Quasielastic knockout of light fragments from 12C and 16O nuclei by intermediate-energy pions

Quasielastic deuteron and triton knockout from ¹²C and ¹⁶O nuclei has been studied infull kinematics using a 0.72-GeV/c pion beam. The momentum distributions of the intranuclear quasideuteron motion, excitation-energy spectra of the residual nuclei, and the effective numbers N _d ^eff of quasideuterons are determined. The parameters of the quasideuteron intranuclear motion are in reasonable agreement with the results obtained in other beams. The N _d ^eff in the nuclei from ⁶Li to ¹⁶O measured in full kinematics are virtually independent of the atomic number in contrast to the analogous values in the inclusive deuteron-knockout reaction induced by protons. The phenomenon of triton knockout from these nuclei is observed, which makes possible estimation of the cross section of backward pion-triton elastic scattering in yet unexplored regions of energy and momentum transfer.     

Improvement of the proton exchange membrane fuel cell performances by optimization of the hot pressing process for membrane electrode assembly

The present study deals with PEM fuel cells, namely with the optimization of the hot pressing process for membrane electrode assembly (MEA) fabrication. Designs of experiments (DoE) have been used for evaluating the effect of hot pressing parameters (pressure, temperature, and time) on the MEA electrical performances. Full factorial 2³ DoE showed that the most important parameter is the pressing temperature. Surface response methodology indicated a non-monotonous behavior of the MEA electrical performances with respect to the pressing temperature. The MEA electrical performances increased with the pressing temperature in the temperature range from 100 to 115 °C, and decreased significantly in the temperature range from 115 to 130 °C. This behavior was attributed to drastic changes of the Nafion® 112 membrane properties and membrane/electrode interface over this temperature range. Observations of the MEA cross-section structure by scanning electron microscopy confirmed such hypotheses. Thermo-mechanical properties of Nafion® as determined by dynamic scanning calorimetry allowed estimating the glass transition temperature at ca. T _g?≈?117 °C in the conditions of the present study. The higher H₂/air fuel cell performance of ca. 0.8 W cm^?2 was obtained with the optimized pressing temperature for MEA fabrication of ca. 115 °C close to the T _g temperature of Nafion® 112, whereas for higher temperature the structure of the Nafion® membrane and of the membrane–electrode interface is damaged.     

Performance and instabilities of proton exchange membrane fuel cells

Performance of proton exchange fuel cells with different membrane and electrode assembly (MEA) is studied. It is shown that MEA fabricated with catalyst plasma pulverization technology has the maximum performance. Some instabilities in the cell performance, observed with time, are probably due to periodic cathode flooding. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 525–534. The text was submitted by the authors in English.     

Pulse photolysis of ditertbutyl peroxide in benzene

The method of pulse photolysis has been used to determine termination rate constants of primary peroxy radicals in benzene at 295 K. Radicals CH₃O ₂ ^. have been found to decay with the rate constant 2k₆=3.7×10⁸ M^–1 s^–1 and radicals (CH₃)₃ COOC(CH₃)CH₂O ₂ ^. with 2k₈=1.2×10⁸ M^–1 s^–1, the rate constant of cross-recombination for both radicals being 2.4×10⁸ M^–1 s^–1.

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295 K: CH₃O ₂ ^. 3,7·10⁸ (M·c)^–1, (CH₃)₃COOC(CH₃)₂CH₂O ₂ ^. =qt 1,2·10⁸ (M·c)^–1, 2,4·10⁸ (M·c)^–1.

     

Comment on the <Emphasis Type="Italic">A</Emphasis> dependence of quasielastic deuteron knockout from nuclei

The A dependence recently measured in an experiment of our group in full kinematics for quasielastic deuteron knockout by pions revealed that the effective number of quasideuterons in a nucleus is independent of its atomic number. This result differs strongly from the A dependence measured in experiments that studied quasielastic inclusive deuteron knockout by protons, in which case one observes an A ^0.33 power-law dependence. Calculations performed on the basis of a simple deuteron-knockout model show that stronger absorptive effects in measurements under conditions of full kinematics may indeed lead to this change in the A dependence.     

Electrochemical noise diagnostics of PEM fuel cell stack for micro-cogeneration application

Journal of Solid State Electrochemistry - Electrochemical noise (EN) generated by a 3500&nbsp;W PEM fuel cell stack (50 cells) has been measured during micro-cogeneration durability tests. The...     

Synthesis of nanostructural electrocatalytic materials on various carbon substrates by ion plasma sputtering of platinum metals

Carbon-supported platinum electrocatalysts for electrochemical systems with a proton-exchange membrane were prepared by ion plasma sputtering in a DC magnetron sputtering unit. Vulcan XC-72, carbon nanotubes, and nanofibers were used as substrates. The starting substrates were occasionally subjected to preliminary chemical treatment or metallization. The synthesized electrocatalyst samples were analyzed by thermogravimetric, X-ray diffraction, and X-ray fluorescent analysis, scanning and transmission microscopy, and cyclic voltammetry. The electrochemical activity of the synthesized Pt/C and Pt-Pd/C materials was studied in a fuel cell, water electrolyzer, and bifunctional fuel cell with a solid polymer electrolyte. Several samples were found to have high specific surface areas (up to 44 m²/g), chemical purity, and electrochemical activity. The qualitative dependences of the characteristics of the catalysts on the parameters of metal deposition and the properties of the starting substrate were found.     

Pulse photolysis rate constants of the decay of ester peroxide radicals

Pulse photolysis measurements of rate constants of the decay of peroxide radicals for seven saturated acetates have revealed their increase with shortening alkyl chain. It is attributed to the high rate constants of the interaction of -acyloxyperoxide radicals ((3±1)×10⁸l/mol s) compared to those for remote peroxide ones.

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. , - (3±1)×10⁸ /. ) .

     

Cumulative protons in the 9Be(12C,p)X reaction at 0.2–3.2 GeV/nucleon

The spectra of protons were measured in fragmentation of ¹²C ions in the cumulative region at energies of 0.2–3.2 GeV/nucleon. The energy dependence of the slope parameters in the obtained spectra was traced. The probability of the existence of two- and three-nucleon clusters in the carbon nucleus was estimated within the model of quark-gluon strings.