Spin-1/2 Kondo effect in an InAs nanowire quantum dot: the Unitary limit, conductance scaling and Zeeman splitting

We report on a comprehensive study of spin-1/2 Kondo effect in a strongly-coupled quantum dot realized in a high-quality InAs nanowire. The nanowire quantum dot is relatively symmetrically coupled to its two leads, so the Kondo effect reaches the Unitary limit. The measured Kondo conductance demonstrates scaling with temperature, Zeeman magnetic field, and out-of-equilibrium bias. The suppression of the Kondo conductance with magnetic field is much stronger than would be expected based on a g-factor extracted from Zeeman splitting of the Kondo peak. This may be related to strong spin-orbit coupling in InAs.Comment: 12 pages, 7 figures. Revised version accepted for publicatio

Dynamics of capacitively coupled double quantum dots

We consider a double dot system of equivalent, capacitively coupled semiconducting quantum dots, each coupled to its own lead, in a regime where there are two electrons on the double dot. Employing the numerical renormalization group, we focus here on single-particle dynamics and the zero-bias conductance, considering in particular the rich range of behaviour arising as the interdot coupling is progressively increased through the strong coupling (SC) phase, from the spin-Kondo regime, across the SU(4) point to the charge-Kondo regime; and then towards and through the quantum phase transition to a charge-ordered (CO) phase. We first consider the two-self-energy description required to describe the broken symmetry CO phase, and implications thereof for the non-Fermi liquid nature of this phase. Numerical results for single-particle dynamics on all frequency scales are then considered, with particular emphasis on universality and scaling of low-energy dynamics throughout the SC phase. The role of symmetry breaking perturbations is also briefly discussed.Comment: 14 pages, 6 figure

The impact of tensioning device mal-positioning on strand tension during Anterior Cruciate Ligament reconstruction

<p>Abstract</p> <p>Background</p> <p>In order to confer optimal strength and stiffness to the graft in Anterior Cruciate Ligament (ACL) reconstruction, the maintenance of equal strand tension prior to fixation, is desired; positioning of the tensioning device can significantly affect strand tension This study aimed to determine the effect of tensioning device mal-positioning on individual strand tension in simulated cadaveric ACL reconstructions.</p> <p>Methods</p> <p>Twenty cadaveric specimens, comprising bovine tibia and tendon harvested from sheep, were used to simulate ACL reconstruction with a looped four-strand tendon graft. A proprietary tensioning device was used to tension the graft during tibial component fixation with graft tension recorded using load cells. The effects of the tensioning device at extreme angles, and in various locking states, was evaluated.</p> <p>Results</p> <p>Strand tension varied significantly when the tensioning device was held at extreme angles (p < 0.001) or in 'locked' configurations of the tensioning device (p < 0.046). Tendon position also produced significant effects (p < 0.016) on the resultant strand tension.</p> <p>Conclusion</p> <p>An even distribution of tension among individual graft strands is obtained by maintaining the tensioning device in an unlocked state, aligned with the longitudinal axis of the tibial tunnel. If the maintenance of equal strand tension during tibial fixation of grafts is important, close attention must be paid to positioning of the tensioning device in order to optimize the resultant graft tension and, by implication, the strength and stiffness of the graft and ultimately, surgical outcome.</p

Renormalization group study of capacitively coupled double quantum dots

The numerical renormalization group is employed to study a double quantum (DQD) dot system consisting of two equivalent single-level dots, each coupled to its own lead and with a mutual capacitive coupling embodied in an interdot interaction U', in addition to the intradot Coulomb interaction U. We focus on the regime with two electrons on the DQD, and the evolution of the system on increasing U'/U. The spin-Kondo effect arising for U'=0 (SU(2) x SU(2)) is found to persist robustly with increasing U'/U, before a rapid but continuous crossover to (a) the SU(4) point U'=U where charge and spin degrees of freedom are entangled and the Kondo scale strongly enhanced; and then (b) a charge-Kondo state, in which a charge-pseudospin is quenched on coupling to the leads/conduction channels. A quantum phase transition of Kosterlitz-Thouless type then occurs from this Fermi liquid, strong coupling (SC) phase, to a broken symmetry, non-Fermi liquid charge ordered (CO) phase at a critical U'_c. Our emphasis in this paper is on the structure, stability and flows between the underlying RG fixed points, on the overall phase diagram in the (U,U')-plane and evolution of the characteristic low-energy Kondo scale inherent to the SC phase; and on static physical properties such as spin- and charge-susceptibilities (staggered and uniform), including universality and scaling behaviour in the strongly correlated regime. Some exact results for associated Wilson ratios are also obtained.Comment: 27 pages, 12 figure

Single-particle dynamics of the Anderson model: a two-self-energy description within the numerical renormalization group approach

Single-particle dynamics of the Anderson impurity model are studied using both the numerical renormalization group (NRG) method and the local moment approach (LMA). It is shown that a 'two-self-energy' description of dynamics inherent to the LMA, as well as a conventional 'single-self-energy' description, arise within NRG; each yielding correctly the same local single-particle spectrum. Explicit NRG results are obtained for the broken symmetry spectral constituents arising in a two-self-energy description, and the total spectrum. These are also compared to analytical results obtained from the LMA as implemented in practice. Very good agreement between the two is found, essentially on all relevant energy scales from the high-energy Hubbard satellites to the low-energy Kondo resonance.Comment: 12 pages, 6 figure

Bases anatómicas para el estudio de las neurociencias

Hace tiempo nos planteábamos entre los amigos de la Cátedra de Anatomía la necesidad de tener algún elemento que nos permita sentar ciertos conceptos, previo a la realización de los trabajos prácticos. Este elemento no debía tener la amplitud de los clásicos tratados de Neuroanatomía, ni caer tampoco en la simpleza de dar sólo pequeñas ideas aisladas. Era algo con lo que el alumno debía contar para ser utilizado como guía previa a la posterior lectura de algún tratado sobre el tema. Es así como surgió la propuesta de escribir estas líneas, que nosotros consideramos como las: Bases Anatómicas para el estudio de las Neurociencias. Entendiendo por ello, nada más que eso. Son sólo las bases de un gran capítulo, las “Neurociencias”, en una época en estas cobran cada vez mayor importancia. Así nos parece que una formación anatómica sólida, en cuanto al conocimiento de la Neuroanatomía, abre a los estudiantes y jóvenes profesionales las puertas para atravesar la que hasta hace poco se consideraba como la última gran frontera del conocimiento científico.Facultad de Ciencias Médica

Secuestro pulmonar : Importancia anatómo-quirúrgica

Los secuestros pulmonares son malformaciones congénitas de origen mixto bronquial y arterial, no comunicado con la vía aérea, que se caracterizan por una zona de tejido pulmonar embrionario quístico y no funcionante cuya vascularización se hace a través de una arteria sistémica anómala. Es una patología de origen congénita y de baja incidencia un caso cada 1000 nacimientos.Representa el 0,15-6,4% del conjunto de las malformaciones congénitas pulmonares.Facultad de Ciencias Médica

The Transition Between Quantum Coherence and Incoherence

We show that a transformed Caldeira-Leggett Hamltonian has two distinct families of fixed points, rather than a single unique fixed point as often conjectured based on its connection to the anisotropic Kondo model. The two families are distinguished by a sharp qualitative difference in their quantum coherence properties and we argue that this distinction is best understood as the result of a transition in the model between degeneracy and non-degeneracy in the spectral function of the ``spin-flip'' operator.Comment: some typos corrected and a reference adde

Modelo de simulación para el entrenamiento en cirugía videotoracoscópica : Etapa II

El empleo de la cirugía video asistida en la patología torácica se ha convertido en una importante herramienta para el tratamiento de pacientes que tradicionalmente se resolvían con cirugía convencional, lo que convierte a este procedimiento en una opción de utilidad y gran valor en la cirugía actual. A tal efecto es de vital importancia el entrenamiento y aprendizaje básico de la técnica de la cirugía video asistida mediante la utilización de modelos de simulación en técnicas videotoracoscópica.Facultad de Ciencias Médica

Reparos anatomo-quirúrgicos para la realización de una duodenopancreatectomía

Objetivo: Indicar los jalones anatómicos que nos permiten realizar con seguridad una duodenopancreatectomía presentando variantes vasculares que determinan cambios en la táctica quirúrgica.Facultad de Ciencias Médica