973 research outputs found
Boundary conditions and Berry phase in magnetic nanostructures
The effect of micromagnetic boundary conditions on the Berry curvature and topological Hall effect in granular nanostructures is investi- gated by model calculations. Both free surfaces and grain boundaries between interacting particles or grains affect the spin structure. The Dzyaloshinskii-Moriya interactions yield corrections to the Erdmann-Weierstrass boundary conditions, but the Berry curvature remains an exclusive functional of the local spin structure, which greatly simplifies the treatment of nanostructures. An explicit example is a model nanostructure with cylindrical symmetry whose spin structure is described by Bessel function and which yields a mean-field-type Hall-effect contribution that can be related to magnetic-force-microscopy images
Self-vacancies in Gallium Arsenide: an ab initio calculation
We report here a reexamination of the static properties of vacancies in GaAs
by means of first-principles density-functional calculations using localized
basis sets. Our calculated formation energies yields results that are in good
agreement with recent experimental and {\it ab-initio} calculation and provide
a complete description of the relaxation geometry and energetic for various
charge state of vacancies from both sublattices. Gallium vacancies are stable
in the 0, -, -2, -3 charge state, but V_Ga^-3 remains the dominant charge state
for intrinsic and n-type GaAs, confirming results from positron annihilation.
Interestingly, Arsenic vacancies show two successive negative-U transitions
making only +1, -1 and -3 charge states stable, while the intermediate defects
are metastable. The second transition (-/-3) brings a resonant bond relaxation
for V_As^-3 similar to the one identified for silicon and GaAs divacancies.Comment: 14 page
Noncollinear spin structure in Fe3+xCo3−xTi2 (x = 0, 2, 3) from neutron diffraction
Neutron powder diffraction has been used to investigate the spin structure of the hard-magnetic alloy Fe3+xCo3−xTi2 (x = 0, 2, 3). The materials are produced by rapid quenching from the melt, they possess a hexagonal crystal structure, and they are nanocrystalline with crystallite sizes D of the order of 40 nm. Projections of the magnetic moment onto both the crystalline c axis and the basal plane were observed. The corresponding misalignment angle exhibits a nonlinear decrease with x, which we explain as a micromagnetic effect caused by Fe-Co site disorder. The underlying physics is a special kind of random-anisotropy magnetism that leads to the prediction of 1/D1/4 power-law dependence of the misalignment angle on the crystallite size
Systems approaches and algorithms for discovery of combinatorial therapies
Effective therapy of complex diseases requires control of highly non-linear
complex networks that remain incompletely characterized. In particular, drug
intervention can be seen as control of signaling in cellular networks.
Identification of control parameters presents an extreme challenge due to the
combinatorial explosion of control possibilities in combination therapy and to
the incomplete knowledge of the systems biology of cells. In this review paper
we describe the main current and proposed approaches to the design of
combinatorial therapies, including the empirical methods used now by clinicians
and alternative approaches suggested recently by several authors. New
approaches for designing combinations arising from systems biology are
described. We discuss in special detail the design of algorithms that identify
optimal control parameters in cellular networks based on a quantitative
characterization of control landscapes, maximizing utilization of incomplete
knowledge of the state and structure of intracellular networks. The use of new
technology for high-throughput measurements is key to these new approaches to
combination therapy and essential for the characterization of control
landscapes and implementation of the algorithms. Combinatorial optimization in
medical therapy is also compared with the combinatorial optimization of
engineering and materials science and similarities and differences are
delineated.Comment: 25 page
4-Chloro-2-[(2,6-diisopropylÂphenÂyl)iminoÂmethÂyl]phenol
The asymmetric unit of the title compound, C19H22ClNO, contains two independent molÂecules in which the dihedral angles between the aromatic rings are 76.45 (9) and 74.69 (9)°. An intraÂmolecular O—H⋯N hydrogen bond occurs in each molÂecule. The crystal structure features weak C—H⋯π interÂactions
Boundary conditions and Berry phase in magnetic nanostructures
The effect of micromagnetic boundary conditions on the Berry curvature and topological Hall effect in granular nanostructures is investi- gated by model calculations. Both free surfaces and grain boundaries between interacting particles or grains affect the spin structure. The Dzyaloshinskii-Moriya interactions yield corrections to the Erdmann-Weierstrass boundary conditions, but the Berry curvature remains an exclusive functional of the local spin structure, which greatly simplifies the treatment of nanostructures. An explicit example is a model nanostructure with cylindrical symmetry whose spin structure is described by Bessel function and which yields a mean-field-type Hall-effect contribution that can be related to magnetic-force-microscopy images
Electronic and Optical Studies of PbO with Oxygen Defect: A DFT Approach
ABSTRACT The GGA exchange correlation with PBE functional has been taken to analyze PbO with and without oxygen defect. It was observed the structural stability and the density of states in the PbO super cell with oxygen defects -33537.19eV and 5.70eV. The HOMO-LUMO level of PbO was observed in DFT method, while oxygen defects in the super cell the energy level was reduced simultaneously -3.68 eV and -3.11 eV
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