156 research outputs found
Hydrogen adsorption on Pd(133) surface
In this study used is an approach based on measurements of the total energy
distribution (TED) of field emitted electrons in order to examine the
properties of Pd (133) from the aspect of both hydrogen adsorption and surface
hydrides formation. The most favourable sites offered to a hydrogen atom to be
adsorbed have been indicated and an attempt to describe the peaks of the
enhancement factor R spectrum to the specific adsorption sites has also been
made.Comment: to be submitted to the Centr. Eur. J. Phy
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Comparative experimental study of x-ray absorption spectroscopy and electron energy loss spectroscopy on passivated U surfaces
X-ray absorption spectroscopy and electron energy loss spectroscopy are complementary analytical techniques on energy and spatial resolution. These techniques are based on the same fundamental physical process of core excitation with either an incident photon or incident electron. In the proper experimental configuration the electron and photon inelastic scattering amplitudes are comparable and thus the x-ray and electron absorption edges look identical. We have applied these two complementary analytical techniques to investigate the electronic structure of C ion implanted U. Implantation of C{sup +} ions into U{sup 238} has been shown to produce a physically and chemically modified surface layer that passivates the surface preventing further air oxidation and corrosion. Comparison of the resultant spectra reveal that transitions between the initial state and a series of final states yield numerous strong features at the absorption edge that can provide structural information and information on the local chemical environment, including the character of the U 5f state
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Recipes for high resolution time-of-flight detectors
The authors discuss the dynamics, construction, implementation and benefits of a time-of-flight (TOF) detector with count rates an order of magnitude higher and resolution three to four times better than that obtainable with a surface barrier detector. The propose use of design criteria for a time-of-flight detector is outlined, and the determination of a TOF detector`s total relative timing error and how this value determines the mass resolution are illustrated using a graphical analysis. They present simulation and experimental examples employing light ions and discuss advantages and pitfalls of medium-energy heavy ion TOF spectrometry
Theory of adsorbate induced surface reconstruction on W(100)
We report results of a theoretical study on an adsorbate induced surface
reconstruction. Hydrogen adsorption on a W(100) surface causes a switching
transition in the symmetry of the displacements of the W atoms within the
ordered c(2x2) phase. This transition is modeled by an effective Hamiltonian,
where the hydrogen degrees of freedom are integrated out. Based on extensive
Monte Carlo renormalisation group calculations we show that the switching
transition is of second order at high temperatures and of first order at low
temperatures. This behavior is qualitatively explained in terms of an XY model
where there is an interplay between four and eight fold anisotropy fields. We
also compare the calculated phase diagrams with a simple mean field theory.Comment: CSC Preprint, 31 pages (plain TeX file, no figures
Adsorption energies and ordered structures of hydrogen on Pd(111) from density functional periodic calculations
Nirsevimab for Prevention of Hospitalizations Due to RSV in Infants
Copyright \ua9 2023 Massachusetts Medical Society.BACKGROUND: The safety of the monoclonal antibody nirsevimab and the effect of nirsevimab on hospitalizations for respiratory syncytial virus (RSV)-associated lower respiratory tract infection when administered in healthy infants are unclear. METHODS: In a pragmatic trial, we randomly assigned, in a 1:1 ratio, infants who were 12 months of age or younger, had been born at a gestational age of at least 29 weeks, and were entering their first RSV season in France, Germany, or the United Kingdom to receive either a single intramuscular injection of nirsevimab or standard care (no intervention) before or during the RSV season. The primary end point was hospitalization for RSV-associated lower respiratory tract infection, defined as hospital admission and an RSV-positive test result. A key secondary end point was very severe RSV-associated lower respiratory tract infection, defined as hospitalization for RSV-associated lower respiratory tract infection with an oxygen saturation of less than 90% and the need for supplemental oxygen. RESULTS: A total of 8058 infants were randomly assigned to receive nirsevimab (4037 infants) or standard care (4021 infants). Eleven infants (0.3%) in the nirsevimab group and 60 (1.5%) in the standard-care group were hospitalized for RSV-associated lower respiratory tract infection, which corresponded to a nirsevimab efficacy of 83.2% (95% confidence interval [CI], 67.8 to 92.0; P<0.001). Very severe RSV-associated lower respiratory tract infection occurred in 5 infants (0.1%) in the nirsevimab group and in 19 (0.5%) in the standard-care group, which represented a nirsevimab efficacy of 75.7% (95% CI, 32.8 to 92.9; P = 0.004). The efficacy of nirsevimab against hospitalization for RSV-associated lower respiratory tract infection was 89.6% (adjusted 95% CI, 58.8 to 98.7; multiplicity-adjusted P<0.001) in France, 74.2% (adjusted 95% CI, 27.9 to 92.5; multiplicity-adjusted P = 0.006) in Germany, and 83.4% (adjusted 95% CI, 34.3 to 97.6; multiplicity-adjusted P = 0.003) in the United Kingdom. Treatment-related adverse events occurred in 86 infants (2.1%) in the nirsevimab group. CONCLUSIONS: Nirsevimab protected infants against hospitalization for RSV-associated lower respiratory tract infection and against very severe RSV-associated lower respiratory tract infection in conditions that approximated real-world settings. (Funded by Sanofi and AstraZeneca; HARMONIE ClinicalTrials.gov number, NCT05437510)
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Silicon-Germanium Films Deposited by Low Frequency PE CVD: Effect of H2 and Ar Dilution
We have studied structure and electrical properties of Si{sub 1-Y}Ge{sub Y}:H films deposited by low frequency PE CVD over the entire composition range from Y=0 to Y=1. The deposition rate of the films and their structural and electrical properties were measured for various ratios of the germane/silane feed gases and with and without dilution by Ar and by H{sub 2}. Structure and composition was studied by Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and Fourier transform infrared (FTIR) spectroscopy. Surface morphology was characterized by atomic force microscopy (AFM). We found: (1) The deposition rate increased with Y maximizing at Y=1 without dilution. (2) The relative rate of Ge and Si incorporation is affected by dilution. (3) Hydrogen preferentially bonds to silicon. (4) Hydrogen content decreases for increasing Y. In addition, optical measurements showed that as Y goes for 0 to 1, the Fermi level moves from mid gap to the conduction band edge, i.e. the films become more n-type. No correlation was found between the pre-exponential and the activation energy of conductivity. The behavior of the conductivity {gamma}-factor suggests a local minimum in the density of states at E {approx} 0.33 eV for the films grown with or without H-dilution and E {approx} 0.25 eV for the films with Ar dilution
Three options for citation tracking: Google Scholar, Scopus and Web of Science
BACKGROUND: Researchers turn to citation tracking to find the most influential articles for a particular topic and to see how often their own published papers are cited. For years researchers looking for this type of information had only one resource to consult: the Web of Science from Thomson Scientific. In 2004 two competitors emerged – Scopus from Elsevier and Google Scholar from Google. The research reported here uses citation analysis in an observational study examining these three databases; comparing citation counts for articles from two disciplines (oncology and condensed matter physics) and two years (1993 and 2003) to test the hypothesis that the different scholarly publication coverage provided by the three search tools will lead to different citation counts from each. METHODS: Eleven journal titles with varying impact factors were selected from each discipline (oncology and condensed matter physics) using the Journal Citation Reports (JCR). All articles published in the selected titles were retrieved for the years 1993 and 2003, and a stratified random sample of articles was chosen, resulting in four sets of articles. During the week of November 7–12, 2005, the citation counts for each research article were extracted from the three sources. The actual citing references for a subset of the articles published in 2003 were also gathered from each of the three sources. RESULTS: For oncology 1993 Web of Science returned the highest average number of citations, 45.3. Scopus returned the highest average number of citations (8.9) for oncology 2003. Web of Science returned the highest number of citations for condensed matter physics 1993 and 2003 (22.5 and 3.9 respectively). The data showed a significant difference in the mean citation rates between all pairs of resources except between Google Scholar and Scopus for condensed matter physics 2003. For articles published in 2003 Google Scholar returned the largest amount of unique citing material for oncology and Web of Science returned the most for condensed matter physics. CONCLUSION: This study did not identify any one of these three resources as the answer to all citation tracking needs. Scopus showed strength in providing citing literature for current (2003) oncology articles, while Web of Science produced more citing material for 2003 and 1993 condensed matter physics, and 1993 oncology articles. All three tools returned some unique material. Our data indicate that the question of which tool provides the most complete set of citing literature may depend on the subject and publication year of a given article
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Epitaxial growth of ultrathin palladium films on Re{0001}
Ultrathin bimetallic layers create unusual magnetic
and surface chemical effects through the modification of electronic structure brought on by low dimensionality, polymorphism, reduced screening, and epitaxial strain. Previous studies have related valence and core-level shifts to surface reactivity through the d-band model of Hammer and Nørskov, and in heteroepitaxial films this band position is determined by competing effects of coordination, strain, and hybridization of substrate and overlayer states. In this study we employ the epitaxially matched Pd on Re{0001} system to grow films with no lateral strain. We use a recent advancement in low-energy electron diffraction to expand the data range sufficiently for a reliable determination of the growth sequence and out-of-plane surface relaxation as a function of film thickness. The results are supported by scanning tunneling
microscopy and X-ray photoemission spectroscopy, which show that the growth is layer-by-layer with significant core-level shifts due to changes in film structure, morphology, and bonding
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