Modelling a general standby system and evaluation of its performance

Redundancy or standby is a technique that has been widely applied to improving system reliability and availability in system design. In this paper, a general method for modelling standby system is proposed and system performance measures are derived. It is shown that the proposed general standby system includes the cases of cold, hot and warm standby systems with units of exponential distribution, which were studied in the literature, as special cases. An optimal allocation problem for a standby system is also discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis and tentative structure elucidation of new anthocyanins in fruit peel of Vitis coignetiae Pulliat (meoru) using LC‐MS/MS: Contribution to the overall antioxidant activity

The skin of Vitis coignetiae Pulliat (meoru) grown wild in the Republic of Korea was analyzed for anthocyanins via HPLC coupled to ESI‐MS/MS in positive ion mode. Chromatographic separation was conducted via RP HPLC using a C₁₈ column, with a 50‐min gradient from 0 to 80% methanol in water containing 0.5% formic acid. A total of 18 anthocyanins were identified. Among them, nine compounds were newly determined by comparing the retention time (t_R) and mass fragmentation patterns with those of the previously reported anthocyanins for other grape varieties: malvidin hexose, peonidin 3‐galactoside, malvidin 3‐galactoside, cyanidin, petunidin, petunidin 3‐(6″‐coumaroyl)‐5‐diglucoside, peonidin, malvidin, and malvidin 3‐(6″‐coumaroyl)‐5‐diglucoside. The antioxidant activity of the V. coignetiae Pulliat anthocyanins was determined via 2,2‐diphenyl‐2‐picrylhydrazyl radical scavenging and 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) radical cation assays in a range of concentration from 25 to 500 mg/L. The capacity increased with concentration. The IC₅₀ values, defined as the concentration of sample required to scavenge 50% of free radicals, were calculated as follows: 189.63±11.31 mg/L and 141.29±6.70 mg/L for 2,2‐diphenyl‐2‐picrylhydrazyl and 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) radical cation, respectively. The antioxidant activity of the V. coignetiae Pulliat anthocyanins is substantially higher than that of ascorbic acid and is similar to the effects of the extracts obtained from other grape varieties.     

Highly improved oxygen reduction performance over Pt/C-dispersed nanowire network catalysts

Electrochemical reduction of oxygen is studied over a novel nanowire network catalyst made of highly-dispersed Pt nanoparticles into electrospun Pt nanowire network architecture, which shows an excellent mass activity increase by 50% or higher per equal Pt mass than the conventional cathode electrocatalysts of Pt/C in polymer electrolyte membrane fuel cells.     

Preparation of ultrahigh‐molecular‐weight syndiotactic poly(vinyl pivalate) monodisperse microspheres by low‐temperature suspension polymerization of vinyl pivalate

The particle size distributions of poly(vinyl pivalate) (PVPi) produced from low‐temperature suspension polymerization of vinyl pivalate (VPi) with 2,2′‐azobis(4‐methoxy‐2,4‐dimethylvaleronitrile) (AMDMVN) as an initiator have been studied. By controlling various synthesis parameters, near‐monodisperse PVPi microspheres from 100 to 400 μm were obtained that are expected to be precursors of near‐monodisperse syndiotactic poly(vinyl alcohol) (PVA) microspheres for biomedical embolic applications. The mean particle diameter follows the relationship: the volume average diameter, D_vad ∝ Y^0.26[VPi]^0.52[AMDMVN]^?0.25[PVA]^0.40T^?8.35Rpm^?0.67, where Y, [VPi], [AMDMVN], [PVA], T, and Rpm are the fractional conversion, concentrations of VPi, AMDMVN, and suspending agent, polymerization temperature, and agitation speed during the polymerization of VPi, respectively. The polydispersity of the particle size distribution of PVPi decreased with decreasing conversion, [AMDMVN], T, and Rpm and with increasing [VPi]. In the case of [PVA], optimization of the suspension stability led to a narrow particle size distribution. Ultrahigh‐molecular‐weights PVPi and PVA (number‐average degrees of polymerization of PVPi (25,000–32,000) and PVA (14,000–17,500), of high syndiotactic diad content (63%), and of high ultimate conversion of VPi into PVPi (85–95%) were obtained by suspension polymerization at 10 °C, followed by saponification. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 789–800, 2005     

Distinct critical fluctuations and molecular motions manifest in a model biomembrane

Lattice dynamics in bis-(n-C₁₆H₃₇NH₃)₂SnCl₆, where the hydrocarbon part is analogous to lipid membrane, was investigated by means of 200 MHz ¹H nuclear magnetic resonance. As a result, critical fluctuations and molecular dynamics associated with the phase transitions, an order-disorder and a conformational phase transition, were distinguished in a wide temperature range. The dynamical origin of the critical fluctuations, observed in the long-chain compounds but not in the short-chain compounds, by the laboratory frame spin-lattice relaxation measurements, is revealed and discussed in this work.     

Aromatic oxadiazole‐based conjugated polymers with excited‐state intramolecular proton transfer: Their synthesis and sensing ability for explosive nitroaromatic compounds

Aromatic polyoxadiazole derivatives containing 9,9′‐dioctylfluorene were successfully synthesized via the Suzuki coupling reaction. The oxadiazole moiety in the polymer backbone was linked with the bis(hydroxyphenyl) group in its 2‐position to exhibit a large Stokes shift in the emission spectrum due to the excited‐state intramolecular proton transfer. To prepare the polymer via the Suzuki cross‐coupling reaction, the hydroxyl group in the monomer was protected with the t‐butoxycarbonyl group before polymerization and removed after polymerization to a desirable extent. The polymer with the free hydroxyl group showed a considerable sensitivity for nitroaromatic compounds, exhibiting fluorescence quenching in a chloroform solution. The interaction between the electron‐donating OH group and electron‐deficient nitroaromatic compounds seemed to play a decisive role in fluorescence quenching. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2059–2068, 2006     

Optical Security System Based on the Biometrics Using Holographic Storage Technique with a Simple Data Format

We implement a first practical holographic security system using electrical biometrics that combines optical encryption and digital holographic memory technologies. Optical information for identification includes a picture of face, a name, and a fingerprint, which has been spatially multiplexed by random phase mask used for a decryption key. For decryption in our biometric security system, a bit-error-detection method that compares the digital bit of live fingerprint with of fingerprint information extracted from hologram is used.     

Synthesis and isodimorphic cocrystallization behavior of poly(1,4-cyclohexylenedimethylene terephthalate-co-1,4-cyclohexylenedimethylene 2,6-naphthalate) copolymers

A series of poly(1,4-cyclohexylenedimethylene terephthalate-co-1,4-cyclohexylenedimethylene 2,6-naphthalate) [P(CT-co-CN)] copolymers were synthesized, and their cocrystallization behavior was investigated using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). Although the P(CT-co-CN) copolymers synthesized have statistical random distribution of CT and CN units, all the copolymers show clear melting and crystallization peaks in DSC thermograms over entire copolymer composition, and have an eutectic melting temperature in the plot of melting temperature versus copolymer composition. WAXD patterns of all the samples show sharp diffraction peaks, and are largely divided into two classes according to the copolymer composition, that is, PCT-type and PCN-type diffraction patterns. These facts lead us to conclude that P(CT-co-CN) copolymers show isodimorphic cocrystallization. The eutectic composition at which the crystal transition from PCT-type to PCN-type crystal occurs was estimated ca. 40 mol % CN content. When the defect Gibbs free energy was estimated by using the equilibrium inclusion model proposed by Wendling and Suter, the value (7.18 kJ/mol) in the case of incorporation of CT units in the PCN crystals were larger than the case (3.32 kJ/mol) of incorporation of CN units in the PCT crystals. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 177–187, 2004