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71.
Sarma D.K. Konwar M. Sharma S. Pal S. Das J. De U.K. Viswanathan G. 《Geoscience and Remote Sensing, IEEE Transactions on》2008,46(6):1689-1696
An integrated regional model is proposed for rain-rate retrievals over land/ocean from the brightness temperature (Tb) values of the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The polarization-corrected temperature calculated from the 85.5-GHz channels is also considered as one of the inputs along with the nine channel Tb values. This model is applicable over the region between and . For this purpose, an artificial neural network is utilized. The collocated precipitation radar (PR) near-surface rain rates as given by a 2A25 data product is considered as a target value. The methodology consists of the separation of land and ocean pixels, the separation of stratiform and convective pixels over land/ocean, and the selection of important features (inputs) for the multilayer perceptron network by the feature selection technique for each group. For the separation of land/ocean pixels, the Tb values of the 10.65-GHz vertical channel are utilized. The values are utilized to separate the stratiform and convective pixels both over land and ocean. The rain retrieval from the developed model is validated with TRMM PR. Overall result shows the better agreement of the model-retrieved rain rate with the PR observation compared to the TMI (2A12) rain rate particularly over land. The rain retrieved from the developed model is further validated with Doppler weather radar. A reasonably good agreement is observed between these two estimations. 相似文献
72.
Howard Huang Harish Viswanathan Andrew Blanksby Mohamed A. Haleem 《The Journal of VLSI Signal Processing》2002,30(1-3):55-69
A High Data Rate (HDR) system has been proposed for providing downlink wireless packet service by using a channel-aware scheduling algorithm to transmit to users in a time-division multiplexed manner. In this paper, we propose using multiple antennas at the transmitter and/or at the receiver to improve performance of an HDR system. We consider the design tradeoffs between scheduling and multi-antenna transmission/detection strategies and investigate the average Shannon capacity throughput as a function of the number of antennas assuming ideal channel estimates and rate feedback. The highest capacities are achieved using multiple antennas at both the transmitter and receiver. For such systems, the best performance is achieved using a multi-input multi-output capacity-achieving transmission scheme such as BLAST (Bell Labs Layered Space-Time) in which the transmitted signal is coded in space and time, and the receive antennas are used to resolve the spatial interference. In the second part of the paper, we discuss practical transmitter and receiver architectures using BLAST for approaching the theoretical gains promised by the capacity analysis. Because the terminal receivers will be portable devices with limited computational and battery power, we perform a computational complexity analysis of the receiver and make high-level assessments on its feasibility. We conclude that the overall computational requirements are within the reach of current hardware technology. 相似文献
73.
S. Karthika Vasudevan Prathibha Mary K. A. Ann Vidyadharan Viji P. R. Biju N. V. Unnikrishnan 《Journal of Electronic Materials》2014,43(2):447-451
A sol–gel method was used to prepare titania-zirconia matrices doped with Sm3+/CdS nanocrystallites. The structural properties of the matrices were characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier-transform infrared spectroscopy studies. The thermal stability of the material was determined by TGA/DTA analysis. The absorption spectrum shows the characteristic peaks of the Sm3+ ions and the absorption peak corresponding to the CdS nanocrystallites. The optical bandgap and size of the CdS nanoparticles were calculated from the absorption spectrum. From TEM, the interplanar distance (d) was estimated to be 3.533 Å, which matches with the (1 0 0) plane of bulk CdS. The measurements yield a nanocrystallite size of around 7.8 nm. The optical absorption and emission spectra confirmed the formation of CdS nanoparticles along with samarium ions in the titania-zirconia matrices. The fluorescence intensity of the samarium ions was found to be greatly enhanced by codoping with CdS nanocrystallites. 相似文献
74.
Vasudevan PrathibhaS. Karthika Joseph CyriacC. Sudarasanakumar N.V. Unnikrishnan 《Materials Letters》2011,65(4):664-666
Anatase TiO2 nanocrystals in the TiO2- SiO2 matrix were prepared by the ultra hydroylsis sol-gel route. The samples were heat treated at 350 °C and 500 °C. The structural analyses of the samples were carried out using X-ray diffraction technique, Raman spectroscopy and Transmission electron microscopy. The size of the nanocrystals from the XRD spectra (8.3 nm) and TEM (5-8 nm) is well in agreement. The spacing for the crystal planes was also determined using the ImageJ program. The Raman peaks further confirmed the formation of only the anatase phase within the matrix. 相似文献
75.
N. Sabari Arul D. Mangalaraj Pao Chi Chen N. Ponpandian C. Viswanathan 《Materials Letters》2011,65(17-18):2635-2638
Highly uniform and well-dispersed cerium oxide quantum dots were successfully synthesized by simple precipitation method by using cerium ammonium nitrate and ammonium hydroxide as precursor materials with suitable conditions. The X-ray diffraction pattern indicates the formation of cubic phase CeO2. The average particle size of cerium oxide from high resolution transmission electron microscopy (HRTEM) was found to be 3 nm. The X-ray photoelectron (XPS) spectrum confirms the presence of Ce3+ in CeO2. Optical studies by UV–vis spectroscopy for the synthesized CeO2 nanoparticles exhibit a blue shift (Eg = 3.78 eV) with respect to the bulk material (Eg = 3.15 eV) due to quantum confined exciton absorption. 相似文献
76.
Gelcast Tooling: Net Shape Casting and Green Machining 总被引:8,自引:0,他引:8
Mark A. Janney Weiju Ren Glen H. Kirby Stephen D. Nunn Srinath Viswanathan 《Materials and Manufacturing Processes》1998,13(3):389-403
Gelcasting is an advanced powder forming process. It is most commonly used to form ceramic or metal powders into complex, near-net shapes. Turbine rotors, gears, nozzles, and crucibles have been successfully gelcast in silicon nitride, alumina, nickel-based superalloy, and several steels. Gelcasting can also be used to make blanks that can be green machined to near-net shape and then high fired. Green machining has been successfully applied to both ceramic and metal gelcast blanks. Recently, we have used gelcasting to make toolinj; for metal casting applications. Most of the work has centered on H13 tool steel. We have demonstrated an ability to gelcast and sinter H13 to near net shape for metal casting tooling. We have also been successful in green machining gelcast blanks using a three-axis CNC milling machine. 相似文献
77.
The aqueous ring-opening metathesis polymerization of the exo-Diels-Alder adduct of furan and maleimide was accomplished using an “activated Ruthenium” catalyst present in the supernatant of a RuCl3-catalyzed aqueous polymerization of furan-dimethylacetylene dicarboxylate adduct. The polymer was characterized by solution 1H? and 13C-NMR, IR, DSC, and viscometry. Characterization revealed an intact imide group and the possibility of high-temperature applications. © 1993 John Wiley & Sons, Inc. 相似文献
78.
R Viswanathan S N Yedave S T Bendre S M Kanetkar S M Chaudhari S B Ogale 《Bulletin of Materials Science》1991,14(2):435-441
Ion beam and thermally-induced interface reactions between highT
c superconducting thin film of Y1Ba2Cu3O7−x
and metal overlayer of Ag are studied with a view to control the interfacial property of contact resistance. The interface
reaction is induced by 100 keV Ar+ ion beam with different ion dose values ranging from 5 × 1013 to 3×1014 ions/cm2. The YBaCuO film-metal interface is characterized by using the small angle XRD to study the structural properties of the
interfacial phases. The electrical property of the interface, specifically contact resistance, has been investigated for different
dose values and thermal treatments. Three-probe vs four-probe configuration has been adopted to measure the contact resistance. 相似文献
79.
F Khanum KR Anilakumar KR Sudarshanakrishna KR Viswanathan 《Canadian Metallurgical Quarterly》1998,68(3):208-213
Two studies were conducted during which 23 patients with chronic migraine were exposed to pulsing electromagnetic fields over the inner thigh. In an open study, 11 subjects kept a 2-week headache log before and after 2 to 3 weeks of exposure to pulsing electromagnetic fields for 1 hour per day, 5 days per week. The number of headaches per week decreased from 4.03 during the baseline period to 0.43 during the initial 2-week follow-up period and to 0.14 during the extended follow-up which averaged 8.1 months. In a double-blind study, 9 subjects kept a 3-week log of headache activity and were randomly assigned to receive 2 weeks of real or placebo pulsing electromagnetic field exposures as described above. They were subsequently switched to 2 weeks of the other mode, after which they kept a final 3-week log. Three additional subjects in the blind study inadvertently received half-power pulsing electromagnetic field exposures. The 6 subjects exposed to the actual device first showed a change in headache activity from 3.32 per week to 0.58 per week. The 3 subjects exposed to only half the dose showed no change in headache activity. Large controlled studies should be performed to determine whether this intervention is actually effective. 相似文献
80.
R Govindaraj R Rajaraman K P Gopinathan B Viswanathan 《Bulletin of Materials Science》1998,21(5):427-431
Time differential perturbed angular correlation (TDPAC) and positron life-time measurements on cold-worked and hydrogen chargedNbHf indicate a strong binding of hydrogen decorated vacancy clusters with Hf impurities. Both TDPAC and positron lifetime results
are mutually consistent on this aspect. Transformation of H-vacancy clusters into H-bubbles is indicated by the positron lifetime
behaviour at annealing temperatures beyond 900 K. Impurity effects like oxygen pickup and coating of voids cannot be ruled
out at elevated temperatures. 相似文献