1,145 research outputs found
Did cultural and artistic education in the Netherlands increase student participation in high cultural events?
Did cultural and artistic education in the Netherlands increase student participation in high cultural events?
Stabilization and vibration isolation of a contactless electromagnetic isolator : a frequency-shaped sliding surface approach
A Frequency-Shaped Sliding Surface Control (FSSSC) approach is applied to an unstable model of a candidate Electro-Magnetic Isolator (EMI) design which has three Degrees Of Freedom (DOF). The EMI is designed to achieve contactless passive gravity compensation for heavy load by permanent magnets. The 3-DOF model can be regarded as three exactly the same double-integrators disturbed by the nonlinear and coupled passive force which results in its inherent instability. The sliding surface is designed based on relative displacement and payload acceleration feedback to achieve low-frequency vibration isolation. To avoid the algebraic control loop, a linear converging controller is designed instead of the conventional switching control. Regardless of the plant uncertainties, the closed-loop transmissibility converges to the designed transmissibility with increasing open-loop gain. A sufficient condition for the closed-loop stability is developed. Both time domain and frequency domain performance of the designed controller is evaluated by simulation. It shows that robust vibration isolation performance is achieved despite of the nonlinear and coupled passive force
Taking Nothing for Granted in Management Education: A Systemic Perspective on the Role of Reflective Questioning
Questioning is one of the most critical behaviors in management education and learning. In this article we explore the antecedents, processes, and outcomes of reflective questioning, as a key element of management learning and education. Reflective questioning involves raising tentative, nonrhetorical questions. By reviewing and synthesizing the literature, we develop a model of reflective questioning in the form of a causal loop diagram. This model implies that reflective questioning can be taught through particular forms of management education, but is also contingent on the psychological safety of the group setting, the individual need for cognition, and challenging tasks and experiences
An unusual case of unilateral supernumerary extensor carpi radialis muscle
An uncommon anatomical variant of muscle that can be considered as a supernumerary extensor carpi radialis muscle was found during the dissection of the forearm region. The identified extensor carpi radialis muscle has origin on the lateral supraepicondylar ridge of the humerus, and an unusual insertion on the tubercle of the scaphoid bone. The presence of this supernumerary muscle may cause diagnostic errors in the forearm region, and can produce a debilitating pain syndrome by secondary compression of adjacent nerves, vessels or tendons due to its course along the anterior compartment of the forearm
Water-gas shift (WGS) Operation of Pre-combustion CO2 Capture Pilot Plant at the Buggenum IGCC
AbstractIn the Nuon/Vattenfall CO2 Catch-up project, a pre-combustion CO2 capture pilot plant was built and operated at the Buggenum IGCC power plant, the Netherlands. The pilot consist of sweet water-gas shift, physical CO2 absorption and CO2 compression. The technology performance was verified and validated models were obtained. This paper describes the validation of a WGS reactor model and the excellent catalyst resistance to carbiding at steam/CO=1.5 mol·mol-1 testing. Model-based optimization shows that compared to conventional operation at steam/CO=2.65, applying steam/CO=1.5 leads to a 10% lower CO2 capture of penalty of 1155 MJelectric·tCO2−1, albeit at a decreased optimum CO2 capture efficiency of 78.5% versus 87.5%
Patterning of ultrathin YBCO nanowires using a new focused-ion-beam process
Manufacturing superconducting circuits out of ultrathin films is a
challenging task when it comes to patterning complex compounds, which are
likely to be deteriorated by the patterning process. With the purpose of
developing high-T superconducting photon detectors, we designed a novel
route to pattern ultrathin YBCO films down to the nanometric scale. We believe
that our method, based on a specific use of a focused-ion beam, consists in
locally implanting Ga^{3+} ions and/or defects instead of etching the film.
This protocol could be of interest to engineer high-T superconducting
devices (SQUIDS, SIS/SIN junctions and Josephson junctions), as well as to
treat other sensitive compounds.Comment: 13 pages, 7 figure
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Optical Spectroscopy Of X-Ray Sources In The Extended Chandra Deep Field South
We present the first results of our optical spectroscopy program aimed to provide redshifts and identifications for the X-ray sources in the Extended Chandra Deep Field South. A total of 339 sources were targeted using the IMACS spectrograph at the Magellan telescopes and the VIMOS spectrograph at the VLT. We measured redshifts for 186 X-ray sources, including archival data and a literature search. We find that the active galactic nucleus (AGN) host galaxies have on average redder rest-frame optical colors than nonactive galaxies, and that they live mostly in the "green valley." The dependence of the fraction of AGNs that are obscured on both luminosity and redshift is confirmed at high significance and the observed AGN spatial density is compared with the expectations from existing luminosity functions. These AGNs show a significant difference in the mid-IR to X-ray flux ratio for obscured and unobscured AGNs, which can be explained by the effects of dust self-absorption on the former. This difference is larger for lower luminosity sources, which is consistent with the dust opening angle depending on AGN luminosity.National Aeronautics and Space Administration PF8-90055, NAS8-03060NSF AST0407295Spitzer JPL RSA1288440Natural Science and Engineering Research Council of Canada (NSERC)National Academy of SciencesNASA/INTEGRAL NNG05GM79GAstronom
Galaxy downsizing evidenced by hybrid evolutionary tracks
An unified picture of stellar and halo mass build-up as a function of mass is
presented. Inferred stellar-dark halo mass relations of galaxies, Ms-Mh, out to
z=4 together with average LCDM halo mass aggregation histories (MAHs) are used
for inferring average Ms growth histories, the Galaxian Hybrid Evolutionary
Tracks (GHETs). The more massive the galaxy, the earlier transited in average
from an active regime of Ms growth to a passive one:
log(Mtran/Msun)=10.30+0.55z ("population downsizing"), where Mtran is the
typical transition stellar mass. This result agrees with independent
observational determinations based on the evolution of the galaxy stellar mass
function decomposition into blue and red galaxies. The specific star formation
rate, SSFR, predicted from the derivative of the GHET is consistent with direct
measures of the SSFR for galaxies at different z's. The average GHETs of
galaxies smaller than Mtran at z=0 (Ms~10^10.3 Msun) did not reach the
quiescent regime, and for them, the lower the mass, the faster the later Ms
growth rate ("downsizing in SSFR"). The GHETs allow to predict the transition
rate in number density of active to passive population; the predicted values
agree with direct estimates of growth rate in number density for the (massive)
red population up to z~1. We show that LCDM-based models of disk galaxy
evolution are able to reproduce the low-mass side of the Ms-Mh relation at z~0,
but at higher z's disagree strongly with the GHETs: models do not reproduce the
downsizing in SSFR and the high SSFR of low mass galaxies. (Abridged)Comment: 14 pages, 9 figures. To appear in ApJ. References updated/corrected,
minor typos correcte
Spin degree of freedom in two dimensional exciton condensates
We present a theoretical analysis of a spin-dependent multicomponent
condensate in two dimensions. The case of a condensate of resonantly
photoexcited excitons having two different spin orientations is studied in
detail. The energy and the chemical potentials of this system depend strongly
on the spin polarization . When electrons and holes are located in two
different planes, the condensate can be either totally spin polarized or spin
unpolarized, a property that is measurable. The phase diagram in terms of the
total density and electron-hole separation is discussed.Comment: 4 pages, 3 figures, Accepted for publication in Physical Review
Letter
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