Large-Scale Turbulent Vortical Structures inside a Sudden Expansion Cylinder Chamber

A large eddy simulation (LES) is performed for turbulent flow around a bluff body inside a sudden expansion cylinder chamber, a configuration which resembles a premixed gas turbine combustor. To promote turbulent mixing and to accommodate flame stability, a flame holder is installed inside the combustion chamber. The Smagorinsky model and the Lagrangian dynamic subgrid-scale model are employed and tested. The calculated Reynolds number is 5,000 based on the bulk velocity and the diameter of inlet pipe. The simulation code is constructed by using a general coordinate system based on the physical contravariant velocity components. The predicted turbulent statistics are evaluated by comparing with the laser-doppler velocimetry (LDV) measurement data. The agreement of LES with the experimental data is shown to be satisfactory. Emphasis is placed on the time-dependent evolutions of turbulent vortical structures behind the flame holder. The numerical flow visualizations depict the behavior of large-scale vortices. The turbulent behavior behind the flame holder is analyzed by visualizing the sectional views of vortical structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Consensus protocol design for discrete‐time networks of multiagent with time‐varying delay via logarithmic quantizer

This article considers the problem of consensus for discrete‐time networks of multiagent with time‐varying delays and quantization. It is assumed that the logarithmic quantizer is utilized between the information flow through the sensor of each agent, and its quantization error is included in the proposed method. By constructing a suitable Lyapunov‐Krasovskii functional and utilizing matrix theory, a new consensus criterion for the concerned systems is established in terms of linear matrix inequalities (LMIs) which can be easily solved by various effective optimization algorithms. Based on the consensus criterion, a designing method of consensus protocol is introduced. One numerical example is given to illustrate the effectiveness of the proposed method. © 2014 Wiley Periodicals, Inc. Complexity 21: 163–176, 2015     

An investigation of teachers’ intentions and reflections about using Standards-based and traditional textbooks in the classroom

This study analyzed teachers’ intentions for and reflections on their use of Standards-based [Connected Mathematics Program (CMP)] textbooks and traditional (non-CMP) mathematics textbooks to guide instruction. In this investigation of the interplay between textbooks and instruction, we focused on learning goals, instructional tasks, teachers’ anticipation of students’ difficulties, and their perceptions of students’ achievement of learning goals. All of these are aspects of teachers’ intentions and reflections that have proved fruitful in comparing the roles of the CMP and non-CMP mathematics textbooks in our Longitudinal Investigation of the Effect of Curriculum on Algebra Learning project. Whereas the cognitive level of the teachers’ intended learning goals appeared generally to reflect the emphases of their respective textbooks, we found that the CMP teachers’ intended learning goals were not as well aligned with the CMP textbooks as the non-CMP teachers’ learning goals were aligned with their non-CMP textbooks. The CMP and non-CMP teachers’ implementations of the lessons seemed to reduce the degree of difference between the cognitive levels of their intended goals. Even so, we found that significantly more CMP lessons than non-CMP lessons were implemented at a high level of cognitive demand. Although the non-CMP teachers’ intended learning goals were better aligned with their textbook’s learning goals, we found that the CMP teachers were more likely than the non-CMP teachers to follow the guidance of their textbooks in designing and selecting instructional tasks for a lesson. Future research should consider other aspects of teachers’ intentions and reflections that may shed a broader light on the role of textbooks and curriculum materials in teachers’ crafting of instructional experiences for their students.     

Particle size control of PbTe quantum dots incorporated in the germano-silicate glass optical fiber by heat treatment

The effect of heat treatment of the germano-silicate glass optical fiber incorporated with PbTe quantum dots on the absorption characteristics was investigated. Incorporation of the PbTe QDs in the fiber core was confirmed by the absorption peaks that appeared at 687 nm and 1055 nm and their shift upon heat treatment. The absorption peak was found to shift linearly toward a longer wavelength after heat treatment at 700 °C, 1000 °C, and 1100 °C for 1 h. The red shift of the excitonic absorption peak was attributed to the increase in the average size of the PbTe QDs in the fiber core.     

Excited-state lifetime of adenine near the first electronic band origin

The excited-state lifetime of supersonically cooled adenine was measured in the gas phase by femtosecond pump-probe transient ionization as a function of excitation energy between 36?100 and 37?500cm(-1). The excited-state lifetime of adenine is ～2ps around the 0-0 band of the (1)L(b) ππ(?) state (36?105cm(-1)). The lifetime drops to ～1ps when adenine is excited to the (1)L(a) ππ(?) state with the pump energy at 36?800cm(-1) and above. The excited-state lifetimes of (1)L(a) and (1)L(b) ππ(?) states are differentiated in accordance with previous frequency-resolved and computational studies.     

Liquid–liquid equilibrium for binary and ternary systems containing di-isopropyl ether (DIPE) and an imidazolium-based ionic liquid at different temperatures

Liquid–liquid equilibrium (LLE) data were determined for two binary systems {di-isopropyl ether (DIPE) + 1-ethyl-3-methylimidazolium-ethylsulfate (EMISE)} and {DIPE + 1-butyl-3-methylimidazolium-tetrafluoroborate([Bmim][BF₄])}at temperatures between 293.15 K and 313.15 K. LLE data for six ternary systems {DIPE + water + EMISE} and {DIPE + water + [Bmim][BF₄]} at 293.15 K, 303.15 K, and 313.15 K were also reported. Experiments were carried out at atmospheric pressure using stirred and thermo-regulated cells. The experimental data were correlated with the well-known NRTL and UNIQUAC activity coefficient models. In addition, distribution coefficients and selectivities of the ionic liquids EMISE and [Bmim][BF₄] for water in the DIPE phase were measured.     

Layer-by-layer assembled multilayer TiO(x) for efficient electron acceptor in polymer hybrid solar cells

We demonstrate that TiO(x) nanocomposite films fabricated using electrostatic layer-by-layer (LbL) assembly improve the power conversion efficiency of photovoltaic cells compared to conventional TiO(x) films fabricated via the sol-gel process. For this study, titanium precursor/poly(allylamine hydrochloride) (PAH) multilayer films were first deposited onto indium tin oxide-coated glass to produce TiO(x) nanocomposites (TiO(x)NC). The specific effect of the LbL processed TiO(x) on photovoltaic performance was investigated using the planar bilayer TiO(x)NC and highly regioregular poly(3-hexylthiophene) (P3HT) solar cells, and the P3HT/LbL TiO(x)NC solar cells showed a dramatic increase in power efficiency, particularly in terms of the short current density and fill factor. The improved efficiency of this device is mainly due to the difference in the chemical composition of the LbL TiO(x)NC films, including the much higher Ti(3+)/Ti(4+) ratio and the highly reactive facets of crystals as demonstrated by XPS and XRD measurement, thus enhancing the electron transfer between electron donors and acceptors. In addition, the grazing incidence wide-angle X-ray scattering (GIWAXS) study revealed the presence of more highly oriented P3HT stacks parallel to the substrate on the LbL TiO(x)NC film compared to those on the sol-gel TiO(x) films, possibly influencing the hole mobility of P3HT and the energy transfer near and at the interface between the P3HT and TiO(x) layers. The results of this study demonstrate that this approach is a promising one for the design of hybrid solar cells with improved efficiency.     

New thiophene‐phenylene‐thiophene acceptor random conjugated copolymers for optoelectronic applications

New low band gap thiophene‐phenylene‐thiophene ( TPT )‐based donor‐acceptor‐donor random copolymers were synthesized for optoelectronic device applications by a palladium‐catalyzed Stille coupling reaction under microwave heating. The acceptors included 2,3‐bis(4‐(2‐ethylhexyloxy)phenyl)‐5,8‐bis[5′‐bromo‐dithien‐2‐yl‐quinoxalines] ( DTQ ) and 3,6‐bis(5‐bromothiophen‐2‐yl)‐2,5‐bis(2‐ethyl‐hexyl)‐pyrrolo[3,4‐c]‐pyrrole‐1,4‐dione ( DPP ). The prepared random copolymers were named as PTPTDTQ_0.55 , PTPTDTQ_0.34DPP_0.14 , and PTPTDTQ_0.26DPP_0.34 depending on the copolymer ratio. The optical band gaps (E) of PTPTDTQ_0.55 , PTPTDTQ_0.34DPP_0.14 , and PTPTDTQ_0.26DPP_0.34 were 1.74, 1.56, and 1.48 eV, respectively. The hole mobility obtained from the field‐effect transistor devices prepared from PTPTDTQ_0.55 , PTPTDTQ_0.34DPP_0.14 , and PTPTDTQ_0.26DPP_0.34 were 2.2 × 10^?3, 2.4 × 10^?3, and 4.7 × 10^?3 cm² V^?1 s^?1, respectively, with the on‐off ratios of 4.0 × 10⁴, 4.0 × 10⁴, and 5.3 × 10⁴. It suggested that the significant intramolecular charge transfer between the TPT and acceptor led to the band gap reduction and hole mobility enhancement. Polymer solar cells of these TPT ‐based copolymers blended with 1‐(3‐methoxycarbonyl)propyl‐1‐phenyl‐[6,6]‐C‐71 (PC₇₁BM) under illumination of AM 1.5G (100 mW cm^?2) solar simulator exhibited a power conversion efficiency (PCE) as high as 3.71%. Besides, the near‐infrared photodetector device prepared from PTPTDTQ_0.26DPP_0.34 showed a high external quantum efficiency exceeding 32% at 700 nm (under ?3 V bias) and fast‐speed response. This study suggests that the prepared TPT ‐based donor‐acceptor random copolymers exhibited promising and versatile applications on optoelectronic devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2351–2360, 2010