26,378 research outputs found
Theory of Local Dynamical Magnetic Susceptibilities from the Korringa-Kohn-Rostoker Green Function Method
Within the framework of time-dependent density functional theory combined
with the Korringa-Kohn-Rostoker Green function formalism, we present a real
space methodology to investigate dynamical magnetic excitations from
first-principles. We set forth a scheme which enables one to deduce the correct
effective Coulomb potential needed to preserve the spin-invariance signature in
the dynamical susceptibilities, i.e. the Goldstone mode. We use our approach to
explore the spin dynamics of 3d adatoms and different dimers deposited on a
Cu(001) with emphasis on their decay to particle-hole pairs.Comment: 32 pages (preprint), 6 figures, one tabl
Resolving the chemical substructure of Orion-KL
The Kleinmann-Low nebula in Orion (Orion-KL) is the nearest example of a
high-mass star-forming environment. For the first time, we complemented 1.3 mm
Submillimeter Array (SMA) interferometric line survey with IRAM 30 m
single-dish observations of the Orion-KL region. Covering a 4 GHz bandwidth in
total, this survey contains over 160 emission lines from 20 species (25
isotopologues), including 11 complex organic molecules (COMs).
At a spatial resolution of 1200 AU, the continuum substructures are resolved.
Extracting the spectra from individual substructures and providing the
intensity-integrated distribution map for each species, we studied the
small-scale chemical variations in this region. Our main results are: (1) We
identify lines from the low-abundance COMs CH3COCH3 and CH3CH2OH, as well as
tentatively detect CH3CHO and long carbon-chains C6H and HC7N. (2) We find that
while most COMs are segregated by type, peaking either towards the hot core
(e.g., N-bearing species) or the compact ridge (e.g., O-bearing species like
HCOOCH3 and CH3OCH3), while the distributions of others do not follow this
segregated structure (e.g., CH3CH2OH, CH3OH, CH3COCH3). (3) We find a second
velocity component of HNCO, SO2, 34SO2, and SO lines, which may be associated
with a strong shock event in the low-velocity outflow. (4) Temperatures and
molecular abundances show large gradients between central condensations and the
outflow regions, illustrating a transition between hot molecular core and
shock-chemistry dominated regimes.
Our observations of spatially resolved chemical variations in Orion-KL
provide the nearest reference source for hot molecular core and outflow
chemistry, which will be an important example for interpreting the chemistry of
more distant HMSFRs.Comment: 51 pages, 17 figures, accepted on 12 March 2015 Dashed lines in
Figure 10 of the published paper was missin
Carbon nanotube: a low-loss spin-current waveguide
We demonstrate with a quantum-mechanical approach that carbon nanotubes are
excellent spin-current waveguides and are able to carry information stored in a
precessing magnetic moment for long distances with very little dispersion and
with tunable degrees of attenuation. Pulsed magnetic excitations are predicted
to travel with the nanotube Fermi velocity and are able to induce similar
excitations in remote locations. Such an efficient way of transporting magnetic
information suggests that nanotubes are promising candidates for memory devices
with fast magnetization switchings
Spin Orbit Coupling and Spin Waves in Ultrathin Ferromagnets: The Spin Wave Rashba Effect
We present theoretical studies of the influence of spin orbit coupling on the
spin wave excitations of the Fe monolayer and bilayer on the W(110) surface.
The Dzyaloshinskii-Moriya interaction is active in such films, by virtue of the
absence of reflection symmetry in the plane of the film. When the magnetization
is in plane, this leads to a linear term in the spin wave dispersion relation
for propagation across the magnetization. The dispersion relation thus assumes
a form similar to that of an energy band of an electron trapped on a
semiconductor surfaces with Rashba coupling active. We also show SPEELS
response functions that illustrate the role of spin orbit coupling in such
measurements. In addition to the modifications of the dispersion relations for
spin waves, the presence of spin orbit coupling in the W substrate leads to a
substantial increase in the linewidth of the spin wave modes. The formalism we
have developed applies to a wide range of systems, and the particular system
explored in the numerical calculations provides us with an illustration of
phenomena which will be present in other ultrathin ferromagnet/substrate
combinations
Studying inhomogeneity of organic coatings using wire beam multielectrode and physicomechanical testing
The effect of thickness, curing temperature and solvent on the structural inhomogeneity of several types of organic coatings has been investigated. The local distribution of electrochemical resistance was studied using a wire beam multielectrode array, while the inhomogeneity at a larger scale was examined using ∼3 cm2 area detached coatings. Physicomechanical tests were also employed to address the structural changes occurring because of variation in curing temperature and the type (or absence) of solvent. Results acquired by wire beam electrode and from the detached coatings showed that increasing the thickness and curing temperature improves the homogeneity of the coating as does elimination of solvent. Waterborne coatings exhibited a relatively homogeneous low resistance with a resistance lower than the threshold required for effective corrosion protection. Results of physicomechanical examination suggest that unreacted functional groups and water absorption are of the main causes of formation of structural defects in organic coatings
Many-body Green's function approach to attosecond nonlinear X-ray spectroscopy
Closed expressions are derived for resonant multidimensional X-ray
spectroscopy using the quasiparticle nonlinear exciton representation of
optical response. This formalism is applied to predict coherent four wave
mixing signals which probe single and two core-hole states. Nonlinear X-ray
signals are compactly expressed in terms of one- and two- particle Green's
functions which can be obtained from the solution of Hedin-like equations at
the level.Comment: 10 pages and 3 figures (To appear in Physical Review B
Is there a link between treatments with exogenous corticosteroids and dog behaviour problems?
Possible side effects of exogenous corticosteroids have been described in both humans and laboratory animals, with recent studies highlighting this issue in dogs. In this paper the behaviour of 345 dogs drawn from the caseload of a behaviour clinic based in the north of Italy between February 2012 and November 2014 were analysed. Possible relationships between dogs that received treatment with corticosteroids versus dogs that received treatment with drugs other than corticosteroids and positive or negative affective states, aggression towards people, other behaviour problems apart from aggression, occurrence of severe bites, and prescription of psychoactive drugs were initially assessed using a Pearson's chi-squared test. Regression analysis was then performed in order to evaluate the best predictors of the investigated items. The goal of this retrospective survey was to investigate possible relationships between the affective states associated with the behavioural complaint of dogs and their previous history of treatment with corticosteroids. Results showed that a history of corticosteroid treatment was a significant predictor of a range of behaviour problems associated with negative affective state, but this result may be confounded by age-related effects
Evaluation of Education and Other Influential Factors on the Perceptions of Influenza Vaccinations
Influenza is a potentially deadly contagious viral infection that attacks the respiratory system. The 1918 influenza pandemic infected approximately 1/3 of the world’s population and resulted in an estimated 50 million deaths globally. Research has led to the production of influenza vaccinations. Unfortunately, there continues to be influenza epidemics that are responsible for killing numerous people annually. One reason for the continued death toll from influenza is the lack of people receiving a yearly flu vaccination. In order to gain more public acceptance for influenza vaccinations, it is important to understand the factors influencing the choice to be vaccinated. A study was conducted on 191 undergraduate general psychology students at the University of Central Arkansas to test if specific factors determine the predictability of vaccination acceptance. Education and positive influential factors toward flu vaccinations are two important factors presented in the study that have influence on participants receiving the vaccine. The study results are beneficial in understanding why people reject flu vaccines and what can be done to reverse those decisions
Stabilisation of fluvial bed sediments by invasive quagga mussels (Dreissena bugensis)
River gravel mobility is an important control on river behaviour, morphology, and ecosystem processes. Gravel stability is dependent on abiotic flow and sediment properties, alongside less widely acknowledged biotic processes. The quagga mussel (Dreissena bugensis), a highly invasive bivalve, frequently occurs at high population densities in rivers and lakes. Quagga mussels attach to benthic sediments using byssal threads, which might affect sediment stability and thereby broader river geomorphology. We aimed to (1) characterise controls of quagga mussel sediment attachment by conducting a field survey in an invaded river, (2) investigate resultant changes in the critical shear stress needed to entrain fluvial bed materials via an ex-situ flume experiment, for measured average (135 m-2) and potential future (270 m-2) mussel densities, and (3) model how this may affect sediment transport rates. From field surveys, mean quagga mussel density was 122 m 2, attaching to an average of 591 g m 2 of mineral bed sediments. Across the survey reach, mussels attached to all grain sizes available, with attachment driven by grain availability, rather than active selection of particular grain sizes. In the ex-situ flume experiment, densities of 135 mussels m-2 did not significantly increase the critical shear stress of fluvial bed materials, but a density of 270 mussels m-2 significantly increased critical shear stress by 40%. Estimates of the proportion of time these critical stresses are exceeded at the field site indicated high densities of quagga mussels may reduce the occurrence of a geomorphically active flood event from Q30 to Q2. These results present feasible invasion scenarios, as quagga mussels frequently reach benthic densities orders of magnitude greater than observed here. This study indicates that substantial alterations to bedload sediment transport may occur following quagga mussel invasion. Future geomorphic modelling should include biology to better understand rates and processes of landscape development
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