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排序方式: 共有358条查询结果,搜索用时 15 毫秒
31.
水泥颗粒生长与黏结的微观分析(英文) 总被引:2,自引:0,他引:2
水泥微观结果的变化是一个十分复杂的过程,其中包含了水泥颗粒的生长、黏联、絮凝以及其它反应。了解这些水泥颗粒的行为对于更好地掌握水泥基材料早期性能非常重要。采用扫描电子显微镜内安装的Quantomix密封舱系统,原位观察了3种不同的水泥浆体的微观结构。基于这个系统可连续观察水泥浆体微结构发展的优点,研究了水化过程中单个颗粒的生长与颗粒间的连接。通过显微照片的图像分析获得水泥颗粒的灰度变化,用于上述研究。对这些水泥浆体中水泥颗粒的生长与连接情况进行了定量研究。 相似文献
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33.
Fluorescence quenching effect of single walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) on three most common fluorophores fluorescein, rhodamine 6G and quinine sulphate has been studied and compared. Comparative studies of quenching efficiency shows that SWCNTs are more efficient fluorescence quencher than the MWCNTs. Nature of Stern–Volmer plot was found to be highly non-linear indicating combined effect of dynamic and static quenching. The contribution of dynamic quenching component was assessed through the fluorescence lifetime measurements. Studies on vacuum annealed SWCNTs with low defect contents suggest that structural defects primarily contribute to the large quenching. Fluorescence quenching was found to be dominant even in the cases where adsorption was low implying that surface adsorption play a minor role in the quenching, except for rhodamine 6G. Adsorption isotherms have been studied using Langmuir and Freundlich models. Freundlich model was found to be closer in behaviour implying a multilayer adsorption of molecules on the surface. The contributions of metal nanoparticles and carbon impurities present in different allotropic forms to the fluorescence quenching were also assessed. We speculate that defect mediated nonradiative energy transfer through dipole–dipole coupling may be the dominant mechanism of high efficiency quenching by SWCNTs. 相似文献
34.
Biodegradation of endosulfan isomers in broth culture and soil microcosm by Pseudomonas fluorescens isolated from soil 总被引:2,自引:0,他引:2
Krishna Giri 《The International journal of environmental studies》2013,70(5):729-742
Bacterial isolates from endosulfan-contaminated soil were grown in minimal medium and screened for endosulfan degradation. The isolate which used endosulfan and showed maximum growth was selected for detailed study. Maximum degradation in shake flask culture by Pseudomonas fluorescens was 92.80% of α and 79.35% of β endosulfan isomers in 15?days at 20?mg/L concentration, followed by 50 and 100?mg/L, while the corresponding values in static condition were 69.15 and 51.39%, respectively. Endosulfan concentration degradation declined significantly at 50 and 100?mg/L. Concomitant to degradation, release of chloride ion exhibited positive relation, while pH decreased from 7.0 to 4.53 in agitating and 7.0–5.18 in static condition. The soil microcosm study revealed maximum endosulfan degradation in sterilized soil amended with P. fluorescens. Endosulfan diol and endosulfan ether were among the products of endosulfan metabolism in broth culture, but only endosulfan ether was detected in the soil microcosm. Endosulfan sulphate, a persistent and toxic metabolite of endosulfan, was not detected in either case. The study showed that P. fluorescens could be used effectively for bioremediation of the pesticide contaminated sites. 相似文献
35.
Sandeep Rawat Harish Andola Lalit Giri Praveen Dhyani Arun Jugran 《International Journal of Food Properties》2013,16(3):703-712
Three Himalayan medicinal plants (Habenaria intermedia, H. edgeworthii, and Roscoea procera), widely used in vitality strengthening Ayurvedic formulations in India, were assessed for nutritional phytochemical constituents, and antioxidant activity. These target species emerged as a good source of minerals and possessed important micro elements. Individually, H. intermedia contained a high content of total phenols, thiamins, tannins, and calcium; R. procera was rich in potassium and iron content; and H. edgeworthii emerged as a good source of sodium. While various antioxidant assays provided evidences on the antioxidant potential of target species, greater antioxidant potential of H. intermedia as compared to the other two species was revealing. This study, therefore, highlighted the possibilities of harnessing nutritional and antioxidant potential of these species. 相似文献
36.
B. C. Giri A. K. Jalan K. S. Chaudhuri 《International Transactions in Operational Research》2005,12(2):235-245
In this paper, an economic production quantity model is developed for a production–inventory system where the demand rate increases with time, the production rate is finite and adjustable in each cycle over an infinite planning horizon and shortages are permitted. The cost of adjusting the production rate depends linearly on the magnitude of the change in the production rate. During the stock‐out period, a known fraction of the unsatisfied demands is backordered while the remaining fraction is lost. The model is formulated taking the demand rate as a general increasing function of time and the optimal production policy is obtained for the special case of a linearly increasing demand rate. The proposed model is also shown to be suitable for a prescribed time horizon. A procedure to find approximately the minimum total cost of the system over a finite time horizon is suggested. A numerical example is taken to illustrate the solution procedure of the developed model. 相似文献
37.
Nyffeler M. Braendli B. Reusser B. Doerr E. Giri D.V. Tomer E.R. 《Electromagnetic Compatibility, IEEE Transactions on》1992,34(4):471-477
The authors address the problem of the interaction of electromagnetic fields with wire cage structures. The two canonical shapes considered are cubes and cylinders. The motivation for this work comes from a need to investigate electromagnetic field coupling (transient or broadband CW) to communication facilities or buildings with metallic rebar elements in the perimeter walls. Coupling calculations are performed by using NEC-2 computer codes and the experiments were performed at the Swiss MEMPS facility. MEMPS is a hybrid type of nuclear electromagnetic pulse (NEMP) simulator consisting of an impedance loaded elliptical structure with either a transient or a broadband CW excitation. Both types of excitations have been used in experimentally studying the coupling characteristics. In the case of cylindrical wire cage structures, both polarizations, i.e., incident electric field and incident magnetic field parallel to the cylinder axis, have been investigated. Good agreement is seen between the computed and measured result 相似文献
38.
An isothermal spectroscopic technique called time analyzed transient spectroscopy (TATS) in the constant capacitance (CC)
mode has been used to characterize electrically active defects in the MeV Ar+ implanted silicon. The problems associated with high defect density and the presence of damaged region in the as-implanted
material are overcome by CC-TATS method. The CC-TATS spectra of the as-implanted sample shows two positive peaks and an attendant
negative peak. Two distinct traps have also been identified using thermally stimulated capacitance method modified to operate
in constant capacitance mode. Variable pulse width measurements using CC-TATS show exponential capture kinetics in contrast
to extremely slow capture observed in conventional deep level transient spectroscopy (DLTS) experiment. The results indicate
that trapping behaviour is due to point-like defects associated with extended defects such as dislocation and stacking fault. 相似文献
39.
S. Suganya J. Venugopal S. Agnes Mary S. Ramakrishna B. S. Lakshmi V. R. Giri Dev 《Iranian Polymer Journal》2014,23(3):237-248
Aloe vera (AV) is one of the medicinal herbs with a well-established spectrum of wound healing, antimicrobial and anti-inflammatory property. AV-mediated therapeutics present significant tissue regenerative activity by modulating the inflammatory and proliferative phases of wound healing. The purpose of the present work was to combine the biological properties of AV and the advantages of electrospun meshes to prepare a potent transdermal biomaterial. The polycaprolactone (PCL) containing 5 and 10 wt % of lyophilized powder of AV was studied for electrospinning into nanoscale fiber mats and compared with PCL/Collagen blend for dermal substitutes. SEM revealed the average diameters of PCL, PCL-AV 5 %, PCL-AV 10 % and PCL/Collagen nanofiber scaffolds in the range of 519 ± 28, 264 ± 46, 215 ± 63 and 249 ± 52 nm, respectively. PCL-AV 10 % nanofiber scaffolds showed finer fiber morphology with improved hydrophilic properties and higher tensile strength of 6.28 MPa with a Young’s modulus of 16.11 MPa desirable for skin tissue engineering. The nanofibers were then used to investigate differences in biological responses in terms of proliferation and cell morphology of mice dermal fibroblasts. It was found that PCL-AV 10 % nanofibrous matrix favored cell proliferation compared to other scaffolds which almost increased linearly by (p ≤ 0.01) 17.79 % and (p ≤ 0.01) 21.28 % compared to PCL on sixth and ninth day. CMFDA dye expression, secretion of collagen and F-actin expression were significantly increased in PCL-AV 10 % scaffolds compared to other nanofibrous scaffolds. The obtained results proved that the PCL-AV 10 % nanofibrous scaffold is a potential biomaterial for skin tissue regeneration. 相似文献
40.
Oxidative stress in a tissue activates phospholipase A2 which releases free arachidonic acid. In addition, a low grade oxidative tone also stimulates the tissue cyclooxygenase activity. Cyclooxygenase-dependent arachidonic acid metabolites such as PGF 2 alpha are known to play an important role in the development and maintenance of hyperplasia in skin in response to the application of tumor promoters. In this study we show that Fe-NTA, an oxidant renal tumor promoter induces PGF 2 alpha which was maximum at 12 hours after Fe-NTA treatment. However, at all time points studied, the elevated levels of PGF 2 alpha have been observed. As a result of the induction of PGF 2 alpha, the hyperplastic response can also be observed in the histopathology of the tissue. Additionally, an increased incorporation of [3H]thymidine in renal DNA has also been observed. Pretreatment of animals with indomethacin suppresses Fe-NTA-mediated hyperproliferation suggesting a role of cyclooxygenase in Fe-NTA-mediated stimulation of hyperplastic activity. The pretreatment of animals with the chain breaking antioxidants, Vit. E, BHA and BHT were only partially effective in inhibiting Fe-NTA-mediated PGF2 alpha production, further suggesting a role of non-free radical-dependent mechanism in its production. Our data suggest that Fe-NTA-induced PGF2 alpha through the activation of cyclooxygenase is responsible for the development and maintenance of hyperplasia in kidney. 相似文献