1,529 research outputs found
Dynamic Programming and Learning Models for Management of a Nonnative Species
Nonnative invasive species result in sizeable economic damages and expensive control costs. Because dynamic optimization models break down if controls depend in complex ways on past controls, non-uniform or scale-dependent spatial attributes, etc., decision support systems that allow learning may be preferred. We compare three models of an invasive weed in California’s grazing lands: (1) a stochastic dynamic programming model, (2) a reinforcement-based, experience-weighted attraction (EWA) learning model, and (3) an EWA model that also includes stochastic forage growth and penalties for repeated application of environmentally harmful control techniques. Results indicate that EWA learning models may be appropriate for invasive species management.Invasive weed species, optimal control, adaptive management
CaCu_3Ti_4O_12/CaTiO_3 Composite Dielectrics: A Ba/Pb-free Ceramics with High Dielectric Constants
We have measured dielectric properties of CaCuTiO
( = 0, 0.1, 0.5, 1, 1.5, 2, 2.9 and 3), and have found that
CaCuTiO (a composite of CaCuTiO and
CaTiO) exhibits a high dielectric constant of 1800 with a low dissipation
factor of 0.02 below 100 kHz from 220 to 300 K. These are comparable to (or
even better than) those of the Pb/Ba-based ceramics, which could be attributed
to a barrier layer of CaTiO on the surface of the CaCuTiO
grains. The composite dielectric ceramics reported here are environmentally
benign as they do not contain Ba/Pb.Comment: 4 pages, 4 figures, Appl. Phys. Lett. (scheduled on July 25, 2005
Effect of ferroelectric layers on the magnetocapacitance properties of superlattices-based oxide multiferroics
A series of superlattices composed of ferromagnetic
LaCaMnO (LCMO) and ferroelectric/paraelectric
BaSrTiO (0x1) were deposited on SrTiO
substrates using the pulsed laser deposition. Films of epitaxial nature
comprised of spherical mounds having uniform size are obtained.
Magnetotransport properties of the films reveal a ferromagnetic Curie
temperature in the range of 145-158 K and negative magnetoresistance as high as
30%, depending on the type of ferroelectric layers employed for their growth
(\QTR{it}{i.e.} '\QTR{it}{x'} value). Ferroelectricity at temperatures ranging
from 55 K to 105 K is also observed, depending on the barium content. More
importantly, the multiferroic nature of the film is determined by the
appearance of negative magnetocapacitance, which was found to be maximum around
the ferroelectric transition temperature (3% per \QTR{it}{tesla}). These
results are understood based on the role of the ferroelectric/paraelectric
layers and strains in inducing the multiferroism.Comment: Accepted to Applied Physics Letter
Surface reconstruction and ferroelectricity in PbTiO thin films
Surface and ferroelectric properties of PbTiO thin films are investigated
using an interatomic potential approach with parameters computed from
first-principles calculations. We show that a model developed for the bulk
describes properly the surface properties of PbTiO. In particular, the
antiferrodistortive surface reconstruction, recently observed from X-ray
scattering, is correctly reproduced as a result of the change in the balance of
long-range Coulombic and short-range interactions at the surface. The effects
of the surface reconstruction on the ferroelectric properties of ultrathin
films are investigated. Under the imposed open-circuit electrical boundary
conditions, the model gives a critical thickness for ferroelectricity of 4 unit
cells. The surface layer, which forms the antiferrodistortive reconstruction,
participates in the ferroelectricity. A decrease in the tetragonality of the
films leads to the stabilization of a phase with non-vanishing in-plane
polarization. A peculiar effect of the surface reconstruction on the in-plane
polarization profile is found.Comment: 6 pages, 5 figure
Modelling frontotemporal dementia using patient-derived induced pluripotent stem cells
Frontotemporal dementia (FTD) describes a group of clinically heterogeneous conditions that frequently affect people under the age of 65 (1). There are multiple genetic causes of FTD, including coding or splice-site mutations in MAPT, GRN mutations that lead to haploinsufficiency of progranulin protein, and a hexanucleotide GGGGCC repeat expansion in C9ORF72. Pathologically, FTD is characterised by abnormal protein accumulations in neurons and glia. These aggregates can be composed of the microtubule-associated protein tau (observed in FTD with MAPT mutations), the DNA/RNA-binding protein TDP-43 (seen in FTD with mutations in GRN or C9ORF72 repeat expansions) or dipeptide proteins generated by repeat associated non-ATG translation of the C9ORF72 repeat expansion. There are currently no disease-modifying therapies for FTD and the availability of in vitro models that recapitulate pathologies in a disease-relevant cell type would accelerate the development of novel therapeutics. It is now possible to generate patient-specific stem cells through the reprogramming of somatic cells from a patient with a genotype/phenotype of interest into induced pluripotent stem cells (iPSCs). iPSCs can subsequently be differentiated into a plethora of cell types including neurons, astrocytes and microglia. Using this approach has allowed researchers to generate in vitro models of genetic FTD in human cell types that are largely inaccessible during life. In this review we explore the recent progress in the use of iPSCs to model FTD, and consider the merits, limitations and future prospects of this approach
Structural, electronic and magnetic properties of SrRuO under epitaxial strain
Using density functional theory within the local spin density approximation,
structural, electronic and magnetic properties of SRO are investigated. We
examine the magnitude of the orthorhombic distortion in the ground state and
also the effects of applying epitaxial constraints, whereby the influence of
large (in the range of ) in-plane strain resulting from coherent
epitaxy, for both [001] and [110] oriented films, have been isolated and
investigated. The overall pattern of the structural relaxations reveal coherent
distortions of the oxygen octahedra network, which determine stability of the
magnetic moment on the Ru ion. The structural and magnetic parameters exhibit
substantial changes allowing us to discuss the role of symmetry and
possibilities of magneto-structural tuning of \SRO-based thin film structures.Comment: 11 page
Insoluble Residues of the Lower Mississippian Limestones of the Madison Group
The correlation of non-fossiliferous drill samples is one of the difficult problems that is enÂcountered in sub-surface stratigraphy. In order to truly correlate a formation, it must have some dis tinctive features and have an areal persistence of these features. These requirements are probably met best by limestone
First principles investigation of ferroelectricity in epitaxially strained PbTiO
The structure and polarization of the as-yet hypothetical Ruddlesden-Popper
compound PbTiO are investigated within density-functional theory. Zone
enter phonons of the high-symmetry KNiF-type reference structure, space
group , were calculated. At the theoretical ground-state lattice
constants, there is one unstable infrared-active phonon. This phonon freezes in
to give the ferroelectric state. As a function of epitaxial strain, two
additional ferroelectric phases are found, with space groups and
at compressive and tensile strains, respectively.Comment: 4 pages, 4 figure
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