Electron Transport through Nanosystems Driven by Coulomb Scattering

Electron transmission through nanosystems is blocked if there are no states connecting the left and the right reservoir. Electron-electron scattering can lift this blockade and we show that this feature can be conveniently implemented by considering a transport model based on many-particle states. We discuss typical signatures of this phenomena, such as the presence of a current signal for a finite bias window.Comment: final version, to appear in Physical Beview B (6 pages and 6 figures included in text, simulation details added and discussion clarified in comparison to first version

Optimal control of ventilation system

Hoy en día la mayoría de los sistemas de ventilación en uso se calibran manualmente. Teniendo en cuenta esto con la necesidad de asegurar buena ventilación en todas las oficinas, normalmente los sistemas funcionan a mayor capacidad de la necesaria. Debido a esto se puede conseguir ahorrar energía introduciendo estrategias de control con la objetivo de asegurar una buena ventilación al mínimo consumo. Para lograr esto, sistemas de ventilación con válvulas controlables han sido consideradas en este proyecto. Estrategias de control optimas dan los requerimientos necesarios con el mínimo consumo de energía para cada situación. Para realizar este control, el primer paso es saber las ecuaciones del sistema y como funcionan estos sistemas. Para implementar el control tienen que conocerse los parámetros que lo gobiernan. Algunos parámetros como los de los ventiladores y las válvulas son conocidos pero otros como las perdidas de carga en las tuberías pueden no ser conocidos. Por lo tanto los parámetros no conocidos tienen que ser estimados. En este proyecto el objetivo es diseñar como estimar los parámetros de sistemas de ventilación. Cuando los parámetros son conocidos, el sistema puede ser conducido a trabajar con un mínimo consumo para cada situación. De esta manera se alcanzará mayor eficiencia en estos sistemas

Dynamic Coupling of Piezoelectric Effects, Spontaneous Polarization, and Strain in Lattice-Mismatched Semiconductor Quantum-Well Heterostructures

A static and dynamic analysis of the combined and self-consistent influence of spontaneous polarization, piezoelectric effects, lattice mismatch, and strain effects is presented for a three-layer one-dimensional AlN/GaN wurtzite quantum-well structure with GaN as the central quantum-well layer . It is shown that, contrary to the assumption of Fonoberov and Balandin [J. Appl. Phys. 94, 7178 (2003); J. Vac. Sci. Technol. B 22, 2190 (2004)], even in cases with no current transport through the structure, the strain distributions are not well captured by minimization of the strain energy only and not, as is in principle required, the total free energy including electric and piezoelectric coupling and spontaneous polarization contributions. Furthermore, we have found that, when an ac signal is imposed through the structure, resonance frequencies exist where strain distributions are even more strongly affected by piezoelectric-coupling contributions depending on the amount of mechanical and electrical losses in the full material system

Coherent Transport through an interacting double quantum dot: Beyond sequential tunneling

Various causes for negative differential conductance in transport through an interacting double quantum dot are investigated. Particular focus is given to the interplay between the renormalization of the energy levels due to the coupling to the leads and the decoherence of the states. The calculations are performed within a basis of many-particle eigenstates and we consider the dynamics given by the von Neumann-equation taking into account also processes beyond sequential tunneling. A systematic comparison between the levels of approximation and also with different formalisms is performed. It is found that the current is qualitatively well described by sequential processes as long as the temperature is larger than the level broadening induced by the contacts.Comment: 11 pages, 5 figures included in tex

Longitudinal trajectory patterns of plasma albumin and C-reactive protein levels around diagnosis, relapse, bacteraemia, and death of acute myeloid leukaemia patients

BACKGROUND: No study has evaluated C-reactive protein (CRP) and plasma albumin (PA) levels longitudinally in patients with acute myeloid leukaemia (AML). METHODS: We studied defined events in 818 adult patients with AML in relation to 60,209 CRP and PA measures. We investigated correlations between CRP and PA levels and daily CRP and PA levels in relation to AML diagnosis, AML relapse, or bacteraemia (all ±30 days), and death (─30-0 days). RESULTS: On the AML diagnosis date (D0), CRP levels increased with higher WHO performance score (PS), e.g. patients with PS 3/4 had 68.1 mg/L higher CRP compared to patients with PS 0, adjusted for relevant covariates. On D0, the PA level declined with increasing PS, e.g. PS 3/4 had 7.54 g/L lower adjusted PA compared to PS 0. CRP and PA levels were inversely correlated for the PA interval 25-55 g/L (R = - 0.51, p < 10-5), but not for ≤24 g/L (R = 0.01, p = 0.57). CRP increases and PA decreases were seen prior to bacteraemia and death, whereas no changes occurred up to AML diagnosis or relapse. CRP increases and PA decreases were also found frequently in individuals, unrelated to a pre-specified event. CONCLUSIONS: PA decrease is an important biomarker for imminent bacteraemia in adult patients with AML.publishersversionpublishe

The Ben Daniel-Duke model in general nanowire structures

A simple computationally effective method is developed for solving the Ben Daniel - Duke equations for nanowire semiconductor heterostructures. The method allows eigenstates and associated energy levels of nanowires with varying cross- sectional shape and/ or varying composition to be obtained, and is based on expanding the envelope function eigenstates on local eigenstates of the corresponding cross- sectional problem. In this way, the original partial differential equation problem is reduced to a set of coupled ordinary differential equations ( this set can to a good approximation be limited to a small number of coupled equations). In the first part of the paper, the model equation framework is derived; it can be easily modified to account for a more general set of partial differential equations. In the second part of the paper, three different cases of axisymmetrical nanowire problems are analysed in terms of eigenstates and energy eigenvalues. The cases considered are ( a) conical nanowires, ( b) a nanowire with a step in radius, and ( c) a conical GaAs/ GaAlAs nanowire. Comparison with computationally more expensive finite- element results on a two- dimensional domain is made, and good agreement is found