Insights into surface reactivity: formic acid oxidation on Cu(110) studied using STM and a molecular beam reactor

Using a combination of STM and molecular beam reactor data we summarise some important features of a model reaction (formic acid oxidation on Cu(110)) which is of general significance to surface reactivity and to catalysis. Three such features are highlighted here. The first concerns the role of weakly held species (possibly physisorbed) in surface reactions. These species, although of very short lifetime on the surface, can, nevertheless, diffuse over long distances to “find” a sparse distribution of active sites. Thus a very low coverage of oxygen on the surface of Cu(110) increases the sticking probability of all the formic acid molecules which strike the surface to high value (0.82), even though the clean surface is relatively unreactive. The important concept here is the “diffusion circle” or “collection zone” which represents the area of surface visited by the molecule in its short sojourn in the weakly held state. The second theme concerns the concept of the “flexible surface”. We show that the involvement of surface atoms in reactions directs the structure and reactivity for a particular reaction. For formic acid oxidation the liberation of Cu atoms during the removal of oxygen as water leads to gross restructuring of the surface and can lead to “compression” of one reactant (the oxygen in this case) into a lower area, higher local coverage, unreactive state (the c(6×2) oxygen structure). Thirdly, and finally, it is proposed that, for many surface reactions, the surface acts in an analogous way to a solvent, supporting a “dissolved” (highly mobile and fluxional) phase of intermediates at low coverage, which crystallise out above a critical coverage (the 2D “solubility limit”). This revised version was published online in July 2006 with corrections to the Cover Date.     

Aggressive versus withdrawn unpopular children: variations in peer and self-perceptions in multiple domains

The present study examines whether subgroups of unpopular children differ in terms of competence in multiple domains. Specifically, subgroups of aggressive unpopular, withdrawn unpopular, and aggressive-withdrawn unpopular and average status children were identified on the basis of peer evaluations. The subgroups were then compared in terms of peer and self-perceptions of competence in various nonsocial and social domains. Results indicated that the 3 subgroups of unpopular children exhibited distinct profiles according to peer perceptions, with aggressive-withdrawn unpopular children being viewed as deficient in virtually every area assessed, and aggressive unpopular and withdrawn unpopular children viewed as exhibiting particular strengths and weaknesses across domains. In terms of self-perceptions, results indicated that withdrawn-unpopular children expressed more accurate, but negative self-evaluations, while children in the aggressive subgroups tended to overestimate their competencies.     

Structure sensitivity in CO oxidation over rhodium

The rates of CO oxidation on the (110) and (111) planes of rhodium have been directly compared using a thermal molecular beam reactor. When the surfaces are largely covered by CO the reaction rate is the same on the two crystal planes. At higher temperatures, where CO desorbs and the surface becomes oxygen covered, the reaction becomes structure sensitive, being markedly faster on the more open (110) plane.     

Accommodation response during a prolonged visual search task

The visual accommodative response is measured during dark field viewing and while engaged in a visual search task. A laser optometer is used to compare performance using microfiche and hard-copy displays. Results indicate a marked bias in the direction of the individual's resting accommodative state during all conditions of display viewing. Implications of these results and those from other studies are discussed with respect to future research in display design.     

Impact of carcass scalding and chilling on muscle proteins and meat quality of broiler breast fillets

The objective of this study was to determine the effects of broiler carcass scalding and chilling methods on meat quality and muscle proteins. During processing, carcasses were hard (60 °C, 1.5 min) or soft (52.8 °C, 3 min) scalded, and either immersion chilled (IC: 0.5 °C, 40 min) or air chilled (AC: 0.5 °C, 120 min). Breast fillets were deboned at 4 h postmortem and used for measuring meat quality and muscle protein characteristics. Scalding by chilling treatment interaction effects on meat quality were not observed. Air chilled carcasses had greater pH₂₄, and reduced drip loss and shear force compared to IC carcasses. Cook yield, color (L*a*b*), and moisture content were not different between chilling treatments. Scalding treatments did not influence quality traits. Sarcoplasmic protein solubility was not influenced by chilling treatment, but was greater in hard versus soft scalded carcasses. Myofibrillar protein solubility was greater in fillets from soft scalded IC carcasses. Alterations in the electrophoretic profiles of the myofibrillar and sarcoplasmic proteins due to treatments indicated minor changes in protein degradation and solubility. Data suggest that while only chilling method influenced meat quality, both scalding and chilling methods influenced protein solubility and degradation in breast fillets deboned 4 h postmortem.     

Myosin heavy chain isoforms influence myofibrillar ATPase activity under simulated postmortem pH, calcium, and temperature conditions

The pH and Ca(2+) sensitivity of myofibrillar ATPase activity plays an integral role in regulating postmortem muscle ATP utilization and likely paces postmortem glycolysis. The objective of this study was to determine the influence of pH and Ca(2+) concentration on the ATPase activity of myofibrils from red semitendinosus (RST) and white semitendinosus (WST) porcine muscles. Myofibrillar ATPase was measured at 39 °C over a pH range 5-7.5 and a [Ca(2+)] range pCa 4-9 (10(-4)-10(-9)M). At maximum Ca(2+)-dependent activation (pCa 4), RST myofibrils had lower (p<0.0001) ATPase activity than WST myofibrils. This maximum activity of myofibrils from both muscle regions was not influenced from pH 7.5 to 6.5, declined between pH 6.5 and 5.75 (Hill coefficient, n(H)=2.7-3.4; pH at half maximum activity, pH(50)=5.97) and was near zero at pH 5.5. At pH 7, pCa-activity relationships showed that RST required less Ca(2+) for half-maximum activation (higher pCa(50); 6.50) than WST myofibrils (pCa(50)=6.35) but had no difference in n(H). At pH 7, both RST and WST myofibrils had maximum Ca(2+)-dependent, actin-activated ATPase activity at pCa ?6 and Ca(2+)-independent myosin ATPase activity at pCa ?6.75. pCa-activity relationships at different pH levels indicated that pCa(50) decreased with pH from pH 6.5 to 6.125 in both RST and WST myofibrils. At pH <5.75, [Ca(2+)] did not influence ATPase activity in RST or WST myofibrils. These data show that myofibrils with predominantly fast MyHC (WST) have a higher actin-activated myosin ATPase activity than myofibrils with primarily slow MyHC isoforms (RST) at Ca(2+) concentrations and pH values characteristic of postmortem muscle.     

Direct synthesis of formate from methanol oxidation on the CuPd[85∶15]{110}p(2×1) surface: induction of a new reaction pathway via a ligand effect

Thermal molecular beam studies of the oxidative dehydrogenation of methanol over the 1/4 ML and 1/2 ML oxygen predosed CuPd[85 15]{110}p(2 × 1) surfaces has been performed. Post reaction thermal desorption spectroscopy (TDS) clearly shows that during these experiments observable levels of formate are produced. This is in contrast to the results of similar experiments performed over oxidised Cu{110} surfaces which showed little formate production. It is hypothesised that the alloying in the surface region causes this new reaction pathway to appear as a consequence of a modification of the stability of one or more of the reactive intermediates produced in this reaction. It is proposed that these modifications of adsorbate stability are due to a ligand effect arising from the presence of Pd in the second layer of the selvedge.