Few-Particle Effects in Semiconductor Quantum Dots: Observation of Multi-Charged-Excitons

We investigate experimentally and theoretically few-particle effects in the optical spectra of single quantum dots (QDs). Photo-depletion of the QD together with the slow hopping transport of impurity-bound electrons back to the QD are employed to efficiently control the number of electrons present in the QD. By investigating structurally identical QDs, we show that the spectral evolutions observed can be attributed to intrinsic, multi-particle-related effects, as opposed to extrinsic QD-impurity environment-related interactions. From our theoretical calculations we identify the distinct transitions related to excitons and excitons charged with up to five additional electrons, as well as neutral and charged biexcitons.Comment: 4 pages, 4 figures, revtex. Accepted for publication in Physical Review Letter

Enhancement of the Binding Energy of Charged Excitons in Disordered Quantum Wires

Negatively and positively charged excitons are identified in the spatially-resolved photoluminescence spectra of quantum wires. We demonstrate that charged excitons are weakly localized in disordered quantum wires. As a consequence, the enhancement of the "binding energy" of a charged exciton is caused, for a significant part, by the recoil energy transferred to the remaining charged carrier during its radiative recombination. We discover that the Coulomb correlation energy is not the sole origin of the "binding energy", in contrast to charged excitons confined in quantum dots.Comment: 4 Fig

Carrier relaxation in GaAs v-groove quantum wires and the effects of localization

Carrier relaxation processes have been investigated in GaAs/AlGaAs v-groove quantum wires (QWRs) with a large subband separation (46 meV). Signatures of inhibited carrier relaxation mechanisms are seen in temperature-dependent photoluminescence (PL) and photoluminescence-excitation (PLE) measurements; we observe strong emission from the first excited state of the QWR below ~50 K. This is attributed to reduced inter-subband relaxation via phonon scattering between localized states. Theoretical calculations and experimental results indicate that the pinch-off regions, which provide additional two-dimensional confinement for the QWR structure, have a blocking effect on relaxation mechanisms for certain structures within the v-groove. Time-resolved PL measurements show that efficient carrier relaxation from excited QWR states into the ground state, occurs only at temperatures > 30 K. Values for the low temperature radiative lifetimes of the ground- and first excited-state excitons have been obtained (340 ps and 160 ps respectively), and their corresponding localization lengths along the wire estimated.Comment: 9 pages, 8 figures, submitted to Phys. Rev. B Attempted to correct corrupt figure

Cross-cultural adaptation, reliability, internal consistency and validation of the Trinity Amputation and Prosthetic Experience Scales-Revised (TAPES-R) for French speaking patients with lower limb amputation

AimThe aim of this study was the French cross-cultural adaptation and validation of The Trinity Amputation and Prosthetic Experience Scales-Revised (TAPES-R-F), in a lower limb amputation population. This self-reported multidimensional amputee-specific questionnaire [1] evaluates with 33 items psychosocial adjustment (3 subscales), activity restriction (1 subscale) and satisfaction with prosthesis (2 subscales).Patients and methodsOne hundred and twenty-nine patients with a mean age of 62 years and with lower limb amputations for at least 1 year were recruited in 5 clinical centers. Translation and cross-cultural adaptation were made according to international guidelines. Internal consistency of each subscale was measured with Cronbach's alpha. Test-retest reliability was assessed by intraclass correlation in a sub- group of 24 subjects who completed the TAPES-R twice with an interval of 7 days. Construct validity was estimated through correlations with 2 main components of SF-36 (MCS, PCS). Correlations were also calculated with 3 scales of the Brief Pain Inventory (BPI).ResultsCronbach's alpha was high, ranging from 0.85 to 0.95. Reliability was acceptable to high (ICC=0.72 to 0.91) for all subscales with the exception of the Social adjustment (ICC=0.67) and Adjustment to limitation (ICC=0.42) subscales. The 2 component of SF-36 was significantly correlated with all subscales (PCS: r=0.24 to 0.66); MCS: r=0.30 to 0.58), except with aesthetic satisfaction and adjustment to limitation. Regarding the BPI, significant correlations were found for all subscales (r=–0.20 to –0.68) with the exception of adjustment to limitation. Ceiling or floor effects (>15%) were found for all but Activity Restriction and Functional Satisfaction Scales.DiscussionThe TAPES-R-F has acceptable psychometric properties for most of its subscales. Our results may suggest that the French version is more useful in a population research perspective than in an individual perspective. Other studies are necessary to clarify the role and the psychometric properties of this measurement

Mott transition from a diluted exciton gas to a dense electron-hole plasma in a single V-shaped quantum wire

We report on the study of many-body interactions in a single high quality V-shaped quantum wire by means of continuous and time-resolved microphotoluminescence. The transition from a weakly interacting exciton gas when the carrier density n is less than 10^5 cm^-1 (i.e. n aX < 0.1, with aX the exciton Bohr radius), to a dense electron-hole plasma (n > 10^6 cm^-1, i.e. n aX > 1) is systematically followed in the system as the carrier density is increased. We show that this transition occurs gradually : the free carriers first coexist with excitons for n aX > 0.1, then the electron-hole plasma becomes degenerate at n aX = 0.8. We also show that the non-linear effects are strongly related to the kind of disorder and localization properties in the structure especially in the low density regime.Comment: 5 figure

Creation of a brochure for amputees: Living with an amputation.

A lower limb amputation is a major event for a patient with many questions arising for him and his family. Individual and environmental factors could influence patient's quality of life and adaptation to amputation. Most of the time brochures concern post operative care after limb amputation (surgery type, stump medical care, prosthetics…). Rehabilitation is often only briefly dealt with these brochures. OBJECTIVES OF THIS STUDY: (1) To write a brochure specifically concerning rehabilitation for lower limb amputees. (2) To assess patients' opinion and satisfaction concerning the relevance and quality of this brochure. (1) Creation of a multidisciplinary team. Creation of a brochure concerning rehabilitation. Modification after 5 amputees' opinion (2 patients in rehabilitation and 3 after discharge). (2) Brochure's evaluation by lower limb amputees, living at home, with questions concerning: clarity, choice of themes selected and illustrations, reassurance, usability and utility. Open-ended and closed-ended questions. (1) Illustrated brochure with 15 questions-and-answers concerning the following themes: "my preparation for active rehabilitation", "recovering my autonomy" and "return to everyday life". Topics are: pain management, body image, physiotherapy, prosthetics, gait rehabilitation, driving adaptations, home adaptations, professional life, leisure and sports activities, place in society, insurances. Illustrations by a cartoonist. (2) Brochure sent to a hundred patients. Compilation of results ongoing. An illustrated brochure concerning rehabilitation after an amputation was written and issued in digital format and in paper. Data recording is ongoing but the first findings are positive and very encouraging. This document including patients' questions and professionals' answers could form basis for discussion with patients and constitute a preliminary stage to a therapeutic education program

A low-power CMOS super-regenerative receiver at 1 GHz

A low-power and low-voltage super-regenerative receiver operating at 1 GHz and implemented in a 0.35-μm CMOS process is described. The receiver includes an low-noise amplifier, a super-regenerative oscillator, an envelope detector, an AGC circuitry with sample/hold function, and a baseband amplifier. The die surface is equal to 0.25 mm2. The power consumption is less than 1.2 mW at VDD = 1.5 V. A 100-KHz saw tooth quench signal is used to achieve a rejection of -36 dB at 500 KHz from the central frequency