Long-term evolution of the aerosol debris cloud produced by the 2009 impact on Jupiter     

A. Sánchez-Lavega  G.S. Orton  R. Hueso  L.N. Fletcher  E. García-Melendo  I. de Pater  H.B. Hammel  A. Simon-Miller  F. Marchis  O. Mousis  J. García-Rojas  M. Cecconi  K. Noll  S. Pedraz  P. Kalas  W. Golisch  P. Sears  V. Reddy  R. Binzel  W. Grundy  J. Emery  A. Rivkin  C. Thomas  D. Trilling  K. Bjorkman  A.J. Burgasser  H. Campins  T.M. Sato  Y. Kasaba  J. Ziffer  R. Mirzoyan  H. Bouy 《Icarus》2011,214(2):462-476

We present a study of the long-term evolution of the cloud of aerosols produced in the atmosphere of Jupiter by the impact of an object on 19 July 2009 (Sánchez-Lavega, A. et al. [2010]. Astrophys. J. 715, L155-L159). The work is based on images obtained during 5 months from the impact to 31 December 2009 taken in visible continuum wavelengths and from 20 July 2009 to 28 May 2010 taken in near-infrared deep hydrogen-methane absorption bands at 2.1-2.3 μm. The impact cloud expanded zonally from ∼5000 km (July 19) to 225,000 km (29 October, about 180° in longitude), remaining meridionally localized within a latitude band from 53.5°S to 61.5°S planetographic latitude. During the first two months after its formation the site showed heterogeneous structure with 500-1000 km sized embedded spots. Later the reflectivity of the debris field became more homogeneous due to clump mergers. The cloud was mainly dispersed in longitude by the dominant zonal winds and their meridional shear, during the initial stages, localized motions may have been induced by thermal perturbation caused by the impact’s energy deposition. The tracking of individual spots within the impact cloud shows that the westward jet at 56.5°S latitude increases its eastward velocity with altitude above the tropopause by 5-10 m s⁻¹. The corresponding vertical wind shear is low, about 1 m s⁻¹ per scale height in agreement with previous thermal wind estimations. We found evidence for discrete localized meridional motions with speeds of 1-2 m s⁻¹. Two numerical models are used to simulate the observed cloud dispersion. One is a pure advection of the aerosols by the winds and their shears. The other uses the EPIC code, a nonlinear calculation of the evolution of the potential vorticity field generated by a heat pulse that simulates the impact. Both models reproduce the observed global structure of the cloud and the dominant zonal dispersion of the aerosols, but not the details of the cloud morphology. The reflectivity of the impact cloud decreased exponentially with a characteristic timescale of 15 days; we can explain this behavior with a radiative transfer model of the cloud optical depth coupled to an advection model of the cloud dispersion by the wind shears. The expected sedimentation time in the stratosphere (altitude levels 5-100 mbar) for the small aerosol particles forming the cloud is 45-200 days, thus aerosols were removed vertically over the long term following their zonal dispersion. No evidence of the cloud was detected 10 months after the impact.  相似文献   

The Maria asteroid family: Genetic relationships and a plausible source of mesosiderites near the 3:1 Kirkwood Gap     

Sherry K. Fieber-Beyer  Michael J. Gaffey  Michael S. Kelley  Vishnu Reddy  Chalbeth M. Reynolds 《Icarus》2011,213(2):524-537

We present a mineralogical assessment of 12 Maria family asteroids, using near-infrared spectral data obtained over the years 2000-2009 combined with visible spectral data (when available) to cover the spectral interval of 0.4-2.5 μm. Our analysis indicates the Maria asteroid family, which is located adjacent to the chaotic region of the 3:1 Kirkwood Gap, appears to be a true genetic family composed of assemblages analogous to mesosiderite-type meteorites. Dynamical models by Farinella et al. (Farinella, P., Gunczi, R., Froeschlé, Ch., Froeschlé, C., [1993]. Icarus 101, 174-187) predict this region should supply meteoroids into Earth-crossing orbits. Thus, the Maria family is a plausible source of some or all of the mesosiderites in our meteorite collections. These individual asteroids were most likely once part of a larger parent object that was broken apart and dispersed. One of the Maria dynamical family members investigated, ((695) Bella), was found to be unrelated to the genetic Maria family members. The parameters of (695) Bella indicate an H-chondrite assemblage, and that Bella may be a sister or daughter of Asteroid (6) Hebe.  相似文献   

Biodegradation and environmental behavior of biodiesel mixtures in the sea: An initial study     

DeMello JA  Carmichael CA  Peacock EE  Nelson RK  Samuel Arey J  Reddy CM 《Marine pollution bulletin》2007,54(7):894-904

Biodiesel, a mixture of fatty acid methyl esters (FAMEs) derived from animal fats or vegetable oils, is rapidly moving towards the mainstream as an alternative source of energy. However, the behavior of biodiesel, or blends of biodiesel with fossil diesel, in the marine environment have yet to be fully understood. Hence, we performed a series of initial laboratory experiments and simple calculations to evaluate the microbial and environmental fate of FAMEs. Aerobic seawater microcosms spiked with biodiesel or mixtures of biodiesel and fossil diesel revealed that the FAMEs were degraded at roughly the same rate as n-alkanes, and more rapidly than other hydrocarbon components. The residues extracted from these different microcosms became indistinguishable within weeks. Preliminary results from physical-chemical calculations suggest that FAMEs in biodiesel mixtures will not affect the evaporation rates of spilled petroleum hydrocarbons but may stabilize oil droplets in the water column and thereby facilitate transport.  相似文献   

GIS-enabled historiography to determine travel routes during the Western Han period via agent-based models and least-cost path analysis     

Raja Sengupta  Griet Vankeerberghen  Ruoxuan Wen  Jing Rao  Yanbing Chen 《Transactions in GIS》2023,27(4):1090-1103

GIS-enabled historiography allows us to shed light on missing or poorly understood aspects of historical events. Here, we use agent-based models (ABMs), least cost path analysis (LCPA), and space–time paths to recreate and evaluate possible modes and routes of travel undertaken by Shi Rao, a Western Han official. A diary was found in Shi Rao's tomb that includes information about his travels over 1 year (11 BCE), including start and end times of his journeys. But it leaves out details regarding modes of transport or exact routes. Using Tan Qixiang's historical atlas, we digitized river networks and utilized modern topographic data to digitally recreate the landscape as it was during Shi Rao's travels. This was then used to evaluate possible journeys via rivers (using ABMs) and roads (using LCPA), and compared to historical speed of boats, carts and horses, with findings indicating that horseback may have been the viable option.  相似文献   

A site-specific study on the measurement of sorption coefficients for radionuclides     

A. A. Dalvi  S. D. Kumar  A. V. R. Reddy 《International Journal of Environmental Science and Technology》2014,11(3):617-622

A study on the potential of geological media from the vicinity of the mining site in Tummalapalle region of Andhra Pradesh in India for retardation of radionuclide migration in groundwater was conducted. The studies included the measurement of sorption coefficients for six radionuclides, uranium, thorium, lead, bismuth, radium and polonium, between two groundwater simulants and two site-specific samples of geological media. Initial parametric studies involving chemical composition, pH, calcium carbonate and organic carbon contents of both geological media and ground water simulants were carried out. Significant differences in sorption coefficients were observed as a result of varying pH, calcium carbonate and presence of trace quantities of organic contents in simulant solutions. For example, uranium has a hundred fold lower distribution coefficient in the case of simulant solution having higher carbonate content. Similarly, in the case of the geological media having higher calcium carbonate and organic carbon contents, higher distribution coefficients were obtained for all radionuclides. Among the six radionuclides studied thorium showed the largest and radium the smallest distribution coefficient values for the soil samples assessed. The site-specific sorption coefficients will be used for contaminant transport study.  相似文献   

Hydrogeological processes controlling the release of arsenic in parts of 24 Parganas district,West Bengal     

Neha Singh  Ravi Prakash Singh  Saumitra Mukherjee  Kyle McDonald  K. J. Reddy 《Environmental Earth Sciences》2014,72(1):111-118

A study was conducted to understand the hydrogeological processes dominating in the North 24 Parganas and South 24 Parganas based on representative 39 groundwater samples collected from selected area. The abundance of major ions was in the order of Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ > Fe²⁺ for cations and HCO₃ ^? > PO₄ ^3? > Cl^? > SO₄ ^2? > NO₃ ^? for anions. Piper trilinear diagram was plotted to understand the hydrochemical facies. Most of the samples are of Ca-HCO₃ type. Based on conventional graphical plots for (Ca + Mg) vs. (SO₄ + HCO₃) and (Na + K) vs. Cl, it is interpreted that silicate weathering and ion exchange are the dominant processes within the study area. Previous studies have reported quartz, feldspar, illite, and chlorite clay minerals as the major mineral components obtained by the XRD analysis of sediments. Mineralogical investigations by SEM and EDX of aquifer materials have shown the occurrence of arsenic as coating on mineral grains in the silty clay as well as in the sandy layers. Excessive withdrawal of groundwater for irrigation and drinking purposes is responsible for fluctuation of the water table in the West Bengal. Aeration beneath the ground surface caused by fluctuation of the water table may lead to the formation of carbonic acid. Carbonic acid is responsible for the weathering of silicate minerals, and due to the formation of clay as a product of weathering, ion exchange also dominates in the area. These hydrogeological processes may be responsible for the release of arsenic into the groundwater of the study area, which is a part of North 24 Parganas and South 24 Parganas.  相似文献   

Stratigraphic status,age, and paleobathymetry of the Grey shale Member,Dalmiapuram Formation,Cauvery Basin,India     

R. Nagendra  P. Sathiyamoorthy  A. N. Reddy  Harry Gilbert  B. C. Jaiprakash 《Arabian Journal of Geosciences》2014,7(10):4133-4144

Grey shale Member of the Dalmiapuram Formation, Ariyalur Group, Cauvery Basin, India was studied for its stratigraphic position, age, and paleobathymetry with a re-look into the lithological relationship and foraminifer assemblages in the deepened limestone mine excavations at M/s Dalmia Cements, Dalmiapuram. Twenty grey shale samples from Kovandankurchchi (pit-4) and Kallakkudi mines yielded diversified calcareous, benthic, and rare index planktic foraminifera. The foraminiferal assemblages suggest a latest Albian age and middle neritic depositional conditions. The abundance of kaolinite and smectite clay minerals relate to warm/humid climate which corroborate with rising relative sea level during grey shale deposition. The grey shale occurs in patches within the marl bedded limestone member which exhibits cyclic deposition of limestone and marl. The limestone mine sections demonstrate that the grey shale forms part of basal marl bedded limestone, directly overlying the coral algal limestone. The present study demonstrates that the grey shale outcrops in Dalmiapuram Formation should be placed stratigraphically as part of marl bedded limestone. The member status for grey shale which is current usage stands discounted.  相似文献   

One-dimensional dispersion in unsteady flow in an adsorbing porous medium: An analytical solution     

Raja Ram Yadava  Ram Raj Vinda  Naveen Kumar 《水文研究》1990,4(2):189-196

Analytical solutions describing the concentration distribution along one-dimensional unsteady seepage flow through adsorbing saturated finite porous medium have been obtained. An exponential function concentration is enforced at the source of the dispersion, while the change in the concentration is zero at the other boundary. A new time variable has been introduced to solve the unsteady flow problem and the solution is illustrated.  相似文献   

Exact bianchi type-II,VIII, and IX cosmological models with matter and electromagnetic fields in Lyra's manifold     

R. Venkateswarlu  D. R. K. Reddy 《Astrophysics and Space Science》1991,182(1):97-103

Spatially-homogeneous and anisotropic Bianchi type-II, VIII, and IX stiff-fluid cosmological models in the presence of source-free electromagnetic fields are obtained in Lyra's manifold. Some properties of the models are also discussed.  相似文献   

Bianchi type-II,VIII, and IX cosmologies with conformally-invariant scalar field and electromagnetic fields     

R. Venkateswarlu  D. R. K. Reddy 《Astrophysics and Space Science》1991,184(1):153-156

In the expansive nondecelerative universe creation of matter happens as a result of a fundamental relationship and mutual compatibility of the field and matter.  相似文献