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| 2. |
- Linke, H, et al.
(författare)
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Quantum ratchets and quantum heat pumps
- 2002
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Ingår i: Applied Physics A: Materials Science & Processing. - : Springer Science and Business Media LLC. - 1432-0630. ; 75:2, s. 237-246
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Tidskriftsartikel (refereegranskat)abstract
- Quantum ratchets are Brownian motors in which the quantum dynamics of particles induces qualitatively new behavior. We review a series of experiments in which asymmetric semiconductor devices of sub-micron dimensions are used to study quantum ratchets for electrons. In rocked quantum-dot ratchets electron-wave interference is used to create a non-linear voltage response, leading to a ratchet effect. The direction of the net ratchet current in this type of device can be sensitively controlled by changing one of the following experimental variables: a small external magnetic field, the amplitude of the rocking force, or the Fermi energy. We also describe a tunneling ratchet in which the current direction depends on temperature. In our discussion of the tunneling ratchet we distinguish between three contributions to the non-linear current-voltage characteristics that lead to the ratchet effect: thermal excitation over energy barriers, tunneling through barriers, and wave reflection from barriers. Finally, we discuss the operation of adiabatically rocked tunneling ratchets as heat pumps.
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| 3. |
- Löfgren, Anneli, et al.
(författare)
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Symmetry of magnetoconductance fluctuations of quantum dots in the nonlinear response regime
- 2006
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 73:23
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the symmetry of magnetoconductance fluctuations of phase-coherent, two-terminal quantum dots in the nonlinear regime of transport. Specifically, we consider open, ballistic quantum dots (electron billiards) with and without symmetry axes parallel and perpendicular to the current direction and formulate a set of novel symmetry relations not observed in devices with lower symmetry. We experimentally confirm these relations, demonstrating that high-quality materials and modern semiconductor technology allow the fabrication of devices with almost perfect symmetry. Small deviations from the intended symmetry, presumably due to impurities and fabrication limitations, do exist and can be detected. We also take into account circuit-induced asymmetries of the measured conductance due to bias-dependent depletion and demonstrate that this effect can be experimentally distinguished from rectification effects that are due to a lack of device symmetry. Some open questions regarding the role of a magnetic field in the nonlinear regime of transport are highlighted.
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| 4. |
- Marlow, CA, et al.
(författare)
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Surviving conduction symmetries in non-linear response
- 2003
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Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036. ; 34:3-6, s. 173-177
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Tidskriftsartikel (refereegranskat)abstract
- In linear response, the electric conductance of mesoscopic, two-terminal devices is symmetric with respect to the direction of an external magnetic field. The conductance symmetry, in general, breaks down in the non-linear regime of transport. Here we consider semiconductor quantum dots and show certain symmetries survive in the non-linear conductance with respect to the bias voltage and magnetic field that can be measured. (C) 2004 Published by Elsevier Ltd.
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| 5. |
- Martin, TP, et al.
(författare)
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The influence of confining wall profile on quantum interference effects in etched Ga0.25In0.75As/InP billiards
- 2003
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Ingår i: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036. ; 34:3-6, s. 179-184
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of the potential profile of etched GaInAs/InP billiards and show that their energy gradients are an order of magnitude steeper than those of surface-gated GaAs/AlGaAs billiards. Previously observed in GaAs/AlGaAs billiards, fractal conductance fluctuations are predicted to be critically sensitive to the billiard profile. Here we show that, despite the increase in energy gradient, the fractal conductance fluctuations persist in the harder GaInAs/InP billiards. (C) 2004 Elsevier Ltd. All rights reserved.
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| 6. |
- Piepoli, MF, et al.
(författare)
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Exercise training meta-analysis of trials in patients with chronic heart failure (ExTraMATCH)
- 2004
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Ingår i: BMJ: British Medical Journal. - 1756-1833. ; 328:7433, s. 189-192
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Tidskriftsartikel (refereegranskat)abstract
- Objective To determine the effect of exercise training on survival in patients with heart failure due to left ventricular systolic dysfunction. Design Collaborative meta-analysis. Inclusion criteria Randomised parallel group controlled trials of exercise training, for at least eight weeks with individual patient data on survival for at least three months. Studies reviewed Nine datasets, totalling 801 patients: 395 received exercise training and 406 were controls. Main outcome measure Death from all causes. Results During a mean (SD) follow up of 705 (729) days there were 88 (22%) deaths in the exercise arm and 105 (26%) in the control arm. Exercise training significantly reduced mortality (hazard ratio 0.65, 95% confidence interval, 0.46 to 0.92; log rank chi(2) = 5.9; P = 0.015). The secondary end point of death or admission to hospital was also reduced (0.72, 0.56 to 0.93; log rank chi(2) = 6.4; P = 0.011). No statistically significant subgroup specific treatment effect was observed. Conclusion Meta-analysis of randomised trials to date gives no evidence that properly supervised medical training programmes for patients with heart failure might be dangerous, and indeed there is clear evidence of an overall reduction in mortality. Further research should focus on optimising exercise programmes and identifying appropriate patient groups to target.
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