Fluid penetration

Increase pore size to increase rate of fluid penetration. Decrease pore size to increase extent of fluid penetration. Modify particle size distrihiition of feed ingredients. Alter milling, classification or formation conditions of feed if appropriate to modify particle size distrihiition. 

Significance. What is the significance of these observations For succinoglycan solutions the answer is obvious, above the transition temperature they have little or no viscosity, which may be undesirable. Such polymers are usually used as viscosifiers or for particle suspension. On the other hand, a drop in viscosity may be an advantage if fluid penetrates a formation hotter than the well as there could be little or no subsequent formation damage. 

The effect of fluid penetration rate and the extent of penetration on granule size distribution from drum granulation experiments is illustrated in Fig. 20 (since no example for fluidized bed granulation is available). From Fig. 20, it is clear that for fluids with a similar extent of penetration, increasing the penetration rate increases the average granule size for various levels of liquid loading. 

GaiUard J et al. Cerebrospinal fluid penetration of amikacin in children with community-acquired bacterial meningitis. Antimicrob Agents Chemother 1995 39 253-255. 

Drug concentrations in pleural fluid, peritoneal fluid, synovial fluid, aqueous humor, and vitreous humor approach two-thirds of the serum concentration when local inflammation is present. Meningeal and am-niotic fluid penetration, with or without local inflammation, is uniformly poor. Measurement of serum, urine, or cerebrospinal fluid drug levels has not been used clinically. 

A horizontal interface between two fluids such that the lower fluid is the less dense tends to deform by the process known as Rayleigh-Taylor instability (see Section UFA). Spikes of the denser fluid penetrate downwards, until the interface is broken up and one fluid is dispersed into the other. This is observed, for example, in formation of drops from a wet ceiling, and of bubbles in film boiling. For low-viscosity fluids, the equivalent diameter of the particle formed is of order Ja/gAp. 

Pharmacokinetics and cerebrospinal fluid penetration of hypericin were studied after i.v. dose of 2 mg/kg in monkeys (Table 2) (70). Mean peak plasma concentration of hypericin following this dose was 71.7pg/mL (142 pM). Elimination of hypericin from plasma was biexponential, with an average terminal half-life of 26 14 hours. The 2 mg/kg dose in nonhuman primates was sufficient to maintain plasma concentrations above 5.1 pg/mL (10 pM) for up to 12 hours (the in vitro concentration required for growth inhibition of human glioma cell lines is greater than 10 pM). 

Fox E, Murphy RF, McCully CL, Adamson PC. Plasma pharmacokinetics and cerebrospinal fluid penetration of hypericin in nonhuman primates. Cancer Chemother Pharmacol 2001 47 41-44. 

Although the terminal half-life of cidofovir is 2.6 hours, the active metabolite, cidofovir diphosphate, has a prolonged intracellular half-life of 17-65 hours, thus allowing infrequent dosing. A separate metabolite, cidofovir phosphocholine, has a half-life of at least 87 hours and may serve as an intracellular reservoir of active drug. Cerebrospinal fluid penetration is poor. Elimination is by active renal tubular secretion. High-flux hemodialysis has been shown to reduce the serum levels of cidofovir by approximately 75%. 

Indinavir requires an acidic environment for optimum solubility and therefore must be consumed on an empty stomach or with a small, low-fat, low-protein meal for maximal absorption (60-65%). The serum half-life is 1.5-2 hours, protein binding is approximately 60%, and the drug has a high level of cerebrospinal fluid penetration (up to 76% of serum levels). Excretion is primarily fecal. An increase in AUC by 60% and in half-life to 2.8 hours in the setting of hepatic insufficiency necessitates dose reduction. 

Most antimicrobial agents are well distributed to most body tissues and fluids. Penetration into the cerebrospinal fluid is an exception. Most do not penetrate uninflamed meninges to an appreciable extent. In the presence of meningitis, however, the cerebrospinal fluid concentrations of many antimicrobials increase (Table 51-6). 

Supercritical Fluid Extraction. Conditions can be generated that allow materials to behave differently from their native state. For example, boiling points are defined as that temperature at which a liquid changes to a gas. If the liquid is contained and pressure exerted, the boiling point changes. For a particular liquid, a combination of pressure and temperature will be reached, called the critical point, at which the material is neither a liquid nor a gas. Above this point exists a region, called the supercritical region, at which increases in both pressure and temperature will have no effect on the material (i.e., it will neither condense nor boil). This so-called supercritical fluid will exhibit properties of both a liquid and a gas. The supercritical fluid penetrates materials as if it were a gas and has solvent properties like a liquid. 

Most solids of high surface area are to some extent porous. The texture of such materials is defined by the detailed geometry of the void and pore space. Porosity, , is a concept related to texture and refers to the pore space in a material. An open pore is a cavity or channel communicating with the surface of a particle, as opposed to a closed pore. Void is the space or interstice between particles. In the context of adsorption and fluid penetration powder porosity is the ratio of the volume of voids plus the volume of open pores to the total volume occupied by the powder. Similarly, particle porosity is the ratio of the volume of open pores to the total volume of the particle. It should be noted that these definitions place the emphasis on the accessibility of pore space to the adsorptive. 

Stool softener laxatives - increase the amount of fluid penetrating the stool and decrease surface tension. 

During the first 10 ptsec of drop impact, the initially spherical drop spreads out, bulging at the edges, then recoUing. By 20—80 psec, the drop reaches a static configm ation, roughly the same diameter as the final spot size, and then begins to shrink as fluid penetrates... 

Hydrothermal circulation causes extensive alteration of the upper ocean crust, reflected both in mineralization of the crust and in changes to physical properties of the basement (Alt, 1995). The direction and extent of chemical and isotopic exchange between seawater and oceanic crust depends on variations in temperature and fluid penetration and, thus, vary strongly as a function of depth. Extensive mineralization of the upper... 

Wise R, Gee T, Andrews JM, Dvorchik B, Marshall G. Pharmacokinetics and inflammatory fluid penetration of intravenous daptomycin in volunteers. Antimicrob Agents Chemother 2002 46(l) 31-3. 

Scotton PG, Pea F, Giobbia M, Baraldo M, VagUa A, Furlanut M. Cerebrospinal fluid penetration of levofloxacin in patients with spontaneous acute bacterial meningitis. Qin Infect Dis 2001 33(9) el09-ll. 

Jimenez-Mejias ME, Pichardo-Guerrero C, Marquez-Rivas FJ, Martin-Lozano D, Prados T, Pachon J. Cerebrospinal fluid penetration and pharmacokinetic/phar-macodynamic parameters of intravenously administered colistin in a case of multidrug-resistant Acinetobacter bau-mannii meningitis. Eur J CUn Microbiol Infect Dis 2002 21(3) 212-14. 

There are also some nice computer simulations, such as those by Cieplak and Robbins ), demonstrating the influence of the contact angle on fluid penetration into a two-dimensional porous material and providing an example of self-organized criticality. 

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