Spectral density of an interacting dot coupled indirectly to conducting leads

We study the spectral density of electrons rho in an interacting quantum dot (QD) with a hybridization lambda to a non-interacting QD, which in turn is coupled to a non-interacting conduction band. The system corresponds to an impurity Anderson model in which the conduction band has a Lorentzian density of states of width Delta2. We solved the model using perturbation theory in the Coulomb repulsion U (PTU) up to second order and a slave-boson mean-field approximation (SBMFA). The PTU works surprisingly well near the exactly solvable limit Delta2 -> 0. For fixed U and large enough lambda or small enough Delta2, the Kondo peak in rho(omega) splits into two peaks. This splitting can be understood in terms of weakly interacting quasiparticles. Before the splitting takes place the universal properties of the model in the Kondo regime are lost. Using the SBMFA, simple analytical expressions for the occurrence of split peaks are obtained. For small or moderate Delta2, the side bands of rho(omega) have the form of narrow resonances, that were missed in previous studies using the numerical renormalization group. This technique also has shortcomings for describing properly the split Kondo peaks. As the temperature is increased, the intensity of the split Kondo peaks decreases, but it is not completely suppressed at high temperatures.Comment: 13 pages, 13 figures, accepted in Phys. Rev.

Explicit minimal Scherk saddle towers of arbitrary even genera in R3\R^3

Starting from works by Scherk (1835) and by Enneper-Weierstra\ss \ (1863), new minimal surfaces with Scherk ends were found only in 1988 by Karcher (see \cite{Karcher1,Karcher}). In the singly periodic case, Karcher's examples of positive genera had been unique until Traizet obtained new ones in 1996 (see \cite{Traizet}). However, Traizet's construction is implicit and excludes {\it towers}, namely the desingularisation of more than two concurrent planes. Then, new explicit towers were found only in 2006 by Martin and Ramos Batista (see \cite{Martin}), all of them with genus one. For genus two, the first such towers were constructed in 2010 (see \cite{Valerio2}). Back to 2009, implicit towers of arbitrary genera were found in \cite{HMM}. In our present work we obtain {\it explicit} minimal Scherk saddle towers, for any given genus $2k$, $k\ge3$

Conductance through an array of quantum dots

We propose a simple approach to study the conductance through an array of $N$ 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 $N$, when the parameters are such that electron-hole symmetry is induced, we obtain perfect conductance $G_0=2e^2/h$. The validity of the approach is discussed in detail.Comment: to appear in Phys. Rev.

Manipulating Majorana Fermions in Quantum Nanowires with Broken Inversion Symmetry

We study a Majorana-carrying quantum wire, driven into a trivial phase by breaking the spatial inversion symmetry with a tilted external magnetic field. Interestingly, we predict that a supercurrent applied in the proximate superconductor is able to restore the topological phase and therefore the Majorana end-states. Using Abelian bosonization, we further confirm this result in the presence of electron-electron interactions and show a profound connection of this phenomenon to the physics of a one-dimensional doped Mott-insulator. The present results have important applications in e.g., realizing a supercurrent assisted braiding of Majorana fermions, which proves highly useful in topological quantum computation with realistic Majorana networks.Comment: 5 pages, 3 figures, Supplementary Material is adde

Dissipation-driven superconductor-insulator transition in linear arrays of Josephson junctions capacitively coupled to metallic films

We study the low-temperature properties of linear Josephson-junction arrays capacitively coupled to a proximate two-dimensional diffusive metal. Using bosonization techniques, we derive an effective model for the array and obtain its critical properties and phases at T = 0 using a renormalization group analysis and a variational approach. While static screening effects given by the presence of the metal can be absorbed in a renormalization of the parameters of the array, backscattering originated in the dynamically screened Coulomb interaction produces a non-trivial stabilization of the insulating groundstate and can drive a superconductor-insulator transition. We study the consequences for the transport properties in the low-temperature regime. In particular, we calculate the resisitivity as a function of the temperature and the parameters of the array, and obtain clear signatures of a superconductor-insulator transition that could be observed in experiments.Comment: 10 pages, 5 figures, submitted to Physical Review

Estilos de vida en relación a la alimentación y hábitos alimentarios dentro y

Lobos, G (Lobos, German). Univ Talca, Fac Ciencias Empresariales, Escuela Ingn Comercial, Talca, ChileResumen Objetivo: Distinguir tipologías de consumidores en base a su estilo de vida en relación a la alimentación en las principales comunas de la Región Metropolitana de Santiago, Chile, y caracterizarlas según sus hábitos de consumo de alimentos dentro y fuera del hogar, características sociodemográficas y su nivel de satisfacción con su alimentación. Material y método: Se aplicó un cuestionario estructurado a una muestra de 951 personas en las principales comunas de la Región Metropolitana de Santiago (más de 100.000 habitantes). El instrumento de recogida de información incluyó una adaptación del cuestionario de estilos de vida en relación a la alimentación (FRL) y la escala SWFL (Satisfaction with Food-related Life). Se consultaron los hábitos de consumo de alimentos dentro y fuera del hogar y variables de clasificación sociodemográfica de los encuestados. Resultados: Mediante análisis cluster se distinguieron cinco tipologías con diferencias significativas en los cinco componentes obtenidos del FRL, con análisis factorial de componentes principales. Las tipologías presentaron distinto perfil de género, edad y nivel socioeconómico y difirieron en los puntajes obtenidos en la SWFL. Se diferenciaron en la frecuencia en que la persona almuerza, toma once y cena en su hogar. Respecto a las comidas fuera del hogar, las tipologías se distinguieron según la frecuencia de comidas en restaurantes, locales de comida rápida y en la compra de comida preparada. Conclusiones: Un estilo de vida en relación a la alimentación con baja implicación y disfrute de los alimentos se asocia con un mayor nivel socioeconómico y menor edad de las personas. Adicionalmente, se asocia con comportamientos alimentarios poco saludables y no beneficiosos para las personas, como una mayor frecuencia de comidas en restaurantes y de compra de comida preparada, junto a una menor frecuencia de comidas en el hogar, lo que estaría influyendo en un nivel inferior de satisfacción con la alimentación

Aceptación de una hortaliza con denominación de origen en dos ciudades del sur de Chile

Considering that the regional origin of foods can increase consumer acceptance, the relative importance of the designation of origin (DO) in the decision to purchase tomatoes in Temuco and Puerto Montt, Chile was evaluated, consumer segments were distinguished according to their preferences by administering a survey to 400 people. A conjoint analysis was used to determine that the variety of tomato (41.8%) was more important than DO (19.5%) and price (17.0%). Presentation and size were the least important attributes. Consumers preferred long-life tomatoes and in bunch, with Angol DO at the lowest price. A hierarchical cluster analysis distinguished three segments. The first (52.5%) was sensitive to variety. The second (13.0%) was also sensitive to variety, but they preferred to pay the highest price. The third (34.5%) was sensitive to price. All three segments preferred the tomato with Angol DO. The segments differed significantly according to gender, size of family group and level of satisfaction with their food-related life. The results indicate a good acceptance of tomatoes with Angol DO; however, particular relevance must be given to the variety of tomato produced.Considerando que la región de origen de los alimentos puede aumentar la aceptación de los consumidores, se evaluó la importancia relativa de la información referida a la denominación de origen (DO) en la decisión de compra de tomates en Temuco y Puerto Montt, Chile, y se diferenciaron segmentos de consumidores según sus preferencias, mediante una encuesta a 400 personas. Utilizando análisis conjunto se determinó que la variedad de tomate (41,8%) fue más importante que la DO (19,5%) y el precio (17,0%). La presentación y el tamaño fueron atributos poco importantes. Los consumidores prefirieron tomate larga vida y en racimo, con DO de Angol, al menor precio. Mediante análisis de conglomerados jerárquicos se diferenciaron tres segmentos. El primero (52,5%) fue sensible a la variedad. El segundo (13,0%) también fue sensible a la variedad, pero prefirieron pagar el precio más elevado. El tercero (34,5%) fue sensible al precio. Los tres segmentos prefirieron el tomate con DO de Angol. Los segmentos se diferenciaron significativamente según género, tamaño del grupo familiar y nivel de satisfacción con su alimentación. Los resultados indican buena aceptación hacia tomates con DO de Angol, sin embargo, se debe dar especial relevancia a la variedad de tomate a producir.Fil: Schnettler, Berta. Universidad de La Frontera (Chile). Facultad de Ciencias Agropecuarias y Forestales. Departamento de Producción Agropecuaria.Fil: Pihán, Rodolfo. Universidad de La Frontera (Chile). Facultad de Ciencias Agropecuarias y Forestales. Departamento de Producción Agropecuaria.Fil: Valdevenito, Ana. Universidad de La Frontera (Chile). Facultad de Ciencias Agropecuarias y Forestales. Departamento de Producción Agropecuaria.Fil: Miranda, Horacio. Universidad de La Frontera (Chile). Facultad de Ciencias Agropecuarias y Forestales. Departamento de Producción Agropecuaria.Fil: Lobos, Germán. Universidad de Talca (Chile)Fil: Grunert, Klaus G.. Universidad de Aarhus (Dinamarca

Aislamiento de bacterias periodontopáticas desde hemocultivos y ateromas obtenidos de pacientes con aterosclerosis y periodontitis

Carlos Padilla E. Laboratorio de Investigación Microbiológica, Facultad de Ciencias de la Salud, Universidad de Talca. Talca. Chile. Fono: 71-200492. Fax: 71-200439. E mail: [email protected]: Periodontitis is a common oral disease produced by bacterial species that reside in the subgingival plaque. These microorganisms have been associated to atherosclerosis and it is suggested that periodontitis is a cardiovascular risk factor. Aim: To isolate periodontal bacteria from blood and atheroma samples, from patients with atherosclerosis and periodontitis. Material and methods: Twelve patients with periodontitis and a clinical diagnosis of atherosclerosis and 12 patients with periodontitis but without atherosclerosis were studied. Blood samples were obtained immediately before and after scaling and root planing. The samples were incubated in aerobic and anaerobic conditions. One week after scaling, atheromatous plaques were obtained during endarterectomy in the 12 patients with atherosclerosis. These were homogenized and cultured for aerobic and anaerobic bacteria. Microorganisms were identified by means ofPCR. Results: Five patients with and two without atherosclerosis, had bacteremia after scaling and root planing. Bacterial species isolated from blood samples were the same found in periodontic pockets. Four atheromatous plaques of patients with bacteremia yielded positive cultures. The isolated bacteria were the same found in blood samples and periodontal pockets. Conclusions: Bacteremia occurred in seven of 24 patients after scaling and root planing. In four patients, the same species found in periodontic pockets and blood cultures were detected in atherosclerotic plaques obtained one week after the dental procedure