Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “VISCOSITY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,117 records · Page 62Linked to original sources
PubMed2003

Noninvasive measurement of viscosity from damping of capillary waves.

Capillary waves are surface waves on fluids with wavelengths in the millimeter range. The determination of viscosity from the damping of capillary waves is of great practical importance as it affords the possibility of measuring the viscosity of fluids noninvasively. In this paper a noncontact method for generation and detection of capillary waves on fluid is described. A miniature laser interferometer is employed to measure noninvasively the wave amplitude and its attenuation with a resolution of about 10 nm. As a test case, the attenuation data for capillary waves on pure water are used to obtain the kinematic viscosity of water as a function of temperature. The results compare favorably with the most reliable published data on the subject.

Capillary Action↗
PubMedDate not supplied

Beverage viscosity is inversely related to postprandial hunger in humans.

Accumulating evidence indicates that energy-yielding beverages evoke weaker appetitive responses than more solid food items, but the properties responsible have not been characterized. The present study attempted to isolate an influence of viscosity. At weekly intervals, 84 adults ingested 325-ml (220 kcal) shakes that were matched on weight, volume, temperature, energy, macronutrient content, energy density, rate of consumption, cognitive expectations, palatability, appearance, and requirements for mechanical processing, but varied in viscosity. Twice appetitive ratings were obtained over the subsequent 4 h, while all intake was proscribed, and twice ratings were kept until the first spontaneous eating occasion comprised of > or =100 kcal. Dietary intake was recorded over the 24 h after shake ingestion. Significantly greater and more prolonged reductions of hunger were observed with the thicker shake. No significant differences were noted in the size or time to first meal or 24 h energy intake. These data indicate viscosity exerts an independent inverse effect on hunger in humans.

Adult↗
PubMed1976

Effect of low-dose subcutaneous heparin on whole-blood viscosity.

The change in blood-viscosity at low shear-rates (0.77 s-1 and 2-62 s-1 was measured in eighteen normal subjects and postoperatively in sixteen patients after administration of 5000 I.U. of subcutaneous heparin. In both groups there was a significant decrease in the mean blood-viscosity 4 to 6 hours after the injection of heparin. This fall in blood-viscosity may be involved in the prophylactic effect of low-dose subcutaneous heparin in preventing venous thrombosis.

Blood Viscosity↗
PubMed1976

Abnormal blood viscosity in Raynaud's phenomenon.

The exact cause of Raynaud's phenomenon is still unknown. Since the principal feature of this condition is the precipitation of the attacks by cold, blood viscosity was measured in ten patients and in ten normal controls at 27 degrees C and 37 degrees C. The viscosity of the patients' blood was significantly higher (p less than 0.05) at 27 degrees C than that of the controls when measured at a low shear-rate (0.77 s-1). This, as well as the higher yield stress of the patients' blood, suggests that Raynaud's phenomenon may be caused by an abnormal local increase in the viscosity and yield stress of the blood in response to a fall in temperature.

Adolescent↗
PubMed2002

Viscosity of alpha-crystallin solutions.

Accommodation in the mammalian lens requires flexure of lens fibres and some redistribution of their contents involving limited viscous flow. Shear-dependent viscosity of bovine alpha-crystallin solutions was determined with the Contraves Low-Shear Rheometer between 4.4 and 347 mg ml(-1), and at 15.5, 25, 30, and 37 degrees C. All solutions showed significant shear thinning, with markedly higher viscosity at physiological levels of approximately 300 mg ml(-1). Viscosity-concentration graphs were similar at low (1.0 s(-1)) and high (94.5 s(-1)) shear rates, indicating low molecular interaction in solution. Arrhenius plots which might have indicated the size of the energy barrier to displacement of molecules or aggregates were inconclusive.

Animals↗
PubMed1999

The effect of phase viscosity ratio on the rheology of liquid two phase gelatin-locust bean gum systems.

The rheological behaviour of liquid two phase gelatin-locust bean gum (LBG) systems, comprising of (a) liquid LBG enriched continuous phase, and (b) flow-deformable gelatin-enriched dispersed particles seems to be determined, at the same phase composition, by phase viscosity ratio (mu). In the mu range from 0.03 to 0.21, viscosity dropped to values noticeably lower (13-40 times) than those of the corresponding LBG solution. Decrease in the viscosity of the mixtures was not observed at mu = 0.5-0.6, corresponding that to the maximum energy scatter inside the droplets, in agreement with Mason's conception of droplet deformation and disruption of liquid Newtonian emulsions.

Galactans↗
PubMed1997

Concentration and temperature dependence of viscosity in lysozyme aqueous solutions.

The paper presents the results of viscosity determinations on aqueous solutions of hen egg-white lysozyme at a wide range of concentrations and at temperatures ranging from 5 degrees C to 55 degrees C. It has been proved that, at each fixed concentration, the viscosity-temperature dependence may be quantitatively described by the modified Arrhenius formula. On the basis of the generalized Arrhenius formula, the parameters of the Mooney approximation were calculated. It has been concluded that lysozyme molecules in aqueous solution behave as hard quasi-spherical particles. By applying an asymptotic form of the generalized Arrhenius formula, such rheological quantities as the intrinsic viscosity and Huggins coefficient were calculated.

Animals↗
PubMedDate not supplied

A new microviscometer for determining the viscosity of middle ear effusion.

A new microviscometer has been developed based on the capillary viscometer method. The device uses a glass sensor tube for aspirating 15-microliter samples. The relative viscosity of the samples was estimated from the negative pressure required for aspiration of the fluid. These pressures ranged widely from 1 centipoise (cp) to 10,000 cp. Measurement of the viscosity of middle ear effusions in 119 samples from 110 otitis media with effusion patients using this device revealed a close relation between their values and their gross appearance (serous less than seromucoid less than mucoid). The microviscometer is useful to determine the relative viscosity of a very small amount of fluid such as middle ear effusion.

Exudates and Transudates↗
PubMed2001

A morphological and tensile bond strength evaluation of an unfilled adhesive with low-viscosity composites and a filled adhesive in one and two coats.

OBJECTIVE: The purpose of this study was to measure the tensile bond strength (TBS) testing of resin composite to dentin of three low-viscosity composites, in association with an unfilled adhesive, and a filled adhesive one and two coats respectively, and to evaluate and compare the SEM morphological observations. METHODS: The labial surface of 120 bovine lower incisors were ground to obtain a flat dentin surface allowing demarcation of a 4 mm diameter area with adhesive tape. The teeth were randomly divided in six groups of 20 each. The dentin of each ground surface was etched with 35% H(3)PO(4) for 15s, followed by application of the respective adhesive: Single Bond (SB) for Groups 1, 2, 3 and 6; Optibond Solo (OS) for Groups 4 and 5. In Groups 1 and 4, a resin composite rod with a wire loop was luted directly to the adhesive surface with Z100. Group 2 received an intermediate layer of Flow It (FI) composite; Group 3 received an intermediate layer of Protect Liner F (PLF) composite; Group 5 received a second coat of OS; and Group 6 received an intermediate layer of an experimental low-viscosity composite (EM). A resin composite rod was luted to the surface of each specimen with Z100 resin composite. All specimens were stored in distilled water at 37 degrees C for 24h prior to TBS testing. Each specimen was inspected by SEM and classified according to adhesive or cohesive failure mode. One specimen of each group was cut longitudinally, polished and prepared for SEM observation. RESULTS: The TBS values were: Group 1 (7.86MPa+/-2.28), Group 2 (7.62MPa+/-1.85), Group 3 (7.60MPa+/-2.14), Group 4 (7.96MPa+/-2.36), Group 5 (7.50MPa+/-2.70) and Group 6 (7.18MPa+/-2.40). No significant statistical differences were observed among the groups. However, the analyses of the failure mode presented a considerable variation. SIGNIFICANCE: The use of a filled adhesive or an unfilled adhesive along with a low-viscosity composite as an intermediate layer may provide a stress absorbing layer, whereby improving the preservation of the bonded interface area.

Adhesives↗
PubMed1998

Intrinsic viscosity calculated out of single point measurements for chondroitin-4-sulfate and chondroitin-6-sulfate solutions.

The differences in the structure of polymer chain between the chondroitin-4-sulfate (C4-S) and the chondroitin-6-sulfate (C6-S) are reflected in the intrinsic viscosity values calculated starting from the traditional methods of Huggins, Kraemer, Mead and Fouss, and Martin, and by the method for a single-point determination of intrinsic viscosity [eta]. For the range between 0.4 and 0.5% (w/v) concentrations, we get an agreement in the intrinsic viscosity values. The chains of both polymers present a flexible structure and are not ramified between 0.28 and 1.00% (w/v) concentrations.

Algorithms↗
PubMed1999

Intraoperative changes of transcranial Doppler velocity: relation to arterial oxygen content and whole-blood viscosity.

The association of arterial oxygen content (CaO2) and viscosity with transcranial Doppler (TCD) blood flow velocity in the middle cerebral artery was studied in 20 adults without cerebrovascular disease undergoing abdominal surgery associated with significant fluctuations in hematology. TCD measurements and arterial blood samples were obtained before and directly after surgery but before blood transfusion. There was an inverse association between baseline mean velocity and CaO2 (r = -0.56), hematocrit (r = -0.50), hemoglobin (r = -0.51), and high-shear viscosity (r = -0.46). After intraoperative blood loss, intraindividual fluctuations of TCD measurements, blood oxygenation, and rheologic factors were studied. In multiple regression analysis, changes in CaO2 had the strongest association with changes in TCD values, accounting for 55% of the variation in mean velocity. Addition of hematocrit and viscosity could not account for more variation in mean velocity than CaO2 alone.

Abdomen↗
PubMed1998

Effect of elevated viscosity in the upper gastrointestinal tract on drug absorption in dogs.

The objectives of these studies were, first, to determine the effect of elevated luminal viscosity on the gastrointestinal absorption of four model drugs and, second, to identify the key processes influencing drug absorption under elevated viscosity conditions. Studies were conducted in vitro and in healthy female mongrel dogs under fasting conditions. In the canine model, both the rate and extent of paracetamol and hydrochlorothiazide absorption were significantly decreased by the coadministration of 15 g guar gum dissolved in 500 ml normal saline. In the case of cimetidine, the rate but not extent of absorption was decreased. Owing to the high variability in the data, no statistically based conclusion could be drawn about the effects of coadministered guar gum on the oral absorption of the poorly soluble mefenamic acid. Based on the in vitro data, it appears that substantial reductions in the dissolution rate of paracetamol, hydrochlorothiazide and cimetidine account for the effects observed in vivo. It is concluded that the effect of an elevation in the intraluminal viscosity on drug absorption is greatest for highly soluble drugs, and results from a combination of a decrease in dissolution rate and gastric emptying rate.

Acetaminophen↗
PubMed1999

Utilizing vehicle imbibition by a microporous membrane and vehicle viscosity to control release rate of salbutamol.

The possibility to control the release rate of salbutamol through the hydrophobic Celgard 2500 polypropylene membrane by varying the composition and the viscosity of hydrophilic drug vehicles was investigated. The use of the polypropylene membrane as a control membrane for reservoir-type drug delivery systems was envisaged and water, glycerol, isopropyl alcohol and ethanol, pure or as binary mixtures were studied as vehicles. With varying composition of the vehicle, a sharp change of its imbibition by the membrane from practically none to a complete filling of the membrane pores occurred, which coincided with a steep rise of the drug permeability for the membrane. From this was inferred that the vehicle-filled pores were the dominant permeation pathway, while when no vehicle was imbibed, transport took place by way of the polymer domain of the membrane. In case of imbibition, the permeation rate could be modulated in a predictable fashion by adjusting the viscosity of the vehicle. This demonstrated that drug release could be controlled by utilizing the in situ interaction of the vehicles with this membrane, leading to imbibition and establishment of a permeation pathway with pre-determined viscosity in the pores of the membrane.

Albuterol↗
PubMed2005

Effect of electrolyte concentration on the viscosity and voltammetry of supercritical solutions.

The viscosity of a supercritical electrolyte solution is measured for the first time using a modified quartz crystal microbalance, and it is shown that ionic solvation leads to a significant structuring of the solvent and an appreciable increase in solution viscosity. Voltammetric investigations in the electrolyte solutions are used to confirm the magnitude of the viscosity changes, and these account for the appreciably lower than expected peak currents.

Borates↗
PubMed1994

Influence of poly(ethylene glycol) and aqueous viscosity on the rotational diffusion of membranous Na,K-ATPase.

The Na,K-ATPase [ATP phosphohydrolase (Na+/K(+)-transporting), E.C. 3.6.1.37] in native membranes from the salt gland of Squalus acanthias has been spin-labeled covalently with a chloromercuri nitroxide derivative, and the rotational diffusion of the protein has been studied, as a function of the concentration of glycerol or poly(ethylene glycol) in the suspending medium, by means of saturation-transfer electron spin resonance spectroscopy. The effective rotational correlation time of the protein increases linearly with the viscosity of the aqueous glycerol medium, with a gradient whose value indicates that ca. 50-70% of the volume of the Na,K-ATPase protein is external to the membrane. The effective rotational correlation times of the protein in poly(ethylene glycol) solutions are considerably greater than those in glycerol solutions of the same viscosity and increase nonlinearly with the viscosity of the suspending medium, indicating that increasing concentrations of poly(ethylene glycol) induce aggregation of the integral proteins within the membrane. The value reached at 50% poly(ethylene glycol) corresponds to a degree of aggregation of the proteins between 2 and 5 depending on whether the ethylene glycol polymer is excluded from the membrane surface region. The results are discussed with respect to hydration forces and poly(ethylene glycol)-induced cell fusion.

Animals↗
PubMed1997

Viscosity dependence of the electron transfer rate from bound cytochrome c to P840 in the photosynthetic reaction center of the green sulfur bacterium Chlorobium tepidum.

Anomalous high viscosity dependence was found in the rate of reaction between the bound cytochrome c and the primary donor bacteriochlorophyll dimer (P840) of the reaction center complex purified from the green sulfur bacterium Chlorobium tepidum. The cytochrome has a primary structure with the N-terminal three membrane-spanning helices connected to the extended C-terminal heme-containing hydrophilic moiety. The rate constant of the reaction decreased from 5.0 x 10(3) s-1 to 1.0 x 10 s-1 as the glycerol concentration increased from 0 to 60% (v/v) at 295 K, showing a linear dependence on the -2.4th power of the specific viscosity. The glycerol effect was fully reversible. The extraordinary high viscosity dependence cannot be explained by the simple diffusive Brownian fluctuation model and suggests that the electron transfer mechanism is dependent on the unique conformational fluctuations of the heme-containing moiety of cytochrome c.

Amino Acid Sequence↗
PubMed2006

Superior solubility of polysaccharides in low viscosity, polar, and halogen-free 1,3-dialkylimidazolium formates.

We successfully prepared low viscosity, polar, and halogen-free ionic liquids as potential solvents for a wide range of polysaccharides. A series of 1,3-dialkylimidazolium formates were produced as liquids having strong hydrogen bond acceptability. These formates had significantly lower viscosity than previously reported polar ionic liquids, in particular 1-allyl-3-methylimidazolium formate (viscosity 66cP at 25 degrees C) and 1-allyl-3-ethylimidazolium formate (67cP at 25 degrees C). Because of their strong hydrogen bond ability, various polysaccharides including amylose and (scarcely soluble) cellulose were dissolved in high concentrations under mild condition.

Halogens↗
PubMed2004

A limiting speed for protein folding at low solvent viscosity.

Because protein folding dynamics are heavily overdamped, Kramers theory predicts the rate of folding to scale inversely with the reaction friction, which is usually interpreted to mean the solvent viscosity. This does not mean, however, that the speed of folding can increase without limit as solvent viscosity decreases. We show that, in a sufficiently fast-folding protein, the folding speed approaches a finite limit at low solvent viscosity, indicating a reaction controlled by internal friction.

Glucose↗