67,966 research outputs found
Creation of blenders in the conservative setting
In this work we prove that each C^r conservative diffeomorphism with a pair
of hyperbolic periodic points of co-index one can be C^1-approximated by C^r
conservative diffeomorphisms having a blender.Comment: 4 figures, 16 figure
Surface Waves and Forced Oscillations in QHE Planar Samples
Dispersion relations and polarizations for surface waves in infinite planar
samples in the QHE regime are explicitly determined in the small wavevector
limit in which the dielectric tensor can be considered as local. The wavelength
and frequency regions of applicability of the results extends to the infrared
region for typical experimental conditions. Then, standard samples with
millimetric sizes seem to be able to support such excitations. Forced
oscillations are also determined which should be generated in the 2DEG by
external electromagnetic sources. They show an almost frequency independent
wavevelength which decreases with the magnetic field. A qualitative model based
in these solutions is also presented to describe a recently found new class of
resonances appearing near the edge of a 2DEG in the QHE regime.Comment: latex file, 18 pages, 3 figures, spelling correcte
Scalar Sector in the Minimal Supersymmetric 3-3-1 model
We consider the minimal supersymmetric extension of the 3-3-1 model and we
study the mass spectra in the scalar sector of this model without the
anti-sextet. We show that all our lighest scalars are in agreement with the
experimental limits.Comment: It was included on the introduction of the article the motivation to
> study the model, and we moved the sections 4.1 and 4.2 to the appendix. It
has 22 pages, 9 figures. It was accepted to be published at International
Journal of Modern Physics
The Non-Mesonic Weak Decay of Double-Lambda Hypernuclei: A Microscopic Approach
The non--mesonic weak decay of double-- hypernuclei is studied
within a microscopic diagrammatic approach. Besides the nucleon--induced
mechanism, , widely studied in single-- hypernuclei,
additional hyperon--induced mechanisms, ,
and , are
accessible in double-- hypernuclei and are investigated here. As in
previous works on single-- hypernuclei, we adopt a nuclear matter
formalism extended to finite nuclei via the local density approximation and a
one--meson exchange weak transition potential (including the ground state
pseudoscalar and vector octets mesons) supplemented by correlated and
uncorrelated two--pion--exchange contributions. The weak decay rates are
evaluated for hypernuclei in the region of the experimentally accessible light
hypernuclei Be and B. Our
predictions are compared with a few previous evaluations. The rate for the
decay is dominated by --, -- and
--exchange and turns out to be about 2.5\% of the free decay
rate, , while the total rate for the and decays, dominated by
--exchange, amounts to about 0.25\% of . The
experimental measurement of these decays would be essential for the beginning
of a systematic study of the non--mesonic decay of strangeness
hypernuclei. This field of research could also shed light on the possible
existence and nature of the --dibaryon.Comment: 17 pages, 2 figure
Spin fluctuations and superconductivity in powders of Fe_1+xTe_0.7Se_0.3 as a function of interstitial iron concentration
Using neutron inelastic scattering, we investigate the role of interstitial
iron on the low-energy spin fluctuations in powder samples of
Fe_{1+x}Te_{0.7}Se_{0.3}. We demonstrate how combining the principle of
detailed balance along with measurements at several temperatures allows us to
subtract both temperature-independent and phonon backgrounds from S(Q,\omega)
to obtain purely magnetic scattering. For small values of interstitial iron
(x=0.009(3)), the sample is superconducting (T_{c}=14 K) and displays a spin
gap of 7 meV peaked in momentum at wave vector q_{0}=(\pi,\pi) consistent with
single crystal results. On populating the interstitial iron sites, the
superconducting volume fraction decreases and we observe a filling in of the
low-energy magnetic fluctuations and a decrease of the characteristic wave
vector of the magnetic fluctuations. For large concentrations of interstitial
iron (x=0.048(2)) where the superconducting volume fraction is minimal, we
observe the presence of gapless spin fluctuations at a wave vector of
q_{0}=(\pi,0). We estimate the absolute total moment for the various samples
and find that the amount of interstitial iron does not change the total
magnetic spectral weight significantly, but rather has the effect of shifting
the spectral weight in Q and energy. These results show that the
superconducting and magnetic properties can be tuned by doping small amounts of
iron and are suggestive that interstitial iron concentration is also a
controlling dopant in the Fe_{1+x}Te_{1-y}Se_{y} phase diagram in addition to
the Te/Se ratio.Comment: (10 pages, 8 figures, to be published in Phys. Rev. B
Consumer Perception of Vegetables Resulting From Conventional Field or Greenhouse Agricultural Methods
This survey studies the way in which French consumers perceive fruits and vegetables, be they local, domestic or imported, resulting from conventional field or greenhouse agricultural methods, in terms of a health and hedonic, then a sustainability, point of view. The method employed, focus groups with individual questionnaires and the use of real-to-life scenarios, allows to get findings concerning the knowledge of the various cultivation methods, attitudes concerning these various methods, the role of information, to expose three representational profiles and, the results of the producer scenario, distributor scenario and consumer scenario study. On a general level, this study brings to light the negative image associated with greenhouse growers but consumer perception varies according to the representational profiles (Traditionalists, Spendthrifts and Responsible). ...French Abstract : Cette étude s'intéresse à la façon dont les consommateurs français perçoivent les fruits et légumes, locaux, nationaux ou importés, issus de l'agriculture conventionnelle ou de production sous serre, du point de vue de la santé, des aspects hédoniques et de la durabilité. Des focus groups complétés par des questionnaires individuels et par une étude de scénarios ont permis de mettre en évidence les niveaux de connaissance et les attitudes concernant les différentes méthodes de production, le rÎle de l'information, de présenter trois profils de représentation et les réponses des consommateurs face aux scénarios producteur, distributeur et consommateur. De façon générale, cette étude montre que l'image associée à la production sous serre est négative, mais les perceptions varient selon les profils de représentations (Traditionalistes, Economes, Responsables).SUSTAINABILITY; CONSUMER; FOOD CONSUMPTION; SCENARIOS METHOD; FOCUS GROUPS; AGRICULTURAL PRODUCTION METHODS; DURABILITE; CONSOMMATEUR; CONSOMMATION ALIMENTAIRE; METHODE DES SCENARIOS; METHODES DE PRODUCTION AGRICOLES
The Berry-Tabor conjecture for spin chains of Haldane-Shastry type
According to a long-standing conjecture of Berry and Tabor, the distribution
of the spacings between consecutive levels of a "generic'' integrable model
should follow Poisson's law. In contrast, the spacings distribution of chaotic
systems typically follows Wigner's law. An important exception to the
Berry-Tabor conjecture is the integrable spin chain with long-range
interactions introduced by Haldane and Shastry in 1988, whose spacings
distribution is neither Poissonian nor of Wigner's type. In this letter we
argue that the cumulative spacings distribution of this chain should follow the
"square root of a logarithm'' law recently proposed by us as a characteristic
feature of all spin chains of Haldane-Shastry type. We also show in detail that
the latter law is valid for the rational counterpart of the Haldane-Shastry
chain introduced by Polychronakos.Comment: LaTeX with revtex4, 6 pages, 6 figure
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