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41.
42.
Anthropogenic and seasonal influences on the dynamics of selected heavy metals in Lake Naivasha, Kenya 总被引:1,自引:0,他引:1
Joseph Nyingi Kamau Anthony Gachanja Catherine Ngila Johnson Michael Kazungu Mingzhe Zhai 《Lakes & Reservoirs: Research and Management》2008,13(2):145-154
Lake Naivasha is a freshwater lake in the Eastern Rift Valley of Kenya (0°45′S and 36°20′E). It has no surface outlet and is perceived to be under anthropogenic stress. Being situated at the basin of the rift valley, the lake acts as a sink for wastes from the town of Naivasha and the surrounding horticultural industry. Flux experiments were conducted to investigate the dynamics of heavy metals between the sediment–water interface in Lake Naivasha. In situ benthic flux experiments were conducted at two sites, one near the municipal wastewater inflow to the lake (site SS), and one at the papyrus field near the horticultural farms (site SH). Sediment samples from the exposed riparian land were collected during the dry season after the lake has receded, and the fluxes of selected metals were determined in the laboratory under simulated conditions. Aluminium in situ benthic flux at site SS averaged 7 mmol m?2 h?1, and was correlated positively with pH (Pearson correlation coefficient (r) = 0.89). While the in situ benthic flux of aluminium at site SH averaged 1 mmol m?2 h?1. In situ benthic fluxes of copper and manganese were predominantly positive at site SS, but not at site SH. The papyrus field at site SH played an important role in buffering of the lake in regard to the selected metals investigated in this study. Redox‐sensitive metals were precipitated in the benthic flux experiment for this site. 相似文献
43.
In this paper we present long-reach fiber access links supporting transmission of Worldwide Interoperability for Microwave Access (WiMAX) compliant signals. We present bi-directional full-duplex transmission of 256-state quadrature amplitude modulation (256-QAM) modulated WiMAX-compliant signals on a 2.4-GHz RF carrier over an 80-km long-reach access link at 100 Mb/s (down) and 64 Mb/s (up). Transmission of 64-QAM and 256-QAM-modulated signals on a 5.8-GHz RF carrier over a 118.8-km access link converged with four baseband differential quadrature phase shift keying (DQPSK) modulated wireline channels, along with ultra-wide band (UWB) and phase shift keying (PSK) radio-over-fiber (RoF) wireless signals over a deployed optical fiber link is also presented. 相似文献
44.
The biodiversity and growth dynamics of Lactic Acid Bacteria (LAB) in farm-house Ossau-Iraty cheeses were investigated from vat milk to 180 days of ripening in six independent batches made from six raw ewe’s milks using five typical cheese-making methods. Commercial starter S1 was used for three batches, starter S1 combined with S2 for one batch and no starter for two batches.Up to ten LAB species from five genera and up to two strains per species were identified per milk; up to eleven species from five genera and up to three strains per species were identified per cheese. Lactococcus lactis, Lactobacillus paracasei, Enterococcus faecalis, Enterococcus faecium, Enterococcus durans, and Leuconostoc mesenteroides were detected in all cheeses. Lactococci reached the highest counts irrespective of the milk and starter used. Lactococci and enterococci increased during manufacture, and mesophilic lactobacilli increased during ripening. Strain and species numbers, the percentage of isolates originating from the raw milk, maximum counts of each genus/species and time for reaching them, all varied according to whether or not a starter was used and the composition of the starter. The genotypes of strains within species varied according to the raw milk used. This generated distinct LAB microbiotas throughout manufacture and ripening that will certainly impact on the characteristics of the ripened cheeses. 相似文献
45.
研发了以生活垃圾焚烧灰渣为增强相,制备铝/生活垃圾灰渣复合材料的新工艺.对铝与生活垃圾灰渣配比、烧结温度、保温时间等因素对铝/生活垃圾灰渣复合材料的性能影响进行了实验研究.试验表明:当铝与生活垃圾灰渣配比为8:2,烧结温度为900℃,保温时间为1.5h,在纯N2保护性气氛的条件下制得的复合材料具有良好的机械性能,如热膨胀系数为0.3,密度为2.43g/cm^3,弹性模量为3014.3MPa,耐磨性能比铝镁合金提高了1.3倍. 相似文献
46.
Peter J. Wan Mukana wa Muanda Jesse E. Covey 《Journal of the American Oil Chemists' Society》1992,69(9):876-879
Refined and bleached soybean oil was hydrogenated with and without ultrasonic energy in a batch system. Reactions were carried
out at 170°C with 0.02% nickel catalyst (Nysel, Harshaw/Filtron Partnership, Cleveland, OH) or 50 ppm nickel in the oil. Hydrogen
pressure was varied from 15 to 90 psig. After 20 min, the average reaction rate was about five times faster in the presence
of ultrasonic energy. Hydrogenation rate generally increased with increasing hydrogen pressure when ultrasonic energy was
applied. However, the increasing rate is more sinusoidal in nature than linear. 相似文献
47.
Abdulkader Baki Amani Remmo Norbert Lwa Frank Wiekhorst Regina Bleul 《International journal of molecular sciences》2021,22(12)
Colloidal stability of magnetic iron oxide nanoparticles (MNP) in physiological environments is crucial for their (bio)medical application. MNP are potential contrast agents for different imaging modalities such as magnetic resonance imaging (MRI) and magnetic particle imaging (MPI). Applied as a hybrid method (MRI/MPI), these are valuable tools for molecular imaging. Continuously synthesized and in-situ stabilized single-core MNP were further modified by albumin coating. Synthesizing and coating of MNP were carried out in aqueous media without using any organic solvent in a simple procedure. The additional steric stabilization with the biocompatible protein, namely bovine serum albumin (BSA), led to potential contrast agents suitable for multimodal (MRI/MPI) imaging. The colloidal stability of BSA-coated MNP was investigated in different sodium chloride concentrations (50 to 150 mM) in short- and long-term incubation (from two hours to one week) using physiochemical characterization techniques such as transmission electron microscopy (TEM) for core size and differential centrifugal sedimentation (DCS) for hydrodynamic size. Magnetic characterization such as magnetic particle spectroscopy (MPS) and nuclear magnetic resonance (NMR) measurements confirmed the successful surface modification as well as exceptional colloidal stability of the relatively large single-core MNP. For comparison, two commercially available MNP systems were investigated, MNP-clusters, the former liver contrast agent (Resovist), and single-core MNP (SHP-30) manufactured by thermal decomposition. The tailored core size, colloidal stability in a physiological environment, and magnetic performance of our MNP indicate their ability to be used as molecular magnetic contrast agents for MPI and MRI. 相似文献
48.
Else Breval Chiping Wang Joseph P. Dougherty Kamau wa Gachigi 《Journal of the American Ceramic Society》2005,88(2):437-442
The room temperature phase diagram of PLZT, (Pb,La)(Zr,Ti)O3 , or L / Z / T for L <12 and T <10 was constructed using X-ray diffraction patterns of sintered and crushed PLZT material. The orthorhombic antiferroelectric phase, a tetragonal phase, the rhombohedral (hexagonal) ferroelectric phases, and the mixed La-rich zone were identified. Increasing substitution of La for Pb in the structure of orthorhombic PLZT leads to a change toward the cubic structure with less anisotropy in a direction corresponding to the cubic 200 direction. At La above ∼8 to 11 mol%, La2 Zr2 O7 appears in the mixed zone. With increasing substitution of Ti for Zr, there is no change toward a cubic structure as the anisotropy is nearly unchanged. However, at a Ti substitution above ∼6 mol%, a rhombohedral and a tetragonal structure appear. 相似文献
49.
K. Yamakawa K. W. A. Gachigi S. Trolier-McKinstry J. P. Dougherty 《Ferroelectrics Letters Section》1996,20(5):149-155
Phase transitions in antiferroelectric lead zirconate thin films were studied at room temperature and at 77 K. The lead zirconate films were prepared on Pt coated Si substrates by a reactive magnetron co-sputtering mthod followed by a rapid thermal annealing process at 700 °C. An electric field induced antiferroelectric — ferroelectric phase transition was observed at room temperature with a maximum polarization value of 70 μC/cm2. The average field required to induce the ferroelectric state and that for the reversion to the antiferroelectric state were 294 kV/cm and 179 kV/cm respectively. At 77 K a metastable ferroelectric — ferroelectric transition was observed with a maximum polarization of 58 μC/cm2. These transitions were found to be coincident with those of lead zirconate single crystals. 相似文献