Ultraviolet observations of Mars and Saturn by the TDIA and OAO-2 satellites     

John Caldwell 《Icarus》1977,32(2):190-209

Ultraviolet photometric and spectrophotometric observations of Mars and Saturn obtained by two Earth-orbiting satellites are combined in this report. High-resolution data from the S59 experiment aboard TD1A reveal no definite absorption features in the spectra of either planet. The absence of a prominent absorption in the Mars data near 2150 Å can be reconciled with the preliminary Viking measurement of NO only if that gas is preferentially concentrated at high Martian altitudes. Broadband photometry from OAO-2 shows that atmospheric dust on Mars during the great dust storm of 1971–1972 reduced the ultraviolet geometric albedo by a factor of ?3 at the height of the storm. This atmospheric energy deposition is probably an important mechanism in the storm dynamics. Diurnal variation in the ultraviolet brightness of Mars appears to be marginally detectable during the dust storm. A real brightness variation during a clear season is observed. The combined Saturn data from the two satellites strongly suggest that NH₃ does not influence the ultraviolet spectrum of Saturn, but that some other absorber does. A candidate for such an absorber, H₂S, is investigated. OAO-2 broadband photometry of Jupiter and of Saturn demonstrate that these planets have very similar albedos from 2100 to 2500 Å. This implies a common ultraviolet absorber on both planets, other than NH₃.  相似文献   

Spatially resolved infrared observations of Saturn III. 10- and 20-μm disk scans at B′ = −11°.8     

A.T. Tokunaga  J. Caldwell  F.C. Gillett  I.G. Nolt 《Icarus》1979,39(1):46-53

Disk scans of Saturn at 10 and 20 μm were obtained when the Saturnicentric solar declination (B′) was ?11°.8. The scans show little change from scans obtained when B′ was ?16°.3, and this could result from the long radiative time constant of the Saturnian atmosphere. The observations at 20 μm, in the H₂ continuum, show positively that the temperature inversion at the south pole has a higher temperature than at any other point on the disk. In addition, the 12.1- and 20-μm scans indicate that the temperature of the inversion region is higher at the equator compared to the temperate zone. The data also suggest that enhanced 20-μm emission is correlated with the strength of the ultraviolet absorption.  相似文献   

Quintessential Cosmology Novel Models of Cosmological Structure Formation     

R.R. Caldwell  R. Dave  P.J. Steinhardt 《Astrophysics and Space Science》1998,261(1-4):303-310

We examine the possibility that a substantial fraction of the total energy density in a spatially flat Universe is composed of a time-dependent and spatially inhomogeneous component whose equation-of-state differs from that of baryons, neutrinos, dark matter, or radiation. In this lecture, we report on our investigations of the case in which the additional energy component, dubbed "quintessence", is due to a dynamical scalar field evolving in a potential. We have computed the effects on the background cosmological evolution, the cosmic microwave background (CMB) and mass power spectrum, finding a broad range of cosmologically viable models. We stress three important features of the quintessence or Q-component: the time evolution of the equation-of-state; the length-scale dependence of the speed of propagation of the fluctuations in the Q-component; and, the contribution of quintessence fluctuations to the CMB anisotropy spectrum. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The Promise of Structure Formation with Cosmic Strings in an Open Universe     

P. P. Avelino  R. R. Caldwell  C. J. A. P. Martins 《Astrophysics and Space Science》1998,261(1-4):319-320

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The magnetotelluric phase tensor   总被引：31，自引：0，他引：31  

T. Grant Caldwell  Hugh M. Bibby  Colin Brown 《Geophysical Journal International》2004,158(2):457-469

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The use of selected genotoxicity assays in green-lipped mussels (Perna viridis): a validation study in Hong Kong coastal waters     

Siu SY  Lam PK  Martin M  Caldwell CW  Richardson BJ 《Marine pollution bulletin》2008,57(6-12):479-492

In Hong Kong, discharges of domestic and industrial wastewaters and disposal of contaminated muds into coastal waters have resulted in high levels of persistent organic contaminants in the water column, biota and bottom sediments. Although the acute toxicity of effluents has been tested by government regulators using mortality-based bioassays, the sublethal effects of many of the pollutants, including environmental carcinogens, have not been well studied. The objective of the present work was to examine the efficiency and efficacy of using: (1) DNA strand breaks (comet assay and alkaline agarose gel electrophoresis assay); (2) oxidative DNA damage (levels of 8-hydroxy-2-deoxyguanosine in cellular DNA) and (3) micronuclei (MN) formation as early warning toxicological indicators of potential environmental carcinogen exposure. Green-lipped mussels (Perna viridis) were transplanted to study sites and retrieved after 4, 8, 12, 16 and 30 days. The bioaccumulation of organic pollutants, including the polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OC pesticides) and polychlorinated biphenyls (PCBs) was observed, and compared with biomarker assays. Some significant dose- and time-dependent inductions of the genotoxic biomarkers, including 8-OHdG, DNA strand breaks and micronuclei were observed. In particular, several very strong (r>0.9) and significantly positive relationships were found at all sites during days 0-12. In addition, significant strong relationships between certain organic contaminants (carcinogenic PAHs and 4 common OC pesticides) and micronuclei were detected at the polluted sites, Tsim Sha Tsui and Sai Wan Ho. The results suggest that the use of micronuclei as a biomarker is potentially effective, especially at the more polluted sites. Nonetheless, further research is required to validate their effectiveness under varying field conditions, especially to elucidate responses under lower contaminant loads, interactions between the environmental and physiological factors affecting organisms in differing coastal environments, and changes in biotransformation and DNA repair enzymes in test organisms.  相似文献   

The seedbed microclimate and active revegetation of disturbed lands in the Mojave Desert     

T.G. Caldwell  E.V. McDonald  M.H. Young 《Journal of Arid Environments》2009,73(4-5):563-573

One of the greatest challenges to the U.S. Department of Defense is maintaining the sustainability of military lands while maximizing their use for training activities. Restoration of disturbed lands in the Mojave Desert has proven to be a challenge, particularly revegetation from seed. This study presents soil moisture dynamics from three restoration sites at the National Training Center, Ft. Irwin, CA. The soil microclimate (matric potential, water balance, and temperature) was monitored beneath various surface treatments to better assess their effects on seed germination and establishment. Results show that under the typically hot and dry climatic conditions that prevail, the soil microclimate is a hostile environment. Irrigation had the most positive effect on the seedbed. Surface mulches including gravel, straw, emulsion, and bark had limited benefits often detrimental. Although seedlings germinated, survival after three months was negligible. Results presented here suggest that successful seeding with broadcast sprinkler irrigation in the central Mojave Desert is not possible unless the seedbed area is limited or advantageous environmental conditions prevail. Improved knowledge of the germination requirements and applied numerical modeling would result in more successful seedbed management.  相似文献   

Recovery in rubble fields: long-term impacts of blast fishing     

Fox HE  Pet JS  Dahuri R  Caldwell RL 《Marine pollution bulletin》2003,46(8):1024-1031

This paper presents initial results from a study of factors that inhibit or enhance hard coral recovery in rubble fields created by blast fishing in Komodo National Park and Bunaken National Park, Indonesia. Within nine sites monitored since 1998, there was no significant natural recovery. Levels of potential source coral larvae were assessed with settlement tiles in the rubble fields and in nearby high coral cover sites. Rubble movement was measured and shown to be detrimental to small scleractinians, especially in high current areas. In shallow water (2-6 m deep), rubble is often overgrown by soft corals and corallimorpharians, which inhibit hard coral survival. There is increased scleractinian recruitment in quadrats cleared of soft coral, and Acropora nubbins transplanted into soft coral fields suffer greater mortality than those transplanted above the soft coral canopy. Gaining an understanding of the prognosis for coral recovery is essential not only in order to assess the long-term impacts of blast fishing, but also to improve management decisions about protection of intact reefs and potential restoration of damaged areas.  相似文献   

New observational constraints on the temperature inversions of Uranus and Neptune     

A.T. Tokunaga  G.S. Orton  J. Caldwell 《Icarus》1983,53(1):141-146

We present 20-μm photometry of Uranus and Neptune which confirms the presence of a temperature inversion in the lower stratospheres in both planets. We find the brightness temperature difference between 17.8 and 19.6 μm to be 0.8 ± 0.5°K for Uranus and 1.8 ± 0.6°K for Neptune. These results indicate that the temperature inversions on both planets are weaker than previously thought. Comparison to model atmospheres by J. Appleby [Ph.D. thesis, SUNY at Stony Brook 1980] indicates that the temperature inversions can be understood as arising from heating by the absorption of sunlight by CH₄ and aerosols. However, the stratospheric CH₄ mixing ratio on Neptune must be higher than that at the temperature minimum.  相似文献   

Evaluation and Mitigation of Landfill Gas Impacts on Cadmium Leaching from Native Soils     

A.E. McGrath  G.L. Upson  M.D. Caldwell 《Ground Water Monitoring & Remediation》2007,27(4):99-109

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