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171.
The equation of radiative transfer for an inhomogenous dispersive finite medium subject to general boundary conditions is solved. The Padé approximation technique is used to calculate the angular distribution of radiation. Numerical results for the [0/1] Padé approximant lead to numerical results that compared with the exact results. 相似文献
172.
O. M. El Mekki 《Solar physics》1985,96(2):397-411
Over-reflection of propagating hydromagnetic planetary-gravity waves incident on the current sheets of the helmet streamers and magnetic sectors of the solar corona is investigated.It is shown that over-reflection arises only if the wavenumbers, or the energy fluxes per unit mass, perpendicular to the current sheet of the incident and the transmitted waves in both cases are in opposite directions. The over-reflected waves then draw magnetic energy from the sun's field and communicate it to the interplanetary magnetic field.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
173.
We have constructed a chemical reaction model in a contracting interstellar cloud including 104 species which are involved in a network of 557 reactions. The chemical kinetic equations were integrated as a function of time by using gear package. The evolution of the system was followed in the density range 10–107 particles cm-3.The calculated fractional abundances of the charged species are in good agreement with those given by other investigators. The charge density has been followed in diffuse, intermediate and dense regions. The most dominant ionic species are metallic ions, HCO+ and H
3
+
in the shielded regions and atomic ions H+, C+, Si+, He+, S+ and metal ions in the diffuse and intermediate regions. The abundances of negatively charged ions were found to be negligible. The results of the calculations on the different metallic ions are interpreted. 相似文献
174.
Matyasovszky István Makra László Tusnády Gábor Csépe Zoltán Nyúl László G. Chapman Daniel S. Sümeghy Zoltán Szűcs Gábor Páldy Anna Magyar Donát Mányoki Gergely Erostyák János Bodnár Károly Bergmann Karl-Christian Deák Áron József Thibaudon Michel Albertini Roberto Bonini Maira Šikoparija Branko Radišić Predrag Gehrig Regula Rybníček Ondřej Severova Elena Rodinkova Victoria Prikhodko Alexander Maleeva Anna Stjepanović Barbara Ianovici Nicoleta Berger Uwe Seliger Andreja Kofol Weryszko-Chmielewska Elżbieta Šaulienė Ingrida Shalaboda Valentina Yankova Raina Peternel Renata Ščevková Jana Bullock James M. 《Theoretical and Applied Climatology》2018,133(1-2):277-295
Theoretical and Applied Climatology - The drivers of spatial variation in ragweed pollen concentrations, contributing to severe allergic rhinitis and asthma, are poorly quantified. We analysed the... 相似文献
175.
Asim Jilani Syed Zajif Hussain Mohd Hafiz Dzarfan Othman Usama Zulfiqar Muhammad Bilal Shakoor Imran Ullah Khan Javed Iqbal Attieh A. Al-Ghamdi Ahmed Alshahrie 《Journal of Atmospheric Chemistry》2018,75(3):271-283
In this work, the X-ray Photoelectron Spectroscopy (XPS) technique is utilized to analyze the surface chemical composition of particulate matter (PM) which was collected from various locations at Jeddah, Saudi Arabia. The main elements found on the surface of PM are carbon (C), oxygen (O) and silicon (Si) with combined percentage of 89.4–94.9 while traces of nitrogen (N), calcium (Ca), aluminum (Al), sodium (Na), chlorine (Cl), manganese (Mg), and sulfur (S) were also present. The analyzed XPS chemical state of C, O and Si was further used to determine their bonding with other elements occurring over the surface of PM. Carbon was found in the form of carbides (18.86%), fluorides (2.39%) and carbonates (78.75%); oxygen was observed as oxides (21.05%) and hydroxides (73.42%) of other metals; and silicon was detected as silicones (12.16%), nitrides (82.53%) and silicates (5.25%). The particle size of a PM is also of great concern for health issues, and thus has been investigated by the Field Emission Scanning Electron Microscope (FESEM). The Energy Dispersive X-ray Spectroscopy (EDS) was employed for cross verification of detected elements by XPS. 相似文献
176.
Optimum reaction time, performance and exhaust emissions of biodiesel produced by microwave irradiation 总被引:3,自引:3,他引:0
A. A. Refaat S. T. El Sheltawy K. U. Sadek 《International Journal of Environmental Science and Technology》2008,5(3):315-322
While transesterification is well established, there remain considerable inefficiencies in existing transesterification processes. In this study an alternative energy stimulant, “microwave irradiation” was used for the production of the alternative energy source, biodiesel. The optimum parametric conditions obtained from the conventional technique were applied using microwave irradiation in order to compare both systems. The results showed that application of radio frequency microwave energy offers a fast, easy route to this valuable biofuel with advantages of enhancing the reaction rate and improving the separation process. The methodology allows for the use of high free fatty acid content feedstock, including used cooking oil; hence it helps to reduce the cost of production which constitutes a major hurdle towards widespread commercialization of biodiesel. The study also showed that the optimum reaction time for microwave-enhanced biodiesel production should be highly respected. Exceeding the optimum reaction time will lead to deterioration of both biodiesel yield and purity. This paper also reported the performance and exhaust emissions from a diesel engine when fuelled with a petroleum diesel fuel and two different biodiesel fuels; one obtained by the conventional technique and the other by microwave irradiation. It was concluded that microwave-enhanced biodiesel is not, at least, inferior to that produced by the conventional technique. 相似文献
177.
Modification of thermal and oxidative properties of biodiesel produced from vegetable oils 总被引:1,自引:1,他引:0
G. El Diwani Ph.D. S. El Rafie Ph.D. 《International Journal of Environmental Science and Technology》2008,5(3):391-400
Trans esterification of three vegetable oils, sunflower oil, linseed oil and mixed oils as; sunflower-soyabean and olein were carried out using methanol, and potasium hydroxide as catalyst. The methyl esters of the corresponding oils were separated from the crude glycerol and characterized by physical-chemical methods to evaluate their thermal properties. This methods are determination of densities, cloud points, pour points, flash points, kinematic viscosities, hydrogen/carbon ratios, sulfur contents, ash contents and triglycerides. The physico-chemical characteristic of biodiesel treated with ozone showed improvement of pour point and flash point indicating higher degree of safety for fuel. Methyl esters mixed with their corresponding ozonated oil were subjected to comparison and evaluation for their thermal properties by the thermo gravimetric analysis differential thermal analysis from which the calculated heat of enthalpy and comparison with the heat of conventional diesel. The results showed that the oxygen content of biodiesel samples treated with ozone increased weight % and resulted in more extensive chemical reaction, promoted combustion characteristics and less carbon residue was produced. Gas chromatography appeared more suitable to address the problem of determining/verifying biodiesel methyl ester and showed that methyl ester content was impurity free. Ultra violet-detection was used for rapid quantization of triglycerols. From the analyses performed biodiesel treated with ozone modified the thermal and oxidative stability shown by the high combustion efficiency indicated by the high heat of enthalpy and reducing the emission of particulate matter. 相似文献
178.
Safae Berrah El Kheir Jamal Oubbih Nadia Saidi Abdelhak Bouabdli 《Arabian Journal of Geosciences》2008,1(2):87-95
Contaminated soils and mine tailings pose major environmental and agricultural problems worldwide. These problems may be partially
solved by an emerging new technology: phytoremediation. This technique uses plants to extract soil contaminants from the ground.
Thlaspi caerulescens is known to accumulate in their tissues several heavy metals from soil and aerial deposition. This study was conducted to
screen plants growing on a contaminated site to determine their potential for metal accumulation. Seeds of T. caerulescens metallicolous have been collected in the vicinity of F.T. Laurent le Minier in the Pb–Zn mining district of les Malines (North
of Montpellier, Southern France), and seeds of T. caerulescens non-metallicolous were sampled on Larzac Plateau (North of Montpellier, Southern France). Soil substrates were collected
from a mine site of Mibladen and Zaida (West, Morroco). Cultivated plant and surface soil samples were analyzed for zinc,
lead, and cadmium concentrations by inductively coupled plasma mass spectrometry. A non-metallicolous (NM) ecotype of T. caerulescens and a metallicolous (M) ecotype are compared for Pb, Cd, and Zn accumulation in shoot and root in five metal-contaminated
soils and one uncontaminated soil. The growth of individuals from uncontaminated soil was greater than that of individuals
from metal-contaminated soils. The NM populations had markedly higher root/shoot ratio compared to M populations. The results
indicate that both ecotypes of T. caerulescens are highly tolerant of zinc and Cd. Ecotype NM had constitutively higher Zn uptake capacity than the M ecotype. T. caerulescens species accumulate higher amount of Zn and Cd in their tissues in polluted soil and, in both of the two ecotypes, the root
Pb concentrations were much greater than those of the shoot Pb contents. From both uncontaminated and metal-contaminated soils,
we conclude that T. caerulescens are interesting material for phytoremediation of zinc and cadmium. 相似文献
179.
A. El Mandour F. El Yaouti Y. Fakir Y. Zarhloule J. Benavente 《Environmental Geology》2008,54(3):491-503
The Bou-Areg plain in the Mediterranean coast at the North-eastern of Morocco is characterized by a semi-arid climate. The
aquifer consists of two sedimentary formations of Plio-quaternary age: the upper formation of fine silts and the lower one
of coarse silts with sand and gravels. The aquifer is underlain by marly bedrock of Miocene age that dips toward the coastal
lagoon of Bou-Areg. The hydrodynamic characteristics vary between 10−4 and 10−3 m/s; and transmissivities range between 10−4 and 10−1 m2/s. The general direction of flow is SW to NE, toward the lagoon. The aquifer is crossed by the river Selouane, which also
ends in the lagoon. The groundwater is characterized by a high salinity that can reach 7.5 g/l. The highest values are observed
in the upstream and in the downstream sectors of the aquifer. The temporal evolution of the physico-chemical parameters depends
on the climatic conditions and piezometric variations. The analysis of the spatio-temporal distribution of the physico-chemical
parameters suggests different sources of groundwater salinization: the seawater intrusion, the influence of marly gypsum-bearing
terrains, and the influence of anthropogenic products as the agricultural fertilizers, which cause great nitrate concentrations
that vary between 80 and 140 mg/l. 相似文献
180.
Groundwater of Egypt: “an environmental overview” 总被引:1,自引:0,他引:1
Although Egypt has the great Nile River, which is the main supply of water, Egypt’s water is limited to 55.5 billion m3 per annum. Owing to the rapid growth of the population and the increasing consumption of water in agriculture, industry,
domestic use, etc., it is expected that Egypt will rely to some extent on groundwater to develop the new projects such as
Tushka in Upper Egypt and East Oweinat. Issues related to groundwater in Egypt are identified with the common geological features
associated with formation of the aquifers and demonstrating the location of the main resources of groundwater, followed by
the main objective of this paper, which is addressing the environmental issues related to groundwater in Egypt. Several studies
have been reviewed and personal communication made with the authorities to introduce this work and provide an overview of
the groundwater quality problems in Egypt with examples from different parts of the country. 相似文献