Nonparametric analysis of clustered data in diagnostic trials: Estimation problems in small sample sizes

In diagnostic trials, clustered data are obtained when several subunits (e.g., organs or vessels) of the same patient are observed where no, several, or all subunits may be diseased or non-diseased as classified by a gold standard. In such a design, repeated measures appear in a natural way since the same patient is observed under different conditions by several readers and the repeated measures may have a quite involved correlation structure. A nonparametric method for clustered data in multiple reader studies to estimate the area under the ROC curve has been previously considered. The disadvantage of this procedure is that the test statistic (a quadratic form) can become negative in case of small samples. Therefore, a slightly different approach by weighting the estimators of the areas under the curves (AUC) is proposed. It is shown that the proposed new estimator of the covariance matrix of the weighted AUC estimators is always positive semidefinite. Simulation studies show that the new statistic maintains the pre-assigned type-I error level quite well even in case of small sample sizes. The method is motivated by a real data example where the previously suggested statistic becomes negative. This example demonstrates the advantage of the new method.     

A decomposition theorem for finite persistent transition systems

In this paper, we consider finite labelled transition systems. We show that if such transition systems are deterministic, persistent, and weakly periodic, then they can be decomposed in the following sense. There exists a finite set of label-disjoint cycles such that any other cycle is Parikh-equivalent to a multiset of cycles from this set.     

Alternating current electrical field effects on lettuce (Lactuca sativa) growing in hydroponic culture with and without cadmium contamination

The aim of the present study was to investigate the effect of a 10 Hz alternating current (10 Hz 1 V cm⁻¹) and a 50 Hz alternating current (50 Hz 1 V cm⁻¹) on the lettuce plant (Lactuca sativa) growing in a hydroponic (soil-free) culture. Thirty lettuce plants were pre-germinated, and then 15 of them were treated with cadmium solution (CdCl₂) of 5 mg/L in concentration. Ten plants (five plants with Cd and five plants without Cd) were subjected to a 10 Hz alternating current (AC) electrical field; 10 plants were subjected to a 50 Hz AC field. The rest of the plants were used as a control. The lettuce plants were harvested after a growth of 60 days. The chlorophyll content, biomass and metal content of the lettuce plants were determined. The biomass of the plants growing in non-contaminated medium was 28 and 106% higher under the 10 and the 50 Hz AC fields respectively compared to the control. Although the plant biomass was reduced by the presence of Cd in the growth medium, the biomass of the plants growing in Cd contaminated medium was 40 and 63% higher respectively for 10 and 50 Hz AC field compared to the plant growing in Cd contaminated medium without electrical treatment. Increased uptake of Cd in the plant shoot was found with the 50 Hz AC field. Significant accumulation and uptake of Cu in plant roots and shoots was found under both electrical treatments.     

Disrupted temporal control in the R6/2 mouse model of Huntington’s disease.

Huntington’s disease is characterized by corticostriatal dysfunction and degeneration of the striatum with progressive loss of the medium spiny neurons. These circuits are important for instrumental responding, interval timing, and temporal control over motor output. We investigated the acquisition of timed operant responding in two R6/2 Huntington’s Disease models, differing in CAG repeat length and genetic background (115 and 250 CAG repeats, and a mixed CBAxC57 or pure C57 background) and their corresponding wild type controls using the peak procedure. Both mouse lines exhibited similar response control deficits. In unreinforced peak trials, mice either did not learn to terminate an ongoing response past reinforcement time or required more trials to acquisition compared to the wild type mice. While transgenic and wild type mice did not exhibit differences in temporal accuracy, response curves were flatter in transgenic mice, suggesting decreased temporal control over operant responding. The results are discussed in terms of the neurobiology of interval timing, instrumental responding, and the neuropathology of HD and R6/2 mice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Elektronenstrahltesten: Genauigkeit von Zeitmessungen im ps-Bereich

Übersicht Die Entwicklung integrierter Mikrowellenschaltungen für analoge und digitale Anwendungen mit hohen Geschwindigkeiten erfordert neue Meßmethoden. Für die Prozeß- und Schaltungsentwicklung ist vor allem die belastungsfreie Messung interner Signale notwendig. Die bereits bewährte Elektronenstrahlmeßtechnik konnte diesen neuen Anforderungen angepaßt werden. Zeitkritische Größen sind sowohl Signalanstiegszeiten als auch Phasenlagen verschiedener Signale zueinander. Signalanstiegszeiten können gegenwärtig bis herab zu 15 ps mit einem Fehler unter 10% gemessen werden. Für Messungen von Phasenlagen zwischen Signalen, die innerhalb von 3 Stunden aufgezeichnet wurden, ergibt sich eine Genauigkeit von±2 ps.

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Electron-beam testing: accuracy of time measurements in the ps range

Contents The development of integrated microwave circuits for analogue and digital applications with higher speeds requires new testing methods. The process and circuit development primarily require non loding measurements of internal signals. The adaptation of the proven technique of e-beam testing to these new requirements was successfull. Signal rise times as well as phase relations between different signals are critical quantities in the time scale. Presently, rise times can be measured down to 15 ps with an error of less than 10%. Measurements between signals being recorded within 3 hours are possible with an accuracy of±2 ps.

     

Clinical application of volume estimation based on three-dimensional ultrasonography

The development of three-dimensional sonography represents a milestone in the history of diagnostic ultrasound. It has become possible to evaluate a region of interest not only in the horizontal and vertical planes but also in a third, i.e. the frontal, plane. Among other possible applications, this technique greatly facilitates volume estimation. The objective of the present study was to evaluate the accuracy and precision of volumetry based on three-dimensional sonography. The results demonstrate a good correlation between estimated volumes and the volumes measured by transvaginal needle-guided follicle aspiration performed under sonographic visualization. Our findings confirm the conclusion of previous studies that three-dimensional sonography is making a valuable contribution to imaging techniques.     

NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase from Thermoproteus tenax. The first identified archaeal member of the aldehyde dehydrogenase superfamily is a glycolytic enzyme with unusual regulatory properties

The hyperthermophilic archaeum Thermoproteus tenax possesses two glyceraldehyde-3-phosphate dehydrogenases differing in cosubstrate specificity and phosphate dependence of the catalyzed reaction. NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase catalyzes the phosphate-independent irreversible oxidation of D-glyceraldehyde 3-phosphate to 3-phosphoglycerate. The coding gene was cloned, sequenced, and expressed in Escherichia coli. Sequence comparisons showed no similarity to phosphorylating glyceraldehyde-3-phosphate dehydrogenases but revealed a relationship to aldehyde dehydrogenases, with the highest similarity to the subgroup of nonphosphorylating glyceraldehyde-3-phosphate dehydrogenases. The activity of the enzyme is affected by a series of metabolites. All effectors tested influence the affinity of the enzyme for its cosubstrate NAD+. Whereas NADP(H), NADH, and ATP reduce the affinity for the cosubstrate, AMP, ADP, glucose 1-phosphate, and fructose 6-phosphate increase the affinity for NAD+. Additionally, most of the effectors investigated induce cooperativity of NAD+ binding. The irreversible catabolic oxidation of glyceraldehyde 3-phosphate, the control of the enzyme by energy charge of the cell, and the regulation by intermediates of glycolysis and glucan degradation identify the NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase as an integral constituent of glycolysis in T. tenax. Its regulatory properties substitute for those lacking in the reversible nonregulated pyrophosphate-dependent phosphofructokinase in this variant of the Embden-Meyerhof-Parnas pathway.     

Electronic Measuring Cup for the Blind

A simple electronic measuring cup for the blind is described. It uses an array of infrared level detectors, which are immersed in the medium to be measured. When used with a standard 1-liter glass, the filling level is indicated acoustically in increments of 50 ml.