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PubMed2000

Equilibrium distribution of heavy quarks in fokker-planck dynamics

We obtain an explicit generalization, within Fokker-Planck dynamics, of Einstein's relation between drag, diffusion, and the equilibrium distribution for a spatially homogeneous system, considering both the transverse and longitudinal diffusion for dimension n>1. We provide a complete characterization of the equilibrium distribution in terms of the drag and diffusion transport coefficients. We apply this analysis to charm quark dynamics in a thermal quark-gluon plasma for the case of collisional equilibration.

Journal Article↗
PubMed2001

Surface smoothing of rough amorphous films by irradiation-induced viscous flow.

Surface roughening and smoothing reactions on vapor codeposited glassy Zr65Al7.5Cu27.5 films by 1.8 MeV Kr+ ion beam irradiation is investigated. Irradiation causes significant smoothing of initially rough surfaces, and nearly atomically smooth films can be achieved. Smooth surfaces roughen at high doses and long wavelengths. By a Fourier analysis, radiation-induced viscous flow is identified as the dominant surface relaxation mechanism. Two noise terms are identified, which operate on different length scales: One is due to sputtering and the other to thermal spikes. The irradiation-induced viscosity is compared with radiation-enhanced diffusion.

Journal Article↗
PubMed1977

Dynamic aspects of biological membranes.

Several aspects of membrane structure and function have been treated in which the dynamic properties of membrane components are particularly significant. The establishment and maintenance of asymmetries across the membrane, and heterogeneities in the plane of the membrane, place certain restrictions on the nature and extent of membrane fluid properties. Long-range order, which may give differential restrictions to rotational versus translational diffusion, requires specific interactions between membrane components that are strong enough to overcome thermal energy. Processes such as membrane fusion are likely to involve local areas in the membrane where certain membrane proteins are sequestered. And finally, the budding of virus membranes by mechanisms that specifically exclude host cell membrane proteins will require specialized interpretations in view of the fluid membrane model. These and other membrane phenomena illustrate the importance of the dynamic properties of membranes.

Animals↗
PubMed1994

[Experimental study of effect on lung in pig supported with RVAD].

Ventricular assist device (VAD) has a potent assist effect in the treatment of severe cases of acute heart failure, exhibiting excellent results at present. Right ventricular assist device (RVAD) has a potent flow volume assist effect in severe right heart failure, but in possibly induces aggravation because of pulmonary function disturbance, left heart failure, etc, since it supplies blood to the low-pressure pulmonary circulation system. However, its assist effects and drawbacks have not yet been examined sufficiently. These points, an acute experiment was performed on the effect of RVAD-induced changes in assist flow volume on hemodynamic changes and the lungs. Pulmonary arterial trunk of pigs weighting 40 +/- 3.4 kg were strangulated to obtain right heart failure models of pulmonary arterial blood flow reduced to about 60%. RVAD was then set to run on the models at a fixed rate (100 beats/min, S/D 35%). The models with RVAD flow about 30% of Ao flow were defined as Group I (low flow assist group: N = 9) and those with RVAD flow about 60% of Ao flow were defined as Group II (high flow assist group: N = 9), and results were compared between both groups. RVAD showed remarkable right ventricular preload relieving effect in both groups. The left cardiac function in Group II after 3 hours of RVAD run differed significantly from Group I in LVRDF, LAP, AoP, and Ao flow, and tended to aggravate them when the left cardiac function was reduced. Pulmonary function changes in Group II in terms of PaO2, PaCO2, SaO2, and A-aDO2 change rates suggested retention to some extent of gas exchange capacity and gradual decrease in gas diffusion capacity. In Group II after 3 hours of RVAD run, pulmonary extravascular thermal volume increased significantly, ACE levels decreased significantly, and the lungs presented morphologically high-level edematous changes, suggesting the possible damage to the lung physiological function in Group II. It was considered that excess flow volume assist during right ventricular assist alone may possibly induce left heart failure and that the assist volume should be decided carefully with attention paid to the left ventricular and pulmonary function.

Animals↗
PubMed2003

Diffuse X-ray scattering from 4,4'-dimethoxybenzil, C16H14O4: analysis via automatic refinement of a Monte Carlo model.

A recently developed method for fitting a Monte Carlo computer-simulation model to observed single-crystal diffuse X-ray scattering has been used to study the diffuse scattering in 4,4'-dimethoxybenzil, C16H14O4. A model involving only nine parameters, consisting of seven intermolecular force constants and two intramolecular torsional force constants, was refined to give an agreement factor, omegaR = [sigma omega(deltaI)2/sigma omegaI2(obs)](1/2), of 18.1% for 118 918 data points in two sections of data. The model was purely thermal in nature. The analysis has shown that the most prominent features of the diffraction patterns, viz. diffuse streaks that occur normal to the [101] direction, are due to longitudinal displacement correlations along chains of molecules extending in this direction. These displacements are transmitted from molecule to molecule via contacts involving pairs of hydrogen bonds between adjacent methoxy groups. In contrast to an earlier study of benzil itself, it was not found to be possible to determine, with any degree of certainty, the torsional force constants for rotations about the single bonds in the molecule. It is supposed that this result may be due to the limited data available in the present study.

Journal Article↗
PubMed1977

Metabolic component in the epithelial intracellular potential of rabbit cornea.

Effects of the change of external ionic composition and the addition of metabolic inhibitors on rabbit cornea were studied by recording the epithelial intracellular potential. High K and Li Ringer's solutions, applied to the corneal endothelial side, caused a marked depolarization of the epithelial cells, but no potential change was seen when applied to the epithelial side. Ouabain, MIAA and NaCN applied to the endothelial side reduced the epithelial potential, while those applied to the epithelial side did not change the potential. DNP and FDNB also had no effect when applied to the epithelial side only. The thermal dependence of the epithelial intracellular potentials of whole eye (0.85 mV/degrees C) and excised cornea (2.01 mV/degrees C) preparations were greater than about 0.2 mV/degrees C predicted by the Nernst equation. It is concluded that the epithelial cell layer of rabbit cornea act as a tight barrier against diffusion of K ion and metabolic inhibitors from the tear side to the epithelial basal cell. A high thermal dependence of the epithelial intracellular potential may depend greatly on the pump ingibition.

Action Potentials↗
PubMed2006

Diffusion rate limitations in actin-based propulsion of hard and deformable particles.

The mechanism by which actin polymerization propels intracellular vesicles and invasive microorganisms remains an open question. Several recent quantitative studies have examined propulsion of biomimetic particles such as polystyrene microspheres, phospholipid vesicles, and oil droplets. In addition to allowing quantitative measurement of parameters such as the dependence of particle speed on its size, these systems have also revealed characteristic behaviors such a saltatory motion of hard particles and oscillatory deformation of soft particles. Such measurements and observations provide tests for proposed mechanisms of actin-based motility. In the actoclampin filament end-tracking motor model, particle-surface-bound filament end-tracking proteins are involved in load-insensitive processive insertion of actin subunits onto elongating filament plus-ends that are persistently tethered to the surface. In contrast, the tethered-ratchet model assumes working filaments are untethered and the free-ended filaments grow as thermal ratchets in a load-sensitive manner. This article presents a model for the diffusion and consumption of actin monomers during actin-based particle propulsion to predict the monomer concentration field around motile particles. The results suggest that the various behaviors of biomimetic particles, including dynamic saltatory motion of hard particles and oscillatory vesicle deformations, can be quantitatively and self-consistently explained by load-insensitive, diffusion-limited elongation of (+)-end-tethered actin filaments, consistent with predictions of the actoclampin filament-end tracking mechanism.

Actins↗
PubMed2003

Site determination and thermally assisted tunneling in homogenous nucleation.

A combined low-temperature scanning tunneling microscopy and density functional theory study on the binding and diffusion of copper monomers, dimers, and trimers adsorbed on Cu(111) is presented. Whereas atoms in trimers are found in fcc sites only, monomers as well as atoms in dimers can occupy the fcc as well as the metastable hcp site. In fact the dimer fcc-hcp configuration is only 1.3 meV less favorable with respect to the fcc-fcc configuration. This enables a confined intracell dimer motion, which at temperatures below 5 K is dominated by thermally assisted tunneling.

Journal Article↗
PubMed1992

Dynamic light scattering studies on hydrodynamic properties of fibrinogen-fibronectin complex.

A high molecular weight 'cryogel' was obtained as insoluble complexes by cold incubation at near-freezing temperatures from heparinized plasma of patients with rheumatoid arthritis. After the cryogel was solubilized at 37 degrees C, 1:1 complex of fibrinogen and fibronectin was purified at room temperature by affinity chromatography on a gelatin-Sepharose 4B. Hydrodynamic properties of the complex were investigated as a function of temperature and NaCl concentration using a dynamic light scattering. The diffusion coefficients of the complex at 20 degrees C decreased with increasing of NaCl concentration as free fibronectin. The complex appears to be a more compact form at low ionic concentration, which is associated with conformational changes of fibronectin. The diffusion coefficient of the complex at 20 degrees C in 0.05 M TrisHCl(pII7.4) containing 0.5 M NaCl was estimated as 8.5 x 10(-8) cm2s-1. The complex did not dissociate over the temperature range from 20 to 37 degrees C. The diffusion coefficients of the complex decreased significantly at 12 degrees C and 40 degrees C. The thermal denaturation of fibrinogen molecule in the complex was observed at 40 degrees C. The CONTIN analysis of the light scattering data showed that the complex associated to form higher aggregates at 15 degrees C, but not at near-freezing temperature. The equilibrium between the complex and higher aggregates appeared reversible.

Diffusion↗
PubMed1990

Functional significance of metabolic responses to thermal acclimation in fish muscle.

Compensatory increases of the aerobic capacity of fish swimming muscle are frequently observed in response to cold acclimation. Such thermal compensation occurs both in fish that remain active in the cold and in fish that become dormant at cold temperatures. For cold-active fish, positive thermal compensation is best explained by conservation of the capacity for aerobic metabolic flux at low temperatures. The compensatory responses of cold-active species can be used to suggest the temperature range over which the activities of glycolytic and tricarboxylic acid cycle enzymes in a muscle, i.e., the muscle's "metabolic profile," can suffice. Analysis of the available data suggests that a 16 degrees C range of temperatures cannot be covered by one metabolic profile, even when the preferred temperatures are centered between the acclimation temperatures. For cold-inactive species that remain normoxic during winter dormancy, the compensatory metabolic modifications may facilitate lipid catabolism. Alternately, an increased aerobic capacity may be adaptive during the relatively cold periods that precede and follow winter dormancy. For goldfish and carp that encounter hypoxia and anoxia during winter dormancy, increased mitochondrial abundance could facilitate ethanol production during anoxia and the diffusion of oxygen to mitochondria during hypoxia. Finally, metabolic modifications during natural acclimatization indicate both thermal compensation and direct thermal effects and suggest that thermal compensation may be masked by reproductive and feeding activities.

Acclimatization↗
PubMed1985

The effect of hyperthermia on glucose transport in normal and thermal-tolerant Chinese hamster ovary cells.

The effect of hyperthermia on glucose transport was studied in CHO cells to test the hypothesis that interference with membrane transport might be related to cell death at elevated temperatures. It was shown that passive diffusion of 2-deoxyglucose increases steadily over the temperature range 4-50 degrees C. Facilitated diffusion increases from 4 degrees C to 35 degrees C then exhibits a broad optimum before decreasing rapidly above 45 degrees C. The temperature dependence of glucose transport in thermally resistant cells was not however different from that of normal cells suggesting that this membrane transport process is not a critical target in cell killing by heat.

Animals↗
PubMed2004

Dynamics of pinned membranes with application to protein diffusion on the surface of red blood cells.

We present a theoretical treatment and simulation algorithm for the dynamics of Helfrich elastic membrane surfaces in the presence of general harmonic perturbations and hydrodynamic coupling to the surrounding solvent. In the limit of localized and strong interactions, this harmonic model can be used to pin the membrane to intracellular/intercellular structures. We consider the case of pinning to the cytoskeleton and use such a model to estimate the macroscopic diffusion constant for band 3 protein on the surface of human erythrocytes. Comparison to experimental results suggests that thermal undulations of the membrane surface should play a significant role in protein mobility on the red blood cell.

Adsorption↗
PubMed1994

Direct imaging of reptation for semiflexible actin filaments.

According to the reptation model of polymer diffusion, a polymer chain exhibits snake-like motion through the entangled mesh of surrounding molecules, in which the undulations of the chain are restricted to a tube-like region. The reptation model can account for many of the dynamic properties of entangled polymer solutions and melts, and has received support from observations of block copolymer diffusion across an interface; but reptative motion has not previously been imaged directly. Here we report such a direct observation of reptation, obtained by video microscopy of fluorescently labelled single, semiflexible filaments of actin in a solution of unlabelled actin filaments. From the restricted thermal undulations of these filaments we can measure the diameter of the confining tube, and we also observe the characteristic thermally excited sliding of the filament out of the end of the tube. We find that the chain self-diffusion coefficient decreases approximately linearly as the filament length increases, in agreement with the reptation model.

Actins↗
PubMed1987

Lipid fluidity and membrane protein dynamics.

Membrane fluidity plays an important role in cellular functions. Membrane proteins are mobile in the lipid fluid environment; lateral diffusion of membrane proteins is slower than expected by theory, due to both the effect of protein crowding in the membrane and to constraints from the aqueous matrix. A major aspect of diffusion is in macromolecular associations: reduction of dimensionality for membrane diffusion facilitates collisional encounters, as those concerned with receptor-mediated signal transduction and with electron transfer chains. In mitochondrial electron transfer, diffusional control is prevented by the excess of collisional encounters between fast-diffusing ubiquinone and the respiratory complexes. Another aspect of dynamics of membrane proteins is their conformational flexibility. Lipids may induce the optimal conformation for catalytic activity. Breaks in Arrhenius plots of membrane-bound enzymes may be related to lipid fluidity: the break could occur when a limiting viscosity is reached for catalytic activity. Viscosity can affect protein conformational changes by inhibiting thermal fluctuations to the inner core of the protein molecule.

Diffusion↗
PubMed1990

Thermally induced optical property changes in myocardium at 1.06 microns.

Light in the visible and near-infrared region is diffusely scattered in tissues by macromolecules. It was therefore hypothesized that tissue coagulation caused by high-power continuous wave laser irradiation might significantly alter tissue optical properties, resulting in a redistribution of laser energy during the laser ablation process. Infrared transmittance studies confirmed the hypothesis by demonstrating an irreversible decrease in light transmittance (45%) during heating of a 0.75 mm thick slice of tissue. Absorption and scattering coefficients were then determined from transmittance and reflectance measurements on thin slices of raw and coagulated myocardium irradiated with a Nd:YAG laser (1.06 microns). The scattering coefficient was found to increase fourfold (0.427 mm-1----1.74 mm-1) during tissue coagulation, while the absorption coefficient remained relatively unchanged (0.044 mm-1----0.051 mm-1). Calculations indicate that the coagulation-induced changes in tissue optical properties substantially increase surface back-scattering and reduce tissue penetration.

Animals↗
PubMed1984

Correlations between changes in indicators of gastric mucosal barrier integrity at time of exposure to "barrier breakers" and extent of hemorrhagic erosions one hour later.

We have examined the effects of seven different "barrier breakers" (including ethanol, aspirin, salicylic acid, isobutyric acid, Na taurocholate, thermal injury, and hyperosmotic glucose) on chambered gastric mucosae of rats in an attempt to identify variations in accepted indicators of mucosal barrier integrity which would accurately predict the extent of subsequent hemorrhagic erosion. When results from all experimental groups were considered, only the initial decrease in transmucosal potential difference (PD) showed significant correlation with final damage (lesion area). When the results were analyzed as separate subgroups, significant correlations were also found between net K+ efflux during the first 10 min after luminal infusion and final lesion area. Only in the subgroup containing ethanol, salicylates, and thermal injury was there a correlation between net loss of luminal H+ (back-diffusion) and lesion area. These results are considered in terms of their implications for the ulcerogenic actions of each group of agents.

Animals↗
PubMed1992

Modified Arrhenius equation for the frequency dependence of the transition temperature of polymers--a note on some further observations.

Activation energies obtained from differential mechanical thermal analysis work on polymers have been observed to relate to similar behaviour of diffusion coefficients of gases in polymers. Comparison of the two techniques showed the additional energy terms to be virtually identical and the pre-exponential factors to relate to segmental motion of a five-unit carbon atom.

Biocompatible Materials↗
PubMed1993

Heat conductance, diffusion theory and intracellular metabolic regulation.

Diffusion theory played a major role in the development of biology as an exact science. The question is raised, however, as to its relevance and applicability in the molecular interactions which occur in metabolism in the living cell. This review looks at diffusion theory from its inception and subsequent introduction into biology, its shortcomings with regard not only to whole-body physiology, but more pertinently at the intracellular level, with its failure to offer a rational basis for metabolic regulation in the internum of the cell. The conclusion is reached that although diffusion inevitably occurs within cells, its role is of little importance with regard to most metabolic activity. In comparison, perfusion of the internal surfaces of the cell by streaming of the fluid compartment of the cytoplasm seems to be the modus operandi which allows molecular interactions to occur at rates far beyond those that diffusion would permit, and at the same time offers a mechanism which permits sensitive control of metabolic activity.

Animals↗