Physical processes leading to surface inhomogeneities: the case of rotation

In this lecture I discuss the bulk surface heterogeneity of rotating stars, namely gravity darkening. I especially detail the derivation of the omega-model of Espinosa Lara & Rieutord (2011), which gives the gravity darkening in early-type stars. I also discuss the problem of deriving gravity darkening in stars owning a convective envelope and in those that are members of a binary system.Comment: 23 pages, 11 figure, Lecture given to the school on the cartography of the Sun and the stars (May 2014 in Besan\c{c}on), to appear in LNP, Neiner and Rozelot edts V2: typos correcte

Simulation of static and random errors on Grover's search algorithm implemented in a Ising nuclear spin chain quantum computer with few qubits

We consider Grover's search algorithm on a model quantum computer implemented on a chain of four or five nuclear spins with first and second neighbour Ising interactions. Noise is introduced into the system in terms of random fluctuations of the external fields. By averaging over many repetitions of the algorithm, the output state becomes effectively a mixed state. We study its overlap with the nominal output state of the algorithm, which is called fidelity. We find either an exponential or a Gaussian decay for the fidelity as a function of the strength of the noise, depending on the type of noise (static or random) and whether error supression is applied (the 2pi k-method) or not.Comment: 18 pages, 8 figures, extensive revision with new figure

Broadband probing magnetization dynamics of the coupled vortex state permalloy layers in nanopillars

Broadband magnetization response of coupled vortex state magnetic dots in layered nanopillars was explored as a function of in-plane magnetic field and interlayer separation. For dipolarly coupled circular Py(25 nm)/Cu(20 nm)/Py(25 nm) nanopillars of 600 nm diameter, a small in-plane field splits the eigenfrequencies of azimuthal spin wave modes inducing an abrupt transition between in-phase and out-of-phase kinds of the low-lying coupled spin wave modes. The critical field for this splitting is determined by antiparallel chiralities of the vortices in the layers. Qualitatively similar (although more gradual) changes occur also in the exchange coupled Py(25 nm)/Cu(1 nm)/Py(25 nm) tri-layer nanopillars. These findings are in qualitative agreement with micromagnetic dynamic simulations

Carry a big stick, or no stick at all: punishment and endowment heterogeneity in the trust game

We investigate the effect of costly punishment in a trust game with endowment heterogeneity. Our findings indicate that the difference between the investor and the allocator’s initial endowments determines the effect of punishment on trust and trustworthiness. Punishment fosters trust only when the investor is wealthier than the allocator. Otherwise, punishment fails to promote trusting behavior. As for trustworthiness, the effect is just the opposite. The higher the difference between the investor and the allocator’s initial endowments, the less willing allocators are to pay back. We discuss the consistency of our findings with social preference models (like inequality aversion, reciprocity), the capacity of punishment (i.e., the deterrence hypothesis) and hidden costs of punishment (i.e., models of intrinsic and extrinsic motivation). Our results are hardly coherent with the first two (inequality aversion and deterrence), but roughly consistent with the latter

Observation of propagating edge spin waves modes

The following article appeared in Journal of Applied Physics 114.7 (2013): 213905 and may be found at http://scitation.aip.org/content/aip/journal/jap/114/21/10.1063/1.4839315Broadband magnetization response of equilateral triangular 1000 nm Permalloy dots has been studied under an in-plane magnetic field, applied parallel (buckle state), and perpendicular (Y state) to the triangles base. Micromagnetic simulations identify edge spin waves (E-SWs) in the buckle state as SWs propagating along the two adjacent edges. These quasi one-dimensional spin waves emitted by the vertex magnetic charges gradually transform from propagating to standing due to interference and are weakly affected by dipolar interdot interaction and variation of the aspect ratio. Spin waves in the Y state have a two dimensional character. These findings open perspectives for implementation of the E-SWs in magnonic crystals and thin films.This work has been supported by the Spanish MINECO (MAT2012-32743, CONSOLIDER CSD2007-00010), Comunidad de Madrid (P2009/MAT-1726) and by the U.S. NSF, grant ECCS-0823813 Grants

Microwave-stimulated superconductivity due to presence of vortices

The response of superconducting devices to electromagnetic radiation is a core concept implemented in diverse applications, ranging from the currently used voltage standard to single photon detectors in astronomy. Suprisingly, a sufficiently high power subgap radiation may stimulate superconductivity itself. The possibility of stimulating type II superconductors, in which the radiation may interact also with vortex cores, remains however unclear. Here we report on superconductivity enhanced by GHz radiation in type II superconducting Pb films in the presence of vortices. The stimulation effect is more clearly observed in the upper critical field and less pronounced in the critical temperature. The magnetic field dependence of the vortex related microwave losses in a film with periodic pinning reveals a reduced dissipation of mobile vortices in the stimulated regime due to a reduction of the core size. Results of numerical simulations support the validy of this conclusion. Our findings may have intriguing connections with holographic superconductors in which the possibility of stimulation is under current debateThis work has been supported in parts by Spanish MINECO (MAT2012-32743), and Comunidad de Madrid (NANOFRONTMAG-CM S2013/MIT-2850) and NANO-SC COST-Action MP-1201. A. Lara thanks UAM for FPI-UAM fellowship. The work of A.V.S. was partially supported by Mandat ‘‘d’Impulsion Scientifique’’ of the F.R.S.-FNR

Floristic Composition and Diversity of a Transect in a Locality of the Lowland Evergreen Forest of the Amazon of Cuyabeno City

The present research determined the high diversity and structure of the lowland evergreen forest of the Amazon in a locality (Rey de los Andes) of Cuyabeno city, since there is no updated information on this important biome. The linear transect methodology of 0.1 hectares was applied along the river and separated 2 m from the edge, all trees and shrubs with a diameter at breast height greater than 10 cm were measured, fertile botanical samples were collected and were processed and identified in the CHEP Herbarium. A total of 86 individuals were obtained between trees and shrubs distributed in 20 families, 39 genera, and 41 species, and a basal area of 10.95 m2 was obtained. The dominant family was Fabaceae with seven genera and the most frequent species were Astrocaryum urostachys, Celtis sp., and Leonia crassa. The highest importance value index was 15.56% for Astrocaryum urostachys and 10.33% for Otoba glycycarpa and the Simpson Diversity Index was 0.96. The diameters obtained were classified into 3 diameter classes, where Class I was made up of 68 individuals, which represents 79.07% of the total. It is concluded that the forest of the Rey de los Andes community has a high diversity of tree and shrub species. Likewise, considering the type of vegetation found, list of species, site, and diameters obtained, it can be stated that it is a well-preserved forest. Keywords: Floristic composition, Lowland evergreen forest, Cuyabeno. Resumen La presente investigación determinó la alta diversidad y estructura del bosque siempreverde de tierras bajas de la amazonía de una localidad (Rey de los Andes) del Cantón Cuyabeno; ya que no se cuenta con información actualizada de este importante bioma. Se aplicó la metodología de transecto lineal de 0,1 hectáreas a lo largo del río y separado a dos metros del borde, se midió todos los árboles y arbustos con diámetro a la altura del pecho mayor a 10 centímetros, se recolectó muestras botánicas fértiles y fueron procesadas e identificadas en el Herbario CHEP. Se obtuvo un total de 86 individuos entre árboles y arbustos distribuidos en 20 familias, 39 géneros y 41 especies y se obtuvo un área basal de 10,95 m2; la familia dominante fue Fabaceae con siete géneros y las especies más frecuentes fueron Astrocaryum urostachys, Celtis sp. y Leonia crassa. El Índice de Valor de Importancia más alto fue de 15,56% para Astrocaryum urostachys y de 10,33% para Otoba glycycarpa y el Índice de Diversidad de Simpson fue de 0,96. Los diámetros obtenidos fueron clasificados en 3 clases diamétricas, donde la Clase I estuvo conformada por 68 individuos lo que representa al 79,07% del total. Se concluye que el bosque de la comunidad Rey de los Andes posee una alta diversidad de especies de árboles y arbustos; así mismo tomando en cuenta el tipo de vegetación encontrada, listado de especies, sitio y diámetros obtenidos, se puede manifestar que se trata de un bosque bien conservado. Palabras Clave: Composición florística, Bosque siempreverde, Cuyaben