Microstructural Finite-Element Analysis of Influence of Localized Strain Distribution on Asphalt Mix Properties

Hot mix asphalt (HMA) is a composite material that consists of mineral aggregates, asphalt binders, and air voids. A finite element model of the HMA microstructure is developed to study the influence of localized strain distribution on the HMA mechanical response. Image analysis techniques are used to capture the HMA microstructure. Due to limitations on the image resolution, the microstructure is divided into two phases: aggregates larger than 0.3 mm and mastic (binder and aggregates smaller than 0.3 mm). A viscoelastic constitutive relationship is used to represent the mastic phase of the HMA microstructure. The mastic viscoelastic properties are obtained from the results of testing asphalt binders in a dynamic shear rheometer and microstructure analysis of idealized mastic. A step-wise finite element procedure is employed in order to account for the influence of the localized high strains on the mastic viscoelastic properties, and HMA mechanical response. The mastic and binder elements of the microstructure are shown to exhibit high strain values within the nonlinear viscoelastic range. The HMA viscoelastic properties are calculated at different strain levels, and the results are compared with experimental data obtained from the frequency sweep shear test.     

Performance of the Production Band 3 receivers (84-116 GHz) for the Atacama Large Millimeter Array (ALMA)

This paper presents the performance of production Band 3 receivers (84-116 GHz) for the Atacama Large Millimeter Array (ALMA) that operate in Chile at 5000 m altitude. The fabrication, and testing of a total of 73 receivers necessitated stringent quality control during assembly and custom designed automated test set for accurate and reproducible measurement results. Interfaces to the ALMA receiver system are described in details. The average single side band noise temperature of band 3 production receivers is 33.2 K, with a minimum of 24.4 K and a maximum of 45.5 K. As for image rejection, the average is 18 dB, with a minimum at 12 dB and a maximum of 21 dB. Other performances with test methodology are described such as gain variation within the IF band, the gain and phase stability, gain compression, and beam patterns. This paper also describes the interfaces to the ALMA front end system, the testing methodology used, and the test results.