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Dielectric Permittivity and Viscoelastic Measurements οf Two Tricomponent Mixtures Consisting οf Laterally Fluorinated Terphenyl Derivatives

100%
Basak S., Dasgupta P., Das B., Das M., Dabrowski R.
Acta Physica Polonica A
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2013
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vol. 123
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issue 4
714-719
EN
Two tricomponent room temperature nematic eutectic mixtures ABC and ABD with laterally fluorinated constituents A and B were prepared as base mixtures for vertically aligned mode LCD's. The physical properties of these mixtures viz. birefringence, dielectric anisotropy, bend elastic constant, relaxation time and rotational viscosities were determined in order to compare with the optimum values required to achieve the target specifications of VA mode materials. The dielectric anisotropy, Δ ε, and optical birefringence, Δ n, of these mixtures were found to be in the range of (-1.3 to -1.4) and (0.13 and 0.14), respectively, at around 20°C. The figure of merit for the ABD mixture has been found to be higher than that of ABC mixture throughout the entire temperature range. The pretilt angle effect in the physical parameters has also been studied. At T=20°C, the response time decreases to 25% and 35% for mixture ABC for 2° and 5° pretilt respectively in comparison to zero pretilt. On the other hand, at the same temperature for the ABD mixture these values are reduced by 16% and 35%, respectively.
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Analysis of Complex Viscosity in a Group of Patients with Circulation Disorders

100%
Marcinkowska-Gapińska A., Kowal P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1A
A-54-A-56
EN
Rheology of viscoelastic fluids is a complex phenomenon. Full blood is an example of a body fluid of non-Newtonian character with pronounced viscoelastic properties. Blood flow in the circulatory system depends not only on the physical and physico-chemical properties of blood but also on the structure and properties of the vascular system. Blood viscosity is one of the most important factor determining the blood flow. Its value depends on the shear rate, hematocrit, erythrocyte aggregability and deformability, and on the plasma viscosity and composition. In the course of the investigation we utilized oscillatory methods, called also dynamic mechanical analysis. The technique principle is based on the measurement of the amplitude and phase of oscillations of the sample subject to a harmonic force with certain amplitude and frequency. The results of dynamic mechanical analysis were used to determine the viscoelastic properties of blood samples. We performed also the standard flow curve measurements of the blood plasma samples, that is shear stress as a function of shear rate in the rotary mode. All measurements were performed by means of a Contraves LS-40 rheometer on blood samples taken from two groups of patients. One group contained patients after heart attack, while the second one - after cerebral infarction. In none of the groups the patients were in an acute state. Information obtained from oscillatory measurements indicate increased erythrocyte aggregability in both groups of patients.
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Analysis of the Effect of Magnetostimulation on Viscoelastic Properties of Blood in Patients with Lasting Pain

86%
Marcinkowska-Gapińska A., Kowal P.
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vol. 125
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issue 4A
A-24-A-26
EN
The aim of the current work was to analyze the influence of alternating magnetic field on the viscoelastic properties of blood in vivo in patients with lasting pain problems. Oscillatory techniques, also called the dynamic mechanical analysis, have been used in the current work to study the viscoelastic properties of blood. The blood samples were collected from patients of a neurological ward complaining about spinal cord and lower limbs pain. Altogether 25 patients took part in the study. A blood sample was collected from each patient twice: before the magnetostimulation and after five treatments. For each blood sample, the hematocrit value was measured using the standard method. Plasma viscosity and the complex whole blood viscosity were measured by means of a rotary-oscillating rheometer Contraves LS40. Magnetic field was generated by the instrument Viofor JPS and the magnetostimulation treatments were performed using different programs. The analysis of the results included estimation of the hematocrit value, plasma viscosity, complex whole blood viscosity and its components: viscous and elastic viscosity at four chosen amplitudes of the shear rate as a function of the applied treatment program. The results obtained in the study suggest that rheological properties of blood change depending on the applied magnetostimulation program.
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