Resistance to penetration

Such a unique hierarchical stmcture gives leather several advantages (/) transformabiUty into any desired shape, (2) resistance to penetration of wind, water, and other materials, (3) breathabiUty (water vapor and air permeabiUty, and water absorption), (4) flexibiUty, and (5) processibiUty into finished forms having a grain or suede surface. 

A more polar comonomer, eg, an AN comonomer, increases the water-vapor transmission more than VC when other factors are constant. For the same reason, AN copolymers are more resistant to penetrants of low cohesive energy density. AH VDC copolymers, however, are very impermeable to ahphatic hydrocarbons. Comonomers that lower T and increase the free volume in the amorphous phase increase permeability more than the polar comonomers higher acrylates are an example. Plasticizers increase permeabiUty for similar reasons. 

The anatomical stmcture of wood affects strength properties, appearance, resistance to penetration by water and chemicals, resistance to decay, pulp quabty, and the chemical reactivity of wood (5). To use wood most effectively requires a knowledge of not only the amounts of various substances that make up wood, but also how those substances are distributed ia the cell walls. 

Resistance to penetration by micro-organisms is covered by EN 374-2 and protection from low temperatures in EN 511. Careful handling and regular inspection are essential since chemicals and abrasion will eventually cause deterioration of gloves. Rinsing in clean water and drying naturally will prolong their life. 

California bearing ratio tests are used to evaluate subgrades for pavements. These tests may be carried out in the field or in the laboratory. Such tests determine the resistance to penetration of a subgrade soil relative to that of a standard crushed-rock base. 

In double-layer nickel coatings however, a flat-based pit is formed in the nickel coating, giving marked resistance to penetration to the basis metal. Figure 13.8 shows a pit in a double-layer nickel plus chromium coating after 58 months service. 

Typical pore size distributions result in mean pore diameters of around 15 //m. Even long and intensive efforts did not succeed in decreasing this value decisively in order to enable production of micropo-rous pocketing material resistant to penetration [65, 66], In practice PVC separators prove themselves in starter batteries in climatically warmer areas, where the battery life is however noticeably reduced because of increased corrosion rates at elevated temperature and vibration due to the road condition. The failure modes are similar for all leaf separator versions shedding of positive active mass fills the mud room at the bottom of the container and leads to bottom shorts there, unless — which is the normal case — the grids of the positive electrodes are totally corroded beforehand. 

Since stab detonators contain no restraining anvil as do percussion primers, the resistance to penetration of the firing pin becomes quite im-. portant. This is the role of compression or density of the mixt. With higher density, the kinetic energy of the firing pin is dissipated over... 

Three main routes exist for the spread of cancer cells throughout the body. These involve the lymphatic system, the blood system, and direct extension into body cavities. Spread by the lymphatic system is thought to be important for carcinomas. The walls of these channels offer little mechanical resistance to penetration by tumor cells. Malignant cells readily invade the walls of these vessels and are carried to regional lymph nodes. In the lymph node, the cancer cells can arrest, proliferate and produce a metastatic tumor. Malignant cells may later detach from the lymph node and be carried in the bloodstream to other sites throughout the body. 

Film thickness is measured in gauge or mils. According to test results reported by several manufacturers, film thickness appears to affect resistance to penetration/ tearing, with thicker films being more resistant to penetration and tearing. However, the application of a thicker film did not decrease glass fragmentation. 

Adding sizing to impart resistance to penetration by liquids. Most sizing is a soap or wax emulsion precipitated by the alum. This produces a gelatinous film on the fiber and a hardened surface. 

In the event that a short delay is desired but space limitations preclude the incorporation of any baffle, the BkPdr pellet should be pressed very strongly to offer resistance to penetration by the high velocity particles... 

Leonard Katzin I want to make two comments, one on this last point in relation to the point that Dr. Margerum made about substituents. Chromium (I II) in the hexahyd rated state is quite resistant to penetration of the coordination shell by nitrate ion. Yet if one takes the% violet chromium nitrate hexahydrate in solid state and treats it with liquid tributylphosphate, within a matter of minutes one gets chromium compound in solution by the mechanism of substituting tributylphosphate for water. So this reaction is fast. This initial solution is violet Within the space of an hour or two it is green. And we have had for some years now infrared evidence that this color change is accompanied by penetration of the nitrate ion into the coordination sphere (4). So this again is a matter of the substituent s changing the relationship of the water. 

The resistance to penetration defined in this sense is called by F. Auerbach the absolute hardness of a body, and he has designed an apparatus for measuring this property. 

Magazine walls or doors of construction resistant to penetration of a bullet of 150-grain M2 ball ammunition having a nominal muzzle velocity of 2700 feet per second fired from a. 30 caliber rifle from a distance of 100 feet perpendicular to the wall or door. 

The stratum corneum has been estimated to contribute 1000 times the diffusional resistance to chemical penetration as the layers beneath it, except for extremely lipid-soluble compounds with tissue/water partition coefficients greater than 400. As in most other epithelial tissues, the two other layers of the skin (dermis and subcutaneous tissue) offer little resistance to penetration. Once a substance has penetrated the outer epithelium, these tissues are rapidly traversed. This may not be true for highly lipid-soluble compounds, because the dermis may function as an additional aqueous barrier preventing a chemical that has penetrated the epidermis from being absorbed into the blood. 

Carbonation begins at exposed surfaces, and spreads inwards at a rate proportional to the square root of time (K66). The thickness of the affected layer can be approximately determined by testing a section with phcnol-phthalein. Chloride ion from an external source similarly penetrates inwards. The age at which corrosion is liable to begin thus depends on the minimum thickness of concrete covering the reinforcement, the resistance to penetration and the conditions to which the concrete is subjected. The depth of cover needed to provide protection over a given period can be calculated (SI 17.B154). 

Figure 19.5. Resistance to penetration of a yoghurt gel as a fiinetion of the degree of p-lg (genetie variant B) denaturation resulting from milk heating pre-treatment sm skim milk, wm whole milk (Dannenberg 1986).

Fig. 93 Soil resistance to penetration and fine-root length density in the soil beneath cutter ant nests (Atta sexdens) and beneath neighboring forest without nest influence.

For steric reasons bifunctional or trifunctional silanes can react with either one only or, at most, two silanol groups on the silica gel surface (second reaction in Fig. 1.8A). Thus, some of the functional (Cl or alkoxy) groups remain unreacted and easily hydrolyse to form new silanol groups. If the reaction mixture contains even traces of water, the hydrolysis occurs during chemical modification of silica and the new silanol groups react with excess molecules of reagents to form a polymerised surface layer (Fig. 1.8B). These bonded phases may be more stable and usually show stronger retention than monomeric phases at low pH. However, the reaction is difficult to reproduce and various batches of the same material may have different properties, so that the reproducibility of separation is poorer than with monomeric phases. Polymeric phases are more resistant to penetration of analytes and may show increased mass-transfer resistance and decreased efficiency (plate number) of separation [- 91. 

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