Interaction of oxygen with Al(111) at elevated temperatures

The interaction of oxygen with Al(111) was investigated by STM at temperatures between 350 and 530 K, by annealing an oxygen precovered surface and by adsorption of oxygen on the hot surface. For exposures up to 10 L and temperatures up to 470 K a considerable part of the oxygen exists still in the chemisorbed state, another part transforms into Al oxide. In contrast to 300 K chemisorbed Oad atoms are mobile at elevated temperatures, and compact, hexagonal (1×1)Oad islands develop by an ordinary nucleation and growth scheme. This evidences attractive interactions between the oxygen atoms on (1×1) sites. From the lateral distribution of Oad islands a diffusion barrier of 1.0–1.1 eV is derived. The imaging of the islands of the (1×1) phase by STM depends on their size, which is understood by a different imaging of the Oad/Al adsorbate complexes at the island borders. Defects in the islands and bright features at the edges are interpreted as nuclei of aluminum oxide. Additional features which appear as topographic holes may be attributed to nonconducting Al oxide grains

Tests of Transfer Reaction Determinations of Astrophysical S-Factors

The ${}^{16}O ({}^{3}He,d) {}^{17}F$ reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of ${}^{17}F$. The coefficients provide the normalization for the tails of the overlap functions for ${}^{17}F \to{}^{16}O + p$ and allow us to calculate the S-factors for ${}^{16}O (p,\gamma){}^{17}F$ at astrophysical energies. The calculated S-factors are compared to measurements and found to be in very good agreement. This provides the first test of this indirect method to determine astrophysical direct capture rates using transfer reactions. In addition, our results yield S(0) for capture to the ground and first excited states in $^{17}F$, without the uncertainty associated with extrapolation from higher energies.Comment: 6 pages, 2 figure

Alpha scattering and capture reactions in the A = 7 system at low energies

Differential cross sections for $^3$He-$\alpha$ scattering were measured in the energy range up to 3 MeV. These data together with other available experimental results for $^3$He $+ \alpha$ and $^3$H $+ \alpha$ scattering were analyzed in the framework of the optical model using double-folded potentials. The optical potentials obtained were used to calculate the astrophysical S-factors of the capture reactions $^3$He$(\alpha,\gamma)^7$Be and $^3$H$(\alpha,\gamma)^7$Li, and the branching ratios for the transitions into the two final $^7$Be and $^7$Li bound states, respectively. For $^3$He$(\alpha,\gamma)^7$Be excellent agreement between calculated and experimental data is obtained. For $^3$H$(\alpha,\gamma)^7$Li a $S(0)$ value has been found which is a factor of about 1.5 larger than the adopted value. For both capture reactions a similar branching ratio of $R = \sigma(\gamma_1)/\sigma(\gamma_0) \approx 0.43$ has been obtained.Comment: submitted to Phys.Rev.C, 34 pages, figures available from one of the authors, LaTeX with RevTeX, IK-TUW-Preprint 930540

Validity, practical utility, and reliability of the activPAL in preschool children

<p>Purpose: With the increasing global prevalence of childhood obesity, it is important to have appropriate measurement tools for investigating factors (e.g. sedentary time) contributing to positive energy balance in early childhood. For pre-school children, single unit monitors such as the activPALTM are promising. However, validation is required as activity patterns differ from adults.</p> <p>Methods: Thirty pre-school children participated in a validation study. Children were videoed for one hour undertaking usual nursery activity while wearing an activPALTM. Video (criterion method) was analyzed on a second-by-second basis to categorise posture and activity. This was compared with the corresponding activPALTM output. In a subsequent sub-study investigating practical utility and reliability, 20 children wore an activPALTM for seven consecutive 24-hour periods.</p> <p>Results: A total of 97,750 seconds of direct observation from 30 children were categorized as sit/lie (46%), stand (35%), walk (16%); with 3% of time in nonsit/lie/upright postures (e.g. crawl/crouch/kneel-up). Sensitivity for the overall total time matched seconds detected as activPALTM ‘sit/lie’ was 86.7%, specificity 97.1%, and positive predictive value (PPV) 96.3%. For individual children, the median (interquartile range) sensitivity for activPALTM sit/lie was 92.8% (76.1-97.4), specificity 97.3% (94.9-99.2), PPV 97.0% (91.5-99.1). The activPALTM underestimated total time spent sitting (mean difference -4.4%, p<0.01), and overestimated time standing (mean difference 7.1%, p<0.01). There was no difference in overall % time categorised as ‘walk’ (p=0.2). The monitors were well tolerated by children during a seven day period of free-living activity. In the reliability study, at least five days of monitoring were required to obtain an intraclass correlation coefficient of ≥0.8 for time spent sit/lie according to activPALTM output.</p> <p>Conclusion: The activPAL had acceptable validity, practical utility, and reliability for the measurement of posture and activity during freeliving activities in pre-school children.</p&gt

Phosphine-Catalyzed Formation of Carbon-Sulfur Bonds: Catalytic Asymmetric Synthesis of gamma-Thioesters

Supporting Information Available: Experimental procedures and compound characterization data. This material is available free of charge via the Internet at http://pubs.acs.org.A method for catalytic asymmetric γ sulfenylation of carbonyl compounds has been developed. In the presence of an appropriate catalyst, thiols not only add to the γ position of allenoates, overcoming their propensity to add to the β position in the absence of a catalyst, but do so with very good enantioselectivity. Sulfur nucleophiles are now added to the three families of nucleophiles (carbon, nitrogen, and oxygen) that had earlier been shown to participate in catalyzed γ additions. The phosphine catalyst of choice, TangPhos, had previously only been employed as a chiral ligand for transition metals, not as an efficient enantioselective nucleophilic catalyst.National Institutes of Health (U.S.)National Institute of General Medical Sciences (U.S.) (R01-GM57034)Merck & Co.Novartis (Firm

A Study of Cosmic Ray Composition in the Knee Region using Multiple Muon Events in the Soudan 2 Detector

Deep underground muon events recorded by the Soudan 2 detector, located at a depth of 2100 meters of water equivalent, have been used to infer the nuclear composition of cosmic rays in the "knee" region of the cosmic ray energy spectrum. The observed muon multiplicity distribution favors a composition model with a substantial proton content in the energy region 800,000 - 13,000,000 GeV/nucleus.Comment: 38 pages including 11 figures, Latex, submitted to Physical Review

A Model for Liver Homeostasis Using Modified Mean-Reverting Ornstein–Uhlenbeck Process

Short of a liver biopsy, hepatic disease and drug-induced liver injury are diagnosed and classified from clinical findings, especially laboratory results. It was hypothesized that a healthy hepatic dynamic equilibrium might be modelled by an Ornstein–Uhlenbeck (OU) stochastic process, which might lead to more sensitive and specific diagnostic criteria. Using pooled data from healthy volunteers in pharmaceutical clinical trials, this model was applied using maximum likelihood (ML) methods. It was found that the exponent of the autocorrelation function was proportional to the square root of time rather than time itself, as predicted by the OU model. This finding suggests a stronger autocorrelation than expected and may have important implications regarding the use of laboratory testing in clinical diagnosis, in clinical trial design, and in monitoring drug safety. Besides rejecting the OU hypothesis for liver test homeostasis, this paper presents ML estimates for the multivariate Gaussian distribution for healthy adult males. This work forms the basis for a new approach to mathematical modelling to improve both the sensitivity and specificity of clinical measurements over time