Oxidation of formic acid at a high surface area supported platinum modified by foreign metal adatoms

The anodic oxidation of formic acid was studied on platinum distributed in the form of small particles in a porous substrate modified by metal adatoms deposited at underpotentials. The rate of the reaction was greatly enhanced on the commercial catalyst Powercat 3000 (PC 3000). The hydrogen adsorption and the underpotential deposition of several metals at PC 3000 were shown to be dissimilar to that at smooth polycrystalline Pt. Steady-state and long-term experiments were performed to determine the stability of this electrode.     

Nonstoichiometry and Defect Chemistry of Ceria Solid Solutions

Ceria solid solutions are potential electrolytes for solid oxidefuel cells (SOFC). At the anode side of SOFCs at low oxygen partialpressures ceria is partially reduced. The nonstoichiometry ofCeO_2-x solid solutions with 20 mol%SmO_1.5, 20 mol% GdO_1.5 and 10 mol%CaO were investigated by isothermal coulometric titration in a zirconia cellin the temperature range from 700 to 900°C and in the oxygen partialpressure range from 10^-12 to 10^-25 atm. Theresults of the 3 different compositions at 900°C are comparable to thosefor pure ceria. At lower temperatures, pure ceria is more stable againstreduction than ceria solid solutions. The dependence of nonstoichiometry onoxygen partial pressure suggests a defect model with oxygen vacancies andtheir associates with reduced cerium cations and dopant cations. Low oxygennonstoichiometries of x = 0.005 to 0.008 can be expected for ceria solidsolutions at 700° under SOFC operating conditions.     

The influence of the degree of heterogeneity on the elastic properties of random sphere packings

The macroscopic mechanical properties of colloidal particle gels strongly depend on the local arrangement of the powder particles. Experiments have shown that more heterogeneous microstructures exhibit up to one order of magnitude higher elastic properties than their more homogeneous counterparts at equal volume fraction. In this paper, packings of spherical particles are used as model structures to computationally investigate the elastic properties of coagulated particle gels as a function of their degree of heterogeneity. The discrete element model comprises a linear elastic contact law, particle bonding and damping. The simulation parameters were calibrated using a homogeneous and a heterogeneous microstructure originating from earlier Brownian dynamics simulations. A systematic study of the elastic properties as a function of the degree of heterogeneity was performed using two sets of microstructures obtained from Brownian dynamics simulation and from the void expansion method. Both sets cover a broad and to a large extent overlapping range of degrees of heterogeneity. The simulations have shown that the elastic properties as a function of the degree of heterogeneity are independent of the structure generation algorithm and that the relation between the shear modulus and the degree of heterogeneity can be well described by a power law. This suggests the presence of a critical degree of heterogeneity and, therefore, a phase transition between a phase with finite and one with zero elastic properties.     

发挥咨询业作用,推进工程项目管理

承包商对工程的具体掌控力要远高于业主方,业主方面对工程实施中的各种问题往往鞭长莫及。为了帮助业主方从源头上实现项目的成功管理,就要发挥工程咨询机构的作用。本文论述了工程咨询机构在招标阶段项目管理的核心内容,指明了其在招标阶段的关键工作,在一定程度上实现了项目资源的优化配置,为业主节约了成本和效益最大化。同时,也分析了我国目前项目管理发展中存在的问题,并参照国内外先进管理思想和管理模式提出了我国工程咨询机构的发展方向及相应对策,对我国工程咨询业的发展有一定的参考价值。     

CeO2−CoO Phase Diagram

Phase equilibria in the CeO₂−CoO system at temperatures above 1500°C were investigated. The microstructures and the phase compositions of the DTA (differential thermal analysis) samples and the quenched solid pellets were analyzed using SEM (scanning electron microscope), EDX (energy dispersive X-ray), and WDX (wavelength dispersive X-ray). A eutectic reaction was found at 1645 ± 5°C. The eutectic point was calculated to be at 82 ± 1.5 mol% CoO. The eutectic phases were the CeO₂-rich phase (containing <5 mol% CoO) and the CoO-rich phase (containing ∼0.5 mol% CeO₂). At 1580°C, the solubility of CoO in CeO₂ was ∼3 mol%.     

Wet-etching of precipitation-based thin film microstructures for micro-solid oxide fuel cells

In micro-solid oxide fuel cells (μ-SOFCs) ceramic thin films are integrated as free-standing membranes on micromachinable substrates such as silicon or Foturan^® glass ceramic wafers. The processing of μ-SOFCs involves unavoidable dry- or wet-chemical etching for opening the substrate below the free-standing fuel cell membranes. In the first part of this paper current dry- and wet-chemical etchants for structuring of ceria-based electrolyte materials are reviewed, and compared to the etch-rates of common μ-SOFCs substrates. Wet-chemical etchants such as hydrofluoric acid are of high interest in μ-SOFC processing since they allow for homogeneous etching of ceria-based electrolyte thin films contrary to common dry-etching methods. In addition, HF acid is the only choice for substrate etching of μ-SOFC based on Foturan^® glass ceramic wafers. Etching of Ce_0.8Gd_0.2O_1.9?x spray pyrolysis electrolyte thin films with 10% HF:H₂O is investigated. The etch-resistance and microstructures of these films show a strong dependency on post deposition annealing, i.e. degree of crystallinity, and damage for low acid exposure times. Their ability to act as a potential etch-resistance for μ-SOFC membranes is broadly discussed. Guidance for thermal annealing and etching of Ce_0.8Gd_0.2O_1.9?x thin films for the fabrication of Foturan^®-based μ-SOFCs is given.     

Structurally related peptide agonist, partial agonist, and antagonist occupy a similar binding pocket within the cholecystokinin receptor. Rapid analysis using fluorescent photoaffinity labeling probes and capillary electrophoresis

The molecular basis of ligand binding to receptors provides important insights for drug development. Here, we explore domains of the cholecystokinin (CCK) receptor that are critical for ligand binding, using a novel series of fluorescent photolabile probes, receptor proteolysis, and rapid high resolution separation of peptide fragments by capillary electrophoresis. Each probe incorporated the same fluorophore and a photolabile p-benzoylphenylalanine at the amino terminus of the pharmacophoric domain (residue 24 of CCK-33) of CCK analogues representing full agonist, partial agonist, and antagonist of this receptor. Each was used to label the CCK receptor expressed on Chinese hamster ovary-CCKR cells, with the labeled domain then released by cyanogen bromide cleavage. Capillary electrophoresis with laser-induced fluorescence detection achieved an on-capillary mass sensitivity of 1.6 attomoles (10(-18) mol), with an excellent signal-to-noise ratio. Each of the biologically divergent, but structurally similar probes saturably and specifically labeled the same receptor domain, consistent with conservation of "docking" determinants. This had an apparent mass of 2.9 kDa, most consistent with the first extracellular loop domain. An additional probe having its site of covalent attachment in a different region of the probe (residue 29 of CCK-33) labeled a distinct receptor fragment with differential migration on capillary electrophoresis (third extracellular loop). Identification of the specific receptor residue(s) covalently linked to the amino-terminal probes must await further fragmentation and sequence analysis.     

A study of rural Latino women seeking cancer-detection examinations

Not only the ovarian steroids but a number of proteins have an effect on the endometrium and its capability to accept an implanting embryo and to establish a pregnancy. In this study we have selected the placental protein 14 (PP14) which is, in spite of its name, produced by the glandular epithelium of the endometrium. Pregnancy-specific beta 1-glycoprotein (SP1) was also investigated. This marker is trophoblast-specific but it has been chosen since some patients repeatedly exhibit weak but detectable serum SP1 when no embryo is present. There seems to be a negative correlation between the chance of obtaining a pregnancy and the occurrence of such abnormal serum SP1 signals; they could originate from the endometrium itself or from another maternal source influencing the endometrium indirectly. The full-cycle time course was determined for these two proteins as well as for estradiol and progesterone. A total of 66 cycles were analyzed, of which 16 were from ovulating volunteers without any hormonal treatment (controls) and 13 were from women taking oral contraceptives. The remaining 37 cycles were from 32 patients undergoing conventional in vitro fertilization (IVF) treatment. Eight pregnancies were achieved in this group during the study period. We found that abnormal positive SP1 signals occurred predominantly in the unsuccessful IVF subgroup, but also in the control groups (with or without contraceptive pills), and this in a cycle-independent manner. PP14, on the other hand, exhibited cyclic patterns in the IVF and ovulating control cycles as did progesterone. However, in seven out of 13 cycles under oral contraception (and suppressed progesterone), a midcycle rise in PP14 was observed. Moreover, midcycle PP14 levels were generally higher in this group when compared to the ovulating controls as well as to the cycles under controlled ovarian stimulation for IVF. This confirms that PP14 is influenced by progesterone but only in an indirect way or under the additional effect of other hormones. It is unlikely that SP1 plays this role since it was not correlated to any of the other proteins or steroids studied. Nevertheless, SP1 did not occur randomly over the different groups.     

Supplementation with isoflavonoid phytoestrogens does not alter serum lipid concentrations: a randomized controlled trial in humans

Isoflavonoids are a class of flavonoids that are derived in the human diet mainly from soybean-based foods. The major dietary isoflavonoids, genistein and daidzein, have estrogen-like activity and are classed as phytoestrogens. Because estrogens can lower serum LDL cholesterol and raise HDL cholesterol, the objective of this study was to determine if isoflavonoids could improve serum lipids in healthy subjects. Forty-six men and 13 postmenopausal women not receiving hormone replacement therapy completed a randomized, double-blind, placebo-controlled trial of two-way parallel design and 8 wk duration. One tablet containing 55 mg of isoflavonoids (predominantly in the form of genistein) or one placebo tablet was taken daily with the evening meal. Subjects maintained their usual diet and physical activity, which were unchanged throughout the intervention. Measurement of isoflavonoids and their metabolites in 24-h urine samples provided an assessment of compliance and of isoflavonoid metabolism. Serum total, LDL, HDL and HDL subclass cholesterol, triglycerides and lipoprotein (a) were assessed at baseline and during the last week of intervention. After adjustment for baseline values, no significant differences in postintervention serum lipid and lipoprotein (a) concentrations between groups were identified. Further adjustment for age, gender and weight change did not alter the results. In addition, changes in urinary isoflavonoids were not significantly correlated with changes in serum lipids and lipoprotein (a). Therefore, this study does not support the hypothesis that isoflavonoid phytoestrogens can improve the serum lipids, at least in subjects with average serum cholesterol concentrations.