1,720,968 research outputs found
Hygrometric applications of microwave quasi-spherical resonators
Full text linkIn this work, triggered by the initial suggestion and the preliminary results obtained at the National Institute for Standards and Technology (NIST), we have explored the possible application of a microwave resonant cavity to realise a reference standard hygrometer. Particularly, we have measured the microwave resonance frequencies of a small volume (69 cm^3) triaxial elipsoidal cavity to determine the water vapor mole fraction x_w of H2O/N2 and H2O/air mixtures. The mixtures were prepared using the INRiM standard humidity generator for frost-point temperatures T_fp in the range between 241 K and 270 K and a commercial two-pressure humidity generator operated at dew-point temperature T_dp between 272 K and 291 K. Following these tests, we demonstrated the performance of the QSR operated as a condensation hygrometer. For this demonstration, a suitable experiment was prepared in cooperation with the National Physical Laboratory (NPL), which allowed to compare the performance of the QSR with that of a calibrated chilled-mirror hygrometer. Finally, with the aim of reducing the uncertainty currently associated to the literature values of the constants in the Debye equation, we have measured the dielectric constant of pure water vapour in the temperature range from 320 K to 470 K at pressures up to 1.7 MPa. As a whole, the results obtained in these experiments demonstrated the validity and satisfactory performance of the microwave technique for hygrometr
Strain-rate and temperature dependent material properties of Agar and Gellan Gum used in biomedical applications
Full text linkAgar and Gellan Gum are biocompatible polymers extensively used in several fields of tissue engineering research (e.g. tissue replacement, tissue support, tissue mimicking), due to their mechanical behaviour effectively representative of actual biological tissues. Since mechanical properties of artificial tissues are related to biocompatibility and functionality of medical implants and significantly influence adhesion, growth and differentiation of cells in tissue-engineering scaffolds, an accurate characterization of Young׳s modulus and relaxation time processes is needed. In this study, the strain-rate and temperature dependent material properties of Agarose and one among the numerous kind of Gellan Gum commercially available, known as Phytagel®, have been investigated. Nine hydrogel samples have been realized with different mechanical properties: the first one Agar-based as a reference material, the further eight samples Gellan Gum based in which the effect of dispersed solid particles like kieselguhr and SiC, as enhancing mechanical properties factors, have been investigated as a function of concentration. Stress-strain has been investigated in compression and relaxation time has been evaluated by means of the Kohlrausch-Williams-Watts time decay function. Mechanical properties have been measured as a function of temperature between 20°C and 35°C and at different strain rates, from ~10-3s-1 and ~10-2s-1 (or deformation rate from ~0.01mms-1 to ~0.1mms-1). From experimental data, the combined temperature and strain-rate dependence of hydrogels Young׳s modulus is determined on the basis of a constitutive model. In addition to a dependence of Young׳s modulus on temperature, a remarkable influence of strain-rate has been observed, especially in the sample containing solid particles; in same ranges of temperature and strain-rate, also relaxation time variations have been monitored in order to identify a possible dependence of damping properties on temperature and strain-rate. The result is the impossibility to determine univocally mechanical properties of studied biomaterials without a proper definition of boundary conditions at which they have been obtained
Functional mechanical attributes of natural and synthetic gel-based scaffolds in tissue engineering: strain-stiffening effects on apparent elastic modulus and compressive toughness
Full text linkThe accurate identification and determination of elastic modulus and toughness, as well as other functional mechanical attributes of artificial tissues, are of paramount importance in several fields of tissue science, tissue engineering and technology, since biomechanical and biophysical behavior is strongly linked to biological features of the medical implants and tissue-engineering scaffolds. When soft or ultra-soft materials are investigated, a relevant dispersion of elastic modulus values can be achieved, due to the strain-stiffening effects, inducing a typical non-linear behavior of these materials, as a function of strain-range. In this short communication, the Apparent elastic modulus strain-range dependence is estimated from a segmentation of the strain stiffening curve, and the related compressive toughness is investigated and discussed, based on experimental evidence, for 6 different kinds of gels, used for artificial tissue fabrication; experimental results are compared to mechanical properties of native human tissues
Application of acoustic methods for a non-destructive evaluation of the elastic properties of several typologies of materials
No full textIn solid phase materials, differently from what happens in the fluid phase, elastic waves propagate both through longitudinal and transverse waves. From the speed of propagation of longitudinal and transverse waves, it is possible to evaluate important elastic properties of the solids under study, namely the Young's modulus, the Poisson's coefficient, the bulk modulus and the shear modulus. This work suggests an accurate method for measuring wave propagation speeds in homogeneous and non-homogeneous materials with the purpose to evaluate their mechanical properties and the associated uncertainty.
First of all, to assess the performance of the proposed methodology, based on the "pulse-echo" technique, in terms of accuracy and precision, measurements of wave propagation speeds have been carried out, in atmospheric conditions, in well-known homogeneous and isotropic materials, such as copper, aluminum, stainless steel and also polymethyl methacrylate (Plexiglas (R)), Teflon (R) and optical glass BK7. These results were compared with the values reported in literature (if present), showing how published speed of sound data are very disperse and not so reliable owing to the lack of a precise uncertainty evaluation and of the temperature value associated to the measurement. Then, the same experimental apparatus was used for measuring speed of sound as a function of temperature (from 274.15 to 313.15 K) for 304 stainless steel and oxygen free copper, showing a good accuracy of the results also for temperature conditions far from ambient. Finally, the same procedure was applied to a non-homogeneous solid, obtaining some very preliminary results in typical mediterranean building material, as Carrara marble
Assessment of the INRIM trace water generator and analysis of the uncertainty components down to -100 °C frost-point temperature
Full text linkA low frost-point generator (INRIM 03) able to operate at sub-atmospheric pressure has been recently designed,
constructed, and assessed at the Istituto Nazionale di Ricerca Metrologica (INRiM) with the aim of providing the
metrological traceability both to instruments developed for the measurement of humidity in atmosphere and to sensors
and analysers used in industry for controlling and measuring the amount of water vapour in manufacturing processes.
The humidity generator operates in a single temperature single pressure mode, letting the carrier gas (nitrogen) achieve
saturation in a single passage through an isothermal saturator. Its working range encompasses a frost-point temperature
range from -100 °C to -20 °C, in a pressure range between 200 hPa and 1100 hPa, corresponding to an amount of water
fraction range from 13·10-9 mol·mol-1 to 6.2·10-3 mol·mol-1.
In a previous work its performance was assessed in the frost-point temperature range from -75 °C to -20 °C [2]. In this
work, a comprehensive set of tests for its characterisation and performance evaluation between -75 °C and -100 °C is
presented. A detailed uncertainty analysis in the above temperature range is reported, taking into account all the sources
of uncertainty that affect the humid gas generation. An expanded uncertainty (k=2) of 0.07 °C was found for frost-point
temperature measurements between -75 °C and -95 °C, while an expanded uncertainty of 0.26 °C resulted at a frost-point
temperature of -100 °C. The relative expanded uncertainty (k=2) associated with water vapour amount fraction
measurements was estimated equal to or better than 1.2 % between 35·10-9 mol·mol-1 and 6.1·10-3 mol·mol-1, increasing
up to 6.5 % at 13∙10-9 mol·mol-1
CAPACITÀ DI MISURA E TARATURA DEL LABORATORIO PRIMARIO DI IGROMETRIA DELL’INRIM
No full textIl laboratorio primario di igrometria dell’INRIM sviluppa e mantiene i campioni primari e secondari delle grandezze termo-igrometriche: umidità relativa, temperatura di rugiada/brina e temperatura dell’aria. Le capacità di misura e taratura del laboratorio - pubblicate sul database KCDB del Bureau International des Poids et Mesures e riconosciute a livello internazionale - sono:
• Misura dell’umidità relativa tra 10 % e 95 % con temperatura dell’aria inclusa tra -10 °C e 70 °C e incertezza da 0.2 % a 0.5 %
• Misura della temperatura di rugiada/brina tra -70 °C e 80 °C e incertezza da 0.08 °C a 0.04 °C.
• Misura della temperatura dell’aria tra -20 °C e 80 °C e incertezza da 0.03 °C a 0.04 °C.
I campioni del laboratorio primario che verranno discussi, impiegati sia per attività scientifiche sia per servizi metrologici, includono un insieme di apparati volte ad assicurare la riferibilità delle misure termo-igrometriche in Italia. In particolare sono a disposizione:
• Un generatore primario di gas umido INRIM-01 che genera un gas a temperatura di rugiada costante tra -20 °C e +95 °C. Il generatore è basato su un sistema a ricircolo a singola pressione.
• Un generatore primario di gas umido INRIM-02 che genera un gas a temperatura di brina costante tra 0 °C e -85 °C. Il generatore è basato su un sistema a ricircolo a singola pressione.
• Un generatore di umidità relativa TS2500. Il generatore è basato sul principio delle 2 Pressioni –2 Temperature e copre il campo delle CMC di umidità relativa. Può anche essere impiegato come generatore secondario di gas umido con temperatura di rugiada/brina compresa tra -36 °C e +70 °C e per la misura della temperatura dell’aria tra -10 °C e +70 °C.
• Sistema di riferimento per la misura della temperatura dell’aria costituito da una camera termostatica, una sottocamera e un termometro campione nell’intervallo tra 70 °C e +180 °C.
L’attività di sviluppo e validazione dei campioni poggia su numerosi progetti di ricerca nazionali e internazionali per la misura dell’umidità dei gas e, più recentemente, per la misura dell’umidità nei solidi. Il laboratorio offre servizi di disseminazione delle grandezze termo-igrometriche quali:
• Taratura di misuratori di temperatura di rugiada/brina
• Taratura di sensori per la misura dell’umidità relativa
• Taratura di termometri per la misura della temperatura dell’aria
• Confronti interlaboratorio (ILC) in termo-igrometria
• ILC per gli ambienti climatici e termostatici
• Collaborazioni di ricerca con l’industria per lo sviluppo di nuovi sensori/metodi di misura
Development of a low-frost point generator operating at sub-atmospheric pressure
Full text linkA low frost point generator (INRIM 03) operating at sub-atmospheric pressure has been designed and constructed at the Istituto Nazionale di Ricerca Metrologica (INRiM) as part of a calibration facility for upper-air sounding instruments. This new humidity generator covers the frost point temperature range between -99 °C and -20 °C and works at any controlled pressure between 200 hPa and 1100 hPa, achieving a complete saturation of the carrier gas (nitrogen) in a single passage through a stainless steel isothermal saturator. The generated humid gas contains a water vapour amount fraction between 14bold dot10-9 mol/mol and 5bold dot10-3 mol/mol. In this work the design of the generator is reported together with characterisation and performance evaluation tests. A preliminary validation of the INRIM 03 against one of the INRIM humidity standards in the common region is also included. Basing on experimental test results, an initial uncertainty evaluation of the generated frost-point temperature, Tfp, and water vapour amount fraction, xw, in the limited range down to -75 °C at atmospheric pressure is reported. For the frost-point temperature, the uncertainty budget yields a total expanded uncertainty (k=2) of less than 0.028 °C, while for the mole fraction the budget yields a total expanded uncertainty of less than 10-6 mol/mol
Acoustical characterization of polysaccharide polymers tissue-mimicking materials
No full textTissue-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.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. (C) 2014 Elsevier B.V. All rights reserved
Trace Water Measurement Standards in Process and Energy Gases
No full textL'abstract è presente nell'allegato / the abstract is in the attachmen
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