inner B ring. The A ring deviates significantly from such a model, consistent with previous suggestions that this region may be closer to a monolayer. An additional complication here is the azimuthally-variable average optical depth associated with “self-gravity wakes” in this region and the fact that much of the A ring may be a mixture of almost opaque wakes and relatively transparent interwake zones. Consistently with previous studies, we find that the near-infrared spectra of all main ring regions are dominated by water ice, with a typical regolith grain radius of 5-20 μm, while the steep decrease in visual reflectance shortward of 0.6 μm is suggestive of an organic contaminant, perhaps tholin-like. Although no materials other than H₂O ice have been identified with any certainty in the VIMS spectra of the rings, significant radial variations are seen in the strength of the water-ice absorption bands. Across the boundary between the C and B rings, over a radial range of ∼7000 km, the near-IR band depths strengthen considerably. A very similar pattern is seen across the outer half of the Cassini Division and into the inner A ring, accompanied by a steepening of the red slope in the visible spectrum shortward of 0.55 μm. We attribute these trends—as well as smaller-scale variations associated with strong density waves in the A ring—to differing grain sizes in the tholin-contaminated icy regolith that covers the surfaces of the decimeter-to-meter sized ring particles. On the largest scale, the spectral variations seen by VIMS suggest that the rings may be divided into two larger ‘ring complexes,’ with similar internal variations in structure, optical depth, particle size, regolith texture and composition. The inner complex comprises the C and B rings, while the outer comprises the Cassini Division and A ring.  相似文献   

Narrow associated quasi-stellar object absorbers: clustering, outflows and the line-of-sight proximity effect     

Vivienne Wild  Guinevere Kauffmann  Simon White  Donald York  Matthew Lehnert  Timothy Heckman  Patrick B. Hall  Pushpa Khare  Britt Lundgren  Donald P. Schneider  Daniel Vanden Berk 《Monthly notices of the Royal Astronomical Society》2008,388(1):227-241

Using data from the Sloan Digital Sky Survey data release 3 (SDSS DR3), we investigate how narrow (<700 km s⁻¹) C  iv and Mg  ii quasar absorption-line systems are distributed around quasars. The C  iv absorbers lie in the redshift range 1.6 < z < 4 and the Mg  ii absorbers in the range 0.4 < z < 2.2. By correlating absorbers with quasars on different but neighbouring lines of sight, we measure the clustering of absorbers around quasars on comoving scales between 4 and 30 Mpc. The observed comoving correlation lengths are   r _o∼ 5 h ⁻¹Mpc  , similar to those observed for bright galaxies at these redshifts. Comparing correlations between absorbers and the quasars, in whose spectra they are identified, then implies: (i) that quasars destroy absorbers to comoving distances of ∼300 kpc (C  iv ) and ∼800 kpc (Mg  ii ) along their lines of sight; (ii) that ≳40 per cent of C  iv absorbers within 3000 km s⁻¹ of the quasi-stellar object are not a result of large-scale clustering but rather are directly associated with the quasar itself; (iii) that this intrinsic absorber population extends to outflow velocities of the order of 12 000 km s⁻¹; (iv) that this outflow component is present in both radio-loud and radio-quiet quasars and (v) that a small high-velocity outflow component is also observed in the Mg  ii population. We also find an indication that absorption systems within 3000 km s⁻¹ are more abundant for radio-loud quasars than for radio-quiet quasars. This suggests either that radio-loud objects live in more massive haloes, or that their radio activity generates an additional low-velocity outflow, or both.  相似文献   

The 2dF-SDSS LRG and QSO Survey: evolution of the clustering of luminous red galaxies since z= 0.6     

David A. Wake  Ravi K. Sheth  Robert C. Nichol  Carlton M. Baugh  Joss Bland-Hawthorn  Matthew Colless  Warrick J. Couch  Scott M. Croom  Roberto De Propris  Michael J. Drinkwater  Alastair C. Edge  Jon Loveday  Tsz Yan Lam  Kevin A. Pimbblet  Isaac G. Roseboom  Nicholas P. Ross  Donald P. Schneider  Tom Shanks  Robert G. Sharp 《Monthly notices of the Royal Astronomical Society》2008,387(3):1045-1062

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Linking the Abundance of Estuarine Fish and Crustaceans in Nearshore Waters to Shoreline Hardening and Land Cover     

Matthew S. Kornis  Denise Breitburg  Richard Balouskus  Donna M. Bilkovic  Lori A. Davias  Steve Giordano  Keira Heggie  Anson H. Hines  John M. Jacobs  Thomas E. Jordan  Ryan S. King  Christopher J. Patrick  Rochelle D. Seitz  Heather Soulen  Timothy E. Targett  Donald E. Weller  Dennis F. Whigham  Jim UphoffJr 《Estuaries and Coasts》2017,40(5):1464-1486

Human alteration of land cover (e.g., urban and agricultural land use) and shoreline hardening (e.g., bulkheading and rip rap revetment) are intensifying due to increasing human populations and sea level rise. Fishes and crustaceans that are ecologically and economically valuable to coastal systems may be affected by these changes, but direct links between these stressors and faunal populations have been elusive at large spatial scales. We examined nearshore abundance patterns of 15 common taxa across gradients of urban and agricultural land cover as well as wetland and hardened shoreline in tributary subestuaries of the Chesapeake Bay and Delaware Coastal Bays. We used a comprehensive landscape-scale study design that included 587 sites in 39 subestuaries. Our analyses indicate shoreline hardening has predominantly negative effects on estuarine fauna in water directly adjacent to the hardened shoreline and at the larger system-scale as cumulative hardened shoreline increased in the subestuary. In contrast, abundances of 12 of 15 species increased with the proportion of shoreline comprised of wetlands. Abundances of several species were also significantly related to watershed cropland cover, submerged aquatic vegetation, and total nitrogen, suggesting land-use-mediated effects on prey and refuge habitat. Specifically, abundances of four bottom-oriented species were negatively related to cropland cover, which is correlated with elevated nitrogen and reduced submerged and wetland vegetation in the receiving subestuary. These empirical relationships raise important considerations for conservation and management strategies in coastal environments.  相似文献   

Modelling malaria susceptibility using geographic information system     

Matthew Biniyam Kursah 《GeoJournal》2017,82(6):1101-1111

Identifying and/or predicting the geography of malaria will help decision makers locate the particular area with the health problem, and to design area-specific interventions. Using GIS (ArcMap 10.1), a spatial analysis of environmental factors that contribute to the spread of malaria vector was conducted to develop a malaria susceptibility model that could be used in effective malaria control planning. The study first determined malaria susceptibility index and combined it with geospatial modelling to predict malaria susceptibility. Clinical malaria cases were then geocoded and tested to determine the accuracy of the prediction. The results show that 72.3, 24.5, 3.1 and 0.1 % of the clinical malaria incidence were found in areas that were predicted to have very high, high, low and very low susceptibility levels. Hence, the model, to a large extent, predicted malaria occurrences. The conclusion is that modelling such as this can help determine spatio-temporal prediction and mapping of malaria incidence to aid in the design and administration of appropriate interventions.  相似文献   

A public health frame arouses hopeful emotions about climate change   总被引：1，自引：1，他引：0  

Teresa A. Myers  Matthew C. Nisbet  Edward W. Maibach  Anthony A. Leiserowitz 《Climatic change》2012,113(3-4):1105-1112

Communication researchers and practitioners have suggested that framing climate change in terms of public health and/or national security may make climate change more personally relevant and emotionally engaging to segments of the public who are currently disengaged or even dismissive of the issue. To evaluate these assumptions, using a nationally representative online survey of U.S. residents (N?=?1,127) conducted in December, 2010, we randomly assigned six previously identified audience segments on climate change to one of three experimental conditions. Subjects were asked to read uniquely framed news articles about climate change emphasizing either the risks to the environment, public health, or national security and the benefits of mitigation and adaptation-related actions. Results show that across audience segments, the public health focus was the most likely to elicit emotional reactions consistent with support for climate change mitigation and adaptation. Findings also indicated that the national security frame may possibly boomerang among audience segments already doubtful or dismissive of the issue, eliciting unintended feelings of anger.  相似文献   

Regional climate model simulation of the AMMA Special Observing Period #3 and the pre-Helene easterly wave     

Leonard M. Druyan  Matthew Fulakeza  Patrick Lonergan  Erik Noble 《Meteorology and Atmospheric Physics》2009,105(3-4):191-210

The study examines results of dynamic downscaling of two global analyses: the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis II and the Global Forecast System final analysis (FNL). Downscaling to a 0.5° grid over West Africa and the adjacent Atlantic Ocean is accomplished by each of two regional models, the Regional Model, version 3 (RM3) of the Center for Climate Systems Research and the Weather, Research and Forecasting model (WRF). Simulations are for September 2006, the African Monsoon Multidisciplinary Analysis (AMMA) Special Observing Period #3 (SOP-3). The aim of this study is to exploit the increased spatial detail in the simulations and representations of climate fields by the regional models to analyze meteorological systems within the SOP-3 area of interest and time frame. In particular, the paper focuses on the regional models’ representations of the structure and movement of a prominent easterly wave during September 10–13th, the precursor of Tropical Storm/Hurricane Helene. It describes the RM3 simulated structure of the developing storm in terms of circulation, precipitation, vertical motion, cumulus heating rates, and cross-sections of wind and geopotential height anomalies. Simulated cumulus heating rates within the wave’s main precipitation area imply a lowering of the bases of active cumulus in the transition from the African continent to the Atlantic, indicating that the ocean environment promotes greater upward latent heat flux that in turn intensifies overlying storms. RM3 circulation, precipitation patterns, and storm trajectory are reasonably consistent with observational evidence. Experiments show that precipitation rates near 6°N over the eastern North Atlantic are sensitive to vertical thermal stability, such that they are enhanced by warmer in situ sea-surface temperatures (SSTs) and diminished by colder SSTs. However, prescribing colder SST causes increases in precipitation north of 9°N within areas of large scale upward vertical motion where rainfall rates are less sensitive to in situ SSTs. The evaluation of WRF indicates that its storm propagation is too fast over West Africa, where associated WRF precipitation rates are exaggerated, but its performance is improved over the Atlantic.  相似文献   

Variability and comparison of hyporheic water temperatures and seepage fluxes in a small Atlantic salmon stream   总被引：2，自引：0，他引：2  

Alexander MD  Caissie D 《Ground water》2003,41(1):72-82

Ground water discharge is often a significant factor in the quality of fish spawning and rearing habitat and for highly biologically productive streams. In the present study, water temperatures (stream and hyporheic) and seepage fluxes were used to characterize shallow ground water discharge and recharge within thestreambed of Catamaran Brook, a small Atlantic salmon (Salmo salar) stream in central New Brunswick, Canada. Three study sites were instrumented using a total of 10 temperature sensors and 18 seepage meters. Highly variable mean seepage fluxes, ranging from 1.7 x 10(-4) to 2.5 cm3 m(-2) sec(-1), and mean hyporheic water temperatures, ranging from 10.5 degrees to 18.0 degrees C, at depths of 20 to 30 cm in the streambed were dependent on streambed location (left versus right stream bank and site location) and time during the summer sampling season. Temperature data were usefulfor determining if an area of the streambed was under discharge (positive flux), recharge (negative flux), or parallel flow (no flux) conditions and seepage meters were used to directly measure the quantity of water flux. Hyporheic water temperature measurements and specific conductance measurements of the seepage meter sample water, mean values ranging from 68.8 to 157.9 microS/cm, provided additional data for determining flux sources. Three stream banks were consistently under discharge conditions, while the other three stream banks showed reversal from discharge to recharge conditions over the sampling season. Results indicate that the majority of the water collected in the seepage meters was composed of surface water. The data obtained suggests that even though a positive seepage flux is often interpreted as ground water discharge, this discharging water may be of stream water origin that has recently entered the hyporheic zone.The measurement of seepage flux in conjunction with hyporheic water temperature or other indicators of water origin should be considered when attempting to quantify the magnitude of exchange and the source of hyporheic water.  相似文献   

An Alpine Lacustrine Record of Early Holocene North American Monsoon Dynamics from Dry Lake, Southern California (USA)     

Broxton W. Bird  Matthew E. Kirby 《Journal of Paleolimnology》2006,35(1):179-192

Dry Lake (2763 m), located in the San Bernardino Mountains of southern California, USA, provides a high-resolution climate record from the coastal southwest depicting early Holocene terrestrial climate. 27 AMS ¹⁴C dates and multi-proxy analyses, including magnetic susceptibility, total organic mater, microfossil counts, and grain size, suggest the early Holocene was significantly wetter then present, due to an enhanced North American Monsoon (NAM). Elevated insolation at 9000 cal year B.P., raised summer sea surface temperatures in the Gulf of California and the eastern tropical Pacific, as well as land surface temperatures, extending the NAM into southern California. The data also provide evidence of the 8.2 ka event, which registers as a 300-year cool period characterized by reduced monsoonal precipitation, depressed basin productivity, and increased erosion. We suggest this event is the most likely period for the early to middle Holocene (9000–5000 cal year B.P.) glacial advance in the San Bernardino Mountains proposed by Owen et al. (2003, Geology 31: 729–732).  相似文献