Numerical study on strained InGaAsP/InGaP quantum wells for 850-nm vertical-cavity surface-emitting lasers

The physical and optical properties of compressively strained InGaAsP/InGaP quantum wells for 850-nm vertical-cavity surface-emitting lasers are numerically studied. The simulation results show that the maximum optical gain, transparency carrier densities, transparency radiative current densities, and differential gain of InGaAsP quantum wells can be efficiently improved by employing a compressive strain of approximately 1.24% in the InGaAsP quantum wells. The simulation results suggest that the 850-nm InGaAsP/InGaP vertical-cavity surface-emitting lasers have the best laser performance when the number of quantum wells is one, which is mainly attributed to the non-uniform hole distribution in multiple quantum wells due to high valence band offset. PACS 42.55.Px; 78.20.-e; 78.20.Bh; 78.30.Fs     

Flexible nanocrystalline‐titania/polyimide hybrids with high refractive index and excellent thermal dimensional stability

In this study, a novel synthetic route was developed to prepare polyimide–nanocrystalline–titania hybrid optical films with a relatively high titania content (up to 50 wt %) and thickness (20–30 μm) from soluble polyimides containing hydroxyl groups. Two series of newly soluble polyimides were synthesized from the hydroxy‐substituted diamines with various commercial tetracarboxylic dianhydrides. The hydroxyl groups on the backbone of the polyimides could provide the organic–inorganic bonding and resulted in homogeneous hybrid solutions by controlling the mole ratio of titanium butoxide/hydroxyl group. AFM, SEM, TEM, and XRD results indicated the formation of well‐dispersed nanocrystalline‐titania. The flexible hybrid films could be successfully obtained and revealed relatively good surface planarity, thermal dimensional stability, tunable refractive index, and high optical transparency. A three‐layer antireflection coating based on the hybrid films was prepared and showed a reflectance of less than 0.5% in the visible range indicated its potential optical applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1433–1440, 2010     

Numerical study on InGaAsN/GaAs multiple-quantum-well laser with GaAsP and GaAsN barriers

In this work, the multiple-quantum-well InGaAsN laser structures with indirect-GaAsP and direct-GaAsN barriers are investigated by using LASTIP simulation program. We vary the quantum-well number, from 1 to 5, to find appropriate barrier material for InGaAsN laser structures. The simulation results show that InGaAsN laser structure has higher characteristic temperature regardless of what quantum-well number is if the indirect-GaAsP barrier is utilized. Furthermore, for InGaAsN laser structure, the usage of indirect-GaAsP barrier is beneficial for reducing the threshold current when the quantum-well number is from 1 to 2 and the usage of direct-GaAsN barrier is beneficial for reducing the threshold current when the quantum-well number is from 3 to 5.     

Strong convergence of an iterative method for nonexpansive mappings with new control conditions

The purpose of this paper is to study the convergence problem of an iterative method for nonexpansive mappings in Banach spaces under some new control conditions on parameters.     

New P‐type of poly(4‐methoxy‐triphenylamine)s derived by coupling reactions: Synthesis,electrochromic behaviors,and hole mobility

Methoxy‐substituted poly(triphenylamine)s, poly‐4‐methoxytriphenylamine ( PMOTPA ), and poly‐N,N‐bis(4‐methoxyphenyl)‐N′,N′‐diphenyl‐p‐phenylenediamine ( PMOPD ), were synthesized from the nickel‐catalyzed Yamamoto and oxidative coupling reaction with FeCl₃. All synthesized polymers could be well characterized by ¹H and ¹³C NMR spectroscopy. These polymers possess good solubility in common organic solvent, thermal stability with relatively high glass‐transition temperatures (T_gs) in the range of 152–273 °C, 10% weight‐loss temperature in excess of 480 °C, and char yield at 800 °C higher than 79% under a nitrogen atmosphere. They were amorphous and showed bluish green light (430–487 nm) fluorescence with quantum efficiency up to 45–62% in NMP solution. The hole‐transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. All polymers exhibited reversible oxidation redox peaks and E_onset around 0.44–0.69 V versus Ag/AgCl and electrochromic characteristics with a color change under various applied potentials. The series of PMOTPA and PMOPD also showed p‐type characteristics, and the estimated hole mobility of O ‐ PMOTPA and Y ‐ PMOPD were up to 1.5 × 10^?4 and 5.6 × 10^?5 cm² V^?1 s^?1, respectively. The FET results indicate that the molecular weight, annealing temperature, and polymer structure could crucially affect the charge transporting ability. This study suggests that triphenylamine‐containing conjugated polymer is a multifunctional material for various optoelectronic device applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4037–4050, 2009     

Pulsatile flows in a lateral aneurysm anchored on a stented and curved parent vessel

We present particle tracking velocimetry measurements and flow visualization of pulsatile flow fields in a stented cerebrovascular lateral aneurysm model with a wide ostium anchored on a curved parent vessel. Among the stent parameters, the blocking ratioC _α ranging from 0% to 75% was selected to study its effect on the changes of intra-aneurysmal hemodynamics for the reference of minimally invasive endovascular aneurysm treatment. The Womersley number was 3.9 and the mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 850, and 300, respectively. The results are characterized in terms of velocity vector field, coded streak images, region averaged velocity, vorticity, and wall shear stress. A critical range ofC _α related to the inflow location as well as the shape and number of intra-aneurysmal vortices is identified. The intra-aneurysmal flow activity, vortex strength, and wall shear stress are found to decrease with increasingC _α. Among theC _α examined,C _α=75% is the most favorable in attenuating the risk of aneurysmal rupture and promoting intra-aneurysmal thrombus.     

合金元素及模拟热处理对2205双相不锈钢之孔蚀性质影响

本文研究了Ｎｉ元素及不同模拟焊后热影响区（ＨＡＺ）组织对２２０５双相不锈钢孔蚀性质之影响。结果发现：在研究成分范围内，不同Ｎｉ含量对于底材电化学极化曲线之影响不大，其Ｅｎｐ和Ｅｎｐ均在１１００￣１２００ｍＶ之间。     

Passive automatic exposure mechanism

In this paper, we will propose a passive automatic exposure mechanism. Different from general automatic exposure mechanism, the passive exposure mechanism directly searches suitable exposure images through the content of images. As exposure is one of the main factors to successfully take pictures, how to find an accurate exposure value is an important issue. Passive automatic exposure is the new trend and key issue of image processing. We will experiment and prove that the method we propose is effective.     

Synthesis,photoluminescence, and electrochromism of novel aromatic poly(amine‐1,3,4‐oxadiazole)s bearing anthrylamine chromophores

Two novel poly(amine‐hydrazide)s were prepared from the polycondensation reactions of the dicarboxylic acid, 9‐[N,N‐di(4‐carboxyphenyl)amino]anthracene ( 1 ), with terephthalic dihydrazide ( TPH ) and isophthalic dihydrazide ( IPH ) via the Yamazaki phosphorylation reaction, respectively. The poly(amine‐hydrazide)s were readily soluble in many common organic solvents and could be solution cast into transparent films. Differential scanning calorimetry (DSC) indicated that these hydrazide polymers had glass‐transition temperatures (T_g) in the range of 182–230 °C and could be thermally cyclodehydrated into the corresponding oxadiazole polymers in the range of 300–400 °C. The resulting poly(amine‐1,3,4‐oxadiazole)s had useful levels of thermal stability associated with high T_g (263–318 °C), 10% weight‐loss temperatures in excess of 500 °C, and char yield at 800 °C in nitrogen higher than 55%. These organo‐soluble anthrylamine‐based poly(amine‐hydrazide)s and poly (amine‐1,3,4‐oxadiazole)s exhibited maximum UV‐vis absorption at 346–349 and 379–388 nm in N‐methyl‐2‐pyrrolidone (NMP) solution, respectively. Their photoluminescence spectra in NMP solution showed maximum bands around 490–497 nm in the green region. The poly(amine‐hydrazide) I ‐ IPH showed a green photoluminescence at 490 nm with PL quantum yield of 29.9% and 17.0% in NMP solution and film state, respectively. The anthrylamine‐based poly(amine‐1,3,4‐oxadiazole)s revealed a electrochromic characteristics with changing color from the pale yellow neutral form to the red reduced form when scanning potentials negatively from 0.00 to ?2.20 V. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1584–1594, 2009     

Novel family of triphenylamine‐containing,hole‐transporting,amorphous, aromatic polyamides with stable electrochromic properties

We report the preparation and characterization of a series of novel electrochromic, aromatic poly(amine amide)s with pendent triphenylamine units. The synthesis proceeded via direct phosphorylation polycondensation between a novel diamine, N,N‐bis(4‐aminophenyl)‐N′,N′‐diphenyl‐1,4‐phenylenediamine, and various aromatic dicarboxylic acids. All the poly(amine amide)s were amorphous and readily soluble in many common organic solvents and could be solution‐cast into transparent, tough, and flexible films with good mechanical properties. They exhibited good thermal stability and 10% weight‐loss temperatures above 540 °C. Their glass‐transition temperatures were 263–290 °C. These polymers in N‐methyl‐2‐pyrrolidinone solutions exhibited strong ultraviolet–visible absorption peaks at 307–358 nm and photoluminescence peaks around 532–590 nm in the green region. The hole‐transporting and electrochromic properties were studied with electrochemical and spectroelectrochemical methods. Cyclic voltammograms of poly(amine amide) films prepared by the casting of polymer solutions onto an indium tin oxide coated glass substrate exhibited two reversible oxidation redox couples at 0.65 and 1.03 V versus Ag/AgCl in an acetonitrile solution. All the poly(amine amide)s showed excellent stability with respect to their electrochromic characteristics; the color of the films changed from pale yellow to green and then blue at 0.85 and 1.25 V, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2085–2098, 2005