Electrocatalyst materials for fuel cells based on the polyoxometalates—K7 or H7[(P2W17O61)Fe(H2O)] and Na12 or H12[(P2W15O56)2Fe4(H2O)2]

Free acids of the iron substituted heteropoly acids (HPA), H₇[(P₂W₁₇O₆₁)Fe^III(H₂O)] (HFe1) and H₁₈[(P₂W₁₅O₅₆)₂Fe^III₂(H₂O)₂] (HFe2) were prepared from the salts K₇[(P₂W₁₇O₆₁)Fe^III(H₂O)] (KFe1) and Na₁₂[(P₂W₁₅O₅₆)₂Fe^III₄(H₂O)₂] (NaFe4), respectively. The iron-substituted HPA were adsorbed on to XC-72 carbon based GDLs to form HPA doped GDEs after water washing with HPA loadings of ca. 1 μmol. The HPA was detected throughout the GDL by EDX. Solution electrochemistry of the free acids are reported for the first time in sulfate buffer, pH 1-3. The hydrogen oxidation reaction was catalyzed by KFe1 at 0.33 V, with an exchange current density of 38 mA/cm². Moderate activity for the oxygen reduction reaction was observed for the iron substituted HPA, which was dramatically improved by selectively removing oxygen atoms from the HPA by cycling the fuel cell cathode under N₂ followed by reoxidation to give a restructured oxide catalyst. The nanostructured oxide achieved an OCV of 0.7 V with a Tafel slope of 115 mV/decade. Cycling the same catalysts in oxygen resulted in an improved catalyst/ionomer/carbon configuration with a slightly higher Tafel slope, 128 mV/decade but a respectable current density of 100 mA/cm² at 0.2 V.     

Synthesis and characterization of organosoluble luminescent poly(amide-imide)s

Poly(amide-imide)s (PAIs) were synthesized from 9,9’-bis(4-aminophenyl)fluorene (APF) and different diimide-dicarboxylic acids (DIDA). The aromatic fluorene group is isolated by DIDA. The structure of the polymer was confirmed by ¹H NMR, ¹³C NMR, and FTIR. These PAIs were soluble in polar aprotic solvents, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide. The crystallinity of the polymers is estimated by means of wide-angle X-ray diffraction. The resultant PAIs exhibited nearly amorphous nature. Thermal stability of the PAIs was characterized by differential scanning calorimetry and thermogravimetric analysis. No obvious glass transition temperatures were detected and the 5% weight loss temperatures of the PAIs were in the range 296–453 °C in nitrogen. The optical properties were studied by Ultraviolet–visible (UV/VIS) spectra and photoluminescent (PL) in solution and film states. The results show similar absorbance and emission to those of the constituting APF monomer. The highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) were estimated from cyclic voltammograms. The values of HOMO and LUMO are -6.67 to -6.72, and -3.54 to -3.58, respectively. Their optical and electrochemical properties are not changed significantly by different DIDA.     

铁皮石斛多糖调控线虫寿命及抗氧化作用的研究

摘 要: 目的 基于秀丽隐杆线虫自然衰老模型, 探讨铁皮石斛多糖(Dendrobium candidum polysaccharides, DOP)抗衰老作用及其机制。方法 将秀丽隐杆线虫野生型N2随机分为对照组和铁皮石斛多糖组(低、中、高), 观察铁皮石斛多糖对线虫N2寿命、运动能力和咽泵能力的影响; 通过检测氧化应激、抗氧化酶试剂盒以及活性氧评估铁皮石斛多糖对N2线虫抗氧化能力的影响。基于skn-1基因缺陷型突变株(EU1)线虫及带有荧光标记的转基因线虫CL2166分析铁皮石斛多糖延长健康寿限的可能作用途径; 采用实时荧光定量聚合酶链反应技术测定铁皮石斛多糖作用下线虫抗氧化、胰岛素信号途径相关基因转录水平。结果 铁皮石斛多糖中剂量组(250 μg/mL)可显著延长线虫N2的寿命, 平均延寿率达12.73%, 可显著提高运动、咽泵、抗氧化应激能力; 显著提高过氧化氢酶(catalase, CAT)、超氧化物歧化酶(superoxide disumutase, SOD)活性和谷胱甘肽(glutathione, GSH)含量, 降低活性氧(reactive oxygen species, ROS)水平和丙二醛(malondialdehyde, MDA)含量; 铁皮石斛多糖干预处理对skn-1基因缺陷线虫的延寿效果缺失; 但能够增强CL2166线虫的荧光强度; 同时上调sod-5、sod-3、ctl-1、ctl-2、daf-16和skn-1基因的表达水平, 下调daf-2基因的表达水平。结论 铁皮石斛多糖可能通过激活Nrf2/SKN-1和DAF-16途径拮抗氧化应激从而延缓线虫衰老。     

Analysis of Field Data on Computer Failures

This paper emphasizes the importance of making field measurements for effective and realistic dependability evaluatians.Two examples are given,both based on real data from IBM mainframes.The first evaluates the imnact of the operating environment on system failure characteristics and the second shows how an accurate model depicting this interaction can be extracted from real data.     

A 50 GHz Divide-by-4 Injection Lock Frequency Divider Using Matching Method

A fully integrated divide-by-4 frequency divider has been designed, fabricated, and measured in the standard bulk 0.18-m complementary metal-oxide semiconductor (CMOS) technology. A newly proposed matching technique was used to eliminate the unwanted low frequency mixing terms at the common node of the circuit so as to achieve a high division ratio of 4. The frequency divider exhibits a measured operation range of 5 GHz from 45.9 to 50.9 GHz. It consumes a dc power of 7.56 mW at a 1.2 V supply in the steady state operation. The phase noise of the free running divider is 88.51 dBc/Hz at 1 MHz offset and the locked divider is 110.74 dBc/Hz at 1 MHz offset. The chip size is only 0.35 mm 0.5 mm including the pad frame. To our knowledge, this divider has the highest operation frequency to date among the high division ratio injection-lock type frequency dividers in commercial CMOS 0.18-m process.     

A 21 GHz Complementary Transformer Coupled CMOS VCO

A new topology for low power voltage controlled oscillators (VCOs) using a 0.18-mum CMOS foundry process is presented in this letter. From the measured results, the VCO exhibits a tuning range of 3% at 21.3 GHz. Using complementary topology, the core power consumption and the output power are 9.6 mW and -3 dBm, respectively. With the broadside coupled transformer, the VCO achieves a good phase noise of -106 dBc/Hz at 1 MHz offset and a compact chip size of 350 times 470 mum². It is the first time that the broadside coupled transformer approach is applied to transformer coupled CMOS VCOs.     

Effects of IS characteristics on e-business success factors of small- and medium-sized enterprises

The current research presents a theoretically sound model of the effects of the characteristics of information systems (IS) on the perception of end-users regarding computer self-efficacy and outcome expectations. The relationships among factors of small- and medium-sized enterprises in Taiwan are examined based on the IS success model and social cognitive theory. A mail survey was conducted, generating 284 usable responses with a total response rate of 51.64%. Structural equation modeling was employed to assess the relationships among related constructs. Data analysis shows that (1) no direct links exist between computer self-efficacy and either information quality or service quality, although certain effects are observable on system quality; (2) the relationships between outcome expectations and both system quality and service quality are significant; however, the relationship with information quality is insignificant; and (3) outcome expectations mediate the effects of computer self-efficacy on end-user satisfaction. The implications of the results are provided, and directions for future research are discussed in the study.     

Thermoplastic Polyurethane Reinforced with Continuous Carbon Fiber Tows: Manufacturing Technique and Fabric Property Evaluation

Co-extrusion technique is used to combine carbon fiber tows and thermoplastic polyurethane (TPU) blends into composite carbon fibers (CCFs). The TPU blends serve as the shell and the carbon fiber tows serve as the core. CCFs are fabricated into woven composites and knitted composites with electromagnetic interference shielding effectiveness (EMI SE). The effects of the content of carbon fiber tows on different fabrics are examined. The failure mechanism of CCFs is improved as the fiber slippage along the axial direction replaces the fiber fracture. Fabrics made of CCFs are soft. The laminated woven composites have an average EMI SE of -27.20 dB at 0–3000 MHz and -44.99 dB at 2450 MHz, suggesting a good EMI attenuation capability. This study proposes the use of co-extrusion technique followed coating and fabrication of carbon fibers. This brand-new concept would be vital in the development of carbon fiber composites.

     

Tensile strength,peel load,and static puncture resistance of laminated composites reinforced with nonwoven fabric

Nonwoven fabrics were used as reinforcement to laminated composites to improve the mechanical properties and damage behaviors. The needle-punched Kevlar/LMPET nonwoven interlayer and two TPU covers were combined via thermal bonding to form the laminated composites. Tensile strength, peel load, and static puncture resistance of the laminated composites were evaluated in terms of needle punching rate and depth of the nonwoven interlayer. Results showed that tensile strength and static puncture resistance depended on the needle punching depth, primarily on the tangled fiber points. The peel load was dependent on the needle punching rate, especially on the resulting melted LMPET fibers. The laminated composites exhibited desirable tensile properties, peel load, and static puncture resistance.     

Salivary cotinine concentration versus self-reported cigarette smoking: Three patterns of inconsistency in adolescence.

The present study examined the extent and sources of discrepancies between self-reported cigarette smoking and salivary cotinine concentration among adolescents. The data are from household interviews with a cohort of 1,024 adolescents from an urban school system. Histories of tobacco use in the last 7 days and saliva samples were obtained. Logistic regressions identified correlates of three inconsistent patterns: (a) Pattern 1-self-reported nonsmoking among adolescents with cotinine concentration above the 11.4 ng/mg cutpoint (n = 176), (b) Pattern 2-low cotinine concentration (below cutpoint) among adolescents reporting having smoked within the last 3 days (n = 155), and (c) Pattern 3-high cotinine concentration (above cutpoint) among adolescents reporting not having smoked within the last 3 days (n = 869). Rates of inconsistency were high among smokers defined by cotinine levels or self-reports (Pattern 1 = 49.1%; Pattern 2 = 42.0%). Controlling for other covariates, we found that reports of nonsmoking among those with high cotinine (Pattern 1) were associated with younger age, having few friends smoking, little recent exposure to smokers, and being interviewed by the same interviewer as the parent and on the same day. Low cotinine concentration among self-reported smokers (Pattern 2) was negatively associated with older age, being African American, number of cigarettes smoked, depth of inhalation, and exposure to passive smoke but positively associated with less recent smoking and depressive symptoms. High cotinine concentrations among self-reported nonsmokers was positively associated with exposure to passive smoke (Pattern 3). The data are consonant with laboratory findings regarding ethnic differences in nicotine metabolism rate. The inverse relationship of cotinine concentration with depressive symptoms has not previously been reported. Depressed adolescent smokers may take in smaller doses of nicotine than nondepressed smokers; alternatively, depressed adolescents may metabolize nicotine more rapidly.