18,018 research outputs found
Leakage currents in high-permittivity thin films
Quite often leakage current data through high-permittivity thin films exhibit straight lines in the "Schottky" plot, i.e., log (current density j) versus sqrt (mean applied field), which suggests an electrode-limited current by field-enhanced thermionic emission. Unfortunately, the extracted permittivity at optical frequencies seldom is in agreement with experimental values and often is unacceptably small, i.e., <1. We suggest a model demonstrating that the leakage current in high-permittivity thin films is bulk-limited, but still is showing the characteristic dependence of thermionic emission. This is due to a combination of boundary conditions of the model, low-permittivity thin layers ("dead layer") at the electrodes and current injection/recombination terms at the injecting/collecting electrodes, respectively. (C) 2003 American Institute of Physics
Resistivity of non-crystalline carbon in the 1-100eV range
A resistivity model for non-crystalline, solid-density carbon and hydrocarbons is presented for such materials heated by short-pulse, ultra-intense lasers. Electron-impact excitation of C atoms and ions was included in this model,and calculation of resistivity curves with and without accounting for excitations indicates that excitations contribute >50% of the resistivity in the 3â20 eV range. This implies that electron-impact excitations make a similar contribution to electron-ion scattering, and thus models not accounting for electron-impact excitation may underestimate the resistivity of dense plasmas in this temperature range
Resistivity of non-crystalline carbon in the 1-100eV range
A resistivity model for non-crystalline, solid-density carbon and hydrocarbons is presented for such materials heated by short-pulse, ultra-intense lasers. Electron-impact excitation of C atoms and ions was included in this model,and calculation of resistivity curves with and without accounting for excitations indicates that excitations contribute >50% of the resistivity in the 3â20 eV range. This implies that electron-impact excitations make a similar contribution to electron-ion scattering, and thus models not accounting for electron-impact excitation may underestimate the resistivity of dense plasmas in this temperature range
Intrinsic and extrinsic x-ray absorption effects in soft x-ray diffraction from the superstructure in magnetite
We studied the (001/2) diffraction peak in the low-temperature phase of
magnetite (Fe3O4) using resonant soft x-ray diffraction (RSXD) at the Fe-L2,3
and O-K resonance. We studied both molecular-beam-epitaxy (MBE) grown thin
films and in-situ cleaved single crystals. From the comparison we have been
able to determine quantitatively the contribution of intrinsic absorption
effects, thereby arriving at a consistent result for the (001/2) diffraction
peak spectrum. Our data also allow for the identification of extrinsic effects,
e.g. for a detailed modeling of the spectra in case a "dead" surface layer is
present that is only absorbing photons but does not contribute to the
scattering signal.Comment: to appear in Phys. Rev.
Studying Flow Close to an Interface by Total Internal Reflection Fluorescence Cross Correlation Spectroscopy: Quantitative Data Analysis
Total Internal Reflection Fluorescence Cross Correlation Spectroscopy
(TIR-FCCS) has recently (S. Yordanov et al., Optics Express 17, 21149 (2009))
been established as an experimental method to probe hydrodynamic flows near
surfaces, on length scales of tens of nanometers. Its main advantage is that
fluorescence only occurs for tracer particles close to the surface, thus
resulting in high sensitivity. However, the measured correlation functions only
provide rather indirect information about the flow parameters of interest, such
as the shear rate and the slip length. In the present paper, we show how to
combine detailed and fairly realistic theoretical modeling of the phenomena by
Brownian Dynamics simulations with accurate measurements of the correlation
functions, in order to establish a quantitative method to retrieve the flow
properties from the experiments. Firstly, Brownian Dynamics is used to sample
highly accurate correlation functions for a fixed set of model parameters.
Secondly, these parameters are varied systematically by means of an
importance-sampling Monte Carlo procedure in order to fit the experiments. This
provides the optimum parameter values together with their statistical error
bars. The approach is well suited for massively parallel computers, which
allows us to do the data analysis within moderate computing times. The method
is applied to flow near a hydrophilic surface, where the slip length is
observed to be smaller than 10nm, and, within the limitations of the
experiments and the model, indistinguishable from zero.Comment: 18 pages, 12 figure
Temperature dependence of surface reconstructions of Au on Pd(110)
Surface reconstructions of Au film on Pd(110) substrate are studied using a
local Einstein approximation to quasiharmonic theory with the Sutton-Chen
interatomic potential. Temperature dependent surface free energies for
different coverages and surface structures are calculated. Experimentally
observed transformations from to and
structures can be explained in the framework of this model. Also conditions for
Stranski-Krastanov growth mode are found to comply with experiments. The domain
of validity of the model neglecting mixing entropy is analyzed.Comment: 7 pages, REVTeX two-column format, 3 postscript figures available on
request from [email protected] To appear in Phys. Rev. Letter
The MobyDick Project: A Mobile Heterogeneous All-IP Architecture
Proceedings of Advanced Technologies, Applications and Market Strategies for 3G (ATAMS 2001). Cracow, Poland: 17-20 June, 2001.This paper presents the current stage of an IP-based architecture for heterogeneous environments, covering UMTS-like W-CDMA wireless access technology, wireless and wired LANs, that is being developed under the aegis of the IST Moby Dick project. This architecture treats all transmission capabilities as basic physical and data-link layers, and attempts to replace all higher-level tasks by IP-based strategies.
The proposed architecture incorporates aspects of mobile-IPv6, fast handover, AAA-control, and Quality of Service. The architecture allows for an optimised control on the radio link layer resources. The Moby dick architecture is currently under refinement for implementation on field trials. The services planned for trials are data transfer and voice-over-IP.Publicad
Modification of the Ames 40- by 80-foot wind tunnel for component acoustic testing for the second generation supersonic transport
The development of a large-scale anechoic test facility where large models of engine/airframe/high-lift systems can be tested for both improved noise reduction and minimum performance degradation is described. The facility development is part of the effort to investigate economically viable methods of reducing second generation high speed civil transport noise during takeoff and climb-out that is now under way in the United States. This new capability will be achieved through acoustic modifications of NASA's second largest subsonic wind tunnel: the 40-by 80-Foot Wind Tunnel at the NASA Ames Research Center. Three major items are addressed in the design of this large anechoic and quiet wind tunnel: a new deep (42 inch (107 cm)) test section liner, expansion of the wind tunnel drive operating envelope at low rpm to reduce background noise, and other promising methods of improving signal-to-noise levels of inflow microphones. Current testing plans supporting the U.S. high speed civil transport program are also outlined
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