555 research outputs found
Theoretical study of the mechanism of dry oxidation of 4H-SiC
Possible defect structures, arising from the interaction of O-2 molecules with an ideal portion of the SiC/SiO2 interface, have been investigated systematically using density functional theory. Based on the calculated total energies and assuming thermal quasiequilibrium during oxidation, the most likely routes leading to complete oxidation have been determined. The defect structures produced along these routes will remain at the interface in significant concentration when stopping the oxidation process. The results obtained for their properties are well supported by experimental findings about the SiC/SiO2 interface. It is found that carbon-carbon bonds can explain most of the observed interface states but not the high density near the conduction band of 4H-SiC
Thickness-dependent magnetic structure of ultrathin Fe/Ir(001) films: from spin-spiral states towards ferromagnetic order
We present a detailed study of the ground-state magnetic structure of
ultrathin Fe films on the surface of fcc Ir(001). We use the spin-cluster
expansion technique in combination with the relativistic disordered local
moment scheme to obtain parameters of spin models and then determine the
favored magnetic structure of the system by means of a mean field approach and
atomistic spin dynamics simulations. For the case of a single monolayer of Fe
we find that layer relaxations very strongly influence the ground-state spin
configurations, whereas Dzyaloshinskii-Moriya (DM) interactions and biquadratic
couplings also have remarkable effects. To characterize the latter effect we
introduce and analyze spin collinearity maps of the system. While for two
monolayers of Fe we find a single-q spin spiral as ground state due to DM
interactions, for the case of four monolayers the system shows a noncollinear
spin structure with nonzero net magnetization. These findings are consistent
with experimental measurements indicating ferromagnetic order in films of four
monolayers and thicker.Comment: 9 pages, 7 figure
INVESTIGATION OF THE HOMOGENIZATION EFFICIENCY OF THE SCREW AGITATOR, HELICAL RIBBON AGITATOR, GATE TYPE ANCHOR IMPELLER AND THE MULTI-PADDLE AGITATOR IN THE MIXING OF HIGH-VISCOSITY NEWTONIAN LIQUIDS
Presented by Prof. Dr. P. FOLDE
Metallic magnetism at finite temperatures studied by relativistic disordered moment description: Theory and applications
We develop a self-consistent relativistic disordered local moment (RDLM)
scheme aimed at describing finite temperature magnetism of itinerant metals
from first principles. Our implementation in terms of the
Korringa--Kohn--Rostoker multiple scattering theory and the coherent potential
approximation allows to relate the orientational distribution of the spins to
the electronic structure, thus a self-consistent treatment of the distribution
is possible. We present applications for bulk bcc Fe, L1-FePt and FeRh
ordered in the CsCl structure. The calculations for Fe show significant
variation of the local moments with temperature, whereas according to the mean
field treatment of the spin fluctuations the Curie temperature is
overestimated. The magnetic anisotropy of FePt alloys is found to depend
strongly on intermixing between nominally Fe and Pt layers, and it shows a
power-law behavior as a function of magnetization for a broad range of chemical
disorder. In case of FeRh we construct a lattice constant vs. temperature phase
diagram and determine the phaseline of metamagnetic transitions based on
self-consistent RDLM free energy curves.Comment: 11 pages, 8 figure
GINA - A Polarized Neutron Reflectometer at the Budapest Neutron Centre
The setup, capabilities and operation parameters of the neutron reflectometer
GINA, the recently installed "Grazing Incidence Neutron Apparatus" at the
Budapest Neutron Centre, are introduced. GINA, a dance-floor-type,
constant-energy, angle-dispersive reflectometer is equipped with a 2D
position-sensitive detector to study specular and off-specular scattering.
Wavelength options between 3.2 and 5.7 {\AA} are available for unpolarized and
polarized neutrons. Spin polarization and analysis are achieved by magnetized
transmission supermirrors and radio-frequency adiabatic spin flippers. As a
result of vertical focusing by the five-element (pyrolytic graphite)
monochromator the reflected intensity from a 20x20 mm sample has doubled. GINA
is dedicated to studies of magnetic films and heterostructures, but unpolarized
options for non-magnetic films, membranes and other surfaces are also provided.
Shortly after its startup, reflectivity values as low as 3x10-5 have been
measured on the instrument. The facility is now open for the international user
community, but its development is continuing mainly to establish new sample
environment options, the spin analysis of off-specularly scattered radiation
and further decrease of the background
The role of law and ethics in developing business management as a profession
Currently, business management is far from being recognised as a profession. This paper suggests that a professional spirit should be developed which could function as a filter of commercial reasoning. Broadly, management will not be organised within the framework of a well-established profession unless formal knowledge, licensing, professional autonomy and professional codes of conduct are developed sufficiently. In developing business management as a profession, law may play a key role. Where the idea is that business management should be more professsionalised, managers must show that they are willing to adopt ethical values, while arriving at business decisions. The paper argues that ethics cannot survive without legal regulation, which, in turn, will not be supported by law unless lawyers can find alternative solutions to the large mechanisms of the official society, secured by the monopolised coercion of the nation state. From a micro perspective of law and business ethics, communities can be developed with their own conventions, rules and standards that are generated and sanctioned within the boundaries of the communities themselves
Role of oxygen vacancy defect states in the n-type conduction of β-Ga[sub 2]O[sub 3]
Based on semiempirical quantum-chemical calculations, the electronic band structure of β-Ga2O3 is presented and the formation and properties of oxygen vacancies are analyzed. The equilibrium geometries and formation energies of neutral and doubly ionized vacancies were calculated. Using the calculated donor level positions of the vacancies, the high temperature n-type conduction is explained. The vacancy concentration is obtained by fitting to the experimental resistivity and electron mobility
NDVI as a Proxy for Estimating Sedimentation and Vegetation Spread in Artificial Lakes — Monitoring of Spatial and Temporal Changes by Using Satellite Images Overarching Three Decades
Observing wetland areas and monitoring changes are crucial to understand hydrological and ecological processes. Sedimentation-induced vegetation spread is a typical process in the succession of lakes endangering these habitats. We aimed to survey the tendencies of vegetation spread of a Hungarian lake using satellite images, and to develop a method to identify the areas of risk. Accordingly, we performed a 33-year long vegetation spread monitoring survey. We used the Normalized Difference Vegetation Index (NDVI) and the Modified Normalized Difference Water Index
(MNDWI) to assess vegetation and open water characteristics of the basins. We used these spectral indices to evaluate sedimentation risk of water basins combined with the fact that the most abundant plant species of the basins was the water caltrop (Trapa natans) indicating shallow water. We proposed a 12-scale Level of Sedimentation Risk Index (LoSRI) composed from vegetation cover data derived from
satellite images to determine sedimentation risk within any given water basin. We validated our results with average water basin water depth values, which showed an r = 0.6 (p < 0.05) correlation. We also pointed on the most endangered locations of these sedimentation-threatened areas, which can provide crucial information for management planning of water directorates and management organizations
Defects in SiO2 as the possible origin of near interface traps in the SiC∕SiO2 system: A systematic theoretical study
A systematic study of the level positions of intrinsic and carbon defects in SiO2 is presented, based on density functional calculations with a hybrid functional in an alpha-quartz supercell. The results are analyzed from the point of view of the near interface traps (NIT), observed in both SiC/SiO2 and Si/SiO2 systems, and assumed to have their origins in the oxide. It is shown that the vacancies and the oxygen interstitial can be excluded as the origin of such NIT, while the silicon interstitial and carbon dimers give rise to gap levels in the energy range inferred from experiments. The properties of these defects are discussed in light of the knowledge about the SiC/SiO2 interface
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