1,281 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
Multi-source self-calibration: Unveiling the microJy population of compact radio sources
Context. Very Long Baseline Interferometry (VLBI) data are extremely
sensitive to the phase stability of the VLBI array. This is especially
important when we reach {\mu}Jy r.m.s. sensitivities. Calibration using
standard phase referencing techniques is often used to improve the phase
stability of VLBI data but the results are often not optimal. This is evident
in blank fields that do not have in-beam calibrators. Aims. We present a
calibration algorithm termed Multi-Source Self-Calibration (MSSC) which can be
used after standard phase referencing on wide-field VLBI observations. This is
tested on a 1.6 GHz wide-field VLBI data set of the Hubble Deep Field-North and
the Hubble Flanking Fields. Methods. MSSC uses multiple target sources detected
in the field via standard phase referencing techniques and modifies the
visibili- ties so that each data set approximates to a point source. These are
combined to increase the signal to noise and permit self-calibration. In
principle, this should allow residual phase changes caused by the troposphere
and ionosphere to be corrected. By means of faceting, the technique can also be
used for direction dependent calibration. Results. Phase corrections, derived
using MSSC, were applied to a wide-field VLBI data set of the HDF-N comprising
of 699 phase centres. MSSC was found to perform considerably better than
standard phase referencing and single source self-calibration. All detected
sources exhibited dramatic improvements in dynamic range. Using MSSC, one
source reached the detection threshold taking the total detected sources to
twenty. 60% of these sources can now be imaged with uniform weighting compared
to just 45% with standard phase referencing. The Parseltongue code which
implements MSSC has been released and made publicly available to the
astronomical community (https://github.com/jradcliffe5/multi_self_cal).Comment: 7 pages, 4 figures, accepted to A&
Generalising some results about right-angled Artin groups to graph products of groups
We prove three results about the graph product G=\G(\Gamma;G_v, v \in
V(\Gamma)) of groups over a graph . The first result generalises
a result of Servatius, Droms and Servatius, proved by them for right-angled
Artin groups; we prove a necessary and sufficient condition on a finite graph
for the kernel of the map from to the associated direct product to
be free (one part of this result already follows from a result in S. Kim's
Ph.D. thesis). The second result generalises a result of Hermiller and Sunic,
again from right-angled Artin groups; we prove that for a graph with
finite chromatic number, has a series in which every factor is a free
product of vertex groups. The third result provides an alternative proof of a
theorem due to Meier, which provides necessary and sufficient conditions on a
finite graph for to be hyperbolic
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
Proof of an entropy conjecture for Bloch coherent spin states and its generalizations
Wehrl used Glauber coherent states to define a map from quantum density
matrices to classical phase space densities and conjectured that for Glauber
coherent states the mininimum classical entropy would occur for density
matrices equal to projectors onto coherent states. This was proved by Lieb in
1978 who also extended the conjecture to Bloch SU(2) spin-coherent states for
every angular momentum . This conjecture is proved here. We also recall our
1991 extension of the Wehrl map to a quantum channel from to , with corresponding to the Wehrl map to classical densities.
For each and we show that the minimal output entropy for
these channels occurs for a coherent state. We also show that coherent
states both Glauber and Bloch minimize any concave functional, not just
entropy.Comment: Version 2 only minor change
On the semiclassical treatment of anharmonic quantum oscillators via coherent states - The Toda chain revisited
We use coherent states as a time-dependent variational ansatz for a
semiclassical treatment of the dynamics of anharmonic quantum oscillators. In
this approach the square variance of the Hamiltonian within coherent states is
of particular interest. This quantity turns out to have natural interpretation
with respect to time-dependent solutions of the semiclassical equations of
motion. Moreover, our approach allows for an estimate of the decoherence time
of a classical object due to quantum fluctuations. We illustrate our findings
at the example of the Toda chain.Comment: 12 pages, some remarks added. Version to be published in J. Phys. A:
Math. Ge
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