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T Amand

Publications and source records attributed to T Amand.

10 recordsLinked to original sources

Electrical control of hole spin relaxation in charge tunable InAs/GaAs quantum dots.

We report on optical orientation of singly charged excitons (trions) in charge-tunable self-assembled InAs/GaAs quantum dots. When the charge varies from 0 to -2, the trion photoluminescence of a single quantum dot shows up and under quasiresonant excitation gets progressively polarized from zero to approximately 100%. This behavior is interpreted as the electric control of the trion thermalization process, which subsequently acts on the hole-spin relaxation driven in nanosecond time scale by the anisotropic electron-hole exchange. This is supported by the excitation spectroscopy and time-resolved measurements of a quantum dot ensemble.

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Direct observation of the electron spin relaxation induced by nuclei in quantum dots.

We have studied the electron spin relaxation in semiconductor InAs/GaAs quantum dots by time-resolved optical spectroscopy. The average spin polarization of the electrons in an ensemble of p-doped quantum dots decays down to 1/3 of its initial value with a characteristic time T(Delta) approximately 500 ps, which is attributed to the hyperfine interaction with randomly oriented nuclear spins. We show that this efficient electron spin relaxation mechanism can be suppressed by an external magnetic field as small as 100 mT.

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Optically driven spin memory in n-doped InAs-GaAs quantum dots.

We show that the spin state of the resident electron in an n-doped self-assembled InAs-GaAs quantum dot can be written and read using nonresonant, circularly polarized optical pumping. A simple theoretical model is presented and accounts for the remarkable dynamics producing counterpolarized photoluminescence.

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Levels of inflammatory markers in the blood processed by autotransfusion devices during cardiac surgery associated with cardiopulmonary bypass circuit.

Intraoperative blood salvage devices allowing a reinfusion of red blood cells (RBCs) after processing of shed blood and stagnant blood in the mediastinal cavity are more and more used to reduce homologous blood requirements in cardiac surgery with cardiopulmonary bypass (CPB). As the proinflammatory activity of the shed blood also contributes to morbidity during CPB, we conducted a prospective study in order to examine the quality of autologous blood before and after processing with five different devices [BRAT2, Sequestra, Compact Advanced, Cell Saver 5 (CS5), Continuous Autologous Transfusion System (CATS)]. All systems resulted in an excellent haemoconcentration, ranging from 53.7% (Compact) to 68.9% (CATS). The concentrations and elimination rates of several inflammatory markers [IL-1beta, IL-2, IL-8, TNFalpha, myeloperoxidase (MPO), elastase] were examined. Except for the Sequestra, an important increase in concentration of IL-1beta (between 30% and 220%) has been observed after processing with each device. In contrast, the attenuation rate of IL-6 and TNFalpha (95%) was optimal for all investigated blood salvages systems. Regarding IL-8, only the CATS and CS5 systems were able to attenuate this biological parameter with an excellent efficacy. The rate of attenuation in MPO and elastase, as markers of leukocyte activation, was higher than 80% for all devices. In conclusion, the different RBC washing systems tested in this study resulted in a significant attenuation of the inflammatory response. Increased levels of IL-1beta after processing remained, however, unclear. According to the type of protocol, based on inlet haematocrit, fill and wash speeds, and wash volumes, small variations in reducing the inflammatory response have been observed from one device to another.

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Spin relaxation quenching in semiconductor quantum dots.

We have studied the spin dynamics in self-organized InAs/GaAs quantum dots by time-resolved photoluminescence performed under strictly resonant excitation. At low temperature, we observe strictly no decay of both the linear and the circular luminescence polarization. This demonstrates that the carrier spins are totally frozen on the exciton lifetime scale.

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