3,421 research outputs found
X-ray flare modeling in the single giant HR 9024
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 10cm (), 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.
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 Irelandâs 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
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
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
Great Lakes ; North American Free Trade Agreement ; Canada ; Manufactures
X-ray Properties of Low-Mass Pre-Main Sequence Stars in the Orion Trapezium Cluster
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 erg/s, in
some cases exceeding 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 cm 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 cm. 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
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 â personal response systems and digital image management â 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 â les systĂšmes de rĂ©ponse personnelle et les interfaces de gestion numĂ©rique des mĂ©dia â 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
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
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
© 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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