Optothermal properties of fibers. VIII. Structure orientation study of annealed Egyptian polyester fibers

A two-beam interferometric method is used to study the change of optical orientation functions and the molecular structure of annealed Egyptian poly(ethylene terephthalate) (PET) fibers. The acoustic method was used for measuring the density. The density results were used to calculate the degree of crystallinity of PET. It was found that annealing causes alignment to the fiber chains in the directions of the fiber axis. This alignment gives an increase in the optical orientation function and decrease in orientation angle. The value of Δα/3α₀, which depends upon the molecular structure of the polymer, remains constant. The obtained results of the optical and the density clarify that new reorientations occurred due to annealing at different conditions. The changes of the refractive index profile of annealed PET fibers are given. Microinterferograms and curves are given for illustration. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2031–2050, 1997     

Digital computer studies of the surge response of a transmission line tower

In this paper, the transmission line tower response and behaviour are described when a lightning stroke terminates on the tower apex. The accompanied overvoltages on different points on the tower and under different conditions are covered. The effect of tower representation and modelling on the overvoltages produced and the tower travel time is also included.     

Throughput behavior of link adaptive 802.11 DCF with MUD capable access node

Conventional IEEE 802.11 medium access control (MAC) protocol discourages simultaneous transmission to avoid collisions. With fast advances in physical layer technologies, multi-user detection (MUD) capable receivers which can detect multiple frames from different users simultaneously become available. If we are to utilize them in today's wireless LAN, however, it is not entirely clear how we should change the MAC and how much benefit is available and can be obtained by doing so. The primary objective of this paper is to investigate such questions. We approach this objective by developing a new throughput expression for 802.11 distributed coordination function (DCF). The derived expression has been verified in simulation. We show that significant throughput gain can be garnered with slight modification in 802.11 DCF.     

A scalable optical WDM multicast Beneš network with multi-channel wavelength converters

An optical wavelength division multiplexing (WDM) multicast network interconnects an input signal on a given wavelength to one or more output fibers, possibly on different wavelengths (via wavelength conversion), while maintaining the signal in the optical domain. A key challenge in the design of scalable multicast networks is to reduce conversion complexity without affecting the switching capability and signal quality. In this article, we propose a scalable WDM multicast Beneš interconnection network with minimized conversion complexity. The proposed network is based on the Copy-and-Route architecture, and it uses multi- channel WCs (MCWCs) for wavelength conversion. The conversion complexity of the proposed design is O(F log₂ W) (where F is the number of fibers and W is the number of wavelengths per fiber), which is smaller than the O(FW) complexity of the optimal design based on conventional single-channel WCs (SCWCs). We prove that, for W >  64 and for any value of F, the conversion complexity of the new design is strictly less than that of the optimal SCWC-based design regardless of the total number of wavelengths simultaneously converted by each MCWCs. Analyzes of conversion complexity of the proposed design for large values of W confirm considerable savings compared to the optimal SCWC-based design. For instance, for W = 256 and an for an arbitrary value of F, a practical implementation of the proposed design achieves 87% reduction in conversion complexity as compared to the optimal SCWC-based design.     

Adsorption kinetics and surface modeling of aqueous methylene blue onto activated carbonaceous wood sawdust

In this work, Sawdust was used to develop a new low-cost adsorbent and study its application to remove methylene blue dye from aqueous solution. Sawdust was calcined under air atmosphere at three different temperatures (300°C, 400°C, and 500°C) using phosphoric acid (H₃PO₄) as an activating agent. The structure, morphology, surface functions and the chemical composition of adsorbent were characterized by Fourier Transform Infrared spectra (FTIR), X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), specific surface area (BET) and Boehm method. Different operational parameters such as pH, adsorbent loading, contact time and were investigated to evaluate experimental data. The adsorption of MB on SD-300, SD-400, and SD-500 show that the pseudo-second-order and Langmuir models fitted better the experimental results of MB adsorption onto all adsorbents. The maximum capacities based on the Langmuir model were 416.7 mg.g^?1 for SD-300, 526.3 mg.g^?1 for SD-400, and 819.7 mg.g^?1 for SD-500. The positive values of ΔG, ΔH, and ΔS implied that the adsorption process was non-spontaneous and endothermic nature. Finally, Regeneration of the SD-500 was investigated and optimization was performed using CCD combined with RSM.     

Different methods for estimating thermal diffusivity of a heat process

The purpose of this study is to compare three different methods for determining the thermal diffusivity of a one dimensional heat diffusion process. A modifiedA?ngstro¨m's method, an on-line least squares method and a maximum likelihood method have been applied to data obtained from experiments on a long copper rod. The accuracy, the amount of computation, the storage capacity and in general the advantages and the limitations of the different methods are discussed.