3,432 research outputs found
Two Dimensional Spin-Polarized Electron Gas at the Oxide Interfaces
The formation of a novel spin-polarized 2D electron gas at the LaMnO
monolayer embedded in SrMnO is predicted from the first-principles
density-functional calculations. The La (d) electrons become confined in the
direction normal to the interface in the potential well of the La layer,
serving as a positively-charged layer of electron donors. These electrons
mediate a ferromagnetic alignment of the Mn t spins near the interface
via the Anderson-Hasegawa double exchange and become, in turn, spin-polarized
due to the internal magnetic fields of the Mn moments.Comment: 5 pages, 6 figure
Strain and Electric Field Modulation of the Electronic Structure of Bilayer Graphene
We study how the electronic structure of the bilayer graphene (BLG) is
changed by electric field and strain from {\it ab initio} density-functional
calculations using the LMTO and the LAPW methods. Both hexagonal and Bernal
stacked structures are considered. The BLG is a zero-gap semiconductor like the
isolated layer of graphene. We find that while strain alone does not produce a
gap in the BLG, an electric field does so in the Bernal structure but not in
the hexagonal structure. The topology of the bands leads to Dirac circles with
linear dispersion in the case of the hexagonally stacked BLG due to the
interpenetration of the Dirac cones, while for the Bernal stacking, the
dispersion is quadratic. The size of the Dirac circle increases with the
applied electric field, leading to an interesting way of controlling the Fermi
surface. The external electric field is screened due to polarization charges
between the layers, leading to a reduced size of the band gap and the Dirac
circle. The screening is substantial in both cases and diverges for the Bernal
structure for small fields as has been noted by earlier authors. As a biproduct
of this work, we present the tight-binding parameters for the free-standing
single layer graphene as obtained by fitting to the density-functional bands,
both with and without the slope constraint for the Dirac cone.Comment: 7 pages, 7 figure
Parameter Estimates of General Failure Rate Model: A Bayesian Approach
The failure rate function plays an important role in studying the lifetime
distributions in reliability theory and life testing models. A study of the
general failure rate model , under squared error loss
function taking and independent exponential random variables has been
analyzed in the literature. In this article, we consider and not
necessarily independent. The estimates of the parameters and under
squared error loss, linex loss and entropy loss functions are obtained here
Enzyme activity and electrophoretic pattern of isoenzymes of amylase, catalase and peroxidase in photo- and gibberellin-induced plants of Impatiens balsamina L. var. rose
Floral buds were induced either by 8 h photoperiods or by the application of GA3 and GA13 in Impatiens balsamina. Total enzyme activity was not directly related to floral morphogenesis although some interesting qualitative correlations existed. Thus, the presence of a new isoenzyme of amylase (RF 0·05) may be related to flower formation since it was present only in the induced plants and not in the vegetative ones, regardless of whether the flowering was caused by inductive photoperiods or by gibberellin treatment. Catalase activity, as well as its isoenzyme forms, could not be detected in the stem and the isoenzyme profile in leaves did not alter with photoperiodic or gibberellin treatment. Treatment with gibberellins induced the synthesis of new isoenzymes of peroxidase but inductive photoperiods did not. The enzyme profiles in relation to photoperiod and gibberellin application are discussed
A Note on the Thermodynamics of the Wet-and Dry-Bulb Hygrometer
The paper deals with the thermodynamic study of the wet-and-dry bulb
hygrometer as applied to other liquids besides water. Hygroscopic liquids are also included.
The theory is found in reasonable accord with experiment
Electronic and Magnetic Structure of the (LaMnO)/(SrMnO) Superlattices
We study the magnetic structure of the (LaMnO)/(SrMnO)
superlattices from density-functional calculations. In agreement with the
experiments, we find that the magnetism changes with the layer thickness `n'.
The reason for the different magnetic structures is shown to be the varying
potential barrier across the interface, which controls the leakage of the
Mn-e electrons from the LMO side to the SMO side. This in turn affects the
interfacial magnetism via the carrier-mediated Zener double exchange. For n=1
superlattice, the Mn-e electrons are more or less spread over the entire
lattice, so that the magnetic behavior is similar to the equivalent alloy
compound LaSrMnO. For larger n, the e electron transfer
occurs mostly between the two layers adjacent to the interface, thus leaving
the magnetism unchanged and bulk-like away from the interface region.Comment: 5 pages, 5 figure
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