Design∕Control Optimization of Cross‐Ply Laminates Under Buckling and Vibration

The optimal layer thicknesses and optimal feedback control function are determined for a symmetric, cross‐ply laminate. The objectives of the optimization are to maximize the biaxial buckling load (design objective) and to minimize the dynamic response to external disturbances (control objective) subject to a constraint on the expenditure of control energy. The design∕control problem is formulated as a multiobjective optimization problem by employing a performance index that combines the design and control objectives in a weighted sum. Numerical results are given for a laminate made of an advanced composite material. Comparisons of controlled and uncontrolled laminates as well as optimally designed and nonoptimal laminates indicate the benefits of treating the design and control problems in unified formulation. The implications of solving these two problems are discussed. The values of optimal design and control variables are given for a number of problem parameters.     

Maximum Principle for Optimal Boundary Control of Vibrating Structures with Applications to Beams

A maximum principle is derived for open-loop boundary control of one dimensional structures undergoing transverse vibrations. The optimal control law is obtained using a maximum principle and the applicability of the results to the boundary control of vibrating beams is demonstrated. The method of solution involves the transformation of the original problem into one with homogeneous boundary conditions for a general set of boundary forces and torques. An adjoint variable is introduced and used in the formulation of a Hamiltonian function which in turn leads to the derivation of the maximum principle. The effectiveness of the proposed control mechanism is illustrated numerically and it is shown that the implementation of the optimal boundary control using one force actuator can lead to substantial decrease in the dynamic response of a vibrating beam.     

Time-domain surface impedances of lossless Debye media

In a previous paper, a surface impedance formalism was given. Its application to interfaces modelling between homogeneous and frequency dependent media, was of great interest in the finite difference timedomain (fdtd) codes. In this paper, an extension of the method to dispersive media is presented. Applying this formalism to lossless Debye medium, the analytical expressions of the time- domain surface impedances are given. The implementation in a fdtd code permits then a numerical verification of the results in relation to the Fresnel method.     

Thermodynamics of HCl in water—ethylene carbonate mixtures

The emf of the cell: Pt; H₂ (1 atm.)/HCl (m), Ethylene carbonate (x), H₂O (100?x)/AgCl, Ag is measured at 5° interval in the temperature range 25 to 45°C. The standard potential of the silver—silver chloride electrode, E^o_m, is determined in each solvent mixture covering the range 0–78% EC. The temperature coefficient is calculated using the method of least squares. The mean activity coefficient of HCl, γ_±, is determined for molalities between 0.01 and 0.05 m in each case. The primary, secondary and total medium effects are calculated. From the variation of the mean activity coefficient with temperature, the relative partial molal heat content $\text{L}$₂ of HCl is computed. $\text{L}$₂ passes through a minimum at 30% for 0.05 m HCl at all temperatures. The effect of temperature on $\text{L}$₂ permits the evaluation of the corresponding relative partial molal specific heat $\text{J}$₂.     

Rigorous comparison of parabolically tapered and conventional multimode-interference-based 3-dB power splitters in InGaAsP/InP waveguides

Design issues such as optical transmission, interference mechanisms, the splitting ratio, the polarization dependence, and the fabrication tolerances of a compact parabolically tapered multimode-interference (MMI)-based 3-dB power splitter on an InP-based deeply etched ridge waveguide, by use of the finite-element-based beam-propagation method, are presented. The benefits and drawbacks of the use of the tapered structure, in comparison with an untapered MMI-based 3-dB splitter, have also been investigated.     

Effect of various steps of purification on ash content and ash constitution of cellulose. I. Cellulose prepared from cotton linters

The effect of the various steps of purification on the ash content and ash constitution of cellulose prepared from cotton linters has been examined. After each step of purification, samples were analysed for total ash, SiO₂, Ca, Mg, Fe, Al, Cu and Mn. Two methods of bleaching were investigated. The first involves double treatment of cellulose with sodium hypochlorite solution, and the second one treatment with hypochlorite followed by another treatment with sodium chlorite solution. The second method has a better effect in diminishing the ash content.     

Dynamic optimization of framed structures

An analytical procedure for the determination of the least weight structure which satisfies a specific frequency requirement plus upper and lower bounds on the design variables is presented. The design algorithm is an iterative solution of the Kuhn-Tucker optimality criterion. The procedure is to modify an existing design to first obtain the correct structural frequency and then, while the frequency is held constant, to minimize the weight. This is accomplished using gradient equations derived in matrix notation for direct application to the finite element method of analysis.

The most important features of the algorithm are: (a) a small number of design iterations are needed to reach optimal or near-optimal design, (b) structural elements with a wide variety of size stiffness may be used.

The procedure has been completely automated in a computer program. Results of two numerical examples show that the method is convergent and that optimized configurations can be determined in as few as 10 redesign cycles.     

Thermal–hydraulic modeling of the onset of flow instability in MTR reactors

Prediction of the onset of the flow instability (OFI) in steady and transient sub-cooled flow boiling is an important consideration in the design and operation of nuclear reactors, in particular for materials testing reactors (MTR). In this study, a predictive model for OFI in the MTR has been developed. The model is based on both the heat balance during the bubble generation and condensation processes, and the force balance for the detached bubbles at the onset of significant void (OSV). The only adjustable coefficient involved in the proposed model is quantified by comparison with the experimental data of Whittle and Forgan [Whittle, R.H., Forgan, R., 1967. A correlation for the minima in the pressure drop versus flow-rate curves for sub-cooled water flowing in narrow heated channels. Nucl. Eng. Des. 6, 89–99], which covers the wide range of MTR operating conditions. The model predictions are compared with predictions of some previous models, and it is shown that the present model results in smaller deviation from the experimental data. A correlation for the heat flux at OFI is also developed based on the present model. The developed correlation gives lower deviation from the experimental data than the well-known correlation of Whittle and Forgan. The model is also used to predict the OFI locus during a transient, where it shows good agreement with the short transient data of Lee and Bankoff [Lee, S.C., Bankoff, S.G., 1993. Prediction of the onset of flow instability in transient sub-cooled flow boiling. J. Nucl. Eng. Des. 139, 149–159] as well.     

Experimental Analysis of Punch-Through Conditions in Power P-I- N Diodes

Commercial power diodes are optimized to feature punch-through behavior. However, a tradeoff between the width and the doping level of the diode epitaxial layer leads to various levels of optimization. For a given breakdown voltage, a shorter epitaxial layer width leads to better transient performances. Device datasheets do not cover this issue and a simple experimental setup is presented to assess the optimization conditions inside the diode epitaxial layer. Three commercial devices are tested and experimental results are confronted to device simulations. A good agreement is found     

Location Management in PCS Networks by Caching Two-Level Forwarding-Pointers

One of the challenging tasks in Personal Communication Services (PCS) is to efficiently maintain the location of PCS subscribers who move from one region to another (hereafter called mobile users). When a mobile user receives a call, the network has to quickly determine its current location. The existing location management scheme suffers from high signaling traffic in locating the mobile users. Two-level forwarding pointer scheme has been proposed from per-user forwarding pointer scheme to reduce the cost of signaling traffic. In this paper, we enhance the two-level forwarding pointer scheme. When a mobile user moves from its current Registered Area (RA), which is served by Mobile Switching Center (MSC), to another RA the local switch that acts as a parent of those two MSCs maintains this movement in its memory (hereafter called cache entry). A cache entry is used to locate rapidly the mobile user instead of querying the Home Location Register (HLR) and waiting for its reply. HLR is centralized in the network and far away from the mobile users so that the signaling traffic crossing it is expensive. Sometimes the cache entry may be failed to reach the mobile user then a two-level forwarding pointers will be created from the corresponding Visitor Location Register (VLR), attached to its MSC, through a correct path to locate the mobile user. Thus, there is a saving in cost of querying the underlying HLR. The analytical results indicate that such proposal efficiently reduces the signaling traffic cost for all values of Call to Mobility Ratio (CMR), this is especially considerable when CMR ≥1, without any increase in the call setup delay. Salah M. Ramadan (samohra@yahoo.com) received the BS and MS degrees from Computers Engineering Department, Al-Azhar University, Cairo, Egypt, in 1995 and 2002, respectively. From 2002, he was a Ph.D. student in Computers Engineering Department at Al-Azhar University and is currently pursuing the Ph.D. degree, where he is a research assistant in the Wireless Networks Branch. His research interests include traffic management in ATM networks, routing protocols, mobility management in PCS networks, and mobile computing. He is currently an instructor in Cisco Academy, Egypt. Ahmed M. El-Sherbini (Sherbini@mcit.gov.eg) received the Ph.D. in Electrical and Communication Engineering, Case Western University, U.S.A. March 1983 and M.Sc. in Communication Engineering, Cairo University, Giza, Egypt, June 1980. (M. Sc. Research Studies at the Ecole Nationale Superieure des Telecommunications (ENST), Paris, France). He is the Director, National Telecommunication Institute – Ministry of Communications and Information Technology, Egypt and Professor of Electrical and Communication Engineering Dept. Faculty of Engineering, Cairo University, Egypt. M. I. Marie received his B.Sc., M.Sc. and Ph.D. in electronic and communication engineering from Cairo University on 1972, 1981, 1985, respectively. Now he is a professor of communications at Computer and System Engineering department Al-Azhar University, Cairo, Egypt. His fields of interest includes digital communication, computer networks and protocols development. M. Zaki (azhar@mailer.scu.eun.eg) is the professor of software engineering, Computer and System Engineering Department, Faculty of Engineering, Al-Azhar University at Cairo. He received his B.Sc. and M.Sc. degrees in electrical engineering from Cairo University in 1968 and 1973 respectively. He received his Ph.D. degrees in computer engineering from Warsaw Technical University, Poland in 1977. His fields of interest include artificial intelligence, soft computing, and distributed system.