Static cylindrically symmetric gravitational field with cosmological constant     

A. Banerjee  Antares Kleber  Nilton O. Santos 《Astrophysics and Space Science》1996,245(1):139-149

We show that a class of solutions for a vacuum cylindrically symmetric gravitational field with nonvanishing cosmological constant reduce to the welknown Levi-Civita metric close to the axis. All the circular geodesics in this generalized vacuum are time like, null or space like depending on the relative magnitudes of the two parameters appearing in the solutions.For other particles moving inZ=constant plane there are some cases where the trapping of timelike and null trajectories occur, while in other cases some of the particles may orbit round the axis in a fixed zone bounded by two limiting radii.  相似文献   

On the Use of Random Material in Dam Cores: Case of the Manso Dam,Brazil     

Ferreira  Breno S.  Almeida  Marcio S. S.  Lopes  Francisco R.  Reis Cavalcanti  Maria do Carmo  Pires Filho  Celso José 《Geotechnical and Geological Engineering》2022,40(4):1973-1987

Geotechnical and Geological Engineering - The Manso Dam, in the Brazilian State of Mato Grosso, intended for flood control and electricity generation, was built by a state-owned energy company in...  相似文献   

A global model study of natural bromine sources and the effects on tropospheric chemistry using MOZART4     

Gabriela Sousa Santos  Sebastian Rast 《Journal of Atmospheric Chemistry》2013,70(1):69-89

Halogens in the atmosphere chemically destroy ozone. In the troposphere, bromine has higher ozone destruction efficiency than chlorine and is the halogen species with the widest geographical spread of natural sources. We investigate the relative strength of various sources of reactive tropospheric bromine and the influence of bromine on tropospheric chemistry using a 6-year simulation with the global chemistry transport model MOZART4. We consider the following sources: short-lived bromocarbons (CHBr₃, CH₂BrCl, CHBr₂Cl, CHBrCl₂, and CH₂Br₂) and CH₃Br, bromine from airborne sea salt particles, and frost flowers and sea salt on or in the snowpack in polar regions. The total bromine emissions in our simulations add up to 31.7 Gmol(Br)/yr: 63 % from polar sources, 24.6 % from short-lived bromocarbons and 12.4 % from airborne sea salt particles. We conclude from our analysis that our global bromine emission is likely to be on the lower end of the range, because of too low emissions from airborne sea salt. Bromine chemistry has an effect on the oxidation capacity of the troposphere, not only due to its direct influence on ozone concentrations, but also by reactions with other key chemical species like HO _x and NO _x . Globally, the impact of bromine chemistry on tropospheric O₃ is comparable to the impact of gas-phase sulfur chemistry, since the inclusion of bromine chemistry in MOZART4 leads to a decrease of the O₃ burden in the troposphere by 6 Tg, while we get an increase by 5 Tg if gas-phase sulfur chemistry is switched off in the standard model. With decreased ozone burden, the simulated oxidizing capacity of the atmosphere decreases thus affecting species associated with the oxidation capacity of the atmosphere (CH₃OOH, H₂O₂).  相似文献   

Orbital Elements of 2004 Perseid Meteoroids Perturbed by Jupiter     

Josep Maria Trigo-Rodriguez  Jeremie Vaubaillon  José Luís Ortiz  Alberto Castro-Tirado  Jordi Llorca  Esko Lyytinen  Martin Jelínek  Antonio de Ugarte Postigo  Pablo Santos Sanz  Francisco J. Aceituno Castro  Albert Sánchez Caso  Antonio Bernal González  Juan Pastor Erades  Francisco Ocaña 《Earth, Moon, and Planets》2005,97(3-4):269-278

Jupiter and Saturn produce important gravitational impulses on meteoroids released by comet 109P/Swift-Tuttle. The meteoroids from this comet once released follow retrograde orbits that during their periodic approaches to these planets (within 1.6 and 0.9 A.U., respectively) are impulsed gaining orbital energy. This perturbation effect is translated into a net inward shift in the node of the perturbed meteoroids. Such geometry with Jupiter occurred in 2004 over a meteoroid trail ejected by this comet during the 1862 A.D. return of the comet to perihelion. In order to study the predicted outburst produced by one-revolution meteoroids, the Spanish Photographic Meteor Network (SPMN) performed an extensive campaign. As a part of this observational effort here are presented 10 accurate meteoroid orbits. We discuss their origin by comparing them with the theoretical orbital elements of the dust trails intercepting the Earth during the 2004 Perseid return.  相似文献   

Production of H ⁺₃  via photodissociation of organic molecules in interstellar clouds     

S. Pilling  D. P. P. Andrade  R. Neves  A. M. Ferreira-Rodrigues  A. C. F. Santos  H. M. Boechat-Roberty 《Monthly notices of the Royal Astronomical Society》2007,375(4):1488-1494

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Anisotropic viscous-fluid cosmological model     

A. Banerjee  M. B. Ribeiro  N. O. Santos 《Astrophysics and Space Science》1987,136(2):331-336

We present exact solutions of a Bianchi type VI₀ viscous fluid cosmological model. It is a generalization of the model proposed by Banerjee and Santos (1983) for Bianchi type I.  相似文献   

Three years statistics of simple 3 solar bursts     

Oscar T. Matsuura  P. Marques Dos Santos 《Solar physics》1971,17(2):402-407

A plasmoid may be ejected during a flare and condensed by a radiative instability. The spectral shape of the mean fluxes of Simple 3 (or long-enduring) solar events is interpreted in terms of a thermal emission from this transient condensation in the higher levels of the solar atmosphere. This condensation is thick enough to block the radiation from the underlying S-component. This explanation fits the observed polarization changes, as well as the thermal character of the bursts time profiles. A clue for solar activity forecasting as well as for detailed studies of active sources is indicated.  相似文献   

An analysis of carrier phase differential kinematic GPS positioning using DynaPos     

Karen?M.?CoveEmail author  Marcelo?C.?Santos 《GPS Solutions》2004,8(4):210-216

A series of activities have been carried out at the University of New Brunswick in an effort to evaluate advances in long-range marine kinematic differential positioning. These activities involved processing and analysis of GPS carrier phase kinematic data sets. Some of the data was collected by UNB and some was provided by The XYZs of GPS Inc. Data were collected using Trimble 5700 and Ashtech Z-12 receivers. The data sets were processed using the software DynaPos provided by the The XYZs of GPS Inc. The best results obtained in our analysis indicate an agreement of 5 cm RMS for the horizontal component and 12 cm RMS for the vertical component between two ionospheric-delay free solutions, in baselines varying from 40 to 100 km.  相似文献   

Trace metal contamination and benthic assemblages in Subaé estuarine system, Brazil     

Hatje V  Barros F  Figueiredo DG  Santos VL  Peso-Aguiar MC 《Marine pollution bulletin》2006,52(8):982-987

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Ideal width of transects for monitoring source-related categories of plastics on beaches     

de Araújo MC  Santos PJ  Costa MF 《Marine pollution bulletin》2006,52(8):957-961

Although there is a consensus on the necessity of monitoring solid wastes pollution on beaches, the methods applied vary widely. Therefore, creating, testing and recommending a method that not only allows comparisons of places and periods, but also the detection of source signals, will be important to reach the objectives of the source-prevention principle. This will also allow the optimisation of time, resources, and processing of samples and data. A classification of the items found into specific categories was made according to their most probable source/use (fisheries, food packaging, hazardous, sewage/personal hygiene, beach user, general home). This study tested different widths of sampling transects to be used in the detection of plastics contamination on beaches, until all the categories were significantly represented. Each transect had its total width (50m) sub-divided into eight intervals of 0-2.5m; 2.5-5m; 5-10m; 10-15m; 15-20m; 20-30m; 30-40m; and 40-50m. The accumulated number of categories in the 50m (up to 2.5m; up to 5m and so on) was used to determine the minimal width necessary to qualitatively characterize the area regarding plastics contamination. The diversity of the categories was directly related to the area of the sampling transect. These results indicate that a significant increase in the number of categories in the first intervals tend to stabilize from 15-20m onwards.  相似文献