24,129 research outputs found
Symmetry-enhanced supertransfer of delocalized quantum states
Coherent hopping of excitation rely on quantum coherence over physically
extended states. In this work, we consider simple models to examine the effect
of symmetries of delocalized multi-excitation states on the dynamical
timescales, including hopping rates, radiative decay, and environmental
interactions. While the decoherence (pure dephasing) rate of an extended state
over N sites is comparable to that of a non-extended state, superradiance leads
to a factor of N enhancement in decay and absorption rates. In addition to
superradiance, we illustrate how the multi-excitonic states exhibit
`supertransfer' in the far-field regime: hopping from a symmetrized state over
N sites to a symmetrized state over M sites at a rate proportional to MN. We
argue that such symmetries could play an operational role in physical systems
based on the competition between symmetry-enhanced interactions and localized
inhomogeneities and environmental interactions that destroy symmetry. As an
example, we propose that supertransfer and coherent hopping play a role in
recent observations of anomolously long diffusion lengths in nano-engineered
assembly of light-harvesting complexes.Comment: 6 page
A community of teachers: Using Activity Theory to investigate the implementation of ICTE in a remote Indigenous school
In 2001-2002, an innovative project entitled Reach In-Reach Out has been conducted in Far North Queensland. Its aim was to use telecommunications and Internet tools to facilitate communication between the children of Lockhart River who attend secondary school in such centres as Cairns, Townsville and Herberton and their families. This study was the first (of three) to investigate the impact of this project. Its focus is on the teachers of Lockart River State School and the changes made to their practice by the implementation of the project. The study described in this paper was conducted in Lockhart River which is situated on Kanthanumpu (Southern Kuuku Ya'u) land in Far North Queensland. The current population is estimated between 650 (Education Queensland, 2001a) and 800 (Lockhart River Land and Sea Management Agency, 2001) residents. The student population of Lockhart River State School in 2001was 26 (Kindy), 105 (Primary) and 30 (Alternate secondary/VET) programs) (Education Queensland, 2001a). At the end of 1999, the secondary school of Lockhart River was closed following a community decision to do so. This necessitated the majority of post-primary students having to leave Lockhart River to continue their education at boarding school. At the beginning of 2002, 38 students left the Lockhart River Community to attend boarding schools (and 8 remained to take part in the Alternate Secondary/VET program offered at the school). Table 1 details the secondary enrolments of Lockhart River students from 1998 to 2001, including the period covered by this study (2001)
A high-speed bi-polar outflow from the archetypical pulsating star Mira A
Optical images and high-dispersion spectra have been obtained of the ejected
material surrounding the pulsating AGB star Mira A. The two streams of knots on
either side of the star, found in far ultra-viollet (FUV) GALEX images, have
now been imaged clearly in the light of Halpha. Spatially resolved profiles of
the same line reveal that the bulk of these knots form a bi-polar outflow with
radial velocity extremes of +- 150 km/s with respect to the central star. The
South stream is approaching and the North stream receding from the observer. A
displacement away from Mira A between the position of one of the South stream
knots in the new Halpha image and its position in the previous Palomar
Observatory Sky Survey (POSS I) red plate has been noted. If interpreted as a
consequence of expansion proper motions the bipolar outflow is tilted at 69deg
+- 2deg to the plane of the sky, has an outflow velocity of 160 +- 10 km/s and
is ~1000 y old.Comment: 8 pages, 5 figures. Accepted for pubication by A&
VLT observations of the asymmetric Etched Hourglass Nebula, MyCn 18
Context. The mechanisms that form extreme bipolar planetary nebulae remain
unclear. Aims. The physical properties, structure, and dynamics of the bipolar
planetary nebula, MyCn 18, are investigated in detail with the aim of
understanding the shaping mechanism and evolutionary history of this object.
Methods. VLT infrared images, VLT ISAAC infrared spectra, and long-slit optical
Echelle spectra are used to investigate MyCn 18. Morpho-kinematic modelling was
used to firmly constrain the structure and kinematics of the source. A
timescale analysis was used to determine the kinematical age of the nebula and
its main components. Results. A spectroscopic study of MyCn 18's central and
offset region reveals the detailed make-up of its nebular composition.
Molecular hydrogen, atomic helium, and Bracket gamma emission are detected from
the central regions of MyCn 18. ISAAC spectra from a slit position along the
narrow waist of the nebula demonstrate that the ionised gas resides closer to
the centre of the nebula than the molecular emission. A kinematical age of the
nebula and its components were obtained by the P-V arrays and timescale
analysis. Conclusions. The structure and kinematics of MyCn 18 are better
understood using an interactive 3-D modelling tool called shape. A dimensional
and timescale analysis of MyCn 18's major components provides a possible
mechanism for the nebula's asymmetry. The putative central star is somewhat
offset from the geometric centre of the nebula, which is thought to be the
result of a binary system. We speculate that the engulfing and destruction of
an exoplanet during the AGB phase may have been a key event in shaping MyCn 18
and generating of its hypersonic knotty outflow.Comment: 15 pages, 3 tables, 13 figures. Accepted for publication by A&
Count Me In: The dimensions of social inclusion through culture and sport
This study was set up to examine claims made for the ability of cultural projects to promote social inclusion (cultural projects are here taken to include those incorporating sport, the arts, media, heritage and outdoor adventure). This was to be achieved primarily by collecting evidence from a sample of 14 projects selected from some 200 that had volunteered their services. The report to the government’s Social Exclusion Unit (SEU) from the Policy Action Team (PAT10) (1999)2 noted the potential. In his foreword, Chris Smith (then Secretary of State for the Department for Culture Media and Sport (DCMS)) wrote: “… art and sport can not only make a valuable contribution to delivering key outcomes of lower long term unemployment, less crime, better health and better qualifications, but can also help to develop the individual pride, community spirit and capacity for responsibility that enable communities to run regeneration programmes themselves”. Similar statements have followed from other politicians, particularly in the recent Commons debate on sport and social exclusion (22/11/01), and again in the public health debate (13/12/01). However, the PAT 10 report also came to the same conclusion as previous commentators (e.g. Glyptis, 19893; Allison & Coalter, 19964; Long & Sanderson, 19985) that there is little ‘hard’ evidence of the social benefits that accrue
Count Me In: The Dimensions of social inclusion through Culture, Media & Sport (Executive Summary)
This study was set up to examine claims made for the ability of cultural projects to promote social inclusion (cultural projects are here taken to include those incorporating sport, the arts, media, heritage and outdoor adventure). This was to be achieved primarily by collecting evidence from a sample of 14 projects selected from some 200 that had volunteered their services. The report to the government’s Social Exclusion Unit (SEU) from the Policy Action Team (PAT10) (1999) noted the potential. In his foreword, Chris Smith (then Secretary of State for the Department for Culture Media and Sport (DCMS)) wrote: “… art and sport can not only make a valuable contribution to delivering key outcomes of lower long term unemployment, less crime, better health and better qualifications, but can also help to develop the individual pride, community spirit and capacity for responsibility that enable communities to run regeneration programmes themselves”. Similar statements have followed from other politicians, particularly in the recent Commons debate on sport and social exclusion (22/11/01), and again in the public health debate (13/12/01). However, the PAT 10 report also came to the same conclusion as previous commentators (e.g. Glyptis, 19893; Allison & Coalter, 19964; Long & Sanderson, 1998) that there is little ‘hard’ evidence of the social benefits that accrue
Tight Binding Hamiltonians and Quantum Turing Machines
This paper extends work done to date on quantum computation by associating
potentials with different types of computation steps. Quantum Turing machine
Hamiltonians, generalized to include potentials, correspond to sums over tight
binding Hamiltonians each with a different potential distribution. Which
distribution applies is determined by the initial state. An example, which
enumerates the integers in succession as binary strings, is analyzed. It is
seen that for some initial states the potential distributions have
quasicrystalline properties and are similar to a substitution sequence.Comment: 4 pages Latex, 2 postscript figures, submitted to Phys Rev Letter
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