3,157 research outputs found
Atmospheric Argon Free burning Arcs with a Simplified Unified Model Using CFD-Arc Modeling
Free burning arcs, where the work piece acts as an anode, are frequently used for a number of applications. Our investigation is exclusively concerned with a simplified unified model of arcs and their electrodes under steady state conditions at atmospheric pressure. The model is used to make predictions of arc and electrode temperatures and arc voltage for a 200 A arc in argon. The computed temperatures along the axis between the cathode tip and the anode surface compare well the measured data
Nucleon cosmological constant term and flavor structure of the gravitational form factors
The gravitational form factors furnish information on the mechanics of the
nucleon. It is essential to compute the generalized isovector-vector form
factors to examine the flavor structure of the gravitational form factors. The
flavor-decomposed form factors reveal the internal structure of the nucleon.
The up quark dominates over the down quark for the mass and spin of the
nucleon, whereas the down quark takes over the up quark for the -term form
factor. We investigate for the first time the isovector cosmological constant
term of the nucleon and its physical implications. The flavor-decomposed
cosmological constant terms of the nucleon unveil how the up-quark contribution
is exactly canceled by the down-quark contribution inside a nucleon within the
framework of the pion mean-field approach. While the nucleon cosmological
constant term does not contribute to the nucleon mass, its flavor structure
sheds light on how the strong force fields due to the cosmological constant
term characterize the stability of the nucleon.Comment: 7 pages and 4 figures. The text was improved and extende
Gravitational form factors of the baryon octet with flavor SU(3) symmetry breaking
We investigate the gravitational form factors of the baryon octet within the
framework of the SU(3) chiral quark-soliton model, considering the effects of
flavor SU(3) symmetry breaking, and the corresponding energy-momentum tensor
distributions. We examine the effects of flavor SU(3) symmetry breaking to the
mass, angular momentum, pressure, and shear force distributions of the baryon
octet. We first find that a heavier baryon is energetically more compact than a
lighter one. For the spin distributions of the baryon octet, they are properly
normalized to their spins and are decomposed into the flavor-singlet axial
charge and the orbital angular momentum even when the flavor SU(3) symmetry is
broken. While the effects of the flavor SU(3) symmetry breaking differently
contribute to the angular momentum distributions for the octet baryons, they
are found to be rather small. The spin and orbital angular momentum almost
equally contribute to the angular momentum distributions for the octet baryons.
We also estimate the effects of the flavor SU(3) symmetry breaking to the
pressure and shear force distributions. Interestingly, even if we include the
effects of the SU(3) flavor symmetry breaking, the shear force distributions
are kept to be positive over . It indicates that the Polyakov & Schweitzer
local stability condition is kept to be intact with the flavor SU(3) symmetry
broken. Lastly, we discuss how much the gravitational form factors vary with
the effects of flavor SU(3) symmetry breaking considered.Comment: 27 pages, 8 figure
Mesenchymal Stem Cells Improve Wound Healing In Vivo via Early Activation of Matrix Metalloproteinase-9 and Vascular Endothelial Growth Factor
We investigated the effects of mesenchymal stem cells (MSCs) on wound healing using a three-dimensional (3D) collagen gel scaffold. Three circular full-thickness skin defects were created on the back of Sprague-Dawley rats. One site was covered with a 3D collagen gel containing 2 Ć 106 MSCs (MSCs+/3D collagen+). Another site was replaced with a 3D collagen gel without MSCs and the third site was left empty. The wound size was significantly reduced in the MSCs+/3D collagen+ sites. MSCs+/3D collagen+ sites exhibited the most neovascularization. FISH showed that Y-chromosome possessing cells were found within the dermis of MSCs+/3D collagen+ sites. Gelatin zymography revealed that the most intense expression of MMP-9 was detected early in the MSCs+/3D collagen+ sites. Our results indicate that MSCs upregulate the early expression of MMP-9 which induces the early mobilization of VEGF. Thus, MSCs appear to accelerate significantly wound healing via early activation of MMP-9 and VEGF
ZnO Nanorod Biosensor for Highly Sensitive Detection of Specific Protein Binding
We report on the fabrication of electrical biosensors based on functionalized ZnO nanorod surfaces with biotin for highly sensitive detection of biological molecules. Due to the clean interface and easy surface modification, the ZnO nanorod sensors can easily detect streptavidin binding down to a concentration of 25 nM, which is more sensitive than previously reported one-dimensional (1D) nanostructure electrical biosensors. In addition, the unique device structure with a micrometer-scale hole at the center of the ZnO nanorod's conducting channel reduces the leakage current from the aqueous solution, hence enhancing device sensitivity. Moreover, ZnO nanorod field-effect-transistor (FET) sensors may open up opportunities to create many other oxide nanorod electrical sensors for highly sensitive and selective real-time detection of a wide variety of biomolecules.The authors thank Prof. Hee Cheul Choi at POSTECH for helpful discussion. This work was supported by the Korea Research Foundation Grant (KRF-2003-041-C00132)
Time-resolved photoluminescence of the size-controlled ZnO nanorods
Size dependence of the time-resolved photoluminescence (TRPL) has been investigated for the ZnO nanorods fabricated by catalyst-free metalorganic chemical vapor deposition. The nanorods have a diameter of 35 nm and lengths in the range of 150 nm to 1.1 mum. The TRPL decay rate decreases monotonically as the length of the nanorods increases in the range of 150 to 600 nm. Decrease of the radiative decay rate of the exciton-polariton has been invoked to account for the results
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