Capillary barriers

A major advantage of DNA as a carrier is that no chemical synthesis or manipulations are needed to obtain DNA-drug complex. The efficacy of the DNA-drug complex depends on stability in the bloodstream, endocytic behavior of normal and tumor cells, presence of extra-cellular deoxyribonuclease activity in the tumor tissues, and capillary barriers that separate normal and tumor cells from the bloodstream. 

Exercise 2 Capillary Barrier ET Cover at Lake County Landfill,... 

Capillary barrier cover systems consist of a finer-grained soil layer (like that of a monolithic cover system) overlying a coarser-grained material layer, usually sand or gravel, as shown conceptually in Figure 25.3. The differences in the unsaturated hydraulic properties between the two layers minimize percolation into the coarser-grained (lower) layer under unsaturated conditions. 

FIGURE 25.3 Conceptual design of a capillary barrier ET final cover.15... 

The finer-grained layer of a capillary barrier cover system has the same function as the monolithic soil layer that is, it stores water until it is removed from the soil by evaporation or transpiration mechanisms. The coarser-grained layer forms a capillary break at the interface of the two layers, which allows the finer-grained layer to retain more water than a monolithic cover system of equal thickness. Capillary forces hold the water in the finer-grained layer until the soil near the interface approaches saturation. If saturation of the finer-grained layer occurs, the water will move relatively quickly into and through the coarser-grained layer and to the waste below. 

Capillary barrier ET cover systems may also eliminate the need for a separate biointrusion and/ or gas collection layer. The coarser-grained layer can act as a biointrusion layer to resist root penetration and animal intrusion, due to its particle size and low water content. The coarser-grained layer can also act as a gas collection layer, because the soil properties and location within the cover system are comparable with a typical gas collection layer in a conventional cover system.3944... 

Finer-grained materials such as silts and clayey silts are typically used for monolithic ET cover systems and the top layer of a capillary barrier ET cover system because they contain finer particles and provide a greater storage capacity than sandy soils. Sandy soils are typically used for the bottom layer of the capillary barrier cover system to provide a contrast in unsaturated hydraulic properties between the two layers. Many ET covers are constructed of soils that include clay loam, silty loam, silty sand, clays, and sandy loam. 

Control layers, such as those used to minimize animal intrusion, promote drainage, and control and collect landfill gas, are often included for conventional cover systems and may also be incorporated into ET cover system designs. For example, a proposed monolithic ET cover at Sandia National Laboratories in New Mexico will have a biointrusion fence with 1/4-in. squares between the topsoil layer and the native soil layer to prevent animals from creating preferential pathways, potentially resulting in percolation. The biointrusion layer, however, will not inhibit root growth to allow for transpiration. At another site, Monticello Uranium Mill Tailings Site in Utah, a capillary barrier ET design has a 12-in. soil/rock admixture as an animal intrusion layer located 44 in. below the surface, directly above the capillary barrier layer. 

In addition, previous studies have been conducted that monitored the performance of ET covers. Selected studies include the following integrated test plot experiment in Los Alamos, New Mexico, which monitored both types of ET covers from 1984 to 198786 Hill Air Force Base alternative cover study in Utah, which evaluated three different covers (RCRA Subtitle D, monolithic ET, and capillary barrier ET) over a 4-year period87 and Hanford field lysimeter test facility in Richland, Washington, DC, which monitored ET covers for 6 years.88... 

A searchable on-line database has been developed by U.S. EPA with information about ET cover systems.92 As of September 2003, the database contained 56 projects with monolithic ET cover systems and 21 projects with capillary barrier ET cover systems these systems have been proposed, tested, or installed at 64 sites located throughout the United States. Some sites have multiple projects, and some projects have multiple covers and/or cover types. 

The database provides project profiles that include site background information (e.g., site type, climate, and precipitation), project information (e.g., purpose, scale, and status), cover information (e.g., design, vegetation, and installation), performance and cost information, points of contact, and references. Table 25.5 provides a summary of key information from the database for 34 recent projects with monolithic ET or capillary barrier ET covers.15... 

Capillary Barrier ET Covers- Gaffey Street Sanitary Landfill, Wilmington, CA —Full-Scale Projects MSW landfill Installation NA... 

Capillary Barrier ET Covers—Demonstration Projects Douglas County Landfill, Bennington, NE (ACAP project) MSW landfill Operational August 2000... 

Cover designs The capillary barrier test section was installed in November 1999. From the surface downward, it is composed of 6 in. of topsoil, 18 in. of moderately compacted silt, and 24 in. of sandy gravel. The cover was seeded in March 2000 with a mixture of grasses, forbs, and shrubs, including bluegrass, wheatgrass, alfalfa, and prickly rose shrubs. A conventional composite cover test section was also constructed at the site. 

Performance data Percolation is being measured with a lysimeter connected to flow monitoring systems, soil moisture is being measured with water content reflectometers, and soil matric potential and soil temperature are being monitored with heat dissipation units. From November 1999 to July 2002, the capillary barrier cover system had a cumulative percolation of 0.5 mm. Total precipitation was 837 mm over the 32-month period. Additional field data were collected through 2005. 

The U.S. DOE has sponsored the ALCD, which is a large-scale field test of two conventional designs (RCRA Subtitle C and Subtitle D) and four alternative landfill covers (monolithic ET cover, capillary barrier ET cover, geosynthetic clay liner cover, and anisotropic—layered capillary barrier—ET cover). The test was conducted at Sandia National Laboratories, located on Kirtland Air Force Base in Albuquerque, New Mexico.84 The ALCD has collected information on the construction, cost, and performance that are needed to compare alternative cover designs with conventional covers. The... 

Stormont, J.C., Incorporating capillary barriers in surface cover systems, Environmental Science and Research Foundation, Proceedings, Landfill Capping in the Semi-Arid West Problems, Perspectives, and Solution, Grand Teton National Park, WY, ESRF-019, May 21-22, 1997, pp. 39-51. 

Pulmonary absorption of volatile anesthetics across the alveolar-capillary barrier is very rapid because of the relatively high lipid-water partition coefficients and small molecular radii of such agents. The driving force for diffusion is a combination of the blood-air partition coefficient (which is a measure of the capacity of blood to dissolve drug) and the difference in partial pressure between the alveoli and the arterial and venous blood. Agents with high blood-air partition coefficients require more drug to be dissolved in the blood for equilibrium to be reached. 

Fig. 3 Aquaporin deletion reduces osmotic water permeability in lung, but does not impair active fluid absorption, a AQP expression in epithelia and endothelia in nasopharyngeal cavity, upper and lower airways, and alveoli, b Osmotically driven water transport across the airspace/capillary barrier in perfused lungs from wildtype and indicated AQP null mice. Note the remarkable slowing of osmotic equilibration in mice lacking AQPl or AQP5. c Alveolar fluid clearance measured from the increased concentration of a volume marker 15 min after instillation of isosmolar fluid at 37°C. Where indicated, fluid absorption was inhibited by amiloride or stimulated by isoproterenol. From Bat et al. (1999) and Ma et al. (2000a)...

Figure 3. Schematic diagram of a sample holder using capillary barriers for water injection and withdrawal experiments. Liquid enters the sample from the bottom while air escapes from the top.

It is generally agreed that proteins can cross the alveolar-capillary barrier of the lung, but the quantitative importance and mechanisms of uptake via this route are not clear. Several mechanisms have been proposed for protein transport in the... 

Hermanns MI, Unger RE, Kehe K, et al. Lung epithelial cell lines in coculture with human microvascular endothelial cells development of an alveolo-capillary barrier in vitro. Lab Invest 2004 84 736-752. 

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