1,422 research outputs found
Wigner Oscillators, Twisted Hopf Algebras and Second Quantization
By correctly identifying the role of central extension in the centrally
extended Heisenberg algebra h, we show that it is indeed possible to construct
a Hopf algebraic structure on the corresponding enveloping algebra U(h) and
eventually deform it through Drinfeld twist. This Hopf algebraic structure and
its deformed version U^F(h) are shown to be induced from a more fundamental
Hopf algebra obtained from the Schroedinger field/oscillator algebra and its
deformed version, provided that the fields/oscillators are regarded as
odd-elements of the super-algebra osp(1|2n). We also discuss the possible
implications in the context of quantum statistics.Comment: 23 page
Obesity in Switzerland: do estimates depend on how body mass index has been assessed?
In Switzerland monitoring of obesity in the general population is based on body mass index (BMI) derived from self-reported weight and height. This approach may lead to misclassification of obese subjects and misinterpretation of obesity prevalence and trends. In order to explore this potential bias, we compared studies with measured and self-reported data.
We analysed five studies based on measured BMI and five studies based on self-reported BMI, all of which were carried out in Switzerland between 1977 and 2004 and encompassed men and women aged 35-74 years. Obesity was defined as BMI>or=30 kg/m2.
The prevalence of obesity was markedly higher (1.6 times) in studies with measured BMI in both sexes: 14.2% vs 8.8% in men and 12.5% vs 7.9% in women. These differences tended to increase with age in both sexes. However, a similar upward trend in the prevalence of obesity was observed with both methods (absolute increase per year in men and women respectively: 0.24% and 0.25% using measured BMI vs 0.17% and 0.20% using self-reported BMI).
In Switzerland obesity prevalence in adults has clearly increased in the past three decades. Although the use of self-reported height and weight leads to a valid estimation of this increase, it results in a considerable underestimation of obesity prevalence rates in Switzerland. The type of assessment of height and weight should be taken into consideration when comparing prevalences of obesity between studies or regions or when using these prevalences to assess associated health risks or costs
Self-energy of a scalar charge near higher-dimensional black holes
We study the problem of self-energy of charges in higher dimensional static
spacetimes. Application of regularization methods of quantum field theory to
calculation of the classical self-energy of charges leads to model-independent
results. The correction to the self-energy of a scalar charge due to the
gravitational field of black holes of the higher dimensional
Majumdar-Papapetrou spacetime is calculated exactly. It proves to be zero in
even dimensions, but it acquires non-zero value in odd dimensional spacetimes.
The origin of the self-energy correction in odd dimensions is similar to the
origin the conformal anomalies in quantum field theory in even dimensional
spacetimes.Comment: 9 page
Wigner phase space distribution as a wave function
We demonstrate that the Wigner function of a pure quantum state is a wave
function in a specially tuned Dirac bra-ket formalism and argue that the Wigner
function is in fact a probability amplitude for the quantum particle to be at a
certain point of the classical phase space. Additionally, we establish that in
the classical limit, the Wigner function transforms into a classical
Koopman-von Neumann wave function rather than into a classical probability
distribution. Since probability amplitude need not be positive, our findings
provide an alternative outlook on the Wigner function's negativity.Comment: 6 pages and 2 figure
Hard diffraction in hadron--hadron interactions and in photoproduction
Hard single diffractive processes are studied within the framework of the
triple--Pomeron approximation. Using a Pomeron structure function motivated by
Regge--theory we obtain parton distribution functions which do not obey
momentum sum rule. Based on Regge-- factorization cross sections for hard
diffraction are calculated. Furthermore, the model is applied to hard
diffractive particle production in photoproduction and in
interactions.Comment: 13 pages, Latex, 13 uuencoded figure
Evaluating the land and ocean components of the global carbon cycle in the CMIP5 earth system models
PublishedJournal ArticleThe authors assess the ability of 18 Earth system models to simulate the land and ocean carbon cycle for the present climate. These models will be used in the next Intergovernmental Panel on Climate Change (IPCC) Fifth AssessmentReport (AR5) for climate projections, and such evaluation allows identification of the strengths and weaknesses of individual coupled carbon-climate models as well as identification of systematic biases of themodels. Results show thatmodels correctly reproduce the main climatic variables controlling the spatial and temporal characteristics of the carbon cycle. The seasonal evolution of the variables under examination is well captured. However, weaknesses appear when reproducing specific fields: in particular, considering the land carbon cycle, a general overestimation of photosynthesis and leaf area index is found for most of the models, while the ocean evaluation shows that quite a few models underestimate the primary production. The authors also propose climate and carbon cycle performance metrics in order to assess whether there is a set of consistently better models for reproducing the carbon cycle. Averaged seasonal cycles and probability density functions (PDFs) calculated from model simulations are compared with the corresponding seasonal cycles and PDFs from different observed datasets. Although the metrics used in this study allow identification of somemodels as better or worse than the average, the ranking of this study is partially subjective because of the choice of the variables under examination and also can be sensitive to the choice of reference data. In addition, it was found that the model performances show significant regional variations. © 2013 American Meteorological Society.This work was supported by the European Commission's 7th Framework Programme under Grant Agreements 238366 (GREENCYCLESII) and 282672 (EMBRACE), while Dr. Jones was supported by the Joint DECC/Defra Met Office Hadley Centre Climate Program (GA01101)
Dynamical noncommutativity
The model of dynamical noncommutativity is proposed. The system consists of
two interrelated parts. The first of them describes the physical degrees of
freedom with coordinates q^1, q^2, the second one corresponds to the
noncommutativity r which has a proper dynamics. After quantization the
commutator of two physical coordinates is proportional to the function of r.
The interesting feature of our model is the dependence of nonlocality on the
energy of the system. The more the energy, the more the nonlocality. The
lidding contribution is due to the mode of noncommutativity, however, the
physical degrees of freedom also contribute in nonlocality in higher orders in
\theta.Comment: published versio
Higher-Derivative Boson Field Theories and Constrained Second-Order Theories
As an alternative to the covariant Ostrogradski method, we show that
higher-derivative relativistic Lagrangian field theories can be reduced to
second differential-order by writing them directly as covariant two-derivative
theories involving Lagrange multipliers and new fields. Despite the intrinsic
non-covariance of the Dirac's procedure used to deal with the constraints, the
explicit Lorentz invariance is recovered at the end. We develop this new
setting on the grounds of a simple scalar model and then its applications to
generalized electrodynamics and higher-derivative gravity are worked out. For a
wide class of field theories this method is better suited than Ostrogradski's
for a generalization to 2n-derivative theoriesComment: 31 pages, Plain Te
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