Carbon dioxide transport through enzymatically active synthetic membranes

The facilitated transport of CO₂ through thin liquid membranes, Millipore filter membranes, and cross-linked protein membranes has been investigated using a tracer ¹⁴CO₂ technique. Both the uncatalyzed reactions and the enzymatic reactions catalyzed by carbonic anhydrase in homogeneous solution and immobilized in several membrane configurations were studied. The steady-state transport data were reduced in terms of an analytical model for simultaneous reaction and diffusion which permitted the direct determination of the diffusional and enzyme kinetic parameters. The experimental method illustrates a powerful technique for measuring rapid reaction kinetics. In addition, a general multi-layer membrane model is developed which is capable of treating membrane kinetic heterogeneities. The multi-layer model yields a useful definition for the reaction boundary layer and provides a comparison among different membrane kinetic configurations for membrane design purposes.     

Clinical trials and tribulations: lessons learned from recruiting pregnant ex-smokers for relapse prevention.

The development of smoking cessation and relapse prevention interventions for pregnant and postpartum women is a public health priority. However, researchers have consistently reported substantial difficulty in recruiting this population into clinical trials. The problem is particularly acute for relapse prevention studies, which must recruit women who have already quit smoking because of their pregnancy. Although these individuals are an important target for tobacco control efforts, they represent an extremely small subgroup of the general population. This paper describes multiple recruitment strategies used for a clinical trial of a self-help relapse prevention program for pregnant women. The effectiveness of the strategies and the direct expense per participant recruited are provided. A proactive recruitment strategy (telephoning women whose phone numbers were purchased from a marketing firm) was ultimately much more successful than a variety of reactive strategies (advertisements, press releases, direct mail, Web placement, health care provider outreach). We found few differences between proactively and reactively recruited participants on baseline variables. The primary difference was that the former had smoked fewer cigarettes per day and reported lower nicotine dependence prior to quitting. Strengths and limitations of the recruitment strategies are discussed.     

Engineering in Genomics [variable number tandem repeats as agents of functional regulation in the genome]

The explosion of genetic data availability in the last decade has opened up many new avenues for the application of genetics to the improvement of human health, particularly, the common and complex disorders, which previously largely defied researchers seeking to understand their etiology. However, the utilization of this data in healthcare and by the pharmaceutical industry is still in its infancy, with the current focus being almost solely on two forms of genetic variation single nucleotide polymorphisms (SNPs), involving the substitution of one base in DNA for another and copy number variations, involving the deletion and multiplication of regions > 1,000 base pairs (bp). However, there is currently a relative paucity of funding and general interest in a third form of variation called microsatellites and mini- satellites.     

Temporal changes in macroinvertebrate assemblages following experimental flooding in permanent and temporary wetlands in an Australian floodplain forest

The River Murray, Australia, is a highly regulated river from which almost 80% of mean annual flow is removed for human use, primarily irrigated agriculture. Consequent changes to the pattern and volume of river flow are reflected in floodplain hydrology and, therefore, the wetting/drying patterns of floodplain wetlands. To explore the significance of these changes, macroinvertebrate samples were compared between permanent and temporary wetlands following experimental flooding in a forested floodplain of the River Murray. Weekly samples from two permanent wetlands and four associated temporary sites were used to track changes in macroinvertebrate assemblage composition. Non‐metric multidimensional scaling was used to ordinate the macroinvertebrate data, indicating consistent differences between the biota of permanent and temporary wetlands and between the initial and later assemblages in the temporary sites. There were marked changes over time, but little sign that the permanent and temporary assemblages were becoming more alike over the 25‐week observation period. The apparent heterogeneity of these systems is of particular importance in developing river management plans which are likely to change flooding patterns. Such plans need to maintain a mosaic of wetland habitats if floodplain biodiversity is to be supported. Copyright © 2002 John Wiley & Sons, Ltd.     

Accounting for uncertainty in control-relevant statistics

To make appropriate decisions based on common indices used in control, both the point estimates and their uncertainties must be known. Many control-relevant statistics, such as model predictions, gain margins and other frequency domain quantities, are functions of parameters of process models. Confidence regions for these quantities are most often calculated under the assumption that these quantities have an asymptotic limiting normal distribution. These confidence regions may be erroneous, and very misleading, as the asymptotic results ignore the influence of parameter nonlinearities. In addition, proximity of the model parameters to stability/invertibility boundaries also distorts the confidence regions from those predicted from asymptotic theory. Generalized profiling is a flexible numerical method for constructing confidence intervals and confidence regions for model parameters, and functions of model parameters. Applications in nonlinear regression [D. Bates, D. Watts, Nonlinear Regression Analysis and Its Applications, John Wiley & Sons, New York, 1988] indicate that it provides a much more accurate representation of uncertainty in those instances when the asymptotic uncertainty results are inaccurate or misleading. Generalized profiling is based on the likelihood approach to quantifying uncertainty. The numerical construction of these likelihood uncertainty regions requires solution to a series of constrained optimization problems. Computationally efficient diagnostic tests, motivated by profiling, are developed. These can be effectively employed as screening tools to indicate when the asymptotic results are most likely to be inadequate.     

Nationwide survey of fluoroscopy: radiation dose and image quality

PURPOSE: To determine the average abdominal entrance air kerma, low-contrast sensitivity, and spatial resolution in upper gastrointestinal tract fluoroscopy in the United States. MATERIALS AND METHODS: A random sample of fluoroscopic facilities was selected to be surveyed for the Nationwide Evaluation of X-ray Trends program. Measurements were performed by using a newly developed fluoroscopic phantom. The surveys were conducted by state radiation control personnel. RESULTS: Average air kerma rates 1 cm above the tabletop, free in air, were 43 mGy/min (n = 340). The rate increased to 64 mGy/min when a 1.6-mm-thick copper filter, which simulated the use of barium contrast medium, was added to increase attenuation. The average entrance air kerma, free in air, for radiographs was 3.4 mGy, and an average of 12 radiographs were obtained per examination. Of 352 facilities surveyed, 306 (87%) were able to resolve wire mesh with 20 or more lines per inch. Of 339 facilities for which percentage contrast could be calculated, 192 (57%) had minimum percentage contrast values of 4% or more. CONCLUSION: Spatial resolution for fluoroscopy is adequate for most of the facilities surveyed, but a substantial proportion of facilities could not visualize low-contrast test objects, which strongly suggests image quality problems.     

Facilitated transport of benzylpenicillin through immobilized liquid membrane

The rate of benzylpenicillin transport, as an ionic pair with a tetrabutyl ammonium cation, from aqueous media through a liquid membrane consisting of n-decanol supported in a porous Teflon membrane has been investigated as a function of the chemical composition of the system and the hydrodynamic conditions at 25°C. The measured transfer rates have been explained in terms of the diffusion of the ionic pair species through the liquid membrane. The results are in agreement with theoretical predictions and it is demonstrated that the transport of benzylpenicillin takes place against a concentration gradient.     

Methanethiosulfonate derivatives inhibit current through the ryanodine receptor/channel

To identify regions of the ryanodine receptor (RyR) important for ion conduction we modified the channel with sulfhydryl-reacting compounds. After addition of methanethiosulfonate (MTS) compounds channel conductance was decreased while other channel properties, including channel regulation by ATP, caffeine, or Ca, were unaffected. The site of action was accessible to the MTS compounds from the cytoplasmic, but not the luminal, side of the channel. In addition, the hydrophilic MTS compounds were only effective when the channel was open, suggesting that the compounds covalently modify the channel from within the water-filled ion conducting pathway. The decrease in channel current amplitude occurred in a step-wise fashion and was irreversible and cumulative over time, eventually leading to the complete block of channel current. However, the time required for each consecutive modification during continuous exposure to the MTS compounds increased, suggesting that successive modification by the MTS compounds is not independent. These results are consistent with the hypothesis that the channel forms a wide vestibule on the cytoplasmic side and contains a much smaller opening on the luminal side. Furthermore, our results indicate that the MTS compounds can serve as functional markers for specific residues of the RyR to be identified in molecular studies.