Search results for "Thermal Conductivity"
showing 10 items of 160 documents
Maximizing phonon thermal conductance for ballistic membranes
2007
At low temperatures, phonon scattering can become so weak that phonon transport becomes ballistic. We calculate the ballistic phonon conductance G for membranes using elasticity theory, considering the transition from three to two dimensions. We discuss the temperature and thickness dependence and especially concentrate on the issue of material parameters. For all membrane thicknesses, the best conductors have, counter-intuitively, the lowest speed of sound.
Thermoplastic Properties of Endodontic Gutta-percha: A Thermographic In Vitro Study
2014
Abstract Introduction Endodontic gutta-percha undergoes deformation at temperatures above 65°C. The temperature influence of heat carriers on gutta-percha cones was investigated in vitro. Methods Six single-rooted extracted teeth were embedded in resin and fixed. The root canals were prepared (ProFile; Dentsply Maillefer, Ballaiques, Switzerland) to different tapers and bisected. Thermographic images when heating the gutta-percha cones (Roeko, Langenau, Germany) with a heat carrier (ML .12; SybronEndo, Orange, CA) at 1 and 5 mm from the working length were made with an infrared thermal imaging camera (ThermaCam P640; Flir Systems, Taby, Sweden). The device temperature was preset at 200°C. T…
High resolution remote estimation of soil surface water content by a thermal inertia approach
2009
Summary The spatial distribution of soil surface water content in a bare soil was evaluated by a thermal inertia approach from high resolution visible/near infrared (VIS/NIR) and thermal infrared (TIR) airborne data. Given that the relationship between the thermal inertia and the soil water content strongly depends on the accurate estimation of the soil thermal conductivity, two different empirical models were applied to estimate it. Remotely estimated water contents were tested with time domain reflectometry (TDR) measurements collected on a 110 × 90 m 2 bare field in coincidence with airborne over-flights. The thermal conductivity model by Johansen (1975) produced more accurate estimates …
Reducing Electric and Thermal Energy Needs in Buildings by Using Innovative Envelope Materials
2018
The life style of building occupants is continuously arising towards conditions that are more comfortable involving, on turn, the growing of the electric energy consumptions for climatization purposes. This calls for the improvement of the efficiencies of equipment along with environmental performance of building materials. Laboratory analyses of samples of mixed materials, utilizing tomato stems harvested in Sicily and Cataluna, have been conducted Thermal conductance and mechanical properties have been detected for different rates of bio-component and inert materials. First results of the thermal properties seem to situate such bio-composites among the insulating building materials, for a…
In-plane conductive heat tansfer in solid and porous planar structures
2011
Methods for determining the in-plane thermal diffusivity in a planar sample geometry were developed. These methods were tested and verified by measuring planar metal samples with known thermal properties. The techniques used were based on heating the sample at one edge and recording the evolution of the temperature field in the sample by a thermographic camera. The temperature fields at different times were processed and then fitted by a solution to a heat equation describing the experimental setup, thermal diffusivity as one of the fitting parameters. In the first experimental setup the sample was placed in a weak constant flow of air, and the situation was improved in the second setup by …
Gold vs. platinum-iridium tip catheter for cavotricuspid isthmus ablation: the AURUM 8 study
2010
Aims Gold electrodes have the theoretical advantage of creating bigger lesions than platinum–iridium (Pt–Ir) electrodes. We performed a prospective randomized study to compare the clinical efficacy of standard 8 mm Pt–Ir tip catheter (control) and 8 mm gold-tip catheters in the ablation of the cavotricuspid isthmus (CTI)-dependent atrial flutter. Methods and results A total of 463 patients undergoing CTI ablation in 19 clinical centres were randomized to receive the treatment by gold-tip or control catheter. The primary endpoint was cumulative radiofrequency (RF) application duration until achieving bidirectional CTI block. It did not differ significantly for the two catheters. The gold-tip…
Towards higher zT in early transition metal oxides: optimizing the charge carrier concentration of the WO3-x compounds
2018
Abstract Thermoelectric devices are believed to play an important role in the energy research for the next decades. Thanks to their low costs coupled with high stability and sustainability, metal oxides are very promising materials even if their efficiencies still need improvements to ensure a wide applicability. Slightly reduced early transition metal oxides show intrinsic defects in the crystal structure which guarantee very low values of the thermal conductivity. The challenge to fulfil the “phonon-glass electron-crystal” concept is to decouple the optimization of the electronic properties from the thermal transport properties. In this contribution we report the optimization of the charg…
Dielectric Dispersion and Ion Conductivity in High-Pressure LixNaw1-xNbO3Solid Solutions
2009
Thermal behaviour and dispersion of dielectric permeability and thermal behaviour of conductivity measured in ferroelectric ceramic solid solutions of Li x Na 1−x NbO 3 (x = 0.17, 0.25) synthesized at high pressure and possessing extended region of homogeneity are reported. The Li x Na 1−x NbO 3 (x = 0.17, 0.25) solid solutions of perovskite structure are found to be super-ionic conductors at rather low temperatures O ≥ 400 K. Dielectric dispersion and anomalous behaviour of dielectric permeability are observed in the thermal range of super-ionic conductivity corresponding to structural transformations in the high-pressure solid solutions.
On the adoption of the Monte Carlo method to solve one-dimensional steady state thermal diffusion problems for non-uniform solids
2013
Abstract The present paper is focussed on the investigation of the potential adoption of the Monte Carlo method to solve one-dimensional, steady state, thermal diffusion problems for continuous solids characterised by an isotropic, space-dependent conductivity tensor and subjected to non-uniform heat power deposition. To this purpose the steady state form of Fourier’s heat diffusion equation relevant to a continuous, heterogeneous and isotropic solid, undergoing a space-dependent heat power density has been solved in a closed analytical form for the general case of Cauchy’s boundary conditions. The thermal field obtained has been, then, put in a peculiar functional form, indicating that it …
Magnetic field dependent thermal conductance in La0.67Ca0.33MnO3
2015
Abstract Using the differential 3 ω technique we measured the low-temperature out-of-plane thermal conductance of heteroepitaxial thin film La0.67Ca0.33MnO3 (LCMO). The magnetic field dependence of the thermal conductance reached values of up to 23%. The effect was observed to be largest in the vicinity of the metal–insulator transition, since the enhancement in thermal conductance is triggered by the colossal magnetoresistance effect increasing the electronic contribution to the thermal conductance. The point of the maximal change was adjusted by post-annealing the samples in an oxygen atmosphere. Samples with a higher transition temperature and lower epitaxial strain displayed a lower mag…