Passive barrier

A membrane is defined as an intervening phase separating two phases forming an active or passive barrier to the transport of matter. Membrane processes can be operated as (1) Dead-end filtration and (2) Cross-flow filtration. Dead-end filtration refers to filtration at one end. A problem with these systems is frequent membrane clogging. Cross-flow filtration overcomes the problem of membrane clogging and is widely used in water and wastewater treatment. 

Capital cost of passive barriers (for example, containment dikes, and vacant land to provide spacing, required by codes, regulations and insurers). 

Honeywell has also been active in developing a combined active-passive oxygen barrier system for polyamide-6 materials [201]. Passive barrier characteristics are provided by nanoclay particles incorporated via melt processing techniques, while active contribution comes from an oxygen-scavenging ingredient (undisclosed). Oxygen transmission results reveal substantial... 

Membranes are not merely passive barriers. They include an array of proteins specialized for promoting or... 

Although the stratum corneum acts as a simple physical barrier to outside influences, skin tissue as a whole is very active. It is crucial in maintaining the body s homeostasis, its essential steady-state environment. Skin maintains temperature and balance of electrolytes, the dissolved salts in internal body fluids. It is metabolically active and participates in hormonal and immune regulatory processes. More than serving as a passive barrier, it is proactive in response to xenobiotic insults and can be damaged in the defensive process by developing rashes and other symptoms. 

Since one major motivation behind the use of plasma BPSG was to provide an improved passivation barrier, the better crack resistance is an advantage, but the greater sodium penetration is a negative. Therefore, it is not clear if it would be advantageous to make this replacement11 for a final passivation film. Its use as an inter-metallic dielectric may be more useful. 

Subcellular localization studies have identified P-450-dependent monooxygenase activity in adult hairless mice sebaceous glands. Phase II conjugation pathways have also been identified in skin. Extracellular enzymes including esterases are present in skin, which has been utilized to formulate lipid-soluble ester prodrugs which penetrate the stratum corneum and then are cleaved to release active drug into the systemic circulation. Finally, co-administration of enzyme inducers and inhibitors modulate cutaneous biotransformation and thus alter the systemic toxicity profile. These metabolic interactions that occur in skin have attracted a great deal of research attention and clearly illustrate that skin is more than a passive barrier to toxin absorption. 

A simplified working definition of a membrane can be conveniently stated as a semipermeable active or passive barrier which, under a certain driving force, permits preferential passage of one or more selected species or components (molecules, particles or polymers) of a gaseous and/or Uquid mixture or solution (Figure 1.1). 

The membrane in a contactor acts as a passive barrier and as a means of bringing two immiscible fluid phases (such as gas and hquid, or an aqueous hquid and an organic hquid, etc.) in contact with each other without dispersion. The phase interface is immobilized at the membrane pore surface, with the pore volume occupied by one of the two fluid phases that are in contact. Since it enables the phases to come in direct contact, the membrane contactor functions as a continuous-contact mass transfer device, such as a packed tower. However, there is no need to physically disperse one phase into the other, or to separate the phases after separation is completed. Several conventional chemical engineering separation processes that are based on mass exchange between phases (e.g., gas absorption, gas stripping, hquid-hquid extraction, etc.) can therefore be carried out in membrane contactors. 

The view of the lipid bilayer in membranes as a passive barrier, with the embedded proteins assigned all functionality, has stood unchallenged for about half a century. Numerous results during the last decade have drastically changed this picture. It is now well established that the lipid molecules also participate in biochemical processes related to many basic membrane functions. An illustrative example is cell activation due to an... 

According to a definition given by the European Membrane Society, the membrane is an intervening phase separating two phases and/or acting as an active or passive barrier... 

Membrane contactors can be made out of flat sheet membranes, which have some commercial applications. However, the most common commercial membrane contactors are made from small-diameter microporous hollow-fiber (or capillary) membranes with fine pores that run from the inner surface to the outer surface of the hollow-fiber wall. The contactor resembles a tube-in-shell configuration with inlet-outlet ports for the shell side and tube side. These kinds of membranes are typically made of hydrophobic materials such as polypropylene (PP), polyethylene (PE), polytetrafluoroethylene (PTFE), poly(tetrafluoroethylene-co-perfluorovinylether) (PEA), or polyvinylidene fluoride (PVDE). The membrane in a contactor acts as a passive barrier and as a means of bringing two immiscible fluid phases, such as gas and liquid or an aqueous liquid and an organic liquid, into contact with each other... 

Appropriate passive barriers, (i.e., fuel clad, coolant system boundaries, containment) to prevent or minimize potent i a I rad i oact i ve re I eases ... 

Personal protective equipment is sometimes included in this category, although generally it provides marginal protection in comparison to more substantial passive barriers. It normally represents the last line of defense, and its use and effectiveness may rely on procedures and training. 

As can be seen from the schematic diagram in Fig. 1.11., four independent, passive barriers prevent the release of fission products from the fuel to the environment in the case of accident ... 

As has been discussed in the preceding sections, the containment of a nuclear power plant represents a very effective passive barrier, at least for a certain period of time, for confining the radionuclides released from the reactor core and from the primary system in a severe accident. This renders possible their plate-out from the containment atmosphere by natural processes such as deposition of aerosols or, as regards iodine, formation of non-volatile compounds, as well as by the action of engineered safety features (e. g. sprays). Nevertheless, in safety considerations it has to be assumed that the containment is not a permanent and absolutly tight confinement, but that there would be several fundamental mechanisms by which a certain fraction of the radionuclides could escape from the containment. The most important of these mechanisms are... 

Until recently, the emphasis has been on passive barriers, which just sit there and act as a barrier between the environment and the product. Such materials are often mixed so... 

As a matter of conclusion, there are a large number of materials as well as the ability to combine them in a lot of different ways to produce passive barriers of all kinds, but the next step is bound to be the active packages. 

ABSTRACT Oil spill removal techniques have been developed as passive barriers to reduce the severity of adverse impacts of oil spills on the environment. Among different oil spill removal methods, combination of skimmers and booms are more preferable environmentally, as they can recover the spilt oil from sea permanently. However, a number of factors such as harsh Arctic climatic conditions, presence of sea ice, remote distances, poor visibility, and less developed infrastructure threaten the overall performance of skimmers. Therefore, identifying such influencing parameters and evaluating their impacts on the overall performance of skimmers is of the utmost importance. In this study, the overall performance of skimmers in the Arctic offshore is discussed from the viewpoints of effectiveness and availability performance. Several operational conditions and their impacts on the availability performance of skimmers and their effectiveness in the Arctic offshore are further reviewed and discussed. Changes in physical and chemical properties of spilt oil and their contribution to the window-of-opportunity for a successful skinmiing operation are described, taking into account the severe Arctic climatic conditions. 

The increasing trend of oil and gas activities in the Arctic offshore has raised major concerns about oil spills and their impacts on the Arctic s ecologically sensitive environment. To decrease the severity of such impacts, oil spill clean-up technologies are developed as passive barriers to oil spills. Various techniques are available for removal of offshore oil spills, such as in-situ burning, use of dispersants, and mechanical methods. Oil skimmers are one of the essential categories of mechanical recovery methods that generally are used in combination with containment booms (Fingas 2011, Potter et al. 2012). 

Omit the barriers whose performance cannot be controlled (e.g. inherent design issues) gravel pack and erosion/corrosion allowance are passive barriers and for this reason were omitted. 

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