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1

Electron Inelastic-Mean-Free-Path Database  

National Institute of Standards and Technology Data Gateway

SRD 71 NIST Electron Inelastic-Mean-Free-Path Database (PC database, no charge)   This database provides values of electron inelastic mean free paths (IMFPs) for use in quantitative surface analyses by AES and XPS.

2

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

SciTech Connect

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

Gordon, F.I. (Department of Physics, Essex University, Colchester CO4 3SQ (United Kingdom)); Djaoui, A. (Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX (United Kingdom))

1992-12-01

3

The experimental electron mean-free-path in Si under typical (S)TEM conditions.  

PubMed

The electron mean-free-path in Si was measured by EELS using the test structure with the certified dimensions as a calibration standard. In a good agreement with the previous CBED measurements, the mean-free-path is 150nm for 200keV and 179nm for 300keV energy of primary electrons at large collection angles. These values are accurately predicted by the model of Iakoubovskii et al. while the model of Malis et al. incorporated in common microscopy software underestimates the mean-free-path by 15% at least. Correspondingly, the thickness of TEM samples reported in many studies of the Si-based materials last decades might be noticeably underestimated. PMID:24954136

Potapov, P L

2014-12-01

4

Long-mean-free-path ballistic hot electrons in high-purity GaAs B. Brill and M. Heiblum  

E-print Network

Long-mean-free-path ballistic hot electrons in high-purity GaAs B. Brill and M. Heiblum Braun, Rehovot 76100, Israel Received 18 July 1996 The mean free path mfp of hot ballistic electrons, injected device, utilizing the cyclotron motion of ballistic electrons in tilted magnetic fields. We find the mfp

Heiblum, Mordehai "Moty"

5

Mapping the density of scattering centers limiting the electron mean free path in graphene.  

PubMed

Recently, giant carrier mobility ? (>10(5) cm(2) V(-1) s(-1)) and micrometer electron mean free path (l) have been measured in suspended graphene or in graphene encapsulated between inert and ultraflat BN layers. Much lower ? values (10000-20000 cm(2) V(-1) s(-1)) are typically reported in graphene on common substrates (SiO(2), SiC) used for device fabrication. The debate on the factors limiting graphene electron mean free path is still open with charged impurities (CI) and resonant scatterers (RS) indicated as the most probable candidates. As a matter of fact, the inhomogeneous distribution of such scattering sources in graphene is responsible of nanoscale lateral inhomogeneities in the electronic properties, which could affect the behavior of graphene nanodevices. Hence, high resolution two-dimensional (2D) mapping of their density is very important. Here, we used scanning capacitance microscopy/spectroscopy to obtain 2D maps of l in graphene on substrates with different dielectric permittivities, that is, SiO(2) (?(SiO2) = 3.9), 4H-SiC (0001) (?(SiC) = 9.7) and the very-high-? perovskite strontium titanate, SrTiO(3) (001), briefly STO (?(STO) = 330). After measuring l versus the gate bias V(g) on an array of points on graphene, maps of the CI density (N(CI)) have been determined by the neutrality point shift from V(g) = 0 V in each curve, whereas maps of the RS density (N(RS)) have been extracted by fitting the dependence of l on the carrier density (n). Laterally inhomogeneous densities of CI and RS have been found. The RS distribution exhibits an average value ?3 × 10(10) cm(-2) independently on the substrate. For the first time, a clear correlation between the minima in the l map and the maxima in the N(CI) map is obtained for graphene on SiO(2) and 4H-SiC, indicating that CI are the main source of the lateral inhomogeneity of l. On the contrary, the l and N(CI) maps are uncorrelated in graphene on STO, while a clear correlation is found between l and N(RS) maps. This demonstrates a very efficient dielectric screening of CI in graphene on STO and the role of RS as limiting factor for electron mean free path. PMID:21981146

Giannazzo, Filippo; Sonde, Sushant; Nigro, Raffaella Lo; Rimini, Emanuele; Raineri, Vito

2011-11-01

6

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

7

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

SciTech Connect

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

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

2008-03-01

8

Experimental and numerical investigation of phonon mean free path distribution  

E-print Network

Knowledge of phonon mean free path (MFP) distribution is critically important to engineering size effects. Phenomenological models of phonon relaxation times can give us some sense about the mean free path distribution, ...

Zeng, Lingping

2013-01-01

9

The excess mean free path transport condensed history algorithm  

Microsoft Academic Search

A new Condensed History algorithm is introduced to enhance the Monte Carlo simulation of electron transport problems. Unlike established multiple scattering algorithms, this method is a true transport process--it simulates a transport equation that approximates the exact Boltzmann equation. The new equation has a larger mean free path than, and preserves two angular moments of, the Boltzmann equation. Thus, the

E W Larsen; D R Tolar

1999-01-01

10

Thermal Conductivity Spectroscopy Technique to Measure Phonon Mean Free Paths  

E-print Network

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

Schmidt, A. J.

11

Nanoscale three-dimensional reconstruction of elastic and inelastic mean free path lengths by electron holographic tomography  

NASA Astrophysics Data System (ADS)

Electron holography at medium resolution simultaneously probes projected electrostatic and magnetostatic potentials as well as elastic and inelastic attenuation coefficients with a spatial resolution of a few nanometers. In this work, we derive how the elastic and inelastic attenuation can be disentangled. Using that result, we perform the first three dimensional tomographic reconstruction of potential and (in)elastic attenuation in parallel. The technique can be applied to distinguish between functional potentials and composition changes in nanostructures, as demonstrated using the example of a GaAs—Al0.33Ga0.67As core-shell nanowire.

Lubk, A.; Wolf, D.; Kern, F.; Röder, F.; Prete, P.; Lovergine, N.; Lichte, H.

2014-10-01

12

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

13

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

14

Magnon thermal mean free path in yttrium iron garnet  

NASA Astrophysics Data System (ADS)

The magnetothermal properties of monocrystalline yttrium iron garnet (YIG) are reported. The magnon contribution to both the thermal conductivity and specific heat at low temperatures has been determined by measuring these properties under an applied magnetic field, which allows us to freeze the magnon modes and isolate the phonon contribution relative to the zero-field behavior. These results are interpreted within the framework of a simple kinetic gas model for magnon heat conduction that allows us to estimate the magnon thermal mean free path, i.e., the inelastic scattering length scale for thermally driven bulk magnons. We observe this parameter to reach as high as approximately 100 ?m at 2 K. It tracks the acoustic phonon thermal mean free path closely and decreases rapidly as the temperature is increased. This relatively short length scale suggests that magnon modes at thermal energies in YIG are not solely or directly responsible for coherent macroscale thermal spin transport (e.g., in the spin Seebeck effect) at high temperatures. Instead, these results support a growing consensus that subthermal magnons, i.e., those at energies below about 30 ± 10 K, are important for spin transport in YIG at all temperatures. These results also emphasize that magnon effects should be considered wavelength dependent, and that magnon-magnon interactions may be just as important for thermal spin transport as magnon-phonon scattering. This, in turn, has implications for understanding the characteristic temperature and length scales involved in spin caloritronic phenomena.

Boona, Stephen R.; Heremans, Joseph P.

2014-08-01

15

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

PubMed Central

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

Liu, Qixin; Cai, Zhiyong

2014-01-01

16

Nucleon mean free path in asymmetric nuclear matter at finite temperature  

NASA Astrophysics Data System (ADS)

The nucleon mean free path in symmetric and asymmetric nuclear matter is investigated in the framework of the finite temperature Brueckner theory. The realistic Bonn B two-body nucleon–nucleon interaction in combination with a consistent microscopic three-body force is adopted in the calculations. The results of the nucleon mean free path at zero temperature are in good agreement with the experimental data. The temperature and density and isospin dependence of the mean free path are studied systematically in asymmetric nuclear matter.

Bao, X. J.; Zhang, H. F.; Lombardo, U.; Dong, J. M.; Zuo, W.

2014-10-01

17

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

NASA Astrophysics Data System (ADS)

We analyse 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.

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

2014-04-01

18

Frequency-dependent phonon mean free path in carbon nanotubes from non-equilibrium molecular dynamics  

E-print Network

Owing to their long phonon mean free paths (MFPs) and high thermal conductivity, carbon nanotubes (CNTs) are ideal candidates for, e.g., removing heat from electronic devices. It is unknown, however, how the intrinsic phonon MFPs depend on vibrational frequency in non-equilibrium. We determine the spectrally resolved phonon MFPs in isotopically pure CNTs from the spectral phonon transmission function calculated using non-equilibrium molecular dynamics, fully accounting for the resistive phonon-phonon scattering processes through the anharmonic terms of the interatomic potential energy function. Our results show that the effective room temperature MFPs of low-frequency phonons ($fdetermined MFPs directly reflect the resistance to energy flow, they can be used to accurately predict the thermal conductivity for arbitrary tube lengths by calculating a single frequency integral. The...

Sääskilahti, K; Volz, S; Tulkki, J

2014-01-01

19

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

PubMed Central

Thermal conductivity in non-metallic crystalline materials results from cumulative contributions of phonons that have a broad range of mean free paths. Here we use high frequency surface temperature modulation that generates non-diffusive phonon transport to probe the phonon mean free path spectra of GaAs, GaN, AlN, and 4H-SiC at temperatures near 80?K, 150?K, 300?K, and 400?K. We find that phonons with MFPs greater than 230 ± 120?nm, 1000 ± 200?nm, 2500 ± 800?nm, and 4200 ± 850?nm contribute 50% of the bulk thermal conductivity of GaAs, GaN, AlN, and 4H-SiC near room temperature. By non-dimensionalizing the data based on Umklapp scattering rates of phonons, we identified a universal phonon mean free path spectrum in small unit cell crystalline semiconductors at high temperature. PMID:24129328

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

2013-01-01

20

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

PubMed

Thermal conductivity in non-metallic crystalline materials results from cumulative contributions of phonons that have a broad range of mean free paths. Here we use high frequency surface temperature modulation that generates non-diffusive phonon transport to probe the phonon mean free path spectra of GaAs, GaN, AlN, and 4H-SiC at temperatures near 80?K, 150?K, 300?K, and 400?K. We find that phonons with MFPs greater than 230 ± 120?nm, 1000 ± 200?nm, 2500 ± 800?nm, and 4200 ± 850?nm contribute 50% of the bulk thermal conductivity of GaAs, GaN, AlN, and 4H-SiC near room temperature. By non-dimensionalizing the data based on Umklapp scattering rates of phonons, we identified a universal phonon mean free path spectrum in small unit cell crystalline semiconductors at high temperature. PMID:24129328

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

2013-01-01

21

Tunable transport mean free path of light in xerogel matrixes embedded with polystyrene spheres  

E-print Network

Xerogel matrices, made by sol-gel techniques, are embedded with polystyrene spheres to promote multiple scattering of light. Varying the concentration of the spheres inside the matrix allows one to adjust the transport mean free path of light inside the material. Coherent backscattering measurements show that a range of transport mean free paths from 90 to 600 nm is easily achieved. The determination of the matrix refractive index permits a direct comparison to multiple scattering and Mie theory. Such tunable diffusive sol-gel samples can be further optimized as random laser materials.

Bret, B P J; Amaro, M; Nunes-Pereira, E J; Belsley, M

2008-01-01

22

Interplanetary gas. XVIII - Models and the mean free path of protons at 1 astronomical unit.  

NASA Technical Reports Server (NTRS)

Velocity distribution functions of solar-wind protons obtained by the Vela 3 satellites have been analyzed to obtain a microscopic determination of the momentum flux along magnetic field lines with respect to a reference frame moving at the bulk speed. The determination from macroscopic parameters allows the calculation of an effective mean free path for protons at 1 AU which averages 0.06 AU and is relatively independent of solar-wind velocity w. For quiet times when w is from 300 to 400 km/sec, the experimental mean free path is 2 to 3 times smaller than the value from plasma theory. For w greater than 400 km/sec, the experimental value is 10 to 100 times smaller than the theoretical value.

Brandt, J. C.; Thayer, N. N.; Wolff, C. L.; Hundhausen, A. J.

1973-01-01

23

Photon mean free paths, scattering, and ever-increasing telescope resolution  

E-print Network

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

Judge, Philip; Uitenbroek, Han; Rempel, Matthias; Suematsu, Yoshinori; Tsuneta, Saku

2014-01-01

24

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

25

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

26

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

27

Thermal conductivity of graphene and graphite: collective excitations and mean free paths.  

PubMed

We characterize the thermal conductivity of graphite, monolayer graphene, graphane, fluorographane, and bilayer graphene, solving exactly the Boltzmann transport equation for phonons, with phonon-phonon collision rates obtained from density functional perturbation theory. For graphite, the results are found to be in excellent agreement with experiments; notably, the thermal conductivity is 1 order of magnitude larger than what found by solving the Boltzmann equation in the single mode approximation, commonly used to describe heat transport. For graphene, we point out that a meaningful value of intrinsic thermal conductivity at room temperature can be obtained only for sample sizes of the order of 1 mm, something not considered previously. This unusual requirement is because collective phonon excitations, and not single phonons, are the main heat carriers in these materials; these excitations are characterized by mean free paths of the order of hundreds of micrometers. As a result, even Fourier's law becomes questionable in typical sample sizes, because its statistical nature makes it applicable only in the thermodynamic limit to systems larger than a few mean free paths. Finally, we discuss the effects of isotopic disorder, strain, and chemical functionalization on thermal performance. Only chemical functionalization is found to play an important role, decreasing the conductivity by a factor of 2 in hydrogenated graphene, and by 1 order of magnitude in fluorogenated graphene. PMID:25343716

Fugallo, Giorgia; Cepellotti, Andrea; Paulatto, Lorenzo; Lazzeri, Michele; Marzari, Nicola; Mauri, Francesco

2014-11-12

28

Linear response theory and neutrino mean free path using Brussels-Montreal Skyrme functionals  

E-print Network

The Brussels-Montreal Skyrme functionals have been successful to describe properties of both finite nuclei and infinite homogeneous nuclear matter. In their latest version, these functionals have been equipped with two extra density-dependent terms in order to reproduce simultaneously ground state properties of nuclei and infinite nuclear matter properties while avoiding at the same time the arising of ferromagnetic instabilities. In the present article, we extend our previous results of the linear response theory to include such extra terms at both zero and finite temperature in pure neutron matter. The resulting formalism is then applied to derive the neutrino mean free path. The predictions from the Brussels-Montreal Skyrme functionals are compared with ab-initio methods.

A. Pastore; M. Martini; D. Davesne; J. Navarro; S. Goriely; N. Chamel

2014-08-12

29

Linear response theory and neutrino mean free path using Brussels-Montreal Skyrme functionals  

E-print Network

The Brussels-Montreal Skyrme functionals have been successful to describe properties of both finite nuclei and infinite homogeneous nuclear matter. In their latest version, these functionals have been equipped with two extra density-dependent terms in order to reproduce simultaneously ground state properties of nuclei and infinite nuclear matter properties while avoiding at the same time the arising of ferromagnetic instabilities. In the present article, we extend our previous results of the linear response theory to include such extra terms at both zero and finite temperature in pure neutron matter. The resulting formalism is then applied to derive the neutrino mean free path. The predictions from the Brussels-Montreal Skyrme functionals are compared with ab-initio methods.

Pastore, A; Davesne, D; Navarro, J; Goriely, S; Chamel, N

2014-01-01

30

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

SciTech Connect

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

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

2012-03-01

31

Damping Rates and Mean Free Paths of Soft Fermion Collective Excitations in a Hot Fermion-Gauge-Scalar Theory  

E-print Network

We study the transport coefficients, damping rates and mean free paths of soft fermion collective excitations in a hot fermion-gauge-scalar plasma with the goal of understanding the main physical mechanisms that determine transport of chirality in scenarios of non-local electroweak baryogenesis. The focus is on identifying the different transport coefficients for the different branches of soft collective excitations of the fermion spectrum. These branches correspond to collective excitations with opposite ratios of chirality to helicity and different dispersion relations. By combining results from the hard thermal loop (HTL) resummation program with a novel mechanism of fermion damping through heavy scalar decay, we obtain a robust description of the different damping rates and mean free paths for the soft collective excitations to leading order in HTL and lowest order in the Yukawa coupling. The space-time evolution of wave packets of collective excitations unambiguously reveals the respective mean free paths. We find that whereas both the gauge and scalar contribution to the damping rates are different for the different branches, the difference of mean free paths for both branches is mainly determined by the decay of the heavy scalar into a hard fermion and a soft collective excitation. We argue that these mechanisms are robust and are therefore relevant for non-local scenarios of baryogenesis either in the Standard Model or extensions thereof.

S. -Y. Wang; D. Boyanovsky; H. J. de Vega; D. -S. Lee; Y. J. Ng

1999-02-01

32

JOURNAL DE PHYSIQUE Colloque C 1, supplement au n 2-3, Tome 32, Fevrier-Mars 1971, page C 1 -539 THE MAGNETIC ANISOTROPY OF Ni AND THE MEAN FREE PATH  

E-print Network

'autre. Abstract. -- The hypothesis is proposed, that the magnetic anisotropy of Ni depends strongly on the mean free path of the electrons. Using this hypothesis the Matthiessen rule for the reciprocal mean free with the resistance ratios ^273/^4.2 = 610 and 230 exhibit according to Franse [1] essentially different torque curves

Paris-Sud XI, Université de

33

Determination of the inelastic mean free path in ice by examination of tilted vesicles and automated most probable loss imaging.  

PubMed

Using electron microscopy, the thickness of ice-embedded vesicles is estimated examining tilted and untilted views and assuming an ellipsoidal shape of the vesicles that appear to be circular in the untilted view. Another thickness measure is obtained from the ratio of the unfiltered and zero-loss-filtered image intensities of the vesicle. From these two measurements, the mean free path A for inelastic scattering of electrons in ice is calculated as 203 +/- 33 nm for 120 kV acceleration voltage. It is found that vesicles in thin ice films (< or = 1.5 lambda) significantly protrude out of the ice film. Due to surface tension the shape becomes an oblate ellipsoid. In holes covered with a thick ice film (> or = 3 lambda) and strong thickness gradients, vesicles are predominantly found in regions where the ice thickness is appropriate for their size. Also, a way of imaging the most probable loss under low-dose conditions involving thickness measurement is proposed. Even at large ice thicknesses zero-loss filtering always gives better image contrast. Most probable loss imaging can only help where there is no intensity in the zero-loss image, at very large thicknesses (lambda > 8). PMID:8921626

Grimm, R; Typke, D; Bärmann, M; Baumeister, W

1996-07-01

34

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

SciTech Connect

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

McLerran, L.

1984-11-01

35

Modification of the Parallel Scattering Mean Free Path of Cosmic Rays in the Presence of Adiabatic Focusing  

NASA Astrophysics Data System (ADS)

The cosmic ray mean free path in a large-scale nonuniform guide magnetic field with superposed magnetostatic turbulence is calculated to clarify some conflicting results in the literature. A new, exact integro-differential equation for the cosmic-ray anisotropy is derived from the Fokker-Planck transport equation. A perturbation analysis of this integro-differential equation leads to an analytical expression for the cosmic ray anisotropy and the focused transport equation for the isotropic part of the cosmic ray distribution function. The derived parallel spatial diffusion coefficient and the associated cosmic ray mean free path include the effect of adiabatic focusing and reduce to the standard forms in the limit of a uniform guide magnetic field. For the illustrative case of isotropic pitch angle scattering, the derived mean free path agrees with the earlier expressions of Beeck & Wibberenz, Bieber & Burger, Kota, and Litvinenko, but disagrees with the result of Shalchi. The disagreement with the expression of Shalchi is particularly strong in the limit of strong adiabatic focusing.

He, H.-Q.; Schlickeiser, R.

2014-09-01

36

Mean free paths of He-fragments produced during the interaction of carbon and silicon nuclei at 4. 5 AGeV/c  

SciTech Connect

This paper reports on interaction mean free paths of He-fragments produced by the collisions of carbon and silicon nuclei at 4.5 A GeV/c in nuclear emulsion for different distances from their production point. The authors do not observe any anomalous effect in the mean free paths of He-fragments.

Ahmad, T.; Irfan, M.; Ahsan, M.Z. (Dept. of Physics, Aligarh Muslim Univ., Aligarh 202002 (IN))

1991-06-14

37

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

SciTech Connect

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

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

2012-06-15

38

Temperature-dependent ballistic transport in a channel with length below the scattering-limited mean free path  

NASA Astrophysics Data System (ADS)

The temperature-dependent ballistic transport, using nonequilibrium Arora distribution function (NEADF), is shown to result in mobility degradation with reduction in channel length, in direct contrast to expectation of a collision-free transport. The ballistic mean free path (mfp) is much higher than the scattering-limited long-channel mfp, yet the mobility is amazingly lower. High-field effects, converting stochastic velocity vectors to streamlined ones, are found to be negligible when the applied voltage is less than the critical voltage appropriate for a ballistic mfp, especially at cryogenic temperatures. Excellent agreement with the experimental data on a metal-oxide-semiconductor field-effect transistor is obtained. The applications of NEADF are shown to cover a wide spectrum, covering regimes from the scattering-limited to ballistic, from nondegenerate to degenerate, from nanowire to bulk, from low- to high-temperature, and from a low electric field to an extremely high electric field.

Arora, Vijay K.; Zainal Abidin, Mastura Shafinaz; Tan, Michael L. P.; Riyadi, Munawar A.

2012-03-01

39

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

40

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

E-print Network

We have obtained spectra of 163 quasars at $z_\\mathrm{em}>4.4$ with the Gemini Multi Object Spectrometers on the Gemini North and South telescopes, the largest publicly available sample of high-quality, low-resolution spectra at these redshifts. From this homogeneous data set, we generated stacked quasar spectra in three redshift intervals at $z\\sim 5$. We have modelled the flux below the rest-frame Lyman limit ($\\lambda_\\mathrm{r}<912$\\AA) to assess the mean free path $\\lambda_\\mathrm{mfp}^{912}$ of the intergalactic medium to HI-ionizing radiation. At mean redshifts $z_\\mathrm{q}=4.56$, 4.86 and 5.16, we measure $\\lambda_\\mathrm{mfp}^{912}=(22.2\\pm 2.3, 15.1\\pm 1.8, 10.3\\pm 1.6)h_{70}^{-1}$ proper Mpc with uncertainties dominated by sample variance. Combining our results with $\\lambda_\\mathrm{mfp}^{912}$ measurements from lower redshifts, the data are well modelled by a simple power-law $\\lambda_\\mathrm{mfp}^{912}=A[(1+z)/5]^\\eta$ with $A=(37\\pm 2)h_{70}^{-1}$ Mpc and $\\eta = -5.4\\pm 0.4$ between $z=2.3$...

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

2014-01-01

41

An enhanced Fourier law derivable from the Boltzmann transport equation and a sample application in determining the mean-free path of nondiffusive phonon modes  

NASA Astrophysics Data System (ADS)

An enhanced Fourier law that we term the unified nondiffusive-diffusive (UND) phonon transport model is proposed in order to account for the effect of low-frequency phonon modes of long mean-free path that propagate concomitantly to the dominant high-frequency modes. The theory is based on spherical harmonic expansions of the phonon distribution functions, wherein the high-frequency mode distribution function is truncated at the first order in the expansion, while the low-frequency mode distribution function, which is farther out of thermal equilibrium, is truncated at the second order. As an illustrative application, the predictions of the proposed model are compared with data from a recent experiment that utilized the transient gratings method to investigate the deviation of thermal transport in a silicon membrane from the predictions of the Fourier law. The good fit of the experimental effective thermal conductivity (ETC) with the analytical solution derived in this work yields quantitative information about the mean-free path of the dominant low-frequency heat-transfer mode in silicon.

Ramu, Ashok T.; Ma, Yanbao

2014-09-01

42

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

43

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

44

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

45

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

46

3HE-rich Solar Particle Mean Free Paths  

NASA Technical Reports Server (NTRS)

The goal of this oral presentation is to attempt to explain why the 3HE-rich events at 1AU appear to be 'scatter-free'. The largest 3HE- rich flux events of Kahler et al. (1985) are used to examine potential wave-particle interactions as the particles travel from the Sun to 1AU.

Tsurutani, B. T.

1995-01-01

47

Influence of the direction of motion on the inelastic interaction between electrons and solid surfaces  

Microsoft Academic Search

Theoretical derivations of the inelastic differential inverse mean free path (DIMFP) and inelastic mean free path (IMFP) for electrons crossing solid surfaces were made for different crossing angles and electron distances relative to the crossing point at the surface. Individual contributions from volume and surface excitations were separated and analyzed for electrons traveling inside and outside the solid. Extended Drude

Y. C. Li; Y. H. Tu; C. M. Kwei; C. J. Tung

2005-01-01

48

Unexpected behavior in a two-path electron interferometer.  

PubMed

We report the observation of an unpredictable behavior of a simple, two-path, electron interferometer. Utilizing an electronic analog of the well-known optical Mach-Zehnder interferometer, with current carrying edge channels in the quantum Hall effect regime, we measured high contrast Aharonov-Bohm (AB) oscillations. Surprisingly, the amplitude of the oscillations varied with energy in a lobe fashion, namely, with distinct maxima and zeros (namely, no AB oscillations) in between. Moreover, the phase of the AB oscillations was constant throughout each lobe period but slipped abruptly by pi at each zero. The periodicity of the lobes defines a new energy scale, which may be a general characteristic of quantum coherence of interfering electrons. PMID:16486497

Neder, I; Heiblum, M; Levinson, Y; Mahalu, D; Umansky, V

2006-01-13

49

Theory of 'which path' dephasing in single electron interference due to trace in conductive environment  

E-print Network

A single-electron two-path interference (Young) experiment is considered theoretically. The decoherence of an electron wave packet due to the 'which path' trace left in the conducting (metallic) plate placed under the electron trajectories is calculated using the many-body quantum description of the electron gas reservoir.

Pawel Machnikowski

2005-11-03

50

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

SciTech Connect

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

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

2010-05-15

51

Electronic structures of polycrystalline ZnO thin films probed by electron energy loss spectroscopy  

E-print Network

Electronic structures of polycrystalline ZnO thin films probed by electron energy loss spectroscopy in polycrystalline ZnO thin films.3 Coherent backscattering3 on ZnO films that has esti- mated the mean free path report the detail studies of the struc- tural and electronic properties of the ZnO thin films by trans

Ho, Seng-Tiong

52

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

53

Radial propagation of solar energetic particles assuming large scattering mean free paths in the interplanetary medium  

NASA Technical Reports Server (NTRS)

Observations of two flares which fit the diffusive model by Beeck et al. (1987) are employed to determine whether large solar-particle events can be explained by the mechanisms of small impulsive events. It is shown that the injection of particles at the source is extended in time and lasts more than approximately 10 hours. The extended injection at the sun is hypothesized to be the reason that large solar particles do not demonstrate the 'pulse/wake' behavior associated with the small impulsive events.

Mason, G. M.; Reames, D. V.; Ng, C. K.

1991-01-01

54

Collision Rates, Mean Free Path, and Diffusion Chemistry 180-213B  

E-print Network

, another applica- tion of this expression is in effusion though a pinhole. If there is a hole of area- topes will escape more slowly (with a 1/mass dependence); hence, effusion through a pinhole is a simple

Ronis, David M.

55

Mean free-path length theory of predator–prey interactions: Application to juvenile salmon migration  

Microsoft Academic Search

Ecological theory traditionally describes predator–prey interactions in terms of a law of mass action in which the prey mortality rate depends on the density of predators and prey. This simplifying assumption makes population-based models more tractable but ignores potentially important behaviors that characterize predator–prey dynamics. Here, we expand traditional predator–prey models by incorporating directed and random movements of both predators

James J. Anderson; Eliezer Gurarie; Richard W. Zabel

2005-01-01

56

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

PubMed Central

The density matrix theory, the ancestor of density functional theory, provides the immediate framework for Path Integral (PI) development, allowing the canonical density be extended for the many-electronic systems through the density functional closure relationship. Yet, the use of path integral formalism for electronic density prescription presents several advantages: assures the inner quantum mechanical description of the system by parameterized paths; averages the quantum fluctuations; behaves as the propagator for time-space evolution of quantum information; resembles Schrödinger equation; allows quantum statistical description of the system through partition function computing. In this framework, four levels of path integral formalism were presented: the Feynman quantum mechanical, the semiclassical, the Feynman-Kleinert effective classical, and the Fokker-Planck non-equilibrium ones. In each case the density matrix or/and the canonical density were rigorously defined and presented. The practical specializations for quantum free and harmonic motions, for statistical high and low temperature limits, the smearing justification for the Bohr’s quantum stability postulate with the paradigmatic Hydrogen atomic excursion, along the quantum chemical calculation of semiclassical electronegativity and hardness, of chemical action and Mulliken electronegativity, as well as by the Markovian generalizations of Becke-Edgecombe electronic focalization functions – all advocate for the reliability of assuming PI formalism of quantum mechanics as a versatile one, suited for analytically and/or computationally modeling of a variety of fundamental physical and chemical reactivity concepts characterizing the (density driving) many-electronic systems. PMID:20087467

Putz, Mihai V.

2009-01-01

57

Path-Integral Renormalization Group Method for Numerical Study of Strongly Correlated Electron Systems  

Microsoft Academic Search

A numerical algorithm for studying strongly correlated electron systems is proposed. The groundstate wavefunction is projected out after a numerical renormalization procedure in the path integral formalism. The wavefunction is expressed from the optimized linear combination of retained states in the truncated Hilbert space with a numerically chosen basis. This algorithm does not suffer from the negative sign problem and

Masatoshi Imada; Tsuyoshi Kashima

2000-01-01

58

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

59

Room-temperature ballistic electron emission luminescence spectroscopy with a scanning tunneling microscope  

E-print Network

Room-temperature ballistic electron emission luminescence spectroscopy with a scanning tunneling electroluminescence in buried luminescent layers at depths greater than the ballistic electron mean free path, ballistic electron emission microscopy BEEM and its associated spectroscopy BEES 1 have been widely used

Russell, Kasey

60

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. PMID:21711643

2011-01-01

61

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

62

Controlled Dephasing of an Electron Interferometer with a Path Detector at Equilibrium  

NASA Astrophysics Data System (ADS)

Controlled dephasing of electrons, via “which path” detection, involves, in general, coupling a coherent system to a current driven noise source. However, here we present a case in which a nearly isolated electron puddle within a quantum dot, at thermal equilibrium and in millikelvin range temperature, fully dephases the interference in a nearby electronic interferometer. Moreover, the complete dephasing is accompanied by an abrupt ? phase slip, which is robust and nearly independent of system parameters. Attributing the robustness of the phenomenon to the Friedel sum rule—which relates a system’s occupation to its scattering phases—proves the universality of this powerful rule. The experiment allows us to peek into a nearly isolated quantum dot, which cannot be accessed via conductance measurements.

Weisz, E.; Choi, H. K.; Heiblum, M.; Gefen, Yuval; Umansky, V.; Mahalu, D.

2012-12-01

63

Dielectric response theory for electron energy loss in clad cylindrical systems  

Microsoft Academic Search

Inelastic interactions between an electron and a clad cylindrical system were investigated using the dielectric response theory. By solving the Poisson equation and applying the boundary conditions, these interactions were formulated in terms of the surface, interface and volume excitations. Formulas of the differential inverse inelastic mean free path (DIIMFP) were derived for electrons moving parallel to the axis of

Y. H. Tu; C. M. Kwei; Y. C. Li; C. J. Tung

2006-01-01

64

Stochastic electron heating in bounded radio-frequency plasmas I. D. Kaganovich,a)  

E-print Network

the mean-free-path is small as compared to and to colli- sional Joule heating. In region B, L, electrons plasma boundary at x L. But contrary to the Joule heating, this hybrid heating is nonlocal: the placeStochastic electron heating in bounded radio-frequency plasmas I. D. Kaganovich,a) V. I. Kolobov

Kaganovich, Igor

65

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

66

The Hall effect and magnetoresistance of a two-dimensional electron gas upon scattering on microinhomogeneities of a magnetic field  

Microsoft Academic Search

The conductivity of a two-dimensional degenerate electron (2DEG) gas has been calculated in a microscopically inhomogeneous magnetic field of Abrikosov's vortices. The mean free path of electrons is assumed to be much larger than the vortex diameter 2 lambda (in this case the vortices play the role of additional asymmetric scatterers). It is shown that the Hall constant for a

A. V. Khaetskii

1991-01-01

67

All-Electron Path Integral Simulations of Warm, Dense Matter: Application to Water and Carbon  

NASA Astrophysics Data System (ADS)

We develop an all-electron path integral Monte Carlo (PIMC) method for warm dense matter and apply it to study water and carbon. PIMC pressures, internal energies, and pair-correlation functions compare well with density functional theory molecular dynamics (DFT-MD) at lower temperatures and enable the construction of a coherent equation of state over a density-temperature range of 3--12 g/cm3 and 102--109 K. PIMC results converge to the Debye-Huckel limiting law at high-temperatures and illuminate the breakdown of DFT pseudopotentials due to core excitations. Funding provided by the NSF (DMS-1025370). Computational resources provided by the National Center for Atmospheric Research and Lawrence Berkeley National Laboratory.

Driver, K. P.; Militzer, B.

2012-12-01

68

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

SciTech Connect

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

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

2006-05-15

69

PHYSICAL REVIEW B 84, 035426 (2011) Abnormal electron paths induced by Klein tunneling in graphene quantum point contacts  

E-print Network

PHYSICAL REVIEW B 84, 035426 (2011) Abnormal electron paths induced by Klein tunneling in graphene quantum point contacts Rui Yang,1 Liang Huang,1,2 Ying-Cheng Lai,1,3,4 and Celso Grebogi4 1 School of Computational Physics and Complex Systems, and Key Laboratory for Magnetism and Magnetic Materials of MOE

Lai, Ying-Cheng

70

Electron energy transport in steep temperature gradients in laser-produced plasmas  

Microsoft Academic Search

The Fokker-Planck equation has been solved numerically in one spatial and two velocity dimensions in order to study thermal conduction in large temperature gradients occurring in laser-produced plasmas. The heat flow is an order of magnitude smaller than that predicted by the classical theory when the temperature scale length is a few electron mean free paths.

A. R. Bell; R. G. Evans; D. J. Nicholas

1981-01-01

71

1928 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 51, NO. 11, NOVEMBER 2004 Briefs___________________________________________________________________________________________  

E-print Network

-current regime have been studied using device simu- lation. The phonon mean-free-path of strained-Si devicesMOS devices due to the smaller energy bandgap and longer phonon mean-free-path. Even though strained device simulations with the phonon mean-free-path parameter determined from the full-band Monte Carlo

Dutton, Robert W.

72

Received 10 Aug 2012 | Accepted 20 Feb 2013 | Published 27 Mar 2013 Broadband phonon mean free path contributions  

E-print Network

in nanostruc- tured materials and devices, where size effects selectively scatter phonons or create nonARTICLE Received 10 Aug 2012 | Accepted 20 Feb 2013 | Published 27 Mar 2013 Broadband phonon mean vibrations called phonons. Thermal conductivity depends on how far phonons travel between scattering events

McGaughey, Alan

73

A time dependent propagator method for long mean free path transport of neutral particles in plasma processing reactors  

E-print Network

processing reactors Wen-yi Tan, Robert J. Hoekstra, and Mark J. Kushnera) Department of Electrical October 1995; accepted for publication 18 December 1995 Plasma etching reactors for microelectronics reactor. The propagator P r,r provides the probability that particles originating at location r will have

Kushner, Mark

74

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

Microsoft Academic Search

Measurements of electron heat flow parallel to B are performed on fully-ionized quiescent plasma column under conditions for which the electron-electron collisional mean free path, 1\\/sub ee\\/, is not small relative to the electron temperature-gradient scale-length. Pulsed microwave heating at one location on the column and nonperturbing microwave resonator measurements of temperature at two locations on the column are used

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

1980-01-01

75

Electron heat transport in a steep temperature gradient  

Microsoft Academic Search

Temporal and spatial measurements of electron heat transport are made in the University of California Davis AURORA device (J. H. Rogers, Ph.D. dissertation, University of California, Davis, 1987). In AURORA, a microwave pulse heats a region of underdense, collisional, plasma (n\\/ncr ≲1, where ncr =1.8×1010 cm?3 is the critical density, Te0 ≊0.15 eV, and the electron scattering mean free path

J. H. Rogers; J. S. De Groot; Z. Abou-Assaleh; J. P. Matte; T. W. Johnston; M. D. Rosen

1989-01-01

76

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

SciTech Connect

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

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

2012-08-15

77

Electron heat transport down steep temperature gradients  

Microsoft Academic Search

Electron heat transport is studied by numerically solving the Fokker-Planck equation, with a spherical harmonic representation of the distribution function. The first two terms (fâ, fâ) suffice, even in steep temperature gradients. Deviations from the Spitzer-Haerm law appear for lambda\\/L\\/sub T\\/ ((mean free path)\\/(temperature gradient length))> or approx. =0.01, as a result of non-Maxwellian fâ. For lambda\\/L\\/sub T\\/> or approx.

J. P. Matte; J. Virmont

1982-01-01

78

Calibration stability of hot cathode ionization gauges: A discussion of the importance of electron path length and gauge constant  

NASA Astrophysics Data System (ADS)

The ion current, i+, in an ionization gauge is given by the equation i+=Ki-P where K is a gas dependent gauge constant, i- is the electron current, and P is the pressure. Values of K for nitrogen for gauges designed for use at ultrahigh vacuum and extreme high vacuum range from 10/Torr to 106/Torr. It is important to know whether calibration stability is sacrificed when K, and the electron path length are large. Using a simple model, the electron path length is estimated as a function of the probability, beta, that an electron will make another pass through the ionizing region. An equation is obtained for K as a function of beta. The fractional change in K, DeltaK/K, is zero for those gauges where the electrons make a single pass, but is increasingly larger for higher sensitivity gauges with greater probabilities of multiple passes. As an example, assume that the probability of the next pass changes by 1%, then the change in sensitivity is 1.5% for a B-A with K=25/Torr, and 9% for a gauge with K=102/Torr. copyright 2002 American Vacuum Society.

Peacock, R. N.

2002-07-01

79

Electronic highways in bilayer graphene.  

PubMed

Bilayer graphene with an interlayer potential difference has an energy gap and, when the potential difference varies spatially, topologically protected one-dimensional states localized along the difference's zero lines. When disorder is absent, electronic travel directions along zero-line trajectories are fixed by valley Hall properties. Using the Landauer-Bu?ttiker formula and the nonequilibrium Green's function technique, we demonstrate numerically that collisions between electrons traveling in opposite directions, due to either disorder or changes in path direction, are strongly suppressed. We find that extremely long mean free paths of the order of hundreds of micrometers can be expected in relatively clean samples. This finding suggests the possibility of designing low power nanoscale electronic devices in which transport paths are controlled by gates which alter the interlayer potential landscape. PMID:21766817

Qiao, Zhenhua; Jung, Jeil; Niu, Qian; Macdonald, Allan H

2011-08-10

80

Electron energy distribution functions in low-pressure inductively coupled bounded plasmas  

SciTech Connect

The electron energy distribution function (EEDF) in a low-pressure inductively coupled plasma confined between two infinite plates separated by 10 cm is investigated using a one-dimensional particle-in-cell simulation including Monte Carlo collisions. At low pressure, where the electron mean free path is of the order of or greater than the system length, the EEDF is close to Maxwellian, except for its tail, depleted at high energy. We give clear evidence that this depletion is mostly due to the high-energy electrons escaping to the walls. As a result of the EEDF nonlocality, the break energy, for which the depletion of the Maxwellian starts, is found to track the plasma potential. At a higher pressure, the electron mean free paths of the various elastic and inelastic collisions become shorter than the system length, resulting in a loss of nonlocality and the break energy of the distribution function moves to energies lower than the plasma potential.

Meige, Albert; Boswell, Rod W. [Space Plasma, Power and Propulsion Group, Research School of Physical Sciences and Engineering, Australian National University, ACT 0200 (Australia)

2006-09-15

81

Temperature-dependent solid-state electron transport through bacteriorhodopsin: experimental evidence for multiple transport paths through proteins.  

PubMed

Electron transport (ETp) across bacteriorhodopsin (bR), a natural proton pump protein, in the solid state (dry) monolayer configuration, was studied as a function of temperature. Transport changes from thermally activated at T > 200 K to temperature independent at <130 K, similar to what we have observed earlier for BSA and apo-azurin. The relatively large activation energy and high temperature stability leads to conditions where bR transports remarkably high current densities above room temperature. Severing the chemical bond between the protein and the retinal polyene only slightly affected the main electron transport via bR. Another thermally activated transport path opens upon retinal oxime production, instead of or in addition to the natural retinal. Transport through either or both of these paths occurs on a background of a general temperature-independent transport. These results lead us to propose a generalized mechanism for ETp across proteins, in which tunneling and hopping coexist and dominate in different temperature regimes. PMID:22296717

Sepunaru, Lior; Friedman, Noga; Pecht, Israel; Sheves, Mordechai; Cahen, David

2012-03-01

82

Analysis of reflection electron energy loss spectra (REELS) for determination of the dielectric function of solids: Fe, Co, Ni  

NASA Astrophysics Data System (ADS)

A simple procedure is developed to simultaneously eliminate multiple scattering contributions from two reflection electron energy-loss spectra (REELS) measured at different energies or for different experimental geometrical configurations. The procedure provides the differential inverse inelastic mean free path (DIIMFP) and the differential surface excitation probability (DSEP). The only required input parameters are the differential cross section for elastic scattering and a reasonable estimate for the inelastic mean free path (IMFP). No prior information on surface excitations is required for the deconvolution. The retrieved DIIMFP and DSEP can be used to determine the dielectric function of a solid by fitting the DSEP and DIIMFP to theory. Eventually, the optical data can be used to calculate the (differential and total) inelastic mean free path and the surface excitation probability. The procedure is applied to Fe, Co and Ni and the retrieved optical data as well as the inelastic mean free paths and surface excitation parameters derived from it are compared to values reported earlier in the literature. In all cases, reasonable agreement is found between the present data and the earlier results, supporting the validity of the procedure.

Werner, Wolfgang S. M.

2007-05-01

83

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

NASA Astrophysics Data System (ADS)

Using first-principles calculations, we study the diffusions of interstitial defects Cd, Cu, Te, and Cl in CdTe. We find that the diffusion behavior is strongly correlated with the electronic structure of the interstitial diffuser. For Cd and Cu, because the defect state is the nondegenerated s -like state under the Td symmetry, the diffusions are almost along the <111 > directions between the tetrahedral sites, although the diffusion of Cu shows some deviation due to the coupling between the Cu d and host s orbitals. The diffusions of the neutral and charged Cd and Cu follow similar paths. However, for Te and Cl atoms, because the defect state is the degenerated p -like state under the Td symmetry, large distortions occur. Therefore the diffusion paths are very different from those of the interstitial Cd and Cu atoms, and depend strongly on the charge states of the interstitial atoms. For Te, we find that the distortion is mostly stabilized by the crystal-field splitting, but for Cl, the exchange splitting plays a more important role.

Ma, Jie; Yang, Jihui; Wei, Su-Huai; Da Silva, Juarez L. F.

2014-10-01

84

Magnetic turbulent electron transport in a reversed field pinch  

SciTech Connect

A model of magnetic turbulent electron transport is presented. The model, based on the thermal conduction theory of Rechester and Rosenbluth, entails a Boltzmann description of electron dynamics in the long mean-free-path limit and quantitatively describes the salient features of superthermal electron measurements in the RFP edge plasma. Included are predictions of the mean superthermal electron energy, current density, and power flux asymmetry. A discussion of the transport model, the assumptions implicit in the model, and the relevance of this work to more general issue of magnetic turbulent transport in toroidal systems is presented. 32 refs., 3 figs.

Schoenberg, K.; Moses, R.

1990-01-01

85

Path-integral theory for evolution of momentum-specified photoemission spectra from broad Gaussian to two-headed Lorentzian due to electron-phonon coupling  

Microsoft Academic Search

Using a path-integral theory, we study the momentum-specified photoemission spectra (MSPES) of one and two dimensional metallic many-electron systems coupled with Einstein phonons. The multiple scatterings of electrons due to phonons are shown to completely dominate the MSPES, even if the electron-phonon coupling strength is intermediate. These multiple scatterings result in spectral evolution from a broad Gaussian to a two-headed

Kai Ji; Hang Zheng; Keiichiro Nasu

2004-01-01

86

Path-Integral Theory of an Electron Gas in a Random Potential  

Microsoft Academic Search

An ideal gas of non-degenerate electrons of mass m in a Gaussian random potential is investigated. The potential is characterized by two parameters: eta whose square is the variance of the potential energy) and L (correlation length). Relevance to the case of a polycrystalline non-degenerate semiconductor is suggested. The autocorrelation function of the potential is taken Gaussian, W(r' - r'

V. Bezak

1970-01-01

87

Ab initio molecular-dynamics method based on the restricted path integral: Application to the electron plasma and liquid alkali metal  

E-print Network

by an effective exchange potential. This path-integral molecular-dynamics method is able to simulate electron of the grand canonical parti- tion function of fermion systems.7 With this method the fer- mion sign problem10,14 to resolve the problem of negative weights to the partition function result- ing from the cross

Deymier, Pierre

88

Role of graphene\\/substrate interface on the local transport properties of the two-dimensional electron gas  

Microsoft Academic Search

The electron mean free path (lgr) is ``locally'' evaluated by scanning capacitance spectroscopy on graphene obtained with different preparation methods and on different substrates, i.e., graphene exfoliated from highly oriented pyrolitic graphite (HOPG) and deposited (DG) on 4H-SiC(0001) and on SiO2 and epitaxial graphene grown on 4H-SiC(0001) (EG). lgr in DG on SiC was more than four times larger than

S. Sonde; F. Giannazzo; C. Vecchio; R. Yakimova; E. Rimini; V. Raineri

2010-01-01

89

Measurements and calculations of the electron recoil spectra from gamma rays emitted by nitrogen for a 14MeV neutron source  

Microsoft Academic Search

The electron recoil spectra from gamma rays produced by the interaction of 14-MeV neutrons with 0.5, 1.0, 3.0, and 7.0 mean-free-paths (mfps) of nitrogen have been measured with NE-213 scintillators positioned at 26, 30, and 120 deg at distances ranging between 7 and 10 m. Thin wall spherical Dewars filled with liquid nitrogen, with radii dimensions equivalent to the above

L. F. Hansen; T. Komoto; E. F. Plechaty; B. A. Pohl; G. S. Sidhu; C. Wong

1977-01-01

90

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

91

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

92

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

NASA Technical Reports Server (NTRS)

Auger electron spectroscopic studies of the grains in oxygen-charged polycrystal-line silver show significant intensity variations as a function of crystallographic orientation. These intensity variations were observed by studies of the Auger images and line scans of the different grains (randomly selected) for each silver transition energy. The results can be attributed to the diffraction of the ejected Auger electrons and interpreted by corresponding changes in the electron mean-free path for inelastic scattering and by oxygen atom accumulation in the subsurface. The subsurface (second layer) octahedral sites increased in size because of surface relaxation and serve as a stable reservoir for the dissolved oxygen.

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

1989-01-01

93

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

SciTech Connect

Emitted electrons are accelerated back into the plasma by the sheath. If their mean free path is large, they can propagate directly to another surface without suffering collisions. We analyze the effects of “transit” on plasma-surface interaction. When transit occurs, surfaces exchanging electrons are intricately coupled. All surfaces float more negatively than they would if the emission collisionally remixed with the bulk plasma. Asymmetries of the system drive a net “transit current” between the surfaces, which influences their potential difference. The larger the initial energy spread of the emitted electrons, the larger the potential difference.

Campanell, Michael [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)] [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Wang, Hongyue [Beijing University of Aeronautics and Astronautics, Beijing (China)] [Beijing University of Aeronautics and Astronautics, Beijing (China)

2013-09-02

94

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...

95

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.

96

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

97

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

98

The semiclassical—classical path theory of direct electron—ion dissociative recombination and e ? + H 3 + recombination  

Microsoft Academic Search

The theory of dissociative recombination (DR) is reviewed. A new semiclassical—classical path theory of DR is presented. It is applicable to DR with or without curve crossing between the potential energy surfaces associated with molecular ion AB? and neutral AB? dissociative states. A new mechanism is proposed for e-H3+ recombination. Rydberg molecules are first formed and the periodic interaction of

M. R. Flannery

1995-01-01

99

Eliashberg Function in an Amorphous Simple Metal Alloy Sn1-Xcux Determined by Electron-Tunneling  

E-print Network

PHYSICAL REVIEW B VOLUME 51, NUMBER 1 1 JANUARY 1995-I Eliashberg function in an amorphous simple metal alloy Sn1 Cu determined by electron tunneling P. W. Watson III NMT-5, MS E506, Los Alamos National Laboratory, Los Alamos, New Mexico 87545... frequencies which was identical to that of Berg- mann. For very short mean free paths (high-resistivity alloys) Meisel and Cote invoked the Pippard condition in an ad hoc fashion and predicted an co dependence. The microscopic models of the electron...

WATSON, PW; Naugle, Donald G.

1995-01-01

100

Path Sensitization in Critical Path Problem  

Microsoft Academic Search

Since the delay of a circuit is determined by the delay of its longest sensitizable paths (such paths are called critical paths), the problem of estimating the delay of a circuit is called critical path problem. One important aspect of the critical path problem is to decide whether a path is sensitizable. A framework which allows various previously proposed path

Hsi-chuan Chen; David Hung-chang Du

1991-01-01

101

Path Pascal  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

102

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

103

Kinetic effects in low-pressure discharges with secondary electron emission  

NASA Astrophysics Data System (ADS)

Secondary electron emission (SEE) from material surfaces can result in efficient plasma cooling and large energy losses from the plasma. This is relevant to Hall thrusters and divertors, where the electron temperature is high enough to provide strong SEE. The SEE reduces negative charge of a wall immersed into a plasma and increases the flux of plasma electrons to the wall. If the plasma is hot enough to produce intense SEE, the plasma potential relative to the wall can be several times lower than that without the SEE. Then the electron heat flux to the wall will be extremely high provided the plasma electron velocity distribution function (EVDF) is Maxwellian, with a large number of electrons flying toward the walls and capable to penetrate the sheath potential barrier. This is the case if the electron mean free path is small compared to the plasma dimensions. Further increase of the electron temperature saturates the wall losses once the space charge limited (SCL) regime of the sheath establishes. In low-pressure plasmas, however, amplification of the electron heat flux to the wall due to the SEE is much weaker because the electron mean free path is large compared to the plasma dimensions. In such plasmas, the EVDF is depleted of the energetic electrons flying toward the walls. This considerably reduces the flux of hot electrons to the walls. The secondary electrons propagate freely between the walls forming electron beams that do not mix with the plasma electrons. The presence of these secondary electron beams with intense current and relatively low energy prevents the occurrence of a steady SCL sheath. Instead, relaxation oscillations of the sheath between the SCL and non-SCL states may occur under conditions with intense anisotropic heating.

Sydorenko, Dmytro

2009-11-01

104

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

PubMed

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

Bass, A D; Sanche, L

1998-12-01

105

Unexpected Behavior in a Two-Path Electron Interferometer I. Neder, M. Heiblum, Y. Levinson, D. Mahalu, and V. Umansky  

E-print Network

edge channels in the quantum Hall effect regime, we measured high contrast Aharonov-Bohm (AB- Bohm (AB) effect [10]. Note that the current in D1 is out of phase with respect to the current in D2. Utilizing an electronic analog of the well-known optical Mach-Zehnder interferometer, with current carrying

Heiblum, Mordehai "Moty"

106

Bond deformation paths and electronic instabilities of ultraincompressible transition metal diborides: Case study of OsB2 and IrB2  

NASA Astrophysics Data System (ADS)

The energetically most stable orthorhombic structure of OsB2 and IrB2 is dynamically stable for OsB2 but unstable for IrB2. Both diborides have substantially lower shear strength in their easy slip systems than their metal counterparts. This is attributed to an easy sliding facilitated by out-of-plane weakening of metallic Os-Os bonds in OsB2 and by an in-plane bond splitting instability in IrB2. A much higher shear resistance of Os-B and B-B bonds than Os-Os ones is found, suggesting that the strengthened Os-B and B-B bonds are responsible for hardness enhancement in OsB2. In contrast, an in-plane electronic instability in IrB2 limits its strength. The electronic structure of deformed diborides suggests that the electronic instabilities of 5d orbitals are their origin of different bond deformation paths. Neither IrB2 nor OsB2 can be intrinsically superhard.

Zhang, R. F.; Legut, D.; Wen, X. D.; Veprek, S.; Rajan, K.; Lookman, T.; Mao, H. K.; Zhao, Y. S.

2014-09-01

107

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.

BEGIN:VCARD VERSION:2.1 FN:Cynthia Ann Radle N:Ann Radle;Cynthia ORG:McCullough High School REV:2005-04-13 END:VCARD

1995-06-30

108

The X-ray Extended Range Technique a model for investigating X-ray and electron collision processes at a synchrotron  

NASA Astrophysics Data System (ADS)

New techniques at synchrotrons can not only drive higher accuracy, structural information and insight in photoabsorption and inelastic scattering of the photon, but also inelastic scattering of the electron. This is important for fields such as XAFS, XANES and powder diffraction, but has also initiated new fields of nanoroughness measurement, measurement of electron inelastic mean free paths, bonding information at an accuracy of crystallographic determination, and similar advances for fluorescence and scattering investigations. We summarise and present some key opportunities for research and development.

Chantler, Christopher T.

2012-11-01

109

Branching and path-deviation of positive streamers resulting from statistical photon transport  

NASA Astrophysics Data System (ADS)

The branching and change in direction of propagation (path-deviation) of positive streamers in molecular gases such as air likely require a statistical process which perturbs the head of the streamer and produces an asymmetry in its space charge density. In this paper, the mechanisms for path-deviation and branching of atmospheric pressure positive streamer discharges in dry air are numerically investigated from the viewpoint of statistical photon transport and photoionization. A statistical photon transport model, based on randomly selected emitting angles and mean-free-path for absorption, was developed and embedded into a fluid-based plasma transport model. The hybrid model was applied to simulations of positive streamer coaxial discharges in dry air at atmospheric pressure. The results show that secondary streamers, often spatially isolated, are triggered by the random photoionization and interact with the thin space charge layer (SCL) of the primary streamer. This interaction may be partly responsible for path-deviation and streamer branching. The general process consists of random remote photo-electron production which initiates a back-traveling electron avalanche, collision of this secondary avalanche with the primary streamer and the subsequent perturbation to its SCL. When the SCL is deformed from a symmetric to an asymmetric shape, the streamer can experience an abrupt change in the direction of propagation. If the SCL is sufficiently perturbed and essentially broken, local maxima in the SCL can develop into new streamers, leading to streamer branching. During the propagation of positive streamers, this mechanism can take place repetitively in time and space, thus producing multi-level branching and more than two branches within one level.

Xiong, Zhongmin; Kushner, Mark J.

2014-12-01

110

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

NASA Astrophysics Data System (ADS)

One of the enduring challenges in graphene research and applications is the extreme sensitivity of its charge carriers to external perturbations, especially those introduced by the substrate. The best available substrates to date, graphite and hexagonal boron nitride (h-BN), still pose limitations: graphite being metallic does not allow gating, while both h-BN and graphite, having lattice structures closely matched to that of graphene, may cause significant band structure reconstruction. Here we show that the atomically smooth surface of exfoliated MoS2 provides access to the intrinsic electronic structure of graphene without these drawbacks. Using scanning tunneling microscopy and Landau-level (LL) spectroscopy in a device configuration that allows tuning of the carrier concentration, we find that graphene on MoS2 is ultraflat, producing long mean free paths, while avoiding band structure reconstruction. Importantly, the screening of the MoS2 substrate can be tuned by changing the position of the Fermi energy with relatively low gate voltages. We show that shifting the Fermi energy from the gap to the edge of the conduction band gives rise to enhanced screening and to a substantial increase in the mean free path and quasiparticle lifetime. MoS2 substrates thus provide unique opportunities to access the intrinsic electronic properties of graphene and to study in situ the effects of screening on electron-electron interactions and transport.

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

2014-10-01

111

Decoupling initial electron beam parameters for Monte Carlo photon beam modelling by removing beam-modifying filters from the beam path  

NASA Astrophysics Data System (ADS)

A new method is presented to decouple the parameters of the incident e- beam hitting the target of the linear accelerator, which consists essentially in optimizing the agreement between measurements and calculations when the difference filter, which is an additional filter inserted in the linac head to obtain uniform lateral dose-profile curves for the high energy photon beam, and flattening filter are removed from the beam path. This leads to lateral dose-profile curves, which depend only on the mean energy of the incident electron beam, since the effect of the radial intensity distribution of the incident e- beam is negligible when both filters are absent. The location of the primary collimator and the thickness and density of the target are not considered as adjustable parameters, since a satisfactory working Monte Carlo model is obtained for the low energy photon beam (6 MV) of the linac using the same target and primary collimator. This method was applied to conclude that the mean energy of the incident e- beam for the high energy photon beam (18 MV) of our Elekta SLi Plus linac is equal to 14.9 MeV. After optimizing the mean energy, the modelling of the filters, in accordance with the information provided by the manufacturer, can be verified by positioning only one filter in the linac head while the other is removed. It is also demonstrated that the parameter setting for Bremsstrahlung angular sampling in BEAMnrc ('Simple' using the leading term of the Koch and Motz equation or 'KM' using the full equation) leads to different dose-profile curves for the same incident electron energy for the studied 18 MV beam. It is therefore important to perform the calculations in 'KM' mode. Note that both filters are not physically removed from the linac head. All filters remain present in the linac head and are only rotated out of the beam. This makes the described method applicable for practical usage since no recommissioning process is required.

DeSmedt, B.; Reynaert, N.; Flachet, F.; Coghe, M.; Thompson, M. G.; Paelinck, L.; Pittomvils, G.; DeWagter, C.; DeNeve, W.; Thierens, H.

2005-12-01

112

Ray Paths  

NSDL National Science Digital Library

For the next two exercises, we will break up into groups of four. Each member of the group will represent one of four waves leaving the source: direct wave, ground roll, reflected wave, and head wave. All four "waves" will leave the source at the same time and travel at a particular speed and path as directed by the instructor. ALL students will record the arrival time of each "wave" at each geophone until all 12 geophones have been used. Plot arrival time versus distance for each "wave". Do any of the time versus distance curves fit a straight line? Do any of them not fit a straight line? Explain why they do or don't fit a straight line. Uses online and/or real-time data Has minimal/no quantitative component

113

Zero-energy bound state at the interface between an s-wave superconductor and a disordered normal metal with repulsive electron-electron interactions  

NASA Astrophysics Data System (ADS)

In recent years, there has been a renewed interest in the proximity effect due to its role in the realization of topological superconductivity. Here, we study a superconductor-normal metal proximity system with repulsive electron-electron interactions in the normal layer. It is known that in the absence of disorder or normal reflection at the superconductor-normal metal interface, a zero-energy bound state forms and is localized to the interface [Fauchère et al., Phys. Rev. Lett. 82, 3336 (1999)., 10.1103/PhysRevLett.82.3336]. Using the quasiclassical theory of superconductivity, we investigate the low-energy behavior of the density of states in the presence of finite disorder and an interfacial barrier. We find that as the mean free path is decreased, the zero-energy peak in the density of states is broadened and reduced. In the quasiballistic limit, the bound state eliminates the minigap pertinent to a noninteracting normal layer and a distinct peak is observed. When the mean free path becomes comparable to the normal layer width, the zero-energy peak is strongly suppressed and the minigap begins to develop. In the diffusive limit, the minigap is fully restored and all signatures of the bound state are eliminated. We find that an interfacial potential barrier does not change the functional form of the density of states peak but does shift this peak away from zero energy.

Reeg, Christopher R.; Maslov, Dmitrii L.

2014-07-01

114

Decoupling initial electron beam parameters for Monte Carlo photon beam modelling by removing beam-modifying filters from the beam path.  

PubMed

A new method is presented to decouple the parameters of the incident e(-) beam hitting the target of the linear accelerator, which consists essentially in optimizing the agreement between measurements and calculations when the difference filter, which is an additional filter inserted in the linac head to obtain uniform lateral dose-profile curves for the high energy photon beam, and flattening filter are removed from the beam path. This leads to lateral dose-profile curves, which depend only on the mean energy of the incident electron beam, since the effect of the radial intensity distribution of the incident e- beam is negligible when both filters are absent. The location of the primary collimator and the thickness and density of the target are not considered as adjustable parameters, since a satisfactory working Monte Carlo model is obtained for the low energy photon beam (6 MV) of the linac using the same target and primary collimator. This method was applied to conclude that the mean energy of the incident e- beam for the high energy photon beam (18 MV) of our Elekta SLi Plus linac is equal to 14.9 MeV. After optimizing the mean energy, the modelling of the filters, in accordance with the information provided by the manufacturer, can be verified by positioning only one filter in the linac head while the other is removed. It is also demonstrated that the parameter setting for Bremsstrahlung angular sampling in BEAMnrc ('Simple' using the leading term of the Koch and Motz equation or 'KM' using the full equation) leads to different dose-profile curves for the same incident electron energy for the studied 18 MV beam. It is therefore important to perform the calculations in 'KM' mode. Note that both filters are not physically removed from the linac head. All filters remain present in the linac head and are only rotated out of the beam. This makes the described method applicable for practical usage since no recommissioning process is required. PMID:16333165

De Smedt, B; Reynaert, N; Flachet, F; Coghe, M; Thompson, M G; Paelinck, L; Pittomvils, G; De Wagter, C; De Neve, W; Thierens, H

2005-12-21

115

Probing Bulk Electronic Structure with Hard X-ray Angle-Resolved Photoemission  

NASA Astrophysics Data System (ADS)

Traditional ultraviolet and 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. I will present the first 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 (Ga,Mn)As, as a technologically-relevant ferromagnetic semiconductor material to illustrate the potential broad applicability of this new technique. The experimental results are compared to free-electron final-state model calculations and more precise one-step photoemission theory including matrix element effects. Some likely future applications areas are discussed.

Gray, Alexander; Minar, Jan; Ueda, Shigenori; Braun, Juergen; Ebert, Hubert; Dubon, Oscar; Kobayashi, Keisuke; Fadley, Charles

2011-11-01

116

Ambient-Pressure X-ray Photoelectron Spectroscopy through Electron Transparent Graphene Membranes  

E-print Network

Photoelectron spectroscopy (PES) and microscopy are highly demanded for exploring morphologically complex solid-gas and solid-liquid interfaces under realistic conditions, but the very small electron mean free path inside the dense media imposes serious experimental challenges. Currently, near ambient pressure PES is conducted using sophisticated and expensive electron energy analyzers coupled with differentially pumped electron lenses. An alternative economical approach proposed in this report uses ultrathin graphene membranes to isolate the ambient sample environment from the PES detection system. We demonstrate that the graphene membrane separating windows are both mechanically robust and sufficiently transparent for electrons in a wide energy range to allow PES of liquid and gaseous water. The reported proof-of-principle experiments also open a principal possibility to probe vacuum-incompatible toxic or reactive samples enclosed inside the hermetic environmental cells.

Kraus, Jurgen; Gunther, Sebastian; Gregoratti, Luca; Amati, Matteo; Kiskinova, Maya; Yulaev, Alexander; Vlassiouk, Ivan; Kolmakov, Andrei

2014-01-01

117

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

118

Electron transport in the solar wind -results from numerical simulations  

NASA Astrophysics Data System (ADS)

A conventional fluid approach is in general insufficient for a correct description of electron trans-port in weakly collisional plasmas such as the solar wind. The classical Spitzer-Hürm theory is a not valid when the Knudsen number (the mean free path divided by the length scale of tem-perature variation) is greater than ˜ 10-2 . Despite this, the heat transport from Spitzer-Hürm a theory is widely used in situations with relatively long mean free paths. For realistic Knud-sen numbers in the solar wind, the electron distribution function develops suprathermal tails, and the departure from a local Maxwellian can be significant at the energies which contribute the most to the heat flux moment. To accurately model heat transport a kinetic approach is therefore more adequate. Different techniques have been used previously, e.g. particle sim-ulations [Landi, 2003], spectral methods [Pierrard, 2001], the so-called 16 moment method [Lie-Svendsen, 2001], and approximation by kappa functions [Dorelli, 2003]. In the present study we solve the Fokker-Planck equation for electrons in one spatial dimension and two velocity dimensions. The distribution function is expanded in Laguerre polynomials in energy, and a finite difference scheme is used to solve the equation in the spatial dimension and the velocity pitch angle. The ion temperature and density profiles are assumed to be known, but the electric field is calculated self-consistently to guarantee quasi-neutrality. The kinetic equation is of a two-way diffusion type, for which the distribution of particles entering the computational domain in both ends of the spatial dimension must be specified, leaving the outgoing distributions to be calculated. The long mean free path of the suprathermal electrons has the effect that the details of the boundary conditions play an important role in determining the particle and heat fluxes as well as the electric potential drop across the domain. Dorelli, J. C., and J. D. Scudder, J. D. 2003, J. Geophys. Res. 108, 1294. Landi, S., and Pantellini, F. G. E. 2003, Astron. Astrophys., 400, 769. Lie-Svendsen, Ø., Leer, E., and Hansteen, V. H. 2001, J. Geophys. Res., 106, 8217. Pierrard, V., Maksimovic, M., and Lemaire, J. 2001, J. Geophys. Res., 106, 29305.

Smith, Håkan; Marsch, Eckart; Helander, Per

119

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

SciTech Connect

The development of a solid oxide fuel cell (SOFC) with a higher efficiency and power density requires an improved understanding and treatment of the irreversibilities. Losses due to the electronic and ionic resistances, which are also known as ohmic losses in the form of Joule heating, can hinder the SOFC’s performance. Ohmic losses can result from the bulk material resistivities as well as the complexities introduced by the cell’s microstructure. In this work, two-dimensional (2D), electronic and ionic transport models are used to develop a method of quantification of the ohmic losses within the SOFC anode microstructure. This quantification is completed as a function of properties determined from a detailed microstructure characterization, namely, the tortuosity of the electronic and ionic phases, phase volume fraction, contiguity, and mean free path. A direct modeling approach at the level of the pore-scale microstructure is achieved through the use of a representative volume element (RVE) method. The correlation of these ohmic losses with the quantification of the SOFC anode microstructure are examined. It is found with this analysis that the contributions of the SOFC anode microstructure on ohmic losses can be correlated with the volume fraction, contiguity, and mean free path.

Grew, Kyle N.; Izzo, Jr., John R.; Chiu, W. K. S.

2011-01-01

120

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

SciTech Connect

The development of a solid oxide fuel cell (SOFC) with a higher efficiency and power density requires an improved understanding and treatment of the irreversibilities. Losses due to the electronic and ionic resistances, which are also known as ohmic losses in the form of Joule heating, can hinder the SOFC's performance. Ohmic losses can result from the bulk material resistivities as well as the complexities introduced by the cell's microstructure. In this work, two-dimensional (2D), electronic and ionic transport models are used to develop a method of quantification of the ohmic losses within the SOFC anode microstructure. This quantification is completed as a function of properties determined from a detailed microstructure characterization, namely, the tortuosity of the electronic and ionic phases, phase volume fraction, contiguity, and mean free path. A direct modeling approach at the level of the pore-scale microstructure is achieved through the use of a representative volume element (RVE) method. The correlation of these ohmic losses with the quantification of the SOFC anode microstructure are examined. It is found with this analysis that the contributions of the SOFC anode microstructure on ohmic losses can be correlated with the volume fraction, contiguity, and mean free path.

Grew, Kyle N.; Izzo, John R.; Chiu, Wilson K.S.

2011-08-16

121

757 Path Loss Measurements  

NASA Technical Reports Server (NTRS)

Path Loss Measurements were obtained on three (3) GPS equipped 757 aircraft. Systems measured were Marker Beacon, LOC, VOR, VHF (3), Glide Slope, ATC (2), DME (2), TCAS, and GPS. This data will provide the basis for assessing the EMI (Electromagnetic Interference) safety margins of comm/nav (communication and navigation) systems to portable electronic device emissions. These Portable Electronic Devices (PEDs) include all devices operated in or around the aircraft by crews, passengers, servicing personnel, as well as the general public in the airport terminals. EMI assessment capability is an important step in determining if one system-wide PED EMI policy is appropriate. This data may also be used comparatively with theoretical analysis and computer modeling data sponsored by NASA Langley Research Center and others.

Horton, Kent; Huffman, Mitch; Eppic, Brian; White, Harrison

2005-01-01

122

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

123

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

E-print Network

: The 1925 Tri- State tornado damage path and associated storm system. Electronic J. Severe Storms Meteor., 8 (2), 1­33. 1 The 1925 Tri-State Tornado Damage Path and Associated Storm System ROBERT H. JOHNS May 2013) ABSTRACT The "Tri-State tornado" event of 18 March 1925, with an official death toll of 695

Doswell III, Charles A.

124

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Effect of temporal fluctuations of the optical path in a system for data storage by cumulative photon echo  

Microsoft Academic Search

An investigation is made of the efficiency of repeated excitation of a sample by laser pulse pairs when data are stored by the photon echo method. Fluctuations of the difference between the pulse phases in different pairs, resulting from instability of the optical path length in the delay line, are shown to prevent cophasal superposition of a set of level-population

A. N. Yashin

1995-01-01

125

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

PubMed Central

Excellent field electron emission properties of a diamond/CoSi2/Si quantum well nanostructure are observed. The novel quantum well structure consists of high quality diamond emitters grown on bulk Si substrate with a nanosized epitaxial CoSi2 conducting interlayer. The results show that the main emission properties were modified by varying the CoSi2 thickness and that stable, low-field, high emission current and controlled electron emission can be obtained by using a high quality diamond film and a thicker CoSi2 interlayer. An electron resonant tunneling mechanism in this quantum well structure is suggested, and the tunneling is due to the long electron mean free path in the nanosized CoSi2 layer. This structure meets most of the requirements for development of vacuum micro/nanoelectronic devices and large-area cold cathodes for flat-panel displays. PMID:23082241

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

2012-01-01

126

Internal tests and improvements of the Krook model for nonlocal electron energy transport in laser produced plasmas  

SciTech Connect

Electron thermal transport in a laser produced plasma cannot be described with a local approximation in many regions of a laser produced plasma because the electron mean free path is longer than the temperature gradient scale length. Since a Krook model for the electron Vlasov equation is analytically solvable in the nonlocal limit, one can find simple expressions for the electron thermal flux in the nonlocal limit, and these can be economically incorporated into fluid simulations. The Krook model provides reasonable descriptions of both preheat and flux limitation. We have analyzed the Krook model in a series of publications. Here we streamline the presentation of the model, show qualitatively just what the model predicts in certain situations, give internal tests to check the validity of the model, and provide more accurate analytic approximations to the integral formulas which the model gives rise to.

Colombant, Denis G.; Manheimer, Wallace M. [Naval Research Laboratory, Code 6730, Plasma Physics Division, Washington, DC 20375 (United States)

2010-11-15

127

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

128

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS: Effect of temporal fluctuations of the optical path in a system for data storage by cumulative photon echo  

NASA Astrophysics Data System (ADS)

An investigation is made of the efficiency of repeated excitation of a sample by laser pulse pairs when data are stored by the photon echo method. Fluctuations of the difference between the pulse phases in different pairs, resulting from instability of the optical path length in the delay line, are shown to prevent cophasal superposition of a set of level-population gratings. The possibility of weakening the negative influence of this effect on the intensity of the read echo signal is considered.

Yashin, A. N.

1995-05-01

129

Wide longitudinal distribution of interplanetary electrons following the 7 February 2010 solar event: Observations and transport modeling  

NASA Astrophysics Data System (ADS)

We analyze 65-105 keV electrons in the 7 February 2010 solar electron event observed simultaneously by STEREO-A, STEREO-B, and ACE. A method to reconstruct the full-electron pitch angle distributions from the four Solar Electron and Proton Telescope sensors on STEREO-A/B and the Solar Electron and Proton Telescope instrument on ACE in the energy range of approximately 60-300 keV for periods of incomplete angular coverage is presented. A transport modeling based on numerical solutions of a three-dimensional particle propagation model which includes pitch angle scattering and focused transport is applied to the intensity and anisotropy profiles measured on all three spacecraft. Based on an analysis of intensity gradients observed between the three spacecraft, we find that the lateral transport of the electrons occurs partially close to the Sun, due to effects of nonradial divergence of magnetic field lines or particle diffusion, and partially in the interplanetary medium. For the mean free paths characterizing the electron diffusion parallel and perpendicular to the interplanetary magnetic field, we derive values of ??˜ 0.1 AU and ??˜ 0.01 AU. In comparison with results from other particle events which we had previously analyzed in a similar manner we discuss whether the diffusion mean free paths parallel and perpendicular to the average magnetic field might be related with each other, and whether the particle transport perpendicular to the average magnetic field is more likely due to particles following meandering magnetic field lines, or due to particles being scattered off individual field lines.

Dröge, W.; Kartavykh, Y. Y.; Dresing, N.; Heber, B.; Klassen, A.

2014-08-01

130

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

131

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

132

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

E-print Network

Hard paths, soft paths or no paths? Cross-cultural perceptions of water solutions Drew Blasco1 to the availability of clean, safe water. In this study we examined cross cultural preferences for soft path vs. hard conceptualize water solutions (hard paths, soft paths, no paths) cross-culturally? 2) What role does development

Hall, Sharon J.

133

Walden's Paths - Ensemble Edition  

NSDL National Science Digital Library

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

2011-01-04

134

Assessing the impact of automated path planning aids in the maritime community  

E-print Network

In the area of merchant maritime navigation, electronic charts are a relatively new tool. As a result, navigational path planning environments that allow users to manually enter a path onto an electronic chart are becoming ...

Buchin, Mariela E

2009-01-01

135

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

136

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

PubMed

Valence electron count is one of the key factors influencing the stability and structure of metals and alloys. However, unlike in molecular compounds, the origins of the preferred electron counts of many metallic phases remain largely mysterious. Perhaps the clearest-cut of such electron counting rules is exhibited by the Nowotny chimney ladder (NCL) phases, compounds remarkable for their helical structural motifs in which transition metal (T) helices serve as channels for a second set of helices formed from main group (E) elements. These phases exhibit density of states pseudogaps or band gaps, and thus special stability and useful physical properties, when their valence electron count corresponds to 14 electrons per T atom. In this Article, we illustrate, using DFT-calibrated Hückel calculations and the reversed approximation Molecular Orbital analysis, that the 14-electron rule of the NCLs is, in fact, a specific instance of an 18 - n rule emerging for T-E intermetallics, where n is the number of E-supported T-T bonds per T atom. The structural flexibility of the NCL series arises from the role of the E atoms as supports for these T-T bonds, which simply requires the E atoms to be as uniformly distributed within the T sublattice as possible. This picture offers a strategy for identifying other intermetallic structures that may be amenable to incommensurability between T and E sublattices. PMID:25215958

Yannello, Vincent J; Fredrickson, Daniel C

2014-10-01

137

Path Integrals and Hamiltonians  

NASA Astrophysics Data System (ADS)

1. Synopsis; Part I. Fundamental Principles: 2. The mathematical structure of quantum mechanics; 3. Operators; 4. The Feynman path integral; 5. Hamiltonian mechanics; 6. Path integral quantization; Part II. Stochastic Processes: 7. Stochastic systems; Part III. Discrete Degrees of Freedom: 8. Ising model; 9. Ising model: magnetic field; 10. Fermions; Part IV. Quadratic Path Integrals: 11. Simple harmonic oscillators; 12. Gaussian path integrals; Part V. Action with Acceleration: 13. Acceleration Lagrangian; 14. Pseudo-Hermitian Euclidean Hamiltonian; 15. Non-Hermitian Hamiltonian: Jordan blocks; 16. The quartic potential: instantons; 17. Compact degrees of freedom; Index.

Baaquie, Belal E.

2014-03-01

138

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

139

Dicalcium nitride as a two-dimensional electride with an anionic electron layer.  

PubMed

Recent studies suggest that electrides--ionic crystals in which electrons serve as anions--are not exceptional materials but rather a generalized form, particularly under high pressure. The topology of the cavities confining anionic electrons determines their physical properties. At present, reported confining sites consist only of zero-dimensional cavities or weakly linked channels. Here we report a layered-structure electride of dicalcium nitride, Ca(2)N, which possesses two-dimensionally confined anionic electrons whose concentration agrees well with that for the chemical formula of [Ca(2)N](+)·e(-). Two-dimensional transport characteristics are demonstrated by a high electron mobility (520?cm(2)?V(-1)?s(-1)) and long mean scattering time (0.6?picoseconds) with a mean free path of 0.12?micrometres. The quadratic temperature dependence of the resistivity up to 120?Kelvin indicates the presence of an electron-electron interaction. A striking anisotropic magnetoresistance behaviour with respect to the direction of magnetic field (negative for the field perpendicular to the conducting plane and positive for the field parallel to it) is observed, confirming diffusive two-dimensional transport in dense electron layers. Additionally, band calculations support confinement of anionic electrons within the interlayer space, and photoemission measurements confirm anisotropic low work functions of 3.5 and 2.6 electronvolts, revealing the loosely bound nature of the anionic electrons. We conclude that Ca(2)N is a two-dimensional electride in terms of [Ca(2)N](+)·e(-). PMID:23364689

Lee, Kimoon; Kim, Sung Wng; Toda, Yoshitake; Matsuishi, Satoru; Hosono, Hideo

2013-02-21

140

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

141

Improved initial guess for minimum energy path calculations  

E-print Network

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 the true minimum energy path using some method of choice for evaluating the energy and atomic forces, for example by ab initio or density functional theory. The optimal path on the IDPP surface is significantly closer to the true 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. Th...

Smidstrup, Søren; Stokbro, Kurt; Jónsson, Hannes

2014-01-01

142

Bootlegging and path dependency  

Microsoft Academic Search

This paper confirms the importance of path dependency in the accumulation of firm-specific technological competencies. It shows that firms are guided by the selective logic of path dependency in their innovation processes, even if management has no part in decisions to invest in a new business idea. The research focuses on the output of bootlegging, defined as research in which

Peter Augsdorfer

2005-01-01

143

The SunPath  

NSDL National Science Digital Library

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

University, Australian N.

144

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

PubMed Central

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

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

2014-01-01

145

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

146

Role of interface band structure on hot electron transport  

NASA Astrophysics Data System (ADS)

Knowledge of electron transport through materials and interfaces is fundamentally and technologically important. For example, metal interconnects within integrated circuits suffer increasingly from electromigration and signal delay due to an increase in resistance from grain boundary and sidewall scattering since their dimensions are becoming shorter than the electron mean free path. Additionally, all semiconductor based devices require the transport of electrons through materials and interfaces where scattering and parallel momentum conservation are important. In this thesis, the inelastic and elastic scattering of hot electrons are studied in nanometer thick copper, silver and gold films deposited on silicon substrates. Hot electrons are electron with energy greater than kBT above the Fermi level (EF). This work was performed utilizing ballistic electron emission microscopy (BEEM) which is a three terminal scanning tunneling microscopy (STM) technique that measures the percentage of hot electrons transmitted across a Schottky barrier interface. Hot electron attenuation lengths of the metals were extracted by measuring the BEEM current as a function of metal overlayer thickness for both hot electron and hot hole injection at 80 K and under ultra high vacuum. The inelastic and elastic scattering lengths were extracted by fitting the energetic dependence of the measured attenuation lengths to a Fermi liquid based model. A sharp increase in the attenuation length is observed at low injection energies, just above the Schottky barrier height, only for metals on Si(001) substrates. In contrast, the attenuation length measured on Si(111) substrates shows a sharp decrease. These results indicate that interface band structure and parallel momentum conservation have significant impact upon the transport of hot electrons across non epitaxial metal-semiconductor interfaces. In addition, they help to separate effects upon hot electron transport that are inherent to the metal film from those associated with the interface and its band structure.

Garramone, John J.

147

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

148

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

149

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

NASA Astrophysics Data System (ADS)

A Monte Carlo model of electron thermalization in inorganic scintillators, which was developed and applied to CsI in a previous publication [Wang et al., J. Appl. Phys. 110, 064903 (2011)], is extended to another material of the alkali halide class, NaI, and to two materials from the alkaline-earth halide class, CaF2 and BaF2. This model includes electron scattering with both longitudinal optical (LO) and acoustic phonons as well as the effects of internal electric fields. For the four pure materials, a significant fraction of the electrons recombine with self-trapped holes and the thermalization distance distributions of the electrons that do not recombine peak between approximately 25 and 50 nm and extend up to a few hundreds of nanometers. The thermalization time distributions of CaF2, BaF2, NaI, and CsI extend to approximately 0.5, 1, 2, and 7 ps, respectively. The simulations show that the LO phonon energy is a key factor that affects the electron thermalization process. Indeed, the higher the LO phonon energy is, the shorter the thermalization time and distance are. The thermalization time and distance distributions show no dependence on the incident ?-ray energy. The four materials also show different extents of electron-hole pair recombination due mostly to differences in their electron mean free paths (MFPs), LO phonon energies, initial densities of electron-hole pairs, and static dielectric constants. The effect of thallium doping is also investigated for CsI and NaI as these materials are often doped with activators. Comparison between CsI and NaI shows that both the larger size of Cs+ relative to Na+, i.e., the greater atomic density of NaI, and the longer electron mean free path in NaI compared to CsI contribute to an increased probability for electron trapping at Tl sites in NaI versus CsI.

Wang, Zhiguo; Xie, YuLong; Campbell, Luke W.; Gao, Fei; Kerisit, Sebastien

2012-07-01

150

Comparison in spatial spreads of secondary electron information between scanning ion and scanning electron microscopy.  

PubMed

Monte Carlo simulations have been carried out to compare the spatial spreads of secondary electron (SE) information in scanning ion microscopy (SIM) with scanning electron microscopy (SEM). Under Ga ion impacts, the SEs are excited by three kinds of collision-partners, that is, projectile ion, recoiled target atom, and target electron. The latter two partners dominantly contribute to the total SE yield gamma for the materials of low atomic number Z2. For the materials of high Z2, on the other hand, the projectile ions dominantly contribute to gamma. These Z2 dependencies generally cause the gamma yield to decrease with an increasing Z2, in contrast with the SE yield delta under electron impacts. Most of the SEs are produced in the surface layer of about 5lambda in depth (lambda: the mean free path of SEs), as they are independent of the incident probe. Under 30 keV Ga ion impacts, the spatial spread of SE information is roughly as small as 10 nm, decreasing with an increasing Z2. Under 10 keV electron impacts, the SEI excited by the primary electrons has a small spatial spread of about 5lambda, but the SEII excited by the backscattered electrons has a large one of several 10 to several 100 nanometers, decreasing with an increasing Z2. The main cause of a small spread of SE information at ion impact is the short ranges of the projectile ions returning to the surface to escape as backscattered ions, the recoiled target atoms, and the target electrons in collision cascade. The 30 keV Ga-SIM imaging is better than the 10 keV SEM imaging in spatial resolution for the structure/material measurements. Here, zero-size probes are assumed. PMID:12926612

Ishitani, Tohru; Ohya, Kaoru

2003-01-01

151

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

152

The reweighted path ensemble.  

PubMed

We introduce a reweighting scheme for the path ensembles in the transition interface sampling framework. The reweighting allows for the analysis of free energy landscapes and committor projections in any collective variable space. We illustrate the reweighting scheme on a two dimensional potential with a nonlinear reaction coordinate and on a more realistic simulation of the Trp-cage folding process. We suggest that the reweighted path ensemble can be used to optimize possible nonlinear reaction coordinates. PMID:21054008

Rogal, Jutta; Lechner, Wolfgang; Juraszek, Jarek; Ensing, Bernd; Bolhuis, Peter G

2010-11-01

153

Electron physics and ambipolarity in the tokamak scrape-off layer  

SciTech Connect

Models of the electron behavior in the scrape-off layer (SOL) of diverted and limited boundary conditions that occurs tokamak plasmas must retain the abrupt change in boundary conditions that occurs across the separatrix or last closed flux surface as well as the electron reflecting Debye sheath established at the limiter or divertor plates. The balance between ion radial diffusion and streaming to the plates sets the SOL width and the electrons must adjust the Debye sheath at the plates to main tain quasineutrality and ambipolarity in the SOL beyond the last closed flux surface. We consider the long mean-free-path limit where a bounce-averaged kinetic electron model results in a steady-state balance in the SOL between radial diffusive feed from the core and velocity space diffusive loss to the plates due to collisional detrapping. In this double diffusion model a velocity space boundary layer occurs about the trapped-passing boundary where strong velocity space gradients must balance the streaming of the newly de-trapped electrons to the plates. The behavior of the electron distribution function in the velocity provides the information needed to evaluate the Debye-sheath-dependent electron loss rate.

Hazeltine, R.D. [Texas Univ., Austin, TX (United States). Inst. for Fusion Studies; Catto, P.J. [Massachusetts Inst. of Tech., Cambridge, MA (United States)

1994-04-01

154

Exploring highly correlated materials via electron pair emission: the case of NiO/Ag(100)  

NASA Astrophysics Data System (ADS)

Metal oxides like NiO are usually termed ‘highly correlated’, because the material properties are decisively determined by the electron-electron interaction. This makes them interesting candidates for electron pair spectroscopy which is particularly sensitive to the electron correlation. We have prepared ultrathin NiO/Ag(100) films and studied the electron pair emission upon electron impact. Compared to the metal substrate we observe an increase of the coincidence intensity by a factor of 8 for NiO. Thickness dependent measurements prove that this enhancement is an intrinsic effect rather than due to a mean free path increase of the oxide. The Néel temperature TN of NiO films displays a thickness dependence which allows us to tune TN. We performed temperature dependent measurements and observed no temperature dependence of the coincidence spectra. This proves that the electron pair emission probes the local correlation rather than long range order. An enhanced coincidence intensity was also found for other oxide phases compared to their corresponding metal phases.

Schumann, F. O.; Behnke, L.; Li, C. H.; Kirschner, J.

2013-03-01

155

A Hot-electron Direct Detector for Radioastronomy  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

156

Sampling diffusive transition paths  

SciTech Connect

We 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 sampling infinitesimal Brownian increments of the path, as well as a different type of stiffness associated with sampling the coarse features of long paths. The fine-features sampling stiffness is eliminated with the use of the fast sampling algorithm (FSA), 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. We use the algorithm to sample the transition path ensemble for the structural interconversion of the 38-atom Lennard-Jones cluster at low temperature.

F. Miller III, Thomas; Predescu, Cristian

2006-10-12

157

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

158

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

159

A Monte Carlo study of reflection electron energy loss spectroscopy spectrum of a carbon contaminated surface  

NASA Astrophysics Data System (ADS)

It has been experimentally found that the carbon surface contamination influences strongly the spectrum signals in reflection electron energy loss spectroscopy (REELS) especially at low primary electron energy. However, there is still little theoretical work dealing with the carbon contamination effect in REELS. Such a work is required to predict REELS spectrum for layered structural sample, providing an understanding of the experimental phenomena observed. In this study, we present a numerical calculation result on the spatially varying differential inelastic mean free path for a sample made of a carbon contamination layer of varied thickness on a SrTiO3 substrate. A Monte Carlo simulation model for electron interaction with a layered structural sample is built by combining this inelastic scattering cross-section with the Mott's cross-section for electron elastic scattering. The simulation results have clearly shown that the contribution of the electron energy loss from carbon surface contamination increases with decreasing primary energy due to increased individual scattering processes along trajectory parts carbon contamination layer. Comparison of the simulated spectra for different thicknesses of the carbon contamination layer and for different primary electron energies with experimental spectra clearly identifies that the carbon contamination in the measured sample was in the form of discontinuous islands other than the uniform film.

Da, B.; Li, Z. Y.; Chang, H. C.; Mao, S. F.; Ding, Z. J.

2014-09-01

160

Stationary electron velocity distribution function in crossed electric and magnetic fields with collisions  

SciTech Connect

Analytical studies and numerical simulations show that the electron velocity distribution function in a Hall thruster discharge with crossed electric and magnetic fields is not Maxwellian. This is due to the fact that the mean free path between collisions is greater than both the Larmor radius and the characteristic dimensions of the discharge channel. However in numerical models of Hall thrusters, a hydrodynamic approach is often used to describe the electron dynamics, because discharge simulation in a fully kinetic approach requires large computing resources and is time consuming. A more accurate modeling of the electron flow in the hydrodynamic approximation requires taking into account the non-Maxwellian character of the distribution function and finding its moments, an approach that reflects the properties of electrons drifting in crossed electric and magnetic fields better than the commonly used Euler or Navier-Stokes approximations. In the present paper, an expression for the electron velocity distribution function in rarefied spatially homogeneous stationary plasma with crossed electric and magnetic fields and predominance of collisions with heavy particles is derived in the relaxation approximation. The main moments of the distribution function including longitudinal and transversal temperatures, the components of the viscous stress tensor, and of the heat flux vector are calculated. Distinctive features of the hydrodynamic description of electrons with a strongly non-equilibrium distribution function and the prospects for further development of the proposed approach for calculating the distribution function in spatially inhomogeneous plasma are discussed.

Shagayda, Andrey [Department of Electrophysics, Keldysh Research Centre, Moscow 125438 (Russian Federation)

2012-08-15

161

Gas Path Seal.  

National Technical Information Service (NTIS)

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 backi...

R. C. Bill, R. D. Johnson

1979-01-01

162

DNA Computing Hamiltonian path  

E-print Network

2014 DNA DNA #12;DNA Computing · Feynman · Adleman · DNASIMD · ... · · · · · DNADNA #12;DNA · DNA · · · · DNA · · #12;2000 2005 2010 1995 Hamiltonian path DNA tweezers DNA tile DNA origami DNA box Sierpinski DNA tile self assembly DNA logic gates Whiplash PCR DNA automaton DNA spider MAYA

Hagiya, Masami

163

World nuclear energy paths  

Microsoft Academic Search

In examing the world nuclear energy paths, the following assumptions were adopted: the world economy will grow somewhat more slowly than in the past, leading to reductions in electricity demand growth rates; national and international political impediments to the deployment of nuclear power will gradually disappear over the next few years; further development of nuclear power will proceed steadily, without

T. J. Connolly; U. Hansen; W. Jaek; K. H. Beckurts

1979-01-01

164

Off the Beaten Path.  

ERIC Educational Resources Information Center

Describes "Off the Beaten Path", a program that takes at-risk students out of the traditional classroom and puts them into a camping atmosphere in order to increase academic achievement, improve self-esteem, and promote better social skills. (WRM)

Grimm, Karen

1999-01-01

165

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

166

Atomic- and electron-beam spectroscopy of rarefied semiquantum media  

NASA Astrophysics Data System (ADS)

The quantum-mechanical collective effects accompanying the propagation of a low-energy atomic or electron beam through a rarefied medium are discussed. An unusual dissipation mechanism due to the inelastic scattering of a test particle with thermal collective modes is considered. The phenomenon in question comes into effect even in a thin target at distances less than the mean free path calculated for direct atomic collisions. This effect provides the possibility to study the collective many-body properties of the medium by means of traditional atomic (electron) spectroscopy. The differential cross sections for the inelastic scattering of a probe particle with fluctuations of density, macroscopic magnetization, and entropy in the target are expressed in terms of the corresponding structure functions and calculated both in the hydrodynamic and collisionless regimes. The spin-flip transitions as well as the nonflip scattering are considered in detail. Possible applications of the theory to semiquantum systems such as gaseous H?, D?, and dilute 3-4He mixtures as well as some aspects of neutron optics and atomic (electron) spectroscopy are briefly discussed.

Bashkin, Eugene P.; Stepaniants, Sergey B.

1995-02-01

167

Fast Advection of Magnetic Fields by Hot Electrons  

SciTech Connect

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

Willingale, L.; Thomas, A. G. R.; Krushelnick, K. [Blackett Laboratory, Imperial College London, London, SW7 2BZ (United Kingdom); Center for Ultrafast Optical Science, Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109-2099 (United States); Nilson, P. M.; Kaluza, M. C.; Dangor, A. E.; Evans, R. G.; Fernandes, P.; Haines, M. G.; Kamperidis, C.; Kingham, R. J.; Ridgers, C. P.; Sherlock, M.; Wei, M. S.; Najmudin, Z. [Blackett Laboratory, Imperial College London, London, SW7 2BZ (United Kingdom); Bandyopadhyay, S.; Notley, M. [Central Laser Facility, Rutherford Appleton Laboratory, Chilton, Oxon, OX11 0QX (United Kingdom); Minardi, S.; Tatarakis, M. [Centre for Plasma Physics and Lasers, Department of Electronics, Technological Educational Institute of Crete, Chania, Crete (Greece); Rozmus, W. [Department of Physics, University of Alberta, Edmonton, Alberta (Canada)

2010-08-27

168

Stabilizing Intelligent Route Control: Randomized Path Monitoring, Randomized Path  

E-print Network

Stabilizing Intelligent Route Control: Randomized Path Monitoring, Randomized Path Switching or History-aware Path Switching? Alexandre Fonte1,2 , Jos´e Martins1 , Marilia Curado1 , and Edmundo Monteiro, Castelo Branco, Portugal Abstract. Multihoming Intelligent Route Control (IRC) plays a signif- icant role

Monteiro, Edmundo

169

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

170

PATHS groundwater hydrologic model  

SciTech Connect

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

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

1980-04-01

171

MINIMUM WEIGHT PATHS TIMEDEPENDENT NETWORKS  

E-print Network

MINIMUM WEIGHT PATHS in TIME­DEPENDENT NETWORKS Ariel Orda Raphael Rom Department of Electrical) ABSTRACT We investigate the minimum weight path problem in networks whose link weights and link delays weight problem always has a solution. We also characterize the structure of an infinite optimal path

Orda, Ariel

172

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

173

Tracking hurricane paths  

NASA Technical Reports Server (NTRS)

The South East coastal region experiences hurricane threat for almost six months in every year. To improve the accuracy of hurricane forecasts, meteorologists would need the storm paths of both the present and the past. A hurricane path can be established if we could identify the correct position of the storm at different times right from its birth to the end. We propose a method based on both spatial and temporal image correlations to locate the position of a storm from satellite images. During the hurricane season, the satellite images of the Atlantic ocean near the equator are examined for the hurricane presence. This is accomplished in two steps. In the first step, only segments with more than a particular value of cloud cover are selected for analysis. Next, we apply image processing algorithms to test the presence of a hurricane eye in the segment. If the eye is found, the coordinate of the eye is recorded along with the time stamp of the segment. If the eye is not found, we examine adjacent segments for the existence of hurricane eye. It is probable that more than one hurricane eye could be found from different segments of the same period. Hence, the above process is repeated till the entire potential area for hurricane birth is exhausted. The subsequent/previous position of each hurricane eye will be searched in the appropriate adjacent segments of the next/previous period to mark the hurricane path. The temporal coherence and spatial coherence of the images are taken into account by our scheme in determining the segments and the associated periods required for analysis.

Prabhakaran, Nagarajan; Rishe, Naphtali; Athauda, Rukshan

1997-01-01

174

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

175

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

176

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

177

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

NASA Astrophysics Data System (ADS)

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.

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

178

Electron heat transport in a steep temperature gradient  

SciTech Connect

Temporal and spatial measurements of electron heat transport are made in the University of California Davis AURORA device (J. H. Rogers, Ph.D. dissertation, University of California, Davis, 1987). In AURORA, a microwave pulse heats a region of underdense, collisional, plasma (n/n/sub cr/ approx. <1, where n/sub cr/ = 1.8 x 10/sup 10/ cm/sup -3/ is the critical density, T/sub e//sub 0/ approx. =0.15 eV, and the electron scattering mean free path lambda/sub perpendicular/approx. >2 cm). In this region, strong thermal heating (T/sub c/ approx. <0.7 eV) as well as suprathermal heating (T/sub h/approx. =3 eV) is observed. The strong heating results in a steep temperature gradient that violates the approximations of classical heat diffusion theory (L/sub T//lambda/sub perpendicular/approx. >3 for thermal electrons, where L/sub T/ = T/sub c/(partialT/sub c//partialz)/sup -1/ is the cold electron temperature scale length. The time evolution of the electron temperature profile is measured using Langmuir probes. The measured relaxation of the temperature gradient after the microwave pulse is compared to calculations using the Fokker--Planck International code (Phys. Rev. Lett. 49, 1936 (1982)) and the multigroup, flux-limited, target design code LASNEX (Comm. Plasma Phys. 2, 51 (1975)). The electron distribution function at the end of the microwave pulse is used as initial conditions for both codes. The Fokker--Planck calculations are found to agree very well with the measurements.

Rogers, J.H.; De Groot, J.S.; Abou-Assaleh, Z.; Matte, J.P.; Johnston, T.W.; Rosen, M.D.

1989-04-01

179

Free Path Lengths in Quasi Crystals  

NASA Astrophysics Data System (ADS)

The Lorentz gas is a model for a cloud of point particles (electrons) in a distribution of scatterers in space. The scatterers are often assumed to be spherical with a fixed diameter d, and the point particles move with constant velocity between the scatterers, and are specularly reflected when hitting a scatterer. There is no interaction between point particles. An interesting question concerns the distribution of free path lengths, i.e. the distance a point particle moves between the scattering events, and how this distribution scales with scatterer diameter, scatterer density and the distribution of the scatterers. It is by now well known that in the so-called Boltzmann-Grad limit, a Poisson distribution of scatterers leads to an exponential distribution of free path lengths, whereas if the scatterer distribution is periodic, the free path length distribution asymptotically behaves as a power law. This paper considers the case when the scatters are distributed on a quasi crystal, i.e. non periodically, but with a long range order. Simulations of a one-dimensional model are presented, showing that the quasi crystal behaves very much like a periodic crystal, and in particular, the distribution of free path lengths is not exponential.

Wennberg, Bernt

2012-06-01

180

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

181

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

PubMed

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

Roy, Kanak; Gopinath, Chinnakonda S

2014-04-15

182

Effects of external magnetic filter on behaviors of fast primary electrons in a volume negative ion source  

SciTech Connect

The relationship between enhancement of hydrogen negative ion H{sup -}, volume production, and behaviors of fast primary electrons is studied theoretically. Trajectories of fast primary electrons are calculated, including collisional effects with hydrogen molecules. Active region of fast electrons depends strongly on the field intensity of the magnetic filter (MF), B{sub MF}, and filament position. Therefore, spatial distributions of ionization and vibrational excitation collision points are also affected with changing B{sub MF}. Although number of vibrational excitation collision points is much smaller than that of ionization collision points due to different mean free path, the relative intensity is varied by changing energy of fast electrons. According to the results and discussions including transport of produced vibrationally excited molecules, for enhancement of H{sup -} production, it is desired that fast electrons should approach the MF position and move into the downstream region as deep as possible without destruction of H{sup -} ions. To realize these conditions, good combination between filament position and the intensity of the MF should be required.

Mori, Shigefumi; Fukumasa, Osamu [Graduate School of Science and Engineering, Yamaguchi University, Tokiwadai 2-16-1, Ube 755-8611 (Japan)

2008-02-15

183

Effects of external magnetic filter on behaviors of fast primary electrons in a volume negative ion source.  

PubMed

The relationship between enhancement of hydrogen negative ion H(-), volume production, and behaviors of fast primary electrons is studied theoretically. Trajectories of fast primary electrons are calculated, including collisional effects with hydrogen molecules. Active region of fast electrons depends strongly on the field intensity of the magnetic filter (MF), B(MF), and filament position. Therefore, spatial distributions of ionization and vibrational excitation collision points are also affected with changing B(MF). Although number of vibrational excitation collision points is much smaller than that of ionization collision points due to different mean free path, the relative intensity is varied by changing energy of fast electrons. According to the results and discussions including transport of produced vibrationally excited molecules, for enhancement of H(-) production, it is desired that fast electrons should approach the MF position and move into the downstream region as deep as possible without destruction of H(-) ions. To realize these conditions, good combination between filament position and the intensity of the MF should be required. PMID:18315147

Mori, Shigefumi; Fukumasa, Osamu

2008-02-01

184

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

Microsoft Academic Search

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

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

1987-01-01

185

Flight Paths of Orbiting Satellites  

NSDL National Science Digital Library

This is an activity to help students visualize the relationship of motion, time and space as it relates to objects orbiting the earth. They will be able to track the path of an orbiting object on a globe, plot the path of an orbiting object on a flat world map, and explain that an object orbiting earth on a plane will produce a flight path which appears as wavy lines on the earths surface.

186

Path Layout in ATM Networks  

Microsoft Academic Search

This paper surveys recent results in the area of virtual path layout in ATM networks. We focus on the one-to-all (or broadcast) and the all-to-all problems. We present a model for theoretical studies of these layouts, which amounts to covering the network with simple paths, under various constraints. The constraints are the hop count (the number of paths traversed between

Shmuel Zaks

1997-01-01

187

Path and path deviation equations for p-branes  

NASA Astrophysics Data System (ADS)

Path and path deviation equations for neutral, charged, spinning and spinning charged test particles, using a modified Bazanski Lagrangian, are derived. We extend this approach to strings and branes. We show how the Bazanski Lagrangian for charged point particles and charged branes arises à la Kaluza-Klein from the Bazanski Lagrangian in 5-dimensions.

Pavši?, Matej; Kahil, Magd E.

2012-04-01

188

Simple model of bulk and surface excitation effects to inelastic scattering in low-energy electron beam irradiation of multi-walled carbon nanotubes  

NASA Astrophysics Data System (ADS)

The effect of bulk and surface excitations to inelastic scattering in low-energy electron beam irradiation of multi-walled carbon nanotubes (MWNTs) is studied using the dielectric formalism. Calculations are based on a semiempirical dielectric response function for MWCNTs determined by means of a many-pole plasmon model with parameters adjusted to available experimental spectroscopic data under theoretical sum-rule constrains. Finite-size effects are considered in the context of electron gas theory via a boundary correction term in the plasmon dispersion relations, thus, allowing a more realistic extrapolation of the electronic excitation spectrum over the whole energy-momentum plane. Energy-loss differential and total inelastic scattering cross sections as a function of electron energy and distance from the surface, valid over the energy range ˜50-30,000 eV, are calculated with the individual contribution of bulk and surface excitations separated and analyzed for the case of normally incident and escaping electrons. The sensitivity of the results to the various approximations for the spatial dispersion of the electronic excitations is quantified. Surface excitations are shown to have a strong influence upon the shape and intensity of the energy-loss differential cross section in the near surface region whereas the general notion of a spatially invariant inelastic mean free path inside the material is found to be of good approximation.

Kyriakou, Ioanna; Emfietzoglou, Dimitris; Garcia-Molina, Rafael; Abril, Isabel; Kostarelos, Kostas

2011-09-01

189

Stabilizing Intelligent Route Control: Randomized Path Monitoring, Randomized Path Switching or History-Aware Path Switching?  

Microsoft Academic Search

Multihoming Intelligent Route Control (IRC) plays a significant role in improving the performance of Internet accesses. However,\\u000a in a competitive environment, IRC systems may introduce persistent route oscillations, causing significant performance degradation.\\u000a In this study, three design alternatives to cope with this issue are investigated: Randomized Path Monitoring, Randomized\\u000a Path Switching and History-aware Path Switching. The simulation results show that

Alexandre Fonte; José Martins; Marilia Curado; Edmundo Monteiro

2008-01-01

190

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

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

191

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

SciTech Connect

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

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

2012-10-15

192

Dependence of the electronic transport on the microstructure in annealed Bi thin films  

NASA Astrophysics Data System (ADS)

Bi thin films, with a thickness ranging from 10 to 100 nm, are deposited by electron-beam evaporation on a thermally oxidized Si(100) substrate. The deposition parameters are optimized in order to maximize the grain size of the polycrystalline films. The evolution of the crystal orientation is examined as a function of the deposition and annealing parameters, by electron back scattering diffraction. Low temperature (21 mK - 150 K) magnetoresistance measurements (up to 15 T) on polycrystalline films reveal weak anti-localization, superimposed by the classical magnetoresistance. The analysis of the weak anti-localization allows us to extract quantum transport parameters, such as the phase coherence and the spin orbit coupling time. From the evolution of the broad magnetoresistance background, we infer the evolution of electronic transport parameters: the mobility, the charge carrier concentration and the mean free path. Magneto-transport and ab initio calculations are combined in order to investigate on the controversial existence of the semimetal-semiconductor transition.

Nhan Bui, Thanh; Raskin, Jean-Pierre; Malet, Loic; Godet, Stephane; Rodrigues Martins, Frederico; Faniel, Sebastien; Gonze, Xavier; Cabosart, Damien; Hackens, Benoit

2013-03-01

193

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

194

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

NASA Astrophysics Data System (ADS)

The electronic stopping power, S , of HfO2 films for proton and alpha particle beams has been measured and calculated. The experimental data have been obtained by the Rutherford backscattering technique and cover the range of 120-900 and 120-3000 keV for proton and alpha particle beams, respectively. Theoretical calculations of the energy loss for the same projectiles have been done by means of the dielectric formalism using the Mermin energy loss function—generalized oscillator strength (MELF-GOS) model for a proper description of the HfO2 target on the whole momentum-energy excitation spectrum. At low projectile energies, a nonlinear theory based on the extended Friedel sum rule has been employed. The calculations and experimental measurements show good agreement for protons and a quite good one for alpha particles. In particular, the experimental maximums of both stopping curves (around 120 and 800 keV, respectively) are well reproduced. On the basis of this good agreement, we have also calculated the inelastic mean-free path (IMFP) and the stopping power for electrons in HfO2 films. Our results predict a minimum value of the IMFP and a maximum value of the S for electrons with energies around 120 and 190 eV, respectively.

Behar, Moni; Fadanelli, Raul C.; Abril, Isabel; Garcia-Molina, Rafael; Denton, Cristian D.; Nagamine, Luiz C. C. M.; Arista, Néstor R.

2009-12-01

195

On shortest paths and sorting  

Microsoft Academic Search

In finding shortest paths, the operation of finding, successively, a minimum from a list of numbers may require more work than the remainder of the algorithm. It is shown how algorithms from sorting literature can be used to accomplish this part of the shortest path algorithm. Bounds on the largest possible amount of work are established, and results of a

Ellis L. Johnson

1972-01-01

196

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

197

Path Jacobians: Theory and Applications  

Microsoft Academic Search

In accordance with Fermat's Variation Principle, a ray path connecting two arbitrary points in a scene via multiple reflectors is given by a non-linear system. If we fix one of the two points and let the other change, the system can be considered as a function relating the reflection points along the path to the varying point. In this paper,

Min Chen; James Arvo

1998-01-01

198

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

199

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

200

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

201

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

SciTech Connect

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

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

2008-05-01

202

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

203

221A Lecture Notes Path Integral  

E-print Network

221A Lecture Notes Path Integral 1 Feynman's Path Integral Formulation Feynman's formulation with a weight factor given by the classical action for each path. Hence the name path integral. This is it. Note of quantum mechanics using the so-called path inte- gral is arguably the most elegant. It can be stated

Murayama, Hitoshi

204

Path Planning with obstacle avoidance  

NASA Technical Reports Server (NTRS)

The research report here summarizes a solution for two dimensional Path Planning with obstacle avoidance in a workspace with stationary obstacles. The solution finds the shortest path for the end effector of a manipulator arm. The program uses an overhead image of the robot work space and the starting and ending positions of the manipulator arm end effector to generate a search graph which is used to find the shortest path through the work area. The solution was originally implemented in VAX Pascal, but was later converted to VAX C.

Krause, Donald M.

1987-01-01

205

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

E-print Network

Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Path Testing Mohammad Mousavi Eindhoven University of Technology, The Netherlands Software Testing, 2012 Mousavi: Path Testing #12;Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Outline Structural

Mousavi, Mohammad

206

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

E-print Network

Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Path Testing Mohammad Mousavi Eindhoven University of Technology, The Netherlands Software Testing, 2013 Mousavi: Path Testing #12;Structural Testing: An Introduction Flow Graphs Path Testing Conclusions Outline Structural

Mousavi, Mohammad

207

Turbulent Pitch-angle Scattering and Diffusive Transport of Hard X-Ray-producing Electrons in Flaring Coronal Loops  

NASA Astrophysics Data System (ADS)

Recent observations from RHESSI have revealed that the number of non-thermal electrons in the coronal part of a flaring loop can exceed the number of electrons required to explain the hard X-ray-emitting footpoints of the same flaring loop. Such sources cannot, therefore, be interpreted on the basis of the standard collisional transport model, in which electrons stream along the loop while losing their energy through collisions with the ambient plasma; additional physical processes, to either trap or scatter the energetic electrons, are required. Motivated by this and other observations that suggest that high-energy electrons are confined to the coronal region of the source, we consider turbulent pitch-angle scattering of fast electrons off low-frequency magnetic fluctuations as a confinement mechanism, modeled as a spatial diffusion parallel to the mean magnetic field. In general, turbulent scattering leads to a reduction of the collisional stopping distance of non-thermal electrons along the loop, and hence to an enhancement of the coronal hard X-ray source relative to the footpoints. The variation of source size L with electron energy E becomes weaker than the quadratic behavior pertinent to collisional transport, with the slope of L(E) depending directly on the mean free path ? associated with the non-collisional scattering mechanism. Comparing the predictions of the model with observations, we find that ? ~ (108-109) cm for ~30 keV, less than the length of a typical flaring loop and smaller than, or comparable to, the size of the electron acceleration region.

Kontar, Eduard P.; Bian, Nicolas H.; Emslie, A. Gordon; Vilmer, Nicole

2014-01-01

208

Learning for informative path planning  

E-print Network

Through the combined use of regression techniques, we will learn models of the uncertainty propagation efficiently and accurately to replace computationally intensive Monte- Carlo simulations in informative path planning. ...

Park, Sooho, S.M. Massachusetts Institute of Technology

2008-01-01

209

Collaborative Authoring of Walden's Paths  

E-print Network

The World Wide Web contains rich collections of digital materials that can be used in education and learning settings. The collaborative authoring prototype of Walden's Paths targets two groups of users: educators and learners. From the perspective...

Li, Yuanling

2012-10-19

210

Morse theory in path space  

E-print Network

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

Yong Seung Cho; Soon-Tae Hong

2007-06-01

211

Formal language constrained path problems  

SciTech Connect

In many path finding problems arising in practice, certain patterns of edge/vertex labels in the labeled graph being traversed are allowed/preferred, while others are disallowed. Motivated by such applications as intermodal transportation planning, the authors investigate the complexity of finding feasible paths in a labeled network, where the mode choice for each traveler is specified by a formal language. The main contributions of this paper include the following: (1) the authors show that the problem of finding a shortest path between a source and destination for a traveler whose mode choice is specified as a context free language is solvable efficiently in polynomial time, when the mode choice is specified as a regular language they provide algorithms with improved space and time bounds; (2) in contrast, they show that the problem of finding simple paths between a source and a given destination is NP-hard, even when restricted to very simple regular expressions and/or very simple graphs; (3) for the class of treewidth bounded graphs, they show that (i) the problem of finding a regular language constrained simple path between source and a destination is solvable in polynomial time and (ii) the extension to finding context free language constrained simple paths is NP-complete. Several extensions of these results are presented in the context of finding shortest paths with additional constraints. These results significantly extend the results in [MW95]. As a corollary of the results, they obtain a polynomial time algorithm for the BEST k-SIMILAR PATH problem studied in [SJB97]. The previous best algorithm was given by [SJB97] and takes exponential time in the worst case.

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

1997-07-08

212

Short paths in expander graphs  

SciTech Connect

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

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

1996-12-31

213

Partnership for Advancing Technologies in Housing (PATH)  

NSF Publications Database

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

214

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

215

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

NASA Technical Reports Server (NTRS)

The release of magnetospheric electrons from Jupiter into interplanetary space is modulated by the Jovian rotation period. The Voyager 1 and 2 observations showed that the modulation period agrees on the average with the synodic period of Jupiter (9h 55m 33.12s), but over intervals of weeks it can differ from the synodic period by several minutes. The lack of exact synchronization is attributed to changes of the plasma population in the Jovian magnetosphere. The Jovian modulation appears to be a persistent feature of the interaction between the solar wind and the magnetosphere and the disappearance of the modulation away from Jupiter is attributed to interplanetary propagation conditions. This leads to the following limits on the diffuse coefficient for interplanetary electrons: kappa perpendicular is or = 8 x 10 to the 19th power sq cm/s and kappa parallel is or = 10 to the 21st power sq cm/s. Modulation was still detectable at 3.8 A.U. behind Jupiter in the far magnetotail. This requires a mean free path in the tail 0.75 A.U. and good field connection along the tail to Jupiter.

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

1982-01-01

216

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

NASA Astrophysics Data System (ADS)

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(? /?)2, where ? is the characteristic diffusion length and ? 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 (?c) and the threshold electric field (EBD) for plasma initiation. The essential features of cyclotron resonance manifested as a sharp drop in ?c, lowering of EBD and enhanced electron energy gain is well reproduced in the constrained random walk.

Bhattacharjee, Sudeep; Dey, Indranuj; Paul, Samit

2013-04-01

217

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

218

Experimental Path Loss Models for Wireless Sensor Networks  

Microsoft Academic Search

Energy conservation is critical in Wireless Sensor Networks. Replacing or recharging batteries is not an option for sensors deployed in hostile environments. Generally communication electronics in the sensor utilizes most energy. This paper studies the effect of changing the transmission power and baud rate on transmission distance. Using Shannon channel capacity formula and Log - Distance Path Loss Model, transmission

Rahul P. Sawant; Qilian Liang; Dan O. Popa; Frank L. Lewis

2007-01-01

219

Gas-path seal technology  

NASA Technical Reports Server (NTRS)

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

Zuk, J.

1976-01-01

220

APEX: An Adaptive Path Index for XML Data Chin-Wan Chung  

E-print Network

for the next generation Web applications including electronic commerce and intelligent Web searching. XML data or path indexes can speed up query evaluation on XML data by restricting the search to only relevantAPEX: An Adaptive Path Index for XML Data Chin-Wan Chung Div. of Computer Science Dept. of EECS

Chung, Chin-Wan

221

Path Abstraction for Combined Navigation and Animation  

NASA Astrophysics Data System (ADS)

Natural motion of virtual characters is crucial in games and simulations. The quality of such motion strongly depends on the path the character walks and the animation of the character locomotion. Therefore, much work has been done on path planning and character animation. However, the combination of both fields has received less attention. Combining path planning and motion synthesis introduces several problems. A path generated by a path planner is often a simplification of the character movement. This raises the question which (body) part of the character should follow the path generated by the path planner and to what extent it should closely follow the path. We will show that enforcing the pelvis to follow the path will lead to unnatural animations and that our proposed solution, using path abstractions, generates significantly better animations.

van Basten, Ben J. H.; Egges, Arjan

222

Crack Path Selection Fatigue crack path imaged via SEM  

E-print Network

phases fail in a brittle manner Fatigue Crack Growth ABSTRACT Advanced aerospace materials continue Crack path selects secondary phases and interface Conclusions ·Nb-Si Alloys tested exhibited toughness at high temperatures. An important property of any high temperature aerospace engineering material is its

Rollins, Andrew M.

223

Multiple paths in complex tasks  

NASA Technical Reports Server (NTRS)

The relationship between utility judgments of subtask paths and the utility of the task as a whole was examined. The convergent validation procedure is based on the assumption that measurements of the same quantity done with different methods should covary. The utility measures of the subtasks were obtained during the performance of an aircraft flight controller navigation task. Analyses helped decide among various models of subtask utility combination, whether the utility ratings of subtask paths predict the whole tasks utility rating, and indirectly, whether judgmental models need to include the equivalent of cognitive noise.

Galanter, Eugene; Wiegand, Thomas; Mark, Gloria

1987-01-01

224

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

PubMed

This study aimed to compare cyclic fatigue and torsional resistances of glide path creating instruments with different tapers and tip sizes. Two sizes (G1 and G2) from G-File system and three sizes (PathFile #1, #2, and #3) from PathFile system were used for torsional resistance and cyclic fatigue resistance tests (n?=?10). The torsional resistance was evaluated at 2-, 3-, 4-, 5-, and 6-mm from the file tip by plotting the torsional load changes until fracture by rotational loading of 2?rpm. The cyclic fatigue resistance was compared by measuring the number of cycles to failure. Data were analyzed statistically using one-way ANOVA and Duncan's post-hoc comparison. The length of the fractured file fragment was also measured. All fractured fragments were observed under a scanning electron microscope (SEM). Although G-2 file showed a lower torsional strength than PathFile #3 at 2- and 3-mm levels (p??0.05). The smaller files of each brand had a significantly higher cyclic fatigue resistance than the bigger ones (p?PathFile #1 and #2 had higher fatigue resistances than G-files (p?PathFile #3, G-2 showed the lowest and PathFile #1 showed the highest resistances among the tested groups (p?path with minimal risk of fracture. SCANNING 36:500-506, 2014. © 2014 Wiley Periodicals, Inc. PMID:24737525

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

2014-09-01

225

The Routing Continuum from Shortest-path to All-path: A Unifying Theory  

E-print Network

The Routing Continuum from Shortest-path to All-path: A Unifying Theory Yanhua Li, Zhi-Li Zhang of data and sensor networks, routing strategies such as shortest-path, multi-path and potential-based ("all-path") routing have been developed. Based on the connection between routing and flow optimization

Boley, Daniel

226

COMPUTER SCIENCE: MISCONCEPTIONS, CAREER PATHS  

E-print Network

Undergraduate Student) #12;Computer Science Misconceptions Intro to Computer Science - Florida International much can I make out of college? Data from the Bureau of Labor Statistics #12;Computer ScienceCOMPUTER SCIENCE: MISCONCEPTIONS, CAREER PATHS AND RESEARCH CHALLENGES School of Computing

Hristidis, Vagelis

227

The Path of Human Evolution  

Microsoft Academic Search

A complex series of evolutionary steps, contingent upon a dynamic environmental context and a long biological heritage, have led to the ascent of Homo sapiens as a dominant component of the modern biosphere. In a field where missing links still abound and new discoveries regularly overturn theoretical paradigms, our understanding of the path of human evolution has made tremendous advances

C. S. Feibel

2004-01-01

228

Advances in steam path technology  

Microsoft Academic Search

For many years, GE has been conducting research to understand better the loss mechanisms that degrade the aerodynamic performance of steam turbine stages, and to develop new computational fluid dynamics (CFD) computer programs to predict these losses accurately. This paper describes a number of new steam path design features that have been introduced in the GE steam turbine product line

John I. Cofer; J. I. IV

1996-01-01

229

Commercializing Biorefineries The Path Forward  

E-print Network

Commercializing Biorefineries The Path Forward Bioenergy ExCo 59 Workshop Golden, CO Lawrence J/R&DFocus Timeframe for R&D Successes & Commercialization 2006 200920082007 20112010 2012: R&D on bench and pilot for commercial demonstration projects 2006: Announced loan guarantee program for projects employing new energy

230

On the Shortest Path Game  

E-print Network

Sep 19, 2014 ... tree, whose child nodes are all leaves, the associated player can reach a decision by simply ... moved to its parent node. In this way, we can ... towards t, since the cost of the path from s to v does not influence the decision in v.

2014-09-19

231

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...

232

Immigration: Rubio's path to presidency?  

E-print Network

Immigration: Rubio's path to presidency? In media blitz retorting conservative critics, he aims Writer Of the four Democratic and four Republican senators who wrote the immigration reform proposal now, both in Congress and nationwide, need more convincing on immigration reform than Democrats. And Rubio

Fernandez, Eduardo

233

Career Paths of Academic Deans.  

ERIC Educational Resources Information Center

This paper examines various career paths leading to deanship and considers the implications of the findings for women and minorities who aspire to this position. The paper is part of a larger study of academic deanship conducted by the Center for Academic Leadership at Washington State University between October 1996 and January 1997. Data for the…

Wolverton, Mimi; Gonzales, Mary Jo

234

A triangular path inverting interferometer  

Microsoft Academic Search

A triangular path inverting interferometer is described with application to the study of thermal 'schlieren'. This is practically free of any vibration and coherence troubles, and possesses the unique feature that either differential or total shear may be obtained only with proper positioning of the object; once aligned, the optical components need not be disturbed further. This simple and stable

D. Chakrabarti; S. P. Basu; M. De

1977-01-01

235

NPRE at Illinois Three Paths  

E-print Network

production; Nuclear power operations and control � Plasma sciences; Applied plasma physics; Nuclear fusionNPRE at Illinois Three Paths Students choose from three concentrations: � Plasma and Fusion � Power and interactions of radiation with matter � Applications of nuclear processes � Nuclear fission for electric power

Gilbert, Matthew

236

Spreading paths in partially observed social networks.  

PubMed

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

Onnela, Jukka-Pekka; Christakis, Nicholas A

2012-03-01

237

Spreading paths in partially observed social networks  

PubMed Central

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

Onnela, Jukka-Pekka; Christakis, Nicholas A.

2012-01-01

238

Spreading paths in partially observed social networks  

NASA Astrophysics Data System (ADS)

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

Onnela, Jukka-Pekka; Christakis, Nicholas A.

2012-03-01

239

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

240

Path Integral Methods in the Su–Schrieffer–Heeger Polaron Problem  

Microsoft Academic Search

I propose a path integral description of the Su–Schrieffer–Heeger Hamiltonian, both in one and two dimensions, after mapping\\u000a the real space model onto the time scale. While the lattice degrees of freedom are classical functions of time and are integrated\\u000a out exactly, the electron particle paths are treated quantum mechanically. The method accounts for the variable range of the\\u000a electronic

Marco Zoli

2007-01-01

241

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

242

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

243

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

244

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

245

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

DOEpatents

An IREB is guided through a curved path by ionizing a channel in a gas with electrons from a filament, and confining the electrons to the center of the path with a magnetic field extending along the path. The magnetic field is preferably generated by a solenoid extending along the path.

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

1988-01-01

246

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

247

A numerical model and scaling relationship for energetic electron beams propagating in air  

SciTech Connect

Scaling relationships for energy loss and scattering are combined with a particle code to construct a purely algebraic expression for the energy deposited by an energetic electron beam injected into field-free homogeneous air. An algebraic formulation is possible because the mean free paths for the major collisional processes depend similarly on density and energy above 1 keV. Accordingly, the spatial behavior of an initially cold pencil beam is approximately self-similar when expressed in terms of the nominal beam range, provided the beam energy at injection exceeds several keV. Since a warm and broad beam can always be decomposed into a series of cold pencil beams, the total energy deposited can be obtained through a simple sum. With such a model, the ionization and excitation generated by a beam can be computed quickly and easily at every point in space. Similar formulations can be developed for other media using particle codes or experimental data. In liquids or solids, the energy deposited is quickly converted to heat and ultimately to melting and/or vaporization of the material.

Fernsler, R. F.; Slinker, S. P. [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375 (United States); Lambrakos, S. G. [Materials Science and Technology Division, Naval Research Laboratory, Washington, DC 20375 (United States)

2008-09-15

248

Shortest Paths for Disc Obstacles  

Microsoft Academic Search

\\u000a Given a number of obstacles in a plane, the problem of computing a geodesic (or the shortest path) between two points has\\u000a been studied extensively. However, the case where the obstacles are circular discs has not been explored as much as it deserves.\\u000a In this paper, we present an algorithm to compute a geodesic among a set of mutually disjoint

Deok-soo Kim; Kwangseok Yu; Youngsong Cho; Donguk Kim; Chee-keng Yap

2004-01-01

249

Path integral on star graph  

NASA Astrophysics Data System (ADS)

In this paper we study path integral for a single spinless particle on a star graph with N edges, whose vertex is known to be described by U(N) family of boundary conditions. After carefully studying the free particle case, both at the critical and off-critical levels, we propose a new path integral formulation that correctly captures all the scale-invariant subfamily of boundary conditions realized at fixed points of boundary renormalization group flow. Our proposal is based on the folding trick, which maps a scalar-valued wave function on star graph to an N-component vector-valued wave function on half-line. All the parameters of scale-invariant subfamily of boundary conditions are encoded into the momentum independent weight factors, which appear to be associated with the two distinct path classes on half-line that form the cyclic group Z2. We show that, when bulk interactions are edge-independent, these weight factors are generally given by an N-dimensional unitary representation of Z2. Generalization to momentum dependent weight factors and applications to worldline formalism are briefly discussed.

Ohya, Satoshi

2012-06-01

250

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

251

Path-Based, Randomized, Oblivious, Minimal Routing  

E-print Network

Path-based, Randomized, Oblivious, Minimal routing (PROM) is a family of oblivious, minimal, path-diverse routing algorithms especially suitable for Network-on-Chip applications with n x n mesh geometry. Rather than choosing ...

Cho, Myong Hyon

2009-01-01

252

CURRENT SHEET REGULATION OF SOLAR NEAR-RELATIVISTIC ELECTRON INJECTION HISTORIES  

SciTech Connect

We present a sample of three large near-relativistic (>50 keV) electron events observed in 2001 by both the ACE and the Ulysses spacecraft, when Ulysses was at high-northern latitudes (>60 Degree-Sign ) and close to 2 AU. Despite the large latitudinal distance between the two spacecraft, electrons injected near the Sun reached both heliospheric locations. All three events were associated with large solar flares, strong decametric type II radio bursts and accompanied by wide (>212 Degree-Sign ) and fast (>1400 km s{sup -1}) coronal mass ejections (CMEs). We use advanced interplanetary transport simulations and make use of the directional intensities observed in situ by the spacecraft to infer the electron injection profile close to the Sun and the interplanetary transport conditions at both low and high latitudes. For the three selected events, we find similar interplanetary transport conditions at different heliolatitudes for a given event, with values of the mean free path ranging from 0.04 AU to 0.27 AU. We find differences in the injection profiles inferred for each spacecraft. We investigate the role that sector boundaries of the heliospheric current sheet (HCS) have on determining the characteristics of the electron injection profiles. Extended injection profiles, associated with coronal shocks, are found if the magnetic footpoints of the spacecraft lay in the same magnetic sector as the associated flare, while intermittent sparse injection episodes appear when the spacecraft footpoints are in the opposite sector or a wrap in the HCS bounded the CME structure.

Agueda, N.; Sanahuja, B. [Departament d'Astronomia i Meteorologia, Institut de Ciencies del Cosmos, Universitat de Barcelona (Spain); Vainio, R. [Department of Physics, University of Helsinki (Finland); Dalla, S. [Jeremiah Horrocks Institute, University of Central Lancashire (United Kingdom); Lario, D. [Applied Physics Laboratory, Johns Hopkins University (United States)

2013-03-10

253

Data-path layout design inside SOC  

Microsoft Academic Search

As more data-path stacks are integrated into system-on-a-chip (SOC), data-path is becoming a critical part of the whole giga-scale integrated circuits (GSI) design. The traditional layout design methodology can not satisfy the data-path performance requirements because it has no knowledge of the data-path bit-sliced structure and the strict performance (such as timing, coupling, and crosstalk) constraints. In this paper, we

Tong Jing; Xian-Long Hong; Yi-Ci Cai; Jing-Yu Xu; Chang-Qi Yang; Yi-Qian Zhang; Qiang Zhou; Weimin Wu

2002-01-01

254

Multiple Paths to Encephalization and Technical Civilizations  

NASA Astrophysics Data System (ADS)

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

Schwartzman, David; Middendorf, George

2011-12-01

255

Functional Equivalence and Spatial Path Memory  

Microsoft Academic Search

Loomis, Klatzky, Avraamides, Lippa & Golledge (2007) suggest that, when it comes to spatial information, verbal description and perceptual experience are nearly functionally equivalent with respect to the cognitive representations they produce. We tested this idea for the case of spatial memory for complex paths. Paths consisted entirely of unit-length segments followed by 90-degree turns, thus assuring that a path

Don R. Lyon; Glenn M. Gunzelmann

2011-01-01

256

The Shortest Path Problem Under Partial Monitoring  

Microsoft Academic Search

Abstract. The on-line shortest path problem is considered under partial monitoring scenarios. At each round, a decision maker has to choose a path between two distinguished vertices of a weighted directed acyclic graph whose edge weights can change in an arbitrary (adversarial) way such that the loss of the chosen path (dened as the sum of the weights of its

András György; Tamás Linder; György Ottucsák

2006-01-01

257

Free Space Path Loss of UWB Communications  

Microsoft Academic Search

Although the Friis' formula is widely used to calculate the free space path loss of narrowband communications, it is considered only single frequency. Therefore, it should be extended to calculate the free space path loss of ultra wideband (UWB) communications by considering the frequency bandwidth. In this paper, the free space path loss of UWB communications is studies. The Friis'

Pichaya Supanakoon; Sathit Aroonpraparat; Sathaporn Promwong; Jun-ichi Takada

258

Path and Trajectory Diversity Theory and Algorithms  

E-print Network

Path and Trajectory Diversity Theory and Algorithms Ross A. Knepper International Conference and Kuffner, SIGGRAPH, 2006] Introduction ConclusionResultsAlgorithmsApproach Theory #12;R.A. Knepper PathResultsAlgorithmsApproach Theory #12;R.A. Knepper Path and Trajectory Diversity 4 Diversity Spectrum Easy to increase diversity

Branicky, Michael S.

259

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

260

Transition Path Theory E. Vanden-Eijnden  

E-print Network

Transition Path Theory E. Vanden-Eijnden Courant Institute of Mathematical Sciences, New York University New York, NY 10012 eve2cims.nyu.edu Eric Vanden-Eijnden E. Vanden-Eijnden: Transition Path Theory State Theory (TST) and Transition Path Sampling (TPS). . . . . . . . . . . . . . . . . . . . . . 455 6

Van Den Eijnden, Eric

261

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

E-print Network

Born­Oppenheimer invariants along nuclear configuration paths Roi Baera) Department of Physical of the wave function. This is done for each calculated state at each nuclear position. Thus he defines a Born to an arbitrary path in nuclear configuration space. We identify invariant electronic states along these paths

Baer, Roi

262

Evolutionary path of UHF secondary imagery dissemination systems (SIDS)  

Microsoft Academic Search

Secondary imagery dissemination (SID) is the process of post-collection and electronic dissemination of digital imagery and associated data. SID systems (SIDS) provide exploited, non-original, annotated, anonymous-source imagery from intelligence, fusion, and dissemination centers. Ultra-high frequency (UHF) operation penetrates double-canopy jungle or heavy rain to provide imagery from an INTEL center to highly-mobile tactical users. The evolutionary path of UHF SIDS

Ernie Franke

2000-01-01

263

Attention trees and semantic paths  

NASA Astrophysics Data System (ADS)

In the last few decades several techniques for image content extraction, often based on segmentation, have been proposed. It has been suggested that under the assumption of very general image content, segmentation becomes unstable and classification becomes unreliable. According to recent psychological theories, certain image regions attract the attention of human observers more than others and, generally, the image main meaning appears concentrated in those regions. Initially, regions attracting our attention are perceived as a whole and hypotheses on their content are formulated; successively the components of those regions are carefully analyzed and a more precise interpretation is reached. It is interesting to observe that an image decomposition process performed according to these psychological visual attention theories might present advantages with respect to a traditional segmentation approach. In this paper we propose an automatic procedure generating image decomposition based on the detection of visual attention regions. A new clustering algorithm taking advantage of the Delaunay- Voronoi diagrams for achieving the decomposition target is proposed. By applying that algorithm recursively, starting from the whole image, a transformation of the image into a tree of related meaningful regions is obtained (Attention Tree). Successively, a semantic interpretation of the leaf nodes is carried out by using a structure of Neural Networks (Neural Tree) assisted by a knowledge base (Ontology Net). Starting from leaf nodes, paths toward the root node across the Attention Tree are attempted. The task of the path consists in relating the semantics of each child-parent node pair and, consequently, in merging the corresponding image regions. The relationship detected in this way between two tree nodes generates, as a result, the extension of the interpreted image area through each step of the path. The construction of several Attention Trees has been performed and partial results will be shown.

Giusti, Christian; Pieroni, Goffredo G.; Pieroni, Laura

2007-02-01

264

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

265

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

266

Communication path for extreme environments  

NASA Technical Reports Server (NTRS)

Methods and systems for using one or more radio frequency identification devices (RFIDs), or other suitable signal transmitters and/or receivers, to provide a sensor information communication path, to provide location and/or spatial orientation information for an emergency service worker (ESW), to provide an ESW escape route, to indicate a direction from an ESW to an ES appliance, to provide updated information on a region or structure that presents an extreme environment (fire, hazardous fluid leak, underwater, nuclear, etc.) in which an ESW works, and to provide accumulated thermal load or thermal breakdown information on one or more locations in the region.

Jorgensen, Charles C. (Inventor); Betts, Bradley J. (Inventor)

2010-01-01

267

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

268

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

269

Verification of surface polarity of O-face ZnO(0 0 0 1\\OverBar) by quantitative modeling analysis of Auger electron spectroscopy  

NASA Astrophysics Data System (ADS)

Is crystalline ZnO(0 0 0 1¯) O-face surface believed to be enriched by Zn atoms? This study may get the answer. We proposed a simplified model to simulate surface concentration ratio on (0 0 0 1¯)-O or (0 0 0 1)-Zn surface based on the hard-sphere model. The simulation ratio was performed by integrating electron signals from the assumed Auger emission, in which the electron mean free path and relative atomic layer arrangements inside the different polarity ZnO crystal surface were considered as relevant parameters. After counting more than 100 experimental observations of Zn/O ratios, the high frequency peak ratio was found at around 0.428, which was near the value predicted by the proposed model using the IMFP database. The ratio larger than the peak value corresponds to that observed in the annealed samples. A downward trend of the ratio evaluated on the post-sputtering sample indicates the possibility of a Zn-enriched phase appearing on the annealed O-face surface. This phenomenon can further elucidate the O-deficiency debate on most ZnO materials.

Su, C. W.; Huang, M. S.; Tsai, T. H.; Chang, S. C.

2012-12-01

270

Mechanism of bifurcation along the reaction path: An application in the case of thioformaldehyde  

Microsoft Academic Search

The mechanism of bifurcation along the reaction path on an adiabatic potential surface is discussed in terms of the second-order Jahn–Teller (SOJT) effect. From the viewpoint of this SOJT effect, bifurcation occurs due to the mixing of the nearest nontotally symmetric electronic excited state into the electronic ground state through a molecular vibration belonging to the same nontotal symmetry. Thus,

Tetsuya Taketsugu; Tsuneo Hirano

1993-01-01

271

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

272

Intricacies of quantum computational paths  

NASA Astrophysics Data System (ADS)

Graph search represents a cornerstone in computer science and is employed when the best algorithmic solution to a problem consists in performing an analysis of a search space representing computational possibilities. Typically, in such problems it is crucial to determine the sequence of transitions performed that led to certain states. In this work we discuss how to adapt generic quantum search procedures, namely quantum random walks and Grover's algorithm, in order to obtain computational paths. We then compare these approaches in the context of tree graphs. In addition we demonstrate that in a best-case scenario both approaches differ, performance-wise, by a constant factor speedup of two, whilst still providing a quadratic speedup relatively to their classical equivalents. We discuss the different scenarios that are better suited for each approach.

Tarrataca, Luís; Wichert, Andreas

2013-02-01

273

The Logic behind Feynman's Paths  

E-print Network

The classical notions of continuity and mechanical causality are left in order to refor- mulate the Quantum Theory starting from two principles: I) the intrinsic randomness of quantum process at microphysical level, II) the projective representations of sym- metries of the system. The second principle determines the geometry and then a new logic for describing the history of events (Feynman's paths) that modifies the rules of classical probabilistic calculus. The notion of classical trajectory is replaced by a history of spontaneous, random an discontinuous events. So the theory is reduced to determin- ing the probability distribution for such histories according with the symmetries of the system. The representation of the logic in terms of amplitudes leads to Feynman rules and, alternatively, its representation in terms of projectors results in the Schwinger trace formula.

Edgardo T. Garcia Alvarez

2010-11-22

274

Choosing Your Geosciences Career Path  

NASA Astrophysics Data System (ADS)

There are many possibilities for rewarding careers in the geosciences including positions in academia, government, industry, and other parts of the private sector. How do you choose the right path to meet your goals and needs and find the right career? What are the tradeoffs and strategic moves that you should make at different stages in your career? Some of the pros and cons between soft-money research, government research, and management and industry positions are discussed from a personal perspective. In addition this presentation will provide some perspective on different career choices as seen by program managers in funding agencies. The competing priorities between work life and private life are discussed with the some thoughts on compromising between "having it all" and finding what works for you.

Paluszkiewicz, T.

2002-12-01

275

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

276

Spatial profiles of electron and metastable atom densities in positive polarity fast ionization waves sustained in helium  

NASA Astrophysics Data System (ADS)

Fast ionization waves (FIWs), often generated with high voltage pulses over nanosecond timescales, are able to produce large volumes of ions and excited states at moderate pressures. The mechanisms of FIW propagation were experimentally and computationally investigated to provide insights into the manner in which these large volumes are excited. The two-dimensional structure of electron and metastable densities produced by short-pulse FIWs sustained in helium were measured using laser-induced fluorescence and laser collision-induced fluorescence diagnostics for times of 100-120 ns after the pulse, as the pressure was varied from 1 to 20 Torr. A trend of center-peaked to volume-filling to wall-peaked electron density profiles was observed as the pressure was increased. Instantaneous FIW velocities, obtained from plasma-induced emission, ranged from 0.1 to 3 × 109 cm s-1, depending on distance from the high voltage electrode and pressure. Predictions from two-dimensional modeling of the propagation of a single FIW correlated well with the experimental trends in electron density profiles and wave velocity. Results from the model show that the maximum ionization rate occurs in the wavefront, and the discharge continues to propagate forward after the removal of high voltage from the powered electrode due to the potential energy stored in the space charge. As the pressure is varied, the radial distribution of the ionization rate is shaped by changes in the electron mean free path, and subsequent localized electric field enhancement at the walls or on the centerline of the discharge.

Weatherford, Brandon R.; Xiong, Zhongmin; Barnat, E. V.; Kushner, Mark J.

2014-09-01

277

Tunneling investigation of the electron scattering effect on the momentum-dependent energy gap distribution in MgB2  

NASA Astrophysics Data System (ADS)

We have studied the effect of electron scattering on the momentum-dependent energy gap distributions in MgB2 by measuring planar tunnel junctions made from epitaxial MgB2 thin films on different substrates, of different thicknesses, with different junction interface properties, and different counter-electrode materials. The phonon features in the tunneling spectra indicated that the native oxide barrier is mainly MgO with estimated barrier thickness ranging from 1.1 to 1.5 nm and the average barrier height from 1.7 to 2.6 eV. When tunneling into the ab-plane occurred in very clean films, both the ? (˜1.8 meV) and ? (˜7.2 meV) gaps were observed with fine structures in the conductance peaks, indicating a distribution of gap values due to anisotropic electron-phonon interaction. The ? gap was enhanced (˜7.9 meV) in MgB2 thin films on SiC substrates which had Tc values over 40 K due to epitaxial tensile strain. As the MgB2 film thickness decreased from 100 nm to 33 nm, the ? gap distribution range was narrowed from ˜1.7 meV to ˜1.4 meV, and the fine peak structures disappeared due to the reduced electron mean free path limited by the film thickness. The fine peak structures were also gradually smeared out when the junction resistance increased. The results show that the electron scattering, either from the MgB2 film or the junction interface or barrier, can smear out the gap distribution structures in the tunneling spectra. Deterioration of the MgB2 film surface was also found to cause an increase in the ? gap value, likely due to an enhancement of interband scattering.

Dai, Wenqing; Chen, Ke; Xi, X. X.; Li, Qi

2013-02-01

278

The Feynman Path Integral: An Historical Slice  

E-print Network

Efforts to give an improved mathematical meaning to Feynman's path integral formulation of quantum mechanics started soon after its introduction and continue to this day. In the present paper, one common thread of development is followed over many years, with contributions made by various authors. The present version of this line of development involves a continuous-time regularization for a general phase space path integral and provides, in the author's opinion at least, perhaps the optimal formulation of the path integral.

John R. Klauder

2003-03-07

279

Maximum Flux Transition Paths of Conformational Change  

PubMed Central

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.

2010-01-01

280

The path integral for dendritic trees  

Microsoft Academic Search

We construct the path integral for determining the potential on any dendritic tree described by a linear cable equation. This is done by generalizing Brownian motion from a line to a tree. We also construct the path integral for dendritic structures with spatially-varying and\\/or time-dependent membrane conductivities due, for example, to synaptic inputs. The path integral allows novel computational techniques

L. F. Abbott; Edward Farhi; Sam Gutmann

1991-01-01

281

Generalized path dependent representations for gauge theories  

SciTech Connect

A set of differential operators acting by continuous deformations on path dependent functionals of open and closed curves is introduced. Geometrically, these path operators are interpreted as infinitesimal generators of curves in the base manifold of the gauge theory. They furnish a representation with the action of the group of loops having a fundamental role. We show that the path derivative, which is covariant by construction, satisfies the Ricci and Bianchi identities. Also, we provide a geometrical derivation of covariant Taylor expansions based on particular deformations of open curves. The formalism includes, as special cases, other path dependent operators such as end point derivatives and area derivatives.

Reyes, Marat C. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, 04510 Mexico D.F. (Mexico) and Universidad Tecnica Federico Santa Maria, Campus Santiago, C.P. 766-0251, Santiago (Chile)

2007-05-15

282

Generalized Path Dependent Representations for Gauge Theories  

E-print Network

A set of differential operators acting by continuous deformations on path dependent functionals of open and closed curves is introduced. Geometrically, these path operators are interpreted as infinitesimal generators of curves in the base manifold of the gauge theory. They furnish a representation with the action of the group of loops having a fundamental role. We show that the path derivative, which is covariant by construction, satisfies the Ricci and Bianchi identities. Also, we provide a geometrical derivation of covariant Taylor expansions based on particular deformations of open curves. The formalism includes, as special cases, other path dependent operators such as end point derivatives and area derivatives.

Marat C. Reyes

2006-11-15

283

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

284

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

285

Design and performance of an optical path cross-connect system based on wavelength path concept  

Microsoft Academic Search

This paper describes the system design and performance of an optical path cross-connect (OPXC) system based on wavelength path concept. The (OPXC) is designed to offer 16 sets of input and output fiber ports with each fiber transporting eight multiwavelength signals for optical paths. Each optical path has a capacity of 2.5 Gb\\/s. Consequently, the total system throughput is 8×16×2.5=320

Masafumi Koga; Yoshiyuki Hamazumi; Atsushi Watanabe; Satoru Okamoto; Hitoshi Obara; Ken-Ichi Sato; Masayuki Okuno; Senichi Suzuki

1996-01-01

286

Path planning by optimal-path-map construction for homogeneous-cost two-dimensional regions  

Microsoft Academic Search

Algorithms to construct optimal-path maps for single isolated homogeneous-cost convex-polygonal regions are discussed. Assuming the ability to construct optimal paths for a certain set of key points, a complete analysis is given of one of the four possible single-region situations, showing how to partition the map into regions of similar path behavior. An algorithm is then proposed for constructing optimal-path

Robert S. Alexander; Neil C. Rowe

1990-01-01

287

On the Representability of Arbitrary Path Sets as Shortest Paths: Theory, Algorithms, and Complexity  

Microsoft Academic Search

\\u000a The question, whether an optional set of routes can be represented as shortest paths, and if yes, then how, has been a rather\\u000a scarcely investigated problem up until now. In turn, an algorithm that, given an arbitrary set of traffic engineered paths,\\u000a can efficiently compute OSPF link weights as to map the given paths to shortest paths may be of

Gábor Rétvári; Róbert Szabó; József Bíró

2004-01-01

288

Path and Path Deviation Equations in Kaluza-Klein Type Theories  

E-print Network

Path and path deviation equations for charged, spinning and spinning charged objects in different versions of Kaluza-Klein (KK) theory using a modified Bazanski Lagrangian have been derived. The significance of motion in five dimensions, especially for a charged spinning object, has been examined. We have also extended the modified Bazanski approach to derive the path and path deviation equations of a test particle in a version of non-symmetric KK theory.

M. E. Kahil

2005-11-07

289

What is Electron Spin?  

E-print Network

distributed for no-profit educational & research purposes. Not for commercial use. An isolated static electron in free space is not a fixed particle at rest. It is always oscillating in a SHM in its own electromagnetic inertia field, rest frame even at zero kelvin temperature. This is non-thermal, standing wave, resonance Compton frequency, oscillation along a linear path or, along an elliptical or a circular (clockwise or anti-clockwise) path, corresponding to the electron’s intrinsic magnetic moment (spin up or spin down). An electron with spin behaves like a tiny magnet. Intrinsic spin does not imply that a subatomic particle is spinning like a toytop about its axis. A hypothetical electron without a charge is like the bob of a simple pendulum without a string. INTRINSIC SPIN & ORBITAL ANGULAR MOMENTUM

Kamal L Rajpal; Copyright Kamal; L Rajpal; All Rights; Reserved May

290

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

291

Path planning and path tracking control of unmanned ground vehicles (UGVs)  

Microsoft Academic Search

Unmanned ground vehicles (UGVs) will be playing increasingly important role in the future battlefields. How to automatically guide and control UGVs under varying environment conditions represents a challenging issue. This paper presents a novel approach to achieving path planning and path tracking of UGVs under dynamic environments. We apply the topology theory to find the optimal path given any starting

Liguo Weng; D. Y. Song

2005-01-01

292

A Continuous-State Version of Discrete Randomized Shortest-Paths, with Application to Path Planning  

E-print Network

are of capital importance in a variety of problems, from robot path planning, to maze solving. Path planning [16] is a well-known problem in the robotics community, described by [26] as "checking the consequences. This distribution, though peaked around optimal paths, let the random walker take a random transition according

Del Moral , Pierre

293

Optical Path Cross-Connect System Scale Evaluation Using Path Accommodation Design for Restricted Wavelength Multiplexing  

Microsoft Academic Search

The optical path (OP) technology, which employs both wavelength-division multiplexing and wavelength routing, will be the key to enhanced network integrity and an ubiquitous broadband integrated services digital network (B-ISDN) in the future. To construct the OP network, path accommodation design that can solve simultaneously the problems of path routing and wavelength assignment must be established. Since optical wavelengths are

Naohide Nagatsu; Satoru Okamoto; Ken-ichi Sato

1996-01-01

294

MODELING DENDRITIC SHAPES Using Path Planning  

E-print Network

the humble to the spectacular: lichens, coral, river systems, and lightning are all examples of naturally of objects exhibiting dendritic shape include lichens, coral, trees, lightning, rivers, crystals least-cost paths through the lattice. Multiple paths from a single starting location (or gen- erator

Mould, David

295

Shortest Paths in Microseconds Rachit Agarwal  

E-print Network

to compute and store a partial shortest path tree (PSPT) for each node. The PSPTs have the property to be an extremely small frac- tion of the entire network; hence, PSPTs can be stored efficiently and each shortest path can be computed ex- tremely quickly. For a real network with 5 million nodes and 69 mil- lion

296

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

297

Katrina'sPath Lake Pontchartrain  

E-print Network

miles to the west · Eye-wall pushes into Pearl River floodplain Impacts · Spillway overtopped into canal #12;Hudson'sPath Future Scenario Hurricane Hudson · Same Katrina path · Intensity increased 3 · 15mph forward speed Jourdan River Basin Pearl River Basin Rolls Royce Test Complex Building 1100

298

Extremal paths on a random Cayley tree  

Microsoft Academic Search

We investigate the statistics of extremal path(s) (both the shortest and the longest) from the root to the bottom of a Cayley tree. The lengths of the edges are assumed to be independent identically distributed random variables drawn from a distribution rho(l). Besides, the number of branches from any node is also random. Exact results are derived for arbitrary distribution

Satya N. Majumdar; P. L. Krapivsky

2000-01-01

299

Evaluation of Calcine Disposition Path Forward  

SciTech Connect

This document describes an evaluation of the baseline and two alternative disposition paths for the final disposition of the calcine wastes stored at the Idaho Nuclear Technology and Engineering Center at the Idaho National Engineering and Environmental Laboratory. The pathways are evaluated against a prescribed set of criteria and a recommendation is made for the path forward.

Birrer, S.A.; Heiser, M.B.

2003-02-26

300

Evaluation of Calcine Disposition - Path Forward  

SciTech Connect

This document describes an evaluation of the baseline and two alternative disposition paths for the final disposition of the calcine wastes stored at the Idaho Nuclear Technology and Engineering Center at the Idaho National Engineering and Environmental Laboratory. The pathways are evaluated against a prescribed set of criteria and a recommendation is made for the path forward.

Steve Birrer

2003-02-01

301

Bounding the error of path loss models  

Microsoft Academic Search

In this paper we analyze the efficacy of basic path loss models at predicting median path loss in urban environments. We attempt to bound the practical error of these models and look at how they may hinder practical wireless applications, and in particular dynamic spectrum access networks. This analysis is made using a large set of measurements from production networks

Caleb Phillips; Douglas Sicker; Dirk Grunwald

2011-01-01

302

Functional test generation for path delay faults  

Microsoft Academic Search

We present a novel test generation technique for path delay faults, based on the growth (G) and disappearance (D) faults of programmable logic arrays (PLA). The circuit is modeled as a PLA that is prime and irredundant with respect to every output. Certain tests for G faults, generated by using known efficient methods are transformed into tests for path delay

Mandyam-komar Srinivas; Vishwani D. Agrawal; Michael L. Bushnell

1995-01-01

303

Path-based control of smoke simulations  

Microsoft Academic Search

In this paper, we propose a novel path-based control method for generating realistic smoke animations. Our method allows an animator to specify a 3D curve for the smoke to follow. Path control is then achieved using a linear (closed) feedback loop to match the velocity field obtained from a 3D flow simulation with a target velocity field. The target velocity

Yootai Kim; Raghu Machiraju; David Thompson

2006-01-01

304

Protecting Location Privacy Through Path Confusion  

Microsoft Academic Search

We present a path perturbation algorithm which can maximize users? location privacy given a quality of service constraint. This work concentrates on a class of applications that continuously collect location samples from a large group of users, where just removing user identifiers from all samples is insufficient because an adversary could use trajectory information to track paths and follow users?

Baik Hoh; Marco Gruteser

2005-01-01

305

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.

306

Control-path Oriented Workflow Intelligence Analyses  

Microsoft Academic Search

This paper proposes two kinds of control-path oriented workflow knowledge analy- sis approaches which will be applied to a workflow intelligence and quality improve- ment framework aiming at the high degree of the workflow traceability and rediscover- ability. The framework needs two kinds of algorithms ? One is for generating the total sequences of the control-paths from a workflow model,

Minjae Park; Kwanghoon Kim

2008-01-01

307

Decision paths in complex tasks  

NASA Technical Reports Server (NTRS)

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

Galanter, Eugene

1991-01-01

308

Path integral for inflationary perturbations  

SciTech Connect

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

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

2010-07-15

309

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

310

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

311

Converging towards the optimal path to extinction  

PubMed Central

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

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

2011-01-01

312

A linearized Fokker-Planck study of ion-eigenmodes in an unmagnetized pair-ion-electron plasma  

SciTech Connect

Two kinds of ion-eigenmodes in an unmagnetized pair-ion-electron plasma, pair-ion-acoustic waves (PIAWs) and ion-Langmuir waves (ILWs), are investigated with Fokker-Planck description. The linearized negative- and positive-ion Fokker-Planck equations and linearized electron Vlasov equation are solved numerically as an eigenvalue problem. The frequencies and damping rates of PIAWs and ILWs are presented as a function of k{lambda}, k{lambda}{sub D}, T{sub e}/T, n{sub -}/n{sub +}, where k is the wave number, {lambda} is the mean-free path of the positive ion, {lambda}{sub D} is the positive ion Debye length, T{sub e} and T are electron and ion temperature, and n{sub -}/n{sub +} is the ratio of negative ion density to positive ion density. It is found that the dispersion relations of PIAWs and ILWs are sensitive to the strength of ion-ion collisions. As k{lambda} increases, it is shown that PIAWs evolve into ILWs smoothly at small negative ion concentration. For large n{sub -}/n{sub +}, PIAWs and ILWs, respectively, exist in a strong-collisional and rare-collisional region, and coexist in the intermediate regime at about k{lambda}{approx}1. For comparison, hydrodynamic description and Vlasov description are also discussed. When the Landau damping is negligible, the two-fluid hydrodynamic description can give good results for ILWs if the friction forces between the negative and positive ions are included.

Zhao Bin; Zheng Jian [CAS Key Laboratory of Basic Plasma Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China) and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2008-08-15

313

All-Optical Monitoring Path Computation Using Lower Bounds of Required Number of Paths  

NASA Astrophysics Data System (ADS)

To reduce the cost of fault management in all-optical networks, it is a promising approach to detect the degradation of optical signal quality solely at the terminal points of all-optical monitoring paths. The all-optical monitoring paths must be routed so that all single-link failures can be localized using route information of monitoring paths where signal quality degradation is detected. However, route computation for the all-optical monitoring paths that satisfy the above condition is time consuming. This paper proposes a procedure for deriving the lower bounds of the required number of monitoring paths to localize all single-link failures, and proposes an efficient monitoring path computation method based on the derived lower bounds. The proposed method repeats the route computation for the monitoring paths until feasible routes can be found, while the assumed number of monitoring paths increases, starting from the lower bounds. With the proposed method, the minimum number of monitoring paths with the overall shortest routes can be obtained quickly by solving several small-scale integer linear programming problems when the possible terminal nodes of monitoring paths are arbitrarily given. Thus, the proposed method can minimize the required number of monitors for detecting the degradation of signal quality and the total overhead traffic volume transferred through the monitoring paths.

Ogino, Nagao; Nakamura, Hajime

314

The Path of Human Evolution  

NASA Astrophysics Data System (ADS)

A complex series of evolutionary steps, contingent upon a dynamic environmental context and a long biological heritage, have led to the ascent of Homo sapiens as a dominant component of the modern biosphere. In a field where missing links still abound and new discoveries regularly overturn theoretical paradigms, our understanding of the path of human evolution has made tremendous advances in recent years. Two major trends characterize the development of the hominin clade subsequent to its origins with the advent of upright bipedalism in the Late Miocene of Africa. One is a diversification into two prominent morphological branches, each with a series of 'twigs' representing evolutionary experimentation at the species or subspecies level. The second important trend, which in its earliest manifestations cannot clearly be ascribed to one or the other branch, is the behavioral complexity of an increasing reliance on technology to expand upon limited inherent morphological specializations and to buffer the organism from its environment. This technological dependence is directly associated with the expansion of hominin range outside Africa by the genus Homo, and is accelerated in the sole extant form Homo sapiens through the last 100 Ka. There are interesting correlates between the evolutionary and behavioral patterns seen in the hominin clade and environmental dynamics of the Neogene. In particular, the tempo of morphological and behavioral innovation may be tracking major events in Neogene climatic development as well as reflecting intervals of variability or stability. Major improvements in analytical techniques, coupled with important new collections and a growing body of contextual data are now making possible the integration of global, regional and local environmental archives with an improved biological understanding of the hominin clade to address questions of coincidence and causality.

Feibel, C. S.

2004-12-01

315

An Analysis of Path-Vector Routing Protocol Convergence Algorithms  

Microsoft Academic Search

Today's Internet uses a path vector routing protocol, BGP, for global routing. After a connectivity change, a path vector protocol tends to explore a potentially large number of alternative paths before converging on new stable paths. Several techniques for improving path vector convergence have been proposed, however there has been no comparative analysis to judge the relative merit of each

Dan Pei; UCLA CSD; Beichuan Zhang; Dan Massey; Lixia Zhang

316

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

317

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

318

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

319

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

320

Transports along paths in Fibre Bundles. I. General Theory  

E-print Network

Transports along path in fibre bundles are axiomatically introduced. Their general functional form and some their simple properties are investigated. The relationships of the transports along paths and lifting of paths are studied.

Bozhidar Z. Iliev

2005-03-01

321

The Transition Temperature of a Thin Type II Superconductor in Contact with a Magnetic Metal.  

National Technical Information Service (NTIS)

Results of the dependence of the superconducting transition temperature on electronic mean free path in a thin alloy superconductor in contact with a ferromagnetic material are in agreement with the predictions of the linearized Ginzburg-Landau theory. (A...

R. P. Groff, R. D. Parks

1966-01-01

322

Nanoscale heat conduction with applications in nanoelectronics and thermoelectrics  

E-print Network

When the device or structure characteristic length scales are comparable to the mean free path and wavelength of energy carriers (electrons, photons, phonons, and molecules) or the time of interest is on the same order as ...

Yang, Ronggui, Ph. D. Massachusetts Institute of Technology

2006-01-01

323

Realistic Human Walking Paths David C. Brogan  

E-print Network

development for entertainment applications and many classes of simulations. We present a novel behav- ioral- served paths in black on the floor. A library exit (a) and a university hallway (b). A realistic walking

Brogan, David

324

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

325

Cooperative optimal path planning for herding problems  

E-print Network

destination following weighted time-optimal and effort-optimal control paths. Simulation of this herding problem is accomplished through dynamic programming by utilizing the SNOPT software in the MATLAB environment. The numerical solution gives us the optimal...

Lu, Zhenyu

2009-05-15

326

Path integration in relativistic quantum mechanics  

E-print Network

The simple physics of a free particle reveals important features of the path-integral formulation of relativistic quantum theories. The exact quantum-mechanical propagator is calculated here for a particle described by the simple relativistic action proportional to its proper time. This propagator is nonvanishing outside the light cone, implying that spacelike trajectories must be included in the path integral. The propagator matches the WKB approximation to the corresponding configuration-space path integral far from the light cone; outside the light cone that approximation consists of the contribution from a single spacelike geodesic. This propagator also has the unusual property that its short-time limit does not coincide with the WKB approximation, making the construction of a concrete skeletonized version of the path integral more complicated than in nonrelativistic theory.

Ian H. Redmount; Wai-Mo Suen

1992-10-28

327

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.

328

Predicting missing links via effective paths  

NASA Astrophysics Data System (ADS)

Recently, in complex network, link prediction has brought a surge of researches, among which similarity based link prediction outstandingly gains considerable success, especially similarity in terms of paths. In investigation of paths based similarity, we find that the effective influence of endpoints and strong connectivity make paths contribute more similarity between two unconnected endpoints, leading to a more accurate link prediction. Accordingly, we propose a so-called effective path index (EP) in this paper to leverage effective influence of endpoints and strong connectivity in similarity calculation. For demonstrating excellence of our index, the comparisons with six mainstream indices are performed on experiments in 15 real datasets and results show a great improvement of performance via our index.

Zhu, Xuzhen; Tian, Hui; Cai, Shimin

2014-11-01

329

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

330

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...

331

Identifying decohering paths in closed quantum systems  

NASA Technical Reports Server (NTRS)

A specific proposal is discussed for how to identify decohering paths in a wavefunction of the universe. The emphasis is on determining the correlations among subsystems and then considering how these correlations evolve. The proposal is similar to earlier ideas of Schroedinger and of Zeh, but in other ways it is closer to the decoherence functional of Griffiths, Omnes, and Gell-Mann and Hartle. There are interesting differences with each of these which are discussed. Once a given coarse-graining is chosen, the candidate paths are fixed in this scheme, and a single well defined number measures the degree of decoherence for each path. The normal probability sum rules are exactly obeyed (instantaneously) by these paths regardless of the level of decoherence. Also briefly discussed is how one might quantify some other aspects of classicality. The important role that concrete calculations play in testing this and other proposals is stressed.

Albrecht, Andreas

1990-01-01

332

Building a path in cell biology  

E-print Network

Setting up a new lab is an exciting but challenging prospect. We discuss our experiences in finding a path to tackle some of the key current questions in cell biology and the hurdles that we have encountered along the way.

Cheeseman, Iain McPherson

333

Non-classical paths in interference experiments  

E-print Network

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

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

2014-01-01

334

Nonclassical paths in quantum interference experiments.  

PubMed

In a double slit interference experiment, the wave function at the screen with both slits open is not exactly equal to the sum of the wave functions with the slits individually open one at a time. The three scenarios represent three different boundary conditions and as such, the superposition principle should not be applicable. However, most well-known text books in quantum mechanics implicitly and/or explicitly use this assumption that is only approximately true. In our present study, we have used the Feynman path integral formalism to quantify contributions from nonclassical paths in quantum interference experiments that provide a measurable deviation from a naive application of the superposition principle. A direct experimental demonstration for the existence of these nonclassical paths is difficult to present. We find that contributions from such paths can be significant and we propose simple three-slit interference experiments to directly confirm their existence. PMID:25279612

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

2014-09-19

335

Path length errors of VLBI antennas  

NASA Astrophysics Data System (ADS)

The performance of single dish radio antennas or telescopes is depending on the surface accuracy of the reflectors in the beam path and the focus/pointing errors induced by deviations/misalignment of the reflectors from a desired direction. For multiple dish VLBI arrays an additional mechanical effect, the path length stability, is a further source of performance degradation. For application at higher frequencies environmental influences as wind and temperature have to be considered additionally to the usually required manufacturing and alignment accuracies. Active measurement ("metrology") of the antenna deformations and their compensation by "active optics" (AO) respectively "flexible body compensation" (FBC) are established methods. For the path length errors AO or FBC are up to now not established methods. The paper describes how to handle the path length errors and the related metrology analogues to the established methods used for surface and focus/pointing error corrections.

Kaercher, Hans J.; Sust, Eberhard; Emde, Peter; Kühn, Jürgen

2010-07-01

336

A chemist building paths to cell biology.  

PubMed

Galileo is reported to have stated, "Measure what is measurable and make measurable what is not so." My group's trajectory in cell biology has closely followed this philosophy, although it took some searching to find this path. PMID:24174456

Weibel, Douglas B

2013-11-01

337

A chemist building paths to cell biology  

PubMed Central

Galileo is reported to have stated, “Measure what is measurable and make measurable what is not so.” My group's trajectory in cell biology has closely followed this philosophy, although it took some searching to find this path. PMID:24174456

Weibel, Douglas B.

2013-01-01

338

Nonclassical Paths in Quantum Interference Experiments  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

339

Unified classical path theories of pressure broadening  

Microsoft Academic Search

A unified classical path theory of pressure broadening is derived using only elementary concepts. It is shown that the theory of Smith, Cooper and Vidal is only correct at all frequencies to first order in the number density of perturbers.

C. Bottcher

1971-01-01

340

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...

341

Animation: Path of 2010 Solar Eclipse  

NASA Video Gallery

On Sunday, 2010 July 11, a total eclipse of the Sun is visible from within a narrow corridor that traverses Earth's southern hemisphere. The path of the Moon's umbral shadow crosses the South Pacif...

342

Potential energy surface exploration with equilibrial paths. Part I: Theory  

Microsoft Academic Search

The equilibrial path concept is further developed. Special attention is spent the symmetry conservation along equilibrial paths and symmetry-breaking. Symmetry-breaking can occur only at singular points. The simple singular points of an equilibrial path are valley–ridge inflection points. In contrast to the intrinsic reaction paths and the gradient extremal paths, the equilibrial paths enable to describe the branching of reaction

Wolfgang Kliesch

2000-01-01

343

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

344

Path Selection and Multipath Congestion Control  

Microsoft Academic Search

In this paper we investigate the potential benefits of coordinated congestion control for multipath data transfers, and contrast with uncoordinated control. For static random path selections, we show the worst-case throughput performance of uncoordinated control behaves as if each user had but a single path (scaling like log(log(N ))\\/ log(N ) where N is the system size, measured in number

Peter B. Key; Laurent Massoulié; Donald F. Towsley

2007-01-01

345

Path-integral formulation of ion heating  

SciTech Connect

A description of the generation and evolution of ionospheric oxygen-ion conic distributions by electromagnetic ion-cyclotron-resonance heating is formulated in terms of a path integral. All of the relevant physics is contained in this path integral, which may be used to calculate measurable properties of the conic distribution. Although the presentation is applied to this specific ionospheric context, the treatment may be generalized to treat other diffusion problems of interest.

Crew, G.B.; Chang, T.

1986-11-01

346

Steam Path Audits on Industrial Steam Turbines  

E-print Network

exhaust, fuel to heat the steam is not a direct cost to producing power in the steam turbine. Increasing turbine efficiency, therefore, benefits the Lyondell facility by increasing power output. DESCRIPTION OF THE STEAM PATH AUDIT The basic approach... National Industrial Energy Technology Conference, Houston, TX, April 22-23, 1992 ---------- ---------- steam path after the initial turbine inlet. The extraction valves cause a large pressure drop between the exhaust of stage 2 and the inlet to stage 3...

Mitchell, D. R.

347

Walden's Paths quiz: system design and implementation  

E-print Network

WAI. DEN'S PATHS QUIZ: SYSTEM DESIGN AND IMPLEMENTATION A Thesis by AVITAL JAYANT ARORA Submitted to the Offtce of Graduate Studies of Texas AJtM University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE... WAI. DEN'S PATHS QUIZ: SYSTEM DESIGN AND IMPLEMENTATION A Thesis by AVITAL JAYANT ARORA Submitted to the Offtce of Graduate Studies of Texas AJtM University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE...

Arora, Avital Jayant

2012-06-07

348

Extremal paths on a random Cayley tree  

Microsoft Academic Search

We investigate the statistics of extremal path(s) (both the shortest and the\\u000alongest) from the root to the bottom of a Cayley tree. The lengths of the edges\\u000aare assumed to be independent identically distributed random variables drawn\\u000afrom a distribution \\\\rho(l). Besides, the number of branches from any node is\\u000aalso random. Exact results are derived for arbitrary distribution

Satya N. Majumdar; P. L. Krapivsky

2000-01-01

349

Path Loss For Short Range Telemetry  

Microsoft Academic Search

The popular Friis transmission formula is used to evaluate the amount of path loss in free space between the transmit and\\u000a receive antennas for the design of wireless transceivers. It is could be also used to estimate the path loss for the link\\u000a of the on-body network when there is no barrier and no body surface in between. Paying special

Yong Liu; Kairaz Contractor; Yunjuan Kang

350

Landmobile satellite excess path loss measurements  

Microsoft Academic Search

This paper describes an experiment conducted with the ATS-6 satellite to determine the additional path loss over free-space loss experienced by land-mobile communication links. This excess path loss is measured as a function of (1) local environment, (2) vehicle heading, (3) link frequency, (4) satellite elevation angle, and (5) street side. An excess loss model developed from the data shows

Garry C. Hess

1979-01-01

351

Landmobile satellite excess path loss measurements  

Microsoft Academic Search

An experiment conducted with the ATS-6 satellite to determine the additional path loss over free-space loss experienced by land-mobile communication links is described. This excess path loss is measured as a function of 1) local environment, 2) vehicle heading, 3) link frequency, 4) satellite elevation angle, and 5) street side. A statistical description of excess loss developed from the data

GARRY C. HESS

1980-01-01

352

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. PMID:24039382

Zhou, Hua; Lange, Kenneth

2013-01-01

353

New England Forests: The Path to Sustainability  

E-print Network

New England Forests: The Path to Sustainability A R E P O R T B Y N E W E N G L A N D F O R E S T R Y F O U N D A T I O N #12;#12;New England Forests: The Path to Sustainability Forests define New tree in a town or state park? Forests are part of New Englanders' daily lives. Nearly all of us rely

Wolfe, Patrick J.

354

SNAPP: Stateless Network-Authenticated Path Pinning  

E-print Network

This paper examines a new building block for next-generation networks: SNAPP, or Stateless Network-Authenticated Path Pinning. SNAPP-enabled routers securely embed their routing decisions in the packet headers of a stream of traffic, effectively pinning a flow’s path between sender and receiver. A sender can use the pinned path (even if routes subsequently change) by including the path embedding in later packet headers. This architectural building block decouples routing from forwarding, which greatly enhances the availability of a path in the face of routing misconfigurations or malicious attacks. To demonstrate the extreme flexibility of SNAPP, we show how it can support a wide range of applications, including sender-controlled paths, expensive route lookups, sender anonymity, and sender accountability. Our analysis shows that SNAPP’s overhead is low, and the system is easily implemented in hardware. We believe that SNAPP is a worthy addition to the network architect’s toolbox, enabling a variety of new designs and trade-offs.

Bryan Parno; Adrian Perrig; Dave Andersen

2008-01-01

355

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

356

i-PI: A Python interface for ab initio path integral molecular dynamics simulations  

E-print Network

Recent developments in path integral methodology have significantly reduced the computational expense of including quantum mechanical effects in the nuclear motion in ab initio molecular dynamics simulations. However, the implementation of these developments requires a considerable programming effort, which has hindered their adoption. Here we describe i-PI, an interface written in Python that has been designed to minimise the effort required to bring state-of-the-art path integral techniques to an electronic structure program. While it is best suited to first principles calculations and path integral molecular dynamics, i-PI can also be used to perform classical molecular dynamics simulations, and can just as easily be interfaced with an empirical forcefield code. To give just one example of the many potential applications of the interface, we use it in conjunction with the CP2K electronic structure package to showcase the importance of nuclear quantum effects in high pressure water.

Ceriotti, Michele; Manolopoulos, David E

2014-01-01

357

Automatic alignment of double optical paths in excimer laser amplifier  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

358

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

SciTech Connect

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.

Pierleoni, C.; Ceperley, D.M.; Bernu, B.; Magro, W.R. (Laboratoire de Physique Theorique des Liquides, Universite Pierre Marie Curie, 4 Place Jussieu, 75252 Paris Cedex 05 (France) Centre Europeen de Calcul Atomique et Moleculaire, Ecole Normale Superieure, 46 Allee d'Italie, 69364 Lyon Cedex 07 (France) National Center for Supercomputing Applications, Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801 (United States))

1994-10-17

359

Choosing Internet Paths with High Bulk Transfer Capacity Jacob A. Strauss  

E-print Network

paper and electronic copies of this thesis and to grant others the right to do so. Author bandwidth TCP can achieve on a path between Internet hosts without performing extensive measurements. More the higher measured BTC. Methods tested include TCP loss rate models, an available bandwidth measuring tool

360

Noise propagation path identification of variable speed drive in time domain via common mode test mode  

Microsoft Academic Search

Electromagnetic Compatibility (EMC) debugging of power electronics systems depends heavily on the experience of specialists due to the complex mechanisms of electromagnetic noise. In this paper, the time domain approach is used instead of the conventional frequency domain method to identify noise propagation path. The proposed test mode switches the upper or lower transistors of the converter legs simultaneously on

D. Zhao; J. A. Ferreira; H. Polinder; A. Roc; F. B. J. Leferink

2008-01-01

361

Noise propagation path identification of variable speed drive in time domain via common mode test mode  

Microsoft Academic Search

Electromagnetic Compatibility (EMC) debugging of power electronics systems depends heavily on the experience of specialists due to the complex mechanisms of electromagnetic noise. In this paper, the time domain approach is used instead of the conventional frequency domain method to identify noise propagation path. The proposed test mode switches the upper or lower transistors of the converter legs simultaneously on

D. Zhao; J. A. Ferreira; H. Polinder; A. Roc'h; F. B. J. Leferink

2007-01-01

362

A CO2 laser scintillometer for C(2) sub n measurements over a many kilometer path  

Microsoft Academic Search

A CO2 laser scintillometer for the measurement of refractive index over pathlengths from 100 m to 10 km is described. Electronic adjustment procedures, calibration, and the operation region of the instrument are outlined. The scintillometer performs well in tests over path lengths of 449, 5900, and 9700 m.

W. Kohsiek

1985-01-01

363

Minimal entropy probability paths between genome families.  

PubMed

We develop a metric for probability distributions with applications to biological sequence analysis. Our distance metric is obtained by minimizing a functional defined on the class of paths over probability measures on N categories. The underlying mathematical theory is connected to a constrained problem in the calculus of variations. The solution presented is a numerical solution, which approximates the true solution in a set of cases called rich paths where none of the components of the path is zero. The functional to be minimized is motivated by entropy considerations, reflecting the idea that nature might efficiently carry out mutations of genome sequences in such a way that the increase in entropy involved in transformation is as small as possible. We characterize sequences by frequency profiles or probability vectors, in the case of DNA where N is 4 and the components of the probability vector are the frequency of occurrence of each of the bases A, C, G and T. Given two probability vectors a and b, we define a distance function based as the infimum of path integrals of the entropy function H( p) over all admissible paths p(t), 0 < or = t< or =1, with p(t) a probability vector such that p(0)=a and p(1)=b. If the probability paths p(t) are parameterized as y(s) in terms of arc length s and the optimal path is smooth with arc length L, then smooth and "rich" optimal probability paths may be numerically estimated by a hybrid method of iterating Newton's method on solutions of a two point boundary value problem, with unknown distance L between the abscissas, for the Euler-Lagrange equations resulting from a multiplier rule for the constrained optimization problem together with linear regression to improve the arc length estimate L. Matlab code for these numerical methods is provided which works only for "rich" optimal probability vectors. These methods motivate a definition of an elementary distance function which is easier and faster to calculate, works on non-rich vectors, does not involve variational theory and does not involve differential equations, but is a better approximation of the minimal entropy path distance than the distance //b-a//(2). We compute minimal entropy distance matrices for examples of DNA myostatin genes and amino-acid sequences across several species. Output tree dendograms for our minimal entropy metric are compared with dendograms based on BLAST and BLAST identity scores. PMID:15133624

Ahlbrandt, Calvin; Benson, Gary; Casey, William

2004-05-01

364

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

SciTech Connect

Purpose: In treatment planning of charged-particle radiotherapy, patient heterogeneity is conventionally modeled as variable-density water converted from CT images to best reproduce the stopping power, which may lead to inaccuracies in the handling of multiple scattering and nuclear interactions. Although similar conversions can be defined for these individual interactions, they would be valid only for specific CT systems and would require additional tasks for clinical application. This study aims to improve the practicality of the interaction-specific heterogeneity correction. Methods: The authors calculated the electron densities and effective densities for stopping power, multiple scattering, and nuclear interactions of protons and ions, using the standard elemental-composition data for body tissues to construct the invariant conversion functions. The authors also simulated a proton beam in a lung-like geometry and a carbon-ion beam in a prostate-like geometry to demonstrate the procedure and the effects of the interaction-specific heterogeneity correction. Results: Strong correlations were observed between the electron density and the respective effective densities, with which the authors formulated polyline conversion functions. Their effects amounted to 10% differences in multiple-scattering angle and nuclear interaction mean free path for bones compared to those in the conventional heterogeneity correction. Although their realistic effect on patient dose distributions would be generally small, it could be at the level of a few percent when a carbon-ion beam traverses a large bone. Conclusions: The present conversion functions are invariant and may be incorporated in treatment planning systems with a common function relating CT number to electron density. This will enable improved beam dose calculation while minimizing initial setup and quality management of the user's specific system.

Kanematsu, Nobuyuki; Inaniwa, Taku; Koba, Yusuke [Department of Accelerator and Medical Physics, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555 (Japan)

2012-02-15

365

Path analysis in genetic epidemiology: a critique.  

PubMed Central

Path analysis, a form of general linear structural equation models, is used in studies of human genetics data to discern genetic, environmental, and cultural factors contributing to familial resemblance. It postulates a set of linear and additive parametric relationships between phenotypes and genetic and cultural variables and then essentially uses the assumption of multivariate normality to estimate and perform tests of hypothesis on parameters. Such an approach has been advocated for the analysis of genetic epidemiological data by D. C. Rao, N. Morton, C. R. Cloninger, L. J. Eaves, and W. E. Nance, among others. This paper reviews and evaluates the formulations, assumptions, methodological procedures, interpretations, and applications of path analysis. To give perspective, we begin with a discussion of path analysis as it occurs in the form of general linear causal models in several disciplines of the social sciences. Several specific path analysis models applied to lipoprotein concentrations, IQ, and twin data are then reviewed to keep the presentation self-contained. The bulk of the critical discussion that follows is directed toward the following four facets of path analysis: (1) coherence of model specification and applicability to data; (2) plausibility of modeling assumptions; (3) interpretability and utility of the model; and (4) validity of statistical and computational procedures. In the concluding section, a brief discussion of the problem of appropriate model selection is presented, followed by a number of suggestions of essentially model-free alternative methods of use in the treatment of complex structured data such as occurs in genetic epidemiology. PMID:6349335

Karlin, S; Cameron, E C; Chakraborty, R

1983-01-01

366

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

367

Perfect discretization of reparametrization invariant path integrals  

SciTech Connect

To obtain a well-defined path integral one often employs discretizations. In the case of gravity and reparametrization-invariant systems, the latter of which we consider here as a toy example, discretizations generically break diffeomorphism and reparametrization symmetry, respectively. This has severe implications, as these symmetries determine the dynamics of the corresponding system. Indeed we will show that a discretized path integral with reparametrization-invariance is necessarily also discretization independent and therefore uniquely determined by the corresponding continuum quantum mechanical propagator. We use this insight to develop an iterative method for constructing such a discretized path integral, akin to a Wilsonian RG flow. This allows us to address the problem of discretization ambiguities and of an anomaly-free path integral measure for such systems. The latter is needed to obtain a path integral, that can act as a projector onto the physical states, satisfying the quantum constraints. We will comment on implications for discrete quantum gravity models, such as spin foams.

Bahr, Benjamin [DAMTP, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); MPI for Gravitational Physics, Am Muehlenberg 1, D-14476 Potsdam (Germany); Dittrich, Bianca; Steinhaus, Sebastian [MPI for Gravitational Physics, Am Muehlenberg 1, D-14476 Potsdam (Germany)

2011-05-15

368

PATHS: Analysis of PATH Duration Statistics and their Impact on Reactive MANET Routing Protocols  

E-print Network

PATHS: Analysis of PATH Duration Statistics and their Impact on Reactive MANET Routing Protocols,fbai,bkrishna,helmy}@usc.edu ABSTRACT We develop a detailed approach to study how mobility im- pacts the performance of reactive MANET. Consequently, Mobile Ad hoc NET- works (MANETs) are attracting a lot of attention from the research community

Krishnamachari, Bhaskar

369

FEM-Based Surface Wave Multimixed-Path Propagator and Path Loss Predictions  

Microsoft Academic Search

A finite element method (FEM)-based surface wave propagation prediction simulator is developed. The simulator is tested and calibrated against analytical ray-mode models that also take into account the Millington recovery effects. It successfully calculates path losses over multimixed propagation paths at MF and HF frequency bands where the surface wave contribution is significant.

Gkhan Apaydin; Levent Sevgi

2009-01-01

370

Multicriteria adaptive paths in stochastic, time-varying networks  

Microsoft Academic Search

In this paper, exact algorithms are proposed for addressing multicriteria adaptive path problems, where arc attributes are stochastic and time-varying. Adaptive paths comprise a set of path strategies that enable the traveler to select a direction among all Pareto-optimal solutions at each node in response to knowledge of the arrival time at the intermediate nodes. Such paths can be viewed

Sathaporn Opasanon; Elise Miller-hooks

2006-01-01

371

Diagnosis for Covariance Structure Models by Analyzing the Path  

ERIC Educational Resources Information Center

When a covariance structure model is misspecified, parameter estimates will be affected. It is important to know which estimates are systematically affected and which are not. The approach of analyzing the path is both intuitive and informative for such a purpose. Different from path analysis, analyzing the path uses path tracing and elementary…

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

2008-01-01

372

An Adaptive Path Planning Algorithm for Cooperating Unmanned Air Vehicles  

SciTech Connect

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

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

2000-09-12

373

Adaptive path planning algorithm for cooperating unmanned air vehicles  

SciTech Connect

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

Cunningham, C T; Roberts, R S

2001-02-08

374

Model Discrepancy in the Saturated Path Hydrology Model: Initial Analysis  

E-print Network

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

Oakley, Jeremy

375

A taxonomy of integral reaction path analysis  

SciTech Connect

W. C. Gardiner observed that achieving understanding through combustion modeling is limited by the ability to recognize the implications of what has been computed and to draw conclusions about the elementary steps underlying the reaction mechanism. This difficulty can be overcome in part by making better use of reaction path analysis in the context of multidimensional flame simulations. Following a survey of current practice, an integral reaction flux is formulated in terms of conserved scalars that can be calculated in a fully automated way. Conditional analyses are then introduced, and a taxonomy for bidirectional path analysis is explored. Many examples illustrate the resulting path analysis and uncover some new results about nonpremixed methane-air laminar jets.

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

2004-12-23

376

Quickest Paths for Different Network Router Mechanisms  

SciTech Connect

The quickest path problem deals with the transmission of a message of size {sigma} from a source to a destination with the minimum end-to-end delay over a network with bandwidth and delay constraints on the links. The authors consider four basic modes and two variations for the message delivery at the nodes reflecting the mechanisms such as circuit switching, Internet protocol, and their combinations. For each of the first three modes, they present O(m{sup 2} + mn log n) time algorithm to compute the quickest path for a given message size {sigma}. For the last mode, the quickest path can be computed in O(m + n log n) time.

Rao, N.S.V.; Grimmell, W.C.; Radhakrishnan, S.; Bang, Y.C.

2000-06-01

377

Constrained Optimization Path Following of Wheeled Robots  

E-print Network

Abstract. A smooth-primitive constrained-optimization-based path-tracking algorithm for mobile robots that compensates for rough terrain, predictable vehicle dynamics, and vehicle mobility constraints has been developed, implemented, and tested on the DARPA LAGR platform. Traditional methods for the geometric path following control problem involve trying to meet position constraints at fixed or velocity dependent look-ahead distances using arcs. We have reformulated the problem as an optimal control problem, using a trajectory generator that can meet arbitrary boundary state constraints. The goal state along the target path is determined dynamically by minimizing a utility function based on corrective trajectory feasibility and cross-track error. A set of field tests compared the proposed method to an implementation of the pure pursuit algorithm and showed that the smooth corrective trajectory constrained optimization approach exhibited higher performance than pure pursuit by achieving rough four times lower average cross-track error and two times lower heading error. 1

Thomas M. Howard; Alonzo Kelly

2006-01-01

378

Molecular path control in zeolite membranes  

PubMed Central

We report molecular simulations of diffusion in confinement showing a phenomenon that we denote as molecular path control (MPC); depending on loading, molecules follow a preferred pathway. MPC raises the important question to which extent the loading may affect the molecular trajectories in nanoporous materials. Through MPC one is able to manually adjust the ratio of the diffusivities through different types of pores, and as an application one can direct the flow of diffusing particles in membranes forward or sideward by simply adjusting the pressure, without the need for mechanical parts like valves. We show that the key ingredient of MPC is the anisotropic nature of the nanoporous material that results in a complex interplay between different diffusion paths as a function of loading. These paths may be controlled by changing the loading, either through a change in pressure or temperature. PMID:16109769

Dubbeldam, D.; Beerdsen, E.; Calero, S.; Smit, B.

2005-01-01

379

A Comparison of Two Path Planners for Planetary Rovers  

NASA Technical Reports Server (NTRS)

The paper presents two path planners suitable for planetary rovers. The first is based on fuzzy description of the terrain, and genetic algorithm to find a traversable path in a rugged terrain. The second planner uses a global optimization method with a cost function that is the path distance divided by the velocity limit obtained from the consideration of the rover static and dynamic stability. A description of both methods is provided, and the results of paths produced are given which show the effectiveness of the path planners in finding near optimal paths. The features of the methods and their suitability and application for rover path planning are compared

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

1999-01-01

380

Bonded Paths and van der Waals Interactions in Orpiment, As2S3  

SciTech Connect

Bond critical properties and bond paths have been calculated for the thioarsenide molecular crystal orpiment, As2S3. In addition to the intramolecular As-S bond paths and van der Waals As-S and S-S bond paths within the layers, intermolecular S-S, As-S and As-As van der Waals paths exist between the layers. The S-S bond paths between the layers are identified with the main interlayer restoring forces responsible for the vibrational internal-mode splitting and the low frequency rigid layer modes previously documented in infrared and Raman studies of orpiment. These S-S bond paths are comparable with those calculated for orthorhombic native sulfur and the As4Sn (n = 3,4,5) molecules for several arsenide molecular crystals. The As-S bond paths show that the two nonequivalent arsenic atoms are each coordinated by a highly distorted octahedral array of sulfur atoms. The octahedra consist of three As-S intramolecular bonded interactions and three longer van der Waals interactions (two intramolecular and one intermolecular). One of the arsenic atoms is also coordinated by an arsenic atom in an interlayer As-As bonded interaction. Laplacian isosurface envelopes calculated for the arsenic and sulfur atoms are comparable with those calculated for native arsenic and orthorhombic sulfur. The intermolecular As-S bond paths connect Lewis acid domains on arsenic and an Lewis base domains on sulfur. Van der Waals interactions are traditionally defined as attractive interactions other than those ascribed to bond formation. However, theoretical evidence and arguments, as well as the connection between the bond paths and the vibrational spectra, indicate that the van der Waals interactions in orpiment are directed bonded interactions in the Slater sense. The experimental bond lengths for the As-S and S-S bonded interactions decrease nonlinearly with the increasing value of the electron density at the bond critical point, concomitant with a decrease in the bonded radii of arsenic and sulfur. On the basis of the local energy density, the intramolecular As-S bonded interactions classify as shared interactions and the intramolecular and intermolecular As-S and S-S bonded interactions and the intermolecular As-As van der Waals interactions classify as closed-shell interactions. The so called planar lone electron pair micelle picture for orpiment is spanned by bond paths, substantiating the claim that the layers in the orpiment structure are linked by weak van der Waals bonded interactions.

Gibbs, Gerald V.; Wallace, Adam F.; Zallen, Richard; Downs, R. T.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.

2010-06-17

381

Which coordinate system for modelling path integration?  

PubMed

Path integration is a navigation strategy widely observed in nature where an animal maintains a running estimate, called the home vector, of its location during an excursion. Evidence suggests it is both ancient and ubiquitous in nature, and has been studied for over a century. In that time, canonical and neural network models have flourished, based on a wide range of assumptions, justifications and supporting data. Despite the importance of the phenomenon, consensus and unifying principles appear lacking. A fundamental issue is the neural representation of space needed for biological path integration. This paper presents a scheme to classify path integration systems on the basis of the way the home vector records and updates the spatial relationship between the animal and its home location. Four extended classes of coordinate systems are used to unify and review both canonical and neural network models of path integration, from the arthropod and mammalian literature. This scheme demonstrates analytical equivalence between models which may otherwise appear unrelated, and distinguishes between models which may superficially appear similar. A thorough analysis is carried out of the equational forms of important facets of path integration including updating, steering, searching and systematic errors, using each of the four coordinate systems. The type of available directional cue, namely allothetic or idiothetic, is also considered. It is shown that on balance, the class of home vectors which includes the geocentric Cartesian coordinate system, appears to be the most robust for biological systems. A key conclusion is that deducing computational structure from behavioural data alone will be difficult or impossible, at least in the absence of an analysis of random errors. Consequently it is likely that further theoretical insights into path integration will require an in-depth study of the effect of noise on the four classes of home vectors. PMID:19962387

Vickerstaff, Robert J; Cheung, Allen

2010-03-21

382

Minefield path planning: architecture and algorithms obeying kinematic constraints  

NASA Astrophysics Data System (ADS)

We have been developing path planning techniques to look for paths that balance the utility and risk associated with different routes through a minefield. Such methods will allow a battlegroup commander to evaluate alternative route options while searching for low risk paths. Extending on previous years' efforts, we have implemented a generalized path planning framework to allow rapid evaluation and integration of new path planning algorithms. We have also implemented a version of Rapidly-Explored Random Trees (RRTs) for mine path planning which integrates path risk, path time, and dynamic and kinematic concerns. Several variants of the RRT algorithm and our existing path planning algorithms were quantitatively evaluated using the generalized path planning framework and an algorithm-dynamic evaluation graphical user interface.

McCubbin, Christopher B.; Piatko, Christine D.; Marshall, Steven J.

2004-09-01

383

Gas path sealing in turbine engines  

NASA Technical Reports Server (NTRS)

Gas path seals are discussed with emphasis on sealing clearance effects on engine component efficiency, compressor pressure ratio, and stall margin. Various case-rotor relative displacements, which affect gas path seal clearances, are identified. Forces produced by nonuniform sealing clearances and their effect on rotor stability are examined qualitatively, and recent work on turbine-blade-tip sealing for high temperatures is described. The need for active clearance control and for engine structural analysis is discussed. The functions of the internal-flow system and its seals are reviewed.

Ludwig, L. P.

1978-01-01

384

Path planning for everday robotics with SANDROS  

SciTech Connect

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

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

1997-02-01

385

Propulsion using the electron spiral toroid  

Microsoft Academic Search

A new propulsion method is proposed which could potentially reduce propellant needed for space travel by three orders of magnitude. It uses the newly patented electron spiral toroid (EST), which stores energy as magnetic field energy. The EST is a hollow toroid of electrons, all spiraling in parallel paths in a thin outer shell. The electrons satisfy the coupling condition,

Clint Seward; Clint

1998-01-01

386

Performance Analysis of Inter-Domain Path Computation Methodologies draft-dasgupta-ccamp-path-comp-analysis-00  

Microsoft Academic Search

This document presents a performance comparison between the per- domain path computation method and the Path Computation Element (PCE) Architecture based Backward Recursive Path Computa- tion (BRPC) procedure. Metrics to capture the significant performance aspects are identified and detailed simulations are carried out on realistic scenarios. A performance analysis for each of the path computation methods is then undertaken.

Sukrit Dasgupta; Jaudelice C. de Oliveira

387

High-order Path Integral Monte Carlo methods for solving quantum dot problems  

E-print Network

The conventional second-order Path Integral Monte Carlo method is plagued with the sign problem in solving many-fermion systems. This is due to the large number of anti-symmetric free fermion propagators that are needed to extract the ground state wave function at large imaginary time. In this work, we show that optimized fourth-order Path Integral Monte Carlo methods, which use no more than 5 free-fermion propagators, can yield accurate quantum dot energies for up to 20 polarized electrons with the use of the Hamiltonian energy estimator.

Chin, Siu A

2014-01-01

388

Path Integral Methods in the Su-Schrieffer-Heeger Polaron Problem  

NASA Astrophysics Data System (ADS)

I propose a path integral description of the Su-Schrieffer-Heeger Hamiltonian, both in one and two dimensions, after mapping the real space model onto the time scale. While the lattice degrees of freedom are classical functions of time and are integrated out exactly, the electron particle paths are treated quantum mechanically. The method accounts for the variable range of the electronic hopping processes. The free energy of the system and its temperature derivatives are computed by summing at any Tover the ensemble of relevant particle paths which mainly contribute to the total partition function. In the low Tregime, the heat capacity over Tratio shows an upturn peculiar to a glass-like behavior. This feature is more sizeable in the square lattice than in the linear chain as the overall hopping potential contribution to the total action is larger in higher dimensionality. The effects of the electron-phonon anharmonic interactions on the phonon subsystem are studied by the path integral cumulant expansion method.

Zoli, Marco

389

Finding the optimal-path maps for path planning across weighted regions  

SciTech Connect

Optimal-path maps tell robots or people the best way to reach a goal point from anywhere in a known terrain area, eliminating most of the need to plan during travel. The authors address the construction of optimal-path maps for two-dimensional polygonal weighted-region terrain, terrain partitioned into polygonal areas such that the cost per unit of distance traveled is homogeneous and isotropic within each area. This is useful for overland route planning across varied ground surfaces and vegetation. The authors propose a new algorithm that recursively partitions terrain into regions of similar optimal-path behavior, and defines corresponding path subspaces for these regions. This process constructs a piecewise-smooth function of terrain position whose gradient direction is everywhere the optimal-path direction, permitting quick path finding. The algorithm used is more complicated than the current path-caching and wavefront-propagation algorithms, but it gives more accurate maps requiring less space to represent. Experiments with an implementation confirm the practicality of the authors' algorithm.

Rowe, N.C.; Alexander, R.S.

2000-02-01

390

Optimizing transmission path utilization in Idaho power  

Microsoft Academic Search

Increased utilization of transmission critical path by wide area real time dynamic rating using Internet based weather data is presented. Economic analysis shows significant benefit of operating transmission lines at higher ratings by taking advantage of favorable weather conditions during overload conditions. A new line current profile based dynamic line rating system has been implemented at Idaho power by real

O. A. Ciniglio; A. K. Deb

2003-01-01

391

No oculomotor plant, no final common path  

Microsoft Academic Search

The assumption that there is an oculomotor plant, a fixed relationship between motoneuron firing rate and eye position, is dis- proved by brainstem recording studies showing that this relationship depends on which supernuclear subsystem determines firing rate. But it remains possible that there is a final common path (FCP), a fixed relationship between firing rate and muscle force. But then,

Joel M. Miller

2003-01-01

392

HAMILTONIAN PATHS ALGORITHMS FOR DISK SCHEDULING  

Microsoft Academic Search

The problem of optimally scheduling the read\\/write requests in a disk storage system is considered. A new class of algorithms for the disk scheduling problem is presented, and the relations between this problem and the shortest hamiltonian path problem on asymmetric graphs are investigated. The problem of deriving realistic upper bounds for the disk utilization factor, one of the main

Giorgio Gallo; Federico Malucelli; Martina Marrè

393

Fusion Development Path Panel Preliminary Report  

E-print Network

Fusion Development Path Panel Preliminary Report Summary for NRC BPAC Panel (Focus on MFE of a demonstration power plant in approximately 35 years. The plan should recognize the capabilities of all fusion facilities around the world, and include both magnetic fusion energy (MFE) and inertial fusion energy (IFE

394

A Complex Path to Haudenosaunee Degree Completion  

ERIC Educational Resources Information Center

This qualitative study describes how 12 Haudenosaunee (Six Nations Iroquois Confederacy) college graduates constructed pathways to degree completion. The participants related their experiences on this path through open-ended interviews. The pathways were found to be complex owing to their unique cultural grounding and dedication to family. The…

Waterman, Stephanie J.

2007-01-01

395

Iran's Tortuous Path Toward “Islamic Liberalism”  

Microsoft Academic Search

This article provides an overview of the intellectual and sociopolitical roots of Iran's tortuous path toward “Islamic liberalism” and reform. It analyzes the shift in the ideological orientation of a major faction within the political elite from a radical to a relatively moderate and liberal interpretation of Islam. The authors trace the roots of this ideological shift to a series

Ahmad Ashraf; Ali Banuazizi

2001-01-01

396

Ambivalent Journey: Teacher Career Paths in Oman  

ERIC Educational Resources Information Center

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

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

2012-01-01

397

Learning to improve path planning performance  

SciTech Connect

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

Chen, Pang C.

1995-04-01

398

CALIFORNIA PATH PROGRAM INSTITUTE OF TRANSPORTATION STUDIES  

E-print Network

, in cooperation with the State of California Business, Transportation, and Housing Agency, Department of Trans from Implementation: Part X Freeway Service Patrols California PATH Working Paper UCB-ITS-PWP-2001 SERVICE PATROLS. David Levinson and Pavithra Kandadai Parthasarathi #12;2 Introduction Incident management

Levinson, David M.

399

PLS Path Modeling and Evolutionary Segmentation  

Microsoft Academic Search

Applications of the partial least squares (PLS) path modeling approach—which have gained increasing dissemination in business research—usually build on the assumption that the data stem from a single population. However, in empirical applications, this assumption of homogeneity is unrealistic. Analyses on the aggregate data level ignore the existence of groups with substantial differences and more often than not result in

Christian M. Ringle; Marko Sarstedt; R. Schlittgen; Charles R. Taylor

2013-01-01

400

Air Path Estimation on Diesel HCCI Engine  

Microsoft Academic Search

In this paper, we address the problem of air path variables estimation for an HCCI engine. Two observers are pro- posed. Both rely on physical assumptions on the com- bustion, but use different sensors. After proving conver- gence in the two cases, we carry out comparisons based on simulation results. We stress the impact of two particu- lar additional sensors

J. Chauvin; N. Petit; P. Rouchon; C. Vigild; Ford Forschungszentrum Aachen

2006-01-01

401

CALIFORNIA PATH PROGRAM INSTITUTE OF TRANSPORTATION STUDIES  

E-print Network

Intelligent SensorValidation and Fusion for Vehicle Guidance Using Probabilistic and Fuzzy Methods Alice-1425 #12;INTELLIGENT SENSOR VALIDATION AND FUSION FOR VEHICLE GUIDANCE USING PROBABILISTIC AND FUZZY MEANS Final Report PATH Project "Intelligent Sensor Validation and Fusion for Reliability and Safety

Agogino, Alice M.

402

The Erratic Path of Hungarian Higher Education  

ERIC Educational Resources Information Center

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

Marcus, Jon

2014-01-01

403

Path matched vibration insensitive Fizeau interferometer  

Microsoft Academic Search

An on-axis, vibration insensitive, polarization Fizeau interferometer is realized through the use of a novel pixelated mask spatial carrier phase shifting technique in conjunction with a low coherence source and a polarization path matching mechanism. In this arrangement, coherence is used to effectively separate out the orthogonally polarized test and reference beam components for interference. With both the test and

Bradley Trent Kimbrough

2006-01-01

404

Current SPE Hydrodynamic Modeling and Path Forward  

SciTech Connect

Extensive work has been conducted on SPE analysis efforts: Fault effects Non-uniform weathered layer analysis MUNROU: material library incorporation, parallelization, and development of non-locking tets Development of a unique continuum-based-visco-plastic strain-rate-dependent material model With corrected SPE data path is now set for a multipronged approach to fully understand experimental series shot effects.

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

2012-08-14

405

Quad-rotor flight path energy optimization  

NASA Astrophysics Data System (ADS)

Quad-Rotor unmanned areal vehicles (UAVs) have been a popular area of research and development in the last decade, especially with the advent of affordable microcontrollers like the MSP 430 and the Raspberry Pi. Path-Energy Optimization is an area that is well developed for linear systems. In this thesis, this idea of path-energy optimization is extended to the nonlinear model of the Quad-rotor UAV. The classical optimization technique is adapted to the nonlinear model that is derived for the problem at hand, coming up with a set of partial differential equations and boundary value conditions to solve these equations. Then, different techniques to implement energy optimization algorithms are tested using simulations in Python. First, a purely nonlinear approach is used. This method is shown to be computationally intensive, with no practical solution available in a reasonable amount of time. Second, heuristic techniques to minimize the energy of the flight path are tested, using Ziegler-Nichols' proportional integral derivative (PID) controller tuning technique. Finally, a brute force look-up table based PID controller is used. Simulation results of the heuristic method show that both reliable control of the system and path-energy optimization are achieved in a reasonable amount of time.

Kemper, Edward

406

Administrator Career Paths and Decision Processes  

ERIC Educational Resources Information Center

Purpose: The purpose of this paper is to present qualitative evidence on the processes and forces that shape school administrator career paths. Design/methodology/approach: An embedded case study approach is used to understand more than 100 administrator career transitions within the Delaware education system. Semi-structured interview data were…

Farley-Ripple, Elizabeth N.; Raffel, Jeffrey A.; Welch, Jennie Christine

2012-01-01

407

Outsmarting the Wolf: Critical Paths to Performance.  

ERIC Educational Resources Information Center

Argues against community colleges opting for a quick fix in difficult times, a tactic designed for continuity rather than change. Adds that financial restrictions confronting community colleges call for drastic change in order to spur sustainable growth. Recommends five paths for strategic resource management and future advantage in the market,…

Alfred, Richard

2003-01-01

408

Behavioral Path Analysis and Environmental Evaluation.  

ERIC Educational Resources Information Center

Behavioral Path Analysis is both a theory and a methodology for studying person-environment interactions. It is designed to be applicable to the evaluation of both environments in use and proposed designed environments. This paper presents the basics of the theory, and some examples of recent applications that have guided its development. The…

Wise, James A.; Kahle, Ellen

409

Planning smooth paths for mobile robots  

Microsoft Academic Search

The authors consider the problem of planning paths for a robot which has a minimum turning radius. This is a first step towards accurately modeling a robot with the kinematics of a car. The technique used is to define a set of canonical trajectories which satisfy the nonholonomic constraints imposed. A configuration space can be constructed for these trajectories in

P. Jacobs; J. Canny

1989-01-01

410

Optimized Cell Planning for Path Loss Reduction  

Microsoft Academic Search

In this paper, an optimized cell planning for path loss reduction has been proposed. A 10 by 10 Km square block is considered as traffic required area (TRA) which consists of number of base stations (BSs) and mobile stations (MSs). The optimization algorithm: Tabu search, is used to optimize the position of base stations in such a way that the

Nagendra Sah

2008-01-01

411

Carrier Frequency Effects on Path Loss  

Microsoft Academic Search

To study the carrier frequency effects on path loss, measurements have been conducted at four discrete frequencies in the range 460-5100 MHz. The transmitter was placed on the roof of a 36 meters tall building and the receive antennas were placed on the roof of a van. Both urban and suburban areas were included in the measurement campaign. The results

Mathias Riback; Jonas Medbo; Jan-erik Berg; Fredrik Harrysson; Henrik Asplund

2006-01-01

412

Paths to Creativity in Security Careers  

E-print Network

to be as creative as we wish How can you encourage creative thinking? Is it obvious why this is keyPaths to Creativity in Security Careers Privacy, Security and Trust 2006 Dr. Gregory Newby Arctic. These people need to be as creative, skilled and innovative as their adversaries. #12;Who is this Guy

Newby, Gregory B.

413

employment opportunities in exciting career paths  

E-print Network

processing and safe handling of all types of food. R&D Scientific Technical Education Sales & Marketing in exciting career paths Food Science Cerificate for BSc graduates Food Science Cerificate for BSc graduates. Because food science is a multidisciplinary applied science, a food science education provides a broad

Barthelat, Francois

414

Service-Learning Partnerships: Paths of Engagement  

ERIC Educational Resources Information Center

This article furthers research and theory on the initiation and development of service-learning partnerships. It identifies three paths of engagement between university and community agencies: tentative engagement, aligned engagement, and committed engagement. This conceptualization helps to understand how service-learning partnerships evolve over…

Dorado, Silvia; Giles, Dwight E., Jr.

2004-01-01

415

Combinatorially Simple Pickup and Delivery Paths  

Microsoft Academic Search

Pickup and delivery problems discussed in the literature of ten allow for only particularly sim- ple solutions in terms of the sequence of visited locations. We study the very simplest pickup and delivery paths which are concatenations of short patter ns visiting one or two requests. This restricted variant, still NP -hard, is close to the traveling salesman problem with

Marco E. Lubbecke

2002-01-01

416

Covariant path integrals on hyperbolic surfaces  

NASA Astrophysics Data System (ADS)

DeWitt's covariant formulation of path integration [B. De Witt, "Dynamical theory in curved spaces. I. A review of the classical and quantum action principles," Rev. Mod. Phys. 29, 377-397 (1957)] has two practical advantages over the traditional methods of "lattice approximations;" there is no ordering problem, and classical symmetries are manifestly preserved at the quantum level. Applying the spectral theorem for unbounded self-adjoint operators, we provide a rigorous proof of the convergence of certain path integrals on Riemann surfaces of constant curvature -1. The Pauli-DeWitt curvature correction term arises, as in DeWitt's work. Introducing a Fuchsian group ? of the first kind, and a continuous, bounded, ?-automorphic potential V, we obtain a Feynman-Kac formula for the automorphic Schrödinger equation on the Riemann surface ?H. We analyze the Wick rotation and prove the strong convergence of the so-called Feynman maps [K. D. Elworthy, Path Integration on Manifolds, Mathematical Aspects of Superspace, edited by Seifert, Clarke, and Rosenblum (Reidel, Boston, 1983), pp. 47-90] on a dense set of states. Finally, we give a new proof of some results in C. Grosche and F. Steiner, "The path integral on the Poincare upper half plane and for Liouville quantum mechanics," Phys. Lett. A 123, 319-328 (1987).

Schaefer, Joe

1997-11-01

417

Judgments of Path, Not Heading, Guide Locomotion  

ERIC Educational Resources Information Center

To steer a course through the world, people are almost entirely dependent on visual information, of which a key component is optic flow. In many models of locomotion, heading is described as the fundamental control variable; however, it has also been shown that fixating points along or near one's future path could be the basis of an efficient…

Wilkie, Richard M.; Wann, John P.

2006-01-01

418

Shortest paths algorithms: theory and experimental evaluation  

Microsoft Academic Search

We conduct an extensive computational study of shortest paths algorithms, including some very recent algorithms. We also suggest new algorithms motivated by the experimental results and prove interesting theoretical results suggested by the experimental data. Our computational study is based on several natural problem classes which identify strengths and weaknesses of various algorithms. These problem classes and algorithm implementations form

Boris V. Cherkassky; Andrew V. Goldberg; Tomasz Radzikt

1994-01-01

419

Path integral quantization of parametrised field theory  

E-print Network

Free scalar field theory on a flat spacetime can be cast into a generally covariant form known as parametrised field theory in which the action is a functional of the scalar field as well as the embedding variables which describe arbitrary, in general curved, foliations of the flat spacetime. We construct the path integral quantization of parametrised field theory in order to analyse issues at the interface of quantum field theory and general covariance in a path integral context. We show that the measure in the Lorentzian path integral is non-trivial and is the analog of the Fradkin- Vilkovisky measure for quantum gravity. We construct Euclidean functional integrals in the generally covariant setting of parametrised field theory using key ideas of Schleich and show that our constructions imply the existence of non-standard `Wick rotations' of the standard free scalar field 2 point function. We develop a framework to study the problem of time through computations of scalar field 2 point functions. We illustrate our ideas through explicit computation for a time independent 1+1 dimensional foliation. Although the problem of time seems to be absent in this simple example, the general case is still open. We discuss our results in the contexts of the path integral formulation of quantum gravity and the canonical quantization of parametrised field theory.

Madhavan Varadarajan

2004-04-06

420

Unified classical path theories of pressure broadening.  

NASA Technical Reports Server (NTRS)

Derivation of a unified classical path theory of pressure broadening, using only elementary concepts. It is shown that the theory of Smith, Cooper and Vidal (1969) is only correct at all frequencies to first order in the number density of perturbers.

Bottcher, C.

1971-01-01

421

Career Paths for Managers in the Arts  

ERIC Educational Resources Information Center

In this article we examine the career paths of top-level managers in the arts. By analysing the training and work history of 23 managers in a variety of arts organisations we evaluate the utility of several existing theories for understanding careers that are characterised by low levels of initial knowledge, the absence of a clear method of entry…

Inglis, Loretta; Cray, David

2012-01-01

422

Path integration in tactile perception of shapes.  

PubMed

Whenever we move the hand across a surface, tactile signals provide information about the relative velocity between the skin and the surface. If the system were able to integrate the tactile velocity information over time, cutaneous touch may provide an estimate of the relative displacement between the hand and the surface. Here, we asked whether humans are able to form a reliable representation of the motion path from tactile cues only, integrating motion information over time. In order to address this issue, we conducted three experiments using tactile motion and asked participants (1) to estimate the length of a simulated triangle, (2) to reproduce the shape of a simulated triangular path, and (3) to estimate the angle between two-line segments. Participants were able to accurately indicate the length of the path, whereas the perceived direction was affected by a direction bias (inward bias). The response pattern was thus qualitatively similar to the ones reported in classical path integration studies involving locomotion. However, we explain the directional biases as the result of a tactile motion aftereffect. PMID:25151621

Moscatelli, Alessandro; Naceri, Abdeldjallil; Ernst, Marc O

2014-11-01

423

Fermionic Path Integral Simulations of Hot, Dense Hydrogen  

NASA Astrophysics Data System (ADS)

Fermionic path integral Monte Carlo simulations have been applied to study the equilibrium properties of the hydrogen and deuterium at high pressure and temperature. We use this technique to determine Hugoniot [1] and compare with recent Laser shock wave experiments by Da Silva et al. Further we investigate the occurence of various species in the hydrogen plasma such as H, H+, e, H2 and H2+ and compare with simulation based on a chemical model. This analysis is connected with the Mott transition, in which electrons move from bound to free states, and the plasma phase transition [2] involving the dissociation of H2. [0.2cm] [1] B. Militzer, W. Magro, and D. Ceperley, ``Fermionic Path-Integral Simulation of Dense Hydrogen'' in Proceedings of the International Conference on Strongly Coupled Coulomb Systems, Boston (1997). [0.2cm] [2] W. R. Magro, D. M. Ceperley , C. Pierleoni and B. Bernu, Phys. Rev. Letts. 76, 1240 (1996).

Militzer, Burkhard; Magro, William; Ceperley, David

1998-03-01

424

Proposal for a QND which-path measurement using photons  

NASA Technical Reports Server (NTRS)

A scheme is proposed for experimentally realizing the famous two-slit gedaenken experiment using photons. As elegantly discussed for electrons by Feynman, a particle's quantum pathways interfere to produce fringes in the probability density for the particle to be found at a particle location. If the path taken by the particle is experimentally determined, the complementarity principle says that the fringes must disappear. To carry out this experiment with photons is difficult because normally the act of determining a photon's location destroys it. We propose to overcome this difficulty by putting a type-2 optical parametric amplifier (OPA) in each arm of a Mach-Zehnder interferometer, and observing fringes at the output. An OPA responds to an input photon by increasing its probability to produce a pair of photons with polarization orthogonal to the input, the detection of which allows partial inference about the path taken by the input photon without destroying it. Thus, the measurement is of the quantum nondemolition (QND) type.

Raymer, M. G.; Yang, S.

1992-01-01

425

Inter-Domain Redundancy Path Computation Methods Based on PCE  

NASA Astrophysics Data System (ADS)

This paper evaluates three inter-domain redundancy path computation methods based on PCE (Path Computation Element). Some inter-domain paths carry traffic that must be assured of high quality and high reliability transfer such as telephony over IP and premium virtual private networks (VPNs). It is, therefore, important to set inter-domain redundancy paths, i. e. primary and secondary paths. The first scheme utilizes an existing protocol and the basic PCE implementation. It does not need any extension or modification. In the second scheme, PCEs make a virtual shortest path tree (VSPT) considering the candidates of primary paths that have corresponding secondary paths. The goal is to reduce blocking probability; corresponding secondary paths may be found more often after a primary path is decided; no protocol extension is necessary. In the third scheme, PCEs make a VSPT considering all candidates of primary and secondary paths. Blocking probability is further decreased since all possible candidates are located, and the sum of primary and secondary path cost is reduced by choosing the pair with minimum cost among all path pairs. Numerical evaluations show that the second and third schemes offer only a few percent reduction in blocking probability and path pair total cost, while the overheads imposed by protocol revision and increase of the amount of calculation and information to be exchanged are large. This suggests that the first scheme, the most basic and simple one, is the best choice.

Hayashi, Rie; Oki, Eiji; Shiomoto, Kohei

426

Common path point diffraction interferometer using liquid crystal phase shifting  

NASA Technical Reports Server (NTRS)

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

Mercer, Carolyn R. (Inventor)

1997-01-01

427

Daytime D region parameters from long-path VLF phase and amplitude  

NASA Astrophysics Data System (ADS)

Observed phases and amplitudes of VLF radio signals propagating on very long paths are used to validate electron density parameters for the lowest edge of the (D region of the) Earth's ionosphere at low latitudes and midlatitudes near solar minimum. The phases, relative to GPS 1 s pulses, and the amplitudes were measured near the transmitters (˜100-150 km away), where the direct ground wave is dominant, and also at distances of ˜8-14 Mm away, over mainly all-sea paths. Four paths were used: NWC (19.8 kHz, North West Cape, Australia) to Seattle (˜14 Mm) and Hawaii (˜10 Mm), NPM (21.4 kHz, Hawaii) and NLK (24.8 kHz, Seattle) to Dunedin, New Zealand (˜8 Mm and ˜12 Mm). The characteristics of the bottom edge of the daytime ionosphere on these long paths were found to confirm and contextualize recently measured short-path values of Wait's traditional height and sharpness parameters, H? and ?, respectively, after adjusting appropriately for the (small) variations of H? and ? along the paths that are due to (1) changing solar zenith angles, (2) increasing cosmic ray fluxes with latitude, and (3) latitudinal and seasonal changes in neutral atmospheric densities from the (NASA) Mass Spectrometer Incoherent Scatter- (MSIS-) E-90 neutral atmosphere model. The sensitivity of this long-path (and hence near-global) phase and amplitude technique is ˜ ± 0.3 km for H? and ˜ ± 0.01 km-1 for ?, thus creating the possibility of treating the height (H? ˜70 km) as a fiduciary mark (for a specified neutral density) in the Earth's atmosphere for monitoring integrated long-term (climate) changes below ˜70 km altitude.

Thomson, Neil R.; Rodger, Craig J.; Clilverd, Mark A.

2011-11-01

428

A Network Architecture with Virtual Path Hopping and Dynamic Virtual Path Allocation Algorithm  

Microsoft Academic Search

Connection oriented packet networks such as IP\\/MPLS can better meet the QoS guarantees in terms of delay jitter, bandwidth etc. required by premium traffic (PT). These connection oriented networks are more vulnerable to failures and they can be classified into link\\/path and degraded failures. Virtual path hopping concept eliminates all terminations of data communications due to degraded type failures detected

Manodha GAMAGE; Mitsuo HAYASAKA; Tetsuya MIKI

2005-01-01

429

X-ray Characterization, Electronic Band Structure, and Thermoelectric Properties of the Cluster Compound Ag2Tl2Mo9Se11.  

PubMed

We report on a detailed investigation of the crystal and electronic band structures and of the transport and thermodynamic properties of the Mo-based cluster compound Ag2Tl2Mo9Se11. This novel structure type crystallizes in the trigonal space group R3?c and is built of a three-dimensional network of interconnected Mo9Se11 units. Single-crystal X-ray diffraction indicates that the Ag and Tl atoms are distributed in the voids of the cluster framework, both of which show unusually large anisotropic thermal ellipsoids indicative of strong local disorder. First-principles calculations show a weakly dispersive band structure around the Fermi level as well as a semiconducting ground state. The former feature naturally explains the presence of both hole-like and electron-like signals observed in Hall effect. Of particular interest is the very low thermal conductivity that remains quasi-constant between 150 and 800 K at a value of approximately 0.6 W·m(-1)·K(-1). The lattice thermal conductivity is close to its minimum possible value, that is, in a regime where the phonon mean free path nears the mean interatomic distance. Such extremely low values likely originate from the disorder induced by the Ag and Tl atoms giving rise to strong anharmonicity of the lattice vibrations. The strongly limited ability of this compound to transport heat is the key feature that leads to a dimensionless thermoelectric figure of merit ZT of 0.6 at 800 K. PMID:25338311

Al Rahal Al Orabi, Rabih; Gougeon, Patrick; Gall, Philippe; Fontaine, Bruno; Gautier, Régis; Colin, Malika; Candolfi, Christophe; Dauscher, Anne; Hejtmanek, Jiri; Malaman, Bernard; Lenoir, Bertrand

2014-11-01

430

Modular electronics packaging system  

NASA Technical Reports Server (NTRS)

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

Hunter, Don J. (Inventor)

2001-01-01

431

Adaptive path planning for flexible manufacturing  

SciTech Connect

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

Chen, Pang C.

1994-08-01

432

Path integral learning of multidimensional movement trajectories  

NASA Astrophysics Data System (ADS)

This paper explores the use of Path Integral Methods, particularly several variants of the recent Path Integral Policy Improvement (PI2) algorithm in multidimensional movement parametrized policy learning. We rely on Dynamic Movement Primitives (DMPs) to codify discrete and rhythmic trajectories, and apply the PI2-CMA and PIBB methods in the learning of optimal policy parameters, according to different cost functions that inherently encode movement objectives. Additionally we merge both of these variants and propose the PIBB-CMA algorithm, comparing all of them with the vanilla version of PI2. From the obtained results we conclude that PIBB-CMA surpasses all other methods in terms of convergence speed and iterative final cost, which leads to an increased interest in its application to more complex robotic problems.

André, João; Santos, Cristina; Costa, Lino

2013-10-01

433

Aerosol optical thickness and atmospheric path radiance  

NASA Technical Reports Server (NTRS)

Simultaneous measurements from the ground of the spectral optical thickness and the atmospheric path radiance from over 30 sites located in many parts of the world and affected by several different aerosol types are reported. These measurements are used to derive the relationship between the optical thickness and the path radiance for a single viewing and illumination geometry and to discuss its implications on remote sensing observations. It is shown that simple measurements performed from the ground can yield empirical relationships that can be used to check some of the common but not validated assumptions about the particle homogeneity, sphericity, composition, and size distribution used in remote sensing models and in estimates of the radiative effects of aerosol. The results are used to test concepts of atmospheric corrections and remote sensing of aerosol from space.

Kaufman, Yoram J.

1993-01-01

434

A path model of aircraft noise annoyance  

NASA Astrophysics Data System (ADS)

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, attitudes toward aircraft operations, sleep interruption and personal sensitivity to noise. The strongest indirect effects are for aircraft Leq(24) and sensitivity. Overall the model explains 41 percent of the variation in the annoyance reported by the 673 survey respondents. The findings both support and extend existing statements in the literature on the antecedents of annoyance.

Taylor, S. M.

1984-09-01

435

Reaction coordinates and rates from transition paths  

PubMed Central

The molecular mechanism of a reaction in solution is reflected in its transition-state ensemble and transition paths. We use a Bayesian formula relating the equilibrium and transition-path ensembles to identify transition states, rank reaction coordinates, and estimate rate coefficients. We also introduce a variational procedure to optimize reaction coordinates. The theory is illustrated with applications to protein folding and the dipole reorientation of an ordered water chain inside a carbon nanotube. To describe the folding of a simple model of a three-helix bundle protein, we variationally optimize the weights of a projection onto the matrix of native and nonnative amino acid contacts. The resulting one-dimensional reaction coordinate captures the folding transition state, with formation and packing of helix 2 and 3 constituting the bottleneck for folding. PMID:15814618

Best, Robert B.; Hummer, Gerhard

2005-01-01

436

Covariant Hamiltonian field theory. Path integral quantization  

E-print Network

The Hamiltonian counterpart of classical Lagrangian field theory is covariant Hamiltonian field theory where momenta correspond to derivatives of fields with respect to all world coordinates. In particular, classical Lagrangian and covariant Hamiltonian field theories are equivalent in the case of a hyperregular Lagrangian, and they are quasi-equivalent if a Lagrangian is almost-regular. In order to quantize covariant Hamiltonian field theory, one usually attempts to construct and quantize a multisymplectic generalization of the Poisson bracket. In the present work, the path integral quantization of covariant Hamiltonian field theory is suggested. We use the fact that a covariant Hamiltonian field system is equivalent to a certain Lagrangian system on a phase space which is quantized in the framework of perturbative field theory. We show that, in the case of almost-regular quadratic Lagrangians, path integral quantizations of associated Lagrangian and Hamiltonian field theories are equivalent.

D. Bashkirov; G. Sardanashvily

2004-02-06

437

Optimizing transmission path utilization in Idaho Power  

Microsoft Academic Search

A new line current profile based dynamic line rating system has been implemented at Idaho Power Company by real-time exchange of data with Energy Management System and real-time weather data from the Internet. Increased utilization of transmission critical path is made possible by wide-area real-time dynamic rating using Internet based weather data. Economic analysis shows significant benefit of operating transmission

Orlando A. Ciniglio; Anjan K. Deb

2004-01-01

438

Path Integrals, and Classical and Quantum Constraints  

E-print Network

Systems with constraints pose problems when they are quantized. Moreover, the Dirac procedure of quantization prior to reduction is preferred. The projection operator method of quantization, which can be most conveniently described by coherent state path integrals, enables one to directly impose a regularized form of the quantum constraints. This procedure also overcomes conventional difficulties with normalization and second class constraints that invalidate conventional Dirac quantization procedures.

John R. Klauder

2005-07-22

439

Buzz Lightyear Connect It!: Flight Path Activity  

NSDL National Science Digital Library

In this activity, "space cadets" (learners) use writing and sequencing skills in addition to directional words/ordered pairs to guide Buzz Lightyear (from the movie "Toy Story") through a grid to reach his orbiter. Learners are encouraged to avoid all obstacles and use as many or as few steps as needed. Once completed, learners give their flight path to a friend and ask him/her to follow the directions to help Buzz reach his orbiter.

Administration, National A.

2011-12-07

440

Vertical flight path steering system for aircraft  

NASA Technical Reports Server (NTRS)

Disclosed is a vertical flight path angle steering system for aircraft, utilizing a digital flight control computer which processes pilot control inputs and aircraft response parameters into suitable elevator commands and control information for display to the pilot on a cathode ray tube. The system yields desirable airplane control handling qualities and responses as well as improvements in pilot workload and safety during airplane operation in the terminal area and under windshear conditions.

Lambregts, Antonius A. (Inventor)

1983-01-01

441

Study Tracks Path of Indian Ocean Tsunami  

NSDL National Science Digital Library

Since the Indian Ocean tsunami of December 26, 2004, scientists have tried to retrace the path of the giant waves to learn how and why the water moved in unexpected directions, even turning corners and producing simultaneous wavefronts coming from different directions. This radio broadcast describes efforts to measure the strength, distance traveled inland, and height of the tsunami, as well as mapping its route. The clip is 4 minutes in length.

442

Flux Control in Networks of Diffusion Paths  

SciTech Connect

A class of optimization problems in networks of intersecting diffusion domains of a special form of thin paths has been considered. The system of equations describing stationary solutions is equivalent to an electrical circuit built of intersecting conductors. The solution of an optimization problem has been obtained and extended to the analogous electrical circuit. The interest in this network arises from, among other applications, an application to wave-particle diffusion through resonant interactions in plasma.

A. I. Zhmoginov and N. J. Fisch

2009-07-08

443

Extremal paths on a random cayley tree  

PubMed

We investigate the statistics of extremal path(s) (both the shortest and the longest) from the root to the bottom of a Cayley tree. The lengths of the edges are assumed to be independent identically distributed random variables drawn from a distribution rho(l). Besides, the number of branches from any node is also random. Exact results are derived for arbitrary distribution rho(l). In particular, for the binary 0,1 distribution rho(l)=pdelta(l,1)+(1-p)delta(l, 0), we show that as p increases, the minimal length undergoes an unbinding transition from a "localized" phase to a "moving" phase at the critical value, p=p(c)=1-b(-1), where b is the average branch number of the tree. As the height n of the tree increases, the minimal length saturates to a finite constant in the localized phase (pp(c)) where the velocity v(min)(p) is determined via a front selection mechanism. At p=p(c), the minimal length grows with n in an extremely slow double-logarithmic fashion. The length of the maximal path, on the other hand, increases linearly as v(max)(p)n for all p. The maximal and minimal velocities satisfy a general duality relation, v(min)(p)+v(max)(1-p)=1, which is also valid for directed paths on finite-dimensional lattices. PMID:11138046

Majumdar; Krapivsky

2000-12-01

444

Generalized canonical transformations and path integrals  

Microsoft Academic Search

Some time-dependent physical systems do not admit, in the general case, either an invariant or auxiliary equation. The study of these systems is then in general made easier by space-time transformation of coordinates. This is true for the case for a rectangular well with a moving wall, which generalized canonical transformations reduce, in the path-integral formalism, to the case of

L. Chetouani; L. Guechi; Théophile F. Hammann

1989-01-01

445

Business engagement on Twitter: a path analysis  

Microsoft Academic Search

Social media services, such as Twitter, enable commercial businesses to participate actively in online word-of-mouth communication.\\u000a In this project, we examined the potential influences of business engagement in online word-of-mouth communication on the\\u000a level of consumers’ engagement and investigated the trajectories of a business’ online word-of-mouth message diffusion in\\u000a the Twitter community. We used path analysis to examine 164,478 tweets

Mimi Zhang; Bernard J. Jansen; Abdur Chowdhury

446

Path-loss prediction model for microcells  

Microsoft Academic Search

Empirical path-loss formulas for microcells in low-rise and high-rise environments are established from measurements conducted in the San Francisco Bay area. Using the 1-km intercepts and slope indexes of the least square fit lines to the measurements at cellular and personal communication services (PCS) frequencies for three base station heights, simple analytic expressions are obtained. Separate formulas are presented for

Dongsoo Har; Howard H. Xia; Henry L. Bertoni

1999-01-01

447

Path Loss Revisited Using Computer Simulation  

Microsoft Academic Search

In this paper, we propose a computer simulation model for the study of the large-scale effects on narrowband wireless transmission systems. The development of the path loss model is based on the ray tracing technique. This study concentrates on the first-order scattering effects, namely each multipath signal is a two-hop signal that involves a single scattering object. The first hop

Hung Huy Khong; Bing W. Kwan; Leonard J. Tung

2009-01-01

448

Improvements to Multiple Path Secure Copy  

Microsoft Academic Search

The demand to move large amounts of data between sites are ubiquitous and growing-particularly among the signal\\/image processing (SIP) community. The Department of Energy (DOE) Sandia Labs has made available a tool called multiple path secure copy (MPSCP), which can move data 4 to 90 times faster than OpenSSHpsilas secure copy (SCP) by using parallel TCP streams. We have enhanced

B. J. Guilfoos; L. R. Humphrey; J. Unpingco

2008-01-01

449

Priming on the path of least resistance  

E-print Network

Check Fluency. Originality Correlations. Discussion. . The Path of Least Resistance and Imagination Frequency. . . Object and Non-object Category Comparisons. . . . . . . . . . . . . . . . Priming Creativity. . 26 . . . . . 26 . 26 . . . . . 29... for the production of new ideas is of central importance. The experiments of this thesis investigated proposed mechanisms of idea generation. Work on creativity and idea generation has led Ward, Smith, and Vaid (1997) to propose a process termed conceptual...

Wruck, Eric Michael

2012-06-07

450

Teaching Career Paths and Teacher Education Reforms  

Microsoft Academic Search

This paper addresses policy issues raised by recent recommendations (e.g., Holmes Group, 1986) to improve the quality of teacher education by moving to fifth-year certification. It describes career patterns of beginning teachers with different undergraduate preparation paths, using data from the 1979 follow-up of the National Longitudinal Study of the High School Class of 1972 (NLS-72) (Riccobono, Henderson, Burkheimer, Place,

Maureen W. McClure; John C. Weidman; Laure M. Sharp

1988-01-01

451

Free Energy Changes, Fluctuations, and Path Probabilities  

E-print Network

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

William G. Hoover; Carol G. Hoover

2011-04-20

452

Predicting Tor path compromise by exit port  

Microsoft Academic Search

Abstract—Tor is currently the most,popular low,latency anonymizing overlay network for TCP-based applications. How- ever, it is well understood that Tor’s path selection algorithm is vulnerable to end-to-end traffic correlation attacks since it chooses Tor routers in proportion to their perceived bandwidth capabilities. Prior work has shown that the fraction of malicious routers and the amount,of adversary-controlled bandwidth are significant factors

Kevin S. Bauer; Dirk Grunwald; Douglas C. Sicker

2009-01-01

453

Covariant path integrals on hyperbolic surfaces  

SciTech Connect

DeWitt{close_quote}s covariant formulation of path integration [B. De Witt, {open_quotes}Dynamical theory in curved spaces. I. A review of the classical and quantum action principles,{close_quotes} Rev. Mod. Phys. {bold 29}, 377{endash}397 (1957)] has two practical advantages over the traditional methods of {open_quotes}lattice approximations;{close_quotes} there is no ordering problem, and classical symmetries are manifestly preserved at the quantum level. Applying the spectral theorem for unbounded self-adjoint operators, we provide a rigorous proof of the convergence of certain path integrals on Riemann surfaces of constant curvature {minus}1. The Pauli{endash}DeWitt curvature correction term arises, as in DeWitt{close_quote}s work. Introducing a Fuchsian group {Gamma} of the first kind, and a continuous, bounded, {Gamma}-automorphic potential V, we obtain a Feynman{endash}Kac formula for the automorphic Schr{umlt o}dinger equation on the Riemann surface {Gamma}{backslash}H. We analyze the Wick rotation and prove the strong convergence of the so-called Feynman maps [K. D. Elworthy, {ital Path Integration on Manifolds, Mathematical Aspects of Superspace}, edited by Seifert, Clarke, and Rosenblum (Reidel, Boston, 1983), pp. 47{endash}90] on a dense set of states. Finally, we give a new proof of some results in C. Grosche and F. Steiner, {open_quotes}The path integral on the Poincare upper half plane and for Liouville quantum mechanics,{close_quotes} Phys. Lett. A {bold 123}, 319{endash}328 (1987). {copyright} {ital 1997 American Institute of Physics.}

Schaefer, J. [Department of Mathematics, State University of New York at Stony Brook, Stony Brook, New York 11794-3651 (United States)] [Department of Mathematics, State University of New York at Stony Brook, Stony Brook, New York 11794-3651 (United States)

1997-11-01

454

Moments of Directed Paths in a Wedge  

NASA Astrophysics Data System (ADS)

A directed path from the origin in the square lattice, and confined to a wedge, exerts a net entropic force on the wedge. If the wedge is formed by the Y -axis and the line Y = rX, then the moment of the force on the line Y = rX about the origin is given by {\\cal M}_\\alpha = \\frac{-\\log \\cot\\alpha}{(1+\\cot\\alpha)^2} \\qquad \\if 0 \\leq \\alpha\\leq \\pi/4 where ? is the vertex angle of the wedge formed by the lines X = 0 and Y = rX in the square lattice. If ? in [ ?/4, ?/2), then the moment about the origin is zero. This model is closely related to a model of a descending directed path crossing a wedge from the point (0, N) to the point (pM, qM) on the line Y = (q/p)X. If lengths in this model are rescaled by pM, while N = lfloor?qMrfloor and (q/p) ? r, where r is an irrational number, then a limiting model of a path crossing the wedge from the point (0, ?) to the point (1, r) on the line Y = rX is obtained. The limiting path exerts a force on the line Y = rX, and the moment of this force about the origin is {\\cal M}_\\alpha = \\frac{-(\\beta-1)\\log((\\beta-1)\\cot\\alpha) }{(1+(\\beta-1)\\cot\\alpha)^2} if ? > 1 and where ? ? [0, ?/2] is the vertex angle of the wedge.

Janse van Rensburg, E. J.

2006-06-01

455

Coherent state path integrals in the continuum  

E-print Network

We discuss the time-continuous path integration in the coherent states basis in a way that is free from inconsistencies. Employing this notion we reproduce known and exact results working directly in the continuum. Such a formalism can set the basis to develop perturbative and non-perturbative approximations already known in the quantum field theory community. These techniques can be proven useful in a great variety of problems where bosonic Hamiltonians are used.

G. Kordas; S. I. Mistakidis; A. I. Karanikas

2014-08-14

456

Toward a consistent interpretation of the QTAIM: tortuous link between chemical bonds, interactions, and bond/line paths.  

PubMed

Currently, bonding analysis of molecules based on the Quantum Theory of Atoms in Molecules (QTAIM) is popular; however, "misinterpretations" of the QTAIM analysis are also very frequent. In this contribution the chemical relevance of the bond path as one of the key topological entities emerging from the QTAIM's topological analysis of the one-electron density is reconsidered. The role of nuclear vibrations on the topological analysis is investigated demonstrating that the bond paths are not indicators of chemical bonds. Also, it is argued that the detection of the bond paths is not necessary for the "interaction" to be present between two atoms in a molecule. The conceptual disentanglement of chemical bonds/interactions from the bonds paths, which are alternatively termed "line paths" in this contribution, dismisses many superficial inconsistencies. Such inconsistencies emerge from the presence/absence of the line paths in places of a molecule in which chemical intuition or alternative bonding analysis does not support the presence/absence of a chemical bond. Moreover, computational QTAIM studies have been performed on some "problematic" molecules, which were considered previously by other authors, and the role of nuclear vibrations on presence/absence of the line paths is studied demonstrating that a bonding pattern consistent with other theoretical schemes appears after a careful QTAIM analysis and a new "interpretation" of data is performed. PMID:24990224

Foroutan-Nejad, Cina; Shahbazian, Shant; Marek, Radek

2014-08-01

457

Conductivity of soils with preferential flow paths  

SciTech Connect

Laboratory soil column experiments were conducted to study the distribution of preferential flow paths resulting from removal of fine-size clay particles. These experiments specifically studied the influence of clay (kaolinite) percentage in sand-clay mixtures and the effect of hydraulic gradients on pore evolution. Analysis of the effluent during the experiments indicated that clay particles were removed from the soil column, accompanied by an increase in porosity and hydraulic conductivity. Dye experiments were conducted on the same columns to stain the pathways where clay particle removal occurred. It was observed that pore formation was fairly uniform in some cases, while other cases showed distinct preferential flow path formation. A physically-based model was used to identify a dimensionless parameter, G, which expresses the ratio of detachment and deposition forces at any space-time location. A model, based on equivalent media theory, is proposed to describe the hydraulic conductivity of soils with preferential flow paths. Future work will test the theoretical expressions for conductivity with experimental results, and investigate the relationship between G and the equivalent conductivity for such soils.

Lin, J.; Govindaraju, R.S. [Kansas State Univ., Manhattan, KS (United States). Dept. of Civil Engineering

1996-12-31

458

Adaptive path planning: Algorithm and analysis  

SciTech Connect

To address the need for a fast path planner, we present a learning algorithm that improves path planning by using past experience to enhance future performance. The algorithm relies on an existing path planner to provide solutions difficult tasks. From these solutions, an evolving sparse work of useful robot configurations is learned to support faster planning. More generally, the algorithm provides a framework in which a slow but effective planner may be improved both cost-wise and capability-wise by a faster but less effective planner coupled with experience. We analyze algorithm by formalizing the concept of improvability and deriving conditions under which a planner can be improved within the framework. The analysis is based on two stochastic models, one pessimistic (on task complexity), the other randomized (on experience utility). Using these models, we derive quantitative bounds to predict the learning behavior. We use these estimation tools to characterize the situations in which the algorithm is useful and to provide bounds on the training time. In particular, we show how to predict the maximum achievable speedup. Additionally, our analysis techniques are elementary and should be useful for studying other types of probabilistic learning as well.

Chen, Pang C.

1995-03-01

459

Average path length for Sierpinski pentagon  

E-print Network

In this paper,we investigate diameter and average path length(APL) of Sierpinski pentagon based on its recursive construction and self-similar structure.We find that the diameter of Sierpinski pentagon is just the shortest path lengths between two nodes of generation 0. Deriving and solving the linear homogenous recurrence relation the diameter satisfies, we obtain rigorous solution for the diameter. We also obtain approximate solution for APL of Sierpinski pentagon, both diameter and APL grow approximately as a power-law function of network order $N(t)$, with the exponent equals $\\frac{\\ln(1+\\sqrt{3})}{\\ln(5)}$. Although the solution for APL is approximate,it is trusted because we have calculated all items of APL accurately except for the compensation($\\Delta_{t}$) of total distances between non-adjacent branches($\\Lambda_t^{1,3}$), which is obtained approximately by least-squares curve fitting. The compensation($\\Delta_{t}$) is only a small part of total distances between non-adjacent branches($\\Lambda_t^{1,3}$) and has little effect on APL. Further more,using the data obtained by iteration to test the fitting results, we find the relative error for $\\Delta_{t}$ is less than $10^{-7}$, hence the approximate solution for average path length is almost accurate.

Junhao Peng; Guoai Xu

2011-12-21

460

Terminal area flight path generation using parallel constraint propagation  

E-print Network

A Flight Path Generator is defined as the module of an automated Air Traffic Control system which plans aircraft trajectories in the terminal area with respect to operational constraints. The flight path plans have to be ...

Sadoune, Michel

1989-01-01