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41.
ABSTRACTBoiling has served as an effective means to dissipate large quantities of heat over small areas. Graphene, a two-dimensional material, has garnered significant attention of researchers due to its excellent thermal properties. In this study, copper test chips are dip coated with a solution consisting of graphene oxide and graphene and its pool boiling performance with distilled water at atmospheric pressure was investigated. The surfaces were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy which confirmed the presence of graphene and graphene oxide. The contact angles measured on the coated surfaces indicated hydrophobic wetting behavior. Four heat transfer surfaces were prepared with dip coating durations of 120 s, 300 s, 600 s, and 1200 s, respectively. A Critical Heat Flux (CHF) of 182 W/cm2 and a heat transfer coefficient (HTC) of 96 kW/m2°C was obtained with the shortest coating duration which translated to an enhancement of 42% in CHF and 47% in HTC when compared to a plain uncoated surface under similar conditions. Contact angle changes were not seen to be responsible, although roughness was seen as an influencing factor contributing to the enhancement. Further studies are needed to explain the enhancement mechanism. 相似文献
42.
The Ferroelectric relaxor ternary system 0.5PZN-(0.5 – x)PFN-xBZN was prepared using the columbite precursor method. The stability of the perovskite phase was studied as a function of BZN content in the system. It was observed that BZN is a good stabilizer of perovskite phase because of the high value of electronegativity difference between its cation and anion. It has also been observed that addition of BZN increases the dielectric maxima peak value and decrease the Curie temperature of the ceramics. The ternary composition 0.5PZN-0.425PFN-0.075BZN has been identified for MLCs applications. It has a T
c of around room temperature with a peak dielectric constant 6400 and tan 0.05. The mechanical properties of relaxor materials have also been studied and reported. 相似文献
43.
Scientometrics of laser research in India and China 总被引:5,自引:0,他引:5
An analysis of 1223 papers published by India (347papers) and China (876papers) at conferences and in journals during 1993
and 1997 in the field of laser S&T indicates that China"s output was twice to that of India. However, Activity Indices for
both the countries in 1993 and 1997 were almost the same. Chinese scientists preferred to publish in domestic journals, while
Indian scientists published in foreign journals. The number of papers by Indian scientists in SCI covered journals and journals
with high-Normalized Impact Factors was more than for China, and, thus India was better connected to the mainstream science
compared to China. The impact made by Indian papers was more than for Chinese papers, as reflected by normalized impact per
paper, proportion of papers in high quality journals, and publication effective index. Indian papers also got more citations
per paper than Chinese papers. Team research appears to be better in China than in India, as reflected by the number of mega-authored
papers produced by the two countries.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
44.
We have studied the operational behaviour of a complex system consisting of two classes of units (with standby redundancy in one class) under two repair disciplines, viz., preemptive-resume and preemptive-repeat. Units have constant failure rate, while repair follows general probability distributions. Supplementary variable and Laplace transform techniques have been used to obtain the transient state probabilities for such a system. From these, steady state behaviour of the complex system has been examined. 相似文献
45.
46.
Saurabh Garg Surjya K. Pal Debabrata Chakraborty 《Neural computing & applications》2007,16(4-5):407-417
This study compares the performance of backpropagation neural network (BPNN) and radial basis function network (RBFN) in predicting
the flank wear of high speed steel drill bits for drilling holes on mild steel and copper work pieces. The validation of the
methodology is carried out following a series of experiments performed over a wide range of cutting conditions in which the
effect of various process parameters, such as drill diameter, feed-rate, spindle speed, etc. on drill wear has been considered.
Subsequently, the data, divided suitably into training and testing samples, have been used to effectively train both the backpropagation
and radial basis function neural networks, and the individual performance of the two networks is then analyzed. It is observed
that the performance of the RBFN fails to match that of the BPNN when the network complexity and the amount of data available
are the constraining factors. However, when a simpler training procedure and reduced computational times are required, then
RBFN is the preferred choice. 相似文献
47.
Jitendra K. Quamara Anu Sharma Maneesha Garg T. Prabha 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,262(2):215-219
Photoconduction behaviour of 75 MeV oxygen ion irradiated (Fluences: 1.8 × 1011, 1.8 × 1012 and 1.8 × 1013 ions/cm2) kapton-H polyimide film in the visible region has been investigated at different temperatures ranging 400-2500 °C and at various electric fields ranging 40-600 kV/cm. A photoinduced exciton formation is the major source for providing charge carriers through thermolization and field-assisted dissociation processes. An attempt has been made to fit the field dependence of the steady state photocurrent to one of the several possible conduction mechanisms. In the high and low fluence (1.8 × 1013 and 1.8 × 1011 ions/cm2) irradiated samples there exists a possibility of Poole-Frankel type of photoconduction mechanism, whereas at intermediate fluence (1.8 × 1012 ions/cm2) a Schottky type photoconduction mechanism may be operative. The log Ips versus 1/T plots consist of two straight lines with a knee point around 800-1000 °C. The activation energy estimated from the slope of these lines is field dependent varying from 0.40 to 0.73 eV and 0.18 to 0.23 eV above and below the knee point, respectively. This indicates the presence of more than one type of trapping levels in irradiated kapton-H polyimide. 相似文献
48.
Singh B.. Garg V.. Bhuvaneswari G.. 《Industrial Electronics, IEEE Transactions on》2007,54(5):2500-2511
This paper presents the design, analysis, and development of a novel autotransformer-based 18-pulse AC-DC converter with reduced kilovoltampere rating, feeding vector-controlled induction-motor drives (VCIMDs) for power-quality improvement at the point of common coupling (PCC). The proposed autotransformer consists of only two single-phase transformers for its realization against three single-phase transformers required in other configurations. The proposed 18-pulse AC-DC converter is suitable for retrofit applications, where, presently, a six-pulse diode bridge rectifier is being used. A set of power-quality parameters, such as total harmonic distortion (THD) and crest factor of AC mains current, power factor, displacement factor, and distortion factor at AC mains, THD of supply voltage at PCC, and DC-bus-voltage ripple factor for a VCIMD fed from an 18-pulse AC-DC converter, are computed to observe its performance. The presented design technique provides flexibility to give an average DC output from the proposed converter, which is the same as that of a conventional three-phase diode bridge rectifier. However, it is also possible to step-up or step-down the output voltage as required. The effect of load variation on VCIMD is also studied to observe the effectiveness of the proposed harmonic mitigator. A laboratory prototype of the proposed autotransformer-based 18-pulse AC-DC converter is developed to validate the design and simulation model. 相似文献
49.
T. P. Gabb J. Telesman P. T. Kantzos A. Garg 《Journal of Failure Analysis and Prevention》2007,7(1):56-65
Increasing service temperatures of gas turbine engines can improve performance and efficiency. Therefore, advanced alloys
are being considered for higher-temperature applications than previously encountered. To support these higher-temperature
applications, failure mode assessments on specimens tested in laboratory test machines can help in understanding prospective
failure scenarios. The effects of temperature on tensile, creep, low-cycle fatigue, and fatigue crack growth failure modes
were evaluated for an advanced powder metallurgy disk superalloy ME3. Conventional tests were performed at temperatures up
to 815 °C on specimens extracted from supersolvus heat treated disks. The failure modes were compared with increasing temperature
for each test type. Fractographic evaluations indicate the failure modes were shifted by increasing temperature, and eventually
became environment-assisted, surface crack initiated failures. 相似文献
50.
Fused deposition modeling (FDM) process is an additive manufacturing technology where objects are manufactured in layers. In the present days, FDM is commercially used to build prototypes, functional components; however, these parts majorly suffer from poor surface quality and dimensional accuracy even for basic part geometries. In the present paper, first the effect of part deposition orientation on surface finish and dimensional accuracy of FDM parts are studied. The part selected for this study is designed in such a way that different primitive geometric features at different directions are present. The parts are built at different orientations (0°, 15°, 30°, 45°, 60°, 75°, 90°) using acrylonitrile butadiene styrene P430 material, and surface finish and dimensional accuracy are measured at different surfaces. Next, the FDM parts are postprocessed by cold vapor treatment of dimethylketone (acetone) and improvement in surface finish and change in dimensional accuracy are investigated. The results show that surface finish of the components is greatly improved by this vapor treatment process with minimal variations in part geometric accuracy after the treatment. 相似文献