A density functional theory study of hydrogen recombination and hydrogen-deuterium exchange on Ga/H-ZSM-5

Density functional theory calculations have been carried out to determine the thermodynamic stability of various Ga species in gallium-exchanged ZSM-5, the thermodynamics of H₂ adsorption, and the most favorable pathway for H₂/D₂ exchange. The portion of the zeolite associated with Ga was represented by a cluster containing 7, 21, or 33 atoms. The B3LYP hybrid method was used to account for the effects of electron exchange and correlation. The most likely form of Ga expected in freshly exchanged and calcined ZSM-5 is ZGa(OH)₂. H₂ reduction of this species is projected to produce ZGa(H)(OH) and ZGa(H)₂. While the thermodynamics of H₂ desorption from ZGa(H)₂ are favorable, the process is projected to be slow because of a high activation barrier. The most favorable pathway for H₂/D₂ exchange over ZGa(H)₂ proceeds via Z(D)(Ga(H)₂(D)) as an intermediate. Similar calculations have been carried out for H₂/D₂ exchange over H-ZSM-5. This revised version was published online in June 2006 with corrections to the Cover Date.     

A systolic array realization of the adaptive decision feedback equalizer

This paper presents a systolic array architecture for the adaptive decision feedback equalizer. The design is based on an algebra developed earlier by Kung and Lin (Proceedings of the Conference of Elliptic Problem Solvers, Monterey, CA, January 1983; Research Report CMU-CS-84-100, Department of Computer Science, Carnegie-Mellon University, Pittsburgh, PA, April 1983.) and is largely made up of two basic processing cells that are computationally equivalent and simple to realize. To maintain accuracy of the algorithm, the array needs to be operated by a clock with a speed twice of that the input. The increase in clock speed can, however, be exploited to reduce the total number of adders and multipliers by about 50%.     

Impact toughness in Al–12Si and Al–12Si–3Cu cast alloys—Part 1: Effect of process variables and microstructure

The charpy impact energy of Al–12Si and Al–12Si–3Cu cast alloys was measured in terms of the total absorbed energy. The standard charpy specimens 10×10×55 mm with a 2 mm V-notch were prepared from the castings. Effect of process variables and microstructural changes on the impact toughness of Al–12Si and Al–12Si–3Cu cast alloys was investigated. The results indicate that combined grain refined and modified Al–12Si–3Cu cast alloys have microstructures consisting of uniformly distributed α-Al dendrites, eutectic Al–Si and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better impact toughness in the cast condition compared with the same alloy subjected to only grain refinement or modification.     

A new approach for medium-access control for data traffic and itsadaptation to the GSM general packet radio services

The inhibit sense multiple access with polling (ISMA/P) is a packet-based medium-access control scheme for statistical multiplexing of data users over a single slotted channel of a time-division multiple-access (TDMA) cellular system. In ISMA/P, the central base station (BS) asserts control over the users by polling data in smaller blocks. This enables ISMA/P to attain a near ideal, steady, and high throughput and low-mean delay performance, which is not usually achievable by contention-reservation-based MAC schemes. In this paper, we describe the ISMA/P algorithm and provide a detailed simulation study of it over a global system for mobile communications (GSM)-like slotted channel for a traffic model adopted from European Railways applications. This study shows that ISMA/P can achieve a steady throughput of 90% over a large range of load. A number of practical advantages of ISMA/P, such as elimination of channel hogging, incorrect channel sensing, battery saving, etc., are also elaborated     

Design of an Ideal Grain-Refiner Alloy for Al-7Si Alloy Using Artificial Neural Networks

An ideal grain refiner has been designed for Al-7Si alloy by performing sensitivity analysis of trained artificial neural network (ANN) model. An ANNs model has been developed for solving these complex grain refinement phenomena in Al-7Si alloy. The model predictions and the analysis are well in agreement with the experimental results and existing metallurgical facts. Uncertainty in predictions helped in finding a new phenomenon at lower addition levels of grain refiner.     

Collapse dynamics of a star of dark matter and dark energy

We study the collapse dynamics of an inhomogeneous spherically symmetric star made of dark matter (DM) and dark energy (DE). The dark matter is taken in the form of a dust cloudwhile an anisotropic fluid is chosen as the candidate for dark energy. It is investigated how dark energy modifies the collapsing process, and it is examined whether dark energy has any effect on the Cosmic Censorship Conjecture. The collapsing star is assumed to be of finite radius, and the space-time is divided into three distinct regions Σ and V ^±, where Σ represents the boundary of the star and V ⁻(V ⁺) denotes the interior (exterior) of the star. The junction conditions for matching V ^± over Σ are specified. The role of Dark energy in the formation of an apparent horizon is studied, and the central singularity is analyzed.     

Compositional and structural analysis of RF magnetron sputtered La3+-modified PZT thin films

In the present work, we report the preparation of lanthanum-modified lead zirconate titanate (PLZT) thin films in pure perovskite phase by RF magnetron sputtering. For this purpose, a 3-in. diameter target of PLZT (8/60/40) was prepared by conventional solid-state reaction route. The chemical composition of PLZT target was determined using gravimetric analysis followed by UV–vis and flame atomic absorption spectrometry. Various deposition parameters such as target-to-substrate spacing, deposition temperature, post-deposition annealing temperature and time have been optimized to obtain PLZT films in pure perovskite phase. The films prepared in pure argon at 100 W RF power without external substrate heating exhibited pure perovskite phase after rapid thermal annealing (RTA) as confirmed by X-ray diffraction (XRD). Compositional analysis of the PLZT film was performed by secondary ion mass spectroscopy (SIMS) using PLZT target as standard sample. Depth profile of the film shows very good stoichiometric uniformity of all elements of PLZT.