Red enhanced YAG:Ce,Pr nanophosphor for white LEDs

Rare earth ion Pr³⁺ was co doped in yellow emitting YAG:Ce nanophosphor to introduce red emission for improving colour rendering property of white LED. Nanocrystalline YAG:Ce, YAG:Ce, Pr was synthesised by a single step auto combustion process. Photoluminescence (PL) emission spectra of YAG:Ce, Pr nanophosphor, when excited by 460?nm blue light, exhibited sharp red emission peaks at 610?nm from Pr³⁺ ions in addition to broad yellow emission from Ce³⁺ peaking at 540?nm due to charge transfer from excited Ce³⁺ 5d band to ³P _J /¹D₂ level of Pr³⁺. Ce³⁺ (yellow) and Pr³⁺ (red) emission decays in tens of nanoseconds and microseconds, respectively. Electroluminescence spectra of blue LED with developed phosphor layer shows colour coordinates (0.30, 0.39) close to ideal white light.     

Fatigue and dielectric properties of undoped and Ce doped PZT thin films

Abstract

Ce doping improves the ferroelectric properties of sol-gel derived PZT thin films by facilitating easier domain wall movement. It also decreases the leakage current densities by reducing the concentration of free carriers through a decrease in concentration of Pb and O vacancies. Ce-PZT films retain good dielectric dispersion characteristics since the concentration of defects and defect dipoles are reduced. Ce doping dramatically improves the fatigue resistance of PZT thin films. We have studied the frequency dependence of fatigue behavior and shown that the loss of polarization due to fatigue follows a universal scaling behavior with N/f², where N is the number of the switching cycles and f is the frequency. The origin of the scaling is attributed to the drift of oxygen vacancies, which is the rate limiting process in the growth of the interface layer responsible for fatigue. Empirical fits for both undoped and cerium doped samples show that switchable polarization follows a stretched exponential decay with time or N/f. Cerium doping is believed to improve fatigue resistance by impeding the motion of oxygen vacancies.     

On the density and discrepancy of a 2D point set with applications to thermal analysis of VLSI chips

In this era of giga-scale integration, thermal analysis has become one of the hot topics in VLSI chip design. Active thermal sources may be abstracted as a set of weighted points on a 2D chip-floor. The conventional notion of discrepancy that deals with the congestion properties of a set of scattered points may not be able to capture properly all real-life instances in this context. In this paper, we have introduced a new concept, called the density of a region to study some of the properties of the distribution of these weighted points. We prove several counter-intuitive results concerning the properties of the regions that have maximum or minimum density. We then outline algorithms for recognizing these regions. We also compare the attributes of density with the existing concept of discrepancy.     

Load sharing and power quality enhanced operation of a distributed microgrid

Control methods for proper load sharing between parallel converters connected in a microgrid and supplied by distributed generators (DGs) are described. It is assumed that the microgrid spans a large area and it supplies loads in both in grid-connected and islanded modes. A control strategy is proposed to improve power quality and proper load sharing in both islanded and grid-connected modes. It is assumed that each of the DGs has a local load connected to it which can be unbalanced and/or non-linear. The DGs compensate the effects of unbalance and non-linearity of the local loads. Common loads are also connected to the microgrid, which are supplied by the utility grid under normal conditions. However, during islanding, each of the DGs supplies its local load and shares the common load through droop characteristics. Both impedance and motor loads are considered to verify the system response. The efficacy of the controller has been validated through simulation for various operating conditions using PSCAD. It has been found through simulation that the total harmonic distortion (THD) of the microgrid voltage is ~10% and the negative and zero sequence components are ~20% of the positive sequence component before compensation. After compensation, the THD remains <0.5%, whereas negative and zero sequence components of the voltages remain <0.02% of the positive sequence component.     

Control of internal fungi of sorghum by fumigation

Laboratory methods of fumigation of food commodities and surface sterilization of grains have been described. Out of eight fumigants tested ethylene oxide, methyl bromide, sulphur dioxide, EDB-MB mixture could give a hundred per cent control of internal fungi of sorghum. Ethylene oxide reduced the viability totally, while sulphur dioxide at 64 mg/l maintained 75 per cent viability. There was increase in the germination percentage over the control with the treatments of ethylene dibromide and phosphine.     

Modeling Color Properties of Tiled Displays

The concept of tiled displays can be successful only if such displays are made to look like a single display perceptually. The two issues that need to be solved to achieve this goal are geometric correction and color seamlessness of images spanning across tiles. Geometric correction algorithms borrow pin‐hole camera models to model projector display geometry. In this paper, we introduce an abstract modeling function that describes the color seen by a viewer when displayed by a display device. Though this function can be used to model color displayed by any common display device, in this paper, we use it to model color in multiprojector display systems. We use the model to explain the reasons for different types of color variations in a multiprojector display, to compare different color correction algorithms, and to derive such algorithms directly from the model.     

A connectionist model for category perception: theory andimplementation

A connectionist model for learning and recognizing objects (or object classes) is presented. The learning and recognition system uses confidence values for the presence of a feature. The network can recognize multiple objects simultaneously when the corresponding overlapped feature train is presented at the input. An error function is defined, and it is minimized for obtaining the optimal set of object classes. The model is capable of learning each individual object in the supervised mode. The theory of learning is developed based on some probabilistic measures. Experimental results are presented. The model can be applied for the detection of multiple objects occluding each other.     

Some properties and fast algorithms of slant transform in image processing

A first order stationary Markov process model has been considered for image processing problems. A relative performance measure of unitary transforms to image data has been defined. It has been proved that the slant transform is superior to Walsh-Hadamard transform in this relative performance measure for positive correlation under the assumed model. A lower bound of relative performance has also been found. Furthermore, fast algorithms for computing diagonal elements of any slant transformed matrix have been presented. Finally, it has been shown how slant transform can be modified to improve the relative performance.     

Performance bound of Walsh-Hadamard transform for feature selection and compression and some related fast algorithms

A fast algorithm of finding the diagonal elements of the covariance matrix of the two-dimensional Walsh-Hadamard (WH) transform of data is described. Its usefulness and other interesting properties of the WH transform are discussed. The performance of the WH transform is compared with the Karhunen-Loeve transform for a first-order stationary Markov process.