133 research outputs found

    The Observational Case for Jupiter Being a Typical Massive Planet

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    We identify a subsample of the recently detected extrasolar planets that is minimally affected by the selection effects of the Doppler detection method. With a simple analysis we quantify trends in the surface density of this subsample in the period - Msin(i) plane. A modest extrapolation of these trends puts Jupiter in the most densely occupied region of this parameter space, thus indicating that Jupiter is a typical massive planet rather than an outlier. Our analysis suggests that Jupiter is more typical than indicated by previous analyses. For example, instead of M_Jup mass exoplanets being twice as common as 2 M_Jup exoplanets, we find they are three times as common.Comment: 17 pages, 6 figures, conforms to version accepted for publication in "Astrobiology", includes new comparison with microlensing constraints on Jupiter-like planet

    What Fraction of Sun-like Stars have Planets?

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    The radial velocities of ~1800 nearby Sun-like stars are currently being monitored by eight high-sensitivity Doppler exoplanet surveys. Approximately 90 of these stars have been found to host exoplanets massive enough to be detectable. Thus at least ~5% of target stars possess planets. If we limit our analysis to target stars that have been monitored the longest (~15 years), ~11% possess planets. If we limit our analysis to stars monitored the longest and whose low surface activity allow the most precise velocity measurements, ~25% possess planets. By identifying trends of the exoplanet mass and period distributions in a sub-sample of exoplanets less-biased by selection effects, and linearly extrapolating these trends into regions of parameter space that have not yet been completely sampled, we find at least ~9% of Sun-like stars have planets in the mass and orbital period ranges Msin(i) > 0.3 M_Jupiter and P 0.1 M_Jupiter and P < 60 years. Even this larger area of the mass-period plane is less than 20% of the area occupied by our planetary system, suggesting that this estimate is still a lower limit to the true fraction of Sun-like stars with planets, which may be as large as ~100%.Comment: Conforms to version accepted by ApJ. Color version and movie available at http://bat.phys.unsw.edu.au/~charley/download/whatfrac

    Mental Processes and Strategic Equilibration: An fMRI Study of Selling Strategies in Second Price Auctions

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    This study is the first to attempt to isolate a relationship between cognitive activity and equilibration to a Nash Equilibrium. Subjects, while undergoing fMRI scans of brain activity, participated in second price auctions against a single competitor following predetermined strategy that was unknown to the subject. For this auction there is a unique strategy that will maximize the subjects' earnings, which is also a Nash equilibrium of the associated game theoretic model of the auction. As is the case with all games, the bidding strategies of subjects participating in second price auctions most often do not reflect the equilibrium bidding strategy at first but with experience, typically exhibit a process of equilibration, or convergence toward the equilibrium. This research is focused on the process of convergence

    The Metallicity of Stars with Close Companions

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    We examine the relationship between the frequency of close companions (stellar and planetary companions with orbital periods < 5 years) and the metallicity of their Sun-like (~ FGK) hosts. We confirm and quantify a ~4 sigma positive correlation between host metallicity and planetary companions. We find little or no dependence on spectral type or distance in this correlation. In contrast to the metallicity dependence of planetary companions, stellar companions tend to be more abundant around low metallicity hosts. At the ~2 sigma level we find an anti-correlation between host metallicity and the presence of a stellar companion. Upon dividing our sample into FG and K sub-samples, we find a negligible anti-correlation in the FG sub-sample and a 3 sigma anti-correlation in the K sub-sample. A kinematic analysis suggests that this anti-correlation is produced by a combination of low-metallicity, high-binarity thick disk stars and higher-metallicity, lower-binarity thin disk stars.Comment: Conforms to version accepted by ApJ. 15 pages formatted with emulateapj.cl

    Development of the DLR Next Generation Train running gear research facility (NGT-FuN)

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    A full-scale prototype of the Next Generation Train (NGT) running gear with a roller rig installation bench will be built as proof of concept of the running gear and its suitability for high-speed traffic. It will be available as the research platform ÔÇťForschungsinfrastruktur NGT-FahrwerkÔÇŁ (FuN) for the German Aerospace Center (DLR) internal and external research activities. This work presents an innovative method and tool chain to develop application software for the automation of a mechatronic running gear (prototype). The methodology, development, and simulation tools that offer a consistent tool chain from model creation to real-time software and measurement data processing are presented. The model and software structures that are necessary for the software environment are described. The software-in-the-loop environment couples the existing multi-body simulations for the development process with signal-based simulation software using a co-simulation interface. The resulting software-in-theloop simulation environment contains a novel interface layer that translates the mechanical states of the multi-body simulation to pseudo-electrical signals that are read or written by the application software. This makes it possible to develop real-time applications and software structures in software-in-the-loop architectures. The real-time software contains a dedicated model structure of input, processing and output submodels, which is based on signal flow and distinct assignment of tasks. On the rapid-control-prototyping hardware, the real-time software is investigated with a virtual installation bench simulation

    How Dry is the Brown Dwarf Desert?: Quantifying the Relative Number of Planets, Brown Dwarfs and Stellar Companions around Nearby Sun-like Stars

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    Sun-like stars have stellar, brown dwarf and planetary companions. To help constrain their formation and migration scenarios, we analyse the close companions (orbital period < 5 years) of nearby Sun-like stars. By using the same sample to extract the relative numbers of stellar, brown dwarf and planetary companions, we verify the existence of a very dry brown dwarf desert and describe it quantitatively. With decreasing mass, the companion mass function drops by almost two orders of magnitude from 1 M_Sun stellar companions to the brown dwarf desert and then rises by more than an order of magnitude from brown dwarfs to Jupiter-mass planets. The slopes of the planetary and stellar companion mass functions are of opposite sign and are incompatible at the 3 sigma level, thus yielding a brown dwarf desert. The minimum number of companions per unit interval in log mass (the driest part of the desert) is at M = 31^{+25}_{-18} M_Jup. Approximately 16% of Sun-like stars have close (P < 5 years) companions more massive than Jupiter: 11% +- 3% are stellar, <1% are brown dwarf and 5% +- 2% are giant planets. The steep decline in the number of companions in the brown dwarf regime, compared to the initial mass function of individual stars and free-floating brown dwarfs, suggests either a different spectrum of gravitational fragmentation in the formation environment or post-formation migratory processes disinclined to leave brown dwarfs in close orbits.Comment: Conforms to version accepted by ApJ. 13 pages formatted with emulateapj.cl

    Increased midgestational IFN-╬│, IL-4 and IL-5 in women bearing a child with autism: A case-control study

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    <p>Abstract</p> <p>Background</p> <p>Immune anomalies have been documented in individuals with autism spectrum disorders (ASDs) and their family members. It is unknown whether the maternal immune profile during pregnancy is associated with the risk of bearing a child with ASD or other neurodevelopmental disorders.</p> <p>Methods</p> <p>Using Luminex technology, levels of 17 cytokines and chemokines were measured in banked serum collected from women at 15 to 19 weeks of gestation who gave birth to a child ultimately diagnosed with (1) ASD (<it>n </it>= 84), (2) a developmental delay (DD) but not autism (<it>n </it>= 49) or (3) no known developmental disability (general population (GP); <it>n </it>= 159). ASD and DD risk associated with maternal cytokine and chemokine levels was estimated by using multivariable logistic regression analysis.</p> <p>Results</p> <p>Elevated concentrations of IFN-╬│, IL-4 and IL-5 in midgestation maternal serum were significantly associated with a 50% increased risk of ASD, regardless of ASD onset type and the presence of intellectual disability. By contrast, elevated concentrations of IL-2, IL-4 and IL-6 were significantly associated with an increased risk of DD without autism.</p> <p>Conclusion</p> <p>The profile of elevated serum IFN-╬│, IL-4 and IL-5 was more common in women who gave birth to a child subsequently diagnosed with ASD. An alternative profile of increased IL-2, IL-4 and IL-6 was more common for women who gave birth to a child subsequently diagnosed with DD without autism. Further investigation is needed to characterize the relationship between these divergent maternal immunological phenotypes and to evaluate their effect on neurodevelopment.</p
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