Estimation of the modulus of elasticity of N-A-S-H and slag-based geopolymer structures containing calcium and magnesium ions as impurities using molecular dynamics simulations

Geopolymers are alkaline cements composed of aluminosilicate units. The molecular structure of some geopolymers is sodium-aluminosilicate hydrate (N-A-S-H). Impurities containing calcium and magnesium are of significant importance in various types of geopolymer materials, as these impurities affect the mechanical properties of the geopolymer. In this study, the effects of different percentages of impurities on the modulus of elasticity of two types of geopolymer structures (N-A-S-H and slag) were investigated using molecular dynamics simulations. A recently introduced and modified N-A-S-H structure was used in the simulations. The molecular structure of blast furnace slag was also used to confirm and validate the molecular simulation results. The main reason for comparing the results of molecular dynamics simulations of the N-A-S-H structure with those of slag was the availability of laboratory results for slag-based geopolymers in the technical literature. The proposed molecular structure of slag based on its constituents is (N,C)-A-S-H. This structure is the most similar to N-A-S-H. The simulation parameters were selected based on data available in the literature. For the amorphous form of N-A-S-H, several simulations were performed to determine the mean modulus of elasticity. Then, additional simulations were carried out to investigate the effect of impurities on the modulus of elasticity of geopolymer materials. The results were in good agreement with the available laboratory results. The results showed that with an increasing percentage of calcium in the N-A-S-H structure, the modulus of elasticity increased. On the other hand, with an increasing percentage of magnesium impurities in the slag and N-A-S-H structures, the modulus of elasticity decreased. The overall results showed that the molecular dynamics simulation method is a good tool to complement laboratory studies for investigating the mechanical properties of geopolymers.     

Design and VLSI implementation for a WCDMA multipath searcher

The third generation (3G) of cellular communications standards is based on wideband CDMA. The wideband signal experiences frequency selective fading due to multipath propagation. To mitigate this effect, a RAKE receiver is typically used to coherently combine the signal energy received on different multipaths. An effective multipath searcher is, therefore, required to identify the delayed versions of the transmitted signal with low probability of false alarm and misdetection. This paper presents an efficient and novel WCDMA multipath searcher design and VLSI architecture that provides a good compromise between complexity, performance, and power consumption. Novel multipath searcher algorithms such as time domain interleaving and peak detection are also presented. The proposed searcher was implemented in 0.18 /spl mu/m CMOS technology and requires only 150 k gates for a total area of 1.5 mm/sup 2/ consuming 6.6 mw at 100 MHz. The functionality and performance of the searcher was verified under realistic conditions using a channel emulator.     

TOPICS IN OPTICAL COMMUNICATIONS - Fundamentals and Challenges of Optical Multiple-Input Multiple-Output Multimode Fiber Links

In this article we discuss the application of MIMO processing to multimode fiber links. MIMO processing is shown to increase the information capacity of communication links linearly as the minimum number of transmitters/receivers increases. The fundamentals of optical MIMO fiber links are presented, and the promises and challenges of such systems are elaborated