The nucleation of faulted dipoles at intersection jogs in γ-TiAl

Single crystal samples of n-(Ti-54.7 at.% Al) deformed to a permanent strain of 2% at room temperature under multiple-slip conditions contain faulted dipoles (FDs) whose density exhibits some dependence on load orientation. Although FDs are hard to observe after compression along [210], they are profuse and congregated in places in the [1 1 8.6] load orientation. They exhibit most of the topological characteristics of FDs formed under single slip as reported by Grégori and Veyssière such as elongation in the screw direction of the primary d011] slip direction and a noticeable shape asymmetry. It is shown further that, in the [1 1 8.6] samples, bundles of FDs originate at jogs that result from intersection with forest dislocations of appropriate Burgers vectors. A mechanism for FD nucleation is proposed on the basis of asymmetrical dissociation of the parent d011] dislocation and specific impingements between the various partials on two adjacent octahedral planes. Implications of the FD nucleation at jogs on the load orientation dependence of the FD density are discussed.     

Investigation of Characteristics of Al2O3/n-In x Ga1−x As (x = 0.53, 0.7, and 1) Metal–Oxide–Semiconductor Structures

The electrical properties of Al₂O₃/n-InGaAs metal–oxide–semiconductor capacitors (MOSCAPs) with In content of 0.53, 0.7, and 1 (InAs) have been investigated. Results show small capacitance–voltage (C–V) frequency dispersion in accumulation (1.70% to 1.85% per decade) for these MOSCAPs, mostly being assigned to border traps in Al₂O₃. With higher In content, shorter minority-carrier response time and smaller C–V hysteresis are observed. The reduction of C–V hysteresis might be related to the reduction of Ga-bearing oxides in Al₂O₃/InGaAs interfaces as indicated by x-ray photoelectron spectroscopy.     

Novel fulleropyrrolidines bearing π-conjugated thiophene derivatives as compatibilizing group for developing highly stable polymer solar cells

A series of new fulleropyrrolidines, which comprise one terthiophene (3T) or dithienyl thienothiophene (2TTT) conjugated segment along with two hexyl (H) or ethylhexyl (EH) chains, abbreviated as 3T-H-C₆₀, 3T-EH-C₆₀, 2TTT-H-C₆₀ and 2TTT-EH-C₆₀, were designed and synthesized to improve their structural compatibility with poly(3-hexylthiophene) (P3HT). These [60]fullerene monoadducts exhibit a characteristic UV–Vis absorption band, associated with the conjugated substituent, and similar optical bandgaps and lowest unoccupied molecular orbital (LUMO) levels of approximately 1.71 eV and −3.72 eV, respectively. The influence of the structure of the substituent in the fulleropyrrolidine on its intermolecular packing within a polymer matrix was investigated. Photoluminescence measurements of the blended films of such C₆₀ derivatives with P3HT reveal that the interfacial area between the two materials is larger in the 3T-based system than in the 2TTT-based system; moreover, the branched ethylhexyl chain is more effective than the linear hexyl group in reducing the size of the phase domains. Transmission electron microscopic images further confirm that relatively serious phase segregation occurs in the 2TTT-C₆₀/P3HT films. Accordingly, solar cells with 3T-C₆₀/P3HT as the active layer have an increased short-circuit current density owing to improved exciton dissociation efficiency, but 2TTT-C₆₀/P3HT devices have a boosted fill factor, owing to the formation of less obstructed pathways for the transport of charge carriers. More interestingly, both 3T-EH-C₆₀/P3HT and 2TTT-EH-C₆₀/P3HT exhibit highly stable blend morphology and the solar cells that are derived from them have extremely steady power conversion efficiency against long-term aging at high temperature.     

Acousto–optical interaction in fishbone-like one-dimensional phoxonic crystal nanobeam

We have investigated the light emission properties in rubrene-doped nematic liquid crystal (LC) cells from the following three standpoints: (i) effect of the heating temperature during the sample preparation, (ii) role of the emissive LC layer thickness, and (iii) role of different LC types used as the emissive layer. As a result, the light-emitting LC cells simultaneously exhibit the features of electrochemiluminescent cells (the carrier transport is governed by an ionic conduction) as well as of organic light-emitting diodes (the luminance strongly depends on the emissive layer thickness). Furthermore, we report that devices with cyano group containing LCs exhibit higher luminance compared to a fluorinated LC.     

A Large-Stroke MEMS Deformable Mirror Fabricated by Low-Stress Fluoropolymer Membrane

This letter presents a deformable mirror (DM) which consists of a 25-mm square flexible membrane and an array of 67 hexagonal electrodes that can pull down a membrane by electrostatic force. The membrane is a 2.15-mum-thick fluoropolymer film and is bonded to an electrode substrate with an 80-mum-thick adhesive acrylic spacer. The fabrication process is completed by a microelectromechanical systems batch process. The surface roughness of polymer membrane is approximately 41 nm. The device demonstrated maximum 38-mum center deflection by applying 250 V because of small residual stress (2.2 MPa) and low Young's modulus (15 GPa) of fluoropolymer film. The response time of the DM is experimentally demonstrated around 10 ms in atmosphere. The proposed device is suitable for large stroke and low sampling rate applications.     

Angle differential‐QAM scheme for resolving phase ambiguity in continuous transmission system

An angle differential quadrature amplitude modulation (ADQAM) scheme is proposed to solve phase ambiguity problem in non‐data‐aided continuous transmission system with square QAM constellation. Starting from the 16‐ADQAM case, we derive differential encoding and decoding schemes in terms of two differential angles and use a solar system analogy for explanation. The 16‐ADQAM system incurs only about 0.5‐dB performance degradation compared with the coherent 16‐QAM system under AWGN channel. Generalization of flat fading channel and higher‐level ADQAM is straightforward. Copyright © 2007 John Wiley & Sons, Ltd.     

Current-Mode Universal Biquadratic Filter with Five Inputs and Two Outputs Using Two Multi-Output CCIIs

A current-mode universal biquadratic filter with five input terminals and two output terminals is presented. The proposed circuit uses two multi-output second generation current conveyors, two grounded capacitors and three resistors. The new circuit offers the following advantages: use of the minimum number of active components, orthogonal controllability of resonance angular frequency and quality factor, use of grounded capacitors and the versatility to synthesize any type of active filter transfer functions.     

Milestones in electron crystallography

Electron crystallography determines the structure of membrane embedded proteins in the two-dimensionally crystallized state by cryo-transmission electron microscopy imaging and computer structure reconstruction. Milestones on the path to the structure are high-level expression, purification of functional protein, reconstitution into two-dimensional lipid membrane crystals, high-resolution imaging, and structure determination by computer image processing. Here we review the current state of these methods. We also created an Internet information exchange platform for electron crystallography, where guidelines for imaging and data processing method are maintained. The server (http://2dx.org) provides the electron crystallography community with a central information exchange platform, which is structured in blog and Wiki form, allowing visitors to add comments or discussions. It currently offers a detailed step-by-step introduction to image processing with the MRC software program. The server is also a repository for the 2dx software package, a user-friendly image processing system for 2D membrane protein crystals.