Probing the inter-tube transport in aligned and random multiwall carbon nanotubes

The temperature and magnetic field dependence of conductivity has been used to probe the inter-tube transport in multiwall carbon nanotubes (MWNTs). The scanning electron microscopy images show highly aligned and random distribution of MWNTs. The conductivity in aligned carbon nanotube (ACNT) and random carbon nanotube (RCNT) samples at low temperature follows T-1/2 (at T < 8 K) and T-3/4 (at T > 8 K) dependence in accordance with the weak localization and electron-electron (e-e) interaction model. The values of diffusion coefficient in ACNT and RCNT are 0.25 x 10(-2) and 0.71 x 10(-2) cm(2) s(-1), respectively, indicating that larger number of inter-tube junctions in later enhances the bulk transport. The positive magnetoconductance (MC) data in both samples show that the weak localization contribution is dominant. However, the saturation of MC at higher fields and lower temperatures indicate that e-e interaction is quite significant in RCNT. The T-3/4 and T-1/2 dependence of inelastic scattering length (l(in)) in ACNT and RCNT samples show that the inelastic e-e scattering is more important in aligned tubes. (C) 2011 American Institute of Physics. doi:10.1063/1.3552911]

Inter And Intramolecular Interactions Of Porphyrins With 5,5′-Dithiobis(2-Nitrobenzoic Acid)

meso-Tetraphenylporphyrin and its metal [zinc(II) and copper(II)] derivatives form both inter and intramolecular complexes with 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB). The nature of interaction is predominantly charge transfer (CT) in origin, with the porphyrin functioning as a II-donor and DTNB as an acceptor. Among the covalently linked intramolecular systems, the magnitude of CT interaction varies with the position (of one of the aryl groups of the porphyrin) to which DTNB is attached as ortho meta > para. Steady-state and time-resolved fluorescence studies revealed electron transfer to be the dominant pathway for the fluorescence quenching in these systems. Steady-state photolysis experiments probed using EPR and optical absorption studies have shown that electron transfer (from the excited singlet state of the porphyrin) to DTNB results in the formation of thiyl radical and production of free thiolate anion. It is found that the products of electrochemical reduction of covalently linked porphyrin-DTNB systems are different from those observed for the photochemical studies.

Engineered dimer interface mutants of triosephosphate isomerase: the role of inter-subunit interactions in enzyme function and stability

The role of inter-subunit interactions in maintaining optimal catalytic activity in triosephosphate isomerase (TIM) has been probed, using the Plasmodium falciparum enzyme as a model. Examination of subunit interface contacts in the crystal structures suggests that residue 75 (Thr, conserved) and residue 13 (Cys, variable) make the largest number of inter-subunit contacts. The mutants Cys13Asp (C13D) and Cys13Glu (C13E) have been constructed and display significant reduction in catalytic activity when compared with wild-type (WT) enzyme (similar to 7.4-fold decrease in k(cat) for the C13D and similar to 3.3-fold for the C13E mutants). Analytical gel filtration demonstrates that the C13D mutant dissociates at concentrations < 1.25 mu M, whereas the WT and the C13E enzymes retain the dimeric structure. The order of stability of the mutants in the presence of chemical denaturants, like urea and guanidium chloride, is WT > Cys13Glu > Cys13Asp. Irreversible thermal precipitation temperatures follow the same order as well. Modeling studies establish that the Cys13Asp mutation is likely to cause a significantly greater structural perturbation than Cys13Glu. Analysis of sequence and structural data for TIMs from diverse sources suggests that residues 13 and 82 form a pair of proximal sites, in which a limited number of residue pairs may be accommodated.

Symplectic integration of nonlinear Hamiltonian systems

There exist several standard numerical methods for integrating ordinary differential equations. However, if one is interested in integration of Hamiltonian systems, these methods can lead to wrong results. This is due to the fact that these methods do not explicitly preserve the so-called 'symplectic condition' (that needs to be satisfied for Hamiltonian systems) at every integration step. In this paper, we look at various methods for integration that preserve the symplectic condition.

Role of Management Decision Variables in Determining Technology Progress and Technical Efficiency in Indian Electronic Industry

This paper analyses the influence of management on Technical Efficiency Change (TEC) and Technological Progress (TP) in the communication equipment and consumer electronics sub-sectors of Indian hardware electronics industry. Each sub-sector comprises 13 sample firms for two time periods.The primary objective is to determine the relative contribution of TP and TEC to TFP Growth (TFPG) and to establish the influence of firm specific operational management decision variables on these two components. The study finds that both the sub-sectors have strived and achieved steady TP but not TEC in the period of economic liberalisation to cope with the intensifying competition. The management decisions with respect to asset and profit utilization, vertical integration, among others, improved TP and TE in the sub-sectors. However, R&D investments and technology imports proved costly for TFP indicating inadequate efforts and/or poor resource utilisation by the management. Management was found to be complacent in terms of improving or developing their own technology as indicated by their higher dependence on import of raw materials and no influence of R&D on TP.

Recent Advances in Low CTE and High Density System-on-a-Package (SOP) Substrate with Thin Film Component Integration

The Packaging Research Center has been developing next generation system-on-a-package (SOP) technology with digital, RF, optical, and sensor functions integrated in a single package/module. The goal of this effort is to develop a platform substrate technology providing very high wiring density and embedded thin film passive and active components using PWB compatible materials and processes. The latest SOP baseline process test vehicle has been fabricated on novel Si-matched CTE, high modulus C-SiC composite core substrates using 10mum thick BCB dielectric films with loss tangent of 0.0008 and dielectric constant of 2.65. A semi-additive plating process has been developed for multilayer microvia build-up using BCB without the use of any vacuum deposition or polishing/CMP processes. PWB and package substrate compatible processes such as plasma surface treatment/desmear and electroless/electrolytic pulse reverse plating was used. The smallest line width and space demonstrated in this paper is 6mum with microvia diameters in the 15-30mum range. This build-up process has also been developed on medium CTE organic laminates including MCL-E-679F from Hitachi Chemical and PTFE laminates with Cu-Invar-Cu core. Embedded decoupling capacitors with capacitance density of >500nF/cm2 have been integrated into the build-up layers using sol-gel synthesized BaTiO3 thin films (200-300nm film thickness) deposited on copper foils and integrated using vacuum lamination and subtractive etch processes. Thin metal alloy resistor films have been integrated into the SOP substrate using two methods: (a) NiCrAlSi thin films (25ohms per square) deposited on copper foils (Gould Electronics) laminated on the build-up layers and two step etch process for resistor definition, and (b) electroless plated Ni-W-P thin films (70 ohms to few Kohms per square) on the BCB dielectric by plasma surface treatment and activation. The electrical design and build-up layer structure along- - with key materials and processes used in the fabrication of the SOP4 test vehicle were presented in this paper. Initial results from the high density wiring and embedded thin film components were also presented. The focus of this paper is on integration of materials, processes and structures in a single package substrate for system-on-a-package (SOP) implementation

Inter and intra crystalline ion exchange equilibria in the system Fe Cr Al O

The tie lines delineating ion-exchange equilibria between FeCr2O4FeAl2O4 spinel solid solution and Cr2O3Al2O3 solid solution with corundum structure have been determined at 1373 K by electron microprobe and EDAX point count analysis of oxide phases equilibrated with metallic iron. Activities in the spinel solid solution are derived from the tie lines and the thermodynamic data on Cr2O3Al2O3 solid solution available in the literature. The oxygen potentials corresponding to the tie-line composition of oxide phases in equilibrium with metallic iron were measured using solid oxide galvanic cells with CaOZrO2 and Y2O3ThO2 electrolytes. These electrochemical measurements also yield activities in the spinel solid solution, in good agreement with those obtained from tie lines. The activity-composition relationship in the spinel solid solution is analysed in terms of the intra-crystalline ion exchange between the tetrahedral and octahedral sites of the spinel structures. The ion exchange is governed by site-preference energies of the cations and the entropy of cations mixing on each site.

Thermodynamic activities in the Pb(Zr1−XTiX)O3 solid solution at 1373K

Although Pb(Zr1−XTiX)O3 solid solution is the cornerstone of the piezoelectric ceramics, there is no information in the literature on thermodynamic activities of the component phases in the solid solution. Using inter-crystalline ion exchange equilibria between Pb(Zr1−XTiX)O3 solid solution with cubic perovskite structure and (Zr1−YTiY)O2 solid solutions with monoclinic and tetragonal structures, activities of PbTiO3 and PbZrO3 in the perovskite solid solution have been derived at 1373 K using the modified Gibbs–Duhem integration technique of Jacob and Jeffes. Tie-lines from the cubic solid solution are skewed towards the ZrO2 corner. Activities in the zirconia-rich (Zr1−YTiY)O2 solid solutions are taken from a recent emf study. The results for the perovskite solid solution at 1373 K can be represented by a sub-regular solution model:View the MathML sourcewhere ΔGE,M is the excess Gibbs energy of mixing of the cubic solid solution and Xi represents the mole fraction of component i. There is a significant positive deviation from ideality for PbTiO3-rich compositions and mild negative deviation near the PbZrO3 corner. The cubic solid solution is intrinsically stable against composition fluctuations at temperatures down to 840 K. The results contrast sharply with the recent calorimetric data on enthalpy of mixing which signal instability of the cubic perovskite solid solution.

A Review of Photo-Induced Inter-Diffusion in Nano-Layered Chalcogenide Films

Abstract | A growing interest in the research of chalcogenide glasses can be currently witnessed, which to a large extent is caused by newly opened fields of applications for these materials. Applications in the field of micro- and opto-electronics, xerography and lithography, acousto-optic and memory switching devices and detectors for medical imaging seem to be most remarkable. Accordingly, photo induced phenomena in chalcogenide glasses are attracting much interest. These phenomena can be found both in uniform thin films as well as multilayered films. Among amorphous multilayers, chalcogenide multilayers are attractive because of the potential it has for tailoring the optical properties. I will be presenting some basic idea of photoinduced effects followed by the diffusion mechanisms of Se, Sb and Bi in to As2S3 films.

Highly fluorescent GFPm2+-based genome integration-proficient promoter probe vector to study Mycobacterium tuberculosis promoters in infected macrophages

Study of activity of cloned promoters in slow-growing Mycobacterium tuberculosis during long-term growth conditions in vitro or inside macrophages, requires a genome-integration proficient promoter probe vector, which can be stably maintained even without antibiotics, carrying a substrate-independent, easily scorable and highly sensitive reporter gene. In order to meet this requirement, we constructed pAKMN2, which contains mycobacterial codon-optimized gfpm2+ gene, coding for GFPm2+ of highest fluorescence reported till date, mycobacteriophage L5 attP-int sequence for genome integration, and a multiple cloning site. pAKMN2 showed stable integration and expression of GFPm2+ from M. tuberculosis and M. smegmatis genome. Expression of GFPm2+, driven by the cloned minimal promoters of M. tuberculosis cell division gene, ftsZ (MtftsZ), could be detected in the M. tuberculosis/pAKMN2-promoter integrants, growing at exponential phase in defined medium in vitro and inside macrophages. Stable expression from genome-integrated format even without antibiotic, and high sensitivity of detection by flow cytometry and fluorescence imaging, in spite of single copy integration, make pAKMN2 useful for the study of cloned promoters of any mycobacterial species under long-term in vitro growth or stress conditions, or inside macrophages.

Electrochemical Integration of Graphene with Light-Absorbing Copper-Based Thin Films

We present an electrochemical route for the integration of graphene with light-sensitive copper-based alloys used in optoelectronic applications. Graphene grown using chemical vapor deposition (CVD) transferred to glass is found to be a robust substrate on which photoconductive CuxS films of 1-2 mu m thickness can be deposited. The effect of growth parameters on the morphology and photoconductivity of CuxS films is presented. Current-voltage (I-V) characterization and photoconductivity decay experiments are performed with graphene as one contact and silver epoxy as the other.

Fuzzy logic based TCSC supplementary controller for damping of inter area oscillations in power system

This paper describes an application of a FACTS supplementary controller for damping of inter area oscillations in power systems. A fuzzy logic controller is designed to regulate a thyristor controlled series capacitor (TCSC) in a multimachine environment to produce additional damping in the system. Simultaneous application of the excitation controller and proposed controller is also investigated. Simulation studies have been done with different types of disturbances and the results are shown to be consistent with the expected performance of the supplementary controller.