211,108 research outputs found
Plasma Lens Backgrounds at a Future Linear Collider
A 'plasma lens' might be used to enhance the luminosity of future linear
colliders. However, its utility for this purpose depends largely on the
potential backgrounds that may be induced by the insertion of such a device in
the interaction region of the detector. In this note we identify different
sources of such backgrounds, calculate their event rates from the elementary
interaction processes, and evaluate their effects on the major parts of a
hypothetical Next Linear Collider (NLC) detector. For plasma lens parameters
which give a factor of seven enhancement of the luminosity, and using the NLC
design for beam parameters as a reference, we find that the background yields
are fairly high, and require further study and improvements in detector
technology to avoid their impact.Comment: 14 pages incl. 3 figures; contributed to the 4th International
Workshop, Electron-Electron Interactions at TeV Energies, Santa Cruz,
California, Dec. 7 - 9, 2001. To be published in Int.Journ. Mod. Phys.
Magnetic correlations on the full chains of Ortho-II YBaCuO
We propose that the NMR line shape on the chain Cu in the stoichiometric
high- superconductor Ortho-II YBaCuO is determined by the
magnetization induced on Cu near O vacancies, due to strong magnetic
correlations in the chains. An unrestricted Hartree-Fock calculation of a
coupled chain-plane Hubbard model with nearest-neighbor d-wave pairing
interaction shows that the broadening of NMR lines is consistent with
disorder-induced magnetization at low temperatures. In addition, we give a
possible explanation of the anomalous bimodal line shape observed at high
temperatures in terms of nonuniform Cu valence in the chains. The proximity
between chains and CuO plane induces anisotropic magnetization on the planar
Cu, and broadens the plane NMR lines in accordance with that of the chain
lines, in agreement with experiment. We discuss implications of the model for
other experiments on underdoped YBCO.Comment: 8 pages, 8 figures, submitted to PR
Optical surface waves in periodic layered medium grown by liquid phase epitaxy
Optical surface waves propagating along the surface of a multilayer stack have been observed. The multilayer stack is grown by liquid phase epitaxy. The transverse intensity distribution measured is found to agree with our theoretical calculation
A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics
Adherend surfaces and fractography were studied using electron spectroscopy for chemical analysis and scanning electron microscopy/energy dispersive analysis of X-rays. In addition, Auger Electron Spectroscopy with depth profiling capability was used. It is shown that contamination of adhesion systems plays an important role not only in determining initial bond strengths but also in the durability of adhesive bonds. It is concluded that the analytical techniques used to characterize and monitor such contamination
Existence of negative differential thermal conductance in one-dimensional diffusive thermal transport
We show that in a finite one-dimensional (1D) system with diffusive thermal
transport described by the Fourier's law, negative differential thermal
conductance (NDTC) cannot occur when the temperature at one end is fixed. We
demonstrate that NDTC in this case requires the presence of junction(s) with
temperature dependent thermal contact resistance (TCR). We derive a necessary
and sufficient condition for the existence of NDTC in terms of the properties
of the TCR for systems with a single junction. We show that under certain
circumstances we even could have infinite (negative or positive) differential
thermal conductance in the presence of the TCR. Our predictions provide
theoretical basis for constructing NDTC-based devices, such as thermal
amplifiers, oscillators and logic devices
A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics
Various surface preparations for titanium 6-4 alloy were studied. An anodizing method was investigated, and compared with the results of other chemical treatments, namely, phosphate/fluoride, Pasa-Jell and Turco. The relative durability of the different surface treatments was assessed by monitoring changes in surface chemistry and morphology occasioned by aging at 505 K (450 F). Basic electron spectroscopic data were collected for polyimide and polyphenylquinoxaline adhesives and synthetic precursors. Fractographic studies were completed for several combinations of adherend, adhesive, and testing conditions
A two-layer multiple-time-scale turbulence model and grid independence study
A two-layer multiple-time-scale turbulence model is presented. The near-wall model is based on the classical Kolmogorov-Prandtl turbulence hypothesis and the semi-empirical logarithmic law of the wall. In the two-layer model presented, the computational domain of the conservation of mass equation and the mean momentum equation penetrated up to the wall, where no slip boundary condition has been prescribed; and the near wall boundary of the turbulence equations has been located at the fully turbulent region, yet very close to the wall, where the standard wall function method has been applied. Thus, the conservation of mass constraint can be satisfied more rigorously in the two-layer model than in the standard wall function method. In most of the two-layer turbulence models, the number of grid points to be used inside the near-wall layer posed the issue of computational efficiency. The present finite element computational results showed that the grid independent solutions were obtained with as small as two grid points, i.e., one quadratic element, inside the near wall layer. Comparison of the computational results obtained by using the two-layer model and those obtained by using the wall function method is also presented
A multiple-time-scale turbulence model based on variable partitioning of turbulent kinetic energy spectrum
A multiple-time-scale turbulence model of a single point closure and a simplified split-spectrum method is presented. In the model, the effect of the ratio of the production rate to the dissipation rate on eddy viscosity is modeled by use of the multiple-time-scales and a variable partitioning of the turbulent kinetic energy spectrum. The concept of a variable partitioning of the turbulent kinetic energy spectrum and the rest of the model details are based on the previously reported algebraic stress turbulence model. Example problems considered include: a fully developed channel flow, a plane jet exhausting into a moving stream, a wall jet flow, and a weakly coupled wake-boundary layer interaction flow. The computational results compared favorably with those obtained by using the algebraic stress turbulence model as well as experimental data. The present turbulence model, as well as the algebraic stress turbulence model, yielded significantly improved computational results for the complex turbulent boundary layer flows, such as the wall jet flow and the wake boundary layer interaction flow, compared with available computational results obtained by using the standard kappa-epsilon turbulence model
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