544 research outputs found
Describing and measuring leadership within school teams by applying a social network perspective
Despite the growing number of studies that acknowledge a crucial role of distributed leadership within schools, limited knowledge exists on how to describe and measure this multi-faceted concept. In a social network study with 130 respondents, from 14 Dutch school teams carrying out collaborative innovation, we theoretically describe three core aspects of the social interaction process of distributed leadership: collective, dynamic, or relational. Furthermore, we empirically explore how to measure all these three aspects of distributed leadership from a social network perspective, whereas most research focuses on either collective or dynamic. Our findings indicate that three network measures (density, reciprocity, indegree centralization) form a coherent combination to measure distributed leadership in school teams in terms of collective, relational, and dynamic, respectively. Furthermore, based on the combination of measures we found differences in distributed leadership between school teams. Thus, adding the relational aspect in addition to the collective and dynamic aspects seems to be informative to measure distributed leadership. Our study motivates to take a social network perspective, instead of the mostly used aggregation approaches, to measure distributed leadership in school teams
The counterrotating core and the black hole mass of IC1459
The E3 giant elliptical galaxy IC1459 is the prototypical galaxy with a fast
counterrotating stellar core. We obtained one HST/STIS long-slit spectrum along
the major axis of this galaxy and CTIO spectra along five position angles. We
present self-consistent three-integral axisymmetric models of the stellar
kinematics, obtained with Schwarzschild's numerical orbit superposition method.
We study the dynamics of the kinematically decoupled core (KDC) in IC1459 and
we find it consists of stars that are well-separated from the rest of the
galaxy in phase space. The stars in the KDC counterrotate in a disk on orbits
that are close to circular. We estimate that the KDC mass is ~0.5% of the total
galaxy mass or ~3*10^9 Msun. We estimate the central black hole mass M_BH of
IC1459 independently from both its stellar and its gaseous kinematics. Some
complications probably explain why we find rather discrepant BH masses with the
different methods. The stellar kinematics suggest that M_BH = (2.6 +/-
1.1)*10^9 Msun (3 sigma error). The gas kinematics suggests that M_BH ~
3.5*10^8 Msun if the gas is assumed to rotate at the circular velocity in a
thin disk. If the observed velocity dispersion of the gas is assumed to be
gravitational, then M_BH could be as high as ~1.0*10^9 Msun. These different
estimates bracket the value M_BH = (1.1 +/- 0.3)*10^9 Msun predicted by the
M_BH-sigma relation. It will be an important goal for future studies to assess
the reliability of black hole mass determinations with either technique. This
is essential if one wants to interpret the correlation between the BH mass and
other global galaxy parameters (e.g. velocity dispersion) and in particular the
scatter in these correlations (believed to be only ~0.3 dex). [Abridged]Comment: 51 pages, LaTeX with 19 PostScript figures. Revised version, with
three new figures and data tables. To appear in The Astrophysical Journal,
578, 2002 October 2
The black hole in IC 1459 from HST observations of the ionized gas disk
The peculiar elliptical galaxy IC 1459 (M_V = -21.19, D = 16.5 Mpc) has a
fast counterrotating stellar core, stellar shells and ripples, a blue nuclear
point source and strong radio core emission. We present results of a detailed
HST study of IC 1459, and in particular its central gas disk, aimed a
constraining the central mass distribution. We obtained WFPC2 narrow-band
imaging centered on the Halpha+[NII] emission lines to determine the flux
distribution of the gas emission at small radii, and we obtained FOS spectra at
six aperture positions along the major axis to sample the gas kinematics. We
construct different dynamical models for the Halpha+[NII] and Hbeta kinematics
that include a supermassive black hole, and in which the stellar mass
distribution is constrained by the observed surface brightness distribution and
ground-based stellar kinematics. All models are consistent with a black hole
mass in the range Mbh=1-4 x 10^8 Msun, and models without a black hole are
always ruled out at high confidence.Comment: 40 pages including 14 figures, Latex; submitted to A
N=2 supergravity in five dimensions revisited
We construct matter-coupled N=2 supergravity in five dimensions, using the
superconformal approach. For the matter sector we take an arbitrary number of
vector-, tensor- and hyper-multiplets. By allowing off-diagonal vector-tensor
couplings we find more general results than currently known in the literature.
Our results provide the appropriate starting point for a systematic search for
BPS solutions, and for applications of M-theory compactifications on Calabi-Yau
manifolds with fluxes.Comment: 35 pages; v.2: A sign changed in a bilinear fermion term in (5.7
Observations of HI Absorbing Gas in Compact Radio Sources at Cosmological Redshifts
We present an overview of the occurrence and properties of atomic gas
associated with compact radio sources at redshifts up to z=0.85. Searches for
HI 21cm absorption were made with the Westerbork Synthesis Radio Telescope at
UHF-high frequencies (725-1200 MHz). Detections were obtained for 19 of the 57
sources with usable spectra (33%). We have found a large range in line depths,
from tau=0.16 to tau<=0.001. There is a substantial variety of line profiles,
including Gaussians of less than 10km/s, to more typically 150km/s, as well as
irregular and multi-peaked absorption profiles, sometimes spanning several
hundred km/s. Assuming uniform coverage of the entire radio source, we obtain
column depths of atomic gas between 1e19 and 3.3e21(Tsp/100K)(1/f)cm^(-2).
There is evidence for significant gas motions, but in contrast to earlier
results at low redshift, there are many sources in which the HI velocity is
substantially negative (up to v=-1420km/s) with respect to the optical
redshift, suggesting that in these sources the atomic gas, rather than falling
into the centre, may be be flowing out, interacting with the jets, or rotating
around the nucleus.Comment: 10 pages, accepted for publication in A&
Influence of nitrogen on diamond growth in oxyacetylene combustion chemical vapor deposition
Validation of the 70-gene signature test (MammaPrint) to identify patients with breast cancer aged ≥ 70 years with ultralow risk of distant recurrence:A population-based cohort study
Introduction: When risk estimation in older patients with hormone receptor positive breast cancer (HR + BC) is based on the same factors as in younger patients, age-related factors regarding recurrence risk and other-cause mortality are not considered. Genomic risk assessment could help identify patients with ultralow risk BC who can forgo adjuvant treatment. However, assessment tools should be validated specifically for older patients. This study aims to determine whether the 70-gene signature test (MammaPrint) can identify patients with HR + BC aged ≥70 years with ultralow risk for distant recurrence. Materials and Methods: Inclusion criteria: ≥70 years; invasive HR + BC; T1-2N0-3M0. Exclusion criteria: HER2 + BC; neoadjuvant therapy. MammaPrint assays were performed following standardized protocols. Clinical risk was determined with St. Gallen risk classification. Primary endpoint was 10-year cumulative incidence rate of distant recurrence in relation to genomic risk. Subdistribution hazard ratios (sHR) were estimated from Fine and Gray analyses. Multivariate analyses were adjusted for adjuvant endocrine therapy and clinical risk. Results: This study included 418 patients, median age 78 years (interquartile range [IQR] 73–83). Sixty percent of patients were treated with endocrine therapy. MammaPrint classified 50 patients as MammaPrint-ultralow, 224 patients as MammaPrint-low, and 144 patients as MammaPrint-high risk. Regarding clinical risk, 50 patients were classified low, 237 intermediate, and 131 high. Discordance was observed between clinical and genomic risk in 14 MammaPrint-ultralow risk patients who were high clinical risk, and 84 patients who were MammaPrint-high risk, but low or intermediate clinical risk. Median follow-up was 9.2 years (IQR 7.9–10.5). The 10-year distant recurrence rate was 17% (95% confidence interval [CI] 11–23) in MammaPrint-high risk patients, 8% (4–12) in MammaPrint-low (HR 0.46; 95%CI 0.25–0.84), and 2% (0–6) in MammaPrint-ultralow risk patients (HR 0.11; 95%CI 0.02–0.81). After adjustment for clinical risk and endocrine therapy, MammaPrint-high risk patients still had significantly higher 10-year distant recurrence rate than MammaPrint-low (sHR 0.49; 95%CI 0.26–0.90) and MammaPrint-ultralow patients (sHR 0.12; 95%CI 0.02–0.85). Of the 14 MammaPrint-ultralow, high clinical risk patients none developed a distant recurrence. Discussion: These data add to the evidence validating MammaPrint's ultralow risk threshold. Even in high clinical risk patients, MammaPrint-ultralow risk patients remained recurrence-free ten years after diagnosis. These findings justify future studies into using MammaPrint to individualize adjuvant treatment in older patients
The inner jet of radio galaxy NGC 315 as observed with Chandra and the VLA
We present Chandra X-ray results for the jet, nucleus, and gaseous atmosphere
of NGC 315, a nearby radio galaxy whose jet kinematics are known through deep
radio mapping. Diffuse X-ray synchrotron emission is detected from the jet out
to 30 arcsec from the nucleus, through regions both of fast bulk flow and
deceleration. The X-ray to radio flux ratio drops considerably where the flow
decelerates, but the X-ray and radio emissions show similar transverse extents
throughout, requiring distributed particle acceleration to maintain the supply
of X-ray-emitting electrons. A remarkable knotty filament within the jet is
seen in both the radio and X-ray, contributing roughly 10 per cent of the
diffuse emission along its extent at both wavelengths. No completely
satisfactory explanation for the filament is found, though its oscillatory
appearance, roughly aligned magnetic field, and requirements for particle
acceleration, suggest that it is a magnetic strand within a shear layer between
fast inner and slower outer flow.Comment: Accepted for publication in the MNRAS. 13 pages,14 figures (some in
colour
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