3D multi-material and multi-joint topology optimization with tooling accessibility constraints

Structural and Multidisciplinary Optimization - This paper proposes a method for performing both multi-material topology optimization and multi-joint topology optimization. The algorithm can...     

Kinematic analysis of three-link spatial mechanisms containing sphere-plane and sphere-groove pairsAnalyse cinématique des mécanismes spatiaux a trois barres contenant les paires sphère-plan et sphère-rainure

Kinematic pairs in a spatial mechanism are viewed either as allowing relative screw motion between links or as constraining the motion of the two chains of the mechanism connected to the two elements of the pair. Using pair geometry constraints of the sphere-plane and sphere-groove kinematic pairs, the displacement, velocity and accelerations equations are derived for, R-Sp-R, 5 R-Sp-P, P-Sp-P, P-Sp-R and R-Sg-C three-link mechanisms. For known values of the input variable, other variables are computed in closed form. The analysis procedures are illustrated using numerical examples.     

Adaptive Filtering Techniques using Cyclic Prefix in OFDM Systems for Multipath Fading Channel Prediction

This paper presents adaptive channel prediction techniques for wireless orthogonal frequency division multiplexing (OFDM) systems using cyclic prefix (CP). The CP not only combats intersymbol interference, but also precludes requirement of additional training symbols. The proposed adaptive algorithms exploit the channel state information contained in CP of received OFDM symbol, under the time-invariant and time-variant wireless multipath Rayleigh fading channels. For channel prediction, the convergence and tracking characteristics of conventional recursive least squares (RLS) algorithm, numeric variable forgetting factor RLS (NVFF-RLS) algorithm, Kalman filtering (KF) algorithm and reduced Kalman least mean squares (RK-LMS) algorithm are compared. The simulation results are presented to demonstrate that KF algorithm is the best available technique as compared to RK-LMS, RLS and NVFF-RLS algorithms by providing low mean square channel prediction error. But RK-LMS and NVFF-RLS algorithms exhibit lower computational complexity than KF algorithm. Under typical conditions, the tracking performance of RK-LMS is comparable to RLS algorithm. However, RK-LMS algorithm fails to perform well in convergence mode. For time-variant multipath fading channel prediction, the presented NVFF-RLS algorithm supersedes RLS algorithm in the channel tracking mode under moderately high fade rate conditions. However, under appropriate parameter setting in \(2\times 1\) space–time block-coded OFDM system, NVFF-RLS algorithm bestows enhanced channel tracking performance than RLS algorithm under static as well as dynamic environment, which leads to significant reduction in symbol error rate.     

Nanostructured biosensor for measuring neuropathy target esterase activity

Neuropathy target esterase (NTE) is a membrane protein found in human neurons and other cells, including lymphocytes. Binding of certain organophosphorus (OP) compounds to NTE is believed to cause OP-induced delayed neuropathy (OPIDN), a type of paralysis for which there is no effective treatment. Mutations in NTE have also been linked with serious neurological diseases, such as motor neuron disease. This paper describes development of the first nanostructured biosensor interface containing a catalytically active fragment of NTE known as NEST. The biosensor was fabricated using the layer-by-layer assembly approach, by immobilizing a layer of NEST on top of multilayers consisting of a polyelectrolyte (poly-L-lysine) and an enzyme (tyrosinase). The biosensor has a response time on the order of seconds and gives a concentration-dependent decrease in sensor output in response to a known NEST (and NTE) inhibitor. Potential applications of the biosensor include screening OP compounds for NTE inhibition and investigating the enzymology of wild-type and mutant forms of NTE. Although the development of a NEST biosensor was the primary purpose of this study, we found that the approach developed for NEST could also be extended to measure the activity of other esterases involved in neural processes, such as acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). On the basis of measured sensitivities, phenyl valerate was the preferred substrate for NEST and BChE, whereas phenyl acetate was better for AChE.     

Indigo: user-level support for building distributed shared abstractions

Distributed systems that consist of workstations connected by high performance interconnects offer computational power comparable to moderate size parallel machines. Middleware like distributed shared memory (DSM) or distributed shared objects (DSO) attempts to improve the programmability of such hardware by presenting to application programmers interfaces similar to those offered by shared memory machines. This paper presents the portable Indigo data sharing library which provides a small set of primitives with which arbitrary shared abstractions are easily and efficiently implemented across distributed hardware platforms. Sample shared abstractions implemented with Indigo include DSM as well as fragmented objects, where the object state is split across different machines and where interfragment communications may be customized to application-specific consistency needs. The Indigo library's design and implementation are evaluated on two different target platforms: a workstation cluster and an IBM SP2 machine. As part of this evaluation, a novel DSM system and consistency protocol are implemented and evaluated with several high performance applications. Application performance attained with the DSM system is compared to the performance experienced when utilizing the underlying basic message-passing facilities or when employing Indigo to construct customized fragmented objects implementing the application's shared state. Such experimentation results in insights concerning the efficient implementation of DSM systems (e.g. how to deal with false sharing). It also leads to the conclusion that Indigo provides a sufficiently rich set of abstractions for efficient implementation of the next generation of parallel programming models for high performance machines. © 1998 John Wiley & Sons, Ltd.     

Heat transfer from multiple row arrays of low aspect ratio pin fins

Pin fin arrays are used in many applications to enhance heat transfer. In modern gas turbines, for example, airfoils are designed with sophisticated internal and external cooling techniques. One method for cooling is routing air from the compressor through intricate cooling channels embedded in turbine airfoils. Heat transfer from the blade to the coolant air can be increased by installing arrays of cylindrical pedestals often referred to as pin fins. Pin fin arrays increase heat transfer by increasing the flow turbulence and surface area of the airfoil exposed to the coolant.For the current study, experiments were conducted to determine the effects of pin spacing on heat transfer and pressure loss through pin fin arrays for a range of Reynolds numbers between 5000 and 30,000. Results showed that spanwise pin spacing had a larger effect than streamwise spacing on array pressure loss while streamwise spacing had a larger effect than spanwise spacing on array heat transfer.     

Development and assessment of the advanced graft copolymers obtained from Hibiscus sabdariffa biomass

In this article, the morphological transformation in Hibiscus sabdariffa stem fiber through graft copolymerization with effective ethyl acrylate (EA) and its binary vinyl monomeric mixtures using ceric ammonium nitrate—nitric acid initiator system has been reported. Different reaction parameters such as temperature, time, initiator concentration, monomer concentration, and pH were optimized to obtain the maximum graft yield (117.3%). The optimized reaction parameters were then used to screen the additive effect of EA with n‐butyl acrylate (BA), acrylic acid (AA), and 4‐vinyl pyridine (4‐VP) in binary vinyl monomer mixtures on percentage grafting, properties, and the behavior of the fiber. The graft copolymers were characterized by FTIR, SEM, XRD, TGA, and DTA techniques and evaluated for physico‐chemical changes. With increase in the P_g a significant physico‐chemico‐thermal resistance, miscibility in organic solvents, hydrophobicity were found to increase, whereas crystallinity, crystallinity index, dye‐uptake, and hydrophylicity decreased, however, the cellulose form I remained unchanged. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Organochlorine pesticide residues in poultry feed,chicken muscle and eggs at a poultry farm in Punjab,India

Animals intended for human food may absorb pesticides from residues in their feed, water or during direct/indirect exposure in the course of pest control. The objective of the present investigation was to monitor organochlorine pesticide residues in poultry feed, chicken muscle and eggs at a selected poultry farm. The samples were Soxhlet extracted for 8 h in 200 mL hexane–acetone (1:1, v/v) mixture. The clean‐up of the samples was performed by silica gel column chromatography and analysis was done on a gas chromatograph equipped with an electron capture detector. The mean total hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT), endosulfan sulfate and heptachlor epoxide residues were 0.65, 0.91, 0.42 and 0.02 mg kg^?1, respectively, in feed while respective values for chicken muscle were 0.11, 0.24, 0.10 and 0.07 mg kg^?1. Higher residues were encountered in eggs as compared to muscle. None of the muscle samples exceeded maximum residue limits (MRL) for organochlorine pesticides, while all egg samples had values above the MRL for HCH and heptachlor epoxide and seven egg samples exceeded MRL for DDT residues. The results indicated that poultry feed could be one of the major sources of contamination for chicken and eggs. These residues are present despite complete ban on the use of technical HCH and DDT for agricultural purposes in India. Copyright © 2005 Society of Chemical Industry