900 research outputs found
Technological and pedagogical convergence between work-based and campus-based learning
There is a strong technological and economic push for higher education providers to adopt online learning strategies. This is driven, in part, by the requirement of industry for lifelong learning on a flexible, just-in-time basis. Simultaneously, there is a rising awareness amongst engineering faculty of the pedagogical issues that underpin good teaching and learning practice, stimulated by revised accreditation approaches and related reviews. These significant drivers of change are often experienced as discordant if not competing issues. This paper presents a case study of work-integrated learning that parallels traditional on-campus learning. Technology and pedagogy begin to converge when: (1) pedagogical assumptions are identified early; (2) flexible learning is not confused with on-line learning; (3) intrinsic and external motivations of stakeholders are aligned; (4) there is broad ownership; and (5) a sustainable development strategy is adopted
Spin squeezing in nonlinear spin coherent states
We introduce the nonlinear spin coherent state via its ladder operator
formalism and propose a type of nonlinear spin coherent state by the nonlinear
time evolution of spin coherent states. By a new version of spectroscopic
squeezing criteria we study the spin squeezing in both the spin coherent state
and nonlinear spin coherent state. The results show that the spin coherent
state is not squeezed in the x, y, and z directions, and the nonlinear spin
coherent state may be squeezed in the x and y directions.Comment: 4 pages, 2 figs, revised version submitted to J. Opt.
Nowhere to Hide: Radio-faint AGN in the GOODS-N field. I. Initial catalogue and radio properties
(Abridged) Conventional radio surveys of deep fields ordinarily have
arc-second scale resolutions often insufficient to reliably separate radio
emission in distant galaxies originating from star-formation and AGN-related
activity. Very long baseline interferometry (VLBI) can offer a solution by
identifying only the most compact radio emitting regions in galaxies at
cosmological distances where the high brightness temperatures (in excess of
K) can only be reliably attributed to AGN activity. We present the first
in a series of papers exploring the faint compact radio population using a new
wide-field VLBI survey of the GOODS-N field. The unparalleled sensitivity of
the European VLBI Network (EVN) will probe a luminosity range rarely seen in
deep wide-field VLBI observations, thus providing insights into the role of AGN
to radio luminosities of the order across cosmic
time. The newest VLBI techniques are used to completely cover an entire 7'.5
radius area to milliarcsecond resolutions, while bright radio sources ( mJy) are targeted up to 25 arcmin from the pointing centre. Multi-source
self-calibration, and a primary beam model for the EVN array are used to
correct for residual phase errors and primary beam attenuation respectively.
This paper presents the largest catalogue of VLBI detected sources in GOODS-N
comprising of 31 compact radio sources across a redshift range of 0.11-3.44,
almost three times more than previous VLBI surveys in this field. We provide a
machine-readable catalogue and introduce the radio properties of the detected
sources using complementary data from the e-MERLIN Galaxy Evolution survey
(eMERGE).Comment: 15 pages, 8 figures, accepted in A&A. Machine-readable table
available upon reques
Two-photon excitation and relaxation of the 3d-4d resonance in atomic Kr
Two-photon excitation of a single-photon forbidden Auger resonance has been observed and investigated using the intense extreme ultraviolet radiation from the free electron laser in Hamburg. At the wavelength 26.9 nm (46 eV) two photons promoted a 3d core electron to the outer 4d shell. The subsequent Auger decay, as well as several nonlinear above threshold ionization processes, were studied by electron spectroscopy. The experimental data are in excellent agreement with theoretical predictions and analysis of the underlying multiphoton processes
SU(N) Coherent States and Irreducible Schwinger Bosons
We exploit the SU(N) irreducible Schwinger boson to construct SU(N) coherent
states. This construction of SU(N) coherent state is analogous to the
construction of the simplest Heisenberg-Weyl coherent states. The coherent
states belonging to irreducible representations of SU(N) are labeled by the
eigenvalues of the SU(N) Casimir operators and are characterized by
complex orthonormal vectors describing the SU(N) group manifold.Comment: 12 pages, 3 figure
The radio emission from active galactic nuclei
Context. For nearly seven decades, astronomers have been studying active galaxies, that is to say, galaxies with actively accreting central supermassive black holes: active galactic nuclei (AGN). A small fraction are characterized by luminous, powerful radio emission: This class is known as radio-loud AGN. A substantial fraction, the so-called radio-quiet AGN population, display intermediate or weak radio emission. However, an appreciable fraction of strong X-ray-emitting AGN are characterized by the absence of radio emission, down to an upper limit of about 10−7 times the luminosity of the most powerful radio-loud AGN.
Aims. We wish to address the nature of these – seemingly radio-silent – X-ray-luminous AGN and their host galaxies to determine if there is any radio emission, and, if so, where it originates.
Methods. Focusing on the GOODS-N field, we examine the nature of these objects, employing stacking techniques on ultra-deep radio data obtained with the JVLA. We combine these radio data with Spitzer far-infrared data.
Results. We establish the absence, or totally insignificant contribution, of jet-driven radio emission in roughly half of the otherwise normal population of X-ray-luminous AGN, which appear to reside in normal star-forming galaxies.
Conclusions. AGN- or jet-driven radio emission is simply a mechanism that may be at work or may be dormant in galaxies with actively accreting black holes. The latter cases can be classified as radio-silent AGN
Education and older adults at the University of the Third Age
This article reports a critical analysis of older adult education in Malta. In educational gerontology, a critical perspective demands the exposure of how relations of power and inequality, in their myriad forms, combinations, and complexities, are manifest in late-life learning initiatives. Fieldwork conducted at the University of the Third Age (UTA) in Malta uncovered the political nature of elder-learning, especially with respect to three intersecting lines of inequality - namely, positive aging, elitism, and gender. A cautionary note is, therefore, warranted at the dominant positive interpretations of UTAs since late-life learning, as any other education activity, is not politically neutral.peer-reviewe
An ultra-deep multi-band VLA survey of the faint radio sky (COSMOS-XS): New constraints on the cosmic star formation history
We make use of ultra-deep 3 GHz Karl G. Jansky Very Large Array observations
of the COSMOS field from the multi-band COSMOS-XS survey to infer radio
luminosity functions (LFs) of star-forming galaxies (SFGs). Using 1300
SFGs with redshifts out to , and fixing the faint and bright end
shape of the radio LF to the local values, we find a strong redshift trend that
can be fitted by pure luminosity evolution with the luminosity parameter given
by . We then combine the
ultra-deep COSMOS-XS data-set with the shallower VLA-COSMOS
large project data-set over the wider COSMOS field in order to fit for joint
density+luminosity evolution, finding evidence for significant density
evolution. By comparing the radio LFs to the observed far-infrared (FIR) and
ultraviolet (UV) LFs, we find evidence of a significant underestimation of the
UV LF by at high redshift (,
integrated down to ). We derive the cosmic star
formation rate density (SFRD) by integrating the fitted radio LFs and find that
the SFRD rises up to and then declines more rapidly than
previous radio-based estimates. A direct comparison between the radio SFRD and
a recent UV-based SFRD, where we integrate both LFs down to a consistent limit
(), reveals that the discrepancy between the radio and
UV LFs translates to a significant (1 dex) discrepancy in the derived
SFRD at , even assuming the latest dust corrections and without accounting
for optically dark sources.Comment: Submitted to ApJ; 27 pages, 13 figures, 4 table
New limits on the 17 keV neutrino
We present results of new measurements of the β spectrum of 35S, using the Caltech double-focusing, iron-free β spectrometer. Our data show no evidence for a heavy neutrino with a mass between 12 and 22 keV admixed to the usual light neutrino. In particular, we rule out, at the 6σ level, a 17 keV neutrino admixed at 0.85%, and give an upper limit (90% C.L.) of 0.2% for such a neutrino admixture. To demonstrate that our experiment is sensitive to spectral features such as those from heavy neutrinos we have induced an artificial kink by means of an absorber foil covering part of the source
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