234 research outputs found

    3-D Kinematics of the HH 110 jet

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    We present new results on the kinematics of the jet HH 110. New proper motion measurements have been calculated from [SII] CCD images obtained with a time baseline of nearly fifteen years. HH 110 proper motions show a strong asymmetry with respect to the outflow axis, with a general trend of pointing towards the west of the axis direction. Spatial velocities have been obtained by combining the proper motions and radial velocities from Fabry-Perot data. Velocities decrease by a factor ~3 over a distance of ~1018^{18} cm, much shorter than the distances expected for the braking caused by the jet/environment interaction. Our results show evidence of an anomalously strong interaction between the outflow and the surrounding environment, and are compatible with the scenario in which HH 110 emerges from a deflection in a jet/cloud collision.Comment: (1)Universitat de Barcelona; (2)UNAM; (3)UPC; (4)University of Hawaii; (5)Southern Astrophysical Research Telescope. 9 pages; 7 Figures Accepted by A&

    Observations and simulations of recurrent novae: U Sco and V394 CrA

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    Observations and analysis of the Aug. 1987 outburst of the recurrent nova V394 CrA are presented. This nova is extremely fast and its outburst characteristics closely resemble those of the recurrent nova U Sco. Hydrodynamic simulations of the outbursts of recurrent novae were performed. Results as applied to the outbursts of V394 CrA and U Sco are summarized

    On the Hydrodynamic Interaction of Shock Waves with Interstellar Clouds. II. The Effect of Smooth Cloud Boundaries on Cloud Destruction and Cloud Turbulence

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    The effect of smooth cloud boundaries on the interaction of steady planar shock waves with interstellar clouds is studied using a high-resolution local AMR technique with a second-order accurate axisymmetric Godunov hydrodynamic scheme. A 3D calculation is also done to confirm the results of the 2D ones. We consider an initially spherical cloud whose density distribution is flat near the cloud center and has a power-law profile in the cloud envelope. When an incident shock is transmitted into a smooth cloud, velocity gradients in the cloud envelope steepen the smooth density profile at the upstream side, resulting in a sharp density jump having an arc-like shape. Such a ``slip surface'' forms immediately when a shock strikes a cloud with a sharp boundary. For smoother boundaries, the formation of slip surface and therefore the onset of hydrodynamic instabilities are delayed. Since the slip surface is subject to the Kelvin-Helmholtz and Rayleigh-Taylor instabilities, the shocked cloud is eventually destroyed in 310\sim 3-10 cloud crushing times. After complete cloud destruction, small blobs formed by fragmentation due to hydrodynamic instabilities have significant velocity dispersions of the order of 0.1 vbv_b, where vbv_b is the shock velocity in the ambient medium. This suggests that turbulent motions generated by shock-cloud interaction are directly associated with cloud destruction. The interaction of a shock with a cold HI cloud should lead to the production of a spray of small HI shreds, which could be related to the small cold clouds recently observed by Stanimirovic & Heiles (2005). The linewidth-size relation obtained from our 3D simulation is found to be time-dependent. A possibility for gravitational instability triggered by shock compression is also discussed.Comment: 62 pages, 16 figures, submitted to Ap

    Evolution of non-kin cooperation:social assortment by cooperative phenotype in guppies

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    © 2019 The Authors. Cooperation among non-kin constitutes a conundrum for evolutionary biology. Theory suggests that non-kin cooperation can evolve if individuals differ consistently in their cooperative phenotypes and assort socially by these, such that cooperative individuals interact predominantly with one another. However, our knowledge of the role of cooperative phenotypes in the social structuring of real-world animal populations is minimal. In this study, we investigated cooperative phenotypes and their link to social structure in wild Trinidadian guppies (Poecilia reticulata). We first investigated whether wild guppies are repeatable in their individual levels of cooperativeness (i.e. have cooperative phenotypes) and found evidence for this in seven out of eight populations, a result which was mostly driven by females. We then examined the social network structure of one of these populations where the expected fitness impact of cooperative contexts is relatively high, and found assortment by cooperativeness, but not by genetic relatedness. By contrast, and in accordance with our expectations, we did not find assortment by cooperativeness in a population where the expected fitness impact of cooperative contexts is lower. Our results provide empirical support for current theory and suggest that assortment by cooperativeness is important for the evolution and persistence of non-kin cooperation in real-world populations

    Odor and Odorous Chemical Emissions from Animal Buildings: Part 1. Project Overview, Collection Methods, and Quality Control

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    Livestock facilities have historically generated public concerns due to their emissions of odorous air and various chemical pollutants. Odor emission factors and identification of principal odorous chemicals are needed to better understand the problem. Applications of odor emission factors include inputs to odor setback models, while chemical emission factors may be compared with regulation thresholds as a means of demonstrating potential health impacts. A companion study of the National Air Emissions Monitoring Study (NAEMS) included measurements necessary for establishing odor and chemical emission factors for confined animal feeding operations. This additional investigation was conducted by the University of Minnesota, Iowa State University, West Texas A&M Agri-Life Center, and Purdue University. The objectives were to (1) determine odor emission rates across swine and dairy facilities and seasons using common protocols and standardized olfactometry methods, (2) develop a chemical library of the most significant odorants, and (3) correlate the chemical library with the olfactometry results. This document describes the sampling and quality assurance methods used in the measurement and evaluation of odor and chemical samples collected at two freestall dairy farms, one sow (gestation/farrowing) facility, and one finishing pig site. Odor samples were collected in Tedlar bags and chemical samples were collected in sorbent tubes at barn inlet and exhaust locations using the NAEMS multiple-location gas sampling systems. Quality assurance protocols included interlaboratory comparison tests, which were evaluated to identify variations between olfactometry labs. While differences were observed, the variations among the labs and samples appeared random and the collected odor data were considered reliable at a 0.5% level of statistical significance. Overall, the study took advantage of groundbreaking opportunities to collect and associate simultaneous odor and chemical information from swine and dairy buildings while maintaining accordance with standard methods and comparability across laboratories

    Model experiment of magnetic field amplification in laser-produced plasmas via the Richtmyer-Meshkov instability

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    A model experiment of magnetic field amplification (MFA) via the Richtmyer-Meshkov instability (RMI) in supernova remnants (SNRs) was performed using a high-power laser. In order to account for very-fast acceleration of cosmic rays observed in SNRs, it is considered that the magnetic field has to be amplified by orders of magnitude from its background level. A possible mechanism for the MFA in SNRs is stretching and mixing of the magnetic field via the RMI when shock waves pass through dense molecular clouds in interstellar media. In order to model the astrophysical phenomenon in laboratories, there are three necessary factors for the RMI to be operative: a shock wave, an external magnetic field, and density inhomogeneity. By irradiating a double-foil target with several laser beams with focal spot displacement under influence of an external magnetic field, shock waves were excited and passed through the density inhomogeneity. Radiative hydrodynamic simulations show that the RMI evolves as the density inhomogeneity is shocked, resulting in higher MFA

    Enhanced brightness of a laser-driven X-ray and particle source by microstructured surfaces of silicon targets

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    The production of intense X-ray and particle sources is one of the most remarkable aspects of high energy laser interaction with a solid target. Wide application of these laser-driven secondary sources requires a high yield, which is partially limited by the amount of laser energy absorbed by the target. Here, we report on the enhancement of laser absorption and X-ray and particle flux by target surface modifications. In comparison to targets with flat front surfaces, our experiments show exceptional laser-to-target performance for our novel cone-shaped silicon microstructures. The structures are manufactured via laser-induced surface structuring. Spectral and spatial studies of reflectance and X-ray generation reveal significant increases of the silicon Kα line and a boost of the overall X-ray intensity, while the amount of reflected light decreases. Also, the proton and electron yields are enhanced, but both temperatures remain comparable to those of flat foil targets. We support the experimental findings with 2D particle in cell simulations to identify the mechanisms responsible for the strong enhancement. Our results demonstrate how custom surface structures can be used to engineer high power laser-plasma sources for future applications
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