4,446 research outputs found
An investigation into the roles and responsibilities of chief unit administrators within multiunit community college districts
The purpose of this study was to identify the roles and responsibilities of chief unit administrators within multiunit community college districts. In addition, the study also included data about the perceptions chief unit administrators had toward their roles and their relationships with other unit administrators and central office administrators;The sample consisted of nine chief unit administrators in three multiunit community college districts located in Iowa, Missouri, and Nebraska. A qualitative approach was implemented to conduct the study and method triangulation was used to collect the data. The collection of data was accomplished through on-site interviews with chief unit administrators, a campus administrator response questionnaire developed by the researcher, and a review of documents from each district. The analysis of responsibilities utilized Mackenzie\u27s management model. The study also compared and contrasted the roles and responsibilities of the administrators in the study;As a result of the analysis of the data, conclusions were made about the responsibilities of the chief unit administrator that could be used for job descriptions, performance evaluations, and in the future planning of the roles and responsibilities of the chief unit administrator. The findings could also be used to increase the understanding of multiunit districts and their administration by sharing the information with university classes and professional organizations;It was evident that the position of chief unit administrators within a multiunit district was one of status and one that impacted both the college/campus and district operations. The management function of directing, which involved facilitating, motivating, delegating, coordinating, and managing change was selected by the chief unit administrators as the one that occupied most of their time. The planning function ranked second. Community involvement and public relations were additional responsibilities identified;The chief unit administrators in the study had positive feelings about the degree of autonomy and authority each of them had to run their campuses, the relationships they had with the other chief administrators in their district, and the status they had as a chief unit administrator
How generic language extensions enable ''open-world'' design in Java
By \emph{open--world design} we mean that collaborating classes are so loosely coupled that changes in one class do not propagate to the other classes, and single classes can be isolated and integrated in other contexts. Of course, this is what maintainability and reusability is all about. In the paper, we will demonstrate that in Java even an open--world design of mere attribute access can only be achieved if static safety is sacrificed, and that this conflict is unresolvable \emph{even if the attribute type is fixed}. With generic language extensions such as GJ, which is a generic extension of Java, it is possible to combine static type safety and open--world design. As a consequence, genericity should be viewed as a first--class design feature, because generic language features are preferably applied in many situations in which object--orientedness seems appropriate. We chose Java as the base of the discussion because Java is commonly known and several advanced features of Java aim at a loose coupling of classes. In particular, the paper is intended to make a strong point in favor of generic extensions of Java
Carbon and oxygen in metal-poor halo stars
Carbon and oxygen are key tracers of the Galactic chemical evolution; in
particular, a reported upturn in [C/O] towards decreasing [O/H] in metal-poor
halo stars could be a signature of nucleosynthesis by massive Population III
stars. We reanalyse carbon, oxygen, and iron abundances in thirty-nine
metal-poor turn-off stars. For the first time, we take into account
three-dimensional (3D) hydrodynamic effects together with departures from local
thermodynamic equilibrium (LTE) when determining both the stellar parameters
and the elemental abundances, by deriving effective temperatures from 3D
non-LTE H profiles, surface gravities from Gaia parallaxes, iron
abundances from 3D LTE Feii equivalent widths, and carbon and oxygen abundances
from 3D non-LTE Ci and Oi equivalent widths. We find that [C/Fe] stays flat
with [Fe/H], whereas [O/Fe] increases linearly up to dex with decreasing
[Fe/H] down to dex. As such [C/O] monotonically decreases towards
decreasing [O/H], in contrast to previous findings, mainly by virtue of less
severe non-LTE effects for Oi at low [Fe/H] with our improved calculations.Comment: 5 pages, 2 figures; published in A&A Letter
Si and Mn Abundances in Damped Lya Systems with Low Dust Content
We have measured the abundances of Zn, Si, Mn, Cr, Fe, and Ni in three damped
Lyman alpha systems at redshifts z < 1 from high resolution echelle spectra of
QSOs recorded with the Keck I telescope. In all three cases the abundances of
Cr, Fe, and Ni relative to Zn indicate low levels of dust depletions. We
propose that when the proportion of refractory elements locked up in dust
grains is less than about 50 percent, it is plausible to assume an
approximately uniform level of depletion for all grain constituents and, by
applying a small dust correction, recover the intrisic abundances of Si and Mn.
We use this approach on a small sample of damped systems for which it is
appropriate, with the aim of comparing the metallicity dependence of the ratios
[Si/Fe] and [Mn/Fe] with analogous measurements in Milky Way stars. The main
conclusion is that the relative abundances of both elements in distant galaxies
are broadly in line with expectations based on Galactic data. Si displays a
mild enhancement at low metallicities, as expected for an alpha-capture
element, but there are also examples of near-solar [Si/Fe] at [Fe/H] < -1. The
underabundance of Mn at low metallicities is possibly even more pronounced than
that in metal-poor stars, and no absorption system has yet been found where
[Mn/Fe] is solar. The heterogeneous chemical properties of damped Lyman alpha
systems, evident even from this limited set of measurements, provide further
support for the conclusion from imaging studies that a varied population of
galaxies gives rise to this class of QSO absorbers.Comment: 29 pages, LaTex, 7 Postscript Figures. Accepted for Publication in
the Astrophysical Journa
Triplicated P-wave measurements for waveform tomography of the mantle transition zone
Triplicated body waves sample the mantle transition zone more extensively than any other wave type, and interact strongly with the discontinuities at 410 km and 660 km. Since the seismograms bear a strong imprint of these geodynamically interesting features, it is highly desirable to invert them for structure of the transition zone. This has rarely been attempted, due to a mismatch between the complex and band-limited data and the (ray-theoretical) modelling methods. Here we present a data processing and modelling strategy to harness such broadband seismograms for finite-frequency tomography. We include triplicated P-waves (epicentral distance range between 14 and 30&deg;) across their entire broadband frequency range, for both deep and shallow sources. We show that is it possible to predict the complex sequence of arrivals in these seismograms, but only after a careful effort to estimate source time functions and other source parameters from data, variables that strongly influence the waveforms. Modelled and observed waveforms then yield decent cross-correlation fits, from which we measure finite-frequency traveltime anomalies. We discuss two such data sets, for North America and Europe, and conclude that their signal quality and azimuthal coverage should be adequate for tomographic inversion. In order to compute sensitivity kernels at the pertinent high body wave frequencies, we use fully numerical forward modelling of the seismic wavefield through a spherically symmetric Earth
The [Y/Mg] clock works for evolved solar metallicity stars
Previously [Y/Mg] has been proven to be an age indicator for solar twins.
Here, we investigate if this relation also holds for helium-core-burning stars
of solar metallicity. High resolution and high signal-to-noise ratio (S/N)
spectroscopic data of stars in the helium-core-burning phase have been obtained
with the FIES spectrograph on the NOT 2.56m telescope and the HIRES
spectrograph on the Keck I 10 m telescope. They have been analyzed to determine
the chemical abundances of four open clusters with close to solar metallicity;
NGC 6811, NGC 6819, M67 and NGC 188. The abundances are derived from equivalent
widths of spectral lines using ATLAS9 model atmospheres with parameters
determined from the excitation and ionization balance of Fe lines. Results from
asteroseismology and binary studies were used as priors on the atmospheric
parameters, where especially the is determined to much higher
precision than what is possible with spectroscopy. It is confirmed that the
four open clusters are close to solar metallicity and they follow the [Y/Mg]
vs. age trend previously found for solar twins. The [Y/Mg] vs. age clock also
works for giant stars in the helium-core burning phase, which vastly increases
the possibilities to estimate the age of stars not only in the solar
neighborhood, but in large parts of the Galaxy, due to the brighter nature of
evolved stars compared to dwarfs.Comment: 5 pages, 3 figures, accepted for publication as a Letter to A&
Towards a better representation of the solar cycle in general circulation models
We introduce the improved Freie UniversitÀt Berlin (FUB) high-resolution radiation scheme FUBRad and compare it to the 4-band standard ECHAM5 SW radiation scheme of Fouquart and Bonnel (FB). Both schemes are validated against the detailed radiative transfer model libRadtran. FUBRad produces realistic heating rate variations during the solar cycle. The SW heating rate response with the FB scheme is about 20 times smaller than with FUBRad and cannot produce the observed temperature signal. A reduction of the spectral resolution to 6 bands for solar irradiance and ozone absorption cross sections leads to a degradation (reduction) of the solar SW heating rate signal by about 20%.
The simulated temperature response agrees qualitatively well with observations in the summer upper stratosphere and mesosphere where irradiance variations dominate the signal.
Comparison of the total short-wave heating rates under solar minimum conditions shows good agreement between FUBRad, FB and libRadtran up to the middle mesosphere (60â70 km) indicating that both parameterizations are well suited for climate integrations that do not take solar variability into account.
The FUBRad scheme has been implemented as a sub-submodel of the Modular Earth Submodel System (MESSy)
IVUS-based imaging modalities for tissue characterization: similarities and differences
Gray-scale intravascular ultrasound (IVUS) is the modality that has been established as the golden standard for in vivo imaging of the vessel wall of the coronary arteries. The use of IVUS in clinical practice is an important diagnostic tool used for quantitative assessment of coronary artery disease. This has made IVUS the de-facto invasive imaging method to evaluate new interventional therapies such as new stent designs and for atherosclerosis progression-regression studies. However, the gray-scale representation of the coronary vessel wall and plaque morphology in combination with the limited resolution of the current IVUS catheters makes it difficult, if not impossible, to identify qualitatively (e.g. visually) the plaque morphology similar as that of histopathology, the golden standard to characterize and quantify coronary plaque tissue components. Meanwhile, this limitation has been partially overcome by new innovative IVUS-based post-processing methods such as: virtual histology IVUS (VH-IVUS, Volcano Therapeutics, Rancho Cordova, CA, USA), iMAP-IVUS (Bostoc Scientific, Santa Clara, CA, USA), Integrated Backscatter IVUS (IB-IVUS) and Automated Differential Echogenicity (ADE)
Symmetric Operation of the Resonant Exchange Qubit
We operate a resonant exchange qubit in a highly symmetric triple-dot
configuration using IQ-modulated RF pulses. At the resulting three-dimensional
sweet spot the qubit splitting is an order of magnitude less sensitive to all
relevant control voltages, compared to the conventional operating point, but we
observe no significant improvement in the quality of Rabi oscillations. For
weak driving this is consistent with Overhauser field fluctuations modulating
the qubit splitting. For strong driving we infer that effective voltage noise
modulates the coupling strength between RF drive and the qubit, thereby
quickening Rabi decay. Application of CPMG dynamical decoupling sequences
consisting of up to n = 32 {\pi} pulses significantly prolongs qubit coherence,
leading to marginally longer dephasing times in the symmetric configuration.
This is consistent with dynamical decoupling from low frequency noise, but
quantitatively cannot be explained by effective gate voltage noise and
Overhauser field fluctuations alone. Our results inform recent strategies for
the utilization of partial sweet spots in the operation and long-distance
coupling of triple-dot qubits.Comment: 6 pages, 5 figure
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