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排序方式: 共有1128条查询结果,搜索用时 78 毫秒
1.
Wireless Personal Communications - In the present scenario, there is a boom in the demand of the users to achieve increased capacity, high data, low latency, and high-performance rates. 5G New... 相似文献
2.
Tek Bahadur Gurung Ram Prasad Dhakal Jay Dev Bista 《Lakes & Reservoirs: Research and Management》2006,11(3):141-148
The seasonal patterns of phytoplankton primary production, chlorophyll‐a concentration, cell number and several other limnological variables in Lake Phewa, located in the active monsoon zone in Central Himalaya, Nepal, were studied for a year beginning in April 2001. During the study period, the gross primary production and chlorophyll‐a concentrations were relatively low during the monsoon season. The phytoplankton cell number, represented by 24 genera, also fluctuated seasonally, but tended to increase in the pre‐ and post‐monsoon period. These results suggest that the monsoon plays a crucial role in the primary production and phytoplankton dynamics for Lake Phewa. Among the phytoplankton species, Microcystis aeruginosa, a representative species for eutrophic lakes, was the dominant phytoplankton. At the same time, however, it is clear that the lake is not yet heavily eutrophic. The present study suggests that the exchange of lake water during the monsoon season contributes to maintaining the health of the lake against further degradation. Nevertheless, the silt carried in the monsoon rain run‐off from the lake's catchment area suggests increasingly serious degradation problems for this small mountainous lake. 相似文献
3.
Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted
calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical
composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX
and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite
particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies
by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give
clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse
to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites
could be useful for hyperthermia. 相似文献
4.
Some substituted coumarins have been synthesized by von-Pechmann condensation using SnCl2 · 2H2O (10 mol %) as catalyst in ethanolic medium. The reactions are simple, easy in handling and environmentally benign. 相似文献
5.
Tek Bahadur Gurung 《Lakes & Reservoirs: Research and Management》2007,12(4):237-246
Lake Rupa is a small, subtropical, shallow lake with a surface area of 100 ha situated 600 m a.s.l. in Central Himalaya, Nepal. This degraded lake was studied between 2000 and 2006, with the goal of determining whether or not it could be restored by a community‐based cooperative of local people living in its catchment. Main threats to the lake, its aquatic life and its very existence include encroachment by excessive aquatic vegetation, sedimentation, and low in‐lake concentrations of dissolved oxygen (DO). Small lakes (≤ 500 ha) are relatively prone to the process of ‘succession and climax’, although they also can be of social, environmental and ecological importance. Thus, their disappearance could spark social chaos and disorder in areas already having to cope with other rapid environmental changes. This means that credible mechanisms for revitalizing or protecting small lakes are an important goal. Accordingly, a lake cooperative of 329 households living in close vicinity to Lake Rupa was formed in 2002, by prioritizing traditional fishers, women and other deprived community members with the goals of respecting the citizenry and equity. Following the cooperative's campaigns directed at weed removal and fish stocking, encroachment of vegetation on the lake margins was halted, its aquatic weeds became under control, and its fisheries improved. In addition to the cooperative's restoration activities, several water quality parameters, including water transparency and DO and chlorophyll‐a concentrations, were monitored on a monthly basis. The measured water transparency was inconsistent, exhibiting large variations between 2000 and 2003. Relatively low, but consistent, values, however, were measured after 2004. The results imply that the removal of weeds, and sufficient nutrients and solar radiation are subsequently available to the lake's phytoplankton communities. Supporting this notion is that the chlorophyll‐a concentration spiked to 205 µg L−1 in November 2006, the water transparency became consistent, and the DO concentration increased to >3.8 mg L−1 during the critical months (March–May) after 2004. These water quality indicators indicated improvement in the degraded Lake Rupa, suggesting that the establishment of cooperatives such as that highlighted in this study could be a powerful and sustainable mechanism for restoring degraded lakes in similar socioeconomic settings by maintaining equity, by connecting communities with their resources, and by facilitating integrity, equity, citizenry and social justice. 相似文献
6.
Arjunan Arulchakkaravarthi Rakesh Kumar Parthasarathy Santhanaraghavan Sivaramakrishnan Muralithar Rengasamy Gopalakrishanan Perumalsamy Ramasamy 《Materials Research Innovations》2002,6(5-6):273-276
Organic molecular scintillating crystals are noted for their good timing and particle discrimination process. Trans-stilbene
is one such candidate noted for its good particle detection characteristics for the past five decades. Progressive strengthening
of detection characteristics of trans-stilbene has been attempted by improving crystal perfection. A series of timing resolution
studies have been carried out for the Bridgman grown trans-stilbene crystals under different experimental conditions. The
results were compared with the previously reported values. Pulse shape discrimination process has been carried out for 241Am and 252Cf sources and good discrimination has been obtained for gamma-alpha and gamma-neutron sources from the grown organic phosphor
crystal.
Electronic Publication 相似文献
7.
Intermetallic phases in Al-Mn alloys 总被引:3,自引:0,他引:3
Aruna Bahadur 《Journal of Materials Science》1988,23(1):48-54
The intermetallic phases present in high-purity and commercial purity Al-Mn alloys (up to 2% Mn) in as-cast and heat-treated conditions were extracted electrolytically in 10% HCl in methanol solution and identified by X-ray diffraction. As iron is known to increase the coarse cast-intermetallic particles and to cause refinement of the grain size after recrystallization, different amounts of iron (up to 0.5%) were added and the resulting intermetallic phases were extracted and identified with and without heat treatment. The unidentified phase -Al (Mn, Fe)Si, reported by Sperry and others, was recognized as corresponding for ASTM card number 6-0669 and the conditions favourable for its formation were determined. This phase may be responsible for refining the grain size after recrystallization in commercial purity alloys as compared to high-purity Al-Mn alloys and may therefore be tried as an inoculant (by adding powdered compound to liquid alloys) for grain refining. 相似文献
8.
Rakesh?Kumar?MahajanEmail author Inderpreet?Kaur Mandeep?Singh?Bakshi 《Journal of surfactants and detergents》2004,7(2):131-134
Poly(vinyl chloride) (PVC) membrane electrodes to determine monomer concentrations of tetradecyltrimethylammonium ion (TTA+) and hexadecylpyridinium ion (HPy+) based on neutral ion-pair carrier complexes of tetradecyltrimethylammonium dodecyl sulfate (TTA+-DS−) and hexadecylpyridinium dodecyl sulfate (HPy+-DS−), respectively, are reported here. The electrodes exhibit a Nernstian slope of 59 mV per decade for TTA+ and a sub-Nernstian slope of 34.5 mV per decade for HPy+ ions. The TTA+ ion-selective electrode (ISE) and the HPy+-ISE can determine the monomer units down to concentrations as low as 4.0×10−4M and 1.66×10−5 M, respectively. The effect of various additives, such as the anionic polyelectrolyte sodium dextran sulfate and macrocyclic
β-cyclodextrin, on the surface activity exhibited by the cationic surfactants TTA+-DS− and HPy+-DS−, in the presence of background concentrations of NaCl was also examined with surfactant-selective sensors. The Gibbs free
energy of micelle formation (ΔG
m
) of both surfactants in the presence of various additives was calculated and found to be less favorable with respect to an
increase in the amount of additives due to less availability of cationic surfactant monomer units. The ion-pair complexes
TTA+-DS− and HPy+-DS− were found to behave as selective carrier compounds in PVC membranes in determining the concentration of monomer units of
both TTA+ and HPy+, respectively. The proposed sensors worked well at a fairly acidic pH of 1–6.5 with response time of 60 s. The sensors responded
well to the surfactant ions even in the presence of additives at lower concentration. The lifetime of the sensors is 3 mon. 相似文献
9.
Different rubber formulations were designed using nitrile rubber and a mixed crosslinking system consisting of sulfur/accelerator and electron beam radiation. Based on the experimental results, an artificial neural network (ANN) was constructed to simulate the mechanical properties and volume fraction of rubber. The ANN could predict accurately the above properties for a series of nitrile rubber compounds. However, the number of training data played a key role in the ANN predictive quality. In addition, the more complex the nonlinear relation between input and output was, the larger was the number of training dataset required. The predicted results were further validated using another mathematical model. The constructed ANN was verified with a completely different styrene butadiene rubber system. The prediction was found to be extremely good. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2227–2237, 2006 相似文献
10.
For complex reactions, the choice of reactor type is important for attaining optimum product yields. Strategies for specifying reactor types have beenIn this paper, product yield in a Van de Vusse reaction scheme has been studied for a wide range of the rate constants, in a reactor system consisting 相似文献