A study of Al2O3:C films on Si(100) grown by low pressure MOCVD

We report the characterization of carbonaceous aluminium oxide, Al2O3:C, films grown on Si(100) by metalorganic chemical vapor deposition. The focus is on the study of the effects of carbon on the dielectric properties of aluminium oxide in a qualitative manner. The carbon present in the aluminium oxide film derives from aluminium acetylacetonate used as the source of aluminium. As-grown films comprise nanometer-sized grains of alumina (∼ 20–50 nm) in an amorphous carbonaceous matrix, as examined by X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The films are shiny; they are smooth as observed by scanning electron microscopy (SEM). An attempt has been made to explore the defects (viz., oxide charge density) in the aluminium oxide films using room temperature high frequency capacitance – voltage (C-V) and current–voltage (I-V) measurements. The hysteresis and stretch-out in the high frequency C-V plots is indicative of charge trapping. The role of heteroatoms, as characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy, in the transport of charge in Al2O3:C films is discussed.

Effect of nortriptyline and paroxetine on measures of chaos of heart rate time series in patients with panic disorder

Tricyclic antidepressants have notable cardiac side effects, and this issue has become important due to the recent reports of increased cardiovascular mortality in patients with depression and anxiety. Several previous studies indicate that serotonin reuptake inhibitors (SRIs) do not appear to have such adverse effects. Apart from the effects of these drugs on routine 12-lead ECG, the effects on beat-to-beat heart rate (HR) and QT interval time series provide more information on the side effects related to cardiac autonomic function. In this study, we evaluated the effects of two antidepressants, nortriptyline (n = 13), a tricyclic, and paroxetine (n = 16), an SRI inhibitor, on HR variability in patients with panic disorder, using a measure of chaos, the largest Lyapunov exponent (LLE) using pre- and posttreatment HR time series. Our results show that nortriptyline is associated with a decrease in LLE of high frequency (HF: 0.15-0.5 Hz) filtered series, which is most likely due to its anticholinergic effect, while paroxetine had no such effect. Paroxetine significantly decreased sympathovagal ratios as measured by a decrease in LLE of LF/HF. These results suggest that paroxetine appears to be safer in regards to cardiovascular effects compared to nortriptyline in this group of patients. (C) 2003 Elsevier Inc. All rights reserved.

Effect of screening of intermicellar interactions on the linear and nonlinear rheology of a viscoelastic gel

We report our studies of the linear and nonlinear rheology of aqueous solutions of the surfactant cetyl trimethylammonium tosylate (CTAT) with varying amounts of sodium chloride (NaCl). The CTAT concentration is fixed at 42 mM, and the salt concentration is varied between 0 and 120 mM. On increasing the salt (NaCl) concentration, we see three distinct regimes in the zero-shear viscosity and the high-frequency plateau modulus data. In regime 1, the zero-shear viscosity shows a weak increase with salt concentration due to enhanced micellar growth. The decrease in the zero-shear viscosities with salt concentration in regimes II and III can be explained in terms of intermicellar branching. The most intriguing feature of our data, however, is the anomalous behavior of the high-frequency plateau modulus in regime II (0.12 less than or equal to [NaCl]/[CTAT] less than or equal to 1.42). In this regime, the plateau modulus increases with an increase in NaCl concentration. This is highly interesting, since the correlation length of concentration fluctuations and hence the plateau modulus G(0) are not expected to change appreciably in the semidilute regime. We propose to explain the changes in regime II in terms of a possible unbinding of the organic counterions (tosylate) from the CTA(+) surfaces on the addition of NaCl. In the nonlinear flow curves of the samples with high salt content, significant deviations from the predictions of the Giesekus model for entangled micelles are observed.

Heat shock protein 70 as a biomarker of heat stress in a simulated hot cockpit

Background: Fighter pilots are frequently exposed to high temperatures during high-speed low-level flight. Heat strain can result in temporary impairment of cognitive functions and when severe, loss of consciousness and consequent loss of life and equipment. Induction of stress proteins is a highly conserved stress response mechanism from bacteria to humans. induced stress protein levels are known to be cytoprotective and have been correlated with stress tolerance. Although many studies on the heat shock response mechanisms have been performed in cell culture and animal model systems, there is very limited information on stress protein induction in human subjects. Hypothesis: Heat shock proteins (Hsp), especially Hsp70, may be induced in human subjects exposed to high temperatures in a hot cockpit designed to simulate heat stress experienced in low flying sorties. Methods: Six healthy volunteers were subjected to heat stress at 55degreesC in a high temperature cockpit simulator for a period of 1 h at 30% humidity. Physiological parameters such as oral and skin temperatures, heart rate, and sweat rate were monitored regularly during this time. The level of Hsp70 in leukocytes was examined before and after the heat exposure in each subject. Conclusions: Hsp70 was found to be significantly induced in all the six subjects exposed to heat stress. The level of induced Hsp70 appears to correlate with other strain indicators such as accumulative circulatory strain and Craig's modified index. The usefulness of Hsp70 as a molecular marker of heat stress in humans is discussed.

The nature of the prompt X-ray and radio emission from SN 2002ap

We report on the combined X-ray and radio observations of the type Ic SN 2002ap, using XMM-Newton TOO observation of M 74 and the Giant Metrewave Radio Telescope ( GMRT). We account for the presence of a nearby source in the pre-supernova Chandra field of view in our measurements of the X-ray flux (0.3-10 KeV) 5.2 days after the explosion. The X-ray spectrum is well fitted by a power law spectrum with photon index alpha = 2.6. Our results suggest that the prompt X-ray emission originates from inverse Compton scattering of photospheric thermal emission by energetic electrons. Radio observations with the GMRT at 610 MHz (8 days after the explosion) and 1420 MHz (70 days after the explosion) are combined with the high frequency VLA observations of SN 2002ap reported by Berger et al. ( 2002), and the early radiospheric properties of SN 2002ap are compared with similar data from two other supernovae. Finally, the GMRT radio map reveals four other X-ray sources in the field of view of M 74 with radio counterparts.

Low-temperature polaronic relaxations with variable range hopping conductivity in FeTiMO(6) (M = Ta,Nb,Sb)

Low-temperature dielectric measurements on FeTiMO(6) (M = Ta,Nb,Sb) rutile-type oxides at frequencies from 0.1 Hz to 10 MHz revealed anomalous dielectric relaxations with frequency dispersion. Unlike the high-temperature relaxor response of these materials, the low-temperature relaxations are polaronic in nature. The relationship between frequency and temperature of dielectric loss peak follows T(-1/4) behavior. The frequency dependence of ac conductivity shows the well-known universal dielectric response, while the dc conductivity follows Mott variable range hopping (VRH) behavior, confirming the polaronic origin of the observed dielectric relaxations. The frequency domain analysis of the dielectric spectra shows evidence for two relaxations, with the high-frequency relaxations following Mott VRH behavior more closely. Significantly, the Cr- and Ga-based analogs, CrTiNbO(6) and GaTiMO(6) (M = Ta,Nb), that were also studied, did not show these anomalies.

Doubly spectral stochastic finite element method (DSSFEM) for random field problems

Uncertainties in complex dynamic systems play an important role in the prediction of a dynamic response in the mid- and high-frequency ranges. For distributed parameter systems, parametric uncertainties can be represented by random fields leading to stochastic partial differential equations. Over the past two decades, the spectral stochastic finite-element method has been developed to discretize the random fields and solve such problems. On the other hand, for deterministic distributed parameter linear dynamic systems, the spectral finite-element method has been developed to efficiently solve the problem in the frequency domain. In spite of the fact that both approaches use spectral decomposition (one for the random fields and the other for the dynamic displacement fields), very little overlap between them has been reported in literature. In this paper, these two spectral techniques are unified with the aim that the unified approach would outperform any of the spectral methods considered on their own. An exponential autocorrelation function for the random fields, a frequency-dependent stochastic element stiffness, and mass matrices are derived for the axial and bending vibration of rods. Closed-form exact expressions are derived by using the Karhunen-Loève expansion. Numerical examples are given to illustrate the unified spectral approach.

A DCT Based Filtering of Biomedical Images

Image filtering techniques have numerous potential applications in biomedical imaging and image processing. The design of filters largely depends on the a-priori knowledge about the type of noise corrupting the image and image features. This makes the standard filters to be application and image specific. The most popular filters such as average, Gaussian and Wiener reduce noisy artifacts by smoothing. However, this operation normally results in smoothing of the edges as well. On the other hand, sharpening filters enhance the high frequency details making the image non-smooth. An integrated general approach to design filters based on discrete cosine transform (DCT) is proposed in this study for optimal medical image filtering. This algorithm exploits the better energy compaction property of DCT and re-arrange these coefficients in a wavelet manner to get the better energy clustering at desired spatial locations. This algorithm performs optimal smoothing of the noisy image by preserving high and low frequency features. Evaluation results show that the proposed filter is robust under various noise distributions.

Robust Fixed Order Lateral H2 Controller for Micro Air Vehicle

This paper presents a robust fixed order H2controller design using strengthened discrete optimal projection equations, which approximate the first order necessary optimality condition. The novelty of this work is the application of the robust H2controller to a micro aerial vehicle named Sarika2 developed in house. The controller is designed in discrete domain for the lateral dynamics of Sarika2 in the presence of low frequency atmospheric turbulence (gust) and high frequency sensor noise. The design specification includes simultaneous stabilization, disturbance rejection and noise attenuation over the entire flight envelope of the vehicle. The resulting controller performance is comprehensively analyzed by means of simulation

Improved utilisation of an HF transformer in DC–AC application

Power conversion using high frequency (HF) link converters is popular because of compact size and light weight of highfrequency transformer. This study focuses on improved utilisation of HF transformer in DC–AC applications. In practical application, the operating condition of the power converter deviates significantly from the designed considerations. These deviating factors are commutation requirements (dead-time, overlap), mismatch in device drops and presence of the fundamental frequency in load current. As a result, the HF transformer handles some amount of low-frequency components (including DC) other than desired HF components. This causes the operating point in B-H curve to shift away from its normal or idealised position and hence results poor utilisation of the HF transformer and unwanted losses. This study investigates the nature of the problem with experimental determination of approximate lumped parameter modelling and saturation behaviour (B-H curve) of the HF transformer. A simple closed-loop control algorithm with online tuning of the controller parameters is proposed to improve the utilisation of the isolation transformer. The simulation and experimental results are presented.

Optimised form of acceleration correction algorithm within SPH-based simulations of impact mechanics

In the context of SPH-based simulations of impact dynamics, an optimised and automated form of the acceleration correction algorithm (Shaw and Reid, 2009a) is developed so as to remove spurious high frequency oscillations in computed responses whilst retaining the stabilizing characteristics of the artificial viscosity in the presence of shocks and layers with sharp gradients. A rational framework for an insightful characterisation of the erstwhile acceleration correction method is first set up. This is followed by the proposal of an optimised version of the method, wherein the strength of the correction term in the momentum balance and energy equations is optimised. For the first time, this leads to an automated procedure to arrive at the artificial viscosity term. In particular, this is achieved by taking a spatially varying response-dependent support size for the kernel function through which the correction term is computed. The optimum value of the support size is deduced by minimising the (spatially localised) total variation of the high oscillation in the acceleration term with respect to its (local) mean. The derivation of the method, its advantages over the heuristic method and issues related to its numerical implementation are discussed in detail. (C) 2011 Elsevier Ltd. All rights reserved.

Implementation of a phase array diffuse optical tomographic imager

Diffuse optical tomography (DOT) using near-infrared (NIR) light is a promising tool for noninvasive imaging of deep tissue. This technique is capable of quantitative reconstructions of absorption coefficient inhomogeneities of tissue. The motivation for reconstructing the optical property variation is that it, and, in particular, the absorption coefficient variation, can be used to diagnose different metabolic and disease states of tissue. In DOT, like any other medical imaging modality, the aim is to produce a reconstruction with good spatial resolution and accuracy from noisy measurements. We study the performance of a phase array system for detection of optical inhomogeneities in tissue. The light transport through a tissue is diffusive in nature and can be modeled using diffusion equation if the optical parameters of the inhomogeneity are close to the optical properties of the background. The amplitude cancellation method that uses dual out-of-phase sources (phase array) can detect and locate small objects in turbid medium. The inverse problem is solved using model based iterative image reconstruction. Diffusion equation is solved using finite element method for providing the forward model for photon transport. The solution of the forward problem is used for computing the Jacobian and the simultaneous equation is solved using conjugate gradient search. The simulation studies have been carried out and the results show that a phase array system can resolve inhomogeneities with sizes of 5 mm when the absorption coefficient of the inhomogeneity is twice that of the background tissue. To validate this result, a prototype model for performing a dual-source system has been developed. Experiments are carried out by inserting an inhomogeneity of high optical absorption coefficient in an otherwise homogeneous phantom while keeping the scattering coefficient same. The high frequency (100 MHz) modulated dual out-of-phase laser source light is propagated through the phantom. The interference of these sources creates an amplitude null and a phase shift of 180° along a plane between the two sources with a homogeneous object. A solid resin phantom with inhomogeneities simulating the tumor is used in our experiment. The amplitude and phase changes are found to be disturbed by the presence of the inhomogeneity in the object. The experimental data (amplitude and the phase measured at the detector) are used for reconstruction. The results show that the method is able to detect multiple inhomogeneities with sizes of 4 mm. The localization error for a 5 mm inhomogeneity is found to be approximately 1 mm.

Adaptive Harmonic Elimination Technique in Single Phase PWM Inverters

High frequency PWM inverters produce an output voltage spectrum at the fundamental reference frequency and around the switching frequency. Thus ideally PWM inverters do not introduce any significant lower order harmonics. However, in real systems, due to dead-time effect, device drops and other non-idealities lower order harmonics are present. In order to attenuate these lower order harmonics and hence to improve the quality of output current, this paper presents an \emph{adaptive harmonic elimination technique}. This technique uses an adaptive filter to estimate a particular harmonic that is to be attenuated and generates a voltage reference which will be added to the voltage reference produced by the current control loop of the inverter. This would have an effect of cancelling the voltage that was producing the particular harmonic. The effectiveness and the limitations of the technique are verified experimentally in a single phase PWM inverter in stand-alone as well as g rid interactive modes of operation.

Supercapacitor studies on globular polypyrrole microstructures developed by a facile electrochemical route

Micrometre-scale polypyrrole (PPy) structures are synthesised for electrochemical supercapacitor applications by a facile electrochemical route. Globular polypyrrole microstructures of size <5 mu m are grown on stainless steel (SS-304) substrate by electro-polymerisation of pyrrole on oxygen microbubble templates electrochemically generated and stabilised in the presence of surfactant/supporting electrolyte/dopant beta-naphthalene sulfonic acid (beta-NSA). Microstructures obtained with scan range of 0-1.6 V (against Ag/AgCl) are uniformly distributed over the surface with high coverage density of 5 x 10(5) to 8 x 10 cm(-2). Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed that the formed microstructures are of beta-NSA doped PPy. Scanning electron microscopy showed the uniform spread and good coverage of microstructures over the substrate. Supercapacitor properties of PPy films are investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge methods with 1.0 M KCl as electrolyte in a three-electrode electrochemical cell. Specific capacitance of 583 Fg(-1) is obtained, which is greater than the values (350-400 Fg(-1) highest) usually reported for this material. Electrochemical impedance spectroscopy proves the supercapacitance behaviour and explains the special inductive component of impedance observed in the high-frequency regime because of the globular structures of PPy deposited

Portable HVAC and Pulsed Plasma Sources for Control of NOX in Diesel Engine Exhaust

In this paper studies were carried out on two compact electric discharge plasma sources for controlling nitrogen oxides (NOX) emission in diesel engine exhaust. The plasma sources consist of an old television flyback transformer to generate high frequency high voltage ac (HVAC) and an automobile ignition coil to generate the high voltage pulses (HV Pulse). The compact plasma sources are aimed at retrofitting the existing catalytic converters with electric discharge assisted cleaning technique. To enhance NOX removal efficiency cascaded plasma-adsorbent technique has been used. Studies were reported at different flow rates and load conditions of the diesel engine.