Arsenic Species in Marine Samples

Arsenic occurs in seawater, in predominantly inorganic forms, at concentrations of about 1-2 μg/L. These concentrations are higher than those of most other potentially toxic metals and semimetals. Marine organisms have coped by exploiting the rich organic chemistry of arsenic to transform inorganic arsenic into a range of essentially non-toxic organoarsenic compounds. The resulting diversity of arsenic species found in marine samples is reviewed together with an overview of analytical methods for their determination. The relevance of the chemical form of arsenic to its bioavailability to marine organisms is also discussed

The effects of Verb Network Strengthening Treatment on a group of persons with aphasia: Replication and extension of previous findings

The current study aims to replicate and extend previous findings with a larger number of participants. Specifically, we asked whether training a set of verbs generalizes to production of 1) sentences containing trained verbs (The carpenter measures the lumber.), 2) sentence containing untrained semantically related verbs (The farmer weighs the apples.), 3) sentences unrelated to treatment (The dog watches the cat.), and 4) single word naming of nouns and verbs. Changes to Western Aphasia Battery-Revised (WAB-R) scores and responses to the CETI completed by communication partners (e.g., spouses of participants) were also evaluated

Adjustable current-induced magnetization switching utilizing interlayer exchange coupling

Electrical current-induced deterministic magnetization switching in a magnetic multilayer structure without external magnetic field is realized by utilizing interlayer exchange coupling. Two ferromagnetic Co layers, with in-plane and out-of-plane anisotropy respectively, are separated by a spacer Ta layer, which plays a dual role of inducing antiferromagnetic interlayer coupling, and contributing to the current-induced effective magnetic field through the spin Hall effect. The current-induced magnetization switching behavior can be tuned by pre-magnetizing the in-plane Co layer. The antiferromagnetic exchange coupling field increases with decreasing thickness of the Ta layer, reaching 630 ±5 Oe for a Ta thickness of 1.5nm. The magnitude of the current-induced perpendicular effective magnetic field from spin-orbit torque is 9.2 Oe/(107Acm-2). The large spin Hall angle of Ta, opposite in sign to that of Pt, results in a low critical current density of 9×106A/cm2. This approach is promising for the electrical switching of magnetic memory elements without external magnetic field

Deterministic Magnetization Switching Using Lateral Spin–Orbit Torque

Current-induced magnetization switching by spin-orbit torque (SOT) holds considerable promise for next generation ultralow-power memory and logic applications. In most cases, generation of spin-orbit torques has relied on an external injection of out-of-plane spin currents into the magnetic layer, while an external magnetic field along the electric current direction is generally required for realizing deterministic switching by SOT. Here, we report deterministic current-induced SOT full magnetization switching by lateral spin-orbit torque in zero external magnetic field. The Pt/Co/Pt magnetic structure was locally annealed by a laser track along the in-plane current direction, resulting in a lateral Pt gradient within the ferromagnetic layer, as confirmed by microstructure and chemical composition analysis. In zero magnetic field, the direction of the deterministic current-induced magnetization switching depends on the location of the laser track, but shows no dependence on the net polarization of external out-of-plane spin currents. From the behavior under external magnetic fields, we identify two independent mechanisms giving rise to SOT, i.e. the lateral Pt-Co asymmetry as well as out-of-plane injected spin currents, where the polarization and the magnitude of the SOT in the former case depends on the relative location and the laser power of the annealing track. Our results demonstrate an efficient field-free deterministic full magnetization switching scheme, without requiring out-of-plane spin current injection or complex external stack structures.Comment: 39 Pages, 9 Figure

Properties of metastable alkaline-earth-metal atoms calculated using an accurate effective core potential

The first three electronically excited states in the alkaline-earth-metal atoms magnesium, calcium, and strontium comprise the (nsnp) triplet P^o_J (J=0,1,2) fine-structure manifold. All three states are metastable and are of interest for optical atomic clocks as well as for cold-collision physics. An efficient technique--based on a physically motivated potential that models the presence of the ionic core--is employed to solve the Schroedinger equation for the two-electron valence shell. In this way, radiative lifetimes, laser-induced clock shifts, and long-range interaction parameters are calculated for metastable Mg, Ca, and Sr.Comment: 13 pages, 9 table

Quasi-free-standing AA-stacked bilayer graphene induced by calcium intercalation of the graphene-silicon carbide interface

We study quasi-freestanding bilayer graphene on silicon carbide intercalated by calcium. The intercalation, and subsequent changes to the system, were investigated by low-energy electron diffraction, angle-resolved photoemission spectroscopy (ARPES) and density-functional theory (DFT). Calcium is found to intercalate only at the graphene-SiC interface, completely displacing the hydrogen terminating SiC. As a consequence, the system becomes highly n-doped. Comparison to DFT calculations shows that the band dispersion, as determined by ARPES, deviates from the band structure expected for Bernal-stacked bilayer graphene. Instead, the electronic structure closely matches AA-stacked bilayer graphene on Ca-terminated SiC, indicating a spontaneous transition from AB- to AA-stacked bilayer graphene following calcium intercalation of the underlying graphene-SiC interface.Comment: 14 pages, 3 figure

Molecular beam epitaxy of CuMnAs

We present a detailed study of the growth of the tetragonal polymorph of antiferromagnetic CuMnAs by the molecular beam epitaxy technique. We explore the parameter space of growth conditions and their effect on the microstructural and transport properties of the material. We identify its typical structural defects and compare the properties of epitaxial CuMnAs layers grown on GaP, GaAs and Si substrates. Finally, we investigate the correlation between the crystalline quality of CuMnAs and its performance in terms of electrically induced resistance switching.Comment: 10 pages, 8 figures and supplementary materia

Increasing the Rate of Magnesium Intercalation Underneath Epitaxial Graphene on 6H-SiC(0001)

Magnesium intercalated 'quasi-freestanding' bilayer graphene on 6H-SiC(0001) (Mg-QFSBLG) has many favorable properties (e.g., highly n-type doped, relatively stable in ambient conditions). However, intercalation of Mg underneath monolayer graphene is challenging, requiring multiple intercalation steps. Here, we overcome these challenges and subsequently increase the rate of Mg intercalation by laser patterning (ablating) the graphene to form micron-sized discontinuities. We then use low energy electron diffraction to verify Mg-intercalation and conversion to Mg-QFSBLG, and X-ray photoelectron spectroscopy to determine the Mg intercalation rate for patterned and non-patterned samples. By modeling Mg intercalation with the Verhulst equation, we find that the intercalation rate increase for the patterned sample is 4.5$\pm$1.7. Since the edge length of the patterned sample is $\approx$5.2 times that of the non-patterned sample, the model implies that the increased intercalation rate is proportional to the increase in edge length. Moreover, Mg intercalation likely begins at graphene discontinuities in pristine samples (not step edges or flat terraces), where the 2D-like crystal growth of Mg-silicide proceeds. Our laser patterning technique may enable the rapid intercalation of other atomic or molecular species, thereby expanding upon the library of intercalants used to modify the characteristics of graphene, or other 2D materials and heterostructures.Comment: 24 pages, 4 figure