Proportional Weirs as Velocity Controlling Devices

Of the many factors that govern the settling phenomenon, the flow velocity in the settling tanks can be controlled favorably by fixing suitably designed weirs at the outlets of the tanks. The velocity at the bottom should not dislodge the particles that have already settled. These requirements might be met with by velocities which are controlled to be constant with respect to the depth of flow, or velocities which reduce linearly with increasing depth or velocities that vary inversely with the depth. To achieve these types of velocity control, new proportional weirs have been designed. Very near to the outlet of the tank, over a small length, the flow was found to be turbulent and noncompliant with the expected type of velocity control. This small length of the disturbance may be provided over and above the theoretical settling length of the tank, for efficient sedimentation.

Field-Effect and Frequency Dependent Transport in Semiconductor-Enriched Single-Wall Carbon Nanotube Network Device

The electrical and optical response of a field-effect device comprising a network of semiconductor-enriched single-wall carbon nanotubes, gated with sodium chloride solution is investigated. Field-effect is demonstrated in a device that uses facile fabrication techniques along with a small-ion as the gate electrolyte-and this is accomplished as a result of the semiconductor enhancement of the tubes. The optical transparency and electrical resistance of the device are modulated with gate voltage. A time-response study of the modulation of optical transparency and electrical resistance upon application of gate voltage suggests the percolative charge transport in the network. Also the ac response in the network is investigated as a function of frequency and temperature down to 5 K. An empirical relation between onset frequency and temperature is determined.

Exciton Plasmon Coupling in Hybrid Semiconductor - Metal Nanoparticle Monolayers

Hybrid semiconductor-metal nanoparticles monolayer of Cadmium Sclenide and gold nanoparticles has been prepared, using Langmuir – Blodgett technique. The near field photoluminescence spectra from such monolayer films, shows red shift similar to 75 meV with respect to CdSe QDs monolayer film and splitting similar to 57 meV. The composite spectra are much broader similar to 330 meV compared to the corresponding emission spectra of CdSe monolayer similar to 165 meV. The possible explanation for the observed features are provided in terms of exciton - Plasmon interaction.

RF Sputtered Er2O3 Thin Films as High-k Gate Dielectrics for Germanium MOS Devices

We report the material and electrical properties of Erbium Oxide (Er2O3) thin films grown on n-Ge (100) by RF sputtering. The properties of the films are correlated with the processing conditions. The structural characterization reveals that the films annealed at 550 degrees C, has densified as compared to the as-grown ones. Fixed oxide charges and interface charges, both of the order of 10(13)/cm(2) is observed.

Integrated CMOS Gas Sensors

We present a low power gas sensor system on CMOS platform consisting of micromachined polysilicon microheater, temperature controller circuit, resistance readout circuit and SnO2 transducer film. The design criteria for different building blocks of the system is elaborated The microheaters are optimized for temperature uniformity as well as static and dynamic response. The electrical equivalent model for the microheater is derived by extracting thermal and mechanical poles through extensive laser doppler vibrometer measurements. The temperature controller and readout circuit are realized on 130nm CMOS technology The temperature controller re-uses the heater as a temperature sensor and controls the duty cycle of the waveform driving the gate of the power MOSFET which supplies heater current. The readout circuit, with subthreshold operation of the MOSFETs, is based oil resistance to time period conversion followed by frequency to digital converter Subthreshold operatin of MOSFETs coupled with sub-ranging technique, achieves ultra low power consumption with more than five orders of magnitude dynamic range RF sputtered SnO2 film is optimized for its microstructure to achive high sensitivity to sense LPG gas.

EIT as a tool to observe dual wavelength operation of a semiconductor laser

We propose a simplified technique for dual wavelength operation of an extended cavity semiconductor laser, and its characterization using electromagnetically induced transparency (EIT). In this laser cavity scheme light beam is made converging before it incidences on the cavity grating. The converging angle of the beam creates two longitudinal oscillating modes of resonating cavity. Frequency separation between the longitudinal modes are measured with the help of beat frequency generation in a photodiode and creating pair of EIT spectra in Rb vapor. The pair of EIT dips that are generated due to dual wavelength of this laser (that is used as control laser) can be used to estimate frequency difference between the generated wavelengths. Width of EIT spectra can be used to estimate line width of individual wavelength components.

Synthesis of liquid crystalline benzothiazole base derivatives: A study of their optical and electrical properties

Two new donor-acceptor type liquid crystalline semiconductors based on benzothiazole have been synthesized. Their structural, photophysical and electronic properties were investigated using X-ray diffraction, atomic force microscopy, cyclic voltammetry, UV-Vis, photoluminescence, and Raman spectroscopy. The liquid crystalline behaviour of the molecules was thoroughly examined by differential scanning calorimetry (DSC) and optical polarizing microscope. The DSC and thermogravimetric analysis (TGA) show that these materials posses excellent thermal stability and have decomposition temperatures in excess of 300 degrees C. Beyond 160 degrees C both molecules show a smectic A liquid crystalline phase that exists till about 240 degrees C. Field-effect transistors were fabricated by vacuum evaporating the semiconductor layer using standard bottom gate/top contact geometry. The devices exhibit p-channel behaviour with hole mobilities of 10(-2) cm(2)/Vs. (C) 2009 Elsevier B.V. All rights reserved.

Dynamics and control of buckling type devices using SMA wire integrated beam

An analysis and design study using Shape Memory Alloy (SMA) wire integrated beam and its buckling shape control are reported. The dynamical system performance is analyzed with a mathematical set-up involving nonlocal and rate sensitive kinetics of phase transformation in the SMA wire. A standard phenomenological constitutive model reported by Brinson (1993) is modified by considering certain consistency conditions in the material property tensors and by eliminating spurious singularity. Considering the inhomogeneity effects, a finite element model of the SMA wire is developed. Simulations are carried out to study the buckling shape control of a beam integrated with SMA wire.

Influence of magnetic clusters on electrical and magnetic properties of In1-xMnxSb/GaAs dilute magnetic semiconductor grown by liquid phase epitaxy

In1-xMnxSb films have been grown with different Mn doping concentrations (x = 0.0085, 0.018, 0.029 and 0.04) beyond the equilibrium 14 solubility limit by liquid phase epitaxy. We have studied temperature dependent resistivity, the Hall effect, magnetoresistance and magnetization for all compositions. Saturation in magnetization observed even at room temperature suggests the existence of ferromagnetic clusters in the film which has been verified by scanning electron microscopy studies. The anomalous Hall coefficient is found to be negative. Remnant field present on the surface of the clusters seems to affect the anomalous Hall effect at very low fields (below 350 Gauss). In the zero field resistivity, a variable-range hopping conduction mechanism dominates below 3.5 K for all samples above which activated behavior is predominant. The temperature dependence of the magnetization measurement shows a magnetic ordering below 10 K which is consistent with electrical measurements. (c) 2007 Elsevier Ltd. All rights reserved.

Chemically Programmed Ultrahigh Density Two-Dimensional Semiconductor Superlattice Array

Designing an ultrahigh density linear superlattice array consisting of periodic blocks of different semiconductors in the strong confinement regime via a direct synthetic route remains an unachieved challenge in nanotechnology. We report a general synthesis route for the formulation of a large-area ultrahigh density superlattice array that involves adjoining multiple units of ZnS rods by prolate US particles at the tips. A single one-dimensional wire is 300-500 nm long and consists of periodic quantum wells with a barrier width of 5 nm provided by ZnS and a well width of 1-2 nm provided by CdS, defining a superlattice structure. The synthesis route allows for tailoring of ultranarrow laserlike emissions (fwhm approximate to 125 meV) originating from strong interwell energy dispersion along with control of the width, pitch, and registry of the superlattice assembly. Such an exceptional high-density superlattice array could form the basis of ultrahigh density memories in addition to offering opportunities for technological advancement in conventional heterojunction-based device applications.

Space-charge limited conduction in doped polypyrrole devices

Doping dependent current-voltage (I-V) and capacitance-voltage (C-V) measurements were carried out on polypyrrole devices in metal-polymer-metal sandwich structure. Temperature dependent I-V measurements infer that space-charge limited conduction (SCLC) with exponential trap distribution is appropriate for the moderately doped samples, whereas trap-free SCLC is observed in lightly doped samples. Trap densities and energies are estimated, the effective mobility is calculated using the Poole-Frenkel model, and the mobility exhibits thermally activated behavior. Frequency dependent capacitance-voltage characteristics show a peak near zero bias voltage, which implies that these devices are symmetric with a negligible barrier height at the metal-polymer interface. Low frequency capacitance measurements have revealed a negative capacitance at higher voltages due to the processes associated with the injection and redistribution of space-charges. (C) 2010 American Institute of Physics.

Optimal reactive power dispatch based on voltage stability criteria in a large power system with AC/DC and FACTs devices

An algorithm for optimal allocation of reactive power in AC/DC system using FACTs devices, with an objective of improving the voltage profile and also voltage stability of the system has been presented. The technique attempts to utilize fully the reactive power sources in the system to improve the voltage stability and profile as well as meeting the reactive power requirements at the AC-DC terminals to facilitate the smooth operation of DC links. The method involves successive solution of steady-state power flows and optimization of reactive power control variables with Unified Power Flow Controller (UPFC) using linear programming technique. The proposed method has been tested on a real life equivalent 96-bus AC and a two terminal DC system under normal and contingency conditions.

Origin of the Enhanced Photoluminescence from Semiconductor CdSeS Nanocrystals

Internal structures of extraordinarily luminescent semiconductor nanoparticles are probed with photoelectron spectroscopy, establishing a gradient alloy structure as an essential ingredient for the observed phenomenon. Comparative photoluminescence lifetime measurements provide direct evidence for a minimization of nonradiative decay channels because of the removal of interfacial defects due to a progressive change in the lattice parameters in such graded structures, exhibiting a nearly single exponential decay Quantum mechanical, calculations suggest a differential extent of spatial collapse of the electron and the hole wave functions in a way that helps to enhance the photoluminescence efficiency, while at the same time increasing the lifetime of the excited state, as observed in the experiments.