The dependence of reproductive rate on cell size and temperature in freshwater ciliated protozoa

Summary Reproductive rates have been calculated for ten species of ciliated protozoa in defined conditions. Interspecific double log regressions of generation time vs. cell volume have been computed at each of three temperatures (8.5° C, 15° C, and 20° C) indicating a significant dependence of reproductive rate on cell size. Recorded generation times varied from 6.38 h in Vorticella microstoma at 20° C to 1004 h in Spirostomum teres at 8.5° C. These values correspond to a range in r _m (day)^-1 of 2.607 to 0.017 and (day)^-1 of 13.554 to 1.017. The relationship between these data and similar published data for marine ciliates is examined and the value of such regressions in ecological studies of the protozoa is discussed.     

Evaluation of linear finite-element analysis models' assumptions for external fixation devices.

Linear finite-element models (FEMs) have enjoyed an increased use in orthopaedic research, including the use for modeling external fixation devices. These fixator FEMs depend on a number of basic assumptions concerning the overall fixation frame stability and the components' rigidity. Among the more important ones are: (i) rigid fixation at both ends of the pin and sidebar; (ii) that the sidebar can be treated essentially as a rigid entity, with all bending occurring in the bone pins; and (iii) that the system can be treated as linearly elastic. Prior work done by the authors questions some of these assumptions. Thus, this study sought an empirical evaluation of the validity of some of these a priori assumptions. A Hoffmann single half-frame was tested in its standard form and then according to a stepwise protocol wherein the frame was welded to eliminate any possible points of instability. These tests looked at the stability and rigidity in various modes (axial compression, torsion, and medial-lateral and anterior-posterior four-point bending). The basic assumptions concerning the frame stability, frame rigidity and the frame's response to loads were found to be erroneous. Component failure was common under minimal loads and statistically significant differences (p less than 0.05) of up to 75% were noted in frame rigidity among the various frame forms tested. Thus, considerable caution must be exercised when employing the FEM technique for evaluating the fixator properties.     

Cell death and the creation of regional differences in neuronal numbers.

Regional variations in cell death are ubiquitous in the nervous system. In the retina, cell death in retinal ganglion cells is elevated in the retinal periphery and may be important in setting up the initial conditions that produce central retinal specializations such as an area centralis or visual streak. In central visual system structures, pronounced spatial and spatiotemporal inhomogeneities in cell death are seen both in layers and regions of the lateral geniculate nucleus and superior colliculus; similar indications of inhomogeneities are seen in those nonvisual structures that have been examined. Cell death in the cortex is highly nonuniform, by layer and by cortical area. A variety of possible functions for these regional losses are proposed, in the context of a uniform mechanism for cell death that allows it to assume multiple functions.     

New methods for the preparation of biospecific adsorbents and immobilized enzymes utilizing trichloro-s-triazine

Methods for preparing biospecific adsorbents and immobilized enzymes utilizing Sepharose CL as a support and trichloro-s-triazine as the linking agent are described. The difficulties encountered during conventional aqueous and mixed aqueous-phase reactions of trichloro-s-triazine with insoluble polyols, particularly reagent hydrolysis, are avoided by performing the activation reactions in anhydrous organic phase and replacing the second chlorine on the triazine ring by an aromatic amine. Ligands can be coupled to the activated support in either aqueous or organic phase. The methods have been applied to the attachment of a number of different enzymes, proteins, and small-molecule ligands to Sepharose. The superiority of the triazine linkage to the cyanogen bromide linkage is demonstrated.     

In-vivo dose measurements with MOSFET dosimeters during MV portal imaging

BackgroundThe purpose of this study was to investigate the feasibility of MOSFET dosimeter in measuring eye dose during 2D MV portal imaging for setup verification in radiotherapy.Materials and methodsThe in-vivo dose measurements were performed by placing the dosimeters over the eyes of 30 brain patients during the acquisition of portal images in linear accelerator by delivering 1 MU with the field sizes of 10 × 10 cm² and 15 × 15 cm².ResultsThe mean doses received by the left and right eyes of 10 out of 30 patients when both eyes were completely inside the anterior portal field were found to be 2.56 ± 0.2 cGy and 2.75 ± 0.2, respectively. Similarly, for next 10 patients out of the same 30 patients the mean doses to left and right eyes when both eyes were completely out of the anterior portal fields were found to be 0.13 ± 0.02 cGy and 0.17 ± 0.02 cGy, respectively. The mean doses to ipsilateral and contralateral eye for the last 10 patients when one eye was inside the anterior portal field were found to be 3.28 ± 0.2 cGy and 0.36 ± 0.1 cGy, respectively.ConclusionThe promising results obtained during 2D MV portal imaging using MOSFET have shown that this dosimeter is well suitable for assessing low doses during imaging thereby enabling to optimize the imaging procedure using the dosimetric data obtained. In addition, the documentation of the dose received by the patient during imaging procedure is possible with the help of an in-built software in conjunction with the MOSFET reader module.     

Adhesion and motility of fouling diatoms on a silicone elastomer

Recent demands for non-toxic antifouling technologies have led to increased interest in coatings based on silicone elastomers that ‘release’ macrofouling organisms when hydrodynamic conditions are sufficiently robust. However, these types of coatings accumulate diatom slimes, which are not released even from vessels operating at high speeds ( > 30 knots). In this study, adhesion strength and motility of three common fouling diatoms (Amphora coffeaeformis var. perpusilla (Grunow) Cleve, Craspedostauros australis Cox and Navicula perminuta Grunow) were measured on a polydimethylsiloxane elastomer (PDMSE) and acid-washed glass. Adhesion of the three species was stronger to PDMSE than to glass but the adhesion strengths varied. The wall shear stress required to remove 50% of cells from PDMSE was 17 Pa for Craspedostauros, 24 Pa for Amphora and >> 53 Pa for Navicula; the corresponding values for glass were 3, 10 and 25 Pa. In contrast, the motility of the three species showed little or no correlation between the two surfaces. Craspedostauros moved equally well on glass and PDMSE, Amphora moved more on glass initially before movement ceased and Navicula moved more on PDMSE before movement ceased. The results show that fouling diatoms adhere more strongly to a hydrophobic PDMSE surface, and this feature may contribute to their successful colonization of low surface energy, foul-release coatings. The results also indicate that diatom motility is not related to adhesion strength, and motility does not appear to be a useful indicator of surface preference by diatoms.     

A simple method to evaluate the potential for degradation of antifouling biocides

A simple method to measure the degradation of antifouling biocides is described which measures the loss of biocidal activity from seawater by bioassay. The bioassay employs either the ship‐fouling diatom Amphora or the brine shrimp Anemia. Loss of bioaclivity from sterile seawater indicates abiotic degradation whilst loss of bioactivity from natural seawater indicates biodegradation. Results are presented for three biocides, viz. the trihalomethylthio compound, N‐dichlorofluoromethylthio‐N’,N'‐dimethyl‐N‐phenyl‐sulphamide (Preventol A4S), di‐n‐octylamine, and the isothiazolone compound 4,5‐dichloro‐2‐n‐octyl‐4‐isothiazolin‐3‐one (Sea‐Nine 211).     

The effect of genomic information on optimal contribution selection in livestock breeding programs

Background

Long-term benefits in animal breeding programs require that increases in genetic merit be balanced with the need to maintain diversity (lost due to inbreeding). This can be achieved by using optimal contribution selection. The availability of high-density DNA marker information enables the incorporation of genomic data into optimal contribution selection but this raises the question about how this information affects the balance between genetic merit and diversity.

Methods

The effect of using genomic information in optimal contribution selection was examined based on simulated and real data on dairy bulls. We compared the genetic merit of selected animals at various levels of co-ancestry restrictions when using estimated breeding values based on parent average, genomic or progeny test information. Furthermore, we estimated the proportion of variation in estimated breeding values that is due to within-family differences.

Results

Optimal selection on genomic estimated breeding values increased genetic gain. Genetic merit was further increased using genomic rather than pedigree-based measures of co-ancestry under an inbreeding restriction policy. Using genomic instead of pedigree relationships to restrict inbreeding had a significant effect only when the population consisted of many large full-sib families; with a half-sib family structure, no difference was observed. In real data from dairy bulls, optimal contribution selection based on genomic estimated breeding values allowed for additional improvements in genetic merit at low to moderate inbreeding levels. Genomic estimated breeding values were more accurate and showed more within-family variation than parent average breeding values; for genomic estimated breeding values, 30 to 40% of the variation was due to within-family differences. Finally, there was no difference between constraining inbreeding via pedigree or genomic relationships in the real data.

Conclusions

The use of genomic estimated breeding values increased genetic gain in optimal contribution selection. Genomic estimated breeding values were more accurate and showed more within-family variation, which led to higher genetic gains for the same restriction on inbreeding. Using genomic relationships to restrict inbreeding provided no additional gain, except in the case of very large full-sib families.