Control of fine-structure splitting and excitonic binding energies in selected individual InAs/GaAs quantum dots

A systematic study of the impact of annealing on the electronic properties of single InAs/GaAs quantum dots (QDs) is presented. Single QD cathodoluminescence spectra are recorded to trace the evolution of one and the same QD over several steps of annealing. A substantial reduction of the excitonic fine-structure splitting upon annealing is observed. In addition, the binding energies of different excitonic complexes change dramatically. The results are compared to model calculations within eight-band k.p theory and the configuration interaction method, suggesting a change of electron and hole wave function shape and relative position.Comment: 4 pages, 4 figure

Deformation and spallation of shocked Cu bicrystals with Σ3 coherent and symmetric incoherent twin boundaries

We perform molecular dynamics simulations of Cu bicrystals with two important grain boundaries (GBs), Σ3 coherent twin boundaries (CTB), and symmetric incoherent twin boundaries (SITB) under planar shock wave loading. It is revealed that the shock response (deformation and spallation) of the Cu bicrystals strongly depends on the GB characteristics. At the shock compression stage, elastic shock wave can readily trigger GB plasticity at SITB but not at CTB. The SITB can induce considerable wave attenuation such as the elastic precursor decay via activating GB dislocations. For example, our simulations of a Cu multilayer structure with 53 SITBs (∼1.5-μm thick) demonstrate a ∼80% elastic shock decay. At the tension stage, spallation tends to occur at CTB but not at SITB due to the high mobility of SITB. The SITB region transforms into a threefold twin via a sequential partial dislocation slip mechanism, while CTB preserves its integrity before spallation. In addition, deformation twinning is a mechanism for inducing surface step during shock tension stage. The drastically different shock response of CTB and SITB could in principle be exploited for, or benefit, interface engineering and materials design

Left-right loading dependence of shock response of (111)//(112) Cu bicrystals: Deformation and spallation

We investigate with molecular dynamics the dynamic response of Cu bicrystals with a special asymmetric grain boundary (GB), (111)//(112)〈110〉, and its dependence on the loading directions. Shock loading is applied along the GB normal either from the left or right to the GB. Due to the structure asymmetry, the bicrystals demonstrate overall strong left-right loading dependence of its shock response, including compression wave features, compression and tensile plasticity, damage characteristics (e.g., spall strength), effective wave speeds and structure changes, except that spallation remains dominated by the GB damage regardless of the loading directions. The presence or absence of transient microtwinning also depends on the loading directions

Shock compression and spallation of single crystal tantalum

We present molecular dynamics simulations of shock-induced plasticity and spall damage in single crystal Ta described by a recently developed embedded-atom-method (EAM) potential and a volumedependent qEAM potential. We use impact or Hugoniotstat simulations to investigate the Hugoniots, deformation and spallation. Both EAM and qEAM are accurate in predicting, e.g., the Hugoniots and γ - surfaces. Deformation and spall damage are anisotropic for Ta single crystals. Our preliminary results show that twinning is dominant for [100] and [110] shock loading, and dislocation, for [111]. Spallation initiates with void nucleation at defective sites from remnant compressional deformation or tensile plasticity. Spall strength decreases with increasing shock strength, while its rate dependence remains to be explored

Use of the Richtmyer-Meshkov Instability to Infer Yield Stress at High-Energy Densities

We use the Richtmyer-Meshkov instability (RMI) at a metal-gas interface to infer the metal’s yield stress (Y) under shock loading and release. We first model how Y stabilizes the RMI using hydrodynamics simulations with a perfectly plastic constitutive relation for copper (Cu). The model is then tested with molecular dynamics (MD) of crystalline Cu by comparing the inferred Y from RMI simulations with direct stress-strain calculations, both with MD at the same conditions. Finally, new RMI experiments with solid Cu validate our simulation-based model and infer Y~0.47 GPa for a 36 GPa shock

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

Microwave-assisted synthesis and antibacterial propensity of N0-s-benzylidene-2-propylquinoline- 4-carbohydrazide and N0-((s-1H-pyrrol- 2-yl)methylene)-2-propylquinoline- 4-carbohydrazide motifs

Microwave-assisted approach was utilized as green approach to access a series of 2-pro pylquinoline-4-carbohydrazide hydrazone derivatives 10a-j of aromatic and heteroaromatic aldehydes in highly encouraging yields. It involved four steps reaction which was initiated with ring opening reaction of isatin in a basified environment and subsequent cross-coupling with pentan-2-one to produce compound 7. Esterification of 7 in acid medium led to the formation of compound 8 which was reacted with hydrazine hydrate to access 9 which upon microwave-assisted condensed with aromatic and heteroaromatic aldehydes furnished the targeted compounds 10a-j. The structures of 10aj were confirmed by physico-chemical, elemental analyses and spectroscopic characterization which include UV, FT-IR, 1H and 13C NMR as well as DEPT-135. The targeted compounds 10a-j, alongside with gentamicin clinical standard, were investigated for their antibacterial efficacies using agar diffusion method. 2-Propyl-N0-(pyridine-3-ylmethylene) quinoline-4-carbohydrazide 10j emerged a

Patient satisfaction with anaesthesia care: development of a psychometric questionnaire and benchmarking among six hospitals in Switzerland and Austria†‡

Background. We describe the development and comparison of a psychometric questionnaire on patient satisfaction with anaesthesia care among six hospitals. Methods. We used a rigorous protocol: generation of items, construction of the pilot questionnaire, pilot study, statistical analysis (construct validity, factor analysis, reliability analysis), compilation of the final questionnaire, main study, repeated analysis of construct validity and reliability. We compared the mean total problem score and the scores for the dimensions: ‘Information/Involvement in decision‐making', and ‘Continuity of personal care by anaesthetist'. The influence of potential confounding variables was tested (multiple linear regression). Results. The average problem score from all hospitals was 18.6%. Most problems are mentioned in the dimensions ‘Information/Involvement in decision‐making' (mean problem score: 30.9%) and ‘Continuity of personal care by anaesthetist' (mean problem score: 32.2%). The overall assessment of the quality of anaesthesia care was good to excellent in 98.7% of cases. The most important dimension was ‘Information/Involvement in decision‐making'. The mean total problem score was significantly lower for two hospitals than the total mean for all hospitals (significantly higher at two hospitals) (P<0.05). Amongst the confounding variables considered, age, sex, subjective state of health, type of anaesthesia and level of education had an influence on the total problem score and the two dimensions mentioned. There were only marginal differences with and without the influence of the confounding variables for the different hospitals. Conclusions. A psychometric questionnaire on patient satisfaction with anaesthesia care must cover areas such as patient information, involvement in decision‐making, and contact with the anaesthetist. The assessment using summed scores for dimensions is more informative than a global summed rating. There were significant differences between hospitals. Moreover, the high problem scores indicate a great potential for improvement at all hospitals. Br J Anaesth 2002; 89: 863-7