Perpendicularly Aligned,Size‐and Spacing‐Controlled Nanocylinders by Molecular‐Weight Adjustment of a Homopolymer Blended in an Asymmetric Triblock Copolymer

Perpendicularly arrayed and size‐controlled nanocylinders have been prepared by simply blending an asymmetric polystyrene‐block‐polyisoprene‐block‐polystyrene triblock copolymer with polystyrene (the minority component) homopolymers of different molecular weights. The preference for perpendicular orientation or hexagonal ordering of the nanocylinders over a large area in the asymmetric block copolymer can be controlled by adjusting the molecular weight of the blended homopolymer, and the perfection of hexagonal ordering of the perpendicular cylinders can be tuned by using a substrate whose surface tension is much different from that of the majority component of the block copolymer. Such highly controlled nanostructured block‐copolymer materials, which have been obtained by a simple method independent of film thickness and interfacial tension between the blocks and the substrates, have wide‐ranging commercial potential, e.g., for use in membranes and nanotemplates with size‐tunable pores, bandgap‐controlled photonic crystals, and other nanotechnological fields demanding a specific nanosize and nanomorphology.     

Improvement of the cell performance in the ZnS/Cu(In,Ga)Se2 solar cells by the sputter deposition of a bilayer ZnO : Al film

ZnS is a candidate to replace CdS as the buffer layer in Cu(In,Ga)Se₂ (CIGS) solar cells for Cd‐free commercial product. However, the resistance of ZnS is too large, and the photoconductivity is too small. Therefore, the thickness of the ZnS should be as thin as possible. However, a CIGS solar cell with a very thin ZnS buffer layer is vulnerable to the sputtering power of the ZnO : Al window layer deposition because of plasma damage. To improve the efficiency of CIGS solar cells with a chemical‐bath‐deposited ZnS buffer layer, the effect of the plasma damage by the sputter deposition of the ZnO : Al window layer should be understood. We have found that the efficiency of a CIGS solar cell consistently decreases with an increase in the sputtering power for the ZnO : Al window layer deposition onto the ZnS buffer layer because of plasma damage. To protect the ZnS/CIGS interface, a bilayer ZnO : Al film was developed. It consists of a 50‐nm‐thick ZnO : Al plasma protection layer deposited at a sputtering power of 50 W and a 100‐nm‐thick ZnO : Al conducting layer deposited at a sputtering power of 200 W. The introduction of a 50‐nm‐thick ZnO : Al layer deposited at 50 W prevented plasma damage by sputtering, resulting in a high open‐circuit voltage, a large fill factor, and shunt resistance. The ZnS/CIGS solar cell with the bilayer ZnO : Al film yielded a cell efficiency of 14.68%. Therefore, the application of bilayer ZnO : Al film to the window layer is suitable for CIGS solar cells with a ZnS buffer layer. Copyright © 2012 John Wiley & Sons, Ltd.     

A novel hybrid silica wide-band amplifier covering S+C+L bands with 105-nm bandwidth

We report a novel hybrid optical amplifier covering S+C+L bands with 105-nm total bandwidth using a silica fiber. The principle of amplification is based on the stimulated radiative transition of Er-ions for C-band and on the stimulated Raman scattering for S- and L-band, respectively. In this letter, we analyze the amplification characteristics for two types of active fiber mediums through numerical simulation. One is a silica fiber configured with Er-doped cladding and Ge-doped core and the other is a medium consisting of Er-doped fiber and dispersion-compensating fiber. By optimizing parameters such as fiber length and pump power, we newly achieve wide-band amplification with 105-nm bandwidth showing a flat gain characteristic over the entire S+C+L bands.     

A Framework for MPEG‐4 Contents Delivery over DMB

Digital Multimedia Broadcasting (DMB) is an upcoming standard in Korea used to provide mobile multimedia broadcasting service based on the Eureka‐147 Digital Audio Broadcasting (DAB) system. The current dominant multimedia coding standard, MPEG‐4, is foreseen to play an important role in forthcoming DMB services. However, the current approaches for transporting MPEG‐4 content over DMB networks are not optimized. To address this issue we propose a novel MPEG‐4 stream multiplexer, called M4SMux, which provides better stream multiplexing and delivery over DMB networks. M4SMux features an MPEG‐4 elementary‐stream interleaving mechanism that reduces the multiplexing overhead and a multiplex configuration mechanism that utilizes M4SLinkTable for easy content access. In addition, we propose an error correction method which enhances transport efficiency.     

Double-pass resonant Er-Raman amplifier

A new double-pass wideband Er-Raman fibre amplifier is proposed, pumped by a Raman laser oscillating through a medium consisting of Er-doped fibre and dispersion compensating fibre in series.     

A fast fully 4-D incremental gradient reconstruction algorithm for list mode PET data

We describe a fast and globally convergent fully four-dimensional incremental gradient (4DIG) algorithm to estimate the continuous-time tracer density from list mode positron emission tomography (PET) data. Detection of 511-keV photon pairs produced by positron-electron annihilation is modeled as an inhomogeneous Poisson process whose rate function is parameterized using cubic B-splines. The rate functions are estimated by minimizing the cost function formed by the sum of the negative log-likelihood of arrival times, spatial and temporal roughness penalties, and a negativity penalty. We first derive a computable bound for the norm of the optimal temporal basis function coefficients. Based on this bound we then construct and prove convergence of an incremental gradient algorithm. Fully 4-D simulations demonstrate the substantially faster convergence behavior of the 4DIG algorithm relative to preconditioned conjugate gradient. Four-dimensional reconstructions of real data are also included to illustrate the performance of this method.     

Fully aromatic polyimide gate insulators with low temperature processability for pentacene organic thin-film transistors

This paper demonstrates the effects of the imidization ratio of polyimide gate insulators on the performance of organic thin-film transistors (OTFTs). We report the synthetic results of polyimide films imidized at a temperature of 200 °C along with an easily removed organic base catalyst (1,8-diazabicyclo[5.4.0]undec-7-ene, DBU), and their application in gate insulators of organic thin-film transistors. The degree of imidization increased to almost 100% after a thermal treatment at 200 °C for 40 min in the presence of DBU. The performance of the pentacene OTFT dramatically improved by using low temperature cured polyimide film as the gate insulator.     

Broadcasting System Compliant with MPEG‐2/4 IPMPX

In this paper, we present an intellectual property management and protection (IPMP) system in a broadcasting environment to provide mechanisms for copyright and contents protection that are compliant with the MPEG‐2 and MPEG‐4 IPMP Extension (IPMPX) specifications. The technology for processing IPMP related information was exploited, and a terminal model has been successfully designed and implemented. In addition, interoperability, which is the main objective of MPEG‐2/4 IPMPX, has been addressed in detail. The experimental results show that the implemented system performs the IPMP process well, meeting the requirements of a broadcasting environment.     

A 2-Gbaud 0.7-V swing voltage-mode driver and on-chip terminatorfor high-speed NRZ data transmission

A large-swing, voltage-mode driver and an on-chip termination circuit are presented for high-speed nonreturn-to-zero (NRZ) data transmission through a copper cable. The proposed driver with active pull-up and pull-down can generate a 700-mV signal to deliver a 2 Gbaud serial NRZ data stream. Low output impedance offered by simple negative-feedback resistors alleviates the detrimental effect of the parasitic capacitance by supplying fast current impulses. A proposed on-chip termination circuit provides termination impedance to a mid-supply termination voltage with the benefit of reduced parasitic capacitance and better termination characteristics compared with off-chip termination. The driver and termination circuits have been incorporated in a 2 Gbaud transceiver chip and fabricated in 0.35 μm CMOS technology. Measurements show a 1.4 V differential swing with a slew rate of 2.5 V/ns at the receiver output and a 65% reduction of reflection by the on-chip termination circuit with power consumption of 191 mW at 3.3 V supply