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71.
Burak Guzelturk Pedro Ludwig Hernandez Martinez Qing Zhang Qihua Xiong Handong Sun Xiao Wei Sun Alexander O. Govorov Hilmi Volkan Demir 《Laser \u0026amp; Photonics Reviews》2014,8(1):73-93
In the past two decades, semiconductor quantum dots and wires have developed into new, promising classes of materials for next‐generation lighting and display systems due to their superior optical properties. In particular, exciton–exciton interactions through nonradiative energy transfer in hybrid systems of these quantum‐confined structures have enabled exciting possibilities in light generation. This review focuses on the excitonics of such quantum dot and wire emitters, particularly transfer of the excitons in the complex media of the quantum dots and wires. Mastering excitonic interactions in low‐dimensional systems is essential for the development of better light sources, e.g., high‐efficiency, high‐quality white‐light generation; wide‐range color tuning; and high‐purity color generation. In addition, introducing plasmon coupling provides the ability to amplify emission in specially designed exciton–plasmon nanostructures and also to exceed the Förster limit in excitonic interactions. In this respect, new routes to control excitonic pathways are reviewed in this paper. The review further discusses research opportunities and challenges in the quantum dot and wire excitonics with a future outlook. 相似文献
72.
We present the formal derivation of a new unidirectional model for unsteady mixed flows in nonuniform closed water pipes.In the case of free surface incompressible flows,the FS-model is formally obtained,using formal asymptotic analysis,which is an extension to more classical shallow water models.In the same way,when the pipe is full,we propose the P-model,which describes the evolution of a compressible inviscid flow,close to gas dynamics equations in a nozzle.In order to cope with the transition between a free surface state and a pressured(i.e.,compressible) state,we propose a mixed model,the PFS-model,taking into account changes of section and slope variation. 相似文献
73.
Effects of flow oscillations on spectrum of Ultrasound Doppler Velocimetry (UDV) signals were investigated theoretically and numerically. A laminar pipe flow with a superimposed oscillating component was considered. Negative impact of oscillation on the ultrasound signal hence on the flow images was observed in the form of spreading of spectral ultrasound signal energy around mean component, leading to image artifacts. Both analytical and numerical results revealed the strong effect of a group of parameters including Doppler frequency, flow oscillation amplitude and frequency. Exceeding a particular value of the group, 1.45, resulted in artifacts in the flow images. Revealing the mechanisms involved in the deteriorations associated with the flow oscillations is potentially useful in UDV studies involving random flow fluctuations such as turbulence. 相似文献
74.
Jiao Z Wang X Wang J Ke L Demir HV Koh TW Sun XW 《Chemical communications (Cambridge, England)》2012,48(3):365-367
Plate-like hydrated tungsten trioxide (3WO(3)·H(2)O) films were grown on a fluorine doped tin oxide (FTO) coated transparent conductive substrate via an efficient, facile and template-free hydrothermal method. The film exhibited a fast coloration/bleaching response (t(c90%) = 4.3 s and t(b90%) = 1.4 s) and a high coloration efficiency (112.7 cm(2) C(-1)), which were probably due to a large surface area. 相似文献
75.
A new phenolic ester 2-( p-hydroxyphenyl)ethyl eicosaheptanoic acid ester (1) and a known one hexacosylferulate (2) were isolated from the acetone extract of Salvia microphylla. In addition, two sesquiterpenes beta-eudesmol (3) and 8alpha-hydroxy-beta-eudesmol (4), a diterpene carnosic acid 12-methyl ether (12-methoxycarnosic acid) (5), three triterpenes erithrodiol 3-acetate, oleanolic acid, lupeol and beta-sitosterol were obtained as known compounds from this plant extract. The structures of the isolated compounds were elucidated by spectroscopic methods, including one- and two- dimensional 1H- and 13C-NMR and MS spectroscopies. The selected compounds were tested for antimicrobial activity against standard bacterial strains, and only carnosic acid 12-methyl ether showed antimicrobial activity against S. aureus at 78 microg mL(-1). 相似文献
76.
We extend the application of the random neural network to texture classification and retrieval. A neuron in the network corresponds to an image pixel and the neurons are connected according to neighboring relationship between pixels. A texture is represented with the weights of the network and the random neural network is used as an associative memory. In order to assess the performance of the method, texture mosaic images are generated from the popular Brodatz album. We also present a real life application in which a specified texture type is retrieved within a large remote sensing image. Results show that error is comparable to that of previous studies on texture classification which make use of other approaches.This is an extended version of the article presented in 2004 IEEE Southwest Symposium on Image Analysis and Interpretation. 相似文献
77.
Janina Hahn Volkan Filiz Sofia Rangou Juliana Clodt Adina Jung Kristian Buhr Clarissa Abetz Volker Abetz 《Journal of Polymer Science.Polymer Physics》2013,51(4):281-290
For the first time the combination of solution casting and solvent–nonsolvent exchange (phase inversion) has been applied to generate asymmetric membranes with highly ordered hexagonally packed cylinders with perpendicular orientation composed of polystyrene-block-poly(ethylene oxide). The influence of parameters like solvent composition and evaporation time on the membrane formation is presented. The development is based on a study of the solution behavior by dynamic light scattering and the precipitation behavior of the cylinder forming diblock copolymer by turbidity measurements from different solvent and nonsolvent systems. The water flux properties, as an important membrane characteristic, show a time dependent behavior, due to swelling of the polyethylene oxide blocks. The morphologies of the membranes are imaged by scanning electron microscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 相似文献
78.
A series of 2‐mono‐ and 2,2‐disubstituted 1,3‐dioxepin derivatives, two of which also had a carbonyl function in one of their 2‐R groups, were prepared and reacted with dimethyl diazomalonate with copper(II) acetylacetonate as a catalyst. Ylide formation probabilities with allyl ether and/or carbonyl functions were investigated. A chemoselectivity in favor of carbonyl ylide was observed. 相似文献
79.
Reactions of Quino‐Ketenes with C‐Nucleophiles: Syntheses of (2‐Hydroxyphenyl)methanols and 2‐Hydroxyphenyl Ketones 下载免费PDF全文
In this study, we have developed a new, efficient, and one‐step protocol for the synthesis of derivatives of 2,4‐dihydroxyphenyl ketones and/or 2,4‐dihydroxyphenyl/naphthalenyl methanols starting from benzodioxinones/naphthodioxinones and organolithium compounds. Reactions have been performed under thermal conditions without catalyst. This work is the first example of the preparation of these products starting from 2‐hydroxy acids. 相似文献
80.
Yue Wang Kah Ee Fong Shancheng Yang Van Duong Ta Yuan Gao Zeng Wang Venkatram Nalla Hilmi Volkan Demir Handong Sun 《Laser \u0026amp; Photonics Reviews》2015,9(5):507-516
The newly engineered ternary CdZnS/ZnS colloidal quantum dots (CQDs) are found to exhibit remarkably high photoluminescence quantum yield and excellent optical gain properties. However, the underlying mechanisms, which could offer the guidelines for devising CQDs for optimized photonic devices, remain undisclosed. In this work, through comprehensive steady‐state and time‐resolved spectroscopy studies on a series of CdZnS‐based CQDs, we unambiguously clarify that CdZnS‐based CQDs are inherently superior optical gain media in the blue spectral range due to the slow Auger process and that the ultralow threshold stimulated emission is enabled by surface/interface engineering. Furthermore, external cavity‐free high‐Q quasitoroid microlasers were produced from self‐assembly of CdZnS/ZnS CQDs by facile inkjet printing technique. Detailed spectroscopy analysis confirms the whispering gallery mode lasing mechanism of the quasitoroid microlasers. This tempting microlaser fabrication method should be applicable to other solution‐processed gain materials, which could trigger broad research interests.