1,078 research outputs found
Bistability of persistent currents in mesoscopic rings
We study the persistent currents flowing in a mesoscopic ring threaded by a
magnetic flux and connected to a stub of finite length. Multistability
processes and Coulomb blockade are demonstrated to be present in this system.
These properties are functions of the magnetic flux crossing the ring which
plays the role that the external applied potential fulfills in the
multistability behaviour of the standard mesoscopic heterostructures.Comment: 13 pages (Revtex), 4 PostScript figures. Send e-mail to:
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Multiple dinosaur egg-shell occurrence in an Upper Cretaceous nesting site from Patagonia
The discovery of hundreds of megaloolithid-type egg-clutches (some including embryos of an indeterminate species of titanosaur sauropods) in several stratigraphical levels of the Late Cretaceous nesting site of Auca Mahuevo (Chiappe et al., 2005) unveiled important aspects of the reproductive behavior of sauropod dinosaurs and stimulated further work at other Patagonian dinosaur egg sites. In November of 2003, a join expedition of the National University of Comahue (Neuquén), the Museo Carmen Funes (Plaza Huincul) and the Museo de Lamarque (Lamarque) conducted fieldwork in several Late Cretaceous localities of Bajo Santa Rosa (center-north RÃo Negro Province, Argentina) bearing the remains of dinosaur eggs and other terrestrial vertebrates (figure 1). The main focus of this expedition was to assess the diversity of dinosaur eggs, to fine-tune the stratigraphy of the egg-bearing layers, and to document the spatial distribution of the egg-clutches. The overall results of this research were reported elsewhere (Salgado et al., 2007). In this contribution, we make focus in one of the fossil localities worked, Berthe IV, where the association of egg clutches likely belonging to different dinosaur species was detected (figure 1.2). Collected eggshells were observed with a binocular loupe ‘‘Stemi SV6 Zeiss’’, at magnifications of x1.0 and x3.2 (for macrocharacters). Microcharacters were observed in transverse thin section using a polarizing microscope (‘‘Zeiss Axioplan’’) at magnifications of x0.4 and x10. The eggshells were photographed using this polarizing microscope equipped with a digital camera. Prior to analysis, the eggshells were submitted to a process of cleaning using ultrasound (see Salgado et al., 2007 for further methodological details).Fil: Coria, Rodolfo Anibal. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Provincia del Neuquen. Municipalidad de Plaza Huincul. Museo "Carmen Funes"; ArgentinaFil: Salgado, Leonardo. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Museo de Geologia y Paleontologia; ArgentinaFil: Chiappe, Luis M.. Los Angeles County Museum of Natural
History. Dinosaur Institute; Estados Unido
Conductance through an array of quantum dots
We propose a simple approach to study the conductance through an array of
interacting quantum dots, weakly coupled to metallic leads. Using a mapping to
an effective site which describes the low-lying excitations and a slave-boson
representation in the saddle-point approximation, we calculated the conductance
through the system. Explicit results are presented for N=1 and N=3: a linear
array and an isosceles triangle. For N=1 in the Kondo limit, the results are in
very good agreement with previous results obtained with numerical
renormalization group (NRG). In the case of the linear trimer for odd , when
the parameters are such that electron-hole symmetry is induced, we obtain
perfect conductance . The validity of the approach is discussed in
detail.Comment: to appear in Phys. Rev.
Juravenator starki (reptilia, theropoda), ein neuer Raubdinosaurier aus dem Oberjura der Südlichen Frankenalb (Süddeutschland): Skelettanatomie und Weichteilbefunde = Juravenator starki (reptilia), a new theropod dinosaur from the Upper Jurassic of the Southern Franconian Alb (Southern Germany) : skeletal anatomy and soft tissue
Effect of topology on the transport properties of two interacting dots
The transport properties of a system of two interacting dots, one of them
directly connected to the leads constituting a side-coupled configuration
(SCD), are studied in the weak and strong tunnel-coupling limits. The
conductance behavior of the SCD structure has new and richer physics than the
better studied system of two dots aligned with the leads (ACD). In the weak
coupling regime and in the case of one electron per dot, the ACD configuration
gives rise to two mostly independent Kondo states. In the SCD topology, the
inserted dot is in a Kondo state while the side-connected one presents Coulomb
blockade properties. Moreover, the dot spins change their behavior, from an
antiferromagnetic coupling to a ferromagnetic correlation, as a consequence of
the interaction with the conduction electrons. The system is governed by the
Kondo effect related to the dot that is embedded into the leads. The role of
the side-connected dot is to introduce, when at resonance, a new path for the
electrons to go through giving rise to the interferences responsible for the
suppression of the conductance. These results depend on the values of the
intra-dot Coulomb interactions. In the case where the many-body interaction is
restricted to the side-connected dot, its Kondo correlation is responsible for
the scattering of the conduction electrons giving rise to the conductance
suppression
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