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PubMed2001

Moisture effect on the transport of organic vapors in sand.

Vapor-phase affects the transport, lifetime, and fate of volatile organic contaminants in soils. Furthermore, it has an effect on the assessment and the selection of a remediation approach. The diffusion of dichloromethane (DCM), 1,1,1-trichloroethane (TCE) and carbon tetrachloride (CTC) in dry and wet sand media were investigated using a packed column at room temperature. The apparent diffusion coefficients, D(app), which accounts for effective diffusion and sorption of DCM, TCE and CTC were determined by fitting the experimental data to a diffusion model. The apparent diffusion coefficients of DCM, TCE and CTC for wet sand were found to be larger than the corresponding values for dry sand. The presence of water reduced retardation factors expressed in terms of the sorption capacity for each compound. The results indicated that dry mineral surface provided dominant sorption sites. This is reflected in greater amounts of organic vapors adsorbed under dry conditions. On the other hand, lower sorption capacities for organic compounds on vapor-water interface than on vapor-mineral interface and their low solubilities resulted in smaller retardation factors in wet sand. The experiments clearly demonstrate the role of humidity in sorption and transport of vapors in sand.

Adsorption↗
PubMed1992

Quantitation of lateral stress in lipid layer containing nonbilayer phase preferring lipids by frequency-domain fluorescence spectroscopy.

Frequency-resolved fluorescence measurements have been performed to quantitate the lateral stress of the lipid layer containing nonbilayer phase preferring dioleoylphosphatidylethanolamine (DOPE). On the basis of a new rotational diffusion model, the wobbling diffusion constant (Dw), the curvature-related hopping diffusion constant (DH), and the two local orientational order parameters ([P2] and [P4]) of 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5-hexatrienyl)phenyl]ethyl] carbonyl]-3-sn-phosphatidylcholine (DPH-PC) in fully hydrated DOPE and DOPE/dioleoylphosphatidylcholine (DOPC) mixtures were calculated from the frequency-domain anisotropy data. The values of [P2], [P4], and DH for DOPE were found to increase significantly at approximately 12 degrees C, the known lamellar liquid crystalline (L alpha) to inverted hexagonal (HII) phase transition temperature of DOPE. Similar features as well as a decline of Dw were detected in the DOPE/DOPC mixtures as the DOPE content was increased from 85% to 90% at 23 degrees C, corresponding to the known lyotropic phase transition of the DOPE/DOPC. In contrast, for DOPC (0-40 degrees C) and DOPE/DOPC (0-100% DOPE at 3 degrees C), which remained in the L alpha phase, these changes were not detected. The most probable local orientation of DPH-PC in the DOPE/DOPC mixtures shifted progressively toward the normal of the lipid/water interface as the content of DOPE increased. We concluded that the curvature-related lateral stress in the lipid layer increases with the content of the nonbilayer phase preferring lipids.

Diffusion↗
PubMed2006

Proton dynamics in lithium-ammonia solutions and expanded metals.

Quasielastic neutron scattering has been used to study proton dynamics in the system lithium-ammonia at concentrations of 0, 4, 12, and 20 mole percent metal (MPM) in both the liquid and solid (expanded metal) phases. At 230 K, in the homogenous liquid state, we find that the proton self-diffusion coefficient first increases with metal concentration, from 5.6x10(-5) cm2 s(-1) in pure ammonia to 7.8x10(-5) cm2 s(-1) at 12 MPM. At higher concentrations we note a small decrease to a value of 7.0x10(-5) cm2 s(-1) at 20 MPM (saturation). These results are consistent with NMR data, and can be explained in terms of the competing influences of the electron and ion solvation. At saturation, the solution freezes to form a series of expanded metal compounds of composition Li(NH3)4. Above the melting point, at 100 K, we are able to fit our data to a jump-diffusion model, with a mean jump length (l) of 2.1 A and residence time (tau) of 3.1 ps. This model gives a diffusion coefficient of 2.3x10(-5) cm2 s(-1). In solid phase I (cubic, stable from 88.8 to 82.2 K) we find that the protons are still undergoing this jump diffusion, with l=2.0 A and tau=3.9 ps giving a diffusion coefficient of 1.8x10(-5) cm2 s(-1). Such motion gives way to purely localized rotation in solid phases IIa (from 82.2 to 69 K) and IIb (stable from 69 to 25 K). We find rotational correlation times (tau(rot)) of the order of 2.0 and 7.3 ps in phases IIa and IIb, respectively. These values can be compared with a rotational mode in solid ammonia with tau(rot) approximately 2.4 ps at 150 K.

Journal Article↗
PubMed2006

Respiration by buried echidnas Tachyglossus aculeatus.

Short-beaked echidnas have an impressive ability to submerge completely into soil or sand and remain there, cryptic, for long periods. This poses questions about how they manage their respiration, cut off from a free flow of gases. We measured the gradient in oxygen partial pressure (PO2) away from the snouts of buried echidnas and oxygen consumption (VO2) in five individuals under similar conditions, in two substrates with different air-filled porosities (fa). A theoretical diffusion model indicated that diffusion alone was insufficient to account for the flux of oxygen required to meet measured rates of VO2. However, it was noticed that echidnas often showed periodic movements of the anterior part of the body, as if such movements were a deliberate effort to flush the tidal air space surrounding their nostrils. These ;flushing movements' were subsequently found to temporarily increase the levels of interstitial oxygen in the soil around the head region. Flushing movements were more frequent while VO2 was higher during the burrowing process, and also in substrate with lower fa. We conclude that oxygen supply to buried echidnas is maintained by diffusion through the soil augmented by periodic flushing movements, which ventilate the tidal airspace that surrounds the nostrils.

Animals↗
PubMed2001

Promoting mechanism of menthol derivative, 1-O-ethyl-3-buthylcyclohexanol, on the percutaneous absorption of ketoprofen.

Menthol derivatives were synthesized and evaluated for their promoting activity on the percutaneous absorption of ketoprofen and skin irritation in vivo, choosing O-ethylmenthol (MET) as the mother compound. The compound having a C-3 positionned n-butyl group (1-O-ethyl-3-n-buthylcyclohexanol, OEBC) indicated the most promoting activity and caused relatively little skin irritation. In order to understand enhancement mechanism of OEBC an in vitro permeation study of ketoprofen was performed. The time course of the cumulative amounts of drug permeated through the rat skin exhibited a linear relation after an initial lag time. This was analyzed in membrane diffusion model and the diffusion and partition parameters of ketoprofen were estimated. Both parameters were remarkably enhanced when a hydrogel containing a small quantity of OEBC (0.5%) was applied. Furthermore, to clarify the site of action of OEBC, we also investigated in vitro permeation study of ketoprofen employing different skins of state, reversed skin and stratum corneum stripped skin. When OEBC was added to the hydrogels which were applied to the reversed and stripped skins, almost no changes of the flux were observed compared with the control (without OEBC). These results suggested that the site of action of OEBC was stratum corneum. Morphological changes of the stratum corneum surface were microscopically observed with 0-2% OEBC. The spaces between the stratum corneum cells treated with 0.5-2% OEBC became extended and the shape of each cell became clear. This may suggest that the site of action of OEBC was the intercellular of stratum corneum. Furthermore, an electron spin resonance study was performed to investigate the effect of OEBC on the intercellular lipid bilayer fluidity of the stratum corneum and the rotational correlation times were calculated. 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) were used as the spin label. In use of OEBC, the fluidity of TEMPO labeled the stratum corneum lipid increased as the addition of OEBC. The results suggested that OEBC promote the penetration of drugs by enhancing fluidity of the local lipid bilayers around TEMPO.

Algorithms↗
PubMed2005

Estimation of yields of OH radicals in water irradiated by ionizing radiation.

The yield of OH radical induced by ionizing radiation was estimated by an empirical model; a prescribed diffusion model for a spur of single size applying to neutral water. Two representative spur distances were introduced, one for an incident primary charged particle and one for a representative secondary electron, to calculate chemical yields among active species in a spur. The total yield from the track was a combination of these primary and secondary yields. Two coefficients of this combination were the parameters of the present model. Based on an optimization of these parameters by existing experimental Fricke G-values, the present model estimates the yields of OH at the microsecond timescale after an irradiation, in a unified manner from electrons to heavy ions. The predicted yields of OH around the nanosecond timescale after an irradiation may be a relevant basis for a study on the mechanisms of radiation effects. This prediction by the present model was exemplified for electrons, photons and heavy ions (proton, helium, carbon, neon, argon and iron).

Computer Simulation↗
PubMed2000

Explicitly modeling the effects of aging on response time.

Research into the effects of aging on response time has focused on Brinley plots. Brinley plots are constructed by plotting mean response times for older subjects against those for young subjects for a set of experimental conditions. The typical result is a straight line with a slope greater than 1 and a negative intercept. This linear function has been interpreted as showing that aging leads to a general slowing of cognitive processes. In this article, we show that the slope of the Brinley plot is actually a measure of the relative standard deviations of older versus young subjects' response times; it is not a measure of general slowing. We examine current models of the effects of aging on mean response time and show how they might be reinterpreted. We also show how a more comprehensive model, Ratcliff's diffusion model (1978), can account for Brinley plot regularities and, at the same time, provide an account of accuracy rates, the shapes of response time distributions, and the relative speeds of error and correct response times, aspects of the data about which models designed to account for Brinley plots are mute. We conclude by endorsing a research approach that applies explicit models to response time data in aging in order to use the parameters of the model to interpret the effects of aging.

Aging↗
PubMed2001

A diffusion-translocation model for gradient sensing by chemotactic cells.

Small chemotactic cells like Dictyostelium and neutrophils transduce shallow spatial chemoattractant gradients into strongly localized intracellular responses. We show that the capacity of a second messenger to establish and maintain localized signals, is mainly determined by its dispersion range, lambda = the square root of D(m)/k(-1), which must be small compared to the cell's length. Therefore, short-living second messengers (high k(-1)) with diffusion coefficients D(m) in the range of 0-5 microm(2) s(-1) are most suitable. Additional to short dispersion ranges, gradient sensing may include positive feedback mechanisms that lead to local activation and global inhibition of second-messenger production. To introduce the essential nonlinear amplification, we have investigated models in which one or more components of the signal transduction cascade translocate from the cytosol to the second messenger in the plasma membrane. A one-component model is able to amplify a 1.5-fold difference of receptor activity over the cell length into a 15-fold difference of second-messenger concentration. Amplification can be improved considerably by introducing an additional activating component that translocates to the membrane. In both models, communication between the front and the back of the cell is mediated by partial depletion of cytosolic components, which leads to both local activation and global inhibition. The results suggest that a biochemically simple and general mechanism may explain various signal localization phenomena not only in chemotactic cells but also those occurring in morphogenesis and cell differentiation.

Animals↗
PubMed2001

Sliding drops in the diffuse interface model coupled to hydrodynamics.

Using a film thickness evolution equation derived recently combining long-wave approximation and diffuse interface theory [L. M. Pismen and Y. Pomeau, Phys. Rev. E 62, 2480 (2000)] we study one-dimensional surface profiles for a thin film on an inclined plane. We discuss stationary flat film and periodic solutions including their linear stability. Flat sliding drops are identified as universal profiles, whose main properties do not depend on mean film thickness. The flat drops are analyzed in detail, especially how their velocity, advancing and receding dynamic contact angles and plateau thicknesses depend on the inclination of the plane. A study of nonuniversal drops shows the existence of a dynamical wetting transition with hysteresis between droplike solutions and a flat film with small amplitude nonlinear waves.

Journal Article↗
PubMed2001

Adsorption of dyes and phenols from water on the activated carbons prepared from corncob wastes.

Pore structures and physical properties of the activated carbons prepared from corncob wastes at various activation temperatures (830, 860, 890 degrees C.) were first studied. Equilibria and rates of adsorption of two commercial dyes, phenol, and 3-chlorophenol from water on such activated carbons were then measured at 30 degrees C. All adsorption isotherms of the solutes could be well fitted by the Langmuir equation. Three simplified kinetic models including pseudo-first-order equation, pseudo-second-order equation, and intraparticle diffusion model were selected to follow the adsorption processes. It was shown that the adsorption of both phenols could be best described by the pseudo second-order equation, but that of both dyes best by the intraparticle diffusion model. Kinetic parameters of each best-fit model were calculated and discussed.

Adsorption↗
PubMed2000

Prognostic models for diffuse large B-cell lymphoma.

Prognosis of DLCL patients is variable and associated with well-defined risk factors. In the past decade several pretreatment variables have been incorporated into prognostic models to predict the death risk of individual patients. The International Prognostic Index (IPI), developed in an international consensus study, has been one of the most widely accepted of these models. In our study we applied some of the major prognostic models proposed for DLCLs in a cohort of 111 patients uniformly treated with a CHOP-like regimen in order to compare their sensitivity and specificity. We also evaluated the possibility of improving the IPI with the inclusion, from among the variables analysed, of serum beta-2 microglobulin level (beta-2M). The sensitivity, reflecting the ability to predict all failures in the cohort of patients as a whole, has improved from 45 to 73 per cent when the beta-2M-IPI model is compared with IPI, without a significant loss of specificity. Based on these results, the beta-2M-IPI may be useful for identifying the subset of patients with very poor prognoses. Therefore, the use of the serum beta-2M value in addition to the IPI may help in selection of the patients with DLCL at higher risk for treatment failure, and identification of those who may require specifically tailored therapeutic approaches.

Adult↗
PubMed2004

Phase transition of traveling waves in bacterial colony pattern.

Depending on the growth condition, bacterial colonies can exhibit different morphologies. Many previous studies have used reaction diffusion equations to reproduce spatial patterns. They have revealed that nonlinear reaction term can produce diverse patterns as well as nonlinear diffusion coefficient. Typical reaction term consists of nutrient consumption, bacterial reproduction, and sporulation. Among them, the functional form of sporulation rate has not been biologically investigated. Here we report experimentally measured sporulation rate. Then, based on the result, a reaction diffusion model is proposed. One-dimensional simulation showed the existence of traveling wave solution. We study the wave form as a function of the initial nutrient concentration and find two distinct types of solution. Moreover, transition between them is very sharp, which is analogous to phase transition. The velocity of traveling wave also shows sharp transition in nonlinear diffusion model, which is consistent with the previous experimental result. The phenomenon can be explained by separatrix in reaction term dynamics. Results of two-dimensional simulation are also shown and discussed.

Bacillus↗
PubMed1979

Loss of nitroglycerin from aqueous solution into plastic intravenous delivery systems.

The mechanism of potential loss of nitroglycerin stored in plastic and glass containers was studied from an equilibrium and kinetic approach. Plastic strips equilibrated with dilute aqueous solutions of neat nitroglycerin showed that the drug was lost by absorption. Drug loss was followed by an electron-capture GLC assay. The same assay of control solutions in glass showed no drug loss in 48 hr at pH 5.7. The kinetics of nitroglycerin absorption and desorption were determined using synthesized 14C-labeled drug. Absorption can be quantified using a diffusion model, where the concentration in the aqueous phase falls with time. Curve fitting yielded an average diffusion coefficient in plastic of 2.05 x 10(-9) cm2/sec and a partition coefficient of 104 (plastic-water) at 30 degrees. Temperature-dependence studies of absorption showed that the diffusion coefficient followed an Arrhenius relationship with an energy requirement of 19.6 kcal/mole, whereas effects on the partition coefficient were negligible. Nitroglycerin desorption from plastic disks under sink conditions into water can be quantified by assuming a diffusion model where the concentration at the surface of a plane sheet remains constant. Nonlinear least-squares curve fitting generated a diffusion coefficient of 1.14 x 10(-9) cm2/sec for the desorption process at 30 degrees.

Absorption↗
PubMed2000

Mechanism of Adsorption of Dyes and Phenols from Water Using Activated Carbons Prepared from Plum Kernels.

The kinetics and mechanism of adsorption of two commercial dyes (BR22, AB25), phenol, and 3-chlorophenol from water on activated carbons were studied at 30 degrees C. The activated carbons were prepared from plum kernels, and the activation temperature and time tested were in the ranges 750-900 degrees C and 1-4 h, respectively. Three simplified kinetic models including a pseudo-first-order, a pseudo-second-order, and an intraparticle diffusion model were tested. It was shown that the adsorption of both phenols could be fitted to a pseudo-second-order rate law, and that of both dyes could be fitted to an intraparticle diffusion model. Kinetic parameters were calculated and correlated with the physical properties of the adsorbents. Copyright 2000 Academic Press.

Journal Article↗
PubMed1983

Pharmacokinetics of high-dose methotrexate in dogs. An experimental model with diffusion chambers.

The usefulness of a diffusion chamber method for determination of concentrations of cytostatic drugs in the interstitial fluid of tissues was tested. Chambers with a permeable membrane (pore size: 0.45 micrometer) were implanted in the liver, kidney, bladder wall, and prostate of dogs. After administration of high doses of methotrexate (100 mg/kg body wt) the concentrations in the chamber fluid and in serum were measured simultaneously and repeatedly for 72 h. The method proved to be effective for collecting data on the distribution of drugs in different organs. The results show that knowledge of the serum concentration does not permit predictions of the drug concentration in the interstitial fluid of various tissues to be made.

Animals↗