Constraints on galaxy formation theories

NASA Technical Reports Server (NTRS)

Szalay, A. S.

1986-01-01

The present theories of galaxy formation are reviewed. The relation between peculiar velocities, temperature fluctuations of the microwave background and the correlation function of galaxies point to the possibility that galaxies do not form uniformly everywhere. The velocity data provide strong constraints on the theories even in the case when light does not follow mass of the universe.

Poynting Robertson Battery and the Chiral Magnetic Fields of AGN Jets

NASA Technical Reports Server (NTRS)

Kazanas, Demosthenes

2010-01-01

We propose that the magnetic fields in the accretion disks of active galactic nuclei (AGNs) are generated by azimuthal electric currents due to the difference between the plasma electron and ion velocities that arises when the electrons are retarded by interactions with the AGN photons (the Poynting Robertson battery). This process provides a unique relation between the polarity of the poloidal B field to the angular velocity Omega of the accretion disk (B is parallel to Omega), a relation absent in the more popular dynamo B-field generation. This then leads to a unique direction for the toroidal B field induced by disk rotation. Observations of the toroidal fields of 29 AGN jets revealed by parsec-scale Faraday rotation measurements show a clear asymmetry that is consistent with this model, with the probability that this asymmetry comes about by chance being approx.0.06 %. This lends support to the hypothesis that the universe is seeded by B fields that are generated in AGNs via this mechanism and subsequently injected into intergalactic space by the jet outflows.

Tsunami-HySEA model validation for tsunami current predictions

NASA Astrophysics Data System (ADS)

Macías, Jorge; Castro, Manuel J.; González-Vida, José Manuel; Ortega, Sergio

2016-04-01

Model ability to compute and predict tsunami flow velocities is of importance in risk assessment and hazard mitigation. Substantial damage can be produced by high velocity flows, particularly in harbors and bays, even when the wave height is small. Besides, an accurate simulation of tsunami flow velocities and accelerations is fundamental for advancing in the study of tsunami sediment transport. These considerations made the National Tsunami Hazard Mitigation Program (NTHMP) proposing a benchmark exercise focussed on modeling and simulating tsunami currents. Until recently, few direct measurements of tsunami velocities were available to compare and to validate model results. After Tohoku 2011 many current meters measurement were made, mainly in harbors and channels. In this work we present a part of the contribution made by the EDANYA group from the University of Malaga to the NTHMP workshop organized at Portland (USA), 9-10 of February 2015. We have selected three out of the five proposed benchmark problems. Two of them consist in real observed data from the Tohoku 2011 event, one at Hilo Habour (Hawaii) and the other at Tauranga Bay (New Zealand). The third one consists in laboratory experimental data for the inundation of Seaside City in Oregon. Acknowledgements: This research has been partially supported by the Junta de Andalucía research project TESELA (P11-RNM7069) and the Spanish Government Research project DAIFLUID (MTM2012-38383-C02-01) and Universidad de Málaga, Campus de Excelencia Andalucía TECH. The GPU and multi-GPU computations were performed at the Unit of Numerical Methods (UNM) of the Research Support Central Services (SCAI) of the University of Malaga.

Approximation of wave action flux velocity in strongly sheared mean flows

NASA Astrophysics Data System (ADS)

Banihashemi, Saeideh; Kirby, James T.; Dong, Zhifei

2017-08-01

Spectral wave models based on the wave action equation typically use a theoretical framework based on depth uniform current to account for current effects on waves. In the real world, however, currents often have variations over depth. Several recent studies have made use of a depth-weighted current U˜ due to [Skop, R. A., 1987. Approximate dispersion relation for wave-current interactions. J. Waterway, Port, Coastal, and Ocean Eng. 113, 187-195.] or [Kirby, J. T., Chen, T., 1989. Surface waves on vertically sheared flows: approximate dispersion relations. J. Geophys. Res. 94, 1013-1027.] in order to account for the effect of vertical current shear. Use of the depth-weighted velocity, which is a function of wavenumber (or frequency and direction) has been further simplified in recent applications by only utilizing a weighted current based on the spectral peak wavenumber. These applications do not typically take into account the dependence of U˜ on wave number k, as well as erroneously identifying U˜ as the proper choice for current velocity in the wave action equation. Here, we derive a corrected expression for the current component of the group velocity. We demonstrate its consistency using analytic results for a current with constant vorticity, and numerical results for a measured, strongly-sheared current profile obtained in the Columbia River. The effect of choosing a single value for current velocity based on the peak wave frequency is examined, and we suggest an alternate strategy, involving a Taylor series expansion about the peak frequency, which should significantly extend the range of accuracy of current estimates available to the wave model with minimal additional programming and data transfer.

Theoretical implications of the galactic radial acceleration relation of McGaugh, Lelli, and Schombert

NASA Astrophysics Data System (ADS)

Nesbet, Robert K.

2018-05-01

Velocities in stable circular orbits about galaxies, a measure of centripetal gravitation, exceed the expected Kepler/Newton velocity as orbital radius increases. Standard Λ cold dark matter (ΛCDM) attributes this anomaly to galactic dark matter. McGaugh et al. have recently shown for 153 disc galaxies that observed radial acceleration is an apparently universal function of classical acceleration computed for observed galactic baryonic mass density. This is consistent with the empirical modified Newtonian dynamics (MOND) model, not requiring dark matter. It is shown here that suitably constrained ΛCDM and conformal gravity (CG) also produce such a universal correlation function. ΛCDM requires a very specific dark matter distribution, while the implied CG non-classical acceleration must be independent of galactic mass. All three constrained radial acceleration functions agree with the empirical baryonic v4 Tully-Fisher relation. Accurate rotation data in the nominally flat velocity range could distinguish between MOND, ΛCDM, and CG.

Weyl corrections to diffusion and chaos in holography

NASA Astrophysics Data System (ADS)

Li, Wei-Jia; Liu, Peng; Wu, Jian-Pin

2018-04-01

Using holographic methods in the Einstein-Maxwell-dilaton-axion (EMDA) theory, it was conjectured that the thermal diffusion in a strongly coupled metal without quasi-particles saturates an universal lower bound that is associated with the chaotic property of the system at infrared (IR) fixed points [1]. In this paper, we investigate the thermal transport and quantum chaos in the EMDA theory with a small Weyl coupling term. It is found that the Weyl coupling correct the thermal diffusion constant D Q and butterfly velocity v B in different ways, hence resulting in a modified relation between the two at IR fixed points. Unlike that in the EMDA case, our results show that the ratio D Q /( v B 2 τ L ) always contains a non-universal Weyl correction which depends also on the bulk fields as long as the U(1) current is marginally relevant in the IR.

Large-scale Observations of a Subauroral Polarization Stream by Midlatitude SuperDARN Radars: Instantaneous Longitudinal Velocity Variations

NASA Technical Reports Server (NTRS)

Clausen, L. B. N.; Baker, J. B. H.; Sazykin, S.; Ruohoniemi, J. M.; Greenwald, R. A.; Thomas, E. J.; Shepherd, S. G.; Talaat, E. R.; Bristow, W. A.; Zheng, Y.;

The D-material universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elghozi, Thomas; Mavromatos, Nick E.; Sakellariadou, Mairi

In a previous publication by some of the authors (N.E.M., M.S. and M.F.Y.), we have argued that the ''D-material universe'', that is a model of a brane world propagating in a higher-dimensional bulk populated by collections of D-particle stringy defects, provides a model for the growth of large-scale structure in the universe via the vector field in its spectrum. The latter corresponds to D-particle recoil velocity excitations as a result of the interactions of the defects with stringy matter and radiation on the brane world. In this article, we first elaborate further on the results of the previous study onmore » the galactic growth era and analyse the circumstances under which the D-particle recoil velocity fluid may ''mimic'' dark matter in galaxies. A lensing phenomenology is also presented for some samples of galaxies, which previously were known to provide tension for modified gravity (TeVeS) models. The current model is found in agreement with these lensing data. Then we discuss a cosmic evolution for the D-material universe by analysing the conditions under which the late eras of this universe associated with large-scale structure are connected to early epochs, where inflation takes place. It is shown that inflation is induced by dense populations of D-particles in the early universe, with the rôle of the inflaton field played by the condensate of the D-particle recoil-velocity fields under their interaction with relativistic stringy matter, only for sufficiently large brane tensions and low string mass scales compared to the Hubble scale. On the other hand, for large string scales, where the recoil-velocity condensate fields are weak, inflation cannot be driven by the D-particle defects alone. In such cases inflation may be driven by dilaton (or other moduli) fields in the underlying string theory.« less

Electromagnetic energy dispersion in a 5D universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hartnett, John G.

2010-06-15

Electromagnetism is analyzed in a 5D expanding universe. Compared to the usual 4D description of electrodynamics it can be viewed as adding effective charge and current densities to the universe that are static in time. These lead to effective polarization and magnetization of the vacuum, which is most significant at high redshift. Electromagnetic waves propagate but group and phase velocities are dispersive. This introduces a new energy scale to the cosmos. And as a result electromagnetic waves propagate with superluminal speeds but no energy is transmitted faster than the canonical speed of light c.

Forward and inverse kinematics of double universal joint robot wrists

NASA Technical Reports Server (NTRS)

Williams, Robert L., II

1991-01-01

A robot wrist consisting of two universal joints can eliminate the wrist singularity problem found on many individual robots. Forward and inverse position and velocity kinematics are presented for such a wrist having three degrees of freedom. Denavit-Hartenberg parameters are derived to find the transforms required for the kinematic equations. The Omni-Wrist, a commercial double universal joint robot wrist, is studied in detail. There are four levels of kinematic parameters identified for this wrist; three forward and three inverse maps are presented for both position and velocity. These equations relate the hand coordinate frame to the wrist base frame. They are sufficient for control of the wrist standing alone. When the wrist is attached to a manipulator arm; the offset between the two universal joints complicates the solution of the overall kinematics problem. All wrist coordinate frame origins are not coincident, which prevents decoupling of position and orientation for manipulator inverse kinematics.

Spatial interpolation of river channel topography using the shortest temporal distance

NASA Astrophysics Data System (ADS)

Zhang, Yanjun; Xian, Cuiling; Chen, Huajin; Grieneisen, Michael L.; Liu, Jiaming; Zhang, Minghua

2016-11-01

It is difficult to interpolate river channel topography due to complex anisotropy. As the anisotropy is often caused by river flow, especially the hydrodynamic and transport mechanisms, it is reasonable to incorporate flow velocity into topography interpolator for decreasing the effect of anisotropy. In this study, two new distance metrics defined as the time taken by water flow to travel between two locations are developed, and replace the spatial distance metric or Euclidean distance that is currently used to interpolate topography. One is a shortest temporal distance (STD) metric. The temporal distance (TD) of a path between two nodes is calculated by spatial distance divided by the tangent component of flow velocity along the path, and the STD is searched using the Dijkstra algorithm in all possible paths between two nodes. The other is a modified shortest temporal distance (MSTD) metric in which both the tangent and normal components of flow velocity were combined. They are used to construct the methods for the interpolation of river channel topography. The proposed methods are used to generate the topography of Wuhan Section of Changjiang River and compared with Universal Kriging (UK) and Inverse Distance Weighting (IDW). The results clearly showed that the STD and MSTD based on flow velocity were reliable spatial interpolators. The MSTD, followed by the STD, presents improvement in prediction accuracy relative to both UK and IDW.

Evolution of cyclic mixmaster universes with noncomoving radiation

NASA Astrophysics Data System (ADS)

Ganguly, Chandrima; Barrow, John D.

2017-12-01

We study a model of a cyclic, spatially homogeneous, anisotropic, "mixmaster" universe of Bianchi type IX, containing a radiation field with noncomoving ("tilted" with respect to the tetrad frame of reference) velocities and vorticity. We employ a combination of numerical and approximate analytic methods to investigate the consequences of the second law of thermodynamics on the evolution. We model a smooth cycle-to-cycle evolution of the mixmaster universe, bouncing at a finite minimum, by the device of adding a comoving "ghost" field with negative energy density. In the absence of a cosmological constant, an increase in entropy, injected at the start of each cycle, causes an increase in the volume maxima, increasing approach to flatness, falling velocities and vorticities, and growing anisotropy at the expansion maxima of successive cycles. We find that the velocities oscillate rapidly as they evolve and change logarithmically in time relative to the expansion volume. When the conservation of momentum and angular momentum constraints are imposed, the spatial components of these velocities fall to smaller values when the entropy density increases, and vice versa. Isotropization is found to occur when a positive cosmological constant is added because the sequence of oscillations ends and the dynamics expand forever, evolving towards a quasi-de Sitter asymptote with constant velocity amplitudes. The case of a single cycle of evolution with a negative cosmological constant added is also studied.

Factors influencing perceived angular velocity.

PubMed

Kaiser, M K; Calderone, J B

1991-11-01

The assumption that humans are able to perceive and process angular kinematics is critical to many structure-from-motion and optical flow models. The current studies investigate this sensitivity, and examine several factors likely to influence angular velocity perception. In particular, three factors are considered: (1) the extent to which perceived angular velocity is determined by edge transitions of surface elements, (2) the extent to which angular velocity estimates are influenced by instantaneous linear velocities of surface elements, and (3) whether element-velocity effects are related to three-dimensional (3-D) tangential velocities or to two-dimensional (2-D) image velocities. Edge-transition rate biased angular velocity estimates only when edges were highly salient. Element velocities influenced perceived angular velocity; this bias was related to 2-D image velocity rather than 3-D tangential velocity. Despite these biases, however, judgments were most strongly determined by the true angular velocity. Sensitivity to this higher order motion parameter was surprisingly good, for rotations both in depth (y-axis) and parallel to the line of sight (z-axis).

Methods of Measurement of High Air Velocities by the Hot-wire Method

NASA Technical Reports Server (NTRS)

Weske, John R.

1943-01-01

Investigations of strengths of hot wires at high velocities were conducted with platinum, nickel, and tungsten at approximately 200 Degrees Celcius hot-wire temperature. The results appear to disqualify platinum for velocities approaching the sonic range; whereas nickel withstands sound velocity, and tungsten may be used for supersonic velocities under standard atmospheric conditions. Hot wires must be supported by rigid prolongs at high velocities to avoid wire breakage. Resting current measurements for constant temperature show agreement with King's relation.

Shallow water models as tool for tsunami current predictions in ports and harbors. Validation with Tohoku 2011 field data

NASA Astrophysics Data System (ADS)

Gonzalez Vida, J. M., Sr.; Macias Sanchez, J.; Castro, M. J.; Ortega, S.

2015-12-01

Model ability to compute and predict tsunami flow velocities is of importance in risk assessment and hazard mitigation. Substantial damage can be produced by high velocity flows, particularly in harbors and bays, even when the wave height is small. Besides, an accurate simulation of tsunami flow velocities and accelerations is fundamental for advancing in the study of tsunami sediment transport. These considerations made the National Tsunami Hazard Mitigation Program (NTHMP) proposing a benchmark exercise focused on modeling and simulating tsunami currents. Until recently, few direct measurements of tsunami velocities were available to compare and to validate model results. After Tohoku 2011 many current meters measurement were made, mainly in harbors and channels. In this work we present a part of the contribution made by the EDANYA group from the University of Malaga to the NTHMP workshop organized at Portland (USA), 9-10 of February 2015. We have selected three out of the five proposed benchmark problems. Two of them consist in real observed data from the Tohoku 2011 event, one at Hilo Habour (Hawaii) and the other at Tauranga Bay (New Zealand). The third one consists in laboratory experimental data for the inundation of Seaside City in Oregon. For this model validation the Tsunami-HySEA model, developed by EDANYA group, was used. The overall conclusion that we could extract from this validation exercise was that the Tsunami-HySEA model performed well in all benchmark problems proposed. The greater spatial variability in tsunami velocity than wave height makes it more difficult its precise numerical representation. The larger variability in velocities is likely a result of the behaviour of the flow as it is channelized and as it flows around bathymetric highs and structures. In the other hand wave height do not respond as strongly to chanelized flow as current velocity.

Crustal velocity structure of the Northern Victoria Land, Antarctica, from ambient seismic noise tomography

NASA Astrophysics Data System (ADS)

Yoo, H. J.; Park, Y.; Lee, W. S.; Graw, J. H.; Hansen, S. E.; Kang, T. S.

2017-12-01

A shear wave velocity model of the Northern Victoria Land, Antarctica, was derived using Rayleigh-wave group velocity dispersions estimated from the cross correlation of ambient seismic noise. The continuous data, from January to November 2015, recorded on 29 broadband stations operated by Korea Polar Research Institute and Alabama University were used for retrieving the fundamental mode Rayleigh-wave Green's functions of each station pair. Rayleigh-wave group dispersions at period ranging from 3 to 23 s were determined by applying the multi-filter analysis technique. The measured group velocities were inverted to obtain 2-D group velocity maps using a fast marching method. We constructed a pseudo-3-D shear velocity model of the study region using 1-D shear velocity inversions at each node followed by a linear interpolation. The resulting shear velocity maps and cross-sections showed the significant velocity differences in the crust across the East Antarctica, Transantarctic Mountains, and the coastal region. The velocity changes are well correlated with the aeromagnetic lineaments, especially in shallow depth. The velocities in the Transantarctic Mountains are relatively high at shallow depth and lower at deeper depth, while those of the coastal region are relatively low in shallow depth and higher at deeper depth, implying thin crust over this area.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabra, Bassem M.; Saliba, Charbel; Akl, Maya Abi

We explore the connection between the central supermassive black holes (SMBH) in galaxies and the dark matter halo through the relation between the masses of the SMBHs and the maximum circular velocities of the host galaxies, as well as the relationship between stellar velocity dispersion of the spheroidal component and the circular velocity. Our assumption here is that the circular velocity is a proxy for the mass of the dark matter halo. We rely on a heterogeneous sample containing galaxies of all types. The only requirement is that the galaxy has a direct measurement of the mass of its SMBHmore » and a direct measurement of its circular velocity and its velocity dispersion. Previous studies have analyzed the connection between the SMBH and dark matter halo through the relationship between the circular velocity and the bulge velocity dispersion, with the assumption that the bulge velocity dispersion stands in for the mass of the SMBH, via the well-established SMBH mass–bulge velocity dispersion relation. Using intermediate relations may be misleading when one is studying them to decipher the active ingredients of galaxy formation and evolution. We believe that our approach will provide a more direct probe of the SMBH and the dark matter halo connection. We find that the correlation between the mass of SMBHs and the circular velocities of the host galaxies is extremely weak, leading us to state the dark matter halo may not play a major role in regulating the black hole growth in the present Universe.« less

Velocity segregation and systematic biases in velocity dispersion estimates with the SPT-GMOS spectroscopic survey

DOE PAGES

Bayliss, Matthew. B.; Zengo, Kyle; Ruel, Jonathan; ...

2017-03-07

The velocity distribution of galaxies in clusters is not universal; rather, galaxies are segregated according to their spectral type and relative luminosity. We examine the velocity distributions of different populations of galaxies within 89 Sunyaev Zel'dovich (SZ) selected galaxy clusters spanningmore » $ 0.28 < z < 1.08$. Our sample is primarily draw from the SPT-GMOS spectroscopic survey, supplemented by additional published spectroscopy, resulting in a final spectroscopic sample of 4148 galaxy spectra---2868 cluster members. The velocity dispersion of star-forming cluster galaxies is $$17\\pm4$$% greater than that of passive cluster galaxies, and the velocity dispersion of bright ($$m < m^{*}-0.5$$) cluster galaxies is $$11\\pm4$$% lower than the velocity dispersion of our total member population. We find good agreement with simulations regarding the shape of the relationship between the measured velocity dispersion and the fraction of passive vs. star-forming galaxies used to measure it, but we find a small offset between this relationship as measured in data and simulations in which suggests that our dispersions are systematically low by as much as 3\\% relative to simulations. We argue that this offset could be interpreted as a measurement of the effective velocity bias that describes the ratio of our observed velocity dispersions and the intrinsic velocity dispersion of dark matter particles in a published simulation result. Here, by measuring velocity bias in this way suggests that large spectroscopic surveys can improve dispersion-based mass-observable scaling relations for cosmology even in the face of velocity biases, by quantifying and ultimately calibrating them out.« less

Velocity segregation and systematic biases in velocity dispersion estimates with the SPT-GMOS spectroscopic survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bayliss, Matthew. B.; Zengo, Kyle; Ruel, Jonathan

The velocity distribution of galaxies in clusters is not universal; rather, galaxies are segregated according to their spectral type and relative luminosity. We examine the velocity distributions of different populations of galaxies within 89 Sunyaev Zel'dovich (SZ) selected galaxy clusters spanningmore » $ 0.28 < z < 1.08$. Our sample is primarily draw from the SPT-GMOS spectroscopic survey, supplemented by additional published spectroscopy, resulting in a final spectroscopic sample of 4148 galaxy spectra---2868 cluster members. The velocity dispersion of star-forming cluster galaxies is $$17\\pm4$$% greater than that of passive cluster galaxies, and the velocity dispersion of bright ($$m < m^{*}-0.5$$) cluster galaxies is $$11\\pm4$$% lower than the velocity dispersion of our total member population. We find good agreement with simulations regarding the shape of the relationship between the measured velocity dispersion and the fraction of passive vs. star-forming galaxies used to measure it, but we find a small offset between this relationship as measured in data and simulations in which suggests that our dispersions are systematically low by as much as 3\\% relative to simulations. We argue that this offset could be interpreted as a measurement of the effective velocity bias that describes the ratio of our observed velocity dispersions and the intrinsic velocity dispersion of dark matter particles in a published simulation result. Here, by measuring velocity bias in this way suggests that large spectroscopic surveys can improve dispersion-based mass-observable scaling relations for cosmology even in the face of velocity biases, by quantifying and ultimately calibrating them out.« less

Velocity Segregation and Systematic Biases In Velocity Dispersion Estimates with the SPT-GMOS Spectroscopic Survey

NASA Astrophysics Data System (ADS)

Bayliss, Matthew. B.; Zengo, Kyle; Ruel, Jonathan; Benson, Bradford A.; Bleem, Lindsey E.; Bocquet, Sebastian; Bulbul, Esra; Brodwin, Mark; Capasso, Raffaella; Chiu, I.-non; McDonald, Michael; Rapetti, David; Saro, Alex; Stalder, Brian; Stark, Antony A.; Strazzullo, Veronica; Stubbs, Christopher W.; Zenteno, Alfredo

2017-03-01

The velocity distribution of galaxies in clusters is not universal; rather, galaxies are segregated according to their spectral type and relative luminosity. We examine the velocity distributions of different populations of galaxies within 89 Sunyaev Zel’dovich (SZ) selected galaxy clusters spanning 0.28< z< 1.08. Our sample is primarily draw from the SPT-GMOS spectroscopic survey, supplemented by additional published spectroscopy, resulting in a final spectroscopic sample of 4148 galaxy spectra—2868 cluster members. The velocity dispersion of star-forming cluster galaxies is 17 ± 4% greater than that of passive cluster galaxies, and the velocity dispersion of bright (m< {m}* -0.5) cluster galaxies is 11 ± 4% lower than the velocity dispersion of our total member population. We find good agreement with simulations regarding the shape of the relationship between the measured velocity dispersion and the fraction of passive versus star-forming galaxies used to measure it, but we find a small offset between this relationship as measured in data and simulations, which suggests that our dispersions are systematically low by as much as 3% relative to simulations. We argue that this offset could be interpreted as a measurement of the effective velocity bias that describes the ratio of our observed velocity dispersions and the intrinsic velocity dispersion of dark matter particles in a published simulation result. Measuring velocity bias in this way suggests that large spectroscopic surveys can improve dispersion-based mass-observable scaling relations for cosmology even in the face of velocity biases, by quantifying and ultimately calibrating them out.

Passage of the discharge current through the plasma-electrode interface in the electromagnetic rail accelerator channel

NASA Astrophysics Data System (ADS)

Zhukov, B. G.; Reznikov, B. I.; Kurakin, R. O.; Ponyaev, S. A.; Bobashev, S. V.

2016-11-01

We investigate the phenomena that accompany the acceleration of a free plasma piston (without a striker) in the electromagnetic rail accelerator channel filled with different gases (argon, helium). An intense glow appears in the shock-compressed layer (SCL) in the case of strong shock waves that produce a high electron concentration ( 1017-1018 cm-3) behind the front. We have proposed that explosive electron emission (EEE) ensures the high-intensity emission of electrons, the passage of a part of the discharge current through the SCL, and the glow of the SCL. The velocity of a shock wave for which the strong electric field in the Debye layer at the cathode causes EEE from its surface and the passage of the current in the SCL has been determined. It has been concluded that, for high velocities of the plasma, the EEE is a universal mechanism that ensure the passage of a strong current through the interface between the cold electrode and the plasma.

Nonmonotonic velocity dependence of atomic friction.

PubMed

Reimann, Peter; Evstigneev, Mykhaylo

2004-12-03

We propose a theoretical model for friction force microscopy experiments with special emphasis on the realistic description of dissipation and inertia effects. Its main prediction is a nonmonotonic dependence of the friction force upon the sliding velocity of the atomic force microscope tip relative to an atomically flat surface. The region around the force maximum can be approximately described by a universal scaling law and should be observable under experimentally realistic conditions.

Current Issues in Cosmology

NASA Astrophysics Data System (ADS)

Pecker, Jean-Claude; Narlikar, Jayant

2011-09-01

Part I. Observational Facts Relating to Discrete Sources: 1. The state of cosmology G. Burbidge; 2. The redshifts of galaxies and QSOs E. M. Burbidge and G. Burbidge; 3. Accretion discs in quasars J. Sulentic; Part II. Observational Facts Relating to Background Radiation: 4. CMB observations and consequences F. Bouchet; 5. Abundances of light nuclei K. Olive; 6. Evidence for an accelerating universe or lack of A. Blanchard; Part III. Standard Cosmology: 7. Cosmology, an overview of the standard model F. Bernardeau; 8. What are the building blocks of our universe? K. C. Wali; Part IV. Large-Scale Structure: 9. Observations of large-scale structure V. de Lapparent; 10. Reconstruction of large-scale peculiar velocity fields R. Mohayaee, B. Tully and U. Frisch; Part V. Alternative Cosmologies: 11. The quasi-steady state cosmology J. V. Narlikar; 12. Evidence for iron whiskers in the universe N. C. Wickramasinghe; 13. Alternatives to dark matter: MOND + Mach D. Roscoe; 14. Anthropic principle in cosmology B. Carter; Part VI. Evidence for Anomalous Redshifts: 15. Anomalous redshifts H. C. Arp; 16. Redshifts of galaxies and QSOs: the problem of redshift periodicities G. Burbidge; 17. Statistics of redshift periodicities W. Napier; 18. Local abnormal redshifts J.-C. Pecker; 19. Gravitational lensing and anomalous redshifts J. Surdej, J.-F. Claeskens and D. Sluse; Panel discussion; General discussion; Concluding remarks.

Autonomous navigation system and method

DOEpatents

Bruemmer, David J [Idaho Falls, ID; Few, Douglas A [Idaho Falls, ID

2009-09-08

A robot platform includes perceptors, locomotors, and a system controller, which executes instructions for autonomously navigating a robot. The instructions repeat, on each iteration through an event timing loop, the acts of defining an event horizon based on the robot's current velocity, detecting a range to obstacles around the robot, testing for an event horizon intrusion by determining if any range to the obstacles is within the event horizon, and adjusting rotational and translational velocity of the robot accordingly. If the event horizon intrusion occurs, rotational velocity is modified by a proportion of the current rotational velocity reduced by a proportion of the range to the nearest obstacle and translational velocity is modified by a proportion of the range to the nearest obstacle. If no event horizon intrusion occurs, translational velocity is set as a ratio of a speed factor relative to a maximum speed.

A Novel View of Spacetime Permitting Faster-Than-Light Travel

NASA Astrophysics Data System (ADS)

Meholic, Gregory V.

2004-02-01

Recent discoveries across many disciplines of physics have supported a driving need for a ``new'' science to explain the apparent relationship between phenomenon at cosmological scales and those at the quantum, subatomic level while still supporting the classical mechanics of motion, electromagnetism and relativity. A novel view of both the spacetime continuum and the universe is postulated that not only connects these fields of interest, but proposes a method to travel at superluminal speeds by examining the underlying equations of special relativity. The governing mathematics of special relativity describe a symmetrical continuum that supports not just one, but three, independent spacetimes each with a unique set of physical laws founded on the speed of light, c. These spacetimes are the subluminal (where v/c < 1), the luminal (where v/c = 1), and the superluminal (where v/c > 1) comprising a `tri-space' universe. Relativistic symmetry illustrates that there can be up to three velocities (one for each spacetime) for a given absolute energy state. The similar characteristics of mass and energy in each spacetime may permit faster-than-light (FTL) travel through a quantum transformation/exchange of energy and mass (at the quark level or beyond) between the subluminal and superluminal realms. Based on the suggested characteristics of superluminal spacetime, the `trans-space' method of FTL travel would allow a particle to traverse sublight space by traveling through the superlight continuum without incurring the penalties of special relativity or causal relations. In addition, the spacetime construct and superluminal realm of the `tri-space' universe may offer a different perspective than the current ideologies that could better represent physical phenomena including universal expansion, the zero-point field, dark matter, and the source of inertia.

Negative velocity fluctuations and non-equilibrium fluctuation relation for a driven high critical current vortex state.

PubMed

Bag, Biplab; Shaw, Gorky; Banerjee, S S; Majumdar, Sayantan; Sood, A K; Grover, A K

2017-07-17

Under the influence of a constant drive the moving vortex state in 2H-NbS 2 superconductor exhibits a negative differential resistance (NDR) transition from a steady flow to an immobile state. This state possesses a high depinning current threshold ([Formula: see text]) with unconventional depinning characteristics. At currents well above [Formula: see text], the moving vortex state exhibits a multimodal velocity distribution which is characteristic of vortex flow instabilities in the NDR regime. However at lower currents which are just above [Formula: see text], the velocity distribution is non-Gaussian with a tail extending to significant negative velocity values. These unusual negative velocity events correspond to vortices drifting opposite to the driving force direction. We show that this distribution obeys the Gallavotti-Cohen Non-Equilibrium Fluctuation Relation (GC-NEFR). Just above [Formula: see text], we also find a high vortex density fluctuating driven state not obeying the conventional GC-NEFR. The GC-NEFR analysis provides a measure of an effective energy scale (E eff ) associated with the driven vortex state. The E eff corresponds to the average energy dissipated by the fluctuating vortex state above [Formula: see text]. We propose the high E eff value corresponds to the onset of high energy dynamic instabilities in this driven vortex state just above [Formula: see text].

Hydrokinetic canal measurements: inflow velocity, wake flow velocity, and turbulence

DOE Data Explorer

Gunawan, Budi

2014-06-11

The dataset consist of acoustic Doppler current profiler (ADCP) velocity measurements in the wake of a 3-meter diameter vertical-axis hydrokinetic turbine deployed in Roza Canal, Yakima, WA, USA. A normalized hub-centerline wake velocity profile and two cross-section velocity contours, 10 meters and 20 meters downstream of the turbine, are presented. Mean velocities and turbulence data, measured using acoustic Doppler velocimeter (ADV) at 50 meters upstream of the turbine, are also presented. Canal dimensions and hydraulic properties, and turbine-related information are also included.

Aquatic habitat mapping with an acoustic doppler current profiler: Considerations for data quality

USGS Publications Warehouse

Gaeuman, David; Jacobson, Robert B.

2005-01-01

When mounted on a boat or other moving platform, acoustic Doppler current profilers (ADCPs) can be used to map a wide range of ecologically significant phenomena, including measures of fluid shear, turbulence, vorticity, and near-bed sediment transport. However, the instrument movement necessary for mapping applications can generate significant errors, many of which have not been inadequately described. This report focuses on the mechanisms by which moving-platform errors are generated, and quantifies their magnitudes under typical habitat-mapping conditions. The potential for velocity errors caused by mis-alignment of the instrument?s internal compass are widely recognized, but has not previously been quantified for moving instruments. Numerical analyses show that even relatively minor compass mis-alignments can produce significant velocity errors, depending on the ratio of absolute instrument velocity to the target velocity and on the relative directions of instrument and target motion. A maximum absolute instrument velocity of about 1 m/s is recommended for most mapping applications. Lower velocities are appropriate when making bed velocity measurements, an emerging application that makes use of ADCP bottom-tracking to measure the velocity of sediment particles at the bed. The mechanisms by which heterogeneities in the flow velocity field generate horizontal velocities errors are also quantified, and some basic limitations in the effectiveness of standard error-detection criteria for identifying these errors are described. Bed velocity measurements may be particularly vulnerable to errors caused by spatial variability in the sediment transport field.

Nonlinear Dynamics of the Cosmic Neutrino Background

NASA Astrophysics Data System (ADS)

Inman, Derek

At least two of the three neutrino species are known to be massive, but their exact masses are currently unknown. Cosmic neutrinos decoupled from the rest of the primordial plasma early on when the Universe was over a billion times hotter than it is today. These relic particles, which have cooled and are now non-relativistic, constitute the Cosmic Neutrino Background and permeate the Universe. While they are not observable directly, their presence can be inferred by measuring the suppression of the matter power spectrum. This suppression is a linear effect caused by the large thermal velocities of neutrinos, which prevent them from collapsing gravitationally on small scales. Unfortunately, it is difficult to measure because of degeneracies with other cosmological parameters and biases arising from the fact that we typically observe point-like galaxies rather than a continous matter field. It is therefore important to look for new effects beyond linear suppression that may be more sensitive to neutrinos. This thesis contributes to the understanding of the nonlinear dynamics of the cosmological neutrino background in the following ways: (i) the development of a new injection scheme for neutrinos in cosmological N-body simulations which circumvents many issues associated with simulating neutrinos at large redshifts, (ii) the numerical study of the relative velocity field between cold dark matter and neutrinos including its reconstruction from density fields, (iii) the theoretical description of neutrinos as a dispersive fluid and its use in modelling the nonlinear evolution of the neutrino density power spectrum, (iv) the derivation of the dipole correlation function using linear response which allows for the Fermi-Dirac velocity distribution to be properly included, and (v) the numerical study and detection of the dipole correlation function in the TianNu simulation. In totality, this thesis is a comprehensive study of neutrino density and velocity fields that may lead to a new technique for constraining neutrino properties via the dipole correlation function.

A coasting cosmology

NASA Technical Reports Server (NTRS)

Kolb, Edward W.

1989-01-01

A Friedmann-Robertson-Walker cosmology with energy density decreasing in expansion as 1/R-squared, where R is the Robertson-Walker scale factor, is studied. In such a model the universe expands with constant velocity; hence the term coasting cosmology. Observational consequences of such a model include the age of the universe, the luminosity distance-redshift relation (the Hubble diagram), the angular diameter distance-redshift relation, and the galaxy number count as a function of redshift. These observations are used to limit the parameters of the model. Among the interesting consequences of the model are the possibility of an ever-expanding closed universe, a model universe with multiple images at different redshifts of the same object, a universe with Omega - 1 not equal to 0 stable in expansion, and a closed universe with radius smaller than 1/H(0).

Kinematics of AWM and MKW Poor Clusters

NASA Astrophysics Data System (ADS)

Koranyi, Daniel M.; Geller, Margaret J.

2002-01-01

We have measured 1365 redshifts to a limiting magnitude of R~15.5 in 15 AWM/MKW clusters and have collected another 203 from the literature in MKW 4s, MKW 2, and MKW 2s. In AWM 7 we have extended the redshift sample to R~18 in the cluster center. We have identified 704 cluster members in 17 clusters; 201 are newly identified. We summarize the kinematics and distributions of the cluster galaxies and provide an initial discussion of substructure, mass and luminosity segregation, spectral segregation, velocity-dispersion profiles, and the relation of the central galaxy to global cluster properties. We compute optical mass estimates, which we compare with X-ray mass determinations from the literature. The clusters are in a variety of dynamical states, reflected in the three classes of behavior of the velocity-dispersion profile in the core: rising, falling, or flat/ambiguous. The velocity dispersion of the emission-line galaxy population significantly exceeds that of the absorption-line galaxies in almost all of the clusters, and the presence of emission-line galaxies at small projected radii suggests continuing infall of galaxies onto the clusters. The presence of a cD galaxy does not constrain the global cluster properties; these clusters are similar to other poor clusters that contain no cD. We use the similarity of the velocity-dispersion profiles at small radii and the cD-like galaxies' internal velocity dispersions to argue that cD formation is a local phenomenon. Our sample establishes an empirical observational baseline of poor clusters for comparison with simulations of similar systems. Observations reported in this paper were obtained at the Multiple Mirror Telescope Observatory, a facility operated jointly by the University of Arizona and the Smithsonian Institution; at the Whipple Observatory, a facility operated jointly by the Smithsonian Astrophysical Observatory and Harvard University; and at the WIYN Observatory, a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories.

Testing critical point universality along the λ-line

NASA Astrophysics Data System (ADS)

Nissen, J. A.; Swanson, D. R.; Geng, Z. K.; Dohm, V.; Israelsson, U. E.; DiPirro, M. J.; Lipa, J. A.

1998-02-01

We are currently building a prototype for a new test of critical-point universality at the lambda transition in 4He, which is to be performed in microgravity conditions. The flight experiment will measure the second-sound velocity as a function of temperature at pressures from 1 to 30 bars in the region close to the lambda line. The critical exponents and other parameters characterizing the behavior of the superfluid density will be determined from the measurements. The microgravity measurements will be quite extensive, probably taking 30 days to complete. In addition to the superfluid density, some measurements of the specific heat will be made using the low-g simulator at the Jet Propulsion Laboratory. The results of the superfluid density and specific heat measurements will be used to compare the asymptotic exponents and other universal aspects of the superfluid density with the theoretical predictions currently established by renormalization group techniques.

Constraining cosmology with the velocity function of low-mass galaxies

NASA Astrophysics Data System (ADS)

Schneider, Aurel; Trujillo-Gomez, Sebastian

2018-04-01

The number density of field galaxies per rotation velocity, referred to as the velocity function, is an intriguing statistical measure probing the smallest scales of structure formation. In this paper we point out that the velocity function is sensitive to small shifts in key cosmological parameters such as the amplitude of primordial perturbations (σ8) or the total matter density (Ωm). Using current data and applying conservative assumptions about baryonic effects, we show that the observed velocity function of the Local Volume favours cosmologies in tension with the measurements from Planck but in agreement with the latest findings from weak lensing surveys. While the current systematics regarding the relation between observed and true rotation velocities are potentially important, upcoming data from H I surveys as well as new insights from hydrodynamical simulations will dramatically improve the situation in the near future.

The kinematic component of the cosmological redshift

NASA Astrophysics Data System (ADS)

Chodorowski, Michał J.

2011-05-01

It is widely believed that the cosmological redshift is not a Doppler shift. However, Bunn & Hogg have recently pointed out that to solve this problem properly, one has to transport parallelly the velocity four-vector of a distant galaxy to the observer's position. Performing such a transport along the null geodesic of photons arriving from the galaxy, they found that the cosmological redshift is purely kinematic. Here we argue that one should rather transport the velocity four-vector along the geodesic connecting the points of intersection of the world-lines of the galaxy and the observer with the hypersurface of constant cosmic time. We find that the resulting relation between the transported velocity and the redshift of arriving photons is not given by a relativistic Doppler formula. Instead, for small redshifts it coincides with the well-known non-relativistic decomposition of the redshift into a Doppler (kinematic) component and a gravitational one. We perform such a decomposition for arbitrary large redshifts and derive a formula for the kinematic component of the cosmological redshift, valid for any Friedman-Lemaître-Robertson-Walker (FLRW) cosmology. In particular, in a universe with Ωm= 0.24 and ΩΛ= 0.76, a quasar at a redshift 6, at the time of emission of photons reaching us today had the recession velocity v= 0.997c. This can be contrasted with v= 0.96c, had the redshift been entirely kinematic. Thus, for recession velocities of such high-redshift sources, the effect of deceleration of the early Universe clearly prevails over the effect of its relatively recent acceleration. Last but not the least, we show that the so-called proper recession velocities of galaxies, commonly used in cosmology, are in fact radial components of the galaxies' four-velocity vectors. As such, they can indeed attain superluminal values, but should not be regarded as real velocities.

The gas content in starburst galaxies

NASA Technical Reports Server (NTRS)

Mirabel, I. F.; Sanders, D. B.

1987-01-01

The results from two large and homogeneous surveys, one in H I, the other in CO, are used for a statistical review of the gaseous properties of bright infrared galaxies. A constant ratio between the thermal FIR radiation and nonthermal radio emission is a universal property of star formation in spiral galaxies. The current rate of star formation in starburst galaxies is found to be 3-20 times larger than in the Milky Way. Galaxies with the higher FIR luminosities and warmer dust, have the larger mass fractions of molecular to atomic interstellar gas, and in some instances, striking deficiencies of neutral hydrogen are found. A statistical blueshift of the optical systemic velocities relative to the radio systemic velocities, may be due to an outward motion of the optical line-emitting gas. From the high rates of star formation, and from the short times required for the depletion of the interstellar gas, it is concluded that the most luminous infrared galaxies represent a brief but important phase in the evolution of some galaxies, when two galaxies merge changing substantially their overall properties.

Rates of species accumulation and taxonomic diversification during phototrophic biofilm development are controlled by both nutrient supply and current velocity.

PubMed

Larson, Chad A; Passy, Sophia I

2013-03-01

The accumulation of new and taxonomically diverse species is a marked feature of community development, but the role of the environment in this process is not well understood. To address this problem, we subjected periphyton in laboratory streams to low (10-cm · s(-1)), high (30-cm · s(-1)), and variable (9- to 32-cm · s(-1)) current velocity and low- versus high-nutrient inputs. We examined how current velocity and resource supply constrained (i) the rates of species accumulation, a measure of temporal beta-diversity, and (ii) the rates of diversification of higher taxonomic categories, defined here as the rate of higher taxon richness increase with the increase of species richness. Temporal biofilm dynamics were controlled by a strong nutrient-current interaction. Nutrients accelerated the rates of accumulation of new species, when flow velocity was not too stressful. Species were more taxonomically diverse under variable than under low-flow conditions, indicating that flow heterogeneity increased the niche diversity in the high-nutrient treatments. Conversely, the lower diversification rates under high- than under low-nutrient conditions at low velocity are explained with finer resource partitioning among species, belonging to a limited number of related genera. The overall low rates of diversification in high-current treatments suggest that the ability to withstand current stress was conserved within closely related species. Temporal heterogeneity of disturbance has been shown to promote species richness, but here we further demonstrate that it also affects two other components of biodiversity, i.e., temporal beta-diversity and diversification rate. Therefore, management efforts for preserving the inherent temporal heterogeneity of natural ecosystems will have detectable positive effects on biodiversity.

Rates of Species Accumulation and Taxonomic Diversification during Phototrophic Biofilm Development Are Controlled by both Nutrient Supply and Current Velocity

PubMed Central

2013-01-01

The accumulation of new and taxonomically diverse species is a marked feature of community development, but the role of the environment in this process is not well understood. To address this problem, we subjected periphyton in laboratory streams to low (10-cm · s−1), high (30-cm · s−1), and variable (9- to 32-cm · s−1) current velocity and low- versus high-nutrient inputs. We examined how current velocity and resource supply constrained (i) the rates of species accumulation, a measure of temporal beta-diversity, and (ii) the rates of diversification of higher taxonomic categories, defined here as the rate of higher taxon richness increase with the increase of species richness. Temporal biofilm dynamics were controlled by a strong nutrient-current interaction. Nutrients accelerated the rates of accumulation of new species, when flow velocity was not too stressful. Species were more taxonomically diverse under variable than under low-flow conditions, indicating that flow heterogeneity increased the niche diversity in the high-nutrient treatments. Conversely, the lower diversification rates under high- than under low-nutrient conditions at low velocity are explained with finer resource partitioning among species, belonging to a limited number of related genera. The overall low rates of diversification in high-current treatments suggest that the ability to withstand current stress was conserved within closely related species. Temporal heterogeneity of disturbance has been shown to promote species richness, but here we further demonstrate that it also affects two other components of biodiversity, i.e., temporal beta-diversity and diversification rate. Therefore, management efforts for preserving the inherent temporal heterogeneity of natural ecosystems will have detectable positive effects on biodiversity. PMID:23335757

Constraining the baryon-dark matter relative velocity with the large-scale 3-point correlation function of the SDSS BOSS DR12 CMASS galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Slepian, Zachary; Slosar, Anze; Eisenstein, Daniel J.

We search for a galaxy clustering bias due to a modulation of galaxy number with the baryon-dark matter relative velocity resulting from recombination-era physics. We find no detected signal and place the constraint bv <0.01 on the relative velocity bias for the CMASS galaxies. This bias is an important potential systematic of Baryon Acoustic Oscillation (BAO) method measurements of the cosmic distance scale using the 2-point clustering. Our limit on the relative velocity bias indicates a systematic shift of no more than 0.3% rms in the distance scale inferred from the BAO feature in the BOSS 2-point clustering, well belowmore » the 1% statistical error of this measurement. In conclusion, this constraint is the most stringent currently available and has important implications for the ability of upcoming large-scale structure surveys such as DESI to self-protect against the relative velocity as a possible systematic.« less

Constraining the baryon-dark matter relative velocity with the large-scale 3-point correlation function of the SDSS BOSS DR12 CMASS galaxies

DOE PAGES

Slepian, Zachary; Slosar, Anze; Eisenstein, Daniel J.; ...

2017-10-24

We search for a galaxy clustering bias due to a modulation of galaxy number with the baryon-dark matter relative velocity resulting from recombination-era physics. We find no detected signal and place the constraint bv <0.01 on the relative velocity bias for the CMASS galaxies. This bias is an important potential systematic of Baryon Acoustic Oscillation (BAO) method measurements of the cosmic distance scale using the 2-point clustering. Our limit on the relative velocity bias indicates a systematic shift of no more than 0.3% rms in the distance scale inferred from the BAO feature in the BOSS 2-point clustering, well belowmore » the 1% statistical error of this measurement. In conclusion, this constraint is the most stringent currently available and has important implications for the ability of upcoming large-scale structure surveys such as DESI to self-protect against the relative velocity as a possible systematic.« less

Constraining the baryon-dark matter relative velocity with the large-scale three-point correlation function of the SDSS BOSS DR12 CMASS galaxies

NASA Astrophysics Data System (ADS)

Slepian, Zachary; Eisenstein, Daniel J.; Blazek, Jonathan A.; Brownstein, Joel R.; Chuang, Chia-Hsun; Gil-Marín, Héctor; Ho, Shirley; Kitaura, Francisco-Shu; McEwen, Joseph E.; Percival, Will J.; Ross, Ashley J.; Rossi, Graziano; Seo, Hee-Jong; Slosar, Anže; Vargas-Magaña, Mariana

2018-02-01

We search for a galaxy clustering bias due to a modulation of galaxy number with the baryon-dark matter relative velocity resulting from recombination-era physics. We find no detected signal and place the constraint bv < 0.01 on the relative velocity bias for the CMASS galaxies. This bias is an important potential systematic of baryon acoustic oscillation (BAO) method measurements of the cosmic distance scale using the two-point clustering. Our limit on the relative velocity bias indicates a systematic shift of no more than 0.3 per cent rms in the distance scale inferred from the BAO feature in the BOSS two-point clustering, well below the 1 per cent statistical error of this measurement. This constraint is the most stringent currently available and has important implications for the ability of upcoming large-scale structure surveys such as the Dark Energy Spectroscopic Instrument (DESI) to self-protect against the relative velocity as a possible systematic.

Novel test of modified Newtonian dynamics with gas rich galaxies.

PubMed

McGaugh, Stacy S

2011-03-25

The current cosmological paradigm, the cold dark matter model with a cosmological constant, requires that the mass-energy of the Universe be dominated by invisible components: dark matter and dark energy. An alternative to these dark components is that the law of gravity be modified on the relevant scales. A test of these ideas is provided by the baryonic Tully-Fisher relation (BTFR), an empirical relation between the observed mass of a galaxy and its rotation velocity. Here, I report a test using gas rich galaxies for which both axes of the BTFR can be measured independently of the theories being tested and without the systematic uncertainty in stellar mass that affects the same test with star dominated spirals. The data fall precisely where predicted a priori by the modified Newtonian dynamics. The scatter in the BTFR is attributable entirely to observational uncertainty, consistent with a single effective force law.

Superfluid-like turbulence in cosmology

NASA Technical Reports Server (NTRS)

Gradwohl, Ben-Ami

1991-01-01

A network of vortices in a superfluid system exhibits turbulent behavior. It is argued that the universe may have experienced such a phase of superfluid-like turbulence due to the existence of a coherent state with non-topological charge and a network of global strings. The unique feature of a distribution of turbulent domains is that it can yield non-gravitationally induced large-scale coherent velocities. It may be difficult, however, to relate these velocities to the observed large-scale bulk motion.

Magnetic monopoles, Galilean invariance, and Maxwell's equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crawford, F.S.

1992-02-01

Maxwell's equations have space reserved for magnetic monopoles. Whether or not they exist in our part of the universe, monopoles provide a useful didactic tool to help us recognize relations among Maxwell's equations less easily apparent in the approach followed by many introductory textbooks, wherein Coulomb's law, Biot and Savart's law, Ampere's law, Faraday's law, Maxwell's displacement current, etc., are introduced independently, as demanded by experiment.'' Instead a conceptual path that deduces all of Maxwell's equations from the near-minimal set of assumptions: (a) Inertial frames exist, in which Newton's laws hold, to a first approximation; (b) the laws of electrodynamicsmore » are Galilean invariant---i.e., they have the same form in every inertial frame, to a first approximation; (c) magnetic poles (as well as the usual electric charges) exist; (d) the complete Lorentz force on an electric charge is known; (e) the force on a monopole at rest is known; (f) the Coulomb-like field produced by a resting electric charge and by a resting monopole are known. Everything else is deduced. History is followed in the assumption that Newtonian mechanics have been discovered, but not special relativity. (Only particle velocities {ital v}{much lt}{ital c} are considered.) This ends up with Maxwell's equations (Maxwell did not need special relativity, so why should we,) but facing Einstein's paradox, the solution of which is encapsulated in the Einstein velocity-addition formula.« less

Homologies in Physics and Astrophysics

NASA Astrophysics Data System (ADS)

Bartlett, David F.; Cumalat, J. P.

2012-01-01

The genes of humans and chimpanzees are homologs. These genes are - in large measure - identical. From this detailed observation, we naturally suppose that both species evolved from a common ancestor. In particle physics the ordinary observed particles and their superymmetric partners are thought to be homologs, generated by a common "ancestor” , the Higgs particle. Experiments at CERN currently are testing this comfortable analogy of physics with biology. Neither the Higgs boson nor any supersymmetric particle has yet been found. We speculate that a variety of objects are homologs - evidence of an as yet undeveloped quantum theory of gravity to replace Dark Matter. A purely astronomical homology is the Vc - σ o relation which places nearly spherical elliptical galaxies just above well-formed spirals (SA & SB). Here the asymptotically- flat, circular velocity Vc is observed to be between 1 and 2 times the central bulge velocity dispersion σo over the range 60 km/s< σo <400 km/s (Ferrarese 2002, Fig 3). The Vc - σ o relation is difficult to explain with self-consistent equilibrium galaxy models (Courteau et al 2007). Here we give an explanation based on the Sinusoidal Potential, a non-Newtonian potential in which φ =-GM Cos[ko r]/r and ko=2 π /400 pc. We relate the lower limit of 60 km/s to the thermal velocity of protons at the” Broadhurst/Hirano & Hartnett” lookback redshift Z=105.6. This is the redshift where what was 400 pc then expands to 128 h-1 Mpc today. Further, at this Z the temperature of the universe was close to the Hartree Energy of 2 times 13.6 eV, an energy where protons have an rms speed of about 60 km/s.

The Tully-Fisher Relation in Cluster Cl 0024+1654 at z=0.4

NASA Astrophysics Data System (ADS)

Metevier, Anne J.; Koo, David C.; Simard, Luc; Phillips, Andrew C.

2006-06-01

Using moderate-resolution Keck spectra, we have examined the velocity profiles of 15 members of cluster Cl 0024+1654 at z=0.4. WFPC2 images of the cluster members have been used to determine structural parameters, including disk sizes, orientations, and inclinations. We compare two methods of optical rotation curve analysis for kinematic measurements. Both methods take seeing, slit size and orientation, and instrumental effects into account and yield similar rotation velocity measurements. Four of the galaxies in our sample exhibit unusual kinematic signatures, such as noncircular motions. Our key result is that the Cl 0024 galaxies are marginally underluminous (0.50+/-0.23 mag), given their rotation velocities, as compared to the local Tully-Fisher relation. In this analysis, we assume no slope evolution and take into account systematic differences between local and distant velocity and luminosity measurements. Our result is particularly striking considering that the Cl 0024 members have very strong emission lines and local galaxies with similar Hα equivalent widths tend to be overluminous on the Tully-Fisher relation. Cl 0024 Tully-Fisher residuals appear to be correlated most strongly with galaxy rotation velocities, indicating a possible change in the slope of the Tully-Fisher relation. However, we caution that this result may be strongly affected by magnitude selection and by the original slope assumed for the analysis. Cl 0024 residuals also depend weakly on color, emission-line strength and extent, and photometric asymmetry. In a comparison of stellar and gas motions in two Cl 0024 members, we find no evidence for counterrotating stars and gas, an expected signature of mergers. Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology and the University of California. Based in part on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Fluorescence-Doped Particles for Simultaneous Temperature and Velocity Imaging

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; Tiemsin, Pacita I.; Wohl, Chrostopher J.; Verkamp, Max; Lowe, T.; Maisto, P.; Byun, G.; Simpson, R.

2012-01-01

Polystyrene latex microspheres (PSLs) have been used for particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) measurements for several decades. With advances in laser technologies, instrumentation, and data processing, the capability to collect more information about fluid flow beyond velocity is possible using new seed materials. To provide additional measurement capability, PSLs were synthesized with temperature-sensitive fluorescent dyes incorporated within the particle. These multifunctional PSLs would have the greatest impact if they could be used in large scale facilities with minimal modification to the facilities or the existing instrumentation. Consequently, several potential dyes were identified that were amenable to existing laser systems currently utilized in wind tunnels at NASA Langley Research Center as well as other wind and fluid (water) tunnels. PSLs incorporated with Rhodamine B, dichlorofluorescein (DCF, also known as fluorescein 548 or fluorescein 27) and other dyes were synthesized and characterized for morphology and spectral properties. The resulting particles were demonstrated to exhibit fluorescent emission, which would enable determination of both fluid velocity and temperature. They also would allow near-wall velocity measurements whereas laser scatter from surfaces currently prevents near-wall measurements using undoped seed materials. Preliminary results in a wind tunnel facility located at Virginia Polytechnic Institute and State University (Virginia Tech) have verified fluorescent signal detection and temperature sensitivity of fluorophore-doped PSLs.

Tests of Relativity Using a Cryogenic Optical Resonator

NASA Astrophysics Data System (ADS)

Braxmaier, C.; Müller, H.; Pradl, O.; Mlynek, J.; Peters, A.; Schiller, S.

2002-01-01

A 190-day comparison of the optical frequencies defined by an optical cavity and a molecular electronic transition is analyzed for the velocity independence of the speed of light (Kennedy-Thorndike test) and the universality of the gravitational redshift. The modulation of the laboratory velocity and the gravitational potential were provided by Earth's orbital motion around the Sun. We find a velocity-dependence coefficient of (1.9+/-2.1)×10-5, 3 times lower compared to the best previous test. Alternatively, the data confirm the gravitational redshift for an electronic transition at the 4% level. Prospects for significant improvements of the tests are discussed.

A Vs30-derived Near-surface Seismic Velocity Model

NASA Astrophysics Data System (ADS)

Ely, G. P.; Jordan, T. H.; Small, P.; Maechling, P. J.

2010-12-01

Shallow material properties, S-wave velocity in particular, strongly influence ground motions, so must be accurately characterized for ground-motion simulations. Available near-surface velocity information generally exceeds that which is accommodated by crustal velocity models, such as current versions of the SCEC Community Velocity Model (CVM-S4) or the Harvard model (CVM-H6). The elevation-referenced CVM-H voxel model introduces rasterization artifacts in the near-surface due to course sample spacing, and sample depth dependence on local topographic elevation. To address these issues, we propose a method to supplement crustal velocity models, in the upper few hundred meters, with a model derived from available maps of Vs30 (the average S-wave velocity down to 30 meters). The method is universally applicable to regions without direct measures of Vs30 by using Vs30 estimates from topographic slope (Wald, et al. 2007). In our current implementation for Southern California, the geology-based Vs30 map of Wills and Clahan (2006) is used within California, and topography-estimated Vs30 is used outside of California. Various formulations for S-wave velocity depth dependence, such as linear spline and polynomial interpolation, are evaluated against the following priorities: (a) capability to represent a wide range of soil and rock velocity profile types; (b) smooth transition to the crustal velocity model; (c) ability to reasonably handle poor spatial correlation of Vs30 and crustal velocity data; (d) simplicity and minimal parameterization; and (e) computational efficiency. The favored model includes cubic and square-root depth dependence, with the model extending to a depth of 350 meters. Model parameters are fit to Boore and Joyner's (1997) generic rock profile as well as CVM-4 soil profiles for the NEHRP soil classification types. P-wave velocity and density are derived from S-wave velocity by the scaling laws of Brocher (2005). Preliminary assessment of the new model is preformed with ground motion simulations for a selection of likely M > 7 scenario events for Southern California (as define by the SCEC Big Ten project).

Graviton propagation within the context of the D-material universe.

PubMed

Elghozi, Thomas; Mavromatos, Nick E; Sakellariadou, Mairi

2017-01-01

Motivated by the recent breakthrough of the detection of Gravitational Waves (GW) from coalescent black holes by the aLIGO interferometers, we study the propagation of GW in the D-material universe , which we have recently shown to be compatible with large-scale structure and inflationary phenomenology. The medium of D-particles induces an effective mass for the graviton, as a consequence of the formation of recoil-velocity field condensates due to the underlying Born-Infeld dynamics. There is a competing effect, due to a super-luminal refractive index, as a result of the gravitational energy of D-particles acting as a dark-matter component, with which propagating gravitons interact. We examine conditions for the condensate under which the latter effect is sub-leading. We argue that if quantum fluctuations of the recoil velocity are relatively strong, which can happen in the current era of the universe, then the condensate, and hence the induced mass of the graviton, can be several orders of magnitude larger than the magnitude of the cosmological constant today. Hence, we constrain the graviton mass using aLIGO and pulsar-timing observations (which give the most stringent bounds at present). In such a sub-luminal graviton case, there is also a gravitational Cherenkov effect for ordinary high-energy cosmic matter, which is further constrained by means of ultra-high-energy cosmic ray observations. Assuming cosmic rays of extragalactic origin, the bounds on the quantum condensate strength, based on the gravitational Cherenkov effect, are of the same order as those from aLIGO measurements, in contrast to the case where a galactic origin of the cosmic rays is assumed, in which case the corresponding bounds are much weaker.

Testing ΛCDM at the lowest redshifts with SN Ia and galaxy velocities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huterer, Dragan; Shafer, Daniel L.; Scolnic, Daniel M.

2017-05-01

Peculiar velocities of objects in the nearby universe are correlated due to the gravitational pull of large-scale structure. By measuring these velocities, we have a unique opportunity to test the cosmological model at the lowest redshifts. We perform this test, using current data to constrain the amplitude of the ''signal'' covariance matrix describing the velocities and their correlations. We consider a new, well-calibrated ''Supercal'' set of low-redshift SNe Ia as well as a set of distances derived from the fundamental plane relation of 6dFGS galaxies. Analyzing the SN and galaxy data separately, both results are consistent with the peculiar velocitymore » signal of our fiducial ΛCDM model, ruling out the noise-only model with zero peculiar velocities at greater than 7σ (SNe) and 8σ (galaxies). When the two data sets are combined appropriately, the precision of the test increases slightly, resulting in a constraint on the signal amplitude of A = 1.05{sub −0.21}{sup +0.25}, where A = 1 corresponds to our fiducial model. Equivalently, we report an 11% measurement of the product of the growth rate and amplitude of mass fluctuations evaluated at z {sub eff} = 0.02, f σ{sub 8} = 0.428{sub −0.045}{sup +0.048}, valid for our fiducial ΛCDM model. We explore the robustness of the results to a number of conceivable variations in the analysis and find that individual variations shift the preferred signal amplitude by less than ∼0.5σ. We briefly discuss our Supercal SN Ia results in comparison with our previous results using the JLA compilation.« less

Supersonic gas streams enhance the formation of massive black holes in the early universe

NASA Astrophysics Data System (ADS)

Hirano, Shingo; Hosokawa, Takashi; Yoshida, Naoki; Kuiper, Rolf

2017-09-01

Supermassive black holes existed less than a billion years after the Big Bang. Because black holes can grow at a maximum rate that depends on their current mass, it has been difficult to understand how such massive black holes could have formed so quickly. Hirano et al. developed simulations to show that streaming motions—velocity offsets between the gas and dark matter components—could have produced black holes with tens of thousands of solar masses in the early universe. That's big enough to grow into the supermassive black holes that we observe today.

Coastal Storm Model.

DTIC Science & Technology

1976-04-30

hindcasting, whereas a con- stant azimuth and storm velocity are used in forecasting. Tte results of hindcast analysis at several sites are included in... undersea breeze conditions and wave- current interactions in the surf zone; Tech. Report TC-149-4, ONR Contract N00014-69-C-0107, Tetra Tech, Inc., Pasadena...MARYLAND 21043 DEPARTMENT UF GEOSCIENrES PURI)IUL UNIVERSITY -DR. RURERT L. MILLER ___ LAFAYE- TTE , INDIANA 47901 DEPARTMENT OF GEOPHYSICAL SCIENCES

Short-period terrestrial planets and radial velocity stellar jitter.

NASA Astrophysics Data System (ADS)

Dumusque, Xavier

2015-01-01

Stellar jitter is the main limitation to ultra-precise radial velocity (RV) measurements. It currently precludes our ability to detect a planet like the Earth. Short-period terrestrial planets present first the advantage of inducing a stronger RV signal. In addition, the signal produced by these planets have a period completely different than stellar activity. This allows us, when the observational strategy is adequate, to decorrelate the planetary signal from the jitter induced by the star using filtering techniques. I will show the examples of Kepler-78b and Corot-7b, where the amplitude of the planetary signal can be detected, despite the stellar activity jitter that is 5 and 3 times larger, respectively. The cases of Alpha Cen Bb will also be reviewed, with a new reduction of the published data that increases the significance of the planetary signal.This project is funded by ETAEARTH, a transnational collaboration between European countries and the US (the Swiss Space Office, the Harvard Origin of Life Initiative, the Scottish Universities Physics Alliance, the University of Geneva, the Smithsonian Astrophysical Observatory, the Italian National Astrophysical Institute, the University of St. Andrews, Queens University Belfast, and the University of Edinburgh) setup to optimize the synergy between space-and ground-based data whose scientific potential for the characterization of extrasolar planets can only be fully exploited when analyzed together.

Lagrangian statistics of mesoscale turbulence in a natural environment: The Agulhas return current.

PubMed

Carbone, Francesco; Gencarelli, Christian N; Hedgecock, Ian M

2016-12-01

The properties of mesoscale geophysical turbulence in an oceanic environment have been investigated through the Lagrangian statistics of sea surface temperature measured by a drifting buoy within the Agulhas return current, where strong temperature mixing produces locally sharp temperature gradients. By disentangling the large-scale forcing which affects the small-scale statistics, we found that the statistical properties of intermittency are identical to those obtained from the multifractal prediction in the Lagrangian frame for the velocity trajectory. The results suggest a possible universality of turbulence scaling.

Simulation of Non-Uniform Electron Beams in the Gyrotron Electron-Optical System

NASA Astrophysics Data System (ADS)

Louksha, O. I.; Trofimov, P. A.

2018-04-01

New calculated data on the effect of emission inhomogeneities on the quality of the electron beam, which is formed in an electron-optical system of a gyrotron, have been obtained. The calculations were based on emission current density distributions, which were measured for the different cathodes in the gyrotron of Peter the Great St. Petersburg Polytechnic University. A satisfactory agreement between the experimental and calculated data on the influence of emission nonuniformities on the velocity spread of electrons has been shown. The necessity of considering the real distribution of the emission current density over the cathode surface to determine the main parameters of the electron beam—the velocity and energy spreads of the electrons, spatial structure of the beam, and coefficient of reflection of electrons from the magnetic mirror—has been demonstrated. The maximum level of emission inhomogeneities, which are permissible for effective work of gyrotrons, has been discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hurricane, O. A.; Kline, J. L.; Meezan, N.

The current high-foot and related implosions have adequate CR and implosion velocity to ignite, but require improved finesse particularly in, but not limited to, implosion symmetry. This is being pursued. The challenge of controlling drive symmetry is also motivating lower convergence ratio designs. These require higher velocity implosions and are also being pursued.

Explicit wave action conservation for water waves on vertically sheared flows

NASA Astrophysics Data System (ADS)

Quinn, Brenda; Toledo, Yaron; Shrira, Victor

2016-04-01

Water waves almost always propagate on currents with a vertical structure such as currents directed towards the beach accompanied by an under-current directed back toward the deep sea or wind-induced currents which change magnitude with depth due to viscosity effects. On larger scales they also change their direction due to the Coriolis force as described by the Ekman spiral. This implies that the existing wave models, which assume vertically-averaged currents, is an approximation which is far from realistic. In recent years, ocean circulation models have significantly improved with the capability to model vertically-sheared current profiles in contrast with the earlier vertically-averaged current profiles. Further advancements have coupled wave action models to circulation models to relate the mutual effects between the two types of motion. Restricting wave models to vertically-averaged non-turbulent current profiles is obviously problematic in these cases and the primary goal of this work is to derive and examine a general wave action equation which accounts for these shortcoming. The formulation of the wave action conservation equation is made explicit by following the work of Voronovich (1976) and using known asymptotic solutions of the boundary value problem which exploit the smallness of the current magnitude compared to the wave phase velocity and/or its vertical shear and curvature. The adopted approximations are shown to be sufficient for most of the conceivable applications. This provides correction terms to the group velocity and wave action definition accounting for the shear effects, which are fitting for application to operational wave models. In the limit of vanishing current shear, the new formulation reduces to the commonly used Bretherton & Garrett (1968) no-shear wave action equation where the invariant is calculated with the current magnitude taken at the free surface. It is shown that in realistic oceanic conditions, the neglect of the vertical structure of the currents in wave modelling which is currently universal, might lead to significant errors in wave amplitude and the predicted wave ray paths. An extension of the work toward the more complex case of turbulent currents will also be discussed.

Structure and variability of the Western Maine Coastal Current

USGS Publications Warehouse

Churchill, J.H.; Pettigrew, N.R.; Signell, R.P.

2005-01-01

Analyses of CTD and moored current meter data from 1998 and 2000 reveal a number of mechanisms influencing the flow along the western coast of Maine. On occasions, the Eastern Maine Coastal Current extends into the western Gulf of Maine where it takes the form of a deep (order 100 m deep) and broad (order 20 km wide) southwestward flow with geostrophic velocities exceeding 20 cm s -1. This is not a coastally trapped flow, however. In fields of geostrophic velocity, computed from shipboard-CTD data, the core of this current is roughly centered at the 100 m isobath and its onshore edge is no closer than 10 km from the coast. Geostrophic velocity fields also reveal a relatively shallow (order 10 m deep) baroclinic flow adjacent to the coast. This flow is also directed to the southwest and appears to be principally comprised of local river discharge. Analyses of moored current meter data reveal wind-driven modulations of the coastal flow that are consistent with expectations from simple theoretical models. However, a large fraction of the near-shore current variance does not appear to be directly related to wind forcing. Sea-surface temperature imagery, combined with analysis of the moored current meter data, suggests that eddies and meanders within the coastal flow may at times dominate the near-shore current variance. ?? 2005 Elsevier Ltd. All rights reserved.

Estimating Discharge, Depth and Bottom Friction in Sand Bed Rivers Using Surface Currents and Water Surface Elevation Observations

NASA Astrophysics Data System (ADS)

Simeonov, J.; Czapiga, M. J.; Holland, K. T.

2017-12-01

We developed an inversion model for river bathymetry estimation using measurements of surface currents, water surface elevation slope and shoreline position. The inversion scheme is based on explicit velocity-depth and velocity-slope relationships derived from the along-channel momentum balance and mass conservation. The velocity-depth relationship requires the discharge value to quantitatively relate the depth to the measured velocity field. The ratio of the discharge and the bottom friction enter as a coefficient in the velocity-slope relationship and is determined by minimizing the difference between the predicted and the measured streamwise variation of the total head. Completing the inversion requires an estimate of the bulk friction, which in the case of sand bed rivers is a strong function of the size of dune bedforms. We explored the accuracy of existing and new empirical closures that relate the bulk roughness to parameters such as the median grain size diameter, ratio of shear velocity to sediment fall velocity or the Froude number. For given roughness parameterization, the inversion solution is determined iteratively since the hydraulic roughness depends on the unknown depth. We first test the new hydraulic roughness parameterization using estimates of the Manning roughness in sand bed rivers based on field measurements. The coupled inversion and roughness model is then tested using in situ and remote sensing measurements of the Kootenai River east of Bonners Ferry, ID.

Tuning the Fermi velocity in Dirac materials with an electric field.

PubMed

Díaz-Fernández, A; Chico, Leonor; González, J W; Domínguez-Adame, F

2017-08-14

Dirac materials are characterized by energy-momentum relations that resemble those of relativistic massless particles. Commonly denominated Dirac cones, these dispersion relations are considered to be their essential feature. These materials comprise quite diverse examples, such as graphene and topological insulators. Band-engineering techniques should aim to a full control of the parameter that characterizes the Dirac cones: the Fermi velocity. We propose a general mechanism that enables the fine-tuning of the Fermi velocity in Dirac materials in a readily accessible way for experiments. By embedding the sample in a uniform electric field, the Fermi velocity is substantially modified. We first prove this result analytically, for the surface states of a topological insulator/semiconductor interface, and postulate its universality in other Dirac materials. Then we check its correctness in carbon-based Dirac materials, namely graphene nanoribbons and nanotubes, thus showing the validity of our hypothesis in different Dirac systems by means of continuum, tight-binding and ab-initio calculations.

Laminar and Turbulent Dynamos in Chiral Magnetohydrodynamics. I. Theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rogachevskii, Igor; Kleeorin, Nathan; Ruchayskiy, Oleg

2017-09-10

The magnetohydrodynamic (MHD) description of plasmas with relativistic particles necessarily includes an additional new field, the chiral chemical potential associated with the axial charge (i.e., the number difference between right- and left-handed relativistic fermions). This chiral chemical potential gives rise to a contribution to the electric current density of the plasma ( chiral magnetic effect ). We present a self-consistent treatment of the chiral MHD equations , which include the back-reaction of the magnetic field on a chiral chemical potential and its interaction with the plasma velocity field. A number of novel phenomena are exhibited. First, we show that themore » chiral magnetic effect decreases the frequency of the Alfvén wave for incompressible flows, increases the frequencies of the Alfvén wave and of the fast magnetosonic wave for compressible flows, and decreases the frequency of the slow magnetosonic wave. Second, we show that, in addition to the well-known laminar chiral dynamo effect, which is not related to fluid motions, there is a dynamo caused by the joint action of velocity shear and chiral magnetic effect. In the presence of turbulence with vanishing mean kinetic helicity, the derived mean-field chiral MHD equations describe turbulent large-scale dynamos caused by the chiral alpha effect, which is dominant for large fluid and magnetic Reynolds numbers. The chiral alpha effect is due to an interaction of the chiral magnetic effect and fluctuations of the small-scale current produced by tangling magnetic fluctuations (which are generated by tangling of the large-scale magnetic field by sheared velocity fluctuations). These dynamo effects may have interesting consequences in the dynamics of the early universe, neutron stars, and the quark–gluon plasma.« less

The Mug:. on E = mc2 and Relativity Theory in the Mass Culture

NASA Astrophysics Data System (ADS)

Okun, L. B.

2013-11-01

This note is an attempt to explain in simple words why the famous relation E = mc2 misrepresents the essence of Einstein's relativity theory. The first part of the note is addressed to high-school teachers, the rest - to those university professors of Physics who allow themselves to say that the mass of a body increases with its velocity.

Contemporary Deformation within the Snake River Plain and Northern Basin and Range Province, USA

NASA Astrophysics Data System (ADS)

Payne, S. J.; McCaffrey, R.; King, R. W.

2007-05-01

GPS velocities, earthquakes, faults, and volcanic features are used to evaluate contemporary deformation within the Snake River Plain (SRP) and surrounding northern Basin and Range Province. The SRP is a prominent low- relief physiographic feature that extends from eastern Oregon through southern Idaho and into northwestern Wyoming, USA. The Eastern Snake River Plain (ESRP) is a 400-km long, NE-trending volcanic province that is characterized by bimodal volcanism, which represents the track of the Yellowstone Hotspot currently located in Wyoming. The Western Snake River Plain (WSRP) is a 300-km long, NW-trending graben that extends into eastern Oregon. The WSRP is an extensional basin that formed adjacent to an earlier position of the Yellowstone Hotspot in southern Idaho. Previous geodetic investigations suggest the ESRP and, perhaps the WSRP, have GPS velocities indicative of rigid block motion of the SRP along its physiographic boundaries. GPS data compiled for this study are used to test this hypothesis. Several institutions including the National Geodetic Survey, Idaho National Laboratory, Rensselaer Polytechnic Institute, and University of Utah observed GPS stations from 1994 to 2006 within the SRP and surrounding region. Horizontal velocities show generally consistent N110°W orientations with an average rate of 1.5 ± 0.3 mm/yr (for 11 stations) along most of the ESRP and adjacent northwest Basin and Range, although some Basin and Range velocities are less and may be influenced by post viscoelastic relaxation following the 1983 Mw 6.9 normal-faulting Borah Peak, Idaho earthquake. GPS velocities with an average rate of 1.9 ± 0.3 mm/yr (for 5 stations) change orientation to N95°W at a distance of 190 km from the Yellowstone Hotspot within the southern region of the ESRP and adjacent Basin and Range. Within the WSRP, GPS velocities have an average rate of 2.0 ± 0.5 mm/yr (for 7 stations) and change orientation to N40°W. These GPS velocities are more consistent with those in eastern Oregon, a region that is rotating clockwise relative to North America. To assess possible rotations and strain rates, we invert GPS horizontal velocities, geologic fault slip rates, earthquake-derived fault slip vector azimuths, and volcanic dike extension rates. We interpret GPS velocities to describe the relative motions of coherent regions of consistent strain within the SRP and surrounding Basin and Range Province.

Accuracy of velocities from repeated GPS surveys: relative positioning is concerned

NASA Astrophysics Data System (ADS)

Duman, Huseyin; Ugur Sanli, D.

2016-04-01

Over more than a decade, researchers have been interested in studying the accuracy of GPS positioning solutions. Recently, reporting the accuracy of GPS velocities has been added to this. Researchers studying landslide motion, tectonic motion, uplift, sea level rise, and subsidence still report results from GPS experiments in which repeated GPS measurements from short sessions are used. This motivated some other researchers to study the accuracy of GPS deformation rates/velocities from various repeated GPS surveys. In one of the efforts, the velocity accuracy was derived from repeated GPS static surveys using short observation sessions and Precise Point Positioning mode of GPS software. Velocities from short GPS sessions were compared with the velocities from 24 h sessions. The accuracy of velocities was obtained using statistical hypothesis testing and quantifying the accuracy of least squares estimation models. The results reveal that 45-60 % of the horizontal and none of the vertical solutions comply with the results from 24 h solutions. We argue that this case in which the data was evaluated using PPP should also apply to the case in which the data belonging to long GPS base lengths is processed using fundamental relative point positioning. To test this idea we chose the two IGS stations ANKR and NICO and derive their velocities from the reference stations held fixed in the stable EURASIAN plate. The University of Bern's GNSS software BERNESE was used to produce relative positioning solutions, and the results are compared with those of GIPSY/OASIS II PPP results. First impressions indicate that it is worth designing a global experiment and test these ideas in detail.

Red Shifts and Existing Speculations

NASA Astrophysics Data System (ADS)

Aisenberg, Sol

2009-03-01

There are many current flaws, mysteries, and errors in the standard model of the universe - all based upon speculative interpretation of many excellent and verified observations. The most serious cause of some errors is the speculation about the meaning of the redshifts observed in the 1930s by Hubble. He ascribed the redshifts as due to ``an apparent Doppler effect''. This led to speculation that the remote stars were receding, and the universe was expanding -- although without observational proof of the actual receding velocity of the stars. The age of the universe, based upon the Hubble constant is pure speculation because of lack of velocity demonstration. The belief in expansion, the big bang, and of inflation should be reexamined. Also, the redshift cannot always be used as a distance measure, particularly for photons from quasars containing massive black holes that can reduce photon energy through gravitational attraction. If the linear Hubble constant is extrapolated to the most remote super novae and beyond, it would eventually require that the corresponding photon energy go to zero or become negative -- according to Hubble linear relationship. This should require a reexamination of the meaning of the red shift and the speculative consequences and give a model with fewer mysteries.

Gunshot residue particle velocity and deceleration.

PubMed

De Forest, Peter R; Martir, Kirby; Pizzola, Peter A

2004-11-01

The velocity of over 800 gunshot residue particles from eight different sources was determined using high speed stroboscopic photography (spark gap light source). These particles were found to have an average velocity of 500 to 600 ft per second. Many particles acquired considerably higher velocities. Thus, the particles have sufficient energy to embed themselves within certain nearby targets like skin or fabric. The relatively high velocity that the particles acquire explain the formation of stippling on skin in close proximity to a muzzle discharge. These findings also indicate little influence of air currents on particle behavior near the muzzle. The deceleration of less than 100 particles during a 100-microsecond interval was also calculated. The particles experienced rapid rates of deceleration which would explain why few particles are found in test firings beyond 3 ft from the muzzle of a discharged firearm. Because of their relatively high velocity, normal wind velocity would not be expected to significantly influence their motion near the muzzle.

Detection of the Velocity Shear Effect on the Spatial Distributions of the Galactic Satellites in Isolated Systems

NASA Astrophysics Data System (ADS)

Lee, Jounghun; Choi, Yun-Young

2015-02-01

We report a detection of the effect of the large-scale velocity shear on the spatial distributions of the galactic satellites around the isolated hosts. Identifying the isolated galactic systems, each of which consists of a single host galaxy and its satellites, from the Seventh Data Release of the Sloan Digital Sky Survey and reconstructing linearly the velocity shear field in the local universe, we measure the alignments between the relative positions of the satellites from their isolated hosts and the principal axes of the local velocity shear tensors projected onto the plane of sky. We find a clear signal that the galactic satellites in isolated systems are located preferentially along the directions of the minor principal axes of the large-scale velocity shear field. Those galactic satellites that are spirals, are brighter, are located at distances larger than the projected virial radii of the hosts, and belong to the spiral hosts yield stronger alignment signals, which implies that the alignment strength depends on the formation and accretion epochs of the galactic satellites. It is also shown that the alignment strength is quite insensitive to the cosmic web environment, as well as the size and luminosity of the isolated hosts. Although this result is consistent with the numerical finding of Libeskind et al. based on an N-body experiment, owing to the very low significance of the observed signals, it remains inconclusive whether or not the velocity shear effect on the satellite distribution is truly universal.

Responses of caddisfly larvae (Brachycentrus spp. ) to temperature, food availability and current velocity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gallepp, G.W.

1977-07-01

Larvae of the stream caddisflies, Brachycentrus americanus and Brachycentrus occidentalis, were studied in eight simulated stream channels to determine their behavioral responses to temperature, food availability (brine shrimp) and current velocity. For both species, filtering, withdrawn and case-building were the primary behavior patterns of larvae that had attached their cases to the substrate. Most larvae not attached to the substrate were crawling or holding. As temperatures increased above 8 C, B. occidentalis larvae filtered more frequantly; but above 20 C the percentage of larvae filtering steadily decreased and the percentage withdrawn increased dramatically with increasing temperature. Percentages of larvae case-buildingmore » and unattached generally decreased over the range of 4 to 27 C. Despite this decrease in case-building, B. occidentalis larvae generally grew faster as temperature increased from 4 to 16 C. Behavior of B. americanus as a function of temperature was similar to behavior of B. occidentalis. Both species responded to decreased ration by increasing the percentage of time filtering. Although many larvae were unattached and probably grazing in Lawrence Creek, few larvae were unattached in the laboratory, even at the lowest ration (1.2 percent of the body weight per day). Growth and case-building activity of B. americanus larvae were directly related to ration. Over the range of current velocities of 7 to 26 cm/sec, behavior of B. occidentalis changed little. At 5 cm/sec fewer larvae filtered and more were unattached; this suggested a threshold response to current velocity. Increasing temperatures from 10 to 20 C caused the percentage withdrawn at low velocities to increase; however, this trend was hardly noticeable at velocities above 10 cm/sec. In these tests, Brachycentrus were more responsive to temperature and food availability than to current velocity.« less

Surface current dynamics under sea breeze conditions observed by simultaneous HF radar, ADCP and drifter measurements

NASA Astrophysics Data System (ADS)

Sentchev, Alexei; Forget, Philippe; Fraunié, Philippe

2017-04-01

Ocean surface boundary layer dynamics off the southern coast of France in the NW Mediterranean is investigated by using velocity observations by high-frequency (HF) radars, surface drifting buoys and a downward-looking drifting acoustic Doppler current profiler (ADCP). The analysis confirms that velocities measured by HF radars correspond to those observed by an ADCP at the effective depth z f = k -1, where k is wavenumber of the radio wave emitted by the radar. The radials provided by the radars were in a very good agreement with in situ measurements, with the relative errors of 1 and 9 % and root mean square (RMS) differences of 0.02 and 0.04 m/s for monostatic and bistatic radar, respectively. The total radar-based velocities appeared to be slightly underestimated in magnitude and somewhat biased in direction. At the end of the survey period, the difference in the surface current direction, based on HF radar and ADCP data, attained 10°. It was demonstrated that the surface boundary layer dynamics cannot be reconstructed successfully without taking into the account velocity variation with depth. A significant misalignment of ˜30° caused by the sea breeze was documented between the HF radar (HFR-derived) surface current and the background current. It was also found that the ocean response to a moderate wind forcing was confined to the 4-m-thick upper layer. The respective Ekman current attained the maximum value of 0.15 m/s, and the current rotation was found to be lagging the wind by approximately 40 min, with the current vector direction being 15-20° to the left of the wind. The range of velocity variability due to wind forcing was found comparable with the magnitude of the background current variability.

Assessment of tidal circulation and tidal current asymmetry in the Iroise sea with specific emphasis on characterization of tidal energy resources around the Ushant Island.

NASA Astrophysics Data System (ADS)

Thiébaut, Maxime; Sentchev, Alexei

2015-04-01

We use the current velocity time series recorded by High Frequency Radars (HFR) to study circulation in highly energetic tidal basin - the Iroise sea. We focus on the analysis of tidal current pattern around the Ushant Island which is a promising site of tidal energy. The analysis reveals surface current speeds reaching 4 m/s in the North of Ushant Island and in the Fromveur Strait. In these regions 1 m/s is exceeded 60% of time and up to 70% of time in center of Fromveur. This velocity value is particularly interesting because it represents the cut-in-speed of the most of marine turbine devices. Tidal current asymmetry is not always considered in tidal energy site selection. However, this quantity plays an important role in the quantification of hydrokinetic resources. Current velocity times series recorded by HFR highlights the existence of a pronounced asymmetry in current magnitude between the flood and ebb tide ranging from -0.5 to more 2.5. Power output of free-stream devices depends to velocity cubed. Thus a small current asymmetry can generate a significant power output asymmetry. Spatial distribution of asymmetry coefficient shows persistent pattern and fine scale structure which were quantified with high degree of accuracy. The particular asymmetry evolution on both side of Fromveur strait is related to the spatial distribution of the phase lag of the principal semi-diurnal tidal constituent M2 and its higher order harmonics. In Fromveur, the asymmetry is reinforced due to the high velocity magnitude of the sixth-diurnal tidal harmonics. HF radar provides surface velocity speed, however the quantification of hydrokinetic resources has to take into account the decreasing of velocity with depth. In order to highlight this phenomenon, we plot several velocity profiles given by an ADCP which was installed in the HFR study area during the same period. The mean velocity in the water column calculated by using the ADCP data show that it is about 80% of the surface current speed. We consider this value in our calculation of power to make the power estimation of marine turbine devices more realistic. Finally, we demonstrate that in the region of opposing flood-versus ebb-dominated asymmetry occurring over limited spatial scale, it is possible to aggregated free-stream devices to provide balanced power generation over the tidal cycle. Keywords : Tidal circulation, current asymmetry, tidal energy, HF radar, Iroise Sea.

Are We Really Missing Small Galaxies?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-02-01

One long-standing astrophysical puzzle is that of so-called missing dwarf galaxies: the number of small dwarf galaxies that we observe is far fewer than that predicted by theory. New simulations, however, suggest that perhaps theres no mystery after all.Missing DwarfsDark-matter cosmological simulations predict many small galaxy halos for every large halo that forms. [The Via Lactea project]Models of a lambda-cold-dark-matter (CDM) universe predict the distribution of galaxy halo sizes throughout the universe, suggesting there should be many more small galaxies than large ones. In what has become known as the missing dwarf problem, however, we find that while we observe the expected numbers of galaxies at the larger end of the scale, we dont see nearly enough small galaxies to match the predictions.Are these galaxies actually missing? Are our predictions wrong? Or are the galaxies there and were just not spotting them? A recent study led by Alyson Brooks (Rutgers University) uses new simulations to explore whatscausing the difference between theory and observation.The fraction of detectable halos as a function of velocity, according to the authors simulations. Below 35 km/s, the detectability of the galaxies drops precipitously. [Brooks et al. 2017]Simulating Galactic VelocitiesBecause we cant weigh a galaxy directly, one proxy used for galaxy mass is its circular velocity; the more massive a galaxy, the faster gas and stars rotate around its center. The discrepancy between models and observations lies in whats known as the galaxy velocity function, which describes the number density of galaxies for a given circular velocity. While theory and observations agree for galaxies with circular velocities above 100 km/s, theory predicts far more dwarfs below this velocity than we observe.To investigate this problem, Brooks and collaborators ran a series of cosmological simulations based on our understanding of a CDM universe. Instead of exploring the result using only dark matter, however, the team included baryons in their simulations. They then produced mock observations of the resulting galaxy velocities to see what an observed velocity function would look like for their simulated galaxies.No Problem After All?Comparison of theoretical velocity functions to observations. The black dashed line shows the original, dark-matter-only model predictions; the black solid line includes the effects of detectability. Blue lines show the authors new model, including the effects of detectability and inclusion of baryons. The red and teal data points from observations match this corrected model well. [Brooks et al. 2017]Based on their baryon-inclusive simulations, Brooks and collaborators argue that there are two main factors that have contributed to the seeming theory/observation mismatch of the missing dwarf problem:Galaxies with low velocities arent detectable by our current surveys.The authors found that the detectable fraction of their simulated galaxies plunges as soon as galaxy velocity drops below 35 km/s. They conclude that were probably unable to see a large fraction of the smallest galaxies.Were not correctly inferring the circular velocity of the galaxies.Circular velocity is usually measured by looking at the line width of a gas tracer like HI. The authors find that this doesnt trace the full potential wells of the dwarf galaxies, however, resulting in an incorrect interpretation of their velocities.The authors show that the inclusion of these effects in the theoretical model significantly changes the predicted shape of the galaxy velocity function. This new function beautifully matches observations, neatly eliminating the missing dwarf problem. Perhaps this long-standing mystery has been a problem of interpretation all along!CitationAlyson M. Brooks et al 2017 ApJ 850 97. doi:10.3847/1538-4357/aa9576

Diffusive Cosmic-Ray Acceleration at Shock Waves of Arbitrary Speed with Magnetostatic Turbulence. I. General Theory and Correct Nonrelativistic Speed Limit

NASA Astrophysics Data System (ADS)

Schlickeiser, R.; Oppotsch, J.

2017-12-01

The analytical theory of diffusive acceleration of cosmic rays at parallel stationary shock waves of arbitrary speed with magnetostatic turbulence is developed from first principles. The theory is based on the diffusion approximation to the gyrotropic cosmic-ray particle phase-space distribution functions in the respective rest frames of the up- and downstream medium. We derive the correct cosmic-ray jump conditions for the cosmic-ray current and density, and match the up- and downstream distribution functions at the position of the shock. It is essential to account for the different particle momentum coordinates in the up- and downstream media. Analytical expressions for the momentum spectra of shock-accelerated cosmic rays are calculated. These are valid for arbitrary shock speeds including relativistic shocks. The correctly taken limit for nonrelativistic shock speeds leads to a universal broken power-law momentum spectrum of accelerated particles with velocities well above the injection velocity threshold, where the universal power-law spectral index q≃ 2-{γ }1-4 is independent of the flow compression ratio r. For nonrelativistic shock speeds, we calculate for the first time the injection velocity threshold, settling the long-standing injection problem for nonrelativistic shock acceleration.

Conduction velocity is regulated by sodium channel inactivation in unmyelinated axons innervating the rat cranial meninges.

PubMed

De Col, Roberto; Messlinger, Karl; Carr, Richard W

2008-02-15

Axonal conduction velocity varies according to the level of preceding impulse activity. In unmyelinated axons this typically results in a slowing of conduction velocity and a parallel increase in threshold. It is currently held that Na(+)-K(+)-ATPase-dependent axonal hyperpolarization is responsible for this slowing but this has long been equivocal. We therefore examined conduction velocity changes during repetitive activation of single unmyelinated axons innervating the rat cranial meninges. In direct contradiction to the currently accepted postulate, Na(+)-K(+)-ATPase blockade actually enhanced activity-induced conduction velocity slowing, while the degree of velocity slowing was curtailed in the presence of lidocaine (10-300 microm) and carbamazepine (30-500 microm) but not tetrodotoxin (TTX, 10-80 nm). This suggests that a change in the number of available sodium channels is the most prominent factor responsible for activity-induced changes in conduction velocity in unmyelinated axons. At moderate stimulus frequencies, axonal conduction velocity is determined by an interaction between residual sodium channel inactivation following each impulse and the retrieval of channels from inactivation by a concomitant Na(+)-K(+)-ATPase-mediated hyperpolarization. Since the process is primarily dependent upon sodium channel availability, tracking conduction velocity provides a means of accessing relative changes in the excitability of nociceptive neurons.

Peculiar motions, accelerated expansion, and the cosmological axis

NASA Astrophysics Data System (ADS)

Tsagas, Christos G.

2011-09-01

Peculiar velocities change the expansion rate of any observer moving relative to the smooth Hubble flow. As a result, observers in a galaxy like our Milky Way can experience accelerated expansion within a globally decelerating universe, even when the drift velocities are small. The effect is local, but the affected scales can be large enough to give the false impression that the whole cosmos has recently entered an accelerating phase. Generally, peculiar velocities are also associated with dipolelike anisotropies, triggered by the fact that they introduce a preferred spatial direction. This implies that observers experiencing locally accelerated expansion, as a result of their own drift motion, may also find that the acceleration is maximized in one direction and minimized in the opposite. We argue that, typically, such a dipole anisotropy should be relatively small and the axis should probably lie fairly close to the one seen in the spectrum of the cosmic microwave background.

Influence of residual plasma drift velocity on the post-arc sheath expansion of vacuum circuit breakers

NASA Astrophysics Data System (ADS)

Mo, Yongpeng; Shi, Zongqian; Bai, Zhibin; Jia, Shenli; Wang, Lijun

2016-05-01

The residual plasma in the inter-contact region of a vacuum circuit breaker moves towards the post-arc cathode at current zero, because the residual plasma mainly comes from the cathode spots during the arc burning process. In the most previous theoretical researches on the post-arc sheath expansion process of vacuum circuit breakers, only the thermal motion of residual plasma was taken into consideration. Alternately, the residual plasma was even assumed to be static at the moment of current zero in some simplified models. However, the influence of residual plasma drift velocity at current zero on the post-arc sheath expansion process was rarely investigated. In this paper, this effect is investigated by a one-dimensional particle-in-cell model. Simulation results indicate that the sheath expands slower with higher residual plasma drift velocity in the initial sheath expansion stage. However, with the increase of residual plasma drift velocity, the overall plasma density in the inter-contact region decreases faster, and the sheath expansion velocity increases earlier. Consequently, as a whole, it needs shorter time to expel the residual plasma from the inter-contact region. Furthermore, if the residual plasma drift velocity is high enough, the sheath expansion process ceases before it develops to the post-arc anode. Besides, the influence of the collisions between charges and neutrals is investigated as well in terms of the density of metal vapor. It shows that the residual plasma drift velocity takes remarkable effect only if the density of the metal vapor is relatively low, which corresponds to the circumstance of low-current interruptions.

Peculiar velocity measurement in a clumpy universe

NASA Astrophysics Data System (ADS)

Habibi, Farhang; Baghram, Shant; Tavasoli, Saeed

Aims: In this work, we address the issue of peculiar velocity measurement in a perturbed Friedmann universe using the deviations from measured luminosity distances of standard candles from background FRW universe. We want to show and quantify the statement that in intermediate redshifts (0.5 < z < 2), deviations from the background FRW model are not uniquely governed by peculiar velocities. Luminosity distances are modified by gravitational lensing. We also want to indicate the importance of relativistic calculations for peculiar velocity measurement at all redshifts. Methods: For this task, we discuss the relativistic correction on luminosity distance and redshift measurement and show the contribution of each of the corrections as lensing term, peculiar velocity of the source and Sachs-Wolfe effect. Then, we use the SNe Ia sample of Union 2, to investigate the relativistic effects, we consider. Results: We show that, using the conventional peculiar velocity method, that ignores the lensing effect, will result in an overestimate of the measured peculiar velocities at intermediate redshifts. Here, we quantify this effect. We show that at low redshifts the lensing effect is negligible compare to the effect of peculiar velocity. From the observational point of view, we show that the uncertainties on luminosity of the present SNe Ia data prevent us from precise measuring the peculiar velocities even at low redshifts (z < 0.2).

The 6dFGS Fundamental Plane

NASA Astrophysics Data System (ADS)

Springob, Chris M.; Colless, M.; Jones, D. H.; Magoulas, C.; Mould, J. R.; Campbell, L.; Lah, P.; Lucey, J.; Merson, A.; Proctor, R.

2010-01-01

The 6dF Galaxy Survey (6dFGS) is an all southern sky galaxy survey, including 125,000 redshifts and more than 10,000 peculiar velocities, making it the largest peculiar velocity sample to date. In combination with 2MASS surface brightnesses and effective radii, 6dFGS yields the near-infrared Fundamental Plane (FP) for a large and uniform sample. We have fit the FP relation for the galaxies in the peculiar velocity sample using a maximum likelihood method which allows us to precisely account for selection effects and observational errors. We investigate the effects of varying stellar populations and environments on the FP. Finally, we discuss the implications of these results both for our understanding of the origin of the FP for early-type galaxies and bulges and for deriving unbiased distances and peculiar velocities in the local universe.

Quantum chaos on a critical Fermi surface.

PubMed

Patel, Aavishkar A; Sachdev, Subir

2017-02-21

We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of [Formula: see text] species of fermions at nonzero density coupled to a [Formula: see text] gauge field in two spatial dimensions and determine the Lyapunov rate and the butterfly velocity in an extended random-phase approximation. The thermal diffusivity is found to be universally related to these chaos parameters; i.e., the relationship is independent of [Formula: see text], the gauge-coupling constant, the Fermi velocity, the Fermi surface curvature, and high-energy details.

Monitoring surface currents and transport variability in Drake Passage using altimetry and hydrography

NASA Astrophysics Data System (ADS)

Pavic, M.; Cunningham, S. A.; Challenor, P.; Duncan, L.

2003-04-01

Between 1993 and 2001 the UK has completed seven occupations of WOCE section SR1b from Burdwood Bank to Elephant Island across Drake Passage. The section consists of a minimum of 31 full depth CTD stations, shipboard ADCP measurements of currents in the upper 300m, and in three of the years full depth lowered ADCP measurements at each station. The section lies under the satellite track of ERS2. The satellite altimeter can determine the along track slope of the sea surface relative to a reference satellite pass once every 35 days. From this we can calculate the relative SSH slope or geostrophic surface current anomalies. If we measure simultaneously with any satellite pass, we can estimate the absolute surface geostrophic current for any subsequent pass. This says that by combining in situ absolute velocity measurements - the reference velocities with altimetry at one time the absolute geostrophic current can be estimated on any subsequent (or previous) altimeter pass. This is the method of Challenor et al. 1996, though they did not have the data to test this relationship. We have seven estimates of the surface reference velocity: one for each of the seven occupations of the WOCE line. The difference in any pair of reference velocities is predicted by the difference of the corresponding altimeter measurements. Errors in combining the satellite and hydrographic data are estimated by comparing pairs of these differences: errors arise from the in situ observations and from the altimetric measurements. Finally we produce our best estimates of eight years of absolute surface geostrophic currents and transport variability along WOCE section SR1 in Drake Passage.

High-frequency Rayleigh-wave method

USGS Publications Warehouse

Xia, J.; Miller, R.D.; Xu, Y.; Luo, Y.; Chen, C.; Liu, J.; Ivanov, J.; Zeng, C.

2009-01-01

High-frequency (???2 Hz) Rayleigh-wave data acquired with a multichannel recording system have been utilized to determine shear (S)-wave velocities in near-surface geophysics since the early 1980s. This overview article discusses the main research results of high-frequency surface-wave techniques achieved by research groups at the Kansas Geological Survey and China University of Geosciences in the last 15 years. The multichannel analysis of surface wave (MASW) method is a non-invasive acoustic approach to estimate near-surface S-wave velocity. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that simultaneous inversion with higher modes and the fundamental mode can increase model resolution and an investigation depth. The other important seismic property, quality factor (Q), can also be estimated with the MASW method by inverting attenuation coefficients of Rayleigh waves. An inverted model (S-wave velocity or Q) obtained using a damped least-squares method can be assessed by an optimal damping vector in a vicinity of the inverted model determined by an objective function, which is the trace of a weighted sum of model-resolution and model-covariance matrices. Current developments include modeling high-frequency Rayleigh-waves in near-surface media, which builds a foundation for shallow seismic or Rayleigh-wave inversion in the time-offset domain; imaging dispersive energy with high resolution in the frequency-velocity domain and possibly with data in an arbitrary acquisition geometry, which opens a door for 3D surface-wave techniques; and successfully separating surface-wave modes, which provides a valuable tool to perform S-wave velocity profiling with high-horizontal resolution. ?? China University of Geosciences (Wuhan) and Springer-Verlag GmbH 2009.

Questions on universal constants and four-dimensional symmetry from a broad viewpoint. I

NASA Technical Reports Server (NTRS)

Hsu, J. P.

1983-01-01

It is demonstrated that there is a flexibility in clock synchronizations and that four-dimensional symmetry framework can be viewed broadly. The true universality of basic constants is discussed, considering a class of measurement processes based on the velocity = distance/time interval, which always yields some number when used by an observer. The four-dimensional symmetry framework based on common time for all observers is formulated, and related processes of measuring light speed are discussed. Invariant 'action functions' for physical laws in the new four-dimensional symmetry framework with the common time are established to discuss universal constants. Truly universal constants are demonstrated, and it is shown that physics in this new framework and in special relativity are equivalent as far as one-particle systems and the S-matrix in field theories are concerned.

Entrainment, transport and deposition of sediment by saline gravity currents

NASA Astrophysics Data System (ADS)

Zordan, Jessica; Juez, Carmelo; Schleiss, Anton J.; Franca, Mário J.

2018-05-01

Few studies have addressed simultaneously the feedback between the hydrodynamics of a gravity current and the geomorphological changes of a mobile bed. Hydrodynamic quantities such as turbulent and mean velocities, bed shear stress and turbulent stresses undoubtedly govern the processes of entrainment, transport and deposition. On the other hand, the incorporation of entrained sediment in the current may change its momentum by introducing extra internal stresses, introducing thus a feedback process. These two main questions are here investigated. Laboratory experiments of saline gravity currents, produced by lock-exchange, flowing over a mobile bed channel reach, are here reported. Different initial buoyancies of the current in the lock are tested together with three different grain sizes of the non-coherent sediment that form the erodible bed. Results from velocity measurements are combined with the visualization of the sediment movement in the mobile reach and with post-test topographic and photo surveys of the geomorphology modifications of the channel bed. Mean and turbulent velocities are measured and bed shear stress and Reynolds stresses are estimated. We show that the mean vertical component of the velocity and bed shear stress are highly correlated with the first instants of sediment entrainment. Vertical turbulent velocity is similarly related to entrainment, although with lower correlation values, contributing as well to the sediment movement. Bed shear stress and Reynolds shear stress measured near the bed are correlated with sediment entrainment for longer periods, indicating that these quantities are associated to distal transport as well. Geomorphological changes in the mobile bed are strongly related to the impulse caused by the bed shear stress on the sediment. On the other hand, we show that the nature of the grain of the mobile bed reach influences the hydrodynamics of the current which means that a feedback mechanisms between both occurs during the passage of the unsteady gravity current. The signature of this geomorphological changes, which is visible in the form of longitudinal steaks of accumulated sediment downstream the mobile bed, is related to the flow initial buoyancy and to the size of the mobile bed sediment. It is argued that the bed material and near-bed turbulent coherent motion interact and mutually influence each other. The geometry of the front of the gravity currents changes with the incorporation of the sediment, indicating that with the presence of sediment extra energy losses occur in the front of the current.

Dependence of electron peak current on hollow cathode dimensions and seed electron energy in a pseudospark discharge

NASA Astrophysics Data System (ADS)

Cetiner, S. O.; Stoltz, P.; Messmer, P.; Cambier, J.-L.

2008-01-01

The prebreakdown and breakdown phases of a pseudospark discharge are investigated using the two-dimensional kinetic plasma simulation code OOPIC™ PRO. Trends in the peak electron current at the anode are presented as function of the hollow cathode dimensions and mean seed injection velocities at the cavity back wall. The plasma generation process by ionizing collisions is examined, showing the effect on supplying the electrons that determine the density of the beam. The mean seed velocities used here are varied between the velocity corresponding to the energy of peak ionization cross section, 15 times this value and no mean velocity (i.e., electrons injected with a temperature of 2.5eV). The reliance of the discharge characteristics on the penetrating electric field is shown to decrease as the mean seed injection velocity increases because of its ability to generate a surplus plasma independent of the virtual anode. As a result, the peak current increases with the hollow cathode dimensions for the largest average injection velocity, while for the smallest value it increases with the area of penetration of the electric field in the hollow cathode interior. Additionally, for a given geometry an increase in the peak current with the surplus plasma generated is observed. For the largest seed injection velocity used a dependence of the magnitude of the peak current on the ratio of the hole thickness and hollow cathode depth to the hole height is demonstrated. This means similar trends of the peak current are generated when the geometry is resized. Although the present study uses argon only, the variation in the discharge dependencies with the seed injection energy relative to the ionization threshold is expected to apply independently of the gas type. Secondary electrons due to electron and ion impact are shown to be important only for the largest impact areas and discharge development times of the study.

Surveys of water velocities in the vicinity of the discharge-release gates of Salamonie Lake Dam, northeastern Indiana, spring and winter 1998

USGS Publications Warehouse

Morlock, Scott E.; Stewart, James A.

2000-01-01

An acoustic Doppler current profiler (ADCP) mounted on a boat was used to collect velocity and depth data and to compute positions of the velocity and depth data relative to the boat track. A global positioning system (GPS) was used to collect earth-referenced position data, and a GPS base station receiver was used to improve the accuracy of the earth-referenced position data. The earth-referenced position data were used to transform the ADCP-computed positions (which were relative to boat tracks) to positions referenced to a point on the spillway tower.

Current Global Absolute Plate Velocities Inferred from the Trends of Hotspot Tracks: Implications for Motion between Groups of Hotspots and Comparison and Combination with Absolute Velocities Inferred from the Orientation of Seismic Anisotropy

NASA Astrophysics Data System (ADS)

Wang, C.; Gordon, R. G.; Zheng, L.

2016-12-01

Hotspot tracks are widely used to estimate the absolute velocities of plates, i.e., relative to the lower mantle. Knowledge of current motion between hotspots is important for both plate kinematics and mantle dynamics and informs the discussion on the origin of the Hawaiian-Emperor Bend. Following Morgan & Morgan (2007), we focus only on the trends of young hotspot tracks and omit volcanic propagation rates. The dispersion of the trends can be partitioned into between-plate and within-plate dispersion. Applying the method of Gripp & Gordon (2002) to the hotspot trend data set of Morgan & Morgan (2007) constrained to the MORVEL relative plate angular velocities (DeMets et al., 2010) results in a standard deviation of the 56 hotspot trends of 22°. The largest angular misfits tend to occur on the slowest moving plates. Alternatively, estimation of best-fitting poles to hotspot tracks on the nine individual plates, results in a standard deviation of trends of only 13°, a statistically significant reduction from the introduction of 15 additional adjustable parameters. If all of the between-plate misfit is due to motion of groups of hotspots (beneath different plates), nominal velocities relative to the mean hotspot reference frame range from 1 to 4 mm/yr with the lower bounds ranging from 1 to 3 mm/yr and the greatest upper bound being 8 mm/yr. These are consistent with bounds on motion between Pacific and Indo-Atlantic hotspots over the past ≈50 Ma, which range from zero (lower bound) to 8 to 13 mm/yr (upper bounds) (Koivisto et al., 2014). We also determine HS4-MORVEL, a new global set of plate angular velocities relative to the hotspots constrained to consistency with the MORVEL relative plate angular velocities, using a two-tier analysis similar to that used by Zheng et al. (2014) to estimate the SKS-MORVEL global set of absolute plate velocities fit to the orientation of seismic anisotropy. We find that the 95% confidence limits of HS4-MORVEL and SKS-MORVEL overlap substantially and that the two sets of angular velocities differ insignificantly. Thus we combine the two sets of angular velocities to estimate ABS-MORVEL, an optimal set of global angular velocities consistent with both hotspot tracks and seismic anisotropy. ABS-MORVEL has more compact confidence limits than either SKS-MORVEL or HS4-MORVEL.

Evaluation of multiple-frequency, active and passive acoustics as surrogates for bedload transport

USGS Publications Warehouse

Wood, Molly S.; Fosness, Ryan L.; Pachman, Gregory; Lorang, Mark; Tonolla, Diego

2015-01-01

The use of multiple-frequency, active acoustics through deployment of acoustic Doppler current profilers (ADCPs) shows potential for estimating bedload in selected grain size categories. The U.S. Geological Survey (USGS), in cooperation with the University of Montana (UM), evaluated the use of multiple-frequency, active and passive acoustics as surrogates for bedload transport during a pilot study on the Kootenai River, Idaho, May 17-18, 2012. Four ADCPs with frequencies ranging from 600 to 2000 kHz were used to measure apparent moving bed velocities at 20 stations across the river in conjunction with physical bedload samples. Additionally, UM scientists measured the sound frequencies of moving particles with two hydrophones, considered passive acoustics, along longitudinal transects in the study reach. Some patterns emerged in the preliminary analysis which show promise for future studies. Statistically significant relations were successfully developed between apparent moving bed velocities measured by ADCPs with frequencies 1000 and 1200 kHz and bedload in 0.5 to 2.0 mm grain size categories. The 600 kHz ADCP seemed somewhat sensitive to the movement of gravel bedload in the size range 8.0 to 31.5 mm, but the relation was not statistically significant. The passive hydrophone surveys corroborated the sample results and could be used to map spatial variability in bedload transport and to select a measurement cross-section with moving bedload for active acoustic surveys and physical samples.

Spinning fluids in general relativity

NASA Technical Reports Server (NTRS)

Ray, J. R.; Smalley, L. L.

1982-01-01

General relativity field equations are employed to examine a continuous medium with internal spin. A variational principle formerly applied in the special relativity case is extended to the general relativity case, using a tetrad to express the spin density and the four-velocity of the fluid. An energy-momentum tensor is subsequently defined for a spinning fluid. The equations of motion of the fluid are suggested to be useful in analytical studies of galaxies, for anisotropic Bianchi universes, and for turbulent eddies.

Impact Testing for Materials Science at NASA - MSFC

NASA Technical Reports Server (NTRS)

Sikapizye, Mitch

2010-01-01

The Impact Testing Facility (ITF) at NASA - Marshall Space Flight Center is host to different types of guns used to study the effects of high velocity impacts. The testing facility has been and continues to be utilized for all NASA missions where impact testing is essential. The Facility has also performed tests for the Department of Defense, other corporations, as well as universities across the nation. Current capabilities provided by Marshall include ballistic guns, light gas guns, exploding wire gun, and the Hydrometeor Impact Gun. A new plasma gun has also been developed which would be able to propel particles at velocities of 20km/s. This report includes some of the guns used for impact testing at NASA Marshall and their capabilities.

THE ANATOMY OF AN EXTREME STARBURST WITHIN 1.3 Gyr OF THE BIG BANG REVEALED BY ALMA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carilli, C. L.; Riechers, D.; Walter, F.

We present further analysis of the [C II] 158 {mu}m fine structure line and thermal dust continuum emission from the archetype extreme starburst/active galactic nucleus (AGN) group of galaxies in the early universe, BRI 1202-0725 at z = 4.7, using the Atacama Large Millimeter Array. The group has long been noted for having a closely separated (26 kpc in projection) FIR-hyperluminous quasar host galaxy and an optically obscured submillimeter galaxy (SMG). A short ALMA test observation reveals a rich laboratory for the study of the myriad processes involved in clustered massive galaxy formation in the early universe. Strong [C II]more » emission from the SMG and the quasar have been reported earlier by Wagg et al. based on these observations. In this paper, we examine in more detail the imaging results from the ALMA observations, including velocity channel images, position-velocity plots, and line moment images. We present detections of [C II] emission from two Ly{alpha}-selected galaxies in the group, demonstrating the relative ease with which ALMA can detect the [C II] emission from lower star formation rate galaxies at high redshift. Imaging of the [C II] emission shows a clear velocity gradient across the SMG, possibly indicating rotation or a more complex dynamical system on a scale {approx}10 kpc. There is evidence in the quasar spectrum and images for a possible outflow toward the southwest, as well as more extended emission (a {sup b}ridge{sup )}, between the quasar and the SMG, although the latter could simply be emission from Ly{alpha}-1 blending with that of the quasar at the limited spatial resolution of the current observations. These results provide an unprecedented view of a major merger of gas-rich galaxies driving extreme starbursts and AGN accretion during the formation of massive galaxies and supermassive black holes within 1.3 Gyr of the big bang.« less

Remote determination of the velocity index and mean streamwise velocity profiles

NASA Astrophysics Data System (ADS)

Johnson, E. D.; Cowen, E. A.

2017-09-01

When determining volumetric discharge from surface measurements of currents in a river or open channel, the velocity index is typically used to convert surface velocities to depth-averaged velocities. The velocity index is given by, k=Ub/Usurf, where Ub is the depth-averaged velocity and Usurf is the local surface velocity. The USGS (United States Geological Survey) standard value for this coefficient, k = 0.85, was determined from a series of laboratory experiments and has been widely used in the field and in laboratory measurements of volumetric discharge despite evidence that the velocity index is site-specific. Numerous studies have documented that the velocity index varies with Reynolds number, flow depth, and relative bed roughness and with the presence of secondary flows. A remote method of determining depth-averaged velocity and hence the velocity index is developed here. The technique leverages the findings of Johnson and Cowen (2017) and permits remote determination of the velocity power-law exponent thereby, enabling remote prediction of the vertical structure of the mean streamwise velocity, the depth-averaged velocity, and the velocity index.

On the Use of Coupled Wind, Wave, and Current Fields in the Simulation of Loads on Bottom-Supported Offshore Wind Turbines during Hurricanes: March 2012 - September 2015

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Eungsoo; Manuel, Lance; Curcic, Milan

In the United States, potential offshore wind plant sites have been identified along the Atlantic seaboard and in the Gulf of Mexico. It is imperative that we define external conditions associated with hurricanes and severe winter storms and consider load cases for which wind turbines may need to be designed. We selected two hurricanes, Ike (2008) and Sandy (2012), and investigated the effect these tropical storms would have on bottom-supported offshore wind turbines that were hypothetically in or close to their path as they made landfall. For realistic turbine loads assessment, it is important that the coupled influences of themore » changing wind, wave, and current fields are simulated throughout the evolution of the hurricanes. We employed a coupled model--specifically, the University of Miami Coupled Model (UMCM)--that integrates atmospheric, wave, and ocean components to produce needed wind, wave, and current data. The wind data are used to generate appropriate vertical wind profiles and full wind velocity fields including turbulence; the current field over the water column is obtained by interpolated discrete output current data; and short-crested irregular second-order waves are simulated using output directional wave spectra from the coupled model. We studied two monopile-supported offshore wind turbines sited in 20 meters of water in the Gulf of Mexico to estimate loads during Hurricane Ike, and a jacket space-frame platform-supported offshore wind turbine sited in 50 meters of water in the mid-Atlantic region to estimate loads during Hurricane Sandy. In this report we discuss in detail how the simulated hurricane wind, wave, and current output data are used in turbine loads studies. In addition, important characteristics of the external conditions are studied, including the relative importance of swell versus wind seas, aerodynamic versus hydrodynamic forces, current velocity effects, yaw control options for the turbine, hydrodynamic drag versus inertia forces, and soil-structure interaction effects. A detailed framework is presented that explains how coupled inputs can be included in turbine loads studies during a hurricane. This framework can aid in future efforts aimed at developing offshore wind turbine design criteria and load cases related to hurricanes.« less

Evaluation of the Ott Hydromet Qliner for measuring discharge in laboratory and field conditions

USGS Publications Warehouse

McVay, Jason C.

2015-01-01

The U.S. Geological Survey, in collaboration with the University of Iowa IIHR – Hydroscience and Engineering, evaluated the use of the Ott Hydromet Qliner using laboratory flume tests along with field validation tests. Analysis of the flume testing indicates the velocities measured by the Qliner at a 40-second exposure time results in higher dispersion of velocities from the mean velocity of data collected with a 5-minute exposure time. The percent data spread from the mean of a 100-minute mean of Qliner velocities for a 40-second exposure time averaged 16.6 percent for the entire vertical, and a 5-minute mean produced a 6.2 percent data spread from the 100-minute mean. This 16.6 percent variation in measured velocity would result in a 3.32 percent variation in computed discharge assuming 25 verticals while averaging 4 bins in each vertical. The flume testing also provided results that indicate the blanking distance of 0.20 meters is acceptable when using beams 1 and 2, however beam 3 is negatively biased near the transducer and the 0.20-meter blanking distance is not sufficient. Field testing included comparing the measured discharge by the Qliner to the discharge measured by a Price AA mechanical current meter and a Teledyne RDI Rio Grande 1200 kilohertz acoustic Doppler current profiler. The field tests indicated a difference between the discharges measured with the Qliner and the field reference discharge between -14.0 and 8.0 percent; however the average percent difference for all 22 field comparisons was 0.22, which was not statistically significant.

The KMOS Deep Survey: Dynamical Measurements of Star-Forming Galaxies at z 3.5

NASA Astrophysics Data System (ADS)

Turner, Owen; Cirasuolo, Michele; Harrison, Chris; McLure, Ross; Dunlop, James; Swinbank, Mark; Johnson, Helen; Sobral, David; Matthee, Jorryt; Sharples, Ray

2017-07-01

This poster present dynamical measurements from the KMOS (K-band Multi-Object Spectrograph) Deep Survey (KDS), which is comprised of 78 typical star-forming galaxies at z = 3.5 in the mass range 9.0 < log(M*) < 10.5. We fit spatially and spectrally convolved mock datacubes to the observed data, in order to make beam-smearing corrected measurements of the intrinsic velocity dispersions and rotation velocities of 33 galaxies in the sample classed as spatially resolved and isolated. The results suggest that the rotation-dominated galaxies in the sample are offset to lower velocities at fixed stellar mass and have higher velocity dispersions than star-forming galaxies in the local and intermediate redshift universe. Only 1/3 of the galaxies in the sample are dominated by rotation, which hints that random motions are playing an increasingly significant role in supporting the dynamical mass in the systems. When searching for evolution in scaling relations, such as the stellar mass Tully-Fisher relation, it is important to take these random motions into account.

Space-time correlations of fluctuating velocities in turbulent shear flows

NASA Astrophysics Data System (ADS)

Zhao, Xin; He, Guo-Wei

2009-04-01

Space-time correlations or Eulerian two-point two-time correlations of fluctuating velocities are analytically and numerically investigated in turbulent shear flows. An elliptic model for the space-time correlations in the inertial range is developed from the similarity assumptions on the isocorrelation contours: they share a uniform preference direction and a constant aspect ratio. The similarity assumptions are justified using the Kolmogorov similarity hypotheses and verified using the direct numerical simulation (DNS) of turbulent channel flows. The model relates the space-time correlations to the space correlations via the convection and sweeping characteristic velocities. The analytical expressions for the convection and sweeping velocities are derived from the Navier-Stokes equations for homogeneous turbulent shear flows, where the convection velocity is represented by the mean velocity and the sweeping velocity is the sum of the random sweeping velocity and the shear-induced velocity. This suggests that unlike Taylor’s model where the convection velocity is dominating and Kraichnan and Tennekes’ model where the random sweeping velocity is dominating, the decorrelation time scales of the space-time correlations in turbulent shear flows are determined by the convection velocity, the random sweeping velocity, and the shear-induced velocity. This model predicts a universal form of the space-time correlations with the two characteristic velocities. The DNS of turbulent channel flows supports the prediction: the correlation functions exhibit a fair good collapse, when plotted against the normalized space and time separations defined by the elliptic model.

Time-dependent London approach: Dissipation due to out-of-core normal excitations by moving vortices

DOE PAGES

Kogan, V. G.

2018-03-19

The dissipative currents due to normal excitations are included in the London description. The resulting time-dependent London equations are solved for a moving vortex and a moving vortex lattice. It is shown that the field distribution of a moving vortex loses its cylindrical symmetry. It experiences contraction that is stronger in the direction of the motion than in the direction normal to the velocity v. The London contribution of normal currents to dissipation is small relative to the Bardeen-Stephen core dissipation at small velocities, but it approaches the latter at high velocities, where this contribution is no longer proportional tomore » v 2. Here, to minimize the London contribution to dissipation, the vortex lattice is oriented so as to have one of the unit cell vectors along the velocity. This effect is seen in experiments and predicted within the time-dependent Ginzburg-Landau theory.« less

Time-dependent London approach: Dissipation due to out-of-core normal excitations by moving vortices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kogan, V. G.

The dissipative currents due to normal excitations are included in the London description. The resulting time-dependent London equations are solved for a moving vortex and a moving vortex lattice. It is shown that the field distribution of a moving vortex loses its cylindrical symmetry. It experiences contraction that is stronger in the direction of the motion than in the direction normal to the velocity v. The London contribution of normal currents to dissipation is small relative to the Bardeen-Stephen core dissipation at small velocities, but it approaches the latter at high velocities, where this contribution is no longer proportional tomore » v 2. Here, to minimize the London contribution to dissipation, the vortex lattice is oriented so as to have one of the unit cell vectors along the velocity. This effect is seen in experiments and predicted within the time-dependent Ginzburg-Landau theory.« less

Time-dependent London approach: Dissipation due to out-of-core normal excitations by moving vortices

NASA Astrophysics Data System (ADS)

Kogan, V. G.

2018-03-01

The dissipative currents due to normal excitations are included in the London description. The resulting time-dependent London equations are solved for a moving vortex and a moving vortex lattice. It is shown that the field distribution of a moving vortex loses its cylindrical symmetry. It experiences contraction that is stronger in the direction of the motion than in the direction normal to the velocity v . The London contribution of normal currents to dissipation is small relative to the Bardeen-Stephen core dissipation at small velocities, but it approaches the latter at high velocities, where this contribution is no longer proportional to v2. To minimize the London contribution to dissipation, the vortex lattice is oriented so as to have one of the unit cell vectors along the velocity. This effect is seen in experiments and predicted within the time-dependent Ginzburg-Landau theory.

Surface Current Density Mapping for Identification of Gastric Slow Wave Propagation

PubMed Central

Bradshaw, L. A.; Cheng, L. K.; Richards, W. O.; Pullan, A. J.

2009-01-01

The magnetogastrogram records clinically relevant parameters of the electrical slow wave of the stomach noninvasively. Besides slow wave frequency, gastric slow wave propagation velocity is a potentially useful clinical indicator of the state of health of gastric tissue, but it is a difficult parameter to determine from noninvasive bioelectric or biomagnetic measurements. We present a method for computing the surface current density (SCD) from multichannel magnetogastrogram recordings that allows computation of the propagation velocity of the gastric slow wave. A moving dipole source model with hypothetical as well as realistic biomagnetometer parameters demonstrates that while a relatively sparse array of magnetometer sensors is sufficient to compute a single average propagation velocity, more detailed information about spatial variations in propagation velocity requires higher density magnetometer arrays. Finally, the method is validated with simultaneous MGG and serosal EMG measurements in a porcine subject. PMID:19403355

Radial Velocity Detection of Extra-Solar Planetary Systems

NASA Technical Reports Server (NTRS)

Cochran, William D.

2004-01-01

This NASA Origins Program grant supported four closely related research programs at The University of Texas at Austin: 1) The McDonald Observatory Planetary Search (MOPS) Program, using the McDonald Observatory 2.7m Harlan Smith telescope and its 2dcoude spectrometer, 2) A high-precision radial-velocity survey of Hyades dwarfs, using the Keck telescope and its HIRES spectrograph, 3) A program at McDonald Observatory to obtain spectra of the parent stars of planetary systems at R = 210,000, and 4) the start of high precision radial velocity surveys using the Hobby-Eberly Telescope. The most important results from NASA support of these research programs are described. A list of all papers published under support of this grant is included at the end.

Mass, momentum and energy flow from an MPD accelerator. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Cory, J. S.

1971-01-01

The mass, momentum, and energy flows are measured over a current range of 8 to 50 kA and inlet mass flows of 2 to 36q/sec of argon. The momentum flux profile indicates that the accelerator produces a uniform, 2-inch diameter axial jet at the anode which expands into a Gaussian profile at an axial station 11 inches from the anode. The electromagnetic component of the thrust is found to follow the familiar quadratic dependence on arc current, while a more complex empirical relation is needed to correlate the gasdynamic contribution with the current and mass flow rate. Using available time-of-flight velocity profiles at a current of 16 kA and a mass flow of 5.9 g/sec, calculated flux profiles of mass and kinetic energy exhibit a tendency for some fraction of the inlet mass flow to leak out at a low velocity around the central high velocity core.

The OPTIS satellite-improved tests of Special and General Relativity

NASA Astrophysics Data System (ADS)

Scheithauer, Silvia; Laemmerzahl, Claus; Dittus, Hansjoerg; Schiller, Stephan; Peters, Achim

2005-06-01

The OPTIS satellite mission is an international collaboration initiated by three German University institutes aiming at improving tests regarding the foundations of Special and General Relativity. The mission idea - which has already passed the state of the initial feasibility study - is to contribute to the most challenging project of physics in this century - the search for a Theory of Quantum Gravity. This theory should resolve the incompatibilities between the quantum theory and Einstein's General Relativity. All approaches for a Quantum Gravity Theory predict small deviations from Special and General Relativity. If such deviations could be found (e.g. an anisotropy of the speed of light, violations of the universality of gravitational red shift or of the universality of free fall) the way to a new understanding of the time and space structure of the universe would be open. Therefore the goal of the OPTIS satellite mission is an accuracy improvement of tests regarding the foundations of Special and General Relativity by up to three orders of magnitude. For that purpose several experiments will be carried out on board the OPTIS satellite testing (i) the isotropy of the speed of light, (ii) the independence of the speed of light from the velocity of the laboratory system, (iii) the universality of the gravitational redshift, (iv) the absolute gravitational redshift and (v) the special relativistic time-dilation. Furthermore, orbit analyses will be done in order to measure (vi) the Lense-Thirring effect and (vii) perigee advance as well as to test (viii) the Newtonian View the MathML source gravitational potential. The benefit from bringing these experiments into space is the nearly disturbance free environment allowing precise measurements and large measurement times. The OPTIS mission will use already available key technologies like optical cavities, highly stabilised lasers, atomic clocks, frequency combs, capacitive gravitational reference sensors, drag-free control, laser tracking and laser linking systems. For most of the proposed tests the measurements are done by comparing the rates of different clocks. For the test of the isotropy of the velocity of light (Michelson-Morley experiment) the frequencies of resonators ("light clocks") pointing in different directions are compared. Concerning the constancy of the speed of light (Kennedy-Thorndike experiment) a resonator and atomic clocks under varying velocities are compared. For tests of the time dilation the rates of clocks in different states of motion and for testing the universality of the gravitational redshift clocks at different positions in the gravitational field are compared. This paper will give an overview about the OPTIS satellite mission, including the science goals, science requirements, key technologies, measurement principles and devices.

Preflare magnetic and velocity fields

NASA Technical Reports Server (NTRS)

Hagyard, M. J.; Gaizauskas, V.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.; Karpen, J. T.; Martres, M.-J.; Porter, J. G.; Schmeider, B.

1986-01-01

A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares

Light echoes whisper the distance to a star

NASA Astrophysics Data System (ADS)

2008-02-01

Astronomers have used ESO's Very Large Telescope to measure the distribution and motions of thousands of galaxies in the distant Universe. This opens fascinating perspectives to better understand what drives the acceleration of the cosmic expansion and sheds new light on the mysterious dark energy that is thought to permeate the Universe. ESO PR Photo 04a/08 ESO PR Photo 04a/08 Large-scale structures (Computer Simulation) "Explaining why the expansion of the Universe is currently accelerating is certainly the most fascinating question in modern cosmology," says Luigi Guzzo, lead author of a paper in this week's issue of Nature, in which the new results are presented. "We have been able to show that large surveys that measure the positions and velocities of distant galaxies provide us with a new powerful way to solve this mystery." Ten years ago, astronomers made the stunning discovery that the Universe is expanding at a faster pace today than it did in the past. "This implies that one of two very different possibilities must hold true," explains Enzo Branchini, member of the team. "Either the Universe is filled with a mysterious dark energy which produces a repulsive force that fights the gravitational brake from all the matter present in the Universe, or, our current theory of gravitation is not correct and needs to be modified, for example by adding extra dimensions to space." Current observations of the expansion rate of the Universe cannot distinguish between these two options, but the international team of 51 scientists from 24 institutions found a way that could help in tackling this problem. The technique is based on a well-known phenomenon, namely the fact that the apparent motion of distant galaxies results from two effects: the global expansion of the Universe that pushes the galaxies away from each other and the gravitational attraction of matter present in the galaxies' neighbourhood that pulls them together, creating the cosmic web of large-scale structures. ESO PR Photo 04b/08 ESO PR Photo 04b/08 A Cone in the Universe "By measuring the apparent velocities of large samples of galaxies over the last thirty years, astronomers have been able to reconstruct a three-dimensional map of the distribution of galaxies over large volumes of the Universe. This map revealed large-scale structures such as clusters of galaxies and filamentary superclusters," says Olivier Le Fèvre, member of the team. "But the measured velocities also contain information about the local motions of galaxies; these introduce small but significant distortions in the reconstructed maps of the Universe. We have shown that measuring this distortion at different epochs of the Universe's history is a way to test the nature of dark energy." Guzzo and his collaborators have been able to measure this effect by using the VIMOS spectrograph on Melipal, one of the four 8.2-m telescopes that is part of ESO's VLT. As part of the VIMOS-VLT Deep Survey (VVDS), of which Le Fèvre is the Principal Investigator, spectra of several thousands of galaxies in a 4-square-degree field (or 20 times the size of the full Moon) at epochs corresponding to about half the current age of the Universe (about 7 billion years ago) were obtained and analysed. ESO PR Video 04/08 ESO PR Video 04/08 Journey through galaxies "This is the largest field ever covered homogeneously by means of spectroscopy to this depth," declares Le Fèvre. "We have now collected more than 13,000 spectra in this field and the total volume sampled by the survey is more than 25 million cubic light-years." The astronomers compared their result with that of the 2dFGRS survey that probed the local Universe, i.e. measures the distortion at the present time. Within current uncertainties, the measurement of this effect provides an independent indication of the need for an unknown extra energy ingredient in the 'cosmic soup', supporting the simplest form of dark energy, the so-called cosmological constant, introduced originally by Albert Einstein. The large uncertainties do not yet exclude the other scenarios, though. "We have also shown that by extending our measurements over volumes about ten times larger than the VVDS, this technique should be able to tell us whether cosmic acceleration originates from a dark energy component of exotic origin or requires a modification of the laws of gravity," explains Guzzo. "VIMOS on the VLT would certainly be a wonderful tool to perform this future survey and help us answer this fundamental question. This strongly encourages scientists to proceed with even more ambitious surveys of the distant Universe," concludes Le Fèvre.

Numerical and Experimental Investigations on the Hydrodynamic Performance of a Tidal Current Turbine

NASA Astrophysics Data System (ADS)

Su, Xiaohui; Zhang, Jiantao; Zhao, Yong; Zhang, Huiying; Zhao, Guang; Cao, Yao

2017-12-01

In this paper, numerical and experimental investigations are presented on the hydrodynamic performance of a horizontal tidal current turbine (TCT) designed and made by our Dalian University of Technology (DUT) research group. Thus it is given the acronym: DUTTCT. An open source CFD solver, called PimpleDyMFoam, is employed to perform numerical simulations for design analysis, while experimental tests are conducted in a DUT towing tank. The important factors, including self-starting velocity, tip speed ratio (TSR) and yaw angle, which play important roles in the turbine output power, are studied in the investigations. Results obtained show that the maximum power efficiency of the newly developed turbine (DUTTCT) could reach up to 47.6% and all its power efficiency is over 40% in the TSR range from 3.5 to 6; the self-starting velocity of DUTTCT is about 0.745m/s; the yaw angle has negligible influence on its efficiency as it is less than 10°.

Influence of residual plasma drift velocity on the post-arc sheath expansion of vacuum circuit breakers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mo, Yongpeng; Shi, Zongqian; Jia, Shenli

The residual plasma in the inter-contact region of a vacuum circuit breaker moves towards the post-arc cathode at current zero, because the residual plasma mainly comes from the cathode spots during the arc burning process. In the most previous theoretical researches on the post-arc sheath expansion process of vacuum circuit breakers, only the thermal motion of residual plasma was taken into consideration. Alternately, the residual plasma was even assumed to be static at the moment of current zero in some simplified models. However, the influence of residual plasma drift velocity at current zero on the post-arc sheath expansion process wasmore » rarely investigated. In this paper, this effect is investigated by a one-dimensional particle-in-cell model. Simulation results indicate that the sheath expands slower with higher residual plasma drift velocity in the initial sheath expansion stage. However, with the increase of residual plasma drift velocity, the overall plasma density in the inter-contact region decreases faster, and the sheath expansion velocity increases earlier. Consequently, as a whole, it needs shorter time to expel the residual plasma from the inter-contact region. Furthermore, if the residual plasma drift velocity is high enough, the sheath expansion process ceases before it develops to the post-arc anode. Besides, the influence of the collisions between charges and neutrals is investigated as well in terms of the density of metal vapor. It shows that the residual plasma drift velocity takes remarkable effect only if the density of the metal vapor is relatively low, which corresponds to the circumstance of low-current interruptions.« less

Peak Weight and Height Velocity to Age 36 Months and Asthma Development: The Norwegian Mother and Child Cohort Study

PubMed Central

Magnus, Maria C.; Stigum, Hein; Håberg, Siri E.; Nafstad, Per; London, Stephanie J.; Nystad, Wenche

2015-01-01

Background The immediate postnatal period is the period of the fastest growth in the entire life span and a critical period for lung development. Therefore, it is interesting to examine the association between growth during this period and childhood respiratory disorders. Methods We examined the association of peak weight and height velocity to age 36 months with maternal report of current asthma at 36 months (n = 50,311), recurrent lower respiratory tract infections (LRTIs) by 36 months (n = 47,905) and current asthma at 7 years (n = 24,827) in the Norwegian Mother and Child Cohort Study. Peak weight and height velocity was calculated using the Reed1 model through multilevel mixed-effects linear regression. Multivariable log-binomial regression was used to calculate adjusted relative risks (adj.RR) and 95% confidence intervals (CI). We also conducted a sibling pair analysis using conditional logistic regression. Results Peak weight velocity was positively associated with current asthma at 36 months [adj.RR 1.22 (95%CI: 1.18, 1.26) per standard deviation (SD) increase], recurrent LRTIs by 36 months [adj.RR 1.14 (1.10, 1.19) per SD increase] and current asthma at 7 years [adj.RR 1.13 (95%CI: 1.07, 1.19) per SD increase]. Peak height velocity was not associated with any of the respiratory disorders. The positive association of peak weight velocity and asthma at 36 months remained in the sibling pair analysis. Conclusions Higher peak weight velocity, achieved during the immediate postnatal period, increased the risk of respiratory disorders. This might be explained by an influence on neonatal lung development, shared genetic/epigenetic mechanisms and/or environmental factors. PMID:25635872

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erkaev, N. V.; Semenov, V. S.; Biernat, H. K.

Hall magnetohydrodynamic model is investigated for current sheet flapping oscillations, which implies a gradient of the normal magnetic field component. For the initial undisturbed current sheet structure, the normal magnetic field component is assumed to have a weak linear variation. The profile of the electric current velocity is described by hyperbolic functions with a maximum at the center of the current sheet. In the framework of this model, eigenfrequencies are calculated as functions of the wave number for the ''kink'' and ''sausage'' flapping wave modes. Because of the Hall effects, the flapping eigenfrequency is larger for the waves propagating alongmore » the electric current, and it is smaller for the opposite wave propagation with respect to the current. The asymmetry of the flapping wave propagation, caused by Hall effects, is pronounced stronger for thinner current sheets. This is due to the Doppler effect related to the electric current velocity.« less

Flow friction of the turbulent coolant flow in cryogenic porous cables

NASA Technical Reports Server (NTRS)

Hendricks, R. C.; Yeroshenko, V. M.; Zaichik, L. I.; Yanovsky, L. S.

1979-01-01

Considered are cryogenic power transmission cables with porous cores. Calculations of the turbulent coolant flow with injection or suction through the porous wall are presented within the framework of a two-layer model. Universal velocity profiles were obtained for the viscous sublayer and flow core. Integrating the velocity profile, the law of flow friction in the pipe with injection has been derived for the case when there is a tangential injection velocity component. The effect of tangential velocity on the relative law of flow friction is analyzed. The applicability of the Prandtl model to the problem under study is discussed. It is shown that the error due to the acceptance of the model increases with the injection parameter and at lower Reynolds numbers; under these circumstances, the influence of convective terms in the turbulent energy equation on the mechanism of turbulent transport should be taken into account.

Conduction velocity is regulated by sodium channel inactivation in unmyelinated axons innervating the rat cranial meninges

PubMed Central

De Col, Roberto; Messlinger, Karl; Carr, Richard W

2008-01-01

Axonal conduction velocity varies according to the level of preceding impulse activity. In unmyelinated axons this typically results in a slowing of conduction velocity and a parallel increase in threshold. It is currently held that Na+–K+-ATPase-dependent axonal hyperpolarization is responsible for this slowing but this has long been equivocal. We therefore examined conduction velocity changes during repetitive activation of single unmyelinated axons innervating the rat cranial meninges. In direct contradiction to the currently accepted postulate, Na+–K+-ATPase blockade actually enhanced activity-induced conduction velocity slowing, while the degree of velocity slowing was curtailed in the presence of lidocaine (10–300 μm) and carbamazepine (30–500 μm) but not tetrodotoxin (TTX, 10–80 nm). This suggests that a change in the number of available sodium channels is the most prominent factor responsible for activity-induced changes in conduction velocity in unmyelinated axons. At moderate stimulus frequencies, axonal conduction velocity is determined by an interaction between residual sodium channel inactivation following each impulse and the retrieval of channels from inactivation by a concomitant Na+–K+-ATPase-mediated hyperpolarization. Since the process is primarily dependent upon sodium channel availability, tracking conduction velocity provides a means of accessing relative changes in the excitability of nociceptive neurons. PMID:18096592

The Mass of the Candidate Exoplanet Companion to HD 33636 from Hubble Space Telescope Astrometry and High-Precision Radial Velocities

NASA Astrophysics Data System (ADS)

Bean, Jacob L.; McArthur, Barbara E.; Benedict, G. Fritz; Harrison, Thomas E.; Bizyaev, Dmitry; Nelan, Edmund; Smith, Verne V.

2007-08-01

We have determined a dynamical mass for the companion to HD 33636 that indicates it is a low-mass star instead of an exoplanet. Our result is based on an analysis of Hubble Space Telescope (HST) astrometry and ground-based radial velocity data. We have obtained high-cadence radial velocity measurements spanning 1.3 yr of HD 33636 with the Hobby-Eberly Telescope at McDonald Observatory. We combined these data with previously published velocities to create a data set that spans 9 yr. We used this data set to search for, and place mass limits on, the existence of additional companions in the HD 33636 system. Our high-precision astrometric observations of the system with the HST Fine Guidance Sensor 1r span 1.2 yr. We simultaneously modeled the radial velocity and astrometry data to determine the parallax, proper motion, and perturbation orbit parameters of HD 33636. Our derived parallax, πabs=35.6+/-0.2 mas, agrees within the uncertainties with the Hipparcos value. We find a perturbation period P=2117.3+/-0.8 days, semimajor axis aA=14.2+/-0.2 mas, and system inclination i=4.1deg+/-0.1deg. Assuming the mass of the primary star to be MA=1.02+/-0.03 Msolar, we obtain a companion mass MB=142+/-11 MJup=0.14+/-0.01 Msolar. The much larger true mass of the companion relative to its minimum mass estimated from the spectroscopic orbit parameters (Msini=9.3 MJup) is due to the nearly face-on orbit orientation. This result demonstrates the value of follow-up astrometric observations to determine the true masses of exoplanet candidates detected with the radial velocity method. Based on data obtained with the NASA/ESA Hubble Space Telescope (HST) and the Hobby-Eberly Telescope (HET). The HST observations were obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. The HET is a joint project of the University of Texas at Austin, Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität Müenchen, and Georg-August-Universität Göttingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.

The Formation of the First Cosmic Structures and the Physics of the z ~ 20 Universe

NASA Astrophysics Data System (ADS)

O'Leary, Ryan M.; McQuinn, Matthew

2012-11-01

We perform a suite of cosmological simulations in the ΛCDM paradigm of the formation of the first structures in the universe prior to astrophysical reheating and reionization (15 <~ z < 200). These are the first simulations initialized in a manner that self-consistently accounts for the impact of pressure on the rate of growth of modes, temperature fluctuations in the gas, and the dark matter-baryon supersonic velocity difference. Even with these improvements, these are still difficult times to simulate accurately as the Jeans length of the cold intergalactic gas must be resolved while also capturing a representative sample of the universe. We explore the box size and resolution requirements to meet these competing objectives. Our simulations support the finding of recent studies that the dark matter-baryon velocity difference has a surprisingly large impact on the accretion of gas onto the first star-forming minihalos (which have masses of ~106 M ⊙). In fact, the halo gas is often significantly downwind of such halos and with lower densities in the simulations in which the baryons have a bulk flow with respect to the dark matter, modulating the formation of the first stars by the local value of this velocity difference. We also show that dynamical friction plays an important role in the nonlinear evolution of the dark matter-baryon differential velocity, acting to erase this velocity difference quickly in overdense gas, as well as sourcing visually apparent bow shocks and Mach cones throughout the universe. We use simulations with both the GADGET and Enzo cosmological codes to test the robustness of these conclusions. The comparison of these codes' simulations also provides a relatively controlled test of these codes themselves, allowing us to quantify some of the tradeoffs between the algorithms. For example, we find that particle coupling in GADGET between the gas and dark matter particles results in spurious growth that mimics nonlinear growth in the matter power spectrum for standard initial setups. This coupling is alleviated by using adaptive gravitational softening for the gas. In a companion paper, we use the simulations presented here to make detailed estimates for the impact of the dark matter-baryon velocity differential on redshifted 21 cm radiation. The initial conditions generator used in this study, CICSASS, can be publicly downloaded.

Cosmic clocks: a tight radius-velocity relationship for H I-selected galaxies

NASA Astrophysics Data System (ADS)

Meurer, Gerhardt R.; Obreschkow, Danail; Wong, O. Ivy; Zheng, Zheng; Audcent-Ross, Fiona M.; Hanish, D. J.

2018-05-01

H I-selected galaxies obey a linear relationship between their maximum detected radius Rmax and rotational velocity. This result covers measurements in the optical, ultraviolet, and H I emission in galaxies spanning a factor of 30 in size and velocity, from small dwarf irregulars to the largest spirals. Hence, galaxies behave as clocks, rotating once a Gyr at the very outskirts of their discs. Observations of a large optically selected sample are consistent, implying this relationship is generic to disc galaxies in the low redshift Universe. A linear radius-velocity relationship is expected from simple models of galaxy formation and evolution. The total mass within Rmax has collapsed by a factor of 37 compared to the present mean density of the Universe. Adopting standard assumptions, we find a mean halo spin parameter λ in the range 0.020-0.035. The dispersion in λ, 0.16 dex, is smaller than expected from simulations. This may be due to the biases in our selection of disc galaxies rather than all haloes. The estimated mass densities of stars and atomic gas at Rmax are similar (˜0.5 M⊙ pc-2), indicating outer discs are highly evolved. The gas consumption and stellar population build time-scales are hundreds of Gyr, hence star formation is not driving the current evolution of outer discs. The estimated ratio between Rmax and disc scalelength is consistent with long-standing predictions from monolithic collapse models. Hence, it remains unclear whether disc extent results from continual accretion, a rapid initial collapse, secular evolution, or a combination thereof.

Can You Hear That Peak? Utilization of Auditory and Visual Feedback at Peak Limb Velocity

ERIC Educational Resources Information Center

Loria, Tristan; de Grosbois, John; Tremblay, Luc

2016-01-01

Purpose: At rest, the central nervous system combines and integrates multisensory cues to yield an optimal percept. When engaging in action, the relative weighing of sensory modalities has been shown to be altered. Because the timing of peak velocity is the critical moment in some goal-directed movements (e.g., overarm throwing), the current study…

Crustal structure of the Pannonian-Carpathian region, Central Europe, from ambient noise tomography

NASA Astrophysics Data System (ADS)

Ren, Y.; Stuart, G. W.; Houseman, G. A.; Carpathian Basins Project Working Group

2010-12-01

The Pannonian Basin of Central Europe is a major extensional basin surrounded by the Carpathian Mountains. During the evolution of the Carpathian-Pannonian region, extension of the crust and lithosphere created several inter-related basins of which the Pannonian basin is the largest. Imaging the seismic velocity structure of the crust and the upper mantle may help us understand the structure and geodynamic evolution of this part of central Europe. Here, we use ambient noise tomography to investigate the crust and uppermost mantle structure in the region. We have collected and processed continuous data from 56 temporary stations deployed in the Carpathian Basins Project (CBP) for 16 months (2005-2007) and 41 permanent broadband stations; this dataset enables the most well-resolved images of the S-wave structure of the region yet obtained. We computed the cross-correlation between vertical component seismograms from pairs of stations and stacked the correlated waveforms over 1-2 years to estimate the Rayleigh wave Green’s function. Frequency-time analysis is used to measure the group velocity dispersion curves, which are then inverted for the group velocity maps. Our 4-10 s group velocity maps exhibit low velocity anomalies which clearly defined the major sediment depo-centers in the Carpathian region. A broad low velocity anomaly in the center of the 5 s group velocity map can be associated with the Pannonian Basin, whereas an anomaly in the southeastern region is related to the Moesian platform. Further east, the Vienna Basin can also be seen on our maps. A fast anomaly in the central region can be associated with the Mid-Hungarian line. At periods from 18 to 24 seconds, group velocities become increasingly sensitive to crustal thickness. The maps also reveal low-velocity anomalies associated with the Carpathians. The low velocity anomalies are probably caused by deeper crustal roots beneath the mountain ranges which occur due to isostatic compensation. CBP working group: G. Houseman, G. Stuart, Y. Ren, B. Dando, P. Lorinczi, School of Earth and Environment, University of Leeds, UK; E. Hegedus, A. Kovács, I. Török, I. László, R. Csabafi, Eötvös Loránd Geophysical Institute, Budapest, Hungary; E. Brüeckl, H. Hausmann, W. Loderer, T-U Wien, Vienna, Austria; S. Radovanovic, V. Kovacevic, D. Valcic, S. Petrovic-Cacic, G. Krunic, Seismological Survey of Serbia, Belgrade, Serbia; A. Brisbourne, D. Hawthorn, A. Horleston, V. Lane, SEIS-UK, Leicester University, UK.

Twin Paradox in de Sitter Spacetime

ERIC Educational Resources Information Center

Boblest, Sebastian; Muller, Thomas; Wunner, Gunter

2011-01-01

The "twin paradox" of special relativity offers the possibility of making interstellar flights within a lifetime. For very long journeys with velocities close to the speed of light, however, we have to take into account the expansion of the universe. Inspired by the work of Rindler on hyperbolic motion in curved spacetime, we study the worldline…

Cosmic velocity-gravity relation in redshift space

NASA Astrophysics Data System (ADS)

Colombi, Stéphane; Chodorowski, Michał J.; Teyssier, Romain

2007-02-01

We propose a simple way to estimate the parameter β ~= Ω0.6/b from 3D galaxy surveys, where Ω is the non-relativistic matter-density parameter of the Universe and b is the bias between the galaxy distribution and the total matter distribution. Our method consists in measuring the relation between the cosmological velocity and gravity fields, and thus requires peculiar velocity measurements. The relation is measured directly in redshift space, so there is no need to reconstruct the density field in real space. In linear theory, the radial components of the gravity and velocity fields in redshift space are expected to be tightly correlated, with a slope given, in the distant observer approximation, by We test extensively this relation using controlled numerical experiments based on a cosmological N-body simulation. To perform the measurements, we propose a new and rather simple adaptive interpolation scheme to estimate the velocity and the gravity field on a grid. One of the most striking results is that non-linear effects, including `fingers of God', affect mainly the tails of the joint probability distribution function (PDF) of the velocity and gravity field: the 1-1.5 σ region around the maximum of the PDF is dominated by the linear theory regime, both in real and redshift space. This is understood explicitly by using the spherical collapse model as a proxy of non-linear dynamics. Applications of the method to real galaxy catalogues are discussed, including a preliminary investigation on homogeneous (volume-limited) `galaxy' samples extracted from the simulation with simple prescriptions based on halo and substructure identification, to quantify the effects of the bias between the galaxy distribution and the total matter distribution, as well as the effects of shot noise.

VizieR Online Data Catalog: Radial velocities of δ Sagittae (Pugh+, 2015)

NASA Astrophysics Data System (ADS)

Pugh, T.; Gray, D. F.; Griffin, R. F.

2018-01-01

28 spectra were obtained by Gray and Pugh between 2008 July and 2010 October (MJD 2454674-2455479) with the high-resolution (R~100000) coude spectrograph of the Elginfield Observatory of Western University (Gray 2009ApJ...697.1032G). The signal-to-noise ratios in the continuum, estimated from the photon counts, ranged from 152 to 314 with a mean of 220. The spectrograph has a dispersion of ~0.013 Å/mm and can reach a radial-velocity precision of 25 m/s by reference to water vapour lines inside the spectrograph (Gray & Brown 2006PASP..118.1112G). In the current case our measurement errors (based on exposures taken within a few nights of one another) range from 27 to 160 m/s, with a mean value of 90 m/s. The radial velocities were determined by measuring the positions of the spectral lines at 85 per cent of the line depth for 15 neutral metal lines in the λ6250-Å region. (1 data file).

Overview of hydro-acoustic current-measurement applications by the U.S. geological survey in Indiana

USGS Publications Warehouse

Morlock, Scott E.; Stewart, James A.

1999-01-01

The U.S. Geological Survey (USGS) maintains a network of 170 streamflow-gaging stations in Indiana to collect data from which continuous records of river discharges are produced. Traditionally, the discharge record from a station is produced by recording river stage and making periodic discharge measurements through a range of stage, then developing a relation between stage and discharge. Techniques that promise to increase data collection accuracy and efficiency include the use of hydro-acoustic instrumentation to measure river velocities. The velocity measurements are used to compute river discharge. In-situ applications of hydro-acoustic instruments by the USGS in Indiana include acoustic velocity meters (AVM's) at six streamflow-gaging stations and newly developed Doppler velocity meters (DVM's) at two stations. AVM's use reciprocal travel times of acoustic signals to measure average water velocities along acoustic paths, whereas DVM's use the Doppler shift of backscattered acoustic signals to compute water velocities. In addition to the in-situ applications, three acoustic Doppler current profilers (ADCP's) are used to make river-discharge measurements from moving boats at streamflow-gaging stations in Indiana. The USGS has designed and is testing an innovative unmanned platform from which to make ADCP discharge measurements.

Field Measurements to Characterize Turbulent Inflow for Marine Hydrokinetic Devices - Marrowstone Island, WA

NASA Astrophysics Data System (ADS)

Richmond, M. C.; Thomson, J. M.; Durgesh, V.; Polagye, B. L.

2011-12-01

Field measurements are essential for developing an improved understanding of turbulent inflow conditions that affect the design and operation of marine and hydrokinetic (MHK) devices. The Marrowstone Island site in Puget Sound, Washington State is a potential location for installing MHK devices, as it experiences strong tides and associated currents. Here, field measurements from Nodule Point on the eastern side of Marrowstone Island are used to characterize the turbulence in terms of velocity variance as a function of length and time scales. The field measurements were performed using Acoustic Doppler Velocimetry (ADV) and Acoustic Doppler Current Profiler (ADCP) instruments. Both were deployed on a bottom-mounted tripod at the site by the Applied Physics Lab at the University of Washington (APL-UW). The ADV acquired single point, temporally resolved velocity data from 17-21 Feb 2011, at a height of 4.6 m above the seabed at a sampling frequency of 32 Hz. The ADCP measured the velocity profile over the water column from a height of 2.6 m above the seabed up to the sea-surface in 36 bins, with each bin of 0.5 m size. The ADCP acquired data from 11-27 Feb 2011 at a sampling frequency of 2 Hz. Analysis of the ADV measurements shows distinct dynamic regions by scale: anisotropic eddies at large scales, an isotropic turbulent cascade (-5/3 slope in frequency spectra) at mesoscales, and contamination by Doppler noise at small scales. While Doppler noise is an order of magnitude greater for the ADCP measurements, the turbulence bulk statistics are consistent between the two instruments. There are significant variations in turbulence statistics with stage of the tidal currents (i.e., from slack to non-slack tidal conditions), however an average turbulent intensity of 10% is a robust, canonical value for this site. The ADCP velocity profiles are useful in quantifying the variability in velocity along the water column, and the ensemble averaged velocity profiles may be described by a power law, commonly used to characterize boundary layers.

Current induced domain wall dynamics in the presence of spin orbit torques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boulle, O., E-mail: Olivier.boulle@cea.fr; Buda-Prejbeanu, L. D.; Jué, E.

2014-05-07

Current induced domain wall (DW) motion in perpendicularly magnetized nanostripes in the presence of spin orbit torques is studied. We show using micromagnetic simulations that the direction of the current induced DW motion and the associated DW velocity depend on the relative values of the field like torque (FLT) and the Slonczewski like torques (SLT). The results are well explained by a collective coordinate model which is used to draw a phase diagram of the DW dynamics as a function of the FLT and the SLT. We show that a large increase in the DW velocity can be reached bymore » a proper tuning of both torques.« less

Vortex Formation in the Wake of Dark Matter Propulsion

NASA Astrophysics Data System (ADS)

Robertson, G. A.; Pinheiro, M. J.

Future spaceflight will require a new theory of propulsion; specifically one that does not require mass ejection. A new theory is proposed that uses the general view that closed currents pervade the entire universe and, in particular, there is a cosmic mechanism to expel matter to large astronomical distances involving vortex currents as seen with blazars and blackholes. At the terrestrial level, force producing vortices have been related to the motion of wings (e.g., birds, duck paddles, fish's tail). In this paper, vortex structures are shown to exist in the streamlines aft of a spaceship moving at high velocity in the vacuum. This is accomplished using the density excitation method per a modified Chameleon Cosmology model. This vortex structure is then shown to have similarities to spacetime models as Warp-Drive and wormholes, giving rise to the natural extension of Hawking and Unruh radiation, which provides the propulsive method for space travel where virtual electron-positron pairs, absorbed by the gravitational expansion forward of the spaceship emerge from an annular vortex field aft of the spaceship as real particles, in-like to propellant mass ejection in conventional rocket theory.

Current collection in an anisotropic plasma

NASA Technical Reports Server (NTRS)

Li, Wei-Wei

1990-01-01

A general method is given to derive the current-potential relations in anisotropic plasmas. Orbit limit current is assumed. The collector is a conductive sphere or an infinite cylinder. Any distribution which is an arbitrary function of the velocity vector can be considered as a superposition of many mono-energetic beams whose current-potential relations are known. The results for two typical pitch angle distributions are derived and discussed in detail. The general properties of the current potential relations are very similar to that of a Maxwellian plasma except for an effective temperature which varies with the angle between the magnetic field and the charging surface. The conclusions are meaningful to generalized geometries.

Analysis of sediment particle velocity in wave motion based on wave flume experiments

NASA Astrophysics Data System (ADS)

Krupiński, Adam

2012-10-01

The experiment described was one of the elements of research into sediment transport conducted by the Division of Geotechnics of West-Pomeranian University of Technology. The experimental analyses were performed within the framework of the project "Building a knowledge transfer network on the directions and perspectives of developing wave laboratory and in situ research using innovative research equipment" launched by the Institute of Hydroengineering of the Polish Academy of Sciences in Gdańsk. The objective of the experiment was to determine relations between sediment transport and wave motion parameters and then use the obtained results to modify formulas defining sediment transport in rivers, like Ackers-White formula, by introducing basic parameters of wave motion as the force generating bed material transport. The article presents selected results of the experiment concerning sediment velocity field analysis conducted for different parameters of wave motion. The velocity vectors of particles suspended in water were measured with a Particle Image Velocimetry (PIV) apparatus registering suspended particles in a measurement flume by producing a series of laser pulses and analysing their displacement with a high-sensitivity camera connected to a computer. The article presents velocity fields of suspended bed material particles measured in the longitudinal section of the wave flume and their comparison with water velocity profiles calculated for the definite wave parameters. The results presented will be used in further research for relating parameters essential for the description of monochromatic wave motion to basic sediment transport parameters and "transforming" mean velocity and dynamic velocity in steady motion to mean wave front velocity and dynamic velocity in wave motion for a single wave.

Development of a beam ion velocity detector for the heavy ion beam probe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fimognari, P. J., E-mail: PJFimognari@XanthoTechnologies.com; Crowley, T. P.; Demers, D. R.

2016-11-15

In an axisymmetric plasma, the conservation of canonical angular momentum constrains heavy ion beam probe (HIBP) trajectories such that measurement of the toroidal velocity component of secondary ions provides a localized determination of the poloidal flux at the volume where they originated. We have developed a prototype detector which is designed to determine the beam angle in one dimension through the detection of ion current landing on two parallel planes of detecting elements. A set of apertures creates a pattern of ion current on wires in the first plane and solid metal plates behind them; the relative amounts detected bymore » the wires and plates determine the angle which beam ions enter the detector, which is used to infer the toroidal velocity component. The design evolved from a series of simulations within which we modeled ion beam velocity changes due to equilibrium and fluctuating magnetic fields, along with the ion beam profile and velocity dispersion, and studied how these and characteristics such as the size, cross section, and spacing of the detector elements affect performance.« less

Radial Velocity Detection of Extra-Solar Planetary Systems

NASA Technical Reports Server (NTRS)

Cochran, William D.

2004-01-01

This NASA Origins Program grant supported four closely related research programs at The University of Texas at Austin: 1) The McDonald Observatory Planetary Search (MOPS) Program, using the McDonald Observatory 2.7m Harlan Smith telescope and its 2dcoud6 spectrometer, 2) A high-precision radial-velocity survey of Hyades dwarfs, using the Keck telescope and its HIRES spectrograph, 3) A program at McDonald Observatory to obtain spectra of the parent stars of planetary systems at R = 210,000, and 4) the start of high precision radial velocity surveys using the Hobby-Eberly Telescope. The most important results from NASA support of these research programs are described below. A list of all papers published under support of this grant is included at the end.

Water Velocities and the Potential for the Movement of Bed Sediments in Sinclair Inlet of Puget Sound, Washington

USGS Publications Warehouse

Gartner, Jeffrey W.; Prych, E.A.; Tate, G.B.; Cacchione, D.A.; Cheng, R.T.; Bidlake, W.R.; Ferreira, J.T.

1998-01-01

Sinclair Inlet is a small embayment of Puget Sound in the State of Washington. The inlet, about 6.5 kilometers long and 1.5 kilometers wide, is the site of Puget Sound Naval Shipyard. There are concerns that bed sediments in the inlet may have been contaminated as a result of activities at the shipyard, and that these sediments could be resuspended by tide- and wind-driven currents and transported within the inlet or out of the inlet to other parts of Puget Sound. This study was conducted to provide information concerning the potential for sediment resuspension in the inlet. To obtain the necessary data, vertical profiles of water current from about 2 meters above the bed to 2 meters below the water surface were monitored with acoustic Doppler current profilers (ADCPs) at three locations during a 6.5-week winter period and a 4.5-week summer period in 1994. In addition, during the winter period, water velocites between 0.19 and 1.20 meters above the bed were measured with current meters using an instrument package called Geoprobe, which was deployed near one of the ADCPs. Other instruments on the Geoprobe measured light transmissivity, and a camera periodically took photographs of the bottom. Instruments on the Geoprobe and on the ADCPs also measured conductivity (for determining salinity), temperature, and pressure (for determinining tide). Samples of bed sediment and water samples for determining suspended-sediment concentration were collected at each of the current-measurement stations. Wind speed and direction were measured at three stations during a 12-month period, and tide was measured at one of these stations. Water currents measured at the three locations in Sinclair Inlet were relatively weak. Typical speeds were 5 to 10 centimeters per second, and the RMS (root-mean-square) speeds were less than 8 centimeters per second. Tidal and residual currents were of similar magnitude. Residual currents near the bottom typically were flowing in the opposite direction of the prevailing wind, while surface currents were in the same direction as the prevailing wind. During most of the year, the prevailing wind was from the soutwest quadrant; however, during July and August, the prevailing wind was usually from the northeast quadrant. The RMS of the total shear velocity for each ADCP station and measurement period, which was estimated from observed profiles of current velocity, ranged from 0.31 centimeters per second to 0.44 centimeters per second. The skin-friction component of the shear velocity was estimated to be no more than half the total. Critical shear velocity, estimated from particle sizes and density of the bed material, was 0.39 centimeters per second or larger. Comparisons of the skin-friction components of total bottom shear velocities with estimates of the critical shear velocity necessary for resuspension of the bed sediments indicate that resuspension occurs only infrequently, usually at times of maximum current during the tidal cycle. This conclusion is supported by measurements near the bed of light transmissivity, which is related to suspended-sediment concentration.

Reynolds number of transition and self-organized criticality of strong turbulence.

PubMed

Yakhot, Victor

2014-10-01

A turbulent flow is characterized by velocity fluctuations excited in an extremely broad interval of wave numbers k>Λf, where Λf is a relatively small set of the wave vectors where energy is pumped into fluid by external forces. Iterative averaging over small-scale velocity fluctuations from the interval Λf

Reynolds number of transition and self-organized criticality of strong turbulence

NASA Astrophysics Data System (ADS)

Yakhot, Victor

2014-10-01

A turbulent flow is characterized by velocity fluctuations excited in an extremely broad interval of wave numbers k >Λf , where Λf is a relatively small set of the wave vectors where energy is pumped into fluid by external forces. Iterative averaging over small-scale velocity fluctuations from the interval Λf

Sodium Velocity Maps on Mercury

NASA Technical Reports Server (NTRS)

Potter, A. E.; Killen, R. M.

2011-01-01

The objective of the current work was to measure two-dimensional maps of sodium velocities on the Mercury surface and examine the maps for evidence of sources or sinks of sodium on the surface. The McMath-Pierce Solar Telescope and the Stellar Spectrograph were used to measure Mercury spectra that were sampled at 7 milliAngstrom intervals. Observations were made each day during the period October 5-9, 2010. The dawn terminator was in view during that time. The velocity shift of the centroid of the Mercury emission line was measured relative to the solar sodium Fraunhofer line corrected for radial velocity of the Earth. The difference between the observed and calculated velocity shift was taken to be the velocity vector of the sodium relative to Earth. For each position of the spectrograph slit, a line of velocities across the planet was measured. Then, the spectrograph slit was stepped over the surface of Mercury at 1 arc second intervals. The position of Mercury was stabilized by an adaptive optics system. The collection of lines were assembled into an images of surface reflection, sodium emission intensities, and Earthward velocities over the surface of Mercury. The velocity map shows patches of higher velocity in the southern hemisphere, suggesting the existence of sodium sources there. The peak earthward velocity occurs in the equatorial region, and extends to the terminator. Since this was a dawn terminator, this might be an indication of dawn evaporation of sodium. Leblanc et al. (2008) have published a velocity map that is similar.

Relative Seismic Velocity Variations Correlate with Deformation at Kīlauea Volcano.

NASA Astrophysics Data System (ADS)

Donaldson, C.; Caudron, C.; Green, R. G.; White, R. S.

2016-12-01

Passive interferometry using ambient seismic noise is an appealing monitoring tool at volcanoes. The continuous nature of seismic noise provides better temporal resolution than earthquake interferometry and ambient noise may be sensitive to changes at depths that do not deform the volcano surface. Despite this, to our knowledge, no studies have yet comprehensively compared deformation and velocity at a volcano over a significant length of time. We use a volcanic tremor source (approximately 0.3 - 1.0 Hz) at Kīlauea volcano as a source for interferometry to measure relative velocity changes with time. The tremor source that dominates the cross correlations is located under the Halema'uma'u caldera at Kīlauea summit. By cross-correlating the vertical component of day-long seismic records between 200 pairs of stations, we extract coherent and temporally consistent coda wave signals with time lags of up to 70 seconds. Our resulting time series of relative velocity shows a remarkable correlation with the tilt record measured at Kīlauea summit. Kīlauea summit is continually inflating and deflating as the level of the lava lake rises and falls. During these deflation-inflation (DI) events the tilt increases (inflation), as the velocity increases, on the scale of days to weeks. In contrast, we also detect a longer-term velocity decrease between 2011-2015 as the volcano slowly inflates. We suggest that variations in velocity result from opening and closing cracks and pores due to changes in magma pressurization. Early modeling results indicate that pressurizing magma reservoirs at different depths can result in opposite changes in compression/extension at the surface. The consistent correlation of relative velocity and deformation in this study provides an opportunity to better understand the mechanism causing velocity changes, which currently limits the scope of passive interferometry as a monitoring tool.

Constraining the relative velocity effect using the Baryon Oscillation Spectroscopic Survey

DOE PAGES

Beutler, Florian; Seljak, Uroš; Vlah, Zvonimir

2017-05-16

Here, we analyse the power spectrum of the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12 to constrain the relative velocity effect, which represents a potential systematic for measurements of the baryon acoustic oscillation (BAO) scale. The relative velocity effect is sourced by the different evolution of baryon and cold dark matter perturbations before decoupling. Our power spectrum model includes all one-loop redshift-space terms corresponding to vbc parametrized by the bias parameter bmore » $$2\\atop{v}$$ . We also include the linear terms proportional to the relative density, δbc, and relative velocity dispersion, θbc, which we parametrize with the bias parameters b$$bc\\atop{δ}$$ and b$$bc\\atop{θ}$$. This data does not support a detection of the relative velocity effect in any of these parameters. Combining the low- and high-redshift bins of BOSS, we find limits of b$$2\\atop{v}$$=0.012±0.015(±0.031) , b$$bc\\atop{δ}$$=-1.0±2.5(±6.2) and b$$bc\\atop{θ}$$=-114±55(±175) with 68 percent (95 percent) confidence levels. These constraints restrict the potential systematic shift in D A(z), H(z) and fσ8, due to the relative velocity, to 1 percent, 0.8 percent and 2 percent, respectively. Given the current uncertainties on the BAO measurements of BOSS, these shifts correspond to 0.53σ, 0.5σ and 0.22σ for DA(z), H(z) and fσ8, respectively.« less

Constraining the relative velocity effect using the Baryon Oscillation Spectroscopic Survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beutler, Florian; Seljak, Uroš; Vlah, Zvonimir

Here, we analyse the power spectrum of the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12 to constrain the relative velocity effect, which represents a potential systematic for measurements of the baryon acoustic oscillation (BAO) scale. The relative velocity effect is sourced by the different evolution of baryon and cold dark matter perturbations before decoupling. Our power spectrum model includes all one-loop redshift-space terms corresponding to vbc parametrized by the bias parameter bmore » $$2\\atop{v}$$ . We also include the linear terms proportional to the relative density, δbc, and relative velocity dispersion, θbc, which we parametrize with the bias parameters b$$bc\\atop{δ}$$ and b$$bc\\atop{θ}$$. This data does not support a detection of the relative velocity effect in any of these parameters. Combining the low- and high-redshift bins of BOSS, we find limits of b$$2\\atop{v}$$=0.012±0.015(±0.031) , b$$bc\\atop{δ}$$=-1.0±2.5(±6.2) and b$$bc\\atop{θ}$$=-114±55(±175) with 68 percent (95 percent) confidence levels. These constraints restrict the potential systematic shift in D A(z), H(z) and fσ8, due to the relative velocity, to 1 percent, 0.8 percent and 2 percent, respectively. Given the current uncertainties on the BAO measurements of BOSS, these shifts correspond to 0.53σ, 0.5σ and 0.22σ for DA(z), H(z) and fσ8, respectively.« less

Tribute to H. John Caulfield: hijacking of the 'holographic principle' by cosmologists

NASA Astrophysics Data System (ADS)

Roychoudhuri, Chandrasekhar

2013-09-01

I came to know Caulfield as a graduate student while developing suitable techniques to quantitatively evaluate coherence properties of pulsed Ruby and YAG lasers beams during the first decade of their evolutions. We continued our professional acquaintance till 2011 through various yearly conferences. It was at the 2011, 4th biennial conference on, "The nature of light: What are photons?" [1], Caulfield gave a paper on this topic and privately expressed his deep concern that the optical "Holographic Principle" has been hijacked by the cosmologists based upon insufficient understanding of the physical processes behind generation and reconstruction of optical holograms. Unlike our material universe, holographic images do not exist as touchable objects; but the material universe does. Now, in his absence, I have taken the liberty of presenting his views about the holographic principle and extend that to further challenge the prevailing hypothesis that cosmological red shift is purely optical Doppler shift that has led to the postulate that the current universe is expanding rapidly. Rigorously speaking, the core problem is generated when we assign reality to human interpreted information out of experimentally derived data, which can never capture complete behavioral properties of any cosmological object that we try to characterize. In holography, an object is a touch-able reality. Scattered light from an object brings incomplete, but sufficient information about the object to construct a decent hologram. It records phase and amplitude information indirectly as intensity fringes. Further, the reconstructed IMAGE does not represent the original touch-able reality. Besides, the image is further degraded from the insufficient information originally recorded on the hologram. Physical theories should be based upon our need to map physical processes behind the phenomenon under study. Information is a subjective human interpretation of measurable parameters registered by instruments, whose registration fidelities are always less than 100%. We illustrate this point by further criticizing the postulate of "Expanding Universe" by analyzing optical Doppler shift as a function of the two velocities, those of source-atoms and those of detector-atoms, in the coronas of stars in different galaxies with respect to the stationary space, instead of just the relative velocities between all possible pairs of galaxies.

Perspectives on the Current Status of and Emerging Policy Issues for Private Research Universities. AGB Occasional Paper No. 9.

ERIC Educational Resources Information Center

Geiger, Roger L.

1991-01-01

Current trends affecting private research universities include: privatization, more programmatic support of research, dispersion of university research, and a shift in the balance of activities from the center toward the periphery. Differences in finance and control of private universities are related to their disproportionate importance, given…

Is the far border of the Local Void expanding?

NASA Astrophysics Data System (ADS)

Iwata, I.; Chamaraux, P.

2011-07-01

Context. According to models of evolution in the hierarchical structure formation scenarios, voids of galaxies are expected to expand. The Local Void (LV) is the closest large void, and it provides a unique opportunity to test observationally such an expansion. It has been found that the Local Group, which is on the border of the LV, is running away from the void center at ~260 km s-1. Aims: In this study we investigate the motion of the galaxies at the far-side border of the LV to examine the presence of a possible expansion. Methods: We selected late-type, edge-on spiral galaxies with radial velocities between 3000 km s-1 and 5000 km s-1, and carried out HI 21 cm line and H-band imaging observations. The near-infrared Tully-Fisher relation was calibrated with a large sample of galaxies and carefully corrected for Malmquist bias. It was used to compute the distances and the peculiar velocities of the LV sample galaxies. Among the 36 sample LV galaxies with good quality HI line width measurements, only 15 galaxies were selected for measuring their distances and peculiar velocities, in order to avoid the effect of Malmquist bias. Results: The average peculiar velocity of these 15 galaxies is found to be -419+208-251 km s-1, which is not significantly different from zero. Conclusions: Due to the intrinsically large scatter of Tully-Fisher relation, we cannot conclude whether there is a systematic motion against the center of the LV for the galaxies at the far-side boundary of the void. However, our result is consistent with the hypothesis that those galaxies at the far-side boundary have an average velocity of ~260 km s-1 equivalent to what is found at the position of the Local Group. Based on data taken at Nançay radiotelescope operated by Observatoire de Paris, CNRS and Université d'Orléans, Infrared Survey Facility (IRSF) which is operated by Nagoya university under the cooperation of South African Astronomical Observatory, Kyoto University, and National Astronomical Observatory of Japan.This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/ California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

On The Missing Dwarf Problem In Clusters And Around The Nearby Galaxy M33

NASA Astrophysics Data System (ADS)

Keenan, Olivia Charlotte

2017-08-01

This thesis explores possible solutions to the dwarf galaxy problem. This is a discrepancy between the number of dwarf galaxies we observe, and the number predicted from cosmological computer simulations. Simulations predict around ten times more dwarf galaxy satellites than are currently observed. I have investigated two possible solutions: dark galaxies and the low surface brightness universe. Dark galaxies are dark matter halos which contain gas, but few or no stars, hence are optically dark. As part of the Arecibo Galaxy Environment Survey I surveyed the neutral hydrogen gas around the nearby galaxy M33. I found 32 gas clouds, 11 of which are new detections. Amongst these there was one particularly interesting cloud. AGESM33-32 is ring shaped and larger than M33 itself, if at the same distance. It has a velocity width which is similar to the velocity dispersion of gas in a disk galaxy, as well as having a clear velocity gradient across it which may be due to rotation. The fact that it also currently has no observed associated stars means it is a dark galaxy candidate. Optically, dwarf galaxies may be out there, but too faint for us to detect. This means that with newer, deeper, images we may be able to unveil a large, low surface brightness, population of dwarf galaxies. However, the question remains as to how these can be distinguished from background galaxies. I have used Next Generation Virgo Survey (NGVS) data to carry out photometry on 852 Virgo galaxies in four bands. I also measured the photometric properties of galaxies on a background (non-cluster) NGVS frame. I discovered that a combination of colour, magnitude and surface brightness information could be used to identify cluster dwarf galaxies from background field galaxies. The most effective method is to use the surface brightness-magnitude relation.

The Invariant Twist of Magnetic Fields in the Relativistic Jets of Active Galactic Nuclei

NASA Technical Reports Server (NTRS)

Contopoulos, Ioannis; Christodoulou, Dimitris M.; Kazanas, Demosthenes; Gabuzda, Denise C.

2009-01-01

The origin of cosmic magnetic (B) fields remains an open question. It is generally believed that very weak primordial B fields are amplified by dynamo processes, but it appears unlikely that the amplification proceeds fast enough to account for the fields presently observed in galaxies and galaxy clusters. In an alternative scenario, cosmic B fields are generated near the inner edges of accretion disks in Active Galactic Nuclei (AGNs) by azimuthal electric currents due to the difference between the plasma electron and ion velocities that arises when the electrons are retarded by interactions with photons. While dynamo processes show no preference for the polarity of the (presumably random) seed field that they amplify, this alternative mechanism uniquely relates the polarity of the poloidal B field to the angular velocity of the accretion disk, resulting in a unique direction for the toroidal B field induced by disk rotation. Observations of the toroidal fields of 29 AGN jets revealed by parsec-scale Faraday rotation measurements show a clear asymmetry that is consistent with this model, with the probability that this asymmetry came about by chance being less than 1 %. This lends support to the hypothesis that the Universe is seeded by B fields that are generated in AGN via this mechanism

Currently available medical engineering degrees in the UK. Part 2: Postgraduate degrees.

PubMed

Joyce, T

2009-05-01

This paper considers taught medical engineering MSc degrees, based on mechanical engineering, which are provided in the UK. Currently there are 19 institutions which provide such postgraduate degree programmes. These are the University of Aberdeen, University of Bath, University of Bradford, Brunel University, University of Dundee, University of Hull, Imperial College London, Keele University, King's College London, University of Leeds, University of Liverpool, University of Nottingham, University of Oxford, Queen Mary University of London, University of Southampton, University of Strathclyde, University of Surrey, University of Ulster, and University of Warwick. While most courses are delivered on a 1 year full-time basis, other delivery modes are also available. Relatively few modules are offered as distance learning or short courses. A wide range of modules are offered by the various universities for the different taught MSc degrees. Common modules include biomaterials and biomechanics. The medical-engineering-related modules offered by a number of universities are also made available to students on allied MSc programmes and undergraduate degrees in medical engineering.

Analysis of mean velocity and turbulence measurements with ADCPs

NASA Astrophysics Data System (ADS)

De Serio, Francesca; Mossa, Michele

2015-07-01

The present study examines the vertical structure of the coastal current in the inner part of the Gulf of Taranto, located in the Ionian Sea (Southern Italy), including both the Mar Grande and Mar Piccolo basins. To this aim, different measuring stations investigated by both a Vessel Mounted Acoustic Doppler Current Profiler (VM-ADCP) and a bottom fixed ADCP were taken into consideration. Two surveys were carried out in the target area on 29.12.2006 and on 11.06.2007 by the research unit of the Technical University of Bari (DICATECh Department), using a VM-ADCP to acquire the three velocity components along the water column in selected stationing points. The measurements were taken in shallow waters, under non-breaking wave conditions, offshore the surf zone. Due to the recording frequency of the instrument time-averaged vertical velocity profiles could be evaluated in these measuring stations. Water temperature and salinity were also measured at the same time and locations by means of a CTD recorder. A rigidly mounted ADCP, located on the seabed in the North-Eastern area of the Mar Grande basin, provided current data relative to the period 10-20 February 2014. Set to acquire the three velocity components with higher frequency with respect to the VM-ADCP, it allowed us to estimate the turbulent quantities such as Reynolds stresses and turbulent kinetic energy by means of the variance method. Therefore, the present research is made up of two parts. The first part examines the current pattern measured by the VM-ADCP and verifies that, for each station, the classical log law reproduces well the vertical profile of the experimental streamwise velocities extending beyond its typical limit of validity up to the surface i.e. reaching great heights above the sea bed. This behavior is quite new and not always to be expected, being generally limited to boundary layers. It has been convincingly observed in only few limited experimental works. In the present study this occurred when two conditions were met: (i) the flow was mainly unidirectional along the vertical; (ii) the interested layer was non-stratified. The second part of the research studies the turbulent statistics derived from the beam signals of the fixed ADCP by means of the variance method. This technique had the advantage of being able to measure the time evolution of the turbulent mixing throughout the entire water column, thus making it possible to perform a detailed study on momentum transfer and turbulence. The deduced vertical profiles of the Reynolds stresses and of the turbulent kinetic energy TKE showed an increasing trend toward the surface, in agreement with previous results in literature. New data-sets of mean velocities and shear stresses, coming from field measurements, are always needed. In fact they represent the first step to derive reliable reference values of coefficients and parameters for the implementation and calibration of the used mathematical hydrodynamic models. Consequently, an effort was made to evaluate consistent bottom drag and wind drag coefficients, on the basis of the calculated bottom and surface shear stresses, respectively.

The effect of humidity on ionic wind velocity in ambient air

NASA Astrophysics Data System (ADS)

Chen, She; Nobelen, J. C. P. Y.; Nijdam, S.

2016-09-01

Due to the evolution of portable electronics and LED lightning system, advances in air cooling technologies must also keep pace. Active cooling by ionic wind, which is usually generated by corona discharge, can greatly reduce the noise and lifetime issues compared to the mechanical fans. The wind is induced when a gas discharge is formed, and neutral molecules gain their energy by the momentum transfer of ion-neutral collisions. However, there is few discussion about the effect of gas composition such as humidity on the wind generation and the physical mechanism is not clear. In the experiment, a positive 5-20 kV DC voltage is applied to the needle-cylinder electrodes with separation of 20 mm. The ionic wind velocity is measured by hot wire anemometry. As the relative humidity (RH) in the ambient air increases, the velocity is found to be severely inhibited. The current is also measured between the cylinder electrode and earth. The results show that the DC component of corona current decreases when RH increases. Since both the discharge current and the ion mobility are reduced when RH increases, their combined effects determine the ionic wind velocity. This work is supported by STW project 13651.

Fundamental Principles of Proper Space Kinematics

NASA Astrophysics Data System (ADS)

Wade, Sean

It is desirable to understand the movement of both matter and energy in the universe based upon fundamental principles of space and time. Time dilation and length contraction are features of Special Relativity derived from the observed constancy of the speed of light. Quantum Mechanics asserts that motion in the universe is probabilistic and not deterministic. While the practicality of these dissimilar theories is well established through widespread application inconsistencies in their marriage persist, marring their utility, and preventing their full expression. After identifying an error in perspective the current theories are tested by modifying logical assumptions to eliminate paradoxical contradictions. Analysis of simultaneous frames of reference leads to a new formulation of space and time that predicts the motion of both kinds of particles. Proper Space is a real, three-dimensional space clocked by proper time that is undergoing a densification at the rate of c. Coordinate transformations to a familiar object space and a mathematical stationary space clarify the counterintuitive aspects of Special Relativity. These symmetries demonstrate that within the local universe stationary observers are a forbidden frame of reference; all is in motion. In lieu of Quantum Mechanics and Uncertainty the use of the imaginary number i is restricted for application to the labeling of mass as either material or immaterial. This material phase difference accounts for both the perceived constant velocity of light and its apparent statistical nature. The application of Proper Space Kinematics will advance more accurate representations of microscopic, oscopic, and cosmological processes and serve as a foundation for further study and reflection thereafter leading to greater insight.

Capture-ejector satellites

NASA Technical Reports Server (NTRS)

Macconochie, I. O.; Eldred, C. H.; Martin, J. A.

1983-01-01

A satellite in the form of a large rotating rim which can be used to boost spacecraft from low-Earth orbit to higher orbits is described. The rim rotates in the plane of its orbit such that the lower portion of the rim is traveling at suborbital velocity, while the upper portion is travelling at greater than orbital velocity. Ascending spacecraft or payloads arrive at the lowest portion of the rim at suborbital velocities, where the payloads are released on a trajectory for higher orbits; descending payloads employ the reverse procedure. Electric thrusters placed on the rim maintain rim rotational speed and altitude. From the standpoint of currently known materials, the capture-ejector concept may be useful for relatively small velocity increments.

Mach's principle: Exact frame-dragging via gravitomagnetism in perturbed Friedmann-Robertson-Walker universes with K=(±1,0)

NASA Astrophysics Data System (ADS)

Schmid, Christoph

2009-03-01

We show that there is exact dragging of the axis directions of local inertial frames by a weighted average of the cosmological energy currents via gravitomagnetism for all linear perturbations of all Friedmann-Robertson-Walker (FRW) universes and of Einstein’s static closed universe, and for all energy-momentum-stress tensors and in the presence of a cosmological constant. This includes FRW universes arbitrarily close to the Milne Universe and the de Sitter universe. Hence the postulate formulated by Ernst Mach about the physical cause for the time-evolution of inertial axes is shown to hold in general relativity for linear perturbations of FRW universes.—The time-evolution of local inertial axes (relative to given local fiducial axes) is given experimentally by the precession angular velocity Ω→gyro of local gyroscopes, which in turn gives the operational definition of the gravitomagnetic field: B→g≡-2Ω→gyro. The gravitomagnetic field is caused by energy currents J→ɛ via the momentum constraint, Einstein’s G0^i^ equation, (-Δ+μ2)A→g=-16πGNJ→ɛ with B→g=curlA→g. This equation is analogous to Ampère’s law, but it holds for all time-dependent situations. Δ is the de Rham-Hodge Laplacian, and Δ=-curlcurl for the vorticity sector in Riemannian 3-space.—In the solution for an open universe the 1/r2-force of Ampère is replaced by a Yukawa force Yμ(r)=(-d/dr)[(1/R)exp⁡(-μr)], form-identical for FRW backgrounds with K=(-1,0). Here r is the measured geodesic distance from the gyroscope to the cosmological source, and 2πR is the measured circumference of the sphere centered at the gyroscope and going through the source point. The scale of the exponential cutoff is the H-dot radius, where H is the Hubble rate, dot is the derivative with respect to cosmic time, and μ2=-4(dH/dt). Analogous results hold in closed FRW universes and in Einstein’s closed static universe.—We list six fundamental tests for the principle formulated by Mach: all of them are explicitly fulfilled by our solutions.—We show that only energy currents in the toroidal vorticity sector with ℓ=1 can affect the precession of gyroscopes. We show that the harmonic decomposition of toroidal vorticity fields in terms of vector spherical harmonics X→ℓm- has radial functions which are form-identical for the 3-sphere, the hyperbolic 3-space, and Euclidean 3-space, and are form-identical with the spherical Bessel-, Neumann-, and Hankel functions.—The Appendix gives the de Rham-Hodge Laplacian on vorticity fields in Riemannian 3-spaces by equations connecting the calculus of differential forms with the curl notation. We also give the derivation the Weitzenböck formula for the difference between the de Rham-Hodge Laplacian Δ and the “rough” Laplacian ∇2 on vector fields.

Mach's principle: Exact frame-dragging via gravitomagnetism in perturbed Friedmann-Robertson-Walker universes with K=({+-}1,0)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmid, Christoph

We show that there is exact dragging of the axis directions of local inertial frames by a weighted average of the cosmological energy currents via gravitomagnetism for all linear perturbations of all Friedmann-Robertson-Walker (FRW) universes and of Einstein's static closed universe, and for all energy-momentum-stress tensors and in the presence of a cosmological constant. This includes FRW universes arbitrarily close to the Milne Universe and the de Sitter universe. Hence the postulate formulated by Ernst Mach about the physical cause for the time-evolution of inertial axes is shown to hold in general relativity for linear perturbations of FRW universes. -more » The time-evolution of local inertial axes (relative to given local fiducial axes) is given experimentally by the precession angular velocity {omega}-vector{sub gyro} of local gyroscopes, which in turn gives the operational definition of the gravitomagnetic field: B-vector{sub g}{identical_to}-2{omega}-vector{sub gyro}. The gravitomagnetic field is caused by energy currents J-vector{sub {epsilon}} via the momentum constraint, Einstein's G{sup 0-}circumflex{sub i-circumflex} equation, (-{delta}+{mu}{sup 2})A-vector{sub g}=-16{pi}G{sub N}J-vector{sub {epsilon}} with B-vector{sub g}=curl A-vector{sub g}. This equation is analogous to Ampere's law, but it holds for all time-dependent situations. {delta} is the de Rham-Hodge Laplacian, and {delta}=-curl curl for the vorticity sector in Riemannian 3-space. - In the solution for an open universe the 1/r{sup 2}-force of Ampere is replaced by a Yukawa force Y{sub {mu}}(r)=(-d/dr)[(1/R)exp(-{mu}r)], form-identical for FRW backgrounds with K=(-1,0). Here r is the measured geodesic distance from the gyroscope to the cosmological source, and 2{pi}R is the measured circumference of the sphere centered at the gyroscope and going through the source point. The scale of the exponential cutoff is the H-dot radius, where H is the Hubble rate, dot is the derivative with respect to cosmic time, and {mu}{sup 2}=-4(dH/dt). Analogous results hold in closed FRW universes and in Einstein's closed static universe.--We list six fundamental tests for the principle formulated by Mach: all of them are explicitly fulfilled by our solutions.--We show that only energy currents in the toroidal vorticity sector with l=1 can affect the precession of gyroscopes. We show that the harmonic decomposition of toroidal vorticity fields in terms of vector spherical harmonics X-vector{sub lm}{sup -} has radial functions which are form-identical for the 3-sphere, the hyperbolic 3-space, and Euclidean 3-space, and are form-identical with the spherical Bessel-, Neumann-, and Hankel functions. - The Appendix gives the de Rham-Hodge Laplacian on vorticity fields in Riemannian 3-spaces by equations connecting the calculus of differential forms with the curl notation. We also give the derivation the Weitzenboeck formula for the difference between the de Rham-Hodge Laplacian {delta} and the ''rough'' Laplacian {nabla}{sup 2} on vector fields.« less

A new benthic foraminiferal proxy for near-bottom current velocities in the Gulf of Cadiz, northeastern Atlantic Ocean

NASA Astrophysics Data System (ADS)

Schönfeld, Joachim

2002-10-01

Recent benthic foraminiferal assemblages were analyzed in the Gulf of Cadiz, northeastern Atlantic, to study the impact of the Mediterranean Outflow Water (MOW) undercurrent on the benthic environment. Foraminiferal counts and the analysis of specimens attached to hard substrates from 26 surface samples reveal a relationship of epibenthic assemblages with sedimentary and hydrodynamic environment. Epibenthic species make up as much as 60% of the living assemblage at proximal sites with high current velocities and 3-18% in distal areas or near the margins of the MOW flow paths at low velocities. These foraminifers inhabit elevated substrates only within the MOW, which evidently provides an ecological niche for opportunistic suspension feeders. They adapt their settling elevation dynamically and occur at greater heights above the ambient sediment surface under stronger currents. Mobility, fixation strength, suspension feeding, and reproduction efficiency emerge as individual capabilities promoting the occupation of elevated substrates by certain epibenthic species. The active microhabitat selection is pursued as basic strategy of these foraminifers to optimize their food acquisition. A better access to food sources stimulates reproduction and leads to a greater contribution of foraminiferal tests to the surface sediments. Elevated epibenthos percentages from the dead assemblage and current velocities prevailing at the sampling sites are closely correlated. A compilation including other data from southern Portugal, Florida Straits, and the English Channel infers an exponential relationship between epibenthic abundances and flow strength implying that endobenthic species prevail even under high current velocities. A linear model provides a significantly better fit for the Gulf of Cadiz data however. This relation is used for a case study in order to estimate near-bottom current strengths for the late Holocene Peak III contourite in core M39008-3. Trends and absolute values of current velocities, inferred from the benthic foraminiferal proxy, are the same scale as estimates obtained from sediment grain-size distribution and hydrodynamic models. Epibenthic foraminifera thus bear a high potential as proxy for palaeocurrent studies that even may overcome objections by predetermined grain-size distributions in deep-sea cores.

Surface drifter derived circulation in the northern and middle Adriatic Sea: Response to wind regime and season

USGS Publications Warehouse

Ursella, L.; Poulain, P.-M.; Signell, R.P.

2007-01-01

More than 120 satellite-tracked drifters were deployed in the northern and middle Adriatic (NMA) Sea between September 2002 and November 2003, with the purpose of studying the surface circulation at mesoscale to seasonal scale in relation to wind forcing, river runoff, and bottom topography. Pseudo-Eulerian and Lagrangian statistics were calculated from the low-pass-filtered drifter velocity data between September 2002 and December 2003. The structure of the mean circulation is determined with unprecedented high horizontal resolution by the new data. In particular, mean currents, velocity variance, and kinetic energy levels are shown to be maximal in the Western Adriatic Current (WAC). Separating data into seasons, we found that the mean kinetic energy is maximal in fall, with high values also in winter, while it is significantly weaker in summer. High-resolution Local Area Model Italy winds were used to relate the drifter velocities to the wind fields. The surface currents appear to be significantly influenced by the winds. The mean flow during the northeasterly bora regime shows an intensification of the across-basin recirculating currents. In addition, the WAC is strongly intensified both in intensity and in its offshore lateral extension. In the southeasterly sirocco regime, northward flow without recirculation dominates in the eastern half of the basin, while during northwesterly maestro the WAC is enhanced. Separating the data into low and high Po River discharge rates for low-wind conditions shows that the WAC and the velocity fluctuations in front of the Po delta are stronger for high Po River runoff. Lagrangian covariance, diffusivity, and integral time and space scales are larger in the along-basin direction and are maximal in the southern portion of the WAC. Copyright 2006 by the American Geophysical Union.

Normalized velocity profiles of field-measured turbidity currents

USGS Publications Warehouse

Xu, Jingping

2010-01-01

Multiple turbidity currents were recorded in two submarine canyons with maximum speed as high as 280 cm/s. For each individual turbidity current measured at a fixed station, its depth-averaged velocity typically decreased over time while its thickness increased. Some turbidity currents gained in speed as they traveled downcanyon, suggesting a possible self-accelerating process. The measured velocity profiles, first in this high resolution, allowed normalizations with various schemes. Empirical functions, obtained from laboratory experiments whose spatial and time scales are two to three orders of magnitude smaller, were found to represent the field data fairly well. The best similarity collapse of the velocity profiles was achieved when the streamwise velocity and the elevation were normalized respectively by the depth-averaged velocity and the turbidity current thickness. This normalization scheme can be generalized to an empirical function Y = exp(–αXβ) for the jet region above the velocity maximum. Confirming theoretical arguments and laboratory results of other studies, the field turbidity currents are Froude-supercritical.

Extended Task Space Control for Robotic Manipulators

NASA Technical Reports Server (NTRS)

Backes, Paul G. (Inventor); Long, Mark K. (Inventor)

1996-01-01

The invention is a method of operating a robot in successive sampling intervals to perform a task, the robot having joints and joint actuators with actuator control loops, by decomposing the task into behavior forces, accelerations, velocities and positions of plural behaviors to be exhibited by the robot simultaneously, computing actuator accelerations of the joint actuators for the current sampling interval from both behavior forces, accelerations velocities and positions of the current sampling interval and actuator velocities and positions of the previous sampling interval, computing actuator velocities and positions of the joint actuators for the current sampling interval from the actuator velocities and positions of the previous sampling interval, and, finally, controlling the actuators in accordance with the actuator accelerations, velocities and positions of the current sampling interval. The actuator accelerations, velocities and positions of the current sampling interval are stored for use during the next sampling interval.

The influence of current speed and vegetation density on flow structure in two macrotidal eelgrass canopies

USGS Publications Warehouse

Lacy, Jessica R.; Wyllie-Echeverria, Sandy

2011-01-01

The influence of eelgrass (Zostera marina) on near-bed currents, turbulence, and drag was investigated at three sites in two eelgrass canopies of differing density and at one unvegetated site in the San Juan archipelago of Puget Sound, Washington, USA. Eelgrass blade length exceeded 1 m. Velocity profiles up to 1.5 m above the sea floor were collected over a spring-neap tidal cycle with a downward-looking pulse-coherent acoustic Doppler profiler above the canopies and two acoustic Doppler velocimeters within the canopies. The eelgrass attenuated currents by a minimum of 40%, and by more than 70% at the most densely vegetated site. Attenuation decreased with increasing current speed. The data were compared to the shear-layer model of vegetated flows and the displaced logarithmic model. Velocity profiles outside the meadows were logarithmic. Within the canopies, most profiles were consistent with the shear-layer model, with a logarithmic layer above the canopy. However, at the less-dense sites, when currents were strong, shear at the sea floor and above the canopy was significant relative to shear at the top of the canopy, and the velocity profiles more closely resembled those in a rough-wall boundary layer. Turbulence was strong at the canopy top and decreased with height. Friction velocity at the canopy top was 1.5–2 times greater than at the unvegetated, sandy site. The coefficient of drag CD on the overlying flow derived from the logarithmic velocity profile above the canopy, was 3–8 times greater than at the unvegetated site (0.01–0.023 vs. 2.9 × 10−3).

On the break down of reality at superluminal velocities, Quantum entanglement and Singularities (Complex Universe)

NASA Astrophysics Data System (ADS)

Estakhr, Ahmad Reza

2017-09-01

In the real world nothing can move faster than the speed of light. But what convinces you that our world is all real? I realized that reality break down at superluminal velocities (By studying the physics of tachyonic neutrinos), Quantum entanglement and Singularities of Black Holes, I realized that infact our world is complex and has two parts, one part of the world is real (the part that nothing can move faster than the speed of light) but the other part of the world is imaginary. z = a + ib Einstein was wrong because he thought our world is completely real (Of course he was not alone in this belief almost all physicists believe that our world is completely real) Eventually his false interpretation of reality censored imaginary part of the universe. Einstein's Second Postulate of special theory of relativity was a misleading guide to the true nature of reality. He `expected' the true nature of reality will follow to his (false) postulate, But the true nature of reality is unlike what anyone ever `expected'!. Einstein twist facts to suit his theory of relativity instead of theories to suit facts!. This is a dramatic revisions to our conception of the theory of relativity, Reality is complex but We always perceive its real part.

Bulk viscous quintessential inflation

NASA Astrophysics Data System (ADS)

Haro, Jaume; Pan, Supriya

In a spatially-flat Friedmann-Lemaître-Robertson-Walker universe, the incorporation of bulk viscous process in general relativity leads to an appearance of a nonsingular background of the universe that both at early and late times depicts an accelerated universe. These early and late scenarios of the universe can be analytically calculated and mimicked, in the context of general relativity, by a single scalar field whose potential could also be obtained analytically where the early inflationary phase is described by a one-dimensional Higgs potential and the current acceleration is realized by an exponential potential. We show that the early inflationary universe leads to a power spectrum of the cosmological perturbations which match with current observational data, and after leaving the inflationary phase, the universe suffers a phase transition needed to explain the reheating of the universe via gravitational particle production. Furthermore, we find that at late times, the universe enters into the de Sitter phase that can explain the current cosmic acceleration. Finally, we also find that such bulk viscous-dominated universe attains the thermodynamical equilibrium, but in an asymptotic manner.

Estimation of the velocity and trajectory of three-dimensional reaching movements from non-invasive magnetoencephalography signals

NASA Astrophysics Data System (ADS)

Yeom, Hong Gi; Sic Kim, June; Chung, Chun Kee

2013-04-01

Objective. Studies on the non-invasive brain-machine interface that controls prosthetic devices via movement intentions are at their very early stages. Here, we aimed to estimate three-dimensional arm movements using magnetoencephalography (MEG) signals with high accuracy. Approach. Whole-head MEG signals were acquired during three-dimensional reaching movements (center-out paradigm). For movement decoding, we selected 68 MEG channels in motor-related areas, which were band-pass filtered using four subfrequency bands (0.5-8, 9-22, 25-40 and 57-97 Hz). After the filtering, the signals were resampled, and 11 data points preceding the current data point were used as features for estimating velocity. Multiple linear regressions were used to estimate movement velocities. Movement trajectories were calculated by integrating estimated velocities. We evaluated our results by calculating correlation coefficients (r) between real and estimated velocities. Main results. Movement velocities could be estimated from the low-frequency MEG signals (0.5-8 Hz) with significant and considerably high accuracy (p <0.001, mean r > 0.7). We also showed that preceding (60-140 ms) MEG signals are important to estimate current movement velocities and the intervals of brain signals of 200-300 ms are sufficient for movement estimation. Significance. These results imply that disabled people will be able to control prosthetic devices without surgery in the near future.

Rip Current Velocity Structure in Drifter Trajectories and Numerical Simulations

NASA Astrophysics Data System (ADS)

Schmidt, W. E.; Slinn, D. N.

2008-12-01

Estimates of rip current velocity and cross-shore structure were made using surfzone drifters, bathymetric surveys, and rectified video images. Over 60 rip current trajectories were observed during a three year period at a Southern California beach in July 2000, 2001, and 2002. Incident wave heights (Hs) immediately offshore (~7 m depth) were obtained by initializing a refraction model with data from nearby directional wave buoys, and varied from 0.3 to 1.0 m. Tide levels varied over approximately 1 m and winds were light. Numerical simulations using the non-linear shallow water equations and modeled over measured bathymetry also produced similar flows and statistics. Time series of drifter position, sampled at 1 Hz, were first-differenced to produce velocity time series. Maximum observed velocities varied between 25 and 80 cm s-1, whereas model maximum velocities were lower by a factor 2 to 3. When velocity maxima were non-dimensionalized by respective trajectory mean velocity, both observed and modeled values varied between 1.5 and 3.5. Cross-shore location of rip current velocity maxima for both shore-normal and shore-oblique rip currents were strongly coincident with the surfzone edge (Xb), as determined by rectified video (observations) or breakpoint (model). Once outside of the surfzone, observed and modeled rip current velocities decreased to 10% of their peak values within 2 surfzone widths of the shoreline, a useful definition of rip current cross-shore extent.

Steady-state heat conduction in quiescent fluids: Incompleteness of the Navier-Stokes-Fourier equations

NASA Astrophysics Data System (ADS)

Brenner, Howard

2011-10-01

Linear irreversible thermodynamic principles are used to demonstrate, by counterexample, the existence of a fundamental incompleteness in the basic pre-constitutive mass, momentum, and energy equations governing fluid mechanics and transport phenomena in continua. The demonstration is effected by addressing the elementary case of steady-state heat conduction (and transport processes in general) occurring in quiescent fluids. The counterexample questions the universal assumption of equality of the four physically different velocities entering into the basic pre-constitutive mass, momentum, and energy conservation equations. Explicitly, it is argued that such equality is an implicit constitutive assumption rather than an established empirical fact of unquestioned authority. Such equality, if indeed true, would require formal proof of its validity, currently absent from the literature. In fact, our counterexample shows the assumption of equality to be false. As the current set of pre-constitutive conservation equations appearing in textbooks are regarded as applicable both to continua and noncontinua (e.g., rarefied gases), our elementary counterexample negating belief in the equality of all four velocities impacts on all aspects of fluid mechanics and transport processes, continua and noncontinua alike.

Accurate Realization of GPS Vertical Global Reference Frame

NASA Technical Reports Server (NTRS)

Elosegui, Pedro

2004-01-01

The few millimeter per year level accuracy of radial global velocity estimates with the Global Positioning System (GPS) is at least an order of magnitude poorer than the accuracy of horizontal global motions. An improvement in the accuracy of radial global velocities would have a very positive impact on a number of geophysical studies of current general interest such as global sea-level and climate change, coastal hazards, glacial isostatic adjustment, atmospheric and oceanic loading, glaciology and ice mass variability, tectonic deformation and volcanic inflation, and geoid variability. The goal of this project is to improve our current understanding of GPS error sources associated with estimates of radial velocities at global scales. GPS error sources relevant to this project can be classified in two broad categories: (1) those related to the analysis of the GPS phase observable, and (2) those related to the combination of the positions and velocities of a set of globally distributed stations as determined from the analysis of GPS data important aspect in the first category include the effect on vertical rate estimates due to standard analysis choices, such as orbit modeling, network geometry, ambiguity resolution, as well as errors in models (or simply the lack of models) for clocks, multipath, phase-center variations, atmosphere, and solid-Earth tides. The second category includes the possible methods of combining and defining terrestrial reference flames for determining vertical velocities in a global scale. The latter has been the subject of our research activities during this reporting period.

Interplanetary magnetic field effects on high latitude ionospheric convection

NASA Technical Reports Server (NTRS)

Heelis, R. A.

1985-01-01

Relations between the electric field and the electric current in the ionosphere can be established on the basis of a system of mathematical and physical equations provided by the equations of current continuity and Ohm's law. For this reason, much of the synthesis of electric field and plasma velocity data in the F-region is made with the aid of similar data sets derived from field-aligned current and horizontal current measurements. During the past decade, the development of a self-consistent picture of the distribution and behavior of these measurements has proceeded almost in parallel. The present paper is concerned with the picture as it applies to the electric field and plasma drift velocity and its dependence on the interplanetary magnetic field. Attention is given to the southward interplanetary magnetic field and the northward interplanetary magnetic field.

Absolute Plate Velocities from Seismic Anisotropy

NASA Astrophysics Data System (ADS)

Kreemer, Corné; Zheng, Lin; Gordon, Richard

2015-04-01

The orientation of seismic anisotropy inferred beneath plate interiors may provide a means to estimate the motions of the plate relative to the sub-asthenospheric mantle. Here we analyze two global sets of shear-wave splitting data, that of Kreemer [2009] and an updated and expanded data set, to estimate plate motions and to better understand the dispersion of the data, correlations in the errors, and their relation to plate speed. We also explore the effect of using geologically current plate velocities (i.e., the MORVEL set of angular velocities [DeMets et al. 2010]) compared with geodetically current plate velocities (i.e., the GSRM v1.2 angular velocities [Kreemer et al. 2014]). We demonstrate that the errors in plate motion azimuths inferred from shear-wave splitting beneath any one tectonic plate are correlated with the errors of other azimuths from the same plate. To account for these correlations, we adopt a two-tier analysis: First, find the pole of rotation and confidence limits for each plate individually. Second, solve for the best fit to these poles while constraining relative plate angular velocities to consistency with the MORVEL relative plate angular velocities. The SKS-MORVEL absolute plate angular velocities (based on the Kreemer [2009] data set) are determined from the poles from eight plates weighted proportionally to the root-mean-square velocity of each plate. SKS-MORVEL indicates that eight plates (Amur, Antarctica, Caribbean, Eurasia, Lwandle, Somalia, Sundaland, and Yangtze) have angular velocities that differ insignificantly from zero. The net rotation of the lithosphere is 0.25±0.11° Ma-1 (95% confidence limits) right-handed about 57.1°S, 68.6°E. The within-plate dispersion of seismic anisotropy for oceanic lithosphere (σ=19.2° ) differs insignificantly from that for continental lithosphere (σ=21.6° ). The between-plate dispersion, however, is significantly smaller for oceanic lithosphere (σ=7.4° ) than for continental lithosphere (σ=14.7° ). Two of the slowest-moving plates, Antarctica (vRMS=4 mm a-1, σ=29° ) and Eurasia (vRMS=3 mm a-1, σ=33° ), have two of the largest within-plate dispersions, which may indicate that a plate must move faster than ˜5 mm a-1 to result in seismic anisotropy useful for estimating plate motion. We will investigate if these relationships still hold with the new expanded data set and with the alternative set of relative plate angular velocities. We have found systematic differences between the SKS orientations and our predicted plate motion azimuths underneath the Arabia plate, which suggests to us either plate-scale mantle flow process not directly associated with that plate's absolute motion or intrinsic lithospheric anisotropy. We will discuss more of such discrepancies underneath other plates using the enlarged data set.

Universal Dark Halo Scaling Relation for the Dwarf Spheroidal Satellites

NASA Astrophysics Data System (ADS)

Hayashi, Kohei; Ishiyama, Tomoaki; Ogiya, Go; Chiba, Masashi; Inoue, Shigeki; Mori, Masao

2017-07-01

Motivated by a recently found interesting property of the dark halo surface density within a radius, {r}\\max , giving the maximum circular velocity, {V}\\max , we investigate it for dark halos of the Milky Way’s and Andromeda’s dwarf satellites based on cosmological simulations. We select and analyze the simulated subhalos associated with Milky-Way-sized dark halos and find that the values of their surface densities, {{{Σ }}}{V\\max }, are in good agreement with those for the observed dwarf spheroidal satellites even without employing any fitting procedures. Moreover, all subhalos on the small scales of dwarf satellites are expected to obey the universal relation, irrespective of differences in their orbital evolutions, host halo properties, and observed redshifts. Therefore, we find that the universal scaling relation for dark halos on dwarf galaxy mass scales surely exists and provides us with important clues for understanding fundamental properties of dark halos. We also investigate orbital and dynamical evolutions of subhalos to understand the origin of this universal dark halo relation and find that most subhalos evolve generally along the {r}\\max \\propto {V}\\max sequence, even though these subhalos have undergone different histories of mass assembly and tidal stripping. This sequence, therefore, should be the key feature for understanding the nature of the universality of {{{Σ }}}{V\\max }.

Discharge estimation from H-ADCP measurements in a tidal river subject to sidewall effects and a mobile bed

NASA Astrophysics Data System (ADS)

Sassi, M. G.; Hoitink, A. J. F.; Vermeulen, B.; Hidayat, null

2011-06-01

Horizontal acoustic Doppler current profilers (H-ADCPs) can be employed to estimate river discharge based on water level measurements and flow velocity array data across a river transect. A new method is presented that accounts for the dip in velocity near the water surface, which is caused by sidewall effects that decrease with the width to depth ratio of a channel. A boundary layer model is introduced to convert single-depth velocity data from the H-ADCP to specific discharge. The parameters of the model include the local roughness length and a dip correction factor, which accounts for the sidewall effects. A regression model is employed to translate specific discharge to total discharge. The method was tested in the River Mahakam, representing a large river of complex bathymetry, where part of the flow is intrinsically three-dimensional and discharge rates exceed 8000 m3 s-1. Results from five moving boat ADCP campaigns covering separate semidiurnal tidal cycles are presented, three of which are used for calibration purposes, whereas the remaining two served for validation of the method. The dip correction factor showed a significant correlation with distance to the wall and bears a strong relation to secondary currents. The sidewall effects appeared to remain relatively constant throughout the tidal cycles under study. Bed roughness length is estimated at periods of maximum velocity, showing more variation at subtidal than at intratidal time scales. Intratidal variations were particularly obvious during bidirectional flow conditions, which occurred only during conditions of low river discharge. The new method was shown to outperform the widely used index velocity method by systematically reducing the relative error in the discharge estimates.

Multiple Outflows in the Giant Eruption of a Massive Star

NASA Astrophysics Data System (ADS)

Humphreys, Roberta M.; Martin, John C.; Gordon, Michael S.; Jones, Terry J.

2016-08-01

The supernova impostor PSN J09132750+7627410 in NGC 2748 reached a maximum luminosity of ≈-14 mag. It was quickly realized that it was not a true supernova, but another example of a nonterminal giant eruption. PSN J09132750+7627410 is distinguished by multiple P Cygni absorption minima in the Balmer emission lines that correspond to outflow velocities of -400, -1100, and -1600 km s-1. Multiple outflows have been observed in only a few other objects. In this paper we describe the evolution of the spectrum and the P Cygni profiles for 3 months past maximum, the post-maximum formation of a cool, dense wind, and the identification of a possible progenitor. One of the possible progenitors is an infrared source. Its pre-eruption spectral energy distribution suggests a bolometric luminosity of -8.3 mag and a dust temperature of 780 K. If it is the progenitor, it is above the AGB limit, unlike the intermediate-luminosity red transients. The three P Cygni profiles could be due to ejecta from the current eruption, the wind of the progenitor, or previous mass-loss events. We suggest that they were all formed as part of the same high-mass-loss event and are due to material ejected at different velocities or energies. We also suggest that multiple outflows during giant eruptions may be more common than reported. Based on observations obtained with the Large Binocular Telescope (LBT), an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are the University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University and The Research Corporation, on behalf of the University of Notre Dame, University of Minnesota, and University of Virginia.

The Dynamical Properties of Virgo Cluster Galaxies

NASA Astrophysics Data System (ADS)

Ouellette, Nathalie N.-Q.

By virtue of its proximity, the Virgo Cluster is an ideal laboratory for us to test our understanding of the formation of structure in our Universe. In this spirit, we present a dynamical study of 33 gas-poor and 34 gas-rich Virgo galaxies as part of the Spectroscopic and H-band Imaging of Virgo survey. Our final spectroscopic data set was acquired at the 3.5-m telescope at the Apache Point Observatory. Halpha rotation curves for the gas-rich galaxies were modelled with a multi-parameter fit function from which various velocity measurements were inferred. Analog values were measured off of the observed rotation curves, but yielded noisier scaling relations, such as the luminosity-velocity relation (also known as the Tully-Fisher relation). Our best i -band Tully-Fisher relation has slope alpha = --7.2 +/- 0.5 and intercept Mi(2.3) = --21.5 +/- 1.1 mag, matching similar previous studies. Our study takes advantage of our own, as well as literature, data; we plan to continue expanding our compilation in order to build the largest Tully-Fisher relation for a cluster to date. Following extensive testing of the IDL routine pPXF , extended velocity dispersion profiles were extracted for our gas-poor galaxies. Considering the lack of a common standard for the measurement of a fiducial galaxy velocity dispersion in the literature, we have endeavoured to rectify this situation by determining the radius at which the measured velocity dispersion, coupled with the galaxy luminosity, yields the tightest Faber-Jackson relation. We found that radius to be 1.5 R e, which exceeds the extent of most dispersion profiles in other works. The slope of our Faber-Jackson relation is alpha = --4.3 +/- 0.2, which closely matches the virial value of 4. This analysis will soon be applied to a study of the Virgo Cluster Fundamental Plane. Rotation correction of our dispersion profiles will also permit the study of galaxies' velocity dispersion profile shapes in an attempt to refine our understanding of the overall manifold of galaxy structural parameters.

Variations in the electrical short-circuit current decay for recombination lifetime and velocity measurements

NASA Technical Reports Server (NTRS)

Jung, Tae-Won; Lindholm, Fredrik A.; Neugroschel, Arnost

1987-01-01

An improved measurement system for electrical short-circuit current decay is presented that extends applicability of the method to silicon solar cells having an effective lifetime as low as 1 microsec. The system uses metal/oxide/semiconductor transistors as voltage-controlled switches. Advances in theory developed here increase precision and sensitivity in the determination of the minority-carrier recombination lifetime and recombination velocity. A variation of the method, which exploits measurements made on related back-surface field and back-ohmic contact devices, further improves precision and sensitivity. The improvements are illustrated by application to 15 different silicon solar cells.

Assessment of velocity fields through open-channel flows with an empiric law.

PubMed

Bardiaux, J B; Vazquez, J; Mosé, R

2008-01-01

Most sewer managers are currently confronted with the evaluation of the water discharges, that flow through their networks or go to the discharge system, i.e. rivers in the majority of cases. In this context, the Urban Hydraulic Systems laboratory of the ENGEES is working on the relation between velocity fields and metrology assessment through a partnership with the Fluid and Solid Mechanics Institute of Strasbourg (IMFS). The responsibility is clearly to transform a velocity profile measurement, given by a Doppler sensor developed by the IMFS team, into a water discharge evaluation. The velocity distribution in a cross section of the flow in a channel has attracted the interests of many researchers over the years, due to its practical applications. In the case of free surface flows in narrow open channels the maximum velocity is below the free surface. This phenomenon, usually called "dip-phenomenon", amongst other things, raises the problem of the area explored in the section of measurements. The work presented here tries to create a simple relation making possible to associate the flow with the velocity distribution. This step allows to insert the sensor position into the flow calculation.

Radial velocity studies of cool stars.

PubMed

Jones, Hugh R A; Barnes, John; Tuomi, Mikko; Jenkins, James S; Anglada-Escude, Guillem

2014-04-28

Our current view of exoplanets is one derived primarily from solar-like stars with a strong focus on understanding our Solar System. Our knowledge about the properties of exoplanets around the dominant stellar population by number, the so-called low-mass stars or M dwarfs, is much more cursory. Based on radial velocity discoveries, we find that the semi-major axis distribution of M dwarf planets appears to be broadly similar to those around more massive stars and thus formation and migration processes might be similar to heavier stars. However, we find that the mass of M dwarf planets is relatively much lower than the expected mass dependency based on stellar mass and thus infer that planet formation efficiency around low-mass stars is relatively impaired. We consider techniques to overcome the practical issue of obtaining good quality radial velocity data for M dwarfs despite their faintness and sustained activity and emphasize (i) the wavelength sensitivity of radial velocity signals, (ii) the combination of radial velocity data from different experiments for robust detection of small amplitude signals, and (iii) the selection of targets and radial velocity interpretation of late-type M dwarfs should consider Hα behaviour.

Numerical Investigations of an Optimized Airfoil with a Rotary Cylinder

NASA Astrophysics Data System (ADS)

Gada, Komal; Rahai, Hamid

2015-11-01

Numerical Investigations of an optimized thin airfoil with a rotary cylinder as a control device for reducing separation and improving lift to drag ratio have been performed. Our previous investigations have used geometrical optimization for development of an optimized airfoil with increased torque for applications in a vertical axis wind turbine. The improved performance was due to contributions of lift to torque at low angles of attack. The current investigations have been focused on using the optimized airfoil for micro-uav applications with an active flow control device, a rotary cylinder, to further control flow separation, especially during wind gust conditions. The airfoil has a chord length of 19.66 cm and a width of 25 cm with 0.254 cm thickness. Previous investigations have shown flow separation at approximately 85% chord length at moderate angles of attack. Thus the rotary cylinder with a 0.254 cm diameter was placed slightly downstream of the location of flow separation. The free stream mean velocity was 10 m/sec. and investigations have been performed at different cylinder's rotations with corresponding tangential velocities higher than, equal to and less than the free stream velocity. Results have shown more than 10% improvement in lift to drag ratio when the tangential velocity is near the free stream mean velocity. Graduate Assistant, Center for Energy and Environmental Research and Services (CEERS), College of Engineering, California State University, Long Beach.

Improved measurements of mean sea surface velocity in the Nordic Seas from synthetic aperture radar

NASA Astrophysics Data System (ADS)

Wergeland Hansen, Morten; Johnsen, Harald; Engen, Geir; Øie Nilsen, Jan Even

2017-04-01

The warm and saline surface Atlantic Water (AW) flowing into the Nordic Seas across the Greenland-Scotland ridge transports heat into the Arctic, maintaining the ice-free oceans and regulating sea-ice extent. The AW influences the region's relatively mild climate and is the northern branch of the global thermohaline overturning circulation. Heat loss in the Norwegian Sea is key for both heat transport and deep water formation. In general, the ocean currents in the Nordic Seas and the North Atlantic Ocean is a complex system of topographically steered barotropic and baroclinic currents of which the wind stress and its variability is a driver of major importance. The synthetic aperture radar (SAR) Doppler centroid shift has been demonstrated to contain geophysical information about sea surface wind, waves and current at an accuracy of 5 Hz and pixel spacing of 3.5 - 9 × 8 km2. This corresponds to a horizontal surface velocity of about 20 cm/s at 35° incidence angle. The ESA Prodex ISAR project aims to implement new and improved SAR Doppler shift processing routines to enable reprocessing of the wide swath acquisitions available from the Envisat ASAR archive (2002-2012) at higher resolution and better accuracy than previously obtained, allowing combined use with Sentinel-1 and Radarsat-2 retrievals to build timeseries of the sea surface velocity in the Nordic Seas. Estimation of the geophysical Doppler shift from new SAR Doppler centroid shift retrievals will be demonstrated, addressing key issues relating to geometric (satellite orbit and attitude) and electronic (antenna mis-pointing) contributions and corrections. Geophysical Doppler shift retrievals from one month of data in January 2010 and the inverted surface velocity in the Nordic Seas are then addressed and compared to other direct and indirect estimates of the upper ocean current, in particular those obtained in the ESA GlobCurrent project.

Endemism hotspots are linked to stable climatic refugia.

PubMed

Harrison, Susan; Noss, Reed

2017-01-01

Centres of endemism have received much attention from evolutionists, biogeographers, ecologists and conservationists. Climatic stability is often cited as a major reason for the occurrences of these geographic concentrations of species which are not found anywhere else. The proposed linkage between endemism and climatic stability raises unanswered questions about the persistence of biodiversity during the present era of rapidly changing climate. The current status of evidence linking geographic centres of endemism to climatic stability over evolutionary time was examined. The following questions were asked. Do macroecological analyses support such an endemism-stability linkage? Do comparative studies find that endemic species display traits reflecting evolution in stable climates? Will centres of endemism in microrefugia or macrorefugia remain relatively stable and capable of supporting high biological diversity into the future? What are the implications of the endemism-stability linkage for conservation? Recent work using the concept of climate change velocity supports the classic idea that centres of endemism occur where past climatic fluctuations have been mild and where mountainous topography or favourable ocean currents contribute to creating refugia. Our knowledge of trait differences between narrow endemics and more widely distributed species remains highly incomplete. Current knowledge suggests that centres of endemism will remain relatively climatically buffered in the future, with the important caveat that absolute levels of climatic change and species losses in these regions may still be large. © The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Inflation in the early universe.

NASA Astrophysics Data System (ADS)

Carmeli, M.

1998-04-01

In this talk it will be assumed that gravitation is negligible. Under this assumption, the receding velocities of galaxies and the distances between them in the Hubble expansion are united into a four-dimensional pseudo-Euclidean manifold, similarly to space and time in ordinary special relativity. The Hubble law is assumed and is written in an invariant way that enables one to derive a four-dimensional transformation which is similar to the Lorentz transformation. The parameter in the new transformation is the ratio between the cosmic time to the Hubble time. Accordingly, the new transformation relates physical quantities at different cosmic times in the limit of weak or negligible gravitation. The transformation is then applied to the problem of the expansion of the Universe at the very early stage when gravity was negligible and thus the transformation is applicable. The author calculates the ratio of the volumes of the Universe at two different times T1 and T2 after the big bang. The result conforms with the standard inflationary universe theory, but now it is obtained without assuming that the Universe is propelled by antigravity.

Recirculation of the Canary Current in fall 2014

NASA Astrophysics Data System (ADS)

Hernández-Guerra, Alonso; Espino-Falcón, Elisabet; Vélez-Belchí, Pedro; Dolores Pérez-Hernández, M.; Martínez-Marrero, Antonio; Cana, Luis

2017-10-01

Hydrographic measurements together with Ship mounted Acoustic Doppler Current Profilers and Lowered Acoustic Doppler Current Profilers (LADCP) obtained in October 2014 are used to describe water masses, geostrophic circulation and mass transport of the Canary Current System, as the Eastern Boundary of the North Atlantic Subtropical Gyre. Geostrophic velocities are adjusted to velocities from LADCP data to estimate an initial velocity at the reference layer. The adjustment results in a northward circulation at the thermocline layers over the African slope from an initial convergent flow. Final reference velocities and consequently absolute circulation are estimated from an inverse box model applied to an ocean divided into 13 neutral density layers. This allows us to evaluate mass fluxes consistent with the thermal wind equation and mass conservation. Ekman transport is estimated from the wind data derived from the Weather Research and Forecasting model. Ekman transport is added to the first layer and adjusted with the inverse model. The Canary Current located west of Lanzarote Island transports to the south a mass of - 1.5 ± 0.7 Sv (1 Sv = 106 m3 s- 1 ≈ 109 kg s- 1) of North Atlantic Central Water at the surface and thermocline layers ( 0-700 m). In fall 2014, hydrographic data shows that the Canary Current in the thermocline (below at about 80 m depth to 700 m) recirculates to the north over the African slope and flows through the Lanzarote Passage. At intermediate layers ( 700-1400 m), the Intermediate Poleward Undercurrent transports northward a relatively fresh Antarctic Intermediate Water in the range of 0.8 ± 0.4 Sv through the Lanzarote Passage and west of Lanzarote Island beneath the recirculation of the Canary Current.

On the response to ocean surface currents in synthetic aperture radar imagery

NASA Technical Reports Server (NTRS)

Phillips, O. M.

1984-01-01

The balance of wave action spectral density for a fixed wave-number is expressed in terms of a new dimensionless function, the degree of saturation, b, and is applied to an analysis of the variations of this quantity (and local spectral level) at wave-numbers large compared to that of the spectral peak, that are produced by variations in the ocean surface currents in the presence of wind input and wave breaking. Particular care is taken to provide physically based representations of wind input and loss by wave breaking and a relatively convenient equation is derived that specifies the distribution of the degree of saturation in a current field, relative to its ambient (undisturbed) background in the absence of currents. The magnitude of the variations in b depends on two parameters, U(o)/c, where U/(o) is the velocity scale of the current and c the phase speed of the surface waves at the (fixed) wave-number considered or sampled by SAR, and S = (L/lambda) (u*/c)(2), where L is the length scale of the current distribution, lambda the wavelength of the surface waves the length scale of the current distribution, lambda the wavelength of the surface waves and u* the friction velocity of the wind.

Current driven instabilities of an electromagnetically accelerated plasma

NASA Technical Reports Server (NTRS)

Chouetri, E. Y.; Kelly, A. J.; Jahn, R. G.

1988-01-01

A plasma instability that strongly influences the efficiency and lifetime of electromagnetic plasma accelerators was quantitatively measured. Experimental measurements of dispersion relations (wave phase velocities), spatial growth rates, and stability boundaries are reported. The measured critical wave parameters are in excellent agreement with theoretical instability boundary predictions. The instability is current driven and affects a wide spectrum of longitudinal (electrostatic) oscillations. Current driven instabilities, which are intrinsic to the high-current-carrying magnetized plasma of the magnetoplasmadynmic (MPD) accelerator, were investigated with a kinetic theoretical model based on first principles. Analytical limits of the appropriate dispersion relation yield unstable ion acoustic waves for T(i)/T(e) much less than 1 and electron acoustic waves for T(i)/T(e) much greater than 1. The resulting set of nonlinear equations for the case of T(i)/T(e) = 1, of most interest to the MPD thruster Plasma Wave Experiment, was numerically solved to yield a multiparameter set of stability boundaries. Under certain conditions, marginally stable waves traveling almost perpendicular to the magnetic field would travel at a velocity equal to that of the electron current. Such waves were termed current waves. Unstable current waves near the upper stability boundary were observed experimentally and are in accordance with theoretical predictions. This provides unambiguous proof of the existence of such instabilites in electromagnetic plasma accelerators.

Go_LIVE! - Global Near-real-time Land Ice Velocity data from Landsat 8 at NSIDC

NASA Astrophysics Data System (ADS)

Klinger, M. J.; Fahnestock, M. A.; Scambos, T. A.; Gardner, A. S.; Haran, T. M.; Moon, T. A.; Hulbe, C. L.; Berthier, E.

2016-12-01

The National Snow and Ice Data Center (NSIDC) is developing a processing and staging system under NASA funding for near-real-time global ice velocity data derived from Landsat 8 panchromatic imagery: Global Land Ice Velocity Extraction from Landsat (Go_LIVE). The system performs repeat image feature tracking using newly developed Python Correlation (PyCorr) software applied to image pairs covering all glaciers > 5km2 as well as both ice sheets. We correlate each Landsat 8 path-row image with matching path-row images acquired within the previous 400 days. Real-Time (RT) panchromatic Landsat 8 L1T images have geolocation accuracy of 5 meters and high radiometric sensitivity (12-bit), allowing for feature matching over low-contrast snow and ice surfaces. High-pass filters are applied to the imagery to enhance local surface texture and improve correlation returns. Despite the excellent geolocation accuracy of Landsat 8, the remaining error introduces an artificial offset in the velocity returns. To correct this error, we apply a shift to the x and y grids to bring the displacement field to zero over known stationary features such as bedrock. For ice sheet interiors where stationary features do not exist, we use near-zero (<10 ma-1) or slow-moving ice areas (10-25 ma-1) to refine velocities. Go_LIVE will eventually include Landsat 7, 5 and 4 imagery as well. Go_LIVE runs on the University of Colorado's supercomputer and Peta Library storage system to process 10,000 image pairs per hour. We are currently developing a web-based data access site at NSIDC. The data are provided in NetCDF (Network Common Data Format) as geolocated grids of x and y velocity components at 300 m spacing with accompanying error and quality parameters. Extensive data sets currently exist for Alaskan, Antarctic, and Greenlandic ice areas, and are available upon request to NSIDC. Go_LIVE's goal for 2017 is a system that updates global ice velocity at few-day or shorter latency.

Stellar Velocity Dispersion: Linking Quiescent Galaxies to Their Dark Matter Halos

NASA Astrophysics Data System (ADS)

Zahid, H. Jabran; Sohn, Jubee; Geller, Margaret J.

2018-06-01

We analyze the Illustris-1 hydrodynamical cosmological simulation to explore the stellar velocity dispersion of quiescent galaxies as an observational probe of dark matter halo velocity dispersion and mass. Stellar velocity dispersion is proportional to dark matter halo velocity dispersion for both central and satellite galaxies. The dark matter halos of central galaxies are in virial equilibrium and thus the stellar velocity dispersion is also proportional to dark matter halo mass. This proportionality holds even when a line-of-sight aperture dispersion is calculated in analogy to observations. In contrast, at a given stellar velocity dispersion, the dark matter halo mass of satellite galaxies is smaller than virial equilibrium expectations. This deviation from virial equilibrium probably results from tidal stripping of the outer dark matter halo. Stellar velocity dispersion appears insensitive to tidal effects and thus reflects the correlation between stellar velocity dispersion and dark matter halo mass prior to infall. There is a tight relation (≲0.2 dex scatter) between line-of-sight aperture stellar velocity dispersion and dark matter halo mass suggesting that the dark matter halo mass may be estimated from the measured stellar velocity dispersion for both central and satellite galaxies. We evaluate the impact of treating all objects as central galaxies if the relation we derive is applied to a statistical ensemble. A large fraction (≳2/3) of massive quiescent galaxies are central galaxies and systematic uncertainty in the inferred dark matter halo mass is ≲0.1 dex thus simplifying application of the simulation results to currently available observations.

Method for controlling a vehicle with two or more independently steered wheels

DOEpatents

Reister, D.B.; Unseren, M.A.

1995-03-28

A method is described for independently controlling each steerable drive wheel of a vehicle with two or more such wheels. An instantaneous center of rotation target and a tangential velocity target are inputs to a wheel target system which sends the velocity target and a steering angle target for each drive wheel to a pseudo-velocity target system. The pseudo-velocity target system determines a pseudo-velocity target which is compared to a current pseudo-velocity to determine a pseudo-velocity error. The steering angle targets and the steering angles are inputs to a steering angle control system which outputs to the steering angle encoders, which measure the steering angles. The pseudo-velocity error, the rate of change of the pseudo-velocity error, and the wheel slip between each pair of drive wheels are used to calculate intermediate control variables which, along with the steering angle targets are used to calculate the torque to be applied at each wheel. The current distance traveled for each wheel is then calculated. The current wheel velocities and steering angle targets are used to calculate the cumulative and instantaneous wheel slip and the current pseudo-velocity. 6 figures.

How to design low-noise burners

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sams, G.; Jordan, J.

1996-12-01

Frequently, natural draft burner designs used in indirect heaters fail to meet the low noise standard of 85 to 88 dBA three feet from the flame arrestor. Noise encountered with indirect burner designs has been shown to be related to nozzle and firetube gas velocities. Testing shows that when the nozzle velocity is sufficiently greater than the firetube velocity, the low-frequency rumble that accompanies current designs ceases. Data obtained from field testing was used to construct a relationship between burner noise level and gas volume expansion ratio, burner air-to-fuel ratio, mixture flowrate, orifice velocity, burner area, and the number ofmore » burners. The noise from a burner can be predicted if the above easily calculable variables are known.« less

The Structure of the Local Universe and the Coldness of the Cosmic Flow

NASA Astrophysics Data System (ADS)

van de Weygaert, R.; Hoffman, Y.

Unlike the substantial coherent bulk motion in which our local patch of the Cosmos is participating, the amplitude of the random motions around this large scale flow seems to be surprisingly low. Attempts to invoke global explanations to account for this coldness of the local cosmic velocity field have not yet been succesfull. Here we propose a different view on this cosmic dilemma, stressing the repercussions of our cosmic neighbourhood embodying a rather uncharacteristic region of the Cosmos. Suspended between two huge mass concentrations, the Great Attractor region and the Perseus-Pisces chain, we find ourselves in a region of relatively low density yet with a very strong tidal shear. By means of constrained realizations of our local Universe, based on Wiener-filtered reconstructions inferred from the Mark III catalogue of galaxy peculiar velocities, we show that indeed this configuration may induce locally cold regions. Hence, the coldness of the local flow may be a cosmic variance effect.

The Rise of International Relations Programs in the Brazilian Federal Universities: Curriculum Specificities and Current Challenges

ERIC Educational Resources Information Center

Ferreira, Marcos Alan S. V.

2016-01-01

The aim of this reflection is to study the new international relations (IR) programs introduced by Brazilian federal universities, looking comparatively at their curriculum specificities and current challenges. In recent years, Brazil has seen an increase of IR programs launched in several regions. Since 2003, the Ministry of Education is in the…

Marine current energy conversion: the dawn of a new era in electricity production.

PubMed

Bahaj, AbuBakr S

2013-02-28

Marine currents can carry large amounts of energy, largely driven by the tides, which are a consequence of the gravitational effects of the planetary motion of the Earth, the Moon and the Sun. Augmented flow velocities can be found where the underwater topography (bathymetry) in straits between islands and the mainland or in shallows around headlands plays a major role in enhancing the flow velocities, resulting in appreciable kinetic energy. At some of these sites where practical flows are more than 1 m s(-1), marine current energy conversion is considered to be economically viable. This study describes the salient issues related to the exploitation of marine currents for electricity production, resource assessment, the conversion technologies and the status of leading projects in the field. This study also summarizes important issues related to site development and some of the approaches currently being undertaken to inform device and array development. This study concludes that, given the highlighted commitments to establish favourable regulatory and incentive regimes as well as the aspiration for energy independence and combating climate change, the progress to multi-megawatt arrays will be much faster than that achieved for wind energy development.

Local and global dynamical effects of dark energy

NASA Astrophysics Data System (ADS)

Chernin, A. D.

Local expansion flows of galaxies were discovered by Lemaitre and Hubble in 1927-29 at distances of less than 25-30 Mpc. The global expansion of the Universe as a whole was predicted theoretically by Friedmann in 1922-24 and discovered in the 1990s in observations at truly cosmological distances of more than 1 000 Mpc. On all these spatial scales, the flows follow a (nearly) linear velocity-distance relation, known now as Hubble's law. This similarity of local and global phenomena is due to the universal dark energy antigravity which dominates the cosmic dynamics on both local and global spatial scales.

Hubble's Cosmology: From a Finite Expanding Universe to a Static Endless Universe

NASA Astrophysics Data System (ADS)

Assis, A. K. T.; Neves, M. C. D.; Soares, D. S. L.

2009-12-01

We analyze the views of Edwin Hubble (1889-1953) as regards the large scale structure of the universe. In 1929 he initially accepted a finite expanding universe in order to explain the redshifts of distant galaxies. Later on he turned to an infinite stationary universe and a new principle of nature in order to explain the same phenomena. Initially, he was impressed by the agreement of his redshift-distance relation with one of the predictions of de Sitter's cosmological model, namely, the so-called "de Sitter effect'', the phenomenon of the scattering of material particles, leading to an expanding universe. A number of observational evidences, though, made him highly skeptical with such a scenario. They were better accounted for by an infinite static universe. The evidences he found were: (i) the huge values he was getting for the "recession'' velocities of the nebulae (1,800 km s-1 in 1929 up to 42,000 km s-1 in 1942, leading to v/c = 1/7), with the redshifts interpreted as velocity-shifts. All other known real velocities of large astronomical bodies are much smaller than these. (ii) The "number effect'' test, which is the running of nebulae luminosity with redshift. Hubble found that a static universe is, within the observational uncertainties, slightly favored. The test is equivalent to the modern "Tolman effect,'' for galaxy surface brightnesses, whose results are still a matter of dispute. (iii) The smallness of the size and the age of the curved expanding universe, implied by the expansion rate that he had determined, and, (iv) the fact that a uniform distribution of galaxies on large scales is more easily obtained from galaxy counts, when a static and flat model is considered. In an expanding and closed universe, Hubble found that homogeneity was only obtained at the cost of a large curvature. We show, by quoting his works, that Hubble remained cautiously against the big bang until the end of his life, contrary to the statements of many modern authors. In order to account for redshifts, in a non-expanding universe, Hubble called for a new principle of nature, like the "tired-light'' mechanism proposed by Fritz Zwicky in 1929. On the other hand, he was aware of the theoretical difficulties of such a radical assumption. Hubble's approach to cosmology strongly suggests that he would not agree with the present status of the modern cosmological paradigm, since he was, above all, driven by observations and by the consequences derived from them.

Substorm Evolution in the Near-Earth Plasma Sheet

NASA Technical Reports Server (NTRS)

Erickson, Gary M.

2004-01-01

This grant represented one-year, phase-out funding for the project of the same name (NAG5-9110 to Boston University) to determine precursors and signatures of local substorm onset and how they evolve in the plasma sheet using the Geotail near-Earth database. We report here on two accomplishments: (1) Completion of an examination of plasma velocity signature at times of local onsets in the current disruption (CD) region. (2) Initial investigation into quantification of near-Earth flux-tube contents of injected plasma at times of substorm injections.

Resolved H I Observations of Local Analogs to z ∼ 1 Luminous Compact Blue Galaxies: Evidence for Rotation-supported Disks

NASA Astrophysics Data System (ADS)

Rabidoux, Katie; Pisano, D. J.; Garland, C. A.; Guzmán, Rafael; Castander, Francisco J.; Wolfe, Spencer A.

2018-01-01

While bright, blue, compact galaxies are common at z∼ 1, they are relatively rare in the local universe, and their evolutionary paths are uncertain. We have obtained resolved H I observations of nine z∼ 0 luminous compact blue galaxies (LCBGs) using the Giant Metrewave Radio Telescope and Very Large Array in order to measure their kinematic and dynamical properties and better constrain their evolutionary possibilities. We find that the LCBGs in our sample are rotating galaxies that tend to have nearby companions, relatively high central velocity dispersions, and can have disturbed velocity fields. We calculate rotation velocities for each galaxy by measuring half of the velocity gradient along their major axes and correcting for inclination using axis ratios derived from SDSS images of each galaxy. We compare our measurements to those previously made with single dishes and find that single-dish measurements tend to overestimate LCBGs’ rotation velocities and H I masses. We also compare the ratio of LCBGs’ rotation velocities and velocity dispersions to those of other types of galaxies and find that LCBGs are strongly rotationally supported at large radii, similar to other disk galaxies, though within their half-light radii the {V}{rot}/σ values of their H I are comparable to stellar {V}{rot}/σ values of dwarf elliptical galaxies. We find that LCBGs’ disks on average are gravitationally stable, though conditions may be conducive to local gravitational instabilities at the largest radii. Such instabilities could lead to the formation of star-forming gas clumps in the disk, resulting eventually in a small central bulge or bar.

Effects of precipitation on sonic anemometer measurements of turbulent fluxes in the atmospheric surface layer

NASA Astrophysics Data System (ADS)

Zhang, Rongwang; Huang, Jian; Wang, Xin; Zhang, Jun A.; Huang, Fei

2016-06-01

Effects caused by precipitation on the measurements of three-dimensional sonic anemometer are analyzed based on a field observational experiment conducted in Maoming, Guangdong Province, China. Obvious fluctuations induced by precipitation are observed for the outputs of sonic anemometer-derived temperature and wind velocity components. A technique of turbulence spectra and cospectra normalized in the framework of similarity theory is utilized to validate the measured variables and calculated fluxes. It is found that the sensitivity of sonic anemometer-derived temperature to precipitation is significant, compared with that of the wind velocity components. The spectra of wind velocity and cospectra of momentum flux resemble the standard universal shape with the slopes of the spectra and cospectra at the inertial subrange, following the -2/3 and -4/3 power law, respectively, even under the condition of heavy rain. Contaminated by precipitation, however, the spectra of temperature and cospectra of sensible heat flux do not exhibit a universal shape and have obvious frequency loss at the inertial subrange. From the physical structure and working principle of sonic anemometer, a possible explanation is proposed to describe this difference, which is found to be related to the variations of precipitation particles. Corrections for errors of sonic anemometer-derived temperature under precipitation is needed, which is still under exploration.

Deflection of natural oil droplets through the water column in deep-water environments: The case of the Lower Congo Basin

NASA Astrophysics Data System (ADS)

Jatiault, Romain; Dhont, Damien; Loncke, Lies; de Madron, Xavier Durrieu; Dubucq, Dominique; Channelliere, Claire; Bourrin, François

2018-06-01

Numerous recurrent seep sites were identified in the deep-water environment of the Lower Congo Basin from the analysis of an extensive dataset of satellite-based synthetic-aperture radar images. The integration of current data was used to link natural oil slicks with active seep-related seafloor features. Acoustic Doppler current profiler measurements across the water column provided an efficient means to evaluate the horizontal deflection of oil droplets rising through the water column. Eulerian propagation model based on a range of potential ascension velocities helped to approximate the path for rising oil plume through the water column using two complementary methods. The first method consisted in simulating the reversed trajectory of oil droplets between sea-surface oil slick locations observed during current measurements and seep-related seafloor features while considering a range of ascension velocities. The second method compared the spatial spreading of natural oil slicks from 21 years of satellite monitoring observations for water depths ranging from 1200 to 2700 m against the modeled deflections during the current measurement period. The mapped oil slick origins are restricted to a 2.5 km radius circle from associated seep-related seafloor features. The two methods converge towards a range of ascension velocities for oil droplets through the water column, estimated between 3 and 8 cm s-1. The low deflection values validate that the sub-vertical projection of the average surface area of oil slicks at the sea surface can be used to identify the origin of expelled hydrocarbon from the seafloor, which expresses as specific seafloor disturbances (i.e. pockmarks or mounds) known to expel fluids.

Accurate Realization of GPS Vertical Global Reference Frame

NASA Technical Reports Server (NTRS)

Elosegui, Pedro

2005-01-01

The goal of this project is to improve our current understanding of GPS error sources associated with estimates of radial velocities at global scales. An improvement in the accuracy of radial global velocities would have a very positive impact on a large number of geophysical studies of current general interest such as global sea-level and climate change, coastal hazards, glacial isostatic adjustment, atmospheric and oceanic loading, glaciology and ice mass variability, tectonic deformation and volcanic inflation, and geoid variability. A set of GPS error sources relevant to this project are those related to the combination of the positions and velocities of a set of globally distributed stations as determined &om the analysis of GPS data, including possible methods of combining and defining terrestrial reference frames. This is were our research activities during this reporting period have concentrated. During this reporting period, we have researched two topics: (1) The effect of errors on the GPS satellite antenna models (or lack thereof) on global GPS vertical position and velocity estimates; (2) The effect of reference W e definition and practice on estimates of the geocenter variations.

Ward identities and consistency relations for the large scale structure with multiple species

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peloso, Marco; Pietroni, Massimo, E-mail: peloso@physics.umn.edu, E-mail: pietroni@pd.infn.it

2014-04-01

We present fully nonlinear consistency relations for the squeezed bispectrum of Large Scale Structure. These relations hold when the matter component of the Universe is composed of one or more species, and generalize those obtained in [1,2] in the single species case. The multi-species relations apply to the standard dark matter + baryons scenario, as well as to the case in which some of the fields are auxiliary quantities describing a particular population, such as dark matter halos or a specific galaxy class. If a large scale velocity bias exists between the different populations new terms appear in the consistencymore » relations with respect to the single species case. As an illustration, we discuss two physical cases in which such a velocity bias can exist: (1) a new long range scalar force in the dark matter sector (resulting in a violation of the equivalence principle in the dark matter-baryon system), and (2) the distribution of dark matter halos relative to that of the underlying dark matter field.« less

Similarity transformation for equilibrium boundary layers, including effects of blowing and suction

NASA Astrophysics Data System (ADS)

Chen, Xi; Hussain, Fazle

2017-03-01

We present a similarity transformation for the mean velocity profiles in sink flow turbulent boundary layers, including effects of blowing and suction. It is based on symmetry analysis which transforms the governing partial differential equations (for mean mass and momentum) into an ordinary differential equation and yields a new result including an exact, linear relation between the mean normal (V ) and streamwise (U ) velocities. A characteristic length function is further introduced which, under a first order expansion (whose coefficient is η ) in wall blowing and suction velocity, leads to the similarity transformation for U with the value of η ≈-1 /9 . This transformation is shown to be a group invariant and maps different U profiles under different blowing and suction conditions into a (universal) profile for no blowing or suction. Its inverse transformation enables predictions of all mean quantities in the mean mass and momentum equations, in good agreement with DNS data.

Planar maneuvering control of underwater snake robots using virtual holonomic constraints.

PubMed

Kohl, Anna M; Kelasidi, Eleni; Mohammadi, Alireza; Maggiore, Manfredi; Pettersen, Kristin Y

2016-11-24

This paper investigates the problem of planar maneuvering control for bio-inspired underwater snake robots that are exposed to unknown ocean currents. The control objective is to make a neutrally buoyant snake robot which is subject to hydrodynamic forces and ocean currents converge to a desired planar path and traverse the path with a desired velocity. The proposed feedback control strategy enforces virtual constraints which encode biologically inspired gaits on the snake robot configuration. The virtual constraints, parametrized by states of dynamic compensators, are used to regulate the orientation and forward speed of the snake robot. A two-state ocean current observer based on relative velocity sensors is proposed. It enables the robot to follow the path in the presence of unknown constant ocean currents. The efficacy of the proposed control algorithm for several biologically inspired gaits is verified both in simulations for different path geometries and in experiments.

The Eastern California Shear Zone as the northward extension of the southern San Andreas Fault

USGS Publications Warehouse

Thatcher, Wayne R.; Savage, James C.; Simpson, Robert W.

2016-01-01

Cluster analysis offers an agnostic way to organize and explore features of the current GPS velocity field without reference to geologic information or physical models using information only contained in the velocity field itself. We have used cluster analysis of the Southern California Global Positioning System (GPS) velocity field to determine the partitioning of Pacific-North America relative motion onto major regional faults. Our results indicate the large-scale kinematics of the region is best described with two boundaries of high velocity gradient, one centered on the Coachella section of the San Andreas Fault and the Eastern California Shear Zone and the other defined by the San Jacinto Fault south of Cajon Pass and the San Andreas Fault farther north. The ~120 km long strand of the San Andreas between Cajon Pass and Coachella Valley (often termed the San Bernardino and San Gorgonio sections) is thus currently of secondary importance and carries lesser amounts of slip over most or all of its length. We show these first order results are present in maps of the smoothed GPS velocity field itself. They are also generally consistent with currently available, loosely bounded geologic and geodetic fault slip rate estimates that alone do not provide useful constraints on the large-scale partitioning we show here. Our analysis does not preclude the existence of smaller blocks and more block boundaries in Southern California. However, attempts to identify smaller blocks along and adjacent to the San Gorgonio section were not successful.

The Eastern California Shear Zone as the northward extension of the southern San Andreas Fault

NASA Astrophysics Data System (ADS)

Thatcher, W.; Savage, J. C.; Simpson, R. W.

2016-04-01

Cluster analysis offers an agnostic way to organize and explore features of the current GPS velocity field without reference to geologic information or physical models using information only contained in the velocity field itself. We have used cluster analysis of the Southern California Global Positioning System (GPS) velocity field to determine the partitioning of Pacific-North America relative motion onto major regional faults. Our results indicate the large-scale kinematics of the region is best described with two boundaries of high velocity gradient, one centered on the Coachella section of the San Andreas Fault and the Eastern California Shear Zone and the other defined by the San Jacinto Fault south of Cajon Pass and the San Andreas Fault farther north. The ~120 km long strand of the San Andreas between Cajon Pass and Coachella Valley (often termed the San Bernardino and San Gorgonio sections) is thus currently of secondary importance and carries lesser amounts of slip over most or all of its length. We show these first order results are present in maps of the smoothed GPS velocity field itself. They are also generally consistent with currently available, loosely bounded geologic and geodetic fault slip rate estimates that alone do not provide useful constraints on the large-scale partitioning we show here. Our analysis does not preclude the existence of smaller blocks and more block boundaries in Southern California. However, attempts to identify smaller blocks along and adjacent to the San Gorgonio section were not successful.

Generation of electric fields and currents by neutral flows in weakly ionized plasmas through collisional dynamos

NASA Astrophysics Data System (ADS)

Dimant, Y. S.; Oppenheim, M. M.; Fletcher, A. C.

2016-08-01

In weakly ionized plasmas neutral flows drag plasma across magnetic field lines generating intense electric fields and currents. An example occurs in the Earth's ionosphere near the geomagnetic equator. Similar processes take place in the Solar chromosphere and magnetohydrodynamic generators. This paper argues that not all convective neutral flows generate electric fields and currents and it introduces the corresponding universal criterion for their formation, ∇×(U ×B )≠∂B /∂t , where U is the neutral flow velocity, B is the magnetic field, and t is time. This criterion does not depend on the conductivity tensor, σ ̂ . For many systems, the displacement current, ∂B /∂t , is negligible making the criterion even simpler. This theory also shows that the neutral-dynamo driver that generates E-fields and currents plays the same role as the DC electric current plays for the generation of the magnetic field in the Biot-Savart law.

Hydrodynamic and suspended-solids concentration measurements in Suisun Bay, California, 1995

USGS Publications Warehouse

Cuetara, Jay I.; Burau, Jon R.; Schoellhamer, David H.

2001-01-01

Sea level, current velocity, water temperature, salinity (computed from conductivity and temperature), and suspended-solids data collected in Suisun Bay, California, from May 30, 1995, through October 27, 1995, by the U.S. Geological Survey are documented in this report. Data were collected concurrently at 21 sites. Various parameters were measured at each site. Velocity-profile data were collected at 6 sites, single-point velocity measurements were made at 9 sites, salinity data were collected at 20 sites, and suspended-solids concentrations were measured at 10 sites. Sea-level and velocity data are presented in three forms; harmonic analysis results; time-series plots (sea level, current speed, and current direction versus time); and time-series plots of low-pass-filtered time series. Temperature, salinity, and suspended-solids data are presented as plots of raw and low-pass-filtered time series.The velocity and salinity data presented in this report document a period when the residual current patterns and salt field were transitioning from a freshwater-inflow-dominated condition towards a quasi steady-state summer condition when density-driven circulation and tidal nonlinearities became relatively more important as long-term transport mechanisms. Sacramento-San Joaquin River Delta outflow was high prior to and during this study, so the tidally averaged salinities were abnormally low for this time of year. For example, the tidally averaged salinities varied from 0-12 at Martinez, the western border of Suisun Bay, to a maximum of 2 at Mallard Island, the eastern border of Suisun Bay. Even though salinities increased overall in Suisun Bay during the study period, the near-bed residual currents primarily were directed seaward. Therefore, salinity intrusion through Suisun Bay towards the Delta primarily was accomplished in the absence of the tidally averaged, two-layer flow known as gravitational circulation where, by definition, the net currents are landward at the bed. The Folsom Dam spillway gate failure on July 17, 1995, was analyzed to determine the effect on the hydrodynamics of Suisun Bay. The peak flow of the American River reached roughly 1,000 cubic meters per second as a result of the failure, which is relatively small. This was roughly 15 percent of the approximate 7,000 cubic meters per second tidal flows that occur daily in Suisun Bay and was likely attenuated greatly. Based on analysis of tidally averaged near-bed salinity and depth-averaged currents after the failure, the effect was essentially nonexistent and is indistinguishable from the natural variability.

Branching and resonant characteristics of surface plasma waves in a semi-bounded quantum plasma including spin-current effects

NASA Astrophysics Data System (ADS)

Lee, Myoung-Jae; Jung, Gwanyong; Jung, Young-Dae

2018-05-01

The dispersion relation for the waves propagating on the surface of a bounded quantum plasma with consideration of electron spin-current and ion-stream is derived and numerically investigated. We have found that one of the real parts of the wave frequency has the branching behavior beyond the instability domains. In such a region where the frequency branching occurs, the waves exhibit purely propagating mode. The resonant instability has also been investigated. We have found that when the phase velocity of the wave is close to the velocity of ion-stream the wave becomes unstable. However, the resonant growth rate is remarkably reduced by the effect of electron spin-current. The growth rate is also decreased by either the reduction of ion-stream velocity or the increase in quantum wavelength. Thus, the quantum effect in terms of the quantum wave number is found to suppress the resonant instability. It is also found that the increase in Fermi energy can reduce the growth rate of the resonant wave in the quantum plasma.

Domain-wall motion at an ultrahigh speed driven by spin-orbit torque in synthetic antiferromagnets.

PubMed

Yu, Ziyang; Zhang, Yue; Zhang, Zhenhua; Cheng, Ming; Lu, Zhihong; Yang, Xiaofei; Shi, Jing; Xiong, Rui

2018-04-27

In this article, we present our numerical investigation about the spin-orbit-torque induced domain-wall (DW) motion in a synthetic antiferromagnetic multilayer nanotrack. This nanotrack was composed by two ferromagnetic (FM) layers with a RKKY inter-layer antiferromagnetic (AFM) exchange coupling. The velocity of DW was well manipulated by varying parameters including inter-layer exchange constant, the Dzyaloshinskii-Moriya interaction (DMI) strength, the current density and the magnetic anisotropy. The DW velocity was found to be strictly related to the orientation of the moments in the two FM layers. When the interlayer exchange constant or the DMI constant were larger than a critical value, there was a large angle between the moments in one FM layer and that in the other one under the current, and the DW was driven to move at an ultrahigh speed (around 10 000 m s -1 ). However, when the DMI or the AFM exchange coupling was weaker than the critical value, the moments in one FM layer were parallel to that in the other one under the current, and the velocity was significantly reduced.

Experimental investigation of nonlinear characteristics of a smart fluid damper

NASA Astrophysics Data System (ADS)

Rahman, Mahmudur; Ong, Zhi Chao; Chong, Wen Tong; Julai, Sabariah; Ahamed, Raju

2018-05-01

Smart fluids, known as smart material, are used to form controllable dampers in vibration control applications. Magnetorheological(MR) fluid damper is a well-known smart fluid damper which has a reputation to provide high damping force with low-power input. However, the force/velocity of the MR damper is significantly nonlinear and proper characteristic analysis are required to be studied for optimal implementation in structural vibration control. In this study, an experimental investigation is carried out to test the damping characteristics of MR damper. Dynamic testing is performed with a long-stroke MR damper model no RD-80410-1 from Lord corporation on a universal testing machine(UTM). The force responses of MR damper are measured under different stroke lengths, velocities and current inputs and their performances are analyzed. This study will play a key role to implement MR damper in many structural vibration control applications.

Dissipative Effects on Inertial-Range Statistics at High Reynolds Numbers.

PubMed

Sinhuber, Michael; Bewley, Gregory P; Bodenschatz, Eberhard

2017-09-29

Using the unique capabilities of the Variable Density Turbulence Tunnel at the Max Planck Institute for Dynamics and Self-Organization, Göttingen, we report experimental measurements in classical grid turbulence that uncover oscillations of the velocity structure functions in the inertial range. This was made possible by measuring extremely long time series of up to 10^{10} samples of the turbulent fluctuating velocity, which corresponds to O(10^{7}) integral length scales. The measurements were conducted in a well-controlled environment at a wide range of high Reynolds numbers from R_{λ}=110 up to R_{λ}=1600, using both traditional hot-wire probes as well as the nanoscale thermal anemometry probe developed at Princeton University. An implication of the observed oscillations is that dissipation influences the inertial-range statistics of turbulent flows at scales significantly larger than predicted by current models and theories.

Role of turbulence fluctuations on uncertainties of acoutic Doppler current profiler discharge measurements

USGS Publications Warehouse

Tarrab, Leticia; Garcia, Carlos M.; Cantero, Mariano I.; Oberg, Kevin

2012-01-01

This work presents a systematic analysis quantifying the role of the presence of turbulence fluctuations on uncertainties (random errors) of acoustic Doppler current profiler (ADCP) discharge measurements from moving platforms. Data sets of three-dimensional flow velocities with high temporal and spatial resolution were generated from direct numerical simulation (DNS) of turbulent open channel flow. Dimensionless functions relating parameters quantifying the uncertainty in discharge measurements due to flow turbulence (relative variance and relative maximum random error) to sampling configuration were developed from the DNS simulations and then validated with field-scale discharge measurements. The validated functions were used to evaluate the role of the presence of flow turbulence fluctuations on uncertainties in ADCP discharge measurements. The results of this work indicate that random errors due to the flow turbulence are significant when: (a) a low number of transects is used for a discharge measurement, and (b) measurements are made in shallow rivers using high boat velocity (short time for the boat to cross a flow turbulence structure).

Hydrodynamic conditioning of diversity and functional traits in subtidal estuarine macrozoobenthic communities

NASA Astrophysics Data System (ADS)

van der Wal, Daphne; Lambert, Gwladys I.; Ysebaert, Tom; Plancke, Yves M. G.; Herman, Peter M. J.

2017-10-01

Variations in abundance and diversity of estuarine benthic macrofauna are typically described along the salinity gradient. The influence of gradients in water depth, hydrodynamic energy and sediment properties are less well known. We studied how these variables influence the distribution of subtidal macrofauna in the polyhaline zone of a temperate estuary (Westerschelde, SW Netherlands). Macrofauna density, biomass and species richness, combined in a so-called ecological richness, decreased with current velocities and median grain-size and increased with organic carbon of the sediment, in total explaining 39% of the variation. The macrofauna community composition was less well explained by the three environmental variables (approx. 12-15% in total, with current velocity explaining approx. 8%). Salinity, water depth and distance to the intertidal zone had a very limited effect on both ecological richness and the macrofauna community. The proportion of (surface) deposit feeders (including opportunistic species), decreased relative to that of omnivores and carnivores with increasing current velocity and sediment grain-size. In parallel, the proportion of burrowing sessile benthic species decreased relative to that of mobile benthic species that are able to swim. Correspondingly, spatial variations in hydrodynamics yielded distinct hotspots and coldspots in ecological richness. The findings highlight the importance of local hydrodynamic conditions for estuarine restoration and conservation. The study provides a tool based on a hydrodynamic model to assess and predict ecological richness in estuaries.

Does choice of angular velocity affect pain level during isokinetic strength testing of knee osteoarthritis patients?

PubMed

Almosnino, S; Brandon, S C E; Sled, E A

2012-12-01

Thigh musculature strength assessment in individuals with knee osteoarthritis is routinely performed in rehabilitative settings. A factor that may influence results is pain experienced during testing. To assess whether pain experienced during isokinetic testing in individuals with knee osteoarthritis is dependent on the angular velocity prescribed. Experimental, repeated measures. University laboratory. Thirty-five individuals (19 women, 16 men) with tibiofemoral osteoarthritis. Participants performed three randomized sets of five maximal concentric extension-flexion repetitions at 60°/s, 90°/s and 120°/s. Pain intensity was measured immediately after the completion of each set. Strength outcomes for each set were the average peak moment. Across gender, pain level was not significantly affected by testing velocity (P=0.18, η(p)(2) =0.05). There was a trend of women reporting more pain than men across all testing velocities, however this comparison did not reach statistical significance (P=0.18, η(p)(2)=0.05). There was a significant main effect of testing velocity on strength, with the highest level attained at 60°/s. However, no difference in strength was noted when testing was performed at 90°/s or 120°/s. A large variation in pain scores within and across conditions and gender was noted, suggesting that at the current stage: 1) isokinetic angular velocity prescription be performed on an individual patient basis; and 2) improvements in the manner pain is recorded are needed in order to reduce the variations in pain scores. Individual prescription of angular velocity may be necessary for optimal strength output and reduction of pain during effort exertion in this patient population.

Circulation in the eastern North Pacific: results from a current meter array along 152°W

NASA Astrophysics Data System (ADS)

Hall, Melinda M.; Niiler, Pearn P.; Schmitz, William J.

1997-07-01

Data from four, 2-3 year long current meter records, at 28°N, 35°N, 39°N and 42°N, along 152°W in the eastern North Pacific, are used to describe the variability found in mesoscale period (< 200 days) and long period ( > 200 days) motions. Energy in the mesoscale energy band of 40-200 day periodicity is found in the upper ocean at each location, generally decreasing to the north and with depth. The long period flow is not coherent among these locations. Record length mean velocities at 3-4 separate depths were used to provide estimates of reference level velocities for vertical profiles of geostrophic currents derived from historical hydrographic data. The vertical profile of measured east-west vertical shear agrees well with the geostrophically computed value; the north-south measured vertical shear is not in as good agreement. Assuming a vorticity balance of fwz= βv, and with w( z=0) as the Ekman pumping, the vertical velocity profiles were also calculated at 28°N and 42dgN. Using these three-dimensional referenced vertical profiles of mean currents, an examination of the mean advection of density in the thermocline revealed significant residuals in the net three-dimensional advection of density (or heat and salt) above 850 m at 28°N and above 240 m at 42°N. These results are relatively independent of the reference level velocities.

Vegetation as self-adaptive coastal protection: Reduction of current velocity and morphologic plasticity of a brackish marsh pioneer.

PubMed

Carus, Jana; Paul, Maike; Schröder, Boris

2016-03-01

By reducing current velocity, tidal marsh vegetation can diminish storm surges and storm waves. Conversely, currents often exert high mechanical stresses onto the plants and hence affect vegetation structure and plant characteristics. In our study, we aim at analysing this interaction from both angles. On the one hand, we quantify the reduction of current velocity by Bolboschoenus maritimus, and on the other hand, we identify functional traits of B. maritimus' ramets along environmental gradients. Our results show that tidal marsh vegetation is able to buffer a large proportion of the flow velocity at currents under normal conditions. Cross-shore current velocity decreased with distance from the marsh edge and was reduced by more than 50% after 15 m of vegetation. We were furthermore able to show that plants growing at the marsh edge had a significantly larger diameter than plants from inside the vegetation. We found a positive correlation between plant thickness and cross-shore current which could provide an adaptive value in habitats with high mechanical stress. With the adapted morphology of plants growing at the highly exposed marsh edge, the entire vegetation belt is able to better resist the mechanical stress of high current velocities. This self-adaptive effect thus increases the ability of B. maritimus to grow and persist in the pioneer zone and may hence better contribute to ecosystem-based coastal protection by reducing current velocity.

Shear velocity structure of central Eurasia from inversion of surface wave velocities

NASA Astrophysics Data System (ADS)

Villaseñor, A.; Ritzwoller, M. H.; Levshin, A. L.; Barmin, M. P.; Engdahl, E. R.; Spakman, W.; Trampert, J.

2001-04-01

We present a shear velocity model of the crust and upper mantle beneath central Eurasia by simultaneous inversion of broadband group and phase velocity maps of fundamental-mode Love and Rayleigh waves. The model is parameterized in terms of velocity depth profiles on a discrete 2°×2° grid. The model is isotropic for the crust and for the upper mantle below 220 km but, to fit simultaneously long period Love and Rayleigh waves, the model is transversely isotropic in the uppermost mantle, from the Moho discontinuity to 220 km depth. We have used newly available a priori models for the crust and sedimentary cover as starting models for the inversion. Therefore, the crustal part of the estimated model shows good correlation with known surface features such as sedimentary basins and mountain ranges. The velocity anomalies in the upper mantle are related to differences between tectonic and stable regions. Old, stable regions such as the East European, Siberian, and Indian cratons are characterized by high upper-mantle shear velocities. Other large high velocity anomalies occur beneath the Persian Gulf and the Tarim block. Slow shear velocity anomalies are related to regions of current extension (Red Sea and Andaman ridges) and are also found beneath the Tibetan and Turkish-Iranian Plateaus, structures originated by continent-continent collision. A large low velocity anomaly beneath western Mongolia corresponds to the location of a hypothesized mantle plume. A clear low velocity zone in vSH between Moho and 220 km exists across most of Eurasia, but is absent for vSV. The character and magnitude of anisotropy in the model is on average similar to PREM, with the most prominent anisotropic region occurring beneath the Tibetan Plateau.

Brownian motion of massive skyrmions in magnetic thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Troncoso, Roberto E., E-mail: r.troncoso.c@gmail.com; Núñez, Álvaro S., E-mail: alnunez@dfi.uchile.cl

2014-12-15

We report on the thermal effects on the motion of current-driven massive magnetic skyrmions. The reduced equation for the motion of skyrmion has the form of a stochastic generalized Thiele’s equation. We propose an ansatz for the magnetization texture of a non-rigid single skyrmion that depends linearly with the velocity. By using this ansatz it is found that the skyrmion mass tensor is closely related to intrinsic skyrmion parameters, such as Gilbert damping, skyrmion-charge and dissipative force. We have found an exact expression for the average drift velocity as well as the mean-square velocity of the skyrmion. The longitudinal andmore » transverse mobility of skyrmions for small spin-velocity of electrons is also determined and found to be independent of the skyrmion mass.« less

Solar oscillations: time analysis of the GOLF p-mode signal

NASA Astrophysics Data System (ADS)

Renaud, C.; Grec, G.; Boumier, P.; Gabriel, A. H.; Robillot, J. M.; Cortés, T. Roca; Turck-Chièze, S.; Ulrich, R. K.

1999-05-01

We determine the intrinsic phase lag of the GOLF data for the solar p-mode velocity deduced either from one of the narrow band photometers working alternatively on blue and red wing of the sodium lines. The timing of the ``blue wing'' velocity coming from the current GOLF data is given in respect to the ground-based observations. The phase lag for the ``blue'' velocity is 6 s in advance relatively to a velocity coming from a differential device. For individual p modes, the phase lag from the ``blue'' velocity to the ``red'' velocity are not in opposition of phase, as expected in a very simple solar model, but differs from 8(o) to 18(o) from the opposition, depending on the degree and the radial order of the acoustic mode. The measurement of the differential lag between the blue and red wings of the D lines may open a new way to monitor the temperature oscillations with the optical depth.

The evolution of rotating stars. III - Predicted surface rotation velocities for stars which conserve total angular momentum

NASA Technical Reports Server (NTRS)

Endal, A. S.; Sofia, S.

1979-01-01

Predicted surface rotation velocities for Population I stars at 10, 7, 5, 3, and 1.5 solar masses are presented. The surface velocities were computed for angular momentum with no radial redistribution, complete redistribution, and partial redistribution as predicted by consideration of circulation currents in rotating stars. Near the main sequence, rotational effects can reduce the moment of inertia of a star, so nonrotating models underestimate the expected velocities for evolving stars. On the red giant branch, angular momentum redistribution reduces the surface velocity by a factor of 2 or more, relative to the velocity expected for no radial redistribution. This removes the discrepancy between predicted and observed rotation rates for the K giants and makes it unlikely that these stars lose significant amounts of angular momentum by stellar winds. Calculations indicate that improved observations of the red giants in the Hyades cluster can be used to determine how angular momentum is redistributed by convection

Preliminary rotor wake measurements with a laser velocimeter

NASA Technical Reports Server (NTRS)

Hoad, D. R.; Rhodes, D. B.; Meyers, J. F.

1983-01-01

A laser velocimeter (LV) was used to determine rotor wake characteristics. The effect of various fuselage widths and rotor-fuselage spacings on time averaged and detailed time dependent rotor wake velocity characteristics was defined. Definition of time dependent velocity characteristics was attempted with the LV by associating a rotor azimuth position with each velocity measurement. Results were discouraging in that no apparent time dependent velocity characteristics could be discerned from the LV measurements. Since the LV is a relatively new instrument in the rotor wake measurement field, the cause of this lack of periodicity is as important as the basic research objectives. An attempt was made to identify the problem by simulated acquisition of LV-type data for a predicted rotor wake velocity time history. Power spectral density and autocorrelation function estimation techniques were used to substantiate the conclusion that the primary cause of the lack of time dependent velocity characteristics was the nonstationary flow condition generated by the periodic turbulence level that currently exists in the open throat configuration of the wind tunnel.

Quenching of Particle-Gas Combustible Mixtures Using Electric Particulate Suspension (EPS) and Dispersion Methods

NASA Technical Reports Server (NTRS)

Colver, Gerald M.; Goroshin, Samuel; Lee, John H. S.

2001-01-01

A cooperative study is being carried out between Iowa State University and McGill University. The new study concerns wall and particle quenching effects in particle-gas mixtures. The primary objective is to measure and interpret flame quenching distances, flammability limits, and burning velocities in particulate suspensions. A secondary objective is to measure particle slip velocities and particle velocity distribution as these influence flame propagation. Two suspension techniques will be utilized and compared: (1) electric particle suspension/EPS; and (2) flow dispersion. Microgravity tests will permit testing of larger particles and higher and more uniform dust concentrations than is possible in normal gravity.

Lithospheric Structure of Arabia from the Joint Inversion of P- and S-wave Receiver Functions and Dispersion Velocities

NASA Astrophysics Data System (ADS)

Julia, Jordi; Al-Amri, Abdullah; Pasyanos, Michael; Rodgers, Arthur; Matzel, Eric; Nyblade, Andrew

2013-04-01

Seismic imaging of the lithosphere under the Arabian shield and platform is critical to help answer important geologic questions of regional and global interest. The Arabian Shield can be regarded as an amalgamation of several arcs and microplates of Proterozoic age that culminated in the accretion of the Arabian portion of Gondwana during the Pan-African event at ~550 Ma and the role of important geologic features observed on the surface - such as the lineaments and shear zones separating the Proterozoic terrains in the shield - is not completely understood. Also, current models of Precambrian crustal evolution predict that Proterozoic terranes are underlain by fertile (FeO-rich) cratonic roots that should promote the production of mafic magmas and underplating of the Arabian shield terranes, and the shield contains Tertiary and Quaternary volcanic rocks related to the early stages of the Red Sea formation that might also be related to plume-related lithospheric "erosion". In order to better understand these relationships, we are developing new velocity models of litospheric structure for the Arabian shield and platform from the joint inversion of up to four seismic data sets: P-wave receiver functions, S-wave receiver functions, dispersion velocities from surface-waves, and dispersion velocities from ambient-noise cross-correlations. The joint inversion combines constraints on crustal thickness from P-wave receiver functions, constraints on lithospheric thickness from S-wave receiver functions and constraints on S-velocity and S-velocity gradients from dispersion velocities to produce detailed S-velocity profiles under single recording stations. We will present S-velocity profiles for a number of permanent stations operated by the Saudi Geological Survey and the King ing Abdulaziz Center for Science and Technology as well as stations from past temporary deployments and discuss the implications of the velocity models regarding composition and tectonics of the Arabian shield and platform.

Quench propagation in the superconducting 6 kA flexible busbars of the LHC

NASA Astrophysics Data System (ADS)

Herzog, R.; Calvi, M.; Sonnemann, F.; Pelegrin-Carcelen, J. M.

2002-05-01

Flexible superconducting cables with currents up to 6 kA will be used to power magnets individually in the insertion regions of the LHC. In case of a quench, the currents in these circuits will decay very fast (with time constants of about 200 ms) such that relatively small copper cross sections are sufficient for these busbars. Quench propagation experiments on a prototype cable and corresponding simulations led to a detailed understanding of the quench behavior of these busbars and to recommendations for the design and application of the cable. Simulations of the quench process in a multi-strand conductor led to a detailed understanding of the way current crosses from superconducting to pure copper strands and how this affects the quench propagation velocity. At nominal current (6 kA), the quench propagation velocities are high (10 m/s) and the hot spot temperature increases rapidly. In this situation, timely quench detection and energy extraction (current reduction) are vital to prevent damage of circuit components.

Can You Hear That Peak? Utilization of Auditory and Visual Feedback at Peak Limb Velocity.

PubMed

Loria, Tristan; de Grosbois, John; Tremblay, Luc

2016-09-01

At rest, the central nervous system combines and integrates multisensory cues to yield an optimal percept. When engaging in action, the relative weighing of sensory modalities has been shown to be altered. Because the timing of peak velocity is the critical moment in some goal-directed movements (e.g., overarm throwing), the current study sought to test whether visual and auditory cues are optimally integrated at that specific kinematic marker when it is the critical part of the trajectory. Participants performed an upper-limb movement in which they were required to reach their peak limb velocity when the right index finger intersected a virtual target (i.e., a flinging movement). Brief auditory, visual, or audiovisual feedback (i.e., 20 ms in duration) was provided to participants at peak limb velocity. Performance was assessed primarily through the resultant position of peak limb velocity and the variability of that position. Relative to when no feedback was provided, auditory feedback significantly reduced the resultant endpoint variability of the finger position at peak limb velocity. However, no such reductions were found for the visual or audiovisual feedback conditions. Further, providing both auditory and visual cues concurrently also failed to yield the theoretically predicted improvements in endpoint variability. Overall, the central nervous system can make significant use of an auditory cue but may not optimally integrate a visual and auditory cue at peak limb velocity, when peak velocity is the critical part of the trajectory.

Erosive events in dilute pyroclastic density currents

NASA Astrophysics Data System (ADS)

Douillet, G.; Kueppers, U.; Rasmussen, K.; Merrison, J. P.; Dingwell, D. B.

2011-12-01

Our understanding of the dynamics of pyroclastic density currents (PDCs) is largely based on the study of their deposits. However, sedimentological structures reflect only the low energy, depositional phases of a flow. To enlarge the source of information on PDC behaviour, we provided wind-tunnel experiments to measure the minimal velocity necessary to erode dry, volcanic ash. Our results permit to link erosive surfaces that are often found in PDC deposits to the minimum velocity that must have acted to produce them. We apply the method to field examples and discuss the occurrence of hydraulic-jumps in dilute PDCs. We measured the threshold of surface friction-velocity for erosion of two types of volcanic ash: 1) a mixture of fragments of vesiculated scoria containing also lithics and crystals and 2) pumice clasts from the Plinian Laacher See eruption. Both were sampled in quarries from the East Eifel volcanic field (Germany). For each type, we measured the threshold for particles from 63 μm to 2 mm in 1 phi-size steps. Static threshold friction-velocities have been measured experimentally in an open, 6 m-long wind-tunnel at Aarhus University. In order to quickly guarantee the downwind equilibrium-dynamics of the saltating sand-surface, we produced roughness-carpets upstream of the study area. The roughness-carpets consist of particles of the measured sample fixed onto the bed in order to create an appropriate static roughness. The measuring section (1 m in length) is located at the downwind end of the wind-tunnel and covered with 10 mm of sample. The wind velocity in the wind-tunnel was progressively increased until a small but continuous number of grains left the surface. This wind velocity was taken as the threshold, and the associated surface friction-velocity was deduced by calibration from wind-profiles data taken over the fixed surface of material of the same characteristics. We apply our results to sedimentary features found in natural deposits and usually interpreted as "chute and pool" structures. These are characterized by erosional events producing a steep side facing the flow, and lensoidal layers deposited on the stoss face of the un-eroded, remaining strata. Our experimental results allow for quantifying the minimum current-velocity required for the observed erosion. Based on this, we discuss the interpretation of such erosional features as "chute and pool" structures, which are the sedimentary record of hydraulic-jumps. There is no clear evidence of the presence of internal hydraulic-jumps in the sedimentary record of PDCs. Moreover, such flows can decelerate drastically and eventually stop without leaving the supercritical flow regime due to their highly depositional nature. Accordingly, they would not experience a hydraulic-jump.

Is lactate production related to muscular fatigue? A pedagogical proposition using empirical facts.

PubMed

Macedo, Denise Vaz; Lazarim, Fernanda Lorenzi; Catanho da Silva, Fernando Oliveira; Tessuti, Lucas Samuel; Hohl, Rodrigo

2009-12-01

The cause-effect relationship between lactic acid, acidosis, and muscle fatigue has been established in the literature. However, current experiments contradict this premise. Here, we describe an experiment developed by first-year university students planned to answer the following questions: 1) Which metabolic pathways of energy metabolism are responsible for meeting the high ATP demand during high-intensity intermittent exercise? 2) Which metabolic pathways are active during the pause, and how do they influence phosphocreatine synthesis? and 3) Is lactate production related to muscular fatigue? Along with these questions, students received a list of materials available for the experiment. In the classroom, they proposed two protocols of eight 30-m sprints at maximum speed, one protocol with pauses of 120 s and the other protocol with pauses of 20 s between sprints. Their performances were analyzed through the velocity registered by photocells. Blood lactate was analyzed before the first sprint and after the eighth sprint. Blood uric acid was analyzed before exercise and 15 and 60 min after exercises. When discussing the data, students concluded that phosphocreatine restoration is time dependent, and this fact influenced the steady level of performance in the protocol with pauses of 120 s compared with the performance decrease noted in the protocol with pauses of 20 s. As the blood lactate levels showed similar absolute increases after both exercises, the students concluded that lactate production is not related to the performance decrement. This activity allows students to integrate the understanding of muscular energy pathways and to reconsider a controversial concept with facts that challenge the universality of the hypothesis relating lactate production to muscular fatigue.

Screening for fetal growth restriction with universal third trimester ultrasonography in nulliparous women in the Pregnancy Outcome Prediction (POP) study: a prospective cohort study.

PubMed

Sovio, Ulla; White, Ian R; Dacey, Alison; Pasupathy, Dharmintra; Smith, Gordon C S

2015-11-21

Fetal growth restriction is a major determinant of adverse perinatal outcome. Screening procedures for fetal growth restriction need to identify small babies and then differentiate between those that are healthy and those that are pathologically small. We sought to determine the diagnostic effectiveness of universal ultrasonic fetal biometry in the third trimester as a screening test for small-for-gestational-age (SGA) infants, and whether the risk of morbidity associated with being small differed in the presence or absence of ultrasonic markers of fetal growth restriction. The Pregnancy Outcome Prediction (POP) study was a prospective cohort study of nulliparous women with a viable singleton pregnancy at the time of the dating ultrasound scan. Women participating had clinically indicated ultrasonography in the third trimester as per routine clinical care and these results were reported as usual (selective ultrasonography). Additionally, all participants had research ultrasonography, including fetal biometry at 28 and 36 weeks' gestational age. These results were not made available to participants or treating clinicians (universal ultrasonography). We regarded SGA as a birthweight of less than the 10th percentile for gestational age and screen positive for SGA an ultrasonographic estimated fetal weight of less than the 10th percentile for gestational age. Markers of fetal growth restriction included biometric ratios, utero-placental Doppler, and fetal growth velocity. We assessed outcomes for consenting participants who attended research scans and had a livebirth at the Rosie Hospital (Cambridge, UK) after the 28 weeks' research scan. Between Jan 14, 2008, and July 31, 2012, 4512 women provided written informed consent of whom 3977 (88%) were eligible for analysis. Sensitivity for detection of SGA infants was 20% (95% CI 15-24; 69 of 352 fetuses) for selective ultrasonography and 57% (51-62; 199 of 352 fetuses) for universal ultrasonography (relative sensitivity 2·9, 95% CI 2·4-3·5, p<0·0001). Of the 3977 fetuses, 562 (14·1%) were identified by universal ultrasonography with an estimated fetal weight of less than the 10th percentile and were at an increased risk of neonatal morbidity (relative risk [RR] 1·60, 95% CI 1·22-2·09, p=0·0012). However, estimated fetal weight of less than the 10th percentile was only associated with the risk of neonatal morbidity (pinteraction=0·005) if the fetal abdominal circumference growth velocity was in the lowest decile (RR 3·9, 95% CI 1·9-8·1, p=0·0001). 172 (4%) of 3977 pregnancies had both an estimated fetal weight of less than the 10th percentile and abdominal circumference growth velocity in the lowest decile, and had a relative risk of delivering an SGA infant with neonatal morbidity of 17·6 (9·2-34·0, p<0·0001). Screening of nulliparous women with universal third trimester fetal biometry roughly tripled detection of SGA infants. Combined analysis of fetal biometry and fetal growth velocity identified a subset of SGA fetuses that were at increased risk of neonatal morbidity. National Institute for Health Research, Medical Research Council, Sands, and GE Healthcare. Copyright © 2015 Sovio et al. Open Access article distributed under the terms of CC BY. Published by Elsevier Ltd.. All rights reserved.

Perspectives on handedness, life and physics.

PubMed

Axelsson, Sven

2003-08-01

In contrast to motion, matter will be conserved in all eternity. Structure and function will arise by the angular momentum of spinning spherical particles and their composites. Symmetry prevails in physics by equal amounts of left- and right-hand spinning entities, while life is asymmetric in this respect. Very rare deviations from the ubiquitous one-sided handedness in biology will probably explain the inert degradation resistant proteins in 'mad cow' type diseases. Velocities of physical events seems to be a most important feature and will explain for instance brain function and the true nature of neurodegenerative diseases. This biophysics of mind will in turn provide answers to many disputable aspects of physics such as the true nature of waves and gravity. Many current concepts in quantum physics will be invalidated, among them the uncertainty principle, the relativity to a fixed speed of light, the energy equation and the expansion of the Universe. Instead, decay and formation will balance each other in a continuum of matter in an intuitively cyclic Multiverse.

Intermittent Behavior of the Separated Boundary Layer along the Suction Surface of a Low Pressure Turbine Blade under Periodic Unsteady Flow Conditions

NASA Technical Reports Server (NTRS)

Oeztuerk, B; Schobeiri, M. T.; Ashpis, David E.

2005-01-01

The paper experimentally and theoretically studies the effects of periodic unsteady wake flow and aerodynamic characteristics on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experiments were carried out at Reynolds number of 110,000 (based on suction surface length and exit velocity). For one steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, intermittency behaviors were experimentally and theoretically investigated. The current investigation attempts to extend the intermittency unsteady boundary layer transition model developed in previously to the LPT cases, where separation occurs on the suction surface at a low Reynolds number. The results of the unsteady boundary layer measurements and the intermittency analysis were presented in the ensemble-averaged and contour plot forms. The analysis of the boundary layer experimental data with the flow separation, confirms the universal character of the relative intermittency function which is described by a Gausssian function.

A simple device for measuring the minimum current velocity to maintain semi-buoyant fish eggs in suspension

USGS Publications Warehouse

Mueller, Julia S.; Cheek, Brandon D.; Chen, Qingman; Groeschel, Jillian R.; Brewer, Shannon K.; Grabowski, Timothy B.

2013-01-01

Pelagic broadcast spawning cyprinids are common to Great Plains rivers and streams. This reproductive guild produces non-adhesive semi-buoyant eggs that require sufficient current velocity to remain in suspension during development. Although studies have shown that there may be a minimum velocity needed to keep the eggs in suspension, this velocity has not been estimated directly nor has the influence of physicochemical factors on egg buoyancy been determined. We developed a simple, inexpensive flow chamber that allowed for evaluation of minimum current velocity needed to keep semi-buoyant eggs in suspension at any time frame during egg development. The device described here has the capability of testing the minimum current velocity needed to keep semi-buoyant eggs in suspension at a wide range of physicochemical conditions. We used gellan beads soaked in freshwater for 0, 24, and 48 hrs as egg surrogates and evaluated minimum current velocities necessary to keep them in suspension at different combinations of temperature (20.0 ± 1.0° C, 25.0 ± 1.0° C, and 28.0 ± 1.0° C) and total dissolved solids (TDS; 1,000 mg L-1, 3,000 mg L-1, and 6,000 mg L-1). We found that our methodology generated consistent, repeatable results within treatment groups. Current velocities ranging from 0.001–0.026 needed to keep the gellan beads in suspension were negatively correlated to soak times and TDS and positively correlated with temperature. The flow chamber is a viable approach for evaluating minimum current velocities needed to keep the eggs of pelagic broadcast spawning cyprinids in suspension during development.

Measuring the velocity field from type Ia supernovae in an LSST-like sky survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Odderskov, Io; Hannestad, Steen, E-mail: isho07@phys.au.dk, E-mail: sth@phys.au.dk

2017-01-01

In a few years, the Large Synoptic Survey Telescope will vastly increase the number of type Ia supernovae observed in the local universe. This will allow for a precise mapping of the velocity field and, since the source of peculiar velocities is variations in the density field, cosmological parameters related to the matter distribution can subsequently be extracted from the velocity power spectrum. One way to quantify this is through the angular power spectrum of radial peculiar velocities on spheres at different redshifts. We investigate how well this observable can be measured, despite the problems caused by areas with nomore » information. To obtain a realistic distribution of supernovae, we create mock supernova catalogs by using a semi-analytical code for galaxy formation on the merger trees extracted from N-body simulations. We measure the cosmic variance in the velocity power spectrum by repeating the procedure many times for differently located observers, and vary several aspects of the analysis, such as the observer environment, to see how this affects the measurements. Our results confirm the findings from earlier studies regarding the precision with which the angular velocity power spectrum can be determined in the near future. This level of precision has been found to imply, that the angular velocity power spectrum from type Ia supernovae is competitive in its potential to measure parameters such as σ{sub 8}. This makes the peculiar velocity power spectrum from type Ia supernovae a promising new observable, which deserves further attention.« less

Origin of Stability in Particle Sedimentation

NASA Technical Reports Server (NTRS)

Segre, Philip N.

2003-01-01

Particle Image Velocimetry (PIV) is used to study the slow settling motions of spheres in suspensions ranging from dilute to highly concentrated, 0.0001 less than phi less than 0.50. During sedimentation, particle velocity fluctuations are found to be organized into regions of characteristic size xi approximately 11 a phi (exp -1/3). A simple model, based upon buoyant mass fluctuations DELTAm given by random density fluctuations in a region of size xi, accurately predicts the magnitudes of the velocity fluctuations DELTAV. We also find a new universal relation for particle diffusion during sedimentation. It can be written in a Stokes-Einstein form as Dapproximately(DELTAmxi)/(6pietaxi), where the effective temperature DELTAmgxi is the gravitational potential energy of density fluctuations. In addition related experiments examining inertial effects and transient states, that are aimed at uncovering the origin of the new lengthscale xi, will also be given.

Acoustic bed velocity and bed load dynamics in a large sand bed river

USGS Publications Warehouse

Gaeuman, D.; Jacobson, R.B.

2006-01-01

Development of a practical technology for rapid quantification of bed load transport in large rivers would represent a revolutionary advance for sediment monitoring and the investigation of fluvial dynamics. Measurement of bed load motion with acoustic Doppler current profiles (ADCPs) has emerged as a promising approach for evaluating bed load transport. However, a better understanding of how ADCP data relate to conditions near the stream bed is necessary to make the method practical for quantitative applications. In this paper, we discuss the response of ADCP bed velocity measurements, defined as the near-bed sediment velocity detected by the instrument's bottom-tracking feature, to changing sediment-transporting conditions in the lower Missouri River. Bed velocity represents a weighted average of backscatter from moving bed load particles and spectral reflections from the immobile bed. The ratio of bed velocity to mean bed load particle velocity depends on the concentration of the particles moving in the bed load layer, the bed load layer thickness, and the backscatter strength from a unit area of moving particles relative to the echo strength from a unit area of unobstructed bed. A model based on existing bed load transport theory predicted measured bed velocities from hydraulic and grain size measurements with reasonable success. Bed velocities become more variable and increase more rapidly with shear stress when the transport stage, defined as the ratio of skin friction to the critical shear stress for particle entrainment, exceeds a threshold of about 17. This transition in bed velocity response appears to be associated with the appearance of longer, flatter bed forms at high transport stages.

Surface velocity divergence model of air/water interfacial gas transfer in open-channel flows

NASA Astrophysics Data System (ADS)

Sanjou, M.; Nezu, I.; Okamoto, T.

2017-04-01

Air/water interfacial gas transfer through a free surface plays a significant role in preserving and restoring water quality in creeks and rivers. However, direct measurements of the gas transfer velocity and reaeration coefficient are still difficult, and therefore a reliable prediction model needs to be developed. Varying systematically the bulk-mean velocity and water depth, laboratory flume experiments were conducted and we measured surface velocities and dissolved oxygen (DO) concentrations in open-channel flows to reveal the relationship between DO transfer velocity and surface divergence (SD). Horizontal particle image velocimetry measurements provide the time-variations of surface velocity divergence. Positive and negative regions of surface velocity divergence are transferred downstream in time, as occurs in boil phenomenon on natural river free-surfaces. The result implies that interfacial gas transfer is related to bottom-situated turbulence motion and vertical mass transfer. The original SD model focuses mainly on small-scale viscous motion, and this model strongly depends on the water depth. Therefore, we modify the SD model theoretically to accommodate the effects of the water depth on gas transfer, introducing a non-dimensional parameter that includes contributions of depth-scale large-vortex motion, such as secondary currents, to surface renewal events related to DO transport. The modified SD model proved effective and reasonable without any dependence on the bulk mean velocity and water depth, and has a larger coefficient of determination than the original SD model. Furthermore, modeling of friction velocity with the Reynolds number improves the practicality of a new formula that is expected to be used in studies of natural rivers.

A comparison of the technique of the football quarterback pass between high school and university athletes.

PubMed

Toffan, Adam; Alexander, Marion J L; Peeler, Jason

2017-07-28

The purpose of the study was to compare the most effective joint movements, segment velocities and body positions to perform the fastest and most accurate pass of high school and university football quarterbacks. Secondary purposes were to develop a quarterback throwing test to assess skill level, to determine which kinematic variables were different between high school and university athletes as well as to determine which variables were significant predictors of quarterback throwing test performance. Ten high school and ten university athletes were filmed for the study, performing nine passes at a target and two passes for maximum distance. Thirty variables were measured using Dartfish Team Pro 4.5.2 video analysis system, and Microsoft Excel was used for statistical analysis. University athletes scored slightly higher than the high school athletes on the throwing test, however this result was not statistically significant. Correlation analysis and forward stepwise multiple regression analysis was performed on both the high school players and the university players in order to determine which variables were significant predictors of throwing test score. Ball velocity was determined to have the strongest predictive effect on throwing test score (r = 0.900) for the high school athletes, however, position of the back foot at release was also determined to be important (r = 0.661) for the university group. Several significant differences in throwing technique between groups were noted during the pass, however, body position at release showed the greatest differences between the two groups. High school players could benefit from more complete weight transfer and decreased throw time to increase throwing test score. University athletes could benefit from increased throw time and greater range of motion in external shoulder rotation and trunk rotation to increase their throwing test score. Coaches and practitioners will be able to use the findings of this research to help improve these and related throwing variables in their high school and university quarterbacks.

Generation of Currents in Weakly Ionized Plasmas through a Collisional Dynamo

NASA Astrophysics Data System (ADS)

Dimant, Yakov; Oppenheim, Meers; Fletcher, Alex

2016-10-01

Intense electric currents called electrojets occur in weakly ionized magnetized plasmas. An example occurs in the Earth's ionosphere near the magnetic equator where neutral winds drive the plasma across the geomagnetic field. Similar processes take place in the Solar chromosphere and MHD generators. We argue that not all convective neutral flows generate electrojets and it introduces the corresponding universal criterion for the current formation, ∇ × (U-> × B->) ≠ ∂ B-> / ∂ t , where U-> is the neutral flow velocity, B-> is the magnetic field, and t is time. This criterion does not depend on the conductivity tensor, σ̂ . For many systems, the displacement current, ∂ B-> / ∂ t , is negligible, making the criterion even simpler. This theory also shows that the neutral-dynamo driver that generates electrojets plays the same role as the DC electric current plays for the generation of the magnetic field in the Biot-Savart law. Work supported by NSF/DOE Grant PHY-1500439.

Modelling of the combustion velocity in UIT-85 on sustainable alternative gas fuel

NASA Astrophysics Data System (ADS)

Smolenskaya, N. M.; Korneev, N. V.

2017-05-01

The flame propagation velocity is one of the determining parameters characterizing the intensity of combustion process in the cylinder of an engine with spark ignition. Strengthening of requirements for toxicity and efficiency of the ICE contributes to gradual transition to sustainable alternative fuels, which include the mixture of natural gas with hydrogen. Currently, studies of conditions and regularities of combustion of this fuel to improve efficiency of its application are carried out in many countries. Therefore, the work is devoted to modeling the average propagation velocities of natural gas flame front laced with hydrogen to 15% by weight of the fuel, and determining the possibility of assessing the heat release characteristics on the average velocities of the flame front propagation in the primary and secondary phases of combustion. Experimental studies, conducted the on single cylinder universal installation UIT-85, showed the presence of relationship of the heat release characteristics with the parameters of the flame front propagation. Based on the analysis of experimental data, the empirical dependences for determination of average velocities of flame front propagation in the first and main phases of combustion, taking into account the change in various parameters of engine operation with spark ignition, were obtained. The obtained results allow to determine the characteristics of heat dissipation and to assess the impact of addition of hydrogen to the natural gas combustion process, that is needed to identify ways of improvement of the combustion process efficiency, including when you change the throttling parameters.

A Unified Geodetic Vertical Velocity Field (UGVVF), Version 1.0

NASA Astrophysics Data System (ADS)

Schmalzle, G.; Wdowinski, S.

2014-12-01

Tectonic motion, volcanic inflation or deflation, as well as oil, gas and water pumping can induce vertical motion. In southern California these signals are inter-mingled. In tectonics, properly identifying regions that are contaminated by other signals can be important when estimating fault slip rates. Until recently vertical deformation rates determined by high precision Global Positioning Systems (GPS) had large uncertainties compared to horizontal components and were rarely used to constrain tectonic models of fault motion. However, many continuously occupied GPS stations have been operating for ten or more years, often delivering uncertainties of ~1 mm/yr or less, providing better constraints for tectonic modeling. Various processing centers produced GPS time series and estimated vertical velocity fields, each with their own set of processing techniques and assumptions. We compare vertical velocity solutions estimated by seven data processing groups as well as two combined solutions (Figure 1). These groups include: Central Washington University (CWU) and New Mexico Institute of Technology (NMT), and their combined solution provided by the Plate Boundary Observatory (PBO) through the UNAVCO website. Also compared are the Jet Propulsion Laboratory (JPL) and Scripps Orbit and Permanent Array Center (SOPAC) and their combined solution provided as part of the NASA MEaSUREs project. Smaller velocity fields included are from Amos et al., 2014, processed at the Nevada Geodetic Laboratory, Shen et al., 2011, processed by UCLA and called the Crustal Motion Map 4.0 (CMM4) dataset, and a new velocity field provided by the University of Miami (UM). Our analysis includes estimating and correcting for systematic vertical velocity and uncertainty differences between groups. Our final product is a unified velocity field that contains the median values of the adjusted velocity fields and their uncertainties. This product will be periodically updated when new velocity fields become available. A database and scripts to access the database will be available through the University of Miami (http://www.geodesy.miami.edu) website. Figure 1. Vertical velocity comparisons between processing groups (blue dots). Red line indicates equal velocities. Weighted Root Mean Square (WRMS) is shown.

Statistics of the cosmic Mach number from numerical simulations of a cold dark matter universe

NASA Technical Reports Server (NTRS)

Suto, Yasushi; Cen, Renyue; Ostriker, Jeremiah P.

1992-01-01

Results are presented of an analysis of the cosmic Mach number, M, the ratio of the streaming velocity, v, to the random velocity dispersion, sigma, of galaxies in a given patch of the universe, which was performed on the basis of hydrodynamical simulations of the cold dark matter scenario. Galaxy formation is modeled by application of detailed physical processes rather than by the ad hoc assumption of 'bias' between dark matter and galaxy fluctuations. The correlation between M and sigma is found to be very weak for both components. No evidence is found for a physical 'velocity bias' in the quantities which appear in the definition of M. Standard cold-dark-matter-dominated universes are in conflict, at a statistically significant level, with the available observation, in that they predict a Mach number considerably lower than is observed.

FINANCIAL ANALYSIS OF CURRENT OPERATIONS OF COLLEGES AND UNIVERSITIES.

ERIC Educational Resources Information Center

SWANSON, JOHN E.; AND OTHERS

TECHNIQUES FOR DEVELOPING FINANCIAL AND RELATED COST-EFFECTIVENESS DATA FOR PUBLIC AND PRIVATELY SUPPORTED AMERICAN COLLEGES AND UNIVERSITIES WERE STUDIED TO FORMULATE PRINCIPLES, PROCEDURES, AND STANDARDS FOR THE ACCUMULATION AND ANALYSES OF CURRENT OPERATING COSTS. AFTER SEPARATE ANALYSES OF INSTITUTIONAL PROCEDURES AND REPORTS, ANALYTIC UNITS…

A Biomechanical Comparison of the Long Snap in Football Between High School and University Football Players.

PubMed

Chizewski, Michael G; Alexander, Marion J L

2015-08-01

Limited previous research was located that examined the technique of the long snap in football. The purpose of the study was to compare the joint movements, joint velocities, and body positions used to perform fast and accurate long snaps in high school (HS) and university (UNI) athletes. Ten HS and 10 UNI subjects were recruited for filming, each performing 10 snaps at a target with the fastest and most accurate trial being selected for subject analysis. Eighty-three variables were measured using Dartfish Team Pro 4.5.2 video analysis software, with statistical analysis performed using Microsoft Excel and SPSS 16.0. Several significant comparisons to long snapping technique between groups were noted during analysis; however, the body position and movement variables at release showed the greatest number of significant differences. The UNI athletes demonstrated significantly higher release velocity and left elbow extension velocity, with significantly lower release height and release angle than the HS group. Total snap time (release time + total flight time) was determined to have the strongest correlation to release velocity for the HS group (r = -0.915) and UNI group (r = -0.918). The study suggests HS long snappers may benefit from less elbow flexion and more knee flexion in the backswing (set position) to increase release velocity. University long snappers may benefit from increased left elbow extension range of motion during force production and decreased shoulder flexion at critical instant to increase long snap release velocity.

Limits and signatures of relativistic spaceflight

NASA Astrophysics Data System (ADS)

Yurtsever, Ulvi; Wilkinson, Steven

2018-01-01

While special relativity imposes an absolute speed limit at the speed of light, our Universe is not empty Minkowski spacetime. The constituents that fill the interstellar/intergalactic vacuum, including the cosmic microwave background photons, impose a lower speed limit on any object travelling at relativistic velocities. Scattering of cosmic microwave photons from an ultra-relativistic object may create radiation with a characteristic signature allowing the detection of such objects at large distances.

Gödel universes in string theory

NASA Astrophysics Data System (ADS)

Barrow, John D.; Dabrowski, Mariusz P.

1998-11-01

We show that homogeneous Gödel spacetimes need not contain closed timelike curves in low-energy-effective string theories. We find exact solutions for the Gödel metric in string theory for the full O(α') action including both dilaton and axion fields. The results are valid for bosonic, heterotic and super-strings. To first order in the inverse string tension α', these solutions display a simple relation between the angular velocity of the Gödel universe, Ω, and the inverse string tension of the form α'=1/Ω2 in the absence of the axion field. The generalization of this relationship is also found when the axion field is present.

Kolmogorov and scalar spectral regimes in numerical turbulence

NASA Technical Reports Server (NTRS)

Kerr, R. M.

1985-01-01

Velocity and passive-scalar spectra for turbulent fields generated by a forced three-dimensional simulation and Taylormicroscale Reynolds numbers up to 83 are shown to have distinct spectral regimes, including a Kolmogorov inertial subrange. Both one- and three-dimensional spectra are shown for comparison with experiment and theory, respectively. When normalized by the Kolmogorov dissipation scales velocity spectra collapse to a single curve and a high-wavenumber bulge is seen. The bulge leads to an artificially high Kolmogorov constant, but is consistent with recent measurements of the velocity spectrum in the dissipation regime and the velocity-derivative skewness. Scalar spectra, when normalized by the Oboukov-Corrsin scales, collapse to curves which depend only on Prandtl number and show a universal inertial-convective subrange, independent of Prandtl number. When normalized by the Batchelor scales, the scalar spectra show a universal dissipation regime which is independent of Prandtl numbers from 0.1 to 1.0. The time development of velocity spectra is illustrated by energy-transfer spectra in which distinct pulses propagate to high wavenumbers.

Photoelectric return-stroke velocity and peak current estimates in natural and triggered lightning

NASA Technical Reports Server (NTRS)

Mach, Douglas M.; Rust, W. David

1989-01-01

Two-dimensional photoelectric return stroke velocities from 130 strokes are presented, including 86 negative natural, 41 negative triggered, one positive triggered, and two positive natural return strokes. For strokes starting near the ground and exceeding 500 m in length, the average velocity is 1.3 + or - 0.3 X 10 to the 8th m/s for natural return strokes and 1.2 + or - 0.3 X 10 to the 8th m/s for triggered return strokes. For strokes with lengths less than 500 m, the average velocities are slightly higher. Using the transmission line model (TLM), the shortest segment one-dimensional return stroke velocity, and either the maximum or plateau electric field, it is shown that natural strokes have a peak current distribution that is lognormal with a median value of 16 kA (maximum E) or 12 kA (plateau E). Triggered lightning has a medium peak current value of 21 kA (maximum E) or 15 kA (plateau E). Correlations are found between TLM peak currents and velocities for triggered and natural subsequent return strokes, but not between TLM peak currents and natural first return stroke velocities.

A molecular theory for nonohmicity of the ion leak across the lipid-bilayer membrane.

PubMed

Fujitani, Y; Bedeaux, D

1997-10-01

The current-voltage relationship of ion leak (i.e., ion transport involving neither special channels nor carriers) across the lipid-bilayer membrane has been observed to be log-linear above the ohmic regime. The coefficient of the linear term has been found to be universal for membranes and penetrants examined. This universality has been explained in terms of diffusion in an external field, where the ion position is described as a Markovian process. Such a diffusion picture can be questioned, however. It is also probable that a leaking ion gets over the potential barrier before experiencing sufficient random collision in the membrane, considering that each ion is surrounded with long lipid molecules aligned almost unidirectionally. As an alternative, we discuss this ion leak in terms of velocity distribution of the ions entering the membrane and density fluctuation of the lipids. We conclude that we can explain the universality without resorting to the diffusion picture.

GPS Measurements for Detecting Aseismic Creeping in the Ismetpasa Region of North Anatolian Fault Zone, Turkey

NASA Astrophysics Data System (ADS)

Ozener, H.; Dogru, A.; Turgut, B.; Yilmaz, O.; Halicioglu, K.; Sabuncu, A.

2010-12-01

In 1972, a six point-network was established by General Directorate of Mapping in Gerede-Ismetpasa. This region is relatively quiet segment of western NAF which is creeping along steadily. This network was surveyed by terrestrial techniques in 1972 and 1973. The Ismetpasa Network was re-measured in 1982 and in 1992 by the Geodesy Working Group of Istanbul Technical University. Although the same network (with five points) was observed in 2002 and 2007 by Zonguldak Karaelmas University applying GPS technique, with 1-hour site occupation, the characteristics of movement has not been detected implicitly. This type of movement still raises a question about the accumulation of tectonic movements in the region. Geodesy Department of Kandilli Observatory and Earthquake Research Institute (KOERI) of Bogazici University has been re-surveyed the network by campaign-based static GPS surveying (10-hour site occupation) since 2005. The GPS velocities data coming from geodynamic GPS networks of the crustal deformation studies and the analysis of repeated geodetic observations give us significant information about the elastic deformation. Therefore, data gathered in this study is processed using GAMIT/GLOBK software and analyzed together with previously collected data to obtain velocity field and strain accumulation in the study area.

Modeling hydraulic and sediment transport processes in white sturgeon spawning habitat on the Kootenai River, Idaho

USGS Publications Warehouse

McDonald, Richard R.; Nelson, Jonathan M.; Vaughn Paragamian,; Barton, Gary J.

2017-01-01

The Kootenai River white sturgeon currently spawn (2005) in an 18-kilometer reach of the Kootenai River, Idaho. Since completion of Libby Dam upstream from the spawning reach, there has been only one successful year of recruitment of juvenile fish. Where successful in other rivers, white sturgeon spawn over clean coarse material of gravel size or larger. The channel substrate in the current spawning reach is composed primarily of sand and some buried gravel; within a few kilometers upstream there is clean gravel. We used a 2-dimensional flow and sediment-transport model and the measured locations of sturgeon spawning from 1994-2002 to gain insight into the paradox between the current spawning location and the absence of suitable substrate. Spatial correlations between spawning locations and the model simulations of velocity and depth indicate the white sturgeon tend to select regions of highest velocity and depth within any river cross-section to spawn. These regions of high velocity and depth are independent of pre- or post-dam flow conditions. A simple sediment-transport simulation suggests that high discharge and relatively long duration flow associated with pre-dam flow events might be sufficient to scour the sandy substrate and expose existing lenses of gravel and cobble as lag deposits in the current spawning reach.

Currents' spatial structure in the Western, Central and South-Eastern Baltic on the base of numerical model and ADCP data analysis

NASA Astrophysics Data System (ADS)

Golenko, Mariya; Golenko, Nikolay

2014-05-01

Numerical modeling of the currents' spatial structure in some regions of the Baltic Sea is performed on the base of POM (Princeton Ocean Model). The calculations were performed under the westerly (most frequent in the Baltic) and north-easterly wind forcings. In the regions adjacent to the Kaliningrad Region's, Polish and Lithuanian coasts these winds generate oppositely directed geostrophic, drift and others types of currents. On the whole these processes can be considered as downwelling and upwelling. Apart from the regions mentioned above the Slupsk Furrow region, which determines the mass and momentum exchange between the Western and Central Baltic, is also considered. During the analysis of currents not only the whole model velocity but also components directed along and across the barotropic geostrophic current velocity are considered. The along geostrophic component for one's turn is separated into the geostrophic current itself and an ageostrophic part. The across geostrophic component is totally ageostrophic. The velocity components directed along and across the geostrophic current approximately describe the velocity components directed along the coast (along isobathes) and from the coast towards the open sea. The suggested approach allowed to present the currents' spatial structures typical for different wind forcings as two maps with the components directed along and across the barotropic geostrophic current velocity. On these maps the areas of the intensive alongshore currents are clearly depicted (for ex. near the base of the Hel Spit, in the region of the Slupsk Sill). The combined analysis of the vectors of the whole and geostrophic velocities allows to reveal the areas where the geostrophic component is significantly strengthened or weakened by the ageostrophic component. Under the westerly wind such currents' features are clearly observed near the end of the Hel Spit and at the southern boarder of the Slupsk Sill, under the north-easterly wind - near the base of the Hel Spit, at the southern boarder of the Slupsk Furrow, near the Curonian Spit (where the relief is bent). On the maps presenting the spatial distributions of the across shore velocities the areas where the mass and momentum transport from the shore to the open sea in the surface layer and vice versa takes place are discriminated. There are also revealed the areas where sharp changes of different velocity components under the wind changes are expected as well as the areas where such changes are expected to be minimal. The model is validated using the field surveys of current velocities by ADCP in the area adjacent to the Kaliningrad region. The comparison of current velocities has shown a close correspondence. In rather wide area the directions and amplitudes of the model and ADCP surface velocities are close, that is additionally confirmed by the comparison of the local vorticity distributions. On the vertical transects of the ADCP current velocity directed across the shoreline the geostrophic jet is clearly pronounced. Its horizontal and vertical scales are in close correspondence with ones of the model jet. At that the more detail calculations which are allowed during the modeling have shown that the geostrophic currents amount to 40-60% (in average) of the whole velocity; two components of the ageostrophic velocity directed along and across the geostrophic velocity are highly variable (from 10 to 60% of the whole velocity). The ageostrophic component directed along the geostrophic current generally strengthens it (up to 20-40% in average and up to 60-70% near the end of the Hel Spit). But in some regions, for example, in the Slupsk Furrow the ageostrophic component slows down the geostrophic current (to 30-40%). In some narrow local areas immediately adjacent to the coast currents directed oppositely to the general quasi geostrophic jet were registered on both field and model data. Before the comparison with the field data these local jets revealed on the model data were considered as improbable. As a result, the comparative analysis of the field and model data led to more detail understanding of dynamic processes in some coastal parts of the Baltic Sea.

The interaction between water currents and salmon swimming behaviour in sea cages.

PubMed

Johansson, David; Laursen, Frida; Fernö, Anders; Fosseidengen, Jan Erik; Klebert, Pascal; Stien, Lars Helge; Vågseth, Tone; Oppedal, Frode

2014-01-01

Positioning of sea cages at sites with high water current velocities expose the fish to a largely unknown environmental challenge. In this study we observed the swimming behaviour of Atlantic salmon (Salmo salar L.) at a commercial farm with tidal currents altering between low, moderate and high velocities. At high current velocities the salmon switched from the traditional circular polarized group structure, seen at low and moderate current velocities, to a group structure where all fish kept stations at fixed positions swimming against the current. This type of group behaviour has not been described in sea cages previously. The structural changes could be explained by a preferred swimming speed of salmon spatially restricted in a cage in combination with a behavioural plasticity of the fish.

Polydisperse particle-driven gravity currents in non-rectangular cross section channels

NASA Astrophysics Data System (ADS)

Zemach, T.

2018-01-01

We consider a high-Reynolds-number gravity current generated by polydisperse suspension of n types of particles distributed in a fluid of density ρi. Each class of particles in suspension has a different settling velocity. The current propagates along a channel of non-rectangular cross section into an ambient fluid of constant density ρa. The bottom and top of the channel are at z = 0, H, and the cross section is given by the quite general form -f1(z) ≤ y ≤ f2(z) for 0 ≤ z ≤ H. The flow is modeled by the one-layer shallow-water equations obtained for the time-dependent motion. We solve the problem by a finite-difference numerical code to present typical height h, velocity u, and mass fractions of particle (concentrations) (ϕ( j), j = 1, …, n) profiles. The runout length of suspensions in channels of power-law cross sections is analytically predicted using a simplified depth-averaged "box" model. We demonstrate that any degree of polydispersivity adds to the runout length of the currents, relative to that of equivalent monodisperse currents with an average settling velocity. The theoretical predictions are supported by the available experimental data. The present approach is a significant generalization of the particle-driven gravity current problem: on the one hand, now the monodisperse current in non-rectangular channels is a particular case of n = 1. On the other hand, the classical formulation of polydisperse currents for a rectangular channel is now just a particular case, f(z) = const., in the wide domain of cross sections covered by this new model.

Experimental analysis on the dynamic wake of an actuator disc undergoing transient loads

NASA Astrophysics Data System (ADS)

Yu, W.; Hong, V. W.; Ferreira, C.; van Kuik, G. A. M.

2017-10-01

The Blade Element Momentum model, which is based on the actuator disc theory, is still the model most used for the design of open rotors. Although derived from steady cases with a fully developed wake, this approach is also applied to unsteady cases, with additional engineering corrections. This work aims to study the impact of an unsteady loading on the wake of an actuator disc. The load and flow of an actuator disc are measured in the Open Jet Facility wind tunnel of Delft University of Technology, for steady and unsteady cases. The velocity and turbulence profiles are characterized in three regions: the inner wake region, the shear layer region and the region outside the wake. For unsteady load cases, the measured velocity field shows a hysteresis effect in relation to the loading, showing differences between the cases when loading is increased and loading is decreased. The flow field also shows a transient response to the step change in loading, with either an overshoot or undershoot of the velocity in relation to the steady-state velocity. In general, a smaller reduced ramp time results in a faster velocity transient, and in turn a larger amplitude of overshoot or undershoot. Time constants analysis shows that the flow reaches the new steady-state slower for load increase than for load decrease; the time constants outside the wake are generally larger than at other radial locations for a given downstream plane; the time constants of measured velocity in the wake show radial dependence.The data are relevant for the validation of numerical models for unsteady actuator discs and wind turbines, and are made available in an open source database (see Appendix).

Filaments from the galaxy distribution and from the velocity field in the local universe

NASA Astrophysics Data System (ADS)

Libeskind, Noam I.; Tempel, Elmo; Hoffman, Yehuda; Tully, R. Brent; Courtois, Hélène

2015-10-01

The cosmic web that characterizes the large-scale structure of the Universe can be quantified by a variety of methods. For example, large redshift surveys can be used in combination with point process algorithms to extract long curvilinear filaments in the galaxy distribution. Alternatively, given a full 3D reconstruction of the velocity field, kinematic techniques can be used to decompose the web into voids, sheets, filaments and knots. In this Letter, we look at how two such algorithms - the Bisous model and the velocity shear web - compare with each other in the local Universe (within 100 Mpc), finding good agreement. This is both remarkable and comforting, given that the two methods are radically different in ideology and applied to completely independent and different data sets. Unsurprisingly, the methods are in better agreement when applied to unbiased and complete data sets, like cosmological simulations, than when applied to observational samples. We conclude that more observational data is needed to improve on these methods, but that both methods are most likely properly tracing the underlying distribution of matter in the Universe.

Conceptual Design of a 100kW Energy Integrated Type Bi-Directional Tidal Current Turbine

NASA Astrophysics Data System (ADS)

Kim, Ki Pyoung; Ahmed, M. Rafiuddin; Lee, Young Ho

2010-06-01

The development of a tidal current turbine that can extract maximum energy from the tidal current will be extremely beneficial for supplying continuous electric power. The present paper presents a conceptual design of a 100kW energy integrated type tidal current turbine for tidal power generation. The instantaneous power density of a flowing fluid incident on an underwater turbine is proportional to the cubic power of current velocity which is approximately 2.5m/s. A cross-flow turbine, provided with a nozzle and a diffuser, is designed and analyzed. The potential advantages of ducted and diffuser-augmented turbines were taken into consideration in order to achieve higher output at a relatively low speed. This study looks at a cross-flow turbine system which is placed in an augmentation channel to generate electricity bi-directionally. The compatibility of this turbine system is verified using a commercial CFD code, ANSYSCFX. This paper presents the results of the numerical analysis in terms of pressure, streaklines, velocity vectors and performance curves for energy integrated type bi-directional tidal current turbine (BDT) with augmentation.

Best Phd thesis Prize: Statistical analysis of ALFALFA galaxies: insights in galaxy

NASA Astrophysics Data System (ADS)

Papastergis, E.

2013-09-01

We use the rich dataset of local universe galaxies detected by the ALFALFA 21cm survey to study the statistical properties of gas-bearing galaxies. In particular, we measure the number density of galaxies as a function of their baryonic mass ("baryonic mass function") and rotational velocity ("velocity width function"), and we characterize their clustering properties ("two-point correlation function"). These statistical distributions are determined by both the properties of dark matter on small scales, as well as by the complex baryonic processes through which galaxies form over cosmic time. We interpret the ALFALFA measurements with the aid of publicly available cosmological N-body simulations and we present some key results related to galaxy formation and small-scale cosmology.

On the linear stability of sheared and magnetized jets without current sheets - relativistic case

NASA Astrophysics Data System (ADS)

Kim, Jinho; Balsara, Dinshaw S.; Lyutikov, Maxim; Komissarov, Serguei S.

2018-03-01

In our prior series of papers, we studied the non-relativistic and relativistic linear stability analysis of magnetized jets that do not have current sheets. In this paper, we extend our analysis to relativistic jets with a velocity shear and a similar current sheet free structure. The jets that we study are realistic because we include a velocity shear, a current sheet free magnetic structure, a relativistic velocity and a realistic thermal pressure so as to achieve overall pressure balance in the unperturbed jet. In order to parametrize the velocity shear, we apply a parabolic profile to the jets' 4-velocity. We find that the velocity shear significantly improves the stability of relativistic magnetized jets. This fact is completely consistent with our prior stability analysis of non-relativistic, sheared jets. The velocity shear mainly plays a role in stabilizing the short wavelength unstable modes for the pinch as well as the kink instability modes. In addition, it also stabilizes the long wavelength fundamental pinch instability mode. We also visualize the pressure fluctuations of each unstable mode to provide a better physical understanding of the enhanced stabilization by the velocity shear. Our overall conclusion is that combining velocity shear with a strong and realistic magnetic field makes relativistic jets even more stable.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barlow, Brad N.; Wade, Richard A.; Liss, Sandra E.

Hot subdwarf stars with F-K main sequence binary companions have been known for decades, but the first orbital periods for such systems were published just recently. Current observations suggest that most have long periods, on the order of years, and that some are or once were hierarchical triple systems. As part of a survey with the Hobby-Eberly Telescope, we have been monitoring the radial velocities of several composite-spectra binaries since 2005 in order to determine their periods, velocities, and eccentricities. Here we present observations and orbital solutions for two of these systems, PG 1449+653 and PG 1701+359. Similar to themore » other sdB+F/G/K binaries with solved orbits, their periods are long, 909 and 734 days, respectively, and pose a challenge to current binary population synthesis models of hot subdwarf stars. Intrigued by their relatively large systemic velocities, we also present a kinematical analysis of both targets and find that neither is likely a member of the Galactic thin disk.« less

Pulsed electromagnetic gas acceleration

NASA Technical Reports Server (NTRS)

Jahn, R. G.; Vonjaskowsky, W. F.; Clark, K. E.

1974-01-01

Detailed measurements of the axial velocity profile and electromagnetic structure of a high power, quasi-steady MPD discharge are used to formulate a gasdynamic model of the acceleration process. Conceptually dividing the accelerated plasma into an inner flow and an outer flow, it is found that more than two-thirds of the total power in the plasma is deposited in the inner flow, accelerating it to an exhaust velocity of 12.5 km/sec. The outer flow, which is accelerated to a velocity of only 6.2 km/sec, appears to provide a current conduction path between the inner flow and the anode. Related cathode studies have shown that the critical current for the onset of terminal voltage fluctuations, which was recently shown to be a function of the cathode area, appears to reach an asymptote for cathodes of very large surface area. Detailed floating potential measurements show that the fluctuations are confined to the vicinity of the cathode and hence reflect a cathode emission process rather than a fundamental limit on MPD performance.

Return stroke velocities and currents using a solid state silicon detector system

NASA Technical Reports Server (NTRS)

Mach, Douglas M.; Rust, W. David

1988-01-01

A small, portable device has been developed to measure return stroke velocities. With the device, velocities from 135 strokes that consist of 92 natural return strokes and 43 triggered return strokes have been analyzed. The average return stroke velocity for longer channels, greater than 500 meters, is 1.2 + or - 0.3 x 10 to the 8th m/s for both natural and triggered return strokes. For shorter channel lengths, less than 500 m, natural lightning has a statistically higher average return stroke velocity of 1.9 + or - 0.7 x 10 to the 8th m/s than triggered lightning with an average return stroke velocity of 1.4 + or - 0.4 x 10 to the 8th m/s. Using the transmission line model of the return stroke, natural lightning has a peak current distribution that is log-normal with a median value of 19 kA. Return stroke velocities and currents were determined for two distant single stroke natural positive cloud-to-ground flashes. The velocities were 1.0 and 1.7 x 10 to the 8th ms/s while the estimated peak current for each positive flash was over 125 kA.

Vertical mass transfer in open channel flow

USGS Publications Warehouse

Jobson, Harvey E.

1968-01-01

The vertical mass transfer coefficient and particle fall velocity were determined in an open channel shear flow. Three dispersants, dye, fine sand and medium sand, were used with each of three flow conditions. The dispersant was injected as a continuous line source across the channel and downstream concentration profiles were measured. From these profiles along with the measured velocity distribution both the vertical mass transfer coefficient and the local particle fall velocity were determined.The effects of secondary currents on the vertical mixing process were discussed. Data was taken and analyzed in such a way as to largely eliminate the effects of these currents on the measured values. A procedure was developed by which the local value of the fall velocity of sand sized particles could be determined in an open channel flow. The fall velocity of the particles in the turbulent flow was always greater than their fall velocity in quiescent water. Reynolds analogy between the transfer of momentum and marked fluid particles was further substantiated. The turbulent Schmidt number was shown to be approximately 1.03 for an open channel flow with a rough boundary. Eulerian turbulence measurements were not sufficient to predict the vertical transfer coefficient. Vertical mixing of sediment is due to three semi-independent processes. These processes are: secondary currents, diffusion due to tangential velocity fluctuations and diffusion due to the curvature of the fluid particle path lines. The diffusion coefficient due to tangential velocity fluctuations is approximately proportional to the transfer coefficient of marked fluid particles. The proportionality constant is less than or equal to 1.0 and decreases with increasing particle size. The diffusion coefficient due to the curvature of the fluid particle path lines is not related to the diffusion coefficient for marked fluid particles and increases with particle size, at least for sediment particles in the sand size range. The total sediment transfer coefficient is equal to the sum of the coefficient due to tangential velocity fluctuations and the coefficient due to the curvature of the fluid particle path lines. A numerical solution to the conservation of mass equation is given. The effects of the transfer coefficient, fall velocity and bed conditions on the predicted concentration profiles are illustrated.

STRING: A new drifter for HF radar validation.

NASA Astrophysics Data System (ADS)

Rammou, Anna-Maria; Zervakis, Vassilis; Bellomo, Lucio; Kokkini, Zoi; Quentin, Celine; Mantovani, Carlo; Kalampokis, Alkiviadis

2015-04-01

High-Frequency radars (HFR) are an effective mean of remotely monitoring sea-surface currents, based on recording the Doppler-shift of radio-waves backscattered on the sea surface. Validation of HFRs' measurements takes place via comparisons either with in-situ Eulerian velocity data (usually obtained by surface current-meters attached on moorings) or to Lagrangian velocity fields (recorded by surface drifters). The most common surface drifter used for this purpose is the CODE-type drifter (Davis, 1985), an industry-standard design to record the vertical average velocity of the upper 1 m layer of the water column. In this work we claim that the observed differences between the HFR-derived velocities and Lagrangian measurements can be attributed not just to the different spatial scales recorded by the above instruments but also due to the fact that while the HFR-derived velocity corresponds to exponentially weighted vertical average of the velocity field from the surface to 1 m depth (Stewart and Joy, 1974) the velocity estimated by the CODE drifters corresponds to boxcar-type weighted vertical average due to the orthogonal shape of the CODE drifters' sails. After analyzing the theoretical behavior of a drifter under the influence of wind and current, we proceed to propose a new design of exponentially-shaped sails for the drogues of CODE-based drifters, so that the HFR-derived velocities and the drifter-based velocities will be directly comparable, regarding the way of vertically averaging the velocity field.The new drifter, codenamed STRING, exhibits identical behavior to the classical CODE design under relatively homogeneous conditions in the upper 1 m layer, however it is expected to follow a significantly different track in conditions of high vertical shear and stratification. Thus, we suggest that the new design is the instrument of choice for validation of HFR installations, as it can be used in all conditions and behaves identically to CODEs when vertical shear is insignificant. Finally, we present results from three experiments using both drifter types in HFR-covered regions of the Eastern Mediterranean. More experiments are planned, incorporating design improvements dictated by the results of the preliminary field tests. This work was held in the framework of the project "Specifically Targeted for Radars INnovative Gauge (STRING)", funded by the Greek-French collaboration programme "Plato".

Vortex clustering and universal scaling laws in two-dimensional quantum turbulence.

PubMed

Skaugen, Audun; Angheluta, Luiza

2016-03-01

We investigate numerically the statistics of quantized vortices in two-dimensional quantum turbulence using the Gross-Pitaevskii equation. We find that a universal -5/3 scaling law in the turbulent energy spectrum is intimately connected with the vortex statistics, such as number fluctuations and vortex velocity, which is also characterized by a similar scaling behavior. The -5/3 scaling law appearing in the power spectrum of vortex number fluctuations is consistent with the scenario of passive advection of isolated vortices by a turbulent superfluid velocity generated by like-signed vortex clusters. The velocity probability distribution of clustered vortices is also sensitive to spatial configurations, and exhibits a power-law tail distribution with a -5/3 exponent.

Counting statistics of tunneling current

NASA Astrophysics Data System (ADS)

Levitov, L. S.; Reznikov, M.

2004-09-01

The form of electron counting statistics of the tunneling current noise in a generic many-body interacting electron system is obtained and universal relations between its different moments are derived. A generalized fluctuation-dissipation theorem providing a relation between current and noise at arbitrary bias-to-temperature ratio eV/kBT is established in the tunneling Hamiltonian approximation. The third correlator of current fluctuations S3 (the skewness of the charge counting distribution) has a universal Schottky-type relation with the current and quasiparticle charge that holds in a wide bias voltage range, both at large and small eV/kBT . The insensitivity of S3 to the Nyquist-Schottky crossover represents an advantage compared to the Schottky formula for the noise power. We discuss the possibility of using the correlator S3 for detecting quasiparticle charge at high temperatures.

Estimating the Velocity and Transport of the East Australian Current using Argo, XBT, and Altimetry

NASA Astrophysics Data System (ADS)

Zilberman, N. V.; Roemmich, D. H.; Gille, S. T.

2016-02-01

Western Boundary Currents (WBCs) are the strongest ocean currents in the subtropics, and constitute the main pathway through which warm water-masses transit from low to mid-latitudes in the subtropical gyres of the Atlantic, Pacific, and Indian Oceans. Heat advection by WBCs has a significant impact on heat storage in subtropical mode waters formation regions and at high latitudes. The possibility that the magnitude of WBCs might change under greenhouse gas forcing has raised significant concerns. Improving our knowledge of WBC circulation is essential to accurately monitor the oceanic heat budget. Because of the narrowness and strong mesoscale variability of WBCs, estimation of WBC velocity and transport places heavy demands on any potential sampling scheme. One strategy for studying WBCs is to combine complementary data sources. High-resolution bathythermograph (HRX) profiles to 800-m have been collected along transects crossing the East Australian Current (EAC) system at 3-month nominal sampling intervals since 1991. EAC transects, with spatial sampling as fine as 10-15 km, are obtained off Brisbane (27°S) and Sydney (34°S), and crossing the related East Auckland Current north of Auckland. Here, HRX profiles collected since 2004 off Brisbane are merged with Argo float profiles and 1000 m trajectory-based velocities to expand HRX shear estimates to 2000-m and to estimate absolute geostrophic velocity and transport. A method for combining altimetric data with HRX and Argo profiles to mitigate temporal aliasing by the HRX transects and to reduce sampling errors in the HRX/Argo datasets is described. The HRX/Argo/altimetry-based estimate of the time-mean poleward alongshore transport of the EAC off Brisbane is 18.3 Sv, with a width of about 180 km, and of which 3.7 Sv recirculates equatorward on a similar spatial scale farther offshore. Geostrophic transport anomalies in the EAC at 27°S show variability of ± 1.3 Sv at interannual time scale related to ENSO. The present calculation is a case study that will be extended to other subtropical WBCs.

Magnetic Reconnection as Revealed by the Magnetospheric Multiscale Mission

NASA Astrophysics Data System (ADS)

Burch, J. L.; Torbert, R. B.; Moore, T. E.; Giles, B. L.; Phan, T.; Le Contel, O.; Webster, J.; Genestreti, K.; Ergun, R.; Chen, L. J.; Wang, S.; Dorelli, J.; Rager, A. C.; Graham, D.; Gershman, D. J.

2017-12-01

The NASA Magnetospheric Multiscale (MMS) mission has completed its prime mission observations and has now entered an extended mission phase. During the two-year prime mission MMS made fundamental advances in our understanding of magnetic reconnection as enabled by its unprecedentedly high-resolution plasma and field measurements, which were made from 4 identical spacecraft in tetrahedral formations ranging down to 7 km. The primary objective of MMS is to understand reconnection at the electron scale, and this objective was accomplished by detailed analysis of 32 electron diffusion regions at the dayside magnetopause and a significant number in the magnetotail, which are still being captured and analyzed. Significant interplay between theory and experiment has occurred throughout the mission leading to the discovery of agyrotropic "crescent-shaped" electron velocity-space distributions, which carry the out-of-plane current; the electron pressure tensor divergence, which produces the reconnection electric field; standing oblique whistler waves, which produce intense dissipation in sub-gyroscale regions near the X-line and electron stagnation point; beam-plasma interactions leading to whistler-mode and Langmuir waves; electromagnetic drift waves leading to corrugated magnetopause current sheets, and numerous other new reconnection-related phenomena. In this talk the many new aspects of reconnection discovered by MMS will be placed into context and used to evaluate our current level of understanding of this universally important space plasma phenomenon.

Rippability Assessment of Weathered Sedimentary Rock Mass using Seismic Refraction Methods

NASA Astrophysics Data System (ADS)

Ismail, M. A. M.; Kumar, N. S.; Abidin, M. H. Z.; Madun, A.

2018-04-01

Rippability or ease of excavation in sedimentary rocks is a significant aspect of the preliminary work of any civil engineering project. Rippability assessment was performed in this study to select an available ripping machine to rip off earth materials using the seismic velocity chart provided by Caterpillar. The research area is located at the proposed construction site for the development of a water reservoir and related infrastructure in Kampus Pauh Putra, Universiti Malaysia Perlis. The research was aimed at obtaining seismic velocity, P-wave (Vp) using a seismic refraction method to produce a 2D tomography model. A 2D seismic model was used to delineate the layers into the velocity profile. The conventional geotechnical method of using a borehole was integrated with the seismic velocity method to provide appropriate correlation. The correlated data can be used to categorize machineries for excavation activities based on the available systematic analysis procedure to predict rock rippability. The seismic velocity profile obtained was used to interpret rock layers within the ranges labelled as rippable, marginal, and non-rippable. Based on the seismic velocity method the site can be classified into loose sand stone to moderately weathered rock. Laboratory test results shows that the site’s rock material falls between low strength and high strength. Results suggest that Caterpillar’s smallest ripper, namely, D8R, can successfully excavate materials based on the test results integration from seismic velocity method and laboratory test.

Cosmic web and environmental dependence of screening: Vainshtein vs. chameleon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Falck, Bridget; Koyama, Kazuya; Zhao, Gong-Bo, E-mail: bridget.falck@port.ac.uk, E-mail: kazuya.koyama@port.ac.uk, E-mail: gong-bo.zhao@port.ac.uk

Theories which modify general relativity to explain the accelerated expansion of the Universe often use screening mechanisms to satisfy constraints on Solar System scales. We investigate the effects of the cosmic web and the local environmental density of dark matter halos on the screening properties of the Vainshtein and chameleon screening mechanisms. We compare the cosmic web morphology of dark matter particles, mass functions of dark matter halos, mass and radial dependence of screening, velocity dispersions and peculiar velocities, and environmental dependence of screening mechanisms in f(R) and nDGP models. Using the ORIGAMI cosmic web identification routine we find thatmore » the Vainshtein mechanism depends on the cosmic web morphology of dark matter particles, since these are defined according to the dimensionality of their collapse, while the chameleon mechanism shows no morphology dependence. The chameleon screening of halos and their velocity dispersions depend on halo mass, and small halos and subhalos can be environmentally screened in the chameleon mechanism. On the other hand, the screening of halos in the Vainshtein mechanism does not depend on mass nor environment, and their velocity dispersions are suppressed. The peculiar velocities of halos in the Vainshtein mechanism are enhanced because screened objects can still feel the fifth force generated by external fields, while peculiar velocities of chameleon halos are suppressed when the halo centers are screened.« less

Development and application of a standardized flow measurement uncertainty analysis framework to various low-head short-converging intake types across the United States federal hydropower fleet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Brennan T

2015-01-01

Turbine discharges at low-head short converging intakes are difficult to measure accurately. The proximity of the measurement section to the intake entrance admits large uncertainties related to asymmetry of the velocity profile, swirl, and turbulence. Existing turbine performance codes [10, 24] do not address this special case and published literature is largely silent on rigorous evaluation of uncertainties associated with this measurement context. The American Society of Mechanical Engineers (ASME) Committee investigated the use of Acoustic transit time (ATT), Acoustic scintillation (AS), and Current meter (CM) in a short converging intake at the Kootenay Canal Generating Station in 2009. Basedmore » on their findings, a standardized uncertainty analysis (UA) framework for velocity-area method (specifically for CM measurements) is presented in this paper given the fact that CM is still the most fundamental and common type of measurement system. Typical sources of systematic and random errors associated with CM measurements are investigated, and the major sources of uncertainties associated with turbulence and velocity fluctuations, numerical velocity integration technique (bi-cubic spline), and the number and placement of current meters are being considered for an evaluation. Since the velocity measurements in a short converging intake are associated with complex nonlinear and time varying uncertainties (e.g., Reynolds stress in fluid dynamics), simply applying the law of propagation of uncertainty is known to overestimate the measurement variance while the Monte Carlo method does not. Therefore, a pseudo-Monte Carlo simulation method (random flow generation technique [8]) which was initially developed for the purpose of establishing upstream or initial conditions in the Large-Eddy Simulation (LES) and the Direct Numerical Simulation (DNS) is used to statistically determine uncertainties associated with turbulence and velocity fluctuations. This technique is then combined with a bi-cubic spline interpolation method which converts point velocities into a continuous velocity distribution over the measurement domain. Subsequently the number and placement of current meters are simulated to investigate the accuracy of the estimated flow rates using the numerical velocity-area integration method outlined in ISO 3354 [12]. The authors herein consider that statistics on generated flow rates processed with bi-cubic interpolation and sensor simulations are the combined uncertainties which already accounted for the effects of all those three uncertainty sources. A preliminary analysis based on the current meter data obtained through an upgrade acceptance test of a single unit located in a mainstem plant has been presented.« less

Impact of current speed on mass flux to a model flexible seagrass blade

NASA Astrophysics Data System (ADS)

Lei, Jiarui; Nepf, Heidi

2016-07-01

Seagrass and other freshwater macrophytes can acquire nutrients from surrounding water through their blades. This flux may depend on the current speed (U), which can influence both the posture of flexible blades (reconfiguration) and the thickness of the flux-limiting diffusive layer. The impact of current speed (U) on mass flux to flexible blades of model seagrass was studied through a combination of laboratory flume experiments, numerical modeling and theory. Model seagrass blades were constructed from low-density polyethylene (LDPE), and 1, 2-dichlorobenzene was used as a tracer chemical. The tracer mass accumulation in the blades was measured at different unidirectional current speeds. A numerical model was used to estimate the transfer velocity (K) by fitting the measured mass uptake to a one-dimensional diffusion model. The measured transfer velocity was compared to predictions based on laminar and turbulent boundary layers developing over a flat plate parallel to flow, for which K∝U0.5 and ∝U, respectively. The degree of blade reconfiguration depended on the dimensionless Cauchy number, Ca, which is a function of both the blade stiffness and flow velocity. For large Ca, the majority of the blade was parallel to the flow, and the measured transfer velocity agreed with laminar boundary layer theory, K∝U0.5. For small Ca, the model blades remained upright, and the flux to the blade was diminished relative to the flat-plate model. A meadow-scale analysis suggests that the mass exchange at the blade scale may control the uptake at the meadow scale.

The Durham/UKST Galaxy Redshift Survey - VII. Redshift-space distortions in the power spectrum

NASA Astrophysics Data System (ADS)

Outram, P. J.; Hoyle, Fiona; Shanks, T.

2001-03-01

We investigate the effect of redshift-space distortions in the power spectrum parallel and perpendicular to the line of sight of the observer, PS(k∥,k⊥), using the optically selected Durham/UKST Galaxy Redshift Survey. On small, non-linear scales anisotropy in the power spectrum is dominated by the galaxy velocity dispersion; the `Finger of God' effect. On larger, linear scales coherent peculiar velocities caused by the infall of galaxies into overdense regions are the main cause of anisotropy. According to gravitational instability theory these distortions depend only on the density and bias parameters via β~Ωm0.6b. Geometrical distortions also occur if the wrong cosmology is assumed, although these would be relatively small given the low redshift of the survey. To quantify these effects, we assume the real-space power spectrum of the APM Galaxy Survey, and fit a simple model for the redshift-space and geometrical distortions. Assuming a flat Ωm=1 universe, we find values for the one-dimensional pairwise velocity dispersion of σp=410+/-170kms-1, and β=0.38+/-0.17. An open Ωm=0.3, and a flat Ωm=0.3, ΩΛ=0.7 universe yield σp=420kms-1, β=0.40, and σp=440kms-1, β=0.45, respectively, with comparable errors. These results are consistent with estimates using the two-point galaxy correlation function, ξ(σ,π), and favour either a low-density universe with Ωm~0.3 if galaxies trace the underlying mass distribution, or a bias factor of b~2.5 if Ωm=1.

Magnetic diffusion and flare energy buildup

NASA Technical Reports Server (NTRS)

Wu, S. T.; Yin, C. L.; Yang, W.-H.

1992-01-01

Photospheric motion shears or twists solar magnetic fields to increase magnetic energy in the corona, because this process may change a current-free state of a coronal field to force-free states which carry electric current. This paper analyzes both linear and nonlinear 2D force-free magnetic field models and derives relations of magnetic energy buildup with photospheric velocity field. When realistic data of solar magnetic field and photospheric velocity field are used, it is found that 3-4 hours are needed to create an amount of free magnetic energy which is of the order of the current-free field energy. Furthermore, the paper studies situations in which finite magnetic diffusivities in photospheric plasma are introduced. The shearing motion increases coronal magnetic energy, while the photospheric diffusion reduces the energy. The variation of magnetic energy in the coronal region, then, depends on which process dominates.

Why there is no Newtonian backreaction

NASA Astrophysics Data System (ADS)

Kaiser, Nick

2017-07-01

In the conventional framework for cosmological dynamics, the scalefactor a(t) is assumed to obey the 'background' Friedmann equation for a perfectly homogeneous universe while particles move according to equations of motions driven by the gravity of the density fluctuations. It has recently been suggested that the emergence of structure modifies the evolution of a(t) via Newtonian (or 'kinematic') backreaction and that this may avoid the need for dark energy. Here, we point out that the conventional system of equations is exact in Newtonian gravity and there is no approximation in the use of the homogeneous universe equation for a(t). The recently proposed modification of Rácz et al. does not reduce to Newtonian gravity in the limit of low velocities. We discuss the relation of this to the 'generalized Friedmann equation' of Buchert and Ehlers. These are quite different things; their formula describes individual regions and is obtained under the restrictive assumption that the matter behaves like a pressure-free fluid, whereas our result is exact for collisionless dynamics and is an auxiliary relation appearing in the structure equations. We use the symmetry of the general velocity autocorrelation function to show how Buchert's Q tends very rapidly to zero for large volume and that this does not simply arise 'by construction' through the adoption of periodic boundary conditions as has been claimed. We conclude that, to the extent that Newtonian gravity accurately describes the low-z universe, there is no backreaction of structure on a(t) and that the need for dark energy cannot be avoided in this way.

Hybrid Practices? Contributions to the Debate on the Mutation of Science and University

ERIC Educational Resources Information Center

Tuunainen, Juha

2005-01-01

This article reflects on current debate over transformations of scientific research and universities. Four well-known mutation theories (Mode-2 knowledge production, triple helix of university-industry-government relations, academic capitalism and enterprise university), and their recent critiques, are reviewed. It is suggested that a better…

Near-field Oblique Remote Sensing of Stream Water-surface Elevation, Slope, and Surface Velocity

NASA Astrophysics Data System (ADS)

Minear, J. T.; Kinzel, P. J.; Nelson, J. M.; McDonald, R.; Wright, S. A.

2014-12-01

A major challenge for estimating discharges during flood events or in steep channels is the difficulty and hazard inherent in obtaining in-stream measurements. One possible solution is to use near-field remote sensing to obtain simultaneous water-surface elevations, slope, and surface velocities. In this test case, we utilized Terrestrial Laser Scanning (TLS) to remotely measure water-surface elevations and slope in combination with surface velocities estimated from particle image velocimetry (PIV) obtained by video-camera and/or infrared camera. We tested this method at several sites in New Mexico and Colorado using independent validation data consisting of in-channel measurements from survey-grade GPS and Acoustic Doppler Current Profiler (ADCP) instruments. Preliminary results indicate that for relatively turbid or steep streams, TLS collects tens of thousands of water-surface elevations and slopes in minutes, much faster than conventional means and at relatively high precision, at least as good as continuous survey-grade GPS measurements. Estimated surface velocities from this technique are within 15% of measured velocity magnitudes and within 10 degrees from the measured velocity direction (using extrapolation from the shallowest bin of the ADCP measurements). Accurately aligning the PIV results into Cartesian coordinates appears to be one of the main sources of error, primarily due to the sensitivity at these shallow oblique look angles and the low numbers of stationary objects for rectification. Combining remotely-sensed water-surface elevations, slope, and surface velocities produces simultaneous velocity measurements from a large number of locations in the channel and is more spatially extensive than traditional velocity measurements. These factors make this technique useful for improving estimates of flow measurements during flood flows and in steep channels while also decreasing the difficulty and hazard associated with making measurements in these conditions.

Astrometry, Radial Velocity, and Photometry: The HD 128311 System Remixed with Data from HST, HET, and APT

NASA Astrophysics Data System (ADS)

McArthur, Barbara. E.; Benedict, G. Fritz; Henry, Gregory W.; Hatzes, Artie; Cochran, William D.; Harrison, Tom E.; Johns-Krull, Chris; Nelan, Ed

2014-11-01

We have used high-cadence radial velocity measurements from the Hobby-Eberly Telescope with published velocities from the Lick 3 m Shane Telescope, combined with astrometric data from the Hubble Space Telescope (HST) Fine Guidance Sensors to refine the orbital parameters of the HD 128311 system, and determine an inclination of 55.°95 ± 14.°55 and true mass of 3.789 +0.924 -0.432 M JUP for HD 128311 c. The combined radial velocity data also reveal a short period signal which could indicate a third planet in the system with an Msin i of 0.133 ± 0.005 M JUP or stellar phenomena. Photometry from the T12 0.8 m automatic photometric telescope at the Fairborn Observatory and HST are used to determine a photometric period close to, but not within the errors of the radial velocity signal. We performed a cross-correlation bisector analysis of the radial velocity data to look for correlations with the photometric period and found none. Dynamical integrations of the proposed system show long-term stability with the new orbital parameters of over 10 million years. Our new orbital elements do not support the claims of HD 128311 b and c being in mean motion resonance. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen, and observations with T12 0.8 m automatic photoelectric telescope (APT) at Fairborn Observatory.

Time evolving bed shear stress due the passage of gravity currents estimated with ADVP velocity measurements

NASA Astrophysics Data System (ADS)

Zordan, Jessica; Schleiss, Anton J.; Franca, Mário J.

2016-04-01

Density or gravity currents are geophysical flows driven by density gradients between two contacting fluids. The physical trigger mechanism of these phenomena lays in the density differences which may be caused by differences in the temperature, dissolved substances or concentration of suspended sediments. Saline density currents are capable to entrain bed sediments inducing signatures in the bottom of sedimentary basins. Herein, saline density currents are reproduced in laboratory over a movable bed. The experimental channel is of the lock-exchange type, it is 7.5 m long and 0.3 m wide, divided into two sections of comparable volumes by a sliding gate. An upstream reach serves as a head tank for the dense mixture; the current propagates through a downstream reach where the main measurements are made. Downstream of the channel a tank exist to absorb the reflection of the current and thus artifacts due to the limited length of the channel. High performance thermoplastic polyurethane simulating fine sediments forms the movable bed. Measures of 3D instantaneous velocities will be made with the use of the non-intrusive technique of the ADV (Acoustic Doppler Current Profiler). With the velocity measurements, the evolution in time of the channel-bed shear stress due the passage of gravity currents is estimated. This is in turn related to the observed erosion and to such parameters determinant for the dynamics of the current as initial density difference, lock length and channel slope. This work was funded by the ITN-Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7-PEOPLE-2013-ITN under REA grant agreement n_607394-SEDITRANS.

Use of acoustic backscatter and vertical velocity to estimate concentration and dynamics of suspended solids in Upper Klamath Lake, south-central Oregon: Implications for Aphanizomenon flos-aquae

USGS Publications Warehouse

Wood, Tamara M.; Gartner, Jeffrey W.

2010-01-01

Vertical velocity and acoustic backscatter measurements by acoustic Doppler current profilers were used to determine seasonal, subseasonal (days to weeks), and diel variation in suspended solids in a freshwater lake where massive cyanobacterial blooms occur annually. During the growing season, the suspended material in the lake is dominated by the buoyancy-regulating cyanobacteria, Aphanizomenon flos-aquae. Measured variables (water velocity, relative backscatter [RB], wind speed, and air and water temperatures) were averaged over the deployment season at each sample time of day to determine average diel cycles. Phase shifts between diel cycles in RB and diel cycles in wind speed, vertical water temperature differences (delta T(degree)), and horizontal current speeds were found by determining the lead or lag that maximized the linear correlation between the respective diel cycles. Diel cycles in RB were more in phase with delta T(degree) cycles, and, to a lesser extent, wind cycles, than to water current cycles but were out of phase with the cycle that would be expected if the vertical movement of buoyant cyanobacteria colonies was controlled primarily by light. Clear evidence of a diel cycle in vertical velocity was found only at the two deepest sites in the lake. Cycles of vertical velocity, where present, were out of phase with expected vertical motion of cyanobacterial colonies based on the theoretical cycle for light-driven vertical movement. This suggests that water column stability and turbulence were more important factors in controlling vertical distribution of colonies than light. Variations at subseasonal time scales were determined by filtering data to pass periods between 1.2 and 15 days. At subseasonal time scales, correlations between RB and currents or air temperature were consistent with increased concentration of cyanobacterial colonies near the surface when water column stability increased (higher air temperatures or weaker currents) and dispersal of colonies throughout the water column when the water column mixed more easily. RB was used to estimate suspended solids concentrations (SSC). Correlations of depth-integrated SSC with currents or air temperatures suggest that depth-integrated water column mass decreased under conditions of greater water column stability and weaker currents. Results suggest that the use of measured vertical velocity and acoustic backscatter as a surrogate for suspended material has the potential to contribute significant additional insight into dynamics of Aphanizomenon flos-aquae colonies in Upper Klamath Lake, south-central Oregon.

Early Life Processes, Endocrine Mediators and Number of Susceptible Cells in Relation to Breast Cancer Risk

DTIC Science & Technology

2007-04-01

Medicine, Karolinska Institutet / Karolinska University Hospital, SE-171 76 Stockholm, Sweden. Timetable of research accomplishments of CP1 as outlined...velocity with mammographic patterns in adult life” CP2 PI: Prof. Per Hall, Dept. of Medical Epidemiology and Biostatistics, Karolinska Institutet ...Medical Epidemiology and Biostatistics, Karolinska Institutet , P.O. Box 281, SE-171 77 Stockholm, Sweden Timetable of research accomplishments of CP3 as

Global Ocean Vertical Velocity From a Dynamically Consistent Ocean State Estimate

NASA Astrophysics Data System (ADS)

Liang, Xinfeng; Spall, Michael; Wunsch, Carl

2017-10-01

Estimates of the global ocean vertical velocities (Eulerian, eddy-induced, and residual) from a dynamically consistent and data-constrained ocean state estimate are presented and analyzed. Conventional patterns of vertical velocity, Ekman pumping, appear in the upper ocean, with topographic dominance at depth. Intense and vertically coherent upwelling and downwelling occur in the Southern Ocean, which are likely due to the interaction of the Antarctic Circumpolar Current and large-scale topographic features and are generally canceled out in the conventional zonally averaged results. These "elevators" at high latitudes connect the upper to the deep and abyssal oceans and working together with isopycnal mixing are likely a mechanism, in addition to the formation of deep and abyssal waters, for fast responses of the deep and abyssal oceans to the changing climate. Also, Eulerian and parameterized eddy-induced components are of opposite signs in numerous regions around the global ocean, particularly in the ocean interior away from surface and bottom. Nevertheless, residual vertical velocity is primarily determined by the Eulerian component, and related to winds and large-scale topographic features. The current estimates of vertical velocities can serve as a useful reference for investigating the vertical exchange of ocean properties and tracers, and its complex spatial structure ultimately permits regional tests of basic oceanographic concepts such as Sverdrup balance and coastal upwelling/downwelling.

Ion streaming instabilities with application to collisionless shock wave structure

NASA Technical Reports Server (NTRS)

Golden, K. I.; Linson, L. M.; Mani, S. A.

1973-01-01

The electromagnetic dispersion relation for two counterstreaming ion beams of arbitrary relative strength flowing parallel to a dc magnetic field is derived. The beams flow through a stationary electron background and the dispersion relation in the fluid approximation is unaffected by the electron thermal pressure. The dispersion relation is solved with a zero net current condition applied and the regions of instability in the k-U space (U is the relative velocity between the two ion beams) are presented. The parameters are then chosen to be applicable for parallel shocks. It was found that unstable waves with zero group velocity in the shock frame can exist near the leading edge of the shock for upstream Alfven Mach numbers greater than 5.5. It is suggested that this mechanism could generate sufficient turbulence within the shock layer to scatter the incoming ions and create the required dissipation for intermediate strength shocks.

Searching for Planets in the Hyades. V. Limits on Planet Detection in the Presence of Stellar Activity

NASA Astrophysics Data System (ADS)

Paulson, Diane B.; Cochran, William D.; Hatzes, Artie P.

2004-06-01

We present the results of a radial velocity survey of a sample of Hyades stars and discuss the effects of stellar activity on radial velocity measurements. The level of radial velocity scatter due to rotational modulation of stellar surface features for the Hyades is in agreement with the 1997 predictions of Saar & Donahue-the maximum radial velocity rms of up to ~50 m s-1, with an average rms of ~16 m s-1. In this sample of 94 stars we find one new binary, two stars with linear trends indicative of binary companions, and no close-in giant planets. We discuss the limits on extrasolar planet detection in the Hyades and the constraints imposed on radial velocity surveys of young stars. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration (NASA). The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Additional data were obtained with the Hobby-Eberly Telescope, which is operated by McDonald Observatory on behalf of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

Analysis and Comparison with DNS of a Stochastic Model for the Relative Motion of High-Stokes-Number Particles in Isotropic Turbulence

NASA Astrophysics Data System (ADS)

Dhariwal, Rohit; Rani, Sarma; Koch, Donald

2015-11-01

In an earlier work, Rani, Dhariwal, and Koch (JFM, Vol. 756, 2014) developed an analytical closure for the diffusion current in the PDF transport equation describing the relative motion of high-Stokes-number particle pairs in isotropic turbulence. In this study, an improved closure was developed for the diffusion coefficient, such that the motion of the particle-pair center of mass is taken into account. Using the earlier and the new analytical closures, Langevin simulations of pair relative motion were performed for four particle Stokes numbers, Stη = 10 , 20 , 40 , 80 and at two Taylor micro-scale Reynolds numbers Reλ = 76 , 131 . Detailed comparisons of the analytical model predictions with those of DNS were undertaken. It is seen that the pair relative motion statistics obtained from the improved theory show excellent agreement with the DNS statistics. The radial distribution functions (RDFs), and relative velocity PDFs obtained from the improved-closure-based Langevin simulations are found to be in very good agreement with those from DNS. It was found that the RDFs and relative velocity RMS increased with Reλ for all Stη . The collision kernel also increased strongly with Reλ , since it depended on the RDF and the radial relative velocities.

Two-Dimensional Analysis of Conical Pulsed Inductive Plasma Thruster Performance

NASA Technical Reports Server (NTRS)

Hallock, A. K.; Polzin, K. A.; Emsellem, G. D.

2011-01-01

A model of the maximum achievable exhaust velocity of a conical theta pinch pulsed inductive thruster is presented. A semi-empirical formula relating coil inductance to both axial and radial current sheet location is developed and incorporated into a circuit model coupled to a momentum equation to evaluate the effect of coil geometry on the axial directed kinetic energy of the exhaust. Inductance measurements as a function of the axial and radial displacement of simulated current sheets from four coils of different geometries are t to a two-dimensional expression to allow the calculation of the Lorentz force at any relevant averaged current sheet location. This relation for two-dimensional inductance, along with an estimate of the maximum possible change in gas-dynamic pressure as the current sheet accelerates into downstream propellant, enables the expansion of a one-dimensional circuit model to two dimensions. The results of this two-dimensional model indicate that radial current sheet motion acts to rapidly decouple the current sheet from the driving coil, leading to losses in axial kinetic energy 10-50 times larger than estimations of the maximum available energy in the compressed propellant. The decreased available energy in the compressed propellant as compared to that of other inductive plasma propulsion concepts suggests that a recovery in the directed axial kinetic energy of the exhaust is unlikely, and that radial compression of the current sheet leads to a loss in exhaust velocity for the operating conditions considered here.

An experimental study of subaqueous slipface deposition.

USGS Publications Warehouse

Hunter, R.E.; Kocurek, G.

1986-01-01

A flume study indicates that grainflow on slipfaces accounts for most cross-strata formed in unidirectional, shallow-water flows. The slipfaces studied were on small megaripples and delta-like steps (0.06-0.28 m high). During intermittent avalanching, at relatively low flow velocities, periods between avalanches were marked by grainfall onto the slipface, the intensity of which was greatest near the brink of the slipface and increased with current velocity. The lee eddy proved very significant in slipface processes by redistributing grainfall sediments and both promoting and impeding grainflow. -from Authors

Preliminary Seismic Velocity Structure Results from Ambient Noise and Teleseismic Tomography: Laguna del Maule Volcanic Field, Chile

NASA Astrophysics Data System (ADS)

Wespestad, C.; Thurber, C. H.; Zeng, X.; Bennington, N. L.; Cardona, C.; Singer, B. S.

2016-12-01

Laguna del Maule Volcanic Field is a large, restless, rhyolitic system in the Southern Andes that is being heavily studied through several methods, including seismology, by a collaborative team of research institutions. A temporary array of 52 seismometers from OVDAS (the Southern Andean Volcano Observatory), PASSCAL (Portable Array Seismic Studies of the Continental Lithosphere), and the University of Wisconsin-Madison was used to collect the 1.3 years worth of data for this preliminary study. Ambient noise tomography uses surface wave dispersion data obtained from noise correlation functions (NCFs) between pairs of seismic stations, with one of each pair acting as a virtual source, in order to image the velocity structure in 3-D. NCFs were computed for hour-long time windows, and the final NCFs were obtained with phase-weighted stacking. The Frequency-Time Analysis technique was then utilized to measure group velocity between station pairs. NCFs were also analyzed to detect temporal changes in seismic velocity related to magmatic activity at the volcano. With the surface wave data from ambient noise, our small array aperture limits our modeling to the upper crust, so we employed teleseismic tomography to study deeper structures. For picking teleseismic arrivals, we tested two different correlation and stacking programs, which utilize adaptive stacking and multi-channel cross-correlation, to get relative arrival time data for a set of high quality events. Selected earthquakes were larger than magnitude 5 and between 30 and 95 degrees away from the center of the array. Stations that consistently show late arrivals may have a low velocity body beneath them, more clearly visualized via a 3-D tomographic model. Initial results from the two tomography methods indicate the presence of low-velocity zones at several depths. Better resolved velocity models will be developed as more data are acquired.

Currently available medical engineering degrees in the UK. Part 1: Undergraduate degrees.

PubMed

Joyce, T

2009-05-01

This paper reviews mechanical-engineering-based medical engineering degrees which are currently provided at undergraduate level in the UK. At present there are 14 undergraduate degree programmes in medical engineering, offered by the University of Bath, University of Birmingham, University of Bradford, Cardiff University, University of Hull, Imperial College London, University of Leeds, University of Nottingham, University of Oxford, Queen Mary University of London, University of Sheffield, University of Southampton, University of Surrey, and Swansea University. All these undergraduate courses are delivered on a full-time basis, both 3 year BEng and 4 year MEng degrees. Half of the 14 degree courses share a core first 2 years with a mechanical engineering stream. The other seven programmes include medical engineering modules earlier in their degrees. Within the courses, a very wide range of medical-engineering-related modules are offered, although more common modules include biomaterials, biomechanics, and anatomy and physiology.

Dynamic stability during running gait termination: Predictors for successful control of forward momentum in children and adults.

PubMed

Cesar, Guilherme M; Sigward, Susan M

2016-08-01

Reported differences between children and adults with respect to COM horizontal and vertical position to maintain dynamic stability during running deceleration suggest that this relationship may not be as important in children. This study challenged the current dynamic stability paradigm by determining the features of whole body posture that predicted forward velocity and momentum of running gait termination in adults and children. Sixteen adults and 15 children ran as fast as possible and stopped at pre-determined location. Separate regression analyses determined whether COM posterior and vertical positions and functional limb length (distance between COM and stance foot) predicted velocity and momentum for adults and children. COM posterior position was the strongest predictor of forward velocity and momentum in both groups supporting the previously established relationship during slower tasks. COM vertical position also predicted momentum in children, not adults. Higher COM position in children was related to greater momentum; consistent with previously reported differences between children and adults in COM position across running deceleration. COM vertical position was related to momentum but not velocity in children suggesting that strategies used to terminate running may be driven by demands imposed not just by velocity, but also the mass being decelerated. Copyright © 2016. Published by Elsevier B.V.

Past, Present and Future

NASA Astrophysics Data System (ADS)

Castellano, Doc

2001-05-01

'Back to the Future'! Who achieved What, When, Why and How is presented. A chronological Review from Galileo's fundamental concepts to today. An analysis of the validity of said concepts. Especially a critical analysis of Einstein's opinion that the velocity of c is the 'ultimate' Universal velocity. --- The Author presents ``21st C TMP''; per the PhD company's analysis of our dynamic Universe. Namely, X' = X - vt/[square root 1 - (v squared/C squared)]. Capital C equal to or GREATER than c, Einstein's 'ultimate' velocity. --- And " MAPHICS ", (TM); MA from MAthematics; and PHICS from PHysICS. " MAPHICS " the ``Omega Science'' that combines the Philosophy of Mathematics with the Philososphy of Physics into ONE Philosophy. `` MAPHICS '' (TM) is presented and explained. Its claimed speed and power of infinite resolution is demonstrated.

A radial velocity survey of the open cluster IC 4665

NASA Technical Reports Server (NTRS)

Prosser, Charles F.; Giampapa, Mark S.

1994-01-01

A radial velocity survey of the open cluster IC 4665 is reported for a group of candidate members previously identified on the basis of proper motion and photometry. Of those candidates observed, 20 out of 42 have radial velocities consistent with membership; these cluster members populate the F5-K0 dwarf region and represent the first relatively conclusive membership determinations for such solar-type stars in IC 4665. Three new spectroscopic binary members of the cluster have been identified. Rotational velocities have also been derived; the v sin i distribution among IC 4665 members reveals that most apparent G dwarf members of IC 4665 are seen to exhibit substantial rotation (v sin i greater than 10 km/s). When compared to evolutionary isochrones, the current list of intermediate-mass members appears to support earlier suggestions that IC 4665 has an age comparable to the Pleiades.

The magnetically driven plasma jet produces a pressure of 33 GPa on PTS

NASA Astrophysics Data System (ADS)

Xu, Qiang; Dan, Jiakun; Wang, Guilin; Guo, Shuai; Zhang, Siqun; Cai, Hongchun; Ren, Xiao; Wang, Kunlun; Zhou, Shaotong; Zhang, Zhaohui; Huang, Xianbin

2017-01-01

We report on experiments in which a magnetically driven plasma jet was used to hit a 500 μm thick planar aluminum target. The plasma jet was produced by using a 50 μm thick aluminum radial foil, which was subjected to 4 MA, 90 ns rising time current on the primary test stand pulsed power facility. The subsequent magnetic bubbles propagate with radial velocity reaching 200 km/s and an axial velocity of 230 km/s. After the plasma knocks onto the target, a shock forms in the target. When the shock gets to the backside of the target, we measure the velocity of the moving surface using dual laser heterodyne velocimetry. By using the Hugoniot relations, we know that the plasma jet produced a pressure of 33 GPa. According to the measured pressure and the velocity of the plasma jet, the density of the jet can be also roughly estimated.

A New Method for Raising Opening Velocity of Electromagnetic Actuated Vacuum Circuit Breaker

NASA Astrophysics Data System (ADS)

Tsukima, Mitsuru; Takeuchi, Toshie; Koyama, Kenichi; Yoshiyasu, Hajimu

Recently an electromagnetic actuator has been widely used as an operating mechanism for the vacuum circuit breaker (VCB). The opening velocity of the contact is supposed to be strongly related with current interruption performance. This paper presents a simple and new technique that raises opening velocity of the electromagnetic actuated VCB. In order to investigate this reason, we built a numerical simulator that predicts the dynamic characteristics of the VCB contact. It takes into account of the magnetic behavior in the actuator and is also coupled with the external control circuit. According to this simulation, it is shown that it is originated from the sharp rise in the electromagnetic thrust force due to the selective saturation of the magnetic yoke. As the result of our experiments, by this technique the opening velocity was verified to be 1.5 times faster than by the conventional way.

Velocity profile, water-surface slope, and bed-material size for selected streams in Colorado

USGS Publications Warehouse

Marchand, J.P.; Jarrett, R.D.; Jones, L.L.

1984-01-01

Existing methods for determining the mean velocity in a vertical sampling section do not address the conditions present in high-gradient, shallow-depth streams common to mountainous regions such as Colorado. The report presents velocity-profile data that were collected for 11 streamflow-gaging stations in Colorado using both a standard Price type AA current meter and a prototype Price Model PAA current meter. Computational results are compiled that will enable mean velocities calculated from measurements by the two current meters to be compared with each other and with existing methods for determining mean velocity. Water-surface slope, bed-material size, and flow-characteristic data for the 11 sites studied also are presented. (USGS)

Determination of Tsunami Warning Criteria for Current Velocity

NASA Astrophysics Data System (ADS)

Chen, R.; Wang, D.

2015-12-01

Present Tsunami warning issuance largely depends on an event's predicted wave height and inundation depth. Specifically, a warning is issued if the on-shore wave height is greater than 1m. This project examines whether any consideration should be given to current velocity. We apply the idea of force balance to determine theoretical minimum velocity thresholds for injuring people and damaging properties as a function of wave height. Results show that even at a water depth of less than 1m, a current velocity of 2 m/s is enough to pose a threat to humans and cause potential damage to cars and houses. Next, we employ a 1-dimensional shallow water model to simulate Tsunamis with various amplitudes and an assumed wavelength of 250km. This allows for the profiling of current velocity and wave height behavior as the Tsunamis reach shore. We compare this data against our theoretical thresholds to see if any real world scenarios would be dangerous to people and properties. We conclude that for such Tsunamis, the present warning criteria are effective at protecting people against larger events with amplitude greater than ~0.3m. However, for events with amplitude less than ~0.2m, it is possible to have waves less than 1m with current velocity high enough to endanger humans. Thus, the inclusion of current velocity data would help the present Tsunami warning criteria become more robust and efficient, especially for smaller Tsunami events.

Large-scale motions in the universe: Using clusters of galaxies as tracers

NASA Technical Reports Server (NTRS)

Gramann, Mirt; Bahcall, Neta A.; Cen, Renyue; Gott, J. Richard

1995-01-01

Can clusters of galaxies be used to trace the large-scale peculiar velocity field of the universe? We answer this question by using large-scale cosmological simulations to compare the motions of rich clusters of galaxies with the motion of the underlying matter distribution. Three models are investigated: Omega = 1 and Omega = 0.3 cold dark matter (CDM), and Omega = 0.3 primeval baryonic isocurvature (PBI) models, all normalized to the Cosmic Background Explorer (COBE) background fluctuations. We compare the cluster and mass distribution of peculiar velocities, bulk motions, velocity dispersions, and Mach numbers as a function of scale for R greater than or = 50/h Mpc. We also present the large-scale velocity and potential maps of clusters and of the matter. We find that clusters of galaxies trace well the large-scale velocity field and can serve as an efficient tool to constrain cosmological models. The recently reported bulk motion of clusters 689 +/- 178 km/s on approximately 150/h Mpc scale (Lauer & Postman 1994) is larger than expected in any of the models studied (less than or = 190 +/- 78 km/s).

Fram Strait: Atmospheric Forcing of The Sea Ice Flux

NASA Astrophysics Data System (ADS)

Widell, K.; Østerhus, S.; Gammelsrød, T.

Measuring the magnitude and variability of the ice and freshwater flux through Fram Strait is an important element in understanding climate variability in the Arctic. Since the major part of the ice and freshwater that leaves the Arctic passes through Fram Strait, this passage can be considered a key area for estimating the net ice production in the Arctic Ocean. In 1990, the Norwegian Polar Institute (NPI) started a monitoring program in the strait, most years by means of two moorings with Upward Looking Sonars (ULS) measuring ice draft. From 1995 and on, these moorings were also equipped with Doppler Current Meters (DCM) to measure the ice velocity. These measurements give an opportunity to investigate the different forces affecting ice motion in the strait. Maximum correlation coefficient between atmospheric sea level pressure (from NCEP/NCAR reanalysed data) and southward ice velocity is found when using the cross strait pressure difference along 80N between 10W and 5E (R = 0.72) consider- ing monthly means. Subtracting current velocity at 50 m depth (also measured by the DCM) from ice velocity improves the correlation to R = 0.84. This gives insight in the relative importance of current and wind on the ice motion, and indicates that pressure data can be used to make fairly good estimates of the ice velocity in the strait. In combination with data on ice thickness and ice stream width, this result is used to calculate the ice volume transport. By making assumptions on the parameters in- volved, the time series is extended back to 1948, the start of the pressure record. This time series will be presented and compared to literature, and annual and seasonal vari- ation of the ice flux will be discussed.

Two-dimensional velocity, optical risetime, and peak current estimates for natural positive lightning return strokes

NASA Technical Reports Server (NTRS)

Mach, Douglas M.; Rust, W. D.

1993-01-01

Velocities, optical risetimes, and transmission line model peak currents for seven natural positive return strokes are reported. The average 2D positive return stroke velocity for channel segments of less than 500 m in length starting near the base of the channel is 0.8 +/- 0.3 x 10 exp 8 m/s, which is slower than the present corresponding average velocity for natural negative first return strokes of 1.7 +/- 0.7 x 10 exp 8/s. It is inferred that positive stroke peak currents in the literature, which assume the same velocity as negative strokes, are low by a factor of 2. The average 2D positive return stroke velocity for channel segments of greater than 500 m starting near the base of the channel is 0.9 +/- 0.4 x 10 exp 8 m/s. The corresponding average velocity for the present natural negative first strokes is 1.2 +/- 0.6 x 10 exp 8 m/s. No significant velocity change with height is found for positive return strokes.

Effect of soccer shoe upper on ball behaviour in curve kicks

PubMed Central

Ishii, Hideyuki; Sakurai, Yoshihisa; Maruyama, Takeo

2014-01-01

New soccer shoes have been developed by considering various concepts related to kicking, such as curving a soccer ball. However, the effects of shoes on ball behaviour remain unclear. In this study, by using a finite element simulation, we investigated the factors that affect ball behaviour immediately after impact in a curve kick. Five experienced male university soccer players performed one curve kick. We developed a finite element model of the foot and ball and evaluated the validity of the model by comparing the finite element results for the ball behaviour immediately after impact with the experimental results. The launch angle, ball velocity, and ball rotation in the finite element analysis were all in general agreement with the experimental results. Using the validated finite element model, we simulated the ball behaviour. The simulation results indicated that the larger the foot velocity immediately before impact, the larger the ball velocity and ball rotation. Furthermore, the Young's modulus of the shoe upper and the coefficient of friction between the shoe upper and the ball had little effect on the launch angle, ball velocity, and ball rotation. The results of this study suggest that the shoe upper does not significantly influence ball behaviour. PMID:25266788

Effect of soccer shoe upper on ball behaviour in curve kicks

NASA Astrophysics Data System (ADS)

Ishii, Hideyuki; Sakurai, Yoshihisa; Maruyama, Takeo

2014-08-01

New soccer shoes have been developed by considering various concepts related to kicking, such as curving a soccer ball. However, the effects of shoes on ball behaviour remain unclear. In this study, by using a finite element simulation, we investigated the factors that affect ball behaviour immediately after impact in a curve kick. Five experienced male university soccer players performed one curve kick. We developed a finite element model of the foot and ball and evaluated the validity of the model by comparing the finite element results for the ball behaviour immediately after impact with the experimental results. The launch angle, ball velocity, and ball rotation in the finite element analysis were all in general agreement with the experimental results. Using the validated finite element model, we simulated the ball behaviour. The simulation results indicated that the larger the foot velocity immediately before impact, the larger the ball velocity and ball rotation. Furthermore, the Young's modulus of the shoe upper and the coefficient of friction between the shoe upper and the ball had little effect on the launch angle, ball velocity, and ball rotation. The results of this study suggest that the shoe upper does not significantly influence ball behaviour.

Annealing effect on current-driven domain wall motion in Pt/[Co/Ni] wire

NASA Astrophysics Data System (ADS)

Furuta, Masaki; Liu, Yang; Sepehri-Amin, Hossein; Hono, Kazuhiro; Zhu, Jian-Gang Jimmy

2017-09-01

The annealing effect on the efficiency of current-driven domain wall motion governed by the spin Hall effect in perpendicularly magnetized Pt/[Co/Ni] wires is investigated experimentally. Important physical parameters, such as the Dzyaloshinskii-Moriya Interaction (DMI), spin Hall angle, and perpendicular anisotropy field strength, for the domain wall motion are all characterized at each annealing temperature. It is found that annealing of wires at temperatures over 120 °C causes significant reduction of the domain wall velocity. Energy dispersive X-ray spectroscopy analysis shows pronounced Co diffusion across the Pt/Co interface resulted from annealing at relatively high temperatures. The combined modeling study shows that the reduction of DMI caused by annealing is mostly responsible for the domain wall velocity reduction due to annealing.

A Combined Study of Photospheric Magnetic and Current Helicities and Subsurface Kinetic Helicities of Solar Active Regions during 2006-2012

NASA Astrophysics Data System (ADS)

Seligman, Darryl; Petrie, G.; Komm, R.

2014-01-01

We compare the average photospheric current helicity H_c, photospheric twist parameter α (a well-known proxy for the full relative magnetic helicity), and subsurface kinetic helicity K_h for 128 active regions observed between 2006-2012. We use 1436 Hinode photospheric vector magnetograms and subsurface fluid velocity data from GONG Dopplergrams. We find a significant hemispheric bias in all three parameters. The K_h parameter is preferentially positive/negative in the southern/northern hemisphere. The H_c and α parameters have the same bias for strong fields |{B}|>1000 G). We examine the temporal variability of each parameter for each active region and identify a significant subset of regions whose three helicity parameters all exhibit clear increasing or decreasing trends. The temporal profiles of these regions have the same bias: positive/negative helicity in the northern/southern hemisphere. The results are consistent with Longcope et al.'s Σ-effect. This work is carried out through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the NSF REU Program. The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.

The Sun was Not Born in M67

NASA Astrophysics Data System (ADS)

Pichardo, Bárbara; Moreno, Edmundo; Allen, Christine; Bedin, Luigi R.; Bellini, Andrea; Pasquini, Luca

2012-03-01

Using the most recent proper-motion determination of the old, solar-metallicity, Galactic open cluster M67 in orbital computations in a non-axisymmetric model of the Milky Way, including a bar and three-dimensional spiral arms, we explore the possibility that the Sun once belonged to this cluster. We have performed Monte Carlo numerical simulations to generate the present-day orbital conditions of the Sun and M67, and all the parameters in the Galactic model. We compute 3.5 × 105 pairs of orbits Sun-M67 looking for close encounters in the past with a minimum distance approach within the tidal radius of M67. In these encounters we find that the relative velocity between the Sun and M67 is larger than 20 km s-1. If the Sun had been ejected from M67 with this high velocity by means of a three-body encounter, this interaction would have either destroyed an initial circumstellar disk around the Sun or dispersed its already formed planets. We also find a very low probability, much lower than 10-7, that the Sun was ejected from M67 by an encounter of this cluster with a giant molecular cloud. This study also excludes the possibility that the Sun and M67 were born in the same molecular cloud. Our dynamical results convincingly demonstrate that M67 could not have been the birth cluster of our solar system. This work relies partly on observations of the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are The Ohio State University; The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.

A Numerical Model of Seawater Volume and Velocity Dynamic for Marine Currents Power Plant in the Bangka Strait, North Sulawesi, Indonesia

NASA Astrophysics Data System (ADS)

Rompas, P. T. D.; Taunaumang, H.; Sangari, F. J.

2017-03-01

One of equipment as prime movers in the marine current power plant is turbine. Marine current turbines require a data of marine currents velocity in its design. The objective of this study was to get the velocities distribution of marine currents in the Bangka strait. The method used survey, observation, and measurement in the Bangka strait. The data of seawater density conducted measurement in the Bangka strait. The data of width and depth of the strait collected from the map of Bangka strait and its depth of the sea. Problem solving of the study used a numerical model. The velocities distribution of marine current obtained from a numerical model in the form of numerical program. The results showed that the velocities distribution at seawater column when low and high tide currents which the maximum happened at 0.1 Sv were 0-0.9 and 0-1.0 m/s respectively, while at 0.3 Sv were 0-2.7 and 0-3.0 m/s respectively. The results will be a product in analyzing the potential kinetic energy that used to design profile of the turbines as prime mover for marine currents power plant in the Bangka strait, North Sulawesi, Indonesia.

Contribution of irregular semicircular canal afferents to the horizontal vestibuloocular response during constant velocity rotation

NASA Technical Reports Server (NTRS)

Angelaki, D. E.; Perachio, A. A.

1993-01-01

1. The effects of constant anodal currents (100 microA) delivered bilaterally to both labyrinths on the horizontal vestibuloocular response (VOR) were studied in squirrel monkeys during steps of angular velocity in the dark. We report that bilateral anodal currents decreased eye velocity approximately 30-50% during the period of galvanic stimulation without a change in the time constant of VOR. The decrease in eye velocity, present during steps of angular velocity, was not observed during sinusoidal head rotation at 0.2, 0.5, and 1 Hz. The results suggest that responses from irregular vestibular afferents influence VOR amplitude during constant velocity rotation.

Double inflation - A possible resolution of the large-scale structure problem

NASA Technical Reports Server (NTRS)

Turner, Michael S.; Villumsen, Jens V.; Vittorio, Nicola; Silk, Joseph; Juszkiewicz, Roman

1987-01-01

A model is presented for the large-scale structure of the universe in which two successive inflationary phases resulted in large small-scale and small large-scale density fluctuations. This bimodal density fluctuation spectrum in an Omega = 1 universe dominated by hot dark matter leads to large-scale structure of the galaxy distribution that is consistent with recent observational results. In particular, large, nearly empty voids and significant large-scale peculiar velocity fields are produced over scales of about 100 Mpc, while the small-scale structure over less than about 10 Mpc resembles that in a low-density universe, as observed. Detailed analytical calculations and numerical simulations are given of the spatial and velocity correlations.

Influence of Current Velocity on Uranium Adsorption from Seawater Using an Amidoxime-based Polymer Fiber Adsorbent

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ladshaw, Austin; Kuo, Li-Jung; Strivens, Jonathan

2017-02-08

Passive adsorption using amidoxime-based polymeric adsorbents is being developed for uranium recovery from seawater. The local oceanic current velocity where the adsorbent is deployed is a key variable in determining locations that will maximize uranium adsorption rates. Two independent experimental approaches using flow-through columns and recirculating flumes were used to assess the influence of linear velocity on uranium uptake kinetics by the adsorbent. Little to no difference was observed in the uranium adsorption rate vs. linear velocity for seawater exposure in flow-through columns. In contrast, adsorption results from seawater exposure in a recirculating flume showed a nearly linear trend withmore » current velocity. The difference in adsorbent performance between columns and flume can be attributed to (i) flow resistance provided by the adsorbent braid in the flume and (ii) enhancement in braid movement (fluttering) with increasing linear velocity.« less

Influence of Current Velocity on Uranium Adsorption from Seawater Using an Amidoxime-Based Polymer Fiber Adsorbent

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ladshaw, Austin; Kuo, Li-Jung; Strivens, Jonathan

2017-02-17

Passive adsorption using amidoxime-based polymeric adsorbents is being developed for uranium recovery from seawater. The local oceanic current velocity where the adsorbent is deployed is a key variable in determining locations that will maximize uranium adsorption rates. Two independent experimental approaches using flow-through columns and recirculating flumes were used to assess the influence of linear velocity on uranium uptake kinetics by the adsorbent. Little to no difference was observed in the uranium adsorption rate vs. linear velocity for seawater exposure in flow-through columns. In contrast, adsorption results from seawater exposure in a recirculating flume showed a nearly linear trend withmore » current velocity. The difference in adsorbent performance between columns and flume can be attributed to (i) flow resistance provided by the adsorbent braid in the flume and (ii) enhancement in braid movement (fluttering) with increasing linear velocity.« less

Design studies of the Ku-band, wide-band Gyro-TWT amplifier

NASA Astrophysics Data System (ADS)

Jung, Sang Wook; Lee, Han Seul; Jang, Kwong Ho; Choi, Jin Joo; Hong, Yong Jun; Shin, Jin Woo; So, Jun Ho; Won, Jong Hyo

2014-02-01

This paper reports a Ku-band, wide band Gyrotron-Traveling-wave-tube(Gyro-TWT) that is currently being developed at Kwangwoon University. The Gyro-TWT has a two stage linear tapered interaction circuit to obtain a wide operating bandwidth. The linearly-tapered interaction circuit and nonlinearly-tapered magnetic field gives the Gyro-TWT a wide operating bandwidth. The Gyro-TWT bandwidth is 23%. The 2d-Particle-in-cell(PIC) and MAGIC2d code simulation results are 17.3 dB and 24.34 kW, respectively for the maximum saturated output power. A double anode MIG was simulated with E-Gun code. The results were 0.7 for the transvers to the axial beam velocity ratio (=alpha) and a 2.3% axial velocity spread at 50 kV and 4 A. A magnetic field profile simulation was performed by using the Poisson code to obtain the grazing magnetic field of the entire interaction circuit with Poisson code.

Design and Characterization of the UTIAS Anechoic Wind Tunnel

NASA Astrophysics Data System (ADS)

Chow, Derrick H. F.

The anechoic open-jet wind tunnel facility at the University of Toronto Institute for Aerospace Studies was updated and characterized to meet the needs of current and future aeroacoustic experiments. The wind tunnel inlet was resurfaced and flow-conditioning screens were redesigned to improve the freestream turbulence intensity to below 0.4% in the test section. The circular nozzle was replaced with a square secondary contraction that increased the maximum test section velocity to 75 m/s and improved flow uniformity to over 99% across a usable cross-sectional area of 500 mm x 500 mm. Acoustic baffles were installed in front of the wind tunnel inlet and foam wedges were installed in the anechoic chamber. The overall background sound pressure levels in the chamber were improved by 8-18 db over the range of operational freestream velocities. The anechoic chamber cut-off frequency is 170 Hz and the reverberation time for a 60 dB sound power decay is 0.032 s.

Error Analysis of Wind Measurements for the University of Illinois Sodium Doppler Temperature System

NASA Technical Reports Server (NTRS)

Pfenninger, W. Matthew; Papen, George C.

1992-01-01

Four-frequency lidar measurements of temperature and wind velocity require accurate frequency tuning to an absolute reference and long term frequency stability. We quantify frequency tuning errors for the Illinois sodium system, to measure absolute frequencies and a reference interferometer to measure relative frequencies. To determine laser tuning errors, we monitor the vapor cell and interferometer during lidar data acquisition and analyze the two signals for variations as functions of time. Both sodium cell and interferometer are the same as those used to frequency tune the laser. By quantifying the frequency variations of the laser during data acquisition, an error analysis of temperature and wind measurements can be calculated. These error bounds determine the confidence in the calculated temperatures and wind velocities.

Do photons travel faster than gravitons?

NASA Astrophysics Data System (ADS)

Ejlli, Damian

2018-02-01

The vacuum polarization in an external gravitational field due to one loop electron-positron pair and one loop millicharged fermion-antifermion pair is studied. Considering the propagation of electromagnetic (EM) radiation and gravitational waves (GWs) in an expanding universe, it is shown that by taking into account QED effects in curved spacetime, the propagation velocity of photons is superluminal and can exceed that of gravitons. We apply these results to the case of the GW170817 event detected by LIGO. If the EM radiation and GWs are emitted either simultaneously or with a time difference from the same source, it is shown that the EM radiation while propagating with superluminal velocity, would be detected either in advance or in delay with respect to GW depending on the ratio of millicharged fermion relative charge to mass epsilon/mepsilon.

The Contributions of the WIYN Observatory to Undergraduate Education

NASA Astrophysics Data System (ADS)

Hooper, Eric; Consortium, WIYN

2014-01-01

Over its nearly 20 year history the WIYN Observatory has provided crucial data for numerous undergraduate research projects at the partner institutions (University of Wisconsin-Madison, Indiana University, and Yale University) plus others who access the telescope via national time from NOAO. WIYN and its instruments have served both undergraduates who are local to each institution, as well as those who have a temporary tenure as Research Experience for Undergraduates (REU) students. The topics of this work range widely, and only a few examples are listed here. Numerous studies of stars have been undertaken by undergraduates, from rotation velocities of pre-main sequence stars (Rhode et al.) to dynamical heating mechanisms in open clusters (Friel et al.). Extragalactic investigations range from a study of cold ISM in galaxies near the centers of rich clusters (Gallagher & Hooper, et al.) to the stellar populations of post-starburst galaxies hosting low-level AGN (Wolf & Hooper, et al.). Students have made wide use of WIYN's long established suite of facility instruments, which currently includes the Hydra multi-object fiber spectrograph, the SparsePak integral field unit fiber spectrograph, and the WHIRC near-infrared imager. A current undergraduate is a key player in final laboratory testing of two new integral field units that will come to WIYN soon. Finally, the new large format imager pODI currently is in science operation, soon to be followed by an upgrade to nearly four times the current imaging area, a powerful tool that will join the others in contributing to undergraduate research and education. This presentation is a continuation of the overview of WIYN contributions to education that began with a discussion of graduate education at the Indianapolis AAS (Hooper, AAS Meeting #222, #214.23).

Lighting the universe with filaments.

PubMed

Gao, Liang; Theuns, Tom

2007-09-14

The first stars in the universe form when chemically pristine gas heats as it falls into dark-matter potential wells, cools radiatively because of the formation of molecular hydrogen, and becomes self-gravitating. Using supercomputer simulations, we demonstrated that the stars' properties depend critically on the currently unknown nature of the dark matter. If the dark-matter particles have intrinsic velocities that wipe out small-scale structure, then the first stars form in filaments with lengths on the order of the free-streaming scale, which can be approximately 10(20) meters (approximately 3 kiloparsecs, corresponding to a baryonic mass of approximately 10(7) solar masses) for realistic "warm dark matter" candidates. Fragmentation of the filaments forms stars with a range of masses, which may explain the observed peculiar element abundance pattern of extremely metal-poor stars, whereas coalescence of fragments and stars during the filament's ultimate collapse may seed the supermassive black holes that lurk in the centers of most massive galaxies.

Pressure Anisotropy Probe for the Terrestrial Reconnection Experiment (TREX)

NASA Astrophysics Data System (ADS)

Myers, Rachel; Egedal, Jan; Olson, Joseph; Greess, Samuel; Clark, Michael; Nonn, Paul; Wallace, John; Forest, Cary

2016-10-01

The Terrestrial Reconnection Experiment (TREX) at the Wisconsin Plasma Astrophysics Laboratory (WiPAL) studies magnetic reconnection primarily in the collisionless regime. In this regime, electron pressure anisotropy is expected to develop, deviating from traditional Hall reconnection dynamics and driving formation of large-scale current layers. In order to measure the anisotropy, a multi-tip electromagnetic probe similar to the M-probe described by Shadman, consisting of 32 Langmuir probe tips and two magnetic coils, has been constructed. Each tip is biased to a different potential, simultaneously measuring discrete parts of the full I-V characteristic. Pulsing the coil then locally increases the magnetic field, creating a magnetic mirror force to reflect electrons with large values of v⊥ / v . The change in electron velocity modifies the I-V characteristics and can be used to infer p∥ /p⊥ . Analysis with the new probe will be presented. DOE Grant DE-SC0010463, University of Wisconsin-Madison University Fellowship.

Power corrections to the universal heavy WIMP-nucleon cross section

NASA Astrophysics Data System (ADS)

Chen, Chien-Yi; Hill, Richard J.; Solon, Mikhail P.; Wijangco, Alexander M.

2018-06-01

WIMP-nucleon scattering is analyzed at order 1 / M in Heavy WIMP Effective Theory. The 1 / M power corrections, where M ≫mW is the WIMP mass, distinguish between different underlying UV models with the same universal limit and their impact on direct detection rates can be enhanced relative to naive expectations due to generic amplitude-level cancellations at leading order. The necessary one- and two-loop matching calculations onto the low-energy effective theory for WIMP interactions with Standard Model quarks and gluons are performed for the case of an electroweak SU(2) triplet WIMP, considering both the cases of elementary fermions and composite scalars. The low-velocity WIMP-nucleon scattering cross section is evaluated and compared with current experimental limits and projected future sensitivities. Our results provide the most robust prediction for electroweak triplet Majorana fermion dark matter direct detection rates; for this case, a cancellation between two sources of power corrections yields a small total 1 / M correction, and a total cross section close to the universal limit for M ≳ few × 100GeV. For the SU(2) composite scalar, the 1 / M corrections introduce dependence on underlying strong dynamics. Using a leading chiral logarithm evaluation, the total 1 / M correction has a larger magnitude and uncertainty than in the fermionic case, with a sign that further suppresses the total cross section. These examples provide definite targets for future direct detection experiments and motivate large scale detectors capable of probing to the neutrino floor in the TeV mass regime.

Waves plus currents at a right angle: The rippled bed case

NASA Astrophysics Data System (ADS)

Faraci, C.; Foti, E.; Musumeci, R. E.

2008-07-01

The present paper deals with wave plus current flow over a fixed rippled bed. More precisely, modifications of the current profiles due to the superimposition of orthogonal cylindrical waves have been investigated experimentally. Since the experimental setup permitted only the wave dominated regime to be investigated (i.e., the regime where orbital velocity is larger than current velocity), also a numerical k-ɛ turbulence closure model has been developed in order to study a wider range of parameters, thus including the current dominated regime (i.e., where current velocity is larger than wave orbital one). In both cases a different response with respect to the flat bed case has been found. Indeed, in the flat bed case laminar wave boundary layers in a wave dominated regime induce a decrease in bottom shear stresses, while the presence of a rippled bed behaves as a macroroughness, which causes the wave boundary layer to become turbulent and therefore the current velocity near the bottom to be smaller than the one in the case of current only, with a consequent increase in the current bottom roughness.

Miami University Information Manual.

ERIC Educational Resources Information Center

Miami Univ., Oxford, OH.

The 1975 information manual is designed to provide current data on policies, procedures, services, facilities, organization and governance of Miami University and, through the extensive index, quick access to this information. The manual is complementary to the university catalog and directory. Information relating to students is in the Student…

The observation of underwater frazil ice formation and upward sediment transport in an Arctic polynya in the Chukchi Sea

NASA Astrophysics Data System (ADS)

Ito, M.; Ohshima, K. I.; Fukamachi, Y.; Simizu, D.; Mahoney, A. R.; Eicken, H.

2016-12-01

Sea ice is a great contributor to energy- and salt-budget, dense water formation and bio-related material cycle in the polar ocean. In coastal polynya, the ice production becomes maximum when open water is maintained owing to underwater frazil ice formation associated with supercooling. In addition, an interaction between frazil ice and re-suspended sediment can be a major process of sediment incorporation into sea ice. Although these process have been reported from laboratory experiments and numerical simulations, in-situ observations have been limited because the under-ice observation is logistically challenging and detection methods of frazil ice and sedimentary particles have not been well established. Since 2009, mooring observations with ADCPs, Ice-Profiling Sonars and C-T recorders have been continuously carried out off Barrow in the Chukchi Sea, through a collaboration between Hokkaido University and University of Alaska Fairbanks. Recently, some in-situ measurements reported the possibility that an ADCP can detect frazil ice and re-suspended sediment using acoustic backscatter strength data. Thus, we analyzed the ADCP data in the Chukchi Sea, focusing on underwater frazil ice formation and upward sediment transport. In winter, polynyas were formed episodically around the observational sites several times by offshore-ward strong winds of > 10 m/s. During these polynya events, surface-intensified signals were detected throughout the water column at two sites with water depths of 40 - 50 m simultaneously. In these cases, potential supercooling occurred and signals were particularly enhanced at timings of in-situ supercooling. Thus, we interpreted these signals as those of frazil ice. On the other hand, bottom-intensified signals originating from re-suspended sediment were detected throughout the water column just after frazil ice was detected. These signals were associated with strong ocean currents of 1 m/s. Thus, sedimentary particles are likely dispersed from the ocean bottom by the strong currents and subsequently brought up to the ocean surface under turbulent mixing conditions. We estimated the fall velocity of sedimentary particles as 0.4 mm/s based on the vertical profiles of the ADCP backscatter strength. This fall velocity corresponds to that of the particle diameter of 20 μm.

Price current-meter standard rating development by the U.S. geological survey

USGS Publications Warehouse

Hubbard, E.F.; Schwarz, G.E.; Thibodeaux, K.G.; Turcios, L.M.

2001-01-01

The U.S. Geological Survey has developed new standard rating tables for use with Price type AA and pygmy current meters, which are employed to measure streamflow velocity. Current-meter calibration data, consisting of the rates of rotation of meters at several different constant water velocities, have shown that the original rating tables are no longer representative of the average responsiveness of newly purchased meters or meters in the field. The new rating tables are based on linear regression equations that are weighted to reflect the population mix of current meters in the field and weighted inversely to the variability of the data at each calibration velocity. For calibration velocities of 0.3 m/s and faster, at which most streamflow measurements are made, the new AA-rating predicts the true velocities within 1.5% and the new pygmy-meter rating within 2.0% for more than 95% of the meters. At calibration velocities, the new AA-meter rating is up to 1.4% different from the original rating, and the new pygmy-meter rating is up to 1.6% different.

Quantifying riverine surface currents from time sequences of thermal infrared imagery

USGS Publications Warehouse

Puleo, J.A.; McKenna, T.E.; Holland, K.T.; Calantoni, J.

2012-01-01

River surface currents are quantified from thermal and visible band imagery using two methods. One method utilizes time stacks of pixel intensity to estimate the streamwise velocity at multiple locations. The other method uses particle image velocimetry to solve for optimal two-dimensional pixel displacements between successive frames. Field validation was carried out on the Wolf River, a small coastal plain river near Landon, Mississippi, United States, on 26-27 May 2010 by collecting imagery in association with in situ velocities sampled using electromagnetic current meters deployed 0.1 m below the river surface. Comparisons are made between mean in situ velocities and image-derived velocities from 23 thermal and 6 visible-band image sequences (5 min length) during daylight and darkness conditions. The thermal signal was a small apparent temperature contrast induced by turbulent mixing of a thin layer of cooler water near the river surface with underlying warmer water. The visible-band signal was foam on the water surface. For thermal imagery, streamwise velocities derived from the pixel time stack and particle image velocimetry technique were generally highly correlated to mean streamwise current meter velocities during darkness (r 2 typically greater than 0.9) and early morning daylight (r 2 typically greater than 0.83). Streamwise velocities from the pixel time stack technique had high correlation for visible-band imagery during early morning daylight hours with respect to mean current meter velocities (r 2 > 0.86). Streamwise velocities for the particle image velocimetry technique for visible-band imagery had weaker correlations with only three out of six correlations performed having an r 2 exceeding 0.6. Copyright 2012 by the American Geophysical Union.

Electron emission and beam generation using ferroelectric cathodes

NASA Astrophysics Data System (ADS)

Flechtner, Donald D.

1999-06-01

In 1989, researchers at CERN published the discovery of significant electron emission (1-100 A/cm2) from Lead-Lanthanum-Zirconate- Titanate (PLZT). The publication of these results led to international interest in ferroelectric cathodes studies for use in pulsed power devices. At Cornell University in 1991, experiments with Lead-Zirconate-Titanate (PZT) compositions were begun to study the feasibility of using this ferroelectric material as a cathode in the electron gun section of High Power Traveling Wave Tube Amplifier Experiments. Current-voltage characteristics were documented for diode voltages ranging from 50-500,000 V with anode cathode gaps of.5-6 cm. A linear current-voltage relation was found for voltages less than 50 kV. For diode voltages >=200 kV, a typical Child-Langmuir V3/2 dependence was observed. Additional experiments have demonstrated repetition rates of up to 50 Hz with current densities of >=20 A/cm2. These results have been used in the ongoing design and construction of the electron gun for a 500 kV pulse modulator capable of repetitive operation at 1 Hz. The electron gun uses a PZT 55/45 (Pb(Zr.55,Ti.45 )O3) cathode to produce a <=400 A electron beam focused by a converging magnetic field. Studies of the emission process itself indicate the initial electrons are produced by field emission from the metallic grid applied to the front surface of the cathode. The field emission is induced by the application of a fast rising 1-3 kV, 150 ns pulse to the rear electrode of the 1 mm thick ferroelectric. Field emission can lead to explosive emission from microprotrusions and metal-ferroelectric-vacuum triple points forming a diffuse plasma on the surface of the sample. Under long pulse experiments (1-5 μs), plasma velocities of ~2 cm/μs were measured from gap closure rates. Results from an ion Faraday cup experiment showed ion velocities of 1-2 cm/μs. Experimental evidence indicates the electron emission is dependent on the field emission initiated by the voltage applied to rear surface of the ferroelectric; however, for current pulse durations on the order of microseconds, the surface plasma expansion into the gap can dominate current flow.

Modeling a Propagating Sawtooth Flare Ribbon Structure as a Tearing Mode in the Presence of Velocity Shear

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parker, Jacob; Longcope, Dana

On 2014 April 18 (SOL2014-04-18T13:03), an M-class flare was observed by IRIS. The associated flare ribbon contained a quasi-periodic sawtooth pattern that was observed to propagate along the ribbon, perpendicular to the IRIS spectral slit, with a phase velocity of ∼15 km s{sup −1}. This motion resulted in periodicities in both intensity and Doppler velocity along the slit. These periodicities were reported by Brannon et al. to be approximately ±0.″5 in position and ±20 km s{sup −1} in velocity and were measured to be ∼180° out of phase with one another. This quasi-periodic behavior has been attributed by others tomore » bursty or patchy reconnection and slipping occurring during three-dimensional magnetic reconnection. Though able to account for periodicities in both intensity and Doppler velocity, these suggestions do not explicitly account for the phase velocity of the entire sawtooth structure or the relative phasing of the oscillations. Here we propose that the observations can be explained by a tearing mode (TM) instability occurring at a current sheet across which there is also a velocity shear. Using a linear model of this instability, we reproduce the relative phase of the oscillations, as well as the phase velocity of the sawtooth structure. We suggest a geometry and local plasma parameters for the April 18 flare that would support our hypothesis. Under this proposal, the combined spectral and spatial IRIS observations of this flare may provide the most compelling evidence to date of a TM occurring in the solar magnetic field.« less

An Air Force Guide for Effective Meeting Management

DTIC Science & Technology

2011-05-01

The inspection program to ensure its sustainment has faced increasing workload requirements due to structural issues related to heavy use and aging...26 Data Sources /Format...aircraft availability, the High Velocity Maintenance (HVM) concept is being implemented to replace the current PDM process for heavy maintenance

A Preliminary Evaluation of Near-Transducer Velocities Collected with Low-Blank Acoustic Doppler Current Profiler

USGS Publications Warehouse

Gartner, J.W.; Ganju, N.K.; ,

2002-01-01

Many streams and rivers for which the US Geological Survey must provide discharge measurements are too shallow to apply existing acoustic Doppler current profiler techniques for flow measurements of satisfactory quality. Because the same transducer is used for both transmitting and receiving acoustic signals in most Doppler current profilers, some small time delay is required for acoustic "ringing" to be damped out of transducers before meaningful measurements can be made. The result of that time delay is that velocity measurements cannot be made close to the transducer thus limiting the usefulness of these instruments in shallow regions. Manufacturers and users are constantly striving for improvements to acoustic instruments which would permit useful discharge measurements in shallow rivers and streams that are still often measured with techniques and instruments more than a century old. One promising area of advance appeared to be reduction of time delay (blank) required between transmitting and receiving signals during acoustic velocity measurements. Development of a low- or zero-blank transducer by RD Instruments3 held promise that velocity measurements could be made much closer to the transducer and thus in much shallower water. Initial experience indicates that this is not the case; limitation of measurement quality appears to be related to the physical presence of the transducer itself within the flow field. The limitation may be the result of changes to water flow pattern close to the transducer rather than transducer ringing characteristics as a function of blanking distance. Results of field experiments are discussed that support this conclusion and some minimum measurement distances from transducer are suggested based on water current speed and ADCP sample modes.

A GRAVITATIONAL DOUBLE-SCATTERING MECHANISM FOR GENERATING HIGH-VELOCITY OBJECTS DURING HALO MERGERS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samsing, Johan; Department of Astrophysical Sciences, Princeton University, Peyton Hall, Princeton, NJ 08544

2015-02-01

We present a dynamical model that describes how halo particles can receive a significant energy kick from the merger between their own host halo and a target halo. This could provide a possible explanation for some high-velocity objects, including extended systems like globular clusters (GCs). In the model we especially introduce a double-scattering mechanism, where a halo particle receives a significant part of its total energy kick by first undergoing a gravitational deflection by the target halo and subsequently by its original host halo. This generates an energy kick that is due to the relative velocity between the halos duringmore » the deflections. We derive analytically the total kick energy of the particle, which is composed of energy from the double-scattering mechanism and tidal fields, as a function of its position in its original host halo just before merger. In the case of a 1:10 merger, we find that the presented mechanisms can easily generate particles with a velocity approximately two times the virial velocity of the target halo. This motivates us to suggest that the high velocity of the recently discovered GC HVGC-1 can be explained by a head-on halo merger. Finally, we illustrate the orbital evolution of high-velocity particles outside the virial sphere of the target halo by solving the equation of motion in an expanding universe. We find a sweet spot around a scale factor of 0.3-0.5 for ejecting particles into large orbits, which can easily reach beyond approximately five virial radii.« less

Effects of slope on the formation of dunes in dilute, turbulent pyroclastic currents: May 18th, 1980 Mt. St. Helens eruption

NASA Astrophysics Data System (ADS)

Bendana, Sylvana; Brand, Brittany D.; Self, Stephen

2014-05-01

The flanks of Mt St Helens volcano (MSH) are draped with thin, cross-stratified and stratified pyroclastic density current (PDC) deposits. These are known as the proximal bedded deposits produced during the May 18th, 1980 eruption of MSH. While the concentrated portions of the afternoon PDCs followed deep topographic drainages down the steep flanks of the volcano, the dilute overriding cloud partially decoupled to develop fully dilute, turbulent PDCs on the flanks of the volcano (Beeson, D.L. 1988. Proximal Flank Facies of the May 18, 1980 Ignimbrite: Mt. St. Helens, Washington.). The deposits along the flank thus vary greatly from those found in the pumice plain, which are generally thick, massive, poorly-sorted, block-rich deposits associated with the more concentrated portions of the flow (Brand et al, accepted. Dynamics of pyroclastic density currents: Conditions that promote substrate erosion and self-channelization - Mount St Helens, Washington (USA). JVGR). We explore the influence of topography on the formation of these dilute currents and influence of slope on the currents transport and depositional mechanisms. The deposits on steeper slopes (>15°) are fines depleted relative to the proximal bedded deposits on shallower slopes (<15°). Bedform amplitude and wavelength increase with increasing slope, as does the occurrence of regressive dunes. Increasing slope causes an increase in flow velocity and thus an increase in flow turbulence. The fines depleted deposits suggest that fine ash elutriation is more efficient in flows with stronger turbulence. The longer wavelength and amplitudes suggest that bedform morphology is directly related to flow velocity, an important finding since the controls on bedform wavelength and amplitude in density stratified flows remains poorly constrained. The occurrence of regressive dunes, often interpreted as high flow-regime bedforms, on steeper slopes relative to progressive dunes on shallower slopes further attests to the control of velocity and flow regime on bedform morphology. Samples collected from recently exposed deposits and analyzed by grain size measurements, density analyses, and crystal morphoscopy studies further assess modes of origin and transport of dilute PDCs.

Modeling the Internal Kinematics (Rotation and Dispersion) of Distant Galaxies (z ~ 1.0) Using Multi-PA Keck DEIMOS Slit Spectra

NASA Astrophysics Data System (ADS)

Miao, Connie; Chen, Jerry; Torres Hernandez, Jose; Guhathakurta, Puragra; Jang, Hyerin

2017-01-01

The stark difference between the chaotic internal motion of distant galaxies and the ordered rotation of typical local spiral galaxies suggests that disordered galaxies at high redshifts (i.e., early times in the Universe's history) gradually settle into well ordered disk morphologies with ordered rotation. We have used slit spectra obtained with Keck DEIMOS at four different position angles for 133 distant objects (z ~ 1.0) in the GOODS-N field. The emission lines in the 2D spectra of the galaxies were used to calculate the redshift/velocity at each spatial location. For each slit row, the distribution of flux over velocity was modeled as a Gaussian curve from which we obtained the radial velocity and spread of radial velocity. Rotation curves and velocity dispersions for each galaxy at each slit angle were plotted at these values. We qualitatively classified galaxies as regularly rotating, merging, face-on, or unable to be determined by examining overlays of the rotation curves from the four slit angles. We found that regular rotating galaxies tended to have peak velocity dispersion at the center while mergers had fairly constant velocity dispersions. Face-on galaxies had chaotic and inconsistent velocity dispersions between different slit angles. Regularly rotation galaxies represented 45% of our sample and mergers represented 27%. The relative percentage of galaxies that were either regularly rotating or mergers roughly matched those of the literature. This research was supported by NASA and the National Science Foundation. Most of this work was carried out by high school students working under the auspices of the Science Internship Program at UC Santa Cruz.

Shear Wave Velocity Structure beneath the African-Anatolian Subduction Zone in Southwestern Turkey from Inversions of Rayleigh Waves

NASA Astrophysics Data System (ADS)

Teoman, U. M.; Sandvol, E. A.; Kahraman, M.; Sahin, S.; Turkelli, N.

2011-12-01

The ongoing subduction of the African Plate under western Anatolia results in a highly complex tectonic structure especially beneath Isparta Angle (IA) and the surroundings where the Hellenic and Cyprian slabs with different subduction geometries intersect. The primary objective is to accurately image the lithospheric structure at this convergent plate boundary and further understand the reasons responsible for the active deformation. Data was gathered from a temporary seismic network consisting of 10 broadband stations that was installed in August 2006 with the support from University of Missouri and nine more stations deployed in March 2007 with the support from Bogazici Research Fund (project ID:07T203). In addition, 21 permanent stations of Kandilli Observatory and Earthquake Research Institute (KOERI) and two from Süleyman Demirel University (SDU) together with five stations from IRIS/Geofon Network were also included to extend the station coverage. We used earthquakes in a distance range of 30-120 degrees with body wave magnitudes larger than 5.5. Depending on the signal to noise ratio, azimuthal coverage of events, and coherence from station, 81 events provided high-quality data for our analysis. The distribution of events shows a good azimuthal coverage, which is important for resolving both lateral heterogeneity and azimuthal anisotropy. We adopted a two-plane-wave inversion technique of Forsyth and Li (2003) to simultaneously solve for the incoming wave field and phase velocity. This relatively simpler representation of a more complex wavefield provided quite stable patterns of amplitude variations in many cases. To begin with, an average phase velocity dispersion curve was obtained and used as an input for tomographic inversions. Two-dimensional tomographic maps of isotropic and azimuthally anisotropic phase velocity variations were generated. Phase velocities can only tell us integrated information about the upper mantle. Furthermore, we inverted phase velocities for shear wave velocities (Saito,1988) in order to obtain direct information at a depth range of 30-300 km that can be interpreted in terms of major tectonic processes such as extension, slab detachment/tearing, STEP faults, volcanism, temperature anomalies, the presence of melt or dissolved water, etc. Resulting tomograms along horizontal and vertical depth sections provided valuable insights on the crustal and upper mantle structure beneath Southwestern Turkey down to almost 300 km.

In-situ measurements of velocity structure within turbidity currents

USGS Publications Warehouse

Xu, J. P.; Noble, M.A.; Rosenfeld, L.K.

2004-01-01

Turbidity currents are thought to be the main mechanism to move ???500,000 m3 of sediments annually from the head of the Monterey Submarine Canyon to the deep-sea fan. Indirect evidence has shown frequent occurrences of such turbidity currents in the canyon, but the dynamic properties of the turbidity currents such as maximum speed, duration, and dimensions are still unknown. Here we present the first-ever in-situ measurements of velocity profiles of four turbidity currents whose maximum along-canyon velocity reached 190 cm/s. Two turbidity currents coincided with storms that produced the highest swells and the biggest stream flows during the year-long deployment. Copyright 2004 by the American Geophysical Union.

Simultaneous electrical and optical study of spoke rotation, merging and splitting in HiPIMS plasma

NASA Astrophysics Data System (ADS)

Klein, P.; Lockwood Estrin, F.; Hnilica, J.; Vašina, P.; Bradley, J. W.

2017-01-01

To gain more information on the temporal and spatial behaviour of self-organized spoke structures in HiPIMS plasmas, a correlation between the broadband optical image of an individual spoke (taken over 200 ns) and the current it delivers to the target has been made for a range of magnetron operating conditions. As a spoke passes over a set of embedded probes in the niobium cathode target, a distinct modulation in the local current density is observed, (typically up to twice the average value), matching very well the radially integrated optical emission intensities (obtained remotely with an ICCD camera). The dual diagnostic system allows the merging and splitting of a set of spokes to be studied as they rotate. It is observed that in the merger of two spokes, the trailing spoke maintains its velocity while the leading spoke either decreases its velocity or increases its azimuthal length. In the spoke splitting process, the total charge collected by an embedded probe is conserved. A simple phenomenological model is developed that relates the spoke mode number m to the spoke dimensions, spoke velocity and gas atom velocity. The results are discussed in the context of the observations of spoke dynamics made by Hecimovic et al (2015 Plasma Sources Sci. Technol. 24 045005)

Propagation analysis of the helicity-drive Alfven wave in the HIST spherical torus plasmas

NASA Astrophysics Data System (ADS)

Hyobu, T.; Hanao, T.; Hirono, H.; Ito, K.; Matsumoto, K.; Nakayama, T.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

2012-10-01

Coaxial Helicity Injection is an efficient current-drive method used in spherical torus experiments. It is a key issue to investigate the dynamo mechanism required to maintain the plasmas. The behavior of a low frequency Alfven wave being possibly related to the dynamo current drive has been studied on HIST. The observed magnetic fluctuation with about 80 kHz propagates along the open flux column (OFC) region, spreading toward the core region. The parallel phase velocity is estimated at 321 km/s from the propagation velocity measured axially along the OFC. The parallel phase velocity agrees well to the Alfven velocity. The radial perpendicular propagation of the Alfven wave can be calculated by a theory based on cold or warm plasma approximation with the Hall term. The theoretical calculation indicates that there are two resonance points and is a cut-off point. These resonance and cut-off points agree well with the magnetic measurement. A part of fluctuation propagates slowly beyond the first resonance point. The wave polarization is left-handed near the resonance point and then converts to be nearly liner outside the resonance point. From these results, we speculate that the torsional Alfven wave evolves to the kinetic Alfven wave during the radial propagation.

Lithosphere structure across the Dead Sea Transform as constrained by Rayleigh waves observed during the DESERT experiment

NASA Astrophysics Data System (ADS)

Laske, G.; Weber, M.

2008-05-01

The interdisciplinary Dead Sea Rift Transect (DESERT) project that was conducted in Israel, the Palestine Territories and Jordan has provided a rich palette of data sets to examine the crust and uppermost mantle beneath one of Earth's most prominent fault systems, the Dead Sea Transform (DST). As part of the passive seismic component, thirty broad-band sensors were deployed in 2000 across the DST for roughly one year. During this deployment, we recorded 115 teleseismic earthquakes that are suitable for a fundamental mode Rayleigh wave analysis at intermediate periods (35-150s). Our initial analysis reveals overall shear velocities that are reduced by up to 4 per cent with respect to reference Earth model PREM. To the west of the DST, we find a seismically relatively fast but thin lid that is about 80 km thick. Towards the east, shallow seismic velocities are low while a deeper low velocity zone is not detected. This contradicts the currently favoured thermomechanical model for the DST that predicts lithospheric thinning through mechanical erosion by an intruding plume from the Red Sea. On the other hand, our current results are somewhat inconclusive regarding asthenosphere velocities east of the DST due to the band limitation of the recording equipment in Jordan.

Climatology of the relationship of cusp-related density anomaly with zonal wind and large-scale FAC based on CHAMP observations: IMF By and solar cycle dependence

NASA Astrophysics Data System (ADS)

Kervalishvili, Guram; Lühr, Hermann

2014-05-01

We present climatology of the relationship of cusp-related density enhancement with the neutral zonal wind velocity, large-scale field-aligned current (FAC), small-scale FAC, and electron temperature using the superposed epoch analysis (SEA) method. The dependence of these variables on the interplanetary magnetic field (IMF) By component orientation and solar cycle are of particular interest. In addition, the obtained results of relative density enhancement (ρrel), zonal wind, electron temperature and FAC are subdivided into three local seasons of 130 days each: local winter (1 January ±65 days), combined equinoxes (1 April ±32 days and 1 October ±32 days), and local summer (1 July ±65 days). Our investigation is based on CHAMP satellite observations and NASA/GSFC's OMNI online data set for solar maximum (Mar/2002-2007) and minimum (Mar/2004-2009) conditions in the Northern Hemisphere. The SEA technique uses the time and location of the thermospheric mass density anomaly peaks as reference parameters. The relative amplitude of cusp-related density enhancement does on average not depend on the IMF By orientation, solar cycle phase, and local season. Also, it is apparent that the IMF By amplitude does not have a big influence on the relative amplitude of the density anomaly. Conversely, there exists a good correlation between ρrel and the negative amplitude of IMF Bz prevailing about half an hour earlier. In the cusp region, both large-scale FAC distribution and thermospheric zonal wind velocity exhibit a clear dependence on the IMF By orientation. In the case of positive (negative) IMF By there is a systematic imbalance between downward (upward) and upward (downward) FACs peaks equatorward and poleward of the reference point, respectively. The zonal wind velocity is directed towards west i.e. towards dawn in a geomagnetic latitude-magnetic local time (MLat-MLT) frame. This is true for all local seasons and solar conditions. The thermospheric density enhancements appear half way between Region 1 (R1) and Region 0 (R0) field-aligned currents, in closer proximity to the upward FAC region. In our case R0 currents are systematically weaker than R1 ones. Also, around the cusp region we find no sign of Region 2 field-aligned currents. We can conclude that there is a close spatial relationship between FACs and cusp-related density enhancements, but we cannot offer any simple functional relation between field-aligned current strength and density anomaly amplitude. There seem to be other quantities (e.g. precipitating electrons) controlling this relation. All the conclusions drawn above are true for the Northern Hemisphere. There may be differences in the Southern Hemisphere.

Ensemble Mean Density and its Connection to Other Microphysical Properties of Falling Snow as Observed in Southern Finland

NASA Technical Reports Server (NTRS)

Tiira, Jussi; Moisseev, Dmitri N.; Lerber, Annakaisa von; Ori, Davide; Tokay, Ali; Bliven, Larry F.; Petersen, Walter

2016-01-01

In this study measurements collected during winters 2013/2014 and 2014/2015 at the University of Helsinki measurement station in Hyytiala are used to investigate connections between ensemble mean snow density, particle fall velocity and parameters of the particle size distribution (PSD). The density of snow is derived from measurements of particle fall velocity and PSD, provided by a particle video imager, and weighing gauge measurements of precipitation rate. Validity of the retrieved density values is checked against snow depth measurements. A relation retrieved for the ensemble mean snow density and median volume diameter is in general agreement with previous studies, but it is observed to vary significantly from one winter to the other. From these observations, characteristic mass- dimensional relations of snow are retrieved. For snow rates more than 0.2mm/h, a correlation between the intercept parameter of normalized gamma PSD and median volume diameter was observed.

Charged BTZ-like black hole solutions and the diffusivity-butterfly velocity relation

NASA Astrophysics Data System (ADS)

Ge, Xian-Hui; Sin, Sang-Jin; Tian, Yu; Wu, Shao-Feng; Wu, Shang-Yu

2018-01-01

We show that there exists a class of charged BTZ-like black hole solutions in Lifshitz spacetime with a hyperscaling violating factor. The charged BTZ black hole is characterized by a charge-dependent logarithmic term in the metric function. As concrete examples, we give five such charged BTZ-like black hole solutions and the standard charged BTZ metric can be regarded as a special instance of them. In order to check the recent proposed universal relations between diffusivity and the butterfly velocity, we first compute the diffusion constants of the standard charged BTZ black holes and then extend our calculation to arbitrary dimension d, exponents z and θ. Remarkably, the case d = θ and z = 2 is a very special in that the charge diffusion D c is a constant and the energy diffusion D e might be ill-defined, but v B 2 τ diverges. We also compute the diffusion constants for the case that the DC conductivity is finite but in the absence of momentum relaxation.

Ensemble mean density and its connection to other microphysical properties of falling snow as observed in Southern Finland

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiira, Jussi; Moisseev, Dmitri N.; von Lerber, Annakaisa

In this study measurements collected during winters 2013/2014 and 2014/2015 at the University of Helsinki measurement station in Hyytiala are used to investigate connections between ensemble mean snow density, particle fall velocity and parameters of the particle size distribution (PSD). The density of snow is derived from measurements of particle fall velocity and PSD, provided by a particle video imager, and weighing gauge measurements of precipitation rate. Validity of the retrieved density values is checked against snow depth measurements. Here, a relation retrieved for the ensemble mean snow density and median volume diameter is in general agreement with previous studies,more » but it is observed to vary significantly from one winter to the other. From these observations, characteristic mass–dimensional relations of snow are retrieved. For snow rates more than 0.2 mm h -1, a correlation between the intercept parameter of normalized gamma PSD and median volume diameter was observed.« less

Ensemble mean density and its connection to other microphysical properties of falling snow as observed in Southern Finland

DOE PAGES

Tiira, Jussi; Moisseev, Dmitri N.; von Lerber, Annakaisa; ...

2016-09-28

In this study measurements collected during winters 2013/2014 and 2014/2015 at the University of Helsinki measurement station in Hyytiala are used to investigate connections between ensemble mean snow density, particle fall velocity and parameters of the particle size distribution (PSD). The density of snow is derived from measurements of particle fall velocity and PSD, provided by a particle video imager, and weighing gauge measurements of precipitation rate. Validity of the retrieved density values is checked against snow depth measurements. Here, a relation retrieved for the ensemble mean snow density and median volume diameter is in general agreement with previous studies,more » but it is observed to vary significantly from one winter to the other. From these observations, characteristic mass–dimensional relations of snow are retrieved. For snow rates more than 0.2 mm h -1, a correlation between the intercept parameter of normalized gamma PSD and median volume diameter was observed.« less

Representing delayed force feedback as a combination of current and delayed states.

PubMed

Avraham, Guy; Mawase, Firas; Karniel, Amir; Shmuelof, Lior; Donchin, Opher; Mussa-Ivaldi, Ferdinando A; Nisky, Ilana

2017-10-01

To adapt to deterministic force perturbations that depend on the current state of the hand, internal representations are formed to capture the relationships between forces experienced and motion. However, information from multiple modalities travels at different rates, resulting in intermodal delays that require compensation for these internal representations to develop. To understand how these delays are represented by the brain, we presented participants with delayed velocity-dependent force fields, i.e., forces that depend on hand velocity either 70 or 100 ms beforehand. We probed the internal representation of these delayed forces by examining the forces the participants applied to cope with the perturbations. The findings showed that for both delayed forces, the best model of internal representation consisted of a delayed velocity and current position and velocity. We show that participants relied initially on the current state, but with adaptation, the contribution of the delayed representation to adaptation increased. After adaptation, when the participants were asked to make movements with a higher velocity for which they had not previously experienced with the delayed force field, they applied forces that were consistent with current position and velocity as well as delayed velocity representations. This suggests that the sensorimotor system represents delayed force feedback using current and delayed state information and that it uses this representation when generalizing to faster movements. NEW & NOTEWORTHY The brain compensates for forces in the body and the environment to control movements, but it is unclear how it does so given the inherent delays in information transmission and processing. We examined how participants cope with delayed forces that depend on their arm velocity 70 or 100 ms beforehand. After adaptation, participants applied opposing forces that revealed a partially correct representation of the perturbation using the current and the delayed information. Copyright © 2017 the American Physiological Society.

From University to Comprehensive Higher Education: On the Widening Gap between "Lehre und Leben."

ERIC Educational Resources Information Center

Bertilsson, Margareta

1992-01-01

The theory of Wilhelm von Humboldt concerning the role of the university is discussed, focusing on four imperatives regulating its activities--unity of research and teaching; the empirical sciences; science and socialization; and science and universal enlightenment. The current status of the university is assessed in relation to these ideals. (MSE)

Partnerships through Innovative Telecommunications at California State University, Chico.

ERIC Educational Resources Information Center

Meuter, Ralph F.; And Others

California State University (CSU), Chico, has used its relatively isolated location to develop an extensive educational system known as "Instructional Television for Students" (ITFS). Currently, the university is launching plans for new partnerships utilizing satellite technology for the delivery of educational programs. Over the years,…

The effect of beamwidth on the analysis of electron-beam-induced current line scans

NASA Astrophysics Data System (ADS)

Luke, Keung L.

1995-04-01

A real electron beam has finite width, which has been almost universally ignored in electron-beam-induced current (EBIC) theories. Obvious examples are point-source-based EBIC analyses, which neglect both the finite volume of electron-hole carriers generated by an energetic electron beam of negligible width and the beamwidth when it is no longer negligible. Gaussian source-based analyses are more realistic but the beamwidth has not been included, partly because the generation volume is much larger than the beamwidth, but this is not always the case. In this article Donolato's Gaussian source-based EBIC equation is generalized to include the beamwidth of a Gaussian beam. This generalized equation is then used to study three problems: (1) the effect of beamwidth on EBIC line scans and on effective diffusion lengths and the results are applied to the analysis of the EBIC data of Dixon, Williams, Das, and Webb; (2) unresolved questions raised by others concerning the applicability of the Watanabe-Actor-Gatos method to real EBIC data to evaluate surface recombination velocity; (3) the effect of beamwidth on the methods proposed recently by the author to determine the surface recombination velocity and to discriminate between the Everhart-Hoff and Kanaya-Okayama ranges which is the correct one to use for analyzing EBIC line scans.

Current Developments in Public Relations and a Review of their Implications on Public Relations Curriculum in Canada.

ERIC Educational Resources Information Center

Wills, Sandra Judith Abiola

Intended to review the recent professional developments in public relations as they are documented in the literature and to explore the implications of these developments for public relations education in Canada at the university level, this thesis is in six chapters, as follows: (1) Introduction; (2) Defining Public Relations; (3) Current Public…

Satellite Altimetry and Current-Meter Velocities in the Malvinas Current at 41°S: Comparisons and Modes of Variations

NASA Astrophysics Data System (ADS)

Ferrari, Ramiro; Artana, Camila; Saraceno, Martin; Piola, Alberto R.; Provost, Christine

2017-12-01

Three year long current-meter arrays were deployed in the Malvinas Current at 41°S below a satellite altimeter track at about 10 years intervals. Surface geostrophic velocities (SGV) derived from satellite altimetric data are compared with the in situ velocities at the upper current meter (˜300 m). Multisatellite gridded SGV compare better with in situ observations than along-track SGV. In spite of the proximity of the moorings to the complex Brazil-Malvinas Confluence (BMC) region, satellite SGV are significantly correlated with the 20 day low-passed in situ velocities (0.85 for along-isobaths velocities, 0.8 for cross-isobaths velocities). The recent in situ measurement period (2014-2015) stands out in the altimetry record with a long-lasting (4 months) high level of eddy kinetic energy at the mooring site and a southernmost location of the Subantarctic Front (SAF). The first two modes of variations of sea level anomaly (SLA) over the BMC remarkably match the first two modes of the low-passed in situ velocities. The first mode is associated with a latitudinal migration of the SAF, and the second with a longitudinal displacement of the Brazil Current overshoot. The two modes dominate the 24 year long record of SLA in the BMC, with energy peaks at the annual and semiannual periods for the first mode and at 3-5 months for the second mode. The SLA over the Southwest Atlantic was regressed onto the two confluence modes of SLA variations and showed remarkable standing wave train like structures in the Argentine Basin.

Current-driven ion-acoustic and potential-relaxation instabilities excited in plasma plume during electron beam welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trushnikov, D. N., E-mail: trdimitr@yandex.ru; Mladenov, G. M., E-mail: gmmladenov@abv.bg; Koleva, E. G., E-mail: eligeorg@abv.bg

Many papers have sought correlations between the parameters of secondary particles generated above the beam/work piece interaction zone, dynamics of processes in the keyhole, and technological processes. Low- and high-frequency oscillations of the current, collected by plasma have been observed above the welding zone during electron beam welding. Low-frequency oscillations of secondary signals are related to capillary instabilities of the keyhole, however; the physical mechanisms responsible for the high-frequency oscillations (>10 kHz) of the collected current are not fully understood. This paper shows that peak frequencies in the spectra of the collected high-frequency signal are dependent on the reciprocal distancemore » between the welding zone and collector electrode. From the relationship between current harmonics frequency and distance of the collector/welding zone, it can be estimated that the draft velocity of electrons or phase velocity of excited waves is about 1600 m/s. The dispersion relation with the properties of ion-acoustic waves is related to electron temperature 10 000 K, ion temperature 2 400 K and plasma density 10{sup 16} m{sup −3}, which is analogues to the parameters of potential-relaxation instabilities, observed in similar conditions. The estimated critical density of the transported current for creating the anomalous resistance state of plasma is of the order of 3 A·m{sup −2}, i.e. 8 mA for a 3–10 cm{sup 2} collector electrode. Thus, it is assumed that the observed high-frequency oscillations of the current collected by the positive collector electrode are caused by relaxation processes in the plasma plume above the welding zone, and not a direct demonstration of oscillations in the keyhole.« less

Current-driven ion-acoustic and potential-relaxation instabilities excited in plasma plume during electron beam welding

NASA Astrophysics Data System (ADS)

Trushnikov, D. N.; Mladenov, G. M.; Belenkiy, V. Ya.; Koleva, E. G.; Varushkin, S. V.

2014-04-01

Many papers have sought correlations between the parameters of secondary particles generated above the beam/work piece interaction zone, dynamics of processes in the keyhole, and technological processes. Low- and high-frequency oscillations of the current, collected by plasma have been observed above the welding zone during electron beam welding. Low-frequency oscillations of secondary signals are related to capillary instabilities of the keyhole, however; the physical mechanisms responsible for the high-frequency oscillations (>10 kHz) of the collected current are not fully understood. This paper shows that peak frequencies in the spectra of the collected high-frequency signal are dependent on the reciprocal distance between the welding zone and collector electrode. From the relationship between current harmonics frequency and distance of the collector/welding zone, it can be estimated that the draft velocity of electrons or phase velocity of excited waves is about 1600 m/s. The dispersion relation with the properties of ion-acoustic waves is related to electron temperature 10 000 K, ion temperature 2 400 K and plasma density 1016 m-3, which is analogues to the parameters of potential-relaxation instabilities, observed in similar conditions. The estimated critical density of the transported current for creating the anomalous resistance state of plasma is of the order of 3 A.m-2, i.e. 8 mA for a 3-10 cm2 collector electrode. Thus, it is assumed that the observed high-frequency oscillations of the current collected by the positive collector electrode are caused by relaxation processes in the plasma plume above the welding zone, and not a direct demonstration of oscillations in the keyhole.

Discovering frequently recurring movement sequences in team-sport athlete spatiotemporal data.

PubMed

Sweeting, Alice J; Aughey, Robert J; Cormack, Stuart J; Morgan, Stuart

2017-12-01

Athlete external load is typically analysed from predetermined movement thresholds. The combination of movement sequences and differences in these movements between playing positions is also currently unknown. This study developed a method to discover the frequently recurring movement sequences across playing position during matches. The external load of 12 international female netball athletes was collected by a local positioning system during four national-level matches. Velocity, acceleration and angular velocity were calculated from positional (X, Y) data, clustered via one-dimensional k-means and assigned a unique alphabetic label. Combinations of velocity, acceleration and angular velocity movement were compared using the Levenshtein distance and similarities computed by the longest common substring problem. The contribution of each movement sequence, according to playing position and relative to the wider data set, was then calculated via the Minkowski distance. A total of 10 frequently recurring combinations of movement were discovered, regardless of playing position. Only the wing attack, goal attack and goal defence playing positions are closely related. We developed a technique to discover the movement sequences, according to playing position, performed by elite netballers. This methodology can be extended to discover the frequently recurring movements within other team sports and across levels of competition.

Large-Scale Survey of the Structure of the Dayside Magnetopause by MMS

NASA Astrophysics Data System (ADS)

Paschmann, G.; Haaland, S. E.; Phan, T. D.; Sonnerup, B. U. Ö.; Burch, J. L.; Torbert, R. B.; Gershman, D. J.; Dorelli, J. C.; Giles, B. L.; Pollock, C.; Saito, Y.; Lavraud, B.; Russell, C. T.; Strangeway, R. J.; Baumjohann, W.; Fuselier, S. A.

2018-03-01

This paper describes the generation and initial utilization of a database containing 80 vector and scalar quantities, for a total of 8,670 magnetopause and magnetosheath current sheet crossings by MMS1, using plasma and magnetic field data from the Fast Plasma Investigation, Fluxgate Magnetometer, and Hot Plasma Composition Analyzer instruments, augmented by solar wind and interplanetary magnetic field data from CDAWeb. Based on a determination of the current sheet width, measured and calculated vector and scalar quantities are stored for the two sides of the current sheet and for selected times within the current sheet. The only manual operations were the classification of the current sheets according to the type of boundary, the character of the magnetic field transition, and the quality of the current sheet fit. To characterize the database, histograms of selected key quantities are presented. We then give the statistics for the duration, motion, and thicknesses of the magnetopause current sheet, using single-spacecraft techniques for the determination of the normal velocities, obtaining median results of 12.9 s, 38.5 km/s, and 705.4 km, respectively. When scaled to the ion inertial length, the median thickness became 12.6; there were no thicknesses less than one. Next, we apply the Walén relation to find crossings that are rotational discontinuities and thus may indicate ongoing magnetic reconnection. For crossings where the velocities in the outflow region exceed the velocity on the magnetosheath side by at least 250 km/s, 47% meet our rotational discontinuity criteria. If we require the outflow to exceed 250 km/s along the L direction, then the percentage rises to 68%.

Application of acoustic velocity meters for gaging discharge of three low-velocity tidal streams in the St. Johns River basin, northeast Florida

USGS Publications Warehouse

Sloat, J.V.; Gain, W.S.

1995-01-01

Index-velocity data collected with acoustic velocity meters, stage data, and cross-sectional area data were used to calculate discharge at three low-velocity, tidal streamflow stations in north-east Florida. Discharge at three streamflow stations was computed as the product of the channel cross-sectional area and the mean velocity as determined from an index velocity measured in the stream using an acoustic velocity meter. The tidal streamlflow stations used in the study were: Six Mile Creek near Picolata, Fla.; Dunns Creek near Satsuma, Fla.; and the St. Johns River at Buffalo Bluff. Cross-sectional areas at the measurement sections ranged from about 3,000 square feet at Six Mile Creek to about 18,500 square feet at St. Johns River at Buffalo Bluff. Physical characteristics for all three streams were similar except for drainage area. The topography primarily is low-relief, swampy terrain; stream velocities ranged from about -2 to 2 feet per second; and the average change in stage was about 1 foot. Instantaneous discharge was measured using a portable acoustic current meter at each of the three streams to develop a relation between the mean velocity in the stream and the index velocity measured by the acoustic velocity meter. Using least-squares linear regression, a simple linear relation between mean velocity and index velocity was determined. Index velocity was the only significant linear predictor of mean velocity for Six Mile Creek and St. Johns River at Buffalo Bluff. For Dunns Creek, both index velocity and stage were used to develop a multiple-linear predictor of mean velocity. Stage-area curves for each stream were developed from bathymetric data. Instantaneous discharge was computed by multiplying results of relations developed for cross-sectional area and mean velocity. Principal sources of error in the estimated discharge are identified as: (1) instrument errors associated with measurement of stage and index velocity, (2) errors in the representation of mean daily stage and index velocity due to natural variability over time and space, and (3) errors in cross-sectional area and mean-velocity ratings based on stage and index velocity. Standard errors for instantaneous discharge for the median cross-sectional area for Six Mile Creek, Dunns Creek, and St. Johns River at Buffalo Bluff were 94,360, and 1,980 cubic feet per second, respectively. Standard errors for mean daily discharge for the median cross-sectional area for Six Mile Creek, Dunns Creek, and St. Johns River at Buffalo Bluff were 25, 65, and 455 cubic feet per second, respectively. Mean daily discharge at the three sites ranged from about -500 to 1,500 cubic feet per second at Six Mile Creek and Dunns Creek and from about -500 to 15,000 cubic feet per second on the St. Johns River at Buffalo Bluff. For periods of high discharge, the AVM index-velocity method tended to produce estimates accurate with 2 to 6 percent. For periods of moderate discharge, errors in discharge may increase to more than 50 percent. At low flows, errors as a percentage of discharge increase toward infinity.

Sheet Flows, Avalanches, and Dune Evolution on Earth and Mars

NASA Technical Reports Server (NTRS)

2003-01-01

This investigation is a collaboration between researchers at Cornell University, the University of Florida, and the University of Rennes 1, France. Flow modeling at Cornell University focused on mechanisms for the suspension and transport of wind-blown sand that are important in both terrestrial and Martian environments. These mechanisms include the saltation (or jumping) of grains, collisions between grains, and the interaction of grains with the velocity fluctuations of the turbulent wind. Of particular interest are sheet flows; these are relatively thin, highly concentrated regions of grains flowing near the ground under the influence of a strong turbulent wind. In them, the grains are suspended by interparticle collisions. Sheet flows may be relatively rare events, but they have the capacity to move great amounts of sand. In order to describe sheet flows, a turbulent mixture theory was formulated for particles in a fluid in which fluctuations in the volume fiaction of the particles take place on the scale of the turbulent eddies. Ensemble averaged equations for particle and fluid mass, momentum, and energy and fluid rate of dissipation were expressed in terms of Farve (concentration) averaged velocities and the associated velocity fluctuations. Correlations that describe the turbulent suspension of particles and dissipation of turbulent energy of both phases due to fluid particle interactions were modeled and boundary conditions at the bed and at the upper surface of the collisional flow were formulated. The boundary conditions at the upper surface were tested in a numerical simulation developed at the University of Florida. Steady and unsteady solutions for steady and unsteady fully-developed flows were obtained over a range of wind speeds fiom the lowest for which collisional between particles occurred to at which turbulent suspension is found to dominate collisional suspension. Below the value of the wind speed at which collisions between particles were unimportant, numerical solutions were obtained for the velocity distribution function and the resulting fields of concentration, particle and gas mean velocity, and particle shear stress for the steady two-dimensional saltation of spherical sand particles driven by a turbulent wind over a bed characterized by a simple relationship (the splash function) between the properties of incoming particles and those of the rebounding particles and other particles ejected fiom the bed. At the University of Rennes 1, experiments devoted to the characterization of the splash function for beds consisting of either random or ordered arrays of spheres in two- dimensions were completed. These indicated the role played by the packing geometry in the rebound and ejection of grains. Preliminary experiments on response of a three- dimensional collision bed to a collision with a single particle were performed. Data was taken with a single camera focused on the plane of collision. Here, for example, the decrease of the effective coefficient of restitution of the bed with an increase of the angle of incidence of the incoming particle has been measured. Other experiments on avalanches at Rennes studied the properties of the flows of particles that are responsible for the motion of the leeward side of a dune. In these, the dependence of the initiation of avalanches on the packing and depth of the particles was measured. Particle migration was studied in inclined flows of a binary mixture of disks and the mechanisms of diffision and segregation were isolated and characterized. The influence of side wall on dense, rapid inclined flows was measured and shown to be the reason why the angle of the free surface in such flows can exceed the static angle of repose. Future research will be devoted to a better understanding the transition between saltating (collisionless) and collisional flows as the wind speed the increases. This will involve the understanding of the evolution of the splash function as clisions with the bed become more numerous, more frequent, and more violent.

Observations of thermal ion influxes about the space shuttle

NASA Technical Reports Server (NTRS)

Grebowsky, Joe M.; Schaefer, A.

1990-01-01

Ion mass spectrometer measurements made as part of the University of Iowa's Plasma Diagnostic Package on the STS-3 and Spacelab 2 Space Shuttle missions sampled a variety of ion composition and collected ion current responses to gas emissions from the vehicle. The only other shuttle ion measurements were made by an Air Force Geophysics Laboratory (AFGL) quadrupole spectrometer flown on STS-4. Gas emissions change the distribution of the incoming plasma through scattering and charge transfer processes. A background flux of contaminant ion species (mostly relating to water) always exists in the near vicinity of the shuttle with a magnitude which is dependent on the look direction of the spectrometer but which varies differently with changes in the angle of attack than that of the ambient ions. There is a near shuttle wake cavity in the contaminant ion distributions which has a different spatial configuration than the wake of the ambient ions. Although water dumps produce the most persistent ion perturbations, the sources for ion current modification were best delineated from measurements made when only one or two of the Reaction Control System thrusters fired for a relatively long duration. Contaminant ion perturbations associated with such firings were observed to persist for the order of a second after the cessation of the firings. The dense thruster plumes are efficient collisional, charge exchange barriers to the passage of ambient ions. Collected ion current perturbations were more evident for firings of the rear verniers, whose plumes scatter off projecting surfaces, than for the nose thrusters. The effect of the Vernier firings was found to depend not only on the location and attitude of the spectrometer with respect to the shuttle and thruster plume direction, but also on the orientation of the local magnetic field with respect to the shuttle velocity.

A modified beam-to-earth transformation to measure short-wavelength internal waves with an acoustic Doppler current profiler

USGS Publications Warehouse

Scotti, A.; Butman, B.; Beardsley, R.C.; Alexander, P.S.; Anderson, S.

2005-01-01

The algorithm used to transform velocity signals from beam coordinates to earth coordinates in an acoustic Doppler current profiler (ADCP) relies on the assumption that the currents are uniform over the horizontal distance separating the beams. This condition may be violated by (nonlinear) internal waves, which can have wavelengths as small as 100-200 m. In this case, the standard algorithm combines velocities measured at different phases of a wave and produces horizontal velocities that increasingly differ from true velocities with distance from the ADCP. Observations made in Massachusetts Bay show that currents measured with a bottom-mounted upward-looking ADCP during periods when short-wavelength internal waves are present differ significantly from currents measured by point current meters, except very close to the instrument. These periods are flagged with high error velocities by the standard ADCP algorithm. In this paper measurements from the four spatially diverging beams and the backscatter intensity signal are used to calculate the propagation direction and celerity of the internal waves. Once this information is known, a modified beam-to-earth transformation that combines appropriately lagged beam measurements can be used to obtain current estimates in earth coordinates that compare well with pointwise measurements. ?? 2005 American Meteorological Society.

Combining physical training with transcranial direct current stimulation to improve gait in Parkinson's disease: a pilot randomized controlled study.

PubMed

Kaski, D; Dominguez, R O; Allum, J H; Islam, A F; Bronstein, A M

2014-11-01

To improve gait and balance in patients with Parkinson's disease by combining anodal transcranial direct current stimulation with physical training. In a double-blind design, one group (physical training; n = 8) underwent gait and balance training during transcranial direct current stimulation (tDCS; real/sham). Real stimulation consisted of 15 minutes of 2 mA transcranial direct current stimulation over primary motor and premotor cortex. For sham, the current was switched off after 30 seconds. Patients received the opposite stimulation (sham/real) with physical training one week later; the second group (No physical training; n = 8) received stimulation (real/sham) but no training, and also repeated a sequential transcranial direct current stimulation session one week later (sham/real). Hospital Srio Libanes, Buenos Aires, Argentina. Sixteen community-dwelling patients with Parkinson's disease. Transcranial direct current stimulation with and without concomitant physical training. Gait velocity (primary gait outcome), stride length, timed 6-minute walk test, Timed Up and Go Test (secondary outcomes), and performance on the pull test (primary balance outcome). Transcranial direct current stimulation with physical training increased gait velocity (mean = 29.5%, SD = 13; p < 0.01) and improved balance (pull test: mean = 50.9%, SD = 37; p = 0.01) compared with transcranial direct current stimulation alone. There was no isolated benefit of transcranial direct current stimulation alone. Although physical training improved gait velocity (mean = 15.5%, SD = 12.3; p = 0.03), these effects were comparatively less than with combined tDCS + physical therapy (p < 0.025). Greater stimulation-related improvements were seen in patients with more advanced disease. Anodal transcranial direct current stimulation during physical training improves gait and balance in patients with Parkinson's disease. Power calculations revealed that 14 patients per treatment arm (α = 0.05; power = 0.8) are required for a definitive trial. © The Author(s) 2014.

Effect of Inductive Coil Geometry and Current Sheet Trajectory of a Conical Theta Pinch Pulsed Inductive Plasma Accelerator

NASA Technical Reports Server (NTRS)

Hallock, Ashley K.; Polzin, Kurt A.; Bonds, Kevin W.; Emsellem, Gregory D.

2011-01-01

Results are presented demonstrating the e ect of inductive coil geometry and current sheet trajectory on the exhaust velocity of propellant in conical theta pinch pulsed induc- tive plasma accelerators. The electromagnetic coupling between the inductive coil of the accelerator and a plasma current sheet is simulated, substituting a conical copper frustum for the plasma. The variation of system inductance as a function of plasma position is obtained by displacing the simulated current sheet from the coil while measuring the total inductance of the coil. Four coils of differing geometries were employed, and the total inductance of each coil was measured as a function of the axial displacement of two sep- arate copper frusta both having the same cone angle and length as the coil but with one compressed to a smaller size relative to the coil. The measured relationship between total coil inductance and current sheet position closes a dynamical circuit model that is used to calculate the resulting current sheet velocity for various coil and current sheet con gura- tions. The results of this model, which neglects the pinching contribution to thrust, radial propellant con nement, and plume divergence, indicate that in a conical theta pinch ge- ometry current sheet pinching is detrimental to thruster performance, reducing the kinetic energy of the exhausting propellant by up to 50% (at the upper bound for the parameter range of the study). The decrease in exhaust velocity was larger for coils and simulated current sheets of smaller half cone angles. An upper bound for the pinching contribution to thrust is estimated for typical operating parameters. Measurements of coil inductance for three di erent current sheet pinching conditions are used to estimate the magnetic pressure as a function of current sheet radial compression. The gas-dynamic contribution to axial acceleration is also estimated and shown to not compensate for the decrease in axial electromagnetic acceleration that accompanies the radial compression of the plasma in conical theta pinches.

Numerical performance analysis of acoustic Doppler velocity profilers in the wake of an axial-flow marine hydrokinetic turbine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richmond, Marshall C.; Harding, Samuel F.; Romero Gomez, Pedro DJ

The use of acoustic Doppler current profilers (ADCPs) for the characterization of flow conditions in the vicinity of both experimental and full scale marine hydrokinetic (MHK) turbines is becoming increasingly prevalent. The computation of a three dimensional velocity measurement from divergent acoustic beams requires the assumption that the flow conditions are homogeneous between all beams at a particular axial distance from the instrument. In the near wake of MHK devices, the mean fluid motion is observed to be highly spatially dependent as a result of torque generation and energy extraction. This paper examines the performance of ADCP measurements in suchmore » scenarios through the modelling of a virtual ADCP (VADCP) instrument in the velocity field in the wake of an MHK turbine resolved using unsteady computational fluid dynamics (CFD). This is achieved by sampling the CFD velocity field at equivalent locations to the sample bins of an ADCP and performing the coordinate transformation from beam coordinates to instrument coordinates and finally to global coordinates. The error in the mean velocity calculated by the VADCP relative to the reference velocity along the instrument axis is calculated for a range of instrument locations and orientations. The stream-wise velocity deficit and tangential swirl velocity caused by the rotor rotation lead to significant misrepresentation of the true flow velocity profiles by the VADCP, with the most significant errors in the transverse (cross-flow) velocity direction.« less

Design of the Digital Satellite Link Interface for a System That Detects the Precursory Electromagnetic Emissions Associated with Earthquakes

DTIC Science & Technology

1986-12-01

earthquake that is likely to occur in a given louality [Ref. 8:p. 1082]. The accumulation law of seismotectonic movement relates the amount of...mechanism - fault creep anomaly - seismic wave velocity - geomagnetic field - telluric (earth) currents - electromagnetic emissions - resistivity of

Spatial orientation of caloric nystagmus in semicircular canal-plugged monkeys.

PubMed

Arai, Yasuko; Yakushin, Sergei B; Cohen, Bernard; Suzuki, Jun-Ichi; Raphan, Theodore

2002-08-01

We studied caloric nystagmus before and after plugging all six semicircular canals to determine whether velocity storage contributed to the spatial orientation of caloric nystagmus. Monkeys were stimulated unilaterally with cold ( approximately 20 degrees C) water while upright, supine, prone, right-side down, and left-side down. The decline in the slow phase velocity vector was determined over the last 37% of the nystagmus, at a time when the response was largely due to activation of velocity storage. Before plugging, yaw components varied with the convective flow of endolymph in the lateral canals in all head orientations. Plugging blocked endolymph flow, eliminating convection currents. Despite this, caloric nystagmus was readily elicited, but the horizontal component was always toward the stimulated (ipsilateral) side, regardless of head position relative to gravity. When upright, the slow phase velocity vector was close to the yaw and spatial vertical axes. Roll components became stronger in supine and prone positions, and vertical components were enhanced in side down positions. In each case, this brought the velocity vectors toward alignment with the spatial vertical. Consistent with principles governing the orientation of velocity storage, when the yaw component of the velocity vector was positive, the cross-coupled pitch or roll components brought the vector upward in space. Conversely, when yaw eye velocity vector was downward in the head coordinate frame, i.e., negative, pitch and roll were downward in space. The data could not be modeled simply by a reduction in activity in the ipsilateral vestibular nerve, which would direct the velocity vector along the roll direction. Since there is no cross coupling from roll to yaw, velocity storage alone could not rotate the vector to fit the data. We postulated, therefore, that cooling had caused contraction of the endolymph in the plugged canals. This contraction would deflect the cupula toward the plug, simulating ampullofugal flow of endolymph. Inhibition and excitation induced by such cupula deflection fit the data well in the upright position but not in lateral or prone/supine conditions. Data fits in these positions required the addition of a spatially orientated, velocity storage component. We conclude, therefore, that three factors produce cold caloric nystagmus after canal plugging: inhibition of activity in ampullary nerves, contraction of endolymph in the stimulated canals, and orientation of eye velocity to gravity through velocity storage. Although the response to convection currents dominates the normal response to caloric stimulation, velocity storage probably also contributes to the orientation of eye velocity.

Energy input from quasars regulates the growth and activity of black holes and their host galaxies.

PubMed

Di Matteo, Tiziana; Springel, Volker; Hernquist, Lars

2005-02-10

In the early Universe, while galaxies were still forming, black holes as massive as a billion solar masses powered quasars. Supermassive black holes are found at the centres of most galaxies today, where their masses are related to the velocity dispersions of stars in their host galaxies and hence to the mass of the central bulge of the galaxy. This suggests a link between the growth of the black holes and their host galaxies, which has indeed been assumed for a number of years. But the origin of the observed relation between black hole mass and stellar velocity dispersion, and its connection with the evolution of galaxies, have remained unclear. Here we report simulations that simultaneously follow star formation and the growth of black holes during galaxy-galaxy collisions. We find that, in addition to generating a burst of star formation, a merger leads to strong inflows that feed gas to the supermassive black hole and thereby power the quasar. The energy released by the quasar expels enough gas to quench both star formation and further black hole growth. This determines the lifetime of the quasar phase (approaching 100 million years) and explains the relationship between the black hole mass and the stellar velocity dispersion.

Responses of bluegills and black crappies to dissolved oxygen, temperature, and current in backwater lakes of the upper Mississippi River during winter

USGS Publications Warehouse

Knights, B.C.; Johnson, B.L.; Sandheinrich, M.B.

1995-01-01

We conducted a radiotelemetry study to examine the effects of dissolved oxygen (DO), water temperature, and current velocity on winter habitat selection by bluegills Lepomis macrochirus and black crappies Pomoxis nigromaculatus in the Finger Lakes backwater complex, Pool 5, on the upper Mississippi River. When DO was above 2 mg/L, both species selected areas with water temperature greater than 1 degree C and undetectable current. As dissolved oxygen concentrations fell below 2 mg/L, fish moved to areas with higher DO, despite water temperatures of 1 degree C and lower and current velocities of 1 cm/s. Areas with water temperature less than 1 degree C and current velocity greater than 1 cm/s were avoided. To incorporate the winter habitat requirements of bluegills and black crappies into habitat restoration projects, we recommend designs that allow the inflow of oxygenated water to maintain adequate DO without substantially decreasing temperature and increasing current velocity.

Curvature from Strong Gravitational Lensing: A Spatially Closed Universe or Systematics?

NASA Astrophysics Data System (ADS)

Li, Zhengxiang; Ding, Xuheng; Wang, Guo-Jian; Liao, Kai; Zhu, Zong-Hong

2018-02-01

Model-independent constraints on the spatial curvature are not only closely related to important problems, such as the evolution of the universe and properties of dark energy, but also provide a test of the validity of the fundamental Copernican principle. In this paper, with the distance sum rule in the Friedmann–Lemaître–Robertson–Walker metric, we achieve model-independent measurements of the spatial curvature from the latest type Ia supernovae and strong gravitational lensing (SGL) observations. We find that a spatially closed universe is preferred. Moreover, by considering different kinds of velocity dispersion and subsamples, we study possible factors that might affect model-independent estimations for the spatial curvature from SGL observations. It is suggested that the combination of observational data from different surveys might cause a systematic bias, and the tension between the spatially flat universe and SGL observations is alleviated when the subsample only from the Sloan Lens ACS Survey is used or a more complex treatment for the density profile of lenses is considered.

THE STELLAR MASS FUNDAMENTAL PLANE AND COMPACT QUIESCENT GALAXIES AT z < 0.6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zahid, H. Jabran; Damjanov, Ivana; Geller, Margaret J.

2016-04-20

We examine the evolution of the relation between stellar mass surface density, velocity dispersion, and half-light radius—the stellar mass fundamental plane (MFP)—for quiescent galaxies at z < 0.6. We measure the local relation from galaxies in the Sloan Digital Sky Survey and the intermediate redshift relation from ∼500 quiescent galaxies with stellar masses 10 ≲ log( M {sub *}/ M {sub ⊙}) ≲ 11.5. Nearly half of the quiescent galaxies in our intermediate redshift sample are compact. After accounting for important selection and systematic effects, the velocity dispersion distribution of galaxies at intermediate redshifts is similar to that of galaxiesmore » in the local universe. Galaxies at z < 0.6 appear to be smaller (≲0.1 dex) than galaxies in the local sample. The orientation of the stellar MFP is independent of redshift for massive quiescent galaxies at z < 0.6 and the zero-point evolves by ∼0.04 dex. Compact quiescent galaxies fall on the same relation as the extended objects. We confirm that compact quiescent galaxies are the tail of the size and mass distribution of the normal quiescent galaxy population.« less

Equatorial Currents in the Indian Ocean Based on Measurements in February 2017

NASA Astrophysics Data System (ADS)

Neiman, V. G.; Frey, D. I.; Ambrosimov, A. K.; Kaplunenko, D. D.; Morozov, E. G.; Shapovalov, S. M.

2018-03-01

We analyze the results of measurements of the Tareev equatorial undercurrent in the Indian Ocean in February 2017. Sections from 3° S to 3°45' N along 68° and 65° E crossed the current with measurements of the temperature, salinity, and current velocity at oceanographic stations. The maximum velocity of this eastward flow was recorded precisely at the equator. The velocity at a depth of 50 m was approximately 60 cm/s. The transport of the Tareev Current was estimated at 9.8 Sv (1 Sv = 106 m3/s).

Do Invertebrate Activity and Current Velocity Affect Fungal Assemblage Structure in Leaves?

NASA Astrophysics Data System (ADS)

Ferreira, Verónica; Graça, Manuel A. S.

2006-02-01

In this study we assessed the effect of current velocity and shredder presence, manipulated in artificial channels, on the structure of the fungal assemblage colonizing alder (Alnus glutinosa (L.) Gaertner) leaves incubated in coarse and fine mesh bags. Fungal sporulation rates, cumulative conidial production and number of species of aquatic hyphomycetes were higher in leaves exposed to high rather than to low current velocity. The opposite was observed regarding Simpson's index (D) on the fungal assemblage. Some species of aquatic hyphomycetes were consistently stimulated in high current channels. No effect of shredders or of mesh type was observed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polat, Orhan, E-mail: orhan.polat@deu.edu.tr; Özer, Çaglar, E-mail: caglar.ozer@deu.edu.tr; Dokuz Eylul University, The Graduate School of Natural and Applied Sciences, Department of Geophysical Engineering, Izmir-Turkey

In this study; we examined one dimensional crustal velocity structure of Izmir gulf and surroundings. We used nearly one thousand high quality (A and B class) earthquake data which recorded by Disaster and Emergency Management Presidency (AFAD) [1], Bogazici University (BU-KOERI) [2] and National Observatory of Athens (NOA) [3,4]. We tried several synthetic tests to understand power of new velocity structure, and examined phase residuals, RMS values and shifting tests. After evaluating these tests; we decided one dimensional velocity structure and minimum 1-D P wave velocities, hypocentral parameter and earthquake locations from VELEST algorithm. Distribution of earthquakes was visibly improvedmore » by using new minimum velocity structure.« less

Shells, holes, worms, high-velocity gas and the z-distribution of gas in galaxies.

NASA Astrophysics Data System (ADS)

Rand, R. J.

The author gives an overview of the current observational understanding of vertically extended gas components in spiral galaxies and the various phenomena which come under such names as shells, holes, worms, and high-velocity gas. For the most part, the focus is on recent high-resolution interferometric studies. The author concentrates on cold gas, and briefly on warm ionized gas, in the Milky Way and a few nearby spirals. Along the way, it is seen how phenomena such as worms and shells may be related to the formation and maintenance of the vertically extended components.

A summary report on the search for current technologies and developers to develop depth profiling/physical parameter end effectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Q.H.

1994-09-12

This report documents the search strategies and results for available technologies and developers to develop tank waste depth profiling/physical parameter sensors. Sources searched include worldwide research reports, technical papers, journals, private industries, and work at Westinghouse Hanford Company (WHC) at Richland site. Tank waste physical parameters of interest are: abrasiveness, compressive strength, corrosiveness, density, pH, particle size/shape, porosity, radiation, settling velocity, shear strength, shear wave velocity, tensile strength, temperature, viscosity, and viscoelasticity. A list of related articles or sources for each physical parameters is provided.

On tide-induced Lagrangian residual current and residual transport: 1. Lagrangian residual current

USGS Publications Warehouse

Feng, Shizuo; Cheng, Ralph T.; Pangen, Xi

1986-01-01

Residual currents in tidal estuaries and coastal embayments have been recognized as fundamental factors which affect the long-term transport processes. It has been pointed out by previous studies that it is more relevant to use a Lagrangian mean velocity than an Eulerian mean velocity to determine the movements of water masses. Under weakly nonlinear approximation, the parameter k, which is the ratio of the net displacement of a labeled water mass in one tidal cycle to the tidal excursion, is assumed to be small. Solutions for tides, tidal current, and residual current have been considered for two-dimensional, barotropic estuaries and coastal seas. Particular attention has been paid to the distinction between the Lagrangian and Eulerian residual currents. When k is small, the first-order Lagrangian residual is shown to be the sum of the Eulerian residual current and the Stokes drift. The Lagrangian residual drift velocity or the second-order Lagrangian residual current has been shown to be dependent on the phase of tidal current. The Lagrangian drift velocity is induced by nonlinear interactions between tides, tidal currents, and the first-order residual currents, and it takes the form of an ellipse on a hodograph plane. Several examples are given to further demonstrate the unique properties of the Lagrangian residual current.

Identification and calculation of the universal asymptote for drag reduction by polymers in wall bounded turbulence.

PubMed

Benzi, Roberto; De Angelis, Elisabetta; L'vov, Victor S; Procaccia, Itamar

2005-11-04

Drag reduction by polymers in wall turbulence is bounded from above by a universal maximal drag reduction (MDR) velocity profile that is a log law, estimated experimentally by Virk as V+(y+) approximately 11.7logy+ - 17. Here V+(y+) and y+ are the mean streamwise velocity and the distance from the wall in "wall" units. In this Letter we propose that this MDR profile is an edge solution of the Navier-Stokes equations (with an effective viscosity profile) beyond which no turbulent solutions exist. This insight rationalizes the universality of the MDR and provides a maximum principle which allows an ab initio calculation of the parameters in this law without any viscoelastic experimental input.

Molecular Rayleigh Scattering Diagnostic for Dynamic Temperature, Velocity, and Density Measurements

NASA Technical Reports Server (NTRS)

Mielke, Amy R.; Elam, Kristie A.; Sung, Chi-Jen

2006-01-01

A molecular Rayleigh scattering technique is developed to measure dynamic gas temperature, velocity, and density in unseeded turbulent flows at sampling rates up to 16 kHz. A high power CW laser beam is focused at a point in an air jet plume and Rayleigh scattered light is collected and spectrally resolved. The spectrum of the light, which contains information about the temperature and velocity of the flow, is analyzed using a Fabry-Perot interferometer. The circular interference fringe pattern is divided into four concentric regions and sampled at 1 and 16 kHz using photon counting electronics. Monitoring the relative change in intensity within each region allows for measurement of gas temperature and velocity. Independently monitoring the total scattered light intensity provides a measure of gas density. A low speed heated jet is used to validate the measurement of temperature fluctuations and an acoustically excited nozzle flow is studied to validate velocity fluctuation measurements. Power spectral density calculations of the property fluctuations, as well as mean and fluctuating quantities are presented. Temperature fluctuation results are compared with constant current anemometry measurements and velocity fluctuation results are compared with constant temperature anemometry measurements at the same locations.

Backarc spreading and mantle wedge flow beneath the Japan Sea: insight from Rayleigh-wave anisotropic tomography

NASA Astrophysics Data System (ADS)

Liu, Xin; Zhao, Dapeng

2016-10-01

We present the first high-resolution Rayleigh-wave phase-velocity azimuthal anisotropy tomography of the Japan subduction zone at periods of 20-150 s, which is determined using a large number of high-quality amplitude and phase data of teleseismic fundamental-mode Rayleigh waves. The obtained 2-D anisotropic phase-velocity models are then inverted for a 3-D shear-wave velocity azimuthal anisotropy tomography down to a depth of ˜300 km beneath Japan. The subducting Pacific slab is imaged as a dipping high-velocity zone with trench-parallel fast-velocity directions (FVDs) which may indicate the anisotropy arising from the normal faults produced at the outer-rise area near the Japan trench axis, overprinting the slab fossil fabric, whereas the mantle wedge generally exhibits lower velocities with trench-normal FVDs which reflect subduction-driven corner flow and anisotropy. Depth variations of azimuthal anisotropy are revealed in the big mantle wedge beneath the Japan Sea, which may reflect past deformations in the Eurasian lithosphere related to backarc spreading during 21 to 15 Ma and complex current convection in the asthenosphere induced by active subductions of both the Pacific and Philippine Sea plates.

P-wave velocity structure of the uppermost mantle beneath Hawaii from traveltime tomography

USGS Publications Warehouse

Tilmann, F.J.; Benz, H.M.; Priestley, K.F.; Okubo, P.G.

2001-01-01

We examine the P-wave velocity structure beneath the island of Hawaii using P-wave residuals from teleseismic earthquakes recorded by the Hawaiian Volcano Observatory seismic network. The station geometry and distribution of events makes it possible to image the velocity structure between ~ 40 and 100 km depth with a lateral resolution of ~ 15 km and a vertical resolution of ~ 30 km. For depths between 40 and 80 km, P-wave velocities are up to 5 per cent slower in a broad elongated region trending SE-NW that underlies the island between the two lines defined by the volcanic loci. No direct correlation between the magnitude of the lithospheric anomaly and the current level of volcanic activity is apparent, but the slow region is broadened at ~ 19.8??N and narrow beneath Kilauea. In the case of the occanic lithosphere beneath Hawaii, slow seismic velocities are likely to be related to magma transport from the top of the melting zone at the base of the lithosphere to the surface. Thermal modelling shows that the broad elongated low-velocity zone cannot be explained in terms of conductive heating by one primary conduit per volcano but that more complicated melt pathways must exist.

Spatio-temporal characteristics of large scale motions in a turbulent boundary layer from direct wall shear stress measurement

NASA Astrophysics Data System (ADS)

Pabon, Rommel; Barnard, Casey; Ukeiley, Lawrence; Sheplak, Mark

2016-11-01

Particle image velocimetry (PIV) and fluctuating wall shear stress experiments were performed on a flat plate turbulent boundary layer (TBL) under zero pressure gradient conditions. The fluctuating wall shear stress was measured using a microelectromechanical 1mm × 1mm floating element capacitive shear stress sensor (CSSS) developed at the University of Florida. The experiments elucidated the imprint of the organized motions in a TBL on the wall shear stress through its direct measurement. Spatial autocorrelation of the streamwise velocity from the PIV snapshots revealed large scale motions that scale on the order of boundary layer thickness. However, the captured inclination angle was lower than that determined using the classic method by means of wall shear stress and hot-wire anemometry (HWA) temporal cross-correlations and a frozen field hypothesis using a convection velocity. The current study suggests the large size of these motions begins to degrade the applicability of the frozen field hypothesis for the time resolved HWA experiments. The simultaneous PIV and CSSS measurements are also used for spatial reconstruction of the velocity field during conditionally sampled intense wall shear stress events. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1315138.

Experimental and numerical simulation of three-dimensional gravity currents on smooth and rough bottom

NASA Astrophysics Data System (ADS)

La Rocca, Michele; Adduce, Claudia; Sciortino, Giampiero; Pinzon, Allen Bateman

2008-10-01

The dynamics of a three-dimensional gravity current is investigated by both laboratory experiments and numerical simulations. The experiments take place in a rectangular tank, which is divided into two square reservoirs with a wall containing a sliding gate of width b. The two reservoirs are filled to the same height H, one with salt water and the other with fresh water. The gravity current starts its evolution as soon as the sliding gate is manually opened. Experiments are conducted with either smooth or rough surface on the bottom of the tank. The bottom roughness is created by gluing sediment material of different diameters to the surface. Five diameter values for the surface roughness and two salinity conditions for the fluid are investigated. The mathematical model is based on shallow-water theory together with the single-layer approximation, so that the model is strictly hyperbolic and can be put into conservative form. Consequently, a finite-volume-based numerical algorithm can be applied. The Godunov formulation is used together with Roe's approximate Riemann solver. Comparisons between the numerical and experimental results show satisfactory agreement. The behavior of the gravity current is quite unusual and cannot be interpreted using the usual model framework adopted for two-dimensional and axisymmetric gravity currents. Two main phases are apparent in the gravity current evolution; during the first phase the front velocity increases, and during the second phase the front velocity decreases and the dimensionless results, relative to the different densities, collapse onto the same curve. A systematic discrepancy is seen between the numerical and experimental results, mainly during the first phase of the gravity current evolution. This discrepancy is attributed to the limits of the mathematical formulation, in particular, the neglect of entrainment in the mathematical model. An interesting result arises from the influence of the bottom surface roughness; it both reduces the front velocity during the second phase of motion and attenuates the differences between the experimental and numerical front velocities during the first phase of motion.

Current Sierra Nevada-North America motion from very long baseline interferometry: Implications for the kinematics of the western United States

DOE Office of Scientific and Technical Information (OSTI.GOV)

Argus, D.F.; Gordon, R.G.

1991-11-01

The authors use geodetic measurements from very long baseline interferometry to estimate the motion of the Sierra Nevadan microplate. The motion of the Sierra Nevadan microplate relative to the North American plate is described by a right-handed rotation of 0.61{degree}/m.y. about lat 32{degree}N, long 128{degree}W. This Euler pole predicts a significant counterclockwise rotation about a local vertical axis. It further predicts a velocity of the eastern edge of the Sierra Nevada relative to stable North America of 11 {plus minus}1 mm/yr toward N36{degree} {plus minus}3{degree}W, which accounts for about one-fourth of the velocity between the Pacific and North American platesmore » and is {approximately}25{degree} clockwise of many prior estimates. The velocity nearly parallels the boundary between the Sierra Nevada and the Great Basin, which implies that current motion within the Great Basin results in a rotational, noncoaxial deformation. The authors use this velocity to estimate how motion is distributed across the broad deforming zone taking up Pacific-North America plate motion. They find that the vector sum of strike slip along the San Andreas fault and motion of the Sierra Nevada relative to stable North America (taken up by deformation within the Great Basin) differs little from the Pacific-north America plate velocity. The difference can be described at 36{degree}N along the San Andreas fault by a vector of 6 mm/yr directed toward N20{degree}W. This vector resolves into components of 5 mm/yr parallel to the fault and 2 mm/yr perpendicular to the fault with 95% confidence intervals of 0 to 10 mm/yr and {minus}1 to +5 mm/yr, respectively. The authors conclude that motion previously inferred to be taken up by deformation other than strike slip along the San Andreas fault or deformation within the Great Basin is much smaller than previously thought.« less

Equation of state for detonation product gases

NASA Astrophysics Data System (ADS)

Nagayama, Kunihito; Kubota, Shiro

2003-03-01

A thermodynamic analysis procedure of the detonation product equation of state (EOS) together with the experimental data set of the detonation velocity as a function of initial density has been formulated. The Chapman-Jouguet (CJ) state [W. Ficket and W. C. Davis, Detonation: Theory and Experiment (University of California Press, Berkeley 1979)] on the p-ν plane is found to be well approximated by the envelope function formed by the collection of Rayleigh lines with many different initial density states. The Jones-Stanyukovich-Manson relation [W. Ficket and W. C. Davis, Detonation: Theory and Experiment (University of California Press, Berkeley, 1979)] is used to estimate the error included in this approximation. Based on this analysis, a simplified integration method to calculate the Grüneisen parameter along the CJ state curve with different initial densities utilizing the cylinder expansion data has been presented. The procedure gives a simple way of obtaining the EOS function, compatible with the detonation velocity data. Theoretical analysis has been performed for the precision of the estimated EOS function. EOS of the pentaerithrytoltetranitrate explosive is calculated and compared with some of the experimental data such as CJ pressure data and cylinder expansion data.

Zeldovich pancakes in observational data are cold

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brinckmann, Thejs; Lindholmer, Mikkel; Hansen, Steen

The present day universe consists of galaxies, galaxy clusters, one-dimensional filaments and two-dimensional sheets or pancakes, all of which combine to form the cosmic web. The so called ''Zeldovich pancakes' are very difficult to observe, because their overdensity is only slightly greater than the average density of the universe. Falco et al. [1] presented a method to identify Zeldovich pancakes in observational data, and these were used as a tool for estimating the mass of galaxy clusters. Here we expand and refine that observational detection method. We study two pancakes on scales of 10 Mpc, identified from spectroscopically observed galaxiesmore » near the Coma cluster, and compare with twenty numerical pancakes.We find that the observed structures have velocity dispersions of about 100 km/sec, which is relatively low compared to typical groups and filaments. These velocity dispersions are consistent with those found for the numerical pancakes. We also confirm that the identified structures are in fact two-dimensional structures. Finally, we estimate the stellar to total mass of the observational pancakes to be 2 · 10{sup −4}, within one order of magnitude, which is smaller than that of clusters of galaxies.« less

Gravity-wave spectra in the atmosphere observed by MST radar, part 4.2B

NASA Technical Reports Server (NTRS)

Scheffler, A. O.; Liu, C. H.

1984-01-01

A universal spectrum of atmospheric buoyancy waves is proposed based on data from radiosonde, Doppler navigation, not-wire anemometer and Jimsphere balloon. The possible existence of such a universal spectrum clearly will have significant impact on several areas in the study of the middle atmosphere dynamics such as the parameterization of sub-grid scale gravity waves in global circulation models; the transport of trace constituents and heat in the middle atmosphere, etc. Therefore, it is important to examine more global wind data with temporal and spatial resolutions suitable for the investigation of the wave spectra. Mesosphere-stratosphere-troposphere (MST) radar observations offer an excellent opportunity for such studies. It is important to realize that radar measures the line-of-sight velocity which, in general, contains the combination of the vertical and horizontal components of the wave-associated particle velocity. Starting from a general oblique radar observation configuration, applying the dispersion relation for the gravity waves, the spectrum for the observed fluctuations in the line-of-sight gravity-wave spectrum is investigated through a filter function. The consequence of the filter function on data analysis is discussed.

First and second sound in a two-dimensional harmonically trapped Bose gas across the Berezinskii–Kosterlitz–Thouless transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xia-Ji, E-mail: xiajiliu@swin.edu.au; Hu, Hui, E-mail: hhu@swin.edu.au

2014-12-15

We theoretically investigate first and second sound of a two-dimensional (2D) atomic Bose gas in harmonic traps by solving Landau’s two-fluid hydrodynamic equations. For an isotropic trap, we find that first and second sound modes become degenerate at certain temperatures and exhibit typical avoided crossings in mode frequencies. At these temperatures, second sound has significant density fluctuation due to its hybridization with first sound and has a divergent mode frequency towards the Berezinskii–Kosterlitz–Thouless (BKT) transition. For a highly anisotropic trap, we derive the simplified one-dimensional hydrodynamic equations and discuss the sound-wave propagation along the weakly confined direction. Due to themore » universal jump of the superfluid density inherent to the BKT transition, we show that the first sound velocity exhibits a kink across the transition. These predictions might be readily examined in current experimental setups for 2D dilute Bose gases with a sufficiently large number of atoms, where the finite-size effect due to harmonic traps is relatively weak.« less

A Pilot Study to Directly Measure the Dynamical Masses of ULIRGs at Intermediate Redshifts

NASA Astrophysics Data System (ADS)

Rothberg, Barry

2012-02-01

We propose a pilot study to use the Calcium II Triplet stellar absorption lines (rest-frame 0.85 microns) in conjunction with publicly available, high-resolution rest-frame optical HST imaging to directly measure the dynamical masses (M_dyn) and estimate central black hole masses (M_BH) in a small sample of intermediate redshift ULIRGs (0.4 < z < 1.0). It is the same method we have used to measure M_dyn and M_BH in local ULIRGs, and has successfully shown that these systems are statistically indistinguishable from nearby (z < 0.4) QSOs. At 0.4 < z < 1.0, the star-formation rates, gas fractions, and (presumably) masses, are believed to be significantly higher than in the local universe. However, mass is a critical parameter in most galaxy scaling relations, and current methods to estimate mass at intermediate redshifts rely heavily on unproven assumptions. Using stellar velocity dispersions is a straight-forward method to measuring M_dyn, and we will use it to: 1) conf! irm higher masses at 0.4 < z < 1.0; and 2) provide a calibration for other techniques.

How does the cosmic large-scale structure bias the Hubble diagram?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fleury, Pierre; Clarkson, Chris; Maartens, Roy, E-mail: pierre.fleury@uct.ac.za, E-mail: chris.clarkson@qmul.ac.uk, E-mail: roy.maartens@gmail.com

2017-03-01

The Hubble diagram is one of the cornerstones of observational cosmology. It is usually analysed assuming that, on average, the underlying relation between magnitude and redshift matches the prediction of a Friedmann-Lemaître-Robertson-Walker model. However, the inhomogeneity of the Universe generically biases these observables, mainly due to peculiar velocities and gravitational lensing, in a way that depends on the notion of average used in theoretical calculations. In this article, we carefully derive the notion of average which corresponds to the observation of the Hubble diagram. We then calculate its bias at second-order in cosmological perturbations, and estimate the consequences on themore » inference of cosmological parameters, for various current and future surveys. We find that this bias deeply affects direct estimations of the evolution of the dark-energy equation of state. However, errors in the standard inference of cosmological parameters remain smaller than observational uncertainties, even though they reach percent level on some parameters; they reduce to sub-percent level if an optimal distance indicator is used.« less

A Preliminary Investigation of Hall Thruster Technology

NASA Technical Reports Server (NTRS)

Gallimore, Alec D.

1997-01-01

A three-year NASA/BMDO-sponsored experimental program to conduct performance and plume plasma property measurements on two Russian Stationary Plasma Thrusters (SPTs) has been completed. The program utilized experimental facilitates at the University of Michigan's Plasmadynamics and Electric Propulsion Laboratory (PEPL). The main features of the proposed effort were as follows: (1) Characterized Hall thruster (and arcjet) performance by measuring ion exhaust velocity with probes at various thruster conditions; (2) Used a variety of probe diagnostics in the thruster plume to measure plasma properties and flow properties including T(sub e) and n(sub e) ion current density and ion energy distribution, and electric fields by mapping plasma potential; (3) Used emission spectroscopy to identify species within the plume and to measure electron temperatures. A key and unique feature of our research was our collaboration with Russian Hall thruster researcher Dr. Sergey A Khartov, Deputy Dean of International Relations at the Moscow Aviation Institute (MAI). His activities in this program included consulting on and participation in research at PEPL through use of a MAI-built SPT and ion energy probe.

Detiding Tsunami Currents to Validate Velocities in Numerical Simulation Codes using Observations Near Hawaii from the 2011 Tohoku Tsunami

NASA Astrophysics Data System (ADS)

Adams, L. M.; LeVeque, R. J.

2015-12-01

The ability to measure, predict, and compute tsunami flow velocities is ofimportance in risk assessment and hazard mitigation. Until recently, fewdirect measurements of tsunami velocities existed to compare with modelresults. During the 11 March 2001 Tohoku Tsunami, 328 current meters werewere in place around the Hawaiian Islands, USA, that captured time seriesof water velocity in 18 locations, in both harbors and deep channels, ata series of depths. Arcos and LeVeque[1] compared these records againstnumerical simulations performed using the GeoClaw numerical tsunami modelwhich is based on the depth-averaged shallow water equations. They confirmedthat GeoClaw can accurately predict velocities at nearshore locations, andthat tsunami current velocity is more spatially variable than wave formor height and potentially more sensitive for model validation.We present a new approach to detiding this sensitive current data. Thisapproach can be used separately on data at each depth of a current gauge.When averaged across depths, the Geoclaw results in [1] are validated. Withoutaveraging, the results should be useful to researchers wishing to validate their3D codes. These results can be downloaded from the project website below.The approach decomposes the pre-tsunami component of the data into three parts:a tidal component, a fast component (noise), and a slow component (not matchedby the harmonic analysis). Each part is extended to the time when the tsunamiis present and subtracted from the current data then to give the ''tsunami current''that can be compared with 2D or 3D codes that do not model currents in thepre-tsunami regime. [1] "Validating Velocities in the GeoClaw Tsunami Model using Observations NearHawaii from the 2001 Tohoku Tsunami"M.E.M. Arcos and Randall J. LeVequearXiv:1410.2884v1 [physics.geo-py], 10 Oct. 2014.project website: http://faculty.washington.edu/lma3/research.html

Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago

NASA Astrophysics Data System (ADS)

Genzel, R.; Schreiber, N. M. Förster; Übler, H.; Lang, P.; Naab, T.; Bender, R.; Tacconi, L. J.; Wisnioski, E.; Wuyts, S.; Alexander, T.; Beifiori, A.; Belli, S.; Brammer, G.; Burkert, A.; Carollo, C. M.; Chan, J.; Davies, R.; Fossati, M.; Galametz, A.; Genel, S.; Gerhard, O.; Lutz, D.; Mendel, J. T.; Momcheva, I.; Nelson, E. J.; Renzini, A.; Saglia, R.; Sternberg, A.; Tacchella, S.; Tadaki, K.; Wilman, D.

2017-03-01

In the cold dark matter cosmology, the baryonic components of galaxies—stars and gas—are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius—a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.

Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago.

PubMed

Genzel, R; Schreiber, N M Förster; Übler, H; Lang, P; Naab, T; Bender, R; Tacconi, L J; Wisnioski, E; Wuyts, S; Alexander, T; Beifiori, A; Belli, S; Brammer, G; Burkert, A; Carollo, C M; Chan, J; Davies, R; Fossati, M; Galametz, A; Genel, S; Gerhard, O; Lutz, D; Mendel, J T; Momcheva, I; Nelson, E J; Renzini, A; Saglia, R; Sternberg, A; Tacchella, S; Tadaki, K; Wilman, D

2017-03-15

In the cold dark matter cosmology, the baryonic components of galaxies-stars and gas-are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius-a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.

Plasma Disks and Rings with ``High'' Magnetic Energy Densities

NASA Astrophysics Data System (ADS)

Coppi, B.; Rousseau, F.

2006-04-01

The nonlinear theory of rotating axisymmetric thin structures in which the magnetic field energy density is comparable with the thermal plasma energy density is formulated. The only flow velocity included in the theory is the velocity of rotation around a central object whose gravity is dominant. The periodic sequence, in the radial direction, of pairs of opposite current channels that can form is shown to lead to relatively large plasma density and pressure modulations, while the relevant magnetic surfaces can acquire a ``crystal structure.'' A new class of equilibria consisting of a series of plasma rings is identified, in the regimes where the plasma pressure is comparable to the magnetic pressure associated with the fields produced by the internal currents. The possible relevance of this result to the formation of dusty plasma rings is pointed out.

Investigation of the residue in an electric rail gun employing a plasma armature

NASA Technical Reports Server (NTRS)

Bauer, D. P.; Barber, J. P.

1984-01-01

The performance of dc electric rail guns using plasma-armature-accelerated projectiles was studied. It was found that the initial rail launcher acceleration profile was consistent with the simulation, but that after the projectile had traveled approximately 25 to 30 cm along the gun, a considerable portion of the current in the projectile armature commutated into a secondary current path. Also noted were the lower than expected muzzle velocities. It was proposed that the secondary current path was a relatively high conductivity layer of residue on the launcher bore.

Proceedings of the NATO Advanced Study Institute on Physics and Applications of Quantum Wells and Superlattices Held in Erice, Italy on 21 April - 1 May 1987. Series B. Volume 170

DTIC Science & Technology

1987-05-01

possibilities and the latter providing a photodetector with low dark currents . Some mention will also be made of structures devised by Nakagawa7 ,8...developments concerning the growth and the characterization of Hgl_xCdxTe-Cdte SLs and related Hg based superlattice systems. These SLs are now currently ...minority carriers in the base region. When a current is flowing, the drift velocities of minority and majority carriers are oppositely directed, and

Reference measurements on a Francis model turbine with 2D Laser-Doppler-Anemometry

NASA Astrophysics Data System (ADS)

Frey, A.; Kirschner, O.; Riedelbauch, S.; Jester-Zuerker, R.; Jung, A.

2016-11-01

To validate the investigations of a high-resolution CFD simulation of a Francis turbine, measurements with 2D Laser-Doppler-Anemometry are carried out. The turbine is operated in part load, where a rotating vortex rope occurs. To validate both, mean velocities and velocity fluctuations, the measurements are classified relative to the vortex rope position. Several acrylic glass windows are installed in the turbine walls such as upstream of the spiral case inlet, in the vaneless space and in the draft tube. The current investigation is focused on a measurement plane below the runner. 2D velocity components are measured on this whole plane by measuring several narrow spaced radial lines. To avoid optical refraction of the laser beam a plan parallel window is inserted in the cone wall. The laser probe is positioned with a 2D traverse system consisting of a circumferential rail and a radial aligned linear traverse. The velocity data are synchronized with the rotational frequency of the rotating vortex rope. The results of one measurement line show the dependency of the axial and circumferential velocities on the vortex rope position.

Rayleigh Scattering Diagnostic for Measurement of Temperature, Velocity, and Density Fluctuation Spectra

NASA Technical Reports Server (NTRS)

Mielke, Amy F.; Elam, Kristie A.; Sung, Chih-Jen; Panda, Jayanta

2006-01-01

A molecular Rayleigh scattering technique is developed to measure dynamic gas temperature, velocity, and density in unseeded turbulent flows at sampling rates up to 10 kHz. A high power CW laser beam is focused at a point in a heated air jet plume and Rayleigh scattered light is collected and spectrally resolved. The spectrum of the light, which contains information about the temperature, velocity, and density of the flow, is analyzed using a Fabry-Perot interferometer. The circular interference fringe pattern is divided into four concentric regions and sampled at 1 and 10 kHz using photon counting electronics. Monitoring the relative change in intensity within each region allows for measurement of gas temperature and velocity. Independently monitoring the total scattered light intensity provides a measure of gas density. Power spectral density calculations of temperature, velocity, and density fluctuations, as well as mean and fluctuating quantities are demonstrated for various radial locations in the jet flow at a fixed axial distance from the jet exit plane. Results are compared with constant current anemometry and pitot probe measurements at the same locations.

A predictive universal fractional-order differential model of wall-turbulence

NASA Astrophysics Data System (ADS)

Song, Fangying; Karniadakis, George

2017-11-01

Fractional calculus has been around for centuries but its use in computational since and engineering has emerged only recently. Here we develop a relatively simple one-dimensional model for fully-developed wall-turbulence that involves a fractional operator with variable fractional order. We use available DNS data bases to ``learn'' the function that describes the fractional order, which has a high value at the wall and decays monotonically to an asymptotic value at the centerline. We show that this function is universal upon re-scaling and hence it can be used to predict the mean velocity profile at all Reynolds numbers. We demonstrate the accuracy of our universal fractional model for channel flow at high Reynolds number as well as for pipe flow and we obtain good agreement with the Princeton super-pipe data up to Reynolds numbers 35,000,000. This work was supported by an ARO MURI Number: W911NF-15-1-0562.

Indicators of University-Industry Knowledge Transfer Performance and Their Implications for Universities: Evidence from the United Kingdom

ERIC Educational Resources Information Center

Rossi, Federica; Rosli, Ainurul

2015-01-01

The issue of what indicators are most appropriate in order to measure the performance of universities in knowledge transfer (KT) activities remains relatively under-investigated. The main aim of this paper is to identify and discuss the limitations to the current measurements of university-industry KT performance, and propose some directions for…

Trans-dimensional ambient noise tomography of the northeast Asia

NASA Astrophysics Data System (ADS)

Kim, Seongryong; Tkalčić, Hrvoje; Rhie, Junkee; Chen, Youlin

2016-04-01

A trans-dimensional and hierarchical Bayesian tomography is performed to estimate spatial variations of shear wave velocity and provide the uncertainty in the northeast Asia region from the ambient noise data. The method accounts for irregular data distribution and sensitivity using adaptive partition property of Voronoi cells. Importantly, the number of basis functions used to parameterise the Earth model in the inversion and the level of data noise are implicitly balanced by the information contained in the data (and treated as free parameters in the inversions). Thereby more reliable models and their rigorous uncertainties are estimated by avoiding over- or under-estimation and explicit regularisation. We measure Rayleigh wave phase and group velocity (8-70 s) for available inter-station paths between more than 300 broadband stations. The obtained group and phase velocity maps reveal characteristic features beneath the former (East Sea also known as Japan Sea) and the current back-arc (Okinawa trough) regions, where relatively high and low velocities are estimated at intermediate (20-40 s) and longer periods (50-60 s), respectively. We observe that the low velocity anomalies extend to beneath intraplate volcanoes in the northeast China and the Korean Peninsula. Based on the depth sensitivity of surface wave dispersions and previous geological evidences, we argue that the intraplate volcanism in this region might be influenced by sub-lithospheric processes related to the subduction of the Pacific and Philippine Sea plates.

Microcrustacea in flowing water - experimental-analysis of washout times and a field-test

USGS Publications Warehouse

Richardson, W.B.

1992-01-01

1. Flow-chamber experiments were conducted to evaluate the ability of microcrustacea to maintain position in moving water. These results were compared to distributions of zooplankton and water velocity in a stream pool to determine the relationship of animal density to water movement and swimming ability.^2. Cladocerans exhibited negative rheotaxis (directed behaviour against a current) but poor ability to maintain position at velocities >2.5 Cm s-1. Daphnia and scapholeberis were better at avoiding washout than moina and diaphanosoma. At velocities 2.5 Cm s-1, scapholeberis >3.2 Cm s-1 and eucyclops >7.75 Cm s-1. Washout time of daphnia and scapholeberis was positively related to body size and negatively to water velocity and possession of eggs. Washout was inversely related to water velocity for eucyclops.^4. Highest densities of microcrustacea in a stream pool were found in non-flowing or downstream zones of the pool. Benthic (hydracarina, harpacticoid copepods, ostracods) and fast-swimming (cyclopoids) forms were most common in flowing zones. Facultatively benthic cladocera were abundant in regions of no flow. Rotifers and immature copepods were most abundant at the downstream end of the pool.^5. Behavioural mechanisms for remaining in stream pools at times of high flow appear to include: (i) flow avoidance (simocephalus, chydorus, scapholeberis and cyclopoids), (ii) use of benthic habitat (ostracods, harpacticoids, hydracarina), (iii) strong swimming ability (cyclopoids).

Measurement of the Radial Velocity of Vega and SAO 104807 by high resolution spectrometry

NASA Astrophysics Data System (ADS)

Rosas, F.; Ordoñez, J.; Suarez, W.; Quijano, A.

2017-07-01

The radial velocity is the component of the velocity with which a celestial object approaches (blueshift) or go away (redshift) of the observer. The precise measurement of the redshift allowed to Humason and Hubble discover the expansion of the Universe. In 1998 two research teams simultaneously discovered that this expansion is accelerated, for that reason the hypothesis of the dark energy has been raised to explain the existing repulsion. The present work shows the measurement of the radial velocity of Vega and SAO104807 by high resolution spectrometry. Using the instruments of the Astronomical Observatory of the University of Nariño, located in the south of Colombia, was measured the displacement that the spectral lines of both celestial objects suffer due to the Doppler effect. The results obtained were quite close to those recorded in databases such as SIMBAD, according to the used equipment. The instruments used were: Celestron CGE Pro 1400 Telescope, Shelyak LHIRES III High Resolution Spectrometer and SBIG ST-8300 CCD Camera. The characteristics of the spectrometer are: Diffraction grating: 2400 lines/mm, Spectral dispersion (H alpha): 0:012 nm/pixel, Radial velocity resolution: 5 km/s.

Variation of Fundamental Mode Surface Wave Group Velocity Dispersion in Iran and the Surrounding Region

NASA Astrophysics Data System (ADS)

Rham, D. J.; Preistley, K.; Tatar, M.; Paul, A.

2006-12-01

We present group velocity dispersion results from a study of regional fundamental mode Rayleigh and Love waves propagating across Iran and the surrounding region. Data for these measurements comes from field deployments within Iran by the University of Cambridge (GBR) and the Universite Joseph-Fourier (FRA) in conjunction with International Institute of Earthquake Engineering and Seismology (Iran), in addition to data from IRIS and Geofone. 1D path- averaged dispersion measurements have been made for ~5500 source-receiver paths using multiple filter analysis. We combine these observations in a tomographic inversion to produce group velocity images between 10 and 60 s period. Because of the dense path coverage, these images have substantially higher lateral resolution for this region than is currently available from global and regional group velocity studies. We observe variations in short-period wave group velocity which is consistent with the surface geology. Low group velocities (2.00-2.55 km/s) at short periods (10-20 s), for both Rayleigh and Love waves are observed beneath thick sedimentary deposits; The south Caspian Basin, Black Sea, the eastern Mediterranean, the Persian Gulf, the Makran, the southern Turan shield, and the Indus and Gangetic basins. Somewhat higher group velocity (2.80-3.15 km/s for Rayleigh, and 3.00-3.40 km/s for Love) at these periods occur in sediment poor regions, such as; the Turkish-Iranian plateau, the Arabian shield, and Kazakhstan. At intermediate periods (30-40 s) group velocities over most of the region are low (2.65-3.20 km/s for Rayleigh, and 2.80-3.45 km/s for love) compared to Arabia (3.40-3.70 km/s Rayleigh, 3.50-4.0 km/s Love). At longer periods (50-60 s) Love wave group velocities remain low (3.25-3.70 km/s) over most of Iran, but there are even lower velocities (2.80-3.00 km/s) still associated with the thick sediments of the south Caspian basin, the surrounding shield areas have much higher group velocities (3.90-4.45 km/s) at these periods. A similar pattern is seen for longer period Rayleigh waves, with low velocities (2.85-3.60 km/s) beneath the Alpine-Himalaya belt, compared to the velocities (3.80-4.10 km/s) of the Turan and Arabian shields, to the north and south respectively, no large anomaly beneath the south Caspian is observed for these longer period Rayleigh waves.

NASA university program management information system, FY 1985

NASA Technical Reports Server (NTRS)

1985-01-01

The University Program Report provides current information and related statistics for approximately 4200 grants/contracts/cooperative agreements active during the reporting period. NASA Field Centers and certain Headquarters Program Offices provide funds for those research and development activities in universities which contribute to the mission needs of that particular NASA element. This annual report is one means of documenting the NASA-University relationship, frequently denoted, collectively, as NASA's University Program.

NASA university program management information system, FY 1986

NASA Technical Reports Server (NTRS)

1986-01-01

The University Program Report provides current information and related statistics for approximately 4300 grants/contracts/cooperative agreements active during the report period. NASA Field centers and certain Headquarters Program Offices provide funds for those R&D activities in universities which contribute to the mission needs of that particular NASA element. This annual report is one means of documenting the NASA-university relationship, frequently denoted, collectively, as NASA's University Program.

NASA University Program Management Information System: FY 1995

NASA Technical Reports Server (NTRS)

1995-01-01

The University Program Report, Fiscal Year 1995, provides current information and related statistics for grants/contracts/cooperative agreements active during the report period. NASA field centers and certain Headquarters program offices provide funds for those R&D activities in universities which contribute to the mission needs of that particular NASA element. This annual report is one means of documenting the NASA-university relationship, frequently denoted, collectively, as NASA's University Program.

NASA University program management information system, FY 1993

NASA Technical Reports Server (NTRS)

1993-01-01

The University Program Report, Fiscal Year 1993, provides current information and related statistics for 7682 grants/contracts/cooperative agreements active during the report period. NASA field centers and certain Headquarters program offices provide funds for those R&D activities in universities which contribute to the mission needs of that particular NASA element. This annual report is one means of documenting the NASA-university relationship, frequently denoted, collectively, as NASA's University Program.

NASA university program management information system, FY 1994

NASA Technical Reports Server (NTRS)

1994-01-01

The University Program report, Fiscal Year 1994, provides current information and related statistics for 7841 grants/contracts/cooperative agreements active during the reporting period. NASA field centers and certain Headquarters program offices provide funds for those activities in universities which contribute to the mission needs of that particular NASA element. This annual report is one means of documenting the NASA-university relationship, frequently denoted, collectively, as NASA's University Program.

Shock Tunnel Studies of Scramjet Phenomena 1994

NASA Technical Reports Server (NTRS)

Morgan, R. G.; Paull, A.; Stalker, R. J.

1997-01-01

Reports by the research staff and graduate students of the Mechanical Engineering Department at the University of Queensland are collected and presented. These reports cover various studies related to the advancement of scramjet technology and the operation of advanced hypervelocity shock-expansion tubes. The report topics include the experimental studies of mixing and combustion in a scramjet flow path, the measurement of integrated thrust and skin friction, and the development of a free-piston-driven expansion tunnel capable of delivering a test gas at superorbital velocities.

Shock Tunnel Studies of Scramjet Phenomena 1995. Supplement 13

NASA Technical Reports Server (NTRS)

Morgan, R. G.; Stalker, R. J.; Paull, A.

1997-01-01

Reports by the research staff and graduate students of the Mechanical Engineering Department at the University of Queensland are collected and presented. These reports cover various studies related to the advancement of scramjet technology and the operation of advanced hypervelocity shock-expansion tubes. The report topics include the experimental studies of mixing and combustion in a scramjet flow path, the measurement of integrated thrust and skin friction, and the development of a free-piston-driven expansion tunnel capable delivering a test gas at super orbital velocities.

Electric Propulsion: Experimental Research

NASA Technical Reports Server (NTRS)

Ruyten, W. M.; Friedly, V. J.; Keefer, D.

1995-01-01

This paper describes experimental electric propulsion research which was carried out at the University of Tennessee Space Institute with support from the Center for Space Transportation and Applied Research. Specifically, a multiplexed LIF technique for obtaining vector velocities, Doppler temperatures, and relative number densities in the exhaust plumes form electric propulsion devices is described, and results are presented that were obtained on a low power argon arcjet. Also, preliminary Langmuir probe measurements on an ion source are described, and an update on the vacuum facility is presented.

Electric propulsion: Experimental research

NASA Technical Reports Server (NTRS)

Ruyten, W. M.; Friedly, V. J.; Keefer, D.

1992-01-01

This paper describes experimental electric propulsion research which was carried out at the University of Tennessee Space Institute with support from the Center for Space Transportation and Applied Research. Specifically, a multiplexed laser induced fluorescence (LIF) technique for obtaining vector velocities, Doppler temperatures, and relative number densities in the exhaust plumes from electric propulsion devices is described, and results are presented that were obtained on a low power argon arcjet. Also, preliminary Langmuir probe measurements on an ion source are described, and an update on the vacuum facility is presented.

Determining Our Motion Through the Galaxy

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-12-01

Though we dont notice it from our point of view, were hurtling through space at breakneck speed and one of the contributors to our overall motion through the universe is the Suns revolutionaround the center of our galaxy. A recent study uses an unusual approach to measure the speed of this rotation.Moving While Sitting StillWe know that the Sun zips rapidly around the center of the Milky Way our orbitalspeed is somewhere around250 km/s, or 560,000 mph! Getting a precise measurement of this velocity is useful because we can combine it with the observed proper motion of Sgr A*, the black hole at the center of our galaxy, to determine the distance from us to the center of the Milky Way. This is an important baseline for lots of other measurements.Example particle orbits modeled within the galactic potential. The top panel represents a starwith zero angular momentum, which is scattered into a chaotic orbit after interacting with the galactic nucleus. [Hunt et al. 2016]But how can we measure the Suns revolutionspeed accurately? A team of scientists led by Jason Hunt (Dunlap Institute at University of Toronto, Canada) have suggested a unique approach to pin down this value: look for missing stars in the solar neighborhood.Missing StarsThe stars around us should exhibit a distribution of velocities describing their orbits about the galactic center but those stars with zero angular momentum should have plunged directly into the galactic center long ago. These stars would have been scattered onto chaotic halo orbits after their plunge, resulting in a dearth of stars with zero angular momentum around us today.By looking at the relative speeds of the stars moving around us, then, we should see a dip in the velocity distribution corresponding to the missing zero-angular-momentum stars. By noting the relative velocity at which that dip occurs, we cleverly reveal the negative of our motion around the galactic center.Velocity distribution for stars within 700 pc of the Sun. A dip in the distribution (marked with an arrow) is noticeable between 210 and 270 km/s. [Hunt et al. 2016]Where Are We and How Fast Are We Going?Hunt and collaborators use a combination of the first data release from ESAs Gaia mission and a star catalog from the Radial Velocity Experiment to examine the motions of a total of over 200,000 stars in the solar neighborhood. They find that there is indeed a lack of disk stars with velocities close to zero angular momentum. They then compare modeled stellar orbits to the data to estimate the relative speed at which the dip in the velocity distribution occurs.From this information, the authors obtain a measurement of 2399 km/s for the Suns revolutionvelocity around the galactic center. They combine this value with a proper motion measurement of Sgr A* to calculate the distance to the galactic center: 7.90.3 kpc (or about 26,000 light-years).Both of these measurements can be improved with future Gaia data releases, which will contain many orders of magnitude more stars. This clever technique, therefore, proves a useful way of better constraining our position and motion through the Milky Way.CitationJason A. S. Hunt et al 2016 ApJL 832 L25. doi:10.3847/2041-8205/832/2/L25

Accelerated cosmos in a nonextensive setup

NASA Astrophysics Data System (ADS)

Moradpour, H.; Bonilla, Alexander; Abreu, Everton M. C.; Neto, Jorge Ananias

2017-12-01

Here we consider a flat FRW universe whose horizon entropy meets the Rényi entropy of nonextensive systems. In our model, the ordinary energy-momentum conservation law is not always valid. By applying the Clausius relation as well as the Cai-Kim temperature to the apparent horizon of a flat FRW universe, we obtain modified Friedmann equations. Fitting the model to the observational data on the current accelerated universe, some values for the model parameters are also addressed. Our study shows that the current accelerating phase of universe expansion may be described by a geometrical fluid, originated from the nonextensive aspects of geometry, which models a varying dark energy source interacting with the matter field in the Rastall way. Moreover, our results indicate that the probable nonextensive features of spacetime may also be used to model a varying dark energy source which does not interact with the matter field and is compatible with the current accelerated phase of the Universe.

Downstream evolution of the Kuroshio's time-varying transport and velocity structure

NASA Astrophysics Data System (ADS)

Andres, M.; Mensah, V.; Jan, S.; Chang, M.-H.; Yang, Y.-J.; Lee, C. M.; Ma, B.; Sanford, T. B.

2017-05-01

Observations from two companion field programs—Origins of the Kuroshio and Mindanao Current (OKMC) and Observations of Kuroshio Transport Variability (OKTV)—are used here to examine the Kuroshio's temporal and spatial evolution. Kuroshio strength and velocity structure were measured between June 2012 and November 2014 with pressure-sensor equipped inverted echo sounders (PIESs) and upward-looking acoustic Doppler current profilers (ADCPs) deployed across the current northeast of Luzon, Philippines, and east of Taiwan with an 8 month overlap in the two arrays' deployment periods. The time-mean net (i.e., integrated from the surface to the bottom) absolute transport increases downstream from 7.3 Sv (±4.4 Sv standard error) northeast of Luzon to 13.7 Sv (±3.6 Sv) east of Taiwan. The observed downstream increase is consistent with the return flow predicted by the simple Sverdrup relation and the mean wind stress curl field over the North Pacific (despite the complicated bathymetry and gaps along the North Pacific western boundary). Northeast of Luzon, the Kuroshio—bounded by the 0 m s-1 isotach—is shallower than 750 dbar, while east of Taiwan areas of positive flow reach to the seafloor (3000 m). Both arrays indicate a deep counterflow beneath the poleward-flowing Kuroshio (-10.3 ± 2.3 Sv by Luzon and -12.5 ± 1.2 Sv east of Taiwan). Time-varying transports and velocities indicate the strong influence at both sections of westward propagating eddies from the ocean interior. Topography associated with the ridges east of Taiwan also influences the mean and time-varying velocity structure there.

Cosmography and Data Visualization

NASA Astrophysics Data System (ADS)

Pomarède, Daniel; Courtois, Hélène M.; Hoffman, Yehuda; Tully, R. Brent

2017-05-01

Cosmography, the study and making of maps of the universe or cosmos, is a field where visual representation benefits from modern three-dimensional visualization techniques and media. At the extragalactic distance scales, visualization is contributing to our understanding of the complex structure of the local universe in terms of spatial distribution and flows of galaxies and dark matter. In this paper, we report advances in the field of extragalactic cosmography obtained using the SDvision visualization software in the context of the Cosmicflows Project. Here, multiple visualization techniques are applied to a variety of data products: catalogs of galaxy positions and galaxy peculiar velocities, reconstructed velocity field, density field, gravitational potential field, velocity shear tensor viewed in terms of its eigenvalues and eigenvectors, envelope surfaces enclosing basins of attraction. These visualizations, implemented as high-resolution images, videos, and interactive viewers, have contributed to a number of studies: the cosmography of the local part of the universe, the nature of the Great Attractor, the discovery of the boundaries of our home supercluster of galaxies Laniakea, the mapping of the cosmic web, and the study of attractors and repellers.

A systematic search for dwarf counterparts to ultra compact high velocity clouds

NASA Astrophysics Data System (ADS)

Bennet, Paul; Sand, David J.; Crnojevic, Denija; Strader, Jay

2015-01-01

Observations of the Universe on scales smaller than typical, massive galaxies challenge the standard Lambda Cold Dark Matter paradigm for structure formation. It is thus imperative to discover and characterize the faintest dwarf galaxy systems, not just within the Local Group, but in relatively isolated environments as well in order to properly connect them with models of structure formation. Here we report on a systematic search of public ultraviolet and optical archives for dwarf galaxy counterparts to so-called Ultra Compact High Velocity Clouds (UCHVCs), which are compact, isolated HI sources recently found in the Galactic Arecibo L-band Feed Array-HI (GALFA-HI) and Arecibo Legacy Fast ALFA (ALFALFA-HI) surveys. Our search has uncovered at least three strong dwarf galaxy candidates, and we present their inferred star formation rate and structural properties here.

Self-organization of river channels as a critical filter on climate signals.

PubMed

Phillips, Colin B; Jerolmack, Douglas J

2016-05-06

Spatial and temporal variations in rainfall are hypothesized to influence landscape evolution through erosion and sediment transport by rivers. However, determining the relation between rainfall and river dynamics requires a greater understanding of the feedbacks between flooding and a river's capacity to transport sediment. We analyzed channel geometry and stream-flow records from 186 coarse-grained rivers across the United States. We found that channels adjust their shape so that floods slightly exceed the critical shear velocity needed to transport bed sediment, independently of climatic, tectonic, and bedrock controls. The distribution of fluid shear velocity associated with floods is universal, indicating that self-organization of near-critical channels filters the climate signal evident in discharge. This effect blunts the impact of extreme rainfall events on landscape evolution. Copyright © 2016, American Association for the Advancement of Science.

Effectiveness of pictorial health warnings on cigarette packs among Lebanese school and university students.

PubMed

Alaouie, Hala; Afifi, Rema A; Haddad, Pascale; Mahfoud, Ziyad; Nakkash, Rima

2015-03-01

Pictorial health warnings are more effective than text warnings in enhancing motivation to quit and not to start smoking among youth. In Lebanon, packs still have only a very small text warning. The aim of this study was to evaluate the perceived effectiveness of pictorial health warnings on cigarette packs among Lebanese youth. This was a cross-sectional study including school students (n=1412) aged 13-18 years recruited from 28 schools and university students (n=1217) aged 18-25 years recruited from 7 universities. A variety of warnings were adapted from other countries. In all, 4 warnings were tested among school students and 18 among university students. All pictorial warnings were considered more effective than the current text warning on message-related and impact-related variables, including intentions to quit or not to start smoking among school and university students. Selected examples related to the top-ranked pictorial warnings are: among male non-smoking school students, 81% agreed that the 'lung' warning had more impact on their intentions not to start smoking as compared to 57% for the current text warning (p<0.001) with a significant difference compared to the current text warning; among female non-smoking university students, 75% agreed that the 'economic impact' pictorial had more impact on their intentions not to start smoking with significant difference as compared to 43% for the current text warning (p value=0.001); finally, the 'heart attack' pictorial resulted in 52% of male university students smokers stating they intended to quit as opposed to 20% for the current text warning (p value=0.019). The results of the present study add to the general international literature on the impact of pictorial warnings on youth and young adults. This study is also the first to test a non-health pictorial warning about the negative economic consequences of smoking, and to find that such a warning was effective among specific sociodemographic groups. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Basic study on hot-wire flow meter in forced flow of liquid hydrogen

NASA Astrophysics Data System (ADS)

Oura, Y.; Shirai, Y.; Shiotsu, M.; Murakami, K.; Tatsumoto, H.; Naruo, Y.; Nonaka, S.; Kobayashi, H.; Inatani, Y.; Narita, N.

2014-01-01

Liquid hydrogen (LH2) is a key issue in a carbon-free energy infrastructure at the energy storage and transportation stage. The typical features of LH2 are low viscosity, large latent heat and small density, compared with other general liquids. It is necessary to measure a mass flow of liquid hydrogen with a simple and compact method, especially in a two phase separate flow condition. We have proposed applying a hot-wire type flow meter, which is usually used a for gas flow meter, to LH2 flow due to the quite low viscosity and density. A test model of a compact LH2 hot-wire flow meter to measure local flow velocities near and around an inside perimeter of a horizontal tube by resistance thermometry was designed and made. The model flow meter consists of two thin heater wires made of manganin fixed in a 10 mm-diameter and 40 mm-length tube flow path made of GFRP. Each rigid heater wire was set twisted by 90 degrees from the inlet to the outlet along the inner wall. In other words, the wires were aslant with regard to the LH2 stream line. The heated wire was cooled by flowing LH2, and the flow velocity was obtained by means of the difference of the cooling characteristic in response to the flow velocity. In this report, we show results on the basic experiments with the model LH2 hot-wire flow meter. First, the heat transfer characteristics of the two heater wires for several LH2 flow velocities were measured. Second, the heating current was controlled to keep the wire temperature constant for various flow velocities. The relations between the flow velocity and the heating current were measured. The feasibility of the proposed model was confirmed.

Kinematics of nearby K-M dwarfs: first results .

NASA Astrophysics Data System (ADS)

Upgren, A. R.; Boyle, R. P.; Sperauskas, J.; Bartašiūtė, S.

The lists of stars selected spectroscopically by Vyssotsky at the McCormick Observatory and the 4th version of the Catalogue of Nearby Stars (CNS4) are two major sources of nearby K-M dwarfs, which complement each other and provide a kinematically unbiased sample of about 1400 such stars. With the addition of Hipparcos and Tycho astrometry, this stellar sample offers perhaps best insight on the kinematical properties of the lower main sequence stars in the immediate solar neighborhood. Until recently, however, the main limitation in observational data for this sample was the lack of well determined radial velocities, especially for fainter magnitude stars. Therefore our first goal was to perform radial velocity observations for one-third of the sample stars which had no accurate or any radial velocity data. Using the CORAVEL spectrometer of Vilnius University Observatory, attached to the 1.5-m NASA and 1.6-m Kuiper telescopes at Steward Observatory, US, and the 1.6-m telescope at Molėtai Observatory, Lithuania, radial velocities have been recently measured for 475 K-M dwarfs. These observations, together with previous radial-velocity data and available astrometry, are used to derive complete kinematical information on the sample stars. Preliminary analysis shows the presence of different age populations which dominate in different regions of the asymmetric drift: from the young disk component, showing no lag behind the rotational motion of the Sun, to the thick disk stars which make up an extended asymmetric tail. Assuming that the U and W velocity components have zero motion relative to the LSR, and that the asymmetric drift is proportional to sigma 2_U, we find the peculiar motion of the Sun relative to the LSR (U_⊙, V_⊙, W_⊙)= (9.3± 1.3, 5.9± 0.8, 6.9±0.7) km s-1. No attempt was made at this stage of work to determine V_⊙ directly from the mean V-motion of the young disk stars. After completion of the radial-velocity program, the next step will be to evaluate the selection effects within the stellar sample. Hopefully, age related stellar measures will also be provided in a later phase of the program.

Modes of uncontrolled rotational motion of the Progress M-29M spacecraft

NASA Astrophysics Data System (ADS)

Belyaev, M. Yu.; Matveeva, T. V.; Monakhov, M. I.; Rulev, D. N.; Sazonov, V. V.

2018-01-01

We have reconstructed the uncontrolled rotational motion of the Progress M-29M transport cargo spacecraft in the single-axis solar orientation mode (the so-called sunward spin) and in the mode of the gravitational orientation of a rotating satellite. The modes were implemented on April 3-7, 2016 as a part of preparation for experiments with the DAKON convection sensor onboard the Progress spacecraft. The reconstruction was performed by integral statistical techniques using the measurements of the spacecraft's angular velocity and electric current from its solar arrays. The measurement data obtained in a certain time interval have been jointly processed using the least-squares method by integrating the equations of the spacecraft's motion relative to the center of mass. As a result of processing, the initial conditions of motion and parameters of the mathematical model have been estimated. The motion in the sunward spin mode is the rotation of the spacecraft with an angular velocity of 2.2 deg/s about the normal to the plane of solar arrays; the normal is oriented toward the Sun or forms a small angle with this direction. The duration of the mode is several orbit passes. The reconstruction has been performed over time intervals of up to 1 h. As a result, the actual rotational motion of the spacecraft relative to the Earth-Sun direction was obtained. In the gravitational orientation mode, the spacecraft was rotated about its longitudinal axis with an angular velocity of 0.1-0.2 deg/s; the longitudinal axis executed small oscillated relative to the local vertical. The reconstruction of motion relative to the orbital coordinate system was performed in time intervals of up to 7 h using only the angularvelocity measurements. The measurements of the electric current from solar arrays were used for verification.

Velocity distribution in a turbulent flow near a rough wall

NASA Astrophysics Data System (ADS)

Korsun, A. S.; Pisarevsky, M. I.; Fedoseev, V. N.; Kreps, M. V.

2017-11-01

Velocity distribution in the zone of developed wall turbulence, regardless of the conditions on the wall, is described by the well-known Prandtl logarithmic profile. In this distribution, the constant, that determines the value of the velocity, is determined by the nature of the interaction of the flow with the wall and depends on the viscosity of the fluid, the dynamic velocity, and the parameters of the wall roughness.In extreme cases depending on the ratio between the thickness of the viscous sublayer and the size of the roughness the constant takes on a value that does not depend on viscosity, or leads to a ratio for a smooth wall.It is essential that this logarithmic profile is the result not only of the Prandtl theory, but can be derived from general considerations of the theory of dimensions, and also follows from the condition of local equilibrium of generation and dissipation of turbulent energy in the wall area. This allows us to consider the profile as a universal law of velocity distribution in the wall area of a turbulent flow.The profile approximation up to the maximum speed line with subsequent integration makes possible to obtain the resistance law for channels of simple shape. For channels of complex shape with rough walls, the universal profile can be used to formulate the boundary condition when applied to the calculation of turbulence models.This paper presents an empirical model for determining the constant of the universal logarithmic profile. The zone of roughness is described by a set of parameters and is considered as a porous structure with variable porosity.

High-current fast electron beam propagation in a dielectric target.

PubMed

Klimo, Ondrej; Tikhonchuk, V T; Debayle, A

2007-01-01

Recent experiments demonstrate an efficient transformation of high intensity laser pulse into a relativistic electron beam with a very high current density exceeding 10(12) A cm(-2). The propagation of such a beam inside the target is possible if its current is neutralized. This phenomenon is not well understood, especially in dielectric targets. In this paper, we study the propagation of high current density electron beam in a plastic target using a particle-in-cell simulation code. The code includes both ionization of the plastic and collisions of newborn electrons. The numerical results are compared with a relatively simple analytical model and a reasonable agreement is found. The temporal evolution of the beam velocity distribution, the spatial density profile, and the propagation velocity of the ionization front are analyzed and their dependencies on the beam density and energy are discussed. The beam energy losses are mainly due to the target ionization induced by the self-generated electric field and the return current. For the highest beam density, a two-stream instability is observed to develop in the plasma behind the ionization front and it contributes to the beam energy losses.

A complete two-phase model of a porous cathode of a PEM fuel cell

NASA Astrophysics Data System (ADS)

Hwang, J. J.

This paper has developed a complete two-phase model of a proton exchange membrane (PEM) fuel cell by considering fluid flow, heat transfer and current simultaneously. In fluid flow, two momentum equations governing separately the gaseous-mixture velocity (u g) and the liquid-water velocity (u w) illustrate the behaviors of the two-phase flow in a porous electrode. Correlations for the capillary pressure and the saturation level connect the above two-fluid transports. In heat transfer, a local thermal non-equilibrium (LTNE) model accounting for intrinsic heat transfer between the reactant fluids and the solid matrices depicts the interactions between the reactant-fluid temperature (T f) and the solid-matrix temperature (T s). The irreversibility heating due to electrochemical reactions, Joule heating arising from Ohmic resistance, and latent heat of water condensation/evaporation are considered in the present non-isothermal model. In current, Ohm's law is applied to yield the conservations in ionic current (i m) and electronic current (i s) in the catalyst layer. The Butler-Volmer correlation describes the relation of the potential difference (overpotential) and the transfer current between the electrolyte (such as Nafion™) and the catalyst (such as Pt/C).

Measurement of velocities with an acoustic velocity meter, one side-looking and two upward-looking acoustic Doppler current profilers in the Chicago Sanitary and Ship Canal, Romeoville, Illinois

USGS Publications Warehouse

Oberg, Kevin A.; Duncker, James J.

1999-01-01

In 1998, a prototype 300 kHz, side-looking Acoustic Doppler Current Profiler (ADCP) was deployed in the Chicago Sanitary and Ship Canal (CSSC) at Romeoville, Illinois. Additionally, two upward-looking ADCP's were deployed in the same acoustic path as the side-looking ADCP and in the reach defined by the upstream and downstream acoustic velocity meter (AVM) paths. All three ADCP's were synchronized to the AVM clock at the gaging station so that data were sampled simultaneously. The three ADCP's were deployed for six weeks measuring flow velocities from 0.0 to 2.5 ft/s. Velocities measured by each ADCP were compared to AVM path velocities and to velocities measured by the other ADCP's.

Evaluation of new collision-pair selection models in DSMC

NASA Astrophysics Data System (ADS)

Akhlaghi, Hassan; Roohi, Ehsan

2017-10-01

The current paper investigates new collision-pair selection procedures in a direct simulation Monte Carlo (DSMC) method. Collision partner selection based on the random procedure from nearest neighbor particles and deterministic selection of nearest neighbor particles have already been introduced as schemes that provide accurate results in a wide range of problems. In the current research, new collision-pair selections based on the time spacing and direction of the relative movement of particles are introduced and evaluated. Comparisons between the new and existing algorithms are made considering appropriate test cases including fluctuations in homogeneous gas, 2D equilibrium flow, and Fourier flow problem. Distribution functions for number of particles and collisions in cell, velocity components, and collisional parameters (collision separation, time spacing, relative velocity, and the angle between relative movements of particles) are investigated and compared with existing analytical relations for each model. The capability of each model in the prediction of the heat flux in the Fourier problem at different cell numbers, numbers of particles, and time steps is examined. For new and existing collision-pair selection schemes, the effect of an alternative formula for the number of collision-pair selections and avoiding repetitive collisions are investigated via the prediction of the Fourier heat flux. The simulation results demonstrate the advantages and weaknesses of each model in different test cases.

Method to Rapidly Collect Thousands of Velocity Observations to Validate Million-Element 2D Hydrodynamic Models

NASA Astrophysics Data System (ADS)

Barker, J. R.; Pasternack, G. B.; Bratovich, P.; Massa, D.; Reedy, G.; Johnson, T.

2010-12-01

Two-dimensional (depth-averaged) hydrodynamic models have existed for decades and are used to study a variety of hydrogeomorphic processes as well as to design river rehabilitation projects. Rapid computer and coding advances are revolutionizing the size and detail of 2D models. Meanwhile, advances in topo mapping and environmental informatics are providing the data inputs to drive large, detailed simulations. Million-element computational meshes are in hand. With simulations of this size and detail, the primary challenge has shifted to finding rapid and inexpensive means for testing model predictions against observations. Standard methods for collecting velocity data include boat-mounted ADCP and point-based sensors on boats or wading rods. These methods are labor intensive and often limited to a narrow flow range. Also, they generate small datasets at a few cross-sections, which is inadequate to characterize the statistical structure of the relation between predictions and observations. Drawing on the long-standing oceanographic method of using drogues to track water currents, previous studies have demonstrated the potential of small dGPS units to obtain surface velocity in rivers. However, dGPS is too inaccurate to test 2D models. Also, there is financial risk in losing drogues in rough currents. In this study, an RTK GPS unit was mounted onto a manned whitewater kayak. The boater positioned himself into the current and used floating debris to maintain a speed and heading consistent with the ambient surface flow field. RTK GPS measurements were taken ever 5 sec. From these positions, a 2D velocity vector was obtained. The method was tested over ~20 km of the lower Yuba River in California in flows ranging from 500-5000 cfs, yielding 5816 observations. To compare velocity magnitude against the 2D model-predicted depth-averaged value, kayak-based surface values were scaled down by an optimized constant (0.72), which had no negative effect on regression analysis. The r2 value for speed was 0.78 by this method, compared with 0.57 based on 199 points from traditional measurements. The r2 value for velocity direction was 0.77. Although it is not ideal to rely on observed surface velocity to evaluate depth-average velocity predictions, all available velocity-measurement methods have a suite of assumptions and complications. Using this method, the availability of 10-100x more data was so beneficial that the outcome was among the highest model performance outcomes reported in the literature.

Current sheath behavior and its velocity enhancement in a low energy Mather-type plasma focus device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aghamir, F. M.; Behbahani, R. A.

The dynamics of the plasma sheath layer and its velocity enhancement have been studied in a low energy (4.9 kJ) Mather-type plasma focus device. Experiments were performed to study the effect of the Lorentz force variation on the current sheath expansion and movement, as well as the existence of traction between all parts of the sheath layer. Two different shape of anodes (cylindrical and step) along with an axial magnetic probe were used to investigate the effects of various experimental conditions, namely different charging voltages and gas pressures. In order to explore the upper limit of the current sheath velocity,more » a comparison has been made between the experimental data gathered by the probe and the Lee's computational model. The limitations governing the enhancement of the current sheath velocity that can lead to the deterioration of a good focusing phenomenon were also investigated. The increase of the current sheath velocity due to the usage of the step anode on ion generation and hard x-ray emissions have been demonstrated by means of an ion collector and a hard x-ray detector.« less

A seepage meter designed for use in flowing water

USGS Publications Warehouse

Rosenberry, D.O.

2008-01-01

Seepage meters provide one of the most direct means to measure exchange of water across the sediment-water interface, but they generally have been unsuitable for use in fluvial settings. Although the seepage bag can be placed inside a rigid container to minimize velocity head concerns, the seepage cylinder installed in the sediment bed projects into and disrupts the flow field, altering both the local-scale fluid exchange as well as measurement of that exchange. A low-profile seepage meter designed for use in moving water was tested in a seepage meter flux tank where both current velocity and seepage velocity could be controlled. The conical seepage cylinder protrudes only slightly above the sediment bed and is connected via tubing to a seepage bag or flowmeter positioned inside a rigid shelter that is located nearby where current velocity is much slower. Laboratory and field tests indicate that the net effect of the small protrusion of the seepage cylinder into the surface water flow field is inconsequentially small for surface water currents up to 65 cm s-1. Current velocity affects the variability of seepage measurements; seepage standard deviation increased from ???2 to ???6 cm d-1 as current velocity increased from 9 to 65 cm s-1. Substantial bias can result if the shelter is not placed to minimize hydraulic gradient between the bag and the seepage cylinder.

Understanding charge transfer of Li+ and Na+ ions scattered from metal surfaces with high work function

NASA Astrophysics Data System (ADS)

Chen, Lin; Wu, Wen-Bin; Liu, Pin-Yang; Xiao, Yun-Qing; Li, Guo-Peng; Liu, Yi-Ran; Jiang, Hao-Yu; Guo, Yan-Ling; Chen, Xi-Meng

2016-08-01

For Li+ and Na+ ions scattered from high work function metal surfaces, efficient neutralization is observed, and it cannot be explained by the conventional free electron model. In order to explain these experimental data, we investigate the velocity-dependent neutral fraction with the modified Brako-Newns (BN) model. The calculated results are in agreement with the experimental data. We find that the parallel velocity effect plays an important role in neutralizing the Li+ and Na+ ions for large angle scattering. The nonmonotonic velocity behavior of neutral fraction is strongly related to the distance-dependent coupling strength between the atomic level and metal states. Project supported by the National Natural Science Foundation of China (Grant Nos. 11405078 and 11474140), the Fundamental Research Funds for the Central Universities, China (Grant Nos. lzujbky-2014-169 and lzujbky-2015-244), the Project sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, the State Education Ministry, and the National Students’ Innovation and Entrepreneurship Training Program (Grant Nos. 201410730069 and 201510730078).

Gyrokinetic statistical absolute equilibrium and turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu Jianzhou; Hammett, Gregory W.

2010-12-15

A paradigm based on the absolute equilibrium of Galerkin-truncated inviscid systems to aid in understanding turbulence [T.-D. Lee, Q. Appl. Math. 10, 69 (1952)] is taken to study gyrokinetic plasma turbulence: a finite set of Fourier modes of the collisionless gyrokinetic equations are kept and the statistical equilibria are calculated; possible implications for plasma turbulence in various situations are discussed. For the case of two spatial and one velocity dimension, in the calculation with discretization also of velocity v with N grid points (where N+1 quantities are conserved, corresponding to an energy invariant and N entropy-related invariants), the negative temperaturemore » states, corresponding to the condensation of the generalized energy into the lowest modes, are found. This indicates a generic feature of inverse energy cascade. Comparisons are made with some classical results, such as those of Charney-Hasegawa-Mima in the cold-ion limit. There is a universal shape for statistical equilibrium of gyrokinetics in three spatial and two velocity dimensions with just one conserved quantity. Possible physical relevance to turbulence, such as ITG zonal flows, and to a critical balance hypothesis are also discussed.« less

A Large Scale Wind Tunnel for the Study of High Reynolds Number Turbulent Boundary Layer Physics

NASA Astrophysics Data System (ADS)

Priyadarshana, Paththage; Klewicki, Joseph; Wosnik, Martin; White, Chris

2008-11-01

Progress and the basic features of the University of New Hampshire's very large multi-disciplinary wind tunnel are reported. The refinement of the overall design has been greatly aided through consultations with an external advisory group. The facility test section is 73 m long, 6 m wide, and 2.5 m nominally high, and the maximum free stream velocity is 30 m/s. A very large tunnel with relatively low velocities makes the small scale turbulent motions resolvable by existing measurement systems. The maximum Reynolds number is estimated at &+circ;= δuτ/ν˜50000, where δ is the boundary layer thickness and uτ is the friction velocity. The effects of scale separation on the generation of the Reynolds stress gradient appearing in the mean momentum equation are briefly discussed to justify the need to attain &+circ; in excess of about 40000. Lastly, plans for future utilization of the facility as a community-wide resource are outlined. This project is supported through the NSF-EPSCoR RII Program, grant number EPS0701730.

The Dynamical Properties of Virgo Cluster Disk Galaxies

NASA Astrophysics Data System (ADS)

Ouellette, N. N. Q.; Courteau, S.; Holtzman, J. A.; Dalcanton, J. J.; McDonald, M.; Zhu, Y.

2014-03-01

By virtue of its proximity, the Virgo Cluster is an ideal laboratory for testing our understanding of structure formation in the Universe. In this spirit, we present a dynamical study of Virgo galaxies as part of the Spectroscopic and H-band Imaging of Virgo (SHIVir) survey. Hα rotation curves (RC) for our gas-rich galaxies were modeled with a multi-parameter fit function from which various velocity measurements were inferred. Our study takes advantage of archival and our own new data as we aim to compile the largest Tully-Fisher relation (TFR) for a cluster to date. Extended velocity dispersion profiles (VDP) are integrated over varying aperture sizes to extract representative velocity dispersions (VDs) for gas-poor galaxies. Considering the lack of a common standard for the measurement of a fiducial galaxy VD in the literature, we rectify this situation by determining the radius at which the measured VD yields the tightest Fundamental Plane (FP). We found that radius to be at least 1 Re, which exceeds the extent of most dispersion profiles in other works.

Test of multi-object exoplanet search spectral interferometer

NASA Astrophysics Data System (ADS)

Zhang, Kai; Wang, Liang; Jiang, Haijiao; Zhu, Yongtian; Hou, Yonghui; Dai, Songxin; Tang, Jin; Tang, Zhen; Zeng, Yizhong; Chen, Yi; Wang, Lei; Hu, Zhongwen

2014-07-01

Exoplanet detection, a highlight in the current astronomy, will be part of puzzle in astronomical and astrophysical future, which contains dark energy, dark matter, early universe, black hole, galactic evolution and so on. At present, most of the detected Exoplanets are confirmed through methods of radial velocity and transit. Guo shoujing Telescope well known as LAMOST is an advanced multi-object spectral survey telescope equipped with 4000 fibers and 16 low resolution fiber spectrographs. To explore its potential in different astronomical activities, a new radial velocity method named Externally Dispersed Interferometry (EDI) is applied to serve Exoplanet detection through combining a fixed-delay interferometer with the existing spectrograph in medium spectral resolution mode (R=5,000-10,000). This new technology has an impressive feature to enhance radial velocity measuring accuracy of the existing spectrograph through installing a fixed-delay interferometer in front of spectrograph. This way produces an interference spectrum with higher sensitivity to Doppler Effect by interference phase and fixed delay. This relative system named Multi-object Exoplanet Search Spectral Interferometer (MESSI) is composed of a few parts, including a pair of multi-fiber coupling sockets, a remote control iodine subsystem, a multi-object fixed delay interferometer and the existing spectrograph. It covers from 500 to 550 nm and simultaneously observes up to 21 stars. Even if it's an experimental instrument at present, it's still well demonstrated in paper that how MESSI does explore an effective way to build its own system under the existing condition of LAMOST and get its expected performance for multi-object Exoplanet detection, especially instrument stability and its special data reduction. As a result of test at lab, inside temperature of its instrumental chamber is stable in a range of +/-0.5degree Celsius within 12 hours, and the direct instrumental stability without further observation correction is equivalent to be +/-50m/s every 20mins.

What to Do about Being Overwhelmed: Graduate Students, Stress and University Services

ERIC Educational Resources Information Center

Oswalt, Sara B.; Riddock, Christina C.

2007-01-01

Few studies have examined graduate students and stress. At a large, Southeastern university, 223 graduate students completed a survey about factors contributing their stress, current coping strategies and related university services. A majority felt stressed (48.9%) or very stressed (24.7%). There were significant differences in coping strategies…

Exploring Levels of Student-Athlete Burnout at Two Canadian Universities

ERIC Educational Resources Information Center

Dubuc-Charbonneau, Nicole; Durand-Bush, Natalie; Forneris, Tanya

2014-01-01

The purpose of the current study was to examine the levels of burnout among student-athletes at two Canadian universities and to investigate whether there were significant differences related to gender, sport, year of university sport participation, academic year, and academic program. Burnout was measured by administering Raedeke and Smith's…

Entrepreneurial Universities and the Development of Regional Societies: A Spatial View of the Europe of Knowledge

ERIC Educational Resources Information Center

Kitagawa, Fumi

2005-01-01

This article highlights a range of university entrepreneurship activities and regional engagement in relation to current governance and finance issues. A model for networking and developing partnership between universities and their region is presented, which reflects existing and emerging European level policy instruments. This model aims at…

Library Public Relations: Recent Articles on Marketing and Branding in University Libraries

ERIC Educational Resources Information Center

Matuozzi, Robert N.

2009-01-01

Though the core mission of a university library--to provide essential support for teaching and research remains unchanged--the library cannot escape budgetary constraints. It has to compete for resources with other departments and programs in the university. Times are hard, with some states currently reporting unprecedented budget deficits with…

Movement Activity Determination with Health-related Variables of University Students in Kosice.

PubMed

Bakalár, Peter; Zvonar, Martin; Sedlacek, Jaromir; Lenkova, Rut; Sagat, Peter; Vojtasko, Lubos; Liptakova, Erika; Barcalova, Miroslava

2018-06-01

There is currently a strong scientific evidence about the negative health consequences of physical inactivity. One of the potential tools for promoting physical activity at the institutional level of the Ecological model is to create conditions and settings that would enable pupils, students and employees engage in some form of physical activity. However, physical activities as a subject are being eliminated from the study programs at Slovak universities. The purpose of the study was to find current evidence about the level of structured physical activity and health-related variables in university students in Košice. The sample consisted of 1,993 or, more precisely, 1,398 students who attended two universities in Košice. To collect data, students completed a questionnaire and were tested for body height, body weight, circumferential measures and percentage body fat. The university students did not sufficiently engage in a structured physical activity. A large number of students had either low or high values of percentage body fat and BMI and high WHR values. Our findings have shown that the research into physical activity of university students should receive more attention.

3D Finite Element Modeling for Possible Creeping Behavior of Gas Hydrate-related Slipstream Submarine Slide, offshore Vancouver Island, Canada

NASA Astrophysics Data System (ADS)

LONG, S.; He, T.; Lan, K.; Spence, G.; Yelisetti, S.

2017-12-01

Natural gas hydrate-related submarine landslides have been identified on worldwide continental slope. Being a potential risk for marine environment and engineering projects, it has been a hot topic of hydrate research in recent decades. The study target is Slipstream submarine landslide, one of the slope failures on the frontal ridges of the Northern Cascadia accretionary margin, off Vancouver Island, Canada. The previous studies of P- & S-wave velocity structure based on OBS (Ocean Bottom Seismometer) data of SeaJade (Seafloor Earthquake Array - Japan Canada Cascadia Experiment) project indicated that there are two high concentration gas-hydrate layers within the ridge, one is at a depth of 100 mbsf (meter beneath the seafloor) with anomalous high P-wave velocities and the other is just above the prominent BSR (bottom-simulating reflector) at a depth of 265-275 mbsf. In this study we investigated the possible creeping behavior of gas hydrate layer to examine the critical instability of the ridge slope using the finite element method for self weight and additional stress (e.g., mega earthquake) conditions. The elastic and elasticoplasticity moduli of gas hydrate layer were obtained from laboratory measurements for different uniaxial pressure tests, which indicated that the sediments behave elastically for uniaxial pressures below 6 MPa, but elasticoplastically between 6-6.77 MPa. The modeled shear stress distribution indicated that the current sliding surface is more likely connected with the shallow high-velocity gas hydrate layer and sliding process related with gas hydrate starts from the toe of the slope and then progressively retreats to the place of current headwall, in a series of triangular blocks or wedges. Since the study area is in the earthquake belt, the large seismic acceleration will greatly affect the stress field and pore pressure distribution within the ridge, and the landslide is going to happen and supposedly at the shallow high-velocity gas hydrate layer.

Laboratory Experiments Enabling Electron Beam use in Tenuous Space Plasmas

NASA Astrophysics Data System (ADS)

Miars, G.; Leon, O.; Gilchrist, B. E.; Delzanno, G. L.; Castello, F. L.; Borovsky, J.

2017-12-01

A mission concept is under development which involves firing a spacecraft-mounted electron beam from Earth's magnetosphere to connect distant magnetic field lines in real time. To prevent excessive spacecraft charging and consequent beam return, the spacecraft must be neutralized in the tenuous plasma environment of the magnetosphere. Particle-In-Cell (PIC) simulations suggest neutralization can be accomplished by emitting a neutral plasma with the electron beam. Interpretation of these simulations also led to an ion emission model in which ion current is emitted from a quasi-neutral plasma as defined by the space charge limit [1,2]. Experiments were performed at the University of Michigan's Plasmadynamics and Electric Propulsion Laboratory (PEPL) to help validate the ion emission model. A hollow cathode plasma contactor was used as a representative spacecraft and charged with respect to the chamber walls to examine the effect of spacecraft charging on ion emission. Retarding Potential Analyzer (RPA) measurements were performed to understand ion flow velocity as this parameter relates directly to the expected space charge limit. Planar probe measurements were also made to identify where ion emission primarily occurred and to determine emission current density levels. Evidence of collisions within the plasma (particularly charge exchange collisions) and a simple model predicting emitted ion velocities are presented. While a detailed validation of the ion emission model and of the simulation tools used in [1,2] is ongoing, these measurements add to the physical understanding of ion emission as it may occur in the magnetosphere. 1. G.L. Delzanno, J.E. Borovsky, M.F. Thomsen, J.D. Moulton, and E.A. MacDonald, J. Geophys. Res. Space Physics 120, 3647, 2015. 2. G.L. Delzanno, J.E. Borovsky, M.F. Thomsen, and J.D. Moulton, J. Geophys. Res. Space Physics 120, 3588, 2015. ________________________________ * This work is supported by Los Alamos National Laboratory.

Immersed transient eddy current flow metering: a calibration-free velocity measurement technique for liquid metals

NASA Astrophysics Data System (ADS)

Krauter, N.; Stefani, F.

2017-10-01

Eddy current flow meters are widely used for measuring the flow velocity of electrically conducting fluids. Since the flow induced perturbations of a magnetic field depend both on the geometry and the conductivity of the fluid, extensive calibration is needed to get accurate results. Transient eddy current flow metering has been developed to overcome this problem. It relies on tracking the position of an impressed eddy current system that is moving with the same velocity as the conductive fluid. We present an immersed version of this measurement technique and demonstrate its viability by numerical simulations and a first experimental validation.

The SPLASH Survey: A Spectroscopic Analysis of the Metal-Poor, Low-Luminosity M31 dSph Satellite Andromeda X

NASA Astrophysics Data System (ADS)

Kalirai, Jason S.; Zucker, Daniel B.; Guhathakurta, Puragra; Geha, Marla; Kniazev, Alexei Y.; Martínez-Delgado, David; Bell, Eric F.; Grebel, Eva K.; Gilbert, Karoline M.

2009-11-01

Andromeda X (And X) is a newly discovered low-luminosity M31 dwarf spheroidal galaxy (dSph) found by Zucker et al. in the Sloan Digital Sky Survey (SDSS; York et al.). In this paper, we present the first spectroscopic study of individual red giant branch stars in And X, as a part of the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) Survey. Using the Keck II telescope and multiobject DEIMOS spectrograph, we target two spectroscopic masks over the face of the galaxy and measure radial velocities for ~100 stars with a median accuracy of σ v ~ 3 km s-1. The velocity histogram for this field confirms three populations of stars along the sight line: foreground Milky Way dwarfs at small negative velocities, M31 halo red giants over a broad range of velocities, and a very cold velocity "spike" consisting of 22 stars belonging to And X with v rad = -163.8 ± 1.2 km s-1. By carefully considering both the random and systematic velocity errors of these stars (e.g., through duplicate star measurements), we derive an intrinsic velocity dispersion of just σ v = 3.9 ± 1.2 km s-1 for And X, which for its size, implies a minimum mass-to-light ratio of M/LV = 37+26 -19 assuming that the mass traces the light. Based on the clean sample of member stars, we measure the median metallicity of And X to be [Fe/H] = -1.93 ± 0.11, with a slight radial metallicity gradient. The dispersion in metallicity is large, σ([Fe/H]phot) = 0.48, possibly hinting that the galaxy retained much of its chemical enrichment products. And X has a total integrated luminosity (MV = -8.1 ± 0.5) that straddles the classical Local Group dSphs and the new SDSS ultra-low luminosity galaxies. The galaxy is among the most metal-poor dSphs known, especially relative to those with MV < -8, and has the second lowest intrinsic velocity dispersion of the entire sample. Our results suggest that And X is less massive by a factor of 4 when compared to Milky Way dSphs of comparable luminosity (e.g., Draco and Ursa Minor). We discuss the potential for better understanding the formation and evolution mechanisms for M31's system of dSphs through (current) kinematic and chemical abundance studies, especially in relation to the Milky Way sample. Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias; these observations were funded by the Optical Infrared Coordination Network (OPTICON), a major international collaboration supported by the Research Infrastructures Programme of the European Commission's Sixth Framework Programme.

Estimates of bottom roughness length and bottom shear stress in South San Francisco Bay, California

USGS Publications Warehouse

Cheng, R.T.; Ling, C.-H.; Gartner, J.W.; Wang, P.-F.

1999-01-01

A field investigation of the hydrodynamics and the resuspension and transport of participate matter in a bottom boundary layer was carried out in South San Francisco Bay (South Bay), California, during March-April 1995. Using broadband acoustic Doppler current profilers, detailed measurements of turbulent mean velocity distribution within 1.5 m above bed have been obtained. A global method of data analysis was used for estimating bottom roughness length zo and bottom shear stress (or friction velocities u*). Field data have been examined by dividing the time series of velocity profiles into 24-hour periods and independently analyzing the velocity profile time series by flooding and ebbing periods. The global method of solution gives consistent properties of bottom roughness length zo and bottom shear stress values (or friction velocities u*) in South Bay. Estimated mean values of zo and u* for flooding and ebbing cycles are different. The differences in mean zo and u* are shown to be caused by tidal current flood-ebb inequality, rather than the flooding or ebbing of tidal currents. The bed shear stress correlates well with a reference velocity; the slope of the correlation defines a drag coefficient. Forty-three days of field data in South Bay show two regimes of zo (and drag coefficient) as a function of a reference velocity. When the mean velocity is >25-30 cm s-1, the ln zo (and thus the drag coefficient) is inversely proportional to the reference velocity. The cause for the reduction of roughness length is hypothesized as sediment erosion due to intensifying tidal currents thereby reducing bed roughness. When the mean velocity is <25-30 cm s-1, the correlation between zo and the reference velocity is less clear. A plausible explanation of scattered values of zo under this condition may be sediment deposition. Measured sediment data were inadequate to support this hypothesis, but the proposed hypothesis warrants further field investigation.

Determination of 3D surface displacement rates in the Upper Rhine Graben based on GURN (GNSS Upper Rhine Graben Network)

NASA Astrophysics Data System (ADS)

Mayer, M.; Knöpfler, A.; Masson, F.; Ulrich, P.; Heck, B.

2012-04-01

In September 2008, the Institut de Physique du Globe de Strasbourg (Ecole et Observatoire des Sciences de la Terre) and the Geodetic Institute of Karlsruhe University (now: Karlsruhe Institute of Technology) established the transnational cooperation GURN (GNSS Upper Rhine Graben Network). Within the GURN initiative, these institutions are cooperating in order to carry out geo-scientific research in the framework of the transnational project TOPO-WECEP (Western and Central European Platform; link: http://www.topo-wecep.eu/), which succeeded the former project URGENT (Upper Rhine Graben Evolution and NeoTectonics; link: http://comp1.geol.unibas.ch) of the EUCOR universities (European Confederation of Upper Rhine Universities). The Rhine Graben is the central segment of the European Cenozoic rift system, which extends from the North Sea through Germany and France to the Mediterranean coast over a distance of some 1100 km. GURN focusses on the Upper Rhine Graben (URG). The URG is a 300 km long and 40 km wide SSW-NNE trending rift, extending from Basel (Switzerland) to Frankfurt (Germany). It is limited to the west by the Vosges Mountains and to the east by the Black Forest Mountains, culminating in elevations of approx. 1500 m. The uplifted area of the Rhenish Massif bounds the URG to the north. To the south, the Leymen, Ferrette, and Vendlincourt folds represent the northernmost structural front of the Jura fold and thrust belt. Present-day distribution of the seismicity in the URG area is classified as moderate but not null. Expected velocities and strain rates are very low (relative velocities lower than 0.1mm/yr). The research is actually based on data of GNSS (Global Navigation Satellite Systems). A highly precise and highly sensitive geodetic network of permanently operating GNSS sites region has been established in the URG region in order to detect recent short-term (data base starting in year 2002) crustal movements based on displacements of GNSS sites. The regional network GURN actually consists of approx. 80 permanently operating GNSS sites of different data providers in Germany, France and Switzerland. The first work steps in the context of GURN were dominated by a detailed analysis of the GNSS data base (e.g., instrumental change artefacts). This analysis included a comparison of the working group related results (EOST, GIK), where different software packages and data handling strategies were used to derive 3D coordinate time series as basis for the determination of a 3D surface displacement field. Due to very small expected velocities in the URG region, the recent GURN focus is on the reliable derivation of site velocities, therefore effects of datum realisation have to be handled with care. The presentation gives an insight into the joint venture GURN focussing on recent results (e.g., 3D surface velocity field).

Effect of Ion Escape Velocity and Conversion Surface Material on H- Production

NASA Astrophysics Data System (ADS)

Tarvainen, O.; Kalvas, T.; Komppula, J.; Koivisto, H.; Geros, E.; Stelzer, J.; Rouleau, G.; Johnson, K. F.; Carmichael, J.

2011-09-01

According to generally accepted models surface production of negative ions depends on ion escape velocity and work function of the surface. We have conducted an experimental study addressing the role of the ion escape velocity on H- production. A converter-type ion source at Los Alamos Neutron Science Center was employed for the experiment. The ion escape velocity was affected by varying the bias voltage of the converter electrode. It was observed that due to enhanced stripping of H- no direct gain of extracted beam current can be achieved by increasing the converter voltage. The conversion efficiency of H- was observed to vary with converter voltage and follow the existing theories in qualitative manner. We present calculations predicting relative H- yields from different cesiated surfaces with comparison to experimental observations from different types of H- ion sources. Utilizing materials exhibiting negative electron affinity and exposed to UV-light is considered for Cesium-free H-/D- production.

Vortex tubes in turbulence velocity fields at Reynolds numbers Re lambda approximately equal to 300-1300.

PubMed

Mouri, Hideaki; Hori, Akihiro; Kawashima, Yoshihide

2004-12-01

The most elementary structures of turbulence, i.e., vortex tubes, are studied using velocity data obtained in a laboratory experiment for boundary layers with Reynolds numbers Re(lambda) =295-1258 . We conduct conditional averaging for enhancements of a small-scale velocity increment and obtain the typical velocity profile for vortex tubes. Their radii are of the order of the Kolmogorov length. Their circulation velocities are of the order of the root-mean-square velocity fluctuation. We also obtain the distribution of the interval between successive enhancements of the velocity increment as the measure of the spatial distribution of vortex tubes. They tend to cluster together below about the integral length and more significantly below about the Taylor microscale. These properties are independent of the Reynolds number and are hence expected to be universal.

Signal processing related to the vestibulo-ocular reflex during combined angular rotation and linear translation of the head

NASA Technical Reports Server (NTRS)

McCrea, R. A.; Chen-Huang, C.; Peterson, B. W. (Principal Investigator)

1999-01-01

The contributions of vestibular nerve afferents and central vestibular pathways to the angular (AVOR) and linear (LVOR) vestibulo-ocular reflex were studied in squirrel monkeys during fixation of near and far targets. Irregular vestibular afferents did not appear to be necessary for the LVOR, since when they were selectively silenced with galvanic currents the LVOR was essentially unaffected during both far- and near-target viewing. The linear translation signals generated by secondary AVOR neurons in the vestibular nuclei were, on average, in phase with head velocity, inversely related to viewing distance, and were nearly as strong as AVOR-related signals. We suggest that spatial-temporal transformation of linear head translation signals to angular eye velocity commands is accomplished primarily by the addition of viewing distance multiplied, centrally integrated, otolith regular afferent signals to angular VOR pathways.

Low-Energy Impacts onto Lunar Regolith Simulant

NASA Astrophysics Data System (ADS)

Seward, Laura M.; Colwell, J.; Mellon, M.; Stemm, B.

2012-10-01

Low-Energy Impacts onto Lunar Regolith Simulant Laura M. Seward1, Joshua E. Colwell1, Michael T. Mellon2, and Bradley A. Stemm1, 1Department of Physics, University of Central Florida, Orlando, Florida, 2Southwest Research Institute, Boulder, Colorado. Impacts and cratering in space play important roles in the formation and evolution of planetary bodies. Low-velocity impacts and disturbances to planetary regolith are also a consequence of manned and robotic exploration of planetary bodies such as the Moon, Mars, and asteroids. We are conducting a program of laboratory experiments to study low-velocity impacts of 1 to 5 m/s into JSC-1 lunar regolith simulant, JSC-Mars-1 Martian regolith simulant, and silica targets under 1 g. We use direct measurement of ejecta mass and high-resolution video tracking of ejecta particle trajectories to derive ejecta mass velocity distributions. Additionally, we conduct similar experiments under microgravity conditions in a laboratory drop tower and on parabolic aircraft with velocities as low as 10 cm/s. We wish to characterize and understand the collision parameters that control the outcome of low-velocity impacts into regolith, including impact velocity, impactor mass, target shape and size distribution, regolith depth, target relative density, and crater depth, and to experimentally determine the functional dependencies of the outcomes of low-velocity collisions (ejecta mass and ejecta velocities) on the controlling parameters of the collision. We present results from our ongoing study showing the positive correlation between impact energy and ejecta mass. The total ejecta mass is also dependent on the packing density (porosity) of the regolith. We find that ejecta mass velocity fits a power-law or broken power-law distribution. Our goal is to understand the physics of ejecta production and regolith compaction in low-energy impacts and experimentally validate predictive models for dust flow and deposition. We will present our results from one-g and microgravity impact experiments.

Sequence optimization to reduce velocity offsets in cardiovascular magnetic resonance volume flow quantification - A multi-vendor study

PubMed Central

2011-01-01

Purpose Eddy current induced velocity offsets are of concern for accuracy in cardiovascular magnetic resonance (CMR) volume flow quantification. However, currently known theoretical aspects of eddy current behavior have not led to effective guidelines for the optimization of flow quantification sequences. This study is aimed at identifying correlations between protocol parameters and the resulting velocity error in clinical CMR flow measurements in a multi-vendor study. Methods Nine 1.5T scanners of three different types/vendors were studied. Measurements were performed on a large stationary phantom. Starting from a clinical breath-hold flow protocol, several protocol parameters were varied. Acquisitions were made in three clinically relevant orientations. Additionally, a time delay between the bipolar gradient and read-out, asymmetric versus symmetric velocity encoding, and gradient amplitude and slew rate were studied in adapted sequences as exploratory measurements beyond the protocol. Image analysis determined the worst-case offset for a typical great-vessel flow measurement. Results The results showed a great variation in offset behavior among scanners (standard deviation among samples of 0.3, 0.4, and 0.9 cm/s for the three different scanner types), even for small changes in the protocol. Considering the absolute values, none of the tested protocol settings consistently reduced the velocity offsets below the critical level of 0.6 cm/s neither for all three orientations nor for all three scanner types. Using multilevel linear model analysis, oblique aortic and pulmonary slices showed systematic higher offsets than the transverse aortic slices (oblique aortic 0.6 cm/s, and pulmonary 1.8 cm/s higher than transverse aortic). The exploratory measurements beyond the protocol yielded some new leads for further sequence development towards reduction of velocity offsets; however those protocols were not always compatible with the time-constraints of breath-hold imaging and flow-related artefacts. Conclusions This study showed that with current systems there was no generic protocol which resulted into acceptable flow offset values. Protocol optimization would have to be performed on a per scanner and per protocol basis. Proper optimization might make accurate (transverse) aortic flow quantification possible for most scanners. Pulmonary flow quantification would still need further (offline) correction. PMID:21388521

Recent Results of Turbulence Research

NASA Technical Reports Server (NTRS)

Prandtl, L

1933-01-01

The first sections of this report deal with two prominent questions, namely the origin of turbulence and the characteristics of turbulent currents. In the third section conclusions are drawn for the flow along a rough wall, whereby an important relation for the velocity distribution is revealed. The principles are also applied to straight rough and smooth tubes.

Analysis of current-meter data at Columbia River gaging stations, Washington and Oregon

USGS Publications Warehouse

Savini, John; Bodhaine, G.L.

1971-01-01

The U.S. Geological Survey developed equipment to measure stream velocity simultaneously with 10 current meters arranged in a vertical and to measure velocity closer to the streambed than attainable with conventional equipment. With the 10 current meters, synchronous velocities were recorded for a period of 66 minutes at 10 different depths in one vertical of one gaging-station cross section. In addition, with a current meter installed on a special bracket to allow measurements to 0.5 foot above streambed, data were obtained at two to four verticals in four gaging-station cross sections. The mean velocity determined for the 66-minute period of record was 3.30 fps (feet per second). The graphic record of velocity was analyzed on a minute-by-minute basis. It was noted that the shape of the vertical velocity curves (plot of horizontal flow velocities measured in a vertical) changed from one minute to the next, but the change seemed to be random. Velocities obtained at different depths in the, profile fluctuated significantly, with the 1-minute velocities obtained at 0.05 depth (5 percent of total depths measured from the surface at indicated vertical) showing the smallest range--0.66 fps--and those at 0.55 depth the largest range--l.22 fps. The standard deviation, expressed in feet per second, of the velocity at each point in the vertical tended to increase with depth--from 0.16 fps at 0.05 depth to a maximum of 0.24 fps at 0.75 depth. The standard deviation, expressed as a percentage of the mean velocity, ranged from about 4 percent near the surface to 11 percent at 0.95 depth. In spite of the fluctuation in mean velocity that occurred during the 66 minutes and observation period of 4 minutes yields a mean velocity that differs from the 66-minute mean by less than one-half of a percent. Determining the mean velocity by averaging the 10-point observations of the 66minute run proved to be as accurate as by plotting the vertical velocity curvy (from the averaged 10 points) and then integrating the depth-velocity profile. In comparing the velocity obtained by integrating the depth-velocity profile with the 10-point mean velocity for other field data, collected beyond that obtained during the 66-minute run, the difference ranged from -1.3 to +1.7 percent and averaged -0.2 percent. Extension of the curve below the 0.95 depth by use of a power function proved to be fairly accurate (when compared with actual measurements within this reach made with the special current-meter bracket). However, the extension did not improve significantly the accuracy of the integrated-curve mean velocity. Both the one- and two-point methods were found to agree with the 10-point velocity. In computing mean river velocity, values determined by the two-point method ranged from -1.4 to +1.6 percent when compared with the base integrated-curve mean river velocity. The one-point method yielded results that ranged from -1.9 to +4.4 percent and averaged 40.1 percent. In determining river flow by use of the midsection and mean-section methods, the mean-section method uniformly yields lower flows for the same dart.. The range in difference is from -0.2 percent to -1.6 percent, with an average difference of -0.6 percent.

Comparison of large-scale structures and velocities in the local universe

NASA Technical Reports Server (NTRS)

Yahil, Amos

1994-01-01

Comparison of the large-scale density and velocity fields in the local universe shows detailed agreement, strengthening the standard paradigm of the gravitational origin of these structures. Quantitative analysis can determine the cosmological density parameter, Omega, and biasing factor, b; there is virtually no sensitivity in any local analyses to the cosmologial constant, lambda. Comparison of the dipole anisotropy of the cosmic microwave background with the acceleration due to the Infrared Astronomy Satellite (IRAS) galaxies puts the linear growth factor in the range beta approximately equals Omega (exp 0.6)/b = 0.6(+0.7/-0.3) (95% confidence). A direct comparison of the density and velocity fields of nearby galaxies gives beta = 1.3 (+0.7/-0.6), and from nonlinear analysis the weaker limit (Omega greater than 0.45 for b greater than 0.5 (again 95% confidence). A tighter limit (Omega greater than 0.3 (4-6 sigma)), is obtained by a reconstruction of the probability distribution function of the initial fluctuations from which the structures observed today arose. The last two methods depend critically on the smooth velocity field determined from the observed velocities of nearby galaxies by the POTENT method. A new analysis of these velocities, with more than three times the data used to obtain the above quoted results, is now underway and promises to tighten the uncertainties considerably, as well as reduce systematic bias.

Retrieving current and wind vectors from ATI SAR data: airborne evidence and inversion strategy

NASA Astrophysics Data System (ADS)

Martin, Adrien; Gommenginger, Christine; Chapron, Bertrand; Marquez, José; Doody, Sam

2017-04-01

Conventional and along-track interferometric (ATI) Synthetic Aperture Radar (SAR) sense the motion of the ocean surface by measuring the Doppler shift of reflected signals. Together with the water displacement associated with ocean currents, the SAR measurements are also affected by a Wind-wave induced Artefact Surface Velocity (WASV) caused by the velocity of Bragg scatterers and the orbital velocity of ocean surface gravity waves. The WASV has been modelled theoretically in past studies but has been estimated empirically only once using Envisat ASAR. Here we propose, firstly, to evaluate this WASV from airborne ATI SAR data, secondly, to validate the airborne retrieved surface current after correction of the WASV against HF radar measurements and thirdly to examine the best inversion strategy for a an Ocean Surface Current (OSC) satellite mission to retrieve accurately both the ocean surface current vector (OSCV) and the wind vector in the frame of an OSC satellite mission. The airborne ATI SAR data were acquired in the tidally dominated Irish Sea using a Wavemill-type dual-beam SAR interferometer. A comprehensive collection of airborne Wavemill data acquired in a star pattern over a well-instrumented site made it possible to estimate the magnitude and dependence on azimuth and incidence angle of the WASV. The airborne results compare favourably with those reported for Envisat ASAR, empirical model, which has been used to correct for it. Validation of the current retrieval capabilities of the proof-of-concept has been conducted against HF radar giving a precisions typically better than 0.1 m/s for surface current speed and 7° for direction. Comparisons with POLCOMS (1.8 km) indicate that the model reproduces well the overall temporal evolution but does not capture the high spatial variability of ocean surface currents at the maximum ebb flow. Airborne retrieved currents highlight a short-scale spatial variability up to 100m related to bathymetry channels, which are not observed (HF radar, 4km resolution) or simulated (POLCOMS, 1.8km). The inversion strategy points to the need for accurate measurement of both the backscatter amplitude and the Doppler information (either as a Doppler centroid frequency anomaly for SAR DCA, or as an interferometric phase for ATI) as well as the need for dual polarization capability (VV+HH) for non-ambiguous inversion. Preliminary inversion results show that the retrieval accuracy for OSC velocity better than 10 cm/s can be achieved but that the OSC accuracy is strongly sensitive to the wind direction relative to the antennas orientation. This concept is a unique opportunity to improve our understanding of the air-sea interaction, the ocean submesoscale dynamic and its impact on the oceanic vertical transport. This concept is particularly well fitted for these ocean surface current and wind vectors observations in coastal and polar regions.

Discharge Measurements in Shallow Urban Streams Using a Hydroacoustic Current Meter

USGS Publications Warehouse

Fisher, G.T.; Morlock, S.E.; ,

2002-01-01

Hydroacoustic current-meter measurements were evaluated in small urban streams under a range of stages, velocities, and channel-bottom materials. Because flow in urban streams is often shallow, conventional mechanical current-meter measurements are difficult or impossible to make. The rotating-cup Price pygmy meter that is widely used by the U.S. Geological Survey and other agencies should not be used in depths below 0.20 ft and velocities less than 0.30 ft/s. The hydroacoustic device provides measurements at depths as shallow as 0.10 ft and velocities as low as 0.10 ft/s or less. Measurements using the hydroacoustic current meter were compared to conventional discharge measurements. Comparisons with Price-meter measurements were favorable within the range of flows for which the meters are rated. Based on laboratory and field tests, velocity measurements with the hydroacoustic cannot be validated below about 0.07 ft/s. However, the hydroacoustic meter provides valuable information on direction and magnitude of flow even at lower velocities, which otherwise could not be measured with conventional measurements.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donner, Leo J.; O'Brien, Travis A.; Rieger, Daniel

Both climate forcing and climate sensitivity persist as stubborn uncertainties limiting the extent to which climate models can provide actionable scientific scenarios for climate change. A key, explicit control on cloud-aerosol interactions, the largest uncertainty in climate forcing, is the vertical velocity of cloud-scale updrafts. Model-based studies of climate sensitivity indicate that convective entrainment, which is closely related to updraft speeds, is an important control on climate sensitivity. Updraft vertical velocities also drive many physical processes essential to numerical weather prediction. Vertical velocities and their role in atmospheric physical processes have been given very limited attention in models for climatemore » and numerical weather prediction. The relevant physical scales range down to tens of meters and are thus frequently sub-grid and require parameterization. Many state-of-science convection parameterizations provide mass fluxes without specifying vertical velocities, and parameterizations which do provide vertical velocities have been subject to limited evaluation against what have until recently been scant observations. Atmospheric observations imply that the distribution of vertical velocities depends on the areas over which the vertical velocities are averaged. Distributions of vertical velocities in climate models may capture this behavior, but it has not been accounted for when parameterizing cloud and precipitation processes in current models. New observations of convective vertical velocities offer a potentially promising path toward developing process-level cloud models and parameterizations for climate and numerical weather prediction. Taking account of scale-dependence of resolved vertical velocities offers a path to matching cloud-scale physical processes and their driving dynamics more realistically, with a prospect of reduced uncertainty in both climate forcing and sensitivity.« less

Dragging of inertial frames.

PubMed

Ciufolini, Ignazio

2007-09-06

The origin of inertia has intrigued scientists and philosophers for centuries. Inertial frames of reference permeate our daily life. The inertial and centrifugal forces, such as the pull and push that we feel when our vehicle accelerates, brakes and turns, arise because of changes in velocity relative to uniformly moving inertial frames. A classical interpretation ascribed these forces to acceleration relative to some absolute frame independent of the cosmological matter, whereas an opposite view related them to acceleration relative to all the masses and 'fixed stars' in the Universe. An echo and partial realization of the latter idea can be found in Einstein's general theory of relativity, which predicts that a spinning mass will 'drag' inertial frames along with it. Here I review the recent measurements of frame dragging using satellites orbiting Earth.

Controls on gas transfer velocities in a large river

NASA Astrophysics Data System (ADS)

Beaulieu, Jake J.; Shuster, William D.; Rebholz, Jacob A.

2012-06-01

The emission of biogenic gases from large rivers can be an important component of regional greenhouse gas budgets. However, emission rate estimates are often poorly constrained due to uncertainties in the air-water gas exchange rate. We used the floating chamber method to estimate the gas transfer velocity (k) of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in the Markland Pool of the Ohio River, a large tributary of the Mississippi River (U.S.A). We measured k every two weeks for a year at one site and at 15 additional sites distributed across the length of the pool during two summer surveys. We found that k was positively related to both water currents and wind speeds, with 46% of the gas transfer attributable to water currents at low wind speeds (e.g., 0.5 m s-1) and 11% at higher wind speeds (e.g., >2.0 m s-1). Gas transfer velocity was highly sensitive to wind, possibly because the direction of river flow was often directly opposed to the wind direction. Gas transfer velocity values derived for CH4 were consistently greater than those derived for CO2 when standardized to a Schmidt number of 600 (k600), possibly because the transfer of CH4, a poorly soluble gas, was enhanced by surfacing microbubbles. Additional research to determine the conditions that support microbubble enhanced gas transfer is merited.

Distant Supernovae Indicate Ever-Expanding Universe

NASA Astrophysics Data System (ADS)

1998-12-01

ESO Astronomers Contribute towards Resolution of Cosmic Puzzle Since the discovery of the expansion of the Universe by American astronomer Edwin Hubble in the 1920's, by measurement of galaxy velocities, astronomers have tried to learn how this expansion changes with time. Until now, most scientists have been considering two possibilities: the expansion rate is slowing down and will ultimately either come to a halt - whereafter the Universe would start to contract, or it will continue to expand forever. However, new studies by two independent research teams, based on observations of exploding stars ( supernovae ) by ESO astronomers [1] with astronomical telescopes at the La Silla Observatory as well as those of their colleagues at other institutions, appear to show that the expansion of the Universe is accelerating . The results take the discovery of the cosmological expansion one step further and challenge recent models of the Universe. If the new measurements are indeed correct, they show that the elusive "cosmological constant" , as proposed by Albert Einstein , contributes significantly to the evolution of the Universe. The existence of a non-zero cosmological constant implies that a repulsive force, counter-acting gravity, currently dominates the universal expansion , and consequently leads to an ever-expanding Universe. This new research is being named as the "Breakthrough of the Year" by the renowned US science journal Science in the December 18, 1998, issue. A Press Release is published by the journal on this occasion. "Fundamental Parameters" of the Universe Three fundamental parameters govern all cosmological models based on the theory of General Relativity. They are 1. the current expansion rate as described by Hubble's constant , i.e. the proportionality factor between expansion velocity and distance 2. the average matter density in the Universe, and 3. the amount of "other energy" present in space. From the measured values of these fundamental parameters, the age of the Universe and the geometry of space can be derived. They have been the focus of a large number of astronomical programmes over the past decades. Many aspects of the currently preferred cosmological model, the Hot Big Bang , have been impressively confirmed by observations of the expansion of the Universe, the cosmic background radiation, and also the explanation of the synthesis of light elements. Still, our knowledge about the dynamical state of the Universe, as well as the early formation of structures, i.e., of galaxies and stars, is far from complete - this remains a field of active research. Possibly, the simplest way to test our present assumptions in this direction is to measure accurate distances and compare them with the expected cosmic scale. This is where the recent results contribute to our understanding of the Universe. The key role of supernovae The two research teams, both with participation from ESO [1], have concentrated on the study of rare stellar explosions, during which certain old stars undergo internal incineration. In this process, explosive nuclear fusion burns matter into the most stable atomic nucleus, iron, and releases a gigantic amount of energy. ESO PR Photo 50a/98 ESO PR Photo 50a/98 [Preview - JPEG: 800 x 648 pix - 768k] [High-Res - JPEG: 3000 x 2431 pix - 8.5Mb] ESO PR Photo 50b/98 ESO PR Photo 50b/98 [Preview - JPEG: 800 x 649 pix - 784k] [High-Res - JPEG: 3000 x 2432 pix - 8.4Mb] These photos illustrate the follow-up observations on which the new results described in this Press Release are based. Sky fields with clusters of galaxies are monitored with the 4-m telescope at Cerro Tololo Interamerican Observatory (CTIO) in Chile and spectra are obtained of suddenly appearing star-like objects that may be supernovae. Confirmed Type Ia supernovae are then monitored by ESO telescopes at La Silla and at other observatories. In PR Photo 50a/98 , a supernova at redshift z = 0.51 [2] (corresponding to a distance of about 10,000 million light-years) is observed on five dates with the SUSI camera at the 3.6-m New Technology Telescope (NTT). The host galaxy is clearly visible and the supernova reaches its maximum brightness around 13 March 1997, after which it fades. In PR Photo 50b/98 of another supernova that was found at the same time, the image of the host galaxy is barely visible, most probably because it is a low surface brightness galaxy . Here, the redshift of the supernova is z = 0.40 (distance 6,000 million light-years) and the brightness peaks around 16 March 1997. Technical information: All images were obtained through an R (red) optical filtre. The image quality varies somewhat from image to image. Exposure times and seeing values: Photo 50a/98 - 11 March (300 sec; 0.73 arcsec); 13 March (600 sec; 0.79 arcsec); 16 March (600 sec; 0.72 arcsec); 29 March (1200 sec; 1.17 arcsec); 5 April (300 sec; 0.55 arcsec) and Photo 50b/98 - 11 March (300 sec; 0.50 arcsec); 13 March (600 sec; 0.81 arcsec); 16 March (600 sec; 0.90 arcsec); 29 March (1200 sec; 0.83 arcsec); 7 April (300 sec; 1.43 arcsec); 7 May (1800 sec; 1.22 arcsec). These explosions, known as Type Ia Supernovae , are distinguished by their very uniform properties, including their intrinsic brightness; this makes them ideal for the measurement of large distances, cf. ESO PR Photos 50a/98 and 50b/98 , as well as ESO Press Release 09/95. It is by means of observations of remote objects of this type that the all-important distances could be determined with sufficient accuracy. In particular, coordinated observing campaigns of Type Ia Supernovae were carried out at several of the world's major observatories. In this way it became possible to secure the crucial data that provide the basis of the new analysis. Distances to Type Ia Supernovae are larger than expected The new observations show that, compared to their nearby twins, distant supernovae appear too dim, even for a Universe which has been freely coasting (i.e. with no change of the expansion velocity) for the last several billion years (corresponding to redshifts of about 0.5). The only reasonable interpretation of these data implies that the measured distances are larger than what they would be in a "non-braking" Universe. This means that the distances to the supernovae must have increased over and above what they would have been if the rate of expansion did not change with time. This is only possible by the effect of additional acceleration , i.e., the rate of expansion of the Universe increases with time. The acceleration comes from a repulsive force . This concept was introduced by Albert Einstein , as the cosmological constant . Implications There are several important implications from this new result. The corresponding, deduced age of the Universe , now about 14,000 - 15,000 million years, no longer conflicts with that of the oldest known stellar objects in globular clusters. Moreover, the spatial geometry of the Universe appears to be "flat" - this is a strong confirmation of inflation (a short phase of very rapid expansion) in the very early Universe. Ordinary matter, which comprises everything we know - from the atom to the stars - is composed of baryonic matter . It has been realized over the last few years that the matter we observe directly is only a fraction of all mass that is actually present in galaxies and clusters of galaxies, as estimated from measurements of internal motions in these objects. This has been referred to as the "dark matter problem" . Following the new measurements, a new component, "dark energy" (i.e., energy of the vacuum), must be added. It appears that this form of energy is dominating the Universe at the current time. There is a profound philosophical repositioning of humankind implied by this result. This follows the first step which was taken by Copernicus who in the mid-sixteenth century dislodged us from the centre of the Universe. Not only does the material from which the visible galaxies, stars, the Earth and its inhabitants are made comprise only a small fration of the gravitating mass in the Universe. There is now a new component, the "dark energy" which joins the "dark matter" in shaping the large-scale geometric and dynamical structure. Clearly, more observations are needed to further support the findings described here. They will soon be forthcoming, especially from new and large telescopes like the ESO Very Large Telescope (VLT) , that has recently delivered its first, impressive results. But already now, on the verge of the new millenium, we are having a first glimpse of extremely exciting and fundamental aspects in the continuing human quest for the deep truths of nature. Notes: [1] The ESO members of the "High-z Supernova Search" team (see URL: http://cfa-www.harvard.edu/cfa/oir/Research/supernova/HighZ.html) are Bruno Leibundgut and Patrick Woudt (ESO HQ, Garching, Germany) and Jason Spyromilio (Paranal Observatory, Chile). Chris Lidman (La Silla Observatory, Chile) and Isobel Hook (formerly ESO HQ, now Royal Observatory, Edinburgh, UK) are members of the "Supernova Cosmology Project" (see URL: http://www-supernova.lbl.gov/). The astronomers mostly used the ESO 3.6-m and 3.6-m NTT telescopes at La Silla for these research programmes. [2] In astronomy, the redshift (z) denotes the fraction by which the lines in the spectrum of an object are shifted towards longer wavelengths. The observed redshift of a distant galaxy or quasar gives a direct estimate of the universal expansion (i.e. the "recession velocity"). Since this expansion rate increases with the distance, the velocity is itself a function (the Hubble relation) of the distance to the object. For instance, a redshift of z = 0.1 corresponds to a velocity of 30,000 km/sec, and assuming a Hubble constant of 20 km/sec per million light-years, to a distance of about 1,500 million light-years. How to obtain ESO Press Information ESO Press Information is made available on the World-Wide Web (URL: http://www.eso.org ). ESO Press Photos may be reproduced, if credit is given to the European Southern Observatory.

Techniques and equipment required for precise stream gaging in tide-affected fresh-water reaches of the Sacramento River, California

USGS Publications Warehouse

Smith, Winchell

1971-01-01

Current-meter measurements of high accuracy will be required for calibration of an acoustic flow-metering system proposed for installation in the Sacramento River at Chipps Island in California. This report presents an analysis of the problem of making continuous accurate current-meter measurements in this channel where the flow regime is changing constantly in response to tidal action. Gaging-system requirements are delineated, and a brief description is given of the several applicable techniques that have been developed by others. None of these techniques provides the accuracies required for the flowmeter calibration. A new system is described--one which has been assembled and tested in prototype and which will provide the matrix of data needed for accurate continuous current-meter measurements. Analysis of a large quantity of data on the velocity distribution in the channel of the Sacramento River at Chipps Island shows that adequate definition of the velocity can be made during the dominant flow periods--that is, at times other than slack-water periods--by use of current meters suspended at elevations 0.2 and 0.8 of the depth below the water surface. However, additional velocity surveys will be necessary to determine whether or not small systematic corrections need be applied during periods of rapidly changing flow. In the proposed system all gaged parameters, including velocities, depths, position in the stream, and related times, are monitored continuously as a boat moves across the river on the selected cross section. Data are recorded photographically and transferred later onto punchcards for computer processing. Computer programs have been written to permit computation of instantaneous discharges at any selected time interval throughout the period of the current meter measurement program. It is anticipated that current-meter traverses will be made at intervals of about one-half hour over periods of several days. Capability of performance for protracted periods was, consequently, one of the important elements in system design. Analysis of error sources in the proposed system indicates that errors in individual computed discharges can be kept smaller than 1.5 percent if the expected precision in all measured parameters is maintained.

The KMOS Deep Survey (KDS) - I. Dynamical measurements of typical star-forming galaxies at z ≃ 3.5

NASA Astrophysics Data System (ADS)

Turner, O. J.; Cirasuolo, M.; Harrison, C. M.; McLure, R. J.; Dunlop, J. S.; Swinbank, A. M.; Johnson, H. L.; Sobral, D.; Matthee, J.; Sharples, R. M.

2017-10-01

We present dynamical measurements from the KMOS (K-band multi-object spectrograph) Deep Survey (KDS), which comprises 77 typical star-forming galaxies at z ≃ 3.5 in the mass range 9.0 < log (M⋆/M⊙) < 10.5. These measurements constrain the internal dynamics, the intrinsic velocity dispersions (σint) and rotation velocities (VC) of galaxies in the high-redshift Universe. The mean velocity dispersion of the galaxies in our sample is σ _int = 70.8^{+3.3}_{-3.1} km s^{-1}, revealing that the increasing average σint with increasing redshift, reported for z ≲ 2, continues out to z ≃ 3.5. Only 36 ± 8 per cent of our galaxies are rotation-dominated (VC/σint > 1), with the sample average VC/σint value much smaller than at lower redshift. After carefully selecting comparable star-forming samples at multiple epochs, we find that the rotation-dominated fraction evolves with redshift with a z-0.2 dependence. The rotation-dominated KDS galaxies show no clear offset from the local rotation velocity-stellar mass (I.e. VC-M⋆) relation, although a smaller fraction of the galaxies are on the relation due to the increase in the dispersion-dominated fraction. These observations are consistent with a simple equilibrium model picture, in which random motions are boosted in high-redshift galaxies by a combination of the increasing gas fractions, accretion efficiency, specific star formation rate and stellar feedback and which may provide significant pressure support against gravity on the galactic disc scale.

Hydrodynamic pumping of a quantum Fermi liquid in a semiconductor heterostructure

NASA Astrophysics Data System (ADS)

Heremans, J. J.; Kantha, D.; Chen, H.; Govorov, A. O.

2003-03-01

We present experimental results for a pumping mechanism observed in mesoscopic structures patterned on two-dimensional electron systems in GaAs/AlGaAs heterostructures. The experiments are performed at low temperatures, in the ballistic regime. The effect is observed as a voltage or current signal corresponding to carrier extraction from sub-micron sized apertures, when these apertures are swept by a beam of ballistic electrons. The carrier extraction, phenomenologically reminiscent of the Bernoulli pumping effect in classical fluids, has been observed in various geometries. We ascertained linearity between measured voltage and injected current in all experiments, thereby excluding rectification effects. The linear response, however, points to a fundamental difference from the Bernoulli effect in classical liquids, where the response is nonlinear and quadratic in terms of the velocity. The temperature dependence of the effect will also be presented. We thank M. Shayegan (Princeton University) for the heterostructure growth, and acknowledge support from NSF DMR-0094055.

Surface current balance and thermoelectric whistler wings at airless astrophysical bodies: Cassini at Rhea

NASA Astrophysics Data System (ADS)

Teolis, B. D.; Sillanpää, I.; Waite, J. H.; Khurana, K. K.

2014-11-01

Sharp magnetic perturbations found by the Cassini spacecraft at the edge of the Rhea flux tube are consistent with field-aligned flux tube currents. The current system results from the difference of ion and electron gyroradii and the requirement to balance currents on the sharp Rhea surface. Differential-type hybrid codes that solve for ion velocity and magnetic field have an intrinsic difficulty modeling the plasma absorber's sharp surface. We overcome this problem by instead using integral equations to solve for ion and electron currents and obtain agreement with the magnetic perturbations at Rhea's flux tube edge. An analysis of the plasma dispersion relations and Cassini data reveals that field-guided whistler waves initiated by (1) the electron velocity anisotropy in the flux tube and (2) interaction with surface sheath electrostatic waves on topographic scales may facilitate propagation of the current system to large distances from Rhea. Current systems like those at Rhea should occur generally, for plasma absorbers of any size such as spacecraft or planetary bodies, in a wide range of space plasma environments. Motion through the plasma is not essential since the current system is thermodynamic in origin, excited by heat flow into the object. The requirements are a difference of ion and electron gyroradii and a sharp surface, i.e., without a significant thick atmosphere.

Corrected Launch Speed for a Projectile Motion Laboratory

ERIC Educational Resources Information Center

Sanders, Justin M.; Boleman, Michael W.

2013-01-01

At our university, students in introductory physics classes perform a laboratory exercise to measure the range of a projectile fired at an assigned angle. A set of photogates is used to determine the initial velocity of the projectile (the launch velocity). We noticed a systematic deviation between the experimentally measured range and the range…

Prediction of aerodynamic noise in a ring fan based on wake characteristics

NASA Astrophysics Data System (ADS)

Sasaki, Soichi; Fukuda, Masaharu; Tsujino, Masao; Tsubota, Haruhiro

2011-06-01

A ring fan is a propeller fan that applies an axial-flow impeller with a ring-shaped shroud on the blade tip side. In this study, the entire flow field of the ring fan is simulated using computational fluid dynamics (CFD); the accuracy of the CFD is verified through a comparison with the aerodynamic characteristics of a propeller fan of current model. Moreover, the aerodynamic noise generated by the fan is predicted on the basis of the wake characteristics. The aerodynamic characteristic of the ring fan based on CFD can represent qualitatively the variation in the measured value. The main flow domain of the ring fan is formed at the tip side of the blade because blade tip vortex is not formed at that location. Therefore, the relative velocity of the ring fan is increased by the circumferential velocity. The sound pressure levels of the ring fan within the frequency band of less than 200 Hz are larger than that of the propeller fan. In the analysis of the wake characteristics, it revealed that Karman vortex shedding occurred in the main flow domain in the frequency domain lower than 200 Hz; the aerodynamic noise of the ring fan in the vortex shedding frequency enlarges due to increase in the relative velocity and the velocity fluctuation.

Basic principles of coaxial launch technology

NASA Technical Reports Server (NTRS)

Kolm, H.; Mongeau, P.

1984-01-01

Already in the 1930s, a discrete-coil mechanically synchronized launcher was built. At the present time, research is almost entirely directed towards railguns. However, although coaxial accelerators are more complex than railguns, they have certain unique advantages. Some of these advantages are related to the absence of physical contact requirements with the projectile, the possibility of a scale-up to very large projectile size, and the availability of up to 100 times more thrust for a given current. The price of the advantages is the need for a drive current in the form of pulses synchronized precisely with transit of each projectile coil through each drive coil. At high velocities, high voltages are required, and high voltage switching represents the technology limit on launch velocity. Attention is given to inductance gradients, the double hump, methods of excitation, methods of synchronization, projectile configuration, energy supply, fundamental limits, trends, and research needs.

Cosmological perturbation effects on gravitational-wave luminosity distance estimates

NASA Astrophysics Data System (ADS)

Bertacca, Daniele; Raccanelli, Alvise; Bartolo, Nicola; Matarrese, Sabino

2018-06-01

Waveforms of gravitational waves provide information about a variety of parameters for the binary system merging. However, standard calculations have been performed assuming a FLRW universe with no perturbations. In reality this assumption should be dropped: we show that the inclusion of cosmological perturbations translates into corrections to the estimate of astrophysical parameters derived for the merging binary systems. We compute corrections to the estimate of the luminosity distance due to velocity, volume, lensing and gravitational potential effects. Our results show that the amplitude of the corrections will be negligible for current instruments, mildly important for experiments like the planned DECIGO, and very important for future ones such as the Big Bang Observer.

On the Role of Discipline-Related Self-Concept in Deep and Surface Approaches to Learning among University Students

ERIC Educational Resources Information Center

Platow, Michael J.; Mavor, Kenneth I.; Grace, Diana M.

2013-01-01

The current research examined the role that students' discipline-related self-concepts may play in their deep and surface approaches to learning, their overall learning outcomes, and continued engagement in the discipline itself. Using a cross-lagged panel design of first-year university psychology students, a causal path was observed in which…

Circulation patterns in the deep Subtropical Northeast Atlantic with ARGO data

NASA Astrophysics Data System (ADS)

Calheiros, Tomas; Bashmachnikov, Igor

2014-05-01

In this work we study the dominant circulation patterns in the Subtropical Northeast Atlantic using ARGO data [25-45o N, 5-35o W]. The data were obtained from the Coriolis operational data center (ftp://ftp.ifremer.fr) for the years 1999-2013. During this period of time in the study there were available area 376 floats with 15062 float-months of total time. The floats were launched in the depths range between 300 and 2000 m, but most of the floats were concentrated at 1000 m (2000 float-months) and 1500 m (3400 float-months). In the upper 400-m layer there were also about 1000 float-months, but their number and distribution did not allow analysis of the mean currents over the study region. For each float position Lagrangian current velocity was computed as the difference between the position when the buoy started sinking to the reference depth and the consequent position of surfacing of the float, divided by the respective time interval. This allowed reducing the noise related with sea-surface drift of the buoys during the data-transmission periods. Mean Eulerian velocity and its error were computed in each of the 2ox2o square. Whenever in a 2ox2o square more than 150 observations of the Lagrangian velocity were available, the square was split into 4 smaller 1ox1o squares, in each of which the mean Eulerian velocities and their errors were estimated. Eulerian currents at 1000 m, as well as at 1500 m depth formed an overall anticyclonic circulation pattern in the study region. The modal velocity of all buoys at 1000 m level was 4 cm/s with an error of the mean of 1.8 cm/s. The modal velocity of all buoys at 1500m was 3 cm/s with an error of the mean of 1.4 cm/s. The southwestward flows near the Madeira Island and further westwards flow along the zonal band of 25-30o N at 1500 m depth well corresponded to the extension of the deep fraction of the Mediterranean Water salt tong.

Providing a Positive Learning Experience for International Students Studying at UK Universities: A Literature Review

ERIC Educational Resources Information Center

Lillyman, Sue; Bennett, Clare

2014-01-01

Much of the current literature relating to international students at university level tends to highlight their experiences from a deficit perspective and in some cases even problematises the experience for the student and university. Other studies tend to focus on recruitment and motivation rather than the lived experiences of the student, thereby…

Hydrodynamic Controls on Muddy Sedimentary Fabric Development on Low-Gradient Shelves: Atchafalaya Chenier Plain Subaqueous Delta

NASA Astrophysics Data System (ADS)

Denommee, K.; Bentley, S. J.; Harazim, D.; Macquaker, J.

2016-02-01

Short sediment cores and geophysical data collected on the Southwest Louisiana Chenier Plain inner shelf have been studied in order to examine the sedimentary products of current-wave-enhanced sediment gravity flows (CWESGFs), a type of sediment gravity flow where the driving energy required to transport sediment across low-gradient settings is augmented by the near-bed orbital velocity of surface gravity wave and near-bed currents. Sedimentary fabrics observed on the SWLA shelf document the following flow evolution: (1) the erosion of the underlying substrate in response to wave-generated shear stresses in the bottom boundary layer, followed by (2) the deposition of ripple a crossbeded unit during wave-mediated oscillatory motions in low-viscosity suspension; (3) the deposition of subtle intercalated laminae during laminar flow at higher suspended sediment concentrations; followed by the deposition of (4) normally graded sediments during the waning phases of the flow. Significantly, the sedimentary fabrics deposited by CWESGFs on SWLA shelf show diagnostic variations from CWESGF-generated sedimentary fabrics observed on the Eel and Amazon shelves. Differences between the observed sedimentary fabrics are hypothesized to result from variations in the relative contribution of near-bed currents, wave orbital velocities, and bed slope (gravity) to the driving energy of the CWESGF, and as such can be catalogued as diagnostic recognition criteria using a prismatic ternary diagram where current-, wave-, and gravity-dominated end members form the vertices of a triangle, and wave period forms the prism axis. In this framework forcing mechanisms can be represented quantitatively, based on wave period and the relative contribution of each of the CWESGF velocity terms. This framework can be used to explore relationships between hydrodynamics and CWESGF fabrics, providing geologists with a tool with which to better recognize the depositional products of CWESGFs in the rock record; allowing for more accurate paleoenvironmental interpretations of extensive muddy successions.

Planetary Protection Requirements for Mars Sample Return Missions: Recommendations from a 2009 NRC Report

NASA Astrophysics Data System (ADS)

Race, Margaret; Farmer, Jack

A 2009 report by the National Research Council (NRC) reviewed a previous study on Mars Sample Return (1997) and provided updated recommendations for future sample return mis-sions based on our current understanding about Mars and its biological potential, as well as advances in technology and analytical capabilities. The committee* made 12 specific recommen-dations that fall into three general categories—one related to current scientific understanding, ten based on changes in the technical and/or policy environment, and one aimed at public com-munication. Substantive changes from the 1997 report relate mainly to protocols and methods, technology and infrastructure, and general oversight. This presentation provides an overview of the 2009 report and its recommendations and analyzes how they may impact mission designs and plans. The full report, Assessment of Planetary Protection Requirements for Mars Sample Return Missions is available online at: http://www.nap.edu/catalog.php?recordi d = 12576 * Study participants: Jack D. Farmer, Arizona State University (chair) James F. Bell III, Cornell University Kathleen C. Benison, Central Michigan University William V. Boynton, University of Arizona Sherry L. Cady, Portland State University F. Grant Ferris, University of Toronto Duncan MacPherson, Jet Propulsion Laboratory Margaret S. Race, SETI Institute Mark H. Thiemens, University of California, San Diego Meenakshi Wadhwa, Arizona State University

Current sheet characteristics of a parallel-plate electromagnetic plasma accelerator operated in gas-prefilled mode

NASA Astrophysics Data System (ADS)

Liu, Shuai; Huang, Yizhi; Guo, Haishan; Lin, Tianyu; Huang, Dong; Yang, Lanjun

2018-05-01

The axial characteristics of a current sheet in a parallel-plate electromagnetic plasma accelerator operated in gas-prefilled mode are reported. The accelerator is powered by a fourteen stage pulse forming network. The capacitor and inductor in each stage are 1.5 μF and 300 nH, respectively, and yield a damped oscillation square wave of current with a pulse width of 20.6 μs. Magnetic probes and photodiodes are placed at various axial positions to measure the behavior of the current sheet. Both magnetic probe and photodiode signals reveal a secondary breakdown when the current reverses the direction. An increase in the discharge current amplitude and a decrease in pressure lead to a decrease in the current shedding factor. The current sheet velocity and thickness are nearly constant during the run-down phase under the first half-period of the current. The current sheet thicknesses are typically in the range of 25 mm to 40 mm. The current sheet velocities are in the range of 10 km/s to 45 km/s when the discharge current is between 10 kA and 55 kA and the gas prefill pressure is between 30 Pa and 800 Pa. The experimental velocities are about 75% to 90% of the theoretical velocities calculated with the current shedding factor. One reason for this could be that the idealized snowplow analysis model ignores the surface drag force.

HF Radar Sea-echo from Shallow Water.

PubMed

Lipa, Belinda; Nyden, Bruce; Barrick, Don; Kohut, Josh

2008-08-06

HF radar systems are widely and routinely used for the measurement of ocean surface currents and waves. Analysis methods presently in use are based on the assumption of infinite water depth, and may therefore be inadequate close to shore where the radar echo is strongest. In this paper, we treat the situation when the radar echo is returned from ocean waves that interact with the ocean floor. Simulations are described which demonstrate the effect of shallow water on radar sea-echo. These are used to investigate limits on the existing theory and to define water depths at which shallow-water effects become significant. The second-order spectral energy increases relative to the first-order as the water depth decreases, resulting in spectral saturation when the waveheight exceeds a limit defined by the radar transmit frequency. This effect is particularly marked for lower radar transmit frequencies. The saturation limit on waveheight is less for shallow water. Shallow water affects second-order spectra (which gives wave information) far more than first-order (which gives information on current velocities), the latter being significantly affected only for the lowest radar transmit frequencies for extremely shallow water. We describe analysis of radar echo from shallow water measured by a Rutgers University HF radar system to give ocean wave spectral estimates. Radar-derived wave height, period and direction are compared with simultaneous shallow-water in-situ measurements.

HF Radar Sea-echo from Shallow Water

PubMed Central

Lipa, Belinda; Nyden, Bruce; Barrick, Don; Kohut, Josh

2008-01-01

HF radar systems are widely and routinely used for the measurement of ocean surface currents and waves. Analysis methods presently in use are based on the assumption of infinite water depth, and may therefore be inadequate close to shore where the radar echo is strongest. In this paper, we treat the situation when the radar echo is returned from ocean waves that interact with the ocean floor. Simulations are described which demonstrate the effect of shallow water on radar sea-echo. These are used to investigate limits on the existing theory and to define water depths at which shallow-water effects become significant. The second-order spectral energy increases relative to the first-order as the water depth decreases, resulting in spectral saturation when the waveheight exceeds a limit defined by the radar transmit frequency. This effect is particularly marked for lower radar transmit frequencies. The saturation limit on waveheight is less for shallow water. Shallow water affects second-order spectra (which gives wave information) far more than first-order (which gives information on current velocities), the latter being significantly affected only for the lowest radar transmit frequencies for extremely shallow water. We describe analysis of radar echo from shallow water measured by a Rutgers University HF radar system to give ocean wave spectral estimates. Radar-derived wave height, period and direction are compared with simultaneous shallow-water in-situ measurements. PMID:27873776

Death education within health education: current status, future directions.

PubMed

Crase, D

1981-12-01

A national survey was conducted among 205 university level divisions/departments of health education to determine the current status of death education courses within the health education field. Forty-nine college and university health educators currently teaching the course returned usable instruments. Death education receives the same credit, utilizes similar grading systems and is generally managed much like other academic courses. Since the discipline is in its infancy and many teachers are relatively unprepared, respondents called for greater quality control and improved professional preparation. Several concerns accompanying the growth of death education were identified.

Bed particle entrainment and motion in turbulent open-channel flows: a high-resolution experimental study

NASA Astrophysics Data System (ADS)

Nikora, Vladimir; Cameron, Stuart; Amir, Mohammad; Stewart, Mark; Witz, Matthew

2015-04-01

In spite of significant efforts of geoscientists and engineers, the exact mechanics of sediment entrainment and transport by turbulent flows remains unclear and continues to be the focus of many research groups worldwide. The talk outlines current developments in this direction at the University of Aberdeen, where an extensive experimental programme has recently been completed. The experiments were conducted in the Aberdeen Open Channel Facility (AOCF, 20 m long, 1.18 m wide) over wide ranges of flow submergence (1.9-8.0), bulk Reynolds number (4400-83000), and channel aspect ratio (9-39). The flume bed was covered by hexagonally-packed glass beads 16 mm in diameter. For entrainment experiments, selected glass particles were replaced with lighter particles (nylon and delrin). Instantaneous velocity fields before, during, and after entrainment were measured with an advanced multi-mode Particle Image Velocimetry (PIV) system developed by S. Cameron. This system was also used for 3D particle tracking in the entrainment experiments. The main types of experiments included: (1) multi-mode turbulence measurements with fixed-bed conditions to assess the background flow structure (10 min to 120 min duration of velocity records); (2) simultaneous measurements of fluctuating differential pressure acting on 23 fixed particles with in-built pressure sensors, synchronously with PIV; (3) measurements of waiting times for particle entrainment, employing a specially designed system (SMC-1) for automatic placement of the particles on the bed and subsequent measurement of the time before entrainment; (4) long-term direct measurements of the instantaneous drag force acting on a single particle (attached to the bed) at different protrusions, synchronously with PIV; and (5) synchronous measurements of the flow field around a particle before, at, and during entrainment, supplemented with 3D particle tracking. The key results include: (1) the refined turbulence structure of a rough-bed open-channel flow assessed with multiple-order bulk velocity statistics, spectra, correlations, and structure functions; (2) identification and quantification of coherent motions, with particular focus on 'superstructures' (or 'very large scale motions' up to 40 flow depths in length); (3) assessment of secondary current effects on the flow structure; (4) statistical characteristics of fluctuating pressure acting on multiple bed particles, including spatial pressure correlations and their relations to the coherent structures; (5) estimates and statistical tests of waiting time distributions; (6) statistics of particle trajectories with particular focus on the initial stages of motion; and (7) identification of typical flow features accompanying particle entrainment. Among other findings, it has been shown, for the first time, that particle entrainment is likely to be associated with interactions between flow superstructures. The 'collisions' of superstructures, 'meandering' across the flow, generate regions of a particular velocity pattern leading to the particle entrainment. This study was supported by an EPSRC (UK) Grant EP/G056404/1, which was directly linked to DFG (Germany) Grants FR 1593/5-1/2, focus of which was on direct numerical simulations of mobile-bed flows. The authors are grateful to M. Uhlmann and C. Chan-Braun (Karlsruhe Institute of Technology) and J. Frohlich and B. Vowinckel (Dresden Technical University) for their useful suggestions and insightful discussions throughout the course of this project.

Inversion of multicomponent seismic data and rock-physics intepretation for evaluating lithology, fracture and fluid distribution in heterogeneous anisotropic reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ilya Tsvankin; Kenneth L. Larner

2004-11-17

Within the framework of this collaborative project with the Lawrence Livermore National Laboratory (LLNL) and Stanford University, the Colorado School of Mines (CSM) group developed and implemented a new efficient approach to the inversion and processing of multicomponent, multiazimuth seismic data in anisotropic media. To avoid serious difficulties in the processing of mode-converted (PS) waves, we devised a methodology for transforming recorded PP- and PS-wavefields into the corresponding SS-wave reflection data that can be processed by velocity-analysis algorithms designed for pure (unconverted) modes. It should be emphasized that this procedure does not require knowledge of the velocity model and canmore » be applied to data from arbitrarily anisotropic, heterogeneous media. The azimuthally varying reflection moveouts of the PP-waves and constructed SS-waves are then combined in anisotropic stacking-velocity tomography to estimate the velocity field in the depth domain. As illustrated by the case studies discussed in the report, migration of the multicomponent data with the obtained anisotropic velocity model yields a crisp image of the reservoir that is vastly superior to that produced by conventional methods. The scope of this research essentially amounts to building the foundation of 3D multicomponent, anisotropic seismology. We have also worked with the LLNL and Stanford groups on relating the anisotropic parameters obtained from seismic data to stress, lithology, and fluid distribution using a generalized theoretical treatment of fractured, poroelastic rocks.« less

Evaluation of ADCP apparent bed load velocity in a large sand-bed river: Moving versus stationary boat conditions

USGS Publications Warehouse

Jamieson, E.C.; Rennie, C.D.; Jacobson, R.B.; Townsend, R.D.

2011-01-01

Detailed mapping of bathymetry and apparent bed load velocity using a boat-mounted acoustic Doppler current profiler (ADCP) was carried out along a 388-m section of the lower Missouri River near Columbia, Missouri. Sampling transects (moving boat) were completed at 5- and 20-m spacing along the study section. Stationary (fixed-boat) measurements were made by maintaining constant boat position over a target point where the position of the boat did not deviate more than 3 m in any direction. For each transect and stationary measurement, apparent bed load velocity (vb) was estimated using ADCP bottom tracking data and high precision real-time kinematic (RTK) global positioning system (GPS). The principal objectives of this research are to (1) determine whether boat motion introduces a bias in apparent bed load velocity measurements; and (2) evaluate the reliability of ADCP bed velocity measurements for a range of sediment transport environments. Results indicate that both high transport (vb>0.6 m/s) and moving-boat conditions (for both high and low transport environments) increase the relative variability in estimates of mean bed velocity. Despite this, the spatially dense single-transect measurements were capable of producing detailed bed velocity maps that correspond closely with the expected pattern of sediment transport over large dunes. ?? 2011 American Society of Civil Engineers.

Expansion of a multicomponent current-carrying plasma jet into vacuum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krasov, V. I.; Paperny, V. L., E-mail: paperny@math.isu.runnet.ru

An expression for the ion−ion coupling in a multicomponent plasma jet is derived for an arbitrary ratio between the thermal and relative velocities of the components. The obtained expression is used to solve the problem on the expansion of a current-carrying plasma microjet emitted from the cathode surface into vacuum. Two types of plasmas with two ion components are analyzed: (i) plasma in which the ion components of equal masses are in the charge states Z{sub 1}= +1 and Z{sub 2}= +2 and (ii) plasma with ions in equal charge states but with the mass ratio m{sub 1}/m{sub 2} =more » 2. It is shown that, for such plasmas, the difference between the velocities of the plasma components remains substantial (about 10% of the average jet velocity in case (i) and 15% in case (ii)) at distances of several centimeters from the emission center, where it can be measured experimentally, provided that its initial value at the emitting cathode surface exceeds a certain threshold. This effect is investigated as a function of the mass ratio and charge states of the ion components.« less

Application of acoustic-Doppler current profiler and expendable bathythermograph measurements to the study of the velocity structure and transport of the Gulf Stream

NASA Technical Reports Server (NTRS)

Joyce, T. M.; Dunworth, J. A.; Schubert, D. M.; Stalcup, M. C.; Barbour, R. L.

1988-01-01

The degree to which Acoustic-Doppler Current Profiler (ADCP) and expendable bathythermograph (XBT) data can provide quantitative measurements of the velocity structure and transport of the Gulf Stream is addressed. An algorithm is used to generate salinity from temperature and depth using an historical Temperature/Salinity relation for the NW Atlantic. Results have been simulated using CTD data and comparing real and pseudo salinity files. Errors are typically less than 2 dynamic cm for the upper 800 m out of a total signal of 80 cm (across the Gulf Stream). When combined with ADCP data for a near-surface reference velocity, transport errors in isopycnal layers are less than about 1 Sv (10 to the 6th power cu m/s), as is the difference in total transport for the upper 800 m between real and pseudo data. The method is capable of measuring the real variability of the Gulf Stream, and when combined with altimeter data, can provide estimates of the geoid slope with oceanic errors of a few parts in 10 to the 8th power over horizontal scales of 500 km.

Laser characterization of the unsteady 2-D ion flow field in a Hall thruster with breathing mode oscillations

NASA Astrophysics Data System (ADS)

Lucca Fabris, Andrea; Young, Christopher; MacDonald-Tenenbaum, Natalia; Hargus, William, Jr.; Cappelli, Mark

2016-10-01

Hall thrusters are a mature form of electric propulsion for spacecraft. One commonly observed low frequency (10-50 kHz) discharge current oscillation in these E × B devices is the breathing mode, linked to a propagating ionization front traversing the channel. The complex time histories of ion production and acceleration in the discharge channel and near-field plume lead to interesting dynamics and interactions in the central plasma jet and downstream plume regions. A time-resolved laser-induced fluorescence (LIF) diagnostic non-intrusively measures 2-D ion velocity and relative ion density throughout the plume of a commercial BHT-600 Hall thruster manufactured by Busek Co. Low velocity classes of ions observed in addition to the main accelerated population are linked to propellant ionization outside of the device. Effects of breathing mode dynamics are shown to persist far downstream where modulations in ion velocity and LIF intensity are correlated with discharge current oscillations. This work is sponsored by the U.S. Air Force Office of Scientific Research with Dr. M. Birkan as program manager. C.Y. acknowledges support from the DOE NSSA Stewardship Science Graduate Fellowship under contract DE-FC52-08NA28752.

Testing Universal Relations of Neutron Stars with a Nonlinear Matter-Gravity Coupling Theory

NASA Astrophysics Data System (ADS)

Sham, Y.-H.; Lin, L.-M.; Leung, P. T.

2014-02-01

Due to our ignorance of the equation of state (EOS) beyond nuclear density, there is still no unique theoretical model for neutron stars (NSs). It is therefore surprising that universal EOS-independent relations connecting different physical quantities of NSs can exist. Lau et al. found that the frequency of the f-mode oscillation, the mass, and the moment of inertia are connected by universal relations. More recently, Yagi and Yunes discovered the I-Love-Q universal relations among the mass, the moment of inertia, the Love number, and the quadrupole moment. In this paper, we study these universal relations in the Eddington-inspired Born-Infeld (EiBI) gravity. This theory differs from general relativity (GR) significantly only at high densities due to the nonlinear coupling between matter and gravity. It thus provides us an ideal case to test how robust the universal relations of NSs are with respect to the change of the gravity theory. Due to the apparent EOS formulation of EiBI gravity developed recently by Delsate and Steinhoff, we are able to study the universal relations in EiBI gravity using the same techniques as those in GR. We find that the universal relations in EiBI gravity are essentially the same as those in GR. Our work shows that, within the currently viable coupling constant, there exists at least one modified gravity theory that is indistinguishable from GR in view of the unexpected universal relations.

Testing universal relations of neutron stars with a nonlinear matter-gravity coupling theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sham, Y.-H.; Lin, L.-M.; Leung, P. T., E-mail: yhsham@phy.cuhk.edu.hk, E-mail: lmlin@phy.cuhk.edu.hk, E-mail: ptleung@phy.cuhk.edu.hk

Due to our ignorance of the equation of state (EOS) beyond nuclear density, there is still no unique theoretical model for neutron stars (NSs). It is therefore surprising that universal EOS-independent relations connecting different physical quantities of NSs can exist. Lau et al. found that the frequency of the f-mode oscillation, the mass, and the moment of inertia are connected by universal relations. More recently, Yagi and Yunes discovered the I-Love-Q universal relations among the mass, the moment of inertia, the Love number, and the quadrupole moment. In this paper, we study these universal relations in the Eddington-inspired Born-Infeld (EiBI)more » gravity. This theory differs from general relativity (GR) significantly only at high densities due to the nonlinear coupling between matter and gravity. It thus provides us an ideal case to test how robust the universal relations of NSs are with respect to the change of the gravity theory. Due to the apparent EOS formulation of EiBI gravity developed recently by Delsate and Steinhoff, we are able to study the universal relations in EiBI gravity using the same techniques as those in GR. We find that the universal relations in EiBI gravity are essentially the same as those in GR. Our work shows that, within the currently viable coupling constant, there exists at least one modified gravity theory that is indistinguishable from GR in view of the unexpected universal relations.« less

Generation of large-scale magnetic fields by small-scale dynamo in shear flows

NASA Astrophysics Data System (ADS)

Squire, Jonathan; Bhattacharjee, Amitava

2015-11-01

A new mechanism for turbulent mean-field dynamo is proposed, in which the magnetic fluctuations resulting from a small-scale dynamo drive the generation of large-scale magnetic fields. This is in stark contrast to the common idea that small-scale magnetic fields should be harmful to large-scale dynamo action. These dynamos occur in the presence of large-scale velocity shear and do not require net helicity, resulting from off-diagonal components of the turbulent resistivity tensor as the magnetic analogue of the ``shear-current'' effect. The dynamo is studied using a variety of computational and analytic techniques, both when the magnetic fluctuations arise self-consistently through the small-scale dynamo and in lower Reynolds number regimes. Given the inevitable existence of non-helical small-scale magnetic fields in turbulent plasmas, as well as the generic nature of velocity shear, the suggested mechanism may help to explain generation of large-scale magnetic fields across a wide range of astrophysical objects. This work was supported by a Procter Fellowship at Princeton University, and the US Department of Energy Grant DE-AC02-09-CH11466.

Large exchange-dominated domain wall velocities in antiferromagnetically coupled nanowires

NASA Astrophysics Data System (ADS)

Kuteifan, Majd; Lubarda, M. V.; Fu, S.; Chang, R.; Escobar, M. A.; Mangin, S.; Fullerton, E. E.; Lomakin, V.

2016-04-01

Magnetic nanowires supporting field- and current-driven domain wall motion are envisioned for methods of information storage and processing. A major obstacle for their practical use is the domain-wall velocity, which is traditionally limited for low fields and currents due to the Walker breakdown occurring when the driving component reaches a critical threshold value. We show through numerical and analytical modeling that the Walker breakdown limit can be extended or completely eliminated in antiferromagnetically coupled magnetic nanowires. These coupled nanowires allow for large domain-wall velocities driven by field and/or current as compared to conventional nanowires.

A correlation to estimate the velocity of convective currents in boilover.

PubMed

Ferrero, Fabio; Kozanoglu, Bulent; Arnaldos, Josep

2007-05-08

The mathematical model proposed by Kozanoglu et al. [B. Kozanoglu, F. Ferrero, M. Muñoz, J. Arnaldos, J. Casal, Velocity of the convective currents in boilover, Chem. Eng. Sci. 61 (8) (2006) 2550-2556] for simulating heat transfer in hydrocarbon mixtures in the process that leads to boilover requires the initial value of the convective current's velocity through the fuel layer as an adjustable parameter. Here, a correlation for predicting this parameter based on the properties of the fuel (average ebullition temperature) and the initial thickness of the fuel layer is proposed.

Time-and-space resolved comparison of plasma expansion velocities in high-power diodes with velvet cathodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang Jie; Shu Ting; Fan Yuwei

2013-01-28

Time-and-space resolved comparison of the expansion velocities of plasmas in the planar diode with cathodes made of carbon velvet and polymer velvet has been performed. The diode was powered by a 200 kV, 110 ns pulse, and the peak current density was nearly 477 A/cm{sup 2}. A four-channel high speed framing camera (HSFC) was used to observe the formation and subsequent movement of the cathode plasmas. More accurate and valuable information about the two-dimensional (radial and axial) velocity components of the cathode plasmas was also acquired by utilizing the digital image processing methods. Additionally, the perveance model based on themore » Child-Langmuir law was used to calculate the expansion velocities of the diode plasmas from voltage and current profiles. Results from the two diagnostics were compared. Comparing the average values of the radial and axial velocity components indicated that the former was much larger than the latter during the initial period of the current. It was also found that the radial velocity of the carbon velvet cathode (190 cm/{mu}s) was much larger than that (90 cm/{mu}s) of the polymer velvet cathode. Moreover, the average values of both the radial and axial velocity components of the carbon velvet cathode were typically in the range of 2.5 {+-} 1.5 cm/{mu}s, which were smaller than that of the polymer velvet cathode during the current flattop. These results, together with the comparison of calculated values from the perveance model, indicated that the diode with carbon velvet cathode was more robust as compared with the polymer velvet cathode for the same electron current densities.« less

The New Guide to Effective Media Relations. The Best of "CASE Currents."

ERIC Educational Resources Information Center

Raley, Nancy, Ed.; Carter, Laura, Ed.

Developing an effective communications program is crucial for the survival of colleges, universities, and independent schools because they must be well understood and have broad public support. This guide to media relations compiles articles from "CASE Currents" into five sections: "The Basics of a News Service" (17 papers);…

The binary system containing the classical Cepheid T Mon

NASA Technical Reports Server (NTRS)

Evans, Nancy Remage; Lyons, Ronald W.

1994-01-01

Several new results are presented for the binary system containing the 27(sup d) classical Cepheid T Mon. New radial velocities for the Cepheid have been obtained, which confirm the decreasing orbital motion at the current epoch. The spectral type of the companion (B9.8 V) has been determined from an International Ultraviolet Explorer (IUE) low resolution spectrum. An IUE high resolution spectrum has been measured to search for the velocity of the companion. A velocity signal at +36 km/s on JD 2,446,105.21 has been tentatively identified as the velocity of the companion, but confirmation of this velocity would be very valuable. Results based on this tentative identification of the velocity are that the companion does not have a high projected rotation velocity, that the companion is unlikely to be a short period binary, and that the gamma velocity of the system is between 20 and 36 km/s. The luminosity and temperature of both the Cepheid and the companion are well determined from the satellite and ground-based observations and the Cepheid PLC relation. However, the companion is above the ZAMS in the H-R diagram, which is inconsistent with the large luminosity difference between the two stars. High rotation for the companion (viewed pole-on) is a possible explanation. The lower limit to the mass function (from the lower limits to the orbital period and amplitude) requires a very high eccentricity for the system for reasonable estimates for the masses of the two stars.

Estimating Velocities of Glaciers Using Sentinel-1 SAR Imagery

NASA Astrophysics Data System (ADS)

Gens, R.; Arnoult, K., Jr.; Friedl, P.; Vijay, S.; Braun, M.; Meyer, F. J.; Gracheva, V.; Hogenson, K.

2017-12-01

In an international collaborative effort, software has been developed to estimate the velocities of glaciers by using Sentinel-1 Synthetic Aperture Radar (SAR) imagery. The technique, initially designed by the University of Erlangen-Nuremberg (FAU), has been previously used to quantify spatial and temporal variabilities in the velocities of surging glaciers in the Pakistan Karakoram. The software estimates surface velocities by first co-registering image pairs to sub-pixel precision and then by estimating local offsets based on cross-correlation. The Alaska Satellite Facility (ASF) at the University of Alaska Fairbanks (UAF) has modified the software to make it more robust and also capable of migration into the Amazon Cloud. Additionally, ASF has implemented a prototype that offers the glacier tracking processing flow as a subscription service as part of its Hybrid Pluggable Processing Pipeline (HyP3). Since the software is co-located with ASF's cloud-based Sentinel-1 archive, processing of large data volumes is now more efficient and cost effective. Velocity maps are estimated for Single Look Complex (SLC) SAR image pairs and a digital elevation model (DEM) of the local topography. A time series of these velocity maps then allows the long-term monitoring of these glaciers. Due to the all-weather capabilities and the dense coverage of Sentinel-1 data, the results are complementary to optically generated ones. Together with the products from the Global Land Ice Velocity Extraction project (GoLIVE) derived from Landsat 8 data, glacier speeds can be monitored more comprehensively. Examples from Sentinel-1 SAR-derived results are presented along with optical results for the same glaciers.

Tracking moving radar targets with parallel, velocity-tuned filters

DOEpatents

Bickel, Douglas L.; Harmony, David W.; Bielek, Timothy P.; Hollowell, Jeff A.; Murray, Margaret S.; Martinez, Ana

2013-04-30

Radar data associated with radar illumination of a movable target is processed to monitor motion of the target. A plurality of filter operations are performed in parallel on the radar data so that each filter operation produces target image information. The filter operations are defined to have respectively corresponding velocity ranges that differ from one another. The target image information produced by one of the filter operations represents the target more accurately than the target image information produced by the remainder of the filter operations when a current velocity of the target is within the velocity range associated with the one filter operation. In response to the current velocity of the target being within the velocity range associated with the one filter operation, motion of the target is tracked based on the target image information produced by the one filter operation.

Comparison of current meters used for stream gaging

USGS Publications Warehouse

Fulford, Janice M.; Thibodeaux, Kirk G.; Kaehrle, William R.

1994-01-01

The U.S. Geological Survey (USGS) is field and laboratory testing the performance of several current meters used throughout the world for stream gaging. Meters tested include horizontal-axis current meters from Germany, the United Kingdom, and the People's Republic of China, and vertical-axis and electromagnetic current meters from the United States. Summarized are laboratory test results for meter repeatability, linearity, and response to oblique flow angles and preliminary field testing results. All current meters tested were found to under- and over-register velocities; errors usually increased as the velocity and angle of the flow increased. Repeatability and linearity of all meters tested were good. In the field tests, horizontal-axis meters, except for the two meters from the People's Republic of China, registered higher velocity than did the vertical-axis meters.

Three-Dimensional P-wave Velocity Structure Beneath Long Valley Caldera, California, Using Local-Regional Double-Difference Tomography

NASA Astrophysics Data System (ADS)

Menendez, H. M.; Thurber, C. H.

2011-12-01

Eastern California's Long Valley Caldera (LVC) and the Mono-Inyo Crater volcanic systems have been active for the past ~3.6 million years. Long Valley is known to produce very large silicic eruptions, the last of which resulted in the formation of a 17 km by 32 km wide, east-west trending caldera. Relatively recent unrest began between 1978-1980 with five ML ≥ 5.7 non-double-couple (NDC) earthquakes and associated aftershock swarms. Similar shallow seismic swarms have continued south of the resurgent dome and beneath Mammoth Mountain, surrounding sites of increased CO2 gas emissions. Nearly two decades of increased volcanic activity led to the 1997 installation of a temporary three-component array of 69 seismometers. This network, deployed by the Durham University, the USGS, and Duke University, recorded over 4,000 high-frequency events from May to September. A local tomographic inversion of 283 events surrounding Mammoth Mountain yielded a velocity structure with low Vp and Vp/Vs anomalies at 2-3 km bsl beneath the resurgent dome and Casa Diablo hot springs. These anomalies were interpreted to be CO2 reservoirs (Foulger et al., 2003). Several teleseismic and regional tomography studies have also imaged low Vp anomalies beneath the caldera at ~5-15 km depth, interpreted to be the underlying magma reservoir (Dawson et al., 1990; Weiland et al., 1995; Thurber et al., 2009). This study aims to improve the resolution of the LVC regional velocity model by performing tomographic inversions using the local events from 1997 in conjunction with regional events recorded by the Northern California Seismic Network (NCSN) between 1980 and 2010 and available refraction data. Initial tomographic inversions reveal a low velocity zone at ~2 to 6 km depth beneath the caldera. This structure may simply represent the caldera fill. Further iterations and the incorporation of teleseismic data may better resolve the overall shape and size of the underlying magma reservoir.

Going with the flow: Tidal influence on the occurrence of the harbour porpoise (Phocoena phocoena) in the Marsdiep area, The Netherlands

NASA Astrophysics Data System (ADS)

IJsseldijk, Lonneke L.; Camphuysen, Kees C. J.; Nauw, Janine J.; Aarts, Geert

2015-09-01

One of the most important factors explaining the distribution and behaviour of coastal marine mammals are tides. Tidal forces drive a large number of primary and secondary processes, such as changes in water depth, salinity, temperature, current velocity and direction. Unravelling which tidal process is the most influential for a certain species is often challenging, due to a lack of observations of all tide related covariates, strong correlation between them, and the elusive nature of most marine organisms which often hampers their detection. In the Marsdiep area, a tidal inlet between the North Sea and the Dutch Wadden Sea, the presence of harbour porpoises (Phocoena phocoena) was studied as a function of tide related covariates. Observations were carried out in early spring from a ferry crossing the inlet on a half hourly basis. Environmental and sightings data were collected by one observer, while an on-board Acoustic Doppler Current Profiler (ADCP) and temperature sensor continuously recorded current velocity profiles and temperature, respectively. Sea surface temperature and salinity were measured at a nearby jetty. Sightings (n = 134) were linked to tidal elevation, geographical position, local depth-averaged current velocity, water temperature (with and without trend correction) and salinity. Variation in sighting rate was best described by salinity, with highest sighting rate at high levels of salinity (> 30 g kg- 1), indicating that porpoises enter the area in bodies of (more saline) North Sea water. Second best variable was time of day, with the highest sighting rate early morning, and decreasing during the day. However, surveys in the morning happened to coincide more often with high water and hence, the apparent time of day effect could be due to collinearity. Most porpoises were present in the northern part of the Marsdiep, particularly during high tide. Tide dependent sighting rates confirmed that porpoises reside in the North Sea, and enter the western Wadden Sea during the flood and leave during ebb. This tidal influx is most likely related to prey availability, which corresponds to other recent studies in this area showing higher fish abundance during high tide. Documenting information on tide related patterns could be used in practice, when e.g. planning anthropogenic activities or assessing critical habitats for this species.

Large-scale structure after COBE: Peculiar velocities and correlations of cold dark matter halos

NASA Technical Reports Server (NTRS)

Zurek, Wojciech H.; Quinn, Peter J.; Salmon, John K.; Warren, Michael S.

1994-01-01

Large N-body simulations on parallel supercomputers allow one to simultaneously investigate large-scale structure and the formation of galactic halos with unprecedented resolution. Our study shows that the masses as well as the spatial distribution of halos on scales of tens of megaparsecs in a cold dark matter (CDM) universe with the spectrum normalized to the anisotropies detected by Cosmic Background Explorer (COBE) is compatible with the observations. We also show that the average value of the relative pairwise velocity dispersion sigma(sub v) - used as a principal argument against COBE-normalized CDM models-is significantly lower for halos than for individual particles. When the observational methods of extracting sigma(sub v) are applied to the redshift catalogs obtained from the numerical experiments, estimates differ significantly between different observation-sized samples and overlap observational estimates obtained following the same procedure.

An analytical model of iceberg drift

NASA Astrophysics Data System (ADS)

Eisenman, I.; Wagner, T. J. W.; Dell, R.

2017-12-01

Icebergs transport freshwater from glaciers and ice shelves, releasing the freshwater into the upper ocean thousands of kilometers from the source. This influences ocean circulation through its effect on seawater density. A standard empirical rule-of-thumb for estimating iceberg trajectories is that they drift at the ocean surface current velocity plus 2% of the atmospheric surface wind velocity. This relationship has been observed in empirical studies for decades, but it has never previously been physically derived or justified. In this presentation, we consider the momentum balance for an individual iceberg, which includes nonlinear drag terms. Applying a series of approximations, we derive an analytical solution for the iceberg velocity as a function of time. In order to validate the model, we force it with surface velocity and temperature data from an observational state estimate and compare the results with iceberg observations in both hemispheres. We show that the analytical solution reduces to the empirical 2% relationship in the asymptotic limit of small icebergs (or strong winds), which approximately applies for typical Arctic icebergs. We find that the 2% value arises due to a term involving the drag coefficients for water and air and the densities of the iceberg, ocean, and air. In the opposite limit of large icebergs (or weak winds), which approximately applies for typical Antarctic icebergs with horizontal length scales greater than about 12 km, we find that the 2% relationship is not applicable and that icebergs instead move with the ocean current, unaffected by the wind. The two asymptotic regimes can be understood by considering how iceberg size influences the relative importance of the wind and ocean current drag terms compared with the Coriolis and pressure gradient force terms in the iceberg momentum balance.

Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemke, R. W., E-mail: rwlemke@sandia.gov; Dolan, D. H.; Dalton, D. G.

We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as itmore » implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ∼1000 GPa is achieved in all cases. These experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.« less

Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemke, R. W.; Dolan, D. H.; Dalton, D. G.

We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as itmore » implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ~1000 GPa is achieved in all cases. Lastly, these experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.« less

Probing off-Hugoniot states in Ta, Cu, and Al to 1000 GPa compression with magnetically driven liner implosions

DOE PAGES

Lemke, R. W.; Dolan, D. H.; Dalton, D. G.; ...

2016-01-07

We report on a new technique for obtaining off-Hugoniot pressure vs. density data for solid metals compressed to extreme pressure by a magnetically driven liner implosion on the Z-machine (Z) at Sandia National Laboratories. In our experiments, the liner comprises inner and outer metal tubes. The inner tube is composed of a sample material (e.g., Ta and Cu) whose compressed state is to be inferred. The outer tube is composed of Al and serves as the current carrying cathode. Another aluminum liner at much larger radius serves as the anode. A shaped current pulse quasi-isentropically compresses the sample as itmore » implodes. The iterative method used to infer pressure vs. density requires two velocity measurements. Photonic Doppler velocimetry probes measure the implosion velocity of the free (inner) surface of the sample material and the explosion velocity of the anode free (outer) surface. These two velocities are used in conjunction with magnetohydrodynamic simulation and mathematical optimization to obtain the current driving the liner implosion, and to infer pressure and density in the sample through maximum compression. This new equation of state calibration technique is illustrated using a simulated experiment with a Cu sample. Monte Carlo uncertainty quantification of synthetic data establishes convergence criteria for experiments. Results are presented from experiments with Al/Ta, Al/Cu, and Al liners. Symmetric liner implosion with quasi-isentropic compression to peak pressure ~1000 GPa is achieved in all cases. Lastly, these experiments exhibit unexpectedly softer behavior above 200 GPa, which we conjecture is related to differences in the actual and modeled properties of aluminum.« less

Galaxy formation and physical bias

NASA Technical Reports Server (NTRS)

Cen, Renyue; Ostriker, Jeremiah P.

1992-01-01

We have supplemented our code, which computes the evolution of the physical state of a representative piece of the universe to include, not only the dynamics of dark matter (with a standard PM code), and the hydrodynamics of the gaseous component (including detailed collisional and radiative processes), but also galaxy formation on a heuristic but plausible basis. If, within a cell the gas is Jeans' unstable, collapsing, and cooling rapidly, it is transformed to galaxy subunits, which are then followed with a collisionless code. After grouping them into galaxies, we estimate the relative distributions of galaxies and dark matter and the relative velocities of galaxies and dark matter. In a large scale CDM run of 80/h Mpc size with 8 x 10 exp 6 cells and dark matter particles, we find that physical bias b is on the 8/h Mpc scale is about 1.6 and increases towards smaller scales, and that velocity bias is about 0.8 on the same scale. The comparable HDM simulation is highly biased with b = 2.7 on the 8/h Mpc scale. Implications of these results are discussed in the light of the COBE observations which provide an accurate normalization for the initial power spectrum. CDM can be ruled out on the basis of too large a predicted small scale velocity dispersion at greater than 95 percent confidence level.

The influence of negative current collector size on a liquid metal positive electrode

NASA Astrophysics Data System (ADS)

Mohammad, Ibrahim; Ashour, Rakan; Kelley, Douglas

2017-11-01

Fluid mixing in the positive electrode of a liquid metal battery (LMB) governs some performance-related factors such as the rate of charge and discharge of the battery. The negative current collector (NCC) of a LMB is always smaller than the positive current collector, implying that current is convergent at the NCC. Also, different NCC sizes introduce different thermal, electromagnetic, and flow boundary conditions. In this talk, I will show how our lab studies the influence of NCC diameter on the flow in a liquid metal positive electrode driven by electrical current. I will present measurements of the flow velocity taken via Ultrasonic Doppler Velocimetry (UDV) over a range of different currents, at different NCC diameters.

The Hubble Constant.

PubMed

Jackson, Neal

2015-01-01

I review the current state of determinations of the Hubble constant, which gives the length scale of the Universe by relating the expansion velocity of objects to their distance. There are two broad categories of measurements. The first uses individual astrophysical objects which have some property that allows their intrinsic luminosity or size to be determined, or allows the determination of their distance by geometric means. The second category comprises the use of all-sky cosmic microwave background, or correlations between large samples of galaxies, to determine information about the geometry of the Universe and hence the Hubble constant, typically in a combination with other cosmological parameters. Many, but not all, object-based measurements give H 0 values of around 72-74 km s -1 Mpc -1 , with typical errors of 2-3 km s -1 Mpc -1 . This is in mild discrepancy with CMB-based measurements, in particular those from the Planck satellite, which give values of 67-68 km s -1 Mpc -1 and typical errors of 1-2 km s -1 Mpc -1 . The size of the remaining systematics indicate that accuracy rather than precision is the remaining problem in a good determination of the Hubble constant. Whether a discrepancy exists, and whether new physics is needed to resolve it, depends on details of the systematics of the object-based methods, and also on the assumptions about other cosmological parameters and which datasets are combined in the case of the all-sky methods.