Fabrication and Electromechanical Characterization of Silver-Clad BSCCO Tapes

The powder-in-tube technique consisting of industrial processes such as wire drawing and rolling has been widely used to fabricate superconducting tapes. In the present investigation a novel technique was adopted to fabricate BSCCO 2223 tapes. Instead of wire drawing, the silver billet was reduced in size by groove rolling. Stress conditions during groove rolling were analyzed and appropriate changes were incorporated to optimize the deformation process. Subsequent thermomechanical treatment resulted in tapes with average critical current densities of 18,000 A/cm². Phase development and microstructural evolution during the thermomechanical treatment were studied using XRD, SEM, and TEM. The electromechanical properties of monofilament and composite BSCCO tapes were evaluated by subjecting them to in situ tensile tests. The strain tolerance of the composite was found to be better than that of the monofilament BSCCO tape.     

Pulse oximetry theory and calibration for low saturations

Pulse oximetry is a widely used technique in biomedical optics, but currently available pulse oximeters rely on empirical calibration approaches, which perform poorly at low saturations. We present an exact solution for pulse oximetry and show how this can be used as the basis for the development of a semiempirical calibration approach that may be useful, especially at low saturations and variable probe geometries. This new approach was experimentally tested against traditional empirical calibration techniques on transmission pulse oximetry for monitoring of fetal sheep using a minimally invasive spiral probe. The results open the way for the development of more accurate pulse oximetry.     

Segmentation and range sensing using a moving-aperture lens

The use of a novel motorized lens to perform segmentation of image sequences is presented in this paper. The lens has the effect of introducing small, repeating movements of the camera center so that objects appear to translate in the image by an amount that depends on the distance from the plane of focus. For a stationary scene, optical flow magnitudes are therefore directly related to three-dimensional object distance from the observer. We describe a segmentation procedure that exploits these controlled observer movements and present experimental results that demonstrate the successful extraction of objects at different depths. Potential applications of our approach include image compositing, teleconferencing, and range estimation.Received: 4 July 2002, Accepted: 16 December 2002, Published online: 23 July 2003 Correspondence to: Amy E. Bell     

Microstructural and magnetic studies on P/M processed (Nd14.9Dy1.9)(Fe65.0Co8.0Cu1.0Ga1.0Nb0.7) B7.5 alloy

Sintered samples of (Nd_14.9 Dy_1.9) (Fe₆₅ Co₈ Cu_1.0 Ga_1.0 Nb_0.7)B_7.5 were prepared and subjected to stepwise annealing in the temperature range 875 K–675 K. The XRD and metallographic (optical and electron microscopy) studies reveal a multi-phase microstructure with each phase showing different solubility of the alloying additions. This alloy has T _C of 705 K with an intrinsic coercivity of 1000 kA/m and energy product of 250 kJ/m³ at RT. Solubility of Co into the matrix phase and that of Ga and Cu into the Nd-rich grain boundary phase are considered to be the main contributing factors for the significant enhancement in T _C and H _ci respectively of the multi-component alloy when compared to those of ternary NdFeB, wherein H _ci = 720 kA/m and T _C = 585 K.     

Inner-Circle Consistency for Wireless Ad Hoc Networks

This paper proposes and evaluates strategies to build reliable and secure wireless ad hoc networks. Our contribution is based on the notion of inner-circle consistency, where local node interaction is used to neutralize errors/attacks at the source, both preventing errors/attacks from propagating in the network and improving the fidelity of the propagated information. We achieve this goal by combining statistical (a proposed fault-tolerant duster algorithm) and security (threshold cryptography) techniques with application-aware checks to exploit the data/computation that is partially and naturally replicated in wireless applications. We have prototyped an inner-circle framework and used it to demonstrate the idea of inner-circle consistency in two significant wireless scenarios: 1) the neutralization of black hole attacks in AODV networks and 2) the neutralization of sensor errors in a target detection/ localization application executed over a wireless sensor network     

A Multilayer Negative-Refractive-Index Transmission-Line (NRI-TL) Metamaterial Free-Space Lens at X-Band

A volumetric free-space negative-refractive-index (NRI) transmission-line (TL) metamaterial lens is described that employs fully printed interdigitated capacitors and meandered inductors designed to exhibit NRI properties at X-band (8-12 GHz). The volumetric topology is realized in a layer-by-layer fashion without any vias, which facilitates easy and rapid fabrication. The fabricated lens was tested for its transmission and dispersion properties using a free-space X-band measurement system consisting of an Agilent network analyzer, standard gain horn antennas, and Rexolite dielectric lenses fabricated in-house, and showed good correspondence with simulations. The focusing ability of the multilayer NRI-TL lens was also verified using a free-space field probing system based on small shielded-loop antennas affixed to a computer-controlled xyz-translator apparatus. Arguably, these results represent the first experimental evidence of coupling between TL-based metamaterials and sources in free space.     

Long-term trends and decadal solar variability in ozone near the tropopause over the Indian region

To investigate the long-term trends and effects of decadal solar variability in the upper tropospheric ozone, data obtained from the Stratospheric Aerosol and Gas Experiment II (SAGE II) aboard the Earth Radiation Budget Satellite (ERBS) during the period 1985–2005 were analysed using a multifunctional regression model over the Indian region (8–40° N; 65–100° E). Analysis of time series spanning these years shows statistically insignificant trends (at the two-sigma level (95% confidence level)) at upper tropospheric pressure levels (10?16 km). This period covers two solar cycles, one lasting from 1985 to 1995 and the other from 1996 to 2005; these are referred to as decade I and decade II, respectively. Since temporal variation in ozone number density indicates 11 year periodicity, trends are statistically significant when calculated separately during each solar cycle. Trend analysis indicates statistically significant positive trends (0.7 ± 1.7% to 3.9 ± 2.9% year^?1 during decade I, and 2.2 ± 1.6% to 4.5 ± 3.0% year^?1 during decade II). In general, higher ozone trends are observed during decade II. Seasonal variation in trends during decade II shows increasing trends during the pre-monsoon (0.8?3.8% year^?1), monsoon (0.8?7.1% year^?1), and post-monsoon (2.8?8.0% year^?1) seasons. The annually averaged solar signal in ozone is found to be of the order of around??5 ± 4.3% to??13.8 ± 6.7%/(100 sfu). Results obtained in the present study are also compared with those obtained by other researchers.     

Efficient reliability estimate of passive thermal hydraulic safety system with automatic differentiation

An approach for efficient estimation of passive safety system functional reliability has been developed and applied to a simplified model of the passive residual heat transport system typical of sodium cooled fast reactors to demonstrate the reduction in computational time. The method is based on generating linear approximations to the best estimate computer code, using the technique of automatic reverse differentiation. This technique enables determination of linear approximation to the code in a few runs independent of the number of input variables for each response variable. The likely error due to linear approximation is reduced by augmented sampling through best estimate code in the neighborhood of the linear failure surface but in a sub domain where linear approximation error is relatively more. The efficiency of this new approach is compared with importance sampling MCS which uses the linear approximation near the failure region and with Direct Monte-Carlo Simulation. In the importance sampling MCS, variants employing random sampling with Box-Muller algorithm and Markov Chain algorithm are inter-compared. The significance of the results with respect to system reliability is also discussed.     

Closed-Form Solution for System Availability Distribution

Highly reliable systems with long mission time, that can tolerate no down time, have motivated the study of system reliability. The emergence of fault-tolerant computing systems, where small down times may be tolerable, and preventive and corrective maintenance permitted, motivates a revisit to measures like mean availability. Vendors of computer systems are being required to specify the level of availability that will be met by their systems over a finite time interval, and pay a penalty for non-compliance. Since no closed-form solution has been reported in the literature, numerical approaches have often been used to compute systems availability over a finite time, even for simple Markov models. We report a Laplace transform solution for the distribution of availability over a finite interval, for a semi-Markov model. The transform of the distribution is analytically inverted to obtain a closed-form solution for the corresponding Markov model.