221 research outputs found
Single-photon single ionization of W ions: experiment and theory
Experimental and theoretical results are reported for photoionization of
Ta-like (W) tungsten ions. Absolute cross sections were measured in the
energy range 16 to 245 eV employing the photon-ion merged-beam setup at the
Advanced Light Source in Berkeley. Detailed photon-energy scans at 100 meV
bandwidth were performed in the 16 to 108 eV range. In addition, the cross
section was scanned at 50 meV resolution in regions where fine resonance
structures could be observed. Theoretical results were obtained from a
Dirac-Coulomb R-matrix approach. Photoionization cross section calculations
were performed for singly ionized atomic tungsten ions in their , =1/2, ground level and the associated
excited metastable levels with =3/2, 5/2, 7/2 and 9/2. Since the ion beams
used in the experiments must be expected to contain long-lived excited states
also from excited configurations, additional cross-section calculations were
performed for the second-lowest term, 5d^5 \; ^6{\rm S}_{J}, =5/2, and for
the F term, 5d^3 6s^2 \; ^4{\rm F}_{J}, with = 3/2, 5/2, 7/2 and 9/2.
Given the complexity of the electronic structure of W the calculations
reproduce the main features of the experimental cross section quite well.Comment: 23 pages, 7 figures, 1 table: Accepted for publication in J. Phys. B:
At. Mol. & Opt. Phy
Toxic equivalency factors (TEFs) after acute oral exposure of azaspiracid 1,-2 and-3 in mice
Azaspiracids (AZAs) are marine algal toxins that can be accumulated by edible shellfish to cause a foodborne gastrointestinal poisoning in humans. In the European Union, only AZA1, -2 and -3 are currently regulated and their concentration in shellfish is determined through their toxic equivalency factors (TEFs) derived from the intraperitoneal lethal potency in mice. Nevertheless, considering the potential human exposure by oral route, AZAs TEFs should be calculated by comparative oral toxicity data. Thus, the acute oral toxicity of AZA1, -2 and -3 was investigated in female CD-1 mice treated with different doses (AZA1: 135-1100 mu g/kg; AZA2 and AZA3: 300-1100 mu g/kg) and sacrificed after 24 h or 14 days. TEFs derived from the median lethal doses (LD50) were 1.0, 0.7 and 0.5, respectively for AZA1, -2 and -3. In fact, after 24 h from gavage administration, LD(50)s were 443 mu g/kg (AZA1; 95% CL: 350-561 mu g/kg), 626 mu g/kg (AZA2; 95% CL: 430-911 mu g/kg) and 875 mu g/kg (AZA3; 95% CL: 757-1010 mu g/kg). Mice dead more than 5 h after the treatment or those sacrificed after 24 h (doses: = 175 mu g AZA1/kg, >= 500 mu g AZA2/kg and >= 600 mu g AZA3/kg) showed enlarged pale liver, while increased serum markers of liver alteration were recorded even at the lowest doses. Blood chemistry revealed significantly increased serum levels of K+ ions (>= 500 mg/kg), whereas light microscopy showed tissue changes in the gastrointestinal tract, liver and spleen. No lethality, macroscopic, tissue or haematological changes were recorded two weeks post exposure, indicating reversible toxic effects. LC-MS/MS analysis of the main organs showed a dose-dependency in gastrointestinal absorption of these toxins: at 24 h, the highest levels were detected in the stomach and, in descending order, in the intestinal content, liver, small intestine, kidneys, lungs, large intestine, heart as well as detectable traces in the brain. After 14 days, AZA1 and AZA2 were still detectable in almost all the organs and intestinal content
Selectively oxidised vertical cavity surface emitting lasers with 50% power conversion efficiency
Includes bibliographical references (page 209).Index-guided vertical cavity top-surface emitting laser diodes have been fabricated from an all epitaxial structure with conducting mirrors by selective lateral oxidation of AlGaAs. Low voltage, a 78% slope efficiency, and a 350μA threshold current in a single device combine to yield a maximum power conversion efficiency of 50% at less than a 2mA drive current. The device operates in a single mode up to 1.5mW
Signatures of Spin Glass Freezing in NiO Nanoparticles
We present a detailed study of the magnetic properties of sol-gel prepared
nickel oxide nanoparticles of different sizes. We report various measurements
such as frequency, field and temperature dependence of ac susceptibility,
temperature and field dependence of dc magnetization and time decay of
thermoremanent magnetization. Our results and analysis show that the system
behaves as a spin glass.Comment: 8 pages, 9 figure
High-frequency modulation of oxide-confined vertical cavity surface emitting lasers
Includes bibliographical references (page 458).High-speed studies of packaged, submilliampere threshold, oxide-confined vertical cavity surface emitting lasers show modulation bandwidths > 16GHz. Very high modulation current efficiency factors occur at low bias but decrease as the modulation bandwidth and frequency of the relative intensity noise peak saturate at higher currents
Simultaneous ambient pressure X-ray photoelectron spectroscopy and grazing incidence X-ray scattering in gas environments
We have developed an experimental system to simultaneously observe surface
structure, morphology, composition, chemical state, and chemical activity for
samples in gas phase environments. This is accomplished by simultaneously
measuring X-ray photoelectron spectroscopy (XPS) and grazing incidence X-ray
scattering (GIXS) in gas pressures as high as the multi-Torr regime, while also
recording mass spectrometry. Scattering patterns reflect near-surface sample
structures from the nano- to the meso-scale. The grazing incidence geometry
provides tunable depth sensitivity while scattered X-rays are detected across a
broad range of angles using a newly designed pivoting-UHV-manipulator for
detector positioning. At the same time, XPS and mass spectrometry can be
measured, all from the same sample spot and in ambient conditions. To
demonstrate the capabilities of this system, we measured the chemical state,
composition, and structure of Ag-behenate on a Si(001) wafer in vacuum and in
O atmosphere at various temperatures. These simultaneous structural,
chemical, and gas phase product probes enable detailed insights into the
interplay between structure and chemical state for samples in gas phase
environments. The compact size of our pivoting-UHV-manipulator makes it
possible to retrofit this technique into existing spectroscopic instruments
installed at synchrotron beamlines. Because many synchrotron facilities are
planning or undergoing upgrades to diffraction limited storage rings with
transversely coherent beams, a newly emerging set of coherent X-ray scattering
experiments can greatly benefit from the concepts we present here.Comment: 21 pages, 4 figure
Proceedings of the International Haemophilia Prophylaxis Study Group Meeting, November 2003, Montreal, PQ, Canada
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72691/1/j.1365-2516.2005.01053.x.pd
Photoionization of the fullerene ion C60+
Photoionization cross section of the fullerene ion C60+ has been calculated
within a single-electron approximation and also by using a consistent many-body
theory accounting for many-electron correlations.Comment: 8 pages, 3 figure
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