83,470 research outputs found
Duality of N=2 Heterotic -- Type I Compactifications in Four Dimensions
We discuss type I -- heterotic duality in four-dimensional models obtained as
a Coulomb phase of the six-dimensional U(16) orientifold model compactified on
T^2 with arbitrary SU(16) Wilson lines. We show that Kahler potentials, gauge
threshold corrections and the infinite tower of higher derivative F-terms agree
in the limit that corresponds to weak coupling, large T^2 heterotic
compactifications. On the type I side, all these quantities are completely
determined by the spectrum of N=2 BPS states that originate from D=6 massless
superstring modes.Comment: 22 pages, LaTeX; typos corrected and references adde
Vegetation boundaries on ERTS-1 imagery
There are no author-identified significant results in this report
ELF: The electronic learning facilitator
As the worldâwide computer network becomes ubiquitous, new tools have been developed, such as the World Wide Web (WWW), for the delivery of multimedia hypertextâbased documents. Similarly, there has been an explosion in the amount of email, bulletin boards, and Usenet News available. This has led to a major problem of information overload: we are slowly but surely being overwhelmed by the amount of information available to us
Preparing the foundations for video-based, practice-placement support: establishing the role from a studentsâ perspective
Currently, many placement-based health programme students within the UK are supported through face-to-face visits from university staff. Whilst cited in literature as being of value, the face-to-face nature of this contact is not supported. Alternatives including video-based communications methods offer the potential for cost effective, environmentally responsible support. However, in order to establish the fitness for purpose of alternative approaches, the content and purpose of current support needs to be understood. This project aimed to investigate student perceptions of the ideal content and purpose of clinical support visits, and alternatives to the current face-to-face approach. Fifty-six Physiotherapy undergraduate students responded to questionnaires with a further nine participating in a follow-up focus group. Participants emphasised the value of the visit in guiding learning, ensuring progression and resolving arising issues, and highlighted concerns over alternative approaches. Focus group participants discussed the importance of personal and professional confidence in directing requirements for support, and went on to propose a menu of options for methods of communication.Whilst limited in some applications, video technologies may be one of the options. Overall, however, this project supports the need for consideration of individualised learning journeys within curriculum planning
Performance of an ideal turbine in an inviscid shear flow
Although wind and tidal turbines operate in turbulent shear flow, most theoretical results concerning turbine performance, such as the well-known Betz limit, assume the upstream velocity profile is uniform. To improve on these existing results we extend the classical actuator disc model in this paper to investigate the performance of an ideal turbine in steady, inviscid shear flow. The model is developed on the assumption that there is negligible lateral interaction in the flow passing through the disc and that the actuator applies a uniform resistance across its area. With these assumptions, solution of the model leads to two key results. First, for laterally unbounded shear flow, it is shown that the normalised power extracted is the same as that for an ideal turbine in uniform flow, if the average of the cube of the upstream velocity of the fluid passing through the turbine is used in the normalisation. Second, for a laterally bounded shear flow, it is shown that the same normalisation can be applied, but allowance must also be made for the fact that non-uniform flow bypassing the turbine alters the background pressure gradient and, in turn, the turbines âeffective blockageâ (so that it may be greater or less than the geometric blockage, defined as the ratio of turbine disc area to cross-sectional area of the flow). Predictions based on the extended model agree well with numerical simulations approximating the incompressible Euler equations. The model may be used to improve interpretation of model-scale results for wind and tidal turbines in tunnels/flumes, to investigate the variation in force across a turbine and to update existing theoretical models of arrays of tidal turbines
The Transition between Nonorthogonal Polarization Modes in PSR B2016+28 at 1404 MHz
Polarization observations of the radio emission from PSR B2016+28 at 1404 MHz
reveal properties that are consistent with two, very different, interpretations
of the pulsar's viewing geometry. The pulsar's average polarization properties
show a rapid change in position angle (PA) near the pulse center, suggesting
that the observer's sightline nearly intersects the star's magnetic pole. But
single pulse, polarization observations of the pulsar show nearly orthogonal
modes of polarization following relatively flat and parallel PA trajectories
across the pulse, suggesting that the sightline is far from the pole.
Additionally, PA histograms reveal a "modal connecting bridge", of unknown
origin, joining the modal PA trajectories over much of the pulse and following
the rapid PA change shown in the average data. The nonorthogonality of
polarization modes is incorporated in a statistical model of radio polarization
to account for the deviations from mode orthogonality that are observed in the
pulsar. The model is used to interpret the rapid PA change and modal connecting
bridge as a longitudinally-resolved transition between modes of nonorthogonal
polarization. Thus, the modal PA trajectories are argued to reflect the
pulsar's true viewing geometry. This interpretation is consistent with the
pulsar's morphological classification, preserves the Radhakrishnan & Cooke
model of pulsar radio emission, and avoids the complication that the modal
connecting bridge might be produced by some other emission mechanism. The
statistical model's ability to simulate the rich variety of polarization
properties observed in the emission lends additional support to the model's
applicability and its underlying assumption that the polarization modes occur
simultaneously.Comment: Accepted for publication in Ap
A novel mechanism for binding of galactose-terminated glycans by the C-type carbohydrate recognition domain in blood dendritic cell antigen 2
Blood dendritic cell antigen 2 (BDCA-2; also designated CLEC4C or CD303) is uniquely expressed on plasmacytoid dendritic cells. Stimulation of BDCA-2 with antibodies leads to an anti-inflammatory response in these cells, but the natural ligands for the receptor are not known. The C-type carbohydrate recognition domain in the extracellular portion of BDCA-2 contains a signature motif typical of C-type animal lectins that bind mannose, glucose, or GlcNAc, yet it has been reported that BDCA-2 binds selectively to galactose-terminated, biantennary N-linked glycans. A combination of glycan array analysis and binding competition studies with monosaccharides and natural and synthetic oligosaccharides have been used to define the binding epitope for BDCA-2 as the trisaccharide GalÎČ1â3/4GlcNAcÎČ1â2Man. X-ray crystallography and mutagenesis studies show that mannose is ligated to the conserved Ca2+ in the primary binding site that is characteristic of C-type carbohydrate recognition domains, and the GlcNAc and galactose residues make additional interactions in a wide, shallow groove adjacent to the primary binding site. As predicted from these studies, BDCA-2 binds to IgG, which bears galactose-terminated glycans that are not commonly found attached to other serum glycoproteins. Thus, BDCA-2 has the potential to serve as a previously unrecognized immunoglobulin Fc receptor
Off-Road Vehicle Recreation in the West: Implications of a Wyoming Analysis
Community/Rural/Urban Development, Resource /Energy Economics and Policy,
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An atlas of CO2 storage potential in the nearshore waters of the Texas coast â American Recovery and Reinvestment Act â âGulf of Mexico Miocene CO2 site characterization mega-transectâ
Bureau of Economic Geolog
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