Aerial electromagnetic sounding of the lithosphere of Venus     

Robert E. Grimm  Amy C. Barr  Keith P. Harrison  David E. Stillman  Kerry L. Neal  Michael A. Vincent  Gregory T. Delory 《Icarus》2012,217(2):462-473

Electromagnetic (EM) investigation depths are larger on Venus than Earth due to the dearth of water in rocks, in spite of higher temperatures. Whistlers detected by Venus Express proved that lightning is present, so the Schumann resonances ～10–40 Hz may provide a global source of electromagnetic energy that penetrates ～10–100 km. Electrical conductivity will be sensitive at these depths to temperature structure and hence thermal lithospheric thickness. Using 1D analytic and 2D numerical models, we demonstrate that the Schumann resonances—transverse EM waves in the ground-ionosphere waveguide—remain sensitive at all altitudes to the properties of the boundaries. This is in marked contrast to other EM methods in which sensitivity to the ground falls off sharply with altitude. We develop a 1D analytical model for aerial EM sounding that treats the electrical properties of the subsurface (thermal gradient, water content, and presence of conductive crust) and ionosphere, and the effects of both random errors and biases that can influence the measurements. We initially consider specified 1D lithospheric thicknesses 100–500 km, but we turn to 2D convection models with Newtonian temperature-dependent viscosity to provide representative vertical and lateral temperature variations. We invert for the conductivity-depth structure and then temperature gradient. For a dry Venus, we find that the error on temperature gradient obtained from any single local measurement is ～100%—perhaps enough to distinguish “thick” vs. “thin” lithospheres. When averaging over thousands of kilometers, however, the standard deviation of the recovered thermal gradient is within the natural variability of the convection models, <25%. A “wet” interior (hundreds of ppm H₂O) limits EM sounding depths using the Schumann resonances to <20 km, and errors are too large to estimate lithospheric properties. A 30-km conductive crust has little influence on the dry-interior models because the Schumann penetration depths are significantly larger. We conclude that EM sounding of the interior of Venus is feasible from a 55-km high balloon. Lithospheric thickness can be measured if the upper-mantle water content is low. If H₂O at hundreds of ppm is present, the deeper, temperature-sensitive structure is screened, but the “wet” nature of the upper mantle, as well as structure of the upper crust, is revealed.  相似文献   

A Comparison of the 10.7-cm Radio Flux Values and the International Sunspot Numbers for Solar Activity Cycles 19, 20, and 21     

Robert A. Greenkorn 《Solar physics》2012,280(1):205-221

A nonlinear analysis of the daily 10.7-cm radio flux values for each of Solar Cycles 19, 20, and 21 is used to determine if the results match those of the International Sunspot Numbers for each of these cycles. Fractals and chaos are described and a brief review of utilizing fractals and chaos is given. The origin of the 10.7-cm radio flux is discussed and a short review of recent work discussing its measurement and its relation to the international sunspot number and other proxies for solar activity cycles given. The parameters used to describe chaos for the 10.7-cm radio flux are discussed. The length of the data sets for either statistical analysis or nonlinear analysis of the 10.7-cm radio flux values is considered. These results indicate that the 10.7-cm radio flux values appear to be stochastic for Cycle 19 and chaotic for Cycles 20 and 21. The International Sunspot Numbers show similar behavior for these three cycles. A day-by-day comparison of the dimensionless 10.7-cm radio flux values and the dimensionless International Sunspot Numbers differences shows a linear trend. The results remain consistent in that the 10.7-cm radio flux values indicate, as did the International Sunspot Numbers, that there is a transition from stochastic behavior for Cycle 19 to chaotic behavior in Cycles 20 and 21. The day-by-day comparison of the 10.7-cm radio flux values and the International Sunspot Numbers emphasizes that the 10.7?cm radio flux values are responding to the magnetic field associated with the sunspots.  相似文献   

Measuring Tourist’s Water Footprint in a Mountain Destination of Northwest Yunnan, China     

Luc HENS  Robert DE WULF 《山地科学学报》2011,8(5):682-693

Monitoring and minimizing tourist’s water consumption is essential for the sustainable development of mountain destinations in the world. However, available data and a generally accepted protocol on such measurement are still limited. This study uses water footprint accounting to quantify tourist’s water demand in the Liming valley, a World Heritage site and a rapidly growing tourism destination in Northwest Yunnan, China. Both the water for direct and indirect use is taken into account based on the consump...  相似文献   

Model prediction capacity of ephemeral gully evolution in conservation tillage systems     

Eduardo Luquin  Miguel A. Campo-Bescós  Rafael Muñoz-Carpena  Ronald L. Bingner  Richard M. Cruse  Henrique G. Momm  Robert R. Wells  Javier Casalí 《地球表面变化过程与地形》2021,46(10):1909-1925

Ephemeral gully (EG) erosion has an important impact on agricultural soil losses and increases field surface hydrology connectivity and transport of pollutants to nearby water bodies. Watershed models including an EG component are scarce and not yet properly evaluated. The objective of this study is to evaluate the capacity of one such tool, AnnAGNPS, to simulate the evolution of two EG formed in a conservation tillage system. The dataset for model testing included runoff measurements and EG morphological characteristics during 3 years. Model evaluation focused on EG evolution of volume, width, and length model outputs, and included calibration and testing phases and a global sensitivity analysis (GSA). While the model did not fully reproduce width and length, the model efficiency to simulate EG volume was satisfactory for both calibration and testing phases, supporting the watershed management objectives of the model. GSA revealed that the most sensitive factors were EG depth, critical shear stress, headcut detachment exponent coefficient b, and headcut detachment leading coefficient a. For EG outputs the model was additive, showing low sensitivity to interactions between the inputs. Prediction of EG spatial evolution on conservation tillage systems requires improved development of gully erosion components, since many of the processes were developed originally for traditional tillage practices or larger channel systems. Our results identify the need for future research when EG form within conservation tillage systems, in particular to study gully headcut, soil erodibility, and width functions specific to these practices.  相似文献   

Improving Risk-Based Screening at Vapor Intrusion Sites in California     

Matthew A. Lahvis  Robert A. Ettinger 《Ground Water Monitoring & Remediation》2021,41(2):73-86

The attenuation factor (AF) of 0.03 recommended by the U.S. Environmental Protection Agency (USEPA) is increasingly being used by regulatory agencies for the development of subsurface vapor screening levels for vapor intrusion (VI). There are concerns, however, over the database used to derive the AF and the AF's applicability to building types and geographies not included in USEPA database. To derive a more technically defensible AF for subsurface vapor screening in California, a database consisting of 8415 paired indoor and subsurface vapor samples collected from 485 buildings at 36 sites in California was compiled. Filtering was applied to remove data of suspect quality that were potentially affected by background (non-VI) sources. Filtering reduced the size of the database to 788 indoor air and subsurface vapor pairs, 80% of which were trichloroethylene (TCE) measurements. An AF of 0.0008 was derived from only TCE vapor data, based on the ability of the AF to reliably identify buildings with indoor air concentrations above screening levels in 95% of cases where subsurface vapor screening levels were exceeded. The AF derived from this study demonstrated limited sensitivity to the variables typically considered important in VI characterization, which was partially attributed to relatively weak correlation of indoor air and subsurface vapor concentration data. The results of this study can be used to improve VI screening in California and other states and help focus limited resources on sites posing the greatest potential risk.  相似文献   

Titan's atmospheric chemistry: Photolysis of gas mixtures containing hydrogen cyanide and carbon monoxide at 185 and 254 nm     

Buu N. Tran  Robert G. Briggs  Peter Persans 《Icarus》2008,193(1):224-232

The formation of organic compounds in the atmosphere of Titan is an ongoing process of the generation of complex organics from the simplest hydrocarbon, methane. Solar radiation and magnetosphere electrons are the main energy sources that drive the reactions in Titan's atmosphere. Since energy from solar radiation is 200 times greater than that from magnetosphere electrons, we have investigated the products formed by the action of UV radiation (185 and 254 nm) on a mixture of gases containing nitrogen, methane, hydrogen, acetylene, ethylene, and cyanoacetylene, the basic gas mixture (BGM) that simulates aspects of Titan's atmosphere using a flow reactor [Tran, B.N., Ferris, J.P., Chera, J.J., 2003a. Icarus 162, 114-124; Tran, B.N., Joseph, J.C., Force, M., Briggs, R.G., Vuitton, V., Ferris, J.P., 2005. Icarus 177, 106-115]. The present research extends these studies by the addition of carbon monoxide and hydrogen cyanide to the BGM. Quantum yields for the loss of reactants and the formation of volatile products were determined and compared with those measured in the absence of the hydrogen cyanide and carbon monoxide. The GCMS analyses of the volatile photolysis products from the BGM, with added hydrogen cyanide, had a composition similar to that of the BGM while the photolysis products of the BGM with added carbon monoxide contained many oxygenated compounds. The infrared spectrum of the corresponding solid product revealed the absorption band of a ketone group, which was probably formed from the reaction of carbon monoxide with the free radicals generated by photolysis of acetylene and ethylene. Of particular interest was the observation that the addition of HCN to the gas mixture only resulted in a very small change in the C/N ratio and in the intensity of the CN frequency at 2210 cm⁻¹ in the infrared spectrum suggesting that little HCN is incorporated into the haze analog. The C/N ratio of the haze analogs was found to be in the 10-12 range. The UV spectra of the solid products formed when HCN or CO added to the BGM is similar to the UV absorption formed from the BGM alone. This result is consistent with absence of additional UV chromophores to the solid product when these mixtures are photolyzed. The following photoproducts, which were not starting materials in our photochemical studies, have been observed on Titan: acetonitrile, benzene, diacetylene, ethane, propene, propane, and propyne.  相似文献   

Carbon dioxide segregation in 1:4 and 1:9 CO₂:H₂O ices     

Robert Hodyss  Paul V. Johnson  Grazyna E. Orzechowska  Jay D. Goguen  Isik Kanik 《Icarus》2008,194(2):836-842

The mid-infrared spectra of mixed vapor deposited ices of CO₂ and H₂O were studied as a function of both deposition temperature and warming from 15 to 100 K. The spectra of ices deposited at 15 K show marked changes on warming beginning at 60 K. These changes are consistent with CO₂ segregating within the ice matrix into pure CO₂ domains. Ices deposited at 60 and 70 K show a greater degree of segregation, as high as 90% for 1:4 CO₂:H₂O ice mixtures deposited at 70 K. As the ice is warmed above 80 K, preferential sublimation of the segregated CO₂ is observed. The kinetics of the segregation process is also examined. The segregation of the CO₂ as the ice is warmed corresponds to temperatures at which the structure of the water ice matrix changes from the high density amorphous phase to the low density amorphous phase. We show how these microstructural changes in the ice have a profound effect on the photochemistry induced by ultraviolet irradiation. These experimental results provide a framework in which observations of CO₂ on the icy bodies of the outer Solar System can be considered.  相似文献   

Gemini/GMOS spectroscopy of the spheroid and globular cluster system of NGC 3923     

Mark A. Norris  Ray M. Sharples  Terry Bridges  Karl Gebhardt  Duncan A. Forbes  Robert Proctor  Favio Raul Faifer  Juan Carlos Forte  Michael A. Beasley  Stephen E. Zepf  David A. Hanes 《Monthly notices of the Royal Astronomical Society》2008,385(1):40-52

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The early-type galaxies NGC 1407 and NGC 1400 – I. Spatially resolved radial kinematics and surface photometry     

Max Spolaor  Duncan A. Forbes  George K. T. Hau  Robert N. Proctor  Sarah Brough 《Monthly notices of the Royal Astronomical Society》2008,385(2):667-674

This is the first paper of a series focused on investigating the star formation and evolutionary history of the two early-type galaxies NGC 1407 and NGC 1400. They are the two brightest galaxies of the NGC 1407 (or Eridanus-A) group, one of the 60 groups studied as part of the Group Evolution Multi-wavelength Study.
Here, we present new high signal-to-noise ratio long-slit spectroscopic data obtained at the ESO 3.6-m telescope and high-resolution multiband imaging data from the Hubble Space Telescope /Advanced Camera for Surveys and wide-field imaging from Subaru Suprime-Cam. We spatially resolved integrated spectra out to ∼0.6 (NGC 1407) and ∼1.3 (NGC 1400) effective radii. The radial profiles of the kinematic parameters v _rot, σ, h ₃ and h ₄ are measured. The surface brightness profiles are fitted to different galaxy light models and the colour distributions analysed. The multiband images are modelled to derive isophotal shape parameters and residual galaxy images. The parameters from the surface brightness profile fitting are used to estimate the mass of the possible central supermassive black hole in NGC 1407. The galaxies are found to be rotationally supported and to have a flat core in the surface brightness profiles. Elliptical isophotes are observed at all radii and no fine structures are detected in the residual galaxy images. From our results, we can also discard a possible interaction between NGC 1400, NGC 1407 and the group intergalactic medium. We estimate a mass of  ∼1.03 × 10⁹ M_⊙  for the supermassive black hole in NGC 1407 galaxy.  相似文献   

Spitzer observations of M33 and the hot star, H ii region connection     

Robert H. Rubin  Janet P. Simpson  Sean W. J. Colgan  Reginald J. Dufour  Gregory Brunner  Ian A. McNabb  Adalbert W. A. Pauldrach  Edwin F. Erickson  Michael R. Haas  Robert I. Citron 《Monthly notices of the Royal Astronomical Society》2008,387(1):45-62

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