650 research outputs found

    An operational system for subject switching between controlled vocabularies: A computational linguistics approach

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    The NASA Lexical Dictionary (NLD), a system that automatically translates input subject terms to those of NASA, was developed in four phases. Phase One provided Phrase Matching, a context sensitive word-matching process that matches input phrase words with any NASA Thesaurus posting (i.e., index) term or Use reference. Other Use references have been added to enable the matching of synonyms, variant spellings, and some words with the same root. Phase Two provided the capability of translating any individual DTIC term to one or more NASA terms having the same meaning. Phase Three provided NASA terms having equivalent concepts for two or more DTIC terms, i.e., coordinations of DTIC terms. Phase Four was concerned with indexer feedback and maintenance. Although the original NLD construction involved much manual data entry, ways were found to automate nearly all but the intellectual decision-making processes. In addition to finding improved ways to construct a lexical dictionary, applications for the NLD have been found and are being developed

    Nitrogenase activity associated with codium species from New Zealand marine habitats

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    Nitrogenase activity, measured as acetylene reduction, was recorded at rates up to 1028 nmol.h \g * dry weight for Codium adhaerens (Cabr.) Ag. var. convolutum Dellow and Codium fragile (Sur.) Hariot subsp. tomentosoides (Van Goor) Silva collected from New Zealand habitats. In both species the ability to reduce acetylene is invariably associated with the presence of a heterocystous blue-green alga, Calothrix sp., epiphytic or embedded in the Codium thallus. A highly significant (P < 0.001) correlation between heterocyst frequency and nitrogenase activity was found. Nitrogenase and net photosynthesis of the Codium-Calothrix system have different steady-state responses to light intensity, and the kinetics of the two processes also differ in that nitrogenase is slow to respond to illumination or darkening. Glucose additions to Codium did not significantly increase nitrogenase activity. Nitrogenase is relatively insensitive to oxygen tension over the range 0-1.0 atm (0-1.033 kgf.cnT2) and still occurs at 1.5 atm (1.55 kgf.cm"2); this condition is unique in all nitrogenase systems thus far reported. Collectively these facts suggest that Calothrix is the agent primarily responsible for nitrogenase activity in these Codium species

    Revisiting the Rigidly Rotating Magnetosphere model for σ\sigma Ori E - II. Magnetic Doppler imaging, arbitrary field RRM, and light variability

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    The initial success of the Rigidly Rotating Magnetosphere (RRM) model application to the B2Vp star sigma OriE by Townsend, Owocki & Groote (2005) triggered a renewed era of observational monitoring of this archetypal object. We utilize high-resolution spectropolarimetry and the magnetic Doppler imaging (MDI) technique to simultaneously determine the magnetic configuration, which is predominately dipolar, with a polar strength Bd = 7.3-7.8 kG and a smaller non-axisymmetric quadrupolar contribution, as well as the surface distribution of abundance of He, Fe, C, and Si. We describe a revised RRM model that now accepts an arbitrary surface magnetic field configuration, with the field topology from the MDI models used as input. The resulting synthetic Ha emission and broadband photometric observations generally agree with observations, however, several features are poorly fit. To explore the possibility of a photospheric contribution to the observed photometric variability, the MDI abundance maps were used to compute a synthetic photospheric light curve to determine the effect of the surface inhomogeneities. Including the computed photospheric brightness modulation fails to improve the agreement between the observed and computed photometry. We conclude that the discrepancies cannot be explained as an effect of inhomogeneous surface abundance. Analysis of the UV light variability shows good agreement between observed variability and computed light curves, supporting the accuracy of the photospheric light variation calculation. We thus conclude that significant additional physics is necessary for the RRM model to acceptably reproduce observations of not only sigma Ori E, but also other similar stars with significant stellar wind-magnetic field interactions.Comment: 16 pages, 17 figures, accepted for publication in MNRA

    Double layer in ionic liquids: Overscreening vs. crowding

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    We develop a simple Landau-Ginzburg-type continuum theory of solvent-free ionic liquids and use it to predict the structure of the electrical double layer. The model captures overscreening from short-range correlations, dominant at small voltages, and steric constraints of finite ion sizes, which prevail at large voltages. Increasing the voltage gradually suppresses overscreening in favor of the crowding of counterions in a condensed inner layer near the electrode. The predicted ion profiles and capacitance-voltage relations are consistent with recent computer simulations and experiments on room-temperature ionic liquids, using a correlation length of order the ion size.Comment: 4 pages + supplementary informatio

    Magnetism in pre-MS intermediate-mass stars and the fossil field hypothesis

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    Today, one of the greatest challenges concerning the Ap/Bp stars is to understand the origin of their slow rotation and their magnetic fields. The favoured hypothesis for the latter is the fossil field, which implies that the magnetic fields subsist throughout the different evolutionary phases, and in particular during the pre-main sequence phase. The existence of magnetic fields at the pre-main sequence phase is also required to explain the slow rotation of Ap/Bp stars. However, until recently, essentially no information was available about the magnetic properties of intermediate-mass pre-main sequence stars, the so-called Herbig Ae/Be stars. The new high-resolution spectropolarimeter ESPaDOnS, installed in 2005 at the Canada-France-Hawaii telescope, provided the capability necessary to perform surveys of the Herbig Ae/Be stars in order to investigate their magnetism and rotation. These investigations have resulted in the detection and/or confirmation of magnetic fields in 8 Herbig Ae/Be stars, ranging in mass from 2 to nearly 15 solar masses. In this contribution I will present the results of our survey, as well as their implications for the origin and evolution of the magnetic fields and rotation.Comment: Proceedings of the CP#AP Workshop held in Vienna in September 200

    Colloquium: The transport properties of graphene: An introduction

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    An introduction to the transport properties of graphene combining experimental results and theoretical analysis is presented. In the theoretical description simple intuitive models are used to illustrate important points on the transport properties of graphene. The concept of chirality, stemming from the massless Dirac nature of the low energy physics of the material, is shown to be instrumental in understanding its transport properties: the conductivity minimum, the electronic mobility, the effect of strain, the weak (anti-)localization, and the optical conductivity.Comment: As publishe

    A novel coupler design and analysis with shielding material tests for a CPT system of electric vehicles based on electromagnetic resonant coupling

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    In this paper, a contactless power transfer (CPT) system using a novel geometrically enhanced energy transfer coupler with three different shielding materials has been built and analysed, along with the evaluations from aspects of electromagnetics and RMS power transmitting based on electromagnetic resonant coupling. A CPT system design improvement with the proposed H-shape ferromagnetic cores and the combined semi-enclosed passive electromagnetic shielding methods have been investigated in terms of generated electromagnetic field characteristics, system power transfer ratings, system efficiency optimization and performances of shielding materials. The results have shown that, across the range of operating frequency of the CPT system, aluminium shielding as a metallic material method could deliver better overall CPT system performance than other two ferromagnetic materials, steel 1010 and ferrite. In addition, the coupler prototype design limitations, misalignment tolerance and the passive shielding design considerations including distance between windings and inner surfaces of shielding shells have been discussed

    Distribution and Diversity of Ascidian in Manado Bay, North Sulawesi

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    The purpose of this study was to determine the distribution and the diversity of ascidians in Manado Bay including species composition, density, diversity, and dominance. This study used the quadrat transect method. This study found differences in the number of ascidian species with water depth, 11 species of 5 families at 15 M depth, and 8 species of 3 families at 7 M depth. The diversity index ranged from 0.868 to 1.844 at 15 M depth and 0.965 to 1.864 at 7 M depth, the evenness index was 0.533 – 0.839 at 15 M depth and 0.600 – 0.897 at 7 M depth, the dominance index was 0.254 – 0.745 at 15 M depth and 0.254 – 0.708 at 7 M depth. Ascidian in Manado Bay had two distribution patterns, a uniform distribution pattern and a clustered distribution pattern. Environmental parameters had a water temperature of 27 oC – 31 oC, the salinity of 30 0/00 – 32 0/00, the brightness of 12 m – 14 m, and pH of 8 – 10.*Keywords: Ascidian; diversity; ecological index; distribution patternAbstrakTujuan dari penelitian ini adalah untuk mengetahui distribusi dan keanekaragaman jenis ascidia di perairan Teluk Manado meliputi: komposisi jenis, kepadatan individu, keanekaragaman, dan dominansi. Serta mengetahui pola distribusi ascidia. Penelitian ini menggunakan metode transek kuadran. Pada penelitian ini ditemukan perbedaan jumlah spesies ascidia menurut kedalaman, 11 spesies dari 5 family pada 15 M dan 8 spesies dari 3 famili pada kedalaman 7 m. Nilai indeks keanekaragaman ascidia di kedalaman 15 m = 0.868 – 1.844 dan 7 m = 0.965 - 1.864, indeks keseragaman 15 m = 0.533 – 0.839 dan 7 m = 0.600 – 0.897, indeks Dominasi15 m = 0.254 – 0.745 dan 7 m = 0.254 – 0.708. Ascdia di perairan Teluk Manado memiliki dua pola distribusi yaitu pola distribusi seragam dan pola distribusi mengelopok. Parameter lingkungan memiliki suhu air 27 oC – 31 oC, salinitas 30 0/00 – 32 0/00, kecerahan 12 m – 14 m, dan pH 8 – 10.*Kata kunci : Ascidia; keanekaragaman; indeks ekologi; pola distribus
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