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21.
Sudhir Singh Bhadauria Dr. Mahesh Chandra Gupta 《Canadian Metallurgical Quarterly》2007,21(3):234-239
Reports of failure of existing concrete structures due to a lack of durability, rather than a deficiency in structural strength, has made concrete technologists, engineers, and researchers focus research on the parameters influencing durability performance with respect to time. Systematic performance monitoring, with respect to chosen durability parameters of existing concrete structures, will decide the direction of future research in this area. Inferences based on laboratory simulations and testing need to be confirmed by in situ field measurements and studies. In situ condition rating and performance monitoring surveys have been conducted by many researchers, scientists, and professional associations, and reported in literature. Inferences of few such studies are summarized and discussed. Deterioration of concrete structures constructed in recent times is observed at relatively faster rates, and has been mainly attributed to cracking. Cracking is associated with the use of faster-hydrating portland cements with increased fineness and the tricalcium silicate (C3S) content to support the high speed of modern construction. In the present research, a case study of deteriorated water tank structures situated in the semitropical region of India is presented. Some selected parameters—such as concrete cover, carbonation depth, chloride concentration, compressive strength, etc. which influence long term durability of structures—have been measured. 相似文献
22.
In this study, an aluminum based metallic matrix (Al-2wt.% Cu) was reinforced with SiC particulates using a conventional casting technique and a new disintegrated melt deposition technique. Microstructural characterization studies conducted on the samples taken from disintegrated melt deposition technique revealed a more uniform distribution of SiC particulates and good interfacial integrity between SiC particulates and metallic matrix when compared to the conventionally cast composite samples. Results of ambient temperature mechanical tests demonstrate an increase in 0.2% YS and ultimate tensile strength of samples taken from disintegrated melt deposition technique when compared with the unreinforced and conventionally cast composite samples. The results of microstructural characterization and mechanical testing were finally rationalized in terms of the nature of processing technique employed to reinforce Al-2wt.% Cu metallic matrix with SiC particulates. 相似文献
23.
J. M. Ballingall P. Ho J. Mazurowski L. Lester K. C. Hwang J. Sutliff S. Gupta J. Whitaker 《Journal of Electronic Materials》1993,22(12):1471-1475
InxGa1−xAs (x=0.25–0.35) grown at low temperature on GaAs by molecular beam epitaxy is characterized by Hall effect, transmission
electron microscopy, and ultrafast optical testing. As with low temperature (LT) GaAs, the resistivity is generally higher
after a brief anneal at 600°C. High-resolution transmission electron microscopy shows all the as-grown epilayers to be heavily
dislocated due to the large lattice mismatch (2–3%). When the layers are annealed, in addition to the dislocations, precipitates
are also generally observed. As with LT-GaAs, the lifetime shortens as growth temperature is reduced through the range 300–120°C;
also, the lifetime in LT-InxGa1−xAs is generally shorter in as-grown samples relative to annealed samples. Metal-semiconductor-metal photodetectors fabricated
on the material exhibit response times of 1–2 picoseconds, comparable to results reported on GaAs grown at low temperature,
and the fastest ever reported in the wavelength range of 1.0–1.3 μm. 相似文献
24.
Ionic conductivity in poly(vinyl butyral) based polymeric electrolytes: Effect of solvents and salts
Li+ conductive solid polymeric electrolytes (SPEs) have been prepared by complexing Li salts LiX (X = I, SCN, CLO4, CF3SO3) with poly(vinyl butyral) (PVB) an amorphous polymer with a low Tg value and well known for its outstanding laminating properties. These self-supporting SPEs have been prepared by the solution cast technique using cyclohexanone, tetrahydrofuran, and n-butyl alcohol as solvents. The XRD and DSC investigations correlated to measured ionic conductivities have revealed that in addition to the amorphous nature of the resulting complex, its Tg value, the concentration and the values of the lattice energies of the complexing salts, the solvent used in making the SPEs also govern the value of ionic conductivity. Highest ionic conductivity values attained in SPEs made with n-butyl alcohol are explained in terms of the interception of the hydrogen bonding due to solvation. 相似文献
25.
Ciby Thomas S. Haldar Manoj Khanna S. Rajesh K.K. Gupta R.S. Gupta 《Microelectronics Reliability》1998,38(12):1955-1961
Analytical model for the transconductance, cut off frequency, transit time and fringing capacitance of LDD MOSFETs is presented with a simple approach. The analysis is carried out considering the LDD device as a conventional MOSFET with a series resistance [Z.-H. Liu et al., Threshold voltage model for submicrometer MOSFETs. IEEE Trans Electron Devices 1993; ED-40: 86–94] and a simple closed form expressions for cut off frequency and transit time is obtained. The total gate capacitance, i.e. the geometric and fringing capacitance, is calculated for both LDD and non-LDD devices and lower fringing capacitance is reported in LDD devices. Lower cut-off frequencies and higher transit time are reported in LDD devices for the same channel length. 相似文献
26.
Quantitation of Cefaclor in Pharmaceutical Dosage Forms Using High Performance Liquid Chromatography
Mary Mathew V. Das Gupta Charlie Bethea 《Drug development and industrial pharmacy》1993,19(14):1723-1729
A stability-indicating high-performance liquid chromatography for the quantitation of cefaclor in pharmaceutical dosage forms has been developed. The method is accurate and precise with a percent relative standard deviation of 1.2 based on 5 readings. A number of inactive ingredients present in the capsules and suspensions did not interfere with the assay procedure. The extraction procedure from the dosage forms is very simple. The recovery from the synthetic mixtures was quantitative. The capsules which had expired 3 years ago lost only 3% of the potency. The drug appears to be very sensitive to strong acids or bases since a 5 minute boiling caused 100% degradation of drug in both the solutions. 相似文献
27.
Mechanical properties of polypropylene-g-poly(methacrylic acid) fibers, prepared by graft copolymerization of methacrylic acid onto polypropylene fiber using simultaneous gamma ray irradiation technique, were evaluated. In general, an improvement in the mechanical behavior of the polypropylene fiber by grafting was observed. Denier and initial modulus of the fiber showed a linear increase with the percent graft, and elongation showed an opposite trend. The results have been explained in terms of reinforcing effect of poly(methacrylic acid) grafts and reduction in the segmental mobility of the polymeric chains. Tenacity also increases up to certain graft level, beyond which a sharp decrease occurs, probably due to the influence on the compactness of the macromolecular chains with the further grafting. 相似文献
28.
29.
M. K. Karthikeyan R. K. Gupta V. Rajesh B. R. Ghosh P. P. Sinha 《Journal of Failure Analysis and Prevention》2007,7(6):429-433
17-4 PH stainless steel is used as internal drive shaft material in liquid engine pumps. One of the drive shafts failed during
operation. The shaft pieces were in contact for short duration after failure, which has resulted in abrasion of fractured
surfaces. Samples from the location of failure were taken, and investigation of the failure was carried out using optical
and scanning electron microscopy. The microstructural analysis of the material and fractographic analysis of the fractured
surface show that the failure was caused by excessive torsion. 相似文献
30.
Gupta R. Hero A.O. III 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(8):1951-1969
We investigate high-rate quantization for various detection and reconstruction loss criteria. A new distortion measure is introduced which accounts for global loss in best attainable binary hypothesis testing performance. The distortion criterion is related to the area under the receiver-operating-characteristic (ROC) curve. Specifically, motivated by Sanov's theorem, we define a performance curve as the trajectory of the pair of optimal asymptotic Type I and Type II error rates of the most powerful Neyman-Pearson test of the hypotheses. The distortion measure is then defined as the difference between the area-under-the-curve (AUC) of the optimal pre-encoded hypothesis test and the AUC of the optimal post-encoded hypothesis test. As compared to many previously introduced distortion measures for decision making, this distortion measure has the advantage of being independent of any detection thresholds or priors on the hypotheses, which are generally difficult to specify in the code design process. A high-resolution Zador-Gersho type of analysis is applied to characterize the point density and the inertial profile associated with the optimal high-rate vector quantizer. The analysis applies to a restricted class of high-rate quantizers that have bounded cells with vanishing volumes. The optimal point density is used to specify a Lloyd-type algorithm which allocates its finest resolution to regions where the gradient of the pre-encoded likelihood ratio has greatest magnitude. 相似文献