Volume 80, Issue 12, December 2009
Index of content:
- THERMOMETRY; THERMAL DIFFUSIVITY; ACOUSTIC; PHOTOTHERMAL AND PHOTOACOUSTIC
Analysis of thermoreflectance signals and characterization of thermal conductivity of metal thin films80(2009); http://dx.doi.org/10.1063/1.3265994View Description Hide Description
The temperature response of the thermal conductivity of metalthin films has been investigated by the thermoreflectance (TR) method. The phase lag of the TR signals depends on the thermal diffusivity when the heating area is small, while on the thermal effusivity when the heating area is large. This enables us to evaluate by analyzing the three-dimensional thermal propagation in the film on the substrate. We show that by analyzing the TR signals, of Cu–Pt alloythin films formed on glass substrates can be estimated. The estimated drastically decreases with an increase in the Pt concentration. Furthermore, we discuss these results by considering the crystallographic properties of the abovementioned thin films investigated by transmission electron microscopy and x-ray diffraction.
New methodology for simultaneous volumetric and calorimetric measurements: Direct determination of and for liquids under pressure80(2009); http://dx.doi.org/10.1063/1.3270258View Description Hide Description
A new batch cell has been developed to measure simultaneously both isobaric thermal expansion and isobaric heat capacity from calorimetric measurements. The isobaric thermal expansion is directly proportional to the linear displacement of an inner flexible below and the heat capacity is calculated from the calorimetric signal. The apparatus used was a commercial Setaram C-80 calorimeter and together with this type of vessels can be operated up to 20 MPa and in the temperature range of 303.15–523.15 K, In this work, calibration was carried out using 1-hexanol and subsequently both thermophysical properties were determined for 3-pentanol, 3-ethyl-3-pentanol, and 1-octanol at atmospheric pressure, 5 and 10 MPa, and from 303.15 to 423.15 K in temperature. Finally experimental values were compared with the literature in order to validate this new methodology, which allows a very accurate determination of isobaric thermal expansion and isobaric heat capacity.
Improvement of energy efficiency via spectrum optimization of excitation sequence for multichannel simultaneously triggered airborne sonar system80(2009); http://dx.doi.org/10.1063/1.3272078View Description Hide Description
Both the energy efficiency and correlation characteristics are important in airborne sonar systems to realize multichannel ultrasonic transducers working together. High energy efficiency can increase echo energy and measurement range, and sharp autocorrelation and flat cross correlation can help eliminate cross-talk among multichannel transducers. This paper addresses energy efficiency optimization under the premise that cross-talk between different sonartransducers can be avoided. The nondominated sorting genetic algorithm-II is applied to optimize both the spectrum and correlation characteristics of the excitation sequence. The central idea of the spectrum optimization is to distribute most of the energy of the excitation sequence within the frequency band of the sonartransducer; thus, less energy is filtered out by the transducers. Real experiments show that a sonar system consisting of eight-channel Polaroid 600 series electrostatic transducers excited with 2 ms optimized pulse-position-modulation sequences can work together without cross-talk and can measure distances up to 650 cm with maximal 1% relative error.