Criteria for accurate usage of block models

The results of block model calculations for multiple discretizations of a dielectric sphere and circular cylinder suggest that it is essential that the cells must be arranged for a best-fit of the body being modeled, the matrix elements must be reasonably accurate, and the cells must be small enough so that the pulse-function basis approximation is not blatantly unreasonable. When these criteria are approximately satisfied the remaining errors appear to be mainly due to imperfect representation of the shape of the object being modeled. It appears that the accuracy can be improved by using discretizations having cells of reduced size near the surface of the object. Geometric factors are defined which allow testing the potential accuracy of a solution without dimensioning or inverting a large matrix. Several unique procedures for discretization are also described that have the potential of partially mitigating the errors due to inaccurate representation of the shape of a scatterer.     

An exemplar-based random walk model of speeded classification

The authors propose and test an exemplar-based random walk model for predicting response times in tasks of speeded, multidimensional perceptual classification. The model combines elements of R. M. Nosofsky's (1986) generalized context model of categorization and G. D. Logan's (1988) instance-based model of automaticity. In the model, exemplars race among one another to be retrieved from memory, with rates determined by their similarity to test items. The retrieved exemplars provide incremental information that enters into a random walk process for making classification decisions. The model predicts correctly effects of within- and between-categories similarity, individual-object familiarity, and extended practice on classification response times. It also builds bridges between the domains of categorization and automaticity.     

Experimental and model investigations of bleaching and saturation of fluorescence in flow cytometry

We investigated the fluorescence emission from three fluorophores commonly used for labeling cells in flow cytometry. We have demonstrated that the fluorescence emission from cells labeled with fluorescein-isothiocyanate (FITC), phycoerythrin (PE), and allophycocyanin (APC) is considerably saturated and bleached in standard flow cytometric conditions. Therefore, for optimization of fluorescence detection in a flow cytometer, it is important to know the emission kinetics in detail. We made a mathematical model of the optical processes involved: absorption, fluorescence emission, nonradiative decay, photodestruction, and triplet state occupation. The validity of the model was experimentally tested with a set of averaged fluorescence pulses, measured in a large range of intensities and illumination times. The fluorescence of APC could be completely described by the model and produced the following rate constants: photodestruction rate kb1 = 6 x 10(3) s(-1), triplet state population rate k12 = 2 x 10(5) s(-1), and depopulation rate k20 = 5 x 10(4) s(-1). The fluorescence kinetics of FITC- and PE-labeled cells could not be fitted with only three parameters over the entire range, indicating that other optical processes are involved. We used the model to determine the sensitivity of our flow cytometer and to calculate the optimum conditions for the detection of APC. The results show that in principle a single APC molecule on a cell can be detected in the presence of background, i.e., autofluorescence and Raman scattering by water.     

Trypanosoma cruzi: nitrogenous-base-containing phosphatides in trypomastigote forms--isolation and chemical analysis

Increasingly clinicians attempt to base decisions regarding patient management on the results of clinical studies in addition to expert opinion and their own practical experience. In this article, the author reviews the published studies available to assist clinicians to make evidence-based decisions in three topics related to small volume red blood cell (RBC) transfusions for preterm infants; namely, studies examining the effects of RBC transfusions on possible symptoms of anemia such as tachypnea, apnea or other cardiorespiratory irregularities, studies investigating the collection and transfusion of umbilical cord blood and finally studies addressing the duration of storage and use of additive solutions for RBCs for transfusion to neonates. Based on the review of these studies, guidelines for small volume RBC transfusions in preterm infants are suggested.     

Evaluation of humoral immune responses in cattle grazing endophyte-infected or endophyte-free fescue

Anecdotal reports suggest cattle with fescue toxicosis may not respond to vaccination and thus, experience increased incidence of Bovine Respiratory Disease Complex (BRDC) when shipped to feedlots. Fescue toxicosis causes hypoprolactemia in cattle. Hypoprolactemia decreases humoral immune responses in mice. Therefore, a study was conducted to compare the magnitude of primary and secondary humoral immune responses against specific antigens in cattle grazing endophyte-infected or endophyte-free fescue. Angus steers were blocked by weight and allocated into four groups. Two groups grazed endophyte-infected (EI) fescue and the other two groups grazed endophyte-free (EF) fescue. All steers were injected IM on d 0 and 21 with lysozyme without adjuvant and concanavalin. A (Con A) with sheep red blood cells (SRBC) in incomplete adjuvant of Freund. Steers were bled on days 0, 21 and 35 post-vaccination. Average daily gains (ADG), alkaline phosphatase (ALP) activity, cholesterol concentrations, rectal temperatures, and serum prolactin concentrations were measured to confirm fescue toxicosis in steers grazing EI fescue. Antibodies to Con A and SRBC were determined by ELISA and hemagglutination assay, respectively. The ADG were decreased for the EI group during the first month. Rectal temperature were elevated and serum prolactin concentrations were decreased in the EI group. Cholesterol and ALP concentrations also were decreased in the EI group. Primary and secondary immune responses against Con A tended to be increased and were increased against SRBC in the EI group. Antibodies against lysozyme were not induced in either group. In conclusion, cattle grazing EI fescue mounted similar humoral immune responses to vaccination, despite hypoprolactemia, as cattle grazing EF fescue. Increases in bovine respiratory disease in cattle maintained on EI fescue probably is not associated with lack of humoral immune response to vaccination protocols as a result of fescue toxicosis.