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排序方式: 共有1096条查询结果,搜索用时 140 毫秒
91.
Hsin Wang Govindarajan Muralidharan Donovan N. Leonard J. Allen Haynes Wallace D. Porter Roger D. England Michael Hays Gopal Dwivedi Sanjay Sampath 《Journal of Thermal Spray Technology》2018,27(3):371-378
Multilayer, graded ceramic/metal coatings were prepared by an air plasma spray method on Ti-6Al-4V, 4140 steel and graphite substrates. The coatings were designed to provide thermal barriers for diesel engine pistons to operate at higher temperatures with improved thermal efficiency and cleaner emissions. A systematic, progressive variation in the mixture of yttria-stabilized zirconia and bondcoat alloys (NiCoCrAlYHfSi) was designed to provide better thermal expansion match with the substrate and to improve thermal shock resistance and cycle life. Heat transfer through the layers was evaluated by a flash diffusivity technique based on a model of one-dimensional heat flow. The aging effect of the as-sprayed coatings was captured during diffusivity measurements, which included one heating and cooling cycle. The hysteresis of thermal diffusivity due to aging was not observed after 100-h annealing at 800 °C. The measurements of coatings on substrate and freestanding coatings allowed the influence of interface resistance to be evaluated. The microstructure of the multilayer coating was examined using scanning electron microscope and electron probe microanalysis. 相似文献
92.
Mohamed AbuDakka Ahsanulhaq Qurashi Parameswar Hari Mir Wakas Alam 《Materials Science in Semiconductor Processing》2010,13(2):115-118
A cost effective, low-temperature approach has been developed for the large-area deposition of ZnO nanorod/nanotube arrays on a ZnO coated glass substrate by the natural oxidation of zinc metal in formamide/water mixtures. The two-step seed deposition and wet-chemical approach exhibited well-controlled growth of highly oriented and densely packed ZnO nanorod/nanotube arrays with large-area homogeneity and uniform morphologies. In order to investigate the quality and alignment of ZnO nanorod arrays grown on the ZnO seed layer coated substrate, three different methods of ZnO coating have been deposited by ultrahigh vacuum evaporation system, DC sputtering and RF sputtering, respectively. Our results showed that the ZnO seed layer grown by RF sputtering resulted in high quality ZnO nanorod arrays. 相似文献
93.
Anurag Jyoti Poornima Vajpayee Premendra D. Dwivedi Rishi Shanker 《The Science of the total environment》2010,408(6):1256-9002
Low numbers (15-100 CFU) of Salmonella in food or water may pose a public health risk. The management of infections caused by Salmonella spp. during outbreaks or forecasting of contamination of aquatic resources largely depends on rapid, sensitive and accurate diagnostic in few hours. In this study, a real-time PCR assay in Molecular-Beacon format was developed and culture-independent quantitative enumeration of Salmonella spp. in surface and potable water is being reported for the first time from northern part of India. Molecular Beacon was designed in highly conserved region of invA gene (present in wide range of Salmonella serotypes including all subspecies) encoding an essential component of the invasion associated specialized type Ø protein secretion apparatus for detection of Salmonella spp. in water. The assay could detect directly 10 and 1 genomic equivalent of Salmonella typhimurium ATCC 14028 per PCR with detection probability of 100 and 20%, respectively. Further, the assay could detect 10 CFU/PCR or more of reference strain (S. typhimurium ATCC 14028) without any enrichment in the presence of 108 CFU ml− 1 of non-pathogenic E. coli (E. coli DH5α) with 100% detection probability. The assay could enumerate Salmonella spp. in surface (n = 40) and potable waters (n = 10) directly (without enrichment). Results indicate that northern India is at high risk of developing Salmonella borne infections. Further, real-time PCR assay in Molecular Beacon format can be used for identification of critical contamination points in natural water resources and potable water distribution systems, necessary to implement vaccination plan timely for prevention of waterborne outbreaks caused by Salmonella spp. 相似文献
94.
Zhang Qi Cao Wei Nallanathan Arumugam Garg Hari Krishna 《Wireless Communications, IEEE Transactions on》2009,8(3):1171-1176
The differentially-encoded, di-symbol time-division multiuser impulse radio (d2TD-IR) with delay-sum autocorrelation receivers is a low complexity, high efficiency short range wireless communication technology for infrastructure networks. The d2TD-IR system is designed with the assumption that the users are perfectly synchronized. In this letter, we propose a recursive algorithm of combined synchronization and power control. Computer simulation results show that the proposed algorithm has significant performance improvement over the algorithm, in which synchronization and power control are performed separately. 相似文献
95.
This short paper reports both the photoluminescence and the lifetime measurements of a prominent emission transition (5D0→7F2) of Eu3+ both in the presence and absence of the codopant rare earth ion (Dy3+) in an optical glass of the composition (79−x)TeO2+6AlF3+15LiF+xLn2O3 as a function of temperature down to 10 K. 相似文献
96.
R. S. Dwivedi A. B. Kumar K. N. Tewari 《International journal of remote sensing》2013,34(11):2303-2318
The availability of remote sensing data with improved spatial, spectral and radiometric resolution is now available to fully exploit their potential for a specific application subject to the relative merits and the limitations of each sensor's data. Presented here is a case study where Landsat MSS and TM; and SPOT MLA data for part of the Bijapur district, southern India, which were acquired on the same day, have been evaluated for mapping eroded lands. The approach involves the geometric registration of all three data to a common map grid using tie points and third order polynomial transform; and resampling the MSS and TM data to a 20m by 20 m pixel dimension and radiometric normalization. Thematic maps showing eroded lands were generated on a micro-VAXbased DIPIX system using a maximum likelihood classifier. Accuracy estimates were made for the thematic maps following stratified unaligned random sampling technique, and subsequently, computing overall accuracy and Kappa coefficient. Spectral separability and classification accuracy was maximum from SPOT-MLA data followed by a combination of Landsat MSS band 1, SPOT-MLA band 2 and Landsat TM band 4; Landsat TM, a combination of Landsat MSS, TM and SPOT MLA; and Landsat MSS data. 相似文献
97.
98.
Thermodynamic optimisation of phase diagrams is a procedure that requires considerable experience and skill. The purpose of this article is to furnish certain guidelines that might facilitate the work and improve the quality of the thermodynamic optimisation of phase diagrams using the Calphad method. Some particulars regarding experimental data, Gibbs energy models, constraints on model parameters, and performing the optimisation are discussed. 相似文献
99.
Grigoriy Sereda Taejin Kim Aubrey Jones Hari Khatri Christopher L. Marshall H. Subramanian Ranjit T. Koodali 《Catalysis Letters》2011,141(8):1086-1096
Abstract
Catalytic performance of solid supported monovanadate catalysts toward oxidation of propane is significantly affected by the templating effect of: (1) pretreatment of the solid support with calixarene derivatives before deposition of ammonium vanadate, (2) direct deposition of vanadyl phthalocyanine as the vanadate precursor. This effect is believed to be linked to the accessibility of the active sites, and was studied in comparison with a reference mesoporous support. 相似文献100.
Sonal Singhal Amit Kumar Chawla Hari Om Gupta Ramesh Chandra 《Nanoscale research letters》2010,5(2):323-331
Zn0.9Cd0.1S nanoparticles doped with 0.005–0.24 M cobalt have been prepared by co-precipitation technique in ice bath at 280 K. For
the cobalt concentration >0.18 M, XRD pattern shows unidentified phases along with Zn0.9Cd0.1S sphalerite phase. For low cobalt concentration (≤0.05 M) particle size, d
XRD is ~3.5 nm, while for high cobalt concentration (>0.05 M) particle size decreases abruptly (~2 nm) as detected by XRD. However,
TEM analysis shows the similar particle size (~3.5 nm) irrespective of the cobalt concentration. Local strain in the alloyed
nanoparticles with cobalt concentration of 0.18 M increases ~46% in comparison to that of 0.05 M. Direct to indirect energy
band-gap transition is obtained when cobalt concentration goes beyond 0.05 M. A red shift in energy band gap is also observed
for both the cases. Nanoparticles with low cobalt concentrations were found to have paramagnetic nature with no antiferromagnetic
coupling. A negative Curie–Weiss temperature of −75 K with antiferromagnetic coupling was obtained for the high cobalt concentration. 相似文献