Electric Field Directed Growth of Molecular Wires of Charge Transfer Molecules on Prefabricated Metal Electrodes

Molecular wires of charge transfer molecules were formed by co-evaporating the 7 7 8 8-Tetracyanoquinodimethane [TCNQ] (acceptor) and Tetrathiafulvalene [TTF] (donor) molecules across prefabricated metal electrodes. Molecular wires of TTF TCNQ were also formed by evaporating single complex of TTF:TCNQ across prefabricated metal electrodes The prefabricated metal electrodes were made using electron beam lithography on SiO2 and glass cover slip substrates. Even though TTF: TCNQ wires grown from both co-evaporation and evaporation techniques show semiconductor like behavior in temperature dependence of resistance they show different activation energies due the difference in stoichiometry of TTF and TCNQ.

Potential and Electric Field Profiles for Transmission line Insulators

Transmission of bulk power at high voltages over very long distances has become very imperative. At present, throughout the globe, this task has been mostly performed by overhead transmission lines. The dual task of mechanically supporting and electrically isolating the live phase conductors from the support tower is performed by string insulators. Whether in clean condition or under polluted conditions, the electrical stress distribution along the insulators governs the possible flashover, which is quite detrimental to the system. However, a reliable data on stress distribution in commonly employed string insulators are rather scarce. Considering this, the present work has made an attempt to study accurately, the field distribution in 220 kV strings for six different types of porcelain/ceramic insulators (Normal and Antifog discs) used for high voltage transmission. The surface charge simulation method is employed for the required field computation. Voltage and electric stress distribution is deduced and compared across different types of discs. A comparison on normalised surface resistance, which is an indicator for the stress concentration under polluted condition, is also attempted.

The selection of a sugar for transport and storage of carbon in plants

Sugars perform two vital functions in plants: as compatible solutes protecting the cell against osmotic stress and as mobile source of immediate and long-term energy requirement for growth and development. The two sugars that occur commonly in nature are sucrose and trehalose. Sucrose comprises one glucose and one fructose molecule; trehalose comprises two glucose molecules. Trehalose occurs in significant amounts in insects and fungi which greatly outnumber the plants. Surprisingly, in plants trehalose has been found in barely detectable amounts, if at all, raising the question `why did nature select sucrose instead of trehalose as the mobile energy source and as storage sugar for the plants'? Modelling revealed that when attached to the ribbon-shaped beta-1,4 glucan a trehalose molecule is shaped like a hook. This suggests that the beta-1,4 glucan chains with attached trehalose will fail to align to form inter-chain hydrogen bonds and coalesce into a cellulose microfibril, as a result of which in trehalose-accumulating plant cells, the cell wall will tend to become leaky. Thus in plants an evolutionary selection was made in favour of sucrose as the mobile energy source. Genetic engineering of plant cells for combating abiotic stresses through microbial trehalose-producing genes is fraught with risk of damage to plant cell walls.

Fermion Electric Dipole Moments in R-parity violating Supersymmetry

In this talk I discuss some aspects of the study of electric dipole moments (EDMs) of the fermions, in the context of R-parity violating (\rpv) Supersymmetry (SUSY). I will start with a brief general discussion of how dipole moments, in general, serve as a probe of physics beyond the Standard Model (SM) and an even briefer summary of \rpv SUSY. I will follow by discussing a general method of analysis for obtaining the leading fermion mass dependence of the dipole moments and present its application to \rpv SUSY case. Then I will summarise the constraints that the analysis of $e,n$ and $Hg$ EDMs provide for the case of trilinear \rpv SUSY couplings and make a few comments on the case of bilinear \rpv, where the general method of analysis proposed by us does not work.

Transient electric field distribution within the working volume of an NEMP simulator

Nuclear electro-magnetic pulse (NEMP) simulators which are used in the simulation of transient electromagnetic fields due to a high altitude nuclear detonation are generally excited with a double exponential high voltage pulse. This results in a current distribution on the wires of the simulator and hence a transient electric field in the working volume of the simulator where the test object is kept. It is found that for the simulator under study, the current distribution is non-uniform and so is the field distribution along the width of the simulator in the working volume. To make the current distribution uniform, several methods have been suggested and the results of these methods are analyzed and suitable conclusions are arrived at from those results.

Advances in Light-Emitting Doped Semiconductor Nanocrystals

Insertion of just a few impurity atoms in a host semiconductor nanocrystal can drastically alter its phase, shape, and physical properties. Such doped nanomaterials now constitute an important class of optical materials that can provide efficient, stable, and tunable dopant emission in visible and NIR spectral windows. Selecting proper dopants and inserting them in appropriate hosts can generate many new series of such doped nanocrystals with several unique and attractive properties in order to meet current challenges in the versatile field of luminescent materials. However, the synthesis of such doped nanomaterials with a specific dopant in a predetermined host at a desired site leading to targeted optical properties requires fundamental understanding of both the doping process as well as the resulting photophysical properties. Summarizing up to date literature reports, in this Perspective we discuss important advances in synthesis methods and in-depth understanding of the optical properties, with an emphasis on the most widely investigated Mn-doped semiconductor nanocrystals.

Ultrasound-modulated optical tomography: recovery of amplitude of vibration in the insonified region from boundary measurement of light correlation

We address a certain inverse problem in ultrasound-modulated optical tomography: the recovery of the amplitude of vibration of scatterers [p(r)] in the ultrasound focal volume in a diffusive object from boundary measurement of the modulation depth (M) of the amplitude autocorrelation of light [phi(r, tau)] traversing through it. Since M is dependent on the stiffness of the material, this is the precursor to elasticity imaging. The propagation of phi(r, tau) is described by a diffusion equation from which we have derived a nonlinear perturbation equation connecting p(r) and refractive index modulation [Delta n(r)] in the region of interest to M measured on the boundary. The nonlinear perturbation equation and its approximate linear counterpart are solved for the recovery of p(r). The numerical results reveal regions of different stiffness, proving that the present method recovers p(r) with reasonable quantitative accuracy and spatial resolution. (C) 2011 Optical Society of America

Effect of substrate bias voltage on the structure, electric and dielectric properties of TiO(2) thin films by DC magnetron sputtering

Titanium dioxide (TiO(2)) films have been deposited on glass and p-silicon (1 0 0) substrates by DC magnetron sputtering technique to investigate their structural, electrical and optical properties. The surface composition of the TiO(2) films has been analyzed by X-ray photoelectron spectroscopy. The TiO(2) films formed on unbiased substrates were amorphous. Application of negative bias voltage to the substrate transformed the amorphous TiO(2) into polycrystalline as confirmed by Raman spectroscopic studies. Thin film capacitors with configuration of Al/TiO(2)/p-Si have been fabricated. The leakage current density of unbiased films was 1 x10(-6) A/cm(2) at a gate bias voltage of 1.5 V and it was decreased to 1.41 x 10(-7) A/cm(2) with the increase of substrate bias voltage to -150 V owing to the increase in thickness of interfacial layer of SiO(2). Dielectric properties and AC electrical conductivity of the films were studied at various frequencies for unbiased and biased at -150 V. The capacitance at 1 MHz for unbiased films was 2.42 x 10(-10) F and it increased to 5.8 x 10(-10) F in the films formed at substrate bias voltage of -150 V. Dielectric constant of TiO(2) films were calculated from capacitance-voltage measurements at 1 MHz frequency. The dielectric constant of unbiased films was 6.2 while those formed at -150 V it increased to 19. The optical band gap of the films decreased from 3.50 to 3.42 eV with the increase of substrate bias voltage from 0 to -150 V. (C) 2011 Elsevier B. V. All rights reserved.

Structure of the Pyridine-Chloranil Complex in Solution: A Surprise from Depolarized Hyper-Rayleigh Scattering Measurements

In this article, we report the structure of a 1:1 charge transfer complex between pyridine (PYR) and chloranil (CHL) in solution (CHCl(3)) from the measurement of hyperpolarizability (beta(HRS)) and linear and circular depolarization ratios, D and D', respectively, by the hyper-Rayleigh scattering technique and state-of-the-art quantum chemical calculations. Using linearly (electric field vector along X) and circularly polarized incident light, respectively, we have measured two macroscopic depolarization ratios D = I(X,X)(2 omega)/I(X,Z)(2 omega) and D' = I(X,C)(2 omega)/I(Z,C)(2 omega) in the laboratory fixed XYZ frame by detecting the second harmonic (SH) scattered light in a polarization resolved fashion. The stabilization energy and the optical gap calculated through the MP2/cc-pVDZ method using Gaussian09 were not significantly different to distinguish between the cofacial and T-shape structures. Only when the experimentally obtained beta(HRS) and the depolarization ratios, D and D', were matched with the theoretically computed values from single and double configuration interaction (SDCI) calculations performed using the ZINDO-SCRF technique, we concluded that the room temperature equilibrium structure of the complex is cofacial. This is in sharp contrast to an earlier theoretical prediction of the T-shape structure of the complex.

Analysis of light‐induced processes in bacteriorhodopsin and its application for spatial light modulation

A simplified energy‐level scheme is proposed for the photochemical cycle of the bacteriorhodopsin molecule. Rate equations are solved for the detailed light‐induced processes based on this model and the intensity‐induced population densities in various states of the molecule at steady state are computed which are used to obtain an analytic expression for the absorption coefficient of the modulation beam. Modulation of the probe laser‐beam transmission by the modulation‐laser‐beam intensity‐induced population changes is analyzed. It is predicted that for a probe beam at 412 nm up to 82% modulation can be achieved using a laser beam intensity of 3.2 W/cm2 at 570 nm. For temperatures ∼77 K, the transmission at 610 nm can be switched from zero to 81% for modulating laser intensity of 11 W/cm2. Construction of a spatial light modulator based on bacteriorhodopsin molecules is proposed and some of its features are discussed.

Analysis of integrated optofluidic lab-on-a-chip fluorescence biosensor based on transmittance of light through a fluidic gap

Sensitivity analysis is an important aspect to be looked into while designing lab-on-a-chip systems. In this paper we will be showing with appropriate design that the best sensitivity of the fluorescence biosensor is achieved for an optimal width of fluidic gap, corresponding to a particular mode spot size. We will be also showing that the sensitivity of the biosensor is affected by efficiency of light coupling, which is influenced by changes in the width of fluidic gap, refractive index of the fluid and higher order modes.

Diffuse optical tomographic imager using a single light source

Near-infrared diffuse optical tomography (DOT) technique has the capability of providing good quantitative reconstruction of tissue absorption and scattering properties with additional inputs such as input and output modulation depths and correction for the photon leakage. We have calculated the two-dimensional (2D) input modulation depth from three-dimensional (3D) diffusion to model the 2D diffusion of photons. The photon leakage when light traverses from phantom to the fiber tip is estimated using a solid angle model. The experiments are carried for single (5 and 6 mm) as well as multiple inhomogeneities (6 and 8 mm) with higher absorption coefficient in a homogeneous phantom. Diffusion equation for photon transport is solved using finite element method and Jacobian is modeled for reconstructing the optical parameters. We study the development and performance of DOT system using modulated single light source and multiple detectors. The dual source methods are reported to have better reconstruction capabilities to resolve and localize single as well as multiple inhomogeneities because of its superior noise rejection capability. However, an experimental setup with dual sources is much more difficult to implement because of adjustment of two out of phase identical light probes symmetrically on either side of the detector during scanning time. Our work shows that with a relatively simpler system with a single source, the results are better in terms of resolution and localization. The experiments are carried out with 5 and 6 mm inhomogeneities separately and 6 and 8 mm inhomogeneities both together with absorption coefficient almost three times as that of the background. The results show that our experimental single source system with additional inputs such as 2D input/output modulation depth and air fiber interface correction is capable of detecting 5 and 6 mm inhomogeneities separately and can identify the size difference of multiple inhomogeneities such as 6 and 8 mm. The localization error is zero. The recovered absorption coefficient is 93% of inhomogeneity that we have embedded in experimental phantom.

Prebreakdown Current and Sparking Potential in a Nonuniform Electric Field with a Crossed Magnetic Field

Prebreakdown currents in a coaxial cylindrical geometry in nitrogen have been measured with and without a crossed magnetic field. The range of parameters used in the investigation are 2.6 ÿ p ÿ 14.5 torr, 50 ÿ (E/p) ÿ 420 V cm-1 torr-1, and 43.0 ÿ H/p ÿ 1185 Oe torr-1 (p is the pressure, E is the electric field, and H is the magnetic field). The initial photoelectric current is obtained by allowing photons produced in an auxiliary glow discharge to strike the cathode. Ions and electrons produced in the auxiliary discharge are prevented from reaching the main gap by suitable shielding. By modifying the Rice equation for back diffusion, the measured ionization current multiplication without a crossed magnetic field is compared with the multiplication predicted by the Townsend growth equation for nonuniform electric fields. It is observed that over the range of 50 Ã�¿ (E/P)max Ã�¿ 250 [(E/P)max is the value of E/p at the central electrode of the coaxial system] measured and calculated multiplication of current agree with each other. With a crossed magnetic field the prebreakdown currents have been measured and compared with the theoretically calculated currents using the equivalent pressure concept. Agreement between the calculated and measured currents is not satisfactory, and this has been attributed more to the uncertainty in the collision frequency data available than nonuniformity of the electric field. Sparking potentials have been measured with and without a crossed magnetic field.