Showing papers by "James P. Butler published in 2021"

Validating Synthetic Galaxy Catalogs for Dark Energy Science in the LSST Era

Abstract: Large simulation efforts are required to provide synthetic galaxy catalogs for ongoing and upcoming cosmology surveys. These extragalactic catalogs are being used for many diverse purposes covering a wide range of scientific topics. In order to be useful, they must offer realistically complex information about the galaxies they contain. Hence, it is critical to implement a rigorous validation procedure that ensures that the simulated galaxy properties faithfully capture observations and delivers an assessment of the level of realism attained by the catalog. We present here a suite of validation tests that have been developed by the Rubin Observatory Legacy Survey of Space and Time (LSST) Dark Energy Science Collaboration (DESC). We discuss how the inclusion of each test is driven by the scientific targets for static ground-based dark energy science and by the availability of suitable validation data. The validation criteria that are used to assess the performance of a catalog are flexible and depend on the science goals. We illustrate the utility of this suite by showing examples for the validation of cosmoDC2, the extragalactic catalog recently released for the LSST DESC second Data Challenge.

Stress, Strain, and the Inflation of the Lung

Abstract: The lung is an inherently mechanical organ. Central to the process of respiration are the cyclic changes in lung volume in response to changes in the transpulmonary pressure. Pressure is force per unit area and is thus a stress, while changes in lung volume and shape constitute a strain. A fully realistic description of lung mechanical behavior must contend with the fact that the relationship between stress and strain can be nonlinear and nonuniform. Moreover, depending on the timescales of interest, lung tissue exhibits viscoelastic behavior and can thus exhibit time-varying strain even when stress is constant. Fortunately, for most clinical applications, it suffices to model lung stretch during respiration as a uniform change in volume under the influence of the transpulmonary pressure, by analogy to force/length relationships in 1D models. Apart from nonlinearities, nonuniform inflation leads to important consequences in the setting of lung injury. While the viscoelastic nature of lung tissue is well established, as yet there is no convincing evidence that such effects must be routinely accounted for at the bedside.