5,548 research outputs found
Double handbag description of proton-antiproton annihilation into a heavy meson pair
We propose to describe the process in a
perturbative QCD motivated framework where a double-handbag hard process factorizes from transition distribution
amplitudes, which are quasi forward hadronic matrix elements of operators, where q denotes light quarks and c denotes the heavy quark.
We advocate that the charm-quark mass acts as the large scale allowing this
factorization. We calculate this process in the simplified framework of the
scalar diquark model and present the expected cross sections for the PANDA
experiment at GSI-FAIR.Comment: 25 page
-production in -collisions within a double handbag approach
We estimate the scattering amplitude of the process within a double-handbag framework where transition distribution
amplitudes, calculated through an overlap representation, factorize from a hard
subprocess. This process will be measured in the
experiment at GSI-FAIR.Comment: Talk given at the 11th International Conference on Low Energy
Antiproton Physics (LEAP2013
Switched Control of Electron Nuclear Spin Systems
In this article, we study control of electron-nuclear spin dynamics at
magnetic field strengths where the Larmor frequency of the nucleus is
comparable to the hyperfine coupling strength. The quantization axis for the
nuclear spin differs from the static B_0 field direction and depends on the
state of the electron spin. The quantization axis can be switched by flipping
the state of electron spin, allowing for universal control on nuclear spin
states. We show that by performing a sequence of flips (each followed by a
suitable delay), we can perform any desired rotation on the nuclear spins,
which can also be conditioned on the state of the electron spin. These
operations, combined with electron spin rotations can be used to synthesize any
unitary transformation on the coupled electron-nuclear spin system. We discuss
how these methods can be used for design of experiments for transfer of
polarization from the electron to the nuclear spins
A comparison of Random Set and Point Estimate Methods in Finite Element Analysis of Tunnel Excavation
Risk and Reliability in Geotechnical Engineerin
Sustainability assessment of organic dairy farms in mountainous areas of Austria
Dairy farming plays a major role in mountainous regions of Austria, mostly due to high proportion of grasslands. In general, Austria’s dairy farming faces challenges regarding sustainability, e.g. environmental impacts, but specifically for alpine areas low productivity and dependency on direct payments are lowering sustainability. Organic farming is considered as a strategy to overcome these challenges.
Considering this general background, we analysed the sustainability performance and its main drivers of organic dairy farms in mountainous regions of Austria
Critical connectedness of thin arithmetical discrete planes
An arithmetical discrete plane is said to have critical connecting thickness
if its thickness is equal to the infimum of the set of values that preserve its
-connectedness. This infimum thickness can be computed thanks to the fully
subtractive algorithm. This multidimensional continued fraction algorithm
consists, in its linear form, in subtracting the smallest entry to the other
ones. We provide a characterization of the discrete planes with critical
thickness that have zero intercept and that are -connected. Our tools rely
on the notion of dual substitution which is a geometric version of the usual
notion of substitution acting on words. We associate with the fully subtractive
algorithm a set of substitutions whose incidence matrix is provided by the
matrices of the algorithm, and prove that their geometric counterparts generate
arithmetic discrete planes.Comment: 18 pages, v2 includes several corrections and is a long version of
the DGCI extended abstrac
On the Validation of Satellite-Derived Sea Ice Surface Temperature
The surface temperature of sea ice controls the rate of ice growth and heat exchange between the ocean and the atmosphere. An algorithm for the satellite retrieval of ice surface temperature has recently been published, but due to the lack of validation data has not been extensively tested. In this paper, data from a recent Arctic field experiment is used in an attempt to validate that algorithm. While the procedure is, in principle, straightforward, we demonstrate that validation is complicated by a variety of factors, including incorrectly assumed atmospheric conditions, undetected clouds in the satellite data, spatial and temporal variability in the surface temperature field, and surface and satellite measurement errors. Comparisons between surface temperatures determined from upwelling broadband longwave radiation, spatial measurements of narrow-band radiation, thermocouples buried just below the snow surface, and narrow-band satellite data show differences of 1 to 13 degrees C. The range in these independent measurements indicates the need for specially designed validation experiments utilizing narrow-band radiometers on aircraft to obtain broad spatial coverage.Key words: ice surface temperature, Arctic climate, sea ice, AVHRRLa température de la surface de la glace de mer contrôle le taux de croissance de la glace et les échanges thermiques entre l'océan et l'atmosphère. Un algorithme d'extraction par satellite de la température de la surface de la glace a récemment été publié, mais n'a pu être mis à l'essai sur une grande échelle, en raison du manque de données de validation. On tente, dans cet article, de valider cet algorithme à l'aide de données provenant d'une expérience de terrain menée récemment dans l'Arctique. Si la procédure est, en principe, simple, on démontre que divers facteurs viennent compliquer cette validation, dont une évaluation incorrecte des conditions atmosphériques, la présence de nuages non détectés dans les données obtenues par satellite, une variabilité spatiale et temporelle dans la température de surface de l'aire expérimentale, et des erreurs dans les mesures prises sur le terrain même et par satellite. Des comparaisons entre les températures de surface déterminées à partir du rayonnement ascendant des ondes longues à large bande, des mesures spatiales du rayonnement à bande étroite, des thermocouples placés juste sous la surface de la neige et des données de satellite dans la bande étroite révèlent des différences allant de 1 à 3 °C. La différence qui existe dans ces mesures prises indépendamment montre bien la nécessité de mettre sur pied des expériences de validation conçues à des fins spécifiques, qui utilisent des radiomètres à bande étroite sur les avions en vue d'obtenir une grande couverture spatiale.Mots clés: température de la surface de la glace, climat de l’Arctique, glace de mer, radiomètre perfectionné à très haute résolutio
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