排序方式： 共有23条查询结果，搜索用时 15 毫秒
1.
Gerald Cecil 《New Astronomy Reviews》2006,49(10-12):553
An AO-assisted integral-field spectrograph is becoming the most efficient tool with which to explore ionized gas outflows. It maps faint spectral lines that diagnose cloud dust content, gas pressure, excitation mechanism, and chemical abundances. Coupled with recent improvements in photoionization models, the total mass hence flow energetics can be estimated. Establishing a consistent dynamical framework requires linking multi-frequency datasets to track the energy flow through its optimal-contrast emission in the various ISM phases. I show HST results on AGN, starburst nuclei, and Galactic Herbig-Haro Objects that need complementary 3D spectra at comparable spatial resolution to come soon from laser-guided AO + integral-field spectrographs at the William-Herschel and SOAR telescopes. 相似文献
2.
Stanley N. Davis Stephen Moysey DeWayne L. Cecil Marek Zreda 《Hydrogeology Journal》2003,11(2):217-227
Natural production of the radionuclide chlorine-36 (36Cl) has provided a valuable tracer for groundwater studies. The nuclear industry, especially the testing of thermonuclear
weapons, has also produced large amounts of 36Cl that can be detected in many samples of groundwater. In order to be most useful in hydrologic studies, the natural production
prior to 1952 should be distinguished from more recent artificial sources. The object of this study was to reconstruct the
probable preanthropogenic levels of 36Cl in groundwater in the United States. Although significant local variations exist, they are superimposed on a broad regional
pattern of 36Cl/Cl ratios in the United States. Owing to the influence of atmospherically transported ocean salt, natural ratios of 36Cl/total Cl are lowest near the coast and increase to a maximum in the central Rocky Mountains of the United States.
Electronic Publication 相似文献
3.
Stephen?MoyseyEmail author Stanley?N.?Davis Marek?Zreda L.?DeWayne?Cecil 《Hydrogeology Journal》2003,11(6):615-627
The natural distribution of 36Cl/Cl in groundwater across the continental United States has recently been reported by Davis et al. (2003). In this paper, the large-scale processes and atmospheric sources of 36Cl and chloride responsible for controlling the observed 36Cl/Cl distribution are discussed.The dominant process that affects 36Cl/Cl in meteoric groundwater at the continental scale is the fallout of stable chloride from the atmosphere, which is mainly derived from oceanic sources. Atmospheric circulation transports marine chloride to the continental interior, where distance from the coast, topography, and wind patterns define the chloride distribution. The only major deviation from this pattern is observed in northern Utah and southern Idaho where it is inferred that a continental source of chloride exists in the Bonneville Salt Flats, Utah.In contrast to previous studies, the atmospheric flux of 36Cl to the land surface was found to be approximately constant over the United States, without a strong correlation between local 36Cl fallout and annual precipitation. However, the correlation between these variables was significantly improved (R
2=0.15 to R
2=0.55) when data from the southeastern USA, which presumably have lower than average atmospheric 36Cl concentrations, were excluded. The total mean flux of 36Cl over the continental United States and total global mean flux of 36Cl are calculated to be 30.5±7.0 and 19.6±4.5 atoms m–2 s–1, respectively.The 36Cl/Cl distribution calculated by Bentley et al. (1986) underestimates the magnitude and variability observed for the measured 36Cl/Cl distribution across the continental United States. The model proposed by Hainsworth (1994) provides the best overall fit to the observed 36Cl/Cl distribution in this study. A process-oriented model by Phillips (2000) generally overestimates 36Cl/Cl in most parts of the country and has several significant local departures from the empirical data.
Resumen Davis et al. (2003) han informado de la distribución natural de la proporción 36Cl/Cl en las aguas subterráneas de la parte continental de los Estados Unidos de América [EUA]. En este artículo, se discute cuáles son los procesos a gran escala y las fuentes atmosféricas del 36Cl y del cloruro que dan lugar a la distribución observada de 36Cl/Cl.El proceso dominante que afecta a la relación 36Cl/Cl en las aguas subterráneas de origen meteórico a escala continental es el aporte de cloruro estable desde la atmósfera, que procede principalmente de los océanos. La circulación atmosférica transporta el cloruro marino hacia el interior, donde la distancia a la costa, topografía y corrientes del viento definen la distribución del cloruro. La única desviación principal de este esquema tiene lugar al norte de Utah y en el sur de Idaho, donde se deduce que existe una fuente continental de cloruro en los Rellanos Salados de Bonneville (Salt Flats).En contraste con estudios previos (Knies et al. 1994; Phillips 2000), se ha descubierto que el flujo atmosférico de 36Cl hacia la superficie terrestre es aproximadamente constante en todos los estados, sin deducirse una correlación fuerte entre el aporte de 36Cl y la precipitación anual. Sin embargo, la correlación entre estas variables se ve mejorada de forma significativa, con coeficientes de regresión comprendidos entre 0,15 y 0,55, cuando se excluyen los datos recogidos en el sudeste de los EUA, que tienen concentraciones de 36Cl atmosférico presuntamente inferiores a la media. El flujo medio total de 36Cl calculado en la zona continental de los Estados Unidos vale 30,5±7,0 átomos por metro cuadrado y segundo, mientras que el flujo total global de 36Cl es de 19,6±4,5 átomos por metro cuadrado y segundo.La distribución de 36Cl/Cl calculada por Bentley et al. (1986) infravalora la magnitud y variabilidad observada en los valores medidos a lo largo de los Estados Unidos. El modelo propuesto por Hainsworth (1994) proporciona el mejor ajuste conjunto a la distribución observada de 36Cl/Cl en este estudio. El modelo orientado a procesos de Phillips (2000) sobreestima por lo general la distribución de 36Cl/Cl en la mayoría del país y difiere significativamente de algunos valores locales empíricos.
Résumé La distribution naturelle du rapport 36Cl/Cl dans les eaux souterraines des États-Unis a été récemment présentée par Davis et al. (2003). Dans ce travail, les processus à grande échelle et les sources atmosphériques de 36Cl et de chlorure responsables du contrôle de la distribution observée du rapport 36Cl/Cl sont discutés. Le processus dominant qui affecte le rapport 36Cl/Cl dans les eaux souterraines dorigine météorique à léchelle continentale est lapport atmosphérique de chlorure stable, qui provient pour lessentiel de sources océaniques. La circulation atmosphérique transporte des chlorures marins vers lintérieur des continents, où la distribution de chlorure est définie par la distance à la côte, la topographie et les régimes des vents. La seule exception majeure à ce schéma est observée dans le nord de lUtah et le sud de lIdaho où lon suppose quil existe une source continentale de chlorure dans les bas-fonds salés de Bonneville. Au contraire de précédentes études (Knies et al. 1994; Phillips 2000), on trouve que le flux atmosphérique de 36Cl vers le sol est approximativement constant sur lensemble des États-Unis, sans forte corrélation entre la retombée locale de 36Cl et les précipitations annuelles. Cependant, la corrélation entre ces variables devient significative (R 2=0.15 à 0.55) lorsquon supprime les données du sud-est des États-Unis, dont on pense quelles présentent des concentrations en 36Cl atmosphérique inférieures à la moyenne. Le flux total moyen de 36Cl sur les États-Unis continentaux et le flux moyen global de 36Cl sont respectivement évalués à 30.5 ± 7.0 et 19.6 ± 4.5 atomes.m–2.s–1. La distribution du rapport 36Cl/Cl calculée par Bentley et al. (1986) sous-estime lordre de grandeur et la variabilité observés pour la distribution mesurée du rapport 36Cl/Cl sur les États-Unis continentaux. Le modèle proposé par Hainsworth (1994) fournit le meilleur ajustement densemble à la distribution du rapport 36Cl/Cl observée dans cette étude. Un modèle orienté vers les processus proposé par Phillips (2000) surestime dans lensemble le rapport 36Cl/Cl dans la plupart des régions du pays et présente plusieurs désaccords locaux avec les données empiriques.相似文献
4.
Ole H. Caspersen MSc PhD. Cecil C. Konijnendijk Anton S. Olafsson 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):7-20
Geografisk Tidsskrift, Danish Journal of Geography 106(2):7–20, 2006 In its Regional Plan of 2005, The Greater Copenhagen Authority (abbreviated as “HUR” in Danish) places special emphasis on the future recreational values associated with the regional green structure. In this paper, the development of the urban green structure in Greater Copenhagen is elaborated upon, focusing on land use changes and the effectiveness of regionally coordinated planning measures. EU MOLAND data are used to analyse the development of the region's green structure during the period 1954 to 1998. Analysis of two “green wedges” within the green structure illustrates that the development of the green recreational areas is the result of both formal and more informal planning initiatives. Development has shown equal phases that correspond to the applied regional planning measures and the general economic conditions. However, local preferences in the involved municipalities likewise have played an important role and have resulted in different urbanisation pressure within the two wedges. Land use has transformed from an agricultural to a primarily recreational landscape. In some areas, however, urbanisation pressure has resulted in residential and green industrial areas instead of the planned recreational land use. Based on its historical development it is concluded that future preservation and development of the green structure in Greater Copenhagen requires regional planning measures to be incorporated into municipal plans. In this way the increasingly independent municipalities will comply to objectives of the Regional Plan 2005. 相似文献
5.
Marine archaeology is a new discipline which seeks to increase knowledge of man's past activities on the sea, through the study of the remains of his ships and other relics on the ocean floor. The author argues that marine archaeology, through its combination of techniques taken from marine ecology, geology, sedimentology and other sciences, has evolved to the point in the UK where it may be classified as a science in its own right. He discusses legal and social problems of the field, and points out the need for a ‘systems approach’ in marine archaeological projects. 相似文献
6.
Galactic winds are important in recycling energy and metals in galaxies. They are also suspected to be the primary mechanism
in the enrichment of the intergalactic medium. New observations are revealing the ubiquity of galactic winds, particularly
at high redshift. We review the observational evidence for them in nearby star-forming and active galaxies and in the high-redshift
universe. 相似文献
7.
Cecil Seethal 《GeoJournal》2002,57(1-2):61-73
The issue of the quality of life of rural South Africans has become a key focus of attention of the national and provincial
governments in postapartheid South Africa. This focus stems from legislation that enshrines concurrent responsibility for
rural development to both these spheres of government. However, post-1995 legislation including the introduction of wall-to-wall
municipal authorities and the subsequent initiatives by municipalities to assume responsibility for service delivery in their
areas have infused considerable complexity into the development landscape at the local level. Within this context and against
the background of different perspectives and strategies for rural development, this paper examines, in a case study of the
Limehill Complex within the Ndaka Municipality in KwaZulu-Natal, the specific development problems that the `deep' rural communities
experience. The paper then discusses strategic interventions that the Ndaka Municipality, in conjunction with other role players
and the different spheres of government, needs to consider for implementation in order to regenerate the rural economy of
the Limehill Complex and assist in the alleviation of widespread poverty in the area.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Walter Dehnen Jonathan Bland-Hawthorn Andreas Quirrenbach Gerald N. Cecil 《Astrophysics and Space Science》1997,248(1-2):33-42
We present the kinematics of the ionized gas over the inner 140″ (10 kpc) from observations with the HIFI Fabry-Perot interferometer.
There is clear evidence for density wave streaming and bar-driven streaming across the field, with bi-symmetric arms that
penetrate to within 200 pc of the nucleus. CO maps show linear structures along (although slightly offset from) the bar consistent
with a strong shock. Along the spiral arms which encircle the bar, the H II regions lie downstream of the CO gas in the rest
frame of the bar, as do the dust lanes, only if the gas outruns the stellar bar. As a first step towards understanding the
details of the gas kinematics, and attempting to determine the mass inflow rate towards the nucleus, we build a mass model
for the central disk constrained by near-infrared images. We plan to use this model as gravitational background potential
for hydrodynamical simulations of the gas response to the bar. Comparing these with the data presented should enable us to
constrain various quantities such as pattern speed, stellar mass-to-light ratio, central mass concentration, and gas fueling
rate.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
J. Bland-Hawthorn S.L. Lumsden G.M. Voit G.N. Cecil J.C. Weisheit 《Astrophysics and Space Science》1997,248(1-2):177-190
The radio jet axis of NGC 1068 is characterised by energetic activity from x-ray to radio wavelengths. Detailed kinematic
and polarization studies have shown that this activity is confined to bipolar cones centered on the AGN which intersect the
plane of the disk. Thus, molecular clouds at 1 kpc distance along this axis are an important probe of the nuclear ionizing
luminosity and spectrum. Extended 10.8μm emission coincident with the clouds is reasonably understood by dust heated to high
temperatures by the nuclear radiation field. This model predicts that the nuclear spectrum is quasar-like (power law + blue
excess) with a luminosity 2-5 times higher than inferred by Pier et al. (1994). Consequently, there is little or no polyaromatic
hydrocarbon (PAH) emission associated with the radio-axis molecular clouds. We review this model in the light of new observations.
A multi-waveband collage is included to illustrate the possible orientations of the double cones to our line of sight and
the galaxian plane.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
K–Ca ages of Cambrian glauconites from the Llano uplift, central Texas, were determined in order to re-evaluate the ability
of the K–Ca system to constrain the timing of deposition of sedimentary packages. All of the K–Ca ages presented here were
found to be younger than their stratigraphic ages. In addition to being too young, the K–Ca ages are also highly variable,
ranging in age from Silurian to Permian. The oldest subset of glauconite ages are in agreement with previously published Rb–Sr
ages from the same outcrop and provide further evidence for there having been a post-depositional thermal or recrystallization
event that reset both the Rb–Sr and K–Ca systems. The range of younger glauconite K–Ca ages is similar to the distribution
of available apatite fission track ages for the Llano basement. K–Ca ages are interpreted as thermochronologic data reflecting
partial retention of Ca in thermally fluctuating basin conditions. Estimates of the closure temperature of Ca in glauconite
are found to be 60–90°C for cooling rates of ~0.5–1°C/My. The K–Ca system is potentially useful as a low-temperature thermochronometer
with closure temperatures <100°C for glauconite. 相似文献