201 research outputs found
Lasing oscillation in a three-dimensional photonic crystal nanocavity with a complete bandgap
We demonstrate lasing oscillation in a three-dimensional photonic crystal
nanocavity. The laser is realized by coupling a cavity mode, which is localized
in a complete photonic bandgap and exhibits the highest quality factor of
~38,500, with high-quality semiconductor quantum dots. We show a systematic
change in the laser characteristics, including the threshold and the
spontaneous emission coupling factor by controlling the crystal size, which
consequently changes the strength of photon confinement in the third dimension.
This opens up many interesting possibilities for realizing future ultimate
light sources and three-dimensional integrated photonic circuits and for more
fundamental studies of physics in the field of cavity quantum electrodynamics.Comment: 14 pages, 4 figure
Validation Préliminaire en contexte français de la tâche Head-Toes-Knees-Shoulders (HTKS, Ponitz, McClelland et al., 2009) évaluant le contrôle inhibiteur chez des enfants de Grande Section de Maternelle
International audienceL’inhibition jouant un rôle essentiel dans le développement de l’enfant, cet article examine les propriétés psychométriques d’une tâche de contrôle inhibiteur (Head-Toes-Knees-Shoulders) auprès de 180 enfants âgés de 5 ans et demi. Les résultats attestent de la sensibilité de l’épreuve et de sa validité convergente. Conformément à la littérature, un léger effet du sexe (en faveur des filles) et un effet plus net du niveau d’étude de la mère (en faveur des mères de niveau élevé) sont observés
The Global School Adaptation score: a new neurodevelopmental assessment tool for very preterm children at five years of age
Objective
To determine the usefulness of a neurodevelopmental assessment tool consisting of a questionnaire administered to teachers to measure the Global School Adaptation (GSA) scores of very preterm children at the age of 5 years.
Study design
A sample of 445 very preterm children (<35 weeks of gestation) was assessed at 5 years of age using GSA and IQ scores. According to the consistency between the scores, children were determined to be well classified, intermediately classified, or misclassified. The differences between groups were assessed through univariate and multivariate logistic regression.
Results
The GSA score was highly or intermediately consistent with the IQ score for 89.2% of the children, and 10.8% were considered misclassified. Children with a higher GSA than IQ score had more autonomy and self-confidence (PÂ < .01), and those with a lower GSA than IQ score had more behavioral problems (PÂ < .01). Analysis by logistic regression showed that sex and gestational age significantly affected the consistency between the 2 scores. Thus, girls were less likely to have a lower GSA than IQ score (aOR = 0.45; 95% CI: 0.24-0.84;Â PÂ = .01), and a lower gestational age significantly increased the likelihood of having a higher GSA than IQ score (for children born between 24 and 28 weeks of gestation: aOR = 2.70; 95% CI: 1.23-5.92;Â PÂ = .01).
Conclusions
The GSA score is a simple, inexpensive, and reliable screening tool for assessing neurodevelopment in very preterm children at 5 years of age
Vertical-external-cavity surface-emitting lasers and quantum dot lasers
The use of cavity to manipulate photon emission of quantum dots (QDs) has
been opening unprecedented opportunities for realizing quantum functional
nanophotonic devices and also quantum information devices. In particular, in
the field of semiconductor lasers, QDs were introduced as a superior
alternative to quantum wells to suppress the temperature dependence of the
threshold current in vertical-external-cavity surface-emitting lasers
(VECSELs). In this work, a review of properties and development of
semiconductor VECSEL devices and QD laser devices is given. Based on the
features of VECSEL devices, the main emphasis is put on the recent development
of technological approach on semiconductor QD VECSELs. Then, from the viewpoint
of both single QD nanolaser and cavity quantum electrodynamics (QED), a
single-QD-cavity system resulting from the strong coupling of QD cavity is
presented. A difference of this review from the other existing works on
semiconductor VECSEL devices is that we will cover both the fundamental aspects
and technological approaches of QD VECSEL devices. And lastly, the presented
review here has provided a deep insight into useful guideline for the
development of QD VECSEL technology and future quantum functional nanophotonic
devices and monolithic photonic integrated circuits (MPhICs).Comment: 21 pages, 4 figures. arXiv admin note: text overlap with
arXiv:0904.369
Spatial regularity of InAs-GaAs quantum dots: quantifying the dependence of lateral ordering on growth rate.
The lateral ordering of arrays of self-assembled InAs-GaAs quantum dots (QDs) has been quantified as a function of growth rate, using the Hopkins-Skellam index (HSI). Coherent QD arrays have a spatial distribution which is neither random nor ordered, but intermediate. The lateral ordering improves as the growth rate is increased and can be explained by more spatially regular nucleation as the QD density increases. By contrast, large and irregular 3D islands are distributed randomly on the surface. This is consistent with a random selection of the mature QDs relaxing by dislocation nucleation at a later stage in the growth, independently of each QD's surroundings. In addition we explore the statistical variability of the HSI as a function of the number N of spatial points analysed, and we recommend N > 10(3) to reliably distinguish random from ordered arrays
Intermediate-band dynamics of quantum dots solar cell in concentrator photovoltaic modules
We report for the first time a successful fabrication and operation of an InAs/GaAs quantum dot based
intermediate band solar cell concentrator photovoltaic (QD-IBSC-CPV) module to the IEC62108 standard
with recorded power conversion efficiency of 15.3%. Combining the measured experimental results at
Underwriters Laboratory (ULH) licensed testing laboratory with theoretical simulations, we confirmed that
the operational characteristics of the QD-IBSC-CPV module are a consequence of the carrier dynamics via
the intermediate-band at room temperature
Clinical relevance of genetic instability in prostatic cells obtained by prostatic massage in early prostate cancer
We investigated whether genetic lesions such as loss of heterozygosity (LOH) are detected in prostatic cells obtained by prostatic massage during early diagnosis of prostate cancer (CaP) and discussed their clinical relevance. Blood and first urine voided after prostatic massage were collected in 99 patients with total prostate-specific antigen (PSA) between 4 and 10 ng ml−1, prior to prostate biopsies. Presence of prostatic cells was confirmed by quantitative RT–PCR analysis of PSA mRNA. Genomic DNA was analysed for LOH on six chromosomal regions. One or more allelic deletions were found in prostatic fluid from 57 patients analysed, of whom 33 (58%) had CaP. Sensitivity and specificity of LOH detection and PSA free to total ratio <15% for positive biopsy were respectively 86.7 and 44% (P=0.002) for LOH, and 55 and 74% (P=0.006) for PSA ratio <15%. Analysis of LOH obtained from prostatic tumours revealed similar patterns compared to prostatic fluid cells in 86% of cases, confirming its accuracy. The presence of LOH of urinary prostatic cells obtained after prostatic massage is significantly associated with CaP on biopsy and may potentially help to identify a set of patients who are candidates for further prostate biopsies
High-Capacity Conductive Nanocellulose Paper Sheets for Electrochemically Controlled Extraction of DNA Oligomers
Highly porous polypyrrole (PPy)-nanocellulose paper sheets have been evaluated as inexpensive and disposable electrochemically controlled three-dimensional solid phase extraction materials. The composites, which had a total anion exchange capacity of about 1.1 mol kg−1, were used for extraction and subsequent release of negatively charged fluorophore tagged DNA oligomers via galvanostatic oxidation and reduction of a 30–50 nm conformal PPy layer on the cellulose substrate. The ion exchange capacity, which was, at least, two orders of magnitude higher than those previously reached in electrochemically controlled extraction, originated from the high surface area (i.e. 80 m2 g−1) of the porous composites and the thin PPy layer which ensured excellent access to the ion exchange material. This enabled the extractions to be carried out faster and with better control of the PPy charge than with previously employed approaches. Experiments in equimolar mixtures of (dT)6, (dT)20, and (dT)40 DNA oligomers showed that all oligomers could be extracted, and that the smallest oligomer was preferentially released with an efficiency of up to 40% during the reduction of the PPy layer. These results indicate that the present material is very promising for the development of inexpensive and efficient electrochemically controlled ion-exchange membranes for batch-wise extraction of biomolecules
A Virtual Testing Approach for Laminated Composites Based on Micromechanics
International audienceThe chapter deals with a crucial question for the design of composite structures: how can one predict the evolution of damage up to and including final fracture? Virtual testing, whose goal is to drastically reduce the huge number of industrial tests involved in current characterization procedures, constitutes one of today’s main industrial challenges. In this work, one revisits our multiscale modeling answer through its practical aspects. Some complements regarding identification, kinking, and crack initiation are also given. Finally, the current capabilities and limits of this approach are discussed, as well as the computational challenges that are inherent to “Virtual Structural Testing.
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