Optical properties of nano-silicon

We investigated the optical properties of silicon clusters and Si nanocrystallites using photolumine-scence (PL) and Raman scattering technique. Broad luminescence band in the red region was observed from Si-doped SiO₂ thin films deposited by co-sputtering of Si and SiO₂ onp-type Si (100) substrates, annealed in Ar and O₂ atmosphere. Nanocrystalline Si particles fabricated by pulsed plasma processing technique showed infrared luminescence from as grown film at room temperature. Raman spectra from these films consisted of broad band superimposed on a sharp line near 516 cm⁻¹ whose intensity, frequency, and width depend on the particle sizes arising from the phonon confinement in the nanocrystalline silicon. We also performed PL, Raman and resonantly excited PL measurements on porous silicon film to compare the optical properties of Si nanostructures grown by different techniques. An extensive computer simulation using empirical pseudo-potential method was carried out for 5–18 atoms Si clusters and the calculated gap energies were close to our PL data. Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore.     

Energy efficient cluster head formation in wireless sensor network

Microsystem Technologies - In clarification of wireless sensor network (WSN) clustering process at household and overseas, an energy efficient cluster head formation technique for WSN are set forth...     

Carboxymethylation of cellulosic material (average degree of polymerization 2600) isolated from cotton (Gossypium) linters with respect to degree of substitution and rheological behavior

Carboxymethylation of cellulosic material (average degree of polymerization 2600) containing 76.5% cellulose and 23.6% xylose isolated from cotton (Gossypium) linters was studied under varying reaction conditions with respect to maximum degree of substitution (DS). The influence of reaction conditions on the apparent viscosity of the prepared derivatives was also studied. The conditions optimized were sodium hydroxide concentration 3.75M, monochloroacetic acid concentration 2.05 mol/AGU, carboxymethylation time 3.5 h, and temperature 55°C, to yield carboxymethyl cellulose of DS 0.77. Rheological studies of 1 and 2% solutions of the optimized product revealed their non‐Newtonian pseudoplastic behavior. Repeating units of the optimized product were also determined by HPLC after complete depolymerization of the polymer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1477–1482, 2005     

Calcium ion-sensor based on polyindole-camphorsulfonic acid composite

We hereby report a new conducting polymer-based calcium ion exchanger, namely polyindole-camphorsulfonic acid (PIn-CSA) composite, and its application in the development of calcium ion-selective electrode. The processable PIn-CSA composite is developed by homogenizing equimolar ratio of chemically synthesized PIn and CSA in tetrahydrofuran. The homogenized PIn-CSA composite is cast over the Pt disc electrode under ambient conditions. The ion-sensor exhibits near Nernstian response for Ca²⁺ over a concentration range of 2 × 10⁻⁵ to 1 × 10⁻² M with a response time of 8 s. The sensor can be used for a period of over 3 months without any major drift in its baseline potential. The useful pH range of the ion-sensor was found out to be 4.0−8.0. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Finite element crash simulations of the human body: Passive and active muscle modelling

Conventional dummy based testing procedures suffer from known limitations. This report addresses issues in finite element human body models in evaluating pedestrian and occupant crash safety measures. A review of material properties of soft tissues and characterization methods show a scarcity of material properties for characterizing soft tissues in dynamic loading. Experiments imparting impacts to tissues and subsequent inverse finite element mapping to extract material properties are described. The effect of muscle activation due to voluntary and non-voluntary reflexes on injuries has been investigated through finite element modelling.     

Spectroscopic investigation of end products obtained by ammonolysis of poly (ethylene terephthalate) waste in the presence of zinc acetate as a catalyst

The effect of catalyst on the degradation of poly (ethylene terephthalate) (PET) waste by ammonolysis was investigated at ambient temperature and atmospheric pressure. The products obtained by ammonolysis in the presence and absence of catalyst were separated and characterized by spectroscopic techniques namely FTIR and Mass Spectrometry (MS) together with Scanning Electron Microscopy (SEM) and Differential Thermal Analysis (DTA). The end products were characterized as 1, 4-benzene dicarboxamide in both the cases and were found to be same throughout the course of reaction. The absence of peak for PET and appearance of peak for 1, 4-benzene dicarboxamide in the FTIR spectra of end product along with MS, SEM and thermal analysis confirms the completion of the reaction. The results show that the catalyst cut shorts the time of completion of reaction from 45 to 15 days only.     

Effects of anisotropy and annealing on microhardness of In x Bi2−x Te3 (x=0·1 to 0·5) single crystals

The crystals of In _x Bi_2−x Te₃ (x=0·1 to 0·5) have been grown by zone-melting method. In order to study anisotropy exhibited by the (0001) plane of the crystals, the directional hardness was determined by producing indentations at various azimuthal orientations of the indentor with respect to the surface over a range 0–180°. The crystal was rotated about the indentor axis in steps of 15° while keeping applied load and loading time constant at 50 g and 20 sec, respectively. For annealing study, the sample was kept at a temperature of 375°C. It was observed that softening of crystal takes place and the hardness decreases to a considerable extent.     

Diversity sustains an evolving network

We study an evolutionary model of a complex system that evolves under catalytic dynamics and Darwinian selection and exhibits spontaneous growth, stasis and then a collapse of its structure. We find that the typical lifetime of the system increases sharply with the diversity of its components or species. We also find that the prime reason for crashes is a naturally occurring internal fragility of the system. This fragility is captured in the network organizational character and is related to a reduced multiplicity of pathways or feedback loops between its components. These results apply to several generalizations of the model as well. This work suggests new parameters for understanding the robustness of evolving molecular networks, ecosystems, societies and markets.