Simultaneous Determination of Fe 3p Spin-Orbit and Exchange Splittings in Photoemission

Spin-resolved core-level photoemission data from the 3p level of ultrathin Fe films [1.4–5.1 monolayers (ML)] epitaxially grown on W(110) have been obtained. A nonlinear least-squares analysis, based on a one-particle Hamiltonian that simultaneously includes core-valence exchange and core-hole spin-orbit interactions, is developed. It is first tested on Fe 2p magnetic circular dichroism (MCD) photoemission spectra and shown to successfully describe the MCD asymmetry data. The model is then used to analyze our thin-film 3p data. With increasing film thickness the spin-orbit splitting (0.67±0.02 eV) remains constant (as expected), the exchange splitting increases from 0±0.12 eV to 0.41±0.05 eV, the average Fe film magnetization (=1.2±0.3μB at 1.4 ML) increases, and the singularity index decreases. The analysis highlights the importance of simultaneously considering all relevant photoemission parameters in extracting meaningful values of the spin-orbit and exchange interactions

Surface Core-Level Shifts and Atomic Coordination at a Stepped W(110) Surface

Core-level 4f7/2 photoemission spectra have been measured from a single, bifacial W crystal, which has both a flat W(110) and a vicinal, stepped W(110) [W(320)] surface. This procedure reduces uncertainties in the quantitative description of peaks in the spectra from W(320). Various analyses, including nonlinear least-squares curve fitting, show that the average surface core-level shift (SCS) for W(320) is only ∼-140 meV, compared to -310 meV for W(110) and that, at a maximum, only two of five terrace rows are isoelectronic to W(110) surface atoms. The absence of a large SCS for the step-edge atoms contradicts earlier interpretations of W(320) core-level spectra and departs significantly from expectations based on atomic-coordination models or tight-binding calculations of a bulk truncated surface. We suggest that systematic errors are responsible for the differences in reported core-level shifts for W(320). Implications of possible step-edge-driven atomic rearrangements are discussed

Conduction-Electron Screening in the Bulk and at Low-Index Surfaces of Ta Metal

High-resolution core-level photoemission spectra from Ta(100) have been measured. The well-resolved peak from the first atomic layer allows a separate assessment of bulk and surface-layer screening responses: singularity indices αB=0.10±0.01 and α100=0.205±0.025, respectively, are obtained. The measured surface-atom lifetime broadening of 70±20 meV (compared to 37±5 meV in the bulk) is consistent with published Auger–photoemission coincidence measurements. The result for the bulk singularity index has been applied in the analysis of previous data in order to extract the screening response in the first atomic layer of Ta(111) (α111=0.16±0.01) and Ta(110) (α110=0.150±0.015). The trend in surface α’s implies an increasingly atomic character for the surface-layer atoms as one proceeds from Ta(110) to Ta(111) to Ta(100)

Thermally Induced Core-Electron Binding-Energy Shifts in Transition Metals: An ExperimentalInvestigation of Ta(100)

High-resolution photoemission spectra from the 4f7/2 levels of Ta(100) have been obtained between 77 K and room temperature. The data show an increase in both the surface and bulk core-level binding energies (BE’s) as the temperature is raised: between 77 and 293 K the bulk and surface BE’s increase by 31±3 and 13±2 meV, respectively. A model calculation of the bulk binding-energy increase, which is based upon the lattice expansion of the solid, is in good agreement with the experimental results and indicates that the shifts arise from both initial- and final-state effects that are of comparable magnitude. The model is further used to estimate thermally induced shifts for the whole 5d transition-metal series. © 1996 The American Physical Society

Femtosecond Thermionic Emission in the Space-Charge Limited Regime

We study femtosecond-laser-pulse-induced electron emission from W(100), Al(110), and Ag(lll) in the sub-damage regime (1–44 mJ/cm2 fluence) by simultaneously measuring the incident-light reflectivity, total electron yield, and electron-energy distribution curves of the emitted electrons. The total-yield results are compared with a space-charge-limited extension of the Richardson-Dushman equation for short-time-scale thermionic emission and with particle-in-a-cell computer simulations of femtosecond-pulsed-induced thermionic emission. Quantitative agreement between the experimental results and two calculated temperature-dependent yields is obtained and shows that the yield varies linearly with temperature beginning at a threshold electron temperature of ~0.25 eV The particle-in-a-cell simulations also reproduce the experimental electron-energy distribution curves. Taken together, the experimental results, the theoretical calculations, and the results of the simulations indicate that thermionic emission from nonequilibrium electron heating provides the dominant source of the emitted electrons. Furthermore, the results demonstrate that a quantitative theory of space-charge-limited femtosecond-pulse-induced electron emission is possible

Metallophytes on Zn-Pb mineralised soils and mining wastes in Broken Hill, NSW, Australia

The wastes of metalliferous mining activities produce a substrate that is generally unfavourable for normal plant establishment and growth. However, metallophytes have evolved to grow in hostile environments that are rich in metals. They possess key properties that commend them for revegetation of mines and metal-contaminated sites. This field survey aimed to identify native metallophytes occurring on minerals wastes and mineralised outcrops in Broken Hill (New South Wales, Australia). Foliar concentrations of minerals were very high compared with non-mineralised soils but within the range expected for plants in such environments. Neither hyperaccumulators nor obligate metallophytes have been found, but they may be present on isolated mineralised outcrops in the wider Broken Hill area; however, a range of facultative metallophytes was identified in this study. These species could be introduced onto mining leases if establishment protocols for such species were developed

X-ray structure of a putative reaction intermediate of 5-aminolaevulinic acid dehydratase

The X-ray structure of yeast 5-aminolaevulinic acid dehydratase, in which the catalytic site of the enzyme is complexed with a putative cyclic intermediate composed of both substrate moieties, has been solved at 0.16 nm (1.6 Å) resolution. The cyclic intermediate is bound covalently to Lys(263) with the amino group of the aminomethyl side chain ligated to the active-site zinc ion in a position normally occupied by a catalytic hydroxide ion. The cyclic intermediate is catalytically competent, as shown by its turnover in the presence of added substrate to form porphobilinogen. The findings, combined with those of previous studies, are consistent with a catalytic mechanism in which the C–C bond linking both substrates in the intermediate is formed before the C–N bond

Herpes Zoster and Cardiovascular Events in Adults: A Systematic Review

Background: Stroke and myocardial infarction have been reported to occur after the development of herpes zoster (shingles), a common and preventable disease. Purpose: To evaluate literature describing the association between herpes zoster and its subtypes with the occurrence of cardiovascular events. Data Sources: PubMed, SCOPUS (Embase), OAIster, Google Scholar (searched in January 2016) Study Selection: Studies published up to January 2016 examining the association between herpes zoster or subtype of herpes zoster with the occurrence of cardiovascular events, including stroke, transient ischemic attack, or an acute coronary event, were selected. Case reports, case studies, and studies of non-general adult populations were excluded. Data Extraction: Data from studies meeting criteria were abstracted on a standardized form, and evaluated following modified set of standard guidelines. Data Synthesis: Nine published articles, with study populations ranging from 2,632 to 4,620,980 patients, met our pre-defined eligibility criteria. Eight studies found at least one positive association between herpes zoster type unspecified and subsequent stroke, transient ischemic attack, or an acute coronary event. Five studies found positive associations between herpes zoster ophthalmicus and stroke or myocardial infarction. Subgroup analyses from three studies were inconsistent regarding the association of cardiovascular events with receipt of antiviral therapy for herpes zoster. Limitations: Excludes non-English publications and non-published evidence. Conclusions: A small number of studies showed greater risks of stroke, transient ischemic attack, and acute cardiac events following the development of herpes zoster and herpes zoster ophthalmicus. Further prospective studies should develop strategies to reduce the risk of cardiovascular disease among patients with herpes zoster

A systematic review and meta-analysis on herpes zoster and the risk of cardiac and cerebrovascular events

BACKGROUND: Patients who develop herpes zoster or herpes zoster ophthalmicus may be at risk for cerebrovascular and cardiac complications. We systematically reviewed the published literature to determine the association between herpes zoster and its subtypes with the occurrence of cerebrovascular and cardiac events. METHODS/RESULTS: Systematic searches of PubMed (MEDLINE), SCOPUS (Embase) and Google Scholar were performed in December 2016. Eligible studies were cohort, case-control, and self-controlled case-series examining the association between herpes zoster or subtypes of herpes zoster with the occurrence of cerebrovascular and cardiac events including stroke, transient ischemic attack, coronary heart disease, and myocardial infarction. Data on the occurrence of the examined events were abstracted. Odds ratios and their accompanying confidence intervals were estimated using random and fixed effects models with statistical heterogeneity estimated with the I2 statistic. Twelve studies examining 7.9 million patients up to 28 years after the onset of herpes zoster met our pre-defined eligibility criteria. Random and fixed effects meta-analyses showed that herpes zoster, type unspecified, and herpes zoster ophthalmicus were associated with a significantly increased risk of cerebrovascular events, without any evidence of statistical heterogeneity. Our meta-analysis also found a significantly increased risk of cardiac events associated with herpes zoster, type unspecified. CONCLUSIONS: Our results are consistent with the accumulating body of evidence that herpes zoster and herpes zoster ophthalmicus are significantly associated with cerebrovascular and cardiovascular events

Observation of magnetic circular dichroism in Fe L_{2,3} x-ray-fluorescence spectra

We report experiments demonstrating circular dichroism in the x-ray-fluorescence spectra of magnetic systems, as predicted by a recent theory. The data, on the L_{2,3} edges of ferromagnetic iron, are compared with fully relativistic local spin density functional calculations, and the relationship between the dichroic spectra and the spin-resolved local density of occupied states is discussed