1,778 research outputs found
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
Elevated n-terminal pro-brain natriuretic peptide is associated with mortality in tobacco smokers independent of airflow obstruction
Background: Tobacco use is associated with an increased prevalence of cardiovascular disease. N-terminal pro-brain natiuretic peptide (NT-proBNP), a widely available biomarker that is associated with cardiovascular outcomes in other conditions, has not been investigated as a predictor of mortality in tobacco smokers. We hypothesized that NT-proBNP would be an independent prognostic marker in a cohort of well-characterized tobacco smokers without known cardiovascular disease. Methods: Clinical data from 796 subjects enrolled in two prospective tobacco exposed cohorts was assessed to determine factors associated with elevated NT-proBNP and the relationship of these factors and NT-proBNP with mortality. Results: Subjects were followed for a median of 562 (IQR 252 - 826) days. Characteristics associated with a NT-proBNP above the median (â„49 pg/mL) were increased age, female gender, and decreased body mass index. By time-to-event analysis, an NT-proBNP above the median (â„49 pg/mL) was a significant predictor of mortality (log rank p = 0.02). By proportional hazard analysis controlling for age, gender, cohort, and severity of airflow obstruction, an elevated NT-proBNP level (â„49 pg/mL) remained an independent predictor of mortality (HR = 2.19, 95% CI 1.07-4.46, p = 0.031). Conclusions: Elevated NT-proBNP is an independent predictor of mortality in tobacco smokers without known cardiovascular disease, conferring a 2.2 fold increased risk of death. Future studies should assess the ability of this biomarker to guide further diagnostic testing and to direct specific cardiovascular risk reduction inventions that may positively impact quality of life and survival. © 2011 Stamm et al
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
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
Atmospheric velocity fields in tepid main sequence stars
The line profiles of the stars with v sin i below a few km/s can reveal
direct signatures of local velocity fields (e.g. convection) in stellar
atmospheres. This effect is well established in cool main sequence stars, and
has been detected and studied in three A stars. This paper reports observations
of main sequence B, A and F stars with two goals: (1) to identify additional
stars having sufficiently low values of v sin i to search for spectral line
profile signatures of local velocity fields, and (2) to explore how the
signatures of the local velocity fields in the atmosphere depend on stellar
parameters such as effective temperature T_eff and peculiarity type.
For stars having T_eff below about 10000 K, we always detect local
atmospheric velocity fields indirectly through a non-zero microturbulence
parameter, but not for hotter stars. Among the A and F stars in our sample
having the sharpest lines, direct tracers of atmospheric velocity fields are
found in six new stars. The velocity field signatures identified include
asymmetric excess line wing absorption, deeper in the blue line wing than in
the red; line profiles of strong lines that are poorly fit by computed
profiles; and strong lines that are broader than they should be for the v sin i
values deduced from weak lines. These effects are found in both normal and Am
stars, but seem stronger in Am stars.
These data still have not been satisfactorily explained by models of
atmospheric convection, including numerical simulations.Comment: Acepted for publication by Astronomy and Astrophysic
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
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
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
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
Precise Modeling of the Exoplanet Host Star and CoRoT Main Target HD 52265
This paper presents a detailed and precise study of the characteristics of
the Exoplanet Host Star and CoRoT main target HD 52265, as derived from
asteroseismic studies. The results are compared with previous estimates, with a
comprehensive summary and discussion. The basic method is similar to that
previously used by the Toulouse group for solar-type stars. Models are computed
with various initial chemical compositions and the computed p-mode frequencies
are compared with the observed ones. All models include atomic diffusion and
the importance of radiative accelerations is discussed. Several tests are used,
including the usual frequency combinations and the fits of the \'echelle
diagrams. The possible surface effects are introduced and discussed. Automatic
codes are also used to find the best model for this star (SEEK, AMP) and their
results are compared with that obtained with the detailed method. We find
precise results for the mass, radius and age of this star, as well as its
effective temperature and luminosity. We also give an estimate of the initial
helium abundance. These results are important for the characterization of the
star-planet system.Comment: 9 pages, 6 figures, 7 tables, to be published in Astronomy and
Astrophysic
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