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1

Wake fields and wake field acceleration  

SciTech Connect

In this lecture we introduce the concepts of wake fields and wake potentials, examine some basic properties of these functions, show how they can be calculated, and look briefly at a few important applications. One such application is wake field acceleration. The wake field accelerator is capable of producing the high gradients required for future very high energy e/sup +/e/sup -/ linear colliders. The principles of wake field acceleration, and a brief description of experiments in progress in this area, are presented in the concluding section. 40 references, 27 figures.

Bane, K.L.F.; Wilson, P.B.; Weiland, T.

1984-12-01

2

Wake field acceleration experiments  

SciTech Connect

Where and how will wake field acceleration devices find use for other than, possibly, accelerators for high energy physics. I don't know that this can be responsibly answered at this time. What I can do is describe some recent results from an ongoing experimental program at Argonne which support the idea that wake field techniques and devices are potentially important for future accelerators. Perhaps this will spawn expanded interest and even new ideas for the use of this new technology. The Argonne program, and in particular the Advanced Accelerator Test Facility (AATF), has been reported in several fairly recent papers and reports. But because this is a substantially new audience for the subject, I will include a brief review of the program and the facility before describing experiments. 10 refs., 7 figs.

Simpson, J.D.

1988-01-01

3

Wake fields and impedance  

Microsoft Academic Search

Knowledge of the electromagnetic interaction between a beam and the surrounding vacuum chamber is necessary in order to optimize the accelerator performance in terms of stored current. Many instability phenomena may occur in the machine because of the fields produced by the beam and acting back on itself as in a feedback device. Basically, these fields produce an extra voltage

L Palumbo; Vittorio G Vaccaro; M Zobov

1994-01-01

4

Wake Fields and Impedance  

Microsoft Academic Search

Knowledge of the electromagnetic interaction between a beam and the surrounding vacuum chamber is necessary in order to optimize the accelerator performance in terms of stored current. Many instability phenomena may occur in the machine because of the fields produced by the beam and acting back on itself as in a feedback device. Basically, these fields produce an extra voltage

L. Palumbo; V. G. Vaccaro; M. Zobov

2003-01-01

5

Transverse fields in dielectric wake field accelerators  

SciTech Connect

Theory is presented for excitation of hybrid electric/magnetic ({ital HEM}) wake-field modes by passage of an electron drive bunch in a dielectric-lined cylindrical waveguide. The drive bunch is moving parallel to the waveguide axis, but is displaced by a radial increment r{sub 0}. Knowledge of the amplitudes of all {ital HEM} modes allows calculation of the transverse forces on a bunch or bunches that follow the displaced drive bunch. Approximate formulas for the transverse forces on a trailing bunch are given, valid in the limit of small r{sub 0}. These transverse forces can lead to beam instability, if cumulative transverse motion is significant on the time-scale of passage of the bunch through the accelerator module. Constructive interference can be present amongst TM{sub 0m} monopole modes that produce highly-peaked spatiotemporally-localized axial wake-fields, with peak fields at the locations of trailing bunches in a multi-bunch train. In this case, the spectrum of dipole (and higher order) {ital HEM} modes may not enjoy the same degree of constructive interference, and may not have the same axial periodicity as the monopole modes. Further analytical and computational study is needed to determine the limitations that transverse wake fields may impose on a multi-bunch dielectric wake-field accelerator. {copyright} {ital 1999 American Institute of Physics.}

Hirshfield, J.L.; Park, S.Y.; Zhang, T. [Omega-P, Inc. 202008 Yale Station, New Haven, Connecticut 06520-2008 (United States); Hirshfield, J.L.; Park, S.Y. [Department of Physics, Yale University, POB 8120, New Haven, Connecticut 06520-8120 (United States)

1999-07-01

6

Transition Wake-Fields in Resistive Tube  

Microsoft Academic Search

The transition wake fields excited by relativistic point charge in cylindrical resistive round pipe are studied. The problem has been solved for the infinite pipe with abrupt change of the walls conductivity from perfect boundary condition to resistive. The analytical presentation of the longitudinal monopole wake field is given.

M. Ivanyan; V. Tsakanov; A. Tsakanian

2005-01-01

7

Collimator wake fields in the SLC final focus  

SciTech Connect

The SLC final focus system accommodates 29 fixed or adjustable collimators for machine protection and background reduction. By amplifying pulse to pulse orbit variations and by generating emittance growth, collimator wake fields may degrade the beam quality at the interaction point (IP). In the SLC final focus, collimator half apertures are larger than the bunch length, so that the standard collimator wake formula of Bane and Morton does not apply. Numerical wake field calculations for SLC parameters agree quite well with the high frequency impedance of a step out transition. Due to the nature of a final focus system, the wake field kicks from all collimators add coherently, and the overall impact on luminosity can be significant. This paper suggests that collimator wake fields in the final focus provide a possible explanation for the 30% discrepancy between expected and measured luminosity in the 1994/95 SLC run.

Zimmermann, F.; Bane, K.L.F.; Ng, C.K.

1996-06-01

8

Experimental study of steady concentration fields in turbulent wakes  

NASA Astrophysics Data System (ADS)

The pollutant transportation process in turbulent wakes is studied experimentally using planar laser-induced fluorescence (PLIF). The concentration fields in the very near wake region behind typical bluff bodies are measured for steady flow. The characteristics of the mean and instantaneous concentration fields behind circular and sinusoidal islands and peninsulas are investigated. The results indicate that the pollutant distribution is closely related with the unsteady vortex shedding in the flow field. Compared with that of the circular island, more pollutants enter into the wake generated by the sinusoidal-shaped island. The time needed for pollutants to accumulate in or drain out of the wake region after the peninsula before reaching a relatively constant value is longer than that for the islands, regardless of the island or peninsula shape. The results will facilitate pollutant control behind sea islands and other natural or man-made structures in water. Also the results provide some fundamental data for checking numerical models.

Jiang, C. B.; Li, Y. L.; Li, Y. S.; Liang, D. F.; Yu, C. Z.

9

Ion acceleration in laser-excited plasma wake fields  

SciTech Connect

The dynamics of the plasma ions in the wake fields of short, ultraintense laser pulses in underdense plasmas are investigated analytically and numerically. Owing to the large ion-to-electron mass ratio, the motion of plasma ions in such wake fields has often been assumed to be neglectable. It is shown that when the laser intensity exceeds 10{sup 20} W/cm{sup 2}, the ion motion can no longer be ignored. In this case, ion momentum peaks appear behind the laser pulse, which correspond with the ion density peaks. The laser-excited wake field appears to be effective for ion acceleration, in particular to ions with high-charge numbers. The dependence of ion acceleration on the laser intensity, pulse width, and background plasma density is discussed.

Yan, F.; Sheng, Z.M.; Dong, Q.L.; Zhang, J.; Yu, W. [Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China)

2006-06-15

10

Waking.  

PubMed

An indubitable aspect of laboring in the realm of hospice care is the "everydayness" of human loss or the stark encounter of death in the human experience. This can pose as opportunity to adopt each day in a particular manner. As such, the focus of my reflection is on transposing certain dynamics of a (funeral) wake to broader professional and personal socioexistential processes. PMID:22811212

Moon, Paul J

2012-07-18

11

Directional Landau damping of wake-field potentials  

SciTech Connect

The wake-field potentials produced by charged particles moving in a plasma are investigated in the presence of finite Landau-damping effects in the wave dispersion relation. In the frame of reference moving with the particle, the phase velocities of the spectrum of waves excited by the moving charge depend on the angle of propagation of the wave vector giving rise to a directional wave-particle resonance condition. As a consequence, the wake structure is seen to decay both along and transverse to the direction of motion of the charged particle.

Bose, Anirban; Janaki, M.S. [Saha Institute of Nuclear Physics 1/AF Bidhannagar, Kolkata 700 064 (India)

2005-10-01

12

Physical mechanisms in the plasma wake-field accelerator  

NASA Astrophysics Data System (ADS)

The acceleration of trapped electrons in the relativistic plasma waves (wake fields) produced by specially shaped charged-particle beams is described by physical, analytic, and two-dimensional simulation models. The effects of competing instabilities, imperfect bunch shapes, transverse dynamics, and dephasing of trapped particles are considered.

Katsouleas, T.

1986-03-01

13

Experimental studies of plasma wake-field acceleration and focusing  

SciTech Connect

More than four years after the initial proposal of the Plasma Wake-field Accelerator (PWFA), it continues to be the object of much investigation, due to the promise of the ultra-high accelerating gradients that can exist in relativistic plasma waves driven in the wake of charged particle beams. These large amplitude plasma wake-fields are of interest in the laboratory, both for the wealth of basic nonlinear plasma wave phenomena which can be studied, as well as for the applications of acceleration of focusing of electrons and positrons in future linear colliders. Plasma wake-field waves are also of importance in nature, due to their possible role in direct cosmic ray acceleration. The purpose of the present work is to review the recent experimental advances made in PWFA research at Argonne National Laboratory, in which many interesting beam and plasma phenomena have been observed. Emphasis is given to discussion of the nonlinear aspects of the PWFA beam-plasma interaction. 29 refs., 13 figs.

Rosenzweig, J.B.; Cole, B.; Ho, C.; Gai, W.; Konecny, R.; Mtingwa, S.; Norem, J.; Rosing, M.; Schoessow, P.; Simpson, J.

1989-07-18

14

Longitudinal- and transverse-wake-field effects in dielectric structures  

NASA Astrophysics Data System (ADS)

A dielectric-loaded circular waveguide structure is a potential high-gradient linear wake-field accelerator. A complete solution is given for the longitudinal electric and magnetic fields excited by a ? function and a Gaussian charge distribution moving parallel to the guide axis. The fields are then given in the limit of particle velocity equal to the speed of light. Example calculations are given for a structure with inner radius of 2 mm, outer radius of 5 mm, dielectric constant of 3, and total charge of 100 nC. Peak wake fields in excess of 200 MV/m are found. Azimuthal modes 0 and 1 are investigated for the particular interest of acceleration and deflection problems.

Rosing, M.; Gai, W.

1990-09-01

15

Longitudinal wake field corrections in circular machines  

SciTech Connect

In computations of longitudinal particle motions in accelerators and storage rings, the fields produced by the interactions of the beam with the cavity in which it circulates are usually calculated by multiplying Fourier components of the beam current by the appropriate impedances. This procedure neglects the slow variation with time of the Fourier coefficients and of the beam revolution frequency. When there are cavity elements with decay times that are comparable with or larger than the time during which changes in the beam parameters occur, these changes can not be neglected. Corrections for this effect have been worked out in terms of the response functions of elements in the ring. The result is expressed as a correction to the impedance which depends on the way in which the beam parameters are changing. A method is presented for correcting a numerical simulation by keeping track of the steady state and transient terms in the response of a cavity.

Symon, Keith R. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States); Dept. of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706 (United States)

1997-02-01

16

Longitudinal wake field corrections in circular machines  

SciTech Connect

In computations of longitudinal particle motions in accelerators and storage rings, the fields produced by the interactions of the beam with the cavity in which it circulates are usually calculated by multiplying Fourier components of the beam current by the appropriate impedances. This procedure neglects the slow variation with time of the Fourier coefficients and of the beam revolution frequency. When there are cavity elements with decay times that are comparable with or larger than the time during which changes in the beam parameters occur, these changes can not be neglected. Corrections for this effect have been worked out in terms of the response functions of elements in the ring. The result is expressed as a correction to the impedance which depends on the way in which the beam parameters are changing. A method is presented for correcting a numerical simulation by keeping track of the steady state and transient terms in the response of a cavity. {copyright} {ital 1997 American Institute of Physics.}

Symon, K.R. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439 (United States)]|[Dept. of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706 (United States)

1997-02-01

17

Nonlinear plasma and beam physics in plasma wake-fields  

SciTech Connect

In experimental studies of the Plasma Wake-field Accelerator performed to date at the Argonne Advanced Accelerator Test Facility, significant nonlinearities in both plasma and beam behavior have been observed. The plasma waves driven in the wake of the intense driving beam in these experiments exhibit three-dimensional nonlinear behavior which has as yet no quantitative theoretical explanation. This nonlinearity is due in part to the self-pinching of the driving beam in the plasma, as the denser self-focused beam can excite larger amplitude plasma waves. The self-pinching is a process with interesting nonlinear aspects: the initial evolution of the beam envelope and the subsequent approach to Bennett equilibrium through phase mixing. 35 refs., 10 figs.

Rosenzweig, J.B.

1990-02-12

18

High-Efficiency Absorber for Damping the Transverse Wake Fields  

SciTech Connect

Transverse wake fields generated by intense beams may propagate long distances in the vacuum chamber and dissipate power in different shielded elements such as bellows, vacuum valves or vacuum pumps. Induced heating in these elements may be high enough to deteriorate vacuum conditions. We have developed a broadband water-cooled bellows-absorber to capture and damp these harmful transverse fields without impacting the longitudinal beam impedance. Experimental results at the PEP-II SLAC B-factory demonstrate high efficiency of this device. This absorber may be useful in other machines like synchrotron light sources or International Linear Collider.

Novokhatski, A.; Seeman, J.; Weathersby, S.; /SLAC

2007-02-28

19

Acceleration of electrons by the wake field of proton bunches  

SciTech Connect

This paper discusses a novel idea to accelerate low-intensity bunches of electrons (or positrons) by the wake field of intense proton bunches travelling along the axis of a cylindrical rf structure. Accelerating gradients in excess of 100 MeV/m and large ''transformer ratios'', which allow for acceleration of electrons to energies in the TeV range, are calculated. A possible application of the method is an electron-positron linear collider with luminosity of 10/sup 33/ cm/sup -2/ s/sup -1/. The relatively low cost and power consumption of the method is emphasized.

Ruggiero, A.G.

1986-01-01

20

Influence of fabrication errors on wake function suppression in NC X-band accelerating structures for linear colliders  

NASA Astrophysics Data System (ADS)

Wake function suppression is effected by ensuring that the mode frequencies of an X-band normal conducting (NC) accelerating structure of multiple cells are detuned and moderately damped by waveguide manifolds attached to the outer wall of the accelerator. We report on the dilution in the wake function suppression that occurs due to errors resulting from the fabrication process. After diffusion bonding 206 cells a non-uniform expansion in the cell geometry forces a substantial shift in the frequencies of select cells. We remap all circuit parameters to these shifted cell frequencies to predict the wake function. Experiments performed on the SLC at the SLAC National Accelerator Laboratory indicate that the wake function is well predicted by the circuit model.

Jones, R. M.; Adolphsen, C. E.; Miller, R. H.; Wang, J. W.; Higo, T.

2009-03-01

21

Field-aligned Currents in Io's Plasma Wake  

NASA Astrophysics Data System (ADS)

Since the discovery of Io-controlled decametric radio emissions, the interaction between Io and Jovian magnetosphere has been studied intensively. Two types of interaction have been proposed so far. One is electric circuit model, in which the induced currents flow between Io and the Jovian ionosphere along the magnetic flux tube threading Io. The other is Alfvén wing model. A wing forms in the perturbed magnetic field lines behind Io, the Alfvénic currents develop in the wing rather than along the magnetic flux tubes. More recently, auroral emission associated with Io's footprint and its trailing emission were observed. Such auroral arc may extend longitudinally westward for more than 100 degrees. This trail of aurora is brightest near Io and dims with increasing downstream distance. There is no clear theoretical understanding of the physics that generates this downstream aurora. However it is generally believed that Io's plasma wake is associated with this phenomenon and field-aligned currents lead to downstream emissions. Along with the above two types of the interaction between Io and its surrounding medium, there are also two theoretical frameworks in which these downstream emissions can be interpreted. The first one is corotational lag. When an Io-perturbed (mass loading and/or Io's conductivity) magnetic flux tube moves slowly relative to Jovian magnetosphere, an electric field would be induced at the equatorial plane of the flux tube, which in turn causes a current perpendicular to the field lines that is connected by field-aligned currents. The Lorentz force due to the perpendicular current would play the role of bring the lagged plasma up to corotation. The second is Alfvén wave, in which the Io-perturbed Alfvén wave is reflected between the Jovian ionosphere and the torus edge, driving particles into loss cone. Our present study attempts to use a MHD method to solve the above problem. MHD simulations of Io-Jupiter interaction has been carried out by several groups and yielded some suggestive results, but these studies concentrated primarily on the vicinity of Io and did not treat the Jovian ionospheric effect realistically. To investigate the mechanism for emissions in the trailing tail, a model extending longitudinally more than 100 degrees and latitudinally from the southern Jovian ionosphere to the northern ionosphere is needed. In particular, such a model should reflect both the non-uniform magnetic field and the non-uniform plasma distributions together with realistic boundary conditions. To tackle this problem with available computer resources, we provide instead an equivalent approach "theory of thin filament motion". Our model is indeed a one-dimensional MHD simulation that satisfies all the above requirements and has the advantage of using much less computer resources than the earlier MHD models, which in turn allows us to try various physical conditions within limited computing time. We assume Io's plasma wake can be regarded as a tail of thin magnetic flux tubes perturbed by Io successively. In this assumption, a flux tube is considered as thin if the pressure variations across the flux tube are negligible compared to the total external pressure (gas plus magnetic pressure) representing the effects of the enveloping magnetized plasma (Jovian magnetosphere). Furthermore we assume that in Io's reference frame the variations of the physical quantities along the downstream distance do not change with time. After converting to the corotating frame, the study of Io's plasma wake can be simplified to investigate the evolution of a magnetic flux tube in Io's wake with appropriate initial conditions. Our simulations suggest that the mechanism for producing wake aurora could not be explained by either Alfvén wave or electric circuit alone, rather, the underlying physics possesses the characteristics typical for both Alfvén wave and corotational lag models. An upstream-coming flux tube must be in contact with Io for approximately 500 seconds, until a tilt angle of about 4 degrees has been develo

Chen, Chuxin

2008-09-01

22

Transverse wake field simulations for the ILC acceleration structure  

SciTech Connect

Details of wake potential simulation in the acceleration structure of ILC, including the RF cavities and input/HOM couplers are presented. Transverse wake potential dependence is described versus the bunch length. Beam emittance dilution caused by main and HOM couplers is estimated, followed by a discussion of possible structural modifications allowing a reduction of transverse wake potential.

Solyak, N.; Lunin, A.; Yakovlev, V.; /Fermilab

2008-06-01

23

Laser wake field acceleration: the highly non-linear broken-wave regime  

Microsoft Academic Search

.   We use three-dimensional particle-in-cell simulations to study laser wake field acceleration (LWFA) at highly relativistic\\u000a laser intensities. We observe ultra-short electron bunches emerging from laser wake fields driven above the wave-breaking\\u000a threshold by few-cycle laser pulses shorter than the plasma wavelength. We find a new regime in which the laser wake takes\\u000a the shape of a solitary plasma cavity.

A. Pukhov; J. Meyer-ter-Vehn

2002-01-01

24

Relativistic wake-field generation by an intense laser pulse in a plasma  

NASA Astrophysics Data System (ADS)

Generation of nonlinear plasma oscillations by an intense laser pulse is considered. It is shown that longitudinal plasma waves with relativistic amplitudes and phase velocities close to the speed of light c can be excited in the wake of a strong single laser pulse in a cold plasma. An analytical and numerical study of the relativistic wake-field generation by laser pulses with realistic shapes is carried out. A nonlinear scheme of the laser wake-field accelerator is suggested.

Berezhiani, V. I.; Murusidze, I. G.

1990-08-01

25

A proposal for the surface roughness wake field measurement at the TESLA Test Facility  

Microsoft Academic Search

The wake fields due to the rough surface of the vacuum chamber have a major influence on the beam dynamics in linear colliders and free electron lasers. These wake fields mainly consists of the fundamental tube mode, modified by the rough boundary condition, which decreases its phase velocity to the speed of light. Its wavelength is proportional to the square

A. Novokhatsky; M. Timm; T. Weiland; H. Schlarb

1999-01-01

26

Wake fields effects due to surface roughness in a circular pipe  

NASA Astrophysics Data System (ADS)

The problem of the wake field generated by a relativistic particle travelling in a long beam pipe with rough surface has been studied by means of a standard theory based on the hybrid modes excited in a periodically corrugated waveguide with circular cross-section. Slow waves synchronous with the particle can be excited in the structure, producing wake fields whose frequency and amplitude depend on the depth of the corrugation. An analytical expression of the wake field is given for very small corrugations.

Angelici, M.; Frezza, F.; Mostacci, A.; Palumbo, L.

2002-08-01

27

Wake fields effects due to surface roughness in a circular pipe  

NASA Astrophysics Data System (ADS)

The problem of the wake field generated by a relativistic particle travelling in a long beam pipe with rough surface has been revisited by means of a standard theory based on the hybrid modes excited in a periodically corrugated waveguide with circular cross section. Slow waves synchronous with the particle can be excited in the structure, producing wake fields whose frequency and amplitude depend on the depth of the corrugation. .

Angelici, M.; Frezza, F.; Mostacci, A.; Palumbo, L.

2001-08-01

28

MHD oseenlet and double wake of a rising sphere under a strong vertical magnetic field  

NASA Astrophysics Data System (ADS)

A flow field of an electrically conducting fluid around a rising sphere is discussed. An asymptotic solution at a large Hartmann number is proposed. A function with a singularity called MHD oseenlet is derived. It gives a double wake unique to MHD flows. Its flow rate across the horizontal plane is a finite value in contrast to the divergent flow rate for stokeslet and zero flow rate for source doublet. We obtain the flow field around a sphere in a series of MHD oseenlet and its derivatives. Fluid in the cone-shaped near wake moves with the rising sphere. The vertical height ± 0.1a H? of the near wake is much larger than its radius a. In far wake, the flow field is reduced to the MHD oseenlet. Tables 2, Figs 5, Refs 8.

Ueno, K.; Yasuda, H.

2003-12-01

29

Wind-flow field measurements in the wake of the Barstow Solar-Thermal Power Plant  

SciTech Connect

A brief flow field measurement study was conducted at the Barstow 10 MW Solar Thermal Power PLant to determine the effect of the plant on the local wind flow field and to identify resulting possible environmental implications. Wind speed measurements were taken at a reference free stream location and at a number of locations in the wake downstream of the plant. Measurements were taken to about 400 m (1312 ft) downstream with wind shear profiles taken to a height of 50 m (164 ft) AGL at each point in the wake. With the heliostats up, the data showed a wake deficit (wind speed reduction) of about 15% from reference extending over the downstream extent of the measurements. This wake is believed to be detectable 1000 to 2000 m (3280 to 6560 ft) downstream of the plant. With the heliostats stowed, no wake deficit was observed. With this modest wind speed reduction, any accumulation of wind blown particulates will occur within the heliostat field or just downstream within 60 m (197 ft) in the near wake. A brief analysis indicated that if a 100 MW array of the same heliostats is constructed, the wake will extend over a height and a downstream extent, roughly similar to the 10 MW plant but increased in size, directly proportional to the linear scale (diameter) of the plant. The magnitude of the wake deficit for a plant of infinite diameter should not exceed twice the deficit observed for the 10 MW plant. Thus, the wind related environmental effects should be essentially of the same magnitude for a 100 MW plant as for the existing 10 MW plant.

Radkey, R.L.; Zambrano, T.G.

1982-11-01

30

Wake fields of a bunch on a general trajectory due to coherent synchrotron radiation  

Microsoft Academic Search

If short bunches travel along trajectories with small bending radii a simple geometrical condition permits strong longitudinal and radial wake fields to act: electromagnetic fields emitted by a particle can `overtake' on a shelter straight trajectory and interact with particles ahead. The bunch then starts to radiate coherently. The electromagnetic fields along the bunch have strong gradients and in general

Martin Dohlus; A. Kabel; T. Limberg

1997-01-01

31

WAKE FIELDS OF A BUNCH ON A GENERAL TRAJECTORY DUE TO COHERENT SYNCHROTRON RADIATION  

Microsoft Academic Search

If short bunches travel along trajectories with small bend- ing radii a simple geometrical condition permits strong lon- gitudinal and radial wake fields to act: electromagnetic fields emitted by a particle can 'overtake' on a shorter straight trajectory and interact with particles ahead. The bunch then starts to radiate coherently. The electromag- netic fields along the bunch have strong gradients

M. Dohlus; A. Kabel; T. Limberg

1998-01-01

32

Longitudinal wake field for an electron beam accelerated through an ultrahigh field gradient  

NASA Astrophysics Data System (ADS)

Electron accelerators with higher and higher longitudinal field gradients are desirable, as they allow for the production of high-energy beams by means of compact and cheap setups. Laser-plasma acceleration technique appears to constitute the more promising breakthrough in this direction, delivering unprecedent field gradients up to TV/m. In this article we give a quantitative description of the impact of longitudinal wake fields on the electron beam. Our paper is based on the solution of Maxwell's equations for the longitudinal field. Our conclusions are valid when the acceleration distance is much smaller than the overtaking length, that is the length that electrons travel as a light signal from the tail of the bunch overtakes the head of the bunch. This condition is well verified for laser-plasma devices. We calculate a closed expression for the impedance and the wake function that may be evaluated numerically. It is shown that the rate of energy loss in the bunch due to radiative interaction is equal to the energy emitted through coherent radiation in the far zone. Furthermore, an expression is found for the asymptotic limit of a large distance of the electron beam from the accelerator compared with the overtaking length. Such expression allows us to calculate analytical solutions for a Gaussian transverse and longitudinal bunch shape. We describe an application of our analytical asymptote by studying the feasibility of a table-top free-electron laser based on laser-plasma driver. Numerical estimations presented in this paper indicate that the effects of the time-dependent energy change induced by the longitudinal wake pose a serious threat to the operation of this device.

Geloni, Gianluca; Saldin, Evgeni; Schneidmiller, Evgeni; Yurkov, Mikhail

2007-07-01

33

Proton entry into the near-lunar plasma wake for magnetic field aligned flow  

NASA Astrophysics Data System (ADS)

We report the first observation of protons in the near-lunar (100-200 km from the surface) and deeper (near anti-subsolar point) plasma wake when the interplanetary magnetic field (IMF) and solar wind velocity (vsw) are parallel (aligned flow; angle between IMF and vsw?10°). More than 98% of the observations during aligned flow condition showed the presence of protons in the wake. These observations are obtained by the Solar Wind Monitor sensor of the Sub-keV Atom Reflecting Analyser experiment on Chandrayaan-1. The observation cannot be explained by the conventional fluid models for aligned flow. Back tracing of the observed protons suggests that their source is the solar wind. The larger gyroradii of the wake protons compared to that of solar wind suggest that they were part of the tail of the solar wind velocity distribution function. Such protons could enter the wake due to their large gyroradii even when the flow is aligned to IMF. However, the wake boundary electric field may also play a role in the entry of the protons into the wake.

Dhanya, M. B.; Bhardwaj, A.; Futaana, Y.; Fatemi, S.; HolmströM, M.; Barabash, S.; Wieser, M.; Wurz, P.; Alok, A.; Thampi, R. S.

2013-06-01

34

Wake-field and fast head-tail instability caused by an electron cloud  

NASA Astrophysics Data System (ADS)

In positron and proton storage rings, electrons produced by photoemission, ionization, and secondary emission accumulate in the vacuum chamber during multibunch operation with close spacing. A positron or proton bunch passing through this ``electron cloud'' experiences a force similar to a short-range wake field. This effective wake field can cause a transverse-mode-coupling instability, if the electron-cloud density exceeds a threshold value. In this report, we compute the electron-cloud induced wake in a region without external magnetic field both analytically and via computer simulation, for parameters representing the low-energy positron ring of KEKB and the LHC proton beam in the CERN SPS. We study the linearity and time dependence of the wake function and its variation with the size of the electron cloud. Using a broadband resonator model for the electron-cloud wake field, we then evaluate theoretical expressions for the transverse-mode-coupling instability based on the linearized Vlasov equation, and for the instability threshold of fast transverse blow up including its dependence on chromaticity.

Ohmi, K.; Zimmermann, F.; Perevedentsev, E.

2002-01-01

35

Pioneer Venus Observations of Plasma and Field Structure in the Near Wake of Venus  

Microsoft Academic Search

Ionospheric plasma density depletions or 'holes' are observed by the Pioneer Venus orbiter in association with radial magnetic fields in the near wake of Venus. This report presents examples of the collected observations of these unexpected features of the Venus nightside ionosphere obtained by the Langmuir probe, magnetometer, ion mass spectrometer, retarding potential analyzer, plasma analyz- er, and electric field

J. G. Luhmann; C. T. Russell; L. H. Brace; H. A. Taylor; W. C. Knudsen; F. L. Scarf; D. S. Colburn; A. Barnes

1982-01-01

36

Traversing field of view and AR-PIV for mid-field wake vortex investigation in a towing tank  

NASA Astrophysics Data System (ADS)

Wake vortex flow experiments are performed in a water tank where a 1:48 scaled model of a large transport aircraft A340-300 is towed at the speed of 3 and 5 ms-1 with values of the angle of attack ?={2°, 4°, 8°}. Particle image velocimetry (PIV) measurements are performed in a plane perpendicular to the towing direction describing the streamwise component of the wake vorticity. The instantaneous field of view (I-FOV) is traversed vertically with an underwater moving-camera device tracking the vortex core during the downward motion. An adaptive resolution (AR) image-processing technique is introduced that enhances the PIV interrogation in terms of spatial resolution and accuracy. The main objectives of the investigation are to demonstrate the applicability of PIV diagnostics in wake vortex research with towing-tank facilities. The specific implementation of the traversing field-of-view (T-FOV) technique and the AR image processing are driven by the need to characterize the vortex wake global properties as well as the vortex decay phenomenon in the mid- and far-field. Relevant aerodynamic information is obtained in the mid-field where the time evolution of the vortex structure (core radius and tangential velocity) and of the overall vortex wake (vortex trajectory, descent velocity, circulation) are discussed.

Scarano, F.; van Wijk, C.; Veldhuis, L. L. M.

2002-08-01

37

Wake field calculation for the TTF-FEL bunch compressor section  

Microsoft Academic Search

The TTF free electron laser needs very short bunches to produce self-amplified spontaneous emission. This short bunch length is produced in a magnetic bunch compressor where the trajectories of particles with different energy have different path length in a way that the bunch is longitudinally compressed. As a parasitic effect the wake fields produced by the passing bunch will have

K. Rothemund; U. Van Rienen

1999-01-01

38

Simulation of Laser Wake Field Acceleration using a 2.5D PIC Code  

NASA Astrophysics Data System (ADS)

A 2.5D PIC simulation code is developed to study the LWFA( Laser WakeField Acceleration ). The electron self-injection and the generation of mono-energetic electron beam in LWFA is briefly discussed through the simulation. And the experiment of this year at SILEX-I laser facility is also introduced.

An, W. M.; Hua, J. F.; Huang, W. H.; Tang, Ch. X.; Lin, Y. Z.

2006-11-01

39

Exposure to pulsed high-frequency electromagnetic field during waking affects human sleep EEG  

Microsoft Academic Search

The aim of the study was to investigate whether the electro- magnetic field (EMF) emitted by digital radiotelephone handsets affects brain physiology. Healthy, young male subjects were exposed for 30 min to EMF (900 MHz; spatial peak specific absorption rate 1 W\\/kg) during the waking period preceding sleep. Compared with the control condition with sham exposure, spectral power of the

Reto Huber; Thomas Graf; Kimberly A. Cote; Lutz Wittmann; Eva Gallmann; Daniel Matter; Jürgen Schuderer; Niels Kuster; Alexander A. Borbély; Peter Achermann

2000-01-01

40

Intrabeam Scattering and Wake Field Effects in Low Emittance Electron Rings  

NASA Astrophysics Data System (ADS)

We present a model to study in a self-consistent way the interplay between intrabeam scattering and wake-field forces in low-emittance high-intensity electron storage rings. The regime of interest is that of the damping rings for the next generation of linear colliders.

Venturini, M.

2002-08-01

41

Intrabeam Scattering and Wake Field Effects in Low Emittance Electron Rings  

SciTech Connect

We present a model to study in a self-consistent way the interplay between intrabeam scattering and wake-fields forces in low emittance high-intensity electron storage rings. The regime of interest is that of the damping rings for the next generation of linear colliders.

Venturini, Marco

2002-08-08

42

Intrabeam scattering and wake field effects in low emittance electron rings  

Microsoft Academic Search

We present a model to study in a self-consistent way the interplay between intrabeam scattering and wake-field forces in low-emittance high-intensity electron storage rings. The regime of interest is that of the damping rings for the next generation of linear colliders

M. Venturini

2001-01-01

43

Investigation on wind turbine wakes: wind tunnel tests and field experiments with LIDARs  

NASA Astrophysics Data System (ADS)

An investigation on the interaction between atmospheric boundary layer flow and wind turbines is carried out with wind tunnel and LIDAR measurements. The former were carried out using hot-wire anemometry and multi-hole pressure probes in the wake of a three-bladed miniature wind turbine. The wind turbine wake is characterized by a strong velocity defect in the proximity of the rotor, and its recovery is found to depend on the characteristics of the incoming atmospheric boundary layer (mean velocity and turbulence intensity profiles). Field experiments were performed using three wind LIDARs. Bi-dimensional scans are performed in order to analyse the wake wind field with different atmospheric boundary layer conditions. Furthermore, simultaneous measurements with two or three LIDARs allow the reconstruction of multi-component velocity fields. Both LIDAR and wind tunnel measurements highlight an increased turbulence level at the wake boundary for heights comparable to the top-tip of the blades; this flow feature can produce dangerous fatigue loads on following wind turbines.

Valerio Iungo, Giacomo; Wu, Ting; Cöeffé, Juliette; Porté-Agel, Fernando

2011-11-01

44

Field investigation of a wake structure downwind of a VAWT in a windfarm array  

Microsoft Academic Search

The effects of upwind turbine wakes on the performance of a FloWind 17-m VAWT were investigated through a series of field experiments conducted at the FloWind windfarm on Cameron Ridge, Tehachapi, California. The field experiment was conducted within a VAWT array consisting of more than nine VAWTs with separations 3D crosswised by 8D downwind (where D is the turbine diameter)

H. T. Liu; J. W. Buck; A. C. Germain; M. E. Hinchee; T. S. Solt; G. M. LeRoy; R. A. Srnsky

1987-01-01

45

The effect of space-charge and wake fields in the Fermilab Booster  

SciTech Connect

We calculate the impedance and the wake functions for laminated structures with parallel-planes and circular geometries. We critically examine the approximations used in the literature for the coupling impedance in laminated chambers and find that most of them are not justified because the wall surface impedance is large. A comparison between the flat and the circular geometry impedance is presented. We use the wake fields calculated for the Fermilab Booster laminated magnets in realistic beam simulations using the Synergia code. We find good agreement between our calculation of the coherent tune shift at injection energy and the experimental measurements. In this paper we calculate the impedance and the wake functions for laminated structures with parallel-planes and circular geometries. First the coupling impedance is derived as a function of the wall surface impedance. Then the surface impedance is calculated by solving Maxwell's equations inside the lamination and the crack regions. We find that the commonly used resistive-wall approximations, good for metallic pipes with small surface impedance, are not valid in the laminated structures where the surface impedance is large. Realistic Synergia simulations of the Booster machine with wake fields predict transverse coherent tune shifts in good agreement with the experiment.

Macridin, Alexandru; Spentzouris, Panagiotis; Amundson, James; /Fermilab; Spentzouris, Linda; McCarron, Daniel; /IIT, Chicago

2011-03-01

46

Complex electric fields near the lunar terminator: The near-surface wake and accelerated dust  

NASA Astrophysics Data System (ADS)

The lunar near-surface electric field in the vicinity of the terminator is very complex, with a surface polarity change from dayside-positive to nightside-negative potentials and the formation of intensely negative potentials due to the low plasma density and increased temperatures in the trailing lunar wake region. Presented is a preliminary map of the terminator near-surface E-field magnitude and a discussion of dust dynamics in this E-field structure, with intense vertical fields tending to give rise to vertically directed dust trajectories (aligned with the surface normal). Application of this process of wake-generated surface E-fields and dust to the more complicated topography at the lunar landing site of Apollo 17 is then used to explain the detection of fast moving (~500 m/sec) but nightside-directed dust in the region. We suggest that local solar wind orographic effects occurring at lunar sunrise/sunset can create a plasma void on the anti-sunward side of obstructing features and associated wake-generated surface E-fields can then be the source of the nightside-directed grains.

Farrell, W. M.; Stubbs, T. J.; Vondrak, R. R.; Delory, G. T.; Halekas, J. S.

2007-07-01

47

Suppressing drift chamber diffusion without magnetic field  

Microsoft Academic Search

The spatial resolution in drift chamber detectors for ionizing radiation is limited by diffusion of the primary electrons. A strong magnetic field along the drift direction is often applied (Fancher et al., Nucl. Instr. and Meth. A 161 (1979) 383) because it suppresses the transverse diffusion, improving the resolution but at considerable increase in cost and complexity. Here we show

C. J. Martoff; D. P. Snowden-Ifft; T. Ohnuki; N. Spooner; M. Lehner

2000-01-01

48

On the Production of Flat Electron Bunches for Laser Wake Field Acceleration  

SciTech Connect

We suggest a novel method for injection of electrons into the acceleration phase of particle accelerators, producing low emittance beams appropriate even for the demanding high energy Linear Collider specifications. In this paper we work out the injection into the acceleration phase of the wake field in a plasma behind a high intensity laser pulse, taking advantage of the laser polarization and focusing. With the aid of catastrophe theory we categorize the injection dynamics. The scheme uses the structurally stable regime of transverse wake wave breaking, when electron trajectory self-intersection leads to the formation of a flat electron bunch. As shown in three-dimensional particle-in-cell simulations of the interaction of a laser pulse in a line-focus with an underdense plasma, the electrons, injected via the transverse wake wave breaking and accelerated by the wake wave, perform betatron oscillations with different amplitudes and frequencies along the two transverse coordinates. The polarization and focusing geometry lead to a way to produce relativistic electron bunches with asymmetric emittance (flat beam). An approach for generating flat laser accelerated ion beams is briefly discussed.

Kando, M.; Fukuda, Y.; Kotaki, H.; Koga, J.; Bulanov, S.V.; Tajima, T.; /JAERI, Kyoto; Chao, A.; Pitthan, R.; /SLAC; Schuler, K.-P.; /DESY; Zhidkov, A.G.; /CRIEPI, Tokyo /Moscow, Inst. General Phys.; Nemoto, K.; /CRIEPI, Tokyo

2006-06-27

49

Effect of forcing on the vorticity field in a confined wake  

NASA Astrophysics Data System (ADS)

Several recent studies have found that when a low Reynolds number, plane wake is forced with sufficient amplitude, the normalized mixing product, measured as the amount of mixed fluid per unit width of the wake, can be increased to levels larger than those seen in high Reynolds number mixing layers. However, no studies examining the velocity and vorticity fields of this flow have been conducted. The present study examines the velocity and vorticity field of a low Reynolds number plane wake within a confining channel in order to better understand the vortex-vortex and vortex-wall interactions in order to shed light on the mechanisms which lead to increases in the amount of mixed fluid within the wake. Molecular Tagging Velocimetry (MTV) is used to measure the velocity field in both the streamwise (u, v velocities in x, y plane) and cross-stream (v, w velocities in y, z plane) measurement planes. The spanwise and streamwise vorticity components are then computed from their respective velocity fields. Measurements in the streamwise plane have found that a distinct spatial periodicity exists in the urms field that is not found in either the unforced case or in unconfined forced flows. A model was developed which relates this spatial periodicity to the phase difference between the forcing input and the rolling up of the vorticity shed from the splitter plate. From these data, it was also determined that the phase at which vorticity is shed is dependent upon the forcing amplitude. The forced wake flow is dominated by the shedding of concentrated, spanwise vortex core rollers. As these cores develop downstream, the levels of peak vorticity within the core decrease. A very small amount of -6w/6z is sufficient to generate a very large decrease in peak vorticity levels. This same quantity has also been found to be a good predictor of the spatial location where mixing enhancement will occur in the forced wake. Mixing enhancement is accomplished by the generation of regions of streamwise vorticity from the reorientation of the primary spanwise vortex cores. A model was developed which describes how these cores develop. The multiple regions of streamwise vorticity are the result of the passage and reorientation of multiple spanwise rollers. These reoriented "legs" of streamwise vorticity interact with the regions of streamwise vorticity resulting from the passage of previous spanwise vortex rollers to generate the additional surface area necessary for mixing enhancement. (Abstract shortened by UMI.)

Cohn, Richard Keith

1999-11-01

50

PERTURBATIONS OF THE INTERPLANETARY MAGNETIC FIELD BY THE LUNAR WAKE  

Microsoft Academic Search

through the leeward riow, an. alternating pattern of magnitude increases and decreases is observed in the penumbra, while generally only an increase is observed in the umbra. Using a theoretical model of plasma flow due to Whang, a first-order solution of the perturbed interplanetary magnetic field is compared with observations. It is concluded that the perturbations can be partially explained

N. F. Ness; K. W. Behannon; H. E. Taylor; Y. C. Whang

1968-01-01

51

Teaching Biology Field Courses in the Wake of Environmental Disasters.  

ERIC Educational Resources Information Center

|A biology field course organized to study the effects of the June 1979 Mexican oil spill on the marine biology of the shores of south Texas and Mexico is described, demonstrating how to effectively couple a biology classroom course with a natural or human caused environmental disaster. (Author/DC)|

Baca, Bart J.

1982-01-01

52

Silicon oxynitride: A field emission suppression coating  

NASA Astrophysics Data System (ADS)

We have studied coatings deposited using our inductively-coupled RF plasma ion implantation and desposition system to suppress field emission from large, 3-D electrode structures used in high voltage applications, like those used by Thomas Jefferson National Accelerator Facility in their DC-field photoelectron gun. Currently time and labor-intensive hand-polishing procedures are used to minimize field emission from these structures. Previous work had shown that the field emission from polished stainless steel (27 muA of field-emitted current at 15 MV/m) could be drastically reduced with simultaneous deposition of sputtered silicon dioxide during nitrogen implantation (167 pA of field-emitted current at 30 MV/m). We have determined that this unique implantation and deposition procedure produces high-purity silicon oxynitride films that can suppress field emission from stainless steel regardless of their initial surface polish. However, when this implantation procedure was applied to large, 3-D substrates, arcs occurred, damaging the coating and causing unreliable and unrepeatable field emission suppression. We have developed a novel reactive sputtering procedure to deposit high-purity silicon oxynitride coatings without nitrogen ion implantation. We can control the stoichometry and deposition rate of these coatings by adjusting the nitrogen pressure and incident RF-power. Using profilometry, Auger electron spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Rutherford backscattering spectrometry, elastic recoil detection analysis, and current-voltage measurements, we have determined that the elemental composition, chemical bonding, density, and electrical properties of the reactively-sputtered silicon oxynitride coatings are similar to those produced by nitrogen implantation during silicon dioxide deposition. Furthermore, high voltage tests determined that both coatings similarly suppress field emission from 6" diameter, polished stainless steel electrodes. We determined a quantitative, predictive electron emission model to describe electron emission from our silicon oxynitride coatings. Although Fowler-Nordheim theory adequately describes field emission from metals, it does not apply to our dielectric coatings. Several models exist in the literature to describe electron emission from dielectrics. Based upon our high voltage field emission results, electron emission from our silicon oxynitride coatings is described by the Schottky and Poole-Frenkel emission models. These models predict that increasing the band gap, dielectric constant, and electron affinity of our silicon oxynitride coatings would further reduce field emission.

Theodore, Nimel D.

53

Three-dimensional island wakes in the field, laboratory experiments and numerical models  

Microsoft Academic Search

Results of field, laboratory and numerical studies are used to describe the three-dimensional circulation in a barotropic island wake in shallow waters. Bottom friction generates a closed circulation characterized by a strong upwelling (typically 10–20 m h?1) in the bulk of the eddy and an even larger downwelling velocity in a narrow zone along the edges of the eddy. This

Eric Wolanski; Takashi Asaeda; Akihiro Tanaka; Eric Deleersnijder

1996-01-01

54

Quantum ring solitons and nonlocal effects in plasma wake field excitations  

SciTech Connect

A theoretical investigation of the quantum transverse beam motion for a cold relativistic charged particle beam travelling in a cold, collisionless, strongly magnetized plasma is carried out. This is done by taking into account both the individual quantum nature of the beam particles (single-particle uncertainty relations and spin) and the self consistent interaction generated by the plasma wake field excitation. By adopting a fluid model of a strongly magnetized plasma, the analysis is carried out in the overdense regime (dilute beams) and in the long beam limit. It is shown that the quantum description of the collective transverse beam dynamics is provided by a pair of coupled nonlinear governing equations. It comprises a Poisson-like equation for the plasma wake potential (driven by the beam density) and a 2D spinorial Schroedinger equation for the wave function, whose squared modulus is proportional to the beam density, that is obtained in the Hartree's mean field approximation, after disregarding the exchange interactions. The analysis of this pair of equations, which in general exhibits a strong nonlocal character, is carried out analytically as well as numerically in both the linear and the nonlinear regimes, showing the existence of the quantum beam vortices in the form of Laguerre-Gauss modes and ring envelope solitons, respectively. In particular, when the relation between the plasma wake field response and the beam probability density is strictly local, the pair of the governing equations is reduced to the 2D Gross-Pitaevskii equation that allows one to establish the conditions for the self focusing and collapse. These conditions include the quantum nature of the beam particles. Finally, when the relation between the plasma wake field response and the beam probability density is moderately nonlocal, the above pair of equations permits to follow the spatio-temporal evolution of a quantum ring envelope soliton. Such a structure exhibits small or violent breathing, but it remains very stable for long time.

Fedele, R.; Tanjia, F. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', and INFN, Napoli (Italy); De Nicola, S. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II', and INFN, Napoli (Italy); Istituto Nazionale di Ottica - C. N. R., Pozzuoli (Italy); Jovanovic, D. [Institute of Physics, University of Belgrade, Belgrade (Serbia); Shukla, P. K. [Center of Advanced Studies in Physical Sciences, Ruhr-Universitaet Bochum, Bochum (Germany)

2012-10-15

55

Mean and Fluctuating Velocity Fields in the Wake of a Freely-Vibrating Cylinder  

NASA Astrophysics Data System (ADS)

In the present work, we study the wake velocity field of an elastically mounted rigid cylinder oscillating transverse to a fluid flow, using DPIV measurements. It is shown that there are large qualitative changes in these velocity fields, depending on the mode of cylinder oscillation. In particular, the characteristic ``recirculation bubble'', usually seen in the mean velocity field behind the nonoscillating cylinder, is found to be present in the case of the `2S' wake formation mode, yet is completely absent for the `2P' mode. For the `2P' mode, we find instead the appearance of a pair of counter-rotating vortices of opposite sign to what is expected, causing a downstream-oriented jet-type flow close to the cylinder, which in turn results in a `double-wake' type velocity profile. Measurements of both the total Reynolds stresses, and the periodic stresses evaluated using phase-averaged velocity data, show that more than 90% of the total stresses are due to the repeatable large-scale coherent structures in the wake, when the body is vibrating. Periodic stresses make up only about 60% of the total stresses, in the case of the stationary body. Interestingly, for the fixed body, the periodic stresses remain relatively unchanged between our experiments (Re=3900) and those of Cantwell & Coles, at Re=140 000, although the total stresses are significantly increased at the larger Re. Our experimental evaluation of Reynolds stress is stimulated by the need for such data in developing turbulence modelling of these flows, as well as to enable detailed comparison with direct numerical simulations.

Govardhan, R.; Williamson, C. H. K.

2001-04-01

56

Electromagnetic field and short-range wake function in a beam pipe of elliptical cross section  

NASA Astrophysics Data System (ADS)

Within the ultrarelativistic limit, analytical expressions are found for the high-frequency resistive-wall coupling impedance of an elliptical cross-section vacuum chamber. Subsequently, the corresponding wake functions are derived by performing inverse Fourier transformations numerically. The electromagnetic fields have been developed working out two systems of solutions, namely for the vacuum and for the resistive wall. The constants involved in these systems have been determined by matching boundary conditions at the interface vacuum wall. Several study cases have been considered concerning the aspect ratio of the elliptical cross section and the transverse position of the leading charge in order to exemplify the behavior of the longitudinal and transverse wake functions.

Lutman, A.; Vescovo, R.; Craievich, P.

2008-07-01

57

Rats hippocampal field potentials feature extraction of wake and sleep stages in Euclidean space.  

PubMed

This paper presents a new methodology of feature extraction of sleep and wake stages of a freely behaving rat based on Continuous Wavelet Transform (CWT). The automatic separation of those stages is very useful for experiments related to learning and memory consolidation since recent scientific evidence indicates that sleep is strongly involved with offline reprocessing of acquired information during waking. Our approach transforms hippocampal Local Field Potentials (LFP) in data vectors that describe the energy distribution pattern of the signal on scaled Morlet wavelets projections. Results indicate that the mathematical analysis used in this work can sensibly describe brain signal patterns that correlate to states of behaviour and that our method can be used for a wider range of applications in neuroscience research. PMID:21097284

Lopes Dos Santos, Vitor; da Costa Souza, Bryan; Belchior, Hindiael Aeraf; Duarte Neto, Adriao Doria

2010-01-01

58

Investigation of Beam Instability Under the Effects of Long-Range Transverse Wake Fields in the Berkeley Future Light Source  

SciTech Connect

An ultra-relativistic charged particle bunch moving through a resonator cavity leaves behind a wake field that will affect subsequent bunches (if the bunch is not ultra-relativistic, the wake field will not be exclusively behind it). If the initial bunch enters the cavity off-axis, it will produce a transverse wake field that can then kick later bunches off the axis. Thus, even bunches that were initially traveling on axis could be displaced and, in turn, produce their own transverse wake fields, affecting following bunches. The offsets obtained by bunches could increase along the bunch train, leading to the so-called multi-bunch beam break-up instability [1]. The purpose of our investigation is to see whether such instability will occur in the superconducting, 1.3 GHz, 2.5GeV linac (see Table 1) planned for the Berkeley future light source (BFLS). We assume an initial steady-state situation established for machine operation; i.e. a continuous process where every bunch follows the same trajectory through the linac, with only small deviations from the axis of the rf structures. We will look at a possible instability arising from a bunch having a small deviation from the established trajectory. Such a deviation would produce a wake field that is slightly different from the one produced by the bunches following the established trajectory. This could lead to subsequent bunches deviating further from the established trajectory. We will assume the deviations are small (at first) and so the difference in the wake field caused by a bunch not traveling along the established trajectory is well approximated by a long-range transverse dipole wake. We are concerned only with deviations from the established trajectory; thus, in our models, a transverse position of zero corresponds to the bunch traveling along the established trajectory. Under this assumption, only the additional long-range transverse dipole wake remains in our models.

Kur, Eugene; Zholents, Alexander A.

2008-08-31

59

Velocity field in the wake of a hydropower farm equipped with Achard turbines  

NASA Astrophysics Data System (ADS)

The study consists of experimental and numerical investigations related to the water flow in the wake of a hydropower farm, equipped with three Achard turbines. The Achard turbine is a French concept of vertical axis cross-flow marine current turbine, with three vertical delta-blades, which operates irrespective of the water flow direction. A farm model built at 1:5 scale has been tested in a water channel. The Achard turbines run in stabilized current, so the flow can be assumed to be almost unchanged in horizontal planes along the vertical z-axis, thus allowing 2D numerical modelling, for different farm configurations: the computational domain is a cross-section of all turbines at a certain z-level. The two-dimensional numerical model of that farm has been used to depict the velocity field in the wake of the farm, with COMSOL Multiphysics and FLUENT software, to compute numerically the overall farm efficiency. The validation of the numerical models with experimental results is performed via the measurement of velocity distribution, by Acoustic Doppler Velocimetry, in the wake of the middle turbine within the farm. Three basic configurations were studied experimentally and numerically, namely: with all turbines aligned on a row across the upstream flow direction; with turbines in an isosceles triangular arrangement pointing downstream; with turbines in an isosceles triangular arrangement pointing upstream. As long as the numerical flow in the wake fits the experiments, the numerical results for the power coefficient (turbine efficiency) are trustworthy. The farm configuration with all turbines aligned on a same row leads to lower values of the experimental velocities than the numerical ones, while the farm configurations where the turbines are in isosceles triangular arrangement, pointing downstream or upstream, present a better match between numerical and experimental data.

Georgescu, A.-M.; Georgescu, S. C.; Cosoiu, C. I.; Alboiu, N.; Hamzu, Al

2010-08-01

60

Field investigation of a wake structure downwind of a VAWT in a windfarm array  

SciTech Connect

The effects of upwind turbine wakes on the performance of a FloWind 17-m VAWT were investigated through a series of field experiments conducted at the FloWind windfarm on Cameron Ridge, Tehachapi, California. The field experiment was conducted within a VAWT array consisting of more than nine VAWTs with separations 3D crosswised by 8D downwind (where D is the turbine diameter) in a staggered configuration. The array is the upwind three rows of VAWTS in a total of six rows that are on top of the Cameron Ridge plateau. The terrain features in the vicinity are reasonably regular, with an upslope of 7 deg on the average; however, several local irregularities are present. The annual hourly averaged wind speed exceeds 8 m/s at the site. The wind field and the power-outputs of nine turbines within the array were measured with wind sensors and power transducers. Nine Gill propeller and 18 Maximum cup anemometers and one direction sensor were mounted on portable and stack-up towers installed upwind and within the turbine array. From the field measurements, the velocity and power/energy deficits were derived under various turbine on/off configurations. Much information was provided to characterize the structure of VAWT wakes and to assess their effects on the performance of downwind turbines. Recommendations are made for optimizing windfarm design and operations as well as for wind energy management.

Liu, H.T.; Buck, J.W.; Germain, A.C.; Hinchee, M.E.; Solt, T.S.; LeRoy, G.M.; Srnsky, R.A.

1987-10-01

61

Mixing, staging, and phasing for a proton-driven wake field accelerator  

SciTech Connect

This paper expands on a few important details of the Wakeatron concept. This is a device where electrons can be accelerated by the wake field of short intense proton bunches travelling along the axis of an rf structure. Specifically, we have examined the consequences of the longitudinal dynamics of both the electron and the proton bunches. Included were ''mixing'' in the proton bunches (crucial to the overall concept) and phase shifts (electron bunches relative to proton bunches) in the acceleration process. Because of the deterioration of the proton bunches, due to the ''mixing'' process, it is required that the Wakeatron is indeed staged in a number of consecutive sections.

Gai, W.; Ruggiero, A.G.; Simpson, J.D.

1987-01-01

62

Kinetic simulation of stratifications and flute structures of charged particle jets and wakes in the ambient magnetic field  

Microsoft Academic Search

General methods are proposed for simulations of time-dependent stratifications and flute structures of charged particle jets and wakes in the ambient magnetic field based on the kinetic approach. The Boltzmann equation solved taking into account the ambient electric and magnetic fields. Using this solution the analytical results are obtained, which describe developing magnetic field aligned stratifications of charged particle jets

M. G. Ponomarjov

1999-01-01

63

Structure of the Velocity and Vorticity Field in a Confined Forced Wake  

NASA Astrophysics Data System (ADS)

Previous results have shown that forcing a low Reynolds number 2D wake inside of a confining channel can lead to large increases in the amount of molecular mixing. The current work is part of an investigation to understand the behavior of this flow based on the structure of its vorticity field. Molecular Tagging Velocimetry (MTV) is used to map the u and v components of the velocity field at several streamwise and spanwise locations within the test section. Approximately 500 measurements are made in each region, which extends about two forcing wavelengths. These measurements allow the examination of the structure of the spanwise vorticity field, which is computed from the velocity data by a 2nd order finite difference scheme. Results show a spatial periodicity in the velocity rms, which can be explained by the existence of a phase difference between the shed spanwise vorticity and the free-stream perturbation. This is different from that usually observed in forced wakes with a steady free-stream. Data also show that the lateral spacing between vortices is highly dependent upon the forcing amplitude.

Cohn, R. K.; Koochesfahani, M. M.

1997-11-01

64

Matched Field Noise Suppression based on Matrix Filter  

Microsoft Academic Search

The tow-ship noise suppression is of the key of towed line array sonar system. Referencing to the novel concept matched field noise suppression (MFNS), the matched field noise suppression based on matrix filter, called MF-CBF in this paper, is proposed to suppress the tow-ship noise. The response of MF- CBF to tow-ship noise is set to be zero and unit

Bo Lei; Kunde Yang; Yuanliang Ma

2007-01-01

65

Field Investigation of a Wake Structure Downwind of a VAWT (Vertical-Axis Wind Turbine) in a Wind Farm Array.  

National Technical Information Service (NTIS)

The effects of upwind turbine wakes on the performance of a FloWind 17-m vertical-axis wind turbine (VAWT) were investigated through a series of field experiments conducted at the FloWind wind farm on Cameron Ridge, Tehachapi, California. From the field m...

H. T. Liu J. W. Buck A. C. Germain M. E. Hinchee T. S. Solt

1988-01-01

66

A Concept of Plasma Wake Field Acceleration Linear Collider (PWFA-LC)  

SciTech Connect

Plasma Wake-Field Acceleration (PWFA) has demonstrated acceleration gradients above 50 GeV/m. Simulations have shown drive/witness bunch configurations that yield small energy spreads in the accelerated witness bunch and high energy transfer efficiency from the drive bunch to the witness bunch, ranging from 30% for a Gaussian drive bunch to 95% for a shaped longitudinal profile. These results open the opportunity for a linear collider that could be compact, efficient and more cost effective that the present microwave technologies. A concept of a PWFA-based Linear Collider (PWFA-LC) has been developed and is described in this paper. The drive beam generation and distribution, requirements on the plasma cells, and optimization of the interaction region parameters are described in detail. The R&D steps needed for further development of the concept are also outlined.

Seryi, Andrei; Hogan, Mark; Pei, Shilun; Raubenheimer, Tor; Tenenbaum, Peter; /SLAC; Katsouleas, Tom; /Duke U.; Huang, Chengkun; Joshi, Chan; Mori, Warren; /UCLA; Muggli, Patric; /Southern California U.

2009-10-30

67

Generating "superponderomotive" electrons due to a non-wake-field interaction between a laser pulse and a longitudinal electric field.  

PubMed

It is shown that electrons with momenta exceeding the "free electron" limit of m(e)ca(0)(2)/2 can be produced when a laser pulse and a longitudinal electric field interact with an electron via a non-wake-field mechanism. The mechanism consists of two stages: the reduction of the electron dephasing rate ? - p(x)/m(e)c by an accelerating region of electric field and electron acceleration by the laser via the Lorentz force. This mechanism can, in principle, produce electrons that have longitudinal momenta that is a significant multiple of m(e)ca(0)(2)/2. 2D particle-in-cell simulations of a relatively simple laser-plasma interaction indicate that the generation of superponderomotive electrons is strongly affected by this "antidephasing" mechanism. PMID:23971580

Robinson, A P L; Arefiev, A V; Neely, D

2013-08-05

68

Simulation of Time-Dependent Energy Modulation by Wake Fields and its Impact on Gain in the VUV free Electron Laser of the TESLA Test Facility  

Microsoft Academic Search

For shorter bunches and narrower undulator gaps the interaction between the electrons in the bunch and the wake fields becomes so large that the FEL amplification is affected. For a typical vacuum chamber of an X-ray or VUV Free Electron Laser three major sources of wake fields exist: a resistance of the beam pipe, a change in the geometric aperture

S. Reiche; H. Schlarb

2000-01-01

69

Proper orthogonal decomposition of velocity gradient fields in a simulated stratified turbulent wake: analysis of vorticity and internal waves  

NASA Astrophysics Data System (ADS)

The characterization of three-dimensional space and time-dependent coherent structures and internal waves in stratified environment is one of the most challenging tasks in geophysical fluid dynamics. Proper orthogonal decomposition (POD) is applied to 2-D slices of vorticity and horizontal divergence obtained from 3-D DNS of a stratified turbulent wake of a towed sphere at Re=5x103 and Fr=4. The numerical method employed solves the incompressible Navier-Stokes equations under the Boussinesq approximation. The temporal discretization consists of three fractional steps: an explicit advancement of the nonlinear terms, an implicit solution of the Poisson equation for the pseudo-pressure (which enforces incompressibility), and an implicit solution of the Helmholtz equation for the viscous terms (where boundary conditions are imposed). The computational domain is assumed to be periodic in the horizontal direction and non-periodic in the vertical direction. The 2-D slices are sampled along the stream-depth (Oxz), span-depth (Oyz) and stream-span planes (Oxy) for 231 times during the interval, Nt ? [12,35] (N is the stratification frequency). During this interval, internal wave radiation from the wake is most pronounced and the vorticity field in the wake undergoes distinct structural transitions. POD was chosen amongst the available statistical tools due to its advantage in characterization of simulated and experimentally measured velocity gradient fields. The computational procedure, applied to any random vector field, finds the most coherent feature from the given ensemble of field realizations. The decomposed empirical eigenfunctions could be referred to as "coherent structures", since they are highly correlated in an average sense with the flow field. In our analysis, we follow the computationally efficient method of 'snapshots' to find the POD eigenfunctions of the ensemble of vorticity field realizations. The results contains of the separate POD modes, along with the reconstructed vorticity and horizontal divergence fields based on the linear combination of the eigenfunctions. Similar to applications of POD to the characterization of coherent structures in turbulent boundary layers, characteristic geometrical features for each eigenmode of vorticity and horizontal divergence are deduced. The results show that in the Oxz plane at the wake centerline the first, most energetic, modes of vorticity reveal a structure similar of the forward-inclined vertical shear layers typical of late-time stratified wakes. In Oxz planes, off-set from the wake centerline, the signature of internal waves in the form of forward-inclined coherent beams extending into the ambient becomes evident. The angle of inclination becomes progressively vertical with increasing POD mode. Lower POD modes on the Oyz planes show a layered structure in the wake core with coherent beams radiating out into the ambient at angles spanning 0 to 75 degrees. The POD analysis of horizontal divergence on the Oxz and Oyz planes reveals similar features with the results for the vorticity field. Two notable exceptions at lower modes are the less organized structure of the wake core and the predominance of beam-like structures in laterally offset Oxz planes. Furthermore, these differences are confirmed through the relative energy spectra distribution of the eigenmodes for the vorticity and the horizontal divergence. Qualitative comparison of the reconstructed low-order velocity gradient fields and the computed flow fields shows the relative contribution of the different mode combinations, to the various flow features such as internal waves and vorticity. It is shown that POD analysis has provided a statistical description of the geometrical features previously observed in instantaneous flow fields of stratified turbulent wake.

Gurka, R.; Diamessis, P.; Liberzon, A.

2009-04-01

70

Generation of parallel electric fields in the Jupiter-Io torus wake region  

NASA Astrophysics Data System (ADS)

Infrared and ultraviolet images have established that auroral emissions at Jupiter caused by the electromagnetic interaction with Io not only produce a bright spot, but an emission trail that extends in longitude from Io's magnetic footprint. Electron acceleration that produces the bright spot is believed to be dominated by Alfvén waves whereas we argue that the trail or wake aurora results from quasi-static parallel electric fields associated with large-scale, field-aligned currents between the Io torus and Jupiter's ionosphere. These currents ultimately transfer angular momentum from Jupiter to the Io torus. We examine the generation and the impact of the quasi-static parallel electric fields in the Io trail aurora. A critical component to our analysis is a current-voltage relation that accounts for the low-density plasma along the magnetic flux tubes that connect the Io torus and Jupiter. This low-density region, ˜ 2 R J from Jupiter's center, can significantly limit the field-aligned current, essentially acting as a “high-latitude current choke.” Once parallel electric fields are introduced, the governing equations that couple Jupiter's ionosphere to the Io torus become nonlinear and, while the large-scale behavior is similar to that expected with no parallel electric field, there are substantial deviations on smaller scales. The solutions, bound by properties of the Io torus and Jupiter's ionosphere, indicate that the parallel potentials are on the order of 1 kV when constrained by peak energy fluxes of a few milliwatts per square meter. The parallel potentials that we predict are significantly lower than earlier reports.

Ergun, R. E.; Ray, L.; Delamere, P. A.; Bagenal, F.; Dols, V.; Su, Y.-J.

2009-05-01

71

Controlling Wake Turbulence  

Microsoft Academic Search

This Letter introduces a control strategy for taming the wake turbulence behind a cylinder. An angular momentum injection scheme is proposed to synchronize the vertical velocity field. We show that the base suction, wake formation length, absolute instability, and the Kármán vortex street are effectively controlled by the angular momentum injection. A control equation is designed to implement the injection.

B. S. V. Patnaik; G. W. Wei

2002-01-01

72

Field investigation of a wake structure downwind of a VANT (Vertical-Axis Wind Turbine) in a wind farm array  

NASA Astrophysics Data System (ADS)

The effects of upwind turbine wakes on the performance of a FloWind 17-m vertical-axis wind turbine (VAWT) were investigated through a series of field experiments conducted at the FloWind wind farm on Cameron Ridge, Tehachapi, California. From the field measurements, we derived the velocity and power/energy deficits under various turbine on/off configurations. Much information was provided to characterize the structure of VAWT wakes and to assess their effects on the performance of downwind turbines. A method to estimate the energy deficit was developed based on the measured power deficit and the wind speed distributions. This method may be adopted for other turbine types and sites. Recommendations are made for optimizing wind farm design and operations, as well as for wind energy management.

Liu, H. T.; Buck, J. W.; Germain, A. C.; Hinchee, M. E.; Solt, T. S.; Leroy, G. M.; Srnsky, R. A.

1988-09-01

73

Ionization effects in the generation of wake-fields by ultra-high contrast femtosecond laser pulses in argon gas  

SciTech Connect

Difference in mechanisms of wake-field generation and electron self-injection by high contrast femtosecond laser pulses in an initially neutral Argon gas and in pre-ionized plasma without ionization is studied via 2D particle-in-cell simulations including optical ionization of the media. For shorter laser pulses, 40 fs, ionization results only in an increase of the charge of accelerated electrons by factor of {approx}3 with qualitatively the same energy distribution. For longer pulses, 80 fs, a more stable wake field structure is observed in the neutral gas with the maximal energy of the accelerated electrons exceeding that in the fixed density plasma. In higher density Argon, an ionizing laser pulse converts itself to a complex system of solitons at a self-induced, critical density ramp.

Makito, K.; Shin, J.-H. [Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka (Japan); Zhidkov, A.; Hosokai, T.; Masuda, S. [Photon Pioneers Center, Osaka University, 2-8, Yamadaoka, Suita, Osaka (Japan); Japan Science and Technology Agency (JST), CREST, 2-8 Yamadaoka, Suita, Osaka (Japan); Kodama, R. [Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka (Japan); Photon Pioneers Center, Osaka University, 2-8, Yamadaoka, Suita, Osaka (Japan); Japan Science and Technology Agency (JST), CREST, 2-8 Yamadaoka, Suita, Osaka (Japan)

2012-10-15

74

Field investigation of a wake structure downwind of a VAWT (vertical-axis wind turbine) in a wind farm array  

SciTech Connect

The effects of upwind turbine wakes on the performance of a FloWind 17-m vertical-axis wind turbine (VAWT) were investigated through a series of field experiments conducted at the FloWind wind farm on Cameron Ridge, Tehachapi, California. From the field measurements, we derived the velocity and power/energy deficits under various turbine on/off configurations. Much information was provided to characterize the structure of VAWT wakes and to assess their effects on the performance of downwind turbines. A method to estimate the energy deficit was developed based on the measured power deficit and the wind speed distributions. This method may be adopted for other turbine types and sites. Recommendations are made for optimizing wind farm design and operations, as well as for wind energy management. 17 refs., 66 figs., 6 tabs.

Liu, H.T.; Buck, J.W.; Germain, A.C.; Hinchee, M.E.; Solt, T.S.; LeRoy, G.M.; Srnsky, R.A.

1988-09-01

75

Preliminary Analysis on Linac Oscillation Data LI05-19 and Wake Field Energy Loss in FACET Commissioning 2012  

SciTech Connect

In this note, preliminary analysis on linac ocsillation data in FACET linac LI05-09 plus LI11-19 is presented. Several quadrupoles are identified to possibly have different strength, compared with their designed strength in the MAD optics model. The beam energy loss due to longitudinal wake fields in the S-band linac is also analytically calculated, also by LITRACK numerical simulations.

Sun, Yipeng; /SLAC

2012-07-23

76

Longitudinal wake field for an electron beam accelerated through an ultrahigh field gradient  

Microsoft Academic Search

Electron accelerators with higher and higher longitudinal field gradients are desirable, as they allow for the production of high-energy beams by means of compact and cheap setups. Laser-plasma acceleration technique appears to constitute the more promising breakthrough in this direction, delivering unprecedent field gradients up to TV\\/m. In this article we give a quantitative description of the impact of longitudinal

Gianluca Geloni; Evgeni Saldin; Evgeni Schneidmiller; Mikhail Yurkov

2007-01-01

77

Numerical simulations of a cylinder wake under a strong axial magnetic field  

NASA Astrophysics Data System (ADS)

We study the flow of a liquid metal in a square duct past a circular cylinder in a strong externally imposed magnetic field. In these conditions, the flow is quasi-two-dimensional, which allows us to model it using a two-dimensional (2D) model. We perform a parametric study by varying the two control parameters Re and Ha (Ha2 is the ratio of Lorentz to viscous forces) in the ranges [0...6000] and [0...2160], respectively. The flow is found to exhibit a sequence of four regimes. The first three regimes are similar to those of the non-magnetohydrodynamic (non-MHD) 2D circular wake, with transitions controlled by the friction parameter Re/Ha. The fourth one is characterized by vortices raising from boundary layer separations at the duct side walls, which strongly disturbs the Kármán vortex street. This provides the first explanation for the breakup of the 2D Kármán vortex street first observed experimentally by Frank, Barleon, and Müller [Phys. Fluids 13, 2287 (2001)]. We also show that, for high values of Ha (Ha>=1120), the transition to the fourth regime occurs for Re~0.56Ha, and that it is accompanied by a sudden drop in the Strouhal number. In the first three regimes, we show that the drag coefficient and the length of the steady recirculation regions located behind the cylinder are controlled by the parameter Re/Ha4/5. Also, the free shear layer that separates the recirculation region from the free stream is similar to a free MHD parallel layer, with a thickness of the order of Ha-1/2 that is quite different to that of the non-MHD case, and therefore strongly influences the dynamics of this region. We also present one case at Re=3×104 and Ha=1120, where this layer undergoes an instability of the Kelvin-Helmholtz-type.

Dousset, Vincent; Pothérat, Alban

2008-01-01

78

Generation of parallel electric fields in the Jupiter–Io torus wake region  

Microsoft Academic Search

Infrared and ultraviolet images have established that auroral emissions at Jupiter caused by the electromagnetic interaction with Io not only produce a bright spot, but an emission trail that extends in longitude from Io's magnetic footprint. Electron acceleration that produces the bright spot is believed to be dominated by Alfvén waves whereas we argue that the trail or wake aurora

R. E. Ergun; L. Ray; P. A. Delamere; F. Bagenal; V. Dols; Y.-J. Su

2009-01-01

79

Suppression of edge-localized modes by magnetic field perturbations  

SciTech Connect

Transport bursts in simulations of edge-localized modes (ELMs) in tokamaks are suppressed by the application of magnetic field perturbations. The amplitude of the applied magnetic field perturbations is characterized by a stochasticity parameter S. When S>1, magnetic flux surfaces are destroyed and the magnetic field lines diffuse in minor radius. As S increases in the simulations, the magnitude of the ELM bursts decreases. The size of bursts is reduced to a very small value while S is still less than unity and most of the magnetic flux surfaces are still preserved. Magnetic field line stochasticity is not a requirement for the stabilization of ELMs by the magnetic field perturbations. The magnetic field perturbations act by suppressing the growth of the resistive ballooning instability that underlies the ELM bursts.

Kleva, Robert G.; Guzdar, Parvez N. [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742-3511 (United States)

2010-11-15

80

Electron trapping in a plasma wake field accelerator by an ultra relativistic electron beam in the presence of ionization  

NASA Astrophysics Data System (ADS)

An ultra relativistic (28.5 GeV) ultra short (˜30 fs) electron beam produced at the Stanford linear accelerator center creates a plasma wave with very large accelerating gradients (>30 GeV/m). Although 1D theories of wave breaking for highly relativistic waves predict that the wave breaking and trapping would require fields on the order of TV/m, we observed self trapped plasma electrons. We also observed a clear onset for the particle trapping which was done by controlling the plasma wave amplitude by controlling the drive bunch length. We attribute this lower trapping threshold to effect of self ionizing plasma which causes electrons to be born in a more favorable place inside the wake for trapping. The trapping occurs in the boundary regions of a lithium column confined by a helium gas. the Lithium electrons support the wake however, the higher ionization potential Helium electrons are born inside the wake in the transition region the measured trapping threshold of 32 GV/m is in excellent agreement with predictions of an analytical model and detailed PIC code simulations of the experiment. Other optical diagnostics supported by PIC simulations showed that the trapped electrons reach multi GeV energies, are produced in multiple buckets and has ultra short features (˜2fs) emitting visible coherent light.

Pz, Erdem

2006-10-01

81

Velocity field in the wake of a hydropower farm equipped with Achard turbines  

Microsoft Academic Search

The study consists of experimental and numerical investigations related to the water flow in the wake of a hydropower farm, equipped with three Achard turbines. The Achard turbine is a French concept of vertical axis cross-flow marine current turbine, with three vertical delta-blades, which operates irrespective of the water flow direction. A farm model built at 1:5 scale has been

A.-M. Georgescu; S. C. Georgescu; C. I. Cosoiu; N. Alboiu; Al Hamzu

2010-01-01

82

The velocity field of the turbulent very near wake of a circular cylinder  

Microsoft Academic Search

Hot-wire measurements were conducted in the very near wake (x\\/d?10) of a circular cylinder at a Reynolds number based on cylinder diameter, Red of 3900. Measurements of the streamwise velocity component with the use of single sensor hot-wire probes were found to be inaccurate for such flowfields where high flow angles are present. An X-array probe provided detailed streamwise and

L. Ong; J. Wallace

1996-01-01

83

The Dynamic Lunar Wake  

NASA Astrophysics Data System (ADS)

Bodies that lack a significant atmosphere and internal magnetic fields, such as the Moon, are obstacles to the solar wind. The solar wind ions and electrons directly impact the surface of the Moon due to the lack of atmosphere, and the interplanetary magnetic field passes through the obstacle relatively undisturbed. Since the solar wind is absorbed by the bodies, a wake is created behind the object. This wake is gradually filled by solar wind plasma downstream of the body, through thermal expansion and the resulting ambipolar electric field, along the magnetic field lines. Here we investigate the global Moon-solar wind interaction using a hybrid model (particle ions, fluid electrons). We focus in particular on the morphology of the wake region, and how it responds to changing solar wind conditions. The model predictions are compared to plasma observations by NASA's ARTEMIS spacecrafts.

Holmstrom, M.; Halekas, J. S.

2011-12-01

84

Traversing field of view and AR-PIV for mid-field wake vortex investigation in a towing tank  

Microsoft Academic Search

Wake vortex flow experiments are performed in a water tank where a 1:48 scaled model of a large transport aircraft A340-300 is towed at the speed of 3 and 5 ms-1 with values of the angle of attack alpha={2°, 4°, 8°}. Particle image velocimetry (PIV) measurements are performed in a plane perpendicular to the towing direction describing the streamwise component

F. Scarano; C. van Wijk; L. L. M. Veldhuis

2002-01-01

85

Traversing field of view and AR-PIV for mid-field wake vortex investigation in a towing tank  

Microsoft Academic Search

Wake vortex flow experiments are performed in a water tank where a 1:48 scaled model of a large transport aircraft A340-300 is towed at the speed of 3 and 5 ms-1 with values of the angle of attack !={2°, 4°, 8°}. Particle image velocimetry (PIV) measurements are performed in a plane perpendicular to the towing direction describing the streamwise component

F. Scarano; C. van Wijk; L. Veldhuis

2002-01-01

86

Enhancement and suppression in the visual field under perceptual load  

PubMed Central

The perceptual load theory of attention proposes that the degree to which visual distractors are processed is a function of the attentional demands of a task—greater demands increase filtering of irrelevant distractors. The spatial configuration of such filtering is unknown. Here, we used steady-state visual evoked potentials (SSVEPs) in conjunction with time-domain event-related potentials (ERPs) to investigate the distribution of load-induced distractor suppression and task-relevant enhancement in the visual field. Electroencephalogram (EEG) was recorded while subjects performed a foveal go/no-go task that varied in perceptual load. Load-dependent distractor suppression was assessed by presenting a contrast reversing ring at one of three eccentricities (2, 6, or 11°) during performance of the go/no-go task. Rings contrast reversed at 8.3 Hz, allowing load-dependent changes in distractor processing to be tracked in the frequency-domain. ERPs were calculated to the onset of stimuli in the load task to examine load-dependent modulation of task-relevant processing. Results showed that the amplitude of the distractor SSVEP (8.3 Hz) was attenuated under high perceptual load (relative to low load) at the most proximal (2°) eccentricity but not at more eccentric locations (6 or 11°). Task-relevant ERPs revealed a significant increase in N1 amplitude under high load. These results are consistent with a center-surround configuration of load-induced enhancement and suppression in the visual field.

Parks, Nathan A.; Beck, Diane M.; Kramer, Arthur F.

2013-01-01

87

Electric field suppression of ultracold confined chemical reactions  

SciTech Connect

We consider ultracold collisions of polar molecules confined in a one-dimensional optical lattice. Using a quantum scattering formalism and a frame transformation method, we calculate elastic and chemical quenching rate constants for fermionic molecules. Taking {sup 40}K{sup 87}Rb molecules as a prototype, we find that the rate of quenching collisions is enhanced at zero electric field as the confinement is increased but that this rate is suppressed when the electric field is turned on. For molecules with 500 nK of collision energy, for realistic molecular densities, and for achievable experimental electric fields and trap confinements, we predict lifetimes for KRb molecules to be 1 s. We find a ratio of elastic to quenching collision rates of about 100, which may be sufficient to achieve efficient evaporative cooling of polar KRb molecules.

Quemener, Goulven; Bohn, John L. [JILA, NIST and University of Colorado, Boulder, Colorado 80309-0440 (United States)

2010-06-15

88

Simulation of Time-Dependent Energy Modulation by Wake Fields and its Impact on Gain in the VUV free Electron Laser of the TESLA Test Facility  

NASA Astrophysics Data System (ADS)

For shorter bunches and narrower undulator gaps the interaction between the electrons in the bunch and the wake fields becomes so large that the FEL amplification is affected. For a typical vacuum chamber of an X-ray or VUV Free Electron Laser three major sources of wake fields exist: a resistance of the beam pipe, a change in the geometric aperture and the surface roughness of the beam pipe. The generated wake fields, which move along with the electrons, change the electron energy and momentum, depending on the electron longitudinal and transverse position. In particular, the accumulated energy modulation shifts the electrons away from the resonance condition. Based on an analytic model the energy loss by the wake fields has been incorporated into the time-dependent FEL simulation code GENESIS 1.3. For the parameters of the TESLA Test Facility the influence of the bunch length, beam pipe diameter and surface roughness has been studied. The results are presented in this paper.

Reiche, S.; Schlarb, H.

2000-05-01

89

2.5D Numerical Simulation of Excitation of Coherent Chain of Electron Wake-Field Bubbles by Optimal Non-Resonant Chain of Dense Relativistic Electron Bunches  

SciTech Connect

It is shown that optimal difference of frequencies of following of electron bunches and following of wake-field bubbles exists, so N-1 drive-bunches strengthen chain of wakefield bubbles and N-th bunch gets in maximal accelerating wakefield.

Maslov, V. I.; Lotov, K. V. [Budker Institute of Nuclear Physics, 630090, Novosibirsk (Russian Federation); Onishchenko, I. N.; Svistun, O. M. [Karazin Kharkov National University, Kharkov, 61108 (Ukraine)

2010-06-16

90

Jovian plasma torus interaction with Europa. Plasma wake structure and effect of inductive magnetic field: 3D hybrid kinetic simulation  

NASA Astrophysics Data System (ADS)

The hybrid kinetic model supports comprehensive simulation of the interaction between different spatial and energetic elements of the Europa moon-magnetosphere system with respect to a variable upstream magnetic field and flux or density distributions of plasma and energetic ions, electrons, and neutral atoms. This capability is critical for improving the interpretation of the existing Europa flyby measurements from the Galileo Orbiter mission, and for planning flyby and orbital measurements (including the surface and atmospheric compositions) for future missions. The simulations are based on recent models of the atmosphere of Europa (Cassidy et al., 2007; Shematovich et al., 2005). In contrast to previous approaches with MHD simulations, the hybrid model allows us to fully take into account the finite gyroradius effect and electron pressure, and to correctly estimate the ion velocity distribution and the fluxes along the magnetic field (assuming an initial Maxwellian velocity distribution for upstream background ions). Photoionization, electron-impact ionization, charge exchange and collisions between the ions and neutrals are also included in our model. We consider the models with O++ and S++ background plasma, and various betas for background ions and electrons, and pickup electrons. The majority of O2 atmosphere is thermal with an extended non-thermal population (Cassidy et al., 2007). In this paper, we discuss two tasks: (1) the plasma wake structure dependence on the parameters of the upstream plasma and Europa's atmosphere (model I, cases (a) and (b) with a homogeneous Jovian magnetosphere field, an inductive magnetic dipole and high oceanic shell conductivity); and (2) estimation of the possible effect of an induced magnetic field arising from oceanic shell conductivity. This effect was estimated based on the difference between the observed and modeled magnetic fields (model II, case (c) with an inhomogeneous Jovian magnetosphere field, an inductive magnetic dipole and low oceanic shell conductivity).

Lipatov, A. S.; Cooper, J. F.; Paterson, W. R.; Sittler, E. C., Jr.; Hartle, R. E.; Simpson, D. G.

2013-03-01

91

Controlling wake turbulence.  

PubMed

This Letter introduces a control strategy for taming the wake turbulence behind a cylinder. An angular momentum injection scheme is proposed to synchronize the vertical velocity field. We show that the base suction, wake formation length, absolute instability, and the Kármán vortex street are effectively controlled by the angular momentum injection. A control equation is designed to implement the injection. The Navier-Stokes equations, along with the control equation, are solved. The occurrence of a new recirculation free zone is identified. PMID:11863732

Patnaik, B S V; Wei, G W

2002-01-17

92

Wake-field and space charge effects on high brightness beams calculations and measured results for the laser driven photoelectrons at BNL-ATF  

SciTech Connect

We discuss the formalism used to study the effects of the interactions between the highly charged particles and the fields in the accelerating structure, including space charge and wake fields. Some of our calculations and numerical simulation results obtained for the Brookhaven National Laboratory (BNL) high-brightness photoelectron beam at the Accelerator Test Facility (ATF) and the measured data at ATF are also included.

Parsa, Z.

1993-05-01

93

Study of the turbulent characteristics of the near-wake field of a medium-sized wind turbine operating in high wind conditions  

SciTech Connect

The near-wake turbulent structure that is downwind of a medium-sized, horizontal axis wind turbine at a distance of one rotor diameter is discussed. The experimental site is the Samos Island Wind Park comprising nine wind turbines installed on the top of a 400 m-high saddle. The analysis is based on experimental data obtained mainly under strong wind conditions by two masts erected upstream and downstream of a wind turbine. The field of wind turbulence is examined both in integral and spectral form. Consideration of the perturbation produced by the tower construction is crucial in the interpretation of results. Observations show that the turbulent field varies from the edge to the center of the wake and strongly depends on the incident wind speed. Increased turbulent levels are observed near the blade tips, with evidence of a similar trend around the hub height for all wind speeds. Decreases of wind turbulence are observed in mid frequencies inside the wake due to the reduced shear associated with the flat crosswind velocity profile. This effect seems to dominate in the variation of the integral values of the longitudinal wind component variance. The low frequency portion of wind spectra reverses behavior in high wind speeds, i.e., an increase in energy relative to background values is observed. This is probably due to the shape of the turbine characteristic power curve. Cross-wind profiles of turbulent shear stresses at the lower boundary of the wake are also discussed. 15 refs., 15 figs., 4 tabs.

Papadopoulos, K.H.; Helmis, C.G.; Soilemes, A.T.; Papageorgas, P.G.; Asimakopoulos, D.N. [Lab. of Meteorology, Athens (Greece)

1995-07-01

94

A multi-beam, multi-terawatt Ti:sapphire laser system for laser wake-field acceleration studies  

NASA Astrophysics Data System (ADS)

The Lasers, Optical Accelerator Systems Integrated Studies (L'OASIS) Lab of LBNL operates a highly automated and remotely controlled Ti:sapphire chirped pulse amplification (CPA) laser system that provides synchronized beams of 2×1.0 TW, 12 TW, and 100 TW peak-power, in a unique, radiation shielded facility. The system has been specially designed for studying high field laser-plasma interactions and particularly aimed for the investigations of laser wake-field particle acceleration. It generates and recombines multiple beams having different pulse durations, wavelengths, and pulse energies for various stages of plasma preparation, excitation, and diagnostics. The amplifier system is characterized and continuously monitored via local area network (LAN) from a radiation shielded control room by an array of diagnostics, including beam profile monitoring cameras, remote controlled alignment options, self-correcting beam-pointing stabilization loops, pulse measurement tools, such as single-shot autocorrelator for pulse duration and third-order correlator for contrast measurements, FROG for pulse shape studies.

Tóth, Cs.; Geddes, C. G. R.; van Tilborg, J.; Leemans, W. P.

2004-12-01

95

Wind-Flow Field Measurements in the Wake of the Barstow Solar-Thermal Power Plant.  

National Technical Information Service (NTIS)

A brief flow field measurement study was conducted at the Barstow 10 MW Solar Thermal Power PLant to determine the effect of the plant on the local wind flow field and to identify resulting possible environmental implications. Wind speed measurements were...

R. L. Radkey T. G. Zambrano

1982-01-01

96

Space charge and wake field analysis for a high brightness electron source  

SciTech Connect

We present a brief overview of the formalism used, and some simulation results for transverse and longitudinal motion of a bunch of particles moving through a cavity (e.g., the Brookhaven National Laboratory high brightness photocathode gun), including effects of the accelerating field, space charge forces (e.g., arising from the interaction of the cavity surface and the self field of the bunch). 3 refs., 12 figs.

Parsa, Z.

1991-01-01

97

Flow-Field Survey of an Empennage Wake Interacting with a Pusher Propeller.  

National Technical Information Service (NTIS)

The flow field between a model empennage and a 591-mm-diameter pusher propeller was studied in the Ames 7- by 10-Foot Wind Tunnel with directional pressure probes and hot-wire anemometers. The region probed was bounded by the empennage trailing edge and d...

W. C. Horne P. T. Soderman

1988-01-01

98

Study of electron trapping by a transversely ellipsoidal bubble in the laser wake-field acceleration  

NASA Astrophysics Data System (ADS)

We present electron trapping in an ellipsoidal bubble which is not well explained by the spherical bubble model by [Kostyukov et al., Phys. Rev. Lett. 103, 175003 (2009)]. The formation of an ellipsoidal bubble, which is elongated transversely, frequently occurs when the spot size of the laser pulse is large compared to the plasma wavelength. First, we introduce the relation between the bubble size and the field slope inside the bubble in longitudinal and transverse directions. Then, we provide an ellipsoidal model of the bubble potential and investigate the electron trapping condition by numerical integration of the equations of motion. We found that the ellipsoidal model gives a significantly less restrictive trapping condition than that of the spherical bubble model. The trapping condition is compared with three-dimensional particle-in-cell simulations and the electron trajectory in test potential simulations.

Cho, Myung-Hoon; Kim, Young-Kuk; Hur, Min Sup

2013-09-01

99

Effect of wakes from moving upstream rods on boundary layer separation from a high lift airfoil  

NASA Astrophysics Data System (ADS)

Highly loaded airfoils in turbines allow power generation using fewer airfoils. High loading, however, can cause boundary layer separation, resulting in reduced lift and increased aerodynamic loss. Separation is affected by the interaction between rotating blades and stationary vanes. Wakes from upstream vanes periodically impinge on downstream blades, and can reduce separation. The wakes include elevated turbulence, which can induce transition, and a velocity deficit, which results in an impinging flow on the blade surface known as a ``negative jet.'' In the present study, flow through a linear cascade of very high lift airfoils is studied experimentally. Wakes are produced with moving rods which cut through the flow upstream of the airfoils, simulating the effect of upstream vanes. Pressure and velocity fields are documented. Wake spacing and velocity are varied. At low Reynolds numbers without wakes, the boundary layer separates and does not reattach. At high wake passing frequencies separation is largely suppressed. At lower frequencies, ensemble averaged velocity results show intermittent separation and reattachment during the wake passing cycle.

Volino, Ralph J.

2011-11-01

100

Repetition suppression and expectation suppression are dissociable in time in early auditory evoked fields.  

PubMed

Repetition of a stimulus, as well as valid expectation that a stimulus will occur, both attenuate the neural response to it. These effects, repetition suppression and expectation suppression, are typically confounded in paradigms in which the nonrepeated stimulus is also relatively rare (e.g., in oddball blocks of mismatch negativity paradigms, or in repetition suppression paradigms with multiple repetitions before an alternation). However, recent hierarchical models of sensory processing inspire the hypothesis that the two might be separable in time, with repetition suppression occurring earlier, as a consequence of local transition probabilities, and suppression by expectation occurring later, as a consequence of learnt statistical regularities. Here we test this hypothesis in an auditory experiment by orthogonally manipulating stimulus repetition and stimulus expectation and, using magnetoencephalography, measuring the neural response over time in human subjects. We found that stimulus repetition (but not stimulus expectation) attenuates the early auditory response (40-60 ms), while stimulus expectation (but not stimulus repetition) attenuates the subsequent, intermediate stage of auditory processing (100-200 ms). These findings are well in line with hierarchical predictive coding models, which posit sequential stages of prediction error resolution, contingent on the level at which the hypothesis is generated. PMID:23015429

Todorovic, Ana; de Lange, Floris P

2012-09-26

101

Electron energy boosting in laser-wake-field acceleration with external magnetic field Bapprox1 T and laser prepulses  

SciTech Connect

Hundred-mega-electron-volt electron beams with quasi-monoenergetic distribution, and a transverse geometrical emittance as small as approx0.02 pi mm mrad are generated by low power (7 TW, 45 fs) laser pulses tightly focused in helium gas jets in an external static magnetic field, Bapprox1 T. Generation of monoenergetic beams strongly correlates with appearance of a straight, at least 2 mm length plasma channel in a short time before the main laser pulse and with the energy of copropagating picosecond pedestal pulses (PPP). For a moderate energy PPP, the multiple or staged electron self-injection in the channel gives several narrow peaks in the electron energy distribution.

Hosokai, Tomonao [Photon Pioneers Center, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan and Japan Science and Technology Agency (JST), CREST, 2-1, Yamadaoka, Suita, Osaka 565-0871 (Japan); Zhidkov, Alexei [Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa 240-0196 (Japan); Yamazaki, Atsushi [Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603 (Japan); Mizuta, Yoshio [Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871 (Japan); Uesaka, Mitsuru [Graduate School of Engineering, University of Tokyo, 22-2 Shirane-shirakata, Tokai, Naka, Ibaraki 319-1188 (Japan); Kodama, Ryosuke [Photon Pioneers Center, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871 (Japan) and Japan Science and Technology Agency (JST), CREST, 2-1, Yamadaoka, Suita, Osaka 565-0871 (Japan); Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871 (Japan)

2010-03-22

102

Active Control of a Cylinder Wake Using Surface Plasma  

NASA Astrophysics Data System (ADS)

An experimental investigation has been undertaken using high-speed Particle Image Velocimetry to study the possibility of controlling the global flow field in the near wake of a circular cylinder at Re = 6,500.Surface plasma actuators were mounted at strategic locations around the cylinder (both fore and aft of the separation point) and used for flow control by producing a body force close to the wall.It was found that the plasma can significantly alter the vortex shedding in the wake of the cylinder, with effectiveness depending upon the actuator location and forcing frequency.The most dramatic effects were observed when the plasma was located very close to the natural laminar separation point.Here, amplification of the shedding was observed when the plasma was excited at the natural vortex shedding frequency (St f ? 0.2; St K = 0.206).This was accompanied by periodic flow reattachment to at least the rearward stagnation point.At higher forcing frequency (St f ? 0.8), the plasma completely suppressed the vortex shedding process which lead to a short and narrow wake, reduced turbulence intensity, and 60% reduction in the wake momentum thickness.At still higher frequency (St f ? 2.0; St SL = 1.7), only the shear layers were excited and the vortex street remained unaltered.

Jukes, T.; Choi, K.-S.

103

Emittance growth due to the wake field driven by an electron beam accelerated in an RF-gun of free electron laser ``ELSA''  

NASA Astrophysics Data System (ADS)

It appears that the ease of the parameter chosen for ``ELSA'' photo injector, the influence of the exit aperture, in terms of beam quality, is slight concerning the transverse emittance: (???/??)(z)~3% at maximum, and negligible concerning the axial emittance. To complete this paper, we recall the results previously obtained concerning the wake field of a closed or open cavity for a beam approaching the anode [6,7]. They had quantitatively specified the expected deep assymetry between the conducting walls regarding their contribution to the total wake field, besides the space-charge contribution. (Given that the radial walls have no time to contribute, these conducting walls are the cathode and the anode.) Thus, concerning the effects on whole-beam emittances, the correction (???/??)(z) entailed by taking the anode contribution into account had been found to be less than 5% at maximum (a maximum reached for t=tg, and for E0=30MV/m). The field map perturbation due to the aperture in the anode [7] has an effect of the same order of magnitude, i.e. small, on the transverse emittance of a beam reaching this exit aperture. As shown in Fig. /3, this correction is of order of 3% for E0=30MV/m. It could be of the order of 10% for E0=10MV/M.

Salah, W.; Dolique, J.-M.

2000-09-01

104

Matched field noise suppression: Principle with application to towedhydrophone line array  

Microsoft Academic Search

Discrete noise source suppression in underwa- ter acoustic channel has attracted great attention in recent years. The paper proposes a new principle for dealing with the problem. This new principle is called matched field noise suppression (MFNS). Based on a previous work of the au- thors group, a full understanding about how a discrete noise source shows effects on the

Yuanliang MA; Shefeng Yan; Kunde Yang

2003-01-01

105

Dynamics and control of hydrofoil wakes  

Microsoft Academic Search

The problem of rotor-stator interaction has been an issue in the turbomachinery field for more than forty years. Manipulation of the stator wakes is one method to minimize the problem. In order to explore this concept, a comprehensive experimental program was carried out in a water tunnel utilizing a series of NACA 0015 hydrofoils. Baseline wake data were collected with

Roger Arndt; Morten Kjeldsen; Martin Wosnik

2006-01-01

106

Ion cyclotron waves in Io's wake region  

NASA Astrophysics Data System (ADS)

When Galileo flew almost directly through the center of Io's wake in December 1995 it encountered a region of depressed field strength, devoid of the strong ion cyclotron waves that were present inbound and outbound on either side of the wake. In August 2001 Galileo made an almost orthogonal pass, parallel to the wake axis, passing within 200 km of the Io surface, and staying close to 1 RIo above the center of the wake. Downstream from Io (but not upstream) strong ion cyclotron waves were seen. The very low frequency of these waves, well below the local SO 2+ gyro frequency, suggests that they were created in the low field of Io's wake. Thus in contrast to implications of the December 1995, near-Io, wake passage, ion cyclotron waves are produced in the Io wake. Furthermore, these waves persisted beyond 6.7 RIo downstream, with little sign of recovery in frequency, indicating that Io's depressed field wake extends well downstream of Io.

Russell, C. T.; Blanco-Cano, X.; Kivelson, M. G.

2003-03-01

107

A Limited Role for Suppression in the Central Field of Individuals with Strabismic Amblyopia  

PubMed Central

Background Although their eyes are pointing in different directions, people with long-standing strabismic amblyopia typically do not experience double-vision or indeed any visual symptoms arising from their condition. It is generally believed that the phenomenon of suppression plays a major role in dealing with the consequences of amblyopia and strabismus, by preventing images from the weaker/deviating eye from reaching conscious awareness. Suppression is thus a highly sophisticated coping mechanism. Although suppression has been studied for over 100 years the literature is equivocal in relation to the extent of the retina that is suppressed, though the method used to investigate suppression is crucial to the outcome. There is growing evidence that some measurement methods lead to artefactual claims that suppression exists when it does not. Methodology/Results Here we present the results of an experiment conducted with a new method to examine the prevalence, depth and extent of suppression in ten individuals with strabismic amblyopia. Seven subjects (70%) showed no evidence whatsoever for suppression and in the three individuals who did (30%), the depth and extent of suppression was small. Conclusions Suppression may play a much smaller role in dealing with the negative consequences of strabismic amblyopia than previously thought. Whereas recent claims of this nature have been made only in those with micro-strabismus our results show extremely limited evidence for suppression across the central visual field in strabismic amblyopes more generally. Instead of suppressing the image from the weaker/deviating eye, we suggest the visual system of individuals with strabismic amblyopia may act to maximise the possibilities for binocular co-operation. This is consistent with recent evidence from strabismic and amblyopic individuals that their binocular mechanisms are intact, and that, just as in visual normals, performance with two eyes is better than with the better eye alone in these individuals.

Barrett, Brendan T.; Panesar, Gurvinder K.; Scally, Andrew J.; Pacey, Ian E.

2012-01-01

108

Wake Turbulence Training Aid.  

National Technical Information Service (NTIS)

The goal of the Wake Turbulence Training Aid is to reduce the number of wake-turbulence related accidents and incidents by improving the pilot's and air traffic controller's decision making and situational awareness through increased and shared understand...

G. C. Hay R. H. Passman

1995-01-01

109

Spectral element discontinuous Galerkin simulations for wake potential calculations : NEKCEM.  

SciTech Connect

In this paper we present high-order spectral element discontinuous Galerkin simulations for wake field and wake potential calculations. Numerical discretizations are based on body-conforming hexagonal meshes on Gauss-Lobatto-Legendre grids. We demonstrate wake potential profiles for cylindrically symmetric cavity structures in 3D, including the cases for linear and quadratic transitions between two cross sections. Wake potential calculations are carried out on 2D surfaces for various bunch sizes.

Min, M.; Fischer, P. F.; Chae, Y.-C.

2008-01-01

110

Resource competition and suppression of plants colonizing early successional old fields.  

PubMed

Early colonizing annual plants are rapidly suppressed in secondary succession on fertile midwestern old fields, while later colonizing perennials persist. Differences in competitive ability for above- and belowground resources may be partly responsible for differences in species persistence during succession, as both light and nutrient availability may change rapidly. We found that, although both above- and belowground competition suppress growth of colonizing plants, belowground competition was the dominant factor in the suppression of the annual Ambrosia artemisiifolia in 2nd-year-old fields near the W.K. Kellogg Biological Station in southwestern Michigan. Despite an ability to persist in later successional fields, seedling transplants of the perennial Achillea millefolium were also suppressed by above- and belowground competition, with belowground competition having the strongest effect. As in many old fields, nitrogen availability is the primary factor limiting plant productivity. There was no clear difference between the species in ability to compete for (15)N from an enriched patch, although there was an indication of greater precision of foraging by Achillea. Life history differences between these species and consequent differences in the phenology of root growth relative to other old-field plants are likely to play a large role in the persistence of Achillea in successional fields where Ambrosia is suppressed. PMID:20135162

Kosola, K R; Gross, K L

1999-01-01

111

Background gradient suppression in stimulated echo NMR diffusion studies using magic pulsed field gradient ratios  

Microsoft Academic Search

By evaluating the spin echo attenuation for a generalized 13-interval PFG NMR sequence consisting of pulsed field gradients with four different effective intensities (Fp\\/r and Gp\\/r), magic pulsed field gradient (MPFG) ratios for the prepare (Gp\\/Fp) and the read (Gr\\/Fr) interval are derived, which suppress the cross term between background field gradients and the pulsed field gradients even in the

Petrik Galvosas; Frank Stallmach; Jörg Kärger

2004-01-01

112

Numerical simulations of wake structure generated by rotating blades using a time marching, free vortex blob method  

Microsoft Academic Search

Vorticity fields in the wake generated by rotating blades are calculated using a time accurate, free vortex blob method without a non physical model of the far wake. The computed free wake geometry of single rotor in hover is represented by the three wake regions: well defined tip vortex region, intermediate entangled region, and initially generated wake bundle. The air

Duck-Joo Lee; Seon-Uk Na

1997-01-01

113

Suppression of current fluctuations in carbon nanotube field-effect transistors by applying alternating current  

Microsoft Academic Search

A method of suppressing current fluctuations in carbon nanotube field-effect transistors (CNTFETs) is proposed. We compared the time dependences of the drain current for direct current (DC) measurement and alternating current (AC) measurement with a lock-in amplifier. Drain-current fluctuations were highly suppressed by the AC with lock-in method in the small gate voltage regime. On the other hand, the current

Yasuhide Ohno; Kenzo Maehashi; Koichi Inoue; Kazuhiko Matsumoto

2008-01-01

114

Current-induced suppression of superconductivity in tantalum thin films at zero magnetic field  

Microsoft Academic Search

We report our findings on the mechanism of current-induced suppression of superconductivity in amorphous tantalum films as thin as 5nm under zero applied magnetic field. Our results indicate that the applied current generates magnetic vortices threading the films, and the dynamics of these vortices leads to the suppression of the superconductivity. Our findings also imply that the motion of current-generated

Yongho Seo; Yongguang Qin; Kyusang Choi; Jongsoo Yoon

2005-01-01

115

Suppression of the Richtmyer-Meshkov Instability in the Presence of a Magnetic Field  

SciTech Connect

We present numerical evidence from two dimensional simulations that the growth of the Richtmyer-Meshkov instability is suppressed in the presence of a magnetic field. A bifurcation occurs during the refraction of the incident shock on the density interface which transports baroclinically generated vorticity away from the interface to a pair of slow or intermediate magnetosonic shocks. Consequently, the density interface is devoid of vorticity and its growth and associated mixing is completely suppressed.

Ravi Samtaney

2003-03-21

116

Wake-induced unsteady flows: Their impact on rotor performance and wake rectification  

SciTech Connect

The impact of wake-induced unsteady flows on blade row performance and the wake rectification process is examined by means of numerical simulation. The passage of a stator wake through a downstream rotor is first simulated using a three-dimensional unsteady viscous flow code. The results from this simulation are used to define two steady-state inlet conditions for a three-dimensional viscous flow simulation of a rotor operating in isolation. The results obtained from these numerical simulations are then compared to those obtained form the unsteady simulation both to quantify the impact of the wake-induced unsteady flow field on rotor performance and to identify the flow processes which impact wake rectification. Finally, the results from this comparison study are related to an existing model, which attempts to account for the impact of wake-induced unsteady flows on the performance of multistage turbomachinery.

Adamczyk, J.J. [National Aeronautics and Space Administration, Brook Park, OH (United States). Lewis Research Center; Celestina, M.L. [Sverdrup Technology, Inc., Brook Park, OH (United States). Dept. of Aeromechanics; Chen, J.P. [Mississippi State Univ., MS (United States). NSF Engineering Research Center

1996-01-01

117

Background gradient suppression in stimulated echo NMR diffusion studies using magic pulsed field gradient ratios  

NASA Astrophysics Data System (ADS)

By evaluating the spin echo attenuation for a generalized 13-interval PFG NMR sequence consisting of pulsed field gradients with four different effective intensities (Fp/r and Gp/r), magic pulsed field gradient (MPFG) ratios for the prepare (Gp/Fp) and the read (Gr/Fr) interval are derived, which suppress the cross term between background field gradients and the pulsed field gradients even in the cases where the background field gradients may change during the z-store interval of the pulse sequence. These MPFG ratios depend only on the timing of the pulsed gradients in the pulse sequence and allow a convenient experimental approach to background gradient suppression in NMR diffusion studies with heterogeneous systems, where the local properties of the (internal) background gradients are often unknown. If the pulsed field gradients are centered in the ?-intervals between the ? and ?/2 rf pulses, these two MPFG ratios coincide to ?=Gp/r/Fp/r=1-8/[1+(1/3)(?/?)2]. Since the width of the pulsed field gradients (?) is bounded by 0<=?<=?, ? can only be in the range of 5<=-?<=7. The predicted suppression of the unwanted cross terms is demonstrated experimentally using time-dependent external gradients which are controlled in the NMR experiment as well as spatially dependent internal background gradients generated by the magnetic properties of the sample itself. The theoretical and experimental results confirm and extend the approach of Sun et al. (J. Magn. Reson. 161 (2003) 168), who recently introduced a 13-interval type PFG NMR sequence with two asymmetric pulsed magnetic field gradients suitable to suppress unwanted cross terms with spatially dependent background field gradients.

Galvosas, Petrik; Stallmach, Frank; Kärger, Jörg

2004-02-01

118

Building wake diffusion  

SciTech Connect

A recent review of building-wake diffusion models for the Nuclear Regulatory Commission (NRC) compares model predictions of centerline concentrations in building wakes with concentrations observed in experiments at seven nuclear reactors. In general, the model predictions are conservative in that they tend to predict concentrations that are greater than those actually observed. However, the models show little skill in accounting for variations in the observed concentrations. Analysis of experimental data indicates that the general form of the standard wake diffusion models is inconsistent with observed variation of concentrations in the wakes. The inconsistency is especially marked for ground-level releases. As an interim measure, multiple linear regression techniques have been used to develop a statistical building wake model alternative to the current models. This paper describes the statistical wake model and compares it with other models. 11 refs., 4 figs.

Ramsdell, J.V.

1989-01-01

119

Suppression of electron scattering by the longitudinal components of tightly focused laser fields  

Microsoft Academic Search

Relativistic electron scattering by a high intensity linearly polarized Gaussian (TEM00 mode) laser beam is studied in detail using three-dimensional numerical simulations. It is observed that the longitudinal components of the electromagnetic field in a tight focus effectively suppress transverse electron scattering in the relativistic laser ponderomotive acceleration scheme. The simulations show that the relativistic ponderomotive acceleration can produce high

S. Masuda; M. Kando; H. Kotaki; K. Nakajima

2005-01-01

120

Suppression of nematophagous fungi by enchytraeid worms: a field exclosure experiment  

Microsoft Academic Search

The feeding biology of Enchytraeus crypticus and other enchytraeids is poorly understood as is their effect on nematophagous fungi. Because enchytraeids had been associated\\u000a with nematophagous fungi in the field and had suppressed these fungi in soil microcosms, we tested the hypothesis that exclusion\\u000a of enchytraeids, largely E. crypticus, would improve establishment of certain nematophagous fungi in field plots. The

B. A. Jaffee; P. F. Santos; A. E. Muldoon

1997-01-01

121

Mixing in the wake of an aircraft carrier  

Microsoft Academic Search

A computational model, originally developed to study ship microbubble wakes, is to study the dispersal of shipboard discharge and possible resuspension of bottom sediment, in the near field of the wake of an aircraft carrier. The near field solution is then used to specify the initial condition for a second model which computes the far field particle dispersion and dilution

Mark Hyman; Jim Rohr; Jon Schoonmaker; Toby Ratcliffe; Bart Chadwick; Ken Richter; Scott Jenkins; J. Wasyl

1995-01-01

122

Contrast-dependent variations in the excitatory classical receptive field and suppressive nonclassical receptive field of cat primary visual cortex.  

PubMed

In area V1 of cat and monkey, there is a surround region beyond the classical receptive field (CRF) which alone is unresponsive but may modulate the cell's response. This field is referred to as the "nonclassical receptive field" (nCRF). It has been reported in monkey that the extent of CRF and/or nCRF of V1 neurons is not fixed but varies with stimulus contrast. We reexamined the contrast dependence of V1 neurons in cat to determine whether this differs from previous studies in macaque. By fitting the spatial summation curves obtained at different contrasts with a difference of Gaussians model, we estimated quantitatively the effect of contrast on the spatial extent of the CRF and nCRF as well as the strength of surround suppression. Our results showed that both the CRF and nCRF expanded at low contrast, but the expansion is more marked for the CRF than for the nCRF. Although the effect of contrast on surround suppression was varied, the overall suppression increased significantly at high contrast. Moreover, the contrast-dependent change in the extent of CRF is independent of the change in suppression strength. Overall, our results in cat are in agreement with those obtained in macaque money. PMID:22302117

Chen, Ke; Song, Xue-Mei; Li, Chao-Yi

2012-02-02

123

Cylinder wakes in flowing soap films  

Microsoft Academic Search

We present an experimental characterization of cylinder wakes in flowing soap films. From instantaneous velocity and thickness fields, we find the vortex-shedding frequency, mean-flow velocity, and mean-film thickness. Using the empirical relationship between the Reynolds and Strouhal numbers obtained for cylinder wakes in three dimensions, we estimate the effective soap-film viscosity and its dependence on film thickness. We also compare

Peter Vorobieff; Robert E. Ecke

1999-01-01

124

Status of wake and array loss research  

SciTech Connect

In recent years, many projects have evaluated wind turbine wake effects and resultant array losses in both Europe and the United States. This paper examines the status of current knowledge about wake effects and array losses and suggests future research. Single-turbine wake characteristics have been studied extensively and are generally described well by existing theoretical models. Field measurements of wake effects in wind turbine arrays are largely limited to small arrays, with 2 to 4 rows of turbines. Few data have been published on wake effects within large arrays. Measurements of wake deficits downwind of large arrays that deficits are substantially larger and extend farther downwind than expected. Although array design models have been developed, these models have been tested and verified using only limited data from a few rows of wind turbines in complex terrain, whereas some of the largest arrays have more than 40 rows of wind turbines. Planned cooperative efforts with the wind industry will obtain existing data relevant to analyzing energy deficits within large arrays and identifying data sets for potential use in array model verification efforts. Future research being considered include a cooperative research experiment to obtain more definitive data on wake deficits and turbulence within and downwind of large arrays. 16 refs., 9 figs., 1 tab.

Elliott, D.L.

1991-09-01

125

Dynamics and control of hydrofoil wakes  

Microsoft Academic Search

The problem of rotor-stator interaction (RSI) is an issue within the field of turbomachinery. The flow field entering the rotor cascade will depend on the stator blade to blade velocity distributions, and the viscous wake trailing cascade blades. This flow field is also dependent on the mode of operation, e.g by changing the angle of each blade in hydroturbines. Manipulating

Morten Kjeldsen; Martin Wosnik; Roger Arndt

2008-01-01

126

Laser wake-field acceleration in pre-formed plasma channel created by pre-pulse pedestal of terawatt laser pulse  

SciTech Connect

The role of nanosecond duration pre-pulse pedestal (Amplified Spontaneous Emission (ASE) pre-pulse) in the propagation of 45 fs, 4 TW Ti:Sapphire laser pulse through a helium gas jet target has been investigated. We observed that the pre-pulse pedestal of about 1 ns duration and intensity 3 x 10{sup 12} W/cm{sup 2} creates pre-formed plasma with optical guiding channel like structure in the gas-jet at density around 3 x 10{sup 19} cm{sup -3}. Guiding of the 45 fs laser pulse (I{sub L} = 3 x 10{sup 18} W/cm{sup 2}) in the pre-formed plasma channel, over a distance much longer than the Rayleigh length was also observed. The guiding of the laser pulse resulted in the generation of high energy electron beam by laser wake-field acceleration of self-injected electrons. The accelerated electron beam was quasi-monoenergetic with peak energy up to 50 MeV, low divergence in the range of 3-6 mrad, and bunch charge up to 100 pC.

Sanyasi Rao, Bobbili; Chakera, Juzer Ali; Naik, Prasad Anant; Kumar, Mukund; Gupta, Parshotam Dass [Laser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013 (India)

2011-09-15

127

Laser wake-field acceleration in pre-formed plasma channel created by pre-pulse pedestal of terawatt laser pulse  

NASA Astrophysics Data System (ADS)

The role of nanosecond duration pre-pulse pedestal (Amplified Spontaneous Emission (ASE) pre-pulse) in the propagation of 45 fs, 4 TW Ti:Sapphire laser pulse through a helium gas jet target has been investigated. We observed that the pre-pulse pedestal of about 1 ns duration and intensity 3 × 1012 W/cm2 creates pre-formed plasma with optical guiding channel like structure in the gas-jet at density around 3 × 1019 cm-3. Guiding of the 45 fs laser pulse (IL = 3 × 1018 W/cm2) in the pre-formed plasma channel, over a distance much longer than the Rayleigh length was also observed. The guiding of the laser pulse resulted in the generation of high energy electron beam by laser wake-field acceleration of self-injected electrons. The accelerated electron beam was quasi-monoenergetic with peak energy up to 50 MeV, low divergence in the range of 3-6 mrad, and bunch charge up to 100 pC.

Sanyasi Rao, Bobbili; Chakera, Juzer Ali; Naik, Prasad Anant; Kumar, Mukund; Gupta, Parshotam Dass

2011-09-01

128

Active control of a cylinder wake flow by using a streamwise oscillating foil  

NASA Astrophysics Data System (ADS)

In this study, numerical experiments are carried out to control the vortex shedding of a circular cylinder by utilizing an oscillating foil. The thin foil of elliptic shape undergoes prescribed harmonic oscillations in the streamwise direction in the near wake region. This simplified model is intended to study how wake dynamics are modified via localized wake disturbance, and then to stabilize the global wake instability. The results show that, at proper gap spacing, the oscillating foil can completely suppress the wake unsteadiness and recover the recirculating bubble type flow. The global instability suppression is then established on the imposition of local symmetry into the reversed flow behind the cylinder. It is revealed that the dynamic interaction between the main shears layer and oscillatory boundary layers is responsible for the wake stabilization mechanism. In addition, the kinematic/dynamic parameters related to foil motions and flow properties are widely discussed to reveal their effects on the performance of wake stabilization and drag reduction.

Bao, Y.; Tao, J.

2013-05-01

129

Ionization suppression of Cl{sub 2} molecules in intense laser fields  

SciTech Connect

The strong field ionization of Cl{sub 2} molecules is investigated by using an ultrashort pulse Ti:sapphire laser. A spatial imaging technique is used in such measurements to reduce the effect of spatial integration. Cl{sub 2} shows strong ionization suppression as do other diatomic molecules having valence orbitals with antibonding symmetry (O{sub 2},S{sub 2}) when compared with the field ionization of atoms with nearly identical ionization potential. A more general molecular tunneling ionization model is proposed, and the calculations are in reasonable agreement with the measurements. Our results support that antibonding leads to ionization suppression, a trend that only F{sub 2} goes against and that needs to be further investigated.

Benis, E.P.; Xia, J.F.; Tong, X.M.; Faheem, M.; Zamkov, M.; Shan, B.; Richard, P.; Chang, Z. [J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506-2604 (United States)

2004-08-01

130

The disappearance of laminar and turbulent wakes in complex flows  

Microsoft Academic Search

The singular effects of steady large-scale external strain on the viscous wake generated by a rigid body and the overall flow field are analysed. In an accelerating flow strained at a positive rate, the vorticity field is annihilated owing to positive and negative vorticity either side of the wake centreline diffusing into one another and the volume flux in the

J. C. R. Hunt; I. Eames

2002-01-01

131

Nonlinear spacing and frequency effects of an oscillating cylinder in the wake of a stationary cylinder  

NASA Astrophysics Data System (ADS)

Nonlinear responses to a transversely oscillating cylinder in the wake of a stationary upstream cylinder are studied theoretically by using an immersed-boundary method at Re=100. Response states are investigated in the three flow regimes for a tandem-cylinder system: the ``vortex suppression'' regime, the critical spacing regime, and the ``vortex formation'' regime. When the downstream cylinder is forced to oscillate at a fixed frequency and amplitude, the response state of flow around the two cylinders varies with different spacing between the two cylinders, while in the same flow regime, the response state can change with the oscillating frequency and amplitude of the downstream cylinder. Based on velocity phase portraits, each of the nonlinear response states can be categorized into one of the three states in the order of increasing chaotic levels: lock-in, transitional, or quasiperiodic. These states can also be correlated with velocity spectral behaviors. The discussions are conducted using near-wake velocity phase portraits, spectral analyses, and related vorticity fields. A general trend in the bifurcation diagrams of frequency spacing shows the smaller the spacing, frequency, or amplitude, the less chaotic the response state of the system and more likely the downstream and upstream wakes are in the same response state. The system is not locked-in in any case when the spacing between the cylinders is larger than the critical spacing. The near-wake velocity spectral behaviors correspond to the nonlinear response states, with narrow-banded peaks shown at the oscillation frequency and its harmonics in the lock-in cases. High frequency harmonic peaks, caused by interactions between the upstream wake and the downstream oscillating cylinder, are reduced in the near-wake velocity spectra of the upstream cylinder when the spacing increases.

Yang, Xiaofan; Zheng, Zhongquan Charlie

2010-04-01

132

Outward expansion of the lunar wake: ARTEMIS observations  

NASA Astrophysics Data System (ADS)

Magnetohydrodynamics (MHD) predicts that lunar wake expands outward at magnetosonic velocities in all directions perpendicular to background solar wind; however, fluid theories emphasize that lunar wake expands outward at sound speeds mainly along the interplanetary magnetic field (IMF). Early observations supported the MHD predictions in the near-moon region despite lack of solar wind and IMF observations. Thanks to the special orbit design of the ARTEMIS mission, the solar wind conditions are well determined at the time of concurrent observations in the lunar wake. 164 wake crossings made by ARTEMIS are statistically studied in this paper. Observations indicated that, in either distant or near-Moon regions, the lunar wake expands outward at the fast MHD wave velocities. This simple model provides a powerful way to determine wake boundaries, particularly at large distances where the boundary signatures are indistinct, thus allowing further studies on the Moon-solar wind/crustal field-solar wind interactions.

Zhang, H.; Khurana, K. K.; Zong, Q.-G.; Kivelson, M. G.; Hsu, T.-S.; Wan, W. X.; Pu, Z. Y.; Angelopoulos, V.; Cao, X.; Wang, Y. F.; Shi, Q. Q.; Liu, W. L.; Tian, A. M.; Tang, C. L.

2012-09-01

133

A multi-beam, multi-terawatt Ti:sapphire laser system for laser wake-field acceleration studies  

Microsoft Academic Search

The Lasers, Optical Accelerator Systems Integrated Studies (L'OASIS) Lab of LBNL operates a highly automated and remotely controlled Ti:sapphire chirped pulse amplification (CPA) laser system that provides synchronized beams of 2x1.0 TW, 12 TW, and 100 TW peak- power, in a unique, radiation shielded facility. The system has been specially designed for studying high field laser-plasma interactions and particularly aimed

Csaba Tóth; Cameron G. R. Geddes; Jeroen van Tilborg; Eric Esarey; Carl B. Schroeder; Wim P. Leemans

134

A multi-beam, multi-terawatt Ti:sapphire laser system for laser wake-field acceleration studies  

Microsoft Academic Search

The Lasers, Optical Accelerator Systems Integrated Studies (L'OASIS) Lab of LBNL operates a highly automated and remotely controlled Ti:sapphire chirped pulse amplification (CPA) laser system that provides synchronized beams of 2×1.0 TW, 12 TW, and 100 TW peak-power, in a unique, radiation shielded facility. The system has been specially designed for studying high field laser-plasma interactions and particularly aimed for

Cs. Tóth; C. G. R. Geddes; J. van Tilborg; W. P. Leemans

2004-01-01

135

A multi-beam, multi-terawatt Ti:sapphire laser system for laser wake-field acceleration studies  

Microsoft Academic Search

The Lasers, Optical Accelerator Systems Integrated Studies (L’OASIS) Lab of LBNL operates a highly automated and remotely controlled Ti:sapphire chirped pulse amplification (CPA) laser system that provides synchronized beams of 2×1.0 TW, 12 TW, and 100 TW peak-power, in a unique, radiation shielded facility. The system has been specially designed for studying high field laser-plasma interactions and particularly aimed for

Cs. To´th; C. G. R. Geddes; J. van Tilborg; W. P. Leemans

2004-01-01

136

Nonlinear collisionless plasma wakes of small particles  

SciTech Connect

The wake behind a spherical particle smaller than the Debye length ({lambda}{sub De}) in flowing plasma is calculated using a particle-in-cell code. The results with different magnitudes of charge reveal substantial nonlinear effects down to values that for a floating particle would correspond to a particle radius {approx}10{sup -2{lambda}}{sub De}. The peak potential in the oscillatory wake structure is strongly suppressed by nonlinearity, never exceeding {approx}0.4 times the unperturbed ion energy. By contrast, the density peak arising from ion focusing can be many times the ambient. Strong heating of the ions occurs in the nonlinear regime. Direct ion absorption by the particle is not important for the far wake unless the radius exceeds 10{sup -1{lambda}}{sub De}, and is therefore never significant (for the far wake) in the linear regime. Reasonable agreement with full-scale linear response calculations are obtained in the linear regime. The wake wavelength is confirmed and an explanation, in terms of the conical potential structure, is proposed for experimentally-observed oblique alignment of different-sized grains.

Hutchinson, I. H. [Plasma Science and Fusion Center and Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2011-03-15

137

Low-mass Planets in Protoplanetary Disks with Net Vertical Magnetic Fields: The Planetary Wake and Gap Opening  

NASA Astrophysics Data System (ADS)

Some regions in protoplanetary disks are turbulent, while some regions are quiescent (e.g. the dead zone). In order to study how planets open gaps in both inviscid hydrodynamic disk (e.g. the dead zone) and the disk subject to magnetorotational instability (MRI), we carried out both shearing box two-dimensional inviscid hydrodynamical simulations and three-dimensional unstratified magnetohydrodynamical (MHD) simulations (having net vertical magnetic fields) with a planet at the box center. We found that, due to the nonlinear wave steepening, even a low mass planet can open gaps in both cases, in contradiction to the "thermal criterion" for gap opening. In order to understand if we can represent the MRI turbulent stress with the viscous ? prescription for studying gap opening, we compare gap properties in MRI-turbulent disks to those in viscous HD disks having the same stress, and found that the same mass planet opens a significantly deeper and wider gap in net vertical flux MHD disks than in viscous HD disks. This difference arises due to the efficient magnetic field transport into the gap region in MRI disks, leading to a larger effective ? within the gap. Thus, across the gap, the Maxwell stress profile is smoother than the gap density profile, and a deeper gap is needed for the Maxwell stress gradient to balance the planetary torque density. Comparison with previous results from net toroidal flux/zero flux MHD simulations indicates that the magnetic field geometry plays an important role in the gap opening process. We also found that long-lived density features (termed zonal flows) produced by the MRI can affect planet migration. Overall, our results suggest that gaps can be commonly produced by low mass planets in realistic protoplanetary disks, and caution the use of a constant ?-viscosity to model gaps in protoplanetary disks.

Zhu, Zhaohuan; Stone, James M.; Rafikov, Roman R.

2013-05-01

138

Plasma wake-field effects on high-current relativistic electron beam transport in the ion-focused regime  

NASA Astrophysics Data System (ADS)

Modulation of the beam current has recently been observed during ion-focused regime (IFR) transport of a high-power relativistic electron beam propagating through a low-density background plasma. Injecting a high-current, high-energy electron beam into an IFR channel immersed in a background plasma induces plasma oscillations. These background plasma oscillations, induced by the rise-time portion of the beam ejecting plasma electrons from the vicinity of the beam into the background plasma, give rise to a modulated axial electric field. This field travels with the beam leading to beam energy and current oscillations. In the experiment, a 1.7 MeV, 1 kA, rise-time-sharpened electron beam is propagated on a KrF excimer laser-produced IFR channel in trimethylamine (TMA) gas, which is immersed in a low-density plasma-filled transport tube. Experimental measurements, analytical theory, and detailed computer simulations are presented demonstrating modulation of this high-current relativistic electron beam near the low-density background plasma frequency.

Miller, J. D.; Schneider, R. F.; Weidman, D. J.; Nguyen, K. T.

1992-12-01

139

Analysis of rotor wake aerodynamics during maneuvering flight using a free-vortex wake methodology  

NASA Astrophysics Data System (ADS)

The problem of helicopter rotor wake aerodynamics during maneuvering flight conditions was analyzed using a time-accurate, free-vortex wake methodology. The free-vortex method consists of a Lagrangian representation of the rotor flow field using vortex elements, where the evolution of the flow field is simulated by tracking the free motion of these vortex elements and calculating their induced velocity field. Traditionally, free-vortex methods are inviscid, incompressible models, but in the present approach the viscous effects are incorporated using a viscous splitting method where the viscous and inviscid terms are modeled as successive sub-processes. The rotor aerodynamics and rigid blade flapping dynamics are closely coupled with the wake model and solved for in a consistent manner using the same numerical scheme. Validations of the methodology with experimental data were performed to study the wake response to perturbations in collective and cyclic pitch inputs. The numerical simulations captured all the essential wake dynamics observed in flow visualization. The predictions of the transient inflow and airloads response were found to be in excellent agreement with the available experimental measurements. It was observed that the rotor wake was extremely sensitive to perturbations in collective and cyclic blade pitch inputs. The characteristic wake response was found to be the bundling of the wake vorticity into a vortex ring structure. The evolution, convection and subsequent breakdown of this bundled ring of tip-vortices was found to be highly nonlinear, and occurs with a temporal lag. The nonlinear induced velocity field associated with unsteady wake evolution can cause considerable fluctuations in the rotor airloads time-history if the bundled tip-vortex structure comes into close proximity to the rotor blades. Furthermore, the interaction of these tip-vortices with the blades results in steep gradients in the rotor airloads across the rotor disk, thereby contributing to impulsive rotor noise. Several free-flight maneuver simulations were analyzed to gain better insight into the unsteady, nonlinear wake development under high-rate, large-amplitude maneuvers such as roll to starboard or port, roll reversals, and the quickstop maneuver. It is shown that the rotor wake response in almost all maneuvering flight conditions is highly nonlinear and emphasizes the need to accurately predict the transient wake aerodynamics to obtain accurate estimates of the unsteady rotor airloads and the resulting rotor acoustics.

Ananthan, Shreyas

140

Differential study on molecular suppressed ionization in intense linearly and circularly polarized laser fields  

SciTech Connect

We present a differential study on above-threshold ionization of the O{sub 2} (N{sub 2}) molecule as well as the companion atom Xe (Ar) (with close ionization potential) produced by linearly and circularly polarized laser fields (25 fs, 795 nm). The photoelectron angular distributions of the companion target are similar at the same laser condition. In both linearly and circularly polarized fields, we observe that the photoelectron yields of O{sub 2} are suppressed in the entire energy spectral range as compared with Xe with fully differential measurements, but not for the N{sub 2}-Ar pair. This is different from the prediction of photoelectron energy spectra by the model including the interference terms [Phys. Rev. Lett. 85, 2280 (2000)], from which the low-energy photoelectrons of O{sub 2} were expected to be strongly suppressed in both linearly and circularly polarized laser fields. Resorting to the basic strong-field ionization picture, we believe that the lower orbital-dependent multiphoton excitation or tunneling possibility of O{sub 2} as compared with Xe is responsible for this effect. High-resolution fully differential data pose a stringent test on the current strong-field calculations on molecules.

Deng Yongkai; Liu Yunquan; Liu Xianrong; Liu Hong; Yang Yudong; Wu Chengyin; Gong Qihuang [Department of Physics and State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871 (China)

2011-12-15

141

Optical Influence of Ship Wakes  

NASA Astrophysics Data System (ADS)

The optical variations observed within ship wakes are largely due to the generation of copious amounts of air bubbles in the upper ocean, a fraction of which accumulate as foam at the surface, where they release scavenged surfactants. Field experiments were conducted to test previous theoretical predictions of the variations in optical properties that result from bubble injection in the surface ocean. Variations in remote-sensing reflectance and size distribution of bubbles within the ship-wake zone were determined in three different optical water types: the clear equatorial Pacific Ocean, moderately turbid coastal waters, and very turbid coastal waters, the latter two of which were offshore of New Jersey. Bubbles introduced by moving vessels increased the backscattering in all cases, which in turn enhanced the reflectance over the entire visible and infrared wave bands. The elevated reflectance had different spectral characteristics in the three locations. The color of ship wakes appears greener in the open ocean, whereas little change in color was observed in near-coastal turbid waters, consistent with predictions. Colorless themselves, bubbles increase the reflected radiance and change the color of the ocean in a way that depends on the spectral backscattering and absorption of the undisturbed background waters. For remote observation from aircraft or satellite, the foam and added surfactants further enhance the reflectance to a degree dependent on the illumination and the viewing geometry.

Zhang, Xiaodong; Lewis, Marlon; Bissett, W. Paul; Johnson, Bruce; Kohler, Dave

2004-05-01

142

Suppression of Ultracold Neutron Depolarization on Material Surfaces with Magnetic Holding Fields  

NASA Astrophysics Data System (ADS)

The depolarization of Ultracold Neutrons(UCN) was measured within 1-m long, 2 3/4" diameter electropolished copper, diamondlike carbon-coated copper, and stainless steel guide tubes as a function of magnetic holding field. The UCN were trapped between a 6 Tesla solenoidal magnetic field and a 3/8" copper aperture. A series of Helmholtz coils produced a magnetic field over the length of the test guide of either 10 or 250 Gauss. The surface depolarization was observed to be suppressed at the higher holding field on the measured copper guides. These measurements will aid in the determination of the upper limit of depolarization of UCN in the UCN beta asymmetry measurement at LANL (UCNA) and in understanding the mechanisms for depolarization in non-magnetic guides.

Rios, Raymond

2009-05-01

143

Waking with the hypothalamus  

Microsoft Academic Search

An essential component of the whole-body homoeostasis provided by the hypothalamus is the management of available energy.\\u000a This includes the regulation of sleeping and waking, feeding and drinking, body temperature and activity, as well as the endocrinium.\\u000a The waking brain, in particular the cerebral cortex, needs to be activated through neuronal pathways ascending from the brainstem\\u000a reticular formation (ascending reticular

Helmut L. Haas; Jian-Sheng Lin

144

The Lunar Wake Current Systems  

NASA Astrophysics Data System (ADS)

Direct impact of the solar wind plasma with the non-conductive body of the Moon, with no atmosphere and no global magnetic field, neutralizes the plasma in the lunar day-side, leaves a plasma void and forms an expanding rarefaction region, confined into a plasma Mach cone downstream. We show that in the transition regions between the plasma void, the rarefaction region, and the interplanetary plasma there are three main currents flowing around these regions in the lunar wake. The generated currents induce magnetic fields within these regions, perturb the field lines there and confine the field perturbations within the lunar Mach cone. We use a three-dimensional, self-consistent hybrid model of plasma (particle ions and fluid electrons) to show the flow of these three currents. First we identify the different plasma regions, separated by the currents, then we show how the currents depend on the interplanetary magnetic field direction. Finally we discuss the current closures in the lunar wake.

Fatemi, Shahab; Holmström, Mats; Futaana, Yoshifumi; Barabash, Stas; Lue, Charles

2013-04-01

145

Acceleration of nonmonoenergetic electron bunches injected into a wake wave  

SciTech Connect

The trapping and acceleration of nonmonoenergetic electron bunches in a wake field wave excited by a laser pulse in a plasma channel is studied. Electrons are injected into the region of the wake wave potential maximum at a velocity lower than the phase velocity of the wave. The paper analyzes the grouping of bunch electrons in the energy space emerging in the course of acceleration under certain conditions of their injection into the wake wave and minimizing the energy spread for such electrons. The factors determining the minimal energy spread between bunch electrons are analyzed. The possibility of monoenergetic acceleration of electron bunches generated by modern injectors in a wake wave is analyzed.

Kuznetsov, S. V., E-mail: shenau@rambler.ru [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

2012-07-15

146

Bounding bubbles: The vertex representation of 3d group field theory and the suppression of pseudomanifolds  

NASA Astrophysics Data System (ADS)

Based on recent work on simplicial diffeomorphisms in colored group field theories, we develop a representation of the colored Boulatov model, in which the group field theory (GFT) fields depend on variables associated to vertices of the associated simplicial complex, as opposed to edges. On top of simplifying the action of diffeomorphisms, the main advantage of this representation is that the GFT Feynman graphs have a different stranded structure, which allows a direct identification of subgraphs associated to bubbles, and their evaluation is simplified drastically. As a first important application of this formulation, we derive new scaling bounds for the regularized amplitudes, organized in terms of the genera of the bubbles, and show how the pseudomanifold configurations appearing in the perturbative expansion are suppressed as compared to manifolds. Moreover, these bounds are proved to be optimal.

Carrozza, Sylvain; Oriti, Daniele

2012-02-01

147

An Analytical Model of Wake Deflection Due to Shear Flow  

Microsoft Academic Search

The main motivation behind this work is to create a purely analytical engineering model for wind turbine wake upward deflection due to shear flow, by developing a closed form solution of the velocity field due to an oblique vortex ring. The effectiveness of the model is evaluated by comparing the results with those of a free-wake model. The solution of

D. Micallef; C. J. Simao Ferreira; T. Sant; G. J. W. Van Bussel

2010-01-01

148

Assimilation Experiment of Lidar Measurements for Wake Turbulence  

Microsoft Academic Search

Numerical simulation of wake turbulence was performed by integrating the lidar measurements using four-dimensional variational method. A bogus vortex technique was adopted to ensure the existence of wake vortices in the flow field. The validation of the method was performed by an idealized test case using virtual lidar measurement which was produced by the reference simulation of a vortex pair.

Takashi Misaka; Takeshi Ogasawara; Shigeru Obayashi; Izumi Yamada; Yoshinori Okuno

2008-01-01

149

Population-wide bias of surround suppression in auditory spatial receptive fields of the owl's midbrain.  

PubMed

The physical arrangement of receptive fields (RFs) within neural structures is important for local computations. Nonuniform distribution of tuning within populations of neurons can influence emergent tuning properties, causing bias in local processing. This issue was studied in the auditory system of barn owls. The owl's external nucleus of the inferior colliculus (ICx) contains a map of auditory space in which the frontal region is overrepresented. We measured spatiotemporal RFs of ICx neurons using spatial white noise. We found a population-wide bias in surround suppression such that suppression from frontal space was stronger. This asymmetry increased with laterality in spatial tuning. The bias could be explained by a model of lateral inhibition based on the overrepresentation of frontal space observed in ICx. The model predicted trends in surround suppression across ICx that matched the data. Thus, the uneven distribution of spatial tuning within the map could explain the topography of time-dependent tuning properties. This mechanism may have significant implications for the analysis of natural scenes by sensory systems. PMID:22855796

Wang, Yunyan; Shanbhag, Sharad J; Fischer, Brian J; Peña, José L

2012-08-01

150

The Human Aerodynamic Wake  

NASA Astrophysics Data System (ADS)

The wake that trails behind a walking person in still air is, in effect, that of an irregular 3-D cylinder. At a brisk walking speed of 1.3 m/s (3 mph), the human wake is characterized by a Reynolds number of about 50,000. It is thus turbulent with underlying large-scale vortex motion. We show that buoyancy plays no role at this Reynolds number, even though it is dominant in the plume of a standing person. Computational Navier-Stokes solutions and laser-light-sheet experiments with a human subject reveal a large recirculation zone behind the torso and flow between the legs. The decay of a passive scalar introduced on the human body is found to be exponential with downstream distance. The volume flux in the human wake is roughly constant with downstream distance until the recirculation closes, whence it grows due to turbulent entrainment. Further experiments reveal the development of the wake from the human thermal plume as the Reynolds number (proportional to walking speed) is increased from zero to 50,000. These results pertain to the sensing of chemical traces in the wakes of walking persons for aviation security. Supported by FAA Grant 99-G-040.

Settles, Gary; Moyer, Zachary; Paterson, Eric; Edge, Brian

2003-11-01

151

Turbulent Elliptic Wakes  

NASA Astrophysics Data System (ADS)

This paper describes results of an experimental study on turbulent wake of an elliptic disk set normal to the main flow, whose major diameter is 2.0 or 3.0 minor diameters, Reynolds number being 2.0x104on the basis of the minor diameter D. Two periodic components of velocity fluctuations were found in the wake. One is centred around the minor plane, being due to the alternate shedding of rolled-up, hairpin-like vortices. The other is centred around the major plane, which is likely to be due to a meandering motion of the wake. The axis switching, which is a cross-over of half-widths in the major and minor planes plotted against the streamwise distance, occurred at approximately 4.0 D downstream of the disk. The mechanism of the axis switching is different from that in elliptic jets, and it is proposed that it is due to a difference in the growth rate of the fundamental Fourier modes in the minor and major planes. The structure of the wake is studied by flow visualization and a survey of the time-mean velocity, turbulence intensities and Reynolds shear stresses. Wavelet analysis of the velocity fluctuations disclosed a low-frequency unsteadiness in the wake. This unsteadiness has different representative frequencies in the major and minor planes, being approximately one-fifth of the frequency of the corresponding periodic component in both planes.

Kiya, M.; Abe, Y.

1999-10-01

152

Enhancement and decrease of critical current due to suppression of superconductivity by a magnetic field  

NASA Astrophysics Data System (ADS)

We present experimental results on the transport properties of a superconducting aluminum loop connected to reservoirs. As function of the applied magnetic field, an unexpected behavior is found—a steep enhancement (for temperatures close to the critical temperature) and a sharp drop (at lower temperatures) of the critical current at some value of the magnetic field Ba*(T) . These effects are a consequence of a sudden suppression of superconductivity at Ba=Ba* in the banks to which the loop is attached by the current leads. As a result, the normal metal-superconductor boundaries appear at the ends of the current leads and the quasiparticle distribution function f(E) in the superconductor deviates strongly from its equilibrium value. Calculations based on the Usadel equations show that the critical current should be enhanced at high temperature (due to the penetration of the normal current from the normal metal-superconductor boundaries), whereas at low temperatures, the suppression of the order parameter by the nonequilibrium f(E) dominates and the critical current decreases. The latter provides a direct experimental verification of the recently proposed mechanism of the destruction of superconductivity by an applied voltage [R. S. Keizer, M. G. Flokstra, J. Aarts, and T. M. Klapwijk, Phys. Rev. Lett. 96, 147002 (2006)].

Vodolazov, D. Y.; Golubovi?, D. S.; Peeters, F. M.; Moshchalkov, V. V.

2007-10-01

153

Wake survey techniques for objects with highly turbulent wakes  

Microsoft Academic Search

The primary objective of this study is to develop practical and accurate wake survey techniques for determining the drag of bluff bodies that have highly turbulent wakes. The commonly used wake survey method, the simplified Jones' equation with pneumatic probe measurements, was found to be inadequate in such cases. This study consisted of an experimental investigation of several wind-tunnel models,

Biao Lu

2003-01-01

154

Cylinder wakes in flowing soap films  

SciTech Connect

We present an experimental characterization of cylinder wakes in flowing soap films. From instantaneous velocity and thickness fields, we find the vortex-shedding frequency, mean-flow velocity, and mean-film thickness. Using the empirical relationship between the Reynolds and Strouhal numbers obtained for cylinder wakes in three dimensions, we estimate the effective soap-film viscosity and its dependence on film thickness. We also compare the decay of vorticity with that in a simple Rankine vortex model with a dissipative term to account for air drag. [copyright] [ital 1999] [ital The American Physical Society

Vorobieff, P.; Ecke, R.E. (Center for Nonlinear Studies, Condensed Matter and Thermal Physics Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)); Vorobieff, P. (Dynamic Experimentation Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States))

1999-09-01

155

Cylinder wakes in flowing soap films.  

PubMed

We present an experimental characterization of cylinder wakes in flowing soap films. From instantaneous velocity and thickness fields, we find the vortex-shedding frequency, mean-flow velocity, and mean-film thickness. Using the empirical relationship between the Reynolds and Strouhal numbers obtained for cylinder wakes in three dimensions, we estimate the effective soap-film viscosity and its dependence on film thickness. We also compare the decay of vorticity with that in a simple Rankine vortex model with a dissipative term to account for air drag. PMID:11970100

Vorobieff, P; Ecke, R E

1999-09-01

156

Waking Up to Waste  

ERIC Educational Resources Information Center

|All homes and schools produce waste. Children may have been astonished at how much people throw away, and this could be the "wake-up call" that arouses their interest. At Carymoor Environmental Centre (an Eco-Centre in South Somerset) getting children involved in active waste reduction and recycling is a priority. Carymoor tries to model waste…

Vrdlovcova, Jill

2005-01-01

157

Suppression of convection using gradient magnetic fields during crystal growth of NiSO4.6H2O  

NASA Astrophysics Data System (ADS)

A magnetic field was successfully used to suppress buoyancy driven convection during solution growth of a NiSO4.6H2O crystal. The disappearance of the convection plume and the expansion of the depletion zones, typical for crystal growth in the absence of gravity, were observed with schlieren microscopy when the product of magnetic field and field gradient corresponds to the condition that for all relevant concentrations buoyancy is compensated by paramagnetic counterforces. We show both theoretically and experimentally, that levitation of the growth solution is not the correct condition to suppress convection.

Poodt, P. W. G.; Heijna, M. C. R.; Tsukamoto, K.; de Grip, W. J.; Christianen, P. C. M.; Maan, J. C.; van Enckevort, W. J. P.; Vlieg, E.

2005-11-01

158

Suppression of Ultracold Neutron Depolarization on Material Surfaces with Magnetic Holding Fields  

NASA Astrophysics Data System (ADS)

Experiments involving polarized Ultracold Neutrons (UCN) for high precision measurements require the use of high Fermi potential materials with a low spin flip probability per bounce. Previous studies show that the spin flip probability for materials vary on the order of 10-3 to 10-6. In this study, the depolarization of UCN was measured within 1-m long, 2 3/4" diameter bare copper, electropolished copper, diamond-like carbon-coated copper, and stainless steel guide tubes as a function of the magnetic holding field. The UCN were trapped between a 6 Tesla solenoidal magnet and a copper plate. A series of Helmholtz coils produced a magnetic holding field over the length of the test guide at 10, 100, or 250 Gauss. The surface depolarization was observed to be suppressed at higher holding fields. These measurements will aid in the determination of an upper limit on depolarization of UCN in the UCNA beta asymmetry measurement at LANL and in understanding the mechanisms for depolarization in non-magnetic guides.

Rios, Raymond

2009-10-01

159

Human Factors in Field Experimentation Design and Analysis of Analytical Suppression Model.  

National Technical Information Service (NTIS)

The primary objective of this study was to provide a contribution to the phenomenon 'Suppression' as an aspect within the military environment. Analytical models explaining these aspects were developed in order to identify the influences to suppression. T...

M. P. Mueller K. H. Pietsch

1978-01-01

160

Role of the basal ganglia in the control of sleep and wakefulness.  

PubMed

The basal ganglia (BG) act as a cohesive functional unit that regulates motor function, habit formation, and reward/addictive behaviors, but the debate has only recently started on how the BG maintain wakefulness and suppress sleep to achieve all these fundamental functions of the BG. Neurotoxic lesioning, pharmacological approaches, and the behavioral analyses of genetically modified animals revealed that the striatum and globus pallidus are important for the control of sleep and wakefulness. Here, we discuss anatomical and molecular mechanisms for sleep-wake regulation in the BG and propose a plausible model in which the nucleus accumbens integrates behavioral processes with wakefulness through adenosine and dopamine receptors. PMID:23465424

Lazarus, Michael; Chen, Jiang-Fan; Urade, Yoshihiro; Huang, Zhi-Li

2013-04-24

161

Brain Wake-Ups  

NSDL National Science Digital Library

Wake-Up_Brain - Fire up those synapses each Monday morning. It's Monday morning and caffeine is slowly percolating into your system but your brain is still covered with weekend sludge. You need something to get those synapses firing, a brain booster to stimulate those billions of gray matter cells. You need Good Morning Thinkers! ... an absolutely free brain wake-up service offered to you by the Innovative Thinking Network, a professional membership association of leaders forging the revitalization of organizations through the powerful use of Innovation, Creativity and Group Thinking Skills. Every Monday morning subscribers receive a short, light-hearted message designed to help wipe away the fog and open the door to more powerful, creative thinking.

1997-01-01

162

Suppression of ambipolar behavior in metallic source/drain metal-oxide-semiconductor field-effect transistors  

NASA Astrophysics Data System (ADS)

We present a study on suppressing the ambipolar behavior of Schottky barrier metal-oxide-semiconductor field-effect transistors (MOSFET). Inserting a silicon nitride layer of appropriate thickness between the metallic source/drain electrodes and the silicon yields a low Schottky-barrier and simultaneously tunes the properties of the contact from metal-semiconductor-like to the behavior of a doped contact. Moreover, device characteristics of pseudo-MOSFETs reveal an efficient suppression of ambipolar behavior. Comparison with an alternative way of achieving low Schottky-barrier contacts, i.e., by inserting a strong dipole layer such as LiF between the metal and the silicon, reveals that the suppression is not a result of shifting the Fermi level closer to the conduction band but is caused by a reduction of metal-induced gap states. The trade-off between suppression of the ambipolar behavior, contact length and on-state current is investigated with simulations.

Ghoneim, H.; Knoch, J.; Riel, H.; Webb, D.; Björk, M. T.; Karg, S.; Lörtscher, E.; Schmid, H.; Riess, W.

2009-11-01

163

EEG microstates of wakefulness and NREM sleep.  

PubMed

EEG-microstates exploit spatio-temporal EEG features to characterize the spontaneous EEG as a sequence of a finite number of quasi-stable scalp potential field maps. So far, EEG-microstates have been studied mainly in wakeful rest and are thought to correspond to functionally relevant brain-states. Four typical microstate maps have been identified and labeled arbitrarily with the letters A, B, C and D. We addressed the question whether EEG-microstate features are altered in different stages of NREM sleep compared to wakefulness. 32-channel EEG of 32 subjects in relaxed wakefulness and NREM sleep was analyzed using a clustering algorithm, identifying the most dominant amplitude topography maps typical of each vigilance state. Fitting back these maps into the sleep-scored EEG resulted in a temporal sequence of maps for each sleep stage. All 32 subjects reached sleep stage N2, 19 also N3, for at least 1 min and 45 s. As in wakeful rest we found four microstate maps to be optimal in all NREM sleep stages. The wake maps were highly similar to those described in the literature for wakefulness. The sleep stage specific map topographies of N1 and N3 sleep showed a variable but overall relatively high degree of spatial correlation to the wake maps (Mean: N1 92%; N3 87%). The N2 maps were the least similar to wake (mean: 83%). Mean duration, total time covered, global explained variance and transition probabilities per subject, map and sleep stage were very similar in wake and N1. In wake, N1 and N3, microstate map C was most dominant w.r.t. global explained variance and temporal presence (ratio total time), whereas in N2 microstate map B was most prominent. In N3, the mean duration of all microstate maps increased significantly, expressed also as an increase in transition probabilities of all maps to themselves in N3. This duration increase was partly--but not entirely--explained by the occurrence of slow waves in the EEG. The persistence of exactly four main microstate classes in all NREM sleep stages might speak in favor of an in principle maintained large scale spatial brain organization from wakeful rest to NREM sleep. In N1 and N3 sleep, despite spectral EEG differences, the microstate maps and characteristics were surprisingly close to wakefulness. This supports the notion that EEG microstates might reflect a large scale resting state network architecture similar to preserved fMRI resting state connectivity. We speculate that the incisive functional alterations which can be observed during the transition to deep sleep might be driven by changes in the level and timing of activity within this architecture. PMID:22658975

Brodbeck, Verena; Kuhn, Alena; von Wegner, Frederic; Morzelewski, Astrid; Tagliazucchi, Enzo; Borisov, Sergey; Michel, Christoph M; Laufs, Helmut

2012-05-30

164

First lunar wake passage of ARTEMIS: Discrimination of wake effects and solar wind fluctuations by 3D hybrid simulations  

NASA Astrophysics Data System (ADS)

The spacecraft P1 of the new ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) mission passed the lunar wake for the first time on February 13, 2010. We present magnetic field and plasma data of this event and results of 3D hybrid simulations. As the solar wind magnetic field was highly dynamic during the passage, a simulation with stationary solar wind input cannot distinguish whether distortions were caused by these solar wind variations or by the lunar wake; therefore, a dynamic real-time simulation of the flyby has been performed. The input values of this simulation are taken from NASA OMNI data and adapted to the P1 data, resulting in a good agreement between simulation and measurements. Combined with the stationary simulation showing non-transient lunar wake structures, a separation of solar wind and wake effects is achieved. An anisotropy in the magnitude of the plasma bulk flow velocity caused by a non-vanishing magnetic field component parallel to the solar wind flow and perturbations created by counterstreaming ions in the lunar wake are observed in data and simulations. The simulations help to interpret the data granting us the opportunity to examine the entire lunar plasma environment and, thus, extending the possibilities of measurements alone: A comparison of a simulation cross section to theoretical predictions of MHD wave propagation shows that all three basic MHD modes are present in the lunar wake and that their expansion governs the lunar wake refilling process.

Wiehle, S.; Plaschke, F.; Motschmann, U.; Glassmeier, K.-H.; Auster, H. U.; Angelopoulos, V.; Mueller, J.; Kriegel, H.; Georgescu, E.; Halekas, J.; Sibeck, D. G.; McFadden, J. P.

2011-06-01

165

Electric field coupling suppression using via fences for magnetic near-field shielded-loop coil probes in low temperature co-fired ceramics  

Microsoft Academic Search

Two types of low-cost and robust magnetic near-field probes manufactured in low temperature co-fired ceramics (LTCC) are presented in this paper. The shielded-loop coil and via fences are used in the probes to provide better electric field coupling suppression. Type I probe is designed to receive horizontal magnetic field, via fences are inserted in the loop aperture and along sides

Yien-Tien Chou; Hsin-Chia Lu

2011-01-01

166

Aircraft Wake Vortices: From Fundamental Research to Operational Application  

NASA Astrophysics Data System (ADS)

Aircraft trailing vortices constitute both a kaleidoscope of instructive fluid dynamics phenomena and a challenge for the sustained development of the safety and capacity of the air-transportation system. This section gives an overview of the wake vortex issue commencing at its historical roots, proceeding with a sketch of the nature and characteristics of wake vortices resulting from field measurement and numerical simulation, and concluding with a depiction of the design and performance of wake vortex simulation systems established for the prediction of dynamic aircraft separations in different flight phases and for sensitivity and risk analysis.

Holzäpfel, Frank; Gerz, Thomas

167

RF interference suppression in a cardiac synchronization system operating in a high magnetic field NMR imaging system  

SciTech Connect

An electrocardiographic (ECG) unit suitable for cardiac-synchronized nuclear magnetic resonance imaging in high magnetic fields is presented. The unit includes lossy transmission lines as ECG leads in order to suppress radio frequency (RF) interference in the electrocardiogram. The unit's immunity to RF interference is demonstrated.

Damji, A.A.; Snyder, R.E.; Ellinger, D.C.; Witkowski, F.X.; Allen, P.S.

1988-11-01

168

Suppression of ionization instability in a magnetohydrodynamic plasma by coupling with a radio-frequency electromagnetic field  

NASA Astrophysics Data System (ADS)

We describe the suppression of ionization instability and the control of a magnetohydrodynamic electrical power-generating plasma by coupling with a radio-frequency (rf) electromagnetic field. The rf heating stabilizes the unstable plasma behavior and homogenizes the nonuniform plasma structure, whereby the power-generating performance is significantly improved.

Murakami, Tomoyuki; Okuno, Yoshihiro; Yamasaki, Hiroyuki

2005-05-01

169

Harmonics suppression of fields arising from vacuum chamber eddy currents with application to SSC low-energy-booster magnets  

NASA Astrophysics Data System (ADS)

An expression for eddy currents induced in a thin-walled conductor due to a time-dependent electromagnet field excitation is formulated, allowing subsequent analytical development of a closed form expression predicting field harmonics in ac iron-core multipole electromagnets arising from eddy currents in the vacuum chamber. A passive technique for harmonics suppression is presented with specific application to the design of the Superconducting Super Collider (SSC) low-energy-booster (LEB) magnets.

Schlueter, R. D.; Halbach, K.

1994-07-01

170

Temporal study of wake formation behind a conducting body  

SciTech Connect

The temporal evolution of the wake of a conducting body is studied experimentally in a pulsed plasma device. Three-dimensional measurements of the plasma potential, density, particle energy distribution, and ion currents are measured throughout the near- and mid-wake regions during the wake formation. It is found that the potential behind the conducting body is initially negative. This negative potential is caused by the higher mobility of the electrons, allowing them to flow into the ion free wake region. The negative potential in the wake region induces an electric field that pulls ions into the region behind the conducting body. However, the dominant factor in determining the length of the near wake is the thermal energy spread of the ions. At later times, as the sheath forms around the conducting body, ions are deflected by the potential gradient in the sheath region. This deflection, in addition to the thermal energy spread of the ions, determines the length of the near wake.

Meassick, S.; Chan, C.; Qian, Y.; Sroda, T.; Azar, T.; Allen, R.C. (Northeastern Univ., Boston, MA (USA))

1991-08-01

171

Perceptual suppression revealed by adaptive multi-scale entropy analysis of local field potential in monkey visual cortex.  

PubMed

Generalized flash suppression (GFS), in which a salient visual stimulus can be rendered invisible despite continuous retinal input, provides a rare opportunity to directly study the neural mechanism of visual perception. Previous work based on linear methods, such as spectral analysis, on local field potential (LFP) during GFS has shown that the LFP power at distinctive frequency bands are differentially modulated by perceptual suppression. Yet, the linear method alone may be insufficient for the full assessment of neural dynamic due to the fundamentally nonlinear nature of neural signals. In this study, we set forth to analyze the LFP data collected from multiple visual areas in V1, V2 and V4 of macaque monkeys while performing the GFS task using a nonlinear method - adaptive multi-scale entropy (AME) - to reveal the neural dynamic of perceptual suppression. In addition, we propose a new cross-entropy measure at multiple scales, namely adaptive multi-scale cross-entropy (AMCE), to assess the nonlinear functional connectivity between two cortical areas. We show that: (1) multi-scale entropy exhibits percept-related changes in all three areas, with higher entropy observed during perceptual suppression; (2) the magnitude of the perception-related entropy changes increases systematically over successive hierarchical stages (i.e. from lower areas V1 to V2, up to higher area V4); and (3) cross-entropy between any two cortical areas reveals higher degree of asynchrony or dissimilarity during perceptual suppression, indicating a decreased functional connectivity between cortical areas. These results, taken together, suggest that perceptual suppression is related to a reduced functional connectivity and increased uncertainty of neural responses, and the modulation of perceptual suppression is more effective at higher visual cortical areas. AME is demonstrated to be a useful technique in revealing the underlying dynamic of nonlinear/nonstationary neural signal. PMID:23578055

Hu, Meng; Liang, Hualou

2013-03-03

172

Speech-induced suppression of evoked auditory fields in children who stutter  

Microsoft Academic Search

Auditory responses to speech sounds that are self-initiated are suppressed compared to responses to the same speech sounds during passive listening. This phenomenon is referred to as speech-induced suppression, a potentially important feedback-mediated speech-motor control process. In an earlier study, we found that both adults who do and do not stutter demonstrated a reduced amplitude of the auditory M50 and

Deryk S. Beal; Maher A. Quraan; Douglas O. Cheyne; Margot J. Taylor; Vincent L. Gracco; Luc F. De Nil

2011-01-01

173

Suppression of guidance force decay of HTS bulk exposed to AC magnetic field perturbation in a maglev vehicle system  

NASA Astrophysics Data System (ADS)

Superconducting maglev vehicle was one of the most promising applications of HTS bulks. In such a system, the HTS bulks were always exposed to AC external magnetic field, which was generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, it was observed that the guidance force of the YBCO bulk over the NdFdB guideway used in the high-temperature superconducting maglev vehicle system was decayed by the application of the AC external magnetic field. In this paper, we adopted a method to suppress the decay by altering the field-cooled height of the bulk. From the experimental results, it was found that the decay rate of the guidance force was smaller at lower field-cooled height. So we could suppress the guidance force decay of HTS bulk exposed to AC external magnetic field perturbation in the maglev vehicle system by reducing the field-cooled height of the bulk. Furthermore, all the experimental results in this paper were explained based on Bean critical-state model.

Zhang, Longcai; Wang, Suyu; Wang, Jiasu

2009-07-01

174

The effect of propranolol on cAMP concentration in the rat preoptic region during the wake-sleep cycle.  

PubMed

In control conditions preoptic cAMP concentration during wakefulness was significantly higher than during synchronized sleep. No differences in nucleotide concentration were observed in the cerebral cortex. Propranolol decreases brain cAMP concentration. This change was associated with the suppression of the difference observed between wakefulness and synchronized sleep in the preoptic region. PMID:2547404

Perez, E; Zamboni, G; Amici, R; Fadiga, L; Calasso, M; Parmeggiani, P L

1989-01-01

175

Speech-induced suppression of evoked auditory fields in children who stutter.  

PubMed

Auditory responses to speech sounds that are self-initiated are suppressed compared to responses to the same speech sounds during passive listening. This phenomenon is referred to as speech-induced suppression, a potentially important feedback-mediated speech-motor control process. In an earlier study, we found that both adults who do and do not stutter demonstrated a reduced amplitude of the auditory M50 and M100 responses to speech during active production relative to passive listening. It is unknown if auditory responses to self-initiated speech-motor acts are suppressed in children or if the phenomenon differs between children who do and do not stutter. As stuttering is a developmental speech disorder, examining speech-induced suppression in children may identify possible neural differences underlying stuttering close to its time of onset. We used magnetoencephalography to determine the presence of speech-induced suppression in children and to characterize the properties of speech-induced suppression in children who stutter. We examined the auditory M50 as this was the earliest robust response reproducible across our child participants and the most likely to reflect a motor-to-auditory relation. Both children who do and do not stutter demonstrated speech-induced suppression of the auditory M50. However, children who stutter had a delayed auditory M50 peak latency to vowel sounds compared to children who do not stutter indicating a possible deficiency in their ability to efficiently integrate auditory speech information for the purpose of establishing neural representations of speech sounds. PMID:21095231

Beal, Deryk S; Quraan, Maher A; Cheyne, Douglas O; Taylor, Margot J; Gracco, Vincent L; De Nil, Luc F

2010-11-21

176

Speech-induced suppression of evoked auditory fields in children who stutter  

PubMed Central

Auditory responses to speech sounds that are self-initiated are suppressed compared to responses to the same speech sounds during passive listening. This phenomenon is referred to as speech-induced suppression, a potentially important feedback-mediated speech-motor control process. In an earlier study, we found that both adults who do and do not stutter demonstrated reduced amplitude of the auditory M50 and M100 responses to speech during active production relative to passive listening. It is unknown if auditory responses to self-initiated speech-motor acts are suppressed in children or if the phenomenon differs between children who do and do not stutter. As stuttering is a developmental speech disorder, examining speech-induced suppression in children may identify possible neural differences underlying stuttering close to its time of onset. We used magnetoencephalography to determine the presence of speech-induced suppression in children and to characterize the properties of speech-induced suppression in children who stutter. We examined the auditory M50 as this was the earliest robust response reproducible across our child participants and the most likely to reflect a motor-to-auditory relation. Both children who do and do not stutter demonstrated speech-induced suppression of the auditory M50. However, children who stutter had a delayed auditory M50 peak latency to vowel sounds compared to children who do not stutter indicating a possible deficiency in their ability to efficiently integrate auditory speech information for the purpose of establishing neural representations of speech sounds.

Beal, Deryk S.; Quraan, Maher A.; Cheyne, Douglas O.; Taylor, Margot J.; Gracco, Vincent L.; De Nil, Luc F.

2011-01-01

177

Momentum transfer between the Io plasma wake and Jupiter's ionosphere  

NASA Astrophysics Data System (ADS)

The interaction between Io and Jupiter is dramatically illustrated by recent ultraviolet and infrared imaging of Jupiter's ionosphere. Bright auroral emissions are observed at the base of Io's flux tube with emissions at the footprint of Io's wake extending large distances downstream (roughly 100° around Jupiter). We propose as a possible explanation for the persisting wake emissions a subcorotating torus flux tube downstream from Io that results in high-latitude parallel electric fields. The transfer of momentum to the subcorotating Iogenic plasma from first the corotating torus and eventually the Jovian ionosphere via the Alfvénic interaction result in intense field-aligned currents which can lead to the formation of parallel electric fields. By comparing the field-aligned current density of the initial Alfvénic disturbance generated by the stagnated flow in Io's wake to the required current density for steady state acceleration of the flux tube we infer a current limitation, or momentum decoupling, caused by a high-latitude field-aligned potential drop. As a result, the subcorotating flux tube is partially decoupled from the Jovian ionosphere and auroral emissions persist for large distances downstream of the initial Io-disturbed flux tube. Model results suggest that the extended wake emissions are initially driven by a ˜70 kV cross-wake potential, which is consistent with observed auroral emissions caused by electron precipitation with energy on the order of tens of keV.

Delamere, P. A.; Bagenal, F.; Ergun, R.; Su, Y.-J.

2003-06-01

178

Field induced suppression of the vortex lattice melting transition in twinned YBa2Cu3O7-?  

NASA Astrophysics Data System (ADS)

We present magneto-resistance data for a high quality, twinned YBaCu3O7-? crystal, taken with the current applied along the ab plane. The crystal was examined at a number of angles to an applied magnetic field, of up to 20T, in order to observe the influence of correlated and point-like disorder on the vortex dynamics. When the applied field was orientated at 15° to the crystalline c-axis (? = 15°), for fields below H* = 12T, we observed the kink in ?(T) associated with vortex lattice melting. We found that when the field exceeded this value, there was a complete suppression of this kink and the ?(T) curves resembled those of crystals with extensive point disorder. This suppression in melting occurs abruptly between 11T and 12T. The melting transition is recovered when the angle between the c-axis and the field is increased. An analysis of features around 12T in ?(T) and ?(?) has been performed for a number of fields and angles.

Langan, R. M.; Gordeev, S. N.; Oussena, M.; Pinfold, S.; de Groot, P. A. J.; Jansen, L.; Gagnon, R.; Taillefer, L.

1997-08-01

179

Wake survey techniques for objects with highly turbulent wakes  

NASA Astrophysics Data System (ADS)

The primary objective of this study is to develop practical and accurate wake survey techniques for determining the drag of bluff bodies that have highly turbulent wakes. The commonly used wake survey method, the simplified Jones' equation with pneumatic probe measurements, was found to be inadequate in such cases. This study consisted of an experimental investigation of several wind-tunnel models, a theoretical analysis of turbulence effects on pressure measurements, and an analysis of wake drag equations. The experimental investigation was performed in the Illinois 3- by 4-foot low-speed wind tunnel. In the test, the wake of a 1-inch diameter cylinder and two airfoils, an S809 and NACA 0012, with and without various ice simulations were surveyed in detail using several Pitot-static probes with different nose shapes and an X-hotwire. The cylinder results were used to validate the wake survey techniques. The drag of the airfoils with and without ice accretions was determined using the validated wake survey techniques. A theoretical analysis of the turbulence effect on total and static pressure measurements was presented and compared with experimental data. Methods for correcting the turbulence effect on pressure measurements were provided, and a technique for estimating the turbulence kinetic pressure using the uncorrected pressure measurements was developed. Turbulence was also found to play an important role in drag determination through Reynolds stresses and static pressure deficit in the wake. A new wake drag equation was derived to include the turbulence effects. It was found the turbulence contribution to profile drag was over 17% in the cylinder test, and over 10% in the test of airfoils with ice accretions. This dissertation for the first time analyzed the turbulence effect on the simplified Jones' equation with measurements using a Pitot probe, and found that this method includes a portion of the turbulence effect into account implicitly, depending on the nose shape of the probe. A method for estimating this implicit correction was developed. Finally, wake survey techniques for determining the drag of objects with highly turbulent wakes were recommended.

Lu, Biao

180

Interplay between Kondo suppression and Lifshitz transitions in YbRh2Si2 at high magnetic fields.  

PubMed

We investigate the magnetic field dependent thermopower, thermal conductivity, resistivity, and Hall effect in the heavy fermion metal YbRh2Si2. In contrast to reports on thermodynamic measurements, we find in total three transitions at high fields, rather than a single one at 10 T. Using the Mott formula together with renormalized band calculations, we identify Lifshitz transitions as their origin. The predictions of the calculations show that all experimental results rely on an interplay of a smooth suppression of the Kondo effect and the spin splitting of the flat hybridized bands. PMID:23829750

Pfau, H; Daou, R; Lausberg, S; Naren, H R; Brando, M; Friedemann, S; Wirth, S; Westerkamp, T; Stockert, U; Gegenwart, P; Krellner, C; Geibel, C; Zwicknagl, G; Steglich, F

2013-06-19

181

Irregular sleep-wake syndrome  

MedlinePLUS

... have a different condition, such as shift work sleep disorder or jet lag syndrome. ... Zee PC, Vitello MV. Circadian rhythm sleep disorder: irregular sleep wake rhythm. Sleep Med Clin 4;2009:213-218.

182

The Sleep–Wakefulness Cycle  

Microsoft Academic Search

\\u000a Wakefulness (W) is necessary for a thoughtful and precise knowledge of things, allowing us to recognize our essential attributes\\u000a and the changes that we experience in ourselves. We spend about two-thirds of our life in W. This state is circadian and homeostatically\\u000a regulated and precisely meshed with sleep into the sleep–wakefulness cycle (SWC). Sleep is also a necessary, active, periodic,

Fernando Reinoso-Suárez; Isabel Andrés; Miguel Garzón

183

The waking brain: an update  

Microsoft Academic Search

Wakefulness and consciousness depend on perturbation of the cortical soliloquy. Ascending activation of the cerebral cortex\\u000a is characteristic for both waking and paradoxical (REM) sleep. These evolutionary conserved activating systems build a network\\u000a in the brainstem, midbrain, and diencephalon that contains the neurotransmitters and neuromodulators glutamate, histamine,\\u000a acetylcholine, the catecholamines, serotonin, and some neuropeptides orchestrating the different behavioral states. Inhibition

Jian-Sheng Lin; Christelle Anaclet; Olga A. Sergeeva; Helmut L. Haas

2011-01-01

184

RNA interference suppression of lignin biosynthesis increases fermentable sugar yields for biofuel production from field-grown sugarcane.  

PubMed

The agronomic performance, cell wall characteristics and enzymatic saccharification efficiency of transgenic sugarcane plants with modified lignin were evaluated under replicated field conditions. Caffeic acid O-methyltransferase (COMT) was stably suppressed by RNAi in the field, resulting in transcript reduction of 80%-91%. Along with COMT suppression, total lignin content was reduced by 6%-12% in different transgenic lines. Suppression of COMT also altered lignin composition by reducing syringyl units and p-coumarate incorporation into lignin. Reduction in total lignin by 6% improved saccharification efficiency by 19%-23% with no significant difference in biomass yield, plant height, stalk diameter, tiller number, total structural carbohydrates or brix value when compared with nontransgenic tissue culture-derived or transgenic control plants. Lignin reduction of 8%-12% compromised biomass yield, but increased saccharification efficiency by 28%-32% compared with control plants. Biomass from transgenic sugarcane lines that have 6%-12% less lignin requires approximately one-third of the hydrolysis time or 3- to 4-fold less enzyme to release an equal or greater amount of fermentable sugar than nontransgenic plants. Reducing the recalcitrance of lignocellulosic biomass to saccharification by modifying lignin biosynthesis is expected to greatly benefit the economic competitiveness of sugarcane as a biofuel feedstock. PMID:23551338

Jung, Je Hyeong; Vermerris, Wilfred; Gallo, Maria; Fedenko, Jeffrey R; Erickson, John E; Altpeter, Fredy

2013-04-02

185

Wake potentials of the ILC Interaction Region  

SciTech Connect

The vacuum chamber of the ILC Interaction Region (IR) is optimized for best detector performance. It has special shaping to minimize additional backgrounds due to the metal part of the chamber. Also, for the same reason this thin vacuum chamber does not have water cooling. Therefore, small amounts of power, which may be deposited in the chamber, can be enough to raise the chamber to a high temperature. One of the sources of 'heating' power is the electromagnetic field of the beam. This field diffracts by non-regularities of the beam pipe and excites free-propagating fields, which are then absorbed by the pipe wall. In addition we have a heating power of the image currents due to finite conductivity of the metallic wall. We will discuss these effects as updating the previous results. The conclusions of this report are: (1) The amount of the beam energy loss in IR is almost equal to the energy loss in one ILC (TESLA) accelerating cryo-module; (2) Addition energy spread at IR is very small; (3) Spectrum of the wake fields is limited 300 GHz; (4) Average power of the wake fields excited in IR is 30 W for nominal ILC parameters; and (5) Pulse power in this case is 6 kilowatts.

Novokhatski, A.; /SLAC

2011-08-16

186

Experimental estimation of a D-shaped cylinder wake using body-mounted sensors  

Microsoft Academic Search

The effectiveness of a small array of body-mounted sensors, for estimation and eventually feedback flow control of a D-shaped\\u000a cylinder wake is investigated experimentally. The research is aimed at suppressing unsteady loads resulting from the von-Kármán\\u000a vortex shedding in the wake of bluff-bodies at a Reynolds number range of 100–1,000. A low-dimensional proper orthogonal decomposition\\u000a (POD) procedure was applied to

Oksana Stalnov; Vitali Palei; Ilan Fono; Kelly Cohen; Avi Seifert

2007-01-01

187

The Computer Code NOVO for the Calculation of Wake Potentials of the Very Short Ultra-relativistic Bunches  

SciTech Connect

The problem of electromagnetic interaction of a beam and accelerator elements is very important for linear colliders, electron-positron factories, and free electron lasers. Precise calculation of wake fields is required for beam dynamics study in these machines. We describe a method which allows computation of wake fields of the very short bunches. Computer code NOVO was developed based on this method. This method is free of unphysical solutions like ''self-acceleration'' of a bunch head, which is common to well known wake field codes. Code NOVO was used for the wake fields study for many accelerator projects all over the world.

Novokhatski, Alexander; /SLAC

2005-12-01

188

Echo characteristic analysis of the nonequilibrium wakes of reentry vehicle  

NASA Astrophysics Data System (ADS)

The article makes use of a method to calculate the flow fields of pure air nonequilibrium reentry vehicle wakes. It analyzes the effects of wake plasma body fields on radar wave frequencies. In conjunction with this, it takes a step further in calculations of radar scattering cross sections under several types of elevation conditions. It explains several important factors influencing cross section size and distribution. Analyses and calculations clearly show that, after taking the Reynolds number, which is verified with the diameter of the bottom section or base of the object and environmental parameters, and arriving at turning point or transition values in fully developed turbulent flow wakes, it is possible to show the appearance of the phenomenon of abrupt increase in scattering cross sections.

Jiayu, Niu

1992-01-01

189

Kirchhoff's Integral Representation and a Cavity Wake Potential  

SciTech Connect

A method is proposed for the calculation of the short-range wake field potentials of an ultra-relativistic bunch passing near some irregularities in a beam pipe. The method is based on the space-time domain integration of Maxwell's equations using Kirchhoff's formulation. We demonstrate this method on two cases where we obtain the wake potentials for the energy loss of a bunch traversing an iris-collimator in a beam pipe and for a cavity. Likewise, formulas are derived for Green's functions that describe the transverse force action of wake fields. Simple formulas for the total energy loss of a bunch with a Gaussian charge density distribution are derived as well. The derived estimates are compared with computer results and predictions of other models.

Novokhatski, Alexander; /SLAC

2012-02-17

190

Synergistic Effects of Turbine Wakes and Atmospheric Stability on Power Production at an Onshore Wind Farm  

Microsoft Academic Search

This report examines the complex interactions between atmospheric stability and turbine-induced wakes on downwind turbine wind speed and power production at a West Coast North American multi-MW wind farm. Wakes are generated when the upwind flow field is distorted by the mechanical movement of the wind turbine blades. This has two consequences for downwind turbines: (1) the downwind turbine encounters

S Wharton; J K Lundquist; N Marjanovic

2012-01-01

191

Detailed structure and dynamics in particle-in-cell simulations of the lunar wake  

Microsoft Academic Search

The solar wind plasma from the Sun interacts with the Moon, generating a wake structure behind it, since the Moon is to a good approximation an insulator, has no intrinsic magnetic field and a very thin atmosphere. The lunar wake in simplified geometry has been simulated via a 112D electromagnetic particle-in-cell code, with high resolution in order to resolve the

Paul C. Birch; Sandra C. Chapman

2001-01-01

192

Measurements in a Two Dimensional Wake Merging into a Boundary Layer.  

National Technical Information Service (NTIS)

Extensive measurements of mean and fluctuating quantities in a two dimensional wake shed from flat plate and in the flow field of a two dimensional wake merging into a boundary layer are described. The experiments were carried out in a low speed wind tunn...

P. J. Pot

1979-01-01

193

Tomographic particle image velocimetry of desert locust wakes: instantaneous volumes combine to reveal hidden vortex elements and rapid wake deformation.  

PubMed

Aerodynamic structures generated by animals in flight are unstable and complex. Recent progress in quantitative flow visualization has advanced our understanding of animal aerodynamics, but measurements have hitherto been limited to flow velocities at a plane through the wake. We applied an emergent, high-speed, volumetric fluid imaging technique (tomographic particle image velocimetry) to examine segments of the wake of desert locusts, capturing fully three-dimensional instantaneous flow fields. We used those flow fields to characterize the aerodynamic footprint in unprecedented detail and revealed previously unseen wake elements that would have gone undetected by two-dimensional or stereo-imaging technology. Vortex iso-surface topographies show the spatio-temporal signature of aerodynamic force generation manifest in the wake of locusts, and expose the extent to which animal wakes can deform, potentially leading to unreliable calculations of lift and thrust when using conventional diagnostic methods. We discuss implications for experimental design and analysis as volumetric flow imaging becomes more widespread. PMID:22977102

Bomphrey, Richard J; Henningsson, Per; Michaelis, Dirk; Hollis, David

2012-09-12

194

Drastic high magnetic field effect on suppression of Escherichia coli death  

Microsoft Academic Search

When Escherichia coli B was aerobically grown in a medium containing one-fourth the concentration of the LB medium supplemented with glutamic acid at 43°C under an inhomogeneous 5.2–6.1 T magnetic field, the number of cells in the stationary phase under the high magnetic field was 100,000 times higher than that under a geomagnetic field. The finding that the amount of

Shin-ichiro Horiuchi; Yoshimasa Ishizaki; Kazumasa Okuno; Takashi Ano; Makoto Shoda

2001-01-01

195

Suppression of drinking by exposure to a high-strength static magnetic field  

Microsoft Academic Search

High-strength static magnetic fields of 7 T and above have been shown to have both immediate and delayed effects on rodents, such as the induction of locomotor circling and the acquisition of conditioned taste aversions. In this study, the acute effects of magnet field exposure on drinking were examined. Exposure to a 14.1-T magnetic field for as little as 5 min significantly

Thomas A. Houpt; Jennifer A. Cassell; Christina Riccardi; Bumsup Kwon; James C. Smith

2007-01-01

196

Approaches to Validation of CFD Models for Far Ship Wake  

NASA Astrophysics Data System (ADS)

The centerline wake of surface ships can extend to tens of kilometers on synthetic aperture radar (SAR) images. However, the hydrodynamics of far wakes of ships are not well understood. Our assumption is that far from the ship, the pattern of flows comprising the wake is represented by longitudinal coherent vortices, which gross parameters only slowly change in the direction along the wake. In order to model this process, we have run a set of non-hydrostatic simulations. The simulations also included dynamics of freshwater plumes in the upper ocean because such types of formations often produce sharp fronts, which can be confused with ship wakes. We have used 2D and 3D setups with slippery and free upper boundary and with several turbulence closure schemes including k-?, standard LES, and Hybrid LES. The models have been implemented in CFD Fluent and simulated such processes as wind-wake and wind-plume interactions and formation of sharp frontal lines on the sea surface. In order to justify the choice of grid and model parameters, we have performed a series of validation tests. These tests included grid and time convergence, sensitivity to geometric parameters, and comparison to available experimental data including photo and SAR images of ship wakes. The Hybrid LES turbulence model has demonstrated a more realistic performance than the other two tested turbulence closure models. The application of CFD to these problems has resulted in a qualitative level of information. Providing information on the level of absolute quantities requires validation with the data from specialized field and laboratory experiments.

Fujimura, A.; Soloviev, A.

2008-12-01

197

Numerical Simulations of the Wake of a Maneuvering Body in a Stratified Fluid  

NASA Astrophysics Data System (ADS)

The turbulent wake that exits behind a submersed body moving in a stratified fluid is the subject of many experimental and numerical investigations, no doubt due to its great importance to the field of submersible vehicle design and operation. In practice a submersible body moves at a constant speed, but frequently experiences unsteady motion (i.e. acceleration, deceleration, change in direction). However, this case has received little attention and instead other idealized flows more amenable to the current experimental and numerical tools available are used as surrogate flows to make inferences about characteristics of the wake. The maneuvers are characterized by the ratio of the thrust and drag coefficients and a geometric factor relating the thrust and drag regions. Results for the maneuvering wake include wake height, wake width, peak defect velocity for 1wake, 1 and are presented. In the far wake, x/D > 100, two and three dimensional contours and isosurfaces of the vertical vorticity are presented. Differences between the maneuvering wake and the more well understood towed wake will be highlighted and discussed in terms of the aforementioned quantities.

Brucker, Kyle; Sarkar, Sutanu

2008-11-01

198

Intergrain forces in low-Mach-number plasma wakes.  

PubMed

Large-scale particle-in-cell calculations of the plasma wake interactions of two negatively charged grains smaller than the Debye length are carried out using the coptic code over a wide range of subsonic plasma flow velocities. In plasmas with the temperature ratio T(e)/T(i)=100, it is found that a single grain's oscillatory wake disappears for flow Mach numbers M less than approximately 0.3, which is the parameter regime where Landau damping is expected to be strong. Neutral collisions suppress potential oscillations above M=0.3, but not the trailing attractive potential peak caused by ion focusing. The transverse (grain-aligning) force on a downstream particle in the wake of another is obtained rigorously from the code in three-dimensional simulations. It shows general agreement with the force that would be deduced from the single-grain wake potential gradient. Except for relatively large grains in the nonlinear collisional regime, the grain-aligning force is very small for slow flow. PMID:23005230

Hutchinson, I H

2012-06-28

199

Oral gabapentin suppresses pentylenetetrazole-induced seizure-like behavior and cephalic field potential in adult zebrafish.  

PubMed

We report the effect of orally administered gabapentin (GBP) on pentylenetetrazole (PTZ)-induced seizure-like activity in adult zebrafish. Zebrafish were pretreated with vehicle or GBP using a novel method of precise oral administration, followed by an intraperitoneal administration of PTZ. Behavioral assessment was carried out using locomotion-based video-tracking analysis and seizure score assignment using visual observation. Cephalic field potential recordings of the zebrafish brain were conducted using an electrical data acquisition system. Orally administered GBP significantly suppressed the seizure-like locomotor activity and strong slow-wave (~3Hz) activity in the cephalic field potential caused by PTZ. This work is the first report of the activity of an orally delivered anticonvulsant in adult zebrafish. Our study provides behavioral and physiological evidence in support of an adult zebrafish model for studying seizures including excitotoxic brain injury and a novel in vivo framework for the evaluation of pharmacological modulators of epilepsy. PMID:23466252

Banote, Rakesh Kumar; Koutarapu, Srinivas; Chennubhotla, Keerthana Sarma; Chatti, Kiranam; Kulkarni, Pushkar

2013-03-05

200

Total Suppression of Superconductivity by High Magnetic Fields in YBa2Cu3O6.6  

NASA Astrophysics Data System (ADS)

We have studied the variation of transverse magnetoresistance of underdoped YBCO6.6 crystals, either pure or with reduced Tc down to 3.5 K by electron irradiation, in fields up to 60 T. We find evidence that the superconducting fluctuation contribution to the conductivity is suppressed only above a threshold field Hc'(T), which is found to vanish at Tc'>Tc. In the pure YBCO6.6 sample, Hc' is already 50 T at Tc. We find that increasing disorder weakly depresses Hc'(0), Tc', and T?, the onset of the Nernst signal. Thus, these energy scales appear more characteristic of the 2D local pairing than the pseudogap temperature which is not modified by disorder.

Rullier-Albenque, F.; Alloul, H.; Proust, Cyril; Lejay, P.; Forget, A.; Colson, D.

2007-07-01

201

Suppression of error-field-induced magnetic islands by Alfvén resonance effect in rotating plasmas  

Microsoft Academic Search

Error-field penetration is numerically studied in cylindrical tokamak geometry with plasma rotation. For a static error field, non-rotating magnetic islands are generated in the steady state. The penetrated perturbed magnetic flux is effectively reduced by the plasma rotation at small resistivity. Twin current sheets are formed at the Alfvén resonance positions when the plasma rotation is fast enough, and thereby

M. Furukawa; L.-J. Zheng

2009-01-01

202

Suppressing the Excitability of Spinal Motoneurons by Extracellularly-Applied Electrical Fields: Insights from Computer Simulations  

Microsoft Academic Search

The effect of extracellularly applied electrical fields on neuronal excitability and firing behavior is attributed to the interaction between neuronal morphology and the spatial distribution and level of differential polarization induced by the applied field in different elements of the neuron. The presence of voltage-gated ion channels that mediate persistent inward currents (PICs) on the dendrites of spinal motoneurons enhances

Sherif M. Elbasiouny; Vivian K. Mushahwar

2007-01-01

203

Strong Reduction of Tc Suppression by Magnetic Field in YBa2Cu3O7+x Films with Dispersed Nanoparticles  

NASA Astrophysics Data System (ADS)

Improvements in the critical current density Jc in applied magnetic fields are of great importance for applications of the YBa2Cu3O7-x coated conductors. Nanosize inclusions have shown to be effective in increasing Jc, but the precise physical mechanisms of their action remains elusive. A broader range of experiments is needed in order to elucidate the physics of this phenomenon. Here we discuss the magnetic field H- and temperature T-dependence of the resistivity of thin films in the normal state and near Tc. Pure YBCO films will be compared with those that contain either dispersed Y2O3 nanoparticles or BaSnO3 nanorods. The resistance of highly c-axis oriented YBCO films was measured by the Montgomery method in the range 20 K < T < 300 K and in fields up to 9 T. The films with inclusions show a much sharper and less broadened in-field transition (smaller Tc suppression by field) than pure YBCO. This correlates well with increased Jc measured by conventional methods and indicates increased pinning strength at all temperatures. In order to further identify the signatures of the nano-inclusions, the samples were annealed in air at 420 deg C. The changes induced by the annealing will be discussed. This work was partially supported by AFOSR and the AFRL Propulsion Directorate.

Cimpoiasu, E.; Feldmann, J. D.; Varanasi, C. V.; Haugan, T. J.; Barnes, P. N.; Levin, G. A.

2009-03-01

204

Content Analysis of Dreams and Waking Narratives  

Microsoft Academic Search

This study investigated the specificity of dream content and its continuity with waking life. For each subject (125 men and 125 women, between the ages of 19 and 29 years), a dream and a waking episode were collected according to \\

Alfio Maggiolini; Chiara Cagnin; Franca Crippa; Anna Persico; Pietro Rizzi

2010-01-01

205

Wake Turbulence Mitigation for Arrivals (WTMA).  

National Technical Information Service (NTIS)

The preliminary Wake Turbulence Mitigation for Arrivals (WTMA) concept of operations is described in this paper. The WTMA concept provides further detail to work initiated by the Wake Vortex Avoidance System Concept Evaluation Team and is an evolution of ...

A. C. Trujillo D. M. Williams G. W. Lohr

2008-01-01

206

Quick profile-reoriganization driven by helical field perturbation for suppressing tokamak major disruptions  

NASA Astrophysics Data System (ADS)

Disruptive behavior of magnetic field configuration leading to tokamak major disruption is found to be controlled by a mild mini-disruption which is induced by the compact external modular multipole-field coils with m=3/n=2 dominant helical field component in the JIPP T-IIU tokamak. This mini-disruption ergodizes the m=2/n=1 magnetic island quickly but mildly and then prevents the profile of electron temperature from flattening. This quick profile-reorganization is effective to avoid the two-step disruption (pre- and major disruptions) responsible for the catastrophic current termination.

Yamazaki, K.; Kawahata, K.; Ando, R.; Matsuoka, K.; Hirokura, S.; Kitagawa, S.; Mohri, A.; Tanahashi, S.; Taniguchi, Y.; Toi, K.

1986-09-01

207

Suppression of Secondary Emission in a Magnetic Field Using a Sawtooth and Isosceles Triangle Surface  

SciTech Connect

The effect of surface roughness on the secondary electron emission from a sawtooth and isosceles triangle surface in a magnetic field under electron bombardment is investigated using a Monte-Carlo method. Some of the secondary electrons emitted from the surface return to the surface within their first few gyrations, resulting in a low effective secondary electron yield. Both sawtooth and isosceles triangle surface in magnetic field can significantly reduce the secondary emission yield below the multipacting threshold with weak dependence on the size of surface and magnetic field.

Wang, L.; Raubenheimer, T.O.; Stupakov, G.; /SLAC

2006-09-26

208

Ballistic Wake of Turbulence in a Plasma Shock Wave  

Microsoft Academic Search

The role of ballistic term in the turbulence that occurs in plasma shock waves is discussed. For electrostatic turbulence these terms are shown to give rise to a wake behind a shock wave in which the energy density in the fluctuating fields decays spatially as x?3 for a class of distribution functions including resonance functions. The importance of the ballistic

Nicholas A. Krall; Derek A. Tidman

1969-01-01

209

Suppression of secondary emission in a magnetic field using triangular and rectangular surfaces  

NASA Astrophysics Data System (ADS)

The effect of surface roughness on the secondary electron emission from a sawtooth and isosceles triangular surface as well as a rectangular surface in a magnetic field under electron bombardment is investigated using a Monte-Carlo method. In all cases, some of the secondary electrons emitted from the surface return to the surface within their first few gyrations, resulting in a low effective secondary electron yield. Either sawtooth or isosceles triangle surface can significantly reduce the secondary emission yield in a magnetic field below the multipacting threshold with a weak dependence on the size of the surface and magnetic field. Rectangular surfaces can also reduce SEY below 1.0 but have a large sensitivity to the size of the grooves and the magnetic field. The impedance as well as other implementations of the grooved surfaces are also discussed.

Wang, L.; Raubenheimer, T. O.; Stupakov, G.

2007-02-01

210

Island wakes in the Southern California Bight  

Microsoft Academic Search

Wind- and current-induced island wakes were investigated using a multiplatform approach of in situ, remote sensing, and numerical model simulations for the Southern California Bight (SCB). Island wind wakes are a result of sheltering from the wind, with weak wind mixing, strong heat storage, and consequent high sea surface temperature (SST). Wind wakes around Santa Catalina Island are most persistent

R. M. A. Caldeira; P. Marchesiello; N. P. Nezlin; P. M. DiGiacomo; J. C. McWilliams

2005-01-01

211

Cooling Signs in Wake Debate  

ERIC Educational Resources Information Center

|More than a year after dismantling a student-assignment policy based on socioeconomic diversity and setting off a wave of reaction that drew national attention, the Wake County, North Carolina, school board took a step that may turn down the temperature of the intense debate. The board, which has been deeply split on an assignment plan for the…

Samuels, Christina A.

2011-01-01

212

Nighttime Wakefulness Associated with Infant  

Microsoft Academic Search

Parent-infant cosleeping occurs in human and nonhuman primates, yet stud- ies on the impact of cosleeping on parental sleep patterns have been limited to human mothers. We examined the effects of cosleeping on the nighttime wake- fulness of a biparental New World primate, Wied's black tufted-ear marmoset (Callithrix kuhlii). We compared the sleep patterns of marmoset parents caring for young

Jeffrey E. Fite; Jeffrey A. French; Kimberly J. Patera; Elizabeth C. Hopkins; Michael Rukstalis; Heather A. Jensen; Corinna N. Ross

213

Control of sleep and wakefulness.  

PubMed

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making. PMID:22811426

Brown, Ritchie E; Basheer, Radhika; McKenna, James T; Strecker, Robert E; McCarley, Robert W

2012-07-01

214

Self-generated electric field suppressing the ferroelectric to antiferroelectric phase transition in ferroelectric ceramics under shock wave compression  

NASA Astrophysics Data System (ADS)

Kinetics of the ferroelectric (FE) to antiferroelectric (AFE) phase transformation under shock wave compression is critical to design the shock-activated power supply and can be characterized in terms of both a transition rate and a limiting degree of transition. By measuring the depoling currents under the short-circuit and high-impedance conditions, we investigated the influence of self-generated electric field on the phase transition kinetics of tin-modified lead zirconate titanate ceramics (Pb0.99Nb0.02[(Zr0.90Sn0.10)0.96Ti0.04]0.98O3) in the pressure range from 0.61 to 4.50 GPa. Experimental results indicate that the self-generated electric field does not appear to have a significant effect on the depoling currents at high shock pressures, but has a strong effect at low pressures. At 0.61 and 1.03 GPa, transition rate and degree diminish with increasing the electric field, illustrating that the self-generated electric field suppresses the FE-to-AFE phase transition. These observations are found to be generally consistent with many ferroelectric materials and results under hydrostatic compression. Fundamental issues are discussed from the perspective of the soft mode theory.

Jiang, Dongdong; Du, Jinmei; Gu, Yan; Feng, Yujun

2012-01-01

215

Suppression of T-lymphocyte cytotoxicity following exposure to 60-Hz sinusoidal electric fields  

SciTech Connect

A significant 25% inhibition (P less than .005) of allogeneic cytotoxicity of the target cell MPC-11 by the murine cytotoxic T-lymphocyte line CTLL-1 was observed when the 4-h cytotoxicity assay was conducted immediately following a 48-h pre-exposure of the effector lymphocytes to a 10-mV/cm (rms) 60-Hz sinusoidal electric field. At 1.0 mV/cm a significant 19% inhibition (P less than .0005) was seen. At 0.1 mV/cm a nonsignificant 7% inhibition of cytotoxicity was noted. When the 4-h cytotoxicity assay was conducted in the presence of the field using previously unexposed effector lymphocytes, cytotoxicity was not significantly reduced. Cell proliferation in the presence of interleukin-2 was unaffected by the field. These data suggest a dose response and threshold (between 0.1 and 1.0 mV/cm) for inhibition of cytotoxicity in clonal T-lymphocytes by exposure to a 60-Hz sinusoidal electric field. These results suggest mechanisms by which 60-Hz electric fields could affect the function of cells of the immune system.

Lyle, D.B.; Ayotte, R.D.; Sheppard, A.R.; Adey, W.R.

1988-01-01

216

Suppression of electric field domains in semiconductor superlattices with side shunting layer  

NASA Astrophysics Data System (ADS)

We have numerically studied the electronic transport properties of a weakly-coupled semiconductor superlattice that possesses a conductive side shunting layer, using a model that includes lateral dynamics in each quantum well of the superlattice [1]. Depending on the lateral size of the superlattice quantum wells and the quality of the connection between the shunt layer and the superlattice, the shunt may inhibit the formation of electric field domains in the superlattice under conditions of negative differential resistance (NDR). We determine conditions to achieve a stable spatially-uniform electric field distribution, an important condition for practical NDR devices such as superlattice THz oscillators. For a superlattice with small lateral extent, a high quality shunt stabilizes the uniform field configuration in the entire structure, whereas a lower quality shunt leads to current oscillations and/or static field domains. We characterize the bifurcations associated with the transitions between these different behaviors. [1] A. Amann and E. Sch"oll, Phys. Rev. B 72, 165319 (2005).

Xu, Huidong; Amann, Andreas; Schöll, Eckehard; Teitsworth, Stephen

2009-03-01

217

Reflection suppression and absorption enhancement of optical field at thin metal gratings with narrow slits.  

PubMed

Optically thin metal gratings of high filling factor can support surface plasmon polariton modes at their horizontal metal boundaries and vertical cavity modes inside their slits. These modes are coupled through the metal stripes and the slits. This letter shows that the resonant interactions between the modes critically influence the optical field distribution near the grating and substantially enhance several phenomena such as low reflection, low transmission, and high absorption of the electromagnetic radiation. A high degree of energy confinement is obtained, especially when the energy is stored almost exclusively on the far side of the grating, away from the incident radiation. It is numerically shown that this phenomenon originates from the interaction of field modes with the collective motion of free electrons, as considered in the Drude model. PMID:23041850

Roszkiewicz, A; Nasalski, W

2012-09-15

218

Suppression of small baryonic structures due to a primordial magnetic field  

NASA Astrophysics Data System (ADS)

We investigate the impact of the existence of a primordial magnetic field on the filter mass, characterizing the minimum baryonic mass that can form in dark matter (DM) haloes. For masses below the filter mass, the baryon content of DM haloes are severely depressed. The filter mass is the mass when the baryon to DM mass ratio in a halo is equal to half the baryon to DM ratio of the Universe. The filter mass has previously been used in semi-analytic calculations of galaxy formation, without taking into account the possible existence of a primordial magnetic field. We examine here its effect on the filter mass. For homogeneous comoving primordial magnetic fields of B0 ~ 1 or 2nG and a re-ionization epoch that starts at a redshift zs = 11 and is completed at zr = 8, the filter mass is increased at redshift 8, for example, by factors of 4.1 and 19.8, respectively. The dependence of the filter mass on the parameters describing the re-ionization epoch is investigated. Our results are particularly important for the formation of low-mass galaxies in the presence of a homogeneous primordial magnetic field. For example, for B0 ~ 1nG and a re-ionization epoch of zs ~ 11 and zr ~ 7, our results indicate that galaxies of total mass M ~ 5 × 108Msolar need to form at redshifts zF >~ 2.0, and galaxies of total mass M ~ 108Msolar at redshifts zF >~ 7.7.

Rodrigues, Luiz Felippe S.; de Souza, Rafael S.; Opher, Reuven

2010-07-01

219

Structure of the lunar wake: Two-dimensional global hybrid simulations  

NASA Astrophysics Data System (ADS)

We study the structure and properties of the lunar wake with these solar wind parameters: the angle $\\theta$sw between directions of the solar wind velocity vsw and the ambient interplanetary magnetic field (IMF) B $\\theta$sw = 45° and 90° and vsw = 6vA (where vA denotes solar wind Alfvén velocity). We examine the structure of the wake-tail formed behind the obstacle. In agreement with in situ observations the lunar wake is formed by two counterstreaming beams which fill the wake with a relatively cold, inhomogeneous and highly anisotropic plasma. The results of this study suggest that for given solar wind conditions the downstream region of the lunar wake is dominated by electromagnetic turbulence with the frequencies near the local proton gyrofrequency. The properties and possible generating mechanisms of the low-frequency electromagnetic turbulence are discussed.

Trávní?ek, Pavel; Hellinger, Petr; Schriver, David; Bale, Stuart D.

2005-03-01

220

Brain mechanisms that control sleep and waking  

NASA Astrophysics Data System (ADS)

This review paper presents a brief historical survey of the technological and early research that laid the groundwork for recent advances in sleep-waking research. A major advance in this field occurred shortly after the end of World War II with the discovery of the ascending reticular activating system (ARAS) as the neural source in the brain stem of the waking state. Subsequent research showed that the brain stem activating system produced cortical arousal via two pathways: a dorsal route through the thalamus and a ventral route through the hypothalamus and basal forebrain. The nuclei, pathways, and neurotransmitters that comprise the multiple components of these arousal systems are described. Sleep is now recognized as being composed of two very different states: rapid eye movements (REMs) sleep and non-REM sleep. The major findings on the neural mechanisms that control these two sleep states are presented. This review ends with a discussion of two current views on the function of sleep: to maintain the integrity of the immune system and to enhance memory consolidation.

Siegel, Jerome

221

Wake effects in a Fayette 95-IIS wind turbine array  

SciTech Connect

A group of 35 wind turbines on the Castello Ranch in Altamont Pass, California, was investigated to quantify array wake effects (losses in energy production due to operation of upwind turbines) and the factors influencing them. Approximately 65 hours of field measurements were made in summer 1986, with turbine energy production and wind velocity data recorded for various scenarios of array operation. Customized software and hardware were developed and installed by Fayette to facilitate these measurements. The existence of wake effects was fairly well established. Relative energy-production losses averaged 6% at the second row, when the first row was operating, and 7 to 8% at the third row, when the first two were operating. Apparently, then, the impact of the first row on the third (at a 21-rotor-diameter distance) was minimal. Ambient wind speed did not appear to affect the relative wind speed pattern within the array due to wakes, but because of the shape of the performance curve, it did affect relative energy production losses (particularly for the low-RPM mode of machine operation). The influences of ambient atmospheric conditions, such as stability, turbulence, and shear on the array wakes, were also investigated by testing over a range of the conditions available during a typical 24-hour day at the test site. None of these variables showed any significant effect on the degree of wake-induced energy losses. While the results of this study apply only to this specific array and type of wind turbine, the methodology could be applied to study wake effects at other wind farms. 6 refs., 7 figs., 20 tabs.

Simon, R.L.; Matson, D.F.; Fuchs, J.M.

1987-09-01

222

Distributed control in a mean-field cortical network model: Implications for seizure suppression  

NASA Astrophysics Data System (ADS)

Brain electrical stimulation (BES) has long been suggested as a means of controlling pathological brain activity. In epilepsy, control of a spatially localized source, the seizure focus, may normalize neuronal dynamics. Consequently, most BES research has been directed at controlling small, local, neuronal populations. At a higher level, pathological seizure activity can be viewed as a network event that may begin without a clear spatial focus or in multiple sites and spread rapidly through a distributed cortical network. In this paper, we begin to address the implications of local control in a network scenario. To do so, we explore the efficacy of local BES when deployed over a larger-scale neuronal network, for instance, using a grid of stimulating electrodes on the cortex. By introducing a mean-field model of neuronal interactions we are able to identify limitations in network controllability based on physiological constraints that suggest the need for more nuanced network control strategies.

Ching, ShiNung; Brown, Emery N.; Kramer, Mark A.

2012-08-01

223

Distributed control in a mean-field cortical network model: implications for seizure suppression.  

PubMed

Brain electrical stimulation (BES) has long been suggested as a means of controlling pathological brain activity. In epilepsy, control of a spatially localized source, the seizure focus, may normalize neuronal dynamics. Consequently, most BES research has been directed at controlling small, local, neuronal populations. At a higher level, pathological seizure activity can be viewed as a network event that may begin without a clear spatial focus or in multiple sites and spread rapidly through a distributed cortical network. In this paper, we begin to address the implications of local control in a network scenario. To do so, we explore the efficacy of local BES when deployed over a larger-scale neuronal network, for instance, using a grid of stimulating electrodes on the cortex. By introducing a mean-field model of neuronal interactions we are able to identify limitations in network controllability based on physiological constraints that suggest the need for more nuanced network control strategies. PMID:23005798

Ching, ShiNung; Brown, Emery N; Kramer, Mark A

2012-08-21

224

Wake Instabilities Behind Bluff Bodies  

Microsoft Academic Search

\\u000a The observation by Bénard of a vortex street in the wake of a circular cylinder has been commonly associated with the stability\\u000a analysis of the double alternate street proposed by von Kármán. After a short historical review of these studies, we present\\u000a the main progress in understanding this instability during the last decade. New experiments and the control of two-dimensional

Michel Provansal

225

Passive propulsion in vortex wakes  

NASA Astrophysics Data System (ADS)

A dead fish is propelled upstream when its flexible body resonates with oncoming vortices formed in the wake of a bluff cylinder, despite being well outside the suction region of the cylinder. Within this passive propulsion mode, the body of the fish extracts sufficient energy from the oncoming vortices to develop thrust to overcome its own drag. In a similar turbulent wake and at roughly the same distance behind a bluff cylinder, a passively mounted high-aspect-ratio foil is also shown to propel itself upstream employing a similar flow energy extraction mechanism. In this case, mechanical energy is extracted from the flow at the same time that thrust is produced. These results prove experimentally that, under proper conditions, a body can follow at a distance or even catch up to another upstream body without expending any energy of its own. This observation is also significant in the development of low-drag energy harvesting devices, and in the energetics of fish dwelling in flowing water and swimming behind wake-forming obstacles.

Beal, D. N.; Hover, F. S.; Triantafyllou, M. S.; Liao, J. C.; Lauder, G. V.

226

Recent results about fan noise: Its generation, radiation and suppression  

NASA Astrophysics Data System (ADS)

Fan noise including its generation, radiation characteristics, and suppression by acoustic treatment is studied. In fan noise generation, results from engine and fan experiments, using inflow control measures to suppress noise sources related to inflow distortion and turbulence, are described. The suppression of sources related to inflow allows the experiments to focus on the fan or engine internal sources. Some of the experiments incorporated pressure sensors on the fan blades to sample the flow disturbances encountered by the blades. From these data some inferences can be drawn about the origins of the disturbances. Also, hot wire measurements of a fan rotor wake field are presented and related to the fan's noise signature. The radiation and the suppression of fan noise are dependent on the acoustic modes generated by the fan. Fan noise suppression and radiation is described by relating these phenomena to the mode cutoff ratio parameter. In addition to its utility in acoustic treatment design and performance prediction, cutoff ratio was useful in developing a simple description of the radiation pattern for broadband fan noise. Some of the findings using the cutoff ratio parameter are presented.

Feiler, C. E.

227

Neurophysiology of sleep and wakefulness.  

PubMed

Wakefulness, NREM sleep, and REM sleep are three distinct states of existence. Each state has characteristic behavioral and physiologic patterns,and each has specific neurophysiologic mechanisms associated with its generation and control. Structures in the brainstem use various neurotransmitters to influence higher brain structures in the midbrain and cortex. The ARAS provides cholinergic, noradrenergic, and glutaminergic stimulation to the thalamus, hypothalamus, and basal forebrain resulting in cholinergic and glutaminergic excitation of the cortex. An active cortex that exhibits a characteristic pattern of desynchronized EEG manifests wakefulness. Various factors affect the need and timing of sleep onset. These factors influence the nucleus tractus solitarius, causing its noradrenergic projections to midbrain and forebrain structures to inhibit activity in the ARAS, resulting inactivation of inhibitory GABAergic thalamocortical projections to the cor-tex. During a state of decreased activation, the cortex exhibits a pattern of synchronized EEG. Transition between NREM sleep and REM sleep is controlled by noradrenergic neurons in the loci coeruleus and serotoninergic neurons in the raphe called REM-off cells and cholinergic neurons in the nucleus reticularis pontis oralis called REM-on cells. Other brain structures are involved in generation and control of REM sleep-related phenomena, such as eye movement and muscle atonia. During wakefulness, there is increased sympathetic tone and decreased parasympathetic tone that maintains most organ systems in a state of action or readiness. During NREM sleep, there is decreased sympathetic tone and increased parasympathetic activity that creates a state of reduced activity. REM sleep is characterized by increased parasympathetic activity and variable sympathetic activity associated with increased activation of certain brain functions. The states of wakefulness and sleep are characterized as stages that are defined by stereotypical EEG, EMG, and EOG patterns. Wakefulness stage has an EEG pattern predominated by the alpha rhythm. With onset of stage 1 sleep, the alpha rhythm attenuates, and an EEG pattern of relatively low voltage and mixed frequency is seen. Progression to stage 2 sleep is defined by the appearance of sleep spindles or K-complexes. Further progression into the deepest sleep stages 3 and 4 is defined by the occurrence of high-amplitude, low-frequency EEG activity. The progression of sleep stages occurs in cycles of 60 to 120 minutes throughout the sleep period. Various circadian environmental and ontologic factors affect the pattern of sleep stage occurrence. PMID:16303589

Harris, Cameron D

2005-12-01

228

If waking and dreaming consciousness became de-differentiated, would schizophrenia result?  

PubMed

If both waking and dreaming consciousness are functional, their de-differentiation would be doubly detrimental. Differentiation between waking and dreaming is achieved through neuromodulation. During dreaming, without external sensory data and with mesolimbic dopaminergic input, hyper-cholinergic input almost totally suppresses the aminergic system. During waking, with sensory gates open, aminergic modulation inhibits cholinergic and mesocortical dopaminergic suppresses mesolimbic. These neuromodulatory systems are reciprocally interactive and self-organizing. As a consequence of neuromodulatory reciprocity, phenomenologically, the self and the world that appear during dreaming differ from those that emerge during waking. As a result of self-organizing, the self and the world in both states are integrated. Some loss of self-organization would precipitate a degree of de-differentiation between waking and dreaming, resulting in a hybrid state which would be expressed heterogeneously, both neurobiologically and phenomenologically. As a consequence of progressive de-differentiation, certain identifiable psychiatric disorders may emerge. Ultimately, schizophrenia, a disorganized-fragmented self, may result. PMID:21498086

Llewellyn, Sue

2011-04-16

229

Spatiotemporal spectral analysis of a forced cylinder wake  

NASA Astrophysics Data System (ADS)

The wake of a circular cylinder performing rotary oscillations is studied using hydrodynamic tunnel experiments at Re=100. Two-dimensional particle image velocimetry on the midplane perpendicular to the axis of a cylinder is used to characterize the spatial development of the flow and its stability properties. The lock-in phenomenon that determines the boundaries between regions of the forcing parameter space where the wake is globally unstable or convectively unstable [see Thiria and Wesfreid, J. Fluids Struct.0889-974610.1016/j.jfluidstructs.2009.04.002 25, 654 (2009) for a review] is scrutinized using the experimental data. A method based on the analysis of power density spectra of the flow allows us to give a detailed description of the forced wake, shedding light on the energy distribution in the different frequency components and in particular on a cascade-like mechanism evidenced for a high amplitude of the forcing oscillation. In addition, a calculation of the drag from the velocity field is performed, allowing us to relate the resulting force on the body to the wake properties.

D'Adamo, Juan; Godoy-Diana, Ramiro; Wesfreid, José Eduardo

2011-11-01

230

Experimental Study of Rotor Vortex Wakes in Descent  

NASA Astrophysics Data System (ADS)

An experimental study is performed on a three-bladed rotor model in a water towing tank. The blade pitch and rotational velocity, the rotor plane angle of attack, and the carriage speed are all varied in order to simulate a wide range of rotorcraft operating states. Circulation Reynolds numbers are of order 105 and blade Reynolds numbers are of order 104. Flow visualization is done using air bubbles or dye injected from the blade tips to mark the vortex core, showing the development of an instability on the helical vortices in the wake. PIV data provide quantitative measures of the flow field as the wake develops. Strain gages are also used to record transient load measurements, allowing a correlation to be made between the rotor performance and the development of the vortex wake. The data so far indicate that as the instability develops, the adjacent vortices merge and form thick vortex rings, especially during descent. The vorticity spreads and is periodically shed from the wake, resulting in significant fluctuations in the rotor loading.

Stack, James; Carradonna, Frank; Savas, Omer

2002-11-01

231

Self-preservation in stratified momentum wakes  

Microsoft Academic Search

A general model is described for drag wakes in a linearly stratified fluid, based on the self-preservation of the flow. It is assumed that the buoyancy-controlled self-similar wake expands in the horizontal direction due to turbulent diffusion and in the vertical direction due to viscous diffusion. The mean characteristics of the wake (height, width and velocity defect) are analytically derived

Patrice Meunier; Peter J. Diamessis; Geoffrey R. Spedding

2006-01-01

232

Recent NASA Wake-Vortex Flight Tests, Flow-Physics Database and Wake-Development Analysis  

Microsoft Academic Search

A series of flight tests over the ocean of a four engine tur- boprop airplane in the cruise configuration have provided a data set for improved understanding of wake vortex physics and atmospheric interaction. An integrated data- base has been compiled for wake-characterization and validation of wake-vortex computational models. This paper describes the wake-vortex flight tests, the data pro- cessing,

Dan D. Vicroy; Paul M. Vijgen; Heidi M. Reimer; Joey L. Gallegos; Philippe R. Spalart

233

Effect of differential spoiler settings (DSS) on the wake vortices of a wing at high-lift-configuration (HLC)  

Microsoft Academic Search

An experimental investigation has been carried out to evaluate the capabilities of differential spoiler setting (DSS) in modifying the wingspan loading. The particle image velocimetery (PIV) technique was used in a low speed wind tunnel facility to measure wake velocities at four locations downstream of the half model in the near wake field. The model was investigated at a high

Omer A. Elsayed; Ashraf A. Omar; Waqar Asrar; Kijung Kwon

2011-01-01

234

Laser-induced wakes in ion crystals  

NASA Astrophysics Data System (ADS)

Wakes in a Coulomb crystal are produced by ``pushing'' with radiation pressure on a rotating spheroidal cloud of laser-cooled 9Be+ ions. The wakes are stationary in the lab frame and are caused by the interference of ``drum-head'' type oscillations. Velocity images of these wakes are obtained directly through the dependence of the ion fluorescence on Doppler shifts, and new analytical calculations accurately reproduce these experimental wake images. The technique demonstrates a way to excite and study modes, that were not accessible with previous techniques. .

Kriesel, J. M.; Bollinger, J. J.; Mitchell, T. B.; King, L. B.; Dubin, D. H. E.

2002-01-01

235

Electromagnetic scattering model of the Kelvin wake and turbulent wake by a moving ship  

Microsoft Academic Search

Taking the attenuation character of the Kelvin wake and the limitation of the traditional two-scale method into account, the practical electromagnetic (EM) scattering model of the Kelvin wake is obtained by using a facet-based model; and for a turbulent ship wake, it is produced by dealing with the wave energy loss rate due to turbulence with the width of turbulent

Rong-Qing Sun; Gen Luo; Min Zhang; Chao Wang

2011-01-01

236

Ketamine, not fentanyl, suppresses pain-related magnetic fields associated with trigeminally innervated area following CO2 laser stimulation.  

PubMed

A variety of pharmacological agents are clinically used to treat pain-related diseases, including in the orofacial region. The effects of analgesics upon cerebral sites responsible for pain perception have yet to be determined. The aim of the present study was to examine the effects of ketamine, an N-methyl-d-aspartate (NMDA) antagonist, and fentanyl, a narcotic analgetic, on pain-related somatosensory-evoked magnetic fields (pain-SEFs) induced by CO(2) laser stimulation of the trigeminally innervated area. Two peaks with latencies of approximately 120 and 200 ms were observed in pain-SEFs after CO(2) laser stimulation. Peaks with approximately 120 ms latency were detected in the bilateral secondary somatosensory cortices. Amplitude of pain-SEFs after CO(2) laser stimulation increased in an intensity-dependent manner. Ketamine suppressed amplitude and prolonged latency of pain-SEFs, whilst fentanyl did not. This suggests that ketamine inhibits NMDA receptor-mediated neurotransmission in a pain input pathway to the cerebral cortex, thereby exerting an analgesic effect. Fentanyl, which acts via opioid receptors, is believed to act differently to ketamine in the pain input process. PMID:18655812

Matsuura, Nobuyuki; Shibukawa, Yoshiyuki; Kato, Motoichiro; Ichinohe, Tatsuya; Suzuki, Takashi; Kaneko, Yuzuru

2008-07-05

237

The role of the oxygen/water redox couple in suppressing electron conduction in field-effect transistors  

NASA Astrophysics Data System (ADS)

Much like with organic semiconductor FETs, a characteristic of carbon nanotube based devices has been their almost exclusive p-type character in air. Electron transport can be observed only under certain conditions, for instance devices annealed in vacuum. We investigated the impact of the chemical nature of the substrate and of ambient adsorbates on the field-effect switching behavior of both nanoscale and thin-film FETs. Our study, using carbon nanotubes as the testbed, revealed that the intrinsic material properties are modified when an adsorbed water layer containing solvated oxygen is present on the SiO2 surface and lead to the reduction of n-type conduction. This finding demonstrates that an electrochemical charge transfer reaction between the semiconducting channel and the aqueous oxygen redox couple is the underlying phenomenon governing the suppression of electron conduction in these devices. This effect should be considered when measuring the transport properties of nanostructures such as nanowires, organic materials, nanotubes, graphene conducted on SiO2/Si substrates.

Levesque, Pierre L.; Aguirre, Carla M.; Paillet, Matthieu; Lapointe, François; St-Antoine, Benoit C.; Desjardins, Patrick; Martel, Richard

2009-03-01

238

Stark interaction of identical particles with the vacuum electromagnetic field as quantum Poisson process suppressing collective spontaneous emission  

SciTech Connect

The effective Hamiltonian describing resonant interaction of an ensemble of identical quantum particles with a photon-free vacuum electromagnetic field has been obtained with allowance for terms of second order in the coupling constant (the Stark interaction) by means of the perturbation theory on the basis of the unitary transformation of the system quantum state. It has been shown that in the Markov approximation the effective Hamiltonian terms of first order in the coupling constant are represented by the quantum Wiener process, whereas terms of second order are expressed by the quantum Poisson process. During the course of the investigation, it was established that the Stark interaction played a significant role in the ensemble dynamics, thus influencing the collective spontaneous decay of the ensemble of an appreciably high number of identical particles. Fundamental effects have been discovered, i.e., the excitation conservation in a sufficiently dense ensemble of identical particles and superradiance suppression in the collective decaying process of an excited ensemble with a determined number of particles.

Basharov, A. M. [RRC ''Kurchatov Institute'', Moscow (Russian Federation)

2011-07-15

239

Pediatric sleep-wake disorders.  

PubMed

Sleep-wake problems are common during childhood and adolescence. They are of diverse cause, and can contribute significantly to alterations in behavior, cognition, and learning. Obstructive sleep apnea, central hypoventilation syndrome, narcolepsy, periodic hypersomnia, delayed sleep phase syndrome, restless legs syndrome, parasomnias, and sleep disruption consequent to psychiatric disorders are some of the commonly encountered conditions. Some aspects of sleep architecture and its organization change with age and maturation. Diagnostic criteria and sleep laboratory techniques and findings for some childhood sleep disorders differ from those of adults. Most pharmacologic agents used to treat pediatric sleep disorders are off-label. PMID:23099134

Kotagal, Suresh; Chopra, Amit

2012-11-01

240

Collisionless Damping of Laser Wakes in Plasma Channels  

SciTech Connect

Excitation of accelerating modes in transversely inhomogeneous plasma channels is considered as an initial value problem. Discrete eigenmodes are supported by plasma channels with sharp density gradients. These eigenmodes are collisionlessly damped as the gradients are smoothed. Using collisionless Landau damping as the analogy, the existence and damping of these "quasi-modes" is studied by constructing and analytically continuing the causal Green's function of wake excitation into the lower half of the complex frequency plane. Electromagnetic nature of the plasma wakes in the channel makes their excitation nonlocal. This results in the algebraic decay of the fields with time due to phase-mixing of plasma oscillations with spatially-varying fequencies. Characteristic decay rate is given by the mixing time, which corresponds to the dephasing of two plasma fluid elements separated by the collisionless skin depth. For wide channels the exact expressions for the field evolution are derived. Implications for electron acceleration in plasma channels are discussed.

Li, X.; Shvets, G.

1998-08-01

241

Linear and nonlinear auditory response properties of interneurons in a high-order avian vocal motor nucleus during wakefulness.  

PubMed

Motor-related forebrain areas in higher vertebrates also show responses to passively presented sensory stimuli. However, sensory tuning properties in these areas, especially during wakefulness, and their relation to perception, are poorly understood. In the avian song system, HVC (proper name) is a vocal-motor structure with auditory responses well defined under anesthesia but poorly characterized during wakefulness. We used a large set of stimuli including the bird's own song (BOS) and many conspecific songs (CON) to characterize auditory tuning properties in putative interneurons (HVC(IN)) during wakefulness. Our findings suggest that HVC contains a diversity of responses that vary in overall excitability to auditory stimuli, as well as bias in spike rate increases to BOS over CON. We used statistical tests to classify cells in order to further probe auditory responses, yielding one-third of neurons that were either unresponsive or suppressed and two-thirds with excitatory responses to one or more stimuli. A subset of excitatory neurons were tuned exclusively to BOS and showed very low linearity as measured by spectrotemporal receptive field analysis (STRF). The remaining excitatory neurons responded well to CON stimuli, although many cells still expressed a bias toward BOS. These findings suggest the concurrent presence of a nonlinear and a linear component to responses in HVC, even within the same neuron. These characteristics are consistent with perceptual deficits in distinguishing BOS from CON stimuli following lesions of HVC and other song nuclei and suggest mirror neuronlike qualities in which "self" (here BOS) is used as a referent to judge "other" (here CON). PMID:22205651

Raksin, Jonathan N; Glaze, Christopher M; Smith, Sarah; Schmidt, Marc F

2011-12-28

242

Linear and nonlinear auditory response properties of interneurons in a high-order avian vocal motor nucleus during wakefulness  

PubMed Central

Motor-related forebrain areas in higher vertebrates also show responses to passively presented sensory stimuli. However, sensory tuning properties in these areas, especially during wakefulness, and their relation to perception, are poorly understood. In the avian song system, HVC (proper name) is a vocal-motor structure with auditory responses well defined under anesthesia but poorly characterized during wakefulness. We used a large set of stimuli including the bird's own song (BOS) and many conspecific songs (CON) to characterize auditory tuning properties in putative interneurons (HVCIN) during wakefulness. Our findings suggest that HVC contains a diversity of responses that vary in overall excitability to auditory stimuli, as well as bias in spike rate increases to BOS over CON. We used statistical tests to classify cells in order to further probe auditory responses, yielding one-third of neurons that were either unresponsive or suppressed and two-thirds with excitatory responses to one or more stimuli. A subset of excitatory neurons were tuned exclusively to BOS and showed very low linearity as measured by spectrotemporal receptive field analysis (STRF). The remaining excitatory neurons responded well to CON stimuli, although many cells still expressed a bias toward BOS. These findings suggest the concurrent presence of a nonlinear and a linear component to responses in HVC, even within the same neuron. These characteristics are consistent with perceptual deficits in distinguishing BOS from CON stimuli following lesions of HVC and other song nuclei and suggest mirror neuronlike qualities in which “self” (here BOS) is used as a referent to judge “other” (here CON).

Raksin, Jonathan N.; Glaze, Christopher M.; Smith, Sarah

2012-01-01

243

Impact of wake on downstream adjacent rotor in low-speed axial compressor  

Microsoft Academic Search

This paper investigates the effect of upstream wake on unsteady separated flow field of downstream adjacent vanes by solving\\u000a 2D unsteady Reynolds-averaged Navier-Stokes equations discretized by a high-order scheme. The results indicated that the maximum\\u000a relative reduction of loss coefficient was 27.2% when the relative passing frequency (the ratio of wake passing frequency\\u000a to the characteristic frequency of trailing-vortex shedding

Xinqian Zheng; Sheng Zhou

2004-01-01

244

High-resolution measurement of surface-active film redistribution in ship wakes  

Microsoft Academic Search

Results are presented from an analysis of measurements of the cross-wake surface tension distributions, obtained during a Navy Field Experiment in January 1989 conducted to examine the effects of ship operating parameters and environmental conditions on the origin and persistence of these ship-generated surfactant bands. The cross-wake surface tension profiles obtained, together with the surface film pressure area and elasticity

R. D. Peltzer; O. M. Griffin; W. R. Barger; J. A. C. Kaiser

1992-01-01

245

Experimental study of low precessing frequencies in the wake of a turbulent annular jet  

Microsoft Academic Search

This paper investigates the flow structure in the wake behind the centrebody of an annular jet using time-resolved stereoscopic\\u000a PIV measurements. Although the time-averaged flow field is symmetric, the instantaneous wake is asymmetric. It consists of\\u000a a central toroidal vortex (CTV), which closes downstream at the stagnation point. This stagnation point lies off-axis and\\u000a hence the axis of the CTV

Maarten Vanierschot; Eric Van den Bulck

2011-01-01

246

Thrust Production and Wake Structure of an Actuated Lamprey Model  

NASA Astrophysics Data System (ADS)

Thrust generation is studied for a flexible lamprey model which is actuated periodically to produce a streamwise traveling wave. Shape memory alloy actuators are used to achieve this deformation. The flow field is investigated using DPIV and flow visualization for a range of Strouhal numbers based on peak-to-peak amplitude of the trailing edge. The vortex kinematics in the spanwise and streamwise planes are examined, and a three-dimensional unsteady vortex model of the wake will be discussed.

Buchholz, James; Smits, Alexander

2004-11-01

247

A Statistical Study of the Lunar Plasma Wake using ARTEMIS Measurements  

NASA Astrophysics Data System (ADS)

The Moon does not have an intrinsic magnetic field and lacks the conductivity necessary to develop an induced magnetosphere. Therefore, the interaction of the Moon with the solar wind is dominated by impact absorption on the day side and the generation of a plasma wake on the night side. The ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) spacecraft mission is a two-probe lunar mission derived from the THEMIS (Time History of Events and Macroscale Interactions During Substorms) mission, repurposed to study the lunar space and planetary environment. Over the course of the mission there have been numerous passes of the ARTEMIS spacecraft through the lunar wake, starting on February 13, 2010. The wake fly-bys have occurred in a variety of orbit geometries and distances from the planet, ranging up to many lunar radii downstream. They have also occurred for a variety of external conditions. In this presentation, we will share a statistical study of the numerous wake-crossing events of the ARTEMIS probes, using data primarily from the ARTEMIS fluxgate magnetometer (FGM) and electrostatic analyzers (ESAs) to identify when the spacecraft entered and exited the wake. Using the morphology of the wake boundary, we will determine the spatial extent of the lunar wake as a function of distance behind the Moon and its response to external conditions.

Ames, W. F.; Brain, D.; Poppe, A.; Halekas, J. S.; Bonnell, J. W.; McFadden, J. P.; Glassmeier, K.; Angelopoulos, V.

2011-12-01

248

Wake structure measurements at the Mod-2 cluster test facility at Goodnoe Hills  

SciTech Connect

A field measurement progam was carried out at the cluster of three MOD-2 wind turbines located at Goodnoe Hills, Washington, to determine the rate of decay of wake velocity deficit with downwind distance in various meteorological conditions. Measurements were taken at hub height (200 ft) between July 12 and August 1, 1982. Wake wind speeds were measured using a radiosonde suspended from a tethered balloon, its position being determined from a grid of ground stakes. Measurments were also made downwind with the turbine off to determine the magnitude of terrain-induced variations in wind speed. The balloon system used to measure downstream wind data proved to be reliable and convenient. Downstream distances of 900, 1500, 2100, and 2700 ft from the turbine were investigated. Differences between the instrumentation systems required that corrections be made to the data. After correction, averaged terrain-induced wind speed variations were regarded as insignificant. Turbine-on velocity ratios showed scatter, suggesting that only some measurements were, in fact, representative of wake centerline velocities, and that others were made off centerline due to wake meander or wind shift. Isolation of the high wind speed (30 to 45 mph) velocity ratios, however, revealed velocity deficits downstream. Measurements at greater downstream distances showed no wake deficit within the limits of resolution of the experiment, indicating that the wake had recovered to free stream conditions. Comparison with the AeroVironment wake model using common values for rotor drag coefficient and turbulence showed similar trends.

Lissaman, P.B.S.; Zambrano, T.G.; Gyatt, G.W.

1983-03-01

249

The effect of wake passing on turbine blade film cooling  

NASA Astrophysics Data System (ADS)

The effect of upstream blade row wake passing on the showerhead film cooling performance of a downstream turbine blade has been investigated through a combination of experimental and computational studies. The experiments were performed in a steady-flow annular turbine cascade facility equipped with an upstream rotating row of cylindrical rods to produce a periodic wake field similar to that found in an actual turbine. Spanwise, chordwise, and temporal resolution of the blade surface temperature were achieved through the use of an array of nickel thin-film surface gauges covering one unit cell of showerhead film hole pattern. Film effectiveness and Nusselt number values were determined for a test matrix of various injectants, injectant blowing ratios, and wake Strouhal numbers. Results indicated a demonstrable reduction in film effectiveness with increasing Strouhal number, as well as the expected increase in film effectiveness with blowing ratio. An equation was developed to correlate the span-average film effectiveness data. The primary effect of wake unsteadiness was found to be correlated well by a chordwise-constant decrement of 0.094*St. Measurable spanwise film effectiveness variations were found near the showerhead region, but meaningful unsteady variations and downstream spanwise variations were not found. Nusselt numbers were less sensitive to wake and injection changes. Computations were performed using a three-dimensional turbulent Navier-Stokes code which was modified to model wake passing and film cooling. Unsteady computations were found to agree well with steady computations provided the proper time-average blowing ratio and pressure/suction surface flow split are matched. The remaining differences were isolated to be due to the enhanced mixing in the unsteady solution caused by the wake sweeping normally on the pressure surface. Steady computations were found to be in excellent agreement with experimental Nusselt numbers, but to overpredict experimental film effectiveness values. This is likely due to the inability to match actual hole exit velocity profiles and the absence of a credible turbulence model for film cooling.

Heidmann, James David

250

Turbulence characteristics in wind-turbine wakes  

Microsoft Academic Search

An analysis of the evolution of turbulence characteristics in wind-turbine wakes has been carried out. Based on experimental results and on numerical results obtained with a CFD code, complemented with some theoretical considerations, simple analytical expressions are proposed for the estimation of the turbulent kinetic energy, k, and its dissipation rate, ?. To obtain the turbulence spectra in the wake

A. Crespo; J. Herna´ndez

1996-01-01

251

Modelling Wind Turbine Wakes in Complex Terrain  

Microsoft Academic Search

Existing engineering-type models for wakes have been developed and calibrated for flat terrain applications. However to consider the effects of the atmospheric boundary layer in a complex terrain environment, including flow separation and wind rose narrowing, requires the application of advanced methods. A method of modeling the wind turbine wakes using a Navier-Stokes solver along with the k-? turbulence model

J. M. Prospathopoulos; E. S Politis; P. K. Chaviaropoulos

252

Wake Filling by Active Tail Articulation  

Microsoft Academic Search

In a viscous fluid, the no slip boundary condition results in a surface drag force on a moving streamlined body, such as a hydrofoil, which causes a downstream wake velocity defect. In this paper, experimental results are presented which show that articulation of a trailing edge tail flap on a hydrofoil is sufficient to diminish the mean wake velocity defect.

Daniel Macumber; David Beal; Anuradha Annaswamy; Charles Henoch; Stephen Huyer

2004-01-01

253

Periodic Wake Effects on Turbulent Juncture Flows  

Microsoft Academic Search

The horseshoe vortex (HV) that develops in juncture geometries with a turbulent approach flow has been shown to exhibit a periodic behavior that correlates with the bursting frequency of the impinging turbulent boundary layer. To examine the additional complication of impinging blade wakes on such juncture flows, as encountered in turbomachinery environments, periodic wakes were systematically introduced upstream of a

Daniel Sabatino; Charles Smith

2000-01-01

254

Impact of wake on downstream adjacent rotor in low-speed axial compressor  

NASA Astrophysics Data System (ADS)

This paper investigates the effect of upstream wake on unsteady separated flow field of downstream adjacent vanes by solving 2D unsteady Reynolds-averaged Navier-Stokes equations discretized by a high-order scheme. The results indicated that the maximum relative reduction of loss coefficient was 27.2% when the relative passing frequency (the ratio of wake passing frequency to the characteristic frequency of trailing-vortex shedding of downstream adjacent rotor) is less than 2.5. The amplitude of wake defect exists a threshold value and the aerodynamic performance is enhanced monotonically with the amplitude of wake defect basically. The effective range of incidence must be greater than 8°, which is near the stall boundary.

Zheng, Xinqian; Zhou, Sheng

2004-05-01

255

Dynamic Hybrid Simulation of the Lunar Wake During ARTEMIS Crossing  

NASA Astrophysics Data System (ADS)

The interaction of the highly dynamic solar wind with the Moon is simulated with the A.I.K.E.F. (Adaptive Ion Kinetic Electron Fluid) code for the ARTEMIS P1 flyby on February 13, 2010. The A.I.K.E.F. hybrid plasma simulation code is the improved version of the Braunschweig code. It is able to automatically increase simulation grid resolution in areas of interest during runtime, which greatly increases resolution as well as performance. As the Moon has no intrinsic magnetic field and no ionosphere, the solar wind particles are absorbed at its surface, resulting in the formation of the lunar wake at the nightside. The solar wind magnetic field is basically convected through the Moon and the wake is slowly filled up with solar wind particles. However, this interaction is strongly influenced by the highly dynamic solar wind during the flyby. This is considered by a dynamic variation of the upstream conditions in the simulation using OMNI solar wind measurement data. By this method, a very good agreement between simulation and observations is achieved. The simulations show that the stationary structure of the lunar wake constitutes a tableau vivant in space representing the well-known Friedrichs diagram for MHD waves.

Wiehle, S.; Plaschke, F.; Angelopoulos, V.; Auster, H.; Glassmeier, K.; Kriegel, H.; Motschmann, U. M.; Mueller, J.

2010-12-01

256

Computational Simulation of a Heavy Vehicle Trailer Wake  

SciTech Connect

To better understand the flow mechanisms that contribute to the aerodynamic drag of heavy vehicles, unsteady large-eddy simulations are performed to model the wake of a truncated trailer geometry above a no-slip surface. The truncation of the heavy vehicle trailer is done to reduce the computational time needed to perform the simulations. Both unsteady and time-averaged results are presented from these simulations for two grids. A comparison of velocity fields with those obtained from a wind tunnel study demonstrate that there is a distinct di.erence in the separated wake of the experimental and computational results, perhaps indicating the influence of the geometry simplification, turbulence model, boundary conditions, or other aspects of the chosen numerical approach.

Ortega, J M; Dunn, T; McCallen, R; Salari, K

2002-12-04

257

Molecular Dynamic Studies of Particle Wake Potentials in Plasmas  

NASA Astrophysics Data System (ADS)

Fast Ignition studies require a detailed understanding of electron scattering, stopping, and energy deposition in plasmas with variable values for the number of particles within a Debye sphere. Presently there is disagreement in the literature concerning the proper description of these processes. Developing and validating proper descriptions requires studying the processes using first-principle electrostatic simulations and possibly including magnetic fields. We are using the particle-particle particle-mesh (P^3M) code ddcMD to perform these simulations. As a starting point in our study, we examined the wake of a particle passing through a plasma. In this poster, we compare the wake observed in 3D ddcMD simulations with that predicted by Vlasov theory and those observed in the electrostatic PIC code BEPS where the cell size was reduced to .03?D.

Ellis, Ian; Graziani, Frank; Glosli, James; Strozzi, David; Surh, Michael; Richards, David; Decyk, Viktor; Mori, Warren

2010-11-01

258

Neuromedin U(2) receptor signaling mediates alteration of sleep-wake architecture in rats.  

PubMed

Growing evidence indicates that neuromedin U (NmU) neuropeptide system plays an integral role in mediating the stress response through the corticotrophin-releasing factor (CRF) pathways. Stress is often associated with alteration in sleep-wake architecture both in human and laboratory animals. Here, we investigated whether activation of the NmU? receptor, a major high affinity receptor for NmU predominantly expressed in the brain, affects sleep behavior in rats. Effects of single (acute) intracebroventricular (icv) infusion of 2.5 nmol of the full agonists porcine NmU8 and rat NmU23 were assessed on sleep-wake architecture in freely moving rats, which were chronically implanted with EEG and EMG electrodes. In addition, repeated once daily administration of NmU8 at 2.5 nmol during 8 consecutive days (sub-chronic) was studied. Acute icv infusion of NmU23 elicited a robust alteration in sleep-wake architecture, namely enhanced wakefulness and suppressed sleep during the first 4h after administration. Acute infusion NmU8 had no effect on spontaneous sleep-wake architecture. However, sub-chronic icv infusion of NmU8 increased the amount of rapid eye movement (REM) sleep and intermediate stage (IS), while decreased light sleep. Additionally, NmU8 increased transitions from sleep states towards wakefulness suggesting a disruption in sleep continuity. The present results show that central-activation of NmU? receptor markedly reduced sleep duration and disrupted the mechanisms underlying NREM-REM sleep transitions. Given that sleep-wakefulness cycle is strongly influenced by stress and the role of NmU/NmU? receptor signaling in stress response, the disruption in sleep pattern associated with peptides species may support at least some signs of stress. PMID:21296417

Ahnaou, A; Drinkenburg, W H I M

2011-02-05

259

Multiple statistical approaches of community fingerprint data reveal bacterial populations associated with general disease suppression arising from the application of different organic field management strategies  

Microsoft Academic Search

Multiple statistical analyses of terminal restriction fragment length polymorphism (T-RFLP) data were used to screen and identify bacterial populations involved in general disease suppression in an organically managed soil. Prior to sampling three different management strategies (i.e. mixed hay (H), tilled fallowing and open-field vegetables production) were used during the transition from conventional to organic farming, with and without compost

María-Soledad Benítez; Fulya Baysal Tustas; Dorith Rotenberg; Mathew D. Kleinhenz; John Cardina; Deborah Stinner; Sally A. Miller; Brian B. McSpadden Gardener

2007-01-01

260

Vorticity and potential vorticity in mountain wakes  

SciTech Connect

A wake is traditionally defined as the region of nearly stagnant flow downstream of a body in a uniform stream. In a stratified fluid, the motions and density surfaces downstream of an obstacle become primarily horizontal; the vertical component of the vorticity associated with the wake, coexisting with the stable vertical density stratification, implies that there is potential vorticity (PV) in the lake. Recent work has demonstrated that dissipation aloft, associated with a breaking mountain wave over an isolated peak, produces a dipole in PV downstream; the dipolar vertical vorticity of the wake is associated with the PV dipole. Although one may infer the existence of vorticity downstream, the PV argument is silent on the question. Where does the wake vorticity come from? To answer this question, a weakly nonlinear model for PV production and wake formation in the case of a small-amplitude mountain has been analyzed, and numerical simulations pertaining to the strongly nonlinear large-amplitude case have been carried out. The simple model indicates that even with dissipation in the system, the vertical vorticity of the wake arises through the tilting of baroclinically generated horizontal vorticity by the dissipating mountain wave. This analysis shows that there need not be any direct effect of friction in the vorticity equation on the tilting term. Analysis of numerical simulations of the large-amplitude case shows that the conclusions from the weakly nonlinear model regarding the source of wake vorticity continue to hold in the strongly nonlinear type.

Rotunno, R.; Grubisic, V.; Smolarkiewicz, P.K. [National Center for Atmospheric Research, Boulder, CO (United States)

1999-08-15

261

Temperatures of wakes in Saturn's A ring  

NASA Astrophysics Data System (ADS)

The physical temperatures of the Saturn's A ring measured by the Cassini Composite Infrared Spectrometer (CIRS) show quadraople azimuthal modulations besides temperature drops in Saturn's shadow. These azimuthal modulations are likely to be caused by self-gravity wakes. In this paper, we develop a new thermal model in which wakes are modeled as elliptical cylinders ignoring inter-wake particles. All the heat fluxes are calculated explicitly taking into account inter-wake shadowing and heating. We apply our model to azimuthal scans of the A ring obtained by the CIRS. The thermal inertia estimated from the eclipse data (data only inside and near Saturn's shadow) of the low phase scans is found to be about 10 in MKS units. With this value of the thermal inertia, the amplitude of the azimuthal temperature modulation is overestimated in our model as compared with those observed. This is likely to be because our model ignores inter-wake particles. The bolometric reflectance of wakes is estimated to be 0.35-0.4 although lower values are required to reproduce temperatures at low solar phase angles. This apparent phase dependence of the reflectance indicates that roughness on the wake surfaces is necessary.

Morishima, Ryuji; Spilker, L.; Turner, N.; Cassini CIRS ring Team

2013-10-01

262

Large HAWT wake measurement and analysis  

NASA Astrophysics Data System (ADS)

From the theoretical fluid dynamics point of view, the wake region of a large horizontal-axis wind turbine has been defined and described, and numerical models of wake behavior have been developed. Wind tunnel studies of single turbine wakes and turbine array wakes have been used to verify the theory and further refine the numerical models. However, the effects of scaling, rotor solidity, and topography on wake behavior are questions that remain unanswered. In the wind tunnel studies, turbines were represented by anything from scaled models to tea strainers or wire mesh disks whose solidity was equivalent to that of a typical wind turbine. The scale factor compensation for the difference in Reynolds number between the scale model and an actual turbine is complex, and not typically accounted for. Though it is wise to study the simpler case of wakes in flat topography, which can be easily duplicated in the wind tunnel, current indications are that wind turbine farm development is actually occurring in somewhat more complex terrain. Empirical wake studies using large horizontal-axis wind turbines have not been thoroughly composited, and, therefore, the results have not been applied to the well-developed theory of wake structure. The measurement programs have made use of both in situ sensor systems, such as instrumented towers, and remote sensors, such as kites and tethered, balloonborne anemometers. We present a concise overview of the work that has been performed, including our own, which is based on the philosophy that the MOD-2 turbines are probably their own best detector of both the momentum deficit and the induced turbulence effect downwind. Only the momentum deficit aspects of the wake/machine interactions have been addressed. Both turbine power output deficits and wind energy deficits as measured by the onsite meteorological towers have been analyzed from a composite data set. The analysis has also evidenced certain topographic influences on the operation of spatially diverse wind turbines.

Miller, A. H.; Wegley, H. L.; Buck, J. W.

1995-05-01

263

Complex wakes behind objects in multispecies plasmas  

NASA Astrophysics Data System (ADS)

Many space, astrophysical, technological and laboratory plasmas are multispecies. Using particle-in-cell (PIC) numerical simulations, the novel features of the wake structures behind finite-sized objects in multispecies collisionless plasma flows are studied. In electropositive plasmas, different ion species can form separate wakes with distinct ion focus regions, and give rise to polarization of the plasma. In electronegative plasmas, with a large fraction of heavy negative ions, the polarization can be stronger due to substantial ion density reduction in the wake.

Miloch, W. J.; Vladimirov, S. V.; Yaroshenko, V. V.

2013-01-01

264

Results from the first lunar-wake flyby of ARTEMIS on wake potential, electron beams, and electrostatic waves  

NASA Astrophysics Data System (ADS)

The ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun) mission is a new two-probe lunar mission derived from the THEMIS (Time History of Events and Macroscale Interactions During Substorms) mission. On Feb 13, 2010, one of the two probes, ARTEMIS P1 (formerly THEMIS-B), made the first lunar-wake flyby of the mission. Halekas et al. [2010] reported observations of electron beams and derived the wake potential along this flyby. They suggested that the electron beams result from the net potential across the wake. In this presentation, we will show that the net potential is a result of the asymmetric electron distribution function of the solar wind and the quasi-neutrality condition. The electric field waveforms of both low-frequency and high-frequency electrostatic waves associated with the electron beams from the on-board Electric Field Instrument (EFI) will be reported. The low-frequency waves around ion cyclotron frequency showed oblique propagation, and seemed to be associated with the deceleration of the electron beams. The high-frequency electrostatic waves had a broadband spectrogram that is consistent with beam mode. We derived the wave number of the high-frequency waves using high time-resolution EFI data, and performed 1D Vlasov simulations to study the generation mechanism of the high-frequency waves. The results of the simulations are consistent with the observations of the electron beams and the derived potential structure by Halekas, et al. [2010]. Reference: Halekas, et al., 2010. First results from ARTEMIS, a new two-spacecraft lunar mission: Counter-streaming plasma populations in the lunar plasma wake. Space Sci. Rev., submitted.

Tao, J.; Ergun, R. E.; Andersson, L.; Angelopoulos, V.; Bonnell, J. W.; Newman, D. L.; McFadden, J. P.; Halekas, J. S.; Cully, C. M.; Glassmeier, K.; Roux, A.; Lecontel, O.; Larson, D. E.; Baumjohann, W.; Goldman, M. V.; Auster, H.

2010-12-01

265

Review of CFD for wind-turbine wake aerodynamics  

Microsoft Academic Search

This article reviews the state of the art of the numerical calculation of wind-turbine wake aerodynamics. Different CFD techniques for modeling the rotor and the wake are discussed. Regarding rotor modeling, recent advances in the generalized actuator approach and the direct model are discussed, as far as it attributes to the wake description. For the wake, the focus is on

B. Sanderse; Pijl van der S. P; B. Koren

2010-01-01

266

Interaction of wake turbulence with a free surface  

Microsoft Academic Search

The turbulent wake of a flat plate aligned with a uniform water flow and extending through the free surface was investigated experimentally. Laser-Doppler velocimetry (LDV) measurements show good agreement with published data for a two-dimensional wake, except in a shallow layer near the free surface. In this surface layer, the wake width is observed to double while the wake centerline

Larry M. Logory; Amir Hirsa; Douglas G. Anthony

1996-01-01

267

Exploring a flight deck based wake turbulence situational awareness tool  

Microsoft Academic Search

As NextGen concepts move toward increasing en route and terminal throughput, wake turbulence separation may become a limiting factor in the pursuit of capacity improvements. Better knowledge of the probable location of wakes (for air traffic controllers as well as pilots) could help provide safe separation from wake turbulence while avoiding unnecessary restrictions to operations. The Wake Turbulence Avoidance Automation

Clark Lunsford; Marshall Koch; H. Peter Stassen; Steven Estes; Brendan Hogan

2012-01-01

268

[Central mechanisms of sleep-wakefulness cycle].  

PubMed

Brief anatomical, physiological and neurochemical basics of the regulation of wakefulness, slow wave (NREM) sleep and paradoxical (REM) sleep are regarded as representing by the end of the first decade of the second millennium. PMID:21950094

Koval'zon, V M

269

Wake collapse in a stratified fluid.  

PubMed

A two-dimensional model is used to obtain quantitative data on characteristics of turbulently mixed wakes of bodies submerged in stratified fluids (more dense below than above). The time between turbulent mixing and maximum expansion of the wake before vertical collapse starts is 0.44 T, where T is the local Väisälä-Brunt period. Time after mixing for maximum rate of horizontal spreading is about 2.0 T. The average Väisälä-Brunt period for the oceans and atmosphere is discussed. It is predicted that the wake collapse phenomenon is not unusual in these environments. The characteristic time for the most active phase of vertical wake collapse should be between a few minutes to several tens of minutes. Qualitative observations of aircraft vapor trails tend to confirm that the phenomenon does occur at full scale. PMID:17798697

Schooley, A H

1967-07-28

270

[Physiology of sleep-wakefulness rhythms].  

PubMed

As the most important site for sleep-wakefulness change, the role of the hypothalamus is particularly emphasized based on our long term experimental data. After rostral midbrain transection, ECoG of the isolated forebrain recovered sleep-wakefulness change, with circadian rhythm, one week after transection. In this preparation, after additional bilateral preoptic or posterior hypothalamic lesions, ECoG "insomnia" or "coma" pattern appeared, respectively. Therefore, the mechanism of sleep-wakefulness change of the forebrain primarily does not depend on the lower brain stem structures such as the raphe nuclei and midbrain reticular formation. Hypothalamic sleep-wakefulness mechanism usually receives strong influence from the suprachiasmatic nucleus, but it can exert its own ultradian "rhythms" (very irregular though) in intact rats or in rats with suprachiasmatic lesions. PMID:9503822

Kawamura, H

1998-02-01

271

Nonuniqueness in wakes and boundary layers  

NASA Astrophysics Data System (ADS)

Instreamlined flow past a flat plate aligned with a uniform stream, it is shown that the Goldstein near wake and the Blasius boundary layer are nonunique solutions locally for the classical boundary layer equations, whereas the Rott-Hakkien very near wake appears to be unique. Concerning non-streamlined flow, new similarity forms are described for the pressure free vicous symmetric closure of a predominantly slender long wake beyond a large-scale separation. Features arising include nonuniqueness, singularities and algebraic behavior, consistent with non-entraining shear layers with algebraic decay. Nonuniqueness also seems possible in reattachment onto a solid surface and for nonsymmetric or pressure controlled flows including the wake of a symmetric cascade.

Smith, F. T.

1983-05-01

272

Visualization of airflow in the wake of a ship superstructure  

NASA Astrophysics Data System (ADS)

Helicopter landings on naval surface ships, such as cruisers and destroyers, must take place in the presence of an air wake created by flow over the ship superstructure. Wake turbulence over the flight deck makes piloted landings dangerous and difficult, and poses significant problems for the use of unmanned rotorcraft. To address this problem, a comprehensive set of experimental and simulation data are being collected via concurrent field tests, wind tunnel measurements, and CFD simulations. These data will facilitate an understanding of the wake turbulence produced under a variety of weather conditions, and will allow assessment of the fidelity of lower order flowfield estimates. A U.S. Navy Auxiliary Patrol (YP) Craft is used as a representative ship platform. The YP is over 100 ft long, has a similar shape to a modern destroyer, and has been modified to include a flight deck and hangar-like superstructure. Presented here are preliminary CFD results along with results from a large-scale flow visualization experiment. Qualitative information gleaned from the flow visualization is being used in the experimental design of upcoming quantitative air velocity measurements.

Brownell, C. J.; Stillman, W. P.; Golden, J. H.; Simpson, S. A.; Luznik, L.; Miklosovic, D. S.; White, G.; Burks, J. S.; Snyder, M. R.

2009-11-01

273

Effect of Velocity Ratio on the Streamwise Vortex Structures in the Wake of a Stack  

NASA Astrophysics Data System (ADS)

The time-averaged velocity and streamwise vorticity fields within the wake of a short stack were investigated in a low-speed wind tunnel using a seven-hole pressure probe. The stack was mounted normal to a ground plane and was partially immersed in a flat-plate turbulent boundary layer. The jet-to-cross-flow velocity ratio was varied from R = 0 to 3, which covered the downwash, cross-wind-dominated and jet-dominated flow regimes. In the downwash and cross-wind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip-vortex pair and base-vortex pair were similar to those found in the wake of a finite circular cylinder, located close to the free end and the base of the stack, respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair has the same orientation as the base vortex pair and is associated with the jet rise.

Adaramola, M. S.; Sumner, D.; Bergstrom, D. J.

274

Numerical Simulation and Wake Modeling of Wind Turbine Rotor as AN Actuator Disk  

NASA Astrophysics Data System (ADS)

Numerical simulations of flow fields around the wind turbine rotor simplified as an actuator disk (AD) with zero thickness have been made to investigate the flow structure and wake development in different operation states. A N-S solver has been used and the energy extracted by the rotor is represented by a discontinuous pressure jump through the actuator disk. Axial pressure and velocity development from far upstream to far downstream is fully described by the simulations, which could never be obtained by the momentum theory. It is showed that there are significant differences in wake development between inviscid and viscous conditions. In inviscid simulations, the axial velocity keeps decreasing along the oncoming flow direction, which is consistent with the momentum theory. In viscous simulations, however, the axial velocity first decreases but then gradually recovers approaching to the undisturbed velocity, due to momentum transport from outer flow to wake flow by viscous shear effect. Based on the numerical analysis, the work of this paper is also focused on wake modeling. A new two-dimensional models based on nonlinear wake development has been developed, which is capable to describe the far wake more accurately.

Shen, Xiang; Wang, Tongguang; Zhong, Wei

275

A comparison of application methods for suppressing the pecan weevil (Coleoptera: Curculionidae) with Beauveria bassiana under field conditions  

Technology Transfer Automated Retrieval System (TEKTRAN)

The pecan weevil, Curculio caryae (Horn), is a key pest of pecans. The entomopathogenic fungus Beauveria bassiana is pathogenic to C. caryae. Our objective was to compare different application methods for suppression of C. caryae adults. Treatments included direct application of B. bassiana (GHA...

276

An overview of experimental results and dispersion modelling of nanoparticles in the wake of moving vehicles.  

PubMed

Understanding the transformation of nanoparticles emitted from vehicles is essential for developing appropriate methods for treating fine scale particle dynamics in dispersion models. This article provides an overview of significant research work relevant to modelling the dispersion of pollutants, especially nanoparticles, in the wake of vehicles. Literature on vehicle wakes and nanoparticle dispersion is reviewed, taking into account field measurements, wind tunnel experiments and mathematical approaches. Field measurements and modelling studies highlighted the very short time scales associated with nanoparticle transformations in the first stages after the emission. These transformations strongly interact with the flow and turbulence fields immediately behind the vehicle, hence the need of characterising in detail the mixing processes in the vehicle wake. Very few studies have analysed this interaction and more research is needed to build a basis for model development. A possible approach is proposed and areas of further investigation identified. PMID:21193254

Carpentieri, Matteo; Kumar, Prashant; Robins, Alan

2010-12-28

277

Onset of the second wake: Dependence on the Reynolds number  

Microsoft Academic Search

The second wake transition occurs in the far wake of a bluff body. This transition destroys the Benard-von Karman vortex street originating in the near wake and produces a secondary vortex street with a lower characteristic frequency. We characterize the onset of the second wake for Reynolds numbers 50-1\\/2 power law. Our two-dimensional far-wake numerical simulations are in good agreement

Peter Vorobieff; Daniel Georgiev; Marc S. Ingber

2002-01-01

278

Waking dreams and other metachoric experiences.  

PubMed

This paper summarizes the development of the concept of metachoric experiences from 1961 onwards. The name of metachoric experience was given to one in which the whole of the environment was replaced by a hallucinatory one, although this may provide a precise replica of the physical world and appear to be completely continuous with normal experience. Prior to 1968 three types of metachoric experiences had been recognized; lucid dreams, out-of-the-body experiences (OBEs) and false awakenings, all of which showed interrelationships. The Institute's 1968 appeal for apparitional experiences led to a recognition that many of these were probably metachoric. This was suggested among other things by certain cases in which the lighting of the whole field of view changes, thus indicating that the experience was completely hallucinatory. The study of apparitions led also to the concept of waking dreams, i.e. completely hallucinatory experiences which may be initiated and terminated without any awareness of discontinuity on the part of the subject. These experiences seem to be capable of considerable apparent extension in time, thus providing a possible explanation of some reports of UFO sightings and of some of the more anomalous experiences of psychical research. In this connection the paper discusses the well-known Versailles experience of Miss Moberly and Miss Jourdain, and a published case of C.G. Jung. In conclusion some of the most obvious similarities and differences between the different types of metachoric experiences are discussed. PMID:2374788

Green, C

1990-06-01

279

HISTAMINE IN THE REGULATION OF WAKEFULNESS  

PubMed Central

The histaminergic system is exclusively localized within the posterior hypothalamus with projection to almost all the major regions of the central nervous system. Strong and consistent evidence exist to suggest that histamine, acting via H1 and/or H3 receptor has a pivotal role in the regulation of sleep-wakefulness. Administration of histamine or H1 receptor agonists induced wakefulness, whereas administration of H1 receptor antagonists promoted sleep. The H3 receptor functions as an auto-receptor and regulates the synthesis and release of histamine. Activation of H3 receptor decreased histamine release and promoted sleep. Conversely, blockade of H3 receptor promoted wakefulness. Histamine release in the hypothalamus and other target regions was highest during wakefulness. The histaminergic neurons displayed maximal activity during the state of vigilance, and cease their activity during NREM and REM sleep. The cerebrospinal levels of histamine were reduced in diseased states where hypersomnolence was a major symptom. The histamine deficient HDC KO mice displayed sleep fragmentation and increased REM sleep during the light period along with profound wakefulness deficit at dark onset, and in novel environment. Similar results were obtained when histamine neurons were lesioned. These studies strongly implicate the histaminergic neurons of the TMN to play a critical role in the maintenance of high vigilance state during wakefulness.

Thakkar, Mahesh M.

2010-01-01

280

Statistics of waves within a ship wake  

NASA Astrophysics Data System (ADS)

High-amplitude water waves induced by high-speed ferries are regularly observed in Tallinn Bay, the Baltic Sea causing intense beach erosion and disturbing marine habitants in the coastal zone. Such a strong impact on coast can be a result of a group structure of the wake and it is studied experimentally at Pikakari beach, Tallinn Bay. The most energetic vessel waves at this location have amplitudes of about 1 m and periods of 8-10 sec with maximum run-up heights up to 1.4 m. These wakes represent a certain structure, where the largest and longest waves come first and waves of smaller amplitude and period after. Sometimes the groups of different heights and periods can be separated even within one wake. The wave heights within a wake are well-described by the Weibull distribution, which has different parameters for wakes from different ships. Wave runup heights can also be described by Weibull distribution and its parameters can be connected to the parameters of the distribution of wave heights. Finally, the runup of individual waves within a wake is studied. It is shown that the largest amplification occurs for waves of weak amplitude and is in a good agreement with an estimate for the nonbreaking runup of a sinusoidal wave. The largest waves are strongly affected by the wave breaking and their runup is modeled numerically in the framework of the nonlinear shallow-water theory.

Didenkulova, I.; Rodin, A.

2012-04-01

281

Histamine in the regulation of wakefulness.  

PubMed

The histaminergic system is exclusively localized within the posterior hypothalamus with projection to almost all the major regions of the central nervous system. Strong and consistent evidence exist to suggest that histamine, acting via H? and/or H? receptor has a pivotal role in the regulation of sleep-wakefulness. Administration of histamine or H? receptor agonists induces wakefulness, whereas administration of H? receptor antagonists promotes sleep. The H? receptor functions as an auto-receptor and regulates the synthesis and release of histamine. Activation of H? receptor reduces histamine release and promotes sleep. Conversely, blockade of H? receptor promotes wakefulness. Histamine release in the hypothalamus and other target regions is highest during wakefulness. The histaminergic neurons display maximal activity during the state of high vigilance, and cease their activity during non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. The cerebrospinal levels of histamine are reduced in diseased states where hypersomnolence is a major symptom. The histamine deficient L-histidine decarboxylase knockout (HDC KO) mice display sleep fragmentation and increased REM sleep during the light period along with profound wakefulness deficit at dark onset, and in novel environment. Similar results have been obtained when histamine neurons are lesioned. These studies strongly implicate the histaminergic neurons of the TMN to play a critical role in the maintenance of high vigilance state during wakefulness. PMID:20851648

Thakkar, Mahesh M

2010-09-20

282

Wind tunnel simulations of wind turbine wake interactions in neutral and stratified wind flow.  

NASA Astrophysics Data System (ADS)

A second programme of work is about to commence as part of a further four years of funding for the UK-EPSRC SUPERGEN-Wind large-wind-farm consortium. The first part of the initial programme at Surrey was to establish and set up appropriate techniques for both on- and off-shore boundary layers (though with an emphasis on the latter) at a suitable scale, and to build suitable rotating model wind turbines. The EnFlo wind tunnel, a UK-NCAS special facility, is capable of creating scaled neutral, stable and unstable boundary layers in its 20m long working section. The model turbines are 1/300-scale of 5MW-size, speed controlled with phase-lock measurement capability, and the blade design takes into account low Reynolds-number effects. Velocity measurements are primarily made using two-component LDA, combined with a ‘cold-wire' probe in order to measure the local turbulent heat flux. Simulation of off-shore wakes is particularly constrained because i) at wind tunnel scale the inherently low surface roughness can be below that for fully rough conditions, ii) the power required to stratify the flow varies as the square of the flow speed, and could easily be impractically large, iii) low blade Reynolds number. The boundary layer simulations, set up to give near-equilibrium conditions in terms of streamwise development, and the model turbines have been designed against these constraints, but not all constraints can be always met simultaneously in practice. Most measurements so far have been made behind just one or two turbines in neutral off- and on-shore boundary layers, at stations up to 12 disk diameters downstream. These show how, for example, the wake of a turbine affects the development of the wake of a downwind turbine that is laterally off-set by say half or one diameter, and how the unaffected part from the first turbine merges with the affected wake of the second. As expected a lower level of atmospheric turbulence causes the wakes to develop and fill-in more slowly compared with the on-shore case. A turbine can also suppress the level of atmospheric turbulence below hub height. In neutral flow, the wakes grow in width and height. However, even in mild stable stratification the vertical development of the wake deficit can be completely inhibited; at least some reduction would be expected arising from the stabilizing influence on vertical fluctuations. The width in contrast develops at about the same rate. As anticipated, the wake development is slower still in the stable case because of the lower level ambient turbulence. The maximum deficit is at a lower height than it is for neutral flow. Various aspects of the turbulence in the wake have been investigated. Second-phase work will examine a larger number of wake-turbine and wake-wake interactions, make a more detailed study of how turbines alter the atmospheric turbulence, and examine more cases of stratification. Work is also in hand related to turbines in or near forested regions, and it is expected that aspects of the physics will have links with the effect a large wind farm will have on the ABL and on the wind resource for a downwind farm. The work will produce a series of test cases to assist in the development of better wake and wind resource prediction models as well as a better understanding of wake physics.

Hancock, P. E.; Pascheke, F.

2010-09-01

283

Suppression of Divergence of Low Energy Ion Beams by Space Charge Neutralization with Low Energy Electrons Emitted from Field Emitter Arrays  

SciTech Connect

Suppression of divergence of low energy neon ion beam was experimentally demonstrated by neutralizing the space charge of ion beam with low energy electrons emitted from silicon field emitter arrays (Si-FEAs). Treatment of the FEAs with trifluoromethane plasma realized surface carbonization which was efficient to elongate the lifetime of the FEA and to improve the electron energy distribution. Together with the improvement of the performance of Si-FEA, we have developed a novel electron deceleration system to produce low energy electrons. A low energy neon ion beam was produced and the beam property was investigated with and without the electron supply from surface carbonized Si-FEA (Si:C-FEA). As a result, the divergence of the neon ion beam was largely suppressed with presence of the electrons.

Ishikawa, Junzo [Department of Electronics and Information Engineering, Chubu University, 1200 Matsumoto-cho, Kasugai, 487-8501 (Japan); Gotoh, Yasuhito; Taguchi, Shuhei; Nicolaescu, Dan; Tsuji, Hiroshi; Kimoto, Tsunenobu [Department of Electronic Science and Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan); Takeuchi, Mitsuaki [JST Innovation Plaza Kyoto, Goryo-ohara, Nishiky-ku, Kyoto 615-, Japan and Photonics and Electronics Research Center, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan); Sakai, Shigeki [Nissin Ion Equpment Co., Ltd., 575 Kuze-Tonoshiro-cho, Minami-ku, Kyoto 601-8205 (Japan)

2011-01-07

284

Analysis of the radar reflectivity of aircraft vortex wakes  

NASA Astrophysics Data System (ADS)

Radar has been proposed as a way of tracking wake vortices to reduce aircraft spacing and tests have revealed radar echoes from aircraft wakes in clear air. The mechanism causing refractive index gradients in these tests is thought to be the same as that for homogeneous and isotropic atmospheric turbulence in the Kolmogorov inertial range, for which there is a scattering analysis due to Tatarski. In reality, however, the structure of aircraft wakes has a significant coherent part superimposed with turbulence, about whose structure very little is known. This work adopts a picture of a coherent (in fact two-dimensional) wake to perform a scattering analysis and calculate the reflected power. In particular, two simple mechanisms causing refractive index gradients are considered: (A) radial pressure (and therefore density) gradient in a columnar vortex arising from the rotational flow; (B) adiabatic transport of atmospheric fluid within a descending oval surrounding a vortex pair. In the scattering analysis, Tatarski's weak scattering approximation is kept but the usual assumptions of a far field and a uniform incident wave are dropped. Neither assumption is generally valid for a wake that is coherent across the radar beam. For analytical insight, an approximate analysis that invokes, in addition to weak scattering, the far-field and wide cylindrical beam assumptions, is also developed and compared with the more general analysis. Reflectivities calculated for the oval (mechanism B) are within 2 13 dB m2 of the measurements ([approximate][minus sign]70 dB m2) of MIT Lincoln Laboratory at Kwajalein atoll. However, the present predictions have a cut-off away from normal incidence which is not present in the measurements. This implies that the two-dimensional picture is not entirely complete. Estimates suggest that the thin layer of vorticity which is baroclinically generated at the boundary of the oval is turbulent and this may account for reflectivity away from normal incidence. The reflectivity of a vortex (mechanism A) is comparable to that of the oval (mechanism B) but occurs at a frequency (about 50 MHz) that is lower than those considered in all the experiments to date. This result may be useful because: (i) existing atmospheric radars (known as ST radars) already operate at this frequency and so the present prediction could be verified; (ii) rain clutter is not a problem at this frequency; (iii) mechanism A is more robust because it is independent of atmospheric stratification.

Shariff, Karim; Wray, Alan

2002-07-01

285

An experimental and analytical study of the stability of counter-rotating vortex pairs with applications for aircraft wake turbulence control  

NASA Astrophysics Data System (ADS)

Aircraft trailing vortex wakes are commonly referred to as `wake turbulence' and may pose a flight safety hazard to other aircraft that may encounter the wake. This hazard is of critical interest during the take-off and landing stages of flight, where aircraft are in the closest proximity to one another. During these flight stages, it is common for transport aircraft to be in a high-lift, or flaps down, configuration. In an effort to study these wakes a generic four-vortex wake is generated experimentally, such that the results are independent of a specific wing loading condition. Three principle objectives served to focus the research project that is presented in this dissertation. The first two objectives were to develop an improved understanding of the wake configurations that were conducive to large instability growth rates and to subsequently use quantitative methods to identify the instability modes that dominate the far-field wake dynamic. With a clear understanding of the physics of an unstable aircraft wake, the third objective of the research project was to use this newly attained information to recommend methods for a reliable wake control strategy. A compilation of flow visualization results shows a design space of counter-rotating wake configurations, defined by the circulation and span ratios, where rapidly amplifying instabilities are consistently seen to exist. This design space is also seen to encompass rigidly-translating wake systems. A combination of quantitative flow visualization estimates, hot-wire anemometry and an analytical stability analysis was successful in identifying two forms of bending wave instability, namely the long and short-wavelength modes. Having identified two bending instability modes in the experimental wake, it was possible to suggest a strategy by which these modes could be exploited for the control of aircraft wakes.

Babie, Brian Matthew

286

Response of a circular cylinder wake to a symmetric actuation by non-thermal plasma discharges  

NASA Astrophysics Data System (ADS)

In this study, the flow past a circular cylinder is manipulated by two plasma discharges placed on both sides of the model (at ±50°). A parametric investigation by force balance is conducted to define the sensitivity of the flow field to unsteady perturbations imparted by plasma actuators (dielectric barrier discharge) at 15.6 m/s ( Re D = 40,000). Effects of simple sinusoidal waveform, burst modulation and amplitude modulation are compared for low-frequency excitations. Regardless of the excitation mode, the cylinder experiences a large increase in the drag coefficient. The larger drag increase is observed for excitation related to the lock-on regime. Fast PIV measurements and triple decomposition by proper orthogonal decomposition are performed to extract the dynamical changes in the cylinder wake and to discriminate the control effects on the coherent and fluctuating turbulence. As expected, the control principally acts on the coherent flow structures. When forced, the vortices form closer to the base of the cylinder regardless of the actuation mode. This results in the drag increase observed by force measurements. The effectiveness of burst modulation is also due to the suppression of irregular shedding that is observed in the natural flow sequence and to a high level of correlation between the upper and lower vortex shedding. Finally, flow visualizations indicate that similar results can be obtained at higher Reynolds number ( Re D = 128,000, 50 m/s).

Benard, N.; Moreau, E.

2013-02-01

287

Effect of velocity ratio on the streamwise vortex structures in the wake of a stack  

NASA Astrophysics Data System (ADS)

The time-averaged velocity and streamwise vorticity fields within the wake of a stack were investigated in a low-speed wind tunnel using a seven-hole pressure probe. The experiments were conducted at a Reynolds number, based on the stack external diameter, of ReD=2.3×104. The stack, of aspect ratio AR=9, was mounted normal to a ground plane and was partially immersed in a flat-plate turbulent boundary layer, where the ratio of the boundary layer thickness to the stack height was ?/H?0.5. The jet-to-cross-flow velocity ratio was varied from R=0 to 3, which covered the downwash, crosswind-dominated and jet-dominated flow regimes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip vortex pair located close to the free end of the stack, and the base vortex pair located close to the ground plane within the flat-plate boundary layer, were similar to those found in the wake of a finite circular cylinder, and were associated with the upwash and downwash flow fields within the stack wake, respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair had the same orientation as the base vortex pair and was associated with the jet rise. The peak vorticity and strength of the streamwise vortex structures were functions of the jet-to-cross-flow velocity ratio. For the tip vortex structures, their peak vorticity and strength reduced as the jet-to-cross-flow velocity ratio increased.

Adaramola, M. S.; Sumner, D.; Bergstrom, D. J.

2010-01-01

288

A CFD model of the wake of an offshore wind farm: using a prescribed wake inflow  

Microsoft Academic Search

An CFD model of the wake of an offshore wind farm, expanding existing measurements is proposed. The method is based on solving the Navier Stokes equation in a large domain downstream an offshore wind farm. The inflow of the domain is estimated using existing met mast measurements from both free stream and directly in-wake conditions. A comparison between the simulation

P-E Réthoré; A Bechmann; N N Sørensen; S T Frandsen; J Mann; H E Jørgensen; O Rathmann; S E Larsen

2007-01-01

289

Four-dimensional characterization of inflow to and wakes from a multi-MW turbine: overview of the Turbine Wake and Inflow Characterization Study (TWICS2011)  

NASA Astrophysics Data System (ADS)

To support substantial deployment of renewably-generated electricity from the wind, critical information about the variability of wind turbine wakes in the real atmosphere from multi-MW turbines is required. The assessment of the velocity deficit and turbulence associated with industrial-scale turbines is a major issue for wind farm design, particularly with respect to the optimization of the spacing between turbines. The significant velocity deficit and turbulence generated by upstream turbines can reduce the power production and produce harmful vibrations in downstream turbines, which can lead to excess maintenance costs. The complexity of wake effects depends on many factors arising from both hardware (turbine size, rotor speed, and blade geometry, etc.) and from meteorological considerations such as wind velocity, gradients of wind across the turbine rotor disk, atmospheric stability, and atmospheric turbulence. To characterize the relationships between the meteorological inflow and turbine wakes, a collaborative field campaign was designed and carried out at the Department of Energy's National Wind Technology Center (NREL/NWTC) in south Boulder, Colorado, in spring 2011. This site often experiences channeled flow with a consistent wind direction, enabling robust statistics of wake velocity deficits and turbulence enhancements. Using both in situ and remote sensing instrumentation, measurements upwind and downwind of multi-megawatt wind turbine in complex terrain quantified the variability of wind turbine inflow and wakes from an industrial-scale turbine. The turbine of interest has a rated power of 2.3 MW, a rotor diameter of 100m, and a hub height of 80m. In addition to several meteorological towers, one extending to hub height (80m) and another extending above the top of the rotor disk (135m), a Triton mini-sodar and a Windcube lidar characterized the inflow to the turbine and the variability across the site. The centerpiece instrument of the TWICS campaign was the NOAA High Resolution Doppler lidar (HRDL), a scanning lidar which captured three-dimensional images of the turbine inflow and wake. Over several weeks, 48+ hours of HRDL observations during a variety of wind speed and atmospheric stability conditions were collected using three scanning strategies. Wake features such as lofting, meandering, intersection with the ground, and expansion factors are identified and discussed. Observations of a remarkably long-distance wake are presented and compared with existing wake models.

Lundquist, J. K.; Banta, R. M.; Pichugina, Y.; Brewer, A.; Alvarez, R. J.; Sandberg, S. P.; Kelley, N. D.; Aitken, M.; Clifton, A.; Mirocha, J. D.

2011-12-01

290

[Sleep-wake regulation by prostaglandin D2 and adenosine].  

PubMed

Prostaglandin (PG) D2 and adenosine are potent endogenous somnogens that accumulate in the brain during prolonged wakefulness. Lipocalin-type PGD synthase (L-PGDS) catalyzes the isomerization of PGH2, a common precursor of various prostanoids, to produce PGD2. L-PGDS is localized in the leptomeninges, choroid plexus, and oligodendrocytes of the central nervous system. PGD2 stimulates DP1 receptors localized in the basal forebrain and increases the local extracellular concentration of adenosine, a paracrine signaling molecule, to promote sleep. Adenosine activates adenosine A2A receptor-expressing neurons in the basal forebrain and ventrolateral preoptic area (VLPO) and inhibits adenosine A1 receptor-possessing arousal neurons. Sleep-promoting neurons in the VLPO send inhibitory signals to suppress the histaminergic neurons in the tuberomammillary nucleus (TMN); the histaminergic neurons contribute to arousal through histamine H1 receptors. GABAergic inhibition of TMN is involved in the induction of non-rapid eye movement (non-REM) sleep by PGD2 and adenosine A2A agonists. The neural network between the VLPO and TMN is considered to play a key role in regulation of vigilance states. Administering an L-PGD inhibitor (SeCl4), DP1 antagonist (ONO-4127Na), or adenosine A2A receptor antagonist (caffeine) suppresses both non-REM and REM sleep, indicating that the PGD2-adenosine system is crucial for maintaining physiological sleep. Selective gene-deletion strategies based on Cre/loxP technology and focal RNA interference have been used for silencing the expression of the A2A receptor by local infection with adeno-associated virus carrying Cre-recombinase or short hairpin RNA. The results of these studies have shown that the A2Asubreceptors in the shell region of the nucleus accumbens are responsible for the effect of caffeine on wakefulness. PMID:22647469

Nagata, Nanae; Urade, Yoshihiro

2012-06-01

291

Transition mechanisms in laminar separation bubbles with and without incoming wakes and synthetic jet effects  

NASA Astrophysics Data System (ADS)

Laminar separation and transition processes of the boundary layer developing under a strong adverse pressure gradient, typical of Ultra-High-Lift turbine profiles, have been experimentally investigated for a low Reynolds number case. The boundary layer development has been surveyed for different conditions: with steady inflow, with incoming wakes and with the synchronized forcing effects due to both incoming wakes and synthetic jet (zero net mass flow rate jet). In this latter case, the jet Strouhal number has been set equal to half the wake-reduced frequency to synchronize the unsteady forcing effects on the boundary layer. Measurements have been taken by means of a single-sensor hot-wire anemometer. For the steady inflow case, particle image velocimetry has been employed to visualize the large-scale vortical structures shed as a consequence of the Kelvin-Helmholtz instability mechanism. For the unsteady inflow cases, a phase-locked ensemble averaging technique, synchronized with the wake and the synthetic jet frequencies, has been adopted to reconstruct the boundary layer space-time evolution. Results have been represented as color plots, for several time instants of the forcing effect period, in order to provide an overall view of the time-dependent transition and separation processes in terms of ensemble-averaged velocity and unresolved unsteadiness distributions. The phase-locked distributions of the unresolved unsteadiness allowed the identification of the instability mechanisms driving transition as well as the Kelvin-Helmholtz structures that grow within the separated shear layer during the incoming wake interval and the synthetic jet operating period. Incoming wakes and synthetic jet effects in reducing and/or suppressing flow separation are investigated in depth.

Simoni, Daniele; Ubaldi, Marina; Zunino, Pietro; Bertini, Francesco

2012-07-01

292

Interaction of exhaust jets and aircraft wake vortices: small-scale dynamics and potential microphysical-chemical transformations  

NASA Astrophysics Data System (ADS)

This paper summarizes recent progress made in the understanding of the interaction between exhaust jets and trailing vortices, in the near field of an aircraft wake. Emphasis is placed on the effects of the jet on the wake vortex dynamics and the effects of the wake on the exhaust dispersion, as well as their potential microphysical and chemical transformations. We discuss in detail results of high-resolution numerical simulations of jet/vortex interaction that include microscale turbulent mixing, gas-phase chemistry and contrail formation. To cite this article: R. Paoli, F. Garnier, C. R. Physique 6 (2005).

Paoli, Roberto; Garnier, François

2005-05-01

293

Progress toward 3D wake structure measurements of aquatic animals using SCUVA  

NASA Astrophysics Data System (ADS)

Recent developments in multi-camera DPIV techniques now enable measurement of three-dimensional wake structure in aquatic animals. The present goal is to integrate those techniques with a self-contained underwater velocimetry apparatus (SCUVA), in order to facilitate in situ measurements of 3D wake structure by SCUBA divers in the field. SCUVA presents an additional constraint in that the flow imaging must be accomplished by a single camera viewing the flow from a single direction. We present progress toward the incorporation of 3D wake measurement techniques into a single-camera platform. The approach relies on the image defocusing concept and calculation of Lagrangian coherent structures directly from fluid particle trajectories. The results may benefit laboratory methods as well as the field techniques that are the present focus.

Dabiri, John; Katija, Kakani

2007-11-01

294

Suppression of ballistic electron transmission through a semiconductor II-structure by an external transverse electric field  

Microsoft Academic Search

We have conducted numerical studies of ballistic electron transport in a semiconductor II-structure when an external transverse electric field is applied. The device conductance as a function of electron energy and the strength of the transverse electric field is calculated on the basis of tight-binding Green's function formalism. The calculations show that a relatively weak electric field can induce very

Sheng Wei-dong; Xia Jian-bai

1996-01-01

295

Spatial characterization of vortical structures and internal waves in a stratified turbulent wake using proper orthogonal decomposition  

NASA Astrophysics Data System (ADS)

Proper orthogonal decomposition (POD) has been applied to two-dimensional transects of vorticity obtained from numerical simulations of the stratified turbulent wake of a towed sphere at a Reynolds number Re=(UD)/?=5×103 and Froude number Fr=2U/(ND)=4 (U and D are characteristic velocity and length scales and N is the stratification frequency). At 231 times during the interval 12field inside the wake core in terms of the relative influence of buoyancy on flow dynamics. The geometry of the individual eigenmodes shows a vorticity structure that is buoyancy-controlled at the lowest modes and is increasingly more actively turbulent as modal index is increased. In the wake ambient, i.e., the initially quiescent region outside the turbulent wake, the geometry of the POD modes consists of distinct internal wave rays whose angle to the horizontal is strongly dependent on modal index. Reconstruction of vorticity fields from subranges of POD modes indicates that, both inside the wake core but also in the wave-dominated ambient, each modal subrange is not only associated with a particular flow structure but also a characteristic timescale of motion. These preliminary findings suggest that POD may be a highly suitable alternative to globally defined basis functions in analyzing spatially localized internal wave fields emitted from a turbulent source that are also localized in space. In particular, it may serve as a platform toward an improved understanding of two fundamental questions associated with the nonequilibrium regime of stratified wake evolution: the structural transitions of the vorticity field within the wake core and the radiation of internal waves by the wake.

Diamessis, Peter J.; Gurka, Roi; Liberzon, Alex

2010-08-01

296

Delayed Orexin Signaling Consolidates Wakefulness and Sleep: Physiology and Modeling  

PubMed Central

Orexin-producing neurons are clearly essential for the regulation of wakefulness and sleep because loss of these cells produces narcolepsy. However, little is understood about how these neurons dynamically interact with other wake- and sleep-regulatory nuclei to control behavioral states. Using survival analysis of wake bouts in wild-type and orexin knockout mice, we found that orexins are necessary for the maintenance of long bouts of wakefulness, but orexin deficiency has little impact on wake bouts <1 min. Since orexin neurons often begin firing several seconds before the onset of waking, this suggests a surprisingly delayed onset (>1 min) of functional effects. This delay has important implications for understanding the control of wakefulness and sleep because increasing evidence suggests that different mechanisms are involved in the production of brief and sustained wake bouts. We incorporated these findings into a mathematical model of the mouse sleep/wake network. Orexins excite monoaminergic neurons and we hypothesize that orexins increase the monoaminergic inhibition of sleep-promoting neurons in the ventrolateral preoptic nucleus. We modeled orexin effects as a time-dependent increase in the strength of inhibition from wake- to sleep-promoting populations and the resulting simulated behavior accurately reflects the fragmented sleep/wake behavior of narcolepsy and leads to several predictions. By integrating neurophysiology of the sleep/wake network with emergent properties of behavioral data, this model provides a novel framework for investigating network dynamics and mechanisms associated with normal and pathologic sleep/wake behavior.

Diniz Behn, C. G.; Kopell, N.; Brown, E. N.; Mochizuki, T.; Scammell, T. E.

2011-01-01

297

Formulations of the endophytic bacterium Bacillus subtilis Tu-100 suppress Sclerotinia sclerotiorum on oilseed rape and improve plant vigor in field trials conducted at separate locations.  

PubMed

Sclerotinia sclerotiorum causes serious yield losses in crops in the People's Republic of China. Two formulations of oilseed rape seed containing the bacterium Bacillus subtilis Tu-100 were evaluated for suppression of this pathogen in field trials conducted at two independent locations. The pellet formulation significantly reduced disease (incidence and disease index) and increased plant dry mass, while the wrap formulation significantly reduced disease incidence and significantly increased plant dry mass at both field locations. Mean seed yield per 120 plants with both formulations of isolate Tu-100 was significantly greater than the appropriate controls, but at only one of the locations. Both formulations provided stable B. subtilis Tu-100 biomass (?10(5) CFU·g(-1)) and seed germination (?85%) over a 6 month period at room temperature. Polymerase chain reaction and DNA sequence analysis identified ituC and ituD, and bacAB and bacD in the genome of isolate Tu-100. These genes are involved in the biosynthesis of iturin and bacilysin. Iturin was detected in culture filtrates from isolate Tu-100, with thin layer chromatography. Detection of bacilysin was not attempted. Experiments reported here indicate the commercial viability of B. subtilis Tu-100 for suppression of S. sclerotiorum on oilseed rape. PMID:21767217

Hu, Xiaojia; Roberts, Daniel P; Maul, Jude E; Emche, Sarah E; Liao, Xing; Guo, Xuelan; Liu, Yeying; McKenna, Laurie F; Buyer, Jeffrey S; Liu, Shengyi

2011-07-18

298

Some dream mechanisms in Finnegans Wake.  

PubMed

This paper does not purport to offer a psychoanalytic reading of Finnegans Wake, but rather to demonstrate how, in recreating the mechanisms of the dream, Joyce's masterpiece offers to psychoanalysis a uniquely rich opportunity to explore the shadowy play of the dream in the permanence of a work of art. In particular, the manner in which Finnegans Wake tells its story through the distortions of dream narrative while bodying forth its protagonists in the substitutions of dream-identity are explored, with the help of certain Freudian and Lacanian concepts of unconscious structure. PMID:8407134

Cox, O

1993-08-01

299

WAKEX 86: A Ship Wake/Films Exploratory Experiment.  

National Technical Information Service (NTIS)

In an exploratory experiment on Chesapeake Bay we examined several aspects of ship wakes and their interaction with natural and artificial surface films. We used aerial photography to record these interactions, the geometries of white water wakes and the ...

J. A. Kaiser W. D. Garrett S. E. Ramberg R. D. Peltzer D. M. Andrews

1988-01-01

300

Wake Turbulence Training Aid (on CD-ROM).  

National Technical Information Service (NTIS)

The goal of the Wake Turbulence Training Aid is to reduce the number of wake turbulence-related accidents and incidents by improving the pilot's and air traffic controller's decision making and situational awareness through increased and shared understand...

1995-01-01

301

Trailing Edge Wake Flow Characteristics of Upper Surface Blown Configurations.  

National Technical Information Service (NTIS)

Mean and fluctuating flow characteristics in the wake of upper surface blown flap configurations are presented. Relative importance of the longitudinal and the transverse components of the wake flow turbulence for noise generation are evaluated using corr...

N. N. Reddy

1978-01-01

302

Ion-wake-mediated particle interaction in a magnetized-plasma flow.  

PubMed

The interaction forces between dust grains in a flowing plasma are strongly modified by the formation of ion wakes. Here, we study the interparticle forces mediated by ion wakes in the presence of a strong magnetic field parallel to the ion flow. For increasing magnetic flux densities a continuous decay of the interaction force is observed. This transition occurs at parameters, where the ion cyclotron frequency starts to exceed the ion plasma frequency, which is in agreement with theoretical predictions. The modification of the interparticle forces is important for the understanding of the structure and dynamics of magnetized dusty plasmas. PMID:23030094

Carstensen, Jan; Greiner, Franko; Piel, Alexander

2012-09-27

303

Identification of vortex pairs in aircraft wakes from sectional velocity data  

Microsoft Academic Search

The dynamics of multiple-vortex wake systems behind aircraft endangering air traffic can be assessed also from physical modelling.\\u000a Large-scale laboratory investigations of multiple-vortex systems have been performed in a free-flight laboratory and in a\\u000a water towing tank. Specialized PIV measurements provide time-resolved flow velocity fields normal to the wake axis. The applicability\\u000a of various ?u-based vortex identification schemes to planar

Carl F. v. Carmer; Robert Konrath; Andreas Schröder; Jean-Claude Monnier

2008-01-01

304

Experimental study of the near-wake structure of a wind turbine operating over complex terrain  

SciTech Connect

Wind parks are often cited in complex terrain whose features determine the wind flow over the area. Results from a field experiment, comprising in-situ and remote sensing techniques (high-resolution acoustic sounders), concerning the upwind area and the near-wake region behind a single medium-sized wind turbine are presented. The experimental site is the Samos Island Wind Park installed on top of a 390 m-high saddle. Because of the topography, wind speed acceleration and channeling effects are expected; thus, the commonly used logarithmic profile is not valid, and the choice of a representative surface roughness length z{sub o} is difficult. Interesting features of the profiles of the standard deviation of the ambient wind speed are also presented. The obtained results reveal a nonlinear interaction of the near wake with the turbine-tower shadowing, while cross-wind wake profiles indicate a potential core structure. The effect of ambient turbulence is apparent, especially at lower wind speeds, even at a distance of one rotor diameter (1 D) behind the turbine. The wake centerline at distances greater than 1 D is often observed at heights greater than the hub-height and attributed to the wind flow characteristics over the Wind Park. Finally, evidence of rotational motion inside the wake is identified. 40 refs., 18 figs., 3 tabs.

Helmis, C.G.; Papadopoulos, K.H.; Asimakopoulos, D.N.; Papageorgas, P.G.; Soilemes, A.T. [Univ. of Athens (Greece)

1995-06-01

305

Experimental Study of the Temporal Nature of an Actively Controlled Three Dimensional Turret Wake  

NASA Astrophysics Data System (ADS)

Experimental measurements have been performed to characterize the actively controlled wake of a three-dimensional, non- conformal turret which is a bluff body commonly used for housing optical systems on airborne platforms. As a bluff body, turrets can generate strong turbulent flow fields that degrade the performance of the optical systems and the aircraft. Experiments were performed in a low-speed wind tunnel at Syracuse University using particle image velocimetry and dynamic pressure measurements with the objective of developing a better understanding of the spatial and temporal nature of the wake flow field. Active control was achieved using dynamic suction in the vicinity of the turret aperture and was found to have a significant impact on the structure of the wake as well as the temporal characteristics of the flow field. With a better understanding of the wake characteristics, closed-loop, active flow control systems will be developed to help reduce fluctuating loading and aero- optical distortions associated with the turbulent flow field.

Shea, Patrick; Glauser, Mark

2011-11-01

306

Vortex wake investigation behind a wing-flap model with jet simulations  

Microsoft Academic Search

To get a better insight in the effect of jets on vortex development and decay, stereo-PIV measurements were performed in a towing tank behind a flapped aircraft model. The experimental data set yields the wake vortex behavior in a range that extends from the vortex formation stage up to the mid-field (approximately t* =2 corresponding to 100 wingspans for a

L. L. M. Veldhuis; R. De Kat

2008-01-01

307

Stability characteristics of counter-rotating vortex pairs in the wakes of triangular-flapped airfoils  

Microsoft Academic Search

A rapidly growing instability is observed to develop between unequal strength, counter-rotating vortex pairs in the wakes of airfoils with outboard triangular flaps. To investigate the physical mechanisms for this instability, a linear stability analysis is performed on a single vortex pair. This analytical model reveals that the instability is driven by the strain rate field from one vortex acting

Jason Marc Ortega

2001-01-01

308

Flow and deformation of the capillary glycocalyx in the wake of a leukocyte  

Microsoft Academic Search

An analysis is presented of the axisymmetric axial and radial flow and deformation fields throughout the endothelial-cell glycocalyx surface layer in the wake region behind a leukocyte moving steadily through a capillary. The glycocalyx, modeled as a thin poroelastic surface layer lining the capillary wall, is assumed to consist of a binary mixture of a linearly viscous fluid constituent and

Edward R. Damiano; Thomas M. Stace

2005-01-01

309

Look at the Influence of Building Orientation on Plume Dispersion in the Wake of a Building.  

National Technical Information Service (NTIS)

Observations of mean pollutant concentration profiles downwind of a block-sized model building are reported. These data are part of a more comprehensive field model study of building wake effects conducted in the U.S. Environmental Protection Agency's Flu...

A. H. Huber

1986-01-01

310

Research article An overview of a Lagrangian method for analysis of animal wake dynamics  

Microsoft Academic Search

Summary The fluid dynamic analysis of animal wakes is becoming increasingly popular in studies of animal swimming and flying, due in part to the development of quantitative flow visualization techniques such as digital particle imaging velocimetry (DPIV). In most studies, quasi-steady flow is assumed and the flow analysis is based on velocity and\\/or vorticity fields measured at a single time

Jifeng Peng; John O. Dabiri

311

First results from ARTEMIS lunar wake crossing: observations and hybrid simulation  

Microsoft Academic Search

The Moon does not have an intrinsic magnetic field and its conductivity is not sufficient to facilitate the development of an induced magnetosphere. The interaction of the Moon with the unperturbed solar wind (SW) is, hence, dominated by the absorption of SW particles on its surface and the consequent generation of a lunar wake on the night side. The SW

F. Plaschke; S. Wiehle; V. Angelopoulos; H. Auster; E. Georgescu; K. Glassmeier; U. M. Motschmann; D. G. Sibeck

2010-01-01

312

Wind tunnel studies of a ship model using vortex generators to improve wake velocities  

Microsoft Academic Search

Severe vibration during trials of a 13,000 ton displacement cargo ship was attributed to the propeller working in a strongly non-uniform velocity field. This report gives the results of a series of wind tunnel experiments performed on a reflex model fitted with vortex generators which substantially improved the wake velocity distribution. It was recommended that these generators be geometrically scaled

N. Matheson

1974-01-01

313

LOOK AT THE INFLUENCE OF BUILDING ORIENTATION ON PLUME DISPERSION IN THE WAKE OF A BUILDING  

EPA Science Inventory

Observations of mean pollutant concentration profiles downwind of a block-sized model building are reported. These data are part of a more comprehensive field model study of building wake effects conducted in the U.S. Environmental Protection Agency's Fluid Modeling Facility. The...

314

Interactions in the far wake behind a pair of cylinders  

Microsoft Academic Search

We present an experimental study of far wakes behind a pair of cylinders (diameter D) separated by a cross-flow axis-to-axis distance S in a quasi-two-dimensional gravity-driven soap-film flow. A secondary vortex street forms in the far wake of each cylinder. As we decrease S, we observe coupling between the structures in the far wake. Visualization of the far wake behind

Tanveer Shakeel; Daniel Georgiev; Jesse Vigil; Peter Vorobieff

2002-01-01

315

Hypothalamic Arousal Regions Are Activated during Modafinil- Induced Wakefulness  

Microsoft Academic Search

Modafinil is an increasingly popular wake-promoting drug used for the treatment of narcolepsy, but its precise mechanism of action is unknown. To determine potential pathways via which modafinil acts, we administered a range of doses of modafinil to rats, recorded sleep\\/wake activity, and studied the pattern of neuronal activation using Fos immunohistochemistry. To contrast modafinil-induced wakefulness with spontaneous wakefulness, we

Thomas E. Scammell; Ivy V. Estabrooke; Marie T. McCarthy; Richard M. Chemelli; Masashi Yanagisawa; Matthew S. Miller; Clifford B. Saper

2000-01-01

316

Injection of Tunnel Ionized Electrons into Laser-Produced Wakes  

NASA Astrophysics Data System (ADS)

The injection of electrons via tunneling ionization into a laser driven wakefield accelerator has been studied with experiments, theory and simulations. In this work the large difference in ionization potentials between successive ionization states of trace atoms, is used as the mechanism for injecting electrons into a laser driven wakefield. Here a mixture of helium and trace amounts of either nitrogen or methane (CH4) gas was used. Electrons from the K shell of either nitrogen or carbon were tunnel ionized near the peak of the laser pulse and injected directly into the wake. The wake was created by electrons from majority helium atoms with contributions, depending on which gas mixture was used, from the either the L shell of nitrogen or the hydrogen and the L shell of carbon. Using the helium nitrogen gas mixture, the threshold intensity at which trapping was observed to occur corresponded to the intensity required to ionize the 6th electron from nitrogen (i.e. the first electron within the K shell). This indicates ionization of the K-shell of nitrogen triggers injection, and the subsequent trapping and acceleration of electrons. The electron energy spectrum was observed to be quasi-continuous for a laser ao ? 2. This spectral shape is a result of the continuous ionization and injection which occurs as long as the magnitude of the laser field remains above that required to ionize the K-shell of the nitrogen. The relative amount of charge accelerated, the intensity threshold, and spectral shape of accelerated electrons were found to be in good agreement with 3-D particle in cell code simulations which modeled the interaction. The trapping of electrons into a wakefield was studied theoretically using a 3-D Hamiltonian description of an electron within a electromagnetic field. From this description, a constant of motion can be found which relates the scalar and vector potentials of the wake and laser to the momentum of an electron. In this manner the required potential difference that an electron must experience to become trapped can be solved for. This estimate of the required potential difference for trapping to occur was found to be in good agreement with that observed in 2-D particle in cell code simulations. Using the 3-D scaling laws for the laser wakefield accelerator in the blowout regime, it was found injecting electrons directly into the wakefield, as they are when injected via ionization, significantly increases the potential difference, or the amount of energy available to the electron, to become trapped. This increase in available potential can in turn be used to lower the absolute wake amplitude necessary for trapping to occur. This reduction in wake amplitude means that electrons can be trapped into wakes with lower amplitudes driven by lasers with lower peak powers. The acceleration of electrons at reduced laser powers using ionization injection has been confirmed experimentally. Using the helium nitrogen or helium methane gas mixtures, accelerated electrons have been routinely observed using laser powers 2--4 times lower than what has been required to accelerate electrons from plasmas created from pure helium gas at similar densities.

Pak, Arthur

317

Increase in the mitotic recombination frequency in Drosophila melanogaster by magnetic field exposure and its suppression by vitamin E supplement  

Microsoft Academic Search

In order to estimate possible mutagenic and\\/or carcinogenic activity of electromagnetic fields, wing spot tests were performed in Drosophila melanogaster. A DNA repair defective mutation mei-41D5 was introduced into the conventional mwh\\/flr test system to enhance mutant spot frequency. Third instar larvae were exposed to a 5-Tesla static magnetic field for 24 h, and after molting, wings were examined under

Takao Koana; Mikie O Okada; Masateru Ikehata; Masayoshi Nakagawa

1997-01-01

318

46 CFR 277.1 - Guam, Midway and Wake.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false Guam, Midway and Wake. 277.1 Section...FOREIGN TRADE; INTERPRETATIONS § 277.1 Guam, Midway and Wake. Steamship service...States mainland and ports in the islands of Guam, Midway and Wake is not âdomestic...

2012-10-01

319

The neural circuit of orexin (hypocretin): maintaining sleep and wakefulness  

Microsoft Academic Search

Sleep and wakefulness are regulated to occur at appropriate times that are in accordance with our internal and external environments. Avoiding danger and finding food, which are life-essential activities that are regulated by emotion, reward and energy balance, require vigilance and therefore, by definition, wakefulness. The orexin (hypocretin) system regulates sleep and wakefulness through interactions with systems that regulate emotion,

Takeshi Sakurai

2007-01-01

320

Wakefulness and visual responsiveness of low medical risk preterms  

Microsoft Academic Search

Wakefulness and visual responsiveness were studied in 45 (24 males, 21 females) low medical risk preterms at expected date of birth and 23 (9 males, 14 females) term healthy neonates of the same racial and social background. Three measures of wakefulness and two responsiveness measures were used. Preterms were more wakeful but not more visually responsive than full?term infants. Moreover,

Sarah l. Friedman; Blanche S. Jacobs; Milton W. Jacobs Jr

1984-01-01

321

Approaches to Validation of CFD Models for Far Ship Wake  

Microsoft Academic Search

The centerline wake of surface ships can extend to tens of kilometers on synthetic aperture radar (SAR) images. However, the hydrodynamics of far wakes of ships are not well understood. Our assumption is that far from the ship, the pattern of flows comprising the wake is represented by longitudinal coherent vortices, which gross parameters only slowly change in the direction

A. Fujimura; A. Soloviev

2008-01-01

322

Power density in theta/alpha frequencies of the waking EEG progressively increases during sustained wakefulness.  

PubMed

Electroencephalogram (EEG) power density and self-rated fatigue were assessed in nine healthy women during a 40-hour period of sustained wakefulness under constant behavioral and environmental conditions (constant routine protocol). Waking EEG recordings were performed for 4 minutes after 3, 10, 27 and 34 hours of prior wakefulness. EEG power density in the 6.25- to 9.0-Hz frequency range progressively increased across the four recordings, suggesting an endogenous homeostatic component in the regulation of the theta/alpha frequencies under constant conditions. Subjective fatigue also exhibited an increasing component in the course of the constant routine protocol, with a clear circadian modulation. Fatigue ratings and the theta/ alpha power density of the waking EEG recorded at the same four time points during the constant routine protocol correlated significantly. Our data demonstrate the presence of a homeostatic component in the control of EEG power density in the 6.25- to 9.0-Hz range. PMID:8746397

Cajochen, C; Brunner, D P; Kräuchi, K; Graw, P; Wirz-Justice, A

1995-12-01

323

Radiative forcing over ocean by Ship Wakes  

NASA Astrophysics Data System (ADS)

Changes in surface albedo represent one of the main forcing agents that can counteract, to some extent, the positive forcing from increasing greenhouse gas concentrations. Here, we report on enhanced ocean reflectance from ship wakes over the Pacific Ocean near the California coast, where we determined, based on airborne radiation measurements that ship wakes can increase reflected sunlight by more than 100%. We assessed the importance of this increase to climate forcing, where we estimated the global radiative forcing of ship wakes to be -0.00014 ± 53% Wm^-2 assuming a global distribution of 32331 ships of size ?100000 gross tonnage. The forcing is smaller than the forcing of aircraft contrails (-0.007 to +0.02 Wm^-2), but considering that the global shipping fleet has rapidly grown in the last five decades and this trend is likely to continue because of the need of more inter-continental transportation as a result of economic globalization, we argue that the radiative forcing of wakes is expected to be increasingly important especially in harbors and coastal regions.

Gatebe, C. K.; Wilcox, E. M.; Poudyal, R.; Wang, J.

2011-12-01

324

Wall Temperature Effects on Laminar Wakes.  

National Technical Information Service (NTIS)

An experimental investigation was made of the effects of cold wall conditions on the structure of the laminar near wake of a 7 degree half-angle right circular cone with a sharp nose at zero pitch and yaw. Free stream Mach number and Reynolds number were ...

A. R. Ahmadi M. Finston

1975-01-01

325

Explicit expressions of impedances and wake functions  

SciTech Connect

Sections 3.2.4 and 3.2.5 of the Handbook of Accelerator Physics and Engineering on Landau damping are combined and updated. The new addition includes impedances and wakes for multi-layer beam pipe, optical model, diffraction model, and cross-sectional transition.

Ng, K.Y.; /Fermilab; Bane, K,; /SLAC

2010-10-01

326

Instability and unsteadiness of aircraft wake vortices  

Microsoft Academic Search

This paper presents a review of theoretical and experimental results on stability and other unsteady properties of aircraft wakes. The basic mechanisms responsible for the propagation and the amplification of perturbation along vortices, namely the Kelvin waves and the cooperative instabilities, are first detailed. These two generic unsteady mechanisms are described by considering asymptotic linear stability analysis of model flows

L. Jacquin; D. Fabre; D. Sipp; H. Vollmers; Camille Soul

327

Explicit Expressions of Impedances and Wake Functions  

SciTech Connect

Sections 3.2.4 and 3.2.5 of the Handbook of Accelerator Physics and Engineering on Landau damping are combined and updated. The new addition includes impedances and wakes for multi-layer beam pipe, optical model, diffraction model, and cross-sectional transition.

Ng, K.Y.; /Fermilab; Bane, K,; /SLAC

2012-06-11

328

Wake County Public School System Design Guidelines.  

ERIC Educational Resources Information Center

|The Wake County Public School System has published its guidelines for planning and design of functional, cost effective, and durable educational facilities that are attractive and enhance the students' educational experience. The guidelines present basic planning requirement and design criteria for the entire construction process, including:…

Wake County Public School System, Raleigh, NC.

329

Wake County Public School System Design Guidelines.  

ERIC Educational Resources Information Center

The Wake County Public School System has published its guidelines for planning and design of functional, cost effective, and durable educational facilities that are attractive and enhance the students' educational experience. The guidelines present basic planning requirement and design criteria for the entire construction process, including: codes…

Wake County Public School System, Raleigh, NC.

330

Waking effectiveness of visual alerting signals  

Microsoft Academic Search

People who are unable to hear acoustic alarm signals because they have a complete or partial hearing loss must rely on visual or tactile signals to warn them in the event of an emergency. However, consumers report that personal smoke detector devices which provide a visual alarm do not wake people reliably . We examined the ability of visual alerting

Sherry K. Bowman; Donald G. Jamieson; Robert D. Ogilvie

331

Calibration of P-3/SAR Wake Data.  

National Technical Information Service (NTIS)

Calibration constants were generated using trihedral comer reflector data collected by the ERIM/NADC P-3 SAR during the 1989 ONR Ship Wake Experiment. These values will be applied to the ONR data to generate absolutely calibrated radar cross-section (RCS)...

N. Malinas

1992-01-01

332

Apparatus for Control of Stator Wakes.  

National Technical Information Service (NTIS)

This patent application discloses an apparatus that controls the wake of stator blades on an underwater vehicle. The apparatus comprises one or more stator blades, each with a movable trailing edge that when actuated in a controlled manner produces a peri...

D. N. Beal

2009-01-01

333

Island wakes in shallow coastal waters  

Microsoft Academic Search

Rattray Island, northeast Australia, is 1.5 km long, 300 m wide, and lies in well-mixed water approximately 25 m deep. Its long axis is inclined at about 60° into the direction of the dominant semidiurnal tidal current. The length of the wake in the lee of the island, as documented by aerial photographs and satellite imagery, appears to equal that

E. Wolanski; J. Imberger; M. L. Heron

1984-01-01

334

A Wake Boundary Layer Mixing Experiment.  

National Technical Information Service (NTIS)

The mixing of a boundary layer was investigated under zero pressure gradient with a two dimensional wake shed from a plate. Measurements of mean and fluctuating quantities were carried out for this flow in particular, as well as for one of the component f...

P. J. Pot

1979-01-01

335

Computation of rotor wake turbulence noise  

Microsoft Academic Search

A major source of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a Reynolds averaged Navier–Stokes code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-in source diagnostic

M. Nallasamy; E. Envia

2005-01-01

336

A New Green's Function for the Wake Potential Calculation of the SLAC S-band Constant Gradient Accelerating Section  

SciTech Connect

The behavior of the longitudinal wake fields excited by a very short bunch in the SLAC S-band constant gradient accelerating structures has been studied. Wake potential calculations were performed for a bunch length of 10 microns using the author's code to obtain a numerical solution of Maxwell's equations in the time domain. We have calculated six accelerating sections in the series (60-ft) to find the stationary solution. While analyzing the computational results we have found a new formula for the Green's function. Wake potentials, which are calculated using this Green's function are in amazingly good agreement with numerical results over a wide range of bunch lengths. The Green's function simplifies the wake potential calculations and can be easily incorporated into the tracking codes. This is very useful for beam dynamics studies of the linear accelerators of LCLS and FACET.

Novokhatski, A,; /SLAC

2012-02-17

337

A new Green's function for the wake potential calculation of the SLAC S-band constant gradient accelerating section  

NASA Astrophysics Data System (ADS)

The behavior of the longitudinal wake fields excited by a very short bunch in the SLAC S-band constant gradient accelerating structures has been studied. Wake potential calculations were performed for a bunch length of 10?m using the author's code to obtain a numerical solution of Maxwell's equations in the time domain. We have calculated six accelerating sections in the series (60-ft) to find the stationary solution. While analyzing the computational results we have found a new formula for Green's function. Wake potentials, which are calculated using this Green's function are in amazingly good agreement with numerical results over a wide range of bunch lengths. Green's function simplifies the wake potential calculations and can be easily incorporated into the tracking codes. This is very useful for beam dynamics studies of the linear accelerators of LCLS [1] and FACET [2].

Novokhatski, A.

2012-08-01

338

Efficacy and residues of phloxine B and uranine for the suppression of Mediterranean fruit fly in coffee fields.  

PubMed

The field efficacy of a bait containing phloxine B, uranine and Provesta 621 protein was tested against Mediterranean fruit fly (Ceratitis capitata; Medfly) by aerial and ground spraying in about 84 ha of coffee fields in Kauai, Hawaii, USA. Concurrently, soil and crop samples were collected from the aerially sprayed field and its unsprayed control field for residue studies. Efficacy of the sprays was assessed through trapping with both protein-baited and trimedlure-baited traps and through the infestation level of coffee cherries collected at least three-quarters ripe. The C capitata population was low at the start of the aerial and ground spray studies, but dramatically increased in the control fields. This increase coincided with initial ripening of coffee cherries. During times of peak population levels, C capitata populations were reduced by more than 91% in the ground-sprayed field and 99% in the aerial-sprayed field, relative to the populations in their respective control fields and based on protein-baited trap catches. Results of residue analyses indicated that uranine dissipated quickly compared with phloxine B on coffee and soil. Coffee samples collected at pre-spray periods had phloxine B residues of 7.2-25.5 ng g-1 on berries. Phloxine B concentrations were much higher on coffee leaves (163-1120 ng g-1). Lower concentrations of the dye were found from coffee samples collected during rainy days. Average phloxine B concentrations immediately after spraying were 56 and 2840 ng g-1 in coffee berries and leaves, respectively. Dissipation of phloxine B on berries was fast, with a half-life (t1/2) of 3 days. Dissipation of phloxine B on leaves was fitted to two linear phases: the initial (0-4 days) with a shorter t1/2 of 3 days and the later phase (4-28 days) with a longer t1/2 of 15 days. Average concentrations of phloxine B in the top soil ranged from 50 to 590 ng g-1 at pre-spray. Phloxine B initial concentration (770 ng g-1) reached a plateau immediately after the last spraying, but showed a steady decline over time with t1/2 of 16 days. Fast dissipation of the dyes in the field indicates that these chemicals may be environmentally compatible and therefore a promising alternative for fruit fly control. PMID:11838283

Licudine, Jocelyn A; McQuate, Grant T; Cunningham, Roy T; Liquido, Nicanor J; Li, Qing X

2002-01-01

339

First results from ARTEMIS lunar wake crossing: observations and hybrid simulation  

NASA Astrophysics Data System (ADS)

The Moon does not have an intrinsic magnetic field and its conductivity is not sufficient to facilitate the development of an induced magnetosphere. The interaction of the Moon with the unperturbed solar wind (SW) is, hence, dominated by the absorption of SW particles on its surface and the consequent generation of a lunar wake on the night side. The SW magnetic field is basically convected through the Moon; the pressure imbalance in lunar wake, however, accounts for a slight increase in magnetic pressure in the lunar wake center. The wake is slowly filled up with SW particles due to their thermal motion, which generates a magnetohydrodynamic (MHD) rarefaction wave propagating away from the wake in the SW frame of reference. Over the last 3 years the Time History of Events and Macroscale Interactions During Substorms (THEMIS) mission provided excellent data helping the scientific community in drawing a detailed picture of the physical processes associated with the development of substorms in the terrestrial magnetotail. Two of the five THEMIS spacecraft are currently being sent into stationary orbits around the Moon in a follow-up mission called Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS). The ARTEMIS P1 spacecraft (formerly THEMIS-B) has recently passed through the lunar wake in a flyby maneuver on February 13, 2010. We show first results of two hybrid code simulations with static and, for the first time, dynamically changing SW input. Adapted SW monitor data of the NASA OMNI database is used as input for the simulations. During the wake crossing the spin stabilized spacecraft P1 was in lunar shadow and, hence, its spin period cannot be determined from sun sensor data. Therefore, an eclipse-spin model is applied to bridge the gap of missing spin period data in order to recover vector measurements. A comparison of the simulation results with correctly despun magnetic field and particle measurements of ARTEMIS P1 allows for a separation of static lunar wake and, due to SW variations, transient features in the observations.

Plaschke, F.; Wiehle, S.; Angelopoulos, V.; Auster, H.; Georgescu, E.; Glassmeier, K.; Motschmann, U. M.; Sibeck, D. G.

2010-12-01

340

A parabolized Navier-Stokes analysis of wake/boundary-layer flow along a cable in tow  

SciTech Connect

A parabolized Navier-Stokes analysis of a turbulent, compressible, wake/boundary-layer flow field for a cable in tow is discussed. It is assumed that the cable is being towed by a missile-like configuration whose total drag coefficient is known. The cable is assumed to be perfectly aligned with the missile axis and is subjected to its wake. Modeled in the analysis is the far wake behind the missile, coupled with the turbulent boundary layer growth along the cable. An analytical starting solution for a parabolized Navier-Stokes code is presented. The starting solution is applicable downstream of the towing body's near wake and, therefore, circumvents the complex task of computing the towing body's flow field. An algebraic wake/boundary-layer turbulence model is used to simulate turbulent flow in both the decaying wake and growing boundary layer along the cable. Results are presented for a towing-body freestream Mach number of 5 and a Reynolds number of 36.0 {times} 10{sup 6} per ft at select distances along a thin cable. 18 refs., 7 figs., 2 tabs.

Barnette, D.W.

1991-01-01

341

Anderson lattice with explicit Kondo coupling revisited: metamagnetism and the field-induced suppression of the heavy fermion state  

NASA Astrophysics Data System (ADS)

We apply the extended (statistically consistent, SCA) Gutzwiller-type approach to the periodic Anderson model (PAM) in an applied magnetic field and in the strong-correlation limit. The finite-U corrections are included systematically by transforming the PAM into the form with the Kondo-type interaction and the residual hybridization, both appearing at the same time and on equal footing. This effective Hamiltonian represents the essence of our Anderson-Kondo lattice model. We show that in ferromagnetic phases the low-energy single-particle states are strongly affected by the presence of the applied magnetic field. We also find that for large values of hybridization strength the system enters the so-called locked heavy fermion state introduced earlier. In this state the chemical potential lies in the majority-spin hybridization gap and, as a consequence, the system evolution is insensitive to further increase of the applied field. However, for a sufficiently strong magnetic field, the system transforms from the locked state to the fully spin-polarized phase. This is accompanied by a metamagnetic transition, as well as by a drastic reduction of the effective mass of the quasiparticles. In particular, we observe no effective mass enhancement in the fully polarized state. The findings are in overall agreement with experimental results for the Ce compounds in high magnetic fields. The mass enhancement for the spin-minority electrons may also diminish with the increasing field, unlike for the quasiparticle states in a single narrow band in the same limit of strong correlations.

Howczak, Olga; Spa?ek, Jozef

2012-05-01

342

Wake Filling by Active Tail Articulation  

NASA Astrophysics Data System (ADS)

In a viscous fluid, the no slip boundary condition results in a surface drag force on a moving streamlined body, such as a hydrofoil, which causes a downstream wake velocity defect. In this paper, experimental results are presented which show that articulation of a trailing edge tail flap on a hydrofoil is sufficient to diminish the mean wake velocity defect. A 3 inch chord length NACA 0020 hydrofoil with a 1 inch long flapping trailing edge section was mounted in the research water tunnel at NUWC, Newport. Tests were conducted at speeds of 1, 2, and 4 m/s and the tail was flapped sinusoidally with amplitudes of 5, 10, and 20 degrees at varying frequencies. Time averaged velocity data was taken 1 chord length downstream by laser doppler velocimetry, LDV. Measurements with zero tail deflection show a velocity defect behind the hydrofoil of magnitude u/U = 0.88 and coefficient of drag, Cd, of approximately 0.02. Active articulation measurements show two regimes of wake filling. At very low Strouhal numbers it was found that tail articulation increases drag and is not useful for wake filling. In this range Cd is a function of flap deflection amplitude, St, and Re. However, above a certain threshold value, approximately St = 0.01, tail articulation begins to lessen the mean drag until Cd goes to zero around St = 0.06. At even higher St, tail articulation begins to produce thrust, resulting in a negative value of Cd. In the useful wake filling region, St 0.01, Cd seems to collapse to be a function of St only.

Macumber, Daniel; Beal, David; Annaswamy, Anuradha; Henoch, Charles; Huyer, Stephen

2004-11-01

343

Activation of 5-HT6 receptors modulates sleep-wake activity and hippocampal theta oscillation.  

PubMed

The modulatory role of 5-HT neurons and a number of different 5-HT receptor subtypes has been well documented in the regulation of sleep-wake cycles and hippocampal activity. A high level of 5-HT(6) receptor expression is present in the rat hippocampus. Further, hippocampal function has been shown to be modulated by both 5-HT(6) agonists and antagonists. In the current study, the potential involvement of 5-HT(6) receptors in the control of hippocampal theta rhythms and sleep-wake cycles has been investigated. Hippocampal activity was recorded by intracranial hippocampal electrodes both in anesthetized (n = 22) and in freely moving rats (n = 9). Theta rhythm was monitored in different sleep-wake states in freely moving rats and was elicited by stimulation of the brainstem reticular formation under anesthesia. Changes in theta frequency and power were analyzed before and after injection of the 5-HT(6) antagonist (SAM-531) and the 5-HT(6) agonist (EMD386088). In freely moving rats, EMD386088 suppressed sleep for several hours and significantly decreased theta peak frequency, while, in anesthetized rats, EMD386088 had no effect on theta power but significantly decreased theta frequency, which could be blocked by coadministration of SAM-531. SAM-531 alone did not change sleep-wake patterns and had no effect on theta parameters in both unanesthetized and anesthetized rats. Decreases in theta frequency induced by the 5-HT(6) receptor agonist correspond to previously described electrophysiological patterns shared by all anxiolytic drugs, and it is in line with its behavioral anxiolytic profile. The 5-HT(6) antagonist, however, failed to potentiate theta power, which is characteristic of many pro-cognitive substances, indicating that 5-HT(6) receptors might not tonically modulate hippocampal oscillations and sleep-wake patterns. PMID:23336058

Ly, Susanna; Pishdari, Bano; Lok, Ling Ling; Hajos, Mihaly; Kocsis, Bernat

2012-12-10

344

Sleep-wake behavior in the rat: ultradian rhythms in a light-dark cycle and continuous bright light.  

PubMed

Ultradian rhythms are a prominent but little-studied feature of mammalian sleep-wake and rest-activity patterns. They are especially evident in long-term records of behavioral state in polyphasic animals such as rodents. However, few attempts have been made to incorporate ultradian rhythmicity into models of sleep-wake dynamics, and little is known about the physiological mechanisms that give rise to ultradian rhythms in sleep-wake state. This study investigated ultradian dynamics in sleep and wakefulness in rats entrained to a 12-h:12-h light-dark cycle (LD) and in rats whose circadian rhythms were suppressed and free-running following long-term exposure to uninterrupted bright light (LL). We recorded sleep-wake state continuously for 7 to 12 consecutive days and used time-series analysis to quantify the dynamics of net cumulative time in each state (wakefulness [WAKE], rapid eye movement sleep [REM], and non-REM sleep [NREM]) in each animal individually. Form estimates and autocorrelation confirmed the presence of significant ultradian and circadian rhythms; maximum entropy spectral analysis allowed high-resolution evaluation of multiple periods within the signal, and wave-by-wave analysis enabled a statistical evaluation of the instantaneous period, peak-trough range, and phase of each ultradian wave in the time series. Significant ultradian periodicities were present in all 3 states in all animals. In LD, ultradian range was approximately 28% of circadian range. In LL, ultradian range was slightly reduced relative to LD, and circadian range was strongly attenuated. Ultradian rhythms were found to be quasiperiodic in both LD and LL. That is, ultradian period varied randomly around a mean of approximately 4 h, with no relationship between ultradian period and time of day. PMID:23223374

Stephenson, Richard; Lim, Joonbum; Famina, Svetlana; Caron, Aimee M; Dowse, Harold B

2012-12-01

345

Detection of Suppressiveness against Rotylenchulus reniformis in Soil from Cotton (Gossypium hirsutum) fields in Texas and Louisiana  

Technology Transfer Automated Retrieval System (TEKTRAN)

Rotylenchulus reniformis is a major problem confronting cotton production in the central part of the cotton belt of the United States of America. In this study, the hypothesis that natural antagonists in some cases are responsible for unusually low densities of the nematode in certain fields was te...

346

Receptive fields of simple cells from a taxonomic study of natural images and suppression of scale redundancy  

Microsoft Academic Search

Much effort has been carried out to propose models of the early visual pathway based on the statistical analysis of natural images. These conventional frameworks lead to predictions on the RFs of simple cells which do not fit well their observed properties (D.L. Ringach, Spatial structure and symmetry of simple-cell receptive fields in macaque primary visual cortex, J. Neurophysiol. 2002

José M. Delgado; Antonio Turiel; Néstor Parga

2006-01-01

347

Axisymmetric Turbulent Wakes with New Nonequilibrium Similarity Scalings  

NASA Astrophysics Data System (ADS)

The recently discovered nonequilibrium turbulence dissipation law implies the existence of axisymmetric turbulent wake regions where the mean flow velocity deficit decays as the inverse of the distance from the wake-generating body and the wake width grows as the square root of that distance. This behavior is different from any documented boundary-free turbulent shear flow to date. Its existence is confirmed in wind tunnel experiments of wakes generated by plates with irregular edges placed normal to an incoming free stream. The wake characteristics of irregular bodies such as buildings, bridges, mountains, trees, coral reefs, and wind turbines are critical in many areas of environmental engineering and fluid mechanics.

Nedi?, J.; Vassilicos, J. C.; Ganapathisubramani, B.

2013-10-01

348

Comparison of application methods for suppressing the pecan weevil (Coleoptera: Curculionidae) with Beauveria bassiana under field conditions.  

PubMed

The pecan weevil, Curculio caryae (Horn), is a key pest of pecans. The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin is pathogenic to C. caryae. One approach to managing C. caryae may be application of B. bassiana directed toward adult weevils as they emerge from the soil to attack nuts in the tree canopy. Our objective was to compare different application methods for suppression of C. caryae adults. Treatments included direct application of B. bassiana (GHA strain) to soil under the tree canopy, soil application followed by cultivation, soil application in conjunction with a cover crop (Sudan grass), direct application to the tree trunk, and application to the trunk with an UV radiation-protecting adjuvant. The study was conducted in a pecan orchard in Byron, GA, in 2005 and 2006. Naturally emerging C. caryae adults, caught after crawling to the trunk, were transported to the laboratory to determine percentage mortality and signs of mycosis. When averaged over the 15-d sampling period, weevil mortality and signs of mycosis were greater in all treatments than in the nontreated control in 2005 and 2006; >75% average mortality was observed with the trunk application both years and in the trunk application with UV protection in 2005. Results indicated trunk applications can produce superior efficacy relative to ground application, particularly if the ground application is followed by cultivation. Efficacy in the cover crop treatment, however, did not differ from other application approaches. Future research should focus on elucidating the causes for treatment differences we observed and the extent to which B. bassiana-induced C. caryae mortality reduces crop damage. PMID:18348807

Shapiro-Ilan, David I; Gardner, Wayne A; Cottrell, Ted E; Behle, Robert W; Wood, Bruce W

2008-02-01

349

Exploration of the vortex wake behind of wind turbine rotor  

NASA Astrophysics Data System (ADS)

The present paper describes a wind tunnel study of flow downstream a small horizontal axis wind turbine (HAWT). The experimental investigations were carried out with the use of particle image velocimetry (PIV). To obtain the flow field in the rotating frame of reference, the phase-locked technique was applied. Explorations were carried out in azimuth planes with different angles. The 3D velocity field was reconstituted by processing the images resulting from the explored azimuth planes. In addition to PIV investigations, hot-wire measurements were also carried out immediately behind the wind turbine rotor at different radial and axial distances. The obtained results are very useful to analyze wind turbine wake and to constitute a reference for CFD computation.

Massouh, F.; Dobrev, I.

2007-07-01

350

The near wake of a freely flying European starling  

NASA Astrophysics Data System (ADS)

The wake of a freely flying European starling (Sturnus vulgaris) has been measured using high speed, time-resolved, particle image velocimetry, simultaneously with high speed cameras which imaged the bird. These have been used to generate vector maps that can be associated with the bird's location and wing configuration in the wind tunnel. Time series of measurements have been expressed as composite wake plots which depict segments of the wing beat cycle for various spanwise locations in the wake. Measurements indicate that downwash is not produced during the upstroke, suggesting that the upstroke does not generate lift. As well, the wake velocities imply the presence of streamwise vortical structures, in addition to tip vortices. These two characteristics indicate similarities between the wake of a bird and the wake of a bat, which may be general features of the wakes of flapping wings.

Kirchhefer, Adam J.; Kopp, Gregory A.; Gurka, Roi

2013-05-01

351

Suppression of experimental allergic encephalomyelitis is specific to the frequency and intensity of nocturnally applied, intermittent magnetic fields in rats  

Microsoft Academic Search

Female Lewis rats (n=72) were inoculated with an emulsion of spinal cord and complete Freund's adjuvant. They were then exposed for approximately 6 min every hour between midnight and 08:00 h for 2 weeks to either 7 or 40 Hz amplitude-modulated magnetic fields whose temporal pattern was designed to simulate a (geomagnetic) storm sudden commencement. The peak strengths of the

L. L Cook; M. A Persinger

2000-01-01

352

Magnetic field suppression in collision-less shocks generated during the expansion of a dense plasma into a rarefied medium  

NASA Astrophysics Data System (ADS)

A two-dimensional numerical study of the expansion of a dense plasma through a more rarefied one is reported. The electrostatic ion-acoustic shock, which is generated during the expansion, accelerates the electrons of the rarefied plasma inducing a superthermal population which reduces electron thermal anisotropy. The Weibel instability is therefore not triggered and no self-generated magnetic fields are observed, in contrast with published theoretical results dealing with plasma expansion into vacuum.

Sarri, G.; Dieckmann, M. E.; Kourakis, I.; Borghesi, M.

2012-02-01

353

Experimental investigation of an actively controlled three-dimensional turret wake  

NASA Astrophysics Data System (ADS)

Hemispherical turrets are bluff bodies commonly used to house optical systems on airborne platforms. These bluff bodies develop complex, three-dimensional flow fields that introduce high mean and fluctuating loads to the turret as well as the airframe support structure which reduce the performance of both the optical systems and the aircraft. An experimental investigation of the wake of a three-dimensional, non-conformal turret was performed in a low-speed wind tunnel at Syracuse University to develop a better understanding of the fundamental flow physics associated with the turret wake. The flow field was studied at a diameter based Reynolds number of 550,000 using stereoscopic particle image velocimetry and dynamic pressure measurements both with and without active flow control. Pressure measurements were simultaneously sampled with the PIV measurements and taken on the surrounding boundary layer plate and at several locations on the turret geometry. Active flow control of the turret wake was performed around the leading edge of the turret aperture using dynamic suction in steady open-loop, unsteady open-loop, and simple closed-loop configurations. Analysis of the uncontrolled wake provided insight into the complex three-dimensional wake when evaluated spatially using PIV measurements and temporally using spectral analysis of the pressure measurements. Steady open-loop suction was found to significantly alter the spatial and temporal nature of the turret wake despite the control being applied locally to the aperture region of the turret. Unsteady open-loop and simple closed-loop control were found to provide similar levels of control to the steady open-loop forcing with a 45% reduction in the control input as calculated using the jet momentum coefficient. The data set collected provides unique information regarding the development of the baseline three-dimensional wake and the wake with three different active flow control configurations. These data can be used to help guide future studies, both experimental and computational, of similar geometries and to provide insight for developing active control systems for complex, three-dimensional flows.

Shea, Patrick R.

354

Suppression of superconductivity by strong magnetic fields in PbTe/PbS heterostructures with a superconducting interface  

NASA Astrophysics Data System (ADS)

This is a comprehensive study of the effect of strong magnetic fields on superconductivity in PbTe/PbS heterostructures with semiconducting layers of different thicknesses. Metallic conductivity and superconductivity (critical temperature Tc <= 6.5 K) in PbTe/PbS heterostructures are caused by inversion of bands along a continuous network of misfit dislocations that develops at the interfaces between semiconductor layers of sufficient thickness (d > 80 nm). With decreasing d the continuity of the superconducting interface is disrupted, Tc decreases, and the metallic conductivity changes to a semiconducting type. Disruption of the continuity of the superconducting interface is found to be a necessary condition for observing a magnetic-field induced superconductor-insulator transition (SIT) and has a significant influence on its features: a fan-like set of resistance curves R(T); intersection of the R(B) curves for fields perpendicular, as well as parallel, to the interface; and, negative magnetoresistance. A scaling analysis based on Fisher's theoretical model is carried out for these samples. No evidence of a SIT was observed in heterostructures with a perfect interface. It appears that the SIT effect is related to percolation phenomena characteristic of granular superconductors.

Bengus, S. V.; Sipatov, A. Yu.; Yuzephovich, S. I.

2013-08-01

355

Beam loading by electrons in nonlinear plasma wakes  

SciTech Connect

An analytical theory for the interaction of an electron bunch with a nonlinear plasma wave is developed to make it possible to design efficient laser- and/or beam-driven accelerators that generate high quality monoenergetic electron beams. This theory shows how to choose the charge, the shape, and the placing of the bunch so that the conversion efficiency from the fields of the bubble to the accelerating electrons reaches nearly 100% and the beam quality is optimized. For intense drivers the nonlinear wake is described by the shape of the bubble and beam loading arises when the radial space-charge force of the beam acts back on the electron sheath surrounding the ion channel. The modification of the wake due to the presence of flat-top electron bunches is studied and it is shown that the energy spread of an externally injected flat-top electron bunch can be kept low. The bunch profile that leads to zero energy spread is also derived.

Tzoufras, M. [Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Lu, W. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Tsung, F. S.; Huang, C. [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Mori, W. B. [Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Katsouleas, T. [Pratt School of Engineering, Duke University, Durham, North Carolina 27708 (United States); Vieira, J.; Fonseca, R. A.; Silva, L. O. [GoLP/Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, 1049-001 Lisboa (Portugal)

2009-05-15

356

The Role of Wakes in Modelling Tidal Current Turbines  

NASA Astrophysics Data System (ADS)

The eventual proper development of arrays of Tidal Current Turbines (TCT) will require a balance which maximizes power extraction while minimizing environmental impacts. Idealized analytical analogues and simple 2-D models are useful tools for investigating questions of a general nature but do not represent a practical tool for application to realistic cases. Some form of 3-D numerical simulations will be required for such applications and the current project is designed to develop a numerical decision-making tool for use in planning large scale TCT projects. The project is predicated on the use of an existing regional ocean modelling framework (the Regional Ocean Modelling System - ROMS) which is modified to enable the user to account for the effects of TCTs. In such a framework where mixing processes are highly parametrized, the fidelity of the quantitative results is critically dependent on the parameter values utilized. In light of the early stage of TCT development and the lack of field scale measurements, the calibration of such a model is problematic. In the absence of explicit calibration data sets, the device wake structure has been identified as an efficient feature for model calibration. This presentation will discuss efforts to design an appropriate calibration scheme which focuses on wake decay and the motivation for this approach, techniques applied, validation results from simple test cases and limitations shall be presented.

Conley, Daniel; Roc, Thomas; Greaves, Deborah

2010-05-01

357

Kinetic instabilities in the lunar wake: ARTEMIS observations  

NASA Astrophysics Data System (ADS)

The Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission is a new two-probe lunar mission derived from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. On 13 February 2010, one of the two probes, ARTEMIS P1 (formerly THEMIS-B), made the first lunar wake flyby of the mission. We present detailed analysis of the electrostatic waves observed on the outbound side of the flyby that were associated with electron beams. Halekas et al. (2011) derived a net potential across the lunar wake from observations and suggested that the net potential generated the observed electron beams and the electron beams in turn excited the observed electrostatic waves due to kinetic instabilities. The wavelengths and velocities of the electrostatic waves are estimated, using high-resolution electric field instrument data with cross-spectrum analysis and cross-correlation analysis. In general, the estimated wavelengths vary from a few hundred meters to a couple of thousand meters. The estimated phase velocities are on the order of 1000 km s-1. In addition, we perform 1-D Vlasov simulations to help identify the mode of the observed electrostatic waves. We conclude that the observed electrostatic waves are likely on the electron beam mode branch.

Tao, J. B.; Ergun, R. E.; Newman, D. L.; Halekas, J. S.; Andersson, L.; Angelopoulos, V.; Bonnell, J. W.; McFadden, J. P.; Cully, C. M.; Auster, H.-U.; Glassmeier, K.-H.; Larson, D. E.; Baumjohann, W.; Goldman, M. V.

2012-03-01

358

Dopamine agonist suppression of rapid-eye-movement sleep is secondary to sleep suppression mediated via limbic structures  

SciTech Connect

The effects of pergolide, a direct dopamine receptor agonist, on sleep and wakefulness, motor behavior and /sup 3/H-spiperone specific binding in limbic structures and striatum in rats was studied. The results show that pergolide induced a biphasic dose effect, with high doses increasing wakefulness and suppressing sleep while low dose decreased wakefulness, but increased sleep. It was shown that pergolide-induced sleep suppression was blocked by ..cap alpha..-glupenthixol and pimozide, two dopamine receptor antagonists. It was further shown that pergolide merely delayed the rebound resulting from rapid-eye-movement (REM) sleep deprivation, that dopamine receptors stimulation had no direct effect on the period, phase or amplitude of the circadian rhythm of REM sleep propensity and that there was no alteration in the coupling of REM sleep episodes with S/sub 2/ episodes. Rapid-eye-movement sleep deprivation resulted in increased sensitivity to the pergolide-induced wakefulness stimulation and sleep suppression and pergolide-induced motor behaviors of locomotion and head bobbing. /sup 3/H-spiperone specific binding to dopamine receptors was shown to be altered by REM sleep deprivation in the subcortical limbic structures. It is concluded that the REM sleep suppressing action of dopamine receptor stimulation is secondary to sleep suppression per se and not secondary to a unique effect on the REM sleep. Further, it is suggested that the wakefulness stimulating action of dopamine receptor agonists is mediated by activation of the dopamine receptors in the terminal areas of the mesolimbocortical dopamine projection system.

Miletich, R.S.

1985-01-01

359

An endogenous glutamatergic drive onto somatic motoneurons contributes to the stereotypical pattern of muscle tone across the sleep-wake cycle.  

PubMed

Skeletal muscle tone is modulated in a stereotypical pattern across the sleep-wake cycle. Abnormalities in this modulation contribute to most of the major sleep disorders; therefore, characterizing the neurochemical substrate responsible for transmitting a sleep-wake drive to somatic motoneurons needs to be determined. Glutamate is an excitatory neurotransmitter that modulates motoneuron excitability; however, its role in regulating motoneuron excitability and muscle tone during natural sleep-wake behaviors is unknown. Therefore, we used reverse-microdialysis, electrophysiology, pharmacological, and histological methods to determine how changes in glutamatergic neurotransmission within the trigeminal motor pool contribute to the sleep-wake pattern of masseter muscle tone in behaving rats. We found that blockade of non-NMDA and NMDA glutamate receptors (via CNQX and d-AP-5) on trigeminal motoneurons reduced waking masseter tone to sleeping levels, indicating that masseter tone is maximal during alert waking because motoneurons are activated by an endogenous glutamatergic drive. This wake-related drive is switched off in non-rapid eye movement (NREM) sleep, and this contributes to the suppression of muscle tone during this state. We also show that a functional glutamatergic drive generates the muscle twitches that characterize phasic rapid-eye movement (REM) sleep. However, loss of a waking glutamatergic drive is not sufficient for triggering the motor atonia that characterizes REM sleep because potent activation of either AMPA or NMDA receptors on trigeminal motoneurons was unable to reverse REM atonia. We conclude that an endogenous glutamatergic drive onto somatic motoneurons contributes to the stereotypical pattern of muscle tone during wakefulness, NREM sleep, and phasic REM sleep but not during tonic REM sleep. PMID:18448642

Burgess, Christian; Lai, Diane; Siegel, Jerome; Peever, John

2008-04-30

360

A comparison of dispersion calculations in bluff body wakes using LES and unsteady RANS  

SciTech Connect

Accurate modeling of the dispersion behavior of sprays or particles is critical for a variety of problems including combustion, urban pollution or release events, and splash and spray transport around heavy vehicles. Bluff body wakes are particularly challenging since these flows are both highly separated and strongly unsteady. Attempting to model the dispersion of droplets or particles interacting with bluff body wakes is even more difficult since small differences in the flow field encountered by particles can lead to large differences in the dispersion behavior. Particles with finite inertia can exhibit additional complicating effects such as preferential concentration. In this preliminary study, we consider the dispersion of solid particles in the wake of a rectangular plane at a Reynolds number (Re) of 10000 and that of droplets in the wake of a simplified tractor-trailer geometry at Re = 2 x 10{sup 6} using both the Large Eddy Simulation (LES) and Unsteady Reynolds-Averaged Navier-Stokes (URANS) turbulence modeling approaches. The calculations were performed using identical meshes for both the LES and URANS models. Particle stresses are not backcoupled to the carrier fluid velocity solution. In the case of the rectangular plane wake, the LES calculation predicts a finer-scale and more persistent wake structure than the URANS one; the resulting particle dispersion is considerably ({approx} 40%) underpredicted for low inertia particles. For the case of the simplified tractor-trailer geometry, although the LES is underresolved, similar trends are observed with strong differences in the vertical and horizontal dispersion of the smallest particles. These results suggest that it may be necessary to use LES to accurately capture the dispersion behavior of small, low inertia particles or droplets, but that URANS may be sufficient for problems in which only large particles with substantial inertia are of primary concern.

Paschkewitz, J S

2006-01-19

361

Fire Suppression  

Microsoft Academic Search

\\u000a Water sprinkler sprays (with relatively large droplet sizes) in residential and commercial structures are probably the most\\u000a well-known application of sprays in fire suppression. In more recent years, water mists (characterized by reduced droplet\\u000a sizes, which may contain additives) have been considered as a replacement for Halon 1301, the most common fire suppressant\\u000a chemical aboard aircraft and ships, but banned

C. Presser; J. C. Yang

362

Optogenetic Probing of Hypocretins’ Regulation of Wakefulness  

Microsoft Academic Search

\\u000a In mammals, sleep is commonly defined as “a rapidly reversible state of (behavioral) immobility and greatly reduced sensory\\u000a responsiveness to environmental stimuli” [1]. Sleep and wake states have been strongly conserved during evolution, and “sleep-like”\\u000a states exist in most organisms, including worms, flies, and fish [2], suggesting common underlying neural circuits and endocrine\\u000a systems. During the last decades, neural circuits

Antoine Adamantidis; Luis de Lecea

363

Wake development in turbulent subsonic axisymmetric flows  

Microsoft Academic Search

The development of the wake velocity and turbulence profiles behind a cylindrical blunt based body aligned with a subsonic\\u000a uniform stream was experimentally investigated as a function of the momentum thickness of the approaching boundary layer and\\u000a the transfer of mass into the recirculating region. Measurements were made just outside of the recirculating region at distances\\u000a of 1.5, 2 and

J. L. F. Porteiro; V. Perez-Villar

1996-01-01

364

Stability characteristics of counter-rotating vortex pairs in the wakes of triangular-flapped airfoils  

NASA Astrophysics Data System (ADS)

A rapidly growing instability is observed to develop between unequal strength, counter-rotating vortex pairs in the wakes of airfoils with outboard triangular flaps. To investigate the physical mechanisms for this instability, a linear stability analysis is performed on a single vortex pair. This analytical model reveals that the instability is driven by the strain rate field from one vortex acting on the perturbations of its neighboring vortex. Another linear stability analysis is conducted to include the effects of the other counter-rotating vortex pair. The qualitative features of the instability, such as its wavelength and non-linear evolution, are examined by flow visualization measurements that are made in a towing tank facility at a chord-based Reynolds number of O(105). From these observations, a sinuous instability is seen to develop on the weaker flap vortices and have a wavelength of order one wingspan. The instability wavelengths that are observed in the flow visualization data compare favorably with those predicted by the two- and four-vortex linear stability analyses, demonstrating that the analytical models capture the essential physics of the instability growth. Quantitative measurements of the vortex wakes are made with a PIV technique, allowing the vortex structure, trajectories, kinetic energy, and distribution to be assessed up to several hundred wingspans downstream of the airfoils. Additionally, the circulation-based Reynolds number is seen to be of O(105). The PIV data indicate that the wake's two-dimensional kinetic energy decreases substantially as the instability transforms the two-dimensional nature of the wake into a three- dimensional one. Finally, the wake alleviation properties of this instability are measured by computing the maximum rolling moment and downwash that a following wing might experience if it were placed in the wakes of these airfoils. These calculations show that by 75 wingspans, the wakes of the triangular-flapped airfoils have rolling moments and downwash that are always less than those of a conventional rectangular airfoil. This rapid reduction in the rolling moment and downwash leads to the conclusion that this instability between unequal strength, counter- rotating vortex pairs has the potential to solve the wake hazard problem.

Ortega, Jason Marc

365

Ship wakes and their manifestations on the sea surface  

NASA Astrophysics Data System (ADS)

Spatial/temporal evolution of turbulence generated by surface ships and the effect of the wake on short wind waves has been studied on the Black Sea and on the Gorky Water Reservoir. Measurements of currents in ship wakes were conducted using an Acoustic Doppler Current Profiler deployed from a motor boat. It was obtained that the temporal/spatial evolution of the wake width could be described approximately by a 0.4-power dependence, and the wake depth remained nearly constant at its initial stage. This allowed one to consider the wake widening as a one-dimensional process. We have developed a simple one-dimensional model of ship wake evolution using a semi-empirical theory of turbulence, and the initial stage of the wake widening (when neglecting dissipation) was described by the equation of turbulent energy balance with the pulse initial condition. Mean circulating currents in the wake zone resulting in the wind wave intensification ("suloi" areas) at the boundaries of the wake were detected in experiment. The asymmetry of the "suloi" bands was observed when the wind was blowing nearly perpendicular to the wake axis. It was shown that the later stage of the wake evolution is characterized by the formation of slick bands at the edges of the wake. The slick bands is a result of the transport of surfactants to the water surface by air bubbles in the wake and their compression due to the mean circulating currents. The work was supported by RFBR (projects 12-05-31237, 11-05-00295), the Program RAN Radiophysics, and by the Russian Government (Grants No. 11.G34.31.0048 and 11.G34.31.0078).

Ermakov, Stanislav; Kapustin, Ivan; Kalimulin, Rashid

2013-04-01

366

Identification of characteristic properties in different vessel wake signals  

NASA Astrophysics Data System (ADS)

The potential threat in terms of environmental protection and safe navigation posed by wake waves from high-speed ferries and fast conventional ships is well documented. Vessels that travel in the near-critical regime (depth Froude number ? 1) at some sections along their ship tracks can generate packets of large, solitonic, very long and long crested waves. The heights and periods of the leading waves, excited at near-critical speeds, may be much larger than those of conventional ferries or vessels travelling at even slightly slower speeds. However, it is difficult to determine a general characterization of such wakes at the coast, due to the transient and nonlinear nature of this phenomenon, and the fact that wake impact is influenced by the local bathymetry and coastline configuration. Such a characterization is required in order to set reasonable limits to wake wash that are sufficient for protection but not excessively restrictive for ship navigation. This paper investigates the potential benefits of wake analysis by means of a time-frequency technique (windowed Fourier transform), which is well known in signal analysis but has only recently been applied in wake analysis. Analysis of ship wakes have been performed based on instrumental data of sea surface elevation recorded at different sites in Tallinn Bay, the Baltic Sea, which is characterized by very intense ship traffic and provides a very rich collection of vessel-wake signals. Results show that the wake signals are easily identified in spectrograms. The method is particularly useful for identification of low frequency signals that may easily be masked by high frequency noise in the wave record. Furthermore, the spectrogram provides an image of the wake that makes it possible to associate wake events with individual ships at a given location. This approach also opens a new direction for the statistical description of wakes, applicable to the characterization of the "wake climate" for sites with intense vessel traffic.

Didenkulova, Ira; Sheremet, Alex; Torsvik, Tomas; Soomere, Tarmo

2013-04-01

367

Suppression of type I collagen in human scleral fibroblasts treated with extremely low-frequency electromagnetic fields  

PubMed Central

Purpose To investigate the expression differences of type I collagen (COL1A1) and its underlying mechanisms in human fetal scleral fibroblasts (HFSFs) that were treated with conditioned medium from retinal pigment epithelial (RPE) cells under extremely low-frequency electromagnetic fields (ELF-EMFs). Methods The ELF-EMFs used in this study were established by slidac and artificial coils. Growth of the treated HFSFs was evaluated by a cell-counting kit-8 assay. The expression of COL1A1 and matrix metalloproteinases-2 (MMP-2) in the treated HFSFs was detected by reverse transcription PCR (RT-PCR) and western blot, and the expression of transforming growth factor-?2 (TGF-?2) and basic fibroblast growth factor-2 (FGF-2) in RPE cells exposed to EMFs was detected by RT-PCR. The expression of COL1A1 and MMP-2 in HFSFs was further confirmed by immunofluorescence staining. Activation of extracellular signal-regulated kinase 1/2 (ERK1/2 also called p44/p42 mitogen-activated protein kinases [MAPK]) and p38 in HFSFs was measured by western blot. Results We found that exposure to ELF-EMFs resulted in a decreased proliferation rate of HFSFs and that addition of RPE supernatant medium could enhance this effect. Compared with that of the control cells, a significant decrease in collagen synthesis was detected in HFSFs under ELF-EMFs. However, the expression of MMP-2 was upregulated, which could be further enhanced via an RPE supernatant additive. The activities of ERK1/2 and p38 were significantly increased in HFSFs exposed to ELF-EMFs, and this effect could be enhanced by RPE supernatant medium additive. Conclusions Our results suggested that ELF-EMFs can inhibit the expression of type I collagen in HFSFs and contribute to the remodeling of the sclera.

Wang, Jie; Cui, Jiefeng

2013-01-01

368

Preliminary Velocity Measurements in the Wake of a Submarine Model  

NASA Astrophysics Data System (ADS)

Preliminary Particle Image Velocimetry (PIV) over a submarine shape has been conducted in a low speed wind tunnel at Princeton University. The model is a 1/67 replica of the USS Albacore, an experimental submarine designed to achieve maximum underwater performance, and based on "bodies of revolution." The model is tested with a sail, and different tail appendages. Velocity vector fields and flow visualizations in the wake region are presented for Reynolds numbers based on model length up to 10^5. The experiments establish the groundwork for future investigations of submarine models in the new High Reynolds Number Test Facility (http://www.princeton.edu/ gasdyn/HRTF.html). Supported by ONR Grants N00014-97-1-0325, N00014-97-1-0340 and N00014-97-1-0618.

Jimenez, J. M.; Reynolds, R.; Smits, A. J.

2000-11-01

369

Modeling the temporal architecture of rat sleep-wake behavior.  

PubMed

The fine architecture of sleep-wake behavior shows a distinct dynamic structure with distributions of rat sleep and wake bout durations displaying qualitatively different profiles. Wake bout durations follow a power-law relation whereas sleep bout durations are exponentially distributed. We show that a physiologically-based sleep-wake regulatory network model with an underlying deterministic structure governing neuronal interactions can generate realistic rat sleep-wake behavior as assessed by both standard summary statistics and survival analysis of bout distributions. Obtaining appropriate bout duration distributions depended on stochastic elements included in the model, the existence of multiple mechanisms for state transitions, and specific relationships among time constants governing state maintenance. This model provides a novel framework for exploring the disruptions of sleep-wake architecture associated with pharmacological, genetic, and disease states. PMID:22255390

Diniz Behn, Cecilia G; Booth, Victoria

2011-01-01

370

Low-dimensional modelling of a transient cylinder wake using double proper orthogonal decomposition  

NASA Astrophysics Data System (ADS)

For the systematic development of feedback flow controllers, a numerical model that captures the dynamic behaviour of the flow field to be controlled is required. This poses a particular challenge for flow fields where the dynamic behaviour is nonlinear, and the governing equations cannot easily be solved in closed form. This has led to many versions of low-dimensional modelling techniques, which we extend in this work to represent better the impact of actuation on the flow. For the benchmark problem of a circular cylinder wake in the laminar regime, we introduce a novel extension to the proper orthogonal decomposition (POD) procedure that facilitates mode construction from transient data sets. We demonstrate the performance of this new decomposition by applying it to a data set from the development of the limit cycle oscillation of a circular cylinder wake simulation as well as an ensemble of transient forced simulation results. The modes obtained from this decomposition, which we refer to as the double POD (DPOD) method, correctly track the changes of the spatial modes both during the evolution of the limit cycle and when forcing is applied by transverse translation of the cylinder. The mode amplitudes, which are obtained by projecting the original data sets onto the truncated DPOD modes, can be used to construct a dynamic mathematical model of the wake that accurately predicts the wake flow dynamics within the lock-in region at low forcing amplitudes. This low-dimensional model, derived using nonlinear artificial neural network based system identification methods, is robust and accurate and can be used to simulate the dynamic behaviour of the wake flow. We demonstrate this ability not just for unforced and open-loop forced data, but also for a feedback-controlled simulation that leads to a 90% reduction in lift fluctuations. This indicates the possibility of constructing accurate dynamic low-dimensional models for feedback control by using unforced and transient forced data only.

Siegel, Stefan G.; Seidel, J.?Rgen; Fagley, Casey; Luchtenburg, D. M.; Cohen, Kelly; McLaughlin, Thomas

371

Genetic and anatomical basis of the barrier separating wakefulness and anesthetic-induced unresponsiveness.  

PubMed

A robust, bistable switch regulates the fluctuations between wakefulness and natural sleep as well as those between wakefulness and anesthetic-induced unresponsiveness. We previously provided experimental evidence for the existence of a behavioral barrier to transitions between these states of arousal, which we call neural inertia. Here we show that neural inertia is controlled by processes that contribute to sleep homeostasis and requires four genes involved in electrical excitability: Sh, sss, na and unc79. Although loss of function mutations in these genes can increase or decrease sensitivity to anesthesia induction, surprisingly, they all collapse neural inertia. These effects are genetically selective: neural inertia is not perturbed by loss-of-function mutations in all genes required for the sleep/wake cycle. These effects are also anatomically selective: sss acts in different neurons to influence arousal-promoting and arousal-suppressing processes underlying neural inertia. Supporting the idea that anesthesia and sleep share some, but not all, genetic and anatomical arousal-regulating pathways, we demonstrate that increasing homeostatic sleep drive widens the neural inertial barrier. We propose that processes selectively contributing to sleep homeostasis and neural inertia may be impaired in pathophysiological conditions such as coma and persistent vegetative states. PMID:24039590

Joiner, William J; Friedman, Eliot B; Hung, Hsiao-Tung; Koh, Kyunghee; Sowcik, Mallory; Sehgal, Amita; Kelz, Max B

2013-09-05

372

Genetic and Anatomical Basis of the Barrier Separating Wakefulness and Anesthetic-Induced Unresponsiveness  

PubMed Central

A robust, bistable switch regulates the fluctuations between wakefulness and natural sleep as well as those between wakefulness and anesthetic-induced unresponsiveness. We previously provided experimental evidence for the existence of a behavioral barrier to transitions between these states of arousal, which we call neural inertia. Here we show that neural inertia is controlled by processes that contribute to sleep homeostasis and requires four genes involved in electrical excitability: Sh, sss, na and unc79. Although loss of function mutations in these genes can increase or decrease sensitivity to anesthesia induction, surprisingly, they all collapse neural inertia. These effects are genetically selective: neural inertia is not perturbed by loss-of-function mutations in all genes required for the sleep/wake cycle. These effects are also anatomically selective: sss acts in different neurons to influence arousal-promoting and arousal-suppressing processes underlying neural inertia. Supporting the idea that anesthesia and sleep share some, but not all, genetic and anatomical arousal-regulating pathways, we demonstrate that increasing homeostatic sleep drive widens the neural inertial barrier. We propose that processes selectively contributing to sleep homeostasis and neural inertia may be impaired in pathophysiological conditions such as coma and persistent vegetative states.

Hung, Hsiao-Tung; Koh, Kyunghee; Sowcik, Mallory; Sehgal, Amita; Kelz, Max B.

2013-01-01

373

Approach towards self-preservation of turbulent cylinder and screen wakes  

Microsoft Academic Search

Two-dimensional wakes generated from a circular cylinder and a 50% solidity screen have significantly different initial conditions. Accordingly, the approach towards self-preservation is quite different for the two wakes. For the cylinder wake, the normalized Reynolds stresses and spanwise vorticity decrease with increasing distance from the wake generator; the inverse occurs in the screen wake. Distributions of mean velocity, Reynolds

R. A. Antonia; J. Mi

1998-01-01

374

The Effect of Shape on the Wake of Low-Aspect-Ratio Wall-Mounted Obstacles  

NASA Astrophysics Data System (ADS)

Wall-mounted bodies in boundary layer flows are ubiquitous in nature and engineering applications. We evaluate the role of shape on the wakes around three different low-aspect-ratio wall-mounted obstacles in shallow boundary-layer flow: semi-ellipsoids with the major axis of the base ellipse aligned in the transverse and streamwise directions, and a sphere. Despite their geometric simplicity, the obstacles create extremely complex, highly three-dimensional and unsteady flow fields for which the transport mechanisms of momentum and scalars are still not well-understood. All three obstacles have the same height and the aspect ratios considered are 0.67, 0.89 and 1, respectively. DPIV was used to interrogate the flow. Streamwise structures observed in the mean wake include tip, base, and horseshoe vortex pairs, which vary significantly in strength with changes in obstacle geometry. Significant variation in the strength of these structures with streamwise location suggests a complex connectivity with the mean spanwise arch structure in the near wake. The three-dimensional topology of the mean wake will be discussed.

Hajimirzaie, Seyed; Buchholz, James

2011-11-01

375

The Effect of Geometry on the Wake Structure of a Surface Mounted Obstacle  

NASA Astrophysics Data System (ADS)

Experiments were conducted to better understand the flow structure in the wake of a square cylinder as a function of its height and develop a parameterization for tall buildings for the QUIC-URB wind model. The experiments were conducted in an open-circuit wind tunnel in a fully turbulent boundary layer. 2D PIV was used to measure the flow field along the vertical symmetry plane of the model buildings. Numerous experimental cases were run in which the geometry was varied by increasing the wall-normal height H of a square cylinder (where W=L; L is streamwise length and W is spanwise width) from H/L=1 to H/L=3 in increments of 0.3L. Preliminary results indicate that a saddle point appears for heights greater than H/L=1.6. The saddle is accompanied by a significant modification of the wake structure. This change can be attributed to the enhanced flux of momentum around the sidewall into the near-wake as the height of the model building is increased. Future work will include horizontal plane measurements in the wake of the model building to further explore the mechanisms that lead to the change in the flow structure.

Addepalli, Bhagirath; Pardyjak, Eric; Brown, Michael

2007-11-01

376

A mathematical model of the sleep\\/wake cycle  

Microsoft Academic Search

We present a biologically-based mathematical model that accounts for several features of the human sleep\\/wake cycle. These\\u000a features include the timing of sleep and wakefulness under normal and sleep-deprived conditions, ultradian rhythms, more frequent\\u000a switching between sleep and wakefulness due to the loss of orexin and the circadian dependence of several sleep measures.\\u000a The model demonstrates how these features depend

Michael J. Rempe; Janet Best; David Terman

2010-01-01

377

A new wake-potential calculation method using orthogonal polynomials  

SciTech Connect

We present, in this paper, a new method for calculating the wake potential of a bunched beam of arbitrary charge distribution, directly from the wake potential of a shorter bunch, by using orthogonal polynomial expansions. Combined with the table-look-up technique, this method leads to an effective computation scheme for repetitive evaluation of wake potentials of different charge distributions under the same boundary conditions. 15 refs.

Wang, Tai-Sen, F. (Los Alamos National Lab., NM (USA)); Zotter, B. (European Organization for Nuclear Research, Geneva (Switzerland))

1991-01-01

378

Transient Resistive Wall Wake for Very Short Bunches  

SciTech Connect

The catch up distance for the resistive wall wake in a round pipe is approximately equal to the square of the pipe radius divided by the bunch length. The standard formulae for this wake are applicable at distances much larger than the catch up distance. In this paper, we calculate the resistive wall wake at distances compared with the catch up distance assuming a constant wall conductivity.

Stupakov, G.; /SLAC

2005-05-13

379

Breaking of a wake wave excited by a narrow laser pulse in a low-density plasma  

SciTech Connect

The spatial structure of a wake wave excited in a low-density plasma by a laser pulse with a small focal spot radius is studied both analytically and numerically. Numerical study shows that, in a small-amplitude laser field, a wake wave breaks after the formation of an off-axis density maximum, which grows in height away from the pulse to become infinitely high after several periods. Analytical and numerical calculations show that the singularity in the density arises from the intersection of the trajectories of neighboring particles. Numerical simulations demonstrate that, as the laser field amplitude increases, the breaking point of the wake wave rapidly approaches the pulse trailing edge. For weakly nonlinear conditions, an analytic dependence of the coordinate of the breaking point on the amplitude and transverse size of the laser pulse is obtained.

Frolov, A. A. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation); Chizhonkov, E. V. [Moscow State University (Russian Federation)

2011-08-15

380

Flow visualization study of the MOD-2 wind turbine wake  

SciTech Connect

The specific objectives of the study reported were: to determine the geometry of the MOD-2 wind turbine wake in terms of wake height and width as a function of downstream distance under two conditions of atmospheric stability; to estimate the mean velocity deficit at several downstream stations in the turbine wake; and to investigate the behavior of the rotor-generated vortices, particularly their configuration and persistence. The background of the wake problem is briefly examined, including a discussion of the critical issues that the flow visualization study addresses. Experimental techniques and data analysis methods are described in detail. (LEW)

Liu H.T.; Waite, J.W.; Hiester, T.R.; Tacheron, P.H.; Srnsky, R.A.

1983-06-01

381

Plasma particle simulations of wake formation behind a spacecraft with thin wire booms  

NASA Astrophysics Data System (ADS)

Double-probe electric field sensors installed on scientific spacecraft are often deployed using wire booms with radii much less than typical Debye lengths of magnetospheric plasmas (millimeters compared to tens of meters). However, in tenuous and cold-streaming plasmas seen in the polar cap and lobe regions, the wire booms, electrically grounded at the spacecraft, have a high positive potential due to photoelectron emission and can strongly scatter approaching ions. Consequently, an electrostatic wake formed behind the spacecraft is further enhanced by the presence of the wire booms. We reproduce this process for the case of the Cluster satellite by performing plasma particle-in-cell (PIC) simulations, which include the effects of both the spacecraft body and the wire booms in a simultaneous manner. The simulations reveal that the effective thickness of the booms for the Cluster Electric Field and Wave (EFW) instrument is magnified from its real diameter (2.2mm) to several meters, when the spacecraft potential is at tens of volts. Such booms enhance the wake electric field magnitude by a factor of 1.5-2 depending on the spacecraft potential and play a principal role in explaining the in situ Cluster EFW data showing sinusoidal spurious electric fields with about 10mV/m amplitude. The boom effects are quantified by comparing PIC simulations with and without wire booms and also by examining the wake formation for various spacecraft potentials.

Miyake, Y.; Cully, C. M.; Usui, H.; Nakashima, H.

2013-09-01

382

Recent NASA Wake-Vortex Flight Tests, Flow-Physics Database and Wake-Development Analysis.  

National Technical Information Service (NTIS)

A series of flight tests over the ocean of a four engine turboprop airplane in the cruise configuration have provided a data set for improved understanding of wake vortex physics and atmospheric interaction. An integrated database has been compiled for wa...

D. D. Vicroy P. M. Vijgen H. M. Reimer J. L. Gallegos P. R. Spalart

1998-01-01

383

The structure of three-dimensional turbulent wakes \\/Case - Turbulent wake behind a crossed circular cylinder  

Microsoft Academic Search

The paper discusses the mean flow properties of the crossed circular cylinder wake. The U-component velocity distribution was determined from the momentum equation on the basis of local similarity, confirming that this profile almost coincided with the experimental value in the region beyond the value of x\\/d of 130. The dependence of reference scale of velocity and length on x

H. Osaka; H. Yamada; Y. Kageyama

1979-01-01

384

Hyperfine Interaction in Diatomics as a Tool for Suppression of Systemics and Verification of Theoretical Values for the Effective Electric Field on Electron for the Electron Edm Experiments  

NASA Astrophysics Data System (ADS)

An important feature of the effective electric field (E_{ eff}) acting on electrons is that it cannot be obtained in an experiment and the electronic structure calculation is required for its evaluation. Therefore, an accuracy check must be provided by calculating the experimentally known hyperfine constants which, similarly to E_{ eff}, depend on the electron spin density near heavy nuclei. As was shown the knowledge of the A_allel and A_perp constants for molecules with dominant one-electron s-p mixed molecular orbital contribution (?=1/2) provide the most important information for the E_{ eff} accuracy check. Howewer, the hyperfine structure for the ?=1 molecules, for a good approximation, is mainly determined by only one constant, A_allel. We show, nevertheless, that perturbation of the hyperfine structure of the ^3?_1 state of WC, HfF^+ and others molecules can be detected in an experiment giving missing information for the E_{ eff} accuracy check. Besides we show that the difference between g-factors for the Omega-doublet levels in diatomics with hyperfine structure can be converged to zero for some electric field. The latter is important for suppressing systematic effects and is one of the factors which determines the sensitivity limit in the eEDM search experiments. We show that in order to reproduce the experimental hyperfine structure of PbF obtained with high accuracy one must take into account the dependence of the hyperfine constants on the internuclear distance. A.V. Titov, N.S. Mosyagin, A.N. Petrov, T.A. Isaev, D.P. DeMille, Progr. Theor. Chem. Phys. B 15, 253 (2006) M.G. Kozlov, J. Phys. B: At. Mol. Opt. Phys. 30, L607 (1997) A. N. Petrov, Phys. Rev. A 83, 024502 (2011) R. J. Mawhorter et al, Phys. Rev. A 84, 022508 (2011)

Petrov, A. N.; Skripnikov, L. V.; Mosyagin, N. S.; Titov, A. V.

2013-06-01

385

Wake Forest University Physics Demonstration Videos  

NSDL National Science Digital Library

Physics is plenty exciting on its own, but this clutch of physics demonstration videos offered up by Wake Forest University's Physics departments will probably have students running out to learn more about string theory and cosmology. Teachers will definitely appreciate this resource, as they can use these videos in the classroom or just recommend to their students. Visitors can view the videos in their entirety by subject headings, which include "Motion", "Heat", "Optics", and not surprisingly, "Newton". All told there are dozens of videos, including "Bed of Nails", "Cartesian Diver", and the surreal yet appropriately titled "Marshmallow Man". Overall, this resource is a delightful find.

386

Geometrical Wake of a Smooth Flat Collimator  

SciTech Connect

A transverse geometrical wake generated by a beam passing through a smooth flat collimator with a gradually varying gap between the upper and lower walls is considered. Based on generalization of the approach recently developed for a smooth circular taper we reduce the electromagnetic problem of the impedance calculation to the solution of two much simpler static problems - a magnetostatic and an electrostatic ones. The solution shows that in the limit of not very large frequencies, the impedance increases with the ratio h/d where h is the width and d is the distance between the collimating jaws. Numerical results are presented for the NLC Post Linac collimator.

Stupakov, G.V.; /SLAC

2011-09-09

387

Wake Behind a Sphere Second Bifurcation  

NASA Astrophysics Data System (ADS)

The objective was to study second transition phenomenon and to make transition between second and third regimes better known. We present in this communication very controlled experiments concerning second instabilities in the wake of the sphere. We discuss the first transition from homogenous flow to a stationary instability and we present original results about peristaltic instability preceeding the hairpins shedding. From our results we proposed now a new insight on the generation of hairpins-vortex shedding phenomena. We obtained a new scenario ``precursor'' of the hairpin vortex shedding, with a peristaltic instability of oscillations of the two parallel counter-rotating vortices behind a sphere.

Gumowski, Konrad; Miedzik, Jan; Goujon-Durand, Sophie; Jenffer, Patrice; Bouchet, Gilles; Wesfreid, Jose-Euardo

2007-11-01

388

Velocity perturbations induced by the longitudinal vortices in a cylinder wake  

Microsoft Academic Search

This paper presents data showing the three-dimensional vortical structures in the near wake region of circular cylinders. The in-plane velocity field was measured using a digital Particle Image Velocimetry (PIV) technique. The vortical structures are found to include inclined counter-rotating longitudinal vortices in the braids joining consecutive Karman vortices. A simple vortex-pair model is proposed to estimate velocity perturbation induced

J. Wu; M. C. Welsh; J. Sheridan

1996-01-01

389

Wave breaking induced surface wakes and jets observed during a bora event  

Microsoft Academic Search

An observational and modeling study of a bora event that occurred during the field phase of the Mesoscale Alpine Programme is presented. Research aircraft in-situ measurements and airborne remote-sensing observations indicate the presence of strong low-level wave breaking and alternating surface wakes and jets along the Croatian coastline over the Adriatic Sea. The observed features are well captured by a

Qingfang Jiang; James D. Doyle

2005-01-01

390

The Effect of Geometry on the Wake Structure of a Surface Mounted Obstacle  

Microsoft Academic Search

Experiments were conducted to better understand the flow structure in the wake of a square cylinder as a function of its height and develop a parameterization for tall buildings for the QUIC-URB wind model. The experiments were conducted in an open-circuit wind tunnel in a fully turbulent boundary layer. 2D PIV was used to measure the flow field along the

Bhagirath Addepalli; Eric Pardyjak; Michael Brown

2007-01-01

391

Near-Wake Turbulence Properties around a Circular Cylinder at High Reynolds Number  

Microsoft Academic Search

The present study investigates the turbulent properties of the flow around a circular cylinder in the near-wake and in the\\u000a near-wall upstream region at the Reynolds number 140,000. A detailed cartography of the mean and turbulent velocity fields\\u000a using a moderate blockage and aspect ratio is provided in order to use the present results for direct comparisons with realisable\\u000a 3D

H. Djeridi; M. Braza; R. Perrin; G. Harran; E. Cid; S. Cazin

2003-01-01

392

Effect of wing-wake interaction on aerodynamic force generation on a 2D flapping wing  

NASA Astrophysics Data System (ADS)

This paper is motivated by the works of Dickinson et al. (Science 284:1954-1960, 1999) and Sun and Tang (J Exp Biol 205:55-70, 2002) which provided two different perspectives on the influence of wing-wake interaction (or wake capture) on lift generation during flapping motion. Dickinson et al. (Science 284:1954-1960, 1999) hypothesize that wake capture is responsible for the additional lift generated at the early phase of each stroke, while Sun and Tang (J Exp Biol 205:55-70, 2002) believe otherwise. Here, we take a more fundamental approach to study the effect of wing-wake interaction on the aerodynamic force generation by carrying out simultaneous force and flow field measurements on a two-dimensional wing subjected to two different types of motion. In one of the motions, the wing at a fixed angle of attack was made to follow a motion profile described by "acceleration-constant velocity-deceleration". Here, the wing was first linearly accelerated from rest to a predetermined maximum velocity and remains at that speed for set duration before linearly decelerating to a stop. The acceleration and deceleration phase each accounted for only 10% of the stroke, and the stroke covered a total distance of three chord lengths. In another motion, the wing was subjected to the same above-mentioned movement, but in a back and forth manner over twenty strokes. Results show that there are two possible outcomes of wing-wake interaction. The first outcome occurs when the wing encounters a pair of counter-rotating wake vortices on the reverse stroke, and the induced velocity of these vortices impinges directly on the windward side of the wing, resulting in a higher oncoming flow to the wing, which translates into a higher lift. Another outcome is when the wing encounters one vortex on the reverse stroke, and the close proximity of this vortex to the windward surface of the wing, coupled with the vortex suction effect (caused by low pressure region at the center of the vortex), causes the net force on the wing to decrease momentarily. These results suggest that wing-wake interaction does not always lead to lift enhancement, and it can also cause lift reduction. As to which outcome prevails depend very much on the flapping motion and the timing of the reverse stroke.

Lua, K. B.; Lim, T. T.; Yeo, K. S.

2011-07-01

393

An inverse agonist of the histamine H(3) receptor improves wakefulness in narcolepsy: studies in orexin-/- mice and patients.  

PubMed

Narcolepsy is characterized by excessive daytime sleepiness (EDS), cataplexy, direct onsets of rapid eye movement (REM) sleep from wakefulness (DREMs) and deficiency of orexins, neuropeptides that promote wakefulness largely via activation of histamine (HA) pathways. The hypothesis that the orexin defect can be circumvented by enhancing HA release was explored in narcoleptic mice and patients using tiprolisant, an inverse H(3)-receptor agonist. In narcoleptic orexin(-/-) mice, tiprolisant enhanced HA and noradrenaline neuronal activity, promoted wakefulness and decreased abnormal DREMs, all effects being amplified by co-administration of modafinil, a currently-prescribed wake-promoting drug. In a pilot single-blind trial on 22 patients receiving a placebo followed by tiprolisant, both for 1 week, the Epworth Sleepiness Scale (ESS) score was reduced from a baseline value of 17.6 by 1.0 with the placebo (p>0.05) and 5.9 with tiprolisant (p<0.001). Excessive daytime sleep, unaffected under placebo, was nearly suppressed on the last days of tiprolisant dosing. H(3)-receptor inverse agonists could constitute a novel effective treatment of EDS, particularly when associated with modafinil. PMID:18295497

Lin, Jian-Sheng; Dauvilliers, Yves; Arnulf, Isabelle; Bastuji, Hélène; Anaclet, Christelle; Parmentier, Régis; Kocher, Laurence; Yanagisawa, Masashi; Lehert, Philippe; Ligneau, Xavier; Perrin, David; Robert, Philippe; Roux, Michel; Lecomte, Jeanne-Marie; Schwartz, Jean-Charles

2007-12-27

394

The structure of cosmic string wakes  

SciTech Connect

The clustering of baryons and cold dark matter induced by a single moving string is analyzed numerically, making use of the new three-dimensional Eulerian cosmological hydrocode of Sornborger {ital et al.}, which uses the piecewise parabolic method to track the baryons and the particle-in-cell method to evolve the dark matter particles. A long straight string moving with a speed comparable to c induces a planar overdensity (a {open_quotes}wake{close_quotes}). Since the initial perturbation is a velocity kick toward the plane behind the string and there is no initial Newtonian gravitational line source, the baryons are trapped in the center of the wake, leading to an enhanced baryon to dark matter ratio. The cold coherent flow leads to very low postshock temperatures of the baryonic fluid. In contrast, long strings with small-scale structure (which can be described by adding a Newtonian gravitational line source) move slowly and form filamentary objects. The large central pressure due to the gravitational potential causes the baryons to be expelled from the central regions and leads to a relative deficit in the baryon to dark matter ratio. In this case, the velocity of the baryons is larger, leading to high postshock temperatures. {copyright} {ital 1997} {ital The American Astronomical Society}

Sornborger, A. [Department of Applied Mathematics and Theoretical Physics, University of Cambridge, 3 Silver Street, Cambridge CB3 9EW, England (United Kingdom); Brandenberger, R. [Physics Department, Brown University, Providence, Rhode Island 02912 (United States); Fryxell, B.; Olson, K. [Institute for Computational Science and Informatics, George Mason University, Fairfax, Virginia 22030 (United States)

1997-06-01

395

[Biological principles of sleep and wake].  

PubMed

Electrophysiologically measurable sleep is divided into rapid eye movement (REM) sleep and nonREM sleep--the latter is further structured into several sleep stages, including deep sleep. This internal sleep regulation is explained by the reciprocal interaction model that was validated in 1975. The interdependence of not only the reciprocal discharge of cholinergic REM-on, but also serotonergic and noradrenergic (REM-off) cell populations distributed over the brain stem results in the alternating pattern of nonREM and REM sleep. The timing of sleep onset and waking is described using the two-process model. Thereby, the theoretical sum of all circadian processes (process C) interacts with the homeostatic sleep drive (process S). Because the occurrence of REM sleep also depends on circadian factors, the decrease of deep sleep during the night is accepted as a physiological correlate of process S. Social activity and daylight synchronize the circadian process with the external 24-h day. With the help of the orexin system, the flip-flop model explains why both sleep and wake can be sustained over longer periods. Dependency on age and physiological short and long sleepers are the most prominent variations of normal sleep behavior. Newer therapeutic concepts in sleep medicine have taken into consideration these biological basics, e.g., in the selection of sleep medication and in the development of new sleep-inducing medications. PMID:22116476

Rodenbeck, A

2011-12-01

396

Characterizing cylinder and hydrofoil wake dynamics  

NASA Astrophysics Data System (ADS)

A number of high speed PIV measurements of wakes trailing a NACA 0015, c=0.081m, and a cylinder D= 0.0127m, in the speed range 2 through 9 m/s have been made in the high speed water tunnel at SAFL- UMN. The cylinder vortex shedding follows closely St=0.2, while that off the hydrofoil is more irregular. Although the hydrofoil shows a more irregular nature a measure for both shedding frequencies and vortex strength of is of great interest also for drag analysis. The direct approach mapping individual structures, e.g. vorticity based analysis, can be obscured by the quality of the measurements made, hence other methods to reveal frequency and strength are in demand. A study were the mapping of time variation of the main flow direction impulse flux integrated over the wake at, minimum two, downstream positions has been made. A cross-correlation analysis of the impulse flux can reveal structure transport speeds, the frequency spectrum will reflect the shedding frequency, while the temporal variation represents the strength. For the hydrofoil it's shown that a significant cross- correlation is present. In terms of spectra even the more structured shedding from cylinders are hard to capture, and finally the vortex strength found using the cited algorithm seems somewhat unreliable. A thorough comparison between the suggested measure and traditional measures is given.

Kjeldsen, Morten; Seim, Bjarte G.; Arndt, Roger E. A.

2009-11-01

397

Investigation on 3D t wake flow structures of swimming bionic fish  

NASA Astrophysics Data System (ADS)

A bionic experimental platform was designed for the purpose of investigating time accurate three-dimensional flow field, using digital particle image velocimetry (DSPIV). The wake behind the flapping trail of a robotic fish model was studied at high spatial resolution. The study was performed in a water channel. A robot fish model was designed and built. The model was fixed onto a rigid support framework using a cable-supporting method, with twelve stretched wires. The entire tail of the model can perform prescribed motions in two degrees of freedom, mainly in carangiform mode, by driving its afterbody and lunate caudal fin respectively. The DSPIV system was set up to operate in a translational manner, measuring velocity field in a series of parallel slices. Phase locked measurements were repeated for a number of runs, allowing reconstruction of phase average flow field. Vortex structures with phase history of the wake were obtained. The study reveals some new and complex three-dimensional flow structures in the wake of the fish, including "reverse hairpin vortex" and "reverse Karman S-H vortex rings", allowing insight into physics of this complex flow.

Shen, G.-X.; Tan, G.-K.; Lai, G.-J.

2012-10-01

398

Dynamic Wind Loads and Vortex Structures in the Wake of a Wind Turbine  

NASA Astrophysics Data System (ADS)

We report an experimental study to characterize the dynamic wind loads and evolution of wake vortex flow structures downstream of a horizontal axis wind turbine (HAWT). The experiments were conducted in a wind tunnel with a wind turbine model placed in a boundary layer flow developed over rough and smooth surfaces in order to study the effects of roughness and the resulting velocity and turbulence fields on the wake characteristics and fatigue loads acting on the wind turbine. In addition to measuring dynamic wind loads (both aerodynamic forces and moments) acting on the wind turbine model using a six-component load cell, a high-resolution Particle Image Velocimetry (PIV) system was used to make phase-locked flow field measurements to quantify the time-evolution of the wake vortex and turbulence flow structures shedding from wind turbine blades. The detailed flow field measurements were correlated with the wind load measurements to elucidate the underlying physics associated with turbine power generation and fatigue loads acting on wind turbines.

Hu, Hui; Yang, Zifeng; Sarkar, Partha

2010-11-01

399

Relationship between vortex ring in tail fin wake and propulsive force  

NASA Astrophysics Data System (ADS)

Our aim was to investigate the three-dimensional (3D) vortex ring in the wake of a tail fin and to clarify the propulsion mechanism of dolphins and fish. In this study, we replaced a tail fin in pitching motion with an oscillating wing having a drive unit. The flow fields around the wing were measured by stereoscopic particle image velocimetry. To visualize the 3D structure of the vortex in the wake, we determined the flow fields in equally spaced cross-sectional planes. We reconstructed the 3D velocity fields from the velocity data with three components in two dimensions. We visualized the 3D vortex structure from these velocity data and plotted an iso-vorticity surface. As a result, we found that the vortex ring was generated by the kick-down and kick-up motions of the wing and that the wake structure was comparable with that obtained numerically. Moreover, we calculated the propulsive forces from the temporal variations in circulation and in the area surrounded by the vortex ring.

Imamura, Naoto; Matsuuchi, Kazuo

2013-10-01

400

Wake Vortex Tracking Using a 35 GHz Pulsed Doppler Radar  

Microsoft Academic Search

A 35 GHz, pulsed-Doppler radar system has been designed and assembled for wake vortex detection and tracking in low visibility conditions. Aircraft wake vortices continue to be an important factor in determining safe following distances or spacings for aircraft in the terminal area. Currently, under instrument meteorological conditions (IMC), aircraft adhere to conservative, fixed following-distance guidelines based primarily on aircraft

Robert T. Neecea; Charles L. Brittb; Joseph H. Whitec; Ashok Mudukutored; Chi Nguyene; Bill Hooperf

401

32 CFR 707.10 - Wake illumination light.  

Code of Federal Regulations, 2013 CFR

...2013-07-01 2013-07-01 false Wake illumination light. 707.10 Section 707.10 National Defense...RULES WITH RESPECT TO ADDITIONAL STATION AND SIGNAL LIGHTS § 707.10 Wake illumination light. Naval vessels may display a white spot...

2013-07-01

402

Analysis of the radar reflectivity of aircraft vortex wakes  

Microsoft Academic Search

Radar has been proposed as a way of tracking wake vortices to reduce aircraft spacing and tests have revealed radar echoes from aircraft wakes in clear air. The mechanism causing refractive index gradients in these tests is thought to be the same as that for homogeneous and isotropic atmospheric turbulence in the Kolmogorov inertial range, for which there is a

Karim Shariff; Alan Wray

2002-01-01

403

Wake Forest U. Joins Ranks of Test-Optional Colleges  

ERIC Educational Resources Information Center

|Wake Forest University will no longer require applicants to submit standardized test scores, the university announced last week. The move makes Wake Forest, in Winston-Salem, North Carolina, one of the most prominent institutions with a "test optional" admissions policy. The university's decision reveals the increasing complexity of the national…

Hoover, Eric; Supiano, Beckie

2008-01-01

404

Theoretical analysis of wake-induced parachute collapse  

Microsoft Academic Search

During recent drop tests of a prototype weapon system, the parachute collapsed soon after it became fully inflated. The magnitude and duration of the collapses were severe enough to degrade parachute performance drastically. A computer-assisted analysis is presented which models parachute inflation, forebody and parachute wake generation, and interaction between the wake and the inflating or collapsing parachute. Comparison of

H. R. Spahr; D. F. Wolf

1981-01-01

405

Wake-related activity of tuberomammillary neurons in rats  

Microsoft Academic Search

Histaminergic neurons of the tuberomammillary nucleus (TMN) are hypothesized to promote wakefulness, but little is known about the activity of these cells during spontaneous behavior. We measured histaminergic neuron activity in the dorsomedial, ventrolateral, and caudal TMN at four different times using Fos and adenosine deaminase immunohistochemistry and recordings of sleep\\/wake behavior. Because circadian factors could influence neuronal activity, we

Emily M. Ko; Ivy V. Estabrooke; Marie McCarthy; Thomas E. Scammell

2003-01-01

406

Aryl-heteroaryl derivatives as novel wake-promoting agents.  

PubMed

In search of a next generation molecule to the novel wake-promoting agent modafinil, a series of aryl-heteroayl-derived wakefulness enhancing agents (in rats) was developed. From this work, compound 16 was separated into its enantiomers to profile them individually. PMID:23110414

Lesur, Brigitte; Lin, Yin G; Marcy, Val R; Aimone, Lisa D; Gruner, John; Bacon, Edward R; Chatterjee, Sankar

2012-12-26

407

Flight safety, aircraft vortex wake and airport operation capacity  

Microsoft Academic Search

One of the major problems that challenge today's aeronautics is the problem of improving flight safety. A zone of increased hazard is the aerospace in the vicinity of an airport. Here, one of aircraft accidents' causes is wake turbulence generated by aircraft. The encountering of an aircraft on take-off or landing with the vortex wake of a preceding aircraft can

Victor V. Vyshinsky

2001-01-01

408

Vortical patterns in the wake of an oscillating airfoil  

Microsoft Academic Search

The vortical flow patterns in the wake of a NACA 0012 airfoil pitching at small amplitudes are studied in a low-speed water channel. It is shown that a great deal of control can be exercised on the structure of the wake by the control of the frequency, amplitude, and also the shape of the oscillation waveform. An important observation in

Manoochehr M. Koochesfahani

1989-01-01

409

Multiscale plant wakes, turbulence and non linear scaling flexible effects  

Microsoft Academic Search

We present velocity ADV measurements and flow visualization of the turbulent wakes behind plant arrays, as these are often fractal in nature, we compare the multifractal spectra and the turbulence structure behind the wakes. Both statistical measures allowing to calculate integral lengthscales and their profiles modified by the plant cannopies [1,2] as well as intermittency and spectral behaviour are also

Teresa Vila; Jose M. Redondo; David Velasco

2010-01-01

410

A modified law of the wake for turbulent shear layers  

Microsoft Academic Search

A simple polynomial expression is proposed for the modification to the wake function for turbulent shear layers that satisfies the condition of zero slope of the velocity profile at the outer edge of the shear layer. The modified and unmodified law of the wake are compared with some experimental cases, and it is seen that the present modified law of

P. S. Granville

1976-01-01

411

Acoustic-gravity waves generated by wake flows  

NASA Astrophysics Data System (ADS)

The wavy wall analogy framework is used to obtain a model problem for the acoustic-gravity wave field generated by a three-dimensional wave packet, that may be seen as a model for wake flow instabilities. In this study, we use asymptotic methods to analyse the manner in which the pressure field structure changes, and more specifically, we estimate the properties of acoustic and gravity waves in terms of saddle-point contributions. The saddle-points are computed from the general dispersion relation that we deduce from a compressible model with earth rotation and non-Boussinesq effects. Particular attention is paid to the far-field limit for which a single saddle-point contribution enables the description of both acoustic and gravity waves, also depending on the streamwise phase velocity of the wave packet. The transition from low-frequency acoustic waves (or infrasounds) to gravity waves can be treated in the same way as the acoustic radiation of supersonic two-dimensional shear layers.

Millet, Christophe; Le Dizès, Stéphane

2010-11-01

412

Multi-component wind measurements of wind turbine wakes performed with three LiDARs  

NASA Astrophysics Data System (ADS)

Field measurements of the wake flow produced from the interaction between atmospheric boundary layer and a wind turbine are performed with three wind LiDARs. The tested wind turbine is a 2 MW Enercon E-70 located in Collonges, Switzerland. First, accuracy of mean values and frequency resolution of the wind measurements are surveyed as a function of the number of laser rays emitted for each measurement. Indeed, measurements performed with one single ray allow maximizing sampling frequency, thus characterizing wake turbulence. On the other hand, if the number of emitted rays is increased accuracy of mean wind is increased due to the longer sampling period. Subsequently, two-dimensional measurements with a single LiDAR are carried out over vertical sections of the wind turbine wake and mean wake flow is obtained by averaging 2D measurements consecutively performed. The high spatial resolution of the used LiDAR allows characterizing in details velocity defect present in the central part of the wake and its downstream recovery. Single LiDAR measurements are also performed by staring the laser beam at fixed directions for a sampling period of about ten minutes and maximizing the sampling frequency in order to characterize wake turbulence. From these tests wind fluctuation peaks are detected in the wind turbine wake at blade top-tip height for different downstream locations. The magnitude of these turbulence peaks is generally reduced by moving downstream. This increased turbulence level at blade top-tip height observed for a real wind turbine has been already detected from previous wind tunnel tests and Large Eddy simulations, thus confirming the presence of a source of dangerous fatigue loads for following wind turbines within a wind farm. Furthermore, the proper characterization of wind fluctuations through LiDAR measurements is proved by the detection of the inertial subrange from spectral analysis of these velocity signals. Finally, simultaneous measurements with two LiDARs are performed over the mean vertical symmetry plane of the wind turbine wake, while a third LiDAR measures the incoming wind over a vertical plane parallel to the mean wind direction and lying outside of the wake. One LiDAR is placed in proximity of the wind turbine location and measures pointing downstream, whereas a second LiDAR is located along the mean wind direction at a downstream distance of 6.5 diameters and measures pointing upstream. For these measurements axial and vertical velocity components are retrieved only for measurement points where the two laser beams result to be roughly orthogonal. Statistics of the two velocity components show in the near wake at hub height strong flow fluctuations with magnitudes about 30% of the mean value, and a gradual reduction for downstream distances larger than three rotor diameters.

Iungo, G. V.; Wu, Y.-T.; Porté-Agel, F.

2012-04-01

413

Experimental investigation of wake vortex in a water towing tank  

NASA Astrophysics Data System (ADS)

Wake vortex behind an aircraft would introduce great hazard to the following aircraft and threaten to the flight safety. Generic model using two rectangular airfoils was employed for generating wake vortex system to investigate the method of wake vortex alliviation. The investigation was carried out in a water towing tank equipt with Particle Image Velocimetry system. Characteristics of double-vortex flow were analyzed for selected cases, proving that the intensity of the vortex is reduced with respect to the interaction between the wake vortices. The study exhibited that the R-L instability was most effectively triggered with parameter combinations of ?1=10°, ?2=8°and b=50mm respectively. As a result, the circulation of the wake vortices was alleviated by nearly 40% accordingly.

Liu, Yue; Wang, Junwei; Liu, Zhirong; Bao, Feng

2012-10-01

414

Effects and mechanisms of wakefulness on local cortical networks  

PubMed Central

SUMMARY Mammalian brains generate internal activity independent of environmental stimuli. Internally generated states may bring about distinct cortical processing modes. To investigate how brain state impacts cortical circuitry, we recorded intracellularly from the same neurons, under anesthesia and subsequent wakefulness, in rat barrel cortex. In every cell examined throughout layers 2–6, wakefulness produced a temporal pattern of synaptic inputs differing markedly from those under anesthesia. Recurring periods of synaptic quiescence, prominent under anesthesia, were abolished by wakefulness, which produced instead a persistently depolarized state. This switch in dynamics was unaffected by elimination of afferent synaptic input from thalamus, suggesting that arousal alters cortical dynamics by neuromodulators acting directly on cortex. Indeed, blockade of noradrenergic, but not cholinergic, pathways induced synaptic quiescence during wakefulness. We conclude that global brain states can switch local recurrent networks into different regimes via direct neuromodulation. Our results provide a basis for understanding how sleep/wake cycles alter synaptic integration in cortical neurons.

Constantinople, Christine M.; Bruno, Randy M.

2011-01-01

415

Wakes of Self-propelled Bodies in Stratified Fluids  

NASA Astrophysics Data System (ADS)

Using high Reynolds number (Re=10^4-10^5) experiments, the dynamics of stratified momentum wakes of self-propelled underwater and surface bodies were studied in (i) deep linearly stratified (deep ocean pycnocline), (ii) two layer (shallow pycnocline), and (iii) surface stratified (turbocline) fluids, and theoretical models wee advanced to explain the flow behavior. These models: (i) predict conditions under which submerged wakes signatures penetrate to the water surface, as expressed by the Confinement and Contrast numbers, and (ii) describe IR (infra-red) surface wakes signatures, as expressed by the Contrast and modified Froude numbers. If decaying turbulence is present surrounding the wake, the penetration of wake signature to the surface is still possible. Estimates for typical oceanic cases are given. PIV, LIF and high sensitivity Infrared Imaging cameras were employed for flow diagnostics.

Voropayev, S. I.; Fernando, H. J. S.

2008-11-01

416

Tau protein role in sleep-wake cycle.  

PubMed

Evidence has shown that the lack of tau produces subtle changes in neuronal structure and modest impairment in complex behaviors, suggesting compensatory mechanisms carried out by other neuronal microtubule-associated proteins. Here we show major abnormalities in sleep-wake cycle of tau-deficient animals including increased wakefulness duration and decreased non-rapid eye movement (NREM) sleep time, a higher number of state transitions between NREM and wake, and shortened sleep bouts. Altered sleep structure in tau-/- mice was accompanied by a significant decline in delta power together with an enhanced spectral density of sleep spindles during NREM sleep. No significant differences were observed in rapid eye movement (REM) sleep between the two mouse strains. Taken together, these results suggest that tau indirectly participates in the regulation of the sleep-wake cycle modulating not only the control and maintenance of global brain states but also the cerebral oscillatory patterns underlying sleep-wake states. PMID:20555133

Cantero, Jose L; Hita-Yañez, Eva; Moreno-Lopez, Bernardo; Portillo, Federico; Rubio, Alicia; Avila, Jesus

2010-01-01

417

Axisymmetric turbulent wakes with new nonequilibrium similarity scalings.  

PubMed

The recently discovered nonequilibrium turbulence dissipation law implies the existence of axisymmetric turbulent wake regions where the mean flow velocity deficit decays as the inverse of the distance from the wake-generating body and the wake width grows as the square root of that distance. This behavior is different from any documented boundary-free turbulent shear flow to date. Its existence is confirmed in wind tunnel experiments of wakes generated by plates with irregular edges placed normal to an incoming free stream. The wake characteristics of irregular bodies such as buildings, bridges, mountains, trees, coral reefs, and wind turbines are critical in many areas of environmental engineering and fluid mechanics. PMID:24138244

Nedi?, J; Vassilicos, J C; Ganapathisubramani, B

2013-10-02

418

Large-scale structures in dipole and quadrupole wakes of a wall-mounted finite rectangular cylinder  

NASA Astrophysics Data System (ADS)

Large-scale quasi-periodic vortex structures shed behind a wall-mounted rectangular cylinder were reconstructed from conditional averaging of several planar particle image velocimetry measurements based on the phase of the pressure at the cylinder surface. The measurements were taken for a square cross-section cylinder with height-to-width ratio of h/d = 8 partially immersed in two nominally thin turbulent boundary layers of thickness-to-height ratios of ?/h = 0.09 and 0.32. The Reynolds number based on the diameter was 12,000. For the thinner boundary layer in the time-averaged wake, one stream wise vortex pair was present at the free end (dipole wake) while for the thicker boundary layer, another pair was also observed at the wall junction (quadrupole wake). The detailed description of the shed structures giving rise to these time-averaged vortex pairs indicates more complex connections than previously proposed arch-type structures, which implies different vortex dynamic processes in the wake. The structures obtained for the dipole and quadrupole wakes were similar at the free end but significantly different at the junction resulting in distinct imprint on the mean and turbulent fields.

Hosseini, Z.; Bourgeois, J. A.; Martinuzzi, R. J.

2013-09-01

419

Aspects of the influence of an oscillating mini-flap upon the near wake of an airfoil NACA 4412  

Microsoft Academic Search

A NACA 4412 airfoil was tested, in a boundary layer wind tunnel, with the aim to study the effect of a Gurney mini-flap, as an active and passive flow control device submitted to a turbulent flow field. The main objective was the experimental determination of flow pattern characteristics downstream the airfoil in the near wake. The untwisted wing model used

J. S. Delnero; J. Marañón Di Leo; J. Colman; M. García Sainz; F. Muñoz; N. Hérouard; M. E. Camocardi

2011-01-01

420

Exploration of the Relationship Between Wake Vortex Parameters and Thrust Force on Oscillating Airfoils Using a Vortex Array Model  

NASA Astrophysics Data System (ADS)

Recently, we demonstrated the ability of a simple model, based on an array of finite-core Gaussian vortices, to accurately reproduce the unsteady velocity field in the wake of, and drag/thrust force acting on harmonically/non-harmonically pitching airfoils. In the present work, this model is employed to explore how the thrust force varies with wake vortex parameters; i.e. circulation, core radius and streamwise/cross-flow spacing of the vortices. Insight from this investigation will be helpful to draw links between trailing-edge flexibility and the detailed process of generation of wake vortices. Such links may have the potential for providing a path towards a rational, yet efficient, approach for tailoring trailing-edge flexibility to obtain desirable force characteristics for flapping-wings Micro Air Vehicles.

Naguib, Ahmed; Koochesfahani, Manoochehr

2011-11-01

421

Radar monitoring of a wake vortex: Electromagnetic reflection of wake turbulence in clear air  

Microsoft Academic Search

This article deals with X-band radar trial campaigns in 2006 and 2007 at Orly Airport, and in June 2008 at Paris-CDG Airport. An X-band Doppler radar has been deployed to assess short range (inferior to 2000 m) wake vortex monitoring capabilities in all weather conditions (dry and wet conditions). Recorded data have been correlated with electromagnetic and fluid mechanical models

Frédéric Barbaresco; Uwe Meier

2010-01-01

422

3D-simulation of the turbulent wake behind a wind turbine  

NASA Astrophysics Data System (ADS)

The paper relates to the simulation of the airflow around a wind turbine (WT) of the type ENERCON E66 with emphasis on the turbulent wake. The simulations were undertaken with the Computational Fluid Dynamics (CFD) software ANSYS FLUENT 6.3 using the LES technique for turbulence modeling. It is the aim of the work to capture the full three-dimensional turbulent flow behind a WT in a sufficient spatial and temporal resolution to generate information for wind loads of WTs in wind farm configuration. This information shall help to optimize wind farm layouts in the future. Using an incoming wind field that matches the requirements of the IEC-61400 for wind fields used in load calculations it was possible to simulate a full meandering turbulent wake. The turbulent features of the WT wake could be reproduced with numerical methods not using further assumptions but solely based on the WT geometry and the solution of the governing physical equations. The project is supported by ENERCON GmbH, Germany.

Wußow, Steffen; Sitzki, Lars; Hahm, Thomas

2007-07-01

423

Shining light on wakefulness and arousal.  

PubMed

Alterations in arousal states are associated with multiple neuropsychiatric disorders, including generalized anxiety disorders, addiction, schizophrenia, and depression. Therefore, elucidating the neurobiological mechanisms controlling the boundaries between arousal, hyperarousal, and hypoarousal is a crucial endeavor in biological psychiatry. Substantial research over several decades has identified distinct arousal-promoting neural populations in the brain; however, how these nuclei act individually and collectively to promote and maintain wakefulness and various arousal states is unknown. We have recently applied optogenetic technology to the repertoire of techniques used to study arousal. Here, we discuss the recent results of these experiments and propose future use of this approach as a way to understand the complex dynamics of neural circuits controlling arousal and arousal-related behaviors. PMID:22440618

de Lecea, Luis; Carter, Matthew E; Adamantidis, Antoine

2012-03-20

424

Shining Light on Wakefulness and Arousal  

PubMed Central

Alterations in arousal states are associated with multiple neuropsychiatric disorders including generalized anxiety disorders, addiction, schizophrenia, and depression. Therefore, elucidating the neurobiological mechanisms controlling the boundaries between arousal, hyperarousal, and hypoarousal is a crucial endeavor in biological psychiatry. Substantial research over several decades has identified distinct arousal-promoting neural populations in the brain; however, how these nuclei act individually and collectively to promote and maintain wakefulness and various arousal states is unknown. We have recently applied optogenetic technology to the repertoire of techniques used to study arousal. Here, we discuss the recent results of these experiments and propose future use of this approach as a way to understand the complex dynamics of neural circuits controlling arousal and arousal-related behaviors.

de Lecea, Luis; Carter, Matthew E.; Adamantidis, Antoine

2013-01-01

425

Prediction of BVI noise patterns and correlation with wake interaction locations  

NASA Astrophysics Data System (ADS)

High resolution fluctuating airloads data were acquired during a test of a contemporary design United Technologies model rotor in the Duits-Nederlandse Windtunnel (DNW). The airloads are used as input to the noise prediction program WOPWOP, in order to predict the blade-vortex interaction (BVI) noise field on a large plane below the rotor. Trends of predicted advancing and retreating side BVI noise levels and directionality as functions of flight condition are presented. The measured airloads have been analyzed to determine the BVI locations on the blade surface, and are used to interpret the predicted BVI noise radiation patterns. Predicted BVI locations are obtained using the free wake model in CAMRAD/JA, the UTRC Generalized Forward Flight Distorted Wake Model, and the UTRC FREEWAKE analysis. These predicted BVI locations are compared with those obtained from the measured pressure data.

Marcolini, Michael A.; Martin, Ruth M.; Lorber, Peter F.; Egolf, T. A.

426

Molecular Tagging Velocimetry and Thermometry in the Wake of a Heated Circular Cylinder  

NASA Astrophysics Data System (ADS)

We report improvements to the Molecular Tagging Velocimetry and Thermometry (MTV)technique for simultaneous velocity and temperature measurements in liquids. Using phosphorescent molecules, a pulsed laser "tags" the regions of interest, and these regions are interrogated at two successive times within the emission lifetime of the molecules. The Lagrangian displacement of the tagged regions gives the estimate of the velocity. The temperature mapping relied on the temperature dependence of phosphorescence lifetime, estimated from the intensity ratio of the images. This technique is used to perform simultaneous velocity and temperature measurements in the wake of a heated cylinder. Significant modification of the wake structure is observed as the Richardson number increases toward unity. Results are discussed in terms of the mean and fluctuating velocity and temperature fields, the velocity-temperature correlation, and the shedding frequency.

Hu, H.; Koochesfahani, M.

2003-11-01

427

Numerical analysis of the tip and root vortex position in the wake of a wind turbine  

NASA Astrophysics Data System (ADS)

The stability of tip and root vortices are studied numerically in order to analyse the basic mechanism behind the break down of tip and root vortices. The simulations are performed using the CFD program "EllipSys3D". In the computations the so-called Actuator Line Method is used, where the blades are represented by lines of body forces representing the loading. The forces on the lines are implemented using tabulated aerodynamic aerofoil data. In this way, computer resources are used more efficiently since the number of mesh points locally around the blade is decreased, and they are instead concentrated in the wake behind the blades. We here present results of computed flow fields and evaluate the flow behaviour in the wake. In particular we compare the position of the root vortices as to the azimuthal position of the tip votices.

Ivanell, S.; Sørensen, J. N.; Mikkelsen, R.; Henningson, D.

2007-07-01

428

Identification of vortex pairs in aircraft wakes from sectional velocity data  

NASA Astrophysics Data System (ADS)

The dynamics of multiple-vortex wake systems behind aircraft endangering air traffic can be assessed also from physical modelling. Large-scale laboratory investigations of multiple-vortex systems have been performed in a free-flight laboratory and in a water towing tank. Specialized PIV measurements provide time-resolved flow velocity fields normal to the wake axis. The applicability of various ? u-based vortex identification schemes to planar velocity data is addressed and demonstrated for unequal-strength co- and counter-rotating vortex pairs. Large vortices shed off the wing tips and flaps are identified employing a ? u-based criterion. Their cooperative mechanisms of generation and decay are evidenced from iso-surfaces of squared swirling strength and from further characteristic vortex parameters.

Carmer, Carl F. V.; Konrath, Robert; Schröder, Andreas; Monnier, Jean-Claude

2008-03-01

429

Statistical structure and mean dynamics of developing turbulent shear-wake flows  

NASA Astrophysics Data System (ADS)

Shear-wake flows formed from the interaction of two turbulent boundary layers are investigated. Primary focus is on the near-field downstream of the splitter plate. Two velocity ratios and two trailing edge geometries are explored via well-resolved hotwire traverses. Comparison with boundary layer data reveals that the loss of the no-slip condition is at first most apparent in the wall-normal velocity fluctuations. Estimates of the terms in the mean momentum equation are examined. Post-separation, the inertial terms in the mean momentum equation rapidly become dominant throughout the flow. Farther downstream the mean effect of turbulent inertia continues to change sign between the wake center and the freestream, as it does between the wall and freestream in the boundary layer. Unlike in the boundary layer, the mean and turbulent inertia terms retain leading order importance over the viscous force term everywhere.

Bamberger, M.; Klewicki, J.

2013-01-01

430

Stratospheric aircraft exhaust plume and wake chemistry  

NASA Astrophysics Data System (ADS)

Progress to date in an ongoing study to analyze and model emissions leaving a proposed High Speed Civil Transport (HSCT) from when the exhaust gases leave the engine until they are deposited at atmospheric scales in the stratosphere is documented. A kinetic condensation model was implemented to predict heterogeneous condensation in the plume regime behind an HSCT flying in the lower stratosphere. Simulations were performed to illustrate the parametric dependence of contrail droplet growth on the exhaust condensation nuclei number density and size distribution. Model results indicate that the condensation of water vapor is strongly dependent on the number density of activated CN. Incorporation of estimates for dilution factors into a Lagrangian box model of the far-wake regime with scale-dependent diffusion indicates negligible decrease in ozone and enhancement of water concentrations of 6-13 times background, which decrease rapidly over 1-3 days. Radiative calculations indicate a net differential cooling rate of the plume about 3K/day at the beginning of the wake regime, with a total subsidence ranging between 0.4 and 1 km. Results from the Lagrangian plume model were used to estimate the effect of repeated superposition of aircraft plumes on the concentrations of water and NO(y) along a flight corridor. Results of laboratory studies of heterogeneous chemistry are also described. Kinetics of HCl, N2O5 and ClONO2 uptake on liquid sulfuric acid were measured as a function of composition and temperature. Refined measurements of the thermodynamics of nitric acid hydrates indicate that metastable dihydrate may play a role in the nucleation of more stable trihydrates PSC's.

Miake-Lye, R. C.; Martinez-Sanchez, M.; Brown, R. C.; Kolb, C. E.; Worsnop, D. R.; Zahniser, M. S.; Robinson, G. N.; Rodriguez, J. M.; Ko, M. K. W.; Shia, R.-L.

1993-07-01

431

The acute soporific action of daytime melatonin administration: effects on the EEG during wakefulness and subjective alertness.  

PubMed

Melatonin has been reported to have soporific effects; following daytime administration, it induces sleepiness and reduces sleep onset latency. However, subjective sleepiness is masked by a variety of stimuli and behaviors; thus, it is important to be able to delineate objective psychophysiological sequelae of melatonin administration. Alertness decrements during wakefulness are correlated with augmented theta/alpha power in the waking electroencephalogram (EEG). This has been validated in a constant routine protocol. In a variety of experiments with melatonin administration (5 mg), the authors have shown that the EEG changes can be measured immediately, before any subjective soporific effects are recognized. These increases in theta/alpha power occur when melatonin is administered during the day (1300 or 1800 h) but are less visible when near the endogenous melatonin rise in the evening (2040 h). Importantly, both subjective and objective measures of sleepiness are suppressed when subjects change posture from supine to standing. PMID:9406039

Cajochen, C; Kräuchi, K; Wirz-Justice, A

1997-12-01

432

First Results from ARTEMIS, a New Two-Spacecraft Lunar Mission: Counter-Streaming Plasma Populations in the Lunar Wake  

NASA Astrophysics Data System (ADS)

We present observations from the first passage through the lunar plasma wake by one of two spacecraft comprising ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun), a new lunar mission that re-tasks two of five probes from the THEMIS magnetospheric mission. On Feb 13, 2010, ARTEMIS probe P1 passed through the wake at ˜3.5 lunar radii downstream from the Moon, in a region between those explored by Wind and the Lunar Prospector, Kaguya, Chandrayaan, and Chang'E missions. ARTEMIS observed interpenetrating proton, alpha particle, and electron populations refilling the wake along magnetic field lines from both flanks. The characteristics of these distributions match expectations from self-similar models of plasma expansion into vacuum, with an asymmetric character likely driven by a combination of a tilted interplanetary magnetic field and an anisotropic incident solar wind electron population. On this flyby, ARTEMIS provided unprecedented measurements of the interpenetrating beams of both electrons and ions naturally produced by the filtration and acceleration effects of electric fields set up during the refilling process. ARTEMIS also measured electrostatic oscillations closely correlated with counter-streaming electron beams in the wake, as previously hypothesized but never before directly measured. These observations demonstrate the capability of the comprehensively instrumented ARTEMIS spacecraft and the potential for new lunar science from this unique two spacecraft constellation.

Halekas, J. S.; Angelopoulos, V.; Sibeck, D. G.; Khurana, K. K.; Russell, C. T.; Delory, G. T.; Farrell, W. M.; McFadden, J. P.; Bonnell, J. W.; Larson, D.; Ergun, R. E.; Plaschke, F.; Glassmeier, K. H.

2011-12-01

433

Morphine inhibits sleep-promoting neurons in the ventrolateral preoptic area via mu receptors and induces wakefulness in rats.  

PubMed

Morphine is the most efficacious and widely prescribed treatment for pain. However, it decreases the total amount of deep sleep and rapid eye movement sleep in humans. Acute morphine administration at low doses causes wakefulness in animal models. To clarify the mechanism by which morphine affects sleep-wake behavior, we investigated the effects of morphine on the sleep-promoting neurons of the ventrolateral preoptic area (VLPO), a putative sleep-active nucleus, using in vitro brain slices by the patch-clamp technique. We also examined the effects of morphine on sleep-wake profiles after administration of opioid receptor antagonist to the VLPO using EEG and electromyogram recordings in freely moving rats. The results showed that morphine inhibited the firing rate of sleep-promoting neurons and hyperpolarized their membrane potentials without affecting interneurons in the VLPO. Morphine-induced hyperpolarization of membrane potentials could be reversed by, D-Phe-Cys-Thr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), a mu receptor antagonist, in the presence of tetrodotoxin. However, after the mu receptors were blocked by CTOP, morphine still suppressed the firing of the sleep-promoting neurons. This effect was antagonized by nor-BIN, a kappa receptor antagonist. Activation of kappa receptor by U50488H inhibited the firing of the sleep-promoting neurons. These results indicate that morphine could inhibit the activity of sleep-promoting neurons in the VLPO through mu and kappa receptors. EEG recordings revealed that morphin