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1

Electron Mean Free Path in Epitaxial Ta(001) Layers  

NASA Astrophysics Data System (ADS)

Epitaxial tantalum layers were grown on MgO(001) by ultrahigh vacuum magnetron sputter deposition at 650 °C to thicknesses d ranging from 5 nm to 2 mum. X-ray diffraction including o-2theta, o rocking curve, and ? scans confirm that the layers are Ta(001) single crystals, while X-ray reflectivity indicates that their roughness is < 0.1 nm for short lateral length scales. The measured room temperature resistivity increases from 12.6+/-0.6 muO-cm for large d to 42.1+/-0.9 muO-cm for d = 5 nm. This increase is well described by the Fuchs-Sondheimer model, yielding a Ta room temperature bulk electron mean free path of lambda294K = 28+/-1 nm. Corresponding measurements in liquid nitrogen yield lambda77K = 65+/-5 nm. These values are approximately an order of magnitude larger than 2.35 and 8.36 nm, respectively, expected from the free electron model. This large discrepancy is attributed to the highly non-spherical Ta Fermi surface. More importantly, the ratio of the measured mean free path lambda77K/ lambda 294K= 2.32 is 1.5x smaller than the ratio of the measured bulk resistivities rho294Krho77K. This suggests that either (i) the mean free path is strongly band dependent, (ii) surface roughness contributes greatly to electron scattering at low temperatures in films of thickness on the order of the mean free path, or (iii) the electron mean free path at low temperature is restricted by the presence of impurities, evidenced by a measured residual resistivity.

Guan, Daniel

2

Effective electron mean free path in TiN(001)  

NASA Astrophysics Data System (ADS)

The measured resistivity ? of smooth stoichiometric epitaxial TiN(001) is 13 and 3.0 ?? cm at 298 and 77 K for bulk layers but is 8 and 25 times higher when the layer thickness d is reduced to 2 nm. The increase in ? with decreasing d is attributed to diffuse electron-surface scattering and is well described by the classical Fuchs-Sondheimer (F-S) model. This is unexpected because the F-S model is based on the nearly free electron model, while TiN exhibits a highly non-spherical Fermi surface and three bands crossing the Fermi-level. The measured room temperature effective electron mean free path ? for bulk scattering is 45 ± 4 nm, which is an order of magnitude larger than the free-electron prediction. This deviation is attributed to ˜93% of charge transport in TiN being due to two slightly filled bands which represent only 4% of conduction electrons. The F-S model is applicable to TiN because these two bands are nearly parabolic and nearly degenerate, yielding a single value for ?, which is estimated based on the published band structure to be 49 nm, in excellent agreement with the experimental 45 nm. These results demonstrate that the F-S model is applicable to metals with non-spherical Fermi-surfaces as long as the charge transport is dominated by a single (or multiple degenerate) band(s).

Chawla, J. S.; Zhang, X. Y.; Gall, D.

2013-02-01

3

Electron mean free path from angle-dependent photoelectron spectroscopy of aerosol particles  

E-print Network

We propose angle-resolved photoelectron spectroscopy of aerosol particles as an alternative way to determine the electron mean free path of low energy electrons in solid and liquid materials. The mean free path is obtained from fits of simulated photoemission images to experimental ones over a broad range of different aerosol particle sizes. The principal advantage of the aerosol approach is twofold. Firstly, aerosol photoemission studies can be performed for many different materials, including liquids. Secondly, the size-dependent anisotropy of the photoelectrons can be exploited in addition to size-dependent changes in their kinetic energy. These finite size effects depend in different ways on the mean free path and thus provide more information on the mean free path than corresponding liquid jet, thin film, or bulk data. The present contribution is a proof of principle employing a simple model for the photoemission of electrons and preliminary experimental data for potassium chloride aerosol particles.

Goldmann, Maximilian; West, Adam H C; Yoder, Bruce L; Signorell, Ruth

2015-01-01

4

Density dependence of electron mean-free paths from low to high energies  

NASA Astrophysics Data System (ADS)

The mean-free path of an electron scattering inelastically in a degenerate electron gas at zero temperature has been calculated, using the dielectric function/self-energy formalism of Ritchie [Phys. Rev. 114, 644 (1959)]. The objective of this work is to model accurately the mean-free path as a function of photoelectron energy and density for use in the calculation of extended x-ray absorption fine structure (EXAFS) [Rev. Mod. Phys. 53, 1 (1981)] of fluids and plasmas whose structure can be described by a radial distribution function. Results are compared with proposed universal mean-free path formulas and it is found that a more generalized version of a power law provides an adequate fit. A table of the best-fit parameters of this law at a range of densities of interest for the EXAFS colliding shock experiments on foil targets is presented.

Gordon, F. I.; Djaoui, A.

1992-12-01

5

Energy losses and mean free paths of electrons in silicon dioxide  

SciTech Connect

Theoretical models and calculations are combined with experimental optical data to determine a model energy-loss function for SiO/sub 2/. Sumrule checks and comparisons with experimental information are made to insure overall consistency of the model. The model energy-loss function is employed to calculate electron inelastic mean free paths and stopping powers for electrons with energies less than or equal to 10 keV in SiO/sub 2/.

Ashley, J.C.; Anderson, V.E.

1981-01-01

6

Photocurrent in bulk heterojunction solar cells with similar electron and hole mean free path  

SciTech Connect

We present photocurrents at several temperatures carried out in a bulk heterojunction photovoltaic device. To explain the results, we developed an analytical model assuming non-injecting contacts and equal mean free paths for electrons and holes. The fitting of the equation to the experimental data provided the temperature evolution of the charge transfer state dissociation probability (P) and ??, where ? is the charge carrier mobility and ? is the charge carrier lifetime. The photocurrent expression tends towards a saturation value of eGPL for high electric fields, where GP is the generation rate of charge carriers.

Coutinho, Douglas José; Faria, Roberto Mendonça, E-mail: faria@ifsc.usp.br [Instituto de Física de São Carlos, Universidade de São Paulo, C.P. 369, 13560-970 São Carlos, SP (Brazil)

2013-11-25

7

Extended Mermin Method for Calculating the Electron Inelastic Mean Free Path  

NASA Astrophysics Data System (ADS)

We propose an improved method for calculating electron inelastic mean free paths (IMFPs) in solids from experimental energy-loss functions based on the Mermin dielectric function. The "extended Mermin" method employs a nonlimited number of Mermin oscillators and allows negative oscillators to take into account not only electronic transitions, as is common in the traditional approaches, but also infrared transitions and inner shell electron excitations. The use of only Mermin oscillators naturally preserves two important sum rules when extending to infinite momentum transfer. Excellent agreement is found between calculated IMFPs for Cu and experimental measurements from elastic peak electron spectroscopy. Notably improved fits to the IMFPs derived from analyses of x-ray absorption fine structure measurements for Cu and Mo illustrate the importance of the contribution of infrared transitions in IMFP calculations at low energies.

Da, B.; Shinotsuka, H.; Yoshikawa, H.; Ding, Z. J.; Tanuma, S.

2014-08-01

8

Mean free path and energy loss of electrons in the solar corona and the inner heliosphere  

NASA Astrophysics Data System (ADS)

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.

Estel, C.; Mann, G.

1999-05-01

9

Electron mean free path of tungsten and the electrical resistivity of epitaxial (110) tungsten films  

NASA Astrophysics Data System (ADS)

This work describes a study of the classical electrical resistivity size effect in tungsten. The important length scale for this size effect is the isotropic average electron mean free path (EMFP), which was determined to be 19.1 nm for W at 293 K by employing density functional theory. To explore the size effect experimentally, (110) oriented epitaxial W films with thicknesses ranging from 9.8 to 299.7 nm were prepared by sputter deposition onto (112¯0) Al2O3 substrates at 520 °C followed by postdeposition annealing in Ar-4%H2 at 850 °C. Film resistivities were measured at room temperature and at liquid He temperature. The Fuchs-Sondheimer (FS) surface scattering model with a low specularity parameter (p = 0.11) was shown to provide a good description of the film resistivity as a function of film thickness. Further, it is shown that an upper bound to the EMFP cannot be established by fitting resistivity data to the FS model, whereas a lower bound can be assessed.

Choi, Dooho; Kim, Chang Soo; Naveh, Doron; Chung, Suk; Warren, Andrew P.; Nuhfer, Noel T.; Toney, Michael F.; Coffey, Kevin R.; Barmak, Katayun

2012-07-01

10

Effects of finite electron mean free path on the attenuation, electromagnetic generation, and detection of ultrasonic shear waves in superconductors  

Microsoft Academic Search

Use of the general many-body formalism allows us to derive a system of equations describing the propagation of electromagnetic shear waves coupled to ultrasonic shear waves in normal and superconducting metals with arbitrary electron mean free paths. From this system of equations we derive general expressions in terms of correlation functions for the attenuation coefficient as well as for the

Kurt Scharnberg

1978-01-01

11

Measurement of the hot electron mean free path and the momentum relaxation rate in GaN  

NASA Astrophysics Data System (ADS)

We present a method for measuring the mean free path and extracting the momentum relaxation time of hot electrons in GaN using the hot electron transistor (HET). In this device, electrons are injected over a high energy emitter barrier into the base where they experience quasi-ballistic transport well above the conduction band edge. After traversing the base, high energy electrons either surmount the base-collector barrier and become collector current or reflect off the barrier and become base current. We fabricate HETs with various base thicknesses and measure the common emitter transfer ratio (?) for each device. The mean free path is extracted by fitting ? to a decaying exponential as a function of base width and the relaxation time is computed using a suitable injection velocity. For devices with an injection energy of ˜1 eV, we measure a hot electron mean free path of 14 nm and calculate a momentum relaxation time of 16 fs. These values are in agreement with theoretical calculations where longitudinal optical phonon scattering is the dominant momentum relaxation mechanism.

Suntrup, Donald J.; Gupta, Geetak; Li, Haoran; Keller, Stacia; Mishra, Umesh K.

2014-12-01

12

Calculations of mean free paths and stopping powers of low energy electrons (? 10 keV) in solids using a statistical model  

Microsoft Academic Search

A statistical model is described and employed to calculate inverse mean free paths and stopping powers for electrons of energies from a few eV to 10 keV above the Fermi level in Al, Si, Ni, Cu, Ag, and Au. Brief tables of mean free paths and stopping powers for these solids are presented. In some cases graphical displays of inverse

J. C. Ashley; C. J. Tungt; R. H. Ritchie; V. E. Anderson

1976-01-01

13

Comment on Observation of a Linear Mean-Free-Path Dependence of the Electron-Phonon Scattering Rate in Thick AuPd Films  

NASA Technical Reports Server (NTRS)

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).

Karasik, B. S.; Sergeev, A. V.

1998-01-01

14

Mean free path of inelastic electron scattering in elemental solids and oxides using transmission electron microscopy: Atomic number dependent oscillatory behavior  

SciTech Connect

Mean free path of inelastic electron scattering {lambda} has been measured with a 200 keV transmission electron microscope for the majority of stable elemental solids and their oxides. An oscillating behavior vs atomic number Z has been revealed, such that within one row of the Periodic Table, the minimum (maximum) of {lambda} is observed for elements with completed (empty) outer d shells. A significantly weaker {lambda}(Z) dependence is observed for the oxides. The {lambda}(Z) variation is ascribed to the three major factors: atomic density, number of 'free' electrons per atom, and contribution of atomic core-loss transitions.

Iakoubovskii, Konstantin; Mitsuishi, Kazutaka; Nakayama, Yoshiko; Furuya, Kazuo [Quantum Dot Research Center, National Institute for Materials Science, 3-13 Sakura, Tsukuba 305-0005 (Japan); High Voltage Microscopy Station, National Institute for Materials Science, 3-13 Sakura, Tsukuba 305-0005 (Japan)

2008-03-01

15

Thermal Conductivity Spectroscopy Technique to Measure Phonon Mean Free Paths  

E-print Network

Size effects in heat conduction, which occur when phonon mean free paths (MFPs) are comparable to characteristic lengths, are being extensively explored in many nanoscale systems for energy applications. Knowledge of MFPs ...

Schmidt, A. J.

16

Calculations of stopping powers and inelastic mean free paths for 20 eV-20 keV electrons in 11 types of human tissue.  

PubMed

Systematic calculations are performed for determining the stopping powers (SP) and inelastic mean free paths (IMFP) for 20 eV-20 keV electrons in 11 types of human tissue. The calculations are based on a dielectric model, including the Born-Ochkur exchange correction. The optical energy loss functions (OELF) are empirically evaluated, because of the lack of available experimental optical data for the 11 tissues under consideration. The evaluated OELFs are examined by the f-sum rule expected from the dielectric response theory, and by calculation of the mean excitation energy. The calculated SPs are compared with those for PMMA (polymethylmethacrylate, a tissue equivalent material) and liquid water. The SP and IMFP data presented here are the results for the 11 human tissues over the energy range of 20 eV-20 keV, and are of importance in radiotherapy planning and for studies of various radiation effects on human tissues. PMID:24144616

Tan, Zhenyu; Liu, Wei

2013-12-01

17

Stopping powers and inelastic mean free path of 200eV-50keV electrons in polymer PMMA, PE, and PVC.  

PubMed

The stopping power (SP) and inelastic mean free path (IMFP) of three polymers: polymethyl methacrylate (PMMA), polyethylene (PE), and polyvinyl chloride (PVC) for electron energies from 200eV to 50keV have been determined based on dielectric models. The energy loss function (ELF) is the main input in the calculation of the SP and IMFP for the dielectric models. ELF in this study was determined from a previously published quantitative analysis of reflection electron energy loss spectroscopy (REELS) spectra. The SP of PMMA, PE and PVC decreases and the IMFP increases with increasing electron energies up to 50keV. For comparison, data from the National Institute of Standards and Technology (NIST) database for electron energies from 10 to 50keV were used and show that SP in this study is lowered by 10-15%. The obtained IMFP for PE was compared with those calculated using the TPP2M predictive equations and shows that a reasonable agreement with a root-mean-square (rms) is 7.01Å. The present approach has high potential for the experimental determination of SP and IMFP from the REELS spectra. PMID:25464178

Tahir, Dahlang; Suarga; Sari, Nur Harmila; Yulianti

2014-10-14

18

The scattering mean free path in the Uranian atmosphere  

NASA Technical Reports Server (NTRS)

New measurements of the equivalent widths of the 4.0 S(0) and S(1) H2 quadrupole lines in the Uranian spectrum have been obtained using high dispersion (4.12 A/mm) image-tube spectrography. The measured equivalent widths are 62 plus or minus 19 mA and 58 plus or minus 13 mA for the S(0) and S(1) lines, respectively. Curve-of-growth analysis in terms of a reflecting layer model yields an H2 column density of 780 (+940 or -330) km amagat and a temperature of 78 (+80 or -24) K. Interpretation using a semiinfinite, homogeneous, isotropically scattering model for line formation yields a scattering mean free path at 6400 A of 550 plus or minus 250 km amagat. Quoted errors for both the H2 column density and the scattering mean free path include the effect of uncertainty in the choice of atmospheric temperature. The results are discussed in terms of current models for the Uranian atmosphere.

Price, M. J.

1973-01-01

19

Study on the Characteristics of Gas Molecular Mean Free Path in Nanopores by Molecular Dynamics Simulations  

PubMed Central

This paper presents studies on the characteristics of gas molecular mean free path in nanopores by molecular dynamics simulation. Our study results indicate that the mean free path of all molecules in nanopores depend on both the radius of the nanopore and the gas-solid interaction strength. Besides mean free path of all molecules in the nanopore, this paper highlights the gas molecular mean free path at different positions of the nanopore and the anisotropy of the gas molecular mean free path at nanopores. The molecular mean free path varies with the molecule’s distance from the center of the nanopore. The least value of the mean free path occurs at the wall surface of the nanopore. The present paper found that the gas molecular mean free path is anisotropic when gas is confined in nanopores. The radial gas molecular mean free path is much smaller than the mean free path including all molecular collisions occuring in three directions. Our study results also indicate that when gas is confined in nanopores the gas molecule number density does not affect the gas molecular mean free path in the same way as it does for the gas in unbounded space. These study results may bring new insights into understanding the gas flow’s characteristic at nanoscale. PMID:25046745

Liu, Qixin; Cai, Zhiyong

2014-01-01

20

Electron Interaction Cross Sections in Al and Al2O3; Calculations of Mean Free Paths, Stopping Powers, and Electron SlowingDown Spectra  

Microsoft Academic Search

The prospects for obtaining better theoretical calculations of experimentally interesting electron interaction effects, over a wide range of electron energies, are now considerably improved through the development of models for valence electron excitation in simple insulators and through the availability of theoretical atomic generalized oscillator strengths for inner shell electron excitation in several low-Z atomic systems. We describe briefly the

J. C. Ashley; C. J. Tung; R. H. Ritchie

1975-01-01

21

Shielding of resonant magnetic perturbations in the long mean-free path regime  

NASA Astrophysics Data System (ADS)

The effect of diamagnetic drifts and of long electron mean free path on the shielding of resonant magnetic perturbations by plasma rotation is investigated. The nature of the force exerted on a moving plasma by a resonant perturbation is qualitatively altered by both drift and long mean-free-path effects. The force is found to have three minima, each of which is a possible locus for discontinuous transitions in plasma velocity. Between these minima are two points where the force exerted by the perturbation is resonant. These points describe locked states where shielding is ineffective and a magnetic island will grow. They correspond to rotation velocities such that either the electrons or the ions are at rest in the frame of the perturbation. The ion root, however, is unstable.

Waelbroeck, F. L.

2003-10-01

22

Mean free paths in single-walled carbon nanotubes measured by Kelvin probe force microscopy  

NASA Astrophysics Data System (ADS)

The inelastic mean free path ?MFP is a critical parameter for electronic devices. Here, we demonstrate Kelvin probe force microscopy (KPFM) as a technique for studying ?MFP in biased, semi-metallic single-walled carbon nanotubes (SWNTs). Having one of the longest room-temperature ?MFP values of any known material, SWNTs provide a unique platform for probing mesoscopic transport. KPFM directly determined ?MFP as a function of bias, quantitatively determined the contributions of different scattering mechanisms, and enabled comparative study of individual SWNTs with and without disorder. The room-temperature mean free paths for optical phonon and surface plasmon-polariton scattering were measured to be 62 ± 20 nm and 260 ± 50 nm, respectively. The optical phonon scattering length is significantly longer than inferred from previous measurements, and it resolves a longstanding discrepancy between SWNT theory and experiment, suggesting that KPFM could become a preferred quantitative technique for studying transport in nanoscale systems.

Fuller, Elliot J.; Pan, Deng; Corso, Brad L.; Gul, O. Tolga; Collins, Philip G.

2014-06-01

23

The scattering mean free path of cosmic ray particles in isotropic damped plasma wave turbulence  

NASA Astrophysics Data System (ADS)

An analytical expression for the mean free path of single-charged cosmic ray particles, especially for positrons, is derived in isotropic plasma wave turbulence, where the crucial scattering of cosmic ray particles with small pitch-angle cosines is caused by resonant cyclotron interactions with oblique magnetosonic waves. In this calculation, viscous damping effects are included, which results in broadening of the resonance function. It is demonstrated that including resonance function broadening ensures a finite mean free path for cosmic ray energies, for which previously reported types of turbulence predicted an infinitely large mean free path.

Vukcevic, M.

2013-07-01

24

The mean free path of protons and neutrons in isospin-asymmetric nuclear matter  

E-print Network

We calculate the mean free path of protons and neutrons in symmetric and asymmetric nuclear matter, based on microscopic in-medium nucleon-nucleon cross sections. Those are obtained from calculations of the G-matrix including relativistic "Dirac" effects. The dependence of the mean free path on energy and isospin asymmetry is discussed. We conclude by suggesting possible ways our microscopic predictions may be helpful in conjunction with studies of rare isotopes.

Francesca Sammarruca

2007-12-24

25

Inelastic Mean Free Path Data for Si Corrected for Surface Excitation  

NASA Astrophysics Data System (ADS)

Surface-sensitive electron spectroscopies, like Auger electron spectroscopy, X-ray photoelectron spectroscopy and elastic peak electron spectroscopy (EPES) are suitable techniques to investigate surfaces and thin layers. A theoretical model for electron transport is needed to process the observed electron spectra. Electron transport descriptions are based on the differential elastic cross sections for the sample atoms and the inelastic mean free path (IMFP) of backscattered electrons. An electron impinging on the sample can lose energy either due to surface or volume excitations. In the present work a Monte Carlo (MC) simulation of the elastic peak of Si, Ag, Ni, Cu, and Au for surface analysis is presented. The IMFP of Si was determined applying the EPES method. The integrated elastic peak ratio of Si with the standard metal reference samples corrected for surface excitation provided IMFP values of Si in the energy range E = 0.2 2.0 keV. Experiments were made with the ESA 31 HSA (ATOMKI) and with the DESA-100 (Staib) spectrometers. Surface correction was based on the application of Chen's model and material parameters. The Monte Carlo simulations of elastically backscattered electron trajectories were made using new EPESWIN software of Jablonski. An improvement of IMFP experimental results was achieved applying the presented procedure.

Tamás Orosz, Gábor; Gergely, György; Gurbán, Sándor; Menyhard, Miklós; Jablonski, Aleksander

2005-12-01

26

Triggering waves in nonlinear lattices: Quest for anharmonic phonons and corresponding mean-free paths  

NASA Astrophysics Data System (ADS)

Guided by a stylized experiment we develop a self-consistent anharmonic phonon concept for nonlinear lattices which allows for explicit "visualization." The idea uses a small external driving force which excites the front particles in a nonlinear lattice slab and subsequently one monitors the excited wave evolution using molecular dynamics simulations. This allows for a simultaneous, direct determination of the existence of the phonon mean-free path with its corresponding anharmonic phonon wave number as a function of temperature. The concept for the mean-free path is very distinct from known prior approaches: the latter evaluate the mean-free path only indirectly, via using both a scale for for the phonon relaxation time and yet another one for the phonon velocity. Notably, the concept here is neither limited to small lattice nonlinearities nor to small frequencies. The scheme is tested for three strongly nonlinear lattices of timely current interest which either exhibit normal or anomalous heat transport.

Liu, Sha; Liu, Junjie; Hänggi, Peter; Wu, Changqin; Li, Baowen

2014-11-01

27

Universal phonon mean free path spectra in crystalline semiconductors at high temperature  

PubMed Central

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

Freedman, Justin P.; Leach, Jacob H.; Preble, Edward A.; Sitar, Zlatko; Davis, Robert F.; Malen, Jonathan A.

2013-01-01

28

Neutrino mean free path in asymmetric nuclear matter at high density  

SciTech Connect

We calculate the neutrino mean free path for neutrino-nucleon scattering in highly asymmetric nuclear matter ({ital N}{gt}{ital Z}) at densities typical for the core of a neutron star. Nuclear matter is described by means of a relativistic field theory of nucleons coupled to neutral, scalar ({sigma}), and vector ({omega}) mesons and to charged vector mesons ({ital d}). The correlation effects induced by the strong interaction of nucleons are taken into account within a self-consistent mean field approximation. The contribution of the exchange terms to the nucleon-nucleon interaction is also included. We present results for physical situations which are expected to occur in the cooling of neutron stars. Exchange terms have the effect of increasing the neutrino mean free path by about 50{percent}. {copyright} {ital 1996 The American Physical Society.}

Fabbri, G.; Matera, F. [Dipartimento di Fisica, Universita degli Studi di Firenze and Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, L.go E. Fermi 2, I-50125, Firenze (Italy)] [Dipartimento di Fisica, Universita degli Studi di Firenze and Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, L.go E. Fermi 2, I-50125, Firenze (Italy)

1996-10-01

29

Photon Mean Free Paths, Scattering, and Ever-Increasing Telescope Resolution  

NASA Astrophysics Data System (ADS)

We revisit an old question: what are the effects of observing stratified atmospheres on scales below a photon mean free path? The mean free path of photons emerging from the solar photosphere and chromosphere is near 100 km. Using current 1m-class telescopes, the mean free path is on the order of the angular resolution. But the Daniel K. Inoue Solar Telescope will have a diffraction limit of 0.020'' near the atmospheric cutoff at 310nm, corresponding to 14 km at the solar surface. Even a small amount of scattering in the source function leads to physical smearing due to this solar 'fog', with effects similar to a degradation of the telescope PSF. We discuss a unified picture that depends simply on the nature and amount of scattering in the source function. Scalings are derived from which the scattering in the solar atmosphere can be transcribed into an effective Strehl ratio, a quantity useful to observers. Observations in both permitted (e.g., Fe I 630.2 nm) and forbidden (Fe I 525.0 nm) lines will shed light on both instrumental performance as well as on small scale structures in the solar atmosphere.

Judge, P. G.; Kleint, L.; Uitenbroek, H.; Rempel, M.; Suematsu, Y.; Tsuneta, S.

2015-01-01

30

Measuring the scattering mean free path of Rayleigh waves on a volcano from spatial phase decoherence  

NASA Astrophysics Data System (ADS)

We analyze the statistics of phase fluctuations of seismic signals obtained from a temporary small aperture array deployed on a volcano in the French Auvergne. We demonstrate that the phase field satisfies Circular Gaussian statistics. We then determine the scattering mean free path of Rayleigh waves from the spatial phase decoherence. This phenomenon, observed for diffuse wavefields, is found to yield a good approximation of the scattering mean free path. Contrary to the amplitude, spatial phase decoherence is free from absorption effects and provides direct access to the scattering mean free path. Our method may find applications in various areas of seismology where the effects of scattering are prominent and a knowledge of the scattering properties is necessary to describe the propagation. As an example, an unbiased estimate of the scattering mean free path is crucial for the localization of changes in multiply scattering media, where a sensitivity kernel based on diffusion theory is used (Larose et al. 2010; Obermann et al. 2013a,b). Our experimental approach may also provide independent estimates of the scattering mean free path in volcanic areas where particularly strong scattering has been proposed, based on the fitting of energy envelopes using energy transport approaches (Wegler & Lühr 2001; Yamamoto & Sato 2010). References: Larose, E., Planès, T., Rossetto, V. & Margerin, L., 2010. Locating a small change in a multiple scattering environment, Appl. Phys. Lett., 96(204101), 1-3. Obermann, A., Planès, T., Larose, E. & Campillo, M., 2013a. Imaging pre and co-eruptive structural and mechanical changes on a volcano with ambient seismic noise, J. geophys. Res., 118, 1-10. Obermann, A., Planès, T., Larose, E., Sens-Schönfelder, C. & Campillo,M., 2013b. Depth sensitivity of seismic coda waves to velocity perturbations in an elastic heterogeneous medium, Geophys. J. Int., 194(1), 372-382. Wegler, U. & Lühr, B.G., 2001. Scattering behaviour at Merapi volcano (Java) revealed from an active seismic experiment, Geophys. J. Int., 145(3), 579-592. Yamamoto, M. & Sato, H., 2010. Multiple scattering and mode conversion revealed by an active seismic experiment at Asama volcano, Japan, J. geophys. Res., 115(B7), doi:10.1029/2009JB007109.

Obermann, Anne; Larose, Eric; Margerin, Ludovic; Rossetto, Vincent

2014-05-01

31

Heat transport by long mean free path vibrations in amorphous silicon nitride near room temperature  

NASA Astrophysics Data System (ADS)

We present measurements of thermal transport in 500-nm-thick, 35-?m-wide, and 806-?m-long micromachined suspended silicon nitride (Si-N) bridges over the temperature range of 77 to 325 K. The measured thermal conductivity of Si-N (for material grown by low-pressure chemical vapor deposition in two different furnaces) deviates somewhat from previously reported measurements and also shows surprising dependence on surface variation at these relatively high temperatures. Addition of discontinuous gold films causes the thermal conductance of Si-N bridges to drop through the entire measured temperature range, before rising again when thicker, continuous films are added. Similar effects occur when continuous but very low-thermal-conductivity alumina films are deposited. The reduction in thermal conductance upon modification of the Si-N surface is strong evidence that vibrational excitations with long mean free paths carry significant heat even at these high temperatures. By measuring a series of film thicknesses the surface-scattering effects can be mitigated, and the resulting experimental values of the thermal conductivity of alumina and Au thin films compare very well to known values or to predictions of the Wiedemann-Franz law. We also present a modified model for the phonon mean free path in thin-film geometries, and use it along with atomic force microsope scans to show that a very small population of phonons with mean free path on the order of 1 ?m and wavelength much longer than the expected thermal wavelengths carry up to 50% of the heat in Si-N at room temperature.

Sultan, Rubina; Avery, A. D.; Underwood, J. M.; Mason, S. J.; Bassett, D.; Zink, B. L.

2013-06-01

32

Isotope effect of the phonons mean free path in graphene by micro-Raman measurement  

NASA Astrophysics Data System (ADS)

The isotope labeled graphene was synthesized in the concentration of 13C carbon atom in 1%, 25%, 50%, 75% and 99%. The isotope effect on the phonon behavior in graphene was investigated based on the micro-Raman analysis of 13C isotope labeled graphene samples. We found that the phonon scattering is affected by the isotopic carbon atom as a point defect. Based on the experiment results, the Klemens-Callaway model and uncertainty principle were used to obtain the mean free path of the G and D phonons. The results agree with the thermal conductivity measurement by non-contact optical method and with other theoretical calculations.

Zhang, CanKun; Li, QiongYu; Tian, Bo; Huang, ZhiYi; Lin, WeiYi; Li, HongYang; He, DaHai; Zhou, YingHui; Cai, WeiWei

2014-10-01

33

Shear viscosity of hot nuclear matter by the mean free path method  

NASA Astrophysics Data System (ADS)

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.

Fang, D. Q.; Ma, Y. G.; Zhou, C. L.

2014-04-01

34

Phonon mean free path of graphite along the c-axis  

SciTech Connect

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.

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

35

Shear viscosity of hot nuclear matter by the mean free path method  

E-print Network

The shear viscosity of hot nuclear matter is investigated by using the mean free path method within the framework of IQMD 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 $\\rho\\sim\\rho_0$, which is consistent with the previous studies on nuclear matter formed during heavy-ion collisions. At $\\rho\\sim\\frac{1}{2}\\rho_0$, a minimum of $\\eta/s$ is seen at around $T=10$ MeV and a maximum of the multiplicity of intermediate mass fragment ($M_{\\text{IMF}}$) is also observed at the same temperature which is an indication of the liquid-gas phase transition.

D. Q. Fang; Y. G. Ma; C. L. Zhou

2014-04-17

36

A DIRECT METHOD TO DETERMINE THE PARALLEL MEAN FREE PATH OF SOLAR ENERGETIC PARTICLES WITH ADIABATIC FOCUSING  

SciTech Connect

The parallel mean free path of solar energetic particles (SEPs), which is determined by physical properties of SEPs as well as those of solar wind, is a very important parameter in space physics to study the transport of charged energetic particles in the heliosphere, especially for space weather forecasting. In space weather practice, it is necessary to find a quick approach to obtain the parallel mean free path of SEPs for a solar event. In addition, the adiabatic focusing effect caused by a spatially varying mean magnetic field in the solar system is important to the transport processes of SEPs. Recently, Shalchi presented an analytical description of the parallel diffusion coefficient with adiabatic focusing. Based on Shalchi's results, in this paper we provide a direct analytical formula as a function of parameters concerning the physical properties of SEPs and solar wind to directly and quickly determine the parallel mean free path of SEPs with adiabatic focusing. Since all of the quantities in the analytical formula can be directly observed by spacecraft, this direct method would be a very useful tool in space weather research. As applications of the direct method, we investigate the inherent relations between the parallel mean free path and various parameters concerning physical properties of SEPs and solar wind. Comparisons of parallel mean free paths with and without adiabatic focusing are also presented.

He, H.-Q.; Wan, W., E-mail: hqhe@mail.iggcas.ac.cn, E-mail: wanw@mail.iggcas.ac.cn [Beijing National Observatory of Space Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029 (China)

2012-03-01

37

Damping rates and mean free paths of soft fermion collective excitations in a hot fermion-gauge-scalar theory  

SciTech Connect

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.

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

38

Mean free paths, viscosity, and the limitations of perfect fluid hydrodynamics in the description of the quark-gluon plasma  

SciTech Connect

The author discusses the applicability of a hydrodynamic description of high energy hadronic collisions. The author reviews the results of recent computations of the mean free paths of quarks and gluons in a quark-gluon plasma, and the corresponding results for viscous coefficients. These quantities are employed to evaluate the limits to the application of perfect fluid hydrodynamics as a description of time evolution of matter produced in various hadronic collisions. 22 references.

McLerran, L.

1984-11-01

39

Mean-free-paths in concert and chamber music halls and the correct method for calibrating dodecahedral sound sources.  

PubMed

The Eyring/Sabine equations assume that in a large irregular room a sound wave travels in straight lines from one surface to another, that the surfaces have an average sound absorption coefficient ?av, and that the mean-free-path between reflections is 4?V/Stot where V is the volume of the room and Stot is the total area of all of its surfaces. No account is taken of diffusivity of the surfaces. The 4?V/Stot relation was originally based on experimental determinations made by Knudsen (Architectural Acoustics, 1932, pp. 132-141). This paper sets out to test the 4?V/Stot relation experimentally for a wide variety of unoccupied concert and chamber music halls with seating capacities from 200 to 5000, using the measured sound strengths Gmid and reverberation times RT60,mid. Computer simulations of the sound fields for nine of these rooms (of varying shapes) were also made to determine the mean-free-paths by that method. The study shows that 4?V/Stot is an acceptable relation for mean-free-paths in the Sabine/Eyring equations except for halls of unusual shape. Also demonstrated is the proper method for calibrating the dodecahedral sound source used for measuring the sound strength G, i.e., the reverberation chamber method. PMID:24437762

Beranek, Leo L; Nishihara, Noriko

2014-01-01

40

Parallel transport of long mean-free-path plasma along open magnetic field lines: Parallel heat flux  

SciTech Connect

In a long mean-free-path plasma where temperature anisotropy can be sustained, the parallel heat flux has two components with one associated with the parallel thermal energy and the other the perpendicular thermal energy. Due to the large deviation of the distribution function from local Maxwellian in an open field line plasma with low collisionality, the conventional perturbative calculation of the parallel heat flux closure in its local or non-local form is no longer applicable. Here, a non-perturbative calculation is presented for a collisionless plasma in a two-dimensional flux expander bounded by absorbing walls. Specifically, closures of previously unfamiliar form are obtained for ions and electrons, which relate two distinct components of the species parallel heat flux to the lower order fluid moments such as density, parallel flow, parallel and perpendicular temperatures, and the field quantities such as the magnetic field strength and the electrostatic potential. The plasma source and boundary condition at the absorbing wall enter explicitly in the closure calculation. Although the closure calculation does not take into account wave-particle interactions, the results based on passing orbits from steady-state collisionless drift-kinetic equation show remarkable agreement with fully kinetic-Maxwell simulations. As an example of the physical implications of the theory, the parallel heat flux closures are found to predict a surprising observation in the kinetic-Maxwell simulation of the 2D magnetic flux expander problem, where the parallel heat flux of the parallel thermal energy flows from low to high parallel temperature region.

Guo Zehua; Tang Xianzhu [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2012-06-15

41

Initial-state, mean-free-path, and skin-depth dependence of attosecond time-resolved IR-streaked XUV photoemission from single-crystalline magnesium  

NASA Astrophysics Data System (ADS)

We analyze the dependence of attosecond streaked photoelectron spectra and photoemission time delays from valence band (VB) and 2p core-level (CL) states of a single-crystalline Mg(0001) thin film on the (i) modeling of the substrate electronic structure, (ii) electron mean free path (MFP), (iii) screening of the near-infrared (NIR) streaking laser field, and (iv) chirp of the attosecond extreme ultraviolet (XUV) pulse. Our quantum-mechanical numerical simulations predict streaked photoemission spectra that depend sensitively on the XUV chirp and weakly on the screening of the streaking laser field by the substrate. They furthermore show that streaking time delays for VB emission are relatively insensitive to the modeling of the initial quantum states, electron MFP, and NIR skin depth of the Mg substrate, in contrast to the stronger dependence of streaking time delays for 2p CL emission on these factors.

Liao, Q.; Thumm, U.

2014-03-01

42

The Giant Gemini GMOS survey of zem > 4.4 quasars - I. Measuring the mean free path across cosmic time  

NASA Astrophysics Data System (ADS)

We have obtained spectra of 163 quasars at zem > 4.4 with the Gemini Multi Object Spectrometers, the largest publicly available sample of high-quality, low-resolution spectra at these redshifts. From this data set, we generated stacked quasar spectra in three redshift intervals at z ˜ 5 to model the average rest-frame Lyman continuum flux and to assess the mean free path ? _mfp^{912} of the intergalactic medium to H I-ionizing radiation. At mean redshifts zq = (4.56, 4.86, 5.16), we measure ? _mfp^{912}=(22.2 ± 2.3, 15.1 ± 1.8, 10.3 ± 1.6)h_{70}^{-1} proper Mpc with uncertainties dominated by sample variance. Combining our results with measurements from lower redshifts, the data are well modelled by a power law ? _mfp^{912}=A[(1+zright)/5]^? with A=(37 ± 2)h_{70}^{-1} Mpc and ? = -5.4 ± 0.4 at 2.3 < z < 5.5. This rapid evolution requires a physical mechanism - beyond cosmological expansion - which reduces the effective Lyman limit opacity. We speculate that the majority of H I Lyman limit opacity manifests in gas outside galactic dark matter haloes, tracing large-scale structures (e.g. filaments) whose average density and neutral fraction decreases with cosmic time. Our measurements of the mean free path shortly after H I reionization serve as a valuable boundary condition for numerical models thereof. Our measured ? _mfp^{912}? 10 Mpc at z = 5.2 confirms that the intergalactic medium is highly ionized without evidence for a break that would indicate a recent end to H I reionization.

Worseck, Gábor; Prochaska, J. Xavier; O'Meara, John M.; Becker, George D.; Ellison, Sara L.; Lopez, Sebastian; Meiksin, Avery; Ménard, Brice; Murphy, Michael T.; Fumagalli, Michele

2014-12-01

43

A DIRECT APPROACH FOR DETERMINING THE PERPENDICULAR MEAN FREE PATH OF SOLAR ENERGETIC PARTICLES IN A TURBULENT AND SPATIALLY VARYING MAGNETIC FIELD  

SciTech Connect

A direct approach for explicitly determining the perpendicular mean free path of solar energetic particles (SEPs) influenced by parallel diffusion and composite dynamical turbulence in a spatially varying magnetic field is presented. As theoretical applications of the direct approach, we investigate the inherent relations between the perpendicular mean free path and various parameters concerning physical properties of SEPs as well as those of interplanetary conditions such as the solar wind and the turbulent magnetic field. Comparisons of the perpendicular mean free paths with and without adiabatic focusing are also presented. The direct method shows encouraging agreement with spacecraft observations, suggesting it is a reliable and useful tool for use in theoretical investigations and space weather forecasting.

He, H.-Q.; Wan, W., E-mail: hqhe@mail.iggcas.ac.cn, E-mail: wanw@mail.iggcas.ac.cn [Beijing National Observatory of Space Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029 (China)

2012-12-15

44

Time-reversed ultrasonically encoded optical focusing into tissue-mimicking media with thickness up to 70 mean free paths  

PubMed Central

In turbid media such as biological tissue, multiple scattering hinders direct light focusing at depths beyond one transport mean free path. As a solution to this problem, time-reversed ultrasonically encoded (TRUE) optical focusing is proposed based on ultrasonic encoding of diffused laser light and optical time reversal. In TRUE focusing, a laser beam of long coherence length illuminates a turbid medium, where the incident light undergoes multiple scattering and part of it gets ultrasonically encoded within the ultrasonic focal zone. A conjugated wavefront of the ultrasonically encoded light is then generated by a phase conjugate mirror outside the medium, which traces back the trajectories of the ultrasonically encoded diffused light and converges light to the ultrasonic focal zone. Here, we report the latest experimental improvement in TRUE optical focusing that increases its penetration in tissue-mimicking media from a thickness of 3.75 to 7.00 mm. We also demonstrate that the TRUE focus depends on the focal diameter of the ultrasonic transducer. PMID:21895321

Liu, Honglin; Xu, Xiao; Lai, Puxiang; Wang, Lihong V.

2011-01-01

45

ANOMALOUS REACTION MEAN FREE PATHS OF NUCLEAR PROJECTILE FRAGMENTS FROM HEAVY ION COLLISIONS AT 2 AGeV  

SciTech Connect

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.

Friedlander, E.M.; Gimpel, R.W.; Heckman, H.H.; Karant, Y.J.; Judek, B.; Ganssauge, E.

1982-08-01

46

Anomalous reaction mean free paths of nuclear projectile fragments from heavy ion collisions at 2A GeV  

SciTech Connect

We present in detail the description and the analysis of two independent experiments using 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< or =Z< or =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.

Friedlander, E.M.; Gimpel, R.W.; Heckman, H.H.; Karant, Y.J.; Judek, B.; Ganssauge, E.

1983-04-01

47

Parallel transport of long mean-free-path plasmas along open magnetic field lines: Plasma profile variation  

SciTech Connect

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.

Guo Zehua; Tang Xianzhu [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2012-08-15

48

Depolarization and electric-field frequency shift of 3He by magnetic-field inhomogeneities: Local theory for short mean free path and solution in 4He  

NASA Astrophysics Data System (ADS)

The local theory of relaxation of 3He by Brownian motion in an inhomogeneous magnetic field, originally proposed by Gamblin and Carver [Phys. Rev. 138, A946 (1965), 10.1103/PhysRev.138.A946] and by Schearer and Walters [Phys. Rev. 139, A1398 (1965), 10.1103/PhysRev.139.A1398], is reconsidered in detail to clarify (or not) the approximations involved. Notably, a discussion is given of frames rotating at time-dependent angular velocities (both in magnitude and in direction), and attention is drawn to the often overlooked long tail that confinement adds to velocity correlation functions. A stepwise application of the Redfield theory of relaxation eventually provides quantitative predictions for the rate of depolarization and the linear-in-electric-field frequency shift, in terms of the components of the local inhomogeneity tensor and the usual parameters (nuclear magnetic resonance frequency, diffusion coefficient, mean time between collisions, etc.), valid in the common situation of mean free path much smaller than the size of the container. These predictions agree with almost all results of previous publications, most of which are based on the global approach which evaluates correlation functions by reference to the diffusion equation in spite of its limitations for short delays.

Jeener, J.

2015-01-01

49

The Relation between Relaxation Time, Mean Free Path, Collision Time and Drift Velocity--Pitfalls and a Proposal for an Approach Illustrating the Essentials  

ERIC Educational Resources Information Center

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…

Jakoby, Bernhard

2009-01-01

50

Vacuum ultraviolet electronic properties of liquids  

NASA Astrophysics Data System (ADS)

Collective electronic oscillations in the silicone liquid Dow Corning 705 were examined. Newly analyzed data on electron bombardment gave better agreement with results of analyzed vuv optical reflectance values for energy loss than earlier results indicated. As previously reported, electron and photon mean free paths and absolute photoyields were calculated from reanalyzed liquid water data in the 2 to 25 eV region. These electron mean free paths were calculated from formamide electron mean free paths scaled for valence electron density. The formamide mean free paths were derived using Born approximation by Ashley and Williams. An alternate approach to calculation of electron mean free path in organic and inorganic matter proposed by Seah and Dench was followed. A survey of a range of liquids with request to reflectivity and photoemission was completed. As a result, a series of n-ethylene glycols with particularly high dipole moments as chosen for study. Ethylene glycol, diethylene glycol, triethylene glycol and tetraethylene glycol were studied.

Painter, L. R.

51

Path integrals for nonadiabatically coupled electrons and nuclei in molecules: Force analysis for branching nuclear paths and conservation laws  

Microsoft Academic Search

Real-time dynamics in electron-nucleus coupled systems in molecules is studied using the path-integral formalism, with a special emphasis on nonadiabatic interactions. We first establish a formal path-integral description of the entire system. Applying the stationary phase approximation, we then derive coupled equations for the mixed quantum-classical treatment of the system: the equations of motion for electron wave-packet dynamics and those

Kota Hanasaki; Kazuo Takatsuka

2010-01-01

52

Path integrals for nonadiabatically coupled electrons and nuclei in molecules: Force analysis for branching nuclear paths and conservation laws  

NASA Astrophysics Data System (ADS)

Real-time dynamics in electron-nucleus coupled systems in molecules is studied using the path-integral formalism, with a special emphasis on nonadiabatic interactions. We first establish a formal path-integral description of the entire system. Applying the stationary phase approximation, we then derive coupled equations for the mixed quantum-classical treatment of the system: the equations of motion for electron wave-packet dynamics and those for nuclear dynamics driven by what we call the force form. Thus the present theory also serves as a general theory for dynamics in mixed quantum and classical systems. On this theoretical foundation, we analyze two theories of nonadiabatic electron-nucleus coupled systems from the viewpoint of path branching: the semiclassical Ehrenfest theory and the recently developed method of phase-space averaging and natural branching [T. Yonehara, S. Takahashi, and K. Takatsuka, J. Chem. Phys.JCPSA60021-960610.1063/1.3151684 130, 214113 (2009)]. We give a unified account of the essential feature of their physical implications and limitations. Path-integral formalism leads to further refinement of the idea of path branching caused by nonadiabatic coupling, thus giving deeper insight into the nonadiabatic dynamics. Further, we study the conservation laws for energy, linear momentum, and angular momentum in the general mixed quantum-classical representation. We also extend the present path-integral formulation so as to handle nonadiabatic dynamics in laser fields.

Hanasaki, Kota; Takatsuka, Kazuo

2010-05-01

53

Path integrals for nonadiabatically coupled electrons and nuclei in molecules: Force analysis for branching nuclear paths and conservation laws  

SciTech Connect

Real-time dynamics in electron-nucleus coupled systems in molecules is studied using the path-integral formalism, with a special emphasis on nonadiabatic interactions. We first establish a formal path-integral description of the entire system. Applying the stationary phase approximation, we then derive coupled equations for the mixed quantum-classical treatment of the system: the equations of motion for electron wave-packet dynamics and those for nuclear dynamics driven by what we call the force form. Thus the present theory also serves as a general theory for dynamics in mixed quantum and classical systems. On this theoretical foundation, we analyze two theories of nonadiabatic electron-nucleus coupled systems from the viewpoint of path branching: the semiclassical Ehrenfest theory and the recently developed method of phase-space averaging and natural branching [T. Yonehara, S. Takahashi, and K. Takatsuka, J. Chem. Phys. 130, 214113 (2009)]. We give a unified account of the essential feature of their physical implications and limitations. Path-integral formalism leads to further refinement of the idea of path branching caused by nonadiabatic coupling, thus giving deeper insight into the nonadiabatic dynamics. Further, we study the conservation laws for energy, linear momentum, and angular momentum in the general mixed quantum-classical representation. We also extend the present path-integral formulation so as to handle nonadiabatic dynamics in laser fields.

Hanasaki, Kota; Takatsuka, Kazuo [Department of Basic Science, University of Tokyo, Komaba, 153-8902 Tokyo (Japan)

2010-05-15

54

Electron correlation from path resummations: the double-excitation star Alex J. W. Thom,  

E-print Network

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

Alavi, Ali

55

Electronic Transport in Mesoscopic Systems  

Microsoft Academic Search

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

Supriyo Datta

1997-01-01

56

COMPARISON BETWEEN PATH LENGTHS TRAVELED BY SOLAR ELECTRONS AND IONS IN GROUND-LEVEL ENHANCEMENT EVENTS  

SciTech Connect

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.

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

57

PATH  

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.

58

Interrelation of Resistivity and Inelastic Electron-Phonon Scattering Rate in Impure NbC Films  

NASA Technical Reports Server (NTRS)

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.

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

59

COLLISIONLESS ELECTRON HEATING IN RF GAS DISCHARGES: I. QUASILINEAR THEORY  

E-print Network

parameters. Due to the large value of the mean free path (MFP) the main mechanism of electron heating turnsCOLLISIONLESS ELECTRON HEATING IN RF GAS DISCHARGES: I. QUASILINEAR THEORY Yu.M. Aliev1 , I an interest in mechanisms of electron heating and power deposition in the plasma main- tained by radio

Kaganovich, Igor

60

Journal of Electron Spectroscopy and Related Phenomena 122 (2002) 221229 www.elsevier.com/locate/elspec  

E-print Network

Journal of Electron Spectroscopy and Related Phenomena 122 (2002) 221­229 www by a variety of electron spectroscopies. The electron spin can be controlled by using a fully characterized spectroscopies 1. Introduction copies. The main reason for this is the short mean free path of electrons

Marcon, Marco

61

Evaluation of the Phonon Mean Free Path in Thin Films by using Classical Molecular Dynamics  

E-print Network

the possibility of applications as new thermal insulators [1-8]. Many studies were carried out to evaluate as a simulation material. The thermal conductivity of a thin film plays an important role in the design of nano that there is apparently a size effect on the thermal conductivity, which indicates that the microscale system has a lower

Maruyama, Shigeo

62

Effects of elastic and inelastic scattering in giving electrons tortuous paths in matter  

Microsoft Academic Search

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

J. E. Turner; R. N. Hamm

1995-01-01

63

Engineering of an alternative electron transfer path in photosystem II  

PubMed Central

The initial steps of oxygenic photosynthetic electron transfer occur within photosystem II, an intricate pigment/protein transmembrane complex. Light-driven electron transfer occurs within a multistep pathway that is efficiently insulated from competing electron transfer pathways. The heart of the electron transfer system, composed of six linearly coupled redox active cofactors that enable electron transfer from water to the secondary quinone acceptor QB, is mainly embedded within two proteins called D1 and D2. We have identified a site in silico, poised in the vicinity of the QA intermediate quinone acceptor, which could serve as a potential binding site for redox active proteins. Here we show that modification of Lysine 238 of the D1 protein to glutamic acid (Glu) in the cyanobacterium Synechocystis sp. PCC 6803, results in a strain that grows photautotrophically. The Glu thylakoid membranes are able to perform light-dependent reduction of exogenous cytochrome c with water as the electron donor. Cytochrome c photoreduction by the Glu mutant was also shown to significantly protect the D1 protein from photodamage when isolated thylakoid membranes were illuminated. We have therefore engineered a novel electron transfer pathway from water to a soluble protein electron carrier without harming the normal function of photosystem II. PMID:20457933

Larom, Shirley; Salama, Faris; Schuster, Gadi; Adir, Noam

2010-01-01

64

Parasitic Effects of Grounding Paths on Common-Mode EMI Filter's Performance in Power Electronics Systems  

SciTech Connect

High-frequency common-mode (CM) electromagnetic-interference (EMI) noise is difficult to suppress in electronics systems. EMI filters are used to suppress CM noise, but their performance is greatly affected by the parasitic effects of the grounding paths. In this paper, the parasitic effects of the grounding paths on an EMI filter's performance are investigated in a motor-drive system. The effects of the mutual inductance between two grounding paths are explored. Guidelines for the grounding of CM EMI filters are derived. Simulations and experiments are finally carried out to verify the theoretical analysis.

Wang, Shuo [ORNL; Maillet, Yoann [Virginia Polytechnic Institute and State University (Virginia Tech); Wang, Fei [ORNL; Lai, Rixin [General Electric; Luo, Fang [Virginia Polytechnic Institute and State University (Virginia Tech); Boroyevich, Dushan [Virginia Polytechnic Institute and State University (Virginia Tech)

2010-01-01

65

Path Integrals for Electronic Densities, Reactivity Indices, and Localization Functions in Quantum Systems  

PubMed Central

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

Putz, Mihai V.

2009-01-01

66

Silicon electronics on silk as a path to bioresorbable, implantable devices Dae-Hyeong Kim,1  

E-print Network

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

Rogers, John A.

67

Quasilinear theory of collisionless electron heating in radio frequency gas discharges  

E-print Network

parameters. Due to the large value of the mean free path MFP the main mechanism of electron heating turns outQuasilinear theory of collisionless electron heating in radio frequency gas discharges Yu. M. Aliev heating of rf discharges is treated for characteristic scale lengths of the heating field much shorter

Kaganovich, Igor

68

Communication: Predictive partial linearized path integral simulation of condensed phase electron transfer dynamics  

SciTech Connect

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.

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

69

Turn on of new electronic paths in Fe-SiO2 granular thin film  

NASA Astrophysics Data System (ADS)

The electrical properties of Fe-SiO2 have been studied in the low-field regime (e?V ? kBT), varying the injected current and the bias potential. Superparamagnetism and a resistance drop of 4400 ? (for a voltage variation of 15 V) were observed at room temperature. This resistance drop increased at lower temperatures. The electrical properties were described with the "Mott variable range hopping" model explaining the behavior of the electrical resistance and the electronic localization length as due to the activation of new electronic paths between more distant grains. This non-ohmic resistance at room temperature can be important for properties dependent of electrical current (magnetoresistance, Hall effect, and magnetoimpedance).

Boff, M. A. S.; Hinrichs, R.; Canto, B.; Mesquita, F.; Baptista, D. L.; Fraga, G. L. F.; Pereira, L. G.

2014-10-01

70

Electronic quantum effects mapped onto non-Born-Oppenheimer nuclear paths: Nonclassical surmounting over potential barriers and trapping above the transition states due to nonadiabatic path-branching  

SciTech Connect

We develop the path-branching representation for nonadiabatic electron wavepacket dynamics [T. Yonehara and K. Takatsuka, J. Chem. Phys. 132, 244102 (2010)] so as to treat dynamics in an energy range comparable to the barrier height of adiabatic potential energy curves. With this representation two characteristic chemical reaction dynamics are studied, in which an incident nuclear wavepacket encounters a potential barrier, on top of which lies another nonadiabatically coupled adiabatic potential curve: (1) Dynamics of initial paths coming into the nonadiabatic interaction region with energy lower than the barrier height. They branch into two pieces (and repeat branching subsequently), the upper counterparts of which can penetrate into a classically inaccessible high energy region and eventually branch back to the product region on the ground state curve. This is so to say surmounting the potential barrier via nonadiabatically coupled excited state, and phenomenologically looks like the so-called deep tunneling. (2) Dynamics of classical paths whose initial energies are a little higher than the barrier but may be lower than the bottom of the excited state. They can undergo branching and some of those components are trapped on top of the potential barrier, being followed by the population decay down to the lower state flowing both to product and reactant sites. Such expectations arising from the path-branching representation are numerically confirmed with full quantum mechanical wavepacket dynamics. This phenomenon may be experimentally observed as time-delayed pulses of wavepacket trains.

Yamamoto, Kentaro, E-mail: kyamamoto@mns2.c.u-tokyo.ac.jp; Takatsuka, Kazuo, E-mail: kaztak@mns2.c.u-tokyo.ac.jp [Department of Basic Science, The University of Tokyo, Komaba, 153-8902 Tokyo (Japan)] [Department of Basic Science, The University of Tokyo, Komaba, 153-8902 Tokyo (Japan)

2014-03-28

71

Control of long electron quantum paths in high-order harmonic generation by phase-stabilized light pulses  

SciTech Connect

In this work we report on the first experimental demonstration of selection of the long electron quantum paths in the process of high-order harmonic generation by phase-stabilized multiple-cycle light pulses. A complete experimental investigation of the role of intensity and carrier-envelope phase of the driving pulses on the spectral characteristics of the long quantum paths is performed. Simulations based on the nonadiabatic saddle-point method and on a complete nonadiabatic three-dimensional model reproduce the main features of the experimental results. The use of phase-stabilized driving pulses allows one to control, on an attosecond temporal scale, the spectral and temporal characteristics associated with the electron quantum paths involved in the harmonic generation process.

Sansone, G.; Benedetti, E.; Caumes, J.-P.; Stagira, S.; Vozzi, C.; De Silvestri, S.; Nisoli, M. [National Laboratory for Ultrafast and Ultraintense Optical Science - CNR-INFM Department of Physics, Politecnico, Piazza Leonardo da Vinci 32, 20133 Milan (Italy)

2006-05-15

72

Theory of probing attosecond electron wave packets via two-path interference of angle-resolved photoelectrons  

SciTech Connect

We study theoretically the electron wave packet generated by an attosecond pulse train (APT) which is probed with a time-delayed infrared (IR) laser pulse. The APT creates an excited state and a continuum electron wave packet. By ionizing the excited state with an IR, a delayed new continuum electron wave packet is created. The interference of the wave packets from the two paths, as reflected in angle-resolved photoelectron spectra, is analyzed analytically. Using the analytical expressions, we examine the possibility of retrieving information on the electron wave packet generated by the APT.

Choi, N. N. [School of Natural Science, Kumoh National Institute of Technology, Gumi, Gyeongbuk 730-701 (Korea, Republic of); J. R. Macdonald Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506-2604 (United States); Jiang, T. F. [J. R. Macdonald Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506-2604 (United States); Institute of Physics, National Chiao Tung University, Hsinchu 30010, Taiwan (China); Morishita, T. [Department of Applied Physics and Chemistry, University of Electro-Communications, 1-5-1 Chofu-ga-oka, Chofu-shi, Tokyo, 182-8585 (Japan); PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012 (Japan); Lee, M.-H. [School of Natural Science, Kumoh National Institute of Technology, Gumi, Gyeongbuk 730-701 (Korea, Republic of); Lin, C. D. [J. R. Macdonald Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506-2604 (United States)

2010-07-15

73

Nonlocal electron hydrodynamics  

NASA Astrophysics Data System (ADS)

Analytical nonlocal theory of an electron transport in unmagnetized plasmas with arbitrary electron collisionality in the limit of large ion charge has been developed. We have found nonlocal expressions for electron transport coefficients: electric conductivity, thermoelectric coefficient, temperature and heat conductivities, electron-ion friction, and ion flux coefficients. We have shown that our theory properly describes a transition from strongly collisional, hydrodynamical regime into the collisionless, free-streaming limit. The thermoelectric coefficient changes its sign when the perturbation wavelength is comparable to the electron-ion mean free path. Electron and ion low frequency longitudinal and transversal susceptibilities are derived from our nonlocal hydrodynamics and the proper definition of the electron heat conductivity is also discussed.

Brantov, A. V.; Bychenkov, V. Yu.; Tikhonchuk, V. T.; Rozmus, W.

1996-11-01

74

Path integral approach to the photoionization of one active electron atom by a pulsed Fock state: Fluctuations contribution  

SciTech Connect

We model in a fully quantum mechanical way the dynamics of an atom of one optically active electron interacting with a pulsed Fock state which is linearly polarized. We use path integral methods. We derive the system's sign solved propagator which gives full information on its dynamics. We apply our method to the ionization of atomic hydrogen by a one-photon pulsed Fock state and study the contribution of the electromagnetic fluctuations.

Thrapsaniotis, E. G. [52 Vianou street, 13671 Athens, Aharnes (Greece)

2012-08-15

75

On the electron scattering and dephasing by the nuclear spins  

Microsoft Academic Search

We show that scattering of the conduction electrons by nuclear spins via the\\u000ahyperfine interaction may lead the upper limit on the mean free path in clean\\u000ametals. Nuclear spins with s >1\\/2 may cause a strong dephasing in dirty limit\\u000adue to the quadrupole coupling to the random potential fluctuations caused by\\u000astatic impurities and lattice imperfections.

A. M. Dyugaev; I. D. Vagner; P. Wyder

2000-01-01

76

On the origin of the electron blocking effect by an n-type AlGaN electron blocking layer  

SciTech Connect

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.

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

77

Inhibition of electron thermal conduction by electromagnetic instabilities. [in stellar coronas  

NASA Technical Reports Server (NTRS)

Heat flux inhibition by electromagnetic instabilities in a hot magnetized plasma is investigated. Low-frequency electromagnetic waves become unstable due to anisotropy of the electron distribution function. The chaotic magnetic field thus generated scatters the electrons with a specific effective mean free path. Saturation of the instability due to wave-wave interaction, nonlinear scattering, wave propagation, and collisional damping is considered. The effective mean free path is found self-consistently, using a simple model to estimate saturation level and scattering, and is shown to decrease with the temperature gradient length. The results, limited to the assumptions of the model, are applied to astrophysical systems. For some interstellar clouds the instability is found to be important. Collisional damping stabilizes the plasma, and the heat conduction can be dominated by superthermal electrons.

Levinson, Amir; Eichler, David

1992-01-01

78

Chemical-Reaction-Induced Hot Electron Flows on Platinum Colloid Nanoparticles under Hydrogen Oxidation: Impact of Nanoparticle Size.  

PubMed

Generation of hot electron flows and the catalytic activity of Pt nanoparticles (NPs) with different sizes were investigated using catalytic nanodiodes. We show that smaller Pt NPs lead to higher chemicurrent yield, which is associated with the shorter travel length for the hot electrons, compared with their inelastic mean free path. We also show the impact of capping on charge carrier transfer between Pt NPs and their support. PMID:25645508

Lee, Hyosun; Nedrygailov, Ievgen I; Lee, Changhwan; Somorjai, Gabor A; Park, Jeong Young

2015-02-16

79

Magnetic turbulent electron transport in a reversed field pinch  

SciTech Connect

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.

Schoenberg, K.; Moses, R.

1990-01-01

80

Inelastic cross-sections of low-energy electrons in silicon for the simulation of heavy ion tracks with the GEANT4DNA toolkit  

Microsoft Academic Search

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

A. Valentin; M. Raine; J. E. Sauvestre

2010-01-01

81

The path to ubiquitous and low-cost organic electronic appliances on plastic  

Microsoft Academic Search

Organic electronics are beginning to make significant inroads into the commercial world, and if the field continues to progress at its current, rapid pace, electronics based on organic thin-film materials will soon become a mainstay of our technological existence. Already products based on active thin-film organic devices are in the market place, most notably the displays of several mobile electronic

Stephen R. Forrest

2004-01-01

82

Effect of phase on the stopping and range distribution of low-energy electrons in water  

Microsoft Academic Search

Dipole oscillator strength distributions (DOSD) of water in the vapor, liquid, and solid phases have been used to calculate the inelastic mean free path, linear energy transfer (LET), and range straggling of low-energy electrons (less than or equal to10 keV) following an earlier procedure of the authors (J. Phys. Chem. 1985, 89, 930). The DOSD's of the different phases show

Jay A. LaVerne; A. Mozumder

1986-01-01

83

Mechanism and rate of denitrification in an agricultural watershed: Electron and mass balance along groundwater flow paths  

USGS Publications Warehouse

The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards. Both the extent and rate of denitrification varied depending on the groundwater flow path. While little or no denitrification occurred in much of the upland portions of the aquifer, a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer. In contrast, a sharp shallow redox gradient is observed adjacent to a third-order stream as aerobic groundwater enters reduced sediments. An essentially complete loss of nitrate concurrent with increases in excess N2 provide evidence that denitrification occurs as groundwater enters this zone. Electron and mass balance calculations suggest that iron sulfide (e.g., pyrite) oxidation is the primary source of electrons for denitrification. Denitrification rate estimates were based on mass balance calculations using nitrate and excess N2 coupled with groundwater travel times. Travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon-based age dates. Denitrification rates were found to vary considerably between the two areas where denitrification occurs. Denitrification rates in the deep, upland portions of the aquifer were found to range from < 0.01 to 0.14 mM of N per year; rates at the redoxcline along the shallow flow path range from 1.0 to 2.7 mM of N per year. Potential denitrification rates in groundwater adjacent to the stream may be much faster, with rates up to 140 mM per year based on an in situ experiment conducted in this zone.The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards. Both the extent and rate of denitrification varied depending on the groundwater flow path. While little or no denitrification occurred in much of the upland portions of the aquifer, a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer. In contrast, a sharp shallow redox gradient is observed adjacent to a third-order stream as aerobic groundwater enters reduced sediments. An essentially complete loss of nitrate concurrent with increases in excess N2 provide evidence that denitrification occurs as groundwater enters this zone. Electron and mass balance calculations suggest that iron sulfide (e.g., pyrite) oxidation is the primary source of electrons for denitrification. Denitrification rate estimates were based on mass balance calculations using nitrate and excess N2 coupled with groundwater travel times. Travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon-based age dates. Denitrification rates were found to vary considerably between the two areas where denitrification occurs. Denitrification rates in the deep, upland portions of the aquifer were found to range from <0.01 to 0.14 mM of N per year; rates at the redoxcline along the shallow flow path range from 1.0 to 2.7 mM of N per year. Potential denitrification rates in groundwater adjacent to the stream may be much faster, with rates up to 140 mM per year based on an in situ experiment conducted in this zone.

Tesoriero, A.J.; Liebscher, H.; Cox, S.E.

2000-01-01

84

A path: from electroplating through lithographic masks in electronics to LIGA in MEMS  

Microsoft Academic Search

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

L. T. Romankiw

1997-01-01

85

Feynman Path Integral Approach to Electron Diffraction for One and Two Slits: Analytical Results  

ERIC Educational Resources Information Center

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.…

Beau, Mathieu

2012-01-01

86

Multiprobe electron waveguides: Filtering and bend resistances  

NASA Astrophysics Data System (ADS)

Recent work in high-mobility quantum wires suggests that electron waveguide behavior is relevant for transport at low temperature. We therefore study transport in ideal electron waveguides paying particular attention to their multimode properties. In order to address four-probe measurements, junctions between waveguides must be included and we consider systems with both one and two junctions. We find, first, that the junctions strongly filter the electrons, changing the distribution of the electrons among the modes of the waveguide. Second, the junctions give rise to both substantial longitudinal resistance and bend resistances which can be either local or nonlocal. The latter effect is a direct result of the filtering properties and decays on the length scale of a mean free path in a system with disorder. In a system where the disorder is smooth, the decay of the nonlocal bend resistance occurs over a distance much smaller than the transport mean free path but close to the total mean free path. Third, interference in scattering from two junctions leads to an oscillatory dependence of the transmission on the length between the junctions. The period of this oscillation is surprisingly low, being determined by mixing of the various modes in the waveguide, and shows up strongly in the nonlocal resistance. Finally, throughout this work we compare the quantum results to classical calculations in order to separate classical size effects from effects which require coherence. The classical transmission coefficient approach is derived from the Boltzmann equation with suitable boundary conditions. The basic trends are present in the classical calculations; however, there are large quantum deviations in certain cases as well as some phenomena which are strictly quantum mechanical, especially in the few-mode regime.

Baranger, Harold U.

1990-12-01

87

Correlation between the electronic structures and diffusion paths of interstitial defects in semiconductors: The case of CdTe  

NASA Astrophysics Data System (ADS)

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 nondegenerated s -like state under the 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 coupling between the Cu d and host s orbitals. 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 the Td symmetry, large distortions occur. Therefore the diffusion paths are very different from those of the interstitial Cd and Cu atoms, 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; Wei, Su-Huai; Da Silva, Juarez L. F.

2014-10-01

88

The long and twisting path: an efficiency evaluation of an electronic whiteboard system.  

PubMed

Electronic whiteboard systems are becoming increasingly popular as replacements for the dry-erase whiteboards previously used for communication and workflow coordination at Emergency Departments. With this it also becomes increasingly important that these systems do not disrupt or delay the working practices of the departments where they are taken into use. Usability evaluations should therefore be employed as part of developing and implementing these systems. We report on a subset of the results from a larger usability study of a electronic whiteboard and find that there are inefficiencies, which could be mitigated by a relatively simple redesign and thus improve the usability of the system. PMID:23388277

Rasmussen, Rasmus; Kushniruk, Andre

2013-01-01

89

The Path of an Electron Orbiting an Accelerating Nucleus Len Zane, University of Nevada, Las Vegas  

E-print Network

the microscopic force laws governing the motion of an electron with the macroscopic properties of rods and clocks a distance D apart with synchronized watches. To synchronize their watches, the two scientists will meet at point A, the middle of the marked off distance D, simultaneously start their watches, and then walk

Hemmers, Oliver

90

Study of the transverse liquid flow paths in pine and spruce using scanning electron microscopy  

Microsoft Academic Search

Samples of pine (Pinus sylvestris) and spruce (Picea abies) were impregnated with a low-viscous epoxy resin using a vacuum process. The epoxy was cured in situ and the specimens sectioned.\\u000a Deposits of the cured epoxy was then observed in the wood cavities using a scanning electron microscope. The investigation\\u000a concentrated on tracing the transverse movements of a viscous liquid in

Tomas Olsson; Modris Megnis; Janis Varna; Henrik Lindberg

2001-01-01

91

A Deterministic Transport Code for Space Environment Electrons  

NASA Technical Reports Server (NTRS)

A deterministic computational procedure has been developed to describe transport of space environment electrons in various shield media. This code is an upgrade and extension of an earlier electron code. Whereas the former code was formulated on the basis of parametric functions derived from limited laboratory data, the present code utilizes well established theoretical representations to describe the relevant interactions and transport processes. The shield material specification has been made more general, as have the pertinent cross sections. A combined mean free path and average trajectory approach has been used in the transport formalism. Comparisons with Monte Carlo calculations are presented.

Nealy, John E.; Chang, C. K.; Norman, Ryan B.; Blattnig, Steve R.; Badavi, Francis F.; Adamczyk, Anne M.

2010-01-01

92

Modelling the high altitude electron temperature: a modified thermal conductivity  

NASA Astrophysics Data System (ADS)

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.

Denton, M. H.; Bailey, G. J.

2001-10-01

93

Influence of emitted electrons transiting between surfaces on plasma-surface interaction  

SciTech Connect

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.

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

94

Auger electron intensity variations in oxygen-exposed large grain polycrystalline silver  

NASA Technical Reports Server (NTRS)

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.

Lee, W. S.; Outlaw, R. A.; Hoflund, G. B.; Davidson, M. R.

1989-01-01

95

Path-integral approach to the electron density of states at the interface of a single modulation-doped heterojunction  

NASA Astrophysics Data System (ADS)

The electronic density of states (DOS) at the interface of a single modulation-doped heterojunction is calculated both in the fluctuation band tail and in the semiclassical limit using the path-integral method. Due to charge density inhomogeneities in the heavily doped barrier region, random potential fluctuations are generated in whose minima carriers are localized, resulting in a band-tail density spectrum. The screening of the long-range potential fluctuations, which are important for the problem considered, is accounted for by using the two-dimensional Thomas-Fermi model. The statistical properties of the random impurity charge distribution are taken into account using the binary correlation function of the random potential for the specific geometry of the problem in two limiting cases of the general correlation function. Analytical expressions for the dimensionless functions of the exponential and preexponential of the band-tail DOS, as a function of the energy, are obtained in the weak and strong screening limit for the quasi-2D case under consideration and are compared to the respective functions for the general d-dimensional case. The dependence of the band-tail DOS behavior on the relevant parameters of the system, namely, spacer layer thickness, doping layer thickness, 2D EG thickness, and 3D-impurity concentration is studied numerically for AlxGa1-xAs-GaAs modulation doped heterostructures and numerical results for the 2D-DOS are presented. The band-tail results for the 2D-DOS are compared with the Kane approximation derived by taking the limit t-->0 in order to determine ?(E) in the whole energy range. We compare the results from the two computed cases of the path-integral expression for the DOS corresponding to the two limits of the general correlation function with each other. On the other hand, we compare the semiclassical limit and the white Gaussian noise limit of the above results with many other theoretical methods such as the generalized semiclassical method, multiple scattering method and the simulations resulting from the tight-binding model.

Sa-Yakanit, V.; Slavcheva, G.

1998-11-01

96

Electron energy loss spectroscopy investigation through a nano ablated uranium dioxide sample.  

PubMed

A lamella of uranium dioxide (?10 × ?10 × ?0.02-0.20 ?m) was produced by focused ion beam for transmission electron and electron energy loss spectroscopy (EELS) examinations. This sample allows quantitative analysis of the EEL spectra recorded for UO? as a function of the thickness. The M, N, O and P edges were recorded over zero loss to 4000 eV loss. The edges allow reconstruction of the electronic transitions, the lowest energy loss edges for P transitions corresponds to P3 electron transition (17.2 eV) from U6p3/2 level. The edge analysis allows also better interpretation of the loss spectrum with identification of the plasmon peak of the core electron transition edges. In addition, the energy lost was studied through a range of thicknesses going from ?20 to ?200 nm to derive the electron mean free path and cross section for inelastic scattering in the plasmon part of the spectrum. The mean free path of inelastic electron for uranium dioxide is compared with that reported earlier for other oxides from Be to Bi and for 200 keV incidents electrons. The present study emphasises the potential of combining FIB and EELS for the analysis of actinide compounds. PMID:23598145

Degueldre, Claude; Schaeublin, Robin; Krbanjevic, Julijana; Minikus, Eugenia

2013-03-15

97

Inhomogeneous exciton broadening and mean free path in In1-x GaxAsyP1-y-InP heterostructures  

Microsoft Academic Search

Absorption and electroabsorption spectra are investigated at low temperature to derive broadening parameters of excitonic absorption edges in the alloy crystals. A strong increase of the inhomogeneous linewidth of excitons is observed for quaternary material which exceeds significantly the width expected from compositional fluctuations. The linewidth decreases again for phosphorous rich samples. Franz-Keldysh oscillations above the absorption edge contain information

Arndt Jaeger; Gerhard Weiser; Peter Wiedemann

1995-01-01

98

On the role of electron-ion recombination in low vacuum scanning electron microscopy.  

PubMed

Here we demonstrate the effects of electron-ion recombination on imaging signals utilized in low vacuum scanning electron microscopes (SEMs). The presented results show that, under normal operating conditions, recombination of ionized gas molecules with secondary electrons (SEs) suppresses a significant fraction of emitted electrons. If the ion flux (and hence the spatial dependence of the SE-ion recombination rate) is laterally inhomogeneous across the imaged region of a specimen, contrast in SE images can be influenced and in some cases (under conditions of high detector field strength and long ionic mean free path) dominated by variations in the recombination rate. Consequently, SE images of features such as topographic asperities can exhibit edge-darkening, leading to inversion of some topographic contrast. Recognition of the extent and nature of electron-ion recombination is required for a correct understanding of processes occurring in variable pressure SEMs and, subsequently, for models of image formation. PMID:11856384

Toth, M; Thiel, B L; Donald, A M

2002-01-01

99

Evidence of Momentum Conservation at a Nonepitaxial Metal/Semiconductor Interface Using Ballistic Electron Emission Microscopy  

NASA Technical Reports Server (NTRS)

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.

Bell, L. D.

1996-01-01

100

Electron Emission from Slightly Oxidized Depleted Uranium Generated by its Own Radioactivity Measured by Electron Spectroscopy, and Electron-Induced Dissociation and Ionization of Hydrogen Near its Surface.  

SciTech Connect

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.

Siekhaus, W J; Nelson, A J

2011-10-26

101

MetaPath: An Electronic Knowledge Base for Collating, Exchanging and Analyzing Case Studies of Xenobiotic Metabolism  

EPA Science Inventory

A new MetaPath information system was developed through a collaborative effort between the Laboratory of Mathematical Chemistry (Bourgas, Bulgaria), EPA?s Office of Research and Development (NHEERL, MED, Duluth, MN and NERL, ERD, Athens, GA), and EPA?s Office of Chemical Safety a...

102

Absolute and effective cross-sections for low-energy electron-scattering processes within condensed matter.  

PubMed

Within the last two decades, a number of experimental techniques have been developed to measure mean free paths and absolute and effective cross-sections for various processes related to the interaction of low-energy electrons with condensed matter. In all of the experiments, a monochromatic electron beam impinges on a thin multilayer film composed of atoms and/or molecules condensed on a metal or semiconductor substrate held at cryogenic temperatures in an ultra-high-vacuum system. Depending on the apparatus, cross-sections are obtained from low-energy electron transmission (LEET), high-resolution electron energy loss (HREEL), x-ray photoelectron (XPS) spectroscopy, electron-stimulated desorption (ESD) of neutral and ions, or a combination of these techniques. Quasi-elastic and inelastic mean free paths have been extracted from LEET data. This method has also served to generate absolute cross-sections for electron trapping and fragment production from the dissociation of transient molecular anions. In amorphous ice, a complete set of absolute cross-sections for all inelastic losses by 1-20 eV electrons has been obtained from HREEL data. Effective cross-sections for neutral and ionic radical formation were generated by desorption and XPS experiments. These various methods are briefly described in this article, and the corresponding cross-sections in the range 0-20 eV summarized. PMID:10052674

Bass, A D; Sanche, L

1998-12-01

103

Characterization of two-dimensional hexagonal boron nitride using scanning electron and scanning helium ion microscopy  

SciTech Connect

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.

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

104

Light-cone path integral approach to the Landau-Pomeranchuk-Migdal effect and the SLAC data on bremsstrahlung from high energy electrons  

Microsoft Academic Search

The recent data of the SLAC E-146 collaboration on the\\u000aLandau-Pomeranchuk-Migdal effect for bremsstrahlung from 8 and 25 GeV electrons\\u000aare analyzed within a rigorous light-cone path integral approach. Numerical\\u000acalculations have been carried out treating rigorously the Coulomb effects and\\u000aincluding the inelastic processes. Comparison with the experimental data is\\u000aperformed taking into account multi-photon emission and photon absorption.

B. G. Zakharov; L. D. Landau

1998-01-01

105

Tornado Paths  

NSDL National Science Digital Library

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.

Samson, Perry; Michigan, University O.

106

Relaxation of electronic excitations in CaF2 nanoparticles  

NASA Astrophysics Data System (ADS)

The luminescence properties of CaF2 nanoparticles with various sizes (20-140 nm) are studied upon the excitation by VUV and x-ray quanta in order to reveal the influence of ratio of mean free path and thermalization length of charge carriers and nanoparticle size on the self-trapped exciton luminescence. The luminescence intensity for exciting quantum energies corresponding to optical creation of exciton and to the range of electronic excitation multiplication is not so sensitive to nanoparticle size as for quanta with energy of Eg < h? < 2Eg. The dependences of luminescence intensity on nanoparticle size at the excitation by quanta of various energies are discussed in terms of electron-phonon and electron-electron scattering lengths and energy losses on surface defects.

Vistovskyy, V. V.; Zhyshkovych, A. V.; Mitina, N. E.; Zaichenko, A. S.; Gektin, A. V.; Vasil'ev, A. N.; Voloshinovskii, A. S.

2012-07-01

107

Carbon nanotubes: Electrons in one dimension  

NASA Astrophysics Data System (ADS)

The work presented in this thesis will discuss transport measurements on individual single-walled nanotubes (SWNTs) and SWNT bundles. SWNTs, which are essentially rolled-up sheets of graphite, are either one-dimensional (1D) metals or 1D semiconductors depending on how they are rolled-up. Measurements on both metallic and semiconducting SWNTs will be presented. Chapter 1 will present an introductory overview to the thesis, discussing prior related experimental work and introducing basic concepts that are used in subsequent chapters. Chapter 2 discusses the experimental methods we have used to study transport in SWNTs. Chapters 3 and 4 discuss low temperature measurements of metallic SWNTs. Chapter 3 will discuss the low temperature behavior of the conductance of a SWNT bundle, or rope, that shows quantum mechanical effects resulting from the finite size of the sample. Chapter 4 will discuss how these finite size effects can be used to experimentally study the quantum level structure in metallic nanotubes and the effects of an applied magnetic field. In chapters 5 and 6, we discuss transport measurements of semiconducting SWNTs. In chapter 5, we show that semiconducting SWNT's can be doped with potassium. Chapter 6 presents experiment and theory that indicate that the elastic mean free path in metallic tubes is far longer than in semiconducting tubes. Chapters 7 and 8 address the effects of electron-electron (e-e) interactions on the transport properties of metallic SWNTs. Chapter 7 discusses some theoretical aspects of 1D wires when e-e interactions are taken account, giving a simplified picture of the Luttinger-liquid state expected for a 1D system of interacting electrons. Finally, chapter 8 will discuss measurements on metallic samples with extremely long mean free paths. These experiments show evidence of this Luttinger-liquid behavior, in which the electron-electron interactions lead to a qualitatively different ground state than what would be expected with Fermi-liquid theory.

Bockrath, Marc William

108

MoS2 : Choice Substrate for Accessing and Tuning the Electronic Properties of Graphene  

NASA Astrophysics Data System (ADS)

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.

Lu, Chih-Pin; Li, Guohong; Watanabe, K.; Taniguchi, T.; Andrei, Eva Y.

2014-10-01

109

Copper foil provides uniform heat sink path  

NASA Technical Reports Server (NTRS)

Thermal path prevents voids and discontinuities which make heat sinks in electronic equipment inefficient. The thermal path combines the high thermal conductivity of copper with the resiliency of silicone rubber.

Phillips, I. E., Jr.; Schreihans, F. A.

1966-01-01

110

A new path for the electron bulk energization in solar flares: Fermi acceleration by magnetohydrodynamic turbulence in reconnection outflows  

NASA Technical Reports Server (NTRS)

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.

Larosa, T. N.; Moore, R. L.; Shore, S. N.

1994-01-01

111

Path Pascal  

NASA Technical Reports Server (NTRS)

Path Pascal is high-level experimental programming language based on PASCAL, which incorporates extensions for systems and real-time programming. Pascal is extended to treat real-time concurrent systems.

Campbell, R. H.; Kolstad, R. B.; Holle, D. F.; Miller, T. J.; Krause, P.; Horton, K.; Macke, T.

1983-01-01

112

Control of Excitonic and Electron-Hole Processes in Wide-Gap Crystals by Means of Elastic Uniaxial Stress  

NASA Astrophysics Data System (ADS)

The time-resolved emission spectra and the excitation spectra of the main emissions have been measured for the first time in stressed and unstressed RbI crystals using synchrotron radiation of 10-30 eV at 8 K. It has been shown that the applied elastic uniaxial stress (EUS) offers promise for the separation of the elementary multiplication mechanisms of electronic excitations. A different influence of EUS on the self-trapping of excitons or holes at 8 K has been discussed. The mean free path of free excitons decreases, while that of valence holes increases in a stressed RbI crystal.

Lushchik, A.; Lushchik, Ch.; Vasil'chenko, E.; Kirm, M.; Martinson, I.

113

Fast Advection of Magnetic Fields by Hot Electrons  

NASA Astrophysics Data System (ADS)

Experiments where a laser-generated proton beam is used to probe the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target are presented. At intensities of 1015Wcm-2 and under conditions of significant fast electron production and strong heat fluxes, the electron mean-free-path is long compared with the temperature gradient scale length and hence nonlocal transport is important for the dynamics of the magnetic field in the plasma. The hot electron flux transports self-generated magnetic fields away from the focal region through the Nernst effect [A. Nishiguchi , Phys. Rev. Lett. 53, 262 (1984)PRLTAO0031-900710.1103/PhysRevLett.53.262] at significantly higher velocities than the fluid velocity. Two-dimensional implicit Vlasov-Fokker-Planck modeling shows that the Nernst effect allows advection and self-generation transports magnetic fields at significantly faster than the ion fluid velocity, vN/cs?10.

Willingale, L.; Thomas, A. G. R.; Nilson, P. M.; Kaluza, M. C.; Bandyopadhyay, S.; Dangor, A. E.; Evans, R. G.; Fernandes, P.; Haines, M. G.; Kamperidis, C.; Kingham, R. J.; Minardi, S.; Notley, M.; Ridgers, C. P.; Rozmus, W.; Sherlock, M.; Tatarakis, M.; Wei, M. S.; Najmudin, Z.; Krushelnick, K.

2010-08-01

114

Fast advection of magnetic fields by hot electrons  

NASA Astrophysics Data System (ADS)

Experiments where a laser generated proton beam is used to probe the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target are presented. At intensities of 10^15 ; Wcm-2 and under conditions of significant fast electron production and strong heat fluxes, the electron mean-free-path is long compared with the temperature gradient scale-length and hence non-local transport is important for the dynamics of the magnetic field in the plasma. The hot electron flux transports self-generated magnetic fields away from the focal region through the Nernst effect [1] at significantly higher velocities than the fluid velocity. Two-dimensional implicit Vlasov-Fokker-Planck modeling shows that the Nernst effect allows advection and self-generation transports magnetic fields at significantly faster than the ion fluid velocity, vN/cs 10.[4pt] [1] A. Nishiguchi et al., Phys. Rev. Lett., 53, 262 (1984).

Willingale, L.; Thomas, A. G. R.; Krushelnick, K.; Nilson, P. M.; Kaluza, M. C.; Dangor, A. E.; Evans, R. G.; Fernandes, P.; Haines, M. G.; Kamperidis, C.; Kingham, R. J.; Ridgers, C. P.; Sherlock, M.; Wei, M.-S.; Najmudin, Z.; Bandyopadyay, S.; Notley, M.; Minardi, S.; Tatarakis, M.; Rozmus, W.

2010-11-01

115

A Deterministic Computational Procedure for Space Environment Electron Transport  

NASA Technical Reports Server (NTRS)

A deterministic computational procedure for describing the transport of electrons in condensed media is formulated to simulate the effects and exposures from spectral distributions typical of electrons trapped in planetary magnetic fields. The primary purpose for developing the procedure is to provide a means of rapidly performing numerous repetitive transport calculations essential for electron radiation exposure assessments for complex space structures. The present code utilizes well-established theoretical representations to describe the relevant interactions and transport processes. A combined mean free path and average trajectory approach is used in the transport formalism. For typical space environment spectra, several favorable comparisons with Monte Carlo calculations are made which have indicated that accuracy is not compromised at the expense of the computational speed.

Nealy, John E.; Chang, C. K.; Norman, Ryan B.; Blattnig, Steve R.; Badavi, Francis F.; Adamcyk, Anne M.

2010-01-01

116

Simulation of electron transport during electron-beam-induced deposition of nanostructures  

PubMed Central

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

Jeschke, Harald O; Valentí, Roser

2013-01-01

117

MoS 2 MoS2: choice substrate for accessing and tuning the electronic properties of graphene.  

PubMed

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 MoS(2) 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 MoS(2) is ultraflat, producing long mean free paths, while avoiding band structure reconstruction. Importantly, the screening of the MoS(2) 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. MoS(2) 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. PMID:25375733

Lu, Chih-Pin; Li, Guohong; Watanabe, K; Taniguchi, T; Andrei, Eva Y

2014-10-10

118

Effect of Nanoparticles on Electron and Thermoelectric MONA ZEBARJADI,1,5  

E-print Network

applications such as thermoelectric power generators1 and solar cells.2 The advantage of incorporating. They obtained the mean free path of the transport and the energy transport velocity, which were in agreement

119

Measurements of electron heat flow along a dc magnetic field in strong temperature gradients  

SciTech Connect

Measurements of electron heat flow parallel to B are performed on a fully -ionized quiescent plasma column under conditions for which the electron-electron collisional mean free path, l/sub ee/, is not small relative to the electron temperature-gradient scale-length. Pulsed microwave heating at one location on the column and nonperturbing microwave resonator measurements of temperature at two locations on the column are used to create and to measure the heat flow. Results are compared with the predictions of a 1-D heat diffusion code that has a parameter, ..cap alpha.., multiplying the Spitzer heat conductivity coefficient, and that also has provision for limiting the heat flux to q/sub L/ = ..beta..nkT ..sqrt..kt/m (where ..beta.. is an adjustable parameter) in order to model the transition to larger values of (l/sub ee/T)dT/dx/.

Massey, R.S.; Ingraham, J.C.; Wright, B.L.; Dreicer, H.

1980-01-01

120

Characterization and Quantification of Electronic and Ionic Ohmic Overpotential and Heat Generation in a Solid Oxide Fuel Cell Anode  

SciTech Connect

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, John R.; Chiu, Wilson K.S.

2011-08-16

121

Electron and phonon transport in Co-doped FeV0.6Nb0.4Sb half-Heusler thermoelectric materials  

NASA Astrophysics Data System (ADS)

The electron and phonon transport characteristics of n-type Fe1-xCoxV0.6Nb0.4Sb half-Heusler thermoelectric compounds is analyzed. The acoustic phonon scattering is dominant in the carrier transport. The deformation potential of Edef = 14.1 eV and the density of state effective mass m* ? 2.0 me are derived under a single parabolic band assumption. The band gap is calculated to be ˜0.3 eV. Electron and phonon mean free paths are estimated based on the low and high temperature measurements. The electron mean free path is higher than the phonon one above room temperature, which is consistent with the experimental result that the electron mobility decreases more than the lattice thermal conductivity by grain refinement to enhance boundary scattering. A maximum ZT value of ˜0.33 is obtained at 650 K for x = 0.015, an increase by ˜60% compared with FeVSb. The optimal doping level is found to be ˜3.0 × 1020 cm-3 at 600 K.

Fu, Chenguang; Liu, Yintu; Xie, Hanhui; Liu, Xiaohua; Zhao, Xinbing; Jeffrey Snyder, G.; Xie, Jian; Zhu, Tiejun

2013-10-01

122

Electron-phonon interaction in disordered metal films: The resistivity and electron dephasing rate  

NASA Astrophysics Data System (ADS)

The temperature dependence of the resistance of films of Al, Be, and NbC with small values of the electron mean free path l=1.5-10 nm has been measured at 4.2-300 K. The resistance of all the films contains a T2 contribution that is proportional to the residual resistance; this contribution has been attributed to the interference between the elastic electron scattering and the electron-phonon scattering. Fitting the data to the theory of the electron-phonon-impurity interference (M. Yu. Reiser and A. V. Sergeev, Zh. Eksp. Teor. Fiz. 92, 224 (1987) [Sov. Phys. JETP 65, 1291 (1987)]), we obtain constants of interaction of the electrons with transverse phonons, and estimate the contribution of this interaction to the electron dephasing rate in thin films of Au, Al, Be, Nb, and NbC. Our estimates are in a good agreement with the experimental data on the inelastic electron-phonon scattering in these films. This indicates that the interaction of electrons with transverse phonons controls the electron-phonon relaxation rate in thin-metal films over a broad temperature range.

Ptitsina, N. G.; Chulkova, G. M.; Il'in, K. S.; Sergeev, A. V.; Pochinkov, F. S.; Gershenzon, E. M.; Gershenson, M. E.

1997-10-01

123

Term Paths  

NSDL National Science Digital Library

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.

Cynthia Ann Radle (McCullough High School REV)

1995-06-30

124

Unimolecular reaction paths of electronically excited species. III. Production of CH + 3 ions from CH3OH + as an example of isolated state dissociation  

NASA Astrophysics Data System (ADS)

The CH3OH+ ion dissociates to CH+3+OH as soon as the energy of state B˜ 2A' is reached. This fragmentation cannot be described by RRKM theory. Ab initio potential energy surfaces at the CI level have been calculated as a function of the CO bond stretching coordinate R and of the COH angle ? for the lowest 2A', 2A?, 4A', and 4A? states. Several zones of strong nonadiabatic interaction have been detected. They correspond to avoided crossings and account for the existence of internal conversions among the different states. In particular, there exists an avoided crossing with a small energy gap between states B˜ 2A' and à 2A', which is localized in a very restricted range of internuclear distances (R=1.555 Å and ?=69.8°). This avoided crossing plays a very important role because it is the only low-energy de-excitation channel of state B˜. The nonadiabatic coupling matrix elements <Ã??/?q?B˜> have been calculated for coordinates R and ?. They are represented by very narrow Lorentzians and they bring about a very high nonadiabatic transition probability. Thus, the population of the upper electronic states (B˜ 2A', C˜ 2A?, and D˜ 2A') detected in the photoelectron spectrum in the 14-18 eV energy range easily cascades down to states à 2A' via this mechanism. Since the zone of nonadiabatic interaction is very narrow, the population starts its evolution on the potential energy surface of states à with well-defined initial conditions. In the present case, internal conversion is a much more specific preparation than optical excitation. The reactive flux then branches into two paths. One of them leads directly to the CH+3+OH asymptote and escapes statistical energy redistribution. The other path leads to the bottom of the potential energy surface and gives rise to the RRKM/QET component of the mass spectrum, i.e., leads to the other fragmentations. ``Isolated state decay'' thus corresponds to dissociation of the nonrandomized fraction of the population and not to isolation, i.e., to lack of radiationless transition to the lower electronic states. The circumstances which give rise to such a behavior are analyzed.

Galloy, C.; Lecomte, C.; Lorquet, J. C.

1982-11-01

125

Total cross sections for positron and electron scattering from pyrimidine  

NASA Astrophysics Data System (ADS)

In this paper we report original measurements of total cross sections for positron scattering from the important biomolecule pyrimidine. The energy range of these measurements was 0.3-45 eV, while the energy resolution was ~260 meV. In addition, we report theoretical results, calculated within the independent atom-screened additivity rule (IAM-SCAR) formalism, for the corresponding electron impact total cross sections. In that case the energy range is 1-10 000 eV. Total cross sections are very important input data for codes that seek to simulate charged-particle tracks in matter, as they define the mean-free path between collisions. As the present data and computations are to the best of our knowledge the first total cross sections to be reported for either positron or electron scattering from pyrimidine, they fill an important void in our available knowledge in the literature.

Zecca, A.; Chiari, L.; García, G.; Blanco, F.; Trainotti, E.; Brunger, M. J.

2010-11-01

126

Beam Model for Energetic Electron Transport in Laser Produced Plasmas  

NASA Astrophysics Data System (ADS)

Energetic electron transport,in laser target implosion codes, is generally handled with a phenominological flux limit . Other techniques include nonlocal transport algorithms (1), although issues have been raised about both their numerical stability and accuracy (2). We have explored a different approach, a beam deposition model. It reduces to Spitzer thermal conduction in the short mean free path limit, is intuitively reasonable, and with suitable approximations, can be economically incorporated into existing implicit numerical algorithms for the electron heat conduction. While our first formulation is for one dimensional plasmas, the model extends easily to two or three dinensions. Initial results appear to be reasonable, and will be presented. 1. Luciani et al, Phys. Rev. Let., 51, 1664, 1983 2.Prasad and Kershaw, Phys. Fluids. B 1, 2430, 1989, and B3, 3087, 1991

Manheimer, Wallace; Colombant, Denis

2002-11-01

127

Surface excitations in surface electron spectroscopies studied by reflection electron energy-loss spectroscopy and elastic peak electron spectroscopy.  

PubMed

Surface excitations, in addition to bulk excitation, undergone by signal electrons in surface electron spectroscopies, such as Auger electron spectroscopy, and X-ray photoelectron spectroscopy, play an important role in the formation of electron spectra. Those inelastic scattering processes not only induce decay in the peak intensity, but also form background appearing in the lower kinetic energy side of relevant peaks. Information on surface excitation is essential in addition to bulk excitations for the quantification of material surfaces by surface electron spectroscopies, and extensive studies have been devoted to it. In this report, we introduce the basics of the study of surface excitations by reflection electron energy loss spectroscopy (REELS) and elastic peak electron spectroscopy (EPES). The application of several approaches within the schemes of EPES analysis and REELS analysis to the experimental determination of inelastic scattering parameters, such as the surface excitation parameter (SEP), differential SEP (DSEP), inelastic mean free path (IMFP), and dielectric function, are also introduced. Information useful to calculate the values of the IMFP and SEP using predictive equations is provided in Supporting Information as well. PMID:20145317

Nagatomi, Takaharu; Tanuma, Shigeo

2010-01-01

128

Field electron emission based on resonant tunneling in diamond/CoSi2/Si quantum well nanostructures  

NASA Astrophysics Data System (ADS)

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.

Gu, Changzhi; Jiang, Xin; Lu, Wengang; Li, Junjie; Mantl, Siegfried

2012-10-01

129

Direct measurement of product of the electron mobility and mean free drift time of CdZnTe semiconductors using position sensitive single  

E-print Network

ZnTe semiconductors using position sensitive single polarity charge sensing detectors Z. He, G. F. Knoll, and D. KZnTe semiconductors using position sensitive single polarity charge sensing detectors Z. He,a) G. F. Knoll, and D. K in semiconductor detectors. These methods are based on newly developed single polarity charge sensing and depth

He, Zhong

130

Electron Density Distributions Calculated for the Nickel Sulfides Millerite, Vaesite, and Heazlewoodite and Nickel Metal: A Case for the Importance of Ni-Ni Bond Paths for  

E-print Network

-orbitals on the interconnecting S atoms. Vaesite, an insulator at low temperatures and a doped semiconductor at higher and heazlewoodite is pictured as occurring along the bond paths, which behave as networks of atomic size wires temperatures, lacks Ni-Ni bond paths. The net charges conferred on the Ni and S atoms are about a quarter

Downs, Robert T.

131

Electromigration in a quasi-two-dimensional electron gas: Theory of driving force  

NASA Astrophysics Data System (ADS)

We calculate the effective force on an impurity charge present in a quasi-two-dimensional electron layer and the induced charge density around the impurity when an electrostatic field is applied parallel to the layer. Our calculation is based on the quantum-mechanical density-matrix formalism, and the scattering is treated in a weak-charge relaxation-time approximation. Our results are compared with the corresponding results in a three-dimensional electron gas, and implications of these results are discussed. It is found that the driving force for electromigration is well approximated by the Fiks-Huntington ballistic theory when KfL>>1, where Kf is the Fermi wave vector and L is the electron mean free path in the layer. For the Si(100) inversion layer, there are significant corrections to the ballistic expression for KfL<=10.

Dasgupta, Basab B.; Sorbello, Richard S.

1980-05-01

132

The development of the July 1989 1 deg x 1 deg and 30' x 30' terrestrial mean free-air anomaly data bases  

NASA Technical Reports Server (NTRS)

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.

Kim, Jeong-Hee; Rapp, Richard H.

1990-01-01

133

A novel method for patient exit and entrance dose prediction based on water equivalent path length measured with an amorphous silicon electronic portal imaging device.  

PubMed

In vivo dosimetry is one of the quality assurance tools used in radiotherapy to monitor the dose delivered to the patient. Electronic portal imaging device (EPID) images for a set of solid water phantoms of varying thicknesses were acquired and the data fitted onto a quadratic equation, which relates the reduction in photon beam intensity to the attenuation coefficient and material thickness at a reference condition. The quadratic model is used to convert the measured grey scale value into water equivalent path length (EPL) at each pixel for any material imaged by the detector. For any other non-reference conditions, scatter, field size and MU variation effects on the image were corrected by relative measurements using an ionization chamber and an EPID. The 2D EPL is linked to the percentage exit dose table, for different thicknesses and field sizes, thereby converting the plane pixel values at each point into a 2D dose map. The off-axis ratio is corrected using envelope and boundary profiles generated from the treatment planning system (TPS). The method requires field size, monitor unit and source-to-surface distance (SSD) as clinical input parameters to predict the exit dose, which is then used to determine the entrance dose. The measured pixel dose maps were compared with calculated doses from TPS for both entrance and exit depth of phantom. The gamma index at 3% dose difference (DD) and 3 mm distance to agreement (DTA) resulted in an average of 97% passing for the square fields of 5, 10, 15 and 20 cm. The exit dose EPID dose distributions predicted by the algorithm were in better agreement with TPS-calculated doses than phantom entrance dose distributions. PMID:20019398

Kavuma, Awusi; Glegg, Martin; Metwaly, Mohamed; Currie, Garry; Elliott, Alex

2010-01-21

134

Johns, R. H., D. W. Burgess, C. A. Doswell III, M. S. Gilmore, J. A. Hart, and S. F. Piltz, 2013: The 1925 Tri-State tornado damage path and associated storm system. Electronic J. Severe Storms Meteor., 8 (2), 133.  

E-print Network

: 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

Doswell III, Charles A.

135

Nanoscale thin single-crystal silicon and its application to electronics  

NASA Astrophysics Data System (ADS)

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.

Avci, Uygar; Tiwari, Sandip

2004-03-01

136

Path entanglement of surface plasmons  

NASA Astrophysics Data System (ADS)

Metals can sustain traveling electromagnetic waves at their surfaces supported by the collective oscillations of their free electrons in unison. Remarkably, classical electromagnetism captures the essential physics of these ‘surface plasma’ waves using simple models with only macroscopic features, accounting for microscopic electron–electron and electron–phonon interactions with a single, semi-empirical damping parameter. Nevertheless, in quantum theory these microscopic interactions could be important, as any substantial environmental interactions could decohere quantum superpositions of surface plasmons, the quanta of these waves. Here we report a measurement of path entanglement between surface plasmons with 95% contrast, confirming that a path-entangled state can indeed survive without measurable decoherence. Our measurement suggests that elastic scattering mechanisms of the type that might cause pure dephasing in plasmonic systems must be weak enough not to significantly perturb the state of the metal under the experimental conditions we investigated.

Fakonas, James S.; Mitskovets, Anna; Atwater, Harry A.

2015-02-01

137

Conditions for electron runaway under leader breakdown of long gaps  

SciTech Connect

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.

Ul'yanov, K. N. [Lenin All-Russia Electrotechnical Institute (Russian Federation)

2008-04-15

138

Path Coupling and Aggregate Path Coupling  

E-print Network

In this survey paper, we describe and characterize an extension to the classical path coupling method applied statistical mechanical models, referred to as aggregate path coupling. In conjunction with large deviations estimates, we use this aggregate path coupling method to prove rapid mixing of Glauber dynamics for a large class of statistical mechanical models, including models that exhibit discontinuous phase transitions which have traditionally been more difficult to analyze rigorously. The parameter region for rapid mixing for the generalized Curie-Weiss-Potts model is derived as a new application of the aggregate path coupling method.

Kovchegov, Yevgeniy

2015-01-01

139

Generation and accretion of electrons in complex plasmas with cylindrical particles  

SciTech Connect

This paper presents an analytical model for the physical understanding of the charging of cylindrical dust particles in an open complex plasma system. Two different mechanisms, viz., thermionic emission and photoelectric emission have been considered for the electron generation from the charged cylindrical dust particles; the corresponding expressions for the rate of emission of electrons and their mean energy have been derived. A simple approach has been adopted to derive the expression for the rate of electron accretion to the dust particle. Further a new expression for the mean energy associated with the accreted electrons due to cylindrical dust particle has been derived and presented. An interesting comparison of results obtained in the case of spherical and cylindrical dust particles has also been made. Using these expressions, a formalism has been developed for the electronic processes in an illuminated dust cloud with cylindrical particles, on the basis of charge neutrality condition and number and energy balance of electrons; the charge carried by the cylindrical dust particles, electron temperature, and electron density corresponding to a given situation have been determined. The limitation of the applicability of the theory, viz., that the mean free path of an electron for accretion by dust particles be less than the dimension of the dust cloud has been pointed out.

Sodha, Mahendra Singh; Misra, Shikha [Disha Institute of Management and Technology, Satya Vihar, Vidhan Sabha-Chandrakhuri Marg, Mandir Hasaud, Raipur 492101, Chattisgarh (India); Mishra, S. K. [Department of Education Building, University of Lucknow, Lucknow 226007 (India)

2009-12-15

140

A high-energy electron scattering study of the electronic structure and elemental composition of O-implanted Ta films used for the fabrication of memristor devices  

NASA Astrophysics Data System (ADS)

High-energy electron scattering is used to investigate Ta films implanted with 10 keV O ions. These films are of interest as they have been used for the fabrication of memristors. High-energy electron scattering is used with incoming electron energies ranging from 5 to 40 keV. The inelastic mean free path, and hence the probing depth, is at these energies of the same order as the range of the implanted ions. At the same time, we can distinguish the mass of the atom that scattered the electron elastically, due to the dependence of the recoil energy on the mass of the scatterer. This allows us to determine quantitatively the atomic composition near the surface from the signal of electrons that have scattered elastically but not inelastically. Electrons that have scattered inelastically as well as elastically provide us with information on the possible electronic excitations. Their signal is used to monitor the presence of the Ta2O5 phase near the surface (characterised by a significant band gap of ?4.5 eV), and estimate at what depth below the surface pure Ta metal is present. In this way, we obtain a fairly detailed picture of the elemental composition and electronic properties of these films.

Vos, M.; Grande, P. L.; Nandi, S. K.; Venkatachalam, D. K.; Elliman, R. G.

2013-08-01

141

Electron conduction mechanism and band diagram of sputter-deposited Al/ZrO{sub 2}/Si structure  

SciTech Connect

Metal-oxide-semiconductor capacitors that incorporate ZrO{sub 2} gate dielectrics were fabricated by radio frequency magnetron sputtering. In this work, the essential structures and electrical properties of ZrO{sub 2} thin films were investigated. C-V, energy dispersive x-ray spectrometry, and transmission electron microscopy analyses reveal that an interfacial layer was formed, subsequently reducing the k value of the annealed ZrO{sub 2} thin films. Additionally, the mechanisms of conduction of the Al/ZrO{sub 2}/p-Si metal/zirconium oxide/semiconductor structure were studied with reference to plots of standard Schottky emission, modified Schottky emission, and Poole-Frenkel emission. According to those results, the dominant mechanisms at high temperatures (>425 K) are Poole-Frenkel emission and Schottky emission in low electric fields (<0.6 MV/cm) and high electric fields (>1 MV/cm), respectively. Experimental results indicate that the Al/ZrO{sub 2} barrier height is 0.92 eV and the extracted trap level is about 1.1 eV from the conduction band of ZrO{sub 2}. The modified Schottky emission can be applied in an electric field to ensure that the electronic mean free path of the insulator is less than its thickness. According to the modified Schottky emission model, the extracted electronic mobility of ZrO{sub 2} thin films is around 13 cm{sup 2}/V s at 475 K. The mean free path of transported electrons in ZrO{sub 2} thin films is between 16.2 and 17.4 nm at high temperatures (425-{approx}475 K)

Chiu, F.-C.; Lin, Z.-H.; Chang, C.-W.; Wang, C.-C.; Chuang, K.-F.; Huang, C.-Y.; Lee, Joseph Yamin; Hwang, H.-L. [Department of Electrical Engineering and Institute of Electronics Engineering, National Tsing-Hua University, Hsinchu, Taiwan (China)

2005-02-01

142

ELECTRON HEAT CONDUCTION IN THE SOLAR WIND: TRANSITION FROM SPITZER-HAeRM TO THE COLLISIONLESS LIMIT  

SciTech Connect

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.

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

143

Modified predictive formula for the electron stopping power  

SciTech Connect

We report an improved predictive formula for the electron stopping power (SP) based on an analysis and fit of SPs and electron inelastic mean free paths (IMFPs) calculated from optical data for 37 elemental solids and energies between 200 eV and 30 keV. The formula is a function of energy, density, and IMFP, and is recommended for solids with atomic numbers larger than 6. While the mean deviation between predicted and calculated SPs was 7.25%, larger deviations were found for four additional materials, Li (22.2%), Be (17.9%), graphite (15.3%), and diamond (15.7%). The predictive SP formula can be applied to multicomponent materials. Test comparisons for two compounds, guanine and InSb, showed average deviations of 16.0% and 19.1%, respectively. The improved SP formula is expected to be useful in simulations of electron trajectories in solids with the continuous slowing-down approximation (e.g., in Auger-electron spectroscopy and electron microprobe analysis)

Jablonski, A. [Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warsaw (Poland); Tanuma, S. [Materials Analysis Station, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Powell, C. J. [Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8370 (United States)

2008-03-15

144

Monte Carlo simulation of backscattered electrons and energy from thick targets and surface films  

NASA Astrophysics Data System (ADS)

Electron-matter interaction is described by a Monte Carlo procedure in which the mean free path is calculated by using a screened Rutherford formula, while energy loss is computed by using the Kanaya and Okayama semiempirical expression. Monte Carlo simulation results of the backscattering coefficient have been compared with the available experimental data. The examined energy range was 5-30 keV, the atomic number range was 4-92, and the tilt angle range was 0°-80°. The agreement between simulated and experimental data is found to be excellent in the energy range 10-30 keV; also for 5 keV the agreement is very good when the atomic number is lower than 50. Then the mean backscattered energy was computed for bulk targets, unsupported thin films, and surface films.

Dapor, Maurizio

1992-07-01

145

Momentum-dependent lifetime broadening of electron energy loss spectra: Sum rule constraints and an asymmetric rectangle toy model  

NASA Astrophysics Data System (ADS)

Electron energy loss spectra enable a detailed quantification of the electronic loss mechanisms in a target solid, particularly in the low-energy region dominated by plasmon excitations. Models of the electronic response in condensed-matter systems are usually derived from free-electron gas or jellium models, which commonly neglect to account for the lifetime broadening of individual plasmon and single-electron excitations in a constrained, physical manner. This can lead to potentially significant errors in electron energy loss spectra and electron inelastic mean-free-path (IMFP) calculations. We develop a toy model of plasmon and single-electron excitations that incorporates lifetime broadening for each excitation in an energy- and momentum-dependent fashion. The model is physically constrained using optical and electronic sum rules. We demonstrate the necessity of asymmetric excitation broadening, and show that causally permitted variations in the broadening function can have a significant impact on the dielectric response of the material. Our developments are applied to molybdenum, and compared with previous modeling and high-precision experimental results for the IMFP at electron energies below 120 eV.

Chantler, C. T.; Bourke, J. D.

2014-11-01

146

Path planning for UAVs  

Microsoft Academic Search

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

S. A. Bortoff; E. Hartford

2000-01-01

147

Walden's Paths - Ensemble Edition  

NSDL National Science Digital Library

WaldenÂs Paths enables users of digital document collections (e.g. the Web) to exploit these documents by reusing them for previously unintended audiences in an academic setting. Authors of paths (usually educators) overlay a linear, directed meta-structure over the Web documents and recontextualize these by adding explanatory text to achieve their curricular goals. Paths do not modifythe structure or content of the Web resources that they include. The creation of a path over pre-organized content (e.g. books, Web pages) to reorganize and associate related information serves to facilitate easy retrieval and communication. WaldenÂs Paths displays the information that the path points to in conjunction with the textual annotations added by the author of the path.

2011-01-04

148

Orbital origins of helices and magic electron counts in the Nowotny chimney ladders: the 18 - n rule and a path to incommensurability.  

PubMed

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

Yannello, Vincent J; Fredrickson, Daniel C

2014-10-01

149

Electron physics and ambipolarity in the tokamak scrape-off layer  

SciTech Connect

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.

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

150

A Hot-electron Direct Detector for Radioastronomy  

NASA Technical Reports Server (NTRS)

A hot-electron transition-edge superconducting bolometer with adjustable thermal relaxation speed is proposed. The bolometer contacts are made from a superconductor with high critical temperature which blocks the thermal diffusion of hot carriers into the contacts. Thus electron-phonon interaction is the only mechanism for heat removal. The speed of thermal relaxation for hot electrons in a nanometer-size superconducting bolometer with T(sub c) = 100-300 mK is controlled by the elastic electron mean free path l. The relaxation rate behaves as T(sup 4)l at subkelvin temperatures and can be reduced by a factor of 10-100 by decreasing 1. Then an antenna- or wave guide-coupled bolometer with a time constant approx. = 10(exp -3) to 10(exp -4) s will exhibit photon-noise limited performance at millimeter and submillimeter wavelengths. The bolometer will have a figure-of-merit NEPtau = 10(exp -22) - 10(exp -21) W/Hz at 100 mK which is 10(exp 3) to 10(exp 4) times better (ie: smaller) than that of a state-of-the-art bolometer. A tremendous increase in speed and sensitivity will have a significant impact for observational mapping applications.

Karasik, Boris S.; McGrath, William R.; LeDuc, Henry G.; Gershenson, Michael E.

1999-01-01

151

Temperature dependence of ballistic mobility in a metamorphic InGaAs/InAlAs high electron mobility transistor  

NASA Astrophysics Data System (ADS)

We have investigated the temperature dependence of ballistic mobility in a 100 nm-long InGaAs/InAlAs metamorphic high-electron-mobility transistor designed for millimeter-wavelength RF applications. To extract the temperature dependence of quasi-ballistic mobility, our experiment involves measurements of the effective mobility in the low-bias linear region of the transistor and of the collision-dominated Hall mobility using a gated Hall bar of the same epitaxial structure. The data measured from the experiment are consistent with that of modeled ballistic mobility based on ballistic transport theory. These results advance the understanding of ballistic transport in various transistors with a nano-scale channel length that is comparable to the carrier's mean free path in the channel.

Lee, Jongkyong; Gang, Suhyun; Jo, Yongcheol; Kim, Jongmin; Woo, Hyeonseok; Han, Jaeseok; Kim, Hyungsang; Im, Hyunsik

2014-07-01

152

Monte-Carlo modeling of excitation of the electron subsystem of Al2O3 and polyethylene after swift heavy ion impact  

NASA Astrophysics Data System (ADS)

The Monte-Carlo (MC) model simulating the femto-second kinetics of the electron subsystem in a track of a swift heavy ion decelerated in the electronic stopping regime is developed. The complex dielectric function (CDF) formalism is used to calculate the cross sections of interactions of an ion and fast electrons with the electron subsystem of a target. It accounts for all collective modes in the electron ensemble. The applied method of CDF reconstruction from the experimental optical data provided a very good agreement of the calculated electron inelastic mean free paths with the NIST database as well as of the calculated SHI energy loss with those from SRIM and CasP codes. The MC model was applied to determine the radial distributions of delocalized electrons and their energy density in tracks of Au (2187 MeV) ions in insulators (Al2O3 and polyethylene) at different times. The femtosecond electron kinetics reveals two fronts of the spatial propagation: the primary fast delta-electrons form the front of excitations while electrons appearing due to decay of plasmons generated in a track form the second slow front following behind.

Rymzhanov, R. A.; Medvedev, N. A.; Volkov, A. E.

2014-05-01

153

Electron-phonon-impurity interference in the resistivity of thin = metal films  

NASA Astrophysics Data System (ADS)

The temperature dependence of the resistivity of thin (d=3D10-70nm) films of Au, Al, Be, Nb, and NbC has been measured at 4.2Kmean free path of electrons l, dominates at temperatures Telectron-phonon and electron-impurity scattering (M.Yu.Reizer and A.V.Sergeev, Sov.Phys.JETP 65, 1291 (1987)). The electron-phonon interaction constants has been obtained for both longitudinal and transverse phonons, in a good agreement with independent calculations. It was shown that the transverse phonons govern both the inelastic electron-phonon scattering and electron-phonon-impurity interference contribution to the resistance.

Gershenson, M. E.; Ptitsina, N. G.; Chulkova, G. M.; Ilyin, K. S.; Pochinkov, F. S.; Sergeev, A. V.; Gershenzon, E. M.

1996-03-01

154

Advanced Physics: Path Integral  

NSDL National Science Digital Library

A cursor is shown in an x-y graph. The cursor can be dragged around the graph and its path is marked as it is moved. The data are sent to a DataTable which shows x, y, and the value of the path integral, F.dl.

Christian, Wolfgang; Belloni, Mario

2006-01-19

155

The SunPath  

NSDL National Science Digital Library

This site features an interactive applet that models the Sun's path from a geocentric view. It calculates and visualizes the position of the Sun based on latitude and time, and allows students to simulate the Sun's position and path for an hour, a day, a month or a year.

University, Australian N.

156

On brittle fracture paths  

Microsoft Academic Search

Two classes of fracture are defined: I — fracture path completely predictable, and II — fracture path predictable only after initial random propagation. Class I fractures occur when there is a line of principal stress passing through the tip of the initiating notch or slit across which the stress is a maximum away from the tip. All Class II fractures

B. Cotterell

1965-01-01

157

Dissecting the Functional Role of Key Residues in Triheme Cytochrome PpcA: A Path to Rational Design of G. sulfurreducens Strains with Enhanced Electron Transfer Capabilities  

PubMed Central

PpcA is the most abundant member of a family of five triheme cytochromes c7 in the bacterium Geobacter sulfurreducens (Gs) and is the most likely carrier of electrons destined for outer surface during respiration on solid metal oxides, a process that requires extracellular electron transfer. This cytochrome has the highest content of lysine residues (24%) among the family, and it was suggested to be involved in e?/H+ energy transduction processes. In the present work, we investigated the functional role of lysine residues strategically located in the vicinity of each heme group. Each lysine was replaced by glutamine or glutamic acid to evaluate the effects of a neutral or negatively charged residue in each position. The results showed that replacing Lys9 (located near heme IV), Lys18 (near heme I) or Lys22 (between hemes I and III) has essentially no effect on the redox properties of the heme groups and are probably involved in redox partner recognition. On the other hand, Lys43 (near heme IV), Lys52 (between hemes III and IV) and Lys60 (near heme III) are crucial in the regulation of the functional mechanism of PpcA, namely in the selection of microstates that allow the protein to establish preferential e?/H+ transfer pathways. The results showed that the preferred e?/H+ transfer pathways are only established when heme III is the last heme to oxidize, a feature reinforced by a higher difference between its reduction potential and that of its predecessor in the order of oxidation. We also showed that K43 and K52 mutants keep the mechanistic features of PpcA by establishing preferential e?/H+ transfer pathways at lower reduction potential values than the wild-type protein, a property that can enable rational design of Gs strains with optimized extracellular electron transfer capabilities. PMID:25153891

Morgado, Leonor; Lourenço, Sílvia; Londer, Yuri Y.; Schiffer, Marianne; Pokkuluri, P. Raj; Salgueiro, Carlos A.

2014-01-01

158

Path integration in insects.  

PubMed

The most notable advance in our knowledge of path integration in insects is a new understanding of how the honeybee measures the distance that it travels during its foraging trips. Data from two groups show that the bee's odometer records distance in terms of the net amount of image motion over the retina that is accumulated during a flight. Progress has also been made in clarifying the relation between path integration and other navigational strategies. On unfamiliar ground, path integration is the only available means of navigation. In familiar surroundings, however, guidance by landmarks may override guidance by path integration. Path integration then becomes a back-up strategy that is used primarily when landmarks fail. PMID:11240286

Collett, T S; Collett, M

2000-12-01

159

Fracturing the optimal paths.  

PubMed

Optimal paths play a fundamental role in numerous physical applications ranging from random polymers to brittle fracture, from the flow through porous media to information propagation. Here for the first time we explore the path that is activated once this optimal path fails and what happens when this new path also fails and so on, until the system is completely disconnected. In fact many applications can also be found for this novel fracture problem. In the limit of strong disorder, our results show that all the cracks are located on a single self-similar connected line of fractal dimension D(b) approximately = 1.22. For weak disorder, the number of cracks spreads all over the entire network before global connectivity is lost. Strikingly, the disconnecting path (backbone) is, however, completely independent on the disorder. PMID:20366106

Andrade, J S; Oliveira, E A; Moreira, A A; Herrmann, H J

2009-11-27

160

Collisionless electron heating in periodic arrays of inductively coupled plasmas  

NASA Astrophysics Data System (ADS)

A novel mechanism of collisionless heating in large planar arrays of small inductive coils operated at radio frequencies is presented. In contrast to the well-known case of non-local heating related to the transversal conductivity, when the electrons move perpendicular to the planar coil, we investigate the problem of electrons moving in a plane parallel to the coils. Two types of periodic structures are studied. Resonance velocities where heating is efficient are calculated analytically by solving the Vlasov equation. Certain scaling parameters are identified. The concept is further investigated by a single particle simulation based on the ergodic principle and combined with a Monte Carlo code allowing for collisions with Argon atoms. Resonances, energy exchange, and distribution functions are obtained. The analytical results are confirmed by the numerical simulation. Pressure and electric field dependences are studied. Stochastic heating is found to be most efficient when the electron mean free path exceeds the size of a single coil cell. Then the mean energy increases approximately exponentially with the electric field amplitude.

Czarnetzki, U.; Tarnev, Kh.

2014-12-01

161

Simulated performance of the calorimetric electron telescope (CALET) experiment  

NASA Astrophysics Data System (ADS)

CALET is a detector planned to be on-board the Japanese Experiment Module Exposed Facility (JEM-EF) of the International Space Station. The CALET mission aims at revealing unsolved problems in high energy phenomena of the Universe by carrying out a precise measurement of the high energy electrons in 1 GeV-20 TeV, the gamma-rays in 20 MeV to a few TeV and the nuclei in a few 10 GeV-1000 TeV. The main detector is composed of imaging calorimeter (IMC), total absorption calorimeter (TASC), silicon pixel array (SIA) and anti-coincidence detector (ACD) to detect various kinds of particles in very wide energy range. The total absorber thickness is 31 radiation lengths for electromagnetic particles and 1.4 interaction mean free paths for protons. Monte Carlo simulation study has been carried out for optimization of the detector performance in observing each kind of particles. We obtained following performance about the observation of very high energy (>100 GeV) electrons, which is a main target of the CALET experiment: (1) Effective geometrical factor is about 7000 cm2 sr. (2) Energy resolution is better than a few %. (3) Angular resolution is better than 0.1°. (4) Proton rejection power is ˜105 with the electron detection efficiency better than 95%. We also present the simulated performance of the CALET experiment in observing other particles.

Akaike, Y.; Taira, K.; Kasahara, K.; Torii, S.; Shimizu, Y.; Yoshida, K.; CALET Collaboration

2010-03-01

162

Photoinduced electron detachment and proton transfer: the proposal for alternative path of formation of triplet States of Guanine (g) and Cytosine (C) pair.  

PubMed

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

Gu, Jiande; Wang, Jing; Leszczynski, Jerzy

2015-02-12

163

Dynamics of the electric current in an ideal electron gas: a sound mode inside the quasi-particles  

E-print Network

We study the equation of motion for the Noether current in an electron gas within the framework of the Schwinger-Keldysh Closed-Time-Path formalism. The equation is shown to be highly non-linear and irreversible even for a non-interacting, ideal gas of electrons at non-zero density. We truncate the linearised equation of motion, written as the Laurent series in Fourier space, so that the resulting expressions are local in time, both at zero and at small finite temperatures. Furthermore, we show that the one-loop Coulomb interactions only alter the physical picture quantitatively, while preserving the characteristics of the dynamics that the electric current exhibits in the absence of interactions. As a result of the composite nature of the Noether current, composite sound waves are found to be the dominant IR collective excitations at length scales between the inverse Fermi momentum and the mean free path that would exist in an interacting electron gas. We also discuss the difference and the transition between the hydrodynamical regime of an ideal gas, defined in this work, and the hydrodynamical regime in phenomenological hydrodynamics, which is normally used for the description of interacting gases.

Sašo Grozdanov; Janos Polonyi

2015-01-26

164

Dynamics of the electric current in an ideal electron gas: a sound mode inside the quasi-particles  

E-print Network

We study the equation of motion for the Noether current in an electron gas within the framework of the Schwinger-Keldysh Closed-Time-Path formalism. The equation is shown to be highly non-linear and irreversible even for a non-interacting, ideal gas of electrons at non-zero density. We truncate the linearised equation of motion, written as the Laurent series in Fourier space, so that the resulting expressions are local in time, both at zero and at small finite temperatures. Furthermore, we show that the one-loop Coulomb interactions only alter the physical picture quantitatively, while preserving the characteristics of the dynamics that the electric current exhibits in the absence of interactions. As a result of the composite nature of the Noether current, composite sound waves are found to be the dominant IR collective excitations at length scales between the inverse Fermi momentum and the mean free path that would exist in an interacting electron gas. We also discuss the difference and the transition betwee...

Grozdanov, Sašo

2015-01-01

165

Inelastic scattering of electron and light ion beams in organic polymers  

SciTech Connect

We have calculated the inelastic mean free path, stopping power, and energy-loss straggling of swift electron, proton, and {alpha}-particle beams in a broad incident energy range in four organic polymers: poly(methyl methacrylate) (PMMA), Kapton, polyacetylene (PA), and poly(2-vinylpyridine) (P2VP). These calculations have been done through a suitable description of their optical properties and its extension into the whole momentum and energy transfer excitation spectrum. For electrons, we take into account the exchange effect between the projectile and the target electrons, while the charge-state fractions have been considered for ions. Our results are compared with other models and with the available experimental data. An excellent agreement with experimental data is obtained in the case of proton and {alpha}-particle beams in Kapton and a reasonably good agreement has been achieved for electron beams in PMMA, Kapton, and PA. We have parameterized by means of simple analytical expressions our results for electron beams interacting with these four polymers, which can be easily implemented in Monte Carlo calculations.

Vera, Pablo de; Abril, Isabel [Departament de Fisica Aplicada, Universitat d'Alacant, E-03080 Alacant (Spain); Garcia-Molina, Rafael [Departamento de Fisica - Centro de Investigacion en Optica y Nanofisica, Universidad de Murcia, E-30100 Murcia (Spain)

2011-05-01

166

Homotopy and Path Integrals  

E-print Network

This is an introductory review of the connection between homotopy theory and path integrals, mainly focus on works done by Schulman [23] that he compared path integral on SO(3) and its universal covering space SU(2), DeWitt and Laidlaw [15] that they proved the theorem to the case of path integrals on the multiply-connected topological spaces. Also, we discuss the application of the theorem in Aharonov-Bohm effect given by [20,24]. An informal introduction to homotopy theory is provided for readers who are not familiar with the theory.

Fumika Suzuki

2011-08-31

167

Follow the Paths  

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.

168

Theory and simulations of current drive via injection of an electron beam in the ACT-1 device  

SciTech Connect

One- and two-dimensional particle simulations of beam-plasma interaction have been carried out in order to understand current drive experiments that use an electron beam injected into the ACT-1 device. Typically, the beam velocity along the magnetic field is V = 10/sup 9/ cm/sec while the thermal velocity of the background electrons is v/sub t/ = 10/sup 8//cm. The ratio of the beam density to the background density is about 10% so that a strong beam-plasma instability develops causing rapid diffusion of beam particles. For both one- and two- dimensional simulations, it is found that a significant amount of beam and background electrons is accelerated considerably beyond the initial beam velocity when the beam density is more than a few percent of the background plasma density. In addition, electron distribution along the magnetic field has a smooth negative slope, f' (v/sub parallel/) < 0, for v/ sub parallel/ > 0 extending v/sub parallel/ = 1.5 V approx. 2 V, which is in sharp contrast to the predictions from quasilinear theory. An estimate of the mean-free path for beam electrons due to Coulomb collisions reveals that the beam electrons can propagate a much longer distance than is predicted from a quasilinear theory, due to the presence of a high energy tail. These simulation results agree well with the experimental observations from the ACT-1 device.

Okuda, H.; Horton, R.; Ono, M.; Wong, K.L.

1985-02-01

169

Inelastic carrier lifetime in a coupled graphene/electron-phonon system: Role of plasmon-phonon coupling  

NASA Astrophysics Data System (ADS)

We calculate the inelastic scattering rates and the hot-electron inelastic mean free paths for both monolayer and bilayer graphene on a polar substrate. We study the quasiparticle self-energy by taking into account both electron-electron and electron-surface-optical-phonon interactions. In this calculation the leading-order dynamic screening approximation (G0W approximation) is used to obtain the quasiparticle self-energy by treating electrons and phonons on an equal footing. We find that the strong coupling between the surface-optical phonon and the plasmon leads to an additional decay channel for the quasiparticle through the emission of the coupled mode, and gives rise to an abrupt increase in the scattering rate, which is absent in the uncoupled system. In monolayer graphene a single jump in the scattering rate occurs, arising from the emission of the low-energy branch of the coupled plasmon-phonon modes. In bilayer graphene the emission of both low- and high-energy branches of the coupled modes contributes to the scattering rate and gives rise to two abrupt changes in the scattering rate. The jumps in the scattering rate can potentially be used in hot-electron devices such as switching devices and oscillators.

Ahn, Seongjin; Hwang, E. H.; Min, Hongki

2014-12-01

170

Statistical Mechanics of Linear Systems & Quadratic Path Integrals  

E-print Network

Homework 5 Optional Statistical Mechanics of Linear Systems & Quadratic Path Integrals 1. Examine(r) = k 2 x2 . It also represents the imaginary time path integral of an electron in a quadratic potential constraints, the system is free to fluctuate at temperature T. So you can define the partition function with x

Deutsch, Josh

171

1 Statistical Mechanics of Linear Systems and Quadratic Path Integrals  

E-print Network

Homework 6 Due 6/4/08 1 Statistical Mechanics of Linear Systems and Quadratic Path Integrals 1 potential v(r) = k 2 x2 . It also represents the imaginary time path integral of an electron in a quadratic these two constraints, the system is free to fluctuate at temperature T. So you can define the partition

Deutsch, Josh

172

Improved initial guess for minimum energy path calculations  

SciTech Connect

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.

Smidstrup, Søren [QuantumWise A/S, Lersø Parkallé 107, DK-2100 Copenhagen (Denmark); Science Institute and Faculty of Physical Sciences, University of Iceland VR-III, 107 Reykjavík (Iceland); Pedersen, Andreas [Science Institute and Faculty of Physical Sciences, University of Iceland VR-III, 107 Reykjavík (Iceland); Integrated Systems Laboratory, ETH Zurich, 8092 Zurich (Switzerland); Stokbro, Kurt [QuantumWise A/S, Lersø Parkallé 107, DK-2100 Copenhagen (Denmark); Jónsson, Hannes, E-mail: hj@hi.is [Science Institute and Faculty of Physical Sciences, University of Iceland VR-III, 107 Reykjavík (Iceland); Department of Applied Physics, Aalto University, Espoo, FI-00076 (Finland)

2014-06-07

173

Restoration by Path Concatenation: Fast Recovery of MPLS Paths  

E-print Network

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

Kaplan, Haim

174

Restoration by Path Concatenation: Fast Recovery of MPLS Paths  

E-print Network

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

Bremler-Barr, Anat

175

Electron Emission From Slightly Oxidized Delta-stabilized Plutonium Generated by its Radioactivity, and Radiation Induced Ionization and Dissociation of Hydrogen at its Surface  

SciTech Connect

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.

Siekhaus, W J; Nelson, A J

2011-10-26

176

Interaction of massless Dirac electrons with acoustic phonons in graphene at low temperatures  

NASA Astrophysics Data System (ADS)

Interaction of massless electrons with the acoustic phonons is studied in two-dimensional (2D) graphene at low temperatures by calculating phonon drag thermopower Sg and hot-electron energy-loss rate F(T) . Sg and F(T) are studied as a function of temperature T and electron concentration ns . For very low temperatures Sg˜T3 and F(T)˜T4 in contrast to Sg˜T4 and F(T)˜T5 of unscreened deformation-potential coupling in usual 2D systems. We find that Sg is related to the phonon limited mobility ?p by Sg ?p=vs?T-1 ( vs is the phonon velocity and ? is the phonon mean-free path) validating Herring’s law for linear dispersion of electrons in graphene. In the low-temperature limit Sg , F(T)˜ns-1/2 . For comparison diffusion thermopower Sd is calculated and Sd˜T , ns-1/2 . Our results are compared with those in the usual 2D systems.

Kubakaddi, S. S.

2009-02-01

177

Reaction Path Reaction path potential for complex biomolecular systems derived from mixed QM/MM methods  

NASA Astrophysics Data System (ADS)

The reaction path potential (RPP) follows the ideas from the reaction path Hamiltonian of Miller, Handy and Adams for gas phase reactions but is designed specifically for large systems described with QM/MM methods. RPP is an analytical energy expression of the combined QM/MM potential energy along the minimum energy path (J. Chem. Phys. 121, 89, 2004). An expansion around the minimum energy path is made in both the nuclear and the electronic degrees of freedom for the QM subsystem, while the interaction between the QM and MM subsystems is described as the interaction of the MM charges with polarizable QM charges. The input data for constructing the reaction path potential are energies, frequencies and electron density response properties of the QM subsystem. RPP provides a potential energy surface for rigorous statistical mechanics and mixed quantum/classical reaction dynamics calculations of complex systems, as will be shown for several enzymes. Recent further development in determining QM/MM free energy reaction paths will also be presented.

Yang, Weitao

2006-03-01

178

Effect of electron Monte Carlo collisions on a hybrid simulation of a low-pressure capacitively coupled plasma  

NASA Astrophysics Data System (ADS)

Fluid models have been widely used and conducted successfully in high pressure plasma simulations where the drift–diffusion and the local-field approximation are valid. However, fluid models are not able to demonstrate non-local effects related to large electron energy relaxation mean free path in low pressure plasmas. To overcome this weakness, a hybrid model coupling electron Monte Carlo collision (EMCC) method with the fluid model is introduced to obtain precise electron energy distribution functions using pseudo-particles. Steady state simulation results by a one-dimensional hybrid model which includes EMCC method for the collisional reactions but uses drift–diffusion approximation for electron transport in a fluid model are compared with those of a conventional particle-in-cell (PIC) and a fluid model for low pressure capacitively coupled plasmas. At a wide range of pressure, the hybrid model agrees well with the PIC simulation with a reduced calculation time while the fluid model shows discrepancy in the results of the plasma density and the electron temperature.

Hwang, Seok Won; Lee, Ho-Jun; Lee, Hae June

2014-12-01

179

UV photoelectron spectroscopy at near ambient pressures: mapping valence band electronic structure changes from Cu to CuO.  

PubMed

Valence band (VB) changes and hence electronic structure evolution was directly observed with low kinetic energy (KE) electrons at near ambient pressure (NAP) conditions with He I photon source in a custom built laboratory ambient pressure photoelectron spectrometer (Lab-APPES). Polycrystalline Cu surfaces were gradually oxidized in O2 to Cu2O, to a mixture of Cu2O + CuO, and finally to CuO between 300 and 625 K and at NAP. Typical VB features for Cu, Cu2O, and CuO were observed, and the results corroborate well with core level and Auger spectral changes. High mean free path associated with low KE electrons, very low or no inelastic scattering, and effective pumping and the design of electrostatic lens regime help to minimize the electron attenuation at NAP conditions. The present results extend the capabilities of the APPES tool to explore the in situ evolution of electronic structure of materials at NAP and high temperatures. PMID:24601627

Roy, Kanak; Gopinath, Chinnakonda S

2014-04-15

180

Mobile transporter path planning  

NASA Technical Reports Server (NTRS)

The use of a genetic algorithm (GA) for solving the mobile transporter path planning problem is investigated. The mobile transporter is a traveling robotic vehicle proposed for the space station which must be able to reach any point of the structure autonomously. Elements of the genetic algorithm are explored in both a theoretical and experimental sense. Specifically, double crossover, greedy crossover, and tournament selection techniques are examined. Additionally, the use of local optimization techniques working in concert with the GA are also explored. Recent developments in genetic algorithm theory are shown to be particularly effective in a path planning problem domain, though problem areas can be cited which require more research.

Baffes, Paul; Wang, Lui

1990-01-01

181

Energetic electron measurements in the edge of a reversed-field pinch  

SciTech Connect

The edge plasma of the ZT-40M (Fusion Technol. {bold 8}, 1571 (1985)) reversed-field pinch has been studied using a combination of three different plasma probes: a double-swept Langmuir probe, an electrostatic energy analyzer, and a calorimeter--Langmuir probe. The edge plasma has been measured both with and without a movable graphite tile limiter present nearby in the plasma. Without a limiter a fast nonthermal tail of electrons ({ital T}{congruent}350 eV) is detected in the edge plasma with nearly unidirectional flow along {bold B} and having a density between 2% and 10% of the cold edge plasma ({ital T}{congruent}20 eV). The toroidal sense of this fast electron flow is against the force of the applied electric field. A large power flux along {bold B} is measured flowing in the same direction as the fast electrons and is apparently carried by the fast electrons. With the limiter present the fast electrons are still detected in the plasma, but are strongly attenuated in the shadow of the limiter. The measured scrape-off lengths for both the fast electrons and the cold plasma indicate cross-field transport at the rate of, or less than, Bohm diffusion. Estimates indicate that the fast electrons could carry the reversed-field pinch current density at the edge and, from the measured transverse diffusion rates, could also account for the electron energy loss channel in ZT-40 M. The long mean-free-path kinetic nature of these fast electrons suggests that a kinetic process, rather than a magnetohydrodynamic process that is based upon a local Ohm's law formulation, is responsible for their generation.

Ingraham, J.C.; Ellis, R.F.; Downing, J.N.; Munson, C.P.; Weber, P.G.; Wurden, G.A. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (US))

1990-01-01

182

An Unplanned Path  

ERIC Educational Resources Information Center

The authors elucidate what they saw as three important challenges to overcome along the path to becoming elementary school mathematics teacher leaders: marginal interest in math, low self-confidence, and teaching in isolation. To illustrate how these challenges were mitigated, they focus on the stories of two elementary school teachers--Laura and…

McGarvey, Lynn M.; Sterenberg, Gladys Y.; Long, Julie S.

2013-01-01

183

DNA Computing Hamiltonian path  

E-print Network

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

Hagiya, Masami

184

Path to the Profession  

ERIC Educational Resources Information Center

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

Coleman, Toni

2012-01-01

185

Shorter Path Constraints for the Resource Constrained Shortest Path Problem  

Microsoft Academic Search

Recently, new cost-based filtering algorithms for shorter-path con- straints have been developed. However, so far only the theoretical properties of shorter-path constraint filtering have been studied. We provide the first extensive experimental evaluation of the new algorithms in the context of the resource con- strained shortest path problem. We show how reasoning about path-substructures in combination with CP-based Lagrangian relaxation

Thorsten Gellermann; Meinolf Sellmann; Robert Wright

2005-01-01

186

A DATABASE OF >20 keV ELECTRON GREEN'S FUNCTIONS OF INTERPLANETARY TRANSPORT AT 1 AU  

SciTech Connect

We use interplanetary transport simulations to compute a database of electron Green's functions, i.e., differential intensities resulting at the spacecraft position from an impulsive injection of energetic (>20 keV) electrons close to the Sun, for a large number of values of two standard interplanetary transport parameters: the scattering mean free path and the solar wind speed. The nominal energy channels of the ACE, STEREO, and Wind spacecraft have been used in the interplanetary transport simulations to conceive a unique tool for the study of near-relativistic electron events observed at 1 AU. In this paper, we quantify the characteristic times of the Green's functions (onset and peak time, rise and decay phase duration) as a function of the interplanetary transport conditions. We use the database to calculate the FWHM of the pitch-angle distributions at different times of the event and under different scattering conditions. This allows us to provide a first quantitative result that can be compared with observations, and to assess the validity of the frequently used term beam-like pitch-angle distribution.

Agueda, N.; Sanahuja, B. [Departament d'Astronomia i Meteorologia, Institut de Ciencies del Cosmos, Universitat de Barcelona, Barcelona (Spain); Vainio, R. [Department of Physics, University of Helsinki, Helsinki (Finland)

2012-10-15

187

Primary cosmic ray electrons above 10 GeV: Evidence for a spectral break  

NASA Technical Reports Server (NTRS)

A balloon borne measurement of the cosmic ray electron spectrum from 10 to 200 GeV is reported in which two new techniques have been used to remove proton background contamination. First, the depth of the spectrometer was more than 25 radiation lengths, the equivalent of more than 2 mean free paths of material, enabling hadronically and electromagnetically induced cascades to be differentiated for a subset of the data. Second, electromagnetic cascade starting points were determined to within + or - 0.1 radiation lengths based upon a calibration with electrons from 5.4 to 18 GeV at the Stanford Linear Accelerator, greatly reducing the chances for a proton to simulate an electron. The resulting spectrum, when fitted with a power law, is quite steep, -3.2 + or - 0.1, but the chi-square fit is marginal. A significantly better fit is achieved assuming a transition region model in which the source spectral index is 2.7 with a break occurring at about 50 GeV.

Silverberg, R. F.; Ormes, J. F.; Balasubrahmanyan, V. K.

1973-01-01

188

Electronic transport in InGaAs/Al2O3 nFinFETs  

NASA Astrophysics Data System (ADS)

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.

Li, Shengwei; Hu, Yaodong; Wu, Yangqing; Huang, Daming; Ye, Peide D.; Li, Ming-Fu

2014-07-01

189

Energy loss of proton, alpha particle, and electron beams in hafnium dioxide films  

SciTech Connect

The electronic stopping power, S, of HfO{sub 2} films for proton and alpha particle beams has been measured and calculated. The experimental data have been obtained by the Rutherford backscattering technique and cover the range of 120-900 and 120-3000 keV for proton and alpha particle beams, respectively. Theoretical calculations of the energy loss for the same projectiles have been done by means of the dielectric formalism using the Mermin energy loss function--generalized oscillator strength (MELF-GOS) model for a proper description of the HfO{sub 2} target on the whole momentum-energy excitation spectrum. At low projectile energies, a nonlinear theory based on the extended Friedel sum rule has been employed. The calculations and experimental measurements show good agreement for protons and a quite good one for alpha particles. In particular, the experimental maximums of both stopping curves (around 120 and 800 keV, respectively) are well reproduced. On the basis of this good agreement, we have also calculated the inelastic mean-free path (IMFP) and the stopping power for electrons in HfO{sub 2} films. Our results predict a minimum value of the IMFP and a maximum value of the S for electrons with energies around 120 and 190 eV, respectively.

Behar, Moni; Fadanelli, Raul C.; Nagamine, Luiz C. C. M. [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, 91501-970 Porto Alegre, RS (Brazil); Abril, Isabel; Denton, Cristian D. [Departament de Fisica Aplicada, Universitat dAlacant, Apartat 99, E-03080 Alacant (Spain); Garcia-Molina, Rafael [Departamento de Fisica-CIOyN, Universidad de Murcia, Apartado 4021, E-30080 Murcia (Spain); Arista, Nestor R. [Division Colisiones Atomicas, Centro Atomico Bariloche, RA-8400 San Carlos de Bariloche (Argentina)

2009-12-15

190

Surface excitations in electron spectroscopy. Part I: dielectric formalism and Monte Carlo algorithm.  

PubMed

The theory describing energy losses of charged non-relativistic projectiles crossing a planar interface is derived on the basis of the Maxwell equations, outlining the physical assumptions of the model in great detail. The employed approach is very general in that various common models for surface excitations (such as the specular reflection model) can be obtained by an appropriate choice of parameter values. The dynamics of charged projectiles near surfaces is examined by calculations of the induced surface charge and the depth- and direction-dependent differential inelastic inverse mean free path (DIIMFP) and stopping power. The effect of several simplifications frequently encountered in the literature is investigated: differences of up to 100% are found in heights, widths, and positions of peaks in the DIIMFP. The presented model is implemented in a Monte Carlo algorithm for the simulation of the electron transport relevant for surface electron spectroscopy. Simulated reflection electron energy loss spectra are in good agreement with experiment on an absolute scale. Copyright © 2012 John Wiley & Sons, Ltd. PMID:23794766

Salvat-Pujol, F; Werner, W S M

2013-05-01

191

Validation of Non-Local Electron Transport Approaches, Application to Shock Ignition  

NASA Astrophysics Data System (ADS)

For laser-plasma interactions at moderate intensities the conduction of heat cannot be captured by the classical Spitzer-H"arm expression and an accurate treatment for non-local electron transport is necessary. A suitable method needs to discriminate between local electrons, that behave in accordance to the classical thermal conduction, and non-local electrons, that have very long mean free paths and diffuse energy all over the physical domain. Two widely known and promising schemes are examined in detail: SNB [Schurtz et al. PoP (2000)] and CMG [Manheimer et al. PoP (2008)]. Both models have been implemented in the hydrodynamic code DUED and benchmarked against the fully kinetic Vlasov-Fokker-Plank codes OSHUN and KETS. Both schemes calculate the right amount of flux in the limit of steep temperature gradients, and for the test problem of hot-spot relaxation they are both generally well-behaved at hydrodynamic time-scales (˜30 ?ei). However, at kinetic time-scales (up to ˜30 ?ei) the SNB model better approximates the kinetic solution. 1D and 2D shock ignition simulations will be presented and the role of non-local effects in the implosion and ignition stages will be discussed.

Marocchino, Alberto; Atzeni, S.; Schiavi, A.; Tzoufras, M.; Mallet, J.; Nicolaï, Ph. D.; Feugeas, J. L.; Tikhonchuk, V.; Bell, A. R.

2012-10-01

192

Experimental Study on Fast Electrons Transport in Ultra-intense Laser Irradiated Solid Targets by Transition Radiation  

NASA Astrophysics Data System (ADS)

The experiment was performed with SILEX laser facility(Ti-saphhire) at LFRC in China. The SILEX parameter: wavelength 0.8?m, duration 35fs, output power 280TW, contrast 5*105, The focal spot ?10?m(F/1.7), intensity on target surface 1*10^19W/cm^2(F/3). The main diagnostic equipments are the electron spectrometer, OMA spectrometer, optical streak camera. Some experimental results are given: The spectrum of optical emission from rear surface is rather narrow around some particular frequencies(1?, 2?, 3?), We ascribe and confirm that the spike-like spectral line that is coherent transition radiation; The coherent light is also seen on time-integrated image with ring-patter due to Weibel instability of the fast electron transport; Obtained experimental cure of target thickness vs OTR image intensity is relative to mean free path of fast electron; The measuring optical transition radiation(OTR) duration of 171ps much longer than 1ps duration of fast electron transport target, the possible explanation is that the OTR duration to be determined magnetic diffusion time.

Zhijian, Zheng; Guangcan, Wang; Yuqiu, Gu

2008-11-01

193

Probing Hot Electron Flow Generated on Pt Nanoparticles with Au/TiO2 Schottky Diodes during Catalytic CO Oxidation  

SciTech Connect

Hot electron flow generated on colloid platinum nanoparticles during exothermic catalytic carbon monoxide oxidation was directly detected with Au/TiO{sub 2} diodes. Although Au/TiO{sub 2} diodes are not catalytically active, platinum nanoparticles on Au/TiO{sub 2} exhibit both chemicurrent and catalytic turnover rate. Hot electrons are generated on the surface of the metal nanoparticles and go over the Schottky energy barrier between Au and TiO{sub 2}. The continuous Au layer ensures that the metal nanoparticles are electrically connected to the device. The overall thickness of the metal assembly (nanoparticles and Au thin film) is comparable to the mean free path of hot electrons, resulting in ballistic transport through the metal. The chemicurrent and chemical reactivity of nanoparticles with citrate, hexadecylamine, hexadecylthiol, and TTAB (Tetradecyltrimethylammonium Bromide) capping agents were measured during catalytic CO oxidation at pressures of 100 Torr O{sub 2} and 40 Torr CO at 373-513 K. We found that chemicurrent yield varies with each capping agent, but always decreases with increasing temperature. We suggest that this inverse temperature dependence is associated with the influence of charging effects due to the organic capping layer during hot electron transport through the metal-oxide interface.

Park, Jeong Y.; Lee, Hyunjoo; Renzas, J. Russell; Zhang, Yawen; Somorjai, G.A.

2008-05-01

194

Energy-loss- and thickness-dependent contrast in atomic-scale electron energy-loss spectroscopy  

NASA Astrophysics Data System (ADS)

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.

Tan, Haiyan; Zhu, Ye; Dwyer, Christian; Xin, Huolin L.

2014-12-01

195

SOCIAL PATH FOLLOWING Carmine Oliva  

E-print Network

of path following; each agent is now able to avoid static and dynamic obstacles along its path, to predict a specific profile for each agent, our system can also show how different stereotypes of people act in those

Karlsson, Brynjar

196

Helmholtz Path Integrals  

NASA Astrophysics Data System (ADS)

The multidimensional, scalar Helmholtz equation of mathematical physics is addressed. Rather than pursuing traditional approaches for the representation and computation of the fundamental solution, path integral representations, originating in quantum physics, are considered. Constructions focusing on the global, two-way nature of the Helmholtz equation, such as the Feynman/Fradkin, Feynman/Garrod, and Feynman/DeWitt-Morette representations, are reviewed, in addition to the complementary phase space constructions based on the exact, well-posed, one-way reformulation of the Helmholtz equation. Exact, Feynman/Kac, stochastic representations are also briefly addressed. These complementary path integral approaches provide an effective means of highlighting the underlying physics in the solution representation, and, subsequently, exploiting this more transparent structure in natural computational algorithms.

Fishman, Louis

2006-05-01

197

Lander flight path analysis  

NASA Technical Reports Server (NTRS)

The primary functions of the Lander Flight Path Analysis Team (LFPAT) were to (1) design the Viking Lander (VL) descent trajectory and compute the descent guidance parameters for command transmission to the Viking Lander and Viking Orbiter (VO), (2) reconstruct the VL trajectory from separation to touchdown using data transmitted from the VL to Earth via the VO during descent, and (3) predict the VL/VO relay link system performance during descent and post touchdown. The preflight VL capability, the history of proposed descent trajectory designs as the site selection process evolved, and the final trajectory design and guidance parameters for each vehicle are addressed along with the trajectory reconstruction process, including the overall reconstructed VL flight path summary and a detailed discussion of the entry trajectory and atmosphere reconstruction results. The postland relay link prediction function is discussed.

Euler, E. A.; Adams, G. L.; Hopper, F. W.

1979-01-01

198

PATHS groundwater hydrologic model  

SciTech Connect

A preliminary evaluation capability for two-dimensional groundwater pollution problems was developed as part of the Transport Modeling Task for the Waste Isolation Safety Assessment Program (WISAP). Our approach was to use the data limitations as a guide in setting the level of modeling detail. PATHS Groundwater Hydrologic Model is the first level (simplest) idealized hybrid analytical/numerical model for two-dimensional, saturated groundwater flow and single component transport; homogeneous geology. This document consists of the description of the PATHS groundwater hydrologic model. The preliminary evaluation capability prepared for WISAP, including the enhancements that were made because of the authors' experience using the earlier capability is described. Appendixes A through D supplement the report as follows: complete derivations of the background equations are provided in Appendix A. Appendix B is a comprehensive set of instructions for users of PATHS. It is written for users who have little or no experience with computers. Appendix C is for the programmer. It contains information on how input parameters are passed between programs in the system. It also contains program listings and test case listing. Appendix D is a definition of terms.

Nelson, R.W.; Schur, J.A.

1980-04-01

199

Path Integrals in Quantum Mechanics  

Microsoft Academic Search

Jean Zinn-Justin's textbook Path Integrals in Quantum Mechanics aims to familiarize the reader with the path integral as a calculational tool in quantum mechanics and field theory. The emphasis is on quantum statistical mechanics, starting with the partition function Tr exp(-? H) and proceeding through the diffusion equation to barrier penetration problems and their semiclassical limit. The 'real time' path

J Louko

2005-01-01

200

Electronic transport in nanoscale structures  

NASA Astrophysics Data System (ADS)

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.

Lagerqvist, Johan

201

Pick-a-Path  

NSDL National Science Digital Library

This mobile app (available for both iOS and Android devices) was developed by the National Council of Teachers of Mathematics with funding from Verizon Foundation. The app is based on the Decimal Maze from the popular lesson "Too Big or Too Small". The goal is to help Okta reach the target (maximum, minimum, or a specific value) by choosing a path from the top of the maze to the bottom â adding, subtracting, multiplying and dividing as the player goes. Seven levels with seven puzzles in each level test the player's skills with operation with powers of ten, negative numbers, fractions, decimals, and exponents.

2012-01-01

202

The California PATH Database  

NSDL National Science Digital Library

The well known Berkeley Digital Library SunSite, discussed in the February 9, 1996 Scout Report, has recently added a new resource to its collection. The PATH database, maintained by the Harmer E. Davis Transportation Library at the University of California, is "the world's largest bibliographical database pertaining to Intelligent Transportation Systems (ITS)." It is searchable and browsable (Browse by ITS Thesaurus Term), and contains over 9,000 records and abstracts "including monographs, journal articles, conference papers, technical reports, theses and selected media coverage," dating back to the 1940s.

1997-01-01

203

Portage and Path Dependence*  

PubMed Central

We examine portage sites in the U.S. South, Mid-Atlantic, and Midwest, including those on the fall line, a geomorphological feature in the southeastern U.S. marking the final rapids on rivers before the ocean. Historically, waterborne transport of goods required portage around the falls at these points, while some falls provided water power during early industrialization. These factors attracted commerce and manufacturing. Although these original advantages have long since been made obsolete, we document the continuing importance of these portage sites over time. We interpret these results as path dependence and contrast explanations based on sunk costs interacting with decreasing versus increasing returns to scale. PMID:23935217

Bleakley, Hoyt; Lin, Jeffrey

2012-01-01

204

JAVA PathFinder  

NASA Technical Reports Server (NTRS)

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.

Mehhtz, Peter

2005-01-01

205

Size-dependent giant-magnetoresistance in millimeter scale GaAs/AlGaAs 2D electron devices  

PubMed Central

Large changes in the electrical resistance induced by the application of a small magnetic field are potentially useful for device-applications. Such Giant Magneto-Resistance (GMR) effects also provide new insights into the physical phenomena involved in the associated electronic transport. This study examines a “bell-shape” negative GMR that grows in magnitude with decreasing temperatures in mm-wide devices fabricated from the high-mobility GaAs/AlGaAs 2-Dimensional Electron System (2DES). Experiments show that the span of this magnetoresistance on the magnetic-field-axis increases with decreasing device width, W, while there is no concurrent Hall resistance, Rxy, correction. A multi-conduction model, including negative diagonal-conductivity, and non-vanishing off-diagonal conductivity, reproduces experimental observations. The results suggest that a size effect in the mm-wide 2DES with mm-scale electron mean-free-paths is responsible for the observed “non-ohmic” size-dependent negative GMR. PMID:24067264

Mani, R. G.

2013-01-01

206

Size-dependent giant-magnetoresistance in millimeter scale GaAs/AlGaAs 2D electron devices.  

PubMed

Large changes in the electrical resistance induced by the application of a small magnetic field are potentially useful for device-applications. Such Giant Magneto-Resistance (GMR) effects also provide new insights into the physical phenomena involved in the associated electronic transport. This study examines a "bell-shape" negative GMR that grows in magnitude with decreasing temperatures in mm-wide devices fabricated from the high-mobility GaAs/AlGaAs 2-Dimensional Electron System (2DES). Experiments show that the span of this magnetoresistance on the magnetic-field-axis increases with decreasing device width, W, while there is no concurrent Hall resistance, Rxy, correction. A multi-conduction model, including negative diagonal-conductivity, and non-vanishing off-diagonal conductivity, reproduces experimental observations. The results suggest that a size effect in the mm-wide 2DES with mm-scale electron mean-free-paths is responsible for the observed "non-ohmic" size-dependent negative GMR. PMID:24067264

Mani, R G; Kriisa, A; Wegscheider, W

2013-01-01

207

APPLICATIONS OF LASERS AND OTHER PROBLEMS IN QUANTUM ELECTRONICS: Amplitude-time structure of the complete profile of the signal formed by backscattering along a combined atmosphere-hydrosphere path of exciting laser radiation  

NASA Astrophysics Data System (ADS)

A study was made of the structure of the complete profile of a backscattering signal representing the scattering in the atmosphere, in a transition layer, and directly in the hydrosphere. Spatial and temporal anomalies were found in the backscattering signal and these were attributed to the changes in properties along the laser radiation path.

Zenchenko, S. A.; Malevich, I. A.; Pranovich, V. I.; Svetlykh, A. A.; Svintilov, M. V.; Sochilin, Georgii B.; Utenkov, B. I.

1987-11-01

208

Total cross-sections for positron and electron scattering from ?-tetrahydrofurfuryl alcohol  

NASA Astrophysics Data System (ADS)

In this paper, we report original measurements of total cross-sections (TCSs) for positron scattering from an important biomolecule, ?-tetrahydrofurfuryl alcohol (THFA). The energy range of these measurements was 0.15-50.15 eV, whereas the energy resolution was ~260 meV. In addition, we report theoretical results, calculated within the independent-screened additivity rule (IAM-SCAR) formalism, on the corresponding electron impact total cross-sections. In this case, the energy range is 1-10 000 eV. With the advent of new particle track simulation codes, which incorporate accurate atomic and molecular data in order to provide interaction details at the nanoscale, interest in positron and electron TCSs has enjoyed something of a recent renaissance as they specify the mean free path between collisions in such codes. Because the present data are, to the best of our knowledge, the first TCSs to be reported for positron scattering from THFA, they fill an important void in the knowledge available to us from the literature.

Zecca, A.; Chiari, L.; García, G.; Blanco, F.; Trainotti, E.; Brunger, M. J.

2011-06-01

209

Jovian modulation of interplanetary electrons as observed with Voyagers 1 and 2  

NASA Technical Reports Server (NTRS)

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.

Schardt, A. W.; Mcdonald, F. B.; Trainor, J. H.

1982-01-01

210

Outdoor visual path following experiments  

Microsoft Academic Search

In this paper the performance of a topological- metric visual path following framework is investigated in different environments. The framework relies on a monocular camera as the only sensing modality. The path is represented as a series of reference images such that each neighboring pair contains a number of common landmarks. Local 3D geometries are reconstructed between the neighboring reference

Albert Diosi; Anthony Remazeilles; Sinisa Segvic; François Chaumette

2007-01-01

211

Path integrals as discrete sums  

SciTech Connect

We present a new formulation of Feynman's path integral, based on Voronin's theorems on the universality of the Riemann zeta function. The result is a discrete sum over paths,'' each given by a zeta function. A new measure which leads to the correct quantum mechanics is explicitly given.

Bitar, K.; Khuri, N.N.; Ren, H.C. (Supercomputer Computations Research Institute, Florida State University, Tallahasee, Florida (USA) Department of Physics, The Rockefeller University, New York, New York (USA))

1991-08-12

212

Data Generation for Path Testing  

Microsoft Academic Search

We present two stochastic search algorithms for generating test cases that execute specified paths in a program. The two algorithms are: a simulated annealing algorithm (SA), and a genetic algorithm (GA). These algorithms are based on an optimization formulation of the path testing problem which include both integer- and real-value test cases. We empirically compare the SA and GA algorithms

Nashat Mansour; Miran Salame

2004-01-01

213

Ab-initio path integral techniques for molecules  

E-print Network

Path integral Monte Carlo with Green's function analysis allows the sampling of quantum mechanical properties of molecules at finite temperature. While a high-precision computation of the energy of the Born-Oppenheimer surface from path integral Monte Carlo is quite costly, we can extract many properties without explicitly calculating the electronic energies. We demonstrate how physically relevant quantities, such as bond-length, vibrational spectra, and polarizabilities of molecules may be sampled directly from the path integral simulation using Matsubura (temperature) Green's functions (imaginary-time correlation functions). These calculations on the hydrogen molecule are a proof-of-concept, designed to motivate new work on fixed-node path-integral calculations for molecules.

Daejin Shin; Ming-Chak Ho; J. Shumway

2006-11-09

214

Ab-initio path integral techniques for molecules  

E-print Network

Path integral Monte Carlo with Green's function analysis allows the sampling of quantum mechanical properties of molecules at finite temperature. While a high-precision computation of the energy of the Born-Oppenheimer surface from path integral Monte Carlo is quite costly, we can extract many properties without explicitly calculating the electronic energies. We demonstrate how physically relevant quantities, such as bond-length, vibrational spectra, and polarizabilities of molecules may be sampled directly from the path integral simulation using Matsubura (temperature) Green's functions (imaginary-time correlation functions). These calculations on the hydrogen molecule are a proof-of-concept, designed to motivate new work on fixed-node path-integral calculations for molecules.

Shin, D; Shumway, J; Ho, Ming-Chak; Shin, Daejin

2006-01-01

215

Reconfigurable data path processor  

NASA Technical Reports Server (NTRS)

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.

Donohoe, Gregory (Inventor)

2005-01-01

216

British Pathe Newsreels Online  

NSDL National Science Digital Library

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.

2002-01-01

217

Ideal Two-Dimensional Electron Systems with a Giant Rashba-Type Spin Splitting in Real Materials: Surfaces of Bismuth Tellurohalides  

NASA Astrophysics Data System (ADS)

Spintronics is aimed at actively controlling and manipulating the spin degrees of freedom in semiconductor devices. A promising way to achieve this goal is to make use of the tunable Rashba effect that relies on the spin-orbit interaction in a two-dimensional electron system immersed in an inversion-asymmetric environment. The spin-orbit-induced spin splitting of the two-dimensional electron state provides a basis for many theoretically proposed spintronic devices. However, the lack of semiconductors with large Rashba effect hinders realization of these devices in actual practice. Here we report on a giant Rashba-type spin splitting in two-dimensional electron systems that reside at tellurium-terminated surfaces of bismuth tellurohalides. Among these semiconductors, BiTeCl stands out for its isotropic metallic surface-state band with the ?¯-point energy lying deep inside the bulk band gap. The giant spin splitting of this band ensures a substantial spin asymmetry of the inelastic mean free path of quasiparticles with different spin orientations.

Eremeev, S. V.; Nechaev, I. A.; Koroteev, Yu. M.; Echenique, P. M.; Chulkov, E. V.

2012-06-01

218

Three-dimensional electron realm in VSe2 by soft-x-ray photoelectron spectroscopy: origin of charge-density waves.  

PubMed

The resolution of angle-resolved photoelectron spectroscopy (ARPES) in three-dimensional (3D) momentum k is fundamentally limited by ill defined surface-perpendicular wave vector k(perpendicular) associated with the finite photoelectron mean free path. Pushing ARPES into the soft-x-ray energy region sharpens the k(perpendicular) definition, allowing accurate electronic structure investigations in 3D materials. We apply soft-x-ray ARPES to explore the 3D electron realm in a paradigm transition metal dichalcogenide VSe2. Essential to break through the dramatic loss of the valence band photoexcitation cross section at soft-x-ray energies is the advanced photon flux performance of our synchrotron instrumentation. By virtue of the sharp 3D momentum definition, the soft-x-ray ARPES experimental band structure and Fermi surface of VSe2 show a textbook clarity. We identify pronounced 3D warping of the Fermi surface and show that its concomitant nesting acts as the precursor for the exotic 3D charge-density waves in VSe2. Our results demonstrate the immense potential of soft-x-ray ARPES to explore details of 3D electronic structure. PMID:23002761

Strocov, Vladimir N; Shi, Ming; Kobayashi, Masaki; Monney, Claude; Wang, Xiaoqiang; Krempasky, Juraj; Schmitt, Thorsten; Patthey, Luc; Berger, Helmuth; Blaha, Peter

2012-08-24

219

Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Path Testing  

E-print Network

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

Mousavi, Mohammad

220

Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Path Testing  

E-print Network

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

Mousavi, Mohammad

221

Modeling Relativistic Electron Precipitation Bremsstrahlung X-Ray Intensities at 10-100 km Manned Vehicle Altitudes  

NASA Technical Reports Server (NTRS)

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.

Krause, L. Habsh; Gilchrist, B. E.; Nishikawa, Ken-Ichi

2013-01-01

222

Modeling Relativistic Electron Precipitation Bremsstrahlung X-Ray Intensities at 10-100 km Manned Vehicle Altitudes  

NASA Astrophysics Data System (ADS)

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.

Habash Krause, L.; Gilchrist, B. E.; Nishikawa, K.; Williams, A.

2013-12-01

223

Calculations of stopping powers of 100 eV-30 keV electrons in 31 elemental solids  

NASA Astrophysics Data System (ADS)

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).

Tanuma, S.; Powell, C. J.; Penn, D. R.

2008-03-01

224

Design of nanophotonic, hot-electron solar-blind ultraviolet detectors with a metal-oxide-semiconductor structure  

NASA Astrophysics Data System (ADS)

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.

Wang, Zhiyuan; Wang, Xiaoxin; Liu, Jifeng

2014-12-01

225

Partnership for Advancing Technologies in Housing (PATH)  

NSF Publications Database

... Technology Systems Interactions and Whole House Approaches PATH?s mission is to advance technology ... technology arena. Far reaching exploratory research that can lead to breakthrough technologies and ...

226

COMPUTER SCIENCE: MISCONCEPTIONS, CAREER PATHS  

E-print Network

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

Hristidis, Vagelis

227

Morse theory in path space  

E-print Network

We consider the path space of a curved manifold on which a point particle is introduced in a conservative physical system with constant total energy to formulate its action functional and geodesic equation together with breaks on the path. The second variation of the action functional is exploited to yield the geodesic deviation equation and to discuss the Jacobi fields on the curved manifold. We investigate the topology of the path space using the action functional on it and its physical meaning by defining the gradient of the action functional, the space of bounded flow energy solutions and the moduli space associated with the critical points of the action functional. We also consider the particle motion on the $n$-sphere $S^{n}$ in the conservative physical system to discuss explicitly the moduli space of the path space and the corresponding homology groups.

Yong Seung Cho; Soon-Tae Hong

2007-06-01

228

Collaborative Authoring of Walden's Paths  

E-print Network

of educators, the authoring tool allows educators to collaboratively build a Walden's Path by filtering and organizing web pages into an ordered linear structure for the common information needs, which can be extended, tailored and modified into a derivative...

Li, Yuanling

2012-10-19

229

Scattering theory with path integrals  

SciTech Connect

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.

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

230

Quantum Mechanics: Sum Over Paths  

NSDL National Science Digital Library

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.

Taylor, Edwin F.

2009-05-26

231

Formal language constrained path problems  

SciTech Connect

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.

Barrett, C.; Jacob, R.; Marathe, M.

1997-07-08

232

Short paths in expander graphs  

SciTech Connect

Graph expansion has proved to be a powerful general tool for analyzing the behavior of routing algorithms and the interconnection networks on which they run. We develop new routing algorithms and structural results for bounded-degree expander graphs. Our results are unified by the fact that they are all based upon, and extend, a body of work asserting that expanders are rich in short, disjoint paths. In particular, our work has consequences for the disjoint paths problem, multicommodify flow, and graph minor containment. We show: (i) A greedy algorithm for approximating the maximum disjoint paths problem achieves a polylogarithmic approximation ratio in bounded-degree expanders. Although our algorithm is both deterministic and on-line, its performance guarantee is an improvement over previous bounds in expanders. (ii) For a multicommodily flow problem with arbitrary demands on a bounded-degree expander, there is a (1 + {epsilon})-optimal solution using only flow paths of polylogarithmic length. It follows that the multicommodity flow algorithm of Awerbuch and Leighton runs in nearly linear time per commodity in expanders. Our analysis is based on establishing the following: given edge weights on an expander G, one can increase some of the weights very slightly so the resulting shortest-path metric is smooth - the min-weight path between any pair of nodes uses a polylogarithmic number of edges. (iii) Every bounded-degree expander on n nodes contains every graph with O(n/log{sup O(1)} n) nodes and edges as a minor.

Kleinberg, J. [MIT, Cambridge, MA (United States); Rubinfeld, R. [Cornell Univ., Ithaca, NY (United States)

1996-12-31

233

CURRENT SHEET REGULATION OF SOLAR NEAR-RELATIVISTIC ELECTRON INJECTION HISTORIES  

SciTech Connect

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.

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

234

Design and realization of expressway vehicle path recognition and ETC system based on RFID  

Microsoft Academic Search

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

Zhihui Feng; Yanjie Zhu; Pengtao Xue; Mingjie Li

2010-01-01

235

E-beam ionized channel guiding of an intense relativistic electron beam  

DOEpatents

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.

Frost, C.A.; Godfrey, B.B.; Kiekel, P.D.; Shope, S.L.

1988-05-10

236

E-beam ionized channel guiding of an intense relativistic electron beam  

DOEpatents

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.

Frost, Charles A. (Albuquerque, NM); Godfrey, Brendon B. (Albuquerque, NM); Kiekel, Paul D. (Albuquerque, NM); Shope, Steven L. (Albuquerque, NM)

1988-01-01

237

On hallucinated garden paths UC San Diego  

E-print Network

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

238

Torsional and cyclic fatigue resistances of glide path preparation instruments: G-file and PathFile.  

PubMed

This study aimed to compare cyclic fatigue and torsional resistances of glide path creating instruments with different tapers and tip sizes. Two sizes (G1 and G2) from G-File system and three sizes (PathFile #1, #2, and #3) from PathFile system were used for torsional resistance and cyclic fatigue resistance tests (n?=?10). The torsional resistance was evaluated at 2-, 3-, 4-, 5-, and 6-mm from the file tip by plotting the torsional load changes until fracture by rotational loading of 2?rpm. The cyclic fatigue resistance was compared by measuring the number of cycles to failure. Data were analyzed statistically using one-way ANOVA and Duncan's post-hoc comparison. The length of the fractured file fragment was also measured. All fractured fragments were observed under a scanning electron microscope (SEM). Although G-2 file showed a lower torsional strength than PathFile #3 at 2- and 3-mm levels (p??0.05). The smaller files of each brand had a significantly higher cyclic fatigue resistance than the bigger ones (p?PathFile #1 and #2 had higher fatigue resistances than G-files (p?PathFile #3, G-2 showed the lowest and PathFile #1 showed the highest resistances among the tested groups (p?path with minimal risk of fracture. PMID:24737525

Sung, Sang Yup; Ha, Jung-Hong; Kwak, Sang-Won; Abed, Rashid El; Byeon, Kyeongmin; Kim, Hyeon-Cheol

2014-01-01

239

Radial bunch compression: Path-length compensation in an rf photoinjector with a curved cathode  

E-print Network

such as the free-electron laser by making them more compact and with shorter pulse duration, and could provide, France (Received 9 June 2006; published 25 August 2006) Electron bunch lengthening due to space of the electron bunch, a larger initial radius causes path-length differences in both the rf cavity

Boyer, Edmond

240

Cockpit simulation study of use of flight path angle for instrument approaches  

NASA Technical Reports Server (NTRS)

The results of a piloted simulation experiment to evaluate the effect of integrating flight path angle information into a typical transport electronic attitude director indicator display format for flight director instrument landing system approaches are presented. Three electronic display formats are evaluated during 3 deg straight-in approaches with wind shear and turbulence conditions. Flight path tracking data and pilot subjective comments are analyzed with regard to the pilot's tracking performance and workload for all three display formats.

Hanisch, B.; Ernst, H.; Johnston, R.

1981-01-01

241

Gas-path seal technology  

NASA Technical Reports Server (NTRS)

Improved gas-path seals are needed for better fuel economy, longer performance retention, and lower maintenance, particularly in advanced, high-performance gas turbine engines. Problems encountered in gas-path sealing are described, as well as new blade-tip sealing approaches for high-pressure compressors and turbines. These include a lubricant coating for conventional, porous-metal, rub-strip materials used in compressors. An improved hot-press metal alloy shows promise to increase the operating surface temperatures of high-pressure-turbine, blade-tip seals to 1450 K (2150 F). Three ceramic seal materials are also described that have the potential to allow much higher gas-path surface operating temperatures than are possible with metal systems.

Zuk, J.

1976-01-01

242

A 2-dimensional optical architecture for solving Hamiltonian path problem based on micro ring resonators  

NASA Astrophysics Data System (ADS)

The problem of finding the Hamiltonian path in a graph, or deciding whether a graph has a Hamiltonian path or not, is an NP-complete problem. No exact solution has been found yet, to solve this problem using polynomial amount of time and space. In this paper, we propose a two dimensional (2-D) optical architecture based on optical electronic devices such as micro ring resonators, optical circulators and MEMS based mirror (MEMS-M) to solve the Hamiltonian Path Problem, for undirected graphs in linear time. It uses a heuristic algorithm and employs n+1 different wavelengths of a light ray, to check whether a Hamiltonian path exists or not on a graph with n vertices. Then if a Hamiltonian path exists, it reports the path. The device complexity of the proposed architecture is O(n2).

Shakeri, Nadim; Jalili, Saeed; Ahmadi, Vahid; Rasoulzadeh Zali, Aref; Goliaei, Sama

2015-01-01

243

Multiple paths in complex tasks  

NASA Technical Reports Server (NTRS)

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.

Galanter, Eugene; Wiegand, Thomas; Mark, Gloria

1987-01-01

244

Electron Tunneling Studies in Tantalum Overlayers on Niobium and in Tantalum and Niobium Nitride Films  

NASA Astrophysics Data System (ADS)

Tunneling measurements have been performed on tantalum surface layers on niobium. The thickness of the tantalum layer ranges from 10 to 100 A. The critical current, bound-state energy, phonon structure, and oxide barrier shape are investigated. The results are compared with an extended version of the Gallagher theory which accounts for both the finite mean free path in the Ta overlayers and suppression of the I_{rm c}R product due to strong electron-phonon coupling effects. Excellent fits to the data yield a value of the intrinsic scattering probability for electrons at the Ta/Nb interface of r^2 = 0.01. In addition, a new fabrication technique--dual ion-beam sputtering --is used to deposit thin films of NbN. The properties of these films and of tunnel junctions formed with NbN as base electrode and native-oxide as well as artificial barriers are reported. A universal empirical correlation is found between the average barrier height phi and the effective barrier width d for measured junctions. This correlation, which holds both for our data and for available data in the literature for oxide -barrier junctions, is discussed in the general context of oxide growth and compared with results for artificial tunnel barriers. Finally, high quality Ta/PbBi tunnel junction of area <=q1 mu m^2 and current density 10 ^3-10^5 A/cm ^2 are produced using a window geometry. The electrical noise properties of these junctions are investigated. Discrete voltage switching events allow the identification of the effect of single localized states in the oxide barrier. The voltage and temperature dependence of the switching rates are consistent with a microscopic model based on the emission and capture of individual electrons at the localized sites within the barrier.

Track, Elie Khalil

245

Quasi-phasematched acceleration of electrons in a density modulated plasma waveguide  

NASA Astrophysics Data System (ADS)

Two quasi-phasematching schemes are proposed for efficient acceleration of electrons to relativistic energies using moderate intensity laser pulses. In the first scheme, Direct Laser Acceleration (DLA) in a corrugated plasma waveguide is proposed for acceleration of relativistic electrons with sub-terawatt laser systems, using the laser field directly as the accelerating field. The second scheme uses the fact that a plasma wakefield generated by an intense guided pulse in a corrugated plasma waveguide can accelerate relativistic electrons significantly beyond the well-known dephasing limit. In each case, particle-in-cell (PIC) simulations are used to validate the acceleration concept, demonstrating linear acceleration by either the phase matched laser field or phase-matched wakefield. In the phase matched wakefield case, theory and PIC simulations demonstrate a significant increase in energy gain compared to the standard laser wakefield acceleration (LWFA) scheme. Corrugated plasma waveguides can be generated by the interaction between an ionizing laser pulse and an atomic cluster flow interrupted by an array of thin wires,. When the collisional mean free path of the clusters is greater than the wire diameter, shadows of the periodically located wires are imparted on the cluster flow, leading to the production of axially modulated plasma waveguides after laser heating of the flow. This occurs when the population ratio of clusters to monomers in the gas is high. At other limit, dominated by gas monomer flow, shock waves generated off the wires by the supersonic gas flow disrupts modulated waveguide generation. Lastly, we experimentally demonstrate LWFA with ionization injection in a N5+ plasma waveguide. It is first shown that the plasma waveguide is almost completely composed of He-like nitrogen (N5+). It is then shown that intense pulse channeling in the plasma waveguide drives stronger wakefields, while the ionization injection process is critical to lowering the laser intensity threshold for self-trapping.

Yoon, Sung Jun

246

Trajectory reversal approach for electron backscattering from solid surfaces  

NASA Astrophysics Data System (ADS)

The backscattering of medium energy electrons from solid surfaces is investigated by analysis of a linearized Boltzmann-type kinetic equation. A closed expression is derived for the Green’s function in an infinite medium valid for a spherically symmetric potential describing the interaction with the ionic subsystem. The solution is expressed in terms of fluctuations of the energy loss and scattering angles and the collision statistics associated with them. Since the fluctuation part is independent of the boundary conditions of the considered problem, solution of the backscattering problem requires an appropriate treatment of the collision statistics. In this context, the exact solution for the Oswald-Kasper-Gaukler model is derived and its limitations are analyzed. An exact approach is presented and implemented in an efficient Monte Carlo scheme based on the trajectory reversal technique. The resulting procedure is faster than the conventional Monte Carlo algorithm by several orders of magnitude. Results for the angular distribution are compared with conventional Monte Carlo calculations and perfectly agree with the latter within their statistical uncertainty. A second approximate algorithm is also given. The approximation involved in this second procedure turns out to be very reasonable: deviations from direct Monte Carlo calculations remain below ˜5% for energies exceeding 200eV . The integral elastic-backscattering coefficient for normal incidence for a large number of materials in the energy range 50eV-10keV is found to approximately exhibit a universal dependence on the ratio of the inelastic and the transport mean free paths, the so-called scattering parameter.

Werner, Wolfgang S. M.

2005-03-01

247

Spreading paths in partially observed social networks  

PubMed Central

Understanding how and how far information, behaviors, or pathogens spread in social networks is an important problem, having implications for both predicting the size of epidemics, as well as for planning effective interventions. There are, however, two main challenges for inferring spreading paths in real-world networks. One is the practical difficulty of observing a dynamic process on a network, and the other is the typical constraint of only partially observing a network. Using a static, structurally realistic social network as a platform for simulations, we juxtapose three distinct paths: (1) the stochastic path taken by a simulated spreading process from source to target; (2) the topologically shortest path in the fully observed network, and hence the single most likely stochastic path, between the two nodes; and (3) the topologically shortest path in a partially observed network. In a sampled network, how closely does the partially observed shortest path (3) emulate the unobserved spreading path (1)? Although partial observation inflates the length of the shortest path, the stochastic nature of the spreading process also frequently derails the dynamic path from the shortest path. We find that the partially observed shortest path does not necessarily give an inflated estimate of the length of the process path; in fact, partial observation may, counterintuitively, make the path seem shorter than it actually is. PMID:22587148

Onnela, Jukka-Pekka; Christakis, Nicholas A.

2012-01-01

248

Revealing quantum path details in high-field physics  

NASA Astrophysics Data System (ADS)

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.

Kolliopoulos, G.; Bergues, B.; Schröder, H.; Carpeggiani, P. A.; Veisz, L.; Tsakiris, G. D.; Charalambidis, D.; Tzallas, P.

2014-07-01

249

Path-integral seismic imaging  

Microsoft Academic Search

A new type of seismic imaging, based on Feynman path integrals for waveform mod- elling, is capable of producing accurate subsurface images without any need for a reference velocity model. Instead of the usual optimization for traveltime curves with maximal signal semblance, a weighted summation over all representative curves avoids the need for velocity analysis, with its common difficulties of

E. Landa; S. Fomel; T. J. Moser

2006-01-01

250

Path integrals for potential scattering  

Microsoft Academic Search

Two path integral representations for the T matrix in nonrelativistic potential scattering are derived and proved to produce the complete Born series when expanded to all orders. They are obtained with the help of ``phantom'' degrees of freedom which take away explicit phases that diverge for asymptotic times. In addition, energy conservation is enforced by imposing a Faddeev-Popov-like constraint in

R. Rosenfelder

2009-01-01

251

Career Paths in Environmental Sciences  

EPA Science Inventory

Career paths, current and future, in the environmental sciences will be discussed, based on experiences and observations during the author's 40 + years in the field. An emphasis will be placed on the need for integrated, transdisciplinary systems thinking approaches toward achie...

252

BornOppenheimer invariants along nuclear configuration paths Department of Physical Chemistry and the Lise Meitner Minerva Center for Quantum Chemistry,  

E-print Network

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

Baer, Roi

253

Enzymatic reaction paths as determined by transition path sampling  

NASA Astrophysics Data System (ADS)

Enzymes are biological catalysts capable of enhancing the rates of chemical reactions by many orders of magnitude as compared to solution chemistry. Since the catalytic power of enzymes routinely exceeds that of the best artificial catalysts available, there is much interest in understanding the complete nature of chemical barrier crossing in enzymatic reactions. Two specific questions pertaining to the source of enzymatic rate enhancements are investigated in this work. The first is the issue of how fast protein motions of an enzyme contribute to chemical barrier crossing. Our group has previously identified sub-picosecond protein motions, termed promoting vibrations (PVs), that dynamically modulate chemical transformation in several enzymes. In the case of human heart lactate dehydrogenase (hhLDH), prior studies have shown that a specific axis of residues undergoes a compressional fluctuation towards the active site, decreasing a hydride and a proton donor--acceptor distance on a sub-picosecond timescale to promote particle transfer. To more thoroughly understand the contribution of this dynamic motion to the enzymatic reaction coordinate of hhLDH, we conducted transition path sampling (TPS) using four versions of the enzymatic system: a wild type enzyme with natural isotopic abundance; a heavy enzyme where all the carbons, nitrogens, and non-exchangeable hydrogens were replaced with heavy isotopes; and two versions of the enzyme with mutations in the axis of PV residues. We generated four separate ensembles of reaction paths and analyzed each in terms of the reaction mechanism, time of barrier crossing, dynamics of the PV, and residues involved in the enzymatic reaction coordinate. We found that heavy isotopic substitution of hhLDH altered the sub-picosecond dynamics of the PV, changed the favored reaction mechanism, dramatically increased the time of barrier crossing, but did not have an effect on the specific residues involved in the PV. In the mutant systems, we observed changes in the reaction mechanism and altered contributions of the mutated residues to the enzymatic reaction coordinate, but we did not detect a substantial change in the time of barrier crossing. These results confirm the importance of maintaining the dynamics and structural scaffolding of the hhLDH PV in order to facilitate facile barrier passage. We also utilized TPS to investigate the possible role of fast protein dynamics in the enzymatic reaction coordinate of human dihydrofolate reductase (hsDHFR). We found that sub-picosecond dynamics of hsDHFR do contribute to the reaction coordinate, whereas this is not the case in the E. coli version of the enzyme. This result indicates a shift in the DHFR family to a more dynamic version of catalysis. The second inquiry we addressed in this thesis regarding enzymatic barrier passage concerns the variability of paths through reactive phase space for a given enzymatic reaction. We further investigated the hhLDH-catalyzed reaction using a high-perturbation TPS algorithm. Though we saw that alternate reaction paths were possible, the dominant reaction path we observed corresponded to that previously elucidated in prior hhLDH TPS studies. Since the additional reaction paths we observed were likely high-energy, these results indicate that only the dominant reaction path contributes significantly to the overall reaction rate. In conclusion, we show that the enzymes hhLDH and hsDHFR exhibit paths through reactive phase space where fast protein motions are involved in the enzymatic reaction coordinate and exhibit a non-negligible contribution to chemical barrier crossing.

Masterson, Jean Emily

254

Assessing perceptions about hazardous substances (PATHS): the PATHS questionnaire.  

PubMed

How people perceive the nature of a hazardous substance may determine how they respond when potentially exposed to it. We tested a new Perceptions AbouT Hazardous Substances (PATHS) questionnaire. In Study 1 (N = 21), we assessed the face validity of items concerning perceptions about eight properties of a hazardous substance. In Study 2 (N = 2030), we tested the factor structure, reliability and validity of the PATHS questionnaire across four qualitatively different substances. In Study 3 (N = 760), we tested the impact of information provision on Perceptions AbouT Hazardous Substances scores. Our results showed that our eight measures demonstrated good reliability and validity when used for non-contagious hazards. PMID:23104995

Rubin, G James; Amlôt, Richard; Page, Lisa; Pearce, Julia; Wessely, Simon

2013-08-01

255

Path-Based Failure and Evolution Management  

Microsoft Academic Search

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 \\

Mike Y. Chen; Anthony Accardi; Emre Kiciman; David A. Patterson; Armando Fox; Eric A. Brewer

2004-01-01

256

Model for Delay Faults Based upon Paths  

Microsoft Academic Search

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 \\

Gordon L. Smith

1985-01-01

257

Multiple Paths to Encephalization and Technical Civilizations  

NASA Astrophysics Data System (ADS)

We propose consideration of at least two possible evolutionary paths for the emergence of intelligent life with the potential for technical civilization. The first is the path via encephalization of homeothermic animals; the second is the path to swarm intelligence of so-called superorganisms, in particular the social insects. The path to each appears to be facilitated by environmental change: homeothermic animals by decreased climatic temperature and for swarm intelligence by increased oxygen levels.

Schwartzman, David; Middendorf, George

2011-12-01

258

Multiple paths to encephalization and technical civilizations.  

PubMed

We propose consideration of at least two possible evolutionary paths for the emergence of intelligent life with the potential for technical civilization. The first is the path via encephalization of homeothermic animals; the second is the path to swarm intelligence of so-called superorganisms, in particular the social insects. The path to each appears to be facilitated by environmental change: homeothermic animals by decreased climatic temperature and for swarm intelligence by increased oxygen levels. PMID:22139517

Schwartzman, David; Middendorf, George

2011-12-01

259

Equilibrium and Dynamical Path Integral Methods in Bacterial Photosynthesis  

Microsoft Academic Search

Classical molecular dynamics simulations have provided a wealth of information on processes in biological systems. In spite\\u000a of the spectacular success and the insights gained from such simulations, processes involving electron or exciton transfer\\u000a are inherently quantum mechanical and thus not amenable to a classical description. This chapter focuses on the use of path\\u000a integral methods for simulating the equilibrium

Nancy Makri

260

Squeezed states and path integrals  

NASA Technical Reports Server (NTRS)

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.

Daubechies, Ingrid; Klauder, John R.

1992-01-01

261

Accelerating cleanup: Paths to closure  

SciTech Connect

This document was previously referred to as the Draft 2006 Plan. As part of the DOE`s national strategy, the Richland Operations Office`s Paths to Closure summarizes an integrated path forward for environmental cleanup at the Hanford Site. The Hanford Site underwent a concerted effort between 1994 and 1996 to accelerate the cleanup of the Site. These efforts are reflected in the current Site Baseline. This document describes the current Site Baseline and suggests strategies for further improvements in scope, schedule and cost. The Environmental Management program decided to change the name of the draft strategy and the document describing it in response to a series of stakeholder concerns, including the practicality of achieving widespread cleanup by 2006. Also, EM was concerned that calling the document a plan could be misconstrued to be a proposal by DOE or a decision-making document. The change in name, however, does not diminish the 2006 vision. To that end, Paths to Closure retains a focus on 2006, which serves as a point in time around which objectives and goals are established.

Edwards, C.

1998-06-30

262

Multiphoton Path Entanglement by Nonlocal Bunching  

Microsoft Academic Search

Multiphoton path entanglement is created without applying postselection, by manipulating the state of stimulated parametric down-conversion. A specific measurement on one of the two output spatial modes leads to the nonlocal bunching of the photons of the other mode, forming the desired multiphoton path entangled state. We present experimental results for the case of a heralded two-photon path entangled state

H. S. Eisenberg; J. F. Hodelin; G. Khoury; D. Bouwmeester

2005-01-01

263

Multilinear decomposition of human walking paths  

Microsoft Academic Search

In a previous work, the authors have shown how the Principal Components Analysis (PCA) of a set of human walking paths provides sufficient information to derive a linear human-like path generator based on examples. The present work aims to provide an analysis of human walking paths from the perspective of multilinear algebra, using the n-mode Singular Value Decomposition (SVD). This

Christian A. Ramirez; M. Castela?n; G. Arechavaleta

2010-01-01

264

SOME PROPERTIES OF PATH MEASURES CHRISTIAN LEONARD  

E-print Network

an unbounded measure. Indeed, its reversing measure is Lebesgue measure (or any of its positive multiple x Rn . Obviously, this path measure has the same unbounded mass as Lebesgue measure.SOME PROPERTIES OF PATH MEASURES CHRISTIAN L´EONARD Abstract. We call any measure on a path space

Paris-Sud XI, Université de

265

Evaluation of the Learning Path Specification  

ERIC Educational Resources Information Center

Flexible lifelong learning requires that learners can compare and select learning paths that best meet individual needs, not just in terms of learning goals, but also in terms of planning, costs etc. To this end a learning path specification was developed, which describes both the contents and the structure of any learning path, be it formal,…

Janssen, Jose; Berlanga, Adriana J.; Koper, Rob

2011-01-01

266

Quantifying the Causes of Path Inflation  

Microsoft Academic Search

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

Neil Spring; Ratul Mahajan; Thomas Anderson

2003-01-01

267

Test data generation and feasible path analysis  

Microsoft Academic Search

This paper describes techniques used by Test Specifica- tion and Determination Tool (TSDT), an experimental prototype for analysis and testing of critical applica- tions written in Ada. Two problems dominate structural testing of programs: exponential explosion in the num- ber of execution paths and feasible path determination, A path is feasible if there exists some input that will cause the

Robert Jasper; Mike Brennan; Keith E. Williamson; Bill Currier; David Zimmerman

1994-01-01

268

Hypertext Paths and the World-Wide Web: Experiences with Walden's Paths  

Microsoft Academic Search

Walden's Paths applies the concept of hypertextual paths to the World-Wide Web. Walden's Paths is being developed for use in the K-12 school environment. The heterogene- ity of the Web coupled with the desirability of supporting the teacher-student relationship make this an interesting and challenging project. We describe the Walden's Paths imple- mentation, discuss ...

Richard Furuta; Frank M. Shipman III; Catherine C. Marshall; Donald Brenner; Hao-wei Hsieh

1997-01-01

269

Longest Path Problems on Ptolemaic Graphs  

NASA Astrophysics Data System (ADS)

Longest path problem is a problem for finding a longest path in a given graph. While the graph classes in which the Hamiltonian path problem can be solved efficiently are widely investigated, there are few known graph classes such that the longest path problem can be solved efficiently. Polynomial time algorithms for finding a longest cycle and a longest path in a Ptolemaic graph are proposed. Ptolemaic graphs are the graphs that satisfy the Ptolemy inequality, and they are the intersection of chordal graphs and distance-hereditary graphs. The algorithms use the dynamic programming technique on a laminar structure of cliques, which is a recent characterization of Ptolemaic graphs.

Takahara, Yoshihiro; Teramoto, Sachio; Uehara, Ryuhei

270

Timeless path integral for relativistic quantum mechanics  

NASA Astrophysics Data System (ADS)

Starting from the canonical formalism of relativistic (timeless) quantum mechanics, the formulation of a timeless path integral is rigorously derived. The transition amplitude is reformulated as the sum, or functional integral, over all possible paths in the constraint surface specified by the (relativistic) Hamiltonian constraint, and each path contributes with a phase identical to the classical action divided by ?. The timeless path integral manifests the timeless feature as it is completely independent of the parametrization for paths. For the special case that the Hamiltonian constraint is a quadratic polynomial in momenta, the transition amplitude admits the timeless Feynman's path integral over the (relativistic) configuration space. Meanwhile, the difference between relativistic quantum mechanics and conventional nonrelativistic (with time) quantum mechanics is elaborated on in light of the timeless path integral.

Chiou, Dah-Wei

2013-06-01

271

Path Integration: Effect of Curved Path Complexity and Sensory System on Blindfolded Walking  

PubMed Central

Path integration refers to the ability to integrate continuous information of the direction and distance travelled by the system relative to the origin. Previous studies have investigated path integration through blindfolded walking along simple paths such as straight line and triangles. However, limited knowledge exists regarding the role of path complexity in path integration. Moreover, little is known about how information from different sensory input systems (like vision and proprioception) contributes to accurate path integration. The purpose of the current study was to investigate how sensory information and curved path complexity affect path integration. Forty blindfolded participants had to accurately reproduce a curved path and return to the origin. They were divided into four groups that differed in the curved path, circle (simple) or figure-eight (complex), and received either visual (previously seen) or proprioceptive (previously guided) information about the path before they reproduced it. The dependent variables used were average trajectory error, walking speed, and distance travelled. The results indicated that (a) both groups that walked on a circular path and both groups that received visual information produced greater accuracy in reproducing the path. Moreover, the performance of the group that received proprioceptive information and later walked on a figure-eight path was less accurate than their corresponding circular group. The groups that had the visual information also walked faster compared to the group that had proprioceptive information. Results of the current study highlight the roles of different sensory inputs while performing blindfolded walking for path integration. PMID:22840893

Koutakis, Panagiotis; Mukherjee, Mukul; Vallabhajosula, Srikant; Blanke, Daniel J.; Stergiou, Nicholas

2012-01-01

272

Effects of non-local electron transport in one-dimensional and two-dimensional simulations of shock-ignited inertial confinement fusion targets  

SciTech Connect

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.

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

273

An improved time-dependent nonlocal electron heat-flux model and its verification by laser-driven Al foil acceleration experiment  

NASA Astrophysics Data System (ADS)

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.

Sijoy, C. D.; Chaurasia, Shivanand; Mishra, Vinayak; Leshma, P.; Sakthivel, N.; Chaturvedi, Shashank; Sharma, S. M.; Basu, Sekhar

2014-06-01

274

Multiple order common path spectrometer  

NASA Technical Reports Server (NTRS)

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.

Newbury, Amy B. (Inventor)

2010-01-01

275

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.

1998-01-01

276

Enhancement of the stability of resistive switching characteristics by conduction path reconstruction  

NASA Astrophysics Data System (ADS)

In this study, a Pt/BiFeO3/TiN device was fabricated and the resistance switching characteristics were investigated. After the first forming process, the conduction path was formed and exhibited unstable bipolar switching characteristics. Subsequently, the original conduction path was destroyed thoroughly by high negative bias. By reconstructing the conduction path after a second forming process (re-forming process), the device exhibits stable bipolar switching characteristics. Transmission electron microscopy analysis indicates that the stability of switching behavior was enhanced because of the joule heating effect, and is an easy way to improve the resistance switching characteristics.

Huang, Jheng-Jie; Chang, Ting-Chang; Yu, Chih-Cheng; Huang, Hui-Chun; Chen, Yu-Ting; Tseng, Hsueh-Chih; Yang, Jyun-Bao; Sze, Simon M.; Gan, Der-Shin; Chu, Ann-Kuo; Lin, Jian-Yang; Tsai, Ming-Jinn

2013-07-01

277

Optimum gradient of mountain paths.  

PubMed

By combining the experiment results of R. Margaria (Atti Accad. Naz. Lincei Memorie 7: 299-368, 1938), regarding the metabolic cost of gradient locomotion, together with recent insights on gait biomechanics, a prediction about the most economical gradient of mountain paths (approximately 25%) is obtained and interpreted. The pendulum-like mechanism of walking produces a waste of mechanical work against gravity within the gradient range of up to 15% (the overall efficiency is dominated by the low transmission efficiency), whereas for steeper values only the muscular efficiency is responsible for the (slight) metabolic change (per meter of vertical displacement) with respect to gradient. The speeds at the optimum gradient turned out to be approximately 0.65 m/s (+0.16 m/s vertical) and 1.50 m/s (-0.36 m/s vertical), for uphill and downhill walking, respectively, and the ascensional energy expenditure was 0.4 and 2.0 ml O2.kg body mass-1.vertical m-1 climbed or descended. When the metabolic power becomes a burden, as in high-altitude mountaineering, the optimum gradient should be reduced. A sample of real mountain path gradients, experimentally measured, mimics the obtained predictions. PMID:8594031

Minetti, A E

1995-11-01

278

Sequential Path Entanglement for Quantum Metrology  

PubMed Central

Path entanglement is a key resource for quantum metrology. Using path-entangled states, the standard quantum limit can be beaten, and the Heisenberg limit can be achieved. However, the preparation and detection of such states scales unfavourably with the number of photons. Here we introduce sequential path entanglement, in which photons are distributed across distinct time bins with arbitrary separation, as a resource for quantum metrology. We demonstrate a scheme for converting polarization Greenberger-Horne-Zeilinger entanglement into sequential path entanglement. We observe the same enhanced phase resolution expected for conventional path entanglement, independent of the delay between consecutive photons. Sequential path entanglement can be prepared comparably easily from polarization entanglement, can be detected without using photon-number-resolving detectors, and enables novel applications.

Jin, Xian-Min; Peng, Cheng-Zhi; Deng, Youjin; Barbieri, Marco; Nunn, Joshua; Walmsley, Ian A.

2013-01-01

279

Studies of the interactions of ionizing radiations with communications materials  

SciTech Connect

Various models were developed for calculating the energy loss per unit length, or stopping power, and the inelastic mean free path for electrons in a material. We have included both organic materials such as polyethylene and inorganic materials such as SiO/sub 2/. In each case, the calculated values of stopping power and mean free path have been compared with experimental values where available and, in the case of mean free paths for organic materials, with those predicted from our universal formula. In addition the various models for stopping power and mean free path have been compared with each other. Measurements have been made of electron attenuation lengths (approx. = electron mean free paths) as a function of incident electron energy for electrons in amorphous carbon films, as a direct check on the values predicted by our universal formula for electron mean free paths in solid organic insulators. A theory has been developed to describe charged-particle track structure in nonmetallic solids, as the track evolves in time and space. Work has continued in the field of microdosimetry with the calculation of the energy densities deposited by high-energy photons as a function of depth in traversing a SiO/sub 2/ slab sandwiched between two slabs of Si.

Ashley, J.C.; Williams, M.W.

1982-01-01

280

Steam Path Audits on Industrial Steam Turbines  

E-print Network

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...

Mitchell, D. R.

281

Multiphoton Path Entanglement by Nonlocal Bunching  

NASA Astrophysics Data System (ADS)

Multiphoton path entanglement is created without applying postselection, by manipulating the state of stimulated parametric down-conversion. A specific measurement on one of the two output spatial modes leads to the nonlocal bunching of the photons of the other mode, forming the desired multiphoton path entangled state. We present experimental results for the case of a heralded two-photon path entangled state and show how to extend this scheme to higher photon numbers.

Eisenberg, H. S.; Hodelin, J. F.; Khoury, G.; Bouwmeester, D.

2005-03-01

282

Multiphoton Path Entanglement by Nonlocal Bunching  

Microsoft Academic Search

Multiphoton path entanglement is created without applying post-selection, by\\u000amanipulating the state of stimulated parametric down-conversion. A specific\\u000ameasurement on one of the two output spatial modes leads to the non-local\\u000abunching of the photons of the other mode, forming the desired multiphoton path\\u000aentangled state. We present experimental results for the case of a heralded\\u000atwo-photon path entangled state

H. S. Eisenberg; J. F. Hodelin; G. Khoury; D. Bouwmeester

2005-01-01

283

Multiphoton path entanglement by nonlocal bunching.  

PubMed

Multiphoton path entanglement is created without applying postselection, by manipulating the state of stimulated parametric down-conversion. A specific measurement on one of the two output spatial modes leads to the nonlocal bunching of the photons of the other mode, forming the desired multiphoton path entangled state. We present experimental results for the case of a heralded two-photon path entangled state and show how to extend this scheme to higher photon numbers. PMID:15783951

Eisenberg, H S; Hodelin, J F; Khoury, G; Bouwmeester, D

2005-03-11

284

Walden's Paths quiz: system design and implementation  

E-print Network

assessment io guide instruction, to provide fccdback to students, and to plan for further development ol the path or the Web pages included in the path. Cox and Junkin [13] discuss how instructors can use the results of an automatically evaluated test... Walden's Paths Quiz: System Design and Implementation. (December 2002) Avital Jayant Arora, B. E. , Universiiy of Bombay Chair of Advisory Committee: Dr. Richard Furuta Thts thesis describes the motivation for onlme testing, compares the effectiveness...

Arora, Avital Jayant

2012-06-07

285

Microwave propagation over mountain-diffraction paths  

Microsoft Academic Search

An experimental study was undertaken to obtain a more complete picture of wide-band transmission via microwave propagation over mountain-diffraction paths. Such paths are characterized by obstacles of irregular shape, and pathlength very large compared to wavelength. Swept-frequency transmission was used to provide a record of signal-level variations with time and frequency on two different paths. Other observations included polarization dependence,

A. Carlson

1966-01-01

286

Langevin equation path integral ground state.  

PubMed

We propose a Langevin equation path integral ground state (LePIGS) approach for the calculation of ground state (zero temperature) properties of molecular systems. The approach is based on a modification of the finite temperature path integral Langevin equation (PILE) method (J. Chem. Phys. 2010, 133, 124104) to the case of open Feynman paths. Such open paths are necessary for a ground state formulation. We illustrate the applicability of the method using model systems and the weakly bound water-parahydrogen dimer. We show that the method can lead to converged zero point energies and structural properties. PMID:23738885

Constable, Steve; Schmidt, Matthew; Ing, Christopher; Zeng, Tao; Roy, Pierre-Nicholas

2013-08-15

287

Path-integral simulation of solids.  

PubMed

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

Herrero, C P; Ramírez, R

2014-06-11

288

The Logic behind Feynman's Paths  

E-print Network

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.

Edgardo T. Garcia Alvarez

2010-11-22

289

Using computerized tomography to determine ionospheric structures. Part 2, A method using curved paths to increase vertical resolution  

SciTech Connect

A method is presented to unfold the two-dimensional vertical structure in electron density by using data on the total electron content for a series of paths through the ionosphere. The method uses a set of orthonormal basis functions to represent the vertical structure and takes advantage of curved paths and the eikonical equation to reduce the number of iterations required for a solution. Curved paths allow a more thorough probing of the ionosphere with a given set of transmitter and receiver positions. The approach can be directly extended to more complex geometries.

Vittitoe, C.N.

1993-08-01

290

Model Checking Almost All Paths Can Be Less Expensive than Checking All Paths  

E-print Network

Model Checking Almost All Paths Can Be Less Expensive than Checking All Paths Matthias Schmalz 1 and nite-state systems, the two notions of smallness coincide. More importantly, they coincide 1 Matthias.Schmalz

Varacca, Daniele - Laboratoire Preuves, Programmes et Systèmes, Université Paris 7

291

Methodology for Augmenting Existing Paths with Additional Parallel Transects  

SciTech Connect

Visual Sample Plan (VSP) is sample planning software that is used, among other purposes, to plan transect sampling paths to detect areas that were potentially used for munition training. This module was developed for application on a large site where existing roads and trails were to be used as primary sampling paths. Gap areas between these primary paths needed to found and covered with parallel transect paths. These gap areas represent areas on the site that are more than a specified distance from a primary path. These added parallel paths needed to optionally be connected together into a single path—the shortest path possible. The paths also needed to optionally be attached to existing primary paths, again with the shortest possible path. Finally, the process must be repeatable and predictable so that the same inputs (primary paths, specified distance, and path options) will result in the same set of new paths every time. This methodology was developed to meet those specifications.

Wilson, John E.

2013-09-30

292

Relationship between electron density and effective densities of body tissues for stopping, scattering, and nuclear interactions of proton and ion beams  

SciTech Connect

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.

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

293

Characterization of electrostatic potential of compound semiconductors using off-axis electron holography  

NASA Astrophysics Data System (ADS)

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 and GaAs were determined to be 12.1 V and 14.0 V, respectively. Accurate knowledge of these parameters was essential before commencing potential profiling across AlGaAs/GaAs heterojunction devices. The electrostatic potential profiles across AlGaAs/AlAs/GaAs heterostructures containing n- and p-doped AlGaAs layers were measured. Potential drops of 0.5 V, caused by ionized carbon impurities, were observed at the epilayer/substrate interface of both heterostructures. The measured potential profiles in the region of the buffer/substrate interface were simulated by adding a sheet acceptor layer at the buffer/substrate interface. The additional interface impurities pull the conduction band up at the interface relative to the Fermi level. The heavily doped p-n junctions in AlGaAs light-emitting diodes with triangular barriers were investigated with emphasis on the efficiency of dopant activation. Comparison of experimental and simulated p-n junction potential profiles enabled the Si and Be dopant activation to be determined. The low Si activation efficiency of 12 percent at 0.6 Al was attributed to the crossover of gamma and X conduction-band minima near the concentration of 0.43 Al. Simulated band-edge diagrams with nominal and activated dopants showed the effect of AlGaAs barrier shape on carrier transport. The lightly doped p-n junctions in InGaAs light-emitting diodes with linearly graded barriers were also studied, and the effect of unintentional oxygen impurities was investigated in terms of doping efficiency. Overall, the success of these studies has verified the capability of off-axis electron holography to provide unique information about complex heterostructures of compound semiconductors with nanoscale resolution. The technique should become a useful tool for future device development and process optimization.

Chung, Suk

2009-12-01

294

Resynthesis of Combinational Circuts for Path Count Reduction and for Path Delay Fault Testability  

Microsoft Academic Search

Path delay fault model is the most suitable model for detecting distributed manufacturing defects that can cause delay faults. However, the number of paths in a modern design can be extremely large and the path delay testability of many practical designs could be very low. In this paper we show how to resynthesize a combinational circuit in order to reduce

Angela Krstic; Kwang-Ting Cheng

1996-01-01

295

Backup Path Re-optimizations for Shared Path Protection in Multi-domain Networks  

Microsoft Academic Search

Within the context of dynamic routing models for shared path protection in multi-domain networks, we propose a backup path re-optimization phase with possible rerouting of the existing backup paths in order to increase the bandwidth sharing among them while minimizing the network backup cost. The re- optimization phase is activated periodically or when routing a new connection fails because of

B. Jaumard; T. Dieu Linh Truong

2006-01-01

296

Energetic Path Finding Across Massive Terrain Data  

E-print Network

Energetic Path Finding Across Massive Terrain Data Andrew Tsui and Zo¨e Wood California Polytechnic of this work include: ­ Tools for managing and performing energetic analysis on massive out-of- core datasets builds on two previous projects involving human centered paths across terrain data, Energetic Analyst [5

Wood, Zoë J.

297

Career path of a corruption entrepreneur  

Microsoft Academic Search

The study of criminal career paths is necessary to understand the methods of success employed by high-performing criminals. The aim of this article is to focus on the career path of Jack Herbert who set up and maintained extensive corruption networks between organised crime groups and police in the Australian state of Queensland. This study builds on Morselli's work on

Mark Lauchs; Zoe Staines

2012-01-01

298

A Random Walk on a Circular Path  

ERIC Educational Resources Information Center

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.

Ching, W.-K.; Lee, M. S.

2005-01-01

299

Cooperative organic mine avoidance path planning  

NASA Astrophysics Data System (ADS)

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.

McCubbin, Christopher B.; Piatko, Christine D.; Peterson, Adam V.; Donnald, Creighton R.; Cohen, David

2005-06-01

300

Asymmetric fluctuation relaxation paths in FPU models  

NASA Astrophysics Data System (ADS)

A recent theory by Bertini, De Sole, Gabrielli, Jona-Lasinio and Landim predicts a temporal asymmetry in the fluctuation-relaxation paths of certain observables of nonequilibrium systems in local thermodynamic equilibrium. We find temporal asymmetries in the fluctuation-relaxation paths of a form of local heat flow, in the nonequilibrium FPU- ? model of Lepri, Livi and Politi.

Giberti, C.; Rondoni, L.; Vernia, C.

2006-06-01

301

Finding Regular Simple Paths in Graph Databases  

Microsoft Academic Search

We consider the following problem: given a labelled directed graph and a regular expression , find all pairs of nodes connected by a simple path such that theconcatenation of the labels along the path satisfies . The problem is motivated by the observation that many recursive queries in relational databases can be expressed in this form, and by the implementation

Alberto O. Mendelzon; Peter T. Wood

1989-01-01

302

Adaptively Ubiquitous Learning in Campus Math Path  

ERIC Educational Resources Information Center

The purposes of this study are to develop and evaluate the instructional model and learning system which integrate ubiquitous learning, computerized adaptive diagnostic testing system and campus math path learning. The researcher first creates a ubiquitous learning environment which is called "adaptive U-learning math path system". This system…

Shih, Shu-Chuan; Kuo, Bor-Chen; Liu, Yu-Lung

2012-01-01

303

Katrina'sPath Lake Pontchartrain  

E-print Network

'sPath Katrina's Storm Surge #12;Now Scenario Hurricane Toufectis · Approaches from the ESE, traveling WNW · SSC to Katrina #12;Gotwals'Path Now Scenario Hurricane Gotwals · Katrina is as Katrina was · Storm track moved 4 Hurricane Horton · Katrina is as Katrina was · Adding roughly 10" sea level rise (25cm) Impacts · Similar

304

Converging towards the optimal path to extinction  

PubMed Central

Extinction appears ubiquitously in many fields, including chemical reactions, population biology, evolution and epidemiology. Even though extinction as a random process is a rare event, its occurrence is observed in large finite populations. Extinction occurs when fluctuations owing to random transitions act as an effective force that drives one or more components or species to vanish. Although there are many random paths to an extinct state, there is an optimal path that maximizes the probability to extinction. In this paper, we show that the optimal path is associated with the dynamical systems idea of having maximum sensitive dependence to initial conditions. Using the equivalence between the sensitive dependence and the path to extinction, we show that the dynamical systems picture of extinction evolves naturally towards the optimal path in several stochastic models of epidemics. PMID:21571943

Schwartz, Ira B.; Forgoston, Eric; Bianco, Simone; Shaw, Leah B.

2011-01-01

305

A clinical path for adult diabetes.  

PubMed

The use of clinical paths for patient care management was explored by this development team as a mechanism to provide consistent, high-quality care to hospitalized patients in high-volume, high-risk diagnostic categories. Reviewing the historical aspects and importance of clinical paths helped expand the team's perspective to incorporate pre- and posthospitalization phases of patient care into the clinical path being developed. A multidisciplinary team of physicians, nurses, health educators, and dietitians from both inpatient and outpatient departments of Kaiser-Santa Teresa Medical Center in San Jose, California, devised and implemented an Adult Diabetes Mellitus care path. Staff education preceded the implementation of the care paths. Measurements of quality indicators showed improvements in patient satisfaction, patient education, patient knowledge, and nutrition assessments. PMID:9416030

Courtney, L; Gordon, M; Romer, L

1997-01-01

306

Bergman Kernel from Path Integral  

NASA Astrophysics Data System (ADS)

We rederive the expansion of the Bergman kernel on Kähler manifolds developed by Tian, Yau, Zelditch, Lu and Catlin, using path integral and perturbation theory, and generalize it to supersymmetric quantum mechanics. One physics interpretation of this result is as an expansion of the projector of wave functions on the lowest Landau level, in the special case that the magnetic field is proportional to the Kähler form. This is relevant for the quantum Hall effect in curved space, and for its higher dimensional generalizations. Other applications include the theory of coherent states, the study of balanced metrics, noncommutative field theory, and a conjecture on metrics in black hole backgrounds discussed in [24]. We give a short overview of these various topics. From a conceptual point of view, this expansion is noteworthy as it is a geometric expansion, somewhat similar to the DeWitt-Seeley-Gilkey et al short time expansion for the heat kernel, but in this case describing the long time limit, without depending on supersymmetry.

Douglas, Michael R.; Klevtsov, Semyon

2010-01-01

307

Biological path to nanoelectronics devices  

NASA Astrophysics Data System (ADS)

The biology and semiconductor technology have progressed independently. There was a large distance between them and a substantial interdisciplinary research area was left untouched. Recently, this situation is changing. Some researchers are stimulating semiconductor technology to introduce bio-molecules into the nano-fabrication process. We proposed a new process for fabricating functional nano-structure on a solid surface using protein supramolecules, which is named "Bio Nano Process" (BNP). We employed a cage-shaped protein, apoferritin and synthesized several kinds of nanoparticles (NP) in the apoferritin cavity. A two-dimensional array of them was made on the silicon wafer and this array was heat treated or UV/ozone treated. These processes produced a two-dimensional inorganic NP array on the silicon surface. The size of NP is small enough as quantum dots and the floating nanodots memory using this NP array is now under development. We also proposed another process using the obtained nanodot array as the nanometric etching mask. This was realized by the neutral beam etching and 7nm Si nano columns with high aspect ratio were fabricated. These experimental results demonstrated that the BNP can fabricate the inorganic nanostructure using protein supramolecules and the BNP opened up a biological path to nanoelectronics devices.

Yamashita, Ichiro

2005-02-01

308

Path integral for inflationary perturbations  

NASA Astrophysics Data System (ADS)

The quantum theory of cosmological perturbations in single-field inflation is formulated in terms of a path integral. Starting from a canonical formulation, we show how the free propagators can be obtained from the well-known gauge-invariant quadratic action for scalar and tensor perturbations, and determine the interactions to arbitrary order. This approach does not require the explicit solution of the energy and momentum constraints, a novel feature which simplifies the determination of the interaction vertices. The constraints and the necessary imposition of gauge conditions is reflected in the appearance of various commuting and anticommuting auxiliary fields in the action. These auxiliary fields are not propagating physical degrees of freedom but need to be included in internal lines and loops in a diagrammatic expansion. To illustrate the formalism we discuss the tree-level three-point and four-point functions of the inflaton perturbations, reproducing the results already obtained by the methods used in the current literature. Loop calculations are left for future work.

Prokopec, Tomislav; Rigopoulos, Gerasimos

2010-07-01

309

Path Integral for Inflationary Perturbations  

E-print Network

The quantum theory of cosmological perturbations in single field inflation is formulated in terms of a path integral. Starting from a canonical formulation, we show how the free propagators can be obtained from the well known gauge-invariant quadratic action for scalar and tensor perturbations, and determine the interactions to arbitrary order. This approach does not require the explicit solution of the energy and momentum constraints, a novel feature which simplifies the determination of the interaction vertices. The constraints and the necessary imposition of gauge conditions is reflected in the appearance of various commuting and anti-commuting auxiliary fields in the action. These auxiliary fields are not propagating physical degrees of freedom but need to be included in internal lines and loops in a diagrammatic expansion. To illustrate the formalism we discuss the tree-level 3-point and 4-point functions of the inflaton perturbations, reproducing the results already obtained by the methods used in the current literature. Loop calculations are left for future work.

Tomislav Prokopec; Gerasimos Rigopoulos

2010-12-11

310

Path integral for inflationary perturbations  

SciTech Connect

The quantum theory of cosmological perturbations in single-field inflation is formulated in terms of a path integral. Starting from a canonical formulation, we show how the free propagators can be obtained from the well-known gauge-invariant quadratic action for scalar and tensor perturbations, and determine the interactions to arbitrary order. This approach does not require the explicit solution of the energy and momentum constraints, a novel feature which simplifies the determination of the interaction vertices. The constraints and the necessary imposition of gauge conditions is reflected in the appearance of various commuting and anticommuting auxiliary fields in the action. These auxiliary fields are not propagating physical degrees of freedom but need to be included in internal lines and loops in a diagrammatic expansion. To illustrate the formalism we discuss the tree-level three-point and four-point functions of the inflaton perturbations, reproducing the results already obtained by the methods used in the current literature. Loop calculations are left for future work.

Prokopec, Tomislav [Institute for Theoretical Physics and Spinoza Institute, Utrecht University, Leuvenlaan 4, 3584 CE Utrecht (Netherlands); Rigopoulos, Gerasimos [Helsinki Institute of Physics, P.O. Box 64, FIN-00014, University of Helsinki (Finland)

2010-07-15

311

Decision paths in complex tasks  

NASA Technical Reports Server (NTRS)

Complex real world action and its prediction and control has escaped analysis by the classical methods of psychological research. The reason is that psychologists have no procedures to parse complex tasks into their constituents. Where such a division can be made, based say on expert judgment, there is no natural scale to measure the positive or negative values of the components. Even if we could assign numbers to task parts, we lack rules i.e., a theory, to combine them into a total task representation. We compare here two plausible theories for the amalgamation of the value of task components. Both of these theories require a numerical representation of motivation, for motivation is the primary variable that guides choice and action in well-learned tasks. We address this problem of motivational quantification and performance prediction by developing psychophysical scales of the desireability or aversiveness of task components based on utility scaling methods (Galanter 1990). We modify methods used originally to scale sensory magnitudes (Stevens and Galanter 1957), and that have been applied recently to the measure of task 'workload' by Gopher and Braune (1984). Our modification uses utility comparison scaling techniques which avoid the unnecessary assumptions made by Gopher and Braune. Formula for the utility of complex tasks based on the theoretical models are used to predict decision and choice of alternate paths to the same goal.

Galanter, Eugene

1991-01-01

312

Excitation of nucleobases from a computational perspective I: reaction paths.  

PubMed

The main intrinsic photochemical events in nucleobases can be described on theoretical grounds within the realm of non-adiabatic computational photochemistry. From a static standpoint, the photochemical reaction path approach (PRPA), through the computation of the respective minimum energy path (MEP), can be regarded as the most suitable strategy in order to explore the electronically excited isolated nucleobases. Unfortunately, the PRPA does not appear widely in the studies reported in the last decade. The main ultrafast decay observed experimentally for the gas-phase excited nucleobases is related to the computed barrierless MEPs from the bright excited state connecting the initial Franck-Condon region and a conical intersection involving the ground state. At the highest level of theory currently available (CASPT2//CASPT2), the lowest excited (1)(??*) hypersurface for cytosine has a shallow minimum along the MEP deactivation pathway. In any case, the internal conversion processes in all the natural nucleobases are attained by means of interstate crossings, a self-protection mechanism that prevents the occurrence of photoinduced damage of nucleobases by ultraviolet radiation. Many alternative and secondary paths have been proposed in the literature, which ultimately provide a rich and constructive interplay between experimentally and theoretically oriented research. PMID:24264958

Giussani, Angelo; Segarra-Martí, Javier; Roca-Sanjuán, Daniel; Merchán, Manuela

2015-01-01

313

Complementarity with neutron two-path interferences and separated-oscillatory-field resonances  

NASA Astrophysics Data System (ADS)

The implications of complementarity on two-path neutron interferences and on separated-oscillatory-field resonances are discussed. The studies are extensions of those by Furry and Ramsey [Phys. Rev. 118, 623 (1960)] on two-path electron interferences which showed that an apparatus used to determine the electron path introduces uncertainties in the scalar and vector potentials which in turn disturb the phase of the electron wave function so much through the Aharonov-Bohm effects [Phys. Rev. 115, 485 (1959)] that the interference fringes disappear. A similar result is derived here for the neutron, but with the phase uncertainties coming from the magnetic moment's motion through an electric field as discussed by Anandan [Phys. Rev. Lett. 48, 1660 (1982)], and Aharonov and Casher [Phys. Rev. Lett. 53, 319 (1984)]. A corresponding result is also obtained for separated-oscillatory-fields resonances, which can be interpreted as an interference between two different paths in spin space. An interesting difference between the separated-path and separated-oscillatory-field experiments is that the latter may be interpreted classically.

Ramsey, Norman F.

1993-07-01

314

Robot path planning using a genetic algorithm  

NASA Technical Reports Server (NTRS)

Robot path planning can refer either to a mobile vehicle such as a Mars Rover, or to an end effector on an arm moving through a cluttered workspace. In both instances there may exist many solutions, some of which are better than others, either in terms of distance traversed, energy expended, or joint angle or reach capabilities. A path planning program has been developed based upon a genetic algorithm. This program assumes global knowledge of the terrain or workspace, and provides a family of good paths between the initial and final points. Initially, a set of valid random paths are constructed. Successive generations of valid paths are obtained using one of several possible reproduction strategies similar to those found in biological communities. A fitness function is defined to describe the goodness of the path, in this case including length, slope, and obstacle avoidance considerations. It was found that with some reproduction strategies, the average value of the fitness function improved for successive generations, and that by saving the best paths of each generation, one could quite rapidly obtain a collection of good candidate solutions.

Cleghorn, Timothy F.; Baffes, Paul T.; Wang, Liu

1988-01-01

315

The behavioural final common path.  

PubMed

In this paper it is argued that any model of the motivational (i.e. reversible) processes governing the behaviour of an animal can be represented by means of isoclines in a multidimensional 'causal-factor space'. The argument is axiomatic, based upon the two prime assumptions: that (1) it is always possible to classify the behavioural repertoire of a species in such a way that the classes are mutually exclusive in the sense that the members of different classes cannot occur simultaneously, and (2) these incompatible actions are uniquely determined by a particular set of causal factors. The isoclines join all points in the space which present a given 'degree of competitiveness' of a particular 'candidate' for overt behavioural expression. The competition between candidates is an inevitable consequence of the fact that animals cannot 'do more than one thing at a time', and is envisaged as taking place in the behavioural final common path. An empirical method of determining the motivational state (i.e. point in causal-factor space) is outlined. This is a 'relative' method, independent of the arbitrary calibration of the axes of the causal-factor space. It is shown that an arbitrary scale of measurement along any two axes of the causal-factor space is all that is necessary for empirical determination of the shape of a motivational isocline. Experiments in which this method has been applied to the measurement of hunger and thirst in doves are outlined, and the results are discussed in terms of their implications for motivation theory in general. PMID:239416

McFarland, D J; Sibly, R M

1975-05-15

316

Evolution paths for advanced automation  

NASA Technical Reports Server (NTRS)

As Space Station Freedom (SSF) evolves, increased automation and autonomy will be required to meet Space Station Freedom Program (SSFP) objectives. As a precursor to the use of advanced automation within the SSFP, especially if it is to be used on SSF (e.g., to automate the operation of the flight systems), the underlying technologies will need to be elevated to a high level of readiness to ensure safe and effective operations. Ground facilities supporting the development of these flight systems -- from research and development laboratories through formal hardware and software development environments -- will be responsible for achieving these levels of technology readiness. These facilities will need to evolve support the general evolution of the SSFP. This evolution will include support for increasing the use of advanced automation. The SSF Advanced Development Program has funded a study to define evolution paths for advanced automaton within the SSFP's ground-based facilities which will enable, promote, and accelerate the appropriate use of advanced automation on-board SSF. The current capability of the test beds and facilities, such as the Software Support Environment, with regard to advanced automation, has been assessed and their desired evolutionary capabilities have been defined. Plans and guidelines for achieving this necessary capability have been constructed. The approach taken has combined indepth interviews of test beds personnel at all SSF Work Package centers with awareness of relevant state-of-the-art technology and technology insertion methodologies. Key recommendations from the study include advocating a NASA-wide task force for advanced automation, and the creation of software prototype transition environments to facilitate the incorporation of advanced automation in the SSFP.

Healey, Kathleen J.

1990-01-01

317

d self-avoiding path (canonical surface) (fixed point)  

E-print Network

d self-avoiding path 2004 2 1 1 path (canonical surface) (fixed point) canonical surface [1, ] self-avoiding path Self-avoiding path d pre-gasket self-avoiding path d pre-gasket Sierpi´nski gasket d pre-gasket self-avoiding path 1 E-mail: hattori@math.nagoya-u.ac.jp 1 #12;d pre-gasket d pre-gasket 1 2 self

Hattori, Tetsuya

318

Automatic alignment of double optical paths in excimer laser amplifier  

NASA Astrophysics Data System (ADS)

A kind of beam automatic alignment method used for double paths amplification in the electron pumped excimer laser system is demonstrated. In this way, the beams from the amplifiers can be transferred along the designated direction and accordingly irradiate on the target with high stabilization and accuracy. However, owing to nonexistence of natural alignment references in excimer laser amplifiers, two cross-hairs structure is used to align the beams. Here, one crosshair put into the input beam is regarded as the near-field reference while the other put into output beam is regarded as the far-field reference. The two cross-hairs are transmitted onto Charge Coupled Devices (CCD) by image-relaying structures separately. The errors between intersection points of two cross-talk images and centroid coordinates of actual beam are recorded automatically and sent to closed loop feedback control mechanism. Negative feedback keeps running until preset accuracy is reached. On the basis of above-mentioned design, the alignment optical path is built and the software is compiled, whereafter the experiment of double paths automatic alignment in electron pumped excimer laser amplifier is carried through. Meanwhile, the related influencing factors and the alignment precision are analyzed. Experimental results indicate that the alignment system can achieve the aiming direction of automatic aligning beams in short time. The analysis shows that the accuracy of alignment system is 0.63?rad and the beam maximum restoration error is 13.75?m. Furthermore, the bigger distance between the two cross-hairs, the higher precision of the system is. Therefore, the automatic alignment system has been used in angular multiplexing excimer Main Oscillation Power Amplification (MOPA) system and can satisfy the requirement of beam alignment precision on the whole.

Wang, Dahui; Zhao, Xueqing; Hua, Hengqi; Zhang, Yongsheng; Hu, Yun; Yi, Aiping; Zhao, Jun

2013-05-01

319

Identifying decohering paths in closed quantum systems  

NASA Technical Reports Server (NTRS)

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.

Albrecht, Andreas

1990-01-01

320

How Do Paths Look From Different Perspectives?  

NSDL National Science Digital Library

Using both literature (a book featuring a path, such as Little Red Riding Hood) and satellite images, students will identify paths, observe and analyze them from different altitudes, and distinguish natural paths from those made by humans. Students will learn how images can inform the building, use and maintenance of paths. The URL opens to the investigation directory, with links to teacher and student materials, lesson extensions, resources, teaching tips, and assessment strategies. This is Investigation 2 of four found in the Grades K-4 Module 4 of Mission Geography. The Mission Geography curriculum integrates data and images from NASA missions with the National Geography Standards. Each of the four investigations in Module 4, while related, can be done independently. Please see Investigation 1 of this module for a two-page module overview and list of all standards addressed.

321

Nonclassical Paths in Quantum Interference Experiments  

NASA Astrophysics Data System (ADS)

In a double slit interference experiment, the wave function at the screen with both slits open is not exactly equal to the sum of the wave functions with the slits individually open one at a time. The three scenarios represent three different boundary conditions and as such, the superposition principle should not be applicable. However, most well-known text books in quantum mechanics implicitly and/or explicitly use this assumption that is only approximately true. In our present study, we have used the Feynman path integral formalism to quantify contributions from nonclassical paths in quantum interference experiments that provide a measurable deviation from a naive application of the superposition principle. A direct experimental demonstration for the existence of these nonclassical paths is difficult to present. We find that contributions from such paths can be significant and we propose simple three-slit interference experiments to directly confirm their existence.

Sawant, Rahul; Samuel, Joseph; Sinha, Aninda; Sinha, Supurna; Sinha, Urbasi

2014-09-01

322

Non-classical paths in interference experiments  

E-print Network

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.

Rahul Sawant; Joseph Samuel; Aninda Sinha; Supurna Sinha; Urbasi Sinha

2014-08-09

323

Engineering Shortest Path Algorithms Camil Demetrescu1  

E-print Network

Engineering Shortest Path Algorithms Camil Demetrescu1 and Giuseppe F. Italiano2 1 Dipartimento di: italiano@disp.uniroma2.it, URL: http://www.disp.uniroma2.it/users/italiano/ Abstract. In this paper, we

Demetrescu, Camil

324

Building a path in cell biology  

E-print Network

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.

Cheeseman, Iain McPherson

325

Multi-objective stochastic path planning  

E-print Network

The present research formulates the path planning as an optimization problem with multiple objectives and stochastic edge parameters. The first section introduces different variants of the PP problem and discusses existing solutions to the problem...

Dasgupta, Sumantra

2009-05-15

326

X-ray characterization, electronic band structure, and thermoelectric properties of the cluster compound Ag2Tl2Mo9Se11.  

PubMed

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

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

327

A path-following algorithm for missiles  

Microsoft Academic Search

The missile path-following problem has not been studied particularly as much as other vehicles. This fact is the source of our motivation behind this work. In this paper, a path-following algorithm, which is specifically designed for missiles but can be applied to other vehicles as well, is proposed. Presented algorithm is composed of a feedback and feed-forward control rule. Feedback

Gorkem Secer

2012-01-01

328

Path integral approach on Schrodinger's cat  

E-print Network

From the following thought experiments, it is demonstrated that the collapse of wave function of an isolated system is possible without external observer. It will be shown that the analysis by Feynman path integral method supports this conclusion. The argument is based on two assumptions: 1. The condition of Schrodinger's cat experiment 2. Feynman path integral; This could explain Schrodinger's cat paradox and its implication on the black hole information paradox will be discussed.

Zinkoo Yun

2013-10-30

329

Highway Hierarchies Hasten Exact Shortest Path Queries  

Microsoft Academic Search

\\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

Peter Sanders; Dominik Schultes

2005-01-01

330

HomePath: Your On-Line Path to a Home of Your Own  

NSDL National Science Digital Library

Whether you're thinking about if you're ready to buy a home, are in the process of buying a home, or are considering refinancing your current home, there's information for you on Fannie Mae's newest website. Fannie Mae is America's largest source of home mortgage funds, and has designed HomePath to be "your on-line path to a home of your own." There are three different paths through the information on the website: HomeStarterPath has resources for people deciding whether home ownership is right for them, including a comparison of renting vs. buying and a calculator for estimating how much house one can afford to buy; HomePurchasePath offers services for people who are ready to buy, including mortgage application information and how to shop for a lender; HomeRefinancePath helps homeowners determine when refinancing is beneficial, and outlines the costs involved.

331

Quantum cosmology based on discrete Feynman paths  

SciTech Connect

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''.

Chew, Geoffrey F.

2002-10-10

332

An Adaptive Path Planning Algorithm for Cooperating Unmanned Air Vehicles  

SciTech Connect

An adaptive path planning algorithm is presented for cooperating Unmanned Air Vehicles (UAVs) that are used to deploy and operate land-based sensor networks. The algorithm employs a global cost function to generate paths for the UAVs, and adapts the paths to exceptions that might occur. Examples are provided of the paths and adaptation.

Cunningham, C.T.; Roberts, R.S.

2000-09-12

333

Adaptive path planning algorithm for cooperating unmanned air vehicles  

SciTech Connect

An adaptive path planning algorithm is presented for cooperating Unmanned Air Vehicles (UAVs) that are used to deploy and operate land-based sensor networks. The algorithm employs a global cost function to generate paths for the UAVs, and adapts the paths to exceptions that might occur. Examples are provided of the paths and adaptation.

Cunningham, C T; Roberts, R S

2001-02-08

334

Diagnosis for Covariance Structure Models by Analyzing the Path  

ERIC Educational Resources Information Center

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…

Yuan, Ke-Hai; Kouros, Chrystyna D.; Kelley, Ken

2008-01-01

335

The Use of Path Analysis in Program Evaluation. No. 12.  

ERIC Educational Resources Information Center

Path analysis, a technique related to multiple regression analysis is used for ascribing causal relationships among variables. Path analysis involves the construction of explicitly formulated causal models and makes the reasoning explicit in the form of path diagrams and structural equations. Regression analysis is then used to construct path

Smith, Nick L.; Murray, Stephen L.

336

Model Discrepancy in the Saturated Path Hydrology Model: Initial Analysis  

E-print Network

Model Discrepancy in the Saturated Path Hydrology Model: Initial Analysis Tom Fricker University discrepancy in the Saturated Path Hydrology Model (logSPM, Kuczera et al., 2006). The purpose). 1 #12;3 The Saturated Path Hydrology Model We consider the Saturated Path Hydrology Model (log

Oakley, Jeremy

337

Achieving Path Diversity over the Internet using MDS Codes  

Microsoft Academic Search

Path diversity works by setting up multiple parallel connections between the end points using the topological path redundancy of the network. In this paper, Forward Error Correction (FEC) is applied across multiple independent paths to enhance the end- to-end reliability. Internet paths are modeled as erasure Gilbert-Elliot channels (1), (2). First, it is shown that over any erasure channel, Maximum

Shervan Fashandi; Shahab Oveis Gharan; Amir K. Khandani

338

14 CFR 171.265 - Glide path performance requirements.  

Code of Federal Regulations, 2010 CFR

...tone predominating below the path and the 90 Hz tone predominating above the path to at least...angular displacement above and below the glide path of... (o) The DDM below the ISMLS glide path...less than 0.30? above the...

2010-01-01

339

14 CFR 171.265 - Glide path performance requirements.  

Code of Federal Regulations, 2013 CFR

...tone predominating below the path and the 90 Hz tone predominating above the path to at least...angular displacement above and below the glide path of... (o) The DDM below the ISMLS glide path...less than 0.30? above the...

2013-01-01

340

14 CFR 171.265 - Glide path performance requirements.  

Code of Federal Regulations, 2011 CFR

...tone predominating below the path and the 90 Hz tone predominating above the path to at least...angular displacement above and below the glide path of... (o) The DDM below the ISMLS glide path...less than 0.30? above the...

2011-01-01

341

14 CFR 171.265 - Glide path performance requirements.  

Code of Federal Regulations, 2012 CFR

...tone predominating below the path and the 90 Hz tone predominating above the path to at least...angular displacement above and below the glide path of... (o) The DDM below the ISMLS glide path...less than 0.30? above the...

2012-01-01

342

Real-Time Path Integral Approach to Nonequilibrium Many-Body Quantum Systems  

NASA Astrophysics Data System (ADS)

A real-time path-integral Monte Carlo approach is developed to study the dynamics in a many-body quantum system coupled to a phonon background until reaching a nonequilibrium stationary state. The approach is based on augmenting an exact reduced equation for the evolution of the system in the interaction picture which is amenable to an efficient path integral (worldline) Monte Carlo approach. Results obtained for a model of inelastic tunneling spectroscopy reveal the applicability of the approach to a wide range of physically important regimes, including high (classical) and low (quantum) temperatures, and weak (perturbative) and strong electron-phonon couplings.

Mühlbacher, Lothar; Rabani, Eran

2008-05-01

343

The (1+1) Dimensional Dirac Equation With Pseudoscalar Potentials: Path Integral Treatment  

NASA Astrophysics Data System (ADS)

The supersymetric path integrals in solving the problem of relativistic spinning particle interacting with pseudoscalar potentials is examined. The relative propagator is presented by means of path integral, where the spin degrees of freedom are described by odd Grassmannian variables and the gauge invariant part of the effective action has a form similar to the standard pseudoclassical action given by Berezin and Marinov. After integrating over fermionic variables (Grassmannian variables), the problem is reduced to a nonrelativistic one with an effective supersymetric potential. Some explicit examples are considered, where we have extracted the energy spectrum of the electron and the wave functions.

Haouat, S.; Chetouani, L.

2007-06-01

344

A Comparison of Two Path Planners for Planetary Rovers  

NASA Technical Reports Server (NTRS)

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

Tarokh, M.; Shiller, Z.; Hayati, S.

1999-01-01

345

Entanglement, Dephasing, and Phase Recovery via Cross-Correlation Measurements of Electrons  

E-print Network

Determination of the path taken by a quantum particle leads to a suppression of interference and to a classical behavior. We employ here a quantum 'which path' detector to perform accurate path determination in a two-path-electron-interferometer; leading to full suppression of the interference. Following the dephasing process we recover the interference by measuring the cross-correlation between the interferometer and detector currents. Under our measurement conditions every interfering electron is dephased by approximately a single electron in the detector - leading to mutual entanglement of approximately single pairs of electrons.

I. Neder; M. Heiblum; D. Mahalu; V. Umansky

2006-07-13

346

Modular electronics packaging system  

NASA Technical Reports Server (NTRS)

A modular electronics packaging system includes multiple packaging slices that are mounted horizontally to a base structure. The slices interlock to provide added structural support. Each packaging slice includes a rigid and thermally conductive housing having four side walls that together form a cavity to house an electronic circuit. The chamber is enclosed on one end by an end wall, or web, that isolates the electronic circuit from a circuit in an adjacent packaging slice. The web also provides a thermal path between the electronic circuit and the base structure. Each slice also includes a mounting bracket that connects the packaging slice to the base structure. Four guide pins protrude from the slice into four corresponding receptacles in an adjacent slice. A locking element, such as a set screw, protrudes into each receptacle and interlocks with the corresponding guide pin. A conduit is formed in the slice to allow electrical connection to the electronic circuit.

Hunter, Don J. (Inventor)

2001-01-01

347

A taxonomy of integral reaction path analysis  

SciTech Connect

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.

Grcar, Joseph F.; Day, Marcus S.; Bell, John B.

2004-12-23

348

Fermionic path integrals and local anomalies  

NASA Astrophysics Data System (ADS)

No doubt, the subject of path integrals proved to be an immensely fruitful human, i.e. Feynman's idea. No wonder it is more timely than ever. Some even claim that it is the most daring, innovative and revolutionary idea since the days of Heisenberg and Bohr. It is thus likely to generate enthusiasm, if not addiction among physicists who seek simplicity together with perfection. Professor Devreese's long-lasting interest in, if not passion on the subject stems from his firm conviction that, beyond being the tool of choice, path integration provides the key to all quantum phenomena, be it in solid state, atomic, molecular or particle physics as evidenced by the impressive list of publications at the address http://lib.ua.ac.be/AB/a867.html. In this note, I review a pitfall of fermionic path integrals and a way to get around it in situations relevant to the Standard Model of particle physics.

Roepstorff, G.

2003-05-01

349

SILK: Scout Paths in the Linux Kernel  

E-print Network

SILK stands for Scout In the Linux Kernel, and is a port of the Scout operating system to run as a Linux kernel module. SILK forms a replacement networking subsystem for standard Linux 2.4 kernels. Linux applications create and use Scout paths via the Linux socket interface with virtually no modifications to the applications themselves. SILK provides Linux applications with the benefits of Scout paths, including early packet demultiplexing, per-flow accounting of resources, and explicit scheduling of network processing. SILK also introduces the concept of an extended path to provide a framework for application QoS. We demonstrate the utility of SILK by showing how it can provide QoS for the Apache Web server.

Andy Bavier; Thiemo Voigt; Mike Wawrzoniak; Larry Peterson; Per Gunningberg

2002-01-01

350

Tornado intensity estimated from damage path dimensions.  

PubMed

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

Elsner, James B; Jagger, Thomas H; Elsner, Ian J

2014-01-01

351

Tornado Intensity Estimated from Damage Path Dimensions  

PubMed Central

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

Elsner, James B.; Jagger, Thomas H.; Elsner, Ian J.

2014-01-01

352

Gas path sealing in turbine engines  

NASA Technical Reports Server (NTRS)

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.

Ludwig, L. P.

1978-01-01

353

Path Factorization Approach to Stochastic Simulations  

NASA Astrophysics Data System (ADS)

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.

Athènes, Manuel; Bulatov, Vasily V.

2014-12-01

354

Priming on the path of least resistance  

E-print Network

PRIMING ON THE PATH OF LEAST RESISTANCE A Thesis by ERIC MICHAEL WRUCK 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 2001 Major... Subject: Psychology PRIMING ON THE PATH OF LEAST RESISTANCE A Thesis by ERIC MICHAEL WRUCK Submitted to Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved as to style and content by...

Wruck, Eric Michael

2001-01-01

355

Gas Path Sealing in Turbine Engines  

NASA Technical Reports Server (NTRS)

A 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 temperature 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.

Ludwig, L. P.

1978-01-01

356

Path planning for everday robotics with SANDROS  

SciTech Connect

We discuss the integration of the SANDROS path planner into a general robot simulation and control package with the inclusion of a fast geometry engine for distance calculations. This creates a single system that allows the path to be computed, simulated, and then executed on the physical robot. The architecture and usage procedures are presented. Also, we present examples of its usage in typical environments found in our organization. The resulting system is as easy to use as the general simulation system (which is in common use here) and is fast enough (example problems are solved in seconds) to be used interactively on an everyday basis.

Watterberg, P.; Xavier, P. [Sandia National Labs., Albuquerque, NM (United States); Hwang, Y. [Korea Inst. of Science and Technology, Seoul (Korea, Republic of)

1997-02-01

357

A high performance magnetorheological valve with a meandering flow path  

NASA Astrophysics Data System (ADS)

The huge developments in the field of magnetorheological (MR) fluid-based devices will have a great influence on the future of mechatronic applications due to the ease of interfacing between electronic controls and the mechanical components that they provide. Among various MR fluid-based devices, an MR valve would be particularly significant for the development of other devices, if it could be successfully achieved. One of the most challenging obstacles to MR valve development is the difficulty of achieving device miniaturization while, at the same time, improving the achievable performance. This study demonstrates a novel design for an MR valve, using the meandering flow path approach in order to increase the effective area so that the MR fluid can be regulated within a small-sized valve. The meandering flow path is formed by combining multiple annular, radial and orifice flow channels. In order to analyze the valve performance, a mathematical model of the proposed MR valve is derived and combined with numerical simulation using the finite element method, with the intention of predicting the achievable pressure drop that can be generated by the valve. The predicted MR valve performances are then experimentally evaluated using an oscillation-disturbed bypass hydraulic cylinder. The simulation results show that the proposed MR valve design could yield substantial pressure drop improvement, which is confirmed by the experiment.

Imaduddin, Fitrian; Amri Mazlan, Saiful; Rahman, Mohd Azizi Abdul; Zamzuri, Hairi; Ubaidillah; Ichwan, Burhanuddin

2014-06-01

358

Radio Wave Path in the Ionosphere Adaptive Ray Tracing Model  

NASA Astrophysics Data System (ADS)

The process of determining the radio wave path in the ionosphere is called ray tracing. Because of the irregularities in the ionosphere the ray paths of HF waves, which are strongly affected by the ionosphere, are calculated for different elevation angles and different frequencies of the radio wave. In HF communication forecasting it is often convenient to use simplified ionosphere models (like CHIU and IRI model) to determine the geographical distribution of ionosphere contents, so the relationship between the electron density and the ionosphere refractive index could be determined. It was seen that for a fixed elevation angle the apogee height decreases as the transmitted frequency became lower. For a different elevation angle values (20, 30 and 40 degree) and transmitted frequency varying from 4 to 18 MHz, there is no difference between the curves which is drown between the altitude (0 to 250 km) and the ground range (0 to 3500 km) because the refraction in all cases occurred in F region only.

Al-Ubaidi, Najat

359

Path-integral treatment of multi-mode vibronic coupling. II. Correlation expansion of class averages  

NASA Astrophysics Data System (ADS)

A path-integral approach to real-time quantum dynamics is presented which is suitable to treat the dynamics of vibronic coupling or spin boson models. In these models the vibrational dynamics is nonseparable as a consequence of the electronic inter-state coupling. The sum over all possible paths in electronic-state space generated by the usual Trotter procedure is expressed in terms of single-mode averages over classes of paths and statistical mode correlations. The averages for classes of a given length can be calculated iteratively from averages over shorter paths. This expansion is formally exact and finite for a finite number of modes. Usually only a limited number of terms has to be evaluated in order to obtain converged results. The scaling of the computational effort with respect to the number of time steps and the number of modes is given by a low-order power law, depending on the chosen class structure and the order of the expansion. The usual time-dependent wave-packet propagation and the full path enumeration, which exhibit an exponential scaling behavior with respect to either the number of modes or the number of time steps, can be considered as opposite limiting cases of the correlation expansion (CE) of the path integral. The convergence of the CE is tested by application to a two-state four-mode model representing S1-S2 vibronic coupling in pyrazine, for which exact references (time-dependent correlation functions) are available. The potential of the CE approximation for the treatment of multi-mode problems is demonstrated by application to an extended 24-mode vibronic-coupling model. This model is suitable to provide a microscopic description of ultrafast optical dephasing processes in large molecules.

Krempl, Stefan; Winterstetter, Manfred; Domcke, Wolfgang

1995-04-01

360

Path Integration in Desert Ants, Cataglyphis fortis  

Microsoft Academic Search

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

Martin Muller; Rudiger Wehner

1988-01-01

361

LONG PATH LASER OZONE MONITOR EVALUATION  

EPA Science Inventory

The purpose of the study reported here was to evaluate a long path laser air pollution monitor developed for the U.S. Environmental Protection Agency (EPA) by the General Electric (GE) Company. The monitor was known as ILAMS (Infrared Laser Atmospheric Monitoring System) and desi...

362

Fusion Development Path Panel Preliminary Report  

E-print Network

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

363

Path integral Monte Carlo applied to vortices  

Microsoft Academic Search

The thermodynamic properties of the vortex lattice in a high-Tc superconductor can be understood by considering a system of bosons in two dimensions. In this picture, the imaginary time world-line of the boson corresponds to the vortex. The vortex lattice melting transition maps to melting the Bose Wigner crystal by means of increasing hbar. We use Path Integral Monte Carlo

Henrik Nordborg; Gianni Blatter

1996-01-01

364

Folded-path optical analysis gas cell  

DOEpatents

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.

Carangelo, Robert M. (Glastonbury, CT); Wright, David D. (Vershire, VT)

1995-01-01

365

The Erratic Path of Hungarian Higher Education  

ERIC Educational Resources Information Center

This article reviews the path of funding higher education in Hungary, where funding cuts have resulted in understaffing, escalating tuition, growing student debt, and declining enrollment. Graduation rates are low, government policies favor vocational disciplines, and the system of preparation and access gives preference to students from wealthier…

Marcus, Jon

2014-01-01

366

Motion on Cycloid Paths: A Project  

ERIC Educational Resources Information Center

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…

Gluck, P.

2010-01-01

367

Virtual path bandwidth allocation in multiuser networks  

Microsoft Academic Search

We consider a multiuser network that is shared by noncooperative users. Each user sets up virtual paths that optimize its own selfish performance measure. This measure accounts for the guaranteed call level quality of service, as well as for the cost incurred for reserving the resource. The interaction among the user strategies is formalized as a noncooperative game. We show

Aurel A. Lazar; Ariel Orda; Dimitrios E. Pendarakis

1997-01-01

368

A shortest path representation for video summarisation  

Microsoft Academic Search

A novel approach is presented to select multiple key frames within an isolated video shot where there is cam- era motion causing significant scene change. This is achieved by determining the dominant motion between frame pairs whose similarities are represented using a di- rected weighted graph. The shortest path in the graph, found using the search algorithm, designates the key

Sarah V. Porter; Majid Mirmehdi; Barry T. Thomas

2003-01-01

369

2006 Spring Issue Page The Critical Path  

E-print Network

2006 Spring Issue Page The Critical Path Kevin McCarthy's (Code 450) 64 Days with FEMA Watching the Fed- eral Emergency Management Agency (FEMA) requested vol- unteers from other federal agencies list a day or two later. After volunteering, I did not hear from FEMA until I received an email on Sept

Christian, Eric

370

Stochastic Evolutionary Algorithms for Planning Robot Paths  

NASA Technical Reports Server (NTRS)

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.

Fink, Wolfgang; Aghazarian, Hrand; Huntsberger, Terrance; Terrile, Richard

2006-01-01

371

Planning Flight Paths of Autonomous Aerobots  

NASA Technical Reports Server (NTRS)

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.

Kulczycki, Eric; Elfes, Alberto; Sharma, Shivanjli

2009-01-01

372

Ambivalent Journey: Teacher Career Paths in Oman  

ERIC Educational Resources Information Center

This study investigated the career paths of 625 university graduates who prepared to be secondary school teachers in Oman, their assessment of their current work situation, and the extent to which their initial commitment to teaching was related to their subsequent career satisfaction and intention to remain in teaching. While nearly all graduates…

Chapman, David W.; Al-Barwani, Thuwayba; Al Mawali, Fathiya; Green, Elizabeth

2012-01-01

373

ELLIPTIC ENUMERATION OF NONINTERSECTING LATTICE PATHS  

E-print Network

ELLIPTIC ENUMERATION OF NONINTERSECTING LATTICE PATHS MICHAEL SCHLOSSER Abstract. We enumerate degenerate cases including Jackson's 8 #7 and Dougall's 7 F6 summation. By considering nonintersecting and Probabilistic Number Theory''). 1 #12; 2 MICHAEL SCHLOSSER We need the following theorem which is a special case

Schlosser, Michael

374

ELLIPTIC ENUMERATION OF NONINTERSECTING LATTICE PATHS  

E-print Network

ELLIPTIC ENUMERATION OF NONINTERSECTING LATTICE PATHS MICHAEL SCHLOSSER Abstract. We enumerate degenerate cases including Jackson's 87 and Dougall's 7F6 summation. By considering nonintersecting lattice Combinatorics and Probabilistic Number Theory"). 1 #12;2 MICHAEL SCHLOSSER We need the following theorem which

Schlosser, Michael

375

Path detection and the uncertainty principle  

Microsoft Academic Search

QUANTUM mechanics predicts that any detector capable of determining the path taken by a particle through a double slit will destroy the interference. This follows from the principle of complementarity formulated by Niels Bohr: simultaneous observation of wave and particle behaviour is prohibited. But such a description makes no reference to the physical mechanism by which the interference is lost.

Pippa Storey; Sze Tan; Matthew Collett; Daniel Walls

1994-01-01

376

Robust constrained shortest path problems under budgeted ...  

E-print Network

2Department of Mechanical, Energy and Management Engineering, University of ... We study the robust constrained shortest path problem under resource uncertainty. ... can readily extend the algorithms presented in this paper to problems that ... such properties are related to the computational complexity and probabilistic ...

2014-09-12

377

Path Integral Method for DNA Denaturation  

E-print Network

The statistical physics of homogeneous DNA is investigated by the imaginary time path integral formalism. The base pair stretchings are described by an ensemble of paths selected through a macroscopic constraint, the fulfillement of the second law of thermodynamics. The number of paths contributing to the partition function strongly increases around and above a specific temperature $T^*_c$ whereas the fraction of unbound base pairs grows continuosly around and above $T^*_c$. The latter is identified with the denaturation temperature. Thus, the separation of the two complementary strands appears as a highly cooperative phenomenon displaying a smooth crossover versus $T$. The thermodynamical properties have been computed in a large temperature range by varying the size of the path ensemble at the lower bound of the range. No significant physical dependence on the system size has been envisaged. The entropy grows continuosly versus $T$ while the specific heat displays a remarkable peak at $T^*_c$. The location of the peak versus $T$ varies with the stiffness of the anharmonic stacking interaction along the strand. The presented results suggest that denaturation in homogeneous DNA has the features of a second order phase transition. The method accounts for the cooperative behavior of a very large number of degrees of freedom while the computation time is kept within a reasonable limit.

Marco Zoli

2009-03-26

378

Efficient Data Mining for Path Traversal Patterns  

Microsoft Academic Search

In this paper, we explore a new data mining capability that involves mining path traversal patterns in a distributed information-providing environment where documents or objects are linked together to facilitate interactive access. Our solution procedure consists of two steps. First, we derive an algorithm to convert the original sequence of log data into a set of maximal forward references. By

Ming-syan Chen; Jong Soo Park; Philip S. Yu

1998-01-01

379

Folded-path optical analysis gas cell  

DOEpatents

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.

Carangelo, R.M.; Wright, D.D.

1995-08-08

380

Asymmetrical Path Interference Test of Light  

E-print Network

The asymmetrical path interference test of light is put forward in the paper. In the test, two different results would arise under the same experimental conditions if light is regarded as wave or particle. Therefore, the test can help us to comprehend which concept, wave or particle, is more essential for micro-particles.

Mei Xiaochun

2006-03-05

381

Adaptable Path Planning in Regionalized Environments  

E-print Network

Adaptable Path Planning in Regionalized Environments Kai-Florian Richter Transregional Collaborative Research Center SFB/TR 8 Spatial Cognition Universit¨at Bremen, Germany richter@sfbtr8.uni planning and execution of the wayfinding task--at least on the large-scale, environmental level [3, 4

Bremen, Universität

382

Soft energy path works for Hawaii  

Microsoft Academic Search

Constrained by small land mass, total dependence on imported oil, and a high cost of living, Hawaii has adopted soft energy paths. Geothermal energy, ocean energy, wind energy, solar energy, and biomass energy play dominant parts. The volcanic origin of the islands makes it unlikely that any oil or natural gas will ever be found there. The volcanic nature of

Crull

2009-01-01

383

Learning to improve path planning performance  

SciTech Connect

In robotics, path planning refers to finding a short. collision-free path from an initial robot configuration to a desired configuratioin. It has to be fast to support real-time task-level robot programming. Unfortunately, current planning techniques are still too slow to be effective, as they often require several minutes, if not hours of computation. To remedy this situation, we present and analyze a learning algorithm that uses past experience to increase future performance. The algorithm relies on an existing path planner to provide solutions to difficult tasks. From these solutions, an evolving sparse network of useful robot configurations is learned to support faster planning. More generally, the algorithm provides a speedup-learning framework in which a slow but capable planner may be improved both cost-wise and capability-wise by a faster but less capable planner coupled with experience. The basic algorithm is suitable for stationary environments, and can be extended to accommodate changing environments with on-demand experience repair and object-attached experience abstraction. To analyze the algorithm, we characterize the situations in which the adaptive planner is useful, provide quantitative bounds to predict its behavior, and confirm our theoretical results with experiments in path planning of manipulators. Our algorithm and analysis are sufficiently, general that they may also be applied to other planning domains in which experience is useful.

Chen, Pang C.

1995-04-01

384

A modified reconfigurable data path processor  

NASA Technical Reports Server (NTRS)

High throughput is an overriding factor dictating system performance. A configurable data processor is presented which can be modified to optimize performance for a wide class of problems. The new processor is specifically designed for arbitrary data path operations and can be dynamically reconfigured.

Ganesh, G.; Whitaker, S.; Maki, G.

1991-01-01

385

Current SPE Hydrodynamic Modeling and Path Forward  

SciTech Connect

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.

Knight, Earl E. [Los Alamos National Laboratory; Rougier, Esteban [Los Alamos National Laboratory

2012-08-14

386

The Path to Disaster The Deepwater Horizon  

E-print Network

21/08/2013 1 The Path to Disaster The Deepwater Horizon BP's disaster in the Gulf of Mexico was not disconnected · The escaping gas ignited · 11 dead · The drilling rig Deepwater Horizon sank after 2 days #12 · They drilled on to get below the pay-zone · An initial plan was produced on April 12th · Feedback

Pym, David J.

387

Modeling DNA Dynamics by Path Integrals  

NASA Astrophysics Data System (ADS)

Complementary strands in DNA double helix show temporary fluctuational openings which are essential to biological functions such as transcription and replication of the genetic information. Such large amplitude fluctuations, known as the breathing of DNA, are generally localized and, microscopically, are due to the breaking of the hydrogen bonds linking the base pairs (bps). I apply imaginary time path integral techniques to a mesoscopic Hamiltonian which accounts for the helicoidal geometry of a short circular DNA molecule. The bps displacements with respect to the ground state are interpreted as time dependent paths whose amplitudes are consistent with the model potential for the hydrogen bonds. The portion of the paths configuration space contributing to the partition function is determined by selecting the ensemble of paths which fulfill the second law of thermodynamics. Computations of the thermodynamics in the denaturation range show the energetic advantage for the equilibrium helicoidal geometry peculiar of B-DNA. I discuss the interplay between twisting of the double helix and anharmonic stacking along the molecule backbone suggesting an interesting relation between intrinsic nonlinear character of the microscopic interactions and molecular topology.

Zoli, Marco

2013-02-01

388

Using path analysis to measure natural selection  

Microsoft Academic Search

We expand current methods for calculating selection coefficients using path analysis and demonstrate how to analyse nonlinear selection. While this incorporation is a straightforward extension of current procedures, the rules for combining these traits to calculate selection coefficients can be complex. We demonstrate our method with an analysis of selection in an experimental population of Arabidopsis thaliana consisting of 289

Scheiner; H. S. CALLAHAN

2000-01-01

389

Path Planning Algorithms for Multiple Heterogeneous Vehicles  

E-print Network

: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 30 viii LIST OF FIGURES FIGURE Page 1 Example solution of PCATSP : : : : : : : : : : : : : : : : : : : : : : 12 2 Example solutions of Hamiltonian path problem : : : : : : : : : : : : 15 3 Edge subset in an infeasible solution... : : : : : : : : : : : : : : : : : : 17 4 "W" set in an infeasible solution : : : : : : : : : : : : : : : : : : : : 17 5 Edges dictating the "W" cut : : : : : : : : : : : : : : : : : : : : : : 18 6 LP feasible solution : : : : : : : : : : : : : : : : : : : : : : : : : : : 20 7 Remove...

Oberlin, Paul V.

2010-01-16

390

Quad-rotor flight path energy optimization  

NASA Astrophysics Data System (ADS)

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.

Kemper, Edward

391

Applications of Path Compression on Balanced Trees  

Microsoft Academic Search

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

Robert Endre Tarjan

1979-01-01

392

SNMP-based Layer3 Path Discovery  

Microsoft Academic Search

This paper presents a process for discovering the layer-3 path between two endpoints in a computernetwork using information available through SNMP in commonly used MIB objects. The pathinformation is useful for analyzing computer networks (e.g., as needed for Avaya Inc.\\

David T. Stott

2002-01-01

393

A surface hopping algorithm for nonadiabatic minimum energy path calculations.  

PubMed

The article introduces a robust algorithm for the computation of minimum energy paths transiting along regions of near-to or degeneracy of adiabatic states. The method facilitates studies of excited state reactivity involving weakly avoided crossings and conical intersections. Based on the analysis of the change in the multiconfigurational wave function the algorithm takes the decision whether the optimization should continue following the same electronic state or switch to a different state. This algorithm helps to overcome convergence difficulties near degeneracies. The implementation in the MOLCAS quantum chemistry package is discussed. To demonstrate the utility of the proposed procedure four examples of application are provided: thymine, asulam, 1,2-dioxetane, and a three-double-bond model of the 11-cis-retinal protonated Schiff base. © 2015 Wiley Periodicals, Inc. PMID:25564760

Schapiro, Igor; Roca-Sanjuán, Daniel; Lindh, Roland; Olivucci, Massimo

2015-02-15

394

Common path point diffraction interferometer using liquid crystal phase shifting  

NASA Technical Reports Server (NTRS)

A common path point diffraction interferometer uses dyed, parallel nematic liquid crystals which surround an optically transparent microsphere. Coherent, collimated and polarized light is focused on the microsphere at a diameter larger than that of the microsphere. A portion of the focused light passes through the microsphere to form a spherical wavefront reference beam and the rest of the light is attenuated by the dyed liquid crystals to form an object beam. The two beams form an interferogram which is imaged by a lens onto an electronic array sensor and into a computer which determines the wavefront of the object beam. The computer phase shifts the interferogram by stepping up an AC voltage applied across the liquid crystals without affecting the reference beam.

Mercer, Carolyn R. (Inventor)

1997-01-01

395

a New Upper Limit on the Electron Antineutrino Rest-Mass  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. The beta-spectrum of ^3H has been measured near the end-point using a Langmuir-Blodgett film of tritated cadmium palmitate as the source. An upper limit of 35 eV at 95% C.L. has been obtained on the mass of the electron anti-neutrino. This thesis describes the preparatory developments of the Oxford neutrino mass experiment and the final measurement of the electron anti-neutrino mass. To measure the beta-spectrum we used a cylindrical mirror analyser (CMA) which has an optical response of ~27 eV FWHM, primarily determined by the exit slit width. The luminosity of the instrument is ~1 times 10 ^{-2} cm^2 . The electrons were pre-accelerated and analysed at a fixed energy of 22.6 keV and to obtain the beta-spectrum near the end-point, the source voltage was varied from -5 KV to -3.5 KV. The electrons were detected by a liquid nitrogen cooled Si(Li) detector with a resolution of ~2 keV. Our background, primarily due to cosmic rays and natural radioactivity, was ~8 cts hr^{ -1} which was the same as the tritium source rate 60 eV below the end-point. The optical response was determined by Monte Carlo calculations and was checked by use of a thin band source of ^{169}Yb at several positions in the source focal plane. Further measurements on the instrument were carried out by an electron gun which included checks on the grid wires. Langmuir-Blodgett (LB) film sources have been manufactured which minimise uncertainties in the energy loss of electrons within the source, associated with uncertainties in thickness. The energy loss through the source was measured with a 100 keV electron microscope. By using dielectric theory the energy loss for 18.6 keV electrons was deduced and the mean free path for 18.6 keV electrons in cadmium palmitate film was found to be 385 A. A tritium run was performed which lasted for ~27 days. The total number of counts in the last 100 eV below the end-point is 690 cts and using the valine molecular final states spectrum, the best fit value for m{2over nu} is -698 +/- 734 eV^2 . The value for the end-point E_0 is 18573 +/- 10 eV which is in agreement with recent determinations. The 95% confidence level limit on m{2overnu} is 1222 eV^2 above the best fit value which corresponds to m_{ |nu} < 35 eV at 95% C.L.

Alizadeh, Ramin

396

Direct multiple path magnetospheric propagation - A fundamental property of nonducted VLF waves  

NASA Technical Reports Server (NTRS)

An elongation of 20-200 ms, attributed to closely spaced multiple propagation paths between the satellite and the ground, is noted in well defined pulses observed by the ISEE 1 satellite in nonducted whistler mode signals from the Siple Station VLF transmitter. Electric field measurements show a 2 to 10 dB amplitude variation in the observed amplitude fading pattern which is also consistent with direct multiple path propagation. The results obtained for two cases, one outside and one inside the plasmapause, establish that the direct signals transmitted from the ground arrive almost simultaneously at any point in the magnetosphere along two or more closely spaced direct ray paths. It is also shown that multiple paths can be explained by assuming field-aligned irregularities, and the implications of these results for nonducted wave-particle interaction in the magnetosphere are discussed. For reasonable parameters of nonducted, multiple path propagation, a cyclotron-resonant electron will experience a wave Doppler broadening of a few tens to a few hundreds of Hz.

Sonwalkar, V. S.; Bell, T. F.; Helliwell, R. A.; Inan, U. S.

1984-01-01

397

Photon path length retrieval from GOSAT observations  

NASA Astrophysics Data System (ADS)

The influence of clouds on the atmospheric radiation budget is investigated, focussing on the photon path length distributions of the scattered sunlight. Apart from the reflection of incoming solar radiation at the cloud top, clouds can also introduce a large number of additional scattering events causing an enhancement of the photon paths. In certain cloud formations, these scattering events also result in a ``ping-pong`` behaviour between different cloud patches and cloud layers. It has been shown from ground based measurements that it is possible to retrieve photon path lengths by analysis of high resolution oxygen A-band spectra (O. Funk et al.). This study uses similar space based measurements of the oxygen A-band for the path length retrieval. The oxygen A-band spectra are retrieved from the Japanese Greenhouse Gases Observing Satellite (GOSAT) which was successfully launched in 2009. The high spectral resolution of the GOSAT TANSO-FTS instrument allows to almost completely resolve the individual absorption lines. The considered spectral range is particularly suitable for this study because it shows clear absorption structures of different strength. From the analysis of the spectral signatures, cloud properties and the underlying path length distributions can be derived. The retrieval is done by analysis and comparison of the extracted TANSO-FTS spectra with simulations from the Monte Carlo radiative transfer Model McArtim. The model permits modelling of altitude dependent oxygen absorption cross sections and three-dimensional cloud patterns. Case studies of clear and cloudy sky scenarios will be presented. Future studies will focus on more complicated cloud structures, especially considering three-dimensional geometries and heterogeneities.

Kremmling, Beke; Penning de Vries, Marloes; Deutschmann, Tim; Wagner, Thomas

2013-04-01

398

Path Finding on High-Dimensional Free Energy Landscapes  

NASA Astrophysics Data System (ADS)

We present a method for determining the average transition path and the free energy along this path in the space of selected collective variables. The formalism is based upon a history-dependent bias along a flexible path variable within the metadynamics framework but with a trivial scaling of the cost with the number of collective variables. Controlling the sampling of the orthogonal modes recovers the average path and the minimum free energy path as the limiting cases. The method is applied to resolve the path and the free energy of a conformational transition in alanine dipeptide.

Díaz Leines, Grisell; Ensing, Bernd

2012-07-01

399

76 FR 17064 - Shared Use Path Accessibility Guidelines  

Federal Register 2010, 2011, 2012, 2013, 2014

...blended transitions, landings, and gutter areas within the shared use path. Grade...the curb at right angles or meets the gutter grade break at right angles. Running...blended transitions, landings, and gutter areas within the shared use path....

2011-03-28

400

14 CFR 171.267 - Glide path automatic monitor system.  

Code of Federal Regulations, 2010 CFR

...DEPARTMENT OF TRANSPORTATION (CONTINUED) NAVIGATIONAL FACILITIES NON-FEDERAL NAVIGATION FACILITIES Interim Standard Microwave Landing System (ISMLS) § 171.267 Glide path automatic monitor system. (a) The ISMLS glide path...

2010-01-01

401

14 CFR 171.267 - Glide path automatic monitor system.  

Code of Federal Regulations, 2014 CFR

... § 171.267 Glide path automatic monitor system. (a) The ISMLS glide path equipment must provide an automatic monitor system that transmits a warning to designated local and remote control points when any of the...

2014-01-01

402

FOLLOWING CARBON'S EVOLUTIONARY PATH: FROM NUCLEOSYNTHESIS TO THE SOLAR SYSTEM  

E-print Network

FOLLOWING CARBON'S EVOLUTIONARY PATH: FROM NUCLEOSYNTHESIS TO THE SOLAR SYSTEM by Stefanie Nicole by Stefanie Nicole Milam entitled Following Carbon's Evolutionary Path: From Nucleosynthesis to the Solar of Doctor of Philosophy _______________________________________________________________________ Date

403

Inquiry-based learning templates for creating online educational paths  

E-print Network

the appropriate websites are collected for inclusion in a path, the path author still faces the challenge of determining how to organize and present the This thesis follows the style of the Journal of the ACM...

Davis, Sarah Alice

2006-10-30

404

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.

405

Sensitivity of ray paths to initial condition  

E-print Network

Using a parabolic equation, we consider ray propagation in a waveguide with the sound speed profile that corresponds to the dynamics of a nonlinear oscillator. An analytical consideration of the dependence of the travel time on the initial conditions is presented. Using an exactly solvable model and the path integral representation of the travel time, we explain the step-like behavior of the travel time (T) as a function of the starting momentum (p_0) (related to the starting ray grazing angle (\\chi_0) by (p_0=\\tan\\chi_0)). A periodic perturbation of the waveguide along the range leads to wave and ray chaos. We explain an inhomogeneity of distribution of the chaotic ray travel times, which has obvious maxima. These maxima lead to the clustering of rays and each maximum relates to a ray identifier, {\\em i.e.} to the number of ray semi--cycles along the ray path.

A. Iomin; G. M. Zaslavsky

2007-06-03

406

Mining Preferred Traversal Paths with HITS  

NASA Astrophysics Data System (ADS)

Web usage mining can discover useful information hidden in web logs data. However, many previous algorithms do not consider the structure of web pages, but regard all web pages with the same importance. This paper utilizes HITS values and PNT preferences as measures to mine users' preferred traversal paths. Wë structure mining uses HITS (hypertext induced topic selection) to rank web pages. PNT (preferred navigation tree) is an algorithm that finds users' preferred navigation paths. This paper introduces the Preferred Navigation Tree with HITS (PNTH) algorithm, which is an extension of PNT. This algorithm uses the concept of PNT and takes into account the relationships among web pages using HITS algorithm. This algorithm is suitable for E-commerce applications such as improving web site design and web server performance.

Yeh, Jieh-Shan; Lin, Ying-Lin; Chen, Yu-Cheng

407

Adaptive path planning for flexible manufacturing  

SciTech Connect

Path planning needs to be fast to facilitate real-time robot programming. Unfortunately, current planning techniques are still too slow to be effective, as they often require several minutes, if not hours of computation. To overcome this difficulty, we present an adaptive algorithm that uses past experience to speed up future performance. It is a learning algorithm suitable for automating flexible manufacturing in incrementally-changing environments. The algorithm allows the robot to adapt to its environment by having two experience manipulation schemes: For minor environmental change, we use an object-attached experience abstraction scheme to increase the flexibility of the learned experience; for major environmental change, we use an on-demand experience repair scheme to retain those experiences that remain valid and useful. Using this algorithm, we can effectively reduce the overall robot planning time by re-using the computation result for one task to plan a path for another.

Chen, Pang C.

1994-08-01

408

Breakdown of the Coherent State Path Integral: Two Simple Examples  

SciTech Connect

We show how the time-continuous coherent state path integral breaks down for both the single-site Bose-Hubbard model and the spin-path integral. Specifically, when the Hamiltonian is quadratic in a generator of the algebra used to construct coherent states, the path integral fails to produce correct results following from an operator approach. As suggested by previous authors, we note that the problems do not arise in the time-discretized version of the path integral.

Wilson, Justin H.; Galitski, Victor [Joint Quantum Institute and Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States)

2011-03-18

409

Path Diversity over the Internet: Performance Analysis and Rate Allocation  

Microsoft Academic Search

Abstract Path diversity works by setting up multiple parallel connections between,the end points using the topological path redundancy of the network. In this paper, Forward Error Correction (FEC) is applied across multiple independent paths to enhance the endto-end reliability. Internet paths are modeled as erasure Gilbert-Elliot channels [1], [2]. First, it is shown that over any erasure channel, Maximum Distance

Shervan Fashandi; Shahab Oveis Gharan; Amir K. Khandani

2007-01-01

410

High brightness electron sources for MeV ultrafast diffraction and microscopy  

NASA Astrophysics Data System (ADS)

In this paper we review the present status of MeV electron sources for ultrafast diffraction and microscopy applications and trace the path forward to improve the spatio-temporal resolution of electron scattering probes.

Musumeci, P.; Li, R. K.

2014-09-01

411

Quantum rings with Rashba spin-orbit coupling: A path-integral approach  

Microsoft Academic Search

We employ a path-integral real-time approach to compute the dc conductance and spin polarization for electrons transported across a ballistic quantum ring with Rashba spin-orbit interaction. We use a piecewise semiclassical approximation for the particle orbital motion and solve the spin dynamics exactly by accounting for both Zeeman coupling and spin-orbit interaction at the same time. Within our approach, we

P. Lucignano; D. Giuliano; A. Tagliacozzo

2007-01-01

412

A long path, low temperature cell.  

PubMed

Design and performance are given of a multiple traversal low temperature absorption cell that operates routinely at a path length of 230 m. The system is comprised of an f/30-aperture White cell surrounded by an aluminum Dewar. The cell has been used in the temperature range 300-77 K and may be pressurized to 3 atm. Vacuum feedthrough adjustments are employed in order to correct for defocusing of the mirrors during the cooling process. PMID:20068970

Blickensderfer, R P; Ewing, G E; Leonard, R

1968-11-01

413

Variational Methods for Path Integral Scattering  

Microsoft Academic Search

In this master thesis, a new approximation scheme to non-relativistic potential scattering is developed and discussed. The starting points are two exact path integral representations of the T-matrix, which permit the application of the Feynman-Jensen variational method. A simple Ansatz for the trial action is made, and, in both cases, the variational procedure singles out a particular one-particle classical equation

Julien Carron; Roland Rosenfelder; PSI Villigen; Jurg Fr; ETH Zurich

2009-01-01

414

Variational Methods for Path Integral Scattering  

Microsoft Academic Search

In this master thesis, a new approximation scheme to non-relativistic potential scattering is developed and discussed. The starting points are two exact path integral representa- tions of the T-matrix, which permit the application of the Feynman-Jensen variational method. A simple Ansatz for the trial action is made, and, in both cases, the varia- tional procedure singles out a particular one-particle

Roland Rosenfelder; PSI Villigen; Jurg Frohlich; ETH Zurich

415

Feyman path integrals in real time  

Microsoft Academic Search

The numerical calculation of Feynman path integrals (F.P.I.) can be performed in real time, i.e. without continuing to imaginary time, at least for quantum mechanical systems with a small number of degrees of freedom. The algorithm stems from the phase space formulation of the F.P.I. and makes intensive use of the Fast Fourier transform to achieve the required efficiency. Scope

Enrico Onofri; Gian Pietro Tecchiolli

1988-01-01

416

Do-It-Yourself Critical Path Method.  

ERIC Educational Resources Information Center

This report describes the critical path method (CPM), a system for planning and scheduling work to get the best time-cost combination for any particular job. With the use of diagrams, the report describes how CPM works on a step-by-step basis. CPM uses a network to show which parts of a job must be done and how they would eventually fit together…

Morris, Edward P., Jr.

417

Local path control for an autonomous vehicle  

Microsoft Academic Search

A control system for an autonomous robot cart designed to operate in well-structured environments such as offices and factories is described. The onboard navigation system comprises a reference-state generator, an error-feedback controller, and cart-location sensing using odometry. There is a convenient separation between the path guidance and control logic. Under normal operating conditions, the controller ensures that the errors between

Winston L. Nelson; Ingeniar J. Cox

1988-01-01

418

Bagging for Path-Based Clustering  

Microsoft Academic Search

Abstract—A resampling,scheme,for clustering with similarity to bootstrap aggregation,(bagging) is presented. Bagging is used to improve,the quality of path- based clustering, a data clustering method that can extract elongated structures from data in a noise robust way. The results of an agglomerative,optimization method,are influenced by small fluctuations of the input data. To increase the reliability of clustering solutions, a stochastic resampling

Bernd Fischer; Joachim M. Buhmann

2003-01-01

419

Free Energy Changes, Fluctuations, and Path Probabilities  

E-print Network

We illustrate some of the static and dynamic relations discovered by Cohen, Crooks, Evans, Jarzynski, Kirkwood, Morriss, Searles, and Zwanzig. These relations link nonequilibrium processes to equilibrium isothermal free energy changes and to dynamical path probabilities. We include ideas suggested by Dellago, Geissler, Oberhofer, and Schoell-Paschinger. Our treatment is intended to be pedagogical, for use in an updated version of our book: Time Reversibility, Computer Simulation, and Chaos. Comments are very welcome.

William G. Hoover; Carol G. Hoover

2011-04-20

420

Scanning path optimization for ultrasound surgery  

NASA Astrophysics Data System (ADS)

One of the problems in ultrasound surgery is the long treatment times when large tumour volumes are sonicated. Large tumours are usually treated by scanning the tumour volume using a sequence of individual focus points. During the scanning, it is possible that surrounding healthy tissue suffers from undesired temperature rise. The selection of the scanning path so that the tumour volume is treated as fast as possible while temperature rise in healthy tissue is minimized would increase the efficiency of ultrasound surgery. The main purpose of this paper is to develop a computationally efficient method which optimizes the scanning path. The optimization algorithm is based on the minimum time formulation of the optimal control theory. The developed algorithm uses quadratic cost criteria to obtain the desired thermal dose in the tumour region. The derived method is evaluated with numerical simulations in 3D which are applied to ultrasound surgery of the breast in simplified geometry. Results from the simulations show that the treatment time as well as the total applied energy can be decreased from 16% to 43% as compared to standard sonication. The robustness of the optimized scanning path is studied by varying the perfusion and absorption in the tumour region.

Malinen, Matti; Huttunen, Tomi; Kaipio, Jari P.; Hynynen, Kullervo

2005-08-01

421

Toroidal path filter for orbital conjunction screening  

NASA Astrophysics Data System (ADS)

For satellite conjunction prediction containing many objects, timely processing can be a concern. Various filters are used to identify orbiting pairs that cannot come close enough over a prescribed time period to be considered hazardous. Such pairings can then be eliminated from further computation to quicken the overall processing time. One such filter is the orbit path filter (also known as the geometric pre-filter), designed to eliminate pairs of objects based on characteristics of orbital motion. The goal of this filter is to eliminate pairings where the distance (geometry) between their orbits remains above some user-defined threshold, irrespective of the actual locations of the satellites along their paths. Rather than using a single distance bound, this work presents a toroid approach, providing a measure of versatility by allowing the user to specify different in-plane and out-of-plane bounds for the path filter. The primary orbit is used to define a focus-centered elliptical ring torus with user-defined thresholds. An assessment is then made to determine if the secondary orbit can touch or penetrate this torus. The method detailed here can be used on coplanar, as well as non-coplanar, orbits.

Alfano, Salvatore

2012-07-01

422

Ray-tracing studies and path-integrated gains of ELF unducted whistler mode waves in the earth's magnetosphere  

NASA Technical Reports Server (NTRS)

Gyroresonance and Landau resonance interactions between unducted low-frequency whistler waves and trapped electrons in the earth's plasmasphere have been studied. Ray paths for waves launched near the plasmapause have been traced. In agreement with recent findings by Thorne et al. (1979), waves have been found which return through the equatorial zone with field-aligned wave normal angles. However, when the growth along the ray path is calculated for such waves, assuming an electron distribution function of the form E exp -n sin exp m alpha, it is found that for all the waves considered, the local growth rate becomes negative before plasmapause reflection, limiting the total gain to small values. Most waves reach zero gain before reflection. This is the result of Landau damping at oblique propagation angles, which necessarily occurs before reflection can take place. It is concluded that the concept of cyclic ray paths does not provide an explanation for the generation of unguided plasmaspheric hiss.

Huang, C. Y.; Goertz, C. K.

1983-01-01

423

Multiple Damage Progression Paths in Model-based Prognostics  

E-print Network

Multiple Damage Progression Paths in Model-based Prognostics Matthew Daigle University, each resulting in their own damage progression path, overlapping to contribute to the overall, in which the problem of charac- terizing multiple damage progression paths is cast as a joint state

Daigle, Matthew

424

ENERGETIC PATH FINDING ACROSS MASSIVE TERRAIN DATA Presented to  

E-print Network

ENERGETIC PATH FINDING ACROSS MASSIVE TERRAIN DATA A Thesis Presented to the Faculty of California;COMMITTEE MEMBERSHIP TITLE: Energetic Path Finding Across Massive Terrain Data AUTHOR: Andrew Tsui DATE: Chris Buckalew, Ph.D. iii #12;Abstract Energetic Path Finding Across Massive Terrain Data Andrew Tsui

Wood, Zoë J.

425

Systematic Upscaling for Feynman Path Integrals A Progress Report  

E-print Network

Systematic Upscaling for Feynman Path Integrals A Progress Report Mark Zlochin and Achi Brandt The Weizmann Institute of Science, Rehovot 76100, Israel November 24, 2005 1 Path Integrals 1.1 The basic setup The path integral approach was introduced by Feynman in his seminal paper (Feynman, 1948). It provides

426

A GA path planner based on domain knowledge for AUV  

Microsoft Academic Search

Autonomous underwater vehicle (AUV) is extensively used for marine engineering, oceanography research and some other civil area. Path planning is a necessary and fundamental technology for AUV autonomy, its goal is to search an optimized path according to some optimization criteria in a certain environment and makes AUV fulfill its mission objectives along the collision-free path. Based on the theory

WANG Hong-jianl; Bian Xin-qian; ZHAO Jiel; Ding Fu-guang; Xia Guo-qing

2004-01-01

427

Extracting optimal paths from roadmaps for motion planning  

Microsoft Academic Search

We present methods for extracting optimal paths from motion planning roadmaps. Our system enables any combination of opti- mization criteria, such as collision detection, kinematic\\/dynamic constraints, or minimum clearance, and relaxed definitions of the goal state, to be used when selecting paths from roadmaps. Our algorithm is an augmented version of Dijkstra's shortest path algorithm which allows edge weights to

Jinsuck Kim; Roger A. Pearce; Nancy M. Amato

2003-01-01

428

Vector Field Path Following for Miniature Air Vehicles  

Microsoft Academic Search

In this paper, a method for accurate path following for miniature air vehicles is developed. The method is based on the notion of vector fields, which are used to generate desired course inputs to inner-loop attitude control laws. Vector field path following control laws are developed for straight-line paths and circular arcs and orbits. Lyapunov stability arguments are used to

Derek R. Nelson; D. Blake Barber; Timothy W. Mclain; Randal W. Beard

2007-01-01

429

Shortest paths synthesis for a car-like robot  

Microsoft Academic Search

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

P. Soueres; J.-P. Laumond

1996-01-01

430

Robot Path Planning in Uncertain Environments: A Language-Measure-  

E-print Network

Robot Path Planning in Uncertain Environments: A Language-Measure- Theoretic Approach Devesh K. Jha the problem of goal-directed robot path planning in the presence of uncertainties that are induced by bounded, probabilistic finite state automata 1 Motivation and Introduction In general, path planning of robots (e

Ray, Asok

431

Integrated Path Planning and ynamic Steering Control for Autonomous Vehicles  

Microsoft Academic Search

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'.

Bruce P. I. Krogh; Charles E. Thorpe

1986-01-01

432

Integrated path planning and dynamic steering control for autonomous vehicles  

Microsoft Academic Search

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.

B. Krogh; C. Thorpe

1986-01-01

433

Stable periodic billiard paths in obtuse isosceles triangles  

E-print Network

Stable periodic billiard paths in obtuse isosceles triangles W. Patrick Hooper March 27, 2006 Can you place a small billiard ball on a frictionless triangular pool table and hit it so that it comes dynamics s of a periodic billiard path is the bi-infinite sequence of edges the billiard path hits, which

Hooper, Patrick

434

Stable periodic billiard paths in obtuse isosceles triangles  

E-print Network

Stable periodic billiard paths in obtuse isosceles triangles W. Patrick Hooper March 27, 2006 Can you place a small billiard ball on a frictionless triangular pool table and hit it so that it comes dynamics s # of a periodic billiard path # is the bi­infinite sequence of edges the billiard path hits

Hooper, Patrick

435

Unstructured path problems and the making of semirings  

Microsoft Academic Search

The solution of the algebraic path problem, for instance with the algorithm by Floyd and Warshall, is part of the classical repertoire on algorithms. This solution presupposes that path costs are computed in a closed semiring or a similar algebraic structure. The associativity and distributivity laws in such algebraic structures exclude many possible path costs. In the seventies, several authors

T. Lengauer; D. Theune

436

Multiple-Goals Path Planning for Coordinate Measuring Machines  

Microsoft Academic Search

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

Steven N. Spitz; Aristides A. G. Requicha

2000-01-01

437

Spare Capacity Assignment in Telecom Networks using Path Restoration*  

E-print Network

Spare Capacity Assignment in Telecom Networks using Path Restoration* Jeyakesavan Veerasamy and S.C.Sha h Alcatel Network Systems, 1225 N. Alma Road Richardson, TX 75081 Abstract Path restoration scheme to achieve a desired level of protection against link failures. Path restoration planning cor- responds

Venkatesan, S.

438

Snell's law and light traveling along the shortest path  

Microsoft Academic Search

the problem to be analyzed follows: Given a starting point s, an ending point t and a set of n Weighted Faces (or regions) in a 2-dimensional space, find the best path from s to t, where the length of the path is defined as the weighted sum of the Euclidean length of the sub paths inside each region. Let

Carlos Lara

2006-01-01

439

Preferential flow paths: biological ‘hot spots’ in soils  

Microsoft Academic Search

Preferential flow of water in soils is a common phenomenon. Our objective was to investigate whether preferential flow paths have higher microbial biomass and different microbial community structures than the rest of the soil. We stained the preferential flow paths in a forest soil with a food dye and sampled soil material from preferential flow paths and from the soil

M. Bundt; F. Widmer; M. Pesaro; J. Zeyer; P. Blaser

2001-01-01

440

NC machine tool path generation from CSG part  

E-print Network

NC machine tool path generation from CSG part representations James E Bobrow Recent improvements for machine tool path generation. Current machining algorithms require that any port geometric information of numerically controlled (NC) machine tool paths. In this paper, we discuss the widely used APT 1

Bobrow, James E.

441

A Note On Minimum Path Bases Petra M. Gleissa  

E-print Network

A Note On Minimum Path Bases Petra M. Gleissa , Josef Leydoldb , Peter F. Stadlera,c a Institute that there exist two vertices x and y in C, not necessarily distinct, and two paths D1 and #12;Minimum Path Bases of Graphs 3 D2 from u to x and from v to y, respectively, such that D1

Stadler, Peter F.

442

EQUILIBRIUM PATHS OF MECHANICAL SYSTEMS WITH UNILATERAL CONSTRAINTS  

E-print Network

EQUILIBRIUM PATHS OF MECHANICAL SYSTEMS WITH UNILATERAL CONSTRAINTS PART II: DEPLOYABLE REFLECTOR M, by imple- menting the theory for tracing the equilibrium path of a mechanical system with unilateral had not been previously explained, is the existence of a corner limit point on the equilibrium path

Pellegrino, Sergio

443

Module for Business, Management, and Technology Career Path.  

ERIC Educational Resources Information Center

Designed for use with secondary students who have explored career paths and wish to pursue a career in business, management, and technology (BM&T), this module focuses on providing work-based learning experiences. Introductory materials include the following: career paths rationale and philosophy, benefits of using career paths, information on…

Broeker, Arlene M.

444

Discrete Approximation to Continuous Anisotropic Shortest-Path Problem  

E-print Network

-path (CSP) problem in 3D. · Incorporates ellipsoid model of radar cross sections of UAVs. Carlyle, Royset-Risk Path Planning for Groups of UAVs James Riehl João Hespanha INFORMS Meeting November 6, 2007 #12;start + #12;Minimum-Risk Path Planning for Groups of UAVs ( , )x v xi xf · Heterogeneous group of M UAVs · K

Hespanha, João Pedro

445

Patterns of technological learning among the strategic groups in the Korean Electronic Parts Industry  

Microsoft Academic Search

This study attempts to explore the patterns of technological learning among different strategic groups in the Korean Electronic Parts Industry. Three different evolution paths are identified based on a dynamic strategic group analysis of 115 small and medium-sized enterprises (SMEs) in the Korean Electronic Parts Industry for the period of 1990–1995. The first path indicates the evolution from a subcontractor

Youngbae Kim; Byungheon Lee

2002-01-01

446

Generic Equations for Constructing Smooth Paths Along Circles and Tangent Lines With Application to Airport Ground Paths  

NASA Technical Reports Server (NTRS)

The primary purpose of this publication is to develop a mathematical model to describe smooth paths along any combination of circles and tangent lines. Two consecutive circles in a path are either tangent (externally or internally) or they appear on the same (lateral) or opposite (transverse) sides of a connecting tangent line. A path may start or end on either a segment or circle. The approach is to use mathematics common to robotics to design the path as a multilink manipulator. This approach allows a hierarchical view of the problem and keeps the notation manageable. A user simply specifies a few parameters to configure a path. Necessary and sufficient conditions automatically ensure the consistency of the inputs for a smooth path. Two example runway exit paths are given, and an angle to go assists in knowing when to switch from one path element to the next.

Barker, L. Keith

1998-01-01

447

Controlling unboundedness in the gravitational path integral  

NASA Astrophysics Data System (ADS)

New results are presented on the Euclidean path-integral formulation for the partition function and density of states pertinent to spherically symmetric black-hole systems in thermodynamic equilibrium. We extend the path-integral construction of Halliwell and Louko which has already been used by one of us (Louko and Whiting), and investigate further a lack of uniqueness in our previous formulation of the microcanonical density of states and in the canonical partition function. In that work, the method chosen for removing the ambiguity resulted in two specific path-integral contours having finite extent. Physically motivated criteria exercised a dominant influence on that choice, as did the need to overcome the unboundedness from below of the gravitational action. The new results presented here satisfy the same physical criteria, but differ in ways which are physically significant. The unboundedness is not now eliminated directly but, for positive temperatures only, it is dealt with by what may be viewed as the introduction of an effective measure, which nevertheless may be of exponential order. Having chosen to investigate alternative contours which, in fact, have infinite extent, we find that imposing the Wheeler-DeWitt equation automatically selects out particular finite end points for the contours, at which the singularity in the action is canceled. A further important outcome of this work is the emergence of a variational principle for the black hole entropy, which has already proved useful at the level of a zero-loop approximation to the coupling of a shell of quantum matter in equilibrium around a Schwarzschild black hole (Horwitz and Whiting). In the course of enquiring into the nature of the variables in which the path integral is constructed and evaluated, we were able to see how to give a unifying description of several previous results in the literature. A concise review of these separate approaches forms an integral part of our new synthesis, relating their various underlying ideas on Hamilton-Jacobi theory and Hamiltonian reduction in the context of path integration. The new insight we gain finally helps motivate the choice of the integration variables, identification of which has played an important role in our whole analysis.

Melmed, Jeffrey; Whiting, Bernard F.

1994-01-01

448

ammonia would react directly with com-pounds 4a and 4b, and a dissociative path D,  

E-print Network

ammonia would react directly with com- pounds 4a and 4b, and a dissociative path D, in which ammonia would react with a 14- electron complex formed after dissociation of olefin (Scheme 5). The rates and ratios of ammonia to olefin (data and plot are shown in figs. S1 and S2 and table S1). The observable

Collins, Steven H.

449

504 IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL. 50, NO. 3, AUGUST 2008 Path Loss From a Transmitter Inside an Aircraft  

E-print Network

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

Ellingson, Steven W.

450

Dynamic micromagnetic field measurement by stroboscopic electron beam tomography  

Microsoft Academic Search

A stroboscopic electron beam tomography system for measuring the dynamic micromagnetic field of recording heads is presented. A pulsed electron beam, which is synchronized with the recording head driver, is scanned along the recording head surface from all directions. Integration of the magnetic field intensity along the beam path is calculated from the electron beam deflection angle. Intensity distributions of

H. Shinada; S. Fukuhara; S. Seitou; H. Todokoro; S. Otomo; H. Takano; K. Shiiki

1992-01-01

451

On the Feynman Path Integral for Nonrelativistic Quantum Electrodynamics  

NASA Astrophysics Data System (ADS)

The Feynman path integral for regularized nonrelativistic quantum electrodynamics is studied rigorously. We begin with the Lagrangian function of the corresponding classical mechanics and construct the Feynman path integral. In the present paper, the electromagnetic potentials are assumed to be periodic with respect to a large box and quantized through their Fourier coefficients with large wave numbers cut off. Firstly, the Feynman path integral with respect to paths on the space of particles and vector potentials is defined rigorously by means of broken line paths under the constraints. Secondly, the Feynman path integral with respect to paths on the space of particles and electromagnetic potentials is also defined rigorously by means of broken line paths and piecewise constant paths without the constraints. This Feynman path integral is stated heuristically in Feynman and Hibbs' book. Thirdly, the vacuum and the state of photons of given momenta and polarizations are expressed concretely as functions of variables consisting of the Fourier coefficients of vector potentials. It is also proved rigorously in terms of distribution theory that the Coulomb potentials between charged particles naturally appear in the above Feynman path integral approach. This shows that the photons give rise to the Coulomb force.

Ichinose, Wataru

452

Vulnerability of complex networks under path-based attacks  

NASA Astrophysics Data System (ADS)

We investigate vulnerability of complex networks including model networks and real-world networks subject to path-based attacks. Specifically, we remove approximately the longest simple path from a network iteratively until there are no paths left in the network. We propose two algorithms, the random augmenting approach (RPA) and the Hamilton-path based approach (HPA), for finding the approximately longest simple path in a network. Results demonstrate that steps of longest-path attacks increase with network density linearly for random networks, while exponentially increasing for scale-free networks. The more homogeneous the degree distribution is, the more fragile the network, which is different from the previous results of node or edge attacks. HPA is generally more efficient than RPA in the longest-path attacks of complex networks. These findings further help us understand the vulnerability of complex systems, better protect complex systems, and design more tolerant complex systems.

Pu, Cun-Lai; Cui, Wei

2015-02-01

453

Simulated final approach path captures using the microwave landing system  

NASA Technical Reports Server (NTRS)

Computer simulation results are presented for intercepting final approach paths using various Microwave Landing System (MLS) path capture concepts. This study, conducted under the Advanced Transport Operating System (ATOPS) program, simulated these captures using the MD-80 aircraft as the study model. Several different capture concepts were investigated. Systems that could be retrofitted into existing aircraft with minimum hardware and software changes were considered. An enhanced ILS look-alike capture provided improved tracking performance over conventional ILS without using a full-up path computer. The other concepts used waypoint databases and path computers to provide smart captures. These captures included lateral path intercepts as well as vertical path control. Winds, turbulence, and MLS noise were included in the simulation. In all cases, acceptable tracking errors were obtained during transition to the final approach path.

Feather, J. B.

1988-01-01

454

Auditory Perception of Motor Vehicle Travel Paths  

PubMed Central

Objective These experiments address concerns that motor vehicles in electric engine mode are so quiet that they pose a risk to pedestrians, especially those with visual impairments. Background The “quiet car” issue has focused on hybrid and electric vehicles, although it also applies to internal combustion engine vehicles. Previous research has focused on detectability of vehicles, mostly in quiet settings. Instead, we focused on the functional ability to perceive vehicle motion paths. Method Participants judged whether simulated vehicles were traveling straight or turning, with emphasis on the impact of background traffic sound. Results In quiet, listeners made the straight-or-turn judgment soon enough in the vehicle’s path to be useful for deciding whether to start crossing the street. This judgment is based largely on sound level cues rather than the spatial direction of the vehicle. With even moderate background traffic sound, the ability to tell straight from turn paths is severely compromised. The signal-to-noise ratio needed for the straight-or-turn judgment is much higher than that needed to detect a vehicle. Conclusion Although a requirement for a minimum vehicle sound level might enhance detection of vehicles in quiet settings, it is unlikely that this requirement would contribute to pedestrian awareness of vehicle movements in typical traffic settings with many vehicles present. Application The findings are relevant to deliberations by government agencies and automobile manufacturers about standards for minimum automobile sounds and, more generally, for solutions to pedestrians’ needs for information about traffic, especially for pedestrians with sensory impairments. PMID:22768645

Ashmead, Daniel H.; Grantham, D. Wesley; Maloff, Erin S.; Hornsby, Benjamin; Nakamura, Takabun; Davis, Timothy J.; Pampel, Faith; Rushing, Erin G.

2012-01-01

455

Automated generation of weld path trajectories.  

SciTech Connect

AUTOmated GENeration of Control Programs for Robotic Welding of Ship Structure (AUTOGEN) is software that automates the planning and compiling of control programs for robotic welding of ship structure. The software works by evaluating computer representations of the ship design and the manufacturing plan. Based on this evaluation, AUTOGEN internally identifies and appropriately characterizes each weld. Then it constructs the robot motions necessary to accomplish the welds and determines for each the correct assignment of process control values. AUTOGEN generates these robot control programs completely without manual intervention or edits except to correct wrong or missing input data. Most ship structure assemblies are unique or at best manufactured only a few times. Accordingly, the high cost inherent in all previous methods of preparing complex control programs has made robot welding of ship structures economically unattractive to the U.S. shipbuilding industry. AUTOGEN eliminates the cost of creating robot control programs. With programming costs eliminated, capitalization of robots to weld ship structures becomes economically viable. Robot welding of ship structures will result in reduced ship costs, uniform product quality, and enhanced worker safety. Sandia National Laboratories and Northrop Grumman Ship Systems worked with the National Shipbuilding Research Program to develop a means of automated path and process generation for robotic welding. This effort resulted in the AUTOGEN program, which has successfully demonstrated automated path generation and robot control. Although the current implementation of AUTOGEN is optimized for welding applications, the path and process planning capability has applicability to a number of industrial applications, including painting, riveting, and adhesive delivery.

Sizemore, John M. (Northrop Grumman Ship Systems); Hinman-Sweeney, Elaine Marie; Ames, Arlo Leroy

2003-06-01

456

Non-Born-Oppenheimer quantum chemistry on the fly with continuous path branching due to nonadiabatic and intense optical interactions.  

PubMed

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 coupling and/or optical interactions. Such branching paths are determined consistently with the motion of the electron wavepackets. Furthermore, these nuclear paths are quantized in terms of Gaussian wavepackets (action decomposed function), which can be applied to nonclassical paths. Both electronic wavepacket dynamics and quantization of non-Born-Oppenheimer paths are generalized so as to include the direct effects of the classical vector potential of electromagnetic fields. In the second half of this paper, we perform numerical studies to explore nonadiabatic dynamics in a laser field by examining two cases: one is a two-state model system having an avoided crossing, and the other is two-state dynamics in HF molecule on the two low lying ab initio potential curves. Both are placed in laser fields. With the former system, we survey some basic properties of the coupling of nonadiabatic dynamics and laser interaction varying the relevant coupling parameters such as the laser timing with respect to the incident of nonadiabatic transition. This investigation will set a foundation for the future studies of control of electronic states in realistic multidimensional molecular systems. Application to the latter system shows that non-Born-Oppenheimer quantum chemistry in laser fields is indeed useful in the study of dynamics in ab initio level. Through the comparison with full quantum data, we verify that the formalism and methodology developed here work accurately. Furthermore, we attain some basic insight about the characteristics of molecules in laser fields. PMID:20590176

Yonehara, Takehiro; Takatsuka, Kazuo

2010-06-28

457

Multiscale electronic transport in Li(1+x)Ni(1/3-u)Co(1/3-v)Mn(1/3-w)O2: a broadband dielectric study from 40 Hz to 10 GHz.  

PubMed

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

Seid, K A; Badot, J C; Dubrunfaut, O; Caldes, M T; Stephant, N; Gautier, L; Guyomard, D; Lestriez, B

2013-12-01

458

Path integral quantization of generalized quantum electrodynamics  

SciTech Connect

In this paper, a complete covariant quantization of generalized electrodynamics is shown through the path integral approach. To this goal, we first studied the Hamiltonian structure of the system following Dirac's methodology and, then, we followed the Faddeev-Senjanovic procedure to obtain the transition amplitude. The complete propagators (Schwinger-Dyson-Fradkin equations) of the correct gauge fixation and the generalized Ward-Fradkin-Takahashi identities are also obtained. Afterwards, an explicit calculation of one-loop approximations of all Green's functions and a discussion about the obtained results are presented.

Bufalo, R.; Pimentel, B. M.; Zambrano, G. E. R. [Instituto de Fisica Teorica (IFT), UNESP-Sao Paulo State University, Rua Doutor Bento Teobaldo Ferraz 271, Bloco II, Barra Funda CEP 01140-070, Sao Paulo, Sao Paulo (Brazil); Departamento de Fisica, Universidad de Narino, Calle 18 Cuadra 50, San Juan de Pasto, Narino (Colombia)

2011-02-15

459

An expert path through a thermo maze  

NSDL National Science Digital Library

Several studies in recent years have demonstrated that upper-division students struggle with partial derivatives and the complicated chain rules ubiquitous in thermodynamics. We asked several experts (primarily faculty who teach thermodynamics) to solve a challenging and novel thermodynamics problem in order to understand how they navigate through this maze. What we found was a tremendous variety in solution strategies and sense-making tools, both within and between individuals. This case study focuses on one particular expert: his solution paths, use of sense-making tools, and comparison of different approaches.

Kustusch, Mary B.; Roundy, David J.; Dray, Tevian; Manogue, Corinne

2014-02-01

460

The Path to Magnetic Fusion Energy  

SciTech Connect

When the possibility of fusion as an energy source for electricity generation was realized in the 1950s, understanding of the plasma state was primitive. The fusion goal has been paced by, and has stimulated, the development of plasma physics. Our understanding of complex, nonlinear processes in plasmas is now mature. We can routinely produce and manipulate 100 million degree plasmas with remarkable finesse, and we can identify a path to commercial fusion power. The international experiment, ITER, will create a burning (self-sustained) plasma and produce 500 MW of thermal fusion power. This talk will summarize the progress in fusion research to date, and the remaining steps to fusion power.

Prager, Stewart (PPPL) [PPPL

2011-05-04

461

Predicting link directions using local directed path  

NASA Astrophysics Data System (ADS)

Link prediction in directed network is attracting growing interest among many network scientists. Compared with predicting the existence of a link, determining its direction is more complicated. In this paper, we propose an efficient solution named Local Directed Path to predict link direction. By adding an extra ground node to the network, we solve the information loss problem in sparse network, which makes our method effective and robust. As a quasi-local method, our method can deal with large-scale networks in a reasonable time. Empirical analysis on real networks shows that our method can correctly predict link directions, which outperforms some local and global methods.

Wang, Xiaojie; Zhang, Xue; Zhao, Chengli; Xie, Zheng; Zhang, Shengjun; Yi, Dongyun

2015-02-01

462

Time optimal paths and acceleration lines of robotic manipulators  

NASA Technical Reports Server (NTRS)

The concept of acceleration lines and their correlation with time-optimal paths of robotic manipulators is presented. The acceleration lines represent the directions of maximum tip acceleration from a point in the manipulator work-space, starting at a zero velocity. These lines can suggest the number and shapes of time-optimal paths for a class of manipulators. It is shown that nonsingular time-optimal paths are tangent to one of the acceleration lines near the end-points. A procedure for obtaining near-optimal paths, utilizing the acceleration lines, is developed. These paths are obtained by connecting the end-points with B splines tangent to the acceleration lines. The near-minimum paths are shown to yield better traveling times than the straight-line path between the same end-points. The near-minimum paths can be used as initial conditions in existing optimization methods to speed-up convergence and computation time. This method can be used for online robot path planning and for interactive designs of robotic-cell layouts. Examples of time-optimal paths of a two-link manipulator, obtained by other optimization procedures and their acceleration lines, are shown.

Shiller, Zvi; Dubowsky, Steven

1987-01-01

463

AUV path planning: an A* approach to path planning with consideration of variable vehicle speeds and multiple, overlapping, time-dependent exclusion zones  

Microsoft Academic Search

The authors describe an implementation of a path planner suitable for an autonomous underwater vehicle (AUV). The path planning unit is capable of maintaining a quadtree database of depth information, obstacles, and exclusion zones: verifying a previously planned path; generating a new path between successive goal points; and generating a path to the nearest point of a safe region. If

K. P. Carroll; S. R. McClaran; E. L. Nelson; D. M. Barnett; D. K. Friesen; G. N. William

1992-01-01

464

Vibration Analysis of a Split Path Gearbox  

NASA Technical Reports Server (NTRS)

Split path gearboxes can be attractive alternatives to the common planetary designs for rotorcraft, but because they have seen little use, they are relatively high risk designs. To help reduce the risk of fielding a rotorcraft with a split path gearbox, the vibration and dynamic characteristics of such a gearbox were studied. A mathematical model was developed by using the Lagrangian method, and it was applied to study the effect of three design variables on the natural frequencies and vibration energy of the gearbox. The first design variable, shaft angle, had little influence on the natural frequencies. The second variable, mesh phasing, had a strong effect on the levels of vibration energy, with phase angles of 0 deg and 180 deg producing low vibration levels. The third design variable, the stiffness of the shafts connecting the spur gears to the helical pinions, strongly influenced the natural frequencies of some of the vibration modes, including two of the dominant modes. We found that, to achieve the lowest level of vibration energy, the natural frequencies of these two dominant modes should be less than those of the main excitation sources.

Krantz, Timothy L.; Rashidi, Majid

1995-01-01