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101.
Ali Bayram Agah Uguz Ali Durmus 《Journal of Materials Engineering and Performance》2002,11(5):571-576
Three types of material whose fracture toughness tests were previously performed by using circumferentially notched bars,
namely (1) a dual-phase steel with three different morphologies; (2) an Al-Zn-Mg-Cu-wrought alloy; and (3) Al-Si-cast alloys
with three different Si contents, were investigated in terms of accuracy and reliability of the testing method. Also, the
advantages of using circumferentially notched bars for fracture toughness determination of metallic materials were discussed.
With the help of stress concentration factors, which are associated with the bluntness of the notch, correction factors for
the fracture toughness calculations are derived. The corrected fracture toughness values are found to be close to the uncorrected
ones, implying that the testing procedure is reliable. 相似文献
102.
103.
Compact WLAN disc antennas 总被引:1,自引:0,他引:1
McEwan N.J. Abd-Alhameed R.A. Ibrahim E.M. Excell P.S. Ali N.T. 《Antennas and Propagation, IEEE Transactions on》2002,50(12):1862-1864
A novel conical beam patch antenna design, suitable for local area network applications, uses a central cylindrical connection from the disc to ground to achieve a large reduction in resonant size. Results on efficiency, bandwidth, and pattern are reported for several prototypes. 相似文献
104.
105.
Dynamic bandwidth allocation for quality-of-service over Ethernet PONs 总被引:24,自引:0,他引:24
Assi C.M. Yinghua Ye Sudhir Dixit Ali M.A. 《Selected Areas in Communications, IEEE Journal on》2003,21(9):1467-1477
Ethernet-based passive optical network (EPON) technology is being considered as a promising solution for next-generation broadband access networks due to the convergence of low-cost Ethernet equipment and low-cost fiber infrastructures. A major feature for this new architecture is the use of a shared transmission media between all users; hence, medium access control arbitration mechanisms are essential for the successful implementation of EPON: i.e., to ensure a contention-free transmission and provide end users with equal access to the shared media. We propose to use the multipoint control protocol defined by the IEEE 802.3ah task force to arbitrate the transmission of different users, and we present different dynamic bandwidth allocation (DBA) algorithms to allocate bandwidths effectively and fairly between end users. These DBA algorithms are also augmented to support differentiated services, a crucial requirement for a converged broadband access network with heterogeneous traffic. We show that queueing delays under strict bandwidth allocation algorithms result in an unexpected behavior for certain traffic classes, and we suggest the use of DBA with appropriate local queue management to alleviate this inappropriate behavior. We conduct detailed simulation experiments to study the performance and validate the effectiveness of the proposed protocols. 相似文献
106.
BATCH SEQUENCING 总被引:1,自引:0,他引:1
Consider the single machine scheduling problem where there are a number of part types to be processed. A part type is defined as follows: Two parts are of the same part type if the machine does not require a setup in between the processing of these parts. The problem investigated in this paper is to find a sequence of batches of parts (if there are any) where all the requirements for parts are met. A heuristic and an exact algorithm are developed, and computational analysis is performed to measure the performance of the heuristic. The time complexity function of the heuristic is O(n2), and the exact algorithm runs in polynomial time given a fixed upper bound on the number of setups. 相似文献
107.
Ronak A. Kapadia Simant R. Upreti Ali Lohi Ioannis Chatzis 《Journal of Petroleum Science and Engineering》2006,51(3-4):214-222
In this work, a mathematical model is developed and simulated to determine gas dispersion along with solubility during the vapor extraction (Vapex) of live oil from a laboratory scale physical model. The physical model is a rectangular block of homogenous porous medium saturated with heavy oil and bitumen. At a given temperature and pressure, the block is initially exposed on its side to a solvent gas, which diffuses into the medium and gets absorbed. The absorption of gas reduces the viscosity of heavy oil and bitumen causing it to drain under gravity. The low-viscosity “live oil” is produced at the bottom of the porous block. The production of live oil with time is accompanied by the shrinkage of oil in the block as well as its increased exposure to gas from top. These phenomena of Vapex are described by the mathematical model, which is used to calculate live oil production with various values of gas solubility and dispersion. Their optimal values are determined for the vapor extraction of Cold Lake bitumen with butane by matching calculated live oil production with its experimental values published earlier. 相似文献
108.
Karim Mohammad Pour Reza Jalil 《AEUE-International Journal of Electronics and Communications》2005,59(7):392-400
The sinuous antennas have a numerous applications in military and civil systems such as direction finding systems and reflector feeds due to their superior broadband characteristics and simultaneous polarization capability. In this paper, design, construction and measurements of planar sinuous antennas are investigated for 1–5 GHz frequency range. Feeding sections of this antenna are realized by using microstrip tapered baluns. We have determined the microstrip tapered balun dimensions using Ansoft HFSS-simulation program. The performances of the manufactured antenna are measured using HP vector network analyzer. Polarization patterns and return loss characteristics of the designed antenna that have been measured in anechoic chamber, are presented. 相似文献
109.
Hamid Javaherian Naghash Ahmad Reza Momeni Hamid Alian Ahmad Reza Massah Shahla Ataie 《Polymer International》2005,54(11):1564-1571
Poly(methyl methacrylate) (PMMA) gels with varying amounts of silicone and solvent and constant amounts of crosslinker were prepared by solution free radical crosslinking copolymerization of methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), tetraethoxysilane (TEOS) and vinyltriethoxysilane (VTES) comonomer systems. They were then studied in benzene at a total monomer concentration of 3.5 mol L?1 and 70 °C. The conversion of monomer, volume swelling ratio, weight fraction and gel point were measured as a function of the reaction time, silicone concentration and benzene content up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in benzene, gel fraction and Fourier‐transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by SEM. Based on the obtained results, it was concluded that the FTIR data did not have the capacity to show the presence of the VTES or TEOS moiety in these kinds of copolymers. On the other hand, the variation of weight fraction of gel, Wg, and its equilibrium volume swelling ratio in benzene, qv, exhibited the same behaviour as that of MMA/EGDM copolymers. Also, the dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percent of conversion and gel fraction. Finally, TEOS is not an ideal silicone compound for reaction in the MMA/EGDM copolymerization system, whereas VTES is a suitable silicone comonomer for this system and it has been proved useful. Copyright © 2005 Society of Chemical Industry 相似文献
110.
Specimen preparation and image processing and analysis techniques for automated quantification of concrete microcracks and voids 总被引:4,自引:0,他引:4
Parviz Soroushian Mohamed Elzafraney Ali Nossoni 《Cement and Concrete Research》2003,33(12):1949-1962
Specimen preparation and image processing/analysis techniques were developed for use in automated quantitative microstructural investigation of concrete, focusing on concrete microcracks and voids. Different specimen preparation techniques were developed for use in fluorescent and scanning electron microscopy (SEM) of concrete; then techniques produce a sharp contrast between microcracks/voids and the body of concrete. The image processing/analysis techniques developed specifically for use with concrete address the following usages: automatic threshold; development of intersecting microcracks/voids and connected voids; distinction of microcracks form voids based on geometric attributes; and noise filtration. 相似文献