Discovery of context-specific ranking functions for effective information retrieval using genetic programming

The Internet and corporate intranets have brought a lot of information. People usually resort to search engines to find required information. However, these systems tend to use only one fixed ranking strategy regardless of the contexts. This poses serious performance problems when characteristics of different users, queries, and text collections are taken into account. We argue that the ranking strategy should be context specific and we propose a , new systematic method that can automatically generate ranking strategies for different contexts based on genetic programming (GP). The new method was tested on TREC data and the results are very promising.     

A short course in antivirus software testing: seven simple rules for evaluating tests

Antivirus software tests are important when selecting antivirus software. However, there are many different tests, and interpreting the results can be challenging. Additionally, the needs of the corporate customer and home user differ, and it is important to understand these differences in order to evaluate antivirus software tests critically.     

Contribution of Raman scattering to water-leaving radiance: a reexamination

We have reexamined the contribution of Raman scattering to the water-leaving radiance in case 1 waters by carrying out radiative transfer simulations that combine the latest reported measurements of the absorption coefficient of pure water with direct measurements of the spectral variation of the Raman-scattering coefficient. The resulting contribution of Raman scattering is then compared with experimental measurements of the water-leaving radiance, and the fractional contribution of radiance produced by Raman scattering to the total radiance measured at a given wavelength is determined. The results show that (1) the contribution of Raman scattering to the water-leaving radiance in an ocean of pure seawater is as much as 50-100% larger than earlier predictions, and (2) the Raman contribution does not decay as rapidly with increasing concentrations of chlorophyllouslike pigments C as predicted earlier. In fact, the Raman fraction for C 8% at wavelengths of interest in ocean color remote sensing and therefore cannot be ignored in ocean color modeling.     

Plasticity of foraging behavior in garter snakes (Thamnophis sirtalis) reared on different diets.

The ontogeny of foraging was studied in 107 neonatal garter snakes (Thamnophis sirtalis) reared on 3 different diets: fish, leafworms, or mixed. Times to approach, capture, handle, and swallow prey were measured during each snake's first feeding and again after 11 to 12 meals. Overall times to consume prey decreased between the first and last tests for the 3 groups, but both prey type and the relative amounts of prey consumed differentially affected the various feeding phases. Approach latencies significantly decreased for snakes fed worms or fish exclusively but not for the mixed-diet snakes. The degrees to which capturing and swallowing latencies decreased differed among diet groups. Diet had little effect on prey handling duration. Sex and litter effects were reduced after feeding experience. These results reveal flexibility in feeding behavior as well as the costs and benefits of experience with multiple prey classes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quantization improvement in MRI using dual quantizers

The quantization of magnetic resonance imaging (MRI) data can cause information loss due to quantizer/data mismatch. The authors address a method for improved quantization as well as techniques for measuring the improvement in such methods. A dual quantizer scheme is described and simulated which is fast and more accurately quantizes MRI data than conventional methods. The approach is to use two quantizers, one for the high-level data and one for the low-level data. This adaptive, dual quantization scheme is simple and provides significant improvements in image quality, especially for three-dimensional (3-D) acquisition. Results are given which show how well the low frequencies are represented and indicate the increased fidelity of the high-frequency components. These results show a significant improvement in signal-to-noise ratio as well as in detection tasks for both noiseless data and data which include varying amounts of system noise.     

Streak Preventive Image Reconstruction with ART and Adaptive Filtering

Streaks arise in computed tomograms for a variety of reasons, such as presence of high-contrast edges and objects, aliasing errors, patient movement, and use of very few views. The problem appears to be an inherent difficulty with all reconstruction methods, including backprojection (with convolution) and the algebraic reconstruction technique (ART). This paper presents the derivation and results of an ART-like algorithm (SPARTAF) oriented towards prevention of streaks via optimization of a cost function based on features of streaks, subject to the constraints of the given projection data. The object-dependent method employs pattern recognition of streaks and adaptive filtering during iterative reconstruction by ART. Results of experiments with a test pattern and of application of the method to reconstructive tomography from radiographic films are presented and the convergence properties demonstrated.     

Optically pumped submillimeter gas lasers and the prospects for constructing space-qualifiable LO systems

An optically pumped submillimeter laser operating in the 500 μm (600 GHz) to 100 μm (3 THz) spectral range is the primary and, at present, the only available local oscillator (LO) source for laboratory and astronomical heterodyne applications for this wavelength region. A short review of the state-of-the-art of submillimeter lasers as LO sources, with an emphasis given to receiver systems designed for airborne heterodyne observations, will be presented. The characteristics and prospects for constructing a spacequalifiable laser LO system will also be given.