Saturn satellite observations and orbits from the 1980 ring plane crossing     

P.K. Seidelmann  R.S. Harrington  D. Pascu  W.A. Baum  D.G. Currie  J.A. Westphal  G.E. Danielson 《Icarus》1981,47(2):282-287

The ground-based observations of the recently discovered Saturnian satellites, obtained during the 1980 apparition, have been collected from the IAU Circulars and identified with and fit to four orbital groups: (1) the inner pair of coorbital librating satellites, (2) the satellite known as “Dione B” near the L₄ point of Dione-Saturn, (3) the satellites associated with the L₄ and L₅ points of Tethys-Saturn or, alternatively, one satellite unconfortably near the orbit of Tethys, and (4) the F-ring satellites observed by Voyager I.  相似文献   

Saturn's E ring: I. CCD observations of March 1980     

W.A. Baum  T. Kreidl  J.A. Westphal  G.E. Danielson  P.K. Seidelmann  D. Pascu  D.G. Currie 《Icarus》1981,47(1):84-96

The tenuous E ring of Saturn is found to commence abruptly at 3 Saturn radii, to peak sharply in the vicinity of the orbit of the satellite Enceladus (about 4 radii), and to spread out thinly to more than 8 radii. This distribution strongly suggests it to be associated with Enceladus and perhaps to be material ejected from Enceladus. The spread of E-ring material above and below the ring plane is greater in its tenuous outskirts than in its denser inner region, suggesting that the E ring may be at an early stage in its evolution. Thus far, our analysis reveals only a marginal variation of the ring with time or Enceladus azimuth. In this paper we describe the special instrumentation used for photometric observations of the E ring, and we present some of the data obtained in March 1980. In Paper II we shall derive the three-dimensional distribution of material in the E ring and discuss its cosmogonic implications.  相似文献   

The Co‐evolution of Residential Segregation and the Built Environment at the Turn of the 20th Century: A Schelling Model     

Seth Spielman  Patrick Harrison 《Transactions in GIS》2014,18(1):25-45

To what degree does the built environment of cities shape the social environment? In this article we use a Schelling‐like agent‐based model to consider how changes to the built environment of cities relate to changes in residential segregation by income and ethnicity. To develop this model we exploit insights from a high resolution historical GIS which maps 100% of the population of Newark, NJ in 1880. Newark in 1880 had a complex social landscape characterized by areas of significant social and economic segregation and areas of relative integration. We develop a Schelling model capable of reproducing these residential patterns. We use this model to explore the decentralization of housing, a specific phenomenon associated with the demise of the walking city in the late 19th century. Holding agent preferences constant, but allowing the landscape of the Schelling model to evolve in ways that reflect historical changes to the built environment, produces changes to the social landscape that are also consistent with history. Our work suggests that changes in residential segregation do not necessarily imply changes to individual attitudes and preferences. Changes in residential segregation can be generated by changes to the built environment, specifically the geographic distribution of housing.  相似文献   

Enhanced spring convective barrier for monsoons in a warmer world?     

Anji Seth  Sara A. Rauscher  Maisa Rojas  Alessandra Giannini  Suzana J. Camargo 《Climatic change》2011,104(2):403-414

Twenty-first century climate model projections show an amplification of the annual cycle in tropical precipitation with increased strength in both wet and dry seasons, but uncertainty is large and few studies have examined transition seasons. Here we analyze coupled climate model projections of global land monsoons and show a redistribution of precipitation from spring to summer in northern (North America, West Africa and Southeast Asia) and southern (South America, Southern Africa) regions. The annual cycle changes are global in scale. Two mechanisms, remote (based on tropospheric stability) and local (based on low level and surface moisture), are evaluated through the annual cycle. Increases in tropospheric stability persist from winter into spring and are reinforced by a reduction in surface moisture conditions, suggesting that in spring both remote and local mechanisms act to inhibit convection. This enhanced spring convective barrier leads to reduced early season rainfall; however, once sufficient increases in moisture (by transport) are achieved, decreases in tropospheric stability result in increased precipitation during the late rainy season. Further examination of this mechanism is needed in observations and models, as the projected changes would have substantial implications for agriculture, water management, and disaster preparedness.  相似文献   

Thermal and haline variability over the central Bering Sea shelf: Seasonal and interannual perspectives     

S. Danielson  L. EisnerT. Weingartner  K. Aagaard 《Continental Shelf Research》2011,31(6):539-554

We examine multi-year conductivity-temperature-depth (CTD) data to better understand temperature and salinity variability over the central Bering Sea shelf. Particular consideration is given to observations made annually from 2002 to 2007 between August and October, although other seasons and years are also considered. Vertical and horizontal correlation maps show that near-surface and near-bottom salinity anomalies tend to fluctuate in phase across the central shelf, but that temperature anomalies are vertically coherent only in the weakly or unstratified inner-shelf waters. We formulate heat content (HC) and freshwater content (FWC) budgets based on the CTD observations, direct estimates of external fluxes (surface heat fluxes, ice melt, precipitation (P), evaporation (E) and river discharge), and indirect estimates of advective contributions. Ice melt, P−E, river discharge, and along-isobath advection are sufficient to account for the mean spring-to-fall increase in FWC, while summer surface heat fluxes are primarily responsible for the mean seasonal increase in HC, although interannual variability in the HC at the end of summer appears related to variability in the along-isobath advection during the summer months. On the other hand, FWC anomalies at the end of summer are significantly correlated with the mean wind direction and cross-isobath Ekman transport averaged over the previous winter. Consistent with the latter finding, salinities exhibit a weak but significant inverse correlation between the coastal and mid-shelf waters. The cross-shelf transport likely has significant effect on nutrient fluxes and other processes important to the functioning of the shelf ecosystem. Both the summer and winter advection fields appear to result from the seasonal mean position and strength of the Aleutian Low. We find that interannual thermal and haline variability over the central Bering Sea shelf are largely uncoupled.  相似文献   

Importance of soil and elevation characteristics for modeling hurricane-induced power outages     

Steven M. Quiring  Laiyin Zhu  Seth D. Guikema 《Natural Hazards》2011,58(1):365-390

Hurricanes can severely damage the electric power system, and therefore, predicting the potential impact of an approaching hurricane is of importance for facilitating planning and storm-response activities. A data mining approach, classification and regression trees (CART), was employed to evaluate whether the inclusion of soil and topographic variables improved the predictive accuracy of the power outage models. A total of 37 soil variables and 20 topographic variables were evaluated in addition to hurricane, power system, and environmental variables. Hurricane variables, specifically the maximum wind gust and duration of strong winds, were the most important variables for predicting power outages in all models. Although the inclusion of soil and topographic variables did not significantly improve the overall accuracy of outage predictions, soil type and soil texture are useful predictors of hurricane-related power outages. Both of these variables provide information about the soil stability which, in turn, influences the likelihood of poles remaining upright and trees being uprooted. CART was also used to evaluate whether environmental variables can be used instead of power system variables. Our results demonstrated that certain land cover variables (e.g., LC21, LC22, and LC23) are reasonable proxies for the power system and can be used in a CART model, with only a minor decrease in predictive accuracy, when detailed information about the power system is not available. Therefore, CART-based power outage models can be developed in regions where detailed information on the power system is not available.  相似文献   

The local ISM in three dimensions: kinematics,morphology and physical properties     

Jeffrey L. Linsky  Seth Redfield 《Astrophysics and Space Science》2014,354(1):29-34

We summarize the results of our long-term program to study the kinematics, morphology, and physical properties of warm partially ionized interstellar gas located within 100 pc of the Sun. Using the Space Telescope Imaging Spectrograph (STIS) and other spectrographs on the Hubble Space Telescope (HST), we measure radial velocities of neutral and singly ionized atoms that identify comoving structures (clouds) of warm interstellar gas. We have identified 15 of these clouds located within 15 pc of the Sun. Each of them moves with a different velocity vector, and they have narrow ranges of temperature, turbulence, and metal depletions. We compute a three-dimensional model for the Local Interstellar Cloud (LIC), in which the Sun is likely embedded near its edge, and the locations and shapes of the other nearby clouds. These clouds are likely separated by ionized Strömgren sphere gas produced by ? CMa, Sirius B, and other hot white dwarfs. We propose that some of these partially ionized clouds are shells of the Strömgren spheres.  相似文献   

Major ion variation and efflux related to discharge in a mafic piedmont province watershed     

Seth Rose 《水文研究》1994,8(5):481-496

Major-ion variability related to discharge was analysed in a forested 187 km² mafic Piedmont Province watershed using statistical (both parametric and non-parametric), graphical (box-plots) and curve-fitting (log concentration-log discharge) techniques. Baseflow alkalinity and base cation concentrations show systematic temporal variations as a result of the influx of additional water that occurs during the late autumn to early spring. Regression analyses indicate that storm-related discharge and baseflow generated during periods of water surplus are characterized by similar dilution slopes. Mass balance estimates indicate that the additional water, which comprises storm/recession discharge and base-flow from late autumn to early spring, is between about 30 and 80% as concentrated as summer low-flow. The thick clay-rich soil mantle represents a key control on solute concentrations in that it stores water for periods of time sufficient for a high degree of water-mineral interaction to occur. Hence solute-discharge relationships (C = aQ^b, where b is typically < 0) are characterized by relatively low slope values and there is ample acid neutralizing capacity throughout the range of discharge. Owing to the predominance of amphibolite, solute efflux related to rock weathering from the Falling Creek watershed is much greater than other more felsic locations within the region. Statistical analyses (Mest and the non-parametric Mann-Whitney-Wilcoxon test), along with accompanying box-plot representations, provide a useful method of describing systematic annual hydrochemical variation within streamflow. These methods are particularly effective for those instances in which a long-term data set exists, but is limited to relatively few sampling periods per year.  相似文献   

An earthquake swarm on the Chagos—Laccadive Ridge and its tectonic implications     

Seth Stein 《Geophysical Journal International》1978,55(3):577-588

Summary. An unusual, isolated swarm of earthquakes occurred on the Chagos-Laccadive Ridge in the Central Indian Ocean between 1965 and 1970. Sixteen earthquakes were "located at approximately 6.0° S, 71.3°E on the steep west facing scarp of the Chagos Bank. This swarm forms the only major seismic activity in the period 1963–76 on the otherwise aseismic ridge. The mechanisms of the three largest earthquakes were studied using body- and surface-wave data. All are extremely similar shallow normal fault events on an east—west fault plane. Such faulting is difficult to reconcile with that expected from either the trend of the Chagos-Laccadive Ridge or the spreading direction at the nearby Central Indian Ridge. The swarm may have occurred at depth on a cross fracture remaining from the breakup of the Chagos Bank and the Mascarene Plateau and the formation of the present Central Indian Ridge.  相似文献   

Structurally-controlled melt accumulation: Himalayan migmatites and related deformation — Dhauli Ganga valley, Garhwal Himalaya     

A. K. Jain  Puneet Seth  Mrinal Shreshtha  P. K. Mukherjee  Keser Singh 《Journal of the Geological Society of India》2013,82(4):313-318

In the uppermost parts of the Higher Himalayan Crystallines (HHC) of the Great Himalaya, widespread in situ partial melting of sillimanite+K-feldspar gneiss resulted in the formation of migmatite and resultant melt accumulation near the South Tibetan Detachment System (STDS) during various deformation events along the Dhauli Ganga valley in Garhwal. The oldest migmatite phase, designated as the Me1, parallels the main foliation S_m as the stromatite layers and concordant leucogranite bands. Younger melt phases Me2, Me3 and Me5 are recorded along small-scale ductile thrusts, extensional fabric and structureless patches, respectively. It is only the Me4 melting phase that is evidenced by large-scale melt migration along cross-cutting irregular veins. These were possible conduits for migration and accumulation of melt into larger leucogranite bodies like the Malari granite (19.0± 0.5 Ma).  相似文献