A compartmental model for the study of diurnal rhythms in cell proliferation

A mathematical model taking into account the observed diurnal variations in cell kinetics is presented. Its principle is to divide each phase of the cell cycle into a definite number of compartments and to assume time-dependent probabilities of transition from one compartment to the following; general properties of the model are derived.The particular case where the only time-dependent transition probabilities are those corresponding to the G₁ phase is studied. A characterization of the joint percentages of S and M cells variations is given. The application of the model to interpretation of published experimental data obtained in hamster cheek pouch epithelium is given.     

Landau theory of two-component phospholipid bilayers. I. Phosphatidylcholine/phosphatidylethanolamine mixtures

Priest's phenomenological model (Mol. Cryst. Liq. Cryst. 60 (1980) 167.) on one- and two-component PC bilayers is extended here. We constructed a new excess free energy term in the state function to describe the thermodynamic properties of the two-component phospholipid bilayers where the chain lengths and the polar heads of the components can be different simultaneously. By means of this generalized state function, we can calculate the phase diagrams of DPPC/DPPE, DMPC/DMPE, DMPC/DPPE, DPPC/DMPE and DSPC/DMPE mixtures. We obtained complete miscibility both in the liquid crystalline and in the gel phase if the chain lengths of the components were the same. If the chain length of the PE component was longer than that of the PC component, we obtained a peritectic system. A eutectic system was obtained in the reverse case. The results of the model were compared with the experimental data available. Applying the quasichemical approximation, we determined the molecular meaning of the phenomenological model parameters. Namely, sigma and gamma are proportional to the sublimation heat of the CH2 group in the long-chain alkanes and to the hydrogen-bonding energy between the polar heads of the ethanolamines; otherwise the model resulted in--1.94 kcal/mol per CH2 for the sublimation heat and --1.4 kcal/mol for the hydrogen-bond energy.     

The influence of temperature on nest site choice and reproductive strategy in a temperate zone Polistes wasp

Abstract. 1. Field experiments with Polistes fuscutus showed that more nests were initiated, co-foundress groups were larger, broods developed faster, and workers eclosed earlier in sun-warmed sites than in cool ones.
2. These results suggest that colonies nesting in sun-warmed shelters gained a fitness advantage over those in cooler shelters. More rapid brood development means that such colonies reach the ergonomic stage more quickly, which in turn means a higher expectancy of survival and greater productivity at the end of the season.
3. We argue that thermal properties constitute an important component of Polistes nest site quality in temperate regions and that these properties influence joining and usurping strategies as well as nest site choice in spring Polistes females. Other factors being equal, a joining or usurping female should opt for a colony in a warm site over one in a cool site, leading to the larger foundress groups we found in warm shelters.
4. We hypothesize that the selective advantage of philopatry in temperate zone Polistes populations is that it brings spring females to nest sites of proven quality.     

Research experience modifies how participants profit from journal clubs in academia

Because Journal Clubs (JClubs) represent valued educational tools, we often assume optimality of Journal Club practices. We analyze here JClubs records from a research group to identify factors that modify how much attendants benefit from discussing a paper. We demonstrate that attendants benefit most from papers focusing on systems similar to those they work on and that their ability to profit from different contribution types changes with research experience. Common JClubs practices such as the assignment of the paper selection to a single individual could thus compromise participant experience. Our conclusions may also be generalizable to situations outside academia.     

Application of bioluminescence ATP measurement for evaluation of fungal viability of foxing spots on old documents

An adenosine triphosphate (ATP) bioluminescence‐based protocol was tested to assess the viability of fungal species in old documents damaged by foxing. Foxing appears as scattered yellow brownish‐red stains, damaging the aesthetics of documents and their long‐term readability. In the field of cultural heritage conservation, the debate over the mechanism of foxing is ongoing. Previous studies found evidence of mold‐like structures in some coloured areas; however, many species have not yet been identified and their role in the phenomenon is not understood. To better understand their involvement in this type of paper decay, we focused our attention first on their viability. We demonstrated the reliability and sensitivity of the ATP bioluminescence assay compared with conventional methods based on cultivation, which has rarely given rise to in vitro growth from foxed papers. From nine books dating back from the 19th and 20th centuries, the mean ATP amount of foxed spots ranged from 0.29 to 3.63 ng/cm², suggesting the presence of strains inside the brownish spots and providing evidence of their viability. Outside the spots, ATP content was considered negligible, with a mean ATP amount of 0 to 0.03 ng/cm². ATP assay appears to be a useful and robust method for the detection and quantification of viable elements in foxing spots. Copyright © 2012 John Wiley & Sons, Ltd.     

Simultaneous secretion of seven lignocellulolytic enzymes by an industrial second-generation yeast strain enables efficient ethanol production from multiple polymeric substrates

A major hurdle in the production of bioethanol with second-generation feedstocks is the high cost of the enzymes for saccharification of the lignocellulosic biomass into fermentable sugars. Simultaneous saccharification and fermentation with Saccharomyces cerevisiae yeast that secretes a range of lignocellulolytic enzymes might address this problem, ideally leading to consolidated bioprocessing. However, it has been unclear how many enzymes can be secreted simultaneously and what the consequences would be on the C6 and C5 sugar fermentation performance and robustness of the second-generation yeast strain. We have successfully expressed seven secreted lignocellulolytic enzymes, namely endoglucanase, β-glucosidase, cellobiohydrolase I and II, xylanase, β-xylosidase and acetylxylan esterase, in a single second-generation industrial S. cerevisiae strain, reaching 94.5 FPU/g CDW and enabling direct conversion of lignocellulosic substrates into ethanol without preceding enzyme treatment. Neither glucose nor the engineered xylose fermentation were significantly affected by the heterologous enzyme secretion. This strain can therefore serve as a promising industrial platform strain for development of yeast cell factories that can significantly reduce the enzyme cost for saccharification of lignocellulosic feedstocks.     

An Evaluation of Methods for the Estimation of Sensitivity and Specificity of Site-Specific Diagnostic Tests

The performance of diagnostic tests is often evaluated by estimating their sensitivity and specificity with respect to a traditionally accepted standard test regarded as a “gold standard” in making the diagnosis. Correlated samples of binary data arise in many fields of application. The fundamental unit for analysis is occasionally the site rather than the subject in site-specific studies. Statistical methods that take into account the within-subject corelation should be employed to estimate the sensitivity and the specificity of diagnostic tests since site-specific results within a subject can be highly correlated. I introduce several statistical methods for the estimation of the sensitivity and the specificity of sitespecific diagnostic tests. I apply these techniques to the data from a study involving an enzymatic diagnostic test to motivate and illustrate the estimation of the sensitivity and the specificity of periodontal diagnostic tests. I present results from a simulation study for the estimation of diagnostic sensitivity when the data are correlated within subjects. Through a simulation study, I compare the performance of the binomial estimator pCBE, the ratio estimator pCBE, the weighted estimator pCWE, the intracluster correlation estimator pCIC, and the generalized estimating equation (GEE) estimator PCGEE in terms of biases, observed variances, mean squared errors (MSE), relative efficiencies of their variances and 95 per cent coverage proportions. I recommend using PCBE when σ == 0. I recommend use of the weighted estimator PCWE when σ = 0.6. When σ == 0.2 or σ == 0.4, and the number of subjects is at least 30, PCGEE performs well.     

Designs for Discrimination Between Bivariate Binary Response Models

We propose a test statistic for discrimination between alternative bivariate binary response models and the optimal design procedure which is an extension of T-optimality. Under certain conditions we prove that the maximum value of the power can be-obtained when the degrees of freedom of the test statistic is one. The conclusion is the same as that in discrimination between alternative univariate separate models. However the test statistics are different.