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41.
We have proposed that application of singular value decomposition on finite-difference time-domain simulations is best suited for modal analysis of complex real-life electromagnetic problems. This combination of two powerful techniques yields a wealth of information about the complete mode structure which cannot be otherwise obtained. This is particularly important for a real-life system having complex geometry and consisting of a range of materials from good conductors to dielectrics and this is further complicated by the existence of broad-band excitation. This hybrid approach is versatile, accurate, and computationally efficient. 相似文献
42.
A.A Ramadan A Abd-El MongyI.S Ahmed Farag A.M El-ShabinyF.A Radwan H.I IsmailH.M Hashem 《Thin solid films》2003,423(2):146-152
CdTe films were prepared by physical vapour deposition on a substrate at room temperature (RT) as well as on a cold (LT) one using low deposition rate. The thickness-dependence of stoichiometry revealed an abrupt decrease in the Cd/Te ratio as the thickness increases. Change of thickness did not affect the type of observed (111) crystallographic texture, only the degree of preferred orientation is enhanced as the film grows. The internal strain was negligible while the crystallite size increased rapidly at small thickness (up to 400 nm), and less thickness dependence was observed with further film growth. However, thickness dependence of lattice parameters showed a minimum and a maximum at approximately 300 nm in the case of RT and LT, respectively. The observed change in conductivity from n- to p-type and its vital correlation with the stoichiometry and structural characteristics were presented. Based on thickness dependence of stoichiometry and lattice parameters as well as the conductivity type, formation and annihilation of lattice defects were considered. 相似文献
43.
Maher F. El-Zohry Mohamed A. Abd-Alla 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,55(3):209-215
3-(2′-Chloroethyl)-2-methyl-3,4-dihydroquinazolin-4-one was reacted with acetylacetone, ethyl acetoacetate and diethylmalonate in the presence of sodium ethoxide to afford the alkylation products IV, V and VI , Compounds IV, V and VI were reacted with hydrazine hydrate, phenylhydrazine, hydroxylamine hydrochloride, urea and thiourea to yield 3-(2′-heterocyclicethyl)-2-methyl-3,4-dihydroquinazolin-4-one derivatives VII-XV . The structures of the synthesized compounds were elucidated by elemental analyses and spectroscopic (IR and XH-NMR) analyses. The prepared compounds were tested for their antimicrobial activities in comparison with tetracycline as a reference compound. 相似文献
44.
Helmy Ahmed Garg Saurabh Nahata Nitin Pamu Priyatham 《Mobile Networks and Applications》2005,10(1-2):99-113
Traditional protocols for routing in ad hoc networks attempt to obtain optimal or shortest paths, and in doing so may incur significant route discovery overhead. Such approaches may be appropriate for routing long-lived transfers where the initial cost of route discovery may be amortized over the life of the connection. For short-lived connections, however, such as resource discovery and small transfers, traditional shortest path approaches may be quite inefficient. In this paper we propose a novel architecture, CARD, for resource discovery in large-scale wireless ad hoc networks. Our mechanism is suitable for resource discovery as well as routing very small data transfers or transactions in which the cost of data transfer is much smaller than the cost of route discovery. Our architecture avoids expensive mechanisms such as global flooding and complex hierarchy formation and does not require any location information. In CARD resources within the vicinity of a node, up to a limited number of hops, are discovered using a proactive scheme. For resources beyond the vicinity, each node maintains a few distant nodes called contacts. Contacts help in creating a small world in the network and provide an efficient way to query for distant resources. Using contacts, the network view (or reachability) of the nodes increases, reducing the discovery overhead and increasing the success rate. On the other hand, increasing the number of contacts also increases control overhead. We study such trade-off in depth and present mechanisms for contact selection and maintenance that attempt to increase reachability with reduced overhead. Our schemes adapt gracefully to network dynamics and mobility using soft-state periodic mechanisms to validate and recover paths to contacts. Our simulation results show that CARD is scalable and can be configured to provide desirable performance for various network sizes. Comparisons with other schemes show overhead savings reaching over 93% (vs. flooding) and 80% (vs. bordercasting or zone routing) for high query rates in large-scale networks. 相似文献
45.
The problem of estimating the parameter of an exponential distribution when a proportion of the observations are outliers is quite important to reliability applications. The method of weighted likelihood is applied to this problem, and a robust estimator of the exponential parameter is proposed. Interestingly, the proposed estimator is an /spl alpha/-trimmed mean type estimator. The large-sample robustness properties of the new estimator are examined. Further, a Monte Carlo simulation study is conducted showing that the proposed estimator is, under a wide range of contaminated exponential models, more efficient than the usual maximum likelihood estimator in the sense of having a smaller risk, a measure combining bias & variability. An application of the method to a data set on the failure times of throttles is presented. 相似文献
46.
Co-evolution as a computational and cognitive model of design 总被引:6,自引:0,他引:6
Co-evolutionary design has been developed as a computational model that assumes two parallel search spaces: the problem space
and the solution space. The design process iteratively searches each space using the other space as the basis for a fitness
function when evaluating the alternatives. Co-evolutionary design can also be developed as a cognitive model of design by
characterizing the way in which designers iteratively search for a design solution, making revisions to the problem specification.
This paper presents the computational model of co-evolutionary design and then describes a protocol study of human designers
looking for evidence of co-evolution of problem specifications and design solutions. The study shows that co-evolutionary
design is a good cognitive model of design and highlights the similarities and differences between the computational model
and the cognitive model. The results show that the two kinds of co-evolutionary design complement each other, having strengths
in different aspects of the design process.
Electronic Publication 相似文献
47.
Pretreatment of high manganese hot metal is suggested to produce hot metal suitable for further processing to steel in conventional LD converter and rich manganese slags satisfy the requirements for the production of silicomanganese alloys. Manganese distribution between slag and iron represents the efficiency of manganese oxidation from hot metal. The present study has been done to investigate the effect of temperature, slag basicity and composition of oxidizer mixture on the distribution coefficient of manganese between slag and iron. Ferrous oxide activity was determined in molten synthetic slag mixtures of FeO‐MnO‐SiO2–CaO–MgO‐Al2O3. The investigated slags had chemical compositions similar to either oxidizer mixture or slags expected to result from the treatment of high manganese hot metal. The technique used to measure the ferrous oxide activity in the investigated slag systems was the well established one of gas‐slag‐metal equilibration in which molten slags contained in armco iron crucibles are exposed to a flowing gas mixture with a known oxygen potential until equilibrium has been attained. After equilibration, the final chemical analysis of the slags gave compositions having a particular ferrous oxide activity corresponding to the oxygen potential of the gas mixture. The determined values of ferrous oxide activity were used to calculate the equilibrium distribution of manganese between slag and iron. Higher manganese distribution between slag and iron was found to be obtained by using oxidizer containing high active iron oxide under acidic slag and relatively low temperature of about 1350°C. 相似文献
48.
Intercalation of poly[oligo(oxyethylene) methacrylates] onto sodium montmorillonite (MMT) clay has been investigated. A polymer–clay hybrid has been synthesized through intercalation of the monomer followed by its solution free‐radical polymerization. Eight polymer–clay hybrids were prepared using different weight ratios of clay, different oligo(oxyethylene) lengths and different proportions of crosslinker. Evidence of the development of nanostructures is obtained from scanning electron microscopy, and wide‐angle X‐ray diffraction studies support these results which show disappearance of the peak characteristic to d001 spacing. In this hybrid MMT is dispersed homogeneously in the polymer matrix. © 2003 Society of Chemical Industry 相似文献
49.
Vibration and damping analysis of beams with composite coats 总被引:1,自引:0,他引:1
Ahmed Abd El-Hamid Hamada 《Composite Structures》1995,32(1-4):33-38
Numerical and experimental investigations of the dynamic behavior for coated laminate composite beams has been presented and discussed in the present work. A numerical technique is utilized to compute the eigen parameters of coated laminated composite beams. An attempt to study the variations in the natural frequencies and damping properties of laminated composite coated beams taking into account different lamina orientation of coat and various kinds of core isotropic material (steel and aluminium) is introduced. The variations of the eigen parameters vs. the code number of the coated layer with the use of various types of isotropic material are measured by utilizing (the frequency response displayed on) an (FFT) analyzer. The experimental and numerical work is carried out on four different fiber orientations, aligned longitudinally, transversely, making 45 ° with the fibers direction and randomly oriented. Comparison between experimental and numerical results shows a tight connection between them. 相似文献
50.
Dr Maher Boulos Author Vitae 《Metal Powder Report》2004,59(5):16-21
It may be a truism to say that round powders pack better, but spheroidisation of powder particles is one of the successful commercial applications of induction plasma technology and can play a key role in substantial improvement of powder quality and fluidity… 相似文献