Electron Inelastic-Mean-Free-Path Database
National Institute of Standards and Technology Data Gateway
SRD 71 NIST Electron Inelastic-Mean-Free-Path Database (PC database, no charge) This database provides values of electron inelastic mean free paths (IMFPs) for use in quantitative surface analyses by AES and XPS.
The electron mean free path (applicable to quantitative electron spectroscopy)
NASA Astrophysics Data System (ADS)
Tokutaka, H.; Nishimori, K.; Hayashi, H.
1985-01-01
There are two well known methods accepted generally to establish the value of the electron mean free path. One is Seah's method where he compiled many published experimental data. The other is Penn's method which is extensively theoretical. Besides, Tarng and Wehner showed that there is a significant difference between the observed electron mean free paths, according to whether the electron pass through Mo or W. Here, we propose a general method to calculate the electron mean free path for material of any atomic number, using Tarng and Wehner's experimental results (Mo and W) and our experimental data for Cr. Then, we compare and review these three methods of Seah, Penn and ourselves to learn which method is the most accurate, using published AES and XPS experimental data. Among these three methods, our method shows values closest to the experimental ones. Finally, we must add the following sentence: When the AES experimental data are compared with the theoretical values, the attenuation length of the primary electron beam should be considered.
Electron mean free path from angle-dependent photoelectron spectroscopy of aerosol particles
Goldmann, Maximilian; West, Adam H C; Yoder, Bruce L; Signorell, Ruth
2015-01-01
We propose angle-resolved photoelectron spectroscopy of aerosol particles as an alternative way to determine the electron mean free path of low energy electrons in solid and liquid materials. The mean free path is obtained from fits of simulated photoemission images to experimental ones over a broad range of different aerosol particle sizes. The principal advantage of the aerosol approach is twofold. Firstly, aerosol photoemission studies can be performed for many different materials, including liquids. Secondly, the size-dependent anisotropy of the photoelectrons can be exploited in addition to size-dependent changes in their kinetic energy. These finite size effects depend in different ways on the mean free path and thus provide more information on the mean free path than corresponding liquid jet, thin film, or bulk data. The present contribution is a proof of principle employing a simple model for the photoemission of electrons and preliminary experimental data for potassium chloride aerosol particles.
Electron mean free path from angle-dependent photoelectron spectroscopy of aerosol particles
NASA Astrophysics Data System (ADS)
Goldmann, Maximilian; Miguel-Sánchez, Javier; West, Adam H. C.; Yoder, Bruce L.; Signorell, Ruth
2015-06-01
We propose angle-resolved photoelectron spectroscopy of aerosol particles as an alternative way to determine the electron mean free path of low energy electrons in solid and liquid materials. The mean free path is obtained from fits of simulated photoemission images to experimental ones over a broad range of different aerosol particle sizes. The principal advantage of the aerosol approach is twofold. First, aerosol photoemission studies can be performed for many different materials, including liquids. Second, the size-dependent anisotropy of the photoelectrons can be exploited in addition to size-dependent changes in their kinetic energy. These finite size effects depend in different ways on the mean free path and thus provide more information on the mean free path than corresponding liquid jet, thin film, or bulk data. The present contribution is a proof of principle employing a simple model for the photoemission of electrons and preliminary experimental data for potassium chloride aerosol particles.
Electron mean free path from angle-dependent photoelectron spectroscopy of aerosol particles.
Goldmann, Maximilian; Miguel-Sánchez, Javier; West, Adam H C; Yoder, Bruce L; Signorell, Ruth
2015-06-14
We propose angle-resolved photoelectron spectroscopy of aerosol particles as an alternative way to determine the electron mean free path of low energy electrons in solid and liquid materials. The mean free path is obtained from fits of simulated photoemission images to experimental ones over a broad range of different aerosol particle sizes. The principal advantage of the aerosol approach is twofold. First, aerosol photoemission studies can be performed for many different materials, including liquids. Second, the size-dependent anisotropy of the photoelectrons can be exploited in addition to size-dependent changes in their kinetic energy. These finite size effects depend in different ways on the mean free path and thus provide more information on the mean free path than corresponding liquid jet, thin film, or bulk data. The present contribution is a proof of principle employing a simple model for the photoemission of electrons and preliminary experimental data for potassium chloride aerosol particles. PMID:26071707
Ghosh, T; Bardhan, M; Bhattacharya, M; Satpati, B
2015-06-01
We report a simple method for measuring the inelastic mean free path of nanostructures of known geometry using energy filtered transmission electron microscopy imaging. The mean free path of inelastic electrons was measured by using systems having known symmetry, such as cylindrical or cubic, combined with Poisson statistics without employing the knowledge of microscope parameters, namely the convergence angle and the collection angle. Having inherent symmetry of such systems, their absolute thickness can be measured from their two-dimensional projection images. We have calculated mean free path of inelastic scattering of electrons in gold, silver and nickel doing case study research by employing gold nanorod, silver nanocube and nickel nanorod lying on a carbon-coated TEM grid at two different electron energies (viz. 200 and 300 keV) following this alternative approach. Results obtained using such alternative approach were verified using microscope parameters. PMID:25787717
Mean free path of a suddenly created fast electron moving in a degenerate electron gas
NASA Astrophysics Data System (ADS)
Nagy, I.; Echenique, P. M.
2012-03-01
A lower bound on the mean free path (l) of a swift electron moving in a degenerate electron gas is calculated by implementing a standard theoretical framework for the collision rate, 1/?, with a scattering amplitude characterized by the matrix element of a hole-screened interaction potential taken between plane-wave states. The instantaneous hole around a system's electron is considered at the Hartree-Fock level for the ground-state wave function of the degenerate electron gas. The real transitions in the many-body system are considered by following Galitskii's treatment on an almost perfect Fermi gas of neutral atomic constituents. The analytical results show minima both in ? and l, and they appear at (E/EF)?4.6 and (E/EF)?2.5, respectively, where E is the kinetic energy of the fast electron and EF is the Fermi energy of the host. Comparison with mean free path data obtained recently for Cu is made and a reasonable agreement is found.
Spin-resolved inelastic mean free path of slow electrons in Fe.
Zdyb, R; Bauer, E
2013-07-10
The spin-dependent reflectivity of slow electrons from ultrathin Fe films on W(110) has been measured with spin polarized low energy electron microscopy. From the amplitude of the quantum size oscillations observed in the reflectivity curves the spin-dependent inelastic mean free path (IMFP) of electrons in Fe has been determined in the energy range from 5 to 16 eV above the vacuum level. The resulting IMFP values for the spin-up electrons are clearly larger than those for the spin-down electrons and the difference between the two values decreases with increasing electron energy in agreement with theoretical predictions. PMID:23765334
NASA Astrophysics Data System (ADS)
Qiu, Bo; Tian, Zhiting; Vallabhaneni, Ajit; Liao, Bolin; Mendoza, Jonathan M.; Restrepo, Oscar D.; Ruan, Xiulin; Chen, Gang
2015-03-01
The mean free paths (MFPs) of energy carriers are of critical importance to the nano-engineering of better thermoelectric materials. Despite significant progress in the first-principles–based understanding of the spectral distribution of phonon MFPs in recent years, the spectral distribution of electron MFPs remains unclear. In this work, we compute the energy-dependent electron scatterings and MFPs in silicon from first principles. The electrical conductivity accumulation with respect to electron MFPs is compared to that of the phonon thermal conductivity accumulation to illustrate the quantitative impact of nanostructuring on electron and phonon transport. By combining all electron and phonon transport properties from first principles, we predict the thermoelectric properties of the bulk and nanostructured silicon, and find that silicon with 20 nm nanograins can result in a higher than five times enhancement in their thermoelectric figure of merit as the grain boundaries scatter phonons more significantly than that of electrons due to their disparate MFP distributions.
Photocurrent in bulk heterojunction solar cells with similar electron and hole mean free path
Coutinho, Douglas José; Faria, Roberto Mendonça
2013-11-25
We present photocurrents at several temperatures carried out in a bulk heterojunction photovoltaic device. To explain the results, we developed an analytical model assuming non-injecting contacts and equal mean free paths for electrons and holes. The fitting of the equation to the experimental data provided the temperature evolution of the charge transfer state dissociation probability (P) and ??, where ? is the charge carrier mobility and ? is the charge carrier lifetime. The photocurrent expression tends towards a saturation value of eGPL for high electric fields, where GP is the generation rate of charge carriers.
NASA Astrophysics Data System (ADS)
Akkerman, Avraham; Murat, Michael
2015-05-01
The mean free path (MFP) for electron-phonon interactions in pure silicon is an important characteristic needed both for low energy electron transport calculations using Boltzmann transport equation, and for Monte Carlo simulations. Full band calculations present a basic (though complicated) approach to the solution of the problem. Simpler approaches based on analytical presentation of the scattering rates have also been used; however they are valid for a restricted range of electron energies, below 2 eV. In this paper we introduce a hybrid method that utilizes the density of energy states calculated from the full band calculations for electron energies larger than 2 eV, allowing to extend the analytical approach for energies up to 5 eV, where the impact ionization becomes the dominant mechanism of electron interactions within bulk silicon. The resulting MFPs as function of electron energy and lattice temperature, together with the integral probability distribution for given energy losses by phonon emission (or energy gain by absorption of phonons) form the database for Monte Carlo calculations. Using this method, we calculate the electron diffusivity and mobility as function of the electron and lattice temperatures. These parameters are important for solution of the two temperature model, used for calculations of the track structure created by swift ions and nanosecond laser beams.
Material dependence of electron inelastic mean free paths at low energies
Tanuma, S. ); Powell, C.J.; Penn, D.R. )
1990-05-01
We present and discuss electron inelastic mean free path (IMFP) data for aluminum and gold in the 50--200 eV range. These elements serve as examples of IMFP calculations that have been made for 50--2000 eV electrons in 31 materials (27 elements and 4 compounds). Substantial differences are found in the shapes of the IMFP versus energy curves for Al and Au and these can be understood in terms of the different inelastic scattering mechanisms in the two metals. The minimum IMFP value occurs at 40 eV in aluminum and at 120 eV in gold, a result which is consistent with the trends expected from free-electron IMFP calculations. This result differs, however, from that expected from the Seah and Dench attenuation length formula which shows essentially no material dependence at low energies. We have extended a general formula derived earlier to describe the calculated IMFPs over the 200--2000 eV energy range to give the IMFP dependences on material and energy from 50 to 2000 eV.
Effective electron mean free path in TiN(001) J. S. Chawla, X. Y. Zhang, and D. Gall
Gall, Daniel
Effective electron mean free path in TiN(001) J. S. Chawla, X. Y. Zhang, and D. Gall Department of smooth stoichiometric epitaxial TiN(001) is 13 and 3.0 lX cm at 298 and 77 K for bulk layers but is 8-S) model. This is unexpected because the F-S model is based on the nearly free electron model, while TiN
Chantler, C T; Bourke, J D
2014-02-01
We develop the many-pole dielectric theory of UV plasmon interactions and electron energy losses, and couple our advances with recent developments of Kohn-Sham density functional theory to address observed discrepancies between high-precision measurements and tabulated data for electron inelastic mean free paths (IMFPs). Recent publications have demonstrated that a five standard error difference exists between longstanding theoretical calculations and measurements of electron IMFPs for elemental solids at energies below 120 eV, a critical region for analysis of electron energy loss spectroscopy (EELS), X-ray absorption spectroscopy (XAS), and related technologies. Our implementation of improved optical loss spectra and a physical treatment of second-order excitation lifetimes resolves this problem in copper for the first time for energies in excess of 80 eV and substantially improves agreement for lower energy electrons. PMID:24450468
Iakoubovskii, Konstantin; Mitsuishi, Kazutaka; Nakayama, Yoshiko; Furuya, Kazuo
2008-03-01
Mean free path of inelastic electron scattering {lambda} has been measured with a 200 keV transmission electron microscope for the majority of stable elemental solids and their oxides. An oscillating behavior vs atomic number Z has been revealed, such that within one row of the Periodic Table, the minimum (maximum) of {lambda} is observed for elements with completed (empty) outer d shells. A significantly weaker {lambda}(Z) dependence is observed for the oxides. The {lambda}(Z) variation is ascribed to the three major factors: atomic density, number of 'free' electrons per atom, and contribution of atomic core-loss transitions.
Experimental and numerical investigation of phonon mean free path distribution
Zeng, Lingping
2013-01-01
Knowledge of phonon mean free path (MFP) distribution is critically important to engineering size effects. Phenomenological models of phonon relaxation times can give us some sense about the mean free path distribution, ...
NASA Astrophysics Data System (ADS)
Tan, Zhenyu; Xia, Yueyuan; Zhao, Mingwen; Liu, Xiangdong; Li, Feng; Huang, Boda; Ji, Yanju
2004-07-01
An empirical method to obtain optical energy loss functions is presented for a large number of organic compounds, for which optical data are not available, on the basis of structure feature analysis of the existed optical energy loss functions for certain organic compounds. The optical energy loss functions obtained by using this method are in good agreement with the experimental data. Based on the Penn's statistical model, a set of systematic expressions have been given for the calculation of the stopping powers and mean free paths of electrons penetrating into the organic compounds in the energy range of E?10 keV. Detailed comparison of the calculated data with other theoretical results is presented. The stopping powers and mean free paths for a group of important polymers, without available optical data, have been calculated. In the calculations, three different cases have been considered, i.e. exchange correction not being considered, Ashley exchange correction being involved, and Born-Ochkur exchange correction being included. The results indicate that for these compounds the calculated stopping powers agree well with those obtained by using Bethe-Bloch theory at high-energy limit E=10 keV, as expected for a stopping power theory that should be converged to Bethe-Bloch theory at high energies.
Thermal Conductivity Spectroscopy Technique to Measure Phonon Mean Free Paths
Schmidt, A. J.
Size effects in heat conduction, which occur when phonon mean free paths (MFPs) are comparable to characteristic lengths, are being extensively explored in many nanoscale systems for energy applications. Knowledge of MFPs ...
Chantler, C T; Bourke, J D
2014-04-01
X-ray absorption fine structure (XAFS) spectroscopy is one of the most robust, adaptable, and widely used structural analysis tools available for a range of material classes from bulk solids to aqueous solutions and active catalytic structures. Recent developments in XAFS theory have enabled high-accuracy calculations of spectra over an extended energy range using full-potential cluster modelling, and have demonstrated particular sensitivity in XAFS to a fundamental electron transport property-the electron inelastic mean free path (IMFP). We develop electron IMFP theory using a unique hybrid model that simultaneously incorporates second-order excitation losses, while precisely accounting for optical transitions dictated by the complex band structure of the solid. These advances are coupled with improved XAFS modelling to determine wide energy-range absorption spectra for molybdenum. This represents a critical test case of the theory, as measurements of molybdenum K-edge XAFS represent the most accurate determinations of XAFS spectra for any material. We find that we are able to reproduce an extended range of oscillatory structure in the absorption spectrum, and demonstrate a first-time theoretical determination of the absorption coefficient of molybdenum over the entire extended XAFS range utilizing a full-potential cluster model. PMID:24651638
Inertial Mass Dependency on Local Vacuum Fluctuation Mean Free Path
NASA Astrophysics Data System (ADS)
White, H. G.
2007-01-01
The intent of this narrative is to propose a relationship between the vacuum energy density, light-radius of the universe, and the plank force. The equation is proposed to infer a connection between inertial mass and an observer's light horizon. This horizon is conjectured to be the mean free path for vacuum fluctuations as seen by an observer in deep space. This fundamental relationship will then be derived from a gravitational wave equation. Once this has been derived, the results will be extended to derive an equation to calculate the effect local matter has on the mean free path of a vacuum fluctuation, and hence the local vacuum energy density (vacuum fluctuation pileup). The paper will conclude by applying the theoretical framework to calculate expected thrust signals in an externally applied ExB application meant to induce plasma drift in the vacuum fluctuations. Current experimental results from domestic and international labs will be addressed.
The hyperon mean free paths in the relativistic mean field
Q. L. Wang; L. Dang; X. H. Zhong; P. Z. Ning
2005-12-19
The $\\Lambda$- and $\\Xi^-$-hyperon mean free paths in nuclei are firstly calculated in the relativistic mean field (RMF) theory. The real parts of the optical potential are derived from the RMF approach, while the imaginary parts are obtained from those of nucleons with the relations: $U^{\\mathrm{IY}}_{\\mathrm{S}} = \\alpha_{\\sigma \\mathrm{Y}}\\cdot U_{\\mathrm{S}}^{\\mathrm{IN}}$ and $U^{\\mathrm{IY}}_{\\mathrm{V}} = \\alpha_{\\omega \\mathrm{Y}}\\cdot U_{\\mathrm{V}}^{\\mathrm{IN}}$ . With the assumption, the depth of the imaginary potential for $\\Xi^-$ is $W_{\\Xi}\\simeq-$ 3.5 MeV, and for $\\Lambda$ is $W_{\\Lambda}\\simeq-$ 7 MeV at low incident energy. We find that, the hyperon mean free path decreases with the increase of the hyperon incident energies, from 200 MeV to 800 MeV; and in the interior of the nuclei, the mean free path is about $2\\sim 3$ fm for $\\Lambda$, and about $4\\sim 8$ fm for $\\Xi^-$, depending on the hyperon incident energy.
Inelastic interaction mean free path of negative pions in tungsten
NASA Technical Reports Server (NTRS)
Cheshire, D. L.; Huggett, R. W.; Jones, W. V.; Rountree, S. P.; Schmidt, W. K. H.; Kurz, R. J.; Bowen, T.; Delise, D. A.; Krider, E. P.; Orth, C. D.
1975-01-01
The inelastic interaction mean free paths lambda of 5, 10, and 15 GeV/c pions were measured by determining the distribution of first interaction locations in a modular tungsten-scintillator ionization spectrometer. In addition to commonly used interaction signatures of a few (2-5) particles in two or three consecutive modules, a chi2 distribution is used to calculate the probability that the first interaction occurred at a specific depth in the spectrometer. This latter technique seems to be more reliable than use of the simpler criteria. No significant dependence of lambda on energy was observed. In tungsten, lambda for pions is 206 plus or minus 6 g/sq cm.
Liu, Qixin; Cai, Zhiyong
2014-01-01
This paper presents studies on the characteristics of gas molecular mean free path in nanopores by molecular dynamics simulation. Our study results indicate that the mean free path of all molecules in nanopores depend on both the radius of the nanopore and the gas-solid interaction strength. Besides mean free path of all molecules in the nanopore, this paper highlights the gas molecular mean free path at different positions of the nanopore and the anisotropy of the gas molecular mean free path at nanopores. The molecular mean free path varies with the molecule’s distance from the center of the nanopore. The least value of the mean free path occurs at the wall surface of the nanopore. The present paper found that the gas molecular mean free path is anisotropic when gas is confined in nanopores. The radial gas molecular mean free path is much smaller than the mean free path including all molecular collisions occuring in three directions. Our study results also indicate that when gas is confined in nanopores the gas molecule number density does not affect the gas molecular mean free path in the same way as it does for the gas in unbounded space. These study results may bring new insights into understanding the gas flow’s characteristic at nanoscale. PMID:25046745
NASA Astrophysics Data System (ADS)
Gergely, G.; Menyhárd, M.; Péntek, K.; Sulyok, A.; Jablonski, A.; Lesiak, B.; Daróczi, Cs.
1995-07-01
The inelastic mean free path (IMFP) of electrons has been determined for selected elemental solids using elastic peak electron spectroscopy (EPES) and a Ni standard. The IMFP was evaluated for the range of 500-3000 eV on Cr, Mo, Ge and Si materials. The Ni standard surface has been prepared by electrolysis and HV vapour deposition. Its quality was verified by AES and STM. The theoretical model relating the elastic peak intensity to the value of the IMFP was based on relativistic scattering cross sections and the multiple elastic scattering events were simulated by a Monte Carlo procedure. Reasonable agreement of the obtained IMFP values and their dependence on the energy with the data by Tanuma et al. and by Ashley et al. was found.
Anisotropic mean free path in simulations of fluids traveling down a density gradient.
Whitman, Jessica R; Aranovich, Gregory L; Donohue, Marc D
2010-06-14
Hard sphere molecular dynamics simulations are used to study the mean free path of molecules traveling down a density gradient at fluid densities ranging between 0.05sigma(-3) and 0.7sigma(-3). Gradients are developed using semipermeable boundaries in the x-direction and, as a result, a net flow develops in the positive x-direction. Over the course of the simulation, the free paths of colliding molecules are calculated and it was determined that the mean free path in the positive x-direction is greater than the mean free path in the negative x-direction at each density studied. These results are compared to the mean free paths in the positive and negative y- and z-directions (in which there is no net flow) and the distribution of free paths for molecules traveling in the positive and negative x-directions gives insight into the physics of the system. In addition, the dependency of the mean free path on speed is studied and compared to kinetic theory predictions. The results have application in the modification of the classical model of diffusion for low density systems undergoing flow in which the mean free path is finite, large, and can be anisotropic. PMID:20550392
Reconstructing phonon mean-free-path contributions to thermal conductivity using nanoscale membranes
Cuffe, John
Knowledge of the mean-free-path distribution of heat-carrying phonons is key to understanding phonon-mediated thermal transport. We demonstrate that thermal conductivity measurements of thin membranes spanning a wide ...
Neutrino mean free paths in spin-polarized neutron Fermi liquids
M. Angeles Perez-Garcia
2010-01-22
Neutrino mean free paths in magnetized neutron matter are calculated using the Hartree-Fock approximation with effective Skyrme and Gogny forces in the framework of the Landau Fermi Liquid Theory. It is shown that describing nuclear interaction with Skyrme forces and for magnetic field strengths $log_{10} B(G) \\gtrsim 17$, the neutrino mean free paths stay almost unchanged at intermediate densities but they largely increase at high densities when they are compared to the field-free case results. However the description with Gogny forces differs from the previous and mean free paths stay almonst unchanged or decrease at densities $[1-2]\\rho_0$. This different behaviour can be explained due to the combination of common mild variation of the Landau parameters with both types of forces and the values of the nucleon effective mass and induced magnetization of matter under presence of a strong magnetic field as described with the two parametrizations of the nuclear interaction.
Universal phonon mean free path spectra in crystalline semiconductors at high temperature
Freedman, Justin P.; Leach, Jacob H.; Preble, Edward A.; Sitar, Zlatko; Davis, Robert F.; Malen, Jonathan A.
2013-01-01
Thermal conductivity in non-metallic crystalline materials results from cumulative contributions of phonons that have a broad range of mean free paths. Here we use high frequency surface temperature modulation that generates non-diffusive phonon transport to probe the phonon mean free path spectra of GaAs, GaN, AlN, and 4H-SiC at temperatures near 80?K, 150?K, 300?K, and 400?K. We find that phonons with MFPs greater than 230 ± 120?nm, 1000 ± 200?nm, 2500 ± 800?nm, and 4200 ± 850?nm contribute 50% of the bulk thermal conductivity of GaAs, GaN, AlN, and 4H-SiC near room temperature. By non-dimensionalizing the data based on Umklapp scattering rates of phonons, we identified a universal phonon mean free path spectrum in small unit cell crystalline semiconductors at high temperature. PMID:24129328
NASA Astrophysics Data System (ADS)
Wei, Gaosheng; Wang, Lixin; Chen, Lin; Du, Xiaoze; Xu, Chao; Zhang, Xinxin
2015-07-01
This study comprehensively analyzes the mean free path of gas molecules and gaseous thermal conductivity in confined nanoporous structures through a wide range of temperatures and pressures. A simplified unit cell cubic array structure of nanospheres is used to correlate microstructure features with specific surface area and density of nanoporous materials. Zeng's model is used to describe the mean free path of the gas molecules and the gaseous thermal conductivity in confined nanoporous structures, and experimental gaseous thermal conductivity data from the literature is used to validate the model. The results show that a material's nanoporous structure features are directly related to specific surface area and density. The mean free path of gas molecules in a confined nanoporous structure decreases with increasing specific surface area and density. Thus, nanoporous materials with a relatively high specific surface area and a higher density are more favorable for confining gaseous thermal conductivity in nanopores. This work shows that p=104{ Pa} and 106{ Pa} are two characteristic pressures at ambient temperatures for the investigated silica aerogel materials. When p<104{ Pa} , the mean free path of the gas molecules remains constant with varying pressure, while gaseous thermal conductivity approaches zero due to the restrictive effect of the nanoporous structure and the diluted gas molecules. When {p}>106{ Pa} , the limiting effect of the nanoporous structure on the movement of gas molecules can be ignored, and so the mean free path of gas molecules in the nanoporous material approaches the mean free path of gas molecules in free space, while the gaseous thermal conductivity approaches the gaseous thermal conductivity in free space. As temperature increases, there exists a maximum value for gaseous thermal conductivity in confined nanoporous materials, but this maximum increases as pressure increases. The maximum gaseous thermal conductivity for the material is also determined in the paper.
On mean free path statistics of relativistic heavy ions in nuclear emulsion
Haret C. Rosu
1994-12-09
We survey at the general level, and in a rather wide and historical context, some less known mathematical details of various mean free path statistics in nuclear emulsion as applied to relativistic projectile fragmentations. A number of comments are provided on Feller's paradox, ordered, censored, and truncated statistics, Erlang and Poisson observers of nuclear emulsion. All these issues are related to the statistical approaches used about a decade ago at Berkeley Bevalac for anomalons, some of which should be considered as standard methods for mean free paths' estimators of relativistic heavy ions.
Tunable transport mean free path of light in xerogel matrixes embedded with polystyrene spheres
Bret, B P J; Amaro, M; Nunes-Pereira, E J; Belsley, M
2008-01-01
Xerogel matrices, made by sol-gel techniques, are embedded with polystyrene spheres to promote multiple scattering of light. Varying the concentration of the spheres inside the matrix allows one to adjust the transport mean free path of light inside the material. Coherent backscattering measurements show that a range of transport mean free paths from 90 to 600 nm is easily achieved. The determination of the matrix refractive index permits a direct comparison to multiple scattering and Mie theory. Such tunable diffusive sol-gel samples can be further optimized as random laser materials.
Measuring the transport mean free path using a reference random medium
NASA Astrophysics Data System (ADS)
Lisyansky, A. A.; Li, J. H.; Genack, A. Z.
1995-01-01
The transport mean free path of microwave radiation in a random sample is determined from measurements of transmission through a composite sample of the medium with unknown scattering characteristics and a random medium of variable thickness and known scattering parameters. The method can be applied at optical frequencies by use of a ceramic wedge as the medium of variable thickness.
Effective phonon mean-free path and slip heat flow in rarefied phonon hydrodynamics
NASA Astrophysics Data System (ADS)
Carlomagno, I.; Sellitto, A.; Jou, D.
2015-10-01
Non-local effects in generalized heat-transport equations provide a mesoscopic approach to phonon hydrodynamics. In contrast to usual phonon hydrodynamics with non-slip heat flow, we consider, in analogy to rarefied gas dynamics, a slip heat flow along the walls. This way the effective thermal conductivity behaves as Kn-1 instead of as Kn-2, which is the behavior in usual phonon hydrodynamics, Kn being the Knudsen number, i.e., the ratio between the mean-free path of the heat carriers and a characteristic size of the system. Here we revisit previous formulations to provide a more explicit and clearer interpretation of the differences between the effective mean-free path in the non-local term of the generalized transport equation for q, and that in the thermal conductivity.
Frequency-dependent phonon mean free path in carbon nanotubes from nonequilibrium molecular dynamics
NASA Astrophysics Data System (ADS)
Sääskilahti, K.; Oksanen, J.; Volz, S.; Tulkki, J.
2015-03-01
Owing to their long phonon mean free paths (MFPs) and high thermal conductivity, carbon nanotubes (CNTs) are ideal candidates for, e.g., removing heat from electronic devices. It is unknown, however, how the intrinsic phonon MFPs depend on vibrational frequency in nonequilibrium. We determine the spectrally resolved phonon MFPs in isotopically pure CNTs from the spectral phonon transmission function calculated using nonequilibrium molecular dynamics, fully accounting for the resistive phonon-phonon scattering processes through the anharmonic terms of the interatomic potential energy function. Our results show that the effective room temperature MFPs of low-frequency phonons (f <0.5 THz) exceed 10 ? m , while the MFP of high-frequency phonons (f ?20 THz) is in the range 10-100 nm. Because the determined MFPs directly reflect the resistance to energy flow, they can be used to accurately predict the thermal conductivity for arbitrary tube lengths by calculating a single frequency integral. The presented results and methods are expected to significantly improve the understanding of nonequilibrium thermal transport in low-dimensional nanostructures.
NASA Astrophysics Data System (ADS)
Obermann, Anne; Larose, Eric; Margerin, Ludovic; Rossetto, Vincent
2014-05-01
We analyze the statistics of phase fluctuations of seismic signals obtained from a temporary small aperture array deployed on a volcano in the French Auvergne. We demonstrate that the phase field satisfies Circular Gaussian statistics. We then determine the scattering mean free path of Rayleigh waves from the spatial phase decoherence. This phenomenon, observed for diffuse wavefields, is found to yield a good approximation of the scattering mean free path. Contrary to the amplitude, spatial phase decoherence is free from absorption effects and provides direct access to the scattering mean free path. Our method may find applications in various areas of seismology where the effects of scattering are prominent and a knowledge of the scattering properties is necessary to describe the propagation. As an example, an unbiased estimate of the scattering mean free path is crucial for the localization of changes in multiply scattering media, where a sensitivity kernel based on diffusion theory is used (Larose et al. 2010; Obermann et al. 2013a,b). Our experimental approach may also provide independent estimates of the scattering mean free path in volcanic areas where particularly strong scattering has been proposed, based on the fitting of energy envelopes using energy transport approaches (Wegler & Lühr 2001; Yamamoto & Sato 2010). References: Larose, E., Planès, T., Rossetto, V. & Margerin, L., 2010. Locating a small change in a multiple scattering environment, Appl. Phys. Lett., 96(204101), 1-3. Obermann, A., Planès, T., Larose, E. & Campillo, M., 2013a. Imaging pre and co-eruptive structural and mechanical changes on a volcano with ambient seismic noise, J. geophys. Res., 118, 1-10. Obermann, A., Planès, T., Larose, E., Sens-Schönfelder, C. & Campillo,M., 2013b. Depth sensitivity of seismic coda waves to velocity perturbations in an elastic heterogeneous medium, Geophys. J. Int., 194(1), 372-382. Wegler, U. & Lühr, B.G., 2001. Scattering behaviour at Merapi volcano (Java) revealed from an active seismic experiment, Geophys. J. Int., 145(3), 579-592. Yamamoto, M. & Sato, H., 2010. Multiple scattering and mode conversion revealed by an active seismic experiment at Asama volcano, Japan, J. geophys. Res., 115(B7), doi:10.1029/2009JB007109.
Heat transport by long mean free path vibrations in amorphous silicon nitride near room temperature
NASA Astrophysics Data System (ADS)
Sultan, Rubina; Avery, A. D.; Underwood, J. M.; Mason, S. J.; Bassett, D.; Zink, B. L.
2013-06-01
We present measurements of thermal transport in 500-nm-thick, 35-?m-wide, and 806-?m-long micromachined suspended silicon nitride (Si-N) bridges over the temperature range of 77 to 325 K. The measured thermal conductivity of Si-N (for material grown by low-pressure chemical vapor deposition in two different furnaces) deviates somewhat from previously reported measurements and also shows surprising dependence on surface variation at these relatively high temperatures. Addition of discontinuous gold films causes the thermal conductance of Si-N bridges to drop through the entire measured temperature range, before rising again when thicker, continuous films are added. Similar effects occur when continuous but very low-thermal-conductivity alumina films are deposited. The reduction in thermal conductance upon modification of the Si-N surface is strong evidence that vibrational excitations with long mean free paths carry significant heat even at these high temperatures. By measuring a series of film thicknesses the surface-scattering effects can be mitigated, and the resulting experimental values of the thermal conductivity of alumina and Au thin films compare very well to known values or to predictions of the Wiedemann-Franz law. We also present a modified model for the phonon mean free path in thin-film geometries, and use it along with atomic force microsope scans to show that a very small population of phonons with mean free path on the order of 1 ?m and wavelength much longer than the expected thermal wavelengths carry up to 50% of the heat in Si-N at room temperature.
Shaing, K. C.
2006-09-15
It is illustrated that plasma transport processes in the direction of the magnetic field are local in the vicinity of the magnetic island in the long mean-free-path regime where the collisionality parameter {nu}{sub *} is larger than 10{sup -2}, and the width of the island is about 3% of the minor radius or smaller. This is because the plasma temperature variation on the magnetic surface that results from the magnetic reconnection is gentle. Both the electron and the ion parallel transport fluxes including parallel heat flow in the banana regime where {nu}{sub *}<1 are calculated using a model Coulomb collision operator that conserves momentum.
Shear viscosity of hot nuclear matter by the mean free path method
NASA Astrophysics Data System (ADS)
Fang, D. Q.; Ma, Y. G.; Zhou, C. L.
2014-04-01
The shear viscosity of hot nuclear matter is investigated by using the mean free path method within the framework of the isospin-dependent quantum molecular dynamics model. Finite size nuclear sources at different density and temperature are initialized based on the Fermi-Dirac distribution. The results show that shear viscosity to entropy density ratio decreases with the increase of temperature and tends toward a constant value for ? ˜?0, which is consistent with the previous studies on nuclear matter formed during heavy-ion collisions. At ? ˜1/2?0, a minimum of ? /s is seen at around T =10 MeV and a maximum of the multiplicity of intermediate mass fragment (MIMF) is also observed at the same temperature which is an indication of the liquid-gas phase transition.
Phonon mean free path spectrum and thermal conductivity for Si1-xGex nanowires
NASA Astrophysics Data System (ADS)
Xie, Guofeng; Guo, Yuan; Wei, Xiaolin; Zhang, Kaiwang; Sun, Lizhong; Zhong, Jianxin; Zhang, Gang; Zhang, Yong-Wei
2014-06-01
We reformulate the linearized phonon Boltzmann transport equation by incorporating the direction-dependent phonon-boundary scattering, and based on this equation, we study the thermal conductivity of Si1-xGex nanowires and derive their phonon mean free path spectrum. Due to the severe suppression of high-frequency phonons by alloy scattering, the low frequency phonons in Si1-xGex nanowires have a much higher contribution to the thermal conductivity than pure silicon nanowires. We also find that Si1-xGex nanowires possess a stronger length-dependent, weaker diameter-dependent, and weaker surface roughness-dependent thermal conductivity than silicon nanowires. These findings are potentially useful for engineering Si1-xGex nanowires for thermoelectric applications.
Inelastic-interaction mean free path of negative pions in tungsten
NASA Technical Reports Server (NTRS)
Cheshire, D. L.; Huggett, R. W.; Jones, W. V.; Rountree, S. P.; Schmidt, W. K. H.; Kurz, R. J.; Bowen, T.; Delise, D. A.; Krider, E. P.; Orth, C. D.
1975-01-01
The inelastic-interaction mean free paths (lambda) of 5-, 10-, and 15-GeV/c pions have been measured by determining the distribution of first-interaction locations in a modular tungsten-scintillator ionization spectrometer. In addition to commonly used interaction signatures of a few (2-5) particles in two or three consecutive modules, a chi-squared distribution is employed to calculate the probability that the first interaction occurred at a specific depth in the spectrometer. This latter technique seems to be more reliable than use of the simpler criteria. No significant dependence of lambda on energy has been observed. In tungsten, lambda for pions is 206 (plus or minus 6) g/sq cm.
He, H.-Q.; Wan, W., E-mail: hqhe@mail.iggcas.ac.cn, E-mail: wanw@mail.iggcas.ac.cn [Beijing National Observatory of Space Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029 (China)
2012-03-01
The parallel mean free path of solar energetic particles (SEPs), which is determined by physical properties of SEPs as well as those of solar wind, is a very important parameter in space physics to study the transport of charged energetic particles in the heliosphere, especially for space weather forecasting. In space weather practice, it is necessary to find a quick approach to obtain the parallel mean free path of SEPs for a solar event. In addition, the adiabatic focusing effect caused by a spatially varying mean magnetic field in the solar system is important to the transport processes of SEPs. Recently, Shalchi presented an analytical description of the parallel diffusion coefficient with adiabatic focusing. Based on Shalchi's results, in this paper we provide a direct analytical formula as a function of parameters concerning the physical properties of SEPs and solar wind to directly and quickly determine the parallel mean free path of SEPs with adiabatic focusing. Since all of the quantities in the analytical formula can be directly observed by spacecraft, this direct method would be a very useful tool in space weather research. As applications of the direct method, we investigate the inherent relations between the parallel mean free path and various parameters concerning physical properties of SEPs and solar wind. Comparisons of parallel mean free paths with and without adiabatic focusing are also presented.
NASA Astrophysics Data System (ADS)
Wang, S.-Y.; Boyanovsky, D.; de Vega, H. J.; Lee, D.-S.; Ng, Y. J.
2000-03-01
We study the transport coefficients, damping rates, and mean free paths of soft fermion collective excitations in a hot fermion-gauge-scalar plasma with the goal of understanding the main physical mechanisms that determine transport of chirality in scenarios of nonlocal electroweak baryogenesis. The focus is on identifying the different transport coefficients for the different branches of soft collective excitations of the fermion spectrum. These branches correspond to collective excitations with opposite ratios of chirality to helicity and different dispersion relations. By combining results from the hard thermal loop (HTL) resummation program with a novel mechanism of fermion damping through heavy scalar decay, we obtain a robust description of the different damping rates and mean free paths for the soft collective excitations to leading order in HTL and lowest order in the Yukawa coupling. The space-time evolution of wave packets of collective excitations unambiguously reveals the respective mean free paths. We find that whereas both the gauge and scalar contribution to the damping rates are different for the different branches, the difference of mean free paths for both branches is mainly determined by the decay of the heavy scalar into a hard fermion and a soft collective excitation. We argue that these mechanisms are robust and are therefore relevant for nonlocal scenarios of baryogenesis either in the standard model or extensions thereof.
NASA Astrophysics Data System (ADS)
Adhya, Souvik P.; Roy, P. K.; Dutt-Mazumder, Abhee K.
2013-04-01
In this work we have derived the expressions of the mean free path (MFP) and emissivity of the neutrinos by incorporating non-Fermi liquid (NFL) corrections upto next to leading order (NLO). We have shown how such corrections affect the cooling of the neutron star composed of quark matter core.
Wang, S.-Y. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)] [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Boyanovsky, D. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States) [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); LPTHE, Universite Pierre et Marie Curie (Paris VI) et Denis Diderot (Paris VII), Tour 16, 1er. etage, 4, Place Jussieu, 75252 Paris, Cedex 05 (France); Vega, H. J. de [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States) [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); LPTHE, Universite Pierre et Marie Curie (Paris VI) et Denis Diderot (Paris VII), Tour 16, 1er. etage, 4, Place Jussieu, 75252 Paris, Cedex 05, (France); Lee, D.-S. [Department of Physics, National Dong Hwa University, Shoufeng, Hualien 974, Taiwan, Republic of China (China)] [Department of Physics, National Dong Hwa University, Shoufeng, Hualien 974, Taiwan, Republic of China (China); Ng, Y. J. [Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599 (United States)] [Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599 (United States)
2000-03-15
We study the transport coefficients, damping rates, and mean free paths of soft fermion collective excitations in a hot fermion-gauge-scalar plasma with the goal of understanding the main physical mechanisms that determine transport of chirality in scenarios of nonlocal electroweak baryogenesis. The focus is on identifying the different transport coefficients for the different branches of soft collective excitations of the fermion spectrum. These branches correspond to collective excitations with opposite ratios of chirality to helicity and different dispersion relations. By combining results from the hard thermal loop (HTL) resummation program with a novel mechanism of fermion damping through heavy scalar decay, we obtain a robust description of the different damping rates and mean free paths for the soft collective excitations to leading order in HTL and lowest order in the Yukawa coupling. The space-time evolution of wave packets of collective excitations unambiguously reveals the respective mean free paths. We find that whereas both the gauge and scalar contribution to the damping rates are different for the different branches, the difference of mean free paths for both branches is mainly determined by the decay of the heavy scalar into a hard fermion and a soft collective excitation. We argue that these mechanisms are robust and are therefore relevant for nonlocal scenarios of baryogenesis either in the standard model or extensions thereof. (c) 2000 The American Physical Society.
He, H.-Q.; Schlickeiser, R. E-mail: rsch@tp4.rub.de
2014-09-10
The cosmic ray mean free path in a large-scale nonuniform guide magnetic field with superposed magnetostatic turbulence is calculated to clarify some conflicting results in the literature. A new, exact integro-differential equation for the cosmic-ray anisotropy is derived from the Fokker-Planck transport equation. A perturbation analysis of this integro-differential equation leads to an analytical expression for the cosmic ray anisotropy and the focused transport equation for the isotropic part of the cosmic ray distribution function. The derived parallel spatial diffusion coefficient and the associated cosmic ray mean free path include the effect of adiabatic focusing and reduce to the standard forms in the limit of a uniform guide magnetic field. For the illustrative case of isotropic pitch angle scattering, the derived mean free path agrees with the earlier expressions of Beeck and Wibberenz, Bieber and Burger, Kota, and Litvinenko, but disagrees with the result of Shalchi. The disagreement with the expression of Shalchi is particularly strong in the limit of strong adiabatic focusing.
Beranek, Leo L; Nishihara, Noriko
2014-01-01
The Eyring/Sabine equations assume that in a large irregular room a sound wave travels in straight lines from one surface to another, that the surfaces have an average sound absorption coefficient ?av, and that the mean-free-path between reflections is 4?V/Stot where V is the volume of the room and Stot is the total area of all of its surfaces. No account is taken of diffusivity of the surfaces. The 4?V/Stot relation was originally based on experimental determinations made by Knudsen (Architectural Acoustics, 1932, pp. 132-141). This paper sets out to test the 4?V/Stot relation experimentally for a wide variety of unoccupied concert and chamber music halls with seating capacities from 200 to 5000, using the measured sound strengths Gmid and reverberation times RT60,mid. Computer simulations of the sound fields for nine of these rooms (of varying shapes) were also made to determine the mean-free-paths by that method. The study shows that 4?V/Stot is an acceptable relation for mean-free-paths in the Sabine/Eyring equations except for halls of unusual shape. Also demonstrated is the proper method for calibrating the dodecahedral sound source used for measuring the sound strength G, i.e., the reverberation chamber method. PMID:24437762
Lacoste, David
2000-01-01
Waves Random Media 10 (2000) 367Â372. Printed in the UK PII: S0959-7174(00)11429-6 Transport mean free path for magneto-transverse light diffusion: an alternative approach David Lacoste Department 11 April 2000 Abstract. This paper presents a derivation of the transport mean free path for magneto-transverse
Davies, Frederick B
2015-01-01
Extremely large opaque troughs in the Lyman-alpha forest have been interpreted as a sign of an extended reionization process below z~6. Such features are impossible to reproduce with simple models of the intergalactic ionizing background that assume a uniform mean free path of ionizing photons. We build a self-consistent model of the ionizing background that includes fluctuations in the mean free path due to the varying strength of the ionizing background and large-scale density field. The dominant effect is the suppression of the ionizing background in large-scale voids due to "self-shielding" by an enhanced number of optically thick absorbers. Our model results in a distribution of 50 Mpc/h Lyman-alpha forest effective optical depths that significantly improves agreement with the observations at z~5.6. Extrapolation to z~5.4 and z~5.8 appears promising, but matching the mean background evolution requires evolution in the absorber population beyond the scope of the present model. We also demonstrate the need...
NASA Astrophysics Data System (ADS)
Liu, Honglin; Xu, Xiao; Lai, Puxiang; Wang, Lihong V.
2011-08-01
In turbid media such as biological tissue, multiple scattering hinders direct light focusing at depths beyond one transport mean free path. As a solution to this problem, time-reversed ultrasonically encoded (TRUE) optical focusing is proposed based on ultrasonic encoding of diffused laser light and optical time reversal. In TRUE focusing, a laser beam of long coherence length illuminates a turbid medium, where the incident light undergoes multiple scattering and part of it gets ultrasonically encoded within the ultrasonic focal zone. A conjugated wavefront of the ultrasonically encoded light is then generated by a phase conjugate mirror outside the medium, which traces back the trajectories of the ultrasonically encoded diffused light and converges light to the ultrasonic focal zone. Here, we report the latest experimental improvement in TRUE optical focusing that increases its penetration in tissue-mimicking media from a thickness of 3.75 to 7.00 mm. We also demonstrate that the TRUE focus depends on the focal diameter of the ultrasonic transducer.
Proton Inelastic Mean Free Path in a Group of Organic Materials in 0.05-10 MeV Range
NASA Astrophysics Data System (ADS)
Tan, Zhen-Yu; Xia, Yue-Yuan; Zhao, Ming-Wen; Liu, Xiang-Dong
2010-11-01
Inelastic mean free paths (MFPs) of 0.05-10 MeV protons in a group of 10 organic compounds are systematically calculated. The calculations are based on the method newly derived from the Ashley optical-data model and from the higher-order correction terms in stopping power calculations. Especially, in this method the new and empirical Bloch correction for the inelastic MFP is given. An evaluation for the optical energy loss function is incorporated into the present calculations because of the lack of available experimental optical data for the considered organic compounds expect for kapton. The proton inelastic MFPs for these 10 organic compounds in the energy range from 0.05 to 10 MeV are presented here for the first time, and the combination of these inelastic MFP data and our previous data of stopping power calculation for these bioorganic compounds may form a useful database for Monte Carlo track-structure studies of various radiation effects on these materials.
Guo Zehua; Tang Xianzhu [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2012-08-15
Parallel transport of long mean-free-path plasma along an open magnetic field line is characterized by strong temperature anisotropy, which is driven by two effects. The first is magnetic moment conservation in a non-uniform magnetic field, which can transfer energy between parallel and perpendicular degrees of freedom. The second is decompressional cooling of the parallel temperature due to parallel flow acceleration by conventional presheath electric field which is associated with the sheath condition near the wall surface where the open magnetic field line intercepts the discharge chamber. To the leading order in gyroradius to system gradient length scale expansion, the parallel transport can be understood via the Chew-Goldbeger-Low (CGL) model which retains two components of the parallel heat flux, i.e., q{sub n} associated with the parallel thermal energy and q{sub s} related to perpendicular thermal energy. It is shown that in addition to the effect of magnetic field strength (B) modulation, the two components (q{sub n} and q{sub s}) of the parallel heat flux play decisive roles in the parallel variation of the plasma profile, which includes the plasma density (n), parallel flow (u), parallel and perpendicular temperatures (T{sub Parallel-To} and T{sub Up-Tack }), and the ambipolar potential ({phi}). Both their profile (q{sub n}/B and q{sub s}/B{sup 2}) and the upstream values of the ratio of the conductive and convective thermal flux (q{sub n}/nuT{sub Parallel-To} and q{sub s}/nuT{sub Up-Tack }) provide the controlling physics, in addition to B modulation. The physics described by the CGL model are contrasted with those of the double-adiabatic laws and further elucidated by comparison with the first-principles kinetic simulation for a specific but representative flux expander case.
NASA Astrophysics Data System (ADS)
Vigil-Fowler, Derek; Bernardi, Marco; Louie, Steven G.
2015-03-01
The organometallic halide pervoskites have generated enormous interest due to the rapidly increasing efficiency of solar cells fabricated from these materials. Most research on the organometallic halide pervoskites has been experimental due to the challenges posed by these materials to theoretical study, including the size of the unit cell, the presence of many defects, the orientational disorder in of the methyammonium (MA) cation, and the heavy atoms involved with the corresponding large spin-orbit coupling (SOC). We study the room-temperature tetragonal structure of CH3NH3PbI3 using density functional theory (DFT) and a many-body Green's functions approach. We use DFT to study the effect of the dependence of the bandstructure on the orientation of the MA cation, while we perform GW and GW plus Bethe-Salpeter equation (GW-BSE) calculations to study the quasiparticle bandstructure and optical spectra, respectively, paying close attention to convergence and the effect of SOC. We particularly investigate the existence of a proposed charge-transfer state in this material. We also briefly discuss the mean free paths due to electron-phonon and electron-electron scattering in the ideal structure. This work was supported by NSF Grant No. DMR10-1006184, and U.S. DOE Contract No. DE-AC02-05CH11231 and the DOE SciDAC program. Computational resources were provided by NERSC. D.V.-F. acknowledges funding from the NSF's Blue Waters Fellowship.
Wei-Zhou Jiang; Bao-An Li; Lie-Wen Chen
2007-08-19
The mean free paths and in-medium scattering cross sections of energetic nucleons in neutron-rich nucleonic matter are investigated using the nucleon optical potential obtained within the relativistic impulse approximation with the empirical nucleon-nucleon scattering amplitudes and the nuclear densities obtained in the relativistic mean field model. It is found that the isospin-splitting of nucleon mean free paths, sensitive to the imaginary part of the symmetry potential, changes its sign at certain high kinetic energy. The in-medium nucleon-nucleon cross sections are analytically and numerically demonstrated to be essentially independent of the isospin asymmetry of the medium and increase linearly with density in the high energy region where the relativistic impulse approximation is applicable.
Jiang Weizhou; Li Baoan; Chen Liewen
2007-10-15
The mean free paths and in-medium scattering cross sections of energetic nucleons in neutron-rich nucleonic matter are investigated using the nucleon optical potential obtained within the relativistic impulse approximation with the empirical nucleon-nucleon scattering amplitudes and the nuclear densities obtained in the relativistic mean-field model. It is found that the isospin-splitting of nucleon mean free paths, sensitive to the imaginary part of the symmetry potential, changes its sign at certain high kinetic energy. The in-medium nucleon-nucleon cross sections are analytically and numerically demonstrated to be essentially independent of the isospin asymmetry of the medium and increase linearly with density in the high-energy region where the relativistic impulse approximation is applicable.
NASA Astrophysics Data System (ADS)
Tan, Zhenyu; Xia, Yueyuan; Zhao, Mingwen; Liu, Xiangdong
2010-07-01
The systematic calculations of the inelastic mean free paths (MFP) of 0.05-10 MeV protons in a group of eleven important bioorganic compounds, i.e. DNA, five bases, three fatty acids, cellulose and ?-carotene, have been performed. The expressions for the calculations are derived from the Ashley's optical-data model and from the higher-order correction terms in stopping power calculations. Especially, the Bloch correction for the inelastic MFP is proposed empirically in this work. The inelastic MFPs for energetic protons in water are also evaluated and compared with other theoretical calculations. The proton inelastic MFPs for these 11 bioorganic compounds in the energy range from 0.05 to 10 MeV are presented here for the first time, and might be useful for studies of various radiation effects in these materials.
NASA Astrophysics Data System (ADS)
Jeener, J.
2015-01-01
The local theory of relaxation of 3He by Brownian motion in an inhomogeneous magnetic field, originally proposed by Gamblin and Carver [Phys. Rev. 138, A946 (1965), 10.1103/PhysRev.138.A946] and by Schearer and Walters [Phys. Rev. 139, A1398 (1965), 10.1103/PhysRev.139.A1398], is reconsidered in detail to clarify (or not) the approximations involved. Notably, a discussion is given of frames rotating at time-dependent angular velocities (both in magnitude and in direction), and attention is drawn to the often overlooked long tail that confinement adds to velocity correlation functions. A stepwise application of the Redfield theory of relaxation eventually provides quantitative predictions for the rate of depolarization and the linear-in-electric-field frequency shift, in terms of the components of the local inhomogeneity tensor and the usual parameters (nuclear magnetic resonance frequency, diffusion coefficient, mean time between collisions, etc.), valid in the common situation of mean free path much smaller than the size of the container. These predictions agree with almost all results of previous publications, most of which are based on the global approach which evaluates correlation functions by reference to the diffusion equation in spite of its limitations for short delays.
Proton inelastic mean free path in amino acids and protein over the energy range of 0.05-10 MeV
NASA Astrophysics Data System (ADS)
Tan, Zhenyu; Xia, Yueyuan; Liu, Xiangdong; Zhao, Mingwen
2010-09-01
The inelastic mean free paths (MFP) of 0.05-10 MeV protons in a group of 15 amino acids and a protein have been systematically calculated. The calculations are based on the method newly derived from the Ashley's optical-data model and from the higher-order correction terms in stopping power calculations. Especially, in this method the new and empirical Bloch correction for the inelastic MFP was given. An evaluation for the optical energy loss function is incorporated into the present calculations because of the lack of available experimental optical data for the bioorganic compounds under consideration. The proton inelastic MFPs for these 15 amino acids and the protein in the energy range from 0.05 to 10 MeV are presented here for the first time, and the combination of these inelastic MFP data and our previous data of the SP calculations for these bioorganic compounds may form a useful database for Monte Carlo track-structure studies of various radiation effects in these materials.
NASA Astrophysics Data System (ADS)
Tan, Zhenyu; Xia, Yueyuan
2011-02-01
The systematical calculations of the inelastic mean free paths (MFPs) of 0.05-10 MeV protons in 12 elemental solids (Al, Si, Ni, Cu, Mo, Rh, Ag, W, Os, Ir, Pt, Au) have been performed. The calculations are based on the algorithm derived from Ashley's optical-data model including the higher-order corrections to stopping power (SP) for protons. The prominence and necessity of the higher-order corrections are demonstrated by calculating the proton SPs for the 12 solids using Ashley's optical-data model and by comparing the calculated SPs with the experimental results, the tabulated values and other corresponding theoretical evaluations. The algorithm of evaluating the proton inelastic MFP is described. In this algorithm, the Barkas-effect correction and the Bloch correction are taken into account, the minimum impact parameter from Lindhard is used in the Barkas-effect correction, and an empirical estimation of a free parameter involved in the Bloch correction to the inelastic MFP is proposed. The evaluated inelastic MFPs of 0.05-10 MeV protons for the 12 solids under two different cases, i.e. the higher-order corrections not being considered and the Barkas-effect correction and the Bloch correction being included, are presented in the tabulated form and are first results for these solids. These numerical results provide an alternative basic data for the Monte Carlo studies on low-energy proton transport in these 12 solids.
ERIC Educational Resources Information Center
Jakoby, Bernhard
2009-01-01
The collision model is frequently introduced to describe electronic conductivity in solids. Depending on the chosen approach, the introduction of the collision time can lead to erroneous results for the average velocity of the electrons, which enters the expression for the electrical conductivity. In other textbooks, correct results are obtained…
Mean Free Path in Soccer and Gases
ERIC Educational Resources Information Center
Luzuriaga, J.
2010-01-01
The trajectories of the molecules in an ideal gas and of the ball in a soccer game are compared. The great difference between these motions and some similarities are discussed. This example could be suitable for discussing many concepts in kinetic theory in a way that can be pictured by students for getting a more intuitive understanding. It could…
Path of Electrons in Photosynthesis
William Arnold
1976-01-01
Electrons, from the oxidation of water, inside the grana disks (thylakoids) are transferred across the membrane to the outside, to the Calvin cycle or the Hill oxidant. The span in redox level may be 2.3 V. Part of the system II chlorophyll is on the inside of the membrane and part on the outside. An electron trap is embedded in
NASA Astrophysics Data System (ADS)
Krawczyk, M.; Jablonski, A.; Tougaard, S.; Toth, J.; Varga, D.; Gergely, G.
1998-05-01
GaAs samples have been studied with a hemispherical analyser of high resolution (type ESA 31). The analyser covers the energy range 10-5000 eV with controlled energy resolution. Prior to measurements, sample surfaces have been exposed to Ar + ions in order to amorphise the surface layer. This procedure resulted in Ga enrichment (70-85 at.% Ga as determined by XPS). The elastic peak and EELS spectra were measured in the loss range E- El of 50 eV. The elastic peak intensity ratios of GaAs sample and the Ni reference were used to determine the IMFP in GaAs. The relations between these ratios and the IMFP have been determined from Monte Carlo simulation of the elastic backscattering effect. The values of the IMFP resulting from this procedure are in reasonable agreement with the literature data. The inelastic scattering cross-sections have been determined using the Tougaard procedure. The energy loss distributions ?iK are presented in the 0.2-5.0 keV range.
Vacuum ultraviolet electronic properties of liquids
NASA Astrophysics Data System (ADS)
Painter, L. R.
Collective electronic oscillations in the silicone liquid Dow Corning 705 were examined. Newly analyzed data on electron bombardment gave better agreement with results of analyzed vuv optical reflectance values for energy loss than earlier results indicated. As previously reported, electron and photon mean free paths and absolute photoyields were calculated from reanalyzed liquid water data in the 2 to 25 eV region. These electron mean free paths were calculated from formamide electron mean free paths scaled for valence electron density. The formamide mean free paths were derived using Born approximation by Ashley and Williams. An alternate approach to calculation of electron mean free path in organic and inorganic matter proposed by Seah and Dench was followed. A survey of a range of liquids with request to reflectivity and photoemission was completed. As a result, a series of n-ethylene glycols with particularly high dipole moments as chosen for study. Ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol were studied.
Moving down the path to electronic records.
Deming, B
1994-04-01
The national debate over health care reform is drawing attention to how electronic records could improve the quality of care. After more than 20 years of sometimes frustrating effort, the pioneers in the movement to automate health care records are being joined by legions of others who are seeing the potential benefits of automation. In this special report, learn the latest developments in the computerized patient record movement. PMID:10141182
Path-length distribution of electrons reflected elastically from solids
NASA Astrophysics Data System (ADS)
Pázsit, I.; Chakarova, Rumjana
1994-11-01
The transport of electrons, reflected from solids while suffering elastic scattering only, is investigated in detail. The angular path length and the depth distributions of the reflected electrons are calculated by solving the relevant half-space transport problem in the DP1 approximation and with detailed Monte Carlo simulation. The incentive for the investigations is to calculate the energy spectrum of the reflected electrons in the vicinity of the elastic peak. According to a suggestion of Tougaard and Sigmund, this can be obtained from the path-length distribution of the elastically scattered electrons and a suitable energy-loss function. The purpose of the present paper is to determine the path-length distribution. It has been found that for certain elements, notably aluminium, carbon, and copper, at certain energies the path-length and depth distributions are not monotonic. The DP1 approximation is in general better than the P1 approximation, but for the nonmonotonic distributions, it is not satisfactory. The nonmonotonic behavior is shown to be related to certain properties of the scattering kernel.
Path integral Monte Carlo and the electron gas
NASA Astrophysics Data System (ADS)
Brown, Ethan W.
Path integral Monte Carlo is a proven method for accurately simulating quantum mechanical systems at finite-temperature. By stochastically sampling Feynman's path integral representation of the quantum many-body density matrix, path integral Monte Carlo includes non-perturbative effects like thermal fluctuations and particle correlations in a natural way. Over the past 30 years, path integral Monte Carlo has been successfully employed to study the low density electron gas, high-pressure hydrogen, and superfluid helium. For systems where the role of Fermi statistics is important, however, traditional path integral Monte Carlo simulations have an exponentially decreasing efficiency with decreased temperature and increased system size. In this thesis, we work towards improving this efficiency, both through approximate and exact methods, as specifically applied to the homogeneous electron gas. We begin with a brief overview of the current state of atomic simulations at finite-temperature before we delve into a pedagogical review of the path integral Monte Carlo method. We then spend some time discussing the one major issue preventing exact simulation of Fermi systems, the sign problem. Afterwards, we introduce a way to circumvent the sign problem in PIMC simulations through a fixed-node constraint. We then apply this method to the homogeneous electron gas at a large swatch of densities and temperatures in order to map out the warm-dense matter regime. The electron gas can be a representative model for a host of real systems, from simple medals to stellar interiors. However, its most common use is as input into density functional theory. To this end, we aim to build an accurate representation of the electron gas from the ground state to the classical limit and examine its use in finite-temperature density functional formulations. The latter half of this thesis focuses on possible routes beyond the fixed-node approximation. As a first step, we utilize the variational principle inherent in the path integral Monte Carlo method to optimize the nodal surface. By using a ansatz resembling a free particle density matrix, we make a unique connection between a nodal effective mass and the traditional effective mass of many-body quantum theory. We then propose and test several alternate nodal ansatzes and apply them to single atomic systems. Finally, we propose a method to tackle the sign problem head on, by leveraging the relatively simple structure of permutation space. Using this method, we find we can perform exact simulations this of the electron gas and 3He that were previously impossible.
Painter, L.R.
1984-01-01
The work on collective electronic oscillations in the silicone liquid Dow Corning 705 was revised. Newly analyzed data on electron bombardment gave better agreement with results of analyzed vuv optical reflectance values for energy loss than earlier results indicated. As previously reported, electron and photon mean free paths and absolute photoyields were calculated from reanalyzed liquid water data in the 2 to 25 eV region. These electron mean free paths were calculated from formamide electron mean free paths scaled for valence electron density. The formamide mean free paths were derived using Born approximation by Ashley and Williams. An alternate approach to calculation of electron mean free path in organic and inorganic matter proposed by Seah and Dench has been followed. A paper detailing the water data and discrepancies in electron mean free path is in preparation. A survey of a range of liquids with request to reflectivity and photoemission was completed. Absorbance measurements in the 25,000 to 2700 A region were made on a number of the insulating liquids. As a result, a series of n-ethylene glycols with particularly high dipole moments was chosen for study. The main thrust of the current contract period has been a study of these liquids which include ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol.
Data path development for multiple electron beam maskless lithography
NASA Astrophysics Data System (ADS)
Krecinic, Faruk; Lin, Shy-Jay; Chen, Jack J. H.
2011-04-01
Electron beam lithography has been used in the production of integrated circuits for decades. However, due to the limitation of throughput it was not a viable solution for high volume manufacturing and its biggest application is the production of semiconductor masks. For many considerations it has particularly now become desirable to eliminate the semiconductor mask and introduce maskless lithography for semiconductor fabrication. Multiple Electron Beam Maskless Lithography (MEBML2) has been proposed as a solution to overcome the traditional source current limitation of an electron beam system by using many thousands of parallel electron beamlets to write a pattern directly on the wafer. In developing the MEBML2 tool the challenges have shifted and, in absence of the mask, the system data path has emerged as one of the central challenges. The main theme in the data path development is bandwidth. The required raw bandwidth at the patterning beams is determined by throughput and resolution, i.e. pixel size and number of intensity modulation levels. To achieve a production worthy throughput at 10 wafers per hour in a Gaussian-beam-based maskless lithography system, by writing 3.5-nm pixels at 2 levels (on/off) which is required for the 22-nm lithography node, the required aggregate bandwidth at the beam blanker array is up to 45 Tbit/s. Such a large bandwidth requirement means that the data path architecture is mainly characterized by the bandwidth of the data streams in the system. Compression techniques can be used to reduce the intermediate data stream bandwidth requirements and consequently lead to simplifying the system design, reducing power consumption and footprint, but come at the cost of increased data processing complexity and possible limitations on throughput. In this paper we will show results from the development of a prototype data path for the Gaussian-beam-based maskless lithography system. A new concept for data processing and storage is proposed. The vertex-based processing and storage technique is adopted to reduce memory usage considerably, with only modest requirements on the hardware resources. It reveals that a realistically implementable data path system for the maskless lithography tool in high volume manufacturing is feasible.
Tan, Lun C. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Malandraki, Olga E.; Patsou, Ioanna; Papaioannou, Athanasios [Institute of Astronomy and Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, Athens (Greece); Reames, Donald V. [Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742 (United States); Ng, Chee K. [College of Science, George Mason University, Fairfax, VA 22030 (United States); Wang, Linghua, E-mail: ltan@umd.edu [Department of Geophysics, Peking University, Beijing 100871 (China)
2013-05-01
We have examined the Wind/3DP/SST electron and Wind/EPACT/LEMT ion data to investigate the path length difference between solar electrons and ions in the ground-level enhancement (GLE) events in solar cycle 23. Assuming that the onset time of metric type II or decameter-hectometric (DH) type III radio bursts is the solar release time of non-relativistic electrons, we have found that within an error range of {+-}10% the deduced path length of low-energy ({approx}27 keV) electrons from their release site near the Sun to the 1 AU observer is consistent with the ion path length deduced by Reames from the onset time analysis. In addition, the solar longitude distribution and IMF topology of the GLE events examined are in favor of the coronal mass ejection-driven shock acceleration origin of observed non-relativistic electrons. We have also found an increase of electron path lengths with increasing electron energies. The increasing rate of path lengths is correlated with the pitch angle distribution (PAD) of peak electron intensities locally measured, with a higher rate corresponding to a broader PAD. The correlation indicates that the path length enhancement is due to the interplanetary scattering experienced by first arriving electrons. The observed path length consistency implies that the maximum stable time of magnetic flux tubes, along which particles transport, could reach 4.8 hr.
NASA Astrophysics Data System (ADS)
Tan, Lun C.; Malandraki, Olga E.; Reames, Donald V.; Ng, Chee K.; Wang, Linghua; Patsou, Ioanna; Papaioannou, Athanasios
2013-05-01
We have examined the Wind/3DP/SST electron and Wind/EPACT/LEMT ion data to investigate the path length difference between solar electrons and ions in the ground-level enhancement (GLE) events in solar cycle 23. Assuming that the onset time of metric type II or decameter-hectometric (DH) type III radio bursts is the solar release time of non-relativistic electrons, we have found that within an error range of ±10% the deduced path length of low-energy (~27 keV) electrons from their release site near the Sun to the 1 AU observer is consistent with the ion path length deduced by Reames from the onset time analysis. In addition, the solar longitude distribution and IMF topology of the GLE events examined are in favor of the coronal mass ejection-driven shock acceleration origin of observed non-relativistic electrons. We have also found an increase of electron path lengths with increasing electron energies. The increasing rate of path lengths is correlated with the pitch angle distribution (PAD) of peak electron intensities locally measured, with a higher rate corresponding to a broader PAD. The correlation indicates that the path length enhancement is due to the interplanetary scattering experienced by first arriving electrons. The observed path length consistency implies that the maximum stable time of magnetic flux tubes, along which particles transport, could reach 4.8 hr.
NASA Technical Reports Server (NTRS)
Tan, Lun C.; Malandraki, Olga E.; Reames, Donald; NG, Chee K.; Wang, Linghua; Patsou, Ioanna; Papaioannou, Athanasios
2013-01-01
We have examined the Wind/3DP/SST electron and Wind/EPACT/LEMT ion data to investigate the path length difference between solar electrons and ions in the ground-level enhancement (GLE) events in solar cycle 23. Assuming that the onset time of metric type II or decameter-hectometric (DH) type III radio bursts is the solar release time of non-relativistic electrons, we have found that within an error range of plus or minus 10% the deduced path length of low-energy (approximately 27 keV) electrons from their release site near the Sun to the 1 AU observer is consistent with the ion path length deduced by Reames from the onset time analysis. In addition, the solar longitude distribution and IMF topology of the GLE events examined are in favor of the coronal mass ejection-driven shock acceleration origin of observed non-relativistic electrons.We have also found an increase of electron path lengths with increasing electron energies. The increasing rate of path lengths is correlated with the pitch angle distribution (PAD) of peak electron intensities locally measured, with a higher rate corresponding to a broader PAD. The correlation indicates that the path length enhancement is due to the interplanetary scattering experienced by first arriving electrons. The observed path length consistency implies that the maximum stable time of magnetic flux tubes, along which particles transport, could reach 4.8 hr.
A hybrid model for computing nonthermal ion distributions in a long mean-free-path plasma
NASA Astrophysics Data System (ADS)
Tang, Xianzhu; McDevitt, Chris; Guo, Zehua; Berk, Herb
2014-10-01
Non-thermal ions, especially the suprathermal ones, are known to make a dominant contribution to a number of important physics such as the fusion reactivity in controlled fusion, the ion heat flux, and in the case of a tokamak, the ion bootstrap current. Evaluating the deviation from a local Maxwellian distribution of these non-thermal ions can be a challenging task in the context of a global plasma fluid model that evolves the plasma density, flow, and temperature. Here we describe a hybrid model for coupling such constrained kinetic calculation to global plasma fluid models. The key ingredient is a non-perturbative treatment of the tail ions where the ion Knudsen number approaches or surpasses order unity. This can be sharply constrasted with the standard Chapman-Enskog approach which relies on a perturbative treatment that is frequently invalidated. The accuracy of our coupling scheme is controlled by the precise criteria for matching the non-perturbative kinetic model to perturbative solutions in both configuration space and velocity space. Although our specific application examples will be drawn from laboratory controlled fusion experiments, the general approach is applicable to space and astrophysical plasmas as well. Work supported by DOE.
Role of phonon dispersion in studying phonon mean free paths in skutterudites
Zebarjadi, Mona
Experimental thermal conductivity of bulk materials are often modeled using Debye approximation together with functional forms of relaxation time with fitting parameters. While such models can fit the temperature dependence ...
Spiral structure and star formation. I - Formation mechanisms and mean free paths
NASA Technical Reports Server (NTRS)
Roberts, W. W., Jr.; Hausman, M. A.
1984-01-01
The wide variety of optical appearances observed in spiral galaxies has encouraged the growth of two theoretical approaches to explain the spiral patterns exhibited by such young objects as OB associations, giant H II regions, and dark dust lanes. These approaches are related to the density wave theory of spiral structure and 'stochastic, self-propagating star formation'. Levinson and Roberts (1981) tried to reconcile these two theoretical approaches, and considered a disk filled with discrete gas clouds. The present investigation is concerned with refinements and extensions of the model of Levinson and Roberts. Attention is given to gravitational forces and dynamical propagation, cloud-cloud collisions, supernova interactions, computational models, a theory concerning the interactions of the gas cloud and stellar association systems, the time evolution of the gas cloud-stellar association systems, and aspects of collisionally triggered star formation.
Evaluation of the Phonon Mean Free Path in Thin Films by using Classical Molecular Dynamics
Maruyama, Shigeo
the possibility of applications as new thermal insulators [1-8]. Many studies were carried out to evaluate as a simulation material. The thermal conductivity of a thin film plays an important role in the design of nano that there is apparently a size effect on the thermal conductivity, which indicates that the microscale system has a lower
Nonequilibrium heterogeneous catalysis in the long mean-free-path regime
NASA Astrophysics Data System (ADS)
Sheehan, D. P.
2013-09-01
It is shown that a standard principle of traditional catalysis—that a catalyst does not alter the final thermodynamic equilibrium of a reaction—can fail in low-pressure, heterogeneous gas-surface reactions. Kinetic theory for this epicatalysis is presented, and two well-documented experimental examples are detailed: surface ionized plasmas and hydrogen dissociation on refractory metals. This phenomenon should be observable over a wide range of temperatures and pressures, and for a broad spectrum of heterogeneous reactions. By transcending some constraints of equilibrium thermodynamics, epicatalysis might provide additional control parameters and synthetic routes for reactions, and enable product streams boosted in thermochemical energy or desirable species.
Demir, Hilmi Volkan
-wavelength emission method. It is found that the strong polarization induced electric field within the n-EBL reduces the thermal velocity and correspondingly the mean free path of the hot electrons. As a result, the electron capture efficiency of the multiple quantum wells is enhanced, which significantly reduces the electron
Electron paths, tunnelling, and diffraction in the spacetime algebra
Stephen Gull; Anthony Lasenby; Chris Doran
1993-01-01
This paper employs the ideas of geometric algebra to investigate the physical content of Dirac's electron theory. The basis is Hestenes' discovery of the geometric significance of the Dirac spinor, which now represents a Lorentz transformation in spacetime. This transformation specifies a definite velocity, which might be interpreted as that of a real electron. Taken literally, this velocity yields predictions
Wang, Shuo [ORNL; Maillet, Yoann [Virginia Polytechnic Institute and State University (Virginia Tech); Wang, Fei [ORNL; Lai, Rixin [General Electric; Luo, Fang [Virginia Polytechnic Institute and State University (Virginia Tech); Boroyevich, Dushan [Virginia Polytechnic Institute and State University (Virginia Tech)
2010-01-01
High-frequency common-mode (CM) electromagnetic-interference (EMI) noise is difficult to suppress in electronics systems. EMI filters are used to suppress CM noise, but their performance is greatly affected by the parasitic effects of the grounding paths. In this paper, the parasitic effects of the grounding paths on an EMI filter's performance are investigated in a motor-drive system. The effects of the mutual inductance between two grounding paths are explored. Guidelines for the grounding of CM EMI filters are derived. Simulations and experiments are finally carried out to verify the theoretical analysis.
Decay Paths of Interfering Two-Electron Excitations in Helium
Menzel, A.; Frigo, S.P.; Whitfield, S.B.; Caldwell, C.D.; Krause, M.O.; Tang, J.; Shimamura, I.
1995-08-21
Partial photoionization cross sections and photoelectron angular distributions of He in the region of interfering Rydberg series below the {ital n}=5 threshold are measured and compared with theoretical results based on the hyperspherical close-coupling method. At a bandpass of 12 meV for the photon energy, this level of differentiation offers the most critical assessment of the dynamics of the two-electron excitations to date. A good understanding is achieved.
Samyadeb Bhattacharya; Sisir Roy
2015-02-17
In this paper, we have estimated the temperature dependent path predictability for an electronic Mach-Zehnder interferometer. The increment of path predictability can directly be associated with stronger decoherence process. We have also theoretically predicted that placing two detectors in both the paths, which are at the same equilibrium temperature with the system, erases all the memory of path information and hence acts like a quantum eraser.
Path-branching representation for nonadiabatic electron dynamics in conical intersection.
Yonehara, Takehiro; Takatsuka, Kazuo
2013-09-12
Path-branching representation (or phase-space averaging and natural branching method (PSANB) as its approximation) of nonadiabatic electron wavepacket dynamics is now known to work well for avoided crossings in many dimensional nonadiabatic transitions [Yonehara, T.; Hanasaki, K.; Takatsuka, K. Chem. Rev. 2012, 112, 499]. In this paper we examine feasibility of the path-branching representation in the theoretical studies of conical intersection (CI). The most characteristic feature of CI is the Herzberg-Longuet-Higgins phase (or the Berry phase) arising from the electronic part of the total wave function, and accordingly quantum phases of both electronic and nuclear dynamics should be taken into account in a balanced manner. We first show the PSANB can well capture the essential feature of the phase dynamics of CI. However, the nuclear phases, the wavelength of which is far shorter than that of the electronic phases, make the computation of nonadiabatic transition extremely oscillatory, resulting in very slow convergence with respect to the number of sampling paths. A similar difficulty quite often takes place in theoretical chemical dynamics. To cope with this situation, we devise a simple and tractable approximation in the application of PSANB resting on the fact that a small number of PSANB paths already reproduce accurate nonadiabatic transition probability. PMID:23527574
Measurement of the transmission phase of an electron in a quantum two-path interferometer
NASA Astrophysics Data System (ADS)
Takada, S.; Yamamoto, M.; Bäuerle, C.; Watanabe, K.; Ludwig, A.; Wieck, A. D.; Tarucha, S.
2015-08-01
A quantum two-path interferometer allows for direct measurement of the transmission phase shift of an electron, providing useful information on coherent scattering problems. In mesoscopic systems, however, the two-path interference is easily smeared by contributions from other paths, and this makes it difficult to observe the true transmission phase shift. To eliminate this problem, multi-terminal Aharonov-Bohm (AB) interferometers have been used to derive the phase shift by assuming that the relative phase shift of the electrons between the two paths is simply obtained when a smooth shift of the AB oscillations is observed. Nevertheless, the phase shifts using such a criterion have sometimes been inconsistent with theory. On the other hand, we have used an AB ring contacted to tunnel-coupled wires and acquired the phase shift consistent with theory when the two output currents through the coupled wires oscillate with well-defined anti-phase. Here, we investigate thoroughly these two criteria used to ensure a reliable phase measurement, the anti-phase relation of the two output currents, and the smooth phase shift in the AB oscillation. We confirm that the well-defined anti-phase relation ensures a correct phase measurement with a quantum two-path interference. In contrast, we find that even in a situation where the anti-phase relation is less well-defined, the smooth phase shift in the AB oscillation can still occur but does not give the correct transmission phase due to contributions from multiple paths. This indicates that the phase relation of the two output currents in our interferometer gives a good criterion for the measurement of the true transmission phase, while the smooth phase shift in the AB oscillation itself does not.
NASA Astrophysics Data System (ADS)
Huo, Pengfei; Miller, Thomas F.; Coker, David F.
2013-10-01
A partial linearized path integral approach is used to calculate the condensed phase electron transfer (ET) rate by directly evaluating the flux-flux/flux-side quantum time correlation functions. We demonstrate for a simple ET model that this approach can reliably capture the transition between non-adiabatic and adiabatic regimes as the electronic coupling is varied, while other commonly used semi-classical methods are less accurate over the broad range of electronic couplings considered. Further, we show that the approach reliably recovers the Marcus turnover as a function of thermodynamic driving force, giving highly accurate rates over four orders of magnitude from the normal to the inverted regimes. We also demonstrate that the approach yields accurate rate estimates over five orders of magnitude of inverse temperature. Finally, the approach outlined here accurately captures the electronic coherence in the flux-flux correlation function that is responsible for the decreased rate in the inverted regime.
Dornheim, Tobias; Groth, Simon; Filinov, Alexey; Bonitz, Michael
2015-01-01
The uniform electron gas (UEG) at finite temperature is of high current interest due to its key relevance for many applications including dense plasmas and laser excited solids. In particular, density functional theory heavily relies on accurate thermodynamic data for the UEG. Until recently, the only existing first-principle results had been obtained for $N=33$ electrons with restricted path integral Monte Carlo (RPIMC), for low to moderate density, $r_s = \\overline{r}/a_B \\gtrsim 1$. This data has been complemented by Configuration path integral Monte Carlo (CPIMC) simulations for $r_s \\leq 1$ that substantially deviate from RPIMC towards smaller $r_s$ and low temperature. In this work, we present results from an independent third method---the recently developed permutation blocking path integral Monte Carlo (PB-PIMC) approach [T. Dornheim \\textit{et al.}, NJP \\textbf{17}, 073017 (2015)] which we extend to the UEG. Interestingly, PB-PIMC allows us to perform simulations over the entire density range down to...
Iron-Oxide Minerals Affect Extracellular Electron-Transfer Paths of Geobacter spp
Kato, Souichiro; Hashimoto, Kazuhito; Watanabe, Kazuya
2013-01-01
Some bacteria utilize (semi)conductive iron-oxide minerals as conduits for extracellular electron transfer (EET) to distant, insoluble electron acceptors. A previous study demonstrated that microbe/mineral conductive networks are constructed in soil ecosystems, in which Geobacter spp. share dominant populations. In order to examine how (semi)conductive iron-oxide minerals affect EET paths of Geobacter spp., the present study grew five representative Geobacter strains on electrodes as the sole electron acceptors in the absence or presence of (semi)conductive iron oxides. It was found that iron-oxide minerals enhanced current generation by three Geobacter strains, while no effect was observed in another strain. Geobacter sulfurreducens was the only strain that generated substantial amounts of currents both in the presence and absence of the iron oxides. Microscopic, electrochemical and transcriptomic analyses of G. sulfurreducens disclosed that this strain constructed two distinct types of EET path; in the absence of iron-oxide minerals, bacterial biofilms rich in extracellular polymeric substances were constructed, while composite networks made of mineral particles and microbial cells (without polymeric substances) were developed in the presence of iron oxides. It was also found that uncharacterized c-type cytochromes were up-regulated in the presence of iron oxides that were different from those found in conductive biofilms. These results suggest the possibility that natural (semi)conductive minerals confer energetic and ecological advantages on Geobacter, facilitating their growth and survival in the natural environment. PMID:23363619
Fermionic path-integral Monte Carlo results for the uniform electron gas at finite temperature
NASA Astrophysics Data System (ADS)
Filinov, V. S.; Fortov, V. E.; Bonitz, M.; Moldabekov, Zh.
2015-03-01
The uniform electron gas (UEG) at finite temperature has recently attracted substantial interest due to the experimental progress in the field of warm dense matter. To explain the experimental data, accurate theoretical models for high-density plasmas are needed that depend crucially on the quality of the thermodynamic properties of the quantum degenerate nonideal electrons and of the treatment of their interaction with the positive background. Recent fixed-node path-integral Monte Carlo (RPIMC) data are believed to be the most accurate for the UEG at finite temperature, but they become questionable at high degeneracy when the Brueckner parameter rs=a /aB —the ratio of the mean interparticle distance to the Bohr radius—approaches 1. The validity range of these simulations and their predictive capabilities for the UEG are presently unknown. This is due to the unknown quality of the used fixed nodes and of the finite-size scaling from N =33 simulated particles (per spin projection) to the macroscopic limit. To analyze these questions, we present alternative direct fermionic path integral Monte Carlo (DPIMC) simulations that are independent from RPIMC. Our simulations take into account quantum effects not only in the electron system but also in their interaction with the uniform positive background. Also, we use substantially larger particle numbers (up to three times more) and perform an extrapolation to the macroscopic limit. We observe very good agreement with RPIMC, for the polarized electron gas, up to moderate densities around rs=4 , and larger deviations for the unpolarized case, for low temperatures. For higher densities (high electron degeneracy), rs?1.5 , both RPIMC and DPIMC are problematic due to the increased fermion sign problem.
Kaganovich, Igor
are discharge devices for spacecraft propulsion.1 A typical HT has a ceramic coaxial channel in which many The neutral gas pressure in the acceleration region is extremely low and the electron mean free path greatly12 The model developed by the authors consid- ers a plasma slab bounded by dielectric walls with secondary
Turn on of new electronic paths in Fe-SiO2 granular thin film
NASA Astrophysics Data System (ADS)
Boff, M. A. S.; Hinrichs, R.; Canto, B.; Mesquita, F.; Baptista, D. L.; Fraga, G. L. F.; Pereira, L. G.
2014-10-01
The electrical properties of Fe-SiO2 have been studied in the low-field regime (e?V ? kBT), varying the injected current and the bias potential. Superparamagnetism and a resistance drop of 4400 ? (for a voltage variation of 15 V) were observed at room temperature. This resistance drop increased at lower temperatures. The electrical properties were described with the "Mott variable range hopping" model explaining the behavior of the electrical resistance and the electronic localization length as due to the activation of new electronic paths between more distant grains. This non-ohmic resistance at room temperature can be important for properties dependent of electrical current (magnetoresistance, Hall effect, and magnetoimpedance).
Turn on of new electronic paths in Fe-SiO{sub 2} granular thin film
Boff, M. A. S. E-mail: marcoaureliosilveiraboff@gmail.com; Canto, B.; Mesquita, F.; Fraga, G. L. F.; Pereira, L. G.; Hinrichs, R.; Baptista, D. L.
2014-10-06
The electrical properties of Fe-SiO{sub 2} have been studied in the low-field regime (e?V ? k{sub B}T), varying the injected current and the bias potential. Superparamagnetism and a resistance drop of 4400?? (for a voltage variation of 15?V) were observed at room temperature. This resistance drop increased at lower temperatures. The electrical properties were described with the “Mott variable range hopping” model explaining the behavior of the electrical resistance and the electronic localization length as due to the activation of new electronic paths between more distant grains. This non-ohmic resistance at room temperature can be important for properties dependent of electrical current (magnetoresistance, Hall effect, and magnetoimpedance).
InAs High-Electron Mobility Transistors on the Path to THz Operation J. A. del Alamo1
del Alamo, Jesús A.
Foundries, 400 Stonebreak Road, Malta, NY 12020 1. Introduction The invention of the High-Electron MobilityInAs High-Electron Mobility Transistors on the Path to THz Operation J. A. del Alamo1 and D.-H. Kim2 1 Microsystems Technology Laboratories, MIT, Cambridge, MA 02139, USA Phone: +1-617-253-4764, E
Yamamoto, Kentaro; Takatsuka, Kazuo
2014-03-28
We develop the path-branching representation for nonadiabatic electron wavepacket dynamics [T. Yonehara and K. Takatsuka, J. Chem. Phys. 132, 244102 (2010)] so as to treat dynamics in an energy range comparable to the barrier height of adiabatic potential energy curves. With this representation two characteristic chemical reaction dynamics are studied, in which an incident nuclear wavepacket encounters a potential barrier, on top of which lies another nonadiabatically coupled adiabatic potential curve: (1) Dynamics of initial paths coming into the nonadiabatic interaction region with energy lower than the barrier height. They branch into two pieces (and repeat branching subsequently), the upper counterparts of which can penetrate into a classically inaccessible high energy region and eventually branch back to the product region on the ground state curve. This is so to say surmounting the potential barrier via nonadiabatically coupled excited state, and phenomenologically looks like the so-called deep tunneling. (2) Dynamics of classical paths whose initial energies are a little higher than the barrier but may be lower than the bottom of the excited state. They can undergo branching and some of those components are trapped on top of the potential barrier, being followed by the population decay down to the lower state flowing both to product and reactant sites. Such expectations arising from the path-branching representation are numerically confirmed with full quantum mechanical wavepacket dynamics. This phenomenon may be experimentally observed as time-delayed pulses of wavepacket trains. PMID:24697428
Shaing, K. C.
2007-11-15
In Part I [Phys. Fluids B 2, 1190 (1990)] and Part II [Phys. Plasmas 12, 082508 (2005)], it was emphasized that the equilibrium plasma viscous forces when applied for the magnetohydrodynamic (MHD) modes are only rigorously valid at the mode rational surface where m-nq=0. Here, m is the poloidal mode number, n is the toroidal mode number, and q is the safety factor. This important fact has been demonstrated explicitly by calculating the viscous forces in the plateau regime in Parts I and II. Here, the effective viscous forces in the banana regime are calculated for MHD modes by solving the linear drift kinetic equation that is driven by the plasma flows first derived in Part I. At the mode rational surface, the equilibrium plasma viscous forces are reproduced. However, it is found that away from the mode rational surface, the viscous forces for MHD modes decrease, a behavior similar to that observed in the viscous forces for the plateau regime. The proper form of the momentum equation that is appropriate for the modeling of the MHD modes is also discussed.
Raychaudhuri, Pratap
gap , the London penetration depth, the coherence length, and the upper and lower critical fieldsUpper critical field in nanostructured Nb: Competing effects of the reduction in density of states December 2006 We show that the upper critical field in nanometer-sized Nb particles is governed
Sansone, G.; Benedetti, E.; Caumes, J.-P.; Stagira, S.; Vozzi, C.; De Silvestri, S.; Nisoli, M. [National Laboratory for Ultrafast and Ultraintense Optical Science - CNR-INFM Department of Physics, Politecnico, Piazza Leonardo da Vinci 32, 20133 Milan (Italy)
2006-05-15
In this work we report on the first experimental demonstration of selection of the long electron quantum paths in the process of high-order harmonic generation by phase-stabilized multiple-cycle light pulses. A complete experimental investigation of the role of intensity and carrier-envelope phase of the driving pulses on the spectral characteristics of the long quantum paths is performed. Simulations based on the nonadiabatic saddle-point method and on a complete nonadiabatic three-dimensional model reproduce the main features of the experimental results. The use of phase-stabilized driving pulses allows one to control, on an attosecond temporal scale, the spectral and temporal characteristics associated with the electron quantum paths involved in the harmonic generation process.
Lai, Ying-Cheng
2011-01-01
PHYSICAL REVIEW B 84, 035426 (2011) Abnormal electron paths induced by Klein tunneling in graphene quantum point contacts Rui Yang,1 Liang Huang,1,2 Ying-Cheng Lai,1,3,4 and Celso Grebogi4 1 School of Computational Physics and Complex Systems, and Key Laboratory for Magnetism and Magnetic Materials of MOE
On the origin of the electron blocking effect by an n-type AlGaN electron blocking layer
Zhang, Zi-Hui; Ji, Yun; Liu, Wei; Tiam Tan, Swee; Kyaw, Zabu; Ju, Zhengang; Zhang, Xueliang; Hasanov, Namig; Lu, Shunpeng; Zhang, Yiping; Zhu, Binbin; Wei Sun, Xiao, E-mail: exwsun@ntu.edu.sg, E-mail: volkan@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Volkan Demir, Hilmi, E-mail: exwsun@ntu.edu.sg, E-mail: volkan@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Department of Electrical and Electronics, Department of Physics, and UNAM-Institute of Material Science and Nanotechnology, Bilkent University, TR-06800, Ankara (Turkey)
2014-02-17
In this work, the origin of electron blocking effect of n-type Al{sub 0.25}Ga{sub 0.75}N electron blocking layer (EBL) for c+ InGaN/GaN light-emitting diodes has been investigated through dual-wavelength emission method. It is found that the strong polarization induced electric field within the n-EBL reduces the thermal velocity and correspondingly the mean free path of the hot electrons. As a result, the electron capture efficiency of the multiple quantum wells is enhanced, which significantly reduces the electron overflow from the active region and increases the radiative recombination rate with holes.
NASA Astrophysics Data System (ADS)
Persano Adorno, Dominique; Pizzolato, Nicola; Fazio, Claudio
2015-09-01
Within the context of higher education for science or engineering undergraduates, we present an inquiry-driven learning path aimed at developing a more meaningful conceptual understanding of the electron dynamics in semiconductors in the presence of applied electric fields. The electron transport in a nondegenerate n-type indium phosphide bulk semiconductor is modelled using a multivalley Monte Carlo approach. The main characteristics of the electron dynamics are explored under different values of the driving electric field, lattice temperature and impurity density. Simulation results are presented by following a question-driven path of exploration, starting from the validation of the model and moving up to reasoned inquiries about the observed characteristics of electron dynamics. Our inquiry-driven learning path, based on numerical simulations, represents a viable example of how to integrate a traditional lecture-based teaching approach with effective learning strategies, providing science or engineering undergraduates with practical opportunities to enhance their comprehension of the physics governing the electron dynamics in semiconductors. Finally, we present a general discussion about the advantages and disadvantages of using an inquiry-based teaching approach within a learning environment based on semiconductor simulations.
Inhibition of electron thermal conduction by electromagnetic instabilities. [in stellar coronas
NASA Technical Reports Server (NTRS)
Levinson, Amir; Eichler, David
1992-01-01
Heat flux inhibition by electromagnetic instabilities in a hot magnetized plasma is investigated. Low-frequency electromagnetic waves become unstable due to anisotropy of the electron distribution function. The chaotic magnetic field thus generated scatters the electrons with a specific effective mean free path. Saturation of the instability due to wave-wave interaction, nonlinear scattering, wave propagation, and collisional damping is considered. The effective mean free path is found self-consistently, using a simple model to estimate saturation level and scattering, and is shown to decrease with the temperature gradient length. The results, limited to the assumptions of the model, are applied to astrophysical systems. For some interstellar clouds the instability is found to be important. Collisional damping stabilizes the plasma, and the heat conduction can be dominated by superthermal electrons.
Thrapsaniotis, E. G. [52 Vianou street, 13671 Athens, Aharnes (Greece)
2012-08-15
We model in a fully quantum mechanical way the dynamics of an atom of one optically active electron interacting with a pulsed Fock state which is linearly polarized. We use path integral methods. We derive the system's sign solved propagator which gives full information on its dynamics. We apply our method to the ionization of atomic hydrogen by a one-photon pulsed Fock state and study the contribution of the electromagnetic fluctuations.
Tougaard, S.; Chorkendorff, I.
1987-05-01
The possibility of extracting absolute inelastic electron scattering cross sections K(T) (differential in energy loss T and path length) for solids from experimental electron spectra is studied. Assuming homogeneous scattering properties for the solid, a formula is found, which allows a direct determination of (lambdaL/(lambda+L))K(T) from a measured reflected electron-energy-loss spectrum (REELS) resulting from a monoenergetic beam of electrons incident on the surface of the solid. Here lambda is the inelastic electron mean free path and Lapprox. =2lambda/sub 1/ where lambda/sub 1/ is the transport mean free path for elastic electron scattering. The formula is applied to experimental REELS spectra of aluminum. The resulting cross sections are discussed in relation to a theoretical calculation based on dielectric-response theory. The determined cross sections are applied to remove the inelastic background signal from Mg--K..cap alpha..(h..nu..approx. =1254 eV) and synchrotron-radiation-excited (h..nu..approx. =250 eV) photoelectron spectra of aluminum. The resulting primary excitation spectra are discussed in relation to the results of existing procedures.
The path to ubiquitous and low-cost organic electronic appliances on plastic
Stephen R. Forrest
2004-01-01
Organic electronics are beginning to make significant inroads into the commercial world, and if the field continues to progress at its current, rapid pace, electronics based on organic thin-film materials will soon become a mainstay of our technological existence. Already products based on active thin-film organic devices are in the market place, most notably the displays of several mobile electronic
Tesoriero, A.J.; Liebscher, H.; Cox, S.E.
2000-01-01
The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards. Both the extent and rate of denitrification varied depending on the groundwater flow path. While little or no denitrification occurred in much of the upland portions of the aquifer, a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer. In contrast, a sharp shallow redox gradient is observed adjacent to a third-order stream as aerobic groundwater enters reduced sediments. An essentially complete loss of nitrate concurrent with increases in excess N2 provide evidence that denitrification occurs as groundwater enters this zone. Electron and mass balance calculations suggest that iron sulfide (e.g., pyrite) oxidation is the primary source of electrons for denitrification. Denitrification rate estimates were based on mass balance calculations using nitrate and excess N2 coupled with groundwater travel times. Travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon-based age dates. Denitrification rates were found to vary considerably between the two areas where denitrification occurs. Denitrification rates in the deep, upland portions of the aquifer were found to range from < 0.01 to 0.14 mM of N per year; rates at the redoxcline along the shallow flow path range from 1.0 to 2.7 mM of N per year. Potential denitrification rates in groundwater adjacent to the stream may be much faster, with rates up to 140 mM per year based on an in situ experiment conducted in this zone.The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards. Both the extent and rate of denitrification varied depending on the groundwater flow path. While little or no denitrification occurred in much of the upland portions of the aquifer, a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer. In contrast, a sharp shallow redox gradient is observed adjacent to a third-order stream as aerobic groundwater enters reduced sediments. An essentially complete loss of nitrate concurrent with increases in excess N2 provide evidence that denitrification occurs as groundwater enters this zone. Electron and mass balance calculations suggest that iron sulfide (e.g., pyrite) oxidation is the primary source of electrons for denitrification. Denitrification rate estimates were based on mass balance calculations using nitrate and excess N2 coupled with groundwater travel times. Travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon-based age dates. Denitrification rates were found to vary considerably between the two areas where denitrification occurs. Denitrification rates in the deep, upland portions of the aquifer were found to range from <0.01 to 0.14 mM of N per year; rates at the redoxcline along the shallow flow path range from 1.0 to 2.7 mM of N per year. Potential denitrification rates in groundwater adjacent to the stream may be much faster, with rates up to 140 mM per year based on an in situ experiment conducted in this zone.
NASA Astrophysics Data System (ADS)
Zhang, Cheng; Tarasenko, Viktor F.; Shao, Tao; Beloplotov, Dmitry V.; Lomaev, Mikhail I.; Wang, Ruixue; Sorokin, Dmitry A.; Yan, Ping
2015-03-01
Diffuse discharges preionized by runaway electrons can produce large-area homogeneous discharges at elevated pressures, which is an intriguing phenomenon in the physics of pulsed discharges. In this paper, runaway-electron-preionized diffuse discharge (REP DD) was obtained in a wide pressure range (0.05-0.25 MPa), and under certain conditions a positive streamer and a cathode-directed spark leader could be observed to propagate at some angles to the applied (background) electric field lines. For a 16-mm gap at an air pressure of 0.08-0.1 MPa, the percentage of pulses in which such propagation is observed is about 5%-50% of their total number, and in the other pulses such bent paths could not be observed because there is even no streamer or cathode-directed spark leader in diffuse discharges. In our opinion, such propagation of the positive streamer and the cathode-directed spark leader at some angle to the background electric field lines owes to different increase rates of the electron density in different regions of the discharge volume under REP DD conditions. Therefore, during the formation of a REP DD, the increase of the electron density is inhomogeneous and nonsimultaneous, resulting in an electron density gradient at the ionization wave front.
Feynman Path Integral Approach to Electron Diffraction for One and Two Slits: Analytical Results
ERIC Educational Resources Information Center
Beau, Mathieu
2012-01-01
In this paper we present an analytic solution of the famous problem of diffraction and interference of electrons through one and two slits (for simplicity, only the one-dimensional case is considered). In addition to exact formulae, various approximations of the electron distribution are shown which facilitate the interpretation of the results.…
Steepest Descent Path Study of Electron-Transfer Reactions Jianshu Cao
Cao, Jianshu
defines the diffusive solvent trajectory that has the highest probability to induce electron transfer for interpreting the kinetics and dynamics of chemical reactions.1-8 It is generally considered as a charac with the lowest energy. For electron transfer, however, the primary concern has been the rate of change
A path: from electroplating through lithographic masks in electronics to LIGA in MEMS
L. T. Romankiw
1997-01-01
This paper reviews the historic development of electroplating through lithographic mask technology in IBM starting from the 1960 s to the present day, the influence this technology has had on electronics, and the influence it may have in the future on HI-MEMS. The technology of electroplating through lithographic masks onto thin seed layers was born in electronics in the late
A Deterministic Transport Code for Space Environment Electrons
NASA Technical Reports Server (NTRS)
Nealy, John E.; Chang, C. K.; Norman, Ryan B.; Blattnig, Steve R.; Badavi, Francis F.; Adamczyk, Anne M.
2010-01-01
A deterministic computational procedure has been developed to describe transport of space environment electrons in various shield media. This code is an upgrade and extension of an earlier electron code. Whereas the former code was formulated on the basis of parametric functions derived from limited laboratory data, the present code utilizes well established theoretical representations to describe the relevant interactions and transport processes. The shield material specification has been made more general, as have the pertinent cross sections. A combined mean free path and average trajectory approach has been used in the transport formalism. Comparisons with Monte Carlo calculations are presented.
Ma, Jie; Yang, Jihui; Da Silva, J. L.F.; Wei, Su-Huai
2014-10-01
Using first-principles calculations, we study the diffusions of interstitial defects Cd, Cu, Te, and Cl in CdTe. We find that the diffusion behavior is strongly correlated with the electronic structure of the interstitial diffuser. For Cd and Cu, because the defect state is the non-degenerated slike state under Td symmetry, the diffusions are almost along the [111] directions between the tetrahedral sites, although the diffusion of Cu shows some deviation due to the s - d coupling. The diffusions of the neutral and charged Cd and Cu follow similar paths. However, for Te and Cl atoms, because the defect statemore »is the degenerated p-like state under Td symmetry, large distortions occur. Therefore, the diffusion paths are very different from those of Cd and Cu interstitials, and depend strongly on the charge states of the interstitial atoms. For Te, we find that the distortion is mostly stabilized by the crystal-field splitting, but for Cl, the exchange splitting plays a more important role.« less
Conditions for Aeronomic Applicability of the Classical Electron Heat Conduction Formula
NASA Technical Reports Server (NTRS)
Cole, K. D.; Hoegy, W. R.
1998-01-01
Conditions for the applicability of the classical formula for heat conduction in the electrons in ionized gas are investigated. In a fully ionised gas ( V(sub en) much greater than V(sub ei)), when the mean free path for electron-electron (or electron-ion) collisions is much larger than the characteristic thermal scale length of the observed system, the conditions for applicability break down. In the case of the Venus ionosphere this breakdown is indicated for a large fraction of the electron temperature data from altitudes greater than 180 km, for electron densities less than 10(exp 4)/cc cm. In a partially ionised gas such that V(sub en) much greater than V(sub ei) there is breakdown of the formula not only when the mean free path of electrons greatly exceeds the thermal scale length, but also when the gradient of neutral particle density exceeds the electron thermal gradient. It is shown that electron heat conduction may be neglected in estimating the temperature of joule heated electrons by observed strong 100 Hz electric fields when the conduction flux is limited by the saturation flux. The results of this paper support our earlier aeronomical arguments against the hypothesis of planetary scale whistlers for the 100 Hz electric field signal. In turn this means that data from the 100 Hz signal may not be used to support the case for lightning on Venus.
Silicon electronics on silk as a path to bioresorbable, implantable devices
NASA Astrophysics Data System (ADS)
Kim, Dae-Hyeong; Kim, Yun-Soung; Amsden, Jason; Panilaitis, Bruce; Kaplan, David L.; Omenetto, Fiorenzo G.; Zakin, Mitchell R.; Rogers, John A.
2009-09-01
Many existing and envisioned classes of implantable biomedical devices require high performance electronics/sensors. An approach that avoids some of the longer term challenges in biocompatibility involves a construction in which some parts or all of the system resorbs in the body over time. This paper describes strategies for integrating single crystalline silicon electronics, where the silicon is in the form of nanomembranes, onto water soluble and biocompatible silk substrates. Electrical, bending, water dissolution, and animal toxicity studies suggest that this approach might provide many opportunities for future biomedical devices and clinical applications.
Influence of emitted electrons transiting between surfaces on plasma-surface interaction
Campanell, Michael; Wang, Hongyue
2013-09-02
Emitted electrons are accelerated back into the plasma by the sheath. If their mean free path is large, they can propagate directly to another surface without suffering collisions. We analyze the effects of “transit” on plasma-surface interaction. When transit occurs, surfaces exchanging electrons are intricately coupled. All surfaces float more negatively than they would if the emission collisionally remixed with the bulk plasma. Asymmetries of the system drive a net “transit current” between the surfaces, which influences their potential difference. The larger the initial energy spread of the emitted electrons, the larger the potential difference.
Auger electron intensity variations in oxygen-exposed large grain polycrystalline silver
NASA Technical Reports Server (NTRS)
Lee, W. S.; Outlaw, R. A.; Hoflund, G. B.; Davidson, M. R.
1989-01-01
Auger electron spectroscopic studies of the grains in oxygen-charged polycrystal-line silver show significant intensity variations as a function of crystallographic orientation. These intensity variations were observed by studies of the Auger images and line scans of the different grains (randomly selected) for each silver transition energy. The results can be attributed to the diffraction of the ejected Auger electrons and interpreted by corresponding changes in the electron mean-free path for inelastic scattering and by oxygen atom accumulation in the subsurface. The subsurface (second layer) octahedral sites increased in size because of surface relaxation and serve as a stable reservoir for the dissolved oxygen.
Huliq:Breaking News Submit News Login Linear Nanotubes Offer Path To High-Performance Electronics
Rogers, John A.
, and corresponding author of a paper accepted for publication in the journal Nature Nanotechnology, and posted on its, on which th deposit thin strips of iron nanoparticles. The iron acts as a catalyst for the growth of carbon-Chrome.com Nanotechnology Products Agilent Instruments for Electronics Microscopy, Bio & Chemical Analysis www
NASA Astrophysics Data System (ADS)
Samolyuk, German; Daene, Markus; Stocks, George Malcolm; Caro, Jose Alfredo; Stoller, Roger
2015-03-01
High-entropy alloys (HEAs) have recently been developed as nontraditional alloy systems. They are composed of multiple elements at or near equiatomic ratios that form random solid solutions on simple underlying fcc or bcc lattices. In recent years HEAs have attracted significant attention due to their high strength, ductility and possible high radiation resistance. The complexity of the alloys results in very interesting electronic system behavior. Even in thermal equilibrium, disorder, especially extreme disorder, has important impacts on all electronic, atomic, and magnetic properties. In the current work we present results of first principle investigation of the electronic and magnetic properties of Ni-based multicomponent concentrated alloys using the coherent potential approximation (CPA). The influence of electronic structure modifications on the electron mean free path and values of electron-phonon coupling are calculated, together with preliminary results on similar quantities obtained by Time Dependent DFT. We discuss possible effects of tuning the mean free path and energy dissipation mechanisms to defect production and recombination in HEAs under irradiation.
Elastic electron backscattering from surfaces
Jablonski, A.; Gryko, J.; Kraaer, J.; Tougaard, S.
1989-01-01
Elastic electron backscattering from solid surfaces has been studied experimentally and theoretically. It has been shown that the recently published P/sub 1/ approximation gives an inadequate description. Much more realistic results are obtained from the Monte Carlo algorithm based on differential cross sections calculated within the partial-wave expansion method. Excellent agreement has been found between the calculated results and the experimental data obtained in the present work or taken from the literature. The present calculations seem to be valid for electron energies exceeding 200 eV and for low- and medium-atomic-number elements. The possibility of measuring the inelastic mean free path of electrons from the elastically backscattered intensity is discussed.
Downs, Robert T.
, and Heazlewoodite and Nickel Metal: A Case for the Importance of Ni-Ni Bond Paths for Electron Transport G. V. Gibbs and are related to its Ni-Ni metal bonded interactions and to the greater covalent character of its bonds. Local that the Ni-S and Ni-Ni bonded interactions are intermediate in character between ionic and covalent. I
Gibbs, G V.; Downs, R T.; Prewitt, C T.; Rosso, Kevin M.; Ross, Nancy; Cox, David F.
2005-12-24
Bond paths and the bond critical point properties (the electron density, ?, and the Hessian of ? at the bond critical point) have been calculated for the bonded interactions comprising the Ni?sulfide minerals millerite, vaesite and heazlewoodite and Ni metal. The experimental NiS bond lengths decrease linearly as the magnitudes of the properties at the bond critical point, bcp, increase in value. NiNi bond paths exist between the Ni atoms in heazlewoodite and millerite for NiNi separations that match the shortest NiNi separation in Ni metal, an indicator that the Ni atoms are bonded. NiNi bond paths also exist between the Ni atoms in bulk Ni metal. The bcp properties of the NiNi bonded interactions in Ni metal are virtually the same as those in the two Ni sulfides. NiNi bond paths are absent in vaesite where the NiNi separations are 60% longer than those in Ni metal. The bcp properties for the NiNi bonded interactions scatter along protractions of the NiS bond length?bcp property trends, suggesting that the two bonded interactions have similar characteristics. The NiNi bond paths radiate throughout Ni metal and the metallic heazlewoodite structures as continuous networks of interconnected NiNi bond paths whereas the NiNi paths in millerite, a highly covalent d,p metal, are restricted to isolated Ni3 rings of NiNi bond paths interconnected by S atoms. Electron transport in Ni metal and heazlewoodite is pictured as occurring along the bond paths, which behave as networks of atomic size wires that radiate in a contiguous circuit throughout the two structures. Unlike heazlewoodite, the electron transport in millerite is pictured as involving a cooperative hopping of the d?orbital electrons from the Ni3 rings comprising Ni3S9 clusters to Ni3 rings in adjacent clusters via the p?orbitals on the interconnecting S atoms. Vaesite, an insulator at low temperatures and a doped semiconductor at higher temperatures, lacks NiNi bond paths. The net charges conferred on the Ni and S atoms are about a quarter that of their nominal formal valences for the atoms in millerite and vaesite with the net charge on Ni increasing with increasing NiS bond length. The reduced net charge on the Ni atom in heazlewoodite is related to its NiNi metal bonded interactions and the contiguity of the NiNi bond paths.
Electronic thermal conductivity measurements in intrinsic graphene
NASA Astrophysics Data System (ADS)
Yi?en, S.; Tayari, V.; Island, J. O.; Porter, J. M.; Champagne, A. R.
2013-06-01
The electronic thermal conductivity of graphene and two-dimensional Dirac materials is of fundamental interest and can play an important role in the performance of nanoscale devices. We report the electronic thermal conductivity Ke in suspended graphene in the nearly intrinsic regime over a temperature range of 20-300 K. We present a method to extract Ke using two-point dc electron transport at low bias voltages, where the electron and lattice temperatures are decoupled. We find Ke ranging from 0.5 to 11 W/m K over the studied temperature range. The data are consistent with a model in which heat is carried by quasiparticles with the same mean free path and velocity as graphene's charge carriers.
Impact of Si growth rate on coherent electron transport in Si:P delta-doped devices
Goh, K. E. J. [Australian Research Council Centre of Excellence for Quantum Computer Technology and School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); Institute of Materials Research and Engineering, A-STAR (Agency for Science, Technology and Research), 3 Research Link, Singapore 117602 (Singapore); Simmons, M. Y. [Australian Research Council Centre of Excellence for Quantum Computer Technology and School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia)
2009-10-05
We address the impact of Si growth rate on electron transport in Si:P {delta}-doped devices encapsulated by low temperature Si molecular beam epitaxy. Si growth rates ranging from 0.05 to 2.2 A s{sup -1} were used in conjunction with 250 deg. C Si overgrowth. Using a combination of scanning tunneling microscopy and 4.2 K magnetotransport measurements, we find that high growth rates tend to degrade the crystal quality of the Si cap layer resulting in shorter electron mean free path and phase coherence length in such devices.
Gibbs, G V; Downs, R T; Prewitt, C T; Rosso, K M; Ross, N L; Cox, D F
2005-11-24
Bond paths and the bond critical point properties (the electron density (rho) and the Hessian of rho at the bond critical points (bcp's)) have been calculated for the bonded interactions comprising the nickel sulfide minerals millerite, NiS, vaesite, NiS(2), and heazlewoodite, Ni(3)S(2), and Ni metal. The experimental Ni-S bond lengths decrease linearly as the magnitudes of the properties each increases in value. Bond paths exist between the Ni atoms in heazlewoodite and millerite for the Ni-Ni separations that match the shortest separation in Ni metal, an indicator that the Ni atoms are bonded. The bcp properties of the bonded interactions in Ni metal are virtually the same as those in heazlewoodite and millerite. Ni-Ni bond paths are absent in vaesite where the Ni-Ni separations are 60% greater than those in Ni metal. The bcp properties for the Ni-Ni bonded interactions scatter along protractions of the Ni-S bond length-bcp property trends, suggesting that the two bonded interactions have similar characteristics. Ni-Ni bond paths radiate throughout Ni metal and the metallic heazlewoodite structures as continuous networks whereas the Ni-Ni paths in millerite, a p,d-metal displaying ionic and covalent features, are restricted to isolated Ni(3) rings. Electron transport in Ni metal and heazlewoodite is pictured as occurring along the bond paths, which behave as networks of atomic size wires that radiate in a contiguous circuit throughout the two structures. Unlike heazlewoodite, the electron transport in millerite is pictured as involving a cooperative hopping of the d-orbital electrons from the Ni(3) rings comprising Ni(3)S(9) clusters to Ni(3) rings in adjacent clusters via the p-orbitals on the interconnecting S atoms. Vaesite, an insulator at low temperatures and a doped semiconductor at higher temperatures, lacks Ni-Ni bond paths. The net charges conferred on the Ni and S atoms are about a quarter of their nominal charges for the atoms in millerite and vaesite with the net charge on Ni increasing with increasing Ni-S bond length. Reduced net charges are observed on the Ni atoms in heazlewoodite and are related to its Ni-Ni metal bonded interactions and to the greater covalent character of its bonds. Local energy density and bond critical point properties of the electron density distributions indicate that the Ni-S and Ni-Ni bonded interactions are intermediate in character between ionic and covalent. PMID:16853830
Carbon nanotubes: Electrons in one dimension
NASA Astrophysics Data System (ADS)
Bockrath, Marc William
The work presented in this thesis will discuss transport measurements on individual single-walled nanotubes (SWNTs) and SWNT bundles. SWNTs, which are essentially rolled-up sheets of graphite, are either one-dimensional (1D) metals or 1D semiconductors depending on how they are rolled-up. Measurements on both metallic and semiconducting SWNTs will be presented. Chapter 1 will present an introductory overview to the thesis, discussing prior related experimental work and introducing basic concepts that are used in subsequent chapters. Chapter 2 discusses the experimental methods we have used to study transport in SWNTs. Chapters 3 and 4 discuss low temperature measurements of metallic SWNTs. Chapter 3 will discuss the low temperature behavior of the conductance of a SWNT bundle, or rope, that shows quantum mechanical effects resulting from the finite size of the sample. Chapter 4 will discuss how these finite size effects can be used to experimentally study the quantum level structure in metallic nanotubes and the effects of an applied magnetic field. In chapters 5 and 6, we discuss transport measurements of semiconducting SWNTs. In chapter 5, we show that semiconducting SWNT's can be doped with potassium. Chapter 6 presents experiment and theory that indicate that the elastic mean free path in metallic tubes is far longer than in semiconducting tubes. Chapters 7 and 8 address the effects of electron-electron (e-e) interactions on the transport properties of metallic SWNTs. Chapter 7 discusses some theoretical aspects of 1D wires when e-e interactions are taken account, giving a simplified picture of the Luttinger-liquid state expected for a 1D system of interacting electrons. Finally, chapter 8 will discuss measurements on metallic samples with extremely long mean free paths. These experiments show evidence of this Luttinger-liquid behavior, in which the electron-electron interactions lead to a qualitatively different ground state than what would be expected with Fermi-liquid theory.
Anomalous dephasing scattering rate of two-dimensional electrons in double quantum well structures
NASA Astrophysics Data System (ADS)
Pagnossin, I. R.; Meikap, A. K.; Lamas, T. E.; Gusev, G. M.; Portal, J. C.
2008-09-01
The results on the measurement of electrical conductivity and magnetoconductivity of a GaAs double quantum well between 0.5 and 1.1 K are reported. The zero magnetic-field conductivity is well described from the point of view of contributions made by both the weak localization and electron-electron interaction. At low field and low temperature, the magnetoconductivity is dominated by the weak localization effect only. Using the weak localization method, we have determined the electron dephasing times ?? and tunneling times ?t . Concerning tunneling, we concluded that ?t presents a minimum around the balance point; concerning dephasing, we observed an anomalous dependence on temperature and conductivity (or elastic mean free path) of ?? . This anomalous behavior cannot be explained in terms of the prevailing concepts for the electron-electron interaction in high-mobility two-dimensional electron systems.
Eliashberg Function in an Amorphous Simple Metal Alloy Sn1-Xcux Determined by Electron-Tunneling
WATSON, PW; Naugle, Donald G.
1995-01-01
of the phonon wave vector and electron mean free path l. Microscopic calculations of the sound attenuation have reproduced the standard Pippard result, but the question regarding the low-frequency behavior of the Eliashberg func- tion u F(ru) has been more... confused. Bergmann predicted that n F(ru) would be proportional to ro at low frequency on the basis of phase space arguments. Subsequently, Poon and Geballe and Meisel and Cote obtained an expression for a F for low frequencies which was identical...
A new MetaPath information system was developed through a collaborative effort between the Laboratory of Mathematical Chemistry (Bourgas, Bulgaria), EPA’s Office of Research and Development (NHEERL, MED, Duluth, MN and NERL, ERD, Athens, GA), and EPA’s Office of Chemical Safety a...
A new MetaPath information system was developed through a collaborative effort between the Laboratory of Mathematical Chemistry (Bourgas, Bulgaria), EPA?s Office of Research and Development (NHEERL, MED, Duluth, MN and NERL, ERD, Athens, GA), and EPA?s Office of Chemical Safety a...
ERIC Educational Resources Information Center
Shore, M. L.
1980-01-01
There are many uses for the shortest path algorithm presented which are limited only by our ability to recognize when a problem may be converted into the shortest path in a graph representation. (Author/TG)
A Deterministic Computational Procedure for Space Environment Electron Transport
NASA Technical Reports Server (NTRS)
Nealy, John E.; Chang, C. K.; Norman, Ryan B.; Blattnig, Steve R.; Badavi, Francis F.; Adamcyk, Anne M.
2010-01-01
A deterministic computational procedure for describing the transport of electrons in condensed media is formulated to simulate the effects and exposures from spectral distributions typical of electrons trapped in planetary magnetic fields. The primary purpose for developing the procedure is to provide a means of rapidly performing numerous repetitive transport calculations essential for electron radiation exposure assessments for complex space structures. The present code utilizes well-established theoretical representations to describe the relevant interactions and transport processes. A combined mean free path and average trajectory approach is used in the transport formalism. For typical space environment spectra, several favorable comparisons with Monte Carlo calculations are made which have indicated that accuracy is not compromised at the expense of the computational speed.
Simulation of electron transport during electron-beam-induced deposition of nanostructures
Jeschke, Harald O; Valentí, Roser
2013-01-01
Summary We present a numerical investigation of energy and charge distributions during electron-beam-induced growth of tungsten nanostructures on SiO2 substrates by using a Monte Carlo simulation of the electron transport. This study gives a quantitative insight into the deposition of energy and charge in the substrate and in the already existing metallic nanostructures in the presence of the electron beam. We analyze electron trajectories, inelastic mean free paths, and the distribution of backscattered electrons in different compositions and at different depths of the deposit. We find that, while in the early stages of the nanostructure growth a significant fraction of electron trajectories still interacts with the substrate, when the nanostructure becomes thicker the transport takes place almost exclusively in the nanostructure. In particular, a larger deposit density leads to enhanced electron backscattering. This work shows how mesoscopic radiation-transport techniques can contribute to a model that addresses the multi-scale nature of the electron-beam-induced deposition (EBID) process. Furthermore, similar simulations can help to understand the role that is played by backscattered electrons and emitted secondary electrons in the change of structural properties of nanostructured materials during post-growth electron-beam treatments. PMID:24367747
NSDL National Science Digital Library
Perry Samson
This website catalogs all the tornado paths in the United States since 1950. The tornado path data is overlaid onto a Google Maps base for easy browsing and manipulation of the map view. Clicking on individual tornados provides the user with information such as its Fujita rating, the amount of damage caused by the tornado, the size of the path that the tornado made, and the length of time the tornado was on the ground.
Branching and path-deviation of positive streamers resulting from statistical photon transport
NASA Astrophysics Data System (ADS)
Xiong, Zhongmin; Kushner, Mark J.
2014-12-01
The branching and change in direction of propagation (path-deviation) of positive streamers in molecular gases such as air likely require a statistical process which perturbs the head of the streamer and produces an asymmetry in its space charge density. In this paper, the mechanisms for path-deviation and branching of atmospheric pressure positive streamer discharges in dry air are numerically investigated from the viewpoint of statistical photon transport and photoionization. A statistical photon transport model, based on randomly selected emitting angles and mean-free-path for absorption, was developed and embedded into a fluid-based plasma transport model. The hybrid model was applied to simulations of positive streamer coaxial discharges in dry air at atmospheric pressure. The results show that secondary streamers, often spatially isolated, are triggered by the random photoionization and interact with the thin space charge layer (SCL) of the primary streamer. This interaction may be partly responsible for path-deviation and streamer branching. The general process consists of random remote photo-electron production which initiates a back-traveling electron avalanche, collision of this secondary avalanche with the primary streamer and the subsequent perturbation to its SCL. When the SCL is deformed from a symmetric to an asymmetric shape, the streamer can experience an abrupt change in the direction of propagation. If the SCL is sufficiently perturbed and essentially broken, local maxima in the SCL can develop into new streamers, leading to streamer branching. During the propagation of positive streamers, this mechanism can take place repetitively in time and space, thus producing multi-level branching and more than two branches within one level.
Inelastic-electron-scattering cross sections for Si, Cu, Ag, Au, Ti, Fe, and Pd
Tougaard, S.; Kraaer, J. )
1991-01-15
Inelastic-scattering cross sections of 300--10 000-eV electrons in Si, Ti, Fe, and Pd and of 300--2000-eV electrons in Cu, Ag, and Au have been investigated theoretically and experimentally. The product of the inelastic mean free path and the cross section were determined experimentally through an analysis, based on a recent formula, of reflection electron-energy-loss spectra. To study energies above 2000 eV a special experimental setup was developed. Theoretical cross sections were determined through a dielectric-response description of the solid-electron interaction using Drude-Lindhard model dielectric functions. At high energies, good agreement is observed between theoretically and experimentally determined cross sections. At lower energies differences are observed. These are discussed partly in terms of a breakdown of the dielectric model used, and partly surface excitations.
A Hot-Electron Far-Infrared Direct Detector
NASA Technical Reports Server (NTRS)
Karasik, B. S.; McGrath, W. R.; LeDuc, H. G.
2000-01-01
A new approach is proposed to improve the sensitivity of direct-detection bolometers at millimeter, submillimeter and far-infrared wavelengths. The idea is to adjust a speed of the thermal relaxation of hot-electrons in a nanometer size normal metal or super-conductive transition edge bolometer by controlling the elastic electron mean free path. If the bolometer contacts are made of a superconductor with high critical temperature (Nb, Pb etc.) then the thermal diffusion into the contacts is absent because of the Andreev's reflection and the electron-phonon relaxation is the only mechanism for heat removal. The relaxation rate should behave as T(sup 4)l at subkelvin temperatures (l is the electron elastic mean free path) and can be reduced by factor of 10-100 by decreasing l. Then an antenna- or waveguide-coupled bolometer with a time constant about 10(exp -3) to 10(exp -5) s at T approximately equals 0.1-0.3 K will exhibit photon-noise limited performance in millimeter and submillimeter range. The choice of the bolometer material is a tradeoff between a low electron heat capacity and fabrication. A state-of-the-art bolometer currently offers NEP = 10(exp -17) W(Square root of (Hz)) at 100 mK along with a approximately equals 2 msec time constant. The bolometer we propose will have a figure-of-merit, NEP(square root (r)), which is 10(exp 3) times smaller. This will allow for a tremendous increase in speed which will have a significant impact for observational mapping applications. Alternatively, the bolometer could operate at higher temperature with still superior sensitivity. This device can significantly increase a science return and reduce the cost for future observational missions. This research was performed by the Center for Space Microelectronics Technology, Jet Propulsion Laboratory, California Institute of Technology, and was sponsored by NASA, Office of Space Science.
Total cross sections for positron and electron scattering from pyrimidine
NASA Astrophysics Data System (ADS)
Zecca, A.; Chiari, L.; García, G.; Blanco, F.; Trainotti, E.; Brunger, M. J.
2010-11-01
In this paper we report original measurements of total cross sections for positron scattering from the important biomolecule pyrimidine. The energy range of these measurements was 0.3-45 eV, while the energy resolution was ~260 meV. In addition, we report theoretical results, calculated within the independent atom-screened additivity rule (IAM-SCAR) formalism, for the corresponding electron impact total cross sections. In that case the energy range is 1-10 000 eV. Total cross sections are very important input data for codes that seek to simulate charged-particle tracks in matter, as they define the mean-free path between collisions. As the present data and computations are to the best of our knowledge the first total cross sections to be reported for either positron or electron scattering from pyrimidine, they fill an important void in our available knowledge in the literature.
Monte Carlo simulation of electron backscattering from compounds with low mean atomic number.
Howell, P G; Boyde, A
1998-01-01
This paper reports a Monte Carlo simulation where a single atom scattering model is adopted. The element taking part in each electron-atom interaction is selected on the basis of its contribution either to the total elastic cross section or to the electron's mean free path. Both Rutherford and Mott scattering are considered, with the continuous slowing down process of Bethe used to calculate the energy loss to the system. The backscattered electron coefficients show good agreement with experimental results from a large group of low atomic number materials when using a model which selects the scattering atom by its contribution to the whole compound calculated from its atomic fraction of the total elastic cross-section. PMID:9493414
Electron Transport and Band Structure in Phosphorus-Doped Polycrystalline Silicon Films
Young, D. L.; Branz, H. M.; Liu, F.; Reedy, R.; To, B.; Wang, Q.
2009-01-01
We study transport mechanisms, effective mass, and band structure by measuring the resistivity, Hall, and Seebeck and Nernst coefficients in heavily phosphorus-doped polycrystalline silicon films made by thermal crystallization of amorphous silicon. We observe a change in transport mechanism which results in an increase in electron mobility from 10% to 80% of the single-crystal silicon mobility as the carrier concentration increases from 10{sup 19} to 10{sup 20} cm{sup -3}. Our measurements of effective mass at the Fermi level indicate that as the carrier concentration increases, there is a shift from impurity-band transport to conduction-band transport, and that the electron effective mass is lower in the impurity band than in the conduction band of Si. The shift to conduction-band transport improves electron mobility with carrier density by improving intragrain carrier mean free path lengths and relaxation times.
NASA Astrophysics Data System (ADS)
Uhlisch, D.; Appenzeller, J.; Tietze, M. F.; Schäpers, Th.; Hollfelder, M.; Lüth, H.
1998-01-01
Ballistic transport of hot electrons was used to characterize the relevant transport lengths in the two-dimensional electron gas formed in an In0.53Ga0.47As/In0.76Ga0.24As/InP heterostructure. This method allows a distinction between impurity scattering, alloy scattering, and electron-electron scattering. Using adjacent point contacts separated by only a few hundred nanometers, we determine the ballistic mean free path for cold electrons to be approximately Lbal=970 nm. Fitting the electron excess energy-dependent peak height of the focusing maxima, good agreement can be obtained by including the energy dependence of ionized impurity scattering. The mean distance between impurities Limp is determined to be approximately 1.2 ?m and the alloy scattering length Lalloy is 4.5 ?m.
McLaughlin, Kevin; Coderre, Sylvain
2015-08-01
As medical trainees gain clinical experience, they increasingly form diagnoses based on their association with predisposing conditions and clinical features rather than pathophysiological explanations. Knowledge of these associations is housed as scripts in long-term memory, and data from the expertise literature imply that expert performance is largely explained by experts possessing more accurate scripts. In rotation-based clerkships, students typically spend a short period of time involved in the care of patients and are frequently deprived of the opportunity to observe the evolution and resolution of illness and the correct association between predisposing conditions, clinical features, and final diagnosis that is required for accurate script formation. Thanks to the introduction of an electronic health record (EHR), students now have the opportunity to track former patients until the final diagnosis and response to treatment is known. Although former patients are unlikely to benefit from being tracked by medical students, this type of learning experience may help students form more accurate scripts and, thus, improve their diagnostic performance on subsequent patients. But, because the purpose of EHRs is to improve clinical care of patients, is it ethically acceptable to allow students no longer involved in the care of patients to use these data solely for the purposes of learning? In this Commentary, the authors highlight the potential for ethical conflict whenever clinical care and teaching mingle, and discuss how these competing interests can still be balanced in the face of advancing technology by applying universal ethical principles and following the advice of Hippocrates. PMID:25565264
Shemesh, Dorit; Domcke, Wolfgang
2011-07-11
The capped dipeptides Ac-L-Phe-Xxx-NH(2) , Xxx=L-Ala, D-Ala, Aib, where Aib (aminoisobutyric acid) is a non-chiral amino acid, have been investigated by means of UV/IR double-resonance spectroscopy in supersonic jets and density functional theory calculations by Gloaguen et al. [Phys. Chem. Chem. Phys. 2007, 9, 4491]. The UV and IR spectra of five different species were observed and their structures assigned by comparison with calculated vibrational frequencies in the NH-stretching region. The peptides with two chiral residues can form homochiral or heterochiral species. In addition, ?-turns exist as two helical forms (?(D), ?(L)) of opposite handedness. Herein, we explore the excited-state potential-energy surfaces of these dipeptides with ab initio calculations. Vertical and adiabatic excitation energies, excited-state reaction paths and conical intersections are characterized with the ADC(2) propagator method. It is shown that electron/proton transfer along the hydrogen bond of the ?-turn gives rise to efficient radiationless deactivation of the (1)??* state of the chromophore via several conical intersections. While the homo/hetero chirality of the residues appears to have a negligible effect on the photophysical dynamics, we found evidence that the ?(L) conformers may have shorter excited-state lifetimes (and thus higher photostability) than the ?(D) conformers. PMID:21488142
Preferential Path Profiling: Compactly Numbering Interesting Paths
Chilimbi, Trishul
Preferential Path Profiling: Compactly Numbering Interesting Paths Kapil Vaswani Indian Institute@microsoft.com Trishul M. Chilimbi Microsoft Research trishulc@microsoft.com Abstract Path profiles provide a more preferential path profiling (PPP), that reduces the overhead of path profiling. PPP leverages the observation
Electron and light emission from island metal films and generation of hot electrons in nanoparticles
NASA Astrophysics Data System (ADS)
Fedorovich, R. D.; Naumovets, A. G.; Tomchuk, P. M.
2000-04-01
We review experimental and theoretical works devoted to electron and photon emission from island metal films (IMFs) representing ensembles of small metal particles deposited onto a dielectric substrate and coupled via penetrable potential barriers. Electrons and photons are emitted when the films are energized by passage of current through them or by laser irradiation. In either case the primary recipient of the energy is the electron gas, which can be heated up to temperatures much higher than the particle lattice temperature. A theoretical substantiation of the model of hot electrons in nanoparticles is presented. The major physical factor that permits generation of hot electrons in IMFs is the dramatic reduction (by orders of magnitude) of the electron-lattice energy transfer in the particles whose size is smaller than the mean free path of electrons in the volume. In such particles with a ballistic motion of electrons, the energy is being lost mainly in surface scattering acts which are less effective in energy transfer than generation of volume phonons. Thus, the electron temperature can become substantially higher than the lattice temperature provided the absorbed power density is high enough and the lattice of the island is intensively cooled by the substrate. The model of hot electrons is used to interpret experimental data. Non-equilibrium electron heating in IMFs can be observed even under stationary conditions, so the island metal films basically differ in their electronic properties from continuous metal films and bulk metals where hot electrons can be obtained only for very short times (?10 -11 s). Thus, the island metal films represent an important variety of nanomaterials having rather unusual physical properties. IMFs can be utilized to fabricate cathodes having interesting application potentialities in vacuum microelectronics, information display technologies and infrared image conversion. Hot electrons generated in nanoparticles may also play a significant role in various dispersed systems exposed to energy fluxes.
NSDL National Science Digital Library
Cynthia Ann Radle (McCullough High School REV)
1995-06-30
Students follow several pathways using anatomical directions on a simulated "body" produced from a copy of a school building's fire evacuation plan. The main hallways are designated as major blood vessels and the various areas of the school, the head, chest, abdomen, etc. Students complete several pathways using anatomical terms as directions. For example, one of my paths begins, "Ex- ot-, ad- superior, ecto- derm-, peri-frontal, circum- rhino-, " which loosely means, exit the ear, go to the superior region, outside the skin, around the frontal region, around the nose. At the end of each path I leave a clue that lets me know the students actually made it. The combined clues form a sentence.
NASA Astrophysics Data System (ADS)
Bykov, A. A.; Strygin, I. S.; Marchishin, I. V.; Goran, A. V.
2014-05-01
Nonlinear magnetotransport of two-dimensional electrons in square antidot lattices prepared on the basis of selectively doped GaAs/AlAs heterostructures with the period that is much less than the electron mean free path in the initial GaAs quantum wells but is much larger than their Fermi wavelength has been studied. It has been shown that the character of the nonlinear transport of the two-dimensional electrons in the lateral lattices under study changes from classical to quantum with the decrease in the antidot radius. It has been found that the quantum lifetime increases in the magnetic field corresponding to the condition of equality of the cyclotron diameter of two-dimensional electrons and the antidot lattice period.
Differential surface and volume excitation probability of medium-energy electrons in solids
NASA Astrophysics Data System (ADS)
Werner, Wolfgang S. M.
2006-08-01
A procedure is developed to rigorously decompose experimental loss spectra of medium-energy (50eV-50keV) electrons reflected from solid surfaces into contributions due to surface and volume electronic excitations. This can be achieved by analysis of two spectra acquired under different experimental conditions, e.g., measured at two different energies and/or geometrical configurations. The input parameters of this procedure comprise the elastic scattering cross section and the inelastic mean free path for volume scattering. The (normalized) differential inelastic mean free path as well as the differential surface excitation probability are retrieved by this procedure. Reflection electron energy loss spectroscopy (REELS) data for Si, Cu, and Au are subjected to this procedure and the retrieved differential surface and volume excitation probabilities are compared with data from the literature. The present results are compared with earlier proposed procedures in which surface excitations are neglected, in particular the deconvolution formula by Tougaard and Chorkendorff [Phys. Rev. B 35, 6570 (1987)] that is frequently employed for this purpose. It is shown that application of the latter procedure to realistic REELS spectra (that always contain a significant contribution due to surface excitations) does not lead to a single scattering loss distribution of any kind, but rather yields a mixture of contributions of electrons that have suffered an arbitrary number of surface and bulk collisions. Therefore, quantitative interpretation of the retrieved loss distributions is troublesome. On the other hand, the results using the procedure proposed in the present work exhibit satisfactory quantitative agreement with theoretical calculations and verify the commonly accepted model for medium energy electron transport in solids with unprecedented detail.
Differential probability for surface and volume electronic excitations in Fe, Pd and Pt
NASA Astrophysics Data System (ADS)
Werner, Wolfgang S. M.
2005-08-01
The normalized differential mean free path for volume scattering and the differential surface excitation probability for medium energy electrons travelling in Fe, Pd and Pt are extracted from reflection electron energy loss spectra (REELS). This was achieved by means of a recently introduced procedure in which two REELS spectra taken under different experimental conditions are simultaneously deconvoluted. In this way, it is possible to obtain the unique reconstruction for the surface and volume single scattering loss distribution. The employed method is compared with a procedure that is frequently used for this purpose [S. Tougaard, I. Chorkendorff, Phys. Rev. B 35 (1987) 6570]. It is shown, both theoretically and through analysis of model spectra as well as experimental data that the approach by Tougaard and Chorkendorff does not result in a single scattering loss distribution. Rather, it gives a mixture of surface, bulk and mixed scattering of any order.
Time-resolved electron kinetics in swift heavy ion irradiated solids
NASA Astrophysics Data System (ADS)
Medvedev, N. A.; Rymzhanov, R. A.; Volkov, A. E.
2015-09-01
The event-by-event Monte Carlo model, TREKIS, was developed to describe the excitation of the electron subsystems of various solids by a penetrating swift heavy ion (SHI), the spatial spreading of generated fast electrons, and secondary electron and hole cascades. Complex dielectric function formalism is used to obtain relevant cross sections. This allows the recognition of fundamental effects resulting from the collective response of the electron subsystem of a target for excitation that is not possible within the binary collision approximation of these cross sections, e.g. the differences in the electronic stopping of an ion and in the electron mean free paths for different structures (phases) of a material. A systematic study performed with this model for different materials (insulators, semiconductors and metals) revealed effects which may be important for an ion track: e.g. the appearance of a second front of excess electronic energy propagation outwards from the track core following the primary front of spreading of generated electrons. We also analyze how the initial ballistic spatial spreading of fast electrons generated in a track turns to the diffusion ~10 fs after ion passage. Detailed time-resolved simulations of electronic subsystem kinetics helped in understanding the reasons behind enhanced silicon resistance to SHI irradiation in contrast to easily produced damage in this material by femtosecond laser pulses. We demonstrate that the fast spreading of excited electrons from the track core on a sub-100 fs timescale prevents the Si lattice from nonthermal melting in a relaxing SHI track.
Electronic spectrum of twisted bilayer graphene
NASA Astrophysics Data System (ADS)
Sboychakov, A. O.; Rakhmanov, A. L.; Rozhkov, A. V.; Nori, Franco
2015-08-01
We study the electronic properties of twisted bilayer graphene in the tight-binding approximation. The interlayer hopping amplitude is modeled by a function which depends not only on the distance between two carbon atoms, but also on the positions of neighboring atoms as well. Using the Lanczos algorithm for the numerical evaluation of eigenvalues of large sparse matrices, we calculate the bilayer single-electron spectrum for commensurate twist angles in the range 1??? ?30? . We show that at certain angles ? greater than ?c?1 .89? the electronic spectrum acquires a finite gap, whose value could be as large as 80 meV. However, in an infinitely large and perfectly clean sample the gap as a function of ? behaves nonmonotonously, demonstrating exponentially large jumps for very small variations of ? . This sensitivity to the angle makes it impossible to predict the gap value for a given sample, since in experiment ? is always known with certain error. To establish the connection with experiments, we demonstrate that for a system of finite size L ˜ the gap becomes a smooth function of the twist angle. If the sample is infinite, but disorder is present, we expect that the electron mean-free path plays the same role as L ˜. In the regime of small angles ?
NASA Astrophysics Data System (ADS)
Pilgrim, Ian; Scannell, Billy; See, Andrew; Montgomery, Rick; Morse, Peter; Fairbanks, Matt; Marlow, Colleen; Linke, Heiner; Farrer, Ian; Ritchie, David; Hamilton, Alex; Micolich, Adam; Eaves, Laurence; Taylor, Richard
2013-03-01
Since the 1950s, materials scientists have pursued the fabrication of solid-state heterostructure (HS) devices of sufficient purity to replicate electron interference effects originally observed in vacuum. The ultimate goal of HS engineering is to create a semiconductor ``billiard table'' in which electrons travel ballistically in a 2-D plane--that is, with scattering events minimized such that the electron's mean free path exceeds the device size. For the past two decades, the modulation-doped (MD) HS architecture has yielded devices supporting very high electron mobilities. In this architecture, ionized dopants are spatially removed from the plane of the electrons, such that their influence on electron trajectories is felt through presumably negligible small-angle scattering events. However, we observe that thermally induced charge redistribution in the doped layers of AlGaAs/GaAs and GaInAs/InP MD heterostructures significantly alters electron transport dynamics as measured by magnetoconductance fluctuations. This result demonstrates that small-angle scattering plays a far larger role than expected in influencing conduction properties. Since the 1950s, materials scientists have pursued the fabrication of solid-state heterostructure (HS) devices of sufficient purity to replicate electron interference effects originally observed in vacuum. The ultimate goal of HS engineering is to create a semiconductor ``billiard table'' in which electrons travel ballistically in a 2-D plane--that is, with scattering events minimized such that the electron's mean free path exceeds the device size. For the past two decades, the modulation-doped (MD) HS architecture has yielded devices supporting very high electron mobilities. In this architecture, ionized dopants are spatially removed from the plane of the electrons, such that their influence on electron trajectories is felt through presumably negligible small-angle scattering events. However, we observe that thermally induced charge redistribution in the doped layers of AlGaAs/GaAs and GaInAs/InP MD heterostructures significantly alters electron transport dynamics as measured by magnetoconductance fluctuations. This result demonstrates that small-angle scattering plays a far larger role than expected in influencing conduction properties. Funded by the Office of Naval Research, US Air Force, Australian Research Council, and Research Corporation for Science Advancement
Doswell III, Charles A.
: The 1925 Tri- State tornado damage path and associated storm system. Electronic J. Severe Storms Meteor., 8 (2), 133. 1 The 1925 Tri-State Tornado Damage Path and Associated Storm System ROBERT H. JOHNS May 2013) ABSTRACT The "Tri-State tornado" event of 18 March 1925, with an official death toll of 695
Electron heat transport in a steep temperature gradient
NASA Astrophysics Data System (ADS)
Rogers, J. H.; De Groot, J. S.; Abou-Assaleh, Z.; Matte, J. P.; Johnston, T. W.; Rosen, M. D.
1989-04-01
Temporal and spatial measurements of electron heat transport are made in the University of California Davis AURORA device (J. H. Rogers, Ph.D. dissertation, University of California, Davis, 1987). In AURORA, a microwave pulse heats a region of underdense, collisional, plasma (n/ncr ?1, where ncr =1.8×1010 cm-3 is the critical density, Te0 ?0.15 eV, and the electron scattering mean free path ???2 cm). In this region, strong thermal heating (Tc ?0.7 eV) as well as suprathermal heating (Th?3 eV) is observed. The strong heating results in a steep temperature gradient that violates the approximations of classical heat diffusion theory (LT/???3 for thermal electrons, where LT=Tc(?Tc/?z)-1 is the cold electron temperature scale length. The time evolution of the electron temperature profile is measured using Langmuir probes. The measured relaxation of the temperature gradient after the microwave pulse is compared to calculations using the Fokker-Planck International code [Phys. Rev. Lett. 49, 1936 (1982)] and the multigroup, flux-limited, target design code lasnex [Comm. Plasma Phys. 2, 51 (1975)]. The electron distribution function at the end of the microwave pulse is used as initial conditions for both codes. The Fokker-Planck calculations are found to agree very well with the measurements. However, the flux-limited diffusion calculations do not agree with the measurements for any value of the flux limiter.
QUANTUM ELECTRONICS Probing Johnson noise and ballistic
Walsworth, Ronald L.
QUANTUM ELECTRONICS Probing Johnson noise and ballistic transport in normal metals with a single-crystal films, indicative ofa substantial deviation from Ohm's law at length scales below the electron mean free of electrons in the metal, indicating that under the appropriate conditions, nearby electrodes may be used
Kolkowitz, S; Safira, A; High, A A; Devlin, R C; Choi, S; Unterreithmeier, Q P; Patterson, D; Zibrov, A S; Manucharyan, V E; Park, H; Lukin, M D
2015-03-01
Thermally induced electrical currents, known as Johnson noise, cause fluctuating electric and magnetic fields in proximity to a conductor. These fluctuations are intrinsically related to the conductivity of the metal. We use single-spin qubits associated with nitrogen-vacancy centers in diamond to probe Johnson noise in the vicinity of conductive silver films. Measurements of polycrystalline silver films over a range of distances (20 to 200 nanometers) and temperatures (10 to 300 kelvin) are consistent with the classically expected behavior of the magnetic fluctuations. However, we find that Johnson noise is markedly suppressed next to single-crystal films, indicative of a substantial deviation from Ohm's law at length scales below the electron mean free path. Our results are consistent with a generalized model that accounts for the ballistic motion of electrons in the metal, indicating that under the appropriate conditions, nearby electrodes may be used for controlling nanoscale optoelectronic, atomic, and solid-state quantum systems. PMID:25636797
Dicalcium nitride as a two-dimensional electride with an anionic electron layer.
Lee, Kimoon; Kim, Sung Wng; Toda, Yoshitake; Matsuishi, Satoru; Hosono, Hideo
2013-02-21
Recent studies suggest that electrides--ionic crystals in which electrons serve as anions--are not exceptional materials but rather a generalized form, particularly under high pressure. The topology of the cavities confining anionic electrons determines their physical properties. At present, reported confining sites consist only of zero-dimensional cavities or weakly linked channels. Here we report a layered-structure electride of dicalcium nitride, Ca(2)N, which possesses two-dimensionally confined anionic electrons whose concentration agrees well with that for the chemical formula of [Ca(2)N](+)·e(-). Two-dimensional transport characteristics are demonstrated by a high electron mobility (520?cm(2)?V(-1)?s(-1)) and long mean scattering time (0.6?picoseconds) with a mean free path of 0.12?micrometres. The quadratic temperature dependence of the resistivity up to 120?Kelvin indicates the presence of an electron-electron interaction. A striking anisotropic magnetoresistance behaviour with respect to the direction of magnetic field (negative for the field perpendicular to the conducting plane and positive for the field parallel to it) is observed, confirming diffusive two-dimensional transport in dense electron layers. Additionally, band calculations support confinement of anionic electrons within the interlayer space, and photoemission measurements confirm anisotropic low work functions of 3.5 and 2.6 electronvolts, revealing the loosely bound nature of the anionic electrons. We conclude that Ca(2)N is a two-dimensional electride in terms of [Ca(2)N](+)·e(-). PMID:23364689
Generation and accretion of electrons in complex plasmas with cylindrical particles
Sodha, Mahendra Singh; Misra, Shikha [Disha Institute of Management and Technology, Satya Vihar, Vidhan Sabha-Chandrakhuri Marg, Mandir Hasaud, Raipur 492101, Chattisgarh (India); Mishra, S. K. [Department of Education Building, University of Lucknow, Lucknow 226007 (India)
2009-12-15
This paper presents an analytical model for the physical understanding of the charging of cylindrical dust particles in an open complex plasma system. Two different mechanisms, viz., thermionic emission and photoelectric emission have been considered for the electron generation from the charged cylindrical dust particles; the corresponding expressions for the rate of emission of electrons and their mean energy have been derived. A simple approach has been adopted to derive the expression for the rate of electron accretion to the dust particle. Further a new expression for the mean energy associated with the accreted electrons due to cylindrical dust particle has been derived and presented. An interesting comparison of results obtained in the case of spherical and cylindrical dust particles has also been made. Using these expressions, a formalism has been developed for the electronic processes in an illuminated dust cloud with cylindrical particles, on the basis of charge neutrality condition and number and energy balance of electrons; the charge carried by the cylindrical dust particles, electron temperature, and electron density corresponding to a given situation have been determined. The limitation of the applicability of the theory, viz., that the mean free path of an electron for accretion by dust particles be less than the dimension of the dust cloud has been pointed out.
NASA Astrophysics Data System (ADS)
Samoto, Norihiko; Shimizu, Ryuichi
1983-07-01
A new Monte Carlo simulation including generation of secondary electrons has been performed to study ultimate resolution in electron beam lithography. With respect to the simulations of inelastic scattering process of the primary electrons we used Gryzinski's excitation function for single electron excitation processes, generating secondary electrons, while the inelastic mean free path proposed by Seah and Dench for organic material and energy loss spectrum obtained by Ritsko were used for simulating the inelastic scattering processes of the secondaries. The calculations were made to obtain energy dissipation profile for 20-kV electrons, particularly, in the vicinity of the point of incidence on nanometer-scale in 3000-Å-thick films of polymethylmethacrylate (PMMA) on a silicon substrate. The result clearly indicates that the secondary electrons play a most important role in determining the energy dissipation profile in the vicinity of the point of incidence, being the significant source of broadening of the energy dissipation profile. The blurring due to secondary electrons at the surface of the PMMA resist is of the order of 10 nm.
Path entanglement of surface plasmons
NASA Astrophysics Data System (ADS)
Fakonas, James S.; Mitskovets, Anna; Atwater, Harry A.
2015-02-01
Metals can sustain traveling electromagnetic waves at their surfaces supported by the collective oscillations of their free electrons in unison. Remarkably, classical electromagnetism captures the essential physics of these ‘surface plasma’ waves using simple models with only macroscopic features, accounting for microscopic electron–electron and electron–phonon interactions with a single, semi-empirical damping parameter. Nevertheless, in quantum theory these microscopic interactions could be important, as any substantial environmental interactions could decohere quantum superpositions of surface plasmons, the quanta of these waves. Here we report a measurement of path entanglement between surface plasmons with 95% contrast, confirming that a path-entangled state can indeed survive without measurable decoherence. Our measurement suggests that elastic scattering mechanisms of the type that might cause pure dephasing in plasmonic systems must be weak enough not to significantly perturb the state of the metal under the experimental conditions we investigated.
ELECTRON HEAT CONDUCTION IN THE SOLAR WIND: TRANSITION FROM SPITZER-HAeRM TO THE COLLISIONLESS LIMIT
Bale, S. D.; Quataert, E.; Pulupa, M.; Salem, C.; Chen, C. H. K.
2013-06-01
We use a statistically significant set of measurements to show that the field-aligned electron heat flux q{sub Parallel-To} in the solar wind at 1 AU is consistent with the Spitzer-Haerm collisional heat flux q{sub sh} for temperature gradient scales larger than a few mean free paths L{sub T} {approx}> 3.5{lambda}{sub fp}. This represents about 65% of the measured data and corresponds primarily to high {beta}, weakly collisional plasma ({sup s}low solar wind{sup )}. In the more collisionless regime {lambda}{sub fp}/L{sub T} {approx}> 0.28, the electron heat flux is limited to q{sub Parallel-To }/q{sub 0} {approx} 0.3, independent of mean free path, where q{sub 0} is the ''free-streaming'' value; the measured q{sub Parallel-To} does not achieve the full q{sub 0}. This constraint q{sub Parallel-To }/q{sub 0} {approx} 0.3 might be attributed to wave-particle interactions, effects of an interplanetary electric potential, or inherent flux limitation. We also show a {beta}{sub e} dependence to these results that is consistent with a local radial electron temperature profile T{sub e} {approx} r {sup -{alpha}} that is a function of the thermal electron beta {alpha} = {alpha}({beta}{sub e}) and that the {beta} dependence of the collisionless regulation constraint is not obviously consistent with a whistler heat flux instability. It may be that the observed saturation of the measured heat flux is a simply a feature of collisional transport. We discuss the results in a broader astrophysical context.
NASA Technical Reports Server (NTRS)
Horton, Kent; Huffman, Mitch; Eppic, Brian; White, Harrison
2005-01-01
Path Loss Measurements were obtained on three (3) GPS equipped 757 aircraft. Systems measured were Marker Beacon, LOC, VOR, VHF (3), Glide Slope, ATC (2), DME (2), TCAS, and GPS. This data will provide the basis for assessing the EMI (Electromagnetic Interference) safety margins of comm/nav (communication and navigation) systems to portable electronic device emissions. These Portable Electronic Devices (PEDs) include all devices operated in or around the aircraft by crews, passengers, servicing personnel, as well as the general public in the airport terminals. EMI assessment capability is an important step in determining if one system-wide PED EMI policy is appropriate. This data may also be used comparatively with theoretical analysis and computer modeling data sponsored by NASA Langley Research Center and others.
ERIC Educational Resources Information Center
Fanaro, Maria de los Angeles; Arlego, Marcelo; Otero, Maria Rita
2012-01-01
This work comprises an investigation about basic Quantum Mechanics (QM) teaching in the high school. The organization of the concepts does not follow a historical line. The Path Integrals method of Feynman has been adopted as a Reference Conceptual Structure that is an alternative to the canonical formalism. We have designed a didactic sequence…
NASA Astrophysics Data System (ADS)
Wittmaack, Klaus
2015-03-01
The mean attenuation length,
Nonlocal electron transport in magnetized plasmas with arbitrary atomic number
Bennaceur-Doumaz, D.; Bendib, A.
2006-09-15
The numerical solution of the steady-state electron Fokker-Planck equation perturbed with respect to a global equilibrium is presented in magnetized plasmas with arbitrary atomic number Z. The magnetic field is assumed to be constant and the electron-electron collisions are described by the Landau collision operator. The solution is derived in the Fourier space and in the framework of the diffusive approximation which captures the spatial nonlocal effects. The transport coefficients are deduced and used to close a complete set of nonlocal electron fluid equations. This work improves the results of A. Bendib et al. [Phys. Plasmas 9, 1555 (2002)] and of A. V. Brantov et al. [Phys. Plasmas 10, 4633 (2003)] restricted to the local and nonlocal high-Z plasma approximations, respectively. The influence of the magnetic field on the nonlocal effects is discussed. We propose also accurate numerical fits of the relevant transport coefficients with respect to the collisionality parameter {lambda}{sub ei}/L and the atomic number Z, where L is the typical scale length and {lambda}{sub ei} is the electron-ion mean-free-path.
NASA Astrophysics Data System (ADS)
Giannazzo, F.; Deretzis, I.; Nicotra, G.; Fisichella, G.; Ramasse, Q. M.; Spinella, C.; Roccaforte, F.; La Magna, A.
2014-05-01
In this paper, the structural and electronic properties of epitaxial graphene (EG) grown on 8°-off 4H-SiC (0001) by high temperature thermal processes have been extensively investigated by a combination of several high resolution characterization techniques. The increase in the number of graphene layers with the growth temperature (from 1600 to 1700 °C) was studied by microRaman spectroscopy and high resolution transmission electron microscopy (HRTEM) on cross-sectioned samples. The few layers of graphene reside on a stepped SiC surface with alternating (0001) terraces and (11-2n) facets. Peculiar corrugations (wrinkles) in the graphene membrane preferentially oriented perpendicularly to the substrate steps were also observed. Motivated by recent atomic resolution studies of the EG/SiC interface revealing a local delamination of the interfacial C buffer from the (11-2n) facets, we searched for a correlation of these interfacial structural properties with the macroscopic electronic transport in EG field effect transistors (FETs). In particular, electrical characterization of EG top gated FETs fabricated with the channel length parallel or perpendicular to the substrate steps revealed a peculiar anisotropy of the channel conductance with respect to the steps' orientation. This effect was explained in terms of a local enhancement of EG resistance on the (11-2n) facets with respect to the (0001) basal plane, which is consistent with a reduced doping due to the local buffer layer delamination from those facets. Furthermore, scanning probe microscopy-based local electron mean free path measurements on EG showed a ~3× enhancement of mean free path on the buffer-layer-free (11-2n) facets with respect to (0001) terraces, probably associated to a strong reduction of Coulomb scattering effects on graphene's electrons.
Conductance of one-dimensional quantum wires with anomalous electron wave-function localization
NASA Astrophysics Data System (ADS)
Amanatidis, Ilias; Kleftogiannis, Ioannis; Falceto, Fernando; Gopar, Víctor A.
2012-06-01
We study the statistics of the conductance g through one-dimensional disordered systems where electron wave functions decay spatially as |?|˜exp(-?r?) for 0mean free path, here we show that when the wave function is anomalously localized (?<1), the full statistics of the conductance is determined by the average
Wang, Zhiguo; Xie, YuLong; Campbell, Luke W.; Gao, Fei; Kerisit, Sebastien N.
2012-07-01
A Monte Carlo model of electron thermalization in inorganic scintillators, which was developed and applied to CsI in a previous publication [Wang et al., J. Appl. Phys. 110, 064903 (2011)], is extended to another material of the alkali halide class, NaI, and to two materials from the alkaline-earth halide class, CaF2 and BaF2. This model includes electron scattering with both longitudinal optical (LO) and acoustic phonons as well as the effects of internal electric fields. For the four pure materials, a significant fraction of the electrons recombine with self-trapped holes and the thermalization distance distributions of the electrons that do not recombine peak between approximately 25 and 50 {per_thousand}nm and extend up to a few hundreds of nanometers. The thermalization time distributions of CaF2, BaF2, NaI, and CsI extend to approximately 0.5, 1, 2, and 7 ps, respectively. The simulations show that the LO phonon energy is a key factor that affects the electron thermalization process. Indeed, the higher the LO phonon energy is, the shorter the thermalization time and distance are. The thermalization time and distance distributions show no dependence on the incident {gamma}-ray energy. The four materials also show different extents of electron-hole pair recombination due mostly to differences in their electron mean free paths (MFPs), LO phonon energies, initial densities of electron-hole pairs, and static dielectric constants. The effect of thallium doping is also investigated for CsI and NaI as these materials are often doped with activators. Comparison between CsI and NaI shows that both the larger size of Cs+ relative to Na+, i.e., the greater atomic density of NaI, and the longer electron mean free path in NaI compared to CsI contribute to an increased probability for electron trapping at Tl sites in NaI versus CsI.
Wang Zhiguo; Gao Fei; Kerisit, Sebastien; Xie Yulong; Campbell, Luke W.
2012-07-01
A Monte Carlo model of electron thermalization in inorganic scintillators, which was developed and applied to CsI in a previous publication [Wang et al., J. Appl. Phys. 110, 064903 (2011)], is extended to another material of the alkali halide class, NaI, and to two materials from the alkaline-earth halide class, CaF{sub 2} and BaF{sub 2}. This model includes electron scattering with both longitudinal optical (LO) and acoustic phonons as well as the effects of internal electric fields. For the four pure materials, a significant fraction of the electrons recombine with self-trapped holes and the thermalization distance distributions of the electrons that do not recombine peak between approximately 25 and 50 nm and extend up to a few hundreds of nanometers. The thermalization time distributions of CaF{sub 2}, BaF{sub 2}, NaI, and CsI extend to approximately 0.5, 1, 2, and 7 ps, respectively. The simulations show that the LO phonon energy is a key factor that affects the electron thermalization process. Indeed, the higher the LO phonon energy is, the shorter the thermalization time and distance are. The thermalization time and distance distributions show no dependence on the incident {gamma}-ray energy. The four materials also show different extents of electron-hole pair recombination due mostly to differences in their electron mean free paths (MFPs), LO phonon energies, initial densities of electron-hole pairs, and static dielectric constants. The effect of thallium doping is also investigated for CsI and NaI as these materials are often doped with activators. Comparison between CsI and NaI shows that both the larger size of Cs{sup +} relative to Na{sup +}, i.e., the greater atomic density of NaI, and the longer electron mean free path in NaI compared to CsI contribute to an increased probability for electron trapping at Tl sites in NaI versus CsI.
Quantitative Analysis by Auger Electron Spectroscopy
NASA Astrophysics Data System (ADS)
Shimizu, Ryuichi
1983-11-01
A short review is presented of the theoretical background of a physical model for the quantification of Auger electron spectroscopy (AES) for surface analysis. The recent studies on the data-base for the inelastic mean free paths (IMFP) by Seah and Dench and systematic calculations of the backscattering factors (R) by Shimizu and Ichimura have now enabled standard quantitative corrections comparable to those widely used in electron probe microanalysis, to be accomplished. For quantitative corrections of wider practical use, the present paper proposes the use of functional representations of the backscattering factors for different angles of incidence (\\psi) for primary energies ranging from 3 to 10 keV as follows: R{=}1{+}(2.34-2.10Z0.14)× U-0.35{+}(2.58Z0.14-2.98) for \\psi=0°, R{=}1{+}(0.462-0.777Z0.20)× U-0.32{+}(1.15Z0.20-1.05) for \\psi{=}30°, R{=}1{+}(1.21-1.39Z0.13)U-0.33{+}(1.94Z0.13-1.88) for \\psi{=}45°, where U is the ratio of the primary energy to the binding energy, and Z is the atomic number of a sample.
Assessing the impact of automated path planning aids in the maritime community
Buchin, Mariela E
2009-01-01
In the area of merchant maritime navigation, electronic charts are a relatively new tool. As a result, navigational path planning environments that allow users to manually enter a path onto an electronic chart are becoming ...
Ion-induced kinetic electron emission from 6LiF, 7LiF and MgF2 thin films
NASA Astrophysics Data System (ADS)
Ullah, S.; H. Dogar, A.; Ashraf, M.; Qayyum, A.
2010-08-01
Secondary electron yields for Ar+ impact on 6LiF, 7LiF and MgF2 thin films grown on aluminum substrates are measured each as a function of target temperature and projectile energy. Remarkably different behaviours of the electron yields for LiF and MgF2 films are observed in a temperature range from 25 °C to 300 °C. The electron yield of LiF is found to sharply increase with target temperature and to be saturated at about 175 °C. But the target temperature has no effect on the electron yield of MgF2. It is also found that for the ion energies greater than 4 keV, the electron yield of 6LiF is consistently high as compared with that of 7LiF that may be due to the enhanced contribution of recoiling 6Li atoms to the secondary electron generation. A comparison between the electron yields of MgF2 and LiF reveales that above a certain ion energy the electron yield of MgF2 is considerably low as compared with that of LiF. We suggest that the short inelastic mean free path of electrons in MgF2 can be one of the reasons for its low electron yield.
Lee, Jongkyong; Gang, Suhyun; Jo, Yongcheol; Kim, Jongmin; Woo, Hyeonseok; Han, Jaeseok; Kim, Hyungsang Im, Hyunsik
2014-07-28
We have investigated the temperature dependence of ballistic mobility in a 100?nm-long InGaAs/InAlAs metamorphic high-electron-mobility transistor designed for millimeter-wavelength RF applications. To extract the temperature dependence of quasi-ballistic mobility, our experiment involves measurements of the effective mobility in the low-bias linear region of the transistor and of the collision-dominated Hall mobility using a gated Hall bar of the same epitaxial structure. The data measured from the experiment are consistent with that of modeled ballistic mobility based on ballistic transport theory. These results advance the understanding of ballistic transport in various transistors with a nano-scale channel length that is comparable to the carrier's mean free path in the channel.
Da, B.; Li, Z. Y.; Chang, H. C.; Ding, Z. J.; Mao, S. F.
2014-09-28
It has been experimentally found that the carbon surface contamination influences strongly the spectrum signals in reflection electron energy loss spectroscopy (REELS) especially at low primary electron energy. However, there is still little theoretical work dealing with the carbon contamination effect in REELS. Such a work is required to predict REELS spectrum for layered structural sample, providing an understanding of the experimental phenomena observed. In this study, we present a numerical calculation result on the spatially varying differential inelastic mean free path for a sample made of a carbon contamination layer of varied thickness on a SrTiO{sub 3} substrate. A Monte Carlo simulation model for electron interaction with a layered structural sample is built by combining this inelastic scattering cross-section with the Mott's cross-section for electron elastic scattering. The simulation results have clearly shown that the contribution of the electron energy loss from carbon surface contamination increases with decreasing primary energy due to increased individual scattering processes along trajectory parts carbon contamination layer. Comparison of the simulated spectra for different thicknesses of the carbon contamination layer and for different primary electron energies with experimental spectra clearly identifies that the carbon contamination in the measured sample was in the form of discontinuous islands other than the uniform film.
NASA Astrophysics Data System (ADS)
Ghavamian, Parviz; Schwartz, Steven J.; Mitchell, Jeremy; Masters, Adam; Laming, J. Martin
2013-10-01
Collisionless shocks are loosely defined as shocks where the transition between pre-and post-shock states happens on a length scale much shorter than the collisional mean free path. In the absence of collision to enforce thermal equilibrium post-shock, electrons and ions need not have the same temperatures. While the acceleration of electrons for injection into shock acceleration processes to produce cosmic rays has received considerable attention, the related problem of the shock heating of quasi-thermal electrons has been relatively neglected. In this paper we review the state of our knowledge of electron heating in astrophysical shocks, mainly associated with supernova remnants (SNRs), shocks in the solar wind associated with the terrestrial and Saturnian bowshocks, and galaxy cluster shocks. The solar wind and SNR samples indicate that the ratio of electron temperature, ( T e ) to ion temperature ( T p ) declining with increasing shock speed or Alfvén Mach number. We discuss the extent to which such behavior can be understood on the basis of waves generated by cosmic rays in a shock precursor, which then subsequently damp by heating electrons, and speculate that a similar explanation may work for both solar wind and SNR shocks.
Simulated performance of the calorimetric electron telescope (CALET) experiment
NASA Astrophysics Data System (ADS)
Akaike, Y.; Taira, K.; Kasahara, K.; Torii, S.; Shimizu, Y.; Yoshida, K.; CALET Collaboration
2010-03-01
CALET is a detector planned to be on-board the Japanese Experiment Module Exposed Facility (JEM-EF) of the International Space Station. The CALET mission aims at revealing unsolved problems in high energy phenomena of the Universe by carrying out a precise measurement of the high energy electrons in 1 GeV-20 TeV, the gamma-rays in 20 MeV to a few TeV and the nuclei in a few 10 GeV-1000 TeV. The main detector is composed of imaging calorimeter (IMC), total absorption calorimeter (TASC), silicon pixel array (SIA) and anti-coincidence detector (ACD) to detect various kinds of particles in very wide energy range. The total absorber thickness is 31 radiation lengths for electromagnetic particles and 1.4 interaction mean free paths for protons. Monte Carlo simulation study has been carried out for optimization of the detector performance in observing each kind of particles. We obtained following performance about the observation of very high energy (>100 GeV) electrons, which is a main target of the CALET experiment: (1) Effective geometrical factor is about 7000 cm2 sr. (2) Energy resolution is better than a few %. (3) Angular resolution is better than 0.1°. (4) Proton rejection power is ˜105 with the electron detection efficiency better than 95%. We also present the simulated performance of the CALET experiment in observing other particles.
Collisionless electron heating in periodic arrays of inductively coupled plasmas
NASA Astrophysics Data System (ADS)
Czarnetzki, U.; Tarnev, Kh.
2014-12-01
A novel mechanism of collisionless heating in large planar arrays of small inductive coils operated at radio frequencies is presented. In contrast to the well-known case of non-local heating related to the transversal conductivity, when the electrons move perpendicular to the planar coil, we investigate the problem of electrons moving in a plane parallel to the coils. Two types of periodic structures are studied. Resonance velocities where heating is efficient are calculated analytically by solving the Vlasov equation. Certain scaling parameters are identified. The concept is further investigated by a single particle simulation based on the ergodic principle and combined with a Monte Carlo code allowing for collisions with Argon atoms. Resonances, energy exchange, and distribution functions are obtained. The analytical results are confirmed by the numerical simulation. Pressure and electric field dependences are studied. Stochastic heating is found to be most efficient when the electron mean free path exceeds the size of a single coil cell. Then the mean energy increases approximately exponentially with the electric field amplitude.
Theory of electron scattering from solids
NASA Astrophysics Data System (ADS)
Fujikawa, Takashi; Hedin, Lars
1989-12-01
We present a theory which describes effects of the losses which determine the electron's mean free path, and which is valid not only for elastic, but also for inelastic, scattering. The results are given in terms of one-electron expressions involving damped one-electron functions and optical potentials. The operators in these expressions are expectation values over correlated many-electron states for the solid. The development follows similar lines as in recent work on photoemission and extended x-ray-absorption fine-structure spectroscopy by Bardyszewski and Hedin. Some of the present results were obtained by Fujikawa and Hedin in a study of scattering theory based on the Low formulation and a quasiboson representation. The theory involves an expansion in the diagonal (or coherent) operators introduced by Van Hove, and uses Feshbach projection-operator techniques. The theory is developed in three steps. First, we regard the scattering electron as an external particle, and we can then work with a product space of the scattering electron and the electrons in the solid. Second, we account for bare exchange between the scattering and target electrons, but keep different sets of one-electron states for the two types of electrons, and do not allow any coupling terms that annihilate the scattering electron. Third, we sketch a theory allowing intermediate, virtual states, where the scattering electron has been absorbed by the solid into a resonant state. We argue in detail that excited-state and ground-state optical potentials should be simply related in the case of extended excitations. All our results are quite general, i.e., they are valid not only for solids, but also for atoms and molecules. The central objects in our theory, the optical potentials, are discussed in some detail. In particular, they are related to the Van Hove, the Francis-Watson, and the Bell-Squires potentials. Their close relation to the ``GW approximation'' is shown. They are written in terms of fluctuation potentials, which can be obtained from the dielectric response function of the target. In the quasiboson representation the fluctuation potentials also determine the inelastic scattering.
Walden's Paths - Ensemble Edition
NSDL National Science Digital Library
2011-01-04
Walden?s Paths enables users of digital document collections (e.g. the Web) to exploit these documents by reusing them for previously unintended audiences in an academic setting. Authors of paths (usually educators) overlay a linear, directed meta-structure over the Web documents and recontextualize these by adding explanatory text to achieve their curricular goals. Paths do not modifythe structure or content of the Web resources that they include. The creation of a path over pre-organized content (e.g. books, Web pages) to reorganize and associate related information serves to facilitate easy retrieval and communication. Walden?s Paths displays the information that the path points to in conjunction with the textual annotations added by the author of the path.
Self similar nonlocal electron heat flow
NASA Astrophysics Data System (ADS)
Matte, Jean-Pierre
2007-11-01
The well known self similar heat diffusion solutions of Zel'dovich and Raizer [1], for a heat wave advancing from a boundary at a fixed temperature or a fixed heat flux do not keep the ratio R of the scale length to the mean free path constant. Instead, R increases and the solution becomes increasingly valid because Spitzer-Harm [2] heat flow is increasingly applicable. A self similar solution exists which keeps R constant, if one assumes that the boundary heat flux increases in time. Similarly, for the problem of a uniform density plasma heated by a finite width laser beam, a self similar solution keeping R constant can be obtained by assuming that the beam intensity and width increase in time. Such solutions will be studied with the electron kinetic code FPI [3], and compared to simulations with more usual laser characteristics. [1] Ya. B. Zel'dovich and Yu. P. Raizer, ``Physics of Shock Waves '', Academic Press, New York, 1967. [2] L. Spitzer and R. Harm, Phys. Rev. 89, 977 (1953). [3] J.-P. Matte et al., Phys. Rev. Lett. 53, 1461 (1984) ; ibid 49, 1936 (1982).
Dynamics of the electric current in an ideal electron gas: a sound mode inside the quasi-particles
Grozdanov, Sašo
2015-01-01
We study the equation of motion for the Noether current in an electron gas within the framework of the Schwinger-Keldysh Closed-Time-Path formalism. The equation is shown to be highly non-linear and irreversible even for a non-interacting, ideal gas of electrons at non-zero density. We truncate the linearised equation of motion, written as the Laurent series in Fourier space, so that the resulting expressions are local in time, both at zero and at small finite temperatures. Furthermore, we show that the one-loop Coulomb interactions only alter the physical picture quantitatively, while preserving the characteristics of the dynamics that the electric current exhibits in the absence of interactions. As a result of the composite nature of the Noether current, composite sound waves are found to be the dominant IR collective excitations at length scales between the inverse Fermi momentum and the mean free path that would exist in an interacting electron gas. We also discuss the difference and the transition betwee...
Dynamics of the electric current in an ideal electron gas: a sound mode inside the quasi-particles
Sašo Grozdanov; Janos Polonyi
2015-01-26
We study the equation of motion for the Noether current in an electron gas within the framework of the Schwinger-Keldysh Closed-Time-Path formalism. The equation is shown to be highly non-linear and irreversible even for a non-interacting, ideal gas of electrons at non-zero density. We truncate the linearised equation of motion, written as the Laurent series in Fourier space, so that the resulting expressions are local in time, both at zero and at small finite temperatures. Furthermore, we show that the one-loop Coulomb interactions only alter the physical picture quantitatively, while preserving the characteristics of the dynamics that the electric current exhibits in the absence of interactions. As a result of the composite nature of the Noether current, composite sound waves are found to be the dominant IR collective excitations at length scales between the inverse Fermi momentum and the mean free path that would exist in an interacting electron gas. We also discuss the difference and the transition between the hydrodynamical regime of an ideal gas, defined in this work, and the hydrodynamical regime in phenomenological hydrodynamics, which is normally used for the description of interacting gases.
Dynamics of the electric current in an ideal electron gas: a sound mode inside the quasi-particles
Sašo Grozdanov; Janos Polonyi
2015-09-03
We study the equation of motion for the Noether current in an electron gas within the framework of the Schwinger-Keldysh Closed-Time-Path formalism. The equation is shown to be highly non-linear and irreversible even for a non-interacting, ideal gas of electrons at non-zero density. We truncate the linearised equation of motion, written as the Laurent series in Fourier space, so that the resulting expressions are local in time, both at zero and at small finite temperatures. Furthermore, we show that the one-loop Coulomb interactions only alter the physical picture quantitatively, while preserving the characteristics of the dynamics that the electric current exhibits in the absence of interactions. As a result of the composite nature of the Noether current, {\\it composite sound} waves are found to be the dominant IR collective excitations at length scales between the inverse Fermi momentum and the mean free path that would exist in an interacting electron gas. We also discuss the difference and the transition between the hydrodynamical regime of an ideal gas, defined in this work, and the hydrodynamical regime in phenomenological hydrodynamics, which is normally used for the description of interacting gases.
NASA Astrophysics Data System (ADS)
Carelli, Fabio; Gianturco, Francesco Antonio; Franz, Jan; Satta, Mauro
2015-06-01
Electron and positron scattering processes in the gas-phase are analysed for uracil and pyrimidine molecules using a multichannel quantum approach at energies close to threshold. The special effects on the scattering dynamics induced by the large dipole moments in both molecules on the spatial features of the continuum leptonic wavefunctions are here linked to the possible bound states of the Rydberg-like molecular anions or `positroned' molecules which could be reached via further couplings with molecular internal degrees of freedom.
Correlating the Nanostructure and Electronic Properties of InAs Nanowires
Petta, Jason
energies obtained suggest quantum dot formation at defects in the wires. These results reinforce due to the built-in one-dimensional confinement of charge carriers. In particular, III-V nanowires, resulting in the observation of quantum confinement effects at room temperature.5 Mean free paths of over
Christian Fleischhack
2015-03-21
The symmetries of paths in a manifold $M$ are classified with respect to a given pointwise proper action of a Lie group $G$ on $M$. Here, paths are embeddings of a compact interval into $M$. There are at least two types of symmetries: Firstly, paths that are parts of an integral curve of a fundamental vector field on $M$ (continuous symmetry). Secondly, paths that can be decomposed into finitely many pieces, each of which is the translate of some free segment, where possibly the translate is cut at the two ends of the paths (discrete symmetry). Here, a free segment is a path $e$ whose $G$-translates either equal $e$ or intersect it in at most finitely many points. Note that all the statements above are understood up to the parametrization of the paths. We will show, for the category of analytic manifolds, that each path is of exactly one of either types. For the proof, we use that the overlap of a path $\\gamma$ with one of its translates is encoded uniquely in a mapping between subsets of $\\dom\\gamma$. Running over all translates, these mappings form the so-called reparametrization set to $\\gamma$. It will turn out that, up to conjugation with a diffeomorphism, any such set is given by the action of a Lie subgroup of $O(2)$ on $S^1$, restricted in domain and range to some compact interval on $S^1$. Now, the infinite subgroups correspond to the continuous symmetry above, finite ones to the discrete symmetry.
Path Integrals and Hamiltonians
NASA Astrophysics Data System (ADS)
Baaquie, Belal E.
2014-03-01
1. Synopsis; Part I. Fundamental Principles: 2. The mathematical structure of quantum mechanics; 3. Operators; 4. The Feynman path integral; 5. Hamiltonian mechanics; 6. Path integral quantization; Part II. Stochastic Processes: 7. Stochastic systems; Part III. Discrete Degrees of Freedom: 8. Ising model; 9. Ising model: magnetic field; 10. Fermions; Part IV. Quadratic Path Integrals: 11. Simple harmonic oscillators; 12. Gaussian path integrals; Part V. Action with Acceleration: 13. Acceleration Lagrangian; 14. Pseudo-Hermitian Euclidean Hamiltonian; 15. Non-Hermitian Hamiltonian: Jordan blocks; 16. The quartic potential: instantons; 17. Compact degrees of freedom; Index.
Siekhaus, W J; Nelson, A J
2011-10-26
Energy dependent electron emission between zero and 1.4 keV generated by the natural reactivity of plutonium was measured by an electrostatic spectrometer with known acceptance angle and acceptance area. The electron spectral intensity decreases continuously except for a distinctive feature of unknown origin at approximately 180eV. The spectrum was converted to energy dependent electron flux (e/cm{sup 2} s) using the assumption that the emission has a cosine angular distribution. The energy dependent electron mean free path in gases and literature cross sections for electron induced reactions were used to determine the number of ionization and dissociation reactions per cm{sup 2} second, found to be about 8*10{sup 8}/cm{sup 2}s and 1.5*10{sup 8}/cm{sup 2}s, respectively, for hydrogen. These results are to be used with caution until complementary measurements can be made, e.g. independent measurement of the total emitted electron current, since the results here are based on the assumption that the electron emission has a cosine angular distribution. That is unlikely to be correct.
Gu, Jiande; Wang, Jing; Leszczynski, Jerzy
2015-02-12
A viable pathway is proposed for the formation of the triplet state of the GC Watson-Crick base pair. It includes the following steps: (a) a low-energy electron is captured by cytosine in the GC pair, forming the cytosine base-centered radical anion GC(-•); and (b) photoradiation with energy around 5 eV initiates the electron detachment from either cytosine (in the gas phase) or guanine (in aqueous solutions). This triggers interbase proton transfer from G to C, creating the triplet state of the GC pair. Double proton transfer involving the triplet state of GC pair leads to the formation of less stable tautomer G(N2-H)(•)C(O2H)(•). Tautomerization is accomplished through a double proton transfer process in which one proton at the N3 of C(H)(•) migrates to the N1 of G(-H)(•); meanwhile, the proton at the N2 of G transfers to the O2 of C. This process is energetically viable; the corresponding activation energy is around 12-13 kcal/mol. The base-pairing energy of the triplet is found to be ?3-5 kcal/mol smaller than that of the singlet state. Thus, the formation of the triplet state GC pair in DNA double strand only slightly weakens its stability. The obtained highly reactive radicals are expected to cause serious damage in the DNA involved in biochemical processes, such as DNA replication where radicals are exposed in the single strands. PMID:25340559
Random walk and electron energy gain in microwave electric fields: gaseous breakdown revisited
NASA Astrophysics Data System (ADS)
Bhattacharjee, S.; Amemiya, H.; Nakagawa, T.; Kase, M.; Goto, A.; Yano, Y.
2002-11-01
Random walk and electron energy gain in microwave electric fields leading to breakdown of a gas are studied theoretically and by numerical simulation with collision and phase randomized. The square law dependence of the random walk given by N (?/?)^2, where N is the average number of collisions encountered by an electron, ? is the characteristic diffusion length and ? is the mean free path, is strictly valid only for free diffusion or for a weak field approximation (v ng v_th, where v is the velocity attained from the field and v_th is the thermal velocity). This can explain breakdown phenomena at limited pressure regimes satisfying ?/? << 1, where ? is the wave frequency and ? is the electron neutral collision frequency. More accurately, the electron random walk under the impressed wave electric field has to be considered consistently to yield breakdown electric fields. The numerical simulation yields a readily usable emperical relation; N Log(1+ ?/?) which can be used to obtain breakdown fields over a wide pressure regime covering either side of the collision frequency transition (? = ?).
A deterministic computational model for the two dimensional electron and photon transport
NASA Astrophysics Data System (ADS)
Badavi, Francis F.; Nealy, John E.
2014-12-01
A deterministic (non-statistical) two dimensional (2D) computational model describing the transport of electron and photon typical of space radiation environment in various shield media is described. The 2D formalism is casted into a code which is an extension of a previously developed one dimensional (1D) deterministic electron and photon transport code. The goal of both 1D and 2D codes is to satisfy engineering design applications (i.e. rapid analysis) while maintaining an accurate physics based representation of electron and photon transport in space environment. Both 1D and 2D transport codes have utilized established theoretical representations to describe the relevant collisional and radiative interactions and transport processes. In the 2D version, the shield material specifications are made more general as having the pertinent cross sections. In the 2D model, the specification of the computational field is in terms of a distance of traverse z along an axial direction as well as a variable distribution of deflection (i.e. polar) angles ? where -?/2mean-free-path and average trajectory approach is used. For candidate shielding materials, using the trapped electron radiation environments at low Earth orbit (LEO), geosynchronous orbit (GEO) and Jupiter moon Europa, verification of the 2D formalism vs. 1D and an existing Monte Carlo code are presented.
From Path Graphs to Directed Path Graphs Steven Chaplick1
Felsner, Stefan
From Path Graphs to Directed Path Graphs Steven Chaplick1 , Marisa Gutierrez2 , Benjamin LÂ´ev^eque3 time algorithm to greedily orient the edges of a path graph model to obtain a directed path graph model. This algorithm has several interesting conse- quences concerning the relationship between path graphs
NSDL National Science Digital Library
Australian National University
This site features an interactive applet that models the Sun's path from a geocentric view. It calculates and visualizes the position of the Sun based on latitude and time, and allows students to simulate the Sun's position and path for an hour, a day, a month or a year.
NASA Astrophysics Data System (ADS)
Hwang, Seok Won; Lee, Ho-Jun; Lee, Hae June
2014-12-01
Fluid models have been widely used and conducted successfully in high pressure plasma simulations where the drift–diffusion and the local-field approximation are valid. However, fluid models are not able to demonstrate non-local effects related to large electron energy relaxation mean free path in low pressure plasmas. To overcome this weakness, a hybrid model coupling electron Monte Carlo collision (EMCC) method with the fluid model is introduced to obtain precise electron energy distribution functions using pseudo-particles. Steady state simulation results by a one-dimensional hybrid model which includes EMCC method for the collisional reactions but uses drift–diffusion approximation for electron transport in a fluid model are compared with those of a conventional particle-in-cell (PIC) and a fluid model for low pressure capacitively coupled plasmas. At a wide range of pressure, the hybrid model agrees well with the PIC simulation with a reduced calculation time while the fluid model shows discrepancy in the results of the plasma density and the electron temperature.
Kyriakou, Ioanna; Emfietzoglou, Dimitris; Garcia-Molina, Rafael; Abril, Isabel; Kostarelos, Kostas
2011-09-01
The effect of bulk and surface excitations to inelastic scattering in low-energy electron beam irradiation of multi-walled carbon nanotubes (MWNTs) is studied using the dielectric formalism. Calculations are based on a semiempirical dielectric response function for MWCNTs determined by means of a many-pole plasmon model with parameters adjusted to available experimental spectroscopic data under theoretical sum-rule constrains. Finite-size effects are considered in the context of electron gas theory via a boundary correction term in the plasmon dispersion relations, thus, allowing a more realistic extrapolation of the electronic excitation spectrum over the whole energy-momentum plane. Energy-loss differential and total inelastic scattering cross sections as a function of electron energy and distance from the surface, valid over the energy range {approx}50-30,000 eV, are calculated with the individual contribution of bulk and surface excitations separated and analyzed for the case of normally incident and escaping electrons. The sensitivity of the results to the various approximations for the spatial dispersion of the electronic excitations is quantified. Surface excitations are shown to have a strong influence upon the shape and intensity of the energy-loss differential cross section in the near surface region whereas the general notion of a spatially invariant inelastic mean free path inside the material is found to be of good approximation.
Local electronic functionality in carbon nanotube devices
NASA Astrophysics Data System (ADS)
Freitag, Marcus
Single-wall carbon nanotubes (SWNTs) are unique molecular conductors that can act as quantum wires or field-effect transistors. Theory gives us detailed understanding about their one-dimensional electronic structure, but very little is known about the internal functioning of real-world devices made of nanotubes. In particular the role of defects and electronic contacts is poorly understood. Here, we use scanning probe techniques to measure electronic properties of SWNTs on nanometer lengthscales. Atomic resolution scanning tunneling microscopy (STM) shows standing waves that form due to backscattering and interference of electrons. Different patterns are ascribed to scattering with large and small momentum transfer. Electronic transport through SWNT bundles is analyzed locally by tunneling AFM (T-AFM) and scanning gate microscopy (SGM). We resolve the electrochemical potential of individual nanotubes within bundles and find that electron hopping between nanotubes limits the conductivity in metallic bundles. Semiconducting bottlenecks have a profound influence on transport along thin bundles. Electronic devices at junctions between two one-dimensional wires are the ultimate goal in miniaturization. We characterize the 1D Schottky barrier at a metal-semiconductor nanotube cross junction by SGM and find a 10 nm depletion width in reverse bias. Nanotube field-effect transistors (FETs) exhibit two back-to-back Schottky barriers at the contacts to Cr/Au leads. They are responsible for the p-type character of the device. Potential modulations due to disorder along the nanotube length determine the turn-off potential for the FET. We are able to characterize defects one by one and find turn-off surface potentials between 250 mV and 800 mV, corresponding to local Fermi levels between 20 meV and 65 meV. Cobalt-contacted nanotube FETs are found to be n-type due to small Schottky barriers for electrons. They behave complementary to the Cr/Au contacted p-type FETs and have experimentally observable conduction band modulations. Finally, CVD-grown metallic SWNTs have a high contact transparency T ˜ 1/2 and large mean-free path lm ˜ 0.43 mum. At high bias we observe energy dissipation along the nanotube, supporting the theory of optical phonon emission.
Ho, Seng-Tiong
]. To achieve light localization in a three-di- mensional (3-D) disordered system, the IoffeRegel criterion.807178 is the transport mean free path. John first suggested that the IoffeRegel criterion could be more easily met the frequency of the light is near a photonic band edge, the IoffeRegel criterion is replaced by , where
Improved initial guess for minimum energy path calculations
Smidstrup, Søren [QuantumWise A/S, Lersø Parkallé 107, DK-2100 Copenhagen (Denmark); Science Institute and Faculty of Physical Sciences, University of Iceland VR-III, 107 Reykjavík (Iceland); Pedersen, Andreas [Science Institute and Faculty of Physical Sciences, University of Iceland VR-III, 107 Reykjavík (Iceland); Integrated Systems Laboratory, ETH Zurich, 8092 Zurich (Switzerland); Stokbro, Kurt [QuantumWise A/S, Lersø Parkallé 107, DK-2100 Copenhagen (Denmark); Jónsson, Hannes, E-mail: hj@hi.is [Science Institute and Faculty of Physical Sciences, University of Iceland VR-III, 107 Reykjavík (Iceland); Department of Applied Physics, Aalto University, Espoo, FI-00076 (Finland)
2014-06-07
A method is presented for generating a good initial guess of a transition path between given initial and final states of a system without evaluation of the energy. An objective function surface is constructed using an interpolation of pairwise distances at each discretization point along the path and the nudged elastic band method then used to find an optimal path on this image dependent pair potential (IDPP) surface. This provides an initial path for the more computationally intensive calculations of a minimum energy path on an energy surface obtained, for example, by ab initio or density functional theory. The optimal path on the IDPP surface is significantly closer to a minimum energy path than a linear interpolation of the Cartesian coordinates and, therefore, reduces the number of iterations needed to reach convergence and averts divergence in the electronic structure calculations when atoms are brought too close to each other in the initial path. The method is illustrated with three examples: (1) rotation of a methyl group in an ethane molecule, (2) an exchange of atoms in an island on a crystal surface, and (3) an exchange of two Si-atoms in amorphous silicon. In all three cases, the computational effort in finding the minimum energy path with DFT was reduced by a factor ranging from 50% to an order of magnitude by using an IDPP path as the initial path. The time required for parallel computations was reduced even more because of load imbalance when linear interpolation of Cartesian coordinates was used.
Energy loss of proton, ? particle, and electron beams in hafnium dioxide films
NASA Astrophysics Data System (ADS)
Behar, Moni; Fadanelli, Raul C.; Abril, Isabel; Garcia-Molina, Rafael; Denton, Cristian D.; Nagamine, Luiz C. C. M.; Arista, Néstor R.
2009-12-01
The electronic stopping power, S , of HfO2 films for proton and alpha particle beams has been measured and calculated. The experimental data have been obtained by the Rutherford backscattering technique and cover the range of 120-900 and 120-3000 keV for proton and alpha particle beams, respectively. Theoretical calculations of the energy loss for the same projectiles have been done by means of the dielectric formalism using the Mermin energy loss function—generalized oscillator strength (MELF-GOS) model for a proper description of the HfO2 target on the whole momentum-energy excitation spectrum. At low projectile energies, a nonlinear theory based on the extended Friedel sum rule has been employed. The calculations and experimental measurements show good agreement for protons and a quite good one for alpha particles. In particular, the experimental maximums of both stopping curves (around 120 and 800 keV, respectively) are well reproduced. On the basis of this good agreement, we have also calculated the inelastic mean-free path (IMFP) and the stopping power for electrons in HfO2 films. Our results predict a minimum value of the IMFP and a maximum value of the S for electrons with energies around 120 and 190 eV, respectively.
Primary cosmic ray electrons above 10 GeV: Evidence for a spectral break
NASA Technical Reports Server (NTRS)
Silverberg, R. F.; Ormes, J. F.; Balasubrahmanyan, V. K.
1973-01-01
A balloon borne measurement of the cosmic ray electron spectrum from 10 to 200 GeV is reported in which two new techniques have been used to remove proton background contamination. First, the depth of the spectrometer was more than 25 radiation lengths, the equivalent of more than 2 mean free paths of material, enabling hadronically and electromagnetically induced cascades to be differentiated for a subset of the data. Second, electromagnetic cascade starting points were determined to within + or - 0.1 radiation lengths based upon a calibration with electrons from 5.4 to 18 GeV at the Stanford Linear Accelerator, greatly reducing the chances for a proton to simulate an electron. The resulting spectrum, when fitted with a power law, is quite steep, -3.2 + or - 0.1, but the chi-square fit is marginal. A significantly better fit is achieved assuming a transition region model in which the source spectral index is 2.7 with a break occurring at about 50 GeV.
Surface excitations in electron spectroscopy. Part I: dielectric formalism and Monte Carlo algorithm
Salvat-Pujol, F; Werner, W S M
2013-01-01
The theory describing energy losses of charged non-relativistic projectiles crossing a planar interface is derived on the basis of the Maxwell equations, outlining the physical assumptions of the model in great detail. The employed approach is very general in that various common models for surface excitations (such as the specular reflection model) can be obtained by an appropriate choice of parameter values. The dynamics of charged projectiles near surfaces is examined by calculations of the induced surface charge and the depth- and direction-dependent differential inelastic inverse mean free path (DIIMFP) and stopping power. The effect of several simplifications frequently encountered in the literature is investigated: differences of up to 100% are found in heights, widths, and positions of peaks in the DIIMFP. The presented model is implemented in a Monte Carlo algorithm for the simulation of the electron transport relevant for surface electron spectroscopy. Simulated reflection electron energy loss spectra are in good agreement with experiment on an absolute scale. Copyright © 2012 John Wiley & Sons, Ltd. PMID:23794766
Salvat-Pujol, F; Werner, W S M
2013-05-01
The theory describing energy losses of charged non-relativistic projectiles crossing a planar interface is derived on the basis of the Maxwell equations, outlining the physical assumptions of the model in great detail. The employed approach is very general in that various common models for surface excitations (such as the specular reflection model) can be obtained by an appropriate choice of parameter values. The dynamics of charged projectiles near surfaces is examined by calculations of the induced surface charge and the depth- and direction-dependent differential inelastic inverse mean free path (DIIMFP) and stopping power. The effect of several simplifications frequently encountered in the literature is investigated: differences of up to 100% are found in heights, widths, and positions of peaks in the DIIMFP. The presented model is implemented in a Monte Carlo algorithm for the simulation of the electron transport relevant for surface electron spectroscopy. Simulated reflection electron energy loss spectra are in good agreement with experiment on an absolute scale. Copyright © 2012 John Wiley & Sons, Ltd. PMID:23794766
ERIC Educational Resources Information Center
Stegemoller, William; Stegemoller, Rebecca
2004-01-01
The path taken and the turns made as a turtle traces a polygon are examined to discover an important theorem in geometry. A unique tool, the Angle Adder, is implemented in the investigation. (Contains 9 figures.)
Tortuous path chemical preconcentrator
Manginell, Ronald P. (Albuquerque, NM); Lewis, Patrick R. (Albuquerque, NM); Adkins, Douglas R. (Albuquerque, NM); Wheeler, David R. (Albuquerque, NM); Simonson, Robert J. (Cedar Crest, NM)
2010-09-21
A non-planar, tortuous path chemical preconcentrator has a high internal surface area having a heatable sorptive coating that can be used to selectively collect and concentrate one or more chemical species of interest from a fluid stream that can be rapidly released as a concentrated plug into an analytical or microanalytical chain for separation and detection. The non-planar chemical preconcentrator comprises a sorptive support structure having a tortuous flow path. The tortuosity provides repeated twists, turns, and bends to the flow, thereby increasing the interfacial contact between sample fluid stream and the sorptive material. The tortuous path also provides more opportunities for desorption and readsorption of volatile species. Further, the thermal efficiency of the tortuous path chemical preconcentrator is comparable or superior to the prior non-planar chemical preconcentrator. Finally, the tortuosity can be varied in different directions to optimize flow rates during the adsorption and desorption phases of operation of the preconcentrator.
NSDL National Science Digital Library
In this lesson, younger students will be introduced to the various orbital paths that are used for satellites. Using a globe and a satellite model or a large picture of Earth, the teacher will introduce three types of orbital paths (polar, elliptical, and geosynchronous). The students should be able to define 'satellite', define the three types of orbits, describe how satellites orbit the Earth, and understand how they are slowed down by drag from the atmosphere.
Park, Jeong Y.; Lee, Hyunjoo; Renzas, J. Russell; Zhang, Yawen; Somorjai, G.A.
2008-05-01
Hot electron flow generated on colloid platinum nanoparticles during exothermic catalytic carbon monoxide oxidation was directly detected with Au/TiO{sub 2} diodes. Although Au/TiO{sub 2} diodes are not catalytically active, platinum nanoparticles on Au/TiO{sub 2} exhibit both chemicurrent and catalytic turnover rate. Hot electrons are generated on the surface of the metal nanoparticles and go over the Schottky energy barrier between Au and TiO{sub 2}. The continuous Au layer ensures that the metal nanoparticles are electrically connected to the device. The overall thickness of the metal assembly (nanoparticles and Au thin film) is comparable to the mean free path of hot electrons, resulting in ballistic transport through the metal. The chemicurrent and chemical reactivity of nanoparticles with citrate, hexadecylamine, hexadecylthiol, and TTAB (Tetradecyltrimethylammonium Bromide) capping agents were measured during catalytic CO oxidation at pressures of 100 Torr O{sub 2} and 40 Torr CO at 373-513 K. We found that chemicurrent yield varies with each capping agent, but always decreases with increasing temperature. We suggest that this inverse temperature dependence is associated with the influence of charging effects due to the organic capping layer during hot electron transport through the metal-oxide interface.
Energy-loss- and thickness-dependent contrast in atomic-scale electron energy-loss spectroscopy
Tan, Haiyan; Xin, Huolin L.; Zhu, Ye; Dwyer, Christian
2014-12-31
Atomic-scale elemental maps of materials acquired by core-loss inelastic electron scattering often exhibit an undesirable sensitivity to the unavoidable elastic scattering, making the maps counter-intuitive to interpret. Here, we present a systematic study that scrutinizes the energy-loss and sample-thickness dependence of atomic-scale elemental maps acquired using 100 keV incident electrons in a scanning transmission electron microscope. For single-crystal silicon, the balance between elastic and inelastic scattering means that maps generated from the near-threshold Si-L signal (energy loss of 99 eV) show no discernible contrast for a thickness of 0.5? (? is the electron mean-free path, here approximately 110 nm). At greater thicknesses we observe a counter-intuitive “negative” contrast. Only at much higher energy losses is an intuitive “positive” contrast gradually restored. Our quantitative analysis shows that the energy-loss at which a positive contrast is restored depends linearly on the sample thickness. This behavior is in very good agreement with our double-channeling inelastic scattering calculations. We test a recently-proposed experimental method to correct the core-loss inelastic scattering and restore an intuitive “positive” chemical contrast. The method is demonstrated to be reliable over a large range of energy losses and sample thicknesses. The corrected contrast for near-threshold maps is demonstrated to be (desirably) inversely proportional to sample thickness. Implications for the interpretation of atomic-scale elemental maps are discussed.
Monochromatic paths and path squares in infinite graphs
Mildenberger, Heike
Monochromatic paths and path squares in infinite graphs Lajos Soukup AlfrÃ©d RÃ©nyi Institute disjoint monochromatic paths with different colours which cover all vertices of K. #12;The beginning complete graph K is coloured with r colors. Then there are r disjoint monochromatic paths with different
NASA Astrophysics Data System (ADS)
Yang, Weitao
2006-03-01
The reaction path potential (RPP) follows the ideas from the reaction path Hamiltonian of Miller, Handy and Adams for gas phase reactions but is designed specifically for large systems described with QM/MM methods. RPP is an analytical energy expression of the combined QM/MM potential energy along the minimum energy path (J. Chem. Phys. 121, 89, 2004). An expansion around the minimum energy path is made in both the nuclear and the electronic degrees of freedom for the QM subsystem, while the interaction between the QM and MM subsystems is described as the interaction of the MM charges with polarizable QM charges. The input data for constructing the reaction path potential are energies, frequencies and electron density response properties of the QM subsystem. RPP provides a potential energy surface for rigorous statistical mechanics and mixed quantum/classical reaction dynamics calculations of complex systems, as will be shown for several enzymes. Recent further development in determining QM/MM free energy reaction paths will also be presented.
Monte Carlo simulation of kilovolt electron transport in solids
NASA Astrophysics Data System (ADS)
Martínez, J. D.; Mayol, R.; Salvat, F.
1990-03-01
A Monte Carlo procedure to simulate the penetration and energy loss of low-energy electron beams through solids is presented. Elastic collisions are described by using the method of partial waves for the screened Coulomb field of the nucleus. The atomic charge density is approximated by an analytical expression with parameters determined from the Dirac-Hartree-Fock-Slater self-consistent density obtained under Wigner-Seitz boundary conditions in order to account for solid-state effects; exchange effects are also accounted for by an energy-dependent local correction. Elastic differential cross sections are then easily computed by combining the WKB and Born approximations to evaluate the phase shifts. Inelastic collisions are treated on the basis of a generalized oscillator strength model which gives inelastic mean free paths and stopping powers in good agreement with experimental data. This scattering model is accurate in the energy range from a few hundred eV up to about 50 keV. The reliability of the simulation method is analyzed by comparing simulation results and experimental data from backscattering and transmission measurements.
Atmospheric Science Data Center
2014-12-08
... is natural to name each of these different trajectories or paths. For MISR, the path is the generic name (actually the numeric label) of ... that are close to each other in longitude will be covered by paths with similar numbers. The path number is also included in the file name ...
Kontar, Eduard P.; Bian, Nicolas H.; Emslie, A. Gordon; Vilmer, Nicole E-mail: emslieg@wku.edu
2014-01-10
Recent observations from RHESSI have revealed that the number of non-thermal electrons in the coronal part of a flaring loop can exceed the number of electrons required to explain the hard X-ray-emitting footpoints of the same flaring loop. Such sources cannot, therefore, be interpreted on the basis of the standard collisional transport model, in which electrons stream along the loop while losing their energy through collisions with the ambient plasma; additional physical processes, to either trap or scatter the energetic electrons, are required. Motivated by this and other observations that suggest that high-energy electrons are confined to the coronal region of the source, we consider turbulent pitch-angle scattering of fast electrons off low-frequency magnetic fluctuations as a confinement mechanism, modeled as a spatial diffusion parallel to the mean magnetic field. In general, turbulent scattering leads to a reduction of the collisional stopping distance of non-thermal electrons along the loop, and hence to an enhancement of the coronal hard X-ray source relative to the footpoints. The variation of source size L with electron energy E becomes weaker than the quadratic behavior pertinent to collisional transport, with the slope of L(E) depending directly on the mean free path ? associated with the non-collisional scattering mechanism. Comparing the predictions of the model with observations, we find that ? ? (10{sup 8}-10{sup 9}) cm for ?30 keV, less than the length of a typical flaring loop and smaller than, or comparable to, the size of the electron acceleration region.
Qian, Weixian; Zhou, Xiaojun; Lu, Yingcheng; Xu, Jiang
2015-09-15
Both the Jones and Mueller matrices encounter difficulties when physically modeling mixed materials or rough surfaces due to the complexity of light-matter interactions. To address these issues, we derived a matrix called the paths correlation matrix (PCM), which is a probabilistic mixture of Jones matrices of every light propagation path. Because PCM is related to actual light propagation paths, it is well suited for physical modeling. Experiments were performed, and the reflection PCM of a mixture of polypropylene and graphite was measured. The PCM of the mixed sample was accurately decomposed into pure polypropylene's single reflection, pure graphite's single reflection, and depolarization caused by multiple reflections, which is consistent with the theoretical derivation. Reflection parameters of rough surface can be calculated from PCM decomposition, and the results fit well with the theoretical calculations provided by the Fresnel equations. These theoretical and experimental analyses verify that PCM is an efficient way to physically model light-matter interactions. PMID:26371930
Sullivan, Blair D; Seymour, Dr. Paul Douglas
2010-01-01
Say a digraph is k-free if it has no directed cycles of length at most k, for k {element_of} Z{sup +}. Thomasse conjectured that the number of induced 3-vertex directed paths in a simple 2-free digraph on n vertices is at most (n-1)n(n+1)/15. We present an unpublished result of Bondy proving there are at most 2n{sup 3}/25 such paths, and prove that for the class of circular interval digraphs, an upper bound of n{sup 3}/16 holds. We also study the problem of bounding the number of (non-induced) 4-vertex paths in 3-free digraphs. We show an upper bound of 4n{sup 4}/75 using Bondy's result for Thomasse's conjecture.
Mobile transporter path planning
NASA Technical Reports Server (NTRS)
Baffes, Paul; Wang, Lui
1990-01-01
The use of a genetic algorithm (GA) for solving the mobile transporter path planning problem is investigated. The mobile transporter is a traveling robotic vehicle proposed for the space station which must be able to reach any point of the structure autonomously. Elements of the genetic algorithm are explored in both a theoretical and experimental sense. Specifically, double crossover, greedy crossover, and tournament selection techniques are examined. Additionally, the use of local optimization techniques working in concert with the GA are also explored. Recent developments in genetic algorithm theory are shown to be particularly effective in a path planning problem domain, though problem areas can be cited which require more research.
NASA Astrophysics Data System (ADS)
Arenas, Claudio; Henriquez, Ricardo; Moraga, Luis; Muñoz, Enrique; Munoz, Raul C.
2015-02-01
We calculate the electrical resistivity of a metallic specimen, under the combined effects of electron scattering by impurities, grain boundaries, and rough surfaces limiting the film, using a quantum theory based upon the Kubo formalism. Grain boundaries are represented by a one-dimensional periodic array of Dirac delta functions separated by a distance "d" giving rise to a Kronig-Penney (KP) potential. We use the Green's function built from the wave functions that are solutions of this KP potential; disorder is included by incorporating into the theory the probability that an electron is transmitted through several successive grain boundaries. We apply this new theory to analyze the resistivity of samples S1, S2, S7 and S8 measured between 4 and 300 K reported in Appl. Surf. Science273, 315 (2013). Although both the classical and the quantum theories predict a resistivity that agrees with experimental data to within a few percent or better, the phenomena giving rise to the increase of resistivity over the bulk are remarkably different. Classically, each grain boundary contributes to the electrical resistance by reflecting a certain fraction of the incoming electrons. In the quantum description, there are states (in the allowed KP bands) that transmit electrons unhindered, without reflections, while the electrons in the forbidden KP bands are localized. A distinctive feature of the quantum theory is that it provides a description of the temperature dependence of the resistivity where the contribution to the resistivity originating on electron-grain boundary scattering can be identified by a certain unique grain boundary reflectivity R, and the resistivity arising from electron-impurity scattering can be identified by a certain unique ?IMP mean free path attributable to impurity scattering. This is in contrast to the classical theory of Mayadas and Shatzkes (MS), that does not discriminate properly between a resistivity arising from electron-grain boundary scattering and that arising from electron-impurity scattering, for MS theory does not allow parameters (?IMP, R) to be uniquely adjusted to describe the temperature dependence of the resistivity data. The same data can be described using different sets of (R, ?IMP); the latter parameter can be varied by two orders of magnitude in the case of small grained samples d < ?, and by a factor of 4 in the case of samples made out of large grains d > ? (where ? is the bulk mean free path at 300 K). For samples d > ?, the increase of resistivity is attributed not to electrons being partially reflected by the grain boundaries, but to a decrease in the number of states at the Fermi sphere that are allowed bands of the KP potential; hence the reflectivity required by the quantum model turns out to be an order of magnitude smaller than that required by the classical MS theory. For samples d < ?, the resistivity increase originates mainly from Anderson localization induced by electron grain boundary scattering from disordered successive grains characterized by a localization length of the order of 110 nm and not from electrons being partially reflected by grain boundaries; the outcome is that the reflectivity required by the quantum theory turns out to be about 4 times smaller than that required by the classical MS theory.
Bhattacharjee, Sudeep; Paul, Samit [Department of Physics, Indian Institute of Technology, Kanpur 208016, Uttar Pradesh (India); Dey, Indranuj [Kyushu University, Kasuga Kouen 6-1, Kasuga City, 816-8580 (Japan)
2013-04-15
This paper deals with random walk of electrons and collisional crossover in a gas evolving toward a plasma, in presence of electromagnetic (EM) waves and magnetostatic (B) fields, a fundamental subject of importance in areas requiring generation and confinement of wave assisted plasmas. In presence of EM waves and B fields, the number of collisions N suffered by an electron with neutral gas atoms while diffusing out of the volume during the walk is significantly modified when compared to the conventional field free square law diffusion; N=1.5({Lambda}/{lambda}){sup 2}, where {Lambda} is the characteristic diffusion length and {lambda} is the mean free path. There is a distinct crossover and a time scale associated with the transition from the elastic to inelastic collisions dominated regime, which can accurately predict the breakdown time ({tau}{sub c}) and the threshold electric field (E{sub BD}) for plasma initiation. The essential features of cyclotron resonance manifested as a sharp drop in {tau}{sub c}, lowering of E{sub BD} and enhanced electron energy gain is well reproduced in the constrained random walk.
Study of electronic sputtering of CaF2 thin films
NASA Astrophysics Data System (ADS)
Pandey, Ratnesh K.; Kumar, Manvendra; Khan, Saif A.; Kumar, Tanuj; Tripathi, Ambuj; Avasthi, D. K.; Pandey, Avinash C.
2014-01-01
In the present work thin films of CaF2 deposited on Si substrate by electron beam evaporation have been investigated for swift heavy ions induced sputtering and surface modifications. Glancing angle X-ray Diffraction (GAXRD) measurements show that the pristine films are polycrystalline in nature and the grain size increases with increase in film thickness. Rutherford backscattering spectrometry (RBS) of pristine as well as irradiated films was performed to determine the sputter yield of CaF2 and a decrease in sputter yield has been observed with increase in film thickness. Thermal spike model has been applied to explain this. The confinement of energy in the grains having size smaller than the electron mean free path (?) results in a higher sputtering yield. Atomic force microscopy (AFM) studies of irradiated CaF2 thin films show formation of cracks on film surface at a fluence of 5 × 1012 ions/cm2. Also RBS results confirm the removal of film from the surface and more exposure of substrate with increasing dose of ions.
Jovian modulation of interplanetary electrons as observed with Voyagers 1 and 2
NASA Technical Reports Server (NTRS)
Schardt, A. W.; Mcdonald, F. B.; Trainor, J. H.
1982-01-01
The release of magnetospheric electrons from Jupiter into interplanetary space is modulated by the Jovian rotation period. The Voyager 1 and 2 observations showed that the modulation period agrees on the average with the synodic period of Jupiter (9h 55m 33.12s), but over intervals of weeks it can differ from the synodic period by several minutes. The lack of exact synchronization is attributed to changes of the plasma population in the Jovian magnetosphere. The Jovian modulation appears to be a persistent feature of the interaction between the solar wind and the magnetosphere and the disappearance of the modulation away from Jupiter is attributed to interplanetary propagation conditions. This leads to the following limits on the diffuse coefficient for interplanetary electrons: kappa perpendicular is or = 8 x 10 to the 19th power sq cm/s and kappa parallel is or = 10 to the 21st power sq cm/s. Modulation was still detectable at 3.8 A.U. behind Jupiter in the far magnetotail. This requires a mean free path in the tail 0.75 A.U. and good field connection along the tail to Jupiter.
NASA Astrophysics Data System (ADS)
Park, Sora; Kwon, Young-Kyun; Tománek, David
2012-02-01
We study the thermal and electronic transport properties of rigidly-interconnected structures having sp^2 carbon minimal surface called schwarzites. The system consists of core parts composed of schwarzite and interconnection parts with (4,4) carbon nanotube segments [1]. Using direct molecular dynamics simulations with the Tersoff potential, we compute the thermal conductivity of various configurations to explore the dependence on the number of core parts and on the length of interconnection parts. Our calculations show that each core part plays as a scattering center, which reduces the phonon mean free path and thus the thermal conductivity. We also investigate the electronic transport properties of the system by applying the non-equilibrium Green function approach in combination with density functional theory. We explore the effects of different core connectivity and structural defects introduced near the core parts on the electrical conductance. These thermal and electonic properties may be connected to the thermoelectric properties of the schwarzite system.[1] S. Park, K. Kittimanapun, J. S. Ahn, Y.-K. Kwon and D. Tom'anek, J. Phys.: Condens. Matter 22, 334220 (2010).
Total cross-sections for positron and electron scattering from ?-tetrahydrofurfuryl alcohol
NASA Astrophysics Data System (ADS)
Zecca, A.; Chiari, L.; García, G.; Blanco, F.; Trainotti, E.; Brunger, M. J.
2011-06-01
In this paper, we report original measurements of total cross-sections (TCSs) for positron scattering from an important biomolecule, ?-tetrahydrofurfuryl alcohol (THFA). The energy range of these measurements was 0.15-50.15 eV, whereas the energy resolution was ~260 meV. In addition, we report theoretical results, calculated within the independent-screened additivity rule (IAM-SCAR) formalism, on the corresponding electron impact total cross-sections. In this case, the energy range is 1-10 000 eV. With the advent of new particle track simulation codes, which incorporate accurate atomic and molecular data in order to provide interaction details at the nanoscale, interest in positron and electron TCSs has enjoyed something of a recent renaissance as they specify the mean free path between collisions in such codes. Because the present data are, to the best of our knowledge, the first TCSs to be reported for positron scattering from THFA, they fill an important void in the knowledge available to us from the literature.
ERIC Educational Resources Information Center
McGarvey, Lynn M.; Sterenberg, Gladys Y.; Long, Julie S.
2013-01-01
The authors elucidate what they saw as three important challenges to overcome along the path to becoming elementary school mathematics teacher leaders: marginal interest in math, low self-confidence, and teaching in isolation. To illustrate how these challenges were mitigated, they focus on the stories of two elementary school teachers--Laura and…
DNA Computing Hamiltonian path
Hagiya, Masami
2014 DNA DNA #12;DNA Computing · Feynman · Adleman · DNASIMD · ... · · · · · DNADNA #12;DNA · DNA · · · · DNA · · #12;2000 2005 2010 1995 Hamiltonian path DNA tweezers DNA tile DNA origami DNA box Sierpinski DNA tile self assembly DNA logic gates Whiplash PCR DNA automaton DNA spider MAYA
ERIC Educational Resources Information Center
Coleman, Toni
2012-01-01
A growing number of institutions are being more deliberate about bringing in fundraisers who fit the culture of the development department and about assessing skills and providing training that fill specific needs. Development shops are paying more attention to cultivating their staffs, staying attuned to employees' needs and creating career paths…
NSDL National Science Digital Library
CareerPath offers a searchable index of employment ads from six major newspapers: The Boston Globe, Chicago Tribune, Los Angeles Times, The New York Times, The San Jose Mercury News, and The Washington Post. The total ads available on October 21 was 21,442. The site is attractive and easy to use.
ERIC Educational Resources Information Center
Grimm, Karen
1999-01-01
Describes "Off the Beaten Path", a program that takes at-risk students out of the traditional classroom and puts them into a camping atmosphere in order to increase academic achievement, improve self-esteem, and promote better social skills. (WRM)
ERIC Educational Resources Information Center
Rodia, Becky
2004-01-01
This article profiles Diane Stanley, an author and illustrator of children's books. Although she was studying to be a medical illustrator in graduate school, Stanley's path changed when she got married and had children. As she was raising her children, she became increasingly enamored of the colorful children's books she would check out of the…
NASA Technical Reports Server (NTRS)
Bill, R. C.; Johnson, R. D. (inventors)
1979-01-01
A gas path seal suitable for use with a turbine engine or compressor is described. A shroud wearable or abradable by the abrasion of the rotor blades of the turbine or compressor shrouds the rotor bades. A compliant backing surrounds the shroud. The backing is a yieldingly deformable porous material covered with a thin ductile layer. A mounting fixture surrounds the backing.
2013-03-05
where j a differential 1-form on some vector space V and t/Xt is a path in V not necessarily of .... Let C be the algebra of bounded continuous functions from R to R and ... Let OC g be the subspace of elements XAOC such that. jjXjjg :¼ sup t;
Tunable path centrality: Quantifying the importance of paths in networks
NASA Astrophysics Data System (ADS)
Pu, Cun-Lai; Cui, Wei; Yang, Jian
2014-07-01
Centrality is a fundamental measure in network analysis. Specifically, centrality of a path describes the importance of the path with respect to the remaining part of the network. In this paper, we propose a tunable path centrality (TPC) measure, which quantifies the centrality of a path by integrating the path degree (PD) (number of neighbors of the path) and the path bridge (PB) (number of bridges in the path) with a control parameter ?. Considering the complexity of large-scale and dynamical topologies of many real-world networks, both PD and PB are computed with only the local topological structure of a path. We demonstrate the distribution of the three path centralities (TPC, PD and PB) in computer-generated networks and real-world networks. Furthermore, we apply the three path centralities to the network fragility problem, and exploit the distribution of the optimal control parameter ? through simulation and analysis. Finally, the simulation results show that generally TPC is more efficient than PD and PB in the network fragility problem. These path centralities are also applicable in many other network problems including spread, control, prediction and so on.
Geoffrey F. Chew
2008-02-21
Arrowed-time divergence-free rules or cosmological quantum dynamics are formulated through stepped Feynman paths across macroscopic slices of Milne spacetime. Slice boundaries house totally-relativistic rays representing elementary entities--preons. Total relativity and the associated preon Fock space, despite distinction from special relativity (which lacks time arrow), are based on the Lorentz group. Each path is a set of cubic vertices connected by straight, directed and stepped arcs that carry inertial, electromagnetic and gravitational action. The action of an arc step comprises increments each bounded by Planck's constant. Action from extremely-distant sources is determined by universe mean energy density. Identifying the arc-step energy that determines inertial action with that determining gravitational action establishes both arc-step length and universe density. Special relativity is accurate for physics at laboratory spacetime scales far below that of Hubble and far above that of Planck.
Louis Fishman
2006-01-01
The multidimensional, scalar Helmholtz equation of mathematical physics is addressed. Rather than pursuing traditional approaches for the representation and computation of the fundamental solution, path integral representations, originating in quantum physics, are considered. Constructions focusing on the global, two-way nature of the Helmholtz equation, such as the Feynman\\/Fradkin, Feynman\\/Garrod, and Feynman\\/DeWitt-Morette representations, are reviewed, in addition to the complementary phase
Studness, C.M.
1995-05-01
The financial community`s focus on utility competition has been riveted on the proceedings now in progress at state regulatory commissions. The fear that something immediately damaging will come out of these proceedings seems to have diminished in recent months, and the stock market has reacted favorably. However, regulatory developments are only one of four paths leading to competition; the others are the marketplace, the legislatures, and the courts. Each could play a critical role in the emergence of competition.
Parsimonious path openings and closings.
Morard, Vincent; Dokladal, Petr; Decenciere, Etienne
2014-04-01
Path openings and closings are morphological tools used to preserve long, thin, and tortuous structures in gray level images. They explore all paths from a defined class, and filter them with a length criterion. However, most paths are redundant, making the process generally slow. Parsimonious path openings and closings are introduced in this paper to solve this problem. These operators only consider a subset of the paths considered by classical path openings, thus achieving a substantial speed-up, while obtaining similar results. In addition, a recently introduced 1D opening algorithm is applied along each selected path. Its complexity is linear with respect to the number of pixels, independent of the size of the opening. Furthermore, it is fast for any input data accuracy (integer or floating point) and works in stream. Parsimonious path openings are also extended to incomplete paths, i.e., paths containing gaps. Noise-corrupted paths can thus be processed with the same approach and complexity. These parsimonious operators achieve a several orders of magnitude speed-up. Examples are shown for incomplete path openings, where computing times are brought from minutes to tens of milliseconds, while obtaining similar results. PMID:24569442
MINIMUM WEIGHT PATHS TIMEDEPENDENT NETWORKS
Orda, Ariel
MINIMUM WEIGHT PATHS in TIMEDEPENDENT NETWORKS Ariel Orda Raphael Rom Department of Electrical) ABSTRACT We investigate the minimum weight path problem in networks whose link weights and link delays are both functions of time. We demonstrate that in general there exist cases in which no finite path
PATHS groundwater hydrologic model
Nelson, R.W.; Schur, J.A.
1980-04-01
A preliminary evaluation capability for two-dimensional groundwater pollution problems was developed as part of the Transport Modeling Task for the Waste Isolation Safety Assessment Program (WISAP). Our approach was to use the data limitations as a guide in setting the level of modeling detail. PATHS Groundwater Hydrologic Model is the first level (simplest) idealized hybrid analytical/numerical model for two-dimensional, saturated groundwater flow and single component transport; homogeneous geology. This document consists of the description of the PATHS groundwater hydrologic model. The preliminary evaluation capability prepared for WISAP, including the enhancements that were made because of the authors' experience using the earlier capability is described. Appendixes A through D supplement the report as follows: complete derivations of the background equations are provided in Appendix A. Appendix B is a comprehensive set of instructions for users of PATHS. It is written for users who have little or no experience with computers. Appendix C is for the programmer. It contains information on how input parameters are passed between programs in the system. It also contains program listings and test case listing. Appendix D is a definition of terms.
Physics Letters A 166 ( 1992) 24-28 North-Holland
Presilla, Carlo
March 1992; accepted for publication 7 April 1992 Communicated by A.P. Fordy A model for dealing comparable to the mean free path of the tunneling electrons is discussed. The use of tunneling probes is not assured. When the sample has a size smaller than the mean free path for inelastic scattering the energy
Anomalous magnetotransport in chemically doped carbon nanotubes.
Latil, Sylvain; Triozon, François; Roche, Stephan
2005-09-16
We report on anomalous magnetotransport features in chemically doped, weakly disordered carbon nanotubes. Under the application of a magnetic field parallel to the tube axis, hole conduction is shown to be strongly affected by impurity scattering with short mean free path and negative magnetoresistance, strongly different from electron conduction with much longer mean free path and positive magnetoresistance behavior. PMID:16197097
Strocov, Vladimir N; Shi, Ming; Kobayashi, Masaki; Monney, Claude; Wang, Xiaoqiang; Krempasky, Juraj; Schmitt, Thorsten; Patthey, Luc; Berger, Helmuth; Blaha, Peter
2012-08-24
The resolution of angle-resolved photoelectron spectroscopy (ARPES) in three-dimensional (3D) momentum k is fundamentally limited by ill defined surface-perpendicular wave vector k(perpendicular) associated with the finite photoelectron mean free path. Pushing ARPES into the soft-x-ray energy region sharpens the k(perpendicular) definition, allowing accurate electronic structure investigations in 3D materials. We apply soft-x-ray ARPES to explore the 3D electron realm in a paradigm transition metal dichalcogenide VSe2. Essential to break through the dramatic loss of the valence band photoexcitation cross section at soft-x-ray energies is the advanced photon flux performance of our synchrotron instrumentation. By virtue of the sharp 3D momentum definition, the soft-x-ray ARPES experimental band structure and Fermi surface of VSe2 show a textbook clarity. We identify pronounced 3D warping of the Fermi surface and show that its concomitant nesting acts as the precursor for the exotic 3D charge-density waves in VSe2. Our results demonstrate the immense potential of soft-x-ray ARPES to explore details of 3D electronic structure. PMID:23002761
NASA Technical Reports Server (NTRS)
Prabhakaran, Nagarajan; Rishe, Naphtali; Athauda, Rukshan
1997-01-01
The South East coastal region experiences hurricane threat for almost six months in every year. To improve the accuracy of hurricane forecasts, meteorologists would need the storm paths of both the present and the past. A hurricane path can be established if we could identify the correct position of the storm at different times right from its birth to the end. We propose a method based on both spatial and temporal image correlations to locate the position of a storm from satellite images. During the hurricane season, the satellite images of the Atlantic ocean near the equator are examined for the hurricane presence. This is accomplished in two steps. In the first step, only segments with more than a particular value of cloud cover are selected for analysis. Next, we apply image processing algorithms to test the presence of a hurricane eye in the segment. If the eye is found, the coordinate of the eye is recorded along with the time stamp of the segment. If the eye is not found, we examine adjacent segments for the existence of hurricane eye. It is probable that more than one hurricane eye could be found from different segments of the same period. Hence, the above process is repeated till the entire potential area for hurricane birth is exhausted. The subsequent/previous position of each hurricane eye will be searched in the appropriate adjacent segments of the next/previous period to mark the hurricane path. The temporal coherence and spatial coherence of the images are taken into account by our scheme in determining the segments and the associated periods required for analysis.
NASA Technical Reports Server (NTRS)
Mehhtz, Peter
2005-01-01
JPF is an explicit state software model checker for Java bytecode. Today, JPF is a swiss army knife for all sort of runtime based verification purposes. This basically means JPF is a Java virtual machine that executes your program not just once (like a normal VM), but theoretically in all possible ways, checking for property violations like deadlocks or unhandled exceptions along all potential execution paths. If it finds an error, JPF reports the whole execution that leads to it. Unlike a normal debugger, JPF keeps track of every step how it got to the defect.
Bleakley, Hoyt; Lin, Jeffrey
2012-05-01
We examine portage sites in the U.S. South, Mid-Atlantic, and Midwest, including those on the fall line, a geomorphological feature in the southeastern U.S. marking the final rapids on rivers before the ocean. Historically, waterborne transport of goods required portage around the falls at these points, while some falls provided water power during early industrialization. These factors attracted commerce and manufacturing. Although these original advantages have long since been made obsolete, we document the continuing importance of these portage sites over time. We interpret these results as path dependence and contrast explanations based on sunk costs interacting with decreasing versus increasing returns to scale. PMID:23935217
NSDL National Science Digital Library
The well known Berkeley Digital Library SunSite, discussed in the February 9, 1996 Scout Report, has recently added a new resource to its collection. The PATH database, maintained by the Harmer E. Davis Transportation Library at the University of California, is "the world's largest bibliographical database pertaining to Intelligent Transportation Systems (ITS)." It is searchable and browsable (Browse by ITS Thesaurus Term), and contains over 9,000 records and abstracts "including monographs, journal articles, conference papers, technical reports, theses and selected media coverage," dating back to the 1940s.
Bleakley, Hoyt; Lin, Jeffrey
2012-01-01
We examine portage sites in the U.S. South, Mid-Atlantic, and Midwest, including those on the fall line, a geomorphological feature in the southeastern U.S. marking the final rapids on rivers before the ocean. Historically, waterborne transport of goods required portage around the falls at these points, while some falls provided water power during early industrialization. These factors attracted commerce and manufacturing. Although these original advantages have long since been made obsolete, we document the continuing importance of these portage sites over time. We interpret these results as path dependence and contrast explanations based on sunk costs interacting with decreasing versus increasing returns to scale. PMID:23935217
Counting Depth Zero Patterns in Ballot Paths
Niederhausen, Heinrich
Counting Depth Zero Patterns in Ballot Paths Heinrich Niederhausen and Shaun Sullivan Florida it to the enu- meration of certain lattice paths. The lattice paths we consider are ballot paths. A ballot path is a path that stays weakly above the diagonal y = x, starts at the origin, and takes steps from the set f
Calculations of stopping powers of 100 eV-30 keV electrons in 31 elemental solids
Tanuma, S.; Powell, C. J.; Penn, D. R.
2008-03-15
We present calculated electron stopping powers (SPs) for 31 elemental solids (Li, Be, glassy C, graphite, diamond, Na, Mg, K, Sc, Ti, V, Fe, Y, Zr, Nb, Mo, Ru, Rh, In, Sn, Cs, Gd, Tb, Dy, Hf, Ta, W, Re, Os, Ir, and Bi). These SPs were determined with an algorithm previously used for the calculation of electron inelastic mean free paths and from energy-loss functions (ELFs) derived from experimental optical data. The SP calculations were made for electron energies between 100 eV and 30 keV and supplement our earlier SP calculations for ten additional solids (Al, Si, Cr, Ni, Cu, Ge, Pd, Ag, Pt, and Au). Plots of SP versus atomic number for the group of 41 solids show clear trends. Multiple peaks and shoulders are seen that result from the contributions of valence-electron and various inner-shell excitations. Satisfactory agreement was found between the calculated SPs and values from the relativistic Bethe SP equation with recommended values of the mean excitation energy (MEE) for energies above 10 keV. We determined effective MEEs versus maximum excitation energy from the ELFs for each solid. Plots of effective MEE versus atomic number showed the relative contributions of valence-electron and different core-electron excitations to the MEE. For a maximum excitation energy of 30 keV, our effective MEEs agreed well for Be, graphite, Na, Al, and Si with recommended MEEs; a difference for Li was attributed to sample oxidation in the SP measurements for the recommended MEE. Substantially different effective MEEs were found for the three carbon allotropes (graphite, diamond, and glassy C)
NASA Technical Reports Server (NTRS)
Krause, L. Habsh; Gilchrist, B. E.; Nishikawa, Ken-Ichi
2013-01-01
Relativisitic electron precipitation (REP) events occur when beams or bunches of relativistic electrons of magnetospheric origin enter the Earth's atmosphere, typically at auroral latitudes. REP events are associated with a variety of space weather effects, including production of transitional and bremsstrahlung radiation, catalytic depletion of stratospheric ozone, and scintillation of transionospheric radio waves. This study examines the intensities of x-rays produced at airliner, manned balloon, and space reuseable launch vehicles (sRLVs). The monoenergetic beam is modeled in cylindrical symetry using the paraxial ray equation. Bremsstrahlung photon production is calculated using the traditional Sauter-Elwert cross-section, providing x-ray emission spectra differential in energy and angle. Attenuation is computed for a plane-stratified standard atmosphere, and the loss processes include photoionization, Rayleigh and Compton scattering, electron-positron pair production, and photonuclear interaction. Peak altitudes of electron energy deposition and bremsstrahlung x-ray production were calculated for beams of energies from 1 MeV through 100 MeV. The altitude peak of bremsstrahlung deposition was consistently and significantly lower that that of the electron deposition due to the longer mean free paths of x-rays compared to electrons within the atmosphere. For example, for a nadir-directed monoenergetic 5 MeV beam, the peak deposition altitude was calculated to be 42 km, but the resulting bremsstrahlung deposition peaked at 25 km. This has implications for crew and passenger safety, especially with the growth of the space tourism industry. A survey of results covering the 1-100 MeV spectrum for the three altitude ranges of interest will be presented.
Hardwick, R D
1989-01-01
The design and implementation of an Intrusion Path Analysis (IPA) function came about as a result of the upgrades to the security systems at the Savannah River Site (SRS), near Aiken, South Carolina. The stated requirements for IPA were broad, leaving opportunity for creative freedom during design and development. The essential elements were that it: be based on alarm and sensor state data; consider insider as well as outsider threats; be flexible and easily enabled or disabled; not be processor intensive; and provide information to the operator in the event the analysis reveals possible path openings. The final design resulted from many and varied conceptual inputs, and will be implemented in selected test areas at SRS. It fulfils the requirements and: allows selective inclusion of sensors in the analysis; permits the formation of concentric rings of protection around assets; permits the defining of the number of rings which must be breached before issuing an alert; evaluates current sensor states as well as a recent, configurable history of sensor states; considers the sensors' physical location, with respect to the concentric rings; and enables changes for maintenance without software recompilation. 3 figs.
NASA Technical Reports Server (NTRS)
2008-01-01
[figure removed for brevity, see original site] Click on the image for movie of Phoenix's Path to Mars
This artist's animation shows the route NASA's Phoenix Mars Lander took to get from Earth to Mars. The spacecraft's path is shown in yellow, and the orbits of Mars and Earth are shown in red and blue, respectively.
Phoenix was launched from Cape Canaveral Air Force Station, Fla., on Aug. 4, 2007, when Earth and Mars were 195 million kilometers (121 million miles) apart. It will have traveled a total of 679 million kilometers (422 million miles) when it is scheduled to reach Mars on May 25, 2008. At that time, Earth and Mars will be farther apart, at 276 million kilometers (171 million miles).
The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver
NASA Astrophysics Data System (ADS)
Cao, Duc; Moses, Gregory; Delettrez, Jacques
2015-08-01
An implicit, non-local thermal conduction algorithm based on the algorithm developed by Schurtz, Nicolai, and Busquet (SNB) [Schurtz et al., Phys. Plasmas 7, 4238 (2000)] for non-local electron transport is presented and has been implemented in the radiation-hydrodynamics code DRACO. To study the model's effect on DRACO's predictive capability, simulations of shot 60 303 from OMEGA are completed using the iSNB model, and the computed shock speed vs. time is compared to experiment. Temperature outputs from the iSNB model are compared with the non-local transport model of Goncharov et al. [Phys. Plasmas 13, 012702 (2006)]. Effects on adiabat are also examined in a polar drive surrogate simulation. Results show that the iSNB model is not only capable of flux-limitation but also preheat prediction while remaining numerically robust and sacrificing little computational speed. Additionally, the results provide strong incentive to further modify key parameters within the SNB theory, namely, the newly introduced non-local mean free path. This research was supported by the Laboratory for Laser Energetics of the University of Rochester.
Fetzer, Roman; Stadtmüller, Benjamin; Ohdaira, Yusuke; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Taira, Tomoyuki; Uemura, Tetsuya; Yamamoto, Masafumi; Aeschlimann, Martin; Cinchetti, Mirko
2015-01-01
Ultraviolet photoemission spectroscopy (UPS) is a powerful tool to study the electronic spin and symmetry features at both surfaces and interfaces to ultrathin top layers. However, the very low mean free path of the photoelectrons usually prevents a direct access to the properties of buried interfaces. The latter are of particular interest since they crucially influence the performance of spintronic devices like magnetic tunnel junctions (MTJs). Here, we introduce spin-resolved extremely low energy photoemission spectroscopy (ELEPS) to provide a powerful way for overcoming this limitation. We apply ELEPS to the interface formed between the half-metallic Heusler compound Co2MnSi and the insulator MgO, prepared as in state-of-the-art Co2MnSi/MgO-based MTJs. The high accordance between the spintronic fingerprint of the free Co2MnSi surface and the Co2MnSi/MgO interface buried below up to 4?nm MgO provides clear evidence for the high interface sensitivity of ELEPS to buried interfaces. Although the absolute values of the interface spin polarization are well below 100%, the now accessible spin- and symmetry-resolved wave functions are in line with the predicted existence of non-collinear spin moments at the Co2MnSi/MgO interface, one of the mechanisms evoked to explain the controversially discussed performance loss of Heusler-based MTJs at room temperature. PMID:25702631
Path integrals on curved manifolds
NASA Astrophysics Data System (ADS)
Grosche, C.; Steiner, F.
1987-12-01
A general framework for treating path integrals on curved manifolds is presented. We also show how to perform general coordinate and space-time transformations in path integrals. The main result is that one has to subtract a quantum correction ?V˜ h 2 from the classical Lagrangian ?, i.e. the correct effective Lagrangian to be used in the path integral is ?eff = ?- ?V. A general prescription for calculating the quantum correction ? V is given. It is based on a canonical approach using Weyl-ordering and the Hamiltonian path integral defined by the midpoint prescription. The general framework is illustrated by several examples: The d-dimensional rotator, i.e. the motion on the sphere S d-1, the path integral in d-dimensional polar coordinates, the exact treatment of the hydrogen atom in R 2 and R 3 by performing a Kustaanheimo-Stiefel transformation, the Langer transformation and the path integral for the Morse potential.
Iterative path attacks on networks
NASA Astrophysics Data System (ADS)
Pu, Cunlai; Li, Siyuan; Michaelson, Andrew; Yang, Jian
2015-08-01
We investigate a path-attack process on model networks and real-world networks. Based on the local topological structure of a path, we propose an attack centrality measure with a control parameter ? for quantifying the influence of a path. In the path-attack process, we iteratively remove the path with the largest attack centrality from a network. Results demonstrate that, for a specific network, there is an optimal ? which results in maximum attack efficiency. The denser and more homogeneous the networks, the more robust the networks are against iterative path attacks. Our work helps to explain the vulnerability of networks and provides some clues about the protection and design of real complex systems.
CURRENT SHEET REGULATION OF SOLAR NEAR-RELATIVISTIC ELECTRON INJECTION HISTORIES
Agueda, N.; Sanahuja, B. [Departament d'Astronomia i Meteorologia, Institut de Ciencies del Cosmos, Universitat de Barcelona (Spain); Vainio, R. [Department of Physics, University of Helsinki (Finland); Dalla, S. [Jeremiah Horrocks Institute, University of Central Lancashire (United Kingdom); Lario, D. [Applied Physics Laboratory, Johns Hopkins University (United States)
2013-03-10
We present a sample of three large near-relativistic (>50 keV) electron events observed in 2001 by both the ACE and the Ulysses spacecraft, when Ulysses was at high-northern latitudes (>60 Degree-Sign ) and close to 2 AU. Despite the large latitudinal distance between the two spacecraft, electrons injected near the Sun reached both heliospheric locations. All three events were associated with large solar flares, strong decametric type II radio bursts and accompanied by wide (>212 Degree-Sign ) and fast (>1400 km s{sup -1}) coronal mass ejections (CMEs). We use advanced interplanetary transport simulations and make use of the directional intensities observed in situ by the spacecraft to infer the electron injection profile close to the Sun and the interplanetary transport conditions at both low and high latitudes. For the three selected events, we find similar interplanetary transport conditions at different heliolatitudes for a given event, with values of the mean free path ranging from 0.04 AU to 0.27 AU. We find differences in the injection profiles inferred for each spacecraft. We investigate the role that sector boundaries of the heliospheric current sheet (HCS) have on determining the characteristics of the electron injection profiles. Extended injection profiles, associated with coronal shocks, are found if the magnetic footpoints of the spacecraft lay in the same magnetic sector as the associated flare, while intermittent sparse injection episodes appear when the spacecraft footpoints are in the opposite sector or a wrap in the HCS bounded the CME structure.
Interactive cutting path analysis programs
NASA Technical Reports Server (NTRS)
Weiner, J. M.; Williams, D. S.; Colley, S. R.
1975-01-01
The operation of numerically controlled machine tools is interactively simulated. Four programs were developed to graphically display the cutting paths for a Monarch lathe, Cintimatic mill, Strippit sheet metal punch, and the wiring path for a Standard wire wrap machine. These programs are run on a IMLAC PDS-ID graphic display system under the DOS-3 disk operating system. The cutting path analysis programs accept input via both paper tape and disk file.
Handbook of Feynman Path Integrals
NASA Astrophysics Data System (ADS)
Grosche, Christian, Steiner, Frank
The Handbook of Feynman Path Integrals appears just fifty years after Richard Feynman published his pioneering paper in 1948 entitled "Space-Time Approach to Non-Relativistic Quantum Mechanics", in which he introduced his new formulation of quantum mechanics in terms of path integrals. The book presents for the first time a comprehensive table of Feynman path integrals together with an extensive list of references; it will serve the reader as a thorough introduction to the theory of path integrals. As a reference book, it is unique in its scope and will be essential for many physicists, chemists and mathematicians working in different areas of research.
Path Integration in Conical Space
Akira Inomata; Georg Junker
2011-11-24
Quantum mechanics in conical space is studied by the path integral method. It is shown that the curvature effect gives rise to an effective potential in the radial path integral. It is further shown that the radial path integral in conical space can be reduced to a form identical with that in flat space when the discrete angular momentum of each partial wave is replaced by a specific non-integral angular momentum. The effective potential is found proportional to the squared mean curvature of the conical surface embedded in Euclidean space. The path integral calculation is compatible with the Schr\\"odinger equation modified with the Gaussian and the mean curvature.
MultiPath TCP -Architecture MultiPath TCP -Receive-Buffer
Bonaventure, Olivier
MultiPath TCP - Architecture MultiPath TCP - Receive-Buffer MultiPath TCP - Congestion Control MultiPath TCP - Live-Demo MultiPath TCP: From Theory to Practice S´ebastien Barr´e Christoph Paasch - Olivier Bonaventure MultiPath TCP: From Theory to Practice 1 / 17 #12;MultiPath TCP - Architecture Multi
Thermoalgebras and path integral
Khanna, F.C. [Theoretical Physics Institute, University of Alberta, Edmonton, AB T6G 2J1 (Canada); TRIUMF, Vancouver, BC, V6T 2A3 (Canada)], E-mail: khanna@phys.ualberta.ca; Malbouisson, A.P.C. [Centro Brasileiro de Pesquisas Fisicas/MCT, 22290-180 Rio de Janeiro, RJ (Brazil)], E-mail: adolfo@cbpf.br; Malbouisson, J.M.C. [Instituto de Fisicas, Universidade Federal da Bahia, 40210-340 Salvador, BA (Brazil)], E-mail: jmalboui@ufba.br; Santana, A.E. [Instituto de Fisicas, Universidade de Brasilia, 70910-900 Brasilia, DF (Brazil)], E-mail: asantana@fis.unb.br
2009-09-15
Using a representation for Lie groups closely associated with thermal problems, we derive the algebraic rules of the real-time formalism for thermal quantum field theories, the so-called thermo-field dynamics (TFD), including the tilde conjugation rules for interacting fields. These thermo-group representations provide a unified view of different approaches for finite-temperature quantum fields in terms of a symmetry group. On these grounds, a path integral formalism is constructed, using Bogoliubov transformations, for bosons, fermions and non-abelian gauge fields. The generalization of the results for quantum fields in (S{sup 1}){sup d}xR{sup D-d} topology is addressed.
Restoration by Path Concatenation: Fast Recovery of MPLS Paths
Bremler-Barr, Anat
Restoration by Path Concatenation: Fast Recovery of MPLS Paths Yehuda Afek Anat Bremler techniques in MPLS (multiprotocol label switching), to achieve powerful schemes for restoration in MPLS based networks. We thus transform MPLS into a flexible and robust method for forward ing packets
Restoration by Path Concatenation: Fast Recovery of MPLS Paths
Kaplan, Haim
Restoration by Path Concatenation: Fast Recovery of MPLS Paths Yehuda Afek Anat Bremler-Barr Haim techniques in MPLS (multi-protocol label switching), to achieve powerful schemes for restoration in MPLS based networks. We thus transform MPLS into a flexible and robust method for forward- ing packets
Finding Good Paths: Applications of Least Cost Caloric Path Computations
Wood, Zoë J.
for crowds and individuals. 1 Introduction Humans have been traveling by foot for thousands of years and the task of finding good foot-paths to travel from point A to point B is something we all think about with disabilities, an individual planning out his or her path in a freeform race or even in arche- ology, to model
Ab-initio path integral techniques for molecules
Daejin Shin; Ming-Chak Ho; J. Shumway
2006-11-09
Path integral Monte Carlo with Green's function analysis allows the sampling of quantum mechanical properties of molecules at finite temperature. While a high-precision computation of the energy of the Born-Oppenheimer surface from path integral Monte Carlo is quite costly, we can extract many properties without explicitly calculating the electronic energies. We demonstrate how physically relevant quantities, such as bond-length, vibrational spectra, and polarizabilities of molecules may be sampled directly from the path integral simulation using Matsubura (temperature) Green's functions (imaginary-time correlation functions). These calculations on the hydrogen molecule are a proof-of-concept, designed to motivate new work on fixed-node path-integral calculations for molecules.
Virtual heights for oblique path calculations
NASA Astrophysics Data System (ADS)
Reilly, Michael H.
1995-05-01
The propagation model of the Ionospheric Communications Analysis and Predictions Program (IONCAP) program, which is designed for fast throughput calculations in the prediction of high-frequency sky wave system performance, makes use of virtual heights, as calculated from known height profiles of the electron density. Use of these for oblique path calculations relies on the well known flat Earth theorems of Breit-Tuve and Martyn, with additional curved Earth correction terms. These approximate corrections are examined in the light of exact results from other models, and alternative strategies are discussed.
NASA Astrophysics Data System (ADS)
Khrabrov, Alexander V.; Kaganovich, Igor D.; Ventzek, Peter L. G.; Ranjan, Alok; Chen, Lee
2015-10-01
Low-pressure capacitively-coupled discharges with additional dc bias applied to a separate electrode are utilized in plasma-assisted etching for semiconductor device manufacturing. Measurements of the electron velocity distribution function (EVDF) of the flux impinging on the wafer, as well as in the plasma bulk, show a thermal population and additional peaks within a broad range of energies. That range extends from the thermal level up to the value for the ‘ballistic’ peak, corresponding to the bias potential. The non-thermal electron flux has been correlated to alleviating the electron shading effect and providing etch-resistance properties to masking photoresist layers. ‘Middle-energy peak electrons’ at energies of several hundred eV may provide an additional sustaining mechanism for the discharge. These features in the electron velocity (or energy) distribution functions are possibly caused by secondary electrons emitted from the electrodes and interacting with two high-voltage sheaths: a stationary sheath at the dc electrode and an oscillating self-biased sheath at the powered electrode. Since at those energies the mean free path for large-angle scattering (momentum relaxation length) is comparable to, or exceeds the size of the discharge gap, these ‘ballistic’ electrons will not be fully scattered by the background gas as they traverse the inter-electrode space. We have performed test-particle simulations in which the features in the EVDF of electrons impacting the RF electrode are fully resolved at all energies. An analytical model has been developed to predict existence of peaked and step-like structures in the EVDF. Those features can be explained by analyzing the kinematics of electron trajectories in the discharge gap. Step-like structures in the EVDF near the powered electrode appear due to accumulation of electrons emitted from the dc electrode within a portion of the RF cycle, and their subsequent release. Trapping occurs when the RF sheath voltage exceeds the applied bias, and is decreasing. The secondary electrons originating from the dc-biased surface also form a peak near the energy equal to the bias potential. Additional peaks, at lower energies, are formed by the electrons emitted from the RF electrode and eventually escaping to it. The latter can be grouped according to the number of bounces between the sheaths during their residence time in the discharge. Each of such groups may give rise to an individual peak in the distribution. The trap-and-release theory developed in this paper provides a convincing explanation for the observations of the ballistic and ‘middle energy peak’ electrons detected in experiments.
Path Integral Methods Nancy Makri
Makri, Nancy
attractions can be summarized as follows: the path integral formulation offers an ideal way of obtaining approach to many-body problems; and it leads to powerful influence functional meth- ods for studying this expression with the same weight. In the classical limit 0 small variations of a path generally result
Path Integrals for Photonic Crystals
Dimant, Yair
2009-01-01
We develop a path integrals approach for analyzing stationary light propagation appropriate for photonic crystals. The hermitian form of the stationary Maxwell equations is transformed into a quantum mechanical problem of a spin 1 particle with spin-orbit coupling and position dependent mass. After appropriate ordering several path integral representations of a solution are constructed. One leaves the propagation of polarization degrees of freedom in an operator form integrated over paths in coordinate space. The use of spin 1 coherent states allows to represent this part as a path integral over such states. Finally a path integral in transversal momentum space with explicit transversality enforced at every time slice is also given. As an example the geometrical optics limit is discussed and the ray equation is recovered together with the Rytov rotation of the polarization vector.
Automated path length and M{sub 56} measurements at Jefferson Lab
Hardy, D.; Tang, J.; Legg, R.
1997-08-01
Accurate measurement of path length and path length changes versus momentum (M{sub 56}) are critical for maintaining minimum beam energy spread in the CEBAF (Continuous Electron Beam Accelerator Facility) accelerator at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). The relative path length for each circuit of the beam (1256m) must be equal within 1.5 degrees of 1497 MHz RF phase. A relative path length measurement is made by measuring the relative phases of RF signals from a cavity that is separately excited for each pass of a 4.2 {mu}s pulsed beam. This method distinguishes the path length to less than 0.5 path length error. The development of a VME based automated measurement system for path length and M{sub 56} has contributed to faster machine setup time and has the potential for use as a feedback parameter for automated control.
E-beam ionized channel guiding of an intense relativistic electron beam
Frost, Charles A. (Albuquerque, NM); Godfrey, Brendon B. (Albuquerque, NM); Kiekel, Paul D. (Albuquerque, NM); Shope, Steven L. (Albuquerque, NM)
1988-01-01
An IREB is guided through a curved path by ionizing a channel in a gas with electrons from a filament, and confining the electrons to the center of the path with a magnetic field extending along the path. The magnetic field is preferably generated by a solenoid extending along the path.
E-beam ionized channel guiding of an intense relativistic electron beam
Frost, C.A.; Godfrey, B.B.; Kiekel, P.D.; Shope, S.L.
1988-05-10
An IREB is guided through a curved path by ionizing a channel in a gas with electrons from a filament, and confining the electrons to the center of the path with a magnetic field extending along the path. The magnetic field is preferably generated by a solenoid extending along the path. 2 figs.
Reasoning with Temporal Logic on Truncated Paths
Francalanza, Adrian
Reasoning with Temporal Logic on Truncated Paths Cindy Eisner1 Dana Fisman1,2 John Havlicek3 Yoad of reasoning with linear temporal logic on truncated paths. A truncated path is a path which is finite, but not necessarily maximal. Truncated paths arise naturally in several areas, among which are incomplete verification
Reconfigurable data path processor
NASA Technical Reports Server (NTRS)
Donohoe, Gregory (Inventor)
2005-01-01
A reconfigurable data path processor comprises a plurality of independent processing elements. Each of the processing elements advantageously comprising an identical architecture. Each processing element comprises a plurality of data processing means for generating a potential output. Each processor is also capable of through-putting an input as a potential output with little or no processing. Each processing element comprises a conditional multiplexer having a first conditional multiplexer input, a second conditional multiplexer input and a conditional multiplexer output. A first potential output value is transmitted to the first conditional multiplexer input, and a second potential output value is transmitted to the second conditional multiplexer output. The conditional multiplexer couples either the first conditional multiplexer input or the second conditional multiplexer input to the conditional multiplexer output, according to an output control command. The output control command is generated by processing a set of arithmetic status-bits through a logical mask. The conditional multiplexer output is coupled to a first processing element output. A first set of arithmetic bits are generated according to the processing of the first processable value. A second set of arithmetic bits may be generated from a second processing operation. The selection of the arithmetic status-bits is performed by an arithmetic-status bit multiplexer selects the desired set of arithmetic status bits from among the first and second set of arithmetic status bits. The conditional multiplexer evaluates the select arithmetic status bits according to logical mask defining an algorithm for evaluating the arithmetic status bits.
Shape Analysis as a Generalized Path Problem Thomas Reps
Reps, Thomas W.
, Madison, WI 53706. Telephone: (608) 262-1204. Electronic mail: reps@cs.wisc.edu. tions of selection to connect two vertices only if the con- catenation of the labels on the edges of the path is a word on the run- ning time of an algorithm for shape analysis. It also per- mits us to obtain a demand algorithm
Pon, Allison; Jewison, Timothy; Su, Yilu; Liang, Yongjie; Knox, Craig; Maciejewski, Adam; Wilson, Michael; Wishart, David S
2015-07-01
PathWhiz (http://smpdb.ca/pathwhiz) is a web server designed to create colourful, visually pleasing and biologically accurate pathway diagrams that are both machine-readable and interactive. As a web server, PathWhiz is accessible from almost any place and compatible with essentially any operating system. It also houses a public library of pathways and pathway components that can be easily viewed and expanded upon by its users. PathWhiz allows users to readily generate biologically complex pathways by using a specially designed drawing palette to quickly render metabolites (including automated structure generation), proteins (including quaternary structures, covalent modifications and cofactors), nucleic acids, membranes, subcellular structures, cells, tissues and organs. Both small-molecule and protein/gene pathways can be constructed by combining multiple pathway processes such as reactions, interactions, binding events and transport activities. PathWhiz's pathway replication and propagation functions allow for existing pathways to be used to create new pathways or for existing pathways to be automatically propagated across species. PathWhiz pathways can be saved in BioPAX, SBGN-ML and SBML data exchange formats, as well as PNG, PWML, HTML image map or SVG images that can be viewed offline or explored using PathWhiz's interactive viewer. PathWhiz has been used to generate over 700 pathway diagrams for a number of popular databases including HMDB, DrugBank and SMPDB. PMID:25934797
NASA Astrophysics Data System (ADS)
Bae, Hyo Won; Yel Lee, Jung; Lee, Ho-Jun; Lee, Hae June
2011-10-01
Recently, atmospheric pressure plasmas attract lots of interests for the useful applications such as surface modification and bio-medical treatment. In this study, a particle-in-cell Monte Carlo collision (PIC-MCC) simulation was adopted to investigate the discharge characteristics of a planar micro dielectric barrier discharge (DBD) with a driving frequency from 1 MHz to 50 MHz and with a gap distance from 60 to 500 micrometers. The variation of control parameters such as the gap distance, the driving wave form, and the applied voltage results in the change in the electron energy distribution function (EEDF). Through the relation between the ionization mean free path and the gap size, a significant change of EEDFs is achievable with the decrease of gap distance. Therefore, it is possible to categorize the operation range of DBDs for its applications by controlling the interactions between plasmas and neutral gas for the generation of preferable radicals. This work was supported by the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (No. 20104010100670).
An Electromechanical Which-Path Interferometer
A. D. Armour; M. P. Blencowe
2001-08-28
We investigate the possibility of an electromechanical which-path interferometer, in which electrons travelling through an Aharonov-Bohm ring incorporating a quantum dot in one of the arms are dephased by an interaction with the fundamental flexural mode of a radio frequency cantilever. The cantilever is positioned so that its tip lies just above the dot and a bias is applied so that an electric field exists between the dot and the tip. This electric field is modified when an additional electron hops onto the dot, coupling the flexural mode of the cantilever and the microscopic electronic degrees of freedom. We analyze the transmission properties of this system and the dependence of interference fringe visibility on the cantilever-dot coupling and on the mechanical properties of the cantilever. The fringes are progressively destroyed as the interaction with the cantilever is turned up, in part due to dephasing arising from the entanglement of the electron and cantilever states and also due to the thermal smearing that results from fluctuations in the state of the cantilever. When the dwell time of the electron on the dot is comparable to or longer than the cantilever period, we find coherent features in the transmission amplitude. These features are washed out when the cantilever is decohered by its coupling to the environment.
NASA Technical Reports Server (NTRS)
Chandler, J. A.
1983-01-01
Long helical vent path cools and releases hot pyrotechnical gas that exits along its spiraling threads. Current design uses 1/4-28 threads with outer diameter of stud reduced by 0.025 in. (0.62 mm). To open or close gassampler bottle, pyrotechnic charges on either one side or other of valve cylinder are actuated. Gases vented slowly over long path are cool enough to present no ignition hazard. Vent used to meter flow in refrigeration, pneumaticcontrol, and fluid-control systems by appropriately adjusting size and length of vent path.
NASA Astrophysics Data System (ADS)
Weatherford, Brandon R.; Xiong, Zhongmin; Barnat, E. V.; Kushner, Mark J.
2014-09-01
Fast ionization waves (FIWs), often generated with high voltage pulses over nanosecond timescales, are able to produce large volumes of ions and excited states at moderate pressures. The mechanisms of FIW propagation were experimentally and computationally investigated to provide insights into the manner in which these large volumes are excited. The two-dimensional structure of electron and metastable densities produced by short-pulse FIWs sustained in helium were measured using laser-induced fluorescence and laser collision-induced fluorescence diagnostics for times of 100-120 ns after the pulse, as the pressure was varied from 1 to 20 Torr. A trend of center-peaked to volume-filling to wall-peaked electron density profiles was observed as the pressure was increased. Instantaneous FIW velocities, obtained from plasma-induced emission, ranged from 0.1 to 3 × 109 cm s-1, depending on distance from the high voltage electrode and pressure. Predictions from two-dimensional modeling of the propagation of a single FIW correlated well with the experimental trends in electron density profiles and wave velocity. Results from the model show that the maximum ionization rate occurs in the wavefront, and the discharge continues to propagate forward after the removal of high voltage from the powered electrode due to the potential energy stored in the space charge. As the pressure is varied, the radial distribution of the ionization rate is shaped by changes in the electron mean free path, and subsequent localized electric field enhancement at the walls or on the centerline of the discharge.
ELECTRON HEAT FLUX IN THE SOLAR WIND: ARE WE OBSERVING THE COLLISIONAL LIMIT IN THE 1 AU DATA?
Landi, S.; Matteini, L.; Pantellini, F.
2014-07-20
Using statistically significant data at 1 AU, it has recently been shown (Bale et al.) that in the solar wind, when the Knudsen number K {sub T} (the ratio between the electron mean free path and the electron temperature scale height) drops below about 0.3, the electron heat flux q intensity rapidly approaches the classical collisional Spitzer-Härm limit. Using a fully kinetic model including the effect of Coulomb collisions and the expansion of the solar wind with heliocentric distance, we observe that the heat flux strength does indeed approach the collisional value for Knudsen numbers smaller than about 0.3 in very good agreement with the observations. However, closer inspection of the heat flux properties, such as its variation with the heliocentric distance and its dependence on the plasma parameters, shows that for Knudsen numbers between 0.02 and 0.3 the heat flux is not conveniently described by the Spitzer-Härm formula. We conclude that even though observations at 1 AU seem to indicate that the electron heat flux intensity approaches the collisional limit when the Knudsen drops below ?0.3, the collisional limit is not a generally valid closure for a Knudsen larger than 0.01. Moreover, the good agreement between the heat flux from our model and the heat flux from solar wind measurements in the high-Knudsen number regime seems to indicate that the heat flux at 1 AU is not constrained by electromagnetic instabilities as both wave-particle and wave-wave interactions are neglected in our calculations.
Weatherford, Brandon R., E-mail: brweathe@gmail.com, E-mail: zax@esi-group.com, E-mail: evbarna@sandia.gov, E-mail: mjkush@umich.edu; Barnat, E. V., E-mail: brweathe@gmail.com, E-mail: zax@esi-group.com, E-mail: evbarna@sandia.gov, E-mail: mjkush@umich.edu [Sandia National Laboratories, Albuquerque, New Mexico 87185-1423 (United States); Xiong, Zhongmin, E-mail: brweathe@gmail.com, E-mail: zax@esi-group.com, E-mail: evbarna@sandia.gov, E-mail: mjkush@umich.edu; Kushner, Mark J., E-mail: brweathe@gmail.com, E-mail: zax@esi-group.com, E-mail: evbarna@sandia.gov, E-mail: mjkush@umich.edu [Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122, USA. (United States)
2014-09-14
Fast ionization waves (FIWs), often generated with high voltage pulses over nanosecond timescales, are able to produce large volumes of ions and excited states at moderate pressures. The mechanisms of FIW propagation were experimentally and computationally investigated to provide insights into the manner in which these large volumes are excited. The two-dimensional structure of electron and metastable densities produced by short-pulse FIWs sustained in helium were measured using laser-induced fluorescence and laser collision-induced fluorescence diagnostics for times of 100–120 ns after the pulse, as the pressure was varied from 1 to 20 Torr. A trend of center-peaked to volume-filling to wall-peaked electron density profiles was observed as the pressure was increased. Instantaneous FIW velocities, obtained from plasma-induced emission, ranged from 0.1 to 3×10?cm s?¹, depending on distance from the high voltage electrode and pressure. Predictions from two-dimensional modeling of the propagation of a single FIW correlated well with the experimental trends in electron density profiles and wave velocity. Results from the model show that the maximum ionization rate occurs in the wavefront, and the discharge continues to propagate forward after the removal of high voltage from the powered electrode due to the potential energy stored in the space charge. As the pressure is varied, the radial distribution of the ionization rate is shaped by changes in the electron mean free path, and subsequent localized electric field enhancement at the walls or on the centerline of the discharge.
An Introduction to Path Analysis
ERIC Educational Resources Information Center
Wolfe, Lee M.
1977-01-01
The analytical procedure of path analysis is described in terms of its use in nonexperimental settings in the social sciences. The description assumes a moderate statistical background on the part of the reader. (JKS)
COMPUTER SCIENCE: MISCONCEPTIONS, CAREER PATHS
Hristidis, Vagelis
COMPUTER SCIENCE: MISCONCEPTIONS, CAREER PATHS AND RESEARCH CHALLENGES School of Computing Undergraduate Student) #12;Computer Science Misconceptions Intro to Computer Science - Florida International University 2 Some preconceived ideas & stereotypes about Computer Science (CS) are quite common
Survivable paths in multilayer networks
Parandehgheibi, Marzieh
We consider the problem of protection in multilayer networks. In single-layer networks, a pair of disjoint paths can be used to provide protection for a source-destination pair. However, this approach cannot be directly ...
Yong Seung Cho; Soon-Tae Hong
2007-06-01
We consider the path space of a curved manifold on which a point particle is introduced in a conservative physical system with constant total energy to formulate its action functional and geodesic equation together with breaks on the path. The second variation of the action functional is exploited to yield the geodesic deviation equation and to discuss the Jacobi fields on the curved manifold. We investigate the topology of the path space using the action functional on it and its physical meaning by defining the gradient of the action functional, the space of bounded flow energy solutions and the moduli space associated with the critical points of the action functional. We also consider the particle motion on the $n$-sphere $S^{n}$ in the conservative physical system to discuss explicitly the moduli space of the path space and the corresponding homology groups.
Path Planner With Vision Capability
NASA Astrophysics Data System (ADS)
Distante, Arcangelo; Attolico, Giovanni; Radicci, Maria G.; Stella, Ettore
1990-03-01
In this paper we are going to describe an ongoing research project intended to integrate a full vision system in a flexible robot programming environment. The use of the vision system sensors, allows the robot to derive a description of the work cell. This description is used for the collision avoidance problem of robot manipulators. The work cell in assembly context can include moving objects. Without any previous knowledge of the work space, the vision system thus immediately determines the work cell map in its entirely. Successively this map is used as input for the path planner process to find the collision-free path. During the assembly robot operation, the vision system is activated to reflect any changes in the robot environment. In this way the path planner works recursively, updating the collision free path until the goal is reached.
Survivable paths in multilayer networks
Parandehgheibi, Marzieh
2012-01-01
We consider the problem of protection in multilayer networks. In single-layer net- works, a pair of disjoint paths can be used to provide protection for a source-destination pair. However, this approach cannot be directly ...
Formal language constrained path problems
Barrett, C.; Jacob, R.; Marathe, M.
1997-07-08
In many path finding problems arising in practice, certain patterns of edge/vertex labels in the labeled graph being traversed are allowed/preferred, while others are disallowed. Motivated by such applications as intermodal transportation planning, the authors investigate the complexity of finding feasible paths in a labeled network, where the mode choice for each traveler is specified by a formal language. The main contributions of this paper include the following: (1) the authors show that the problem of finding a shortest path between a source and destination for a traveler whose mode choice is specified as a context free language is solvable efficiently in polynomial time, when the mode choice is specified as a regular language they provide algorithms with improved space and time bounds; (2) in contrast, they show that the problem of finding simple paths between a source and a given destination is NP-hard, even when restricted to very simple regular expressions and/or very simple graphs; (3) for the class of treewidth bounded graphs, they show that (i) the problem of finding a regular language constrained simple path between source and a destination is solvable in polynomial time and (ii) the extension to finding context free language constrained simple paths is NP-complete. Several extensions of these results are presented in the context of finding shortest paths with additional constraints. These results significantly extend the results in [MW95]. As a corollary of the results, they obtain a polynomial time algorithm for the BEST k-SIMILAR PATH problem studied in [SJB97]. The previous best algorithm was given by [SJB97] and takes exponential time in the worst case.
Individual carbon nanotubes for quantum electronic and quantum photonic devices
NASA Astrophysics Data System (ADS)
Ai, Nan
2011-12-01
Carbon nanotubes (CNTs) are promising materials since their unique one dimensional geometry leads to remarkable physical properties such as ballistic transport, long mean free path, large direct band gaps, high mechanical tensile strength and strong exciton binding energies, which make them attractive candidates for applications in high-performance nanoelectronics and nanophotonics. CNT-based field-effect transistors (CNT-FETs) are considered to be ideally suited for future nanoelectronics. Single CNT-FETs made by depositing metal electrodes on top of individual CNTs with E-beam lithography have achieved great performance but are limited for massive large area integrated circuit fabrication. Therefore, this thesis demonstrates characteristics of CNT-FETs made by registered in-plane growth utilizing tailored nanoscale catalyst patterns and chemical vapor deposition (CVD), resulting in CNT arrays directly bridging source and drain. The demonstrated access to individual CNTs with pronounced semiconducting behavior opens also the possibility to form more advanced nanoelectronic structures such as CNT quantum dots. CNT-based single electron transistors (CNT-SETS) are promising for quantum electronic devices operating with ultra-low power consumption and allow fundamental studies of electron transport. In addition to existing CNT-SETS based on individual CNTs, we have fabricated the first CNT-SETS based on in-plane grown CNTs using the CVD technique. The demonstrated utilization of registered in-plane growth opens possibilities to create novel SET device geometries which are more complex, i.e. laterally ordered and scalable, as required for advanced quantum electronic devices. Blinking and spectral diffusion are hallmarks of nanoscale light emitters and a challenge for creating stable fluorescent biomarkers or efficient nonclassical light sources. The studies of blinking of CNTs are still in the explorative stage. In this thesis, I show the first experimental demonstration of the suppression of blinking and spectral diffusion of individual CNTs by manipulation of their dielectric environment, resulting in five fold enhanced light emission. Such results open many new device applications in CNT nanophotonics, such as efficient CNT-based single photon sources. CNT-based FETs, SETS and light emitters studied in this thesis demonstrate the great potential for CNTs as optoelectronic material in future nanoelectronic and nanophotonic device applications.
NASA Astrophysics Data System (ADS)
Belof, Jonathan; Dubois, Jonathan
2013-06-01
Warm dense matter (WDM), the regime of degenerate and strongly coupled Coulomb systems, is of great interest due to it's importance in understanding astrophysical processes and high energy density laboratory experiments. Path Integral Monte Carlo (PIMC) presents a particularly attractive formalism for tackling outstanding questions in WDM, in that electron correlation can be calculated exactly, with the nuclear and electronic degrees of freedom on equal footing. Here we present an efficient means of solving the Feynman path integral numerically by variational optimization of a trial density matrix, a method originally proposed for simple potentials by Feynman and Kleinert, and we show that this formalism provides an accurate description of warm dense matter with a number of unique advantages over other PIMC approaches. An exchange interaction term is derived for the variationally optimized path, as well as a numerically efficient scheme for dealing with long-range electrostatics. Finally, we present results for the pair correlation functions and thermodynamic observables of the spin polarized electron gas, warm dense hydrogen and all-electron warm dense carbon within the presented VPT-PIMC formalism. Warm dense matter (WDM), the regime of degenerate and strongly coupled Coulomb systems, is of great interest due to it's importance in understanding astrophysical processes and high energy density laboratory experiments. Path Integral Monte Carlo (PIMC) presents a particularly attractive formalism for tackling outstanding questions in WDM, in that electron correlation can be calculated exactly, with the nuclear and electronic degrees of freedom on equal footing. Here we present an efficient means of solving the Feynman path integral numerically by variational optimization of a trial density matrix, a method originally proposed for simple potentials by Feynman and Kleinert, and we show that this formalism provides an accurate description of warm dense matter with a number of unique advantages over other PIMC approaches. An exchange interaction term is derived for the variationally optimized path, as well as a numerically efficient scheme for dealing with long-range electrostatics. Finally, we present results for the pair correlation functions and thermodynamic observables of the spin polarized electron gas, warm dense hydrogen and all-electron warm dense carbon within the presented VPT-PIMC formalism. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.
Shortest-path problems Proofs Weight of path p = v0 v1 vk
California at Davis, University of
Shortest-path problems Â Proofs Weight of path p = v0 v1 Â· Â· Â· vk: w(p) = k i=1 w(vi-1, vi) Shortest-path weight u ; v (u, v) = min{w(p) : u p ; v} if there exists a path u ; v otherwise Shortest-path u ; v any path p such that w(p) = (u, v) #12;Shortest-paths properties Triangular inequality
NASA Technical Reports Server (NTRS)
Thakoor, Anil
1990-01-01
Viewgraphs on electronic neural networks for space station are presented. Topics covered include: electronic neural networks; electronic implementations; VLSI/thin film hybrid hardware for neurocomputing; computations with analog parallel processing; features of neuroprocessors; applications of neuroprocessors; neural network hardware for terrain trafficability determination; a dedicated processor for path planning; neural network system interface; neural network for robotic control; error backpropagation algorithm for learning; resource allocation matrix; global optimization neuroprocessor; and electrically programmable read only thin-film synaptic array.
Finding the k Shortest Paths David Eppstein
Eppstein, David
constraints beyond having a small length, but those other constraints may be ill-defined or hard to optimize-known shortest path problem, in which not one but several short paths must be produced. The k shortest paths problem, for a given k and a given source-destination pair in a digraph, is to list the k paths
Paths for Z_k parafermionic models
P. Jacob; P. Mathieu
2007-07-03
We present a simple bijection between restricted (Bressoud) lattice paths and RSOS paths in regime II. Both types of paths describe states in Z_k parafermionic irreducible modules. The bijection implies a direct correspondence between a RSOS path and a parafermionic state in a quasi-particle basis.
Disjoint paths in tournaments Maria Chudnovsky1
Scott, Alexander Alexander
Disjoint paths in tournaments Maria Chudnovsky1 Columbia University, New York, NY 10027, USA Alex) (1 i k) of a digraph G, how can we test whether there exist k vertex-disjoint directed paths from G. The k vertex-disjoint paths problem is to determine whether there exist vertex-disjoint paths P1
Optimal Distributed All Pairs Shortest Paths
Optimal Distributed All Pairs Shortest Paths ETH Zurich Distributed Computing Group Stephan = Number of hops of shortest path #12;Diameter of a network · Distance between two nodes = Number of hops of shortest path #12;Diameter of a network · Distance between two nodes = Number of hops of shortest path
Reactive Path Deformation for Nonholonomic Mobile Robots
Lamiraux, Florent
. A collision-free initial path being given for a robot, obstacles detected while following this path can make, [21] proposed a method that enables him to deform on line the path to be fol- lowed by the robot1 Reactive Path Deformation for Nonholonomic Mobile Robots F. Lamiraux, D. Bonnafous, and O
NASA Astrophysics Data System (ADS)
Shakeri, Nadim; Jalili, Saeed; Ahmadi, Vahid; Rasoulzadeh Zali, Aref; Goliaei, Sama
2015-01-01
The problem of finding the Hamiltonian path in a graph, or deciding whether a graph has a Hamiltonian path or not, is an NP-complete problem. No exact solution has been found yet, to solve this problem using polynomial amount of time and space. In this paper, we propose a two dimensional (2-D) optical architecture based on optical electronic devices such as micro ring resonators, optical circulators and MEMS based mirror (MEMS-M) to solve the Hamiltonian Path Problem, for undirected graphs in linear time. It uses a heuristic algorithm and employs n+1 different wavelengths of a light ray, to check whether a Hamiltonian path exists or not on a graph with n vertices. Then if a Hamiltonian path exists, it reports the path. The device complexity of the proposed architecture is O(n2).
Arithmetic area for m planar Brownian paths
Jean Desbois; Stephane Ouvry
2012-02-04
We pursue the analysis made in [1] on the arithmetic area enclosed by m closed Brownian paths. We pay a particular attention to the random variable S{n1,n2, ...,n} (m) which is the arithmetic area of the set of points, also called winding sectors, enclosed n1 times by path 1, n2 times by path 2, ...,nm times by path m. Various results are obtained in the asymptotic limit m->infinity. A key observation is that, since the paths are independent, one can use in the m paths case the SLE information, valid in the 1-path case, on the 0-winding sectors arithmetic area.
Path Integral Invariance under Point Canonical Transformations
Jordan, A; Jordan, Andres; Libedinsky, Matias
1997-01-01
It is often stated in the literature on path integrals that naive changes of coordinates might in general give inequivalent theories. The discrepancy is presumably connected to subtleties in the discretization, to the stochastic nature of quantum paths, or to operator order ambiguities in the canonical quantization. Here we argue that in order to define a path integral one needs not only a Lagrangian but also a set of paths that join succesive points in the discretized paths. If the set of paths is maintained when performing a point canonical transformation the path integral does not change. We explicitly show this with the calculation of the free particle kernel in polar coordinates.
Electron and ion acceleration in relativistic shocks with applications to GRB afterglows
NASA Astrophysics Data System (ADS)
Warren, Donald C.; Ellison, Donald C.; Bykov, Andrei M.; Lee, Shiu-Hang
2015-09-01
We have modelled the simultaneous first-order Fermi shock acceleration of protons, electrons, and helium nuclei by relativistic shocks. By parametrizing the particle diffusion, our steady-state Monte Carlo simulation allows us to follow particles from particle injection at non-relativistic thermal energies to above PeV energies, including the non-linear smoothing of the shock structure due to cosmic ray (CR) backpressure. We observe the mass-to-charge (A/Z) enhancement effect believed to occur in efficient Fermi acceleration in non-relativistic shocks and we parametrize the transfer of ion energy to electrons seen in particle-in-cell (PIC) simulations. For a given set of environmental and model parameters, the Monte Carlo simulation determines the absolute normalization of the particle distributions and the resulting synchrotron, inverse Compton, and pion-decay emission in a largely self-consistent manner. The simulation is flexible and can be readily used with a wide range of parameters typical of ?-ray burst (GRB) afterglows. We describe some preliminary results for photon emission from shocks of different Lorentz factors and outline how the Monte Carlo simulation can be generalized and coupled to hydrodynamic simulations of GRB blast waves. We assume Bohm diffusion for simplicity but emphasize that the non-linear effects we describe stem mainly from an extended shock precursor where higher energy particles diffuse further upstream. Quantitative differences will occur with different diffusion models, particularly for the maximum CR energy and photon emission, but these non-linear effects should be qualitatively similar as long as the scattering mean-free path is an increasing function of momentum.
NASA Astrophysics Data System (ADS)
Jin, Hua; Oh, Suhk Kun; Kang, Hee Jae; Tougaard, Sven
2006-10-01
Quantitative analysis of reflection electron energy loss spectra for ultrathin HfO2, Al2O3, and Hf-Al-O dielectric thin films on Si(100) were carried out by using Tougaard-Yubero [Surf. Interface Anal. 36, 824 (2004)] QUEELS-?(k ,?)-REELS software. Experimental cross sections obtained from reflection electron energy loss spectroscopy were compared with theoretical inelastic scattering cross section Ksc deduced from the simulated energy loss function (ELF). The ELF is expressed as a sum of Drude oscillators. For HfO2, the ELF shows peaks in the vicinity of 10, 17, 22, 27, 37, and 47eV. For Al2O3, a broad peak at 22eV with a very weak shoulder at 14eV and a shoulder at 32eV were observed, while for the Al2O3 doped HfO2, the peak position is similar to that of HfO2. This indicates that when Hf-Al-O film is used as a gate dielectric in a complementary metal-oxide semiconductor transistor, its electronic structure is mainly determined by the d state of Hf. In addition, the inelastic mean free path (IMFP) was also calculated from the theoretical inelastic scattering cross section. The IMFPs at 300eV were about 7.05, 9.62, and 8.48Å and those at 500eV were 11.42, 15.40, and 13.64Å for HfO2, Al2O3, and Hf-Al-O, respectively. The method of determining the IMFP from the ELF is a convenient tool for ultrathin dielectric materials.
Orthogonal Scan Paths for Data Path Logic Robert B. Norwood* and Edward J. McCluskey
Stanford University
Orthogonal Scan Paths for Data Path Logic Robert B. Norwood* and Edward J. McCluskey Center Abstract We have implemented a synthesis-for-test algorithm to implement orthogonal scan paths in data path logic. Orthogonal scan paths [Avra 92] facilitate the sharing of the functional and the test logic
The inverse shortest paths problem with upper bounds on shortest paths costs.
Toint, Philippe
The inverse shortest paths problem with upper bounds on shortest paths costs. by D. Burton 1 W of the inverse shortest paths problem with upper bounds on shortest path costs, and prove that obtaining, Belgium Keywords : computational complexity, shortest paths, inverse problems, traffic modelling. #12; 1
NASA Technical Reports Server (NTRS)
Zuk, J.
1976-01-01
Improved gas-path seals are needed for better fuel economy, longer performance retention, and lower maintenance, particularly in advanced, high-performance gas turbine engines. Problems encountered in gas-path sealing are described, as well as new blade-tip sealing approaches for high-pressure compressors and turbines. These include a lubricant coating for conventional, porous-metal, rub-strip materials used in compressors. An improved hot-press metal alloy shows promise to increase the operating surface temperatures of high-pressure-turbine, blade-tip seals to 1450 K (2150 F). Three ceramic seal materials are also described that have the potential to allow much higher gas-path surface operating temperatures than are possible with metal systems.
Baer, Roi
BornOppenheimer invariants along nuclear configuration paths Roi Baera) Department of Physical of the wave function. This is done for each calculated state at each nuclear position. Thus he defines a Born to an arbitrary path in nuclear configuration space. We identify invariant electronic states along these paths
NASA Astrophysics Data System (ADS)
Wang, Yi-Ting; Woo, Tak-Pong; Lo, S.-T.; Kim, Gil-Ho; Liang, Chi-Te
2014-05-01
In this report, we will discuss the nonmonotonic magnetoresistance (MR) in an AlGaN/GaN high-electron-mobility transistor (HEMT) in a perpendicular magnetic field B in the ballistic region ( kBT?/? < 1) and in the weakly-disordered limit ( kFl = 159 ? 1), where kB, T, ?, ?, k F, and l represent the Boltzmann constant, temperature, elastic scattering time, reduced Planck constant, Fermi wave vector and mean free path, respectively. The MR shows a local maximum between the weak localization (WL) and the Shubnikov-de Haas regions. In the low magnetic field regime, the quantum correction to the conductivity is proportional to T -3/2, which is consistent with a recent theory [T. A. Sedrakyan, and M. E. Raikh, Phys. Rev. Lett. 100, 106806 (2008)]. According to our results, as the temperature is increased, the position of the MR maximum in B increases. These results cannot be explained by present theories. Moreover, in the high-magnetic-field regime, neither the magnetic and nor the temperature dependences of the observed MR is consistent with present theories. We, therefore, suggest that while some features of the observed nonmonotonic MR can be successfully explained, further experimental and theoretical studies are necessary to obtain a thorough understanding of the MR effects.
Multiple paths in complex tasks
NASA Technical Reports Server (NTRS)
Galanter, Eugene; Wiegand, Thomas; Mark, Gloria
1987-01-01
The relationship between utility judgments of subtask paths and the utility of the task as a whole was examined. The convergent validation procedure is based on the assumption that measurements of the same quantity done with different methods should covary. The utility measures of the subtasks were obtained during the performance of an aircraft flight controller navigation task. Analyses helped decide among various models of subtask utility combination, whether the utility ratings of subtask paths predict the whole tasks utility rating, and indirectly, whether judgmental models need to include the equivalent of cognitive noise.
NASA Astrophysics Data System (ADS)
Marocchino, A.; Atzeni, S.; Schiavi, A.
2014-01-01
In some regions of a laser driven inertial fusion target, the electron mean-free path can become comparable to or even longer than the electron temperature gradient scale-length. This can be particularly important in shock-ignited (SI) targets, where the laser-spike heated corona reaches temperatures of several keV. In this case, thermal conduction cannot be described by a simple local conductivity model and a Fick's law. Fluid codes usually employ flux-limited conduction models, which preserve causality, but lose important features of the thermal flow. A more accurate thermal flow modeling requires convolution-like non-local operators. In order to improve the simulation of SI targets, the non-local electron transport operator proposed by Schurtz-Nicolaï-Busquet [G. P. Schurtz et al., Phys. Plasmas 7, 4238 (2000)] has been implemented in the DUED fluid code. Both one-dimensional (1D) and two-dimensional (2D) simulations of SI targets have been performed. 1D simulations of the ablation phase highlight that while the shock profile and timing might be mocked up with a flux-limiter; the electron temperature profiles exhibit a relatively different behavior with no major effects on the final gain. The spike, instead, can only roughly be reproduced with a fixed flux-limiter value. 1D target gain is however unaffected, provided some minor tuning of laser pulses. 2D simulations show that the use of a non-local thermal conduction model does not affect the robustness to mispositioning of targets driven by quasi-uniform laser irradiation. 2D simulations performed with only two final polar intense spikes yield encouraging results and support further studies.
NASA Astrophysics Data System (ADS)
Sijoy, C. D.; Chaurasia, Shivanand; Mishra, Vinayak; Leshma, P.; Sakthivel, N.; Chaturvedi, Shashank; Sharma, S. M.; Basu, Sekhar
2014-06-01
In hydrodynamics simulation of laser driven systems, the time-dependent nonlocal electron heat-flux models predict the saturation (flux inhibition) and delocalization of the heat-flux automatically. Therefore it avoids commonly used time and space-independent ad hoc flux limiting. Previously proposed analytical nonlocal heat-flux model of Luciani et al. [Phys. Rev. Lett., 51, p-1664, (1983)] which fits the results of numerical Fokke-Planck calculations is simple and straight forward to implement in a fluid code. The proposed expression, however, is a convolution of Spitze-Harm heat-flux with a delocalization kernel which depends on classical electron collision mean free path. This is rigorously valid for high temperature non-degenerate plasmas. However, in laser driven systems, the energy transport due to electron thermal conduction is important in regions between the critical density and ablation surface where the plasma is mostly degenerate. We have improved this nonlocal heat-flux model by using a wide-range electron collision frequency model valid from warm-dense matter (degenerate plasmas) to fully ionized plasmas. The effect of this improved nonlocal heat-flux model on the free-surface velocity of laser-accelerated Al foils of thickness 2-10 ?m is studied by using a two-dimensional radiation hydrodynamics code. The simulated free surface velocities are compared with our experimental results for laser intensities in the range 4 × 1013-3 × 1014 W/cm2. Preliminary analysis shows that the simulation results obtained with improved nonlocal heat-flux model yields better agreement with our experimental values.
NASA Astrophysics Data System (ADS)
Li, Wu
2015-08-01
We demonstrate the ab initio electrical transport calculation limited by electron-phonon coupling by using the full solution of the Boltzmann transport equation (BTE), which applies equally to metals and semiconductors. Numerical issues are emphasized in this work. We show that the simple linear interpolation of the electron-phonon coupling matrix elements from a relatively coarse grid to an extremely fine grid can ease the calculational burden, which makes the calculation feasible in practice. For the Brillouin zone (BZ) integration of the transition probabilities involving one ? function, the Gaussian smearing method with a physical choice of locally adaptive broadening parameters is employed. We validate the calculation in the cases of n -type Si and Al. The calculated conductivity and mobility are in good agreement with experiments. In the metal case we also demonstrate that the Gaussian smearing method with locally adaptive broadening parameters works excellently for the BZ integration with double ? functions involved in the Eliashberg spectral function and its transport variant. The simpler implementation is the advantage of the Gaussian smearing method over the tetrahedron method. The accuracy of the relaxation time approximation and the approximation made by Allen [Phys. Rev. B 17, 3725 (1978), 10.1103/PhysRevB.17.3725] has been examined by comparing with the exact solution of BTE. We also apply our method to n -type monolayer MoS2, for which a mobility of 150 cm2 v-1 s-1 is obtained at room temperature. Moreover, the mean free paths are less than 9 nm, indicating that in the presence of grain boundaries the mobilities should not be effectively affected if the grain boundary size is tens of nanometers or larger. The ab initio approach demonstrated in this paper can be directly applied to other materials without the need for any a priori knowledge about the electron-phonon scattering processes, and can be straightforwardly extended to study cases with electron-impurity scattering.
Semiconducting carbon nanotube transistors: Electron and spin transport properties
NASA Astrophysics Data System (ADS)
Chen, Yung-Fu
Single-walled carbon nanotubes (SWNTs) have attracted great interest both scientifically and technologically due to their long mean free paths and high carrier velocities at room temperature, and possibly very long spin-scattering lengths. This thesis will describe experiments to probe the charge-and spin-transport properties of long, clean individual SWNTs prepared by chemical vapor deposition and contacted by metal electrodes. A SWNT field-effect transistor (SWNT-FET) has been shown to be sensitive to single electrons in charge traps. A single charge trap near a SWNT-FET is explored here using both electronic and scanned-probe techniques, and a simple model is developed to determine the capacitances of the trap to the SWNT and gate electrode. SWNTs are contacted with ferromagnetic electrodes in order to explore the transport of spin-polarized current through the SWNT. In some cases spin-dependent transport was observed, verifying long spin scattering lengths in SWNT. However, in many cases no spin-dependent effects were observed; these results will be discussed in the context of the present state of results in the literature. Semiconducting SWNTs (s-SWNTs) with Schottky-barrier contacts are measured at high bias. Nearly symmetric ambipolar transport is observed, with electron and hole currents significantly exceeding 25 muA, the reported current limit in m-SWNTs. Four simple models for the field-dependent velocity (ballistic, current saturation, velocity saturation, and constant mobility) are studied in the unipolar regime; the high-bias behavior is best explained by a velocity saturation model with a saturation velocity of 2 x 107 cm/s. A simple Boltzmann equation model for charge transport in s-SWNTs is developed with two adjustable parameters, the elastic and inelastic scattering lengths. The model predicts velocity saturation rather than current saturation in s-SWNTs, in agreement with experiment. Contact effects in s-SWNT-FET are explored by electrically heating the devices. These experiments resolve the origin of nanotube p-type behavior in air by showing that the observed p-type behavior upon air exposure cannot be explained by change in contact work function, but is instead due to doping of the nanotube. Modest doping of the SWNT narrows the Schottky Barriers and provides a high-conductance Ohmic tunnel contact from electrode to SWNT.
Small Aircraft RF Interference Path Loss
NASA Technical Reports Server (NTRS)
Nguyen, Truong X.; Koppen, Sandra V.; Ely, Jay J.; Szatkowski, George N.; Mielnik, John J.; Salud, Maria Theresa P.
2007-01-01
Interference to aircraft radio receivers is an increasing concern as more portable electronic devices are allowed onboard. Interference signals are attenuated as they propagate from inside the cabin to aircraft radio antennas mounted on the outside of the aircraft. The attenuation level is referred to as the interference path loss (IPL) value. Significant published IPL data exists for transport and regional category airplanes. This report fills a void by providing data for small business/corporate and general aviation aircraft. In this effort, IPL measurements are performed on ten small aircraft of different designs and manufacturers. Multiple radio systems are addressed. Along with the typical worst-case coupling values, statistical distributions are also reported that could lead to better interference risk assessment.
Small Aircraft RF Interference Path Loss Measurements
NASA Technical Reports Server (NTRS)
Nguyen, Truong X.; Koppen, Sandra V.; Ely, Jay J.; Szatkowski, George N.; Mielnik, John J.; Salud, Maria Theresa P.
2007-01-01
Interference to aircraft radio receivers is an increasing concern as more portable electronic devices are allowed onboard. Interference signals are attenuated as they propagate from inside the cabin to aircraft radio antennas mounted on the outside of the aircraft. The attenuation level is referred to as the interference path loss (IPL) value. Significant published IPL data exists for transport and regional category airplanes. This report fills a void by providing data for small business/corporate and general aviation aircraft. In this effort, IPL measurements are performed on ten small aircraft of different designs and manufacturers. Multiple radio systems are addressed. Along with the typical worst-case coupling values, statistical distributions are also reported that could lead to more meaningful interference risk assessment.
Himpsel, Franz J.
95120 Received 30 September 1994; accepted for publication 10 April 1995 The geometric and electronic structure of complex multi-elemental materials.4 Due to the long mean free path of photons in solids 1000 Å
Nanoscale heat conduction with applications in nanoelectronics and thermoelectrics
Yang, Ronggui, Ph. D. Massachusetts Institute of Technology
2006-01-01
When the device or structure characteristic length scales are comparable to the mean free path and wavelength of energy carriers (electrons, photons, phonons, and molecules) or the time of interest is on the same order as ...
Spreading paths in partially observed social networks
NASA Astrophysics Data System (ADS)
Onnela, Jukka-Pekka; Christakis, Nicholas A.
2012-03-01
Understanding how and how far information, behaviors, or pathogens spread in social networks is an important problem, having implications for both predicting the size of epidemics, as well as for planning effective interventions. There are, however, two main challenges for inferring spreading paths in real-world networks. One is the practical difficulty of observing a dynamic process on a network, and the other is the typical constraint of only partially observing a network. Using static, structurally realistic social networks as platforms for simulations, we juxtapose three distinct paths: (1) the stochastic path taken by a simulated spreading process from source to target; (2) the topologically shortest path in the fully observed network, and hence the single most likely stochastic path, between the two nodes; and (3) the topologically shortest path in a partially observed network. In a sampled network, how closely does the partially observed shortest path (3) emulate the unobserved spreading path (1)? Although partial observation inflates the length of the shortest path, the stochastic nature of the spreading process also frequently derails the dynamic path from the shortest path. We find that the partially observed shortest path does not necessarily give an inflated estimate of the length of the process path; in fact, partial observation may, counterintuitively, make the path seem shorter than it actually is.
Perceived Shrinkage of Motion Paths
ERIC Educational Resources Information Center
Sinico, Michele; Parovel, Giulia; Casco, Clara; Anstis, Stuart
2009-01-01
We show that human observers strongly underestimate a linear or circular trajectory that a luminous spot follows in the dark. At slow speeds, observers are relatively accurate, but, as the speed increases, the size of the path is progressively underestimated, by up to 35%. The underestimation imposes little memory load and does not require…
Career Paths in Environmental Sciences
Career paths, current and future, in the environmental sciences will be discussed, based on experiences and observations during the author's 40 + years in the field. An emphasis will be placed on the need for integrated, transdisciplinary systems thinking approaches toward achie...
Horbez, Camille
2012-01-01
We prove that a collection of paths defined in the sphere model of outer space using a surgery process are uniform quasi-geodesics, provided they remain in some thick part of outer space. To do so, we relate the Lipschitz metric on outer space to a notion of intersection numbers.
Immigration: Rubio's path to presidency?
Fernandez, Eduardo
Immigration: Rubio's path to presidency? In media blitz retorting conservative critics, he aims Writer Of the four Democratic and four Republican senators who wrote the immigration reform proposal now, both in Congress and nationwide, need more convincing on immigration reform than Democrats. And Rubio
E J Janse van Rensburg; T Prellberg; A Rechnitzer
2007-06-28
Directed paths have been used extensively in the scientific literature as a model of a linear polymer. Such paths models in particular the conformational entropy of a linear polymer and the effects it has on the free energy. These directed models are simplified versions of the self-avoiding walk, but they do nevertheless give insight into the phase behaviour of a polymer, and also serve as a tool to study the effects of conformational degrees of freedom in the behaviour of a linear polymer. In this paper we examine a directed path model of a linear polymer in a confining geometry (a wedge). The main focus of our attention is $c_n$, the number of directed lattice paths of length $n$ steps which takes steps in the North-East and South-East directions and which is confined to the wedge $Y=\\pm X/p$, where $p$ is an integer. In this paper we examine the case $p=2$ in detail, and we determine the generating function using the iterated kernel method. We also examine the asymtotics of $c_n$. In particular, we show that $$ c_n = [0.67874...]\\times 2^{n-1}(1+(-1)^n) + O((4/3^{3/4})^{n+o(n)}) + o((4/3^{3/4})^n) $$ where we can determine the constant $0.67874...$ to arbitrary accuracy with little effort.
van Rensburg, E J J; Rechnitzer, A
2007-01-01
Directed paths have been used extensively in the scientific literature as a model of a linear polymer. Such paths models in particular the conformational entropy of a linear polymer and the effects it has on the free energy. These directed models are simplified versions of the self-avoiding walk, but they do nevertheless give insight into the phase behaviour of a polymer, and also serve as a tool to study the effects of conformational degrees of freedom in the behaviour of a linear polymer. In this paper we examine a directed path model of a linear polymer in a confining geometry (a wedge). The main focus of our attention is $c_n$, the number of directed lattice paths of length $n$ steps which takes steps in the North-East and South-East directions and which is confined to the wedge $Y=\\pm X/p$, where $p$ is an integer. In this paper we examine the case $p=2$ in detail, and we determine the generating function using the iterated kernel method. We also examine the asymtotics of $c_n$. In particular, we show th...
Aircraft flight path angle display system
NASA Technical Reports Server (NTRS)
Lambregts, Antonius A. (Inventor)
1991-01-01
A display system for use in an aircraft control wheel steering system provides the pilot with a single, quickened flight path angle display to overcome poor handling qualities due to intrinsic flight path angle response lags, while avoiding multiple information display symbology. The control law for the flight path angle control system is designed such that the aircraft's actual flight path angle response lags the pilot's commanded flight path angle by a constant time lag .tau., independent of flight conditions. The synthesized display signal is produced as a predetermined function of the aircraft's actual flight path angle, the time lag .tau. and command inputs from the pilot's column.
Enzymatic reaction paths as determined by transition path sampling
NASA Astrophysics Data System (ADS)
Masterson, Jean Emily
Enzymes are biological catalysts capable of enhancing the rates of chemical reactions by many orders of magnitude as compared to solution chemistry. Since the catalytic power of enzymes routinely exceeds that of the best artificial catalysts available, there is much interest in understanding the complete nature of chemical barrier crossing in enzymatic reactions. Two specific questions pertaining to the source of enzymatic rate enhancements are investigated in this work. The first is the issue of how fast protein motions of an enzyme contribute to chemical barrier crossing. Our group has previously identified sub-picosecond protein motions, termed promoting vibrations (PVs), that dynamically modulate chemical transformation in several enzymes. In the case of human heart lactate dehydrogenase (hhLDH), prior studies have shown that a specific axis of residues undergoes a compressional fluctuation towards the active site, decreasing a hydride and a proton donor--acceptor distance on a sub-picosecond timescale to promote particle transfer. To more thoroughly understand the contribution of this dynamic motion to the enzymatic reaction coordinate of hhLDH, we conducted transition path sampling (TPS) using four versions of the enzymatic system: a wild type enzyme with natural isotopic abundance; a heavy enzyme where all the carbons, nitrogens, and non-exchangeable hydrogens were replaced with heavy isotopes; and two versions of the enzyme with mutations in the axis of PV residues. We generated four separate ensembles of reaction paths and analyzed each in terms of the reaction mechanism, time of barrier crossing, dynamics of the PV, and residues involved in the enzymatic reaction coordinate. We found that heavy isotopic substitution of hhLDH altered the sub-picosecond dynamics of the PV, changed the favored reaction mechanism, dramatically increased the time of barrier crossing, but did not have an effect on the specific residues involved in the PV. In the mutant systems, we observed changes in the reaction mechanism and altered contributions of the mutated residues to the enzymatic reaction coordinate, but we did not detect a substantial change in the time of barrier crossing. These results confirm the importance of maintaining the dynamics and structural scaffolding of the hhLDH PV in order to facilitate facile barrier passage. We also utilized TPS to investigate the possible role of fast protein dynamics in the enzymatic reaction coordinate of human dihydrofolate reductase (hsDHFR). We found that sub-picosecond dynamics of hsDHFR do contribute to the reaction coordinate, whereas this is not the case in the E. coli version of the enzyme. This result indicates a shift in the DHFR family to a more dynamic version of catalysis. The second inquiry we addressed in this thesis regarding enzymatic barrier passage concerns the variability of paths through reactive phase space for a given enzymatic reaction. We further investigated the hhLDH-catalyzed reaction using a high-perturbation TPS algorithm. Though we saw that alternate reaction paths were possible, the dominant reaction path we observed corresponded to that previously elucidated in prior hhLDH TPS studies. Since the additional reaction paths we observed were likely high-energy, these results indicate that only the dominant reaction path contributes significantly to the overall reaction rate. In conclusion, we show that the enzymes hhLDH and hsDHFR exhibit paths through reactive phase space where fast protein motions are involved in the enzymatic reaction coordinate and exhibit a non-negligible contribution to chemical barrier crossing.
Succinct Indices for Path Minimum, with Applications to Path Reporting
Chan, Timothy M.
in O((m, n)) time, and occupies O(m) bits of space in addition to the space required for the input tree weights are within a query range. We achieve three different time/space tradeoffs for path reporting by designing (a) an O(n)-word structure with O(lg n + occ · lg n) query time, where occ is the number of nodes
Time optimal paths for high speed maneuvering
Reister, D.B.; Lenhart, S.M.
1993-01-01
Recent theoretical results have completely solved the problem of determining the minimum length path for a vehicle with a minimum turning radius moving from an initial configuration to a final configuration. Time optimal paths for a constant speed vehicle are a subset of the minimum length paths. This paper uses the Pontryagin maximum principle to find time optimal paths for a constant speed vehicle. The time optimal paths consist of sequences of axes of circles and straight lines. The maximum principle introduces concepts (dual variables, bang-bang solutions, singular solutions, and transversality conditions) that provide important insight into the nature of the time optimal paths. We explore the properties of the optimal paths and present some experimental results for a mobile robot following an optimal path.
Shortest path optimization under limited information
Dahleh, Munther A.
The problem of finding an optimal path in an uncertain graph arises in numerous applications, including network routing, path-planning for vehicles, and the control of finite-state systems. While techniques in robust and ...
Cottage View Ct. Pedestrian/Bike Path
Kostic, Milivoje M.
51N Buses Only Miles Cottage View Ct. Pedestrian/Bike Path Commuter Students ( white circled lots Resources Barsema Hall NIU Convocation Center To NIU Broadcast Center via Bike Path NIU Center for the Study
Visualization of Ant Pheromone Based Path Following
Sutherland, Benjamin T.
2010-07-14
This thesis develops a simulation and visualization of a path finding algorithm based on ant pheromone paths created in 3D space. The simulation is useful as a demonstration of a heuristic approach to NP-complete problems ...
Model for Delay Faults Based upon Paths
Gordon L. Smith
1985-01-01
Delay testing of combinational logic in a clocked environment is analyzed. A model based upon paths is introduced for delay faults. Any path with a total delay exceeding the clock interval is called a \\
Measuring Continuous-Path Accuracies of Robots
NASA Technical Reports Server (NTRS)
Allison, T. A.; Arnold, G. A.
1986-01-01
Sensors yield data on deviation from predetermined path and speed. Accuracy and repeatability of continuous-path robot motion measured with new method. Determines ability of robot to maintain tool orientation. Used with any type of manipulator arm and with separate, coordinated part positioner. Noncontacting eddy-current sensors measure distance from tool to aluminum path plate as robot end effector moves tool at prescribed distance from plate. Flat, sloped, curved, and other shapes used for path plate.
Geodesics on path spaces and double category
Saikat Chatterjee
2015-09-16
Let $M$ be a Riemannian manifold and ${\\mathcal P}M$ be the space of all smooth paths on $M$. We describe geodesics on path space ${\\mathcal P}M$. Normal neighbourhood structure on ${\\mathcal P}M$ has been discussed. We identify paths on $M$ under "back-track" equivalence. Under this identification we show that if $M$ is complete, then geodesics on path space yield a double category.We gave a physical interpretation of this double category.
Spacetime path formalism: localized states
Ed Seidewitz
2010-11-14
This note is an addendum to quant-ph/0507115. In that paper, I present a formalism for relativistic quantum mechanics in which the spacetime paths of particles are considered fundamental, reproducing the standard results of the traditional formulation of relativistic quantum mechanics and quantum field theory. Now, it is well known that there are issues with the ability to localize the position of particles in the usual formulation of relativistic quantum mechanics. The present note shows how, in the spacetime path formalism, the natural representation of on-shell 3-momentum states is effectively a Foldy-Wouthuysen transformation of the traditional representation, addressing the localization issues of position states and, further, providing a straightforward non-relativistic limit.
Physarum can compute shortest paths.
Bonifaci, Vincenzo; Mehlhorn, Kurt; Varma, Girish
2012-09-21
Physarum polycephalum is a slime mold that is apparently able to solve shortest path problems. A mathematical model has been proposed by Tero et al. (Journal of Theoretical Biology, 244, 2007, pp. 553-564) to describe the feedback mechanism used by the slime mold to adapt its tubular channels while foraging two food sources s(0) and s(1). We prove that, under this model, the mass of the mold will eventually converge to the shortest s(0)-s(1) path of the network that the mold lies on, independently of the structure of the network or of the initial mass distribution. This matches the experimental observations by Tero et al. and can be seen as an example of a "natural algorithm", that is, an algorithm developed by evolution over millions of years. PMID:22732274
Filtered backprojection proton CT reconstruction along most likely paths
Rit, Simon; Dedes, George; Freud, Nicolas; Sarrut, David; Letang, Jean Michel [Universite de Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Universite Lyon 1, Centre Leon Berard, 69008 Lyon (France)
2013-03-15
Purpose: Proton CT (pCT) has the potential to accurately measure the electron density map of tissues at low doses but the spatial resolution is prohibitive if the curved paths of protons in matter is not accounted for. The authors propose to account for an estimate of the most likely path of protons in a filtered backprojection (FBP) reconstruction algorithm. Methods: The energy loss of protons is first binned in several proton radiographs at different distances to the proton source to exploit the depth-dependency of the estimate of the most likely path. This process is named the distance-driven binning. A voxel-specific backprojection is then used to select the adequate radiograph in the distance-driven binning in order to propagate in the pCT image the best achievable spatial resolution in proton radiographs. The improvement in spatial resolution is demonstrated using Monte Carlo simulations of resolution phantoms. Results: The spatial resolution in the distance-driven binning depended on the distance of the objects from the source and was optimal in the binned radiograph corresponding to that distance. The spatial resolution in the reconstructed pCT images decreased with the depth in the scanned object but it was always better than previous FBP algorithms assuming straight line paths. In a water cylinder with 20 cm diameter, the observed range of spatial resolutions was 0.7 - 1.6 mm compared to 1.0 - 2.4 mm at best with a straight line path assumption. The improvement was strongly enhanced in shorter 200 Degree-Sign scans. Conclusions: Improved spatial resolution was obtained in pCT images with filtered backprojection reconstruction using most likely path estimates of protons. The improvement in spatial resolution combined with the practicality of FBP algorithms compared to iterative reconstruction algorithms makes this new algorithm a candidate of choice for clinical pCT.
Colloidal quantum dot photovoltaics: a path forward.
Kramer, Illan J; Sargent, Edward H
2011-11-22
Colloidal quantum dots (CQDs) offer a path toward high-efficiency photovoltaics based on low-cost materials and processes. Spectral tunability via the quantum size effect facilitates absorption of specific wavelengths from across the sun's broad spectrum. CQD materials' ease of processing derives from their synthesis, storage, and processing in solution. Rapid advances have brought colloidal quantum dot photovoltaic solar power conversion efficiencies of 6% in the latest reports. These achievements represent important first steps toward commercially compelling performance. Here we review advances in device architecture and materials science. We diagnose the principal phenomenon-electronic states within the CQD film band gap that limit both current and voltage in devices-that must be cured for CQD PV devices to fulfill their promise. We close with a prescription, expressed as bounds on the density and energy of electronic states within the CQD film band gap, that should allow device efficiencies to rise to those required for the future of the solar energy field. PMID:21967723
Squeezed states and path integrals
NASA Technical Reports Server (NTRS)
Daubechies, Ingrid; Klauder, John R.
1992-01-01
The continuous-time regularization scheme for defining phase-space path integrals is briefly reviewed as a method to define a quantization procedure that is completely covariant under all smooth canonical coordinate transformations. As an illustration of this method, a limited set of transformations is discussed that have an image in the set of the usual squeezed states. It is noteworthy that even this limited set of transformations offers new possibilities for stationary phase approximations to quantum mechanical propagators.
Free Space Path Loss of UWB Communications
Pichaya Supanakoon; Sathit Aroonpraparat; Sathaporn Promwong; Jun-ichi Takada
Although the Friis' formula is widely used to calculate the free space path loss of narrowband communications, it is considered only single frequency. Therefore, it should be extended to calculate the free space path loss of ultra wideband (UWB) communications by considering the frequency bandwidth. In this paper, the free space path loss of UWB communications is studies. The Friis'
The area determined by underdiagonal lattice paths
Merlini, Donatella
The area determined by underdiagonal lattice paths Donatella Merlini, Renzo Sprugnoli, M. Cecilia of underdiagonal lattice paths and the main diagonal. This area is important because it is connected to the number of inversions in permutations and to the internal path length in various types of trees. We obtain
Powers of Hamiltonian Paths in Interval Graphs
Isaak, Garth
Powers of Hamiltonian Paths in Interval Graphs Garth Isaak* DEPARTMENT OF MATHEMATICS LEHIGH of a Hamiltonian path are sufficient for the class of interval graphs. The proof is based on showing that a greedy algorithm tests for the existence of Hamiltonian path powers in interval graphs. We will also discuss covers
Realistic Human Walking Paths David C. Brogan
Brogan, David
Realistic Human Walking Paths David C. Brogan Department of Computer Science University of Virginia are influenced by kinematic and dynami- cal constraints. A realistic model of human walking paths is an important model of path planning that extends previous models through its significant use of pedestrian
Chip layout optimization using critical path weighting
A. E. Dunlop; V. D. Agrawal; D. N. Deutsch; M. F. Jukl; P. Kozak; M. Wiesel
1984-01-01
A chip layout procedure for optimizing the performance of critical timing paths in a synchronous digital circuit is presented. The procedure uses the path analysis data produced by a static timing analysis program to generate weights for critical nets on clock and data paths. These weights are then used to bias automatic placement and routing in the layout program. This
Evaluation of the Learning Path Specification
ERIC Educational Resources Information Center
Janssen, Jose; Berlanga, Adriana J.; Koper, Rob
2011-01-01
Flexible lifelong learning requires that learners can compare and select learning paths that best meet individual needs, not just in terms of learning goals, but also in terms of planning, costs etc. To this end a learning path specification was developed, which describes both the contents and the structure of any learning path, be it formal,…
Adaptive Path Planner for Highly Dynamic Environments
Baltes, Jacky
://www.citr.auckland.ac.nz/~jacky Abstract. This paper describes adaptive path planning, a novel ap- proach to path planning for car a collision free path through a set of obstacles from an initial to a goal position. A simple example through objects moving. In fact, RoboCup features an active opponent that tries #12;2 to prevent a robot
Path optimization for oil probe
NASA Astrophysics Data System (ADS)
Smith, O'Neil; Rahmes, Mark; Blue, Mark; Peter, Adrian
2014-05-01
We discuss a robust method for optimal oil probe path planning inspired by medical imaging. Horizontal wells require three-dimensional steering made possible by the rotary steerable capabilities of the system, which allows the hole to intersect multiple target shale gas zones. Horizontal "legs" can be over a mile long; the longer the exposure length, the more oil and natural gas is drained and the faster it can flow. More oil and natural gas can be produced with fewer wells and less surface disturbance. Horizontal drilling can help producers tap oil and natural gas deposits under surface areas where a vertical well cannot be drilled, such as under developed or environmentally sensitive areas. Drilling creates well paths which have multiple twists and turns to try to hit multiple accumulations from a single well location. Our algorithm can be used to augment current state of the art methods. Our goal is to obtain a 3D path with nodes describing the optimal route to the destination. This algorithm works with BIG data and saves cost in planning for probe insertion. Our solution may be able to help increase the energy extracted vs. input energy.
Kanematsu, Nobuyuki; Inaniwa, Taku; Koba, Yusuke
2012-02-15
Purpose: In treatment planning of charged-particle radiotherapy, patient heterogeneity is conventionally modeled as variable-density water converted from CT images to best reproduce the stopping power, which may lead to inaccuracies in the handling of multiple scattering and nuclear interactions. Although similar conversions can be defined for these individual interactions, they would be valid only for specific CT systems and would require additional tasks for clinical application. This study aims to improve the practicality of the interaction-specific heterogeneity correction. Methods: The authors calculated the electron densities and effective densities for stopping power, multiple scattering, and nuclear interactions of protons and ions, using the standard elemental-composition data for body tissues to construct the invariant conversion functions. The authors also simulated a proton beam in a lung-like geometry and a carbon-ion beam in a prostate-like geometry to demonstrate the procedure and the effects of the interaction-specific heterogeneity correction. Results: Strong correlations were observed between the electron density and the respective effective densities, with which the authors formulated polyline conversion functions. Their effects amounted to 10% differences in multiple-scattering angle and nuclear interaction mean free path for bones compared to those in the conventional heterogeneity correction. Although their realistic effect on patient dose distributions would be generally small, it could be at the level of a few percent when a carbon-ion beam traverses a large bone. Conclusions: The present conversion functions are invariant and may be incorporated in treatment planning systems with a common function relating CT number to electron density. This will enable improved beam dose calculation while minimizing initial setup and quality management of the user's specific system.
NASA Astrophysics Data System (ADS)
Gan, Zhaofeng
Off-axis electron holography (EH) has been used to characterize electrostatic potential, active dopant concentrations and charge distribution in semiconductor nanostructures, including ZnO nanowires (NWs) and thin films, ZnTe thin films, Si NWs with axial p-n junctions, Si-Ge axial heterojunction NWs, and Ge/Li xGe core/shell NW. The mean inner potential (MIP) and inelastic mean free path (IMFP) of ZnO NWs have been measured to be 15.3V+/-0.2V and 55+/-3nm, respectively, for 200keV electrons. These values were then used to characterize the thickness of a ZnO nano-sheet and gave consistent values. The MIP and IMFP for ZnTe thin films were measured to be 13.7+/-0.6V and 46+/-2nm, respectively, for 200keV electrons. A thin film expected to have a p-n junction was studied, but no signal due to the junction was observed. The importance of dynamical effects was systematically studied using Bloch wave simulations. The built-in potentials in Si NWs across the doped p-n junction and the Schottky junction due to Au catalyst were measured to be 1.0+/-0.3V and 0.5+/-0.3V, respectively. Simulations indicated that the dopant concentrations were ~1019cm-3 for donors and ~1017 cm-3 for acceptors. The effects of positively charged Au catalyst, a possible n+-n --p junction transition region and possible surface charge, were also systematically studied using simulations. Si-Ge heterojunction NWs were studied. Dopant concentrations were extracted by atom probe tomography. The built-in potential offset was measured to be 0.4+/-0.2V, with the Ge side lower. Comparisons with simulations indicated that Ga present in the Si region was only partially activated. In situ EH biasing experiments combined with simulations indicated the B dopant in Ge was mostly activated but not the P dopant in Si. I-V characteristic curves were measured and explained using simulations. The Ge/LixGe core/shell structure was studied during lithiation. The MIP for LixGe decreased with time due to increased Li content. A model was proposed to explain the lower measured Ge potential, and the trapped electron density in Ge core was calculated to be 3x1018 electrons/cm3. The Li amount during lithiation was also calculated using MIP and volume ratio, indicating that it was lower than the fully lithiated phase.
Model Checking Almost All Paths Can Be Less Expensive than Checking All Paths
Varacca, Daniele - Laboratoire Preuves, Programmes et SystÃ¨mes, UniversitÃ© Paris 7
Model Checking Almost All Paths Can Be Less Expensive than Checking All Paths Matthias Schmalz 1 model checking problems: checking whether a linear-time formula is satised by all paths (which we call universal model checking) and checking whether a formula is satised by almost all paths (which we call fair
Hydrogen molecule ion: Path integral Monte Carlo approach
Kylänpää, I; Rantala, T T
2007-01-01
Path integral Monte Carlo approach is used to study the coupled quantum dynamics of the electron and nuclei in hydrogen molecule ion. The coupling effects are demonstrated by comparing differences in adiabatic Born--Oppenheimer and non-adiabatic simulations, and inspecting projections of the full three-body dynamics onto adiabatic Born--Oppenheimer approximation. Coupling of electron and nuclear quantum dynamics is clearly seen. Nuclear pair correlation function is found to broaden by 0.040 a_0 and average bond length is larger by 0.056 a_0. Also, non-adiabatic correction to the binding energy is found. Electronic distribution is affected less, and therefore, we could say that the adiabatic approximation is better for the electron than for the nuclei.
Nanoscale heat transport via electrons and phonons by molecular dynamics simulations
NASA Astrophysics Data System (ADS)
Lin, Keng-Hua
Nanoscale heat transport has become a crucial research topic due to the growing importance of nanotechnology for manufacturing, energy conversion, medicine and electronics. Thermal transport properties at the nanoscale are distinct from the macroscopic ones since the sizes of nanoscale features, such as free surfaces and interfaces, are comparable to the wavelengths and mean free paths of the heat carriers (electrons and phonons), and lead to changes in thermal transport properties. Therefore, understanding how the nanoscale features and energy exchange between the heat carriers affect thermal transport characteristics are the goals of this research. Molecular dynamics (MD) is applied in this research to understand the details of nanoscale heat transport. The advantage of MD is that the size effect, anharmonicity, atomistic structure, and non-equilibrium behavior of the system can all be captured since the dynamics of atoms are described explicitly in MD. However, MD neglects the thermal role of electrons and therefore it is unable to describe heat transport in metal or metal-semiconductor systems accurately. To address this limitation of MD, we develop a method to simulate electronic heat transport by implementing electronic degrees of freedom to MD. In this research, nanoscale heat transport in semiconductor, metal, and metal-semiconductor systems is studied. Size effects on phonon thermal transport in SiGe superlattice thin films and nanowires are studied by MD. We find that, opposite to the macroscopic trend, superlattice thin films can achieve lower thermal conductivity than nanowires at small scales due to the change of phonon nature caused by adjusting the superlattice periodic length and specimen length. Effects of size and electron-phonon coupling rate on thermal conductivity and thermal interface resistivity in Al and model metal-semiconductor systems are studied by MD with electronic degrees of freedom. The results show that increasing the specimen length or the electron-phonon coupling rate increases the electronic contribution in thermal transport and therefore increases the thermal conductivity; moreover, the thermal interface resistivity in metal-semiconductor systems is observed to depend on the heat flux direction due to the direction-dependent energy transfer pathways between electrons and phonons at the interface. MD with electronic degrees of freedom is also applied to simulate heat transport across the metal-semiconductor interface under the non-equilibrium conditions, mimicking the ultrafast laser heating in transient thermoreflectance measurements. The effect of local and non-local electron-phonon coupling across the interface are examined, since the experimental evidence suggests that non-local electron-phonon coupling occurs under the non-equilibrium conditions. Our results show that non-local electron-phonon coupling not only facilitates energy transfer across the interface but also enhances ballistic transport of the high frequency phonon modes in a semiconductor. In summary, our study provides an insight into the details of nanoscale heat transport in various systems by MD and MD with electronic degrees of freedom.
Characterizing the evolutionary path(s) to early Homo.
Schroeder, Lauren; Roseman, Charles C; Cheverud, James M; Ackermann, Rebecca R
2014-01-01
Numerous studies suggest that the transition from Australopithecus to Homo was characterized by evolutionary innovation, resulting in the emergence and coexistence of a diversity of forms. However, the evolutionary processes necessary to drive such a transition have not been examined. Here, we apply statistical tests developed from quantitative evolutionary theory to assess whether morphological differences among late australopith and early Homo species in Africa have been shaped by natural selection. Where selection is demonstrated, we identify aspects of morphology that were most likely under selective pressure, and determine the nature (type, rate) of that selection. Results demonstrate that selection must be invoked to explain an Au. africanus-Au. sediba-Homo transition, while transitions from late australopiths to various early Homo species that exclude Au. sediba can be achieved through drift alone. Rate tests indicate that selection is largely directional, acting to rapidly differentiate these taxa. Reconstructions of patterns of directional selection needed to drive the Au. africanus-Au. sediba-Homo transition suggest that selection would have affected all regions of the skull. These results may indicate that an evolutionary path to Homo without Au. sediba is the simpler path and/or provide evidence that this pathway involved more reliance on cultural adaptations to cope with environmental change. PMID:25470780
Physarum Can Compute Shortest Paths
Bonifaci, Vincenzo; Varma, Girish
2011-01-01
A mathematical model has been proposed by biologists to describe the feedback mechanism used by the Physarum Polycephalum slime mold to adapt its tubular channels while foraging two food sources $s_0$ and $s_1$. We give a proof of the fact that, under this model, the mass of the mold will eventually converge to the shortest $s_0$-$s_1$ path of the network that the mold lies on, independently of the structure of the network or of the initial mass distribution. This matches the experimental observations by the biologists and can be seen as an example of a "natural algorithm", that is, an algorithm developed by evolution over millions of years.
Communication path for extreme environments
NASA Technical Reports Server (NTRS)
Jorgensen, Charles C. (Inventor); Betts, Bradley J. (Inventor)
2010-01-01
Methods and systems for using one or more radio frequency identification devices (RFIDs), or other suitable signal transmitters and/or receivers, to provide a sensor information communication path, to provide location and/or spatial orientation information for an emergency service worker (ESW), to provide an ESW escape route, to indicate a direction from an ESW to an ES appliance, to provide updated information on a region or structure that presents an extreme environment (fire, hazardous fluid leak, underwater, nuclear, etc.) in which an ESW works, and to provide accumulated thermal load or thermal breakdown information on one or more locations in the region.
Intellimotion: California PATH's Quarterly Newsletter
NSDL National Science Digital Library
The California Partners for Advanced Transit and Highways (PATH) researches methods for increasing highway safety, reducing congestion, and minimizing pollution and energy consumption. Intellimotion is one of its publications that highlights some of the current projects. Although it is labeled as a quarterly newsletter, Intellimotion is released on a very irregular basis. The 2002 issue covers several stories, including a project that makes vehicle navigation with the Global Positioning System extremely accurate. Another article looks at intelligent transportation systems and the issues regarding Bus Rapid Transit. Many past issues of Intellimotion are available on this Web site. This site is also reviewed in the October 25, 2002 Scout Report.
Gibbs Ensembles of Nonintersecting Paths
Alexei Borodin; Senya Shlosman
2008-04-03
We consider a family of determinantal random point processes on the two-dimensional lattice and prove that members of our family can be interpreted as a kind of Gibbs ensembles of nonintersecting paths. Examples include probability measures on lozenge and domino tilings of the plane, some of which are non-translation-invariant. The correlation kernels of our processes can be viewed as extensions of the discrete sine kernel, and we show that the Gibbs property is a consequence of simple linear relations satisfied by these kernels. The processes depend on infinitely many parameters, which are closely related to parametrization of totally positive Toeplitz matrices.
Multiple order common path spectrometer
NASA Technical Reports Server (NTRS)
Newbury, Amy B. (Inventor)
2010-01-01
The present invention relates to a dispersive spectrometer. The spectrometer allows detection of multiple orders of light on a single focal plane array by splitting the orders spatially using a dichroic assembly. A conventional dispersion mechanism such as a defraction grating disperses the light spectrally. As a result, multiple wavelength orders can be imaged on a single focal plane array of limited spectral extent, doubling (or more) the number of spectral channels as compared to a conventional spectrometer. In addition, this is achieved in a common path device.
Staff detection with stable paths.
Dos Santos Cardoso, Jaime; Capela, Artur; Rebelo, Ana; Guedes, Carlos; Pinto da Costa, Joaquim
2009-06-01
The preservation of musical works produced in the past requires their digitalization and transformation into a machine-readable format. The processing of handwritten musical scores by computers remains far from ideal. One of the fundamental stages to carry out this task is the staff line detection. We investigate a general-purpose, knowledge-free method for the automatic detection of music staff lines based on a stable path approach. Lines affected by curvature, discontinuities, and inclination are robustly detected. Experimental results show that the proposed technique consistently outperforms well-established algorithms. PMID:19372615
Noncrossing Linked Partitions and Large (3, 2)-Motzkin Paths
Chen, Bill
Noncrossing Linked Partitions and Large (3, 2)-Motzkin Paths William Y.C. Chen1, Carol J. Wang2 1)-Motzkin paths, where a (3, 2)-Motzkin path can be viewed as a Motzkin path for which there are three types of horizontal steps and two types of down steps. A large (3, 2)- Motzkin path is a (3, 2)-Motzkin path for which
The Feynman trajectories: determining the path of a protein using fixed-endpoint assays.
Ketteler, Robin
2010-03-01
Richard Feynman postulated in 1948 that the path of an electron can be best described by the sum or functional integral of all possible trajectories rather than by the notion of a single, unique trajectory. As a consequence, the position of an electron does not harbor any information about the paths that contributed to this position. This observation constitutes a classical endpoint observation. The endpoint assay is the desired type of experiment for high-throughput screening applications, mainly because of limitations in data acquisition and handling. Quite contrary to electrons, it is possible to extract information about the path of a protein using endpoint assays, and these types of applications are reviewed in this article. PMID:20130209
Vittitoe, C.N.
1993-08-01
A method is presented to unfold the two-dimensional vertical structure in electron density by using data on the total electron content for a series of paths through the ionosphere. The method uses a set of orthonormal basis functions to represent the vertical structure and takes advantage of curved paths and the eikonical equation to reduce the number of iterations required for a solution. Curved paths allow a more thorough probing of the ionosphere with a given set of transmitter and receiver positions. The approach can be directly extended to more complex geometries.
Path-integral simulation of solids.
Herrero, C P; Ramírez, R
2014-06-11
The path-integral formulation of the statistical mechanics of quantum many-body systems is described, with the purpose of introducing practical techniques for the simulation of solids. Monte Carlo and molecular dynamics methods for distinguishable quantum particles are presented, with particular attention to the isothermal-isobaric ensemble. Applications of these computational techniques to different types of solids are reviewed, including noble-gas solids (helium and heavier elements), group-IV materials (diamond and elemental semiconductors), and molecular solids (with emphasis on hydrogen and ice). Structural, vibrational, and thermodynamic properties of these materials are discussed. Applications also include point defects in solids (structure and diffusion), as well as nuclear quantum effects in solid surfaces and adsorbates. Different phenomena are discussed, as solid-to-solid and orientational phase transitions, rates of quantum processes, classical-to-quantum crossover, and various finite-temperature anharmonic effects (thermal expansion, isotopic effects, electron-phonon interactions). Nuclear quantum effects are most remarkable in the presence of light atoms, so that especial emphasis is laid on solids containing hydrogen as a constituent element or as an impurity. PMID:24810944
ANALYSIS OF CROSSING PATH CRASH COUNTERMEASURE SYSTEMS
Wassim G. Najm; Jonathan A. Koopmann; David L. Smith
This paper summarizes the results of an analysis of promising countermeasure systems for crossing path crashes, and thus provides a foundation for setting research priorities under the United States (U.S.) Department of Transportation's Intelligent Vehicle Initiative. Crossing path crashes involve one moving vehicle cutting across the path of another, which amounted to 1.72 million police-reported crashes in the U.S. based
Generalized path dependent representations for gauge theories
Reyes, Marat C. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, 04510 Mexico D.F. (Mexico) and Universidad Tecnica Federico Santa Maria, Campus Santiago, C.P. 766-0251, Santiago (Chile)
2007-05-15
A set of differential operators acting by continuous deformations on path dependent functionals of open and closed curves is introduced. Geometrically, these path operators are interpreted as infinitesimal generators of curves in the base manifold of the gauge theory. They furnish a representation with the action of the group of loops having a fundamental role. We show that the path derivative, which is covariant by construction, satisfies the Ricci and Bianchi identities. Also, we provide a geometrical derivation of covariant Taylor expansions based on particular deformations of open curves. The formalism includes, as special cases, other path dependent operators such as end point derivatives and area derivatives.
Path Deviation Equations in AP-Geometry
NASA Astrophysics Data System (ADS)
Wanas, M. I.; Kahil, M. E.
2006-02-01
Recently, it has been shown that Absolute Parallelism (AP) geometry admits paths that are naturally quantized. These paths have been used to describe the motion of spinning particles in a background gravitational field. In case of a weak static gravitational field limits, the paths are applied successfully to interpret the discrepancy in the motion of thermal neutrons in the Earth's gravitational field (COW-experiment). The aim of the present work is to explore the properties of the deviation equations corresponding to these paths. In the present work the deviation equations are derived and compared to the geodesic deviation equation of the Riemannian geometry.
Revealing genuine optical-path entanglement.
Monteiro, F; Caprara Vivoli, V; Guerreiro, T; Martin, A; Bancal, J-D; Zbinden, H; Thew, R T; Sangouard, N
2015-05-01
How can one detect entanglement between multiple optical paths sharing a single photon? We address this question by proposing a scalable protocol, which only uses local measurements where single photon detection is combined with small displacement operations. The resulting entanglement witness does not require postselection, nor assumptions about the photon number in each path. Furthermore, it guarantees that entanglement lies in a subspace with at most one photon per optical path and reveals genuinely multipartite entanglement. We demonstrate its scalability and resistance to loss by performing various experiments with two and three optical paths. We anticipate applications of our results for quantum network certification. PMID:25978215
Revealing Genuine Optical-Path Entanglement
NASA Astrophysics Data System (ADS)
Monteiro, F.; Vivoli, V. Caprara; Guerreiro, T.; Martin, A.; Bancal, J.-D.; Zbinden, H.; Thew, R. T.; Sangouard, N.
2015-05-01
How can one detect entanglement between multiple optical paths sharing a single photon? We address this question by proposing a scalable protocol, which only uses local measurements where single photon detection is combined with small displacement operations. The resulting entanglement witness does not require postselection, nor assumptions about the photon number in each path. Furthermore, it guarantees that entanglement lies in a subspace with at most one photon per optical path and reveals genuinely multipartite entanglement. We demonstrate its scalability and resistance to loss by performing various experiments with two and three optical paths. We anticipate applications of our results for quantum network certification.
Paths and stochastic order in open systems
Lucia, Umberto
2011-01-01
The principle of maximum irreversible is proved to be a consequence of a stochastic order of the paths inside the phase space; indeed, the system evolves on the greatest path in the stochastic order. The result obtained is that, at the stability, the entropy generation is maximum and, this maximum value is consequence of the stochastic order of the paths in the phase space, while, conversely, the stochastic order of the paths in the phase space is a consequence of the maximum of the entropy generation at the stability.
Escaping path approach for speckle noise reduction
NASA Astrophysics Data System (ADS)
Szczepanski, Marek; Radlak, Krystian
2015-02-01
A novel fast filtering technique for multiplicative noise removal in ultrasound images was presented in this paper. The proposed algorithm utilizes concept of digital paths created on the image grid presented in [1] adapted to the needs of multiplicative noise reduction. The new approach uses special type of digital paths so called Escaping Path Model and modified path length calculation based on topological as well as gray-scale distances. The experiments confirmed that the proposed algorithm achieves a comparable results with the existing state-of-the-art denoising schemes in suppressing multiplicative noise in ultrasound images.
Path Deviation Equations in AP-Geometry
M. I. Wanas; M. E. Kahil
2006-05-06
Recently, it has been shown that Absolute Parallelism (AP) geometry admits paths that are naturally quantized. These paths have been used to describe the motion of spinning particles in a background gravitational field. In case of a weak static gravitational field limits, the paths are applied successfully to interpret the discrepancy in the motion of thermal neutrons in the Earth's gravitational field (COW-experiment). The aim of the present work is to explore the properties of the deviation equations corresponding to these paths. In the present work the deviation equations are derived and compared to the geodesic deviation equation of the Riemannian geometry.
Path integral for Koenigs spaces
Grosche, C., E-mail: Christian.Grosche@desy.d [II Institut fuer Theoretische Physik Universitaet Hamburg (Germany)
2008-05-15
I discuss a path-integral approach for the quantum motion on two-dimensional spaces according to Koenigs, for short 'Koenigs spaces'. Their construction is simple: one takes a Hamiltonian from a two-dimensional flat space and divides it by a two-dimensional superintegrable potential. These superintegrable potentials are the isotropic singular oscillator, the Holt potential, and the Coulomb potential. In all cases, a nontrivial space of nonconstant curvature is generated. We can study free motion and the motion with an additional superintegrable potential. For possible bound-state solutions, we find in all three cases an equation of the eighth order in the energy E. The special cases of the Darboux spaces are easily recovered by choosing the parameters accordingly.
Fragmentation paths in dynamical models
M. Colonna; A. Ono; J. Rizzo
2010-11-05
We undertake a quantitative comparison of multi-fragmentation reactions, as modeled by two different approaches: the Antisymmetrized Molecular Dynamics (AMD) and the momentum-dependent stochastic mean-field (SMF) model. Fragment observables and pre-equilibrium (nucleon and light cluster) emission are analyzed, in connection to the underlying compression-expansion dynamics in each model. Considering reactions between neutron-rich systems, observables related to the isotopic properties of emitted particles and fragments are also discussed, as a function of the parametrization employed for the isovector part of the nuclear interaction. We find that the reaction path, particularly the mechanism of fragmentation, is different in the two models and reflects on some properties of the reaction products, including their isospin content. This should be taken into account in the study of the density dependence of the symmetry energy from such collisions.
Free path lengths in quasicrystals
Jens Marklof; Andreas Strömbergsson
2013-04-07
Previous studies of kinetic transport in the Lorentz gas have been limited to cases where the scatterers are distributed at random (e.g. at the points of a spatial Poisson process) or at the vertices of a Euclidean lattice. In the present paper we investigate quasicrystalline scatterer configurations, which are non-periodic, yet strongly correlated. A famous example is the vertex set of the Penrose tiling. Our main result proves the existence of a limit distribution of the free path length, which answers a question of Wennberg. The limit distribution is characterised by a certain random variable on the space of higher dimensional lattices, and is distinctly different from the exponential distribution observed for random scatterer configurations. The key ingredients in the proofs are equidistribution theorems on homogeneous spaces, which follow from Ratner's measure classification.
Methodology for Augmenting Existing Paths with Additional Parallel Transects
Wilson, John E.
2013-09-30
Visual Sample Plan (VSP) is sample planning software that is used, among other purposes, to plan transect sampling paths to detect areas that were potentially used for munition training. This module was developed for application on a large site where existing roads and trails were to be used as primary sampling paths. Gap areas between these primary paths needed to found and covered with parallel transect paths. These gap areas represent areas on the site that are more than a specified distance from a primary path. These added parallel paths needed to optionally be connected together into a single path—the shortest path possible. The paths also needed to optionally be attached to existing primary paths, again with the shortest possible path. Finally, the process must be repeatable and predictable so that the same inputs (primary paths, specified distance, and path options) will result in the same set of new paths every time. This methodology was developed to meet those specifications.
Flexible-Path Human Exploration
NASA Technical Reports Server (NTRS)
Sherwood, B.; Adler, M.; Alkalai, L.; Burdick, G.; Coulter, D.; Jordan, F.; Naderi, F.; Graham, L.; Landis, R.; Drake, B.; Hoffman, S.; Grunsfeld, J.; Seery, B. D.
2010-01-01
In the fourth quarter of 2009 an in-house, multi-center NASA study team briefly examined "Flexible Path" concepts to begin understanding characteristics, content, and roles of potential missions consistent with the strategy proposed by the Augustine Committee. We present an overview of the study findings. Three illustrative human/robotic mission concepts not requiring planet surface operations are described: assembly of very large in-space telescopes in cis-lunar space; exploration of near Earth objects (NEOs); exploration of Mars' moon Phobos. For each, a representative mission is described, technology and science objectives are outlined, and a basic mission operations concept is quantified. A fourth type of mission, using the lunar surface as preparation for Mars, is also described. Each mission's "capability legacy" is summarized. All four illustrative missions could achieve NASA's stated human space exploration objectives and advance human space flight toward Mars surface exploration. Telescope assembly missions would require the fewest new system developments. NEO missions would offer a wide range of deep-space trip times between several months and two years. Phobos exploration would retire several Marsclass risks, leaving another large remainder set (associated with entry, descent, surface operations, and ascent) for retirement by subsequent missions. And extended lunar surface operations would build confidence for Mars surface missions by addressing a complementary set of risks. Six enabling developments (robotic precursors, ISS exploration testbed, heavy-lift launch, deep-space-capable crew capsule, deep-space habitat, and reusable in-space propulsion stage) would apply across multiple program sequence options, and thus could be started even without committing to a specific mission sequence now. Flexible Path appears to be a viable strategy, with meaningful and worthy mission content.
Noppamas Pukkhem; Martha Evens; Wiwat Vatanawood
2006-01-01
Personalized learning paths are becoming more common in adaptive learning systems. In this paper we extend our earlier work by developing the Content Path Combination Model (CPCM) for integrating the design paths obtained from different instructional designers and making a strongly recommended course object sequence; presenting methodologies for handling two central tasks: (i) creating the linear sequence extensions that are
Optical Constants and Inelastic Electron-Scattering Data for 17 Elemental Metals
NASA Astrophysics Data System (ADS)
Werner, Wolfgang S. M.; Glantschnig, Kathrin; Ambrosch-Draxl, Claudia
2009-12-01
Two new sets of optical data, i.e., values for the real (?1) and imaginary (?2) parts of the complex dielectric constant as well as the energy loss function (ELF) (Im{-1/?}), are presented for 16 elemental metals (Ti, V, Fe, Co, Ni, Cu, Zn, Mo, Pd, Ag, Ta, W, Pt, Au, Pb, and Bi) and 1 semimetal (Te) and are compared to available data in the literature. One data set is obtained from density functional theory (DFT) calculations and gives ? from the infrared to the soft x-ray range of wavelengths. The other set of optical constants, derived from experimental reflection electron energy-loss spectroscopy (REELS) spectra, provides reliable optical data from the near-ultraviolet to the soft x-ray regime. The two data sets exhibit very good mutual consistency and also, overall, compare well with optical data found in the literature, most of which were determined several decades ago. However, exceptions to this rule are also found in some instances, some of them systematic, where the DFT and REELS mutually agree significantly better than with literature data. The accuracy of the experimental data is estimated to be better than 10% for the ELF and ?2 as well as for ?1 for energies above 10eV. For energies below 10eV, the uncertainty in ?1 in the experimental data may exceed 100%, which is a consequence of the fact that energy-loss measurements mainly sample the absorptive part of the dielectric constant. Electron inelastic-scattering data, i.e., the differential inverse inelastic mean free path (IMFP) as well the differential and total surface excitation probabilities are derived from the experimental data. Furthermore, the total electron IMFP is calculated from the determined optical constants by employing linear response theory for energies between 200 and 3000eV. In the latter case, the consistency between the DFT and the REELS data is excellent (better than 5% for all considered elements over the entire energy range considered) and a very good agreement with earlier results is also obtained, except for a few cases for which the earlier optical data deviate significantly from those obtained here.
A Random Sampling Scheme for Path Planning
Latombe, Jean-Claude
precludes any useful application. This negative result has led some researchers to seek heuristic algorithms path planners have been proposed during the last few years. Their at tractiveness stems from for future research. 1 Introduction Robot path planning has been proven a hard problem [40]. There is strong
FESAC Development Path Meeting Draft Agenda
FESAC Development Path Meeting Draft Agenda October 28, 2002 9:00 - 9:35: 1) Structural Materials Development for MFE and IFE - Steve Zinkle What options could be possible for a 35-year Demo? ODS steels Development Path - Mohamed Abdou / Mike Ulrickson Speak about what a blanket is. Range of blanket options
Euclidean path modeling for video surveillance
Imran N. Junejo; Hassan Foroosh
2008-01-01
In this paper, we address the issue of Euclidean path modeling in a single camera for activity monitoring in a multi-camera video surveillance system. The method consists of a path building training phase and a testing phase. During the unsupervised training phase, after auto-calibrating a camera and thereafter metric rectifying the input trajectories, a weighted graph is constructed with trajectories
10 Metric Path Planning Chapter objectives
Sukthankar, Gita Reese
between continuous and event-driven replanning. 10.1 Objectives and Overview Metric path planning navigation focused on subgoals which are gateways or locations where the robot could change its primary heading. The terms "optimal" and "best" have serious ramifications for robotics. In order to say a path
Global path planning for Mars rover exploration
Paul Tompkins; Anthony Stentz; David Wettergreen
2004-01-01
TEMPEST is a planner for long-range planetary navigation that bridges the gap between path planning and classical planning and scheduling. In addition to planning routes, our approach yields the timing and placement of actions to conserve and restore expendable resources and that abide by operational constraints. TEMPEST calls upon the incremental search engine (ISE) to enable heuristic path planning and
Clearance Based Path Optimization for Motion Planning
Utrecht, Universiteit
of information and computing sciences, utrecht university technical report UUCS2003039 www.cs.uu.nl #12Clearance Based Path Optimization for Motion Planning Roland Geraerts Mark Overmars institute; Clearance Based Path Optimization for Motion Planning Roland Geraerts Mark Overmars Institute of Information
Clearance Based Path Optimization for Motion Planning
Utrecht, Universiteit
of information and computing sciences, utrecht university technical report UU-CS-2003-039 www.cs.uu.nl #12Clearance Based Path Optimization for Motion Planning Roland Geraerts Mark Overmars institute;Clearance Based Path Optimization for Motion Planning Roland Geraerts Mark Overmars Institute of Information
Learning Omnidirectional Path Following Using Dimensionality Reduction
Kolter, J. Zico
. INTRODUCTION In this paper we consider the task of omnidirectional path following: moving a four-legged robot in a circle while facing the circle's center, following a straight line while spinning around, or any otherLearning Omnidirectional Path Following Using Dimensionality Reduction J. Zico Kolter and Andrew Y
PARALLEL EVOLUTIONARY ALGORITHMS FOR UAV PATH PLANNING
PARALLEL EVOLUTIONARY ALGORITHMS FOR UAV PATH PLANNING Dong Jia Post-Doctoral Research Associate vehicles (UAVs). Premature convergence prevents evolutionary-based algorithms from reaching global optimal. To overcome this problem, this paper presents a framework of parallel evolutionary algorithms for UAV path
Lattice path combinatorics for multiple product identities
Larry Ericksen
2010-01-01
Lattice paths are enumerated as walks on a lattice under the Delannoy criterion of vertical, horizontal and upward diagonal steps. Delannoy recursions are generalized for arbitrary weights in each of these directions, where the row elements of the Delannoy triangles correspond to lattice paths for all walks at a given length.This paper surveys known connections between generating functions for Delannoy
Adaptively Ubiquitous Learning in Campus Math Path
ERIC Educational Resources Information Center
Shih, Shu-Chuan; Kuo, Bor-Chen; Liu, Yu-Lung
2012-01-01
The purposes of this study are to develop and evaluate the instructional model and learning system which integrate ubiquitous learning, computerized adaptive diagnostic testing system and campus math path learning. The researcher first creates a ubiquitous learning environment which is called "adaptive U-learning math path system". This system…
Stable Billiard Paths on Polygons Yilong Yang
Varadarajan, Veeravalli S.
Stable Billiard Paths on Polygons Yilong Yang April 29, 2013 #12;Contents 1 Preface 2 2 Introduction to Mathematical Billiards 3 2.1 Basic Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.3 Space of Labeled n-gons and Stable Periodic Billiard Path
Shortest path and Schramm-Loewner Evolution
Posé, N.; Schrenk, K. J.; Araújo, N. A. M.; Herrmann, H. J.
2014-01-01
We numerically show that the statistical properties of the shortest path on critical percolation clusters are consistent with the ones predicted for Schramm-Loewner evolution (SLE) curves for ? = 1.04 ± 0.02. The shortest path results from a global optimization process. To identify it, one needs to explore an entire area. Establishing a relation with SLE permits to generate curves statistically equivalent to the shortest path from a Brownian motion. We numerically analyze the winding angle, the left passage probability, and the driving function of the shortest path and compare them to the distributions predicted for SLE curves with the same fractal dimension. The consistency with SLE opens the possibility of using a solid theoretical framework to describe the shortest path and it raises relevant questions regarding conformal invariance and domain Markov properties, which we also discuss. PMID:24975019
Modular electronics packaging system
NASA Technical Reports Server (NTRS)
Hunter, Don J. (Inventor)
2001-01-01
A modular electronics packaging system includes multiple packaging slices that are mounted horizontally to a base structure. The slices interlock to provide added structural support. Each packaging slice includes a rigid and thermally conductive housing having four side walls that together form a cavity to house an electronic circuit. The chamber is enclosed on one end by an end wall, or web, that isolates the electronic circuit from a circuit in an adjacent packaging slice. The web also provides a thermal path between the electronic circuit and the base structure. Each slice also includes a mounting bracket that connects the packaging slice to the base structure. Four guide pins protrude from the slice into four corresponding receptacles in an adjacent slice. A locking element, such as a set screw, protrudes into each receptacle and interlocks with the corresponding guide pin. A conduit is formed in the slice to allow electrical connection to the electronic circuit.
Career Paths in Sport Management
ERIC Educational Resources Information Center
Schwab, Keri A.; Legg, Eric; Tanner, Preston; Timmerman, Danielle; Dustin, Daniel; Arthur-Banning, Skye G.
2015-01-01
Sport management alumni (N = 268) from five universities that offer undergraduate programs with an emphasis in sport management within departments of parks, recreation, and tourism were sampled via an electronic survey. The survey sought to learn where alumni were working, and how they felt about their career choice and undergraduate professional…
Improving WCET by Applying Worst-Case Path Optimizations
Mueller, Frank
the WCET by adapting and applying optimizations designed for frequent paths to the worst-case (WC) paths a timing analyzer to detect the WC paths in a function. Since these path-based optimizations may increase evaluate these WC path optimizations and present results showing the decrease in WCET versus the increase
A NEW IMPLEMENTATION OF YEN'S RANKING LOOPLESS PATHS ALGORITHM 1
Pascoal, Marta Margarida Braz
A NEW IMPLEMENTATION OF YEN'S RANKING LOOPLESS PATHS ALGORITHM 1 Ernesto de Queir' os Vieira algorithm for ranking the K shortest loopless paths between a pair of nodes in a network. In this paper to conclude. Keywords: network, path, loopless path, paths ranking. 1 Introduction The problem of determining
On Third-party Addresses in Traceroute Paths
California at San Diego, University of
On Third-party Addresses in Traceroute Paths Young Hyun, Andre Broido, kc claffy CAIDA, San Diego relative to path beginning distribution relative to path end multihoming Conclusions #12;Motivation) BGP tables at RouteViews and RIPE AS paths derived from traceroute paths #12;Traceroute advantages
Issues and Paths to Magnetic Confinement Fusion Energy
Issues and Paths to Magnetic Confinement Fusion Energy Hutch Neilson Princeton Plasma Physics #12;Issues and Paths to MFE: Outline 2 Issues & Paths to MFE / H. Neilson / AAAS Meeting / 16 February are planning major facilities and next steps beyond ITER on the path to DEMO. Issues & Paths to MFE / H
Weighted Lattice Paths Coworkers: R. Brak, A. J. Guttmann,
Essam, John W.
Weighted Lattice Paths Coworkers: R. Brak, A. J. Guttmann, A. L. Owczarek and H. Lonsdale #12;Binomial Paths and the constant term method Method due to P A MacMahon ,Combinatory Analysis Vol. 2 1916 #12;Dyck and Ballot paths Â· A Dyck path is a lattice path which starts and ends on the x- axis
Periodic billiard paths in right triangles are W. Patrick Hooper
Hooper, Patrick
Periodic billiard paths in right triangles are unstable W. Patrick Hooper January 24, 2007 A billiard path in a triangle T is a bi-infinite path consisting of line segments in the interior of reflection. Billiard paths must never intersect the vertices of T. A periodic billiard path is a billiard
Periodic billiard paths in right triangles are W. Patrick Hooper
Hooper, Patrick
Periodic billiard paths in right triangles are unstable W. Patrick Hooper January 24, 2007 A billiard path ## in a triangle T is a biÂinfinite path consisting of line segments in the interior of reflection. Billiard paths must never intersect the vertices of T . A periodic billiard path is a billiard
Decision paths in complex tasks
NASA Technical Reports Server (NTRS)
Galanter, Eugene
1991-01-01
Complex real world action and its prediction and control has escaped analysis by the classical methods of psychological research. The reason is that psychologists have no procedures to parse complex tasks into their constituents. Where such a division can be made, based say on expert judgment, there is no natural scale to measure the positive or negative values of the components. Even if we could assign numbers to task parts, we lack rules i.e., a theory, to combine them into a total task representation. We compare here two plausible theories for the amalgamation of the value of task components. Both of these theories require a numerical representation of motivation, for motivation is the primary variable that guides choice and action in well-learned tasks. We address this problem of motivational quantification and performance prediction by developing psychophysical scales of the desireability or aversiveness of task components based on utility scaling methods (Galanter 1990). We modify methods used originally to scale sensory magnitudes (Stevens and Galanter 1957), and that have been applied recently to the measure of task 'workload' by Gopher and Braune (1984). Our modification uses utility comparison scaling techniques which avoid the unnecessary assumptions made by Gopher and Braune. Formula for the utility of complex tasks based on the theoretical models are used to predict decision and choice of alternate paths to the same goal.
Gerbertian paths for the Jubilee
NASA Astrophysics Data System (ADS)
Sigismondi, Costantino
2015-04-01
Gerbert before becoming Pope Sylvester II came several times in Rome, as reported in his Letters and in the biography of Richerus. Eight places in Rome can be connected with Gerbertian memories. 1. The Cathedral of St. John in the Lateran where the gravestone of his tumb is still preserved near the Holy Door; 2. the “Basilica Hierusalem” (Santa Croce) where Gerbert had the stroke on May 3rd 1003 which lead him to death on May 12th; 3. the Aventine hill, with the church of the Knights of Malta in the place where the palace of the Ottonian Emperors was located; 4. the church of St. Bartholomew in the Tiber Island built in 997 under Otto III; 5. the Obelisk of Augustus in Montecitorio to remember the relationship between Gerbert, Astronomy and numbers which led the birth of the legends on Gerbert magician; 6. St. Mary Major end of the procession of August 15, 1000; 7. St. Paul outside the walls with the iconography of the Popes and 8. St. Peter's tumb end of all Romaei pilgrimages. This Gerbertian path in Rome suggests one way to accomplish the pilgrimage suggested by Pope Francis in the Bulla Misericordiae Vultus (14) of indiction of the new Jubilee.
Quantum-classical path integral. I. Classical memory and weak quantum nonlocality
Makri, Nancy
nonlocality Roberto Lambert1 and Nancy Makri1,2 1 Department of Physics, University of Illinois, 1110 W. Green in a stepwise fashion along classical trajectories of the free solvent. This simple "classical path" limit with millions of atoms. On the other hand, nonadiabatic effects allowing electronic transitions are commonly
Half-lattice paths and Virasoro characters
Olivier B. -Fournier; Pierre Mathieu; Trevor A. Welsh
2011-09-03
We first briefly review the role of lattice paths in the derivation of fermionic expressions for the M(p,p') minimal model characters of the Virasoro Lie algebra. We then focus on the recently introduced half-lattice paths for the M(p,2p+/-1) characters, reformulating them in such a way that the two cases may be treated uniformly. That the generating functions of these half-lattice paths are indeed M(p,2p+/-1) characters is proved by describing weight preserving bijections between them and the corresponding RSOS lattice paths. Here, the M(p,2p-1) case is derived for the first time. We then apply the methods of Bressoud and Warnaar to these half-lattice paths to derive fermionic expressions for the Virasoro characters X^{p,2p+/-1}_{1,2} that differ from those obtained from the RSOS paths. This work is an extension of that presented by the third author at the "7th International Conference on Lattice Path Combinatorics and Applications", Siena, Italy, July 2010.
Robot path planning using a genetic algorithm
NASA Technical Reports Server (NTRS)
Cleghorn, Timothy F.; Baffes, Paul T.; Wang, Liu
1988-01-01
Robot path planning can refer either to a mobile vehicle such as a Mars Rover, or to an end effector on an arm moving through a cluttered workspace. In both instances there may exist many solutions, some of which are better than others, either in terms of distance traversed, energy expended, or joint angle or reach capabilities. A path planning program has been developed based upon a genetic algorithm. This program assumes global knowledge of the terrain or workspace, and provides a family of good paths between the initial and final points. Initially, a set of valid random paths are constructed. Successive generations of valid paths are obtained using one of several possible reproduction strategies similar to those found in biological communities. A fitness function is defined to describe the goodness of the path, in this case including length, slope, and obstacle avoidance considerations. It was found that with some reproduction strategies, the average value of the fitness function improved for successive generations, and that by saving the best paths of each generation, one could quite rapidly obtain a collection of good candidate solutions.
14 CFR 171.267 - Glide path automatic monitor system.
Code of Federal Regulations, 2011 CFR
2011-01-01
...2011-01-01 false Glide path automatic monitor system. 171.267 Section 171...171.267 Glide path automatic monitor system. (a) The ISMLS glide path equipment must provide an automatic monitor system that transmits a...
14 CFR 171.267 - Glide path automatic monitor system.
Code of Federal Regulations, 2013 CFR
2013-01-01
...2013-01-01 false Glide path automatic monitor system. 171.267 Section 171...171.267 Glide path automatic monitor system. (a) The ISMLS glide path equipment must provide an automatic monitor system that transmits a...
14 CFR 171.267 - Glide path automatic monitor system.
Code of Federal Regulations, 2012 CFR
2012-01-01
...2012-01-01 false Glide path automatic monitor system. 171.267 Section 171...171.267 Glide path automatic monitor system. (a) The ISMLS glide path equipment must provide an automatic monitor system that transmits a...
14 CFR 171.267 - Glide path automatic monitor system.
Code of Federal Regulations, 2014 CFR
2014-01-01
...2014-01-01 false Glide path automatic monitor system. 171.267 Section 171...171.267 Glide path automatic monitor system. (a) The ISMLS glide path equipment must provide an automatic monitor system that transmits a...
14 CFR 171.267 - Glide path automatic monitor system.
Code of Federal Regulations, 2010 CFR
2010-01-01
...2010-01-01 false Glide path automatic monitor system. 171.267 Section 171...171.267 Glide path automatic monitor system. (a) The ISMLS glide path equipment must provide an automatic monitor system that transmits a...
28 CFR 36.403 - Alterations: Path of travel.
Code of Federal Regulations, 2013 CFR
2013-07-01
... 2013-07-01 false Alterations: Path of travel. 36.403 Section 36.403...Alterations § 36.403 Alterations: Path of travel. (a) General. ...that, to the maximum extent feasible, the path of travel to the altered area...
14 CFR 25.123 - En route flight paths.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 2013-01-01 false En route flight paths. 25.123 Section 25.123 Aeronautics...Performance § 25.123 En route flight paths. (a) For the en route configuration, the flight paths prescribed in paragraph (b)...
14 CFR 23.61 - Takeoff flight path.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 2011-01-01 false Takeoff flight path. 23.61 Section 23.61 Aeronautics...Performance § 23.61 Takeoff flight path. For each commuter category airplane, the takeoff flight path must be determined as follows:...
14 CFR 25.123 - En route flight paths.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 2012-01-01 false En route flight paths. 25.123 Section 25.123 Aeronautics...Performance § 25.123 En route flight paths. (a) For the en route configuration, the flight paths prescribed in paragraph (b)...
14 CFR 25.123 - En route flight paths.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 2014-01-01 false En route flight paths. 25.123 Section 25.123 Aeronautics...Performance § 25.123 En route flight paths. (a) For the en route configuration, the flight paths prescribed in paragraph (b)...
14 CFR 25.123 - En route flight paths.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 2011-01-01 false En route flight paths. 25.123 Section 25.123 Aeronautics...Performance § 25.123 En route flight paths. (a) For the en route configuration, the flight paths prescribed in paragraph (b)...
Automatic alignment of double optical paths in excimer laser amplifier
NASA Astrophysics Data System (ADS)
Wang, Dahui; Zhao, Xueqing; Hua, Hengqi; Zhang, Yongsheng; Hu, Yun; Yi, Aiping; Zhao, Jun
2013-05-01
A kind of beam automatic alignment method used for double paths amplification in the electron pumped excimer laser system is demonstrated. In this way, the beams from the amplifiers can be transferred along the designated direction and accordingly irradiate on the target with high stabilization and accuracy. However, owing to nonexistence of natural alignment references in excimer laser amplifiers, two cross-hairs structure is used to align the beams. Here, one crosshair put into the input beam is regarded as the near-field reference while the other put into output beam is regarded as the far-field reference. The two cross-hairs are transmitted onto Charge Coupled Devices (CCD) by image-relaying structures separately. The errors between intersection points of two cross-talk images and centroid coordinates of actual beam are recorded automatically and sent to closed loop feedback control mechanism. Negative feedback keeps running until preset accuracy is reached. On the basis of above-mentioned design, the alignment optical path is built and the software is compiled, whereafter the experiment of double paths automatic alignment in electron pumped excimer laser amplifier is carried through. Meanwhile, the related influencing factors and the alignment precision are analyzed. Experimental results indicate that the alignment system can achieve the aiming direction of automatic aligning beams in short time. The analysis shows that the accuracy of alignment system is 0.63?rad and the beam maximum restoration error is 13.75?m. Furthermore, the bigger distance between the two cross-hairs, the higher precision of the system is. Therefore, the automatic alignment system has been used in angular multiplexing excimer Main Oscillation Power Amplification (MOPA) system and can satisfy the requirement of beam alignment precision on the whole.
Optimization of Loading Paths for Tube Hydroforming
NASA Astrophysics Data System (ADS)
Jirathearanat, Suwat; Altan, Taylan
2004-06-01
An iterative FE simulation approach enhanced with numerical optimization schemes has been implemented for determination of optimum loading paths for tube hydroforming (THF) processes. A general optimization code, PAM-OPT, has been applied to optimize several THF processes simulated by PAM-STAMP. This paper discusses formulations of optimization of loading paths for various THF processes including a Y-shape and a complex structural part. In the process optimization, the loading paths were represented by piecewise-linear curve functions of which the control points were the design variables. Several objective functions and constraints were formulated to express the critical desirable part qualities.
Path planning strategies for autonomous ground vehicles
NASA Astrophysics Data System (ADS)
Gifford, Kevin Kent
Several key issues involved with the planning and executing of optimally generated paths for autonomous vehicles are addressed. Two new path planning algorithms are developed, and examined, which effectively minimize replanning as unmapped hazards are encountered. The individual algorithms are compared via extensive simulation. The search strategy results are implemented and tested using the University of Colorado's autonomous vehicle test-bed, RoboCar, and results show the advantages of solving the single-destination all-paths problem for autonomous vehicle path planning. Both path planners implement a graph search methodology incorporating dynamic programming that solves the single-destination shortest-paths problem. Algorithm 1, termed DP for dynamic programming, searches a state space where each state represents a potential vehicle location in a breadth-first fashion expanding from the goal to all potential start locations in the state space. Algorithm 2, termed DP*, couples the heuristic search power of the well-known A* search procedure (Nilsson-80) with the dynamic programming principle applied to graph searching to efficiently make use of overlapping subproblems. DP* is the primary research contribution of the work contained within this thesis. The advantage of solving the single-destination shortest-paths problem is that the entire terrain map is solved in terms of reaching a specified goal. Therefore, if the robot is diverted from the pre-planned path, an alternative path is already computed. The search algorithms are extended to include a probabilistic approach using empirical loss functions to incorporate terrain map uncertainties into the path considering terrain planning process. The results show the importance of considering terrain uncertainty. If the map representation ignores uncertainty by marking any area with less than perfect confidence as unpassable or assigns it the worst case rating, then the paths are longer than intuitively necessary. A hierarchical software control architecture is introduced that uses as the main guidance function an arbitration-based scheme which is able to efficiently and robustly integrate disparate sensor data. The flexibility provided by such an architecture allows for very easy integration of any type of environmental sensing device into the path planning algorithm.
Extending the application of critical path methods.
Coffey, R J; Othman, J E; Walters, J I
1995-01-01
Most health care organizations are using critical pathways in an attempt to reduce the variation in patient care, improve quality, enhance communication, and reduce costs. Virtually all of the critical path efforts to date have developed tables of treatments, medications, and so forth by day and have displayed them in a format known as a Gantt chart. This article presents a methodology for identifying the true "time-limiting" critical path, describes three additional methods for presenting the information--the network, precedent, and resource formats--and shows how these can significantly enhance current critical path efforts. PMID:10141770
Non Abelian Dual Maps in Path Space
Isbelia Martin
1999-05-04
We study an extension of the procedure to construct duality transformations among abelian gauge theories to the non abelian case using a path space formulation. We define a pre-dual functional in path space and introduce a particular non local map among Lie algebra valued 1-form functionals that reduces to the ordinary Hodge-* duality map of the abelian theories. Further, we establish a full set of equations on path space representing the ordinary Yang Mills equations and Bianchi identities of non abelian gauge theories of 4-dimensional euclidean space.
The terminal area automated path generation problem
NASA Technical Reports Server (NTRS)
Hsin, C.-C.
1977-01-01
The automated terminal area path generation problem in the advanced Air Traffic Control System (ATC), has been studied. Definitions, input, output and the interrelationships with other ATC functions have been discussed. Alternatives in modeling the problem have been identified. Problem formulations and solution techniques are presented. In particular, the solution of a minimum effort path stretching problem (path generation on a given schedule) has been carried out using the Newton-Raphson trajectory optimization method. Discussions are presented on the effect of different delivery time, aircraft entry position, initial guess on the boundary conditions, etc. Recommendations are made on real-world implementations.
Evolution paths for advanced automation
NASA Technical Reports Server (NTRS)
Healey, Kathleen J.
1990-01-01
As Space Station Freedom (SSF) evolves, increased automation and autonomy will be required to meet Space Station Freedom Program (SSFP) objectives. As a precursor to the use of advanced automation within the SSFP, especially if it is to be used on SSF (e.g., to automate the operation of the flight systems), the underlying technologies will need to be elevated to a high level of readiness to ensure safe and effective operations. Ground facilities supporting the development of these flight systems -- from research and development laboratories through formal hardware and software development environments -- will be responsible for achieving these levels of technology readiness. These facilities will need to evolve support the general evolution of the SSFP. This evolution will include support for increasing the use of advanced automation. The SSF Advanced Development Program has funded a study to define evolution paths for advanced automaton within the SSFP's ground-based facilities which will enable, promote, and accelerate the appropriate use of advanced automation on-board SSF. The current capability of the test beds and facilities, such as the Software Support Environment, with regard to advanced automation, has been assessed and their desired evolutionary capabilities have been defined. Plans and guidelines for achieving this necessary capability have been constructed. The approach taken has combined indepth interviews of test beds personnel at all SSF Work Package centers with awareness of relevant state-of-the-art technology and technology insertion methodologies. Key recommendations from the study include advocating a NASA-wide task force for advanced automation, and the creation of software prototype transition environments to facilitate the incorporation of advanced automation in the SSFP.
NASA Astrophysics Data System (ADS)
Feibel, C. S.
2004-12-01
A complex series of evolutionary steps, contingent upon a dynamic environmental context and a long biological heritage, have led to the ascent of Homo sapiens as a dominant component of the modern biosphere. In a field where missing links still abound and new discoveries regularly overturn theoretical paradigms, our understanding of the path of human evolution has made tremendous advances in recent years. Two major trends characterize the development of the hominin clade subsequent to its origins with the advent of upright bipedalism in the Late Miocene of Africa. One is a diversification into two prominent morphological branches, each with a series of 'twigs' representing evolutionary experimentation at the species or subspecies level. The second important trend, which in its earliest manifestations cannot clearly be ascribed to one or the other branch, is the behavioral complexity of an increasing reliance on technology to expand upon limited inherent morphological specializations and to buffer the organism from its environment. This technological dependence is directly associated with the expansion of hominin range outside Africa by the genus Homo, and is accelerated in the sole extant form Homo sapiens through the last 100 Ka. There are interesting correlates between the evolutionary and behavioral patterns seen in the hominin clade and environmental dynamics of the Neogene. In particular, the tempo of morphological and behavioral innovation may be tracking major events in Neogene climatic development as well as reflecting intervals of variability or stability. Major improvements in analytical techniques, coupled with important new collections and a growing body of contextual data are now making possible the integration of global, regional and local environmental archives with an improved biological understanding of the hominin clade to address questions of coincidence and causality.
Nonclassical paths in quantum interference experiments.
Sawant, Rahul; Samuel, Joseph; Sinha, Aninda; Sinha, Supurna; Sinha, Urbasi
2014-09-19
In a double slit interference experiment, the wave function at the screen with both slits open is not exactly equal to the sum of the wave functions with the slits individually open one at a time. The three scenarios represent three different boundary conditions and as such, the superposition principle should not be applicable. However, most well-known text books in quantum mechanics implicitly and/or explicitly use this assumption that is only approximately true. In our present study, we have used the Feynman path integral formalism to quantify contributions from nonclassical paths in quantum interference experiments that provide a measurable deviation from a naive application of the superposition principle. A direct experimental demonstration for the existence of these nonclassical paths is difficult to present. We find that contributions from such paths can be significant and we propose simple three-slit interference experiments to directly confirm their existence. PMID:25279612
Local-time representation of path integrals
Petr Jizba; Vaclav Zatloukal
2015-06-02
We derive a local-time path-integral representation for a generic one-dimensional time-independent system. In particular, we show how to rephrase the matrix elements of the Bloch density matrix as a path integral over x-dependent local-time profiles. The latter quantify the time that the sample paths x(t) in the Feynman path integral spend in the vicinity of an arbitrary point x. Generalization of the local-time representation that includes arbitrary functionals of the local time is also provided. We argue that the results obtained represent a powerful alternative to the traditional Feynman-Kac formula, particularly in the high and low temperature regimes. To illustrate this point, we apply our local-time representation to analyze the asymptotic behavior of the Bloch density matrix at low temperatures. Further salient issues, such as connections with the Sturm-Liouville theory and the Rayleigh-Ritz variational principle are also discussed.
Numerical evaluation of Feynman path integrals
NASA Astrophysics Data System (ADS)
Baird, William Hugh
1999-11-01
The notion of path integration developed by Feynman, while an incredibly successful method of solving quantum mechanical problems, leads to frequently intractable integrations over an infinite number of paths. Two methods now exist which sidestep this difficulty by defining "densities" of actions which give the relative number of paths found at different values of the action. These densities are sampled by computer generation of paths and the propagators are found to a high degree of accuracy for the case of a particle on the infinite half line and in a finite square well in one dimension. The problem of propagation within a two dimensional radial well is also addressed as the precursor to the problem of a particle in a stadium (quantum billiard).
Path Analysis in Genetic Epidemiology and Alternatives.
ERIC Educational Resources Information Center
Karlin, Samuel
1987-01-01
Discusses the application of path analysis in the context of genetic epidemiology. Examines the coherence of model specification, plausibility of modeling assumptions, the interpretability and usefulness of the model, and the validity of statistical procedures. (RB)
Shortest Paths, Network Design and Associated Polyhedra
Magnanti, Thomas L.
We study a specialized version of network design problems that arise in telecommunication, transportation and other industries. The problem, a generalization of the shortest path problem, is defined on an undirected network ...
A chemist building paths to cell biology.
Weibel, Douglas B
2013-11-01
Galileo is reported to have stated, "Measure what is measurable and make measurable what is not so." My group's trajectory in cell biology has closely followed this philosophy, although it took some searching to find this path. PMID:24174456
An Alternate Path To Stoichiometric Problem Solving.
ERIC Educational Resources Information Center
Schmidt, Hans-Jurgen
1997-01-01
Discusses an alternate path to teaching introductory stoichiometry based on research findings. The recommendation is to use problems that can be solved easily by rapid mental calculation as well as by pure logic. (AIM)
Locating ''sneak paths'' in electrical circuitry
NASA Technical Reports Server (NTRS)
Dannback, T. M.
1968-01-01
Use of a matrix system wherein circuit pin connections are assigned arbitrary designators and these used in formation of the matrix is illustrated. The matrix is a format that shows the current paths.
Geomagnetic Reversals: Rates, Timescales, Preferred Paths,
Constable, Catherine G.
Geomagnetic Reversals: Rates, Timescales, Preferred Paths, Statistical Models and Simulations: Geomagnetic reversals, Reversal rates, Paleointensity, Statistics of Geodynamo September 30, 2001 #12;Abstract Paleomagnetic data on geomagnetic reversals are divided into two general categories: times of occurrence
Duality of quantum coherence and path distinguishability
NASA Astrophysics Data System (ADS)
Bera, Manabendra Nath; Qureshi, Tabish; Siddiqui, Mohd Asad; Pati, Arun Kumar
2015-07-01
We derive a generalized wave-particle duality relation for arbitrary multipath quantum interference phenomena. Beyond the conventional notion of the wave nature of a quantum system, i.e., the interference fringe visibility, we introduce a quantifier as the normalized quantum coherence, recently defined in the framework of quantum information theory. To witness the particle nature, we quantify the path distinguishability or the which-path information based on unambiguous quantum state discrimination. Then, the Bohr complementarity principle for multipath quantum interference can be stated as a duality relation between the quantum coherence and the path distinguishability. For two-path interference, the quantum coherence is identical to the interference fringe visibility, and the relation reduces to the well-known complementarity relation. The duality relation continues to hold in the case where mixedness is introduced due to possible decoherence effects.
Riemann Curvature Tensor and Closed Geodesic Paths
ERIC Educational Resources Information Center
Morganstern, Ralph E.
1977-01-01
Demonstrates erroneous results obtained if change in a vector under parallel transport about a closed path in Riemannian spacetime is made in a complete circuit rather than just half a circuit. (Author/SL)
Towards Safest Path Adversarial Coverage (Extended Abstract)
Kaminka, Gal A.
to perform coverage missions in hazardous environments, such as opera- tions in nuclear power plants- plistic heuristic algorithm that generates a coverage path which tries to minimize a cost function, which
Nonclassical Paths in Quantum Interference Experiments
NASA Astrophysics Data System (ADS)
Sawant, Rahul; Samuel, Joseph; Sinha, Aninda; Sinha, Supurna; Sinha, Urbasi
2014-09-01
In a double slit interference experiment, the wave function at the screen with both slits open is not exactly equal to the sum of the wave functions with the slits individually open one at a time. The three scenarios represent three different boundary conditions and as such, the superposition principle should not be applicable. However, most well-known text books in quantum mechanics implicitly and/or explicitly use this assumption that is only approximately true. In our present study, we have used the Feynman path integral formalism to quantify contributions from nonclassical paths in quantum interference experiments that provide a measurable deviation from a naive application of the superposition principle. A direct experimental demonstration for the existence of these nonclassical paths is difficult to present. We find that contributions from such paths can be significant and we propose simple three-slit interference experiments to directly confirm their existence.
Identifying decohering paths in closed quantum systems
NASA Technical Reports Server (NTRS)
Albrecht, Andreas
1990-01-01
A specific proposal is discussed for how to identify decohering paths in a wavefunction of the universe. The emphasis is on determining the correlations among subsystems and then considering how these correlations evolve. The proposal is similar to earlier ideas of Schroedinger and of Zeh, but in other ways it is closer to the decoherence functional of Griffiths, Omnes, and Gell-Mann and Hartle. There are interesting differences with each of these which are discussed. Once a given coarse-graining is chosen, the candidate paths are fixed in this scheme, and a single well defined number measures the degree of decoherence for each path. The normal probability sum rules are exactly obeyed (instantaneously) by these paths regardless of the level of decoherence. Also briefly discussed is how one might quantify some other aspects of classicality. The important role that concrete calculations play in testing this and other proposals is stressed.
Steam Path Audits on Industrial Steam Turbines
Mitchell, D. R.
1992-01-01
areas of performance degradation during a turbine outage. Repair priorities can then be set in accordance with quantitative results from the steam path audit. As a result of optimized repair decisions, turbine efficiency increases, emissions... is to examine the entire turbine steam path in detail and then compare the "as-found" condition with the "new-and-clean" condition of the machine. The new-and-clean performance of the Lyondell steam turbine was modeled in STPE using the valves...
A Path Algorithm for Constrained Estimation
Zhou, Hua; Lange, Kenneth
2013-01-01
Many least-square problems involve affine equality and inequality constraints. Although there are a variety of methods for solving such problems, most statisticians find constrained estimation challenging. The current article proposes a new path-following algorithm for quadratic programming that replaces hard constraints by what are called exact penalties. Similar penalties arise in l1 regularization in model selection. In the regularization setting, penalties encapsulate prior knowledge, and penalized parameter estimates represent a trade-off between the observed data and the prior knowledge. Classical penalty methods of optimization, such as the quadratic penalty method, solve a sequence of unconstrained problems that put greater and greater stress on meeting the constraints. In the limit as the penalty constant tends to ?, one recovers the constrained solution. In the exact penalty method, squared penalties!are replaced by absolute value penalties, and the solution is recovered for a finite value of the penalty constant. The exact path-following method starts at the unconstrained solution and follows the solution path as the penalty constant increases. In the process, the solution path hits, slides along, and exits from the various constraints. Path following in Lasso penalized regression, in contrast, starts with a large value of the penalty constant and works its way downward. In both settings, inspection of the entire solution path is revealing. Just as with the Lasso and generalized Lasso, it is possible to plot the effective degrees of freedom along the solution path. For a strictly convex quadratic program, the exact penalty algorithm can be framed entirely in terms of the sweep operator of regression analysis. A few well-chosen examples illustrate the mechanics and potential of path following. This article has supplementary materials available online. PMID:24039382
HomePath: Your On-Line Path to a Home of Your Own
NSDL National Science Digital Library
Whether you're thinking about if you're ready to buy a home, are in the process of buying a home, or are considering refinancing your current home, there's information for you on Fannie Mae's newest website. Fannie Mae is America's largest source of home mortgage funds, and has designed HomePath to be "your on-line path to a home of your own." There are three different paths through the information on the website: HomeStarterPath has resources for people deciding whether home ownership is right for them, including a comparison of renting vs. buying and a calculator for estimating how much house one can afford to buy; HomePurchasePath offers services for people who are ready to buy, including mortgage application information and how to shop for a lender; HomeRefinancePath helps homeowners determine when refinancing is beneficial, and outlines the costs involved.
Equivalence of trans paths in ion channels
NASA Astrophysics Data System (ADS)
Alvarez, Juan; Hajek, Bruce
2006-04-01
We explore stochastic models for the study of ion transport in biological cells. Analysis of these models explains and explores an interesting feature of ion transport observed by biophysicists. Namely, the average time it takes ions to cross certain ion channels is the same in either direction, even if there is an electric potential difference across the channels. It is shown for simple single ion models that the distribution of a path (i.e., the history of location versus time) of an ion crossing the channel in one direction has the same distribution as the time-reversed path of an ion crossing the channel in the reverse direction. Therefore, not only is the mean duration of these paths equal, but other measures, such as the variance of passage time or the mean time a path spends within a specified section of the channel, are also the same for both directions of traversal. The feature is also explored for channels with interacting ions. If a system of interacting ions is in reversible equilibrium (net flux is zero), then the equivalence of the left-to-right trans paths with the time-reversed right-to-left trans paths still holds. However, if the system is in equilibrium, but not reversible equilibrium, then such equivalence need not hold.
Multi-Level Indoor Path Planning Method
NASA Astrophysics Data System (ADS)
Xiong, Q.; Zhu, Q.; Zlatanova, S.; Du, Z.; Zhang, Y.; Zeng, L.
2015-05-01
Indoor navigation is increasingly widespread in complex indoor environments, and indoor path planning is the most important part of indoor navigation. Path planning generally refers to finding the most suitable path connecting two locations, while avoiding collision with obstacles. However, it is a fundamental problem, especially for 3D complex building model. A common way to solve the issue in some applications has been approached in a number of relevant literature, which primarily operates on 2D drawings or building layouts, possibly with few attached attributes for obstacles. Although several digital building models in the format of 3D CAD have been used for path planning, they usually contain only geometric information while losing abundant semantic information of building components (e.g. types and attributes of building components and their simple relationships). Therefore, it becomes important to develop a reliable method that can enhance application of path planning by combining both geometric and semantic information of building components. This paper introduces a method that support 3D indoor path planning with semantic information.
Bonded Paths and van der Waals Interactions in Orpiment, As2S3
Gibbs, Gerald V.; Wallace, Adam F.; Zallen, Richard; Downs, R. T.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.
2010-06-17
Bond critical properties and bond paths have been calculated for the thioarsenide molecular crystal orpiment, As2S3. In addition to the intramolecular As-S bond paths and van der Waals As-S and S-S bond paths within the layers, intermolecular S-S, As-S and As-As van der Waals paths exist between the layers. The S-S bond paths between the layers are identified with the main interlayer restoring forces responsible for the vibrational internal-mode splitting and the low frequency rigid layer modes previously documented in infrared and Raman studies of orpiment. These S-S bond paths are comparable with those calculated for orthorhombic native sulfur and the As4Sn (n = 3,4,5) molecules for several arsenide molecular crystals. The As-S bond paths show that the two nonequivalent arsenic atoms are each coordinated by a highly distorted octahedral array of sulfur atoms. The octahedra consist of three As-S intramolecular bonded interactions and three longer van der Waals interactions (two intramolecular and one intermolecular). One of the arsenic atoms is also coordinated by an arsenic atom in an interlayer As-As bonded interaction. Laplacian isosurface envelopes calculated for the arsenic and sulfur atoms are comparable with those calculated for native arsenic and orthorhombic sulfur. The intermolecular As-S bond paths connect Lewis acid domains on arsenic and an Lewis base domains on sulfur. Van der Waals interactions are traditionally defined as attractive interactions other than those ascribed to bond formation. However, theoretical evidence and arguments, as well as the connection between the bond paths and the vibrational spectra, indicate that the van der Waals interactions in orpiment are directed bonded interactions in the Slater sense. The experimental bond lengths for the As-S and S-S bonded interactions decrease nonlinearly with the increasing value of the electron density at the bond critical point, concomitant with a decrease in the bonded radii of arsenic and sulfur. On the basis of the local energy density, the intramolecular As-S bonded interactions classify as shared interactions and the intramolecular and intermolecular As-S and S-S bonded interactions and the intermolecular As-As van der Waals interactions classify as closed-shell interactions. The so called planar lone electron pair micelle picture for orpiment is spanned by bond paths, substantiating the claim that the layers in the orpiment structure are linked by weak van der Waals bonded interactions.
High-order path-integral Monte Carlo methods for solving quantum dot problems
NASA Astrophysics Data System (ADS)
Chin, Siu A.
2015-03-01
The conventional second-order path-integral Monte Carlo method is plagued with the sign problem in solving many-fermion systems. This is due to the large number of antisymmetric free-fermion propagators that are needed to extract the ground state wave function at large imaginary time. In this work we show that optimized fourth-order path-integral Monte Carlo methods, which use no more than five free-fermion propagators, can yield accurate quantum dot energies for up to 20 polarized electrons with the use of the Hamiltonian energy estimator.
NASA Astrophysics Data System (ADS)
Jablonski, A.; Salvat, F.; Powell, C. J.
2004-06-01
We have analyzed differential cross sections (DCSs) for the elastic scattering of electrons by neutral atoms that have been derived from two commonly used atomic potentials: the Thomas-Fermi-Dirac (TFD) potential and the Dirac-Hartree-Fock (DHF) potential. DCSs from the latter potential are believed to be more accurate. We compared DCSs for six atoms (H, Al, Ni, Ag, Au, and Cm) at four energies (100, 500, 1000, and 10 000 eV) from two databases issued by the National Institute of Standards and Technology in which DCSs had been obtained from the TFD and DHF potentials. While the DCSs from the two potentials had similar shapes and magnitudes, there can be pronounced deviations (up to 70%) for small scattering angles for Al, Ag, Au, and Cm. In addition, there were differences of up to 400% at scattering angles for which there were deep minima in the DCSs; at other angles, the differences were typically less than 20%. The DCS differences decreased with increasing electron energy. DCSs calculated from the two potentials were compared with measured DCSs for six atoms (He, Ne, Ar, Kr, Xe, and Hg) at energies between 50 eV and 3 keV. For Ar, the atom for which experimental data are available over the largest energy range there is good agreement between the measured DCSs and those calculated from the TFD and DHF potentials at 2 and 3 keV, but the experimental DCSs agree better with the DCSs from the DHF potential at lower energies. A similar trend is found for the other atoms. At energies less than about 1 keV, there are increasing differences between the measured DCSs and the DCSs calculated from the DHF potential. These differences were attributed to the neglect of absorption and polarizability effects in the calculations. We compare transport cross sections for H, Al, Ni, Ag, Au, and Cm obtained from the DCSs for each potential. For energies between 200 eV and 1 keV, the largest differences are about 20% (for H, Au, and Cm); at higher energies, the differences are smaller. We also examine the extent to which three quantities derived from DCSs vary depending on whether the DCSs were obtained from the TFD or DHF potential. First, we compare calculated and measured elastic-backscattered intensities for thin films of Au on a Ni substrate with different measurement conditions, but it is not clear whether DCSs from the TFD or DHF potential should be preferred. Second, we compare electron inelastic mean free paths (IMFPs) derived from relative and absolute measurements by elastic-peak electron spectroscopy and from analyses with DCSs obtained from the TFD and DHF potentials. In four examples, for a variety of materials and measurement conditions, we find differences between the IMFPs from the TFD and DHF potentials ranging from 1.3% to 17.1%. Third, we compare mean escape depths for two photoelectron lines and two Auger-electron lines in solid Au obtained using DCSs from the TFD and DHF potentials. The relative differences between these mean escape depths vary from 4.3% at 70 eV to0.5% at 2016 eV at normal electron emission, and become smaller with increasing emission angle. Although measured DCSs for atoms can differ from DCSs calculated from the DHF potential by up to a factor of 2, we find that the atomic DCSs are empirically useful for simulations of electron transport in solids for electron energies above about 300 eV. The atomic DCSs can also be useful for energies down to at least 200 eV if relative measurements are made.
Ravikumar, B.
Importa Applica Notificat ke Yo ble electron Google gla le electron al of this wor hands-on p kshop is fun Scienc Park, CA 9 4g5YHf @sonoma.ed 5 rable ool G or embedd e of the mo electronics EEE and org am
Theory of extreme correlations using canonical Fermions and path integrals
Shastry, B. Sriram, E-mail: sriram@physics.ucsc.edu
2014-04-15
The t–J model is studied using a novel and rigorous mapping of the Gutzwiller projected electrons, in terms of canonical electrons. The mapping has considerable similarity to the Dyson–Maleev transformation relating spin operators to canonical Bosons. This representation gives rise to a non Hermitian quantum theory, characterized by minimal redundancies. A path integral representation of the canonical theory is given. Using it, the salient results of the extremely correlated Fermi liquid (ECFL) theory, including the previously found Schwinger equations of motion, are easily rederived. Further, a transparent physical interpretation of the previously introduced auxiliary Greens function and the ‘caparison factor’, is obtained. The low energy electron spectral function in this theory, with a strong intrinsic asymmetry, is summarized in terms of a few expansion coefficients. These include an important emergent energy scale ?{sub 0} that shrinks to zero on approaching the insulating state, thereby making it difficult to access the underlying very low energy Fermi liquid behavior. The scaled low frequency ECFL spectral function, related simply to the Fano line shape, has a peculiar energy dependence unlike that of a Lorentzian. The resulting energy dispersion obtained by maximization is a hybrid of a massive and a massless Dirac spectrum E{sub Q}{sup ?}??Q??(?{sub 0}{sup 2}+Q{sup 2}), where the vanishing of Q, a momentum type variable, locates the kink minimum. Therefore the quasiparticle velocity interpolates between (??1) over a width ?{sub 0} on the two sides of Q=0, implying a kink there that strongly resembles a prominent low energy feature seen in angle resolved photoemission spectra (ARPES) of cuprate materials. We also propose novel ways of analyzing the ARPES data to isolate the predicted asymmetry between particle and hole excitations. -- Highlights: •Spectral function of the Extremely Correlated Fermi Liquid theory at low energy. •Electronic origin of low energy kinks in energy dispersion. •Non Hermitian representation of Gutzwiller projected electrons. •Analogy with Dyson–Maleev representation of spins. •Path integral formulation of extremely correlated electrons.
Path integrals from meV to MeV
Sa-yakanit, V. (Chulalongkorn Univ., Bangkok (Thailand)); Sritrakool, W.; Berananda, J.O.; Gutzwiller, M.C.; Inomata, A. (State Univ. of New York, Albany, NY (United States). Dept. of Physics); Lundqvist, S.; Klauder, J.R. (Florida Univ., Gainesville, FL (United States)); Schulman, L.
1989-01-01
This book contains the proceedings of the 3rd international conference on Path integrals from meV to MeV under the following: Feynman and Beyond; 40 years of path integration; Feynman and Hibbs revisited; Path integral application to a polaron in a magnetic field; Time dependent quantum tunnelling; and Two level systems in metals; A path integral approach.
An Adaptive Path Planning Algorithm for Cooperating Unmanned Air Vehicles
Cunningham, C.T.; Roberts, R.S.
2000-09-12
An adaptive path planning algorithm is presented for cooperating Unmanned Air Vehicles (UAVs) that are used to deploy and operate land-based sensor networks. The algorithm employs a global cost function to generate paths for the UAVs, and adapts the paths to exceptions that might occur. Examples are provided of the paths and adaptation.
Adaptive path planning algorithm for cooperating unmanned air vehicles
Cunningham, C T; Roberts, R S
2001-02-08
An adaptive path planning algorithm is presented for cooperating Unmanned Air Vehicles (UAVs) that are used to deploy and operate land-based sensor networks. The algorithm employs a global cost function to generate paths for the UAVs, and adapts the paths to exceptions that might occur. Examples are provided of the paths and adaptation.
Replacement Paths via Fast Matrix Multiplication Oren Weimann
Yuster, Raphael
Replacement Paths via Fast Matrix Multiplication Oren Weimann Department of Computer Science be a directed edge-weighted graph and let P be a shortest path from s to t in G. The replacement paths problem asks to compute, for every edge e on P, the shortest s-to-t path that avoids e. Apart from
Covering Paths for Planar Point Sets Adrian Dumitrescu
Dumitrescu, Adrian
Covering Paths for Planar Point Sets Adrian Dumitrescu D´aniel Gerbner Bal´azs Keszegh Csaba D. T´oth§ February 28, 2013 Abstract Given n points in the plane, a covering path is a polygonal path that visits all the points. If no three points are collinear, every covering path requires at least n/2 segments, and n - 1
Searching Paths of Constant Bandwidth Bernd Borchert and Klaus Reinhardt
Borchert, Bernd
Searching Paths of Constant Bandwidth Bernd Borchert and Klaus Reinhardt Universit¨at T. As a generalization of paths, the notion of paths of band- width w is introduced. We show that, for constant w 1, the corre- sponding search problem for such a path of length k in a given graph is NP-complete and fixed
Road Network Reconstruction for Organizing Paths Daniel Chen
Sun, Jian
Road Network Reconstruction for Organizing Paths Daniel Chen Leonidas J. Guibas John Hershberger Jian Sun Abstract We consider the problem of reconstructing a road net- work from a collection of path to allow efficient path sim- ilarity queries against new query paths on the same road network
Road Network Reconstruction for Organizing Paths Daniel Chen
Guibas, Leonidas J.
Road Network Reconstruction for Organizing Paths Daniel Chen Leonidas J. Guibas John Hershberger Jian Sun Abstract We consider the problem of reconstructing a road net- work from a collection of path efficient path similarity queries against new query paths on the same road network. This is a timely prob
Diagnosis for Covariance Structure Models by Analyzing the Path
ERIC Educational Resources Information Center
Yuan, Ke-Hai; Kouros, Chrystyna D.; Kelley, Ken
2008-01-01
When a covariance structure model is misspecified, parameter estimates will be affected. It is important to know which estimates are systematically affected and which are not. The approach of analyzing the path is both intuitive and informative for such a purpose. Different from path analysis, analyzing the path uses path tracing and elementary…
A Comparison of Two Path Planners for Planetary Rovers
NASA Technical Reports Server (NTRS)
Tarokh, M.; Shiller, Z.; Hayati, S.
1999-01-01
The paper presents two path planners suitable for planetary rovers. The first is based on fuzzy description of the terrain, and genetic algorithm to find a traversable path in a rugged terrain. The second planner uses a global optimization method with a cost function that is the path distance divided by the velocity limit obtained from the consideration of the rover static and dynamic stability. A description of both methods is provided, and the results of paths produced are given which show the effectiveness of the path planners in finding near optimal paths. The features of the methods and their suitability and application for rover path planning are compared
Minimal entropy probability paths between genome families.
Ahlbrandt, Calvin; Benson, Gary; Casey, William
2004-05-01
We develop a metric for probability distributions with applications to biological sequence analysis. Our distance metric is obtained by minimizing a functional defined on the class of paths over probability measures on N categories. The underlying mathematical theory is connected to a constrained problem in the calculus of variations. The solution presented is a numerical solution, which approximates the true solution in a set of cases called rich paths where none of the components of the path is zero. The functional to be minimized is motivated by entropy considerations, reflecting the idea that nature might efficiently carry out mutations of genome sequences in such a way that the increase in entropy involved in transformation is as small as possible. We characterize sequences by frequency profiles or probability vectors, in the case of DNA where N is 4 and the components of the probability vector are the frequency of occurrence of each of the bases A, C, G and T. Given two probability vectors a and b, we define a distance function based as the infimum of path integrals of the entropy function H( p) over all admissible paths p(t), 0 < or = t< or =1, with p(t) a probability vector such that p(0)=a and p(1)=b. If the probability paths p(t) are parameterized as y(s) in terms of arc length s and the optimal path is smooth with arc length L, then smooth and "rich" optimal probability paths may be numerically estimated by a hybrid method of iterating Newton's method on solutions of a two point boundary value problem, with unknown distance L between the abscissas, for the Euler-Lagrange equations resulting from a multiplier rule for the constrained optimization problem together with linear regression to improve the arc length estimate L. Matlab code for these numerical methods is provided which works only for "rich" optimal probability vectors. These methods motivate a definition of an elementary distance function which is easier and faster to calculate, works on non-rich vectors, does not involve variational theory and does not involve differential equations, but is a better approximation of the minimal entropy path distance than the distance //b-a//(2). We compute minimal entropy distance matrices for examples of DNA myostatin genes and amino-acid sequences across several species. Output tree dendograms for our minimal entropy metric are compared with dendograms based on BLAST and BLAST identity scores. PMID:15133624
Local path configuration method considering global path optimality in multilayer networks
NASA Astrophysics Data System (ADS)
Takehara, Takayoshi; Tode, Hideki; Murakami, Koso
2005-10-01
Recently, further high-speed and larger capacity communication is requested in the IP network. And multilayer network that constructs the IP network on an optical network such as IP over WDM is focused on. Under such a network environment, the multipath routing for setting two or more paths between a starting and ending nodes in each network is researched. The multipaths are taken advantage of load balance and path recovery and damaged traffic is switched to other paths at the starting node if a failure happens on a path. However, the traditional routing often finds multipaths overlapping on some links and nodes because of its low "disjoint property". Hence, path recovery is difficult because the multipaths may be interrupted at the same time. In order to resolve the problem in multilayer network, we propose the local path configuration method considering global path optimality. Concretely, we propose a network architecture where networks are connected by multiple edge nodes and multipath routing method with new link cost and parallel calculation of multipaths. As a result, the multipaths are prevented from overlapping and the disjointed multipaths enable efficient path recovery in case of a failure. Moreover, we verify the effectiveness of the disjoint property.
A Continuous-State Version of Discrete Randomized Shortest-Paths, with Application to Path Planning
Del Moral , Pierre
a weighted directed graph G, the RSP considers the policy that minimizes the expected cost (exploitation] is a well-known problem in the robotics community, described by [26] as "checking the consequences entropy [23]. The introduced path randomization allows balancing the load (number of packages) per path
Cross-Layer Path Management in Multi-path Transport Protocol for Mobile Devices
Massachusetts at Amherst, University of
interfaces, such as WiFi and cel- lular. However, wireless path characteristics change frequently in mobile environments, causing challenges for MPTCP: For example, WiFi associated paths often become unavailable as devices move, since WiFi has intermittent connectivity caused by the short signal range and susceptibility
Path analysis in genetic epidemiology: a critique.
Karlin, S; Cameron, E C; Chakraborty, R
1983-01-01
Path analysis, a form of general linear structural equation models, is used in studies of human genetics data to discern genetic, environmental, and cultural factors contributing to familial resemblance. It postulates a set of linear and additive parametric relationships between phenotypes and genetic and cultural variables and then essentially uses the assumption of multivariate normality to estimate and perform tests of hypothesis on parameters. Such an approach has been advocated for the analysis of genetic epidemiological data by D. C. Rao, N. Morton, C. R. Cloninger, L. J. Eaves, and W. E. Nance, among others. This paper reviews and evaluates the formulations, assumptions, methodological procedures, interpretations, and applications of path analysis. To give perspective, we begin with a discussion of path analysis as it occurs in the form of general linear causal models in several disciplines of the social sciences. Several specific path analysis models applied to lipoprotein concentrations, IQ, and twin data are then reviewed to keep the presentation self-contained. The bulk of the critical discussion that follows is directed toward the following four facets of path analysis: (1) coherence of model specification and applicability to data; (2) plausibility of modeling assumptions; (3) interpretability and utility of the model; and (4) validity of statistical and computational procedures. In the concluding section, a brief discussion of the problem of appropriate model selection is presented, followed by a number of suggestions of essentially model-free alternative methods of use in the treatment of complex structured data such as occurs in genetic epidemiology. PMID:6349335
Multiple Manifold Clustering Using Curvature Constrained Path
Babaeian, Amir; Bayestehtashk, Alireza; Bandarabadi, Mojtaba
2015-01-01
The problem of multiple surface clustering is a challenging task, particularly when the surfaces intersect. Available methods such as Isomap fail to capture the true shape of the surface near by the intersection and result in incorrect clustering. The Isomap algorithm uses shortest path between points. The main draw back of the shortest path algorithm is due to the lack of curvature constrained where causes to have a path between points on different surfaces. In this paper we tackle this problem by imposing a curvature constraint to the shortest path algorithm used in Isomap. The algorithm chooses several landmark nodes at random and then checks whether there is a curvature constrained path between each landmark node and every other node in the neighborhood graph. We build a binary feature vector for each point where each entry represents the connectivity of that point to a particular landmark. Then the binary feature vectors could be used as a input of conventional clustering algorithm such as hierarchical clustering. We apply our method to simulated and some real datasets and show, it performs comparably to the best methods such as K-manifold and spectral multi-manifold clustering. PMID:26375819
Interpretation of pressure-temperature-time paths
England, P.C.
1985-01-01
Pressure-temperature-time (PTt) paths inferred from mineral assemblages or compositions in metamorphic rocks are used to place constraints on metamorphic processes on several different scales. The purpose of this paper is to indicate the kind of questions that may be answered, and those that cannot, by interpretation of PTt data. The intensity of regional metamorphism depends both on the intensity of available heat sources and the length of time available for thermal relaxation; consequently the addition of reliable dates to a PT path is a crucial element in containing thermal history. For example, the question as to whether or not Archaean continental thermal regimes were similar to today's cannot be answered without PTt paths dated to a precision of better than 30 Myr. As there is always local perturbation due to tectonic, igneous or other fluid activity it is essential to obtain widespread PTt data before making estimates of thermal budgets for regional metamorphism. However, on the smaller scale, PTt paths may be used to infer tectonic style where structural data are ambiguous or lacking. Particular attention is paid to the problems of inferring extensional events from the PTt paths recorded by rocks from regional metamorphic belts.
Path Integral on the Extreme Field Configurations
NASA Astrophysics Data System (ADS)
Khatsymovsky, V. M.
The canonical Hamiltonian path integral measure obeys certain rule which relates such measure on the paths defined on the whole time axis to the measures on the paths defined on the regions constituting the time axis. We show that this "gluing" rule can be reproduced without referring to Hamiltonian formalism, by substituting field configurations with arbitrarily fast change of the fields at the boundary points of these regions into action and viewing the path integral in the sense of generalized function. Now the coordinate along which gluing proceeds can be not only the time. The piecewise-flat (simplicial) minisuperspace gravity system is considered. Arbitrarily fast change of the (tangential component of) metric between the two 4-simplices with common 3-face is studied. That is, we generalize piecewise-flat anzats by allowing tangential metric to be function of the distance from the 3-face in the neighborhood of this 3-face. The action is nondegenerate (nonsingular) with respect to these additional generalized coordinates. The rule for gluing the path integral measures on separate 4-simplices is found. The resulting general expression covers a large variety of the measures including those usually used in numerical calculations and allows one to specify the measure in some applications.
Chawla, J. S.; Gall, D.
2012-02-15
Epitaxial Ag(001) layers were deposited on MgO(001) in order to study electron surface scattering. X-ray reflection indicates 3D layer nucleation with a high rms surface roughness of 1.0 nm for a layer thickness d = 3.5 nm. X-ray diffraction shows that {l_brace}111{r_brace} twins form at d < 11 nm, followed by 2nd generation twinning for 11 nm < d < 120 nm. Increasing the growth temperature from 25 to 150 deg. C suppresses 2nd generation twinning and reduces the twin density by 2 orders of magnitude. In situ deposition of epitaxial 2.5-nm-thick TiN(001) underlayers prior to Ag deposition results in twin-free single-crystal Ag(001) with 10 x smoother surfaces for d = 3.5 nm. This is attributed to a better wetting on the higher energy TiN(001) than MgO(001) surface, resulting in the absence of 3D nuclei with exposed {l_brace}111{r_brace} facets, which facilitate twin nucleation. The twinned Ag/MgO layers have a higher resistivity {rho} than the single crystal Ag/TiN layers at both 298 and 77 K, due to electron scattering at grain and twin boundaries. The {rho} for single-crystal Ag layers increases with decreasing d, which is well explained with known surface scattering models and provides specularity parameters for the Ag-vacuum and the Ag-air interfaces of p = 0.8 {+-} 0.1 and 0.4 {+-} 0.1, respectively. A comparison with corresponding epitaxial Cu(001) layers shows that {rho}{sub Ag} < {rho}{sub Cu} for d > 50 nm, consistent with known bulk values. However, {rho}{sub Ag} > {rho}{sub Cu} for d < 40 nm. This is attributed to the larger electron mean free path for electron-phonon scattering and a correspondingly higher resistivity contribution from surface scattering in Ag than Cu. In contrast, air exposure causes {rho}{sub Ag} < {rho}{sub Cu} for all d, due to diffuse scattering at the oxidized Cu surface and the correspondingly higher Cu resistivity.
Minimum Path Bases and Relevant Paths Petra M. Gleiss a , Josef Leydold b , Peter F. Stadler a,c
Stadler, Peter F.
Minimum Path Bases and Relevant Paths Petra M. Gleiss a , Josef Leydold b , Peter F. Stadler a GF(2) spanned by the paths with endÂpoints in U and the cycles in G(V, E). We extend Vismara distribution of subgraphs is the same in all minimum length bases, the number of cycles and paths may di
Essam, John W.
Bicoloured Dyck paths and the contact polynomial for n non-intersecting paths in a half Subject Classifications: 05A15 Abstract In this paper configurations of n non-intersecting lattice paths. Such configurations are called Hankel n-paths and their contact polynomial is defined by ^ZH 2r(n; ) r+1 c=1 |H (n) 2
Paris-Sud XI, Université de
- 1 - Orphan innovation, or when path-creation goes stale: a design framework to characterize path,version1-12Jun2012 #12;- 2 - Orphan innovation, or when path-creation goes stale: a design framework to characterize path-dependence in realtime How can we identify whether innovation processes in an organization
Achieving fast and bandwidth-efficient shared-path protection
Yizhi Xiong; Dahai Xu; Chunming Qiao
2003-01-01
Dynamic provisioning of restorable bandwidth guaranteed paths is a challenge in the design of broad-band transport networks, especially next-generation optical networks. A common approach is called (failure-independent) path protection, whereby for every mission-critical active path to be established, a link (or node) disjoint backup path (BP) is also established. To optimize network resource utilization, shared path protection should be adopted,
Space operations center communications path obscuration
NASA Astrophysics Data System (ADS)
Carl, J. R.; Lu, B. P.
Computer assisted techniques were developed to determine the obscuration of a communications path caused by the physical objects that comprise the Space Operations Center (SOC). Of particular interest in this paper is the obscuration of the line-of-sight path from an antenna, mounted somewhere on or in the vicinity of the SOC, to a geosynchronous satellite, such as a Telemetry Data Relay Satellite. The dynamic geometry of this type of problem makes it difficult to visualize, in a complete manner, without the aid of a computer. Blockage is shown graphically by computer-generated displays, and the percentage of time that the path is blocked is calculated. Graphics permit a ready comparison of one antenna location to another.
Fermionic path integrals and local anomalies
NASA Astrophysics Data System (ADS)
Roepstorff, G.
2003-05-01
No doubt, the subject of path integrals proved to be an immensely fruitful human, i.e. Feynman's idea. No wonder it is more timely than ever. Some even claim that it is the most daring, innovative and revolutionary idea since the days of Heisenberg and Bohr. It is thus likely to generate enthusiasm, if not addiction among physicists who seek simplicity together with perfection. Professor Devreese's long-lasting interest in, if not passion on the subject stems from his firm conviction that, beyond being the tool of choice, path integration provides the key to all quantum phenomena, be it in solid state, atomic, molecular or particle physics as evidenced by the impressive list of publications at the address http://lib.ua.ac.be/AB/a867.html. In this note, I review a pitfall of fermionic path integrals and a way to get around it in situations relevant to the Standard Model of particle physics.
Path Integral Invariance under Point Transformations
Andres Jordan; Matias Libedinsky
1998-01-05
We give here a covariant definition of the path integral formalism for the Lagrangian, which leaves a freedom to choose anyone of many possible quantum systems that correspond to the same classical limit without adding new potential terms nor searching for a strange measure, but using as a framework the geometry of the spaces considered. We focus our attention on the set of paths used to join succesive points in the discretization if the time-slicing definition is used to calculate the integral.If this set of paths is not preserved when performing a point transformation, the integral may change. The reasons for this are geometrically explained. Explicit calculation of the Kernel in polar coordinates is made, yielding the same system as in Cartesian coordinates.
Circular common-path point diffraction interferometer.
Du, Yongzhao; Feng, Guoying; Li, Hongru; Vargas, J; Zhou, Shouhuan
2012-10-01
A simple and compact point-diffraction interferometer with circular common-path geometry configuration is developed. The interferometer is constructed by a beam-splitter, two reflection mirrors, and a telescope system composed by two lenses. The signal and reference waves travel along the same path. Furthermore, an opaque mask containing a reference pinhole and a test object holder or test window is positioned in the common focal plane of the telescope system. The object wave is divided into two beams that take opposite paths along the interferometer. The reference wave is filtered by the reference pinhole, while the signal wave is transmitted through the object holder. The reference and signal waves are combined again in the beam-splitter and their interference is imaged in the CCD. The new design is compact, vibration insensitive, and suitable for the measurement of moving objects or dynamic processes. PMID:23027234
A taxonomy of integral reaction path analysis
Grcar, Joseph F.; Day, Marcus S.; Bell, John B.
2004-12-23
W. C. Gardiner observed that achieving understanding through combustion modeling is limited by the ability to recognize the implications of what has been computed and to draw conclusions about the elementary steps underlying the reaction mechanism. This difficulty can be overcome in part by making better use of reaction path analysis in the context of multidimensional flame simulations. Following a survey of current practice, an integral reaction flux is formulated in terms of conserved scalars that can be calculated in a fully automated way. Conditional analyses are then introduced, and a taxonomy for bidirectional path analysis is explored. Many examples illustrate the resulting path analysis and uncover some new results about nonpremixed methane-air laminar jets.
Molecular path control in zeolite membranes
Dubbeldam, D.; Beerdsen, E.; Calero, S.; Smit, B.
2005-01-01
We report molecular simulations of diffusion in confinement showing a phenomenon that we denote as molecular path control (MPC); depending on loading, molecules follow a preferred pathway. MPC raises the important question to which extent the loading may affect the molecular trajectories in nanoporous materials. Through MPC one is able to manually adjust the ratio of the diffusivities through different types of pores, and as an application one can direct the flow of diffusing particles in membranes forward or sideward by simply adjusting the pressure, without the need for mechanical parts like valves. We show that the key ingredient of MPC is the anisotropic nature of the nanoporous material that results in a complex interplay between different diffusion paths as a function of loading. These paths may be controlled by changing the loading, either through a change in pressure or temperature. PMID:16109769
Proposal for a QND which-path measurement using photons
NASA Technical Reports Server (NTRS)
Raymer, M. G.; Yang, S.
1992-01-01
A scheme is proposed for experimentally realizing the famous two-slit gedaenken experiment using photons. As elegantly discussed for electrons by Feynman, a particle's quantum pathways interfere to produce fringes in the probability density for the particle to be found at a particle location. If the path taken by the particle is experimentally determined, the complementarity principle says that the fringes must disappear. To carry out this experiment with photons is difficult because normally the act of determining a photon's location destroys it. We propose to overcome this difficulty by putting a type-2 optical parametric amplifier (OPA) in each arm of a Mach-Zehnder interferometer, and observing fringes at the output. An OPA responds to an input photon by increasing its probability to produce a pair of photons with polarization orthogonal to the input, the detection of which allows partial inference about the path taken by the input photon without destroying it. Thus, the measurement is of the quantum nondemolition (QND) type.
Tornado intensity estimated from damage path dimensions.
Elsner, James B; Jagger, Thomas H; Elsner, Ian J
2014-01-01
The Newcastle/Moore and El Reno tornadoes of May 2013 are recent reminders of the destructive power of tornadoes. A direct estimate of a tornado's power is difficult and dangerous to get. An indirect estimate on a categorical scale is available from a post-storm survery of the damage. Wind speed bounds are attached to the scale, but the scale is not adequate for analyzing trends in tornado intensity separate from trends in tornado frequency. Here tornado intensity on a continuum is estimated from damage path length and width, which are measured on continuous scales and correlated to the EF rating. The wind speeds on the EF scale are treated as interval censored data and regressed onto the path dimensions and fatalities. The regression model indicates a 25% increase in expected intensity over a threshold intensity of 29 m s(-1) for a 100 km increase in path length and a 17% increase in expected intensity for a one km increase in path width. The model shows a 43% increase in the expected intensity when fatalities are observed controlling for path dimensions. The estimated wind speeds correlate at a level of .77 (.34, .93) [95% confidence interval] with a small sample of wind speeds estimated independently from a doppler radar calibration. The estimated wind speeds allow analyses to be done on the tornado database that are not possible with the categorical scale. The modeled intensities can be used in climatology and in environmental and engineering applications. Research is needed to understand the upward trends in path length and width. PMID:25229242
Tornado Intensity Estimated from Damage Path Dimensions
Elsner, James B.; Jagger, Thomas H.; Elsner, Ian J.
2014-01-01
The Newcastle/Moore and El Reno tornadoes of May 2013 are recent reminders of the destructive power of tornadoes. A direct estimate of a tornado's power is difficult and dangerous to get. An indirect estimate on a categorical scale is available from a post-storm survery of the damage. Wind speed bounds are attached to the scale, but the scale is not adequate for analyzing trends in tornado intensity separate from trends in tornado frequency. Here tornado intensity on a continuum is estimated from damage path length and width, which are measured on continuous scales and correlated to the EF rating. The wind speeds on the EF scale are treated as interval censored data and regressed onto the path dimensions and fatalities. The regression model indicates a 25% increase in expected intensity over a threshold intensity of 29 m s?1 for a 100 km increase in path length and a 17% increase in expected intensity for a one km increase in path width. The model shows a 43% increase in the expected intensity when fatalities are observed controlling for path dimensions. The estimated wind speeds correlate at a level of .77 (.34, .93) [95% confidence interval] with a small sample of wind speeds estimated independently from a doppler radar calibration. The estimated wind speeds allow analyses to be done on the tornado database that are not possible with the categorical scale. The modeled intensities can be used in climatology and in environmental and engineering applications. Research is needed to understand the upward trends in path length and width. PMID:25229242
Mars PathFinder Rover Traverse Image
NASA Technical Reports Server (NTRS)
1998-01-01
This figure contains an azimuth-elevation projection of the 'Gallery Panorama.' The original Simple Cylindrical mosaic has been reprojected to the inside of a sphere so that lines of constant azimuth radiate from the center and lines of constant elevation are concentric circles. This projection preserves the resolution of the original panorama. Overlaid onto the projected Martian surface is a delineation of the Sojourner rover traverse path during the 83 Sols (Martian days) of Pathfinder surface operations. The rover path was reproduced using IMP camera 'end of day' and 'Rover movie' image sequences and rover vehicle telemetry data as references.
Connections on decorated path space bundles
Saikat Chatterjee; Amitabha Lahiri; Ambar N. Sengupta
2015-02-11
For a principal bundle $P\\to M$ equipped with a connection ${\\bar A}$, we study an infinite dimensional bundle ${\\mathcal P}^{\\rm dec}_{\\bar A}P$ over the space of paths on $M$, with the points of ${\\mathcal P}^{\\rm dec}_{\\bar A}P$ being horizontal paths on $P$ decorated with elements of a second structure group. We construct parallel transport processes on such bundles and study holonomy bundles in this setting. We explain the relationship with categorical geometry and explore the notion of categorical connections on categorical principal bundles in a concrete differential geometric way.
Path planning for everday robotics with SANDROS
Watterberg, P.; Xavier, P. [Sandia National Labs., Albuquerque, NM (United States); Hwang, Y. [Korea Inst. of Science and Technology, Seoul (Korea, Republic of)
1997-02-01
We discuss the integration of the SANDROS path planner into a general robot simulation and control package with the inclusion of a fast geometry engine for distance calculations. This creates a single system that allows the path to be computed, simulated, and then executed on the physical robot. The architecture and usage procedures are presented. Also, we present examples of its usage in typical environments found in our organization. The resulting system is as easy to use as the general simulation system (which is in common use here) and is fast enough (example problems are solved in seconds) to be used interactively on an everyday basis.
Path Factorization Approach to Stochastic Simulations
NASA Astrophysics Data System (ADS)
Athènes, Manuel; Bulatov, Vasily V.
2014-12-01
The computational efficiency of stochastic simulation algorithms is notoriously limited by the kinetic trapping of the simulated trajectories within low energy basins. Here we present a new method that overcomes kinetic trapping while still preserving exact statistics of escape paths from the trapping basins. The method is based on path factorization of the evolution operator and requires no prior knowledge of the underlying energy landscape. The efficiency of the new method is demonstrated in simulations of anomalous diffusion and phase separation in a binary alloy, two stochastic models presenting severe kinetic trapping.
Quantum Extremism: Effective Potential and Extremal Paths
E. N. Argyres; M. T. M. van Kessel; R. H. P. Kleiss
2009-07-07
The reality and convexity of the effective potential in quantum field theories has been studied extensively in the context of Euclidean space-time. It has been shown that canonical and path-integral approaches may yield different results, thus resolving the `convexity problem'. We discuss the transferral of these treatments to Minkowskian space-time, which also necessitates a careful discussion of precisely which field configurations give the dominant contributions to the path integral. In particular, we study the effective potential for the N=1 linear sigma model.
The calculation of ionospheric ray paths
Koehler, Buford Ray
1967-01-01
to Figure 4-3 show ordinary mode ray path calculations for different angles of incidence, constant direction Figure 4-1 Ordinary mode ray paths with angles of incidence from the vertical varying from 5 to 0 60 , y = 30 , . 7 0 40, dX ~:-0. 005; Scale...: 0. 40 units per inch. 22 Vertical H X 0. 0 X=1. Figure 3-3 Normal index surface curves, ordinary mode, vertical plane; F = 30 , 7 0. 80, dX = 0. 05; Scale: 0. 40 units per inch. 23 Vertical H e X= 0. 0 X= 1. 0 Figure 3-4 Normal index...
A surface hopping algorithm for nonadiabatic minimum energy path calculations.
Schapiro, Igor; Roca-Sanjuán, Daniel; Lindh, Roland; Olivucci, Massimo
2015-02-15
The article introduces a robust algorithm for the computation of minimum energy paths transiting along regions of near-to or degeneracy of adiabatic states. The method facilitates studies of excited state reactivity involving weakly avoided crossings and conical intersections. Based on the analysis of the change in the multiconfigurational wave function the algorithm takes the decision whether the optimization should continue following the same electronic state or switch to a different state. This algorithm helps to overcome convergence difficulties near degeneracies. The implementation in the MOLCAS quantum chemistry package is discussed. To demonstrate the utility of the proposed procedure four examples of application are provided: thymine, asulam, 1,2-dioxetane, and a three-double-bond model of the 11-cis-retinal protonated Schiff base. PMID:25564760
Foroutan-Nejad, Cina; Shahbazian, Shant; Marek, Radek
2014-08-01
Currently, bonding analysis of molecules based on the Quantum Theory of Atoms in Molecules (QTAIM) is popular; however, "misinterpretations" of the QTAIM analysis are also very frequent. In this contribution the chemical relevance of the bond path as one of the key topological entities emerging from the QTAIM's topological analysis of the one-electron density is reconsidered. The role of nuclear vibrations on the topological analysis is investigated demonstrating that the bond paths are not indicators of chemical bonds. Also, it is argued that the detection of the bond paths is not necessary for the "interaction" to be present between two atoms in a molecule. The conceptual disentanglement of chemical bonds/interactions from the bonds paths, which are alternatively termed "line paths" in this contribution, dismisses many superficial inconsistencies. Such inconsistencies emerge from the presence/absence of the line paths in places of a molecule in which chemical intuition or alternative bonding analysis does not support the presence/absence of a chemical bond. Moreover, computational QTAIM studies have been performed on some "problematic" molecules, which were considered previously by other authors, and the role of nuclear vibrations on presence/absence of the line paths is studied demonstrating that a bonding pattern consistent with other theoretical schemes appears after a careful QTAIM analysis and a new "interpretation" of data is performed. PMID:24990224
Path planning in a two-dimensional environment
NASA Astrophysics Data System (ADS)
Fox, Richard K.; Garcia, Antonio, Jr.; Nelson, Michael L.
1999-07-01
This paper presents a path planning algorithm that is part of the STESCA control architecture for autonomous vehicles. The path planning algorithm models an autonomous vehicle's path as a series of line segments in Cartesian space and compares each line segment to a list of known obstacles and hazardous areas to determine if any collisions or hindrances exist. In the event of a detected collision, the algorithm selects a point outside the obstacle or hazardous area, generates two new path segments that avoid the obstruction and recursively checks the new paths for other collisions. Once underway, if the autonomous vehicle encounters previously unknown obstacles or hazardous areas, the path planner operates in a run-time mode that decides how to re-route the path around the obstacle or abort. This paper describes the path planner along with examples of path planning in a two-dimensional environment with a wheeled land-based robotic vehicle.
Inter-Domain Redundancy Path Computation Methods Based on PCE
NASA Astrophysics Data System (ADS)
Hayashi, Rie; Oki, Eiji; Shiomoto, Kohei
This paper evaluates three inter-domain redundancy path computation methods based on PCE (Path Computation Element). Some inter-domain paths carry traffic that must be assured of high quality and high reliability transfer such as telephony over IP and premium virtual private networks (VPNs). It is, therefore, important to set inter-domain redundancy paths, i. e. primary and secondary paths. The first scheme utilizes an existing protocol and the basic PCE implementation. It does not need any extension or modification. In the second scheme, PCEs make a virtual shortest path tree (VSPT) considering the candidates of primary paths that have corresponding secondary paths. The goal is to reduce blocking probability; corresponding secondary paths may be found more often after a primary path is decided; no protocol extension is necessary. In the third scheme, PCEs make a VSPT considering all candidates of primary and secondary paths. Blocking probability is further decreased since all possible candidates are located, and the sum of primary and secondary path cost is reduced by choosing the pair with minimum cost among all path pairs. Numerical evaluations show that the second and third schemes offer only a few percent reduction in blocking probability and path pair total cost, while the overheads imposed by protocol revision and increase of the amount of calculation and information to be exchanged are large. This suggests that the first scheme, the most basic and simple one, is the best choice.
What is optimized in an optimal path?
Sparks, Fraser T; O'Reilly, Kally C; Kubie, John L
2013-10-01
An animal confronts numerous challenges when constructing an optimal navigational route. Spatial representations used for path optimization are likely constrained by critical environmental factors that dictate which neural systems control navigation. Multiple coding schemes depend upon their ecological relevance for a particular species, particularly when dealing with the third, or vertical, dimension of space. PMID:24103621
Stochastic Evolutionary Algorithms for Planning Robot Paths
NASA Technical Reports Server (NTRS)
Fink, Wolfgang; Aghazarian, Hrand; Huntsberger, Terrance; Terrile, Richard
2006-01-01
A computer program implements stochastic evolutionary algorithms for planning and optimizing collision-free paths for robots and their jointed limbs. Stochastic evolutionary algorithms can be made to produce acceptably close approximations to exact, optimal solutions for path-planning problems while often demanding much less computation than do exhaustive-search and deterministic inverse-kinematics algorithms that have been used previously for this purpose. Hence, the present software is better suited for application aboard robots having limited computing capabilities (see figure). The stochastic aspect lies in the use of simulated annealing to (1) prevent trapping of an optimization algorithm in local minima of an energy-like error measure by which the fitness of a trial solution is evaluated while (2) ensuring that the entire multidimensional configuration and parameter space of the path-planning problem is sampled efficiently with respect to both robot joint angles and computation time. Simulated annealing is an established technique for avoiding local minima in multidimensional optimization problems, but has not, until now, been applied to planning collision-free robot paths by use of low-power computers.
Motion on Cycloid Paths: A Project
ERIC Educational Resources Information Center
Gluck, P.
2010-01-01
This article reports a high school laboratory project whose theme is the motion of a small ball on cycloidal tracks. Models were built both of a brachistochrone and of a Huygens pendulum clock whose bob is constrained to move on a cycloidal path. Photogates and a data acquisition system were employed in order to investigate experimentally the…
Asymmetrical Path Interference Test of Light
Mei Xiaochun
2006-03-05
The asymmetrical path interference test of light is put forward in the paper. In the test, two different results would arise under the same experimental conditions if light is regarded as wave or particle. Therefore, the test can help us to comprehend which concept, wave or particle, is more essential for micro-particles.
Gender Differences in Career Paths in Banking.
ERIC Educational Resources Information Center
Morgan, Sandra; And Others
1993-01-01
Analyzed career paths of middle managers in bank. Study of matched pairs found that men (n=25) advanced faster and reached middle management through fewer promotions and positions than did women (n=25). Men had significantly more work experience outside of banking. In banking careers, men held more jobs in lending, whereas women occupied more…
LONG PATH LASER OZONE MONITOR EVALUATION
The purpose of the study reported here was to evaluate a long path laser air pollution monitor developed for the U.S. Environmental Protection Agency (EPA) by the General Electric (GE) Company. The monitor was known as ILAMS (Infrared Laser Atmospheric Monitoring System) and desi...
Quad-rotor flight path energy optimization
NASA Astrophysics Data System (ADS)
Kemper, Edward
Quad-Rotor unmanned areal vehicles (UAVs) have been a popular area of research and development in the last decade, especially with the advent of affordable microcontrollers like the MSP 430 and the Raspberry Pi. Path-Energy Optimization is an area that is well developed for linear systems. In this thesis, this idea of path-energy optimization is extended to the nonlinear model of the Quad-rotor UAV. The classical optimization technique is adapted to the nonlinear model that is derived for the problem at hand, coming up with a set of partial differential equations and boundary value conditions to solve these equations. Then, different techniques to implement energy optimization algorithms are tested using simulations in Python. First, a purely nonlinear approach is used. This method is shown to be computationally intensive, with no practical solution available in a reasonable amount of time. Second, heuristic techniques to minimize the energy of the flight path are tested, using Ziegler-Nichols' proportional integral derivative (PID) controller tuning technique. Finally, a brute force look-up table based PID controller is used. Simulation results of the heuristic method show that both reliable control of the system and path-energy optimization are achieved in a reasonable amount of time.
The Erratic Path of Hungarian Higher Education
ERIC Educational Resources Information Center
Marcus, Jon
2014-01-01
This article reviews the path of funding higher education in Hungary, where funding cuts have resulted in understaffing, escalating tuition, growing student debt, and declining enrollment. Graduation rates are low, government policies favor vocational disciplines, and the system of preparation and access gives preference to students from wealthier…
Visualizing Transmedia Networks: Links, Paths and Peripheries
ERIC Educational Resources Information Center
Ruppel, Marc Nathaniel
2012-01-01
'Visualizing Transmedia Networks: Links, Paths and Peripheries' examines the increasingly complex rhetorical intersections between narrative and media ("old" and "new") in the creation of transmedia fictions, loosely defined as multisensory and multimodal stories told extensively across a diverse media set. In order…
Applications of Path Compression on Balanced Trees
Robert Endre Tarjan
1979-01-01
Several fast algorithms are presented for computing functions defined on paths in trees under various assumpuons. The algorithms are based on tree mampulatton methods first used to efficiently represent equivalence relations. The algorithms have O((m + n)a(m + n, n)) running tunes, where m and n are measures of the problem size and a Is a functional reverse of Ackermann's
A twin path, solid state laser gyroscope
Jeffrey Ian Webb
1991-01-01
A twin path ring laser gyroscope detects rotation as a Sagnac beat frequency shifts between two free-running solid state lasers. The Nd:YAG, monolithic, unidirectional ring lasers operate in a temperature stabilized environment to minimize environmental influences on the beat frequency. The rotation sensitivity is limited by technical noise sources. Diagnostic calculations are presented in which the beat frequency sensitivity to
Path Planning for Planetary Exploration Ioannis Rekleitis
Rekleitis, Ioannis
Exploration Rovers (MERs) Spirit and Opportunity [16] has open the door for future missions to Mars are capable of planning local paths and avoiding obstacles. Future missions such as the "Mars Sci- ence an experiment. All experiments were performed at the Mars Emulation Terrain located at the CSA's facilities
Minimum padding to satisfy short path constraints
Narendra V. Shenoy; Robert K. Brayton; Alberto L. Sangiovanni-Vincentelli
1993-01-01
Combinational circuits are ojlen embedded in synchronous designs with rnernory elements at the input and output ports. A performance metric for a circuit is the cycle time of the clock signal. Correct circuit operatwn requires that all paths have a delay that lies between an upper bound and a lower bound. Traditional approaches in delay optimizatwn for combinational circuits [9,
The Many Paths of Hypervalent Iodine Reactions
Stoltz, Brian M.
The Many Paths of Hypervalent Iodine Reactions Ryan McFadden Stoltz Literature Group Meeting June! In Outline I. What is Hypervalency? A. The Martin-Arduengo Notation B. Bonding in Hypervalent Iodine Compounds C. A Brief History of IBX and DMP II. Oxidation Chemistry of Hypervalent Iodine A. Oxidations
Biometric Secret Path for Mobile User Authentication
Boyer, Edmond
this technology has a relationship between the user and its authenticator. Biometric authentication systems analysis such as fingerprint or face. When using a biometric system, two important steps have devices. In the section 3, we propose a new biometric system combining the secret path representation
Path integral and noncommutative poisson brackets
P. Valtancoli
2015-02-05
We find that in presence of noncommutative poisson brackets the relation between Lagrangian and Hamiltonian is modified. We discuss this property by using the path integral formalism for non-relativistic systems. We apply this procedure to the harmonic oscillator with a minimal length.