6,330 research outputs found
Atomic and magnetic structures of (CuCl)LaNbO and (CuBr)LaNbO: Density functional calculations
The atomic and magnetic structures of (Cu)LaNbO (=Cl and Br)
are investigated using the density-functional calculations. Among several
dozens of examined structures, an orthorhombic distorted structure,
in which the displacement pattern of halogens resembles the model
conjectured previously based on the empirical information is identified as the
most stable one. The displacements of halogens, together with those of Cu
ions, result in the formation of -Cu--Cu- zigzag chains in the two
materials. The nearest-neighbor interaction within the zigzag chains are
determined to be antiferromagnetic (AFM) for (CuCl)LaNbO but
ferromagnetic (FM) for (CuBr)LaNbO. On the other hand, the first two
neighboring interactions between the Cu cations from adjacent chains are found
to be AFM and FM respectively for both compounds. The magnitudes of all these
in-plane exchange couplings in (CuBr)LaNbO are evaluated to be about
three times those in (CuCl)LaNbO. In addition, a sizable AFM
inter-plane interaction is found between the Cu ions separated by two NbO
octahedra. The present study strongly suggests the necessity to go beyond the
square model in order to correctly account for the magnetic property
of (CuLaNbO.Comment: 24 pages, 7 figure
Surface grid generation for complex three-dimensional geometries
An outline is presented for the creation of surface grids from primitive geometry data such as obtained from CAD/CAM systems. The general procedure is applicable to any geometry including full aircraft with wing, nacelle, and empennage. When developed in an interactive graphics environment, a code based on this procedure is expected to substantially improve the turn around time for generating surface grids on complex geometries. Results are shown for a general hypersonic airplane geometry
On F-theory E_6 GUTs
We approach the Minimum Supersymmetric Standard Model (MSSM) from an E_6 GUT
by using the spectral cover construction and non-abelian gauge fluxes in
F-theory. We start with an E_6 singularity unfolded from an E_8 singularity and
obtain E_6 GUTs by using an SU(3) spectral cover. By turning on SU(2) X U(1)^2
gauge fluxes, we obtain a rank 5 model with the gauge group SU(3) X SU(2) X
U(1)^2. Based on the well-studied geometric backgrounds in the literature, we
demonstrate several models and discuss their phenomenology.Comment: 42 pages, 17 tables; typos corrected, clarifications added, and
references adde
Deposit Insurance and the Composition of Bank Suspensions in Developing Economies: Lessons from the State Deposit Insurance Experiments of the 1920S
Eight states established deposit insurance systems between 1908 and 1917. All abandoned the systems between 1921 and 1930. Scholars debate the costs and benefits of these policy experiments. New data drawn from the archives of the Federal Reserve Board of Governors demonstrate that deposit insurance influenced the composition of bank suspensions in these states. In typical years, suspensions due to runs fell. Suspensions due to mismanagement rose. During the penultimate year of each system, the bank failure rate rose to an unsustainable height and the system ceased operations.
Climate Change and Crop Yield Distribution: Some New Evidence From Panel Data Models
This study examines the impact of climate on the yields of seven major crops in Taiwan based on pooled panel data for 15 prefectures over the 1977-1996 period. Unit-root tests and maximum likelihood methods involving a panel data model are explored to obtain reliable estimates. The results suggest that climate has different impacts on different crops and a gradual increase in crop yield variation is expected as global warming prevails. Policy measures to counteract yield variability should therefore be carefully evaluated to protect farmers from exposure to these long-lasting and increasingly climate-related risks.Yield response, Climate change, Panel data, Unit-root test
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