Difference estimators of quantiles in finite populations

This paper deals with the inference of finite populations quantiles by using auxiliary information. The population information considered on the proposed estimatiors is a population quantile of the auxiliary variable with the same order as that of the quantile of the main variable to be estimated. A simulation study based on three real finite populations is performed and comparisons of the proposed estimators with other common estimators for quantile estimation are carried out.     

Robust trend parameters in a multivariate spatial linear model

This article gives a robust estimator of the trend parameters in multivariate spatial linear models. This estimator is presented as an alternative to the classical one which is obtained by using cokriging. The goal focuses on improving predictions of spatial variables when data contain both atypical and high influence observations. The procedure consists of extending robust methods used in linear regression models to the multivariate spatial context. The resulting estimator belongs to the class of GM-estimators and then, it is a bounded influence estimator and it has good robust properties, in particular, a high breakdown point and a high efficiency. An illustrative example is given to show how the proposed estimator works. Research partially supported by Ministerio de Ciencia y Tecnología, Project AGL2000-0978.     

Formation of the La0.03Sr0.255Ba0.7Nb2–yTiyO6–y/2 ferroelectric ceramic system

The study of the formation of the Sr_0.255La_0.03Ba_0.7Nb_{2 – y} Ti _y O_{6 – y/2} ferroelectric ceramic system and the influence of the sintering conditions and titanium concentration on the densification process is reported. A single-phase compound is observed for low titanium content (y 0.1) in the XRD spectra, being isostructural with the tetragonal tungsten bronze SBN phase. For high titanium concentrations (y > 0.1) the XRD patterns show, besides the tetragonal phase reflections, several small peaks evidencing an additional phase in the compound. This second phase was identified as isostructural to hexagonal Ba₆Nb₉Ti₇O₄₂. The grain size shows a linear increase with titanium content in the region of monophasic compositions and a possible liquid phase aided sintering process is analyzed.     

A meta-analysis of writing instruction for adolescent students.

There is considerable concern that the majority of adolescents do not develop the competence in writing they need to be successful in school, the workplace, or their personal lives. A common explanation for why youngsters do not write well is that schools do not do a good job of teaching this complex skill. In an effort to identify effective instructional practices for teaching writing to adolescents, the authors conducted a meta-analysis of the writing intervention literature (Grades 4-12), focusing their efforts on experimental and quasi-experimental studies. They located 123 documents that yielded 154 effect sizes for quality of writing. The authors calculated an average weighted effect size (presented in parentheses) for the following 11 interventions: strategy instruction (0.82), summarization (0.82), peer assistance (0.75), setting product goals (0.70), word processing (0.55), sentence combining (0.50), inquiry (0.32), prewriting activities (0.32), process writing approach (0.32), study of models (0.25), grammar instruction (- 0.32). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cover Picture: Magnetorheological Fluids Based on Ionic Liquids (Adv. Mater. 13/2007)

The use of ionic liquids as carriers of magnetorheological fluids is described by Schubert and co‐workers on p. 1740. Combining the properties of ionic liquids with magnetorheological technology may lead to new, “smart” fluids for application in medical therapies, engineering devices, or multiphase biological and chemical systems. In the presence of a magnetic field the fluids behave as solids owing to a stronger interaction between their suspended magnetic particles. In the absence of the magnetic field, they become liquids again in a fully reversible process.     

AN AI ELECTRICAL GROUND SUPPORT EQUIPMENT FOR CONTROLLING AND TESTING A SPACE INSTRUMENT

A versatile and modular electrical ground support equipment (EGSE) system has been developed using artificial intelligence (AI) techniques to control and test the PESCA instrument and the communication process of the satellite without any human supervision. The PESCA instrument has been designed and built with the purpose of studying solar energetic particles and the anomalous cosmic rays. It will be part of the Russian FOTON satellite payload that is scheduled to be launched in December 2007. The tool allows complete and autonomous control, verification, and validation of the PESCA instrument, although its modularity makes it extensible to other onboard instruments.     

Performance improvement of web caching in Web 2.0 via knowledge discovery

Web 2.0 systems are more unpredictable and customizable than traditional web applications. This causes that performance techniques, such as web caching, limit their improvements. Our study was based on the hypotheses that the use of web caching in Web 2.0 applications, particularly in content aggregation systems, can be improved by adapting the content fragment designs. We proposed to base this adaptation on the analysis of the characterization parameters of the content elements and on the creation of a classification algorithm. This algorithm was deployed with decision trees, created in an off-line knowledge discovery process. We also defined a framework to create and adapt fragments of the web documents to reduce the user-perceived latency in web caches. The experiment results showed that our solution had a remarkable reduction in the user-perceived latency even losses in the cache hit ratios and in the overhead generated on the system, in comparison with other web cache schemes.     

Image processing techniques in a preliminary morphometric characterization of corneal epithelium by scanning electron microscopy

Several processing techniques of digital images allowed us to quantify the percentage of cell surface covered by microprojections (microvilli or microplicae) (SCM), the adhesion between epithelial cells by the parameter intercellular junctions (IJ), the size (cell area), shape (cell shape) and shade (cell shade) of cells on the corneal epithelium of nine rabbits. The data were analyzed and the epithelial cells were classified into three groups by cluster analysis. Assuming the representativeness of the sample, our findings suggest that for a normal corneal epithelium, 80% of the cells could show SCM >41%, and IJ >0.98 (being one a cell to cell junction without disruptions). Standard deviations of cell shade lower than 21 gray levels could indicate a tendency to lose the cell shade mosaic. Normal corneas could show a majority of cells (54–69%) included in group 2 with smaller mean size (80% of cells with cell area <242 μm²), higher SCM (80% of cells with SCM >44.83%), polygonal mean shape and brighter shade. Group 1 (15–30% of cells) could show a larger mean size (80% of cells with cell area >494 μm²), lower SCM (although 80% of cells with SCM >32.61%), circular mean shape and darker electron reflex. Group 3 could display a medium mean size, higher SCM (similar to group 2), circular mean shape (similar to group 1), and brighter shade. These analyses could possibly be used to further assess the corneal response to ocular drugs, contact lens, and surgical procedures or to discriminate between pathology stages. Microsc. Res. Tech. 73:1059–1066, 2010. © 2010 Wiley‐Liss, Inc.     

Simulation of laminar flow inside ducts of irregular geometry using integral transforms

 The Generalized Integral Transform Technique is employed in the hybrid numerical-analytical solution of the steady two-dimensional Navier–Stokes equations, defined within arbitrarily shaped domains, for incompressible laminar channel flow. The formalism is illustrated for the classical test-case of laminar flow in a gradual expansion duct. Numerical results with automatic global accuracy control are obtained for suggested values of Reynolds numbers in the literature, and critically compared against previously reported benchmark solutions for the same problem. The relative merits of the proposed approach are then pointed out. Received 24 May 1999