1,406 research outputs found
Considerations when introducing electronic patient-reported outcome data capture in multicentre oncology randomised controlled trials.
Group theoretical approach to quantum fields in de Sitter space I. The principal series
Using unitary irreducible representations of the de Sitter group, we
construct the Fock space of a massive free scalar field.
In this approach, the vacuum is the unique dS invariant state. The quantum
field is a posteriori defined by an operator subject to covariant
transformations under the dS isometry group. This insures that it obeys
canonical commutation relations, up to an overall factor which should not
vanish as it fixes the value of hbar. However, contrary to what is obtained for
the Poincare group, the covariance condition leaves an arbitrariness in the
definition of the field. This arbitrariness allows to recover the amplitudes
governing spontaneous pair creation processes, as well as the class of alpha
vacua obtained in the usual field theoretical approach. The two approaches can
be formally related by introducing a squeezing operator which acts on the state
in the field theoretical description and on the operator in the present
treatment. The choice of the different dS invariant schemes (different alpha
vacua) is here posed in very simple terms: it is related to a first order
differential equation which is singular on the horizon and whose general
solution is therefore characterized by the amplitude on either side of the
horizon. Our algebraic approach offers a new method to define quantum field
theory on some deformations of dS space.Comment: 35 pages, 2 figures ; Corrected typo, Changed referenc
Kompetenznetz E-Learning Hessen
Mit dem Kompetenznetz e-learning-hessen.de vernetzen sich die hessischen Hochschulen mit Hilfe der Koordination und Unterstützung durch das httc und Förderung durch das Hessische Ministerium für Wissenschaft und Kunst rund um das Thema E-Learning. Dieser Beitrag beschreibt die Ziele des Netzwerks, dessen Maßnahmen und Elemente und die bisherigen Erfahrungen und seine Entwicklung seit dem Jahr 2000. Mit der abschließenden Bewertung werden Anhaltspunkte für eine erfolgreiche Vernetzung von Hochschulen und ein Ausblick auf die geplanten Aktivitäten des hessischen Netzwerkes in den nächsten Jahren gegeben. (DIPF/ Orig.
CPVMatch - Concentrating photovoltaic modules using advanced technologies and cells for highest efficiencies
This paper presents the project Concentrating Photovoltaic modules using advanced technologies and cells for highest efficiencies (CPVMatch), which is funded from the European Union’s Horizon 2020 research and innovation programme. V multi-junction solar cells and CPV modules. Concerning cells, novel wafer bonded four-junction solar cells made of GaInP/GaAs//GaInAs/Ge are optimized with the target of reaching 48% efficiency under concentration at the end of the project. Moreover, multi-junction solar cell technologies with advanced materials - like ternary IV element mixtures (i.e. SiGeSn) and nanostructured anti-reflective coatings - are investigated. Concerning CPV modules the project focuses on both Fresnel-based and mirror-based technologies with a target efficiency of 40% under high concentrations beyond 800x. Achromatic Fresnel lenses for improved light management without secondary optics are investigated. In addition, smart, mirror-based HCPV modules are developed, which include a new mirror-based design, the integration of high efficiency, low cost DC/DC converters and an intelligent tracking sensor (PSD sensor) at module level. A profound life-cycle and environmental assessment and the development of adapted characterization methods of new multi-junction cells and HCPV modules complete the work plan of CPVMatch
Systematic effects in the extraction of the 'WMAP haze'
The extraction of a 'haze' from the WMAP microwave skymaps is based on
subtraction of known foregrounds, viz. free-free (bremsstrahlung), thermal dust
and synchrotron, each traced by other skymaps. While the 408 MHz all-sky survey
is used for the synchrotron template, the WMAP bands are at tens of GHz where
the spatial distribution of the radiating cosmic ray electrons ought to be
quite different because of the energy-dependence of their diffusion in the
Galaxy. The systematic uncertainty this introduces in the residual skymap is
comparable to the claimed haze and can, for certain source distributions, have
a very similar spectrum and latitudinal profile and even a somewhat similar
morphology. Hence caution must be exercised in interpreting the 'haze' as a
physical signature of, e.g., dark matter annihilation in the Galactic centre.Comment: 17 pages, 12 figures; improved diffusion model; extended discussion
of spectral index maps; clarifying comments, figures and references added; to
appear in JCA
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