12,904,736 research outputs found
The Spin Structure of the Constituent Quarks and of the Nucleon
We define a constituent quark within QCD. It is shown that the spin of such a
quark and hence also the spin of the nucleon reduced due to -pairs,
in agreement with experiment. A solution to the spin problem is given.Comment: 7 page
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Participatory online environmental education at the Open University UK
The role of education in helping our societies put sustainability into practice is crucial. The motivation, awareness and empowerment, necessary for citizens to understand the concept and take part in its operationalisation, ought to emerge from environmental education, since we might encounter some difficulty when trying to teach, or impose these notions in a theoretical way. In developing environmental courses, we therefore ought to progressively replace pedagogical approaches based on (relatively 'authoritarian') transfers of information with more interactive and collaborative learning processes: citizens' participation can start with the creation of communities of learners. This paper describes the construction of two web courses: a first level teaching module on environmental systems and a third level interdisciplinary environmental course, both developed at the Open University, specialised in distance and open learning. The themes of the course include participatory processes in decision-making, the perception and representation of environmental systems, alternative leadership, biodiversity, climate change and integrated water management, environmental action and governance. The concepts focused on include sustainability, complexity, uncertainty, globalisation and 'systemic problem solving'. In both courses, the overall pedagogical process is based on the notion of environmental governance. This means that the web has been chosen as a learning platform, because
- it provides various types of up to date information as well as archives,
- it allows various types of users to communicate between different countries, and also
- it encourages collaborative and interactive learning.
This paper describes the experience of the author in creating web environmental courses at the Open University. Components of the courses such as interactive activities are discussed, as well as the pedagogical focus progressively shifted towards more participatory processes of learning
Realistic Neutrino Masses from Multi-brane Extensions of the Randall-Sundrum Model?
Scenarios based on the existence of large or warped (Randall-Sundrum model)
extra dimensions have been proposed for addressing the long standing puzzle of
gauge hierarchy problem. Within the contexts of both those scenarios, a novel
and original type of mechanism generating small (Dirac) neutrino masses, which
relies on the presence of additional right-handed neutrinos that propagate in
the bulk, has arisen. The main objective of the present study is to determine
whether this geometrical mechanism can produce reasonable neutrino masses also
in the interesting multi-brane extensions of the Randall-Sundrum model. We
demonstrate that, in some multi-brane extensions, neutrino masses in agreement
with all relevant experimental bounds can indeed be generated but at the price
of a constraint (stronger than the existing ones) on the bulk geometry, and
that the other multi-brane models even conflict with those experimental bounds.Comment: 29 pages, 3 figures, Latex file. References added, study extende
A description of the ratio between electric and magnetic proton form factors by using space-like, time-like data and dispersion relations
We use the available information on the ratio between the electric and
magnetic proton form factors coming from recently published space-like data and
from the few available time-like data. We apply a dispersive procedure on these
data to evaluate the behaviour of this ratio, as a complex function, for all
values of q^2.Comment: 12 pages, 7 Encapsulated Postscript figures, uses epsfig, rotating,
exscale, amsmath, cite, latexsym, graphics, color packages, added reference
Isospin and symmetry energy effects on nuclear fragment production in liquid-gas type phase transition region
We have demonstrated that the isospin of nuclei influences the fragment
production during the nuclear liquid-gas phase transition. Calculations for
Au197, Sn124, La124 and Kr78 at various excitation energies were carried out on
the basis of the statistical multifragmentation model (SMM). We analyzed the
behavior of the critical exponent tau with the excitation energy and its
dependence on the critical temperature. Relative yields of fragments were
classified with respect to the mass number of the fragments in the transition
region. In this way, we have demonstrated that nuclear multifragmentation
exhibits a 'bimodality' behavior. We have also shown that the symmetry energy
has a small influence on fragment mass distribution, however, its effect is
more pronounced in the isotope distributions of produced fragments.Comment: 8 pages, 9 figures, accepted for publication in EPJ
Measurement of the LT-asymmetry in \pi^0 electroproduction at the energy of the \Delta (1232) resonance
The reaction p(e,e'p)pi^0 has been studied at Q^2=0.2 (GeV/c)^2 in the region
of W=1232 MeV. From measurements left and right of q, cross section asymmetries
\rho_LT have been obtained in forward kinematics \rho_LT(\theta_\pi^0=20deg) =
(-11.68 +/- 2.36_stat +/- 2.36_sys)$ and backward kinematics
\rho_LT(\theta_\pi^0=160deg) =(12.18 +/- 0.27_stat +/- 0.82_sys). Multipole
ratios \Re(S_1+^* M_1+)/|M_1+|^2 and \Re(S_0+^* M_1+)/|M_1+|^2 were determined
in the framework of the MAID2003 model. The results are in agreement with older
data. The unusally strong negative \Re(S_0+^* M_1+)/|M_1+|^2 required to bring
also the result of Kalleicher et al. in accordance with the rest of the data is
almost excluded.Comment: 7 pages, 7 figures, 4 tables. Changed content. Accepted for
publication in EPJ
Quantum Chaos in the Yang-Mills-Higgs System at Finite Temperature
The quantum chaos in the finite-temperature Yang-Mills-Higgs system is
studied. The energy spectrum of a spatially homogeneous SU(2) Yang-Mills-Higgs
is calculated within thermofield dynamics. Level statistics of the spectra is
studied by plotting nearest-level spacing distribution histograms. It is found
that finite temperature effects lead to a strengthening of chaotic effects,
i.e. spectrum which has Poissonian distribution at zero temperature has
Gaussian distribution at finite-temperature.Comment: 6 pages, 5 figures, Revte
One-step generation of high-quality squeezed and EPR states in cavity QED
We show how to generate bilinear (quadratic) Hamiltonians in cavity quantum
electrodynamics (QED) through the interaction of a single driven three-level
atom with two (one) cavity modes. With this scheme it is possible to generate
one-mode mesoscopic squeezed superpositions, two-mode entanglements, and
two-mode squeezed vacuum states (such the original EPR state), without the need
for Ramsey zones and external parametric amplification. The degree of squeezing
achieved is up to 99% with currently feasible experimental parameters and the
errors due to dissipative mechanisms become practically negligible
Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV
We report the first measurement of charged particle elliptic flow in Pb-Pb
collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron
Collider. The measurement is performed in the central pseudorapidity region
(||<0.8) and transverse momentum range 0.2< < 5.0 GeV/. The
elliptic flow signal v, measured using the 4-particle correlation method,
averaged over transverse momentum and pseudorapidity is 0.087 0.002
(stat) 0.004 (syst) in the 40-50% centrality class. The differential
elliptic flow v reaches a maximum of 0.2 near = 3
GeV/. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow
increases by about 30%. Some hydrodynamic model predictions which include
viscous corrections are in agreement with the observed increase.Comment: 10 pages, 4 captioned figures, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/389
Thouless energy of a superconductor from non local conductance fluctuations
We show that a spin-up electron from a normal metal entering a superconductor
propagates as a composite object consisting of a spin-down hole and a pair in
the condensate. This leads to a factorization of the non local conductance as
two local Andreev reflections at both interfaces and one propagation in the
superconductor, which is tested numerically within a one dimensional toy model
of reflectionless tunneling. Small area junctions are characterized by non
local conductance fluctuations. A treatment ignoring weak localization leads to
a Thouless energy inverse proportional to the sample size, as observed in the
numerical simulations. We show that weak localization can have a strong effect,
and leads to a coupling between evanescent quasiparticles and the condensate by
Andreev reflections ``internal'' to the superconductor.Comment: 11 pages, 12 figures, revised manuscrip
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