Measuring thermal conductivity in extreme conditions: sub-Kelvin temperatures and high (27 T) magnetic fields

We present a one-heater-two-thermometer set-up for measuring thermal conductivity and electric resistivity of a bulk sample at low temperatures down to 0.1 K and in magnetic fields up to 27 Tesla. The design overcomes the difficulties emerging in the context of large water-cooled resistive magnets.Comment: 4 pages including 4 figure

Determination of stability constants using genetic algorithms

A genetic algorithm (GA)-simplex hybrid approach has been developed for the determination of stability constants using calorimetric and polarographic data obtained from literature sources. The GA determined both the most suitable equilibrium model for the systems studied and the values of the stability constants and the heats of formation for the calorimetric studies. As such, a variable length chromosome format was devised to represent the equilibrium models and stability constants (and heats of formation). The polarographic data were obtained from studies of cadmium chloride and lead with the crown ether dicyclohexyl-18-crown-6. The calorimetric data were obtained from a study of a two step addition reaction of Hg(CN)2 with thiourea. The stability constants obtained using the GA-simplex hybrid approach compare favourably with the values quoted in the literature

Advances in item response theory and applications: an introduction

Test theories can be divided roughly into two categories. The first is classical test theory, which dates back to Spearman’s conception of the observed test score as a composite of true and error components, and which was introduced to psychologists at the beginning of this century. Important milestones in its long and venerable tradition are Gulliksen’s Theory of Mental Tests (1950) and Lord and Novick’s Statistical Theories of Mental Test Scores (1968). The second is item response theory, or latent trait theory, as it has been called until recently. At the present time, item response theory (IRT) is having a major impact on the field of testing. Models derived from IRT are being used to develop tests, to equate scores from nonparallel tests, to investigate item bias, and to report scores, as well as to address many other pressing measurement problems (see, e.g., Hambleton, 1983; Lord, 1980). IRT differs from classical test theory in that it assumes a different relation of the test score to the variable measured by the test. Although there are parallels between models from IRT and psychophysical models formulated around the turn of the century, only in the last 10 years has IRT had any impact on psychometricians and test users. Work by Rasch (1980/1960), Fischer (1974), 9 Birnbaum (1968), ivrighi and Panchapakesan (1969), Bock (1972), and Lord (1974) has been especially influential in this turnabout; and Lazarsfeld’s pioneering work on latent structure analysis in sociology (Lazarsfeld, 1950; Lazarsfeld & Henry, 1968) has also provided impetus. One objective of this introduction is to review the conceptual differences between classical test theory and IRT. A second objective is to introduce the goals of this special issue on item response theory and the seven papers. Some basic problems with classical test theory are reviewed in the next section. Then, IRT approaches to educational and psychological measurement are presented and compared to classical test theory. The final two sections present the goals for this special issue and an outline of the seven invited papers

Specific mapping of disease resistance genes in tetraploid cut roses

Control of fungal diseases is a major constraint of cut-rose cultivation in greenhouses and in transportation around the world. Therefore, development of resistant cultivars is a promising way to reduce the use of chemicals required for controlling the diseases. Genetic analyses and breeding for resistance, however, are hampered by the high degree of heterozygosity and the polyploid nature of cultivated roses. Nucleotide-binding site (NBS) profiling of Van der Linden et al. (2004) was used as a tool enabling a more directed way of studying the genetics of resistance to pathogens responsible for diseases such as powdery mildew. NBS profiling is a multiplex screening technique, producing amplified resistance gene (R-gene) and resistance gene analogue (RGA) fragments by using degenerated primers based on the conserved motifs present in the NBS domain of resistance genes. Since RGAs are abundantly distributed and highly polymorphic within the plant genome, NBS profiling generates multiple markers of putative resistance genes. Twelve NBS degenerated primer/ restriction enzyme combinations were used to genotype the whole rose tetraploid K5 population (Yan, 2005) and its parents. To generate RGA profiles, the restriction enzymes: AluI, HaeIII, Mse and RsaI were used in combination with degenerated primers NBS1, NBS3, and NBS5a6. The profiles were dominantly scored resulting in 106 polymorphic RGA markers which segregated in a 1:1 or 3:1 ratio. Uni-and bi-parental simplex markers will be mapped on the two available AFLP/SSR K5 maps (Yan, 2005) with Joinmap 4.0. The resulting parental tetraploid maps will be used to dissect the genetic variation for resistance to powdery mildew resistance. Additional Rosaceae SSRs mentioned in the literature are currently tested on the K5 population to obtain allelic bridges between the tetraploid and diploid genetic maps in rose and related species in order to align them. These bridges will improve cross-ploidy comparisons in roses in order to strengthen cut rose breedin

Symptom complexes in patients with seropositive arthralgia and in patients newly diagnosed with rheumatoid arthritis: a qualitative exploration of symptom development

Objective: The aim of this study was to explore symptoms and symptom development during the earliest phases of rheumatoid arthritis (RA) in patients with seropositive arthralgia and patients newly diagnosed with RA