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51.
A.W. Jones R.J. Davis A. Wilkinson G. Giardino S.J. Melhuish H. Asareh R.D. Davies A.N. Lasenby 《Monthly notices of the Royal Astronomical Society》2001,327(2):545-551
We present the joint analysis of two 5-GHz interferometric surveys of the northern sky, taken with different baselines. The two surveys were carried out on the Jodrell Bank 5-GHz interferometer based at Manchester. The Maximum Entropy Method is used to check the consistency of the two surveys and the final two-dimensional maps are used, together with low-frequency full sky surveys, to put constraints on the Galactic spectral index. It is found that synchrotron emission is the dominant process at high Galactic latitudes below 5 GHz. 相似文献
52.
53.
This article describes a method that determines the position of a point relative to a fixed boundary. Its advantage over the other existing algorithms described below is that in most cases it is necessary that only part of the algorithm be executed to determine the position of the point. A possible inconvenience of using this algorithm is that the contour boundary has to be entered as data. For problems where the boundary often changes the algorithm is not suitable in its present form. The applications envisaged here are to cases where the position of a very large number of points have to be determined relative to one fixed polygonal boundary whose shape is known in advance, for example, blanking out of contours in automatic contouring, or selecting drill holes which lie in the particular part of a mineral deposit. 相似文献
54.
A continuum representation for soil which incorporates the concepts of hypoelasticity and critical state theory is proposed. General, three-dimensional constitutive equations are formulated to relate specific volume, stress, rate of deformation and rate of change of stress, resulting in a mathematical material model which exhibits phenomenological features typical of soil response. The general constitutive equations are specialized to represent the particular cases of isotropic compression, constant, volume deformation, uniaxial compression and biaxial deformation. Methods are suggested for determining the model parameters to represent a specific soil using conventional triaxial test data. Comparisons of stress-strain response with published experimental data are shown. 相似文献
55.
New measurements of the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn at 3.1 and 8.6 mm wavelengths are given. The temperatures reported for the planets at 3.1 mm wavelength are higher than previous measurements in this wavelength range and change the interpretation of some planetary spectra. For Mercury, it is found that the mean brightness temperature is independent of wavelength and that a temperature dependent thermal conductivity is not required to match the observations. In the case of Mars, the spectrum is shown to rise in the millimeter region as simple models predict. For Jupiter, the need to recalculate the spectrum with recent models is demonstrated. The flux density scale proposed by Dent (1972) has been revised according to a more accurate determination of the millimeter brightness temperature of Jupiter. 相似文献
56.
57.
The San Francisco Estuary Regional Monitoring Program initiated surveillance monitoring to identify previously unmonitored synthetic organic contaminants in the San Francisco Estuary. Organic extracts of water samples were analyzed using gas chromatography-mass spectrometry in full scan mode. The major contaminant classes identified in the samples were fire retardants, pesticides, personal care product ingredients, and plasticizers. Evidence from the literature suggests that some of these contaminants can persist in the environment, induce toxicity, and accumulate in marine biota and in higher food chain consumers. The major sources of these contaminants into the marine environment are the discharge of municipal and industrial wastewater effluents, urban stormwater, and agricultural runoff. As a proactive effort, it is suggested that surveillance studies be used routinely in monitoring programs to identify and prevent potential problem contaminants from harming the marine environment. 相似文献
58.
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
59.
Kristen E. K. Coppin Christopher J. Davis & Milena Micono 《Monthly notices of the Royal Astronomical Society》1998,301(1):L10-L14
We discuss the formation of spectral features in the decelerating ejecta of gamma-ray bursts, including the possible effect of inhomogeneities. These should lead to blueshifted and broadened absorption edges and resonant features, especially from H and He. An external neutral ISM could produce detectable H and He, as well as Fe X-ray absorption edges and lines. Hypernova scenarios may be diagnosed by Fe Kα and H Lyα emission lines. 相似文献
60.
Fly ash generated by coal-fired power plants is in part collected by filters in the emission stacks while a small portion
is vented into the atmosphere. Since many of the coalfired power plants in the western United States are located in the desnrt,
the ability to monitor fly ash emissions requires a chemical tracer that utilizes desert soil and plant interactions with
the fly ash deposited in the desert environment. This investigation presents the results of a controlled greenhouse experiment
in which a native desert plant, the brittlebush (Encelia farinosa), was grown on admixtures of desert soils and fly ash. The fly ash is strongly enriched in Sr and the brittlebush is a Sr
accumulator. The data demonstrate that (1) the brittlebush isotopically equilibrates with desert soils whose fly ash components
are as low as 0.25% by weight, (2) the fly ash Sr is apparently more available to the plant, than Sr derived from the soils,
and (3) the difference between the87Sr/86Sr ratio of the fly ash (0.70807) and soils (0.71097 to 0.71117) warrants further investigations in the natural environment
to determine the practicality of this method as a natural tracer of fly ash in the environment. 相似文献