1,059 research outputs found
New record of <i>Carapus dubius</i> (Carapidae) off Madagascar?
When checking the identification of the Carapidae in the MNHN collection (Muséum National d’Histoire Naturelle, Paris) a specimen of Eurypleuron owasianum (Matsubara, 1953) (MNHN 1992-0914) caught off Madagascar (20°S, 42°30’E) was found to be incorrectly identified. The specimen is vey close to Carapus dubius (Putnam, 1874), which is known from the Eastern Pacific (Markle and Olney, 1990)
Photon-assisted shot noise in graphene in the Terahertz range
When subjected to electromagnetic radiation, the fluctuation of the
electronic current across a quantum conductor increases. This additional noise,
called photon-assisted shot noise, arises from the generation and subsequent
partition of electron-hole pairs in the conductor. The physics of
photon-assisted shot noise has been thoroughly investigated at microwave
frequencies up to 20 GHz, and its robustness suggests that it could be extended
to the Terahertz (THz) range. Here, we present measurements of the quantum shot
noise generated in a graphene nanoribbon subjected to a THz radiation. Our
results show signatures of photon-assisted shot noise, further demonstrating
that hallmark time-dependant quantum transport phenomena can be transposed to
the THz range.Comment: includes supplemental materia
Evolution of Exoplanets and their Parent Stars
Studying exoplanets with their parent stars is crucial to understand their
population, formation and history. We review some of the key questions
regarding their evolution with particular emphasis on giant gaseous exoplanets
orbiting close to solar-type stars. For masses above that of Saturn, transiting
exoplanets have large radii indicative of the presence of a massive
hydrogen-helium envelope. Theoretical models show that this envelope
progressively cools and contracts with a rate of energy loss inversely
proportional to the planetary age. The combined measurement of planetary mass,
radius and a constraint on the (stellar) age enables a global determination of
the amount of heavy elements present in the planet interior. The comparison
with stellar metallicity shows a correlation between the two, indicating that
accretion played a crucial role in the formation of planets. The dynamical
evolution of exoplanets also depends on the properties of the central star. We
show that the lack of massive giant planets and brown dwarfs in close orbit
around G-dwarfs and their presence around F-dwarfs are probably tied to the
different properties of dissipation in the stellar interiors. Both the
evolution and the composition of stars and planets are intimately linked.Comment: appears in The age of stars - 23rd Evry Schatzman School on Stellar
Astrophysics, Roscoff : France (2013
Coupling of Josephson flux-flow oscillators to an external RC load
We investigate by numerical simulations the behavior of the power dissipated
in a resistive load capacitively coupled to a Josephson flux flow oscillator
and compare the results to those obtained for a d.c. coupled purely resistive
load. Assuming realistic values for the parameters R and C, both in the high-
and in the low-Tc case the power is large enough to allow the operation of such
a device in applications.Comment: uuencoded, gzipped tar archive containing 11 pages of REVTeX text + 4
PostScript figures. To appear in Supercond. Sci. Techno
Kink Chains from Instantons on a Torus
We describe how the procedure of calculating approximate solitons from
instanton holonomies may be extended to the case of soliton crystals. It is
shown how sine-Gordon kink chains may be obtained from CP1 instantons on a
torus. These kink chains turn out to be remarkably accurate approximations to
the true solutions. Some remarks on the relevance of this work to Skyrme
crystals are also made.Comment: latex 17 pages, DAMTP 94-7
Contribution de la biologie moléculaire à la sélection animale: les marqueurs génétiques
Avec la domestication des animaux de rente, les Ă©leveurs ont cherchĂ© d'une part, Ă
accroître les performances de leurs animaux en sélectionnant dans la population mise à leur
disposition les sujets les plus performants pour la (les) caractéristique(s) recherchée(s) et
d'autre part, à réduire l'impact des zoonoses en sélectionnant les animaux résistants. Toutefois,
si cette approche de la sélection a permis inconsciemment de favoriser au sein de la
population les génotypes intéressants pour les critères recherchés, il importe de garder en
mémoire que la production et la santé animale résultent non seulement du potentiel génétique
mais Ă©galement d'interactions entre l'alimentation, le statut physiologique, les facteurs environnementaux et le savoir-faire de l'Ă©leveur
Screening current effects in Josephson junction arrays
The purpose of this work is to compare the dynamics of arrays of Josephson
junctions in presence of magnetic field in two different frameworks: the so
called XY frustrated model with no self inductance and an approach that takes
into account the screening currents (considering self inductances only). We
show that while for a range of parameters the simpler model is sufficiently
accurate, in a region of the parameter space solutions arise that are not
contained in the XY model equations.Comment: Figures available from the author
Shot noise generated by graphene p–n junctions in the quantum Hall effect regime
International audienceGraphene offers a unique system to investigate transport of Dirac Fermions at p–n junctions. In a magnetic field, combination of quantum Hall physics and the characteristic transport across p–n junctions leads to a fractionally quantized conductance associated with the mixing of electron-like and hole-like modes and their subsequent partitioning. The mixing and partitioning suggest that a p–n junction could be used as an electronic beam splitter. Here we report the shot noise study of the mode-mixing process and demonstrate the crucial role of the p–n junction length. For short p–n junctions, the amplitude of the noise is consistent with an electronic beam-splitter behaviour, whereas, for longer p–n junctions, it is reduced by the energy relaxation. Remarkably, the relaxation length is much larger than typical size of mesoscopic devices, encouraging using graphene for electron quantum optics and quantum information processing
Switching between dynamic states in intermediate-length Josephson junctions
The appearance of zero-field steps (ZFS’s) in the current-voltage characteristics of intermediate-length overlap-geometry Josephson tunnel junctions described by a perturbed sine-Gordon equation (PSGE) is associated with the growth of parametrically excited instabilities of the McCumber background curve (MCB). A linear stability analysis of a McCumber solution of the PSGE in the asymptotic linear region of the MCB and in the absence of magnetic field yields a Hill’s equation which predicts how the number, locations, and widths of the instability regions depend on the junction parameters. A numerical integration of the PSGE in terms of truncated series of time-dependent Fourier spatial modes verifies that the parametrically excited instabilities of the MCB evolve into the fluxon oscillations characteristic of the ZFS’s. An approximate analysis of the Fourier mode equations in the presence of a small magnetic field yields a field-dependent Hill’s equation which predicts that the major effect of such a field is to reduce the widths of the instability regions. Experimental measurements on Nb-NbxOy-Pb junctions of intermediate length, performed at different operating temperatures in order to vary the junction parameters and for various magnetic field values, verify the physical existence of switching from the MCB to the ZFS’s. Good qualitative, and in many cases quantitative, agreement between analytic, numerical, and experimental results is obtained
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