Controlling spin in an electronic interferometer with spin-active interfaces

We consider electronic current transport through a ballistic one-dimensional quantum wire connected to two ferromagnetic leads. We study the effects of the spin-dependence of interfacial phase shifts (SDIPS) acquired by electrons upon scattering at the boundaries of the wire. The SDIPS produces a spin splitting of the wire resonant energies which is tunable with the gate voltage and the angle between the ferromagnetic polarizations. This property could be used for manipulating spins. In particular, it leads to a giant magnetoresistance effect with a sign tunable with the gate voltage and the magnetic field applied to the wire.Comment: 5 pages, 3 figures. to be published in Europhysics Letter

Crossidium geheebii (Pottiaceae, Bryophyta), un nuevo registro para el continente americano

Background and Aims: Although the bryoflora of Argentina has been extensively studied, there are still environments to explore and taxa to record. The objective of this work was to report a new record, Crossidium geheebii, for the American continent.Methods: Specimens were collected in the Argentine Patagonia. Using an optical microscope, the morphology and anatomy of the leaves, stems and sporophytes were observed.Key results: A brief description, discussion, distribution map and illustration of the reported species are presented. Moreover, a key to identify the species of the genus Crossidium with distribution in America is included.Conclusions: Crossidium geheebii is reported for the first time for the American continent.Antecedentes y Objetivos: Aunque la brioflora de Argentina ha sido extensamente estudiada, aún quedan ambientes por explorar y taxones que deberán registrarse. El objetivo de este trabajo fue reportar un nuevo registro, Crossidium geheebii, para el continente americano. Métodos: Los especímenes fueron recolectados en la Patagonia argentina. Empleando un microscopio óptico se observó la morfología y anatomía de las hojas, tallos y esporofitos.Resultados clave: Se presenta una breve descripción, discusión, mapa de distribución e ilustración de la especie reportada. También se incluye una clave para identificar las especies del género Crossidium, con distribución en América.Conclusiones: Se registra por primera vez a Crossidium geheebii para el continente americano

Positive cross-correlations in a three-terminal quantum dot with ferromagnetic contacts

We study current fluctuations in an interacting three-terminal quantum dot with ferromagnetic leads. For appropriately polarized contacts, the transport through the dot is governed by a novel dynamical spin blockade, i.e., a spin-dependent bunching of tunneling events not present in the paramagnetic case. This leads for instance to positive zero-frequency cross-correlations of the currents in the output leads even in the absence of spin accumulation on the dot. We include the influence of spin-flip scattering and identify favorable conditions for the experimental observation of this effect with respect to polarization of the contacts and tunneling rates.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Manipulating the Quantum State of an Electrical Circuit

We have designed and operated a superconducting tunnel junction circuit that behaves as a two-level atom: the ``quantronium''. An arbitrary evolution of its quantum state can be programmed with a series of microwave pulses, and a projective measurement of the state can be performed by a pulsed readout sub-circuit. The measured quality factor of quantum coherence Qphi=25000 is sufficiently high that a solid-state quantum processor based on this type of circuit can be envisioned.Comment: 4 figures include

Conserved spin and orbital phase along carbon nanotubes connected with multiple ferromagnetic contacts

We report on spin dependent transport measurements in carbon nanotubes based multi-terminal circuits. We observe a gate-controlled spin signal in non-local voltages and an anomalous conductance spin signal, which reveal that both the spin and the orbital phase can be conserved along carbon nanotubes with multiple ferromagnetic contacts. This paves the way for spintronics devices exploiting both these quantum mechanical degrees of freedom on the same footing.Comment: 8 pages - minor differences with published versio

Un protocolo de tinción mejorado para la visualización de micorrizas arbusculares en briofitas.

The most accepted method for staining arbuscular mycorrhiza (AM) in vascular plants has been one proposed by Phillips & Hayman in 1970. In particular, for the study of AM in bryophytes (s.l.) [Anthocerotophyta, Bryophyta (s.s.), Marchantiophyta] some authors have introduced modifications to this technique. Even though all these protocols stain AM, their main disadvantage is related to the result of material maceration (e.g. over-softening or completely destroying plant cells due to the high temperatures used, the high concentrations of reagents or the long-term exposure to aggressive chemicals). In order to optimise the results for the observation of AM in this group of plants, a modification is presented to the traditional staining technique. In the protocol here proposed, 70% ethanol is used as fixative and first clarifier, 1% potassium hydroxide (KOH) (80 °C, 20 min) as a second clarifier; 1% hydrochloric acid (HCl) (50 °C, 10 min) as an acidifier and 0.05% trypan blue (60 °C, 20 min) for dyeing. This improved protocol is not destructive, it is fast to perform and it is of wide application since it allows staining the AM in bryophytes.Un protocolo de tinción mejorado para la visualización de micorrizas arbusculares en briofitas. El método tradicional más aceptado para la tinción de micorrizas arbusculares (MA) en plantas vasculares es el propuesto por Phillips & Hayman en 1970. En particular, para el estudio de las MA en briofitas (s.l.) [Anthocerotophyta, Bryophyta (s.s.), Marchantiophyta] algunos autores introdujeron modificaciones a esta técnica. Aunque todos estos protocolos tiñen las MA, su principal desventaja está relacionada con el resultado de la maceración del material (e.g. reblandecimiento excesivo o destrucción de las células vegetales por altas temperaturas utilizadas, altas concentraciones de reactivos o exposición prolongada a sustancias químicas agresivas). Para optimizar la observación de las MA en briofitas (s.l.), se desarrolló una adaptación a la técnica de tinción tradicional y sus modificaciones. En el protocolo aquí propuesto, se usa etanol 70% para fijar y como primer clarificador, hidróxido de potasio (KOH) 1% (80 °C, 20 min) como segundo clarificador; ácido clorhídrico (HCl) 1% (50 °C, 10 min) como acidificante y azul de tripán 0,05% (60 °C, 20 min) para teñir. Este protocolo mejorado no es destructivo, es rápido de realizar y es de amplia aplicación ya que permite teñir las MA en briófitas (s.l.)

MUSGOS, SUS PARIENTES Y ASOCIADOS: ¿Conocemos toda la diversidad vegetal que habita la Patagonia? La respuesta es no y aquí se invita a conocer a unas plantas olvidadas: las briofitas.

En este artículo se repasan las características distintivas de las briofitas, su importancia ecológica, sus asociaciones y la forma de estudiarlas. Además, se muestra un ejemplo de investigación realizado en la Patagonia argentina, donde se mencionan algunos de los resultados más destacados que se obtuvieron. Entre ellos se encuentran el relevamiento de 235 especies de briofitas, de las cuales 99 presentan novedades de diversidad, desde continentales hasta regionales. Respecto a la presencia de micorrizas, se encontró únicamente en 11 de las 235 especies sin embargo se observaron estructuras fúngicas en 176 de las especies estudiadas. ARK: ark:/s26185385/kkor9q93

Modeling a Schottky-barrier carbon nanotube field-effect transistor with ferromagnetic contacts

In this study, a model of a Schottky-barrier carbon nanotube field- effect transistor (CNT-FET), with ferromagnetic contacts, has been developed. The emphasis is put on analysis of current-voltage characteristics as well as shot (and thermal) noise. The method is based on the tight-binding model and the non- equilibrium Green's function technique. The calculations show that, at room temperature, the shot noise of the CNT FET is Poissonian in the sub-threshold region, whereas in elevated gate and drain/source voltage regions the Fano factor gets strongly reduced. Moreover, transport properties strongly depend on relative magnetization orientations in the source and drain contacts. In particular, one observes quite a large tunnel magnetoresistance, whose absolute value may exceed 50%.Comment: 8 pages, 4 figure

Global stability of vortex solutions of the two-dimensional Navier-Stokes equation

Both experimental and numerical studies of fluid motion indicate that initially localized regions of vorticity tend to evolve into isolated vortices and that these vortices then serve as organizing centers for the flow. In this paper we prove that in two dimensions localized regions of vorticity do evolve toward a vortex. More precisely we prove that any solution of the two-dimensional Navier-Stokes equation whose initial vorticity distribution is integrable converges to an explicit self-similar solution called ``Oseen's vortex''. This implies that the Oseen vortices are dynamically stable for all values of the circulation Reynolds number, and our approach also shows that these vortices are the only solutions of the two-dimensional Navier-Stokes equation with a Dirac mass as initial vorticity. Finally, under slightly stronger assumptions on the vorticity distribution, we also give precise estimates on the rate of convergence toward the vortex.Comment: 35 pages, no figur