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排序方式: 共有2083条查询结果,搜索用时 812 毫秒
61.
Joseph E. Williams Ramesh Goel Joseph R. V. Flora Radisav Vidic 《Canadian Metallurgical Quarterly》2005,131(11):1583-1588
A two-stage mathematical model was developed to describe adsorbate removal in a dead-end powdered activated carbon/ultrafiltration (PAC/UF) membrane process. Para-nitrophenol (PNP) was used as the model organic compound. The first stage accounted for adsorbate removal during transport from the initial PAC contact with the PNP solution to the membrane system, and the second stage accounted for additional PNP removal due to the retention of the PAC in a growing bed on the membrane surface. The PAC adsorptive capacity was described using the Langmuir isotherm, whose parameters were estimated from isotherm experiments. Transport of the PNP through the PAC particle was described using the homogeneous surface diffusion model and the surface diffusivity was estimated from batch experiments. The two stage model predicted the effluent concentrations from the PAC/UF process during the early stages of the experiments, but model improvements are required to more accurately predict the latter stages. A batch model can be used to describe the effluent PNP concentration from the PAC/UF process if dispersion is neglected. 相似文献
62.
The feasibility of electric current prompted aerobic biodegradation of NH4+–N in an attached growth bioreactor system is demonstrated. Nitrification was induced at electric current densities of 1.25 and 2.5?mA/cm2 and with pure oxygen supplied at a rate equivalent to 1.25?mA/cm2 when the bioreactor was operated in batch mode at 6 days detention time. About 84% (27?mg/L)?NH4+–N loss was observed at the end of each detention period during all three experimental conditions, indicating that the electric current did not negatively impact the rate of nitrification. Nitrite accumulation was observed during the initial stages of nitrification experiments with 1.25?mA/cm2 current intensity, but nitrite did not accumulate during the other two sets of nitrification experiments. A mathematical model formulated to obtain the rates of biological reactions showed that rates of NH4+–N removal are similar for all aeration conditions. Abiotic experiments showed that NH4+–N was not removed electrolytically and via stripping, confirming that NH4+–N disappearance is due to biological activity. 相似文献
63.
A simple analytical method is presented that can be used to predict the intralaminar fracture toughness of multilayered composite laminate based on the failure stresses of its sub laminates. MCCI approach is followed to verify the fracture toughness of a base laminate and the method is validated comparing the available test data on the toughness value of the base laminate with the prediction. It is observed that a better representation of carbon —epoxy base laminate by its sub laminate gives very good agreement in prediction within 3%. 相似文献
64.
K. Ramesh W. G. Lewis S. C. Veldhuis A. Yui 《Materials and Manufacturing Processes》2005,20(6):895-903
Ongoing developments in broadband digital networks and optical devices require mechanical components having nano-metric surface finishes and ultra precision shapes. Such components are processed using the technology of diamond micro-machining in which diamond tools are extensively used. However, these tools are susceptible to chemical attack at high temperatures and induce severe wear, especially when cutting ferrous materials. As a result, these diamond tools need to be redefined (i.e., resharpened) on a regular basis in order to facilitate micro-cutting and to generate nano-metric surface finishes. This paper describes a new way of diamond tool edge re-sharpening and its conditions to achieve both increased accuracy and material removal rate. 相似文献
65.
T. Jiao L. J. Kecskes T. C. Hufnagel K. T. Ramesh 《Metallurgical and Materials Transactions A》2004,35(11):3439-3444
We have investigated the mechanical behavior of a composite material consisting of a Zr57Nb5Al10Cu15.4Ni12.6 metallic glass matrix with 60 vol pct tungsten particles under uniaxial compression over a range of strain rates from 10−4 to 104 s−1. In contrast to the behavior of single-phase metallic glasses, the failure strength of the composite increases with increasing
strain rate. The composite shows substantially greater plastic deformation than the unreinforced glass under both quasi-static
and dynamic loading. Under quasi-static loading, the composite specimens do not fail even at nominal plastic strains in excess
of 30 pct. Under dynamic loading, fracture of the composite specimens is induced by shear bands at plastic strains of approximately
20 to 30 pct. We observed evidence of shear localization in the composite on two distinct length scales. Multiple shear bands
with thicknesses less than 1 μm form under both quasi-static and dynamic loading. The large plastic deformation developed in the composite specimens is
due to the ability of the tungsten particles both to initiate these shear bands and to restrict their propagation. In addition,
the dynamic specimens also show shear bands with thicknesses on the order of 50 μm; the tungsten particles inside these shear bands are extensively deformed. We propose that thermal softening of the tungsten
particles results in a lowered constraint for shear band development, leading to earlier failure under dynamic loading. 相似文献
66.
Laser composite surfacing of AISI 304 stainless steel with titanium boride for improved wear resistance 总被引:2,自引:0,他引:2
The present study concerns development of a hard in situ boride-dispersed composite layer on the surface of AISI 304 stainless steel substrate to improve the wear resistance property. Laser processing was carried out by melting the surface of sand-blasted AISI 304 stainless steel substrate using a continuous wave CO2 laser and simultaneous deposition of a mixture of K2TiF6 (potassium titanium hexafluoride) and KBF6 (potassium hexafloroborate) (in the weight ratio of 2:1) using Ar as shrouding environment. Powder feed rate was maintained constant at 4 g/min. Irradiation results in dissociation of a pre-deposited mixture along with a part of the stainless steel substrate, intermixing and rapid solidification to form the composite layer on the surface. The micro-structure of composite layer consists of dispersion of titanium boride particles in AISI 304 stainless steel matrix. Volume fraction of particles is found to be uniform throughout the composite layer, though varied with laser parameters. The micro-hardness of the surface was improved 250–350 VHN as compared to 220 VHN of the AISI 304 stainless steel substrate with a significant improvement in wear resistance property. The mechanism of wear was found to be a combination of adhesive and abrasive in as-received stainless steel. However, it was predominantly abrasive for laser composite surfaced stainless steel. 相似文献
67.
Hildrun Kretschmer Ramesh Kundra Donald deB. Beaver Theo Kretschmer 《Scientometrics》2012,93(1):135-150
The causes of gender bias favoring men in scientific and scholarly systems are complex and related to overall gender relationships in most of the countries of the world. An as yet unanswered question is whether in research publication gender bias is equally distributed over scientific disciplines and fields or if that bias reflects a closer relation to the subject matter. We expected less gender bias with respect to subject matter, and so analysed 14 journals of gender studies using several methods and indicators. The results confirm our expectation: the very high position of women in co-operation is striking; female scientists are relatively overrepresented as first authors in articles. Collaboration behaviour in gender studies differs from that of authors in PNAS. The pattern of gender studies reflects associations between authors of different productivity, or ??masters?? and ??apprentices?? but the PNAS pattern reflects associations between authors of roughly the same productivity, or ??peers??. It would be interesting to extend the analysis of these three-dimensional collaboration patterns further, to see whether a similar characterization holds, what it might imply about the patterns of authorship in different areas, what those patterns might imply about the role of collaboration, and whether there are differences between females and males in collaboration patterns. 相似文献
68.
69.
Ramesh M. Gohil 《应用聚合物科学杂志》2012,126(1):260-272
We have studied the efficiencies of commercially available barrier resins used for food packaging and beverage bottle applications and compared them with resins made using copolymer and blending approaches. The effects of various copolymer related parameters that influence oxygen barrier performance and the underlying mechanisms for these effects in PET‐based copolymers and blends were investigated. Using these approaches, it is possible to make highly effective PET‐based copolymers for gas barrier applications. Blending of PET with phenolic and other organic materials shows equivalent barrier performance in PET copolymers having comonomer levels of <8‐mole %. Reduction in oxygen permeation rates results from the reduction or elimination of short range molecular motion of polyethylene terephthalate molecules. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
70.
Achuta Kadambi Vage Taamazyan Boxin Shi Ramesh Raskar 《International Journal of Computer Vision》2017,125(1-3):34-51
Analyzing the polarimetric properties of reflected light is a potential source of shape information. However, it is well-known that polarimetric information contains fundamental shape ambiguities, leading to an underconstrained problem of recovering 3D geometry. To address this problem, we use additional geometric information, from coarse depth maps, to constrain the shape information from polarization cues. Our main contribution is a framework that combines surface normals from polarization (hereafter polarization normals) with an aligned depth map. The additional geometric constraints are used to mitigate physics-based artifacts, such as azimuthal ambiguity, refractive distortion and fronto-parallel signal degradation. We believe our work may have practical implications for optical engineering, demonstrating a new option for state-of-the-art 3D reconstruction. 相似文献