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.     

An efficient algorithm for solving general periodic Toeplitzsystems

An efficient algorithm is presented for inverting matrices which are periodically Toeplitz, i.e., whose diagonal and subdiagonal entries exhibit periodic repetitions. Such matrices are not per symmetric and thus cannot be inverted by Trench's (1964) method. An alternative approach based on appropriate matrix factorization and partitioning is suggested. The algorithm provides certain insight on the formation of the inverse matrix, is implementable on a set of circularly pipelined processors and, as a special case, can be used for inverting a set of block Toeplitz matrices without requiring any matrix operation     

A note on methods for analysis of flow through microchannels

The flow problem within a straight microchannel of arbitrary cross section is analyzed. Exact analytical solutions for flow profile of a channel flow with no-slip boundary conditions have been obtained in literature only for simple geometry of channel section. In this paper, a number of problems with more complicated geometries are solved either exactly or approximately. Three general solution methods are discussed, namely, complex function analysis, membrane vibration analogy and variational method. The usefulness of each method is justified with the help of examples.     

Simulation studies on model reference adaptive controller based speed estimation technique for the vector controlled permanent magnet synchronous motor drive

This paper presents a speed estimation technique for the permanent magnet synchronous motor drive. A Model Reference Adaptive System (MRAS) has been formed using the instantaneous and steady-state reactive powers to estimate the speed. It has been shown that such unique MRAS offers several desirable features. The proposed technique is completely independent of stator resistance and is less parameter sensitive, as the estimation-algorithm is only dependent on q-axis stator inductance. Also, the method requires less computational effort as the simplified expressions are used in the MRAS. The stability of the proposed system is achieved through Popov’s Hyperstability criteria. Extensive simulation results are presented to validate the proposed technique. The system is tested at different speeds including zero speed and a very satisfactory performance has been achieved.     

Spectral engineering of terahertz quantum cascade lasers using focused ion beam etched photonic lattices

Focused ion beam etching has been used to introduce one-dimensional photonic lattices, of periods 9.11, 9.24, 9.44 /spl mu/m, between the cleaved facets of three 4.44 THz Fabry-Perot quantum cascade lasers. Singlemode lasing has been achieved at precisely defined wavelengths of 67.59, 68.48, 70.00 /spl mu/m, respectively.