Effect of parameters of Ge(Si)/Si(001) self-assembled islands on their electroluminescence at room temperature

The electroluminescence (EL) of multilayered p-i-n structures with the self-assembled Ge(Si)/Si(001) islands are investigated. It is found that the structures with islands grown at 600°C have the highest intensity of the electroluminescence signal at room temperature in the wavelength range of 1.3–1.55 μm. The annealing of structures with the Ge(Si) islands leads to an increase in the EL-signal intensity at low temperatures and hampers the temperature stability of this signal, which is related to the additional Si diffusion into islands during annealing. The found considerable increase in the electroluminescence-signal intensity with the thickness of the separating Si layer is associated with a decrease in the elastic stresses in the structure with an increase in this layer’s thickness. The highest EL quantum efficiency in the wavelength range of 1.3–1.55 μm obtained in investigated structures amounted to 0.01% at room temperature.     

液晶产业调整形势乐观

Panel makers are making serious adjustments to accom-modate to changing global markets,but those adjustmentsare not only reductions in capex and manufacturing capacity.Indeed,some of the changes anticipate recovering prices anddemand.First,a negative story that appeared on the web lastweek turns out to be not true.     

Dynamic and CW linewidth measurements of 1.55-μm InGaAs-InGaAsPmultiquantum well distributed feedback lasers

Measurement of the CW linewidth and frequency chirp as functions of modulation data rate and bias level for 1.55-μm InGaAsP multiquantum-well distributed feedback lasers grown by low-pressure MOCVD are presented. The results show that the CW linewidth of asymmetric facet-coated multiquantum-well DFB lasers can be as low as 2.0 MHz at 13.5 mW output power. The frequency chirp increases with modulation data rate and is significantly larger if the laser off-state is below threshold than if it is above threshold. The 20 dB down chirp widths are in the range of 1.9-5 Å for 40 mA peak-to-peak modulation current at 10 Gb/s under above-threshold bias     

Dynamic Microcapsules with Rapid and Reversible Permeability Switching

Dynamic microcapsules are reported that exhibit shell membranes with fast and reversible changes in permeability in response to external stimuli. A hydrophobic anhydride monomer is employed in the thiol–ene polymerization as a disguised precursor for the acid‐containing shells; this enables the direct encapsulation of aqueous cargo in the liquid core using microfluidic fabrication of water‐in‐oil‐in‐water double emulsion drops. The poly(anhydride) shells hydrolyze in their aqueous environment without further chemical treatment, yielding cross‐linked poly(acid) microcapsules that exhibit trigger‐responsive and reversible property changes. The microcapsule shell can actively be switched numerous times between impermeable and permeable due to the exceptional mechanical properties of the thiol–ene network that prevent rupture or failure of the membrane, allowing it to withstand the mechanical stresses imposed on the capsule during the dynamic property changes. The permeability and molecular weight cutoff of the microcapsules can dynamically be controlled with triggers such as pH and ionic environment. The reversibly triggered changes in permeability of the shell exhibit a response time of seconds, enabling actively adjustable release profiles, as well as on‐demand capture, trapping, and release of cargo molecules with molecular selectivity and fast on‐off rates.     

Quantification of character-impact odour compounds of roasted beef

Beef was roasted for 7 min in frying pans made of glass (A) or of stainless steel (B). The lower temperature in A yielded a more roasty-sweet flavour and the higher temperature in B a roasty-harsh, more caramellike flavour. Using stable isotope dilution assays the concentration levels of the odour compounds 4-hydroxy-2,5-dimethyl-3(2H)-furanone (I), 2-acetyl-2-thiazoline (II), 2-ethyl-3,5-dimethylpyrazine (III), 2,3-diethyl-5-methylpyrazine (IV), guaiacol (V) and methional (VI) were determined in samples A and B. The data obtained were divided by the corresponding odour thresholds which were evaluated nasally and retronasally. The results indicated that the flavour differences of A and B were preferentially caused by differences in the concentration levels of odorantsI, II, IV, andVI.

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Quantitative Analyse charakteristischer Geruchsstoffe von gebratenem Rindfleisch

Zusammenfassung Rindfleisch wurde 7 min in Pfannen aus Glas (A) und rostfreiem Stahl (B) gebraten. Die niedrigere Temperatur in A führte zu einem stärker röstig-süßen Aroma und die höhere Temperatur in B zu einem röstig-herben, stärker caramelartigen Aroma. Die Konzentrationen der Geruchsstoffe 4-Hydroxy-2,5-dimethyl-3(2H)-furanon (I), 2-Acetyl-2-thiazolin (II), 2-Ethyl-3,5-dimethyl-pyrazin (III), 2,3-Diethyl-5-methylpyrazin (IV), Guajacol (V) und Methional (VI) wurden in den Proben A und B mit Hilfe von Isotopenverdünnungsanalysen bestimmt. Die erhaltenen Werte wurden dividiert durch die entsprechenden nasal und retronasal ermittelten Geruchsschwellen. Die Ergebnisse zeigten, daß die Aromaunterschiede von A und B in erster Linie auf Unterschiede in den Konzentrationen der GeruchsstoffeI,II, IV undVI beruhen.

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Presented in part at the symposium Flavour Precursors, University of Würzburg, Sept. 30th to Oct. 2nd, 1992     

High-resolution venography of the brain using magnetic resonance imaging

The purpose of this study was to evaluate a non-flow related magnetic resonance imaging method to visualize small veins independent of arteries in the human brain. A long TE, high-resolution 3D gradient echo MR acquisition was used to highlight venous information. The method is based on the paramagnetic property of deoxyhemoglobin and the resulting phase difference between veins and brain parenchyma at long echo times. The MR magnitude images were masked with a phase mask filter to enhance small structure visibility.. Venous information down to sub-pixel vessel diameters of several hundred microns is visible. Venous data are displayed in an angiographic manner using a minimum intensity projection algorithm. Both superficial veins and deep white matter veins are visible. The method has been successfully applied in volunteers. Preliminary results in patients with cerebral arteriovenous malformations indicate its potential in clinical applications. The proposed method is easy to implement and does not require administration of a contrast agent or application of specially designed rf pulses to highlight the veins. Rather it exploits the intrinsic magnetic properties (BOLD-effect) and the prolonged T ^_2* of venous blood. The method may be of diagnostic potential in the assessment of arteriovenous malformations or other vascular venous lesions. © 1998 Elsevier Science B.V. All rights reserved.     

Cassini Titan Radar Mapper

The Cassini Titan Radar Mapper is a multimode radar instrument designed to probe the optically inaccessible surface of Titan, Saturn's largest moon. The instrument is to be included in the payload of the Cassini Saturn Mission, scheduled for launch in 1995. The individual modes of Cassini Radar Mapper will allow topographic mapping and surface imaging at few hundred meters resolution. The requirements that lay behind the design are briefly discussed, and the configuration and capability of the instrument are described. The present limited knowledge of Titan's surface and the measurement requirements imposed on the radar instrument are addressed. Also discussed are the Cassini mission and the projected orbits, which imposed another set of design constraints that led to the multitude of modes and to an unconventional antenna configuration. The antenna configuration and the different radar modes are described     

光电子元件市场趋势

随着越来越多的移动电话和笔记本电脑配备短距离红外无线连接特性，随着更广范围的汽车车辆安装了由红外传感器实现的传感系统，以及随着交互式机顶盒和DVD播放机等消费类多媒体系统对综合遥控功能的要求越来越多，光电子元件行业的总体趋势是不断增长。