A novel Pt/Cr/Ru/C cathode catalyst for direct methanol fuel cells (DMFC) with simultaneous methanol tolerance and oxygen promotion

New carbon supported electrocatalysts Pt/Cr/Ru with distinct compositions and preparation methods were studied with the help of different electrochemical and spectroscopic techniques. The purposes of obtaining these catalysts lie on their possibilities towards methanol/oxygen fuel cells. In this sense, the oxygen reduction reaction and methanol oxidation reaction were analyzed using stationary and fluid dynamic methodologies. Pt_7.8/Ru_1.3/Cr_0.5 and Pt_8.0/Ru_2.0/Cr_0.1 were the most interesting prepared substrates, on which the first one shows the best catalytic properties towards methanol oxidation and the second the finest performance towards oxygen reduction reaction. Reaction orders with respect to oxygen for the oxygen reduction reaction were obtained being equal to ½ at potentials lower than 0.80 V for both catalysts. Polarization curves run for this reaction depicted two Tafel slopes, i.e. 0.09 V dec⁻¹ above 0.8 V and 0.20 V dec⁻¹ below 0.8 V for both catalysts. An analysis of the most likely mechanism for the oxygen reduction was proposed on the base of those reaction orders and Tafel slopes.     

Negligible depletion solid-phase microextraction with radiolabeled analytes to study free concentrations and protein binding: an example with [3H]estradiol

A new method is presented that enables sensitive measurement of free concentrations of radiolabeled ligands. Additionally, protein binding of radiochemicals in complex matrixes can be determined with this new technique that combines negligible depletion solid-phase microextraction (nd-SPME) with liquid scintillation counting (LSC) as detection. [3H]Estradiol was taken as an example compound. Possible matrix effects of protein on fiber uptake kinetics were studied. No matrix effect was found, either by fouling of the fiber, or by changed uptake kinetics. The validity of the method was shown in the determination of the affinity constant (Ka) of estradiol for human serum albumin (HSA). The Ka was estimated at 8.9 x 10(4) M(-1), which corresponds well with literature values. This study shows that nd-SPME is suitable to study the free concentration and protein binding of [3H]estradiol. The method described in this paper combines the advantages of nd-SPME with the advantages of radiolabeled analytes, creating a timesaving, simple, and sensitive analytical tool that will be particularly useful in complex matrixes containing many potential interferences for chromatographic methods.     

A comparison of specular reflection and PA-FTIR techniques in the analysis of annealed injection-molded polyamide 6,6

A comparative study between the specular reflectance and photoacoustic FTIR techniques is presented in this work. The potential and limitations of these two methods are investigated by following and analyzing structural variations that take place at the surface in annealed injection-molded polyamide 6,6. Both spectroscopic techniques appear to be quite sensitive in detecting small structural changes that occur in polyamide 6,6 when submitted to different annealing temperatures. However, the presence of distorted bands in the specular reflection spectra makes the photoacoustic FTIR method more attractive for the IR vibrational analysis of difficult materials (e.g., composites, black-filled polymers, paints, etc.) that cannot be easily characterized by conventional transmission FTIR. © 1994 John Wiley & Sons, Inc.     

Finite element method and limit analysis theory for soil mechanics problems

This paper deals with a finite element formulation of problems of limit loads in soil mechanics via limit analysis theory. After recalling the principal results of this theory, the authors describe a numerical formulation for both the static and kinematic approaches of the ultimate load. Thanks to linearization of the yield criterion, the finite element model leads to a linear programming problem. The efficiency of the two proposed computing procedures is demonstrated by their application to the problem of pulling out of foundations and slope stability.     

Crystal growth of alkaline earth fluorides in a reactive atmosphere. Part II

Crystal growth of MF₂ (M = Ca, Sr, and Ba) is carried out under two different reactive atmospheres, HF and HF + CF₄, with the same carrier gas (He). The effect of processing is seen in a comparison of the optical transparency in the near infrared of the single-crystal specimens.     

Congruently melting compounds of CaF2 · rcRF3: Part II

Crystals of congruently melting CaF₂ · r_cRF₃, where R = Gd, Tb, Dy, Ho, Y and Er, were shown to have the tysonite (LaF₃-type) structure. From the lattice constants, crystal composition (r_c) and density (p), these compounds are seen to be an extended form of the hexagonal (tysonite) structure of the corresponding RF₃. In these compounds, Ca²⁺ enters substitutionally compensated by a fluoride ion vacancy. The partial molar volume of RF₃ in the compound is a constant of the class of R and equals 37.6 cm³.     

The quality of mother–infant attachment and its relationship to toddlers' initial sociability with peers.

37 age- and sex-matched toddler dyads were observed between ages 20 and 23 mo in a 30-min play session with mothers present. Assignment to dyad was determined by attachment classification, assessed at 18 mo in the M. D. Ainsworth et al (1978) Strange Situation procedure. Ss classified as securely attached (SAs), anxiously avoidant (AAs), or anxiously resistant (ARs) were paired with SAs. In the play situation, SAs were more sociable and more positively oriented toward both mother and peer. Mothers of SAs were more supportive and appropriately directive and played an important role in successful outcomes for their children. AAs participated actively in the play session but were rated as more negative in their orientation toward both mother and peer. ARs appeared highly stressed by this situation; they ignored most peer offers and were most negative toward their mothers. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Condiciones suficientes para la existencia de solucion optima en un programa semi-infinito

The boundness of the feasible set of a Semi-infinite Programming Problem guarantees, in many cases, the existence of an optimum point. Therefore we study such property in connection with the solution-set of a system of infinitely many constraints. Later on we give existence-theorems for an optimum point, involving the objective function in different ways such as: the generalized Lagrange-function; a specific cone of directions; a special dual problem; and, certain infinite systems associated to the problem.

     

Infrared-transparent glasses derived from the fluorides of zirconium,thorium, and barium

Glasses consisting solely of high-purity ZrF₄, ThF₄, and BaF₂ have been synthesized using reactive atmosphere processing (RAP) techniques. RAP of the individual components and the molten material with anhydrous HF and CCl₄ is described. The glass molds easily at 312°C and 1920 psi with a high-fidelity replication of the die surface. The glass is water insoluble, unusually hard and strong, and continuously transparent from 0.3 to 7 μm.     

Crystal growth of alkaline earth fluorides in a reactive atmosphere

Crystal growth of MF₂ (M = Ca, Sr, or Ba) is carried out in a reactive atmosphere consisting of HF and a carrier gas (He). Single-crystal Bridgman ingots, with the axis oriented at 〈111〉, are grown up to 5.2 cm in diameter. The mechanical strength of these specimens is found to be higher than what has been reported.