2,796 research outputs found

    An Analysis of George Wallace and his First Inaugural Address as Governor of Alabama

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    To understand Governor George Wallace of Alabama, one has to look back at his watershed moment. The 1958 election for governor. From there, one can attempt to explain how Wallace became a figure of tragedy (by his own doing though) and how he had to sell his soul for the governorship. After understanding what made George Wallace tick, I shall move into his inaugural speech in 1963. By explaining this fiery speech through ideological criticism, one will be able to better comprehend the subtleties of both the man and the times. The bulk of the ideological criticism will be on the symbol and idea of the Lost Cause and naturally following that, coded language. From there, an analysis of his use of freedom and faith as a rallying call for white Southerners everywhere

    Carrier transport properties in the vicinity of single seld-assembled quantum dots determined by low-voltage cathodoluminescence imaging

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    Abstract : We propose a method to investigate the carrier transport properties in the ultrathin wetting layer of a self-assembled quantum dot (QD) structure using low-voltage cathodoluminescence (CL) imaging. Measurements are performed on diluted InAs/InP QDs in order to spatially resolve them on CL images at temperature ranging from 5 to 300 K. The mean ambipolar diffusion length extracted from CL intensity profiles across different isolated bright spots is about 300 nm at 300 K. This gives an ambipolar carrier mobility of about 110 cm2/(V s)110 cm2/(V s). Temperature investigation reveals a maximum diffusion length near 120 K

    Development of a System for 3D High-resolution Seismic Reflection Profiling on Lakes

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    A high-resolution three-dimensional (3D) seismic reflection system for small-scale targets in lacustrine settings has been developed. Its main characteristics include navigation and shot-triggering software that fires the seismic source at regular distance intervals (max. error of 0.25m) with real-time control on navigation using differential GPS (Global Positioning System). Receiver positions are accurately calculated (error<0.20m) with the aid of GPS antennas attached to the end of each of three 24-channel streamers. Two telescopic booms hold the streamers at a distance of 7.5m from each other. With a receiver spacing of 2.5m, the bin dimension is 1.25m in inline and 3.75m in crossline direction. To test the system, we conducted a 3D survey of about 1km2 in Lake Geneva, Switzerland, over a complex fault zone. A 5-m shot spacing resulted in a nominal fold of 6. A double-chamber bubble-cancelling 15/15in3 air gun (40-650Hz) operated at 80 bars and 1m depth gave a signal penetration of 300m below water bottom and a best vertical resolution of 1.1m. Processing followed a conventional scheme, but had to be adapted to the high sampling rates, and our unconventional navigation data needed conversion to industry standards. The high-quality data enabled us to construct maps of seismic horizons and fault surfaces in three dimensions. The system proves to be well adapted to investigate complex structures by providing non-aliased images of reflectors with dips up to 30

    Resolved Spectroscopy of the T8.5 and Y0-0.5 Binary WISEPC J121756.91+162640.2AB

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    We present 0.9 - 2.5 um resolved spectra for the ultracool binary WISEPC J121756.91+162640.2AB. The system consists of a pair of brown dwarfs that straddles the currently defined T/Y spectral type boundary. We use synthetic spectra generated by model atmospheres that include chloride and sulfide clouds (Morley et al.), the distance to the system (Dupuy & Kraus), and the radius of each component based on evolutionary models (Saumon & Marley) to determine a probable range of physical properties for the binary. The effective temperature of the T8.5 primary is 550 - 600 K, and that of the Y0 - Y0.5 secondary is 450 K. The atmospheres of both components are either free of clouds or have extremely thin cloud layers. We find that the masses of the primary and secondary are 30 and 22 M_Jup, respectively, and that the age of the system is 4 - 8 Gyr. This age is consistent with astrometric measurements (Dupuy & Kraus) that show that the system has kinematics intermediate between those of the thin and thick disks of the Galaxy. An older age is also consistent with an indication by the H - K colors that the system is slightly metal-poor.Comment: 21 pages which include 6 Figures and 3 Tables. Accepted on November 8 2013 for publication in Ap

    Petrology and geochemistry of Devono-Carboniferous volcanic rocks in Nova Scotia

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    The Devono-Carboniferous volcanic rocks of Nova Scotia include Middle Devonian basalts from the McAras Brook Formation in the northern Antigonlsh Highlands (Ballantynes Cove and McAras Brook areas), Kiddle Devonian and Carboniferous basalts and rhyolites of the Fountain Lake Group In the Cobequid Highlands and the Upper Devonian-Lower Carboniferous basalts and rhyolites of the Fisset Brook Formation in Cape Breton Island. The volcanic rocks were extruded upon the continental crust in an lntraplate setting. The basalts are tholelitic except those from Ballantynes Cove which are alkaline. All these basalts could have been derived from a similar upper mantle source - garnet peridotite. Rhyolites were probably generated by crustal anatexis related to the ascending basaltic magma. The Devono-Carboniferous volcaniant is probably connected with rifting along faults bounding the Magadalen pull-apart basin. In the Cobequid Highlands, the volcanlsm appears to be spatially and temporally associated with plutonism. R&#xC9;SUM&#xC9; Les roches volcaniqu&#xE9;e D&#xE9;vono-Carbonif&#xE8;res de la Nouvelle-&#xC9;cosse comprennent: les basaltes de la formation McAras Brook (D&#xE9;vonian moyen) dans la partie nord des hautes-terres d'Antigonlsh (r&#xE9;gions de Ballantynes Cove et de McAras Brook); les basaltes et les rhyolites du groupe Fountain Lake (D&#xE9;vonien moyen et Carbonif&#xE8;re) des monts Cobequid; et les basaltes et rhyolites (D&#xE9;vonien sup&#xE9;rieur-Carbonif&#xE8;re inf&#xE9;rieur) de la formation Fisset Brook su l’ile du Cap-Breton. Les roches volcaniqu&#xE9;e furent repandues &#xE0; la surface de la cro&#xF9;te continentale dans un contexte intraplaque. Les basaltes sont tous thol&#xE8;iltiques &#xE0; l'exception de ceux de Ballantynes Cove qui sont alcallns. Tous ces basaltes pourralent provenir d'une m&#xEA;me source situ&#xE9;e dans la partie sup&#xE9;rieure de manteau terrestre - p&#xE9;ridotite &#xE0; grenat. Les rhyolites r&#xE9;sultent probablement de l'anatexie de la cro&#xF9;te associ&#xE9;e &#xE0; la mont&#xE9;e du magma basaltique. Le volcanisme D&#xE9;vono-Carbonif&#xE8;re est probablement reli&#xE9; &#xE0; une fissuration le long des failles qui encadrent le bassin de d&#xE9;chirement des Madeleines. Dans les monts Cobequid, le volcanisme semble associ&#xE9; de fa&#xE7;on spatio-temporelle au plutonisine. [Traduit par le Journal

    Limits on the Mass and Initial Entropy of 51 Eri b from Gaia EDR3 Astrometry

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    51 Eri b is one of the only young planets consistent with a wide range of possible initial entropy states, including the cold-start scenario associated with some models of planet formation by core accretion. The most direct way to constrain the initial entropy of a planet is by measuring its luminosity and mass at a sufficiently young age that the initial conditions still matter. We present the tightest upper limit on 51 Eri b's mass yet (M < 11 Mjup at 2σ\sigma) using a cross-calibration of Hipparcos and Gaia EDR3 astrometry and the orbit-fitting code orvara. We also reassess its luminosity using a direct, photometric approach, finding log(Lbol/Lsun) = -5.5±\pm0.2 dex. Combining this luminosity with the 24±\pm3 Myr age of the β\beta Pic moving group, of which 51 Eri is a member, we derive mass distributions from a grid of evolutionary models that spans a wide range of initial entropies. We find that 51 Eri b is inconsistent with the coldest-start scenarios, requiring an initial entropy of >8 kBk_B/baryon at 97% confidence. This result represents the first observational constraint on the initial entropy of a potentially cold-start planet, and it continues the trend of dynamical masses for directly imaged planets pointing to warm- or hot-start formation scenarios.Comment: Accepted for publication in MNRAS (9 pages, 6 figures

    Precise Dynamical Masses of Directly Imaged Companions from Relative Astrometry, Radial Velocities, and Hipparcos-Gaia DR2 Accelerations

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    We measure dynamical masses for five objects--three ultracool dwarfs, one low-mass star, and one white dwarf--by fitting orbits to a combination of the Hipparcos-Gaia Catalog of Accelerations, literature radial velocities, and relative astrometry. Our approach provides precise masses without any assumptions about the primary star, even though the observations typically cover only a small fraction of an orbit. We also perform a uniform re-analysis of the host stars' ages. Two of our objects, HD 4747B and HR 7672B, already have precise dynamical masses near the stellar/substellar boundary and are used to validate our approach. For Gl 758B, we obtain a mass of m=38.1−1.5+1.7m=38.1_{-1.5}^{+1.7} MJupM_{Jup}, the most precise mass measurement of this companion to date. Gl 758B is the coldest brown dwarf with a dynamical mass, and the combination of our low mass and slightly older host-star age resolves its previously noted discrepancy with substellar evolutionary models. HD 68017B, a late-M dwarf, has a mass of m=0.147±0.003m=0.147\pm 0.003 M⊙M_\odot, consistent with stellar theory and previous empirical estimates based on its absolute magnitude. The progenitor of the white dwarf Gl 86B has been debated in the literature, and our dynamical measurement of m=0.595±0.010m=0.595 \pm 0.010 M⊙M_\odot is consistent with a higher progenitor mass and younger age for this planet-hosting binary system. Overall, these case studies represent only five of the thousands of accelerating systems identified by combining Hipparcos and Gaia. Our analysis could be repeated for many of them to build a large sample of companions with dynamical masses.Comment: 33 pages, 24 figures, 9 tables, AJ accepted with minor revision

    Rotational Velocities of Individual Components in Very Low Mass Binaries

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    We present rotational velocities for individual components of 11 very low mass (VLM) binaries with spectral types between M7 and L7.5. These results are based on observations taken with the near-infrared spectrograph, NIRSPEC, and the Keck II laser guide star adaptive optics system. We find that the observed sources tend to be rapid rotators (v sin i > 10 km s^(–1)), consistent with previous seeing-limited measurements of VLM objects. The two sources with the largest v sin i, LP 349–25B and HD 130948C, are rotating at ~30% of their break-up speed, and are among the most rapidly rotating VLM objects known. Furthermore, five binary systems, all with orbital semimajor axes ≾3.5 AU, have component v sin i values that differ by greater than 3σ. To bring the binary components with discrepant rotational velocities into agreement would require the rotational axes to be inclined with respect to each other, and that at least one component is inclined with respect to the orbital plane. Alternatively, each component could be rotating at a different rate, even though they have similar spectral types. Both differing rotational velocities and inclinations have implications for binary star formation and evolution. We also investigate possible dynamical evolution in the triple system HD 130948A–BC. The close binary brown dwarfs B and C have significantly different v sin i values. We demonstrate that components B and C could have been torqued into misalignment by the primary star, A, via orbital precession. Such a scenario can also be applied to another triple system in our sample, GJ 569A–Bab. Interactions such as these may play an important role in the dynamical evolution of VLM binaries. Finally, we note that two of the binaries with large differences in component v sin i, LP 349–25AB and 2MASS 0746+20AB, are also known radio sources

    Nucleation and growth behavior of multicomponent secondary phases in entropy-stabilized oxides

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    The rocksalt structured (Co,Cu,Mg,Ni,Zn)O entropy-stabilized oxide (ESO) exhibits a reversible phase transformation that leads to the formation of Cu-rich tenorite and Co-rich spinel secondary phases. Using atom probe tomography, kinetic analysis, and thermodynamic modeling, we uncover the nucleation and growth mechanisms governing the formation of these two secondary phases. We find that these phases do not nucleate directly, but rather they first form Cu-rich and Co-rich precursor phases, which nucleate in regions rich in Cu and cation vacancies, respectively. These precursor phases then grow through cation diffusion and exhibit a rocksalt-like crystal structure. The Cu-rich precursor phase subsequently transforms into the Cu-rich tenorite phase through a structural distortion-based transformation, while the Co-rich precursor phase transforms into the Co-rich spinel phase through a defect-mediated transformation. Further growth of the secondary phases is controlled by cation diffusion within the primary rocksalt phase, whose diffusion behavior resembles other common rocksalt oxides
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