Absolute Entropy and Energy of Carbon Dioxide Using the Two-Phase Thermodynamic Model

The two-phase thermodynamic (2PT) model is used to determine the absolute entropy and energy of carbon dioxide over a wide range of conditions from molecular dynamics trajectories. The 2PT method determines the thermodynamic properties by applying the proper statistical mechanical partition function to the normal modes of a fluid. The vibrational density of state (DoS), obtained from the Fourier transform of the velocity autocorrelation function, converges quickly, allowing the free energy, entropy, and other thermodynamic properties to be determined from short 20-ps MD trajectories. The anharmonic effects in the vibrations are accounted for by the broadening of the normal modes into bands from sampling the velocities over the trajectory. The low frequency diffusive modes, which lead to finite DoS at zero frequency, are accounted for by considering the DoS as a superposition of gas-phase and solid-phase components (two phases). The analytical decomposition of the DoS allows for an evaluation of properties contributed by different types of molecular motions. We show that this 2PT analysis leads to accurate predictions of entropy and energy of CO2 over a wide range of conditions (from the triple point to the critical point of both the vapor and the liquid phases along the saturation line). This allows the equation of state of CO2 to be determined, which is limited only by the accuracy of the force field. We also validated that the 2PT entropy agrees with that determined from thermodynamic integration, but 2PT requires only a fraction of the time. A complication for CO2 is that its equilibrium configuration is linear, which would have only two rotational modes, but during the dynamics it is never exactly linear, so that there is a third mode from rotational about the axis. In this work, we show how to treat such linear molecules in the 2PT framework.

Nonlinear electrical conduction and broad band noise in the charge-ordered rare earth manganate Nd0.5Ca0.5MnO3

Measurements of the dc transport properties and the low-frequency conductivity noise in films of charge-ordered Nd0.5Ca0.5MnO3 grown on Si substrate reveal the existence of a threshold field in the charge-ordered regime beyond which strong nonlinear conduction sets in along with a large broad band conductivity noise. Threshold-dependent conduction disappears as T --> T-CO, the charge-ordering temperature. This observation suggests that the charge-ordered state gets depinned at the onset of the nonlinear conduction. (C) 1999 American Institute of Physics. [S0003-6951(99)05247-X].

Electrical characterization of Ba(Zr0.1Ti0.9)O-3 thin films grown by pulsed laser ablation technique

In situ annealed thin films of ferroelectric Ba(Zr0.1Ti0.9)O-3 were deposited on platinum substrates by pulsed laser ablation technique. The as grown films were polycrystalline in nature without the evidence of any secondary phases. The polarization hysteresis loop confirmed the ferroelectricity, which was also cross-checked with the capacitance-voltage characteristics. The remnant polarization was about 5.9 muC cm(-2) at room temperature and the coercive field was 45 kV. There was a slight asymmetry in the hysteresis for different polarities, which was thought to be due to the work function differences of different electrodes. The dielectric constant was about 452 and was found to exhibit low frequency dispersion that increased with frequency, This was related to the space-charge polarization. The complex impedance was plotted and this exhibited a semicircular trace, and indicated an equivalent parallel R - C circuit within the sample. This was attributed to the grain response. The DC leakage current-voltage plot was consistent with the space-charge limited conduction theory, but showed some deviation, which was explained by assuming a Poole-Frenkel type conduction to be superimposed on to the usual space-charge controlled current. (C) 2002 Elsevier Science B.V. All rights reserved.

Electrocatalytic efficiency of polyaniline by cyclic voltammetry and electrochemical impedance spectroscopy studies

Electrochemical redox reactions of ferrous/ferric (Fe2+/Fe3+) and hydroquinone/quinone (H(2)Q/Q) were studied on Pt and polyaniline (PANI)-deposited Pt electrodes in 0.5 M H2SO4-supporting electrolyte by cyclic voltammetry and ac impedance spectroscopy. A comparison of the experimental data obtained with the Pt and PANI/Pt electrodes suggested that the reactions were catalyzed by the PANI. Based on a relative increase in peak currents of cyclic voltammograms, catalytic efficiency (gamma(cv)) of the PANI was defined. There was an increase in gamma(cv) with an increase of scan rate and a decrease of concentration of Fe2+/Fe3+ or H(2)Q. The complex plane impedance spectrum of the electrode consisted of a semicircle in high frequency range and a linear spike in low frequency range. The exchange current density (i(0)) calculated using the semicircle part of the impedance showed Butler-Volmer kinetics with respect to concentration dependence. From a relative increase of i(0) on the PANI/Pt electrode, catalytic efficiency (gamma(eis)) was evaluated. (C) 2002 Elsevier Science B.V. All rights reserved.

The use of a fibre anemometer in turbulent flows

Quartz fibre anemometers have been used (as described in subsequent papers) to survey the velocity field of turbulent free convective air flows. This paper discusses the reasons for the choice of this instrument and provides the background information for its use in this way. Some practical points concerning fibre anemometers are mentioned. The rest of the paper is a theoretical study of the response of a fibre to a turbulent flow. An approximate representation of the force on the fibre due to the velocity field and the equation for a bending beam, representing the response to this force, form the basis of a consideration of the mean and fluctuating displacement of the fibre. Emphasis is placed on the behaviour when the spectrum of the turbulence is largely in frequencies low enough for the fibre to respond effectively instantaneously (as this corresponds to the practical situation). Incomplete correlation of the turbulence along the length of the fibre is taken into account. Brief mention is made to the theory of the higher-frequency (resonant) response in the context of an experimental check on the applicability of the low-frequency theory.

Interface states of laser ablated BaTiO3 and Ba0.9Ca0.1TiO3 thin films in MFS structure determined by DLTS and C – V technique

BaTiO3 and Ba0.9Ca0.1TiO3 thin films were deposited on the p – type Si substrate by pulsed excimer laser ablation technique. The Capacitance – Voltage (C-V) measurement measured at 1 MHz exhibited a clockwise rotating hysteresis loop with a wide memory window for the Metal – Ferroelectric – Semiconductor (MFS) capacitor confirming the ferroelectric nature. The low frequency C – V measurements exhibited the response of the minority carriers in the inversion region while at 1 MHz the C – V is of a high frequency type with minimum capacitance in the inversion region. The interface states of both the MFS structures were calculated from the Castagne – Vaipaille method (High – low frequency C – V curve). Deep Level Transient Spectroscopy (DLTS) was used to analyze the interface traps and capture cross section present in the MFS capacitor. There were distinct peaks present in the DLTS spectrum and these peaks were attributed to the presence of the discrete interface states present at the semiconductor – ferroelectric interface. The distribution of calculated interface states were mapped with the silicon energy band gap for both the undoped and Ca doped BaTiO3 thin films using both the C – V and DLTS method. The interface states of the Ca doped BaTiO3 thin films were found to be higher than the pure BaTiO3 thin films.

MFIS and MFS structures using SrBi2Ta2O9 thin films for the FRAM applications

Recently there is an increasing demand and extensive research on high density memories, in particular to the ferroelectric random access memory composed of 1T/1C (1 transistor/1 capacitor) or 2T/2C. FRAM's exhibit fast random acess in read/write mode, non - volatility and low power for good performance. An integration of the ferroelectric on Si is the key importance and in this regard, there had been various models proposed like MFS, MFIS, MFMIS structure etc., Choosing the proper insulator is very essential for the better performance of the device and to exhibit excellent electrical characteristics. ZrTiO4 is a potential candidate because of its excellent thermal stability and lattice match on the Si substrate. SrBi2Ta2O9 and ZrTiO4 thin films were prepared on p - type Si substrate by pulsed excimer laser ablation technique. Optimization of both ZT and SBT thin films in MFS and MFIS structure had been done based on the annealing, oxygen partial pressures and substrate temperatures to have proper texture of the thin films. The dc leakage current, P - E hysteresis, capacitance - voltage and conductance - voltage measurement were carried out. The effect of the frequency dependence on MFIS structure was observed in the C – V curve. It displays a transition of C - V curve from high frequency to low frequency curve on subjection to varied frequencies. Density of interface states has been calculated using Terman and high - low frequency C - V curve. The effect of memory window in the C - V hysteresis were analysed in terms of film thickness and annealing temperatures. DC conduction mechanism were analysed in terms of poole - frenkel, Schottky and space charge limited conduction separately on MFS, MIS structure.

MFIS and MFS structures using SrBi2Ta2O9 thin films for the FRAM applications

Recently there is an increasing demand and extensive research on high density memories, in particular to the ferroelectric random access memory composed of 1T/1C (1 transistor/1 capacitor) or 2T/2C. FRAM's exhibit fast random acess in read/write mode, non - volatility and low power for good performance. An integration of the ferroelectric on Si is the key importance and in this regard, there had been various models proposed like MFS, MFIS, MFMIS structure etc., Choosing the proper insulator is very essential for the better performance of the device and to exhibit excellent electrical characteristics. ZrTiO4 is a potential candidate because of its excellent thermal stability and lattice match on the Si substrate. SrBi2Ta2O9 and ZrTiO4 thin films were prepared on p - type Si substrate by pulsed excimer laser ablation technique. Optimization of both ZT and SBT thin films in MFS and MFIS structure had been done based on the annealing, oxygen partial pressures and substrate temperatures to have proper texture of the thin films. The dc leakage current, P - E hysteresis, capacitance - voltage and conductance - voltage measurement were carried out. The effect of the frequency dependence on MFIS structure was observed in the C – V curve. It displays a transition of C - V curve from high frequency to low frequency curve on subjection to varied frequencies. Density of interface states has been calculated using Terman and high - low frequency C - V curve. The effect of memory window in the C - V hysteresis were analysed in terms of film thickness and annealing temperatures. DC conduction mechanism were analysed in terms of poole - frenkel, Schottky and space charge limited conduction separately on MFS, MIS structure.

Network Rhythms Influence the Relationship between Spike-Triggered Local Field Potential and Functional Connectivity

Characterizing the functional connectivity between neurons is key for understanding brain function. We recorded spikes and local field potentials (LFPs) from multielectrode arrays implanted in monkey visual cortex to test the hypotheses that spikes generated outward-traveling LFP waves and the strength of functional connectivity depended on stimulus contrast, as described recently. These hypotheses were proposed based on the observation that the latency of the peak negativity of the spike-triggered LFP average (STA) increased with distance between the spike and LFP electrodes, and the magnitude of the STA negativity and the distance over which it was observed decreased with increasing stimulus contrast. Detailed analysis of the shape of the STA, however, revealed contributions from two distinct sources-a transient negativity in the LFP locked to the spike (similar to 0 ms) that attenuated rapidly with distance, and a low-frequency rhythm with peak negativity similar to 25 ms after the spike that attenuated slowly with distance. The overall negative peak of the LFP, which combined both these components, shifted from similar to 0 to similar to 25 ms going from electrodes near the spike to electrodes far from the spike, giving an impression of a traveling wave, although the shift was fully explained by changing contributions from the two fixed components. The low-frequency rhythm was attenuated during stimulus presentations, decreasing the overall magnitude of the STA. These results highlight the importance of accounting for the network activity while using STAs to determine functional connectivity.

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.

On numerical prediction of the acoustic source characteristics of an engine exhaust system

The contemporary methods for source characterization rely mainly on experiments. These methods produce inaccurate results in the low‐frequency band, where the characteristics are all the more important. Moreover, the experimental methods cannot be used at the design stage. Hence, a numerical technique to obtain the source characteristics is desirable. In this paper, the pressure‐time history and the mass‐flux‐time history obtained by means of the time‐domain analysis have been used, along with the two‐load method to compute the source characteristics. Two new computational methods for obtaining the source characteristics have been described. These are much simpler, and computationally more economical than the complete time‐domain simulation, which makes use of the method of characteristics.

Input voltage modulated high voltage DC power supply topology for pulsed load applications

High voltage power supplies for radar applications are investigated which are subjected to pulsed load with stringent specifications. In the proposed solution, power conversion is done in two stages. A low power-high frequency converter modulates the input voltage of a high power-low frequency converter. This method satisfies all the performance specifications and takes care of the critical aspects of HV transformer.

Evolution of 1/f α noise during electromigration stressing of metal film: Spectral signature of electromigration process

In this paper we report a systematic study of low-frequency 1/fα resistance fluctuation in a metal film at different stages of electromigration. The resistance fluctuation (noise) measurement was carried out in presence of a dc electromigration stressing current. We observe that in addition to the increase in the spectral power SV(f), the frequency dependence of the spectral power changes as the electromigration process progresses and the exponent α starts to change from 1 to higher value closer to 1.5. We interpret this change in α as arising due to an additional contribution to the spectral power with a 1/f3/2 component, which starts to contribute as the electromigration process progresses. This additional component SV(f) ∼ 1/f3/2 has been suggested to originate from long range diffusion that would accompany any electromigration process. The experimental observation finds support in a model simulation, where we also find that the enhancement of noise during electromigration stressing is accompanied by a change in spectral power frequency dependence.