Activity,selectivity, and methanol tolerance of novel carbon-supported Pt and Pt<Subscript>3</Subscript>Me (Me = Ni,Co) cathode catalysts

The activity, selectivity, and methanol tolerance of novel, carbon supported high-metal loading (40 wt.%) Pt/C and Pt₃Me/C (Me = Ni, Co) catalysts for the O₂ reduction reaction (ORR) were evaluated in model studies under defined mass transport and diffusion conditions, by rotating (ring) disk and by differential electrochemical mass spectrometry. The catalysts were synthesized by the organometallic route, via deposition of pre-formed Pt and Pt₃Me pre-cursors followed by their decomposition into metal nanoparticles. Characteristic properties such as particle sizes, particle composition and phase formation, and active surface area, were determined by transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. For comparison, commercial Pt/C catalysts (20 and 40 wt.%, E-Tek, Somerset, NJ, USA) were investigated as well, allowing to evaluate Pt loading effects and, by comparison with the pre-cursor-based catalyst with their much smaller particle sizes (1.7 nm diameter), also particle size effects. Kinetic parameters for the ORR were evaluated; the ORR activities of the bimetallic catalysts and of the synthesized Pt/C catalyst were comparable and similar to that of the high-loading commercial Pt/C catalyst; at typical cathode operation potentials H₂O₂ formation is negligible for the synthesized catalysts. Due to their lower methanol oxidation activity the bimetallic catalysts show an improved methanol tolerance compared to the commercial Pt/C catalysts. The results indicate that the use of very small particle sizes is a possible way to achieve reasonably good ORR activities at an improved methanol tolerance at DMFC cathode relevant conditions.     

Diagnostic and therapeutic thoracic surgery in leukemia and severe aplastic anemia

We examined the hypothesis that peak magnitude strain gradients are spatially correlated with sites of bone formation. Ten adult male turkeys underwent functional isolation of the right radius and a subsequent 4-week exogenous loading regimen. Full field solutions of the engendered strains were obtained for each animal using animal-specific, orthotropic finite element models. Circumferential, radial, and longitudinal gradients of normal strain were calculated from these solutions. Site-specific bone formation within 24 equal angle pie sectors was determined by automated image analysis of microradiographs taken from the mid-diaphysis of the experimental radii. The loading regimen increased mean cortical area (+/-SE) by 32.3 +/- 10.5% (p = 0.01). Across animals, some periosteal bone formation was observed in every sector. The amount of periosteal new bone area contained within each sector was not uniform. Circumferential strain gradients (r2 = 0.36) were most strongly correlated with the observed periosteal bone formation. SED (a scalar measure of stress/strain magnitude with minimal relation to fluid flow) was poorly correlated with periosteal bone formation (r2 = 0.01). The combination of circumferential, radial, and longitudinal strain gradients accounted for over 60% of the periosteal new bone area (r2 = 0.63). These data indicate that strain gradients, which are readily determined given a knowledge of the bone's strain environment and geometry, may be used to predict specific locations of new bone formation stimulated by mechanical loading.     

Magnetic Properties of the Frustrated fcc – Antiferromagnet HoB12 Above and Below T N

We have investigated the magnetic ordering of the frustrated fcc – antiferromagnet HoB₁₂. Below T_N= 7.4 K antiferromagnetic order and a complex phase diagram is observed. Above T_N neutron scattering experiments show strong diffuse scattering. The diffuse signal indicates strong correlations between rare earth moments along the [111] direction well above T_N. The behavior of this component resembles low dimensional magnets which are known to show long range order only at T = 0. Close to T_N correlations perpendicular to the [111] direction get relevant, they diverge toward T_N. Thus we observe a complex ordering process where the frustration is lifted in steps. The experimental data and their interpretation are presented, some of the possible microscopic origins are discussed.      

Physical adsorption on ferroelectric surfaces: photoinduced and thermal effects

Selective deposition of charged polystyrene (PS) microspheres from an aqueous solution on domain-patterned lithium niobate is investigated. The selectivity of PS microsphere deposition can be varied by controlling the deposition temperature. Selective decoration of the positive domains (positive polarization surface charges) is achieved at room temperature and is attributed to the electrostatic interaction of the charged nanoparticles and the polarization surface charges of the ferroelectric. In contrast, at elevated temperatures, the particles decorate the negative domains. This process is explained by considering the pyroelectric properties of lithium niobate.     

Design and characterization of a high-power laser-induced acoustic desorption probe coupled with a fourier transform ion cyclotron resonance mass spectrometer

We report here the construction and characterization of a high-power laser-induced acoustic desorption (LIAD) probe designed for Fourier transform ion cyclotron resonance mass spectrometers to facilitate analysis of nonvolatile, thermally labile compounds. This "next generation" LIAD probe offers significant improvements in sensitivity and desorption efficiency for analytes with larger molecular weights via the use of higher laser irradiances. Unlike the previous probes which utilized a power-limiting optical fiber to transmit the laser pulses through the probe, this probe employs a set of mirrors and a focusing lens. At the end of the probe, the energy from the laser pulses propagates through a thin metal foil as an acoustic wave, resulting in desorption of neutral molecules from the opposite side of the foil. Following desorption, the molecules can be ionized by electron impact or chemical ionization. Almost an order of magnitude greater power density (up to 5.0x10(9) W/cm2) is achievable on the backside of the foil with the high-power LIAD probe compared to the earlier LIAD probes (maximum power density approximately 9.0x10(8) W/cm2). The use of higher laser irradiances is demonstrated not to cause fragmentation of the analyte. The use of higher laser irradiances increases sensitivity since it results in the evaporation of a greater number of molecules per laser pulse. Measurement of the average velocities of LIAD-evaporated molecules demonstrates that higher laser irradiances do not correlate with higher velocities of the gaseous analyte molecules.     

Behavior of Ni‐base alloy 625 in methanol‐supercritical water systems

Methanol reacts with water under supercritical conditions to form a hydrogen rich gas. This reforming reaction can be performed without the addition of a catalyst. Typical reaction conditions are 25 MPa pressure and 600°C temperature and short residence times. The tubular flow reactor used was made of the nickel base alloy 625. The reactor was operated continuously for more than 1000 hours without problems. The feed concentration was 5 weight‐% methanol. The major component of the product gas was hydrogen (up to more than 70 vol‐%). Methanol conversion was higher than 99% and the liquid effluent was clear and free of soot. After exposure, the reactor has been sectioned and each section has been analyzed. No major corrosion phenomena were observed. Severe ductility loss of the material could be measured in the higher temperature section of the reactor.     

Analysis of base oil fractions by ClMn(H2O)+ chemical ionization combined with laser-induced acoustic desorption/fourier transform ion cyclotron resonance mass spectrometry

Laser-induced acoustic desorption (LIAD), combined with chemical ionization with the ClMn(H(2)O)(+) ion, is demonstrated to facilitate the analysis of base oils by Fourier transform ion cyclotron resonance mass spectrometry. The LIAD/ClMn(H(2)O)(+) method produces only one product ion, [ClMn + M](+), for each component (M) in base oils, thus providing molecular weight (MW) information for the analytes. With the exception of one sample, no fragmentation was observed. The mass spectra indicate the presence of homologous series of ions differing in mass by multiples of 14 Da (i.e., CH(2)). All peaks in the spectra correspond to ions with even m/z values and hence are formed from hydrocarbons with no nitrogen atoms, in agreement with the compositional nature of base oils. The MW distributions measured for two groups of base oil samples cover the range 350-600 Da, which is in excellent agreement with the values determined by gas chromatography. Moreover, the hydrocarbon types (i.e., paraffin and cycloparaffins with different numbers of rings) present in each base oil sample can be determined based on the m/z values of the product ions. Finally, the results obtained by using LIAD/ClMn(H(2)O)(+) indicate that the efficiency of the technique (combined desorption and ionization efficiency) is similar for different hydrocarbon types and fairly uniform over a wide molecular weight range, thus allowing quantitative analysis of the base oils. Hence, the product ions' relative abundances were used to determine the percentage of each type of hydrocarbon in the base oil. In summary, three important parameters (MW distributions, hydrocarbon types, and their relative concentrations) can be obtained in a single experiment. This mass spectrometric technique therefore provides detailed molecular-level information for base oils, which cannot be obtained by other analytical methods.