Electronically Tunable Filters

In this article, a brief introduction to the development of tunable filters was given. A classical design technique based on a combline filter approach was shown, where minimum degradation in passband performance could be obtained across a broad-tuning range. The fundamental disadvantages associated with the conventional resonator tuning approaches were also discussed, recognizing the importance of developing new techniques for realizing tunable microwave filters. It was shown that there is a possibility in realizing an electronically reconfigurable microwave filter based on parallel- coupled switched-delay lines, which possesses the important property of maintaining constant absolute bandwidth over almost an octave of tuning bandwidth. Furthermore, the filter has the ability to incorporate active switching elements in the filter circuit, without sacrificing its loss and linearity performance. With the exceptional linearity performance and power handling capability, the filter is readily adapted to poor environments. Although the use of p-i-n diodes as switching elements would result in large dc consumption, the approach could also be readily adapted for use with any switches, such as pHEMT or RF MEMS switches, to achieve extremely low power consumption. The integration of switchable couplings to enable both bandwidth and center frequency to be reconfigurable would be an enhancement.     

Application of interspersed repetitive sequence polymerase chain reaction for construction of yeast artificial chromosome contigs

This work is devoted to the comprehension of the sorption mechanism of uranyl ions on chitosan particle dispersions. The uranyl concentration measurements were obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) and we considered the role of various physicochemical parameters (pH; nature and concentration of added salts; degree of acetylation, DA). The use of appropriate calculation software allowed us to determine the chemical nature of uranyl species in solution in relation to these different parameters. The optimal pH of fixation has been found to be within 6.5-7.5 and can be related to the necessity of having both deprotonated amino groups and no carbonate ions, which are a strong complexant of uranyl ions, thus inhibiting their interaction with chitosan. The decrease of metal uptake with an increase of DA and the lack of influence of ionic strength, confirm the results obtained with pH and allowed us to suppose the formation of a complex with chitosan amino groups rather than interactions of an electrostatic nature.     

George A. Miller, language, and the computer metaphor and mind.

This article asks why the analogy between humans and computers was understood by cognitive psychologists to mean that "minds exist and that it is our job as psychologists to study them." Earlier psychologists, such as Clark Hull, used analogies between humans and complex machines such as telephone switchboards to defend a rigorous behaviorism. How, then, did the computer metaphor of mind come to be seen as the root concept underlying a paradigm shift from behaviorism to cognitivism? To answer this question, this article examines the life and work of George A. Miller, one of the most prominent of a generation of psychologists who began their careers as "good behaviorists" but later came to embrace cognitivism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A statnet Tutorial

The statnet suite of R packages contains a wide range of functionality for the statistical analysis of social networks, including the implementation of exponential-family random graph (ERG) models. In this paper we illustrate some of the functionality of statnet through a tutorial analysis of a friendship network of 1,461 adolescents.     

Introduction to special issue: The plus ultra of empirical research.

Recent advances in cognitive science and neuroscience (CSN) have allowed scientists to begin to address questions that were heretofore considered the province of the humanities. Growing out of a 2007 conference at Bucknell University, this volume explores recent research in many different areas that combines the methods and perspectives of both the humanities and CSN. This introduction argues that the barriers to such work (such as the opposition between objective scientific research and subjective humanistic research) are purely of our own making and in no way absolute; it further asserts that the articles herein demonstrate that the potential benefits of interdisciplinary study far outweigh the risks. There is no fixed method for interdisciplinarity. Its success depends on respect for the particulars of each research question and the imagination to see what combinations of different disciplines might work best. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nanocomposites from poly(ethylene-co-methacrylic acid) ionomers: effect of surfactant structure on morphology and properties

A detailed study of the structure-property relationships for nanocomposites prepared using melt processing techniques from a sodium ionomer of poly(ethylene-co-methacrylic acid) and a series of organoclays is reported. Transmission electron microscopy, X-ray scattering, stress-strain behavior, and Izod impact analysis were used to evaluate the nanocomposite morphology and physical properties. Four distinct surfactant structural effects lead to improved levels of exfoliation and higher stiffness for these nanocomposites: higher number of alkyl tails on the amine rather than one, longer alkyl tails instead of shorter ones, use of 2-hydroxy-ethyl groups as opposed to methyl groups on the ammonium ion, and an excess amount of the amine surfactant on the clay instead of an equivalent amount. These trends are opposite of what has been seen in nylon 6 based nanocomposites but are similar to those observed in nanocomposites formed from LDPE and LLDPE. Although some organoclays were exfoliated better than others, none of the ionomer-based nanocomposites exhibited exfoliation levels as great as those seen in nylon 6 nanocomposites; nevertheless, these nanocomposites offer promising improvements in performance and may be particularly interesting for barrier applications.     

Agricultural pesticides threaten the ecological integrity of northern prairie wetlands.

The northern Great Plains of North America has millions of small wetlands, and these are often dispersed through cultivated fields. We investigated relationship between pesticide occurrence and precipitation in selected wetlands in a 30.4 x 10(4) km2 area of the Great Plains with relatively uniform farming practices and 1,777,600 wetlands (southern Saskatchewan, Canada). By early July after pesticides have been applied to crops, the mean number of pesticides detected in wetlands ranged from 1.8 in regions with little precipitation (< 21 mm rain during the previous 15 days) to 3.2 in regions under higher rainfall (> 90 mm). The proportion of wetlands in which at least one pesticide exceeded Canadian guidelines for the protection of aquatic life increased from 0% to 60% over this same precipitation range. The maximum number of pesticides detected in a single wetland was six. Concentration of lindane in wetlands increased with increasing precipitation. Using geographic information on rainfall, wetland densities, area seeded to crops, and region specific relationships between pesticides and precipitation, we estimated the number of wetlands in Saskatchewan with elevated levels of pesticides. In early July, during 3 of the 6 years, the number of wetlands subjected to pesticide levels that exceeded guidelines for the protection of aquatic life was significant, ranging from 152,000 to 424,000 wetlands or 9-24%, respectively, of the total. Lindane and triallate exceeded the guidelines most frequently.     

Nutritional consequences of processing soybean oil

A major objective of commercial processing of soybean oil into edible products is to remove unwanted impurities from the oil with the least possible effect on nutritional quality of the oil. Soybean oil is an excellent dietary source of essential linoleic acid and also of tocopherols, which serve as sources of vitamin E and natural antioxidants. The data presented in this report indicate that the nutritional quality of soybean oil is largely retained after typical commercial processing conditions. Hydrogenation does reduce the level of essential fatty acids; however, typical commercial salad and cooking oils and shortenings made from partially hydrogenated soybean oil retain nutritionally significant levels of essential fatty acids. Tocopherols also are present at high levels in the finished oil. Among the unwanted components of crude soybean oil which are effectively removed by processing are pesticide residues, phosphatides, free fatty acids, color pigments, and compounds causing objectionable odors and flavors.