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.
Proton and electron mean free paths: The Palmer consensus revisited
NASA Technical Reports Server (NTRS)
Bieber, John W.; Matthaeus, William H.; Smith, Charles W.; Wanner, Wolfgang; Kallenrode, May-Britt; Wibberenz, Gerd
1994-01-01
We present experimental and theoretical evidence suggesting that the mean free path of cosmic-ray electrons and protons may be fundamentally different at low to intermediate (less than 50 MV) rigidities. The experimental evidence is from Helios observations of solar energetic particles, which show that the mean free path of 1.4 MV electrons is often similar to that of 187 MV protons, even though proton mean free paths continue to decrease comparatively rapidly with decreasing rigidty down to the lowest channels (about 100 MV) observed. The theoretical evidence is from computations of particle scattering in dynamical magnetic turbulence, which predict that electrons will have a larger mean free path than protons of the same rigidity. In the light of these new results, 'consensus' ideas about cosmic-ray mean free paths may require drastic revision.
Electron inelastic mean free paths in cerium dioxide
NASA Astrophysics Data System (ADS)
Krawczyk, M.; Holdynski, M.; Lisowski, W.; Sobczak, J. W.; Jablonski, A.
2015-06-01
Electron transport properties in CeO2 powder samples were studied by elastic-peak electron spectroscopy (EPES). Prior to EPES measurements, the CeO2 sample surface was pre-sputtered by 0.5 keV Ar ion etching. As a result, an altered layer with thickness of 1.3 nm was created. X-ray photoelectron spectroscopy (XPS) analysis revealed two chemical states of cerium Ce4+ (68%) and Ce3+ (32%) at the surface region of CeO2 sample after such treatment. The inelastic mean free path (IMFP), characterizing electron transport, was evaluated as a function of energy within the 0.5-2 keV range. Experimental IMFPs were corrected for surface excitations and approximated by the simple function ? = kEp, where ? was the IMFP, E denoted the energy (in eV), and k = 0.207 and p = 0.6343 were the fitted parameters. The IMFPs measured here were compared with IMFPs resulting from the TPP-2M predictive equation for the measured composition of oxide surface. The measured IMFPs were found to be from 3.1% to 20.3% smaller than the IMFPs obtained from the predictive formula in the energy range of 0.5-2 keV. The EPES IMFP value at 500 eV was related to the altered layer of sputtered CeO2 samples.
Ionization By Impact Electrons in Solids: Electron Mean Free Path Fitted Over A Wide Energy Range
Ziaja, B; London, R A; Hajdu, J
2005-06-09
We propose a simple formula for fitting the electron mean free paths in solids both at high and at low electron energies. The free-electron-gas approximation used for predicting electron mean free paths is no longer valid at low energies (E < 50 eV), as the band structure effects become significant at those energies. Therefore we include the results of the band structure calculations in our fit. Finally, we apply the fit to 9 elements and 2 compounds.
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
Evaluation of Calculated and Measured Electron Inelastic Mean Free Paths Near Solid Surfaces
C. J. Powell; A. Jablonski
1999-01-01
An analysis is given of the consistency of calculated and measured electron inelastic mean free paths (IMFPs) near solid surfaces for electron energies between 50 and 104 eV, the energy range of relevance for surface analysis by Auger electron spectroscopy and x-ray photoelectron spectroscopy. This evaluation is based on IMFPs calculated from experimental optical data and on IMFPs measured by
Long-mean-free-path ballistic hot electrons in high-purity GaAs B. Brill and M. Heiblum
Heiblum, Mordehai "Moty"
Long-mean-free-path ballistic hot electrons in high-purity GaAs B. Brill and M. Heiblum Braun, Rehovot 76100, Israel Received 18 July 1996 The mean free path mfp of hot ballistic electrons, injected device, utilizing the cyclotron motion of ballistic electrons in tilted magnetic fields. We find the mfp
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.
Qiu, Bo
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 ...
Mean free path and energy loss of electrons in the solar corona and the inner heliosphere
NASA Astrophysics Data System (ADS)
Estel, C.; Mann, G.
1999-05-01
We have studied the mean free path of electrons in the solar atmosphere in dependence on their initial velocity and their starting height above the photosphere. The net pitch angle change results from the combined effects of Coulomb scattering and the decreasing field strength of the large-scale magnetic field. We show that above a certain velocity all electrons can travel a distance of at least five AU without deflection. This treshold velocity decreases with increasing starting height. Furthermore the loss of kinetic energy due to Coulomb collisions as a function of distance from the Sun has been calculated. At small distances, up to at least 1.5 Rsun (solar radius), the energy component parallel to the magnetic field (assumed as radial from the Sun) decreases but above 1.5 Rsun this component increases though the total particle energy decreases. If we assume that the injected electrons also have a velocity component perpendicular to the magnetic field (pitch angle theta >0), the radial velocity component will increase even at low coronal heights. The theoretical results are compared with observational data of solar type III radio bursts.
Kohtaro Ishida; Michihiko Mannami; Kenzo Tanaka
1967-01-01
The mean free path of high energy electrons for the plasmon excitation has been measured in a single crystal of aluminium by a Möllenstedt type energy analyser combined with an electron microscope. The mean free path of 50 kV electron is 1000± 100Å when the crystal is far away from the exact Bragg condition to the incident electrons. When the
Russell, Kasey
Hot-electron mean free path of ErAs thin films grown on GaAs determined by metal-base transistor of the hot-electron mean free path in ErAs thin films grown on GaAs. Using an Al/Al2O3/Al tunnel junction as a hot-electron source for ballistic electron emission spectros- copy, we investigate ErAs films
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
NASA Technical Reports Server (NTRS)
Karasik, B. S.; Sergeev, A. V.
1998-01-01
Recent paper has raised again a question about the electron-phonon (EP) relaxation rate in impure metals. From weak localization (WL) measurements the authors have found that the dephasing rate in AuPd disordered films follows the T(sup 2)el-law (el is the mean free path).
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, ...
Mean free path in the relativistic mean field
Rego, R.A. (Instituto de Estudo Avancados, Centro Tecnico Aeroespacial, 12231, Sao Jose dos Campos, Sao Paulo (Brazil))
1991-11-01
An exact expression for the mean free path in a relativistic description of nuclear matter is given. Corrections due to the spatial nonlocality are calculated. While the latter play a significant role in giving reasonable values for the mean free path in nonrelativistic models, they have minor effects in the relativistic description of the nuclear matter mean field.
Liljequist, D.; Ismail, M. (Department of Physics, University of Stockholm, Vanadisv. 9, S-113 46 Stockholm (Sweden)); Salvat, F.; Mayol, R.; Martinez, J.D. (Facultat de Fisica (ECM), Universitat de Barcelona, Societat Catalona de Fisica (IEC), Diagonal 647, 08028 Barcelona (Spain))
1990-10-01
The transport mean free path, or transport cross section, is tabulated for the elastic scattering of electrons and positrons in solid matter by means of a correction factor {Tc} applied to the result of a simple screened Rutherford cross section. The correction factor table is based on differential cross-section calculations using a combination of partial-wave analysis (PWA), the Wentzel--Kramers--Brillouin approximation, and the Born approximation, and covers kinetic energies from 100 eV to 20 MeV. Results at low energies are compared with PWA calculations of higher accuracy. Nuclear size effects are discussed but not explicitly included. Applications are discussed.
R. Teissier; D. Sicault; A. Goujon; J. L. Pelouard; F. Pardo; F. Mollot
1999-01-01
Absolute electroluminescence intensities of InP\\/InGaAs heterostructures are monitored as a function of the position of the active layer from a mirror deposited on the semiconductor surface. The strong observed modulation is explained in terms of confinement of the electromagnetic field in the semi-infinite cavity delimited by the reflecting interface. This effect is shown to be a powerful probe of electron
Neutrino emissivities and mean free paths of degenerate quark matter
N. Iwamoto
1982-01-01
The neutrino properties of quark matter are investigated by calculating the neutrino emissivities and mean free paths. It is shown that the simple ..beta.. decay reactions, d..-->..u+eâ»+nu-bar\\/sub e\\/ and u+eâ»..-->..d+..nu..\\/sub e\\/, are kinematically allowed due to quark-quark interactions, and that as a consequence quark matter has a neutrino emissivity dramatically larger than that of ordinary neutron star matter, and comparable
Effective phonon mean free path in polycrystalline nanostructures
NASA Astrophysics Data System (ADS)
Hori, Takuma; Shiomi, Junichiro; Dames, Chris
2015-04-01
We have calculated the mean free path (MFP) of phonons associated with grain boundary scattering in polycrystalline nanostructures, by developing a Monte Carlo ray tracing transmission model that can be applied to arbitrary geometries. The calculations for various log-normal grain-size distributions realized by Voronoi diagrams and genetic algorithms show that the boundary-scattering MFP in a polycrystalline nanostructure is 20%-30% longer than that in a simple cubic structure with the same average grain size (defined by matching grain volumes). The impact on thermal conductivity is quantified for nanocrystalline silicon by using Matthiessen's rule to combine boundary scattering with intrinsic phonon-phonon scattering. The result reveals that the thermal conductivity depends strongly on the average grain size but only weakly on the breadth of the grain-size distribution, and thus, the simple cubic structure is a reasonable approximation for the polydisperse grain structure of actual materials.
Finite temperature inelastic mean free path and quasiparticle lifetime in graphene
NASA Astrophysics Data System (ADS)
Li, Qiuzi; Das Sarma, S.
2013-02-01
We adopt the GW and random phase approximations to study finite temperature effects on the inelastic mean free path and quasiparticle lifetime by directly calculating the imaginary part of the finite temperature self-energy induced by electron-electron interaction in extrinsic and intrinsic graphene. In particular, we provide the density-dependent leading order temperature correction to the inelastic scattering rate for both single-layer and double-layer graphene systems. We find that the inelastic mean free path is strongly influenced by finite-temperature effects. We present the similarity and the difference between graphene with linear chiral band dispersion and conventional two-dimensional electron systems with parabolic band dispersion. We also compare the calculated finite temperature inelastic scattering length with the elastic scattering length due to Coulomb disorder and comment on the prospects for quantum interference effects showing up in low-density graphene transport. We also carry out inelastic scattering calculation for electron-phonon interaction, which by itself gives rather long carrier mean free paths and lifetimes since the deformation potential coupling is weak in graphene, and therefore electron-phonon interaction contributes significantly to the inelastic scattering only at relatively high temperatures.
Neutrino mean free paths in cold symmetric nuclear matter
Cowell, S.; Pandharipande, V.R. [Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green St., Urbana, Illinois 61801 (United States)
2004-09-01
The neutrino mean free paths (NMFP) for scattering and absorption in cold symmetric nuclear matter (SNM) are calculated using two-body effective interactions and one-body effective weak operators obtained from realistic models of nuclear forces using correlated basis theory. The infinite system is modeled in a box with periodic boundary conditions and the one particle-hole (p-h) response functions are calculated using the Tamm-Dancoff approximation (TDA). For the densities {rho}=(1/2), 1 (3/2){rho}{sub 0}, where {rho}{sub 0} is the equilibrium density of SNM, the strength of the response is shifted to higher energy transfers when compared to a noninteracting Fermi gas (FG). This and the weakness of effective operators compared to the bare operators, significantly reduces the cross sections, enhancing the NMFP by factors of {approx}2.5-3.5 at the densities considered. The NMFP at the equilibrium density {rho}{sub 0} are also calculated using the TDA and random phase approximation (RPA) using zero range Skyrme-like effective interactions with parameters chosen to reproduce the equation of state and spin-isospin susceptibilities of matter. Their results indicate that RPA corrections to correlated TDA may further increase the NMFP by {approx}25% to 3-4 times those in a noninteracting FG. Finally, the sums and the energy weighted sums of the Fermi and Gamow-Teller responses obtained from the correlated ground state are compared with those of the 1 p-h response functions to extract the sum and mean energies of multi p-h contributions to the weak response. The relatively large mean energy of the multi p-h excitations suggests that they may not contribute significantly to low energy NMFP.
Peter J. Catto; Andrei N. Simakov
2004-01-01
Short mean free path descriptions of magnetized plasmas have existed for almost 50 years so it is surprising to find that further modifications are necessary. The earliest work adopted an ordering in which the flow velocity is assumed to be comparable to the ion thermal speed. Later, less well-known studies extended the short mean free path treatment to the normally
Reconstructing phonon mean-free-path contributions to thermal conductivity using nanoscale membranes
NASA Astrophysics Data System (ADS)
Cuffe, John; Eliason, Jeffrey K.; Maznev, A. A.; Collins, Kimberlee C.; Johnson, Jeremy A.; Shchepetov, Andrey; Prunnila, Mika; Ahopelto, Jouni; Sotomayor Torres, Clivia M.; Chen, Gang; Nelson, Keith A.
2015-06-01
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 thickness range can be used to characterize how bulk thermal conductivity is distributed over phonon mean free paths. A noncontact transient thermal grating technique was used to measure the thermal conductivity of suspended Si membranes ranging from 15-1500 nm in thickness. A decrease in the thermal conductivity from 74-13% of the bulk value is observed over this thickness range, which is attributed to diffuse phonon boundary scattering. Due to the well-defined relation between the membrane thickness and phonon mean-free-path suppression, combined with the range and accuracy of the measurements, we can reconstruct the bulk thermal conductivity accumulation vs. phonon mean free path, and compare with theoretical models.
Interaction mean-free-path of cosmic-ray Fe in air
NASA Technical Reports Server (NTRS)
Crane, J. H.; Guo, D. D.; Israel, M. H.; Klarmann, J.
1983-01-01
The interaction mean-free-path of cosmic-ray iron in air has been determined by observing the change in flux as a function of atmospheric depth. A large detector and a large variation in altitude during the balloon flight result in a high precision measurement. The result is in agreement, though slightly larger than the mean-free-path deduced from the measurements of interactions of iron on different targets at the Bevalac accelerator.
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
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.
Peter J. Catto; Andrei N. Simakov
2003-01-01
Short mean free path descriptions of magnetized plasmas have existed for almost 50 years. The earliest work adopted an ordering in which the flow velocity was assumed to be comparable to the ion thermal speed. Later work extended the treatment to the normally more interesting limit in which the pressure times the mean flow velocity is comparable to the diamagnetic
A. Teufel; R. Schlickeiser
2002-01-01
The parallel mean free path of cosmic ray particles in partially turbulent electromagnetic fields is a key input parameter for cosmic ray transport. Here the parallel mean free paths of cosmic ray protons, electrons and positrons are calculated for two particular turbulence models: slab-like dynamical and random sweeping turbulence. After outlining the general quasilinear formalism for deriving the pitch-angle Fokker-Planck
Proton mean-free path in nuclear matter and in finite nuclei
H. J. Yuan; H. L. Lin; G. Fai; S. A. Moszkowski
1989-01-01
The mean-free path of protons is calculated in nuclear matter and in finite nuclei using the extended Skyrme interaction. The Green's function technique is employed for infinite nuclear matter to carry out the calculations analytically. The connection to finite nuclei is established and results are compared to data extracted from reaction cross sections and optical-potential fits for three closed-shell nuclei.
NASA Astrophysics Data System (ADS)
Brunetti, G.; Lazarian, A.
2011-04-01
Direct evidence for in situ particle acceleration mechanisms in the intergalactic medium (IGM) is provided by the diffuse Mpc-scale synchrotron emissions observed from galaxy clusters. It has been proposed that magnetohydrodynamic turbulence, generated during cluster-cluster mergers, may be a source of particle reacceleration in the IGM. Calculations of turbulent acceleration must self-consistently account for the complex non-linear coupling between turbulent waves and particles. This has been calculated in some detail with the assumption that turbulence interacts in a collisionless way with the IGM. In this paper, we explore a different picture of acceleration by compressible turbulence in galaxy clusters, where the interaction between turbulence and the IGM is mediated by plasma instabilities and maintained collisional at scales much smaller than the Coulomb mean free path. In this regime, most of the energy of fast modes is channelled into the reacceleration of relativistic particles and the acceleration process approaches a universal behaviour, being self-regulated by the back-reaction of the accelerated particles on the turbulence itself. Assuming that relativistic protons contribute to several per cent (or less) of the cluster energy, consistent with the Fermi observations of nearby clusters, we find that compressible turbulence at the level of a few per cent of the thermal energy can reaccelerate relativistic electrons at GeV energies, which are necessary to explain the observed diffuse radio emission in the form of giant radio haloes.
Shaing, K. C. [Engineering Physics Department, University of Wisconsin, Madison, Wisconsin 53706 (United States)
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.
Estimation of the Mean Free Path using Cross-Correlations in the Seismic Coda
NASA Astrophysics Data System (ADS)
Clerc, V.; Roux, P.; Campillo, M.; Maynard, R.; Chaput, J. A.
2014-12-01
We present recent results concerning the extraction of Green's functions from coda waves. Campillo and Paul 2003 used earthquakes codas and found that the causal and anticausal parts of the cross-correlation are asymmetrical for some stations, depending on the earthquake source region. The lapse time in the coda window is a key parameter to understand causal to anticausal amplitude ratio. We show that this ratio result from the competition between the source signature (non-symmetric cross-correlations when the distribution of sources is non-isotropic around the receivers) and the scattering processes which tend to restore the time symmetry of the correlations. The theoretical analysis is derived from wave propagation theory for single scattering and multiple scattering as initiated by Roux 2005. We propose to use the temporal evolution of cross-correlation function amplitude in coda waves to estimate the value of the mean free path in the propagation medium. The equipartition of the energy is clearly observed in the numerical simulations conducted in a two-dimensional acoustic medium. The cross-correlations between the distinct time windows in synthetic coda records at two points are measured for a set of events for which we obtain a good estimate of the medium mean free path. We perform the same analysis on a set of icequakes recorded at Mount Erebus. The correlations averaged over sources and time exhibit a temporal evolution that obeys to convergence patterns similar to those observed in numerical studies.
NASA Astrophysics Data System (ADS)
Zhang, Hang; Hua, Chengyun; Ding, Ding; Minnich, Austin J.
2015-03-01
Thermal conductivity measurements over variable lengths on nanostructures such as nanowires provide important information about the mean free paths (MFPs) of the phonons responsible for heat conduction. However, nearly all of these measurements have been interpreted using an average MFP even though phonons in many crystals possess a broad MFP spectrum. Here, we present a reconstruction method to obtain MFP spectra of nanostructures from variable-length thermal conductivity measurements. Using this method, we investigate recently reported length-dependent thermal conductivity measurements on SiGe alloy nanowires and suspended graphene ribbons. We find that the recent measurements on graphene imply that 70% of the heat in graphene is carried by phonons with MFPs longer than 1 micron.
Zhang, Hang; Hua, Chengyun; Ding, Ding; Minnich, Austin J
2015-01-01
Thermal conductivity measurements over variable lengths on nanostructures such as nanowires provide important information about the mean free paths (MFPs) of the phonons responsible for heat conduction. However, nearly all of these measurements have been interpreted using an average MFP even though phonons in many crystals possess a broad MFP spectrum. Here, we present a reconstruction method to obtain MFP spectra of nanostructures from variable-length thermal conductivity measurements. Using this method, we investigate recently reported length-dependent thermal conductivity measurements on SiGe alloy nanowires and suspended graphene ribbons. We find that the recent measurements on graphene imply that 70% of the heat in graphene is carried by phonons with MFPs longer than 1 micron. PMID:25764977
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.
Zhang, Hang; Hua, Chengyun; Ding, Ding; Minnich, Austin J.
2015-01-01
Thermal conductivity measurements over variable lengths on nanostructures such as nanowires provide important information about the mean free paths (MFPs) of the phonons responsible for heat conduction. However, nearly all of these measurements have been interpreted using an average MFP even though phonons in many crystals possess a broad MFP spectrum. Here, we present a reconstruction method to obtain MFP spectra of nanostructures from variable-length thermal conductivity measurements. Using this method, we investigate recently reported length-dependent thermal conductivity measurements on SiGe alloy nanowires and suspended graphene ribbons. We find that the recent measurements on graphene imply that 70% of the heat in graphene is carried by phonons with MFPs longer than 1 micron. PMID:25764977
Phonon mean free path of graphite along the c-axis
Wei, Zhiyong; Yang, Juekuan; Chen, Weiyu; Bi, Kedong; Chen, Yunfei, E-mail: yunfeichen@seu.edu.cn [Jiangsu Key Laboratory for Design and Manufacture of Micro/Nano Biomedical Instruments and School of Mechanical Engineering, Southeast University, Nanjing 210096 (China); Li, Deyu, E-mail: deyu.li@vanderbilt.edu [Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee 37235-1592 (United States)
2014-02-24
Phonon transport in the c-axis direction of graphite thin films has been studied using non-equilibrium molecular dynamics (MD) simulation. The simulation results show that the c-axis thermal conductivities for films of thickness ranging from 20 to 500 atomic layers are significantly lower than the bulk value. Based on the MD data, a method is developed to construct the c-axis thermal conductivity as an accumulation function of phonon mean free path (MFP), from which we show that phonons with MFPs from 2 to 2000?nm contribute ?80% of the graphite c-axis thermal conductivity at room temperature, and phonons with MFPs larger than 100?nm contribute over 40% to the c-axis thermal conductivity. These findings indicate that the commonly believed value of just a few nanometers from the simple kinetic theory drastically underestimates the c-axis phonon MFP of graphite.
Phonon Mean Free Path Spectra Measured by Broadband Frequency Domain Thermoreflectance
NASA Astrophysics Data System (ADS)
Malen, Jonathan
2014-03-01
Nonmetallic crystalline materials conduct heat by the transport of quantized atomic lattice vibrations called phonons. Thermal conductivity depends on how far phonons travel between scattering events -- their mean free paths (MFPs). Due to the breadth of the phonon MFP spectrum, nanostructuring of materials and devices can reduce thermal conductivity from bulk by scattering long MFP phonons, while short MFP phonons are unaffected. We have developed a novel approach called Broadband Frequency Domain Thermoreflectance (BB-FDTR) that uses high-frequency laser heating to generate non-Fourier heat conduction that can sort phonons based on their MFPs. BB-FDTR outputs thermal conductivity as a function of heating frequency. Through non-equilibrium Boltzmann Transport Equation models this data can be converted to thermal conductivity accumulation, which describes how thermal conductivity is summed from phonons with different MFPs. Relative to alternative approaches, BB-FDTR yields order-of-magnitude improvements in the resolution and breadth of the thermal conductivity accumulation function. We will present data for GaAs, GaN, AlN, Si, and SiC that show interesting commonalities near their respective Debye temperatures and suggest that there may be a universal phonon MFP spectrum for small unit cell non-metals in the high temperature limit. At the time of this abstract submission we are also working on measurements of semiconductor alloys and select metals that will be presented if completed by the conference.
Kushner, Mark
October 1995; accepted for publication 18 December 1995 Plasma etching reactors for microelectronicsA time dependent propagator method for long mean free path transport of neutral particles in plasma processing reactors Wen-yi Tan, Robert J. Hoekstra, and Mark J. Kushnera) Department of Electrical
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.
NASA Astrophysics Data System (ADS)
Simakov, Andrei N.; Catto, Peter J.
2005-10-01
Expressions for ion perpendicular viscosity, electron and ion parallel viscosities, gyroviscosities, and heat fluxes, as well as electron-ion energy and momentum exchange terms are derived for arbitrary mean-free path plasmas, in which the lowest order distribution function is a Maxwellian. The latter assumption often holds for plasmas confined by magnetic fields with closed flux surfaces in the absence of strong external driving forces [1], such as neutral beams or radio-frequency waves. In particular, it is always employed in the neoclassical theory. The results are given in terms of a few velocity space integrals of the gyrophase averaged correction to the Maxwellian by assuming the gyroradius is small compared to the shortest perpendicular scale length. The general expressions make possible a hybrid fluid-kinetic description, and correctly reproduce known results in the collisional limit [2].[1] R. D. Hazeltine and J. D. Meiss, Plasma Confinement (Addison-Wesley, Redwood City, CA, 1991).[2] P. J. Catto and A. N. Simakov, Phys. Plasmas 11, 90 (2004).
Sadjadi, Zeinab; Miri, Mirfaez; Shaebani, M Reza; Nakhaee, Sareh
2008-09-01
We study photon diffusion in a two-dimensional random packing of monodisperse disks as a simple model of granular media and wet foams. We assume that the intensity reflectance of disks is a constant r . We present an analytic expression for the transport mean free path l;{*} in terms of the velocity of light in the disks and host medium, radius R and packing fraction of the disks, and the intensity reflectance. For glass beads immersed in air or water, we estimate transport mean free paths about half the experimental ones. For air bubbles immersed in water, l;{*}R is a linear function of 1epsilon , where epsilon is the liquid volume fraction of the model wet foam. This throws light on the empirical law of Vera [Appl. Opt. 40, 4210 (2001)] and promotes more realistic models. PMID:18851007
Friedlander, E.M.; Gimpel, R.W.; Heckman, H.H.; Karant, Y.J.; Judek, B.; Ganssauge, E.
1982-08-01
We present in detail the description and the analysis of two independent experiments using Bevalac beams of {sup 16}O and {sup 56}Fe. From their results it is concluded that the reaction mean free paths of relativistic projectile fragments, 3 {<=} Z {<=} 26, are shorter for a few centimeters after emission than at large distances where they are compatible with values predicted from experiments on beam nuclei. The probability that this effect is due to a statistical fluctuation is <10{sup -3}. The effect is enhanced in later generations of fragments, the correlation between successive generations suggesting a kind of "memory" for the anomaly. Various systematic and spurious effects as well as conventional explanations are discussed mainly on the basis of direct experimental observations internal to our data, and found not to explain our results. The data can be interpreted by the relatively rare occurrence of anomalous fragments that interact with an unexpectedly large cross section. The statistical methods used in the analysis of the observations are fully described.
The Giant Gemini GMOS survey of z>4.4 quasars - I. Measuring the mean free path across cosmic time
Worseck, Gábor; O'Meara, John M; Becker, George D; Ellison, Sara; Lopez, Sebastian; Meiksin, Avery; Ménard, Brice; Murphy, Michael T; Fumagalli, Michele
2014-01-01
We have obtained spectra of 163 quasars at $z_\\mathrm{em}>4.4$ with the Gemini Multi Object Spectrometers on the Gemini North and South telescopes, the largest publicly available sample of high-quality, low-resolution spectra at these redshifts. From this homogeneous data set, we generated stacked quasar spectra in three redshift intervals at $z\\sim 5$. We have modelled the flux below the rest-frame Lyman limit ($\\lambda_\\mathrm{r}<912$\\AA) to assess the mean free path $\\lambda_\\mathrm{mfp}^{912}$ of the intergalactic medium to HI-ionizing radiation. At mean redshifts $z_\\mathrm{q}=4.56$, 4.86 and 5.16, we measure $\\lambda_\\mathrm{mfp}^{912}=(22.2\\pm 2.3, 15.1\\pm 1.8, 10.3\\pm 1.6)h_{70}^{-1}$ proper Mpc with uncertainties dominated by sample variance. Combining our results with $\\lambda_\\mathrm{mfp}^{912}$ measurements from lower redshifts, the data are well modelled by a simple power-law $\\lambda_\\mathrm{mfp}^{912}=A[(1+z)/5]^\\eta$ with $A=(37\\pm 2)h_{70}^{-1}$ Mpc and $\\eta = -5.4\\pm 0.4$ between $z=2.3$...
NASA Astrophysics Data System (ADS)
Guo, Zehua; Tang, Xian-Zhu
2012-08-01
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., qn associated with the parallel thermal energy and qs related to perpendicular thermal energy. It is shown that in addition to the effect of magnetic field strength (B) modulation, the two components (qn and qs) 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? and T?), and the ambipolar potential (?). Both their profile (qn/B and qs/B2) and the upstream values of the ratio of the conductive and convective thermal flux (qn/nuT? and qs/nuT?) 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)
Feng, Tianli; Ruan, Xiulin; Ye, Zhenqiang; Cao, Bingyang
2015-06-01
The spectral phonon properties in defected graphene have been unclear due to the lack of advanced techniques for predicting the phonon-defect scattering rate without fitting parameters. Taking advantage of the extended phonon normal mode analysis, we obtained the spectral phonon relaxation time and mean free path (MFP) in defected graphene and studied the impacts of three common types of defects: Stone-Thrower-Wales (STW) defect, double vacancy (DV), and monovacancy (MV). The phonon-STW defect scattering rate is found to have no significant frequency dependence, and as a result, the relative contribution of long-wavelength phonons sharply decreases. In contrast, the phonon scattering by DVs or MVs exhibits a frequency dependence of ?p-d -1˜?1.1 -1.3 except for a few long-wavelength phonons, revisiting the traditionally used ˜?4 dependence. We note that although MV-defected graphene has the lowest thermal conductivity as compared to the other two defected graphene samples at the same defect concentration, it has a portion of phonons with the longest MFP. The contribution from the long-MFP and long-wavelength phonons does not decrease much as the vacancy concentration increases. STW defect and MV block more out-of-plane modes than in-plane modes, while DV has less bias for which mode to block. As the MV concentration increases from 0 to 1.1%, the relative contribution from out-of-plane modes decreases from 30% to 18%, while that of the transverse acoustic mode remains at around 30%. These findings of spectral phonon properties can provide more insight than the effective properties and benefit the prospective phononic engineering.
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.
Ján Benacka
2008-01-01
The paper gives the analytical solution to the one dimensional hyperbolic heat conduction equation in an insulated slab-shaped\\u000a sample that is heated uniformly on the front face with ? or laser impulse. The solution results in a formula that enables\\u000a to estimate the minimum mean free path of energy carriers in the sample to detect the second sound (i.e. the
A. Teufel; R. Schlickeiser
2003-01-01
The parallel mean free path of cosmic ray particles in partially turbulent electromagnetic fields is calculated for two particular turbulence models: slab-like dynamical and random sweeping turbulence. Using the general results for the pitch-angle Fokker-Planck coefficient from Teufel & Schlickeiser (2002) the rigidity dependence and the absolute value of the mean free path for these specific turbulence models are calculated
Arc-evaporated carbon films: Optical properties and electron mean free paths
E. T. Arakawa; S. M. Dolfini; J. C. Ashley; M. W. Williams
1985-01-01
The real and imaginary parts of the complex refractive index, n(..omega..) = n(..omega..)+ik(..omega..), of arc-evaporated carbon films have been obtained over the range of photon energies h..omega.. from 0.5 to 62.0 eV. Values of k(..omega..) obtained from transmission measurements in this energy range were combined with values of k(..omega..) from the literature in the infrared and soft-x-ray regions. A Kramers-Kronig
Murat Kurudirek; Yüksel Özdemir
2011-01-01
The gamma ray energy absorption (EABF) and exposure buildup factors (EBF) have been calculated for some essential amino acids, fatty acids and carbohydrates in the energy region 0.015–15MeV up to a penetration depth of 40mfp (mean free path). The five parameter geometric progression (G-P) fitting approximation has been used to calculate both EABF and EBF. Variations of EABF and EBF
Magnetic Refocussing of Electron Paths
W. E. Stephens
1934-01-01
A general method of magnetic direction refocussing, i.e., the refocussing of slightly divergent electron paths in a uniform magnetic field, has been found, of which the familiar 180° refocussing is a particular case. If we use a wedge-shaped magnetic field, whose lines of force are perpendicular to the plane of motion of an electron beam, the field being produced by
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
NASA Astrophysics Data System (ADS)
Luzuriaga, J.
2010-09-01
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 be suitable for an introductory course in vacuum techniques or undergraduate courses in kinetic theory of gases. Without going into the slightly harder quantitative results, the analysis presented might be used for introducing some ideas of kinetic theory qualitatively to high school students.
NASA Astrophysics Data System (ADS)
Kurudirek, Murat; Özdemir, Yüksel
2011-01-01
The gamma ray energy absorption ( EABF) and exposure buildup factors ( EBF) have been calculated for some essential amino acids, fatty acids and carbohydrates in the energy region 0.015-15 MeV up to a penetration depth of 40 mfp (mean free path). The five parameter geometric progression (G-P) fitting approximation has been used to calculate both EABF and EBF. Variations of EABF and EBF with incident photon energy, penetration depth and weight fraction of elements have been studied. While the significant variations in EABF and EBF for amino acids and fatty acids have been observed at the intermediate energy region where Compton scattering is the main photon interaction process, the values of EABF and EBF appear to be almost the same for all carbohydrates in the continuous energy region. It has been observed that the fatty acids have the largest EABF and EBF at 0.08 and 0.1 MeV, respectively, whereas the maximum values of EABF and EBF have been observed for aminoacids and carbohydrates at 0.1 MeV. At the fixed energy of 1.5 MeV, the variation of EABF with penetration depth appears to be independent of the variations in chemical composition of the amino acids, fatty acids and carbohydrates. Significant variations were also observed between EABF and EBF which may be due to the variations in chemical composition of the given materials.
A DRIFT ORDERED SHORT MEAN-FREE DESCRIPTION FOR PARTIALLY IONIZED MAGNETIZED PLASMA
SIMAKOV, ANDERI N. [Los Alamos National Laboratory
2007-02-08
Effects of neutral particles, most prominently the associated heat flux and viscosity, can be very important or even dominant at the edge of a tokamak and so must be self-consistently accounted for in a description of magnetized tokamak edge plasma. To the best of our knowledge, this has only been done so far for short mean-free path plasma under MHD-like Braginskii's orderings i.e. assuming that species velocities are on the order of the ion thermal speed. Since plasma flows in modern tokamaks are usually slow compared with the ion thermal speed (at least in the absence of strong external momentum sources) it is more appropriate to use drift orderings in which the plasma flow velocity is instead comparable with the diamagnetic heat flow divided by pressure. Employing drift orderings and evaluating species distribution functions through second order in the small gyroradius and mean-free path expansion parameters allows accounting for the important effects of heat fluxes on species momentum transport (viscosities), which are missing from the large flow ordered treatments. In this work we consider short mean-free path plasma consisting of electrons and single species of singly-charged ions and neutrals. We neglect neutral-neutral and elastic electron-neutral collisions and approximate the neutral-ion charge-exchange cross-section with a constant. We employ drift orderings to evaluate ion, neutral, and electron heat fluxes, viscosity tensors, and momentum and energy exchange terms and formulate a self-consistent system of electron, ion, and neutral fluid equations, thereby generalizing the drift-ordered treatment of fully ionized plasma.
Review Article Prediction of Spectral Phonon Mean Free Path and
Ruan, Xiulin
involves the time domain or frequency domain normal mode analysis. We present the theoretical frameworks-boundary scattering processes. They used this approach to observe the strong modification of acoustic phonon group the original work is properly cited. We give a review of the theoretical approaches for predicting spectral
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.
Paris-Sud XI, Université de
. As we use a monochromatic laser source, there is no difficulty to record the resultant speckle pattern, for instance, if they are detected far from the source, or through a monomode fiber. We have demonstrated
Measuring the Thickness of Aluminium Alloy Thin Foils Using Electron Energy Loss Spectroscopy
A. Bardal; K. Lie
2000-01-01
Combining electron energy loss spectroscopy and convergent beam electron diffraction measurements, we have determined the mean-free-path for inelastic electron scattering for four different aluminium alloys. Electron energy loss spectroscopy spectra were acquired with the transmission electron microscope in image mode, without any objective aperture inserted. The value for pure aluminium was determined as 119 ± 5nm at an incident electron
Electronic Transport in Mesoscopic Systems
Supriyo Datta
1997-01-01
Recent advances in semiconductor technology have made possible the fabrication of structures whose dimensions are much smaller than the mean free path of an electron. This book gives the first thorough account of the theory of electronic transport in such mesoscopic systems. Beginning with coverage of fundamental concepts, the book presents a detailed account of transmission function formalism which is
Interrelation of Resistivity and Inelastic Electron-Phonon Scattering Rate in Impure NbC Films
NASA Technical Reports Server (NTRS)
Il'in, K. S.; Ptitsina, N. G.; Sergeev, A. V.; Goltsman, G. N.; Gershenzon, E. M.; Karasik, B. S.; Pechen, E. V.; Krasnosvobodtsev, S. I.
1998-01-01
A complex study of the electron-phonon interaction in thin NbC films with electron mean free path l=2-13 nm gives strong evidence that electron scattering is significantly modified due to the interference between electron-phonon and elastic electron scattering from impurities.
Electron correlation from path resummations: the double-excitation star Alex J. W. Thom,
Alavi, Ali
Electron correlation from path resummations: the double-excitation star Alex J. W. Thom, George H evaluation of a N-electron path-integral. In particular, we show that the double excitation star graph. In this paper, we concentrate on the case of the star graph, whose form allows its weight to be calculated
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.
Su, S.D.; Baylor, K.J.; Engholm, B.A. (CEGA Corporation, San Diego, CA (United States))
1987-05-01
PATH is a highly flexible shielding code utilizing the common point-kernel integration technique primarily for treating gamma radiation from reactors, radioactive components and from complex piping systems. Major features of the code include complex geometry capability, various source options, extensive data library, simple but flexible input and well-organized output format.
NSDL National Science Digital Library
Started in the 1970s as an agency to assist men and women in gaining access to a variety of birth control methods, PATH has since expanded its focus to provide "sustainable, culturally relevant [health] solutions, enabling communities worldwide to break longstanding cycles of poor health." The PATH website has more than a dozen videos and slideshows available to visitors at the "Our Multimedia" link near the bottom right hand corner of the homepage. A three-minute video entitled "Better Nutrition For Life" educates visitors about an innovative rice product that could bring greater nutrition to millions of malnourished people where rice is a staple food. The product is Ultra Rice, and is actually fortified pasta that looks, cooks, and tastes like rice, but is fortified with nutrients. The "rice" can be fortified with the needed nutrients the particular population being served is lacking. A slideshow about TB in the Ukraine, explains to visitors why there has been a resurgence of TB in Eastern Europe, and how PATH and its partners set out to help control it throughout the region.
Steepest Descent Path Study of Electron-Transfer Reactions Jianshu Cao
Cao, Jianshu
path of solvent polarization, thus providing a new perspective of electron- transfer reactions. Though of initial conditions: E b ) 0(, where is the friction coefficient and Eb is the transition state
Russell, Kasey
Room-temperature ballistic electron emission luminescence spectroscopy with a scanning tunneling electroluminescence in buried luminescent layers at depths greater than the ballistic electron mean free path, ballistic electron emission microscopy BEEM and its associated spectroscopy BEES 1 have been widely used
Electron diffusion in intense high frequency electromagnetic fields
S. Bhattacharjee; I. Dey; S. Jain; H. Amemiya
The phenomenon of electron diffusion in a background gas, in the presence of high frequency electromagnetic fields is investigated. Monte-Carlo simulation procedures were applied to determine the number of collisions N. The dependence of N on the externally controllable parameters like the electron-neutral mean free path ? and the characteristic diffusion length ? (determined by the geometry) were studied. It
Resistive ballooning modes in an axisymmetric toroidal plasma with long mean-free path
Connor, J.W.; Chen, L.
1984-08-01
Tokamak devices normally operate at such high temperatures that the resistive fluid description is inappropriate. In particular, the collision frequency may be low enough for trapped particles to exist. However, on account of the high conductivity of such plasmas, one can identify two separate scale lengths when discussing resistive ballooning modes. By describing plasma motion on one of these, the connection length, in terms of kinetic theory the dynamics of trapped particles can be incorporated. On the resistive scale length, this leads to a description in terms of modified fluid equations in which trapped particle effects appear. The resulting equations are analyzed and the presence of trapped particles is found to modify the stability properties qualitatively.
Effect of adiabatic cooling on the fitted parallel mean free path of solar energetic particles
G. Qin; M. Zhang; J. R. Dwyer
2006-01-01
The focused transport equation without adiabatic energy loss is widely used to model solar energetic particles' (SEP) interplanetary propagation by fitting spacecraft data. We incorporate the adiabatic energy loss effect, provided by the divergence of the solar wind flows, into the focused transport equation. The equation is then solved numerically using a time-backward stochastic integration method. We show the comparison
Mean free-path length theory of predator–prey interactions: Application to juvenile salmon migration
James J. Anderson; Eliezer Gurarie; Richard W. Zabel
2005-01-01
Ecological theory traditionally describes predator–prey interactions in terms of a law of mass action in which the prey mortality rate depends on the density of predators and prey. This simplifying assumption makes population-based models more tractable but ignores potentially important behaviors that characterize predator–prey dynamics. Here, we expand traditional predator–prey models by incorporating directed and random movements of both predators
Afshari, Ehsan
, screening lengths, and mean free paths. Inevitably, quantum effects, and sometimes, single- electron effects. . influences the flow of electrons in the transistor channel. Changes in the transistor current are a measureSuperlattices and Microstructures, Vol. 23, No. 3/4, 1998 Kinetic modelling of electron tunneling
RELAXATION OF HOT ELECTRONS IN SOLIDS OF REDUCED R. PORATH, T. OHMS, M. SCHARTE, J. BEESLEY,
Aeschlimann, Martin
dimensions smaller than the mean free path of the excited electrons. In silver nano-particles, the electron of the increased radiation damping in nano- particles. 2. Introduction A large variety of modern research fields liquids (FLT), which treats the excitation as a quasiparticle. The lifetime ee of a single particle
Impact of electron-phonon scattering on the performance of carbon nanotube interconnects for GSI
Azad Naeemi; James D. Meindl
2005-01-01
While electron mean-free path in carbon nanotubes can be as large as several micrometers for small bias voltages, for large biases electrons get backscattered by optical and zone-boundary phonons and nanotube resistance can increase by more than 100 times. This letter reveals this kind of backscattering has a small impact (error <25%) in most interconnect applications of carbon nanotubes in
A random walk model for the crystallite size effect on the secondary electron yield from insulators
Jacques Cazaux
2003-01-01
A recent model for the random walk of low energy electrons is applied to the crystallite-size effect on the secondary electron yield ? from insulators. The corresponding fitting procedure is successfully applied to the experimental results previously obtained by Ushio et al. on various MgO films (Thin Solid Films 167 (1988) 299). The values of the transport mean free path
Electron paths and double-slit interference in the scanning gate microscopy
NASA Astrophysics Data System (ADS)
Kolasi?ski, K.; Szafran, B.
2015-06-01
We analyze electron paths in a solid-state double-slit interferometer based on two-dimensional electron gas and mapping by scanning gate microscopy (SGM). A device with a quantum point source contact of a split exit and a drain contact for electron detection is considered. We study the SGM maps of source-drain conductance (G) as functions of the probe position, and we find that for a narrow drain, the classical electron paths are clearly resolved without any trace of double-slit interference. The latter is only present in the SGM maps of backscattering (R) probability. Double-slit interference is found in the G maps for a wider drain contact, but at the expense of a loss of information on the electron trajectories. We discuss the interplay of Young's interference and interference effects between various electron paths introduced by the tip and the electron detector. The stability of the G and R maps versus the geometry parameters of the scattering device is also discussed.
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.
Electron Spectroscopic Methods for the Investigation of Liquid Surface Structure
Harald Morgner
1996-01-01
The goal of our work is the elucidation of the surface structure of liquids on the molecular level. We use several electron spectroscopies and related techniques. In photoelectron spectroscopy the observation depth is governed by the mean free path of the photoelectrons which in turn depends on the kinetic energy. Using synchrotron radiation as source of photons the energy and
Effects of elastic and inelastic scattering in giving electrons tortuous paths in matter.
Turner, J E; Hamm, R N
1995-09-01
Heavy charged particles travel in essentially straight lines in matter, while electrons travel in tortuous paths. Frequent multiple elastic Coulomb scattering by atomic nuclei is often cited as the reason for this electron behavior. Heavy charged particles also undergo multiple Coulomb scattering. However, because they are massive, significant deflections occur only in rare, close encounters with nuclei. In contrast to heavy particles, the inelastic interaction of an electron with an atomic electron represents a collision with a particle of equal mass. In principle, therefore, repeated inelastic scattering of an electron can also produce large-angle deflections and thus contribute to the tortuous nature of an electron's track. To investigate the relative importance of elastic and inelastic scattering on determining the appearance of electron tracks, detailed Monte Carlo transport computations have been carried out for monoenergetic pencil beams of electrons normally incident on a water slab with initial energies from 1 keV to 1 MeV. The calculations have been performed with deflections due to (1) inelastic scattering only, (2) elastic scattering only, and (3) both types of scattering. Results are presented to show the spreading of the pencil beams with depth in the slab, the transmission through slabs of different thicknesses, and back-scattering from the slab. The results show that elastic nuclear scattering is indeed the principal physical process that causes electron paths to be tortuous; however, the smaller effect of inelastic electronic scattering is far from negligible. PMID:7635734
Putz, Mihai V.
2009-01-01
The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI) development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr’s quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions – all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving) many-electronic systems. PMID:20087467
Silicon electronics on silk as a path to bioresorbable, implantable devices Dae-Hyeong Kim,1
Rogers, John A.
Silicon electronics on silk as a path to bioresorbable, implantable devices Dae-Hyeong Kim,1 Yun water soluble and biocompatible silk substrates. Electrical, bending, water dissolution, and animal on nanomembranes of silicon, with biodegrad- able thin film substrates of silk protein, to yield a flexible system
Putz, Mihai V
2009-11-01
The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI) development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr's quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions - all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving) many-electronic systems. PMID:20087467
Assurance of Complex Electronics. What Path Do We Take?
NASA Technical Reports Server (NTRS)
Plastow, Richard A.
2007-01-01
Many of the methods used to develop software bare a close resemblance to Complex Electronics (CE) development. CE are now programmed to perform tasks that were previously handled in software, such as communication protocols. For instance, Field Programmable Gate Arrays (FPGAs) can have over a million logic gates while system-on-chip (SOC) devices can combine a microprocessor, input and output channels, and sometimes an FPGA for programmability. With this increased intricacy, the possibility of "software-like" bugs such as incorrect design, logic, and unexpected interactions within the logic is great. Since CE devices are obscuring the hardware/software boundary, we propose that mature software methodologies may be utilized with slight modifications to develop these devices. By using standardized S/W Engineering methods such as checklists, missing requirements and "bugs" can be detected earlier in the development cycle, thus creating a development process for CE that will be easily maintained and configurable based on the device used.
Quantum path interferences of electron trajectories in two-center molecules.
Yang, Weifeng; Song, Xiaohong; Zeng, Zhinan; Li, Ruxin; Xu, Zhizhan
2010-02-01
We report a new quantum path interference effect of electron trajectories in high-order harmonic generation (HHG) from two-center molecules, in which the interference minima are mainly located in the high-energy portion of HHG spectrum. The quantum calculations of the time-frequency analyses and the classical results of the electron trajectories demonstrate very good agreement and reveal that the positions of the interference minima are associated with the cutoff of various kinds of molecular electron trajectories. The interference fringes within a half optical cycle can be clearly seen in the time-frequency analysis spectrum. Moreover, the characteristics of both the HHG in frequency domain and the corresponding attosecond pulse generation in time domain permit tracing back the interference information of these electron trajectories. These interference phenomena offer new possibilities for getting insight into the attosecond electronic dynamics in molecules. PMID:20174084
NASA Technical Reports Server (NTRS)
Ko, H. C.
1973-01-01
The wave-normal emissivity and the ray emissivity formulas for an electron moving along a helical path in a magnetoactive medium are presented. Simplified formulas for the case of an isotropic plasma are also given. Because of the helical motion of the electron, a difference exists between the radiated power per unit solid angle and the received power per unit solid angle. The relation between these two quantities in a magnetoactive medium is shown. Results are compared with those obtained by others, and the sources of discrepancies are pointed out.
Interacting electrons in one dimension: a path integral Monte Carlo study
NASA Astrophysics Data System (ADS)
Lyubartsev, Alexander P.
2007-06-01
Path integral Monte Carlo simulations have been carried out for a system of interacting fermionic particles in one dimension. Due to the fact that the sign problem can be completely eliminated for one-dimensional systems, such simulations allow one to obtain accurate energies and particle densities in arbitrary external potentials. Two cases were considered: electrons in the field of a uniform neutralizing background and in an effective field of atoms on a lattice. In the latter case, a clear asymmetry of the charge density distribution of conducting electrons and holes has been observed.
P. H. J. Nafstad
1967-01-01
Morphology and distribution of the perforant path fibres in the hippocampus and the fascia dentata of the rat have been studied in the electron microscope. Investigations were carried out on normal tissue as well as on tissue degenerating after entorhinal damage. The perforant path fibres were relatively thin and the terminals small. Two terminal fields were found to be of
Huo, Pengfei; Miller, Thomas F. III [Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 (United States)] [Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 (United States); Coker, David F. [Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215 (United States)] [Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215 (United States)
2013-10-21
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.
Suk Chung
2009-01-01
The research of this dissertation involved the use of off-axis electron holography to investigate electrostatic potentials within AlGaAs\\/GaAs heterostructures. The inelastic mean-free-paths of high-energy electrons (200 keV) for AlAs and GaAs have been determined to be 77 nm and 67 nm, respectively, based on comparing thicknesses by electron holography and convergent beam electron diffraction. The mean inner potentials of AlAs
NASA Astrophysics Data System (ADS)
Driver, K. P.; Militzer, B.
2012-03-01
We develop an all-electron path integral Monte Carlo method with free-particle nodes for warm dense matter and apply it to water and carbon plasmas. We thereby extend path integral Monte Carlo studies beyond hydrogen and helium to elements with core electrons. Path integral Monte Carlo results for pressures, internal energies, and pair-correlation functions compare well with density functional theory molecular dynamics calculations at temperatures of (2.5-7.5)×105K, and both methods together form a coherent equation of state over a density-temperature range of 3-12g/cm3 and 104-109K.
Path Integral Monte Carlo finite-temperature electronic structure of quantum dots
NASA Astrophysics Data System (ADS)
Leino, Markku; Rantala, Tapio T.
2003-03-01
Quantum Monte Carlo methods allow a straightforward procedure for evaluation of electronic structures with a proper treatment of electronic correlations. This can be done even at finite temperatures [1]. We apply the Path Integral Monte Carlo (PIMC) simulation method [2] for one and two electrons in a single and double quantum dots. With this approach we evaluate the electronic distributions and correlations, and finite temperature effects on those. Temperature increase broadens the one-electron distribution as expected. This effect is smaller for correlated electrons than for single ones. The simulated one and two electron distributions of a single and two coupled quantum dots are also compared to those from experiments and other theoretical (0 K) methods [3]. Computational capacity is found to become the limiting factor in simulations with increasing accuracy. This and other essential aspects of PIMC and its capability in this type of calculations are also discussed. [1] R.P. Feynman: Statistical Mechanics, Addison Wesley, 1972. [2] D.M. Ceperley, Rev.Mod.Phys. 67, 279 (1995). [3] M. Pi, A. Emperador and M. Barranco, Phys.Rev.B 63, 115316 (2001).
Ultrarelativistic Electron-Positron Plasma
Markus H. Thoma
2008-10-06
Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.
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
Path-Integral Monte Carlo Simulation of the Warm Dense Homogeneous Electron Gas
NASA Astrophysics Data System (ADS)
Brown, Ethan W.; Clark, Bryan K.; DuBois, Jonathan L.; Ceperley, David M.
2013-04-01
We perform calculations of the 3D finite-temperature homogeneous electron gas in the warm-dense regime (rs?(3/4?n)1/3a0-1=1.0-40.0 and ??T/TF=0.0625-8.0) using restricted path-integral Monte Carlo simulations. Precise energies, pair correlation functions, and structure factors are obtained. For all densities, we find a significant discrepancy between the ground state parametrized local density approximation and our results around TF. These results can be used as a benchmark for developing finite-temperature density functionals, as well as input for orbital-free density function theory formulations.
Fermionic path-integral Monte Carlo results for the uniform electron gas at finite temperature.
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. PMID:25871225
Hot ballistic transport and phonon emission in a two-dimensional electron gas
U. Sivan; M. Heiblum; C. P. Umbach
1989-01-01
Hot-electron transport in a 2D electron gas is investigated as a function of the electron's excess energy. The inelastic mean free path at energies below the longitudinal-optical-phonon energy is found to be an order of magnitude longer than theoretical predictions. For higher injection energies, LO-phonon emission is found to be the main scattering mechanism. This, together with the ballistic motion
Shaing, K. C. [Plasma and Space Science Center, and Department of Physics, National Cheng Kung University, Tainan, 701 Taiwan (China) and Engineering Physics Department, University of Wisconsin, Madison, Wisconsin 53706 (United States)
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.
Ruan, Xiulin
-performance thermoelectric materi- als with high ZT require high S, r and low j. PbTe is one of the best thermoelectric October 2011 Keywords: Thermal conductivity Molecular dynamics Thermoelectrics Nanostructure a b s t r a c and temperature. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction High-performance thermoelectric
Electron avalanche and spark evolution along laser path in resonant laser-induced ignition
NASA Astrophysics Data System (ADS)
Adams, Steven; Tolson, Boyd; Hensley, Amber
2014-10-01
A multi-photon ionization scheme is studied that could provide laser-induced ignition within a high-voltage gap across an aircraft combustion chamber. The multi-photon resonant enhanced ionization (REMPI) technique could potentially be applied as a laser trigger from a compact low power laser source leading to breakdown and ignition of an aircraft air-fuel flow. In this experiment, an ultraviolet laser is passed through an aperture in the anode and into the flow chamber. The REMPI process forms an ionized channel between the electrodes and, with an applied electric field, eventually leads to breakdown precisely along the laser path. A delay time of 200 to 1000 ns between the laser pulse and breakdown event is typical for our range of conditions. High speed imaging and spectroscopic data reveal evidence of space charge regions and local field distortion within the interelectrode space during the delay time and a model is applied to simulate the electron avalanche process. Spatially resolved spectroscopic analysis identifies various regions and degrees of laser photoionization, electron impact ionization, radical species and gas heating during the delay time.
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.
Magnetic turbulent electron transport in a reversed field pinch
Schoenberg, K.; Moses, R.
1990-01-01
A model of magnetic turbulent electron transport is presented. The model, based on the thermal conduction theory of Rechester and Rosenbluth, entails a Boltzmann description of electron dynamics in the long mean-free-path limit and quantitatively describes the salient features of superthermal electron measurements in the RFP edge plasma. Included are predictions of the mean superthermal electron energy, current density, and power flux asymmetry. A discussion of the transport model, the assumptions implicit in the model, and the relevance of this work to more general issue of magnetic turbulent transport in toroidal systems is presented. 32 refs., 3 figs.
Field Theoretic Description of Ultrarelativistic Electron-Positron Plasmas
Markus H. Thoma
2009-07-06
Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.
NASA Astrophysics Data System (ADS)
Medvedev, N. A.; Rymzhanov, R. A.; Volkov, A. E.
2013-11-01
Complex dielectric function formalism is applied to obtain the cross-sections, mean free path of electrons, and energy losses of swift heavy ions (SHI) in solid LiF and Y2O3 out of the experimentally known loss function. The calculated electron inelastic mean free paths in these materials agree very well with the NIST database; the inelastic energy losses of swift Pb and Au ions agree well with those calculated with the widely used SRIM and CasP codes. The obtained cross-sections are used in Monte Carlo simulations of the electronic kinetics after SHI impacts. The radial distributions of the electron and valence hole densities as well as their energy densities were calculated.
P3-34: Design of a gridded electron gun using the particle path and the FEM approach
César C. Xavier; Cláudio C. Motta
2010-01-01
The XMGUN was used to design a 30kV, 4.6A and 0.88?Perv axis-symmetric high power electron gun, with grid and shadow grid, working under the space charge limited flow to be used in a TWT. The XMGUN uses the particle path, instead of the motion equation, to perform the macroparticles ray tracing and the FEM approach. It was observed a current
A. Valentin; M. Raine; J. E. Sauvestre
2010-01-01
The Energy-Loss Function (ELF) of silicon has been used to calculate differential and total inelastic cross-sections of incident electrons. The model has been validated in the 16.7 eV-50 keV incident energy range by comparing the stopping powers, mean free paths and ranges to experimental and evaluated ICRU data. The cross sections were then used to simulate low-energy electron tracks in
Liu, I-Lin [Center for Quantum Science and Engineering, Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); Li, Peng-Cheng [Center for Quantum Science and Engineering, Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Chu, Shih-I [Center for Quantum Science and Engineering, Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); Department of Chemistry, University of Kansas, Lawrence, Kansas 66045 (United States)
2011-09-15
We report a mechanism and a realizable approach for the coherent control of the generation of an isolated and ultrashort atto second (as) laser pulse from atoms by optimizing the two-color laser fields with a proper time delay. Optimizing the laser pulse shape allows the control of the electron quantum paths and enables high-harmonic generation from the long- and short-trajectory electrons to be enhanced and split near the cutoff region. In addition, it delays the long-trajectory electron emission time and allows the production of extremely short atto second pulses in a relatively narrow time duration. As a case study, we show that an isolated 30 as pulse with a bandwidth of 127 eV can be generated directly from the contribution of long-trajectory electrons alone.
The Capture and Loss of Electrons by Helium Ions in Helium
Philip Rudnick
1931-01-01
Mean free paths for capture (L1) and loss (L0) of electrons by helium ions in helium have been measured by a method whose chief novelty is the use of an ion source which gives quite strictly homogeneous velocities. In the range of velocities 0.6 × 108 cm\\/sec. to 1.0 × 108 cm\\/sec. L0, reduced to 760 mm, is found to
NASA Astrophysics Data System (ADS)
Runge, Keith; Deymier, Pierre
2013-03-01
Recent progress in orbital-free Density Functional Theory (OF-DFT), particularly with regard to temperature dependent functionals, has promise for the simulation of warm dense matter (WDM) systems. WDM includes systems with densities of an order of magnitude beyond ambient or more and temperatures measured in kilokelvin. A challenge for the development of temperature dependent OF-DFT functionals is the lack of benchmark information with temperature and pressure dependence on simple models under WDM conditions. We present an approach to fill this critical gap using the restricted path-integral molecular dynamics (rPIMD) method. Electrons are described as harmonic necklaces within the discrete path integral representation while quantum exchange takes the form of cross linking between electron necklaces. A molecular dynamics algorithm is used to sample phase space and the fermion sign problem is addressed by restricting the density matrix to positive values. The temperature dependence of kinetic energies for the strongly coupled electron plasma is presented for a number of Wigner-Seitz radii in terms of a fourth order Sommerfeld expansion. Recent progress in orbital-free Density Functional Theory (OF-DFT), particularly with regard to temperature dependent functionals, has promise for the simulation of warm dense matter (WDM) systems. WDM includes systems with densities of an order of magnitude beyond ambient or more and temperatures measured in kilokelvin. A challenge for the development of temperature dependent OF-DFT functionals is the lack of benchmark information with temperature and pressure dependence on simple models under WDM conditions. We present an approach to fill this critical gap using the restricted path-integral molecular dynamics (rPIMD) method. Electrons are described as harmonic necklaces within the discrete path integral representation while quantum exchange takes the form of cross linking between electron necklaces. A molecular dynamics algorithm is used to sample phase space and the fermion sign problem is addressed by restricting the density matrix to positive values. The temperature dependence of kinetic energies for the strongly coupled electron plasma is presented for a number of Wigner-Seitz radii in terms of a fourth order Sommerfeld expansion. Supported by US DoE Grant DE-SC0002139
Electron cyclotron resonance microwave ion sources for thin film processing
Berry, L.A.; Gorbatkin, S.M.
1990-01-01
Plasmas created by microwave absorption at the electron cyclotron resonance (ECR) are increasingly used for a variety of plasma processes, including both etching and deposition. ECR sources efficiently couple energy to electrons and use magnetic confinement to maximize the probability of an electron creating an ion or free radical in pressure regimes where the mean free path for ionization is comparable to the ECR source dimensions. The general operating principles of ECR sources are discussed with special emphasis on their use for thin film etching. Data on source performance during Cl base etching of Si using an ECR system are presented. 32 refs., 5 figs.
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.
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
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.…
Modelling the high altitude electron temperature: a modified thermal conductivity
NASA Astrophysics Data System (ADS)
Denton, M. H.; Bailey, G. J.
2001-10-01
Measured values of the thermal electron temperature are known to be higher than values calculated by hydrodynamic atmospheric models — in some cases, this difference may be as high as 50%. A modification to the classical expression for the electron thermal conductivity is presented and introduced into the Sheffield University Plasmasphere Ionosphere Model (SUPIM). The modification is applicable to the low density region in the topside ionosphere and is based on mean free path arguments originally presented by Mayr and Volland [J. Geophys. Res. 73 (1968) 4851]. The values calculated by SUPIM using this modification are in much closer agreement with the values measured by the EXOS-D satellite.
Auger electron emission from a Si(1 1 1) surface during 11-keV Ar+ ion sputtering
NASA Astrophysics Data System (ADS)
Kawai, K.; Sakuma, Y.; Kato, M.; Soda, K.
2013-11-01
Ion sputtering experiments were carried out for a Si(1 1 1)-7 × 7 surface, irradiated with an 11-keV Ar+ beam. The energy spectra of secondary electrons were measured with a cylindrical mirror analyzer (CMA). The dependence of the Auger electron yield on the ion incidence angle, ?, measured from the surface normal, was studied by varying ? from 0° to 80°. The Auger electron yield increases with increasing incidence angle. This angular dependence is similar to that of the Si sputtering yield. Both angular dependences could be reasonably understood in terms of ion range, escape depths of the sputtered ion and the electron mean free path.
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.
Influence of emitted electrons transiting between surfaces on plasma-surface interaction
Campanell, Michael [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)] [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Wang, Hongyue [Beijing University of Aeronautics and Astronautics, Beijing (China)] [Beijing University of Aeronautics and Astronautics, Beijing (China)
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.
Ma, Jie [National Renewable Energy Lab. (NREL), Golden, CO (United States); Yang, Jihui [National Renewable Energy Lab. (NREL), Golden, CO (United States); Da Silva, J. L.F. [Univ. of Sao Paulo, Sao Carlos (Brazil). Sao Carlos Institute of Chemistry; Wei, Su-Huai [National Renewable Energy Lab. (NREL), Golden, CO (United States)
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 T_{d} 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 state is the degenerated p-like state under T_{d} 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.
Ma, Jie [National Renewable Energy Lab. (NREL), Golden, CO (United States); Yang, Jihui [National Renewable Energy Lab. (NREL), Golden, CO (United States); Da Silva, J. L.F. [Univ. of Sao Paulo, Sao Carlos (Brazil). Sao Carlos Institute of Chemistry; Wei, Su-Huai [National Renewable Energy Lab. (NREL), Golden, CO (United States)
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 state 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.
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
NASA Astrophysics Data System (ADS)
Bonitz, Michael; Schoof, Tim; Groth, Simon
2014-10-01
Thermodynamic properties of the homogeneous electron gas (HEG) at finite temperatures are of high importance for many systems, including dense quantum plasmas, warm dense matter or plasmas in the interior of compact stars. Recently, Restricted Path Integral Monte-Carlo data for low to moderate densities (rs = r /aB >= 1) have been presented, while the high-density regime was not accessible due to the Fermion sign problem. Here we apply the recently developed Configuration PIMC (CPIMC) method to the HEG at high densities (rs <~ 0 . 5) and low to moderate temperatures (? =kB T /EF <= 1). We demonstrate that CPIMC allows for efficient ab-initio quilibrium calculations of thermodynamic properties of highly degenerate, moderately coupled electrons. It is based on the representation of the N-particle density operator in a basis of antisymmetrized N-particle states) and does not suffer from the Fermion sign problem in the non-interacting limit. Deutsche Forschungsgemeinschaft, BO1366-9.
NASA Astrophysics Data System (ADS)
Allen, C. W.
2004-12-01
We've developed an algorithm to iteratively solve the linearized Vlasov equation for growth rates and first-order potentials of instabilities such as collisionless ion-electron tearing in a neutral sheet. It requires no assumptions about the nature of the equilibrium trajectories and can give exact (numerical) results. In this work we describe the algorithm, and its application to study the behavior of the tearing-mode starting from a Harris equilibrium over a range of the control parameters: the current sheet half-width w, (Te)/(T_i), (Me)/(M_i). The method starts with computing and saving several thousand equilibrium particle paths to sample the phase space for a chosen equilibrium state. Then for a given k, the coupled equations for ?c{A1} and ? are solved iteratively with ?c{J1} computed from time-integrals over the saved particle paths. A new ?c{A1} is found using a Green's function to ensure the boundary- conditions are satisfied, while the correction to ? is found from a relation involving integrals of the currents and ?c{A1}. ? 1 is found by assuming quasi-neutrality. The method is stable, converges for any starting values we've tried, requires less than a MB of memory, and 10MB--10GB of disk space for the paths. CPU time on a desktop PC is from ˜ 10 minutes to an hour for each k. The algorithm is similar in spirit to previous work [1], but was developed independently so the implementation is different. Typical dispersion curves, plots of potentials and response functions will be shown. We've found the growth-rates can be fit quite well (correlations of 0.999) by the expression ? (k)= ax kb(1/w-k) where parameters ax, b are determined from the peak growth ? x and wavenumber kx. Preliminary results are that for parameter values (Me)/(M_i)=1, (Te)/(T_i)=1 the dependence of ? x, kx on w, over the range 3--20, is given by kx=0.527 w-1.07 and ? x=0.219 w-2.32 where ? x is scaled by ? i, k and w are scaled by ? i. For (Me)/(M_i)= 1/1836, (Te)/(T_i)=1/2 the dependence is kx=0.451 w-1.11 and ? x=0.0567 w-2.379. [1] M. Brittnacher, K. B. Quest, and H. Karimabadi, J. Geophys. Res., 100, 3551, (1995); W. Daughton, J. Geophys. Res., 103, 29429, (1998).
NASA Astrophysics Data System (ADS)
Campbell, Philip Michael
Functionalization of silicon through the UV attachment of organic monolayers represents a potential method for creating molecular electronics. Prior research has demonstrated that longchain alkenes create highly ordered, robust monolayers on Si(111). However, specific applications, such as double tunnel junctions and quantum dot solar cells, require shorter chain molecules than have been previously studied. Through the use of FTIR and XPS data, UV attachment of several short-chain organics is demonstrated to create dense monolayers. The results reveal that molecules with a seven carbon base chain are extremely stable and can undergo additional functionalization to create an amine terminated surface without compromising the quality. STS curves on gold nanoparticles deposited on these monolayers show evidence of Coulomb staircase behavior. Conversely, chains shorter than seven carbons degrade more quickly when stored in a dry nitrogen environment and cannot withstand the processing steps necessary to be used for this application.
NASA Technical Reports Server (NTRS)
Bell, L. D.
1996-01-01
Ballistic-Electron-Emission Microscopy (BEEM) spectroscopy has been performed on Au/Si(111) structures as a function of Au thickness and temperature. At 77 K a direct signature of parallel momentum conservation at the Au/Si interface is observed in the BEEM spectra. The variation in spectral shape with both Au thickness and temperature places restrictions on allowable values of inelastic and elastic mean-free paths in the metal, and also requires the presence of multiple electron passes within the Au layer. An independent indication of multiple reflections is directly observed in the attenuation of BEEM current with Au thickness.
Stochastic treatment of electron multiplication without scattering in dielectrics
NASA Technical Reports Server (NTRS)
Lin, D. L.; Beers, B. L.
1981-01-01
By treating the emission of optical phonons as a Markov process, a simple analytic method is developed for calculating the electronic ionization rate per unit length for dielectrics. The effects of scattering from acoustic and optical phonons are neglected. The treatment obtains universal functions in recursive form, the theory depending on only two dimensionless energy ratios. A comparison of the present work with other numerical approaches indicates that the effect of scattering becomes important only when the electric potential energy drop in a mean free path for optical-phonon emission is less than about 25% of the ionization potential. A comparison with Monte Carlo results is also given for Teflon.
Siekhaus, W J; Nelson, A J
2011-10-26
Energy dependent electron emission (counts per second) between zero and 1.4 keV generated by the natural reactivity of uranium was measured by an electrostatic spectrometer with known acceptance angle and acceptance area. The electron intensity decreases continuously with energy, but at different rates in different energy regimes, suggesting that a variety of processes may be involved in producing the observed electron emission. 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 flux decreased rapidly from {approx}10{sup 6}/cm{sup 2}s to {approx}10{sup 5}/cm{sup 2}s in the energy range from zero to 200 eV, and then more slowly from {approx}10{sup 5}/cm{sup 2}s to {approx}3*10{sup 4}/cm{sup 2} s in the range from 200 to 1400 eV. The energy dependent electron mean free path in gases together with literature cross sections for electron induced reactions were used to determine the number of ionization and dissociation reactions per cm{sup 2}s within the inelastic mean free path of electrons, and found to be about 1.3*10{sup 8}/cm{sup 2}s and 1.5*10{sup 7}/cm{sup 2}s, respectively, for hydrogen. An estimate of the number of ionization and dissociation reactions occurring within the total range, rather than the mean free path of electrons in gases resulted in 6.2*10{sup 9}/cm{sup 2}s and 1.3*10{sup 9}/cm{sup 2}s, respectively. The total energy flux carried by electrons from the surface is suspiciously close to the total possible energy generated by one gram of uranium. A likely source of error is the assumption that the electron emission has a cosine distribution. Angular distribution measurements of the electron emission would check that assumption, and actual measurement of the total current emanating from the surface are needed to confirm the value of the current calculated in section II. These results must therefore be used with caution - until they are confirmed by other measurements.
Del Rosso, T; Giammanco, F; Anderson, M G; Conti, F; Balvis, A; Isakov, I; Matvienko, V; Strashnoy, G; Waggoner, W; Bonelli, L; Paganini, E; Binderbauer, M W
2012-09-15
We describe the performance of a second-harmonic interferometer (SHI) to measure, on an optical path exceeding 12 m, the electron plasma density of two plasmoids formed in separate theta-pinch chambers and then merged in a central compression chamber after undergoing acceleration and compression. The excellent mechanical stability and a time resolution better than 50 ns suggest the application of SHI, especially in pulsed plasma devices with limited optical accesses. PMID:23041882
Guo, Hongxuan, E-mail: Guo.hongxuan@nims.go.jp, E-mail: msxu@zju.edu.cn [Global Research Center for Environment and Energy Based on Nanomaterials Science National Institute for Materials Science (NIMS) 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Gao, Jianhua; Ishida, Nobuyuki [International Center for Young Scientists, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Xu, Mingsheng, E-mail: Guo.hongxuan@nims.go.jp, E-mail: msxu@zju.edu.cn [State Key Laboratory of Silicon Materials, Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Fujita, Daisuke [Advanced Key Technologies Division, Global Research Center for Environment and Energy Based on Nanomaterials Science, and International Center for Young Scientists, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan)
2014-01-20
Characterization of the structural and physical properties of two-dimensional (2D) materials, such as layer number and inelastic mean free path measurements, is very important to optimize their synthesis and application. In this study, we characterize the layer number and morphology of hexagonal boron nitride (h-BN) nanosheets on a metallic substrate using field emission scanning electron microscopy (FE-SEM) and scanning helium ion microscopy (HIM). Using scanning beams of various energies, we could analyze the dependence of the intensities of secondary electrons on the thickness of the h-BN nanosheets. Based on the interaction between the scanning particles (electrons and helium ions) and h-BN nanosheets, we deduced an exponential relationship between the intensities of secondary electrons and number of layers of h-BN. With the attenuation factor of the exponential formula, we calculate the inelastic mean free path of electrons and helium ions in the h-BN nanosheets. Our results show that HIM is more sensitive and consistent than FE-SEM for characterizing the number of layers and morphology of 2D materials.
MoS2 : Choice Substrate for Accessing and Tuning the Electronic Properties of Graphene
NASA Astrophysics Data System (ADS)
Lu, Chih-Pin; Li, Guohong; Watanabe, K.; Taniguchi, T.; Andrei, Eva Y.
2014-10-01
One of the enduring challenges in graphene research and applications is the extreme sensitivity of its charge carriers to external perturbations, especially those introduced by the substrate. The best available substrates to date, graphite and hexagonal boron nitride (h -BN ), still pose limitations: graphite being metallic does not allow gating, while both h -BN and graphite, having lattice structures closely matched to that of graphene, may cause significant band structure reconstruction. Here we show that the atomically smooth surface of exfoliated MoS2 provides access to the intrinsic electronic structure of graphene without these drawbacks. Using scanning tunneling microscopy and Landau-level (LL) spectroscopy in a device configuration that allows tuning of the carrier concentration, we find that graphene on MoS2 is ultraflat, producing long mean free paths, while avoiding band structure reconstruction. Importantly, the screening of the MoS2 substrate can be tuned by changing the position of the Fermi energy with relatively low gate voltages. We show that shifting the Fermi energy from the gap to the edge of the conduction band gives rise to enhanced screening and to a substantial increase in the mean free path and quasiparticle lifetime. MoS2 substrates thus provide unique opportunities to access the intrinsic electronic properties of graphene and to study in situ the effects of screening on electron-electron interactions and transport.
Electron Transport in Tangled Magenetic Fields
NASA Astrophysics Data System (ADS)
Albright, B. J.; Chandran, B. D. G.; Cowley, S. C.; Loh, M.
1999-11-01
Galaxy clusters are believed to possess tangled magnetic fields that have small correlation lengths compared to the dimensions of the clusters and the collisional mean free paths of the electrons in the clusters. Thermal conduction in galaxy clusters plays a central role in their evolution, and the mass accretion rates in clusters are controlled by this parameter. Heat conduction in cluster plasmas is not well understood, however, and estimates of the thermal conductivity are too high to explain the observed mass accretion rates in cooling flows. This talk will demonstrate how an inhomogeneous magnetic field in a galaxy cluster may inhibit the transport of heat in such a medium by restricting the mobility of electrons both perpendicular to the magnetic field and also parallel to the field. A typical galaxy cluster may experience a reduction by a factor of 100 or more in its thermal conductivity from these effects. This is consistent with observations of cooling flows.
Jinhe Liu; Wanqian Hu; Yuzhe Liu; Yu Liu
2000-01-01
In this paper, the electron rotating radius and the corresponding length above surface of the workpiece where the electron density is notably reduced are calculated on the condition of adding magnetic field in laser welding according to the temperature of plasma and the average velocity of electron motion. The experiments results indicate that on the set condition, the weld area
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.
NASA Technical Reports Server (NTRS)
Larosa, T. N.; Moore, R. L.; Shore, S. N.
1994-01-01
We recently proposed that a magnetohydrodynamic (MHD) turbulent cascade produces the bulk energization of electrons to approximately 25 keV in the impulsive phase of solar flares (LaRosa & Moore 1993). In that scenario, (1) the cascading MHD turbulence is fed by shear-unstable Alfvenic outflows from sites of strongly driven reconnection in the low corona, and (2) the electrons are energized by absorbing the energy that flows down through the cascade. We did not specify the physical mechanism by which the cascading energy is ultimately transferred to the electrons. Here we propose that Fermi acceleration is this mechanism, the process by which the electrons are energized and by which the cascading MHD turbulence is dissipated. We point out that in the expected cascade MHD fluctuations of scale 1 km can Fermi-accelerate electrons from 0.1 keV to approximately 25 keV on the subsecond timescales observed in impulsive flares, provided there is sufficient trapping and scattering of electrons in the MHD turbulence. We show that these same fluctuations provide the required trapping; they confine the electrons within the turbulent region until the turbulence eis dissipated. This results in the energization of all of the lectrons in each large-scale (5 x 10(exp 7)cm) turbulent eddy to 25 keV. The Fermi process also requires efficient scattering so that the pitch-angle distribution of the accelerating electrons remains isotropic. We propose that the electrons undergo resonant scattering by high-frequency plasma R-waves that, as suggested by others (Hamilton & Petrosian 1992), are generated by the reconnection. Ions are not scattered by R-waves. Provided that there is negligible generation of ion-scattering plasma turbulence (e.g., L-waves) by the reconnection or the MHD turbulence, the ions will not Fermi-accelerate and the cascading energy is transferred only to the electrons. We conclude that, given this situation, electron Fermi acceleration can plausibly account for the electron bulk energization in impulsive solar flares.
NASA Astrophysics Data System (ADS)
Liu, Jinhe; Hu, Wanqian; Liu, Yuzhe; Liu, Yu
2000-10-01
In this paper, the electron rotating radius and the corresponding length above surface of the workpiece where the electron density is notably reduced are calculated on the condition of adding magnetic field in laser welding according to the temperature of plasma and the average velocity of electron motion. The experiments results indicate that on the set condition, the weld area is increased by 18% with the weld penetration and the melting efficiency being increased by 22% and 13% respectively when the magnetic flux density added is set at 96 mT.
NASA Astrophysics Data System (ADS)
Kushwaha, Manvir S.; Vasilopoulos, P.
2003-03-01
A theoretical investigation is made of the response of a field-effect transistor (FET) to an incoming electromagnetic radiation in the presence of an applied perpendicular magnetic field. The influence of an external friction (related with electron scattering by impurities and/or phonons) and internal friction (associated with the electron-electron scattering) is also taken into account. The two-dimensional (2D) electron fluid in the FET channel has been treated within the framework of hydrodynamics. The treatment is valid for a nondegenerate electron gas in which the mean free path for electron-electron scattering (?_ee) is much smaller than the device length (L) and the mean free path due to collisions with impurities and/or phonons (?_coll). A magnetic field weak enough to set in the magnetic (Landau) quantization renders the 2D electron fluid abide by the said requirements (i.e., ?_ee << L << ?_coll) and hence fit to be governed by the hydrodynamics. It is demonstrated that a short (long) channel high electron mobility transistor (HEMT) yields a resonant (nonresonant) response to an ac signal induced by the incoming electromagnetic radiation at the plasma oscillation frequencies of the 2D electrons in the device. Keeping the device length and temperature at control, an appplied magnetic field can be tuned to achieve the desired effect on the response of the device. As regards the temperature, it is observed that lower the temperature (i.e., higher the mobility), the higher the responsivity of the device. Such response makes the FET a promising device for new types of sources, detectors, mixers, and multipliers. The HEMT-based devices should, in principle, operate at much higher frequencies than the conventional transit-time limited devices, since the plasma waves propagate much faster than electrons.
NASA Astrophysics Data System (ADS)
Shimawaki, H.; Neo, Y.; Mimura, H.; Wakaya, F.; Takai, M.
2013-04-01
This paper investigates the effect of optical pulses on the electron emission properties of metal-oxide-semiconductor (MOS) cathodes based on nanocrystalline silicon (nc-Si). The emission current is enhanced by about two orders of magnitude by the irradiation of 405 nm laser light. The increase of the emission current under irradiation was proportional to incident laser power. The differential quantum efficiency of the nc-Si based MOS diode itself was estimated to be 3 × 10-2. However, the value of the photoemission current was only 3 × 10-7 due to the short mean free path of hot electron for Pt used as the gate electrode. We obtained a pulsed electron beam from the cathode device by a pulsed laser. The result shows that MOS type cathodes have a suitable structure for optically generating a train of short electron bunches.
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.
Grew, Kyle N.; Izzo, John R.; Chiu, Wilson K.S.
2011-08-16
The development of a solid oxide fuel cell (SOFC) with a higher efficiency and power density requires an improved understanding and treatment of the irreversibilities. Losses due to the electronic and ionic resistances, which are also known as ohmic losses in the form of Joule heating, can hinder the SOFC's performance. Ohmic losses can result from the bulk material resistivities as well as the complexities introduced by the cell's microstructure. In this work, two-dimensional (2D), electronic and ionic transport models are used to develop a method of quantification of the ohmic losses within the SOFC anode microstructure. This quantification is completed as a function of properties determined from a detailed microstructure characterization, namely, the tortuosity of the electronic and ionic phases, phase volume fraction, contiguity, and mean free path. A direct modeling approach at the level of the pore-scale microstructure is achieved through the use of a representative volume element (RVE) method. The correlation of these ohmic losses with the quantification of the SOFC anode microstructure are examined. It is found with this analysis that the contributions of the SOFC anode microstructure on ohmic losses can be correlated with the volume fraction, contiguity, and mean free path.
Grew, Kyle N.; Izzo, Jr., John R.; Chiu, W. K. S.
2011-01-01
The development of a solid oxide fuel cell (SOFC) with a higher efficiency and power density requires an improved understanding and treatment of the irreversibilities. Losses due to the electronic and ionic resistances, which are also known as ohmic losses in the form of Joule heating, can hinder the SOFC’s performance. Ohmic losses can result from the bulk material resistivities as well as the complexities introduced by the cell’s microstructure. In this work, two-dimensional (2D), electronic and ionic transport models are used to develop a method of quantification of the ohmic losses within the SOFC anode microstructure. This quantification is completed as a function of properties determined from a detailed microstructure characterization, namely, the tortuosity of the electronic and ionic phases, phase volume fraction, contiguity, and mean free path. A direct modeling approach at the level of the pore-scale microstructure is achieved through the use of a representative volume element (RVE) method. The correlation of these ohmic losses with the quantification of the SOFC anode microstructure are examined. It is found with this analysis that the contributions of the SOFC anode microstructure on ohmic losses can be correlated with the volume fraction, contiguity, and mean free path.
A Hot-electron Direct Detector for Radioastronomy
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. The idea is to adjust a speed of the thermal relaxation of hot-electrons in a nanometer size normal metal or superconductive transition edge bolometer by controlling the elastic electron mean free path. If the bolometer contacts are made of a superconductor with high critical temperature 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 7(exp 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 approx. 10(exp -3) to 10(exp -5) S at T approx. = 0.1 - 0.3 K will exhibit photon-noise limited performance in millimeter and subn-millimeter range. The bolometer will have a figure-of-merit NEk square root of tau approx. = 10(exp -22) 10(exp -21) W/Hz at 100 mK which is 10(exp 3) times smaller than that of a state-of-the-art bolometer. 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 research was performed by the Center for Space Microelectronics Technology, JPL, California Institute of Technology, under the contract for NASA.
Field electron emission based on resonant tunneling in diamond/CoSi2/Si quantum well nanostructures
Gu, Changzhi; Jiang, Xin; Lu, Wengang; Li, Junjie; Mantl, Siegfried
2012-01-01
Excellent field electron emission properties of a diamond/CoSi2/Si quantum well nanostructure are observed. The novel quantum well structure consists of high quality diamond emitters grown on bulk Si substrate with a nanosized epitaxial CoSi2 conducting interlayer. The results show that the main emission properties were modified by varying the CoSi2 thickness and that stable, low-field, high emission current and controlled electron emission can be obtained by using a high quality diamond film and a thicker CoSi2 interlayer. An electron resonant tunneling mechanism in this quantum well structure is suggested, and the tunneling is due to the long electron mean free path in the nanosized CoSi2 layer. This structure meets most of the requirements for development of vacuum micro/nanoelectronic devices and large-area cold cathodes for flat-panel displays. PMID:23082241
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.
Particle-in-cell simulations of discharges with intense electron emission
NASA Astrophysics Data System (ADS)
Sydorenko, Dmytro
2013-09-01
In many plasma devices, the plasma is bounded by walls which emit electrons due to secondary electron emission or thermionic emission. At low pressures, the electron mean free path exceeds the plasma dimensions, and the emitted electrons accelerated by the intense electric field of the near-wall sheath propagate through the plasma as an electron beam. The beam dynamics in a finite length system is different from theoretical predictions for infinite or periodic plasmas. This presentation gives a summary of numerical studies of beam-plasma interaction in Hall thrusters and dc discharges carried out with a particle-in-cell code. The code resolves one spatial coordinate and three velocity components, it is based on the direct implicit algorithm, the electron-to-ion mass ratio is realistic, numerous collisions between electrons and neutrals and the Coulomb collisions are included, code performance is enhanced with the help of MPI parallelization. The following effects are discussed: vanishing of the two-stream instability due to modification of the bulk electron velocity distribution, sheath instability in Hall thrusters, intermittency and multiple regimes of the two-stream instability in dc discharges. In many plasma devices, the plasma is bounded by walls which emit electrons due to secondary electron emission or thermionic emission. At low pressures, the electron mean free path exceeds the plasma dimensions, and the emitted electrons accelerated by the intense electric field of the near-wall sheath propagate through the plasma as an electron beam. The beam dynamics in a finite length system is different from theoretical predictions for infinite or periodic plasmas. This presentation gives a summary of numerical studies of beam-plasma interaction in Hall thrusters and dc discharges carried out with a particle-in-cell code. The code resolves one spatial coordinate and three velocity components, it is based on the direct implicit algorithm, the electron-to-ion mass ratio is realistic, numerous collisions between electrons and neutrals and the Coulomb collisions are included, code performance is enhanced with the help of MPI parallelization. The following effects are discussed: vanishing of the two-stream instability due to modification of the bulk electron velocity distribution, sheath instability in Hall thrusters, intermittency and multiple regimes of the two-stream instability in dc discharges. In collaboration with I. D. Kaganovich, Y. Raitses, A. V. Khrabrov (Princeton Plasma Physics Laboratory, Princeton, NJ), P. L. G. Ventzek, L. Chen (Tokyo Electron America, Austin, TX), A. Smolyakov (University of Saskatchewan, Saskatoon, SK, Canada).
Electron correlation in narrow band systems
NASA Astrophysics Data System (ADS)
Kishore, R.
1983-03-01
The effect of the electron correlations in narrow bands, such as d(f) bands in the transition (rare earth) metals and their compounds and the impurity bands in doped semiconductors, are studied. The narrow band systems are described by the Hubbard Hamiltonian. By proposing a local self-energy for the interacting electrons, we found that our results are exact in both atomic and band limits and reduce to the Hartree Fock results for U/delta yield 0, where U is the intra-atomic Coulomb interaction and delta is the bandwidth of the noninteracting electrons. For the Lorentzian form of the density of states of the noninteracting electrons, our approximation turns out to be equivalent to the third Hubbard approximation. A simple argument, based on the mean free path obtained from the imaginary part of the self energy, shows how the electron correlations can give rise to a discontinuous metal-nonmetal transition as proposed by Mott. The band narrowing and the existence of the satellite below the Fermi energy in Ni, found in photoemission experiments, can also be understood.
NASA Technical Reports Server (NTRS)
Kim, Jeong-Hee; Rapp, Richard H.
1990-01-01
In June 1986 a 1 x 1 deg/mean free-air anomaly data file containing 48955 anomalies was completed. In August 1986 a 30 x 30 min mean free-air anomaly file was defined containing 31787 values. For the past three years data has been collected to upgrade these mean anomaly files. The primary emphasis was the collection of data to be used for the estimation of 30 min means anomalies in land areas. The emphasis on land areas was due to the anticipated use of 30 min anomalies derived from satellite altimeter data in the ocean areas. There were 10 data sources in the August 1986 file. Twenty-eight sources were added based on the collection of both point and mean anomalies from a number of individuals and organizations. A preliminary 30 min file was constructed from the 38 data sources. This file was used to calculate 1 x 1 deg mean anomalies. This 1 x 1 deg file was merged with a 1 x 1 deg file which was a merger of the June 1986 file plus a 1 x 1 deg file made available by DMA Aerospace Center. Certain bad 30 min anomalies were identified and deleted from the preliminary 30 min file leading to the final 30 min file (the July 1989 30 min file) with 66990 anomalies and their accuracy. These anomalies were used to again compute 1 x 1 deg anomalies which were merged with the previous June 86 DMAAC data file. The final 1 x 1 deg mean anomaly file (the July 89 1 x 1 deg data base) contained 50793 anomalies and their accuracy. The anomaly data files were significantly improved over the prior data sets in the following geographic regions: Africa, Scandinavia, Canada, United States, Mexico, Central and South America. Substantial land areas remain where there is little or no available data.
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.
The calculation of ionospheric ray paths
Koehler, Buford Ray
1967-01-01
Parabolic ionospheric layer of electrons, altitude versus electron density Page 1- 2 Sample ray paths with constant angle of propagation and increasing frequency, parabolic ionosphere of electrons assumed, earth's magnetic field neglected 1- 3 Sample... ray paths with constant frequency and variable angle of propagation and range, parabolic ionosphere of electrons assumed, earth's magnetic field neglected 2- 1 The vertical and lateral deviations of a radio wave propagated in a plane ionosphere...
Nanoscale thin single-crystal silicon and its application to electronics
NASA Astrophysics Data System (ADS)
Avci, Uygar; Tiwari, Sandip
2004-03-01
We demonstrate a method for achieving thin (tens of nanometers) single-crystal silicon films with electronic-quality bulk and surface properties, atomic-scale surface roughness, and suitable for use in complex multilayered structures. The thin silicon film is achieved by defining thickness through the use of oxidation depth as a reference, transfer of film structure by exfoliation, and chemical-mechanical polishing for selective thin film definition. Such structures are useful in a variety of directions: in electronic devices such as field-effect transistors, in characterization studies such as those utilizing vertical transport using thicknesses of the order of mean free path length, etc. We demonstrate its use in a silicon metal-oxide-semiconductor transistor with two gates, one on each side of the thin silicon film on a planar substrate.
Miraglia, J. E. [Instituto de Astronomia y Fisica del Espacio, Consejo Nacional de Investigaciones Cientificas y Tecnicas, Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Casilla de Correo 67, Sucursal 28, 1428 Buenos Aires, (Argentina)
2003-08-01
We introduce a distorted wave method to calculate the nonlinear excitation effects occurring when a fast bare ion penetrates a free-electron gas. The central scheme of this work is to replace the undistorted plane waves leading to the Lindhard dielectric response function (or random phase approximation) by Coulomb waves with an effective charge. This impulse-type approximation is valid for velocities larger than the Fermi velocity. Stopping and mean free path are presented for impact of bare multicharged ions on aluminum free-electron gas. The Barkas effect is theoretically found, i.e., negative heavy particles lose energy at the lower rate than positive particles of the same velocity do. As the projectile charge increases, the single differential cross section per unit energy presents two effects: the plasmon peak sharpens and the binary peak starts to be increasingly noticeable.
Conditions for electron runaway under leader breakdown of long gaps
Ul'yanov, K. N. [Lenin All-Russia Electrotechnical Institute (Russian Federation)
2008-04-15
An original hydrodynamic model in which inelastic collisions in the equations of motion and energy balance play a decisive role is developed and applied to simulate electron avalanches in strong electric fields. The mean energy and drift velocity of electrons, as well as the ionization coefficient and electric field in a wide range of mean electron energies, are determined for helium and xenon. A criterion is derived for the runaway of the average electron in discharges with ionization multiplication. It is shown that runaway can take place at any value of E/p, provided that the momentum mean free path exceeds the gap length. The voltage corresponding to electron runaway is found for helium, xenon, and air as a function of the electric field, the electron mean energy, and the parameter pd. Conditions for the formation of a precursor in electronegative gases are analyzed. It is shown that the presence of a precursor with a high electric conductance is necessary for the formation of a new leader step. The voltage and time ranges corresponding to efficient electron runaway and X-ray generation during leader breakdown in air are determined.
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
NSDL National Science Digital Library
For the next two exercises, we will break up into groups of four. Each member of the group will represent one of four waves leaving the source: direct wave, ground roll, reflected wave, and head wave. All four "waves" will leave the source at the same time and travel at a particular speed and path as directed by the instructor. ALL students will record the arrival time of each "wave" at each geophone until all 12 geophones have been used. Plot arrival time versus distance for each "wave". Do any of the time versus distance curves fit a straight line? Do any of them not fit a straight line? Explain why they do or don't fit a straight line. Uses online and/or real-time data Has minimal/no quantitative component
Photoionization pathways and free electrons in UV-MALDI.
Knochenmuss, Richard
2004-06-01
The recently developed model for primary and secondary UV-MALDI ion formation (Knochenmuss, R. J. Mass Spectrom. 2002, 37, 867-877. Knochenmuss, R. Anal. Chem. 2003, 75, 2199.) is applied to questions regarding photoionization pathways and electron versus negative ion production. Two-photon ionization of the matrix in direct contact with analyte is possible under some circumstances (Kinsel, G.; Knochenmuss, R.; Setz, P.; Land, C. M.; Goh, S.-K.; Archibong, E. F.; Hardesty, J. H.; Marynik, D. J. Mass Spectrom. 2002, 37, 1131-1140.), and is added to the model. When analyte is present in large mole ratios (such as when matrix suppression is desired), this effect contributes modestly to the ion yield. Generally, matrix exciton pooling remains dominant. The interfacial layer of thin samples on a metal substrate may also be ionizable in a 2-photon process. A mechanism is proposed, and the correspondingly modified model gives excellent agreement with electron emission versus laser intensity data. Capture in, or escape of low-energy electrons from a thick sample (or on a nonmetallic substrate) is also examined. Because the mean free path for MALDI electrons in a solid matrix is on the order of 10 nm, below such depths, any electrons generated are captured to form negative ions. Only a surface layer can emit free electrons. This surface emission effect is also well reproduced by the model, up to a laser intensity limit caused by surface charging. This charging phenomenon is investigated and illustrated by molecular dynamics calculations. PMID:15167799
The passage of fast electrons through matter
NASA Astrophysics Data System (ADS)
Sorini, Adam P.
This work regards the passage of fast electrons through matter, and in particular how electrons scatter and lose energy within a solid. The basic quantum theory of these scattering processes was first considered in the early- to mid-20th century by Bohr, Bethe, Fermi, and others. This work extends our understanding of how a relativistic electron scatters off, and loses energy to, a complex many-body system. The main idea of this work is that it is now possible to calculate, from first-principles, the inelastic losses of relativistic electrons in condensed matter. We present ab initio calculations based on a real-space Green's function approach, implemented in the FEFF8 computer program[1]. Our work focuses on three topics: Relativistic stopping power and associated loss parameters, electron energy loss spectroscopy in high energy transmission electron microscopes, and the inelastic electron scattering mixed dynamic form factor. We calculate, for the first time, ab initio stopping powers and inelastic mean free paths in real materials. The stopping powers are calculated over a broad energy range, from ten eV to above ten MeV. We also present the first ab initio calculations of the "mean excitation energy". We develop a relativistic theory of inelastic electron scattering, based on ab initio calculations of dielectric response, and the generalized Lorenz gauge. Using our relativistic dielectric theory, we calculate the EELS magic angle ratio for boron nitride and for graphite. In these anisotropic materials we find large relativistic corrections to the magic angle for high energy electron microscopes. We also predict and calculate large deviations in the EELS magic angle from the relativistic vacuum predictions in the low energy-loss regime. Finally, we present calculations of mixed dynamic form factor.
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
Monte Carlo simulation of positron-stimulated secondary electron emission from solids
NASA Astrophysics Data System (ADS)
Dapor, Maurizio; Miotello, Antonio; Zari, Davide
2000-03-01
We have analyzed the problem of the secondary electrons emitted from a solid irradiated by a positron or electron particle beam. The relevant concepts that form the basis for a theoretical understanding of the secondary electron emission problem are reanalyzed by looking at Wolff's theory. However, to attain analytical results, such a theory must include some simplification, which may be valid in only a limited number of situations. To overcome such a limitation we have elaborated a Monte Carlo procedure for the calculation of the secondary electrons emitted from a solid, irradiated with a positron beam. The choice of a primary positron beam is justified because the experiments involving electron emission are not contaminated by the reemitted primary electrons. The calculations were performed in the positron primary energy range between 50 eV and 2 keV, and for different incidence angles with respect to the surface of a copper sample. Many numerical results are reported, namely: i) the elastic mean-free paths of positrons in copper, ii) the mean number of electrons emitted per positron, iii) the penetration depth of the positrons, and iv) the depths from which the secondary electrons are emitted. Finally, the numerical results concerning the secondary electron energy distribution are compared with the experimental data recently presented by Overton and Coleman showing a general good agreement.
NASA Astrophysics Data System (ADS)
Sheldon, W. R.
2004-05-01
Electron precipitation from the outer belt is an important input of energy and electric charge to the atmosphere. The ionization profile (ionization rate vs. altitude) may be affected by the direction at which electrons enter the top of the atmosphere. Definitive measurements of the angular distribution of precipitating electrons at the top of the atmosphere have not been made; studies of the problem have made a number of assumptions in this regard. Consideration of the mechanism by which electrons in the drift loss cone enter the atmosphere due to eastward drift suggests horizontal entry: an electron in the process of mirroring near the top of the atmosphere encounters a region where its gyro-circumference is equal to its mean-free- path and it collides with an atmospheric molecule. In order to study whether horizontal entry at the top of the atmospere could have a significant effect, we have investigated this question by comparing horizontal to vertical entry with a Monte Carlo study using the FLUKA code. Assuming an energy spectrum typical of outer belt electrons up to 10 MeV at entry, both electrons and X rays were followed down to energies of 100 keV. The Monte Carlo results are compared to measurements in the atmosphere of electrons made below 80 km on rocket-boosted, parachute-deployed payloads, and to measurements of X rays made on balloon payloads at altitudes of about 35 km.
ELECTRON HEAT CONDUCTION IN THE SOLAR WIND: TRANSITION FROM SPITZER-HAeRM TO THE COLLISIONLESS LIMIT
Bale, S. D.; Quataert, E. [Physics Department, University of California, Berkeley (United States); Pulupa, M.; Salem, C.; Chen, C. H. K. [Space Sciences Laboratory, University of California, Berkeley (United States)
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…
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 [Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Xie Yulong [Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Campbell, Luke W. [National Security Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)
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.
NASA Astrophysics Data System (ADS)
Wang, Zhiguo; Xie, YuLong; Campbell, Luke W.; Gao, Fei; Kerisit, Sebastien
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 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 ?-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.
Deymier, Pierre
in the insulating state to long-range order, leading to a thermody- namics transformation and an antiferromagnetic a paramagnetic metallic state with electron gas character, we find that bound electrons form upon expansion theory. For instance, great strides have been made in the understanding of the correlated electron gas
Electron physics and ambipolarity in the tokamak scrape-off layer
Hazeltine, R.D. [Texas Univ., Austin, TX (United States). Inst. for Fusion Studies; Catto, P.J. [Massachusetts Inst. of Tech., Cambridge, MA (United States)
1994-04-01
Models of the electron behavior in the scrape-off layer (SOL) of diverted and limited boundary conditions that occurs tokamak plasmas must retain the abrupt change in boundary conditions that occurs across the separatrix or last closed flux surface as well as the electron reflecting Debye sheath established at the limiter or divertor plates. The balance between ion radial diffusion and streaming to the plates sets the SOL width and the electrons must adjust the Debye sheath at the plates to main tain quasineutrality and ambipolarity in the SOL beyond the last closed flux surface. We consider the long mean-free-path limit where a bounce-averaged kinetic electron model results in a steady-state balance in the SOL between radial diffusive feed from the core and velocity space diffusive loss to the plates due to collisional detrapping. In this double diffusion model a velocity space boundary layer occurs about the trapped-passing boundary where strong velocity space gradients must balance the streaming of the newly de-trapped electrons to the plates. The behavior of the electron distribution function in the velocity provides the information needed to evaluate the Debye-sheath-dependent electron loss rate.
Han, Jaeheon [Department of Electronic Engineering, Kangnam University, 111 Gugal-dong, Giheung-gu, Yongin-city, Gyeonggi-do, Korea 446-702 (Korea, Republic of)
2011-12-23
Short channel GaAs Metal Semiconductor Field Effect Transistors (MESFETs) have been fabricated with gate length to 20 nm, in order to examine the characteristics of sub-50 nm MESFET scaling. Here the rise in the measured transconductance is mainly attributed to electron velocity overshoot. For gate lengths below 40 nm, however, the transconductance drops suddenly. The behavior of velocity overshoot and its degradation is investigated and simulated by using a transport model based on the retarded Langevin equation (RLE). This indicates the existence of a minimum acceleration length needed for the carriers to reach the overshoot velocity. The argument shows that the source resistance must be included as an internal element, or appropriate boundary condition, of relative importance in any model where the gate length is comparable to the inelastic mean free path of the carriers.
NASA Astrophysics Data System (ADS)
Kang, Sungmu
In this thesis, devices using the ballistic transport of two dimensional electron gas (2DEG) in GaAs High Electron Mobility Transistor(HEMT) structure is fabricated and their dc and ac properties are characterized. This study gives insight on operation and applications of modern submicron devices with ever reduced gate length comparable to electron mean free path. The ballistic transport is achieved using both temporal and spatial limits in this thesis. In temporal limit, when frequency is higher than the scattering frequency (1/(2pitau)), ballistic transport can be achieved. At room temperature, generally the scattering frequency is around 500 GHz but at cryogenic temperature (?4K) with high mobility GaAs HEMT structure, the frequency is much lower than 2 GHz. On this temporal ballistic transport regime, effect of contact impedance and different dc mobility on device operation is characterized with the ungated 2DEG of HEMT structure. In this ballistic regime, impedance and responsivity of plasma wave detector are investigated using the gated 2DEG of HEMT at different ac boundary conditions. Plasma wave is generated at asymmetric ac boundary conditions of HEMTs, where source is short to ground and drain is open while rf power is applied to gate. The wave velocity can be tuned by gate bias voltage and induced drain to source voltage(Vds ) shows the resonant peak at odd number of fundamental frequency. Quantitative power coupling to plasma wave detector leads to experimental characterization of resonant response of plasma wave detector as a function of frequency. Because plasma wave resonance is not limited by transit time, the physics learned in this study can be directly converted to room temperature terahertz detection by simply reducing gate length(Lgate) to submicron for the terahertz application such as non destructive test, bio medical analysis, homeland security, defense and space. In same HEMT structure, the dc and rf characterization on device is also carried out in order to compare the conventional HEMT and plasma wave detector. Additionally in spatial limit, the ballistic transport is achieved when gate length is shorter than mean free path of electron. Using depletion gates in GaAs/AlGaAs structure, we make quasi one dimensional channel (quantum point contact) at cryogenic temperature and investigate dc and ac(rf frequency) of 2DEG in spatial ballistic transport.
NASA Astrophysics Data System (ADS)
Sheldon, W. R.; Andersen, V.; Pinsky, L. S.
Electron precipitation from the outer belt is an important input of energy and electric charge to the atmosphere. Its effect on the electrodynamics of the atmosphere depends on the resulting ionization profile (ionization rate vs. altitude). It is likely that the ionization profile is strongly affected by the angular distribution of precipitating electrons absorbed by the atmosphere. Definitive measurements of precipitating electrons at the top of the atmosphere have not been made; the usual assumption for calculations of this problem is that they have an isotropic distribution over the zenithal hemisphere. However, consideration of the mechanism leading to the precipitation of outer belt electrons suggests a different distribution: a trapped electron in the process of mirroring encounters a region near the top of the atmosphere where its gyro-circumference is equal to its mean-free-path and thus collides with an atmospheric molecule. In this case, precipitating electrons are traveling horizontally when they are absorbed in the atmosphere. In order to investigate differences in the ionization profile that may depend on the angular distribution of precipitating electrons, we have conducted a Monte Carlo study of this problem using the FLUKA code. The two angular distributions described previously were assumed with an energy spectrum typical for outer belt electrons up to 10 MeV; both electrons and X-rays were followed down to energies of 100 keV. The Monte Carlo results are compared to measurements of electrons in the atmosphere below 80 km made from rocket-boosted, parachute-deployed payloads, and to measurements of X-rays made on balloon payloads at altitudes of about 35 km. Also, the flux and energy spectrum of backscattered electrons traveling upward from the atmosphere are determined for the two angular distributions of precipitating electrons, isotropic over the zenithal hemisphere and horizontal absorption.
Traveling salesman path problems
Lam, Fumei
2005-01-01
In the Traveling Salesman Path Problem, we are given a set of cities, traveling costs between city pairs and fixed source and destination cities. The objective is to find a minimum cost path from the source to destination ...
Tatsuya Nakamura; Yuji Abe; Seiya Kasai; Hideki Hasegawa; Tamotsu Hashizume
2006-01-01
A new single electron (SE) binary-decision diagram (BDD) node device having a single quantum dot connected to three nanowire branches through tunnel barriers was fabricated using etched AlGaAs\\/GaAs nanowires and nanometer-sized Schottky wrap gates (WPGs), and their operation was characterized experimentally, for the hexagonal BDD quantum circuit. Fabricated devices showed clear and steep single electron pass switching by applying only
S. A. Bortoff; E. Hartford
2000-01-01
In this paper, a two step path-planning algorithm for UAVs is proposed. The algorithm generates a stealthy path through a set of enemy radar sites of known location, and provides an intuitive way to trade-off stealth versus path length. In the first step, a suboptimal rough-cut path is generated through the radar sites by constructing and searching a graph based
Yannello, Vincent J; Fredrickson, Daniel C
2014-10-01
Valence electron count is one of the key factors influencing the stability and structure of metals and alloys. However, unlike in molecular compounds, the origins of the preferred electron counts of many metallic phases remain largely mysterious. Perhaps the clearest-cut of such electron counting rules is exhibited by the Nowotny chimney ladder (NCL) phases, compounds remarkable for their helical structural motifs in which transition metal (T) helices serve as channels for a second set of helices formed from main group (E) elements. These phases exhibit density of states pseudogaps or band gaps, and thus special stability and useful physical properties, when their valence electron count corresponds to 14 electrons per T atom. In this Article, we illustrate, using DFT-calibrated Hückel calculations and the reversed approximation Molecular Orbital analysis, that the 14-electron rule of the NCLs is, in fact, a specific instance of an 18 - n rule emerging for T-E intermetallics, where n is the number of E-supported T-T bonds per T atom. The structural flexibility of the NCL series arises from the role of the E atoms as supports for these T-T bonds, which simply requires the E atoms to be as uniformly distributed within the T sublattice as possible. This picture offers a strategy for identifying other intermetallic structures that may be amenable to incommensurability between T and E sublattices. PMID:25215958
Hard paths, soft paths or no paths? Cross-cultural perceptions of water solutions
Hall, Sharon J.
Hard paths, soft paths or no paths? Cross-cultural perceptions of water solutions Drew Blasco1 to the availability of clean, safe water. In this study we examined cross cultural preferences for soft path vs. hard conceptualize water solutions (hard paths, soft paths, no paths) cross-culturally? 2) What role does development
Photon-noise-limited direct detector based on disorder-controlled electron heating
NASA Astrophysics Data System (ADS)
Karasik, Boris S.; McGrath, William R.; Gershenson, Michael E.; Sergeev, Andrew V.
2000-05-01
We present a concept for a hot-electron direct detector capable of counting single millimeter-wave photons. The detector is based on a microbridge (1 ?m size) transition edge sensor made from a disordered superconducting film. The electron-phonon coupling strength at temperatures of 100-300 mK is proportional to the elastic electron mean free path l and can be reduced by over an order of magnitude by decreasing l. The microbridge contacts are made from a different superconductor with higher critical temperature Nb, which blocks the thermal diffusion of hot carriers into the contacts. The low electron-phonon heat conductance and the high thermal resistance of the contacts determine the noise equivalent power of ˜10-20-10-21 W/?Hz at 100 mK, which is 102-103 times better than that of state-of-the-art bolometers. Due to the effect of disorder, the electron cooling time is ˜10-1-10-2 s at 0.1 K. By exploiting negative electrothermal feedback, the detector time constant can be made as short as 10-3-10-4 s without sacrificing sensitivity.
Low-energy electron (0-100eV) interaction with resists using LEEM
NASA Astrophysics Data System (ADS)
Thete, A.; Geelen, D.; Wuister, S.; van der Molen, S. J.; Tromp, R. M.
2015-03-01
Extreme Ultra Violet (EUV) lithography is a next generation lithographic technique using 13.5 nm wavelength light (91.7eV photon energy) to define sub-20 nm features. This high energy radiation generates lower energy electrons (LEEs) after being absorbed. The mean free path of LEEs increases rapidly below ca. 30 eV allowing them to migrate several nanometers from their point of origin. As LEEs can still have sufficient energy to react with the surrounding resist, this may give rise to pattern blurring, posing a challenge for sub 10 nm features. Here, we introduce Low Energy Electron Microscopy (LEEM) as an extremely useful technique to investigate the interactions of LEEs with EUV resists. Using LEEM we can expose the resist with precise electron energies and doses. We also report the initial results of LEE exposures on poly(methyl methacrylate) PMMA. We have studied the LEE-PMMA interaction depth as a function of electron energy; a distinct exposure threshold is found at ~15 eV, below which the resist responds only very weakly to electron exposure.
Utilization of path length fuzing in the Peacekeeper Weapon System
NASA Astrophysics Data System (ADS)
Jackson, A. D.
This paper presents a discussion of the utilization and implementation of path length fuzing in the Peacekeeper Weapon System. Some background information which introduces the concept of path length fuzing and discusses its applicability to the Peacekeeper is first presented. Mathematical modeling of path length fuzing is discussed, and some novel algorithms and techniques developed by the author for implementation of path length fuzing in the Peacekeeper Operational Flight Program are presented. The scope of this paper is confined to the flight software and targeting aspects of path length fuzing; details of of the fuze hardware and electronics are not addressed.
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.
Computing almost shortest paths
Michael Elkin
2005-01-01
We study the s-sources almost shortest paths(abbreviated s-ASP) problem. Given an unweightedgraph G = (V,E),and a subset S ? Vof s nodes, the goal is to compute almostshortest paths between all the pairs of nodes S× V. We devise an algorithm withrunning timeO(∣E∣n?+ s ·n1 + ?)for this problem that computes the pathsPu,wfor all pairs (u,w) ?S × V such
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
Kyriakou, Ioanna; Emfietzoglou, Dimitris [Medical Physics Lab, University of Ioannina Medical School, 451 10 Ioannina (Greece); Garcia-Molina, Rafael [Departamento de Fisica - CIOyN, Universidad de Murcia, E-30100 Murcia (Spain); Abril, Isabel [Departament de Fisica Aplicada, Universitat d'Alacant, Apartat 99, E-03080 Alacant (Spain); Kostarelos, Kostas [Nanomedicine Lab, Centre for Drug Delivery Research, The School of Pharmacy, University of London, London WC1N 1AX (United Kingdom)
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.
Ab initio reaction paths and direct dynamics calculations
Kim K. Baldridge; Mark S. Gordon; Rozeanne Steckler; Donald G. Truhlar
1989-01-01
A detailed study of methods for generating the minimum energy path of a chemical reaction using ab initio electronic structure calculations is presented; the convergence with respect to step size of the geometry and energy along this path is studied with several algorithms. The investigations are extended to the calculation of chemical reaction rate coefficients by interfacing the polyrate code
Improved initial guess for minimum energy path calculations
NASA Astrophysics Data System (ADS)
Smidstrup, Søren; Pedersen, Andreas; Stokbro, Kurt; Jónsson, Hannes
2014-06-01
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.
Electronic transport in InGaAs/Al2O3 nFinFETs
NASA Astrophysics Data System (ADS)
Li, Shengwei; Hu, Yaodong; Wu, Yangqing; Huang, Daming; Ye, Peide D.; Li, Ming-Fu
2014-07-01
Based on the multiple subbands quasi-ballistic transport theory, we investigate the electronic transport of nano size In0.53Ga0.47As nFinFETs with Al2O3 gate dielectric, emphasizing the saturation current region. 1D mobile charge density and gate capacitance density are introduced for the first time to describe the nano-FinFET transport property under volume inversion. With the extracted effective channel mobility of electrons in the linear region from our experiments, the electron mean free path ? in the channel with the value of 5-9 nm is obtained. With only one fitting parameter ? = 0.31 for the critical length l=L{{\\left( \\frac{kT/q}{{{V}_{d}}} \\right)}^{\\alpha }} in the quasi-ballistic transport theory, the calculated drain current can fit all experimental data for various gate voltage V g, source-drain voltage V d, and temperature (240-332 K) in overall very good agreement. The backscattering coefficient r in the saturation region is larger than 0.8, indicating a large room for improvement for the present InGaAs FinFET technology and performance.
Energy-loss- and thickness-dependent contrast in atomic-scale electron energy-loss spectroscopy
Tan, Haiyan [Universit_e de Toulouse, Toulouse, France (Europe); National Institute of Standards Technology, Gaithersburg, MD (United States); Xin, Huolin L. [Brookhaven National Lab. (BNL), Upton, NY (United States); Zhu, Ye [Monash Univ., Melbourne, VIC (Australia); Dwyer, Christian [Peter Grunberg Institute, Julich, Germany (Europe)
2014-12-01
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.
Energy-loss- and thickness-dependent contrast in atomic-scale electron energy-loss spectroscopy
NASA Astrophysics Data System (ADS)
Tan, Haiyan; Zhu, Ye; Dwyer, Christian; Xin, Huolin L.
2014-12-01
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 counterintuitive 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 counterintuitive "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.
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.
NASA Astrophysics Data System (ADS)
Petnikova, V. M.; Tret'yakov, Evgeniy V.; Shuvalov, Vladimir V.
2006-11-01
It is shown that the stability of the Henyey—Greenstein phase function allows the calculation rate of light propagation through strongly scattering objects to be drastically increased by using the same a priori information on interaction processes as in the initial formulation of the problem. The increase in the calculation rate is accompanied by a gradual impairment of simulation accuracy from the accuracy of the Monte-Carlo method to that of the diffusion approximation. By using a standard assumption about the statistical independence of the photon mean free path and photon scattering angle, an exact analytic expression relating the effective number of scattering events with the optical path is obtained.
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,natali,haimkg@math.tau.ac.il, fedith,mischug@research.att.com Abstract A new general theory about restoration of network paths is first introduced. The theory pertains to restoration of shortest paths in a network following failure, e.g., we
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,natali,haimk}@math.tau.ac.il, {edith,mischu}@research.att.com Abstract A new general theory about restoration of network paths is first introduced. The theory pertains to restoration of shortest paths in a network following failure, e.g., we
Hot-electron distribution function in high-Z materials
Lindman, E.L.
1982-01-01
An analytic expression is obtained for the distribution of hot electrons as a function of distance into a cold material slab in which ..nu../sub E/ = ..gamma../sub E/v/sup -..cap alpha../ and ..nu..perpendicular to = ..gamma..v/sup -..beta../ are the assumed velocity dependences of the energy loss collision frequency and the scattering collision frequency and ..nu../sub E/ << ..nu..perpendicular to. For a time independent source, a time independent solution exists with a characteristic penetration length equal to (lambda/sub E/lambdaperpendicular to)/sup 1/2/ where lambda/sub E/ and lambdaperpendicular to are the mean-free-paths corresponding to ..nu../sub E/ and ..nu..perpendicular to. The distribution function at large distance from the source is proprtional to v/sub ..cap alpha..-3/ for v less than a critical velocity. For v greater than the critical velocity, the velocity dependence of the Maxwellian source reappears causing an exponential cutoff.
Electron transport in nanostructures: A key to high temperature superconductivity?
NASA Astrophysics Data System (ADS)
Roeser, H. P.; Haslam, D. T.; Hetfleisch, F.; López, J. S.; von Schoenermark, M. F.; Stepper, M.; Huber, F. M.; Nikoghosyan, A. S.
2010-09-01
Nanostructured GaAs Schottky barrier diodes are used as low noise THz heterodyne detectors. Different diodes show that the electron transport is ballistic and given by an optimized depletion thickness DDepl which is shorter than the mean free path length. The best THz mixer noise temperature is achieved when the depletion thickness is twice the doping distance in GaAs with DDepl=2 x. There also is a linear relation between the depletion thickness and the carrier mobility ? by (2 x) 2? h/(2 e) ?. Since the mobility is proportional to 1/energy and because of many similarities when comparing with properties of high temperature superconductors (HTSC) it has been investigated if the doping distance x in HTSCs is connected with 1/( kTc). It turns out that there is also a strong correlation between x and the critical transition temperature Tc given by (2 x) 2˜1/ Tc. A detailed analysis and comparison suggest that the correlation equation for HTSCs is linked to the transition temperature Tc, the density of states in a 1D quantum wire, the lowest energy E1 in a 1D quantum well, and to the Fermi energy EF.
From (2,3)-Motzkin Paths to Schröder Paths
NASA Astrophysics Data System (ADS)
Yan, Sherry H. F.
2007-08-01
In this paper, we provide a bijection between the set of restricted (2,3)-Motzkin paths of length n and the set of Schroder paths of semilength n. Furthermore, we give a one-to-one correspondence between the set of (2,3)-Motzkin paths of length n and the set of little Schroder paths of semilength n+1. By applying the bijections, we get the enumerations of Schroder paths according to the statistics "number of udd's" and "number of hd's".
Electronic transport in nanoscale structures
NASA Astrophysics Data System (ADS)
Lagerqvist, Johan
In this dissertation electronic transport in nanoscale structures is discussed. An expression for the shot noise, a fluctuation in current due to the discreteness of charge, is derived directly from the wave functions of a nanoscale system. Investigation of shot noise is of particular interest due to the rich fundamental physics involved. For example, the study of shot noise can provide fundamental insight on the nature of electron transport in a nanoscale junction. We report calculations of the shot noise properties of parallel wires in the regime in which the interwire distance is much smaller than the inelastic mean free path. The validity of quantized transverse momenta in a nanoscale structure and its effect on shot noise is also discussed. We theoretically propose and show the feasibility of a novel protocol for DNA sequencing based on the electronic signature of single-stranded DNA while it translocates through a nanopore. We find that the currents for the bases are sufficiently different to allow for efficient sequencing. Our estimates reveal that sequencing of an entire human genome could be done with very high accuracy in a matter of hours, e.g., orders of magnitude faster than present techniques. We also find that although the overall magnitude of the current may change dramatically with different detection conditions, the intrinsic distinguishability of the bases is not significantly affected by pore size and transverse field strength. Finally, we study the ability of water to screen charges in nanopores by using all-atom molecular dynamics simulations coupled to electrostatic calculations. Due to the short length scales of the nanopore geometry and the large local field gradient of a single ion, the energetics of transporting an ion through the pore is strongly dependent on the microscopic details of the electric field. We show that as long as the pore allows the first hydration shell to stay intact, e.g., ˜6 nearby water molecules, the electric field of the ion can be well screened. We also discuss the consequences of the formation of hydration layers and of the discrete nature of polarization at atomic length scales for the applicability of continuum dielectric models.
Sullivan, Blair D [ORNL; Seymour, Dr. Paul Douglas [Princeton University
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.
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.
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.
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…
Jeffrey Michael Hebert
2001-01-01
This dissertation explores optimal path planning for air vehicles. An air vehicle exposed to illumination by a tracking radar is considered and the problem of determining an optimal planar trajectory connecting two prespecified points is addressed. An analytic solution yielding the trajectory minimizing the received radar energy reflected from the target is derived using the Calculus of Variations. Additionally, the
Danil Sokolov; Ivan Poliakov; Alexandre Yakovlev
2007-01-01
A token-based model for asynchronous data path is formally defined and three token game semantics, spread token, antitoken and counterflow, are introduced. These semantics are studied and their advantages and drawbacks are highlighted. For analysis and comparison a software tool is developed which integrates these models into a consistent framework. The models are verified by mapping them into Petri nets
Dynamic Shortest Paths Containers
Dorothea Wagner; Thomas Willhalm; Christos D. Zaroliagis
2004-01-01
Using a set of geometric containers to speed up shortest path queries in a weighted graph has been proven a useful tool for dealing with large sparse graphs. Given a layout of a graph G = (V; E), we store, for each edge (u; v) 2 E, the bounding box of all nodes t 2 V for which a shortest
Geometric Shortest Path Containers
Dorothea Wagner; Thomas Willhalm; Christos Zaroliagis
2004-01-01
In this paper, we consider Dijkstra's algorithm for the single source single target shortest path problem in large sparse graphs. The goal is to reduce the response time for on-line queries by using precomputed information. Due to the size of the graph, preprocessing space requirements can be only linear in the number of nodes. We assume that a layout of
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
Atmospheric Science Data Center
2014-12-08
... every 233 revolutions around the Earth, it is natural to name each of these different trajectories or paths. For MISR, the path is the generic name (actually the numeric label) of all orbits that observe the same areas ...
Assessing the Impact of Automated Path Planning Aids in the Maritime Community
Cummings, Mary "Missy"
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 to newer technology for navigation is taking longer, as there is higher risk due to the weapons
Bike path Schools Bike friendly
Crews, Stephen
Bike path Schools Parks Greenways Bike lane Bike friendly Bike path on sidewalk (uphill only a left turn, merge with motor vehicle traffic well in advance of the intersection. When bicycle paths stopping distance in inclement weather. Use a backpack or bike bag to carry items. Reasons to Bike
Autonomous ground vehicle path tracking
Jeff Wit; Carl D. Crane III; David G. Armstrong II
2004-01-01
Autonomous ground vehicle navigation requires the integration of many technologies such as path planning, position and orientation sensing, vehicle control, and obstacle avoidance. The work presented here focuses on the control of a nonholonomic ground vehicle as it tracks a given path. A new path tracking technique called ''vector pursuit'' is presented. This new technique is based on the theory
NASA Astrophysics Data System (ADS)
Bhasker, H. P.; Thakur, Varun; Shivaprasad, S. M.; Dhar, S.
2015-06-01
The depth distribution of the transport properties as well as the temperature dependence of the low field magneto-conductance for c -axis oriented GaN nanowall network samples grown with different average wall-widths ({{t}\\text{av}} ) are investigated. Magneto-conductance recorded at low temperatures shows clear signature of weak localization effect in all samples studied here. The scattering mean free path {{l}e} and the phase coherence time {??} , are extracted from the magneto-conductance profile. Electron mobility estimated from {{l}e} is found to be comparable with those estimated previously from room temperature conductivity data for these samples, confirming independently the substantial mobility enhancement in these nanowalls as compared to bulk. Our study furthermore reveals that the high electron mobility region extends down to several hundreds of nanometer below the tip of the walls. Like mobility, phase coherence length ({{l}?} ) is found to increase with the reduction of the average wall width. Interestingly, for samples with lower values of the average wall width, {{l}?} is estimated to be as high as 60 ?m, which is much larger than those reported for GaN/AlGaN heterostructure based two-dimensional electron gas (2DEG) systems.
NASA Astrophysics Data System (ADS)
Habash Krause, L.; Gilchrist, B. E.; Nishikawa, K.; Williams, A.
2013-12-01
Relativistic 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 suborbital Reusable Launch Vehicle (sRLV) altitudes. The monoenergetic beam is modeled in cylindrical symmetry 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 bremmstrahlung deposition peaked at 25 km. This has implications for crew and passenger safety, especially with the growth of the space tourism industry that relies on sRLVs with a nominal apogee of 100 km. A survey of results covering the 1-100 MeV spectrum for the three altitude ranges of interest will be presented.
NASA Astrophysics Data System (ADS)
Wang, Zhiyuan; Wang, Xiaoxin; Liu, Jifeng
2014-12-01
Solar-blind ultraviolet (UV) detection refers to photon detection specifically in the wavelength range of 200 nm–320 nm. Without background noises from solar radiation, it has broad applications from homeland security to environmental monitoring. The most commonly used solid state devices for this application are wide band gap (WBG) semiconductor photodetectors (Eg > 3.5 eV). However, WBG semiconductors are difficult to grow and integrate with Si readout integrated circuits (ROICs). In this paper, we design a nanophotonic metal-oxide-semiconductor structure on Si for solar-blind UV detectors. Instead of using semiconductors as the active absorber, we use Sn nano-grating structures to absorb UV photons and generate hot electrons for internal photoemission across the Sn/SiO2 interfacial barrier, thereby generating photocurrent between the metal and the n-type Si region upon UV excitation. Moreover, the transported hot electron has an excess kinetic energy >3 eV, large enough to induce impact ionization and generate another free electron in the conduction band of n-Si. This process doubles the quantum efficiency. On the other hand, the large metal/oxide interfacial energy barrier (>3.5 eV) also enables solar-blind UV detection by blocking the less energetic electrons excited by visible photons. With optimized design, ˜75% UV absorption and hot electron excitation can be achieved within the mean free path of ˜20 nm from the metal/oxide interface. This feature greatly enhances hot electron transport across the interfacial barrier to generate photocurrent. The simple geometry of the Sn nano-gratings and the MOS structure make it easy to fabricate and integrate with Si ROICs compared to existing solar-blind UV detection schemes. The presented device structure also breaks through the conventional notion that photon absorption by metal is always a loss in solid-state photodetectors, and it can potentially be extended to other active metal photonic devices.
Calculations of stopping powers of 100 eV-30 keV electrons in 31 elemental solids
NASA Astrophysics Data System (ADS)
Tanuma, S.; Powell, C. J.; Penn, D. R.
2008-03-01
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 100eV and 30keV 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 10keV. 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 30keV, 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.
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.
Thermoalgebras and path integral
NASA Astrophysics Data System (ADS)
Khanna, F. C.; Malbouisson, A. P. C.; Malbouisson, J. M. C.; Santana, A. E.
2009-09-01
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 (S1)d×R topology is addressed.
pathChirp: Efficient Available Bandwidth Estimation for Network Paths
Cottrell, Les
2003-04-30
This paper presents pathChirp, a new active probing tool for estimating the available bandwidth on a communication network path. Based on the concept of ''self-induced congestion,'' pathChirp features an exponential flight pattern of probes we call a chirp. Packet chips offer several significant advantages over current probing schemes based on packet pairs or packet trains. By rapidly increasing the probing rate within each chirp, pathChirp obtains a rich set of information from which to dynamically estimate the available bandwidth. Since it uses only packet interarrival times for estimation, pathChirp does not require synchronous nor highly stable clocks at the sender and receiver. We test pathChirp with simulations and Internet experiments and find that it provides good estimates of the available bandwidth while using only a fraction of the number of probe bytes that current state-of-the-art techniques use.
NASA Astrophysics Data System (ADS)
Fetzer, Roman; Stadtmüller, Benjamin; Ohdaira, Yusuke; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Taira, Tomoyuki; Uemura, Tetsuya; Yamamoto, Masafumi; Aeschlimann, Martin; Cinchetti, Mirko
2015-02-01
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.
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
NASA Astrophysics Data System (ADS)
Hebert, Jeffrey Michael
This dissertation explores optimal path planning for air vehicles. An air vehicle exposed to illumination by a tracking radar is considered and the problem of determining an optimal planar trajectory connecting two prespecified points is addressed. An analytic solution yielding the trajectory minimizing the received radar energy reflected from the target is derived using the Calculus of Variations. Additionally, the related problem of an air vehicle tracked by a passive sensor is also solved. Using the insights gained from the single air vehicle radar exposure minimization problem, a hierarchical cooperative control law is formulated to determine the optimal trajectories that minimize the cumulative exposure of multiple air vehicles during a rendezvous maneuver. The problem of one air vehicle minimizing exposure to multiple radars is also addressed using a variational approach, as well as a sub-optimal minmax argument. Local and global optimality issues are explored. A novel decision criterion is developed determining the geometric conditions dictating when it is preferable to go between or around two radars. Lastly, an optimal minimum time control law is obtained for the target identification and classification mission of an autonomous air vehicle. This work demonstrates that an awareness of the consequences of embracing sub-optimal and non-globally optimal solutions for optimization problems, such as air vehicle path planning, is essential.
Internet's critical path horizon
NASA Astrophysics Data System (ADS)
Valverde, S.; Solé, R. V.
2004-03-01
Internet is known to display a highly heterogeneous structure and complex fluctuations in its traffic dynamics. Congestion seems to be an inevitable result of user's behavior coupled to the network dynamics and it effects should be minimized by choosing appropriate routing strategies. But what are the requirements of routing depth in order to optimize the traffic flow? In this paper we analyse the behavior of Internet traffic with a topologically realistic spatial structure as described in a previous study [S.-H. Yook et al., Proc. Natl Acad. Sci. USA 99, 13382 (2002)]. The model involves self-regulation of packet generation and different levels of routing depth. It is shown that it reproduces the relevant key, statistical features of Internet's traffic. Moreover, we also report the existence of a critical path horizon defining a transition from low-efficient traffic to highly efficient flow. This transition is actually a direct consequence of the web's small world architecture exploited by the routing algorithm. Once routing tables reach the network diameter, the traffic experiences a sudden transition from a low-efficient to a highly-efficient behavior. It is conjectured that routing policies might have spontaneously reached such a compromise in a distributed manner. Internet would thus be operating close to such critical path horizon.
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.
Collaborative Authoring of Walden's Paths
Li, Yuanling
2012-10-19
COLLABORATIVE AUTHORING OF WALDEN’S PATHS A Thesis by YUANLING LI Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE... August 2012 Major Subject: Computer Science Collaborative Authoring of Walden’s Paths Copyright 2012 Yuanling Li COLLABORATIVE AUTHORING OF WALDEN’S PATHS A Thesis by YUANLING LI...
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.
Path planning for virtual bronchoscopy.
Negahdar, Mohamadreza; Ahmadian, Alireza; Navab, Nassir; Firouznia, Kavous
2006-01-01
We have developed an automated path planning method, which enables virtual bronchoscopic 3D multidetector computed tomography (MDCT) image analysis and follow on image-guided bronchoscopy. The method fundamentals are novel combination of distance transformation and snake-based models. The computation time of our algorithm is faster than similar works and there were no missing or false branches in the final path of airways. The planned path is suitable for quantitative airway analysis and smooth virtual navigation. PMID:17946384
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.
Particle-in-cell simulations of electron dynamics in low pressure discharges with magnetic fields
NASA Astrophysics Data System (ADS)
Sydorenko, Dmytro
In modern low pressure plasma discharges, the electron mean free path often exceeds the device dimensions. Under such conditions the electron velocity distribution function may significantly deviate from Maxwellian, which strongly affects the discharge properties. The description of such plasmas has to be kinetic and often requires the use of numerical methods. This thesis presents the study of kinetic effects in inductively coupled plasmas and Hall thrusters carried out by means of particle-in-cell simulations. The important result and the essential part of the research is the development of particle-in-cell codes. An advective electromagnetic 1d3v particle-in-cell code is developed for modelling the inductively coupled plasmas. An electrostatic direct implicit 1d3v particle-in-cell code EDIPIC is developed for plane geometry simulations of Hall thruster plasmas. The EDIPIC code includes several physical effects important for Hall thrusters: collisions with neutral atoms, turbulence, and secondary electron emission. In addition, the narrow sheath regions crucial for plasma-wall interaction are resolved in simulations. The code is parallelized to achieve fast run times. Inductively coupled plasmas sustained by the external RF electromagnetic field are widely used in material processing reactors and electrodeless lighting sources. In a low pressure inductive discharge, the collisionless electron motion strongly affects the absorption of the external electromagnetic waves and, via. the ponderomotive force, the density profile. The linear theory of the anomalous skin effect based on the linear electron trajectories predicts a strong decrease of the ponderomotive force for warm plasmas. Particle-in-cell simulations show that the nonlinear modification of electron trajectories by the RF magnetic field partially compensates the effects of electron thermal motion. As a result, the ponderomotive force in warm collisionless plasmas is stronger than predicted by linear kinetic theory. A new model of secondary electron emission in a bounded plasma slab, allowing for emission due to the counter-propagating secondary electron beams, is developed. It is shown that in bounded plasmas the average energy of plasma bulk electrons is far less important for the space charge saturation of the sheath than it is in purely Maxwellian plasmas. A new regime with relaxation oscillations of the sheath has been identified in simulations. Recent experimental studies of Hall thrusters indirectly support the simulation results with respect to the electron temperature saturation and the channel width effect on the thruster discharge. (Abstract shortened by UMI.)
Shortest Path Algorithm What is the Shortest Path Problem?
Razak, Saquib
at vertex B: The resulting vertex-weighted graph is: #12;Data structures required · The implementation. · The method returns a vertex-weighted Digraph from which the shortest path from s to any vertex can be found;What is the shortest path problem? · In an edge-weighted graph, the weight of an edge measures the cost
Path detection in video surveillance
Dimitrios Makris; Tim Ellis
2002-01-01
This paper addresses the problem of automatically extracting frequently used pedestrian pathways from video sequences of natural outdoor scenes. Path models are learnt from the accumulation of trajectory data over long time periods, and can be used to augment the classification of subseq uent track data. In particular, labelled paths provide an efficient means for compressing the trajectory data for
Using Runtime Paths for Macroanalysis
Mike Y. Chen; Emre Kiciman; Anthony Accardi; Armando Fox; Eric A. Brewer
2003-01-01
We introduce macroanalysis, an approach used to infer the high-level properties of dynamic, distributed systems, and an indispensable tool when faced with tasks where lo- cal context and individual component details are insuffi- cient. We present a new methodology, runtime path anal- ysis, where paths are traced through software components and then aggregated to understand global system behav- ior via
Path Analysis: A Brief Introduction.
ERIC Educational Resources Information Center
Carducci, Bernardo J.
Path analysis is presented as a technique that can be used to test on a priori model based on a theoretical conceptualization involving a network of selected variables. This being an introductory source, no previous knowledge of path analysis is assumed, although some understanding of the fundamentals of multiple regression analysis might be…
NASA Astrophysics Data System (ADS)
Su, C. W.; Huang, M. S.; Tsai, T. H.; Chang, S. C.
2012-12-01
Is crystalline ZnO(0 0 0 1¯) O-face surface believed to be enriched by Zn atoms? This study may get the answer. We proposed a simplified model to simulate surface concentration ratio on (0 0 0 1¯)-O or (0 0 0 1)-Zn surface based on the hard-sphere model. The simulation ratio was performed by integrating electron signals from the assumed Auger emission, in which the electron mean free path and relative atomic layer arrangements inside the different polarity ZnO crystal surface were considered as relevant parameters. After counting more than 100 experimental observations of Zn/O ratios, the high frequency peak ratio was found at around 0.428, which was near the value predicted by the proposed model using the IMFP database. The ratio larger than the peak value corresponds to that observed in the annealed samples. A downward trend of the ratio evaluated on the post-sputtering sample indicates the possibility of a Zn-enriched phase appearing on the annealed O-face surface. This phenomenon can further elucidate the O-deficiency debate on most ZnO materials.
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.
Hard paths, soft paths or no paths? Cross-cultural perceptions of water solutions
NASA Astrophysics Data System (ADS)
Wutich, A.; White, A. C.; Roberts, C. M.; White, D. D.; Larson, K. L.; Brewis, A.
2013-06-01
In this study, we examine how development status and water scarcity shape people's perceptions of "hard path" and "soft path" water solutions. Based on ethnographic research conducted in four semi-rural/peri-urban sites (in Bolivia, Fiji, New Zealand, and the US), we use content analysis to conduct statistical and thematic comparisons of interview data. Our results indicate clear differences based on development status and, to a lesser extent, water scarcity. People in less developed sites were more likely to suggest hard path solutions, less likely to suggest soft path solutions, and more likely to see no path to solutions than people in more developed sites. Thematically, people in less developed sites envisioned solutions that involve small-scale water infrastructure and decentralized, community based solutions, while people in more developed sites envisioned solutions that involve large-scale infrastructure and centralized, regulatory water solutions. People in water-scarce sites were less likely to suggest soft path solutions and more likely to see no path to solutions (but no more likely to suggest hard path solutions) than people in water-rich sites. Thematically, people in water-rich sites seemed to perceive a wider array of unrealized potential soft path solutions than those in water-scarce sites. On balance, our findings are encouraging in that they indicate that people are receptive to soft path solutions in a range of sites, even those with limited financial or water resources. Our research points to the need for more studies that investigate the social feasibility of soft path water solutions, particularly in sites with significant financial and natural resource constraints.
Hard paths, soft paths or no paths? Cross-cultural perceptions of water solutions
NASA Astrophysics Data System (ADS)
Wutich, A.; White, A. C.; White, D. D.; Larson, K. L.; Brewis, A.; Roberts, C.
2014-01-01
In this study, we examine how development status and water scarcity shape people's perceptions of "hard path" and "soft path" water solutions. Based on ethnographic research conducted in four semi-rural/peri-urban sites (in Bolivia, Fiji, New Zealand, and the US), we use content analysis to conduct statistical and thematic comparisons of interview data. Our results indicate clear differences associated with development status and, to a lesser extent, water scarcity. People in the two less developed sites were more likely to suggest hard path solutions, less likely to suggest soft path solutions, and more likely to see no path to solutions than people in the more developed sites. Thematically, people in the two less developed sites envisioned solutions that involve small-scale water infrastructure and decentralized, community-based solutions, while people in the more developed sites envisioned solutions that involve large-scale infrastructure and centralized, regulatory water solutions. People in the two water-scarce sites were less likely to suggest soft path solutions and more likely to see no path to solutions (but no more likely to suggest hard path solutions) than people in the water-rich sites. Thematically, people in the two water-rich sites seemed to perceive a wider array of unrealized potential soft path solutions than those in the water-scarce sites. On balance, our findings are encouraging in that they indicate that people are receptive to soft path solutions in a range of sites, even those with limited financial or water resources. Our research points to the need for more studies that investigate the social feasibility of soft path water solutions, particularly in sites with significant financial and natural resource constraints.
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 for reasoning about truncated paths, and analyze its characteristics. 1 Introduction Traditional ltl semantics
Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Path Testing
Mousavi, Mohammad
Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Path Testing Mohammad Mousavi Eindhoven University of Technology, The Netherlands Software Testing, 2012 Mousavi: Path Testing #12;Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Outline Structural
Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Path Testing
Mousavi, Mohammad
Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Path Testing Mohammad Mousavi Eindhoven University of Technology, The Netherlands Software Testing, 2013 Mousavi: Path Testing #12;Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Outline Structural
British Pathe Newsreels Online
NSDL National Science Digital Library
2002-01-01
British Pathe, one of the oldest media companies in the world, recently made available its entire 3500-hour film archive, covering "news, sport, social history and entertainment from 1896 to 1970." At the Web site, users can search by keyword or try out advanced search, if details such as reel numbers or exact titles are known. Casual users may prefer the "Lucky Dip" search, which provides a random selection of films to see. After a search returns a hit list of films, choices include "Preview Film: a page of stills, with a textual description of the clip;" "Download Now: a free, low resolution clip;" or "Add to basket, to purchase higher resolutions of the film." (A rate card giving prices for low and high resolution clips is provided.) One hint for first-time users, though: if files do not seem to download properly, check your email, because you will be sent the URL to retrieve your film. After just a bit of finagling on our first visit, we watched the Beatles at a water-skiing show, Charlie Chaplin, and Sir Ernest Shackleton and his sled dogs photographed in 1916 on returning from their Antarctic expedition.
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.
Coherent state path integral and Langevin equation of interacting fermions
B. Mieck
2002-01-01
Interacting fermions, electrons and holes in a semiconductor, are coupled to a thermal reservoir of bosons which yield the fluctuating noise. We use a coherent state path integral formulation on the time contour for non-equilibrium systems in terms of anticommuting variables which replace the fermionic creation- and annihilation operators in the time development operator. An auxiliary commuting field ?x(tp), defined
Evaluating go-path measurements to determine faulty components \\
Larry V. Kirkland; Nathan Wilson; Floyd Berghout
2004-01-01
This paper describes the use of multiple go-path measurements, in combination with algorithmic test sequences, to aid in improving test efficiency and accuracy and diagnostics. As an electronic device or circuit is tested, the output of the unit under tests (UUT) may be considered as a function of the input. Through the use of multiple tests designed to exercise system
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).
Hydrogen molecule ion: Path-integral Monte Carlo approach
I. Kylänpää; M. Leino; T. T. Rantala
2007-01-01
The 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 nonadiabatic simulations, and inspecting projections of the full three-body dynamics onto the adiabatic Born-Oppenheimer approximation. Coupling of the electron and nuclear quantum dynamics is clearly seen.
Pon, Allison; Jewison, Timothy; Su, Yilu; Liang, Yongjie; Knox, Craig; Maciejewski, Adam; Wilson, Michael; Wishart, David S.
2015-01-01
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
Two-path solid-state interferometry using ultra-subwavelength two-dimensional plasmonic waves
Ham, Donhee
Two-path solid-state interferometry using ultra-subwavelength two-dimensional plasmonic waves Kitty at microwave frequencies. Two plasmonic paths are defined with GaAs/AlGaAs 2D electron gas 80 nm below, we develop a high-resolution 2D plasmonic inter- ferometer at microwave frequencies
Design and realization of expressway vehicle path recognition and ETC system based on RFID
Zhihui Feng; Yanjie Zhu; Pengtao Xue; Mingjie Li
2010-01-01
With the development of expressway, the vehicle path recognition based on RFID is designed and an Electronic Toll Collection system of expressway will be implemented. It uses a passive RFID tag as carrier to identify Actual vehicle path in loop road. The ETC system will toll collection without parking, also census traffic flow and audit road maintenance fees. It is
Energy-loss- and thickness-dependent contrast in atomic-scale electron energy-loss spectroscopy
Tan, Haiyan; Xin, Huolin L.; Zhu, Ye; Dwyer, Christian
2014-12-01
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). Atmore »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.« less
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.
Learning for informative path planning
Park, Sooho, S.M. Massachusetts Institute of Technology
2008-01-01
Through the combined use of regression techniques, we will learn models of the uncertainty propagation efficiently and accurately to replace computationally intensive Monte- Carlo simulations in informative path planning. ...
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
An introduction to critical paths.
Coffey, Richard J; Richards, Janet S; Remmert, Carl S; LeRoy, Sarah S; Schoville, Rhonda R; Baldwin, Phyllis J
2005-01-01
A critical path defines the optimal sequencing and timing of interventions by physicians, nurses, and other staff for a particular diagnosis or procedure. Critical paths are developed through collaborative efforts of physicians, nurses, pharmacists, and others to improve the quality and value of patient care. They are designed to minimize delays and resource utilization and to maximize quality of care. Critical paths have been shown to reduce variation in the care provided, facilitate expected outcomes, reduce delays, reduce length of stay, and improve cost-effectiveness. The approach and goals of critical paths are consistent with those of total quality management (TQM) and can be an important part of an organization's TQM process. PMID:15739581
Scattering theory with path integrals
Rosenfelder, R. [Particle Theory Group, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland)] [Particle Theory Group, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland)
2014-03-15
Starting from well-known expressions for the T-matrix and its derivative in standard nonrelativistic potential scattering, I rederive recent path-integral formulations due to Efimov and Barbashov et al. Some new relations follow immediately.
Shortest Paths in Euclidean Graphs
Robert Sedgewick; Jeffrey Scott Vitter
1986-01-01
We analyze a simple method for finding shortest paths inEuclidean graphs (where vertices are points in a Euclidean space and edge weights are Euclidean distances between points). For many graph\\u000a models, the average running time of the algorithm to find the shortest path between a specified pair of vertices in a graph\\u000a withV vertices andE edges is shown to beO(V)
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.
Quantum Mechanics: Sum Over Paths
NSDL National Science Digital Library
Taylor, Edwin F.
Created by Edwin F. Taylor a former professor at the Department of Physics at the Massachusetts Institute of Technology, this material describes methods of presenting quantum mechanics using the path-integral formulation. Included are links to a paper and presentation outlining the method, software to simulate the path integrals, and student workbook materials. This course has been used for introducing quantum physics to high school teachers.
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.
A combinatorial approach to the electron correlation problem Alex J. W. Thom and Ali Alavia
Alavi, Ali
A combinatorial approach to the electron correlation problem Alex J. W. Thom and Ali Alavia for the Monte Carlo evaluation of the energy of a correlated electronic system. The path-integral expression electrons.1 In its "real-space imaginary-time" formulation, the path integral represents a sum over paths
On hallucinated garden paths UC San Diego
On hallucinated garden paths Roger Levy UC San Diego Department of Linguistics 2010 LSA Annual., 1995) #12;Garden-pathing in incremental parsing · Garden-path sentence a consequence of incrementality recent examples don't match this definition · Tabor et al. (2004): garden-paths on continuous substrings
Cooperative organic mine avoidance path planning
Christopher B. McCubbin; Christine D. Piatko; Adam V. Peterson; Creighton R. Donnald; David Cohen
2005-01-01
The JHU\\/APL Path Planning team has developed path planning techniques to look for paths that balance the utility and risk associated with different routes through a minefield. Extending on previous years' efforts, we investigated real-world Naval mine avoidance requirements and developed a tactical decision aid (TDA) that satisfies those requirements. APL has developed new mine path planning techniques using graph
Graphs and Paths Page 1 Introduction
Allan, Vicki H.
? For example: I want to travel every bike path in Logan (assuming they had any ) but I don't want to everGraphs and Paths Page 1 Chapter 9 Graphs Introduction What are some characteristics of a binary travel on the same path twice. Can I begin at my home, visit every path, and then return? The data
Complexity of path discovery game problems
Hiroaki Tohyama; Akeo Adachi
2000-01-01
In this paper path discovery games are introduced, and complexity of the game problems is studied. It is shown that the path discovery game problem played on directed graphs is PSPACE-complete, and the path discovery game problem played on undirected graphs is in the class SSPACE(nlogn). Moreover, it is shown that the acyclic path discovery game problems played on directed
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.
A linearized Fokker-Planck study of ion-eigenmodes in an unmagnetized pair-ion-electron plasma
Zhao Bin; Zheng Jian [CAS Key Laboratory of Basic Plasma Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China) and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)
2008-08-15
Two kinds of ion-eigenmodes in an unmagnetized pair-ion-electron plasma, pair-ion-acoustic waves (PIAWs) and ion-Langmuir waves (ILWs), are investigated with Fokker-Planck description. The linearized negative- and positive-ion Fokker-Planck equations and linearized electron Vlasov equation are solved numerically as an eigenvalue problem. The frequencies and damping rates of PIAWs and ILWs are presented as a function of k{lambda}, k{lambda}{sub D}, T{sub e}/T, n{sub -}/n{sub +}, where k is the wave number, {lambda} is the mean-free path of the positive ion, {lambda}{sub D} is the positive ion Debye length, T{sub e} and T are electron and ion temperature, and n{sub -}/n{sub +} is the ratio of negative ion density to positive ion density. It is found that the dispersion relations of PIAWs and ILWs are sensitive to the strength of ion-ion collisions. As k{lambda} increases, it is shown that PIAWs evolve into ILWs smoothly at small negative ion concentration. For large n{sub -}/n{sub +}, PIAWs and ILWs, respectively, exist in a strong-collisional and rare-collisional region, and coexist in the intermediate regime at about k{lambda}{approx}1. For comparison, hydrodynamic description and Vlasov description are also discussed. When the Landau damping is negligible, the two-fluid hydrodynamic description can give good results for ILWs if the friction forces between the negative and positive ions are included.
NASA Astrophysics Data System (ADS)
Ishii, Katsuhiro; Iwai, Toshiaki; Uozumi, Jun; Asakura, Toshimitsu
1998-07-01
A free-path-length distribution function (FPDF) of multiply backscattered light is theoretically derived for a fractal aggregate of particles. An effective mean-free path-length l D is newly introduced as a measure of randomness analogous with a homogeneously random medium. We confirm the validity of the FPDF by demonstrating agreement between the dimensions designed for a particle distribution generated by a random walk based on the derived FPDF and estimated by the radius of gyration method. The FPDF is applied to Monte Carlo simulations for copolarized multiply backscattered light from the fractal aggregate of particles. It is shown that a copolarized intensity peak of enhanced backscattering in the far field decreases in accordance with 2 D and has an angular width of l D . This spatial feature of the backscattering enhancement corresponds to that of the copolarized intensity peak produced from a homogeneously random medium with a dimension of D 3 . As a result, the validity of the model for the fractal structure of particle aggregates and the applicability of the derived FPDF are confirmed by the numerical results.
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
mirror detector with FADC type electronics. The UV sensitive camera of each mirror holds 256, the exponential index of the deep part of the Xmax distribu- tion was related to the proton mean free path
. The effective mean free path of electrons () in a CNT is the combined effect of various acoustic and optical Barbara, CA 93106, USA *Center for Microwave and RF Technology, Shanghai Jiao Tong University, Shanghai
Exploring Carbon Nanotube Bundle Global Interconnects for Chip Multiprocessor Applications
Pasricha, Sudeep
. Conventional copper (Cu) global interconnects have become increasingly susceptible to electromigration at high owing to longer electron mean free path (MFP) lengths in the micrometer range, compared to nanometer
Revealing quantum path details in high-field physics
NASA Astrophysics Data System (ADS)
Kolliopoulos, G.; Bergues, B.; Schröder, H.; Carpeggiani, P. A.; Veisz, L.; Tsakiris, G. D.; Charalambidis, D.; Tzallas, P.
2014-07-01
The fundamental mechanism underlying harmonic emission in the strong-field regime is governed by tunnel ionization of the atom, followed by the motion of the electron wave packet in the continuum, and finally by its recollision with the atomic core. Due to the quantum nature of the process, the properties of the electron wave packet strongly correlate with those of the emitted radiation. Here, by spatially resolving the interference pattern generated by overlapping the harmonic radiation emitted by different interfering electron quantum paths, we have succeeded in unravelling the intricacies associated with the recollision process. This has been achieved by mapping the spatial extreme-ultraviolet (EUV)-intensity distribution onto a spatial ion distribution, produced in the EUV focal area through the linear and nonlinear processes of atoms. By in situ manipulation of the intensity-dependent motion of the electron wave packets, we have been able to directly measure the difference between the harmonic emission times and electron path lengths resulting from different electron trajectories. Due to the high degree of accuracy that the present approach provides, we have been able to demonstrate the quantum nature of the recollision process. This is done by quantitatively correlating the photoemission time and the electron quantum path-length differences, taking into account the energy-momentum transfer from the driving laser field into the system. This information paves the way for electron-photon correlation studies at the attosecond time scale, while it puts the recollision process from the semiclassical prospective into a full quantum-mechanical context.
Evaluation of steam path audits
Caudill, M.B. [Tri-State Generation and Transmission Association, Inc., Montrose, CO (United States); Griebenow, R.D. [SAIC, Huntersville, NC (United States)
1995-06-01
Tri-State Generation and Transmission association is the operating agent for the 1350 megawatt Craig Generating Station, located in northwestern Colorado. Tri-State has recently incorporated turbine steam path audits into their aggressive performance improvement program. The intent of the audits are to quantify and attain the most cost effective increase in turbine performance as a result of a major outage. Valuable information about performance losses in the turbine has been obtained from steam path audits conducted on the three Craig Units. However, accurate audit results often depend on the quality of measurements and the experience of the auditor. Without a second method to verify the results of a steam path audit, repairs might be performed on a non-cost effective basis, or significant performance degradations might be overlooked. In addition, an inaccurate audit may lead to erroneous expectations for performance improvements resulting from the maintenance performed during the outage.
Phase Diagram of Optimal Paths
Alex Hansen; Janos Kertesz
2004-02-17
We show that choosing appropriate distributions of the randomness, the search for optimal paths links diverse problems of disordered media like directed percolation, invasion percolation, directed and non-directed spanning polymers. We also introduce a simple and efficient algorithm, which solves the d-dimensional model numerically in order N^(1+d_f/d) steps where d_f is the fractal dimension of the path. Using extensive simulations in two dimensions we identify the phase boundaries of the directed polymer universality class. A new strong-disorder phase occurs where the optimum paths are self-affine with parameter-dependent scaling exponents. Furthermore, the phase diagram contains directed and non-directed percolation as well as the directed random walk models at specific points and lines.
Path Integral Monte Carlo Methods for Fermions
NASA Astrophysics Data System (ADS)
Ethan, Ethan; Dubois, Jonathan; Ceperley, David
2014-03-01
In general, Quantum Monte Carlo methods suffer from a sign problem when simulating fermionic systems. This causes the efficiency of a simulation to decrease exponentially with the number of particles and inverse temperature. To circumvent this issue, a nodal constraint is often implemented, restricting the Monte Carlo procedure from sampling paths that cause the many-body density matrix to change sign. Unfortunately, this high-dimensional nodal surface is not a priori known unless the system is exactly solvable, resulting in uncontrolled errors. We will discuss two possible routes to extend the applicability of finite-temperatue path integral Monte Carlo. First we extend the regime where signful simulations are possible through a novel permutation sampling scheme. Afterwards, we discuss a method to variationally improve the nodal surface by minimizing a free energy during simulation. Applications of these methods will include both free and interacting electron gases, concluding with discussion concerning extension to inhomogeneous systems. Support from DOE DE-FG52-09NA29456, DE-AC52-07NA27344, LLNL LDRD 10- ERD-058, and the Lawrence Scholar program.
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.
Marocchino, A.; Atzeni, S.; Schiavi, A. [Dipartimento SBAI, Università di Roma “La Sapienza” and CNISM, Roma 00161 (Italy)] [Dipartimento SBAI, Università di Roma “La Sapienza” and CNISM, Roma 00161 (Italy)
2014-01-15
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.
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.
Optimized Fermion Path Integral Monte Carlo
NASA Astrophysics Data System (ADS)
Khairallah, Saad; Draeger, Erik; Shumway, John
2011-03-01
We present the latest developments in a new path integral Monte Carlo method for continuum fermions. The new formalism uses the maximum entropy principle to map the approximated density matrix to an effective bosonic problem. Verification and performance results are presented for both free electrons and compressed hydrogen, showing accurate results with a substantial performance gain over reference slice fPIMC, particularly at lower temperatures where ergodicity issues can significantly impact sampling efficiency. The limiting approximations in the method are identified and discussed, and suggest the need for improved nodal models. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Alternative Nuclear Paths To 2050
Ivan Vera; Evelyne Bertel; Geoffrey Stevens
he circumstances surrounding nuclear power worldwide and the importance that may be given to issues affecting its future development point toward very different alternative paths over the next 50 years. Economic deregulation, lack of competitiveness in some countries, negative public perception and concerns about waste issues suggest that nuclear power might decrease progressively with a potential phase-out of the technology
Gilbert, Matthew
NPRE at Illinois Three Paths Students choose from three concentrations: · Plasma and Fusion · Power,312,815 Research Facilities · Beckman Institute (beckman.illinois.edu) · Center for Plasma-Material Interactions (cpmi.illinois.edu) · Institute for Genomic Biology (igb.illinois.edu) · Micro and Nanotechnology
Moldovan employment relations: “path dependency”?
Claudio Morrison; Richard Croucher
2010-01-01
Purpose – The paper aims to examine the theory that trade unions' functions in a transitional economy are characterised by “path dependency”. Design\\/methodology\\/approach – The research is based on case studies of employment relations in enterprises operating in Moldova. The approach is realist (critical materialism). An ethnographic approach is taken to analysing social relations in three locally and foreign-owned companies
Noncommutative Geometry and Path Integrals
Mikhail Kapranov
2006-01-01
\\u000a We argue that there should exist a “noncommutative Fourier transform” which should identify functions of noncommutative variables\\u000a (say, of matrices of indeterminate size) and ordinary functions or measures on the space of paths. Some examples are considered.
WHEELCHAIR NEGOTIABLE PATHS ACCESSIBLE ENTRANCE
Huang, Jianyu
NEGOTIABLE PATHS ACCESSIBLE ENTRANCE ACCESSIBLE PARKING SPACE ELEVATOR ACCESS KEY PPUBLIC PARKING BUS STOP ENTRANCE ACCESSIBLE PARKING SPACE ELEVATOR ACCESS KEY PPUBLIC PARKING BUS STOP (EAGLE ESCORT) BLUE LIGHT SPACE ELEVATOR ACCESS KEY PPUBLIC PARKING BUS STOP (EAGLE ESCORT) BLUE LIGHT EMERGENCY PHONE #12
Acyclic orientations with path constraints
Rosa M. V. Figueiredo; Valmir C. Barbosa; Nelson Maculan; Cid C. Souza
2005-01-01
Many well-known combinatorial optimization problems can be stated over the set of acyclic orientations of an undirected graph. For example, acyclic orientations with certain diameter constraints are closely related to the optimal solutions of the vertex coloring and frequency assignment problems. In this paper we introduce a linear programming formulation of acyclic orientations with path constraints, and discuss its use
SSME propellant path leak detection
NASA Technical Reports Server (NTRS)
Crawford, Roger; Shohadaee, Ahmad Ali
1989-01-01
The complicated high-pressure cycle of the space shuttle main engine (SSME) propellant path provides many opportunities for external propellant path leaks while the engine is running. This mode of engine failure may be detected and analyzed with sufficient speed to save critical engine test hardware from destruction. The leaks indicate hardware failures which will damage or destroy an engine if undetected; therefore, detection of both cryogenic and hot gas leaks is the objective of this investigation. The primary objective of this phase of the investigation is the experimental validation of techniques for detecting and analyzing propellant path external leaks which have a high probability of occurring on the SSME. The selection of candidate detection methods requires a good analytic model for leak plumes which would develop from external leaks and an understanding of radiation transfer through the leak plume. One advanced propellant path leak detection technique is obtained by using state-of-the-art technology infrared (IR) thermal imaging systems combined with computer, digital image processing, and expert systems for the engine protection. The feasibility of IR leak plume detection is evaluated on subscale simulated laboratory plumes to determine sensitivity, signal to noise, and general suitability for the application.
Fano resonances in electronic transport through a single-electron transistor
J. Göres; D. Goldhaber-Gordon; S. Heemeyer; M. A. Kastner; Hadas Shtrikman; D. Mahalu; U. Meirav
2000-01-01
We have observed asymmetric Fano resonances in the conductance of a single-electron transistor resulting from interference between a resonant and a nonresonant path through the system. The resonant component shows all the features typical of single-electron addition to the confined droplet within the transistor, but the origin of the nonresonant path is unclear. A feature of this experimental system, compared
Electronics 2010: A New Systems Approach to Teaching Electronics
NSDL National Science Digital Library
These are the slides for the MATEC NetWorks Webinar that was held on May 9, 2008 for Electronics 2010: A New Systems Approach to Teaching Electronics. Presented by Tom McGlew, a thirty year veteran to the electronics field, the presentation discusses new paths for electronics and the changing role of the technician, and the implications for curriculum. The goals of the eSyst project are also discussed, the needed curriculum changes and updates, and ideas for assessment.
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 \\
Path-Based Failure and Evolution Management
Mike Y. Chen; Anthony Accardi; Emre Kiciman; David A. Patterson; Armando Fox; Eric A. Brewer
2004-01-01
We present a new approach to managing failures and evolution in large, complex distributed systems using runtime paths. We use the paths that requests follow as they move through the system as our core abstraction, and our \\
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.
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.
Hydrogen molecule ion: Path integral Monte Carlo approach
I. Kylanpaa; M. Leino; T. T. Rantala
2008-01-01
Path integral Monte Carlo approach is used to study the coupled quantum dynamics of the electron\\u000d\\u000aand nuclei in hydrogen molecule ion. The coupling effects are demonstrated by comparing differences\\u000d\\u000ain adiabatic Born–Oppenheimer and non-adiabatic simulations, and inspecting projections of the\\u000d\\u000afull three-body dynamics onto adiabatic Born–Oppenheimer approximation.\\u000d\\u000aCoupling of electron and nuclear quantum dynamics is clearly seen. Nuclear pair
Kanematsu, Nobuyuki; Inaniwa, Taku; Koba, Yusuke [Department of Accelerator and Medical Physics, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555 (Japan)
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.
Configuration Path Integral Monte Carlo
NASA Astrophysics Data System (ADS)
Bonitz, Michael; Schoof, Tim; Groth, Simon; Filinov, Alexei; Hochstuhl, David
2011-10-01
A novel path integral Monte Carlo (PIMC) approach for correlated many-particle systems with arbitrary pair interaction in continuous space at low temperatures is presented. It is based on a representation of the N-particle density operator in a basis of (anti-)symmetrized N-particle states (``configurations'' of occupation numbers). The path integral is transformed into a sum over trajectories with the same topology and, finally, the limit of M to infinity, (M is the number of high-temperature factors), is analytically performed. This yields exact expressions for the thermodynamic quantities and allows to perform efficient simulations for fermions at low temperature and weak to moderate coupling. Our method is applicable to dense quantum plasmas in the regime of strong degeneracy where conventional PIMC, e.g., fails due to the fermion sign problem. This work is supported by the Deutsche Forschungsgemeinschaft.
Path Planning for Autonomous Underwater Vehicles
Clément Pêtrès; Yan Pailhas; Pedro Patrón; Yvan R. Petillot; Jonathan Evans
2007-01-01
Efficient path planning algorithms are a crucial issue for modern autonomous underwater vehicles. Classical path planning algorithms in artificial intelligence are not designed to deal with wide continuous environments prone to currents. We present a novel Fast Marching based approach to address the following issues. First, we develop an algorithm we call FM* to efficiently extract a continuous path from
Quantifying the Causes of Path Inflation
Neil Spring; Ratul Mahajan; Thomas Anderson
2003-01-01
Researchers have shown that the Internet exhibits path inflation - end-to-end paths can be significantly longer than necessary. We present a trace-driven study of 65 ISPs that characterizes the root causes of path inflation, namely topology and routing policy choices within an ISP, between pairs of ISPs, and across the global Inter- net. To do so, we develop and validate
Disjoint Paths in Densely Embedded Graphs
Jon M. Kleinberg; Eva Tardoss
1995-01-01
We consider the following maximum disjoint paths problem (mdpp). We are given a large network, and pairs of nodes that wish to communicate over paths through the network — the goal is to simultaneously connect as many of these pairs as possible in such a way that no two communication paths share an edge in the network. This classical problem
Continuous Path Planning with Multiple Constraints
Mitchell, Ian
paths for unmanned aerial vehicles through enviroments with varying levels of threat. Paths an algorithm which generates paths whose costs lie on the Pareto optimal surface for each possible destina destination can be rapidly evaluated. To handle constraints, we sample the Pareto optimal surface looking
Circular Shortest Path on Regular Grids
Changming Sun; Stefano Pallottino Csiro
2002-01-01
Shortest path algorithms have been used for a number of applications such as crack detection, road orlinear feature extraction on images. There are applications where the starting and ending positionsof the shortest path needs to be constrained. In this paper, we presents several new algorithms forthe extraction of a circular shortest path within an image such that the starting and
Path and Trajectory Diversity Theory and Algorithms
Branicky, Michael S.
Path and Trajectory Diversity Theory and Algorithms Ross A. Knepper International Conference. Kuffner #12;R.A. Knepper Path and Trajectory Diversity 2 Applications [Knepper and Mason, ISER, 2008][Lau and Trajectory Diversity 3 Not all path sets are created equal Introduction Conclusion
Scripted documents: a hypermedia path mechanism
Polle T. ZelIweger
1989-01-01
The concept of a path, or ordered traversal of some links in a hypertext, has been a part of the hypertext notion from its early formation. Although paths can help to solve two major problems with hypertext systems, namely user disorientation and high cognitive overhead for users, their value has not been recognized. Paths can also provide the backbone for
Code of Federal Regulations, 2011 CFR
2011-01-01
...surface to the end of the takeoff path. (d) The takeoff path must be determined by a continuous demonstrated takeoff or by synthesis from segments. If the takeoff path is determined by the segmental method— (1) The segments must be clearly...
Removing False Paths from Combinational Modules 1
Yuji Kukimoto; Robert K. Brayton
The existence of false paths complicates the task of accurate tim- ing analysis significantly. A technique to remove false paths from a combinational circuit without degrading its performance h as a prac- tical value since topological timing analysis is then good e nough to estimate the performance of false-path-free circuits accu rately. One can think of the KMS algorithm (1)
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
Chip layout optimization using critical path weighting
A. E. Dunlop; V. D. Agrawal; D. N. Deutsch; M. F. Jukl; P. Kazak
1988-01-01
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
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.
Lévy flights over quantum paths
NASA Astrophysics Data System (ADS)
Laskin, Nick
2007-02-01
An impact of integration over the paths of the Lévy flights on the quantum mechanical kernel has been studied. Analytical expression for a free particle kernel has been obtained in terms of the Fox H-function. A new equation for the kernel of a particle in the box has been found. New general results include the well known quantum formulae for a free particle kernel and particle in box kernel.
Acyclic Orientations with Path Constraints
Rosa M. V. Figueiredo; Valmir C. Barbosa; Nelson Maculan; Cid C. de Souza
2008-01-01
Many well-known combinatorial optimization problems can be stated over the\\u000aset of acyclic orientations of an undirected graph. For example, acyclic\\u000aorientations with certain diameter constraints are closely related to the\\u000aoptimal solutions of the vertex coloring and frequency assignment problems. In\\u000athis paper we introduce a linear programming formulation of acyclic\\u000aorientations with path constraints, and discuss its use
Imaging Electron Interferometer
NASA Astrophysics Data System (ADS)
Bleszynski, A. C.; Aidala, K. E.; LeRoy, B. J.; Westervelt, R. M.; Heller, E. J.; Maranowski, K. D.; Gossard, A. C.
2005-06-01
An imaging electron interferometer was created in a two-dimensional electron gas (2DEG) using a liquid-He cooled scanning probe microscope (SPM). Electron waves emitted from a quantum point contact (QPC) return to the QPC along two paths: reflection from a concave mirror formed by a gate, and backscattering from the depleted disc underneath the charged SPM tip. Interference of these waves when they return to the QPC produces strong interference fringes in images of electron flow. A quantum phase shifter is formed by moving the mirror via its gate voltage — the fringes move a corresponding amount. The coherent fringes are robust to thermal averaging when the lengths of the two paths are within lT = ?vF/?kBT of each other.
A. Farrel
Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering (TE) Label Switched Paths (LSPs) may be computed by Path Computation Elements (PCEs). Where the TE LSP crosses multiple domains, such as Autonomous Systems (ASes), the path may be computed by multiple PCEs that cooperate, with each responsible for computing a segment of the path. However, in some cases (e.g.,
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.
Harmonic-based gain compensation method in optic sensors with separate light paths.
Perciante, César Daniel; Ferrari, José A; Garbusi, Eugenio
2003-06-10
We describe a method for the compensation of gain unbalance in optical sensors with separate light path that involve two separate detection and conditioning electronic devices. The method is based on the digital measurement of harmonics of the output intensities from each path by means of the fast Fourier transform algorithm. The quotient of the amplitude of harmonics allows us to calculate the unbalance between paths and to compensate for it. In particular, this method can be applied electric power and current sensors that use Faraday and Pockels cells to measure current and voltage, respectively. PMID:12816322
Reduction of secondary-electron yields by collective electric fields within metals
Joseph E. Borovsky; David M. Suszcynsky
1991-01-01
A fast ion passing through a metal target drives electrons out of its path by means of Coulomb scattering. Some of these electrons escape the target and are denoted as secondary electrons. The rapid displacement of electrons from the ion's path produces a charge separation in the metal, which gives rise to an electric field in the wake of the
Arithmetic area for m planar Brownian paths
NASA Astrophysics Data System (ADS)
Desbois, Jean; Ouvry, Stéphane
2012-05-01
We pursue the analysis made in Desbois and Ouvry (2011 J. Stat. Mech. P05024) on the arithmetic area enclosed by m closed Brownian paths. We pay particular attention to the random variable Sn1, n2,..., nm(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,..., and nm times by path m. Various results are obtained in the asymptotic limit m\\to \\infty . A key observation is that, since the paths are independent, one can use in the m-path case the SLE information, valid in the one-path case, on the zero-winding sectors arithmetic area.
Mechanics of the crack path formation
NASA Technical Reports Server (NTRS)
Rubinstein, Asher A.
1991-01-01
A detailed analysis of experimentally obtained curvilinear crack path trajectories formed in a heterogeneous stress field is presented. Experimental crack path trajectories were used as data for the numerical simulations, recreating the actual stress field governing the development of the crack path. Thus, the current theories of crack curving and kinking could be examined by comparing them with the actual stress field parameters as they develop along the experimentally observed crack path. The experimental curvilinear crack path trajectories were formed in the tensile specimens with a hole positioned in the vicinity of a potential crack path. The numerical simulation, based on the solution of equivalent boundary value problems with the possible perturbations of the crack path, is presented.
Mechanics of the crack path formation
NASA Technical Reports Server (NTRS)
Rubinstein, Asher A.
1989-01-01
A detailed analysis of experimentally obtained curvilinear crack path trajectories formed in a heterogeneous stress field is presented. Experimental crack path trajectories were used as data for numerical simulations, recreating the actual stress field governing the development of the crack path. Thus, the current theories of crack curving and kinking could be examined by comparing them with the actual stress field parameters as they develop along the experimentally observed crack path. The experimental curvilinear crack path trajectories were formed in the tensile specimens with a hole positioned in the vicinity of a potential crack path. The numerical simulation, based on the solution of equivalent boundary value problems with the possible perturbations of the crack path, is presented here.
Inquiry-based learning templates for creating online educational paths
Davis, Sarah Alice
2006-10-30
(with annotation enlarged)............................................. 49 9 Second Stop in Density Path (with annotation enlarged) ........................................ 49 10 Third Stop in Density Path..........................................................................................50 11 Fourth Stop in Density Path..................................................................................... 50 12 Last Stop in Density Path (with annotation enlarged)............................................. 50 13 Opening...
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.
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.
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.
Effective path length corrections in beam-beam scattering experiments
NASA Technical Reports Server (NTRS)
Brinkmann, R. T.; Trajmar, S.
1981-01-01
The effect of the change of scattering geometry with scattering angle in beam-beam experiments is investigated. Atomic (molecular) target distributions associated with static gas, orifice, tube, capillary array (with and without further collimation), and jet sources have been considered in model calculations for a number of commonly used electron scattering geometries. The relationship between scattering intensity, cross section, and the geometrical integral called 'effective path length' is derived. Volume correction factors (the reciprocal of effective path length) have been calculated for sample cases to illustrate the effect of various beam and scattering geometry characteristics. The validity of the model calculation has been experimentally verified. Most of the commonly used scattering geometries require significant correction of the scattering intensity distributions, but with proper planning scattering geometries can be designed such that the intensity and the cross section angular distribution are identical within 1%.
Generating transition paths by Langevin bridges
NASA Astrophysics Data System (ADS)
Orland, Henri
2011-05-01
We propose a novel stochastic method to generate paths conditioned to start in an initial state and end in a given final state during a certain time tf. These paths are weighted with a probability given by the overdamped Langevin dynamics. We show that these paths can be exactly generated by a non-local stochastic differential equation. In the limit of short times, we show that this complicated non-solvable equation can be simplified into an approximate local stochastic differential equation. For longer times, the paths generated by this approximate equation do not satisfy the correct statistics, but this can be corrected by an adequate reweighting of the trajectories. In all cases, the paths are statistically independent and provide a representative sample of transition paths. The method is illustrated on the one-dimensional quartic oscillator.
Duality of Quantum Coherence and Path Distinguishability
Manabendra Nath Bera; Tabish Qureshi; Mohd Asad Siddiqui; Arun Kumar Pati
2015-03-10
We derive a generalized wave-particle duality relation for arbitrary dimensional multi-path quantum interference phenomena. Beyond the traditional signature of the wave nature of a quantum system, i.e., the fringe visibility, we introduce a novel quantifier as the normalized quantum coherence, recently defined in the frame-work 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 multi-path 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-know complementarity relation. The new duality relation continues to hold in the case where mixedness is introduced due to possible decoherence effects.
Al Rahal Al Orabi, Rabih; Gougeon, Patrick; Gall, Philippe; Fontaine, Bruno; Gautier, Régis; Colin, Malika; Candolfi, Christophe; Dauscher, Anne; Hejtmanek, Jiri; Malaman, Bernard; Lenoir, Bertrand
2014-11-01
We report on a detailed investigation of the crystal and electronic band structures and of the transport and thermodynamic properties of the Mo-based cluster compound Ag2Tl2Mo9Se11. This novel structure type crystallizes in the trigonal space group R3?c and is built of a three-dimensional network of interconnected Mo9Se11 units. Single-crystal X-ray diffraction indicates that the Ag and Tl atoms are distributed in the voids of the cluster framework, both of which show unusually large anisotropic thermal ellipsoids indicative of strong local disorder. First-principles calculations show a weakly dispersive band structure around the Fermi level as well as a semiconducting ground state. The former feature naturally explains the presence of both hole-like and electron-like signals observed in Hall effect. Of particular interest is the very low thermal conductivity that remains quasi-constant between 150 and 800 K at a value of approximately 0.6 W·m(-1)·K(-1). The lattice thermal conductivity is close to its minimum possible value, that is, in a regime where the phonon mean free path nears the mean interatomic distance. Such extremely low values likely originate from the disorder induced by the Ag and Tl atoms giving rise to strong anharmonicity of the lattice vibrations. The strongly limited ability of this compound to transport heat is the key feature that leads to a dimensionless thermoelectric figure of merit ZT of 0.6 at 800 K. PMID:25338311
Hydrogen molecule ion: Path-integral Monte Carlo approach
Kylaenpaeae, I.; Leino, M.; Rantala, T. T. [Institute of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere (Finland)
2007-11-15
The 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 nonadiabatic simulations, and inspecting projections of the full three-body dynamics onto the adiabatic Born-Oppenheimer approximation. Coupling of the electron and nuclear quantum dynamics is clearly seen. The nuclear pair correlation function is found to broaden by 0.040a{sub 0}, and the average bond length is larger by 0.056a{sub 0}. Also, a nonadiabatic correction to the binding energy is found. The electronic distribution is affected less than the nuclear one upon inclusion of nonadiabatic effects.
Hydrogen molecule ion: Path-integral Monte Carlo approach
NASA Astrophysics Data System (ADS)
Kylänpää, I.; Leino, M.; Rantala, T. T.
2007-11-01
The 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 nonadiabatic simulations, and inspecting projections of the full three-body dynamics onto the adiabatic Born-Oppenheimer approximation. Coupling of the electron and nuclear quantum dynamics is clearly seen. The nuclear pair correlation function is found to broaden by 0.040a0 , and the average bond length is larger by 0.056a0 . Also, a nonadiabatic correction to the binding energy is found. The electronic distribution is affected less than the nuclear one upon inclusion of nonadiabatic effects.
Continuous-curvature paths for autonomous vehicles
Winston Nelson
1989-01-01
The paths followed by autonomously guided vehicles (AGVs) are generally made up of line and circular-arc segments. For most AGVs, the steering functions required to keep the position and heading of the cart continuously aligned with such paths have discontinuities at the line-arc-line transitions points, because the curvature of the path is discontinuous at these points. For applications where continuous-curvature
Steam Path Audits on Industrial Steam Turbines
Mitchell, D. R.
steam Path Audits on Industrial steam Turbines DOUGLAS R. MITCHELL. ENGINEER. ENCOTECH, INC., SCHENECTADY, NEW YORK ABSTRACT The electric utility industry has benefitted from steam path audits on steam turbines for several years. Benefits... include the ability to identify 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...
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
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.
Ramaswamy, Ramkumar
2004-12-10
This paper addresses sensitivity analysis questions concerning the shortest path problem and the maximum capacity path problem in an undirected network. For both problems, we determine the maximum and ...
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.
The Logic behind Feynman's Paths
Edgardo T. Garcia Alvarez
2010-11-22
The classical notions of continuity and mechanical causality are left in order to refor- mulate the Quantum Theory starting from two principles: I) the intrinsic randomness of quantum process at microphysical level, II) the projective representations of sym- metries of the system. The second principle determines the geometry and then a new logic for describing the history of events (Feynman's paths) that modifies the rules of classical probabilistic calculus. The notion of classical trajectory is replaced by a history of spontaneous, random an discontinuous events. So the theory is reduced to determin- ing the probability distribution for such histories according with the symmetries of the system. The representation of the logic in terms of amplitudes leads to Feynman rules and, alternatively, its representation in terms of projectors results in the Schwinger trace formula.
Choosing Your Geosciences Career Path
NASA Astrophysics Data System (ADS)
Paluszkiewicz, T.
2002-12-01
There are many possibilities for rewarding careers in the geosciences including positions in academia, government, industry, and other parts of the private sector. How do you choose the right path to meet your goals and needs and find the right career? What are the tradeoffs and strategic moves that you should make at different stages in your career? Some of the pros and cons between soft-money research, government research, and management and industry positions are discussed from a personal perspective. In addition this presentation will provide some perspective on different career choices as seen by program managers in funding agencies. The competing priorities between work life and private life are discussed with the some thoughts on compromising between "having it all" and finding what works for you.
The path to adaptive microsystems
NASA Astrophysics Data System (ADS)
Zolper, John C.; Biercuk, Michael J.
2006-05-01
Scaling trends in microsystems are discussed frequently in the technical community, providing a short-term perspective on the future of integrated microsystems. This paper looks beyond the leading edge of technological development, focusing on new microsystem design paradigms that move far beyond today's systems based on static components. We introduce the concept of Adaptive Microsystems and outline a path to realizing these systems-on-a-chip. The role of DARPA in advancing future components and systems research is discussed, and specific DARPA efforts enabling and producing adaptive microsystems are presented. In particular, we discuss efforts underway in the DARPA Microsystems Technology Office (MTO) including programs in novel circuit architectures (3DIC), adaptive imaging and sensing (AFPA, VISA, MONTAGE, A-to-I) and reconfigurable RF/Microwave devices (SMART, TFAST, IRFFE).
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.
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.
Leak Path Development in CO2 Wells
NASA Astrophysics Data System (ADS)
Torsater, M.; Todorovic, J.; Opedal, N.; Lavrov, A.
2014-12-01
Wells have in numerous scientific works been denoted the "weak link" of safe and cost-efficient CO2 Capture and Storage (CCS). Whether they are active or abandoned, all wells are man-made intrusions into the storage reservoir with sealing abilities depending on degradable materials like steel and cement. If dense CO2 is allowed to expand (e.g. due to leakage) it will cool down its surroundings and cause strong thermal and mechanical loading on the wellbore. In addition, CO2 reacts chemically with rock, cement and steel. To ensure long-term underground containment, it is therefore necessary to study how, why, where and when leakage occurs along CO2wells. If cement bonding to rock or casing is poor, leak paths can form already during drilling and completion of the well. In the present work, we have mapped the bonding quality of cement-rock and cement-steel interfaces - and measured their resistance towards CO2 flow. This involved a large experimental matrix including different rocks, steels, cement types and well fluids. The bonding qualities were measured on composite cores using micro computed tomography (µ-CT), and CO2 was flooded through the samples to determine leakage rates. These were further compared to numerical simulations of leakage through the digitalized µ-CT core data, and CO2chemical interactions with the materials were mapped using electron microscopy. We also present a new laboratory set-up for measuring how well integrity is affected by downhole temperature variations - and we showcase some initial results. Our work concludes that leak path development in CO2 wells depends critically on the drilling fluids and presflushes/spacers chosen already during drilling and completion of a well. Fluid films residing on rock and casing surfaces strongly degrade the quality of cement bonding. The operation of the well is also important, as even slight thermal cycling (between 10°C and 95°C on casing) leads to significant de-bonding of the annular cement.
Relationship between phase path and effective path for oblique ionospheric propagation
P. J. D. Gething
1965-01-01
The effects of earth curvature were neglected by Appleton in deriving the well-known relationship between phase path P and effective path P' for oblique propagation of a signal of frequency . It is shown that this equation is still rigorously satisfied when earth curvature is taken into account. An expression for phase path, correct to first order curvature terms, is
PathExpander: Architectural Support for Increasing the Path Coverage of Dynamic Bug Detection #
Zhou, Yuanyuan
PathExpander: Architectural Support for Increasing the Path Coverage of Dynamic Bug Detection,pinzhou,liuwei,yyzhou,torrellas}@cs.uiuc.edu Abstract Dynamic software bug detection tools are commonly used be cause they leverage runtime information. However, they suffer from a fundamental limitation, the Path Coverage Problem: they detect bugs
PathExpander: Architectural Support for Increasing the Path Coverage of Dynamic Bug Detection
Torrellas, Josep
PathExpander: Architectural Support for Increasing the Path Coverage of Dynamic Bug Detection Shan,pinzhou,liuwei,yyzhou,torrellas}@cs.uiuc.edu Abstract Dynamic software bug detection tools are commonly used be- cause they leverage run-time information. However, they suffer from a fundamental limitation, the Path Coverage Problem: they detect bugs
Mach flow angularity probes for scramjet engine flow path diagnostics
Jalbert, P.A.; Hiers, R.S. Jr. [Sverdrup Technology, Inc., Arnold AFS, TN (United States)
1993-12-31
Mach-flow angularity (MFA) probes were developed for use in scramjet flow path probe rakes. Prototype probes were fabricated to demonstrate the assembly processes (numerical control machining, furnace brazing, and electron beam welding). Tests of prototype probes confirmed the thermal durability margins and life cycle. Selected probes were calibrated in air at Mach numbers from 1.75 to 6.0. Acceptance criteria for the production probes stressed thermal durability and pressure (and, consequently, Mach number) measurement quality. This new water-cooled MFA probe has 0.397-cm shaft diameter and is capable of withstanding heat fluxes of 2.724 kW/sq cm.
Path Matching in Compressed Control Flow Traces
Gupta, Rajiv
Path Matching in Compressed Control Flow Traces Youtao Zhang Rajiv Gupta Dept. of Computer Science in compressed form generated using SEQUITUR. The occurrence of an intraprocedural path in the WPP cannot with large amounts of data are often stored in compressed form and one of the commonly used compression
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 and as an educational tool...
't Hooft's quantum determinism -- path integral viewpoint
Massimo Blasone; Petr Jizba; Hagen Kleinert
2005-04-07
We present a path integral formulation of 't Hooft's derivation of quantum from classical physics. Our approach is based on two concepts: Faddeev-Jackiw's treatment of constrained systems and Gozzi's path integral formulation of classical mechanics. This treatment is compared with our earlier one [quant-ph/0409021] based on Dirac-Bergmann's method.
PATH PLANNING BY MULTIHEURISTIC SEARCH VIA SUBGOALS
Pekka Isto
1996-01-01
An efficient path planning algorithm for general 6 degrees of freedom robots is presented in the paper. The path planner is based on multiheuristic A * search algorithm with dynamic subgoal generation for rapid escaping from deep local-minimum wells. The algorithm has been implemented as an extension to a robot off-line programming and simulation system for testing. The presented test
Cooperative organic mine avoidance path planning
NASA Astrophysics Data System (ADS)
McCubbin, Christopher B.; Piatko, Christine D.; Peterson, Adam V.; Donnald, Creighton R.; Cohen, David
2005-06-01
The JHU/APL Path Planning team has developed path planning techniques to look for paths that balance the utility and risk associated with different routes through a minefield. Extending on previous years' efforts, we investigated real-world Naval mine avoidance requirements and developed a tactical decision aid (TDA) that satisfies those requirements. APL has developed new mine path planning techniques using graph based and genetic algorithms which quickly produce near-minimum risk paths for complicated fitness functions incorporating risk, path length, ship kinematics, and naval doctrine. The TDA user interface, a Java Swing application that obtains data via Corba interfaces to path planning databases, allows the operator to explore a fusion of historic and in situ mine field data, control the path planner, and display the planning results. To provide a context for the minefield data, the user interface also renders data from the Digital Nautical Chart database, a database created by the National Geospatial-Intelligence Agency containing charts of the world's ports and coastal regions. This TDA has been developed in conjunction with the COMID (Cooperative Organic Mine Defense) system. This paper presents a description of the algorithms, architecture, and application produced.
Multi-Path Time Protocols Alexander Shpiner
Segall, Adrian
IP networks. Keywords: multiple paths, slave diversity, IEEE 1588, PTP, NTP, time protocol, clock are the Network Time Protocol (NTP) [1], and the Precision Time Protocol (PTP) [2]. In both protocols the master transport types. Our Multi-path Time Protocol approach is an extension to the PTP and NTP protocols
Dynamic Shortest Paths Containers Dorothea Wagnera,1
Zaroliagis, Christos D.
of nodes. In [17], angular sectors were introduced to speed up the processing of such shortest path queries of Patras, 26500 Patras, Greece Abstract Using a set of geometric containers to speed up shortest path is quite large (though sparse), and hence space requirements are only acceptable to be linear in the number
Shortest Path Problems on a Polyhedral Surface
Atlas F. Cook; Carola Wenk
2009-01-01
We develop algorithms to compute edge sequences, Voronoi diagrams, shortest path maps, the Fréchet distance, and the diameter for a polyhedral surface. Dis- tances on the surface are measured either by the length of a Euclidean shortest path or by link distance.
Multiresolution Path Planning Via Sector Decompositions
Tsiotras, Panagiotis
Multiresolution Path Planning Via Sector Decompositions Compatible to On-Board Sensor Data that includes actual path length along with a risk-induced metric. We use a multi-resolution cell decomposition or popup threats. Several multi-resolution or hierarchical algorithms have been proposed in the literature
A Random Walk on a Circular Path
ERIC Educational Resources Information Center
Ching, W.-K.; Lee, M. S.
2005-01-01
This short note introduces an interesting random walk on a circular path with cards of numbers. By using high school probability theory, it is proved that under some assumptions on the number of cards, the probability that a walker will return to a fixed position will tend to one as the length of the circular path tends to infinity.
Fast path planning in virtual colonoscopy.
Lee, Jeongjin; Kim, Gyehyun; Lee, Ho; Shin, Byeong-Seok; Shin, Yeong Gil
2008-09-01
We propose a fast path planning algorithm using multi-resolution path tree propagation and farthest visible point. Initial path points are robustly generated by propagating the path tree, and all internal voxels locally most distant from the colon boundary are connected. The multi-resolution scheme is adopted to increase computational efficiency. Control points representing the navigational path are successively selected from the initial path points by using the farthest visible point. The position of the initial path point in a down-sampled volume is accurately adjusted in the original volume. Using the farthest visible point, the number of control points is adaptively changed according to the curvature of the colon shape so that more control points are assigned to highly curved regions. Furthermore, a smoothing step is unnecessary since our method generates a set of control points to be interpolated with the cubic spline interpolation. We applied our method to 10 computed tomography datasets. Experimental results showed that the path was generated much faster than using conventional methods without sacrificing accuracy, and clinical efficiency. The average processing time was approximately 1s when down-sampling by a factor of 2, 3, or 4. We concluded that our method is useful in diagnosing colon cancer using virtual colonoscopy. PMID:18707681
Using Runtime Paths for Macro Analysis
Mike Chen; Emre Kiciman; Anthony Accardi; Armando Fox; Eric Brewer
2002-01-01
We introduce macro analysis, an approach used to infer the high-level properties of dynamic, distributed systems , and an indispensable tool when faced with tasks where lo- cal context and individual component details are insuffi- cient. We present a new methodology,runtime path analysis, where paths are traced through software components and then aggregated to understand global system behavior via statistical
Career Path Guide for Adult Career Choices.
ERIC Educational Resources Information Center
Case, Clydia
Intended for adults who are considering career choices or changes, this booklet provides opportunities for self-study and reflection in six career paths. The booklet begins with tips for long-term career survival and myths and realities of career planning. After a brief career survey, readers are introduced to six career paths: arts and…
Fatigue failure paths for offshore platform inspection
Demir I. Karsan; Ashok Kumar
1990-01-01
A closed- form, reliability-based procedure is developed to identify fatigue failure paths of offshore structures and assess the notional probability of system failure through these paths. The procedure utilizes the Miners rule node fatigue failure reliability model developed by Wirsching. Effects of load redistribution following the fatigue failure of a node on the time to failure of remaining unfailed nodes
Shortest path and Schramm-Loewner Evolution
NASA Astrophysics Data System (ADS)
Posé, N.; Schrenk, K. J.; Araújo, N. A. M.; Herrmann, H. J.
2014-06-01
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.
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
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
Precision Cleaning - Path to Premier
NASA Technical Reports Server (NTRS)
Mackler, Scott E.
2008-01-01
ITT Space Systems Division s new Precision Cleaning facility provides critical cleaning and packaging of aerospace flight hardware and optical payloads to meet customer performance requirements. The Precision Cleaning Path to Premier Project was a 2007 capital project and is a key element in the approved Premier Resource Management - Integrated Supply Chain Footprint Optimization Project. Formerly precision cleaning was located offsite in a leased building. A new facility equipped with modern precision cleaning equipment including advanced process analytical technology and improved capabilities was designed and built after outsourcing solutions were investigated and found lacking in ability to meet quality specifications and schedule needs. SSD cleans parts that can range in size from a single threaded fastener all the way up to large composite structures. Materials that can be processed include optics, composites, metals and various high performance coatings. We are required to provide verification to our customers that we have met their particulate and molecular cleanliness requirements and we have that analytical capability in this new facility. The new facility footprint is approximately half the size of the former leased operation and provides double the amount of throughput. Process improvements and new cleaning equipment are projected to increase 1st pass yield from 78% to 98% avoiding $300K+/yr in rework costs. Cost avoidance of $350K/yr will result from elimination of rent, IT services, transportation, and decreased utility costs. Savings due to reduced staff expected to net $4-500K/yr.
Path Integral Molecular Dynamics for Hydrogen with Orbital-Free Density Functional Theory
NASA Astrophysics Data System (ADS)
Runge, Keith; Karasiev, Valentin; Deymier, Pierre
2014-03-01
The computational bottleneck for performing path-integral molecular dynamics (PIMD) for nuclei on a first principles electronic potential energy surface has been the speed with which forces from the electrons can be generated. Recent advances in orbital-free density functional theory (OF-DFT) not only allow for faster generation of first principles forces but also include the effects of temperature on the electron density. We will present results of calculations on hydrogen in warm dense matter conditions where the protons are described by PIMD and the electrons by OF-DFT. Work supported by U.S. Dept. of Energy, grant DE-SC0002139.
ISSN 1055-1425 This work was performed as part of the California PATH Program of the
Levinson, David M.
a model to maximize social welfare associated with the toll plaza. A payment choice model estimates OF CALIFORNIA, BERKELEY Deploying Electronic Tolls UCB-ITS-PRR-2000-11 California PATH Research Report David Levinson Elva Chang CALIFORNIA PARTNERS FOR ADVANCED TRANSIT AND HIGHWAYS #12;Deploying Electronic Tolls 1
Yeong-Lieh Lin
1995-01-01
We investigate quantum interference effects--due to electron motion on lattices immersed in a magnetic field --in a variety of condensed matter systems. These effects arise from the interference between magnetic phase factors associated with different electron paths. The spirit of our approach follows Feynman's programme: to derive physical quantities in terms of \\
FINDING SENSING COVERAGE AND BREACH PATHS IN SURVEILLANCE WIRELESS SENSOR NETWORKS
, planned, etc.) and sink deployment. Depending on the range and the number of sensors, the sensing coverageFINDING SENSING COVERAGE AND BREACH PATHS IN SURVEILLANCE WIRELESS SENSOR NETWORKS Ertan Onur of Computer Engineering BUSIM Laboratory, Department of Electrical and Electronics Engineering Bogazic
P. R. Bueno; E. R. Leite
2003-01-01
This paper describes the mechanisms of ion and electron transport in nanostructured insertion electrode materials such as metal oxide electrochromics and\\/or Li ion batteries. A general description is given of cases of insertion into a short path region predicted by the geometric disposition of insertion materials in nanostructural electrodes, designed mainly by connected spherical-like particles and nanofibers, both protruding from
Nonholonomic catheter path reconstruction using electromagnetic tracking
NASA Astrophysics Data System (ADS)
Lugez, Elodie; Sadjadi, Hossein; Akl, Selim G.; Fichtinger, Gabor
2015-03-01
Catheter path reconstruction is a necessary step in many clinical procedures, such as cardiovascular interventions and high-dose-rate brachytherapy. To overcome limitations of standard imaging modalities, electromagnetic tracking has been employed to reconstruct catheter paths. However, tracking errors pose a challenge in accurate path reconstructions. We address this challenge by means of a filtering technique incorporating the electromagnetic measurements with the nonholonomic motion constraints of the sensor inside a catheter. The nonholonomic motion model of the sensor within the catheter and the electromagnetic measurement data were integrated using an extended Kalman filter. The performance of our proposed approach was experimentally evaluated using the Ascension's 3D Guidance trakStar electromagnetic tracker. Sensor measurements were recorded during insertions of an electromagnetic sensor (model 55) along ten predefined ground truth paths. Our method was implemented in MATLAB and applied to the measurement data. Our reconstruction results were compared to raw measurements as well as filtered measurements provided by the manufacturer. The mean of the root-mean-square (RMS) errors along the ten paths was 3.7 mm for the raw measurements, and 3.3 mm with manufacturer's filters. Our approach effectively reduced the mean RMS error to 2.7 mm. Compared to other filtering methods, our approach successfully improved the path reconstruction accuracy by exploiting the sensor's nonholonomic motion constraints in its formulation. Our approach seems promising for a variety of clinical procedures involving reconstruction of a catheter path.
Functional equivalence and spatial path memory.
Lyon, Don R; Gunzelmann, Glenn M
2011-11-01
Loomis, Klatzky, Avraamides, Lippa and Golledge ( 2007 ) suggest that, when it comes to spatial information, verbal description and perceptual experience are nearly functionally equivalent with respect to the cognitive representations they produce. We tested this idea for the case of spatial memory for complex paths. Paths consisted entirely of unit-length segments followed by 90-degree turns, thus assuring that a path could be described with equal precision using either an egocentric verbal description or a virtual self-motion experience. The verbal description was analogous to driving directions (e.g., turn left and go one block, then turn right, etc.) except in three dimensions (allowing rotation followed by up or down movement). Virtual self-motion was depicted as first-person travel through a 3D grid of featureless corridors. Comparison of these two conditions produced a result that may be surprising to some, but nevertheless appears to support the notion of functional equivalence: Virtual self-motion does not produce better path memory than verbal description, when care is taken to present equally precise path information. This result holds for even very complex paths and despite evidence from proximity-based interference that the memory representation of the path is spatial. PMID:22044400
14 CFR 29.59 - Takeoff path: Category A.
Code of Federal Regulations, 2010 CFR
2010-01-01
...2010-01-01 false Takeoff path: Category A. 29.59 Section 29.59 ...AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Flight Performance § 29.59 Takeoff path: Category A. (a) The takeoff path...
14 CFR 29.59 - Takeoff path: Category A.
Code of Federal Regulations, 2011 CFR
2011-01-01
...2011-01-01 false Takeoff path: Category A. 29.59 Section 29.59 ...AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Flight Performance § 29.59 Takeoff path: Category A. (a) The takeoff path...
Path Selection Methods for Localized Quality of Service Routing
Yuan, Xin
performance, local- ized QoS routing must effectively select the predetermined set of candi- date paths was used to select candi- date paths. This paper fills in the gap by studying path selec- tion schemes
Current path in light emitting diodes based on nanowire ensembles
NASA Astrophysics Data System (ADS)
Limbach, F.; Hauswald, C.; Lähnemann, J.; Wölz, M.; Brandt, O.; Trampert, A.; Hanke, M.; Jahn, U.; Calarco, R.; Geelhaar, L.; Riechert, H.
2012-11-01
Light emitting diodes (LEDs) have been fabricated using ensembles of free-standing (In, Ga)N/GaN nanowires (NWs) grown on Si substrates in the self-induced growth mode by molecular beam epitaxy. Electron-beam-induced current analysis, cathodoluminescence as well as biased ?-photoluminescence spectroscopy, transmission electron microscopy, and electrical measurements indicate that the electroluminescence of such LEDs is governed by the differences in the individual current densities of the single-NW LEDs operated in parallel, i.e. by the inhomogeneity of the current path in the ensemble LED. In addition, the optoelectronic characterization leads to the conclusion that these NWs exhibit N-polarity and that the (In, Ga)N quantum well states in the NWs are subject to a non-vanishing quantum confined Stark effect.
Unusual bond paths in organolithium compounds
Bachrach, S.M.; Ritchie, J.P.
1986-01-01
We have applied the topological method to a number of organolithium compounds. The wavefunctions were determined with GAUSSIAN-82 using 3-21G basis set and fully optimized geometries. Gradient paths were obtained using the RHODER package and critical points were located using EXTREME. These results indicate the unusual nature of organolithium compounds. The strange bond paths arise mainly from the ionic nature of the C-Li interaction. We suggest that the term ''bond path'' may best be suited for covalent bonds. 4 figs., 1 tab.
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)
Steam Path Audits on Industrial Steam Turbines
Mitchell, D. R.
1992-01-01
The electric utility industry has benefitted from steam path audits on steam turbines for several years. Benefits include the ability to identify areas of performance degradation during a turbine outage. Repair priorities can then be set...
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.
Non-classical paths in interference experiments
Rahul Sawant; Joseph Samuel; Aninda Sinha; Supurna Sinha; Urbasi Sinha
2014-08-09
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 which is only approximately true. In our present study, we have used the Feynman path integral formalism to quantify contributions from non-classical paths in quantum interference experiments which provide a measurable deviation from a naive application of the superposition principle. A direct experimental demonstration for the existence of these non-classical paths is hard. We find that contributions from such paths can be significant and we propose simple three-slit interference experiments to directly confirm their existence.
Multi-objective stochastic path planning
Dasgupta, Sumantra
2009-05-15
of multiple objectives and stochastic edge parameters. 2. Identify candidate constraints where clustering based multi-level programming can be applied to eliminate infeasible edges. 3. Provide an exact O (V.E) algorithm for building redundant shortest paths. 4...
Building a path in cell biology
Cheeseman, Iain McPherson
Setting up a new lab is an exciting but challenging prospect. We discuss our experiences in finding a path to tackle some of the key current questions in cell biology and the hurdles that we have encountered along the way.
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.
Walden's Paths quiz: system design and implementation
Arora, Avital Jayant
2002-01-01
This thesis describes the motivation for online testing, compares the effectiveness of online tests versus conventional tests and outlines the features of online-testing mechanisms. It details the features and implementation of the Walden's Paths...
Code of Federal Regulations, 2011 CFR
2011-01-01
...by a continuous demonstrated takeoff. (e) The takeoff path to 35 feet above the takeoff surface must be determined by synthesis from segments; and (1) The segments must be clearly defined and must be related to distinct changes in...
Code of Federal Regulations, 2010 CFR
2010-01-01
...by a continuous demonstrated takeoff. (e) The takeoff path to 35 feet above the takeoff surface must be determined by synthesis from segments; and (1) The segments must be clearly defined and must be related to distinct changes in...
Predicting missing links via effective paths
NASA Astrophysics Data System (ADS)
Zhu, Xuzhen; Tian, Hui; Cai, Shimin
2014-11-01
Recently, in complex network, link prediction has brought a surge of researches, among which similarity based link prediction outstandingly gains considerable success, especially similarity in terms of paths. In investigation of paths based similarity, we find that the effective influence of endpoints and strong connectivity make paths contribute more similarity between two unconnected endpoints, leading to a more accurate link prediction. Accordingly, we propose a so-called effective path index (EP) in this paper to leverage effective influence of endpoints and strong connectivity in similarity calculation. For demonstrating excellence of our index, the comparisons with six mainstream indices are performed on experiments in 15 real datasets and results show a great improvement of performance via our index.
Electron matter optics and an electron Mach-Zehnder interferometer
NASA Astrophysics Data System (ADS)
Gronniger, Glen Everet
The diffraction of electrons by natural crystal structures was first observed in 1927. Before the start of this work, it was not clear whether or not the high quality gratings currently available could be used for electron diffraction due to image charge and other electron grating interactions. We observe for the first time electron diffraction from man made diffraction gratings of 100 nm periodicity. The high quality of diffraction and the ability to "pick" the periodicity allowed us to construct the first Mach-Zehnder electron interferometer using these gratings. Multiple approaches, including a prototype of our current interferometer and the combination of a grating with an electron bi-prism, were unsuccessful. Many stabilization issues must be overcome to observe electron interference fringes in the interferometer. Many experimental design ideas were used to reach proper stabilization requirements. The final interferometer design constructed was the only interferometer to obtain electron interference fringes. The theoretical model used to analyze the data is based on the path integral formalism. This calculates the amplitude associated with all classical paths through the experimental device. The sum of all amplitudes, the path integral, yields the resulting probability at the detection screen. We obtain good fits between our path integral calculations and experimental data. Alternate explanations of our data, such as the possibilities of Talbot Lau and classical Moire interferometers are ruled out in favor of the Mach-Zehnder explanation. This type of interferometer could be used for future experiments. An experiment for which the fundamental quantum mechanical experiment has never been done; observing the dispersion-less nature of the Aharonov-Bohm Effect, may lend itself to the characteristics of this type of interferometer. Preliminary calculations have been performed to investigate the feasibility of using the grating technology to perform the required experiment.
Highway Hierarchies Hasten Exact Shortest Path Queries
Peter Sanders; Dominik Schultes
2005-01-01
\\u000a We present a new speedup technique for route planning that exploits the hierarchy inherent in real world road networks. Our\\u000a algorithm preprocesses the eight digit number of nodes needed for maps of the USA or Western Europe in a few hours using linear\\u000a space. Shortest (i.e. fastest) path queries then take around eight milliseconds to produce exact shortest paths. This
Optimization of Loading Paths for Tube Hydroforming
Suwat Jirathearanat; Taylan Altan
2004-01-01
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
New England Forests: The Path to Sustainability
Wolfe, Patrick J.
New England Forests: The Path to Sustainability A R E P O R T B Y N E W E N G L A N D F O R E S T R Y F O U N D A T I O N #12;#12;New England Forests: The Path to Sustainability Forests define New tree in a town or state park? Forests are part of New Englanders' daily lives. Nearly all of us rely
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.
Quantum cosmology based on discrete Feynman paths
Chew, Geoffrey F.
2002-10-10
Although the rules for interpreting local quantum theory imply discretization of process, Lorentz covariance is usually regarded as precluding time quantization. Nevertheless a time-discretized quantum representation of redshifting spatially-homogeneous universe may be based on discrete-step Feynman paths carrying causal Lorentz-invariant action--paths that not only propagate the wave function but provide a phenomenologically-promising elementary-particle Hilbert-space basis. In a model under development, local path steps are at Planck scale while, at a much larger ''wave-function scale'', global steps separate successive wave-functions. Wave-function spacetime is but a tiny fraction of path spacetime. Electromagnetic and gravitational actions are ''at a distance'' in Wheeler-Feynman sense while strong (color) and weak (isospin) actions, as well as action of particle motion, are ''local'' in a sense paralleling the action of local field theory. ''Nonmaterial'' path segments and ''trivial events'' collaborate to define energy and gravity. Photons coupled to conserved electric charge enjoy privileged model status among elementary fermions and vector bosons. Although real path parameters provide no immediate meaning for ''measurement'', the phase of the complex wave function allows significance for ''information'' accumulated through ''gentle'' electromagnetic events involving charged matter and ''soft'' photons. Through its soft-photon content the wave function is an ''information reservoir''.
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.
Development Paths in Archaeological Surveying
NASA Astrophysics Data System (ADS)
Tabbagh, A.
2005-05-01
Geophysical surveys of archaeological sites began in 1938, when an electrical survey was performed at the historical site of Williamsburg (Virginia, USA). Its full development, however, has been achieved by several European teams, which have continuously worked on it since the fifties. Geophysical survey is one step of archaeological site reconnaissance, which comprises many other non-invasive techniques such as document studies, field walking, air photo interpretation...Nevertheless solely geophysical techniques allow a direct exploration of the underground itself over a significant depth of investigation. Several physical properties can be measured to detect and map archaeological features and/or remains but electrical resistivity and magnetisation has been commonly used for fifty years and dielectric permittivity more recently. The major path of the technical evolution was to increase both the speed of the survey and the size of the area by using short measurement duration (less than 0.1 s) and to incorporate mechanical systems that allow the continuous pulling of the sensors on the field. Magnetic measurements are thus achieved either by fluxgate or optically pumped sensors, while electrical measurements are achieved by mobile multi-pole systems simultaneously over two or three different depths. In such surveys the mesh grid is 1 x 1 m or 0.5 x 0.5 m. Another aim is to limit the size of the surveyed area but to increase the geometrical resolution by using ground penetrating radars (GPR) with a very fine mesh (0.2 x 0.2 m) and by processing the data by `time slices' which allow to follow precisely the extension in depth of the different features. In addition for magnetic features, the simultaneous inversion of magnetic field and susceptibility (and soon viscosity) measurements using linear filtering allows the differentiation among the types of magnetization and allows for an improved determination of the depths of magnetic property contrasts. By considering the geological context, global magnetic susceptibility values in the field is also an indication of possible settlement and of the type of land use in the past.
Solar corona electron density distribution
P. B. Esposito; Peter Edenhofer; Ernst Lueneburg
1980-01-01
The paper discusses the three and one-half months of single-frequency time delay data which were acquired from the Helios 2 spacecraft around the time of its solar occultation. The excess time delay due to integrated effect of free electrons along the signal's ray path could be separated and modeled following the determination of the spacecraft trajectory. An average solar corona
Electron beam gaseous pollutants treatment
A. G. Chmielewski
1995-01-01
Summary form only given, as follows. High energy electrons create thousands of ions and free radicals along their path. In consequence radiolytical processes take place that with usage of additional reactants at proper physical gas conditions may lead to new air pollution control technologies. Three examples are discussed: SO2 and NOx removal (combustion flue gases); volatile organic compounds removal (industrial
High-order path-integral Monte Carlo methods for solving quantum dot problems.
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. PMID:25871047
Electronic-Photonic Convergence on Silicon
Lionel C. Kimerling
The silicon-based electronics industry has grown by exponentially increasing performance at constant cost through dimensional shrinking of devices. That path came to an abrupt halt in 2005 as conventional scaling rules were replaced by increasing the parallelism in systems. In addition, the common paradigm of electronics for signal processing and photonics for communication has failed to provide the projected performance
Approximate path seeking for statistical iterative reconstruction
NASA Astrophysics Data System (ADS)
Wu, Meng; Yang, Qiao; Maier, Andreas; Fahrig, Rebecca
2015-03-01
Statistical iterative reconstruction (IR) techniques have demonstrated many advantages in X-ray CT reconstruction. The statistical iterative reconstruction approach is often modeled as an optimization problem including a data fitting function and a penalty function. The tuning parameter values that regulate the strength of the penalty function are critical for achieving good reconstruction results. However, appropriate tuning parameter values that are suitable for the scan protocols and imaging tasks are often difficult to choose. In this work, we propose a path seeking algorithm that is capable of generating a series of IR images with different strengths of the penalty function. The path seeking algorithm uses the ratio of the gradients of the data fitting function and the penalty function to select pixels for small fixed size updates. We describe the path seeking algorithm for penalized weighted least squares (PWLS) with a Huber penalty function in both the directions of increasing and decreasing tuning parameter value. Simulations using the XCAT phantom show the proposed method produces path images that are very similar to the IR images that are computed via direct optimization. The root-mean- squared-error of one path image generated by the proposed method relative to full iterative reconstruction is about 6 HU for the entire image and 10 HU for a small region. Different path seeking directions, increment sizes and updating percentages of the path seeking algorithm are compared in simulations. The proposed method may reduce the dependence on selection of good tuning parameter values by instead generating multiple IR images, without significantly increasing the computational load.
Minefield path planning: architecture and algorithms obeying kinematic constraints
Christopher B. McCubbin; Christine D. Piatko; Steven J. Marshall
2004-01-01
We have been developing path planning techniques to look for paths that balance the utility and risk associated with different routes through a minefield. Such methods will allow a battlegroup commander to evaluate alternative route options while searching for low risk paths. Extending on previous years' efforts, we have implemented a generalized path planning framework to allow rapid evaluation and
Path Analysis: A Link between Family Theory and Reseach.
ERIC Educational Resources Information Center
Rank, Mark R.; Sabatelli, Ronald M.
This paper discusses path analysis and the applicability of this methodology to the field of family studies. The statistical assumptions made in path analysis are presented along with a description of the two types of models within path analysis, i.e., recursive and non-recursive. Methods of calculating in the path model and the advantages of…
An Overview of Autonomous Mobile Robot Path Planning Algorithms
N. Sariff; N. Buniyamin
2006-01-01
Determination of a collision free path for a robot between start and goal positions through obstacles cluttered in a workspace is central to the design of an autonomous robot path planning. This paper presents an overview of autonomous mobile robot path planning focusing on algorithms that produce an optimal path for a robot to navigate in an environment. To complete
Best-path planning for public transportation systems
Chao-Lin Liu
2002-01-01
The author examines methods for a special class of path planning problems in which the routes are constrained. General search algorithms assume that we can move around in the traffic network freely, so they extend the partial paths from the very last location to each of its neighbors to form more partial paths. The best partial paths are then selected
Advanced path interpolation in high performance motion control systems
Dongjun Zhang; Zexiang Li; Shuang Cong; Hong Wu
2010-01-01
In the path following motion control system, the reference tool path of the machine tool is geometric curves predetermined by applications. The reference motion command for servo control system is generated based on the geometric tool path and the feedrate. The command generation module is called path interpolation. It is a classical problem in the motion control system. However, a
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…
Multiple paths extraction in images using a constrained expanded trellis.
Sun, Changming; Appleton, Ben
2005-12-01
Single shortest path extraction algorithms have been used in a number of areas such as network flow and image analysis. In image analysis, shortest path techniques can be used for object boundary detection, crack detection, or stereo disparity estimation. Sometimes one needs to find multiple paths as opposed to a single path in a network or an image where the paths must satisfy certain constraints. In this paper, we propose a new algorithm to extract multiple paths simultaneously within an image using a constrained expanded trellis (CET) for feature extraction and object segmentation. We also give a number of application examples for our multiple paths extraction algorithm. PMID:16355660
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
The formal path integral and quantum mechanics
Johnson-Freyd, Theo [Department of Mathematics, University of California - Berkeley, 970 Evans Hall, Berkeley, California 94720 (United States)
2010-11-15
Given an arbitrary Lagrangian function on R{sup d} and a choice of classical path, one can try to define Feynman's path integral supported near the classical path as a formal power series parameterized by 'Feynman diagrams', although these diagrams may diverge. We compute this expansion and show that it is (formally, if there are ultraviolet divergences) invariant under volume-preserving changes of coordinates. We prove that if the ultraviolet divergences cancel at each order, then our formal path integral satisfies a 'Fubini theorem' expressing the standard composition law for the time evolution operator in quantum mechanics. Moreover, we show that when the Lagrangian is inhomogeneous quadratic in velocity such that its homogeneous-quadratic part is given by a matrix with constant determinant, then the divergences cancel at each order. Thus, by 'cutting and pasting' and choosing volume-compatible local coordinates, our construction defines a Feynman-diagrammatic 'formal path integral' for the nonrelativistic quantum mechanics of a charged particle moving in a Riemannian manifold with an external electromagnetic field.
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,
Shortest Path Computation with No Information Leakage
Mouratidis, Kyriakos
2012-01-01
Shortest path computation is one of the most common queries in location-based services (LBSs). Although particularly useful, such queries raise serious privacy concerns. Exposing to a (potentially untrusted) LBS the client's position and her destination may reveal personal information, such as social habits, health condition, shopping preferences, lifestyle choices, etc. The only existing method for privacy-preserving shortest path computation follows the obfuscation paradigm; it prevents the LBS from inferring the source and destination of the query with a probability higher than a threshold. This implies, however, that the LBS still deduces some information (albeit not exact) about the client's location and her destination. In this paper we aim at strong privacy, where the adversary learns nothing about the shortest path query. We achieve this via established private information retrieval techniques, which we treat as black-box building blocks. Experiments on real, large-scale road networks assess the pract...
Information Flow Analysis via Path Condition Refinement
NASA Astrophysics Data System (ADS)
Taghdiri, Mana; Snelting, Gregor; Sinz, Carsten
We present a new approach to information flow control (IFC), which exploits counterexample-guided abstraction refinement (CEGAR) technology. The CEGAR process is built on top of our existing IFC analysis in which illegal flows are characterized using program dependence graphs (PDG) and path conditions (as described in [12]). Although path conditions provide an already precise abstraction that can be used to generate witnesses to the illegal flow, they may still cause false alarms. Our CEGAR process recognizes false witnesses by executing them and monitoring their executions, and eliminates them by automatically refining path conditions in an iterative way as needed. The paper sketches the foundations of CEGAR and PDG-based IFC, and describes the approach in detail. An example shows how the approach finds illegal flow, and demonstrates how CEGAR eliminates false alarms.
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.
Quickest Paths for Different Network Router Mechanisms
Rao, N.S.V.; Grimmell, W.C.; Radhakrishnan, S.; Bang, Y.C.
2000-06-01
The quickest path problem deals with the transmission of a message of size {sigma} from a source to a destination with the minimum end-to-end delay over a network with bandwidth and delay constraints on the links. The authors consider four basic modes and two variations for the message delivery at the nodes reflecting the mechanisms such as circuit switching, Internet protocol, and their combinations. For each of the first three modes, they present O(m{sup 2} + mn log n) time algorithm to compute the quickest path for a given message size {sigma}. For the last mode, the quickest path can be computed in O(m + n log n) time.
Line transect sampling from a curving path.
Hiby, L; Krishna, M B
2001-09-01
Cutting straight line transects through dense forest is time consuming and expensive when large areas need to be surveyed for rare or highly clustered species. We argue that existing paths or game trails may be suitable as transects for line transect sampling even though they will not, in general, run straight. Formulas and software currently used to estimate local density using perpendicular distance data can be used with closest approach distances measured from curving transects. Suitable paths or trails are those for which the minimum radius of curvature is rarely less than the width of the shoulder in the detection probability function. The use of existing paths carries the risk of bias resulting from unrepresentative sampling of available habitats, and this must be weighed against the increase in coverage available. PMID:11550921
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
Exploiting Deterministic TPG for Path Delay Testing
Xiaowei Li; Paul Y. S. Cheung
2000-01-01
Detection of path delay faults requires two-pattern tests. BIST technique provides a low-cost test solution. This paper proposes\\u000a an approach to designing a cost-effective deterministic test pattern generator (TPG) for path delay testing. Given a set of\\u000a pre-generated test-pairs with pre-determined fault coverage, a deterministic TPG is synthesized to apply the given test-pair\\u000a set in a limited test time. To
Multi-objective stochastic path planning
Dasgupta, Sumantra
2009-05-15
[6, 7]. Genetic Algorithms have been applied to generate the non-dominated Pareto optimal set in multi- criteria path planning [8]. Potential and value-function approaches have been reported for multi-criteria path planning in [9, 10]. C... per grid, source node, s and destination node, d. The first parameter is the average height (normalized) of the grid and the second parameter is the type of vegetation in the terrain. To be navigable, the average normalized height is set to 3...
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.
Gas path sealing in turbine engines
NASA Technical Reports Server (NTRS)
Ludwig, L. P.
1978-01-01
Survey of gas path seals is presented with particular attention given to sealing clearance effects on engine component efficiency. The effects on compressor pressure ratio and stall margin are pointed out. Various case-rotor relative displacements, which affect gas path seal clearances, are identified. Forces produced by nonuniform sealing clearances and their effect on rotor stability are discussed qualitatively, and recent work on turbine-blade-tip sealing for high temperatures is described. The need for active clearance control and for engine structural analysis is discussed. The functions of the internal-flow system and its seals are reviewed.
Gas path sealing in turbine engines
NASA Technical Reports Server (NTRS)
Ludwig, L. P.
1978-01-01
Gas path seals are discussed with emphasis on sealing clearance effects on engine component efficiency, compressor pressure ratio, and stall margin. Various case-rotor relative displacements, which affect gas path seal clearances, are identified. Forces produced by nonuniform sealing clearances and their effect on rotor stability are examined qualitatively, and recent work on turbine-blade-tip sealing for high temperatures is described. The need for active clearance control and for engine structural analysis is discussed. The functions of the internal-flow system and its seals are reviewed.
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.
Path factorization approach to stochastic simulations.
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. PMID:25526107
Common-path interference and oscillatory Zener tunneling in bilayer graphene p-n junctions
Nandkishore, Rahul; Levitov, Leonid
2011-01-01
Interference and tunneling are two signature quantum effects that are often perceived as the yin and yang of quantum mechanics: a particle simultaneously propagating along several distinct classical paths versus a particle penetrating through a classically inaccessible region via a single least-action path. Here we demonstrate that the Dirac quasiparticles in graphene provide a dramatic departure from this paradigm. We show that Zener tunneling in gapped bilayer graphene, which governs transport through p-n heterojunctions, exhibits common-path interference that takes place under the tunnel barrier. Due to a symmetry peculiar to the gapped bilayer graphene bandstructure, interfering tunneling paths form conjugate pairs, giving rise to high-contrast oscillations in transmission as a function of the gate-tunable bandgap and other control parameters of the junction. The common-path interference is solely due to forward-propagating waves; in contrast to Fabry–Pérot-type interference in resonant-tunneling structures, it does not rely on multiple backscattering. The oscillations manifest themselves in the junction I–V characteristic as N-shaped branches with negative differential conductivity. The negative dI/dV, which arises solely due to under-barrier interference, can enable new high-speed active-circuit devices with architectures that are not available in electronic semiconductor devices. PMID:21825159
Jue, Jason P.
Abstract-- Path protection requires finding a working path and a protection path that are link disjoint. In this paper, we consider the dynamic lightpath protection problem in WDM mesh networks under-disjoint lightpaths on a single wavelength; however, such algorithms fail if the working and protection lightpaths
Jue, Jason P.
Abstract-- Path protection requires finding a working path and a protection path that are link disjoint. In this paper, we consider the dynamic lightpath protection problem in WDM mesh networks where-- Optical network, lightpath protection, shared risk link group, risk disjoint, integer linear program (ILP
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
self-avoiding path dSG self-avoiding path
Hattori, Tetsuya
0: SAP on dSG (Self-Avoiding Path) w : Z+ G L(w) = inf{i | w(j) = w(i), j i} W0 = {w : Z+ G, 6, Â· Â· Â· dSG, d = 2, 3, SAP SAP path dSG SAP SAP #12;( ) (i) (path ) ( ) (ii) (iii) dSG SAP (re- cursion) #12;recursion SAP (A) SAP Â· d = 2: I2 = {(1), (2)} {Ov1} ( ) {Ov1v2} ( ) Â· I3 = {(1), (2), (3
Seid, K A; Badot, J C; Dubrunfaut, O; Caldes, M T; Stephant, N; Gautier, L; Guyomard, D; Lestriez, B
2013-12-01
This work is the first detailed study concerning the multiscale electronic transport and its temperature dependence in the LiNi1/3Co1/3Mn1/3O2 (NMC) family, high-capacity electrode materials for lithium ion batteries. Powders with two different mean cluster sizes (3 ?m and 10 ?m) but the same particle sizes (0.4 to 1.3 ?m) were measured. The detailed formula of the studied compound is Li1.04Ni(2+)0.235Ni(3+)0.09Mn(4+)0.315Co(3+)0.32O2. Different electrical relaxations are evidenced, resulting from the polarizations at the different scales of the powder architecture. When the frequency increases, three dielectric relaxations are detected in the following order due to: (a) space-charge polarization (low-frequency range) owing to the interface between the sample and the conductive metallic layer deposited on it; (b) polarization of NMC clusters (micronic scale) induced by the existence of resistive junctions between them; and (c) polarization of NMC particles (at sub-micronic scale) induced by resistive junctions between them. High interatomic level conductivity of about 20 S m(-1) was evidenced and attributed to the contribution of the extended states and to a Brownian motion of the charge carriers with mean free path similar to the lattice constant. The ratio between sample and local conductivity is more than 10(5). The large conductivity drop of 3 to 4 orders of magnitude is observed from the particle to the cluster scale. A very large number of charge carriers are blocked by the interparticle junctions within the clusters. The conductivity drop from the cluster to the sample scale is comparatively very small, owing to the dense architecture of the NMC sample in which the spherical clusters are very piled up on each other. PMID:24145999
Electron pairing in dilute liquid metal-metal halide solutions
Selloni, A.; Car, R.; Parrinello, M.; Carnevali, P.
1987-09-10
Spin density functional theory is used to describe the interaction between solvated electrons in KCl in the high dilution limit. In agreement with recent calculations based on the path integral method our results for antiparallel spin predict a strong tendency to form localized bielectronic complexes. At variance with numerical path integral, our method can efficiently treat the case of parallel spins. For this case we find that electrons repel each other and localize into separate F-center-like states.
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…
COUNTING NONINTERSECTING LATTICE PATHS WITH TURNS
Krattenthaler, Christian
COUNTING NONINTERSECTING LATTICE PATHS WITH TURNS C. Krattenthaler Institut fÂ¨ur Mathematik der points and a given total number of North-East turns. These formulas are important for the computation with given starting and end points and a given total number of turns in certain regions. If one forgets about
2005 Spring Quarter Page The Critical Path
Christian, Eric
2005 Spring Quarter Page The Critical Path GOES-N About to Launch GOES-R Coming Down the Line February 6, 1975. SMS-C heralded the GOES era when it was named GOES-A. (GOES Continued on page 6) GOES-N/GOES-R
Fusion Development Path Panel Preliminary Report
Fusion Development Path Panel Preliminary Report Summary for NRC BPAC Panel (Focus on MFE of a demonstration power plant in approximately 35 years. The plan should recognize the capabilities of all fusion facilities around the world, and include both magnetic fusion energy (MFE) and inertial fusion energy (IFE
Building a path in cell biology
Voeltz, Gia; Cheeseman, Iain
2012-01-01
Setting up a new lab is an exciting but challenging prospect. We discuss our experiences in finding a path to tackle some of the key current questions in cell biology and the hurdles that we have encountered along the way. PMID:23112222
Path Integration in Desert Ants, Cataglyphis fortis
Martin Muller; Rudiger Wehner
1988-01-01
Foraging desert ants, Cataglyphis fortis, continually keep track of their own positions relative to home--i.e., integrate their tortuous outbound routes and return home along straight (inbound) routes. By experimentally manipulating the ants' outbound trajectories we show that the ants solve this path integration problem not by performing a true vector summation (as a human navigator does) but by employing a
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
is organized as follows. Section 2 is dedicated to the state of the art on biometric authentication on mobile. STATE OF THE ART In the literature, biometric based mobile authentication is an emerging issueBiometric Secret Path for Mobile User Authentication: A Preliminary Study Michael Beton National
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
Folded-path optical analysis gas cell
Carangelo, Robert M. (Glastonbury, CT); Wright, David D. (Vershire, VT)
1995-01-01
A folded-path gas cell employs an elliptical concave mirror in confronting relationship to two substantially spherical concave mirrors. At least one of the spherical mirrors, and usually both, are formed with an added cylindrical component to increase orthogonal focii coincidence and thereby to increase the radiation energy throughput characteristic of the cell.
Folded-path optical analysis gas cell
Carangelo, R.M.; Wright, D.D.
1995-08-08
A folded-path gas cell employs an elliptical concave mirror in confronting relationship to two substantially spherical concave mirrors. At least one of the spherical mirrors, and usually both, are formed with an added cylindrical component to increase orthogonal foci coincidence and thereby to increase the radiation energy throughput characteristic of the cell. 10 figs.
Fractional quantum mechanics and Lévy path integrals
NASA Astrophysics Data System (ADS)
Laskin, Nikolai
2000-04-01
A new extension of a fractality concept in quantum physics has been developed. The path integrals over the Lévy paths are defined and fractional quantum and statistical mechanics have been developed via new fractional path integrals approach. A fractional generalization of the Schrödinger equation has been found. The new relation between the energy and the momentum of non-relativistic fractional quantum-mechanical particle has been established. We have derived a free particle quantum-mechanical kernel using Fox's H-function. The equation for the fractional plane wave function has been obtained. As a physical application of the developed fQM we have proposed a new fractional approach to the QCD problem of quarkonium. A fractional generalization of the motion equation for the density matrix has been found. The density matrix of a free particle has been expressed in term of the Fox's H-function. We also discuss the relationships between fractional and the well-known Feynman path integral approaches to quantum and statistical mechanics.
Judgments of Path, Not Heading, Guide Locomotion
Richard M. Wilkie; John P. Wann
2006-01-01
To steer a course through the world, people are almost entirely dependent on visual information, of which a key component is optic flow. In many models of locomotion, heading is described as the fundamental control variable; however, it has also been shown that fixating points along or near one's future path could be the basis of an efficient control solution.
Four Paths that Led to Careers.
ERIC Educational Resources Information Center
Witherspoon, W. Roger
1989-01-01
Traces the alternative career paths that four minority individuals followed to professional journalism. Includes a potential doctoral candidate in 17th century poetry, a future aeronautical engineer, a jazz musician, and possible pharmacist. Contends that minorities must often approach the profession through alternative routes in order to succeed.…
Shortest Paths in Microseconds Rachit Agarwal
, the goal is to minimize latency while maintaining feasible memory requirements. We present ASAP, a system that achieves this goal by exploiting the structure of social networks. ASAP preprocesses a given network edges, ASAP computes a shortest path for most node pairs in less than 49 microseconds per pair. ASAP
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.
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.
Optimal Distributed All Pairs Shortest Paths
Optimal Distributed All Pairs Shortest Paths ETH Zurich Distributed Computing Group Stephan Holzer ETH Zürich Roger Wattenhofer ETH Zürich #12;Distributed network Graph G of n nodes 2 4 5 1 3 #12;Distributed network Graph G of n nodes 2 4 5 1 3 Unique IDs #12;Distributed network Graph G of n nodes 2 4 5 1
Planning Flight Paths of Autonomous Aerobots
NASA Technical Reports Server (NTRS)
Kulczycki, Eric; Elfes, Alberto; Sharma, Shivanjli
2009-01-01
Algorithms for planning flight paths of autonomous aerobots (robotic blimps) to be deployed in scientific exploration of remote planets are undergoing development. These algorithms are also adaptable to terrestrial applications involving robotic submarines as well as aerobots and other autonomous aircraft used to acquire scientific data or to perform surveying or monitoring functions.
Crack path prediction near an elliptical inclusion
E. M. Patton; M. H. Santare
1993-01-01
A technique is presented which will predict the path of a naturally growing crack where the stress field can be modeled as two-dimensional. The Green function for an arbitrarily oriented edge dislocation interacting with a rigid inclusion (or void) is used in an integral formulation of the elasticity problem. The technique uses a boundary integral approach to solve for the
Volcanic eruption induced WWVB transmission path interruption
H. A. Buckmaster; C. H. Hansen
1985-01-01
It is reported that the 60 kHz transmission of WWVB from Fort Collins, Colorado, was not received in Calgary, Alberta, Canada, for about 11 h from 1109 UT to 2153 UT on July 23, 1980. It is suggested that this transmission path interruption is correlated with the 15 km height ash cloud due to the July 22, 1980 volcanic eruption
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…
New formulas for tropospheric scatter path loss
Steen A. Parl
1979-01-01
The predicted performance of tropospheric scatter transmission is investigated in terms of spectrum slope, refractive index variance, and scale of turbulence. The common volume integral is evaluated to yield a useful expression for path loss in terms of these parameters. Formulas for the coupling loss in the asymptotic case of very wide and very narrow antenna beams are derived. Approximate
Current SPE Hydrodynamic Modeling and Path Forward
Knight, Earl E. [Los Alamos National Laboratory; Rougier, Esteban [Los Alamos National Laboratory
2012-08-14
Extensive work has been conducted on SPE analysis efforts: Fault effects Non-uniform weathered layer analysis MUNROU: material library incorporation, parallelization, and development of non-locking tets Development of a unique continuum-based-visco-plastic strain-rate-dependent material model With corrected SPE data path is now set for a multipronged approach to fully understand experimental series shot effects.
PATH. Gamma Dose Calculations and Shielding Analysis
Su, S.D.; Baylor, K.J.; Engholm, B.A. [CEGA Corporation, San Diego, CA (United States)
1988-02-01
PATH is a highly flexible shielding code utilizing the common point-kernel integration technique primarily for treating gamma radiation from reactors, radioactive components and from complex piping systems. Major features of the code include complex geometry capability, various source options, extensive data library, simple but flexible input and well-organized output format.
Analysis on free Riemannian path spaces
Shizan Fang; Feng-Yu Wang
2005-01-01
The gradient operator is defined on the free path space with reference measure P?, the law of the Brownian motion on the base manifold with initial distribution ?, where ? has strictly positive density w.r.t. the volume measure. The formula of integration by parts is established for the underlying directional derivatives, which implies the closability of the gradient operator so
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,
Arto Annila
2011-01-01
The variational principle in its original form á la Maupertuis is used to delineate paths of light through varying energy densities and to associate shifts in frequency and changes in momentum. The gravitational bending and Doppler shift are in this way found as mere manifestations of least-time energy dispersal. In particular, the general principle of least action due to Maupertuis
employment opportunities in exciting career paths
Barthelat, Francois
IN FOOD SCIENCE McGillMcGillMcGILL UNIVERSITY Photos: © USDA. Used with permission Design © 2006/03 HCR) 398-7977 e-mail: foodscience@mcgill.ca We are also on the web: www.mcgill.ca/foodscience/ McGill Food in exciting career paths Food Science Cerificate for BSc graduates Food Science Cerificate for BSc graduates
Shielded transient self-interaction of a bunch entering a circle from a straight path
NASA Astrophysics Data System (ADS)
Li, Rui; Bohn, Courtlandt L.; Bisognano, Joseph J.
1997-11-01
Recent developments in electron-gun and injector technologies enable production of short, high-charge bunches. In this parameter regime,the curvature effect on the bunch self-interaction, by way of coherent synchrotron radiation (CSR) and space-charge forces as the beam traverse magnet bends, may cause serious emittance degradation. In this paper, we study an electron bunch orbiting between two infinite, parallel conducting plates. The bunch moves on a trajectory from a straight path to a circular orbit and begins radiating. Transient effects, arising from CSR and space-charge forces generated from source particles both on the bend and on the straight path prior to the bend, are analyzed using Lienard-Wiechert fields, and their overall net effect is obtained. The influence of the plates on the transients is contrasted to their shielding of the steady- state radiated power. Results for emittance degradation induced by this self-interaction are also presented.
A methodology for predicting minimum travel paths using real-time traffic network data
Liu, Chang
1991-01-01
presents the examples of the program results. Appendix B contains the computer program listing. BACKGROUND Based on the advances in electronics, communication, and computer information processing technologies, Intelligent Vehicle/Highway Systems (IVHS... of MASTER OF SCIENCE December 1991 Major Subject: Civil Engineering A METHODOLOGY FOR PREDICTING MINIMUM TRAVEL PATHS USING REAL-TIME TRAFFIC NETWORK DATA A Thesis by Chang Liu Approved as to style and content by: Daniel B. Fambro (Chair...
On the effect of winding parallel paths in synchronous permanent magnet electric machine drives
D. M. Ionel; I. P. Brown
2010-01-01
The described study involved interior permanent magnet (IPM) motors with distributed and concentrated (non-overlapping) stator windings. The machines were operated with sine-wave current-regulated power electronic drives. A coupled finite element model was used for the electromagnetic field and electric circuit analysis. Special instrumentation was employed for the measurement of 3D forces. It is shown that stator winding parallel paths can
Paths in the minimally weighted path model are incompatible with Schramm-Loewner evolution
NASA Astrophysics Data System (ADS)
Norrenbrock, C.; Melchert, O.; Hartmann, A. K.
2013-03-01
We study numerically the geometrical properties of minimally weighted paths that appear in the minimally weighted path (MWP) model on two-dimensional lattices assuming a combination of periodic and free boundary conditions (BCs). Each realization of the disorder consists of a random fraction (1-?) of bonds with unit strength and a fraction ? of bond strengths drawn from a Gaussian distribution with zero mean and unit width. For each such sample, a path is forced to span the lattice along the direction with the free BCs. The path and a set of negatively weighted loops form a ground state. A ground state on such a lattice can be determined performing a nontrivial transformation of the original graph and applying sophisticated matching algorithms. Here we examine whether the geometrical properties of the paths are in accordance with the predictions of the Schramm-Loewner evolution (SLE). Measuring the fractal dimension, considering the winding angle statistics, and reviewing Schramm's left passage formula indicate that the paths cannot be described in terms of SLE.
Role of closed paths in the path integral approach of statistical thermodynamics
NASA Astrophysics Data System (ADS)
Badiali, Jean-Pierre
2015-04-01
Thermodynamics is independent of a description at a microscopic level consequently statistical thermodynamics must produce results independent of the coordinate system used to describe the particles and their interactions. In the path integral formalism the equilibrium properties are calculated by using closed paths and an euclidean coordinate system. We show that the calculations on these paths are coordinates independent. In the change of coordinate systems we consider those preserving the physics on which we focus. Recently it has been shown that the path integral formalism can be built from the real motion of particles. We consider the change of coordinates for which the equations of motion are unchanged. Thus we have to deal with the canonical transformations. The Lagrangian is not uniquely defined and a change of coordinates introduces in hamiltonians the partial time derivative of an arbitrary function. We have show that the closed paths does not contain any arbitrary ingredients. This proof is inspired by a method used in gauge theory. Closed paths appear as the keystone on which we may describe the equilibrium states in statistical thermodynamics.
Path ORAM: An Extremely Simple Oblivious RAM Protocol
Stefanov, Emil
We present Path ORAM, an extremely simple Oblivious RAM protocol with a small amount of client storage. Partly due to its simplicity, Path ORAM is the most practical ORAM scheme for small client storage known to date. We ...
14 CFR 23.61 - Takeoff flight path.
Code of Federal Regulations, 2011 CFR
2011-01-01
...UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Performance § 23.61 Takeoff flight path. For each commuter category...distance determined in accordance with § 23.59. (b) The net takeoff flight path data must be determined so that...
14 CFR 23.61 - Takeoff flight path.
Code of Federal Regulations, 2010 CFR
2010-01-01
...UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Flight Performance § 23.61 Takeoff flight path. For each commuter category...distance determined in accordance with § 23.59. (b) The net takeoff flight path data must be determined so that...
14 CFR 25.115 - Takeoff flight path.
Code of Federal Regulations, 2011 CFR
2011-01-01
...AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Performance § 25.115 Takeoff flight path. (a) The takeoff...as appropriate for the runway surface condition. (b) The net takeoff flight path data must be determined so that they...
14 CFR 25.115 - Takeoff flight path.
Code of Federal Regulations, 2010 CFR
2010-01-01
...AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Flight Performance § 25.115 Takeoff flight path. (a) The takeoff...as appropriate for the runway surface condition. (b) The net takeoff flight path data must be determined so that they...
Real-Time Feynman Path Integral Realization of Instantons
Aleksey Cherman; Mithat Unsal
2014-08-19
In Euclidean path integrals, quantum mechanical tunneling amplitudes are associated with instanton configurations. We explain how tunneling amplitudes are encoded in real-time Feynman path integrals. The essential steps are borrowed from Picard-Lefschetz theory and resurgence theory.
Mission Geography: Paths (title provided or enhanced by cataloger)
NSDL National Science Digital Library
Mission Geography uses existing NASA data and images where possible to engage students in active, hands-on inquiry, modeling the scientific method and developing students' understanding of environment-society relations and Earth science. This module looks at many different kinds of paths and considers why paths are where they are and how they look from space. People and animals make paths that take into account the terrain and other features of the landscape. Rivers, lava, smoke, and other natural phenomena follow paths. The module contains four investigations in which students interpret paths in their immediate environment, use literature to investigate paths, inspect unusual paths, and use satellite images to view paths of natural disasters. Each investigation is complete with overview, a list of materials and supplies, content preview, classroom procedures, worksheets, background, and evaluation.
1. AERIAL VIEW OF THE PATH TRANSIT SYSTEM BRIDGE, LOOKING ...
1. AERIAL VIEW OF THE PATH TRANSIT SYSTEM BRIDGE, LOOKING NORTHEAST. THE CONRAIL BRIDGE (HAER No. NJ-43) AND THE NEWARK TURNPIKE ARE VISIBLE IN THE BACKGROUND - Path Transit System Bridge, Spanning Hackensack River, Kearny, Hudson County, NJ
Dual-path receiver for state reconstruction of propagating
Gross, Rudolf
WMI Dual-path receiver for state reconstruction of propagating quantum microwaves Diploma Thesis homodyning for microwave setups . . . . . . . . . . . 6 2.3 Dual-path method (classical emulator . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.1.2 Heterodyne converter
Jun Yeup Kim; Le-Yin Zhang
2008-01-01
Jun Yeup Kim and Le-Yin Zhang Formation of foreign direct investment clustering – a new path to local economic development? The case of Qingdao, Regional Studies. This paper investigates the clustering of Chinese electronics manufacturers, large and small, alongside established foreign producers in Qingdao, North China. It examines how the supplier–buyer linkages between foreign invested enterprises (FIEs) and local firms
Ellingson, Steven W.
a Transmitter Inside an Aircraft Cabin to an Exterior Fuselage-Mounted Antenna Kathy Wei Hurst and Steven W and equipment on large aircraft may increase the like- lihood of interference with the aircraft's electronic systems. Thus, the "interference path loss" from a transmitting device inside the cabin of such aircraft
Takehiro Yonehara; Kazuo Takatsuka
2010-01-01
We extend our formerly proposed theory for non-Born-Oppenheimer electronic and nuclear wavepacket dynamics within on-the-fly scheme [T. Yonehara, S. Takahashi, and K. Takatsuka, J. Chem. Phys. 130, 214113 (2009)] to a case of nonadiabatic dynamics under an intense laser field: electron wavepacket in a molecule is propagated in attosecond time-scale along non-Born-Oppenheimer nuclear paths that smoothly branch due to nonadiabatic
Dynamic Path Planning of Mobile Robots Based on ABC Algorithm
Qianzhi Ma; Xiujuan Lei
2010-01-01
\\u000a For the global path planning of mobile robot under the dynamic uncertain environment, a path planning method combined time\\u000a rolling window strategy and artificial bee colony (ABC) algorithm was proposed. To meet the real time requirement, the global\\u000a path was replaced by local paths within a series of rolling windows. Due to the ability of global optimization, and rapid\\u000a convergence
A Combinatorial Interpretation of the Area of Schroder Paths
Pinzani, Renzo
A Combinatorial Interpretation of the Area of SchrÂ¨oder Paths E. Pergola, R. Pinzani Dipartimento. Abstract An elevated SchrÂ¨oder path is a lattice path that uses the steps (1; 1), (1; \\Gamma1), and (2; 0 of elevated SchrÂ¨oder paths of length 2n + 2 satisfies the recurrence f n+1 = 6f n \\Gamma f n\\Gamma1 , n â?? 2
NASA Astrophysics Data System (ADS)
Zou, X. D.; Hovmoeller, S.
2008-01-01
Different techniques for structure determination from transmission electron microscopy and electron diffraction are reviewed, including three-dimensional reconstruction, the precession technique and ultrafast electron crystallography. Examples of electron-crystallography applications are given.
Degenerate optimal paths in thermally isolated systems
NASA Astrophysics Data System (ADS)
Acconcia, Thiago V.; Bonança, Marcus V. S.
2015-04-01
We present an analysis of the work performed on a system of interest that is kept thermally isolated during the switching of a control parameter. We show that there exists, for a certain class of systems, a finite-time family of switching protocols for which the work is equal to the quasistatic value. These optimal paths are obtained within linear response for systems initially prepared in a canonical distribution. According to our approach, such protocols are composed of a linear part plus a function which is odd with respect to time reversal. For systems with one degree of freedom, we claim that these optimal paths may also lead to the conservation of the corresponding adiabatic invariant. This points to an interesting connection between work and the conservation of the volume enclosed by the energy shell. To illustrate our findings, we solve analytically the harmonic oscillator and present numerical results for certain anharmonic examples.
Bosonization in the path integral formulation
NASA Astrophysics Data System (ADS)
Fujikawa, Kazuo; Suzuki, Hiroshi
2015-03-01
We establish the direct d =2 on-shell bosonization ?L(x+)=ei ? (x+) and ?R†(x-)=ei ? (x-) in path integral formulation by deriving the off-shell relations ?L(x )?R†(x )=exp [i ? (x )] and ?R(x )?L†(x )=exp [-i ? (x )] . Similarly, the on-shell bosonization of the bosonic commuting spinor, ?L(x+)=i e-i ? (x+)?+e-i ? (x+) , ?R†(x-)=e-i ? (x-)-i ? (x-) and ?R(x-)=i ei ? (x-)?-e+i ? (x-) , ?L†(x+)=ei ? (x+)+i ? (x+) , is established in path integral formulation by deriving the off-shell relations ?L(x )?R†(x )=i e-i ? (x )?+e-i ? (x ) and ?R(x )?L†(x )=i ei ? (x )?-ei ? (x ) .
Gauge Freedom in the Path Integral Formalism
NASA Astrophysics Data System (ADS)
Sakoda, S.
2007-04-01
We investigate 't Hooft's technique of changing the gauge parameter of the linear covariant gauge from the point of view of the path integral with respect to the gauge freedom. Extension of the degrees of freedom allows us to formulate a system with extended gauge symmetry. The gauge fixing for this extended symmetry yields the 't Hooft averaging as a path integral over the additional degrees of freedom. Another gauge fixing is found as a non-abelian analogue of the type II gaugeon formalism of Yokoyama and Kubo. In this connection, the 't Hooft average can be viewed as the analogue of the type I gaugeon formalism. As a result, we obtain gauge covariant formulations of non-abelian gauge theories, which allow us to understand 't Hoot's technique also from the canonical fromalism.
Common-path spectral phase microscopy
NASA Astrophysics Data System (ADS)
Cardenas, Nelson; Mohanty, Samarendra
2011-10-01
Quantitative phase microscopy is an emerging non-contact method for quantifying physical properties (refractive index, thickness) of materials. The high spatial resolution achieved with millisecond-scale resolution using this non-staining method over a wide-field of view is highly advantageous for mapping dynamic changes in the sample properties due to temperature, pressure and molecular interactions. Since refractive index dispersion is intrinsic to a material, he spectral measurement of refractive index changes will allow characterization and analytical quantification of material. Here, we introduce common-path spectral phase microscopic (CP-SPM) imaging of microscopic objects. CP-SPM is based on a common path interferometer with a tunable laser beam With this method, we are able to characterize both the refractive index of particles over a continuous wavelength band, and also the characteristics of several types of particles simultaneously.
Volcanic eruption induced WWVB transmission path interruption
NASA Astrophysics Data System (ADS)
Buckmaster, H. A.; Hansen, C. H.
1985-07-01
It is reported that the 60 kHz transmission of WWVB from Fort Collins, Colorado, was not received in Calgary, Alberta, Canada, for about 11 h from 1109 UT to 2153 UT on July 23, 1980. It is suggested that this transmission path interruption is correlated with the 15 km height ash cloud due to the July 22, 1980 volcanic eruption of Mount St. Helens as it drifted eastward interrupting both the ground- and first hop sky-wave paths and that this ash cloud is the source of the conductivity and/or ionization necessary to produce this interruption. Small phase retardations are also reported which could be correlated with other Mount St. Helens volcanic events during May-July 1980.
Wavelet shrinkage on paths for denoising of scattered data
Plonka, Gerlind
for image denoising. In this paper, we want to propose a new adaptive wavelet threshold scheme for scatteWavelet shrinkage on paths for denoising of scattered data Dennis Heinen and Gerlind Plonka; Sec- ondary 68U10. Keywords. scattered data denoising, wavelet shrinkage, path vectors, easy path
Integrated path planning and dynamic steering control for autonomous vehicles
B. Krogh; C. Thorpe
1986-01-01
A method is presented for combining two previously proposed algorithms for path-planning and dynamic steering control into a computationally feasible scheme for real-time feedback control of autonomous vehicles in uncertain environments. In the proposed approach to vehicle guidance and control, Path Relaxation is used to compute critical points along a globally desirable path using a priori information and sensor data.
Integrated Path Planning and ynamic Steering Control for Autonomous Vehicles
Bruce P. I. Krogh; Charles E. Thorpe
1986-01-01
A method is presented for combining two previously proposed algorithms for path-planning and dynamic steering control into a computationally feasible scheme for real-time feedback control of autonomous vehicles in uncertain environments. In the proposed approach to vehicle guidance and control, Path Relaxation is used to compute critical points along a globally desirable path using a priori information and sensor data'.
EFFET KONDO PATH INTEGRAL THEORY OF MAGNETIC ALLOYS
Paris-Sud XI, UniversitÃ© de
EFFET KONDO PATH INTEGRAL THEORY OF MAGNETIC ALLOYS by D. R. HAMANN Bell Telephone Laboratories-d. Une evaluation approxin~ativede ce (( path integral)) restreint donne la temperature de Kondo caracte and Yuval. Approximate evaluation of this restricted path integral yields the characteristic Kondo
Multiple-Goals Path Planning for Coordinate Measuring Machines
Steven N. Spitz; Aristides A. G. Requicha
2000-01-01
Path planning is a crucial step in automatic programming of coor- dinate measuring machines (CMMs). The goal is to generate an efficient and collision-free path for the CMM to inspect a collec- tion of points. Previous research concentrates on path plan ning be- tween two points, or sequencing the points without regard to obsta- cles and collisions. In this paper
Path planning in the Proteus rapid prototyping system
Konstantinos A. Tarabanis
2001-01-01
Presents algorithms for determining the paths employed by the Proteus rapid prototyping system when building three-dimensional parts. Proteus is a fused deposition modeling system that extrudes a thermoplastic in beads through a nozzle. Determines within each layer of the layered manufacturing process, the material deposition paths as well as the regions where local structures are required to support these paths.
Optimal robot path planning based on danger degree map
Yinghua Xue; Guohui Tian; Bin Huang
2009-01-01
A modified path planning approach is presented for mobile robot in the paper. First a new environment model called danger degree map (DDM) is constructed in order to provide more rich environment information than grids map. Then the equidistant distributed PSO whose fitness function is the weighted sum of the path length and the path danger degree is introduced to
Adaptive tool path planning applied in manufacturing optimization
J. Radej; L. Budin; Z. Mihajlovic
2004-01-01
Paper describes research done on algorithms for the generation of gouge-free nonisoparametric tool paths across surface plane segments obtained through triangulation partitioning. Along with contiguous trajectory sequences, adaptive tool path planning introduces partially discontinuous tool trajectories. Algorithm achieves the necessary trajectory continuity by the insertion of the auxiliary tool-orientation trajectories. The tool passes over the path gaps are accomplished through
Rapid approximation for optimal paths in phase space
Chyon Hae Kim; Hiroshi Tsujino; Shigeki Sugano
2011-01-01
This paper addresses optimal motion for general machines. Approximation for optimal motion needs a global path planning algorithm that precisely calculates the whole dynamics of a machine in a brief calculation. We propose a path planning algorithm that is composed of a path searching algorithm and a pruning algorithm. The pruning algorithm is based on our analysis for the resemblances
Spare Capacity Assignment in Telecom Networks Using Path Restoration
Jeyakesavan Veerasamy; S. Venkatesant; Jay C. Shah
1995-01-01
Path restoration scheme can be used in augmentingexisting telecommunication networks with adequatespare capacity to achieve a desired level of protectionagainst link failures. Path restoration planning correspondsto the multi--commodity flow problem, whichis computationally hard. In this paper, we present thedetails of an approximation scheme for the path basedrestoration planning problem and an implementation.We then compare the performance of link and pathrestoration
Shortest paths synthesis for a car-like robot
P. Soueres; J.-P. Laumond
1996-01-01
This paper deals with the complete characterization of the shortest paths for a car-like robot. Previous works have shown that the search for a shortest path may be limited to a simple family of trajectories. Our work completes this study by providing a way to select inside this family an optimal path to link any two configurations. We combine the
A Schroder Generalization of Haglund's Statistic on Catalan Paths
Killpatrick, Kendra
A SchrÂ¨oder Generalization of Haglund's Statistic on Catalan Paths Eric S. Egge Department generalize Haglund's statistic to Sn,d, the set of SchrÂ¨oder paths from (0, 0) to (n, n) with with d diagonal is equidistributed with a known extension of the area statistic to SchrÂ¨oder paths. We conjecture