Model Predictive Static Programming: A Computationally Efficient Technique For Suboptimal Control Design

Combining the philosophies of nonlinear model predictive control and approximate dynamic programming, a new suboptimal control design technique is presented in this paper, named as model predictive static programming (MPSP), which is applicable for finite-horizon nonlinear problems with terminal constraints. This technique is computationally efficient, and hence, can possibly be implemented online. The effectiveness of the proposed method is demonstrated by designing an ascent phase guidance scheme for a ballistic missile propelled by solid motors. A comparison study with a conventional gradient method shows that the MPSP solution is quite close to the optimal solution.

Defect-selective photothermal imaging: a sensitive tool for damage mapping in optical coatings

A defect-selective photothermal imaging system for the diagnostics of optical coatings is demonstrated. The instrument has been optimized for pump and probe parameters, detector performance, and signal processing algorithm. The imager is capable of mapping purely optical or thermal defects efficiently in coatings of low damage threshold and low absorbance. Detailed mapping of minor inhomogeneities at low pump power has been achieved through the simultaneous action of a low-noise fiber optic photothermal beam defection sensor and a common-mode-rejection demodulation (CMRD) technique. The linearity and sensitivity of the sensor have been examined theoretically and experimentally, and the signal to noise ratio improvement factor is found to be about 110 compared to a conventional bicell photodiode. The scanner is so designed that mapping of static or shock sensitive samples is possible. In the case of a sample with absolute absorptance of 3.8 x 10(-4), a change in absorptance of about 0.005 x 10(-4) has been detected without ambiguity, ensuring a contrast parameter of 760. This is about 1085% improvement over the conventional approach containing a bicell photodiode, at the same pump power. The merits of the system have been demonstrated by mapping two intentionally created damage sites in a MgF2 coating on fused silica at different excitation powers. Amplitude and phase maps were recorded for thermally thin and thick cases, and the results are compared to demonstrate a case which, in conventional imaging, would lead to a deceptive conclusion regarding the type and location of the damage. Also, a residual damage profile created by long term irradiation with high pump power density has been depicted.

Structural, optical and electrical properties of sulfur-incorporated amorphous carbon films

Amorphous carbon-sulfur (a-C:S) composite films were prepared by vapor phase pyrolysis technique. The structural changes in the a-C:S films were investigated by electron microscopy. A powder X-ray diffraction (XRD) study depicts the two-phase nature of a sulfur-incorporated a-C system. The optical bandgap energy shows a decreasing trend with an increase in the sulfur content and preparation temperature. This infers a sulfur incorporation and pyrolysis temperature induced reduction in structural disorder or increase in sp (2) or pi-sites. The presence of sulfur (S 2p) in the a-C:S sample is analyzed by the X-ray photoelectron spectroscopy (XPS). The sp (3)/sp (2) hybridization ratio is determined by using the XPS C 1s peak fitting, and the results confirm an increase in sp (2) hybrids with sulfur addition to a-C. The electrical resistivity variation in the films depends on both the sulfur concentration and the pyrolysis temperature.

Structural and optical investigations of TiO2 films deposited on transparent substrates by sol-gel technique

An inexpensive and effective simple method for the preparation of nano-crystalline titanium oxide (anatase) thin films at room temperature on different transparent substrates is presented. This method is based on the use of peroxo-titanium complex, i.e. titanium isopropoxide as a single initiating organic precursor. Post-annealing treatment is necessary to convert the deposited amorphous film into titanium oxide (TiO2) crystalline (anatase) phase. These films have been characterized for X-ray diffraction (XRD) studies, atomic force microscopic (AFM) studies and optical measurements. The optical constants such as refractive index and extinction coefficient have been estimated by using envelope technique. Also, the energy gap values have been estimated using Tauc's formula for on glass and quartz substrates are found to be 3.35 eV and 3.39 eV, respectively.

Some studies on TiO2 films deposited by sol-gel technique

TiO2 films are extensively used in various applications including optical multi-layers, sensors, photo catalysis, environmental purification, and solar cells etc. These are prepared by both vacuum and non-vacuum methods. In this paper, we present the results on TiO2 thin films prepared by a sol-gel spin coating process in non-aqueous solvent. Titanium isopropoxide is used as TiO2 precursor. The films were annealed at different temperatures up to 3000 C for 5 hours in air. The influence of the various deposition parameters like spinning speed, spinning time and annealing temperature on the thickness of the TiO2 films has been studied. The variation of film thickness with time in ambient atmosphere was also studied. The optical, structural and morphological characteristics were investigated by optical transmittance-reflectance measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The refractive index and extinction coefficient of the films were determined by envelope technique and spectroscopic ellipsometry. TiO2 films exhibited high transparency (92%) in the visible region with a refractive index of 2.04 at 650 nm. The extinction coefficient was found to be negligibly small. The X-ray diffraction analysis showed that the TiO2 film deposited on glass substrate changes from amorphous to crystalline (anatase) phase with annealing temperature above 2500 C. SEM results show that the deposited films are uniform and crack free.

The Influence of Processing Parameters on Characteristics of an Aluminum Alloy Spray Deposition

In the present investigation, two nozzle configurations are used for spray deposition, convergent nozzle (nozzle-A), and convergent nozzle with 2 mm parallel portion attached at its end (nozzle-C) without changing the exit area. First, the conditions for subambient aspiration pressure, i.e., pressure at the tip of the melt delivery tube, are established by varying the protrusion length of the melt delivery tube at different applied gas pressures for both of the nozzles. Using these conditions, spray deposits in a reproducible manner are successfully obtained for 7075 Al alloy. The effect of applied gas pressure, flight distance, and nozzle configuration on various characteristics of spray deposition, viz., yield, melt flow rate, and gas-to-metal ratio, is examined. The over-spray powder is also characterized with respect to powder size distribution, shape, and microstructure. Some of the results are explained with the help of numerical analysis presented in an earlier article.

Structural and optical investigations of TiO2 films deposited on transparent substrates by sol-gel technique

An inexpensive and effective simple method for the preparation of nano-crystalline titanium oxide (anatase) thin films at room temperature on different transparent substrates is presented. This method is based on the use of peroxo-titanium complex, i.e. titanium isopropoxide as a single initiating organic precursor. Post-annealing treatment is necessary to convert the deposited amorphous film into titanium oxide (TiO2) crystalline (anatase) phase. These films have been characterized for X-ray diffraction (XRD) studies, atomic force microscopic (AFM) studies and optical measurements. The optical constants such as refractive index and extinction coefficient have been estimated by using envelope technique. Also, the energy gap values have been estimated using Tauc's formula for on glass and quartz substrates are found to be 3.35 eV and 3.39 eV, respectively. (C) 2008 Elsevier B.V. All rights reserved.

A fuzzy multistage evolutionary (FUME) clustering technique

n this paper, a multistage evolutionary scheme is proposed for clustering in a large data base, like speech data. This is achieved by clustering a small subset of the entire sample set in each stage and treating the cluster centroids so obtained as samples, together with another subset of samples not considered previously, as input data to the next stage. This is continued till the whole sample set is exhausted. The clustering is accomplished by constructing a fuzzy similarity matrix and using the fuzzy techniques proposed here. The technique is illustrated by an efficient scheme for voiced-unvoiced-silence classification of speech.

A technique for steady-state polarisation of stationary solid electrodes and its applications

A new technique has been devised to achieve a steady-state polarisation of a stationary electrode with a helical shaft rotating coaxial to it. A simplified theory for the convective hydrodynamics prevalent under these conditions has been formulated. Experimental data are presented to verify the steady-state character of the current-potential curves and the predicted dependence of the limiting current on the rotation speed of the rotor, the bulk concentration of the depolariser and the viscosity of the solution. Promising features of the multiple-segment electrodes concentric to a central disc electrode are pointed out.

Bayesian and Decision Tree Approaches for Pattern Recognition Including Feature Measurement Costs

The minimum cost classifier when general cost functionsare associated with the tasks of feature measurement and classification is formulated as a decision graph which does not reject class labels at intermediate stages. Noting its complexities, a heuristic procedure to simplify this scheme to a binary decision tree is presented. The optimizationof the binary tree in this context is carried out using ynamicprogramming. This technique is applied to the voiced-unvoiced-silence classification in speech processing.

Optimum choice of wavelengths in the anomalous scattering technique with synchrotron radiation

A formula has been derived for the mean-square error in the phases of crystal reflections determined through the multiwavelength anomalous scattering method.The error is written in terms of a simple function of the positions in the complex plane of the 'centres' corresponding to the different wavelengths. For the case of three centres, the mean-square error is inversely proportional to the area of the triangle formed by them.

A DLTS technique for surface state capture cross-section measurement of MOS diodes

A modified DLTS technique is proposed for the direct measurement of capture cross-section of MOS surface states. The nature of temperature and energy dependence σn is inferred from data analysis. Temperature dependence of σn is shown to be consistent with the observed DLTS line shapes.

Hybrid constant factor incremental delta modulators

The paper presents a new adaptive delta modulator, called the hybrid constant factor incremental delta modulator (HCFIDM), which uses instantaneous as well as syllabic adaptation of the step size. Three instantaneous algorithms have been used: two new instantaneous algorithms (CFIDM-3 and CFIDM-2) and the third, Song's voice ADM (SVADM). The quantisers have been simulated on a digital computer and their performances studied. The figure of merit used is the SNR with correlated, /?C-shaped Gaussian signals and real speech as the input. The results indicate that the hybrid technique is superior to the nonhybrid adaptive quantisers. Also, the two new instantaneous algorithms developed have improved SNR and fast response to step inputs as compared to the earlier systems.

A Spectral Iteration Technique For The Analysis Of Yagi-Uda Arrays

The paper present a spectral iteration technique for the analysis of linear arrays of unequally spaced dipoles of unequal lengths. As an example, the Yagi-Uda array is considered for illustration. Analysis is carried out in both the spatial as well as the spectral domains, the two being linked by the Fourier transform. The fast Fourier transform algorithm is employed to obtain an iterative solution to the electric field integral equation and the need for matrix inversion is circumvented. This technique also provides a convenient means for testing the satisfaction of the boundary conditions on the array elements. Numerical comparison of the input impedance and radiation pattern have been made with results deduced elsewhere by other methods. The computational efficency of this technique has been found to be significant for large arrays.

A Novel Operator-Splitting Technique for One-Dimensional Laminar Premixed Flames

This paper is concerned the calculation of flame structure of one-dimensional laminar premixed flames using the technique of operator-splitting. The technique utilizes an explicit method of solution with one step Euler for chemistry and a novel probabilistic scheme for diffusion. The relationship between diffusion phenomenon and Gauss-Markoff process is exploited to obtain an unconditionally stable explicit difference scheme for diffusion. The method has been applied to (a) a model problem, (b) hydrazine decomposition, (c) a hydrogen-oxygen system with 28 reactions with constant Dρ 2 approximation, and (d) a hydrogen-oxygen system (28 reactions) with trace diffusion approximation. Certain interesting aspects of behaviour of the solution with non-unity Lewis number are brought out in the case of hydrazine flame. The results of computation in the most complex case are shown to compare very favourably with those of Warnatz, both in terms of accuracy of results as well as computational time, thus showing that explicit methods can be effective in flame computations. Also computations using the Gear-Hindmarsh for chemistry and the present approach for diffusion have been carried out and comparison of the two methods is presented.