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1

Ionization By Impact Electrons in Solids: Electron Mean Free Path Fitted Over A Wide Energy Range  

SciTech Connect

We propose a simple formula for fitting the electron mean free paths in solids both at high and at low electron energies. The free-electron-gas approximation used for predicting electron mean free paths is no longer valid at low energies (E < 50 eV), as the band structure effects become significant at those energies. Therefore we include the results of the band structure calculations in our fit. Finally, we apply the fit to 9 elements and 2 compounds.

Ziaja, B; London, R A; Hajdu, J

2005-06-09

2

Spin-resolved inelastic mean free path of slow electrons in Fe.  

PubMed

The spin-dependent reflectivity of slow electrons from ultrathin Fe films on W(110) has been measured with spin polarized low energy electron microscopy. From the amplitude of the quantum size oscillations observed in the reflectivity curves the spin-dependent inelastic mean free path (IMFP) of electrons in Fe has been determined in the energy range from 5 to 16 eV above the vacuum level. The resulting IMFP values for the spin-up electrons are clearly larger than those for the spin-down electrons and the difference between the two values decreases with increasing electron energy in agreement with theoretical predictions. PMID:23765334

Zdyb, R; Bauer, E

2013-07-10

3

Angular distribution of elastic electron backscattering from surfaces: determination of the electron inelastic mean free path  

NASA Astrophysics Data System (ADS)

The development of analytical techniques based on measurements of electron elastic-backscattering probabilities stimulated an interest in the theoretical description of such phenomena. The most accurate and reliable theoretical models involve Monte Carlo (MC) simulations of electron trajectories in solids; however, this approach generally requires considerable computer effort. It has been shown that the performance of a modified analytical theory originally proposed by Oswald et al (1993 J. Electron Spectrosc. Relat. Phenom. 61 251), designated with the acronym OKGM, compares reasonably well with MC calculations. The MC data are usually underestimated by the OKGM model, and the mean percentage deviation, averaged over nine elements and five energies up to 5 keV, is equal to 8.8% for typical experimental configurations. However, the agreement between ratios of backscattering probabilities from MC simulations and the OKGM model agree much better due to the fact that underestimation of backscattering probability by the OMGM theory is partially cancelled. The percentage deviation between ratios from these theoretical models decreases to 3.14%. The OKGM model should then be useful for determining inelastic mean free paths (IMFPs) from measured elastic-peak intensities. The accuracy of the obtained IMFPs is comparable with IMFPs from MC simulations.

Jablonski, A.

2014-02-01

4

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

NASA Astrophysics Data System (ADS)

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

2013-11-01

5

Determination of the inelastic mean free path of electrons in polythiophenes using elastic peak electron spectroscopy method  

Microsoft Academic Search

The inelastic mean free path (IMFP) is an important parameter for quantitative surface characterisation by Auger electron spectroscopy, X-ray photoelectron spectroscopy or electron energy loss spectroscopy. An extensive database of the IMFPs for selected elements, inorganic and organic compounds has been recently published by Powell and Jablonski. As it follows from this compilation, the published material on IMFPs for conductive

B. Lesiak; A. Kosinski; A. Jablonski; L. Kövér; J. Tóth; D. Varga; I. Cserny; M. Zagorska; I. Kulszewicz-Bajer; G. Gergely

2001-01-01

6

Experimental determination of the mean free path of screened edge magnetoplasmons in a two-dimensional electron gas  

Microsoft Academic Search

Magnetic oscillations of the photovoltage in a two-dimensional electron system with the back gate, exposed to microwave radiation,\\u000a are studied. The oscillations result from the interference of screened edge magnetoplasmons (EMPs). The mean free path of\\u000a the EMPs is quantitatively determined by analyzing the dependence of the oscillation amplitude on the electron density. The\\u000a dependences of the mean free path

V. M. Muravev; I. V. Andreev; I. V. Kukushkin; J. H. Smet; K. von Klitzing

2008-01-01

7

Inelastic interactions of low-energy electrons with organic solids: simple formulae for mean free paths and stopping powers  

SciTech Connect

A theoretical description of the inelastic interactions of low-energy electrons (E less than or equal to 10 keV) with solid organic insulators is presented. The response of the valence electrons to energy and momentum transfers is inferred from a model for the energy-loss function with parameters fixed by optical data. With this model energy-loss function, inverse mean free path and stopping power due to interactions with the valence electrons are calculated for several organic solids. Contributions to the inverse mean free path and stopping power due to K-shell ionization in carbon, nitrogen, and oxygen are obtained from theoretical atomic generalized oscillator strengths. Simple, analytical formulae are deduced which allow predictions of mean free paths and stopping powers for electrons in the energy range 100 eV less than or equal to E less than or equal to 10 keV to be made for a large group of organic solids.

Ashley, J.C.

1980-12-01

8

Determination of the inelastic mean free path of electrons in polythiophenes using elastic peak electron spectroscopy method  

NASA Astrophysics Data System (ADS)

The inelastic mean free path (IMFP) is an important parameter for quantitative surface characterisation by Auger electron spectroscopy, X-ray photoelectron spectroscopy or electron energy loss spectroscopy. An extensive database of the IMFPs for selected elements, inorganic and organic compounds has been recently published by Powell and Jablonski. As it follows from this compilation, the published material on IMFPs for conductive polymers is very limited. Selected polymers, such as polyacetylenes and polyanilines, have been investigated only recently. The present study is a continuation of the research on IMFPs determination in conductive polymers using the elastic peak electron spectroscopy (EPES) method. In the present study three polythiophene samples have been studied using high energy resolution spectrometer and two standards: Ni and Ag. The resulting experimental IMFPs are compared to the respective IMFP values determined using the predictive formulae proposed by Tanuma and Powell (TPP-2M) and by Gries (G1), showing a good agreement. The scatter between the experimental and predicted IMFPs in polythiophenes is evaluated. The statistical and systematic errors, their sources and the possible contributions to the systematic error due to influence of the accuracy of the input parameters, such as the surface composition and density, on the IMFPs derived from the experiments and Monte Carlo calculations, are extensively discussed.

Lesiak, B.; Kosinski, A.; Jablonski, A.; Kövér, L.; Tóth, J.; Varga, D.; Cserny, I.; Zagorska, M.; Kulszewicz-Bajer, I.; Gergely, G.

2001-04-01

9

Inelastic mean-free paths and surface excitation parameters by absolute reflection electron-energy loss measurements  

SciTech Connect

An analytical approach is proposed for simultaneously determining the inelastic mean-free path (IMFP), the surface excitation parameter (SEP), and the differential SEP (DSEP) in absolute units from an absolute reflection electron energy loss spectroscopy (REELS) spectrum under the assumption that the normalized differential inelastic mean-free path for bulk excitations and the elastic scattering cross section are known. This approach was applied to an analysis of REELS spectra for Ni, and the IMFP, SEP, and DSEP in Ni for 300-3000 eV electrons were determined. The resulting IMFPs showed good agreement with those calculated using the TPP-2M predictive equations and with those calculated from optical data. The deduced DSEPs show a reasonable agreement with those theoretically predicted. The obtained SEPs were compared with those calculated using several predictive equations. The present SEP results agreed well with the Chen formula with a material parameter proposed for Ni. The present approach has high potential for the experimental determination of IMFPs, SEPs, and DSEPs in absolute units.

Nagatomi, T. [Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); Goto, K. [National Institute of Advanced Industrial Science and Technology (AIST) Chubu, Moriyama-ku, Nagoya, Aichi 463-8560 (Japan)

2007-06-15

10

Determination of the inelastic mean free path of electrons in GaAs and InP after surface cleaning by ion bombardment using elastic peak electron spectroscopy  

Microsoft Academic Search

The inelastic mean free path (IMFP) of electrons is an important material parameter needed for quantitative AES, EELS and non-destructive depth profiling. The distinction between the terms for IMFP and the attenuation length (AL) has been established by ASTM standards. A practical experimental method for determining values of the IMFP is elastic peak electron spectroscopy (EPES). In this method, experimentally

L. Zommer; B. Lesiak; A. Jablonski; G. Gergely; M. Menyhard; A. Sulyok; S. Gurban

1998-01-01

11

Electron inelastic mean free paths in biological matter based on dielectric theory and local-field corrections  

NASA Astrophysics Data System (ADS)

The inelastic mean free path (IMFP) of electrons with energies up to a few keV is calculated from the dielectric electron-gas theory for densities corresponding to those of biological matter. The effect of the many-body local-field correction on the Lindhard dielectric response function is examined using some of the available analytical approximations to its static limit. We have tested the performance of several Hubbard-type local-field corrections along with the formula proposed by Corradini and co-workers [M. Corradini, R. Del Sole, G. Onida, M. Palumno, Phys. Rev. B 57 (1998) 14569] which is extensively used in connection with the exchange-correlation kernel of time-dependent density functional theory. It is shown that the Lindhard dielectric function provides reasonable estimates of electron IMFPs below about 50 eV, where the majority of semi-empirical dielectric calculations based on the extended-optical-data methodology fail. The use of LFC results in a sizeable reduction of the IMFP which, at low energies, may reach ˜20%.

Emfietzoglou, D.; Kyriakou, I.; Abril, I.; Garcia-Molina, R.; Petsalakis, I. D.; Nikjoo, H.; Pathak, A.

2009-01-01

12

Mean free paths of charge carriers in CZT crystal  

NASA Astrophysics Data System (ADS)

The asymmetrical distortion of the Cadmium Zinc Telluride ((CZT) energy spectrum is mainly caused by the hole trapping in the CZT crystal, and it can be characterized by the mean free path of hole. The mean free paths of the charge carriers in the CZT crystal can be extracted from fitting the peak shape of the measured energy spectrum. The energy spectra of ?-rays from 241Am, and that of ? particles from 238Pu were measured with a CZT with 5×5×5 mm 3. The mean free path of the electron was determined from the bias dependence of ?-particle response. The energy spectra of ?-ray were simulated with EGSnrc code, in which Hecht equation was included, and the mean free path of the hole was determined by comparing the measured spectrum with the simulated one. The energy spectrum of 662 keV ?-ray was measured with the CZT detector, and it was compared with the simulated spectrum, in which newly determined mean free paths of the electron and the hole were used.

Park, Se-Hwan; Kim, Yong-Kyun; Jeon, Sung-Dae; Ha, Jang-Ho; Hong, Duk-Geun

2007-08-01

13

Electron stopping power and inelastic mean free path in amino acids and protein over the energy range of 20–20,000 eV  

Microsoft Academic Search

Systematic calculations of stopping power (SPs) and inelastic mean free path (IMFP) values for 20–20,000 eV electrons in a group of 15 amino acids and a simple protein have been performed. The calculations are based on the dielectric response model and take into account the exchange effect between the incident electron and target electrons. The optical energy-loss functions for the 15

Zhenyu Tan; Yueyuan Xia; Mingwen Zhao; Xiangdong Liu

2006-01-01

14

Determination of mass attenuation coefficients, effective atomic and electron numbers, mean free paths and kermas for PbO, barite and some boron ores  

NASA Astrophysics Data System (ADS)

The total mass attenuation coefficients, ? m, for PbO, barite, colemanite, tincal and ulexite were determined at 80.1, 302.9, 356.0, 661.7 and 1250.0 keV photon energies by using NaI (Tl) scintillation detector. Effective atomic number, Z eff, effective electron number, N eff, total atomic cross-section, ? t, total electronic cross-section, ? e, mean free path, mfp, and kerma relative to air were determined experimentally and theoretically. The theoretical mass attenuation coefficients were estimated using mixture rule. The calculated values were compared with the experimental values for all samples.

Un, A.; Sahin, Y.

2011-07-01

15

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

16

Stopping power and mean free path for low-energy electrons in ten scintillators over energy range of 20-20,000 eV.  

PubMed

Systematic calculations of the stopping powers (SP) and inelastic mean free paths (IMFP) for 20-20,000eV electrons in a group of 10 important scintillators have been carried out. The calculations are based on the dielectric model including the Born-Ochkur exchange correction and the optical energy loss functions (OELFs) are empirically evaluated because of the lack of available experimental optical data for the scintillators under consideration. The evaluated OELFs are examined by both the f-sum rule and the calculation of mean ionization potential. The SP and IMFP data presented here are the first results for the 10 scintillators over the energy range of 20-20,000eV, and are of key importance for the investigation of liquid scintillation counting. PMID:21880497

Tan, Zhenyu; Xia, Yueyuan

2012-01-01

17

The mean free path of low-rigidity cosmic rays  

NASA Technical Reports Server (NTRS)

The paper presents a simple heuristic argument that suggests that the large rigidity independent mean free paths observed for low-rigidity solar and galactic cosmic rays can be understood in terms of weak turbulence diffusion theory. This is shown to be possible if it is assumed that the interplanetary magnetic turbulence consists of a combination of Alfven waves propagating with constant field magnitude and a small (about 5-10 percent) admixture of compressive fluctuations.

Goldstein, M. L.

1980-01-01

18

The mean free path of low rigidity cosmic rays  

NASA Technical Reports Server (NTRS)

A simple heuristic argument is presented which suggests that the large rigidity independent mean free paths observed for low rigidity solar and galactic cosmic rays can be understood in terms of weak turbulence diffusion theory if one assumes that the interplanetary magnetic turbulence consists of a combination of Alfven waves propagating with constant field magnitude and a small (approximately 5-10%) admixture of compressive fluctuations.

Goldstein, M. L.

1979-01-01

19

Inelastic interaction mean free path of negative pions in tungsten  

NASA Technical Reports Server (NTRS)

The inelastic interaction mean free paths lambda of 5, 10, and 15 GeV/c pions were measured by determining the distribution of first interaction locations in a modular tungsten-scintillator ionization spectrometer. In addition to commonly used interaction signatures of a few (2-5) particles in two or three consecutive modules, a chi2 distribution is used to calculate the probability that the first interaction occurred at a specific depth in the spectrometer. This latter technique seems to be more reliable than use of the simpler criteria. No significant dependence of lambda on energy was observed. In tungsten, lambda for pions is 206 plus or minus 6 g/sq cm.

Cheshire, D. L.; Huggett, R. W.; Jones, W. V.; Rountree, S. P.; Schmidt, W. K. H.; Kurz, R. J.; Bowen, T.; Delise, D. A.; Krider, E. P.; Orth, C. D.

1975-01-01

20

Neutrino mean free paths in cold symmetric nuclear matter  

NASA Astrophysics Data System (ADS)

The neutrino mean free paths (NMFP) for scattering and absorption in cold symmetric nuclear matter (SNM) are calculated using two-body effective interactions and one-body effective weak operators obtained from realistic models of nuclear forces using correlated basis theory. The infinite system is modeled in a box with periodic boundary conditions and the one particle-hole ( p-h ) response functions are calculated using the Tamm-Dancoff approximation (TDA). For the densities ?= 1 /2 , 1, 3 /2 ?0 , where ?0 is the equilibrium density of SNM, the strength of the response is shifted to higher energy transfers when compared to a noninteracting Fermi gas (FG). This and the weakness of effective operators compared to the bare operators, significantly reduces the cross sections, enhancing the NMFP by factors of ˜2.5 3.5 at the densities considered. The NMFP at the equilibrium density ?0 are also calculated using the TDA and random phase approximation (RPA) using zero range Skyrme-like effective interactions with parameters chosen to reproduce the equation of state and spin-isospin susceptibilities of matter. Their results indicate that RPA corrections to correlated TDA may further increase the NMFP by ˜25% to 3 4 times those in a noninteracting FG. Finally, the sums and the energy weighted sums of the Fermi and Gamow-Teller responses obtained from the correlated ground state are compared with those of the 1 p-h response functions to extract the sum and mean energies of multi p-h contributions to the weak response. The relatively large mean energy of the multi p-h excitations suggests that they may not contribute significantly to low energy NMFP.

Cowell, S.; Pandharipande, V. R.

2004-09-01

21

Finite temperature inelastic mean free path and quasiparticle lifetime in graphene  

NASA Astrophysics Data System (ADS)

We adopt the GW and random phase approximations to study finite temperature effects on the inelastic mean free path and quasiparticle lifetime by directly calculating the imaginary part of the finite temperature self-energy induced by electron-electron interaction in extrinsic and intrinsic graphene. In particular, we provide the density-dependent leading order temperature correction to the inelastic scattering rate for both single-layer and double-layer graphene systems. We find that the inelastic mean free path is strongly influenced by finite-temperature effects. We present the similarity and the difference between graphene with linear chiral band dispersion and conventional two-dimensional electron systems with parabolic band dispersion. We also compare the calculated finite temperature inelastic scattering length with the elastic scattering length due to Coulomb disorder and comment on the prospects for quantum interference effects showing up in low-density graphene transport. We also carry out inelastic scattering calculation for electron-phonon interaction, which by itself gives rather long carrier mean free paths and lifetimes since the deformation potential coupling is weak in graphene, and therefore electron-phonon interaction contributes significantly to the inelastic scattering only at relatively high temperatures.

Li, Qiuzi; Das Sarma, S.

2013-02-01

22

Mean Free Path of Protons in Nuclei and the Nuclear Radius.  

National Technical Information Service (NTIS)

The mean free path (lambda) of protons in nuclei in the energy range 40-1000 MeV was determined. The concept of mean free path of a nucleon in nuclei was discussed. This topic attracted much attention because of the discrepancy between the phenomenologica...

R. Dymarz T. Kohmura

1982-01-01

23

Mean Free Path of a Nucleon in Nucleus-Nucleus Collision  

Microsoft Academic Search

The mean free path of a nucleon for two colliding nuclei has been calculated in terms of the imaginary part of the optical potential and the k effective mass. The energy range 10-30 MeV\\/nucleon appears to be optimum for mean free paths in the range 3-4 fm.

Bikash Sinha

1983-01-01

24

Broadband mean free path of diffuse light in polydisperse ensembles of scatterers for white light-emitting diode lighting.  

PubMed

We study the diffuse transport of light through polymer slabs containing TiO(2) scattering particles. The slabs are diffuser plates typical of a commercial white light-emitting diode (LED) module (Fortimo). We have measured the diffuse transmission and reflection properties over a broad wavelength range (470-840 nm) from which we derive the transport mean free path using the theory of light diffusion. With increasing scatterer density, the mean free path becomes shorter. The mean free path increases with wavelength; hence, blue light is scattered more strongly than red light. To interpret the results, we propose an ab initio model without adjustable parameters for the mean free path by using Mie theory. We include inhomogeneous broadening as a result of the size distribution of the scattering particles as measured by dynamic light scattering. Surprisingly, the calculated mean free path decreases with wavelength, at variance with our experiments, which is caused by particles with radii R in excess of 0.25 ?m. Close inspection of the scatterers by electron microscopy reveals that large particles (R>0.4 ?m) consist of clusters of small particles (R<0.13 ?m). Therefore, we have improved our model by only taking into account the individual scatterers within the clusters. This model predicts mean free paths in good agreement with our experimental results. We discuss consequences of our results to white LED lighting modules. PMID:23669667

Vos, Willem L; Tukker, Teus W; Mosk, Allard P; Lagendijk, Ad; IJzerman, Wilbert L

2013-04-20

25

Determination of absolute thickness and mean free path of thin foil specimen by zeta-factor method.  

PubMed

The zeta-factor method is applied to the thickness determination of thin amorphous specimens where the convergent-beam electron diffraction method is not applicable. Characteristic X-ray intensities are first measured using standard specimens in order to determine zeta-factors. These zeta-factors are then used to determine local thicknesses of an amorphous Si and an amorphous Al alloy. Electron energy-loss spectroscopy (EELS) spectra are acquired at the same positions as for the X-ray measurements. Thus, using the thicknesses measured from the zeta-factor method, the electron mean-free path is determined through the EELS log-ratio method. The mean free path is measured as a function of the collection semi-angle, beta, and specimen thickness, and it is also compared with theoretical values. Furthermore, the mean free path of amorphous Si is compared with that of the crystalline Si. PMID:15180208

Ohshima, Katsunori; Kaneko, Kenji; Fujita, Takeshi; Horita, Zenji

2004-01-01

26

Inelastic and elastic mean free paths from FIB samples of metallic glasses.  

PubMed

We have used focused ion beam (FIB) milling and scanning electron microscopy (SEM) to prepare samples of known thickness for measurement of the electron scattering elastic and inelastic mean free paths (EMFP and IMFP respectively) of three metallic glasses, Cu(64.5)Zr(35.5), Zr(50)Cu(45)Al(5), and Al(87)Y(7)Fe(5)Cu. After measuring the EMFP and IMFP in a scanning transmission electron microscope, we used the FIB to coat the lamellae with carbon on the top and bottom surfaces, which eliminated secondary electron emission from those surfaces and made SEM measurements of their thickness more reliable. At 200 kV, we find IMFP/ EMFP values of 146±2/43±1, 163±1/41±1, and 149±1/85±1 nm, respectively for the three glass compositions. Our results differ from available models for the IMFP by as much as 50%. PMID:23154031

Schweiss, D T; Hwang, Jinwoo; Voyles, P M

2013-01-01

27

Electron mean-free pathlengths through monolayers of cadmium arachidate  

Microsoft Academic Search

The inelastic mean-free pathlengths lambda, of 1042-1402 eV electrons through cadmium arachidate (C19H39COO)2Cd, monolayers have been determined from attenuation measurements of the core level photoemission (XPS) signals from gold, silver and indium substrates. Both fixed angle-variable overlayer thickness experiments and variable angle-fixed overlayer thickness experiments were performed. We derive a preferred value of 3.6 nm at 1117 eV and an

C. R. Brundle; H. Hopster; J. D. Swalen

1979-01-01

28

Electron mean-free pathlengths through monolayers of cadmium arachidate  

Microsoft Academic Search

The inelastic mean-free pathlengths ?, of 1042–1402 eV electrons through cadmium arachidate (C19H39COO)2Cd, monolayers have been determined from attenuation measurements of the core level photoemission (XPS) signals from gold, silver and indium substrates. Both fixed angle-variable overlayer thickness experiments and variable angle-fixed overlayer thickness experiments were performed. We derive a preferred value of 3.6 nm at 1117 eV and an

C. R. Brundle; H. Hopster; J. D. Swalen

1979-01-01

29

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

30

Inelastic mean free path data for Si corrected for surface excitation.  

PubMed

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. PMID:17481337

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

2005-12-01

31

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.

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

2013-01-01

32

Wave-particle interaction in parallel transport of long mean-free-path plasmas along open field magnetic field lines  

NASA Astrophysics Data System (ADS)

A tokamak fusion reactor dumps a large amount of heat and particle flux to the divertor through the scrape-off plasma (SOL). Situation exists either by necessity or through deliberate design that the SOL plasma attains long mean-free-path along large segments of the open field lines. The rapid parallel streaming of electrons requires a large parallel electric field to maintain ambipolarity. The confining effect of the parallel electric field on electrons leads to a trap/passing boundary in the velocity space for electrons. In the normal situation where the upstream electron source populates both the trapped and passing region, a mechanism must exist to produce a flux across the electron trap/passing boundary. In a short mean-free-path plasma, this is provided by collisions. For long mean-free-path plasmas, wave-particle interaction is the primary candidate for detrapping the electrons. Here we present simulation results and a theoretical analysis using a model distribution function of trapped electrons. The dominating electromagnetic plasma instability and the associated collisionless scattering, that produces both particle and energy fluxes across the electron trap/passing boundary in velocity space, are discussed.

Guo, Zehua; Tang, Xianzhu

2012-03-01

33

Experimental and Theoretical Studies on Phonon Mean Free Path in Thermoelectric Materials  

Microsoft Academic Search

Nanostructured thermoelectric materials have shown improved thermoelectric figure of merit due to reduced phonon thermal conductivity. To design nanostructures that effectively scatter phonons via interface and boundary scattering, it is important to know the phonon mean free path of thermoelectric materials in their bulk form. In this talk, we will present recent progress in experimental and theoretical investigation of phonon

Gang Chen

2011-01-01

34

Hydrodynamic force measurements under precisely controlled conditions: Correlation of slip parameters with the mean free path  

NASA Astrophysics Data System (ADS)

A customized atomic force microscope has been utilized in dynamic mode to measure hydrodynamic forces between a sphere and a flat plate, both coated with gold. In order to study the influence of the mean free path on slippage without systematic errors due to varying surface properties, all data have been acquired at precisely the same spot on the plate. Local accommodation coefficients and slip lengths have been extracted from experimental data for He, Ne, Ar, Kr, as well as N2, CO2, and C2H6, at Knudsen numbers between 3 × 10-4 and 3. We found that slippage is effectively suppressed if the mean free path of the fluid is lower than the roughness amplitude on the surface, while we could not observe a clear correlation between the accommodation coefficient and the molecular mass.

Sedmik, René I. P.; Borghesani, Armando F.; Heeck, Kier; Iannuzzi, Davide

2013-04-01

35

The proton scattering mean free path for the May 7, 1978, solar flare event  

SciTech Connect

The scattering mean free paths of solar flare protons in the rigidity ranges 195-396 MV (20-80 MeV) and from about 1.5 to 5 GV for the May 7, 1978, solar cosmic ray event were found to be 1.7 {plus minus} 0.1 AU and 3.9 {plus minus} 0.4 AU, respectively. These scattering mean free paths are compared with those deduced for other scatter-free solar cosmic ray events. The rigidity dependence of {lambda}{sub 11} can be described by {lambda}(AU) = 2.0 (P(GV)){sup 0.4} for 0.1 < P < 5 GV.

Debrunner, H.; Graedel, H. (Univ. of Bern (Switzerland)); Lockwood, J.A. (Univ. of New Hampshire, Durham (USA))

1991-05-01

36

On the mean free path for a periodic array of spherical obstacles  

SciTech Connect

We prove theorems pertaining to periodic arrays of spherical obstacles which show how the macroscopic limit of the mean free path depends on the scaling of the size of the obstacles. We treat separately the cases where the obstacles are totally and partially absorbing, and we also distinguish between two-dimensional arrays, where our results are optimal, and higher dimensional arrays, where they are not. The cubically symmetric arrays to which these results apply do not have finite horizon.

Dumas, H.S. [Univ. of Cincinnati, OH (United States); Dumas, L. [Universite Paris VII (France); Golse, F. [Universite Paris VII (France)]|[Ecole Normale Superieure, Paris (France)

1996-03-01

37

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

38

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

39

Isovector-channel role of relativistic mean field models in the neutrino mean free path  

SciTech Connect

An improvement in the treatment of the isovector channel of relativistic mean field (RMF) models based on effective field theory (E-RMF) is suggested, by adding an isovector scalar ({delta}) meson and using a similar procedure to the one used by Horowitz and Piekarewicz to adjust the isovector-vector channel in order to achieve a softer density dependent symmetry energy of the nuclear matter at high density. Their effects on the equation of state (EOS) at high density and on the neutrino mean free path (NMFP) in neutron stars are discussed.

Sulaksono, A.; Hutauruk, P.T.P.; Mart, T. [Departemen Fisika, FMIPA, Universitas Indonesia, Depok, 16424 (Indonesia)

2005-12-15

40

Neutron fraction and neutrino mean free path predictions in relativistic mean field models  

SciTech Connect

The equation of state (EOS) of dense matter and neutrino mean free path (NMFP) in a neutron star have been studied by using relativistic mean field models motivated by effective field theory. It is found that the models predict too large proton fractions, although one of the models (G2) predicts an acceptable EOS. This is caused by the isovector terms. Except G2, the other two models predict anomalous NMFP's. In order to minimize the anomaly, besides an acceptable EOS, a large M* is favorable. A model with large M* retains the regularity in the NMFP even for a small neutron fraction.

Hutauruk, P.T.P.; Williams, C.K.; Sulaksono, A.; Mart, T. [Departemen Fisika, FMIPA, Universitas Indonesia, Depok 16424 (Indonesia)

2004-12-01

41

Extending the collisional fluid equations into the long mean-free-path regime in toroidal plasmas. III. Parallel heat conduction  

SciTech Connect

It is illustrated that plasma transport processes in the direction of the magnetic field are local in the vicinity of the magnetic island in the long mean-free-path regime where the collisionality parameter {nu}{sub *} is larger than 10{sup -2}, and the width of the island is about 3% of the minor radius or smaller. This is because the plasma temperature variation on the magnetic surface that results from the magnetic reconnection is gentle. Both the electron and the ion parallel transport fluxes including parallel heat flow in the banana regime where {nu}{sub *}<1 are calculated using a model Coulomb collision operator that conserves momentum.

Shaing, K. C. [Engineering Physics Department, University of Wisconsin, Madison, Wisconsin 53706 (United States)

2006-09-15

42

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

43

Empirical quantitative relationships among grain size, mean free path, contiguity and cobalt content in WC-Co hardmetal  

Microsoft Academic Search

Measured values of WC mean grain size, mean free path in cobalt and contiguity, have been plotted against each other and\\/or against the cobalt content for a set of WC-Co alloys having a wide range of grain sizes and cobalt contents. The relationships between these parameters are shown in graph form as well as by means of analytical expressions, allowing

SILVANA LUYCKX; ANNE D LOVE

2003-01-01

44

Non-Fermi liquid correction to the neutrino mean free path and emissivity in neutron star beyond the leading order  

NASA Astrophysics Data System (ADS)

In this work we have derived the expressions of the mean free path (MFP) and emissivity of the neutrinos by incorporating non-Fermi liquid (NFL) corrections upto next to leading order (NLO). We have shown how such corrections affect the cooling of the neutron star composed of quark matter core.

Adhya, Souvik P.; Roy, P. K.; Dutt-Mazumder, Abhee K.

2013-04-01

45

Critical Fields of Thin Superconducting Films. II. Mean Free Path Effects in Indium-Tin Alloy Films  

Microsoft Academic Search

In a previous paper, a theoretical model was presented from which the critical magnetic fields of thin superconducting films could be calculated. The model was worked out for the nonlocal model of Pippard, but only thickness effects were discussed in detail and compared to experimental data on pure indium films. In this paper, mean free path effects as well as

A. M. Toxen; M. J. Burns

1963-01-01

46

Extraction of mean free path of charge carriers in CdZnTe crystals from measured full-energy peaks  

NASA Astrophysics Data System (ADS)

The mean free path of electrons ( ?e) and holes ( ?h) in a CdZnTe crystal were extracted from measured ?-ray spectra. First, distortion due to Gaussian broadening was unfolded from full-energy peaks in the ?-ray spectra. As a result, only tailing was left in the unfolded peaks. Second, ?e and ?h were determined by fitting tailing of full-energy peaks in calculated response functions to that in the unfolded ?-ray spectra. The response functions were calculated using EGS4 with the Hecht equation coded. 2.5×10 2 cm for ?e and 5.0×10 -2 cm for ?h were obtained in an electric field of 2500 V/ cm: the ?? products were found to be 1.0×10 -1 cm2/ V for electrons and 2.0×10 -5 cm2/ V for holes. This method is reasonable to obtain ?e and ?h, which are necessary to correct the distortion caused by tailing in X-ray spectra.

Miyajima, Satoshi; Sakuragi, Hideaki; Matsumoto, Masao

2002-06-01

47

Horizontally aligned carbon nanotube bundles for interconnect application: diameter-dependent contact resistance and mean free path  

NASA Astrophysics Data System (ADS)

We have demonstrated the fabrication of horizontally aligned carbon nanotube (CNT) bundles on Si substrate for interconnect line application. By controlling the catalyst thickness, we fabricated multi-walled CNT and few-walled CNT bundles with different diameters. We measured the resistances of the CNTs as a function of the length and the diameter. The dependence of the contact resistance between the CNT and the metal on the CNT diameter was extracted from the resistance plots. We investigated and experimentally validated the relationship between the diameter and the mean free path of the CNT.

Chai, Yang; Xiao, Zhiyong; Chan, Philip C. H.

2010-06-01

48

Fluctuation of mean free path and transition temperature induced vortex pinning in (Ba,K)Fe2As2 superconductors  

NASA Astrophysics Data System (ADS)

The vortex pinning mechanisms of Ba0.72K0.28Fe2As2 single crystal have been studied systematically as a function of temperature and magnetic field. The temperature dependence of the critical current density, Jc(T), was analysed within the collective pinning model at different magnetic fields. It was found that both the ?l pinning mechanism, i.e., pinning associated with charge-carrier mean free path fluctuation, and the ?Tc pinning mechanism, which is associated with spatial fluctuations of the transition temperature, coexist in the Ba0.72K0.28Fe2As2 single crystal in fields smaller than 4 T. Their contributions are strongly temperature and magnetic field dependent. At lower temperature and B <= 4 T, the ?l pinning is the dominant mechanism, and its contributions decrease with increasing temperature. At temperatures close to the critical temperature, however, there is evidence for ?Tc pinning. At magnetic fields larger than 4 T, the ?l pinning mechanism is the only effect.

Ghorbani, S. R.; Wang, X. L.; Shahbazi, M.; Dou, S. X.; Lin, C. T.

2012-05-01

49

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

50

A comparison of the solution of pitch angle transport equation with the simulation - The case of a long scattering mean free path  

NASA Astrophysics Data System (ADS)

For the case of a long scattering mean free path, the solution of pitch angle transport equation using the method of KOTA et al. (1982) (KMJKGO) is compared with the simulation which follows the trajectories of particles in a simulated random magnetic field. The comparison shows that the KMJKGO method gives similar time profiles of the intensity to those obtained by the simulation, even with the anisotropic injection of particle at the source. It is found that the time profile is very sensitive to the direction of the velocity cone with respect to the ambient magnetic field at the point of injection, even though the same scattering mean free path is used. Thus, the direction of the velocity cone at the injection of the particles may be an important parameter when interpreting the propagation of solar cosmic rays from the time profile of intensity.

Sakai, Takasuke

51

Proton inelastic mean free path in a group of bioorganic compounds and water in 0.05-10 MeV range - Including higher-order corrections  

NASA Astrophysics Data System (ADS)

The systematic calculations of the inelastic mean free paths (MFP) of 0.05-10 MeV protons in a group of eleven important bioorganic compounds, i.e. DNA, five bases, three fatty acids, cellulose and ?-carotene, have been performed. The expressions for the calculations are derived from the Ashley's optical-data model and from the higher-order correction terms in stopping power calculations. Especially, the Bloch correction for the inelastic MFP is proposed empirically in this work. The inelastic MFPs for energetic protons in water are also evaluated and compared with other theoretical calculations. The proton inelastic MFPs for these 11 bioorganic compounds in the energy range from 0.05 to 10 MeV are presented here for the first time, and might be useful for studies of various radiation effects in these materials.

Tan, Zhenyu; Xia, Yueyuan; Zhao, Mingwen; Liu, Xiangdong

2010-07-01

52

Magnetization hysteresis and time decay measurements in FeSe0.50Te0.50: Evidence for fluctuation in mean free path induced pinning  

NASA Astrophysics Data System (ADS)

We present results of magnetic measurements relating to vortex phase diagram in a single crystal of FeSe0.5Te0.5 which displays a second magnetization peak anomaly for H?c. The possible role of the crystalline anisotropy on vortex pinning is explored via magnetic torque magnetometry. We present evidence in favor of pinning related to spatial variations of the charge carrier mean free path leading to small bundle vortex pinning by randomly distributed (weak) pinning centers for both H?c and H?c. This is further corroborated using magnetization data for H?c in a single crystal of FeSe0.35Te0.65. Dynamical response across the second magnetization peak (SMP) anomaly in FeSe0.5Te0.5 has been compared with that across the well-researched phenomenon of peak effect (PE) in a single crystal of CeRu2.

Das, P.; Thakur, Ajay D.; Yadav, Anil K.; Tomy, C. V.; Lees, M. R.; Balakrishnan, G.; Ramakrishnan, S.; Grover, A. K.

2011-12-01

53

The Path of Electrons  

NSDL National Science Digital Library

Students engage in an interactive "hot potato" demonstration to gain an appreciation for the flow of electrons through a circuit. Students role play the different parts of a simple circuit and send small items representing electrons (paper or candy pieces) through the circuit.

Integrated Teaching And Learning Program

54

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

55

Mean free path in soccer and gases  

NASA Astrophysics Data System (ADS)

The trajectories of the molecules in an ideal gas and of the ball in a soccer game are compared. The great difference between these motions and some similarities are discussed. This example could be suitable for discussing many concepts in kinetic theory in a way that can be pictured by students for getting a more intuitive understanding. It could be suitable for an introductory course in vacuum techniques or undergraduate courses in kinetic theory of gases. Without going into the slightly harder quantitative results, the analysis presented might be used for introducing some ideas of kinetic theory qualitatively to high school students.

Luzuriaga, J.

2010-09-01

56

Mean Free Path in Soccer and Gases  

ERIC Educational Resources Information Center

The trajectories of the molecules in an ideal gas and of the ball in a soccer game are compared. The great difference between these motions and some similarities are discussed. This example could be suitable for discussing many concepts in kinetic theory in a way that can be pictured by students for getting a more intuitive understanding. It could…

Luzuriaga, J.

2010-01-01

57

A comprehensive study on energy absorption and exposure buildup factors for some essential amino acids, fatty acids and carbohydrates in the energy range 0.015-15 MeV up to 40 mean free path  

NASA Astrophysics Data System (ADS)

The gamma ray energy absorption ( EABF) and exposure buildup factors ( EBF) have been calculated for some essential amino acids, fatty acids and carbohydrates in the energy region 0.015-15 MeV up to a penetration depth of 40 mfp (mean free path). The five parameter geometric progression (G-P) fitting approximation has been used to calculate both EABF and EBF. Variations of EABF and EBF with incident photon energy, penetration depth and weight fraction of elements have been studied. While the significant variations in EABF and EBF for amino acids and fatty acids have been observed at the intermediate energy region where Compton scattering is the main photon interaction process, the values of EABF and EBF appear to be almost the same for all carbohydrates in the continuous energy region. It has been observed that the fatty acids have the largest EABF and EBF at 0.08 and 0.1 MeV, respectively, whereas the maximum values of EABF and EBF have been observed for aminoacids and carbohydrates at 0.1 MeV. At the fixed energy of 1.5 MeV, the variation of EABF with penetration depth appears to be independent of the variations in chemical composition of the amino acids, fatty acids and carbohydrates. Significant variations were also observed between EABF and EBF which may be due to the variations in chemical composition of the given materials.

Kurudirek, Murat; Özdemir, Yüksel

2011-01-01

58

Study on the characteristics of gas molecular mean free pathin nanopores by molecular dynamics simulations.  

PubMed

This paper presents studies on the characteristics of gas molecular mean freepath in nanopores by molecular dynamics simulation. Our study results indicate that themean free path of all molecules in nanopores depend on both the radius of the nanoporeand the gas-solid interaction strength. Besides mean free path of all molecules in thenanopore, this paper highlights the gas molecular mean free path at different positions ofthe nanopore and the anisotropy of the gas molecular mean free path at nanopores. Themolecular mean free path varies with the molecule's distance from the center of thenanopore. 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 isconfined in nanopores. The radial gas molecular mean free path is much smaller than themean free path including all molecular collisions occuring in three directions. Our studyresults also indicate that when gas is confined in nanopores the gas molecule number densitydoes not affect the gas molecular mean free path in the same way as it does for the gas inunbounded space. These study results may bring new insights into understanding the gasflow's characteristic at nanoscale. PMID:25046745

Liu, Qixin; Cai, Zhiyong

2014-01-01

59

A DRIFT ORDERED SHORT MEAN-FREE DESCRIPTION FOR PARTIALLY IONIZED MAGNETIZED PLASMA  

SciTech Connect

Effects of neutral particles, most prominently the associated heat flux and viscosity, can be very important or even dominant at the edge of a tokamak and so must be self-consistently accounted for in a description of magnetized tokamak edge plasma. To the best of our knowledge, this has only been done so far for short mean-free path plasma under MHD-like Braginskii's orderings i.e. assuming that species velocities are on the order of the ion thermal speed. Since plasma flows in modern tokamaks are usually slow compared with the ion thermal speed (at least in the absence of strong external momentum sources) it is more appropriate to use drift orderings in which the plasma flow velocity is instead comparable with the diamagnetic heat flow divided by pressure. Employing drift orderings and evaluating species distribution functions through second order in the small gyroradius and mean-free path expansion parameters allows accounting for the important effects of heat fluxes on species momentum transport (viscosities), which are missing from the large flow ordered treatments. In this work we consider short mean-free path plasma consisting of electrons and single species of singly-charged ions and neutrals. We neglect neutral-neutral and elastic electron-neutral collisions and approximate the neutral-ion charge-exchange cross-section with a constant. We employ drift orderings to evaluate ion, neutral, and electron heat fluxes, viscosity tensors, and momentum and energy exchange terms and formulate a self-consistent system of electron, ion, and neutral fluid equations, thereby generalizing the drift-ordered treatment of fully ionized plasma.

SIMAKOV, ANDERI N. [Los Alamos National Laboratory

2007-02-08

60

Measurement of the mean free path of edge magnetoplasmons revealed in the spectra of magnetic oscillations of photovoltage in a two-dimensional electron system under microwave radiation  

Microsoft Academic Search

In the spectrum of photovoltage oscillations that are periodic with respect to the magnetic field and appear on Hall structures\\u000a under microwave irradiation, two frequency components of oscillations are observed and analyzed. The appearance of these two\\u000a frequencies in photovoltage oscillations is explained by the existence of two trajectories of edge magnetoplasmons and by\\u000a the effects of the interference of

V. M. Murav’ev; I. V. Kukushkin; A. L. Parakhonski?; J. Smet; K. von Klitzing

2006-01-01

61

Path-Integral Molecular Dynamics Calculations of Electron Plasma  

NASA Astrophysics Data System (ADS)

We introduce a first-principles molecular dynamics method based on the discretized path integral representation of quantum particles. Fermi statistics is automatically generated by an effective exchange potential. This path-integral molecular dynamics method is able to simulate exchange in electron plasmas at the border of the degenerate regime with a satisfactory level of accuracy.

Oh, Ki-Dong; Deymier, P. A.

1998-10-01

62

Electron wave packets: Quantum statistics in path integral representation  

SciTech Connect

Fundamental relations between ensemble-averaged kinetic energy, pressure, and virial are obtained for quantum many-particle systems at finite temperatures. A path-integral method is developed for calculating kinetic energy for mixed (quantum-classical) systems. The method eliminates the problem of divergent variance. Path-integral Monte Carlo simulations are performed to validate the method as applied to single-electron and electron-pair wave packets, with exact treatment of exchange symmetry and spin states. Quantitative results are compared with corresponding characteristics calculated for point charges.

Shevkunov, S. V., E-mail: root@svsh.tu.neva.ru [St. Petersburg State Polytechnic University (Russian Federation)

2008-01-15

63

Electronic medical records: a path forward.  

PubMed

Health systems are moving to implement comprehensive electronic medical record (EMR) systems, or significant pieces of them, in the belief that EMR can be integrated into clinical practice and lead to improved patient outcomes and enhanced safety. There are substantial roadblocks to implementing EMR, including significant cost, the competency needed to implement, the political environment, organization infrastructure and culture, and how organization leaders understand return on investment. Complicating factors include the drive to implement EMR to meet meaningful use standards to qualify for a federal incentive program and recently publicized studies that question the value equation of the EMR as it relates to patient care improvements. We offer our experiences on the successful implementation of the EMR across the large health systems we lead. We offer practical advice and tips on how to achieve successful implementation, evidence that successful implementations improve patient care and safety, and a glimpse of how EMR is a significant foundation in a future of collaborative models that provide continuum-based care. PMID:21961380

Bernd, David L; Fine, Peter S

2011-01-01

64

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.

65

1 Degree X 1 Degree Mean Free - Air Gravity Anomalies.  

National Technical Information Service (NTIS)

The publication contains a set of 1 degree x 1 degree mean free-air anomaly (MFAA) values for portions of the world where sufficient gravity data is available for anomaly computation. The values are referred to the International Ellipsoid and represent th...

C. A. Lechner G. Larry J. J. Gillespie

1971-01-01

66

New model of electron free path in multiple layers for Monte Carlo simulation  

Microsoft Academic Search

A new model of an electron free path in multiple layers is proposed for Monte Carlo simulation of electron trajectories. In this model, the free path is calculated taking into account not only the scattering probability in the layer involving the initial scattering point but also that in the layers along the scattering direction. The result, simulated with the new

Seiji Horiguchi; Masanori Suzuki; Toshio Kobayashi; Hideo Yoshino; Yutaka Sakakibara

1981-01-01

67

The optimal path of logistics distribution in electronic commerce  

Microsoft Academic Search

Efficient and fast logistics distribution system is of paramount significance for enterprises, especially for the development of e-commerce. At present, the problem that e-commerce puzzles businessmen is logistics distribution. Based on Dijkstra's shortest path algorithm, an intelligent optimal path algorithm is presented with the aid of the thoughts of state space searching and dynamic cut branch in artificial intelligence. The

Zhang Yong-mei; Ma Li

2010-01-01

68

Path Integral Monte Carlo finite-temperature electronic structure of quantum dots  

Microsoft Academic Search

Quantum Monte Carlo methods allow a straightforward procedure for evaluation of electronic structures with a proper treatment of electronic correlations. This can be done even at finite temperatures [1]. We apply the Path Integral Monte Carlo (PIMC) simulation method [2] for one and two electrons in a single and double quantum dots. With this approach we evaluate the electronic distributions

Markku Leino; Tapio T. Rantala

2003-01-01

69

Phonon temperature and electron temperature in thermoelectric coupling  

NASA Astrophysics Data System (ADS)

We develop a mesoscopic model of thermoelectric coupling in nanosystems, allowing for different phonon and electron temperatures, and mutual energy exchange. Its compatibility with the second law of thermodynamics is proved. By comparisons with other theoretical proposals, the different coefficients involved in the model are identified. We consider two illustrations: (a) for systems where the electron mean-free path is considerably shorter than the phonon mean-free path, the non-equilibrium phonon temperature may be different with respect to the local-equilibrium temperature of electrons; (b) for systems with large electron mean-free path, one may have the so-called "hot electrons," namely, electrons having a higher temperature than that of the phonons.

Jou, David; Sellitto, Antonio; Cimmelli, Vito A.

2013-12-01

70

Engineering of an alternative electron transfer path in photosystem II.  

PubMed

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 Q(B), is mainly embedded within two proteins called D1 and D2. We have identified a site in silico, poised in the vicinity of the Q(A) 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

2010-05-25

71

Spiral structure and star formation. I - Formation mechanisms and mean free paths  

NASA Technical Reports Server (NTRS)

The wide variety of optical appearances observed in spiral galaxies has encouraged the growth of two theoretical approaches to explain the spiral patterns exhibited by such young objects as OB associations, giant H II regions, and dark dust lanes. These approaches are related to the density wave theory of spiral structure and 'stochastic, self-propagating star formation'. Levinson and Roberts (1981) tried to reconcile these two theoretical approaches, and considered a disk filled with discrete gas clouds. The present investigation is concerned with refinements and extensions of the model of Levinson and Roberts. Attention is given to gravitational forces and dynamical propagation, cloud-cloud collisions, supernova interactions, computational models, a theory concerning the interactions of the gas cloud and stellar association systems, the time evolution of the gas cloud-stellar association systems, and aspects of collisionally triggered star formation.

Roberts, W. W., Jr.; Hausman, M. A.

1984-01-01

72

Nonequilibrium heterogeneous catalysis in the long mean-free-path regime.  

PubMed

It is shown that a standard principle of traditional catalysis-that a catalyst does not alter the final thermodynamic equilibrium of a reaction-can fail in low-pressure, heterogeneous gas-surface reactions. Kinetic theory for this epicatalysis is presented, and two well-documented experimental examples are detailed: surface ionized plasmas and hydrogen dissociation on refractory metals. This phenomenon should be observable over a wide range of temperatures and pressures, and for a broad spectrum of heterogeneous reactions. By transcending some constraints of equilibrium thermodynamics, epicatalysis might provide additional control parameters and synthetic routes for reactions, and enable product streams boosted in thermochemical energy or desirable species. PMID:24125231

Sheehan, D P

2013-09-01

73

Domain-wall velocity, mobility, and mean-free-path in permalloy films  

Microsoft Academic Search

Domain-wall velocity was measured for vacuum-deposited permalloy films in the thickness range of from 310 to 3000 Å. The dependence of the velocity on drive field amplitude was non-linear for all of the forty-two films. The ?-H characteristics were clearly separated into two regions (low and high field), except for the thick films ( > 2500 Å). The high field

SUSUMU KONISHI; SHOICHI YAMADA; T. Kusuda

1971-01-01

74

Modeling Gridded Inertial-Electrostatic Fusion Devices with Short Mean Free Paths  

Microsoft Academic Search

Gridded inertial-electrostatic confinement (IEC) devices accelerate and focus ions using voltage differences between nearly transparent concentric grids in spherical or cylindrical geometry. Voltages of 50-100 kV can be produced relatively easily between the grids, giving the accelerated ions energies with substantial fusion cross sections. The resulting fusion products potentially can produce radioisotopes useful for positron emission tomography and other applications.

J. F. Santarius; R. P. Ashley; G. L. Kulcinski; G. R. Piefer; K. M. Subramanian

2000-01-01

75

Nonequilibrium heterogeneous catalysis in the long mean-free-path regime  

NASA Astrophysics Data System (ADS)

It is shown that a standard principle of traditional catalysis—that a catalyst does not alter the final thermodynamic equilibrium of a reaction—can fail in low-pressure, heterogeneous gas-surface reactions. Kinetic theory for this epicatalysis is presented, and two well-documented experimental examples are detailed: surface ionized plasmas and hydrogen dissociation on refractory metals. This phenomenon should be observable over a wide range of temperatures and pressures, and for a broad spectrum of heterogeneous reactions. By transcending some constraints of equilibrium thermodynamics, epicatalysis might provide additional control parameters and synthetic routes for reactions, and enable product streams boosted in thermochemical energy or desirable species.

Sheehan, D. P.

2013-09-01

76

Strong tunneling in the electron box: a path integral Monte Carlo analysis  

Microsoft Academic Search

Strong electron tunneling effects in the single-electron box are investigated by means of a path integral Monte Carlo analysis. Our results for the effective capacitance of the box are compared to previous theoretical predictions and Monte Carlo simulations. We discuss the accuracy of our simulations and convergence of our results as a function of the Trotter number used in the

C. P. Herrero; G. Schön; A. D. Zaikin

2000-01-01

77

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

78

Path Integral Monte Carlo Calculation of the Momentum Distribution of the Homogeneous Electron Gas at Finite Temperature  

Microsoft Academic Search

Path integral Monte Carlo (PIMC) simulations are used to calculate the momentum distribution of the homogeneous electron gas at finite temperature. This is done by calculating the off-diagonal elements of the real-space density matrix, represented in PIMC by open paths. It is demonstrated how the restricted path integral Monte Carlo methods can be extended in order to deal with open

B. Militzer; E. L. Pollock; D. M. Ceperley

2003-01-01

79

Relaxation of electrons on impurities in super conductors  

Microsoft Academic Search

The method of kinetic equations with self-consistent field for the generalized electron density matrix of a superconductor is used to study the evolution of the density matrix in time with allowance for scattering of electrons on impurities for an arbitrary ratio of the mean free path to the correlation radius of the superconducting electrons. For this, the theory of multiple

V. P. Galaiko

1975-01-01

80

Computational investigation of electron path inside SEM chamber in mirror effect phenomenon.  

PubMed

Present work aims at describe the behaviour of an accelerated probing electron that orientated towards a charged insulator sample and hence producing mirror images. The distribution of the trapped charges at the sample surface is approximated as a point charge. Hence, analytical derivation for the path equation of this electron has been presented. The derived model expresses the probing electron path in terms of the scanning potential, incident angle, trapped charges and the sample relative permittivity. Some of experimental data are import from published literatures so as to justify the introduced procedure. The obtained results have shown that important information could be predictable through the use of this procedure. Hence this procedure may be considered as a tool for describing, analysing and providing hints for further investigation of electron mirror images. PMID:23896651

Al-Obaidi, Hassan N; Khaleel, Imad H

2013-08-01

81

Simulations of one- and two-electron systems by Bead-Fourier path integral molecular dynamics  

NASA Astrophysics Data System (ADS)

The Bead-Fourier path integral molecular dynamics technique introduced earlier [S. D. Ivanov, A. P. Lyubartsev, and A. Laaksonen, Phys. Rev. E 67 066710 (2003)] is applied for simulation of electrons in the simplest molecules: molecular hydrogen, helium atom, and their ions. Special attention is paid to the correct description of electrons in the core region of a nucleus. In an attempt to smooth the Coulomb potential at small distances, a recipe is suggested. The simulation results are in excellent agreement with the analytical solution for the ``harmonic helium atom'', as well as with the vibrational potential of the H2 molecule and He ionization energies. It is demonstrated, that the Bead-Fourier path integral molecular dynamics technique is able to provide the accuracy required for the description of electron structure and chemical bonds in cases when electron exchange effects need not be taken into account.

Ivanov, Sergei D.; Lyubartsev, Alexander P.

2005-07-01

82

Simulations of one- and two-electron systems by Bead-Fourier path integral molecular dynamics.  

PubMed

The Bead-Fourier path integral molecular dynamics technique introduced earlier [S. D. Ivanov, A. P. Lyubartsev, and A. Laaksonen, Phys. Rev. E 67 066710 (2003)] is applied for simulation of electrons in the simplest molecules: molecular hydrogen, helium atom, and their ions. Special attention is paid to the correct description of electrons in the core region of a nucleus. In an attempt to smooth the Coulomb potential at small distances, a recipe is suggested. The simulation results are in excellent agreement with the analytical solution for the "harmonic helium atom", as well as with the vibrational potential of the H(2) molecule and He ionization energies. It is demonstrated, that the Bead-Fourier path integral molecular dynamics technique is able to provide the accuracy required for the description of electron structure and chemical bonds in cases when electron exchange effects need not be taken into account. PMID:16080728

Ivanov, Sergei D; Lyubartsev, Alexander P

2005-07-15

83

Path integrals for electronic densities, reactivity indices, and localization functions in quantum systems.  

PubMed

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

2009-11-01

84

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.

Putz, Mihai V.

2009-01-01

85

Comparison between solar electron and ion path lengths traveled during the Ground-Level Enhancement events in solar cycle 23  

NASA Astrophysics Data System (ADS)

The inconsistency of electron and ion path lengths during Solar Energetic Particle (SEP) events remains an open issue. In order to investigate the difference between the electron and ion path lengths during the Ground-Level Enhancement (GLE) events in solar cycle 23, electron and ion data from the WIND/3DP/SST and WIND/EPACT/LEMT instruments respectively have been used. The electron path lengths were determined for the GLEs in solar cycle 23 assuming that the solar release time of non-relativistic electrons is well represented by the onset time of metric type II or decametre-hectometric (DH) type III radio bursts. The values estimated for low-energy electrons (~ 27 keV) were compared to the ion path lengths deduced by Reames for the GLEs in solar cycle 23 based on the onset-time analysis and consistency within an error range of 10% was found. In addition, the electron path lengths were found to increase with increasing electron energies, with the increasing rate of path lengths corresponding to broader position angle distribution (PAD) of electrons, which suggests that electron path length enhancement is due to interplanetary scattering experienced by first-arriving electrons. Furthermore, the solar longitude distribution and IMF topology of the GLE events examined support that the non-relativistic electrons observed have been accelerated in shocks driven by CMEs. Finally, it should be stressed that the observed path length consistency leads to stability of magnetic flux tubes along which particles travel, with a maximum stability time of ~ 4.8 hours, which could be very important for forecasting since, based on the observed onset time of the electron event, it is possible to observe the arrival and duration of the proton event.

Malandraki, Olga; Tan, Lun; Reames, Donald; Ng, Chee; Wang, Linghua; Patsou, Ioanna; Papaioannou, Athanasios

2014-05-01

86

Thermovoltaic evidence for electronic Knudsen flow through silicon microcontacts  

NASA Astrophysics Data System (ADS)

Asymmetric heat generation is detected by Seebeck-voltage measurements in current-carrying microcontacts, produced by adjoining two wedges of n-type silicon in ultrahigh vacuum. Decreasing the contact dimensions increases this asymmetry, which arises in the Knudsen regime of ballistic electron transport when the geometric dimensions of the contacts are sufficiently reduced to become comparable to the electron mean free path.

Gerlach-Meyer, U.; Queisser, H. J.

1983-11-01

87

Path integral study of the correlated electronic states of Na4–Na6  

Microsoft Academic Search

Feynman’s path integral formulation of quantum mechanics is used to study the correlated electronic states of Na4–Na6. Two types of simulations are performed: in the first, the nuclei are allowed to move at finite temperature in order to find the most stable geometries. In agreement with previous calculations, we find that planar structures are the most stable and that there

Randall W. Hall

1990-01-01

88

Lateral homogeneity of the electronic properties in pristine and ion-irradiated graphene probed by scanning capacitance spectroscopy  

PubMed Central

In this article, a scanning probe method based on nanoscale capacitance measurements was used to investigate the lateral homogeneity of the electron mean free path both in pristine and ion-irradiated graphene. The local variations in the electronic transport properties were explained taking into account the scattering of electrons by charged impurities and point defects (vacancies). Electron mean free path is mainly limited by charged impurities in unirradiated graphene, whereas an important role is played by lattice vacancies after irradiation. The local density of the charged impurities and vacancies were determined for different irradiated ion fluences.

2011-01-01

89

Motion of Electrons in Electric and Magnetic Fields: Introductory Laboratory and Computer Studies.  

ERIC Educational Resources Information Center

Describes a series of laboratory experiments and computer simulations of the motion of electrons in electric and magnetic fields. These experiments, which involve an inexpensive student-built electron gun, study the electron mean free path, magnetic focusing, and other aspects. (Author/HM)

Huggins, Elisha R.; Lelek, Jeffrey J.

1979-01-01

90

Gyrosynchrotron radiation formulae. [analysis of electron moving along a helical path in a magnetoactive medium  

NASA Technical Reports Server (NTRS)

The wave-normal emissivity and the ray emissivity formulas for an electron moving along a helical path in a magnetoactive medium are presented. Simplified formulas for the case of an isotropic plasma are also given. Because of the helical motion of the electron, a difference exists between the radiated power per unit solid angle and the received power per unit solid angle. The relation between these two quantities in a magnetoactive medium is shown. Results are compared with those obtained by others, and the sources of discrepancies are pointed out.

Ko, H. C.

1973-01-01

91

Path Integral Monte Carlo Calculation of the Momentum Distribution of the Homogeneous Electron Gas at Finite Temperature  

Microsoft Academic Search

Path integral Monte Carlo (PIMC) simulations are used to calculate the\\u000amomentum distribution of the homogeneous electron gas at finite temperature.\\u000aThis is done by calculating the off-diagonal elements of the real-space density\\u000amatrix, represented in PIMC by open paths. It is demonstrated how the\\u000arestricted path integral Monte Carlo methods can be extended in order to deal\\u000awith open

B. Militzer; E. L. Pollock; D. M. Ceperley

2003-01-01

92

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

93

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

NASA Astrophysics Data System (ADS)

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.; Coker, David F.

2013-10-01

94

Thick-film gold and platinum conducing paths for high temperature electronics  

NASA Astrophysics Data System (ADS)

A new thick film gold conductive composition for high temperature electronics was elaborated and tested. This paste was designed for metallization of the alumina substrates (Al2O3) for electrical interconnection system, e.g. for a silicon carbide Schotky diode. Also platinum pastes for conductive paths resistant to high temperatures (over 600°C) were elaborated by the authors. Several gold and platinum powders and glasses, as well as bonding oxides were examined to design a suitable composition. The influence of the paste composition and firing temperature on the layer properties was shown. The obtained layers were aged a 1000 hours at elevated temperatures (350°C). Sheet resistance of platinum and gold paths was measured. Mechanical strength and electrical resistance of wire bonds to the gold layers after aging were also examined. The electrical measurements were performed at room temperature and elevated temperature (150°C, 250°C, 350°C), using precise four-wire method. The microstructure of layers was also shown.

Jakubowska, Ma?gorzata; Kalenik, Jerzy; Kie?basi?ski, Konrad; M?o?niak, Anna; Zwierkowska, El?bieta

2008-01-01

95

Universal quantum computation with electron spins in quantum dots based on superpositions of spacetime paths and Coulomb blockade  

Microsoft Academic Search

Using electrostatic gates to control the electron positions, we present a new controlled-NOT gate based on quantum dots. The qubit states are chosen to be the spin states of an excess conductor electron in the quantum dot; and the main ingredients of our scheme are the superpositions of space-time paths of electrons and the effect of Coulomb blockade. All operations

Cyrus C. Y. Lin; Chopin Soo; Yin-Zhong Wu; Wei-Min Zhang

2004-01-01

96

All-electron path integral Monte Carlo simulations of warm dense matter: application to water and carbon plasmas.  

PubMed

We develop an all-electron path integral Monte Carlo method with free-particle nodes for warm dense matter and apply it to water and carbon plasmas. We thereby extend path integral Monte Carlo studies beyond hydrogen and helium to elements with core electrons. Path integral Monte Carlo results for pressures, internal energies, and pair-correlation functions compare well with density functional theory molecular dynamics calculations at temperatures of (2.5-7.5)×10(5) K, and both methods together form a coherent equation of state over a density-temperature range of 3-12 g/cm(3) and 10(4)-10(9) K. PMID:22540485

Driver, K P; Militzer, B

2012-03-16

97

Iron-Oxide Minerals Affect Extracellular Electron-Transfer Paths of Geobacter spp  

PubMed Central

Some bacteria utilize (semi)conductive iron-oxide minerals as conduits for extracellular electron transfer (EET) to distant, insoluble electron acceptors. A previous study demonstrated that microbe/mineral conductive networks are constructed in soil ecosystems, in which Geobacter spp. share dominant populations. In order to examine how (semi)conductive iron-oxide minerals affect EET paths of Geobacter spp., the present study grew five representative Geobacter strains on electrodes as the sole electron acceptors in the absence or presence of (semi)conductive iron oxides. It was found that iron-oxide minerals enhanced current generation by three Geobacter strains, while no effect was observed in another strain. Geobacter sulfurreducens was the only strain that generated substantial amounts of currents both in the presence and absence of the iron oxides. Microscopic, electrochemical and transcriptomic analyses of G. sulfurreducens disclosed that this strain constructed two distinct types of EET path; in the absence of iron-oxide minerals, bacterial biofilms rich in extracellular polymeric substances were constructed, while composite networks made of mineral particles and microbial cells (without polymeric substances) were developed in the presence of iron oxides. It was also found that uncharacterized c-type cytochromes were up-regulated in the presence of iron oxides that were different from those found in conductive biofilms. These results suggest the possibility that natural (semi)conductive minerals confer energetic and ecological advantages on Geobacter, facilitating their growth and survival in the natural environment.

Kato, Souichiro; Hashimoto, Kazuhito; Watanabe, Kazuya

2013-01-01

98

Restricted Path-Integral Molecular Dynamics for Simulating the Correlated Electron Plasma in Warm Dense Matter  

NASA Astrophysics Data System (ADS)

Several areas of study including heavy ion beam, large scale laser, and high pressure or Thomson scattering studies necessitate a fundamental understanding of warm dense matter (WDM) i.e. matter at high temperature and high density. The WDM regime, however, lacks any adequate highly developed class of simulation methods. Recent progress to address this deficit has been the development of orbital-free Density Functional Theory (ofDFT). However, scant benchmark information is available on temperature and pressure dependence of simple but realistic models in WDM regime. The present work aims to fill this critical gap using the restricted path-integral molecular dynamics (rPIMD) method. Within the discrete path integral representation, electrons are described as harmonic necklaces. Quantum exchange takes the form of cross linking between electron necklaces. The fermion sign problem is addressed by restricting the density matrix to positive values. The molecular dynamics algorithm is employed to sample phase space. Here, we focus on the behavior of strongly correlated electron plasmas under WDM conditions. We compute the kinetic and potential energies and compare them to those obtained with the ofDFT method.

Kapila, Vivek; Deymier, Pierre; Runge, Keith

2011-11-01

99

Path-Integral Monte Carlo Simulation of the Warm Dense Homogeneous Electron Gas  

NASA Astrophysics Data System (ADS)

We perform calculations of the 3D finite-temperature homogeneous electron gas in the warm-dense regime (rs?(3/4?n)1/3a0-1=1.0-40.0 and ??T/TF=0.0625-8.0) using restricted path-integral Monte Carlo simulations. Precise energies, pair correlation functions, and structure factors are obtained. For all densities, we find a significant discrepancy between the ground state parametrized local density approximation and our results around TF. These results can be used as a benchmark for developing finite-temperature density functionals, as well as input for orbital-free density function theory formulations.

Brown, Ethan W.; Clark, Bryan K.; DuBois, Jonathan L.; Ceperley, David M.

2013-04-01

100

Electron energy transport in ion waves and its relevance to laser-produced plasmas  

Microsoft Academic Search

Electron energy transport in plasmas is examined in the context of ion waves which are intermediate between collisionless isothermal ion acoustic waves and collisional adiabatic sound waves. The conductivity is found to be much less than the Spitzer-Haerm result for wavelengths less than 1000 electron mean free paths. This is expected to be relevant to laser-produced ablating plasmas in which

A. R. Bell

1983-01-01

101

Molecular Dynamics. VI. Free-Path Distributions and Collision Rates for Hard-Sphere and Square-Well Molecules  

Microsoft Academic Search

Free-path distributions and collision rates for systems of hard-sphere and square-well molecules are computed and compared to simple models. Mean free paths for solids and dense fluids are found to be within 2% of those predicted by dividing the kinetic-theory mean free path by the relative probability of two molecules in contact. These mean free paths are much smaller than

T. Einwohner; B. J. Alder

1968-01-01

102

Production of Relativistic Electrons Following Storms and Substorms: Results from Stepwise Multiple Regression and Path Analysis  

NASA Astrophysics Data System (ADS)

A number of parameters of the solar wind and magnetosphere are correlated with the production of relativistic electrons. These include the level of relativistic electrons at storm onset, seed electron flux, solar wind velocity and number density, IMF Bz, AE and Kp indices, and ULF and VLF wave power. However, as all these variables may be intercorrelated between each other as well, simple correlations between each predictor variable and electron flux may not tell the whole story. We identified 166 storms and substorms (1992-2002) with at least 72 storm free hours after the minimum Dst. We obtained hourly averaged electron fluxes for relativistic electrons (> 1.5 MeV) and seed electrons (100 keV) from several spacecraft (Los Alamos National Laboratory geosynchronous energetic particle instruments). For each storm or substorm event, we found the log10 maximum relativistic electron flux for each satellite following the end of the main phase of each storm. No spacecraft was in operation for this entire period, so we averaged over all available satellites in each hour. As each satellite was calibrated differently, we first converted each observation to a standardized score with mean 0 and standard deviation of 1. We performed a stepwise multiple regression using solar wind velocity and flow angles (both latitude and longitude), number density, standard deviation of velocity and number density, a ULF index (Kozyreva et al., 2007, Planet. Space Sci., 55, 755-769), VLF (.5-1.0 kHz), AE, Kp, Dst, IMF Bz, Bz RMS standard deviation , and log10 of seed electron and onset relativistic electron fluxes as predictor variables. We also performed regressions entering physical variables first (e.g., solar wind velocity) and adding indices second (e.g., Dst) to determine if physical variables were more predictive. We subsequently performed a path analysis, showing the relationships between the predictor variables, as well as their influence on electron flux following each event. The rise in relativistic electron flux following storms and substorms is best explained by a set of variables rather than by one or two factors. Vsw, ULF, main phase seed electron flux, and either IMF Bz or Dst are the most significant explanatory variables. AE (relating to substorm activity) and Kp show somewhat less influence.

Simms, L. E.; Engebretson, M. J.; Pilipenko, V.; Reeves, G. D.

2012-12-01

103

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.  

PubMed

We develop the path-branching representation for nonadiabatic electron wavepacket dynamics [T. Yonehara and K. Takatsuka, J. Chem. Phys. 132, 244102 (2010)] so as to treat dynamics in an energy range comparable to the barrier height of adiabatic potential energy curves. With this representation two characteristic chemical reaction dynamics are studied, in which an incident nuclear wavepacket encounters a potential barrier, on top of which lies another nonadiabatically coupled adiabatic potential curve: (1) Dynamics of initial paths coming into the nonadiabatic interaction region with energy lower than the barrier height. They branch into two pieces (and repeat branching subsequently), the upper counterparts of which can penetrate into a classically inaccessible high energy region and eventually branch back to the product region on the ground state curve. This is so to say surmounting the potential barrier via nonadiabatically coupled excited state, and phenomenologically looks like the so-called deep tunneling. (2) Dynamics of classical paths whose initial energies are a little higher than the barrier but may be lower than the bottom of the excited state. They can undergo branching and some of those components are trapped on top of the potential barrier, being followed by the population decay down to the lower state flowing both to product and reactant sites. Such expectations arising from the path-branching representation are numerically confirmed with full quantum mechanical wavepacket dynamics. This phenomenon may be experimentally observed as time-delayed pulses of wavepacket trains. PMID:24697428

Yamamoto, Kentaro; Takatsuka, Kazuo

2014-03-28

104

TOPICAL REVIEW: Electron dynamics in inhomogeneous magnetic fields  

Microsoft Academic Search

This review explores the dynamics of two-dimensional electrons in magnetic potentials that vary on scales smaller than the mean free path. The physics of microscopically inhomogeneous magnetic fields relates to important fundamental problems in the fractional quantum Hall effect, superconductivity, spintronics and graphene physics and spins out promising applications which will be described here. After introducing the initial work done

Alain Nogaret

2010-01-01

105

Path-integral approach in the calculation of the electron density of states at the semiconductor-insulator interface  

Microsoft Academic Search

The electron density of states near the semiconductor-insulator interface is calculated using the Feynman's path-integral method. Statistical interface charge distribution properties have been taken into account and the Fourier transform of the binary correlation function of the random potential has been computed. Finally the electron density of states in the band tail in a first cumulant approximation is obtained. The

G. Slavcheva; I. Yanchev

1996-01-01

106

Spatial correlations in the electron gas: Path integral Monte Carlo simulation  

SciTech Connect

Thermally excited states of the three-dimensional electron gas in a neutralizing background are computed by path integral Monte Carlo simulation for values of the Wigner-Seitz radius within the interval 5 < r{sub s} < 15. Coulomb and exchange interactions, permutation symmetry, and spin state are treated explicitly. Variation of electron correlation functions with density and temperature is analyzed. Quantum effects suppress and enhance spatial correlation at low and high densities, respectively. Transition between the electron-gas states characterized by these opposite trends corresponds to a density of approximately 2.5 x 10{sup 21} cm{sup -3}. A transition line between liquid-like and gaslike phases is determined in the temperature-density diagram. Weak anisotropy of many-body correlations in the liquid-like state stimulates excitation of spherically symmetric collective rotational modes. The effective short-range pseudopotential exhibits strong temperature dependence due to exchange effects. For strongly correlated systems, the characteristic screening length deviates from that predicted by the Thomas-Fermi screening model ({approx}{radical}r{sub s}), approaching a linear function of r{sub s}. The effective short-range interaction substantially differs from the Yukawa potential in mean field theory. Coulomb interaction shifts the Fermi level up by an order of magnitude or higher, and this effect becomes stronger with decreasing density.

Shevkunov, S. V. [St. Petersburg State Polytechnic University (Russian Federation)], E-mail: root@svsh.tu.neva.ru

2006-07-15

107

Mean Free Air Anomalies: Sources of Information on Heterogeneities in the Earth'S Mantle.  

National Technical Information Service (NTIS)

Maps of mean free air anomalies of the entire earth by data of I. D. Zhongolovich, W. A. Heiskanen and W. M. Kaula are presented. These anomalies which are a substitute for the isostatic anomalies are evidently connected with the heterogeneities in the ma...

M. E. Artemev

1967-01-01

108

All-Electron Path Integral Monte Carlo Simulations of Small Atoms and Molecules  

Microsoft Academic Search

Imaginary-time Feynman path integrals describe quantum mechanics at finite temperatures. Monte Carlo simulations using path integrals have many ap- plications to nanoscale physics. Fermions introduce negative terms in the partition function, which we remove with a fixed-node approximation. In this article, we give an introduction to path integral Monte Carlo simulations. We focus on a difficult problem: the direct application

J. Shumway

109

Extending the collisional fluid equations into the long mean-free-path regime in toroidal plasmas. IV. Banana regime  

SciTech Connect

In Part I [Phys. Fluids B 2, 1190 (1990)] and Part II [Phys. Plasmas 12, 082508 (2005)], it was emphasized that the equilibrium plasma viscous forces when applied for the magnetohydrodynamic (MHD) modes are only rigorously valid at the mode rational surface where m-nq=0. Here, m is the poloidal mode number, n is the toroidal mode number, and q is the safety factor. This important fact has been demonstrated explicitly by calculating the viscous forces in the plateau regime in Parts I and II. Here, the effective viscous forces in the banana regime are calculated for MHD modes by solving the linear drift kinetic equation that is driven by the plasma flows first derived in Part I. At the mode rational surface, the equilibrium plasma viscous forces are reproduced. However, it is found that away from the mode rational surface, the viscous forces for MHD modes decrease, a behavior similar to that observed in the viscous forces for the plateau regime. The proper form of the momentum equation that is appropriate for the modeling of the MHD modes is also discussed.

Shaing, K. C. [Plasma and Space Science Center, and Department of Physics, National Cheng Kung University, Tainan, 701 Taiwan (China) and Engineering Physics Department, University of Wisconsin, Madison, Wisconsin 53706 (United States)

2007-11-15

110

Plasmaspheric electron content in the GPS ray paths over Japan under magnetically quiet conditions at high solar activity  

Microsoft Academic Search

Vertical total electron content (GPS-TEC) data obtained from the dual-frequency GPS receiver network (GEONET) in Japan are compared with those calculated using the Sheffield University plasmasphere-ionosphere model (SUPIM). The model is also used to estimate the electron content in the plasmaspheric sections of GPS ray paths for the three seasons of high solar activity (F10.7 = 165) under magnetically quiet

N. Balan; Y. Otsuka; T. Tsugawa; S. Miyazaki; T. Ogawa; K. Shiokawa

2002-01-01

111

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

112

A model and computer code for the Monte Carlo simulation of relativistic electron and positron penetration through matter  

Microsoft Academic Search

A model and Monte Carlo code were developed as a subroutine dealing with electron and positron transport in a computer program simulating the response of a multimaterial nuclear detector. The variable scattering angle model and the variable screened Rutherford model are used for scattering. In both models, an artificial mean free path with fixed, computationally convenient length is used. The

M. Ismail; D. Liljequist

1986-01-01

113

Electronic and atomic structure of liquid potassium via path integral molecular dynamics with non-local quantum exchange  

NASA Astrophysics Data System (ADS)

We develop a novel first-principle molecular dynamics method based on the discretized path integral formalism of quantum mechanics. This method which includes quantum exchange is used to simulate the behavior of liquid potassium at high temperature. We compute the energy as well as the electronic and atomic structural properties of the liquid metal. These results compare favorably with previous calculations and experimental results.

Deymier, P. A.; Jabbour, G. E.; Weinberg, J. D.; Cherne, F. J.

1996-03-01

114

Coherent control of the electron quantum paths for the generation of single ultrashort atto second laser pulse  

SciTech Connect

We report a mechanism and a realizable approach for the coherent control of the generation of an isolated and ultrashort atto second (as) laser pulse from atoms by optimizing the two-color laser fields with a proper time delay. Optimizing the laser pulse shape allows the control of the electron quantum paths and enables high-harmonic generation from the long- and short-trajectory electrons to be enhanced and split near the cutoff region. In addition, it delays the long-trajectory electron emission time and allows the production of extremely short atto second pulses in a relatively narrow time duration. As a case study, we show that an isolated 30 as pulse with a bandwidth of 127 eV can be generated directly from the contribution of long-trajectory electrons alone.

Liu, I-Lin [Center for Quantum Science and Engineering, Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); Li, Peng-Cheng [Center for Quantum Science and Engineering, Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Chu, Shih-I [Center for Quantum Science and Engineering, Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); Department of Chemistry, University of Kansas, Lawrence, Kansas 66045 (United States)

2011-09-15

115

Simulation of the Correlated Electron Plasma in the Warm Dense Matter Regime by Restricted Path-Integral Molecular Dynamics  

NASA Astrophysics Data System (ADS)

Warm dense matter (WDM) can be characterized by electron temperatures of a few eV and densities an order of magnitude or more beyond ambient. This regime currently lacks any adequate highly developed class of simulation methods. Recent developments in orbital-free Density Functional Theory (ofDFT) aim to provide such a simulation method, however, little benchmark information is available on temperature and pressure dependence of simple but realistic models in WDM regime. The present work aims to fill this critical gap using the restricted path-integral molecular dynamics (rPIMD) method. Within the discrete path integral representation, electrons are described as harmonic necklaces, while, quantum exchange takes the form of cross linking between electron necklaces. The fermion sign problem is addressed by restricting the density matrix to positive values and a molecular dynamics algorithm is employed to sample phase space. Here, we focus on the behavior of strongly correlated electron plasmas under WDM conditions. We compute the kinetic and potential energies and compare them to those obtained with the ofDFT method.

Kapila, Vivek; Deymier, Pierre; Runge, Keith

2012-02-01

116

Electron-phonon coupling in Ba 0.6K 0.4BiO 3 by discretized quantum path integral molecular dynamics  

NASA Astrophysics Data System (ADS)

We calculated the electron-phonon interaction energy and estimated the electron-phonon coupling constant in Ba 0.6K 0.4BiO 3 using a quantum path integral molecular dynamics. We determined the electron-phonon coupling constant at room temperature to be about 1.34.

Lee, C. Y.; Deymier, P. A.

1992-01-01

117

Temperature Dependence of the Kinetic Energy of the Correlated Electron Plasma by Restricted Path-Integral Molecular Dynamics  

NASA Astrophysics Data System (ADS)

Recent progress in orbital-free Density Functional Theory (OF-DFT), particularly with regard to temperature dependent functionals, has promise for the simulation of warm dense matter (WDM) systems. WDM includes systems with densities of an order of magnitude beyond ambient or more and temperatures measured in kilokelvin. A challenge for the development of temperature dependent OF-DFT functionals is the lack of benchmark information with temperature and pressure dependence on simple models under WDM conditions. We present an approach to fill this critical gap using the restricted path-integral molecular dynamics (rPIMD) method. Electrons are described as harmonic necklaces within the discrete path integral representation while quantum exchange takes the form of cross linking between electron necklaces. A molecular dynamics algorithm is used to sample phase space and the fermion sign problem is addressed by restricting the density matrix to positive values. The temperature dependence of kinetic energies for the strongly coupled electron plasma is presented for a number of Wigner-Seitz radii in terms of a fourth order Sommerfeld expansion.

Runge, Keith; Deymier, Pierre

2013-03-01

118

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

119

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

120

Electron energy transport in ion waves and its relevance to laser-produced plasmas  

Microsoft Academic Search

Electron energy transport in plasmas is examined in the context of ion waves which are intermediate between collisionless isothermal ion acoustic waves and collisional adiabatic sound waves. The conductivity is found to be much less than the Spitzer-Ha¨rm result for wavelengths less than 1000 electron mean free paths. This is expected to be relevant to laser-produced ablating plasmas in which

A. R. Bell

1983-01-01

121

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

122

Identification of the CHClF2 molecule fragmentation paths by electron impact  

NASA Astrophysics Data System (ADS)

CFC compounds in the atmosphere play a crucial role to the environment, being the main responsible for the enlargement of the ozone hole. Recent studies show that electron impact can be a significant process for the fragmentation of these molecules; for this reason, the collisional processes of CHClF2 by electron impact were studied. Total and partial cross sections have been obtained, showing the predominance of the release of neutral chlorine, which is the main responsible for the breaking down of ozone molecules. There is a strong indication that this chlorine is being released as a result of the ionization of electrons from both chlorine and fluorine orbitals.

Sigaud, L.; Ferreira, Natalia; de Jesus, V. L. B.; Wolff, W.; de Barros, A. L. F.; dos Santos, A. C. F.; Menezes, R. S.; Rocha, A. B.; Shah, M. B.; Montenegro, E. C.

2012-11-01

123

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

124

Electron transport in single-walled carbon nanotubes  

NASA Astrophysics Data System (ADS)

We present electron transport experiments on single walled carbon nanotubes (SWNTs). By measuring the linear scaling of resistance with length, we determine an unusually long mean free path of Lm ˜1 mum at room temperature. From the temperature dependence of the mean free path for over 10 samples we show that inelastic scattering with acoustic phonons are the main source of scattering at room temperature and experimentally determine the electron-acoustic phonon strength. Disorder ultimately limits the low temperature mean free path (Lm ˜10 mum), which we show by employing scanning gate microscopy. We analyze the non-linear scaling of resistance with length and temperature to further elucidate the nature of this disorder. In general, we find that transport in 1-dimension is dominated by the strongest defect along the channel. For larger source-drain voltage (VSD > 0.2 V), we show that L m is significantly reduced in both metallic and semiconducting SWNTs, due to electrons scattering with the higher energy phonons. In semiconducting samples, when the Fermi energy is close to the energy band gap, we observe an anomalous conductance dip. Finally, we utilize locally controlled gate structures to fabricate a series of tunable barriers to form a superlattice and observe its mini-band structure superimposed on that of the nanotubes.

Purewal, Meninder S.

125

Silicon electronics on silk as a path to bioresorbable, implantable devices  

NASA Astrophysics Data System (ADS)

Many existing and envisioned classes of implantable biomedical devices require high performance electronics/sensors. An approach that avoids some of the longer term challenges in biocompatibility involves a construction in which some parts or all of the system resorbs in the body over time. This paper describes strategies for integrating single crystalline silicon electronics, where the silicon is in the form of nanomembranes, onto water soluble and biocompatible silk substrates. Electrical, bending, water dissolution, and animal toxicity studies suggest that this approach might provide many opportunities for future biomedical devices and clinical applications.

Kim, Dae-Hyeong; Kim, Yun-Soung; Amsden, Jason; Panilaitis, Bruce; Kaplan, David L.; Omenetto, Fiorenzo G.; Zakin, Mitchell R.; Rogers, John A.

2009-09-01

126

Silicon electronics on silk as a path to bioresorbable, implantable devices  

PubMed Central

Many existing and envisioned classes of implantable biomedical devices require high performance electronics?sensors. An approach that avoids some of the longer term challenges in biocompatibility involves a construction in which some parts or all of the system resorbs in the body over time. This paper describes strategies for integrating single crystalline silicon electronics, where the silicon is in the form of nanomembranes, onto water soluble and biocompatible silk substrates. Electrical, bending, water dissolution, and animal toxicity studies suggest that this approach might provide many opportunities for future biomedical devices and clinical applications.

Kim, Dae-Hyeong; Kim, Yun-Soung; Amsden, Jason; Panilaitis, Bruce; Kaplan, David L.; Omenetto, Fiorenzo G.; Zakin, Mitchell R.; Rogers, John A.

2009-01-01

127

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

Microsoft Academic Search

Within the last two decades, a number of experimental techniques have been developed to measure mean free paths and absolute\\u000a and effective cross-sections for various processes related to the interaction of low-energy electrons with condensed matter.\\u000a In all of the experiments, a monochromatic electron beam impinges on a thin multilayer film composed of atoms and\\/or molecules\\u000a condensed on a metal

Andrew D. Bass; Léon Sanche

1998-01-01

128

Electron-Phonon Interaction in Barium-Potassium Bismuth-Oxygen Superconductor by Quantum Path Integral Molecular Dynamics  

NASA Astrophysics Data System (ADS)

We have introduced two different techniques in this paper to investigate the high Tc superconductor BaK BiO_3. The first one is the rigid -ion molecular dynamics model to calculate classical properties of the crystal. This method provides the ionic anisotropic vibrational spectra. It is found that the oxygen modes dominate the vibrational spectrum from 150 cm^ {-1} up to 820 cm^{ -1}. An increase in the number of substituted K around an oxygen favors high frequency vibrational modes. We have also determined by experiment IR spectrum. The absorption peaks are between 380 to 880 cm^{-1 }. Our experimental and computational data are in good agreement in the high frequency region. The second technique used to investigate this high Tc superconductor is based on a quantum path integral molecular dynamics. It has been applied for the first time to the determination of electron-phonon interaction energy. We estimate the electron phonon coupling constant at about 1.34. This value represents a weak to moderate electron-phonon coupling inBa_{1-x}K_{x}BiO _3 in agreement with current views of this pairing mechanism in this material.

Lee, Chong Yong

1990-01-01

129

Two-electron states in Ba0.6K0.4BiO3 via discretized path integral molecular dynamics  

NASA Astrophysics Data System (ADS)

We report for the calculation of the electronic singlet and triplet states in Ba0.6K0.4BiO3 by a discretized path integral molecular dynamics which includes quantum indistinguishability. We show that two nonpolarized electrons form a bound complex within a single Bi ion. Two polarized electrons are located on different Bi sites. The singlet-triplet splitting is found to be ˜0.6 eV.

Lee, C. Y.; Deymier, P. A.

1997-06-01

130

Injection of ballistic hot electrons and cool holes in a two-dimensional electron gas  

NASA Astrophysics Data System (ADS)

We have constructed a novel magnetic spectrometer to study the dynamics of hot electrons and cool missing electron states injected by quantum point contacts in the two-dimensional electron gas of a GaAs-Al xGa 1- x As heterostructure. The mean free path of these quasi-particles is found to be longer than recent theoretical estimates. The injection energy of the particles is found to be anomalously low as the point contact approaches pinch-off, and also for high bias voltages.

Williamson, J. G.; van Houten, H.; Beenakker, C. W. J.; Broekaart, M. E. I.; Spendeler, L. I. A.; van Wees, B. J.; Foxon, C. T.

1990-04-01

131

Hot-electron drift velocity in III V semiconductors under the condition of impact ionization  

NASA Astrophysics Data System (ADS)

A calculation has been carried out for the drift velocity of electrons in the highfield region under the condition of impact ionization in III V semiconductor compounds. The energy-balance equation of the one-electron model has been solved considering alloy scattering and carrier-carrier interaction, in addition to optical phonon and ionization scattering. Fairly good agreement is obtained for GaAs with the available experimental and Monte-Carlo results. Graphs for the high-field drift velocity has also been plotted for Ga1- x InxAs ( x = 0.53) at different ratios of ionization mean-free path and optical phonon mean-free path. The plot of high-field drift velocity versus ionization rate reveals that the high-field drift velocity strongly depends on the ionization rate of carriers, and vice versa.

Singh, S. R.; Pal, B. B.

1987-05-01

132

Using Exact Particle Paths in the Calculation of Linear Ion-Electron Tearing and Dependence on the Equilibrium State Parameters  

NASA Astrophysics Data System (ADS)

We've developed an algorithm to iteratively solve the linearized Vlasov equation for growth rates and first-order potentials of instabilities such as collisionless ion-electron tearing in a neutral sheet. It requires no assumptions about the nature of the equilibrium trajectories and can give exact (numerical) results. In this work we describe the algorithm, and its application to study the behavior of the tearing-mode starting from a Harris equilibrium over a range of the control parameters: the current sheet half-width w, (Te)/(T_i), (Me)/(M_i). The method starts with computing and saving several thousand equilibrium particle paths to sample the phase space for a chosen equilibrium state. Then for a given k, the coupled equations for ?c{A1} and ? are solved iteratively with ?c{J1} computed from time-integrals over the saved particle paths. A new ?c{A1} is found using a Green's function to ensure the boundary- conditions are satisfied, while the correction to ? is found from a relation involving integrals of the currents and ?c{A1}. ? 1 is found by assuming quasi-neutrality. The method is stable, converges for any starting values we've tried, requires less than a MB of memory, and 10MB--10GB of disk space for the paths. CPU time on a desktop PC is from ˜ 10 minutes to an hour for each k. The algorithm is similar in spirit to previous work [1], but was developed independently so the implementation is different. Typical dispersion curves, plots of potentials and response functions will be shown. We've found the growth-rates can be fit quite well (correlations of 0.999) by the expression ? (k)= ax kb(1/w-k) where parameters ax, b are determined from the peak growth ? x and wavenumber kx. Preliminary results are that for parameter values (Me)/(M_i)=1, (Te)/(T_i)=1 the dependence of ? x, kx on w, over the range 3--20, is given by kx=0.527 w-1.07 and ? x=0.219 w-2.32 where ? x is scaled by ? i, k and w are scaled by ? i. For (Me)/(M_i)= 1/1836, (Te)/(T_i)=1/2 the dependence is kx=0.451 w-1.11 and ? x=0.0567 w-2.379. [1] M. Brittnacher, K. B. Quest, and H. Karimabadi, J. Geophys. Res., 100, 3551, (1995); W. Daughton, J. Geophys. Res., 103, 29429, (1998).

Allen, C. W.

2004-12-01

133

Electron spin resonance and exchange paths in the orthorhombic dimer system Sr2VO4  

NASA Astrophysics Data System (ADS)

We report on susceptibility and electron spin resonance (ESR) measurements at X- and Q-band frequencies of Sr2VO4 with orthorhombic symmetry. In this dimer system, the V4+ ions are in tetrahedral environment and are coupled by an antiferromagnetic intradimer exchange constant J/kB? 100 K to form a singlet ground state without any phase transitions between room temperature and 2 K. Based on an extended Hückel tight-binding analysis, we identify the strongest exchange interaction to occur between two inequivalent vanadium sites via two intermediate oxygen ions. The ESR absorption spectra can be well fitted by a single Lorentzian line and the temperature dependence of the ESR intensity, and the dc susceptibility can be modeled by using the Bleaney-Bowers approach for independent dimers. The temperature dependence of the ESR linewidth at X-band frequency can be modeled by a superposition of a linear increase with temperature with a slope ? =1.35 Oe/K and a thermally activated behavior with an activation energy ?/kB =1418 K, both of which point to spin-phonon coupling as the dominant relaxation mechanism in this compound.

Deisenhofer, J.; Schaile, S.; Teyssier, J.; Wang, Zhe; Hemmida, M.; von Nidda, H.-A. Krug; Eremina, R. M.; Eremin, M. V.; Viennois, R.; Giannini, E.; van der Marel, D.; Loidl, A.

2012-12-01

134

Photoelectron angular distributions from liquid water: effects of electron scattering.  

PubMed

Photoelectron angular distributions (PADs) from the liquid-water surface and from bulk liquid water are reported for water oxygen-1s ionization. Although less so than for the gas phase, the measured PADs from the liquid are remarkably anisotropic, even at electron kinetic energies lower than 100 eV, when elastic scattering cross sections for the outgoing electrons with other water molecules are large. The PADs reveal that theoretical estimates of the inelastic mean free path are likely too long at low kinetic energies, and hence the electron probing depth in water, near threshold ionization, appears to be considerably smaller than so far assumed. PMID:24206487

Thürmer, Stephan; Seidel, Robert; Faubel, Manfred; Eberhardt, Wolfgang; Hemminger, John C; Bradforth, Stephen E; Winter, Bernd

2013-10-25

135

Electron cyclotron resonance microwave ion sources for thin film processing  

SciTech Connect

Plasmas created by microwave absorption at the electron cyclotron resonance (ECR) are increasingly used for a variety of plasma processes, including both etching and deposition. ECR sources efficiently couple energy to electrons and use magnetic confinement to maximize the probability of an electron creating an ion or free radical in pressure regimes where the mean free path for ionization is comparable to the ECR source dimensions. The general operating principles of ECR sources are discussed with special emphasis on their use for thin film etching. Data on source performance during Cl base etching of Si using an ECR system are presented. 32 refs., 5 figs.

Berry, L.A.; Gorbatkin, S.M.

1990-01-01

136

Electronic States of Nickel Effected By Magnetic Doping  

NASA Astrophysics Data System (ADS)

Spin currents have a great potential to replace charge currents. This would revolutionize how we read/write information. The generation and switching of spin currents however must be well understood. Transport measurements suggest that magnetic impurities can alter the mean free path of carriers and thereby create spin currents. Angle-resolved photoemission is used to determine the change in the electronic states of Ni induced by doping with iron, chromium, and manganese near the Fermi Energy. The samples were single crystals of nickel(110) with variable amounts of dopant diffused into it. Alloy single crystals were used over epitaxial thin films due to the sharper features at the Fermi Energy that they produced. The mean free path, magnetic splitting, and carrier density are affected by a few percent of each of the dopants. Iron suppresses the mean free path of minority spins only, while chromium and manganese suppresses both spins and decreases the magnetic splitting. The strong variation of these affects from one impurity to the other supports the concept of tailoring spin transport by magnetic doping. [1] K. N. Altmann et al., Phys. Rev. Lett. 87, 137201 (2001) [2] K.R. Podolak, Ph.D. Thesis, Penn. State (2008)

Podolak, Ken; Smith, Jamie

2012-02-01

137

Electron Density Distributions Calculated For The Ni-Sulfides Millerite, Vaesite and Heazlewoodite and Nickel Metal: A case for The Importance Of NiNi Bond Paths For Electron Transport  

SciTech Connect

Bond paths and the bond critical point properties (the electron density, ?, and the Hessian of ? at the bond critical point) have been calculated for the bonded interactions comprising the Ni?sulfide minerals millerite, vaesite and heazlewoodite and Ni metal. The experimental NiS bond lengths decrease linearly as the magnitudes of the properties at the bond critical point, bcp, increase in value. NiNi bond paths exist between the Ni atoms in heazlewoodite and millerite for NiNi separations that match the shortest NiNi separation in Ni metal, an indicator that the Ni atoms are bonded. NiNi bond paths also exist between the Ni atoms in bulk Ni metal. The bcp properties of the NiNi bonded interactions in Ni metal are virtually the same as those in the two Ni sulfides. NiNi bond paths are absent in vaesite where the NiNi separations are 60% longer than those in Ni metal. The bcp properties for the NiNi bonded interactions scatter along protractions of the NiS bond length?bcp property trends, suggesting that the two bonded interactions have similar characteristics. The NiNi bond paths radiate throughout Ni metal and the metallic heazlewoodite structures as continuous networks of interconnected NiNi bond paths whereas the NiNi paths in millerite, a highly covalent d,p metal, are restricted to isolated Ni3 rings of NiNi bond paths interconnected by S atoms. Electron transport in Ni metal and heazlewoodite is pictured as occurring along the bond paths, which behave as networks of atomic size wires that radiate in a contiguous circuit throughout the two structures. Unlike heazlewoodite, the electron transport in millerite is pictured as involving a cooperative hopping of the d?orbital electrons from the Ni3 rings comprising Ni3S9 clusters to Ni3 rings in adjacent clusters via the p?orbitals on the interconnecting S atoms. Vaesite, an insulator at low temperatures and a doped semiconductor at higher temperatures, lacks NiNi bond paths. The net charges conferred on the Ni and S atoms are about a quarter that of their nominal formal valences for the atoms in millerite and vaesite with the net charge on Ni increasing with increasing NiS bond length. The reduced net charge on the Ni atom in heazlewoodite is related to its NiNi metal bonded interactions and the contiguity of the NiNi bond paths.

Gibbs, G V.; Downs, R T.; Prewitt, C T.; Rosso, Kevin M.; Ross, Nancy; Cox, David F.

2005-12-24

138

Effect of electron collisions on transport coefficients induced by the inverse bremsstrahlung absorption in plasmas  

SciTech Connect

The transport coefficients of fully ionized plasmas under the influence of a high-frequency electric field are derived solving numerically the electron Fokker-Planck equation using a perturbation method, parametrized as a function of the electron mean-free-path {lambda}{sub ei} compared to the spatial scales L. The isotropic and anisotropic contributions of the inverse bremsstrahlung heating are considered. Electron-electron collision terms are kept in the analysis, which allows us to consider with sufficient accuracy to describe plasmas with arbitrary atomic number Z. Practical numerical fits of the transport coefficients are proposed as functions of Z and the collisionality parameter {lambda}{sub ei}/L.

Bendib, A.; Tahraoui, A.; Bendib, K.; Mohammed El Hadj, K.; Hueller, S. [Laboratoire d'Electronique Quantique, Faculte de Physique, USTHB, El Alia BP 32, Bab Ezzouar 16111, Algiers (Algeria); Centre de Physique Theorique, Ecole Polytechnique, F-91128 Palaiseau Cedex (France)

2005-03-01

139

Carbon KVV Auger electron emission from highly oriented pyrolytic graphite bombarded by fast protons  

NASA Astrophysics Data System (ADS)

We have studied carbon KVV Auger electron emission from highly oriented pyrolytic graphite (HOPG) by ion-induced 180° electron spectroscopy. In obliquely emitting directions across the HOPG (0 0 0 1) surface, the Auger peak yield induced by MeV protons becomes lower than in the surface normal direction. An analysis based on mean free path for inelastic scattering indicates that the observed reduction of the Auger yield can be explained by increased inelastic collisions with valence electrons above the surface. The experimental results provide information about the production sites of the KVV Auger electrons in the layer structure.

Kudo, Hiroshi; Haruyama, Katsuhiro; Kinoshita, Takao; Seki, Seiji; Narumi, Kazumasa; Naramoto, Hiroshi

2002-05-01

140

Shortest Paths.  

ERIC Educational Resources Information Center

There are many uses for the shortest path algorithm presented which are limited only by our ability to recognize when a problem may be converted into the shortest path in a graph representation. (Author/TG)

Shore, M. L.

1980-01-01

141

Observations of the HF induced total electron content variations along the paths of the gps signals above the sura facility  

NASA Astrophysics Data System (ADS)

Recently several authors reported experimental evidences total electron content (TEC) varia-tions along the paths of GPS satellite signals caused by the HF heating of the F2 region of the ionosphere [1,2]. Here we present results on TEC variations caused by the vertical pumping of the ionosphere by radiation of the SURA facility at a frequency 4.3 MHz. In our experiments we used differ-ent pump radiation schedules, like [30 s "on", 30 s "off"]; [2 minutes "on" 2 minutes "off"]; [2 min "on" 4 minutes "off"]; and continuous pumping. The most reliable evidence of the pump-induced TEC variations was obtained on August 27, 2009. During the experiment the continuous pumping of the ionosphere with effective radiated power 60 MW started approxi-mately 5 minutes prior to Ionospheric Penetration Point (IPP) for GPS G21 signal entrance to the heated volume of the ionosphere (at (-3) dB level of the heater beam). The TEC variations were observed during whole IPP pass across the heated volume (from 17:45 to 18:22 UT, LT DST=UT+4 hours) despite of the switch of the pumping schedule from continuous one to [2 minutes "on", 4 minutes "off"] after the IPP passed the culmination point (18:05 UT, 6° to the South from zenith above the SURA facility). The TEC variations achieved a value 0.3 TECU (1 TEC Unit = 1.0 · 1016 el/m2 ), which was approximately 0.7% of the average measured TEC. Estimations performed with the use of ionograms, IRI 2007 model and existing knowledge of the large scale pump induced irregularities in the F2 region of the ionosphere have shown that the TEC variations observed can be attributed to the irregularities with the scales ˜ 5-15 km along the IPP track (i.e. across the pump beam) and 100 km along the geomagnetic field. The work is supported by RFBR grants 10-02-00642, 09-02-01150 and Federal Special-purpose Program "Scientific and pedagogical personnel of innovative Russia". [1] G. Milikh, A.Gurevich, K. Zybin, J. Secan, Geophys. Res. Lett., 2008, 35, L22102, doi:10.1029/2008GL035527. [2] E.D. Tereshchenko, A.N. Milichenko, V.L. Frolov, R.Yu. Yurik., Radiophys and Quantum Electron, 2008, 51, 842-846.

Grach, Savely; Ryabov, Alexander; Kotik, Dmitry; Sergeev, Evgeny; Shindin, Alexey

142

The absorption spectrum of the solvated electron in fluid helium by maximum entropy inversion of imaginary time correlation functions from path integral Monte Carlo simulations  

Microsoft Academic Search

The dipole absorption spectrum of an electron in fluid helium is calculated by the maximum entropy method (MEM) numerical inversion of quantum Monte Carlo data obtained from a path integral Monte Carlo (PIMC) simulation at 309 K at the reduced densities &rgr;*=0.1, 0.3, 0.5, 0.7, and 0.9. Our results agree with the RISM-polaron theory results of Nichols and Chandler [A.

E. Gallicchio; B. J. Berne

1994-01-01

143

Effect of temperature on the formation of electronic bound states in an expanded bcc hydrogenoid crystal: A restricted path-integral molecular dynamics simulation  

NASA Astrophysics Data System (ADS)

We have used the restricted path-integral molecular dynamics method to study the correlated electronic structure of a half-filled expanded three-dimensional hydrogenoid body-centered cubic lattice at finite temperatures. Starting from a paramagnetic metallic state with electron gas character, we find that bound electrons form upon expansion of the lattice. The bound electrons are spatially localized with their center for the motion of gyration located on ionic positions. The region of coexistence of bound and unbound states in the temperature-density plane is reminiscent of that associated with a first-order transition. At constant temperature, the number of bound electrons increases monotonously with decreasing density. The width of the region of coexistence narrows with increasing temperature.

Oh, Ki-Dong; Deymier, P. A.

2004-04-01

144

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

145

Auger electron emission from a Si(1 1 1) surface during 11-keV Ar+ ion sputtering  

NASA Astrophysics Data System (ADS)

Ion sputtering experiments were carried out for a Si(1 1 1)-7 × 7 surface, irradiated with an 11-keV Ar+ beam. The energy spectra of secondary electrons were measured with a cylindrical mirror analyzer (CMA). The dependence of the Auger electron yield on the ion incidence angle, ?, measured from the surface normal, was studied by varying ? from 0° to 80°. The Auger electron yield increases with increasing incidence angle. This angular dependence is similar to that of the Si sputtering yield. Both angular dependences could be reasonably understood in terms of ion range, escape depths of the sputtered ion and the electron mean free path.

Kawai, K.; Sakuma, Y.; Kato, M.; Soda, K.

2013-11-01

146

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.

147

Conditions for Aeronomic Applicability of the Classical Electron Heat Conduction Formula  

NASA Technical Reports Server (NTRS)

Conditions for the applicability of the classical formula for heat conduction in the electrons in ionized gas are investigated. In a fully ionised gas ( V(sub en) much greater than V(sub ei)), when the mean free path for electron-electron (or electron-ion) collisions is much larger than the characteristic thermal scale length of the observed system, the conditions for applicability break down. In the case of the Venus ionosphere this breakdown is indicated for a large fraction of the electron temperature data from altitudes greater than 180 km, for electron densities less than 10(exp 4)/cc cm. In a partially ionised gas such that V(sub en) much greater than V(sub ei) there is breakdown of the formula not only when the mean free path of electrons greatly exceeds the thermal scale length, but also when the gradient of neutral particle density exceeds the electron thermal gradient. It is shown that electron heat conduction may be neglected in estimating the temperature of joule heated electrons by observed strong 100 Hz electric fields when the conduction flux is limited by the saturation flux. The results of this paper support our earlier aeronomical arguments against the hypothesis of planetary scale whistlers for the 100 Hz electric field signal. In turn this means that data from the 100 Hz signal may not be used to support the case for lightning on Venus.

Cole, K. D.; Hoegy, W. R.

1998-01-01

148

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

149

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...

150

An electron-transfer path through an extended disulfide relay system: the case of the redox protein ALR.  

PubMed

The oxidative folding mechanism in the intermembrane space of human mitochondria underpins a disulfide relay system consisting of the import receptor Mia40 and the homodimeric FAD-dependent thiol oxidase ALR. The flavoprotein ALR receives two electrons per subunit from Mia40, which are then donated through one-electron reactions to two cytochrome c molecules, thus mediating a switch from two-electron to one-electron transfer. We dissect here the mechanism of the electron flux within ALR, characterizing at the atomic level the ALR intermediates that allow electrons to rapidly flow to cytochrome c. The intermediate critical for the electron-transfer process implies the formation of a specific inter-subunit disulfide which exclusively allows electron flow from Mia40 to FAD. This finding allows us to present a complete model for the electron-transfer pathway in ALR. PMID:22224850

Banci, Lucia; Bertini, Ivano; Calderone, Vito; Cefaro, Chiara; Ciofi-Baffoni, Simone; Gallo, Angelo; Tokatlidis, Kostas

2012-01-25

151

Convoy electron production by heavy ions in solids  

SciTech Connect

The term convoy electron refers to those electrons ejected in fast ion-atom and ion-solid collisions closely matched in vector velocity to that of the incident heavy particles responsible for their ejection. Similarities and differences among electrons ejected into such states through binary electron capture to continuum and electron loss to continuum processes in single ion-atom encounters are compared and contrasted to more complex ejection processes occurring in solid targets. Puzzles posed by the apparent strong projectile Z dependence but weak emergent ion charge dependence of the yield in the case of solid targets are reviewed. Very recent progress in resolving these puzzles has been made by recent observations that the apparent mean free path for electron scattering out of the forward direction within the target is observed to be an order of magnitude greater than that for free electrons of equal velocity provided the projectile charge is high. 13 references, 2 figures, 1 table.

Sellin, I.A.

1984-01-01

152

Current driven due to localized electron power deposition in DIII-D  

SciTech Connect

Due to spatial localization of electron cyclotron wave injection in DIII-D, electrons heated in an off-axis region must toroidally transit the tokamak 25--50 times before re-entering the heating region. This distance is of the order of the mean free path. The effect of such RF localization is simulated with a time-dependent Fokker-Planck code which is 2D-in-velocity, 1D-in-space-along-B, and periodic in space. An effective parallel electric field arises to maintain continuity of the driven current. Somewhat surprisingly, the localized current drive efficiency remains equal to that for a uniform medium.

Harvey, R.W. [CompX, Del Mar, CA (United States); Lin-Liu, Y.R.; Luce, T.C.; Prater, R. [General Atomics, San Diego, CA (United States); Sauter, O. [Ecole Polytechnique Federale de Lausanne (Switzerland); Smirnov, A.P. [Moscow State Univ. (Russian Federation)

1999-05-01

153

Path Finder  

NSDL National Science Digital Library

Finding certain files on a computer can be an onerous chore from time to time, and Path Finder is a good solution for anyone who's been bedeviled by such a task. The application includes a dual pane browser, cut and paste support, and a website that includes an interactive tour through its other features. This version of Path Finder is compatible with systems running Mac OS X 10.5 and newer. Also, this is a 30-day free trial version, and a full paid license is required after that point.

154

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

155

Electron propagation in orientationally disordered fullerides  

SciTech Connect

We study the electronic spectrum for doped electronic states in the orientationally disordered [ital M][sub 3]C[sub 60] fullerides. Momentum-resolved Green's functions are calculated within a cluster-Bethe-lattice model and compared with results from calculations on periodically repeated supercells containing quenched orientational disorder. Despite the relatively strong scattering from orientational fluctuations, the electronic states near the Fermi energy are well described by propagating states characterized by an effective Bloch wave vector and a mean free path [ital l][approx]20 A. The effective Fermi surface is calculated in this model. This differs from that previously calculated for the orientationally ordered crystal, but is relatively well described within a disorder-averaged virtual-crystal Hamiltonian, which we derive.

Mele, E.J.; Erwin, S.C. (Department of Physics and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States))

1994-07-15

156

Solar Energetic Electrons propagation in converging Interplanetary Magnetic structures by the Ulysses spacecraft (event of day 081,1995)  

NASA Astrophysics Data System (ADS)

Fine time resolution observations of energetic (40-112 KeV) electrons made by the HI-SCALE experiment onboard the Ulysses spacecraft, during the onset of a major solar electron event on day 81 of the year 1995 and the technique of mapping the solar wind at the solar corona, are used, in order to obtain the large-angle scattering distance of these particles in a converging structure of the large scale interplanetary magnetic field. Consequently, effective mean free paths are determined.

Marhavilas, P.; Sarris, E.; Anagnostopoulos, G.; Trochoutsos, P.

157

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

158

Path Clearance  

Microsoft Academic Search

In military scenarios, agents (i.e., troops of soldiers, convoys, and unmanned vehicles) may often have to traverse environments with only a limited intelligence about the locations of adversaries. We study a particular instance of this problem that we refer to as path clearance problem.This article presents a survey of our work on scalable and suitable for real-time use approaches to

Maxim Likhachev; Anthony Stentz

2009-01-01

159

Local field corrections in two-dimensional coupled electron-LO phonon systems  

NASA Astrophysics Data System (ADS)

We theoretically investigate the effects of vertex corrections on the many-body properties of a two-dimensional electron gas system in which the electrons are coupled to the LO phonons under adiabatic conditions. We calculate the vertex-corrected electron self-energy, spectral function, damping rate, lifetime and inelastic mean free path in a coupled electron-LO phonon system at zero temperature. Because of the adiabatic situation, we neglect the phonon vertex correction in our calculations. We go beyond the random phase approximation (RPA) and consider the short-range exchange and correlation interactions by using the Hubbard and Singwi-Tosi-Land-Sjölander (STLS) approximations. In general, our results show that by decreasing the electron density, the vertex effects become more significant and the STLS approximation has a stronger effect than does the Hubbard approximation. We find that including the vertex corrections yields sharper quasiparticle peaks compared with the RPA approach. In addition, longer quasiparticle lifetimes and mean free paths are obtained when the vertex corrections are taken into account.

Vazifehshenas, T.; Rostami, S.

2011-07-01

160

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

161

Correlation of Electron Path Lengths Observed in the Highly Wound Outer Region of Magnetic Clouds with the Slab Fraction of Magnetic Turbulence in the Dissipation Range  

NASA Astrophysics Data System (ADS)

Three magnetic cloud events, in which solar impulsive electron events occurred in their outer region, are employed to investigate the difference of path lengths L 0eIII traveled by non-relativistic electrons from their release site near the Sun to the observer at 1 AU, where L 0eIII = v l × (t l – t III), v l and t l being the velocity and arrival time of electrons in the lowest energy channel (~27 keV) of the Wind/3DP/SST sensor, respectively, and t III being the onset time of type III radio bursts. The deduced L 0eIII value ranges from 1.3 to 3.3 AU. Since a negligible interplanetary scattering level can be seen in both L 0eIII > 3 AU and ~1.2 AU events, the difference in L 0eIII could be linked to the turbulence geometry (slab or two-dimensional) in the solar wind. By using the Wind/MFI magnetic field data with a time resolution of 92 ms, we examine the turbulence geometry in the dissipation range. In our examination, ~6 minutes of sampled subintervals are used in order to improve time resolution. We have found that, in the transverse turbulence, the observed slab fraction is increased with an increasing L 0eIII value, reaching ~100% in the L 0eIII > 3 AU event. Our observation implies that when only the slab spectral component exists, magnetic flux tubes (magnetic surfaces) are closed and regular for a very long distance along the transport route of particles.

Tan, Lun C.; Reames, Donald V.; Ng, Chee K.; Shao, Xi; Wang, Linghua

2014-05-01

162

Test of validity of the V -type approach for electron trajectories in reflection electron energy loss spectroscopy  

NASA Astrophysics Data System (ADS)

An electron reaching the detector after being backscattered from a solid surface in a reflection electron energy loss spectroscopy (REELS) experiment follows a so-called V -type trajectory if it is reasonable to consider that it has only one large elastic scattering event along its total path length traveled inside the solid. V -type trajectories are explicitly assumed in the dielectric model developed by Yubero [Phys. Rev. B 53, 9728 (1996)] for quantification of electron energy losses in REELS experiments. However, the condition under which this approximation is valid has not previously been investigated explicitly quantitatively. Here, we have studied to what extent these REELS electrons can be considered to follow near V -type trajectories. To this end, we have made Monte Carlo simulations of trajectories for electrons traveling at different energies in different experimental geometries in solids with different elastic scattering properties. Path lengths up to three to four times the corresponding inelastic mean free paths have been considered to account for 80-90% of the total electrons having one single inelastic scattering event. On this basis, we have made detailed and systematic studies of the correlation between the distribution of path lengths, the maximum depth reached, and the fraction of all electrons that have experienced near V -type trajectories. These investigations show that the assumption of V -type trajectories for the relevant path lengths is, in general, a good approximation. In the rare cases, when the detection angle corresponds to a scattering angle with a deep minimum in the cross section, very few electrons have experienced true V -type trajectories. However, even in these extreme cases, a large fraction of the relevant electrons have near V -type trajectories.

Yubero, F.; Pauly, N.; Dubus, A.; Tougaard, S.

2008-06-01

163

Path Planning Control.  

National Technical Information Service (NTIS)

Viewgraphs on path planning control are presented. Topics covered include: model based path planning; sensor based path planning; hybrid path planning; proximity sensor array; and applications for fuzzy logic.

M. Mcroberts

1990-01-01

164

Path planning control  

NASA Technical Reports Server (NTRS)

Viewgraphs on path planning control are presented. Topics covered include: model based path planning; sensor based path planning; hybrid path planning; proximity sensor array; and applications for fuzzy logic.

Mcroberts, Malcolm

1990-01-01

165

Electron dynamics in inhomogeneous magnetic fields.  

PubMed

This review explores the dynamics of two-dimensional electrons in magnetic potentials that vary on scales smaller than the mean free path. The physics of microscopically inhomogeneous magnetic fields relates to important fundamental problems in the fractional quantum Hall effect, superconductivity, spintronics and graphene physics and spins out promising applications which will be described here. After introducing the initial work done on electron localization in random magnetic fields, the experimental methods for fabricating magnetic potentials are presented. Drift-diffusion phenomena are then described, which include commensurability oscillations, magnetic channelling, resistance resonance effects and magnetic dots. We then review quantum phenomena in magnetic potentials including magnetic quantum wires, magnetic minibands in superlattices, rectification by snake states, quantum tunnelling and Klein tunnelling. The third part is devoted to spintronics in inhomogeneous magnetic fields. This covers spin filtering by magnetic field gradients and circular magnetic fields, electrically induced spin resonance, spin resonance fluorescence and coherent spin manipulation. PMID:21393794

Nogaret, Alain

2010-06-30

166

Thickness measurements with electron energy loss spectroscopy.  

PubMed

Measurements of thickness using electron energy loss spectroscopy (EELS) are revised. Absolute thickness values can be quickly and accurately determined with the Kramers-Kronig sum method. The EELS data analysis is even much easier with the log-ratio method, however, absolute calibration of this method requires knowledge of the mean free path of inelastic electron scattering lambda. The latter has been measured here in a wide range of solids and a scaling law lambda approximately rho(-0.3) versus mass density rho has been revealed. EELS measurements critically depend on the excitation and collection angles. This dependence has been studied experimentally and theoretically and an efficient model has been formulated. PMID:18454473

Iakoubovskii, K; Mitsuishi, K; Nakayama, Y; Furuya, K

2008-08-01

167

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

168

A deterministic computational procedure for space environment electron transport  

NASA Astrophysics Data System (ADS)

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.; Adamczyk, Anne M.

2010-08-01

169

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.

Jeschke, Harald O; Valenti, Roser

2013-01-01

170

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

PubMed

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

Salvat-Pujol, Francesc; Jeschke, Harald O; Valentí, Roser

2013-01-01

171

Microwave photoresistance of a two-dimensional electron gas in a ballistic microbar  

NASA Astrophysics Data System (ADS)

The effect of millimeter microwave radiation on the electron transport of two-dimensional (2D) ballistic microbars formed on the basis of individual GaAs quantum wells at a temperature of T = 4.2 K in magnetic fields B < 0.6 T has been investigated. Differences have been revealed in the magnetic field dependences of the microwave photoresistance of a 2D electron gas in Hall bars with a length L and a width W for the cases L, W > l p and L, W < l p , where l p is the electron mean free path for momentum. The microwave photoresistance in macroscopic bars ( L, W > l p ) is a periodic alternating function of the inverse magnetic field; in microbars ( L, W < l p ), it is a periodic positive function of 1/ B. The experimental results indicate that the mechanisms of the microwave photoresistance of a 2D electron gas are different for macroscopic and microscopic bars.

Bykov, A. A.

2009-08-01

172

Electron-electron scattering in three-dimensional highly degenerate semiconductors  

NASA Astrophysics Data System (ADS)

We have measured the low-field magnetoresistances of a series of Sn-doped indium oxide thick films in the temperature T range of 4\\text{-}35\\ \\text{K} . The electron dephasing rate 1/\\tau_{\\varphi} as a function of T for each film was extracted by comparing the magnetoresistance data with the three-dimensional weak-localization theoretical predictions. We found that the extracted 1/\\tau_{\\varphi} varies linearly with T^{3/2} . Furthermore, at a given T, 1/\\tau_{\\varphi} varies linearly with k_F^{-5/2}l^{-3/2} , where kF is the Fermi wave number, and l is the electron elastic mean free path. These features are well explained in terms of the small-energy-transfer electron-electron scattering time in three-dimensional disordered conductors. This electron dephasing mechanism dominates over the electron-phonon scattering process because the carrier concentrations in our films are ? 3 orders of magnitude lower than those in typical metals, which resulted in a greatly suppressed electron-phonon relaxation rate. Our result is the first quantitative demonstration of this unique three-dimensional electron-electron scattering time in experiments.

Zhang, Y. J.; Li, Z. Q.; Lin, J. J.

2013-08-01

173

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

174

Locality of information obtained from proximity-electron-tunneling spectroscopy  

SciTech Connect

The locality of the information obtained by the technique of proximity-electron tunneling (PETS) is analyzed, with particular attention to the effects on the measured effective-phonon spectrum ..cap alpha../sup 2/F(..omega..) is disorder or impurities near the surface of the superconductor electrode. As in conventional tunnel junctions it is determined that the (energy-dependent) electron mean free path determines the maximum depth of the superconductor of which the measured phonon spectrum is characterized. An averaging length L(E) is defined and found to be typically larger in proximity junctions than in conventional junctions. This can make PET results inherently less susceptible than conventional results to surface disorder of the superconductor.

Arnold, G.B.; Wolf, E.L.

1982-02-01

175

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

176

Quantum corrections to the conductivity of disordered graphene on SiC (000\\overline {1}) : weak localization and current-bias dependent electron-electron interactions  

NASA Astrophysics Data System (ADS)

The properties of epitaxial graphene grown via thermal decomposition of silicon carbide are extremely sensitive to annealing conditions. Here we show how the surface morphologies resulting from a range of UHV growth protocols affect the electron scattering rates associated with various quantum corrections to the conductivity. Detailed analysis of magnetotransport data provides insight into the degree of disorder via fits to weak localization and weak antilocalization models, while additional fitting is used to identify more subtle contributions from electron-electron (e-e) interaction effects. This second contribution is found to be current-bias dependent, and is seen only for more disordered samples, which is attributed to the shorter mean free path in these materials.

Creeth, G. L.; Strudwick, A. J.; Sadowski, J. T.; Marrows, C. H.

2014-01-01

177

Secondary electron emission from diamond surfaces  

SciTech Connect

Diamond exhibits very high, but widely varying, secondary-electron yields. In this study, we identified some of the factors that govern the secondary-electron yield from diamond by performing comparative studies on polycrystalline films with different dopants (boron or nitrogen), doping concentrations, and surface terminations. The total electron yield as a function of incident-electron energy and the energy distribution of the emitted secondary electrons showed that both bulk properties and surface chemistry are important in the secondary-electron-emission process. The dopant type and doping concentration affect the transport of secondary electrons through the sample bulk, as well as the electrical conductivity needed to replenish the emitted electrons. Surface adsorbates affect the electron transmission at the surface-vacuum interface because they change the vacuum barrier height. The presence of hydrogen termination at the diamond surface, the extent of the hydrogen coverage, and the coadsorption of hydrocarbon-containing species all correlated with significant yield changes. Extraordinarily high secondary-electron yields (as high as 84) were observed on B-doped diamond samples saturated with surface hydrogen. The secondary electrons were predominantly low-energy quasithermalized electrons residing in the bottom of the diamond conduction band. Two key reasons for the unusually high yields are (1) the wide band gap which allows the low-energy secondary electrons to have long mean-free paths, and (2) the very low or even negative electron affinity at the surface which permits the low-energy quasithermalized electrons that reach the surface to escape into vacuum.

Shih, A.; Yater, J.; Pehrsson, P.; Butler, J.; Hor, C.; Abrams, R. [Naval Research Laboratory, Washington, DC 20375 (United States)] [Naval Research Laboratory, Washington, DC 20375 (United States)

1997-08-01

178

Effects of macroscopic inhomogeneities on electron mobility in semi-insulating GaAs  

NASA Technical Reports Server (NTRS)

It is shown that defect inhomogeneities of sizes larger than the electron mean free path are responsible for the low values and anomalous temperature dependence of the electron mobility in semi-insulating (SI) GaAs. The room-temperature electron mobility values below about 6000 sq cm/V s cannot be uniquely used for the determination of the concentration of ionized defects, since the contribution from inhomogeneities usually exceeds that from scattering by ionized impurities. The effects of the macroscopically inhomogeneous distribution of residual acceptors and the major deep donor EL2 diminish at elevated temperatures between 600 and 900 K, which offers a means for identification of inhomogeneities, and furthermore explains recently reported steplike mobility versus temperature behavior in SI-GaAs.

Walukiewicz, W.; Wang, L.; Pawlowicz, L. M.; Lagowski, J.; Gatos, H. C.

1986-01-01

179

DISCUSS: Critical Path Analysis  

NSDL National Science Digital Library

This module, by Barrie Baker and Neville Hunt of Coventry University, introduces critical path analysis and addresses the following topics: Networks, Critical paths, Floats, Activity-on-node (AON) networks. Excel spreadsheets are used to provide examples and exercises.

Baker, Barrie; Hunt, Neville

2009-04-23

180

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

181

Long Path Problems  

Microsoft Academic Search

We demonstrate the interesting, counter-intuitive result that simple paths to the global optimum can be so long that climbing the path is intractable. This means that a unimodal search space, which consists of a single hill and in which each point in the space is on a simple path to the global optimum, can be difficult for a hillclimber to

Jeffrey Horn; David E. Goldberg; Kalyanmoy Deb

1994-01-01

182

Thinnest Path Problem.  

National Technical Information Service (NTIS)

We consider the thinnest path problem for secure communication in wireless ad hoc networks. For a given source and a destination, the thinnest path problem asks for a path from the source to the destination that results in the minimum number of nodes hear...

A. Swami J. Gao Q. Zhao

2013-01-01

183

Spin Path Integrals and Generations  

Microsoft Academic Search

The spin of a free electron is stable but its position is not. Recent quantum information research by G. Svetlichny, J. Tolar,\\u000a and G. Chadzitaskos have shown that the Feynman position path integral can be mathematically defined as a product of incompatible states; that is, as a product of mutually unbiased\\u000a bases (MUBs). Since the more common use of MUBs

Carl Brannen

2010-01-01

184

Nonlinear magnetotransport in a two-dimensional electron system in a square array of antidots in GaAs/AlAs heterostructures  

NASA Astrophysics Data System (ADS)

Nonlinear magnetotransport of two-dimensional electrons in square antidot lattices prepared on the basis of selectively doped GaAs/AlAs heterostructures with the period that is much less than the electron mean free path in the initial GaAs quantum wells but is much larger than their Fermi wavelength has been studied. It has been shown that the character of the nonlinear transport of the two-dimensional electrons in the lateral lattices under study changes from classical to quantum with the decrease in the antidot radius. It has been found that the quantum lifetime increases in the magnetic field corresponding to the condition of equality of the cyclotron diameter of two-dimensional electrons and the antidot lattice period.

Bykov, A. A.; Strygin, I. S.; Marchishin, I. V.; Goran, A. V.

2014-05-01

185

Path Relaxation: Path Planning for a Mobile Robot  

Microsoft Academic Search

Path Relaxation is a method of planning safe paths around obstacles for mobile robots. It works in two steps: a global grid starch that finds a rough path, followed by a local relaxation step that adjusts each node on the path to lower the overall path cost. The representation used by Path Relaxation allows an explicit tradeoff among length of

Charles E. Thorpe; L. Matthies

1984-01-01

186

Path planning using optically computed potential fields  

NASA Technical Reports Server (NTRS)

An algorithm for the optical computation of potential field maps suitable for mobile robot navigation is described and experimentally produced maps and paths are presented. The parallel analog optical computation employs a two-dimensional spatial light modulator on which an image of the potential field map is generated. Optically calculated fields contain no local minima, tend to produce paths centered in gaps between obstacles, and produce paths which give preference to wide gaps. Calculation of 128 x 128 pixel fields at a few hertz are possible with current technology, and calculation time vs. map size scales favorably in comparison to digital electronic computation.

Reid, Max B.

1993-01-01

187

Shortest path algorithms  

Microsoft Academic Search

Theshortest path problem is considered from a computational point of view. Eight algorithms which solve theshortest path tree problem on directed graphs are presented, together with the results of wide-ranging experimentation designed to compare their relative performances on different graph topologies. The focus of this paper is on the implementation of the different data structures used in the algorithms. A

Giorgio Gallo; Stefano Pallottino

1988-01-01

188

Path Following Robot.  

National Technical Information Service (NTIS)

Given a desired path to be followed by a Robot, a set of commands must be given to the Robot joint servos so that the Robot Tip, or Endpoint, can follow that path. These commands must be synchronized in time and scaled so as to maintain accuracy in the pr...

S. G. Goodway

1987-01-01

189

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

190

Operational transfer path analysis  

NASA Astrophysics Data System (ADS)

One of the tools used to study the NVH behaviour of a system is the transfer path analysis. It aims to identify the operational forces and the propagation paths of the vibrations and is especially interesting in the case when the system is composed of different subsystems. The classical techniques identify the transfer paths when the system is disassembled. This way one eliminates flanking transfer paths. Yet it is very time-consuming and the boundary conditions are not correct anymore. The presented method makes it possible to identify the transfer paths without disassembling the system. The advantages are that the overall testing time is reduced and that the real boundary conditions are present. In this article the theory will be reviewed and it will be validated using data generated by finite element simulations.

De Sitter, Gert; Devriendt, Christof; Guillaume, Patrick; Pruyt, Erik

2010-02-01

191

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

192

Spatial plasma potentials and electron energy distributions in inductively and capacitively coupled plasmas under a weakly collisional and nonlocal electron kinetic regime  

NASA Astrophysics Data System (ADS)

Spatial profiles of the plasma potential and electron energy distribution function (EEDF) were measured in inductively and capacitively coupled plasmas (ICP and CCP) under weakly collisional and nonlocal electron kinetic regimes [1]. The measured EEDF at the discharge center was a bi-Maxwellain distribution with low (T1) and high (T2) electron temperature groups at both the ICP and the CCP, while the EEDF at the radial boundary was closely Maxwellian distribution in the ICP due to cutting of the low energy electrons by relatively large ambipolar potential in this discharge regime. The ambipolar potential in the entire radial region was in the scale of Teff -1.5 Teff, where Teff is the effective electron temperature. At the boundary region with the ion mean free path scale, the ambipolar potential increased abruptly and was about Teff,edge/2, where the Teff,edge is the effective electron temperature at the boundary, which corresponds to the presheath scale. These results of the ICP, which are contrary to the ambipolar potential of the CCP in a nearly free-fall regime [2], are caused by relatively high T1 and a small portion of low energy electron group density to total electron density in the ICP under the weakly collisional and nonlocal electron kinetic regimes. [4pt] [1] H. C. Lee and C. W. Chung, Phys. Plasmas 19 033514 (2012).[0pt] [2] V. A. Godyak, V. P. Meytlis, and H. R. Strauss, IEEE Trans. Plasma Sci. 23 728 (1995).

Lee, Hyo-Chang; Chung, Chin-Wook

2012-10-01

193

Path Relaxation: Path Planning for a Mobile Robot.  

National Technical Information Service (NTIS)

Path Relaxation is a method of planning safe paths around obstacles for mobile robots. It works in two steps: a global grid search that finds a rough path, followed by a local relaxation step that adjusts each node on the path to lower the overall path co...

C. E. Thorpe

1984-01-01

194

The passage of fast electrons through matter  

NASA Astrophysics Data System (ADS)

This work regards the passage of fast electrons through matter, and in particular how electrons scatter and lose energy within a solid. The basic quantum theory of these scattering processes was first considered in the early- to mid-20th century by Bohr, Bethe, Fermi, and others. This work extends our understanding of how a relativistic electron scatters off, and loses energy to, a complex many-body system. The main idea of this work is that it is now possible to calculate, from first-principles, the inelastic losses of relativistic electrons in condensed matter. We present ab initio calculations based on a real-space Green's function approach, implemented in the FEFF8 computer program[1]. Our work focuses on three topics: Relativistic stopping power and associated loss parameters, electron energy loss spectroscopy in high energy transmission electron microscopes, and the inelastic electron scattering mixed dynamic form factor. We calculate, for the first time, ab initio stopping powers and inelastic mean free paths in real materials. The stopping powers are calculated over a broad energy range, from ten eV to above ten MeV. We also present the first ab initio calculations of the "mean excitation energy". We develop a relativistic theory of inelastic electron scattering, based on ab initio calculations of dielectric response, and the generalized Lorenz gauge. Using our relativistic dielectric theory, we calculate the EELS magic angle ratio for boron nitride and for graphite. In these anisotropic materials we find large relativistic corrections to the magic angle for high energy electron microscopes. We also predict and calculate large deviations in the EELS magic angle from the relativistic vacuum predictions in the low energy-loss regime. Finally, we present calculations of mixed dynamic form factor.

Sorini, Adam P.

195

Electron Transport In Magnetized Laser Hohlraum Plasmas  

NASA Astrophysics Data System (ADS)

The plasma conditions we expect to encounter in hohlraum experiments on the National Ignition Facility span from the familiar, relatively benign conditions of Nova and Omega to much more hostile environments in which electron temperatures may be 10s of keV. In any of these situations simple estimates indicate that heat flow is very non-local, making the local diffusion approximation typically used in hydrocodes invalid. However, large, mega gauss magnetic fields which are generated primarily at the wall and fill the body of the hohlraum will tend to localize the electron transport. In this paper we use the Fokker-Planck code IMPACT to study heat flow as a function of plasma scale lengths compared to the electron mean free path, and as a function of magnetization and compare the results with local and non-local theory for plasma conditions of relevance to hohlraums driven by the National ignition Facility. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

Friesen, Lorien; Edwards, John; Town, Richard; Kingham, Robert; Rozmus, Wojciech

2003-10-01

196

Critical-Path-whitepaper  

Cancer.gov

NEGOTIATING THE CRITICAL PATH..................................................................................................7 SCIENTIFIC AND TECHNICAL DIMENSIONS ALONG THE CRITICAL PATH...................................9 A BETTER PRODUCT DEVELOPMENT TOOLKIT IS URGENTLY NEEDED ..................................11 TOOLS FOR ASSESSING SAFETY......................................................................................................16 Towards a Better Safety Toolkit................................................................................................17 Getting to the Right Safety Standards......................................................................................20 TOOLS FOR DEMONSTRATING MEDICAL UTILITY .......................................................................20 Towards a Better Effectiveness Toolkit ...................................................................................21 Getting to the Right Effectiveness Standards .........................................................................25 TOOLS FOR CHARACTERIZATION AND MANUFACTURING .........................................................25 Towards a Better Manufacturing Toolkit.................................................................................27 Getting to the Right Manufacturing Standards .......................................................................28 A PATH FORWARD .............................................................................................................................29 The Orphan Products Grant Program.

197

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

198

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

199

Critical Path Method Reports.  

National Technical Information Service (NTIS)

The computer system for the Critical Path Method Reports consists of three programs. The programs are CPM Calculation, CPM Calendar Dating and CPM Time-Sequence Plot. The CPM Calculations Program is used for doing the arithmetic calculations associated wi...

R. C. Tennent

1964-01-01

200

Air Vehicle Path Planning.  

National Technical Information Service (NTIS)

This dissertation explores optimal path planning for air vehicles. An air vehicle exposed to illumination by a tracking radar is considered and the problem of determining an optimal planar trajectory connecting two prespecified points is addressed. An ana...

J. M. Hebert

2001-01-01

201

Tortuous path chemical preconcentrator  

DOEpatents

A non-planar, tortuous path chemical preconcentrator has a high internal surface area having a heatable sorptive coating that can be used to selectively collect and concentrate one or more chemical species of interest from a fluid stream that can be rapidly released as a concentrated plug into an analytical or microanalytical chain for separation and detection. The non-planar chemical preconcentrator comprises a sorptive support structure having a tortuous flow path. The tortuosity provides repeated twists, turns, and bends to the flow, thereby increasing the interfacial contact between sample fluid stream and the sorptive material. The tortuous path also provides more opportunities for desorption and readsorption of volatile species. Further, the thermal efficiency of the tortuous path chemical preconcentrator is comparable or superior to the prior non-planar chemical preconcentrator. Finally, the tortuosity can be varied in different directions to optimize flow rates during the adsorption and desorption phases of operation of the preconcentrator.

Manginell, Ronald P. (Albuquerque, NM); Lewis, Patrick R. (Albuquerque, NM); Adkins, Douglas R. (Albuquerque, NM); Wheeler, David R. (Albuquerque, NM); Simonson, Robert J. (Cedar Crest, NM)

2010-09-21

202

A Path to Discovery  

ERIC Educational Resources Information Center

The path taken and the turns made as a turtle traces a polygon are examined to discover an important theorem in geometry. A unique tool, the Angle Adder, is implemented in the investigation. (Contains 9 figures.)

Stegemoller, William; Stegemoller, Rebecca

2004-01-01

203

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.

204

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

205

Edge spin accumulation in two-dimensional electron and hole systems in a quasiballistic regime  

NASA Astrophysics Data System (ADS)

We consider a two-dimensional structure with spin-orbit-related splitting of the electron (hole) spectrum and calculate the edge spin density which appears due to the intrinsic mechanism of spin-orbit interaction in the presence of a charge current through the structure. We concentrate on the quasiballistic case when a mean-free path, being much smaller than the sample size, is larger than the spin precession length determined by the value of the spin-orbit splitting. We show that regardless of the presence or absence of the bulk spin current, the main source of the edge spin density is the boundary scattering itself. The character of the edge spin density depends on the smoothness of the bulk impurity potential. We have calculated the edge spin density profile for an arbitrary smoothness of the scattering potential in the bulk, and discussed relation to the existing experiments for two-dimensional holes.

Khaetskii, Alexander

2014-05-01

206

Production of electron-positron pairs by a photon propagating in a strongly magnetized thermal bath  

SciTech Connect

The production of electron-positron pairs by a photon propagating in a thermal bath in both zero and strong (B Much-Greater-Than 4.41 Multiplication-Sign 10{sup 13} G) magnetic fields has been considered. The mean free path has been calculated for the high-energy photon propagating through a thermodynamically equilibrium photon gas along the magnetic field lines so that the {gamma} {yields} e{sup -}e{sup +} decay is kinematically forbidden. It has been shown that the strong magnetic field suppresses the probability of the {gamma}{gamma} Prime {yields} e{sup -}e{sup +} process. The analyzed process can be useful for analysis of possible mechanisms of the generation of the e{sup -}e{sup +} plasma in the regions of the polar caps of magnetars.

Dunaev, M. A., E-mail: yarosla@rambler.ru; Mikheev, N. V., E-mail: mikheev@uniyar.ac.ru [Yaroslavl State University (Russian Federation)

2012-03-15

207

Conductance of one-dimensional quantum wires with anomalous electron wave-function localization  

NASA Astrophysics Data System (ADS)

We study the statistics of the conductance g through one-dimensional disordered systems where electron wave functions decay spatially as |?|˜exp(-?r?) for 0mean free path, here we show that when the wave function is anomalously localized (?<1), the full statistics of the conductance is determined by the average and the power ?. Our theoretical predictions are verified numerically by using a random hopping tight-binding model at zero energy, where due to the presence of chiral symmetry in the lattice there exists an anomalous localization; this case corresponds to the particular value ?=1/2. To test our theory for other values of ?, we introduce a statistical model for random hopping in the tight-binding Hamiltonian.

Amanatidis, Ilias; Kleftogiannis, Ioannis; Falceto, Fernando; Gopar, Víctor A.

2012-06-01

208

High resolution study of structural and electronic properties of epitaxial graphene grown on off-axis 4H–SiC (0001)  

NASA Astrophysics Data System (ADS)

In this paper, the structural and electronic properties of epitaxial graphene (EG) grown on 8°-off 4H–SiC (0001) by high temperature thermal processes have been extensively investigated by a combination of several high resolution characterization techniques. The increase in the number of graphene layers with the growth temperature (from 1600 to 1700 °C) was studied by microRaman spectroscopy and high resolution transmission electron microscopy (HRTEM) on cross-sectioned samples. The few layers of graphene reside on a stepped SiC surface with alternating (0001) terraces and (11?2n) facets. Peculiar corrugations (wrinkles) in the graphene membrane preferentially oriented perpendicularly to the substrate steps were also observed. Motivated by recent atomic resolution studies of the EG/SiC interface revealing a local delamination of the interfacial C buffer from the (11?2n) facets, we searched for a correlation of these interfacial structural properties with the macroscopic electronic transport in EG field effect transistors (FETs). In particular, electrical characterization of EG top gated FETs fabricated with the channel length parallel or perpendicular to the substrate steps revealed a peculiar anisotropy of the channel conductance with respect to the steps' orientation. This effect was explained in terms of a local enhancement of EG resistance on the (11?2n) facets with respect to the (0001) basal plane, which is consistent with a reduced doping due to the local buffer layer delamination from those facets. Furthermore, scanning probe microscopy-based local electron mean free path measurements on EG showed a ~3× enhancement of mean free path on the buffer-layer-free (11?2n) facets with respect to (0001) terraces, probably associated to a strong reduction of Coulomb scattering effects on graphene's electrons.

Giannazzo, F.; Deretzis, I.; Nicotra, G.; Fisichella, G.; Ramasse, Q. M.; Spinella, C.; Roccaforte, F.; La Magna, A.

2014-05-01

209

Energy transfer: On the right path  

NASA Astrophysics Data System (ADS)

Controlled energy-transfer on a molecular scale is a goal in many areas of science, from artificial photosynthesis to molecular electronics. Now, DNA origami has been used to direct the transfer of energy from an excited input dye down one of two paths by precisely arranging a mediator dye.

Albinsson, Bo

2011-04-01

210

Monte Carlo simulations of electron thermalization in alkali iodide and alkaline-earth fluoride scintillators  

SciTech Connect

A Monte Carlo model of electron thermalization in inorganic scintillators, which was developed and applied to CsI in a previous publication [Wang et al., J. Appl. Phys. 110, 064903 (2011)], is extended to another material of the alkali halide class, NaI, and to two materials from the alkaline-earth halide class, CaF{sub 2} and BaF{sub 2}. This model includes electron scattering with both longitudinal optical (LO) and acoustic phonons as well as the effects of internal electric fields. For the four pure materials, a significant fraction of the electrons recombine with self-trapped holes and the thermalization distance distributions of the electrons that do not recombine peak between approximately 25 and 50 nm and extend up to a few hundreds of nanometers. The thermalization time distributions of CaF{sub 2}, BaF{sub 2}, NaI, and CsI extend to approximately 0.5, 1, 2, and 7 ps, respectively. The simulations show that the LO phonon energy is a key factor that affects the electron thermalization process. Indeed, the higher the LO phonon energy is, the shorter the thermalization time and distance are. The thermalization time and distance distributions show no dependence on the incident {gamma}-ray energy. The four materials also show different extents of electron-hole pair recombination due mostly to differences in their electron mean free paths (MFPs), LO phonon energies, initial densities of electron-hole pairs, and static dielectric constants. The effect of thallium doping is also investigated for CsI and NaI as these materials are often doped with activators. Comparison between CsI and NaI shows that both the larger size of Cs{sup +} relative to Na{sup +}, i.e., the greater atomic density of NaI, and the longer electron mean free path in NaI compared to CsI contribute to an increased probability for electron trapping at Tl sites in NaI versus CsI.

Wang Zhiguo; Gao Fei; Kerisit, Sebastien [Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Xie Yulong [Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Campbell, Luke W. [National Security Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)

2012-07-01

211

Sampling diffusive transition paths.  

PubMed

The authors address the problem of sampling double-ended diffusive paths. The ensemble of paths is expressed using a symmetric version of the Onsager-Machlup formula, which only requires evaluation of the force field and which, upon direct time discretization, gives rise to a symmetric integrator that is accurate to second order. Efficiently sampling this ensemble requires avoiding the well-known stiffness problem associated with the sampling of infinitesimal Brownian increments of the path, as well as a different type of stiffness associated with the sampling of the coarse features of long paths. The fine-feature sampling stiffness is eliminated with the use of the fast sampling algorithm, and the coarse-feature sampling stiffness is avoided by introducing the sliding and sampling (S&S) algorithm. A key feature of the S&S algorithm is that it enables massively parallel computers to sample diffusive trajectories that are long in time. The authors use the algorithm to sample the transition path ensemble for the structural interconversion of the 38-atom Lennard-Jones cluster at low temperature. PMID:17444696

Miller, Thomas F; Predescu, Cristian

2007-04-14

212

Low thermal conductivity of the layered oxide (Na,Ca)Co2O4: Another example of a phonon glass and an electron crystal  

NASA Astrophysics Data System (ADS)

The thermal conductivity of polycrystalline samples of (Na,Ca)Co2O4 is found to be unusually low, 20 mW/cmK at 280 K. On the assumption of the Wiedemann-Franz law, the lattice thermal conductivity is estimated to be 18 mW/cm K at 280 K, and it does not change appreciably with the substitution of Ca for Na. A quantitative analysis has revealed that the phonon mean free path is comparable with the lattice parameters, where the point-defect scattering plays an important role. Electronically the same samples show a metallic conduction down to 4.2 K, which strongly suggests that NaCo2O4 exhibits a glasslike poor thermal conduction together with a metal-like good electrical conduction. The present study further suggests that a strongly correlated system with layered structure can act as a material of a phonon glass and an electron crystal.

Takahata, K.; Iguchi, Y.; Tanaka, D.; Itoh, T.; Terasaki, I.

2000-05-01

213

Improved initial guess for minimum energy path calculations.  

PubMed

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. PMID:24907989

Smidstrup, Søren; Pedersen, Andreas; Stokbro, Kurt; Jónsson, Hannes

2014-06-01

214

Improved initial guess for minimum energy path calculations  

NASA Astrophysics Data System (ADS)

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; Pedersen, Andreas; Stokbro, Kurt; Jónsson, Hannes

2014-06-01

215

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

216

Behavior of VLF Ray Paths in the Ionosphere.  

National Technical Information Service (NTIS)

Two dimensional VLF ray paths have been computed for a model ionosphere with a centered dipole magnetic field and a diffusive equilibrium distribution of electrons and H+, He+ and O+ ions. The behavior of these ray paths are illustrated for variations wit...

S. D. Shawhan

1967-01-01

217

Investigating the thermal stability of electron transport properties in modulation-doped semiconductor heterostructure systems  

NASA Astrophysics Data System (ADS)

Since the 1950s, materials scientists have pursued the fabrication of solid-state heterostructure (HS) devices of sufficient purity to replicate electron interference effects originally observed in vacuum. The ultimate goal of HS engineering is to create a semiconductor ``billiard table'' in which electrons travel ballistically in a 2-D plane---that is, with scattering events minimized such that the electron's mean free path exceeds the device size. For the past two decades, the modulation-doped (MD) HS architecture has yielded devices supporting very high electron mobilities. In this architecture, ionized dopants are spatially removed from the plane of the electrons, such that their influence on electron trajectories is felt through presumably negligible small-angle scattering events. However, we observe that thermally induced charge redistribution in the doped layers of AlGaAs/GaAs and GaInAs/InP MD heterostructures significantly alters electron transport dynamics as measured by magnetoconductance fluctuations. This result demonstrates that small-angle scattering plays a far larger role than expected in influencing conduction properties.

Pilgrim, Ian; Scannell, Billy; See, Andrew; Montgomery, Rick; Morse, Peter; Fairbanks, Matt; Marlow, Colleen; Linke, Heiner; Farrer, Ian; Ritchie, David; Hamilton, Alex; Micolich, Adam; Eaves, Laurence; Taylor, Richard

2013-03-01

218

Electron energy distributions and anomalous skin depth effects in high-plasma-density inductively coupled discharges  

NASA Astrophysics Data System (ADS)

Electron transport in low pressure (<10s mTorr), moderate frequency (<10s MHz) inductively coupled plasmas (ICPs) displays a variety of nonequilibrium characteristics due to their operation in a regime where the mean free paths of electrons are significant fractions of the cell dimensions and the skin depth is anomalous. Proper analysis of transport for these conditions requires a kinetic approach to resolve the dynamics of the electron energy distribution (EED) and its non-Maxwellian character. To facilitate such an investigation, a method was developed for modeling electron-electron collisions in a Monte Carlo simulation and the method was incorporated into a two-dimensional plasma equipment model. Electron temperatures, electron densities, and EEDs obtained using the model were compared with measurements for ICPs sustained in argon. It was found that EEDs were significantly depleted at low energies in regimes dominated by noncollisional heating, typically within the classical electromagnetic skin depth. Regions of positive and negative power deposition were observed for conditions where the absorption of the electric field was both monotonic and nonmonotonic.

Vasenkov, Alex V.; Kushner, Mark J.

2002-12-01

219

Oxygen Self-Diffusion in HfO_{2} Studied by Electron Spectroscopy.  

PubMed

High-resolution measurement of the energy of electrons backscattered from oxygen atoms makes it possible to distinguish between ^{18}O and ^{16}O isotopes as the energy of elastically scattered electrons depends on the mass of the scattering atom. Here we show that this approach is suitable for measuring oxygen self-diffusion in HfO_{2} using a Hf^{16}O_{2}(20??nm)/Hf^{18}O_{2} bilayers (60 nm). The mean depth probed (for which the total path length equals the inelastic mean free path) is either 5 or 15 nm in our experiment, depending on the geometry used. Before annealing, the elastic peak from O is thus mainly due to electrons scattered from ^{16}O in the outer layer, while after annealing the signal from ^{18}O increases due to diffusion from the underlying Hf^{18}O_{2} layer. For high annealing temperatures the observed interdiffusion is consistent with an activation energy of 1 eV, but at lower temperatures interdiffusion decreases with increasing annealing time. We interpret this to be a consequence of defects, present in the layers early on and enhancing the oxygen diffusivity, disappearing during the annealing process. PMID:24836258

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

2014-05-01

220

Oxygen Self-Diffusion in HfO2 Studied by Electron Spectroscopy  

NASA Astrophysics Data System (ADS)

High-resolution measurement of the energy of electrons backscattered from oxygen atoms makes it possible to distinguish between O18 and O16 isotopes as the energy of elastically scattered electrons depends on the mass of the scattering atom. Here we show that this approach is suitable for measuring oxygen self-diffusion in HfO2 using a HfO162(20nm)/HfO182 bilayers (60 nm). The mean depth probed (for which the total path length equals the inelastic mean free path) is either 5 or 15 nm in our experiment, depending on the geometry used. Before annealing, the elastic peak from O is thus mainly due to electrons scattered from O16 in the outer layer, while after annealing the signal from O18 increases due to diffusion from the underlying HfO182 layer. For high annealing temperatures the observed interdiffusion is consistent with an activation energy of 1 eV, but at lower temperatures interdiffusion decreases with increasing annealing time. We interpret this to be a consequence of defects, present in the layers early on and enhancing the oxygen diffusivity, disappearing during the annealing process.

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

2014-05-01

221

Following the Path  

ERIC Educational Resources Information Center

This article profiles Diane Stanley, an author and illustrator of children's books. Although she was studying to be a medical illustrator in graduate school, Stanley's path changed when she got married and had children. As she was raising her children, she became increasingly enamored of the colorful children's books she would check out of the…

Rodia, Becky

2004-01-01

222

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

223

Gas path seal  

NASA Technical Reports Server (NTRS)

A gas path seal suitable for use with a turbine engine or compressor is described. A shroud wearable or abradable by the abrasion of the rotor blades of the turbine or compressor shrouds the rotor bades. A compliant backing surrounds the shroud. The backing is a yieldingly deformable porous material covered with a thin ductile layer. A mounting fixture surrounds the backing.

Bill, R. C.; Johnson, R. D. (inventors)

1979-01-01

224

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

225

CareerPath  

NSDL National Science Digital Library

CareerPath offers a searchable index of employment ads from six major newspapers: The Boston Globe, Chicago Tribune, Los Angeles Times, The New York Times, The San Jose Mercury News, and The Washington Post. The total ads available on October 21 was 21,442. The site is attractive and easy to use.

226

Electron Transport Behavior on Gate Length Scaling in Sub-50 nm GaAs Metal Semiconductor Field Effect Transistors  

SciTech Connect

Short channel GaAs Metal Semiconductor Field Effect Transistors (MESFETs) have been fabricated with gate length to 20 nm, in order to examine the characteristics of sub-50 nm MESFET scaling. Here the rise in the measured transconductance is mainly attributed to electron velocity overshoot. For gate lengths below 40 nm, however, the transconductance drops suddenly. The behavior of velocity overshoot and its degradation is investigated and simulated by using a transport model based on the retarded Langevin equation (RLE). This indicates the existence of a minimum acceleration length needed for the carriers to reach the overshoot velocity. The argument shows that the source resistance must be included as an internal element, or appropriate boundary condition, of relative importance in any model where the gate length is comparable to the inelastic mean free path of the carriers.

Han, Jaeheon [Department of Electronic Engineering, Kangnam University, 111 Gugal-dong, Giheung-gu, Yongin-city, Gyeonggi-do, Korea 446-702 (Korea, Republic of)

2011-12-23

227

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

228

Linearized path integral approach for calculating nonadiabatic time correlation functions  

PubMed Central

We show that quantum time correlation functions including electronically nonadiabatic effects can be computed by using an approach in which their path integral expression is linearized in the difference between forward and backward nuclear paths while the electronic component of the amplitude, represented in the mapping formulation, can be computed exactly, leading to classical-like equations of motion for all degrees of freedom. The efficiency of this approach is demonstrated in some simple model applications.

Bonella, Sara; Montemayor, Daniel; Coker, David F.

2005-01-01

229

Electron Energy Distributions and Non-Collisional Heating in Magnetically Enhanced Inductively Coupled Plasmas  

NASA Astrophysics Data System (ADS)

Magnetically Enhanced Inductively Coupled Plasmas (MEICPs) can deposit power in the volume of reactors at locations deeper than the conventional skin depth. Mechanisms for power deposition and electron energy transport in MEICPs have been computationally investigated using a 2-dimensional plasma equipment model. Using a tensor conductivity in solution of Maxwell's equations, 3-d components of the inductively coupled electric field are produced from an m = 0 antenna and 2-d static applied magnetic fields. These fields are used in an electron Monte Carlo Simulation to generate electron energy distributions (EEDs), transport coefficients and electron impact source functions. For MEICPs operating at < 10s mTorr in Ar and Ar/molecular gas mixtures, significant power deposition occurs downstream when the radial and axial components of the electric field are commensurate to the azimuthal component. For B > 100s G and p < 10 mTorr, the tail of the EED (> 20-30 eV) is heated in the downstream region. This results from non-collisional heating by the axial electric field for electrons in the tail of the EED having long mean-free-paths while low energy electrons are is still somewhat collisional.

Kinder, Ronald L.; Kushner, Mark J.

2000-10-01

230

Noncollisional heating and electron energy distributions in magnetically enhanced inductively coupled and helicon plasma sources  

NASA Astrophysics Data System (ADS)

The ability to deposit power in the volume of plasma reactors at locations deeper than the conventional skin depth makes magnetically enhanced inductively coupled plasma (MEICP) and helicon sources appealing for use in materials processing. Mechanisms for power deposition and electron energy transport in MEICPs have been computationally investigated using a two-dimensional (2D) plasma equipment model. Using a tensor conductivity in the solution of Maxwell's equations, three-dimensional components of the inductively coupled electric field are produced from an m=0 antenna and 2D applied magnetic fields. These fields are then used in a Monte Carlo simulation to generate electron energy distributions (EEDs), transport coefficients, and electron impact source functions. The electrostatic component of the wave is resolved by estimating the charge density using an oscillatory perturbed electron density. For MEICPs operating at pressures less than 10 mTorr in Ar, significant power deposition occurs downstream when the radial and axial components of the electric field are commensurate with the azimuthal component. For magnetic fields above 100 G, the tail of the EED (>20-30 eV) is enhanced in the downstream region. This enhancement results from noncollisional heating by the axial electric field for electrons in the tail of the EED which have long mean free paths, while lower energy electrons are still somewhat collisional.

Kinder, Ronald L.; Kushner, Mark J.

2001-10-01

231

Electron-Ion Temperature Equilibration in Collisionless Shocks: The Supernova Remnant-Solar Wind Connection  

NASA Astrophysics Data System (ADS)

Collisionless shocks are loosely defined as shocks where the transition between pre-and post-shock states happens on a length scale much shorter than the collisional mean free path. In the absence of collision to enforce thermal equilibrium post-shock, electrons and ions need not have the same temperatures. While the acceleration of electrons for injection into shock acceleration processes to produce cosmic rays has received considerable attention, the related problem of the shock heating of quasi-thermal electrons has been relatively neglected. In this paper we review the state of our knowledge of electron heating in astrophysical shocks, mainly associated with supernova remnants (SNRs), shocks in the solar wind associated with the terrestrial and Saturnian bowshocks, and galaxy cluster shocks. The solar wind and SNR samples indicate that the ratio of electron temperature, ( T e ) to ion temperature ( T p ) declining with increasing shock speed or Alfvén Mach number. We discuss the extent to which such behavior can be understood on the basis of waves generated by cosmic rays in a shock precursor, which then subsequently damp by heating electrons, and speculate that a similar explanation may work for both solar wind and SNR shocks.

Ghavamian, Parviz; Schwartz, Steven J.; Mitchell, Jeremy; Masters, Adam; Laming, J. Martin

2013-10-01

232

Tunable path centrality: Quantifying the importance of paths in networks  

NASA Astrophysics Data System (ADS)

Centrality is a fundamental measure in network analysis. Specifically, centrality of a path describes the importance of the path with respect to the remaining part of the network. In this paper, we propose a tunable path centrality (TPC) measure, which quantifies the centrality of a path by integrating the path degree (PD) (number of neighbors of the path) and the path bridge (PB) (number of bridges in the path) with a control parameter ?. Considering the complexity of large-scale and dynamical topologies of many real-world networks, both PD and PB are computed with only the local topological structure of a path. We demonstrate the distribution of the three path centralities (TPC, PD and PB) in computer-generated networks and real-world networks. Furthermore, we apply the three path centralities to the network fragility problem, and exploit the distribution of the optimal control parameter ? through simulation and analysis. Finally, the simulation results show that generally TPC is more efficient than PD and PB in the network fragility problem. These path centralities are also applicable in many other network problems including spread, control, prediction and so on.

Pu, Cun-Lai; Cui, Wei; Yang, Jian

2014-07-01

233

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

234

Consequences of different interstellar electron spectra on 16 MeV electron modulation  

NASA Astrophysics Data System (ADS)

The local interstellar spectrum (LIS) for galactic electrons is an important parameter in heliospheric modulation studies, and is still basically unknown at energies of interest to modulation. In this work the effects of different published LIS scenarios on model computations are shown, and in particular compared to the ˜16 MeV Pioneer 10 observations. The modulation of galactic and Jovian electrons is studied using a fully three-dimensional, steady-state model based on Parker's transport equation including the Jovian source. Compatibility between the model computations and observations gives an indication as to the magnitude of the diffusion coefficients because electron modulation responds directly to the energy dependence of the diffusion coefficients below ˜500 MeV. Comparing the different parallel mean free paths needed to compute compatible solutions with observations an upper and lower limit to the electron LIS are proposed. 1. Introduction The local interstellar spectrum (LIS) for galactic electrons is important for the study of the heliospheric modulation of cosmic ray electrons. Because of solar modulation it is impossible to determine a realistic LIS from observed modulated electron spectra at Earth because of the lack of knowledge of the transport coefficients (e.g., Potgieter, 1996; Langner et al., 2001). The LIS is therefore still basically unknown at energies of interest (e.g., Langner et al., 2001). Fortunately, ~16 MeV electron measurements had been made by the Pioneer 10 spacecraft up to ~70 AU (Lopate, 1991). The measurements include an encounter with the Jovian magnetosphere which is a relatively strong source of electrons with energies up to at least ~30 MeV (e.g., Simpson et al., 1974; Teegarden et al., 1974). The modulation of cosmic rays in the heliosphere is generally simulated by numerical models where the LIS is introduced as an initial condition. Ferreira et al. (2001b) compared model calculations with ~7 MeV observations from Ulysses, which covered a wide variety of latitudes in the inner heliosphere. This was followed by Ferreira et al. (2001c) who compared model solutions with ~16 MeV electrons observations from Pioneer 10 that stayed close to the equatorial regions up to ~70 AU. These studies provided new insights of model parameters (especially the transport coefficients) necessary to compute solutions compatible to observations. Strong et al. (1994) produced a LIS by using a sophisticated galactic propagation model in combination with gamma ray and radio synchrotron data. This spectrum has been used extensively as the LIS in modulation studies (e.g., Potgieter, 1996; Ferreira et al., 2000). Strong et al. (2000) argued that this LIS was too high for energies < ~200 MeV and proposed new, much lower spectra. Recently, Langner et al. (2001) also determined a new electron LIS, using a phenomenological approach. In this paper, the effects of these proposed LIS on modulation model computations are shown as different scenarios, comparing the computed results with the observed Pioneer 10 intensities. 2. Modulation model and parameters The model is based on the numerical solution of Parker's [1965] transport equation (TPE) : ? ? ? ? f f f t f R = - + < > ?? + ?? ?? + ? ? +( ) ( ) ( ) ln V v VD Ks Q 1 3 , (1) where f (r,P,t) is the cosmic ray distribution function; P is rigidity, r is position, and t is time. Terms on the right-hand side represent convection, gradient and curvature drifts, diffusion, adiabatic energy changes and a source function, respectively, with V the solar wind velocity. The symmetric tensor Ks consists of a parallel diffusion coefficient K|| and two perpendicular diffusion coefficients, namely K?r the perpendicular diffusion coefficient in the radial/azimuthal direction, and K?? the perpendicular diffusion coefficient in the polar direction. The parallel mean free path is given by

Ferreira, S. E. S.; Potgieter, M. S.; Langner, U. W.; de Jager, O. C.

2001-08-01

235

Finding the k Shortest Paths  

Microsoft Academic Search

We describe algorithms for finding the k shortest paths connectinga given pair of vertices in a digraph (allowing cycles). Our algorithmsoutput an implicit representation of the paths as an unordered setin time O(m + n log n + k). The paths can be output in order bylength in total time O(m + n log n + k log k). We

David Eppstein

1994-01-01

236

Shortest Paths for Line Segments  

Microsoft Academic Search

Abstract We study the problem of shortest paths for a line segment in the plane. As a measure of the distance traversed by a path, we take the average curve length of the orbits of prescribed points on the line segment. This problem is nontrivial even in free space (i.e., in the absence of obstacles). We characterize all shortest paths

Christian Icking; Giinter Rote; Emo Welzl; Chee-keng Yap

1993-01-01

237

Self similar nonlocal electron heat flow  

NASA Astrophysics Data System (ADS)

The well known self similar heat diffusion solutions of Zel'dovich and Raizer [1], for a heat wave advancing from a boundary at a fixed temperature or a fixed heat flux do not keep the ratio R of the scale length to the mean free path constant. Instead, R increases and the solution becomes increasingly valid because Spitzer-Harm [2] heat flow is increasingly applicable. A self similar solution exists which keeps R constant, if one assumes that the boundary heat flux increases in time. Similarly, for the problem of a uniform density plasma heated by a finite width laser beam, a self similar solution keeping R constant can be obtained by assuming that the beam intensity and width increase in time. Such solutions will be studied with the electron kinetic code FPI [3], and compared to simulations with more usual laser characteristics. [1] Ya. B. Zel'dovich and Yu. P. Raizer, ``Physics of Shock Waves '', Academic Press, New York, 1967. [2] L. Spitzer and R. Harm, Phys. Rev. 89, 977 (1953). [3] J.-P. Matte et al., Phys. Rev. Lett. 53, 1461 (1984) ; ibid 49, 1936 (1982).

Matte, Jean-Pierre

2007-11-01

238

Formally exact path integral Monte Carlo calculations using approximate projection operators  

Microsoft Academic Search

A class of approximate projection operators is used to reduce the variance in path integral Monte Carlo calculations in a formally exact manner. Paths are classified according to the projection operators, allowing the identification of paths whose contribution to the variance is negligible. The approach is applied to two canonical systems: Two like-spin electrons in a three dimensional harmonic well

Randall W. Hall

1992-01-01

239

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

240

Byrds Flight Path  

NSDL National Science Digital Library

The Ohio State Universitys Library web site notes As a navigational aviator, Byrd pioneered in the technology that would be the foundation for modern polar exploration and investigation. As a decorated and much celebrated hero, Byrd drew popular attention to areas of the world that became focal points of scientific investigation in numerous disciplines. More information about Admiral Richard E. Byrd can be found at (http:--www.lib.ohio-state.edu-arvweb-polar-byrd-byrd.htm). The next animation, #1001, shows Byrds plane as it follows the flight path presented in this animation.

Biddlecome, Tom; Snodgrass, Stuart; Newcombe, Marte; Jezek, Ken

1999-11-08

241

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.

Bleakley, Hoyt; Lin, Jeffrey

2012-01-01

242

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

243

Geometry of optimal path hierarchies  

NASA Astrophysics Data System (ADS)

We investigate the hierarchy of optimal paths in a disordered landscape, based on the best path, the second best path and so on in terms of an energy. By plotting each path at a height according to its energy above some zero level, a landscape appears. This landscape is self-affine and controlled by two Hurst exponents: the one controlling the height fluctuations is 1/3 and the one controlling the fluctuations of the equipotential lines in the landscape is 2/3. These two exponents correspond to the exponents controlling energy and shape fluctations in the directed polymer problem. We furthermore find that the density of spanning optimal paths scale as the length of the paths to -2/3 and the histogram of energy differences between consecutive paths scale as a power law in the difference size with exponent -2.5.

Talon, Laurent; Auradou, Harold; Pessel, Marc; Hansen, Alex

2013-08-01

244

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

245

Orientational disorder and electronic states in C sub 60 and A sub 3 C sub 60 , where A is an alkali metal  

SciTech Connect

Orientational disorder appears to persist in solid C{sub 60} even at low temperature, and similar static disorder is likely to exist in {ital A}{sub 3}c{sub 60}. The effects of such disorder on their electronic structures are studied by three-band tight-binding models for the C{sub 60} and {ital A}{sub 3}C{sub 60} conduction bands. The densities of states for the disordered systems are quite different from those in the ordered systems. Participation-ratio analyses suggest that most of the states are delocalized, but there should nonetheless be a host of experimental consequences associated with short mean free paths.

Gelfand, M.P.; Lu, J.P. (Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States))

1992-02-17

246

Photodeactivation paths in norbornadiene.  

PubMed

The first high level ab initio quantum-chemical calculations of potential energy surfaces (PESs) for low-lying singlet excited states of norbornadiene in the gas phase are presented. The optimization of the stationary points (minima and conical intersections) and the recalculation of the energies were performed using the multireference configuration interaction with singles (MR-CIS) and the multiconfigurational second-order perturbation (CASPT2) methods, respectively. It was shown that the crossing between valence V2 and Rydberg R1 states close to the Franck-Condon (FC) point permits an easy population switch between these states. Also, a new deactivation path in which the doubly excited state with (?3)(2) configuration (DE) has a prominent role in photodeactivation from the R1 state due to the R1/DE and the DE/V1 conical intersections very close to the R1 and DE minima, respectively, was proposed. Subsequent deactivation from the V1 to the ground state goes through an Olivucci-Robb-type conical intersection that adopts a rhombic distorted geometry. The deactivation path has negligible barriers, thereby making ultrafast radiationless decay to the ground state possible. PMID:23553256

Antol, Ivana

2013-06-30

247

Phoenix's Path to Mars  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Click on the image for movie of Phoenix's Path to Mars

This artist's animation shows the route NASA's Phoenix Mars Lander took to get from Earth to Mars. The spacecraft's path is shown in yellow, and the orbits of Mars and Earth are shown in red and blue, respectively.

Phoenix was launched from Cape Canaveral Air Force Station, Fla., on Aug. 4, 2007, when Earth and Mars were 195 million kilometers (121 million miles) apart. It will have traveled a total of 679 million kilometers (422 million miles) when it is scheduled to reach Mars on May 25, 2008. At that time, Earth and Mars will be farther apart, at 276 million kilometers (171 million miles).

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver

2008-01-01

248

Probability and shape of the spectral line of a single bulk characteristic energy loss of a fast electron in a medium with electron absorption and strong spatial dispersion  

NASA Astrophysics Data System (ADS)

The probability of single characteristic energy loss of a fast electron in a reflection experiment has been calculated. Unlike many works concerning this subject, the bremsstrahlung of bulk plasmons in the non- Cherenkov ranges of frequencies and wavevectors of a plasmon has been taken into account. The contributions to the probability of single loss and to the shape of the spectral line from a quantum correction that is due to the interference of elastic and inelastic electron scattering events have been determined. The probability has been calculated in the kinetic approximation for the relative permittivity, where the short-wavelength range of the plasmon spectrum is correctly taken into account. In view of these circumstances, the expression for the mean free path of the electron with respect to the emission of a bulk plasmon that was obtained by Pines [D. Pines, Elementary Excitations in Solids (Benjamin, New York, 1963)] has been refined. The coherence length of the fast electron in the medium-energy range under consideration has been estimated. The shape of the spectral line of energy losses in the non-Cherenkov frequency range has been determined. It has been shown that the probability of the single emission of the bulk plasmon incompletely corresponds to the Poisson statistics.

Libenson, B. N.

2011-10-01

249

Probability and shape of the spectral line of a single bulk characteristic energy loss of a fast electron in a medium with electron absorption and strong spatial dispersion  

SciTech Connect

The probability of single characteristic energy loss of a fast electron in a reflection experiment has been calculated. Unlike many works concerning this subject, the bremsstrahlung of bulk plasmons in the non- Cherenkov ranges of frequencies and wavevectors of a plasmon has been taken into account. The contributions to the probability of single loss and to the shape of the spectral line from a quantum correction that is due to the interference of elastic and inelastic electron scattering events have been determined. The probability has been calculated in the kinetic approximation for the relative permittivity, where the short-wavelength range of the plasmon spectrum is correctly taken into account. In view of these circumstances, the expression for the mean free path of the electron with respect to the emission of a bulk plasmon that was obtained by Pines [D. Pines, Elementary Excitations in Solids (Benjamin, New York, 1963)] has been refined. The coherence length of the fast electron in the medium-energy range under consideration has been estimated. The shape of the spectral line of energy losses in the non-Cherenkov frequency range has been determined. It has been shown that the probability of the single emission of the bulk plasmon incompletely corresponds to the Poisson statistics.

Libenson, B. N., E-mail: libenson-b@yandex.ru [St. Petersburg State Polytechnic University (Russian Federation)

2011-10-15

250

Path ensembles and path sampling in nonequilibrium stochastic systems.  

PubMed

Markovian models based on the stochastic master equation are often encountered in single molecule dynamics, reaction networks, and nonequilibrium problems in chemistry, physics, and biology. An efficient and convenient method to simulate these systems is the kinetic Monte Carlo algorithm which generates continuous-time stochastic trajectories. We discuss an alternative simulation method based on sampling of stochastic paths. Utilizing known probabilities of stochastic paths, it is possible to apply Metropolis Monte Carlo in path space to generate a desired ensemble of stochastic paths. The method is a generalization of the path sampling idea to stochastic dynamics, and is especially suited for the analysis of rare paths which are not often produced in the standard kinetic Monte Carlo procedure. Two generic examples are presented to illustrate the methodology. PMID:17867733

Harland, Ben; Sun, Sean X

2007-09-14

251

Hydrogen and surface excitation in electron spectra of polyethylene  

NASA Astrophysics Data System (ADS)

The inelastic mean free path (IMFP) of electrons of polyethylene was determined by elastic peak electron spectroscopy (EPES). Hydrogen cannot be detected directly by conventional electron spectroscopies, such as Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), reflection electron energy loss spectroscopy (REELS) and EPES. The evaluation of electron spectra on polyethylene (PE) and other polymers needs corrections for hydrogen and surface excitation. Electron elastic backscattering on H atoms appears in the splitting of the elastic peak, shifting and Doppler broadening of the H peak produced by recoil effect. This shift is 0.34-3.8 eV for E=0.2-2.0 keV. Experiments resulted in separating the very low H elastic signal from the background. Surface excitation is characterised by the parameter Pse( E) which was described by formulae of Tanuma, Werner and Chen, using different definitions. The Pse( E) of PE was determined by our new procedure. Si and Ag were used as reference samples for its determination by EPES experiments. Experiments were made with a HSA spectrometer of high energy resolution. Their Monte Carlo evaluation was based on the NIST 64 database and IMFP of Tanuma et al., Gries and Cumpson. Pse( E) of PE was determined by best fit of experimental parameters, comparing the different IMFPs and surface excitation correction factors of Chen and Werner et al. The criteria of best fit are the RMS deviations from the different corrections. The total backscattering spectra (elastic and inelastic) of PE, C and Cu resulted in indirect observation of H.

Orosz, G. T.; Gergely, G.; Menyhard, M.; Tóth, J.; Varga, D.; Lesiak, B.; Jablonski, A.

2004-09-01

252

Numerical evidence of mixing in rooms using the free path temporal distribution.  

PubMed

The ergodic propriety of a room has strong effects on its reverberation. If the room is ergodic, the reverberation can be broken up in two steps: a deterministic process followed by a stochastic one. The late reverberation can be then modeled by a reverberation algorithm instead of more computationally consuming methods. In this study, the free path temporal distribution obtained by ray-tracing is used as an indicator of the room's mixing: the energetic average of the path lengths is computed at each time step. Ergodic rooms are thus characterized by rapidly convergent distributions. The free path value becomes independent of time. On the other hand, path selection mechanism and orbits are observed in non-ergodic rooms. The transition time from the deterministic process to the stochastic one is also studied through the evaluation of the room's time constant. It is shown that its value depends only on the mean free path and the boundaries scattering value. An empirical expression is obtained which agrees well with simulations carried out in a concert hall. This transition time from a deterministic model to a stochastic one can be used to speed up the acoustical predictions and auralizations in ergodic rooms. PMID:21895079

Billon, Alexis; Embrechts, Jean-Jacques

2011-09-01

253

pathChirp: Efficient Available Bandwidth Estimation for Network Paths  

Microsoft Academic Search

This paper presents pathChirp, a new active probing tool for estimating the available bandwidth on a communication network path. Based on the concept of ''self-induced congestion,'' pathChirp features an exponential flight pattern of probes we call a chirp. Packet chips offer several significant advantages over current probing schemes based on packet pairs or packet trains. By rapidly increasing the probing

Les

2003-01-01

254

Electron Transport Modeling in Inertial Confinement Fusion Experiments  

NASA Astrophysics Data System (ADS)

Thermal transport plays an important role in inertial confinement fusion. The Spitzer--Harm model has conventionally been used in hydrocodes. Such a model, however, breaks when the electron mean free path exceeds a few percent of the spatial scale length in a plasma. To extend the validity of the model, a flux limiter f is introduced and the Spitzer flux qSH is replaced by a fraction of the free-stream flux fqFS in regions where qSH> fqFS. Alternatively, a convolution form and multigroup diffusion model of the thermal flux have been proposed in the past. In this talk, a new nonlocal model is presented which takes into account the finite deposition range of electrons. Such a model is based on the solution of a simplified kinetic equation. Heat flux, calculated with the model, is used in the hydrocode LILAC to simulate ICF experiments. Comparison of the results of such simulations with both the experimental data and Fokker--Planck simulations will be presented. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460.

Goncharov, V. N.

2005-10-01

255

Path Integral Monte Carlo Calculation of Interatomic Forces  

Microsoft Academic Search

The calculation of electronic forces with quantum Monte Carlo has, for many years, been an outstanding problem. One can calculate interatomic forces with Path Integral Monte Carlo(PIMC) as the coordinate derivatives of the partition function. Advantages of using PIMC are that effects of thermal electronic excitations and correlations are included, no trial functions are involved and the force estimator is

Fenghua Zong; David Ceperley

1997-01-01

256

Shortest Paths Without a Map  

Microsoft Academic Search

Papadimitriou, C.H. and M. Yannakakis, Shortest paths without a map, Theoretical Computer Science 84 (1991) 127-150. We study several versions of the shortest-path problem when the map is not known in advance, but is specified dynamically. We are seeking dynamic decision rules that optimize the worst-case ratio of the distance covered to the length of the (statically) optimal path. We

Christos H. Papadimitriou; Mihalis Yannakakis

1989-01-01

257

Interactive cutting path analysis programs  

NASA Technical Reports Server (NTRS)

The operation of numerically controlled machine tools is interactively simulated. Four programs were developed to graphically display the cutting paths for a Monarch lathe, Cintimatic mill, Strippit sheet metal punch, and the wiring path for a Standard wire wrap machine. These programs are run on a IMLAC PDS-ID graphic display system under the DOS-3 disk operating system. The cutting path analysis programs accept input via both paper tape and disk file.

Weiner, J. M.; Williams, D. S.; Colley, S. R.

1975-01-01

258

Path planning for virtual bronchoscopy.  

PubMed

We have developed an automated path planning method, which enables virtual bronchoscopic 3D multidetector computed tomography (MDCT) image analysis and follow on image-guided bronchoscopy. The method fundamentals are novel combination of distance transformation and snake-based models. The computation time of our algorithm is faster than similar works and there were no missing or false branches in the final path of airways. The planned path is suitable for quantitative airway analysis and smooth virtual navigation. PMID:17946384

Negahdar, Mohamadreza; Ahmadian, Alireza; Navab, Nassir; Firouznia, Kavous

2006-01-01

259

Handbook of Feynman Path Integrals  

NASA Astrophysics Data System (ADS)

The Handbook of Feynman Path Integrals appears just fifty years after Richard Feynman published his pioneering paper in 1948 entitled "Space-Time Approach to Non-Relativistic Quantum Mechanics", in which he introduced his new formulation of quantum mechanics in terms of path integrals. The book presents for the first time a comprehensive table of Feynman path integrals together with an extensive list of references; it will serve the reader as a thorough introduction to the theory of path integrals. As a reference book, it is unique in its scope and will be essential for many physicists, chemists and mathematicians working in different areas of research.

Grosche, Christian, Steiner, Frank

260

Electron affinity of pentacene thin film studied by radiation-damage free inverse photoemission spectroscopy  

NASA Astrophysics Data System (ADS)

The electron affinity of pentacene thin films has been evaluated during the last decades, but it is still under controversial due to varieties of film quality and radiation damages of the films introduced during inverse photoemission spectroscopy (IPES) experiment together with insufficient energy resolution of the instruments. We employed the near-ultraviolet IPES with a better energy resolution 0.27 ~ 0.32 eV and using lower energy electron beams (0 eV <= Ei <= 4.9 eV) to study the unoccupied states of pentacene thin film. Due to a large mean-free-path of the electron in this energy region, the threshold electron affinity of the bulk of pentacene film was precisely determined to be 2.70 +/- 0.03 eV. Using the threshold ionization energy of 4.90 +/- 0.05 eV determined by ultraviolet photoemission spectroscopy, the band-gap energy of the pentacene film is obtained to be 2.20 +/- 0.06 eV.

Han, Weining; Yoshida, Hiroyuki; Ueno, Nobuo; Kera, Satoshi

2013-09-01

261

Probing bulk electronic structure with hard X-ray angle-resolved photoemission.  

PubMed

Traditional ultraviolet/soft X-ray angle-resolved photoemission spectroscopy (ARPES) may in some cases be too strongly influenced by surface effects to be a useful probe of bulk electronic structure. Going to hard X-ray photon energies and thus larger electron inelastic mean-free paths should provide a more accurate picture of bulk electronic structure. We present experimental data for hard X-ray ARPES (HARPES) at energies of 3.2 and 6.0 keV. The systems discussed are W, as a model transition-metal system to illustrate basic principles, and GaAs, as a technologically-relevant material to illustrate the potential broad applicability of this new technique. We have investigated the effects of photon wave vector on wave vector conservation, and assessed methods for the removal of phonon-associated smearing of features and photoelectron diffraction effects. The experimental results are compared to free-electron final-state model calculations and to more precise one-step photoemission theory including matrix element effects. PMID:21841798

Gray, A X; Papp, C; Ueda, S; Balke, B; Yamashita, Y; Plucinski, L; Minár, J; Braun, J; Ylvisaker, E R; Schneider, C M; Pickett, W E; Ebert, H; Kobayashi, K; Fadley, C S

2011-10-01

262

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

263

Anomalous paths in quantum mechanical path-integrals  

NASA Astrophysics Data System (ADS)

We investigate modifications of the discrete-time lattice action, for a quantum mechanical particle in one spatial dimension, that vanish in the naïve continuum limit but which, nevertheless, induce non-trivial effects due to quantum fluctuations. These effects are seen to modify the geometry of the paths contributing to the path-integral describing the time evolution of the particle, which we investigate through numerical simulations. In particular, we demonstrate the existence of a modified lattice action resulting in paths with any fractal dimension, df, between one and two. We argue that df=2 is a critical value, and we exhibit a type of lattice modification where the fluctuations in the position of the particle becomes independent of the time step, in which case the paths are interpreted as superdiffusive Lévy flights. We also consider the jaggedness of the paths, and show that this gives an independent classification of lattice theories.

Grimsmo, Arne L.; Klauder, John R.; Skagerstam, Bo-Sture K.

2013-11-01

264

Monte Carlo simulation of electron drift velocity in low-temperature-grown gallium arsenide in a Schottky-barrier model  

NASA Astrophysics Data System (ADS)

We present a method of simulating the electron transport in low-temperature-grown GaAs by the Monte Carlo method. Low-temperature-grown GaAs contains microscopic inclusions of As and these inhomogeneities render impossible the standard Monte Carlo mobility simulations. Our method overcomes this difficulty and allows the quantitative prediction of electron transport on the basis of principal microscopic material parameters, including the impurity and the precipitate concentrations and the precipitate size. The adopted approach involves simulations of a single electron trajectory in real space, while the influence of As precipitates on the GaAs matrix is treated in the framework of a Schottky-barrier model. The validity of this approach is verified by evaluation of the drift velocity in homogeneous GaAs where excellent agreement with other workers' results is reached. The drift velocity as a function of electric field in low-temperature-grown GaAs is calculated for a range of As precipitate concentrations. Effect of compensation ratio on drift velocity characteristics is also investigated. It is found that the drift velocity is reduced and the electric field at which the onset of the negative differential mobility occurs increases as the precipitate concentration increases. Both these effects are related to the reduced electron mean free path in the presence of precipitates. Additionally, comparatively high low-field electron mobilities in this material are theoretically explained.

Arifin, P.; Goldys, E.; Tansley, T. L.

1995-08-01

265

Path Analysis: A Brief Introduction.  

ERIC Educational Resources Information Center

Path analysis is presented as a technique that can be used to test on a priori model based on a theoretical conceptualization involving a network of selected variables. This being an introductory source, no previous knowledge of path analysis is assumed, although some understanding of the fundamentals of multiple regression analysis might be…

Carducci, Bernardo J.

266

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

267

Analysis of Crossing Path Crashes.  

National Technical Information Service (NTIS)

This report defines the problem of crossing path crashes in the United States. This crash type involves one moving vehicle that cuts across the path of another when their initial approach comes from either lateral or opposite directions and they typically...

W. G. Najm J. D. Smith D. L. Smith

2001-01-01

268

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

269

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

270

Hard paths, soft paths or no paths? Cross-cultural perceptions of water solutions  

NASA Astrophysics Data System (ADS)

In this study, we examine how development status and water scarcity shape people's perceptions of "hard path" and "soft path" water solutions. Based on ethnographic research conducted in four semi-rural/peri-urban sites (in Bolivia, Fiji, New Zealand, and the US), we use content analysis to conduct statistical and thematic comparisons of interview data. Our results indicate clear differences associated with development status and, to a lesser extent, water scarcity. People in the two less developed sites were more likely to suggest hard path solutions, less likely to suggest soft path solutions, and more likely to see no path to solutions than people in the more developed sites. Thematically, people in the two less developed sites envisioned solutions that involve small-scale water infrastructure and decentralized, community-based solutions, while people in the more developed sites envisioned solutions that involve large-scale infrastructure and centralized, regulatory water solutions. People in the two water-scarce sites were less likely to suggest soft path solutions and more likely to see no path to solutions (but no more likely to suggest hard path solutions) than people in the water-rich sites. Thematically, people in the two water-rich sites seemed to perceive a wider array of unrealized potential soft path solutions than those in the water-scarce sites. On balance, our findings are encouraging in that they indicate that people are receptive to soft path solutions in a range of sites, even those with limited financial or water resources. Our research points to the need for more studies that investigate the social feasibility of soft path water solutions, particularly in sites with significant financial and natural resource constraints.

Wutich, A.; White, A. C.; White, D. D.; Larson, K. L.; Brewis, A.; Roberts, C.

2014-01-01

271

Hard paths, soft paths or no paths? Cross-cultural perceptions of water solutions  

NASA Astrophysics Data System (ADS)

In this study, we examine how development status and water scarcity shape people's perceptions of "hard path" and "soft path" water solutions. Based on ethnographic research conducted in four semi-rural/peri-urban sites (in Bolivia, Fiji, New Zealand, and the US), we use content analysis to conduct statistical and thematic comparisons of interview data. Our results indicate clear differences based on development status and, to a lesser extent, water scarcity. People in less developed sites were more likely to suggest hard path solutions, less likely to suggest soft path solutions, and more likely to see no path to solutions than people in more developed sites. Thematically, people in less developed sites envisioned solutions that involve small-scale water infrastructure and decentralized, community based solutions, while people in more developed sites envisioned solutions that involve large-scale infrastructure and centralized, regulatory water solutions. People in water-scarce sites were less likely to suggest soft path solutions and more likely to see no path to solutions (but no more likely to suggest hard path solutions) than people in water-rich sites. Thematically, people in water-rich sites seemed to perceive a wider array of unrealized potential soft path solutions than those in water-scarce sites. On balance, our findings are encouraging in that they indicate that people are receptive to soft path solutions in a range of sites, even those with limited financial or water resources. Our research points to the need for more studies that investigate the social feasibility of soft path water solutions, particularly in sites with significant financial and natural resource constraints.

Wutich, A.; White, A. C.; Roberts, C. M.; White, D. D.; Larson, K. L.; Brewis, A.

2013-06-01

272

The path planning of UAV based on orthogonal particle swarm optimization  

NASA Astrophysics Data System (ADS)

To ensure the attack mission success rate, a trajectory with high survivability and accepted path length and multiple paths with different attack angles must be planned. This paper proposes a novel path planning algorithm based on orthogonal particle swarm optimization, which divides population individual and speed vector into independent orthogonal parts, velocity and individual part update independently, this improvement advances optimization effect of traditional particle swarm optimization in the field of path planning, multiple paths are produced by setting different attacking angles, this method is simulated on electronic chart, the simulation result shows the effect of this method.

Liu, Xin; Wei, Haiguang; Zhou, Chengping; Li, Shujing

2013-10-01

273

Multiresolution path planning for mobile robots  

Microsoft Academic Search

The problem of automatic collision-free path planning is central to mobile robot applications. An approach to automatic path planning based on a quadtree representation is presented. Hierarchical path-searching methods are introduced, which make use of this multiresolution representation, to speed up the path planning process considerably. The applicability of this approach to mobile robot path planning is discussed.

S. Kambhampati; L. S. Davis

1986-01-01

274

Planning multiple paths with evolutionary speciation  

Microsoft Academic Search

This paper demonstrates a new approach to multidimensional path planning that is based on multiresolution path representation, where explicit configuration space computation is not required, and incorporates an evolutionary algorithm for solving the multimodal optimization problem, generating multiple alternative paths simultaneously. The multiresolution path representation reduces the expected search length for the path-planning problem and accordingly reduces the overall computational

Cem Hocaoglu; Arthur C. Sanderson

2001-01-01

275

Overcoming path dependency: path generation in open systems  

Microsoft Academic Search

Studies on societal path dependencies tend to focus on mechanisms that anchor and stabilize national trajectories while paying\\u000a less attention to transnational interactions and multilevel governance. This paper explores processes of path transformation\\u000a in societies that are presumed to have the characteristics of open systems. Two pairs of case studies are presented and compared.\\u000a The first illustrates institutional change through

Marie-Laure Djelic; Sigrid Quack

2007-01-01

276

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

277

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

278

Partial intensity approach for quantitative analysis of reflection-electron-energy-loss spectra  

NASA Astrophysics Data System (ADS)

We have considered a formalism, known as partial intensity approach (PIA), previously developed to quantitatively analyze reflection electron energy loss (REEL) spectra [1,2]. The aim of the approach is, in particular, to recover the single scattering distribution of energy losses and to separate it into bulk and surface contributions, respectively referred to as the differential inverse inelastic mean free path (DIIMFP) and the differential surface excitation parameter (DSEP). As compared to [1] and [2], we have implemented a modified approach, and we have applied it to the specific geometry of the cylindrical mirror analyzer (CMA), used to acquire the REEL spectra shown here. Silicon, a material with well-defined surface and bulk plasmons, is taken as a case study to investigate the approach as a function of electron energy over the energy range typical of REELS, i.e. from 250 eV to 2 keV. Our goal is, on the one hand, to examine possible limits for the applicability of the approach and, on the other hand, to test a basic assumption of the PIA, namely that a unique DIIMFP and a unique DSEP account for REEL spectra, whatever the acquisition conditions (i.e. electron energy or angle of surface crossing) are. We find that a minimum energy exists below which the PIA cannot be applied and that the assumption of REEL spectra accounted for by unique DIIMFP and DSEP is indeed an approximation.

Calliari, L.; Filippi, M.; A. Varfolomeev

2011-08-01

279

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

PubMed Central

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.

Salvat-Pujol, F; Werner, W S M

2013-01-01

280

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

281

Path Characterization Algorithms for FASCODE.  

National Technical Information Service (NTIS)

This report has described the results of a study undertaken at AER to identify and implement a state of the art nonlinear retrieval approach to characterize line of sight variability of atmospheric thermal and constituent environments. This path character...

B. L. Linder J. L. Moncet R. G. Isaacs S. A. Clough S. D. Worsham

1990-01-01

282

Shortest paths on a polyhedron  

Microsoft Academic Search

We present an algorithm for determining the shortest path between a source point and any destination point along the surface of a polyhedron (need not be convex). Our algorithm uses a new approach which deviates from the conventional “continuous Dijkstra” technique. It takes &Ogr;(n2) time and ⊖(n) space to determine the shortest path and to compute the inward layout which

Jindong Chen; Yijie Han

1990-01-01

283

Shortest Paths in Euclidean Graphs  

Microsoft Academic Search

We analyze a simple method for finding shortest paths inEuclidean graphs (where vertices are points in a Euclidean space and edge weights are Euclidean distances between points). For many graph\\u000a models, the average running time of the algorithm to find the shortest path between a specified pair of vertices in a graph\\u000a withV vertices andE edges is shown to beO(V)

Robert Sedgewick; Jeffrey Scott Vitter

1986-01-01

284

Path integration on Darboux spaces  

Microsoft Academic Search

In this paper, the Feynman path integral technique is applied to two-dimensional spaces of nonconstant curvature: these spaces\\u000a are called Darboux spaces D\\u000a I-D\\u000a IV. We start each consideration in terms of the metric and then analyze the quantum theory in the separable coordinate systems.\\u000a The path integral in each case is formulated and then solved in the majority of

Christian Grosche; Theoretische Physik

2006-01-01

285

Backup Path Classification Based on Failure Risks for Efficient Backup Path Computation  

Microsoft Academic Search

Abstract. We propose a new approach exploiting the failure risk (node, link or Shared Risk Link Group) structures to enhance the backup path computation. Upon failure, our approach classifies the backup paths into two categories: operative backup paths and inoperative backup,paths. An operative backup path is an active backup path which really receives traffic of some affected communications while an

Mohand Yazid Saidi; Bernard Cousin; Jean-louis Le Roux

2009-01-01

286

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

DOEpatents

An Intense Relativistic Electron Beam (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, C.A.; Godfrey, B.B.; Kiekel, P.D.; Shope, S.L.

1986-04-25

287

Path Integral Simulations of Heavy, Warm Dense Matter  

NASA Astrophysics Data System (ADS)

We develop an all-electron path integral Monte Carlo (PIMC) method for warm dense matter composed of elements with core electrons. For several second- and third-row elements, PIMC pressures, internal energies, and pair-correlation functions compare well with density functional theory molecular dynamics (DFT-MD) at low temperatures and enable the construction of coherent equations of state over a wide range of temperatures and densities. Details of the method and results will be discussed.

Driver, Kevin; Militzer, Burkhard

2013-03-01

288

New Sufficient Conditions for Hamiltonian Paths  

PubMed Central

A Hamiltonian path in a graph is a path involving all the vertices of the graph. In this paper, we revisit the famous Hamiltonian path problem and present new sufficient conditions for the existence of a Hamiltonian path in a graph.

Kaykobad, M.

2014-01-01

289

An Appraisal of Some Shortest Path Algorithms.  

National Technical Information Service (NTIS)

A critical review of the literature of shortest paths in networks that examines methods for determining (1) the shortest path between two specified nodes; (2) the shortest path between all pairs of nodes; (3) the second, third, etc., shortest path; (4) th...

S. E. Dreyfus

1967-01-01

290

From force fields to dynamics: Classical and quantal paths  

SciTech Connect

Reaction path provides a powerful tool for bridging the gap between electronic structure and chemical dynamics. Classical mechanical reaction paths may usually be understood in terms of the force field in the vicinity of a minimum energy path (MEP). When there is a significant component of hydrogenic motion along the MEP and a barrier much higher than the average energy of reactants, quantal tunneling paths must be considered, and these tend to be located on the corner-cutting side of the MEP. As the curvature of the MEP in mass-scaled coordinates is increased, the quantal reaction paths may deviate considerably from the classical ones, and the force field must be mapped out over a wider region, called the reaction swath. The required force fields may be presented by global or semiglobal analytic functions, or the dynamics may be computed directly from the electronic structure results without the intermediacy of potential energy functions. Applications to atom and diatom reactions in the gas phase and at gas-solid interfaces and to reactions of polyatomic molecules in the gas phase, in clusters, and in aqueous solution are discussed as examples. 106 refs., 2 figs.

Truhlar, D.G. (Univ. of Minnesota, Minneapolis (USA)); Gordon, M.S. (North Dakota State Univ., Fargo (USA))

1990-08-03

291

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

292

Study of electronic sputtering of CaF2 thin films  

NASA Astrophysics Data System (ADS)

In the present work thin films of CaF2 deposited on Si substrate by electron beam evaporation have been investigated for swift heavy ions induced sputtering and surface modifications. Glancing angle X-ray Diffraction (GAXRD) measurements show that the pristine films are polycrystalline in nature and the grain size increases with increase in film thickness. Rutherford backscattering spectrometry (RBS) of pristine as well as irradiated films was performed to determine the sputter yield of CaF2 and a decrease in sputter yield has been observed with increase in film thickness. Thermal spike model has been applied to explain this. The confinement of energy in the grains having size smaller than the electron mean free path (?) results in a higher sputtering yield. Atomic force microscopy (AFM) studies of irradiated CaF2 thin films show formation of cracks on film surface at a fluence of 5 × 1012 ions/cm2. Also RBS results confirm the removal of film from the surface and more exposure of substrate with increasing dose of ions.

Pandey, Ratnesh K.; Kumar, Manvendra; Khan, Saif A.; Kumar, Tanuj; Tripathi, Ambuj; Avasthi, D. K.; Pandey, Avinash C.

2014-01-01

293

Electron random walk and collisional crossover in a gas in presence of electromagnetic waves and magnetostatic fields  

SciTech Connect

This paper deals with random walk of electrons and collisional crossover in a gas evolving toward a plasma, in presence of electromagnetic (EM) waves and magnetostatic (B) fields, a fundamental subject of importance in areas requiring generation and confinement of wave assisted plasmas. In presence of EM waves and B fields, the number of collisions N suffered by an electron with neutral gas atoms while diffusing out of the volume during the walk is significantly modified when compared to the conventional field free square law diffusion; N=1.5({Lambda}/{lambda}){sup 2}, where {Lambda} is the characteristic diffusion length and {lambda} is the mean free path. There is a distinct crossover and a time scale associated with the transition from the elastic to inelastic collisions dominated regime, which can accurately predict the breakdown time ({tau}{sub c}) and the threshold electric field (E{sub BD}) for plasma initiation. The essential features of cyclotron resonance manifested as a sharp drop in {tau}{sub c}, lowering of E{sub BD} and enhanced electron energy gain is well reproduced in the constrained random walk.

Bhattacharjee, Sudeep; Paul, Samit [Department of Physics, Indian Institute of Technology, Kanpur 208016, Uttar Pradesh (India); Dey, Indranuj [Kyushu University, Kasuga Kouen 6-1, Kasuga City, 816-8580 (Japan)

2013-04-15

294

Random walk of electrons in a gas in the presence of polarized electromagnetic waves: Genesis of a wave induced discharge  

SciTech Connect

The average number of collisions N of seed electrons with neutral gas atoms during random walk in escaping from a given volume, in the presence of polarized electromagnetic waves, is found to vary as N=B({lambda}/{lambda}){sup 2}/[1+C({lambda}/{lambda})]{sup 2}, indicating a modification to the conventional field free square law N=A({lambda}/{lambda}){sup 2}, where {lambda} is the characteristic diffusion length and {lambda} the mean free path. It is found that for the field free case A=1.5 if all the electrons originate at the center and is 1.25 if they are allowed to originate at any random point in the given volume. The B and C coefficients depend on the wave electric field and frequency. Predictions of true discharge initiation time {tau}{sub c} can be made from the temporal evolution of seed electrons over a wide range of collision frequencies. For linearly polarized waves of 2.45 GHz and electric field in the range (0.6-1.0)x10{sup 5} V/m, {tau}{sub c}=5.5-1.6 ns for an unmagnetized microwave driven discharge at 1 Torr argon.

Bhattacharjee, Sudeep; Paul, Samit [Department of Physics, Indian Institute of Technology, Kanpur 208016 (India)

2009-10-15

295

A comparison study on the electronic structures, lattice dynamics and thermoelectric properties of bulk silicon and silicon nanotubes  

NASA Astrophysics Data System (ADS)

In order to investigate the mechanism of the electron and phonon transport in a silicon nanotube (SiNT), the electronic structures, the lattice dynamics, and the thermoelectric properties of bulk silicon (bulk Si) and a SiNT have been calculated in this work using density functional theory and Boltzmann transport theory. Our results suggest that the thermal conductivity of a SiNT is reduced by a factor of 1, while its electrical conductivity is improved significantly, although the Seebeck coefficient is increased slightly as compared to those of the bulk Si. As a consequence, the figure of merit (ZT) of a SiNT at 1200 K is enhanced by 12 times from 0.08 for bulk Si to 1.10. The large enhancement in electrical conductivity originates from the largely increased density of states at the Fermi energy level and the obviously narrowed band gap. The significant reduction in thermal conductivity is ascribed to the remarkably suppressed phonon thermal conductivity caused by a weakened covalent bonding, a decreased phonon density of states, a reduced phonon vibration frequency, as well as a shortened mean free path of phonons. The other factors influencing the thermoelectric properties have also been studied from the perspective of electronic structures and lattice dynamics.

Lu, Peng-Xian; Qu, Ling-Bo; Cheng, Qiao-Huan

2013-11-01

296

Far-Infrared Studies of 2D and 1D Electrons in Ultra High-Mobility Gated Semiconductor Structures  

NASA Astrophysics Data System (ADS)

Far-infrared (FIR) photoconductivity experiments are reported for extremely high-mobility gated GaAs-AlGaAs 1D and 2D structures in which the electron density and confining potential are separately adjustable by surface gates. Unprecedented mean free paths in excess of 100 ?m are observed in ballistic transport measurements in 2D, and conductance quantisation is observed in 5 ?m long 1D quantum wires. The electron density is tunable over two orders of magnitude. This allows detailed studies of cyclotron resonance (CR) at differing Landau level filling factors, ?. The samples are undoped, carriers being introduced by a top-gate, so comparisons can be drawn with similar studies in modulation-doped structures, in particular CR measurements in the extreme quantum limit (?<<1) where a splitting of the CR line has previously been used to probe correlated electron physics. The extension of this work to FIR studies of quantum wires at milli-Kelvin temperatures is expected to provide a spectroscopic probe of 2D-1D coupling and correlation effects in 1D (Luttinger liquid), where the absence of random disorder becomes increasingly important.

Heron, R. J.; Lewis, R. A.; Rickel, D. G.; Clark, R. G.; Starrett, R. P.; Kane, B. E.; Facer, G. R.; Lumpkin, N. E.; Dzurak, A. S.; Pfeiffer, L. N.; West, K. W.

1998-03-01

297

Quantitative analysis of electron energy loss spectra and modelling of optical properties of multilayer systems for extreme ultraviolet radiation regime  

NASA Astrophysics Data System (ADS)

Ruthenium capped multilayer coatings for use in the extreme ultraviolet (EUV) radiation regime have manifold applications in science and industry. Although the Ru cap shall protect the reflecting multilayers, the surface of the heterostructures suffers from contamination issues and surface degradation. In order to get a better understanding of the effects of these impurities on the optical parameters, reflection electron energy loss spectroscopy (REELS) measurements of contaminated and H cleaned Ru multilayer coatings were taken at various primary electron beam energies. Experiments conducted at low primary beam energies between 100 eV and 1000 eV are very surface sensitive due to the short inelastic mean free path of the electrons in this energy range. Therefore, influences of the surface condition on the above mentioned characteristics can be appraised. In this paper, it can be shown that carbon and oxide impurities on the mirror surface decrease the transmission of the Ru cap by about 0.75% and the overall reflectance of the device is impaired as the main share of the non-transmitted EUV light is absorbed in the contamination layer.

Gusenleitner, S.; Handick, E.; Hauschild, D.; Reinert, F.

2014-03-01

298

Optical Path, Phase, and Interference  

NASA Astrophysics Data System (ADS)

A powerful tool in wave optics is the concept of optical path length, a notion usually introduced with Fermat's principle.1-3 The analysis of Fermat's principle requires the application of the calculus of variations and the concept of an extremum, ideas too advanced for beginning students. However, the concept has proven its usefulness in the analysis4 of interference experiments such as those of Michelson and Fabry-Perot. In this paper we shall show how optical path length can aid in the analysis of a modified two-slit Young experiment.

Newburgh, Ronald

2005-11-01

299

Fixed-Phase Path Integral Monte Carlo Simulations in Quantum Dots in Magnetic Fields  

Microsoft Academic Search

We have developed a fixed-phase approximation for path integral Monte Carlo (PIMC) simulations. With the fixed phase approximation, the difficulties created by phases in path integrals for magnetic systems are managed in a practical way. We first demonstrate the method on electrons in a 2-D parabolic dot in a magnetic field. The PIMC method allows us to extend the simulation

Daejin Shin; John Shumway

2005-01-01

300

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

301

Triple quantum dots: Two path transport and electrostatic stability diagram  

NASA Astrophysics Data System (ADS)

We present analysis of measurements on a triple quantum dot with a two path setup. The electron transport along both paths is recorded as well as charging data measured with a quantum point contact. The results are compared with an electrostatic model. This model allows for the full visualization of the three dimensional stability diagram for triple quantum dots. It is found that this diagram contains a central diamond shaped plane at which one specific quantum cellular automata (QCA) process occurs. Moreover quadruple points are found with four degenerate charge configurations. The QCA process defines the quadruple points and limits their number to six.

Rogge, M. C.; Haug, R. J.

2010-02-01

302

Electron Localization in Water Clusters.  

National Technical Information Service (NTIS)

Electron attachment to water clusters was explored by the quantum path integral molecular dynamics method, demonstrating that the energetically favored localization mode involves a surface state of the excess electron, rather than the precursor of the hyd...

U. Landman R. N. Barnett C. L. Cleveland J. Jortner

1987-01-01

303

Path Analysis with Composite Variables.  

ERIC Educational Resources Information Center

Six methods for fitting path models with weighted composites of variables replacing latent variables (of which five are easily implemented with conventional computer software) are introduced and related to "soft" modeling by Partial Least Squares. Criteria for comparing their performance are devised, and some evaluative remarks are offered.…

McDonald, Roderick P.

1996-01-01

304

Randomized distributed shortest paths algorithms  

Microsoft Academic Search

This paper is concerned with distributed algorithm for finding shortest paths in an asynchronous communication network. For the problem of Breadth First Search, the best previously known algorithms required either &THgr;(V) time, or &THgr; (E + V · D) communication. We present new algorithm, which requires O(D1+?) time, and O(E1+?) messages, for any ? > 0. (Here, V is number

B. Awerbuch

1989-01-01

305

Perceived Shrinkage of Motion Paths  

ERIC Educational Resources Information Center

We show that human observers strongly underestimate a linear or circular trajectory that a luminous spot follows in the dark. At slow speeds, observers are relatively accurate, but, as the speed increases, the size of the path is progressively underestimated, by up to 35%. The underestimation imposes little memory load and does not require…

Sinico, Michele; Parovel, Giulia; Casco, Clara; Anstis, Stuart

2009-01-01

306

Moldovan employment relations: “path dependency”?  

Microsoft Academic Search

Purpose – The paper aims to examine the theory that trade unions' functions in a transitional economy are characterised by “path dependency”. Design\\/methodology\\/approach – The research is based on case studies of employment relations in enterprises operating in Moldova. The approach is realist (critical materialism). An ethnographic approach is taken to analysing social relations in three locally and foreign-owned companies

Claudio Morrison; Richard Croucher

2010-01-01

307

Thinking on the Write Path  

ERIC Educational Resources Information Center

The present paper underscores the importance of the cognitive orientation of English as a Foreign Language (EFL) students in their success in writing courses. A few suggestions are made as to how EFL teachers can put their students on the right cognitive path in their writings.

Salmani-Nodoushan, Mohammad Ali

2007-01-01

308

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...

309

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.

Onnela, Jukka-Pekka; Christakis, Nicholas A.

2012-01-01

310

Optimal Communication Path Routing in a System Employing Interconnected Integrated Circuit Technology.  

National Technical Information Service (NTIS)

An electronic system is described in which integrated circuits employing cornered I/O are arranged in a framework including an optional path manager and at least one updateable routing table. Packet routing options are described with solutions being provi...

B. Tourancheau C. Koch-Hofer X. F. Vigouroux

2005-01-01

311

Small Aircraft RF Interference Path Loss  

NASA Technical Reports Server (NTRS)

Interference to aircraft radio receivers is an increasing concern as more portable electronic devices are allowed onboard. Interference signals are attenuated as they propagate from inside the cabin to aircraft radio antennas mounted on the outside of the aircraft. The attenuation level is referred to as the interference path loss (IPL) value. Significant published IPL data exists for transport and regional category airplanes. This report fills a void by providing data for small business/corporate and general aviation aircraft. In this effort, IPL measurements are performed on ten small aircraft of different designs and manufacturers. Multiple radio systems are addressed. Along with the typical worst-case coupling values, statistical distributions are also reported that could lead to better interference risk assessment.

Nguyen, Truong X.; Koppen, Sandra V.; Ely, Jay J.; Szatkowski, George N.; Mielnik, John J.; Salud, Maria Theresa P.

2007-01-01

312

Small Aircraft RF Interference Path Loss Measurements  

NASA Technical Reports Server (NTRS)

Interference to aircraft radio receivers is an increasing concern as more portable electronic devices are allowed onboard. Interference signals are attenuated as they propagate from inside the cabin to aircraft radio antennas mounted on the outside of the aircraft. The attenuation level is referred to as the interference path loss (IPL) value. Significant published IPL data exists for transport and regional category airplanes. This report fills a void by providing data for small business/corporate and general aviation aircraft. In this effort, IPL measurements are performed on ten small aircraft of different designs and manufacturers. Multiple radio systems are addressed. Along with the typical worst-case coupling values, statistical distributions are also reported that could lead to more meaningful interference risk assessment.

Nguyen, Truong X.; Koppen, Sandra V.; Ely, Jay J.; Szatkowski, George N.; Mielnik, John J.; Salud, Maria Theresa P.

2007-01-01

313

A path integral Monte Carlo study of quantum solutes in liquid ammonia and ammonia clusters  

Microsoft Academic Search

The path integral Monte Carlo method is applied to some solvation problems involving quantum solutes. Thermodynamics quantities like partial molar volume and entropy change associated with the electron solvaton process are calculate. The ionization of alkali atoms in liquid ammonia and the electron attachment to ammonia clusters are investigated.\\u000aPath integral MC simulations at constant pressure lead to an expansion

Massimo Marchi

1988-01-01

314

Theory of bright-field scanning transmission electron microscopy for tomography  

SciTech Connect

Radiation transport theory is applied to electron microscopy of samples composed of one or more materials. The theory, originally due to Goudsmit and Saunderson, assumes only elastic scattering and an amorphous medium dominated by atomic interactions. For samples composed of a single material, the theory yields reasonable parameter-free agreement with experimental data taken from the literature for the multiple scattering of 300-keV electrons through aluminum foils up to 25 {mu}m thick. For thin films, the theory gives a validity condition for Beer's law. For thick films, a variant of Moliere's theory [V. G. Moliere, Z. Naturforschg. 3a, 78 (1948)] of multiple scattering leads to a form for the bright-field signal for foils in the multiple-scattering regime. The signal varies as [t ln(e{sup 1-2{gamma}}t/{tau})]{sup -1} where t is the path length of the beam, {tau} is the mean free path for elastic scattering, and {gamma} is Euler's constant. The Goudsmit-Saunderson solution interpolates numerically between these two limits. For samples with multiple materials, elemental sensitivity is developed through the angular dependence of the scattering. From the elastic scattering cross sections of the first 92 elements, a singular-value decomposition of a vector space spanned by the elastic scattering cross sections minus a delta function shows that there is a dominant common mode, with composition-dependent corrections of about 2%. A mathematically correct reconstruction procedure beyond 2% accuracy requires the acquisition of the bright-field signal as a function of the scattering angle. Tomographic reconstructions are carried out for three singular vectors of a sample problem with four elements Cr, Cu, Zr, and Te. The three reconstructions are presented jointly as a color image; all four elements are clearly identifiable throughout the image.

Levine, Zachary H. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8410 (United States)

2005-02-01

315

SEM Technique for Experimentally Locating Latch-Up Paths in Integrated Circuits.  

National Technical Information Service (NTIS)

A technique is presented for using the scanning electron microscope (SEM) in the electron-beam-induced current (EBIC) mode to delineate latch-up paths in CMOS ICs. In the EBIC mode, the current produced by the collection and separation of the electron-bea...

P. V. Dressendorfer M. G. Armendariz

1980-01-01

316

Path-Integral Molecular Dynamics Simulation for Water Anion Clusters of Various Sizes  

NASA Astrophysics Data System (ADS)

Small water molecule clusters to which an electron is attached have been investigated by path-integral molecular dynamics for electron. A solvated electron (interior state) and a dipole captured one (surface state) were obtained for large and small clusters, respectively, after producing several hundred clusters in various structures and sizes.

Ikeshoji, T.

317

Path similarity skeleton graph matching.  

PubMed

This paper presents a novel framework to for shape recognition based on object silhouettes. The main idea is to match skeleton graphs by comparing the shortest paths between skeleton endpoints. In contrast to typical tree or graph matching methods, we completely ignore the topological graph structure. Our approach is motivated by the fact that visually similar skeleton graphs may have completely different topological structures. The proposed comparison of shortest paths between endpoints of skeleton graphs yields correct matching results in such cases. The skeletons are pruned by contour partitioning with Discrete Curve Evolution, which implies that the endpoints of skeleton branches correspond to visual parts of the objects. The experimental results demonstrate that our method is able to produce correct results in the presence of articulations, stretching, and occlusion. PMID:18550909

Bai, Xiang; Latecki, Longin Jan

2008-07-01

318

Large margin shortest path routing  

Microsoft Academic Search

A new discriminative approach to routing inspired by the large margin criterion serving as a basis for support vector machines\\u000a is presented. The proposed formulation uses the benefit of the dualization convex program, and it is possible for standard\\u000a solvers to learn the weighting metrics of the shortest path routing. In order to demonstrate this and due to its simplicity,

Yadamsuren Lutbat; Rentsen Enkhbat; Won-Joo Hwang

319

Quasi-Randomized Path Planning  

Microsoft Academic Search

We propose the use of quasi-random sampling techniquesfor path planning in high-dimensional congurationspaces. Following similar trends from relatednumerical computation elds, we show several advantagesoered by these techniques in comparison to randomsampling. Our ideas are evaluated in the contextof the probabilistic roadmap (PRM) framework.Two quasi-random variants of PRM-based plannersare proposed: 1) a classical PRM with quasi-randomsampling, and 2) a quasi-random Lazy-PRM....

Micliael S. Branicky; Steven M. Lavalle; Kari Olson; Libo Yang

2001-01-01

320

Deterministic technique of path summation  

SciTech Connect

A numerical method, based on the Euclidean path integral formulation of quantum mechanics, to evaluate the ground state energy and wave function of a quantum system is discussed. The method is illustrated in one-dimensional cases, and then applied to a two-body system interacting through central and tensor potentials. A detailed discussion of the deuteron problem with a realistic nuclear potential is given.

Rosa-Clot, M.; Taddei, S. (Dipartimento di Fisica, Universita degli Studi di Firenze and Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, Largo Enrico Fermi 2, I-50125, Firenze (Italy))

1994-08-01

321

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

322

A theory of the electrical properties of liquid metals. I: The monovalent metals  

Microsoft Academic Search

The mean free path of an electron in a liquid metal depends on scattering by the ions. The cross section of each ion depend on its ‘pseudo-potential’, which can be estimated from the band gap in the solid. If the ions scattered independently, the mean free path would be much too short. But there is strong correlation between the positions

J. M. Ziman

1961-01-01

323

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

324

Multiresolution Path Planning for Mobile Robots.  

National Technical Information Service (NTIS)

The problem of automatic collision-free path planning is central to mobile robot applications. This report presents an approach to automatic two dimensional path planning based on a quadtree representation. (A quadtree is a recursive decomposition of a 2-...

S. Kambhampati L. S. Davis

1985-01-01

325

Path Integral Methods for Inelastic Scattering.  

National Technical Information Service (NTIS)

Corrections to the primitive semi-classical amplitude for multiple inelastic scattering are obtained from a path integral formulation of scattering theory. The path integrals are calculated by making an expansion about a classical orbit describing elastic...

C. V. Sukumar D. M. Brink

1983-01-01

326

Surface Waves: Source and Path Properties.  

National Technical Information Service (NTIS)

Several characteristics of oceanic surface waves can be altered by low rigidity sediments along the propagation path. Specifically spectral shape of both Love and Rayleigh waves as well as path phase velocity can be affected. The theoretical Love wave spe...

D. J. Weidner

1975-01-01

327

Ab initio reaction paths and direct dynamics calculations  

SciTech Connect

A detailed study of methods for generating the minimum energy path of a chemical reaction using ab initio electronic structure calculations is presented; the convergence with respect to step size of the geometry and energy along this path is studied with several algorithms. The investigations are extended to the calculation of chemical reaction rate coefficients by interfacing the polyrate code for variational transition-state theory and semiclassical tunneling calculations with a locally modified Gaussian 82 electronic structure package that now contains reaction path following capabilities at both the Hartree-Fock and perturbation theory levels. This combined package is used to study the kinetics of the abstraction reaction CH{sub 3} + H{sub 2} {yields} CH{sub 4} + H, which is considered as a prototype organic reaction. They report calculations of reaction rates based on electronic structure theory and generalized transition-state theory, including a multidimensional tunneling correction, without performing an analytic fit to the potential surface. The calculation of dynamical processes directly from ab initio electronic structure input without the intermediary of a potential surface fit is called direct dynamics, and this paper demonstrates the feasibility of this approach for bimolecular reactions.

Baldridge, K.K.; Gordon, M.S. (North Dakota State Univ., Fargo (USA)); Steckler, R.; Truhlar, D.G. (Univ. of Minnesota, Minneapolis (USA))

1989-06-29

328

Output-Sensitive Reporting of Disjoint Paths  

Microsoft Academic Search

A k-path query on a graph consists of computing k vertex-disjoint paths between two givenvertices of the graph, whenever they exist. In this paper, we study the problem of performingk-path queries, with k 3, in a graph G with n vertices. We denote with ` the total length ofthe paths reported. For k 3, we present an optimal data structure

Giuseppe Di Battista; Roberto Tamassia; Luca Vismara

1999-01-01

329

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

330

Wavelet formulation of path integral Monte Carlo  

Microsoft Academic Search

A wavelet formulation of path integral Monte Carlo (PIMC) is constructed. Comparison with Fourier path integral Monte Carlo is presented using simple one-dimensional examples. Wavelet path integral Monte Carlo exhibits a few advantages over previous methods for PIMC. The efficiency of the current method is at least comparable to other techniques.

Art E. Cho; J. D. Doll; David L. Freeman

2002-01-01

331

Removing False Paths from Combinational Modules 1  

Microsoft Academic Search

The existence of false paths complicates the task of accurate tim- ing analysis significantly. A technique to remove false paths from a combinational circuit without degrading its performance h as a prac- tical value since topological timing analysis is then good e nough to estimate the performance of false-path-free circuits accu rately. One can think of the KMS algorithm (1)

Yuji Kukimoto; Robert K. Brayton

332

Chip layout optimization using critical path weighting  

Microsoft Academic Search

A chip layout procedure for optimizing the performance of critical timing paths in a synchronous digital circuit is presented. The procedure uses the path analysis data produced by a static timing analysis program to generate weights for critical nets on clock and data paths. These weights are then used to bias automatic placement and routing in the layout program. This

A. E. Dunlop; V. D. Agrawal; D. N. Deutsch; M. F. Jukl; P. Kazak

1988-01-01

333

Fast Algorithms for Solving Path Problems  

Microsoft Academic Search

Let G = (V, E) be a directed graph with a distinguished source vertex s. The single-source path expression problem is to find, for each vertex v, a regular expression P(s, v) which represents the set of all paths in G from s to v A solution to this problem can be used to solve shortest path problems, solve sparse

Robert Endre Tarjan

1981-01-01

334

Global path planning using artificial potential fields  

Microsoft Academic Search

The author describes a path planning technique for robotic manipulators and mobile robots in the presence of stationary obstacles. The planning consists of applying potential fields around configuration-space obstacles and using these fields to select a safe path for the robot to follow. The advantage of using potential fields in path planning is that they offer a relatively fast and

Charles W. Warren

1989-01-01

335

Path diversity for enhanced media streaming  

Microsoft Academic Search

Media streaming over best effort packet networks such as the Internet is quite challenging because of the dynamic and unpredictable available bandwidth, loss rate, and delay. Recently, streaming over multiple paths to provide path diversity has emerged as an approach to help overcome these problems. This article provides an overview of the benefits and use of path diversity for media

John G. Apostolopoulos; Mitchell D. Trott

2004-01-01

336

SCTP Performance Issue on Path Delay Differential  

Microsoft Academic Search

This paper studies the effect of path delay on SCTP performance. It focuses on the SCTP fast retransmit algorithm and demonstrates that the performance in the current retransmission strategy will degrade acutely when the secondary path delay is less than the primary path delay at a certain level. The performance degradation is due to the disordered SACKs and constant congestion

Yuansong Qiao; Enda Fallon; Liam Murphy; John Murphy; Austin Hanley; Xiaosong Zhu; Adrian Matthews; Eoghan Conway; Gregory Hayes

2007-01-01

337

Path delay fault simulation of sequential circuits  

Microsoft Academic Search

To analyze path delay faults in synchronous sequential circuits, stimuli are simulated in a dual-vector mode. The signal states represent the logic and transition conditions for two consecutive vectors. After the simulation of each vector, only the activated paths are traced and the corresponding fault effect, if propagated to a flip-flop, is added to its fault list. A path numbering

Soumitra Bose; Prathima Agrawal; Vishwani D. Agrawal

1993-01-01

338

Path Integral Analyses of the Hydrogen Atom  

Microsoft Academic Search

The path integral analysis of the hydrogen atom problem are presented in this dissertation. The Green's function for the hydrogen atom is calculated exactly by path integration. The scattering phase shifts are also expressed in terms of path integrals and evaluated for the Coulomb potential with or without additional modifying potentials. First, the hydrogen atom in two dimensions is treated

Roger Chung Chor Ho

1982-01-01

339

Path integral analyses of the hydrogen atom  

Microsoft Academic Search

The path integral analysis of the hydrogen atom problem are presented in this dissertation. The Green's function for the hydrogen atom is calculated exactly by the path integration. The scattering phase shifts are also expressed in terms of path integrals and evaluated for the Coulomb potential with or without additional modifying potentials. First, the hydrogen atom in two dimensions is

1982-01-01

340

14 CFR 25.111 - Takeoff path.  

Code of Federal Regulations, 2010 CFR

...2009-01-01 2009-01-01 false Takeoff path. 25.111 Section 25.111 Aeronautics and...AIRPLANES Flight Performance § 25.111 Takeoff path. (a) The takeoff path extends from a standing start to a point...

2009-01-01

341

14 CFR 25.111 - Takeoff path.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 2010-01-01 false Takeoff path. 25.111 Section 25.111 Aeronautics and...AIRPLANES Flight Performance § 25.111 Takeoff path. (a) The takeoff path extends from a standing start to a point...

2010-01-01

342

14 CFR 23.57 - Takeoff path.  

Code of Federal Regulations, 2010 CFR

...2009-01-01 2009-01-01 false Takeoff path. 23.57 Section 23.57 Aeronautics...Flight Performance § 23.57 Takeoff path. For each commuter category airplane, the takeoff path is as follows: (a) The...

2009-01-01

343

Randomized path coloring on binary trees  

Microsoft Academic Search

Motivated by the problem of WDM routing in all-optical networks, we study the following NP-hard problem. We are given a directed binary tree T and a set R of directed paths on T. We wish to assign colors to paths of R, in such way that no two paths that share a directed arc of T are assigned the same

Vincenzo Auletta; Ioannis Caragiannis; Christos Kaklamanis; Pino Persiano

2002-01-01

344

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

345

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

346

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

347

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

348

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

SciTech Connect

We present calculated electron stopping powers (SPs) for 31 elemental solids (Li, Be, glassy C, graphite, diamond, Na, Mg, K, Sc, Ti, V, Fe, Y, Zr, Nb, Mo, Ru, Rh, In, Sn, Cs, Gd, Tb, Dy, Hf, Ta, W, Re, Os, Ir, and Bi). These SPs were determined with an algorithm previously used for the calculation of electron inelastic mean free paths and from energy-loss functions (ELFs) derived from experimental optical data. The SP calculations were made for electron energies between 100 eV and 30 keV and supplement our earlier SP calculations for ten additional solids (Al, Si, Cr, Ni, Cu, Ge, Pd, Ag, Pt, and Au). Plots of SP versus atomic number for the group of 41 solids show clear trends. Multiple peaks and shoulders are seen that result from the contributions of valence-electron and various inner-shell excitations. Satisfactory agreement was found between the calculated SPs and values from the relativistic Bethe SP equation with recommended values of the mean excitation energy (MEE) for energies above 10 keV. We determined effective MEEs versus maximum excitation energy from the ELFs for each solid. Plots of effective MEE versus atomic number showed the relative contributions of valence-electron and different core-electron excitations to the MEE. For a maximum excitation energy of 30 keV, our effective MEEs agreed well for Be, graphite, Na, Al, and Si with recommended MEEs; a difference for Li was attributed to sample oxidation in the SP measurements for the recommended MEE. Substantially different effective MEEs were found for the three carbon allotropes (graphite, diamond, and glassy C)

Tanuma, S. [Materials Analysis Station, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Powell, C. J.; Penn, D. R. [National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8370 (United States)

2008-03-15

349

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

350

Electron transport in p-wave superconductor-normal metal junctions  

NASA Astrophysics Data System (ADS)

We study low-temperature electron transport in p-wave superconductor-insulator-normal metal junctions. In diffusive metals, the p-wave component of the order parameter is strongly suppressed at distances greater than the mean free path l. At the superconductor-normal metal boundary, due to spin-orbit interaction, there is a triplet to singlet conversion of the superconducting order parameter. The singlet component survives at distances much larger than l from the boundary. It is this component that controls the low-temperature resistance of the junctions. As a result, the resistance of the system strongly depends on the angle between the insulating boundary and the d vector characterizing the spin structure of the triplet superconducting order parameter. We also analyze the spatial dependence of the electric potential in the presence of the current and show that the electric field is suppressed in the insulating boundary as well as in the normal metal at distances of order of the coherence length away from the boundary. This is very different from the case of the normal metal-insulator-normal metal junctions, where the voltage drop takes place predominantly at the insulator.

Keles, A.; Andreev, A. V.; Spivak, B. Z.

2014-01-01

351

Processor Would Find Best Paths On Map  

NASA Technical Reports Server (NTRS)

Proposed very-large-scale integrated (VLSI) circuit image-data processor finds path of least cost from specified origin to any destination on map. Cost of traversal assigned to each picture element of map. Path of least cost from originating picture element to every other picture element computed as path that preserves as much as possible of signal transmitted by originating picture element. Dedicated microprocessor at each picture element stores cost of traversal and performs its share of computations of paths of least cost. Least-cost-path problem occurs in research, military maneuvers, and in planning routes of vehicles.

Eberhardt, Silvio P.

1990-01-01

352

Switching mesh with broadcast path redundancy  

US Patent & Trademark Office Database

One embodiment disclosed relates to a method of broadcasting packets through a network of switches. A packet is received to be broadcast through the network of switches. A broadcast path is selected from a plurality of generated broadcast paths. A broadcast path tag associated with the selected broadcast path is created and inserted into the packet. A determination is made of the port(s) by which to forward the packet, and the packet is transmitted via the port(s) to next switch(es) in accordance with the selected broadcast path.

2008-11-04

353

Feynman path integrals in the young double-slit experiment  

Microsoft Academic Search

An estimate for the value of the nonlinear interference term in the Young double-slit experiment is found using the Feynman path-integral method. In our time-dependent calculation the usual interference term becomes multiplied by 1+e withe proportional to cos(2m? L\\/ hT), where ? is the distance between the two slits (holes) andL is the length of the shortest trajectory of electrons

H. Yabuki

1986-01-01

354

Feynman Path Integrals in the Young Double-Slit Experiment  

NASA Astrophysics Data System (ADS)

An estimate for the value of the nonlinear interference term in the Young double-slit experiment is found using the Feynman path-integral method. In our time-dependent calculation the usual interference term becomes multiplied by 1+ e with e proportional to cos(2 m? L/ ? T), where ? is the distance between the two slits (holes) and L is the length of the shortest trajectory of electrons between the source and the observation point.

Yabuki, H.

1986-02-01

355

Feynman path integrals in the young double-slit experiment  

SciTech Connect

An estimate for the value of the nonlinear interference term in the Young double-slit experiment is found using the Feynman path-integral method. In our time-dependent calculation the usual interference term becomes multiplied by 1 + e with e proportional to cos(2mlambdaL//eta/T), where lambda is the distance between the two slits (holes) and L is the length of the shortest trajectory of electrons between the source and the observation point.

Yabuki, H.

1986-02-01

356

Colloidal quantum dot photovoltaics: a path forward.  

PubMed

Colloidal quantum dots (CQDs) offer a path toward high-efficiency photovoltaics based on low-cost materials and processes. Spectral tunability via the quantum size effect facilitates absorption of specific wavelengths from across the sun's broad spectrum. CQD materials' ease of processing derives from their synthesis, storage, and processing in solution. Rapid advances have brought colloidal quantum dot photovoltaic solar power conversion efficiencies of 6% in the latest reports. These achievements represent important first steps toward commercially compelling performance. Here we review advances in device architecture and materials science. We diagnose the principal phenomenon-electronic states within the CQD film band gap that limit both current and voltage in devices-that must be cured for CQD PV devices to fulfill their promise. We close with a prescription, expressed as bounds on the density and energy of electronic states within the CQD film band gap, that should allow device efficiencies to rise to those required for the future of the solar energy field. PMID:21967723

Kramer, Illan J; Sargent, Edward H

2011-11-22

357

Evaluation of guidewire path reproducibility.  

PubMed

The number of minimally invasive vascular interventions is increasing. In these interventions, a variety of devices are directed to and placed at the site of intervention. The device used in almost all of these interventions is the guidewire, acting as a monorail for all devices which are delivered to the intervention site. However, even with the guidewire in place, clinicians still experience difficulties during the interventions. As a first step toward understanding these difficulties and facilitating guidewire and device guidance, we have investigated the reproducibility of the final paths of the guidewire in vessel phantom models on different factors: user, materials and geometry. Three vessel phantoms (vessel diameters approximately 4 mm) were constructed having tortuousity similar to the internal carotid artery from silicon tubing and encased in Sylgard elastomer. Several trained users repeatedly passed two guidewires of different flexibility through the phantoms under pulsatile flow conditions. After the guidewire had been placed, rotational c-arm image sequences were acquired (9 in. II mode, 0.185 mm pixel size), and the phantom and guidewire were reconstructed (512(3), 0.288 mm voxel size). The reconstructed volumes were aligned. The centerlines of the guidewire and the phantom vessel were then determined using region-growing techniques. Guidewire paths appear similar across users but not across materials. The average root mean square difference of the repeated placement was 0.17 +/- 0.02 mm (plastic-coated guidewire), 0.73 +/- 0.55 mm (steel guidewire) and 1.15 +/- 0.65 mm (steel versus plastic-coated). For a given guidewire, these results indicate that the guidewire path is relatively reproducible in shape and position. PMID:18561663

Schafer, Sebastian; Hoffmann, Kenneth R; Noël, Peter B; Ionita, Ciprian N; Dmochowski, Jacek

2008-05-01

358

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

359

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

360

Mechanics of the crack path formation  

NASA Technical Reports Server (NTRS)

A detailed analysis of experimentally obtained curvilinear crack path trajectories formed in a heterogeneous stress field is presented. Experimental crack path trajectories were used as data for numerical simulations, recreating the actual stress field governing the development of the crack path. Thus, the current theories of crack curving and kinking could be examined by comparing them with the actual stress field parameters as they develop along the experimentally observed crack path. The experimental curvilinear crack path trajectories were formed in the tensile specimens with a hole positioned in the vicinity of a potential crack path. The numerical simulation, based on the solution of equivalent boundary value problems with the possible perturbations of the crack path, is presented here.

Rubinstein, Asher A.

1989-01-01

361

Mechanics of the crack path formation  

NASA Technical Reports Server (NTRS)

A detailed analysis of experimentally obtained curvilinear crack path trajectories formed in a heterogeneous stress field is presented. Experimental crack path trajectories were used as data for the numerical simulations, recreating the actual stress field governing the development of the crack path. Thus, the current theories of crack curving and kinking could be examined by comparing them with the actual stress field parameters as they develop along the experimentally observed crack path. The experimental curvilinear crack path trajectories were formed in the tensile specimens with a hole positioned in the vicinity of a potential crack path. The numerical simulation, based on the solution of equivalent boundary value problems with the possible perturbations of the crack path, is presented.

Rubinstein, Asher A.

1991-01-01

362

SSME propellant path leak detection  

NASA Technical Reports Server (NTRS)

The primary objective of this phase of the investigation is the experimental validation of techniques for detecting and analyzing propellant path external leaks which have a high probability of occurring on the SSME. The selection of candidate detection methods requires a good analytic model for leak plumes which would develop from external leaks and an understanding of radiation transfer through the leak plume. One advanced propellant path leak detection technique is obtained by using state-of-art technology of infrared (IR) thermal imaging systems combined with computer, digital image processing and expert systems for the engine protection. The feasibility of the IR leak plume detection will be evaluated on subscale simulated laboratory plumes to determine sensitivity, signal to noise, and general suitability for the application. The theoretical analysis was undertaken with the objective of developing and testing simple, easy-to-use models to predict the amount of radiation coming from a radiation source, background plate (BP), which can be absorbed, emitted and scattered by the gas leaks.

Crawford, Roger; Shohadaee, Ahmad Ali; Powers, W. T.

1995-01-01

363

Electron-hole quantum physics in ZnO  

NASA Astrophysics Data System (ADS)

This dissertation describes several new aspects of the quantum physics of electrons and holes in zinc oxide (ZnO), including a few possible applications. Zinc oxide is a II-VI semiconductor with a direct band gap in the ultraviolet. Experimental and theoretical studies have been performed, both on bulk ZnO and on ZnO nanowires. Chapter 2 presents a new technique for an ultrafast all-optical shutter, based on two-photon absorption in a ZnO crystal. This shutter can be used for luminescence experiments requiring extremely high time-resolution. Chapter 3 describes a time-resolved study on the electron-hole many-body effects in highly excited ZnO at room temperature, in particular band-filling, band-gap renormalization, and the disappearance of the exciton resonance due to screening. In Chapter 4, the quantum many-body theory developed and experimentally verified in Chapter 3, is used to explain laser action in ZnO nanowires, and compared with experimental results. In contrast to current opinion, the results indicate that excitons are not involved in the laser action. The measured emission wavelength, the laser threshold, and the spectral distance between the laser modes are shown to be excellently explained by our quantum many-body theory. Multiple scattering of light in a forest of nanowires can be employed to enhance light absorption in solar cells. Optimization of this technique requires better understanding of light diffusion in such a nanowire forest. In Chapter 5 we demonstrate a method, based on two-photon absorption, to directly measure the residence time of light in a nanowire forest, and we show that scanning electron microscope (SEM) images can be used to predict the photon mean free path. In Chapter 6 we present a new ultrafast all-optical transistor, consisting of a forest of ZnO nanowires. After excitation, laser action in this forest causes rapid recombination of the majority of the electrons and holes, limiting the amplification to 1.2 picoseconds only . This ultrafast ultraviolet transistor may have applications in all-optical computing and in pump-probe experiments. Finally, Chapter 7 presents our discovery of preformed electron-hole Cooper pairs. A ZnO crystal has been highly excited via three-photon absorption at cryogenic temperatures. A new peak appears in the measured emission spectra when the crystal is cooled below a certain temperature, and also when it is excited above a certain density. Comparison with light amplification spectra, calculated from quantum many-body theory, demonstrates that this new peak is due to amplified spontaneous emission (ASE) from preformed electron-hole Cooper pairs.

Versteegh, M. A. M.

2011-09-01

364

Selection of potentially testable path delay faults for test generation  

Microsoft Academic Search

We present a method of path selection and test generation for path delay faults. The proposed method addresses the fact that logic circuits typically have very large numbers of paths, and a large percentage of these paths are typically untestable. The proposed method selects a set of potentially testable long paths by utilizing non-enumerative identification of untestable paths and removing

Atsushi Murakami; Seiji Kajihara; Tsutomu Sasao; Irith Pomeranz; Sudhakar M. Reddy

2000-01-01

365

OSL—optimal single-loop guide paths for AGVS  

Microsoft Academic Search

This study deals with the Automated Guided Vehicle System guide path design problem. We suggest a single closed loop guide path layout configuration as an alternative to conventional but more complex guide path designs. The benefits of using a simple guide path versus more complicated guide paths are discussed. A procedure for designing an optimal single loop guide path for

J. M. A. TANCHOCOf; DAVID SINRIECH

1992-01-01

366

Free Path Lengths in Quasicrystals  

NASA Astrophysics Data System (ADS)

Previous studies of kinetic transport in the Lorentz gas have been limited to cases where the scatterers are distributed at random (e.g., at the points of a spatial Poisson process) or at the vertices of a Euclidean lattice. In the present paper we investigate quasicrystalline scatterer configurations, which are non-periodic, yet strongly correlated. A famous example is the vertex set of a Penrose tiling. Our main result proves the existence of a limit distribution for the free path length, which answers a question of Wennberg. The limit distribution is characterised by a certain random variable on the space of higher dimensional lattices, and is distinctly different from the exponential distribution observed for random scatterer configurations. The key ingredients in the proofs are equidistribution theorems on homogeneous spaces, which follow from Ratner's measure classification.

Marklof, Jens; Strömbergsson, Andreas

2014-03-01

367

The path to adaptive microsystems  

NASA Astrophysics Data System (ADS)

Scaling trends in microsystems are discussed frequently in the technical community, providing a short-term perspective on the future of integrated microsystems. This paper looks beyond the leading edge of technological development, focusing on new microsystem design paradigms that move far beyond today's systems based on static components. We introduce the concept of Adaptive Microsystems and outline a path to realizing these systems-on-a-chip. The role of DARPA in advancing future components and systems research is discussed, and specific DARPA efforts enabling and producing adaptive microsystems are presented. In particular, we discuss efforts underway in the DARPA Microsystems Technology Office (MTO) including programs in novel circuit architectures (3DIC), adaptive imaging and sensing (AFPA, VISA, MONTAGE, A-to-I) and reconfigurable RF/Microwave devices (SMART, TFAST, IRFFE).

Zolper, John C.; Biercuk, Michael J.

2006-06-01

368

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

369

Spatial and frequency coherence of oblique, one-hop, high-frequency paths  

SciTech Connect

We consider the effect of random index of refraction fluctuations upon long-distance, ionospherically-reflected, hf paths. Along with deterministic effects such as multipath and dispersion, such fluctuations have a deleterious impact on hf communication including nonabsorptive fading, time-of-arrival spread, angle-of-arrival spread, and Doppler spread. We develop a formalism to calculate the mutual coherence functions for spatial and frequency separations based upon a path integral solution of the parabolic wave equation for a single refracted path through an ionosphere which contains random electron density fluctuations. The statistics of the hf path depend directly on the strength and statistics of the electron density fluctuations; we model the spatial power spectrum of the density fluctuation as a power law behavior versus frequency and with outer and inner scales.

Fitzgerald, T.J.

1995-10-01

370

Atomic and molecular quantum mechanics by the path integral molecular dynamics method  

NASA Astrophysics Data System (ADS)

The quantum path integral molecular dynamics method was applied to studies of excess electron localization by a Na + ion and by a NaCl molecule. Spatial and energetic characterization of the ground state of the excess electron compare favorably with results of model potential calculations for Na and with SCF Cl calculations for NaCl -.

Scharf, Dafna; Jortner, Joshua; Landman, Uzi

1986-10-01

371

ANALYSIS OF CROSSING PATH CRASH COUNTERMEASURE SYSTEMS  

Microsoft Academic Search

This paper summarizes the results of an analysis of promising countermeasure systems for crossing path crashes, and thus provides a foundation for setting research priorities under the United States (U.S.) Department of Transportation's Intelligent Vehicle Initiative. Crossing path crashes involve one moving vehicle cutting across the path of another, which amounted to 1.72 million police-reported crashes in the U.S. based

Wassim G. Najm; Jonathan A. Koopmann; David L. Smith

372

Elastic Bands: Connecting Path Planning and Control  

Microsoft Academic Search

Elastic bands are proposed as the basis for a new framework to close the gap between global path planning and real-time sensor-based robot control. An elastic band is a deformable collision-free path. The initial shape of the elastic is the free path generated by a planner. Subjected to artificial forces, the elastic band deforms in real time to a short

Sean Quinlan; Oussama Khatib

1993-01-01

373

Multiple-path execution for chip multiprocessors  

Microsoft Academic Search

The increased dependence of clock cycle time on interconnect delay favors chip multiprocessors (CMP) for future microprocessor designs. This paper studies multiple-path execution (MPE) on a CMP to provide speedup on unmodified sequential code by exploring different paths of a conditional branch on separate processors. MPE performance due to processor complexity and count, cache and branch prediction architecture, processor-to-path allocation

Matthew C. Chidester; Alan D. George; Matthew A. Radlinski

2003-01-01

374

Ant navigation: resetting the path integrator  

Microsoft Academic Search

Desert ants use path integration as their predominant system of long-distance navigation, but they also make use of route-defining and nest-defining visual landmarks. Such landmark-gained information might override the information provided by the path integrator, but nevertheless the path integrator keeps running. Here we show that only cues that are associated with the ant being inside the nest are able

Markus Knaden; Rüdiger Wehner

2006-01-01

375

Maximum Flux Transition Paths of Conformational Change.  

PubMed

Given two metastable states A and B of a biomolecular system, the problem is to calculate the likely paths of the transition from A to B. Such a calculation is more informative and more manageable if done for a reduced set of collective variables chosen so that paths cluster in collective variable space. The computational task becomes that of computing the "center" of such a cluster. A good way to define the center employs the concept of a committor, whose value at a point in collective variable space is the probability that a trajectory at that point will reach B before A. The committor "foliates" the transition region into a set of isocommittors. The maximum flux transition path is defined as a path that crosses each isocommittor at a point which (locally) has the highest crossing rate of distinct reactive trajectories. This path is based on the same principle as the minimum resistance path of Berkowitz et al (1983), but it has two advantages: (i) the path is invariant with respect to a change of coordinates in collective variable space and (ii) the differential equations that define the path are simpler. It is argued that such a path is nearer to an ideal path than others that have been proposed with the possible exception of the finite-temperature string method path. To make the calculation tractable, three approximations are introduced, yielding a path that is the solution of a nonsingular two-point boundary-value problem. For such a problem, one can construct a simple and robust algorithm. One such algorithm and its performance is discussed. PMID:20890401

Zhao, Ruijun; Shen, Juanfang; Skeel, Robert D

2010-08-10

376

Path integral analyses of the hydrogen atom  

SciTech Connect

The path integral analysis of the hydrogen atom problem are presented in this dissertation. The Green's function for the hydrogen atom is calculated exactly by the path integration. The scattering phase shifts are also expressed in terms of path integrals and evaluated for the Coulomb potential with or without additional modifying potentials. First, the hydrogen atom in two dimensions is treated by path integration in parabolic coordinates. Feynman's path integral for the hydrogen atom in R/sup 2/, which cannot be directly integrated, is reduced to the exactly solvable path integral for an oscillator in R/sup 2/. The reduction procedure consists of the path-dependent time rescaling and the Levi-Civita transformation from Cartesian to parabolic coordinates. A path-dependent scaling of the global time and a nonlinear transformation of global coordinated are not necessarily valid in a path integral. Therefore, the reduction procedure is applied to each well-defined short time integral. The two-dimensional problem is studied by both the Lagrangian and the Hamiltonian path integral. The exact results are obtained for the Green's function and the energy spectrum of the hydrogen atom in R/sup 2/. The reduction procedure is then generalized to solve the hydrogen atom in three dimensions. The same time scaling is adopted. Since the three-dimensional counterpart of the Levi-Cavita transformation does not exist, the Kustaanheimo-Steifel transformation, which maps Cartesian variables in R/sup 3/ into Cartesian variables in R/sup 4/, is modified to transform the Coulomb path integral into an oscillator in R/sup 4/. An extra dimension introduced for the transformation is eliminated after path integration. The Green's function and the energy spectrum are found for the hydrogen atom in R/sup 3/.

Ho, R.C.C.

1982-01-01

377

Randomized path coloring on binary trees  

Microsoft Academic Search

Motivated by the problem of WDM routing in all-optical networks, we study the following NP-hard problem. We are given a di- rected binary tree T and a set R of directed paths on T.W e wish to assign colors to paths in R, in such a way that no two paths that share ad irected arc ofT are assigned the

Vincenzo Auletta; Ioannis Caragiannis; Christos Kaklamanis; Pino Persiano

2000-01-01

378

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

379

Path Deviation Equations in AP-Geometry  

NASA Astrophysics Data System (ADS)

Recently, it has been shown that Absolute Parallelism (AP) geometry admits paths that are naturally quantized. These paths have been used to describe the motion of spinning particles in a background gravitational field. In case of a weak static gravitational field limits, the paths are applied successfully to interpret the discrepancy in the motion of thermal neutrons in the Earth's gravitational field (COW-experiment). The aim of the present work is to explore the properties of the deviation equations corresponding to these paths. In the present work the deviation equations are derived and compared to the geodesic deviation equation of the Riemannian geometry.

Wanas, M. I.; Kahil, M. E.

2006-02-01

380

Path-integral simulation of solids  

NASA Astrophysics Data System (ADS)

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.

Herrero, C. P.; Ramírez, R.

2014-06-01

381

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

382

Path-integral molecular dynamics simulation of diamond  

NASA Astrophysics Data System (ADS)

Diamond is studied by path-integral molecular dynamics simulations of the atomic nuclei in combination with a tight-binding Hamiltonian to describe its electronic structure and total energy. This approach allows us to quantify the influence of quantum zero-point vibrations and finite temperatures on both the electronic and vibrational properties of diamond. The electron-phonon coupling mediated by the zero-point vibration reduces the direct electronic gap of diamond by 10%. The calculated decrease of the direct gap with temperature shows good agreement with the experimental data available up to 700K . Anharmonic vibrational frequencies of the crystal have been obtained from a linear-response approach based on the path integral formalism. In particular, the temperature dependence of the zone-center optical phonon has been derived from the simulations. The anharmonicity of the interatomic potential produces a red shift of this phonon frequency. At temperatures above 500K , this shift is overestimated in comparison to available experimental data. The predicted temperature shift of the elastic constant c44 displays reasonable agreement with the available experimental results.

Ramírez, Rafael; Herrero, Carlos P.; Hernández, Eduardo R.

2006-06-01

383

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

384

Construction of Optimal-Path Maps for Homogeneous-Cost-Region Path-Planning Problems.  

National Technical Information Service (NTIS)

Fast path-planning algorithms are needed for autonomous vehicles and tactical terrain-analysis tools. We explore a new approach using 'optimal-path maps', that give the best path to a goal point from any given start point in cross-country two-dimensional ...

R. S. Alexander

1989-01-01

385

Electron Heat Flux in the Solar Wind: Are We Observing the Collisional Limit in the 1 AU Data?  

NASA Astrophysics Data System (ADS)

Using statistically significant data at 1 AU, it has recently been shown (Bale et al.) that in the solar wind, when the Knudsen number K T (the ratio between the electron mean free path and the electron temperature scale height) drops below about 0.3, the electron heat flux q intensity rapidly approaches the classical collisional Spitzer-Härm limit. Using a fully kinetic model including the effect of Coulomb collisions and the expansion of the solar wind with heliocentric distance, we observe that the heat flux strength does indeed approach the collisional value for Knudsen numbers smaller than about 0.3 in very good agreement with the observations. However, closer inspection of the heat flux properties, such as its variation with the heliocentric distance and its dependence on the plasma parameters, shows that for Knudsen numbers between 0.02 and 0.3 the heat flux is not conveniently described by the Spitzer-Härm formula. We conclude that even though observations at 1 AU seem to indicate that the electron heat flux intensity approaches the collisional limit when the Knudsen drops below ~0.3, the collisional limit is not a generally valid closure for a Knudsen larger than 0.01. Moreover, the good agreement between the heat flux from our model and the heat flux from solar wind measurements in the high-Knudsen number regime seems to indicate that the heat flux at 1 AU is not constrained by electromagnetic instabilities as both wave-particle and wave-wave interactions are neglected in our calculations.

Landi, S.; Matteini, L.; Pantellini, F.

2014-07-01

386

Traffic equilibrium problem with nonadditive path costs.  

National Technical Information Service (NTIS)

In this paper the authors present a version of the (static) traffic equilibrium problem in which the cost incurred on a path is not simply the sum of the costs on the arcs that constitute that path. The authors motivate this nonadditive version of the pro...

S. A. Gabriel D. Bernstein

1995-01-01

387

More Efficient Path-Finding Algorithm.  

National Technical Information Service (NTIS)

In this paper, we present a new routing algorithm, which we call path-finding algorithm (PFA). It drastically reduces the possibility of temporary routing loops, which accounts for its fast convergence properties. Like other path-finding algorithms, PFA o...

J. J. Garcia-Luna-Aceves S. Murthy

2006-01-01

388

Next Generation Science Standards (NGSS) Path Finder  

NSDL National Science Digital Library

This interactive visual 'path finder' from the Concord Consortium allows users to explore the component pieces of the Next Generation Science Standards. After selecting the appropriate practices, core ideas, and crosscutting concepts, the path finder will suggest relevant resources from the Concord Consortium's collection.

Consortium, The C.

389

The stable paths problem and interdomain routing  

Microsoft Academic Search

Dynamic routing protocols such as RIP and OSPF essentially implement distributed algorithms for solving the shortest paths problem. The border gateway protocol (BGP) is currently the only interdomain routing protocol deployed in the Internet. BGP does not solve a shortest paths problem since any interdomain protocol is required to allow policy-based metrics to override distance-based metrics and enable autonomous systems

Timothy G. Griffin; F. Bruce Shepherd; Gordon T. Wilfong

2002-01-01

390

Another adaptive distributed shortest path algorithm  

Microsoft Academic Search

The authors give a distributed algorithm to compute shortest paths in a network with changing topology. The authors analyze its behavior. The proof of correctness is discussed. It does not suffer from the routing table looping behavior associated with the Ford-Bellman distributed shortest path algorithm although it uses truly distributed processing. Its time and message complexities are evaluated. Comparisons with

Pierre A. Humblet

1991-01-01

391

Optimizing Path Expressions Using Navigational Algebraic Operators  

Microsoft Academic Search

Object-oriented database systems are more and more used in real applications due to their rich data model and query language mixing declarative assertions and navigations. Queries may frequently involve multiple collection traversais (i.e., path expression). Moreover, quantifiers like exist, any, all can also be included inside path expressions. These bring new challenges for object query optimization. In order to efficiently

Zhao-hui Tang; Georges Gardarin; Veronique Smahi

1996-01-01

392

Global Path Planning Approach for Redundant Manipulators.  

National Technical Information Service (NTIS)

A new approach for global path planning of redundant manipulators is proposed. It poses the path planning problem as a finite time nonlinear control problem. The solution is found by a Newton-Raphson type algorithm. This technique is capable of handling v...

S. Seereeram J. Wen

1993-01-01

393

Randomized Query Processing in Robot Path Planning  

Microsoft Academic Search

The subject of this paper is the analysis of a randomized preprocessing scheme that has been used for query processing in robot path planning. The attractiveness of the scheme stems from its general applicability to virtually any path-planning problem, and its empirically observed success. In this paper we initiate a theoretical basis for explaining this empirical success. Under a simple

Lydia E. Kavraki; Jean-claude Latombe; Rajeev Motwani; Prabhakar Raghavan

1998-01-01

394

Analysis of probabilistic roadmaps for path planning  

Microsoft Academic Search

We provide an analysis of a path planning method which uses probabilistic roadmaps. This method has proven very successful in practice, but the theoretical understanding of its performance is still limited. Assuming that a path ? exists between two configurations a and b of the robot, we study the dependence of the failure probability to connect a and b, on:

Lydia E. Kavraki; Mihail N. Kolountzakis; Jean-claude Latombe

1998-01-01

395

Coverage Path Planning: The Boustrophedon Cellular Decomposition  

Microsoft Academic Search

Coverage path planning is the determination ofa path that a robot must take in order to passover each point in an environment. Applicationsinclude vacuuming, floor scrubbing, andinspection. We developed the boustrophedoncellular decomposition, which is an exact cellulardecomposition approach, for the purposesof coverage. Each cell in the boustrophedonis covered with simple back and forth motions.Once each cell is covered, then the

Howie Choset; Philippe Pignon

1997-01-01

396

A path model of aircraft noise annoyance  

Microsoft Academic Search

This paper describes the development and testing of a path model of aircraft noise annoyance by using noise and social survey data collected in the vicinity of Toronto International Airport. Path analysis is used to estimate the direct and indirect effects of seventeen independent variables on individual annoyance. The results show that the strongest direct effects are for speech interference,

S. M. Taylor

1984-01-01

397

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

398

Traceroute and BGP AS Path Incongruities  

Microsoft Academic Search

Researchers investigating topics such as performance, stability, and growth of the Internet often turn to BGP routing tables to obtain Internet topology. BGP routing tables provide a mapping from address prefixes to autonomous system (AS) paths. Our study, based on hundreds of thousands of traceroutes from three locations worldwide, categorizes differences between AS paths obtained from BGP routing tables and

Young Hyun; Andre Broido; K. C. Claffy

2003-01-01

399

Path integration on Hermitian hyperbolic space  

Microsoft Academic Search

In this paper, the path integral technique is applied to the quantum motion on the Hermitian hyperbolic space HH(2). The Schrödinger equation on this space separates in 12 coordinate systems which are closely related to the coordinate systems on the two-dimensional hyperboloid. For six coordinate systems out of the twelve it is possible to find a path integral solution.

Christian Grosche; Theoretische Physik

2005-01-01

400

Outdoor Path Labeling Using Polynomial Mahalanobis Distance  

Microsoft Academic Search

Autonomous robot navigation in outdoor environ- ments remains a challenging and unsolved problem. A key issue is our ability to identify safe or navigable paths far enough ahead of the robot to allow smooth trajectories at acceptable speeds. Colour or texture-based labeling of safe path regions in image sequences is one way to achieve this far field prediction. A challenge

Gregory Z. Grudic; Jane Mulligan

2006-01-01

401

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

402

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

403

Symbolic modeling and evaluation of data paths  

Microsoft Academic Search

We present an automata model which concisely cap- tures the constraints imposed by a data-path, such as bus hazards, register constraints, and control encoding limita- tions. A set of uniform base components for depicting gen- eral data-paths and techniques for systematic translation of such depictions into Boolean functions are described. Finally, this model is expanded to represent the limitations of

Chuck Monahan; Forrest Brewer

1995-01-01

404

UAV Path Planning for Passive Emitter Localization  

Microsoft Academic Search

A path planning algorithm is presented for uninhabited aerial vehicles (UAVs) trying to geolocate an emitter using passive payload sensors. The objective is to generate a sequence of waypoints for each vehicle that minimizes localization uncertainty. The path planning problem is cast as a nonlinear programming problem using an approximation of the Fisher information matrix (FIM) and solved at successive

Kutluyil Dogancay

2012-01-01

405

Study on tire noise transfer path identification  

Microsoft Academic Search

Improvement of vehicle interior noise has been becoming more important for driving perception. Since NVH refinement on powertrain has achieved a lot of effectiveness, other noise sources like tire noise begin dominant. On the basis of analyzing wheel excitation force and transmission, structure transfer path of tire noise was modeled in this paper and experimental transfer path analysis was carried

Jin Chang; Wang WanYing; Jin XiaoXiong

2010-01-01

406

Precision Cleaning - Path to Premier  

NASA Technical Reports Server (NTRS)

ITT Space Systems Division s new Precision Cleaning facility provides critical cleaning and packaging of aerospace flight hardware and optical payloads to meet customer performance requirements. The Precision Cleaning Path to Premier Project was a 2007 capital project and is a key element in the approved Premier Resource Management - Integrated Supply Chain Footprint Optimization Project. Formerly precision cleaning was located offsite in a leased building. A new facility equipped with modern precision cleaning equipment including advanced process analytical technology and improved capabilities was designed and built after outsourcing solutions were investigated and found lacking in ability to meet quality specifications and schedule needs. SSD cleans parts that can range in size from a single threaded fastener all the way up to large composite structures. Materials that can be processed include optics, composites, metals and various high performance coatings. We are required to provide verification to our customers that we have met their particulate and molecular cleanliness requirements and we have that analytical capability in this new facility. The new facility footprint is approximately half the size of the former leased operation and provides double the amount of throughput. Process improvements and new cleaning equipment are projected to increase 1st pass yield from 78% to 98% avoiding $300K+/yr in rework costs. Cost avoidance of $350K/yr will result from elimination of rent, IT services, transportation, and decreased utility costs. Savings due to reduced staff expected to net $4-500K/yr.

Mackler, Scott E.

2008-01-01

407

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.

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

2011-01-01

408

Shortest path and Schramm-Loewner Evolution  

PubMed Central

We numerically show that the statistical properties of the shortest path on critical percolation clusters are consistent with the ones predicted for Schramm-Loewner evolution (SLE) curves for ? = 1.04 ± 0.02. The shortest path results from a global optimization process. To identify it, one needs to explore an entire area. Establishing a relation with SLE permits to generate curves statistically equivalent to the shortest path from a Brownian motion. We numerically analyze the winding angle, the left passage probability, and the driving function of the shortest path and compare them to the distributions predicted for SLE curves with the same fractal dimension. The consistency with SLE opens the possibility of using a solid theoretical framework to describe the shortest path and it raises relevant questions regarding conformal invariance and domain Markov properties, which we also discuss.

Pose, N.; Schrenk, K. J.; Araujo, N. A. M.; Herrmann, H. J.

2014-01-01

409

Optimal robust path planning in general environments  

SciTech Connect

The authors address robust path planning for a mobile agent in a general environment by finding minimum cost source-destination paths having prescribed widths. The main result is a new approach that optimally solves the robust path planning problem using an efficient network flow formulation. Their algorithm represents a significant departure from conventional shortest-path or graph search based methods; it not only handles environments with solid polygonal obstacles, but also generalizes to arbitrary cost maps that may arise in modeling incomplete or uncertain knowledge of the environment. Simple extensions allow them to address higher dimensional problems instances and minimum-surface computations; the latter is a result of independent interest. They use an efficient implementation to exhibit optimal path-planning solutions for a variety of test problems. The paper concludes with open issues and directions for future work.

Hu, T.C. (Univ. of California, San Diego, La Jolla, CA (United States). Computer Science and Engineering Dept.); Kahng, A.B. (Univ. of California, Los Angeles, CA (United States). Computer Science Dept.); Robins, G. (Univ. of Virginia, Charlottesville, VA (United States). Dept. of Computer Science)

1993-12-01

410

The Feynman trajectories: determining the path of a protein using fixed-endpoint assays.  

PubMed

Richard Feynman postulated in 1948 that the path of an electron can be best described by the sum or functional integral of all possible trajectories rather than by the notion of a single, unique trajectory. As a consequence, the position of an electron does not harbor any information about the paths that contributed to this position. This observation constitutes a classical endpoint observation. The endpoint assay is the desired type of experiment for high-throughput screening applications, mainly because of limitations in data acquisition and handling. Quite contrary to electrons, it is possible to extract information about the path of a protein using endpoint assays, and these types of applications are reviewed in this article. PMID:20130209

Ketteler, Robin

2010-03-01

411

Hydrogen molecule ion: Path-integral Monte Carlo approach  

SciTech Connect

The path-integral Monte Carlo approach is used to study the coupled quantum dynamics of the electron and nuclei in hydrogen molecule ion. The coupling effects are demonstrated by comparing differences in adiabatic Born-Oppenheimer and nonadiabatic simulations, and inspecting projections of the full three-body dynamics onto the adiabatic Born-Oppenheimer approximation. Coupling of the electron and nuclear quantum dynamics is clearly seen. The nuclear pair correlation function is found to broaden by 0.040a{sub 0}, and the average bond length is larger by 0.056a{sub 0}. Also, a nonadiabatic correction to the binding energy is found. The electronic distribution is affected less than the nuclear one upon inclusion of nonadiabatic effects.

Kylaenpaeae, I.; Leino, M.; Rantala, T. T. [Institute of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere (Finland)

2007-11-15

412

Effect of horizontal gradients on ionospherically reflected or transionospheric paths using a precise homing-in method  

NASA Astrophysics Data System (ADS)

A homing-in method is presented for determining ionospheric reflected or transionospheric paths between fixed transmitter and receiver locations in the presence of ionospheric gradients or ripples. Both initial elevation and azimuth are automatically adjusted to find the path that arrives exactly at the receiver. The method can be used for any 3D ionospheric model to find precise ray paths and phase and group delays for both magneto-ionic modes. The method takes full account of path location, geomagnetic field orientation and the bending of the ray path resulting from horizontal as well as vertical gradients of electron density. It can also find multiple paths e.g. low and high angle, 1- and 2-hops for both ordinary and extraordinary modes. Examples of its use are given for both terrestrial HF links and Earth to Satellite paths. For paths reflected from the ionosphere, the effect of gradients of both critical frequency and height of maximum electron density are determined and the comparative effect of gradients on high and low angle and 1- and 2-hops paths for both magneto-ionic modes investigated. Path variation with frequency for a fixed link is also studied and the bandwidth of the ionospheric background channel (dispersive bandwidth) and its reciprocal (the pulse rise time), important for wideband digital HF broadcasting or spread spectrum HF communications, is estimated for a range of frequencies, for high- and low-angle rays and 1- and 2-hop paths. For Earth-satellite paths, the effect of the ionosphere and horizontal ionospheric gradients is determined for a range of frequencies and elevation angles. It is shown that the method can also enable the determination of second-order errors in satellite navigation methods, such as GPS, due to ionospheric gradients and the effect of the geomagnetic field.

Strangeways, H. J.

2000-10-01

413

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

414

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

415

Path-integral approach of ionization by ultrashort laser pulses  

SciTech Connect

In the present paper, we model in a fully quantum-mechanical way the dynamics of an atom with one active electron interacting with a coherent linearly polarized ultrashort photonic pulse. We use path-integral methods. We derive the system's propagator in its discrete form and develop a Monte Carlo method to study its dynamics. To avoid any additional complication, we apply our method to the ionization of atomic hydrogen from its ground state supposing that the photon energy is greater than the ionization threshold and give the ionization probability. In fact, the present method can be applied to the ionization of any atom or molecule.

Thrapsaniotis, E.G. [Department of Applied Mathematics, University of Crete, 71409 Heraklion, Crete (Greece)

2004-09-01

416

Crack-path effect on material toughness  

NASA Technical Reports Server (NTRS)

The main features of a toughening mechanism associated with a curvilinear crack path are examined using a model consisting of a macrocrack in a brittle solid with a curvilinear segment at the crack tip. A numerical procedure for finite and semiinfinite cracks is formulated and evaluated using an example which has an exact solution (a finite crack in the form of a circular arc in a uniform stress field). It is shown that, for a relatively small amplitude of crack path oscillations, the toughening ratio can be taken equal to the ratio of the corresponding crack path lengths.

Rubinstein, Asher A.

1990-01-01

417

Path Integrals and Anomalies in Curved Space  

NASA Astrophysics Data System (ADS)

Path integrals provide a powerful method for describing quantum phenomena. This book introduces the quantum mechanics of particles moving in curved space by employing path integrals and then using them to compute anomalies in quantum field theories. These anomalies provide enormous constraints in the search for physical theories such as those of elementary particles, quantum gravity and string theories. An advanced text for researchers and graduate students of quantum field theory and string theory, the first part is also a stand-alone introduction to path integrals in quantum mechanics.

Bastianelli, Fiorenzo; van Nieuwenhuizen, Peter

418

Optimization of Loading Paths for Tube Hydroforming  

NASA Astrophysics Data System (ADS)

An iterative FE simulation approach enhanced with numerical optimization schemes has been implemented for determination of optimum loading paths for tube hydroforming (THF) processes. A general optimization code, PAM-OPT, has been applied to optimize several THF processes simulated by PAM-STAMP. This paper discusses formulations of optimization of loading paths for various THF processes including a Y-shape and a complex structural part. In the process optimization, the loading paths were represented by piecewise-linear curve functions of which the control points were the design variables. Several objective functions and constraints were formulated to express the critical desirable part qualities.

Jirathearanat, Suwat; Altan, Taylan

2004-06-01

419

Formation of bound states in expanded metal studied via path integral molecular dynamics  

NASA Astrophysics Data System (ADS)

The usefulness of the restricted path integral molecular dynamics method for the study of strongly correlated electrons is demonstrated by studying the formation of bound electronic states in a half-filled expanded three-dimensional hydrogenoid body-centred cubic lattice at finite temperature. Starting from a metallic state with one-component plasma character, we find that bound electrons form upon expansion of the lattice. The bound electrons are spatially localized with their centre for the motion of gyration located at ionic positions. The number of bound electrons increases monotonically with decreasing density.

Deymier, P. A.; Oh, Ki-Dong

2004-03-01

420

28 CFR 36.403 - Alterations: Path of travel.  

Code of Federal Regulations, 2010 CFR

...Alterations] [Sec. 36.403 - Alterations: Path of travel.] 28 JUDICIAL ADMINISTRATION...Alterations Sec. 36.403 Alterations: Path of travel. (a) General. An alteration...to the maximum extent feasible, the path of travel to the altered...

2009-07-01

421

Path discrepancies between great circle and rhumb line  

NASA Technical Reports Server (NTRS)

A simulation of a mathematical model to compute path discrepancies between great circle and rhumb line flight paths is presented. The model illustrates that the path errors depend on the latitude, the bearing, and the trip length of the flight.

Kaul, Rajan

1987-01-01

422

An Alternate Path To Stoichiometric Problem Solving.  

ERIC Educational Resources Information Center

Discusses an alternate path to teaching introductory stoichiometry based on research findings. The recommendation is to use problems that can be solved easily by rapid mental calculation as well as by pure logic. (AIM)

Schmidt, Hans-Jurgen

1997-01-01

423

IRIS Optical Instrument and Light Paths  

NASA Video Gallery

The optical portion of the instrument and the light paths from the primary and secondary mirror of the telescope assembly into the spectrograph. The spectrograph then breaks the light into 2 Near U...

424

Asymptotic Optimality of Shortest Path Routing.  

National Technical Information Service (NTIS)

Many communication networks use adaptive shortest path routing. By this the authors mean that each network link is periodically assigned a length that depends on its congestion level during the preceding period, and all traffic generated between length up...

E. M. Gafni D. P. Pertsekas

1983-01-01

425

Limited path percolation in complex networks.  

PubMed

We study the stability of network communication after removal of a fraction q=1-p of links under the assumption that communication is effective only if the shortest path between nodes i and j after removal is shorter than al(ij)(a> or =1) where l(ij) is the shortest path before removal. For a large class of networks, we find analytically and numerically a new percolation transition at p(c)=(kappa(0)-1)((1-a)/a), where kappa(0) [triple bond] / and k is the node degree. Above p(c), order N nodes can communicate within the limited path length al(ij), while below p(c), N(delta) (delta<1) nodes can communicate. We expect our results to influence network design, routing algorithms, and immunization strategies, where short paths are most relevant. PMID:17995444

López, Eduardo; Parshani, Roni; Cohen, Reuven; Carmi, Shai; Havlin, Shlomo

2007-11-01

426

Orbital Path of the International Space Station  

NASA Video Gallery

Astronauts Don Pettit, Andre Kuipers and Dan Burbank explain the orbital path of the International Space Station. Earth video credit: Image Science and Analysis Laboratory, NASA's Johnson Space Cen...

427

Locating ''sneak paths'' in electrical circuitry  

NASA Technical Reports Server (NTRS)

Use of a matrix system wherein circuit pin connections are assigned arbitrary designators and these used in formation of the matrix is illustrated. The matrix is a format that shows the current paths.

Dannback, T. M.

1968-01-01

428

Path Integral Quantization in the Temporal Gauge.  

National Technical Information Service (NTIS)

The quantization of non-Abelian gauge theories in the temporal gauge is studied within Feynman's path integral approach. The standard asymptotic boundary conditions are only imposed on the transverse gauge fields. The fictituous longitudinal gauge quanta ...

B. Scholz F. Steiner

1983-01-01

429

Riemann Curvature Tensor and Closed Geodesic Paths  

ERIC Educational Resources Information Center

Demonstrates erroneous results obtained if change in a vector under parallel transport about a closed path in Riemannian spacetime is made in a complete circuit rather than just half a circuit. (Author/SL)

Morganstern, Ralph E.

1977-01-01

430

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.

431

Circular free-electron laser  

DOEpatents

A high efficiency, free electron laser utilizing a circular relativistic electron beam accelerator and a circular whispering mode optical waveguide for guiding optical energy in a circular path in the circular relativistic electron beam accelerator such that the circular relativistic electron beam and the optical energy are spatially contiguous in a resonant condition for free electron laser operation. Both a betatron and synchrotron are disclosed for use in the present invention. A free electron laser wiggler is disposed around the circular relativistic electron beam accelerator for generating a periodic magnetic field to transform energy from the circular relativistic electron beam to optical energy.

Brau, Charles A. (Los Alamos, NM); Kurnit, Norman A. (Santa Fe, NM); Cooper, Richard K. (Los Alamos, NM)

1984-01-01

432

Circular free-electron laser  

DOEpatents

A high efficiency, free electron laser is described utilizing a circular relativistic electron beam accelerator and a circular whispering mode optical waveguide for guiding optical energy in a circular path in the circular relativistic electron beam accelerator such that the circular relativistic electron beam and the optical energy are spatially contiguous in a resonant condition for free electron laser operation. Both a betatron and synchrotron are disclosed for use in the present invention. A free electron laser wiggler is disposed around the circular relativistic electron beam accelerator for generating a periodic magnetic field to transform energy from the circular relativistic electron beam to optical energy.

Brau, C.A.; Kurnit, N.A.; Cooper, R.K.

1982-01-26

433

The prediction of radio-path characteristics  

NASA Astrophysics Data System (ADS)

The paper examines algorithms for the long-term prediction of radio-path characteristics in the ionosphere, the main characteristic being the MUF at a given distance. The proposed approach is based on long-term memories called DATA BANKS. Attention is given to the characteritics of the various banks, including the BANK OF CITIES, the BANK OF RADIO PATHS, the REFERENCE DATA BANK, and the OUTPUT DATA BANK.

Gitina, G. M.; Kalinin, Iu. K.

434

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

435

A Path Algorithm for Constrained Estimation  

PubMed Central

Many least-square problems involve affine equality and inequality constraints. Although there are a variety of methods for solving such problems, most statisticians find constrained estimation challenging. The current article proposes a new path-following algorithm for quadratic programming that replaces hard constraints by what are called exact penalties. Similar penalties arise in l1 regularization in model selection. In the regularization setting, penalties encapsulate prior knowledge, and penalized parameter estimates represent a trade-off between the observed data and the prior knowledge. Classical penalty methods of optimization, such as the quadratic penalty method, solve a sequence of unconstrained problems that put greater and greater stress on meeting the constraints. In the limit as the penalty constant tends to ?, one recovers the constrained solution. In the exact penalty method, squared penalties!are replaced by absolute value penalties, and the solution is recovered for a finite value of the penalty constant. The exact path-following method starts at the unconstrained solution and follows the solution path as the penalty constant increases. In the process, the solution path hits, slides along, and exits from the various constraints. Path following in Lasso penalized regression, in contrast, starts with a large value of the penalty constant and works its way downward. In both settings, inspection of the entire solution path is revealing. Just as with the Lasso and generalized Lasso, it is possible to plot the effective degrees of freedom along the solution path. For a strictly convex quadratic program, the exact penalty algorithm can be framed entirely in terms of the sweep operator of regression analysis. A few well-chosen examples illustrate the mechanics and potential of path following. This article has supplementary materials available online.

Zhou, Hua; Lange, Kenneth

2013-01-01

436

Continuous-Discrete Path Integral Filtering  

Microsoft Academic Search

A summary of the relationship between the Langevin equation,\\u000aFokker-Planck-Kolmogorov forward equation (FPKfe) and the Feynman path integral\\u000adescriptions of stochastic processes relevant for the solution of the\\u000acontinuous-discrete filtering problem is provided in this paper. The practical\\u000autility of the path integral formula is demonstrated via some nontrivial\\u000aexamples. Specifically, it is shown that the simplest approximation of the

Bhashyam Balaji

2009-01-01

437

Balancing minimum spanning and shortest path trees  

Microsoft Academic Search

This paper give a simple linear-time algorithm that, given a weighted\\u000adigraph, finds a spanning tree that simultaneously approximates a shortest-path\\u000atree and a minimum spanning tree. The algorithm provides a continuous\\u000atrade-off: given the two trees and epsilon > 0, the algorithm returns a\\u000aspanning tree in which the distance between any vertex and the root of the\\u000ashortest-path

Samir Khuller; Balaji Raghavacharit; Neal E. Young

1993-01-01

438

The Number of Shortest Paths in the  

Microsoft Academic Search

\\u000a We enumerate all of the shortest paths between any vertex v and the identity vertex in an (n, k)-star graph by enumerating the minimum factorizations of v in terms of the transpositions corresponding to edges in that graph. This result generalizes a previous one for the star\\u000a graph, and can be applied to obtain the number of the shortest paths

Eddie Cheng; Ke Qiu; Zhi Zhang Shen

2010-01-01

439

Path planning using a potential field representation  

Microsoft Academic Search

An approach to two-dimensional as well as three-dimensional findpath problems that divides each problem into two steps is presented. Rough paths are found based only on topological information. This is accomplished by assigning to each obstacle an artificial potential similar to electrostatic potential to prevent the moving object from colliding with the obstacles, and then locating minimum-potential valleys. The paths

Yong Koo Hwang; Narendra Ahuja

1988-01-01

440

A more efficient path-finding algorithm  

Microsoft Academic Search

Presents a new routing algorithm, which the authors call a path-finding algorithm (PFA). It drastically reduces the possibility of temporary routing loops, which accounts for its fast convergence properties. Like other path-finding algorithms, the PFA operates by specifying the second-to-last hop to each destination, in addition to the distance to the destination. A detailed proof of correctness and complexity is

Shree Murthy; J. J. Garcia-Luna-Aceves

1994-01-01

441

Path Planning by Negotiation for Decentralized Agents  

Microsoft Academic Search

This paper presents a real-time path-planning algorithm for decentralized agents, which provides guaranteed collision-free paths for the agents towards their desired destinations. The algorithm is run locally on the agents, which can exchange information using wireless communication. The algorithm is robust with respect to arbitrary delays in the wireless traffic, possible sources being transmission time, error correction, and others. Agents

Oliver Purwin; R. D'Andrea

2007-01-01

442

UAV Path Planning Using Evolutionary Algorithms  

Microsoft Academic Search

Evolutionary Algorithms have been used as a viable candidate to solve path planning problems effectively and provide feasible\\u000a solutions within a short time. In this work a Radial Basis Functions Artificial Neural Network (RBF-ANN) assisted Differential\\u000a Evolution (DE) algorithm is used to design an off-line path planner for Unmanned Aerial Vehicles (UAVs) coordinated navigation\\u000a in known static maritime environments. A

Ioannis K. Nikolos; Eleftherios S. Zografos; Athina N. Brintaki

2007-01-01

443

Characterization of gallium nitride-based high electron mobility transistor devices  

NASA Astrophysics Data System (ADS)

High electron mobility transistors (HEMTs) consisting of aluminum gallium nitride (AlGaN) - gallium nitride (GaN) heterostructures have been characterized by advanced electron microscopy methods including off-axis electron holography, nanoscale chemical analysis, and in situ electrical biasing. The research was divided into three parts: (1) Site-specific sample preparation using focused-ion-beam (FIB) and other complementary techniques; (2) Off-axis electron holography to image electrostatic fields in unbiased and biased devices; and (3) Chemical and micro-structural analysis of as-grown and stressed devices. The FIB shortcut-liftout method was used to prepare specimens suitable for quantitative electron holography observation. The nature and extent of ion-beam damage was quantified for several ion-beam energies. The impact of ion implantation and specimen amorphization on potential profiles of AlGaN/GaN heterostructures was also evaluated, and methods suitable for reducing and removing FIB damage were explored. The inelastic mean-free-path (IMFP), an important parameter for local thickness measurements by electron holography, was determined for 200 kiloelectron-volt electrons in GaN. Potential profiles were calculated from reconstructed phase images for HEMT structures prepared by wedge-polishing, argon-milling and FIB using an IMFP of 69.5 nanometers. The profiles matched closely after accounting for the thickness of amorphous layers in the potential calculation. The potential profiles across AlGaN/GaN heterostructures were mapped in real devices, and characteristic profiles were identified beneath the Schottky gate, insulating SiN layer, and ohmic source and drain. In all cases, the expected built-in piezoelectric field was absent in the AlGaN layer. These devices were also mounted for in situ electrical biasing utilizing a moveable electrode to ground the gate contact. Current-voltage (I-V) curves measured in situ resembled that of a diode, rather than a functioning transistor, suggesting that parasitic channels for electrical current had became active for bias voltages above 3V. Moreover, the HEMT devices failed at biases above 10V due to migration of the FIB-deposited Pt protective layers. Finally, the site-selectivity of the FIB was utilized to prepare specimens at the location of hot spots identified during reverse-bias step-stress testing. Although a V-type defect was observed at the site of one hot spot, microstructural breakdown was not normally evident.

Cullen, David A.

444

Non-monotonic magnetoresistance in an AlGaN/GaN high-electron-mobility transistor structure in the ballistic region  

NASA Astrophysics Data System (ADS)

In this report, we will discuss the nonmonotonic magnetoresistance (MR) in an AlGaN/GaN high-electron-mobility transistor (HEMT) in a perpendicular magnetic field B in the ballistic region ( kBT?/? < 1) and in the weakly-disordered limit ( kFl = 159 ? 1), where kB, T, ?, ?, k F, and l represent the Boltzmann constant, temperature, elastic scattering time, reduced Planck constant, Fermi wave vector and mean free path, respectively. The MR shows a local maximum between the weak localization (WL) and the Shubnikov-de Haas regions. In the low magnetic field regime, the quantum correction to the conductivity is proportional to T -3/2, which is consistent with a recent theory [T. A. Sedrakyan, and M. E. Raikh, Phys. Rev. Lett. 100, 106806 (2008)]. According to our results, as the temperature is increased, the position of the MR maximum in B increases. These results cannot be explained by present theories. Moreover, in the high-magnetic-field regime, neither the magnetic and nor the temperature dependences of the observed MR is consistent with present theories. We, therefore, suggest that while some features of the observed nonmonotonic MR can be successfully explained, further experimental and theoretical studies are necessary to obtain a thorough understanding of the MR effects.

Wang, Yi-Ting; Woo, Tak-Pong; Lo, S.-T.; Kim, Gil-Ho; Liang, Chi-Te

2014-05-01

445

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

446

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.

1997-01-01

447

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

448

Electronics 2010: A New Systems Approach to Teaching Electronics  

NSDL National Science Digital Library

These are the slides for the MATEC NetWorks Webinar that was held on May 9, 2008 for Electronics 2010: A New Systems Approach to Teaching Electronics. Presented by Tom McGlew, a thirty year veteran to the electronics field, the presentation discusses new paths for electronics and the changing role of the technician, and the implications for curriculum. The goals of the eSyst project are also discussed, the needed curriculum changes and updates, and ideas for assessment.

2008-11-26

449

Current path in light emitting diodes based on nanowire ensembles  

NASA Astrophysics Data System (ADS)

Light emitting diodes (LEDs) have been fabricated using ensembles of free-standing (In, Ga)N/GaN nanowires (NWs) grown on Si substrates in the self-induced growth mode by molecular beam epitaxy. Electron-beam-induced current analysis, cathodoluminescence as well as biased ?-photoluminescence spectroscopy, transmission electron microscopy, and electrical measurements indicate that the electroluminescence of such LEDs is governed by the differences in the individual current densities of the single-NW LEDs operated in parallel, i.e. by the inhomogeneity of the current path in the ensemble LED. In addition, the optoelectronic characterization leads to the conclusion that these NWs exhibit N-polarity and that the (In, Ga)N quantum well states in the NWs are subject to a non-vanishing quantum confined Stark effect.

Limbach, F.; Hauswald, C.; Lähnemann, J.; Wölz, M.; Brandt, O.; Trampert, A.; Hanke, M.; Jahn, U.; Calarco, R.; Geelhaar, L.; Riechert, H.

2012-11-01

450

A unified scheme for ab initio molecular orbital theory and path integral molecular dynamics  

NASA Astrophysics Data System (ADS)

We present a general approach for accurate calculation of chemical substances which treats both nuclei and electrons quantum mechanically, adopting ab initio molecular orbital theory for the electronic structure and path integral molecular dynamics for the nuclei. The present approach enables the evaluation of physical quantities dependent on the nuclear configuration as well as the electronic structure, within the framework of Born-Oppenheimer adiabatic approximation. As an application, we give the path integral formulation of electric response properties-dipole moment and polarizability, which characterize the changes both in electronic structure and nuclear configuration at a given temperature when uniform electrostatic field is present. We also demonstrate the calculation of a water molecule using the present approach and the result of temperature and isotope effects is discussed.

Shiga, Motoyuki; Tachikawa, Masanori; Miura, Shinichi

2001-11-01

451

Open-path millimeter-wave spectroscopy in the 225--315 GHz range.  

National Technical Information Service (NTIS)

This paper discusses the development of an open-path millimeter-wave (mm-wave) spectroscopy system in the 225--315 GHz atmospheric window. The new system is primarily a monostatic swept-frequency radar consisting of a mm-wave sweeper, hot-electron-bolomet...

N. Gopalsami S. Bakhtiari A. C. Raptis

1996-01-01

452

Efficient path-integral Monte Carlo technique for ultrasmall device applications  

Microsoft Academic Search

The ability to model equilibrium electronic properties of ultrasmall devices using a path-integral Monte Carlo (PIMC) method is demonstrated. First, a direct sampling PIMC method and its advantages over Metropolis importance sampling PIMC methods in this application are described. Then two potential structures typical of ultrasmall devices, a single and a coupled double finite square well potential, are analyzed and

L. F. Register; M. A. Stroscio; M. A. Littlejohn

1989-01-01

453

Equation of state of the hydrogen plasma by path integral Monte Carlo simulation  

Microsoft Academic Search

The equation of state of hydrogen plasma is calculated by the restricted path integral Monte Carlo method. We have investigated the plasma from the classical weak coupling regime to the quantum strongly coupled regime. Good agreement is found with the existing theories for low electronic degeneracy. Inception of molecular formation is observed at low densities and temperatures.

C. Pierleoni; D. M. Ceperley; B. Bernu; W. R. Magro

1994-01-01

454

Unbiased sampling of lattice Hamilton path ensembles  

NASA Astrophysics Data System (ADS)

Hamilton paths, or Hamiltonian paths, are walks on a lattice which visit each site exactly once. They have been proposed as models of globular proteins and of compact polymers. A previously published algorithm [Mansfield, Macromolecules 27, 5924 (1994)] for sampling Hamilton paths on simple square and simple cubic lattices is tested for bias and for efficiency. Because the algorithm is a Metropolis Monte Carlo technique obviously satisfying detailed balance, we need only demonstrate ergodicity to ensure unbiased sampling. Two different tests for ergodicity (exact enumeration on small lattices, nonexhaustive enumeration on larger lattices) demonstrate ergodicity unequivocally for small lattices and provide strong support for ergodicity on larger lattices. Two other sampling algorithms [Ramakrishnan et al., J. Chem. Phys. 103, 7592 (1995); Lua et al., Polymer 45, 717 (2004)] are both known to produce biases on both 2×2×2 and 3×3×3 lattices, but it is shown here that the current algorithm gives unbiased sampling on these same lattices. Successive Hamilton paths are strongly correlated, so that many iterations are required between statistically independent samples. Rules for estimating the number of iterations needed to dissipate these correlations are given. However, the iteration time is so fast that the efficiency is still very good except on extremely large lattices. For example, even on lattices of total size 10×10×10 we are able to generate tens of thousands of uncorrelated Hamilton paths per hour of CPU time.

Mansfield, Marc L.

2006-10-01

455

Curved paths in raptor flight: Deterministic models.  

PubMed

Two deterministic models for flight of Peregrine Falcons and possibly other raptors as they approach their prey are examined mathematically. Both models make two assumptions. The first, applicable to both models, is that the angle of sight between falcon and prey is constant, consistent with observations that the falcon keeps its head straight during flight and keeps on course by use of the deep foveal region in its eye which allows maximum acuity at an angle of sight of about 45 degrees . The second assumption for the first model (conical spiral), is that the initial direction of flight determines the overall path. For the second model (flight constrained to a tilted plane), a parameter that fixes the orientation of the plane is required. A variational calculation also shows that the tilted plane flight path is the shortest total path, and, consequently, the conical spiral is another shortest total path. Numerical calculations indicate that the flight paths for the two models are very similar for the experimental conditions under which observations have been made. However, the angles of flight and bank differ significantly. More observations are needed to investigate the applicability of the two models. PMID:16757000

Lorimer, John W

2006-10-21

456

The formal path integral and quantum mechanics  

SciTech Connect

Given an arbitrary Lagrangian function on R{sup d} and a choice of classical path, one can try to define Feynman's path integral supported near the classical path as a formal power series parameterized by 'Feynman diagrams', although these diagrams may diverge. We compute this expansion and show that it is (formally, if there are ultraviolet divergences) invariant under volume-preserving changes of coordinates. We prove that if the ultraviolet divergences cancel at each order, then our formal path integral satisfies a 'Fubini theorem' expressing the standard composition law for the time evolution operator in quantum mechanics. Moreover, we show that when the Lagrangian is inhomogeneous quadratic in velocity such that its homogeneous-quadratic part is given by a matrix with constant determinant, then the divergences cancel at each order. Thus, by 'cutting and pasting' and choosing volume-compatible local coordinates, our construction defines a Feynman-diagrammatic 'formal path integral' for the nonrelativistic quantum mechanics of a charged particle moving in a Riemannian manifold with an external electromagnetic field.

Johnson-Freyd, Theo [Department of Mathematics, University of California - Berkeley, 970 Evans Hall, Berkeley, California 94720 (United States)

2010-11-15

457

Transhorizon cochannel interference path measurements in Europe  

NASA Astrophysics Data System (ADS)

Existing methods for predicting co-channel interference levels are very inadequate, and development of these methods has been severely limited by the lack of suitable data. There are particular problems within Europe because there is a wide range of climatic and geographical conditions. COST Project 210 was set up to provide suitable data and prediction methods. The prime objective is to develop and evaluate models to serve as a basis for frequency planning co-ordination procedures and interference calculations, in order to improve the organization of further radio communication systems within Europe. After giving an up-to-date statement on the COST 210 activities set out above, early results obtained from three representative areas of study are given: (1) statistics of high signal level, and case studies, essentially in clear-air conditions, on paths of 150 to 300 km from France to the U.K. (in collaboration with CNET (Paris), CNET (Lannion), Portsmouth Polytechnic, IBA and RSGB); (2) hydrometeor scatter studies using a 10 cm wavelength dual-polarization radar at RAL, where a radar-derived raincell database is being used to simulate interference paths and to examine relative effects of ice and rain, etc; and (3) hydrometeor scatter statistics and case studies on a 131 km overland path (in collaboration with DTI), and a 48 km overland path, both in conjunction with the radar mentioned above, and two oversea paths of 201 and 302 km (in collaboration with CNET).

Hall, Martin P. M.

1988-12-01

458

Oscillatory fracture paths in thin elastic sheets  

NASA Astrophysics Data System (ADS)

We report results on a novel mode of quasi-static oscillatory crack propagation in thin elastic sheets [1]. A cutting tip of width w is perpendicularly driven through a thin brittle polymer film, held along its lateral boundaries, that progressively cuts the material as it advances [2]. For thin enough cutting tips (w < wc with w_c=0.2mm) the fracture path is straight. However, for w > w_c, the crack follows a well defined and highly reproducible oscillatory path. The amplitude and wavelength of the oscillatory crack paths scale linearly with the width of the cutting tip over a wide range of length scales but are independent of both of the cutting speed and the width of the sheet. We develop a model for this phenomena, based on the coupling between crack propagation and out-of-plane deformations of the film, which exhibits behaviour in remarkably good agreement with the experimental crack paths. [1] B. Roman, P.M. Reis, B. Audoly , S. DeVilliers, V. Viguié, D. Vallet, Oscillatory fracture paths in thin elastic sheets C.R. de Mecanique, vol 331, no 12, p. 811--816 (2003). [2] http://www.lmm.jussieu.fr/platefracture/

Reis, Pedro Miguel; Audoly, Basile; Roman, Benoit

2004-03-01

459

Asymmetric exclusion model and weighted lattice paths  

NASA Astrophysics Data System (ADS)

We show that the known matrix representations of the stationary state algebra of the asymmetric simple exclusion process (ASEP) can be