Development and Characterization of Novel Alumina Based Ceramic Matrix Composites for Energy Efficient Sliding Applications

Friction, wear, and lubrication have direct influence on performance, reliability, and service life of mechanical systems with moving components. The useful life of these systems and their efficiency can be improved by improving the surface properties/ performance at sliding interfaces. Further, the usage of materials for sliding systems is limited in extreme environments, such as high temperature, and space, etc., due to their limited surface properties. This thesis focuses on the development of a new class of composites with superior surface properties, i.e., low friction and high wear resistance for extreme environmental conditions. Alumina, a well understood material for its tribological performance, is a merit choice for applications where high wear resistance is required, such as pump bearings, seal rings, valve seats, piston components, gears, cutting tool inserts and artificial joints. We propose to develop a novel alumina based ceramic composite to enhance its surface and tribological properties using a powder compaction technique. The newly developed composites will be characterized by X-ray Diffraction (XRD), Fourier Transform Infrared spectroscope (FTIR), Optical microscope, Environmental Scanning Electron Microscope (E-SEM), Goniometer and Surface profilometer. In-situ formation of high temperature stable phases, effect of sintering temperature, and percentage of reinforcement on phase formation will be studied. Investigation of effect of sintering temperature and percentage of reinforcement on density, porosity, and grain size will be conducted. The composites will be characterized for their tribological properties (friction and wear). The mechanisms for modified friction and wear will be proposed. The process parameters and compositions will be optimized. XRD results confirmed the formation of Al18B4O33, and AlB2 and FTIR confirmed the presence of B2O3. Increase in sintering temperature and wt % of boron affected the porosity, grain size, and hardness of the composites. The coefficient of friction was lower for the composites compared to pure alumina ceramic. The coefficient of friction decreased with increase in sintering temperature. The wear mechanism was found to be micro-fracture using ESEM and SEM studies

Long-term morphological and power spectral studies of VHF amplitude scintillations recorded over Waltair (17.7°N, 83.3°E), India

This research reports on recently recorded 250 MHz amplitude scintillations at Waltair (17.7°N, 83.3°E), a low-latitude station in India, using the signals radiated from a geostationary satellite (FLEETSAT, 73°E) during a six-year period (2008 - 2013), which covers extremely low and higher solar activity years (2008 and 2013). The morphological features in terms of local time, month, and season during different geophysical conditions are presented. The scintillation patches (segregated based on their occurrence durations) have shown an increasing trend with the increasing sunspot activity. The scintillation patches with 30-min duration show increasing trends with increasing sunspot activity, and their occurrence frequencies also show increasing trends with increasing sunspot activity. The scintillation activity during disturbed epochs (Kp index lies between 3+ and 9) is found to be less compared to its quiet day counterparts. The plausible mechanisms for these observational results are discussed. In addition, power spectral characteristics, including Fresnel frequency, upper role of frequency and spectral slope of scintillations are calculated and the salient results are presented

Optimized cross-layer forward error correction coding for H.264 AVC video transmission over wireless channels

Forward error correction (FEC) codes that can provide unequal error protection (UEP) have been used recently for video transmission over wireless channels. These video transmission schemes may also benefit from the use of FEC codes both at the application layer (AL) and the physical layer (PL). However, the interaction and optimal setup of UEP FEC codes at the AL and the PL have not been previously investigated. In this paper, we study the cross-layer design of FEC codes at both layers for H.264 video transmission over wireless channels. In our scheme, UEP Luby transform codes are employed at the AL and rate-compatible punctured convolutional codes at the PL. In the proposed scheme, video slices are first prioritized based on their contribution to video quality. Next, we investigate the four combinations of cross-layer FEC schemes at both layers and concurrently optimize their parameters to minimize the video distortion and maximize the peak signal-to-noise ratio. We evaluate the performance of these schemes on four test H.264 video streams and show the superiority of optimized cross-layer FEC design.Peer reviewedElectrical and Computer Engineerin

Experiments with range computations using extrapolation

The natural interval extension (NIE) used widely in interval analysis has the first order convergence property, i.e., the excess width of the range enclosures obtained with the NIE goes down at least linearly with the domain width. Here, we show how range approximations of higher convergence orders can be obtained from the sequence of range enclosures generated with the NIE and uniform subdivision. We combine the well-known Richardson Extrapolation Process (Sidi, A., Practical Extrapolation Methods, Cambridge University Press, Cambridge, 2003) with Brezinski's error control method (Brezinski, C., Error Control in Convergence Acceleration Processes, IMA J. Nunerical Analysis 3 (1983), pp. 65-80) to generate non-validated range approximations to the true range. We demonstrate the proposed method for accelerating the convergence orders on several multidimensional examples, varying from one to six dimensions. These numerical experiments also show that considerable computational savings can be obtained with the proposed procedure. However, the theoretical basis of the proposed method remains to be investigated

Extrapolation based interval approach to compute the frequency responses of non-rational transfer functions with nonlinear parametric dependencies

We consider the problem of computing the frequency response of a non-rational transfer function having uncertainties in the parameters. A complete characterization of the frequency plots of such a transfer function is provided and an efficient and guaranteed algorithm for computing the envelope of the Bode plot using interval analysis (IA) is devised. In particular, it is shown that the range enclosure property of the interval analysis can be used to compute the Bode envelopes of the non-rational transfer function with parametric dependencies. The range enclosures computed using IA are guaranteed to contain the minima and maxima of the function over a given box. The IA is combined with uniform subdivision technique to obtain the range enclosures of desired accuracy. We also show, how the well known Richardson extrapolation technique helps in accelerating the convergence process of the algorithm

Gamma-Delta T Cell Acute Lymphoblastic Leukemia: A Single-Center Experience

Gamma-delta (γδ) T cell neoplasms are a rare disease entity characterized by an aggressive clinical course [1,2]. The management of these neoplasms associated with high incidence of induction failures and poor clinical outcomes [3]. Here we present two cases of gamma-delta T cell acute lymphoblastic leukemia (γδ T-ALL) successfully treated with chemotherapy and allogeneic stem cell transplant at our institution. We also review the literature and summarize what is known about this disease. In our experience, induction chemotherapy followed by allogeneic stem cell transplantation has been an effective strategy in producing durable remissions.</p