808 research outputs found
On thin plate spline interpolation
We present a simple, PDE-based proof of the result [M. Johnson, 2001] that
the error estimates of [J. Duchon, 1978] for thin plate spline interpolation
can be improved by . We illustrate that -matrix
techniques can successfully be employed to solve very large thin plate spline
interpolation problem
Genetic clustering on the hippocampal surface for genome-wide association studies
Imaging genetics aims to discover how variants in the human genome influence brain measures derived from images. Genome-wide association scans (GWAS) can screen the genome for common differences in our DNA that relate to brain measures. In small samples, GWAS has low power as individual gene effects are weak and one must also correct for multiple comparisons across the genome and the image. Here we extend recent work on genetic clustering of images, to analyze surface-based models of anatomy using GWAS. We performed spherical harmonic analysis of hippocampal surfaces, automatically extracted from brain MRI scans of 1254 subjects. We clustered hippocampal surface regions with common genetic influences by examining genetic correlations (rg) between the normalized deformation values at all pairs of surface points. Using genetic correlations to cluster surface measures, we were able to boost effect sizes for genetic associations, compared to clustering with traditional phenotypic correlations using Pearson's r
Antagonistic effects of transforming growth factor-beta on vitamin D3 enhancement of osteocalcin and osteopontin transcription: reduced interactions of vitamin D receptor/retinoid X receptor complexes with vitamin E response elements
Osteocalcin and osteopontin are noncollagenous proteins secreted by
osteoblasts and regulated by a complex interplay of systemic and locally
produced factors, including growth factors and steroid hormones. We
investigated the mechanism by which transforming growth factor-beta (TGF
beta) inhibits 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3)-enhanced expression
of the osteocalcin (OC) and osteopontin (OP) genes. ROS 17/2.8 cells, in
which both genes are expressed, were transfected with reporter constructs
driven by native (i.e. wild-type) rat OC and mouse OP promoters. TGF beta
abrogated the 1,25-(OH)2D3 enhanced transcription of both the OC and OP
genes. The inhibitory TGF beta response for each requires vitamin D
response element (VDRE) sequences, although there are additional
contributions from proximal basal regulatory elements. These
transcriptional effects were further investigated for contribution of the
trans-activating factors, which interact with OC and OP VDREs, involving
the vitamin D receptor (VDR) and retinoid X receptor (RXR). Gel mobility
shift assays show that TGF beta significantly reduces induction of the
heterodimers VDR/RXR complexes in 1,25-(OH)2D3-treated ROS 17/2.8 cells.
However, Western blot and ligand binding analysis reveal that TGF beta
does not affect nuclear availability of the VDR. We also show that
activator protein-1 activity is up-regulated by TGF beta; thus, activator
protein-1 binding sites in the OC promoter may potentially contribute to
inhibitory effects of TGF beta on basal transcription. Our studies
demonstrate that the inhibitory action of TGF beta on the 1,25-(OH)2D3
enhancement of OC and OP transcription in osteoblastic cells results from
modulations of protein-DNA interactions at the OC and OP VDRE, which
cannot be accounted for by changes in VDR protein levels. As OC and OP
participate in bone turnover, our results provide insight into the
contributions of TGF beta and 1,25-(OH)2D3 to VDR-mediated gene regulatory
mechanism operative in bone formation and/or resorption events
Nonlinear porous medium flow with fractional potential pressure
We study a porous medium equation, with nonlocal diffusion effects given by
an inverse fractional Laplacian operator. We pose the problem in n-dimensional
space for all t>0 with bounded and compactly supported initial data, and prove
existence of a weak and bounded solution that propagates with finite speed, a
property that is nor shared by other fractional diffusion models.Comment: 32 pages, Late
Charge Fluctuations on Membrane Surfaces in Water
We generalize the predictions for attractions between over-all neutral
surfaces induced by charge fluctuations/correlations to non-uniform systems
that include dielectric discontinuities, as is the case for mixed charged lipid
membranes in an aqueous solution. We show that the induced interactions depend
in a non-trivial way on the dielectric constants of membrane and water and show
different scaling with distance depending on these properties. The generality
of the calculations also allows us to predict under which dielectric conditions
the interaction will change sign and become repulsive
Implementation and Validation of Schapery-Rand Anisotropic Viscoelasticity Model for Super-Pressure Balloons
The thin film used for the NASA Ultra Long Duration Balloons (ULDB) shows con-siderable time-dependent behaviour. Furthermore, experiments on scaled ULDB balloons have revealed that wrinkles are present over a wide range of pressures. A numerical model has been developed describing the nonlinear anisotropic viscoelastic material behaviour by means of a Schapery-type model and this model has been extended to model wrinkling by means of a user-defined subroutine in the finite-element package ABAQUS. After a description of the viscoelastic modelling approach, a lobe of a 48 gore ULDB flat facet balloon is modelled and compared to experimental results. Additionally two test cases of anisotropic wrinkling are presented, one involving a flat membrane and one a cylindrical balloon structure. I
Imprints of the Quantum World in Classical Mechanics
The imprints left by quantum mechanics in classical (Hamiltonian) mechanics
are much more numerous than is usually believed. We show Using no physical
hypotheses) that the Schroedinger equation for a nonrelativistic system of
spinless particles is a classical equation which is equivalent to Hamilton's
equations.Comment: Paper submitted to Foundations of Physic
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