An evaluation of self-adjusting binary search tree techniques

Much has been said in praise of self-adjusting data structures, particularly self-adjusting binary search trees. Self-adjusting trees are most suited to skewed key-access distributions as the techniques attempt to place the most commonly accessed keys near the root of the tree. Theoretical bounds on worst-case and amortized performance (i.e. performance over a sequence of operations) have been derived which compare well with those for optimal binary search trees. In this paper, we compare the performance of three different techniques for self-adjusting trees with that of AVL and random binary search trees. Comparisons are made for various tree sizes, levels of key-access-frequency skewness and ratios of insertions and deletions to searches. The results show that, because of the high cost of maintaining self-adjusting trees, in almost all cases the AVL tree outperforms all the self-adjusting trees and in many cases even a random binary search tree has better performance, in terms of CPU time, than any of the self-adjusting trees. Self-adjusting trees seem to perform best in a highly dynamic environment, contrary to intuition.     

On the choice of spatial and categorical scale in remote sensing land cover classification

Our interest in this paper is on the choice of spatial and categorical scale, and their interaction, in creating classifications of land cover from remotely sensed measurements. We note that in discussing categorical scale, the concept of spatial scale naturally arises, and in discussing spatial scale, the issue of aggregation of measurements must be considered. Therefore, and working towards an ultimate goal of producing multiscale, multigranular characterizations of land cover, we address here successively and in a cumulative fashion the topics of (1) aggregation of measurements across multiple scales, (2) adaptive choice of spatial scale, and (3) adaptive choice of categorical scale jointly with spatial scale. We show that the use of statistical finite mixture models with groups of original pixel-scale measurements, at successive spatial scales, offers improved pixel-wise classification accuracy as compared to the commonly used technique of label aggregation. We then show how a statistical model selection strategy may be used with the finite mixture models to provide a data-adaptive choice of spatial scale, varying by location (i.e., multiscale), from which classifications at least as accurate as those of any single spatial scale may be achieved. Finally, we extend this paradigm to allow for jointly adaptive selection of spatial and categorical scale. Our emphasis throughout is on the empirical quantification of the role of the various elements above, and a comparison of their performance with standard methods, using various artificial landscapes. The methods proposed in this paper should be useful for a variety of scale-related land cover classification tasks.     

Modeling of the zero-bias resistance-area product of long wavelength infrared HgCdTe-on-Si diodes fabricated from molecular beam epitaxy-grown epitaxial layers

The electrical effects of dislocations has been studied by modeling zero-bias resistance-area product (R₀A) of long wavelength infrared diodes fabricated in molecular beam epitaxy (MBE)-grown HgCdTe-Si epitaxial films. Results show that dislocations influence both 40 K and 78 K R₀A products in high dislocation density (HgCdTe/Si) material. In low dislocation density samples (HgCdTe/CdZnTe), the variations in 78 K R₀A are limited by the composition (x) variations in Hg_1-xCd_xTe material, whereas dislocation contribution dominates the variations at 40 K. The origin of relatively large spread in 40 K R₀A in both types of samples is traced to the statistical variations in the core charges of dislocations. It is concluded that additional alternatives besides the reduction of dislocation density (such as control of core charges), may also need attention in order to make Si a viable substrate material for the growth of HgCdTe epitaxial layers suitable for devices operating at 40 K.     

Liquid-phase sintering of TiN-enriched T15-grade high-speed steels and their mechanical properties

The present investigation is an attempt to develop composites based on high-speed steel through liquid-phase sintering route using a powder metallurgical technique. Water-atomised annealed T15-grade HSS powder, lubricant and various mass percents of TiN (0–8%) were blended and axially compacted into green pellets at 850 MPa at room temperature. During sintering studies carried out in vacuum (10^?2 torr), optimum temperature for full densification was determined for each composition. Only full dense sintered samples (density ≥98% theoretical) were selected for further heat treatment and the evaluation of mechanical properties. Mechanical properties like hardness, transverse rupture strength and hot compressive yield strength were evaluated. Both qualitative and quantitative metallographic studies were carried out and chemical analysis of various phases in sintered as well as heat-treated composites were determined using SEM-EDX. The results confirm that fully dense composites containing up to 2% TiN exhibit equivalent mechanical properties, although some differences in service behaviour e.g. wear resistance are to be expected.     

Depth from defocus: A spatial domain approach

A new method named STM is described for determining distance of objects and rapid autofocusing of camera systems. STM uses image defocus information and is based on a new Spatial-Domain Convolution/Deconvolution Transform. The method requires only two images taken with different camera parameters such as lens position, focal length, and aperture diameter. Both images can be arbitrarily blurred and neither of them needs to be a focused image. Therefore STM is very fast in comparison with Depth-from-Focus methods which search for the lens position or focal length of best focus. The method involves simple local operations and can be easily implemented in parallel to obtain the depth-map of a scene. STM has been implemented on an actual camera system named SPARCS. Experiments on the performance of STM and their results on real-world planar objects are presented. The results indicate that the accuracy of STM compares well with Depth-from-Focus methods and is useful in practical applications. The utility of the method is demonstrated for rapid autofocusing of electronic cameras.     

Effect of rotation on the heat penetration characteristics of thermally processed tuna in oil in retort pouches

Tuna in oil was processed in retort pouches (20 × 17 cm) to a, F₀ value of 10. Heat penetration characteristics were determined using a rotary retort to an F₀ value of 10 and the results compared with a stationary retort. For studying the changes in heat penetration during rotation, tuna in oil was packed into retort pouches, subjected to different rotation speeds (2, 4 and 6 r.p.m.) and thermally processed to the same F₀ value. For the same F₀ value of 10, although there was a reduction in process time with increasing rotation speed up to 6 r.p.m., the magnitude of the reduction in processing time decreased with increase in speed of rotation. However up to 2 r.p.m. there was a considerable reduction in process time.     

Transcritical CO2 Heat Pump Dryer: Part 1. Mathematical Model and Simulation

In this study, a mathematical model and simulation code has been developed to investigate the performance of a transcritical CO₂ heat pump dryer. The model takes into account detailed heat and mass transfer and pressure drop phenomena occurring in each component of the system. To take care of the variable heat transfer properties, the heat exchanger components were divided into several infinitesimal segments to examine the state, heat and mass balance and pressure drop for both refrigerant and air, and hence accurate results are expected. In Part 2 of the article, the model developed has been validated with experimental data and then the model was used to investigate effects of important operating parameters on the performance.     

Contribution of dislocations to the zero-bias resistance-area product of LWIR HgCdTe photodiodes at low temperatures

Dislocations in the base material are shown to significantly influence zero-bias impedance of long wavelength infrared HgCdTe photodiodes by acting as a shunt, and by influencing their minority carrier lifetime. Consequently, temperature dependence of zero-bias resistance-area product (R/sub 0/A) of these photodiodes can be described very well over a broad temperature range, down to 25 K, after taking into account the temperature and dislocation dependence of the minority carrier lifetime in addition to the shunt resistance contribution of dislocations. Further, based on the theoretical prediction that the shunt resistance contribution of a dislocation is a sensitive function of the magnitude of the charge around its core, it is proposed that the scatter of the R/sub 0/A experimental data in diodes with dislocation densities of less than 1/spl times/10/sup 7/ cm/sup -2/ could be the result of statistical variations in the charge around the core of dislocations. Interaction of dislocations among themselves may be responsible for deviations above dislocation densities of 1/spl times/10/sup 7/ cm/sup -2/.     

Endophthalmitis in eyes following vitrectomy

The authors describe two patients who underwent pars plana vitrectomy for nonclearing vitreous hemorrhage. Both patients had severe pain, increased intraocular pressure, and orbital swelling. The anterior chamber became flat in a phakic eye. The infection progressed rapidly, and ultimately evisceration was required in both cases. The presence of a flat anterior chamber in gas-filled, phakic eyes and a severe orbital inflammatory reaction in the early postoperative period should alert the physician to the possibility of endophthalmitis.     

Route optimization in mobile ATM networks

This paper presents an algorithm for optimizing the route of a connection that becomes suboptimal due to operations such as handoffs and location-based reroutes, and applies this algorithm to the handoff management problem in mobile ATM (Asynchronous Transfer Mode) networks based on the PNNI (Private Network-to-Network Interface) standard. The route optimization algorithm uses hierarchical route information of the connection and summarized topology and loading information of the network to determine a “crossover node” such that adjusting the connection from that crossover node results in an optimally routed connection. Handoff management schemes that perform local rerouting of connections have been proposed in order to support fast handoffs. These methods result in suboptimally routed connections. In this paper, we demonstrate how this route optimization algorithm can be used to optimize the route of a connection after such a handoff is executed, as the second phase of a two-phase handoff scheme. This route optimization procedure can also be executed as part of the handoff procedure resulting in a one-phase handoff scheme. Applying this route optimization algorithm, we propose two one-phase schemes, the one-phase optimal scheme and the one-phase minimal scheme. A comparative performance analysis of one- and two-phase handoff schemes is presented. Measures of comparison are handoff latency and the amount of network resources used by a connection. Handoff latency in the one-phase optimal scheme is greater than that in the two-phase schemes, and handoff latency in the one-phase minimal scheme is smaller than that in the two-phase schemes. The one-phase methods show a significant increase in efficiency of the connection compared to the two-phase methods. This revised version was published online in June 2006 with corrections to the Cover Date.