Department of Electrical Engineering

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IIT Jodhpur

A new approach is presented to analyze sliding mode control in discrete-time systems using an established reaching law, whereby the ultimate band is obtained to be lesser than any previous analysis done with the same reaching law. Multirate Output Feedback technique of fast output sampling is used to calculate the control action. The controller parameters are evaluated according to the ultimate band that is desired, giving rise to a negative switching gain, contradicting popular notion of non-negative switching gains used in sliding mode control. © 2012 IEEE.

World University root node

2012 7th International Conference on Electrical and Computer Engineering, ICECE 2012

Minimal quasi sliding mode band with multirate output feedback

The paper presents a new control law for higher order sliding mode control. The control law keeps a constraint in 2-sliding mode such that the finite time stabilization of triple integrator is achieved. The switching function from non-singular terminal sliding mode is used to achieve the goal. The switching function is designed to have relative degree two with respect the input and thus the twisting controller can be exploited for finite time convergence. The fractional powers are carefully designed to prevent the unboundedness or singularity arising because of some constraint being kept at zero. The disturbance rejection is a natural consequence of use of twisting controller. © 2012 IEEE.

Proceedings of IEEE International Workshop on Variable Structure Systems

An algorithm for third order sliding mode control by keeping a 2-sliding constraint

We study the use of machine learning for visual quality evaluation with comprehensive singular value decomposition (SVD)-based visual features. In this paper, the two-stage process and the relevant work in the existing visual quality metrics are first introduced followed by an in-depth analysis of SVD for visual quality assessment. Singular values and vectors form the selected features for visual quality assessment. Machine learning is then used for the feature pooling process and demonstrated to be effective. This is to address the limitations of the existing pooling techniques, like simple summation, averaging, Minkowski summation, etc., which tend to be ad hoc. We advocate machine learning for feature pooling because it is more systematic and data driven. The experiments show that the proposed method outperforms the eight existing relevant schemes. Extensive analysis and cross validation are performed with ten publicly available databases (eight for images with a total of 4042 test images and two for video with a total of 228 videos). We use all publicly accessible software and databases in this study, as well as making our own software public, to facilitate comparison in future research. © 2006 IEEE.

IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics

SVD-based quality metric for image and video using machine learning

In this paper, we propose a new image quality assessment (IQA) scheme, with emphasis on gradient similarity. Gradients convey important visual information and are crucial to scene understanding. Using such information, structural and contrast changes can be effectively captured. Therefore, we use the gradient similarity to measure the change in contrast and structure in images. Apart from the structural/contrast changes, image quality is also affected by luminance changes, which must be also accounted for complete and more robust IQA. Hence, the proposed scheme considers both luminance and contrast-structural changes to effectively assess image quality. Furthermore, the proposed scheme is designed to follow the masking effect and visibility threshold more closely, i.e., the case when both masked and masking signals are small is more effectively tackled by the proposed scheme. Finally, the effects of the changes in luminance and contrast-structure are integrated via an adaptive method to obtain the overall image quality score. Extensive experiments conducted with six publicly available subject-rated databases (comprising of diverse images and distortion types) have confirmed the effectiveness, robustness, and efficiency of the proposed scheme in comparison with the relevant state-of-the-art schemes. © 2011 IEEE.

IEEE Transactions on Image Processing

Image quality assessment based on gradient similarity

Bit-depth expansion is an art of converting low bit-depth image into high bit-depth image. Bit-depth of an image represents the number of bits required to represent an intensity value of the image. Bit-depth expansion is an important field since it directly affects the display quality. In this paper, we propose a novel method for bit-depth expansion which uses Minimum Risk Based Classification to create high bit-depth image. Blurring and other annoying artifacts are lowered in this method. Our method gives better objective (PSNR) and superior visual quality as compared to recently developed bit-depth expansion algorithms. © 2012 IEEE.

2012 IEEE Visual Communications and Image Processing, VCIP 2012

Bit-depth expansion using minimum risk based classification

In this paper we present two computationally simple algorithms that can be used for prediction of pixels of images. In one of the algorithms, prediction is made by estimating intensity value variations in four directions and their reciprocals are used to make prediction of unknown pixel. This algorithm captures local characteristics of the unknown pixel well as it uses only a small number of neighborhood pixels. The other algorithm finds slope as the relative intensity-value variations and classifies image pixels in fourteen bins by classifying the slope in the same number of bins. LS based predictors are estimated for pixels belonging to each of the bins and hence the they represent global characteristics of these pixels. Since one algorithm takes care of local characteristics while the other one represents global feature, we propose a switching method for these two algorithms that takes advance of both the algorithms. Switching is done on a pixel-by-pixel basis and the same gives approximately 0.10 bpp better performance as compared to some of the computationally complex methods reported in literature at a lower computational complexity. © 2012 IEEE.

2012 IEEE I2MTC - International Instrumentation and Measurement Technology Conference, Proceedings

A lossless image prediction algorithm using slope estimation and least square optimization

The temperature dependent current transport properties of nonpolar a-plane (11 2 0) InN/GaN heterostructure Schottky junction were investigated. The barrier height ( b) and ideally factor (η) estimated from the thermionic emission (TE) model were found to be temperature dependent in nature. The conventional Richardson plot of the ln(I s/T 2) versus 1/kT has two regions: the first region (150-300 K) and the second region (350-500 K). The values of Richardson constant (A +) obtained from this plot are found to be lower than the theoretical value of n-type GaN. The variation in the barrier heights was explained by a double Gaussian distribution with mean barrier height values ( b ) of 1.17 and 0.69 eV with standard deviation (σ s) of 0.17 and 0.098 V, respectively. The modified Richardson plot in the temperature range 350-500 K gives the Richardson constant which is close to the theoretical value of n-type GaN. Hence, the current mechanism is explained by TE by assuming the Gaussian distribution of barrier height. At low temperature 150-300 K, the absence of temperature dependent tunneling parameters indicates the tunneling assisted current transport mechanism. © 2012 American Institute of Physics.

Fulltext

Journal of Applied Physics

Current transport in nonpolar a-plane InN/GaN heterostructures Schottky junction

Hexagonal Ge3N4 layer was prepared on Ge surface by in situ direct atomic source nitridation and it is promising buffer layer to grow GaN on Ge (111). The valence band offset (VBO) of GaN/Ge3N4/Ge heterojunctions is determined by X-ray photoemission spectroscopy. The valence band (VB) of Ge3N4 is found to be 0.38±0.04eV above the GaN valance band and 1.14±0.04eV below the Ge. The GaN/Ge3N4 and Ge3N4/Ge are found type-II and type-I heterojunctions, respectively. The exact measurements of the VBO and conduction band offset (CBO) are important for use of GaN/Ge3N4/Ge (111) heterosystems. © 2012 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Physica Status Solidi (B) Basic Research

Determination of MBE grown wurtzite GaN/Ge3N4/Ge heterojunctions band offset by X-ray photoelectron spectroscopy

Ultra thin films of pure β-Si 3N 4 (0001) were grown on Si (111) surface by exposing the surface to radio- frequency nitrogen plasma with a high content of nitrogen atoms. Using β-Si 3N 4 layer as a buffer layer, GaN epilayers were grown on Si (111) substrate by plasma-assisted molecular beam epitaxy. The valence band offset (VBO) of GaN/β-Si 3N 4/Si heterojunctions is determined by X-ray photoemission spectroscopy. The VBO at the β-Si3N4 / Si interface was determined by valence-band photoelectron spectra to be 1.84 eV. The valence band of GaN is found to be 0.41 ± 0.05 eV below that of β-Si 3N 4 and a type-II heterojunction. The conduction band offset was deduced to be ~ 2.36 eV, and a change of the interface dipole of 1.29 eV was observed for GaN/β-Si 3N 4 interface formation. © 2012 Elsevier B.V. All rights reserved.

Thin Solid Films

Valence band offset at GaN/β-Si 3N 4 and β-Si 3N 4/Si(111) heterojunctions formed by plasma-assisted molecular beam epitaxy

We present the study involving the dependence of carrier concentration of InN films, grown on GaN templates using the plasma assisted molecular beam epitaxy system, on growth temperature. The influence of InN carrier concentration on the electrical transport behavior of InN/GaN heterostructure based Schottky junctions is also discussed. The optical absorption edge of InN film was found to be strongly dependent on carrier concentration, and was described by Kane's k.p model, with non-parabolic dispersion relation for carrier in the conduction band. The position of the Fermi-level in InN films was modulated by the carrier concentration in the InN films. The barrier height of the heterojunctions as estimated from I-V characteristic was also found to be dependent on the carrier concentration of InN. © 2012 Elsevier Ltd. All rights reserved.