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PubMed2001

A new vogel-like law: ionic conductivity, dielectric relaxation, and viscosity near the glass transition.

A model is developed that describes temperature and pressure dependence of dielectric relaxation, ionic conductivity, and viscosity of glass-forming liquids near the glass transition temperature. The expressions for ionic conductivity are compared with experimental results for two polymer electrolytes. Those for dielectric relaxation are compared with data for poly(propylene oxide) and poly(vinyl acetate). The theoretical viscosity law is compared with experiment for propylene carbonate.

Journal Article↗
PubMed2001

Energy landscapes and the non-Newtonian viscosity of liquids and glasses.

An inherent structure analysis of viscosity is developed based on results of nonequilibrium molecular dynamics simulations. The viscosity is separated into a "structural" contribution associated with the energy minima that the system visits, and a "vibrational" contribution associated with displacements within the energy minima. The structural contribution is shear thinning due to strain-activated relaxations caused by the disappearance of high-stress energy minima, while the vibrational contribution is Newtonian.

Journal Article↗
PubMed2003

Shear viscosity of langmuir monolayers in the low-density limit.

We have measured the shear viscosity in the liquid phase of several Langmuir monolayers with an accuracy better than 30%. The method is based on the optical monitoring of the Brownian diffusion of submicron latex spheres floating at the air-water interface. The values are between 1 and 11x10(-10) N s m(-1), which is 10 to 100 times lower than previous data on similar systems. For N-palmitoyl-6-n-penicillanic acid and L-alpha-dipalmitoylphosphatidylcholine, the variation of the shear viscosity with surface density agrees with a classical free area model, whereas for pentadecanoic acid we observe a compensation effect.

Journal Article↗
PubMed2004

Bistability and "negative" viscosity for a suspension of insulating particles in an electric field.

It is shown that a suspension of insulating particles in a liquid with low conductivity possesses bistability and has a "negative" effective viscosity effect in the electric field due to internal rotations. By Brownian dynamics simulation it has been found that thermal fluctuations of the angular velocity of particles in this bistable system can have a large effect on the viscosity of the suspension.

Journal Article↗
PubMed2004

Shear flows and shear viscosity in a two-dimensional Yukawa system (dusty plasma).

The shear viscosity of a two-dimensional liquid-state dusty plasma was measured experimentally. A monolayer of highly charged polymer microspheres, with a Yukawa interaction, was suspended in a plasma sheath. Two counterpropagating Ar+ laser beams pushed the particles, causing shear-induced melting of the monolayer and a shear flow in a planar Couette configuration. By fitting the particle velocity profiles in the shear flow to a Navier-Stokes model, the kinematic viscosity was calculated; it was of order 1 mm(2) s(-1), depending on the monolayer's parameters and shear stress applied.

Journal Article↗
PubMed2005

Preventing transition to turbulence: a viscosity stratification does not always help.

In channel flows a step on the route to turbulence is the formation of streaks, often due to algebraic growth of disturbances. While a variation of viscosity in the gradient direction often plays a large role in laminar-turbulent transition in shear flows, we show that it has, surprisingly, little effect on the algebraic growth. Nonuniform viscosity therefore may not always work as a flow-control strategy for maintaining the flow as laminar.

Journal Article↗
PubMed2006

Shear viscosity and shear thinning in two-dimensional Yukawa liquids.

A two-dimensional Yukawa liquid is studied using two different nonequilibrium molecular dynamics simulation methods. Shear viscosity values in the limit of small shear rates are reported for a wide range of Coulomb coupling parameter and screening lengths. At high shear rates it is demonstrated that this liquid exhibits shear thinning; i.e., the viscosity eta diminishes with increasing shear rate. It is expected that two-dimensional dusty plasmas will exhibit this effect.

Journal Article↗
PubMed2006

Velocity autocorrelations and viscosity renormalization in sheared granular flows.

The decay of the velocity autocorrelation function in a sheared granular flow is analyzed in the limit where the wavelength of fluctuations is larger than the "conduction length," so that energy is a nonconserved variable. The decay of the velocity autocorrelation function is much faster than that in a fluid at equilibrium for which energy is a conserved variable. Specifically, the autocorrelation function in a sheared granular flow decays proportional to t-3 in 2D and t-9/2 in 3D, in contrast with the decay proportional to t-1 in 2D and t-3/2 in 3D for a fluid at equilibrium. The renormalization of the viscosity due to mode coupling is evaluated using this form of the decay of the autocorrelation function. It is found that the logarithmic divergence in the viscosity in 2D, and the divergence of the Burnett coefficients in 3D, which is characteristic of a fluid of elastic particles at equilibrium, is absent in a sheared granular flow.

Journal Article↗
PubMed2006

Bulk viscosity, thermoacoustic boundary layers, and adsorption near the critical point of xenon.

We present an improved model for the dissipation and dispersion in an acoustic resonator filled with xenon near its critical temperature Tc. We test the model with acoustic measurements in stirred xenon that have a temperature resolution of (T - Tc)/Tc approximately 7 x 10(-6). The model includes the frequency-dependent bulk viscosity calculated numerically from renormalization-group theory and it includes critical-point adsorption. Because the density of adsorbed xenon exceeds the critical density, the bulk viscosity's effect on surface dissipation is reduced, thereby improving the agreement between theory and experiment.

Journal Article↗
PubMed1982

Temperature effects on seed imbibition and leakage mediated by viscosity and membranes.

The possible involvement of membranes and water viscosity in the temperature effects on imbibition and solute leakage of radish (Raphanus sativa var. Early Scarlet Globe) seeds and excised sugar pine (Pinus lambertiana Dougl.) embryos was evaluated. In these two seed materials, the temperature effect on initial rates of imbibition and solute leakage could be accounted for primarily by changes in water viscosity, the relationship being approximately linear. It appears that membranes are involved both in water uptake and solute leakage. Heat-killed radish seeds and sugar pine embryos exhibited significantly higher rates of imbibition and solute leakage than did viable ones. In addition, sugar pine embryos exhibited an abrupt change in rates of imbibition and solute leakage between 15 and 20 degrees C, resulting in abnormally high water uptake and solute leakage above this temperature.

Journal Article↗
PubMed2005

Influence of viscosity on the diffraction of sound by a periodic array of screens.

The paper contains an analysis of the transmission of a pressure wave through a periodic grating including the influence of the air viscosity. The system of equations in this case consists of the compressible Navier-Stokes equations associated with no-slip boundary conditions on solid surfaces. The problem is reduced to two hypersingular integral equations for determining the velocity components along the slits. These equations are solved by using Galerkin's method with some special trial functions. The results can be applied in designing protective screens for miniature microphones realized in the technology of micro-electro-mechanical systems (MEMS). In this case, the physical dimensions of the device are on the order of the viscous boundary layer so that the viscosity cannot be neglected. The microfluidic model of the screen consists of a periodic array of slits in a substrate. The analysis indicates that the openings in the screen should be on the order of 10 microm in order to avoid excessive attenuation of the signal.

Models, Theoretical↗
PubMed1999

Instability of magma flow from volatile-dependent viscosity

Volatiles dissolved in silicic magma at depth exsolve as the magma nears the surface and cause an increase in viscosity of the magma. A model of a volcanic conduit within an elastic medium and a viscosity dependent on the volatile content of the magma produces oscillatory magma flow for a critical range of steady input flow rates. Oscillatory flow is recognized as a fundamental mode of behavior at silicic volcanoes, and understanding it allows improved short-term forecasting of timing and eruption style.

Journal Article↗
PubMedDate not supplied

Cardiovascular effects in viscose rayon workers exposed to carbon disulfide.

The objectives of this study were to investigate the cardiovascular effects in workers currently exposed to carbon disulfide (CS2) below the threshold limit value (TLV) of 31 mg/m3 and to determine the prevalence of coronary heart disease (CHD) after long-term exposure. 172 men (91 workers exposed to CS2 in a viscose rayon factory and 81 referent workers) were examined using a medical and job history questionnaire, Rose's questionnaire, and electrocardiography at rest, and by measuring blood pressure and serum lipids and lipoproteins. Personal exposures were monitored simultaneously with active sampling and findings were analyzed according to the NIOSH 1600 method. As a result of technical and organizational improvements, personal CS2 exposures were well below the TLV (5.4-13.02 mg/m3). No significant effect of CS2 on blood pressure or lipids (total cholesterol, HDL and LDL cholesterol, triglycerides, and apolipoproteins AI and B) was found, even after allowance for confounding factors. The prevalence of CHD (ECG abnormalities and chest pain) was higher in the viscose rayon workers than in the workers with no exposure but reached statistical significance for men with exposure histories often years and more only (cumulative CS9 index > or = 150 mg/m3, the most highly exposed group). The findings suggest that the coronary risk is increased in workers previously exposed to high CS2 concentrations but not in those exposed to CS2 levels below the current TLV.

Adult↗
PubMed1990

Comparative study of gentamicin release from normal and low viscosity acrylic bone cement.

The pharmacokinetics of gentamicin were studied after total hip joint arthroplasties in 2 groups of 10 patients. The prosthesis was performed in the first group with 'Palacos R plus gentamicin' (normal viscosity), manufactured by Schering, and in the second group with 'Cerafix genta R' (low viscosity) manufactured by Ceraver-Osteal. Both cements included similar concentrations of gentamicin. Urine was collected at 12-hour intervals for 15 days after operation, and drainage fluids for 48, 72 or 108 hours. Blood samples were taken 3 and/or 5 hours after prosthesis implantation. In both cases, high concentrations of gentamicin were found in drainage fluids and urine during the early postoperative period. Mean gentamicin excretion curves were calculated by a computer-aided design program (SIAM) for the 2 cements. The release of gentamicin was biphasic in both cases, although the slow elimination phase appeared to be longer for 'Cerafix'. In the first postoperative period, the drug had a better bioavailability during the rapid elimination phase in the case of 'Palacos'. The calculated peak blood concentration was in the same range for both compounds. The conclusion is drawn that, in patients undergoing total hip joint arthroplasties, gentamicin concentrations reach local levels higher than the minimum inhibitory concentrations of most of the likely sensitive pathogens. However, in both cases, as blood concentrations appear to be low, patients will not be protected against systemic infections. Both cements have similar antibacterial properties but the mechanical properties of 'Cerafix' are the better of the two.

Adult↗
PubMed1986

Fatty fish-induced changes in membrane lipid composition and viscosity of human erythrocyte suspensions.

The effect of a daily supplement of 75-100 g fatty fish, providing 3 g of omega 3 fatty acids, on the lipid composition and deformability of erythrocytes was studied in six healthy male subjects. After 4 weeks of the fish supplementation the mean degree of unsaturation, expressed as double bond index, of erythrocyte phosphatidyl choline (PC) and phosphatidyl ethanolamine (PE) had increased significantly by 10% and 4%, respectively. The mean cholesterol/phospholipid ratio (C/P ratio) in the membranes had increased by 28% (p less than 0.001). No change was seen in the distribution of the four major phospholipid classes. After withdrawal of the supplement for 4 weeks the changes in PC were reversed, but the changes in PE persisted and the mean C/P ratio still was higher than basal by 16% (p less than 0.01). The effect on the C/P ratio by the fatty fish is in contrast with the previously observed lack in effect of cod-liver oil. The viscosity of erythrocyte suspensions with a packed cell volume fraction of 0.80 and measured at shear rates less than or equal to 8.11 s-1 was decreased after the fish. We suggest that the fall in the viscosity of erythrocyte suspensions, reflecting increased cell deformability, is probably due to the change in the fatty acid composition of erythrocyte PC.

Adult↗
PubMed1986

The fate of ultra-low viscosity 14C-hydroxypropyl methylcellulose in rats following gavage administration.

The disposition of 14C-Hydroxypropyl methylcellulose (HPMC) with a viscosity of 2.25 centipoise was studied in male and female Sprague-Dawley rats following a single 500 mg/kg body weight gavage dose, or five consecutive daily doses. Recoveries for the single dose were: feces, greater than 99%; urine, approximately 1%; carcass and tissues, approximately 0.2%; expired air, 0.07%; and bile, 0.05%. Plasma radioactivity had a monophasic excretion half-life of approximately 2 hours for either sex. The majority of the residual radioactivity in the tissues was found in the gastrointestinal tract. The absorbed radioactivity in the urine, based on thin layer chromatography (TLC) analyses, represented methyl ethers of glucose and oligomers; this amounted to 0.56% recovered in a study in which urine samples were isolated from possible contamination by radioactivity in the feces. The 0.56% correlated well with the 0.53% portion of the original dosing solution which consisted of cellulose units with an average molecular weight of less than 1000. Recovery of radioactivity in the feces of rats on the 5-day dosing regimen was 97% and 102% for males and females, respectively, without any evidence for accumulation in tissues. Approximately 1% was recovered in the urine. Thus, the results of this work show that ultra-low viscosity 2.25 centipoise HPMC was only minimally absorbed with essentially all of a single 500 mg/kg gavage dose, or 5 daily consecutive doses, being excreted unabsorbed in the feces.

Administration, Oral↗
PubMed1993

Low- vs high-viscosity cement in hip arthroplasty. No radiographic difference in 226 arthrosis cases followed for 5 years.

In 1984 and 1985, 352 hips were randomly assigned to total hip arthroplasty with either low- or high-viscosity cement at 5 Swedish orthopedic departments. Of the 267 hips finally included in the study, 226 were examined clinically and radiographically after 54-77 months. Radiographically, 21 definite stem loosenings and 1 probable stem loosening were observed (10 percent) and 4 additional stems had been exchanged before the 5-year examination. In the survivorship analysis, 261 stem prostheses were included and using this method, 7 percent were radiographically loose after 5 years. There were 4 definitely loose and 8 probably loose acetabular cups. No difference was found between cement of high and low viscosity with regard to prosthetic fixation.

Aged↗
PubMed1976

Systolic time intervals as a measure of left ventricular function in viscose rayon workers exposed to carbon disulfide.

In a group of viscose rayon workers exposed to carbon disulfide the systolic time intervals were calculated. They were determined from the simultaneous recording of an ECG, a phonocardiogram, and arterial pulse tracings. Results indicate a shortened left ventricular ejection time (lvet) and a prolonged isovolumetric contraction time (ICT), together with an increase in the ratio of ICT to LVET. These alterations, which occurred in the absence of any clinical signs or symptoms of heart disease, are interpreted as a consequence of an impaired left ventricular contractility, comparable to mild coronary dysfunction. Literature data support the hypothesis that the biochemical mechanisms involved in the effect of carbon disulfide on myocardial cells are (a) an interference with energy metabolism from the inadequate availability of thiamine and nicotinamide or a direct inhibition of cytochrome or (b) an interference with catecholamine metabolism and defective hormonal control of the energy utilization process. Impaired left ventricular function in rayon viscose workers exposed to carbon disulfide represents an early and highly sensitive sign of carbon disulfide intoxication, and the use of systolic time intervals as a noninvasive measure of myocardial performance may be a useful method for monitoring carbon disulfide exposed people.

Air Pollutants↗

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