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Jet Propulsion Laboratory
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Division of Chemistry and Chemical Engineering
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Division of Biology
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    ABSTRACT: We present rest-frame 15 and 24 μm luminosity functions (LFs) and the corresponding star-forming LFs at z < 0.3 derived from the 5MUSES sample. Spectroscopic redshifts have been obtained for ∼98% of the objects and the median redshift is ∼0.12. The 5–35 μm Infrared Spectrograph spectra allow us to estimate accurately the luminosities and build the LFs. Using a combination of starburst and quasar templates, we quantify the star formation (SF) and active galactic nucleus (AGN) contributions in the mid-IR spectral energy distribution. We then compute the SF LFs at 15 and 24 μm, and compare with the total 15 and 24 μm LFs. When we remove the contribution of AGNs, the bright end of the LF exhibits a strong decline, consistent with the exponential cutoff of a Schechter function. Integrating the differential LF, we find that the fractional contribution by SF to the energy density is 58% at 15 μm and 78% at 24 μm, while it goes up to ∼86% when we extrapolate our mid-IR results to the total IR luminosity density. We confirm that the AGNs play more important roles energetically at high luminosities. Finally, we compare our results with work at z ∼ 0.7 and confirm that evolution on both luminosity and density is required to explain the difference in the LFs at different redshifts.
    The Astrophysical Journal 01/2016; 734(1):40-11. DOI:10.1088/0004-637X/734/1/40
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    ABSTRACT: Comets rarely come close enough to be studied intensively with Earth-based radar. The most recent such occurrence was when Comet 103P/Hartley 2 passed within 0.12 AU in late 2010 October, less than two weeks before the EPOXI flyby. This offered a unique opportunity to improve pre-encounter trajectory knowledge and obtain complementary physical data for a spacecraft-targeted comet. 103P/Hartley 2 is only the fourth comet nucleus to be imaged with radar and already the second to be identified as an elongated, bilobate object based on its delay-Doppler signature. The images show the dominant spin mode to be a rotation about the short axis with a period of 18.2 hr. The nucleus has a low radar albedo consistent with a surface density of 0.5–1.0 g cm −3 . A separate echo component was detected from large (>cm) grains ejected anisotropically with velocities of several to tens of meters per second. Radar shows that, in terms of large-grain production, 103P/Hartley 2 is an unusually active comet for its size.
    The Astrophysical Journal Letters 01/2016; 734(1):2-4. DOI:10.1088/2041-8205/734/1/L2
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    ABSTRACT: The crack initiation phenomenon in a metallic material under cyclic loadings is due to the localization of the deformation in some grains at the microstructure scale which induces damage. However, the engineering way to design structures conduct to establish macroscopic fatigue criteria which finally consider mean value of the mechanical fields, at the scale of a representative volume of material. In the last decades, a lot of phenomenological models have been proposed in this way, based on macroscopic stress or strain tensors but none are com-pletely satisfactory, essentially due to the lack of physical basis. An alternative way consists in considering energy based approach, in particular by studying the evolution of stored energy during cycling. In this aim, a first step consists in defining a theoretical framework based on dissipation which enables to explain previous experimental works studying the evolution of temperature of specimen during cyclic loading. Such a framework has been proposed by Charkaluk and Constantinescu and is based on shakedown concepts and a micro-macro transition. However, due to the heterogeneous behavior of polycristalline metallic aggregates, some grains can exhibit plastic strains whereas other still undergo a pure elastic response and, in fatigue, this can conduct to crack initiation in such plastic grains even if the macroscopic be-havior of the specimen remains elastic. Therefore, the second step consists in the development of a method enabling to access to a full-field measurement of both kinematical and thermal fields of a same zone at the grains scale, in order to be able, in future work, to realize energy balance at the microstructure scale. The principle of such an experimental method supposes i) the determination of thermal fields thanks to an infrared camera equipped with a high mag-nification lens, ii) the computation of kinematical fields based on images coming from a CCD camera and analyzed with an image correlation technique and, iii) the use of a special coating and a dichroic lens to realise both measurements at the same time, in the same area.
    7 th EUROMECH Solid Mechanics Conference, Lisbon (Portugal); 07/2015


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