Diffusion, extraordinary

Du Pont called this new lubricant material Krytox (64,65) and initially it had such extraordinary properties that it sold for 200/kg ( 187kg ca 1993). Krytox was and is used ia most of the vacuum pumps and diffusion oil pumps for the microelectronics iadustry ia this country and ia Japan because it produces no hydrocarbon (or fluorocarbon) vapor contamination. It has also found important appHcations ia the lubrication of computer tapes and ia other data processiag appHcations as weU as military and space appHcations. 

Quite extraordinary diffusion coefficients of impurities from odier parts of die Periodic Table are found, and especially in die important case of lidiium or copper diffusion, where die eidiancement over self-diffusion is by six to eight orders of magnitude. This indicates diat diese atoms do not form part of die sp network in die sUmcture, but more closely resemble separate atoms in die sp iiiaUix. 

Root exudation of extraordinary high amounts of specific carboxy lutes (e.g ci-u-ate, malate. oxalate, pbytosiderophores) in response to nutritional deficiency stress or Al toxicity in some plant species cannot simply be attributed to diffusion processes. The controlled release of these compounds, involved in mobilization of mineral nutrients and in detoxification of Al. may be mediated by more specific mechanisms. Inhibitory effects by exogenous application of various anion chan-... 

Carbenes are such highly reactive intermediates that their direct observation requires extraordinary efforts. One set of conditions that has proved quite valuable is low temperature isolation. Carbenes can be generated by irradiation of an appropriate precursor within a glass or more ordered inert matrix at very low temperatures. The low temperature of the experiment stops or slows reactions of the carbene with the matrix material. Also, the rigidity of the medium prevents diffusion and the dimerization of the carbene is stopped. Many carbenes can be stabilized at the boiling point of nitrogen (77 K) others require liquid helium temperatures (4 K). 

Since its first appearance in 1967, the Topics in Stereochemistry series has stood as the standard-bearer for advances in the broad field of stereochemistry. The visionary founders of the series anticipated, with remarkable foresight, the extraordinary growth and impact that stereochemistry has had on all reaches of the chemical enterprise. Fortunately, there is no cease of interest in the importance of stereochemistry as the discipline of chemistry evolves and its borders expand and diffuse into the related fields of biology, medicine, physics, materials science, chemical engineering, and environmental science. 

Mechanistic Ideas. The ordinary-extraordinary transition has also been observed in solutions of dinucleosomal DNA fragments (350 bp) by Schmitz and Lu (12.). Fast and slow relaxation times have been observed as functions of polymer concentration in solutions of single-stranded poly(adenylic acid) (13 14), but these experiments were conducted at relatively high salt and are interpreted as a transition between dilute and semidilute regimes. The ordinary-extraordinary transition has also been observed in low-salt solutions of poly(L-lysine) (15). and poly(styrene sulfonate) (16,17). In poly(L-lysine), which is the best-studied case, the transition is detected only by QLS, which measures the mutual diffusion coefficient. The tracer diffusion coefficient (12), electrical conductivity (12.) / electrophoretic mobility (18.20.21) and intrinsic viscosity (22) do not show the same profound change. It appears that the transition is a manifestation of collective particle dynamics mediated by long-range forces but the mechanistic details of the phenomenon are quite obscure. 

Schmitz and Lu (12) have also considered coupling of translational and rotational modes for rigid rods in congested solutions as an explanation for the extraordinary diffusion regime. They concluded that, for 350 bp dinucleosomal DNA, the coupled ion model gave better agreement with the data. Since our DNA molecules are even shorter, 150 bp, the coupled translation -rotation model can seemingly be ruled out. 

Strassman speculates that DMT, released by the pineal after death, could diffuse to nearby brain areas, allowing the soul to transit. His hypothesis is that the pineal gland produces psychedelic amounts of DMT at extraordinary times in our lives and at death. As we die, our life force leaves the body through the pineal gland, which releases a flood of DMT. Pineal DMT may be produced for a few hours even after we are dead, which could affect any lingering consciousness. The pineal gland is close to the brain s visual, auditory, and emotional centers and thus would be strategically positioned to alter our inner experiences. 

Hydrides. According to X-ray and neutron diffraction and metallographic studies of the Nb-H system,524 the H may be considered a lattice gas with phase transitions. In the a-, a -, j6-, and -phases of the system, H occupies tetrahedral interlattice positions. Whereas direct reaction between niobium metal and hydrogen occurs only after repeated activation of the metal by hydrogen absorption at ca. 7 atm and 350 °C, NbH2 is formed at temperatures as low as 22 °C in mixtures of LaNi5H6 7 and Nb.525 The extraordinary catalytic effect of the lanthanum-nickel complex is attributed to the presence of surface-absorbed atomic hydrogen species which are able to diffuse into the niobium lattice. There has been a review of the T a-H system.526... 

Nonsteady-state diffusion through oil-water multilaminates has been used extensively as a model for the optimal biological response of a series of congeners with respect to partition coefficient (3,7, 8). Actual solution of this model reveals the deficiencies of multilaminates as a model for biological transport, but it does show the extraordinary separation factors of these multilaminates in the nonsteady-state regime. 

The solution to this series of diffusion equations demonstrates (Figure 2) the extraordinary capability of these oil-water multilaminates to separate permeants based on partition coefficient. Let PMA be the partition coefficient for maximum transport. For P MAX t le total transport CR(t) depends exponentially on, the number of oil layers for p>>pjIAX> cR(t) depends exponentially on n-1, the number of water laminates. 

Owing to its extraordinary chemical stability, diamond is a prospective electrode material for use in theoretical and applied electrochemistry. In this work studies performed during the last decade on boron-doped diamond electrochemistry are reviewed. Depending on the doping level, diamond exhibits properties either of a superwide-gap semiconductor or a semimetal. In the first case, electrochemical, photoelectrochemical and impedance-spectroscopy studies make the determination of properties of the semiconductor diamond possible. Among them are the resistivity, the acceptor concentration, the minority carrier diffusion length, the flat-band potential, electron phototransition energies, etc. In the second case, the metal-like diamond appears to be a corrosion-stable electrode that is efficient in the electrosyntheses (e.g., in the electroreduction of hard to reduce compounds) and electroanalysis. Kinetic characteristics of many outer-sphere... 

Closely linked to its extraordinary solvent capacities is water s role in transporting dissolved materials throughout the organism. With the exception of air-filled channels like the tracheal systems of insects, most of the transport processes of organisms involve movement of dissolved solutes. Diffusion of solutes within water is rapid, as is the translational and rotational movement of water itself. The extensive networks of hydrogen bonds that form among water molecules and between water and solutes do not impede this dynamic move-... 

The physical separation between genotype and phenotype has an extraordinary consequence, because mental genotypes can be directly instructed by mental phenotypes, and this means that cultural heredity is based on a transmission of acquired characters. Cultural inheritance, in other words, is transmitted with a Lamarckian mechanism, whereas biological inheritance relies on a Mendelian mechanism which is enormously slower. As a result, cultural evolution is much faster than biological evolution, and almost all differences between biology and culture can be traced back to the divide that exists in their hereditary mechanisms. The discovery that human artifacts (i.e. cultural phenotypes) obey the Lotka-Volterra equations has two outstanding consequences. The first is that selection accounts for all types of adaptive evolution natural selection is the mechanism hy which all phenotypes - biological as well as cultural - diffuse in the world. 

It has long been a mystery why diffusion coefficients of polymer-diluent systems, especially when the diluent is a good solvent for a given polymer, exhibit so pronounced a concentration dependence that it looks extraordinary. Several proposals have been made for the interpretation of this dependence. Thus Park (1950) attempted to explain it in terms of the thermodynamic non-ideality of polymer-diluent mixtures, but it was found that such an effect was too small to account for the actual data. Fujita (1953) suggested immobilization of penetrant molecules in the polymer network, which, however, was not accepted by subsequent workers. Recently, Barrer and Fergusson (1958) reported that their diffusion coefficient data for benzene in rubber could be analyzed in terms of the zone theory of diffusion due to Barrer (1957). Examination shows, however, that their conclusion is never definitive, since it resorted to a less plausible choice of the value for a certain basic parameter. 

In the past decade a number of physical techniques have been used to evaluate the unique barrier properties of mammalian skin [1]. This chapter deals with the use of another physical technique, fluorescence spectroscopy, to study the barrier properties of the human stratum corneum (SC), specifically with respect to the transport of ions and water. The SC is the outermost layer of the human epidermis and consists of keratinized epithelial cells (comeo-cytes), physically isolated from one another by extracellular lipids arranged in multiple lamellae [2]. Due to a high diffusive resistance, this extracellular SC lipid matrix is believed to form the major barrier to the transport of ions and water through the human skin [3-5]. The objective of the fluorescence studies described here is to understand how such extraordinary barrier properties are achieved. First the phenomenon of fluorescence is described, followed by an evaluation of the use of anthroyloxy fatty acid fluorescent probes to study the physical properties of solvents and phospholipid membranes. Finally, the technique is applied to the SC to study its diffusional barrier to iodide ions and water. 

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