1,977 research outputs found
[Fe II] and H2 filaments in the Supernova Remnant G11.2-0.3: Supernova Ejecta and Presupernova Circumstellar Wind
We present the results of near-infrared imaging and spectroscopic
observations of the young, core-collapse supernova remnant (SNR) G11.2-0.3. In
the [Fe II] 1.644 um image, we first discover long, clumpy [Fe II] filaments
within the radio shell of the SNR, together with some faint, knotty features in
the interior of the remnant. We have detected several [Fe II] lines and HI Br-G
line toward the peak position of the bright southeastern [Fe II] filament. The
derived extinction is large (Av=13 mag) and it is the brightest [Fe II]
filament detected toward SNRs to date. By analyzing two [Fe II] 1.644 um images
obtained in 2.2 yrs apart, we detect a proper motion corresponding to an
expansion rate of 0.''035 (0.''013) /yr [or 830 (310) km/s]. We also discover
two small H2 filaments. One is bright and along the SE boundary of the radio
shell, while the other is faint and just outside of its NE boundary. We have
detected H2 (2-1) S(3) line toward the former filament and derive an excitation
temperature of 2,100 K. We suggest that the H2 filaments are dense clumps in a
presupernova circumstellar wind swept up by the SNR shock while the [Fe II]
filaments are probably composed of both shocked wind material and shocked
supernova (SN) ejecta. The distribution of [Fe II] filaments may indicate that
the SN explosion in G11.2-0.3 was asymmetric as in Cassiopeia A. Our results
support the suggestion that G11.2-0.3 is a remnant of a SN IIL/b interacting
with a dense red supergiant wind.Comment: 30 pages with 10 figures, To appear in the Astrophysical Journa
Infrared Excess and Molecular Gas in the Galactic Worm GW46.4+5.5
We have carried out high-resolution (~3') HI and CO line observations along
one-dimensional cuts through the Galactic worm GW46.4+5.5. By comparing the HI
data with IRAS data, we have derived the distributions of I_100 excess and
tau_100 excess, which are respectively the 100 mum intensity and 100 mum
optical depth in excess of what would be expected from HI emission. In two
observed regions, we were able to make a detailed comparison of the infrared
excess and the CO emission. We have found that tau_100 excess has a very good
correlation with the integrated intensity of CO emission, W_CO, but I_100
excess does not. There are two reasons for the poor correlation between I_100
excess and W_CO: firstly, there are regions with enhanced infrared emissivity
without CO, and secondly, dust grains associated with molecular gas have a low
infrared emissivity. In one region, these two factors completely hide the
presence of molecular gas in the infrared. In the second region, we could
identify the area with molecular gas, but I_100 excess significantly
underestimates the column density of molecular hydrogen because of the second
factor mentioned above. We therefore conclude that tau_100 excess, rather than
I_100 excess, is an accurate indicator of molecular content along the line of
sight. We derive tau_100/N(H)=(1.00+-0.02)*10^-5~(10^20 cm^-2)^-1, and
X=N(H_2)/W_CO=~0.7*10^20 cm^-2 (K km s^-1)^-1. Our results suggest that I_100
excess could still be used to estimate the molecular content if the result is
multiplied by a correction factor xi_c=_HI/_H_2 (~2 in
the second region), which accounts for the different infrared emissivities of
atomic and molecular gas. We also discuss some limitations of this work.Comment: 10 pages, 9 postscript figures, uses aas2pp4.sty to be published in
Astrophyslcal Journa
Governance of Offshore IT Outsourcing at Shell Global Functions IT-BAM Development and Application of a Governance Framework to Improve Outsourcing Relationships
The lack of effective IT governance is widely recognized as a key inhibitor to successful global IT outsourcing relationships. In this study we present the development and application of a governance framework to improve outsourcing relationships. The approach used to developing an IT governance framework includes a meta model and a customization process to fit the framework to the target organization. The IT governance framework consists of four different elements (1) organisational structures, (2) joint processes between in- and outsourcer, (3) responsibilities that link roles to processes and (4) a diverse set of control indicators to measure the success of the relationship. The IT governance framework is put in practice in Shell GFIT BAM, a part of Shell that concluded to have a lack of management control over at least one of their outsourcing relationships. In a workshop the governance framework was used to perform a gap analysis between the current and desired governance. Several gaps were identified in the way roles and responsibilities are assigned and joint processes are set-up. Moreover, this workshop also showed the usefulness and usability of the IT governance framework in structuring, providing input and managing stakeholders in the discussions around IT governance
The integrated academic information system support for education 3.0 in higher education institution: lecturer perspective
Education 3.0 has been implemented in many higher education institutions (HEIs). Education 3.0 has been directed the institution toward better educational experience. But on the other hands, the implementation of Education 3.0 also caused some problems. Previous research has found administrative problem experienced by the lecturer. This research explores deeper from the lecturer and suggested the solution from lecturer perspective, combined with information technology capabilities owned by the HEIs. The research used a case study as the method and conducted a qualitative research with a semi-structured interview. The interview analysis has found that the increase of the administrative processes is caused by online and offline administrative activities. The online activities are from e-learning and the offline activities are from traditional learning (face-to-face). The administrative processes also involved the academic information system (AIS). Simplified all of the administrative processes are more preferred. To overcome the problems, integrating the AIS and e-learning become necessary. This research suggests transforming the existing AIS into an integrated AIS and hopes the solution can simplify the administration process
Validity of the rigid band picture for the t-J model
We present an exact diagonalization study of the doping dependence of the
single particle Green's function in 16, 18 and 20 site clusters of t-J model.
We find evidence for rigid-band behaviour starting from the half-filled case:
upon doping, the topmost states of the quasiparticle band observed in the
photoemisson spectrum at half-filling cross the chemical potential and reappear
as the lowermost states of the inverse photoemission spectrum. Features in the
inverse photoemission spectra which are inconsistent with rigid-band behaviour
are shown to originate from the nontrivial point group symmetry of the ground
state with two holes, which enforces different selection rules than at
half-filling. Deviations from rigid band behaviour which lead to the formation
of the `large Fermi surface' in the momentum distribution occur only at
energies far from the chemical potential. A Luttinger Fermi surface and a
nearest neighbor hopping band do not exist.Comment: Remarks: Revtex file + 7 figures attached as compressed postscript
files Figures can also be obtained by ordinary mail on reques
Photo-centric variability of quasars caused by variations in their inner structure: Consequences on Gaia measurements
We study the photocenter position variability due to variations in the quasar
inner structure. We consider variability in the accretion disk emissivity and
torus structure variability due to different illumination by the central
source. We discuss possible detection of these effects by Gaia. Observations of
the photocenter variability in two AGNs, SDSS J121855+020002 and SDSS
J162011+1724327 have been reported and discussed. With investigation of the
variations in the quasar inner structure we explore how much this effect can
affect the position determination and whether it can be (or not) detected with
Gaia mission. We used (a) a model of a relativistic disk, including the
perturbation that can increase brightness of a part of the disk, and
consequently offset the photocenter position, and (b) a model of a dusty torus
which absorbs and re-emits the incoming radiation from accretion disk. We
estimated the value of the photocenter offset due to these two effects. We
found that perturbations in the inner structure can significantly offset the
photocenter. It depends on the characteristics of perturbation and accretion
disk and structure of the torus. In the case of two considered QSOs the
observed photocenter offsets cannot be explained by variations in the accretion
disk and other effects should be considered. We discussed possibility of
exploding stars very close to the AGN source, and also possibility that there
are two variable sources in the center of these two AGNs that may indicate a
binary super-massive black hole system on a kpc (pc) scale. The Gaia mission
seems to be very perspective, not only for astrometry, but also for exploring
the inner structure of AGNs. We conclude that variations in the quasar inner
structure can affect the observed photocenter (up to several mas). There is a
chance to observe such effect in the case of bright and low-redshifted QSOs.Comment: 12 pages, 8 figures, 3 tables. Accepted for publication in Astronomy
and Astrophysics. Language improved, typos correcte
Hole-Hole Contact Interaction in the t-J Model
Using an analytical variational approach we calculate the hole-hole contact
interaction on the N\'{e}el background. Solution of the Bethe-Salpeter equation
with this interaction gives bound states in - and p-waves with binding
energies close to those obtained by numerical methods. At the
bound state disappears. In conclusion we discuss the relation between short
range and long range interactions and analogy with the problem of pion
condensation in nuclear matter.Comment: 11 pp. (LATEX), 7 figures (PostScript) appended, report N
Shocked Molecular Gas in the Supernova Remnant HB 21
We report the discovery of the shocked molecular gas in the supernova remnant
HB 21. We derive the physical parameters of the shocked gas from CO J=1-0 and
J=2-1 line observations. We discuss the correlation of the shocked molecular
gas with the previously detected, shocked atomic gas and the associated
infrared emission.Comment: 24 pages, 10 figures, To appear in the ApJ, scheduled for the April
10, 2001 issue (v551
Radio Continuum and Recombination Line Study of UC HII Regions with Extended Envelopes
We have carried out 21 cm radio continuum observations of 16 UC HII regions
using the VLA (D-array) in search of associated extended emission. We have also
observed H76 recombination line towards all the sources and
He76 line at the positions with strong H76 line emission. The
UC HII regions have simple morphologies and large (>10) ratios of single-dish
to VLA fluxes. Extended emission was detected towards all the sources. The
extended emission consists of one to several compact components and a diffuse
extended envelope. All the UC HII regions but two are located in the compact
components, where the UC HII regions always correspond to their peaks. The
compact components with UC HII regions are usually smaller and denser than
those without UC HII regions. Our recombination line observations indicate that
the ultracompact, compact, and extended components are physically associated.
The UC HII regions and their associated compact components are likely to be
ionized by the same sources on the basis of the morphological relations
mentioned above. This suggests that almost all of the observed UC HII regions
are not `real' UC HII regions and that their actual ages are much greater than
their dynamical age (<10000 yr). We find that most of simple UC HII regions
previously known have large ratios of single-dish to VLA fluxes, similar to our
sources. Therefore, the `age problem' of UC HII regions does not seem to be as
serious as earlier studies argued. We present a simple model that explains
extended emission around UC HII regions. Some individual sources are discussed.Comment: 29 pages, 28 postscript figures, Accepted for publication in Ap
Phenology and temperatureâdependent development of Ceutorhynchus assimilis, a potential biological control agent for Lepidium draba
Lepidium draba (Brassicaceae) is a major concern for agriculture and biodiversity in the western United States. As current control methods do not provide long-term, sustainable solutions, research has been conducted to find biological control agents. Ceutorhynchus assimilis is one of the currently investigated candidates. Known as oligophagous in the literature, a specialist clade of this root-galling weevil exists in southern Europe. This raised the question of its ability to survive in colder climates in the target range. We investigated the phenology of C. assimilis in the field in southern France (specialist clade) and Romania (generalist clade) and measured various temperature-dependent parameters in the laboratory. In both ranges, weevils were univoltine. Oviposition in autumn started later in France compared to Romania, while mature larvae exited galls (to pupate in the soil) earlier the following year. On average, 25% and 32% of galls from France and Romania were completely below the soil surface, respectively, and this appeared to depend on soil substrate. Weevils transported from France to Romania were able to develop, but at a much lower rate than Romanian weevils. Mortality of overwintering larvae of both clades increased with decreasing temperature and exposure time. At â5°C, lethal times Lt50 and Lt95 were 15 and 42 days for the specialist clade and 26 and 72 days for the generalist clade. A higher proportion of third instar larvae compared to first and second instar larvae survived. Pupation time at different temperatures did not differ between weevils from France or Romania. A climate match model (comparing winter temperatures) indicated that the specialist clade of C. assimilis from France has the potential to establish in some parts of the target range (e.g. Washington, Oregon, California). However, temperature extremes and winters without snow cover will likely limit its establishment unless rapid adaptive evolution takes place
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