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991.
992.
Norbert Hertkorn Ronald Benner Philippe Schmitt-Kopplin Karl Kaiser John I. Hedges 《Geochimica et cosmochimica acta》2006,70(12):2990-3010
Refractory carboxyl-rich alicyclic molecules (CRAM) are characterized in marine dissolved organic matter (DOM) using nuclear magnetic resonance spectroscopy and ultrahigh resolution mass spectrometry. CRAM are distributed throughout the water column and are the most abundant components of deep ocean DOM ever characterized. CRAM are comprised of a complex mixture of carboxylated and fused alicyclic structures with a carboxyl-C:aliphatic-C ratio of 1:2 to 1:7. CRAM are expected to constitute a strong ligand for metal binding, and multiple coordination across cations could promote aggregation and marine gel formation thereby affecting CRAM reactivity and the bioavailability of nutrients and trace metals. It appears CRAM are ultimately derived from biomolecules with structural similarities to sterols and hopanoids. The occurrence of CRAM in freshwater and terrestrial environments seems likely, considering the global distribution of biomolecules and the similarities of biogeochemical processes among environments. 相似文献
993.
Manuela A. Fehr Mark Rehkämper Alex N. Halliday Maria Schönbächler Bodo Hattendorf 《Geochimica et cosmochimica acta》2006,70(13):3436-3448
Tellurium isotope data acquired by multiple-collector inductively coupled plasma-mass spectrometry (MC-ICPMS) are presented for sequential acid leachates of the carbonaceous chondrites Orgueil, Murchison, and Allende. Tellurium isotopes are produced by a broad range of nucleosynthetic pathways and they are therefore of particular interest given the isotopic anomalies previously identified for other elements in these meteorites. In addition, the data provide new constraints on the initial solar system abundance of the r-process nuclide 126Sn, which decays to 126Te with a half-life of 234,500 years. The 126Te/128Te ratios of all leachates were found to be identical, within uncertainty, despite variations in 124Sn/128Te of between about 0.002 and 1.4. The data define a 126Sn/124Sn ratio of <7.7 × 10−5 at the time of last isotopic closure, consistent with the value of <18 × 10−5 previously reported for bulk carbonaceous chondrites. How close this is to the initial 126Sn/124Sn ratio of the solar system depends on when the investigated samples last experienced redistribution of Sn and Te. No clear evidence is found for nucleosynthetic anomalies in the abundances of p-, s-, and r-process nuclides. The largest effect detected in this study is a small excess of the r-process nuclide 130Te in a nitric acid leachate of Murchison. This fraction displays an anomalous ε130Te of +3.5 ± 2.5. Although barely resolvable given the analytical uncertainties, this is consistent with the presence of a small excess r-process component or an s-process deficit. The general absence of anomalies contrasts with previous results obtained for K, Cr, Zr, Mo, and Ba isotopes in similar leachates, which display nucleosynthetic anomalies of up to 3.8%. The reason for this discrepancy is unclear but it may reflect volatility and more efficient mixing of Te in the solar nebula. 相似文献
994.
This study provides a detailed magnetostratigraphy of sediments composing the Cold Creek cataclysmic flood bar in the Pasco Basin, Washington. Our interpretation suggests onset of Missoula floods or similar events prior to 1.1 myr, later than previously suggested by Bjornstad et al. [Bjornstad, B.N., Fecht, K.R., Pluhar, C.J., 2001. Long history of pre-Wisconsin, Ice Age cataclysmic floods: evidence from southeastern Washington State. Journal of Geology 109 (6), 695-713]. Nonetheless these data suggest that Channeled Scabland features formed over a much longer timespan than commonly cited, that continental ice sheets of the early Pleistocene reached as far south as those of the late Pleistocene, and that similar physiography existed in eastern Washington and perhaps Montana to both generate and route Missoula-flood-like events. This study adds paleomagnetic polarity results from 213 new samples of silts and sands derived from nine new drill cores penetrating the Cold Creek cataclysmic flood bar to our previous database of 53 samples from four boreholes, resulting in a much more robust and detailed magnetostratigraphy. Rock magnetic studies on these sediments show pure magnetite to be the predominant remanence-carrying magnetic mineral, ruling out widespread remagnetization by secondary mineralization. The magnetostratigraphy at eastern Cold Creek bar is characterized by a normal polarity interval bracketed by reversed polarities. Equating the normal zone with the Jaramillo subchron (0.99-1.07 myr) affords the simplest correlation to the magnetic polarity timescale. Western Cold Creek bar was likely deposited during the Brunhes chron (0-0.78 myr) since it exhibits mainly normal polarities with only two thin reversed-polarity horizons that we interpret as magnetic excursions during the Brunhes. 相似文献
995.
I. C. Okoli DVM M. Sc. Ph.D. C. U. Nweke B.S. Agric. Tech. C. G. Okoli B.Sc M. Sc. Ph.D. M. N. Opara DVM M.Sc 《International Journal of Environmental Science and Technology》2006,3(1):9-14
This study was carried out to identify the common moulds growing in selected commercial poultry feed sold in Owerri, Imo State, Nigeria. Forty-eight bulk samples derived froml92 bags of feeds were collected from broiler starter (BS), broiler finishers (BF), grower mash (GM) and layer mash (LM) across 4 different brands of ommercial poultry feeds, which included Livestock (LF), Top (TF) Guinea (GF) and Vital (VF) feeds. The feed samples were collected during the rainy season months of June, July and August. The common moulds isolated from these feeds were Aspergillus sp., Peicillium sp.,Mucor sp., Yeast sp., Rhizopus sp., Epicoecum sp., Gymnoaseus sp., Cladosporium sp., Mortierella sp. as well as Bacteria. Generally, more organisms were isolated in June than the other months with Mortierella sp. being the only one not isolated in that month. Vital feed with 8 different isolates had the highest diversity of fungal species while the others had between 4 and 5 species. Prevalence rates across the feed types, generally ranged from 18.76% in layer mash to 30.03% in broiler finisher. The four Aspergillus sp. isolated came from GM and BF. This study highlights the need for constant monitoring of moulds in commercial feedstuff produced in the humid tropical environments such as Imo state, Nigeria. There is also the need to routinely include fungal growth nhibitors in commercial feeds since moulds are capable of reducing the nutritional values of feedstuff as well as elaborating pathogenic toxins. 相似文献
996.
S. N. Jamal B. Sc. M. Sc. M. Zafar Iqbal B.Sc. M.Sc Ph.D. M. Athar M.Sc MPhil. Ph.D. D.Sc 《International Journal of Environmental Science and Technology》2006,3(1):53-58
The study deals with the effect of metal toxicity (aluminum, chromium and combination of both the metals) on seed germination, root length, shoot length, seedling length and dry biomass of Vigna radiata and V. sinensis. Chromium adversely affected the seedling by significantly reducing the growth whereas aluminum did not show such effect in both the species. Percentage of germination was good in both the species at different concentration of treatment (aluminum, chromium and combined treatment). Shoot length was also not much affected in V. sinensis as it was greatly inhibited in V. radiata. Both the species showed the purpling of stem. Dry biomass of V. radiata showed positive effect than V. sinensis. However, dry biomass decreased to a lesser extent when treated with aluminum, chromium and combined treatment as compared to control. 相似文献
997.
A. A. Rassafi M. Vaziri A. N. Azadani 《International Journal of Environmental Science and Technology》2006,3(1):59-68
The current paper is an attempt to find a sustainable fuel strategy for passenger cars in Iran. Currently, most of Iran’s passenger cars consume gasoline, a non-renewable fossil fuel. This fuel has well-known environmental impacts, including various kinds of pollutions, as well as the threat of quick running out. These general negative characteristics of gasoline are amplified by the high consumption rate of Iran’s transportation sector, (e.g. about three times more than that of UK). The objective of this paper is firstly selecting possible alternative fuels for Iran’s transportation sector, and then proposing the percent of cars consuming these alternative fuels (along with gasoline). The best strategies are proposed based on environmental and economic considerations, and hence are more sustainable decisions comparing with the other strategies. The best strategies are found using partial order theory and Hasse diagram technique, which is a multi-criteria decision analysis (MCDA) tool. 相似文献
998.
Hydrocyclones are widely used in the mining and chemical industries. An attempt has been made in this study, to develop a CFD (computational fluid dynamics) model, which is capable of predicting the flow patterns inside the hydrocyclone, including accurate prediction of flow split as well as the size of the air-core. The flow velocities and air-core diameters are predicted by DRSM (differential Reynolds stress model) and LES (large eddy simulations) models were compared to experimental results. The predicted water splits and air-core diameter with LES and RSM turbulence models along with VOF (volume of fluid) model for the air phase, through the outlets for various inlet pressures were also analyzed. The LES turbulence model led to an improved turbulence field prediction and thereby to more accurate prediction of pressure and velocity fields. This improvement was distinctive for the axial profile of pressure, indicating that air-core development is principally a transport effect rather than a pressure effect. 相似文献
999.
L.D. Chrosniak L.N. Smith C.G. McDonald B.F. Jones J.M. Flinn 《Journal of Geochemical Exploration》2006,88(1-3):91
Ingestion of enhanced zinc can cause memory impairments and copper deficiencies. This study examined the effect of zinc supplementation, with and without copper, on two types of memory. Rats raised pre- and post-natally on 10 mg/kg ZnCO3 or ZnSO4 in the drinking water were tested in a fear-conditioning experiment at 11 months of age. Both zinc groups showed a maladaptive retention of fearful memories compared to controls raised on tap water. Rats raised on 10 mg/kg ZnCO3, 10 mg/kg ZnCO3 + 0.25 mg/kg CuCl2, or tap water, were tested for spatial memory ability at 3 months of age. Significant improvements in performance were found in the ZnCO3 + CuCl2 group compared to the ZnCO3 group, suggesting that some of the cognitive deficits associated with zinc supplementation may be remediated by addition of copper. 相似文献
1000.
N. Kosheleva E. Karabanov A. Kositskiy D. Williams S. Armstrong 《Journal of Geochemical Exploration》2006,88(1-3):118
A channel account approach is proposed to estimate longitudinal changes in runoff along large river systems. This new method provides a quantitative basis for describing the fluvial transport of suspended particulate material and dissolved substances. This method includes an evaluation of basic elements of water balance in separate sections of the river network and subsequent correction of channel accounting equations for the entire system using a maximum likelihood principle. To calculate water discharges of tributaries that have no hydrological information, structural analysis of river network is performed. This approach provides less error in comparison with traditional methods of estimating lateral inflow. The method is used to trace water discharge with increasing distance along the Lena river basin and to evaluate the contribution of geologically and lithologically uneven sub-basins in water discharge formation during a summer low water period. 相似文献