Experimental densities of subcooled deuterium oxide at pressures up to 160 MPa.

In this work, the experimental results of deuterium oxide density at high pressure and in a wide range of temperatures, by means of the pseudo-isochoric method, are presented. A specific stainless steel cell was devised to be used as a pycnometer and filled with variable mass of heavy water. The latter was measured by weighing with an analytical balance and using the substitution method. The volume of the pycnometric cell was measured by the gravimetric method and corrected for the effect of temperature and pressure. Each measurement cycle was performed at constant mass, measuring pressure as a function of temperature at equilibrium. From the mass and volume values, density was calculated according to its definition. Heavy water density was measured for temperatures down to 253 K and for pressures up to 163 MPa, thus both in stable and supercooled metastable states. All terms contributing to the uncertainty in determining the volume and the mass were considered, obtaining an expanded relative uncertainty of deuterium oxide density of 0.04%.

Density measurements of subcooled water in the temperature range of (243 and 283) K and for pressures up to 400 MPa.

In this work, accurate density measurements of subcooled water (freshly double-distilled water) were performed along eight constant-mass curves in the temperature range of (243 to 283) K and in the pressure range of (140 to 400) MPa, by a pseudo-isochoric method. The experimental apparatus mainly consisted of a high pressure vessel, especially designed for this experiment, of known volume as a function of temperature and pressure, used to perform measurements in the T-p range under study. The density of subcooled water was obtained by measuring the equilibrium pressure at different temperatures, keeping the mass constant. All terms contributing to the uncertainty of subcooled water density measurements were considered; the estimated relative uncertainty, in the investigated temperature and pressure range, is about 0.07%. The experimental results were compared with the literature densities. In particular, the trend of density versus temperature for a constant mass of sample observed experimentally differs from the trend calculated by the equation provided by the International Association for Properties of Water and Steam (IAPWS-95) outside the range of validity, i.e., in the metastable region.

Acoustical characterization of polysaccharide polymers tissue-mimicking materials.

Tissue-mimicking phantoms play a crucial role in medical ultrasound research because they can simulate biological soft tissues. In last years, many types of polymeric tissues have been proposed and characterized from an acoustical and a thermal point of view, but, rarely, a deep discussion about the quality of the measurements, in terms of the uncertainty evaluation, has been reported. In this work, considering the necessity to develop laboratory standards for the measurement of ultrasonic exposure and dose quantities, a detailed description of the experimental apparatuses for the sound speed and the attenuation coefficient measurements is given, focusing the attention on the uncertainty evaluation both of the results and analysis algorithms. In particular, this algorithm reveals a novel empirical relation, fixing a limit to the energy content (therefore limits the number of cycles) of the three parts in which the authors have proposed to divide the acoustical signal. Furthermore, the realisation of multi-components phantoms, Agar and Phytagel based tissue-mimicking gels along with others long chain molecules (dextrane or polyvinyl alcohol) and scattering materials (silicon carbide and kieselguhr) are investigated. This paper reports accurate speed of sound and attenuation coefficient measurements. Speed of sound is measured by a pulse-echo technique in far-field condition, using an optical glass buffer rod; while attenuation coefficient is determined by an insertion technique, using demineralized water as reference material. The experimental sound speed results are subjected to an overall estimated relative uncertainty of about 1.5% and the attenuation coefficient uncertainty is less than 2.5%. For the development of laboratory standards, a detailed analysis of the measurement uncertainty is fundamental to make sample properties comparable. The authors believe this study could represent the right direction to make phantoms characterizations referable and traceable.