Department of Electrical Engineering

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Whenever we compute control using digital computer, the states measured need to be converted to digital word before processing in the computer. This conversion gives rise to quantization error in state measurement which in turn affects the applied control to the plant. This would cause the system dynamics to deviate from the behaviour predicted by any theoretical analysis which does not consider the effect of such quantization. Here an analysis has been presented taking into consideration the error due to quantization for Quasi Sliding Mode Control with state feedback. © 2011 IEEE.

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IECON Proceedings (Industrial Electronics Conference)

Quasi sliding mode control with quantization in state measurement

2,2′-(Benzo[c][1,2,5]thiadiazol-4,7-diyl)-4,4′-dialkyl-bis(4H- dithieno[3,2-b:2′,3′-d]pyrrole) (DTP-BTD-DTP) donor-acceptor-donor (D-A-D) and 4-alkyl-2,6-bis(benzo[c][1,2,5]thiadiazol-4-yl)-4H-dithieno[3,2-b: 2′,3′-d]pyrrole (BTD-DTP-BTD) acceptor-donor-acceptor (A-D-A) triads, with or without additional alkylation in the DTP 6- or BTD 7-positions, respectively, have been synthesized using Stille coupling reactions, characterized using UV-vis absorption spectroscopy and electrochemistry, modeled using density functional theory calculations, and used as charge-transport materials in field-effect transistors. The choice of alkyl substitution pattern has only minor effects on the optical and redox behavior but can be used to modify the thermal properties and solubility of these compounds. The D-A-D and A-D-A triads show long-wavelength absorption maxima at 566-588 and 517-521 nm, respectively, in solution. These transitions are attributed to excitation from a delocalized HOMO to a BTD-localized LUMO and, accordingly, are bathochromically shifted from those of analogous compounds in which the BDT moieties are replaced by benzene rings (393-417 nm). The triads are oxidized at potentials of +0.01 to +0.37 V vs ferrocenium/ferrocene and are reduced at potentials of -1.95 to -1.74 V, with the D-A-D species being both the most easily oxidized and most easily reduced. Field-effect transistors based on solution-processed films of some of the triads showed p-channel behavior; the highest average hole mobility value measured was 5.9 × 10-3 cm2 V -1 s-1 for 2,2′-(benzo[c][1,2,5]thiadiazol-4,7-diyl) -4,4′-di-n-dodecyl-bis(4H-dithieno[3,2-b:2′,3′-d]pyrrole) and was accompanied by an on/off current ratio of ca. 103. © 2011 American Chemical Society.

Journal of Physical Chemistry C

Benzothiadiazole-dithienopyrrole donor-acceptor-donor and acceptor-donor-acceptor triads: Synthesis and optical, electrochemical, and charge-transport properties

In this chapter, a nonlinear sliding surface is discussed to improve the transient response for general discrete-time multiple input multiple output linear systems with matched perturbations. The nonlinear surface modulates the closed loop damping ratio from an initial low to final high value to achieve better transient performance. The control law is based on the discrete-time sliding mode equivalent control and thus eliminates chattering. The control law is proposed based on two approaches: (1) reaching law based approach which needs only disturbance bounds and (2) disturbance observer based approach. Multirate output feedback is used to relax the need of the entire state vector for implementation of the control law. A possible extension of the nonlinear surface to input-delay systems is also presented. © 2011 Springer-Verlag Berlin Heidelberg.

Lecture Notes in Control and Information Sciences

Discrete-time sliding mode control using output feedback and nonlinear surface

This paper presents a new image interpolation technique for enhancement of spatial resolution of images. The proposed algorithm uses the switching of existing Soft-decision Adaptive Interpolation (SAI) algorithm and Single Pass Interpolation Algorithm (SPIA) methods. We learn the error pattern in the interpolation process of SAI method and SPIA Method after interpolating downsampled version of LR image. Then we deviced a mechanism to correct the error pattern. Emperically we found that SAI methods works better on smooth images (variation among the pixels is less) while SPIA method works better on detailed images (more variation among the pixels), because of the type of pixels used in the interpolation. So, a hybrid scheme of combining SAI method and SPIA method is proposed for best prediction of high resolution (HR) image. The proposed algorithm produces the best results in different varieties of images in terms of both PSNR measurement and subjective visual quality. © 2011 IEEE.

Proceedings - IEEE International Symposium on Circuits and Systems

An efficient image interpolation algorithm based upon the switching and self learned characteristics for natural images

Photoluminescence (PL) of high quality GaN epitaxial layer grown on β-Si3N4/Si (1 1 1) substrate using nitridationannealingnitridation method by plasma-assisted molecular beam epitaxy (PA-MBE) was investigated in the range of 5300 K. Crystallinity of GaN epilayers was evaluated by high resolution X-ray diffraction (HRXRD) and surface morphology by Atomic Force Microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). The temperature-dependent photoluminescence spectra showed an anomalous behaviour with an 'S-like' shape of free exciton (FX) emission peaks. Distant shallow donoracceptor pair (DAP) line peak at approximately 3.285 eV was also observed at 5 K, followed by LO replica sidebands separated by 91 meV. The activation energy of the free exciton for GaN epilayers was also evaluated to be ∼27.8±0.7 meV from the temperature-dependent PL studies. Low carrier concentrations were observed ∼4.5±2×1017 cm-3 by measurements and it indicates the silicon nitride layer, which not only acts as a growth buffer layer, but also effectively prevents Si diffusion from the substrate to GaN epilayers. The absence of yellow band emission at around 2.2 eV signifies the high quality of film. The tensile stress in GaN film calculated by the thermal stress model agrees very well with that derived from Raman spectroscopy. © 2010 Elsevier B.V.

Journal of Luminescence

Temperature-dependent photoluminescence of GaN grown on β-Si 3N4/Si (1 1 1) by plasma-assisted MBE

The present work explores the electrical transport and infrared (IR) photoresponse properties of InN nanorods (NRs)/n-Si heterojunction grown by plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN NRs is verified by the X-ray diffraction and transmission electron microscopy. Raman measurements show that these wurtzite InN NRs have sharp peaks E 2(high) at 490.2 cm -1 and A1 (LO) at 591 cm -1. The current transport mechanism of the NRs is limited by three types of mechanisms depending on applied bias voltages. The electrical transport properties of the device were studied in the range of 80 to 450 K. The faster rise and decay time indicate that the InN NRs/n-Si heterojunction is highly sensitive to IR light. © 2011 Kumar et al.

Fulltext

Nanoscale Research Letters

Transport and infrared photoresponse properties of InN nanorods/Si heterojunction

InN quantum dots (QDs) were grown on Si (111) by epitaxial Stranski-Krastanow growth mode using plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN QDs was verified by the x-ray diffraction and transmission electron microscopy. Scanning tunneling microscopy has been used to probe the structural aspects of QDs. A surface bandgap of InN QDs was estimated from scanning tunneling spectroscopy (STS) I-V curves and found that it is strongly dependent on the size of QDs. The observed size-dependent STS bandgap energy shifts with diameter and height were theoretical explained based on an effective mass approximation with finite-depth square-well potential model. © 2011 American Institute of Physics.

Journal of Applied Physics

Size dependent bandgap of molecular beam epitaxy grown InN quantum dots measured by scanning tunneling spectroscopy

Comparative studies have been carried out on the performance of the photovoltaic devices with dissimilar shapes of the InN nanostructures fabricated on p-Si (100). The devices fabricated with the nanodots show a superior performance compared to the devices fabricated with the nanorods. The discussions have been carried out on the superior junction property, larger effective junction area and inherent random pyramidal topographical texture of the cell fabricated with nanodots. Such single junction devices exhibit a promising fill factor and external quantum efficiency of 38% and 27%, respectively, under concentrated AM1.5 illumination. © 2012 Materials Research Society.

Materials Research Society Symposium Proceedings

Comparative studies on photovoltaic performance of InN nanostructures/p- Si(100) heterojunction devices grown by molecular beam epitaxy

Here we show how the electromechanical properties of silicon nanowires (NWs) are modified when they are subjected to extreme mechanical deformations (buckling and buckling mode transitions), such as those appearing in flexible devices. Flexible devices are prone to frequent dynamic stress variations, especially buckling, while the small size of NWs could give them an advantage as ultra-sensitive electromechanical stress sensors embedded in such devices. We evaluated the NWs post-buckling behavior and the effects of buckling mode transition on their piezoresistive gauge factor (GF). Polycrystalline silicon NWs were embedded in SiO2 microbridges to facilitate concurrent monitoring of their electrical resistance without problematic interference, while an external stylus performed controlled deformations of the microbridges. At points of instability, the abrupt change in the buckling configuration of the microbridge corresponded to a sharp resistance change in the embedded NWs, without altering the NWs' GF. These results also highlight the importance of strategically positioning the NW in the devices, since electrical monitoring of buckling mode transitions is feasible when the deformations impact a region where the NW is placed. The highly flexible NWs also exhibited unusually large fracture strength, sustaining tensile strains up to 5.6%; this will prove valuable in demanding flexible sensors. © 2010 IOP Publishing Ltd.

Nanotechnology

The electromechanical response of silicon nanowires to buckling mode transitions

The work establishes the asymptotic rate of decay for the probability of node isolation in bounded wireless sensor networks, in the high density regime. In this regime, the exposition reveals the role of the most isolated neighborhoods of the bounding region in exponentially increasing the average probability of isolation. The problem is treated for a large family of random spatial distributions of nodes, random shapes of node coverage areas and random topography of the network's bounding region. Different examples are presented to insightfully describe the detrimental effect of boundedness in network isolation. Finally we address different aspects relating to extremely isolating bounding regions and densities that vary exponentially in time. {\textcopyright} 2010 IEEE.