Influence of karst hydrology on water quality management in southeast South Australia     

A. J. Emmett  A. L. Telfer 《Environmental Geology》1994,23(2):149-155

Southeast South Australia has large reserves of potable groundwater, generally close to the surface. European settlement has had a major impact on groundwater quality due to the presence of extensive karst in the unconfined aquifer. Historically, industries such as cheese factories were often sited close to karst features (e.g. caves and sinkholes) because they provided a convenient means of waste disposal. Although most have long since closed, they have left a legacy of pollution plumes of varying sizes. In Mount Gambier, the main regional centre, the presence of both exposed and subterranean karst features provided a perfect system for the disposal of stormwater. Prior to the provision of a sewerage system within Mount Gambier, all toilet and household wastewaters were disposed to ground. These activities and the subsequent problems that began emerging in the 1960s have led to a concerted effort over the last 20 years to change the philosophy of waste disposal and to generate an understanding and responsibility by those who live in the region and depend on groundwater for the major part of their water supply. Mount Gambier's water supply comes from the Blue Lake. Groundwater inflow from a highly karstic Tertiary limestone aquifer provides 90% of the recharge to the Blue Lake. The lake is a high-value resource in a high-risk environment and in order to minimize this risk, a water-quality management plan for the lake is currently being developed.  相似文献   

An evaluation of residential air radon concentrations and related variables in southeast Michigan,USA     

L. G. Kodosky 《Environmental Geology》1994,23(1):65-72

Analysis of 153 residential air radon (Rn-222) screening measurements from southeast Michigan indicates that basements host Rn levels two to three times higher than upper-level rooms. Compared to unfinished basements, finished (e.g., paneled walls, tiled floors) basements apparently reduce indoor air Rn levels while partially finished basements may not. Factor analysis of residence questionnaire data explains 59 percent of the Rn data variance. The volume of pathways (e.g., foundation cracks/holes, uncapped sumps) allowing Rn seepage into the dwelling controls the largest portion, 23 percent, of the explained data variance. The residence water source explains 11 percent of the Rn data variance. Groundwater Rn levels contribute to the air Rn data variability, but the study data cannot quantitatively assess this contribution. Seven percent of the Rn data variance is likely controlled by house depressurization facilitated by residence structural properties. Residences with foundation cracks or poorly sealed joints and low-volume indoor-outdoor air exchange are more prone to this effect. Eighteen percent of the explained Rn data variance correlates with the residence's primary heat source. Evidently, operating combustion sources also induce house depressurization and allow Rn to be drawn into the house through entry paths. Twenty-four percent of the analyses equal or exceed 4 pCi/1 Rn. In residences occupied 5 years by the same individuals, 17 percent of the Rn data are 4 pCi/l; here the arithmetic mean air Rn level is 8.3 pCi/l and the average occupancy period 17.4 years.  相似文献   

Connection between X-ray and optical variability in NGC 4151     

V. L. Oknyanskij 《Astrophysics and Space Science》1994,222(1-2):157-169

We have used long light curves in the X-ray (ARIEL V, EXOSAT, Ginga and others), UV (IUE), and optical (data of intensive ground-based monitoring) ranges of NGC 4151 to investigate connections between variations in these spectral fields. Applying Fourier (CLEAN algorithm) and modern cross-correlation analysis, we revealed the different character of the variability and the cross-correlation between high and low states of the nucleus. In contrast to earlier results, we found that X-ray and optical fluxes correlate in the active state without any apparent delay.In the power spectrum of the optical and X-ray light curves in the high state we found the existence of the same period of about 65 days, which disappeared in the low state.We confirmed previous data that X-ray variations correlate more strongly with UV and optical continuum variability during the low state, but it is possible that the optical variations appear to lag behind those involving X-rays by several tens of days.Strong variations in H line profile and [Fe X]6374 line intensity variations correlate with the observed X-ray covering dip in 1990 (Yaqoobet al., 1993).We discuss briefly the implications of these results.  相似文献   

Once more on quasar periodicities     

Ágnes Holba  I. Horváth  B. Lukács  G. Paál 《Astrophysics and Space Science》1994,222(1-2):65-83

In an earlier paper Arp, Bi, Chu and Zhu investigated various quasar samples and recognized a periodicity of remarkable degree in them. Their conclusion was that the existence of such a periodicity is a counterevidence against the cosmological origin of quasar redshifts. Since this question is of great importance in a cosmological context, here we reanalyze some of the samples together with a galaxy sample of the pencil-beam survey of Broadhurstet al. Our result is that on the plane of cosmological parameters (₀, ₀) there is a non-negligible region where two quasar samples and the galaxy sample are simultaneously fairly periodic. Pure periodicity is still compatible with cosmological principles, at least on length scales much longer than the period length. So the regularities can fit into a cosmological context.  相似文献   

Long,accurate time series measurements of radial velocities of solar-type stars     

R. S. Mcmillan  T. L. Moore  M. L. Perry  P. H. Smith 《Astrophysics and Space Science》1994,212(1-2):271-280

We have been measuring changes in the radial velocities (RV's) of solar-type stars to search for gravitational perturbations by planets. We transmit violet starlight through a Fabry-Perot etalon interferometer and sense changes in Doppler shift from changes in the fluxes of light on the slopes of stellar absorption lines. Our data now span 6 years. Our observations of the Sun showed earlier that both our technique and the profiles of solar photospheric violet absorption lines can be stable enough to reveal planetary perturbations. We now carry this validation to the spectra of other near-solar-type stars. Annual averages of our RV's of Draconis and Virginis are stable to ±6 m s^–1. The slope of our five-year series of RV's of Bootis A is consistent with the star's well-determined visual astrometric orbit about Bootis B. The Fabry-Perot technique of Doppler shift measurement is fully capable of detecting perturbations due to planets with masses and orbits similar to those of Jupiter.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.  相似文献   

The project “spice”     

D. Rouan  N. Epchtein  M. De Muizon  F. Lacombe  P. Puget  D. Tiphene  F. Boulanger  X. Desert  G. Guyot  L. D'Hendecourt  J -M. Lamarre  A. Leger  F. Pajot  J -L. Puget  E. Caux  M. Giard  G. Serra  C. Cesarsky  L. Vigroux  A. Omont 《Astrophysics and Space Science》1994,217(1-2):41-44

Proposed to both the French and the European Space Agency as one possible small mission, SPICE is a project for a dedicated small satellite for a near-IR spectroscopic all-sky survey. The instrument would cover the spectral range 1.8 - 3.6µm, possibly extended to 1.8 - 7µm, at a resolution of 100, with pixels of 1 arc-min. The excellent sensitivity (0.02 MJy sr-1) results from: i) the quasi-zero level of background due to the efficient passive cooling of the whole experiment; ii) the use of large format arrays; iii) the non-stop observing mode (drift-scanning). The spectral domain, complementing the one of ISO, partially opaque from the ground, is specially rich in spectral features tracing stars and all components of the Interstellar Medium (molecular, atomic and ionized gas, dust). With a cooling below 80 K of the focal instrument, then it becomes possible to consider doubling the spectral domain and to cover the whole 1.8 - 7µm range.  相似文献   

A coronal loop model for the production of X-ray and radio flares in the RS CVn binary HR 1099     

D. F. Falla  L. M. Bartlett  M. H. L. Smith  R. R. Hillier 《Astrophysics and Space Science》1994,211(1):115-126

The RS CVn binary stellar system HR 1099 is a source of both X-ray and radio flares. We present here a model of the system in which the two types of flare are produced by the same population of mildly-relativistic ( 10) electrons, injected into a coronal loop. After reviewing possible radiation mechanisms we conclude that, given the probable conditions in the flaring region, the radio emission is gyrosynchrotron radiation and the X-ray emission is thermal bremsstrahlung. The thermal X-ray source must lie in the stellar chromosphere, but the apparent absence of plasma absorption at radio frequencies indicates that the radio source is located high in the coronal loop. Using the relationships given by Dulk and Marsh (1982) for the radio emission from a power-law electron energy spectrum,N() ( - 1)^–, we conclude that 3 7, with 30% of the electron population trapped in the radio source. Some implications of these results for one particular version of the model are discussed.  相似文献   

Nonthermal radio emission from hot star winds     

Wan Chen  Richard L. White 《Astrophysics and Space Science》1994,221(1-2):259-273

Nonthermal radio emission has been observed from some of the most luminous hot star winds. It is understood to be synchrotron radiation of the relativistic electrons in the winds. To understand how the electrons are accelerated to such high energies and to correctly explain the observed radio flux and spectra require an exhaustive investigation of all the relevant physical processes involved and possibly point to a complex wind structure. In this paper we discuss the logical path toward a comprehensive model of the nonthermal radio emission from hot star winds. Based on the available observational data and fundamental theoretical considerations, we found that the only physically viable and self-consistent scenario is:the nonthermal radio emission is synchrotron radiation of relativistic electrons the electrons are accelerated by shocks via the first-order Fermi mechanism the acceleration has to be in situ in the radio emitting region the shocks formed at the base of the winds have to propagate to beyond the radio photosphere).  相似文献   

A photochemical model of the martian atmosphere     

Nair H  Allen M  Anbar AD  Yung YL  Clancy RT 《Icarus》1994,111(1):124-150

The factors governing the amounts of CO, O2, and O3 in the martian atmosphere are investigated using a minimally constrained, one-dimensional photochemical model. We find that the incorporation of temperature-dependent CO2 absorption cross sections leads to an enhancement in the water photolysis rate, increasing the abundance of OH radicals to the point where the model CO abundance is smaller than observed. Good agreement between models and observations of CO, O2, O3, and the escape flux of atomic hydrogen can be achieved, using only gas-phase chemistry, by varying the recommended rate constants for the reactions CO + OH and OH + HO2 within their specified uncertainties. Similar revisions have been suggested to resolve discrepancies between models and observations of the terrestrial mesosphere. The oxygen escape flux plays a key role in the oxygen budget on Mars; as inferred from the observed atomic hydrogen escape, it is much larger than recent calculations of the exospheric escape rate for oxygen. Weathering of the surface may account for the imbalance. Quantification of the escape rates of oxygen and hydrogen from Mars is a worthwhile objective for an upcoming martian upper atmospheric mission. We also consider the possibility that HOx radicals may be catalytically destroyed on dust grains suspended in the atmosphere. Good agreement with the observed CO mixing ratio can be achieved via this mechanism, but the resulting ozone column is much higher than the observed quantity. We feel that there is no need at this time to invoke heterogeneous processes to reconcile models and observations.  相似文献   

On the statistical wind rose analysis     

B. Zelenko  I. Lisac 《Theoretical and Applied Climatology》1994,48(4):209-214

Summary In this paper an approximation of the occurrence probability of wind direction classes by means of a mixture distribution consisting of several component distributions is described. In particular, undetermined parameter values of a mixture distribution describing a wind rose are estimated by minimizing an appropriate function. Deviations of the obtained frequencies from the wind rose data are subjected to a chi-square test. Every component of the mixture distribution is expected to have an occurrence probability equal to the probability of the corresponding airflow type. This method has been applied to approximately two hundred wind data samples based on particular parts of a day and year. Results of two characteristic examples are discussed. It is expected that the statistically obtained components can be explained by meteorological and topoclimatological parameters.With 3 Figures  相似文献