Download or read book The Living Barrier written by Roy J. Levin and published by Butterworth-Heinemann. This book was released on 2013-10-22 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Living Barrier: A Primer on Transfer across Biological Membranes provides information pertinent to the movement of molecules across cell membranes. This book covers a variety of topics, including cell membrane, membrane transfer, water transfer, and movement of charged solutes. Organized into nine chapters, this book begins with an overview of the basic ideas of the cell membrane and reviews the experimental evidence about the structure of the cell membrane. This text then reviews the classical electron microscope pictures of membranes. Other chapters consider the interactions between electrical potentials and the movements of charged substances, which make the membrane transfer of these substances much more complicated than those of neutral molecules. This book discusses as well the aspects of water structure and its influence on membrane permeability. The final chapter deals with the methods by which membranes are synthesized. This book is a valuable resource for biochemists, physiologists, pharmacologists, and botanists.
Download or read book Molecular Biology of The Cell written by Bruce Alberts and published by . This book was released on 2002 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Reactive Membrane Barriers for Containment of Subsurface Contamination written by and published by . This book was released on 2007 with total page 62 pages. Available in PDF, EPUB and Kindle. Book excerpt: The overall goal of this project was to develop reactive membrane barriers--a new and flexible technique to contain and stabilize subsurface contaminants. Polymer membranes will leak once a contaminant is able to diffuse through the membrane. By incorporating a reactive material in the polymer, however, the contaminant is degraded or immobilized within the membrane. These processes increase the time for contaminants to breakthrough the barrier (i.e. the lag time) and can dramatically extend barrier lifetimes. In this work, reactive barrier membranes containing zero-valent iron (Fe°) or crystalline silicotitanate (CST) were developed to prevent the migration of chlorinated solvents and cesium-137, respectively. These studies were complemented by the development of models quantifying the leakage/kill time of reactive membranes and describing the behavior of products produced via the reactions within the membranes. First, poly(vinyl alcohol) (PVA) membranes containing Fe° and CST were prepared and tested. Although PVA is not useful in practical applications, it allows experiments to be performed rapidly and the results to be compared to theory. For copper ions (Cu{sup 2+}) and carbon tetrachloride, the barrier was effective, increasing the time to breakthrough over 300 times. Even better performance was expected, and the percentage of the iron used in the reaction with the contaminants was determined. For cesium, the CST laden membranes increased lag times more than 30 times, and performed better than theoretical predictions. A modified theory was developed for ion exchangers in reactive membranes to explain this result. With the PVA membranes, the effect of a groundwater matrix on barrier performance was tested. Using Hanford groundwater, the performance of Fe° barriers decreased compared to solutions containing a pH buffer and high levels of chloride (both of which promote iron reactivity). For the CST bearing membrane, performance improved by a factor of three when groundwater was used in place of deionized water. The performance of high density polyethylene (HDPE) membranes containing Fe° was then evaluating using carbon tetrachloride as the target contaminant. Only with a hydrophilic additive (glycerol), was the iron able to extend lag times. Lag times were increased by a factor of 15, but only 2-3% of the iron was used, likely due to formation of oxide precipitates on the iron surface, which slowed the reaction. With thicker membranes and lower carbon tetrachloride concentrations, it is expected that performance will improve. Previous models for reactive membranes were also extended. The lag time is a measurement of when the barrier is breached, but contaminants do slowly leak through prior to the lag time. Thus, two parameters, the leakage and the kill time, were developed to determine when a certain amount of pollutant has escaped (the kill time) or when a given exposure (concentration x time) occurs (the leakage). Finally, a model was developed to explain the behavior of mobile reaction products in reactive barrier membranes. Although the goal of the technology is to avoid such products, it is important to be able to predict how these products will behave. Interestingly, calculations show that for any mobile reaction products, one half of the mass will diffuse into the containment area and one half will escape, assuming that the volumes of the containment area and the surrounding environment are much larger than the barrier membrane. These parameters/models will aid in the effective design of barrier membranes.
Download or read book Liquid Separations with Membranes written by Karl W. Böddeker and published by Springer Science & Business Media. This book was released on 2007-12-14 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt: The plan of this book is to present the relevant thermodynamic features of fluid mixtures in contact with semipermeable barriers, then to apply this information in deriving the design requirements of individual membrane separation processes. The membranes, by this approach, are introduced by way of the mass transport and selectivity demands which they are to meet. This book gives a survey, in systematic order, of the terms and concepts by which barrier separations operate.
Download or read book Polymer Membranes Containing Zero valent Iron as Contaminant Barriers written by Tsutomu Shimotori and published by . This book was released on 2005 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Membrane Permeability 100 Years Since Ernest Overton written by and published by Academic Press. This book was released on 1999-05-21 with total page 443 pages. Available in PDF, EPUB and Kindle. Book excerpt: Membrane permeability is fundamental to all cell biology and subcellular biology. The cell exists as a closed unit. Import and export depend upon a number of sophisticated mechanisms, such as active transport, endocytosis, exocytosis, and passive diffusion. These systems are critical for the normal housekeeping physiological functions. However, access to the cell is also taken advantage of by toxic microbes (such as cholera or ptomaine) and when designing drugs. Ernest Overton, one of the pioneers in lipid membrane research, put forward the first comprehensive theory of lipid membrane structure. His most quoted paper on the osmotic properties of cells laid the foundation for the modern concepts of membrane function, most notably important in anesthesia. This book is designed to celebrate the centennial anniversary (in the first chapter) of Overton's work. Subsequent chapters present readers with up-to-date concepts of membrane structure and function and the challenge they pose for new explorations. Provides an historical perspective of Overton's contributions to the theory of narcosis Presents an overview of each permeability mechanism, including active transport, endocytosis, exocytosis, and passive diffusion
Download or read book Membranes and Barriers written by and published by . This book was released on 1995 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Guidance on the Use of Plastic Membranes As VOC Vapour Barriers written by Steve Wilson (Civil engineer) and published by . This book was released on 2014-10 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: Buildings are often constructed on sites where volatile organic compounds (VOCs) such as benzene, toluene, chlorinated solvents, ethers etc. are in the ground. The usual remedial solution is to provide a gas membrane under or over the floor slab, of the same type as used to prevent methane and carbon dioxide migration into buildings. This guide provides a summary of the functions of a vapour membrane and the factors that may affect the performance of the membrane in a protection system for a building on land contaminated by VOCs.
Download or read book Flake filled Reactive Barrier Membranes written by Nancy Kristina Lape and published by . This book was released on 2004 with total page 314 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Cerebral Circulation written by Marilyn J. Cipolla and published by Biota Publishing. This book was released on 2016-07-28 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt: This e-book will review special features of the cerebral circulation and how they contribute to the physiology of the brain. It describes structural and functional properties of the cerebral circulation that are unique to the brain, an organ with high metabolic demands and the need for tight water and ion homeostasis. Autoregulation is pronounced in the brain, with myogenic, metabolic and neurogenic mechanisms contributing to maintain relatively constant blood flow during both increases and decreases in pressure. In addition, unlike peripheral organs where the majority of vascular resistance resides in small arteries and arterioles, large extracranial and intracranial arteries contribute significantly to vascular resistance in the brain. The prominent role of large arteries in cerebrovascular resistance helps maintain blood flow and protect downstream vessels during changes in perfusion pressure. The cerebral endothelium is also unique in that its barrier properties are in some way more like epithelium than endothelium in the periphery. The cerebral endothelium, known as the blood-brain barrier, has specialized tight junctions that do not allow ions to pass freely and has very low hydraulic conductivity and transcellular transport. This special configuration modifies Starling's forces in the brain microcirculation such that ions retained in the vascular lumen oppose water movement due to hydrostatic pressure. Tight water regulation is necessary in the brain because it has limited capacity for expansion within the skull. Increased intracranial pressure due to vasogenic edema can cause severe neurologic complications and death.
Download or read book Synthesizing High Quality Graphene Membranes for Engineering Diffusion Barriers written by Susmit Singha Roy and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: We demonstrate significant advances in the fundamental understanding and engineering of scalable graphene diffusion barriers. Experimental studies have established that defect-free non-scalable graphene is an excellent barrier material, however its scalable counterparts are still well behind in terms of performance. The latter's ability to perform as a barrier membrane is compromised primarily by the presence of three major problems - high density of defects, self-degradation in ambient environment and induced electrochemical oxidation of the underlying material. First, we develop an in-depth understanding of how diffusion occurs through monolayer graphene grown via chemical vapor deposition. It is shown that the atomic membrane is impenetrable in the pristine regions, however it is easily penetrated by oxygen and water at grain boundaries and intrinsic pinholes. Second, we study in detail the self-deterioration of graphene in ambient and quantify the evolution, kinetics, and energetics of the degradation process both in the pristine and intrinsically defective regions of graphene. It is also found that the degradation process is accelerated in the presence of water vapor. Third, we find that the overall defect density of a graphene membrane is primarily determined by the density of its intrinsic pinholes and grain boundaries. We demonstrate that the density on intrinsic pinholes can be significantly reduced by reducing the surface roughness of the growth substrate which is achieved by regulating the pre-growth annealing time and temperature. The density of the grain boundaries can be altered by varying the internucleation distance during the growth of the membrane. Fourth, when graphene is used as a corrosion barrier for metals, we establish that the electrochemical corrosion of the metal can be drastically reduced by adding an ultra-thin electrically insulating layer between the graphene and the metal. In addition, the barrier performance is enhanced greatly by stacking more layers of graphene top of the first layer. Finally, we combine all the results and knowledge from these previous studies to design the best performing scalable graphene barrier until date. We expect this study to serve as a foundation for engineering next-generation graphene barriers with performance comparable to its pristine and theoretical counterparts.
Download or read book Assessment of the Performance of Engineered Waste Containment Barriers written by National Research Council and published by National Academies Press. This book was released on 2007-09-22 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt: President Carter's 1980 declaration of a state of emergency at Love Canal, New York, recognized that residents' health had been affected by nearby chemical waste sites. The Resource Conservation and Recovery Act, enacted in 1976, ushered in a new era of waste management disposal designed to protect the public from harm. It required that modern waste containment systems use "engineered" barriers designed to isolate hazardous and toxic wastes and prevent them from seeping into the environment. These containment systems are now employed at thousands of waste sites around the United States, and their effectiveness must be continually monitored. Assessment of the Performance of Engineered Waste Containment Barriers assesses the performance of waste containment barriers to date. Existing data suggest that waste containment systems with liners and covers, when constructed and maintained in accordance with current regulations, are performing well thus far. However, they have not been in existence long enough to assess long-term (postclosure) performance, which may extend for hundreds of years. The book makes recommendations on how to improve future assessments and increase confidence in predictions of barrier system performance which will be of interest to policy makers, environmental interest groups, industrial waste producers, and industrial waste management industry.
Download or read book Barrier Membranes with High Concentrations of Aligned Impermeable Flakes written by Jonathan P. DeRocher and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Diffusion in Flake filled Barrier Membranes written by Diana Marie Eitzman and published by . This book was released on 1992 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Synthesizing High Quality Graphene Membranes for Engineering Diffusion Barriers written by Susmit Singha Roy and published by . This book was released on 2015 with total page 328 pages. Available in PDF, EPUB and Kindle. Book excerpt: We demonstrate significant advances in the fundamental understanding and engineering of scalable graphene diffusion barriers. Experimental studies have established that defect-free non-scalable graphene is an excellent barrier material, however its scalable counterparts are still well behind in terms of performance. The latter’s ability to perform as a barrier membrane is compromised primarily by the presence of three major problems - high density of defects, self-degradation in ambient environment and induced electrochemical oxidation of the underlying material. First, we develop an in-depth understanding of how diffusion occurs through monolayer graphene grown via chemical vapor deposition. It is shown that the atomic membrane is impenetrable in the pristine regions, however it is easily penetrated by oxygen and water at grain boundaries and intrinsic pinholes. Second, we study in detail the self-deterioration of graphene in ambient and quantify the evolution, kinetics, and energetics of the degradation process both in the pristine and intrinsically defective regions of graphene. It is also found that the degradation process is accelerated in the presence of water vapor. Third, we find that the overall defect density of a graphene membrane is primarily determined by the density of its intrinsic pinholes and grain boundaries. We demonstrate that the density on intrinsic pinholes can be significantly reduced by reducing the surface roughness of the growth substrate which is achieved by regulating the pre-growth annealing time and temperature. The density of the grain boundaries can be altered by varying the internucleation distance during the growth of the membrane. Fourth, when graphene is used as a corrosion barrier for metals, we establish that the electrochemical corrosion of the metal can be drastically reduced by adding an ultra-thin electrically insulating layer between the graphene and the metal. In addition, the barrier performance is enhanced greatly by stacking more layers of graphene top of the first layer. Finally, we combine all the results and knowledge from these previous studies to design the best performing scalable graphene barrier until date. We expect this study to serve as a foundation for engineering next-generation graphene barriers with performance comparable to its pristine and theoretical counterparts.
Download or read book Localized Barriers in the Plasma Membrane written by Barry Gumbiner and published by . This book was released on 1985 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Comparative Analysis of Fluid Applied Air Barrier Products written by Katherine S. Wissink and published by . This book was released on 2014 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fluid-applied air-barrier/water-resistive-barrier membranes for use in exterior wall systems are relatively new products and are increasingly being specified and used by designers and building owners. These membranes can serve as the primary air barrier and water-resistive barrier, as well as the vapor retarder depending on the vapor permeance of the membrane. The integrity and continuity of this membrane is essential, given that this single material may perform up to three critical functions and will govern the performance of the wall system in terms of moisture migration and waterproofing. The lack of widely accepted industry standards of material property performance for these products makes it difficult for designers to compare products from different manufacturers. Further, because these products are relatively new, their long-term performance is not well established. As such, durability testing of these membranes is important to help designers and building owners anticipate long-term performance prior to specifying these products on projects. This article compares material properties and durability of 14 fluid-applied air barriers, both vapor-permeable and -impermeable products, as determined by laboratory testing. Properties tested include adhesion to common substrates, elongation, and water absorption. The laboratory testing program also addresses the durability of the membranes by testing the effect of freezing temperatures, exposure to water and UV radiation, and aging on the material properties noted above. This article discusses the development of the laboratory testing program, outlines methods of testing and accelerated weathering, and summarizes the test results.
