Limits of compensation in a failed antenna array

In large antenna arrays, the possibility of occurrence of faults in some of the radiating elements cannot be precluded at all times. In such situations, the radiation pattern of the array gets distorted, mostly with an increase in sidelobe level and decrease in gain. Although it is not possible to restore the pattern fully by rearranging the excitations of the functioning elements, compensation methods have been reported in the literature for restoring one performance parameter of the array and making a trade‐off on some other parameter. In this article, we have made a study on the tolerance level of this compensation process. One part of the study deals with the thinning in the failed array, that is, to find a limit on the minimum number of functioning elements of the array that can restore the digital beamforming of the failed array. The second part of study deals with finding the maximum number of element failures that can be compensated. The study was carried out by optimizing the amplitude excitations of the failed array. Instead of classical optimization techniques, particle swarm optimization was used for the compensation process. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:635–645, 2014.     

An efficient bi-layer content based image retrieval system

Multimedia Tools and Applications - Large amount of multi-media content, generated by various image capturing devices, is shared and downloaded by millions of users across the globe, every second....     

A parallel computational approach for similarity search using Bloom filters

Finding similar items in a large and unstructured dataset is a challenging task in many applications of data science, such as searching, indexing, and retrieval. With the increasing data volume and demand for real time responses, similarity search has gained much consideration. In this paper, a parallel computational approach for similarity search using Bloom filters (PCASSB) has been proposed, which uses Bloom filter for the representation of features of document and comparison with user's query. Query features are stored in integer query array (^IQ_A), an array of integer. The PCASSB, an approximate similarity search technique, has been implemented on graphics processing unit with compute unified device architecture as the programming platform. To compute the similarity score between query and reference dataset, Dice coefficient has been used as a baseline method. The accuracy of the results generated by PCASSB is compared with the baseline method and other state‐of‐the‐art methods. The experimental results show that the proposed technique is quite effective in processing large number of text documents as it takes less computational time.     

Investigations on fractal frequency selective diaphragms in rectangular waveguide

In this article, self‐similarity and space‐filling properties of fractal structures are explored as frequency selective diaphragms in rectangular waveguide, which can find applications in the design of compact, lightweight, and multiband waveguide filters with better out‐of‐band rejection ratio. Some self‐affine fractal structures, based on Sierpinski gasket and plus shape fractals, are proposed, and the effect of scaling factor on the location of transmission bands is investigated. Self‐similar structures like Hilbert curve, Koch curve, and Minkowski fractals are shown to be efficient in reducing resonant frequency of the diaphragm. Numerical results are presented along with the results obtained from HFSS, which show a good agreement. A typical application of the fractal diaphragm in the design of waveguide bandstop filter has also been demonstrated. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Reliability analysis of a system with a mixture of warm and cold standby

A single-server two-unit standby system with two modes of each unit—normal and total failure—is considered. The standby units are repeatedly interconverted after a random time from warm to cold and cold to warm. Upon failure of the operative unit, the standby unit, if it is warm, starts to operate instantaneously; otherwise, the system goes down until the cold standby starts to operate. System failure occurs when both units fail totally. Identifying the system at suitable regenerative epochs, the integral equations are set up and the expressions for reliability and mean time to system failure (MTSF) are obtained. The graphical behaviour of MTSF is also studied in a particular case.     

Profit analysis of two-unit priority standby system with rest period of the operator

This paper deals with profit analysis of a single-server two-unit (one priority and the other ordinary) cold standby system with two modes—normal and total failure. The priority unit gets preference both for operation and repair. After working a random amount of time, the operator of the system needs rest for a random amount of time and during the rest period of the operator the system becomes down but not failed. the system failure occurs when both the units are in total failure mode. Identifying the system at suitable regenerative epochs, the integral equations are set up for the probabilities of system being in the ‘up’, ‘down’ or ‘failed’ state and to solve these equations Laplace transform technique is adopted. Various reliability characteristics are obtained to carry out the cost-benefit analysis and numerical results pertaining to particular cases are also presented.     

Cost analysis of a three-unit standby system subject to random shocks and linearly increasing failure rates

This paper deals with the cost analysis of a single-server three identical unit cold standby system. The operating unit is subject to random shocks occurring from time to time. Due to each shock it may happen with a fixed known probability that (i) the operating unit is not at all affected, (ii) the failure rate of the unit increases and the unit is said to work in quasi-normal mode, and (iii) the operating unit fails totally. Failure time distributions of the operative unit are taken to be Rayleigh with different parameters while the repair and shock time distributions are negative exponentials. The system is observed at suitable regenerative epochs in order to obtain various interesting measures of system effectiveness.