3,421 research outputs found

    X-ray flare modeling in the single giant HR 9024

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    We analyze a Chandra-HETGS observation of the single G-type giant HR 9024. The high flux allows us to examine spectral line and continuum diagnostics at high temporal resolution, to derive plasma parameters (thermal distribution, abundances, temperature, ...). A time-dependent 1D hydrodynamic loop model with semi-length 1012^{12}cm (∌R⋆\sim R_{\star}), and impulsive footpoint heating triggering the flare, satisfactorily reproduces the observed evolution of temperature and emission measure, derived from the analysis of the strong continuum emission. The observed characteristics of the flare appear to be common features in very large flares in active stars (also pre-main sequence stars), possibly indicating some fundamental physics for these very dynamic and extreme phenomena in stellar coronae.Comment: 2 pages, 4 figures. To be included in the proceedings of the 'X-ray universe 2005 meeting' held in San Lorenzo de El Escorial (Spain), 26-30 Sep 200

    Direct regulation is an efficient approach to industrial environmental improvement: empirical evidence and perceptions from chemical manufacturers in Ireland and Italy.

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    Industrial production is a major source of global pollution, and it is widely recognised that regulation is required to reduce this pollution for the benefit of society. However, there is considerable debate about the most effective approach to environmental regulation with respect to both environmental and competitive performance. This paper integrates complementary empirical evidence from two entirely separate projects with different approaches (scientific and econometric), from different countries (Ireland and Italy), in order to assess the effectiveness and efficiency of direct environmental regulation in practice. Quantitative pollution avoidance and compliance cost data from Ireland’s pharmaceutical-manufacturing sector were combined with questionnaire responses from 20 Irish pharmaceutical manufacturers and 25 Italian manufacturers of chemicals for building products. We conclude that direct command-and-control regulation is a highly effective approach, and that the efficiency of such regulation is often underestimated.environmental regulation, environmental performance, competitiveness.

    X-ray Spectroscopy of the Contact Binary VW Cephei

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    Short-period binaries represent extreme cases in the generation of stellar coronae via a rotational dynamo. Such stars are important for probing the origin and nature of coronae in the regimes of rapid rotation and activity saturation. VW Cep (P=0.28 d) is a relatively bright, partially eclipsing, and very active object. Light curves made from Chandra/HETGS data show flaring and rotational modulation, but no eclipses. Velocity modulation of emission lines indicates that one component dominates the X-ray emission. The emission measure is highly structured, having three peaks. Helium-like triplet lines give electron densities of about 3.0E+10 - 18.0E+10 /cm^3. We conclude that the corona is predominantly on the polar regions of the primary star and compact.Comment: Accepted for publication in the Astropysical Journal, 23 June 2006; 22 pages, 15 figure

    Chandra/HETGS Observations of the Capella System: the Primary as a Dominating X-ray Source

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    Using the Chandra/High Energy Transmission Grating Spectrometer (hereafter HETGS) we have detected Doppler motion of Capella's X-ray emission lines in the 6 -- 25AA wave-band. The observed motion follows the expected orbital motion of Capella's primary. This finding implies that the primary G8 III star, not the secondary G1 III star in the Hertzsprung gap, has been the dominant source of hot 10^{6.8} -- 10^{7}K plasma at least in the last six years. In addition, the results demonstrate the long-term stability of the HETGS and demonstrate small uncertainties of 25 and 33 km/s in the velocity determination with the HEG and MEG, respectively.Comment: 4 pages, 4 figures, accepted by Astrophysical Journal Letter

    The binational Great Lakes economy

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    Great Lakes ; North American Free Trade Agreement ; Canada ; Manufactures

    X-ray Properties of Low-Mass Pre-Main Sequence Stars in the Orion Trapezium Cluster

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    The Chandra High Energy Transmission Gratings (HETG) Orion Legacy Project (HOLP) is the first comprehensive set of observations of a very young massive stellar cluster which provides high resolution X-ray spectra of very young stars over a wide mass range (0.7 - 2.3 Msun). In this paper, we focus on the six brightest X-ray sources with T Tauri stellar counterparts which are well-characterized at optical and infra-red wavelengths. All stars show column densities which are substantially smaller than expected from optical extinction indicating that the sources are located on the near side of the cluster with respect to the observer as well as that these stars are embedded in more dusty environments. Stellar X-ray luminosities are well above 103110^{31} erg/s, in some cases exceeding 103210^{32} erg/s for a substantial amount of time. The stars during these observations show no flares but are persistently bright. The spectra can be well fit with two temperature plasma components of 10 MK and 40 MK, of which the latter dominates the flux by a ratio 6:1 on average. The total EMs range between 3 - 8×1054\times10^{54} cm−3^{-3} and are comparable to active coronal sources. Limits on the forbidden to inter-combination line ratios in the He-Like K-shell lines show that we observe a predominantely optically thin plasma with electron densities below 101210^{12} cm−3^{-3}. Observed abundances compare well with active coronal sources underlying the coronal nature of these sources. The surface flux in this sample of 0.6 to 2.3 Msun classical T Tauri stars shows that coronal activity and possibly coronal loop size increase significantly between ages 0.1 to 10 Myrs.Comment: 13 pages, 12 figures, submitted to the Astrophysical Journa

    From Internet Users to Digital Historians: A Student Project Praxis Developed between an Historian and a Librarian-Technologist

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    In the context of a reevaluation of the standards of the Relationship between teacher and student, and within the context of an encouragement of enhancing a digital pedagogy with university courses in general, Professor David Del Testa and Ms. Abby Clobridge collaborated with one another to create a module of instruction with an introductory history course which used the topic of the Second World War as a vehicle to teach research methods. Utilizing two forms of digital technologies – personal response systems and digital image management – Clobridge and Del Testa let students act as professional historians, with positive results. They argue that only their presence as co-instructors in this course, with a visible crossing of the frontiers of expertise, and the leveling of access to research tools created by these technologies, permitted such a result, and that digital technologies enhanced the results that were achievedDans le contexte d'une Ă©valuation de la qualitĂ© de l'enseignement Ă  l'universitĂ© de Bucknell (Pennsylvanie, USA) et suite Ă  une forte incitation Ă  renforcer la prĂ©sence d'outils de pĂ©dagogie numĂ©riques dans les cours universitaires en gĂ©nĂ©ral, le professeur David Del Testa et Mme Abby Clobridge ont dĂ©veloppĂ© en collaboration un module d'enseignement intĂ©grĂ© dans un cours d'histoire de premier cycle. Cet enseignement propose une initiation aux mĂ©thodes de recherche de l'historien Ă  travers l'exemple de la DeuxiĂšme Guerre Mondiale. L'emploi de deux formes de technologie numĂ©rique – les systĂšmes de rĂ©ponse personnelle et les interfaces de gestion numĂ©rique des mĂ©dia – a permis Ă  Clobridge et Del Testa de crĂ©er les conditions nĂ©cessaires pour « laisser agir » les Ă©tudiants en tant qu'historiens professionnels, avec des rĂ©sultats apprĂ©ciables. Ces rĂ©sultats ont pu ĂȘtre obtenus grĂące Ă  la prĂ©sence de Clobridge et Del Testa en tant que co-instructeurs dans le cours, ce qui a permis un croisement visible de leurs domaines d'expertise, et grĂące Ă  l'accĂšs aux outils de recherche numĂ©riques qui ont amĂ©liorĂ© considĂ©rablement la qualitĂ© du travail des Ă©tudiants

    X-ray Flares of EV Lac: Statistics, Spectra, Diagnostics

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    We study the spectral and temporal behavior of X-ray flares from the active M-dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare parameters by fitting an empirical function which characterizes the amplitude, shape, and scale. The flares range from very short (<1 ks) to long (10 ks) duration events with a range of shapes and amplitudes for all durations. We extract spectra for composite flares to study their mean evolution and to compare flares of different lengths. Evolution of spectral features in the density-temperature plane shows probable sustained heating. The short flares are significantly hotter than the longer flares. We determined an upper limit to the Fe K fluorescent flux, the best fit value being close to what is expected for compact loops.Comment: 9 pages; 9 figures; latex/emulateapj style; Submitted to The Astrophysical Journa

    Evidence for Accretion in the High-resolution X-ray Spectrum of the T Tauri Star System Hen 3-600

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    We present high-resolution X-ray spectra of the multiple T Tauri star system Hen 3-600, obtained with the High Energy Transmission Grating Spectrograph on the Chandra X-ray Observatory. Two binary components were detected in the zeroth-order image. Hen 3-600-A, which has a large mid-infrared excess, is a 2-3 times fainter in X-rays than Hen 3-600-B, due to a large flare on B. The dispersed X-ray spectra of the two primary components overlap spatially; spectral analysis was performed on the combined system. Analysis of the individual spectra was limited to regions where the contributions of A and B can be disentangled. This analysis results in two lines of evidence indicating that the X-ray emission from Hen 3-600 is derived from accretion processes: line ratios of O VII indicate that the characteristic density of its X-ray-emitting plasma is large; a significant component of low-temperature plasma is present and is stronger in component A. These results are consistent with results obtained from X-ray gratings spectroscopy of more rapidly accreting systems. All of the signatures of Hen 3-600 that are potential diagnostics of accretion activity -- X-ray emission, UV excess, H-alpha emission, and weak infrared excess -- suggest that its components represent a transition phase between rapidly accreting, classical T Tauri stars and non-accreting, weak-lined T Tauri stars.Comment: latex, 27 pages, 12 figures, 6 tables; accepted by Ap

    The use of lng as a marine fuel: Civil liability considerations from an international perspective

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    © 2017. Oxford University Press. All rights reserved. Recent regulations in the maritime domain have placed increasing pressure on the shipping industry to reduce exhaust emissions from ships. Using LNG, which produces virtually 0% sulphur dioxide emissions, as an alternative fuel has thus become an attractive option to shipowners. However, the absence of a comprehensive legal framework in this regard is noteworthy, particularly in view of the fact that the issue of liability for pollution damage and the corresponding issue of compensation is a lacuna in the domain of international maritime law. This article examines this issue in detail and proposes that there is an urgent need to develop an international legal regime, and within the current framework and without abandoning the established regimes, amending the Carriage of Hazardous and Noxious Substances by Sea may well be a better option
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