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1

Wake fields and energy spread for the ERHIC ERL  

SciTech Connect

Wake fields in high-current ERLs can cause significant beam quality degradations. Here we summarize effects of coherent synchrotron radiation, resistive wall, accelerating cavities and wall roughness for ERL parameters of the eRHIC project. A possibility of compensation of such correlated energy spread is also presented. An emphasis in the discussion is made on the suppression of coherent synchrotron radiation due to shielding and a possible reduction of wall roughness effects for realistic surfaces.

Fedotov, A.; Kayran, D.

2011-10-16

2

DIELECTRIC WAKE FIELD RESONATOR ACCELERATOR MODULE  

SciTech Connect

Results are presented from experiments, and numerical analysis of wake fields set up by electron bunches passing through a cylindrical or rectangular dielectric-lined structure. These bunches excite many TM-modes, with Ez components of the wake fields sharply localized on the axis of the structure periodically behind the bunches. The experiment with the cylindrical structure, carried out at ATF Brookhaven National Laboratory, used up to three 50 MeV bunches spaced by one wake field period (21 cm) to study the superposition of wake fields by measuring the energy loss of each bunch after it passed through the 53-cm long dielectric element. The millimeter-wave spectrum of radiation excited by the passage of bunches is also studied. Numerical analysis was aimed not only to simulate the behavior of our device, but in general to predict dielectric wake field accelerator performance. It is shown that one needs to match the radius of the cylindrical dielectric channel with the bunch longitudinal rms-length to achieve optimal performance.

Hirshfield, Jay L.

2013-11-06

3

Wake Fields in the Super B Factory Interaction Region  

SciTech Connect

The geometry of storage ring collider interaction regions present an impedance to beam fields resulting in the generation of additional electromagnetic fields (higher order modes or wake fields) which affect the beam energy and trajectory. These affects are computed for the Super B interaction region by evaluating longitudinal loss factors and averaged transverse kicks for short range wake fields. Results indicate at least a factor of 2 lower wake field power generation in comparison with the interaction region geometry of the PEP-II B-factory collider. Wake field reduction is a consderation in the Super B design. Transverse kicks are consistent with an attractive potential from the crotch nearest the beam trajectory. The longitudinal loss factor scales as the -2.5 power of the bunch length. A factor of 60 loss factor reduction is possible with crotch geometry based on an intersecting tubes model.

Weathersby, Stephen; /SLAC; Novokhatski, Alexander; /SLAC

2011-06-02

4

Fast polynomial approach to calculating wake fields  

SciTech Connect

In the computation of transverse wake field effects in accelerators, it is necessary to compute expressions of the form given in equations (1). It is usually desired to compute this a large number of times, the values of z{sub i} and x{sub i} being different at each iteration, other quantities remaining the same. The problem in practical applications is that the computational work grows as N{sub m}{sup 2}. Thus even using parallel computation to achieve speedup, the elapsed time to obtain a result still increases linearly with N{sub m}. The authors introduce here an approximate method of evaluating the sum in (1) whose computational work increases only as N{sub m}logN{sub m}. It involves some significant initial computation which does not have to be repeated at each subsequent iteration. The basis of the approach is to replace the individual contributions of a group of distant macroparticles with a local series expansion. In this respect it is similar in spirit to the so called fast multipole method.

Goldstein, C.I.; Peierls, R.F. [Brookhaven National Lab., Upton, NY (United States). Dept. of Applied Science

1997-06-15

5

Plasma wake field XUV radiation source  

DOEpatents

A XUV radiation source uses an interaction of electron beam pulses with a gas to create a plasma radiator. A flowing gas system (10) defines a circulation loop (12) with a device (14), such as a high pressure pump or the like, for circulating the gas. A nozzle or jet (16) produces a sonic atmospheric pressure flow and increases the density of the gas for interacting with an electron beam. An electron beam is formed by a conventional radio frequency (rf) accelerator (26) and electron pulses are conventionally formed by a beam buncher (28). The rf energy is thus converted to electron beam energy, the beam energy is used to create and then thermalize an atmospheric density flowing gas to a fully ionized plasma by interaction of beam pulses with the plasma wake field, and the energetic plasma then loses energy by line radiation at XUV wavelengths Collection and focusing optics (18) are used to collect XUV radiation emitted as line radiation when the high energy density plasma loses energy that was transferred from the electron beam pulses to the plasma.

Prono, Daniel S. (Los Alamos, NM); Jones, Michael E. (Los Alamos, NM)

1997-01-01

6

Wake fields and energy spread for the eRHIC ERL  

SciTech Connect

Wake fields in high-current ERLs can cause significant beam quality degradations. Here we summarize effects of coherent synchrotron radiation, resistive wall, accelerating cavities and wall roughness for ERL parameters of the eRHIC project. A possibility of compensation of such correlated energy spread is also presented. An emphasis in the discussion is made on the suppression of coherent synchrotron radiation due to shielding and a possible reduction of wall roughness effects for realistic surfaces. In this report we discuss the wake fields with a focus on their effect on the energy spread of the beam. Other effects of wake fields are addressed elsewhere. An energy spread builds up during a pass though a very long beam transport in the eRHIC ERL under design. Such energy spread become important when beam is decelerated to low energy, and needs to be corrected. Several effects, such as Coherent Synchrotron Radiation (CSR), Resistive Wall (RW), accelerating RF cavities (RF) and Wall Roughness (WR) were considered. In this paper, we briefly summarize major contributions to energy spread from the wake fields for eRHIC parameters, and present possible energy spread compensation for decelerated beam. In the rest of the report we discuss effects which we believe are suppressed for the eRHIC parameters.

Fedotov, A.; Kayran, D.

2011-10-16

7

Wake Vortex Field Measurement Program at Memphis, Tennessee: Data Guide  

NASA Technical Reports Server (NTRS)

Eliminating or reducing current restrictions in the air traffic control system due to wake vortex considerations would yield increased capacity, decreased delays, and cost savings. Current wake vortex separation standards are widely viewed as very conservative under most conditions. However, scientific uncertainty about wake vortex behavior under different atmospheric conditions remains a barrier to development of an adaptive vortex spacing system. The objective of the wake vortex field measurement efforts during December, 1994 and August, 1995 at Memphis, TN were to record wake vortex behavior for varying atmospheric conditions and types of aircraft. This effort is part of a larger effort by the NASA Langley Research Center to develop an Aircraft Vortex Spacing System (AVOSS) as an element of the Terminal Area Productivity (TAP) program. The TAP program is being performed in concert with the FAA Terminal Air Traffic Control Automation (TATCA) program and ATC Automation. Wake vortex behavior was observed using a mobile continuous-wave (CW) coherent laser Doppler radar (lidar) developed at Lincoln Laboratory. This lidar features a number of improvements over previous systems, including the first-ever demonstration of an automatic wake vortex detection and tracking algorithm.

Campbell, S. D.; Dasey, T. J.; Freehart, R. E.; Heinrichs, R. M.; Mathews, M. P.; Perras, G. H.; Rowe, G. S.

1997-01-01

8

Mariner 10 magnetic field observations of the Venus wake  

NASA Technical Reports Server (NTRS)

Magnetic field measurements made over a 21-hour interval during the Mariner 10 encounter with Venus were used to study the down-stream region of the solar wind-Venus interaction over a distance of approximately 100 R sub v. For most of the day before closest approach the spacecraft was located in a sheath-like region which was apparently bounded by planetary bow shock on the outer side and either a planetary wake boundary or transient boundary-like feature on the inner side. The spacecraft made multiple encounters with the wake-like boundary during the 21-hour interval with an increasing frequency as it approached the planet. Each pass into the wake boundary from the sheath region was consistently characterized by a slight decrease in magnetic field magnitude, a marked increase in the frequency and amplitude of field fluctuations, and a systematic clockwise rotation of the field direction when viewed from above the plane of the planet orbit.

Lepping, R. P.; Behannon, K. W.

1977-01-01

9

Wake field in dielectric acceleration structures L. Schachter,1  

E-print Network

particle accel- erators relies on dielectric slow-wave structures confining a laser field. Conceptually, but eventually any practical accelerator will consist of a series of extended slow-wave structures that needWake field in dielectric acceleration structures L. Scha¨chter,1 R. L. Byer,2 and R. H. Siemann3 1

Byer, Robert L.

10

Field-aligned currents in Io's plasma wake  

NASA Astrophysics Data System (ADS)

In Io's reference frame, the downstream distribution of various physical quantities in Io's plasma wake can be regarded as unchangeable with respect to time. A magnetic flux tube in a specific position in the wake can be related to a state of its evolution after been perturbed by Io. Thus the investigation of the wake can be transferred to the study of an Io-perturbed flux tube in the Jovian corotational frame. A magnetohydrodynamics approach called "The theory of a thin filament motion" is employed here. Our simulations suggest that 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 developed, before it is released downstream. A perturbed flux tube would undergo a subcorotational motion in Io's plasma wake. This motion is inevitably modulated by Alfvén wave bouncing back and forth inside the Io plasma torus. The scale of the subcorotation region is in the order of one Jovian radius. The distribution of the simulated field-aligned currents downstream is consistent with the observed wake aurora brightness profile; in particular, the periodic structure in the current distribution is in agreement with recent infrared and FUV observations showing the presence of secondary spots in the auroral emissions.

Chen, Chuxin

2008-09-01

11

ARTEMIS observations of extreme diamagnetic fields in the lunar wake  

NASA Astrophysics Data System (ADS)

We present two Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) observations of diamagnetic fields in the lunar wake at strengths exceeding twice the ambient magnetic field during high plasma beta conditions. The first observation was 350 km from the lunar surface while the Moon was located in the terrestrial magnetosheath with elevated particle temperatures. The second observation was in the solar wind ranging from 500 to 2000 km downstream, with a relatively low magnetic field strength of approximately 1.6 nT. In both cases, the plasma beta exceeded 10. We discuss the observations and compare the data to hybrid plasma simulations in order to validate the model under such extreme conditions and to elucidate the global structure of the lunar wake during these observations. The extreme nature of the diamagnetic field in the lunar wake provides an important end-member test case for theoretical and modeling studies of the various plasma processes operating in the lunar wake.

Poppe, A. R.; Fatemi, S.; Halekas, J. S.; Holmström, M.; Delory, G. T.

2014-06-01

12

Field measurements in the wake of a model wind turbine  

NASA Astrophysics Data System (ADS)

As a first step to study the dynamics of a wind farm' we experimentally explored the flow field behind a single wind turbine of diameter 1.17 m at a hub height of 6.25 m. A 10 m tower upstream of the wind farm characterizes the atmospheric conditions and its influence on the wake evolution. A vertical rake of sonic anemometers is clustered around the hub height on a second tower' 6D downstream of the turbine. We present preliminary observations from a 1- hour block of data recorded in near-neutral atmospheric conditions. The ratio of the standard deviation of power to the inflow velocity is greater than three' revealing adverse effects of inflow turbulence on the power and load fluctuations. Furthermore' the wake defect and Reynolds stress and its gradient are pronounced at 6D. The flux of energy due to Reynolds stresses is similar to that reported in wind tunnel studies. The swirl and mixing produces a constant temperature wake which results in a density jump across the wake interface. Further field measurements will explore the dynamics of a model wind farm' including the effects of atmospheric variability.

Pol, Suhas; Taylor, Amelia; Bilbao, Argenis; Doostalab, Ali; Novoa, Santiago; Westergaard, Carsten; Hussain, Fazle; Sheng, Jian; Ren, Beibei; Giesselmann, Michael; Glauser, Mark; Castillo, Luciano

2014-06-01

13

Wouthuysen-Field absorption trough in cosmic string wakes  

NASA Astrophysics Data System (ADS)

The baryon density enhancement in cosmic string wakes leads to a stronger coupling of the spin temperature to the gas kinetic temperate inside these string wakes than in the intergalactic medium (IGM). The Wouthuysen-Field (WF) effect has the potential to enhance this coupling to such an extent that it may result in the strongest and cleanest cosmic string signature in the currently planned radio telescope projects. Here we consider this enhancement under the assumption that x-ray heating is not significant. We show that the size of this effect in a cosmic string wake leads to a brightness temperature at least two times more negative than in the surrounding IGM. If the SCI-HI [T. C. Voytek et al., Astrophys. J. 782, L9 (2014), J. B. Peterson et al., arXiv:1409.2774] or EDGES [J. D. Bowman and A. E. E. Rogers Nature (London) 468, 796 (2010), J. D. Bowman et al., Astrophys. J. 676, 1 (2008)] experiments confirm a WF absorption trough in the cosmic gas, then cosmic string wakes should appear clearly in 21 cm redshift surveys of z =10 to 30.

Hernández, Oscar F.

2014-12-01

14

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

15

Beam-shape distortion caused by transverse wake fields  

SciTech Connect

As a particle bunch in a storage ring passes through a region with a transverse impedance, it generates a transverse wake electromagnetic field that is proportional to the transverse displacement of the bunch in the region. The field acts back on the bunch, causing various effects (such as instabilities) in the motion of the bunch. We study one such effect in which a transverse impedance causes the beam to be distorted in its shape. Observed at a fixed location in the storage ring, this distortion does not change from turn to turn; rather, the distortion is static in time. To describe the distortion, the bunch is considered to be divided longitudinally into many slices and the centers of change of the slices are connected into a curve. In the absence of transverse impedance, this curve is a straight line parallel to the direction of motion of the bunch. Perturbed by the transverse wake field, the curve becomes distorted. What we find in this paper is the shape of such a curve. The results obtained are applied to the PEP storage ring. The impedance is assumed to come solely from the rf cavities. We find that the beam shape is sufficiently distorted and hence that loss of luminosity due to this effect becomes a possibility.

Chao, A.W.; Kheifets, S.

1983-02-01

16

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

17

A prescribed wake rotor inflow and flow field prediction analysis, user's manual and technical approach  

NASA Technical Reports Server (NTRS)

A user's manual is provided which includes the technical approach for the Prescribed Wake Rotor Inflow and Flow Field Prediction Analysis. The analysis is used to provide the rotor wake induced velocities at the rotor blades for use in blade airloads and response analyses and to provide induced velocities at arbitrary field points such as at a tail surface. This analysis calculates the distribution of rotor wake induced velocities based on a prescribed wake model. Section operating conditions are prescribed from blade motion and controls determined by a separate blade response analysis. The analysis represents each blade by a segmented lifting line, and the rotor wake by discrete segmented trailing vortex filaments. Blade loading and circulation distributions are calculated based on blade element strip theory including the local induced velocity predicted by the numerical integration of the Biot-Savart Law applied to the vortex wake model.

Egolf, T. A.; Landgrebe, A. J.

1982-01-01

18

COAXIAL TWO-CHANNEL DIELECTRIC WAKE FIELD ACCELERATOR  

SciTech Connect

Theory, computations, and experimental apparatus are presented that describe and are intended to confirm novel properties of a coaxial two-channel dielectric wake field accelerator. In this configuration, an annular drive beam in the outer coaxial channel excites multimode wakefields which, in the inner channel, can accelerate a test beam to an energy much higher than the energy of the drive beam. This high transformer ratio is the result of judicious choice of the dielectric structure parameters, and of the phase separation between drive bunches and test bunches. A structure with cm-scale wakefields has been build for tests at the Argonne Wakefield Accelerator Laboratory, and a structure with mm-scale wakefields has been built for tests at the SLAC FACET facility. Both tests await scheduling by the respective facilities.

Hirshfield, Jay L. [Omega-P, Inc.

2013-04-30

19

Measurement of velocity and vorticity fields in the wake of an airfoil in periodic pitching motion  

NASA Technical Reports Server (NTRS)

The velocity field created by the wake of an airfoil undergoing a prescribed pitching motion was sampled using hot wire anemometry. Data analysis methods concerning resolution of velocity components from cross wire data, computation of vorticity from velocity time history data, and calculation of vortex circulation from vorticity field data are discussed. These data analysis methods are applied to a flow field relevant to a two dimensional blade-vortex interaction study. Velocity time history data were differentiated to yield vorticity field data which are used to characterize the wake of the pitching airfoil. Measurement of vortex strength in sinusoidal and nonsinusoidal wakes show vortices in the sinusoidal wake have stronger circulation and more concentrated vorticity distributions than the tailored nonsinusoidal wake.

Booth, Earl R., Jr.

1987-01-01

20

Nonthermal Lorentzian wake-field effects on collision processes in complex dusty plasmas  

NASA Astrophysics Data System (ADS)

The influence of nonthermal Lorentzian wake-field on the electron-dust grain collision is investigated in complex dusty plasmas. The Eikonal method and the effective interaction potential are applied to obtain the Eikonal scattering phase shift, the differential Eikonal collision cross section, and the total Eikonal collision cross section as functions of the collision energy, the impact parameter, the Mach number, and the spectral index of Lorentzian plasma. It is found that the nonthermal effect enhances the Eikonal scattering phase shift and, however, suppresses the Eikonal collision cross section for the electron-dust grain in Lorentzian complex dusty plasmas. It is also found that the Eikonal scattering phase shift decreases with increasing Mach number and spectral index. In addition, the Eikonal collision cross section increases with an increase of the spectral index and Mach number in Lorentzian complex dusty plasmas.

Hong, Woo-Pyo; Jung, Young-Dae

2014-10-01

21

Nonthermal Lorentzian wake-field effects on collision processes in complex dusty plasmas  

SciTech Connect

The influence of nonthermal Lorentzian wake-field on the electron-dust grain collision is investigated in complex dusty plasmas. The Eikonal method and the effective interaction potential are applied to obtain the Eikonal scattering phase shift, the differential Eikonal collision cross section, and the total Eikonal collision cross section as functions of the collision energy, the impact parameter, the Mach number, and the spectral index of Lorentzian plasma. It is found that the nonthermal effect enhances the Eikonal scattering phase shift and, however, suppresses the Eikonal collision cross section for the electron-dust grain in Lorentzian complex dusty plasmas. It is also found that the Eikonal scattering phase shift decreases with increasing Mach number and spectral index. In addition, the Eikonal collision cross section increases with an increase of the spectral index and Mach number in Lorentzian complex dusty plasmas.

Hong, Woo-Pyo [Department of Electronics Engineering, Catholic University of Daegu, Hayang 712-702 (Korea, Republic of); Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590 (United States); Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)

2014-10-15

22

Effect of self-injection on ultraintense laser wake-field acceleration.  

PubMed

The self-injection of plasma electrons which have been accelerated to relativistic energies by a laser pulse moving with a group velocity less than the speed of light with I lambda(2)>5 x 10(19) W microm(2)/cm(2) is found via particle-in-cell simulation to be efficient for laser wake-field acceleration. When the matching condition a(0)> or =(2(1/4)omega/omega(pl))(2/3) is met, the self-injection, along with wave breaking, dominates monoenergetic electron acceleration yielding up to 100 MeV energies by a 100 TW, 20 fs laser pulse. In contrast to the injection due to wave-breaking processes, self-injection allows suppression of production of a Maxwell distribution of accelerated particles and the extraction of a beam-quality bunch of energetic electrons. PMID:15089350

Zhidkov, A; Koga, J; Kinoshita, K; Uesaka, M

2004-03-01

23

Clutter suppression and classification using twin inverted pulse sonar in ship wakes.  

PubMed

Twin inverted pulse sonar (TWIPS) is here deployed in the wake of a moored rigid inflatable boat (RIB) with propeller turning, and then in the wake of a moving tanker of 4580 dry weight tonnage (the Whitchallenger). This is done first to test its ability to distinguish between scatter from the wake and scatter from the seabed, and second to test its ability to improve detectability of the seabed through the wake, compared to conventional sonar processing techniques. TWIPS does this by distinguishing between linear and nonlinear scatterers and has the further property of distinguishing those nonlinear targets which scatter energy at the even-powered harmonics from those which scatter in the odd-powered harmonics. TWIPS can also, in some manifestations, require no range correction (and therefore does not require the a priori environment knowledge necessary for most remote detection technologies). PMID:22088017

Leighton, T G; Finfer, D C; Chua, G H; White, P R; Dix, J K

2011-11-01

24

Flow field in the wake of a bluff body driven through a steady recirculating flow  

NASA Astrophysics Data System (ADS)

The wake produced by a bluff body driven through a steady recirculating flow is studied experimentally in a water facility using particle image velocimetry. The bluff body has a rectangular cross section of height, , and width, , such that the aspect ratio, AR = H/ D, is equal to 3. The motion of the bluff body is uniform and rectilinear, and corresponds to a Reynolds number based on width, Re D = 9,600. The recirculating flow is confined within a hemicylindrical enclosure and is generated by planar jets emanating from slots of width, , such that . Under these conditions, experiments are performed in a closed-loop facility that enables complete optical access to the near-wake. Velocity fields are obtained up to a distance of downstream of the moving body. Data include a selection of phase-averaged velocity fields representative of the wake for a baseline case (no recirculation) and an interaction case (with recirculation). Results indicate that the transient downwash flow typically observed in wakes behind finite bodies of small aspect ratio is significantly perturbed by the recirculating flow. The wake is displaced from the ground plane and exhibits a shorter recirculation zone downstream of the body. In summary, it was found that the interaction between a bluff body wake and a recirculating flow pattern alters profoundly the dynamics of the wake, which has implications on scalar transport in the wake.

Poussou, Stephane B.; Plesniak, Michael W.

2015-02-01

25

Electrons on closed field lines of lunar crustal fields in the solar wind wake  

NASA Astrophysics Data System (ADS)

Plasma signature around crustal magnetic fields is one of the most important topics of the lunar plasma sciences. Although recent spacecraft measurements are revealing solar-wind interaction with the lunar crustal fields on the dayside, plasma signatures around crustal fields on the night side have not been fully studied yet. Here we show evidence of plasma trapping on the closed field lines of the lunar crustal fields in the solar-wind wake, using SELENE (Kaguya) plasma and magnetic field data obtained at 14-15 km altitude from the lunar surface. In contrast to expectation on plasma cavity formation at the strong crustal fields, electron flux is enhanced above Crisium Antipode (CA) anomaly which is one of the strongest lunar crustal fields. The enhanced electron fluxes above CA are characterised by (1) occasional bi-directional field-aligned beams in the lower energy range (<150 eV) and (2) a medium energy component (150-300 eV) that has a double loss-cone distribution representing bounce motion between the two footprints of the crustal magnetic fields. The low-energy electrons on the closed field lines may come from the lunar night side surface, while supply mechanism of medium-energy electrons on the closed field line remains to be solved. We also report that a density cavity in the wake is observed not above the strongest magnetic field but in its vicinity.

Nishino, Masaki N.; Saito, Yoshifumi; Tsunakawa, Hideo; Takahashi, Futoshi; Fujimoto, Masaki; Harada, Yuki; Yokota, Shoichiro; Matsushima, Masaki; Shibuya, Hidetoshi; Shimizu, Hisayoshi

2015-04-01

26

Numerical Simulation of Wake Vortices Measured During the Idaho Falls and Memphis Field Programs  

NASA Technical Reports Server (NTRS)

A numerical large-eddy simulation model is under modification and testing for application to aircraft wake vortices. The model, having a meteorological framework, permits the interaction of wake vortices with environments characterized by crosswind shear, stratification, and humidity. As part of the validation process, model results are compared with measured field data from the 1990 Idaho Falls and the 1994-1995 Memphis field experiments. Cases are selected that represent different aircraft and a cross section of meteorological environments. Also included is one case with wake vortex generation in ground effect. The model simulations are initialized with the appropriate meteorological conditions and a post roll-up vortex system. No ambient turbulence is assumed in our initial set of experiments, although turbulence can be self generated by the interaction of the model wakes with the ground and environment.

Proctor, Fred H.

1996-01-01

27

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

NASA Technical Reports Server (NTRS)

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 downstream propeller. The wake properties, including effects of propeller operation on the empennage wake, were investigated for two empennage geometries: one, a vertical tail fin, the other, a Y-tail with a 34 deg dihedral. Results showed that the effect of the propeller on the empennage wake upstream of the propeller was not strong. The flow upstream of the propeller was accelerated in the streamwise direction by the propeller, but the empennage wake width and velocity defect were relatively unaffected by the presence of the propeller. The peak turbulence in the wake near the propeller tip station, 0.66 diameter behind the vertical tail fin, was approximately 3 percent of the free-stream velocity. The velocity field data can be used in predictions of the acoustic field due to propeller-wake interaction.

Horne, W. Clifton; Soderman, Paul T.

1988-01-01

28

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

29

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

PubMed

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. PMID:11800799

Ohmi, K; Zimmermann, F; Perevedentsev, E

2002-01-01

30

Magnetic Fields in the Lunar Wake and Its Responses to the External Solar Wind Conditions  

NASA Astrophysics Data System (ADS)

The Moon has no thick atmosphere and no global magnetic field. When the solar wind plasma impacts with the Moon, particles can be mostly absorbed by the lunar surface, so it leaves a plasma void downstream, i.e., the lunar wake. Considering the pressure balance, people could expect that the magnetic field may have an enhancement in the central lunar wake. Such an enhancement has been detected earlier [Ogilvie et al., 1996; Owen et al., 1996; Halekas et al., 2005]. Besides the observational analysis, lots of theoretical studies and numerical modeling have also been used to investigate this process, e.g., in MHD [Xie et al., 2012], 3D hybrid model [Wiehle et al., 2011; Wang et al., 2011; Holmström et al., 2012] as well as PIC model [Birch and Chapman, 2011]. In the present study, we find that the enhancement of magnetic field in the central part is larger in the deep lunar wake than that in the far downtail region with the observations from the two ARTEMIS probes. However, in the wake boundary, there are usually two depletion dips on the two sides. As the distances from the lunar center increase, the slope of the enhancement of magnetic field strength becomes smoother. It means that the enhancement of magnitude in the deep lunar wake is sharpest from the boundary to the center. Another signature observed is that the magnitude of magnetic field decreases in the wake center as the distance from the body increases. So the distributions of magnetic field strength across the cross section as a function of distances from the lunar center are different. We have also tried to find the responses of the magnetic field distributions in the lunar wake to the angle of the IMF with respect to the direction of the solar wind flow. In the near wake, the dependence of field distributions on the angle is not obvious in the observational data. However, in the far downstream region from the lunar body, as the angle decreases, the amplitude of the magnetic field fluctuations becomes higher. And the effects of IMF directions to magnetic field disturbance across different lunar distances are very distinct. All these indicate that the magnetic field distributions are depending on the orientation of IMF in the far downtail region. The detailed mechanism implied in this refilling process of plasma cavity along the tailward distance needs further research in the future.

Wong, H.; Ma, Y.; Ip, W.; Xu, X.

2013-12-01

31

Blunt body near wake flow field at Mach 6  

NASA Technical Reports Server (NTRS)

Tests were conducted in a Mach 6 flow to examine the reattachment process of an axisymmetric free shear layer associated with the near wake of a 70 deg. half angle, spherically blunted cone with a cylindrical after body. Model angle of incidence was fixed at 0 deg. and free-stream Reynolds numbers based on body diameter ranged from 0.5 x 10(exp 6) to 4 x 10(exp 6). The sensitivity of wake shear layer transition on reattachment heating was investigated. The present perfect gas study was designed to compliment results obtained previously in facilities capable of producing real gas effects. The instrumented blunted cone model was designed primarily for testing in high enthalpy hypervelocity shock tunnels in both this country and abroad but was amenable for testing in conventional hypersonic blowdown wind tunnels as well. Surface heating rates were inferred from temperature - time histories from coaxial surface thermocouples on the model forebody and thin film resistance gages along the model base and cylindrical after body. General flow feature (bow shock, wake shear layer, and recompression shock) locations were visually identified by schlieren photography. Mean shear layer position and growth were determined from intrusive pitot pressure surveys. In addition, wake surveys with a constant temperature hot-wire anemometer were utilized to qualitatively characterize the state of the shear layer prior to reattachment. Experimental results were compared to laminar perfect gas predictions provided by a 3-D Navier Stokes code (NSHYP). Shear layer impingement on the instrumented cylindrical after body resulted in a localized heating maximum that was 21 to 29 percent of the forebody stagnation point heating. Peak heating resulting from the reattaching shear layer was found to be a factor of 2 higher than laminar predictions, which suggested a transitional shear layer. Schlieren flow visualization and fluctuating voltage time histories and spectra from the hot wire surveys across the shear layer substantiate this observation. The sensitivity of surface heating to forebody roughness was characterized for a reattaching shear layer. For example, at R(sub infinity), d = 4 x 10(exp 6), when the shear layer was transitional, the magnitude of peak heating from shear layer impingement was reduced by approximately 24 percent when transition grit was applied to the forebody. The spatial location of the local peak, however, remained unchanged.

Horvath, Thomas J.; McGinley, Catherine B.; Hannemann, Klaus

1996-01-01

32

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

Microsoft Academic Search

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

R. L. Radkey; T. G. Zambrano

1982-01-01

33

Autoinjection of electrons into a wake field using a capillary with attached cone  

SciTech Connect

By using a cone attached to a capillary, electrons generated through a laser interaction were autoinjected and accelerated in a low-density wake field. The cone attached to the entrance of the capillary serves as an electron supplier. It increases the number of electrons from below the detection limit to 1.1 pC and the energy from 4 to 30 MeV. A two-dimensional particle-in-cell simulation reveals that a significant number of energetic electrons are extracted from the surface of the cone and are subsequently trapped in the wake field and accelerated in the capillary.

Mori, Y.; Kitagawa, Y. [Graduate School for the Creation of New Photonics, 1955-1 Kurematsu-cho, Hamamatsu, Shizuoka 431-1202 (Japan); Sentoku, Y. [Department of Physics, University of Nevada, 5625 Fox Avenue, Reno, Nevada 89506 (United States); Kondo, K.; Tsuji, K.; Nakanii, N.; Fukumochi, S.; Kashihara, M.; Kimura, K.; Tanaka, K. A.; Norimatsu, T.; Tanimoto, Tsuyoshi; Nakamura, H.; Kodama, R. [Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan); Graduate School of Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan); Takeda, K.; Tampo, M.; Mima, K. [Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan); Miura, E. [National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)

2009-12-15

34

Simulation of ultrashort electron pulse generation from optical injection into wake-field plasma waves  

E-print Network

dealt only with one-dimensional models. In this paper two-dimensional particle-in-cell simulations of magnitude higher than those in conventional rf linacs, be- cause they are not limited by dielectric breakdown. Nor- mally, electrons oscillating in the plasma wave cannot be accelerated by the wake field

Umstadter, Donald

35

Suppressive Surrounds of Receptive Fields In Monkey Frontal Eye Field  

PubMed Central

A critical step in determining how a neuron contributes to visual processing is determining its visual receptive field (RF). While recording from neurons in frontal eye field (FEF) of awake monkeys (Macaca mulatta), we probed the visual field with small spots of light and found excitatory RFs that decreased in strength from RF center to periphery. However, presenting stimuli with different diameters centered on the RF revealed suppressive surrounds that overlapped the previously determined excitatory RF, and reduced responses 84% on average. Consequently, in that overlap area, stimulation produced excitation or suppression, depending on the stimulus. Strong stimulation of the RF periphery with annular stimuli allowed us to quantify this effect. A modified Difference of Gaussians (DoG) model that independently varied center and surround activation accounted for the nonlinear activity in the overlap area. Our results suggest that: 1) the suppressive surrounds found in FEF are fundamentally the same as those in V1 except for the size and strength of excitatory and suppressive mechanisms, 2) methodically assaying suppressive surrounds in FEF is essential for correctly interpreting responses to large and/or peripheral stimuli and therefore understanding the effects of stimulus context, 3) regulating the relative strength of the surround clearly changes neuronal responses, and may therefore play a significant part in the neuronal changes resulting from visual attention and stimulus salience. PMID:22933810

Cavanaugh, James; Joiner, Wilsaan M.; Wurtz, Robert H.

2012-01-01

36

Characterizing rotor stator interaction (RSI) using CFD and experimentally obtained wake flow fields  

NASA Astrophysics Data System (ADS)

RSI is a major reason for noise and vibration, and reduced performance of turbomachinery. The stationary cascade upstream of the impeller stage is a source of variations in velocity due to angular momentum transfer, creating a cascade blade-to-blade variation. In addition a number of secondary flow fields due to boundary layer dynamics, such as wake flows, emerge from the cascade. At UMN a number of TR PIV fields have been captured downstream of a hydrofoil in liquid water, c=81mm and Re,c= (5 to 8)e5, for different AoAs and for selected passive flow control techniques. The wake trailing the foil is characterized by swirling structures, albeit far from regular shedding. One line of analysis of the captured wake flow fields has been to characterize the structures by a statistical averaged energy analysis over the structures. A second approach has been to use the experimentally obtained data as input in CFD analysis of the impingement of the wake on a rotating vane. Both the procedure and results are described.

Kjeldsen, Morten; Finstad, Pal H. E.; Arndt, Roger E. A.

2010-11-01

37

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

38

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

39

Volumetric visualization of the near- and far-field wake in flapping wings.  

PubMed

The flapping wings of flying animals create complex vortex wake structure; understanding its spatial and temporal distribution is fundamental to animal flight theory. In this study, we applied the volumetric 3-component velocimetry to capture both the near- and far-field flow generated by a pair of mechanical flapping wings. For the first time, the complete three-dimensional wake structure and its evolution throughout a wing stroke were quantified and presented experimentally. The general vortex wake structure maintains a quite consistent form: vortex rings in the near field and two shear layers in the far field. Vortex rings shed periodically from the wings and are linked to each other in successive strokes. In the far field, the shed vortex rings evolve into two parallel shear layers with dominant vorticity convected from tip and root vortices. The shear layers are nearly stationary in space compared to the periodic vortex rings shed in the near field. In addition, downwash passes through the centers of the vortex rings and extends downward between the two shear layers. PMID:23924871

Liu, Yun; Cheng, Bo; Barbera, Giovanni; Troolin, Daniel R; Deng, Xinyan

2013-09-01

40

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; Nemoto, K.; /CRIEPI, Tokyo

2006-06-27

41

Terahertz radiation from oscillating electrons in laser-induced wake fields  

SciTech Connect

Strong terahertz (1 THz=10{sup 12} Hz) radiation can be generated by the electron oscillation in fs-laser-induced wake fields. The interaction of a fs-laser pulse with a low-density plasma layer is studied in detail using numerical simulations. The spatial distribution and temporal evolution of terahertz electron current developed in a low-density plasma layer are presented, which enables us to calculate the intensity distribution of THz radiation. It is shown that laser and plasma parameters, such as laser intensity, pulse width, and background plasma density, are of key importance to the process. The optimum condition for wake-field excitation and terahertz emission is discussed upon the simulation results. Radiation peaked at 6.4 THz, with 900 fs duration and 9% bandwidth, can be generated in a plasma of density 5x10{sup 17} cm{sup -3}. It turns out that the maximum radiation intensity scales as n{sub 0}{sup 3}a{sub 0}{sup 4} when wake field is resonantly excited, where n{sub 0} and a{sub 0} are, respectively, the plasma density and the normalized field amplitude of the laser pulse.

Cao Lihua; Zheng Chunyang; Liu Zhanjun; Li Bin [Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Yu Wei; Xu Han [Shanghai Institute of Optics and Fine Mechanics, Shanghai 201800 (China); Bogaerts, A. [Department of Chemistry, University of Antwerp, B-2610 Wilrijk-Antwerp (Belgium)

2004-10-01

42

Generation of vortex rings by nonstationary laser wake field  

SciTech Connect

A new concept of generating quasistatic magnetic fields, vortex rings, and electron jets in an isotropic homogeneous plasma is presented. The propagation of plasma waves, generated by a relativistically intense short pulse laser, is investigated by using the kinetic model and a novel nonpotential, time-dependent ponderomotive force is derived by obtaining a hydrodynamic equation of motion. This force can in turn generate quasistatic magnetic fields, vortex rings, and electron jets. It is also shown that the vortex rings can become a means for accelerating electrons, which are initially in equilibrium. The conservation of canonical momentum circulation and the frozen-in condition for the vorticity is discussed. The excitation of the vortex waves by the modulation of the amplitude of the plasma waves is considered. These vortex waves, which generate a lower hybrid mode propagating across the generated magnetic field, are also investigated.

Tsintsadze, N.L.; Murtaza, G.; Shah, H.A. [Department of Physics, Tbilisi State University, Chavchavadze 3 (Georgia); National Centre for Mathematics, G.C. University, Lahore 54000 (Pakistan); Department of Physics, G.C. University, Lahore 54000 (Pakistan)

2006-01-15

43

Numerical Simulation of Wake Vortices Measured During the Idaho Falls and Memphis Field Programs  

Microsoft Academic Search

A numerical large-eddy simulation model isunder modification and testing for application to aircraftwake vortices. The model, having a meteorologicalframework, permits the interaction of wake vortices withenvironments characterized by crosswind shear, stratification,and humidity. As part of the validation process,model results are compared with measured field datafrom the 1990 Idaho Falls and the 1994-1995 Memphisfield experiments. Cases are selected that representdifferent aircraft...

Fred H. Proctor

1996-01-01

44

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

45

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

46

The Junction Point Model: A Field Model of Waking, Sleeping, and Dreaming, Relating Dream Witnessing, the Waking\\/Sleeping Transition, and Transcendental Meditation in Terms of a Common Psychophysiologic State  

Microsoft Academic Search

A field model of waking, sleeping, and dreaming, called the junction point model, portrays waking, NREM-sleep, and REM-dreaming as expressions of a single, undifferentiated state. EEG data are presented that support this model: (1) in the transitions between waking, NREM-sleep, and REM-dreaming, bursts of similar frequency EEG—7 to 9 Hz—are seen that do not seem generated by known sleep mechanisms,

Frederick Travis

1994-01-01

47

Small-scale electron density and magnetic-field structures in the wake of an ultraintense laser pulse.  

PubMed

We investigate the interaction of a high intensity ultrashort laser pulse with an underdense collisionless plasma in the regime where the Langmuir wake wave excited behind the laser pulse is loaded by fast particle beams, formed during the wake wave breaking. The beam loading causes the deterioration of the central part of the wake wave near the pulse axis, and the formation of bunches of sharply focalized ultrarelativistic electrons. The bunches of electrons generate a fast propagating magnetic field, which we interpret in terms of the magnetic component of the Lienard-Wiechert potential of a moving electric charge. PMID:11970504

Liseikina, T V; Califano, F; Vshivkov, V A; Pegoraro, F; Bulanov, S V

1999-11-01

48

Effects of Magnetic Field on the Turbulent Wake of a Cylinder in MHD Channel Flow  

SciTech Connect

Results from a free-surface MHD flow experiment are presented detailing the modi cation of vortices in the wake of a circular cylinder with its axis parallel to the applied magnetic fi eld. Experiments were performed with a Reynolds number near Re ~ 104 as the interaction parameter, N = |j x#2; B| / |? (? ? ?), was increased through unity. By concurrently sampling the downstream fluid velocity at sixteen cross-stream locations in the wake, it was possible to extract an ensemble of azimuthal velocity profi les as a function of radius for vortices shed by the cylinder at varying strengths of magnetic field. Results indicate a signi cant change in vortex radius and rotation as N is increased. The lack of deviations from the vortex velocity pro file at high magnetic fi elds suggests the absence of small-scale turbulent features. By sampling the wake at three locations downstream in subsequent experiments, the decay of the vortices was examined and the effective viscosity was found to decrease as N-049±0.4. This reduction in effective viscosity is due to the modi cation of the small-scale eddies by the magnetic fi eld. The slope of the energy spectrum was observed to change from a k-1.8 power-law at low N to a k-3.5 power-law for N > 1. Together, these results suggest the flow smoothly transitioned to a quasi-two-dimensional state in the range 0 < N < 1.

John Rhoads, Eric Edlund and Hantao Ji

2013-04-17

49

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

50

Wakeatron: acceleration of electrons on the wake field of a proton bunch  

SciTech Connect

We explore in this note the idea of accelerating a low intensity electron or positron bunch, travelling through a linear rf structure, following at a short distance an intense proton bunch which leaves behind a wake field. This device acts like a transformer where two beams are involved: one made of protons at high current and low energy, the other made of either electrons or positrons, at low current and high energy. The two beams are coupled electromagnetically to each other by a specially designed rf structure made of a long sequence of cavities.

Ruggiero, A.G.

1985-01-01

51

Strong-field-ionization suppression by light-field control  

NASA Astrophysics Data System (ADS)

In recent attempts to control strong-field phenomena such as molecular dissociation, undesired ionization sometimes seriously limited the outcome. In this work we examine the capability of quantum optimal control theory to suppress the ionization by rational pulse shaping. Using a simple model system and the ground-state occupation as the target functional, we show that optimal control generally leads to a significant suppression of the ionization, although the fluence and the pulse length are kept fixed. In the low-frequency regime the ionization is reduced mainly by avoiding high peaks in the intensity and thus preventing tunneling. In contrast, at high frequencies in the extreme ultraviolet regime the optimized pulses strongly couple with the (de)-excitations of the system, which leads to different pulse characteristics. Finally, we show that the applied target functional works, to some extent, for the enhancement of the high-order-harmonic generation, although further developments in optimal control theory to find proper target functionals are required.

Räsänen, Esa; Madsen, Lars Bojer

2012-09-01

52

The velocity and vorticity fields of the turbulent near wake of a circular cylinder  

NASA Technical Reports Server (NTRS)

The purpose of this research is to provide a detailed experimental database of velocity and vorticity statistics in the very near wake (x/d less than 10) of a circular cylinder at Reynolds number of 3900. This study has determined that estimations of the streamwise velocity component in flow fields with large nonzero cross-stream components are not accurate. Similarly, X-wire measurements of the u and v velocity components in flows containing large w are also subject to the errors due to binormal cooling. Using the look-up table (LUT) technique, and by calibrating the X-wire probe used here to include the range of expected angles of attack (+/- 40 deg), accurate X-wire measurements of instantaneous u and v velocity components in the very near wake region of a circular cylinder has been accomplished. The approximate two-dimensionality of the present flow field was verified with four-wire probe measurements, and to some extent the spanwise correlation measurements with the multisensor rake. Hence, binormal cooling errors in the present X-wire measurements are small.

Wallace, James; Ong, Lawrence; Moin, Parviz

1995-01-01

53

Observation of high-resolution wind fields and offshore wind turbine wakes using TerraSAR-X imagery  

NASA Astrophysics Data System (ADS)

1. Introduction Numerous large-scale offshore wind farms have been built in European waters and play an important role in providing renewable energy. Therefore, knowledge of behavior of wakes, induced by large wind turbines and their impact on wind power output is important. The spatial variation of offshore wind turbine wake is very complex, depending on wind speed, wind direction, ambient atmospheric turbulence and atmospheric stability. In this study we demonstrate the application of X-band TerraSAR-X (TS-X) data with high spatial resolution for studies on wind turbine wakes in the near and far field of the offshore wind farm Alpha Ventus, located in the North Sea. Two cases which different weather conditions and different wake pattern as observed in the TS-X image are presented. 2. Methods The space-borne synthetic aperture radar (SAR) is a unique sensor that provides two-dimensional information on the ocean surface. Due to their high resolution, daylight and weather independency and global coverage, SARs are particularly suitable for many ocean and coastal applications. SAR images reveal wind variations on small scales and thus represent a valuable means in detailed wind-field analysis. The general principle of imaging turbine wakes is that the reduced wind speed downstream of offshore wind farms modulates the sea surface roughness, which in turn changes the Normalized Radar Cross Section (NRCS, denoted by ?0) in the SAR image and makes the wake visible. In this study we present two cases at the offshore wind farm Alpha Ventus to investigate turbine-induced wakes and the retrieved sea surface wind field. Using the wind streaks, visible in the TS-X image and the shadow behind the offshore wind farm, induced by turbine wake, the sea surface wind direction is derived and subsequently the sea surface wind speed is calculated using the latest generation of wind field algorithm XMOD2. 3. Case study alpha ventus Alpha Ventus is located approximately 45 km from the coast of Borkum, Germany, and consists of twelve 5-Megawatt wind power turbines. The retrieved results are validated by comparing with QuikSCAT measurements, the results of the German Weather Service (DWD) atmospheric model and in-situ measurements of wind speed and wind direction, obtained from the research platform FiNO1, installed 400 m west of Alpha Ventus. 4. Conclusion In the presented case study we quantify the wake characteristics of wake length, wake width, maximum velocity de?cit, wake merging and wake meandering. We show that SAR has the capability to map the sea surface two-dimensionally in high spatial resolution which provides a unique opportunity to observe spatial characteristics of offshore wind turbine wakes. The SAR derived information can support offshore wind farming with respect to optimal siting and design and help to estimate their effects on the environment.

Gies, Tobias; Jacobsen, Sven; Lehner, Susanne; Pleskachevsky, Andrey

2014-05-01

54

Powerful terahertz emission from laser wake fields excited in inhomogeneous plasmas  

SciTech Connect

Powerful coherent emission of broadband few-terahertz radiation can be produced from a laser wake field by linear mode conversion. This occurs when the laser pulse is incident obliquely to the density gradient of inhomogeneous plasmas. The emission spectrum and conversion efficiency predicted by mode conversion theory are in agreement with particle-in-cell simulations. The energy conversion efficiency from laser pulses to this low-frequency emission scales proportional to their frequency ratio by ({omega}/{omega}{sub 0}){sup 3} and increases with the laser intensity and the plasma density scale length. By adjusting the laser pulse duration and plasma density profiles, one can control the emission frequency, bandwidth, and duration. In two- and three-dimensional geometry, conical wake emission is found in the backward direction when the laser pulse propagates along the density gradient. This can be explained well by the linear mode conversion. To avoid conical emission, a laser pulse incident obliquely to the density gradient can be deployed so that collimated emission becomes dominant in the 'specular reflection' direction, suitable for practical applications.

Sheng Zhengming; Mima, Kunioki; Zhang Jie [Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871 (Japan); Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China)

2005-12-15

55

Compensation of wake-field-driven energy spread in Energy Recovery Linacs  

E-print Network

Energy Recovery Linacs provide high-energy beams, but decelerate those beams before dumping them, so that their energy is available for the acceleration of new particles. During this deceleration, any relative energy spread that is created at high energy is amplified by the ratio between high energy and dump energy. Therefore, Energy Recovery Linacs are sensitive to energy spread acquired at high energy, e.g. from wake fields. One can compensate the time-correlated energy spread due to wakes via energy-dependent time-of-flight terms in appropriate sections of an Energy Recovery Linac, and via high-frequency cavities. We show that nonlinear time-of-flight terms can only eliminate odd orders in the correlation between time and energy, if these terms are created by a beam transport within the linac that is common for accelerating and decelerating beams. If these two beams are separated, so that different beam transport sections can be used to produce time-of-flight terms suitable for each, also even-order terms ...

Hoffstaetter, Georg H

2008-01-01

56

High-quality electron beam from laser wake-field acceleration in laser produced plasma plumes  

NASA Astrophysics Data System (ADS)

Generation of highly collimated (?div ˜10 mrad), quasi-monoenergetic electron beam with peak energy 12 MeV and charge ˜50 pC has been experimentally demonstrated from self-guided laser wake-field acceleration (LWFA) in a plasma plume produced by laser ablation of solid nylon (C12H22N2O2)n target. A 7 TW, 45 fs Ti:sapphire laser system was used for LWFA, and the plasma plume forming pulse was derived from the Nd:YAG pump laser of the same system. The results show that a reproducible, high quality electron beam could be produced from this scheme which is simple, low cost and has the capability for high repetition rate operation.

Sanyasi Rao, Bobbili; Moorti, Anand; Rathore, Ranjana; Ali Chakera, Juzer; Anant Naik, Prasad; Dass Gupta, Parshotam

2013-06-01

57

High-quality electron beam from laser wake-field acceleration in laser produced plasma plumes  

SciTech Connect

Generation of highly collimated ({theta}{sub div}{approx}10 mrad), quasi-monoenergetic electron beam with peak energy 12 MeV and charge {approx}50 pC has been experimentally demonstrated from self-guided laser wake-field acceleration (LWFA) in a plasma plume produced by laser ablation of solid nylon (C{sub 12}H{sub 22}N{sub 2}O{sub 2}){sub n} target. A 7 TW, 45 fs Ti:sapphire laser system was used for LWFA, and the plasma plume forming pulse was derived from the Nd:YAG pump laser of the same system. The results show that a reproducible, high quality electron beam could be produced from this scheme which is simple, low cost and has the capability for high repetition rate operation.

Sanyasi Rao, Bobbili; Moorti, Anand; Rathore, Ranjana; Ali Chakera, Juzer; Anant Naik, Prasad; Dass Gupta, Parshotam [Laser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)] [Laser Plasma Division, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India)

2013-06-10

58

Comparison of the Dynamic Wake Meandering Model, Large-Eddy Simulation, and Field Data at the Egmond aan Zee Offshore Wind Plant: Preprint  

SciTech Connect

The focus of this work is the comparison of the dynamic wake meandering model and large-eddy simulation with field data from the Egmond aan Zee offshore wind plant composed of 36 3-MW turbines. The field data includes meteorological mast measurements, SCADA information from all turbines, and strain-gauge data from two turbines. The dynamic wake meandering model and large-eddy simulation are means of computing unsteady wind plant aerodynamics, including the important unsteady meandering of wakes as they convect downstream and interact with other turbines and wakes. Both of these models are coupled to a turbine model such that power and mechanical loads of each turbine in the wind plant are computed. We are interested in how accurately different types of waking (e.g., direct versus partial waking), can be modeled, and how background turbulence level affects these loads. We show that both the dynamic wake meandering model and large-eddy simulation appear to underpredict power and overpredict fatigue loads because of wake effects, but it is unclear that they are really in error. This discrepancy may be caused by wind-direction uncertainty in the field data, which tends to make wake effects appear less pronounced.

Churchfield, M. J.; Moriarty, P. J.; Hao, Y.; Lackner, M. A.; Barthelmie, R.; Lundquist, J.; Oxley, G. S.

2014-12-01

59

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

60

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

61

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 RJ 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 ~1 miliWatt per meter squared. 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.

2008-12-01

62

Simulations of field-aligned currents: Application of theory of thin filament motion to Io's plasma wake  

NASA Astrophysics Data System (ADS)

Io's plasma wake was treated as a tail of magnetic flux tubes perturbed by Io successively. The evolution of an Io-perturbed flux tube was studied numerically via magnetohydrodynamics (MHD) approach of a thin filament. 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 s, until a tilt angle of about 4° has been developed, before it is released downstream. A magnetic field depression forms downstream as a result of the continual departure of the flux tubes from Io, which in turn has significant influence on the motion of a flux tube. A perturbed flux tube would undergo a subcorotational motion in Io's plasma wake. This motion is inevitably modulated by Alfvén wave bouncing back and forth between the equatorial plane and the boundary of Io plasma torus. The scale of the subcorotation region is in the order of 1 Jovian radius (RJ). The distribution of the simulated field-aligned currents downstream is consistent with the observed wake aurora brightness profile; in particular, the periodic structure in the current distribution is in agreement with recent infrared and FUV observations showing the presence of secondary spots in the auroral emissions.

Chen, C. X.

2007-03-01

63

Measurements of surface-pressure and wake-flow fluctuations in the flow field of a whitcomb supercritical airfoil  

NASA Technical Reports Server (NTRS)

Measurements of surface pressure and wake flow fluctuations were made as part of a transonic wind tunnel investigation into the nature of a supercritical airfoil flow field. Emphasis was on a range of high subsonic Mach numbers and moderate lift coefficients corresponding to the development of drag divergence and buffeting. Fluctuation data were analyzed statistically for intensity, frequency content, and spatial coherence. Variations in these parameters were correlated with changes in the mean airfoil flow field.

Roos, F. W.; Riddle, D. W.

1977-01-01

64

The Role of Turbulence in Chemical and Dynamical Processes in the Near-Field Wake of Subsonic Aircraft  

NASA Technical Reports Server (NTRS)

During this grant, covering the period from September 1998 to December 2001, we continued the investigation of the role of turbulent mixing in the wake of subsonic aircraft initiated in 1994 for NASA's Atmospheric Effects of Aviation Project. The goal of the research has been to provide sufficient understanding and quantitative analytical capability to assess the dynamical, chemical, and microphysical interactions in the near-field wake that have the greatest potential to influence the global atmospheric impact of the projected fleet of subsonic aircraft. Through large-eddy simulations we have shown that turbulence in the early wake dynamics can have a strong effect on both the ice microphysics of contrail evolution and on wake chemistry. The wake vortex dynamics are the primary determinant of the vertical extent of the contrail; this together with the local wind shear largely determines the horizontal extent. The fraction of the initial ice crystals surviving the wake vortex dynamics, their spatial distribution, and the ice mass distribution are all sensitive to the aircraft type, assumed initial ice crystal number, and ambient humidity and turbulence conditions. Our model indicates that there is a significant range of conditions for which a smaller aircraft such as a B737 produces as significant a persistent contrail as a larger aircraft such as a B747, even though the latter consumes almost five times as much fuel. Large-eddy simulations of the near wake of a B757 provided a fine-grained chemical-dynamical representation of simplified NOx - HOx chemistry in wakes of ages from a few seconds to several minutes. By sampling the simulated data in a manner similar to that of in situ aircraft measurements it was possible to provide a likely explanation for a puzzle uncovered in the 1996 SUCCESS flight measurements of OH and HO2 The results illustrate the importance of considering fluid dynamics effects in interpreting chemistry results when mixing rates and species fluctuations are large, and demonstrate the feasibility of using 3D unsteady LES with coupled chemistry to study such phenomena.

Lewellen, D. C.; Lewellen, W. Steve

2002-01-01

65

Analysis of the wake field effects in the PEP-II storage rings with extremely high currents  

NASA Astrophysics Data System (ADS)

We present the history and analysis of different wake field effects throughout the operational life of the PEP-II SLAC B-factory. Although the impedance of the high and low energy rings is small, the intense high-current beams generated a lot of power. The effects from these wake fields are: heating and damage of vacuum beam chamber elements like RF seals, vacuum valves, shielded bellows, BPM buttons and ceramic tiles; vacuum spikes, vacuum instabilities and high detector background; and beam longitudinal and transverse instabilities. We also discuss the methods used to eliminate these effects. Results of this analysis and the PEP-II experience may be very useful in the design of new storage rings and light sources.

Novokhatski, A.; Seeman, J.; Sullivan, M.

2014-01-01

66

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

67

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

NASA Astrophysics Data System (ADS)

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 ˜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.; Zhidkov, A.; Hosokai, T.; Shin, J.-H.; Masuda, S.; Kodama, R.

2012-10-01

68

Wake fields in 9-cell TESLA accelerating structures : Spectral Element Discontinuous Galerkin (SEDG) simulations.  

SciTech Connect

Using our recently developed high-order accurate Maxwell solver, NEKCEM, we carried out longitudinal wakefield calculations for a 9-cell TESLA cavity structure in 3D. Indirect method is used for wake potential calculations. Computational results with NEKCEM are compared with those of GdfidL. NEKCEM uses a spectral element discontinuous Galerkin (SEDG) method based on a domain decomposition approach using spectral-element discretizations on Gauss-Lobatto-Legendre grids with body-conforming hexahedral meshes. The numerical scheme is designed to ensure high-order spectral accuracy, using the discontinuous Galerkin form with boundary conditions weakly enforced through a flux term between elements. Concerns related to implementation on wake potential calculations are discussed, and wake potential calculations with indirect method by NEKCEM compared with the results of the finite difference time-domain code GdfidL.

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

2007-01-01

69

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

70

Exhaust jet mixing and condensation effects in the near field of aircraft wakes  

Microsoft Academic Search

In order to investigate the process of contrail formation, an integral model and a two-dimensional direct numerical simulation have been used to analyse the mixing and entrainment processes of the engine exhaust through their interaction with the vortex wake of various aircraft. The objective of this study is to evaluate the partial vapour pressure of water and temperature in the

F Garnier; A Laverdant

1999-01-01

71

Scaling of far-field wake angle of nonaxisymmetric pressure disturbance  

NASA Astrophysics Data System (ADS)

It has been recently emphasized that the angle of maximum wave amplitude ? in the wake of a disturbance of finite size can be significantly narrower than the maximum value ?K=sin-1(1/3)?19.47? predicted by the classical analysis of Kelvin. For axisymmetric disturbance, a simple argument based on the Cauchy-Poisson initial-value problem suggests that the wake angle decreases following a Mach-like law at large velocity, ? ?FrL-1, where FrL=U/?gL is the Froude number based on the disturbance velocity U, its size L, and gravity g. In this paper we extend this analysis to the case of nonaxisymmetric disturbances, relevant to real ships. We find that, for intermediate Froude numbers, the wake angle follows an intermediate scaling law ? ?FrL-2, in agreement with the recent prediction of Noblesse et al. [Eur. J. Mech. B/Fluids 46, 164 (2014), 10.1016/j.euromechflu.2014.03.012]. We show that beyond a critical Froude number, which scales as A1/2 (where A is the length-to-width aspect ratio of the disturbance), the asymptotic scaling ? ?FrB-1 holds, where now FrB=A1/2FrL is the Froude number based on the disturbance width. We propose a simple model for this transition, and provide a regime diagram of the scaling of the wake angle as a function of parameters (A,FrL).

Moisy, F.; Rabaud, M.

2014-06-01

72

Wake flowfields for Jovian probe  

NASA Technical Reports Server (NTRS)

The wake flow field developed by the Galileo probe as it enters the Jovian atmosphere was modeled. The wake produced by the probe is highly energetic, yielding both convective and radiative heat inputs to the base of the probe. A component mathematical model for the inviscid near and far wake, the viscous near and far wake, and near wake recirculation zone was developed. Equilibrium thermodynamics were used for both the ablation and atmospheric species. Flow fields for three entry conditions were calculated. The near viscous wave was found to exhibit a variable axial pressure distribution with the neck pressure approximately three times the base pressure. Peak wake flow field temperatures were found to be in proportion to forebody post shock temperatures.

Engel, C. D.; Hair, L. M.

1980-01-01

73

Compression and Suppression of Shifting Receptive Field Activity in Frontal Eye Field Neurons  

PubMed Central

Before each saccade, neurons in frontal eye field anticipate the impending eye movement by showing sensitivity to stimuli appearing where the neuron's receptive field will be at the end of the saccade, referred to as the future field (FF) of the neuron. We explored the time course of this anticipatory activity in monkeys by briefly flashing stimuli in the FF at different times before saccades. Different neurons showed substantial variation in FF time course, but two salient observations emerged. First, when we compared the time span of stimulus probes before the saccade to the time span of FF activity, we found a striking temporal compression of FF activity, similar to compression seen for perisaccadic stimuli in human psychophysics. Second, neurons with distinct FF activity also showed suppression at the time of the saccade. The increase in FF activity and the decrease with suppression were temporally independent, making the patterns of activity difficult to separate. We resolved this by constructing a simple model with values for the start, peak, and duration of FF activity and suppression for each neuron. The model revealed the different time courses of FF sensitivity and suppression, suggesting that information about the impending saccade triggering suppression reaches the frontal eye field through a different pathway, or a different mechanism, than that triggering FF activity. Recognition of the variations in the time course of anticipatory FF activity provides critical information on its function and its relation to human visual perception at the time of the saccade. PMID:24227735

Cavanaugh, James; Wurtz, Robert H.

2013-01-01

74

HIGH-GRADIENT, HIGH-TRANSFORMER-RATIO, DIELECTRIC WAKE FIELD ACCELERATOR  

SciTech Connect

The Phase I work reported here responds to DoE'ss stated need "...to develop improved accelerator designs that can provide very high gradient (>200 MV/m for electrons...) acceleration of intense bunches of particles." Omega-P'�s approach to this goal is through use of a ramped train of annular electron bunches to drive a coaxial dielectric wakefield accelerator (CDWA) structure. This approach is a direct extension of the CDWA concept from acceleration in wake fields caused by a single drive bunch, to the more efficient acceleration that we predict can be realized from a tailored (or ramped) train of several drive bunches. This is possible because of a much higher transformer ratio for the latter. The CDWA structure itself has a number of unique features, including: a high accelerating gradient G, potentially with G > 1 GeV/m; continuous energy coupling from drive to test bunches without transfer structures; inherent transverse focusing forces for particles in the accelerated bunch; highly stable motion of high charge annular drive bunches; acceptable alignment tolerances for a multi-section system. What is new in the present approach is that the coaxial dielectric structure is now to be energized by-not one-�but by a short train of ramped annular-shaped drive bunches moving in the outer coaxial channel of the structure. We have shown that this allows acceleration of an electron bunch traveling along the axis in the inner channel with a markedly higher transformer ratio T than for a single drive bunch. As described in this report, the structure will be a GHz-scale prototype with cm-scale transverse dimensions that is expected to confirm principles that can be applied to the design of a future THz-scale high gradient (> 500 MV/m) accelerator with mm-scale transverse dimensions. We show here a new means to significantly increase the transformer ratio T of the device, and thereby to significantly improve its suitability as a flexible and effective component in a future high energy, high gradient accelerator facility. We predict that the T of a high gradient CDWA can be increased by a substantial factor; this enhancement is dramatically greater than what has been demonstrated heretofore. This large enhancement in T that we predict arises from using a train of three or four drive bunches in which the spacing of the bunches and their respective charges are selected according to a simple principle that requires each bunch lose energy to the wakefields at the same rate, so as not to sacrifice drive beam efficiency�¢����as would be the case if one bunch exhausted its available energy while others had not. It is anticipated that results from the study proposed here can have a direct impact on design of the dielectric accelerator in a TeV-scale collider concept, and in the accelerator for an x-ray FEL.

Jay L. Hirshfield

2012-04-12

75

Measurements of fish's wake by PIV  

NASA Astrophysics Data System (ADS)

In this paper an experiment on measurements of the wake of Goldfish carassius auratus swimming unrestricted was conducted in a water tunnel. Color liquid was used to visualize the wake of the fish and PIV was used to measure velocity field of the wake. Results show that there is reverse Karman vortex street in symmetrical plane of the fish's wake and the Strouhal frequency of the fish is about 0.35 udner the different experimental conditions. The distribution of velocity and vorticity in the wake of Goldfish was measured by PIV and formation of reverse Karman vortex street in the wake was studied in a model experiment.

Li, Xuemin; Wu, Yanfeng; Lu, Xiyun; Yin, Xiezhen

2003-04-01

76

Maleic hydrazide: sprout suppression of potatoes in the field.  

PubMed

In 2005, the active substance maleic hydrazide was released on the Belgian market. Maleic hydrazide is authorized in potatoes as foliar treatment for instore sprout suppression and control of volunteers. The mode of action is based on blocking cell division whilst cell elongation is not affected. The product must be applied at once during the growing season, only after at least 80% of the tubers have reached 25 mm diameter and not later than 3 weeks before haulm killing. The first 24 h after application, no meaningful precipitation should occur to insure sufficiently uptake of the product by the crop. Field trials were set up for 4 years (2005-2008) and 4 locations per year with application of maleic hydrazide in four different cultivars (Bintje, Fontane, Asterix and Cilena). After application, the cultivar Asterix showed almost every year a temporarily phytotoxicity (bronze discoloration). On the first place yield was determined. When maleic hydrazide was applied too early (80% tubers % 25mm diameter) yield was negatively affected (3 years on 4) except for the cultivar Cilena (fresh market). Internal quality (dry matter and fry quality) was not influenced by the application of maleic hydrazide. Only Fontane had a slightly lower dry matter content. Maleic hydrazide also influenced appearance of secondary growth. However, the results were very variable depending on cultivar, location and time of application. After harvest, the tubers were kept in storage and assessed monthly on germination. Potatoes treated late in the growing season, showed a shorter dormancy period. A part of the tubers was replanted the following spring to verify volunteer control. Additional trials were set up by the Flemish government for two years (2010-2011). The results of previous trials were confirmed. Additional, the influence of maleic hydrazide on internal germination during storage was examined on the cultivar Innovator. The tests clearly showed a positive effect for this parameter. PMID:23878989

De Blauwer, V; Demeulemeester, K; Demeyere, A; Hofmans, E

2012-01-01

77

Jovian Plasmas Torus Interaction with Europa. Plasma Wake Structure and Effect of Inductive Magnetic Field: 3D Hybrid Kinetic Simulation  

NASA Technical Reports Server (NTRS)

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 Oþ þ and Sþ þ 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, David G.

2013-01-01

78

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

SciTech Connect

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 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.

Toth, Cs.; Geddes, C.G.R.; Tilborg, J. van; Leemans, W.P. [L'OASIS Group, Accelerator and Fusion Research Division, Lawrence Berkeley National Laboratory, BLDG 71R0259, 1 Cyclotron Rd., Berkeley, CA 94720 (United States)

2004-12-07

79

The suppression effect of external magnetic field on the high-power microwave window multipactor phenomenon  

NASA Astrophysics Data System (ADS)

To suppress the surface multipactor phenomenon and improve the transmitting power of the high-power microwave window, the application of external magnetic fields is theoretically analyzed and simulated. A Monte Carlo algorithm is used to track the secondary electron trajectories and study the multipactor scenario on the surface of a cylinder window. It is confirmed that over-resonant magnetic fields (an external magnetic field whose magnitude is slightly greater than that of a resonant magnetic field) will generate a compensating trajectory and collision, which can suppress the secondary electron avalanche. The optimal value of this external magnetic field that will avoid the multipactor phenomenon on cylinder windows is discussed.

Zhang, Xue; Wang, Yong; Fan, Junjie

2015-02-01

80

Magnetic field suppression of melt flow in crystal growth  

Microsoft Academic Search

The p-version least-squares finite element method was used for prediction of solidification from a melt under the influence of an externally applied magnetic field. The computational results indicate significantly different flow-field patterns and thermal fields in the melt and the accrued solid in the cases of full gravity, reduced gravity, and an applied uniform magnetic field.

Brian H. Dennis; George S. Dulikravich

2002-01-01

81

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

Microsoft Academic Search

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

Sue Llewellyn

2011-01-01

82

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

SciTech Connect

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 [School of Natural Science, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of)] [School of Natural Science, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of); Kim, Young-Kuk; Hur, Min Sup [School of Electrical and Computer Engineering, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of)] [School of Electrical and Computer Engineering, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of)

2013-09-15

83

Power suppression from disparate mass scales in effective scalar field theories of inflation and quintessence  

SciTech Connect

A scalar potential coupled to other fields of large disparate masses will exhibit power suppression of the quantum loop corrections from these massive fields. Quintessence fields in the dark energy regime and inflaton fields during inflation often have a very large background field value. Thus any other field with its mass dependent on the quintessence/inflaton background field value through a moderate coupling will become very massive during the dark energy/inflation phase and its quantum corrections to the scalar effective potential will be suppressed. This concept is developed in this paper using the decoupling theorem. The problem then reduces to a quantitative question of the size of suppression effects within the parameter space of coupling constants, scalar field background value and renormalization scale. Some numerical examples are presented both for inflation and quintessence, but the approach is general and can be applied to any scalar field effective potential. The consequences to dark energy of the decoupling effect developed here is that the quintessence field need not just be an incredibly weakly interacting field, often included as an add-on to generate dark energy and having no other purpose. Instead, this quintessence field could play a central role in the particle physics dynamics at early times and then the other fields simply decouple from it at late times before the onset of the dark energy phase. For inflation a consequence is coupling of the inflaton to other heavy fields can be much larger.

Bastero-Gil, Mar [Departamento de Física Teórica y del Cosmos, Universidad de Granada, Granada-18071 (Spain); Berera, Arjun [School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ (United Kingdom); Jackson, Brendan M., E-mail: mbg@ugr.es, E-mail: ab@ph.ed.ac.uk, E-mail: bmj@roe.ac.uk [Institute for Astronomy, School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3HJ (United Kingdom)

2011-07-01

84

Characterization of cavity wakes  

NASA Astrophysics Data System (ADS)

Scope and Method of Study. This research focused on flow over deep cavities at subsonic speeds with emphasis on the wake downstream of the cavity. Cavity wake behaviors have not been studied in detail and are a major concern for air vehicles with cavities and in particular for optical sensor systems installed in cavities. Other key behaviors for sensor survival and performance are cavity resonance and turbulence scales in the shear layer. A wind tunnel test apparatus was developed to explore cavity and wake characteristics. It consisted of a test section insert for the OSU Indraft Wind Tunnel with an additional contraction cone for significantly increased speed. The test section included a variable depth cavity in a boundary layer splitter plate/fairing assembly, a Y-Z traverse and pitot rake with in-situ pressure transducers for high frequency response. Flows were measured over clean cavities with length to depth (L/D) ratios of 4 to 1/2 and on cavities with a porous fence for resonance suppression. Measurements were taken in streamwise and cross-stream sections to three cavity lengths downstream of the cavity trailing edge. Flow visualization using laser sheet and smoke injection was also used. Findings and Conclusions. The high speed insert demonstrated a significant new capability for the OSU wind tunnel, reaching speeds of 0.35 Mach (390 feet/second) in a 14"x14" test section. Inlet room flow was found to be quite unsteady and recommendations are made for improved flow and quantitative visualization. Key findings for cavity wake flow include its highly three dimensional nature with asymmetric peaks in cross section with boundary layer thicknesses and integral length scales several times that of a normal flat plate turbulent boundary layer (TBL). Turbulent intensities (TI) of 35% to 55% of freestream speeds were measured for the clean configuration. Fence configuration TI's were 20% to 35% of free stream and, in both configurations, TI's decayed to approximately that of a flat plate TBL by 3 cavity lengths downstream from the cavity trailing edge. Fence flow visualization showed edge vortices and jets through the perforations that suggest the potential for minimizing turbulence intensity and scales while still suppressing cavity resonance.

Kidd, James A.

85

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

86

Wake characteristics of a model ornithopter  

NASA Astrophysics Data System (ADS)

This paper details unsteady wake measurements from a model Ornithopther flying in a wind tunnel at representative flight conditions. Testing over a range of Strouhal number, 0.1-0.3, shows that the unsteady wake is composed of coherent vortical structures that resemble vortex rings. A single ring is formed in the wake of each wing during one wing beat. Momentum balance from velocity field measurements are reconciled with unsteady lift and drag measurements from a drag balance.

Juarez, Alfredo; Harlow, Jacob; Allen, James; Ferreira de Sousa, Paulo

2006-03-01

87

Dynamics and control of hydrofoil wakes  

NASA Astrophysics Data System (ADS)

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 the stator viscous wakes is one method to minimize the problems associated RSI; i.e. noise and vibration. In order to explore this concept, a comprehensive experimental program was carried out in a high-speed water tunnel utilizing a series of NACA 0015 hydrofoils. Baseline wake data were collected with a hydraulically smooth foil and compared with two foils modified with two sizes of vortex generators (VG) positioned close to the leading edge of the foil. Not only was the effect of the modifications on wake spreading investigated but also the effect on wake dynamics such as vortex shedding was studied. A high frame-rate PIV system was used at recording rates of 1 and 10 kHz to map the near wake region, extending roughly 1 chord-length downstream the trailing edge, over a range of angles of attack and velocities. The results show that wake dynamics and wake characteristics, i.e. velocity deficit and width, scale with average drag. It was demonstrated that the use of VGs can improve both the dynamics and spreading characteristics of the wake.

Kjeldsen, Morten; Wosnik, Martin; Arndt, Roger

2008-11-01

88

Efficient and stable transgene suppression via RNAi in field-grown poplars.  

PubMed

The efficiency and stability of RNA interference (RNAi) in perennial species, particularly in natural environments, is poorly understood. We studied 56 independent poplar RNAi transgenic events in the field over 2 years. A resident BAR transgene was targeted with two different types of RNAi constructs: a 475-bp IR of the promoter sequence and a 275-bp IR of the coding sequence, each with and without the presence of flanking matrix attachment regions (MARs). RNAi directed at the coding sequence was a strong inducer of gene silencing; 80% of the transgenic events showed more than 90% suppression. In contrast, RNAi targeting the promoter resulted in only 6% of transgenic events showing more than 90% suppression. The degree of suppression varied widely but was highly stable in each event over 2 years in the field, and had no association with insert copy number or the presence of MARs. RNAi remained stable during a winter to summer seasonal cycle, a time when expression of the targeted transgene driven by an rbcS promoter varied widely. When strong gene suppression was induced by an IR directed at the promoter sequence, it was accompanied by methylation of the homologous promoter region. DNA methylation was also observed in the coding region of highly suppressed events containing an IR directed at the coding sequence; however, the methylation degree and pattern varied widely among those suppressed events. Our results suggest that RNAi can be highly effective for functional genomics and biotechnology of perennial plants. PMID:17929189

Li, Jingyi; Brunner, Amy M; Shevchenko, Olga; Meilan, Richard; Ma, Cathleen; Skinner, Jeffrey S; Strauss, Steven H

2008-08-01

89

Suppression of Marangoni convection in the FZ melt by high-frequency magnetic field  

Microsoft Academic Search

The effect of high-frequency magnetic field on the Marangoni convection in the floating zone (FZ) silicon melt has been investigated numerically. The purpose of the study is to clarify the applicability of the high-frequency magnetic field on the suppression of the Marangoni convection. The numerically obtained results reveal that the high-frequency magnetic field has the dumping effect for the Marangoni

Tetsuo Munakata; Satoshi Someya; Ichiro Tanasawa

2002-01-01

90

Airloads, wakes, and aeroelasticity  

NASA Technical Reports Server (NTRS)

Fundamental considerations regarding the theory of modeling of rotary wing airloads, wakes, and aeroelasticity are presented. The topics covered are: airloads and wakes, including lifting-line theory, wake models and nonuniform inflow, free wake geometry, and blade-vortex interaction; aerodynamic and wake models for aeroelasticity, including two-dimensional unsteady aerodynamics and dynamic inflow; and airloads and structural dynamics, including comprehensive airload prediction programs. Results of calculations and correlations are presented.

Johnson, Wayne

1990-01-01

91

Caught in the act: a field gone suppressive for common scab?  

Technology Transfer Automated Retrieval System (TEKTRAN)

Potato varieties are evaluated for resistance to common scab (CS) in fields with high CS disease pressure. Occasionally, disease pressure naturally declines in a CS nursery; this is termed disease suppression. We have data on severity of potato CS in a scab nursery in Maine for 6 years between 2001...

92

Emergence of spatially heterogeneous burst suppression in a neural field model of electrocortical activity.  

PubMed

Burst suppression in the electroencephalogram (EEG) is a well-described phenomenon that occurs during deep anesthesia, as well as in a variety of congenital and acquired brain insults. Classically it is thought of as spatially synchronous, quasi-periodic bursts of high amplitude EEG separated by low amplitude activity. However, its characterization as a "global brain state" has been challenged by recent results obtained with intracranial electrocortigraphy. Not only does it appear that burst suppression activity is highly asynchronous across cortex, but also that it may occur in isolated regions of circumscribed spatial extent. Here we outline a realistic neural field model for burst suppression by adding a slow process of synaptic resource depletion and recovery, which is able to reproduce qualitatively the empirically observed features during general anesthesia at the whole cortex level. Simulations reveal heterogeneous bursting over the model cortex and complex spatiotemporal dynamics during simulated anesthetic action, and provide forward predictions of neuroimaging signals for subsequent empirical comparisons and more detailed characterization. Because burst suppression corresponds to a dynamical end-point of brain activity, theoretically accounting for its spatiotemporal emergence will vitally contribute to efforts aimed at clarifying whether a common physiological trajectory is induced by the actions of general anesthetic agents. We have taken a first step in this direction by showing that a neural field model can qualitatively match recent experimental data that indicate spatial differentiation of burst suppression activity across cortex. PMID:25767438

Bojak, Ingo; Stoyanov, Zhivko V; Liley, David T J

2015-01-01

93

Emergence of spatially heterogeneous burst suppression in a neural field model of electrocortical activity  

PubMed Central

Burst suppression in the electroencephalogram (EEG) is a well-described phenomenon that occurs during deep anesthesia, as well as in a variety of congenital and acquired brain insults. Classically it is thought of as spatially synchronous, quasi-periodic bursts of high amplitude EEG separated by low amplitude activity. However, its characterization as a “global brain state” has been challenged by recent results obtained with intracranial electrocortigraphy. Not only does it appear that burst suppression activity is highly asynchronous across cortex, but also that it may occur in isolated regions of circumscribed spatial extent. Here we outline a realistic neural field model for burst suppression by adding a slow process of synaptic resource depletion and recovery, which is able to reproduce qualitatively the empirically observed features during general anesthesia at the whole cortex level. Simulations reveal heterogeneous bursting over the model cortex and complex spatiotemporal dynamics during simulated anesthetic action, and provide forward predictions of neuroimaging signals for subsequent empirical comparisons and more detailed characterization. Because burst suppression corresponds to a dynamical end-point of brain activity, theoretically accounting for its spatiotemporal emergence will vitally contribute to efforts aimed at clarifying whether a common physiological trajectory is induced by the actions of general anesthetic agents. We have taken a first step in this direction by showing that a neural field model can qualitatively match recent experimental data that indicate spatial differentiation of burst suppression activity across cortex.

Bojak, Ingo; Stoyanov, Zhivko V.; Liley, David T. J.

2015-01-01

94

SURFACE FILMS TO SUPPRESS FIELD EMISSION IN HIGH-POWER MICROWAVE COMPONENTS  

SciTech Connect

Results are reported on attempts to reduce the RF breakdown probability on copper accelerator structures by applying thin surface films that could suppress field emission of electrons. Techniques for application and testing of copper samples with films of metals with work functions higher than copper are described, principally for application of platinum films, since platinum has the second highest work function of any metal. Techniques for application of insulating films are also described, since these can suppress field emission and damage on account of dielectric shielding of fields at the copper surface, and on account of the greater hardness of insulating films, as compared with copper. In particular, application of zirconium oxide films on high-field portions of a 11.424 GHz SLAC cavity structure for breakdown tests are described.

Hirshfield, Jay l

2014-02-07

95

Analysis of shot noise suppression in mesoscopic cavities in a magnetic field  

Microsoft Academic Search

We present a numerical investigation of shot noise suppression in mesoscopic\\u000acavities and an intuitive semiclassical explanation of the behavior observed in\\u000athe presence of an orthogonal magnetic field. In particular, we conclude that\\u000athe decrease of shot noise for increasing magnetic field is the result of the\\u000ainterplay between the diameter of classical cyclotron orbits and the width of

P. Marconcini; M. Macucci; G. Iannaccone; B. Pellegrini; G. Marola

2006-01-01

96

Suppression of high-power microwave dielectric multipactor by resonant magnetic field  

NASA Astrophysics Data System (ADS)

Through dynamic calculation and electromagnetic particle-in-cell simulation, high-power microwave dielectric multipactor is discovered to be suppressed by utilizing external dc magnetic field parallel to the surface, perpendicular to the rf field and satisfying the gyrofrequency close to the rf frequency ? ˜?. It is found that multipactor electrons emitted from the surface can be resonantly accelerated to obtain the impact energy ?e higher than the second crossover energy, leading to secondary emission yield lower than one. Besides, the corresponding flight time gets close to the rf period, also the period of the vector Erf×B, resulting in secondary electrons immediately pulled away without multipactoring along the surface. What is more, with the rf field increasing, suppression effect can be further enhanced due to ?e rising.

Chang, C.; Liu, G. Z.; Tang, C. X.; Chen, C. H.; Shao, H.; Huang, W. H.

2010-03-01

97

Commercial aircraft wake vortices  

Microsoft Academic Search

This paper discusses the problem of wake vortices shed by commercial aircraft. It presents a consolidated European view on the current status of knowledge of the nature and characteristics of aircraft wakes and of technical and operational procedures of minimizing and predicting the vortex strength and avoiding wake encounters. Methodological aspects of data evaluation and interpretation, like the description of

Thomas Gerza; Frank Holz

98

The psychology of waking  

Microsoft Academic Search

More than 200 dreams were secured and all the results were in harmony. The dream is recalled as the cause of and as occurring at the time of waking. The dream presents a situation that is strange, frightful, astonishing, puzzling, surprising, unreal or otherwise shocking––a crisis. In regular waking it is least shocking and very elusive. In voluntary waking at

N. B. Bond

1929-01-01

99

Suppression of cooling by strong magnetic fields in white dwarf stars.  

PubMed

Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young. PMID:25327247

Valyavin, G; Shulyak, D; Wade, G A; Antonyuk, K; Zharikov, S V; Galazutdinov, G A; Plachinda, S; Bagnulo, S; Machado, L Fox; Alvarez, M; Clark, D M; Lopez, J M; Hiriart, D; Han, Inwoo; Jeon, Young-Beom; Zurita, C; Mujica, R; Burlakova, T; Szeifert, T; Burenkov, A

2014-11-01

100

Suppression of cooling by strong magnetic fields in white dwarf stars  

NASA Astrophysics Data System (ADS)

Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young.

Valyavin, G.; Shulyak, D.; Wade, G. A.; Antonyuk, K.; Zharikov, S. V.; Galazutdinov, G. A.; Plachinda, S.; Bagnulo, S.; Fox Machado, L.; Alvarez, M.; Clark, D. M.; Lopez, J. M.; Hiriart, D.; Han, Inwoo; Jeon, Young-Beom; Zurita, C.; Mujica, R.; Burlakova, T.; Szeifert, T.; Burenkov, A.

2014-11-01

101

Experimental evaluation of a flat wake theory for predicting rotor inflow-wake velocities  

NASA Technical Reports Server (NTRS)

The theory for predicting helicopter inflow-wake velocities called flat wake theory was correlated with several sets of experimental data. The theory was developed by V. E. Baskin of the USSR, and a computer code known as DOWN was developed at Princeton University to implement the theory. The theory treats the wake geometry as rigid without interaction between induced velocities and wake structure. The wake structure is assumed to be a flat sheet of vorticity composed of trailing elements whose strength depends on the azimuthal and radial distributions of circulation on a rotor blade. The code predicts the three orthogonal components of flow velocity in the field surrounding the rotor. The predictions can be utilized in rotor performance and helicopter real-time flight-path simulation. The predictive capability of the coded version of flat wake theory provides vertical inflow patterns similar to experimental patterns.

Wilson, John C.

1992-01-01

102

A study of rotor wake development and wake/body interactions in hover  

NASA Technical Reports Server (NTRS)

Experiments were conducted to document the wake geometry and interactional effects between a hovering rotor and a body representing a simplified helicopter fuselage. The wide-field shadowgraph technique was used to visualize the rotor wake vortices and to obtain quantitative information on the wake trajectories, with and without the presence of the body. Particular attention was paid to visualizing and quantifying the wake geometry during the direct impingement of tip vortices on the body surface. The rotor performance with and without the fuselage is also discussed.

Bagai, A.; Leishman, J. G.; Samak, D. K.

1991-01-01

103

Near-Field Analysis of Bright and Dark Modes on Plasmonic Metasurfaces Showing Extraordinary Suppressed Transmission  

E-print Network

Plasmonic metasurfaces are investigated that consist of a sub wavelength line pattern in an ultrathin (~ 10 nm) silver film, designed for extraordinarily suppressed transmission (EOST) in the visible spectral range. Measurements with a near-field scanning optical microscope (NSOM) demonstrate that far field irradiation creates resonant excitations of antenna like (bright) modes that are localized on the metal ridges. In contrast, bound (dark) surface plasmon polaritons (SPPs) launched from an NSOM tip propagate well across the metasurface, preferentially perpendicular to the grating lines.

Dobmann, Sabine; Ploss, Daniel; Peschel, Ulf

2014-01-01

104

Visualization on fish's wake  

NASA Astrophysics Data System (ADS)

In this paper an experiment on wake of Goldfish swimming unrestricted was conducted in a water tunnel. Method of color liquid was used to visualize the wake. Results show that there is reverse Karman vortex street in symmetrical plane of the wake and the Strouhal frequency of the fish is in the range 0.25-0.35. A 3D vortex ring chain model was presented.

Li, Xuemin; Lu, Xiyun; Yin, Xiezhen

2002-05-01

105

The Reykjavik wake  

NASA Astrophysics Data System (ADS)

We present preliminary results from the wake flights in the MOSO 2 campaign that took place in Iceland, autumn 2011. The results include RPAS measurements (soundings) of an orographic wake in southwestern Iceland during a northerly wind storm. The results reveal a wake structure dominated by the local as well as the larger scale topography. The RPAS dataset is augmented with measurements from a network of automatic weather stations and simulations from a numerical weather model.

Jonassen, Marius O.; Ólafsson, Haraldur; Rögnvaldsson, Ólafur; Ágústsson, Hálfdán

2013-04-01

106

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

107

Wind tunnel measurements for dispersion modelling of vehicle wakes  

NASA Astrophysics Data System (ADS)

Wind tunnel measurements downwind of reduced scale car models have been made to study the wake regions in detail, test the usefulness of existing vehicle wake models, and draw key information needed for dispersion modelling in vehicle wakes. The experiments simulated a car moving in still air. This is achieved by (i) the experimental characterisation of the flow, turbulence and concentration fields in both the near and far wake regions, (ii) the preliminary assessment of existing wake models using the experimental database, and (iii) the comparison of previous field measurements in the wake of a real diesel car with the wind tunnel measurements. The experiments highlighted very large gradients of velocities and concentrations existing, in particular, in the near-wake. Of course, the measured fields are strongly dependent on the geometry of the modelled vehicle and a generalisation for other vehicles may prove to be difficult. The methodology applied in the present study, although improvable, could constitute a first step towards the development of mathematical parameterisations. Experimental results were also compared with the estimates from two wake models. It was found that they can adequately describe the far-wake of a vehicle in terms of velocities, but a better characterisation in terms of turbulence and pollutant dispersion is needed. Parameterised models able to predict velocity and concentrations with fine enough details at the near-wake scale do not exist.

Carpentieri, Matteo; Kumar, Prashant; Robins, Alan

2012-12-01

108

Suppression of strong-field ionization by optimal pulse shaping: Application to hydrogen and the hydrogen molecular ion  

NASA Astrophysics Data System (ADS)

We investigate the ability of quantum optimal control theory to shape pulses suppressing strong-field ionization of a hydrogen atom and a H2+ molecule. We show that considerable suppression of the ionization yield can be achieved for both H and H2+ with optimal pulse shaping for a fixed fluence and pulse length. The mechanisms responsible for ionization suppression and the shape of the optimized pulse are different for infrared and ultraviolet laser fields. In the low-frequency regime the optimized pulse reduces the ionization yield by suppressing the highest peaks of the laser field. For the higher laser frequencies considered the ionization yield of H can be decreased by exciting low-lying resonances.

Shvetsov-Shilovski, N. I.; Madsen, L. B.; Räsänen, E.

2015-02-01

109

Cosmic string wakes  

NASA Technical Reports Server (NTRS)

Accretion of matter onto wakes left behind by horizon-sized pieces of cosmic string is investigated, and the effects of wakes on the large-scale structure of the universe are determined. Accretion of cold matter onto wakes, the effects of a long string on fluids with finite velocity dispersion or sound speeds, the interactions between loops and wakes, and the conditions for wakes to survive disruption by loops are discussed. It is concluded that the most important wakes are those which were formed at the time of equal matter and radiation density. This leads to sheetlike overdense regions of galaxies with a mean separation in agreement with the scale of the bubbles of de Lapparent, Geller, and Huchra (1986). However, for the value of G(mu) favored from galaxy formation considerations in a universe with cold dark matter, a wake accretes matter from a distance of only about 1.5 Mpc, which is much less than the distance between the wakes.

Stebbins, Albert; Veeraraghavan, Shoba; Silk, Joseph; Brandenberger, Robert; Turok, Neil

1987-01-01

110

Secondary energy growth and turbulence suppression in conducting channel flow with streamwise magnetic field  

NASA Astrophysics Data System (ADS)

The effects of a streamwise magnetic field on conducting channel flow are studied by analyzing secondary linear perturbations evolving on streamwise streaks and by direct numerical simulations of relaminarization. By means of an optimal perturbation approach, magnetic damping is found to increase the streamwise wavelength of the most amplified secondary perturbations and to reduce their amplification level. Complete suppression of secondary instability is observed at a critical magnetic interaction parameter that depends on the streak amplitude and on the Reynolds number when the transient evolution of the streaky basic flow is taken into account. Relaminarization in the direct numerical simulation occurs at lower values of the interaction parameter than the critical values from the stability computations for the streak amplitudes considered. The dependence of these threshold values of the interaction parameters on the Reynolds number is fairly similar between simulations and stability analysis. Relaminarization thresholds from the simulations are also in good agreement with experiments on pipe flow with streamwise magnetic field.

Dong, Shuai; Krasnov, Dmitry; Boeck, Thomas

2012-07-01

111

Wind and Wake Sensing with UAV Formation Flight: System Development and Flight Testing  

NASA Astrophysics Data System (ADS)

Wind turbulence including atmospheric turbulence and wake turbulence have been widely investigated; however, only recently it become possible to use Unmanned Aerial Vehicles (UAVs) as a validation tool for research in this area. Wind can be a major contributing factor of adverse weather for aircraft. More importantly, it is an even greater risk towards UAVs because of their small size and weight. Being able to estimate wind fields and gusts can potentially provide substantial benefits for both unmanned and manned aviation. Possible applications include gust suppression for improving handling qualities, a better warning system for high wind encounters, and enhanced control for small UAVs during flight. On the other hand, the existence of wind can be advantageous since it can lead to fuel savings and longer duration flights through dynamic soaring or thermal soaring. Wakes are an effect of the lift distribution across an aircraft's wing or tail. Wakes can cause substantial disturbances when multiple aircraft are moving through the same airspace. In fact, the perils from an aircraft flying through the wake of another aircraft is a leading cause of the delay between takeoff times at airports. Similar to wind, though, wakes can be useful for energy harvesting and increasing an aircraft's endurance when flying in formation which can be a great advantage to UAVs because they are often limited in flight time due to small payload capacity. Formation flight can most often be seen in manned aircraft but can be adopted for use with unmanned systems. Autonomous flight is needed for flying in the "sweet spot" of the generated wakes for energy harvesting as well as for thermal soaring during long duration flights. For the research presented here formation flight was implemented for the study of wake sensing and gust alleviation. The major contributions of this research are in the areas of a novel technique to estimate wind using an Unscented Kalman filter and experimental wake sensing data using UAVs in formation flight. This has been achieved and well documented before in manned aircraft but very little work has been done on UAV wake sensing especially during flight testing. This document describes the development and flight testing of small unmanned aerial system (UAS) for wind and wake sensing purpose including a Ground Control Station (GCS) and UAVs. This research can be stated in four major components. Firstly, formation flight was obtained by integrating a formation flight controller on the WVU Phastball Research UAV aircraft platform from the Flight Control Systems Laboratory (FCSL) at West Virginia University (WVU). Second, a new approach to wind estimation using an Unscented Kalman filter (UKF) is discussed along with results from flight data. Third, wake modeling within a simulator and wake sensing during formation flight is shown. Finally, experimental results are used to discuss the "sweet spot" for energy harvesting in formation flight, a novel approach to cooperative wind estimation, and gust suppression control for a follower aircraft in formation flight.

Larrabee, Trenton Jameson

112

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

SciTech Connect

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 wind flows with reduced velocity and (2) the downwind turbine encounters increased turbulence across multiple length scales via mechanical turbulence production by the upwind turbine. This increase in turbulence on top of ambient levels may increase aerodynamic fatigue loads on the blades and reduce the lifetime of turbine component parts. Furthermore, ambient atmospheric conditions, including atmospheric stability, i.e., thermal stratification in the lower boundary layer, play an important role in wake dissipation. Higher levels of ambient turbulence (i.e., a convective or unstable boundary layer) lead to higher turbulent mixing in the wake and a faster recovery in the velocity flow field downwind of a turbine. Lower levels of ambient turbulence, as in a stable boundary layer, will lead to more persistent wakes. The wake of a wind turbine can be divided into two regions: the near wake and far wake, as illustrated in Figure 1. The near wake is formed when the turbine structure alters the shape of the flow field and usually persists one rotor diameter (D) downstream. The difference between the air inside and outside of the near wake results in a shear layer. This shear layer thickens as it moves downstream and forms turbulent eddies of multiple length scales. As the wake travels downstream, it expands depending on the level of ambient turbulence and meanders (i.e., travels in non-uniform path). Schepers estimates that the wake is fully expanded at a distance of 2.25 D and the far wake region begins at 2-5 D downstream. The actual distance traveled before the wake recovers to its inflow velocity is dependent on the amount ambient turbulence, the amount of wind shear, and topographical and structural effects. The maximum velocity deficit is estimated to occur at 1-2 D but can be longer under low levels of ambient turbulence. Our understanding of turbine wakes comes from wind tunnel experiments, field experiments, numerical simulations, and from studies utilizing both experimental and modeling methods. It is well documented that downwind turbines in multi-Megawatt wind farms often produce less power than upwind turbine rows. These wake-induced power losses have been estimated from 5% to up to 40% depending on the turbine operating settings (e.g., thrust coefficient), number of turbine rows, turbine size (e.g., rotor diameter and hub-height), wind farm terrain, and atmospheric flow conditions (e.g., ambient wind speed, turbulence, and atmospheric stability). Early work by Elliott and Cadogan suggested that power data for different turbulent conditions be segregated to distinguish the effects of turbulence on wind farm power production. This may be especially important for downwind turbines within wind farms, as chaotic and turbulent wake flows increase stress on downstream turbines. Impacts of stability on turbine wakes and power production have been examined for a flat terrain, moderate size (43 turbines) wind farm in Minnesota and for an offshore, 80 turbine wind farm off the coast of Denmark. Conzemius found it difficult to distinguish wakes (i.e., downwind velocity deficits) when the atmosphere was convective as large amounts of scatter were present in the turbine nacelle wind speed data. This suggested that high levels of turbulence broke-up the wake via large buoyancy effects, which are generally on the order of 1 km in size. On the other hand, they found pronounced wake effects when the atmosphere was very stable and turbulence was either suppressed or the length scale was reduced as turbulence in this case was mechanically produced (i.e., friction forces). This led to larger reductions at downwind turbines and maximum ve

Wharton, S; Lundquist, J K; Marjanovic, N

2012-01-25

113

Dissipation of Turbulence in the Wake of a Wind Turbine  

NASA Astrophysics Data System (ADS)

The wake of a wind turbine is characterized by increased turbulence and decreased wind speed. Turbines are generally deployed in large groups in wind farms, and so the behaviour of an individual wake as it merges with other wakes and propagates downwind is critical in assessing wind-farm power production. This evolution depends on the rate of turbulence dissipation in the wind-turbine wake, which has not been previously quantified in field-scale measurements. In situ measurements of winds and turbulence dissipation from the wake region of a multi-MW turbine were collected using a tethered lifting system (TLS) carrying a payload of high-rate turbulence probes. Ambient flow measurements were provided from sonic anemometers on a meteorological tower located near the turbine. Good agreement between the tower measurements and the TLS measurements was established for a case without a wind-turbine wake. When an operating wind turbine is located between the tower and the TLS so that the wake propagates to the TLS, the TLS measures dissipation rates one to two orders of magnitude higher in the wake than outside of the wake. These data, collected between two and three rotor diameters downwind of the turbine, document the significant enhancement of turbulent kinetic energy dissipation rate within the wind-turbine wake. These wake measurements suggest that it may be useful to pursue modelling approaches that account for enhanced dissipation. Comparisons of wake and non-wake dissipation rates to mean wind speed, wind-speed variance, and turbulence intensity are presented to facilitate the inclusion of these measurements in wake modelling schemes.

Lundquist, J. K.; Bariteau, L.

2015-02-01

114

Development and testing of laser Doppler system components for wake vortex monitoring. Volume 1: Scanner development, laboratory and field testing and system modeling  

NASA Technical Reports Server (NTRS)

A servo-controlled range/elevation scanner for the laser Doppler velocimeter (LDV) was developed and tested in the field to assess its performance in detecting and monitoring aircraft trailing vortices in an airport environment. The elevation scanner provides a capability to manually point the LDV telescope at operator chosen angles from 3.2 deg. to 89.6 deg within 0.2 deg, or to automatically scan the units between operator chosen limits at operator chosen rates of 0.1 Hz to 0.5 Hz. The range scanner provides a capability to manually adjust the focal point of the system from a range of 32 meters to a range of 896 meters under operator control, or to scan between operator chosen limits and at rates from 0.1 Hz to 6.9 Hz. The scanner controls are designed to allow simulataneous range and elevation scanning so as to provide finger scan patterns, arc scan patterns, and vertical line scan patterns. The development and testing of the unit is discussed, along with a fluid dynamic model of the wake vortex developed in a laser Doppler vortex sensor simulation program.

Wilson, D. J.; Krause, M. C.; Coffey, E. W.; Huang, C. C.; Edwards, B. B.; Shrider, K. R.; Jetton, J. L.; Morrison, L. K.

1974-01-01

115

Cancellation of the ion deflection due to electron-suppression magnetic field in a negative-ion accelerator  

SciTech Connect

A new magnetic configuration is proposed for the suppression of co-extracted electrons in a negative-ion accelerator. This configuration is produced by an arrangement of permanent magnets embedded in one accelerator grid and creates an asymmetric local magnetic field on the upstream and downstream sides of this grid. Thanks to the “concentration” of the magnetic field on the upstream side of the grid, the resulting deflection of the ions due to magnetic field can be “intrinsically” cancelled by calibrating the configuration of permanent magnets. At the same time, the suppression of co-extracted electrons can be improved.

Chitarin, G., E-mail: chitarin@igi.cnr.it [Consorzio RFX, Association EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy); Dept. of Management and Engineering, University of Padova, Strad. S. Nicola 3, 36100 Vicenza (Italy); Agostinetti, P.; Aprile, D.; Marconato, N.; Veltri, P. [Consorzio RFX, Association EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy)] [Consorzio RFX, Association EURATOM-ENEA, Corso Stati Uniti 4, 35127 Padova (Italy)

2014-02-15

116

Cancellation of the ion deflection due to electron-suppression magnetic field in a negative-ion accelerator.  

PubMed

A new magnetic configuration is proposed for the suppression of co-extracted electrons in a negative-ion accelerator. This configuration is produced by an arrangement of permanent magnets embedded in one accelerator grid and creates an asymmetric local magnetic field on the upstream and downstream sides of this grid. Thanks to the "concentration" of the magnetic field on the upstream side of the grid, the resulting deflection of the ions due to magnetic field can be "intrinsically" cancelled by calibrating the configuration of permanent magnets. At the same time, the suppression of co-extracted electrons can be improved. PMID:24593594

Chitarin, G; Agostinetti, P; Aprile, D; Marconato, N; Veltri, P

2014-02-01

117

Fast fat-suppressed reduced field-of-view temperature mapping using 2DRF excitation pulses  

NASA Astrophysics Data System (ADS)

The purpose of this study is to develop a fast and accurate temperature mapping method capable of both fat suppression and reduced field-of-view (rFOV) imaging, using a two-dimensional spatially-selective RF (2DRF) pulse. Temperature measurement errors caused by fat signals were assessed, through simulations. An 11 × 1140 ?s echo-planar 2DRF pulse was developed and incorporated into a gradient-echo sequence. Temperature measurements were obtained during focused ultrasound (FUS) heating of a fat-water phantom. Experiments both with and without the use of a 2DRF pulse were performed at 3 T, and the accuracy of the resulting temperature measurements were compared over a range of TE values. Significant inconsistencies in terms of measured temperature values were observed when using a regular slice-selective RF excitation pulse. In contrast, the proposed 2DRF excitation pulse suppressed fat signals by more than 90%, allowing good temperature consistency regardless of TE settings. Temporal resolution was also improved, from 12 frames per minute (fpm) with the regular pulse to 28 frames per minute with the rFOV excitation. This technique appears promising toward the MR monitoring of temperature in moving adipose organs, during thermal therapies.

Yuan, Jing; Mei, Chang-Sheng; Madore, Bruno; McDannold, Nathan J.; Panych, Lawrence P.

2011-05-01

118

Modeling Flow Suppression of Error-field-induced Magnetic Islands in Tokamaks  

NASA Astrophysics Data System (ADS)

Small deviations from axisymmetry in applied tokamak magnetic fields can induce island formation at magnetic surfaces whose rotational transform resonates with the perturbation. These islands have a braking effect on plasma rotation that can destabilize resistive wall modes. The IPEC codefootnotetextJ.K. Park, et al., Phys. Plasmas 14, 052110 (2007). is useful for computing plasma response to harmonic perturbations in the infinite-conducting limit, assuming perfect shielding at the resonant surface, but cannot predict the nonlinear effects of finite-sized islands. Using the nonlinear extended MHD code M3D,footnotetextW. Park, et al., Phys. Plasmas 6, 1796 (1999). we explore the effects of a 2,1 perturbation on the nonlinear evolution of a family of equilibria with finite resistivity. Particular attention is paid to the effects of toroidal flow on suppressing island formation, making contact with the analytic theory of Fitzpatrick.footnotetextR. Fitzpatrick, Phys. Plasmas 5, 3325 (1998). Island suppression is shown to depend strongly on the tearing mode stability properties of the equilibrium.

Breslau, J. A.; Park, W.

2009-11-01

119

Fast fat-suppressed reduced field-of-view temperature mapping using 2DRF excitation pulses.  

PubMed

The purpose of this study is to develop a fast and accurate temperature mapping method capable of both fat suppression and reduced field-of-view (rFOV) imaging, using a two-dimensional spatially-selective RF (2DRF) pulse. Temperature measurement errors caused by fat signals were assessed, through simulations. An 11×1140?s echo-planar 2DRF pulse was developed and incorporated into a gradient-echo sequence. Temperature measurements were obtained during focused ultrasound (FUS) heating of a fat-water phantom. Experiments both with and without the use of a 2DRF pulse were performed at 3T, and the accuracy of the resulting temperature measurements were compared over a range of TE values. Significant inconsistencies in terms of measured temperature values were observed when using a regular slice-selective RF excitation pulse. In contrast, the proposed 2DRF excitation pulse suppressed fat signals by more than 90%, allowing good temperature consistency regardless of TE settings. Temporal resolution was also improved, from 12 frames per minute (fpm) with the regular pulse to 28 frames per minute with the rFOV excitation. This technique appears promising toward the MR monitoring of temperature in moving adipose organs, during thermal therapies. PMID:21371923

Yuan, Jing; Mei, Chang-Sheng; Madore, Bruno; McDannold, Nathan J; Panych, Lawrence P

2011-05-01

120

Wake Vortex Minimization  

NASA Technical Reports Server (NTRS)

A status report is presented on research directed at reducing the vortex disturbances of aircraft wakes. The objective of such a reduction is to minimize the hazard to smaller aircraft that might encounter these wakes. Inviscid modeling was used to study trailing vortices and viscous effects were investigated. Laser velocimeters were utilized in the measurement of aircraft wakes. Flight and wind tunnel tests were performed on scale and full model scale aircraft of various design. Parameters investigated included the effect of wing span, wing flaps, spoilers, splines and engine thrust on vortex attenuation. Results indicate that vortives may be alleviated through aerodynamic means.

1977-01-01

121

Cavities of Weak Magnetic Field Strength in the Wake of FTEs: Results from Global Magnetospheric MHD Simulations  

NASA Technical Reports Server (NTRS)

We use the global magnetohydrodynamic (MHD) code BATS-R-US to model multipoint observations of Flux Transfer Event (FTE) signatures. Simulations with high spatial and temporal resolution predict that cavities of weak magnetic field strength protruding into the magnetosphere trail FTEs. These predictions are consistent with recently reported multi-point Cluster observations of traveling magnetopause erosion regions (TMERs).

Kuznetsova, M. M.; Sibeck, D. G.; Hesse, M.; Wang, Y.; Rastaetter, L.; Toth, G.; Ridley, A.

2009-01-01

122

NASA wake vortex research  

NASA Technical Reports Server (NTRS)

NASA is conducting research that will enable safe improvements in the capacity of the nation's air transportation system. The wake-vortex hazard is a factor in establishing the minimum safe spacing between aircraft during landing and takeoff operations and, thus, impacts airport capacity. The ability to accurately model the wake hazard and determine safe separation distances for a wide range of aircraft and operational scenarios may provide the basis for significant increases in airport capacity. Current and planned NASA research is described which is focused on increasing airport capacity by safely reducing wake-hazard-imposed aircraft separations through advances in a number of technologies including vortex motion and decay prediction, vortex encounter modeling, wake-vortex hazard characterization, and in situ flow sensing.

Stough, H. P., III; Greene, George C.; Stewart, Eric C.; Stuever, Robert A.; Jordan, Frank L., Jr.; Rivers, Robert A.; Vicroy, Dan D.

1993-01-01

123

Wake Signature Detection  

NASA Astrophysics Data System (ADS)

An accumulated body of quantitative evidence shows that bluff-body wakes in stably stratified environments have an unusual degree of coherence and organization, so characteristic geometries such as arrays of alternating-signed vortices have very long lifetimes, as measured in units of buoyancy timescales, or in the downstream distance scaled by a body length. The combination of pattern geometry and persistence renders the detection of these wakes possible in principle. It now appears that identifiable signatures can be found from many disparate sources: Islands, fish, and plankton all have been noted to generate features that can be detected by climate modelers, hopeful navigators in open oceans, or hungry predators. The various types of wakes are reviewed with notes on why their signatures are important and to whom. A general theory of wake pattern formation is lacking and would have to span many orders of magnitude in Reynolds number.

Spedding, Geoffrey R.

2014-01-01

124

Suppressive effect of electromagnetic field on analgesic activity of tramadol in rats.  

PubMed

The electromagnetic fields (EMFs) have been shown to alter animal and human behavior, such as directional orientation, learning, pain perception (nociception or analgesia) and anxiety-related behaviors. The aim of this study was to evaluate the influence of electromagnetic fields of high-frequency microwaves on pain perception and anti-nociceptive activity of tramadol (TRAM) - analgetic effective in the treatment of moderate to severe acute and chronic pain states. Electromagnetic fields exposures of a)1500 MHz frequency and b) modulated, 1800 MHz (which is identical to that generated by mobile phones) were applied. Paw withdrawal latency (PWL) to thermal stimulus was measured in vehicle or tramadol (TRAM) treated animals before and after 30, 60 and 90 minutes from injections. The differences in the level of pain (PWL) between control group and rats exposed to EMF alone in three measurements, were not observed. Tramadol alone significantly increased PWLs to thermal stimulus in comparison to vehicle results at 30 (p < 0.001) and 60 minutes (p < 0.05) after drug injection. EMF exposure of both frequencies transiently suppressed analgesic effect of tramadol, significantly reducing paw withdrawal latency in animals treated with this drug at 30 minutes from the drug injection. PMID:22708363

Bodera, P; Stankiewicz, W; Antkowiak, B; Paluch, M; Kieliszek, J; Sobiech, J; Zdanowski, R; Wojdas, A; Siwicki, A K; Skopi?ska-Rózewska, E

2012-01-01

125

Turbulent Plane Wakes Subjected to Successive Strains  

NASA Technical Reports Server (NTRS)

Six direct numerical simulations of turbulent time-evolving strained plane wakes have been examined to investigate the response of a wake to successive irrotational plane strains of opposite sign. The orientation of the applied strain field has been selected so that the flow is the time-developing analogue of a spatially developing wake evolving in the presence of either a favourable or an adverse streamwise pressure gradient. The magnitude of the applied strain rate a is constant in time t until the total strain e(sup at) reaches about four. At this point, a new simulation is begun with the sign of the applied strain being reversed (the original simulation is continued as well). When the total strain is reduced back to its original value of one, yet another simulation is begun with the sign of the strain being reversed again back to its original sign. This process is done for both initially "favourable" and initially "adverse" strains, providing simulations for each of these strain types from three different initial conditions. The evolution of the wake mean velocity deficit and width is found to be very similar for all the adversely strained cases, with both measures rapidly achieving exponential growth at the rate associated with the cross-stream expansive strain e(sup at). In the "favourably" strained cases, the wake widths approach a constant and the velocity deficits ultimately decay rapidly as e(sup -2at). Although all three of these cases do exhibit the same asymptotic exponential behaviour, the time required to achieve this is longer for the cases that have been previously adversely strained (by at approx. equals 1). These simulations confirm the generality of the conclusions drawn in Rogers (2002) regarding the response of plane wakes to strain. The evolution of strained wakes is not consistent with the predictions of classical self-similar analysis; a more general equilibrium similarity solution is required to describe the results. At least for the cases considered here, the wake Reynolds number and the ratio of the turbulent kinetic energy to the square of the wake mean velocity deficit are determined nearly entirely by the total strain. For these measures the order in which the strains are applied does not matter and the changes brought about by the strain are nearly reversible. The wake mean velocity deficit and width, on the other hand, differ by about a factor of three when the total strain returns to one, depending on whether the wake was first "favourably" or "adversely" strained. The strain history is important for predicting the evolution of these quantities.

Rogers, Michael M.

2003-01-01

126

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

127

Evaluation of a Wake Vortex Upset Model Based on Simultaneous Measurements of Wake Velocities and Probe-Aircraft Accelerations  

NASA Technical Reports Server (NTRS)

Simultaneous measurements were made of the upset responses experienced and the wake velocities encountered by an instrumented Learjet probe aircraft behind a Boeing 747 vortex-generating aircraft. The vortex-induced angular accelerations experienced could be predicted within 30% by a mathematical upset response model when the characteristics of the wake were well represented by the vortex model. The vortex model used in the present study adequately represented the wake flow field when the vortices dissipated symmetrically and only one vortex pair existed in the wake.

Short, B. J.; Jacobsen, R. A.

1979-01-01

128

Studies of a flat wake rotor theory  

NASA Technical Reports Server (NTRS)

A computer code was developed at Princeton University to calculate the velocity components in the flow field near a lifting rotor. The induced velocity components in the rotor flow field predicted by this theory are compared with experiment. It appears that on balance, this relatively simple theory gives a reasonable prediction of the average induced velocities in a rotor flow and is quite suitable for such applications as estimating the influence of the rotor wake on the tail surfaces of rotorcraft. The theory predicts that significant induced velocity components are present in all three flow directions in the wake at a lifting rotor. It should be noted , however, that there are a few experimental measurements of the longitudinal and lateral induced velocity components in the rotor wake. This theory, known as the flat wake theory, is essentially the rotary wing analog of Prandtl's lifting line theory. The theory is described in this report. Calculations based on the theory are presented and compared with a modern free wake theory.

Curtiss, H. C., Jr.; Mckillip, R. M., Jr.

1992-01-01

129

Use of disease-suppressive Brassica rotation crops in potato production: overview of 10 years of field trials  

Technology Transfer Automated Retrieval System (TEKTRAN)

Disease-suppressive Brassica rotation crops have shown promise for management of soilborne diseases and enhanced yield in a variety of crop production systems. Over the last 10 years, numerous field trials have focused on how to best use Brassica crops in potato rotations in the Northeast, including...

130

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

131

Dissipation of turbulence in the wake of a wind turbine  

NASA Astrophysics Data System (ADS)

The wake of a wind turbine is characterized by increased turbulence and decreased wind speed. Turbines are generally deployed in large groups in wind farms, and so the behavior of an individual wake as it merges with other wakes and propagates downwind is of great importance in assessing wind farm power production as well as impacts of wind energy deployment on local and regional environments. The rate of turbulence dissipation in the wake quantifies the wake behavior as it propagates. In situ field measurements of turbulence dissipation rate in the wake of wind turbines have not been previously collected although correct modeling of dissipation rate is required for accurate simulations of wake evolution. In Fall 2012, we collected in situ measurements of winds and turbulence dissipation from the wake region of a multi-MW turbine, using the University of Colorado at Boulder's Tethered Lifting System (TLS). The TLS is a unique state-of-the-art tethersonde, proven in numerous boundary-layer field experiments to be able to measure turbulence kinetic energy dissipation rates. Ambient flow measurements were provided from sonic anemometers on a meteorological tower located upwind of the turbine, from a profiling lidar upwind, and from a scanning lidar measuring both inflow to and wake from the turbine. Measurements collected within the wake indicate that dissipation rates are higher in the turbine wake than in the ambient flow. Profiles of dissipation and turbulence throughout the rotor disk suggest that dissipation peaks near the hub height of the turbine. Suggestions for incorporating this information into wind turbine modeling approaches will be provided.

Lundquist, J. K.; Bariteau, L.

2013-12-01

132

Wake Vortex Sensors Requirements Overview  

NASA Technical Reports Server (NTRS)

The presentation includes discussions of primary wake vortex system requirements, evolution models, sensor evolution, site specific sensor tradeoffs, wake sensor functions, deployment considerations, the operational test bed system and additional sensor requirements.

Hinton, David A.

1997-01-01

133

Wake Studies of Ornithopters  

NASA Astrophysics Data System (ADS)

This paper details experiments using a mechanical ornithopter flying in a low speed wind tunnel. Experiments were conducted for a Strouhal number of 0.3 and Reynolds number of 2300, Particle Image Velocimetry (PIV) and flow visualization was used to develop quantitative and qualitative information about the nature of the wake. The data shows that the wake is made of a series of discrete vortex rings. The impulse of these rings has been estimated with PIV data and the results correlate well with the lift required to sustain the ornithopter in flight.

Juarez, Alfredo; Harlow, Jacob; Allen, James; Ferreira de Sousa, Paulo

2006-11-01

134

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

135

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

136

Wake-promoting pharmacotherapy for psychiatric disorders.  

PubMed

Medications promoting wakefulness are currently used in psychopharmacology in different contexts and with different objectives. In particular, they may be used for the treatment of syndromes that primarily show significant impairment in alertness/wakefulness (e.g., excessive sleepiness and other sleep disorders) as well as for the symptomatic treatment of different neuropsychiatric disorders that, in turn, are not exclusively characterized by sleep-wake disturbances (like mood disorders, for instance). In addition, several psychotropic compounds, including some antipsychotics, mood stabilizers, antidepressants, and anxiolytics have well-established sedating side effects that may go beyond the therapeutic target and require the symptomatic use of wake-promoting agents. Even though such a clinical scenario reflects millions of individuals affected (alterations of wakefulness have a prevalence rate of 20-43% in the general population), relatively few pharmacotherapies are available, mainly including compounds with psychostimulating effects, such as methylphenidate, modafinil, and armodafinil and some amphetaminic agents. In light of their side effects and potential for abuse, such compounds have received FDA approval only for a limited number of psychiatric disorders. Nonetheless, their clinical application has recently become more widespread, including attention deficit hyperactivity disorder, narcolepsy, treatment-resistant depression, bipolar disorder, shift work sleep disorder, schizophrenia, and addictions. Wake-promoting agents have different mechanisms of action, peculiar clinical strengths and specific limitations, with novel drugs in the field under extensive investigation. The present review is aimed to provide an updated overview of the aforementioned compounds as well as investigational drugs in the field, in terms of mechanism of action, indications and use in clinical practice. PMID:25312027

Dell'Osso, Bernardo; Dobrea, Cristina; Cremaschi, Laura; Arici, Chiara; Altamura, A Carlo

2014-12-01

137

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

PubMed Central

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

2013-01-01

138

Pedestal Bifurcation and Resonant Field Penetration at the Threshold of Edge-Localized Mode Suppression in the DIII-D Tokamak.  

PubMed

Rapid bifurcations in the plasma response to slowly varying n=2 magnetic fields are observed as the plasma transitions into and out of edge-localized mode (ELM) suppression. The rapid transition to ELM suppression is characterized by an increase in the toroidal rotation and a reduction in the electron pressure gradient at the top of the pedestal that reduces the perpendicular electron flow there to near zero. These events occur simultaneously with an increase in the inner-wall magnetic response. These observations are consistent with strong resonant field penetration of n=2 fields at the onset of ELM suppression, based on extended MHD simulations using measured plasma profiles. Spontaneous transitions into (and out of) ELM suppression with a static applied n=2 field indicate competing mechanisms of screening and penetration of resonant fields near threshold conditions. Magnetic measurements reveal evidence for the unlocking and rotation of tearinglike structures as the plasma transitions out of ELM suppression. PMID:25815938

Nazikian, R; Paz-Soldan, C; Callen, J D; deGrassie, J S; Eldon, D; Evans, T E; Ferraro, N M; Grierson, B A; Groebner, R J; Haskey, S R; Hegna, C C; King, J D; Logan, N C; McKee, G R; Moyer, R A; Okabayashi, M; Orlov, D M; Osborne, T H; Park, J-K; Rhodes, T L; Shafer, M W; Snyder, P B; Solomon, W M; Strait, E J; Wade, M R

2015-03-13

139

Pedestal Bifurcation and Resonant Field Penetration at the Threshold of Edge-Localized Mode Suppression in the DIII-D Tokamak  

NASA Astrophysics Data System (ADS)

Rapid bifurcations in the plasma response to slowly varying n =2 magnetic fields are observed as the plasma transitions into and out of edge-localized mode (ELM) suppression. The rapid transition to ELM suppression is characterized by an increase in the toroidal rotation and a reduction in the electron pressure gradient at the top of the pedestal that reduces the perpendicular electron flow there to near zero. These events occur simultaneously with an increase in the inner-wall magnetic response. These observations are consistent with strong resonant field penetration of n =2 fields at the onset of ELM suppression, based on extended MHD simulations using measured plasma profiles. Spontaneous transitions into (and out of) ELM suppression with a static applied n =2 field indicate competing mechanisms of screening and penetration of resonant fields near threshold conditions. Magnetic measurements reveal evidence for the unlocking and rotation of tearinglike structures as the plasma transitions out of ELM suppression.

Nazikian, R.; Paz-Soldan, C.; Callen, J. D.; deGrassie, J. S.; Eldon, D.; Evans, T. E.; Ferraro, N. M.; Grierson, B. A.; Groebner, R. J.; Haskey, S. R.; Hegna, C. C.; King, J. D.; Logan, N. C.; McKee, G. R.; Moyer, R. A.; Okabayashi, M.; Orlov, D. M.; Osborne, T. H.; Park, J.-K.; Rhodes, T. L.; Shafer, M. W.; Snyder, P. B.; Solomon, W. M.; Strait, E. J.; Wade, M. R.

2015-03-01

140

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

141

Wake Vortex Advisory System (WakeVAS) Concept of Operations  

NASA Technical Reports Server (NTRS)

NASA Langley Research Center has a long history of aircraft wake vortex research, with the most recent accomplishment of demonstrating the Aircraft VOrtex Spacing System (AVOSS) at Dallas/Forth Worth International Airport in July 2000. The AVOSS was a concept for an integration of technologies applied to providing dynamic wake-safe reduced spacing for single runway arrivals, as compared to current separation standards applied during instrument approaches. AVOSS included state-of-the-art weather sensors, wake sensors, and a wake behavior prediction algorithm. Using real-time data AVOSS averaged a 6% potential throughput increase over current standards. This report describes a Concept of Operations for applying the technologies demonstrated in the AVOSS to a variety of terminal operations to mitigate wake vortex capacity constraints. A discussion of the technological issues and open research questions that must be addressed to design a Wake Vortex Advisory System (WakeVAS) is included.

Rutishauser, David; Lohr, Gary; Hamilton, David; Powers, Robert; McKissick, Burnell; Adams, Catherine; Norris, Edward

2003-01-01

142

Electromagnetic signature of human cortical dynamics during wakefulness and sleep  

E-print Network

Electromagnetic signature of human cortical dynamics during wakefulness and sleep Signature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.5 Spatial reach of LFP & Electromagnetic Lead field . . . . . . . . . . . . . . . 35 2 Studies 45 4 Overview 47 4.1 Electromagnetic properties of the extracellular medium

Destexhe, Alain

143

Interaction of Aircraft Wakes From Laterally Spaced Aircraft  

NASA Technical Reports Server (NTRS)

Large Eddy Simulations are used to examine wake interactions from aircraft on closely spaced parallel paths. Two sets of experiments are conducted, with the first set examining wake interactions out of ground effect (OGE) and the second set for in ground effect (IGE). The initial wake field for each aircraft represents a rolled-up wake vortex pair generated by a B-747. Parametric sets include wake interactions from aircraft pairs with lateral separations of 400, 500, 600, and 750 ft. The simulation of a wake from a single aircraft is used as baseline. The study shows that wake vortices from either a pair or a formation of B-747 s that fly with very close lateral spacing, last longer than those from an isolated B-747. For OGE, the inner vortices between the pair of aircraft, ascend, link and quickly dissipate, leaving the outer vortices to decay and descend slowly. For the IGE scenario, the inner vortices ascend and last longer, while the outer vortices decay from ground interaction at a rate similar to that expected from an isolated aircraft. Both OGE and IGE scenarios produce longer-lasting wakes for aircraft with separations less than 600 ft. The results are significant because concepts to increase airport capacity have been proposed that assume either aircraft formations and/or aircraft pairs landing on very closely spaced runways.

Proctor, Fred H.

2009-01-01

144

Direct Numerical Simulation of a Weakly Stratified Turbulent Wake  

NASA Technical Reports Server (NTRS)

Direct numerical simulation (DNS) is used to investigate a time-dependent turbulent wake evolving in a stably stratified background. A large initial Froude number is chosen to allow the wake to become fully turbulent and axisymmetric before stratification affects the spreading rate of the mean defect. The uncertainty introduced by the finite sample size associated with gathering statistics from a simulation of a time-dependent flow is reduced, compared to earlier simulations of this flow. The DNS reveals the buoyancy-induced changes to the turbulence structure, as well as to the mean-defect history and the terms in the mean-momentum and turbulence-kinetic-energy budgets, that characterize the various states of this flow - namely the three-dimensional (essentially unstratified), non-equilibrium (or 'wake-collapse') and quasi-two-dimensional (or 'two-component') regimes observed elsewhere for wakes embedded in both weakly and strongly stratified backgrounds. The wake-collapse regime is not accompanied by transfer (or 'reconversion') of the potential energy of the turbulence to the kinetic energy of the turbulence, implying that this is not an essential feature of stratified-wake dynamics. The dependence upon Reynolds number of the duration of the wake-collapse period is demonstrated, and the effect of the details of the initial/near-field conditions of the wake on its subsequent development is examined.

Redford, J. A.; Lund, T. S.; Coleman, Gary N.

2014-01-01

145

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

E-print Network

with the solar wind were found by the IMP-1 satellite (Ness et al., 1964; Ness, 1965). Later, the magnetic field the existence of a lunar wake (Ness et al., 1967). This pioneering mission revealed the low electric

California at Berkeley, University of

146

Passive Wake Vortex Control  

SciTech Connect

The collapse of the Soviet Union and ending of the Cold War brought about many significant changes in military submarine operations. The enemies that the US Navy faces today and in the future will not likely be superpowers armed with nuclear submarines, but rather smaller, rogue nations employing cheaper diesel/electric submarines with advanced air-independent propulsion systems. Unlike Cold War submarine operations, which occurred in deep-water environments, future submarine conflicts are anticipated to occur in shallow, littoral regions that are complex and noisy. Consequently, non-acoustic signatures will become increasingly important and the submarine stealth technology designed for deep-water operations may not be effective in these environments. One such non-acoustic signature is the surface detection of a submarine's trailing vortex wake. If a submarine runs in a slightly buoyant condition, its diving planes must be inclined at a negative angle of attack to generate sufficient downforce, which keeps the submarine from rising to the surface. As a result, the diving planes produce a pair of counter-rotating trailing vortices that propagate to the water surface. In previous deep-water operations, this was not an issue since the submarines could dive deep enough so that the vortex pair became incoherent before it reached the water surface. However, in shallow, littoral environments, submarines do not have the option of diving deep and, hence, the vortex pair can rise to the surface and leave a distinct signature that might be detectable by synthetic aperture radar. Such detection would jeopardize not only the mission of the submarine, but also the lives of military personnel on board. There has been another attempt to solve this problem and reduce the intensity of trailing vortices in the wakes of military submarines. The research of Quackenbush et al. over the past few years has been directed towards an idea called ''vortex leveraging.'' This active concept works by placing shape memory alloy (SMA) control surfaces on the submarine's diving planes and periodically oscillating them. The modulated control vortices generated by these surfaces interact with the tip vortices on the diving planes, causing an instability to rapidly occur. Though several numerical simulations have been presented, experimental verification does not appear to be available in the open literature. The authors address this problem through a concept called passive wake vortex control (PWVC), which has been demonstrated to rapidly break apart a trailing vortex wake and render it incoherent. PWVC functions by introducing unequal strength, counter-rotating control vortices next to the tip vortices. The presence of these control vortices destabilizes the vortex wake and produces a rapidly growing wake instability.

Ortega, J M

2001-10-18

147

Particle Access and Charging Environments in the Lunar Wake  

NASA Technical Reports Server (NTRS)

A plasma wake a region of low density, high temperature plasma forms on the far side of the Moon when solar wind, magnetosheath, and magnetotail plasma flows past the Moon [Manka, 1973; Ogilvie et al., 1996; Farrell et al., 1998; Halekas et al., 2005]. Ion populations in these flows typically have much smaller thermal velocity than bulk speed and are therefore excluded from the plasma wake while the large thermal electron velocity allows the lighter negatively charged particles to stream ahead of the ions into the wake. Charge separation due to electrons streaming ahead of the ions into the wake from the wake boundary establishes an ambipolar electric field which impedes the motion of electron flow and accelerates ions into the wake [Ogilvie et al., 1996; Farrell et al., 1997]. We have conducted a theoretical study of acceleration (and deceleration) of charged particles in lunar plasma environments, which investigated the mechanisms responsible for allowing solar wind entry into the lunar wake, and for producing energetic particle distributions observed within the lunar wake. To this end, the investigation utilized a macroscale 3D hybrid particle-in-cell numerical model of the interaction of the Moon with external plasma environments to compute electric fields in the lunar environment for a variety of external plasma conditions and interplanetary magnetic field orientations. Ion dynamics were attained from the hybrid code while electron dynamics were determined by considering electron test particle trajectories through the fields established in the hybrid code. Results from the code will be presented to evaluate charging environments within the lunar wake.

Parker, Linda; Minow, Joseph; Singh, Nagendra; Araveti, Venkata S.; Venkiteswaran, Karthik

2010-01-01

148

Speckle suppression via sparse representation for wide-field imaging through turbid media.  

PubMed

Speckle suppression is one of the most important tasks in the image transmission through turbid media. Insufficient speckle suppression requires an additional procedure such as temporal ensemble averaging over multiple exposures. In this paper, we consider the image recovery process based on the so-called transmission matrix (TM) of turbid media for the image transmission through the media. We show that the speckle left unremoved in the TM-based image recovery can be suppressed effectively via sparse representation (SR). SR is a relatively new signal reconstruction framework which works well even for ill-conditioned problems. This is the first study to show the benefit of using the SR as compared to the phase conjugation (PC) a de facto standard method to date for TM-based imaging through turbid media including a live cell through tissue slice. PMID:24977910

Jang, Hwanchol; Yoon, Changhyeong; Chung, Euiheon; Choi, Wonshik; Lee, Heung-No

2014-06-30

149

First Lunar Wake Passage of ARTEMIS: Discrimination of Wake Effects and Solar Wind Fluctuations by 3D Hybrid Simulations  

NASA Technical Reports Server (NTRS)

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.

2011-01-01

150

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.

151

Statistical Study of the Lunar Plasma Wake Outer Boundary  

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 of solar wind particles on the day side and the generation of a plasma wake on the night side. A plasma density gradient forms between the flowing solar wind and the plasma wake, causing solar wind plasma to gradually refill the wake region. Electrons fill the wake first, pulling ions in after them via ambi-polar diffusion. Despite the existence of comprehensive new plasma measurements of the lunar wake region, relatively little attention has been devoted to the shape and variability in location of its outer boundary. Improved knowledge of this boundary condition for the physical processes associated with wake refilling would provide useful tests for simulations and theoretical models of the lunar plasma interaction. 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, at distances of up to seven lunar radii from the Moon. They have occurred for a variety of external conditions. We present a statistical study of tens of selected wake-crossing events of the ARTEMIS probes in 2011, using data primarily from the ARTEMIS fluxgate magnetometers (FGMs) and electrostatic analyzers (ESAs) to identify when the spacecraft entered and exited the wake. We study the shape of the outer wake boundary and its response to external conditions using two different techniques: one defines the wake boundary by a sharp decrease in ion density, the other by a decrease in magnetic field magnitude. We investigate how the wake boundary changes in response to solar wind parameters such as plasma beta, ion velocity, ion temperature, and magnetic field cone and clock angles. These results are compared with earlier wake crossing studies and computational modeling.

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

2012-12-01

152

Evidence of Magnetic Breakdown on the Defects With Thermally Suppressed Critical Field in High Gradient SRF Cavities  

SciTech Connect

At SRF 2011 we presented the study of quenches in high gradient SRF cavities with dual mode excitation technique. The data differed from measurements done in 80's that indicated thermal breakdown nature of quenches in SRF cavities. In this contribution we present analysis of the data that indicates that our recent data for high gradient quenches is consistent with the magnetic breakdown on the defects with thermally suppressed critical field. From the parametric fits derived within the model we estimate the critical breakdown fields.

Eremeev, Grigory [JLAB; Palczewski, Ari [JLAB

2013-09-01

153

Speech-induced suppression of evoked auditory fields in children who stutter Deryk S. Beal a,  

E-print Network

Gill University, Montreal, Qc., Canada g Haskins Laboratories, New Haven, CT, USA h Toronto Western Research Institute, University Health Network, Toronto, Ont., Canada a b s t r a c ta r t i c l e i n f o Article, examining speech-induced suppression in children may identify possible neural differences underlying

154

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

2013-08-01

155

Wake in faint television meteors  

NASA Technical Reports Server (NTRS)

The two component dustball model was used in numerical lag computation. Detached grain lag is typically less than 2 km, with expected wakes of a few hundred meters. True wake in television meteors is masked by apparent wake due to the combined effects of image persistence and blooming. To partially circumvent this problem, we modified a dual MCP intensified CID video system by addition of a rotating shutter to reduce the effective exposure time to about 2.0 ms. Preliminary observations showed that only 2 of 27 analyzed meteors displayed statistically significant wake.

Robertson, M. C.; Hawkes, Robert L.

1992-01-01

156

Wake-Up Call  

NSDL National Science Digital Library

The main character of this case is Denise, who we first meet in the early morning hours as she wakes up in a cold sweat, gasping for breath. But it is her husband, Jeremy, who has been diagnosed with heart disease, not her. What’s going on? In this interrupted case study, in which the other main character is Denise’s heart (who we get to know through a series of “interior” monologues), students learn about the risk factors, symptoms, and consequences of a heart attack. The case is suitable for a course in pathophysiology, first year nursing, enzymology, advanced biology or anatomy, or nutrition.

Lisa Marie Rubin

2002-01-01

157

Phantom for assessment of fat suppression in large field-of-view diffusion-weighted magnetic resonance imaging  

NASA Astrophysics Data System (ADS)

We present the development and application of a phantom for assessment and optimization of fat suppression over a large field-of-view in diffusion-weighted magnetic resonance imaging at 1.5 T and 3 T. A Perspex cylinder (inner diameter 185 mm, height 300 mm) which contains a second cylinder (inner diameter 140 mm) was constructed. The inner cylinder was filled with water doped with copper sulphate and sodium chloride and the annulus was filled with corn oil, which closely matches the spectrum and longitudinal relaxation times of subcutaneous abdominal fat. Placement of the phantom on the couch at 45° to the z-axis presented an elliptical cross-section, which was of a similar size and shape to axial abdominal images. The use of a phantom for optimization of fat suppression allowed quantitative comparison between studies without the differences introduced by variability between human subjects. We have demonstrated that the phantom is suitable for selection of inversion delay times, spectral adiabatic inversion recovery delays and assessment of combinatorial methods of fat suppression. The phantom is valuable in protocol development and the assessment of new techniques, particularly in multi-centre trials.

Winfield, J. M.; Douglas, N. H. M.; deSouza, N. M.; Collins, D. J.

2014-05-01

158

Chitin Amendment Increases Soil Suppressiveness toward Plant Pathogens and Modulates the Actinobacterial and Oxalobacteraceal Communities in an Experimental Agricultural Field  

PubMed Central

A long-term experiment on the effect of chitin addition to soil on the suppression of soilborne pathogens was set up and monitored for 8 years in an experimental field, Vredepeel, The Netherlands. Chitinous matter obtained from shrimps was added to soil top layers on two different occasions, and the suppressiveness of soil toward Verticillium dahliae, as well as plant-pathogenic nematodes, was assessed, in addition to analyses of the abundances and community structures of members of the soil microbiota. The data revealed that chitin amendment had raised the suppressiveness of soil, in particular toward Verticillium dahliae, 9 months after the (second) treatment, extending to 2 years following treatment. Moreover, major effects of the added chitin on the soil microbial communities were detected. First, shifts in both the abundances and structures of the chitin-treated soil microbial communities, both of total soil bacteria and fungi, were found. In addition, the abundances and structures of soil actinobacteria and the Oxalobacteraceae were affected by chitin. At the functional gene level, the abundance of specific (family-18 glycoside hydrolase) chitinase genes carried by the soil bacteria also revealed upshifts as a result of the added chitin. The effects of chitin noted for the Oxalobacteraceae were specifically related to significant upshifts in the abundances of the species Duganella violaceinigra and Massilia plicata. These effects of chitin persisted over the time of the experiment. PMID:23811512

Cretoiu, Mariana Silvia; Korthals, Gerard W.; Visser, Johnny H. M.

2013-01-01

159

Wake Measurements in ECN's Scaled Wind Farm  

NASA Astrophysics Data System (ADS)

In ECN's scaled wind farm the wake evolution is studied in two different situations. A single wake is studied at two different locations downstream of a turbine and a single wake is studied in conjunction with a triple wake. Here, the wake is characterized by the relative wind speed, the turbulence intensity, the vertical wind speed and the turbulence (an)isotropy. Per situation all wake measurements are taken simultaneously together with the inflow conditions.

Wagenaar, J. W.; Schepers, J. G.

2014-12-01

160

A new methodology for free wake analysis using curved vortex elements  

NASA Technical Reports Server (NTRS)

A method using curved vortex elements was developed for helicopter rotor free wake calculations. The Basic Curve Vortex Element (BCVE) is derived from the approximate Biot-Savart integration for a parabolic arc filament. When used in conjunction with a scheme to fit the elements along a vortex filament contour, this method has a significant advantage in overall accuracy and efficiency when compared to the traditional straight-line element approach. A theoretical and numerical analysis shows that free wake flows involving close interactions between filaments should utilize curved vortex elements in order to guarantee a consistent level of accuracy. The curved element method was implemented into a forward flight free wake analysis, featuring an adaptive far wake model that utilizes free wake information to extend the vortex filaments beyond the free wake regions. The curved vortex element free wake, coupled with this far wake model, exhibited rapid convergence, even in regions where the free wake and far wake turns are interlaced. Sample calculations are presented for tip vortex motion at various advance ratios for single and multiple blade rotors. Cross-flow plots reveal that the overall downstream wake flow resembles a trailing vortex pair. A preliminary assessment shows that the rotor downwash field is insensitive to element size, even for relatively large curved elements.

Bliss, Donald B.; Teske, Milton E.; Quackenbush, Todd R.

1987-01-01

161

. . . are going to wake up!  

E-print Network

, Number one, March 1906. Quote: Sooner or later the American people are going to wake up! Emma Goldman. . . are going to wake up! Sooner or later the American people . . . #12;With high hopes: A Documentary History of the American Years 1890-1919, our four-volume series. Volume 1: Made for America 1890

California at Berkeley, University of

162

Binocular Neurons in Parastriate Cortex: Interocular ‘Matching’ of Receptive Field Properties, Eye Dominance and Strength of Silent Suppression  

PubMed Central

Spike-responses of single binocular neurons were recorded from a distinct part of primary visual cortex, the parastriate cortex (cytoarchitectonic area 18) of anaesthetized and immobilized domestic cats. Functional identification of neurons was based on the ratios of phase-variant (F1) component to the mean firing rate (F0) of their spike-responses to optimized (orientation, direction, spatial and temporal frequencies and size) sine-wave-luminance-modulated drifting grating patches presented separately via each eye. In over 95% of neurons, the interocular differences in the phase-sensitivities (differences in F1/F0 spike-response ratios) were small (?0.3) and in over 80% of neurons, the interocular differences in preferred orientations were ?10°. The interocular correlations of the direction selectivity indices and optimal spatial frequencies, like those of the phase sensitivies and optimal orientations, were also strong (coefficients of correlation r ?0.7005). By contrast, the interocular correlations of the optimal temporal frequencies, the diameters of summation areas of the excitatory responses and suppression indices were weak (coefficients of correlation r ?0.4585). In cells with high eye dominance indices (HEDI cells), the mean magnitudes of suppressions evoked by stimulation of silent, extra-classical receptive fields via the non-dominant eyes, were significantly greater than those when the stimuli were presented via the dominant eyes. We argue that the well documented ‘eye-origin specific’ segregation of the lateral geniculate inputs underpinning distinct eye dominance columns in primary visual cortices of mammals with frontally positioned eyes (distinct eye dominance columns), combined with significant interocular differences in the strength of silent suppressive fields, putatively contribute to binocular stereoscopic vision. PMID:24927276

Wang, Chun; Dreher, Bogdan

2014-01-01

163

An analysis of wake-stator interaction in airfoil cascades  

NASA Astrophysics Data System (ADS)

A computational study has been conducted in order to provide insight into the details of the unsteady flow in the leading-edge region of airfoil cascades during wake-stator interaction. The calculations are performed at off-design operating conditions, since the flow at conditions near to those at which stall onset occurs is of particular interest in helping to understand the mechanisms responsible for compressor stall. A thorough understanding of these mechanisms will provide the underpinnings needed to design compressors with favorable stall characteristics, using fewer design iterations than are typical with the present state of the art. The results obtained during this study show that the use of highly refined grids leads to the resolution of complex unsteady phenomena associated with wake-stator interaction. The structure of the interaction is shown to change significantly as the magnitude of the wake deficit is increased, with shedding from the leading-edge separation bubble suppressed compared to that observed for the cases with small wake deficit or no wake disturbance.

Barnett, M.; Sondak, D. L.

1995-03-01

164

Mesoscale Simulation Data for Initializing Fast-Time Wake Transport and Decay Models  

NASA Technical Reports Server (NTRS)

The fast-time wake transport and decay models require vertical profiles of crosswinds, potential temperature and the eddy dissipation rate as initial conditions. These inputs are normally obtained from various field sensors. In case of data-denied scenarios or operational use, these initial conditions can be provided by mesoscale model simulations. In this study, the vertical profiles of potential temperature from a mesoscale model were used as initial conditions for the fast-time wake models. The mesoscale model simulations were compared against available observations and the wake model predictions were compared with the Lidar measurements from three wake vortex field experiments.

Ahmad, Nashat N.; Proctor, Fred H.; Vanvalkenburg, Randal L.; Pruis, Mathew J.; LimonDuparcmeur, Fanny M.

2012-01-01

165

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 (PPPM) code ddcMD and the particle-in-cell (PIC) code BEPS to perform these simulations. As a starting point in our study, we examine the wake of a particle passing through a plasma in 3D electrostatic simulations performed with ddcMD and with BEPS using various cell sizes. In this poster, we compare the wakes we observe in these simulations with each other and predictions from Vlasov theory.

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

2011-11-01

166

A Circuit-Level Model of Hippocampal Place Field Dynamics Modulated by Entorhinal Grid and Suppression-Generating Cells  

PubMed Central

Hippocampal “place cells” and the precession of their extracellularly recorded spiking during traversal of a “place field” are well-established phenomena. More recent experiments describe associated entorhinal “grid cell” firing, but to date only conceptual models have been offered to explain the potential interactions among entorhinal cortex (EC) and hippocampus. To better understand not only spatial navigation, but mechanisms of episodic and semantic memory consolidation and reconsolidation, more detailed physiological models are needed to guide confirmatory experiments. Here, we report the results of a putative entorhinal-hippocampal circuit level model that incorporates recurrent asynchronous-irregular non-linear (RAIN) dynamics, in the context of recent in vivo findings showing specific intracellular–extracellular precession disparities and place field destabilization by entorhinal lesioning. In particular, during computer-simulated rodent maze navigation, our model demonstrate asymmetric ramp-like depolarization, increased theta power, and frequency (that can explain the phase precession disparity), and a role for STDP and KAHP channels. Additionally, we propose distinct roles for two entorhinal cell populations projecting to hippocampus. Grid cell populations transiently trigger place field activity, while tonic “suppression-generating cell” populations minimize aberrant place cell activation, and limit the number of active place cells during traversal of a given field. Applied to place-cell RAIN networks, this tonic suppression explains an otherwise seemingly discordant association with overall increased firing. The findings of this circuit level model suggest in vivo and in vitro experiments that could refute or support the proposed mechanisms of place cell dynamics and modulating influences of EC. PMID:21151359

Jayet Bray, Laurence C.; Quoy, Mathias; Harris, Frederick C.; Goodman, Philip H.

2010-01-01

167

An optically modulated zero-field atomic magnetometer with suppressed spin-exchange broadening  

SciTech Connect

We demonstrate an optically pumped {sup 87}Rb magnetometer in a microfabricated vapor cell based on a zero-field dispersive resonance generated by optical modulation of the {sup 87}Rb ground state energy levels. The magnetometer is operated in the spin-exchange relaxation-free regime where high magnetic field sensitivities can be achieved. This device can be useful in applications requiring array-based magnetometers where radio frequency magnetic fields can induce cross-talk among adjacent sensors or affect the source of the magnetic field being measured.

Jiménez-Martínez, R. [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States) [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States); Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States); Knappe, S.; Kitching, J. [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States)] [Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States)

2014-04-15

168

Enhancement or Suppression of the Near-Field Radiative Heat Transfer Between Two Materials  

Microsoft Academic Search

Control of near-field radiative heat transfer is significant due to its practical applications. We propose an approach to control near-field thermal radiation between two closely spaced bodies by inserting a suspended thin film. Numerical simulations are carried out for different material combinations of doped silicon and aluminum (Al). Investigation showed that the heat flux between the two bodies can be

Z. H. Zheng; Y. M. Xuan

2011-01-01

169

Suppressing decoherence of spin waves in a warm atomic vapor by applying a guiding magnetic field  

NASA Astrophysics Data System (ADS)

We report an experimental and theoretical investigation to extend lifetimes of light storages by applying guiding magnetic fields in a room-temperature atomic vapor. The storages are based on dynamic electromagnetically induced transparency. Retrieval efficiencies versus storage time are experimentally measured for different strengths of the guiding magnetic fields. The measured results show that the 1/e storage times are ˜6 ?s and ˜59 ?s for the guiding field B0z = 0 and B0z = 93 mG, respectively. Physical processes causing decoherence in an atomic ensemble have been discussed and analyzed. A theory model which is used to evaluate the decoherence caused by fluctuations of transverse magnetic fields is developed. Based on this evaluation, the fact that storage lifetimes can be increased by applying guiding magnetic fields is well explained.

Tian, Long; Li, Shujing; Zhang, Zhiying; Wang, Hai

2015-02-01

170

Bubbly wake of surface vessels  

NASA Astrophysics Data System (ADS)

We study the length of the bubbly wake of surface vessels. This wake is important for the boat security since it can extend to several ship length and thus increases the detectability of the ship by torpedoes. The image analysis of the wake of real scale ships reveals the sensitivity of the length to propellers. We have thus conducted a systematic study in the laboratory of the interaction bubble/propeller, trying to address several questions:- what is the role of cavitation?- is the propeller able to attract the bubbles present along the ship at the sea surface?- if attracted, can these bubble be broken by the propeller?

Caillé, François; Magnaudet, Jacques; Clanet, Christophe

2006-11-01

171

Wake Turbulence Mitigation for Arrivals (WTMA)  

NASA Technical Reports Server (NTRS)

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 the Wake Turbulence Mitigation for Departure concept. Anticipated benefits about reducing wake turbulence separation standards in crosswind conditions, and candidate WTMA system considerations are discussed.

Williams, Daniel M.; Lohr, Gary W.; Trujillo, Anna C.

2008-01-01

172

Wind Turbine Wake Experiment - Wieringermeer (WINTWEX-W)  

NASA Astrophysics Data System (ADS)

The Wind Turbine Wake Experiment - Wieringermeer (WINTWEX-W) is a cooperative wake measurement campaign conducted by the Norwegian Centre of Offshore Wind Energy (Norcowe) and the Energy Research Centre of the Netherlands (ECN). A scanning, four static Windcubes as well as a downstream looking nacelle LiDAR are placed for half a year downstream of one of five research wind turbines in ECNs' wind turbine test farm Wieringermeer. In order to capture wake characteristics under different weather conditions a 60° sector for three different elevations and two vertical cross-sections are scanned every minute with additional wind profile information every second at 2, 5 and 12 rotor diameter distances. Another static Windcube, a forward-looking nacelle LiDAR and three Sonics are placed upstream to measure the undisturbed approaching flow field. During the campaign several scanning algorithms are tested to capture most wake features. The aim of the campaign is a qualitative and quantitative description of single wind turbine wake evolution, propagation and persistency, as well as to improve CFD wake models by delivering a detailed data set of several real atmospheric conditions.

Kumer, Valerie; Reuder, Joachim; Svardal, Benny; Eecen, Peter

2014-05-01

173

The POLAR code wake model: Comparison with in situ observations  

SciTech Connect

Measurements of the ion and electron densities associated with the wake of the shuttle orbiter were made by the Plasma Diagnostics Package (PDP) during the 1985 Spacelab 2 mission. Cross sections of the wake at distances of 50-250 m downstream and measurements along the wake axis from 5 to 100 m were obtained. The POLAR wake model, developed for The Air Force Geophysics Laboratory to study charging of spacecraft in low-altitude high-inclination orbits, was used to perform a three-dimensional simulation of the plasma wake evaluated at points along relative trajectory of the PDP. The POLAR code uses several simplifying assumptions to predict wake densities. These include neglecting the magnetic field and assuming that the plasma is quasi-neutral. The code models plasma density ahead of the expansion front, using a neutral approximation, and models the plasma density behind the expansion front by using the self-similar solution of the expansion of a plasma into a vacuum. For cases where T{sub i} {approx} T{sub e}, the front is not sharp and thermal motion can account for most of the expansion. This approach is computationally very efficient. The results presented here are the first known comparison between such a model and actual in situ data obtained for objects of scale size {approx} 10{sup 4} {lambda}{sub d}. Excellent qualitative and quantitative agreement are found at distances greater than {approx} 30 m.

Murphy, G. (Jet Propulsion Lab., Pasadena, CA (USA)); Katz, I. (S-Cubed, La Jolla, CA (USA))

1989-07-01

174

Atmospheric-wake vortex interactions  

NASA Technical Reports Server (NTRS)

The interactions of a vortex wake with a turbulent stratified atmosphere are investigated with the computer code WAKE. It is shown that atmospheric shear, turbulence, and stratification can provide the dominant mechanisms by which vortex wakes decay. Computations included the interaction of a vortex wake with a viscous ground plane. The observed phenomenon of vortex bounce is explained in terms of secondary vorticity produced on the ground. This vorticity is swept off the ground and advected about the vortex pair, thereby altering the classic hyperbolic trajectory. The phenomenon of the solitary vortex is explained as an interaction of a vortex with crosswind shear. Here, the vortex having the sign opposite that of the sign of the vorticity in the shear is dispersed by a convective instability. This instability results in the rapid production of turbulence which in turn disperses the smoke marking the vortex.

Bilanin, A. J.; Hirsh, J. E.; Teske, M. E.; Hecht, A. M.

1978-01-01

175

Irregular sleep-wake syndrome  

MedlinePLUS

... normal, but the body clock loses its normal circadian cycle. People with changing work shifts and travelers ... Kanuther N, Harrington J, Lee-Chiong T. Circadian rhythm sleep ... rhythm sleep disorder: irregular sleep wake rhythm. Sleep ...

176

Mach-like capillary-gravity wakes.  

PubMed

We determine experimentally the angle ? of maximum wave amplitude in the far-field wake behind a vertical surface-piercing cylinder translated at constant velocity U for Bond numbers Bo(D)=D/?(c) ranging between 0.1 and 4.2, where D is the cylinder diameter and ?(c) the capillary length. In all cases the wake angle is found to follow a Mach-like law at large velocity, ??U(-1), but with different prefactors depending on the value of Bo(D). For small Bo(D) (large capillary effects), the wake angle approximately follows the law ??c(g,min)/U, where c(g,min) is the minimum group velocity of capillary-gravity waves. For larger Bo(D) (weak capillary effects), we recover a law ???[gD]/U similar to that found for ship wakes at large velocity [Rabaud and Moisy, Phys. Rev. Lett. 110, 214503 (2013)]. Using the general property of dispersive waves that the characteristic wavelength of the wave packet emitted by a disturbance is of order of the disturbance size, we propose a simple model that describes the transition between these two Mach-like regimes as the Bond number is varied. We show that the new capillary law ??c(g,min)/U originates from the presence of a capillary cusp angle (distinct from the usual gravity cusp angle), along which the energy radiated by the disturbance accumulates for Bond numbers of order of unity. This model, complemented by numerical simulations of the surface elevation induced by a moving Gaussian pressure disturbance, is in qualitative agreement with experimental measurements. PMID:25215822

Moisy, Frédéric; Rabaud, Marc

2014-08-01

177

Mach-like capillary-gravity wakes  

NASA Astrophysics Data System (ADS)

We determine experimentally the angle ? of maximum wave amplitude in the far-field wake behind a vertical surface-piercing cylinder translated at constant velocity U for Bond numbers BoD=D/?c ranging between 0.1 and 4.2, where D is the cylinder diameter and ?c the capillary length. In all cases the wake angle is found to follow a Mach-like law at large velocity, ? ˜U-1, but with different prefactors depending on the value of BoD. For small BoD (large capillary effects), the wake angle approximately follows the law ? ?cg ,min/U, where cg ,min is the minimum group velocity of capillary-gravity waves. For larger BoD (weak capillary effects), we recover a law ? ˜?gD /U similar to that found for ship wakes at large velocity [Rabaud and Moisy, Phys. Rev. Lett. 110, 214503 (2013), 10.1103/PhysRevLett.110.214503]. Using the general property of dispersive waves that the characteristic wavelength of the wave packet emitted by a disturbance is of order of the disturbance size, we propose a simple model that describes the transition between these two Mach-like regimes as the Bond number is varied. We show that the new capillary law ? ?cg ,min/U originates from the presence of a capillary cusp angle (distinct from the usual gravity cusp angle), along which the energy radiated by the disturbance accumulates for Bond numbers of order of unity. This model, complemented by numerical simulations of the surface elevation induced by a moving Gaussian pressure disturbance, is in qualitative agreement with experimental measurements.

Moisy, Frédéric; Rabaud, Marc

2014-08-01

178

Suppression of metal-insulator transition in VO2 by electric field-induced oxygen vacancy formation.  

PubMed

Electrolyte gating with ionic liquids is a powerful tool for inducing novel conducting phases in correlated insulators. An archetypal correlated material is vanadium dioxide (VO(2)), which is insulating only at temperatures below a characteristic phase transition temperature. We show that electrolyte gating of epitaxial thin films of VO(2) suppresses the metal-to-insulator transition and stabilizes the metallic phase to temperatures below 5 kelvin, even after the ionic liquid is completely removed. We found that electrolyte gating of VO(2) leads not to electrostatically induced carriers but instead to the electric field-induced creation of oxygen vacancies, with consequent migration of oxygen from the oxide film into the ionic liquid. This mechanism should be taken into account in the interpretation of ionic liquid gating experiments. PMID:23520104

Jeong, Jaewoo; Aetukuri, Nagaphani; Graf, Tanja; Schladt, Thomas D; Samant, Mahesh G; Parkin, Stuart S P

2013-03-22

179

Gravitational wakes in Saturn's rings  

Microsoft Academic Search

Numerical simulations, including both gravitational interactions and dissipative impacts between particles, are used here to study realistic models for Saturn's rings. For the C-ring there is no instability, but for the B- and A-rings gravitational wakes form. In the A-ring these wakes are so strong that particles trapped in them from meter-sized aggregate particles, which themselves lead to further instability.

H. Salo

1992-01-01

180

Suppression outside the classical cortical receptive field GARY A. WALKER, IZUMI OHZAWA, and RALPH D. FREEMAN  

E-print Network

D. FREEMAN Group in Vision Science, School of Optometry, University of California, Berkeley, CA) is a useful and quick approximation of CRF dimensions, but is unsuitable for demarcating the spatial extent, 1990). Still, the minimum response field, and subtle vari- ations using qualitative criteria, have been

Freeman, Ralph D.

181

An experimental investigation of bending wave instability modes in a generic four-vortex wake  

NASA Astrophysics Data System (ADS)

An experimental study of a planar wake consisting of four vortices that simulate the trailing vortex wakes generated by transport airplanes in either takeoff or landing configurations is presented. The objective of this study was to examine naturally occurring wake instabilities. Specifically, the focus of the study was centered on bending wave instabilities of which the Crow instability represents a particular case. A unique method of generating a four-vortex wake was developed for this study. The four-vortex wake generating device permitted direct variation of the spacing between vortices as well as control over the vortex circulation strength. Two quantitative flow visualization experiments were instrumental in identifying wake configurations that were conducive to the rapid growth of bending wave modes and in the identification of the long-wavelength mode. Detailed experiments were also conducted to examine the flow structure in the near-field or roll-up region using a four sensor, hot-wire probe that could measure all three velocity components in the wake simultaneously. The results of both the flow visualization and hot-wire experiments indicate that the long-wavelength mode and the first short-wavelength mode likely dominate the far-field wake physics and may potentially be utilized in a wake control strategy.

Babie, Brian M.; Nelson, Robert C.

2010-07-01

182

A Study of Wake Development and Structure in Constant Pressure Gradients  

NASA Technical Reports Server (NTRS)

Motivated by the application to high-lift aerodynamics for commercial transport aircraft, a systematic investigation into the response of symmetric/asymmetric planar turbulent wake development to constant adverse, zero, and favorable pressure gradients has been conducted. The experiments are performed at a Reynolds number of 2.4 million based on the chord of the wake generator. A unique feature of this wake study is that the pressure gradients imposed on the wake flow field are held constant. The experimental measurements involve both conventional LDV and hot wire flow field surveys of mean and turbulent quantities including the turbulent kinetic energy budget. In addition, similarity analysis and numerical simulation have also been conducted for this wake study. A focus of the research has been to isolate the effects of both pressure gradient and initial wake asymmetry on the wake development. Experimental results reveal that the pressure gradient has a tremendous influence on the wake development, despite the relatively modest pressure gradients imposed. For a given pressure gradient, the development of an initially asymmetric wake is different from the initially symmetric wake. An explicit similarity solution for the shape parameters of the symmetric wake is obtained and agrees with the experimental results. The turbulent kinetic energy budget measurements of the symmetric wake demonstrate that except for the convection term, the imposed pressure gradient does not change the fundamental flow physics of turbulent kinetic energy transport. Based on the turbulent kinetic energy budget measurements, an approach to correct the bias error associated with the notoriously difficult dissipation estimate is proposed and validated through the comparison of the experimental estimate with a direct numerical simulation result.

Thomas, Flint O.; Nelson, R. C.; Liu, Xiaofeng

2000-01-01

183

Complex geophysical wake flows. Madeira Archipelago case study  

NASA Astrophysics Data System (ADS)

Idealized studies of island wakes often use a cylinder-like island to generate the wake, whereas most realistic studies use a close representation of the oceanic bathymetry immersed in a complex representation of the "ambient" geophysical flows. Here, a system of multiple islands was placed into numerical and experimental channels, in order to focus on the complexity of the archipelago wake, including (a) the influence of small neighboring islands and (b) the role of the island-shelf. The numerical geostrophic and stratified channel was built using a three-dimensional primitive equation model, considering a realistic representation of the Madeira archipelago bathymetry, with prescribed initial and boundary conditions. Results from the simulations show that the neighboring islands alter the near-field wake. Small eddies generated by the neighboring islands lead to destabilization of the shear layers of the larger island. Laboratory experiments carried out in the Coriolis rotating tank corroborated this near-field disruptive mechanism. The neighboring island perturbation effect was present whatever the direction of the incoming flow, but under different regimes. North-south wakes produced geostrophic eddies (? R d), whereas west-east wakes produced (exclusively) ageostrophic submesoscale eddies (< < R d) which traveled offshore with wave-like motion. The archipelago shelf contributed to the asymmetric vertical migration of oceanic vorticity. Cyclonic vorticity dominated the surface dynamics, whereas anticyclonic circulation prevailed at the bottom part of the linearly stratified upper layer. This study identifies several likely wake scenarios induced by the Madeira archipelago, and may serve as guide for future multiscale numerical studies and in situ campaigns.

Caldeira, Rui Miguel A.; Sangrà, Pablo

2012-05-01

184

ROTORCRAFT WAKE MODELING: PAST, PRESENT AND Narayanan Komerath Marilyn J. Smith  

E-print Network

extension of this re- search is in the field of sustainable energy, particularly wind turbine design. This requires full understanding of and the ability to control the wake to minimize noise due to blade and analysis. The knowledge and accurate convection and dissipation of individual wakes in wind farms

185

The spectral analysis on PIV testing data in Near wake of the wind turbine  

Microsoft Academic Search

The measure on instantaneous velocity field in near wake of horizontal axis wind turbine (HAWT) were carried out using cross correlation particle image velocimetry (PIV) and axis-coder positioning period sampling system at wind tunnel opening. Near wake spectral characteristics were obtained by spectral analysis on PIV testing data at six tip speed ratios. The research result serves as a reference

Zhiying Gao; Jianwen Wang

2010-01-01

186

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

187

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

188

Suppression of Amblyomma americanum (Ixodida: Ixodidae) for short-term field operations utilizing cypermethrin and lambda-cyhalothrin.  

PubMed

Tick-borne diseases pose significant risks to U.S. military personnel who conduct operations, both domestic and abroad. To determine the feasibility of protecting personnel from tick vectors during short-term field deployments, acaricides cypermethrin (Demon WP, Syngenta, Greensboro, NC) and lambda-cyhalothrin (Surrender Pestabs, CSI, Pasadena, TX) were applied to plots within two separate field sites on Camp Blanding Joint Training Center in Starke, FL, from May to June 2011. We analyzed their effectiveness in reducing tick counts for 6 wk after application. In total, 8,193 ticks were identified and counted, of which > 99% were a mix of nymphs and adult-stage Amblyomma americanum (L.). Our results indicate that both cypermethrin and lambda-cyhalothrin were effective in significantly reducing tick numbers and preventing entry into treated plots for 6 wk after application. Thus, these two acaracides can be used to effectively suppress tick populations and provide residual protection in small geographic areas of recreation or public health significance. PMID:24897866

Hughes, Tony H; Richardson, Alec G; Hoel, David F; Mejeoumov, Tracy; Farooq, Mohammad; Stoops, Craig A

2014-05-01

189

Canopy wake measurements using multiple scanning wind LiDARs  

NASA Astrophysics Data System (ADS)

Canopy wakes have been shown, in controlled wind tunnel experiments, to significantly affect the fluxes of momentum, heat and other scalars at the land and water surface over distances of ~O(1 km), see Markfort et al. (EFM, 2013). However, there are currently no measurements of the velocity field downwind of a full-scale forest canopy. Point-based anemometer measurements of wake turbulence provide limited insight into the extent and details of the wake structure, whereas scanning Doppler wind LiDARs can provide information on how the wake evolves in space and varies over time. For the first time, we present measurements of the velocity field in the wake of a tall patch of forest canopy. The patch consists of two uniform rows of 35-meter tall deciduous, plane trees, which border either side of the Allée de Dorigny, near the EPFL campus. The canopy is approximately 250 m long, and it is 35 m wide, along the direction of the wind. A challenge faced while making field measurements is that the wind rarely intersects a canopy normal to the edge. The resulting wake flow may be deflected relative to the mean inflow. Using multiple LiDARs, we measure the evolution of the wake due to an oblique wind blowing over the canopy. One LiDAR is positioned directly downwind of the canopy to measure the flow along the mean wind direction and the other is positioned near the canopy to evaluate the transversal component of the wind and how it varies with downwind distance from the canopy. Preliminary results show that the open trunk space near the base of the canopy results in a surface jet that can be detected just downwind of the canopy and farther downwind dissipates as it mixes with the wake flow above. A time-varying recirculation zone can be detected by the periodic reversal of the velocity vector near the surface, downwind of the canopy. The implications of canopy wakes for measurement and modeling of surface fluxes will be discussed.

Markfort, Corey D.; Carbajo Fuertes, Fernando; Valerio Iungo, Giacomo; Stefan, Heinz; Porté-Agel, Fernando

2014-05-01

190

Formation and Recovery of Cold Wake during Typhoon Fanapi (2010)  

NASA Astrophysics Data System (ADS)

Cold anomaly of sea surface temperature (SST) is often created after the passage of a moving hurricane or typhoon. The SST reduction within these cold anomalies or cold wakes may reach 2C to 4C. The cold wakes may have important impact on the development of a tropical cyclone due to their control on the surface energy fluxes. This work is aimed at understanding the evolution of cold wake and its impacts on the boundary layers on both sides of the air-sea interface. During 2010 typhoon season, coupled Naval Research Laboratory COAMPS-Tropical Cyclone was used to provide real-time forecasts for ITOP (Impact of Typhoons on the Ocean in the Pacific) field experiment. Typhoon Fanapi started as a tropical depression on September 14, and turned into a Category 4 typhoon on September 18. Along its passage, Typhoon Fanapi produced a large area of cold wake, leading to about 2 degree C reductions in SST. The coupled COAMPS-TC realistically predicted the cold wake formation and recovery as well as the typhoon's track and intensity in general. We use combined coupled COAMPS-TC prediction and observation data collected during the ITOP IOP to investigate the characteristics of the cold wake evolution, evolution of atmospheric as well as oceanic boundary layers. The cold wake was predicted by the model on the right hand side of the storm track; it is driven by the strong shear mixing in the ocean mixed layer. The predicted maximum SST reduction within the wake is 2.5 C, a value very close to the AXBT and satellite observations. Because of this decrease in SST, a stable atmospheric boundary layer is formed, leading to decreases in the surface wind speed, sensible and latent heat fluxes. The predicted warming rate in the cold wake recovery process is comparable with the satellite observation, even though diurnal signal is much more significant in the model prediction. An important question is what determines the recovery time scale. Given the similar solar warming rate between the cold wake and undisturbed environment, this time scale should depend on the differences in the surface turbulence and longwave radiative fluxes and the depth of the ocean surface layer. Currently, we are investigating this issue by analyzing surface energy budget from observation data and model results.

Wang, S.; Jin, H.; Black, P. G.; Chen, S.; Doyle, J.; O'Neill, L. W.

2012-12-01

191

Improving actuator disk wake model  

NASA Astrophysics Data System (ADS)

The wind energy industry has traditionally relied on simple wake models for estimating Wind Turbine (WT) wake losses. Despite limitations, low requirements in terms of detailed rotor information makes their use feasible, unlike more complex models, such as Blade Element Method (BEM) or Actuator Line. Froude's Actuator Disk (AD) does not suffer the simpler model's limitation of prescribing the wake through a closed set of equations, while sharing with them the low rotor data requirements. On the other hand they require some form of parametrization to close the model and calculate total thrust acting on the flow. An Actuator Disk model was developed, using an iterative algorithm based on Froude's one-dimensional momentum theory to determine the WT's performance, proving to be successful in estimating the performance of both machines in undisturbed flow and in the wake of an upstream machines. Before Froude's AD limitations compared to more complex rotor models, load distributions emulating those of a BEM model were tested. The results show that little impact is obtained at 3 rotor diameters downstream and beyond, agreeing with common definition of a far-wake that starts at 1-2 diameters downstream, where rotor characteristics become negligible and atmospheric flow effects dominate.

Costa Gomes, V. M. M. G.; Palma, J. M. L. M.; Silva Lopes, A.

2014-06-01

192

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

PubMed Central

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

2012-01-01

193

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  

Technology Transfer Automated Retrieval System (TEKTRAN)

Sclerotinia sclerotiorum causes serious yield losses in crops in The People’s Republic of China. Two formulations of oilseed rape seed containing the endophytic bacterium Bacillus subtilis Tu-100 were evaluated for suppression of this pathogen in field trials conducted at two independent locations....

194

Study of a Wake Recovery Mechanism in a High-Speed Axial Compressor Stage  

NASA Technical Reports Server (NTRS)

This work addresses the significant differences in compressor rotor wake mixing loss which exist in a stage environment relative to a rotor in isolation. The wake decay for a rotor in isolation is due solely to viscous dissipation which is an irreversible process and thus leads to a loss in both total pressure and efficiency. Rotor wake decay in the stage environment is due to both viscous mixing and the inviscid strain imposed on the wake fluid particles by the stator velocity field. This straining process, referred to by Smith (1993) as recovery, is reversible and for a 2D rotor wake leads to an inviscid reduction of the velocity deficit of the wake. A model for the rotor wake decay process is developed and used to quantify the viscous dissipation effects relative to those of inviscid wake stretching. The model is verified using laser anemometer measurements acquired in the wake of a transonic rotor operated in isolation and in a stage configuration at near peak efficiency and near stall operating conditions. Additional insight is provided by a time-accurate 3D Navier-Stokes simulation of the compressor stator flow field at the corresponding stage loading levels. Results from the wake decay model exhibit good agreement with the experimental data. Data from the model, laser anemometer measurements, and numerical simulations indicate that for the rotor/stator spacing used in this work, which is typical of core compressors, rotor wake straining (stretching) is the primary decay process in the stator passage with viscous mixing playing only a minor role. The implications of these results on compressor stage design are discussed.

VanZante, Dale E.

1998-01-01

195

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

196

Magnetic Fluctuations and Turbulence in the Venus Magnetosheath and Wake  

E-print Network

Recent research has shown that distinct physical regions in the Venusian induced magnetosphere are recognizable from the variations of strength and of wave/fluctuation activity of the magnetic field. In this paper the statistical properties of magnetic fluctuations are investigated in the Venusian magnetosheath, terminator, and wake regions. The latter two regions were not visited by previous missions. We found 1/f fluctuations in the magnetosheath, large-scale structures near the terminator and more developed turbulence further downstream in the wake. Location independent short-tailed non-Gaussian statistics was observed.

Z. Vörös; T. L. Zhang; M. P. Leubner; M. Volwerk; M. Delva; W. Baumjohann; K. Kudela

2008-06-11

197

Analytical model of rotor wake aerodynamics in ground effect  

NASA Technical Reports Server (NTRS)

The model and the computer program developed provides the velocity, location, and circulation of the tip vortices of a two-blade helicopter in and out of the ground effect. Comparison of the theoretical results with some experimental measurements for the location of the wake indicate that there is excellent accuracy in the vicinity of the rotor and fair amount of accuracy far from it. Having the location of the wake at all times enables us to compute the history of the velocity and the location of any point in the flow. The main goal of out study, induced velocity at the rotor, can also be calculated in addition to stream lines and streak lines. Since the wake location close to the rotor is known more accurately than at other places, the calculated induced velocity over the disc should be a good estimate of the real induced velocity, with the exception of the blade location, because each blade was replaced only by a vortex line. Because no experimental measurements of the wake close to the ground were available to us, quantitative evaluation of the theoretical wake was not possible. But qualitatively we have been able to show excellent agreement. Comparison of flow visualization with out results has indicated the location of the ground vortex is estimated excellently. Also the flow field in hover is well represented.

Saberi, H. A.

1983-01-01

198

Numerical Modeling Studies of Wake Vortices: Real Case Simulations  

NASA Technical Reports Server (NTRS)

A three-dimensional large-eddy simulation model, TASS, is used to simulate the behavior of aircraft wake vortices in a real atmosphere. The purpose for this study is to validate the use of TASS for simulating the decay and transport of wake vortices. Three simulations are performed and the results are compared with the observed data from the 1994-1995 Memphis field experiments. The selected cases have an atmospheric environment of weak turbulence and stable stratification. The model simulations are initialized with appropriate meteorological conditions and a post roll-up vortex system. The behavior of wake vortices as they descend within the atmospheric boundary layer and interact with the ground is discussed.

Shen, Shao-Hua; Ding, Feng; Han, Jongil; Lin, Yuh-Lang; Arya, S. Pal; Proctor, Fred H.

1999-01-01

199

Wakes in Inertial Fusion Plasmas  

NASA Astrophysics Data System (ADS)

Plasma wave wakes, which are the collective oscillatory response near the plasma frequency to the propagation of particles or electromagnetic waves through a plasma, play a critical role in many plasma processes. New results from backwards stimulated Raman scattering (BSRS), in which wakes with phase velocities much less than the speed of light are induced by the beating of counter-propagating light waves, and from electron beam stopping, in which the wakes are produced by the motion of relativistically propagating electrons through the dense plasma, are discussed. Both processes play important roles in Inertial Confinement Fusion (ICF). In BSRS, laser light is scattered backwards out of the plasma, decreasing the energy available to compress the ICF capsule and affecting the symmetry of where the laser energy hits the hohlraum wall in indirect drive ICF. The plasma wave wake can also generate superthermal electrons that can preheat the core and/or the ablator. Electron beam stopping plays a critical role in the Fast Ignition (FI) ICF concept, in which a beam of relativistic electrons is used to heat the target core to ignition temperatures after the compression stage. The beam stopping power determines the effectiveness of the heating process. This dissertation covers new discoveries on the importance of plasma wave wakes in both BSRS and electron beam stopping. In the SRS studies, 1D particle-in-cell (PIC) simulations using OSIRIS are performed, which model a short-duration (˜500/?0 --1FWHM) counter-propagating scattered light seed pulse in the presence of a constant pump laser with an intensity far below the absolute instability threshold for plasma waves undergoing Landau damping. The seed undergoes linear convective Raman amplification and dominates over the amplification of fluctuations due to particle discreteness. The simulation results are in good agreement with results from a coupled-mode solver when special relativity and the effects of finite size PIC simulation particles are accounted for. Linear gain spectra including both effects are discussed. Extending the PIC simulations past when the seed exits the simulation domain reveals bursts of large-amplitude scattering in many cases, which do not occur in simulations without the seed pulse. These bursts can have amplitudes several times greater than the amplified seed pulse, and an examination of the orbits of particles trapped in the wake illustrates that the bursts are caused by a reduction of Landau damping due to particle trapping. This large-amplitude scattering is caused by the seed inducing a wake earlier in the simulation, thus modifying the distribution function. Performing simulations with longer duration seeds leads to parts of the seeds reaching amplitudes several times more than the steady-state linear theory results, similarly caused by a reduction of Landau damping. Simulations with continuous seeds demonstrate that the onset of inflation depends on the seed wavelength and incident intensity, and oscillations in the reflectivity are observed at a frequency equal to the difference between the seed frequency and the frequency at which the inflationary SRS grows. In the electron beam stopping studies, 3D PIC simulations are performed of relativistic electrons with a momentum of 10mec propagating in a cold FI core plasma. Some of the simulations use one simulation particle per real particle, and particle sizes much smaller than the interparitcle spacing. The wake made by a single electron is compared against that calculated using cold fluid theory assuming the phase velocity of the wake is near the speed of light. The results agree for the first wavelength of the wake. However, the shape of the wake changes for succeeding wavelengths and depends on the background plasma temperature, with the concavity pointing in the direction the electron is moving in cold plasmas and in the opposite direction as the plasma temperature increases. In the warm plasma the curvature is described by electrostatic Vlasov theory (for vparticle >> vth) and is due

Ellis, Ian Norman

200

Normal Component of Induced Velocity for Entire Field of a Uniformly Loaded Lifting Rotor with Highly Swept Wake as Determined by Electromagnetic Analog  

NASA Technical Reports Server (NTRS)

Values of the normal component of induced velocity throughout the entire field of a uniformly loaded r(rotor at high high speed are presented in the form of charts and tables. Many points were found by an electromagnetic analog, details of which are given. Comparisons of computed and analog values for the induced velocity indicate that the latter are sufficiently accurate for engineering purposes.

Castles, Walter, Jr.; Durham, Howard L., Jr.; Kevorkian, Jirair

1959-01-01

201

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

NASA Technical Reports Server (NTRS)

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 wake characterization and validation of wake-vortex computational models. This paper describes the wake-vortex flight tests, the data processing, the database development and access, and results obtained from preliminary wake-characterization analysis using the data sets.

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

1998-01-01

202

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

203

Problem solving: Waking and dreaming  

Microsoft Academic Search

Investigated whether problem-solving ability is either quantitatively or qualitatively superior following an interval of sleep including dreaming than it is following an equal interval of waking time. 24 college students were tested on matched problems before and after these 2 conditions on 3 problem types: crossword puzzles, Remote Associates Test, and Thematic Apperception Test story completions. These were predicted to

Rosalind D. Cartwright

1974-01-01

204

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

205

CONTROL OF SLEEP AND WAKEFULNESS  

PubMed Central

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.

2013-01-01

206

Effects of atmospheric stability on the evolution of wind turbine wakes: Volumetric LiDAR scans  

NASA Astrophysics Data System (ADS)

Aerodynamic optimization of wind farm layout is a fundamental task to reduce wake effects on downstream wind turbines, thus to maximize wind power harvesting. However, downstream evolution and recovery of wind turbine wakes are strongly affected by the characteristics of the incoming atmospheric boundary layer (ABL) flow, like the vertical profiles of the mean wind velocity and the turbulence intensity, which are in turn affected by the ABL stability regime. Therefore, the characterization of the variability of wind turbine wakes under different ABL stability regimes becomes fundamental to better predict wind power harvesting and improve wind farm efficiency. To this aim, wind velocity measurements of the wake produced by a 2 MW Enercon E-70 wind turbine were performed with three scanning Doppler wind Light Detection and Ranging (LiDAR) instruments. One LiDAR was typically devoted to the characterization of the incoming wind, in particular wind velocity, shear and turbulence intensity at the height of the rotor disc. The other two LiDARs performed scans in order to characterize the wake velocity field produced by the tested wind turbine. The main challenge in performing field measurements of wind turbine wakes is represented by the varying wind conditions, and by the consequent adjustments of the turbine yaw angle needed to maximize power production. Consequently, taking into account possible variations of the relative position between LiDAR measurement volume and wake location, different LiDAR measurement procedures were carried out in order to perform 2-D and 3-D characterizations of the mean wake velocity field. However, larger measurement volumes and higher spatial resolution require longer sampling periods; thus, to investigate wake turbulence tests were also performed by staring the LiDAR laser beam over fixed directions and with the maximum sampling frequency. Furthermore, volumetric scans of the wind turbine wake were performed under different wind conditions via two simultaneous LiDARs. Through the evaluation of the minimum wake velocity deficit as a function of the downstream distance, it is shown that the stability regime of the ABL has a significant effect on the wake evolution; specifically the wake recovers faster under convective conditions. This result suggests that atmospheric inflow conditions, and particularly thermal stability, should be considered for improved wake models and predictions of wind power harvesting.

Valerio Iungo, Giacomo; Porté-Agel, Fernando

2014-05-01

207

Wind tunnel measurements in the wake of a simple structure in a simulated atmospheric flow  

NASA Technical Reports Server (NTRS)

Measurements of longitudinal mean velocity and turbulence intensity were made in the wake of a rectangular model building in a simulated atmospheric boundary-layer wind. The model building was a 1:50 scale model of a structure used in a wake measurement program at the George C. Marshall Space Flight Center 8-tower boundary-layer facility. The approach wind profile and measurement locations were chosen to match the field site conditions. The wakes of the building in winds from azimuths of 0 and 47 degrees referenced to the normal to the building long axis were examined. The effect of two lines of trees upwind of the building on the wake and the importance of the ratio of the building height to boundary-layer thickness on the extent of the wake were determined.

Hansen, A. C.; Peterka, J. A.; Cermak, J. E.

1975-01-01

208

Prediction and Control of Vortex Dominated and Vortex-wake Flows  

NASA Technical Reports Server (NTRS)

This report describes the activities and accomplishments under this research grant, including a list of publications and dissertations, produced in the field of prediction and control of vortex dominated and vortex wake flows.

Kandil, Osama

1996-01-01

209

Vortex shedding in compressor blade wakes  

NASA Technical Reports Server (NTRS)

The wakes of highly loaded axial compressor blades were often considered to be turbulent, unstructured flows. Recent work has suggested that the blade wakes are in fact dominated by a vortex street-like structure. The work on the wake structure at MIT is reviewed, the results of a viscous numerical simulation are presented, the blade wake vortices are compared to those shed from a cylinder, and the implications of the wake structure on compressor performance are discussed. In particular, a two-dimensional, time accurate, viscous calculation shows both a periodic wake structure and time variations in the passage shock strength. The numerical calculations are compared to laser anemometer and high frequency response probe data. The effect of the wake structure on the entropy production and apparent adiabatic efficiency of the compressor rotor is discussed.

Epstein, A. H.; Gertz, J. B.; Owen, P. R.; Giles, M. B.

1987-01-01

210

Absolute instability of the Gaussian wake profile  

NASA Technical Reports Server (NTRS)

Linear parallel-flow stability theory has been used to investigate the effect of viscosity on the local absolute instability of a family of wake profiles with a Gaussian velocity distribution. The type of local instability, i.e., convective or absolute, is determined by the location of a branch-point singularity with zero group velocity of the complex dispersion relation for the instability waves. The effects of viscosity were found to be weak for values of the wake Reynolds number, based on the center-line velocity defect and the wake half-width, larger than about 400. Absolute instability occurs only for sufficiently large values of the center-line wake defect. The critical value of this parameter increases with decreasing wake Reynolds number, thereby indicating a shrinking region of absolute instability with decreasing wake Reynolds number. If backflow is not allowed, absolute instability does not occur for wake Reynolds numbers smaller than about 38.

Hultgren, Lennart S.; Aggarwal, Arun K.

1987-01-01

211

Wake shed by an accelerating carangiform fish  

NASA Astrophysics Data System (ADS)

We reveal an important fact that momentum change observed in the wake of an accelerating carangiform fish does not necessarily elucidate orientations of propulsive forces produced. An accelerating Crucian Carp (Carassius auratus) was found to shed a wake with net forward fluid momentum, which seemed drag-producing. Based on Newton's law, however, an accelerating fish is expected to shed a thrust wake with net rearward fluid momentum, rather than a drag wake. The unusual wake pattern observed is considered to be resulted primarily from the effect of pressure gradient created by accelerating movements of the fish. Ambient fluids tend to be sucked into low pressure zones behind an accelerating fish, resulting in forward orientations of jets recognizable in the wake. Accordingly, as to an accelerating fish, identifying force orientations from the wake requires considering also the effect of pressure gradient.

Ting, Shang-Chieh; Yang, Jing-Tang

2008-11-01

212

Planetary Ion fluxes in the Venus Wake  

NASA Astrophysics Data System (ADS)

Measurements conducted with the ASPERA-4 instrument and the magnetometer of the Venus Express spacecraft show that the kinetic pressure of planetary O+ ions measured in the Venus wake can be significantly larger than the local magnetic pressure and, as a result, those ions are not being driven by magnetic forces but by the kinetic energy of the solar wind. Beams of planetary O+ ions with those properties have been detected in several orbits of the Venus Express through the wake as the spacecraft traverses by the noon-midnight plane along its near polar trajectory. Peak values of the kinetic pressure of the O+ ions are sufficient to produce superalfvenic flow conditions. It is suggested that such O+ ion beams are eroded from the magnetic polar regions of the Venus ionosphere where the solar wind carves out plasma channels that extend downstream from those regions. Issues related to the acceleration of planetary ions as the solar wind interacts with the Venus ionosphere are related to the energetics of the plasma. When the kinetic pressure of the particle populations involved in the interaction is smaller than the local magnetic pressure the latter will be dominant and hence the particles will follow trajectories dictated by the magnetic field. Such conditions should occur by the magnetic barrier that is formed over the dayside Venus ionosphere where the interplanetary magnetic fluxes pile up thus leading to enhanced values of the magnetic field intensity. Different conditions are expected when the kinetic pressure of the plasma is larger than the local magnetic pressure. In this case the latter will be convected by the particle fluxes as it occurs in the superalfvenic solar wind. Plasma conditions applicable to the planetary ions that stream in the Venus wake and that have been removed from the Venus ionosphere can be examined using the plasma and magnetic field data obtained from the Venus Express (VEX) measurements. A suitable example is provided by the plasma and the magnetic pressure profiles that were obtained from the data in orbit 123 on August 22-2006 and that are reproduced in Figure 1. The profiles in the lower panel show that the peak kinetic pressure of the O+ ions becomes substantially larger than the local magnetic pressure (between 01:48 UT and 02:00 UT) and also that within a wide region of the wake (between ~02:00 UT and ~02:25 UT) the kinetic pressure becomes smaller than the magnetic pressure. Values of the ratio of the kinetic to the magnetic pressure that are obtained from both profiles are given in the upper panel to show that in the region where the peak kinetic pressure of the O+ ions are measured that ratio is substantially larger than one thus indicating that the local ions move under superalfvenic conditions. The opposite is true in other regions of the wake where values of that ratio are smaller than one and thus the plasma is subalfvenic.

Pérez-de-Tejada, H.; Lundin, R.; Durand-Manterola, H.; Barabash, S.; Zhang, T. L.; Sauvaud, J. A.; Reyes-Ruiz, M.

2012-09-01

213

Experimental and Numerical Investigation of Pressure Gradient Effects on Asymmetric Wake Development  

NASA Astrophysics Data System (ADS)

In a multielement airfoil used for high-lift applications, the wake generated by the leading edge slat is usually higly-asymmeric in shape and invariably develops in a strong pressure gradient environment. In this study, the near wake behavior of an initially asymmetric wake which develops in zero, favorable and adverse pressure gradients is investigated both experimentally and numerically. The asymmetric wake is generated by a splitter plate with tapered trailing edge. Passive flow control of the boundary layer development on both sides of the splitter plate gives rise to the wake asymmetry. The pressure gradients are imposed as the wake passes through a wind tunnel diffuser test section with fully adjustable top and bottom wall contours. Flow field surveys are conducted by LDV and constant temperature anemometry. The numerical simulations are based on a thin-shear layer form of the Navier Stokes equation in conjunction with an implementation of both the Spalart-Allmaras and the Wilcox k-? model. Experimental and numerical results show that the imposed pressure gradients and wake asymmetry have a significant effect on the wake flow structure. Preliminary measurements of the turbulence kinetic energy budget including convection, diffusion, production and most of the dissipation terms will also be presented.

Liu, Xiaofeng; Thomas, Flint O.; Nelson, Robert C.

1999-11-01

214

Measurement procedures for characterization of wind turbine wakes with scanning Doppler wind LiDARs  

NASA Astrophysics Data System (ADS)

The wake flow produced from an Enercon E-70 wind turbine is investigated through three scanning Doppler wind LiDARs. One LiDAR is deployed upwind to characterize the incoming wind, while the other two LiDARs are located downstream to carry out wake measurements. The main challenge in performing measurements of wind turbine wakes is represented by the varying wind conditions, and by the consequent adjustments of the turbine yaw angle needed to maximize power production. Consequently, taking into account possible variations of the relative position between the LiDAR measurement volume and wake location, different measuring techniques were carried out in order to perform 2-D and 3-D characterizations of the mean wake velocity field. However, larger measurement volumes and higher spatial resolution require longer sampling periods; thus, to investigate wake turbulence tests were also performed by staring the LiDAR laser beam over fixed directions and with the maximum sampling frequency. The characterization of the wake recovery along the downwind direction is performed. Moreover, wake turbulence peaks are detected at turbine top-tip height, which can represent increased fatigue loads for downstream wind turbines within a wind farm.

Iungo, G. V.; Porté-Agel, F.

2013-05-01

215

Dynamics of wake structure in clapping propulsion  

NASA Astrophysics Data System (ADS)

Some animals such as insects and frogs use a pair of symmetric flaps for locomotion. In some cases, these flappers operate in close proximity or even touch each other. In order to understand the underlying physics of these kinds of motion, we have studied the wake structures induced by clapping and their associated thrust performance. A simple mechanical model with two acrylic plates was used to simulate the power stroke of the clapping motion and three-dimensional flow fields were obtained using defocusing digital particle image velocimetry. Our studies show that the process of vortex connection plays a critical role in forming a downstream closed vortex loop. Under some kinematic conditions, this vortex loop changes its shape dynamically, which is analogous to the process of an elliptical vortex ring switching its minor and major axis. As the length of the plate along the rotating shaft decreases to change an aspect ratio, the downstream motion of the vortex is retarded due to the outward motion of side edge vortices and less propulsive force is generated per the surface area of the plate. The impact of compliance and stroke angle of the plate on wake structures and thrust magnitudes are also presented.

Kim, Daegyoum; Gharib, Morteza

2009-11-01

216

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

217

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

218

An integrated Navier-Stokes - full potential - free wake method for rotor flows  

NASA Astrophysics Data System (ADS)

The strong wake shed from rotary wings interacts with almost all components of the aircraft, and alters the flow field thus causing performance and noise problems. Understanding and modeling the behavior of this wake, and its effect on the aerodynamics and acoustics of helicopters have remained as challenges. This vortex wake and its effect should be accurately accounted for in any technique that aims to predict rotor flow field and performance. In this study, an advanced and efficient computational technique for predicting three-dimensional unsteady viscous flows over isolated helicopter rotors in hover and in forward flight is developed. In this hybrid technique, the advantages of various existing methods have been combined to accurately and efficiently study rotor flows with a single numerical method. The flow field is viewed in three parts: (i) an inner zone surrounding each blade where the wake and viscous effects are numerically captured, (ii) an outer zone away from the blades where wake is modeled, and (iii) a Lagrangean wake which induces wake effects in the outer zone. This technique was coded in a flow solver and compared with experimental data for hovering and advancing rotors including a two-bladed rotor, the UH-60A rotor and a tapered tip rotor. Detailed surface pressure, integrated thrust and torque, sectional thrust, and tip vortex position predictions compared favorably against experimental data. Results indicated that the hybrid solver provided accurate flow details and performance information typically in one-half to one-eighth cost of complete Navier-Stokes methods.

Berkman, Mert Enis

1998-12-01

219

Field Evaluations of Augmentative Releases of Delphastus catalinae (Horn) (Coleoptera: Coccinellidae) for Suppression of Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) Infesting Cotton  

Microsoft Academic Search

In 1992 and 1993, field evaluations were conducted to determine the efficacy of Delphastus catalinae (Horn) releases for the suppression of Bemisia argentifolii Bellows & Perring infesting cotton in the Imperial Valley of California. Augmentative releases of adult beetles, totaling 3.5 and 5.5 beetles per plant for 1992 and 1993, respectively, were made into four 0.2-hectare cotton plots and four

Kevin M. Heinz; James R. Brazzle; Michael P. Parrella; Charles H. Pickett

1999-01-01

220

Neurons containing orexin or melanin concentrating hormone reciprocally regulate wake and sleep  

PubMed Central

Neurons containing orexin (hypocretin), or melanin concentrating hormone (MCH) are intermingled with each other in the perifornical and lateral hypothalamus. Each is a separate and distinct neuronal population, but they project to similar target areas in the brain. Orexin has been implicated in regulating arousal since loss of orexin neurons is associated with the sleep disorder narcolepsy. Microinjections of orexin into the brain or optogenetic stimulation of orexin neurons increase waking. Orexin neurons are active in waking and quiescent in sleep, which is consistent with their role in promoting waking. On the other hand, the MCH neurons are quiet in waking but active in sleep, suggesting that they could initiate sleep. Recently, for the first time the MCH neurons were stimulated optogenetically and it increased sleep. Indeed, optogenetic activation of MCH neurons induced sleep in both mice and rats at a circadian time when they should be awake, indicating the powerful effect that MCH neurons have in suppressing the wake-promoting effect of not only orexin but also of all of the other arousal neurotransmitters. Gamma-Aminobutyric acid (GABA) is coexpressed with MCH in the MCH neurons, although MCH is also inhibitory. The inhibitory tone of the MCH neurons is opposite to the excitatory tone of the orexin neurons. We hypothesize that strength in activity of each determines wake vs. sleep. PMID:25620917

Konadhode, Roda Rani; Pelluru, Dheeraj; Shiromani, Priyattam J.

2015-01-01

221

Large-Eddy Simulations and Lidar Measurements of Vortex-Pair Breakup in Aircraft Wakes  

NASA Technical Reports Server (NTRS)

Results of large-eddy simulations of an aircraft wake are compared with results from ground-based lidar measurements made at NASA Langley Research Center during the Subsonic Assessment Near-Field Interaction Flight Experiment field tests. Brief reviews of the design of the field test for obtaining the evolution of wake dispersion behind a Boeing 737 and of the model developed for simulating such wakes are given. Both the measurements and the simulations concentrate on the period from a few seconds to a few minutes after the wake is generated, during which the essentially two-dimensional vortex pair is broken up into a variety of three-dimensional eddies. The model and experiment show similar distinctive breakup eddies induced by the mutual interactions of the vortices, after perturbation by the atmospheric motions.

Lewellen, D. C.; Lewellen, W. S.; Poole, L. R.; DeCoursey, R. J.; Hansen, G. M.; Hostetler, C. A.; Kent, G. S.

1998-01-01

222

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.

223

Multiple-LiDAR measurements of wind turbine wakes: effect of the atmospheric stability  

NASA Astrophysics Data System (ADS)

Aerodynamic design and optimization of a wind farm layout are mainly based on the evaluation of wind turbine wake recovery by moving downstream, and on the characterization of wake interactions within a wind farm. Indeed, the power production of downstream wind turbine rows is strictly affected by the cumulative wake produced by the turbines deployed upstream. Wind turbine wakes are dependent on their aerodynamic features, and being immersed in the atmospheric boundary layer (ABL), they are also affected by surface heterogeneity, e.g. site topography and surface coverage, and atmospheric stability. The ABL stability is typically classified as neutral, convective or stable. In a neutral ABL the mechanical turbulent production is the dominating phenomenon. Conversely, for a convective ABL the turbulent kinetic energy and vertical transport phenomena are enhanced by positive buoyancy. Finally, for a stable ABL, a lower turbulence level is typically observed with an increased wind shear. For the present campaign convective ABL was typically observed during day-time, and neutral ABL for early morning and sunset periods. The aim of the present work is the evaluation of the influence of the ABL stability on downstream evolution of wind turbine wakes, which is mainly controlled by different ABL turbulence characteristics. Field measurements of the wake produced from a 2 MW Enercon E-70 wind turbine were performed with three scanning Doppler wind LiDARs. The wind and atmospheric conditions were characterized through a sonic anemometer deployed in proximity of the wind turbine. One LiDAR was placed at a distance about 12 rotor diameters upstream of the turbine in order to characterize the incoming wind. Two additional LiDARs were typically used to perform wake measurements. Tests were performed over the wake vertical symmetry plane in order to characterize wake recovery. Measurements were also carried out over conical surfaces in order to investigate the wind turbine wake with varying wind direction, thus different turbine yaw angles. Moreover, a 3D characterization of the wind turbine wake was performed by scanning the LiDAR over a 3D measurement volume. However, the large sampling period required for the 3D scans does not allow the investigation of wake dynamics. The LiDAR measurements show that wake evolution is significantly affected by the stability conditions of the ABL, thus by the different turbulence characteristics of the incoming wind. In particular, a faster wake recovery is observed in the presence of an increased turbulence of the incoming wind and for more convective atmospheric flows.

Valerio Iungo, Giacomo; Porté-Agel, Fernando

2013-04-01

224

Ship wake signatures in radar/optical images of the sea surface: observations and physical mechanisms  

NASA Astrophysics Data System (ADS)

Ship wakes can be clearly seen in satellite radar and optical images of the sea surface, and understanding of physical mechanisms responsible for the wake signatures is very important to develop methods of ship detection/identification. The wake surface signatures at small and intermediate stages are characterized by a smooth centerline area where surface waves are depressed due to the vessel turbulence and by a pair of rough bands at the sides of the centerline wake. At large wake ages two slick bands (a "railroad track" wake) appear instead of the rough bands, while the smooth centerline band is practically absent. In this paper results of field studies of the mean flow structure near the wake are presented. It is shown that two mean circulating currents ("rolls") rotating in the opposite directions are formed at two sides of the median vertical plane of the wake. Near the water surface the rolls result in diverging horizontal flows, decreasing near the wake edges. Wind waves propagating against the diverging currents are amplified due to a wave straining mechanism thus increasing the surface roughness. Film sampling was carried out when crossing the wakes and analysis of films collected within the "railroad" slick bands and outside the bands has revealed enhanced surface wave damping, obviously due to accumulation of surfactants in the slick bands; the surfactant compression is explained by the action of the diverging currents. The diverging currents as part of the rolls and the surfactant transport to the water surface are supposed to be associated with air bubbles generated by ship propellers.

Ermakov, S.; Kapustin, I.; Lazareva, T.

2014-10-01

225

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). PMID:22205651

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

2012-01-01

226

Evaluation of Fast-Time Wake Vortex Models using Wake Encounter Flight Test Data  

NASA Technical Reports Server (NTRS)

This paper describes a methodology for the integration and evaluation of fast-time wake models with flight data. The National Aeronautics and Space Administration conducted detailed flight tests in 1995 and 1997 under the Aircraft Vortex Spacing System Program to characterize wake vortex decay and wake encounter dynamics. In this study, data collected during Flight 705 were used to evaluate NASA's fast-time wake transport and decay models. Deterministic and Monte-Carlo simulations were conducted to define wake hazard bounds behind the wake generator. The methodology described in this paper can be used for further validation of fast-time wake models using en-route flight data, and for determining wake turbulence constraints in the design of air traffic management concepts.

Ahmad, Nashat N.; VanValkenburg, Randal L.; Bowles, Roland L.; Limon Duparcmeur, Fanny M.; Gloudesman, Thijs; van Lochem, Sander; Ras, Eelco

2014-01-01

227

RWF rotor-wake-fuselage code software reference guide  

NASA Technical Reports Server (NTRS)

The RWF (Rotor-Wake-Fuselage) code was developed from first principles to compute the aerodynamics associated with the complex flow field of helicopter configurations. The code is sized for a single, multi-bladed main rotor and any configuration of non-lifting fuselage. The mathematical model for the RWF code is based on the integration of the momentum equations and Green's theorem. The unknowns in the problem are the strengths of prescribed singularity distributions on the boundaries of the flow. For the body (fuselage) a surface of constant strength source panels is used. For the rotor blades and rotor wake a surface of constant strength doublet panels is used. The mean camber line of the rotor airfoil is partitioned into surface panels. The no-flow boundary condition at the panel centroids is modified at each azimuthal step to account for rotor blade cyclic pitch variation. The geometry of the rotor wake is computers at each time step of the solution. The code produces rotor and fuselage surface pressures, as well as the complex geometry of the evolving rotor wake.

Berry, John D.

1991-01-01

228

Preliminary rotor wake measurements with a laser velocimeter  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

229

Plasma wakefield acceleration studies using the quasi-static code WAKE  

NASA Astrophysics Data System (ADS)

The quasi-static code WAKE [P. Mora and T. Antonsen, Phys. Plasmas 4, 217 (1997)] is upgraded to model the propagation of an ultra-relativistic charged particle beam through a warm background plasma in plasma wakefield acceleration. The upgraded code is benchmarked against the full particle-in-cell code OSIRIS [Hemker et al., Phys. Rev. Spec. Top. Accel. Beams 3, 061301 (2000)] and the quasi-static code QuickPIC [Huang et al., J. Comput. Phys. 217, 658 (2006)]. The effect of non-zero plasma temperature on the peak accelerating electric field is studied for a two bunch electron beam driver with parameters corresponding to the plasma wakefield acceleration experiments at Facilities for Accelerator Science and Experimental Test Beams. It is shown that plasma temperature does not affect the energy gain and spread of the accelerated particles despite suppressing the peak accelerating electric field. The role of plasma temperature in improving the numerical convergence of the electric field with the grid resolution is discussed.

Jain, Neeraj; Palastro, John; Antonsen, T. M.; Mori, Warren B.; An, Weiming

2015-02-01

230

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...

231

TWO-CHANNEL DIELECTRIC WAKE FIELD ACCELERATOR  

SciTech Connect

Experimental results are reported for test beam acceleration and deflection in a two-channel, cm-scale, rectangular dielectric-lined wakefield accelerator structure energized by a 14-MeV drive beam. The dominant waveguide mode of the structure is at {approx}30 GHz, and the structure is configured to exhibit a high transformer ratio ({approx}12:1). Accelerated bunches in the narrow secondary channel of the structure are continuously energized via Cherenkov radiation that is emitted by a drive bunch moving in the wider primary channel. Observed energy gains and losses, transverse deflections, and changes in the test bunch charge distribution compare favorably with predictions of theory.

Jay L. Hirshfield

2012-05-30

232

GPU Based Fast Free-Wake Calculations For Multiple Horizontal Axis Wind Turbine Rotors  

NASA Astrophysics Data System (ADS)

Unsteady free-wake solutions of wind turbine flow fields involve computationally intensive interaction calculations, which generally limit the total amount of simulation time or the number of turbines that can be simulated by the method. This problem, however, can be addressed easily using high-level of parallelization. Especially when exploited with a GPU, a Graphics Processing Unit, this property can provide a significant computational speed-up, rendering the most intensive engineering problems realizable in hours of computation time. This paper presents the results of the simulation of the flow field for the NREL Phase VI turbine using a GPU-based in-house free-wake panel method code. Computational parallelism involved in the free-wake methodology is exploited using a GPU, allowing thousands of similar operations to be performed simultaneously. The results are compared to experimental data as well as to those obtained by running a corresponding CPU-based code. Results show that the GPU based code is capable of producing wake and load predictions similar to the CPU- based code and in a substantially reduced amount of time. This capability could allow free- wake based analysis to be used in the possible design and optimization studies of wind farms as well as prediction of multiple turbine flow fields and the investigation of the effects of using different vortex core models, core expansion and stretching models on the turbine rotor interaction problems in multiple turbine wake flow fields.

Türkal, M.; Novikov, Y.; Ü?enmez, S.; Sezer-Uzol, N.; Uzol, O.

2014-06-01

233

The 3-D wake measurements near a hovering rotor for determining profile and induced drag  

NASA Technical Reports Server (NTRS)

Primarily an experimental effort, this study focuses on the velocity and vorticity fields in the near wake of a hovering rotor. Drag terminology is reviewed, and the theory for separately determining the profile-and-induced-drag components from wake quantities is introduced. Instantaneous visualizations of the flow field are used to center the laser velocimeter (LV) measurements on the vortex core and to assess the extent of the positional mandering of the trailing vortex. Velocity profiles obtained at different rotor speeds and distances behind the rotor blade clearly indicate the position, size, and rate of movement of the wake sheet and the core of the trailing vortex. The results also show the distribution of vorticity along the wake sheet and within the trailing vortex.

Mcalister, K. W.; Schuler, C. A.; Branum, L.; Wu, J. C.

1995-01-01

234

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

235

Comparison of Wake Model Simulations with Offshore Wind Turbine Wake Profiles Measured by Sodar  

E-print Network

Comparison of Wake Model Simulations with Offshore Wind Turbine Wake Profiles Measured by Sodar R of most of the commonly used models for predicting wind speed decrease (wake) downstream of a wind turbine a ship-mounted sodar at a small offshore wind farm. The experiments were conducted at varying distances

Pryor, Sara C.

236

Feasibility of wake vortex monitoring systems for air terminals  

NASA Technical Reports Server (NTRS)

Wake vortex monitoring systems, especially those using laser Doppler sensors, were investigated. The initial phases of the effort involved talking with potential users (air traffic controllers, pilots, etc.) of a wake vortex monitoring system to determine system requirements from the user's viewpoint. These discussions involved the volumes of airspace to be monitored for vortices, and potential methods of using the monitored vortex data once the data are available. A subsequent task led to determining a suitable mathematical model of the vortex phenomena and developing a mathematical model of the laser Doppler sensor for monitoring the vortex flow field. The mathematical models were used in combination to help evaluate the capability of laser Doppler instrumentation in monitoring vortex flow fields both in the near vicinity of the sensor (within 1 kilometer and at long ranges(10 kilometers).

Wilson, D. J.; Shrider, K. R.; Lawrence, T. R.

1972-01-01

237

Near-wake vortex motions behind a circular cylinder at low Reynolds number  

Microsoft Academic Search

A topological point of view is taken to investigate vortex motions in the near-wake region of a circular cylinder, where the Taylor hypothesis does not hold. Three-dimensional flow fields in the wake-transition regime are constructed by synthesizing time-resolved PIV data obtained in several planes of view. The convection velocities of the Kármán and secondary vortices are evaluated from the trajectories

J. Sung; J. Y. Yoo

2003-01-01

238

Effects of Solar Wind Conditions on the Plasma Wake Within a Polar Crater: Preliminary Results  

NASA Technical Reports Server (NTRS)

As the solar wind sweeps horizontally past a shadowed lunar crater it simultaneously diffuses toward the surface through an ambipolar process, forming a plasma wake (e.g., Figure 1). Importantly, the resulting electric field structure diverts solar wind protons toward the cold crater floor where they may represent a source of surficial hydrogen. We present a handful of two-dimensional kinetic simulations exploring the range of wake structures and surface particle fluxes possible under various background plasma conditions.

Zimmerman, M. I.; Farrell, W. M.; Stubbs, T. J.

2011-01-01

239

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

240

Kinetic energy entrainment in wind turbine and actuator disc wakes: an experimental analysis  

NASA Astrophysics Data System (ADS)

The present experimental study focuses on the comparison between the wake of a two-bladed wind turbine and the one of an actuator disk. The flow field at the middle plane of the wake is measured with a stereoscopic particle image velocimetry setup, in the low-speed Open Jet Facility wind tunnel of the Delft University of Technology. The wind turbine wake is characterized by the complex dynamics of the tip vortex development and breakdown. Analysis of the flow statistics show anisotropic turbulent fluctuations in the turbine wake, with stronger components in the radial direction. The wake of the actuator disc is instead characterized by isotropic random fluctuations. The mixing process in the shear layer is further analysed in terms of flux of mean flow kinetic energy, to show the main differences between the kinetic energy entrainment in the actuator and the turbine wake. This project is intended to provide the basis for understanding the origin of the limitations of the current wake models based on the actuator disc assumption.

Lignarolo, L. E. M.; Ragni, D.; Simão Ferreira, C. J.; van Bussel, G. J. W.

2014-06-01

241

Effect of the solar-wind proton entry into the deepest lunar wake  

NASA Astrophysics Data System (ADS)

We study effect of the solar wind (SW) proton entry deep into the near-Moon wake that was recently discovered by the SELENE mission. Because previous lunar-wake models are based on electron domination, no effect of SW proton entry on the near-Moon wake environment has been taken into account so far. Recent SELENE observations revealed that a part of the SW protons are reflected at the lunar dayside surface and picked-up by the SW electric field (Saito et al., GRL, 2008), and some of them access the deepest lunar wake; this process is called type-II entry (Nishino et al., GRL, 2009). Here we show that the type-II entry of SW protons forms proton-governed region (PGR) to drastically change the electromagnetic environment of the lunar wake. Broadband electrostatic noise found in the PGR is manifestation of electron two-stream instability, which is attributed to the counter-streaming electrons absorbed from the ambient SW to maintain the quasi-neutrality. Acceleration of the absorbed electrons up to ~1 keV means a superabundance of positive charges of 10-4-10-7 cm-3 in the near-Moon wake, which should be immediately canceled out by the incoming high-speed electrons. This is a general phenomenon in the lunar wake, because PGR does not necessarily require peculiar SW condition for its formation.

Nishino, Masaki N.; Fujimoto, Masaki; Saito, Yoshifumi; Yokota, Shoichiro; Kasahara, Yoshiya; Tsunakawa, Hideo; Terasawa, Toshio

2010-05-01

242

Pluto's plasma wake oriented away from the ecliptic plane  

NASA Astrophysics Data System (ADS)

Conditions similar to those observed in the solar wind interaction with Venus and Mars where there is a planetary atmosphere in the absence of a global intrinsic magnetic field may also be applicable to Pluto. With up to 24 ?bars inferred for the Pluto atmosphere it is possible that the feeble solar photon radiation flux that reaches by its orbit, equivalent to ?10-3 that at Earth, is sufficient to produce an ionization component that can be eroded by the solar wind. In view of the reduced solar wind density (?10-3 with respect to that at 1 AU) that should be available by Pluto its total kinetic energy will be significantly smaller than that at Earth. However, the parameter values that are implied for the interaction process between the solar wind and the local upper ionosphere are sufficient to produce a plasma wake that should extend downstream from Pluto. In view of its low gravity force the plasma wake should have a wider cross-section than that in the Venus and Mars plasma environment. Since Pluto rotates with the axis tilted ?30° away from the ecliptic plane the plasma wake will be influenced by a Magnus force that has a large component is the north-south solar polar direction. That force will be responsible for propelling the plasma wake with a component that can be directed away from that plane. It is estimated that transport of solar wind momentum to the upper Pluto's ionosphere implies rotation periods smaller than that of the solid body, and thus large values of the Magnus force that can increase the orientation of the plasma wake away from the ecliptic plane.

Pérez-de-Tejada, H.; Durand-Manterola, H.; Reyes-Ruiz, M.; Lundin, R.

2015-01-01

243

Pluto's Plasma Wake Oriented Away from the Ecliptic Plane  

NASA Astrophysics Data System (ADS)

Conditions similar to those observed in the solar wind interaction with Venus and Mars with a planetary atmosphere and in the absence of an intrinsic magnetic field should also be applicable to Pluto. With up to 24 ?bars inferred for the Pluto atmosphere it is possible that the feeble solar photon radiation flux that reaches by its orbit, equivalent to ~10-3 of that at earth, is sufficient to produce an ionization component that can be eroded by the solar wind. In view of the reduced solar wind density (~ 10-3 with respect to that by 1 AU) that should be available by Pluto its kinetic energy will be significantly smaller than that by earth. However, the parameter values that are implied for the interaction process between the solar wind and the local upper ionosphere are sufficient to produce a plasma wake that should extend downstream from Pluto. In view of its low gravity force the plasma wake should have a wider cross-section than that in the Venus and Mars plasma environment. Since Pluto rotates with its rotational axis tilted close to its orbital plane the plasma wake will be influenced by a Magnus force that is nearly north-south oriented. That force will be responsible for propelling the plasma wake with a component that can be directed away from the ecliptic plane. It is estimated that transport of solar wind momentum to the upper Pluto's ionosphere implies rotation periods smaller than that of the solid body, and thus larger values of the Magnus force that can increase the orientation of the plasma wake away from the ecliptic plane.

Perez De Tejada, H. A.; Durand-Manterola, H.; Lundin, R. N.; Reyes-Ruiz, M.

2013-12-01

244

The Effect of Wake Passing on Turbine Blade Film Cooling  

NASA Technical Reports Server (NTRS)

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 demonstratable 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

1996-01-01

245

Wake Vortex Detection: Phased Microphone vs. Linear Infrasonic Array  

NASA Technical Reports Server (NTRS)

Sensor technologies can make a significant impact on the detection of aircraft-generated vortices in an air space of interest, typically in the approach or departure corridor. Current state-of-the art sensor technologies do not provide three-dimensional measurements needed for an operational system or even for wake vortex modeling to advance the understanding of vortex behavior. Most wake vortex sensor systems used today have been developed only for research applications and lack the reliability needed for continuous operation. The main challenges for the development of an operational sensor system are reliability, all-weather operation, and spatial coverage. Such a sensor has been sought for a period of last forty years. Acoustic sensors were first proposed and tested by National Oceanic and Atmospheric Administration (NOAA) early in 1970s for tracking wake vortices but these acoustic sensors suffered from high levels of ambient noise. Over a period of the last fifteen years, there has been renewed interest in studying noise generated by aircraft wake vortices, both numerically and experimentally. The German Aerospace Center (DLR) was the first to propose the application of a phased microphone array for the investigation of the noise sources of wake vortices. The concept was first demonstrated at Berlins Airport Schoenefeld in 2000. A second test was conducted in Tarbes, France, in 2002, where phased microphone arrays were applied to study the wake vortex noise of an Airbus 340. Similarly, microphone phased arrays and other opto-acoustic microphones were evaluated in a field test at the Denver International Airport in 2003. For the Tarbes and Denver tests, the wake trajectories of phased microphone arrays and lidar were compared as these were installed side by side. Due to a built-in pressure equalization vent these microphones were not suitable for capturing acoustic noise below 20 Hz. Our group at NASA Langley Research Center developed and installed an infrasonic array at the Newport News-Williamsburg International Airport early in the year 2013. A pattern of pressure burst, high-coherence intervals, and diminishing-coherence intervals was observed for all takeoff and landing events without exception. The results of a phased microphone vs. linear infrasonic array comparison will be presented.

Shams, Qamar A.; Zuckerwar, Allan J.; Sullivan, Nicholas T.; Knight, Howard K.

2014-01-01

246

Field trial analysis of nitrate reductase co-suppression: a comparative study of 38 combinations of transgene loci  

Microsoft Academic Search

Co-syppression of host genes and 35S transgenes encoding nitrate reductase was previously reported in transgenic tobacco plants (Nicotiana tabacum cv. Paraguay or Burley) using either a full-length cDNA or fragments devoid of the 3' and\\/or 5' UTR. Co-suppression was previously shown to affect a limited fraction of the progeny of one transgenic tobacco line homozygous for a single transgene locus,

Jean-Christophe Palauqui; Hervé Vaucheret

1995-01-01

247

SAR observation and numerical modeling of tidal current wakes at the East China Sea offshore wind farm  

NASA Astrophysics Data System (ADS)

A TerraSAR-X (TS-X) Synthetic Aperture Radar (SAR) image acquired at the East China Sea offshore wind farm presents distinct wakes at a kilometer scale on the lee of the wind turbines. The presumption was that these wakes were caused by wind movement around turbine blades. However, wind analysis using spaceborne radiometer data, numerical weather prediction, and in situ measurements suggest that the prevailing wind direction did not align with the wakes. By analyzing measurement at the tidal gauge station and modeling of the tidal current field, these trailing wakes are interpreted to have formed when a strong tidal current impinged on the cylindrical monopiles of the wind turbines. A numerical simulation was further conducted to reproduce the tidal current wake under such conditions. Comparison of the simulated surface velocity in the wake region with the TS-X sea surface backscatter intensity shows a similar trend. Consequently, turbulence intensity (T.I.) of the tidal current wakes over multiple piles is studied using the TS-X observation. It is found that the T.I. has a logarithmic relation with distance. Furthermore, another case study showing wakes due to wind movement around turbine blades is presented to discuss the differences in the tidal current wakes and wind turbine wakes. The conclusion is drawn that small-scale wakes formed by interaction of the tidal current and the turbine piles could be also imaged by SAR when certain conditions are satisfied. The study is anticipated to draw more attentions to the impacts of offshore wind foundations on local hydrodynamic field.

Li, XiaoMing; Chi, Lequan; Chen, Xueen; Ren, YongZheng; Lehner, Susanne

2014-08-01

248

Experimental Results on Rotor Wakes Narayanan Komerath  

E-print Network

Engineering Georgia Institute of Technology, Atlanta The wake of a rotor is at once an extremely complex these advances, shown both experimentally and through analysis and computation, it has become possible. Meanwhile, the ancient disconnect between the correct wake geometry as calculated from blade loading

249

Dream bizarreness and waking thought in schizophrenia  

Microsoft Academic Search

Dream diaries and reports of daytime waking thought were collected from five schizophrenia patients and matched controls. It was more difficult for blind judges to differentiate the patients' than the controls' dream reports from reports of waking thought, and patients reported shorter but more bizarre dreams than did the controls.

Valdas Noreika; Katja Valli; Juha Markkula; Katriina Seppälä; Antti Revonsuo

2010-01-01

250

Continuity between waking activities and dream activities  

Microsoft Academic Search

Empirical studies largely support the continuity hypothesis of dreaming. Despite 11 of previous research efforts, the exact formulation of the continuity hypothesis re- 12 mains vague. The present paper focuses on two aspects: (1) the differential incor- 13 poration rate of different waking-life activities and (2) the magnitude of which 14 interindividual differences in waking-life activities are reflected in corresponding

Michael Schredl; Friedrich Hofmann

2002-01-01

251

Continuity between waking activities and dream activities  

Microsoft Academic Search

Empirical studies largely support the continuity hypothesis of dreaming. Despite of previous research efforts, the exact formulation of the continuity hypothesis remains vague. The present paper focuses on two aspects: (1) the differential incorporation rate of different waking-life activities and (2) the magnitude of which interindividual differences in waking-life activities are reflected in corresponding differences in dream content. Using a

Michael Schredl; Friedrich Hofmann

2003-01-01

252

Suppression of Floating Body Effects by Controlling Potential Profile in the Lower Body Region of Silicon-on-Insulator Metal-Oxide-Semiconductor Field Effect Transistors  

NASA Astrophysics Data System (ADS)

This paper describes a promising way to suppress floating body effects (FBE) in fully depleted (FD) silicon-on-insulator metal-oxide-semiconductor field-effect transistors (SOI MOSFETs), which is applicable to the complementary MOS (CMOS) structure. The FBE is suppressed by controlling the potential profile by supplying an adequate positive substrate voltage (VSUB). FD SOI NMOSFETs show a strong dependence of VT on VD in the higher VD range, which is induced by the FBE@. The accumulation in the body of holes generated through impact ionization raises the body potential, and hence lowers VT. A positive VSUB improves the anomalous subthreshold slope, and thereby weakens the dependence of VT on VD. This is mainly because the positive VSUB lowers the potential barrier height for holes in the lower body region, which enhances the flow of holes in the body into the source, and thus suppresses the increase in body potential. The decrease in the potential barrier height for holes is supported by two-dimensional device simulation. Supplying a positive VSUB causes hardly any changes in the characteristics of SOI P-channel MOSFETs (PMOSFETs). Therefore, supplying a positive voltage to the substrate is useful for the SOI CMOS structure.

Sato, Yasuhiro; Tsuchiya, Toshiaki

2000-06-01

253

Monitoring Wake Vortices for More Efficient Airports  

NASA Technical Reports Server (NTRS)

Wake vortices are generated by all aircraft during flight. The larger the aircraft, the stronger the wake, so the Federal Aviation Administration (FAA) separates aircraft to ensure wake turbulence has no effect on approaching aircraft. Currently, though, the time between planes is often larger than it needs to be for the wake to dissipate. This unnecessary gap translates into arrival and departure delays, but since the wakes are invisible, the delays are nearly inevitable. If, however, the separation between aircraft can be reduced safely, then airport capacity can be increased without the high cost of additional runways. Scientists are currently studying these patterns to identify and introduce new procedures and technologies that safely increase airport capacity. NASA, always on the cutting edge of aerospace research, has been contributing knowledge and testing to these endeavors.

2005-01-01

254

Turbulent kinetic energy dissipation rate observations in the cold wake of Typhoon Fanapi  

NASA Astrophysics Data System (ADS)

Typhoon Fanapi formed in the western North Pacific Ocean, and became a named storm on September 14, 2010 in the vicinity of 129.1 E, 19.6 N. It subsequently traveled westward across the Philippine Sea and came ashore near Hualien, Tawain as a category 3 storm on the Saffir-Simpson scale (winds of 120 miles per hour) on September 19, 2010. The storm created a strong cold wake in the ocean along its path. Following the landfall of the typhoon, a research cruise abroad the R/V Revelle was undertaken to study the structure, evolution, and decay of the cold wake as part of the Impact of Typhoons on the Pacific (ITOP) study. Here we present observations of the cold wake revealing the residual turbulent kinetic energy after the storm. Hydrographic and velocity observations were made with coincident turbulence observations, made with a tethered free-falling profiler measuring shear microstructure. This data record allows us document the turbulent kinetic energy dissipation rate over a period spanning 3 to 18 days after the passage of the storm. In the near-surface layer (z<50-m depth), turbulent kinetic energy (TKE) dissipation rates were suppressed in the cold wake, relative to levels outside the wake, as a result of the increased stratification. It would appear that any enhancement of turbulence occurring in the near-surface layer had dissipated by the 3rd day after the storm's passage. However, below the cold wake, TKE dissipation rate levels decayed in the 2-week period after the storm, consistent with the decay on near-inertial energy. The results suggest that cold wakes may be an effective way to boost mixing through the mixed-layer/thermocline transition zone that links surface forcing to ocean interior processes.

St Laurent, L.; Jayne, S. R.; Lambert, S.; Douglass, E.; Rainville, L.; Lee, C. M.

2012-12-01

255

Computation of rotor aerodynamic loads with a constant vorticity contour free wake model  

NASA Technical Reports Server (NTRS)

An analytical method is presented which facilitates the study of isolated rotors with an improved approach to wake simulation. Vortex filaments are simulated along contours of constant sheet strength for the sheet of vorticity resulting from each rotor blade. Curved vortex elements comprise the filaments which can be distorted by the local velocity field. Called the Constant Vorticity Contour wake model, the approach permits the simulation of the blades' wakes corresponding to the full span of the rotor blade. The discretization of the wake of the rotor blade produces spacing and structure that are consistent with the spatial and temporal variations in the loading. A vortex-lattice aerodynamic model of the blade is also included which introduces a finite-element structural model of the blade and consideration of the force and moment trim analysis. Results of the present version of the simulation, called RotorCRAFT, are found to correlate well with H-34 flight-test data.

Quackenbush, Todd R.; Wachspress, Daniel A.; Boschitsch, Alexander H.

1991-01-01

256

POD Analysis of a Wind Turbine Wake in a Turbulent Atmospheric Boundary Layer  

NASA Astrophysics Data System (ADS)

The wake of a single wind turbine is modeled using an actuator disk model and large eddy simulations. As inflow condition a numerically generated turbulent atmospheric boundary layer is used. The proper orthogonal decomposition (POD) is applied to a plane perpendicular to the main flow in the far wake of the turbine. Reconstructions of the field are investigated depending on the numbers of POD modes used. Even though a great number of modes is needed to recover a great part of the turbulent kinetic energy, our results indicate that relevant aspects of a wake flow can be recovered using only a few modes. Particularly, the dynamics of the average velocity over a potential disk in the wake can partially be captured using only three modes.

Bastine, D.; Witha, B.; Wächter, M.; Peinke, J.

2014-06-01

257

Study for prediction of rotor/wake/fuselage interference, part 1  

NASA Technical Reports Server (NTRS)

A method was developed which allows the fully coupled calculation of fuselage and rotor airloads for typical helicopter configurations in forward flight. To do this, an iterative solution is carried out based on a conventional panel representation of the fuselage and a blade element representation of the rotor where fuselage and rotor singularity strengths are determined simultaneously at each step and the rotor wake is allowed to relax (deform) in response to changes in rotor wake loading and fuselage presence. On completion of the iteration, rotor loading and inflow, fuselage singularity strength (and, hence, pressure and velocity distributions) and rotor wake are all consistent. The results of a fully coupled calculation of the flow around representative helicopter configurations are presented. The effect of fuselage components on the rotor flow field and the overall wake structure is detailed and the aerodynamic interference between the different parts of the aircraft is discussed.

Clark, D. R.; Maskew, B.

1985-01-01

258

Study for prediction of rotor/wake/fuselage interference. Part 2: Program users guide  

NASA Technical Reports Server (NTRS)

A method was developed which permits the fully coupled calculation of fuselage and rotor airloads for typical helicopter configurations in forward flight. To do this, an iterative solution is carried out based on a conventional panel representation of the fuselage and a blade element representation of the rotor where fuselage and rotor singularity strengths are determined simultaneously at each step and the rotor wake is allowed to relax (deform) in response to changes in rotor wake loading and fuselage presence. On completion of the iteration, rotor loading and inflow, fuselage singularity strength (and, hence, pressure and velocity distributions) and rotor wake are all consistent. The results of a fully coupled calculation of the flow around representative helicopter configurations are presented. The effect of fuselage components on the rotor flow field and the overall wake structure is discussed as well as the aerodynamic interference between the different parts of the aircraft. Details of the computer program are given.

Clark, D. R.; Maskew, B.

1985-01-01

259

Wake interaction and power production of variable height model wind farms  

NASA Astrophysics Data System (ADS)

Understanding wake dynamics is an ongoing research topic in wind energy, since wakes have considerable effects on the power production when wind turbines are placed in a wind farm. Wind tunnel experiments have been conducted to study the wake to wake interaction in a model wind farm in tandem with measurements of the extracted power. The aim is to investigate how alternating mast height influences the interaction of the wakes and the power production. Via the use of stereo-particle image velocimetry, the flow field was obtained in the first and last rows of the wind turbine array as a basis of comparison. It was found that downstream of the exit row wind turbine, the power was increased by 25% in the case of a staggered height configuration. This is partly due to the fact that the taller turbines reach into a flow area with a softened velocity gradient. Another aspect is that the wake downstream of a tall wind turbine to some extent passes above the standard height wind turbine. Overall the experiments show that the velocity field downstream of the exit row changes considerably when the mast height is alternating.

Vested, M. H.; Hamilton, N.; Sørensen, J. N.; Cal, R. B.

2014-06-01

260

A Critical Review of the Transport and Decay of Wake Vortices in Ground Effect  

NASA Technical Reports Server (NTRS)

This slide presentation reviews the transport and decay of wake vortices in ground effect and cites a need for a physics-based parametric model. The encounter of a vortex with a solid body is always a complex event involving turbulence enhancement, unsteadiness, and very large gradients of velocity and pressure. Wake counter in ground effect is the most dangerous of them all. The interaction of diverging, area-varying, and decaying aircraft wake vortices with the ground is very complex because both the vortices and the flow field generated by them are altered to accommodate the presence of the ground (where there is very little room to maneuver) and the background turbulent flow. Previous research regarding vortex models, wake vortex decay mechanisms, time evolution within in ground effect of a wake vortex pair, laminar flow in ground effect, and the interaction of the existing boundary layer with a convected vortex are reviewed. Additionally, numerical simulations, 3-dimensional large-eddy simulations, a probabilistic 2-phase wake vortex decay and transport model and a vortex element method are discussed. The devising of physics-based, parametric models for the prediction of (operational) real-time response, mindful of the highly three-dimensional and unsteady structure of vortices, boundary layers, atmospheric thermodynamics, and weather convective phenomena is required. In creating a model, LES and field data will be the most powerful tools.

Sarpkaya, T.

2004-01-01

261

Transitions in the vortex wake behind the plunging profile  

NASA Astrophysics Data System (ADS)

In this study we investigate numerically the vortex wake formation behind the profile performing simple harmonic motion known in the literature as plunging. This research was inspired by the flapping motion which is appropriate for birds, insects and fishes. We assume the two dimensional model of flow. Depending on the parameters such as plunging amplitude, frequency and the Reynolds number, we demonstrate many different types of vortex street behind the profile. It is well known that the type of vortex wake determines the hydrodynamic forces acting on the profile. Dependences of the plunging amplitude, the Strouhal number and various topology vortices are established by constructing the phase transition diagram. The areas in the diagram related to the drag, thrust, and lift force generation are captured. We notice also the areas where the vorticity field is disordered. The disordered vorticity field does not allow maintenance of the periodic forces on the profile. An increase in the Reynolds number leads to the transition of the vortex wake behind the profile. The transition is caused by the phenomenon of boundary layer eruption. Further increase of the Reynolds number causes the vortex street related to the generation of the lift force to vanish.

Koz?owski, Tomasz; Kudela, Henryk

2014-12-01

262

Non-linear plasma wake growth of electron holes  

NASA Astrophysics Data System (ADS)

An object's wake in a plasma with small Debye length that drifts across the magnetic field is subject to electrostatic electron instabilities. Such situations include, for example, the moon in the solar wind and probes in magnetized laboratory plasmas. The instability drive mechanism can equivalently be considered drift down the potential-energy gradient or drift up the density-gradient. The gradients arise because the plasma wake has a region of depressed density and electrostatic potential into which ions are attracted along the field. The non-linear consequences of the instability are analysed in this paper. At physical ratios of electron to ion mass, neither linear nor quasilinear treatment can explain the observation of large-amplitude perturbations that disrupt the ion streams well before they become ion-ion unstable. We show here, however, that electron holes, once formed, continue to grow, driven by the drift mechanism, and if they remain in the wake may reach a maximum non-linearly stable size, beyond which their uncontrolled growth disrupts the ions. The hole growth calculations provide a quantitative prediction of hole profile and size evolution. Hole growth appears to explain the observations of recent particle-in-cell simulations.

Hutchinson, I. H.; Haakonsen, C. B.; Zhou, C.

2015-03-01

263

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

264

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

265

Three-dimensional lunar wake reconstructed from ARTEMIS data  

NASA Astrophysics Data System (ADS)

Data from the two-spacecraft Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun mission to the Moon have been exploited to characterize the lunar wake with unprecedented fidelity. The differences between measurements made by a spacecraft in the solar wind very near the Moon and concurrent measurements made by a second spacecraft in the near lunar wake are small but systematic. They enabled us to establish the perturbations of plasma density, temperature, thermal, magnetic and total pressure, field, and flow downstream of the Moon to distances of 12 lunar radii (RM). The wake disturbances are initiated immediately behind the Moon by the diamagnetic currents at the lunar terminator. Rarefaction waves propagate outward at fast MHD wave velocities. Beyond ~6.5 RM, all plasma and field parameters are poorly structured which suggests the presence of instabilities excited by counter-streaming particles. Inward flowing plasma accelerated through pressure gradient force and ambipolar electric field compresses the magnetic field and leads to continuous increase in magnitude of magnetic perturbations. Besides the downstream distance, the field perturbation magnitude is also a function of the solar wind ion beta and the angle between the solar wind and the interplanetary magnetic field (IMF). Both ion and electron temperatures increase as a consequence of an energy dispersion effect, whose explanation requires fully kinetic models. Downstream of the Moon, the IMF field lines are observed to bulge toward the Moon, which is unexpected and may be caused by a plasma pressure gradient force or/and the pickup of heavy charged dust grains behind the Moon.

Zhang, H.; Khurana, K. K.; Kivelson, M. G.; Angelopoulos, V.; Wan, W. X.; Liu, L. B.; Zong, Q.-G.; Pu, Z. Y.; Shi, Q. Q.; Liu, W. L.

2014-07-01

266

Bubbly wake: the role of the propeller  

NASA Astrophysics Data System (ADS)

We study the length of the bubbly wake of surface vessels. This wake is important for the boat security since it can extend to several ship length and thus increases the detectability of the ship by torpedoes. The image analysis of the wake of real scale ships reveals the sensitivity of the length to propellers. We have thus conducted a systematic study in the laboratory of the interaction bubble/propeller, trying to address several questions:- what is the role of cavitation?- is the propeller able to attract the bubbles present along the ship at the sea surface?- if attracted, can these bubble be broken by the propeller?

Caille, Francois

2005-11-01

267

Aircraft control in wake vortex wind shear  

NASA Technical Reports Server (NTRS)

In the past, there have been a number of fatal incidents attributable to wake vortex encounters, involving both general aviation and commercial aircraft. In fact, the wake vortex hazard is considered to be the single dominant safety issue determining the aircraft spacing requirements at airports. As the amount of air traffic increases, the number of dangerous encounters is likely only to increase. It is therefore imperative that a means be found to reduce the danger. That is the purpose of this research: to use nonlinear inverse dynamic (NID) control methods in the design of an aircraft control system which can improve the safety margin in a wake vortex encounter.

Wold, Gregory R.

1995-01-01

268

The symmetric turbulent wake of a flat plate  

NASA Technical Reports Server (NTRS)

Detailed measurements of mean flow and turbulence in the developing symmetric wake of a smooth, flat plate are presented. The results are discussed in the light of previous data and theories for near and far wakes. It is shown that evolution of the upstream boundary layers into the classical asymptotic wake occurs in three quite distinct stages and takes about 350 wake momentum thicknesses.

Ramaprian, B. R.; Patel, V. C.; Sastry, M. S.

1982-01-01

269

Enhancement of high-energy electron generation through suppression of Raman backscattering  

SciTech Connect

The effect of Raman backscattering (RBS) on high-energy electron generation in laser-plasma interaction has been investigated for laser intensities well above the wave breaking and electron trapping threshold. One-dimensional particle-in-cell simulations show that suppression of RBS increases the high-energy electron yield in this regime. RBS-induced heating causes heavy beam loading and damping of the laser wake. Its suppression leads to higher wake amplitudes and higher particle energies. RBS suppression through direct stimulation of Raman forward scatter is demonstrated. The implications for high-energy electron production through laser-plasma interaction are discussed.

Trines, R.M.G.M.; Kamp, L.P.J.; Schep, T.J.; Leemans, W.P.; Esarey, E.H.; Sluijter, F.W.

2004-05-27

270

Suppression of quantum decoherence via infrared-driven coherent exciton-plasmon coupling: Undamped field and Rabi oscillations  

SciTech Connect

We show that when a semiconductor quantum dot is in the vicinity of a metallic nanoparticle and driven by a mid-infrared laser field, its coherent dynamics caused by interaction with a visible laser field can become free of quantum decoherence. We demonstrate that this process, which can offer undamped Rabi and field oscillations, is the result of coherent normalization of the “effective” polarization dephasing time of the quantum dot (T{sub 2}{sup *}). This process indicates formation of infrared-induced coherently forced oscillations, which allows us to control the value of T{sub 2}{sup *} using the infrared laser. The results offer decay-free ultrafast modulation of the effective field experienced by the quantum dot when neither the visible laser field nor the infrared laser changes with time.

Sadeghi, S. M., E-mail: seyed.sadeghi@uah.edu [Department of Physics, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States); Nano and Micro Device Center, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States); Patty, K. D. [Department of Physics, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States)

2014-02-24

271

Analysis of long distance wakes behind a row of turbines - a parameter study  

NASA Astrophysics Data System (ADS)

Large Eddy Simulations (LES) of the long distance wake behind a row of 10 turbines are conducted to predict wake recovery. The Navier-Stokes solver EllipSys3D is used in combination with the actuator disc concept. Neutral atmospheric conditions are assumed in combination with synthetic turbulence using the Mann method. Both the wind shear profile and turbulence are introduced into the flow field using body forces. Previous simulations using the same simulation method to model the Horns Rev wind farm showed a higher wake recovery at long distances compared to measurements. The current study investigates further the sensitivity to parameters such as the grid resolution, Reynolds number, the turbulence characteristics as well as the impact of using different internal turbine spacings. The clearest impact on the recovery behind the farm could be seen from the turbulence intensity of the incoming flow. The impact of the wind shear on the turbulence intensity in the domain needs further studies. A lower turbulence level gives slower wake recovery as expected. A slower wake recovery can also be seen for a higher grid resolution. The Reynolds number, apart from when using a very low value, has a small impact on the result. The variation of the internal spacing is seen to have a relatively minor impact on the farm wake recovery.

Eriksson, O.; Nilsson, K.; Breton, S.-P.; Ivanell, S.

2014-06-01

272

Hippocampal corticosterone impairs memory consolidation during sleep but improves consolidation in the wake state  

PubMed Central

We studied the interaction between glucocorticoid (GC) level and sleep/wake state during memory consolidation. Recent research has accumulated evidence that sleep supports memory consolidation in a unique physiological process, qualitatively distinct from consolidation occurring during wakefulness. This appears particularly true for memories that rely on the hippocampus, a region with abundant expression of GC receptors. Against this backdrop we hypothesized that GC effects on consolidation depend on the brain state, i.e., sleep and wakefulness. Following exploration of two objects in an open field, during 80 min retention periods rats received an intrahippocampal infusion of corticosterone (10 ng) or vehicle while asleep or awake. Then the memory was tested in the hippocampus-dependent object-place recognition paradigm. GCs impaired memory consolidation when administered during sleep but improved consolidation during the wake retention interval. Intrahippocampal infusion of GC or sleep/wake manipulations did not alter novel-object recognition performance that does not require the hippocampus. This work corroborates the notion of distinct consolidation processes occurring in sleep and wakefulnesss, and identifies GCs as a key player controlling distinct hippocampal memory consolidation processes in sleep and wake conditions. © 2014 Wiley Periodicals, Inc. PMID:24596244

Kelemen, Eduard; Bahrendt, Marie; Born, Jan; Inostroza, Marion

2014-01-01

273

PIV and LDA measurements of the wake behind a wind turbine model  

NASA Astrophysics Data System (ADS)

In the present work we review the results of a series of measurements of the flow behind a model scale of a horizontal axis wind turbine rotor carried out at the water flume at Technical University of Denmark (DTU). The rotor is three-bladed and designed using Glauert theory for tip speed ratio ? =5 with a constant design lift coefficient along the span, CLdesign= 0.8. The measurements include dye visualization, Particle Image Velocimetry and Laser Doppler Anemometry. The wake instability has been studied in the range ? =3 - 9 at different cross-sections from the very near wake up to 10 rotor diameters downstream from the rotor. The initial flume flow was subject to a very low turbulence level with a uniform velocity profile, limiting the influence of external disturbances on the development of the inherent vortex instability. Using PIV measurements and visualizations, special attention was paid to detect and categorize different types of wake instabilities and the development of the flow in the near and the far wake. In parallel to PIV, LDA measurements provided data for various rotor regimes, revealing the existence of three main regular frequencies governing the development of different processes and instabilities in the rotor wake. In the far wake a constant frequency corresponding to the Strouhal number was found for the long-scale instabilities. This Strouhal number is in good agreement with the well-known constant that usually characterizes the oscillation in wakes behind bluff bodies. From associated visualizations and reconstructions of the flow field, it was found that the dynamics of the far wake is associated with the precession (rotation) of a helical vortex core. The data indicate that Strouhal number of this precession is independent of the rotor angular speed.

Naumov, I. V.; Mikkelsen, R. F.; Okulov, V. L.; Sørensen, J. N.

2014-06-01

274

Simulations of accelerating currents in Io's plasma wake  

NASA Astrophysics Data System (ADS)

The evolution of an Io-perturbed flux tube was studied numerically via magnetohydrodynamics MHD approach of a thin filament Our simulations suggest that the mechanism for producing wake aurora could not be explained by either Alfvén wave or electric circuit alone 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 developed before it is released downstream A magnetic field depression forms downstream as a result of the continual departure of the flux tubes from Io which in turn has significant influence on the motion of a flux tube A perturbed flux tube would undergo a subcorotational motion in Io s plasma wake This motion is inevitably modulated by Alfvén wave bouncing back and forth between the equatorial plane and the boundary of Io plasma torus The scale of the subcorotation region is in the order of 1 Jovian radius The distribution of the simulated accelerating currents downstream is consistent with the observed wake aurora brightness profile

Chen, C. X.

275

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

276

Use of Individual Flight Corridors to Avoid Vortex Wakes  

NASA Technical Reports Server (NTRS)

Vortex wakes of aircraft pose a hazard to following aircraft until the energetic parts of their flow fields have decayed to a harmless level. It is suggested here that in-trail spacings between aircraft can be significantly and safely reduced by designing an individual, vortex-free flight corridor for each aircraft. Because each aircraft will then have its own flight corridor, which is free of vortex wakes while in use by the assigned aircraft, the time intervals between aircraft operations can be safely reduced to the order of seconds. The productivity of airports can then be substantially increased. How large the offset distances between operational corridors need to be to have them vortex free, and how airports need to be changed to accommodate an individual flight-corridor process for landing and takeoff operations, are explored. Estimates are then made of the productivity of an individual flight-corridor system as a function of the in-trail time interval between operations for various values of wake decay time, runway width, and the velocity of a sidewind. The results confirm the need for short time intervals between aircraft operations if smaller offset distances and increased productivity are to be achieved.

Rossow, Vernon J.

2001-01-01

277

Investigation of aircraft vortex wake structure  

NASA Astrophysics Data System (ADS)

In this work we analyze the mechanisms of formation of the vortex wake structure of aircraft with different wing shape in the plan flying close to or away from the underlying surface cleaned or released mechanization wing.

Baranov, N. A.; Turchak, L. I.

2014-11-01

278

NASA Wake Vortex Research for Aircraft Spacing  

NASA Technical Reports Server (NTRS)

The National Aeronautics and Space Administration (NASA) is addressing airport capacity enhancements during instrument meteorological conditions through the Terminal Area Productivity (TAP) program. Within TAP, the Reduced Spacing Operations (RSO) subelement at the NASA Langley Research Center is developing an Aircraft Vortex Spacing System (AVOSS). AVOSS will integrate the output of several inter-related areas to produce weather dependent, dynamic wake vortex spacing criteria. These areas include current and predicted weather conditions, models of wake vortex transport and decay in these weather conditions, real-time feedback of wake vortex behavior from sensors, and operationally acceptable aircraft/wake interaction criteria. In today's ATC system, the AVOSS could inform ATC controllers when a fixed reduced separation becomes safe to apply to large and heavy aircraft categories. With appropriate integration into the Center/TRACON Automation System (CTAS), AVOSS dynamic spacing could be tailored to actual generator/follower aircraft pairs rather than a few broad aircraft categories.

Perry, R. Brad; Hinton, David A.; Stuever, Robert A.

1996-01-01

279

Three-Phased Wake Vortex Decay  

NASA Technical Reports Server (NTRS)

A detailed parametric study is conducted that examines vortex decay within turbulent and stratified atmospheres. The study uses a large eddy simulation model to simulate the out-of-ground effect behavior of wake vortices due to their interaction with atmospheric turbulence and thermal stratification. This paper presents results from a parametric investigation and suggests improvements for existing fast-time wake prediction models. This paper also describes a three-phased decay for wake vortices. The third phase is characterized by a relatively slow rate of circulation decay, and is associated with the ringvortex stage that occurs following vortex linking. The three-phased decay is most prevalent for wakes imbedded within environments having low-turbulence and near-neutral stratification.

Proctor, Fred H.; Ahmad, Nashat N.; Switzer, George S.; LimonDuparcmeur, Fanny M.

2010-01-01

280

On the wake of a Darrieus turbine  

NASA Technical Reports Server (NTRS)

The theory and experimental measurements on the aerodynamic decay of a wake from high performance vertical axis wind turbine are discussed. In the initial experimental study, the wake downstream of a model Darrieus rotor, 28 cm diameter and a height of 45.5 cm, was measured in a Boundary Layer Wind Tunnel. The wind turbine was run at the design tip speed ratio of 5.5. It was found that the wake decayed at a slower rate with distance downstream of the turbine, than a wake from a screen with similar troposkein shape and drag force characteristics as the Darrieus rotor. The initial wind tunnel results indicated that the vertical axis wind turbines should be spaced at least forty diameters apart to avoid mutual power depreciation greater than ten per cent.

Base, T. E.; Phillips, P.; Robertson, G.; Nowak, E. S.

1981-01-01

281

Model of the Human Sleep Wake System  

E-print Network

A model and analysis of the human sleep/wake system is presented. The model is derived using the known neuronal groups, and their various projections, involved with sleep and wake. Inherent in the derivation is the existence of a slow time scale associated with homeostatic regulation, and a faster time scale associated with the dynamics within the sleep phase. A significant feature of the model is that it does not contain a periodic forcing term, common in other models, reflecting the fact that sleep/wake is not dependent upon a diurnal stimulus. Once derived, the model is analyzed using a linearized stability analysis. We then use experimental data from normal sleep-wake systems and orexin knockout systems to verify the physiological validity of the equations.

Rogers, Lisa

2012-01-01

282

Secure Wake-Up Scheme for WBANs  

NASA Astrophysics Data System (ADS)

Network life time and hence device life time is one of the fundamental metrics in wireless body area networks (WBAN). To prolong it, especially those of implanted sensors, each node must conserve its energy as much as possible. While a variety of wake-up/sleep mechanisms have been proposed, the wake-up radio potentially serves as a vehicle to introduce vulnerabilities and attacks to WBAN, eventually resulting in its malfunctions. In this paper, we propose a novel secure wake-up scheme, in which a wake-up authentication code (WAC) is employed to ensure that a BAN Node (BN) is woken up by the correct BAN Network Controller (BNC) rather than unintended users or malicious attackers. The scheme is thus particularly implemented by a two-radio architecture. We show that our scheme provides higher security while consuming less energy than the existing schemes.

Liu, Jing-Wei; Ameen, Moshaddique Al; Kwak, Kyung-Sup

283

Review of Idealized Aircraft Wake Vortex Models  

NASA Technical Reports Server (NTRS)

Properties of three aircraft wake vortex models, Lamb-Oseen, Burnham-Hallock, and Proctor are reviewed. These idealized models are often used to initialize the aircraft wake vortex pair in large eddy simulations and in wake encounter hazard models, as well as to define matched filters for processing lidar observations of aircraft wake vortices. Basic parameters for each vortex model, such as peak tangential velocity and circulation strength as a function of vortex core radius size, are examined. The models are also compared using different vortex characterizations, such as the vorticity magnitude. Results of Euler and large eddy simulations are presented. The application of vortex models in the postprocessing of lidar observations is discussed.

Ahmad, Nashat N.; Proctor, Fred H.; Duparcmeur, Fanny M. Limon; Jacob, Don

2014-01-01

284

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

2011-03-01

285

Wake-up effects in Si-doped hafnium oxide ferroelectric thin films  

SciTech Connect

Hafnium oxide based ferroelectric thin films have shown potential as a promising alternative material for non-volatile memory applications. This work reports the switching stability of a Si-doped HfO{sub 2} film under bipolar pulsed-field operation. High field cycling causes a “wake-up” in virgin “pinched” polarization hysteresis loops, demonstrated by an enhancement in remanent polarization and a shift of negative coercive voltage. The rate of wake-up is accelerated by either reducing the frequency or increasing the amplitude of the cycling field. We suggest de-pinning of domains due to reduction of the defect concentration at bottom electrode interface as origin of the wake-up.

Zhou, Dayu, E-mail: zhoudayu@dlut.edu.cn [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China) [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Key Laboratory for Materials Modification by Laser, Ion and Electron Beams, Ministry of Education, Dalian University of Technology, Dalian 116024 (China); State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China); Xu, Jin [Department of Electronic Engineering, Dalian Neusoft University of Information, Dalian 116023 (China)] [Department of Electronic Engineering, Dalian Neusoft University of Information, Dalian 116023 (China); Li, Qing; Guan, Yan [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China)] [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Cao, Fei; Dong, Xianlin [Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China)] [Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Müller, Johannes [Fraunhofer IPMS-CNT, Koengisbruecker Strasse 180, 01109 Dresden (Germany)] [Fraunhofer IPMS-CNT, Koengisbruecker Strasse 180, 01109 Dresden (Germany); Schenk, Tony; Schröder, Uwe [Namlab gGmbH/TU Dresden, Noethnitzer Strasse 64, 01187 Dresden (Germany)] [Namlab gGmbH/TU Dresden, Noethnitzer Strasse 64, 01187 Dresden (Germany)

2013-11-04

286

Suppression of antiferromagnetic ordering by magnetic field in Ce0.6La0.4In3  

NASA Astrophysics Data System (ADS)

Electrical resistivity and specifc heat measurements were performed at high magnetic fields up to 45 T in Ce0.6La0.4In3, which is the La-substituted material to heavy fermion antiferromagnet CeIn3. In Ce0.6La0.4In3, the H-T phase diagram was drawn and the critical magnetic field was estimated to be approximately at 39 T. The critical field of Ce0.6La0.4In3 is about 20 T lower than that at 60 T of CeIn3. Lower critical field facilitates observing Fermi surfaces when crossing phase boundary between antiferromagnetic and paramagnetic phases. Thus, the phase diagram obtained from our results should be a guide when we compare the Fermi surface topology in antiferromagnetic phase to that in paramagnetic phase.

Ebihara, T.; Silhanek, A. V.; Jaime, M.; Harrison, N.

2015-03-01

287

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

288

Mesoscale wake clouds in Skylab pictures.  

NASA Technical Reports Server (NTRS)

The recognition of cloud patterns formed in the wake of orographic obstacles was investigated using pictures from Skylab, for the purpose of estimating atmospheric motions. The existence of ship-wake-type wave clouds in contrast to vortex sheets were revealed during examination of the pictures, and an attempt was made to characterize the pattern of waves as well as the transition between waves and vortices. Examples of mesoscale cloud patterns which were analyzed photogrammetrically and meteorologically are presented.

Fujita, T. T.; Tecson, J. J.

1974-01-01

289

Wake-Vortex Hazards During Cruise  

NASA Technical Reports Server (NTRS)

Even though the hazard posed by lift-generated wakes of subsonic transport aircraft has been studied extensively for approach and departure at airports, only a small amount of effort has gone into the potential hazard at cruise altitude. This paper reports on a studio of the wake-vortex hazard during cruise because encounters may become more prevalent when free-flight becomes available and each aircraft, is free to choose its own route between destinations. In order to address the problem, the various fluid-dynamic stages that vortex wakes usually go through as they age will be described along with estimates of the potential hazard that each stage poses. It appears that a rolling-moment hazard can be just as severe at cruise as for approach at airports, but it only persists for several minutes. However, the hazard posed by the downwash in the wake due to the lift on the generator aircraft persists for tens of minutes in a long narrow region behind the generating aircraft. The hazard consists of severe vertical loads when an encountering aircraft crosses the wake. A technique for avoiding vortex wakes at cruise altitude will be described. To date the hazard posed by lift-generated vortex wakes and their persistence at cruise altitudes has been identified and subdivided into several tasks. Analyses of the loads to be encounter and are underway and should be completed shortly. A review of published literature on the subject has been nearly completed (see text) and photographs of vortex wakes at cruise altitudes have been taken and the various stages of decay have been identified. It remains to study and sort the photographs for those that best illustrate the various stages of decay after they are shed by subsonic transport aircraft at cruise altitudes. The present status of the analysis and the paper are described.

Rossow, Vernon J.; James, Kevin D.; Nixon, David (Technical Monitor)

1998-01-01

290

Secure Wake-Up Scheme for WBANs  

Microsoft Academic Search

Network life time and hence device life time is one of the fundamental metrics in wireless body area networks (WBAN). To prolong it, especially those of implanted sensors, each node must conserve its energy as much as possible. While a variety of wake-up\\/sleep mechanisms have been proposed, the wake-up radio potentially serves as a vehicle to introduce vulnerabilities and attacks

Jing-Wei Liu; Moshaddique Al Ameen; Kyung-Sup Kwak

2010-01-01

291

Vortex interactions and decay in aircraft wakes  

NASA Technical Reports Server (NTRS)

The dynamic interaction of aircraft wake vortices was investigated using both inviscid and viscous models. For the viscous model, a computer code was developed using a second-order closure model of turbulent transport. The phenomenon of vortex merging which results in the rapid aging of a vortex wake was examined in detail. It was shown that the redistribution of vorticity during merging results from both convective and diffusive mechanisms.

Bilanin, A. J.; Teske, M. E.; Dupdonaldson, C.; Williamson, G. G.

1977-01-01

292

Abstract--This paper presents the comparison of sleep-wake classification using electroencephalogram (EEG) and  

E-print Network

/wake identification has been used both in clinical fields and personal health/wellness fields. Clinically, polysomnography (PSG) has been used to monitor sleep and identify sleep disorders in sleep labs as a gold standard multiple sensors (accelerometer, photoplethysmogram, etc). Due to advances in device technology, more

293

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

294

Computation of wake/exhaust mixing downstream of advanced transport aircraft  

NASA Technical Reports Server (NTRS)

The mixing of engine exhaust with the vortical wake of high speed aircraft operating in the stratosphere can play an important role in the formation of chemical products that deplete atmospheric ozone. An accurate analysis of this type of interaction is therefore necessary as a part of the assessment of the impact of proposed High Speed Civil Transport (HSCT) designs on atmospheric chemistry. This paper describes modifications to the parabolic Navier-Stokes flow field analysis in the UNIWAKE unified aircraft wake model to accommodate the computation of wake/exhaust mixing and the simulation of reacting flow. The present implementation uses a passive chemistry model in which the reacting species are convected and diffused by the fluid dynamic solution but in which the evolution of the species does not affect the flow field. The resulting analysis, UNIWAKE/PCHEM (Passive CHEMistry) has been applied to the analysis of wake/exhaust flows downstream of representative HSCT configurations. The major elements of the flow field model are described, as are the results of sample calculations illustrating the behavior of the thermal exhaust plume and the production of species important to the modeling of condensation in the wake. Appropriate steps for further development of the UNIWAKE/PCHEM model are also outlined.

Quackenbush, Todd R.; Teske, Milton E.; Bilanin, Alan J.

1993-01-01

295

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

296

Analysis of the Radar Reflectivity of Aircraft Vortex Wakes  

NASA Technical Reports Server (NTRS)

Radar has been proposed as a way to track wake vortices to reduce aircraft spacing and tests have revealed radar echoes from aircraft wakes in clear air. The results are always interpreted qualitatively using Tatarski's theory of weak scattering by isotropic atmospheric turbulence. The goal of the present work was to predict the value of the radar cross-section (RCS) using simpler models. This is accomplished in two steps. First, the refractive index is obtained. Since the structure of the aircraft wakes is different from atmospheric turbulence, three simple mechanisms specific to vortex wakes are considered: (1) Radial density gradient in a two-dimensional vortex, (2) three-dimensional fluctuations in the vortex cores, and (3) Adiabatic transport of the atmospheric fluid in a two-dimensional oval surrounding the pair of vortices. The index of refraction is obtained more precisely for the two-dimensional mechanisms than for the three-dimensional ones. In the second step, knowing the index of refraction, a scattering analysis is performed. 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, a simpler approximation 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. The predicted RCS values for the oval surround the vortices (mechanism C) agree with the experiments of Bilson conducted over a wide range of frequencies. However, the predictions have a cut-off away from normal incidence which is not present in the measurements. Estimates suggest that this is due to turbulence in the baroclinic vorticity generated at the boundary of the oval. The reflectivity of a vortex itself (mechanism A) is comparable to that of the oval (mechanism C) but cuts-off at frequencies lower than those considered in all the experiments to date. The RCS of a vortex happens to peak at the frequency (about 49 MHz) where atmospheric radars (known as ST radars) operate and so the present prediction could be verified in the future. Finally , we suggest that hot engine exhaust could increase RCE by 40 db and reveal vortex circulation, provided its mixing with the surroundings is prevented in the laminarising flow of the vortices.

Shariff, Karim; Wray, Alan; Yan, Jerry (Technical Monitor)

2000-01-01

297

Do trout swim better than eels? Challenges for estimating performance based on the wake of self-propelled bodies  

NASA Astrophysics Data System (ADS)

Engineers and biologists have long desired to compare propulsive performance for fishes and underwater vehicles of different sizes, shapes, and modes of propulsion. Ideally, such a comparison would be made on the basis of either propulsive efficiency, total power output or both. However, estimating the efficiency and power output of self-propelled bodies, and particularly fishes, is methodologically challenging because it requires an estimate of thrust. For such systems traveling at a constant velocity, thrust and drag are equal, and can rarely be separated on the basis of flow measured in the wake. This problem is demonstrated using flow fields from swimming American eels, Anguilla rostrata, measured using particle image velocimetry (PIV) and high-speed video. Eels balance thrust and drag quite evenly, resulting in virtually no wake momentum in the swimming (axial) direction. On average, their wakes resemble those of self-propelled jet propulsors, which have been studied extensively. Theoretical studies of such wakes may provide methods for the estimation of thrust separately from drag. These flow fields are compared with those measured in the wakes of rainbow trout, Oncorhynchus mykiss, and bluegill sunfish, Lepomis macrochirus. In contrast to eels, these fishes produce wakes with axial momentum. Although the net momentum flux must be zero on average, it is neither spatially nor temporally homogeneous; the heterogeneity may provide an alternative route for estimating thrust. This review shows examples of wakes and velocity profiles from the three fishes, indicating challenges in estimating efficiency and power output and suggesting several routes for further experiments. Because these estimates will be complicated, a much simpler method for comparing performance is outlined, using as a point of comparison the power lost producing the wake. This wake power, a component of the efficiency and total power, can be estimated in a straightforward way from the flow fields. Although it does not provide complete information about the performance, it can be used to place constraints on the relative efficiency and cost of transport for the fishes.

Tytell, Eric D.

2007-11-01

298

Do trout swim better than eels? Challenges for estimating performance based on the wake of self-propelled bodies  

NASA Astrophysics Data System (ADS)

Engineers and biologists have long desired to compare propulsive performance for fishes and underwater vehicles of different sizes, shapes, and modes of propulsion. Ideally, such a comparison would be made on the basis of either propulsive efficiency, total power output or both. However, estimating the efficiency and power output of self-propelled bodies, and particularly fishes, is methodologically challenging because it requires an estimate of thrust. For such systems traveling at a constant velocity, thrust and drag are equal, and can rarely be separated on the basis of flow measured in the wake. This problem is demonstrated using flow fields from swimming American eels, Anguilla rostrata, measured using particle image velocimetry (PIV) and high-speed video. Eels balance thrust and drag quite evenly, resulting in virtually no wake momentum in the swimming (axial) direction. On average, their wakes resemble those of self-propelled jet propulsors, which have been studied extensively. Theoretical studies of such wakes may provide methods for the estimation of thrust separately from drag. These flow fields are compared with those measured in the wakes of rainbow trout, Oncorhynchus mykiss, and bluegill sunfish, Lepomis macrochirus. In contrast to eels, these fishes produce wakes with axial momentum. Although the net momentum flux must be zero on average, it is neither spatially nor temporally homogeneous; the heterogeneity may provide an alternative route for estimating thrust. This review shows examples of wakes and velocity profiles from the three fishes, indicating challenges in estimating efficiency and power output and suggesting several routes for further experiments. Because these estimates will be complicated, a much simpler method for comparing performance is outlined, using as a point of comparison the power lost producing the wake. This wake power, a component of the efficiency and total power, can be estimated in a straightforward way from the flow fields. Although it does not provide complete information about the performance, it can be used to place constraints on the relative efficiency and cost of transport for the fishes.

Tytell, Eric D.

299

Deep Water Oceanic Wakes: a simple case study  

NASA Astrophysics Data System (ADS)

In present study we investigate the formation and evolution of oceanic wakes generated by obstacle of a real island shape (in our case - Madeira island) but without consideration of bathymetry around it. Numerical simulations using Regional Ocean Modeling System (ROMS) are presented. ROMS is a free-surface, terrain-following, primitive equations ocean model (Shchepetkin and McWilliams, 2005). Numerical models are often used to study the formation and evolution of the leeward, mesoscale and sub-mesoscale flows around of islands (Dietrich et al., 1996; Dong et al., 2007; Heywood et al., 1996). Madeira archipelago is a group of deep-sea islands located at Northeast Atlantic at about 33°N, 17°W. The biggest island of the archipelago is Madeira Island with about 50 km in east-west and 20 km in north-south direction. Its obstruction to the incoming oceanic and atmospheric flows induces leeward wake instabilities. This phenomena is observed using remote sensing and field data (Caldeira et al., 2002). We use the similar methodology to study Madeira island wakes problem as it was presented at Dong et al., 2007. The main difference between their study and ours is that they carried out experiences with an idealized cylindrical obstacle and we are using an island with its real shape at the surface and with vertical sides. The island was centered in a geostrophic channel like configuration with a prescribed surface intensified meridional (southward) inflow at the upstream boundary (i.e., our study is dedicated to the wakes, generated at the eastern and western part of Madeira Island). Eastern and Western channel boundaries were set to slippery-tangential and zero normal conditions, whereas boundaries around the island were set to zero-normal and no-slip flow. A clamped condition with a sponge layer was applied at the southern outflow boundary for outgoing current and density profile. The initial conditions for the entire domain were set equal to the upstream boundary condition expect at the island points. Our numerical simulations were devoted to study of various dynamical flow regimes. Obtained results showed that oceanic wakes formations were sensitive to three dimensionless parameters that representing a ratio between inertial and frictional forces - Reynolds number (Re), rotational effects - Rossby number (Ro) and stratification effects - Burger number (Bu). Wake asymmetries induce different behaviour for cyclonic and anti-cyclonic eddies than that showed by Dong et al., 2007. References: Caldeira, R.M.A., S. Groom, P. Miller, D. Pilgrim and N. Nezlin, 2002: Sea-surface signatures of the island mass effect phenomena around Madeira Island, Northeast Atlantic, Remote Sensing of the Environment, 80, 336-360. Dietrich, D.E., M.J. Bowman, C.A. Lin and A. Mestas-Nunez, 1996: Numerical studies of small island wakes, Geophysics, Astrophysics and Fluid Dynamics, 83, 195-231. Dong, C., J.C. McWilliams and A. Shchepetkin, 2007: Island Wakes in Deep Water, Journal of Physical Oceanography, 37, 962-981. Heywood, K.J., D.P Stevens, G.R. Bigg, 1996: Eddy formation behind the tropical island of Aldabra, Deep-Sea Research I, 43, 555-578. Shchepetkin, A.F., and J.C. McWilliams, 2005: The Regional Ocean Modeling System: A split-explicit, free-surface, topography-following-coordinate oceanic model, Ocean Modelling, 9, 347-404.

Luis, E. A.; Boutov, D.

2009-04-01

300

Wake deficit measurements on the Jess and Souza Ranches, Altamont Pass  

SciTech Connect

This report is ninth in a series of documents presenting the findings of field test under DOE's Cooperative Field Test Program (CFTP) with the wind industry. This report provides results of a project conducted by Altamont Energy Corp. (AEC) to measure wake deficits on the Jess and Sousa Ranches in Altamont Pass, CA. This research enhances and complements other DOE-funded projects to refine estimates of wind turbine array effects. This project will help explain turbine performance variability caused by wake effects. 4 refs., 28 figs., 106 tabs.

Nierenburg, R. (Altamont Energy Corp., San Rafael, CA (USA))

1990-04-01

301

Evolution and breakdown of helical vortex wakes behind a wind turbine  

NASA Astrophysics Data System (ADS)

The wake behind a three-bladed Glauert model rotor in a water channel was investigated. Planar particle image velocimetry was used to measure the velocity fields on the wake centre-line, with snapshots phase-locked to blade position of the rotor. Phase- locked averages of the velocity and vorticity fields are shown, with tip vortex interaction and entanglement of the helical filaments elucidated. Proper orthogonal decomposition and topology-based vortex identification are used to filter the PIV images for coherent structures and locate vortex cores. Application of these methods to the instantaneous data reveals unsteady behaviour of the helical filaments that is statistically quantifiable.

Nemes, A.; Sherry, M.; Lo Jacono, D.; Blackburn, H. M.; Sheridan, J.

2014-12-01

302

JOURNAL OF DISPLAY TECHNOLOGY, VOL. 6, NO. 6, JUNE 2010 229 Color Breakup Suppression in Field-Sequential  

E-print Network

%, as compared to the three-primary LCDs. Index Terms--Color breakup, liquid crystal display (LCD), multi liquid crystal display (LCD) devices, especially for large screen TVs. The two most lossy components--Field-sequential-color liquid crystal displays (FSC LCDs) exhibit a 3 higher optical efficiency and 3 higher res- olution

Wu, Shin-Tson

303

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...

304

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

305

User's guide for a flat wake rotor inflow/wake velocity prediction code, DOWN  

NASA Technical Reports Server (NTRS)

A computer code named DOWN was created to implement a flat wake theory for the calculation of rotor inflow and wake velocities. A brief description of the code methodology and instructions for its use are given. The code will be available from NASA's Computer Software Management and Information Center (COSMIC).

Wilson, John C.

1991-01-01

306

Simulation of wind turbine wakes using the actuator line technique.  

PubMed

The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated snapshots of the wake. PMID:25583862

Sørensen, Jens N; Mikkelsen, Robert F; Henningson, Dan S; Ivanell, Stefan; Sarmast, Sasan; Andersen, Søren J

2015-02-28

307

Dynamic wake prediction and visualization with uncertainty analysis  

NASA Technical Reports Server (NTRS)

A dynamic wake avoidance system utilizes aircraft and atmospheric parameters readily available in flight to model and predict airborne wake vortices in real time. A novel combination of algorithms allows for a relatively simple yet robust wake model to be constructed based on information extracted from a broadcast. The system predicts the location and movement of the wake based on the nominal wake model and correspondingly performs an uncertainty analysis on the wake model to determine a wake hazard zone (no fly zone), which comprises a plurality of wake planes, each moving independently from another. The system selectively adjusts dimensions of each wake plane to minimize spatial and temporal uncertainty, thereby ensuring that the actual wake is within the wake hazard zone. The predicted wake hazard zone is communicated in real time directly to a user via a realistic visual representation. In an example, the wake hazard zone is visualized on a 3-D flight deck display to enable a pilot to visualize or see a neighboring aircraft as well as its wake. The system substantially enhances the pilot's situational awareness and allows for a further safe decrease in spacing, which could alleviate airport and airspace congestion.

Holforty, Wendy L. (Inventor); Powell, J. David (Inventor)

2005-01-01

308

Interference suppression in the two-photon annihilation of an electron positron pair in the light wave field  

Microsoft Academic Search

Nonresonant two-photon annihilation of an electron-positron pair in the field of a moderately strong circularly polarized wave is investigated theoretically. The partial cross-section can be summed over all processes of emission and absorption of photons. It is shown that all essentially quantum contributions caused by the Bunkin-Fedorov quantum parameter are compensated for both Feynman diagrams and are not compensated for

O. I. Denisenko; S. P. Roshchupkin; A. I. Voroshilo

2006-01-01

309

Chronic decrease in wakefulness and disruption of sleep-wake behavior after experimental traumatic brain injury.  

PubMed

Traumatic brain injury (TBI) can cause sleep-wake disturbances and excessive daytime sleepiness. The pathobiology of sleep disorders in TBI, however, is not well understood, and animal models have been underused in studying such changes and potential underlying mechanisms. We used the rat lateral fluid percussion (LFP) model to analyze sleep-wake patterns as a function of time after injury. Rapid-eye movement (REM) sleep, non-REM (NREM) sleep, and wake bouts during light and dark phases were measured with electroencephalography and electromyography at an early as well as chronic time points after LFP. Moderate TBI caused disturbances in the ability to maintain consolidated wake bouts during the active phase and chronic loss of wakefulness. Further, TBI resulted in cognitive impairments and depressive-like symptoms, and reduced the number of orexin-A-positive neurons in the lateral hypothalamus. PMID:25242371

Skopin, Mark D; Kabadi, Shruti V; Viechweg, Shaun S; Mong, Jessica A; Faden, Alan I

2015-03-01

310

Characteristics of Low-Frequency Waves at the Lunar Wake Boundary  

NASA Astrophysics Data System (ADS)

The Moon has generally been considered to be a simple absorbing body that does not have a complex interaction with the solar wind. Recent studies using Kaguya and Chandrayaan, however, how demonstrated that this is not the case. The ARTEMIS spacecraft (formerly THEMIS-B and -C) entered lunar orbit in July 2011 and now provide an opportunity to make robust, long-term observations of this plasma interaction. During a November 2012 wake crossing, when the IMF was steady and nearly radial, Halekas et al. [2013] documented a previously unseen feature of the Moon environment. As ARTEMIS P2 approached the wake, it observed low-amplitude fast magnetonic waves that were convected from upstream; inside the rarefaction region, the compressional strength of these waves intensified; and through the wake boundary, the waves changed from correlated to anti-correlated density and field fluctuations. Halekas et al. explained this structure as the superposition of the magnetosonic waves and lateral wake motion driven by the same. In this study, we use wake observations through the ARTEMIS mission to characterize the presence and behavior of these waves as a function of the solar wind and IMF conditions and of spacecraft location relative to the Moon. With this survey, we test the Halekas et al. predictions that these phenomena will be most common during radial IMF conditions, but will still be observable in oblique fields. Finally, we discuss what implications these results have for the more common situation where a bow shock is present.

Leisner, J. S.; Glassmeier, K.; Constantinescu, D. O.; Halekas, J. S.; Fornacon, K.

2013-12-01

311

Recent Developments on Airborne Forward Looking Interferometer for the Detection of Wake Vortices  

NASA Technical Reports Server (NTRS)

A goal of these studies was development of the measurement methods and algorithms necessary to detect wake vortex hazards in real time from either an aircraft or ground-based hyperspectral Fourier Transform Spectrometer (FTS). This paper provides an update on research to model FTS detection of wake vortices. The Terminal Area Simulation System (TASS) was used to generate wake vortex fields of 3-D winds, temperature, and absolute humidity. These fields were input to the Line by Line Radiative Transfer Model (LBLRTM), a hyperspectral radiance model in the infrared, employed for the FTS numerical modeling. An initial set of cases has been analyzed to identify a wake vortex IR signature and signature sensitivities to various state variables. Results from the numerical modeling case studies will be presented. Preliminary results indicated that an imaging IR instrument sensitive to six narrow bands within the 670 to 3150 per centimeter spectral region would be sufficient for wake vortex detection. Noise floor estimates for a recommended instrument are a current research topic.

Daniels, Taumi S.; Smith, William L.; Kirev, Stanislav

2012-01-01

312

Wind tunnel simulation of a wind turbine wake in neutral, stable and unstable wind flow  

NASA Astrophysics Data System (ADS)

Measurements of mean velocity, Reynolds stresses, temperature and heat flux have been made in the wake of a model wind turbine in the EnFlo meteorology wind tunnel, for three atmospheric boundary layer states: the base-line neutral case, stable and unstable. The full-to-model scale is approximately 300:1. Primary instrumentation is two-component LDA combine with cold-wire thermometry to measure heat flux. In terms of surface conditions, the stratified cases are weak, but there is a strong 'imposed' condition in the stable case. The measurements were made between 0.5D and 10D, where D is the turbine disk diameter. In the stable case the velocity deficit decreases more slowly; more quickly in the unstable case. Heights at which quantities are maximum or minimum are greater in the unstable case and smaller in the stable case. In the stable case the wake height is suppressed but the width is increased, while in the unstable case the height is increased and the width (at hub height) reaches a maximum and then decreases. The turbulence in the wake behaves in a complex way. Further work needs to be done, to cover stronger levels of surface condition, requiring more extensive measurements to properly capture the wake development.

Hancock, P. E.; Zhang, S.; Pascheke, F.; Hayden, P.

2014-12-01

313

Stability analysis of shallow wake flows  

NASA Astrophysics Data System (ADS)

Experimentally observed periodic structures in shallow (i.e. bounded) wake flows are believed to appear as a result of hydrodynamic instability. Previously published studies used linear stability analysis under the rigid-lid assumption to investigate the onset of instability of wakes in shallow water flows. The objectives of this paper are: (i) to provide a preliminary assessment of the accuracy of the rigid-lid assumption; (ii) to investigate the influence of the shape of the base flow profile on the stability characteristics; (iii) to formulate the weakly nonlinear stability problem for shallow wake flows and show that the evolution of the instability is governed by the Ginzburg Landau equation; and (iv) to establish the connection between weakly nonlinear analysis and the observed flow patterns in shallow wake flows which are reported in the literature. It is found that the relative error in determining the critical value of the shallow wake stability parameter induced by the rigid-lid assumption is below 10% for the practical range of Froude number. In addition, it is shown that the shape of the velocity profile has a large influence on the stability characteristics of shallow wakes. Starting from the rigid-lid shallow-water equations and using the method of multiple scales, an amplitude evolution equation for the most unstable mode is derived. The resulting equation has complex coefficients and is of Ginzburg Landau type. An example calculation of the complex coefficients of the Ginzburg Landau equation confirms the existence of a finite equilibrium amplitude, where the unstable mode evolves with time into a limit-cycle oscillation. This is consistent with flow patterns observed by Ingram & Chu (1987), Chen & Jirka (1995), Balachandar et al. (1999), and Balachandar & Tachie (2001). Reasonable agreement is found between the saturation amplitude obtained from the Ginzburg Landau equation under some simplifying assumptions and the numerical data of Grubi[sbreve]ic et al. (1995). Such consistency provides further evidence that experimentally observed structures in shallow wake flows may be described by the nonlinear Ginzburg Landau equation. Previous works have found similar consistency between the Ginzburg Landau model and experimental data for the case of deep (i.e. unbounded) wake flows. However, it must be emphasized that much more information is required to confirm the appropriateness of the Ginzburg Landau equation in describing shallow wake flows.

Kolyshkin, A. A.; Ghidaoui, M. S.

2003-11-01

314

Electrically-activated source extension graphene nanoribbon field effect transistor: Novel attributes and design considerations for suppressing short channel effects  

NASA Astrophysics Data System (ADS)

In this paper a double gate graphene nanoribbon field effect transistor with electrically-activated source extension is proposed. Source region of the proposed structure includes two sections, an electrically-activated extension and a doped section. The electrically extension, which is located between doped source section and gate region, is biased independent of the gate to form a virtual extension for source. The electrically-activated extension creates a step in potential profile which increases the horizontal distance between conduction and valance bands at channel to source junction. This step reduces the probability of band to band tunneling, lowers the leakage current and improves drain induced barrier lowering. The devices have been simulated based on self consistent solution of Poisson and Schrodinger equations within non-equilibrium Green's function formalism. In addition, the effects of the edge and third nearest neighbor are included for more accurate outcomes. Simulations show that the proposed structure is a more reliable device because of its higher ON/Off current ratio, shorter delay time, and smaller power delay product beside lower subthreshold swing than conventional graphene nanoribbon field effect transistor.

Naderi, Ali; Keshavarzi, Parviz

2014-08-01

315

Effect of solar-wind proton entry into the deepest lunar wake  

NASA Astrophysics Data System (ADS)

We study effect of solar wind (SW) proton entry deep into the near-Moon wake that was recently discovered by the SELENE mission. It has been accepted that the high-speed electrons in the ambient SW determine the lunar night-side environment. Therefore, previous lunar-wake models are based on the electron domination, and no effect of SW proton entry on the near-Moon wake environment has been taken into account so far. Recent SELENE observations revealed that a part of the SW protons are reflected at the lunar dayside surface and picked-up by the SW electric field (Saito et al., GRL, 2008), and some of them access the deepest lunar wake; this process is called type-II entry (Nishino et al., GRL, 2009). Here we show that the type-II entry of SW protons forms proton-governed region (PGR) to drastically change the electromagnetic environment of the lunar wake. Broadband electrostatic noise found in the PGR is manifestation of electron two-stream instability, which is attributed to the counter-streaming electrons absorbed from the ambient SW to maintain the quasi-neutrality. An acceleration of the absorbed electrons up to ˜1 keV means a superabundance of positive charges of 10-5 ˜10-7 cm-3 in the near-Moon wake, which should be immediately canceled out by the incoming high-speed electrons. This is a general phenomenon in the lunar wake, because PGR does not necessarily require peculiar SW condition for its formation.

Nishino, Masaki N.; Fujimoto, Masaki; Saito, Yoshifumi; Yokota, Shoichiro; Kasahara, Yoshiya; Omura, Yoshiharu; Goto, Yoshitaka; Hashimoto, Kozo; Kumamoto, Atsushi; Ono, Takayuki; Tsunakawa, Hideo; Matsushima, Masaki; Takahashi, Futoshi; Shibuya, Hidetoshi; Shimizu, Hisayoshi; Terasawa, Toshio

316

Effects of a three-dimensional hill on the wake characteristics of a model wind turbine  

NASA Astrophysics Data System (ADS)

The spatial evolution of a turbine wake downwind of a three-dimensional sinusoidal hill is studied using large-eddy simulations and wind tunnel measurements. The computed flow fields behind the hill show good agreement with wind tunnel measurements. Three different heights of the hill, i.e., hhill = zh - 0.5D, ? zh and =zh + 0.5D (where zh is the turbine hub height and D is the diameter of the turbine rotor), were considered. The effect of the hill turbine spacing was investigated through a comparative analysis with the turbine wake results in the undisturbed turbulent boundary layer. It is observed that the turbine wakes downwind of the hill with hhill ? zh and hhill = zh + 0.5D recover faster because of the increased entrainment of ambient flow into the turbine wake, which is due to the enhanced turbulent transport in both spanwise and vertical directions. In comparison with the turbine only case, significant increases in the turbulence kinetic energy (TKE) in the turbine wake are observed for the hill-turbine cases with hhill ? zh and hhill = zh + 0.5D. A velocity scale UT, defined in terms of the thrust force acting on the turbine, is introduced for the turbine-added velocity deficit and TKE. For the turbine-added velocity deficit, UT is shown to be an appropriate scale at wake locations sufficiently far downwind of the turbine (i.e., greater than or equal to 8D). The vertical profiles of the turbine-added TKE normalized by UT 2 are shown to nearly collapse in the wake both for the turbine only and hill-turbine cases at all locations greater than 4D downwind of the turbine. A simple model for the turbine-added TKE in complex terrain is also proposed based on the new physical insights obtained from our simulations.

Yang, Xiaolei; Howard, Kevin B.; Guala, Michele; Sotiropoulos, Fotis

2015-02-01

317

Magnetoelectric phenomena in manganites R0.6Ca0.4MnO3(R = Pr, Nd) with charge ordering suppressed by a magnetic field  

NASA Astrophysics Data System (ADS)

A change in electric polarization (up to 300 ?C/m2) upon magnetic-field suppression of a charge-ordered antiferromagnetic state upon a transition to the ferromagnetic conducting phase ( H cr ˜ 65-80 kOe at 4.2 K) is discovered in Pr0.6Ca0.4MnO3 and Nd0.6Ca0.4MnO3 single crystals. The transition is also accompanied by a jump in magnetization and magnetostriction. The dependence of the induced polarization sign on the polarity of the electric field in which the sample was preliminarily cooled indicates the existence of spontaneous electric polarization. The effect is the strongest in Nd0.6Ca0.4MnO3 and is weaker by a factor of 5-10 in Pr0.6Ca0.4MnO3, for which the tolerance factor is higher. The observed effect may be associated with recently predicted noncentrosymmetric structures in doped manganites with x ˜ 0.5 (see D.V. Efremov, J. van den Brink, and D.I. Khomskii, Nature Materials 3, 853 (2004)), in which e g electrons are not localized upon charge and orbital ordering at one manganese ion, but are distributed among neighboring ions, thus forming an ordered polar dimer structure.

Kadomtseva, A. M.; Popov, Yu. F.; Vorob'ev, G. P.; Kamilov, K. I.; Ivanov, V. Yu.; Mukhin, A. A.; Balbashov, A. M.

2008-01-01

318

Wake Vortex Tracking Using a 35 GHz Pulsed Doppler Radar  

NASA Technical Reports Server (NTRS)

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 weight classifications. When ambient conditions are such that vortices will either drift or dissipate, leaving the flight corridor clear, the prescribed spacings are unnecessarily long and result in decreased airport throughput. There is a potential for significant airport efficiency improvement, if a system can be employed to aid regulators and pilots in setting safe and efficient following distances based on airport conditions. The National Aeronautics and Space Administration (NASA), the Federal Aviation Agency, and Volpe National Transportation Systems Center have promoted and worked to develop systems that would increase airport capacity and provide for safe reductions in aircraft separation. The NASA Aircraft Vortex Spacing System (AVOSS), a wake vortex spacing system that can provide dynamic adjustment of spacings based on real-time airport weather conditions, has demonstrated that Lidar systems can be successfully used to detect and track vortices in clear air conditions. To fill the need for detection capability in low-visibility conditions, a 35 GHz, pulsed-Doppler radar system is being investigated for use as a complimentary, low-visibility sensor for wake vortices. The radar sensor provides spatial and temporal information similar to that provided by Lidar, but under weather conditions that a Lidar cannot penetrate. Currently, we are analyzing the radar design based upon the data and experience gained during the wake vortex Lidar deployment with AVOSS at Dallas/Fort Worth International Airport. As part of this study, two numerical models were utilized in system simulations. The results of this study improve our understanding of the method of detection, resolution requirements for range and azimuth, pulse compression, and performance prediction. Simulations applying pulse compression techniques show that detection is good in heavy fog to greater than 2000 m. Both compressed and uncompressed short pulses show the vortex structure. To explore operational challenges, siting and scanning strategies were also analyzed. Simulation results indicate that excellent wake vortex detection, tracking and classification is possible in drizzle (+15 dBZ) and heavy fog (- 13 dBZ) using short pulse techniques (<99ns) at ranges on the order of 900 m, with a modest power of 500 W output. At 1600 m, detection can be expected at reflectivities as low as -13 dBZ (heavy fog). The radar system, as designed and built, has the potential to support field studies of a wake vortex spacing system in low-visibility conditions ranging from heavy fog to rain, when sited within 2000m of the flight path.

Neece, Robert T.; Britt, Charles L.; White, Joseph H.; Mudukutore, Ashok; Nguyen, Chi; Hooper, Bill

2005-01-01

319

[Sleep and wakefulness in Callorhinus ursinus].  

PubMed

Sleep and wakefulness of northern fur seals were studied on three subadult bulls carrying the implanted electrodes for recording the electrocorticogram of the two hemispheres, the neck electromiogram, the electrooculogram and the electrocardiogram. The active wakefulness accounted for 32.0 +/- 5.3% of total recording time, the relaxed wakefulness -31.7 +/- 3.1%, the slow wave sleep -30.5 +/- 5.1% and the paradoxical sleep -5.8 +/- 0.9%. The sleep cycle averaged 22,6 +/- 1.2 minutes. Interhemispheric asymmetry of the ECoG slow waves was pronounced in all three animals. Different forms of the asymmetry occupied 15.0 +/- 0.7% of total recording time. Such interhemispheric asymmetry was found in pinnipeds for the first time, in this respect the northern fur seals differ from the Caspean seals but resemble the dolphins. PMID:6475297

Mukhametov, L M; Liamin, O I; Poliakova, I G

1984-01-01

320

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. PMID:23592926

Wang, Jie; Cui, Jiefeng

2013-01-01

321

Fetal behavioural states: sleep and wakefulness?  

PubMed

The behaviour of fetuses in utero is often described using terms that were originally devised to describe behaviour after birth. This article considers a definition of the states of coma, sleep, and wakefulness, using criteria that might equally be applied before and after birth. Current knowledge of behaviour of the sheep and human fetus is discussed in the light of such criteria. It is concluded that these species do not appear to be comatose in utero. At present there is insufficient evidence to conclude that sleep and wakefulness exist in utero. PMID:1598421

Parkes, M J

1992-04-01

322

Effects of incoming surface wind conditions on the wake characteristics and dynamic wind loads acting on a wind turbine model  

NASA Astrophysics Data System (ADS)

An experimental investigation was conducted to examine the effects of incoming surface wind conditions on the wake characteristics and dynamic wind loads acting on a wind turbine model. The experimental study was performed in a large-scale wind tunnel with a scaled three-blade Horizontal Axial Wind Turbine model placed in two different types of Atmospheric Boundary Layer (ABL) winds with distinct mean and turbulence characteristics. In addition to measuring dynamic wind loads acting on the model turbine by using a force-moment sensor, a high-resolution Particle Image Velocimetry system was used to achieve detailed flow field measurements to characterize the turbulent wake flows behind the model turbine. The measurement results reveal clearly that the discrepancies in the incoming surface winds would affect the wake characteristics and dynamic wind loads acting on the model turbine dramatically. The dynamic wind loads acting on the model turbine were found to fluctuate much more significantly, thereby, much larger fatigue loads, for the case with the wind turbine model sited in the incoming ABL wind with higher turbulence intensity levels. The turbulent kinetic energy and Reynolds stress levels in the wake behind the model turbine were also found to be significantly higher for the high turbulence inflow case, in comparison to those of the low turbulence inflow case. The flow characteristics in the turbine wake were found to be dominated by the formation, shedding, and breakdown of various unsteady wake vortices. In comparison with the case with relatively low turbulence intensities in the incoming ABL wind, much more turbulent and randomly shedding, faster dissipation, and earlier breakdown of the wake vortices were observed for the high turbulence inflow case, which would promote the vertical transport of kinetic energy by entraining more high-speed airflow from above to re-charge the wake flow and result in a much faster recovery of the velocity deficits in the turbine wake.

Tian, Wei; Ozbay, Ahmet; Hu, Hui

2014-12-01

323

Three-Centimeter Doppler Radar Observations of Wingtip-Generated Wake Vortices in Clear Air  

NASA Technical Reports Server (NTRS)

This report documents a high risk, high pay-off experiment with the objective of detecting, for the first time, the presence of aircraft wake vortices in clear air using X-band Doppler radar. Field experiments were conducted in January 1995 at the Wallops Flight Facility (WFF) to demonstrate the capability of the 9.33 GHz (I=3 cm) radar, which was assembled using an existing nine-meter parabolic antenna reflector at VVTT and the receiver/transmitter from the NASA Airborne Windshear Radar-Program. A C-130-aircraft, equipped with wingtip smoke generators, created visually marked wake vortices, which were recorded by video cameras. A C-band radar also observed the wake vortices during detection attempts with the X-band radar. Rawinsonde data was used to calculate vertical soundings of wake vortex decay time, cross aircraft bearing wind speed, and water vapor mixing ratio for aircraft passes over the radar measurement range. This experiment was a pathfinder in predicting, in real time, the location and persistence of C-130 vortices, and in setting the flight path of the aircraft to optimize X-band radar measurement of the wake vortex core in real time. This experiment was conducted in support of the NASA Aircraft Vortex Spacing System (AVOSS).

Marshall, Robert E.; Mudukutore, Ashok; Wissel, Vicki L. H.; Myers, Theodore

1997-01-01

324

The effect of flow perturbations on the near wake characteristics of a circular cylinder  

NASA Astrophysics Data System (ADS)

The mean and fluctuating velocity fields in the near wake of a circular cylinder subjected to an incident mean flow with periodic velocity perturbations superimposed upon it were examined using laser Doppler anemometry. From these measurements the wake was characterized in terms of the recirculation bubble length, vortex formation length, maximum intensity of the velocity fluctuations and the wavelength of the vortex street. The well-known `lock-on' phenomenon was observed for perturbation frequencies around two times the natural vortex shedding frequency. It is shown that the wake structure is modified in a systematic manner within the lock-on range. The forced wake shares many basic characteristics as that of a cylinder oscillating either transversely or in line, relative to the flow direction. These include the shortening of the recirculation bubble and the vortex formation region as well as the variation of the longitudinal vortex spacing with perturbation frequency. Differences but also similarities between forced wakes at low (less than 350) and relatively higher Reynolds numbers (greater than 350) are discussed.

Konstantinidis, E.; Balabani, S.; Yianneskis, M.

2003-09-01

325

Study of the Mutual Interaction Between a Wing Wake and an Encountering Airplane  

NASA Technical Reports Server (NTRS)

In an effort to increase airport productivity, several wind-tunnel and flight-test programs are currently underway to determine safe reductions in separation standards between aircraft. These programs are designed to study numerous concepts from the characteristics and detection of wake vortices to the wake-vortex encounter phenomenon. As part of this latter effort, computational tools are being developed and utilized as a means of modeling and verifying wake-vortex hazard encounters. The objective of this study is to assess the ability of PMARC, a low-order potential-flow panel method, to predict the forces and moments imposed on a following business-jet configuration by a vortex interaction. Other issues addressed include the investigation of several wake models and their ability to predict wake shape and trajectory, the validity of the velocity field imposed on the following configuration, modeling techniques and the effect of the high-lift system and the empennage. Comparisons with wind-tunnel data reveal that PMARC predicts the characteristics for the clean wing-body following configuration fairly well. Non-linear effects produced by the addition of the high-lift system and empennage, however, are not so well predicted.

Walden, A. B.; vanDam, C. P.

1996-01-01

326

To what extent do neurobiological sleep-waking processes support psychoanalysis?  

PubMed

Sigmund Freud's thesis was that there is a censorship during waking that prevents memory of events, drives, wishes, and feelings from entering the consciousness because they would induce anxiety due to their emotional or ethical unacceptability. During dreaming, because the efficiency of censorship is decreased, latent thought contents can, after dream-work involving condensation and displacement, enter the dreamer's consciousness under the figurative form of manifest content. The quasi-closed dogma of psychoanalytic theory as related to unconscious processes is beginning to find neurobiological confirmation during waking. Indeed, there are active processes that suppress (repress) unwanted memories from entering consciousness. In contrast, it is more difficult to find neurobiological evidence supporting an organized dream-work that would induce meaningful symbolic content, since dream mentation most often only shows psychotic-like activities. PMID:20870071

Gottesmann, Claude

2010-01-01

327

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...

328

[Frontiers in Bioscience 8, s1056-1067, September 1, 2003] SLEEP, WAKING AND NEUROBEHAVIOURAL PERFORMANCE  

E-print Network

sleep loss 6. Countermeasures to neurobehavioural deficits associated with sleep loss 6.1. Naps 6.1.1. Laboratory studies 6.1.2. Prophylactic napping 6.1.3. Field studies 6.2. Sleep inertia 6.3.Rest breaks, but rather in counteracting them, via the use of countermeasures, such as naps and wake promoting compounds

Pennsylvania, University of

329

Laser Doppler velocimeter system simulation for sensing aircraft wake vortices  

NASA Technical Reports Server (NTRS)

A hydrodynamic model of aircraft vortex wakes in an irregular wind shear field near the ground is developed and used as a basis for modeling the characteristics of a laser Doppler detection and vortex location system. The trailing vortex sheet and the wind shear are represented by discrete free vortices distributed over a two-dimensional grid. The time dependent hydrodynamic equations are solved by direct numerical integration in the Boussinesq approximation. The ground boundary is simulated by images, and fast Fourier Transform techniques are used to evaluate the vorticity stream function. The atmospheric turbulence was simulated by constructing specific realizations at time equal to zero, assuming that Kolmogoroff's law applies, and that the dissipation rate is constant throughout the flow field. The response of a simulated laser Doppler velocimeter is analyzed by simulating the signal return from the flow field as sensed by a simulation of the optical/electronic system.

Thomson, J. A. L.; Meng, J. C. S.

1974-01-01

330

Properties of aircraft wake vortices measured by ground-based continuous-wave Doppler lidar  

NASA Astrophysics Data System (ADS)

The DLR ground-based cw Doppler lidar has been developed for wind and turbulence measurements in the Atmospheric Boundary Layer. Moreover, it is used for experimental investigations of aircraft wake vortices. By the present paper measurements of wake vortices generated by military-type fixed-wing as well as rotor-wing aircraft will be presented. The experimental data has been analyzed regarding the structure and circulation of wake vortices, partly also regarding their temporal development. The influence of flight parameters has been measured during several consecutive fly-bys. Small variations in the velocity profiles could be observed which were overlayed by the signatures of the variable wind and turbulence field, a problem which can only be solved by statistical treatment. The influence of the aircraft design could be demonstrated by comparison of the vortex signatures generated by two B707-type aircraft with pronounced differences in aircraft design.

Koepp, Friedrich

1999-05-01

331

Wake pattern and wave resistance for anisotropic moving disturbances  

NASA Astrophysics Data System (ADS)

We present a theoretical study of gravity waves generated by an anisotropic moving disturbance. We model the disturbance by an elliptical pressure field of given aspect ratio W. We study the wake pattern as a function of W and the longitudinal hull Froude number Fr = V/sqrt{gL}, where V is the velocity, g is the acceleration of gravity, and L is the size of the disturbance in the direction of motion. For large hull Froude numbers, we analytically show that the rescaled surface profiles for which sqrt{W}/Fr is kept constant coincide. In particular, the angle outside which the surface is essentially flat remains constant and equal to the Kelvin angle, and the angle corresponding to the maximum amplitude of the waves scales as sqrt{W}/Fr, thus showing that previous work on the wake's angle for isotropic objects can be extended to anisotropic objects of given aspect ratio. We then focus on the wave resistance and discuss its properties in the case of an elliptical Gaussian pressure field. We derive an analytical expression for the wave resistance in the limit of very elongated objects and show that the position of the speed corresponding to the maximum wave resistance scales as sqrt{gL}/sqrt{W}.

Benzaquen, Michael; Darmon, Alexandre; Raphaël, Elie

2014-09-01

332

Observations of the trade wind wakes of Kauai and Oahu  

E-print Network

[1] The Hawaiian islands of Kauai and Oahu stand in the path of the east-northeasterly trade winds, creating wakes in the lee. For the first time, the structure of the wakes and their diurnal cycle were observed on a cruise during 18–20 December 2006. The dynamic wakes, characterized by reduced

Yang Yang; Jian Ma; Shang-ping Xie

333

Active Wake Redirection Control to Improve Energy Yield (Poster)  

SciTech Connect

Wake effects can dramatically reduce the efficiency of waked turbines relative to the unwaked turbines. Wakes can be deflected, or 'redirected,' by applying yaw misalignment to the turbines. Yaw misalignment causes part of the rotor thrust vector to be pointed in the cross-stream direction, deflecting the flow and the wake. Yaw misalignment reduces power production, but the global increase in wind plant power due to decreased wake effect creates a net increase in power production. It is also a fairly simple control idea to implement at existing or new wind plants. We performed high-fidelity computational fluid dynamics simulations of the wake flow of the proposed Fishermen's Atlantic City Windfarm (FACW) that predict that under certain waking conditions, wake redirection can increase plant efficiency by 10%. This means that by applying wake redirection control, for a given watersheet area, a wind plant can either produce more power, or the same amount of power can be produced with a smaller watersheet area. With the power increase may come increased loads, though, due to the yaw misalignment. If misalignment is applied properly, or if layered with individual blade pitch control, though, the load increase can be mitigated. In this talk we will discuss the concept of wake redirection through yaw misalignment and present our CFD results of the FACW project. We will also discuss the implications of wake redirection control on annual energy production, and finally we will discuss plans to implement wake redirection control at FACW when it is operational.

Churchfield, M. J.; Fleming, P.; DeGeorge, E.; Bulder, B; White, S. M.

2014-10-01

334

Observations of the trade wind wakes of Kauai and Oahu  

Microsoft Academic Search

The Hawaiian islands of Kauai and Oahu stand in the path of the east-northeasterly trade winds, creating wakes in the lee. For the first time, the structure of the wakes and their diurnal cycle were observed on a cruise during 18–20 December 2006. The dynamic wakes, characterized by reduced trades, extend about 1 km in height with strong wind shear

Yang Yang; Jian Ma; Shang-Ping Xie

2008-01-01

335

Observations of the trade wind wakes of Kauai and Oahu  

Microsoft Academic Search

The Hawaiian islands of Kauai and Oahu stand in the path of the east-northeasterly trade winds, creating wakes in the lee. For the first time, the structure of the wakes and their diurnal cycle were observed on a cruise during 18-20 December 2006. The dynamic wakes, characterized by reduced trades, extend about 1 km in height with strong wind shear

Yang Yang; Jian Ma; Shang-Ping Xie

2008-01-01

336

Sleep in the Unresponsive Wakefulness Syndrome and Minimally Conscious State  

E-print Network

Sleep in the Unresponsive Wakefulness Syndrome and Minimally Conscious State Victor Cologan,1 Laureys1,7 Abstract The goal of our study was to investigate different aspects of sleep, namely the sleep-wake cycle and sleep stages, in the vegetative state/unresponsive wakefulness syndrome (VS

Delorme, Arnaud

337

Analysis of noise measured from a propeller in a wake  

Microsoft Academic Search

In this experimental study, the acoustic characteristics of a propeller operating in a wake were studied. The propeller performance and noise were measured from two 0.25 scale propellers operating in an open jet anechoic flow environment with and without a wake. One propeller had NACA 16 series sections; the other, ARA-D. Wake thicknesses of 1 and 3 propeller chords were

P. J. W. Block

1984-01-01

338

Memory of initial conditions in stratified wakes at late times?  

Microsoft Academic Search

Late wakes of bluff bodies traveling through stratified fluids at sufficiently high Reynolds and internal Froude number appear to possess certain general characteristics that depend only weakly, if at all, on details of the initial conditions. However, the possible influence of body geometry (for example) on the late wake has not been investigated explicitly. The far wakes of various towed-bodies

P. Meunier; G. R. Spedding

2002-01-01

339

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

340

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

341

Suppression of unimolecular decay of laser desorbed peptide and protein ions by entrainment in rarefied supersonic gas jets under weak electric fields.  

PubMed

Unimolecular decay of sample ions imposes a limit on the usable laser fluence in matrix-assisted laser desorption/ionization (MALDI) ion sources. Traditionally, some modest degree of collisional sample ion cooling has been achieved by connecting MALDI ion sources directly to gas-filled radio frequency (RF) multipoles. It was also discovered in the early 1990s that gas-filled RF multipoles exhibit increased ion transmission efficiency due to collisional ion focusing effects. This unexpected experimental finding was later supported by elementary Monte Carlo simulations. Both experiments and simulations assumed a resting background gas with typical pressures of the order of 1 Pa. However, considerable additional improvements can be achieved if laser desorbed sample ions are introduced immediately after desorption, still within the ion source, in an axisymmetric rarefied supersonic gas jet with peak pressure of the order of 100 Pa and flow velocities >300 m/s, and under weak electric fields. We describe here the design principle and report performance data of an ion source coined "MALDI-2," which incorporates elements of both rarefied aerodynamics and particle optics. Such a design allows superb suppression of metastable fragmentation due to rapid collisional cooling in <10 ?s and nearly perfect injection efficiency into the attached RF ion guide, as numerous experiments have confirmed. PMID:25669372

Hieke, Andreas

2014-01-21

342

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.

343

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

344

Experiments in Waking Hypnosis for Instructional Purposes  

Microsoft Academic Search

The author discusses the theory of hypnotism and the possibility of employing it for experimental purposes in the class-room. He distinguishes between sleeping and waking hypnosis, justifying his use of the latter term with a wealth of historical and contemporary evidence. He reports the success of class experiments in both types of hypnosis, particularly the latter which he describes minutely.

W. R. Wells

1924-01-01

345

Experimental investigation of a stratified buoyant wake  

E-print Network

of the Rayleigh-Taylor mixing layer. The development of the near wake in the presence of unstable stratification is examined, in addition to the recovery of the buoyancy driven mixing layer. Planar laser induced fluorescence (PLIF) is used to visualize the mixing...

Kraft, Wayne Neal

2004-11-15

346

Holographic flow visualization. [of aircraft wakes  

NASA Technical Reports Server (NTRS)

Holographic visualization techniques are presented of the vortex wake of a lifting wing. The motions of tracer particles in vortical flows are described along with the development of a liquid-drop tracer generator. An analysis is presented of the motion of particles of arbitrary density and size in solid body and potential vortex flows.

Charwat, A. F.; Fourney, M. E.

1976-01-01

347

Radiative Forcing Over Ocean by Ship Wakes  

NASA Technical Reports Server (NTRS)

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 plus or minus 53% Watts per square meter assuming a global distribution of 32331 ships of size of greater than or equal to 100000 gross tonnage. The forcing is smaller than the forcing of aircraft contrails (-0.007 to +0.02 Watts per square meter), 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, Charles K.; Wilcox, E.; Poudyal, R.; Wang, J.

2011-01-01

348

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

349

The calculation of near-wake flows  

Microsoft Academic Search

Calculated flow properties are compared with measurements obtained in two- dimensional isothermal wakes with and without recirculation. The equations of continuity and momentum were solved numerically together with equations which formed a turbulence model. Calculations were made using three turbulence models : the first comprised transport equations for turbulence kinetic energy and the rate of turbulence dissipation; the second and

S. B. Pope; J. H. Whitelaw

1976-01-01

350

Ram side of Wake Shield Facility  

NASA Technical Reports Server (NTRS)

The ram side of the Wake Shield Facility (WSF) is in the grasp of the Space Shuttle Discovery's Remote Manipulator System (RMS) arm in this 70mm frame. Clouds over the Atlantic Ocean and the blackness of space share the backdrop for the picture.

1994-01-01

351

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

352

Vortex shedding in high-speed compressor blade wakes  

NASA Technical Reports Server (NTRS)

The wakes of highly loaded compressor blades are generally considered to be turbulent flows. Recent work has suggested that the blade wakes are dominated by a vortex streetlike structure. The experimental evidence supporting the wake vortex structure is reviewed. This structure is shown to redistribute thermal energy within the flowfield. The effect of the wake structure on conventional aerodynamic measurements of compressor performance is noted. A two-dimensional, time-accurate, viscous numerical simulation of the flow exhibits both vortex shedding in the wake and a lower-frequency flow instability that modulates the shedding. The numerical results are shown to agree quite well with the measurement from transonic compressor rotors.

Epstein, A. H.; Gertz, J. B.; Owen, P. R.; Giles, M. B.

1988-01-01

353

Wind-tunnel measurements in the wakes of structures  

NASA Technical Reports Server (NTRS)

Detailed measurements of longitudinal mean velocity, turbulence intensity, space correlations, and spectra made in the wake of two rectangular scaled models in simulated atmospheric boundary-layer winds are presented. The model buildings were 1:50 scale models of two trailers. Results of a flow visualization study of the wake geometry are analyzed with some singular point theorems. Two hypothetical flow patterns of the detailed wake geometry are proposed. Some preliminary studies of the vortex wake, effects of the model size, model aspect ratios, and boundary layer characteristics on the decay rate and extent of the wake are also presented and discussed.

Woo, H. G. C.; Peterka, J. A.; Cermak, J. E.

1977-01-01

354

Intercropping leeks to suppress weeds  

Microsoft Academic Search

Many field vegetables such as leek are weak competitors against weeds, causing high costs for weed management practice. Using celery as a companion cash crop was suggested to improve the weed suppression of leek. Three field experiments were carried out to study the intra- and interspecific competition in a leek:celery intercrop with and without additional weed competition. Results from this

D. T. Baumann; M. J. Kropff; L. Bastiaans

2000-01-01

355

Structure of the wake of a magnetic obstacle.  

PubMed

We use a combination of numerical simulations and experiments to elucidate the structure of the flow of an electrically conducting fluid past a localized magnetic field, called magnetic obstacle. We demonstrate that the stationary flow pattern is considerably more complex than in the wake behind an ordinary body. The steady flow is shown to undergo two bifurcations (rather than one) and to involve up to six (rather than just two) vortices. We find that the first bifurcation leads to the formation of a pair of vortices within the region of magnetic field that we call inner magnetic vortices, whereas a second bifurcation gives rise to a pair of attached vortices that are linked to the inner vortices by connecting vortices. PMID:17501279

Votyakov, E V; Kolesnikov, Yu; Andreev, O; Zienicke, E; Thess, A

2007-04-01

356

Cosmic string wakes and large-scale structure  

NASA Technical Reports Server (NTRS)

The formation of structure from infinite cosmic string wakes is modeled for a universe dominated by cold dark matter (CDM). Cross-sectional slices through the wake distribution tend to outline empty regions with diameters which are not inconsistent with the range of sizes of the voids in the CfA slice of the universe. The topology of the wake distribution is found to be spongy rather than cell-like. Correlations between CDM wakes do not extend much beyond a horizon length, so it is unlikely that CDM wakes are responsible for the correlations between clusters of galaxies. An estimate of the fraction of matter to accrete onto CDM wakes indicates that wakes could be more important in galaxy formation than previously anticipated.

Charlton, Jane C.

1988-01-01

357

Proceedings of the NASA First Wake Vortex Dynamic Spacing Workshop  

NASA Technical Reports Server (NTRS)

A Government and Industry workshop on wake vortex dynamic spacing systems was conducted on May 13-15, 1997, at the NASA Langley Research Center. The purpose of the workshop was to disclose the status of ongoing NASA wake vortex R&D to the international community and to seek feedback on the direction of future work to assure an optimized research approach. Workshop sessions examined wake vortex characterization and physics, wake sensor technologies, aircraft/wake encounters, terminal area weather characterization and prediction, and wake vortex systems integration and implementation. A final workshop session surveyed the Government and Industry perspectives on the NASA research underway and related international wake vortex activities. This document contains the proceedings of the workshop including the presenters' slides, the discussion following each presentation, the wrap-up panel discussion, and the attendees' evaluation feedback.

Creduer, Leonard (Editor); Perry, R. Brad (Editor)

1997-01-01

358

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

359

Numerical simulations of the near wake of a sphere moving in a steady, horizontal motion through a linearly stratified fluid at Re = 1000  

NASA Astrophysics Data System (ADS)

A numerical investigation of the near wake of a sphere moving horizontally through a linearly stratified fluid is presented. Simulations are first performed on a flow with Reynolds number Re = 200 for a range of internal Froude number, 0.1 ? Fr ? ?. The simulations capture buoyant characteristic behavior, the presence of vortex shedding at low Fr, and lee waves. Simulations at higher Reynolds number, Re = 1000, for 1 ? Fr ? ? provide a description and parametrization of the near wake, including the density field. At Re = 1000, the effects of utilizing two different averaging techniques in the unsteady near wake region are discussed. Perturbation quantities in the stratified near wake are anisotropic, and based on the oscillations of the centerline vertical perturbation velocity, the Fr at which the stratified near wake may be considered indistinguishable from the uniform density near wake is suggested to be O(100). Parametrization of the near wake is accomplished using the parameterized vertical wake height, downstream distance from the sphere, and Fr as parameters.

Orr, Trevor S.; Domaradzki, J. Andrzej; Spedding, Geoffrey R.; Constantinescu, George S.

2015-03-01

360

A CFD code comparison of wind turbine wakes  

NASA Astrophysics Data System (ADS)

A comparison is made between the EllipSys3D and SnS CFD codes. Both codes are used to perform Large-Eddy Simulations (LES) of single wind turbine wakes, using the actuator disk method. The comparison shows that both LES models predict similar velocity deficits and stream-wise Reynolds-stresses for four test cases. A grid resolution study, performed in EllipSys3D and SnS, shows that a minimal uniform cell spacing of 1/30 of the rotor diameter is necessary to resolve the wind turbine wake. In addition, the LES-predicted velocity deficits are also compared with Reynolds-Averaged Navier Stokes simulations using EllipSys3D for a test case that is based on field measurements. In these simulations, two eddy viscosity turbulence models are employed: the k-epsilon model and the k-epsilon-fp model. Where the k-epsilon model fails to predict the velocity deficit, the results of the k-epsilon-fP model show good agreement with both LES models and measurements.

van der Laan, M. P.; Storey, R. C.; Sørensen, N. N.; Norris, S. E.; Cater, J. E.

2014-06-01

361

Separation of circadian and wake duration-dependent modulation of EEG activation during wakefulness  

NASA Technical Reports Server (NTRS)

The separate contribution of circadian rhythmicity and elapsed time awake on electroencephalographic (EEG) activity during wakefulness was assessed. Seven men lived in an environmental scheduling facility for 4 weeks and completed fourteen 42.85-h 'days', each consisting of an extended (28.57-h) wake episode and a 14.28-h sleep opportunity. The circadian rhythm of plasma melatonin desynchronized from the 42.85-h day. This allowed quantification of the separate contribution of circadian phase and elapsed time awake to variation in EEG power spectra (1-32 Hz). EEG activity during standardized behavioral conditions was markedly affected by both circadian phase and elapsed time awake in an EEG frequency- and derivation-specific manner. The nadir of the circadian rhythm in alpha (8-12 Hz) activity in both fronto-central and occipito-parietal derivations occurred during the biological night, close to the crest of the melatonin rhythm. The nadir of the circadian rhythm of theta (4.5-8 Hz) and beta (20-32 Hz) activity in the fronto-central derivation was located close to the onset of melatonin secretion, i.e. during the wake maintenance zone. As time awake progressed, delta frequency (1-4.5 Hz) and beta (20-32 Hz) activity rose monotonically in frontal derivations. The interaction between the circadian and wake-dependent increase in frontal delta was such that the intrusion of delta was minimal when sustained wakefulness coincided with the biological day, but pronounced during the biological night. Our data imply that the circadian pacemaker facilitates frontal EEG activation during the wake maintenance zone, by generating an arousal signal that prevents the intrusion of low-frequency EEG components, the propensity for which increases progressively during wakefulness.

Cajochen, C.; Wyatt, J. K.; Czeisler, C. A.; Dijk, D. J.

2002-01-01

362

The three-dimensional wake of a cylinder undergoing a combination of translational and rotational oscillation in a quiescent fluid  

NASA Astrophysics Data System (ADS)

Previous two-dimensional numerical studies have shown that a circular cylinder undergoing both oscillatory rotational and translational motions can generate thrust so that it will actually self-propel through a stationary fluid. Although a cylinder undergoing a single oscillation has been thoroughly studied, the combination of the two oscillations has not received much attention until now. The current research reported here extends the numerical study of Blackburn et al. [Phys. Fluids 11, L4 (1999)] both experimentally and numerically, recording detailed vorticity fields in the wake and using these to elucidate the underlying physics, examining the three-dimensional wake development experimentally, and determining the three-dimensional stability of the wake through Floquet stability analysis. Experiments conducted in the laboratory are presented for a given parameter range, confirming the early results from Blackburn et al. [Phys. Fluids 11, L4 (1999)]. In particular, we confirm the thrust generation ability of a circular cylinder undergoing combined oscillatory motions. Importantly, we also find that the wake undergoes three-dimensional transition at low Reynolds numbers (Re?100) to an instability mode with a wavelength of about two cylinder diameters. The stability analysis indicates that the base flow is also unstable to another mode at slightly higher Reynolds numbers, broadly analogous to the three-dimensional wake transition mode for a circular cylinder, despite the distinct differences in wake/mode topology. The stability of these flows was confirmed by experimental measurements.

Nazarinia, M.; Lo Jacono, D.; Thompson, M. C.; Sheridan, J.

2009-06-01

363

IEA-Task 31 WAKEBENCH: Towards a protocol for wind farm flow model evaluation. Part 2: Wind farm wake models  

NASA Astrophysics Data System (ADS)

Researchers within the International Energy Agency (IEA) Task 31: Wakebench have created a framework for the evaluation of wind farm flow models operating at the microscale level. The framework consists of a model evaluation protocol integrated with a web-based portal for model benchmarking (www.windbench.net). This paper provides an overview of the building-block validation approach applied to wind farm wake models, including best practices for the benchmarking and data processing procedures for validation datasets from wind farm SCADA and meteorological databases. A hierarchy of test cases has been proposed for wake model evaluation, from similarity theory of the axisymmetric wake and idealized infinite wind farm, to single-wake wind tunnel (UMN-EPFL) and field experiments (Sexbierum), to wind farm arrays in offshore (Horns Rev, Lillgrund) and complex terrain conditions (San Gregorio). A summary of results from the axisymmetric wake, Sexbierum, Horns Rev and Lillgrund benchmarks are used to discuss the state-of-the-art of wake model validation and highlight the most relevant issues for future development.

Moriarty, Patrick; Sanz Rodrigo, Javier; Gancarski, Pawel; Chuchfield, Matthew; Naughton, Jonathan W.; Hansen, Kurt S.; Machefaux, Ewan; Maguire, Eoghan; Castellani, Francesco; Terzi, Ludovico; Breton, Simon-Philippe; Ueda, Yuko

2014-06-01

364

Effect of periodic wakes on jets injected into turbulent boundary layers  

NASA Astrophysics Data System (ADS)

Surfaces subject to high temperature flow are often cooled using lower temperature jets injected through the surface. The jets typically have low velocity and are inclined at shallow angles so that they remain near the surface, forming a protective film. The technique is known as ``film cooling.'' The process can be complicated by periodic turbulent wakes shed from objects moving upstream of the cooled surface. In the present study, jets with various velocities were injected into turbulent boundary layers on a flat-plate test wall. Periodic wakes were generated with a spoked wheel, located upstream in the wind tunnel. The jet behavior was determined through instantaneous flow temperature measurements made with a traversing cold-wire (constant current) probe. The measurements were ensemble averaged to show the temperature field at various phases during the wake passing cycle. The wakes tend to force the jets closer to the surface, enhancing their cooling effectiveness, but the associated turbulence has the opposite effect and accelerates coolant dispersal. The net effect depends on the jet velocity. Results, including animations of the experimentally measured flow temperature fields, will be presented.

Volino, Ralph

2007-11-01

365

Three-dimensional vortex wake structure of a flapping-wing micro aerial vehicle in forward flight configuration  

NASA Astrophysics Data System (ADS)

This paper investigates the formation and evolution of the unsteady three-dimensional wake structures generated by the flapping wings of the DelFly II micro aerial vehicle in forward flight configuration. Time-resolved stereoscopic particle image velocimetry (Stereo-PIV) measurements were carried out at several spanwise-aligned planes in the wake, so as to allow a reconstruction of the temporal development of the wake of the flapping wings throughout the complete flapping cycle. Simultaneous thrust-force measurements were performed to explore the relation between the wake formation and the aerodynamic force generation mechanisms. The three-dimensional wake configuration was subsequently reconstructed from the planar PIV measurements by two different approaches: (1) a spatiotemporal wake reconstruction obtained by convecting the time-resolved, three-component velocity field data of a single measurement plane with the free-stream velocity; (2) for selected phases in the flapping cycle a direct three-dimensional spatial wake reconstruction is interpolated from the data of the different measurement planes, using a Kriging regression technique. Comparing the results derived from both methods in terms of the behavior of the wake formations, their phase and orientation indicate that the spatiotemporal reconstruction method allows to characterize the general three-dimensional structure of the wake, but that the spatial reconstruction method can reveal more details due to higher streamwise resolution. Comparison of the wake reconstructions for different values of the reduced frequency allows assessing the impact of the flapping frequency on the formation and interaction characteristics of the vortical structures. For low values of the reduced frequency, it is observed that the vortex structure formation of instroke and outstroke is relatively independent of each other, but that increasing interaction occurs at higher reduced frequencies. It is further shown that there is a phase lag in the appearance of the structures for increasing flapping frequency, which is in correlation with the generation of the forces. Comparison of thrust generated during the instroke and the outstroke phases of the flapping motion in conjunction with the development of the wake structures indicates that wing-wing interaction at the start of outstroke (peel motion) becomes a dominant feature for reduced frequencies greater than 0.62.

Percin, M.; van Oudheusden, B. W.; Eisma, H. E.; Remes, B. D. W.

2014-09-01

366

Studies of particle wake potentials in plasmas  

NASA Astrophysics Data System (ADS)

A detailed understanding of electron stopping and scattering in plasmas with variable values for the number of particles within a Debye sphere is still not at hand. Presently, there is some disagreement in the literature concerning the proper description of these processes. Theoretical models assume electrostatic (Coulomb force) interactions between particles and neglect magnetic effects. Developing and validating proper descriptions requires studying the processes using first-principle plasma simulations. We are using the particle-particle particle-mesh (PPPM) code ddcMD and the particle-in-cell (PIC) code BEPS to perform these simulations. As a starting point in our study, we examine the wake of a particle passing through a plasma in 3D electrostatic simulations performed with ddcMD and BEPS. In this paper, we compare the wakes observed in these simulations with each other and predictions from collisionless kinetic theory. The relevance of the work to Fast Ignition is discussed.

2011-09-01

367

CFD Simulations for the Effect of Unsteady Wakes on the Boundary Layer of a Highly Loaded Low-Pressure Turbine Airfoil (L1A)  

NASA Technical Reports Server (NTRS)

This report is the third part of a three-part final report of research performed under an NRA cooperative Agreement contract. The first part was published as NASA/CR-2012-217415. The second part was published as NASA/CR-2012-217416. The study of the very high lift low-pressure turbine airfoil L1A in the presence of unsteady wakes was performed computationally and compared against experimental results. The experiments were conducted in a low speed wind tunnel under high (4.9%) and then low (0.6%) freestream turbulence intensity for Reynolds number equal to 25,000 and 50,000. The experimental and computational data have shown that in cases without wakes, the boundary layer separated without reattachment. The CFD was done with LES and URANS utilizing the finite-volume code ANSYS Fluent (ANSYS, Inc.) under the same freestream turbulence and Reynolds number conditions as the experiment but only at a rod to blade spacing of 1. With wakes, separation was largely suppressed, particularly if the wake passing frequency was sufficiently high. This was validated in the 3D CFD efforts by comparing the experimental results for the pressure coefficients and velocity profiles, which were reasonable for all cases examined. The 2D CFD efforts failed to capture the three dimensionality effects of the wake and thus were less consistent with the experimental data. The effect of the freestream turbulence intensity levels also showed a little more consistency with the experimental data at higher intensities when compared with the low intensity cases. Additional cases with higher wake passing frequencies which were not run experimentally were simulated. The results showed that an initial 25% increase from the experimental wake passing greatly reduced the size of the separation bubble, nearly completely suppressing it.

Vinci, Samuel, J.

2012-01-01

368

Suppression of the metal-insulator transition by magnetic field in (Pr{sub 1?y}Y{sub y}){sub 0.7}Ca{sub 0.3}CoO{sub 3} (y?=?0.0625)  

SciTech Connect

The (Pr{sub 1?y}Y{sub y}){sub 0.7}Ca{sub 0.3}CoO{sub 3} compound (y?=?0.0625, T{sub MI-SS}=40?K), at the lower limit for occurrence of the first-order metal-insulator (MI) and simultaneous spin-state (SS) transitions, has been studied using electrical resistivity and magnetization measurements in magnetic fields up to 17?T. The isothermal experiments demonstrate that the low-temperature insulating phase can be destabilized by an applied field and the metallic phase returns well below the transition temperature T{sub MI-SS}. The reverse process with decreasing field occurs with a significant hysteresis. The temperature scans taken at fixed magnetic fields reveal a parabolic-like decrease in T{sub MI-SS} with increasing field strength and a complete suppression of the MI-SS transition in fields above 9?T.

Naito, Tomoyuki, E-mail: tnaito@iwate-u.ac.jp; Fujishiro, Hiroyuki [Faculty of Engineering, Iwate University, Morioka 020-8551 (Japan); Nishizaki, Terukazu; Kobayashi, Norio [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Hejtmánek, Ji?í; Knížek, Karel; Jirák, Zden?k [Institute of Physics, ASCR, Cukrovarnická 10, 162 00 Prague 6 (Czech Republic)

2014-06-21

369

Suppression of the metal-insulator transition by magnetic field in (Pr1-yYy)0.7Ca0.3CoO3 (y = 0.0625)  

NASA Astrophysics Data System (ADS)

The (Pr1-yYy)0.7Ca0.3CoO3 compound (y = 0.0625, TMI-SS=40 K), at the lower limit for occurrence of the first-order metal-insulator (MI) and simultaneous spin-state (SS) transitions, has been studied using electrical resistivity and magnetization measurements in magnetic fields up to 17 T. The isothermal experiments demonstrate that the low-temperature insulating phase can be destabilized by an applied field and the metallic phase returns well below the transition temperature TMI-SS. The reverse process with decreasing field occurs with a significant hysteresis. The temperature scans taken at fixed magnetic fields reveal a parabolic-like decrease in TMI-SS with increasing field strength and a complete suppression of the MI-SS transition in fields above 9 T.

Naito, Tomoyuki; Fujishiro, Hiroyuki; Nishizaki, Terukazu; Kobayashi, Norio; Hejtmánek, Ji?í; Knížek, Karel; Jirák, Zden?k

2014-06-01

370

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. PMID:24039590

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

2013-01-01

371

Wake Vortex Advisory System (WakeVAS) Evaluation of Impacts on the National Airspace System  

NASA Technical Reports Server (NTRS)

This report is one of a series that describes an ongoing effort in high-fidelity modeling/simulation, evaluation and analysis of the benefits and performance metrics of the Wake Vortex Advisory System (WakeVAS) Concept of Operations being developed as part of the Virtual Airspace Modeling and Simulation (VAMS) project. A previous study, determined the overall increases in runway arrival rates that could be achieved at 12 selected airports due to WakeVAS reduced aircraft spacing under Instrument Meteorological Conditions. This study builds on the previous work to evaluate the NAS wide impacts of equipping various numbers of airports with WakeVAS. A queuing network model of the National Airspace System, built by the Logistics Management Institute, Mclean, VA, for NASA (LMINET) was used to estimate the reduction in delay that could be achieved by using WakeVAS under non-visual meteorological conditions for the projected air traffic demand in 2010. The results from LMINET were used to estimate the total annual delay reduction that could be achieved and from this, an estimate of the air carrier variable operating cost saving was made.

Smith, Jeremy C.; Dollyhigh, Samuel M.

2005-01-01

372

THE RELATION OF WAKING FANTASY TO DREAMING  

Microsoft Academic Search

This study investigated the relationship between fantasy immersion (fantasy proneness, absorption, and positive-constructive daydreaming) and qualities of nocturnal dreaming in a large non-clinical community-based sample (n = 288). The results indicate a strong linear relationship between all of the waking fantasy measures, especially positive-constructive daydreaming style, and phenomenal qualities of dreaming. Further, men and women differed significantly, both in how

ROSS LEVIN; HUGH YOUNG

2002-01-01

373

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

374

Entry of solar-wind ions into the wake of a small unmagnetized body: A global Vlasov simulation  

NASA Astrophysics Data System (ADS)

The interaction between a plasma flow and a small dielectric body with a weak intrinsic global magnetic field is studied by means of a five-dimensional full electromagnetic Vlasov simulation with two configuration and three velocity spaces. In the present study, entry processes of ions into the nightside wake tail are examined. The simulation result shows that solar-wind ions are reflected at the dayside magnetopause and are picked up by the interplanetary magnetic field. Then, a small part of the reflected ions are taken into the deep wake tail near the body by the ExB cycloid motion.

Umeda, T.; Ito, Y.

2013-12-01

375

Sleep and dream suppression following a lateral medullary infarct: A first-person account  

Microsoft Academic Search

Consciousness can be studied only if subjective experience is documented and quantified, yet first-person accounts of the effects of brain injury on conscious experience are as rare as they are potentially useful. This report documents the alterations in waking, sleeping, and dreaming caused by a lateral medullary infarct. Total insomnia and the initial suppression of dreaming was followed by the

J Allan Hobson

2002-01-01

376

Wake force computation in the time domain for long structures  

SciTech Connect

One is often interested in calculating the wake potentials for short bunches in long structures using TBCI. For ultra-relativistic particles it is sufficient to solve for the fields only over a window containing the bunch and moving along with it. This technique reduces both the memory and the running time required by a factor that equals the ratio of the structure length to the window length. For example, for a bunch with sigma/sub z/ of one picosecond traversing a single SLAC cell this improvement factor is 15. It is thus possible to solve for the wakefields in very long structures: for a given problem, increasing the structure length will not change the memory required while only adding linearly to the CPU time needed.

Bane, K.; Weiland, T.

1983-07-01

377

Experimental study of rotor wake/body interactions in hover  

NASA Technical Reports Server (NTRS)

Experiments were conducted to document the tip vortex geometries and interactional effects betwen a hovering rotor and a body representing a simplified helicopter fuselage. The wide-field shadowgraph technique was used to visualize the rotor tip vortices and to obtain quantitative information on the trajectories, with and without the presence of the body. It was found that the effects of the body caused significant changes to both the radial contraction and axial displacements of the tip vortices compared to the isolated case. Direct impingement of the tip vortices on the body surface was also observed, and found to cause large local wake deformations. The rotor performance was significantly affected by the body, producing a higher figure of merit relative to the isolated case.

Bagai, A.; Leishman, J. G.

1992-01-01

378

Changing and shielded magnetic fields suppress c-Fos expression in the navigation circuit: input from the magnetosensory system contributes to the internal representation of space in a subterranean rodent  

PubMed Central

The neural substrate subserving magnetoreception and magnetic orientation in mammals is largely unknown. Previous experiments have demonstrated that the processing of magnetic sensory information takes place in the superior colliculus. Here, the effects of magnetic field conditions on neuronal activity in the rodent navigation circuit were assessed by quantifying c-Fos expression. Ansell's mole-rats (Fukomys anselli), a mammalian model to study the mechanisms of magnetic compass orientation, were subjected to natural, periodically changing, and shielded magnetic fields while exploring an unfamiliar circular arena. In the undisturbed local geomagnetic field, the exploration of the novel environment and/or nesting behaviour induced c-Fos expression throughout the head direction system and the entorhinal–hippocampal spatial representation system. This induction was significantly suppressed by exposure to periodically changing and/or shielded magnetic fields; discrete decreases in c-Fos were seen in the dorsal tegmental nucleus, the anterodorsal and the laterodorsal thalamic nuclei, the postsubiculum, the retrosplenial and entorhinal cortices, and the hippocampus. Moreover, in inactive animals, magnetic field intensity manipulation suppressed c-Fos expression in the CA1 and CA3 fields of the hippocampus and the dorsal subiculum, but induced expression in the polymorph layer of the dentate gyrus. These findings suggest that key constituents of the rodent navigation circuit contain populations of neurons responsive to magnetic stimuli. Thus, magnetic information may be integrated with multimodal sensory and motor information into a common spatial representation of allocentric space within this circuit. PMID:20219838

Burger, Tomáš; Lucová, Marcela; Moritz, Regina E.; Oelschläger, Helmut H. A.; Druga, Rastislav; Burda, Hynek; Wiltschko, Wolfgang; Wiltschko, Roswitha; N?mec, Pavel

2010-01-01

379

Radar monitoring of a wake vortex: Electromagnetic reflection of wake turbulence in clear air  

NASA Astrophysics Data System (ADS)

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 of wake turbulences for better and more accurate understanding of roll-up radar cross section (RCS) and Doppler signature.

Barbaresco, Frédéric; Meier, Uwe

2010-01-01

380

Unsteady vortex lattice techniques applied to wake formation and performance of the statically thrusting propeller  

NASA Technical Reports Server (NTRS)

The application is considered of vortex lattice techniques to the problem of describing the aerodynamics and performance of statically thrusting propellers. A numerical lifting surface theory to predict the aerodynamic forces and power is performed. The chordwise and spanwise loading is modelled by bound vortices fixed to a twisted flat plate surface. In order to eliminate any apriori assumptions regarding the wake shape, it is assumed the propeller starts from rest. The wake is generated in time and allowed to deform under its own self-induced velocity field as the motion of the propeller progresses. The bound circulation distribution is then determined with time by applying the flow tangency boundary condition at certain selected control points on the blades. The aerodynamics of the infinite wing and finite wing are also considered. The details of wake formation and roll-up are investigated, particularly the localized induction effect. It is concluded that proper wake roll-up and roll-up rates can be established by considering the details of motion at the instant of start.

Hall, G. F.

1975-01-01

381

Three-dimensional vortex wake structure of flapping wings in hovering flight.  

PubMed

Flapping wings continuously create and send vortices into their wake, while imparting downward momentum into the surrounding fluid. However, experimental studies concerning the details of the three-dimensional vorticity distribution and evolution in the far wake are limited. In this study, the three-dimensional vortex wake structure in both the near and far field of a dynamically scaled flapping wing was investigated experimentally, using volumetric three-component velocimetry. A single wing, with shape and kinematics similar to those of a fruitfly, was examined. The overall result of the wing action is to create an integrated vortex structure consisting of a tip vortex (TV), trailing-edge shear layer (TESL) and leading-edge vortex. The TESL rolls up into a root vortex (RV) as it is shed from the wing, and together with the TV, contracts radially and stretches tangentially in the downstream wake. The downwash is distributed in an arc-shaped region enclosed by the stretched tangential vorticity of the TVs and the RVs. A closed vortex ring structure is not observed in the current study owing to the lack of well-established starting and stopping vortex structures that smoothly connect the TV and RV. An evaluation of the vorticity transport equation shows that both the TV and the RV undergo vortex stretching while convecting downwards: a three-dimensional phenomenon in rotating flows. It also confirms that convection and secondary tilting and stretching effects dominate the evolution of vorticity. PMID:24335561

Cheng, Bo; Roll, Jesse; Liu, Yun; Troolin, Daniel R; Deng, Xinyan

2014-02-01

382

Three-dimensional vortex wake structure of flapping wings in hovering flight  

PubMed Central

Flapping wings continuously create and send vortices into their wake, while imparting downward momentum into the surrounding fluid. However, experimental studies concerning the details of the three-dimensional vorticity distribution and evolution in the far wake are limited. In this study, the three-dimensional vortex wake structure in both the near and far field of a dynamically scaled flapping wing was investigated experimentally, using volumetric three-component velocimetry. A single wing, with shape and kinematics similar to those of a fruitfly, was examined. The overall result of the wing action is to create an integrated vortex structure consisting of a tip vortex (TV), trailing-edge shear layer (TESL) and leading-edge vortex. The TESL rolls up into a root vortex (RV) as it is shed from the wing, and together with the TV, contracts radially and stretches tangentially in the downstream wake. The downwash is distributed in an arc-shaped region enclosed by the stretched tangential vorticity of the TVs and the RVs. A closed vortex ring structure is not observed in the current study owing to the lack of well-established starting and stopping vortex structures that smoothly connect the TV and RV. An evaluation of the vorticity transport equation shows that both the TV and the RV undergo vortex stretching while convecting downwards: a three-dimensional phenomenon in rotating flows. It also confirms that convection and secondary tilting and stretching effects dominate the evolution of vorticity. PMID:24335561

Cheng, Bo; Roll, Jesse; Liu, Yun; Troolin, Daniel R.; Deng, Xinyan

2014-01-01

383

Plasma wave turbulence due to the wake of an ionospheric sounding rocket  

NASA Astrophysics Data System (ADS)

A sounding rocket moving in the ionosphere generally interacts with surrounding plasma. Because this affects in-situ measurement data, it is very important to understand the physics of the interaction between the ionosphere and a moving vehicle. For instance, a rarefied plasma region called "plasma wake" is formed behind a sounding rocket. Several previous studies based on rocket experiments have suggested that upper-hybrid resonance (UHR) mode waves are excited in a rocket wake. A wake turbulence model has been proposed as a possible explanation for the waves where two stream instability occurs in the wake center owing to the incident plasma flow from the both sides of the wake edges. Thus, plasma waves are generated and have been observed by the wave receivers onboard the rockets. Plasma waves in a wake have been reported not only around sounding rockets but also around solar system bodies such as Moon. As for a rocket wake, the generation mechanism of the waves has been investigated by using wave receivers with time resolutions worse than 500 msec. They are, however, not enough for detailed investigations about the plasma wave generations and propagations. To discuss the properties of the plasma waves caused around a rocket wake, we have analyzed the data of electric fields and electron number density in the S-520-26 sounding rocket experiment, which was performed at Uchinoura, Japan, on January 12, 2012. The rocket reached an altitude of 298 km, and the data has been obtained four or five times in one spin period of the rocket by using a newly developed digital plasma wave monitor and an impedance probe, whose time resolutions are about 260 msec. In the observation, enhancement of plasma waves has been observed in two frequency ranges from 0.02 to 0.9 MHz (LF range), and from 1.3 to 2.4 MHz (MF range). The frequency range of the MF emissions is around the UHR frequency, which is determined based on the IGRF magnetic field model and electron number density measured by the impedance probe. However, the lowest frequency of the emissions is almost the same as the Z-mode cutoff frequency, particularly in higher altitude range than 280 km. The wave spectra are similar to those observed by the previous studies. The frequency range of the LF emissions is found to be that of whistler mode branch. Based on the rocket attitude, it is suggested that the electric fields of the LF and MF emissions are nearly perpendicular and parallel to the wake structure, respectively. If we can assume that the observed waves are generated around the rocket, they have to be electrostatic waves because the wave length should be shorter than the size of the disturbed region. We have performed calculations of plasma dispersion relations with assuming some anisotropic velocity distribution functions of electrons expected around the wake, and deduced the linear growth rates, group velocities, etc. We compare the observational results with calculated ones, and discuss the generation mechanisms of the plasma waves.

Endo, Ken; Kumamoto, Atsushi; Oya, Hiroshi; Ono, Takayuki; Katoh, Yuto

2013-04-01

384

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

385

Wake coupling to full potential rotor analysis code  

NASA Technical Reports Server (NTRS)

The wake information from a helicopter forward flight code is coupled with two transonic potential rotor codes. The induced velocities for the near-, mid-, and far-wake geometries are extracted from a nonlinear rigid wake of a standard performance and analysis code. These, together with the corresponding inflow angles, computation points, and azimuth angles, are then incorporated into the transonic potential codes. The coupled codes can then provide an improved prediction of rotor blade loading at transonic speeds.

Torres, Francisco J.; Chang, I-Chung; Oh, Byung K.

1990-01-01

386

Evaluation of Fast-Time Wake Vortex Prediction Models  

NASA Technical Reports Server (NTRS)

Current fast-time wake models are reviewed and three basic types are defined. Predictions from several of the fast-time models are compared. Previous statistical evaluations of the APA-Sarpkaya and D2P fast-time models are discussed. Root Mean Square errors between fast-time model predictions and Lidar wake measurements are examined for a 24 hr period at Denver International Airport. Shortcomings in current methodology for evaluating wake errors are also discussed.

Proctor, Fred H.; Hamilton, David W.

2009-01-01

387

Initialization and Simulation of Three-Dimensional Aircraft Wake Vortices  

NASA Technical Reports Server (NTRS)

This paper studies the effects of axial velocity profiles on vortex decay, in order to properly initialize and simulate three-dimensional wake vortex flow. Analytical relationships are obtained based on a single vortex model and computational simulations are performed for a rather practical vortex wake, which show that the single vortex analytical relations can still be applicable at certain streamwise sections of three-dimensional wake vortices.

Ash, Robert L.; Zheng, Z. C.

1997-01-01

388

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

PubMed

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, reward and energy homeostasis. PMID:17299454

Sakurai, Takeshi

2007-03-01

389

Rotor wake characteristics of a transonic axial flow fan  

NASA Technical Reports Server (NTRS)

State of the art turbomachinery flow analysis codes are not capable of predicting the viscous flow features within turbomachinery blade wakes. Until efficient 3D viscous flow analysis codes become a reality there is therefore a need for models which can describe the generation and transport of blade wakes and the mixing process within the wake. To address the need for experimental data to support the development of such models, high response pressure measurements and laser anemometer velocity measurements have been obtained in the wake of a transonic axial flow fan rotor.

Hathaway, M. D.; Gertz, J.; Epstein, A.; Strazisar, A. J.

1985-01-01

390

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

391

The three-dimensional evolution of a plane wake  

NASA Technical Reports Server (NTRS)

In the past three decades, linear stability analysis has led to a comprehensive understanding of the linear stages of transition in plane wakes. Our understanding of the nonlinear and turbulent stages is less developed. Nonlinear theory developed by Papageorgiou and Smith was used to study the long-wavelength regime in wakes. The nonlinear and turbulent stages were investigated experimentally, and few numerical studies examined the early nonlinear stages of forced wakes. The evolution of three dimensional disturbances in an incompressible wake is investigated using direct numerical simulations. The instantaneous three-dimaensional structures and corresponding statistics are presented.

Maekawa, H.; Moser, R. D.; Mansour, N. N.

1993-01-01

392

Rotor wake characteristics of a transonic axial flow fan  

NASA Technical Reports Server (NTRS)

State of the art turbomachinery flow analysis codes are not capable of predicting the viscous flow features within turbomachinery blade wakes. Until efficient 3D viscous flow analysis codes become a reality there is therefore a need for models which can describe the generation and transport of blade wakes and the mixing process within the wake. To address the need for experimental data to support the development of such models, high response pressure measurements and laser anemometer velocity measurements were obtained in the wake of a transonic axial flow fan rotor.

Hathaway, M. D.; Gertz, J.; Epstein, A.; Strazisar, A. J.

1985-01-01

393

Numerical simulation of laminar-turbulent transition in a spatially-developing flat plate wake  

NASA Technical Reports Server (NTRS)

Laminar-turbulent transition of an incompressible flat-plate wake is investigated by direct numerical integration of the Navier-Stokes equations. For the numerical integration, a combination of finite-difference and spectral methods along with an ADI/Crank-Nicolson/Adams-Bashforth time integration scheme is employed. Subject to 2D forcing, the wake exhibited a rapidly-growing fundamental disturbance that quickly saturated. This saturation was due partly to the stabilizing effect of the mean flow distortion. Downstream of the saturation point, disturbance energy was concentrated in the fundamental disturbance, the second harmonic, and the mean flow distortion component. At large amplitude levels, a Karman vortex street formed. Variations in the 2D forcing level did not alter the qualitative behavior of the disturbances. Simulations of 3D breakdown indicates that the presence of large-amplitude, 2D disturbances tends to initially suppress small-amplitude 3D disturbance growth. Following this initial suppression, a resumption of 3D growth is observed that may have been due to a secondary instability mechanism. For high levels of 3D disturbance energy, lambda-shaped vortical structures formed between adjacent Karman vortices.

Dratler, D. I.; Fasel, H. F.

1993-01-01

394

Validation of the suppressive subtractive hybridization method in Mycoplasma agalactiae species by the comparison of a field strain with the type strain PG2  

Microsoft Academic Search

The subtractive suppressive hybridization (SSH), a method that allows the identification of sequences that are present in one genome (tester) but not in the other (driver), is a promising technique for the comparison of Mycoplasma agalactiae pathogenic strains. The optimal conditions for SSH were established by subtracting the M. agalactiae type strain PG2 DNA from the M. agalactiae strain 5632

Marc S. Marenda; Edy M. Vilei; Joachim Frey; Xavier Berthelot

2004-01-01

395

Field evaluation of bacterial symbionts of entomopathogenic nematodes for suppression of hairy rose beetle, Tropinota squalida Scop., (Coleoptera: Scarabaeidae) population on cauliflower in Egypt  

Microsoft Academic Search

The potential of bacterial symbionts in suppressing T. squalida populations on cauliflower from transplanting to harvest was evaluated. Significant reductions in plant infestation percentage and population density (\\/m) were recorded throughout the plantation seasons in 2005 and 2006 after spraying the plants. The percentage reduction in numbers\\/m was the highest in March for treatments with X. nematophilus and P. luminescens.

A. S. Abdel-Razek

2010-01-01

396

Aircraft Wake Vortex Spacing System (AVOSS) Performance Update and Validation Study  

NASA Technical Reports Server (NTRS)

An analysis has been performed on data generated from the two most recent field deployments of the Aircraft Wake VOrtex Spacing System (AVOSS). The AVOSS provides reduced aircraft spacing criteria for wake vortex avoidance as compared to the FAA spacing applied under Instrument Flight Rules (IFR). Several field deployments culminating in a system demonstration at Dallas Fort Worth (DFW) International Airport in the summer of 2000 were successful in showing a sound operational concept and the system's potential to provide a significant benefit to airport operations. For DFW, a predicted average throughput increase of 6% was observed. This increase implies 6 or 7 more aircraft on the ground in a one-hour period for DFW operations. Several studies of performance correlations to system configuration options, design options, and system inputs are also reported. The studies focus on the validation performance of the system.

Rutishauser, David K.; OConnor, Cornelius J.

2001-01-01

397

Helicopter rotor wake geometry and its influence in forward flight. Volume 1: Generalized wake geometry and wake effect on rotor airloads and performance  

NASA Technical Reports Server (NTRS)

An analytic investigation to generalize wake geometry of a helicopter rotor in steady level forward flight and to demonstrate the influence of wake deformation in the prediction of rotor airloads and performance is described. Volume 1 presents a first level generalized wake model based on theoretically predicted tip vortex geometries for a selected representative blade design. The tip vortex distortions are generalized in equation form as displacements from the classical undistorted tip vortex geometry in terms of vortex age, blade azimuth, rotor advance ratio, thrust coefficient, and number of blades. These equations were programmed to provide distorted wake coordinates at very low cost for use in rotor airflow and airloads prediction analyses. The sensitivity of predicted rotor airloads, performance, and blade bending moments to the modeling of the tip vortex distortion are demonstrated for low to moderately high advance ratios for a representative rotor and the H-34 rotor. Comparisons with H-34 rotor test data demonstrate the effects of the classical, predicted distorted, and the newly developed generalized wake models on airloads and blade bending moments. Use of distorted wake models results in the occurrence of numerous blade-vortex interactions on the forward and lateral sides of the rotor disk. The significance of these interactions is related to the number and degree of proximity to the blades of the tip vortices. The correlation obtained with the distorted wake models (generalized and predicted) is encouraging.

Egolf, T. A.; Landgrebe, A. J.

1983-01-01

398

Helices in the wake of precipitation fronts  

NASA Astrophysics Data System (ADS)

A theoretical study of the emergence of helices in the wake of precipitation fronts is presented. The precipitation dynamics is described by the Cahn-Hilliard equation and the fronts are obtained by quenching the system into a linearly unstable state. Confining the process onto the surface of a cylinder and using the pulled-front formalism, our analytical calculations show that there are front solutions that propagate into the unstable state and leave behind a helical structure. We find that helical patterns emerge only if the radius of the cylinder R is larger than a critical value R>Rc, in agreement with recent experiments.

Thomas, Shibi; Lagzi, István; Molnár, Ferenc, Jr.; Rácz, Zoltán

2013-08-01

399

Helices in the wake of precipitation fronts.  

PubMed

A theoretical study of the emergence of helices in the wake of precipitation fronts is presented. The precipitation dynamics is described by the Cahn-Hilliard equation and the fronts are obtained by quenching the system into a linearly unstable state. Confining the process onto the surface of a cylinder and using the pulled-front formalism, our analytical calculations show that there are front solutions that propagate into the unstable state and leave behind a helical structure. We find that helical patterns emerge only if the radius of the cylinder R is larger than a critical value R>R(c), in agreement with recent experiments. PMID:24032809

Thomas, Shibi; Lagzi, István; Molnár, Ferenc; Rácz, Zoltán

2013-08-01

400

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.

401

Thermal wake/vessel detection technique  

DOEpatents

A computer-automated method for detecting a vessel in water based on an image of a portion of Earth includes generating a thermal anomaly mask. The thermal anomaly mask flags each pixel of the image initially deemed to be a wake pixel based on a comparison of a thermal value of each pixel against other thermal values of other pixels localized about each pixel. Contiguous pixels flagged by the thermal anomaly mask are grouped into pixel clusters. A shape of each of the pixel clusters is analyzed to determine whether each of the pixel clusters represents a possible vessel detection event. The possible vessel detection events are represented visually within the image.

Roskovensky, John K. (Albuquerque, NM); Nandy, Prabal (Albuquerque, NM); Post, Brian N (Albuquerque, NM)

2012-01-10

402

Wakes from arrays of buildings. [flight safety  

NASA Technical Reports Server (NTRS)

Experiments were carried out in a small wind tunnel in which atmospheric flow around buildings was simulated. Arrays of one, two, three, and four model buildings were tested, and wake profiles of velocity and turbulence were measured. The data indicate the effect of the buildings on the wind environment encountered by aircraft during landing or takeoff operations. It was possible to use the results to locate the boundaries of the air regions affected by the obstacles and to recommend preferred arrangements of buildings to maximize light safety.

Logan, E., Jr.; Lin, S. H.

1982-01-01

403

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

404

Distributed forcing flow control in the wake of a blunt trailing edge profiled body using plasma actuators  

NASA Astrophysics Data System (ADS)

A modern flow control technique for reducing the drag associated with the periodic shedding of von Kármán vortices in the wake of a blunt trailing edge profiled body is presented. The technique involves distributed forcing of the wake flow using an array of dielectric barrier discharge plasma actuators, with a spanwise spacing matched to the spanwise wavelength of the dominant secondary wake instability. The experiments include measurement of the velocity field in multiple vertical and horizontal planes in the wake using particle image velocimetry, as well as base pressure, at Reynolds numbers of 2000, 3000, and 5000 based on trailing edge thickness. The flow control technique causes elongation of the vortex formation region across the span, and significant reduction of the fluctuating and total drag forces, up to a maximum of 94% and 18%, respectively. The effectiveness of the flow control technique is shown to be dependent on the induced momentum coefficient. Proper orthogonal decomposition analysis is used to investigate the mechanism of interaction of the flow control technique with the wake flow. Two distinct flow regimes are observed depending on the induced momentum coefficient. The effect of the control on the wake flow structure in the first regime is similar to those observed in previous studies involving mild spanwise-periodic geometric perturbations at the trailing edge, where control leads to streamwise displacement of the vortices and a shift in shedding frequency. However, an incremental increase in the momentum coefficient leads to a second flow regime similar to those previously observed in the case of large-amplitude geometric perturbations, with an almost complete attenuation of vortex shedding in the near-wake region.

Naghib-Lahouti, A.; Hangan, H.; Lavoie, P.

2015-03-01

405

Radar manifestations of ship wakes in algae bloom zones  

NASA Astrophysics Data System (ADS)

Radar manifestations of ship wakes in zones of phytoplankton bloom are discussed. It is shown that these signatures can be regarded as indicators of biogenic activity. The main data are satellite radar images. Satellite visible (VIS) and infrared (IR) satellite data are also analyzed. The large amount of the available data allowed us to make some generalizations and obtain statistically reliable results concerning spatial and temporal variability of certain type of ship wake manifestations in synthetic aperture radar (SAR) images of the sea surface. Traditional classification of surface ship wakes manifestations in satellite SAR images specifies distinct features such as a dark trailing centreline region (turbulent wake), narrow V-wakes aligned at some angle to the ship's path (the Kelvin wake), and, sometimes, internal wave wakes generated under conditions of shallow stratification. Their characteristic lengths are reported to be up to tens of kilometers and they can last from tens of minutes up to one hour. Instances of radar signatures of the ship wakes dissimilar to the previously described were detected in radar images obtained in the course of a satellite monitoring campaign of the central and south-eastern Baltic. These ship wakes can be seen in satellite radar images as long bright strips of enhanced backscatter with characteristic length of up to several hundred kilometres lasting more than 5 hours. A hypothesis is put forward of the coherence of this type of ship wakes detected in sea surface radar imagery and areas of intensive biogenic activity under conditions of low near-surface winds. Statistics on their seasonal, spatial and year-to-year distribution are drawn. These results are compared with temporal and spatial variations in chlorophyll a concentration and intensity of phytoplankton bloom in the area of interest. Chlorophyll a concentration maps derived from satellite data are used, as well as those based on in situ measurements. The relation between occurrences of this type of ship wake manifestations and areas of algae blooms is established.

Mityagina, Marina I.; Lavrova, Olga Yu.

2014-10-01

406

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

407

Ferromagnetic resonance probe liftoff suppression apparatus  

DOEpatents

A liftoff suppression apparatus utilizing a liftoff sensing coil to sense the amount a ferromagnetic resonance probe lifts off the test surface during flaw detection and utilizing the liftoff signal to modulate the probe's field modulating coil to suppress the liftoff effects.

Davis, Thomas J. (Issaquah, WA); Tomeraasen, Paul L. (West Richland, WA)

1985-01-01

408

Transition and Turbulence Modeling for Blunt-Body Wake Flows  

NASA Technical Reports Server (NTRS)

Aerobraking has been proposed as an efficient means of decelerating spacecraft for planetary missions. Most current aerobrake designs feature a blunt forebody shielding the payload from the intense heat generated during atmospheric entry. Although this forebody will absorb the largest portion of the heat pulse, accurate prediction of heating in the near wake is of great importance, since large local heating values can occur at points of shear-layer impingement. In order to address the various issues associated with these blunt-body wake flowfields, the Advisory Group for Aerospace Research and Development (AGARD) formed Working Group 18 in 1992. One of the objectives of this activity was to examine real-gas effects in high-speed flow fields around a 70 deg. blunted cone. To date, many researchers have conducted experiments using this geometry in various facilities, such as the Large Energy National Shock (LENS) tunnel at Cubric/Calspan and the HEG shock tunnel at DLR-Goettingen. Several computational studies have also been conducted in concert with these tests. Many of the experimental results have indicated the possible presence of a transitional shear layer through a large increase in heat transfer downstream of the reattachment point. The presence of transition could in fact lead to much higher peak heating than if the separated flow is entirely laminar or turbulent. In the shock-tunnel tests, however, it is difficult to separate such viscous-flow phenomena from real-gas effects. In order to help make this distinction, Horvath et al. recently conducted a set of experiments in the NASA Langley 20-Inch Mach 6 Tunnel, and compared the results to laminar Navier-Stokes calculations. They found heat-transfer distributions similar to those obtained in the high-enthalpy facilities, with the measured peak heating along the sting support markedly greater than that predicted by the laminar computations. These trends point to the need to find transitional and turbulent computational solutions for these flowfields.

Nance, Robert P.; Horvath, Thomas J.; Hassan, H. A.

1997-01-01

409

Direct Numerical Simulation of a Temporally Evolving Incompressible Plane Wake: Effect of Initial Conditions on Evolution and Topology  

NASA Technical Reports Server (NTRS)

Direct numerical simulations have been used to examine the effect of the initial disturbance field on the development of three-dimensionality and the transition to turbulence in the incompressible plane wake. The simulations were performed using a new numerical method for solving the time-dependent, three-dimensional, incompressible Navier-Stokes equations in flows with one infinite and two periodic directions. The method uses standard Fast Fourier Transforms and is applicable to cases where the vorticity field is compact in the infinite direction. Initial disturbances fields examined were combinations of two-dimensional waves and symmetric pairs of 60 deg oblique waves at the fundamental, subharmonic, and sub-subharmonic wavelengths. The results of these simulations indicate that the presence of 60 deg disturbances at the subharmonic streamwise wavelength results in the development of strong coherent three-dimensional structures. The resulting strong three-dimensional rate-of-strain triggers the growth of intense fine scale motions. Wakes initiated with 60 deg disturbances at the fundamental streamwise wavelength develop weak coherent streamwise structures, and do not develop significant fine scale motions, even at high Reynolds numbers. The wakes which develop strong three-dimensional structures exhibit growth rates on par with experimentally observed turbulent plane wakes. Wakes which develop only weak three-dimensional structures exhibit significantly lower late time growth rates. Preliminary studies of wakes initiated with an oblique fundamental and a two-dimensional subharmonic, which develop asymmetric coherent oblique structures at the subharmonic wavelength, indicate that significant fine scale motions only develop if the resulting oblique structures are above an angle of approximately 45 deg.

Sondergaard, R.; Cantwell, B.; Mansour, N.

1997-01-01

410

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

411

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

412

Absolute instability in axisymmetric wakes: compressible and density variation effects  

NASA Astrophysics Data System (ADS)

Lesshafft & Huerre (Phys. Fluids, 2007; vol. 19, 024102) have recently studied the transition from