A transfer hamiltonian model for devices based on quantum dot arrays.

We present a model of electron transport through a random distribution of interacting quantum dots embedded in a dielectric matrix to simulate realistic devices. The method underlying the model depends only on fundamental parameters of the system and it is based on the Transfer Hamiltonian approach. A set of noncoherent rate equations can be written and the interaction between the quantum dots and between the quantum dots and the electrodes is introduced by transition rates and capacitive couplings. A realistic modelization of the capacitive couplings, the transmission coefficients, the electron/hole tunneling currents, and the density of states of each quantum dot have been taken into account. The effects of the local potential are computed within the self-consistent field regime. While the description of the theoretical framework is kept as general as possible, two specific prototypical devices, an arbitrary array of quantum dots embedded in a matrix insulator and a transistor device based on quantum dots, are used to illustrate the kind of unique insight that numerical simulations based on the theory are able to provide.

Localized self-heating in large arrays of 1D nanostructures.

One dimensional (1D) nanostructures offer a promising path towards highly efficient heating and temperature control in integrated microsystems. The so called self-heating effect can be used to modulate the response of solid state gas sensor devices. In this work, efficient self-heating was found to occur at random networks of nanostructured systems with similar power requirements to highly ordered systems (e.g. individual nanowires, where their thermal efficiency was attributed to the small dimensions of the objects). Infrared thermography and Raman spectroscopy were used to map the temperature profiles of films based on random arrangements of carbon nanofibers during self-heating. Both the techniques demonstrate consistently that heating concentrates in small regions, the here-called "hot-spots". On correlating dynamic temperature mapping with electrical measurements, we also observed that these minute hot-spots rule the resistance values observed macroscopically. A physical model of a random network of 1D resistors helped us to explain this observation. The model shows that, for a given random arrangement of 1D nanowires, current spreading through the network ends up defining a set of spots that dominate both the electrical resistance and power dissipation. Such highly localized heating explains the high power savings observed in larger nanostructured systems. This understanding opens a path to design highly efficient self-heating systems, based on random or pseudo-random distributions of 1D nanostructures.

[Where are we going with neuroimaging?]. / Hacia dónde vamos con la neuroimagen?

UNLABELLED: OBJECTIVE AND DEVELOPMENT: We present a short revision based on the latest advances in magnetic resonance image and its use in daily practice. Ranging from morphological image to functional imaging, including new three-dimensional capabilities applied as a pre-surgical tool. CONCLUSION: We explore its possibilities in brain pathology and psychiatry beyond morphological changes in order to ascertain the biochemical substratum, in some pathologies, with the use of spectroscopy.

Flexible sensor based on carbon nanofibers with multifunctional sensing features.

Herein, we present the fabrication and characterization of a flexible gas sensor based on carbon nanofibers. The sensing device is composed of interdigitated silver electrodes deposited by inkjet printing on Kapton substrates, subsequently coated with carbon nanofibers as sensing element. Gas sensing response to CO, NH3 and humidity has been characterized in detail. Thermal, mechanical and electromagnetic radiation effects have also been studied and discussed from the point of view of the cross-sensitivity. The obtained results open the door for a new generation of flexible sensors with multifunctional sensing features, which are producible with scalable techniques based on low cost nanomaterials.

Residual Stress Relaxation Induced by Mass Transport Through Interface of the Pd/SrTiO3.

Metal interconnections having a small cross-section and short length can be subjected to very large mass transport due to the passing of high current densities. As a result, nonlinear diffusion and electromigration effects which may result in device failure and electrical instabilities may be manifested. Various thicknesses of Pd were deposited over SrTiO3 substrate. Residual stress of the deposited film was evaluated by measuring the variation of d-spacing versus sin2ψ through conventional X-ray diffraction method. It has been found that the lattice misfit within film and substrate might be relaxed because of mass transport. Besides, the relation between residual intrinsic stress and oxygen diffusion through deposited film has been expressed. Consequently, appearance of oxide intermediate layer may adjust interfacial characteristics and suppress electrical conductivity by increasing electron scattering through metallic films.

The effects of electron-hole separation on the photoconductivity of individual metal oxide nanowires.

The responses of individual ZnO nanowires to UV light demonstrate that the persistent photoconductivity (PPC) state is directly related to the electron-hole separation near the surface. Our results demonstrate that the electrical transport in these nanomaterials is influenced by the surface in two different ways. On the one hand, the effective mobility and the density of free carriers are determined by recombination mechanisms assisted by the oxidizing molecules in air. This phenomenon can also be blocked by surface passivation. On the other hand, the surface built-in potential separates the photogenerated electron-hole pairs and accumulates holes at the surface. After illumination, the charge separation makes the electron-hole recombination difficult and originates PPC. This effect is quickly reverted after increasing either the probing current (self-heating by Joule dissipation) or the oxygen content in air (favouring the surface recombination mechanisms). The model for PPC in individual nanowires presented here illustrates the intrinsic potential of metal oxide nanowires to develop optoelectronic devices or optochemical sensors with better and new performances.

[Moyamoya disease among children. An analysis of a series in the Western world and literature review]. / Moyamoya en la poblacion infantil. Analisis de una serie occidental y revision de la bibliografia.

PATIENTS AND METHODS: A total of 12 patients with moyamoya disease or syndrome with a mean age of 6 years were analyzed in a retrospective fashion. RESULTS: Infarction was the most frequent presentation feature (8 out of 12 patients), 2 had epilepsy and 2 were incidental findings. Seven cases were classified as idiopathic while the other five were related to systemic illnesses. Diagnosis was initially made by magnetic resonance angiography in 9 cases, and conventional angiography in 3 cases. Mean follow-up is 5 years; six patients experienced clinical worsening of symptoms, while 6 cases remained clinically stable. However, all of them showed angiographic progression. Four patients underwent revascularization surgery. Two children died due to complications associated with moyamoya disease, and six have moderate handicaps. CONCLUSION: Due to the fact moyamoya disease is not an indolent disorder and readily progress to cause complications, surgical revascularization should always be considered in the management of these patients.

[Neuroimaging of cerebral ischemia]. / Neuroimagen de la isquemia cerebral.

Diagnostic confirmation of cerebral vascular accidents is of particular interest to neurologists because of the therapeutic and prognostic implications which the added social costs, in both the follow up of these patients, as well as the complications which may develop represent. The different diagnostic imaging techniques are presented with emphasis on magnetic resonance, which, given its multisequential capacity, provides not only simple morphologic data, but also information on the complex chemical structure of the cerebral parenchyma by spectroscopy, with the added value of determining excellent delimitations of the cerebral vascular tree. The new diffusion-perfusion techniques amplify the diagnostic sensitivity during the first hours of clinical admission which are crucial for therapeutic decisions to be effective.

[Magnetic resonance++ with gadolinium in Sturge Weber syndrome]. / Resonancia magnética con gadolinium en el síndrome de Sturge Weber.

We report four patients with Sturge Weber syndrome in which the pial angioma was visualized better with Gd-DOTA enhanced MR imaging. MR alone demonstrated thickened cortex with diminished convolutions, abnormal white matter and prominent subependymal veins. However, Gd-DOTA enhanced MR imaging improved the visualization of the angioma, localizing and demonstrating the extent of the malformation in Sturge Weber syndrome. We believe that this is the procedure of choice to recognize the extent of the intracranial involvement and which would help to select those patients that would benefit from surgical treatment.

[Diagnosis of discitis using MRI in children]. / Diagnóstico de la discitis mediante resonancia magnética en el niño.

Two patients developed unsteady gait and presented pathological neurologic signs in lower extremities which lead to suspect an expansive process in the spinal cord. The radiological exploration was normal in both cases. Magnetic resonance imaging resulted in diagnosis of discitis. A revision has been carried out of the different diagnostic procedures and the possible indications for magnetic resonance imaging.