Cell alignment using patterned biocompatible gold nanoparticle templates

Biocompatible structures are produced for cellular patterning. The biocompatible surfaces are generated to provide protein nonfouling patterns, offering direct communication to the cells for controlling cell adhesion and proliferation. These biofunctional surfaces provide a platform for aligning the cells in the direction of patterns, indicating potential application in the field of tissue engineering.     

Molecular beam epitaxy grown long wavelength infrared HgCdTe on Si detector performance

The use of silicon as a substrate alternative to bulk CdZnTe for epitaxial growth of HgCdTe for infrared (IR) detector applications is attractive because of potential cost savings as a result of the large available sizes and the relatively low cost of silicon substrates. However, the potential benefits of silicon as a substrate have been difficult to realize because of the technical challenges of growing low defect density HgCdTe on silicon where the lattice mismatch is ∼19%. This is especially true for LWIR HgCdTe detectors where the performance can be limited by the high (∼5×10⁶ cm⁻²) dislocation density typically found in HgCdTe grown on silicon. We have fabricated a series of long wavelength infrared (LWIR) HgCdTe diodes and several LWIR focal plane arrays (FPAs) with HgCdTe grown on silicon substrates using MBE grown CdTe and CdSeTe buffer layers. The detector arrays were fabricated using Rockwell Scientific’s planar diode architecture. The diode and FPA and results at 78 K will be discussed in terms of the high dislocation density (∼5×10⁶ cm²) typically measured when HgCdTe is grown on silicon substrates.     

High resolutionV-I characteristics measurements on highT c superconductors

V-I characteristics of sintered superconducting pellets of YBa₂Cu₃O_7−δ was measured with a resolution one order of magnitude better than the usual dc techniques employing nanovoltmeters. For this purpose software-based lock-in-amplifier technique was developed and used. A square-wave excitation current was used. The voltage signal was digitized into a time series and Fourier-analysed on a computer in this technique. Our results show a very small frequency-dependent resistance in some samples which are nominally superconducting. These results help in checking the material quality and defining the critical current densities better.     

Novel high performance fibres

The need for high performance materials for aerospace and other structural engineering applications has led to the development of carbon fibres. At IIT Delhi, an attempt is being made to develop acrylic precursor fibres for manufacturing carbon fibres indigenously. The present study deals with the structural regulation of acrylic precursors during thermo-oxidative stabilization and subsequent carbonization. A new microporous acrylic fibre-acrysorb has also been developed which has high water imbibition and moisture sorption properties. Production of X-ray opaque and antistatic polyester fibres has also been high-lighted.     

Nucleation and Location of Kirkendall Voids at the Tin-Based Solder/Copper Joint: A Review

Void nucleation is a critical issue in wetting because it negatively impacts the solder joint and diminishes its electrical and mechanical properties. Generally, the Kirkendall effect (unbalanced diffusion) and Kirkendall voids (KVs) are developed due to dissimilar diffusivities of species (Cu and Sn) in a diffusion process. However, voids are also nucleated in the supersaturating condition, creating an additional position at or inside the “Kirkendall voids” interface. Various factors (surface modification, reinforcement of fourth elements, substrate type, and impurities) and the environment also support the nucleation of voids. Many researchers have discussed that KVs are nucleated into to intermetallic compounds layers. Reviewing the significant parameters for developing the KV in solid–liquid and solid–solid conditions is essential. Hence, in this review, the potential process of development of the KVs, concepts of thermodynamics, chemical reactions, and growth kinetics are developed. The position and reduction of KVs nucleation are also explained in this paper.     

An automatic 3D mesh generation method for domains with multiple materials

This paper describes an automatic and efficient approach to construct unstructured tetrahedral and hexahedral meshes for a composite domain made up of heterogeneous materials. The boundaries of these material regions form non-manifold surfaces. In earlier papers, we developed an octree-based isocontouring method to construct unstructured 3D meshes for a single material (homogeneous) domain with manifold boundary. In this paper, we introduce the notion of a material change edge and use it to identify the interface between two or several different materials. A novel method to calculate the minimizer point for a cell shared by more than two materials is provided, which forms a non-manifold node on the boundary. We then mesh all the material regions simultaneously and automatically while conforming to their boundaries directly from volumetric data. Both material change edges and interior edges are analyzed to construct tetrahedral meshes, and interior grid points are analyzed for proper hexahedral mesh construction. Finally, edge-contraction and smoothing methods are used to improve the quality of tetrahedral meshes, and a combination of pillowing, geometric flow and optimization techniques is used for hexahedral mesh quality improvement. The shrink set of pillowing schemes is defined automatically as the boundary of each material region. Several application results of our multi-material mesh generation method are also provided.     

Improving scheduling of tasks in a heterogeneous environment

Optimal scheduling of parallel tasks with some precedence relationship, onto a parallel machine is known to be NP-complete. The complexity of the problem increases when task scheduling is to be done in a heterogeneous environment, where the processors in the network may not be identical and take different amounts of time to execute the same task. We introduce a task duplication-based scheduling algorithm for network of heterogeneous systems (TANH), with complexity O(V/sup 2/), which provides optimal results for applications represented by directed acyclic graphs (DAGs), provided a simple set of conditions on task computation and network communication time could be satisfied. The performance of the algorithm is illustrated by comparing the scheduling time with an existing "best imaginary level scheduling (BIL)" scheme for heterogeneous systems. The scalability for a higher or lower number of processors, as per their availability is also discussed. We have shown to provide substantial improvement over existing work on the task duplication-based scheduling algorithm (TDS).     

Effect of the nature and mole fraction of acidic comonomer on the stabilization of polyacrylonitrile

Differential scanning calorimetry (DSC) and thermogravimetric analysis measurements were used to study the influence of the acidic comonomers acrylic acid, methacrylic acid, and itaconic acid on the exothermic reactions occurring during the heat treatment of acrylonitrile copolymers under air atmosphere. The presence of these reactions was noticed in the DSC exotherms of the copolymers, which appear as doublets. These doublets were resolved into their constituent peaks, arising due to the occurrence of oxidative and cyclization reactions, and the area under the resolved peaks was considered as the extent of the reaction. The comonomers under study were found to enhance the secondary oxidation reactions and retard the extent of cyclization reactions. The degree of cyclization decreases abruptly with the increase in the comonomer content beyond ⋍ 2 mol %. © 1996 John Wiley & Sons, Inc.     

Melting behavior of acrylonitrile polymers

Melting of acrylonitrile polymers (which have a tendency to degrade before melting) was detected during their heat treatments at high heating rates (i.e., 80°C min⁻¹ or above). The probable reason for their melting at such higher heating rates is discussed. The melting behavior of acrylonitrile polymers was also studied by sealing the polymer with water in a specially designed pressure pan and then heating it in the differential scanning calorimetry cell. The phenomenon of melting is found to be influenced by the rate and environment of heating, molecular weight, and nature of the comonomer. Water suppresses the melting point (T_m) of the polymer due to its plasticization effect; however, it causes the hydrolysis of some CN groups during this process of melting. The nature of melting endotherm has been correlated with the structure of the polymer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2703–2709, 1998