Search results for "Viscosity."

Are abdominal obesity and body mass index independent predictors of hemorheological parameters?

2012

There is an association between obesity and rheological blood behavior [2, 4–7]. In this sense we have read with interest the recently published article by Brun et al. [1] in this journal. The authors evaluate, in a population of 430 subjects, the relationship between abdominal obesity and body mass index (BMI) with blood viscosity, and conclude that both anthropometric parameters are associated with increased blood viscosity but by different mechanisms, where the waist to hip ratio is a better predictor for blood viscosity than BMI. It is striking that in this study the authors do not indicate the variables included in the stepwise multivariate regression model, where plasma lipids, glucos…

Interaction between pre-landing activities and stiffness regulation of the knee joint musculoskeletal system in the drop jump: implications to perfor…

2002

The purpose of the present study was to investigate the interaction between the pre-landing activities and the stiffness regulation of the knee joint musculoskeletal system and the takeoff speed during a drop jump (DJ). Nine healthy male subjects performed a DJ test from the height of 50 cm. The surface electromyographic (EMG) activity of the vastus lateralis (VL) muscle was recorded to evaluate both the pre-landing and post-landing muscle activation levels. Simultaneous recording of the jumping motion and ground reaction force was performed by a high-speed video camera (100 frames x s(-1)), and a force platform was employed to allow joint moment analysis. Joint stiffness was calculated by …

In Vitro Percutaneous Penetration of Acyclovir from Solvent Systems and Carbopol 971-P Hydrogels: Influence of Propylene Glycol

2005

The mechanism underlying propylene glycol (PG) effects on acyclovir (ACV) penetration through human epidermis were studied. Solvent systems and Carbopol gels containing increasing percentage of PG (from 0% to 70%, w/w) were used. Viscosity studies of both vehicles were carried out to characterise the influence of rheological behaviour. In solvent systems skin permeation values of ACV increase as the concentration of PG increase yielding a maximum enhancement ratio (ER = 10) for 70% PG. The release rate of ACV from gels was determined. Higuchi's model was used to estimate the apparent diffusion coefficient of the drug. These values show a decrease as the content of PG in the vehicle increase…

Hemorheological profile in primary and secondary Raynaud's phenomenon. Influence of microangiopathy.

2013

Raynaud's phenomenon (RP) is an episodic peripheral circulatory disorder characterized by local artery spams in subjects exposed to cold or emotional stress. It is not well-established whether RP patients show an altered rheological profile, mostly due to patient classification and clinical severity. We aimed to compare the hemorheological profile in patients with primary and secondary RP with a healthy control group. Eighteen primary RP, 22 secondary RP and 22 healthy controls, were included in the study. RP patients were also divided according to the presence of digital ulcers (7 with, 33 without). Biochemical and hemorheological variables were analyzed, including glucose, triglycerides, …

Coagulation, fibrinolysis and haemorheology in premenopausal obese women with different body fat distribution

1994

Recently waist/hip ratio (WHR), a marker of body fat distribution, has been described as a risk factor for cardiovascular disease (CVD). The aim of the present study was to evaluate the influence of body fat distribution on metabolic, haemostatic and haemorheological pattern in premenopausal obese women with different WHR. Fourty premenopausal obese women were subdivided into two groups, matched for age and body mass index (BMI): 20 women with abdominal obesity (WHR = 0.94 +/- 0.02) and 20 women with peripheral obesity (WHR = 0.77 +/- 0.03). Twenty nonobese women were recruited as control group. The abdominal obesity group had significantly higher blood glucose, triglycerides, total cholest…

Effect of biomass features on oxygen transfer in conventional activated sludge and membrane bioreactor systems

2019

Abstract The aim of the present study was to compare the oxygen transfer efficiency in a conventional activated sludge and a membrane bioreactor system. The oxygen transfer was evaluated by means of the oxygen transfer coefficient and α-factor calculation, under different total suspended solids concentration, extracellular polymeric substances, sludge apparent viscosity and size of the flocs. The oxygen transfer coefficient and α-factor showed an exponential decreasing trend with total suspended solid, with a stronger oxygen transfer coefficient dependence in the conventional activated sludge compared to the membrane bioreactor. It was noted that the oxygen transfer coefficient in the conve…

Thermodynamic Behavior of Non-Ionic Tri-block Copolymers in Water at Three Temperatures

2006

Apparent molar volumes (V Φ) of aqueous solutions of some copolymers, based on ethylene oxide (EO) and propylene oxide (PO) units, were determined as functions of concentration at three temperatures. Viscosity measurements were also carried out on some of these systems. The effects studied include how the molecular architecture and the molecular weight affect the aggregation of the copolymer, keeping constant the EO/PO ratio. Modeling of the volumetric data yielded the partial molar volume of the copolymer in the standard (V°) and the aggregated (V M) states, as well as the equilibrium constant for micellization and the aggregation number. Analysis of the viscosity data supported the insigh…

1988

Deviations in the determination of the unperturbed dimensions of polymers arising in ternary polymer systems (solvent (1)/solvent (2)/polymer) can be explained by the inaccurate use of an interaction parameter independent of polymer molecular weight. On this basis, a new formalism for the calculation of the second virial coefficient from intrinsic viscosity is proposed. This formalism was tested (and compared with well established formalisms) for all ternary polymer systems with simultaneous intrinsic viscosity and second virial coefficient data in the literature.

1987

The intrinsic viscosities, [η], for the ternary systems alkane (1)/2-butanone (2)/poly(dimethylsiloxane) (PDMS)(3), with the alkanes decane, dodecane and hexadecane, are determined at 20,0°C. The constants a of the Mark-Houwink equation and the constant of the unperturbed dimensions, KΘ, of the polymer are evaluated over the whole composition range of the binary solvent mixture. [η] shows a pronounced maximum at intermediate compositions as found in cosolvent mixtures. In these cosolvent mixtures, the numerical values of KΘ are higher than in the single-component solvents, because the cosolvent mixtures correspond to a mixed solvent with an excess free energy, GE ≥ 0, the increase in KΘ bei…

Zero Viscosity Limit for Analytic Solutions of the Primitive Equations

2016

The aim of this paper is to prove that the solutions of the primitive equations converge, in the zero viscosity limit, to the solutions of the hydrostatic Euler equations. We construct the solution of the primitive equations through a matched asymptotic expansion involving the solution of the hydrostatic Euler equation and boundary layer correctors as the first order term, and an error that we show to be \({O(\sqrt{\nu})}\). The main assumption is spatial analyticity of the initial datum.