14,476 research outputs found
QCD corrections to e+ e- --> 4 jets
We report on the next-to-leading order QCD calculation for e+ e- --> 4 jets.
We explain some modern techniques which have been used to calculate the
one-loop amplitudes efficiently. We further report on the general purpose
numerical program ``Mercutio'', which can be used to calculate any infrared
safe four-jet quantity in electron-positron annihilation at next-to-leading
order.Comment: 4 pages, talk given at the UK Phenomenology Workshop on Collider
Physics, Durham, 19-24 September 199
A causal statistical family of dissipative divergence type fluids
In this paper we investigate some properties, including causality, of a
particular class of relativistic dissipative fluid theories of divergence type.
This set is defined as those theories coming from a statistical description of
matter, in the sense that the three tensor fields appearing in the theory can
be expressed as the three first momenta of a suitable distribution function. In
this set of theories the causality condition for the resulting system of
hyperbolic partial differential equations is very simple and allow to identify
a subclass of manifestly causal theories, which are so for all states outside
equilibrium for which the theory preserves this statistical interpretation
condition. This subclass includes the usual equilibrium distributions, namely
Boltzmann, Bose or Fermi distributions, according to the statistics used,
suitably generalized outside equilibrium. Therefore this gives a simple proof
that they are causal in a neighborhood of equilibrium. We also find a bigger
set of dissipative divergence type theories which are only pseudo-statistical,
in the sense that the third rank tensor of the fluid theory has the symmetry
and trace properties of a third momentum of an statistical distribution, but
the energy-momentum tensor, while having the form of a second momentum
distribution, it is so for a different distribution function. This set also
contains a subclass (including the one already mentioned) of manifestly causal
theories.Comment: LaTex, documentstyle{article
The psychometric properties of ADCS - activities of daily living inventory and comparison of different ADL scores
Several multi-item activities of daily living (ADL) scales have been developed for assessment of functional status of patients with Alzheimer’s Disease (AD) in the last few decades. A disadvantage of the large number of scales is that scores of different ADL scales cannot be compared directly with each other. ADL scales which are used by McNamee’s (Townsend's disability scale) and Hill’s (Medicare Beneficiary definitions and Katz index of ADL) provide suitable tools for modelling the cost-effectiveness of different treatments in patients with Alzheimer’s disease, since they report empirical results about the relationship between the degree of functional impairment (healthcare costs) and the prevalence of institutionalisation.
The IDEAL trial examines the efficacy of Exelon Patch with the ADCS - Activities of Daily Living Inventory (ADCS-ADL). This ADL instrument is not directly comparable to the ADL scales used by McNamee and Hill. However, the use of the ADL scale from the IDEAL study to predict the prevalence of institutionalisation with scales by Hill and McNamee would be desirable. Because of the generic nature of the ADL construct, and considering the fact that these well validated ADL instruments identify the main physical impairments and functional disabilities in Alzheimer's disease, we should expect high overlap in item content between different ADL instruments. The high overlap in item content between instruments, and the similar wording and scoring criteria, makes it possible to pair each impairment with another. The intention of this study was to establish the link between these ADL scales in order to provide appropriate conditions for further economic analyses on the dataset provided by the IDEAL study
Nonlinear screening and stopping power in two-dimensional electron gases
We have used density functional theory to study the nonlinear screening
properties of a two-dimensional (2D) electron gas. In particular, we consider
the screening of an external static point charge of magnitude Z as a function
of the distance of the charge from the plane of the gas. The self-consistent
screening potentials are then used to determine the 2D stopping power in the
low velocity limit based on the momentum transfer cross-section. Calculations
as a function of Z establish the limits of validity of linear and quadratic
response theory calculations, and show that nonlinear screening theory already
provides significant corrections in the case of protons. In contrast to the 3D
situation, we find that the nonlinearly screened potential supports a bound
state even in the high density limit. This behaviour is elucidated with the
derivation of a high density screening theorem which proves that the screening
charge can be calculated perturbatively in the high density limit for arbitrary
dimensions. However, the theorem has particularly interesting implications in
2D where, contrary to expectations, we find that perturbation theory remains
valid even when the perturbing potential supports bound states.Comment: 23 pages, 15 figures in RevTeX
Report from upper atmospheric science
Most of the understanding of the thermosphere resulted from the analysis of data accrued through the Atmosphere Explorer satellites, the Dynamics Explorer 2 satellite, and observations from rockets, balloons, and ground based instruments. However, new questions were posed by the data that have not yet been answered. The mesosphere and lower thermosphere have been less thoroughly studied because of the difficulty of accessibility on a global scale, and many rather fundamental characteristics of these regions are not well understood. A wide variety of measurement platforms can be used to implement various parts of a measurement strategy, but the major thrusts of the International Solar Terrestrial Physics Program would require Explorer-class missions. A remote sensing mission to explore the mesosphere and lower thermosphere and one and two Explorer-type spacecraft to enable a mission into the thermosphere itself would provide the essential components of a productive program of exploration of this important region of the upper atomsphere. Theoretical mission options are explored
Effect of the channel and interference phenomena in the two-pion transitions of charmonia and bottomonia
The basic shape of di-pion mass spectra in the two-pion transitions of both
charmonia and bottomonia states is explained by an unified mechanism based on
contributions of the , and coupled channels
including their interference. The role of the individual resonances in
shaping the di-pion mass distributions in the charmonia and bottomonia decays
is considered.Comment: 8 pages, 4 figures, Talk at the XXIII International Baldin Seminar on
High Energy Physics Problems "Relativistic Nuclear Physics \& Quantum
Chromodynamics" (Dubna, Russia, 19--24 September 2016). arXiv admin note:
text overlap with arXiv:1610.0789
The interference effects of multi-channel pion-pion scattering contributions to the final states of - and -meson family decays
It is shown that the basic shape of dipion mass distributions in the two-pion
transitions of both charmonia and bottomonia states are explained by an unified
mechanism based on the contribution of the , and
coupled channels including their interference.Comment: 5 pages, 3 figures, talk at the14th International Workshop on Meson
Production, Properties and Interaction (Krakow, Poland, 2nd - 7th June 2016
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