58 research outputs found

    A Survey of Orbits of Co-orbitals of Jupiter

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    working version of a paper planned for Planetary and Space ScienceJupiter’s Trojan asteroids fulfill the prediction of Lagrange that orbits can be stable when a small body orbits in specific locations relative to its ‘parent’ planet and the Sun. The first such Trojan asteroid was discovered in 1906 and subsequently similar asteroids have been discovered associated with Mars and with Neptune. To date no Trojans have been discovered associated with Earth, but several horseshoe asteroids, co-orbital asteroids moving along a large range of the Earth’s orbit, have been found. Other planets also are not known to have Trojan-type asteroids associated with them. Since the number of detected Jupiter Trojans has increased dramatically in the last few years, we have conducted a numerical survey of their orbital motions to see whether any in fact move in horseshoe orbits. We find that none do, although there is some possibility that escaped Trojans have been detected. Here we also use the enlarged database of information about Trojans to summarize their orbital properties as now known

    Inner solar system dynamical analogs of plutinos

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    accepted by Icarus, November 2007By studying orbits of asteroids potentially in 3:2 exterior mean motion resonance with Earth, Venus, and Mars, we have found plutino analogs. We identify at least 27 objects in the inner solar system dynamically protected from encounter through this resonance. These are four objects associated with Venus, six with Earth, and seventeen with Mars. Bodies in the 3:2 exterior resonance (including those in the plutino resonance associated with Neptune) orbit the Sun twice for every three orbits of the associated planet, in such a way that with sufficiently low libration amplitude close approaches to the planet are impossible. As many as 15% of Kuiper Belt objects share the 3:2 resonance, but are poorly observed. One of several resonance sweeping mechanisms during planetary migration is likely needed to explain the origin and properties of 3:2 resonant Kuiper Belt objects. Such a mechanism likely did not operate in the inner solar system. We suggest that scattering by the next planet out allows entry to, and exit from, 3:2 resonance for objects associated with Venus or Earth. 3:2 resonators of Mars, on the other hand, do not cross the paths of other planets, and have a long lifetime. There may exist some objects trapped in the 3:2 Mars resonance which are primordial, with our tests on the most promising objects known to date indicating lifetimes of at least tens of millions of years. Identifying 3:2 resonant systems in the inner Solar System permits this resonance to be studied on shorter timescales and with better determined orbits than has been possible to date, and introduces new mechanisms for entry into the resonant configuration

    Inner solar system dynamical analogs for plutinos

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    By studying orbits of near-Earth asteroids potentially in 2:3 mean motion resonance with Earth, Venus, and Mars, we have found plutino analogs. We identify 23 objects in the inner solar system dynamically protected from encounter through this resonance. Plutinos in the Kuiper belt share similar remarkable 2:3 mean motion resonant properties of Pluto with respect to Neptune. These objects orbit the Sun twice for every three Neptune orbits, in such a way that close approaches to Neptune are impossible. Inner solar system “plutinos” avoid their respective associated planet in much the same way. As many as 15% of Kuiper Belt objects share the 2:3 resonance, but are poorly observed. Since the resonant condition does not allow the secondary body to have ever been near the primary, a resonance sweeping mechanism is preferred to explain the origin of Pluto and plutinos. This mechanism likely did not operate in the inner solar system, but scattering by the next outer planet is a potential entry to 3:2 resonance with Venus and Earth. Mars plutinos, on the other hand, may be primordial objects as they are not planet crossing. The analogue resonant systems apparently arise from a different mechanism than the resonance sweeping and scattering thought to apply in the Kuiper Belt

    The Star for Beginners: Introductions to the Magnum Opus of Franz Rosenzweig

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    In "The Star of Redemption", written at the end and after World War I and published in 1921, Franz Rosenzweig presented an epoch-making Jewish-inspired philosophy of religion. In three steps, each with three chapters or "books," Rosenzweig unfolds in it his view of God, the world, and man, their interrelationship, and their contribution and role in the redemption of the world. In this introduction, young and old Rosenzweig scholars take readers by the hand chapter by chapter, book by book. They lead safely through Rosenzweig's argumentation, making sometimes difficult lines of thought comprehensible and plausible. The chapter introductions open up reliable access for interested readers and new perspectives for connoisseurs

    Intercultural business ethics (IBE) : a teaching handbook

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    This book is a practical handbook for lecturers teaching Intercultural Business Ethics (IBE) in higher education. It is the result of collaboration between lecturers from South Africa, China and Switzerland in an ongoing intercultural teaching project. The basic idea is that students discuss ethical dilemmas from the business world in culturally mixed groups and present their joint solution proposals in a short video. The handbook aims to help facilitators of the peaceful coexistence of countries and cultures

    Cathodoluminescence studies of chevron features in semi-polar (1122) InGaN/GaN multiple quantum well structures

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    Epitaxial overgrowth of semi-polar III-nitride layers and devices often leads to arrowhead-shaped surface features, referred to as chevrons. We report on a study into the optical, structural, and electrical properties of these features occurring in two very different semi-polar structures, a blue-emitting multiple quantum well structure, and an amber-emitting light-emitting diode. Cathodoluminescence (CL) hyperspectral imaging has highlighted shifts in their emission energy, occurring in the region of the chevron. These variations are due to different semi-polar planes introduced in the chevron arms resulting in a lack of uniformity in the InN incorporation across samples, and the disruption of the structure which could cause a narrowing of the quantum wells (QWs) in this region. Atomic force microscopy has revealed that chevrons can penetrate over 150 nm into the sample and quench light emission from the active layers. The dominance of non-radiative recombination in the chevron region was exposed by simultaneous measurement of CL and the electron beam-induced current. Overall, these results provide an overview of the nature and impact of chevrons on the luminescence of semi-polar devices

    Planetesimal-driven planet migration in the presence of a gas disk

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    We report here on an extension of a previous study by Kirsh et al. (2009) of planetesimal-driven migration using our N-body code SyMBA (Duncan et al., 1998). The previous work focused on the case of a single planet of mass Mem, immersed in a planetesimal disk with a power-law surface density distribution and Rayleigh distributed eccentricities and inclinations. Typically 10^4-10^5 equal-mass planetesimals were used, where the gravitational force (and the back-reaction) on each planetesimal by the Sun and planetwere included, while planetesimal-planetesimal interactions were neglected. The runs reported on here incorporate the dynamical effects of a gas disk, where the Adachi et al. (1976) prescription of aerodynamic gas drag is implemented for all bodies. In some cases the Papaloizou and Larwood (2000) prescription of Type-I migration for the planet are implemented, as well as a mass distribution. In the gas-free cases, rapid planet migration was observed - at a rate independent of the planet's mass - provided the planet's mass was not large compared to the mass in planetesimals capable of entering its Hill sphere. In such cases, both inward and outward migrations can be self-sustaining, but there is a strong propensity for inward migration. When a gas disk is present, aerodynamic drag can substantially modify the dynamics of scattered planetesimals. For sufficiently large or small mono-dispersed planetesimals, the planet typically migrates inward. However, for a range of plausible planetesimal sizes (i.e. 0.5-5.0 km at 5.0 AU in a minimum mass Hayashi disk) outward migration is usually triggered, often accompanied by substantial planetary mass accretion. The origins of this behaviour are explained in terms of a toy model. The effects of including a size distribution and torques associated with Type-I migration are also discussed.Comment: 37 pages, 17 figures, Accepted for publication in Icaru

    On the accumulation of planetesimals near disc gaps created by protoplanets

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    We have performed three-dimensional two-fluid (gas-dust) hydrodynamical models of circumstellar discs with embedded protoplanets (3 - 333 M\oplu) and small solid bodies (radii 10cm to 10m). We find that high mass planets (\gtrsim Saturn mass) open sufficiently deep gaps in the gas disc such that the density maximum at the outer edge of the gap can very efficiently trap metre-sized solid bodies. This allows the accumulation of solids at the outer edge of the gap as solids from large radii spiral inwards to the trapping region. This process of accumulation occurs fastest for those bodies that spiral inwards most rapidly, typically metre-sized boulders, whilst smaller and larger objects will not migrate sufficiently rapidly in the discs lifetime to benefit from the process. Around a Jupiter mass planet we find that bound clumps of solid material, as large as several Earth masses, may form, potentially collapsing under self-gravity to form planets or planetesimals. These results are in agreement with Lyra et al. (2009), supporting their finding that the formation of a second generation of planetesimals or of terrestrial mass planets may be triggered by the presence of a high mass planet.Comment: 14 pages, 10 figures. Accepted for publication in MNRA

    You do what in your microprobe?! The EPMA as a multimode platform for nitride semiconductor characterization

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    While the use of electron probe microanalysis (EPMA) is widespread in the geological and metallurgical sciences, it remains less prevalent in the field of semiconductor research. For these materials, trace element (i.e. dopant) levels typically lie near or beneath the detection limit of wavelength-dispersive Xray (WDX) spectrometers, while alloy compositions of ternary mixtures and multilayer structures can more readily be determined using X-ray diffraction techniques. The electron beam measurements more commonly applied to semiconductors remain transmission electron microscopy (for structural characterization), and scanning electron microscopy (topographic, optical and electrical information). Despite this, there are many aspects of the EPMA that make it an attractive platform for all of thesetypes of semiconductor characterization, particularly when combining compositional information fromWDX with complementary and simultaneously-acquired signals. These advantages include: built-inlight optics; a stable, quantified and high-current beam; and a combined large-area and high-resolutionmapping capability. This allows the measurement of cathodoluminescence (CL), electron beam-inducedcurrent (EBIC) and electron channelling contrast imaging (ECCI) signals alongside WDX, which weapply to the investigation of visible and UV AlxInyGa1-x-yN materials, devices and nanostructures
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