Experimental Validation of Formula for Calculation Thermal Diffusivity in Superlattices Performed Using a Combination of Two Frequency-Domain Methods: Photothermal Infrared Radiometry and Thermoreflectance

In this paper, we validate two theoretical formula used to characterize thermal transport of superlattices at different temperatures. These formulas are used to measure cross-plane thermal conductivity and thermal boundary resistance, when it is not possible to obtain heat capacity or thermal diffusivity and in-plane thermal conductivity. We find that the most common formula for calculating thermal diffusivity and heat capacity (and density) can be used in a temperature range of −50 °C to 50 °C. This confirms that the heat capacity in the very thin silicon membranes is the same as in bulk silicon, as was preliminary investigated using an elastic continuum model. Based on the obtained thermal parameters, we can fully characterize the sample using a new procedure for characterization of the in-plane and cross-plane thermal transport properties of thin-layer and superlattice semiconductor samples.

Herschel-PACS photometry of the five major moons of Uranus

Aims. We aim to determine far-infrared fluxes at 70, 100, and 160 μm for the five major Uranus satellites, Titania, Oberon, Umbriel, Ariel, and Miranda. Our study is based on the available calibration observations at wavelengths taken with the PACS photometer aboard the Herschel Space Observatory. Methods. The bright image of Uranus was subtracted using a scaled Uranus point spread function (PSF) reference established from all maps of each wavelength in an iterative process removing the superimposed moons. The photometry of the satellites was performed using PSF photometry. Thermophysical models of the icy moons were fitted to the photometry of each measurement epoch and auxiliary data at shorter wavelengths. Results. The best-fit thermophysical models provide constraints for important properties of the moons, such as surface roughness and thermal inertia. We present the first thermal infrared radiometry longward of 50 μm for the four largest Uranian moons, Titania, Oberon, Umbriel, and Ariel, at epochs with equator-on illumination. Due to this inclination geometry, heat transport took place to the night side so that thermal inertia played a role, allowing us to constrain that parameter. Also, we found some indication for differences in the thermal properties of leading and trailing hemispheres. The total combined flux contribution of the four major moons relative to Uranus is 5.7 × 10−3, 4.8 × 10−3, and 3.4 × 10−3 at 70, 100, and 160 μm, respectively. We therefore precisely specify the systematic error of the Uranus flux by its moons when Uranus is used as a far-infrared prime flux calibrator. Miranda is considerably fainter and always close to Uranus, impeding reliable photometry. Conclusions. We successfully demonstrate an image processing technique for PACS photometer data that allows us to remove a bright central source and reconstruct point source fluxes on the order of 10−3 of the central source as close as ≈3 × the half width at half maximum of the PSF. We established improved thermophysical models of the five major Uranus satellites. Our derived thermal inertia values resemble those of trans-neptunian object (TNO) dwarf planets, Pluto and Haumea, more than those of smaller TNOs and Centaurs at heliocentric distances of about 30 AU.

Forward-Looking Infrared Radiometry (FLIR) Application for Detecting Ballast Fouling

This paper is intended to assess the practical aspects of the previously proposed approach for detecting railroad ballast fouling using an off-the-shelf Forward-Looking Infrared Radiometry (FLIR) Technology. FLIR is among the technologies that are becoming more prevalent in railroad applications [1,2]. The method discussed in this paper takes advantage of the temperature differences measured by the FLIR camera between the top surface of clean and partially fouled ballast samples as an indicator of fouling. The method is intended to potentially serve as an efficient and time-effective manner for detecting early stages of ballast fouling prior to it requiring a costly intervention. Ballast fouling is a common maintenance-of-way issue for the railroad industry, which occurs as a result of contaminants clogging up the ballast and preventing water drainage. The water retained at the sublayers diminishes the strength of the foundation and could result in other undesirable conditions such as clay pumping and reduced track strength. In this study, experiments are performed to study the thermal behavior and characteristics of clean, and partially- and fully-fouled ballast using a FLIR camera. The FLIR camera is set up in a stationary configuration for ease of testing and also providing a more direct approach to analyzing the data, to keep the test conditions highly repeatable and reduce any environmental variations. The results indicate that the cooling and heating rate at the top surface for clean, partially fouled, and fouled ballast are different during the daily heat-up cycle. It is determined that although the FLIR camera is able to measure some changes in the ballast temperature for the fouling conditions that are evaluated in the study, the differences may be within the range of variations that could occur in field conditions. The paper includes the range of measured temperature by the FLIR camera and discusses the pros and cons of using this approach in practice. Additional field testing is needed to validate or dispute the initial findings of the study.