726 research outputs found
A New Coupled CFD/Neutron Kinetics System for High Fidelity Simulations of LWR Core Phenomena: Proof of Concept
The Institute for Neutron Physics and Reactor Technology (INR) at the Karlsruhe Institute of Technology (KIT) is investigating the application of the meso- and microscale analysis for the prediction of local safety parameters for light water reactors (LWR). By applying codes like CFD (computational fluid dynamics) and SP3 (simplified transport) reactor dynamics it is possible to describe the underlying phenomena in a more accurate manner than by the nodal/coarse 1D thermal hydraulic coupled codes. By coupling the transport (SP3) based neutron kinetics (NK) code DYN3D with NEPTUNE-CFD, within a parallel MPI-environment, the NHESDYN platform is created. The newly developed system will allow high fidelity simulations of LWR fuel assemblies and cores. In NHESDYN, a heat conduction solver, SYRTHES, is coupled to NEPTUNE-CFD. The driver module of NHESDYN controls the sequence of execution of the solvers as well as the communication between the solvers based on MPI. In this paper, the main features of NHESDYN are discussed and the proof of the concept is done by solving a single pin problem. The prediction capability of NHESDYN is demonstrated by a code-to-code comparison with the DYNSUB code. Finally, the future developments and validation efforts are highlighted
Turbulent friction in flows over permeable walls
Peer reviewedPublisher PD
Bed-load effects on hydrodynamics of rough-bed open-channel flows
Peer reviewedPublisher PD
Clinical and molecular genetic features of pulmonary hypertension in patients with hereditary hemorrhagic telangiectasia
BACKGROUND: Most patients with familial primary pulmonary hypertension have defects in the gene for bone morphogenetic protein receptor II (BMPR2), a member of the transforming growth factor beta (TGF-beta) superfamily of receptors. Because patients with hereditary hemorrhagic telangiectasia may have lung disease that is indistinguishable from primary pulmonary hypertension, we investigated the genetic basis of lung disease in these patients.
METHODS: We evaluated members of five kindreds plus one individual patient with hereditary hemorrhagic telangiectasia and identified 10 cases of pulmonary hypertension. In the two largest families, we used microsatellite markers to test for linkage to genes encoding TGF-beta-receptor proteins, including endoglin and activin-receptor-like kinase 1 (ALK1), and BMPR2. In subjects with hereditary hemorrhagic telangiectasia and pulmonary hypertension, we also scanned ALK1 and BMPR2 for mutations.
RESULTS: We identified suggestive linkage of pulmonary hypertension with hereditary hemorrhagic telangiectasia on chromosome 12q13, a region that includes ALK1. We identified amino acid changes in activin-receptor-like kinase 1 that were inherited in subjects who had a disorder with clinical and histologic features indistinguishable from those of primary pulmonary hypertension. Immunohistochemical analysis in four subjects and one control showed pulmonary vascular endothelial expression of activin-receptor-like kinase 1 in normal and diseased pulmonary arteries.
CONCLUSIONS: Pulmonary hypertension in association with hereditary hemorrhagic telangiectasia can involve mutations in ALK1. These mutations are associated with diverse effects, including the vascular dilatation characteristic of hereditary hemorrhagic telangiectasia and the occlusion of small pulmonary arteries that is typical of primary pulmonary hypertension
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Backlighting prospects for ICF targets
High energy x-ray backlighters are necessary to diagnose the implosion symmetry and stability of intermediate and high density targets. Synchronization requirements between the target irradiating pulse and the radiograph place severe constraints on the type of x-ray sources which can be used and favors laser irradiated backlighters. Data gathered on line emitters as a function of laser pulselength, wavelength and intensity in the 5 to 10 keV region are used to determine which diagnostic instruments will be feasible for ICF target experiments, and the requirements for backlighter irradiation
Dimensional crossover in topological matter: Evolution of the multiple Dirac point in the layered system to the flat band on the surface
We consider the dimensional crossover in the topological matter, which
involves the transformation of different types of topologically protected
zeroes in the fermionic spectrum. In the considered case, the multiple Dirac
(Fermi) point in quasi 2-dimensional system evolves into the flat band on the
surface of the 3-dimensional system when the number of atomic layers increases.
This is accompanied by formation of the spiral nodal lines in the bulk. We also
discuss the topological quantum phase transition at which the surface flat band
shrinks and changes its chirality, while the nodal spiral changes its helicity.Comment: 13 pages, 7 figure
Substrate-induced band gap opening in epitaxial graphene
Graphene has shown great application potentials as the host material for next
generation electronic devices. However, despite its intriguing properties, one
of the biggest hurdles for graphene to be useful as an electronic material is
its lacking of an energy gap in the electronic spectra. This, for example,
prevents the use of graphene in making transistors. Although several proposals
have been made to open a gap in graphene's electronic spectra, they all require
complex engineering of the graphene layer. Here we show that when graphene is
epitaxially grown on the SiC substrate, a gap of ~ 0.26 is produced. This gap
decreases as the sample thickness increases and eventually approaches zero when
the number of layers exceeds four. We propose that the origin of this gap is
the breaking of sublattice symmetry owing to the graphene-substrate
interaction. We believe our results highlight a promising direction for band
gap engineering of graphene.Comment: 10 pages, 4 figures; updated reference
Rotation Symmetry Spontaneous Breaking of Edge States in Zigzag Carbon Nanotubes
Analytical solutions of the edge states were obtained for the (N, 0) type
carbon nanotubes with distorted ending bonds. It was found that the edge states
are mixed via the distortion. The total energies for N=5 and N>=7 are lower in
the asymmetric configurations of ending bonds than those having axial rotation
symmetry. Thereby the symmetry is breaking spontaneously. The results imply
that the symmetry of electronic states at the apex depends on the occupation;
the electron density pattern at the apex could change dramatically and could be
controlled by applying an external field.Comment: 19 pages, 3 figure
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