We obtain bounds on the stability of various self-gravitating astrophysical objects using a new measure of shape complexity known as configurational entropy. We apply the method to Newtonian polytropes, neutron stars with an Oppenheimer-Volkoff equation of state, and to self-gravitating configurations of complex scalar field (boson stars) with different self-couplings, showing that the critical stability region of these stellar configurations obtained from traditional perturbation methods correlates well with critical points of the configurational entropy with accuracy of a few percent or better.

Quantifying the airflow field in building room or vehicle cabin indoor space is crucial for creating a thermal comfortable and healthy indoor environment. Airflow field measurement can provide quantitative information of indoor air distribution and local air velocity around occupants or passengers, which has strong relationship with the ventilation effectiveness, the pollutant transportation and the energy conservation in a building or a vehicle. However, the airflow field in indoor environment is normally characterized by high turbulent level and unsteady due to relatively low air velocity from the diffuser, thermal plume of heat source and unsteady perturbation of occupants' behavior. Generally, it is very difficult to conduct accurate and detailed measurement of such a complex turbulent flow field with point-wise anemometry.

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Studies of neutron stars are extremely timely given the recent detection of gravitational waves from a binary neutron star merger GW170817, and an International Space Station payload NICER currently in operation that aims to determine radii of neutron stars to a precision better than 5%. In many cases, neutron star solutions are constructed numerically due to the complexity of the field equations with realistic equations of state. However, in order to relate observables like the neutron star mass and radius to interior quantities like central density and pressure, it would be useful to provide an accurate, analytic modeling of a neutron star interior. One such solution for static and isolated neutron stars is the Tolman VII solution characterized only by two parameters (e.g. mass and radius), though its agreement with numerical solutions is not perfect. We here introduce an improved analytic model based on the Tolman VII solution by introducing an additional parameter to make the analytic density profile agree better with the numerically obtained one. This additional parameter can be fitted in terms of the stellar mass, radius and central density in an equationof-state-insensitive way. In most cases, we find that the new model more accurately describes realistic profiles than the original Tolman VII solution by a factor of 2-5. Our results are first-step calculations towards constructing analytic interior solutions for more realistic neutron stars under rotation or tidal deformation. arXiv:1904.05954v3 [gr-qc]

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a b s t r a c tBreathing is a high-risk behavior for spreading infectious diseases in enclosed environments, so it is important to investigate the characteristics of human exhalation flow and dispersal of exhaled air to reduce the risk. This paper used two-dimensional time-resolved particle image velocimetry (2D TR-PIV) to measure the exhaled flow from a breathing thermal manikin. Since the exhaled flow is transient and periodic, the phase-averaged method was used to analyze the flow characteristics. The results showed that the velocity profile of the flow exiting the mouth was bell-shaped for exhalation and flat for inhalation. The exhaled flow showed different characteristics during each stage of the exhalation process. In the initial phase, a mushroom-shaped flow arose, while some jet characteristics appeared in the middle phase. The effect of thermal buoyancy and thermal plume on the exhaled flow was analyzed. Clear turbulence characteristics were found in the exhaled flow, and the turbulence fluctuation was very strong in the transition stage between exhalation and inhalation. The last finding was that the distribution and value of vorticity were different in each phase. The results of quantitative PIV provided detailed information about the boundary condition set and validation data for CFD simulation.