Recent advances in bioprocessing application of membrane chromatography

Compared to traditional chromatography using resins in packed-bed columns, membrane chromatography is a relatively new and immature bioseparation technology based on the integration of membrane filtration and liquid chromatography into a single-stage operation. Over the past decades, advances in membrane chemistry have yielded novel membrane devices with high binding capacities and improved mass transfer properties, significantly increasing the bioprocessing efficiency for purification of biomolecules. Due to the disposable nature, low buffer consumption, and reduced equipment costs, membrane chromatography can significantly reduce downstream bioprocessing costs. In this review, we discuss technological merits and disadvantages associated with membrane chromatography as well as recent bioseparation applications with a particular attention on purification of large biomolecules.     

Understanding reproductive allometry in turtles: A slippery “slope”

Measures of reproductive output in turtles are generally positively correlated with female body size. However, a full understanding of reproductive allometry in turtles requires logarithmic transformation of reproductive and body size variables prior to regression analyses. This allows for slope comparisons with expected linear or cubic relationships for linear to linear and linear to volumetric variables, respectively. We compiled scaling data using this approach from published and unpublished turtle studies (46 populations of 25 species from eight families) to quantify patterns among taxa. Our results suggest that for log–log comparisons of clutch size, egg width, egg mass, clutch mass, and pelvic aperture width to shell length, all scale hypoallometrically despite theoretical predictions of isometry. Clutch size generally scaled at ~1.7 to 2.0 (compared to an isometric expectation of 3.0), egg width at ~0.5 (compared to an expectation of 1.0), egg mass at ~1.1 to 1.3 (3.0), clutch mass at ~2.5 to 2.8 (3.0), and pelvic aperture width at 0.8–0.9 (1.0). We also found preliminary evidence that scaling may differ across years and clutches even in the same population, as well as across populations of the same species. Future investigators should aspire to collect data on all these reproductive parameters and to report log–log allometric analyses to test our preliminary conclusions regarding reproductive allometry in turtles.     

Spectrofluorimetric study on fluorescence quenching of tyrosine and l‐tryptophan by the aniracetam cognition enhancer drug: quenching mechanism using Stern–Volmer and double‐log plots

A novel approach on fluorescence quenching of tyrosine and l ‐tryptophan is presented for spectrofluorimetric determination of aniracetam in drug substances and products. The quenching mechanism was investigated using Stern–Volmer plots and ultraviolet spectra figures of quencher–fluorophore mixtures. Binding constant and stoichiometry were calculated using double‐log plots. The spectrofluorimetric method was optimized for the experimental conditions affecting fluorescence quenching including fluorophore concentration, diluent, and reaction time. Moreover, the pH‐rate profile of aniracetam was studied using simple kinetics and found to be stable within the pH range 5–8. Fluorescence quenching of tyrosine and l ‐tryptophan were observed on addition of aniracetam in aqueous medium at pH 5.5–6.5. Aniracetam quenched the fluorescence of tyrosine and l ‐tryptophan in the concentration range 1–20 μg/ml and 0.3–20 μg/ml, respectively, with binomial relationships between quenching values (ΔF) and aniracetam concentration. Limits of detection were found to be 0.10 μg/ml for tyrosine–aniracetam and 0.14 μg/ml for l ‐tryptophan–aniracetam. Method validation was performed as per ICH guidelines and demonstrated that the developed spectrofluorimetric method was accurate, precise, specific, and suitable for analysis of aniracetam in routine quality control laboratories. All experimental materials and solvents used are eco‐friendly, indicating that the cited spectrofluorimetric procedure is an excellent green method.     

红壤水分条件对温州蜜柑果实生长与产量的影响

以宫川温州蜜柑(Citrus unshiu Marc. cv. Miyagawa Wase)橘树为材料,于2003—2004年利用土壤水分探头实时监测柑橘果实膨大期的红壤水分,研究了红壤相对含水量（RSM）对柑橘果实生长及产量构成因子的影响。结果表明：RSM由30%增加到90%,柑橘果实纵径和横径均递增,而纵径/横径比值则递减,周累积果实增量纵径（1.60～1.74 cm）<横径（1.95～2.26 cm）,红壤水分降低对柑橘果实纵向膨大限制影响大于横径;果实产量构成因子呈抛物线趋势变化,且RSM为75%时达到最大值。综合柑橘果实生长及其产量构成因子,RSM在75%时最利于柑橘果实生长及高产。     

A multiple-record systems estimation method that takes observed and unobserved heterogeneity into account

We present a model to estimate the size of an unknown population from a number of lists that applies when the assumptions of (a) homogeneity of capture probabilities of individuals and (b) marginal independence of lists are violated. This situation typically occurs in epidemiological studies, where the heterogeneity of individuals is severe and researchers cannot control the independence between sources of ascertainment. We discuss the situation when categorical covariates are available and the interest is not only in the total undercount, but also in the undercount within each stratum resulting from the cross-classification of the covariates. We also present several techniques for determining confidence intervals of the undercount within each stratum using the profile log likelihood, thereby extending the work of Cormack (1992, Biometrics48, 567-576).     

Nonparametric rank-based methods for group sequential monitoring of paired censored survival data

This research gives methods for nonparametric sequential monitoring of paired censored survival data in the two-sample problem using paired weighted log-rank statistics with adjustments for dependence in survival and censoring outcomes. The joint asymptotic closed-form distribution of these sequentially monitored statistics has a dependent increments structure. Simulations validating operating characteristics of the proposed methods highlight power and size consequences of ignoring even mildly correlated data. A motivating example is presented via the Early Treatment Diabetic Retinopathy Study.     

Evaluation of two methods for assessing gene-environment interactions using data from the Danish case-control study of facial clefts

BACKGROUND: Epidemiological investigations have begun to consider gene-environment (GE) interactions as potential risk factors for many diseases, including several different birth defects. However, traditional methodological approaches for the analysis of case-control data tend to have low power for detection of interaction effects. A log-linear approach that can impose the assumption that the genotype and exposure of interest occur independently in the population has been proposed as a potentially more powerful method for assessing GE interactions but has not been widely applied in the published literature. METHODS: The present analyses were undertaken to compare the results obtained when stratified analyses and a log-linear approach were used to assess potential GE interactions. The analyses were conducted using data from a population-based, case-control study conducted in Denmark and considered associations between nonsyndromic cleft lip with or without cleft palate (CL+/-P), infant genotype for variants of RAR-alpha, TGF-alpha, TGF-beta3, and MSX1, and maternal exposure to smoking, alcohol, and multivitamins. RESULTS: Neither the stratified nor the log-linear analyses provided evidence that that risk of CL+/-P is influenced by any of the GE interactions that were evaluated, despite the potential increase in power offered by the latter approach. Further, the analyses highlight concerns regarding the power to reject the assumption of independence of the genetic and environmental factor of interest in the controls and related concerns regarding the validity of results obtained using the log-linear approach when the underlying assumption is violated. CONCLUSIONS: The potential increase in power offered by the log-linear approach is offset by concerns regarding the validity of this approach when the independence assumption is violated.     

The influence of submerged pulpwood on feeding and condition of fishes in a reservoir

One hundred and forty years of log driving in the Kennebec River, Maine, left an estimated one to two million cords of submerged pulpwood logs, with major accumulations in reservoirs such as Wyman lake. Commercial salvaging of these logs began in 1978, which prompted a study to assess the importance of these logs to fishes and the potential effects of log salvaging. Vertical gill nets were set in Wyman Lake, in areas with and without logs, to measure fish densities and to obtain specimens for analysis of food habits and body conditions. Yellow perch (Perca flavescens) were more abundant in sites without logs (P < .05), but suckers (Catostomus spp.) were more abundant in sites with logs (P < 0.05). Yellow perch preyed primarily on cladocerans in sites without logs and on larger invertebrates in sites with logs, implying a difference in prey availability between study sites. Although the yellow perch and common shiners captured in non-log areas were longer than those in log areas (P < 0.05), their body conditions were not significantly different. Moderate log salvage operations would probably have little effect on the body conditions and abundances of fishes in Wyman Lake, if precautions were taken to avoid disruption of spawning and nursery areas at critical times of the year; impacts would vary in other lakes with differing topography and species compositions.