Electronic coupling in dimetallic complexes with pi-conjugated bridge

Compound 2, [(eta5-C5Me5) Fe(dppe)]2(mu-C[triple bond]C-CH==CH-C[triple bond]C), was prepared by the reaction of compound 1, [eta5-C5Me5) Fe(dppe)]2+ (mu2-C==CH-CH=CH-HC=C).(PF6)2-, with KOBu(t). Compound 2 showed two quasi-reversible one-electron oxidations at -0.674 and -0.253 V, respectively. The comproportionation constant, Kc, was calculated from these measurements. The mixed-valence(MV) radical cation 2+ showed an absorption peak at 1586 nm, which was assigned to the MV pi-pi band of the delocalized complex (Robin-Day Mixed-valence Class III) and the effective coupling parameter, Hab, is consistent with the presence of electronic delocalization.     

Sulfonated poly(ether sulfone)‐based catalyst binder for a proton‐exchange membrane fuel cell

Sulfonated poly(ether sulfone) copolymer (PES 60) and its partially fluorinated analogue (F‐PES 60) were synthesized via the nucleophilic aromatic polycondensation of commercially available monomers to make a polymer electrolyte membrane and a binding material in the electrodes of a membrane–electrode assembly (MEA). PES 60 and F‐PES 60 showed proton conductivities of 0.091 and 0.094 S/cm, respectively, in water at room temperature. The copolymer was dissolved in the mixture of alcohol and water to get a 1 wt % binder solution. A catalyst slurry was prepared with the copolymer solution and sprayed on the copolymer (PES 60 or F‐PES 60) membrane to obtain a MEA. Both PES 60 and F‐PES 60 based MEAs were fabricated with different amounts of their binder in the electrodes to examine the effect of the copolymer binder in the catalyst layer on the fuel cell performance. The MEA with 2 wt % copolymer binder in the electrodes showed the best fuel cell performance. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Assessment of the Efficacy of Intermittent Ozone Disinfection

An example of intermittent disinfection occurs in dental-unit water systems (DUWS), which are disinfected only for a specified time per each day. The efficacy of intermittent ozonation was evaluated using a laboratory-scale, membrane-based ozone disinfection system (MBODS), which delivers bubbleless dissolved ozone to the DUWS. A new tool - the weighted Ct value, or C_w, - was applied to interpret heterotrophic plate counts (HPC) data. To achieve the American Dental Association's (ADA's) criterion (<200 CFU/mL), the required ozone dosage was C_w > 0.07 mg–O₃/L. However, even the highest ozone dosage (C_w > 0.130 mg/L) allowed biofilm HPC to persist at over 10⁴ CFU/cm². Although a higher C_w killed planktonic and biofilm bacteria more thoroughly, it also generated more biodegradable dissolved organic carbon (BDOC). Thus, this research illustrates the inherent trade-off of intermittent ozonation: a higher C_w kills more bacteria during the ozonation period, but creates more BDOC that fosters biofilm regrowth when ozonation is off.     

Fuel cell performance of polymer electrolyte membrane based on hexafluorinated sulfonated poly(ether sulfone)

The potential-current fuel cell characteristics of membrane electrode assemblies (MEAs) using hexafluorinated sulfonated poly(ether sulfone) copolymer are compared to those of Nafion^® based MEAs in the case of proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC). The hexafluorinated copolymer with 60 mol% of monosulfonated comonomer based acid form membrane is chosen for this study due to its high proton conductivity, high thermal stability, low methanol permeability, and its insolubility in boiling water. The catalyst powder is directly coated on the membrane and the catalyst coated membrane is used to fabricate MEAs for both fuel cells. A current density of 530 mA cm^?2 at 0.6 V is obtained at 70 °C with H₂/air as the fuel and oxidant. The peak power density of 110 mW cm^?2 is obtained at 80 °C under specific DMFC operating conditions. Other electrochemical characteristics such as electrochemical impedance spectroscopy, cyclic voltammetry, and linear sweep voltammetry are also studied.     

Fatigue behavior and statistical evaluation of the stress category for a steel-concrete composite bridge deck

The maintenance cost of bridges is rapidly increasing since many existing bridges are deteriorating or reaching their design life all over the world. Moreover, as many long-span bridges are under construction and planning in Korea, research and development on bridge decks with high load-resistance capacity as well as high fatigue strength has become a growing concern. This research gives experimental results of the fatigue behavior of a new-type of steel-concrete composite bridge deck being developed under such circumstances. The proposed composite bridge deck consists of corrugated steel plate, welded steel ribs, stud shear connectors, and reinforced concrete filler. Fatigue tests were conducted under a four-point bending test with four different stress ranges in constant amplitude. In order to determine the influence of the concrete filling, fatigue tests on partial steel specimens containing only plain corrugated steel plates were performed in advance. The partial steel specimens and the steel-concrete composite deck specimens both showed fatigue failure in the tension part concerning the fillet welding part between the corrugated steel plate and steel rib. Finally, the stress category of the fillet welding part of each specimen is evaluated based on a statistical approach of Albrecht’s probability model. The research concludes that the fatigue behavior of such steel-concrete composite decks under sagging moment can be estimated based on the classical S-N approach, focusing on steel components.     

Group Delay Equalized UWB InGaP/GaAs HBT MMIC Amplifier Using Negative Group Delay Circuits

A negative group delay (NGD) circuit has been employed to equalize a group delay variation in a broadband ultra-wideband (UWB) InGaP/GaAs heterojunction bipolar transistor (HBT) monolithic microwave integrated circuit (MMIC) amplifier. Using the NGD circuit, a part of a salient group delay characteristic in the operation band of broadband amplifiers can be suppressed without an increase of the entire group delay. The MMIC amplifier has a steep group delay increase in the lower frequency region of the full-band UWB band (3.1-10.6 GHz) due to the sum of phase variations near the cutoff frequencies of the HBTs. The NGD circuit has been inserted to reduce this increase of the group delay in the UWB band. By adding a three-cell NGD circuit while considering input and output matching at the input side of the MMIC amplifier, the group delay variation is decreased by 78%. However, gain was also decreased by insertion of the multistage NGD circuit. In an attempt to avoid this decrease in gain, a one-cell NGD circuit was inserted into the feedback loop of the MMIC amplifier, and as a result, we were able to decrease the group delay variation by 79%, with minimal gain deterioration.     

Error probabilities of noncoherent and coherent FSK in the presence of frequency and phase offsets for two-hop relay networks

We analyze the error performance of two-hop relay networks adopting frequency shift keying (FSK) over frequencyflat Rayleigh fading channels. It is assumed that relay networks consist of a source, a relay, and a destination without a direct path signal from the source to the destination and the relay adopts the amplify-and-forward protocol with a fixed gain. Firstly, considering imperfect frequency and phase synchronization, we obtain the exact error probability expressions for noncoherent and coherent binary FSK (BFSK). Secondly, assuming perfect frequency and phase synchronization, we derive a closed-form error probability approximation for coherent M-ary FSK (MFSK). The proposed methods can also be used for the error performance analysis of classical one-hop FSK systems with perfect/imperfect frequency and phase synchronization. The obtained error probability expressions will help the design of two-hop relay networks adopting FSK in determining the system parameters such as the transmission power at the source, the amplifying coefficient at the relay, and the maximum affordable frequency and phase offsets to satisfy the required error performance.     

Multilevel Programmable Oxide Diode for Cross-Point Memory by Electrical-Pulse-Induced Resistance Change

A multilevel one-time programmable (OTP) oxide diode for cross-point memory is introduced. The oxide diode is composed of a thin-film p-CuO/n-InZnOx (IZO). By applying negative electrical pulses, the p-CuO/n-IZO diode exhibited multilevel resistance states, and such characteristics of the p-CuO/n-IZO diode could be utilized as the cell of OTP cross-point memory. The resistance-change properties of the p-CuO/n-IZO diode originated possibly from a back-to-back diode phenomenon by oxygen ion migration in the IZO thin film.     

Design and implementation of a uniformity-improving page allocation scheme for flash-based storage systems

Flash memory is being actively employed in a variety of embedded systems such as digital cameras, MP3 players, cell phones, solid state disks (SSDs), and digital media broadcasting (DMB) devices. This paper considers performance issues in file systems that employ Flash memory as a storage medium. Firstly, it explores the characteristics of Flash memory and identifies the cost of block cleaning as the key performance bottleneck for Flash memory analogous to the seek time in disk storage. Then, it defines three performance parameters, namely, utilization, invalidity, and uniformity and derives a formula for block cleaning cost based on these parameters. It is shown that, of these parameters, uniformity exerts the strongest influence on the cost of cleaning and that uniformity is a file system controllable parameter. Finally, we design a uniformity-aware page allocation scheme and analyze how enhanced uniformity affects the block cleaning cost with various workloads. Real implementation experiments conducted on an embedded system show that the scheme proposed here typically reduces the cleaning time by 20 to 30% compared to the traditional sequential allocation scheme that is used in YAFFS.     

Design and implementation of an adaptive recurrent neural networks (ARNN) controller of the pneumatic artificial muscle (PAM) manipulator

This paper presents the design, development and implementation of an adaptive recurrent neural networks (ARNN) controller suitable for real-time manipulator control applications. The unique feature of the ARNN controller is that it has dynamic self-organizing structure, fast learning speed, good generalization and flexibility in learning. The proposed adaptive algorithm focuses on fast and efficient optimization by weighting parameters of inverse recurrent neural models used in the ARNN controller. This approach is employed to implement the ARNN controller with a view to controlling the joint angle position of the highly nonlinear pneumatic artificial muscle (PAM) manipulator in real-time. The performance of this novel proposed controller was found to be superior compared with a conventional PID controller. These results can be applied to control other highly nonlinear systems as well.