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Sample records for infragravity wave contribution

  1. Cross-shore sand transport by infragravity waves as a function of beach steepness

    NASA Astrophysics Data System (ADS)

    Bakker, A. T. M.; Brinkkemper, J. A.; Steen, F.; Tissier, M. F. S.; Ruessink, B. G.

    2016-10-01

    Two field data sets of near-bed velocity, pressure, and sediment concentration are analyzed to study the influence of infragravity waves on sand suspension and cross-shore transport. On the moderately sloping Sand Motor beach (≈1:35), the local ratio of infragravity wave height to sea-swell wave height is relatively small (HIG/HSW<0.4), and sand fluxes are related to the correlation of the infragravity-wave orbital motion with the sea-swell wave envelope, r0. When the largest sea-swell waves are present during negative infragravity velocities (bound wave, negative correlation r0), most sand is suspended here, and the infragravity sand flux qIG is offshore. When r0 is positive, the largest sea-swell waves are present during positive infragravity velocities (free wave), and qIG is onshore directed. For both cases, the infragravity contribution to the total sand flux is, however, relatively small (<20%). In the inner surf zone of the gently (≈1:80) sloping Ameland beach, the infragravity waves are relatively large (HIG/HSW>0.4), most sand is suspended during negative infragravity velocities, and qIG is offshore directed. The infragravity contribution to the total sand flux is considerably larger and reaches up to ≈60% during energetic conditions. On the whole, HIG/HSW is a good indicator for the infragravity-related sand suspension mechanism and the resulting infragravity sand transport direction and relative importance.

  2. Infragravity waves across the oceans

    NASA Astrophysics Data System (ADS)

    Rawat, Arshad; Ardhuin, Fabrice; Aucan, Jerome

    2014-05-01

    The propagation of transoceanic Infragravity (IG) wave was investigated using a global spectral wave model together with deep-ocean pressure recorders. IG waves are generated mostly at the shorelines due to non-linear hydrodynamic effects that transfer energy from the main windsea and swell band, with periods of 1 to 25 s, to periods up to 500 s. IG waves are important for the study of near-shore processes and harbor agitation, and can also be a potential source of errors in satellite altimetry measurements. Setting up a global IG model was motivated by the investigation of these errors for the future planned SWOT mission. Despite the fact that the infragravity waves exhibit much smaller vertical amplitudes than the usual high frequency wind-driven waves, of the order of 1 cm in the deep oceans, their propagation throughout the oceans and signature in the wave spectrum can be clearly observed. Using a simplified empirical parameterization of the nearshore source of free IG waves as a function of the incoming wave parameters we extended to WAVEWATCH III model, used so far for windseas and swell, to the IG band, up to periods of 300 s. The spatial and temporal variability of the modeled IG energy was well correlated to the DART station records, making it useful to interpret the records of IG waves. Open ocean IG wave records appear dominated by trans-oceanic events with well defined sources concentrated on a few days, usually on West coasts, and affecting the entire ocean basin, with amplitude patterns very similar to those of tsunamis. Three particular IG bursts during 2008 are studied, 2 in the Pacific Ocean and 1 in the North Atlantic. It was observed that the liberated IG waves can travel long distances often crossing whole oceans with negligible dissipation. The IG signatures are clearly observed at sensors along their propagation paths.

  3. Infragravity waves in the deep ocean: An upward revision

    NASA Astrophysics Data System (ADS)

    Aucan, J.; Ardhuin, F.

    2013-07-01

    Ocean infragravity waves are surface gravity waves with periods of several minutes and corresponding wavelengths of up to tens of kilometers. When propagating freely in the deep ocean, these waves are typically small, several centimeters at most, so they have been seldom studied. In the context of future wide-swath altimetry missions, these waves need to be better quantified as they have wavelengths that will be resolved by such instruments. Here, we analyze the global climatology and variability of infragravity waves in the deep ocean using data from over 40 open ocean locations, with depths larger than 2000 m. We show that typical infragravity wave heights are higher than previously estimated, with winter-averaged values up to 11 mm off the U.S. West Coast, and typically less than 6 mm in the tropics. The mid to high latitudes exhibit a strong seasonal cycle consistent with the local variability of the wind-waves, while the tropical Pacific has a higher energy level during the Austral winter that does not correlate well with the local wind-waves, suggesting a remote source for the recorded infragravity waves. These infragravity wave energies are expected to be a significant contribution to the error budget for possible measurements of sea level associated to sub-mesoscale currents at horizontal scales around 10 km. Hence, a global numerical model of infragravity waves will likely be necessary for the analysis of the planned Surface Water Ocean Topography mission.

  4. Infragravity waves over a natural barred profile

    USGS Publications Warehouse

    Sallenger, A.H.; Holman, R.A.

    1987-01-01

    Measurements of cross-shore flow were made across the surf zone during a storm as a nearshore bar became better developed and migrated offshore. Measured infragravity band spectra were compared to synthetic spectra calculated numerically over the natural barred profile assuming a white run-up spectrum of leaky mode or high-mode edge waves. The dominant wave observed early in the storm was consistent with Symond and Bowen's (1984) theoretical prediction of resonant amplification of discrete frequencies over a barred profile. -from Authors

  5. Standing infragravity waves over an alongshore irregular rocky bathymetry

    NASA Astrophysics Data System (ADS)

    Winter, G.; Lowe, R. J.; Symonds, G.; Hansen, J. E.; van Dongeren, A. R.

    2017-06-01

    Rocky reef coastlines typically feature highly variable and often abrupt cross-shore and alongshore changes in bathymetry. The effects of this irregular rocky bathymetry on the dynamics of infragravity waves are largely unknown. Most models of infragravity wave dynamics have been developed and validated on smooth alongshore-uniform bathymetries, which may break down over these highly variable bathymetries. A 2 week field experiment was conducted on a rocky reef-fringed beach to investigate how the variable bathymetry affects the spatial and temporal variability of infragravity waves. The height of short (sea-swell) waves decreased over the shallow reef due to breaking, whereas the height of infragravity waves increased toward the shoreline. Both during a storm event (Hm0 = 2.3 m) and under moderate wave conditions (Hm0 = 1.0-1.8 m), the infragravity waves formed a persistent cross-shore standing wave pattern along the entire shoreline, despite the irregular bathymetry. In addition, the alongshore components of infragravity waves refracted by the presence of the nearshore reef were observed to propagate in opposite directions up and down the coast resulting in a local alongshore standing wave pattern. Thus, the presence of highly variable nearshore bathymetry, which commonly occurs along rocky reef coastlines, may produce both cross-shore and alongshore standing wave patterns.

  6. Relevance of infragravity waves in a wave-dominated inlet

    NASA Astrophysics Data System (ADS)

    Bertin, Xavier; Olabarrieta, Maitane

    2016-08-01

    This study investigates the relevance of infragravity (IG) waves at Albufeira Lagoon Inlet, a shallow wave-dominated inlet located on the western coast of Portugal. A field experiment carried out in September 2010 revealed the occurrence of low-frequency oscillations (i.e., 25-300 s) in water levels and current velocities. While these fluctuations were present over the ebb-tidal delta along the whole tidal cycle, they only appeared between the beginning of the flood and up to 2 h after high tide inside the lagoon. The XBeach modeling system was applied to Albufeira Lagoon Inlet and reproduced the generation and propagation of IG waves and their blocking during the ebb. This behavior was explained by blocking due to opposing tidal currents reaching 2.5 m s-1 in shallow water depths. Numerical results suggest that the breakpoint mechanism and the long bound wave shoaling mechanisms contributed significantly to the generation of IG waves in the inlet. IG waves induced fluctuations in flood currents inside the lagoon reaching temporarily 100% of their magnitude. The fact that these fluctuations occur mostly at flood and not at ebb could promote flood dominance in the lagoon. This hypothesis will have to be verified, namely under storm wave conditions.

  7. Relevance of Infragravity Waves in a Wave Dominated Shallow Inlet

    NASA Astrophysics Data System (ADS)

    Olabarrieta, M.; Bertin, X.

    2014-12-01

    Infragravity (IG) waves have received a growing attention over the last decade and they have been shown to partly control dune erosion, barrier breaching, development of seiches in harbors or the circulation on fringing reefs. Although the relevance IG waves in surf and swash zone dynamics is well recognized, their dynamics and effects on tidal inlets and estuaries have not been analyzed. This study investigates the importance of IG waves at Albufeira Lagoon Inlet, a shallow wave-dominated inlet located on the western Coast of Portugal. Water levels and currents were measured synchronously during a two-day field experiment carried out at Albufeira Lagoon Inlet in September 2010. Apart from the tidally induced gravity wave modulations and wave induced setup inside the lagoon, an important IG wave contribution was identified. Low frequency oscillations were noticeable in the free surface elevation records and produced fluctuations of up to 100% in current intensities. While IG waves in the ebb shoal were present during the whole tidal cycle, the absence of IG waves characterized the ebbing tide inside the lagoon. The energy in the IG frequency band gradually increased from low tide to high tide, and disappeared during the ebbing tide. The modeling system Xbeach was applied to hindcast the hydrodynamics during the field experiment period. The model captures the main physics related with the IG wave generation and propagation inside the inlet, and reproduced the IG blocking during the ebb as identified in the measurements. This behavior was explained by the combination of advection and wave blocking induced by opposing tidal currents. Both measurements and numerical results suggested the bound wave release as the dominant mechanism responsible for IG wave generation. The fact that IG waves only propagate at flood tide has strong implications on the sediment balance of the inlet and contribute to inlet infilling under energetic wave conditions. It is expected that IG

  8. A case study on dune response to infragravity waves

    NASA Astrophysics Data System (ADS)

    Li, Wenshan; Wang, Hui; Li, Huan; Wu, Shuangquan; Li, Cheng

    2017-08-01

    A series of numerical simulations were conducted using the process-based model XBeach to investigate dune response under normal and getting rid of infragravity wave conditions with different slopes. Erosion volume upside the dune toe and dune top recession are set as indicators for dune vulnerability as well as defence capacity for its front-beach. Results show that both dune erosion volume and dune top recession decrease with gentler dune slopes. Of all the simulation cases, dune with a face slope of 1/1 lost most sand and supplied most sand for lower-bed. The presence of infragravity waves is validated to be crucial to dune vulnerability. The dune erosion volume is shown to decrease by 44.5%∼61.5% and the dune top recession decreased by 0%∼45.5% correspondingly, in the case that infragravity motion is not taken into account during simulation for different dune slopes.

  9. Observations of nearshore infragravity wave dynamics under high energy swell and wind-wave conditions

    NASA Astrophysics Data System (ADS)

    Inch, Kris; Davidson, Mark; Masselink, Gerd; Russell, Paul

    2017-04-01

    Infragravity waves (0.005-0.04 Hz) can dominate the water motion close to shore on low sloping beaches and play a significant role in beach and dune erosion. A new field data set of water surface elevation at 15 cross-shore locations on a dissipative, fetch-unlimited beach is analysed to investigate the forcing and surf zone behaviour of infragravity waves during a wide range of offshore wave conditions (Ho=0.38-3.88 m; Tp=6-20 s). Infragravity waves approach the shore as bound waves lagging slightly ( 4 s) behind the short wave (0.04-0.33 Hz) envelope and are released in the surf zone as free waves. Infragravity wave heights of up to 1 m are measured close to shore and are best predicted using an offshore forcing parameter that represents the short wave energy flux (Ho2 Tp). Considerable infragravity dissipation is observed in the surf zone and dissipation increases with offshore wave energy. Dissipation is highly frequency-dependant and a frequency-domain Complex Empirical Orthogonal Function analysis reveals (quasi-)standing waves at frequencies <0.017 Hz, but an increasingly progressive wave pattern at higher frequencies with reflection coefficients <0.1, indicative of more than 90% dissipation. Much of the observed dissipation occurs very close to shore and the dependence of the reflection coefficient on a normalised bed slope parameter implies that energy at high infragravity frequencies is dissipated by wave breaking, since these frequencies fit into a mild sloping regime. This is supported by the results of bispectral analysis which show predominantly infragravity-infragravity interactions in shallow water and the development of infragravity harmonics indicative of steepening and eventual breaking of the infragravity waves.

  10. Six years of deep ocean infragravity wave measurements on the Mid-Atlantic Ridge, 37°N

    NASA Astrophysics Data System (ADS)

    Crawford, W. C.; Ballu, V.; Bertin, X.; Karpytchev, M.

    2013-12-01

    Ocean infragravity waves are an important part of the deep ocean climate, can be used to measure subsurface elastic properties, and may contribute to the earth's background seismic noise. They are surface gravity waves with periods from 10s of seconds to 10s of minutes and are generated by non-linear wave-wave interactions, with the strongest infragravity waves believed to be generated by storms near coastlines. The first deep ocean observations of infragravity waves suggested that they were much stronger and more constant in the Pacific Ocean than in the North Atlantic Ocean, presumably because the Pacific Ocean has direct wavepaths to more coastline and, in particular, high-latitude coastlines in both the Northern and Southern Oceans [Webb et al., 1991]. However, a recent study of deep ocean infragravity waves, using data from tsunami buoys at a large number of sites in the Pacific and Atlantic Oceans, suggests that infragravity wave energy is much more variable in the Pacific Ocean, and stronger in the Atlantic Ocean, than was assumed [Aucan & Ardhuin, 2013]. We measured seafloor pressure continuously for six years at a deep ocean site using both differential and absolute pressure gauges. We describe the levels and variability of infragravity wave energy and their correlation with coastal storms. We relate the energy observed at Atlantic and Pacific ocean tsunami gauges to the sensitivity of each site to waves from surrounding coastlines, calculated using a tsunami modeling code. We compare the sensitivity of tsunami buoys and differential pressure gauges to deep ocean infragravity waves.

  11. Infragravity Waves Over Topography: Generation, Dissipation, and Reflection

    DTIC Science & Technology

    2006-09-01

    34" Joseph Pedlosky Chairman, Joint Committee for Physical Oceanography 2 Infragravity Waves over Topography: Generation, Dissipation, and Reflection...members and coauthors, Drs. David Chapman, Robert Guza, Thomas Herbers, Steve Lentz, Joseph Pedlosky, Britt Raubenheimer, and Carl Wunsch, have patiently...curve). The 95% confidence interval, based on a X2 distribution with 42 degrees of freedom [ Priestley , 1981], is shown in the upper right corner. 15 1.3

  12. The sources of deep ocean infragravity waves observed in the North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Crawford, Wayne; Ballu, Valerie; Bertin, Xavier; Karpytchev, Mikhail

    2015-07-01

    Infragravity waves are long-period (25-250 s) ocean surface gravity waves generated in coastal zones through wave-wave interactions or oscillation of the breaking point. Most of the infragravity wave energy is trapped or dissipated near coastlines, but a small percentage escapes into the open oceans. The source of deep ocean infragravity waves is debated, specifically whether they come mostly from regions with strong source waves or from sites with particular morphologies/orientations. We correlate measurements of infragravity waves in the deep North Atlantic Ocean with infragravity wave generation parameters throughout the Atlantic Ocean to find the dominant sources of deep ocean infragravity wave energy in the North Atlantic Ocean. The deep ocean infragravity wave data are from a 5 year deployment of absolute pressure gauges west of the Azores islands (37°N, 35°W) and shorter data sets from seafloor tsunami gauges (DART buoys). Two main sources are identified: one off of the west coast of southern Europe and northern Africa (25°N-40°N) in northern hemisphere winter and the other off the west coast of equatorial Africa (the Gulf of Guinea) in southern hemisphere winter. These regions have relatively weak source waves and weak infragravity wave propagation paths to the main measurement site, indicating that that the site morphology/orientation dominates the creation of deep ocean infragravity waves. Both regions have also been identified as potential sources of global seismological noise, suggesting that the same mechanisms may be behind the generation of deep ocean infragravity waves and global seismological noise in the frequency band from 0.001 to 0.04 Hz.

  13. Surf zone, infragravity wave energy flux, and runup in extreme conditions

    NASA Astrophysics Data System (ADS)

    Fiedler, J. W.; Brodie, K. L.; McNinch, J.; Guza, R. T.

    2014-12-01

    Waves, currents, and sand levels were observed on a 1.4 km-long cross-shore transect extending from the back beach to ~11 m water depth at Agate Beach, Oregon in Fall 2013. Wave runup and water table fluctuations on this low slope (1:80) beach were measured with a cliff-mounted scanning Lidar and buried pressure sensors. Significant wave heights at an offshore buoy in 128m depth ranged from small (0.5m) to extreme (7.5m), with peak periods between 4-22 seconds. Infragravity frequency (nominally 0.01 Hz) horizontal runup excursions exceeded 100m, and infragravity cross-shore velocity exceeded 3 m/s. Cross-shore patterns of infragravity wave energy flux, observed with seven co-located pressure and current meters, indicate 'proto-saturation' of the inner surfzone in extreme conditions. That is, the intensification of incident wave forcing (e.g. higher energy, longer swell) leads to a wider surfzone and an increase in the shoreward infragravity wave energy seaward of the surfzone, but produces more modest increases in flux in the inner surfzone, and in the runup. Nonlinear energy balances, based on the observations, show transfer of energy from sea-swell to infragravity waves, and vice-versa. The infragravity energy balance closes in cases with low energy incident sea-swell. With more energetic incident waves, there is an unexplained inner surfzone energy sink at the lowest IG frequencies (0.004-0.02 Hz). Ongoing work aims to quantify the effect on infragravity energy balances by infragravity wave breaking and bottom friction. Additionally, the estimates may be degraded by contamination with rotational velocities of surfzone eddies. Whatever the dynamical explanation, infragravity wave runup on a low slope beach in high-energy conditions is limited significantly by dissipation. The slow rate of runup increase suggests nascent, or 'proto' saturation. This work was supported by the U.S. Army Corps of Engineers.

  14. Numerical Modeling of Infragravity Wave Runup on Steep and Mildly Sloping Natural Beaches

    NASA Astrophysics Data System (ADS)

    Fiedler, J. W.; Smit, P.; Brodie, K. L.; McNinch, J.; Guza, R. T.; Gallien, T.

    2016-12-01

    We present ongoing work which aims to validate the non-hydrostatic model SWASH for wave runup and infragravity waves generated by a range of different incident wave spectra at the offshore boundary, including the effect of finite directional spread. Flume studies of wave runup are limited to normally incident (1D) sea and infragravity waves, but natural waves are directionally spread (2D), with substantially different dynamics from 1D. For example, refractive trapping (edge waves) is only possible with 2D waves, and the bound infragravity wave response to short wave groups is highly amplified for the special case of normal incidence. Selected case studies are modeled at Agate Beach, Oregon, a low slope (1:80) beach with maximum offshore wave heights greater than 7m, and Cardiff, California, a steep (1:8) beach with maximum wave heights of 2m. Peak periods ranged between 5-20 s at both sites. On both beaches, waves were measured on a transect from approximately 10m depth to the runup, using pressure sensors, current meters, and a scanning lidar. Bulk short wave quantities, wave runup, infragravity frequency spectra and energy fluxes are compared with SWASH. On the low slope beach with energetic incident waves, the observed horizontal runup excursions reach 140m ( 100s periods). Swash front velocities reached up to several m/s, causing short waves to stack up during runup drawdown. On reversal of the infragravity phase, the stacked short waves are swept onshore with the long wave front, effectively enhancing runup by phase coupling long and short waves. Statistical variability and nonlinearity in swash generation lead to time-varying runup heights. Here, we test these observations with 2D SWASH, as well as the sensitivity of modeled runup to the parameterization of bottom friction.

  15. Infragravity wave generation and dynamics over a mild slope beach : Experiments and numerical computations

    NASA Astrophysics Data System (ADS)

    Cienfuegos, R.; Duarte, L.; Hernandez, E.

    2008-12-01

    Charasteristic frequencies of gravity waves generated by wind and propagating towards the coast are usually comprised between 0.05Hz and 1Hz. Nevertheless, lower frequecy waves, in the range of 0.001Hz and 0.05Hz, have been observed in the nearshore zone. Those long waves, termed as infragravity waves, are generated by complex nonlinear mechanisms affecting the propagation of irregular waves up to the coast. The groupiness of an incident random wave field may be responsible for producing a slow modulation of the mean water surface thus generating bound long waves travelling at the group speed. Similarly, a quasi- periodic oscillation of the break-point location, will be accompained by a slow modulation of set-up/set-down in the surf zone and generation and release of long waves. If the primary structure of the carrying incident gravity waves is destroyed (e.g. by breaking), forced long waves can be freely released and even reflected at the coast. Infragravity waves can affect port operation through resonating conditions, or strongly affect sediment transport and beach morphodynamics. In the present study we investigate infragravity wave generation mechanisms both, from experiments and numerical computations. Measurements were conducted at the 70-meter long wave tank, located at the Instituto Nacional de Hidraulica (Chile), prepared with a beach of very mild slope of 1/80 in order to produce large surf zone extensions. A random JONSWAP type wave field (h0=0.52m, fp=0.25Hz, Hmo=0.17m) was generated by a piston wave-maker and measurements of the free surface displacements were performed all over its length at high spatial resolution (0.2m to 1m). Velocity profiles were also measured at four verticals inside the surf zone using an ADV. Correlation maps of wave group envelopes and infragravity waves are computed in order to identify long wave generation and dynamics in the experimental set-up. It appears that both mechanisms (groupiness and break-point oscillation) are

  16. Dynamics of Nearshore Sand Bars and Infra-gravity Waves: The Optimal Theory Point of View

    NASA Astrophysics Data System (ADS)

    Bouchette, F.; Mohammadi, B.

    2016-12-01

    It is well known that the dynamics of near-shore sand bars are partly controlled by the features (location of nodes, amplitude, length, period) of the so-called infra-gravity waves. Reciprocally, changes in the location, size and shape of near-shore sand bars can control wave/wave interactions which in their turn alter the infra-gravity content of the near-shore wave energy spectrum. The coupling infra-gravity / near-shore bar is thus definitely two ways. Regarding numerical modelling, several approaches have already been considered to analyze such coupled dynamics. Most of them are based on the following strategy: 1) define an energy spectrum including infra-gravity, 2) tentatively compute the radiation stresses driven by this energy spectrum, 3) compute sediment transport and changes in the seabottom elevation including sand bars, 4) loop on the computation of infra-gravity taking into account the morphological changes. In this work, we consider an alternative approach named Nearshore Optimal Theory, which is a kind of breakdown point of view for the modeling of near-shore hydro-morphodynamics and wave/ wave/ seabottom interactions. Optimal theory applied to near-shore hydro-morphodynamics arose with the design of solid coastal defense structures by shape optimization methods, and is being now extended in order to model dynamics of any near-shore system combining waves and sand. The basics are the following: the near-shore system state is through a functional J representative of the energy of the system in some way. This J is computed from a model embedding the physics to be studied only (here hydrodynamics forced by simple infra-gravity). Then the paradigm is to say that the system will evolve so that the energy J tends to minimize. No really matter the complexity of wave propagation nor wave/bottom interactions. As soon as J embeds the physics to be explored, the method does not require a comprehensive modeling. Near-shore Optimal Theory has already given

  17. Group bound long waves as a source of infragravity energy in the surf zone

    NASA Astrophysics Data System (ADS)

    Masselink, Gerhard

    1995-11-01

    Measurements of water surface elevation and cross-shore currents were made under moderate-energy conditions ( Hrms = 1.1 m and Tz = 7.5 s) on a low-gradient macrotidal beach in central Queensland, Australia. The infragravity signal (<0.04 Hz) is separated into incoming and outgoing components and compared with the wind wave envelope. The variances associated with the incoming and outgoing infragravity signals are comparable and increase four- to five-fold from a water depth of around 4 m to a depth of 1 m. Cross-correlation and cross-spectral analysis indicate the presence of an incoming bound long wave (BLW) that lags approximately 5 s behind the wind wave envelope. The BLW decouples from the wind wave groups as the incident waves break. The released BLW then travels onshore through the surf zone as a free wave and reflects some distance seaward (5 m) of the shoreline. The superposition of the released BLW and the reflected leaky wave results in standing wave motion in the inner surf zone. Coherence-spectra suggest that about 40% of the incoming infragravity energy is forced by the wind wave envelope.

  18. Infragravity currents in a small ría: Estuary-amplified coastal edge waves?

    NASA Astrophysics Data System (ADS)

    Uncles, R. J.; Stephens, J. A.; Harris, C.

    2014-10-01

    Observations are presented of estuarine infragravity oscillations in a very small estuary, the Ría de Santiuste, northern Spain, that discharges into a bay. Time-scale calculations and measurements indicate that the most likely source of amplified infragravity waves within the estuary are coastal edge waves, which appear to be resonating between the headlands of the bay, and onshore-offshore seiching of waters that may be resonating between the beach and the bay's seaward limit. Infragravity waves in the estuary have a narrow, power-dominant periodicity range of 4.3-4.8 min. Generally, only very weak waves, and at other periodicities, occur within the tidal river when it is unaffected by the tide. Although infragravity water-level amplitudes are small in the tidal river, typically ˜0.01 m during high water, the corresponding velocity amplitudes are significant, typically ˜0.1 m s-1, despite the occurrence of high runoff conditions during these measurements. Within the estuary and close to the mouth, near-bed salinity shows considerable variability that is a consequence of salt wedge oscillations with periodicities that are within the range of 4.3-4.8 min. Model results for simulated neap to spring high-water water levels show that wave periodicities in the range 3.5-4.5 min correspond approximately to 3λ/4 resonances. The model also indicates that an effect of low runoff is to greatly enhance resonant behaviour within the estuary, such that water level amplitudes of 0.02 m at the mouth can produce wave currents as fast as 0.4 m s-1 within the estuary, compared with ˜0.1 m s-1 during high runoff.

  19. Incident wave, infragravity wave, and non-linear low-frequency bore evolution across fringing coral reefs

    NASA Astrophysics Data System (ADS)

    Storlazzi, C. D.; Griffioen, D.; Cheriton, O. M.

    2016-12-01

    Coral reefs have been shown to significantly attenuate incident wave energy and thus provide protection for 100s of millions of people globally. To better constrain wave dynamics and wave-driven water levels over fringing coral reefs, a 4-month deployment of wave and tide gauges was conducted across two shore-normal transects on Roi-Namur Island and two transects on Kwajalein Island in the Republic of the Marshall Islands. At all locations, although incident wave (periods <25 s) heights were an order of magnitude greater than infragravity wave (periods > 250 s) heights on the outer reef flat just inshore of the zone of wave breaking, the infragravity wave heights generally equaled the incident wave heights by the middle of the reef flat and exceeded the incident wave heights on the inner reef flat by the shoreline. The infragravity waves generally were asymmetric, positively skewed, bore-like forms with incident-band waves riding the infragravity wave crest at the head of the bore; these wave packets have similar structure to high-frequency internal waves on an internal wave bore. Bore height was shown to scale with water depth, offshore wave height, and offshore wave period. For a given tidal elevation, with increasing offshore wave heights, such bores occurred more frequently on the middle reef flat, whereas they occurred less frequently on the inner reef flat. Skewed, asymmetric waves are known to drive large gradients in velocity and shear stress that can transport material onshore. Thus, a better understanding of these low-frequency, energetic bores on reef flats is critical to forecasting how coral reef-lined coasts may respond to sea-level rise and climate change.

  20. Beach slope effects on sand suspension and transport rate by infragravity waves

    NASA Astrophysics Data System (ADS)

    de Bakker, A.; Brinkkemper, J.; van der Steen, F.; Tissier, M.; Ruessink, G.

    2016-02-01

    The suspension and transport of sand by infragravity (IG) waves has been investigated in various studies. The diversity in boundary conditions has resulted in observations that contrast in direction and relative importance of IG sand transport as well as in the underlying suspension mechanism. We hypothesize that the relative importance of IG wave energy to sea-swell wave energy, which is affected by beach characteristics and offshore wave conditions, explains these contrasting observations. Here, we investigate this with data from the moderately sloping (1:35) Sand Motor beach, and the gently sloping (1:80) Ameland beach, both in the Netherlands. On each site, wave characteristics, velocities and sand concentrations were collected at up to 4 locations in the intertidal zone. On the moderately sloping Sand Motor beach, the IG waves were typically small compared to sea-swell waves (Hm0IG/Hm0sw< 0.4), despite offshore wave heights close to 5 m. Accordingly, the sand was suspended by the sea-swell waves and the IG transport direction is linked to the correlation of the IG orbital motion with the sea-swell wave envelope. In the shoaling and outer surf zone, the correlation is negative and the IG transport is offshore directed. Further shoreward, the correlation becomes positive as the largest sea-swell waves are present on the IG crest, resulting in onshore IG transport. However, in both cases the IG transport hardly contributed to the total transport. This contrasts with the inner surf zone of the gently sloping Ameland beach, where the IG waves were more energetic (Hm0IG/Hm0sw > 0.4), and their transport contribution was substantial. The IG transport was predominantly offshore directed as the sand was mostly suspended by the negative IG-wave velocity phase. On the whole, our data confirm that the local ratio of IG to sea/swell wave height is a good proxy for the sand suspension mechanism, the IG transport direction, and the relative importance of IG waves to the

  1. Analysis and numerical modeling of the global free infra-gravity wave climate for the SWOT mission

    NASA Astrophysics Data System (ADS)

    Ardhuin, Fabrice; Aucan, Jérome; Rawat, Arshad

    2013-04-01

    All sea level variations of the order of 1 cm at scales under 30 km are of great interest for the future Surface Water Ocean Topography (SWOT) satellite mission. That satellite should provide high-resolution maps of the sea surface height for analysis of meso to sub-mesoscale currents, but that will require a filtering of all gravity wave motions in the data. Free infragravity waves (FIGWs) are generated and radiate offshore when swells and/or wind seas and their associated bound infragravity waves impact exposed coastlines. Free infragravity waves have dominant periods comprised between 1 and 10 minutes and horizontal wavelengths of up to tens of kilometers. Given the length scales of the infragravity waves wavelength and amplitude, the infragravity wave field will can a significant fraction the signal measured by the future SWOT mission. In this study, we analyze the data from recovered bottom pressure recorders of the Deep-ocean Assessment and Reporting of Tsunami (DART) program. This analysis includes data spanning several years between 2006 and 2010, from stations at different latitudes in the North and South Pacific, the North Atlantic, the Gulf of Mexico and the Caribbean Sea. We present and discuss the following conclusions: (1) The amplitude of free infragravity waves can reach several centimeters, higher than the precision sought for the SWOT mission. (2) The free infragravity signal is higher in the Eastern North Pacific than in the Western North Pacific, possibly due to smaller incident swell and seas impacting the nearby coastlines. (3) Free infragravity waves are higher in the North Pacific than in the North Atlantic, possibly owing to different average continental shelves configurations in the two basins. (4) There is a clear seasonal cycle at the high latitudes North Atlantic and Pacific stations that is much less pronounced or absent at the tropical stations, consistent with the generation mechanism of free infragravity waves. Our numerical model

  2. Analysis of the global free infra-gravity wave climate for the SWOT mission, and preliminary results of numerical modelling

    NASA Astrophysics Data System (ADS)

    Rawat, A.; Aucan, J.; Ardhuin, F.

    2012-12-01

    All sea level variations of the order of 1 cm at scales under 30 km are of great interest for the future Surface Water Ocean Topography (SWOT) satellite mission. That satellite should provide high-resolution maps of the sea surface height for analysis of meso to sub-mesoscale currents, but that will require a filtering of all gravity wave motions in the data. Free infragravity waves (FIGWs) are generated and radiate offshore when swells and/or wind seas and their associated bound infragravity waves impact exposed coastlines. Free infragravity waves have dominant periods comprised between 1 and 10 minutes and horizontal wavelengths of up to tens of kilometers. Given the length scales of the infragravity waves wavelength and amplitude, the infragravity wave field will can a significant fraction the signal measured by the future SWOT mission. In this study, we analyze the data from recovered bottom pressure recorders of the Deep-ocean Assessment and Reporting of Tsunami (DART) program. This analysis includes data spanning several years between 2006 and 2010, from stations at different latitudes in the North and South Pacific, the North Atlantic, the Gulf of Mexico and the Caribbean Sea. We present and discuss the following conclusions: (1) The amplitude of free infragravity waves can reach several centimeters, higher than the precision sought for the SWOT mission. (2) The free infragravity signal is higher in the Eastern North Pacific than in the Western North Pacific, possibly due to smaller incident swell and seas impacting the nearby coastlines. (3) Free infragravity waves are higher in the North Pacific than in the North Atlantic, possibly owing to different average continental shelves configurations in the two basins. (4) There is a clear seasonal cycle at the high latitudes North Atlantic and Pacific stations that is much less pronounced or absent at the tropical stations, consistent with the generation mechanism of free infragravity waves. Our numerical model

  3. Modelling Infragravity Waves and Currents across a Fringing Reef: Ningaloo Reef, Western Australia

    NASA Astrophysics Data System (ADS)

    van Dongeren, A. R.; Duong Minh, T.; Lowe, R.; Roelvink, J.; Ranasinghe, R.; Symonds, G.

    2010-12-01

    The majority of the world’s coastlines contain submerged reef structures of various types, i.e. tropical coral reefs, relic temperate limestone platforms, and other submerged rock formations. Relatively little research has been conducted to study nearshore hydrodynamic processes that occur in reef environments. A good understanding of these processes is important because waves and wave-induced currents drive sediment transport, nutrient dynamics, and dispersal of larval coral and fish. Through the development of improved hydrodynamic models, the impact of environmental changes and human impacts on reefs may be accurately assessed. However, predictive models have historically been developed and tested using sandy coast environments. There are some important differences with reefs: wave breaking over the reef results in onshore flows with a higher bed friction coefficient, as well as set-up. Recent field studies (e.g., Lowe et al. JPO, 2009a) have shown the transformation of swell energy on reefs, and numerical model studies (Symonds and Black, JCR 2001, Ranasinghe et al., Coastal Eng. 2006, Lowe et al. J. Geoph. Res. 2009b) have shown that the spatial pattern of mean wave heights and mean currents can be qualitatively reproduced. However, the bulk of the measured variability is often in the infragravity frequency band (Pequignet et al. Geoph. Res. Lett., 2009 and Lowe et al., in prep.). The recently developed open-source model XBeach (Roelvink et al, Coastal Eng. 2009) is specifically designed to model these wave motions and associated sediment transport and has been successfully applied to sandy coasts (McCall et al., Coastal Eng. 2010). The objective of this paper is to apply XBeach to simulate infragravity forcing at Ningaloo Reef, a large fringing coral reef located along the northwest coastline of Western Australia. A field experiment at Ningaloo Reef (Western Australia) conducted in June 2009 by Lowe et al (in prep.) specifically aimed at measuring

  4. Numerical investigation of infragravity wave amplifications during harbor oscillations influenced by variable offshore topography

    NASA Astrophysics Data System (ADS)

    Gao, Junliang; Ji, Chunyan; Ma, Xiaojian; Liu, Yingyi; Gaidai, Oleg

    2017-09-01

    The infragravity (IG) period oscillations inside an elongated rectangular harbor near the offshore fringing reef induced by normal-incident bichromatic short wave groups are simulated using a fully nonlinear Boussinesq model, FUNWAVE 2.0. Based on an IG wave separation procedure, this article presents a systematical investigation on how the maximum IG period component amplitude, the bound and free IG waves, and their relative components inside the harbor change with respect to the plane reef-face slope and the incident short wave amplitude under the condition of the 2nd to the 5th modes. For the given harbor and the ranges of the reef-face slope and the incident short wave amplitude studied in this paper, it is shown that both the maximum IG period component amplitude and the free IG wave component amplitude inside the harbor fluctuate widely with the reef-face slope, and their changing trends with the reef-face slope are almost identical with each other, while the bound IG waves inside the harbor seem insensitive to it. Both the maximum IG period component amplitude and those of the bound and free IG standing waves inside the harbor change cubically with the incident short wave amplitude.

  5. Remote sensing of the correlation between breakpoint oscillations and infragravity waves in the surf and swash zone

    NASA Astrophysics Data System (ADS)

    Moura, T.; Baldock, T. E.

    2017-04-01

    A novel remote sensing methodology to determine the dominant infragravity mechanism in the inner surf and swash zone in the field is presented. Video observations of the breakpoint motion are correlated with the shoreline motion and inner surf zone water levels to determine the relationship between the time-varying breakpoint oscillations and the shoreline motion. The results of 13 field data sets collected from three different beaches indicate that, inside the surf zone, the dominance of bound wave or breakpoint forcing is strongly dependent on the surf zone width and the type of short wave breaking. Infragravity generation by bound wave release was stronger for conditions with relatively narrow surf zones and plunging waves; breakpoint forcing was dominant for wider surf zones and spilling breaker conditions.

  6. Parameterization of Incident and Infragravity Swash Variance

    NASA Astrophysics Data System (ADS)

    Stockdon, H. F.; Holman, R. A.; Sallenger, A. H.

    2002-12-01

    By clearly defining the forcing and morphologic controls of swash variance in both the incident and infragravity frequency bands, we are able to derive a more complete parameterization for extreme runup that may be applicable to a wide range of beach and wave conditions. It is expected that the dynamics of the incident and infragravity bands will have different dependencies on offshore wave conditions and local beach slopes. For example, previous studies have shown that swash variance in the incident band depends on foreshore beach slope while the infragravity variance depends more on a weighted mean slope across the surf zone. Because the physics of each band is parameterized differently, the amount that each frequency band contributes to the total swash variance will vary from site to site and, often, at a single site as the profile configuration changes over time. Using water level time series (measured at the shoreline) collected during nine dynamically different field experiments, we test the expected behavior of both incident and infragravity swash and the contribution each makes to total variance. At the dissipative sites (Iribarren number, \\xi0, <0.3) located in Oregon and the Netherlands, the incident band swash is saturated with respect to offshore wave height. Conversely, on the intermediate and reflective beaches, the amplitudes of both incident and infragravity swash variance grow with increasing offshore wave height. While infragravity band swash at all sites appears to increase linearly with offshore wave height, the magnitudes of the response are somewhat greater on reflective beaches than on dissipative beaches. This means that for the same offshore wave conditions the swash on a steeper foreshore will be larger than that on a more gently sloping foreshore. The potential control of the surf zone slope on infragravity band swash is examined at Duck, North Carolina, (0.3 < \\xi0 < 4.0), where significant differences in the relationship between swash

  7. Observations of Infragravity Waves at the Ocean-Bottom Broadband Seismic Stations Endeavour (KEBB) and Explorer (KXBB)

    NASA Astrophysics Data System (ADS)

    Dolenc, D.; Romanowicz, B.; McGill, P.; Wilcock, W.

    2007-12-01

    The long-period background noise observed at ocean-bottom seismic stations is mainly due to deformation of the seafloor under the pressure forcing by long-period ocean surface gravity waves (infragravity waves; 0.002 to 0.05 Hz). Understanding the nature and characteristics of the coupling between the infragravity waves and the solid earth is important for the study of the infragravity wave generation and dissipation as well as for the study of the earth's hum and structure using non-seismic sources. Ocean-bottom broadband stations KEBB and KXBB were deployed as part of a three-year multidisciplinary experiment funded by the W. M. Keck foundation to monitor the linkages between seismic deformation and hydrothermal fluxes on the northern Juan de Fuca plate. The seismic component of the project was a collaboration between the University of Washington, the University of Oregon, and the Monterey Bay Aquarium Research Institute. Station KEBB was installed 247 km west of Vancouver Island (VI) at a water depth of 2376 m in August 2003. A year later station KXBB was installed 105 km offshore VI at a water depth of 2370 m. Each station comprised a Guralp CMG-1T three-component broadband seismometer, sensitive over a wide frequency range from 50 Hz to 2.8 mHz (360 sec), connected to a recording and battery package. Both seismometers were completely buried in the ocean floor sediments. The two stations recorded data continuously and stored them locally until retrieval once per year. Infragravity waves can be observed at KEBB and KXBB on stormy as well as quiet days in the period band from 30 to 400 sec. When compared to the energy of short-period ocean waves recorded at local buoys, the low- frequency seismic noise is found to be mainly generated when the short-period ocean waves reach the coast, and not when the storm passes directly above the stations. Two types of modulation of the infragravity signal are observed. First, a longer-period modulation of the infragravity

  8. Swell-generated Set-up and Infragravity Wave Propagation Over a Fringing Coral Reef: Implications for Wave-driven Inundation of Atoll Islands

    NASA Astrophysics Data System (ADS)

    Cheriton, O. M.; Storlazzi, C. D.; Rosenberger, K. J.; Quataert, E.; van Dongeren, A.

    2014-12-01

    The Republic of the Marshall Islands is comprised of 1156 islands on 29 low-lying atolls with a mean elevation of 2 m that are susceptible to sea-level rise and often subjected to overwash during large wave events. A 6-month deployment of wave and tide gauges across two shore-normal sections of north-facing coral reef on the Roi-Namur Island on Kwajalein Atoll was conducted during 2013-2014 to quantify wave dynamics and wave-driven water levels on the fringing coral reef. Wave heights and periods on the reef flat were strongly correlated to the water levels. On the fore reef, the majority of wave energy was concentrated in the incident band (5-25 s); due to breaking at the reef crest, however, the wave energy over the reef flat was dominated by infragravity-band (25-250 s) motions. Two large wave events with heights of 6-8 m at 15 s over the fore reef were observed. During these events, infragravity-band wave heights exceeded the incident band wave heights and approximately 1.0 m of set-up was established over the innermost reef flat. This set-up enabled the propagation of large waves across the reef flat, reaching maximum heights of nearly 2 m on the innermost reef flat adjacent to the toe of the beach. XBEACH models of the instrument transects were able to replicate the incident waves, infragravity waves, and wave-driven set-up across the reef when the hydrodynamic roughness of the reef was correctly parameterized. These events led to more than 3 m of wave-driven run-up and inundation of the island that drove substantial morphological change to the beach face.

  9. Removal of Infragravity-Wave-Induced Long-Period Noise from OBS Data and Inversion for Crustal Structure Offshore Eastern Taiwan

    NASA Astrophysics Data System (ADS)

    Kuo, B.; Lin, C.; Hsiao, N.; Liang, W.

    2013-12-01

    Vertical ocean-bottom seismometer (OBS) data at frequencies < 0.05 Hz are contaminated by noise exerted from ocean waves, especially the infragravity waves. We constructed the transfer function between pressure and velocity data of OBSs deployed in Taiwan waters and removed the pressure-induced noise from seismic recordings. Three broadband OBSs S002, S005, and S004 were deployed at 1750, 1900, and 4500 m water depth each for 10 months, and a cabled, shallow-buried sensor EOS1 was installed at 300 m seafloor since late 2011. Removing long-period noise for these OBSs improves the identification of teleseismic phases P, S, Pdiff, and PKIKP which were otherwise unidentifiable. For EOS1, infragravity waves completely mask the P and S waveforms for local events in the period range for CMT solution, i.e., 10-40 s. Application of transfer function yielded clean, prominent P and S waveforms at these periods and aids in the CMT determination of small events jointly with land stations. EOS1 is situated on the Ryukyu ridge 45 km off the NE coast of Taiwan. We are performing inversion of the compliance function for EOS1 for the crustal structure beneath the station.

  10. ON PREDICTING INFRAGRAVITY ENERGY IN THE SURF ZONE.

    USGS Publications Warehouse

    Sallenger,, Asbury H.; Holman, Robert A.; Edge, Billy L.

    1985-01-01

    Flow data were obtained in the surf zone across a barred profile during a storm. RMS cross-shore velocities due to waves in the intragravity band (wave periods greater than 20 s) had maxima in excess of 0. 5 m/s over the bar crest. For comparison to measured spectra, synthetic spectra of cross-shore flow were computed using measured nearshore profiles. The structure, in the infragravity band, of these synthetic spectra corresponded reasonably well with the structure of the measured spectra. Total variances of measured cross-shore flow within the infragravity band were nondimensionalized by dividing by total infragravity variances of synthetic spectra. These nondimensional variances were independent of distance offshore and increased with the square of the breaker height. Thus, cross-shore flow due to infragravity waves can be estimated with knowledge of the nearshore profile and incident wave conditions. Refs.

  11. Experimental investigation of change of energy of infragavity waves in dependence on spectral characteristics of an irregular wind waves in coastal zone

    NASA Astrophysics Data System (ADS)

    Saprykina, Yana; Divinskii, Boris

    2013-04-01

    An infragravity waves are long waves with periods of 20 - 300 s. Most essential influence of infragarvity waves on dynamic processes is in a coastal zone, where its energy can exceed the energy of wind waves. From practical point of view, the infragravity waves are important, firstly, due to their influence on sand transport processes in a coastal zone. For example, interacting with group structure of wind waves the infragravity waves can define position of underwater bars on sandy coast. Secondly, they are responsible on formation of long waves in harbors. Main source of infragravity waves is wave group structure defined by sub-nonlinear interactions of wind waves (Longuet-Higgins, Stewart, 1962). These infragravity waves are bound with groups of wind waves and propagate with wave group velocity. Another type of infragravity waves are formed in a surf zone as a result of migration a wave breaking point (Symonds, et al., 1982). What from described above mechanisms of formation of infragravity waves prevails, till now it is unknown. It is also unknown how energy of infragravity waves depends on energy of input wind waves and how it changes during nonlinear wave transformation in coastal zone. In our work on the basis of the analysis of data of field experiment and numerical simulation a contribution of infragravity waves in total wave energy in depending on integral characteristics of an irregular wave field in the conditions of a real bathymetry was investigated. For analysis the data of field experiment "Shkorpilovtsy-2007" (Black sea) and data of numerical modeling of Boussinesq type equation with extended dispersion characteristics (Madsen et al., 1997) were used. It was revealed that infragravity waves in a coastal zone are defined mainly by local group structure of waves, which permanently changes due to nonlinearity, shoaling and breaking processes. Free infragravity waves appearing after wave breaking exist together with bound infragravity waves. There are

  12. Observations of infragravity motions for reef fringed islands and atolls

    NASA Astrophysics Data System (ADS)

    Becker, J. M.; Merrifield, M. A.; Ford, M.

    2012-12-01

    The frequency of flooding events that affect low lying islands and atolls in the Pacific is expected to increase under current sea level rise projections. Infragravity (IG) motions, with periods ranging from approximately 25 to 400 seconds, are an important component of wave driven flooding events for reef fringed islands and atolls. The IG variability during wave events is analyzed and interpreted dynamically from pressure and current observations at four cross-reef transects in the North Pacific Ocean that include sites in the Republic of the Marshall Islands and Guam. The IG motions are shown to depend upon the spectral properties of the incident wave forcing and reef flat characteristics that include reef flat length (ranging from 100m to 450m at the four sites) and total water level due to setup and tides. A small inundation event at one of the sites is shown to occur due to large shoreline infragravity energy.

  13. The role of beach morphodynamic state on infragravity swash on beaches: field observations.

    NASA Astrophysics Data System (ADS)

    Gomes da Silva, Paula; González, Mauricio; Medina, Raul

    2017-04-01

    The runup generated by waves can be defined as the maximum height above sea water level on the coastline and is an important criterion for costal structures/nourishment design and erosion/flooding risk analysis. Given the complexity of nonlinear processes involved in the runup generation, its prediction is commonly made by means of empirical formulations that relate wave and beach parameters. The most accepted parametrization presented till the moment was proposed by Stockdon et al. (2006), in which the runup exceeded by 2 percent of the waves (R2) is described in terms of setup (η - the steady superelevation of the mean water level caused by breaking waves) and incident and infragravity swash (Sinc and Sig- time-varying fluctuations around the setup caused by non-breaking waves). Such formulation has been widely accepted and its efficiency was appraised in many works. Nevertheless, although empirical parametrization of infragravity swash using incident wave's parameters shows reasonable skill, the correlation can still present considerable scatter. The amount of infragravity energy on swash is directly related to the morphodynamic beach state, in a way that beach profiles classified as reflective (low wave energy, coarse sediment and higher beach slope) tend to show lower Sig values than dissipative ones (high wave energy, fine sediment and lower beach slope). However, since Stockdon's formula for predicting infragravity swash consider only wave parameters, its use implies that beaches receiving the same wave energy but with different grain size and beach slope would present the same Sig values. This work assumed the hypothesis that the scatter verified on the predictions of the infragravity swash is mainly related to the lack of information about the beach state in Stockdon formula. Based on that, a field campaign was designed and carried out in Somo-El Puntal beach, north Spain, with the aim of generating data to be analyzed in terms of infragravity swash. An

  14. CMS-Wave Background and Capabilities: Developed for Coastal and Inlet Applications

    DTIC Science & Technology

    2012-06-01

    2 m, 15 sec from NE with infra-gravity wave without infra-gravity wave Infra-gravity Waves at Humboldt Bay, CA Coastal Modeling System... Mexico Gulf of Mexico Regional grid Local grid Coastal Modeling System Basics Webinar 21 Regional Wave Generation Incident Waves: 12.9 m, 13.8 sec

  15. Surface Wave Processes on the Shelf and Beach

    DTIC Science & Technology

    2016-06-07

    shelf. RESULTS The nonlinear dispersion of random surface gravity waves in shallow water was investigated with Boussinesq theory and extensive field data...Wavenumbers of surface gravity waves observed in shallow water near Duck, NC, are compared with the linear dispersion relation and nonlinear Boussinesq...Thornton, Gravity and shear wave contributions to nearshore infragravity motions, J. Phys. Oceanogr., 29(2), 231-239, 1999. Herbers, T. H. C., S. Elgar

  16. Wave variance partitioning in the trough of a barred beach

    NASA Astrophysics Data System (ADS)

    Howd, Peter A.; Oltman-Shay, Joan; Holman, Robert A.

    1991-07-01

    The wave-induced velocity field in the nearshore is composed of contributions from incident wind waves (ƒ > 0.05 Hz), surface infragravity waves (ƒ < 0.05 Hz, |κ| < (σ2/gβ) and shear waves (ƒ < 0.05 Hz, |κ| > σ2/gβ), where ƒ is the frequency, σ = 2πƒ, κ is the radial alongshore wavenumber (2π/L, L being the alongshore wavelength), β is the beach slope, and g is the acceleration due to gravity. Using an alongshore array of current meters located in the trough of a nearshore bar (mean depth ≈ 1.5 m), we investigate the bulk statistical behaviors of these wave bands over a wide range of incident wave conditions. The behavior of each contributing wave type is parameterized in terms of commonly measured or easily predicted variables describing the beach profile, wind waves, and current field. Over the 10-day period, the mean contributions (to the total variance) of the incident, infragravity, and shear wave bands were 71.5%, 14.3% and 13.6% for the alongshore component of flow (mean rms oscillations of 44, 20, and 19 cm s-1, respectively), and 81.9%, 10.9%, and 6.6% for the cross-shore component (mean rms oscillations of 92, 32, and 25 cm s-1, respectively). However, the values varied considerably. The contribution to the alongshore (cross-shore) component of flow ranged from 44.8-88.4% (58.5-95.8%) for the incident band, to 6.2-26.6% (2.5-32.4%) for the infragravity band, and 3.4-33.1% (0.6-14.3%) for the shear wave band. Incident wave oscillations were limited by depth-dependent saturation over the adjacent bar crest and varied only with the tide. The infragravity wave rms oscillations on this barred beach are best parameterized by the offshore wave height, consistent with previous studies on planar beaches. Comparison with data from four other beaches of widely differing geometries shows the shoreline infragravity amplitude to be a near-constant ratio of the offshore wave height. The magnitude of the ratio is found to be dependent on the Iribarren

  17. Ambient seismic wave field.

    PubMed

    Nishida, Kiwamu

    2017-01-01

    The ambient seismic wave field, also known as ambient noise, is excited by oceanic gravity waves primarily. This can be categorized as seismic hum (1-20 mHz), primary microseisms (0.02-0.1 Hz), and secondary microseisms (0.1-1 Hz). Below 20 mHz, pressure fluctuations of ocean infragravity waves reach the abyssal floor. Topographic coupling between seismic waves and ocean infragravity waves at the abyssal floor can explain the observed shear traction sources. Below 5 mHz, atmospheric disturbances may also contribute to this excitation. Excitation of primary microseisms can be attributed to topographic coupling between ocean swell and seismic waves on subtle undulation of continental shelves. Excitation of secondary microseisms can be attributed to non-linear forcing by standing ocean swell at the sea surface in both pelagic and coastal regions. Recent developments in source location based on body-wave microseisms enable us to estimate forcing quantitatively. For a comprehensive understanding, we must consider the solid Earth, the ocean, and the atmosphere as a coupled system.

  18. Tidally discontinuous ocean forcing in bar-built estuaries: The interaction of tides, infragravity motions, and frictional control

    NASA Astrophysics Data System (ADS)

    Williams, M. E.; Stacey, M. T.

    2016-01-01

    Shallow, bar-built estuaries on wave-dominated coasts in Mediterranean climates experience an intermittent connection to the ocean. In the presence of low streamflow, their inlets may completely close as a result of nearshore sand transport, but even in the open condition, these inlets remain constricted. Extensive field measurements in the highly salt-stratified Pescadero estuary in northern California show that the shallow mouth causes these estuaries to experience discontinuous tidal forcing. While the ocean and estuary are fully connected with near-equal water levels, tidal velocities are slow but infragravity motions in the nearshore induce large velocity oscillations within the estuary. As the ocean tide falls, infragravity forcing is cut off, because the estuarine mouth is perched above the low tide ocean water level, and ebbing velocities are set by bed friction. Observations reveal this oscillation between ocean-forced and frictionally controlled conditions characterizes and sets estuarine hydrodynamics. Additional wave setup of the lagoon emphasizes the dependence of these estuaries on nearshore ocean conditions, but the diurnal or semidiurnal retreat of the ocean below the mouth cuts off this nearshore influence so it too is tidally varying. Here we present detailed observations and a framework for understanding hydrodynamics in small, shallow bar-built estuaries.

  19. Introduction to Phase-Resolving Wave Modeling with FUNWAVE

    DTIC Science & Technology

    2015-07-01

    runup, overtopping, inundation, tsunamis , and ship waves. INTRODUCTION: Modeling nonlinear coastal wave processes, such as inundation, wave runup...bore propagation, tsunami propagation, harbor resonance, ship wakes, and infragravity waves, requires efficient and accurate computing of the evolution...wind-wave propagation, harbor entrances, nonlinear shoaling, runup, overtopping, inundation, tsunamis , and ship waves. 15. SUBJECT TERMS 16

  20. Observations and estimates of wave-driven water level extremes at the Marshall Islands

    NASA Astrophysics Data System (ADS)

    Merrifield, M. A.; Becker, J. M.; Ford, M.; Yao, Y.

    2014-10-01

    Wave-driven extreme water levels are examined for coastlines protected by fringing reefs using field observations obtained in the Republic of the Marshall Islands. The 2% exceedence water level near the shoreline due to waves is estimated empirically for the study sites from breaking wave height at the outer reef and by combining separate contributions from setup, sea and swell, and infragravity waves, which are estimated based on breaking wave height and water level over the reef flat. Although each component exhibits a tidal dependence, they sum to yield a 2% exceedence level that does not. A hindcast based on the breaking wave height parameterization is used to assess factors leading to flooding at Roi-Namur caused by an energetic swell event during December 2008. Extreme water levels similar to December 2008 are projected to increase significantly with rising sea level as more wave and tide events combine to exceed inundation threshold levels.

  1. Contribution of Forced Harmonics Into Wind Wave Spectra

    NASA Astrophysics Data System (ADS)

    Badulin, S. I.; Ivenskikh, N. N.; Resio, D.; Zakharov, V. E.

    Basic equations of weakly nonlinear theory of water waves are written in special vari- ables that are related to original physical variables through a nonlinear transformation. The transformation takes into account an effect of forced harmonics -- corrections to linear theory solutions. This fact is usually ignored in a great number of studies, the nonlinear corrections are considered as vanishingly small for sea wave conditions. In the present work the problem of the transformation from "canonical" to "observed" wave spectra is discussed in the context of kinetic equation for water waves. The ef- fect is specified for model and calculated spectra in deep and shallow water cases. The effect is shown to be significant just in deep water case due to its integral nature and features of water wave spectra -- sharp peak with rather low background in high and low frequencies. For the background these corrections, or, in other words, the forced harmonics contribution can exceed zero-order values. The problem of experimental discrimination of master (zero-order) and forced harmonics contribution is discussed. The research was conducted under the U.S. Army Corps of Engineers, RDT&E pro- gram, grant DACA 42-00-C0044, ONR grant N00014-98-1-0070 and Russian Foun- dation for Basic Research grants N01-05-64603, N01-05-64464.

  2. Contribution of non-resonant wave-wave interactions in the dynamics of long-crested sea wave fields

    NASA Astrophysics Data System (ADS)

    Benoit, Michel

    2017-04-01

    Gravity waves fields at the surface of the oceans evolve under the combined effects of several physical mechanisms, of which nonlinear wave-wave interactions play a dominant role. These interactions transfer energy between components within the energy spectrum and allow in particular to explain the shape of the distribution of wave energy according to the frequencies and directions of propagation. In the oceanic domain (deep water conditions), dominant interactions are third-order resonant interactions, between quadruplets (or quartets) of wave components, and the evolution of the wave spectrum is governed by a kinetic equation, established by Hasselmann (1962) and Zakharov (1968). The kinetic equation has a number of interesting properties, including the existence of self-similar solutions and cascades to small and large wavelengths of waves, which can be studied in the framework of the wave (or weak) turbulence theory (e.g. Badulin et al., 2005). With the aim to obtain more complete and precise modelling of sea states dynamics, we investigate here the possibility and consequences of taking into account the non-resonant interactions -quasi-resonant in practice- among 4 waves. A mathematical formalism has recently been proposed to account for these non-resonant interactions in a statistical framework by Annenkov & Shrira (2006) (Generalized Kinetic Equation, GKE) and Gramstad & Stiassnie (2013) (Phase Averaged Equation, PAE). In order to isolate the non-resonant contributions, we limit ourselves here to monodirectional (i.e. long-crested) wave trains, since in this case the 4-wave resonant interactions vanish. The (stochastic) modelling approaches proposed by Annenkov & Shrira (2006) and Gramstad & Stiassnie (2013) are compared to phase-resolving (deterministic) simulations based on a fully nonlinear potential approach (using a high-order spectral method, HOS). We study and compare the evolution dynamics of the wave spectrum at different time scales (i.e. over

  3. Internal gravity wave contributions to global sea surface variability

    NASA Astrophysics Data System (ADS)

    Savage, A.; Arbic, B. K.; Richman, J. G.; Shriver, J. F.; Buijsman, M. C.; Zamudio, L.; Wallcraft, A. J.; Sharma, H.

    2016-02-01

    High-resolution (1/12th and 1/25th degree) 41-layer simulations of the HYbrid Coordinate Ocean Model (HYCOM), forced by both atmospheric fields and the astronomical tidal potential, are used to construct global maps of sea-surface height (SSH). The HYCOM output has been separated into steric, non-steric, and total sea-surface height and the maps display variance in subtidal, tidal, and supertidal bands. Two of the global maps are of particular interest in planning for the upcoming Surface Water and Ocean Topography (SWOT) wide-swath satellite altimeter mission; (1) a map of the nonstationary tidal signal (estimated after removing the stationary tidal signal via harmonic analysis), and (2) a map of the steric supertidal contributions, which are dominated by the internal gravity wave continuum. Both of these maps display signals of order 1 cm2, the target accuracy for the SWOT mission. Therefore, both non-stationary internal tides and non-tidal internal gravity waves are likely to be important sources of "noise" that must be accurately removed before examination of lower-frequency phenomena can take place.

  4. Microseisms and hum from ocean surface gravity waves

    NASA Astrophysics Data System (ADS)

    Traer, James; Gerstoft, Peter; Bromirski, Peter D.; Shearer, Peter M.

    2012-11-01

    Ocean waves incident on coasts generate seismic surface waves in three frequency bands via three pathways: direct pressure on the seafloor (primary microseisms, PM), standing waves from interaction of incident and reflected waves (double-frequency microseisms, DF), and swell-transformed infragravity wave interactions (the Earth's seismic hum). Beamforming of USArray seismic data shows that the source azimuths of the generation regions of hum, PM and DF microseisms vary seasonally, consistent with hemispheric storm patterns. The correlation of beam power with wave height over all azimuths is highest in near-coastal waters. Seismic signals generated by waves from Hurricane Irene and from a storm in the Southern Ocean have good spatial and temporal correlation with nearshore wave height and peak period for all three wave-induced seismic signals, suggesting that ocean waves in shallow water commonly excite hum (via infragravity waves), PM, and DF microseisms concurrently.

  5. Edge wave response on a barred beach with wind-sea and swell forcing

    NASA Astrophysics Data System (ADS)

    Contardo, Stephanie; Symonds, Graham; Segura, Laura

    2015-04-01

    The occurrence of short period wind-sea associated with a diurnal sea breeze, superimposed on longer period swell in South West Western Australia provides an opportunity to observe the response of infragravity (0.01-0.05 Hz) waves, in the nearshore, to both wind-sea and swell forcing. An alongshore array of pressure sensors and a cross-shore array of current velocity and pressure sensors are deployed at Secret Harbour, a barred beach near Perth. The observations show a stronger infragravity response to longer period incident swell than to short period wind-sea. Infragravity waves at Secret Harbour are generated by two mechanisms: breakpoint forcing and bound wave release. Breakpoint forcing is observed with both swell and wind-sea forcing while bound wave release is only observed in the presence of swell. Two mechanisms generate free infragravity waves during swell periods while only one mechanism is in place during wind-sea periods, providing an explanation for the stronger response to swell than wind-sea. Free infragravity waves propagating offshore after reflection at the shoreline are called leaky waves; those which are trapped to the shoreline by refraction are called edge waves. At Secret Harbour, both edge waves and leaky waves are detected. Leaky waves dominate with swell forcing while edge waves dominate with wind-sea forcing. Amongst edge waves, mode 0 waves are found to dominate in the absence of wind-sea, while higher mode edge waves dominate when wind-sea is present. We calculate the expected wavenumber-frequency distribution of edge wave and leaky wave energy, based on resonance conditions, using wave period, incidence angle and directional spreading, as proposed by Bowen and Guza (1978). Observations and predictions are in good agreement. However the model can be improved by quantifying the infragravity energy generated by both infragravity wave generation mechanisms. Bowen, A. J., and R. T. Guza (1978), Edge waves and surf beat, Journal of

  6. Essential thalamic contribution to slow waves of natural sleep.

    PubMed

    David, François; Schmiedt, Joscha T; Taylor, Hannah L; Orban, Gergely; Di Giovanni, Giuseppe; Uebele, Victor N; Renger, John J; Lambert, Régis C; Leresche, Nathalie; Crunelli, Vincenzo

    2013-12-11

    Slow waves represent one of the prominent EEG signatures of non-rapid eye movement (non-REM) sleep and are thought to play an important role in the cellular and network plasticity that occurs during this behavioral state. These slow waves of natural sleep are currently considered to be exclusively generated by intrinsic and synaptic mechanisms within neocortical territories, although a role for the thalamus in this key physiological rhythm has been suggested but never demonstrated. Combining neuronal ensemble recordings, microdialysis, and optogenetics, here we show that the block of the thalamic output to the neocortex markedly (up to 50%) decreases the frequency of slow waves recorded during non-REM sleep in freely moving, naturally sleeping-waking rats. A smaller volume of thalamic inactivation than during sleep is required for observing similar effects on EEG slow waves recorded during anesthesia, a condition in which both bursts and single action potentials of thalamocortical neurons are almost exclusively dependent on T-type calcium channels. Thalamic inactivation more strongly reduces spindles than slow waves during both anesthesia and natural sleep. Moreover, selective excitation of thalamocortical neurons strongly entrains EEG slow waves in a narrow frequency band (0.75-1.5 Hz) only when thalamic T-type calcium channels are functionally active. These results demonstrate that the thalamus finely tunes the frequency of slow waves during non-REM sleep and anesthesia, and thus provide the first conclusive evidence that a dynamic interplay of the neocortical and thalamic oscillators of slow waves is required for the full expression of this key physiological EEG rhythm.

  7. Essential Thalamic Contribution to Slow Waves of Natural Sleep

    PubMed Central

    David, François; Schmiedt, Joscha T.; Taylor, Hannah L.; Orban, Gergely; Di Giovanni, Giuseppe; Uebele, Victor N.; Renger, John J.; Lambert, Régis C.; Leresche, Nathalie

    2013-01-01

    Slow waves represent one of the prominent EEG signatures of non-rapid eye movement (non-REM) sleep and are thought to play an important role in the cellular and network plasticity that occurs during this behavioral state. These slow waves of natural sleep are currently considered to be exclusively generated by intrinsic and synaptic mechanisms within neocortical territories, although a role for the thalamus in this key physiological rhythm has been suggested but never demonstrated. Combining neuronal ensemble recordings, microdialysis, and optogenetics, here we show that the block of the thalamic output to the neocortex markedly (up to 50%) decreases the frequency of slow waves recorded during non-REM sleep in freely moving, naturally sleeping-waking rats. A smaller volume of thalamic inactivation than during sleep is required for observing similar effects on EEG slow waves recorded during anesthesia, a condition in which both bursts and single action potentials of thalamocortical neurons are almost exclusively dependent on T-type calcium channels. Thalamic inactivation more strongly reduces spindles than slow waves during both anesthesia and natural sleep. Moreover, selective excitation of thalamocortical neurons strongly entrains EEG slow waves in a narrow frequency band (0.75–1.5 Hz) only when thalamic T-type calcium channels are functionally active. These results demonstrate that the thalamus finely tunes the frequency of slow waves during non-REM sleep and anesthesia, and thus provide the first conclusive evidence that a dynamic interplay of the neocortical and thalamic oscillators of slow waves is required for the full expression of this key physiological EEG rhythm. PMID:24336724

  8. Could linear hysteresis contribute to shear wave losses in tissues?

    PubMed

    Parker, Kevin J

    2015-04-01

    For nearly 100 y in the study of cyclical motion in materials, a particular phenomenon called "linear hysteresis" or "ideal hysteretic damping" has been widely observed. More recently in the field of shear wave elastography, the basic mechanisms underlying shear wave losses in soft tissues are in question. Could linear hysteresis play a role? An underlying theoretical question must be answered: Is there a real and causal physical model that is capable of producing linear hysteresis over a band of shear wave frequencies used in diagnostic imaging schemes? One model that can approximately produce classic linear hysteresis behavior, by examining a generalized Maxwell model with a specific power law relaxation spectrum, is described here. This provides a theoretical plausibility for the phenomenon as a candidate for models of tissue behavior.

  9. Observations of wave runup, setup, and swash on natural beaches

    USGS Publications Warehouse

    Stockdon, Hilary F.; Holman, Rob A.

    2011-01-01

    Video-based observations of wave runup, setup, and swash from 10 dynamically diverse field experiments are presented. These data were used to develop widely applicable empirical parameterizations for wave setup, incident band swash height, infragravity band swash height, and the 2-percent exceedance level for wave runup. Details regarding the experiments, data analysis, and empirical parameterizations can be found in Stockdon and others (2006).

  10. The Theory of Plasma Waves: A Perspective of the contributions of Thomas H. Stix

    NASA Astrophysics Data System (ADS)

    Kaw, Predhiman

    2001-10-01

    During the fifties and sixties Thomas H. Stix laid the conceptual foundations of the theory of interaction of radio frequency waves with plasmas. His 1962 book trained a world wide community of plasma scientists and engineers who dedicated their lives to this important field. We see the fruit of all this pioneering work in our concepts of modern fusion reactors where reactor grade plasmas may be produced by electron cyclotron resonance effects, heated by ion cyclotron range of frequencies and maintained in a steady state with non-inductive currents using fast waves and lower hybrid waves. Not only this but the entire field of wave propagation and instabilities in ionospheric, space and astrophysical plasmas has greatly benefited from the pioneering work of Tom Stix. A review of the major contributions of Stix to the physics of plasma waves will be presented .

  11. Relative contributions of formants to the intelligibility of sine-wave sentences in Mandarin Chinese.

    PubMed

    Han, Yiyuan; Chen, Fei

    2017-06-01

    Early sine-wave speech (SWS) studies showed that the first three formants contain sufficient intelligibility information. The present work assessed the relative perceptual contributions of the first three formants. Mandarin sentences were edited to generate two SWS conditions: removal of one of the first three formant trajectories, and preservation of only one formant trajectory. In addition, SWS synthesis was implemented in the absence of sine-wave amplitude modulation. The results consistently showed that the trajectory of the second formant contributed the most to intelligibility, and the effect of amplitude modulation was smaller than that of the formant number.

  12. Predominance of ECH wave contribution to diffuse aurora in Earth's outer magnetosphere

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-Jia; Angelopoulos, Vassilis; Ni, Binbin; Thorne, Richard M.

    2015-01-01

    to its importance for global energy dissipation in the ionosphere, the diffuse aurora has been intensively studied in the past 40 years. Its origin (precipitation of 0.5-10 keV electrons from the plasma sheet without potential acceleration) has been generally attributed to whistler-mode chorus wave scattering in the inner magnetosphere (R < ~8 RE), while the scattering mechanism beyond that distance remains unresolved. By modeling the quasi-linear diffusion of electrons with realistic parameters for the magnetic field, loss cone size, and wave intensity (obtained from Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations as a function of magnetospheric location), we estimate the loss cone filling ratio and electron cyclotron harmonic (ECH) wave-induced electron precipitation systematically throughout the entire data set, from 6 RE out to 31 RE (the THEMIS apogee). By comparing the wave-induced precipitation directly with the equatorially mapped energy flux distribution of the diffuse aurora from ionospheric observations (OVATION Prime model) at low altitudes, we quantify the contribution of auroral energy flux precipitated due to ECH wave scattering. Although the wave amplitudes decrease, as expected, with distance from the Earth, due to the smaller loss cone size and stretched magnetic field topology, ECH waves are still capable of causing sufficient scattering of plasma sheet electrons to account for the observed diffuse auroral dissipation. Our results demonstrate that ECH waves are the dominant driver of the diffuse aurora in the outer magnetosphere, beyond ~8 RE.

  13. Interference between wave modes may contribute to the apparent negative dispersion observed in cancellous bone

    PubMed Central

    Anderson, Christian C.; Marutyan, Karen R.; Holland, Mark R.; Wear, Keith A.; Miller, James G.

    2008-01-01

    Previous work has shown that ultrasonic waves propagating through cancellous bone often exhibit a linear-with-frequency attenuation coefficient, but a decrease in phase velocity with frequency (negative dispersion) that is inconsistent with the causality-imposed Kramers–Kronig relations. In the current study, interfering wave modes similar to those observed in bone are shown to potentially contribute to the observed negative dispersion. Biot theory, the modified Biot–Attenborogh model, and experimental results are used to aid in simulating multiple-mode wave propagation through cancellous bone. Simulations entail constructing individual wave modes exhibiting a positive dispersion using plausible velocities and amplitudes, and then summing the individual modes to create mixed-mode output wave forms. Results of the simulations indicate that mixed-mode wave forms can exhibit negative dispersion when analyzed conventionally under the assumption that only one wave is present, even when the individual interfering waves exhibit positive dispersions in accordance with the Kramers–Kronig relations. Furthermore, negative dispersion is observed when little or no visual evidence of interference exists in the time-domain data. Understanding the mechanisms responsible for the observed negative dispersion could aid in determining the true material properties of cancellous bone, as opposed to the apparent properties measured using conventional data analysis techniques. PMID:19045668

  14. Predominance of Ech Wave Contribution to the Diffuse Auroral Precipitation in Earth's Outer Magnetosphere

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Angelopoulos, V.; Ni, B.; Thorne, R. M.

    2014-12-01

    Due to its importance for global energy dissipation in the ionosphere, the diffuse aurora has been intensively studied in the past 40 years. Its origin (precipitation of 0.5-10 keV electrons from the plasma sheet without potential acceleration) has been generally attributed to whistler-mode chorus wave scattering in the inner magnetosphere (R<~8 RE), while the scattering mechanism beyond that distance remains unresolved. By modeling the quasi-linear diffusion of electrons with realistic parameters for the ambient magnetic field, loss-cone size and electrostatic electron cyclotron harmonic (ECH) wave intensity (obtained from THEMIS observations as a function of magnetospheric location), we estimate the loss-cone filling ratio and ECH wave-induced electron precipitation systematically throughout the entire data set, from 6 RE out to 31 RE (the THEMIS apogee). By comparing the wave-induced precipitation directly with the equatorially mapped energy flux distribution of diffuse aurora from ionospheric observations (OVATION Prime model) at low altitudes, we quantify the contribution of auroral energy flux from ECH wave scattering. Although the wave amplitudes drop, as expected, with distance from the Earth, due to the small loss cone size and stretched magnetic field topology, ECH waves are still capable of causing sufficient scattering of plasma sheet electrons to account for the observed diffuse auroral dissipation. Our results demonstrate that ECH waves are the dominant driver of diffuse aurora in the outer magnetosphere (beyond ~8 RE).

  15. Wave characteristics and hydrodynamics at a reef island on Dongsha Atoll in the South China Sea

    NASA Astrophysics Data System (ADS)

    Su, Shih-Feng; Chiang, Te-Yun; Lin, Yi-Hao; Chen, Jia-Lin

    2017-04-01

    An inhabited coral reef island, located at the Dongsha Atoll in the northern South China Sea, is frequently attacked by typhoon waves. Coastline has suffered severe erosion and coastal inundation during certain typhoon paths. Groins were therefore built surround the island to stabilize the shoreline. However, the engineering structures redistributed the characteristics of hydrodynamics, which resulted in the disappearance of seasonal sediment movements on the reef flat. Additionally, infragravity waves (20-200 sec) on reefs have be found to generate strong resonance during energetic wave events. To understand wave characteristics and nearshore circulations around the reef under typical waves and typhoon waves, a phase-averaged and a phase-resolving wave models validated with previous field experiments are used to simulate significant wave height, wave setup and reef circulations. The phase-resolving model is specially applied to investigate infragravity motions around the island. Model results will illustrate the spatial variations of infragravity-wave field and wave-induced nearshore circulation and can provide information for coastal management and protection.

  16. Morphodynamic modeling of an embayed beach under wave group forcing

    NASA Astrophysics Data System (ADS)

    Reniers, A. J. H. M.; Roelvink, J. A.; Thornton, E. B.

    2004-01-01

    The morphodynamic response of the nearshore zone of an embayed beach induced by wave groups is examined with a numerical model. The model utilizes the nonlinear shallow water equations to phase resolve the mean and infragravity motions in combination with an advection-diffusion equation for the sediment transport. The sediment transport associated with the short-wave asymmetry is accounted for by means of a time-integrated contribution of the wave nonlinearity using stream function theory. The two-dimensional (2-D) computations consider wave group energy made up of directionally spread, short waves with a zero mean approach angle with respect to the shore normal, incident on an initially alongshore uniform barred beach. Prior to the 2-D computations, the model is calibrated with prototype flume measurements of waves, currents, and bed level changes during erosive and accretive conditions. The most prominent feature of the 2-D model computations is the development of an alongshore quasi-periodic bathymetry of shoals cut by rip channels. Without directional spreading, the smallest alongshore separation of the rip channels is obtained, and the beach response is self-organizing in nature. Introducing a small amount of directional spreading (less than 2°) results in a strong increase in the alongshore length scales as the beach response changes from self-organizing to being quasi-forced. A further increase in directional spreading leads again to smaller length scales. The hypothesized correlation between the observed rip spacing and wave group forced edge waves over the initially alongshore uniform bathymetry is not found. However, there is a correlation between the alongshore length scales of the wave group-induced quasi-steady flow circulations and the eventual alongshore spacing of the rip channels. This suggests that the scouring associated with the quasi-steady flow induced by the initial wave groups triggers the development of rip channels via a positive feedback

  17. Using pressure and seismological broadband ocean data to model shear wave velocities in the north Atlantic.

    NASA Astrophysics Data System (ADS)

    Rios, Celia; Dahm, Torsten; Jegen, Marion

    2010-05-01

    Seafloor compliance is the transfer function between pressure and vertical displacement at the seafloor Infragravity waves in the oceanic layer have long periods in the range of 30 - 500 s and obey a simple frequency-wavenumber relation. Seafloor compliance from infragravity waves can be analyzed with single station recordings to determinate sub-seafloor shear wave velocities. Previous studies in the Pacific Ocean have demonstrated that reliable near-surface shear wave profiles can be derived from infragravity wave compliance. However, these studies indicate that, beside the water depth the compliance measurements are limited by instrument sensitivity, calibration uncertainties and possibly other effects. In this work seafloor compliance and infragravity waves are observed at two different locations in the Atlantic Ocean: the Logatchev hydrothermal field at the Mid Atlantic Ridge and the Azores (Sao Miguel Island). The data was acquired with the broadband ocean compliance station developed at the University of Hamburg as well as ocean station from the German instrument pool for amphibian seismology (DEPAS) equipped with broadband seismometers and pressure sensors. Vertical velocity and pressure data were used to calculate power spectral densities and normalized compliance along two profiles (one in each location). Power spectral densities show a dominant peak at low frequencies (0.01-0.035Hz) limited by the expected cut-off frequency, which is dependent on the water depth at each station. The peak has been interpreted as a strong infragravity wave with values between 10-14 and 10-11 (m/s2)2/Hz and 104 and 106 (Pa2)2/Hz for acceleration and pressure respectively. The results show compliance values between 10-10 and 10-8 1/Pa and its estimations take into account the coherence between seismic and pressure signals in order to confirm that the seismic signals in the infragravity waves are caused by pressure sources. Shear wave velocity models, with depth resolution

  18. Typical scenarios of nonlinear wave transformation: criteria of realization and contribution in relief changes.

    NASA Astrophysics Data System (ADS)

    Shtremel, Margarita; Saprykina, Yana; Kuznetsov, Sergey; Andreeva, Nataliya

    2014-05-01

    Coastal zone is area which dynamical regime is formed by wind waves. While propagating to the coast, waves are transforming and then breaking. All energy of waves brought from deep water dissipates in coastal zone causing bottom sediment suspension. Wave asymmetry, which determines bulk and direction of sediment transport, also changes. These processes lead to bottom relief deformations, such as bar formations, beach erosion or accumulation. Occurrence of each situation depends on wave regime and mean bottom slope. Purpose of this work is to find typical examples of manifestation of nonlinear wave transformation and to account its contribution to relief changes. This investigation can be used to classify coastal zones and estimate their vulnerability to wave impact. Waves in coastal zone are weakly nonlinear dispersive due to near-resonant triad interactions between wave components. The main feature of nonlinear wave transformation in intermediate depth is periodical exchange of energy between first and higher harmonics of wave motion. This effect causes fluctuations of higher statistic moments of waves. The periodical fluctuation of amplitudes of nonlinear wave harmonics was used to develop classification of coastal zone. 'Skorpilovtsy-2007' field experiment data was analyzed and four scenarios of nonlinear wave transformation were determined. They were separated from one another depending on character of energy exchange between first and second wave harmonics: 1. Input waves have low second harmonics, their amplitude grows only near the shore 1,5 - 2 periods of energy exchange can be distinguished 2. There is only one full period of energy exchange with high relative amplitude of second harmonic. Second harmonic reaches its maximum within coastal zone 3. There is no obvious maximum of second harmonic and its amplitude changes very little in whole coastal zone. There are 3 and more periods of energy exchange. 4. Amplitude of the second harmonic on the seaward end

  19. Maximum Wave Run-up Measured on a Natural Beach Owing to Extreme Waves

    NASA Astrophysics Data System (ADS)

    Thornton, E. B.; MacMahan, J. H.

    2014-12-01

    Unique field data indicative of maximum run-up owing to extreme wave conditions with a 50 year return period are obtained from the distribution of sea-glass on 10-18 m high dunes. The hypothesis that sea-glass is an indicator of maximum run-up is verified by the observations that new sea-glass on a beach is found at the rackline, the highest point of run-up. The source of the sea-glass is a garbage dump on the dune in southern Monterey Bay from 1937-1951. It is estimated that the dump, located on an erosive shoreline, was falling into the ocean by at least 1960, so that the maximum run-up values have a return period of at least 50 years. Various empirical run-up models based both on extensive laboratory and field measurements are assessed to include contributions from sea-swell and infragravity waves, setup and tidal elevation, which are parameterized on wave height and surf parameter, P, which is a function of wave height, period and beach slope. Deep water hindcast waves (1958-2011) refracted to 4m water depth are used as input to the models. Beach and dune slopes averaged over the run-up region from mean water level to the maximum run-up ranged 0.1 - 0.63 (angle of repose). Reasonable comparison with model predicted run-up with distribution of sea-glass on the dune were obtained for P <2 events, but were underpredicted for large P. Large P events are associated with long period swell waves characteristic of the Pacific Ocean that are outside the empirical parameter space from which the model equations were derived, suggesting a possible deficiency in the models.

  20. Chiral dynamics, S-wave contributions and angular analysis in D→ π π ℓ \\bar{ν }

    NASA Astrophysics Data System (ADS)

    Shi, Yu-Ji; Wang, Wei; Zhao, Shuai

    2017-07-01

    We present a theoretical analysis of the D^-→ π ^+π ^- ℓ \\bar{ν } and \\bar{D}^0→ π ^+π ^0 ℓ \\bar{ν } decays. We construct a general angular distribution which can include arbitrary partial waves of π π . Retaining the S-wave and P-wave contributions we study the branching ratios, forward-backward asymmetries and a few other observables. The P-wave contribution is dominated by ρ ^0 resonance, and the S-wave contribution is analyzed using the unitarized chiral perturbation theory. The obtained branching fraction for D→ ρ ℓ ν , at the order 10^{-3}, is consistent with the available experimental data. The S-wave contribution has a branching ratio at the order of 10^{-4}, and this prediction can be tested by experiments like BESIII and LHCb. Future measurements can also be used to examine the π -π scattering phase shift.

  1. Spin-electron acoustic waves: The Landau damping and ion contribution in the spectrum

    SciTech Connect

    Andreev, Pavel A.

    2016-06-15

    Separated spin-up and spin-down quantum kinetics is derived for more detailed research of the spin-electron acoustic waves (SEAWs). This kinetic theory allows us to obtain the spectrum of the SEAWs including the effects of occupation of quantum states more accurately than the quantum hydrodynamic theory. We derive and apply the quantum kinetic theory to calculate the Landau damping of the SEAWs. We consider the contribution of ions dynamics into the SEAW spectrum. We obtain the contribution of ions in the Landau damping in the temperature regime of classic ions. Kinetic analysis for the ion-acoustic, zero sound, and Langmuir waves at the separated spin-up and spin-down electron dynamics is presented as well.

  2. Background Lamb waves in the Earth's atmosphere

    NASA Astrophysics Data System (ADS)

    Nishida, K.; Kobayashi, N.; Fukao, Y.

    2013-12-01

    Lamb waves of the Earth's atmosphere in the millihertz band have been considered as transient phenomena excited only by large events [e.g. the major volcanic eruption of Krakatoa in 1833, the impact of Siberian meteorite in 1908, the testing of large nuclear tests and the huge earthquakes, Garrett1969]. In a case of the solid Earth, observation of background free oscillations in the millihertz band-now known as Earth's background free oscillations or seismic hum, has been firmly established. Above 5 mHz, their dominant excitation sources are oceanic infragravity waves. At 3.7 and 4.4 mHz an elasto-acoustic resonance between the solid Earth and the atmosphere was observed [Nishida et al., 2000]. These seismic observations show that the contribution of atmospheric disturbances to the seismic hum is dominant below 5 mHz. Such contribution implies background excitations of acoustic-gravity waves in this frequency range. For direct detection of the background acoustic-gravity waves, our group conducted observations using an array of barometers [Nishida et al. 2005]. However, the spatial scale of the array of about 10 km was too small to detect acoustic modes below 10 mHz. Since then, no direct observations of these waves have been reported. In 2011, 337 high-resolution microbarometers were installed on a continental scale at USArray Transportable Array. The large and dense array enables us to detect the background atmospheric waves. Here, we show the first evidence of background Lamb waves in the Earth's atmosphere from 0.2 to 10 mHz, based on the array analysis of microbarometer data from the USArray in 2012. The observations suggest that the excitation sources are atmospheric disturbances in the troposphere. Theoretically, their energy in the troposphere tunnels into the thermosphere at a resonant frequency via thermospheric gravity wave, where the observed amplitudes indeed take a local minimum. The energy leak through the frequency window could partly contribute to

  3. Observations of waves and currents during barrier island inundation

    NASA Astrophysics Data System (ADS)

    Engelstad, A.; Ruessink, B. G.; Wesselman, D.; Hoekstra, P.; Oost, A.; van der Vegt, M.

    2017-04-01

    Overwash and inundation on barrier islands can transport sediment onshore, leading to vertical accretion. These processes could ensure barrier island growth in times of sea-level rise, but wave and current fields during overwash and inundation are not well understood. Field data of water levels, waves, and currents were collected on a barrier island in the Netherlands to investigate the hydrodynamics during island inundation. Observations show that even in shallow water depths (<0.5 m) wave energy was not completely dissipated as waves propagated from the North Sea onshore. Additionally, locally generated wind waves entered the field area from the Wadden Sea and propagated offshore. Infragravity waves were an important part of the wave field, particularly onshore of the beach crest. They were observed to be onshore progressive and displayed a bore-like shape when water depths were shallow. Wave breaking was the dominant dissipation mechanism for high-frequency waves as well as for infragravity waves, which is in agreement with prior research on infragravity wave energy dissipation on mild sloping (closed-boundary) beaches. A large-scale offshore directed water-level gradient between the Wadden Sea and the North Sea side, caused by elevated water levels in the Wadden Sea during the storms, frequently drove an offshore flow if it was large enough to exceed the cross-shore gradient due to wave setup. In addition, elevated water levels in the Wadden Sea decreased current velocities due to a decrease in water-level gradients. This study highlights the influence of back-barrier processes on the hydrodynamics during inundation.

  4. B s → K (*)ℓ, angular analysis, S-wave contributions and | V ub |

    NASA Astrophysics Data System (ADS)

    Meißner, Ulf-G.; Wang, Wei

    2014-01-01

    We analyse the and decays that are valuable for extracting the CKM matrix element | V ub|. We calculate the differential and integrated partial widths in units of | V ub|2 based on various calculations of hadronic form factors and in particular the latest Lattice QCD calculation of the B s → K * form factors. For the decay , we formulate the general angular distributions with the inclusion of the various partial-wavecontributions. Using the results for the Kπ scalar form factor calculated from unitarized chiral perturbation theory, we explore the S-wave effects on angular distribution variables and demonstrate that they may not be negligible, considering the high precision expected in future measurements. We also briefly discuss the impact of the S-wave ππ contributions in the decay and provide estimates for the mode . The studies of these channels in future can not only be used to determine | V ub|, but may also provide valuable information on the Kπ and ππ phase shifts.

  5. Numerical study of contributions of shock wave and gas penetration toward induced rock damage during blasting

    NASA Astrophysics Data System (ADS)

    Lanari, M.; Fakhimi, A.

    2015-06-01

    The authors present an improved version of continuum analysis 2D, a hybrid two-dimensional finite element-discrete element-smoothed particle program for modeling rock blasting. A modified formula governing the interaction of smoothed particles with discrete elements is presented, along with the results of numerical simulations involving detonations within jointed rock. PETN was modeled as the explosive, and Barre granite as the rock specimen. The borehole was simulated both with and without a thin copper lining. The purpose of the copper lining is to prevent gas from penetrating into the induced cracks within the rock, so that the shock wave's contribution toward rock damage can be separated from that of the gas penetration. The results suggest that majority of the cracks are formed due to the shock wave propagating within the rock, whereas the gas penetration mostly separates the already-formed rock fragments and pushes them apart.

  6. Contribution of soil moisture in summer heat waves amplitude in MED-CORDEX simulations

    NASA Astrophysics Data System (ADS)

    Stéfanon, M.

    2012-04-01

    Contribution of soil moisture in summer heat wave amplitude in MED-CORDEX simulations Marc Stéfanon(1), Philippe Drobinski(1), Fabio D'Andrea(1), Cindy-Lebeaupin Brossier(1,2), (1) IPSL/LMD, France; (2) CNRM, France ; Heat waves and droughts are extreme weather events intrinsically linked, through strong coupling between the Earth's energy and water cycles. Their impact in short and medium term can be considerable on our societies in terms of health, socio-economic and ecological damage, as in 2003 in Western Europe or Russia in 2010. They are even more affected by climate change than the average state of the atmosphere and could be more frequent, more intense and more extended in the future. Besides this effect could be enhanced by the fact that Mediterranean, a vulnerable area of important geographic and climatic contrasts, is among the most responsive to global warming. If triggering of heat waves is determined by the large scale, land surface-related processes and feedbacks can amplify or inhibit heat trough several feedback mechanism. In regional climate models (RCMs) the land surface model (LSM) plays a key role in energy and water exchanges between land and atmosphere and determine the partitioning of surface fluxes (the relationship of latent heat flux to sensible heat flux). In the frame of the HyMeX and MED-CORDEX programs, two simulations at 20-km grid resolution have been performed over 1989-2008 with 2 different LSMs (RUC and 5-layer diffusive schemes) on a Mediterranean domain. The control simulation (CTL) corresponds to the RUC configuration, whereas experiment with perturbed soil moisture (WET) corresponds to the 5-layer diffusive scheme. CTL is able to correctly simulates temporal and spatial variations of soil moisture, as drought conditions. WET has a high soil moisture value, constant through time and land use dependant. These simulations are inter-compared to provide an estimate of the soil moisture contribution to heat wave amplitude.

  7. Reduced soil moisture contributes to more intense and more frequent heat waves in northern China

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Liu, Zhenyuan; Chen, Li

    2015-09-01

    Heat waves have attracted increasing attention in recent years due to their frequent occurrence. The present study investigates the heat wave intensity and duration in China using daily maximum temperature from 753 weather stations from 1960 to 2010. In addition, its relationships with soil moisture local forcing on the ten-day period and monthly scales in spring and summer are analyzed using soil moisture data from weather stations and ERA40 reanalysis data. And finally, a mechanistic analysis is carried out using CAM5.1 (Community Atmosphere Model, version 5.1) coupled with CLM2 (Community Land Model, version 2). It is found that the heat wave frequency and duration show a sandwich distribution across China, with high occurrence rates in Southeast China and Northwest China, where the maximum frequency and duration exceeded 2.1 times and 9 days per year, respectively. The increasing trends in both duration and intensity occurred to the north of 35°N. The relationships between heat wave frequency in northern China in July (having peak distribution) and soil moisture in the earlier stage (from March to June) and corresponding period (July) are further analyzed, revealing a strong negative correlation in March, June and July, and thus showing that soil moisture in spring and early summer could be an important contributor to heat waves in July via positive subtropical high anomalies. However, the time scales of influence were relatively short in the semi-humid and humid regions, and longer in the arid region. The contribution in the corresponding period took place via positive subtropical high anomalies and positive surface skin temperature and sensible heat flux anomalies.

  8. Collective mode contributions to the Meissner effect: Fulde-Ferrell and pair-density wave superfluids

    NASA Astrophysics Data System (ADS)

    Boyack, Rufus; Wu, Chien-Te; Anderson, Brandon M.; Levin, K.

    2017-06-01

    In this paper we demonstrate the necessity of including the generally omitted collective-mode contributions in calculations of the Meissner effect for nonuniform superconductors. We consider superconducting pairing with nonzero center-of-mass momentum, as is possibly relevant to high transition temperature cuprates, cold atoms, and color superconductors in quantum chromodynamics. For the concrete example of the Fulde-Ferrell phase we present a quantitative calculation of the superfluid density, showing not only that the collective-mode contributions are appreciable but also that they derive from the amplitude mode of the order parameter. This latter mode is generally viewed as being invisible in conventional superconductors. However, our analysis shows that it is extremely important in pair-density-wave-type superconductors, where it destroys stable superfluidity well before the mean-field order parameter vanishes.

  9. The gravitational wave contribution to cosmic microwave background anisotropies and the amplitude of mass fluctuations from COBE results

    NASA Technical Reports Server (NTRS)

    Lucchin, Francesco; Matarrese, Sabino; Mollerach, Silvia

    1992-01-01

    A stochastic background of primordial gravitational waves may substantially contribute, via the Sachs-Wolfe effect, to the large-scale cosmic microwave background (CMB) anisotropies recently detected by COBE. This implies a bias in any resulting determination of the primordial amplitude of density fluctuations. We consider the constraints imposed on n is less than 1 ('tilted') power-law fluctuation spectra, taking into account the contribution from both scalar and tensor waves, as predicted by power-law inflation. The gravitational wave contribution to CMB anisotropies generally reduces the required rms level of mass fluctuation, thereby increasing the linear bias parameter, even in models where the spectral index is close to the Harrison-Zel'dovich value n = 1. This 'gravitational wave bias' helps to reconcile the predictions of CDM models with observations on pairwise galaxy velocity dispersion on small scales.

  10. Postreceptoral contributions to the light-adapted ERG of mice lacking b-waves.

    PubMed

    Shirato, Suguru; Maeda, Hidetaka; Miura, Gen; Frishman, Laura J

    2008-06-01

    The purpose of this study was to determine the contributions of postreceptoral neurons to the light-adapted ERG of the Nob mouse, a model for complete-type congenital stationary night blindness (CSNB1) that lacks a b-wave from depolarizing bipolar cells. Ganzfeld ERGs were recorded from anesthetized adult control mice, control mice injected intravitreally with L-2-amino-4-phosphonobutyric acid (Control APB mice) to remove On pathway activity, and Nob mice. ERGs also were recorded after PDA (cis-2,3-piperidine-dicarboxylic acid, 3-5mM) was injected to block transmission to hyperpolarizing (Off) bipolar and horizontal cells, and all third-order neurons. Stimuli were brief (<4ms, 0.4-2.5log sc td s) and long (200ms, 2.5-4.6log sc td) LED flashes (lambda(max)=513nm, on a rod suppressing background (2.6log sc td). Sinusoidal modulation of the LEDs (mean, 2.6log sc td; contrast, 100%; 3-36Hz) was used to study flicker ERGs. Brief-flash ERGs of Nob mice presented as long-lasting negative waves with a positive-going intrusion that started about 50ms after the flash and peaked around 120ms. Control APB mice had similar responses, and in both cases, PDA removed the positive-going intrusion. For long flashes, PDA removed a small, slow "d-wave" after light offset. With sinusoidal stimulation, the fundamental (F1) amplitude of control mice ERG peaked at 8Hz ( approximately 70microV). For Nob mice the peak was approximately 20microV at 6Hz before PDA and approximately 10muV at 3Hz or lower after PDA. F1 responses were present up to 21Hz in control and Nob eyes and 15Hz in Nob eyes after PDA. Between 3 and 6Hz, F1 phase was 170-210 degrees more delayed in Nob than control mice; phase was hardly altered by PDA. With vector analysis, a substantial postreceptoral input to the Nob flicker ERG was revealed. In control mice, the second harmonic (F2) response showed peaks of approximately 10mocrpV at 3Hz and 13Hz. Nob mice showed almost no F2. In summary, in this study it was found that

  11. Simple analytical methods for computing the gravity-wave contribution to the cosmic background radiation anisotropy

    SciTech Connect

    Wang, Y.

    1996-01-01

    We present two simple analytical methods for computing the gravity-wave contribution to the cosmic background radiation (CBR) anisotropy in inflationary models; one method uses a time-dependent transfer function, the other methods uses an approximate gravity-mode function which is a simple combination of the lowest order spherical Bessel functions. We compare the CBR anisotropy tensor multipole spectrum computed using our methods with the previous result of the highly accurate numerical method, the {open_quote}{open_quote}Boltzmann{close_quote}{close_quote} method. Our time-dependent transfer function is more accurate than the time-independent transfer function found by Turner, White, and Lindsey; however, we find that the transfer function method is only good for {ital l}{approx_lt}120. Using our approximate gravity-wave mode function, we obtain much better accuracy; the tensor multipole spectrum we find differs by less than 2{percent} for {ital l}{approx_lt}50, less than 10{percent} for {ital l}{approx_lt}120, and less than 20{percent} for {ital l}{le}300 from the {open_quote}{open_quote}Boltzmann{close_quote}{close_quote} result. Our approximate graviton mode function should be quite useful in studying tensor perturbations from inflationary models. {copyright} {ital 1996 The American Physical Society.}

  12. S-wave resonance contributions to in the perturbative QCD factorization approach

    NASA Astrophysics Data System (ADS)

    Ma, Ai-Jun; Li, Ya; Wang, Wen-Fei; Xiao, Zhen-Jun

    2017-08-01

    By employing the perturbative QCD (PQCD) factorization approach, we study the quasi-two-body decays, where the pion pair comes from the S-wave resonance f 0(X). The Breit-Wigner formula for the f 0(500) and f 0(1500) resonances and the Flatté model for the f 0(980) resonance are adopted to parameterize the time-like scalar form factors in the two-pion distribution amplitudes. As a comparison, Bugg's model is also used for the wide f 0(500) in this work. For decay rates, we found the following PQCD predictions: (a) when the contributions from f 0(980) and f 0(1500) are all taken into account; (b) in the Breit-Wigner model and in Bugg's model. Supported by National Natural Science Foundation of China (11235005, 11547038)

  13. Contributions of tropical waves to tropical cyclone genesis over the western North Pacific

    NASA Astrophysics Data System (ADS)

    Wu, Liang; Takahashi, Masaaki

    2017-09-01

    The present study investigates the relationship between the tropical waves and the tropical cyclone (TC) genesis over the western North Pacific (WNP) for the period 1979-2011. Five wave types are considered in this study. It is shown that the TC genesis is strongly related to enhanced low-level vorticity and convection of tropical waves and significant difference are detected in the TC modulation by dynamic and thermodynamic components of the waves. More TCs tend to form in regions of waves with overlapping cyclonic vorticity and active convection. About 83.2% of TCs form within active phase of tropical waves, mainly in a single wave and two coexisting waves. Each wave type-related genesis accounts for about 30% of all TC geneses except for the Kelvin waves that account for only 25.2% of TC geneses. The number of each wave type-related TC genesis consistently varies seasonally with peak in the TC season (July-November), which is attributed to a combined effect of active wave probability and intensity change. The interannual variation in the TC genesis is well reproduced by the tropical wave-related TC genesis, especially in the region east of 150°E. An eastward extension of the enhanced monsoon trough coincides with increased tropical wave activity by accelerated wave-mean flow interaction.

  14. Identifying Contributing Harmonics in the Gravitational Wave Spectrum of Highly Eccentric EMRIs

    NASA Astrophysics Data System (ADS)

    Kaiser, Andrew; Stone, Jordan; Ahrens, Sloan; Kennefick, Daniel

    2016-03-01

    In the study of gravitational waves emitted from extreme mass ratio inspirals highly eccentric orbits are problematic because of the large number of harmonics, and thus the lengthy computation times that were thought to be inherent to it. The issue however, is made simpler because the spectrum is not that broad and is fairly localized. The true complexity lies in finding the peaks of the largest contributors to accurately describe the complete spectrum, since for any given multipole of the spectrum the position of the peak in the emission is difficult to predict. This project uses two methods of finding the peak harmonic of a given spectrum. The first method uses a skipping algorithm to systematically jump over harmonics with insignificant contributions to the total waveform. Because this method is still not completely efficient, a second method uses a Newtonian order approximation given by Peters and Matthews to give an estimate of the frequency of the actual waveform peak, and then fills in around this harmonics to give the spectrum. The two methods are complementary since the skipping algorithm can be used when the Newtonian estimation fails to find the peak immediately.

  15. Challenges in assessing the contribution of climate change to observed record-breaking heat waves

    NASA Astrophysics Data System (ADS)

    Perlwitz, J.; Xu, T.; Quan, X.; Hoerling, M. P.; Dole, R. M.

    2013-12-01

    Record-setting heat waves have large impacts on public health and society due to increased mortality rate, wild fires, property damages and agricultural loss. There is increasing interest in understanding the causes of such extreme events including the role of climate change. We use the example of the link between atmospheric blocking frequency and summertime seasonal temperature extreme to address some challenges in determining the relative contributions of natural variability and climate change on the occurrence and magnitude of extreme climate-related events. We utilize the 62-year record of observational data from 1960 to 2011 and long integrations with the NCARs Community Climate System Model Version 4 (CCSM4). This climate model represents well atmospheric blocking frequency and related weather features over the European/Ural region. Both observations and long climate integrations suggest that seasonal temperature extremes over the Northern European/Ural region are strongly conditioned by blocking. We illustrate that one challenge in climate event attribution is related to the fact that very long records are necessary to sufficiently sample the frequency of occurrence of the principal driver of a record-setting climate event. We further illustrate that there is a strong regional dependence on how the link between blocking frequency and extreme temperature anomalies is modified due to climate change suggesting that event attribution results are often not transferable from one region to another.

  16. Synthesizing ocean bottom pressure records including seismic wave and tsunami contributions: Toward realistic tests of monitoring systems

    NASA Astrophysics Data System (ADS)

    Saito, Tatsuhiko; Tsushima, Hiroaki

    2016-11-01

    The present study proposes a method for synthesizing the ocean bottom pressure records during a tsunamigenic earthquake. First, a linear seismic wave simulation is conducted with a kinematic earthquake fault model as a source. Then, a nonlinear tsunami simulation is conducted using the sea bottom movement calculated in the seismic wave simulation. By using these simulation results, this method can provide realistic ocean bottom pressure change data, including both seismic and tsunami contributions. A simple theoretical consideration indicates that the dynamic pressure change caused by the sea bottom acceleration can contribute significantly until the duration of 90 s for a depth of 4000 m in the ocean. The performance of a tsunami monitoring system was investigated using the synthesized ocean bottom pressure records. It indicates that the system based on the hydrostatic approximation could not measure the actual tsunami height when the time does not elapse enough. The dynamic pressure change and the permanent sea bottom deformation inside the source region break the condition of a simple hydrostatic approximation. A tsunami source estimation method of tFISH is also examined. Even though the synthesized records contain a large dynamic pressure change, which is not considered in the algorithm, tFISH showed a satisfactory performance 5 min after the earthquake occurrence. The pressure records synthesized in this study, including both seismic wave and tsunami contributions, are more practical for evaluating the performance of our monitoring ability, whereas most tsunami monitoring tests neglect the seismic wave contribution.

  17. Comparison of different statistical methods for estimation of extreme sea levels with wave set-up contribution

    NASA Astrophysics Data System (ADS)

    Kergadallan, Xavier; Bernardara, Pietro; Benoit, Michel; Andreewsky, Marc; Weiss, Jérôme

    2013-04-01

    Estimating the probability of occurrence of extreme sea levels is a central issue for the protection of the coast. Return periods of sea level with wave set-up contribution are estimated here in one site : Cherbourg in France in the English Channel. The methodology follows two steps : the first one is computation of joint probability of simultaneous wave height and still sea level, the second one is interpretation of that joint probabilities to assess a sea level for a given return period. Two different approaches were evaluated to compute joint probability of simultaneous wave height and still sea level : the first one is multivariate extreme values distributions of logistic type in which all components of the variables become large simultaneously, the second one is conditional approach for multivariate extreme values in which only one component of the variables have to be large. Two different methods were applied to estimate sea level with wave set-up contribution for a given return period : Monte-Carlo simulation in which estimation is more accurate but needs higher calculation time and classical ocean engineering design contours of type inverse-FORM in which the method is simpler and allows more complex estimation of wave setup part (wave propagation to the coast for example). We compare results from the two different approaches with the two different methods. To be able to use both Monte-Carlo simulation and design contours methods, wave setup is estimated with an simple empirical formula. We show advantages of the conditional approach compared to the multivariate extreme values approach when extreme sea-level occurs when either surge or wave height is large. We discuss the validity of the ocean engineering design contours method which is an alternative when computation of sea levels is too complex to use Monte-Carlo simulation method.

  18. Wave run-up on a high-energy dissipative beach

    USGS Publications Warehouse

    Ruggiero, P.; Holman, R.A.; Beach, R.A.

    2004-01-01

    Because of highly dissipative conditions and strong alongshore gradients in foreshore beach morphology, wave run-up data collected along the central Oregon coast during February 1996 stand in contrast to run-up data currently available in the literature. During a single data run lasting approximately 90 min, the significant vertical run-up elevation varied by a factor of 2 along the 1.6 km study site, ranging from 26 to 61% of the offshore significant wave height, and was found to be linearly dependent on the local foreshore beach slope that varied by a factor of 5. Run-up motions on this high-energy dissipative beach were dominated by infragravity (low frequency) energy with peak periods of approximately 230 s. Incident band energy levels were 2.5 to 3 orders of magnitude lower than the low-frequency spectral peaks and typically 96% of the run-up variance was in the infragravity band. A broad region of the run-up spectra exhibited an f-4 roll off, typical of saturation, extending to frequencies lower than observed in previous studies. The run-up spectra were dependent on beach slope with spectra for steeper foreshore slopes shifted toward higher frequencies than spectra for shallower foreshore slopes. At infragravity frequencies, run-up motions were coherent over alongshore length scales in excess of 1 km, significantly greater than decorrelation length scales on moderate to reflective beaches. Copyright 2004 by the American Geophysical Union.

  19. H-He elastic scattering at low energies: Contribution of nonzero partial waves

    SciTech Connect

    Sinha, Prabal K.; Ghosh, A.S.

    2005-01-01

    The present study reports the nonzero partial wave elastic cross sections together with s-wave results for the scattering of an antihydrogen atom off a gaseous helium target at thermal energies (up to 10{sup -2} a.u.). We have used a nonadiabatic atomic orbital method having different basis sets to investigate the system. The consideration of all the significant partial waves (up to J=24) reduces the oscillatory nature present in the individual partial wave cross section. The added elastic cross section is almost constant up to 10{sup -7} a.u. and then decreases steadily and very slowly with increasing energy.

  20. Overly persistent circulation in climate models contributes to overestimated frequency and duration of heat waves and cold spells

    NASA Astrophysics Data System (ADS)

    Plavcová, Eva; Kyselý, Jan

    2016-05-01

    The study examines links of summer heat waves and winter cold spells in Central Europe to atmospheric circulation and specifically its persistence in an ensemble of regional climate models (RCMs). We analyse 13 RCMs driven by the ERA-40 reanalysis and compare them against observations over reference period 1971-2000. Using objective classification of circulation types and an efficiency coefficient with a block resampling test, we identify circulation types significantly conducive to heat waves and cold spells. We show that the RCMs have a stronger tendency to group together days with very high or low temperature and tend to simulate too many heat waves and cold spells, especially those lasting 5 days and more. Circulation types conducive to heat waves in summer are characterized by anticyclonic, southerly and easterly flow, with increasing importance of warm advection during heat waves. Winter cold spells are typically associated with easterly and anticyclonic flow, and the onset of cold spells tends to be linked to northerly and cyclonic flow with cold advection. The RCMs are generally able to reproduce the links between circulation and heat waves or cold spells, including the radiation-to-advection effect for heat waves and the opposite advection-to-radiation effect for cold spells. They capture relatively well also changes of mean temperature anomalies during sequences of given circulation types, namely the tendency towards temperature increase (decrease) during those types conducive to heat waves (cold spells). Since mean lengths of all circulation supertypes are overestimated in the RCMs, we conclude that the overly persistent circulation in climate models contributes to the overestimated frequency of long heat waves and cold spells. As these biases are rather general among the examined RCMs and similar drawbacks are likely to be manifested in climate model simulations for the twenty-first century, the results also suggest that climate change scenarios for

  1. Thalamic Atrophy Contributes to Low Slow Wave Sleep in Neuromyelitis Optica Spectrum Disorder

    PubMed Central

    Su, Lei; Han, Yujuan; Xue, Rong; Wood, Kristofer; Shi, Fu-Dong; Liu, Yaou; Fu, Ying

    2016-01-01

    Slow wave sleep abnormality has been reported in neuromyelitis optica spectrum disorder (NMOSD), but mechanism for such abnormality is unknown. To determine the structural defects in the brain that account for the decrease of slow wave sleep in NMOSD patients. Thirty-three NMOSD patients and 18 matched healthy controls (HC) were enrolled. Polysomnography was used to monitor slow wave sleep and three-dimensional T1-weighted MRIs were obtained to assess the alterations of grey matter volume. The percentage of deep slow wave sleep decreased in 93% NMOSD patients. Compared to HC, a reduction of grey matter volume was found in the bilateral thalamus of patients with a lower percentage of slow wave sleep (FWE corrected at cluster-level, p < 0.05, cluster size > 400 voxels). Furthermore, the right thalamic fraction was positively correlated with the decrease in the percentage of slow wave sleep in NMOSD patients (p < 0.05, FDR corrected, cluster size > 200 voxels). Our study identified that thalamic atrophy is associated with the decrease of slow wave sleep in NMOSD patients. Further studies should evaluate whether neurotransmitters or hormones which stem from thalamus are involved in the decrease of slow wave sleep. PMID:28053819

  2. Thalamic Atrophy Contributes to Low Slow Wave Sleep in Neuromyelitis Optica Spectrum Disorder.

    PubMed

    Su, Lei; Han, Yujuan; Xue, Rong; Wood, Kristofer; Shi, Fu-Dong; Liu, Yaou; Fu, Ying

    2016-12-01

    Slow wave sleep abnormality has been reported in neuromyelitis optica spectrum disorder (NMOSD), but mechanism for such abnormality is unknown. To determine the structural defects in the brain that account for the decrease of slow wave sleep in NMOSD patients. Thirty-three NMOSD patients and 18 matched healthy controls (HC) were enrolled. Polysomnography was used to monitor slow wave sleep and three-dimensional T1-weighted MRIs were obtained to assess the alterations of grey matter volume. The percentage of deep slow wave sleep decreased in 93% NMOSD patients. Compared to HC, a reduction of grey matter volume was found in the bilateral thalamus of patients with a lower percentage of slow wave sleep (FWE corrected at cluster-level, p < 0.05, cluster size > 400 voxels). Furthermore, the right thalamic fraction was positively correlated with the decrease in the percentage of slow wave sleep in NMOSD patients (p < 0.05, FDR corrected, cluster size > 200 voxels). Our study identified that thalamic atrophy is associated with the decrease of slow wave sleep in NMOSD patients. Further studies should evaluate whether neurotransmitters or hormones which stem from thalamus are involved in the decrease of slow wave sleep.

  3. Standing and Travelling Wave Contributions to the Persistent Ridge-Trough Over North America During Winter 2013/14

    NASA Astrophysics Data System (ADS)

    Watt-Meyer, O.; Kushner, P. J.

    2015-12-01

    The winter season over North America during 2013/14 was dominated by a persistent ridge-trough that brought warm and dry conditions to the southwestern U.S., and markedly cold temperatures to central and eastern North America [Wang et al., 2014; Hartmann, 2015]. In addition, several cold air outbreaks occurred during the winter season, the strongest of which was around 7 January 2014 and led to minimum daily temperature records being set at many weather stations including Atlanta, Austin, Chicago and New York [Screen et al., in press]. This study uses a novel decomposition of wave variability into standing and travelling components [Watt-Meyer and Kushner, 2015] to diagnose the anomalous circulation of the 2013/14 winter season. This spectral decomposition is an improvement on previous methods because it explicitly accounts for the covariance between standing and travelling waves, and because the real-space components of the signal can be easily reconstructed. An index representing the ridge-trough dipole is computed using mid-tropospheric heights and shown to be well correlated with surface temperatures over central and eastern North America. The contributions to this dipole index from standing waves, westward travelling waves, and eastward travelling waves are calculated. The analysis demonstrates that the cold air outbreak of 7 January 2014 was driven by a synoptic wave of record breaking amplitude intensifying a persistent background amplification of the typical ridge-trough structure seen during North American winter.

  4. Indexes of aortic pressure augmentation markedly underestimate the contribution of reflected waves toward variations in aortic pressure and left ventricular mass.

    PubMed

    Booysen, Hendrik L; Woodiwiss, Angela J; Sibiya, Moekanyi J; Hodson, Bryan; Raymond, Andrew; Libhaber, Elena; Sareli, Pinhas; Norton, Gavin R

    2015-03-01

    Although indexes of wave reflection enhance risk prediction, the extent to which measures of aortic systolic pressure augmentation (augmented pressures [Pa] or augmentation index) underestimate the effects of reflected waves on cardiovascular risk is uncertain. In participants from a community sample (age >16), we compared the relative contribution of reflected (backward wave pressures and the reflected wave index [RI]) versus augmented (Pa and augmentation index) pressure wave indexes to variations in central aortic pulse pressure (PPc; n=1185), and left ventricular mass index (LVMI; n=793). Aortic hemodynamics and LVMI were determined using radial applanation tonometry (SphygmoCor) and echocardiography. Independent of confounders, RI and backward wave pressures contributed more than forward wave pressures, whereas Pa and augmentation index contributed less than incident wave pressure to variations in PPc (P<0.0001 for comparison of partial r values). In those <50 years of age, while backward wave pressures (partial r=0.28, P<0.0001) contributed more than forward wave pressures (partial r=0.15, P<0.001; P<0.05 for comparison of r values), Pa (partial r=0.13, P<0.005) contributed to a similar extent as incident wave pressure (partial r=0.22, P<0.0001) to variations in LVMI. Furthermore, in those ≥50 years of age, backward wave pressures (partial r=0.21, P<0.0001), but not forward wave pressures (P=0.98), while incident wave pressure (partial r=0.23, P<0.0001), but not Pa (P=0.80) were associated with LVMI. Pa and augmentation index underestimated the effect of wave reflection on PPc and LVMI in both men and women. Thus, as compared with relations between indexes of aortic pressure augmentation and PPc or LVMI, strikingly better relations are noted between aortic wave reflection and PPc or LVMI. © 2014 American Heart Association, Inc.

  5. Overly persistent circulation in climate models contributes to overestimated frequency and duration of heat waves and cold spells

    NASA Astrophysics Data System (ADS)

    Plavcova, Eva; Kysely, Jan

    2016-04-01

    The study examines links of summer heat waves and winter cold spells in Central Europe to atmospheric circulation and specifically its persistence in an ensemble of regional climate models (RCMs). We analyse 13 RCMs driven by the ERA-40 reanalysis and compare them against observations over 1971-2000. Using objective classification of circulation types and an efficiency coefficient with a block resampling test, we identify circulation types significantly conducive to heat waves and cold spells. We show that the RCMs have a stronger tendency to group together days with very high or low temperature and tend to simulate too many heat waves and cold spells, especially those lasting 5 days and more. Circulation types conducive to heat waves in summer are characterized by anticyclonic, southerly and easterly flow, with increasing importance of warm advection during heat waves. Winter cold spells are typically associated with easterly and anticyclonic flow, and the onset of cold spells tends to be linked to northerly and cyclonic flow with cold advection. The RCMs are generally able to reproduce the links between circulation and heat waves or cold spells, including the radiation-to-advection effect for heat waves and the opposite advection-to-radiation effect for cold spells. They capture relatively well also changes of mean temperature anomalies during sequences of given circulation types, namely the tendency towards an increase (decrease) of temperature during the types conducive to heat waves (cold spells). Since mean lengths of all circulation supertypes are overestimated in the RCMs, we conclude that the overly persistent circulation in climate models contributes to the overestimated frequency of long heat waves and cold spells. As these biases are rather general among the examined RCMs and similar drawbacks are likely to be manifested in climate model simulations for the 21st century, the results also suggest that climate change scenarios for spells of days with high

  6. Assessing the contributions of surface waves and complex rays to far-field Mie scattering by use of the Debye series

    NASA Technical Reports Server (NTRS)

    Hovenac, Edward A.; Lock, James A.

    1991-01-01

    The contributions of complex rays and the secondary radiation shed by surface waves to scattering by a dielectric sphere are calculated in the context of the Debye series expansion of the Mie scattering amplitudes. Also, the contributions of geometrical rays are reviewed and compared with the Debye series. Interference effects between surface waves, complex waves, and geometrical waves are calculated, and the possibility of observing these interference effects is discussed. Experimental data supporting the observation of a surface wave-geometrical pattern is presented.

  7. Modeling the effect of wave-vegetation interaction on wave setup

    NASA Astrophysics Data System (ADS)

    van Rooijen, A. A.; McCall, R. T.; van Thiel de Vries, J. S. M.; van Dongeren, A. R.; Reniers, A. J. H. M.; Roelvink, J. A.

    2016-06-01

    Aquatic vegetation in the coastal zone attenuates wave energy and reduces the risk of coastal hazards, e.g., flooding. Besides the attenuation of sea-swell waves, vegetation may also affect infragravity-band (IG) waves and wave setup. To date, knowledge on the effect of vegetation on IG waves and wave setup is lacking, while they are potentially important parameters for coastal risk assessment. In this study, the storm impact model XBeach is extended with formulations for attenuation of sea-swell and IG waves, and wave setup effects in two modes: the sea-swell wave phase-resolving (nonhydrostatic) and the phase-averaged (surfbeat) mode. In surfbeat mode, a wave shape model is implemented to capture the effect of nonlinear wave-vegetation interaction processes on wave setup. Both modeling modes are verified using data from two flume experiments with mimic vegetation and show good skill in computing the sea-swell and IG wave transformation, and wave setup. In surfbeat mode, the wave setup prediction greatly improves when using the wave shape model, while in nonhydrostatic mode (nonlinear) intrawave effects are directly accounted for. Subsequently, the model is used for a range of coastal geomorphological configurations by varying bed slope and vegetation extent. The results indicate that the effect of wave-vegetation interaction on wave setup may be relevant for a range of typical coastal geomorphological configurations (e.g., relatively steep to gentle slope coasts fronted by vegetation).

  8. Nonreciprocal Oersted field contribution to the current-induced frequency shift of magnetostatic surface waves

    NASA Astrophysics Data System (ADS)

    Haidar, Mohammad; Bailleul, Matthieu; Kostylev, Mikhail; Lao, Yuyang

    2014-03-01

    The influence of an electrical current on the propagation of magnetostatic surface waves is investigated in a relatively thick (40 nm) permalloy film both experimentally and theoretically. Contrary to previously studied thinner films where the dominating effect is the current-induced spin-wave Doppler shift, the magnetic field generated by the current (Oersted field) is found to induce a strong nonreciprocal frequency shift which overcompensates the Doppler shift. The measured current-induced frequency shift is in agreement with the developed theory. The theory relates the sign of the frequency shift to the spin-wave modal profiles. The good agreement between the experiment and the theory confirms a recent prediction of a counterintuitive mode localization for magnetostatic surface waves in the dipole-exchange regime.

  9. Near Source Contributions to Teleseismic P Wave Coda and Regional Phases

    DTIC Science & Technology

    1991-04-27

    coda - 15. NUMBER OF-PAGES Underground explosions Teleseismic, waves -_140 P waves Splain16. -PRICE CODE pP parameters Salto 17. SECURITY CLSSIFICATION...short-period vertical component recordings for underground explosions at the Nevada (NTS) and Novaya Zemlya test sites. The waveforms were recorded at...receiver terms for the two CSN stations from Figure 2 for the 25 Pahute Mesa explosions. The P and P Co6da station’ spectra are showw withl- vertical

  10. CONTRIBUTION OF VELOCITY VORTICES AND FAST SHOCK REFLECTION AND REFRACTION TO THE FORMATION OF EUV WAVES IN SOLAR ERUPTIONS

    SciTech Connect

    Wang, Hongjuan; Liu, Siqing; Gong, Jiancun; Wu, Ning; Lin, Jun

    2015-06-01

    We numerically study the detailed evolutionary features of the wave-like disturbance and its propagation in the eruption. This work is a follow-up to Wang et al., using significantly upgraded new simulations. We focus on the contribution of the velocity vortices and the fast shock reflection and refraction in the solar corona to the formation of the EUV waves. Following the loss of equilibrium in the coronal magnetic structure, the flux rope exhibits rapid motions and invokes the fast-mode shock at the front of the rope, which then produces a type II radio burst. The expansion of the fast shock, which is associated with outward motion, takes place in various directions, and the downward expansion shows the reflection and the refraction as a result of the non-uniform background plasma. The reflected component of the fast shock propagates upward and the refracted component propagates downward. As the refracted component reaches the boundary surface, a weak echo is excited. The Moreton wave is invoked as the fast shock touches the bottom boundary, so the Moreton wave lags the type II burst. A secondary echo occurs in the area where reflection of the fast shock encounters the slow-mode shock, and the nearby magnetic field lines are further distorted because of the interaction between the secondary echo and the velocity vortices. Our results indicate that the EUV wave may arise from various processes that are revealed in the new simulations.

  11. Remote Sensing Characterization of Two-dimensional Wave Forcing in the Surf Zone

    NASA Astrophysics Data System (ADS)

    Carini, R. J.; Chickadel, C. C.; Jessup, A. T.

    2016-02-01

    In the surf zone, breaking waves drive longshore currents, transport sediment, shape bathymetry, and enhance air-sea gas and particle exchange. Furthermore, wave group forcing influences the generation and duration of rip currents. Wave breaking exhibits large gradients in space and time, making it challenging to measure in situ. Remote sensing technologies, specifically thermal infrared (IR) imagery, can provide detailed spatial and temporal measurements of wave breaking at the water surface. We construct two-dimensional maps of active wave breaking from IR imagery collected during the Surf Zone Optics Experiment in September 2010 at the US Army Corps of Engineers' Field Research Facility in Duck, NC. For each breaker identified in the camera's field of view, the crest-perpendicular length of the aerated breaking region (roller length) and wave direction are estimated and used to compute the wave energy dissipation rate. The resultant dissipation rate maps are analyzed over different time scales: peak wave period, infragravity wave period, and tidal wave period. For each time scale, spatial maps of wave breaking are used to characterize wave forcing in the surf zone for a variety of wave conditions. The following phenomena are examined: (1) wave dissipation rates over the bar (location of most intense breaking) have increased variance in infragravity wave frequencies, which are different from the peak frequency of the incoming wave field and different from the wave forcing variability at the shoreline, and (2) wave forcing has a wider spatial distribution during low tide than during high tide due to depth-limited breaking over the barred bathymetry. Future work will investigate the response of the variability in wave setup, longshore currents and rip currents, to the variability in wave forcing in the surf zone.

  12. Destructive tsunami-like wave generated by surf beat over a coral reef during Typhoon Haiyan

    PubMed Central

    Roeber, Volker; Bricker, Jeremy D.

    2015-01-01

    Storm surges cause coastal inundation due to setup of the water surface resulting from atmospheric pressure, surface winds and breaking waves. Here we show that during Typhoon Haiyan, the setup generated by breaking waves near the fringing-reef-protected town of Hernani, the Philippines, oscillated with the incidence of large and small wave groups, and steepened into a tsunami-like wave that caused extensive damage and casualties. Though fringing reefs usually protect coastal communities from moderate storms, they can exacerbate flooding during strong events with energetic waves. Typical for reef-type bathymetries, a very short wave-breaking zone over the steep reef face facilitates the freeing of infragravity-period fluctuations (surf beat) with little energy loss. Since coastal flood planning relies on phase-averaged wave modelling, infragravity surges are not being accounted for. This highlights the necessity for a policy change and the adoption of phase-resolving wave models for hazard assessment in regions with fringing reefs. PMID:26245839

  13. Vibrational structure theory: new vibrational wave function methods for calculation of anharmonic vibrational energies and vibrational contributions to molecular properties.

    PubMed

    Christiansen, Ove

    2007-06-21

    A number of recently developed theoretical methods for the calculation of vibrational energies and wave functions are reviewed. Methods for constructing the appropriate quantum mechanical Hamilton operator are briefly described before reviewing a particular branch of theoretical methods for solving the nuclear Schrödinger equation. The main focus is on wave function methods using the vibrational self-consistent field (VSCF) as starting point, and includes vibrational configuration interaction (VCI), vibrational Møller-Plesset (VMP) theory, and vibrational coupled cluster (VCC) theory. The convergence of the different methods towards the full vibrational configuration interaction (FVCI) result is discussed. Finally, newly developed vibrational response methods for calculation of vibrational contributions to properties, energies, and transition probabilities are discussed.

  14. Contribution of tuned liquid column gas dampers to the performance of offshore wind turbines under wind, wave, and seismic excitations

    NASA Astrophysics Data System (ADS)

    Bargi, Khosrow; Dezvareh, Reza; Mousavi, Seyed Amin

    2016-09-01

    The main intention of the present study is to reduce wind, wave, and seismic induced vibrations of jackettype offshore wind turbines (JOWTs) through a newly developed vibration absorber, called tuned liquid column gas damper (TLCGD). Using a Simulink-based model, an analytical model is developed to simulate global behavior of JOWTs under different dynamic excitations. The study is followed by a parametric study to explore efficiency of the TLCGD in terms of nacelle acceleration reduction under wind, wave, and earthquake loads. Study results indicate that optimum frequency of the TLCGD is rather insensitive to excitation type. In addition, while the gain in vibration control from TLCGDs with higher mass ratios is generally more pronounced, heavy TLCGDs are more sensitive to their tuned frequency such that ill-regulated TLCGD with high mass ratio can lead to destructive results. It is revealed that a well regulated TLCGD has noticeable contribution to the dynamic response of the JOWT under any excitation.

  15. Sustained and Transient Contributions to the Rat Dark-Adapted Electroretinogram b-Wave

    PubMed Central

    Dang, Trung M.; Vingrys, Algis J.; Bui, Bang V.

    2013-01-01

    The most dominant feature of the electroretinogram, the b-wave, is thought to reflect ON-bipolar cell responses. However, a number of studies suggest that the b-wave is made up of several components. We consider the composition of the rat b-wave by subtracting corneal negative components obtained using intravitreal application of pharmacological agents to remove postreceptoral responses. By analyzing the intensity-response characteristic of the PII across a range of fixed times during and after a light step, we find that the rat isolated PII has 2 components. The first has fast rise and decay characteristics with a low sensitivity to light. GABAc-mediated inhibitory pathways enhance this transient-ON component to manifest increased and deceased sensitivity to light at shorter (<160 ms) and longer times, respectively. The second component has slower temporal characteristics but is more sensitive to light. GABAc-mediated inhibition enhances this sustained-ON component but has little effect on its sensitivity to light. After stimulus offset, both transient and sustained components return to baseline, and a long latency sustained positive component becomes apparent. The light sensitivities of transient-ON and sustained-OFF components are consistent with activity arising from cone ON- and OFF-bipolar cells, whereas the sustained-ON component is likely to arise from rod bipolar cells. PMID:23533706

  16. The contribution of activated processes to Q. [stress corrosion cracking in seismic wave attenuation

    NASA Technical Reports Server (NTRS)

    Spetzler, H. A.; Getting, I. C.; Swanson, P. L.

    1980-01-01

    The possible role of activated processes in seismic attenuation is investigated. In this study, a solid is modeled by a parallel and series configuration of dashpots and springs. The contribution of stress and temperature activated processes to the long term dissipative behavior of this system is analyzed. Data from brittle rock deformation experiments suggest that one such process, stress corrosion cracking, may make a significant contribution to the attenuation factor, Q, especially for long period oscillations under significant tectonic stress.

  17. The contribution of activated processes to Q. [stress corrosion cracking in seismic wave attenuation

    NASA Technical Reports Server (NTRS)

    Spetzler, H. A.; Getting, I. C.; Swanson, P. L.

    1980-01-01

    The possible role of activated processes in seismic attenuation is investigated. In this study, a solid is modeled by a parallel and series configuration of dashpots and springs. The contribution of stress and temperature activated processes to the long term dissipative behavior of this system is analyzed. Data from brittle rock deformation experiments suggest that one such process, stress corrosion cracking, may make a significant contribution to the attenuation factor, Q, especially for long period oscillations under significant tectonic stress.

  18. Wave dissipation by muddy seafloors

    NASA Astrophysics Data System (ADS)

    Elgar, Steve; Raubenheimer, Britt

    2008-04-01

    Muddy seafloors cause tremendous dissipation of ocean waves. Here, observations and numerical simulations of waves propagating between 5- and 2-m water depths across the muddy Louisiana continental shelf are used to estimate a frequency- and depth-dependent dissipation rate function. Short-period sea (4 s) and swell (7 s) waves are shown to transfer energy to long-period (14 s) infragravity waves, where, in contrast with theories for fluid mud, the observed dissipation rates are highest. The nonlinear energy transfers are most rapid in shallow water, consistent with the unexpected strong increase of the dissipation rate with decreasing depth. These new results may explain why the southwest coast of India offers protection for fishing (and for the 15th century Portuguese fleet) only after large waves and strong currents at the start of the monsoon move nearshore mud banks from about 5- to 2-m water depth. When used with a numerical nonlinear wave model, the new dissipation rate function accurately simulates the large reduction in wave energy observed in the Gulf of Mexico.

  19. Contributions to the theory of magnetorotational instability and waves in a rotating plasma

    SciTech Connect

    Mikhailovskii, A. B. Lominadze, J. G. Churikov, A. P.; Tsypin, V. S.; Erokhin, N. N.; Erokhin, N. S.; Konovalov, S. V.; Pashitskii, E. A.; Stepanov, A. V.; Vladimirov, S. V.; Galvao, R. M. O.

    2008-01-15

    The one-fluid magnetohydrodynamic (MHD) theory of magnetorotational instability (MRI) in an ideal plasma is presented. The theory predicts the possibility of MRI for arbitrary {beta}, where {beta} is the ratio of the plasma pressure to the magnetic field pressure. The kinetic theory of MRI in a collisionless plasma is developed. It is demonstrated that as in the ideal MHD, MRI can occur in such a plasma for arbitrary {beta}. The mechanism of MRI is discussed; it is shown that the instability appears because of a perturbed parallel electric field. The electrodynamic description of MRI is formulated under the assumption that the dispersion relation is expressed in terms of the permittivity tensor; general properties of this tensor are analyzed. It is shown to be separated into the nonrotational and rotational parts. With this in mind, the first step for incorporation of MRI into the general theory of plasma instabilities is taken. The rotation effects on Alfven waves are considered.

  20. Estimating storm-induced wave runup using numerical and parameterized models

    NASA Astrophysics Data System (ADS)

    Stockdon, H. F.; Thompson, D.; Plant, N. G.; Long, J.

    2014-12-01

    Wave runup during storm conditions can drive extreme changes to coastal environments. Prediction of runup elevation during these events is important for identifying areas at risk to erosion and coastal flooding and for evaluating potential hazards to coastal communities. Parametric models are often used to calculate runup levels that are expected from specific storms or storm scenarios. However, most parameterizations were not developed or tested under highly energetic conditions, principally because observations of runup under these conditions are extremely difficult to collect. Therefore, we used a numerical model, XBeach, to simulate runup during storm conditions and then, using these model-generated data, determine where an existing parameterization (Stockdon et al, 2006) can be extended or modified. First, the accuracy of XBeach-simulated wave runup components (setup and swash) were evaluated using observations collected during the 1997 SandyDuck field experiment in North Carolina. The swash component was split into incident band and infragravity band. Incident-band swash is not modeled explicitly by XBeach and therefore simulated values are significantly lower than observations. Setup and infragravity swash are adequately modeled using XBeach, indicating that these simulated storm-induced water levels can be used as surrogates for actual observations. Generalized wave conditions for category 1-5 hurricanes were then used to model extreme setup and swash. For setup, simulated hurricane results are higher than what would be predicted using the parameterization. Here, interaction of high water levels with the dune face prevents a simple extrapolation of the existing parameterization. XBeach-modeled infragravity swash for hurricane conditions compares well with the parameterization suggesting that we can use simulated data to extend this parameterization to more extreme wave conditions.

  1. New Variants and Age Shift to High Fatality Groups Contribute to Severe Successive Waves in the 2009 Influenza Pandemic in Taiwan

    PubMed Central

    Yang, Ji-Rong; Huang, Yuan-Pin; Chang, Feng-Yee; Hsu, Li-Ching; Lin, Yu-Cheng; Su, Chun-Hui; Chen, Pei-Jer; Wu, Ho-Sheng; Liu, Ming-Tsan

    2011-01-01

    Past influenza pandemics have been characterized by the signature feature of multiple waves. However, the reasons for multiple waves in a pandemic are not understood. Successive waves in the 2009 influenza pandemic, with a sharp increase in hospitalized and fatal cases, occurred in Taiwan during the winter of 2010. In this study, we sought to discover possible contributors to the multiple waves in this influenza pandemic. We conducted a large-scale analysis of 4703 isolates in an unbiased manner to monitor the emergence, dominance and replacement of various variants. Based on the data from influenza surveillance and epidemic curves of each variant clade, we defined virologically and temporally distinct waves of the 2009 pandemic in Taiwan from May 2009 to April 2011 as waves 1 and 2, an interwave period and wave 3. Except for wave 3, each wave was dominated by one distinct variant. In wave 3, three variants emerged and co-circulated, and formed distinct phylogenetic clades, based on the hemagglutinin (HA) genes and other segments. The severity of influenza was represented as the case fatality ratio (CFR) in the hospitalized cases. The CFRs in waves 1 and 2, the interwave period and wave 3 were 6.4%, 5.1%, 15.2% and 9.8%, respectively. The results highlight the association of virus evolution and variable influenza severity. Further analysis revealed that the major affected groups were shifted in the waves to older individuals, who had higher age-specific CFRs. The successive pandemic waves create challenges for the strategic preparedness of health authorities and make the pandemic uncertain and variable. Our findings indicate that the emergence of new variants and age shift to high fatality groups might contribute potentially to the occurrence of successive severe pandemic waves and offer insights into the adjustment of national responses to mitigate influenza pandemics. PMID:22140569

  2. [Neurophysiology of hypnosis. The suggestive process and contributions of the learned control of brain waves].

    PubMed

    Pinelli, P

    1975-10-31

    The contribution that neurophysiological examination, subordinate to psychodynamic analysis, can bring to the investigation of facts and results in the therapeutic application of hypnosis is discussed. Phenomena with a suggestive background are analysed, particularly those of ideomotor transformation with reference to prereflective though (Polanyi & Dyer). A special case is represented by phobic-obsessive disturbances. Here analysis of the process of ideative reinforcement must take account of the untranslatability of certain linguistico-syntactic connotations at this level. The part played by sensorimotor EEG biofeedback training in practical therapeutics is also examined.

  3. Modelling seismic noise surface and body waves

    NASA Astrophysics Data System (ADS)

    Gualtieri, L.; Stutzmann, E.; Capdeville, Y.; Farra, V.; Schimmel, M.; Ardhuin, F.; Mangeney, A.; Morelli, A.

    2013-12-01

    A proper knowledge of seismic noise sources is important to correctly extract properties of the Earth from seismic noise records. We present the theory for modeling both surface and body waves in the secondary microseism period band 3-10 s. We consider noise sources as vertical single forces at the ocean surface and we derive their amplitude from a realistic ocean wave model. We compute the site effect due to the bathymetry for both Rayleigh and body waves by using normal modes and ray theory. We show that it varies strongly with frequency and seismic wave type. We compute the amplitude of noise spectra by using normal mode summation and we show that the fundamental mode of Rayleigh wave is the dominant signal on noise spectra amplitude. For computing Rayleigh wave seismic spectra, we derive an attenuation model that enables to fit well the amplitudes of the noise vertical component whatever the station location in the secondary microseismic period band. Moreover, we estimate the energy amount of Love waves by modelling horizontal components with vertical force sources. The discrepancy between real and synthetic spectra on the horizontal components enables to estimate the amount of Love waves for which a different source mechanism is needed. The same theory is applied to study long period noise (T=20-500 s), considering noise sources as single forces generated by the interaction of ocean infragravity waves. We compute the Rayleigh wave site effect by using normal modes and we show that it is not frequency dependent.

  4. Contribution of mode-coupling and phase-mixing of Alfvén waves to coronal heating

    NASA Astrophysics Data System (ADS)

    Pagano, P.; De Moortel, I.

    2017-05-01

    Context. Phase-mixing of Alfvén waves in the solar corona has been identified as one possible candidate to explain coronal heating. While this scenario is supported by observations of ubiquitous oscillations in the corona carrying sufficient wave energy and by theoretical models that have described the concentration of energy in small-scale structures, it is still unclear whether this wave energy can be converted into thermal energy in order to maintain the million-degree hot solar corona. Aims: The aim of this work is to assess how much energy can be converted into thermal energy by a phase-mixing process triggered by the propagation of Alfvénic waves in a cylindric coronal structure, such as a coronal loop, and to estimate the impact of this conversion on the coronal heating and thermal structure of the solar corona. Methods: To this end, we ran 3D MHD simulations of a magnetised cylinder where the Alfvén speed varies through a boundary shell, and a footpoint driver is set to trigger kink modes that mode couple to torsional Alfvén modes in the boundary shell. These Alfvén waves are expected to phase-mix, and the system allows us to study the subsequent thermal energy deposition. We ran a reference simulation to explain the main process and then we varied the simulation parameters, such as the size of the boundary shell, its structure, and the persistence of the driver. Results: When we take high values of magnetic resistivity and strong footpoint drivers into consideration, we find that i) phase-mixing leads to a temperature increase of the order of 105 K or less, depending on the structure of the boundary shell; ii) this energy is able to balance the radiative losses only in the localised region involved in the heating; and iii) we can determine the influence of the boundary layer and the persistence of the driver on the thermal structure of the system. Conclusions: Our conclusion is that as a result of the extreme physical parameters we adopted and the

  5. Initial-data contribution to the error budget of gravitational waves from neutron-star binaries

    NASA Astrophysics Data System (ADS)

    Tsokaros, Antonios; Mundim, Bruno C.; Galeazzi, Filippo; Rezzolla, Luciano; Uryū, Kōji

    2016-08-01

    As numerical calculations of inspiraling neutron-star binaries reach values of accuracy that are comparable with those of black-hole binaries, a fine budgeting of the various sources of error becomes increasingly important. Among such sources, the initial data are normally not accounted for, the rationale being that the error on the initial spacelike hypersurface is always far smaller than the error gained during the evolution. We here consider critically this assumption and perform a comparative analysis of the gravitational waveforms relative to essentially the same physical binary configuration when computed with two different initial-data codes, and then evolved with the same evolution code. More specifically, we consider the evolution of irrotational neutron-star binaries computed either with the pseudospectral code lorene, or with the newly developed finite-difference code cocal; both sets of initial data are subsequently evolved with the high-order-evolution code whiskythc. In this way we find that although global quantities of the system, like the mass and angular momentum, have differences of the order of ≲0.02 % , local quantities, like rest-mass density, extrinsic curvature or angular velocity, show pointwise differences that are much larger, of the order of ≲1 %. These local differences are then responsible for a dephasing in the gravitational waves at the merger time (after approximately three orbits) of ˜1.4 radians. Our results highlight the importance of using initial data that are pointwisely the same when comparative studies are done and physical parameters are estimated.

  6. Wave scattering from encapsulated microbubbles subject to high-frequency ultrasound: contribution of higher-order scattering modes.

    PubMed

    Chen, Jiusheng; Hunter, Kendall S; Shandas, Robin

    2009-10-01

    The theoretical understanding of encapsulated microbubble response to high-frequency ultrasound (HFUS) excitation is still limited although some novel experimental HFUS contrast imaging techniques have been well developed. In this paper, the higher-order modal (HOM) contributions to the scattered field are studied for such microbubbles driven by 1-100 MHz ultrasound. An exact solution of all small-amplitude vibrational modes of a single encapsulated microbubble in water is given by the wave scattering theory (WST) method and compared to results obtained from Church's Rayleigh-Plesset-like model for the small-amplitude radial oscillation of a microbubble in an incompressible fluid. From numerical results, we show that the HOM field contribution is significant for scattering properties from individual Nycomed microbubbles with normalized frequency > or = 0.2. It is also shown that the multiple scattering is strengthened for monodispersed Definity microbubbles of 3 microm radius at frequencies >40 MHz. However, comparisons between the authors' analyses and known experimental data for polydispersed Definity microbubbles indicate that the HOM contributions are insignificant in attenuation estimation at frequencies <50 MHz. In conclusion, the WST model analysis suggests that HOM scattering is an important consideration for single bubbles but may be less critical in the modeling of polydispersed Definity bubbles at high frequencies.

  7. Wave scattering from encapsulated microbubbles subject to high-frequency ultrasound: Contribution of higher-order scattering modes

    PubMed Central

    Chen, Jiusheng; Hunter, Kendall S.; Shandas, Robin

    2009-01-01

    The theoretical understanding of encapsulated microbubble response to high-frequency ultrasound (HFUS) excitation is still limited although some novel experimental HFUS contrast imaging techniques have been well developed. In this paper, the higher-order modal (HOM) contributions to the scattered field are studied for such microbubbles driven by 1–100 MHz ultrasound. An exact solution of all small-amplitude vibrational modes of a single encapsulated microbubble in water is given by the wave scattering theory (WST) method and compared to results obtained from Church’s Rayleigh–Plesset-like model for the small-amplitude radial oscillation of a microbubble in an incompressible fluid. From numerical results, we show that the HOM field contribution is significant for scattering properties from individual Nycomed microbubbles with normalized frequency ≥0.2. It is also shown that the multiple scattering is strengthened for monodispersed Definity® microbubbles of 3 μm radius at frequencies >40 MHz. However, comparisons between the authors’ analyses and known experimental data for polydispersed Definity® microbubbles indicate that the HOM contributions are insignificant in attenuation estimation at frequencies <50 MHz. In conclusion, the WST model analysis suggests that HOM scattering is an important consideration for single bubbles but may be less critical in the modeling of polydispersed Definity® bubbles at high frequencies. PMID:19813791

  8. Lithospheric and asthenospheric contributions to shear-wave splitting observations in the southeastern United States

    NASA Astrophysics Data System (ADS)

    Wagner, Lara S.; Long, Maureen D.; Johnston, Mignon D.; Benoit, Margaret H.

    2012-08-01

    We present observations of both null and non-null SKS splitting from temporary deployments across the southeastern United States in order to evaluate the relative contributions of lithospheric deformation and asthenospheric flow to regional anisotropy. Data for this study come from four temporary broadband seismic deployments: the Appalachian Seismic Transect (AST), the Test Experiment for Eastern North America (TEENA), the South Carolina Earth Physics Project (SCEPP), and the Florida to Edmonton Array (FLED). In general, we find fast directions aligned roughly parallel to absolute plate motion of the North American plate (APM) within and west of the Southern Appalachians, whereas to the southeast, we find a broad area dominated by complex splitting patterns consisting of well-constrained null splitting measurements over a range of backazimuths along with a very small number of resolved non-null measurements. This change in splitting patterns is consistent with a transition from drag induced asthenospheric flow beneath the older sections of the North American continent to vertical or incoherent mantle flow, likely in combination with complex lithospheric anisotropy, beneath the younger accreted terranes to the southeast. In addition to these general patterns, we find a number of non-null splitting measurements that are not aligned with APM, but are instead aligned with prominent magnetic anomalies that may correspond to ancient continental suture zones or faults. This would suggest that in these areas, a strongly anisotropic (but localized) lithospheric fabric dominates over any ambient asthenospheric anisotropic signature. In areas with generally strong APM parallel splitting, this would imply a thick sheared mantle lithosphere whose deformation-induced anisotropy is strong enough to overprint the anisotropy induced by APM, and is aligned with the shallower crustal structures responsible for generating the observed magnetic anomalies. In the southeastern areas

  9. Wave Mode Processing Algorithms, Product Validation and Assimilation Wave Retrievals and Applications

    NASA Astrophysics Data System (ADS)

    Collard, Fabrice; Johnsen, Harald; Lotfi, Aouf; Chapron, Bertrand

    2013-03-01

    The fourth SAR oceanography workshop, SEASAR 2012 , entitled "Advances in SAR Oceanography", was held in Tromsø, 18th to 22th June 2012. Among the topics highlighted at SEASAR 2012 were ”Wave mode processing algorithms, product validation and assimilation” and ”Wave retrievals and applications”. The last decade of SAR wave research has brought high level of consensus on the various approaches for deriving wave information from SAR images. The main new achievements have been within advance applications of SAR wave derived information such as;1) the investigation of extreme sea states in intense storms; 2) the study of individual exceptional wave states, such as freak (monster) waves; 3) the extension of numerical wave models in the general context of Earth System modelling, including the improved representation of wave-current interactions, air-sea fluxes, and second-order spectral quantities related to infra-gravity and microseism generation, and; 4) improved assimilation of wave data in NWP models. This paper presents a summary of achievements and way forward within these fields since the previous white paper of SeaSAR2003 (ESA SP-565, 2004).

  10. Wave-Group Resolving vs Wave-Resolving Modeling of Surf and Swash Processes

    NASA Astrophysics Data System (ADS)

    Roelvink, J. A.; McCall, R. T.; Mehvar, S.; Dastgheib, A.

    2014-12-01

    Numerical modeling of beach and dune erosion, overwashing and breaching has gained much from inclusion of wave-group related infragravity motions in models such as XBeach (Roelvink et al, 2009). The main assumption in this model is that on the upper beach the incident-band, short waves are to a large extent dissipated, whereas infragravity wave motions have more oomph and are the ones making it to the dune foot and even over it. It is then justified to resolve the variations in short-wave energy and resulting long-wave motions, while parameterizing the short wave motions. This model has been applied successfully in many cases, both lab and field, concerning sandy beaches and dunes. However, as the sand gets coarser and beaches steeper, more and more incident wave energy is found in the swash, and at some point the parameterizations and associated coefficients start dominating the process. For gravel beaches, McCall et al (2014) have made use of a wave-resolving mode of XBeach, which makes use of a one-layer, nonhydrostatic approach developed by Zijlema et al. (2011). They have included a groundwater model and have shown that both the infiltration-exfiltration processes and the incident-band swash are important in getting the swash hydrodynamics on gravel beaches right. This work is continuing with promising results for morphodynamic response during extreme events. At the same time, we are investigating the skill of both approaches for wave runup and overtopping and are testing the morphodynamic behavior of the wave-resolving model in comparison with data and the original XBeach. So far, at the sandy end of the spectrum, both approaches give good and very similar results. In our presentation we will highlight some of these results and will present a sensitivity study where both approaches will be run and compared for a range of coastal profiles, including hard end structures. This will allow us to give clear guidelines for when to use the (much more computer

  11. Factors contributing to record-breaking heat waves over the Great Plains during the 1930s Dust Bowl

    NASA Astrophysics Data System (ADS)

    Cowan, T.; Hegerl, G. C.

    2016-12-01

    Record-breaking summer heat waves that plagued contiguous United States in the 1930s emerged during the decade-long "Dust Bowl" drought. Using high-quality daily temperature observations, the Dust Bowl heat wave characteristics for the Great Plains are assessed using metrics that describe variations in heat wave activity and intensity. We also quantify record-breaking heat waves over the pre-industrial period for 22 CMIP5 model multi-century realisations. The most extreme Great Plains heat wave summers in the Dust Bowl decade (e.g. 1931, 1934, 1936) were pre-conditioned by anomalously dry springs, as measured by proxy drought indices. In general, summer heat waves over the Great Plains develop 15-20 days earlier after anomalously dry springs, and are also significantly longer and hotter, indicative of the importance of land surface feedbacks in heat wave intensification. The majority of pre-industrial climate model experiments capture regionally clustered summer heat waves across North America, although the North Pacific and Atlantic sea surface temperature patterns associated with the heat waves vary considerably between models. Sea surface temperature patterns may be more important for influencing winter and spring precipitation, thus amplifying summer heat waves during drought periods. The synoptic pattern that commonly appeared during the exceptional Dust Bowl heat waves featured an anomalous broad surface pressure ridge straddling an upper level blocking anticyclone over the western United States. This forced significant subsidence and adiabatic warming over the Great Plains, and triggered anomalous southward warm advection over southern regions, prolonging and amplifying the heat waves over central United States. Importantly, the results show that despite the sparsity of stations in the 1930s, homogeneous observations are crucial in accurately quantifying the Dust Bowl decade heat waves, as opposed to solely relying on atmospheric reanalysis.

  12. Contribution of Antisymmetric and Symmetric Waves to the Reflection of Sound in a Fluid by a Thick, Homogeneous Plate.

    DTIC Science & Technology

    1980-10-23

    SOUND IN A FLUID BY A THICK, HOMOGENEOUS PLATE INTRODUCTION In a recent report Rudgers [11 describes the acoustical behavior of thick, fluid-loaded...symmetric waves to the plate-fluid interactions studied by Rudgers (1]. In the present report, the role of antisymmetric and symmetric waves is analyzed...defined by Rudgers (4]. The structural response function of the two types of waves in combination is related to the response functions of the two types

  13. Contribution of backward and forward wave pressures to age-related increases in aortic pressure in a community sample not receiving antihypertensive therapy.

    PubMed

    Hodson, Bryan; Norton, Gavin R; Ballim, Imraan; Sareli, Pinhas; Woodiwiss, Angela J

    2017-08-24

    Reports on the contribution of aortic forward (Pf) and backward (Pb) wave pressures to age-related increases in central aortic pulse pressure (PPc) have been confounded by the use of participants receiving antihypertensive therapy. We assessed the relative contribution of Pf and Pb to age-related increases in PPc (radial applanation tonometry and SphygmoCor software using an assumed triangular wave for wave separation analysis) in 892 community participants not receiving antihypertensive therapy. We validated our results using aortic flow waves (echocardiography) for wave separation analysis in 254 of these participants. In multivariate regression models in those aged <50 years, adjustments for both Pb and a Pf-independent measure of reflected wave function (RM = Pb/Pf), but not Pf abolished the impact of age on PPc. However, in those aged >50 years, adjustments for Pf (β-coefficient: 0.25 ± 0.06 vs. 0.74 ± 0.08; P < .0001) and Pb (0.04 ± 0.04 vs. 0.74 ± 0.08; P < .0001), but not RM markedly decreased the relationship between age and PPc. On product of coefficient mediation analysis, whether assessed in men or in women, in those participants aged <50 years, independent of several confounders and mean arterial pressure, Pb (P < .005), but not Pf contributed to age-related increases in PPc. In contrast, in those participants aged ≥50 years, independent of several confounders and mean arterial pressure, Pb (P < .005) and Pf (P < .01) contributed to age-related increases in PPc, and Pb effects were markedly diminished by adjustments for Pf (0.26 ± 0.002 vs. 0.52 ± 0.003 mm Hg per year, P < .0001 for comparison). In conclusion, independent of the effects of antihypertensive therapy, aortic backward waves contribute to age-related increases in aortic PPc across the adult lifespan, but at an older age, this effect may be attributed in part to the impact of forward on backward wave pressures. Copyright © 2017 American Society of

  14. The relative contribution of waves, tides, and nontidal residuals to extreme total water levels on U.S. West Coast sandy beaches

    NASA Astrophysics Data System (ADS)

    Serafin, Katherine A.; Ruggiero, Peter; Stockdon, Hilary F.

    2017-02-01

    To better understand how individual processes combine to cause flooding and erosion events, we investigate the relative contribution of tides, waves, and nontidal residuals to extreme total water levels (TWLs) at the shoreline of U.S. West Coast sandy beaches. Extreme TWLs, defined as the observed annual maximum event and the simulated 100 year return level event, peak in Washington, and are on average larger in Washington and Oregon than in California. The relative contribution of wave-induced and still water levels (SWL) to the 100 year TWL event is similar to that of the annual maximum event; however, the contribution of storm surge to the SWL doubles across events. Understanding the regional variability of TWLs will lead to a better understanding of how sea level rise, changes in storminess, and possible changes in the frequency of major El Niños may impact future coastal flooding and erosion along the U.S. West Coast and elsewhere.

  15. Dissociating the contributions of slow-wave sleep and rapid eye movement sleep to emotional item and source memory.

    PubMed

    Groch, S; Zinke, K; Wilhelm, I; Born, J

    2015-07-01

    Sleep benefits the consolidation of emotional memories, and this influence is commonly attributed to the rapid eye movement (REM) stage of sleep. However, the contributions of sleep stages to memory for an emotional episode may differ for the event per se (i.e., item memory), and the context in which it occurred (source memory). Here, we examined the effects of slow wave sleep (SWS) and REM sleep on the consolidation of emotionally negative and neutral item (picture recognition) and source memory (recall of picture-location and picture-frame color association) in humans. In Study 1, the participants (n=18) learned 48 negative and 48 neutral pictures which were presented at specific locations and preceded by colored frames that had to be associated with the picture. In a within-subject design, learning was either followed by a 3-h early-night SWS-rich or by a late-night REM sleep-rich retention interval, then retrieval was tested. Only after REM-rich sleep, and not after SWS-rich sleep, was there a significant emotional enhancement, i.e., a significantly superior retention of emotional over neutral pictures. On the other hand, after SWS-rich sleep the retention of picture-frame color associations was better than after REM-rich sleep. However, this benefit was observed only for neutral pictures; and it was completely absent for the emotional pictures. To examine whether this absent benefit reflected a suppressive effect of emotionality on associations of minor task relevance, in Study 2 we manipulated the relevance of the picture-frame color association by combining it with information about monetary reward, following otherwise comparable procedures. Here, rewarded picture-frame color associations were equally well retained over SWS-rich early sleep no matter if the frames were associated with emotional or neutral pictures. Results are consistent with the view that REM sleep favors the emotional enhancement of item memory whereas SWS appears to contribute primarily

  16. Kinetic analysis of spin current contribution to spectrum of electromagnetic waves in spin-1/2 plasma. II. Dispersion dependencies

    NASA Astrophysics Data System (ADS)

    Andreev, Pavel A.

    2017-02-01

    The dielectric permeability tensor for spin polarized plasmas derived in terms of the spin-1/2 quantum kinetic model in six-dimensional phase space obtained in Part I of this work is applied for the study of spectra of high-frequency transverse and transverse-longitudinal waves propagating perpendicular to the external magnetic field. Cyclotron waves are studied in consideration of waves with the electric field directed parallel to the external magnetic field. It is found that the separate spin evolution modifies the spectrum of cyclotron waves. These modifications increase with the increase in spin polarization and the number of the cyclotron resonance. Spin dynamics gives a considerable modification of spectra even if the anomalous part of electron magnetic moment is not included in the model. The account of anomalous magnetic moment leads to a fine structure of each cyclotron resonance. So, each cyclotron resonance splits into three waves. Details of this spectrum and its changes with the change of spin polarization are studied for the first and second cyclotron waves. A cyclotron resonance existing at ω≈0.001 | Ωe| due to the anomalous magnetic moment is also described, where | Ωe| is the cyclotron frequency. The ordinary waves do not have any considerable modification. The electrostatic and electromagnetic Berstein modes are studied during the analysis of waves propagating perpendicular to the external magnetic field with the electric field perturbation directed perpendicular to the external field. A modification of the oscillatory structure caused by the equilibrium spin polarization is found in both regimes. Similar modification is found for the extraordinary wave spectrum.

  17. [Contribution of atrial activation to the segment of the typical atrial flutter wave: an electro-anatomic insight into the electrocardiogram morphology].

    PubMed

    Wang, Jun; Chen, Minglong; Yang, Bing; Ju, Weizhu; Zhang, Fengxiang; Yang, Gang; Li, Mingfang; Cao, Kejiang

    2015-07-01

    To investigate how the intra-cardiac activation was translates into the characterized flutter wave in patients with cavatricuspid isthmus-dependent counter-clockwise atrial flutter (CTI-AFL). A total of 15 hospitalized CTI-AFL patients (mean age: (60 ± 14) years old, 1 female) from October 2012 to February 2014 were enrolled in the study. The activation map was re-constructed during AFL rhythm for left atrium and right atrium using 3-dimensional mapping system. The flutter wave in surface electrocardiogram was analyzed in combination with the intra-cardiac activation. The mean left ventricular ejection fraction was (60.8 ± 6.6)%, and the left atrial diameter was (39.0 ± 3.4) mm. The mean tachycardia cycle length was (220 ± 24) ms. The activation map was completed in all cases. In inferior leads, the flutter wave was divided into three parts: slowly downward part, sharp downward part and the terminal positive part. The three parts corresponded to the fixed activation part of the macro-reentry. The distinctive flutter wave of CTI-AFL was determined by the unique macro-reentry activation in the right atrium. The activation of left atrium contributes to the downward part of the wave.

  18. Evaluation of wave runup predictions from numerical and parametric models

    USGS Publications Warehouse

    Stockdon, Hilary F.; Thompson, David M.; Plant, Nathaniel G.; Long, Joseph W.

    2014-01-01

    Wave runup during storms is a primary driver of coastal evolution, including shoreline and dune erosion and barrier island overwash. Runup and its components, setup and swash, can be predicted from a parameterized model that was developed by comparing runup observations to offshore wave height, wave period, and local beach slope. Because observations during extreme storms are often unavailable, a numerical model is used to simulate the storm-driven runup to compare to the parameterized model and then develop an approach to improve the accuracy of the parameterization. Numerically simulated and parameterized runup were compared to observations to evaluate model accuracies. The analysis demonstrated that setup was accurately predicted by both the parameterized model and numerical simulations. Infragravity swash heights were most accurately predicted by the parameterized model. The numerical model suffered from bias and gain errors that depended on whether a one-dimensional or two-dimensional spatial domain was used. Nonetheless, all of the predictions were significantly correlated to the observations, implying that the systematic errors can be corrected. The numerical simulations did not resolve the incident-band swash motions, as expected, and the parameterized model performed best at predicting incident-band swash heights. An assimilated prediction using a weighted average of the parameterized model and the numerical simulations resulted in a reduction in prediction error variance. Finally, the numerical simulations were extended to include storm conditions that have not been previously observed. These results indicated that the parameterized predictions of setup may need modification for extreme conditions; numerical simulations can be used to extend the validity of the parameterized predictions of infragravity swash; and numerical simulations systematically underpredict incident swash, which is relatively unimportant under extreme conditions.

  19. THz generation by two-color femtosecond filaments with complex polarization states: four-wave mixing versus photocurrent contributions

    NASA Astrophysics Data System (ADS)

    Fedorov, V. Yu; Koulouklidis, A. D.; Tzortzakis, S.

    2017-01-01

    Two-color filamenation in gases is known to produce intense and broadband THz radiation. There are two physical mechanisms responsible for the THz generation in this scheme: four-wave mixing and emission from the induced plasma currents. The case when the main and second harmonic are linearly polarized is well studied including the impact from each of the above mechanisms. However, for the cases when the two-color fields have complex polarization states the role of the four-wave mixing and plasma mechanisms in the formation of the THz polarization is still under-explored. Here we use both the four-wave mixing and photocurrent models in order to consider the THz generation by two-color fields with arbitrary polarizations. We show that under specific polarizations of the two-color field components it is possible to determine which of the mechanisms is responsible for the THz polarization formation.

  20. Contribution of stress wave and cavitation bubble in evaluation of cell-cell adhesion by femtosecond laser-induced impulse

    NASA Astrophysics Data System (ADS)

    Iino, Takanori; Li, Po-Lin; Wang, Wen-Zhe; Deng, Jia-Huei; Lu, Yun-Chang; Kao, Fu-Jen; Hosokawa, Yoichiroh

    2014-10-01

    When an intense femtosecond laser is focused in a cell culture medium, shock wave, stress wave, and cavitation bubble are generated at the laser focal point. Cell-cell adhesion can be broken at the cellular level by the impacts of these factors. We have applied this breaking of the adhesion to an estimation of the cell-cell adhesion strength. In this application, it is important to identify which of these factors is the dominant factor that breaks the adhesion. Here we investigated this issue using streptavidin-coated microbeads adhering to a biotin-coated substrate as a mimic of the cell-cell adhesion. The results indicated that the break was induced mainly by the stress wave, not by the impact of the cavitation bubble.

  1. Relative contributions of external SST forcing and internal atmospheric variability to July-August heat waves over the Yangtze River valley

    NASA Astrophysics Data System (ADS)

    Chen, Xiaolong; Zhou, Tianjun

    2017-08-01

    The Yangtze River valley (YRV), located in central-eastern China, has witnessed increased numbers of heat waves in the summer since 1951. Knowing what factors control and affect the interannual variability of heat waves, especially distinguishing the contributions of anomalous sea surface temperature (SST) forcings and those of internal modes of variability, is important to improving heat wave prediction. After evaluating 70 members of the atmospheric model intercomparison project (AMIP) experiments from the 25 models that participated in the coupled model intercomparison project phase 5 (CMIP5), 13 high-skill members (HSMs) are selected to estimate the SST-forced variability. The results show that approximately 2/3 of the total variability of the July-August heat waves in the YRV during 1979-2008 can be attributed to anomalous SST forcings, whereas the other 1/3 are due to internal variability. Within the SST-forced component, one-half of the influence is from the impact of the El Niño-Southern Oscillation (ENSO) and the other half is from non-ENSO related SST forcings, specifically, the SST anomalies in the North Pacific and the North Atlantic. Both the decaying El Niño and developing La Niña accompanied by a warm Indian Ocean and cold central Pacific, respectively, are favorable to hotter summers in the YRV because these patterns strengthen and extend the western North Pacific Subtropical High (WNPSH) westwards, for which the decaying ENSO plays a dominant role. The internal variability shows a circumglobal teleconnection in which Rossby waves propagate southeastwards over the Eurasian Continent and strengthen the WNPSH. Atmospheric model sensitivity experiments confirm that non-ENSO SST forcings can modulate the WNPSH and heat wave variability by projecting their influences onto the internal mode.

  2. A contribution to computer analysis of coupled-cavity traveling wave tubes. [design study for CTS satellite

    NASA Technical Reports Server (NTRS)

    Connolly, D. J.; Omalley, T. A.

    1977-01-01

    A flexible accurate large-signal computer program has been developed for the design of coupled-cavity traveling wave tubes. The program is written for a TSS-360 time sharing system. The beam is described by a disk model and the slow wave structure by a sequence of cavities or cells. The computational approach is arranged so that each cavity may have different geometrical or electrical parameters than its neighbors. This allows the program user to simulate a tube of almost arbitrary complexity. Input and output couplers, severs, complicated velocity tapers, and other features peculiar to one or a few cavities may be modeled by a correct choice of input data. The beam-wave interaction is handled by a new approach in which the RF fields are expanded in solutions to the TM wave equation retaining all significant space harmonics. The program was used to perform a design study of the TWT developed for the CTS satellite. Good agreement was obtained between the predictions of the program and the measured performance of the flight tube. The internal check on power balance was satisfied within plus or minus 0.2 per cent of input beam power.

  3. Observations of Wave-Orbital Ripple Dynamics at Fire Island, New York

    NASA Astrophysics Data System (ADS)

    Harrison, S. R.

    2016-12-01

    Observations of evolving seabed morphology were collected concurrent with hydrodynamic and wave measurements over a 3-month winter deployment at Fire Island, New York as part of an ongoing regional study to better understand cross-shore sediment transport processes. In order to observe wave-orbital scale ripple dynamics, an active source of cross-shore bedload transport, instruments were deployed at locations between 1-2 km offshore in 12-15 m water depth along the inner-shelf where wave-velocity skewness and asymmetry are thought to influence ripple migration. Flows throughout the water column were measured, with emphasis on the bottom 50 cm, in order to capture interactions between wave-driven flows and the rippled seabed. Ripple geometry and migration were computed from rotary sonar images and consisted of mainly linear ripples (0.7 m wavelength and 0.1 m height) with slight shoreward asymmetry and an estimated net shoreward transport rate of 1.1 m³/yr per alongshore meter. Nearly all ripple migration events were shoreward despite a high occurrence of negative skewness events measured at the freestream above the wave-boundary layer. Convergent-beam pulse-coherent Doppler current profiler data showed wave- velocity skewness and near-bed mean flows from ripple vortex entrainment to vary both vertically and horizontally around the ripple. Skewness was largest midway between the ripple troughs and crests at approximately 3-5 cm above the elevation of the adjacent ripple crest. Skewness was minimal in the bottom 5-8 cm and appeared to be converted to rectified mean-flow jets directed toward the ripple crests. Skewness in the freestream poorly indicated the near-bed velocity where the majority of the sediment transport occurred. Most of the negative skewness was associated with infragravity motion. Removing the infragravity component resulted in positive skewness and a much better indicator of onshore ripple migration.

  4. Wave transformation on a sub-horizontal shore platform, Tatapouri, North Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Ogawa, H.; Dickson, M. E.; Kench, P. S.

    2011-09-01

    Waves are generally considered to be an important control on shore platform evolution but there have been very few detailed studies of wave dynamics on rocky coasts. This study provides a detailed description of wave transformation processes across a shore platform near Gisborne, New Zealand. A field experiment was conducted on an intertidal, 250 m-wide platform that is characterised by a sharp seaward edge. Mean platform elevation is 0.7 m below mean sea-level (MSL) and platform gradient is 0.3°. Four nearly equally spaced pressure gauges were deployed over a 24-h period during fair-weather swell conditions characterised by a mean wave height of 0.4-0.5 m and wave period of 7 s. Wave energy at the seaward edge of the platform was dominated by incident swell waves with peak frequency at 0.09 Hz. At all tidal stages waves broke at the seaward edge of the platform, but changing tidal stage exerted a strong control on the rate of wave energy attenuation across the platform. The relative importance of waves at wind-wave frequencies increased in the centre of the platform as the tidal stage and water level increased, whereas infragravity waves became dominant toward the cliff toe. Three different hydrodynamic zones were distinguished across the shore platform; (i) a breaker zone close to the seaward edge; (ii) a propagation/shoaling zone in the central region of the platform; and (iii) a zone of energy dissipation across the inner part of the platform. The spatial dimensions of the three zones varied with changing tidal stage, enabling different wave processes to operate across different parts of the platform at different times. The experiment showed that wave-height attenuation is strongly controlled by tidal stage, ranging between 93% attenuation of wave height during the initial flooding stage to 44% attenuation at high tide. Wave height was found to be depth-limited, with the ratios of Hmax and Hm0 to water depth calculated as 0.7 and 0.4, respectively. The

  5. On the ultra-low frequency wave contributions to the relativistic electron flux dynamics in the outer Van Allen radiation belt

    NASA Astrophysics Data System (ADS)

    Dal Lago, A.; Marchezi, J. P.; Alves, L. R.; da Silva, L.; Dallaqua, R.; Medeiros, C.; Souza, V. M. C. E. S.; Rockenbach, M.; Vieira, L.; Mendes, O., Jr.; Sibeck, D. G.; Kanekal, S. G.; Kletzing, C.; Baker, D. N.; Wygant, J. R.

    2016-12-01

    Various physical processes can contribute to loss and acceleration of energetic electrons in the Earth's radiation belts. In the range of 1 mHz to 10 Hz, ultra-low frequency (ULF) waves are known to cause significant changes in the energetic particle flux in the radiation belts. On board the Van Allen Probes, the Relativistic Electron Proton Telescope (REPT) measures the relativistic electron flux in the outer radiation belts in the energy range from 1.8 MeV up to 20 MeV. We selected events that have significant electron flux dropouts, classified into two categories regarding the time elapsed between the outer radiation belt dropout and the refurbishing, namely events that time scale had taken (i) a few hours and, (ii) some days. This work aims to investigate the presence of ULF waves using the radial and azimuthal magnetic and electric field components recorded by the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS). The evaluation of the power spectral density of those components unravels the poloidal and toroidal characteristc of the rapid compressional waves. We discuss how these modes can contribute to modifications of the relativistic electron fluxes considering the (i) and (ii) cases.

  6. The contribution of ventricular apicobasal and transmural repolarization patterns to the development of the T wave body surface potentials in frogs (Rana temporaria) and pike (Esox lucius).

    PubMed

    Vaykshnorayte, Marina A; Azarov, Jan E; Tsvetkova, Alena S; Vityazev, Vladimir A; Ovechkin, Alexey O; Shmakov, Dmitry N

    2011-05-01

    The study aimed at the simultaneous determination of the transmural and apicobasal differences in the repolarization timing and the comparison of the contributions of these two repolarization gradients to the development of the body surface T wave potentials in animals with the single heart ventricle (fishes and amphibians). Unipolar potentials were measured on the body surface, epicardium and in the intramural (subepicardial, Epi; midmyocardial; and subendocardial, Endo) ventricular layers of 9 pike and 8 frogs. Activation times, repolarization times and activation-recovery intervals were determined. A transmural gradient in repolarization durations in frogs (Endo>Epi, P<0.024) corresponds to the gradient in repolarization times. No significant transmural difference in repolarization duration is observed in pike that produces a repolarization sequence from Endo to Epi (Endowave in spite of the opposite transmural repolarization patterns. The present study suggests that the apicobasal repolarization gradient provides the major contribution to the development of the T wave potentials on the body surface in pike and frogs.

  7. The Contribution of Environmental Siting and Permitting Requirements to the Cost of Energy for Wave Energy Devices

    SciTech Connect

    Copping, Andrea E.; Geerlofs, Simon H.; Hanna, Luke A.

    2014-06-01

    Responsible deployment of marine and hydrokinetic (MHK) devices in estuaries, coastal areas, and major rivers requires that biological resources and ecosystems be protected through siting and permitting (consenting) processes. Scoping appropriate deployment locations, collecting pre-installation (baseline) and post-installation data all add to the cost of developing MHK projects, and hence to the cost of energy. Under the direction of the U.S. Department of Energy, Pacific Northwest National Laboratory scientists have developed logic models that describe studies and processes for environmental siting and permitting. Each study and environmental permitting process has been assigned a cost derived from existing and proposed tidal, wave, and riverine MHK projects. Costs have been developed at the pilot scale and for commercial arrays for a surge wave energy converter

  8. Resonance vibrations of the Ross Ice Shelf and observations of persistent atmospheric waves

    NASA Astrophysics Data System (ADS)

    Godin, Oleg A.; Zabotin, Nikolay A.

    2016-10-01

    Recently reported lidar observations have revealed a persistent wave activity in the Antarctic middle and upper atmosphere that has no counterpart in observations at midlatitude and low-latitude locations. The unusual wave activity suggests a geographically specific source of atmospheric waves with periods of 3-10 h. Here we investigate theoretically the hypothesis that the unusual atmospheric wave activity in Antarctica is generated by the fundamental and low-order modes of vibrations of the Ross Ice Shelf (RIS). Simple models are developed to describe basic physical properties of resonant vibrations of large ice shelves and their coupling to the atmosphere. Dispersion relation of the long surface waves, which propagate in the floating ice sheet and are responsible for its low-order resonances, is found to be similar to the dispersion relation of infragravity waves in the ice-free ocean. The phase speed of the surface waves and the resonant frequencies determine the periods and wave vectors of atmospheric waves that are generated by the RIS resonant oscillations. The altitude-dependent vertical wavelengths and the periods of the acoustic-gravity waves in the atmosphere are shown to be sensitive to the physical parameters of the RIS, which can be difficult to measure by other means. Predicted properties of the atmospheric waves prove to be in a remarkable agreement with the key features of the observed persistent wave activity.

  9. Resonance Vibrations of the Ross Ice Shelf and Observations of Persistent Atmospheric Waves

    NASA Astrophysics Data System (ADS)

    Zabotin, N. A.; Godin, O. A.

    2016-12-01

    Recently reported lidar observations at McMurdo have revealed a persistent wave activity in the Antarctic middle and upper atmosphere that has no counterpart in observations at mid- and low-latitude locations [Chen et al., JGR Space Physics, 2016]. The unusual wave activity suggests a geographically specific source of atmospheric waves with periods of 3-10 hours. Here, we investigate theoretically the hypothesis that the unusual atmospheric wave activity in Antarctica is generated by the fundamental and low-order modes of vibrations of the Ross Ice Shelf (RIS). Simple models are developed to describe basic physical properties of resonant vibrations of large ice shelves and their coupling to the atmosphere. Dispersion relation of the long surface waves, which propagate in the floating ice sheet and are responsible for its low-order resonances, is found to be similar to the dispersion relation of infragravity waves in the ice-free ocean. The phase speed of the surface waves and the resonant frequencies determine the periods and wave vector of atmospheric waves that are generated by the RIS resonant oscillations. The altitude-dependent vertical wavelengths and the periods of the acoustic-gravity waves in the atmosphere are shown to be sensitive to the physical parameters of the RIS, which can be difficult to measure by other means. Predicted properties of the atmospheric waves prove to be in a remarkable agreement with the key features of the observed persistent wave activity.

  10. The relative contribution of waves, tides, and nontidal residuals to extreme total water levels on U.S. West Coast sandy beaches

    USGS Publications Warehouse

    Serafin, Katherine A.; Ruggiero, Peter; Stockdon, Hilary F.

    2017-01-01

    To better understand how individual processes combine to cause flooding and erosion events, we investigate the relative contribution of tides, waves, and nontidal residuals to extreme total water levels (TWLs) at the shoreline of U.S. West Coast sandy beaches. Extreme TWLs, defined as the observed annual maximum event and the simulated 100 year return level event, peak in Washington, and are on average larger in Washington and Oregon than in California. The relative contribution of wave-induced and still water levels (SWL) to the 100 year TWL event is similar to that of the annual maximum event; however, the contribution of storm surge to the SWL doubles across events. Understanding the regional variability of TWLs will lead to a better understanding of how sea level rise, changes in storminess, and possible changes in the frequency of major El Niños may impact future coastal flooding and erosion along the U.S. West Coast and elsewhere.

  11. Experimental verification of the vaporization's contribution to the shock waves generated by underwater electrical wire explosion under micro-second timescale pulsed discharge

    NASA Astrophysics Data System (ADS)

    Han, Ruoyu; Zhou, Haibin; Wu, Jiawei; Clayson, Thomas; Ren, Hang; Wu, Jian; Zhang, Yongmin; Qiu, Aici

    2017-06-01

    This paper studies pressure waves generated by exploding a copper wire in a water medium, demonstrating the significant contribution of the vaporization process to the formation of shock waves. A test platform including a pulsed current source, wire load, chamber, and diagnostic system was developed to study the shock wave and optical emission characteristics during the explosion process. In the experiment, a total of 500 J was discharged through a copper wire load 0.2 mm in diameter and 4 cm in length. A water gap was installed adjacent to the load so that the current was diverted away from the load after breakdown occurred across the water gap. This allows the electrical energy injection into the load to be interrupted at different times and at different stages of the wire explosion process. Experimental results indicate that when the load was bypassed before the beginning of the vaporization phase, the measured peak pressure was less than 2.5 MPa. By contrast, the peak pressure increased significantly to over 6.5 MPa when the water gap broke down after the beginning of the vaporization phase. It was also found that when bypassing the load after the voltage peak, similar shock waves were produced to those from a non-bypassed load. However, the total optical emission of these bypassed loads was at least an order of magnitude smaller. These results clearly demonstrate that the vaporization process is vital to the formation of shock waves and the energy deposited after the voltage collapse may only have a limited effect.

  12. Autochthonous intestinal bacteria and coprophagy: a possible contribution to the ontogeny and rhythmicity of slow wave sleep in mammals.

    PubMed

    Brown, R; Price, R J; King, M G; Husband, A J

    1988-07-01

    A sleep-inducing substance Factor S (FS) has been identified as a member of the muramyl peptide family of molecules which constitute the cell wall of bacteria. FS-like substances are unable to be synthesized by mammals suggesting that the symbiotic bacteria of the gastrointestinal tract are a prime source of FS. The present paper considers the relationship between the ontogenesis of Slow Wave Sleep (SWS) and the colonization of the intestine with strictly anaerobic bacteria. The practice of coprophagy in rats and rabbits is considered as an efficient method of FS ingestion during the sleep period.

  13. Contributions by Wave Propagation Laboratory to EPA's (Environmental Protection Agency's) complex-terrain model-development project. Technical memo

    SciTech Connect

    Eberhard, W.L.

    1986-12-01

    The Wave Propagation Laboratory (WPL) participated in the Environmental Protection Agency's Complex Terrain Model Development Project, whose objective is development of numerical air-quality models valid in complex terrain. Particular attention was given to impaction of elevated plumes on high terrain during stable (nocturnal) conditions. WPL operated a plume-mapping lidar, acoustic sounders (some with Doppler capability), sonic anemometers, a tethered sonde, and crosswind optical anemometers. Measurements were usually displayed in real time for experimental guidance and later processed with quality assurance for quantitative analysis. A synopsis of data acquisition and archiving is given for each experiment, including a review of the results of scientific analyses already completed.

  14. Intermolecular shielding contributions studied by modeling the 13C chemical-shift tensors of organic single crystals with plane waves

    PubMed Central

    Johnston, Jessica C.; Iuliucci, Robbie J.; Facelli, Julio C.; Fitzgerald, George; Mueller, Karl T.

    2009-01-01

    In order to predict accurately the chemical shift of NMR-active nuclei in solid phase systems, magnetic shielding calculations must be capable of considering the complete lattice structure. Here we assess the accuracy of the density functional theory gauge-including projector augmented wave method, which uses pseudopotentials to approximate the nodal structure of the core electrons, to determine the magnetic properties of crystals by predicting the full chemical-shift tensors of all 13C nuclides in 14 organic single crystals from which experimental tensors have previously been reported. Plane-wave methods use periodic boundary conditions to incorporate the lattice structure, providing a substantial improvement for modeling the chemical shifts in hydrogen-bonded systems. Principal tensor components can now be predicted to an accuracy that approaches the typical experimental uncertainty. Moreover, methods that include the full solid-phase structure enable geometry optimizations to be performed on the input structures prior to calculation of the shielding. Improvement after optimization is noted here even when neutron diffraction data are used for determining the initial structures. After geometry optimization, the isotropic shift can be predicted to within 1 ppm. PMID:19831448

  15. Modeling the contributions of Ca2+ flows to spontaneous Ca2+ oscillations and cortical spreading depression-triggered Ca2+ waves in astrocyte networks.

    PubMed

    Li, Bing; Chen, Shangbin; Zeng, Shaoqun; Luo, Qingming; Li, Pengcheng

    2012-01-01

    Astrocytes participate in brain functions through Ca(2+) signals, including Ca(2+) waves and Ca(2+) oscillations. Currently the mechanisms of Ca(2+) signals in astrocytes are not fully clear. Here, we present a computational model to specify the relative contributions of different Ca(2+) flows between the extracellular space, the cytoplasm and the endoplasmic reticulum of astrocytes to the generation of spontaneous Ca(2+) oscillations (CASs) and cortical spreading depression (CSD)-triggered Ca(2+) waves (CSDCWs) in a one-dimensional astrocyte network. This model shows that CASs depend primarily on Ca(2+) released from internal stores of astrocytes, and CSDCWs depend mainly on voltage-gated Ca(2+) influx. It predicts that voltage-gated Ca(2+) influx is able to generate Ca(2+) waves during the process of CSD even after depleting internal Ca(2+) stores. Furthermore, the model investigates the interactions between CASs and CSDCWs and shows that the pass of CSDCWs suppresses CASs, whereas CASs do not prevent the generation of CSDCWs. This work quantitatively analyzes the generation of astrocytic Ca(2+) signals and indicates different mechanisms underlying CSDCWs and non-CSDCWs. Research on the different types of Ca(2+) signals might help to understand the ways by which astrocytes participate in information processing in brain functions.

  16. The Contribution of Environmental Siting and Permitting Requirements to the Cost of Energy for Oscillating Water Column Wave Energy Devices

    SciTech Connect

    Copping, Andrea E.; Geerlofs, Simon H.; Hanna, Luke A.

    2013-09-01

    Responsible deployment of marine and hydrokinetic (MHK) devices in estuaries, coastal areas, and major rivers requires that biological resources and ecosystems be protected through siting and permitting (consenting) processes. Scoping appropriate deployment locations, collecting pre-installation (baseline) and post-installation data all add to the cost of developing MHK projects, and hence to the cost of energy. Under the direction of the U.S. Department of Energy, Pacific Northwest National Laboratory scientists have developed logic models that describe studies and processes for environmental siting and permitting. Each study and environmental permitting process has been assigned a cost derived from existing and proposed tidal, wave, and riverine MHK projects, as well as expert opinion of marine environmental research professionals. Cost estimates have been developed at the pilot and commercial scale. The reference model described in this document is an oscillating water column device deployed in Northern California at approximately 50 meters water depth.

  17. Transcriptome Analysis Reveals the Contribution of Thermal and the Specific Effects in Cellular Response to Millimeter Wave Exposure

    PubMed Central

    Habauzit, Denis; Le Quément, Catherine; Zhadobov, Maxim; Martin, Catherine; Aubry, Marc; Sauleau, Ronan; Le Dréan, Yves

    2014-01-01

    Radiofrequency radiations constitute a new form of environmental pollution. Among them, millimeter waves (MMW) will be widely used in the near future for high speed communication systems. This study aimed therefore to evaluate the biocompatibility of MMW at 60 GHz. For this purpose, we used a whole gene expression approach to assess the effect of acute 60 GHz exposure on primary cultures of human keratinocytes. Controls were performed to dissociate the electromagnetic from the thermal effect of MMW. Microarray data were validated by RT-PCR, in order to ensure the reproducibility of the results. MMW exposure at 20 mW/cm2, corresponding to the maximum incident power density authorized for public use (local exposure averaged over 1 cm2), led to an increase of temperature and to a strong modification of keratinocyte gene expression (665 genes differentially expressed). Nevertheless, when temperature is artificially maintained constant, no modification in gene expression was observed after MMW exposure. However, a heat shock control did not mimic exactly the MMW effect, suggesting a slight but specific electromagnetic effect under hyperthermia conditions (34 genes differentially expressed). By RT-PCR, we analyzed the time course of the transcriptomic response and 7 genes have been validated as differentially expressed: ADAMTS6, NOG, IL7R, FADD, JUNB, SNAI2 and HIST1H1A. Our data evidenced a specific electromagnetic effect of MMW, which is associated to the cellular response to hyperthermia. This study raises the question of co-exposures associating radiofrequencies and other environmental sources of cellular stress. PMID:25302706

  18. Application of a Coupled Ocean Wave Sediment Transport Modeling System to Investigate Morphological Changes during Hurricane Sandy.

    NASA Astrophysics Data System (ADS)

    Warner, J. C.; List, J. H.; Safak, I.; Liste, M.; Schwab, W. C.

    2016-02-01

    Barrier islands provide a means of defense against large storm impacts. While a vast majority of studies focus on the subaeial areas of barrier islands, a significant component of barrier island geologic framework is submerged. Understanding how barrier islands respond to storms requires a thorough investigation of the complete inner-shelf to surf-zone region. Hurricane Sandy impacted the US east coast in 2012 and was one of the most destructive storms in US history with impacts including flooding, coastal erosion, dune overtopping, breaching. Here we evaluate the oceanographic processes and morphological changes during Hurricane Sandy on Fire Island, NY and the adjacent inner continental shelf using geophysical observations and numerical modeling. Geologic investigations of the seafloor in 2011 and 2014 demonstrate changes of seafloor morphology and modern sediment thickness revealing up to 450 m of lateral movement of sedimentary features and deposition at depths up to 30 m. Physical processes responsible for these morphological changes were investigated using a coupled ocean-wave-sediment modeling system (COAWST) with grid refinement to simulate oceanographic conditions on a regional 5-km grid along the entire US east coast, with increased resolution of 700 m in the NY bight, 100 m along Fire Island, and 5 m at the breach formed due to Hurricane Sandy. Model results identify maximum surge of up to 3 m, surface currents up to 2 m/s, and wave heights up to 8 m. Sediment redistribution along Fire Island showed erosional patterns consistent with geologic observations. Modeling advancements using an infragravity wave component (InWave) identify key aspects of barrier island response during the storm. Total storm water levels along Fire Island are shown to be a combination of surge, tidal, and infragravity signal. During the peak of the storm total water level and wave action was able to create a breach. Models results are compared to field observations.

  19. Observations of Wave, Current, and Wave-Current Induced Sediment Transport in the Inlet of a Small, Shallow Estuary

    NASA Astrophysics Data System (ADS)

    Harvey, M.; Giddings, S. N.; Pawlak, G. R.

    2016-02-01

    The coupling of the hydrodynamics and morphodynamics in a tidal inlet are examined to understand the relative importance of waves, wave-current interactions, and mean currents in sediment transport processes in a low-inflow estuary. This study uses data collected in Los Peñasquitos Lagoon (LPL) in San Diego, CA from Winter 2014 to Winter 2015. LPL is a small, shallow, low-inflow estuary whose mouth is located in the middle of a long, sandy beach in Southern California. Waves and currents drive sand transport from the beach into the mouth of the lagoon where accreting sand forms a sill that intermittently limits or blocks the lagoon's exchange with the ocean. The sill modulates the water level in the lagoon through hydraulic control and regulates the amount of wave energy able to propagate into the lagoon due to depth-limited breaking. Infragravity period waves (>30 second) propagate furthest into the lagoon. The offshore wave field, the tidal phase, and the sill height influence the waves and currents in the lagoon and thus influence the wave-induced and wave-current induced bed stress. The bed stress dictates the amount of sand that can be transported into the lagoon through suspension and bed load. Acoustic Doppler velocimeters (ADVs), deployed during large wave and surge events, are used to measure the wave orbital velocities, currents, turbulence, and bed shear. Optical backscatter sensors, deployed alongside the ADVs, are used to quantify the suspended sediment fluxes during the extreme events. A time-lapse camera directed at the mouth and bathymetric surveys are used to quantify the net sediment movement in the lagoon.

  20. Gravitational waves

    NASA Astrophysics Data System (ADS)

    Trautman, Andrzej

    2017-07-01

    Historical remarks on early theoretical work on the subject. Very early on, Einstein introduced the notion of gravitational waves, but later became convinced that they did not exist as a physical phenomenon. Exact solutions of Einstein’s equations representing waves were found by a number of authors, contributing to their final acceptance as part of physics.

  1. numerical broadband modelling of ocean waves, from 1 to 300 s: implications for seismic wave sources and wave climate studies

    NASA Astrophysics Data System (ADS)

    Ardhuin, F.; Stutzmann, E.; Gualtieri, L.

    2014-12-01

    Ocean waves provide most of the energy that feeds the continuous vertical oscillations of the solid Earth. Three period bands are usually identified. The hum contains periods longer than 30 s, and the primary and secondary peaks are usually centered around 15 and 5 s, respectively. Motions in all three bands are recorded everywhere on our planet and can provide information on both the solid Earth structure and the ocean wave climate over the past century. Here we describe recent efforts to extend the range of validity of ocean wave models to cover periods from 1 to 300 s (Ardhuin et al., Ocean Modelling 2014), and the resulting public database of ocean wave spectra (http://tinyurl.com/iowagaftp/HINDCAST/ ). We particularly discuss the sources of uncertainty for building a numerical model of acoustic and seismic noise on this knowledge of ocean wave spectra. For acoustic periods shorter than 3 seconds, the main uncertainties are the directional distributions of wave energy (Ardhuin et al., J. Acoust. Soc. Amer. 2013). For intermediate periods (3 to 25 s), the propagation properties of seismic waves are probably the main source of error when producing synthetic spectra of Rayleigh waves (Ardhuin et al. JGR 2011, Stutzmann et al. GJI 2012). For the longer periods (25 to 300 s), the poor knowledge of the bottom topography details may be the limiting factor for estimating hum spectra or inverting hum measurements in properties of the infragravity wave field. All in all, the space and time variability of recorded seismic and acoustic spectra is generally well reproduced in the band 3 to 300 s, and work on shorter periods is under way. This direct model can be used to search for missing noise sources, such as wave scattering in the marginal ice zone, find events relevant for solid earth studies (e.g. Obrebski et al. JGR 2013) or invert wave climate properties from microseismic records. The figure shows measured spectra of the vertical ground acceleration, and modeled

  2. Wave Dissipation and Balance - NOPP Wave Project

    DTIC Science & Technology

    2014-09-30

    processes that affect wind-generated ocean gravity waves. The various dissipative processes that contribute to the spectral wave evolution are isolated...over mature ocean surface wave spectra. J. Phys. Oceanogr., 34:3345–2358, 2004. K. Hasselmann. On the non-linear energy transfer in a gravity wave...P. Giovanangeli. Air flow structure over short- gravity breaking water waves. Boundary-Layer Meteorol., 126:477–705, 2008. doi: 10.1007/s10546-007

  3. The Fractional Free Volume of the Sorbed Vapor in Modeling the Viscoelastic Contribution to Polymer-Coated Surface Acoustic Wave Vapor Sensor Responses

    SciTech Connect

    Grate, Jay W. ); Zellers, Edward T.

    1999-12-01

    Surface acoustic wave (SAW) vapor sensors with polymeric sorbent layers can respond to vapors based on mass-loading and modulus decreases of the polymer film. The modulus changes are associated with volume changes that occur as vapor is sorbed by the film. A factor based on the fractional free volume of the vapor as a liquid has been incorporated into a model for the contribution of swelling-induced modulus changes to observed SAW vapor sensor responses. In this model, it is not the entire volume added to the film by the vapor molecules that causes the modulus to decrease. The free volume effect is calibrated from thermal expansion experiments. The amplification of the SAW vapor sensor response due to modulus effects that are predicted by this model have been compared to amplification factors determined by comparing the responses of polymer-coated SAW vapor sensors with the responses of similarly-coated thickness shear mode (TSM) vapor sensors, the latter being gravimetric. Results for six vapors on each of two polymers, poly(isobutylene) and poly(epichlorohydrin), were examined. The model correctly predicts amplification factors are related to the specific volume of the vapor as a liquid. The fractional free volume factor provides a physically meaningful addition to the model and is consistent with conventional polymer physics treatments of the effects of temperature and plasticization on polymer modulus.

  4. Positive dependence of thermal conductivity on temperature in GeTe/Bi2Te3 superlattices: the contribution of electronic and particle wave lattice thermal conductivity

    NASA Astrophysics Data System (ADS)

    Tong, H.; Lan, F.; Liu, Y. J.; Zhou, L. J.; Wang, X. J.; He, Q.; Wang, K. Z.; Miao, X. S.

    2017-09-01

    Temperature-dependent thermal conductivity of phase-change material, GeTe/Bi2Te3 superlattices, has been investigated in the temperature range of 40-300 K. We have found that thermal conductivity increases with increasing temperature, which is contrary to the common results indicated by other works. In this paper, two possible mechanisms are suggested for this result. One is that the thermal conductivity is affected by the thermal boundary resistance at the interfaces between layers, and the other considers the factor of electronic thermal conductivity in the partially coherent regime which is based on the very wave-particle duality of phonons. Finally, the periodic thickness dependence of the thermal conductivity in GeTe/Bi2Te3 superlattices have been measured at room temperature, and the results indicate the main contribution of electron in the total thermal conductivity and the partially coherent regime of phonon. Thus we believe that the second explanation is more reasonable. The work here deepens the understanding of basic mechanisms of thermal transport in phase-change superlattices, and is instructive in modeling and simulation of phase change memories.

  5. Wave-driven Hydrodynamics for Different Reef Geometries and Roughness Scenarios

    NASA Astrophysics Data System (ADS)

    Franklin, G. L.; Marino-Tapia, I.; Torres-Freyermuth, A.

    2013-05-01

    In fringing reef systems where a shallow lagoon is present behind the reef crest, wave breaking appears to dominate circulation, controlling numerous key processes such as the transport and dispersion of larvae, nutrients and sediments. Despite their importance, there is a need for more detailed knowledge on the hydrodynamic processes that take place within the surf zone of these systems and the effects different combinations of geometries and roughness have on them. The present study focuses on the use of two-dimensional (2DV) numerical model simulations and data obtained during a field campaign in Puerto Morelos, Quintana Roo, Mexico to better understand the detailed surf zone processes that occur over a fringing reef. The model used is Cornell Breaking Wave and Structures (COBRAS), which solves Reynolds-Averaged Navier-Stokes (RANS) equations. Reef geometries implemented in the model include a reef flat and two different reef crests. The effect of roughness on wave setup, radiation stress, mean flows, and cross-shore spectral evolution for the model results was studied using different roughness coefficients (Nikuradse) and a bathymetric profile obtained in the field using the bottom track option of an Acoustic Doppler Current Profiler. Field data were also analysed for the configuration and roughness of Puerto Morelos. Model results reveal that for all profiles wave setup increased significantly (~22%) with increasing bed roughness, in agreement with previous findings for sandy beaches.For all wave heights and periods studied, increasing roughness also affected spectral wave evolution across the reef, with a significant reduction in energy, particularly at infragravity frequencies. The presence of a reef crest in the profile resulted in differences in behaviour at infragravity frequencies. For example, preliminary results suggest that there is a shift towards higher frequencies as waves progress into the lagoon when a crest is present, something that does not

  6. Resonance vibrations of the Ross Ice Shelf cause persistent atmospheric waves

    NASA Astrophysics Data System (ADS)

    Godin, Oleg; Zabotin, Nikolay

    2017-04-01

    Recently reported lidar observations have revealed a persistent wave activity in the Antarctic middle and upper atmosphere that has no counterpart in observations at mid- and low-latitude locations [Chen et al., 2016]. The unusual wave activity suggests a geographically specific source of atmospheric waves with periods of 3-10 hours. Here, we investigate theoretically the hypothesis that the unusual atmospheric wave activity in Antarctica is generated by the fundamental and low-order modes of vibrations of the Ross Ice Shelf (RIS). Simple models are developed to describe basic physical properties of resonant vibrations of large ice shelves and their coupling to the atmosphere. Dispersion relation of the long surface waves, which propagate in the floating ice sheet and are responsible for its low-order resonances, is found to be similar to the dispersion relation of infragravity waves in the ice-free ocean. The phase speed of the surface waves and the resonant frequencies determine the periods and wave vectors of atmospheric waves that are generated by the RIS resonant oscillations. The altitude-dependent vertical wavelengths and the periods of the acoustic-gravity waves in the atmosphere are shown to be sensitive to the physical parameters of the RIS, which can be difficult to measure by other means. Predicted properties of the atmospheric waves prove to be in a remarkable agreement with the key features of the observed persistent wave activity], including frequency band, vertical wavelength range, and weak variation of the vertical wavelength with the height. The present work is a motivation for in-depth studies of coupling between vibrations of ice shelves and waves in the upper and middle atmosphere at high latitudes.

  7. MHD Model Estimates of the Contribution of Driven, Linear, Non-Plane Wave Dissipation to Chromospheric Heating Using a Complete Electrical Conductivity Tensor

    NASA Astrophysics Data System (ADS)

    Goodman, M. L.

    2008-12-01

    given heating rate. At magnetic field strengths < 400 G, this value of FCh is achieved only at higher frequencies corresponding to solutions that violate the linear approximation. For the similar special case of Bz = 200 G, Bx1=140 G, and 50 ≤ Bcond(0) ≤ 1500 G the range of the maximum allowed driver frequency that is consistent with the linear approximation is 100.25 ≥ ν ≥ 92.5 mHz. The corresponding range of FCh is 2 × 106 ≤ FCh ≤ 5.4 × 107 ergs-cm-2-sec-1. This raises the possibility that linear MHD waves with periods ~ 10 seconds might make a major contribution to chromospheric heating in regions where the photospheric magnetic field strength is moderate to high. These results support the proposition of Goodman (e.g. Goodman 2000, ApJ, 533, 501; Goodman 2004, A&A, 424, 691; Kazeminezhad & Goodman 2006, ApJ, 166, 613) that the onset of electron and proton magnetization near the local temperature minimum, and their rapid increase with height causes the rate of proton Pedersen current dissipation to rapidly increase by orders of magnitude with height, creating and maintaining the solar chromosphere, and the chromospheres of solar type stars. This mechanism is not restricted to linear waves. It operates on any current generating MHD process. This work was supported by Grant ATM 0650443 from the National Science Foundation to the West Virginia High Technology Consortium Foundation.

  8. On the long waves disturbing ship operations in Ferrol (Spain)

    NASA Astrophysics Data System (ADS)

    Lopez, Mario; Iglesias, Gregorio

    2013-04-01

    Long waves may cause significant disturbances for port operations. This paper is concerned with the long wave problems at Ferrol, a port in NW Spain. Long wave periods range between a few tens of seconds to several hours. In shallow water their wavelengths are on the order of hundreds of meters to kilometres. As a result, these waves can match the natural periods of oscillation of semi-enclosed bodies of water like gulfs, bays, fiords, or harbours, resulting in resonant oscillations. During resonance, the vertical displacement of the free surface increases until the energy input is balanced by losses due to friction, flow separation, boundary absorption, and radiation from the mouth (Okihiro et al., 1993). The induced horizontal displacements of the water mass are responsible for the large movements on ships. The non-linear interaction of long and wind waves and the direct atmospheric forcing are the main sources of long waves in the ocean. In the first case, the long waves are also known as infragravity waves and tend to have relatively small periods. In the second case, the atmospheric forced long waves, different mechanisms have been used to explain their generation. Atmospheric disturbances passing over the continental shelf (Sepic et al., 2008) or wind convection cells (de Jong and Battjes, 2004) are two of the causes for these 'meteorological' waves. Whatever their cause, they tend to have relatively large periods and, therefore, a significant potential to excite the first modes of oscillation of harbours. In addition, other different forcing mechanisms can generate long waves, including submerged landslides (Cecioni and Bellotti, 2010) and seisms (Candella et al., 2008). Disturbances to load and unload operations have been reported from 2005 at the Exterior Port of Ferrol (NW Spain). On-site measurements of sea-level oscillations revealed energy peaks possibly related to resonant processes (López et al., 2012; López and Iglesias, 2013). This work is

  9. Magnetic susceptibility of YBa2Cu3O6 +x crystals: Unusual Curie behavior and small contributions from charge density waves

    NASA Astrophysics Data System (ADS)

    Kokanović, I.; Cooper, J. R.

    2016-08-01

    We report measurements of the magnetic susceptibility of twinned single crystals of YBa2Cu3O6 +x from just above their superconducting transition temperatures to 300 K with magnetic fields of up to 5 T applied parallel and perpendicular to the CuO2 planes at seven values of x . Appropriate analysis allows the relatively small, but still important, Curie terms to be separated from other contributions to the susceptibility. Our data support a picture in which the Curie terms arise from oxygen disorder in the Cu-O chains. This agrees with published work on polycrystalline samples where the sample cooling rate was varied, but here we show that the Curie plots flatten out above 200 K. We identify small effects of charge density wave (CDW) instabilities in the temperature (T ) derivative of the in-plane susceptibility d χa b(T ) /d T and discuss their x dependence. For x =0.67 we make a detailed comparison with published high energy x-ray diffraction data using a minimal model involving Fermi arcs, thereby obtaining values for the CDW energy gap and the Helmholtz free energy in a coherence volume. At 80 and 100 K the latter is comparable with, or smaller than, kBT , respectively, highlighting the probable importance of thermal fluctuations. We note that the effect of the Lorentz force on charge carriers in the Fermi arcs could provide a simple mechanism for enhancing the CDWs in high magnetic fields, as suggested by recent experiments.

  10. Observations of wave transformation over a fringing coral reef and the importance of low-frequency waves and offshore water levels to runup, overwash, and coastal flooding

    USGS Publications Warehouse

    Cheriton, Olivia; Storlazzi, Curt; Rosenberger, Kurt

    2016-01-01

    Many low-lying tropical islands are susceptible to sea level rise and often subjected to overwash and flooding during large wave events. To quantify wave dynamics and wave-driven water levels on fringing coral reefs, a 5 month deployment of wave gauges and a current meter was conducted across two shore-normal transects on Roi-Namur Island in the Republic of the Marshall Islands. These observations captured two large wave events that had waves with maximum heights greater than 6 m with peak periods of 16 s over the fore reef. The larger event coincided with a peak spring tide, leading to energetic, highly skewed infragravity (0.04–0.004 Hz) and very low frequency (0.004–0.001 Hz) waves at the shoreline, which reached heights of 1.0 and 0.7 m, respectively. Water surface elevations, combined with wave runup, reached 3.7 m above the reef bed at the innermost reef flat adjacent to the toe of the beach, resulting in flooding of inland areas. This overwash occurred during a 3 h time window that coincided with high tide and maximum low-frequency reef flat wave heights. The relatively low-relief characteristics of this narrow reef flat may further drive shoreline amplification of low-frequency waves due to resonance modes. These results (1) demonstrate how the coupling of high offshore water levels with low-frequency reef flat wave energetics can lead to large impacts along fringing reef-lined shorelines, such as island overwash, and (2) lend support to the hypothesis that predicted higher sea levels will lead to more frequent occurrences of these extreme events, negatively impacting coastal resources and infrastructure.

  11. Observations of wave transformation over a fringing coral reef and the importance of low-frequency waves and offshore water levels to runup, overwash, and coastal flooding

    NASA Astrophysics Data System (ADS)

    Cheriton, Olivia M.; Storlazzi, Curt D.; Rosenberger, Kurt J.

    2016-05-01

    Many low-lying tropical islands are susceptible to sea level rise and often subjected to overwash and flooding during large wave events. To quantify wave dynamics and wave-driven water levels on fringing coral reefs, a 5 month deployment of wave gauges and a current meter was conducted across two shore-normal transects on Roi-Namur Island in the Republic of the Marshall Islands. These observations captured two large wave events that had waves with maximum heights greater than 6 m with peak periods of 16 s over the fore reef. The larger event coincided with a peak spring tide, leading to energetic, highly skewed infragravity (0.04-0.004 Hz) and very low frequency (0.004-0.001 Hz) waves at the shoreline, which reached heights of 1.0 and 0.7 m, respectively. Water surface elevations, combined with wave runup, reached 3.7 m above the reef bed at the innermost reef flat adjacent to the toe of the beach, resulting in flooding of inland areas. This overwash occurred during a 3 h time window that coincided with high tide and maximum low-frequency reef flat wave heights. The relatively low-relief characteristics of this narrow reef flat may further drive shoreline amplification of low-frequency waves due to resonance modes. These results (1) demonstrate how the coupling of high offshore water levels with low-frequency reef flat wave energetics can lead to large impacts along fringing reef-lined shorelines, such as island overwash, and (2) lend support to the hypothesis that predicted higher sea levels will lead to more frequent occurrences of these extreme events, negatively impacting coastal resources and infrastructure.

  12. [Comparative study of the rod and cone contributions to the generation of b-wave ERG and tectal evoked potential in the dark-adapted carp].

    PubMed

    Garina, N S; Erchenkov, V G; Vorontsov, D D; Semina, T K

    2006-01-01

    Amplitudes and peak latencies as functions of wave length and monochromatic light intensity were investigated for b-wave ERG and tectal evoked potentials (EP) in the dark-adapted carp (Cyprinus carpio L). It was found, that independently of light intensity b-wave action spectra had one maximum in the medium wave band, corresponding to rod sensitivity area. For tectal EP, similar action spectra with maximum in the middle-wave were seen at low light intensity only. The b-wave amplitude growth was significant for the whole band of light intensities, and these changes were accompanied with a slight decrease in peak latency (to 50-100 ms). Tectal EP amplitude increased when low-intensity light was changed for medium intensity light and did not considerably increase to brighter light stimuli. However, tectal EP time latency significantly decreased (to 100-200 ms) during light intensity increasing. This differences show that retinal rod system, which in responsible for ERG b-wave in darkness, is not a key factor in the generation of tectal EP.

  13. Gravity waves

    NASA Technical Reports Server (NTRS)

    Fritts, David

    1987-01-01

    Gravity waves contributed to the establishment of the thermal structure, small scale (80 to 100 km) fluctuations in velocity (50 to 80 m/sec) and density (20 to 30%, 0 to peak). Dominant gravity wave spectrum in the middle atmosphere: x-scale, less than 100 km; z-scale, greater than 10 km; t-scale, less than 2 hr. Theorists are beginning to understand middle atmosphere motions. There are two classes: Planetary waves and equatorial motions, gravity waves and tidal motions. The former give rise to variability at large scales, which may alter apparent mean structure. Effects include density and velocity fluctuations, induced mean motions, and stratospheric warmings which lead to the breakup of the polar vortex and cooling of the mesosphere. On this scale are also equatorial quasi-biennial and semi-annual oscillations. Gravity wave and tidal motions produce large rms fluctuations in density and velocity. The magnitude of the density fluctuations compared to the mean density is of the order of the vertical wavelength, which grows with height. Relative density fluctuations are less than, or of the order of 30% below the mesopause. Such motions may cause significant and variable convection, and wind shear. There is a strong seasonal variation in gravity wave amplitude. Additional observations are needed to address and quantify mean and fluctuation statistics of both density and mean velocity, variability of the mean and fluctuations, and to identify dominant gravity wave scales and sources as well as causes of variability, both temporal and geographic.

  14. Higher-order contributions to ion-acoustic solitary waves in a multicomponent plasma consisting of warm ions and two-component nonisothermal electrons

    SciTech Connect

    Das, K.P.; Majumdar, S.R.; Paul, S.N. ||

    1995-05-01

    An integrated form of the governing equations in terms of pseudopotential higher-order nonlinear and dispersive effects is obtained by applying the reductive perturbation method for ion-acoustic solitary waves in a collisionless unmagnetized multicomponent plasma having warm ions and two-component nonisothermal electrons. The present method is advantageous because instead of solving an inhomogeneous second-order differential equation at each order, as in the standard procedure, we solve a first-order inhomogeneous equation at each order except at the lowest. The expressions of both Mach number and width of the solitary wave are obtained as a function of the amplitude of the wave for third-order nonlinear and dispersive effects. The variations of potential, width, and Mach number against soliton amplitude are shown graphically, taking into consideration the nonisothermality of two-component electrons in the plasma.

  15. Contribution of the ULF wave activity to the global recovery of the outer radiation belt during the passage of a high-speed solar wind stream observed in September 2014

    NASA Astrophysics Data System (ADS)

    Dal Lago, A.; Da Silva, L. A.; Alves, L. R.; Dallaqua, R.; Marchezi, J.; Medeiros, C.; Souza, V. M. C. E. S.; Koga, D.; Jauer, P. R.; Vieira, L.; Rockenbach, M.; Mendes, O., Jr.; De Nardin, C. M.; Sibeck, D. G.

    2016-12-01

    The interaction of the solar wind with the Earth's magnetosphere can either increase or decrease the relativistic electron population in the outer radiation belt. In order to investigate the contribution of the ULF wave activity to the global recovery of the outer radiation belt relativistic electron population, we searched the Van Allen data for a period in which we can clearly distinguish the enhancement of the fluxes from the background. The complex solar wind structure observed from September 12-24, 2014, which resulted from the interaction of two coronal mass ejections (CMEs) and a high-speed stream, presented such a scenario. The CMEs are related to the dropout of the relativistic electron population followed by several days of low fluxes. The global recovery started during the passage of the high-speed stream that was associated with the occurrence of substorms that persisted for several days. Here we estimate the contribution of ULF wave-particle interactions to the enhancement of the relativistic electron fluxes. Our approach is based on estimates of the ULF wave radial diffusion coefficients employing two models: (a) an analytic expression presented by Ozeke et al. (2014); and (b) a simplified model based on the solar wind parameters. The preliminary results, uncertainties and future steps are discussed in details.

  16. Modeling Motu Profile Response to Varying Wave and Storm Climate

    NASA Astrophysics Data System (ADS)

    Ortiz, A. C.; Ashton, A. D.; Donnelly, J. P.

    2014-12-01

    The atolls of the Pacific Ocean are low-lying landforms (less than 5m in elevation), typically consisting of reef-building corals often mounted by subaerial islets, or motu, which encircle a central lagoon. These motu, perched atop old coral reefs, typically consist of sand and gravel, and are sometimes anchored by relict geologic features (highstand coral reefs). Despite the vital role these islets play as home to terrestrial ecosystems and human infrastructure, the morphologic processes responsible for their formation and maintenance remain poorly understood. For example, although extreme events are hypothesized as a formation mechanism, motu are found in regions where hurricanes or tropical cyclones rarely occur and across varying storm gradients and frequency tracks. Here we use hydrodynamic and event-based morphodynamic modeling to better understand the role of storm events on the formation and evolution of motu. Using XBeach, a two-dimensional model of infragravity wave propagation and sediment transport, coupled with the coastal wave model, SWAN (Simulating WAves Nearshore), we simulate the hydrodynamic and morphodynamic impacts of storm events on the nearshore, beach, and backbarrier portions of atolls. We investigate the effect of different representative profile morphology, for example motu height or the distance from the reef edge to the motu, on storm response. We further test the effect of storm intensity and inundation scenarios (i.e. difference in elevated water levels of the lagoon and ocean) on storm hydrodynamics and morphologic change. Model scenarios are informed and compared to basin-wide analysis of the variation of atoll and motu characteristics, such as reef width, motu width, and motu spacing across the Pacific Ocean. Atoll morphologies and storm responses are affected by both geographic location and, locally, the shoreline orientation (compared to storm tracks). Combining these different model scenarios with measured morphometrics allows

  17. Near-source contributions to teleseismic P-wave coda and regional phases. Final report, 1 Jan 89-31 Dec 90

    SciTech Connect

    Lay, T.

    1991-04-27

    This report presents the results of an investigation of near-source effects on teleseismic P-wave and early P-wave coda spectra for underground explosions. The underlying objective of this research has been to determine whether the differential behavior of P and P coda can be exploited to remotely determine near-source properties such as overburden velocity, burial depth, and degree of saturation. The report also contains a review paper on the pP phase, focussed on assessing the various methodologies that have been used to determine pP parameters and trying to reconcile the existing discrepancies in various estimates. The final section of the report is an encyclopedia article on the role of seismological monitoring of nuclear testing treaties. Energy radiated upward from underground nuclear explosions has a complex interaction with the free surface that strongly influences the seismic wavefields recorded at teleseismic and regional distances. This interaction, differing from that for earthquakes primarily due to the much higher strains and strain rates involved, is essential to understand for both explosion yield estimation and event discrimination. Reflection of explosion P wave energy from the free surface, which produces the pP phase, involves frequency-dependent, non-linear processes that are intimately linked to surface spallation.

  18. Improving Short Wave Breaking Behavior In Surfbeat Models

    NASA Astrophysics Data System (ADS)

    Roelvink, J.; Daly, C.; Vandongeren, A. R.; van Thiel de Vries, J.; McCall, R.

    2009-12-01

    In present surfzone modeling three approaches are widely applied: short-wave resolving models, ‘surfbeat’ models, which resolve wave energy modulations on the time-scale of wave groups and their associated infragravity waves, and wave averaged models. In all three approaches, wave breaking is a process that is highly schematized and governed by several empirical coefficients. In this presentation we will focus on the breaking process in ‘surfbeat’ models, such as XBeach (Roelvink et al, 2009). These models need to describe the short wave dissipation by breaking as a function of the slowly-varying short wave energy or wave height. The model usually applied is that by Roelvink (1993), which combines a probability that waves are breaking as function of wave heigth over water depth ratio H/h with a bore-type dissipation formulation similar to that by Battjes and Janssen (1978). A drawback of such a formulation is that there is no ‘memory’ in the breaking process, and the amount of breaking instantly varies with the water depth (though the wave height itself does have a memory). For cases with bichromatic waves, or for long-period swell, this does not reflect reality enough: waves that start breaking do not instantly stop breaking once the water depth increases, but continue until some lower threshold is reached. This concept was captured in Dally’s (1992) wave-by-wave approach, where individual waves are tracked in a probabilistic setting. We have now implemented a similar formulation in XBeach, where the property that waves are breaking is tracked; it is switched on when H/h exceeds a first criterion; this property is propagated using an advection equation and when H/h gets below a second criterion breaking is switched off. This formulation can do two things the previous one can’t: maintain groupiness inside the surf zone and have a maximum of wave breaking in the trough after a steep bar, as was observed for instance in Arcilla et al’s (1994) test 1

  19. Researching of sea waves influence on a coastal line transformation (based on field observation results)

    NASA Astrophysics Data System (ADS)

    Chernov, A.; Kouznetsov, K.; Kurkin, A.; Shevchenko, G.

    2009-04-01

    The long duration registrations of bottom pressure, temperature and meteorological data took place in June - October 2007 on the shelf near 104th - 110th kilometer of interstate road Yuzhno-Sakhalinsk - Okha. Sediment transport and abrasion processes are observed in this place, it is a dangerous factor for road and railroad constructions, it can also be threat for some buildings of Vzmorie town. Distributed network of autonomous pressure gauges was installed for wave structure studying. Gauges were installed in tree lines with 100, 150 and 200 meters far from each other. Gathered data contains information about different wave's regimes under different weather conditions, it's allowed us to make analysis. Different data rows for different wave regimes were taken for analysis. Transformation of wave field along shoreline and opposite was observed. The results of observation are showed that disposition of waves was determined by swell waves with period 8-9 second. Wind waves were weaker than swell waves, conceivably because of big depths in the studied area. Much more interesting results were found in the infragravity waves range (0.5 - 5 min). For example, peaks with period above 150 and 75 seconds are presented in the spectral estimation of record from gauge 23. The same peaks were not observed in other gauges to the North and to the South from 23. However, low frequency peak was much stronger at the storm weather, but 75 seconds peak was stayed non-changed under the different weather conditions. For understanding mechanism of infra-gravitation waves generation group structure of waves were studied. Spectrum characteristics of different data rows for different wave regimes and also for their envelopes were provided. Results of this research allow us to consider that wave packets with common period 7 - 8 seconds make infra-gravitation waves with period above 5 minutes which forcing sediment transport processes. Satellite images of studied place were used in this

  20. Oceanic lithospheric S-wave velocities from the analysis of P-wave polarization at the ocean floor

    NASA Astrophysics Data System (ADS)

    Hannemann, Katrin; Krüger, Frank; Dahm, Torsten; Lange, Dietrich

    2016-12-01

    Our knowledge of the absolute S-wave velocities of the oceanic lithosphere is mainly based on global surface wave tomography, local active seismic or compliance measurements using oceanic infragravity waves. The results of tomography give a rather smooth picture of the actual S-wave velocity structure and local measurements have limitations regarding the range of elastic parameters or the geometry of the measurement. Here, we use the P-wave polarization (apparent P-wave incidence angle) of teleseismic events to investigate the S-wave velocity structure of the oceanic crust and the upper tens of kilometres of the mantle beneath single stations. In this study, we present an up to our knowledge new relation of the apparent P-wave incidence angle at the ocean bottom dependent on the half-space S-wave velocity. We analyse the angle in different period ranges at ocean bottom stations (OBSs) to derive apparent S-wave velocity profiles. These profiles are dependent on the S-wave velocity as well as on the thickness of the layers in the subsurface. Consequently, their interpretation results in a set of equally valid models. We analyse the apparent P-wave incidence angles of an OBS data set which was collected in the Eastern Mid Atlantic. We are able to determine reasonable S-wave-velocity-depth models by a three-step quantitative modelling after a manual data quality control, although layer resonance sometimes influences the estimated apparent S-wave velocities. The apparent S-wave velocity profiles are well explained by an oceanic PREM model in which the upper part is replaced by four layers consisting of a water column, a sediment, a crust and a layer representing the uppermost mantle. The obtained sediment has a thickness between 0.3 and 0.9 km with S-wave velocities between 0.7 and 1.4 km s-1. The estimated total crustal thickness varies between 4 and 10 km with S-wave velocities between 3.5 and 4.3 km s-1. We find a slight increase of the total crustal thickness from

  1. Theory of Seismic Noise Excitation by Ocean Waves

    NASA Astrophysics Data System (ADS)

    Tanimoto, T.

    2009-12-01

    It is becoming increasingly clear that seismic noise, recorded in continuous data, will be an important part of seismic data that will be used for seismic structure study. Causes of noise vary from frequency to frequency but the predominant noise, specifically in the microseismic frequency band (about 0.05-0.4 Hz), is now recognized to be ocean waves. The Hum, seismic noise in a lower frequency band about 0.003-0.015 Hz, may also be excited by this mechanism (Webb, 2007). The detailed excitation mechanism of microseisms by ocean waves is attributed to Longuet-Higgins (1950) (which credits earlier study by Miche, 1944) which beautifully explains one critical aspect of data, the double frequency noise peak. Longuet-Higgins (1950) basically showed how nonlinear advection term in the Navier-Stokes equation and the nonlinear term in the kinematic free-surface boundary condition lead to the generation of pressure when there are colliding ocean waves. In this paper, we will show that excitation of seismic noise can be formulated starting from the original nonlinear terms in the equations, basically skipping the intermediate pressure term derived by Longuet-Higgins. The equivalent body-force term by these nonlinear terms can be expressed in a compact formula and may be used to describe seismic wavefields. We will show 1. The equivalent Longuet-Higgins term arises from our approach but it is exact only for low frequencies below 0.1 Hz. At higher frequencies, depending on ocean depth, deviations up to a factor of 5-10 can arise. 2. At low frequencies (<0.005 Hz), a horizontal force term arises whose effects may become larger than pressure variations due to the Longuet-Higgins mechanism. Webb (2007) and Tanimoto (2007) pointed out this term. This term contains azimuthal effects (radiation pattern), as opposed to the isotropic vertical forcing by the Longuett-Higgins mechanism. 3. We also examine the excitation of the toroidal hum (Kurrle and Widmer, 2008). Infragravity waves

  2. P-wave tomographic images in the Central Betics-Alborán Sea (South Spain) using local earthquakes: Contribution for a continental collision

    NASA Astrophysics Data System (ADS)

    Serrano, Inmaculada; Morales, José; Zhao, Dapeng; Torcal, Federico; Vidal, Francisco

    To investigate the relationship between shallow and intermediate-depth earthquakes and the crust and upper mantle structure beneath the Betic-Cordillera and Alborán sea region, we have applied seismic tomography to 2569 P-wave arrival times from 367 microearthquakes recorded by both permanent and temporary seismic stations deployed in the region. These earthquakes occurred in the depth range of 0 to 110 km beneath the Central Betic Cordilleras and Alborán sea. Our results have revealed significant structural heterogeneities in the crust and upper mantle beneath the study area. In the upper crust there is a high-velocity anomaly at Sierra Gorda (western boundary of the Granada basin) penetrating to 15 km depth, which is in good agreement with the aeromagnetic anomaly. In the Granada basin, a low-velocity anomaly is located in the middle crust, which coincides with a previously detected greater cutoff depth of seismicity, and are considered to be associated with a highly fractured zone generated by an intracrustal detachment. The northern boundary of the Alborán sea (Málaga coast) is well imaged as low velocities from 50 to 90 km depths. This low-velocity zone in the upper mantle is associated with the intermediate-depth seismicity, which outline a section of continental crust related to the collision/subduction beneath the northern part of the Alborán sea-southern part of the Central Betics.

  3. Kinetic analysis of spin current contribution to spectrum of electromagnetic waves in spin-1/2 plasma. I. Dielectric permeability tensor for magnetized plasmas

    NASA Astrophysics Data System (ADS)

    Andreev, Pavel A.

    2017-02-01

    The dielectric permeability tensor for spin polarized plasmas is derived in terms of the spin-1/2 quantum kinetic model in six-dimensional phase space. Expressions for the distribution function and spin distribution function are derived in linear approximations on the path of dielectric permeability tensor derivation. The dielectric permeability tensor is derived for the spin-polarized degenerate electron gas. It is also discussed at the finite temperature regime, where the equilibrium distribution function is presented by the spin-polarized Fermi-Dirac distribution. Consideration of the spin-polarized equilibrium states opens possibilities for the kinetic modeling of the thermal spin current contribution in the plasma dynamics.

  4. The contribution of radio-frequency rectification to field-aligned losses of high-harmonic fast wave power to the divertor in the National Spherical Torus eXperiment

    SciTech Connect

    Perkins, R. J. Hosea, J. C.; Jaworski, M. A.; Diallo, A.; Bell, R. E.; Bertelli, N.; Gerhardt, S.; Kramer, G. J.; LeBlanc, B. P.; Phillips, C. K.; Podestà, M.; Roquemore, L.; Taylor, G.; Wilson, J. R.; Ahn, J.-W.; Gray, T. K.; McLean, A.; Sabbagh, S.

    2015-04-15

    The National Spherical Torus eXperiment (NSTX) can exhibit a major loss of high-harmonic fast wave (HHFW) power along scrape-off layer (SOL) field lines passing in front of the antenna, resulting in bright and hot spirals on both the upper and lower divertor regions. One possible mechanism for this loss is RF sheaths forming at the divertors. Here, we demonstrate that swept-voltage Langmuir probe characteristics for probes under the spiral are shifted relative to those not under the spiral in a manner consistent with RF rectification. We estimate both the magnitude of the RF voltage across the sheath and the sheath heat flux transmission coefficient in the presence of the RF field. Although precise comparison between the computed heat flux and infrared (IR) thermography cannot yet be made, the computed heat deposition compares favorably with the projections from IR camera measurements. The RF sheath losses are significant and contribute substantially to the total SOL losses of HHFW power to the divertor for the cases studied. This work will guide future experimentation on NSTX-U, where a wide-angle IR camera and a dedicated set of coaxial Langmuir probes for measuring the RF sheath voltage directly will quantify the contribution of RF sheath rectification to the heat deposition from the SOL to the divertor.

  5. The Virtual Wave Observatory (VWO)

    NASA Technical Reports Server (NTRS)

    Fung, Shing F.

    2008-01-01

    Heliophysics wave data are currently not easily searchable by computers, making identifying pertinent wave data features for analyses and cross comparisons difficult and laborious. Since wave data analysis requires specialized knowledge about waves, which spans the spectrum of microphysics to macrophysics, researchers having varied expertise cannot easily use wave data. To resolve these difficulties and to allow wave data to contribute more fully to Heliophysics research, we are developing a Virtual Wave Observatory (VWO) whose goal is to enable all Heliophysics wave data to become searchable, understandable and usable by the Heliophysics community. The VWO objective is to enable search of multiple and distributed wave data (from both active and passive measurements). This presentation provides and overview of the VWO, a new VxO component within the emerging distributed Heliophysics data and model environment.

  6. The Virtual Wave Observatory (VWO)

    NASA Technical Reports Server (NTRS)

    Fung, Shing F.

    2008-01-01

    Heliophysics wave data are currently not easily searchable by computers, making identifying pertinent wave data features for analyses and cross comparisons difficult and laborious. Since wave data analysis requires specialized knowledge about waves, which spans the spectrum of microphysics to macrophysics, researchers having varied expertise cannot easily use wave data. To resolve these difficulties and to allow wave data to contribute more fully to Heliophysics research, we are developing a Virtual Wave Observatory (VWO) whose goal is to enable all Heliophysics wave data to become searchable, understandable and usable by the Heliophysics community. The VWO objective is to enable search of multiple and distributed wave data (from both active and passive measurements). This presentation provides and overview of the VWO, a new VxO component within the emerging distributed Heliophysics data and model environment.

  7. Japanese contributions to MAP

    NASA Technical Reports Server (NTRS)

    Kato, S.

    1989-01-01

    Japan contributed much to MAP in many branches. The MU (middle and upper atmosphere) radar, in operation during the MAP period, produced various novel possibilities in observations of middle atmosphere dynamics; possibilities which were fairly well realized. Gravity wave saturation and its spectrum in the mesosphere were observed successfully. Campaign observations by radars between Kyoto and Adelaide were especially significant in tidal and planetary wave observations. In Antarctica, middle atmosphere observation of the dramatic behavior of aerosols in winter is well elucidated together with the ozone hole. Theoretical and numerical studies have been progressing actively since a time much earlier than MAP. Now it is pointed out that gravity waves play an important role in producing the weak wind region in the stratosphere as well as the mesosphere.

  8. Observations of Waves and Currents on an Inundated Barrier Island: the Role of the Back-Barrier Basin

    NASA Astrophysics Data System (ADS)

    Engelstad, A.; van der Vegt, M.; Ruessink, G.; Wesselman, D.

    2016-02-01

    Vertical accretion of sediment on barrier islands is essential in mitigating the effects of sea-level rise and island subsidence. Overwash and the associated onshore sediment transport might ensure aggradation of barrier islands, especially in mesotidal, mixed energy systems. However, artificial sand drift dykes on many barrier islands in the Dutch Wadden Sea effectively prevent overwash. At present the reopening of dunes is considered, but not much field data on overwash is available to substantiate the effects of these measures. Therefore an extensive field campaign was set-up to quantify the hydrodynamic processes during overwash and island inundation across a wide and gently sloping Dutch barrier island spit. Here, we present much-needed field data collected in the course of several storms in the winter of 2014/2015. Waves and currents were observed using Acoustic Doppler Velocimeters (ADVs) and stand-alone pressure sensors along an 1.3 km instrument array spanning across the spit from the North Sea to the Wadden Sea. Most instruments were installed subaerial at locations ranging from -0.2m to 1.6m with respect to the Dutch Ordnance Datum (NAP), and inundation depths measured at the highest location ranged from a few centimeters to 1.3m. The data shows that flooding of the barrier can occur from two sides. During rising tides, water mainly flows from the North Sea across the barrier to the Wadden Sea. During falling tides, water level gradients can be reversed and water can flow towards the sea. Since a flow reversal was not observed during all events, this suggests that a seaward directed water level gradient can be counteracted by wave-induced set-up. The measured wave field showed that infragravity- and swell-waves typically entered the field site from the North Sea side, while locally generated wind waves frequently entered from the Wadden Sea. The results clearly highlight the role of the back-barrier basin.

  9. Ice Waves

    NASA Image and Video Library

    2017-09-27

    Ice Waves - May 21st, 2001 Description: Along the southeastern coast of Greenland, an intricate network of fjords funnels glacial ice to the Atlantic Ocean. During the summer melting season, newly calved icebergs join slabs of sea ice and older, weathered bergs in an offshore slurry that the southward-flowing East Greenland Current sometimes swirls into stunning shapes. Exposed rock of mountain peaks, tinted red in this image, hints at a hidden landscape. Credit: USGS/NASA/Landsat 7 To learn more about the Landsat satellite go to: landsat.gsfc.nasa.gov/ NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Join us on Facebook

  10. A preliminary evaluation of nearhore extreme sea level and wave models for fringing reef environments

    NASA Astrophysics Data System (ADS)

    Hoeke, R. K.; Reyns, J.; O'Grady, J.; Becker, J. M.; Merrifield, M. A.; Roelvink, J. A.

    2016-02-01

    Oceanic islands are widely perceived as vulnerable to sea level rise and are characterized by steep nearshore topography and fringing reefs. In such settings, near shore dynamics and (non-tidal) water level variability tends to be dominated by wind-wave processes. These processes are highly sensitive to reef morphology and roughness and to regional wave climate. Thus sea level extremes tend to be highly localized and their likelihood can be expected to change in the future (beyond simple extrapolation of sea level rise scenarios): e.g. sea level rise may increase the effective mean depth of reef crests and flats and ocean acidification and/or increased temperatures may lead to changes in reef structure. The problem is sufficiently complex that analytic or numerical approaches are necessary to estimate current hazards and explore potential future changes. In this study, we evaluate the capacity of several analytic/empirical approaches and phase-averaged and phase-resolved numerical models at sites in the insular tropical Pacific. We consider their ability to predict time-averaged wave setup and instantaneous water level exceedance probability (or dynamic wave run-up) as well as computational cost; where possible, we compare the model results with in situ observations from a number of previous studies. Preliminary results indicate analytic approaches are by far the most computationally efficient, but tend to perform poorly when alongshore straight and parallel morphology cannot be assumed. Phase-averaged models tend to perform well with respect to wave setup in such situations, but are unable to predict processes related to individual waves or wave groups, such as infragravity motions or wave run-up. Phase-resolved models tend to perform best, but come at high computational cost, an important consideration when exploring possible future scenarios. A new approach of combining an unstructured computational grid with a quasi-phase averaged approach (i.e. only phase

  11. IL-1β is induced in reactive astrocytes in the somatosensory cortex of rats with genetic absence epilepsy at the onset of spike-and-wave discharges, and contributes to their occurrence.

    PubMed

    Akin, Demet; Ravizza, Teresa; Maroso, Mattia; Carcak, Nihan; Eryigit, Tugba; Vanzulli, Ilaria; Aker, Rezzan Gülhan; Vezzani, Annamaria; Onat, Filiz Yılmaz

    2011-12-01

    Interleukin (IL)-1β plays a crucial role in the mechanisms of limbic seizures in rodent models of temporal lobe epilepsy. We addressed whether activation of the IL-1β signaling occurs in rats with genetic absence epilepsy (GAERS) during the development of spike-and-wave discharges (SWDs). Moreover, we studied whether inhibition of IL-1β biosynthesis in GAERS could affect SWD activity. IL-1β expression and glia activation were studied by immunocytochemistry in the forebrain of GAERS at postnatal days (PN)14, PN20, and PN90 and in age-matched non-epileptic control Wistar rats. In PN14 GAERS, when no SWDs have developed yet, IL-1β immunostaining was undetectable, and astrocytes and microglia showed a resting phenotype similar to control Wistar rats. In 3 out of 9 PN20 GAERS, IL-1β was observed in activated astrocytes of the somatosensory cortex; the cytokine expression was associated with the occurrence of immature-type of SWDs. In all adult PN90 GAERS, when mature SWDs are established, IL-1β was observed in reactive astrocytes of the somatosensory cortex but not in adjacent cortical areas or in extra-cortical regions. An age-dependent c-fos activation was found in the somatosensory cortex of GAERS with maximal levels reached in PN90 rats; c-fos was also induced in some thalamic nuclei in PN20 and PN90 GAERS. Inhibition of IL-1β biosynthesis in PN90 GAERS by 4-day systemic administration of a specific ICE/Caspase-1 blocker, significantly reduced both SWD number and duration. These results show that IL-1β is induced in reactive astrocytes of the somatosensory cortex of GAERS at the onset of SWDs. IL-1β has pro-ictogenic properties in this model, and thus it may play a contributing role in the mechanisms underlying the occurrence of absence seizures. Copyright © 2011 Elsevier Inc. All rights reserved.

  12. Wave turbulence

    NASA Astrophysics Data System (ADS)

    Nazarenko, Sergey

    2015-07-01

    Wave turbulence is the statistical mechanics of random waves with a broadband spectrum interacting via non-linearity. To understand its difference from non-random well-tuned coherent waves, one could compare the sound of thunder to a piece of classical music. Wave turbulence is surprisingly common and important in a great variety of physical settings, starting with the most familiar ocean waves to waves at quantum scales or to much longer waves in astrophysics. We will provide a basic overview of the wave turbulence ideas, approaches and main results emphasising the physics of the phenomena and using qualitative descriptions avoiding, whenever possible, involved mathematical derivations. In particular, dimensional analysis will be used for obtaining the key scaling solutions in wave turbulence - Kolmogorov-Zakharov (KZ) spectra.

  13. Tracking Ocean Gravity Waves in Real-time: Highlights of Bottom Pressure Data Recorded on Ocean Networks Canada's NEPTUNE observatory

    NASA Astrophysics Data System (ADS)

    Heesemann, Martin; Mihaly, Steve; Gemmrich, Johannes; Davis, Earl; Thomson, Richard; Dewey, Richard

    2016-04-01

    Ocean Networks Canada operates two cabled ocean observatories off Vancouver Island on Canada's west coast. The regional NEPTUNE observatory spans the entire Juan de Fuca tectonic plate from the coast across the subduction zone to the hydrothermally active Endeavour Segment of the Juan de Fuca Ridge Segment while the VENUS observatory focuses on coastal processes. Both observatories collect data on physical, chemical, biological, and geological aspects of the ocean over long time periods, supporting research on complex earth processes. High-precision bottom pressure recorders (BPR) deployed on the NEPTUNE observatory are capable of detecting a wide range of phenomena related to sea level variations. The observatory BPRs provide observations of nano-resolution (with respect to full scale of the instrument) pressure variations which correspond to sub-millimeter scale surface water displacements in several kilometers of water. Detected signals include tides, tsunamis, infragravity waves, swell, wave-induced microseisms, storm surge, and seismic signals. Spectral analysis reveals many of these phenomena with periods ranging from a few seconds to many hours. Dispersion patterns from distant swells are prominent in the swell and microseism bands. By comparing the difference of arrival times between longer period waves, which arrive first, and shorter period waves we can estimate the distance the swells travelled since they were generated. Using this information, swell can be tracked back to specific storms across the Pacific. The presentation will high-light some examples of the mentioned phenomena in the continuous time-series that in some instances are more than seven years long.

  14. A Joint Monte Carlo Inversion of Seafloor Compliance, Receiver Functions and Rayleigh Wave Dispersion at OBS Stations off New Zealand

    NASA Astrophysics Data System (ADS)

    Ball, J. S.; Sheehan, A. F.; Stachnik, J. C.; Collins, J. A.

    2012-12-01

    Surface wave dispersion measurements, receiver functions and seafloor compliance data were jointly inverted to produce shear velocity profiles at Ocean Bottom Seismic (OBS) stations off the South Island of New Zealand. Receiver function analysis of OBS data presents a technical challenge due largely to the presence of multiply scattered reverberations in the water and low-velocity sediments at OBS sites. Teleseismic arrivals from interfaces of tectonic interest are obscured by sediment-converted shear waves and water column multiples. Mitigation of these effects typically requires accurate characterization of sediment layer shear velocities and thicknesses. The seismic properties of the sediment column can be probed using shallow mode-converted shear arrivals and the seafloor's response to ocean loading from infragravity waves (seafloor compliance). Data for this study were acquired in 2009-2010 by the Marine Observations of Anisotropy Near Aotearoa (MOANA) experiment, which deployed 30 broadband OBS and differential pressure gauges (DPGs) off the South Island of New Zealand. Seafloor compliance was calculated from MOANA DPG pressure and OBS vertical component acceleration power spectra at periods between 50-250s. The resulting compliance values range from 10-10-10-8 Pa-1 and are sensitive to changes in shear modulus at depths that increase with forcing period. Receiver functions were estimated using events of high SNR from epicentral distances of 30-90 degrees. Forward modeling utilized full-wavefield synthetic seismograms to account for the OBS location at the boundary between acoustic and elastic media. Rayleigh wave group velocity dispersion curves at periods from 6-30s were derived from ambient noise tomography. A Bayesian Markov Chain Monte Carlo algorithm was implemented to estimate shear velocity profiles, crustal and sediment thicknesses using these combined observations. Preliminary sediment thickness estimates range from 400m on the Challenger plateau to

  15. Nonlinear Waves.

    DTIC Science & Technology

    1982-09-23

    Similarity in the asymptotic behavior of collision-free hydromagnetic waves and water waves, New York Univ., Courant Inst. Math. Sci., Res. Report NYO -90 L...Long solitary waves in lakes and • estuaries, propagating on the thermocline separating two shallow layers of fluid of almost equal densities, are

  16. Gravity Waves

    Atmospheric Science Data Center

    2013-04-19

    article title:  Gravity Waves Ripple over Marine Stratocumulus Clouds ... Imaging SpectroRadiometer (MISR), a fingerprint-like gravity wave feature occurs over a deck of marine stratocumulus clouds. Similar ... that occur when a pebble is thrown into a still pond, such "gravity waves" sometimes appear when the relatively stable and stratified air ...

  17. Glutamatergic Retinal Waves

    PubMed Central

    Kerschensteiner, Daniel

    2016-01-01

    Spontaneous activity patterns propagate through many parts of the developing nervous system and shape the wiring of emerging circuits. Prior to vision, waves of activity originating in the retina propagate through the lateral geniculate nucleus (LGN) of the thalamus to primary visual cortex (V1). Retinal waves have been shown to instruct the wiring of ganglion cell axons in LGN and of thalamocortical axons in V1 via correlation-based plasticity rules. Across species, retinal waves mature in three stereotypic stages (I–III), in which distinct circuit mechanisms give rise to unique activity patterns that serve specific functions in visual system refinement. Here, I review insights into the patterns, mechanisms, and functions of stage III retinal waves, which rely on glutamatergic signaling. As glutamatergic waves spread across the retina, neighboring ganglion cells with opposite light responses (ON vs. OFF) are activated sequentially. Recent studies identified lateral excitatory networks in the inner retina that generate and propagate glutamatergic waves, and vertical inhibitory networks that desynchronize the activity of ON and OFF cells in the wavefront. Stage III wave activity patterns may help segregate axons of ON and OFF ganglion cells in the LGN, and could contribute to the emergence of orientation selectivity in V1. PMID:27242446

  18. Extreme events in Faraday waves

    NASA Astrophysics Data System (ADS)

    Punzmann, Horst; Shats, Michael; Xia, Hua

    2014-05-01

    Observations of extreme wave events in the ocean are rare due to their low statistical probability. In the laboratory however, the evolution of extreme wave events can be studied in great detail with high spatial and temporal resolution. The reported surface wave experiments in the short wavelength gravity-capillary range aim to contribute to the understanding of some of the underlying mechanisms for rogue wave generation. In this talk, we report on extreme wave events in parametrically excited Faraday waves. Faraday waves appear if a fluid is accelerated (normal to the fluid surface) above a critical threshold. A variety of novel tools have been deployed to characterize the 2D surface elevation. The results presented show spatio-temporal and statistical data on the surface wave conditions leading up to extreme wave events. The peak in wave amplitude during such an event is shown to exceed six times the standard deviation of the average wave field with significantly increased statistical probability compared to the background wave field [1]. The experiments also show that parametrically excited waves can be viewed as assembles of oscillons [2] (or oscillating solitons) where modulation instability seems to play a crucial role in their formation. More detailed studies on the oscillon dynamics reveal that the onset of an increased probability of extreme wave events correlates with the increase in the oscillons mobility and merger [3]. Reference: 1. Xia H., Maimbourg T., Punzmann H., and Shats M., Oscillon dynamics and rogue wave generation in Faraday surface ripples, Physical Review Letters 109, 114502 (2012) 2. Shats M., Xia H., and Punzmann H., Parametrically excited water surface ripples as ensembles of oscillons, Physical Review Letters 108, 034502 (2012) 3. Shats M., Punzmann H., Xia H., Capillary rogue waves, Physical Review Letters, 104, 104503 (2010)

  19. Jupiter Wave

    NASA Image and Video Library

    2015-10-13

    Scientists spotted a rare wave in Jupiter North Equatorial Belt that had been seen there only once before in this false-color close-up from NASA Hubble Telescope. In Jupiter's North Equatorial Belt, scientists spotted a rare wave that had been seen there only once before. It is similar to a wave that sometimes occurs in Earth's atmosphere when cyclones are forming. This false-color close-up of Jupiter shows cyclones (arrows) and the wave (vertical lines). http://photojournal.jpl.nasa.gov/catalog/PIA19659

  20. Making waves

    NASA Astrophysics Data System (ADS)

    Kruse, Karsten

    2017-01-01

    Traveling waves propagating along surfaces play an important role for intracellular organization. Such waves can appear spontaneously in reaction-diffusion systems, but only few general criteria for their existence are known. Analyzing the dynamics of the Min proteins in Escherichia coli, Levine and Kessler (2016 New J. Phys. 18 122001) now identified a new mechanism for the emergence of traveling waves that relies on conservation laws. From their analysis one can expect traveling waves to be a generic feature of systems made of proteins that have a cytoplasmic and a membrane-bound state.

  1. The gravitational wave decade

    NASA Astrophysics Data System (ADS)

    Conklin, John

    2016-03-01

    With the expected direct detection of gravitational waves by Advanced LIGO and pulsar timing arrays in the near future, and with the recent launch of LISA Pathfinder this can arguably be called the decade of gravitational waves. Low frequency gravitational waves in the mHz range, which can only be observed from space, provide the richest science and complement high frequency observatories on the ground. A space-based observatory will improve our understanding of the formation and growth of massive black holes, create a census of compact binary systems in the Milky Way, test general relativity in extreme conditions, and enable searches for new physics. LISA, by far the most mature concept for detecting gravitational waves from space, has consistently ranked among the nation's top priority large science missions. In 2013, ESA selected the science theme ``The Gravitational Universe'' for its third large mission, L3, under the Cosmic Visions Program, with a planned launch date of 2034. NASA has decided to join with ESA on the L3 mission as a junior partner and has recently assembled a study team to provide advice on how NASA might contribute to the European-led mission. This talk will describe these efforts and the activities of the Gravitational Wave Science Interest Group and the L3 Study Team, which will lead to the first space-based gravitational wave observatory.

  2. Assessing wave energy effects on biodiversity: the wave hub experience.

    PubMed

    Witt, M J; Sheehan, E V; Bearhop, S; Broderick, A C; Conley, D C; Cotterell, S P; Crow, E; Grecian, W J; Halsband, C; Hodgson, D J; Hosegood, P; Inger, R; Miller, P I; Sims, D W; Thompson, R C; Vanstaen, K; Votier, S C; Attrill, M J; Godley, B J

    2012-01-28

    Marine renewable energy installations harnessing energy from wind, wave and tidal resources are likely to become a large part of the future energy mix worldwide. The potential to gather energy from waves has recently seen increasing interest, with pilot developments in several nations. Although technology to harness wave energy lags behind that of wind and tidal generation, it has the potential to contribute significantly to energy production. As wave energy technology matures and becomes more widespread, it is likely to result in further transformation of our coastal seas. Such changes are accompanied by uncertainty regarding their impacts on biodiversity. To date, impacts have not been assessed, as wave energy converters have yet to be fully developed. Therefore, there is a pressing need to build a framework of understanding regarding the potential impacts of these technologies, underpinned by methodologies that are transferable and scalable across sites to facilitate formal meta-analysis. We first review the potential positive and negative effects of wave energy generation, and then, with specific reference to our work at the Wave Hub (a wave energy test site in southwest England, UK), we set out the methodological approaches needed to assess possible effects of wave energy on biodiversity. We highlight the need for national and international research clusters to accelerate the implementation of wave energy, within a coherent understanding of potential effects-both positive and negative.

  3. Calcium wave of Brain Astrocytes

    NASA Astrophysics Data System (ADS)

    Cornell Bell, A. H.

    1997-03-01

    Time lapse confocal scanning laser microscopy was used to study hippocampal astrocyte cultures loaded with a calcium indicator, Fluo3-AM (4 uM). kThe neurotransmitter kainate (100uM) overwhelms the Na+-buffering capacity of astrocytes within 100 sec resulting in reversal of the Na+/Ca2+ exchanger. This results in a subcellular site where Ca2+ entering the cytoplasm contributes to a long-distance Ca2+ wave which travels at 20 um/sec without decrement. Image analysis has shown calcium waves not only at a high Kainate dose, but also at a low Kainate dose, e.g. 10uM. These are, however, shortlived and burried in an extremely noisy background and only detectable by analyzing the calcium waves images for spatio-temporal coherence. As the kainate dose increases, more large scale coherent structures with visible geometric features (spiral waves and target waves) can be observed. Multiple spiral waves are produced when the Kainate dose increases to 100 uM. These waves travel at a constant velocity across entire microscope fields for long time periods (>30 mins). Na+ channels have no effect on the Kainate wave. Voltage-gated Ca2+ channels are not involved and Ca2+ enters through reversal of the exchanger. Ca2+ release from stores does not contribute to the kainate wave. Removal of Na+ or Ca2+ from outside and the specific Na+/Ca2+ exchange inhibitor benzamil (10 uM) inhibit the kainate wave. A functional antibody to alpha6-Integrin which is localized to membrane regions between cells inhibits the spread of the kainate wave in a dose and time-dependent manner. Fluorescence Recovery after Photobleach (FRAP) techniques indicate that gap junctions remain open between cells. This would imply that Ca2+ or IP3 need not pass through the gap junction, but reversal of the exchanger would propel the Ca2+ wave at the cell surface.

  4. A global traveling wave on Venus

    NASA Technical Reports Server (NTRS)

    Smith, Michael D.; Gierasch, Peter J.; Schinder, Paul J.

    1993-01-01

    The dominant large-scale pattern in the clouds of Venus has been described as a 'Y' or 'Psi' and tentatively identified by earlier workers as a Kelvin wave. A detailed calculation of linear wave modes in the Venus atmosphere verifies this identification. Cloud feedback by infrared heating fluctuations is a plausible excitation mechanism. Modulation of the large-scale pattern by the wave is a possible explanation for the Y. Momentum transfer by the wave could contribute to sustaining the general circulation.

  5. A global traveling wave on Venus

    NASA Technical Reports Server (NTRS)

    Smith, Michael D.; Gierasch, Peter J.; Schinder, Paul J.

    1992-01-01

    The dominant large-scale pattern in the clouds of Venus has been described as a 'Y' or 'Psi' and tentatively identified by earlier workers as a Kelvin wave. A detailed calculation of linear wave modes in the Venus atmosphere verifies this identification. Cloud feedback by infrared heating fluctuations is a plausible excitation mechanism. Modulation of the large-scale pattern by the wave is a possible explanation for the Y. Momentum transfer by the wave could contribute to sustaining the general circulation.

  6. Dislocations in magnetohydrodynamic waves in a stellar atmosphere.

    PubMed

    López Ariste, A; Collados, M; Khomenko, E

    2013-08-23

    We describe the presence of wave front dislocations in magnetohydrodynamic waves in stratified stellar atmospheres. Scalar dislocations such as edges and vortices can appear in Alfvén waves, as well as in general magnetoacoustic waves. We detect those dislocations in observations of magnetohydrodynamic waves in sunspots in the solar chromosphere. Through the measured charge of all the dislocations observed, we can give for the first time estimates of the modal contribution in the waves propagating along magnetic fields in solar sunspots.

  7. Comments on the Terminology of "Convectively-Coupled Kelvin Waves"

    NASA Technical Reports Server (NTRS)

    Chao, Winston C.

    2006-01-01

    The terminology "convectively-coupled Kelvin waves" has been used frequently in the literature to refer to the 15 m/s eastward-moving planetary and large-scale waves in the tropics. This note points out that this terminology is not appropriate, since these waves contain Rossby waves and mixed Rossby-gravity waves also. The significance of pointing out this misnomer is that a better understanding of these waves may contribute to the search for their cause.

  8. Nonlinear Waves

    DTIC Science & Technology

    1989-06-15

    following surprising situation. Namely associated with the integrable nonlinear Schrodinger equations are standard numerical schemes which exhibit at...36. An Initial Boundary Value Problem for the Nonlinear Schrodinger Equations , A.S. Fokas, Physica D March 1989. 37. Evolution Theory, Periodic... gravity waves and wave excitation phenomena related to moving pressure distributions; numerical approximation and computation; nonlinear optics; and

  9. Microfluidic waves

    PubMed Central

    Utz, Marcel; Begley, Matthew R.; Haj-Hariri, Hossein

    2012-01-01

    The propagation of pressure waves in fluidic channels with elastic covers is discussed in view of applications to flow control in microfluidic devices. A theory is presented which describes pressure waves in the fluid that are coupled to bending waves in the elastic cover. At low frequencies, the lateral bending of the cover dominates over longitudinal bending, leading to propagating, non-dispersive longitudinal pressure waves in the channel. The theory addresses effects due to both the finite viscosity and compressibility of the fluid. The coupled waves propagate without dispersion, as long as the wave length is larger than the channel width. It is shown that in channels of typical microfluidic dimensions, wave velocities in the range of a few 10 m s−1 result if the channels are covered by films of a compliant material such as PDMS. The application of this principle to design microfluidic band pass filters based on standing waves is discussed. Characteristic frequencies in the range of a few kHz are readily achieved with quality factors above 30. PMID:21966667

  10. Third Wave.

    ERIC Educational Resources Information Center

    Reed, Chris

    2000-01-01

    Third Wave is a Christian charity based in Derby (England) that offers training in vocational skills, preindustrial crafts, horticultural and agricultural skills, environmental education, and woodland survival skills to disadvantaged people at city and farm locations. Third Wave employs a holistic approach to personal development in a community…

  11. Atmospheric Waves

    NASA Technical Reports Server (NTRS)

    2007-01-01

    With its Multispectral Visible Imaging Camera (MVIC), half of the Ralph instrument, New Horizons captured several pictures of mesoscale gravity waves in Jupiter's equatorial atmosphere. Buoyancy waves of this type are seen frequently on Earth - for example, they can be caused when air flows over a mountain and a regular cloud pattern forms downstream. In Jupiter's case there are no mountains, but if conditions in the atmosphere are just right, it is possible to form long trains of these small waves. The source of the wave excitation seems to lie deep in Jupiter's atmosphere, below the visible cloud layers at depths corresponding to pressures 10 times that at Earth's surface. The New Horizons measurements showed that the waves move about 100 meters per second faster than surrounding clouds; this is about 25% of the speed of sound on Earth and is much greater than current models of these waves predict. Scientists can 'read' the speed and patterns these waves to learn more about activity and stability in the atmospheric layers below.

  12. Moreton Waves

    NASA Technical Reports Server (NTRS)

    Thompson, B. J.

    1999-01-01

    "Moreton waves," named for the observer who popularized them, are a solar phenomenon also known in scientific literature as "Moreton-Ramsey wave," "flare waves," "flare-associated waves," "MHD blast waves," "chromospheric shock fronts" and various other combinations of terms which connote violently propagating impulsive disturbances. It is unclear whether all of the observations to which these terms have been applied pertain to a single physical phenomenon: there has perhaps been some overlap between the observations and the assumed physical properties of the observed occurrence. Moreton waves are ideally observed in the wings of H alpha, and appear as semi-circular fronts propagating at speeds ranging from several hundred to over a thousand km/sec. They form an arc, or "brow shape" which can span up to 180 degrees. Extrapolating the speed and locations of the arc indicates that the phenomenon's origin intersects well with the impulsive phase of the associated H alpha flare (if the flare exhibits an impulsive phase). However, the arc may not form or may not be observable until it is tens of megameters from the flaring region, and subsequently can propagate to distances exceeding 100 megameters. The high speeds and distances of propagation, plus the associated radio and energetic particle observations, provided strong evidence of a coronal, rather than a chromospheric origin. The H alpha manifestation of the wave is assumed to be the "ground track" or "skirt" of a three-dimensional disturbance.

  13. ASTER Waves

    NASA Image and Video Library

    2000-10-06

    The pattern on the right half of this image of the Bay of Bengal is the result of two opposing wave trains colliding. This ASTER sub-scene, acquired on March 29, 2000, covers an area 18 kilometers (13 miles) wide and 15 kilometers (9 miles) long in three bands of the reflected visible and infrared wavelength region. The visible and near-infrared bands highlight surface waves due to specular reflection of sunlight off of the wave faces. http://photojournal.jpl.nasa.gov/catalog/PIA02662

  14. Waves in Motion

    NASA Astrophysics Data System (ADS)

    McGourty, L.; Rideout, K.

    2005-12-01

    "Waves in Motion" This teaching unit was created by Leslie McGourty and Ken Rideout under the Research Experience for Teachers (RET) program at MIT Haystack Observatory during the summer of 2005. The RET program is funded by a grant from the National Science Foundation. The goals of this teaching unit are to deepen students' understanding about waves, wave motion, and the electromagnetic spectrum as a whole. Specifically students will comprehend the role radio waves play in our daily lives and in the investigation of the universe. The lessons can be used in a high school physics, earth science or astronomy curriculum. The unit consists of a series of interlocking lectures, activities, and investigations that can be used as stand alone units to supplement a teacher's existing curriculum, as an independent investigation for a student, or as a long exploration into radio astronomy with a theme of waves in space: how and where they carry their information. Special emphasis is given to the Relativity theories in honor of the "World Year of Physics" to celebrate Einstein's 1905 contributions. The lessons are currently being implemented at the high school level, the preliminary results of which will be presented. At the end of the academic year, the units will be evaluated and updated, reflecting student input and peer review after which they will be posted on the internet for teachers to use in their classrooms.

  15. Whirling waves in Interference experiments

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  16. Spiral wave dynamics in neocortex

    PubMed Central

    Liang, Jianmin; Takagaki, Kentaroh; Gao, Xin; Wu, Jian-young

    2015-01-01

    Summary Although spiral waves are ubiquitous features of nature, and have been observed in many biological systems, their existence and potential function in mammalian cerebral cortex remains uncertain. Using voltage-sensitive dye imaging, we found that spiral waves occur frequently in the neocortex in vivo, both during pharmacologically induced oscillations and during sleep-like states. While their lifespan is limited, spiral waves can modify ongoing cortical activity by influencing oscillation frequencies and spatial coherence, and by reducing amplitude in the area surrounding the spiral phase singularity. During sleep-like states, the rate of occurrence of spiral waves varies greatly depending on brain states. These results support the hypothesis that spiral waves, as an emergent activity pattern, can organize and modulate cortical population activity on the mesoscopic scale and may contribute to both normal cortical processing and to pathological patterns of activity such as those found in epilepsy. PMID:21145009

  17. Five Years of Data at the Monterey Ocean Bottom Broadband Seismic Station (MOBB)

    NASA Astrophysics Data System (ADS)

    Dolenc, D.; Romanowicz, B.; McGill, P.; Neuhauser, D.; Uhrhammer, R.

    2007-12-01

    We present an overview of the results obtained at MOBB in the past 5.5 years of its continuous operation. In particular we focus on the observations of the long-period ocean surface gravity waves (infragravity waves; 0.002 to 0.05 Hz) and different methods to remove the long-period background and signal-generated noise from the seismic observations. MOBB was installed 40 km offshore in the Monterey Bay at a water depth of 1000 m in April 2002 in collaboration between Berkeley Seismological Laboratory and Monterey Bay Aquarium Research Institute (MBARI). It is located west of the San Gregorio Fault and represents the first step towards extending the onshore broadband seismic network in northern California westward of the Pacific-North America plate boundary. MOBB comprises a three- component broadband seismometer Guralp CMG-1T, sensitive over a wide frequency range, from 50 Hz to 2.8 mHz (360 s), a water current meter measuring current speed and direction, and a differential pressure gauge. At present, the station is autonomous and the data are on average retrieved every 4 months using MBARI's remotely operated vehicle Ventana. Work is under way to connect it to the MARS (Monterey Accelerated Research System) cable so that it will contribute continuous real time data to the northern California earthquake monitoring system. Lessons learned from the MOBB deployment as well as noise removal techniques that are specific to the ocean bottom installation will provide us reference for future installations of broadband seismic stations in the oceans. When compared to the quiet land stations, ocean bottom seismic station MOBB shows increased background noise in the band pass of interest for the study of regional and teleseismic signals. This is mainly due to deformation of the seafloor under the pressure forcing by infragravity waves. Also observed is additional signal- generated noise which is due to the reverberations in the shallow sedimentary layers as well as in the

  18. Novel itinerant transverse spin waves

    NASA Astrophysics Data System (ADS)

    Feldmann, John Delaney

    In 1956, Lev Davidovich Landau put forth his theory on systems of interacting fermions, or fermi liquids. A year later, Viktor Pavlovich Silin described spin waves that such a system of fermions would support. The treatment of the contribution of the molecular field to the spin wave dispersion was a novel aspect of these spin waves. Silin predicted that there would exist a hierarchy of spin waves in a fermi liquid, one for each component of the spherical harmonic expansion of the fermi surface. In 1968, Anthony J. Leggett and Michael J. Rice derived from fermi liquid theory how the behavior of the spin diffusion coefficient of a fermi liquid could be directly experimentally observable via the spin echo effect [24]. Their prediction, that the diffusion coefficient of a fermi liquid would not decay exponentially with temperature, but rather would have a maximum at some non-zero temperature, was a direct consequence of the fermi liquid molecular field and spin wave phenomena, and this was corroborated by experiment in 1971 by Corruccini, et al. [13]. A parallel advancement in the theory of fermi liquid spin waves came with the extension of the theory to describe weak ferromagnetic metals. In 1959, Alexei Abrikosov and I. E. Dzyaloshiski put forth a theoretical description of a ferromagnetic fermi liquid [1]. In 2001, Kevin Bedell and Krastan Blagoev showed that a non-trivial contribution to the dispersion of the ferromagnetic current spin wave arises from the necessary consideration of higher harmonic moments in the distortion of the fermi surface from its ground state [8]. In the chapters to follow, the author presents new results for transverse spin waves in a fermi liquid, which arise from a novel ground state of a fermi liquid-one in which an l = 1 harmonic distortion exists in the ground state polarization. It is shown that such an instability can lead to spin waves with dispersions that are characterized by a linear dependence on the wave number at long

  19. Determining wave direction using curvature parameters.

    PubMed

    de Queiroz, Eduardo Vitarelli; de Carvalho, João Luiz Baptista

    2016-01-01

    The curvature of the sea wave was tested as a parameter for estimating wave direction in the search for better results in estimates of wave direction in shallow waters, where waves of different sizes, frequencies and directions intersect and it is difficult to characterize. We used numerical simulations of the sea surface to determine wave direction calculated from the curvature of the waves. Using 1000 numerical simulations, the statistical variability of the wave direction was determined. The results showed good performance by the curvature parameter for estimating wave direction. Accuracy in the estimates was improved by including wave slope parameters in addition to curvature. The results indicate that the curvature is a promising technique to estimate wave directions.•In this study, the accuracy and precision of curvature parameters to measure wave direction are analyzed using a model simulation that generates 1000 wave records with directional resolution.•The model allows the simultaneous simulation of time-series wave properties such as sea surface elevation, slope and curvature and they were used to analyze the variability of estimated directions.•The simultaneous acquisition of slope and curvature parameters can contribute to estimates wave direction, thus increasing accuracy and precision of results.

  20. Modulation of short waves by long waves. [ocean wave interactions

    NASA Technical Reports Server (NTRS)

    Reece, A. M., Jr.

    1978-01-01

    Wave-tank experiments were performed to investigate the cyclic short-wave energy changes, related in phase to an underlying long wave, which occur during active generation of the short-wave field by wind. Measurements of time series of the short-wave slope were made by a laser-optical system, where the basic long-wave parameters were controlled and wind speeds were accurately reproducible. The short-wave slope variances were found to exhibit cyclic variations that are related to the phase of the long wave. The variations result from two combined effects: (1) the short wave frequency is varied by the long-wave orbital velocity; (2) the energy of the short waves is modulated by the actions of aerodynamic and hydrodynamic couplings that operate on the short waves in a manner related to the long-wave phase.

  1. Capillary waves and ellipsometry experiments

    NASA Astrophysics Data System (ADS)

    Bonn, D.; Wegdam, G. H.

    1992-09-01

    The inclusion of higher-order terms in the capillary-wave Hamiltonian may reduce the contributions of these fluctuations to the ellipsometric coefficients. We show that the renormalization of capillary waves at a fluid-fluid interface by Sengers and van Leeuwen [Phys. Rev. A 39 (1989) 6346] using the wave vector-dependent surface tension that follows from the coupled mode theory by Meunier [Phys. France 48 (1987)1819] yields a satisfactory agreement with recent ellipsometry measurements by Schmidt [Phys. Rev. A 38 (1988) 567]. The interface is viewed upon as an intrinsic interface broadened by capillary waves. We suppose that the cutoff wave vector q_{max} that follows from mode-coupling theory marks the transition from the short-wavelength bulk-like fluctuations that contribute to the bare surface tension to the long-wavelength capillary wave-like fluctuations that contribute to the full surface tension. This enables us to calculate, without any adjustable parameters, both the ratio of the bare and experimental surface tension and the universal constant for the elliptical thickness of the interface. Both agree remarkably well with experimental values.

  2. Numerical procedure for planetary wave solution

    SciTech Connect

    Choi, Woo Kap; Wuebbles, D.J.

    1993-09-01

    The newly-developed LLNL two-dimensional chemical-radiative-transport model requires a knowledge of the EP flux divergence as an input momentum forcing. The major contributions for this forcing term come from the synoptic wave in the troposphere, the planetary wave in the stratosphere and mesosphere and the gravity wave in the upper mesosphere. The major source of the zonal momentum forcing in the middle atmosphere is the nonlinear planetary wave breaking. This planetary wave breaking also plays a significant role of mixing the chemical tracers. Garcia suggested a way of parameterizing the planetary wave breaking by using, linear damping of the primary wave. In this note we describe the procedure of obtaining the wave solution for the parameterization.

  3. Making WAVES.

    ERIC Educational Resources Information Center

    Hindes, Victoria A.; Hom, Keri; Brookshaw, Keith

    About 46% of high school graduates enrolled in California State Universities need remedial courses in both math and English to prepare them for college level. These students typically earned B averages in their high school math and English classes. In order to address this issue, Shasta College launched Operation WAVES (Win by Achieving Valuable…

  4. Wave Condensation

    NASA Astrophysics Data System (ADS)

    Rica, Sergio

    In this article I will review some results, in collaboration with Colm Connaughton, Christophe Josserand, Antonio Picozzi, and Yves Pomeau [Phys. Rev. Lett. 95, 263901 (2005)], on the large-scale condensation of classical waves by considering the defocusing nonlinear Schrödinger equation as a representative model.

  5. Gravity wave initiated convection

    NASA Technical Reports Server (NTRS)

    Hung, R. J.

    1990-01-01

    The vertical velocity of convection initiated by gravity waves was investigated. In one particular case, the convective motion-initiated and supported by the gravity wave-induced activity (excluding contributions made by other mechanisms) reached its maximum value about one hour before the production of the funnel clouds. In another case, both rawinsonde and geosynchronous satellite imagery were used to study the life cycles of severe convective storms. Cloud modelling with input sounding data and rapid-scan imagery from GOES were used to investigate storm cloud formation, development and dissipation in terms of growth and collapse of cloud tops, as well as, the life cycles of the penetration of overshooting turrets above the tropopause. The results based on these two approaches are presented and discussed.

  6. Urban Heat Wave Hazard Assessment

    NASA Technical Reports Server (NTRS)

    Quattrochi, Dale A.; Jedlovec, Gary; Meyer, Paul J.; LaFontaine, Frank J.; Crane, Dakota L.

    2016-01-01

    Heat waves are the largest cause of environment-related deaths globally. On average, over 6,000 people in the United States alone are hospitalized each summer due to excessive heat. Key elements leading to these disasters are elevated humidity and the urban heat island effect, which act together to increase apparent temperature and amplify the effects of a heat wave. Urban demographics and socioeconomic factors also play a role in determining individual risk. Currently, advisories of impending heat waves are often too generalized, with limited or no spatial variability over urban regions. This frequently contributes to a lack of specific response on behalf of the population. A goal of this project is to develop a product that has the potential to provide more specific heat wave guidance invoking greater awareness and action.

  7. On neutron surface waves

    SciTech Connect

    Ignatovich, V. K.

    2009-01-15

    It is shown that neutron surface waves do not exist. The difference between the neutron wave mechanics and the wave physics of electromagnetic and acoustic processes, which allows the existence of surface waves, is analyzed.

  8. Rings and Waves

    NASA Image and Video Library

    2013-09-30

    Saturn A ring is decorated with several kinds of waves. NASA Cassini spacecraft has captured a host of density waves, a bending wave, and the edge waves on the edge of the Keeler gap caused by the small moon Daphnis.

  9. Students dance longitudinal standing waves

    NASA Astrophysics Data System (ADS)

    Ruiz, Michael J.

    2017-05-01

    A demonstration is presented that involves students dancing longitudinal standing waves. The resulting kinaesthetic experience and visualization both contribute towards an understanding of the natural modes of vibrations in open and closed pipes. A video of this fun classroom activity is provided (http://mjtruiz.com/ped/dance/).

  10. Wave Turbulence

    NASA Astrophysics Data System (ADS)

    Newell, Alan C.; Rumpf, Benno

    2011-01-01

    In this article, we state and review the premises on which a successful asymptotic closure of the moment equations of wave turbulence is based, describe how and why this closure obtains, and examine the nature of solutions of the kinetic equation. We discuss obstacles that limit the theory's validity and suggest how the theory might then be modified. We also compare the experimental evidence with the theory's predictions in a range of applications. Finally, and most importantly, we suggest open challenges and encourage the reader to apply and explore wave turbulence with confidence. The narrative is terse but, we hope, delivered at a speed more akin to the crisp pace of a Hemingway story than the wordjumblingtumbling rate of a Joycean novel.

  11. Gravity waves

    NASA Astrophysics Data System (ADS)

    Vanzandt, T. E.

    1985-07-01

    Atmospheric parameters fluctuate on all scales. In the mesoscale these fluctuations are occasionally sinusoidal so that they can be interpreted as gravity waves. Usually, however, the fluctuations are noise like, so that their cause is not immediately evident. Results of mesoscale observations in the 20 to 120 m altitude range that are suitable for incorporation into a model atmosphere are very limited. In the stratosphere and lower mesosphere observations are sparse and very little data has been summarized into appropriate form. There is much more data in the upper mesosphere and lower thermosphere, but again very little of it has been summarized. The available mesoscale spectra of horizontal wind u versus vertical wave number m in the 20 to 120 km altitude range are shown together with a spectrum from the lower atmosphere for comparison. Further information about these spectra is given. In spite of the large range of altitudes and latitudes, the spectra from the lower atmosphere (NASA, 1971 and DEWAN, 1984) are remarkably similar in both shape and amplitude. The mean slopes of -2.38 for the NASA spectrum and -2.7 for the Dewan spectra are supported by the mean slope of -2.75 found by ROSENBERG et al. (1974). The mesospheric spectrum is too short to establish a shape. Its amplitude is about an order of magnitude larger than the NASA spectrum in the same wave number range. The NASA and Dewan spectra suggest that the mesoscale spectra in the lower atmosphere are insensitive to meteorological conditions.

  12. Gravity Waves

    NASA Technical Reports Server (NTRS)

    Vanzandt, T. E.

    1985-01-01

    Atmospheric parameters fluctuate on all scales. In the mesoscale these fluctuations are occasionally sinusoidal so that they can be interpreted as gravity waves. Usually, however, the fluctuations are noise like, so that their cause is not immediately evident. Results of mesoscale observations in the 20 to 120 m altitude range that are suitable for incorporation into a model atmosphere are very limited. In the stratosphere and lower mesosphere observations are sparse and very little data has been summarized into appropriate form. There is much more data in the upper mesosphere and lower thermosphere, but again very little of it has been summarized. The available mesoscale spectra of horizontal wind u versus vertical wave number m in the 20 to 120 km altitude range are shown together with a spectrum from the lower atmosphere for comparison. Further information about these spectra is given. In spite of the large range of altitudes and latitudes, the spectra from the lower atmosphere (NASA, 1971 and DEWAN, 1984) are remarkably similar in both shape and amplitude. The mean slopes of -2.38 for the NASA spectrum and -2.7 for the Dewan spectra are supported by the mean slope of -2.75 found by ROSENBERG et al. (1974). The mesospheric spectrum is too short to establish a shape. Its amplitude is about an order of magnitude larger than the NASA spectrum in the same wave number range. The NASA and Dewan spectra suggest that the mesoscale spectra in the lower atmosphere are insensitive to meteorological conditions.

  13. Gravity Waves

    NASA Technical Reports Server (NTRS)

    Vanzandt, T. E.

    1985-01-01

    Atmospheric parameters fluctuate on all scales. In the mesoscale these fluctuations are occasionally sinusoidal so that they can be interpreted as gravity waves. Usually, however, the fluctuations are noise like, so that their cause is not immediately evident. Results of mesoscale observations in the 20 to 120 m altitude range that are suitable for incorporation into a model atmosphere are very limited. In the stratosphere and lower mesosphere observations are sparse and very little data has been summarized into appropriate form. There is much more data in the upper mesosphere and lower thermosphere, but again very little of it has been summarized. The available mesoscale spectra of horizontal wind u versus vertical wave number m in the 20 to 120 km altitude range are shown together with a spectrum from the lower atmosphere for comparison. Further information about these spectra is given. In spite of the large range of altitudes and latitudes, the spectra from the lower atmosphere (NASA, 1971 and DEWAN, 1984) are remarkably similar in both shape and amplitude. The mean slopes of -2.38 for the NASA spectrum and -2.7 for the Dewan spectra are supported by the mean slope of -2.75 found by ROSENBERG et al. (1974). The mesospheric spectrum is too short to establish a shape. Its amplitude is about an order of magnitude larger than the NASA spectrum in the same wave number range. The NASA and Dewan spectra suggest that the mesoscale spectra in the lower atmosphere are insensitive to meteorological conditions.

  14. Sediment and Crustal Shear Velocity Structure offshore New Zealand from Seafloor Compliance, Receiver Functions and Rayleigh Wave Dispersion

    NASA Astrophysics Data System (ADS)

    Ball, J. S.; Sheehan, A. F.; Stachnik, J. C.; Lin, F.; Collins, J. A.

    2013-12-01

    We have developed a joint Monte Carlo inversion of teleseismic receiver functions, seafloor compliance, and Rayleigh wave dispersion and apply it here to ocean bottom seismic (OBS) data from offshore New Zealand. With this method we estimate sediment and crustal thickness and shear velocity structure beneath the Bounty Trough and the Tasman Sea flanking the South Island of New Zealand. Teleseismic receiver functions and surface wave dispersion measurements provide complementary constraints on shear velocity structure and interface depths beneath seismic stations. At ocean bottom seismic (OBS) stations the interpretation of these measurements is complicated by strong sediment reverberations that obscure deeper impedance contrasts such as the Moho. In principle, the seafloor's response to ocean loading from infragravity waves (seafloor compliance) can be used to determine shallow shear velocity information. This velocity information can subsequently be used to better model the receiver function reverberations, allowing deeper interfaces of tectonic interest to be resolved. Data for this study were acquired in 2009-2010 by the Marine Observations of Anisotropy Near Aotearoa (MOANA) experiment, which deployed 30 broadband OBS and differential pressure gauges (DPGs) off the South Island of New Zealand. High-frequency (5Hz) receiver functions were estimated using multitaper cross-correlation for events in a 30-90 degree epicentral distance range. Coherence-weighted stacks binned by epicentral distance were produced in the frequency domain to suppress noise. Seafloor compliance was measured using multitaper pressure and acceleration spectra averaged from 120 days of continuous data without large transient events. Seafloor compliance measurements on the order of 10-9 Pa-1 are sensitive to shear velocity structure in the uppermost 5km of the crust and sediments. Rayleigh dispersion measurements were obtained at periods of 6-27s from ambient noise cross correlation. Sediment

  15. CMS-Wave

    DTIC Science & Technology

    2015-10-30

    Coastal Inlets Research Program CMS-Wave CMS-Wave is a two-dimensional spectral wind -wave generation and transformation model that employs a forward...estimates. The model can be coupled to the Boussinesq wave model BOUSS-2D for port and harbor applications. CMS-Wave, a phase-averaged spectral wind -wave

  16. Internal Waves and Wave Attractors in Enceladus' Subsurface Ocean

    NASA Astrophysics Data System (ADS)

    van Oers, A. M.; Maas, L. R.; Vermeersen, B. L. A.

    2016-12-01

    One of the most peculiar features on Saturn moon Enceladus is its so-called tiger stripe pattern at the geologically active South Polar Terrain (SPT), as first observed in detail by the Cassini spacecraft early 2005. It is generally assumed that the four almost parallel surface lines that constitute this pattern are faults in the icy surface overlying a confined salty water reservoir. In 2013, we formulated the original idea [Vermeersen et al., AGU Fall Meeting 2013, abstract #P53B-1848] that the tiger stripe pattern is formed and maintained by induced, tidally and rotationally driven, wave-attractor motions in the ocean underneath the icy surface of the tiger-stripe region. Such wave-attractor motions are observed in water tank experiments in laboratories on Earth and in numerical experiments [Maas et al., Nature, 338, 557-561, 1997; Drijfhout and Maas, J. Phys. Oceanogr., 37, 2740-2763, 2007; Hazewinkel et al., Phys. Fluids, 22, 107102, 2010]. Numerical simulations show the persistence of wave attractors for a range of ocean shapes and stratifications. The intensification of the wave field near the location of the surface reflections of wave attractors has been numerically and experimentally confirmed. We measured the forces a wave attractor exerts on a solid surface, near a reflection point. These reflection points would correspond to the location of the tiger stripes. Combining experiments and numerical simulations we conclude that (1) wave attractors can exist in Enceladus' subsurface sea, (2) their shape can be matched to the tiger stripes, (3) the wave attractors cause a localized force at the water-ice boundaries, (4) this force could have been large enough to contribute to fracturing the ice and (5) the wave attractors localize energy (and particles) and cause dissipation along its path, helping explain Enceladus' enigmatic heat output at the tiger stripes.

  17. Wave chaotic experiments and models for complicated wave scattering systems

    NASA Astrophysics Data System (ADS)

    Yeh, Jen-Hao

    Wave scattering in a complicated environment is a common challenge in many engineering fields because the complexity makes exact solutions impractical to find, and the sensitivity to detail in the short-wavelength limit makes a numerical solution relevant only to a specific realization. On the other hand, wave chaos offers a statistical approach to understand the properties of complicated wave systems through the use of random matrix theory (RMT). A bridge between the theory and practical applications is the random coupling model (RCM) which connects the universal features predicted by RMT and the specific details of a real wave scattering system. The RCM gives a complete model for many wave properties and is beneficial for many physical and engineering fields that involve complicated wave scattering systems. One major contribution of this dissertation is that I have utilized three microwave systems to thoroughly test the RCM in complicated wave systems with varied loss, including a cryogenic system with a superconducting microwave cavity for testing the extremely-low-loss case. I have also experimentally tested an extension of the RCM that includes short-orbit corrections. Another novel result is development of a complete model based on the RCM for the fading phenomenon extensively studied in the wireless communication fields. This fading model encompasses the traditional fading models as its high-loss limit case and further predicts the fading statistics in the low-loss limit. This model provides the first physical explanation for the fitting parameters used in fading models. I have also applied the RCM to additional experimental wave properties of a complicated wave system, such as the impedance matrix, the scattering matrix, the variance ratio, and the thermopower. These predictions are significant for nuclear scattering, atomic physics, quantum transport in condensed matter systems, electromagnetics, acoustics, geophysics, etc.

  18. Inhomogeneous plane waves and cylindrical waves in anisotropic anelastic media

    NASA Astrophysics Data System (ADS)

    Krebes, E. S.; Le, Lawrence H. T.

    1994-12-01

    In isotropic anelastic media, the phase velocity of an inhomogeneous plane body wave, which is a function of Q and the degree of inhomogeneity gamma, is significantly less than the corresponding homogeneous wave phase velocity typically only if gamma is very large (unless Q is unusually low). Here we investigate inhomogeneous waves in anisotropic anelastic media, where phase velocities are also functions of the direction of phase propagation theta, and find that (1) the low phase velocities can occur at values of gamma which are substantially less than the isotropic values and that they occur over a limited range of oblique directions theta, and (2) for large positive values of gamma, there are ranges of oblique directions theta in which the inhomogeneous waves cannot propagate at all because there is no physically acceptable solution to the dispersion relation. We show examples of how the waves of case 1 can occur in practice and cause a number of anomalous wave propagation effects. The waves of case 2, though, do not arise in practice (they do not correspond to any points on the horizontal slowness plate). We also show that in the decomposition of a cylindrical wave into plane waves, inhomogeneous plane waves occur whose amplitudes grow in the direction of phase propagation and that this direction is away from the receiver to which they are contributing. The energy in these waves does, however, travel toward the receiver, and their amplitudes decay in the direction of energy propagation. We also show that if the commonly used definition for the quality factor in an isotropic medium, Q = -Re(mu)/Im(mu) where mu is a complex modulus, is applied to an anisotropic anelastic medium in order to study absorption anisotropy, a generally unreliable measure of the anelasticity of inhomogeneous wave propagation in a given arbitrary direction is obtained. The more fundamental definition based on energy loss (i.e., 2pi/Q = Delta E/E) should be used in general, and we present

  19. Making Waves: Seismic Waves Activities and Demonstrations

    NASA Astrophysics Data System (ADS)

    Braile, S. J.; Braile, L. W.

    2011-12-01

    The nature and propagation of seismic waves are fundamental concepts necessary for understanding the exploration of Earth's interior structure and properties, plate tectonics, earthquakes, and seismic hazards. Investigating seismic waves is also an engaging approach to learning basic principles of the physics of waves and wave propagation. Several effective educational activities and demonstrations are available for teaching about seismic waves, including the stretching of a spring to demonstrate elasticity; slinky wave propagation activities for compressional, shear, Rayleigh and Love waves; the human wave activity to demonstrate P- and S- waves in solids and liquids; waves in water in a simple wave tank; seismic wave computer animations; simple shake table demonstrations of model building responses to seismic waves to illustrate earthquake damage to structures; processing and analysis of seismograms using free and easy to use software; and seismic wave simulation software for viewing wave propagation in a spherical Earth. The use of multiple methods for teaching about seismic waves is useful because it provides reinforcement of the fundamental concepts, is adaptable to variable classroom situations and diverse learning styles, and allows one or more methods to be used for authentic assessment. The methods described here have been used effectively with a broad range of audiences, including K-12 students and teachers, undergraduate students in introductory geosciences courses, and geosciences majors.

  20. Capillary rogue waves.

    PubMed

    Shats, M; Punzmann, H; Xia, H

    2010-03-12

    We report the first observation of extreme wave events (rogue waves) in parametrically driven capillary waves. Rogue waves are observed above a certain threshold in forcing. Above this threshold, frequency spectra broaden and develop exponential tails. For the first time we present evidence of strong four-wave coupling in nonlinear waves (high tricoherence), which points to modulation instability as the main mechanism in rogue waves. The generation of rogue waves is identified as the onset of a distinct tail in the probability density function of the wave heights. Their probability is higher than expected from the measured wave background.

  1. Statistical analysis of plasmaspheric EMIC waves

    NASA Astrophysics Data System (ADS)

    Kato, Y.; Miyoshi, Y.; Sakaguchi, K.; Kasahara, Y.; Keika, K.; Shoji, M.; Kitamura, N.; Hasegawa, S.; Kumamoto, A.; Shiokawa, K.

    2014-12-01

    Electromagnetic ion cyclotron (EMIC) waves in the inner magnetosphere are important since EMIC waves cause the pitch angle scattering of ring current ions as well as relativistic electrons of the radiation belts. Although the spatial distributions of EMIC waves have been investigated by several spacecraft such as CRRES, THEMIS and AMPTE/CCE, there have been little studies on plasmaspheric EMIC waves. We investigate statistically EMIC wave data using the Akebono/VLF measurements. The plasmaspheric EMIC waves tend to be distributed at lower L-shell region (L~2) than the slot region. There are no significant MLT dependences, which are different from the EMIC waves outside the plasmapause. The plasmaspheric EMIC wave frequencies depend on the equatorial cyclotron frequency, suggesting that the plasmaspheric EMIC waves are not propagated from high L-shell but generated near the equivalent L-shell magnetic equator. This result is consistent with the result of the dependence of resonance energy. Using the in-situ thermal plasma density measured by the Akebono satellite, we estimate the resonance energy of energetic ions, and the resonance energies of the plasmaspheric EMIC waves are few tens keV to ~ 1 MeV. The results indicate that the ring current and radiation belt ions may contribute the generation of the plasmaspheric EMIC waves.

  2. Physical response of light-time gravitational wave detectors

    NASA Astrophysics Data System (ADS)

    Koop, Michael J.; Finn, Lee Samuel

    2014-09-01

    Gravitational wave detectors are typically described as responding to gravitational wave metric perturbations, which are gauge-dependent and—correspondingly—unphysical quantities. This is particularly true for ground-based interferometric detectors, like LIGO, space-based detectors, like LISA and its derivatives, spacecraft Doppler tracking detectors, and pulsar timing array detectors. The description of gravitational waves, and a gravitational wave detector's response, to the unphysical metric perturbation has lead to a proliferation of false analogies and descriptions regarding how these detectors function, and true misunderstandings of the physical character of gravitational waves. Here we provide a fully physical and gauge-invariant description of the response of a wide class of gravitational wave detectors in terms of the Riemann curvature, the physical quantity that describes gravitational phenomena in general relativity. In the limit of high frequency gravitational waves, the Riemann curvature separates into two independent gauge-invariant quantities: a "background" curvature contribution and a "wave" curvature contribution. In this limit the gravitational wave contribution to the detector response reduces to an integral of the gravitational wave contribution of the curvature along the unperturbed photon path between components of the detector. The description presented here provides an unambiguous physical description of what a gravitational wave detector measures and how it operates, a simple means of computing corrections to a detectors response owing to general detector motion, a straightforward way of connecting the results of numerical relativity simulations to gravitational wave detection, and a basis for a general and fully relativistic pulsar timing formula.

  3. The morning glory wave of southern California

    NASA Astrophysics Data System (ADS)

    Tsai, Victor C.; Kanamori, Hiroo; Artru, Juliette

    2004-02-01

    A pulse-like disturbance traveling across the Los Angeles basin was observed on 12 October 2001 with seismographs of the TriNet network. This wave had a period of about 1000 s and a propagation speed of about 10 m/s, much slower than seismic waves. The seismograph data were compared with barograph data, and a good correlation was found so the wave was determined to be atmospheric in origin. It had amplitude of about 1 mbar, but it was not known what process could produce such a wave. Since the initial finding, we have inspected all the TriNet barograph and seismograph data for a period of two and a half years (from January 2000 to August 2002) and found four more similar events. Each of the events has amplitude between 0.8 and 1.3 mbar, a period between 700 and 1400 s, and a propagation speed between 5 and 25 m/s. We conclude that these waves are internal gravity waves trapped in a stable layer formed by a temperature inversion. Some of these waves have large amplitudes and develop into solitary waves (nonlinear internal gravity waves) similar to the spectacular "morning glory" wave observed in Australia. We call these waves the LA morning glory waves. The LA morning glory wave is probably excited by either stormy weather, winds such as the Santa Ana winds, or large teleseismic events. The morning glory wave could contribute to the recently reported excitation of the background free oscillations of the Earth. Additionally, because of its large amplitude it could have important implications for aviation safety, as was suggested earlier for the morning glory waves in Australia.

  4. Nonlinear Waves.

    DTIC Science & Technology

    1986-05-27

    con- €"" straints:’. *’Permanent address: Dipartimento di Fisica . Universita di Roma 1. 00185 u 11lia. tr(a U(x)) = 0. (7a. 2469 1. Math,. PyS. 26 (10...Tenenblat Universidade de Brasilia Departamento de Matematica Brasilia, Brasil September 1985 , - . Abstract The generalized wave equation and generalized...Permanent addrems: Dipartimento di Fisica . Universita di Roma t3 U, 0. Roma. Italy The linear limit of i3) provides the most general solution ot 2614 J. MatM

  5. CMS-Wave

    DTIC Science & Technology

    2014-10-27

    2014 2. REPORT TYPE 3. DATES COVERED 00-00-2014 to 00-00-2014 4. TITLE AND SUBTITLE CMS -Wave 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM...Program CMS -Wave CMS -Wave is a two-dimensional spectral wind-wave generation and transformation model that employs a forward-marching, finite...difference method to solve the wave action conservation equation. Capabilities of CMS -Wave include wave shoaling, refraction, diffraction, reflection

  6. Wave heating of the solar atmosphere

    PubMed Central

    Arregui, Iñigo

    2015-01-01

    Magnetic waves are a relevant component in the dynamics of the solar atmosphere. Their significance has increased because of their potential as a remote diagnostic tool and their presumed contribution to plasma heating processes. We discuss our current understanding of coronal heating by magnetic waves, based on recent observational evidence and theoretical advances. The discussion starts with a selection of observational discoveries that have brought magnetic waves to the forefront of the coronal heating discussion. Then, our theoretical understanding of the nature and properties of the observed waves and the physical processes that have been proposed to explain observations are described. Particular attention is given to the sequence of processes that link observed wave characteristics with concealed energy transport, dissipation and heat conversion. We conclude with a commentary on how the combination of theory and observations should help us to understand and quantify magnetic wave heating of the solar atmosphere. PMID:25897091

  7. Waves at Navigation Structures

    DTIC Science & Technology

    2014-10-27

    upgrades the Coastal Modeling System’s ( CMS ) wave model CMS -Wave, a phase-averaged spectral wave model, and BOUSS-2D, a Boussinesq-type nonlinear wave...provided by this work unit address these critical needs of the Corps’ navigation mission. Description Issue Addressed CMS -Wave application at Braddock...Bay, NY WaveNet application in Gulf of Mexico CMS -Wave and BOUSS-2D are two numerical wave models, and WaveNet and TideNet are two web-based

  8. ASTER Waves

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The pattern on the right half of this image of the Bay of Bengal is the result of two opposing wave trains colliding. This ASTER sub-scene, acquired on March 29, 2000, covers an area 18 kilometers (13 miles) wide and 15 kilometers (9 miles) long in three bands of the reflected visible and infrared wavelength region. The visible and near-infrared bands highlight surface waves due to specular reflection of sunlight off of the wave faces.

    Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of International Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. science team leader; Moshe Pniel of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The primary goal of the ASTER mission is to obtain high-resolution image data in 14 channels over the entire land surface, as well as black and white stereo images. With revisit time of between 4 and 16 days, ASTER will provide the capability for repeat coverage of changing areas on Earth's surface. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of International Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. science team leader; Moshe Pniel of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The primary goal of the ASTER mission is to obtain high-resolution image data in 14 channels

  9. Interferometry of background acoustic-gravity waves

    NASA Astrophysics Data System (ADS)

    Zabotin, Nikolay A.; Godin, Oleg A.; Sheehan, Anne F.

    2013-04-01

    directivity. The reduction in the averaging time makes it possible to study dynamics on the acoustic-gravity wave field and helps to identify specific wave types that contribute to observed pressure variations. We will discuss implications of the seafloor measurements for observations of acoustic-gravity waves in air above the ocean and feasibility of extending the wave interferometry to other modalities of observation of background acoustic-gravity waves, including ionospheric radio sounding performed with Dynasonde systems.

  10. Waves and Tsunami Project

    ERIC Educational Resources Information Center

    Frashure, K. M.; Chen, R. F.; Stephen, R. A.; Bolmer, T.; Lavin, M.; Strohschneider, D.; Maichle, R.; Micozzi, N.; Cramer, C.

    2007-01-01

    Demonstrating wave processes quantitatively in the classroom using standard classroom tools (such as Slinkys and wave tanks) can be difficult. For example, waves often travel too fast for students to actually measure amplitude or wavelength. Also, when teaching propagating waves, reflections from the ends set up standing waves, which can confuse…

  11. Waves and Tsunami Project

    ERIC Educational Resources Information Center

    Frashure, K. M.; Chen, R. F.; Stephen, R. A.; Bolmer, T.; Lavin, M.; Strohschneider, D.; Maichle, R.; Micozzi, N.; Cramer, C.

    2007-01-01

    Demonstrating wave processes quantitatively in the classroom using standard classroom tools (such as Slinkys and wave tanks) can be difficult. For example, waves often travel too fast for students to actually measure amplitude or wavelength. Also, when teaching propagating waves, reflections from the ends set up standing waves, which can confuse…

  12. Stationary Planetary Wave and Nonmigrating Tidal Composition of Ionospheric Wave-3 & Wave-4 variations in 2007-2011 FORMOSAT-3/COSMIC observations

    NASA Astrophysics Data System (ADS)

    Chang, L. C.; Lin, C.; Yue, J.; Liu, J. G.; Lin, J.

    2013-12-01

    The wave-3 and wave-4 modulations of the Equatorial Ionization Anomalies (EIAs) are a robust feature of the low latitude ionosphere, when viewed in a constant local time reference frame. Although initially associated respectively with the DE2 and DE3 nonmigrating diurnal tides coupling upwards from the mesosphere and lower thermosphere (MLT) region alone, recent results have suggested that the wave-3 and wave-4 components may also have significant contributions from other nonmigrating tidal and stationary planetary wave (SPW) components. In this study, we present observations of tidal and SPW components comprising the ionospheric wave-3 and wave-4 structures from FORMOSAT-3 / COSMIC Total Electron Content (TEC) from 2007-2011. We find that the wave-3 (wave-4) feature is comprised predominately by DE2 (DE3) and SPW3 (SPW4) throughout the entire five year period, with contributions from SE1 (SE2) being less significant. Additionally, the wave-3 component also has recurring contributions from a DW4 component during December/January. The absolute amplitudes of all the aforementioned components are positively correlated to the level of solar activity, as well as the semiannual variation in zonal mean TEC. After normalizing by the zonal mean TEC, the relative amplitudes of the wave-4 related components show an anti-correlation to solar activity through 2010, which is not seen with the wave-3 related components. The seasonal variation and phase relations of the main constituents of wave-3 and wave-4 are consistent from year to year, as evidenced by the inter-annual recurrence in the peak and trough locations of the ionospheric wave-3 and wave-4. Relative amplitudes of DE3 (black) and SPW4 (blue) in COSMIC TECs as a function of time at 15°N (a) and 15°S (b). Units % of maximum daily zonal mean TEC. Range of uncertainties denoted by dotted lines.

  13. PARTICLE ACCELERATION IN SUPERLUMINAL STRONG WAVES

    SciTech Connect

    Teraki, Yuto; Ito, Hirotaka; Nagataki, Shigehiro

    2015-06-01

    We calculate the electron acceleration in random superluminal strong waves (SLSWs) and radiation from them using numerical methods in the context of the termination shocks of pulsar wind nebulae. We pursue the orbit of electrons by solving the equation of motion in the analytically expressed electromagnetic turbulences. These consist of a primary SLS and isotropically distributed secondary electromagnetic waves. Under the dominance of the secondary waves, all electrons gain nearly equal energy. On the other hand, when the primary wave is dominant, selective acceleration occurs. The phase of the primary wave for electrons moving nearly along the wavevector changes very slowly compared with the oscillation of the wave, which is “phase-locked,” and such electrons are continuously accelerated. This acceleration by SLSWs may play a crucial role in pre-shock acceleration. In general, the radiation from the phase-locked population is different from the synchro-Compton radiation. However, when the amplitude of the secondary waves is not extremely weaker than that of the primary wave, the typical frequency can be estimated from synchro-Compton theory using the secondary waves. The primary wave does not contribute to the radiation because the SLSW accelerates electrons almost linearly. This radiation can be observed as a radio knot at the upstream of the termination shocks of the pulsar wind nebulae without counterparts in higher frequency ranges.

  14. Wave reflections in the pulmonary arteries analysed with the reservoir–wave model

    PubMed Central

    Bouwmeester, J Christopher; Belenkie, Israel; Shrive, Nigel G; Tyberg, John V

    2014-01-01

    Conventional haemodynamic analysis of pressure and flow in the pulmonary circulation yields incident and reflected waves throughout the cardiac cycle, even during diastole. The reservoir–wave model provides an alternative haemodynamic analysis consistent with minimal wave activity during diastole. Pressure and flow in the main pulmonary artery were measured in anaesthetized dogs and the effects of hypoxia and nitric oxide, volume loading and positive end-expiratory pressure were observed. The reservoir–wave model was used to determine the reservoir contribution to pressure and flow and once subtracted, resulted in ‘excess’ quantities, which were treated as wave-related. Wave intensity analysis quantified the contributions of waves originating upstream (forward-going waves) and downstream (backward-going waves). In the pulmonary artery, negative reflections of incident waves created by the right ventricle were observed. Overall, the distance from the pulmonary artery valve to this reflection site was calculated to be 5.7 ± 0.2 cm. During 100% O2 ventilation, the strength of these reflections increased 10% with volume loading and decreased 4% with 10 cmH2O positive end-expiratory pressure. In the pulmonary arterial circulation, negative reflections arise from the junction of lobar arteries from the left and right pulmonary arteries. This mechanism serves to reduce peak systolic pressure, while increasing blood flow. PMID:24756638

  15. Surface wave tomography

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.

    1984-01-01

    Vertically polarized shear wave velocity (VSV), determined primarily from fundamental mode Rayleigh waves, and the difference between the velocity of horizontally polarized shear waves (VSH) and VSV, therefore a measure of anisotropy, are shown.

  16. Gravitational-wave astronomy

    NASA Technical Reports Server (NTRS)

    Press, W. H.; Thorne, K. S.

    1972-01-01

    The significance of experimental evidence for gravitational waves is considered for astronomy. Properties, generation, and astrophysical sources of the waves are discussed. Gravitational wave receivers and antennas are described. A review of the Weber experiment is presented.

  17. Wave-function functionals

    SciTech Connect

    Pan Xiaoyin; Slamet, Marlina; Sahni, Viraht

    2010-04-15

    We extend our prior work on the construction of variational wave functions {psi} that are functionals of functions {chi}:{psi}={psi}[{chi}] rather than simply being functions. In this manner, the space of variations is expanded over those of traditional variational wave functions. In this article we perform the constrained search over the functions {chi} chosen such that the functional {psi}[{chi}] satisfies simultaneously the constraints of normalization and the exact expectation value of an arbitrary single- or two-particle Hermitian operator, while also leading to a rigorous upper bound to the energy. As such the wave function functional is accurate not only in the region of space in which the principal contributions to the energy arise but also in the other region of the space represented by the Hermitian operator. To demonstrate the efficacy of these ideas, we apply such a constrained search to the ground state of the negative ion of atomic hydrogen H{sup -}, the helium atom He, and its positive ions Li{sup +} and Be{sup 2+}. The operators W whose expectations are obtained exactly are the sum of the single-particle operators W={Sigma}{sub i}r{sub i}{sup n},n=-2,-1,1,2, W={Sigma}{sub i{delta}}(r{sub i}), W=-(1/2){Sigma}{sub i{nabla}i}{sup 2}, and the two-particle operators W={Sigma}{sub n}u{sup n},n=-2,-1,1,2, where u=|r{sub i}-r{sub j}|. Comparisons with the method of Lagrangian multipliers and of other constructions of wave-function functionals are made. Finally, we present further insights into the construction of wave-function functionals by studying a previously proposed construction of functionals {psi}[{chi}] that lead to the exact expectation of arbitrary Hermitian operators. We discover that analogous to the solutions of the Schroedinger equation, there exist {psi}[{chi}] that are unphysical in that they lead to singular values for the expectations. We also explain the origin of the singularity.

  18. Auroral plasma waves

    NASA Technical Reports Server (NTRS)

    Gurnett, Donald A.

    1989-01-01

    A review is given of auroral plasma wave phenomena, starting with the earliest ground-based observations and ending with the most recent satellite observations. Two types of waves are considered, electromagnetic and electrostatic. Electromagnetic waves include auroral kilometric radiation, auroral hiss, ELF noise bands, and low-frequency electric and magnetic noise. Electrostatic waves include upper hybrid resonance emissions, electron cyclotron waves, lower hybrid waves, ion cyclotron waves and broadband electrostatic noise. In each case, a brief overview is given describing the observations, the origin of the instability, and the role of the waves in the physics of the auroral acceleration region.

  19. Dispersive wave emission from wave breaking.

    PubMed

    Conforti, Matteo; Trillo, Stefano

    2013-10-01

    We show that pulses undergoing wave breaking in nonlinear weakly dispersive fibers radiate, owing to phase-matching (assisted by higher-order dispersion) of linear dispersive waves with the shock-wave front. Our theoretical results perfectly explain the radiation observed recently from pulses propagating in the normal dispersion (i.e., nonsolitonic) regime.

  20. Mesosphere Dynamics with Gravity Wave Forcing. 2; Planetary Waves

    NASA Technical Reports Server (NTRS)

    Mayr, H. G.; Mengel, J. G.; Chan, K. L.; Porter, H. S.; Einaudi, Franco (Technical Monitor)

    2000-01-01

    We present results from a non-linear, 3D, time dependent numerical spectral model (NSM) which extends from the ground up into the thermosphere and incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GW). Our focal point is the mesosphere where wave interactions are playing a dominant role. We discuss planetary waves in the present paper and diurnal and semi-diurnal tides in the companion paper. Without external time dependent energy or momentum sources, planetary waves (PWs) are generated in the model for zonal wavenumbers 1 to 4, which have amplitudes in the mesosphere above 50 km as large as 30 m/s and periods between 2 and 50 days. The waves are generated primarily during solstice conditions, which indicates that the baroclinic instability (associated with the GW driven reversal in the latitudinal temperature gradient) is playing an important role. Results from a numerical experiment show that GWs are also involved directly in generating the PWs. For the zonal wavenumber m = 1, the predominant wave periods in summer are around 4 days and in winter between 6 and 10 days. For m = 2, the periods are in summer and close to 2.5 and 3.5 days respectively For m = 3, 4 the predominant wave periods are in both seasons close to two days. The latter waves have the characteristics of Rossby gravity waves with meridional winds at equatorial latitudes. A common feature of the PWs (m = 1 to 4) generated in summer and winter is that their vertical wavelengths throughout the mesosphere are large which indicates that the waves are not propagating freely but are generated throughout the region. Another common feature is that the PWs propagate preferentially westward in summer and eastward in winter, being launched from the westward and eastward zonal winds that prevail respectively in summer and winter altitudes below 80 km. During spring and fall, for m = 1 and 2 eastward propagating long period PWs are generated that are launched from the smaller

  1. Waving Goodbye

    NASA Image and Video Library

    2017-05-30

    Before NASA's Cassini entered its Grand Finale orbits, it acquired unprecedented views of the outer edges of the main ring system. For example, this close-up view of the Keeler Gap, which is near the outer edge of Saturn's main rings, shows in great detail just how much the moon Daphnis affects the edges of the gap. Daphnis creates waves in the edges of the gap through its gravitational influence. Some clumping of ring particles can be seen in the perturbed edge, similar to what was seen on the edges of the Encke Gap back when Cassini arrived at Saturn in 2004. This view looks toward the sunlit side of the rings from about 3 degrees above the ring plane. The view was acquired at a distance of approximately 18,000 miles (30,000 kilometers) from Daphnis and at a Sun-Daphnis-spacecraft, or phase, angle of 69 degrees. Image scale is 581 feet (177 meters) per pixel. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 16, 2017. https://photojournal.jpl.nasa.gov/catalog/PIA21329

  2. Inherently Unstable Internal Gravity Waves

    NASA Astrophysics Data System (ADS)

    Alam, Reza

    2016-11-01

    Here we show that there exist internal gravity waves that are inherently unstable, that is, they cannot exist in nature for a long time. The instability mechanism is a one-way (irreversible) harmonic-generation resonance that permanently transfers the energy of an internal wave to its higher harmonics. We show that, in fact, there are countably infinite number of such unstable waves. For the harmonic-generation resonance to take place, nonlinear terms in the free surface boundary condition play a pivotal role, and the instability does not obtain for a linearly-stratified fluid if a simplified boundary condition such as rigid lid or linear form is employed. Harmonic-generation resonance discussed here also provides a mechanism for the transfer of the energy of the internal waves to the higher-frequency part of the spectrum where internal waves are more prone to breaking, hence losing energy to turbulence and heat and contributing to oceanic mixing. Yong Liang (yong.liang@berkeley.edu).

  3. Rarefaction wave gun propulsion

    NASA Astrophysics Data System (ADS)

    Kathe, Eric Lee

    A new species of gun propulsion that dramatically reduces recoil momentum imparted to the gun is presented. First conceived by the author on 18 March 1999, the propulsion concept is explained, a methodology for the design of a reasonable apparatus for experimental validation using NATO standard 35mm TP anti-aircraft ammunition is developed, and the experimental results are presented. The firing results are juxtaposed by a simple interior ballistic model to place the experimental findings into a context within which they may better be understood. Rarefaction wave gun (RAVEN) propulsion is an original contribution to the field of armament engineering. No precedent is known, and no experimental results of such a gun have been published until now. Recoil reduction in excess of 50% was experimentally achieved without measured loss in projectile velocity. RAVEN achieves recoil reduction by means of a delayed venting of the breech of the gun chamber that directs the high enthalpy propellant gases through an expansion nozzle to generate forward thrust that abates the rearward momentum applied to the gun prior to venting. The novel feature of RAVEN, relative to prior recoilless rifles, is that sufficiently delayed venting results in a rarefaction wave that follows the projectile though the bore without catching it. Thus, the projectile exits the muzzle without any compromise to its propulsion performance relative to guns that maintain a sealed chamber.

  4. A review of wave mechanics in the pulmonary artery with an emphasis on wave intensity analysis.

    PubMed

    Su, J; Hilberg, O; Howard, L; Simonsen, U; Hughes, A D

    2016-12-01

    Mean pulmonary arterial pressure and pulmonary vascular resistance (PVR) remain the most common haemodynamic measures to evaluate the severity and prognosis of pulmonary hypertension. However, PVR only captures the non-oscillatory component of the right ventricular hydraulic load and neglects the dynamic compliance of the pulmonary arteries and the contribution of wave transmission. Wave intensity analysis offers an alternative way to assess the pulmonary vasculature in health and disease. Wave speed is a measure of arterial stiffness, and the magnitude and timing of wave reflection provide information on the degree of impedance mismatch between the proximal and distal circulation. Studies in the pulmonary artery have demonstrated distinct differences in arterial wave propagation between individuals with and without pulmonary vascular disease. Notably, greater wave speed and greater wave reflection are observed in patients with pulmonary hypertension and in animal models exposed to hypoxia. Studying wave propagation makes a valuable contribution to the assessment of the arterial system in pulmonary hypertension, and here, we briefly review the current state of knowledge of the methods used to evaluate arterial waves in the pulmonary artery. © 2016 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.

  5. A review of wave mechanics in the pulmonary artery with an emphasis on wave intensity analysis

    PubMed Central

    Su, Junjing; Hilberg, Ole; Howard, Luke; Simonsen, Ulf; Hughes, Alun D

    2016-01-01

    Mean pulmonary arterial pressure and pulmonary vascular resistance remain the most common hemodynamic measures to evaluate the severity and prognosis of pulmonary hypertension. However, pulmonary vascular resistance only captures the non-oscillatory component of the right ventricular hydraulic load and neglects the dynamic compliance of the pulmonary arteries and the contribution of wave transmission. Wave intensity analysis offers an alternative way to assess the pulmonary vasculature in health and disease. Wave speed is a measure of arterial stiffness and the magnitude and timing of wave reflection provide information on the degree of impedance mismatch between the proximal and distal circulation. Studies in the pulmonary artery have demonstrated distinct differences in arterial wave propagation between individuals with and without pulmonary vascular disease. Notably, greater wave speed and greater wave reflection are observed in patients with pulmonary hypertension and in animal models exposed to hypoxia. Studying wave propagation makes a valuable contribution to the assessment of the arterial system in pulmonary hypertension and here, we briefly review the current state of knowledge of the methods used to evaluate arterial waves in the pulmonary artery. PMID:27636734

  6. Raman spectroscopy of hypersonic shock waves

    PubMed

    Ramos; Mate; Tejeda; Fernandez; Montero

    2000-10-01

    Raman spectroscopy is shown to be an efficient diagnostic methodology for the study of hypersonic shock waves. As a test, absolute density and rotational population profiles have been measured across five representative normal shock waves of N2 generated in a free jet, spanning the Mach number range 7.7waves shows a largely bimodal rotational distribution function with additional contribution of scattered molecules, in close analogy with the velocity distribution function known from helium shock waves [G. Pham-Van-Diep et al., Science 245, 624 (1989)]. Quantitative data on invariance trends of density profiles and properties of the wake beyond the shock waves are reported.

  7. Phonons, Atoms, and Waves

    ERIC Educational Resources Information Center

    Reid, John S.

    1977-01-01

    Discussed are how the thermal vibrations of a solid are described in terms of lattice waves, how these waves interact with other waves, or with themselves, and how one is led from such a description in terms of waves to the concept of a phonon. (Author/MA)

  8. A Simple Wave Driver

    ERIC Educational Resources Information Center

    Temiz, Burak Kagan; Yavuz, Ahmet

    2015-01-01

    This study was done to develop a simple and inexpensive wave driver that can be used in experiments on string waves. The wave driver was made using a battery-operated toy car, and the apparatus can be used to produce string waves at a fixed frequency. The working principle of the apparatus is as follows: shortly after the car is turned on, the…

  9. Fracture interface waves

    NASA Astrophysics Data System (ADS)

    Gu, Boliang; Nihei, Kurt T.; Myer, Larry R.; Pyrak-Nolte, Laura J.

    1996-01-01

    Interface waves on a single fracture in an elastic solid are investigated theoretically and numerically using plane wave analysis and a boundary element method. The finite mechanical stiffness of a fracture is modeled as a displacement discontinuity. Analysis for inhomogeneous plane wave propagation along a fracture yields two dispersive equations for symmetric and antisymmetric interface waves. The basic form of these equations are similar to the classic Rayleigh equation for a surface wave on a half-space, except that the displacements and velocities of the symmetric and antisymmetric fracture interface waves are each controlled by a normalized fracture stiffness. For low values of the normalized fracture stiffness, the symmetric and antisymmetric interface waves degenerate to the classic Rayleigh wave on a traction-free surface. For large values of the normalized fracture stiffness, the antisymmetric and symmetric interface waves become a body S wave and a body P wave, respectively, which propagate parallel to the fracture. For intermediate values of the normalized fracture stiffness, both interface waves are dispersive. Numerical modeling performed using a boundary element method demonstrates that a line source generates a P-type interface wave, in addition to the two Rayleigh-type interface waves. The magnitude of the normalized fracture stiffness is observed to control the velocities of the interface waves and the partitioning of seismic energy among the various waves near the fracture.

  10. A Simple Wave Driver

    ERIC Educational Resources Information Center

    Temiz, Burak Kagan; Yavuz, Ahmet

    2015-01-01

    This study was done to develop a simple and inexpensive wave driver that can be used in experiments on string waves. The wave driver was made using a battery-operated toy car, and the apparatus can be used to produce string waves at a fixed frequency. The working principle of the apparatus is as follows: shortly after the car is turned on, the…

  11. Finsler p p -waves

    NASA Astrophysics Data System (ADS)

    Fuster, Andrea; Pabst, Cornelia

    2016-11-01

    In this work we present Finsler gravitational waves. These are a Finslerian version of the well-known p p -waves, generalizing the very special relativity line element. Our Finsler p p -waves are an exact solution of Finslerian Einstein's equations in vacuum and describe gravitational waves propagating in an anisotropic background.

  12. Wave-particle energy exchange directly observed in a kinetic Alfvén-branch wave

    NASA Astrophysics Data System (ADS)

    Gershman, Daniel J.; F-Viñas, Adolfo; Dorelli, John C.; Boardsen, Scott A.; Avanov, Levon A.; Bellan, Paul M.; Schwartz, Steven J.; Lavraud, Benoit; Coffey, Victoria N.; Chandler, Michael O.; Saito, Yoshifumi; Paterson, William R.; Fuselier, Stephen A.; Ergun, Robert E.; Strangeway, Robert J.; Russell, Christopher T.; Giles, Barbara L.; Pollock, Craig J.; Torbert, Roy B.; Burch, James L.

    2017-03-01

    Alfvén waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres and astrophysical systems but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASA's Magnetospheric Multiscale (MMS) mission, we utilize Earth's magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfvén wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via nonlinear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations.

  13. Wave-particle energy exchange directly observed in a kinetic Alfvén-branch wave

    DOE PAGES

    Gershman, Daniel J.; F-Viñas, Adolfo; Dorelli, John C.; ...

    2017-03-31

    Alfvén waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres and astrophysical systems but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASA’s Magnetospheric Multiscale (MMS) mission, we utilize Earth’s magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfvén wave. Electronsmore » confined between adjacent wave peaks may have contributed to saturation of damping effects via nonlinear particle trapping. As a result, the investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations.« less

  14. Wave-particle energy exchange directly observed in a kinetic Alfvén-branch wave

    PubMed Central

    Gershman, Daniel J.; F-Viñas, Adolfo; Dorelli, John C.; Boardsen, Scott A.; Avanov, Levon A.; Bellan, Paul M.; Schwartz, Steven J.; Lavraud, Benoit; Coffey, Victoria N.; Chandler, Michael O.; Saito, Yoshifumi; Paterson, William R.; Fuselier, Stephen A.; Ergun, Robert E.; Strangeway, Robert J.; Russell, Christopher T.; Giles, Barbara L.; Pollock, Craig J.; Torbert, Roy B.; Burch, James L.

    2017-01-01

    Alfvén waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres and astrophysical systems but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASA's Magnetospheric Multiscale (MMS) mission, we utilize Earth's magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfvén wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via nonlinear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations. PMID:28361881

  15. Wave-particle energy exchange directly observed in a kinetic Alfvén-branch wave.

    PubMed

    Gershman, Daniel J; F-Viñas, Adolfo; Dorelli, John C; Boardsen, Scott A; Avanov, Levon A; Bellan, Paul M; Schwartz, Steven J; Lavraud, Benoit; Coffey, Victoria N; Chandler, Michael O; Saito, Yoshifumi; Paterson, William R; Fuselier, Stephen A; Ergun, Robert E; Strangeway, Robert J; Russell, Christopher T; Giles, Barbara L; Pollock, Craig J; Torbert, Roy B; Burch, James L

    2017-03-31

    Alfvén waves are fundamental plasma wave modes that permeate the universe. At small kinetic scales, they provide a critical mechanism for the transfer of energy between electromagnetic fields and charged particles. These waves are important not only in planetary magnetospheres, heliospheres and astrophysical systems but also in laboratory plasma experiments and fusion reactors. Through measurement of charged particles and electromagnetic fields with NASA's Magnetospheric Multiscale (MMS) mission, we utilize Earth's magnetosphere as a plasma physics laboratory. Here we confirm the conservative energy exchange between the electromagnetic field fluctuations and the charged particles that comprise an undamped kinetic Alfvén wave. Electrons confined between adjacent wave peaks may have contributed to saturation of damping effects via nonlinear particle trapping. The investigation of these detailed wave dynamics has been unexplored territory in experimental plasma physics and is only recently enabled by high-resolution MMS observations.

  16. Planetary plasma waves

    NASA Technical Reports Server (NTRS)

    Gurnett, Donald A.

    1993-01-01

    The primary types of plasma waves observed in the vicinity of the planets Venus, Mars, Earth, Jupiter, Saturn, Uranus, and Neptune are described. The observations are organized according to the various types of plasma waves observed, ordered according to decreasing distance from the planet, starting from the sunward side of the planet, and ending in the region near the closest approach. The plasma waves observed include: electron plasma oscillations and ion acoustic waves; trapped continuum radiation; electron cyclotron and upper hybrid waves; whistler-mode emissions; electrostatic ion cyclotron waves; and electromagnetic ion cyclotron waves.

  17. Teleseismic S wave microseisms.

    PubMed

    Nishida, Kiwamu; Takagi, Ryota

    2016-08-26

    Although observations of microseisms excited by ocean swells were firmly established in the 1940s, the source locations remain difficult to track. Delineation of the source locations and energy partition of the seismic wave components are key to understanding the excitation mechanisms. Using a seismic array in Japan, we observed both P and S wave microseisms excited by a severe distant storm in the Atlantic Ocean. Although nonlinear forcing of an ocean swell with a one-dimensional Earth model can explain P waves and vertically polarized S waves (SV waves), it cannot explain horizontally polarized S waves (SH waves). The precise source locations may provide a new catalog for exploring Earth's interior.

  18. Instability of Wave Trains and Wave Probabilities

    NASA Astrophysics Data System (ADS)

    Babanin, Alexander

    2013-04-01

    Centre for Ocean Engineering, Science and Technology, Swinburne University of Technology, Melbourne, Australia, ababanin@swin.edu.au Design criteria in ocean engineering, whether this is one in 50 years or one in 5000 years event, are hardly ever based on measurements, and rather on statistical distributions of relevant metocean properties. Of utmost interest is the tail of distribution, that is rare events such as the highest waves with low probability. Engineers have long since realised that the superposition of linear waves with narrow-banded spectrum as depicted by the Rayleigh distribution underestimates the probability of extreme wave heights and crests, which is a critical shortcoming as far as the engineering design is concerned. Ongoing theoretical and experimental efforts have been under way for decades to address this issue. Typical approach is the treating all possible waves in the ocean or at a particular location as a single ensemble for which some comprehensive solution can be obtained. The oceanographic knowledge, however, now indicates that no single and united comprehensive solution is available. We would expect the probability distributions of wave height to depend on a) whether the waves are at the spectral peak or at the tail; b) on wave spectrum and mean steepness in the wave field; c) on the directional distribution of the peak waves; d) on whether the waves are in deep water, in intermediate depth or in shallow water; e) on wave breaking; f) on the wind, particularly if it is very strong, and on the currents if they have suitable horizontal gradients. Probability distributions in the different circumstances according to these groups of conditions should be different, and by combining them together the inevitable scatter is introduced. The scatter and the accuracy will not improve by increasing the bulk data quality and quantity, and it hides the actual distribution of extremes. The groups have to be separated and their probability

  19. Wave Climate and Trends in the Red Sea: Results from a 30-Year Wave Hindcast

    NASA Astrophysics Data System (ADS)

    Langodan, Sabique; Cavaleri, Luigi; Pomaro, Angela; Portilla, Jesus; Viswanadhapalli, Yesubabu; Abu Al-Naja, Yasser; Hoteit, Ibrahim

    2017-04-01

    The deceivingly simple structure of the Red Sea offers very interesting wind and wave conditions, not easily, if ever, found elsewhere. The mountain ranges bordering the Red Sea influence the local dominant wind regimes and transform the Red Sea into a virtual wind channel, where along-axis winds are the dominant feature. Larger and smaller valleys cut across the bordering mountain ridges, creating winds that are relevant to local wind regimes. A unique situation in the Red Sea is the convergence of two wave systems forced by opposite winds over an extended period of time meeting at the center of the Red Sea. This study presents wave climate, variability and their trends in the Red Sea based on a 30-yr wave hindcast. A high-resolution regional atmospheric reanalysis generated using WRF model, initialized with ERA-Interim global reanalysis is employed to drive WAVEWATCH III model from 1985 through 2014. The wind and wave hindcasts were validated against buoys, scatterometers and altimeters, and their quality was found to be good. We explore the contribution of individual wave system that modulates to the variability of wave in the Red Sea and investigate the possible long-term trends in each system. A characterization of the wave conditions based on wave spectra brings out a detailed description of the different wave regimes, their associated meteorological conditions and their variation in time and geographical space.

  20. Weakly nonlinear magnetohydrodynamic wave interactions

    SciTech Connect

    Webb, G.M.; Brio, M.; Kruse, M.T.; Zank, G.P.

    1999-06-01

    Equations describing weakly nonlinear magnetohydrodynamic (MHD) wave interactions in one Cartesian space dimension are discussed. For wave propagation in uniform media, the wave interactions of interest consist of: (a) three-wave resonant interactions in which high frequency waves, may evolve on long space and time scales if the wave phases satisfy the resonance conditions; (b) Burgers self-wave steepening for the magnetoacoustic waves, and (c) mean wave field effects, in which a particular wave interacts with the mean wave field of the other waves. For wave propagation in non-uniform media, further linear wave mixing terms appear in the equations. The equations describe four types of resonant triads: slow-fast magnetosonic wave interaction; Alfv{acute e}n-entropy wave interaction; Alfv{acute e}n-magnetosonic wave interaction; and magnetosonic-entropy wave interaction. The formalism is restricted to coherent wave interactions. {copyright} {ital 1999 American Institute of Physics.}

  1. Vorticity and Wave Motion in a Compressible Protoplanetary Disk

    NASA Technical Reports Server (NTRS)

    Davis, Sanford S.; DeVincenzi, Donald (Technical Monitor)

    2001-01-01

    The impact of an isolated vortex in a compressible Keplerian disk is examined using higher order numerical solutions of the Euler and entropy-conserving Energy equations. The vortex is stretched by the background shear flow with longer lasting anticyclonic vortices persisting for about 10 vortex revolutions. Simultaneously, the vortex emits transient radial waves consisting mainly of axisymmetrical weak shock waves and a slower, nonaxisymmetric Rossby wave. These waves may contribute to certain transient events in protoplanetary disks. The vortex stretching and waves were found to have little long-term feedback on the baseline 'standard solar nebula' disk structure and confirm the extremely stable structure of non self-gravitating disks.

  2. Wave Dissipation and Balance - NOPP Wave Project

    DTIC Science & Technology

    2012-09-30

    ocean with the atmosphere, land and solid Earth. Waves also define in many ways the appearance of the ocean seen by remote- sensing instruments. Beyond...waves, sediments and remote sensing systems, and to improve our forecasting and hindcasting capacity of these phenomena from the global ocean to the...feedback on the wave model quality APPROACH AND WORK PLAN By combining theoretical advances with numerical models, remote sensing and field

  3. On Hokusai's Great wave off Kanagawa: localization, linearity and a rogue wave in sub-Antarctic waters

    PubMed Central

    Dudley, J. M.; Sarano, V.; Dias, F.

    2013-01-01

    The Hokusai woodcut entitled The great wave off Kanagawa has been interpreted as an unusually large storm wave, likely to be classed as a rogue wave, and possibly generated from nonlinear wave dynamics (J. H. E. Cartwright and H. Nakamura, Notes Rec. R. Soc. 63, 119–135 (2009)). In this paper, we present a complementary discussion of this hypothesis, discussing in particular how linear and nonlinear mechanisms can both contribute to the emergence of rogue wave events. By making reference to the Great wave's simultaneous transverse and longitudinal localization, we show that the purely linear mechanism of directional focusing also predicts characteristics consistent with those of the Great wave. In addition, we discuss the properties of a particular rogue wave photographed on the open ocean in sub-Antarctic waters, which shows two-dimensional localization and breaking dynamics remarkably similar to Hokusai's depiction in the woodcut. PMID:24687148

  4. On Hokusai's Great wave off Kanagawa: localization, linearity and a rogue wave in sub-Antarctic waters.

    PubMed

    Dudley, J M; Sarano, V; Dias, F

    2013-06-20

    The Hokusai woodcut entitled The great wave off Kanagawa has been interpreted as an unusually large storm wave, likely to be classed as a rogue wave, and possibly generated from nonlinear wave dynamics (J. H. E. Cartwright and H. Nakamura, Notes Rec. R. Soc.63, 119-135 (2009)). In this paper, we present a complementary discussion of this hypothesis, discussing in particular how linear and nonlinear mechanisms can both contribute to the emergence of rogue wave events. By making reference to the Great wave's simultaneous transverse and longitudinal localization, we show that the purely linear mechanism of directional focusing also predicts characteristics consistent with those of the Great wave. In addition, we discuss the properties of a particular rogue wave photographed on the open ocean in sub-Antarctic waters, which shows two-dimensional localization and breaking dynamics remarkably similar to Hokusai's depiction in the woodcut.

  5. Scattered surface wave energy in the seismic coda

    USGS Publications Warehouse

    Zeng, Y.

    2006-01-01

    One of the many important contributions that Aki has made to seismology pertains to the origin of coda waves (Aki, 1969; Aki and Chouet, 1975). In this paper, I revisit Aki's original idea of the role of scattered surface waves in the seismic coda. Based on the radiative transfer theory, I developed a new set of scattered wave energy equations by including scattered surface waves and body wave to surface wave scattering conversions. The work is an extended study of Zeng et al. (1991), Zeng (1993) and Sato (1994a) on multiple isotropic-scattering, and may shed new insight into the seismic coda wave interpretation. The scattering equations are solved numerically by first discretizing the model at regular grids and then solving the linear integral equations iteratively. The results show that scattered wave energy can be well approximated by body-wave to body wave scattering at earlier arrival times and short distances. At long distances from the source, scattered surface waves dominate scattered body waves at surface stations. Since surface waves are 2-D propagating waves, their scattered energies should in theory follow a common decay curve. The observed common decay trends on seismic coda of local earthquake recordings particular at long lapse times suggest that perhaps later seismic codas are dominated by scattered surface waves. When efficient body wave to surface wave conversion mechanisms are present in the shallow crustal layers, such as soft sediment layers, the scattered surface waves dominate the seismic coda at even early arrival times for shallow sources and at later arrival times for deeper events.

  6. ULF Waves at Mercury

    NASA Astrophysics Data System (ADS)

    Kim, E.-H.; Boardsen, S. A.; Johnson, J. R.; Slavin, J. A.

    2016-02-01

    This chapter provides a brief overview of the observed characteristics of ultra-low-frequency (ULF) waves at Mercury. It shows how field-aligned propagating ULF waves at Mercury can be generated by externally driven fast compressional waves (FWs) via mode conversion at the ion-ion hybrid resonance. Then, the chapter reviews the interpretation that the strong magnetic compressional waves near and its harmonics observed with 20 of Mercury's magnetic equator could be the ion Bernstein wave (IBW) mode. A recent statistical study of ULF waves at Mercury based on MESSENGER data reported the occurrence and polarization of the detected waves. The chapter further introduces the field line resonance and the electromagnetic ion Bernstein waves to explain such waves, and shows that both theories can partially explain the observations.

  7. Density waves in Titan's upper atmosphere

    NASA Astrophysics Data System (ADS)

    Cui, J.; Yelle, R. V.; Li, T.; Snowden, D. S.; Müller-Wodarg, I. C. F.

    2014-01-01

    Analysis of the Cassini Ion Neutral Mass Spectrometer data reveals the omnipresence of density waves in various constituents of Titan's upper atmosphere, with quasi-periodical structures visible for N2, CH4,29N2, and some of the minor constituents. The N2 amplitude lies in the range of ≈4%-16%with a mean of ≈8%. Compositional variation is clearly seen as a sequence of decreasing amplitude with increasing scale height. The observed vertical variation of amplitude implies significant wave dissipation in different constituents, possibly contributed by molecular viscosity for N2but by both molecular viscosity and binary diffusion for the others. A wave train with near horizontally propagating wave energy and characterized by a wavelength of ≈730 km and a wave period of ≈10 h is found to best reproduce various aspects of the observations in a globally averaged sense. Some horizontal and seasonal trends in wave activity are identified, suggesting a connection between the mechanism driving the overall variability in the background atmosphere and the mechanism driving the waves. No clear association of wave activity with magnetospheric particle precipitation can be identified from the data.

  8. Fracture channel waves

    NASA Astrophysics Data System (ADS)

    Nihei, Kurt T.; Yi, Weidong; Myer, Larry R.; Cook, Neville G. W.; Schoenberg, Michael

    1999-03-01

    The properties of guided waves which propagate between two parallel fractures are examined. Plane wave analysis is used to obtain a dispersion equation for the velocities of fracture channel waves. Analysis of this equation demonstrates that parallel fractures form an elastic waveguide that supports two symmetric and two antisymmetric dispersive Rayleigh channel waves, each with particle motions and velocities that are sensitive to the normal and tangential stiffnesses of the fractures. These fracture channel waves degenerate to shear waves when the fracture stiffnesses are large, to Rayleigh waves and Rayleigh-Lamb plate waves when the fracture stiffnesses are low, and to fracture interface waves when the fractures are either very closely spaced or widely separated. For intermediate fracture stiffnesses typical of fractured rock masses, fracture channel waves are dispersive and exhibit moderate to strong localization of guided wave energy between the fractures. The existence of these waves is examined using laboratory acoustic measurements on a fractured marble plate. This experiment confirms the distinct particle motion of the fundamental antisymmetric fracture channel wave (A0 mode) and demonstrates the ease with which a fracture channel wave can be generated and detected.

  9. Interactions between two propagating waves in rat visual cortex

    PubMed Central

    Gao, Xin; Xu, Weifeng; Wang, Zhijie; Takagaki, Kentaroh; Li, Bing; Wu, Jian-young

    2012-01-01

    Sensory-evoked propagating waves are frequently observed in sensory cortex. However, it is largely unknown how an evoked propagating wave affects the activity evoked by subsequent sensory inputs, or how two propagating waves interact when evoked by simultaneous sensory inputs. Using voltage-sensitive dye imaging, we investigated the interactions between two evoked waves in rat visual cortex, and the spatiotemporal patterns of depolarization in the neuronal population due to wave-to-wave interactions. We have found that visually-evoked propagating waves have a refractory period of about 300 ms, within which the response to a subsequent visual stimulus is suppressed. Simultaneous presentation of two visual stimuli at different locations can evoke two waves propagating toward each other, and these two waves fuse. Fusion significantly shortens the latency and half-width of the response, leading to changes in the spatial profile of evoked population activity. The visually-evoked propagating wave may also be suppressed by a preceding spontaneous wave. The refractory period following a propagating wave and the fusion between two waves may contribute to visual sensory processing by modifying the spatiotemporal profile of population neuronal activity evoked by sensory events. PMID:22561730

  10. A Reaction-Diffusion Model of Cholinergic Retinal Waves

    PubMed Central

    Lansdell, Benjamin; Ford, Kevin; Kutz, J. Nathan

    2014-01-01

    Prior to receiving visual stimuli, spontaneous, correlated activity in the retina, called retinal waves, drives activity-dependent developmental programs. Early-stage waves mediated by acetylcholine (ACh) manifest as slow, spreading bursts of action potentials. They are believed to be initiated by the spontaneous firing of Starburst Amacrine Cells (SACs), whose dense, recurrent connectivity then propagates this activity laterally. Their inter-wave interval and shifting wave boundaries are the result of the slow after-hyperpolarization of the SACs creating an evolving mosaic of recruitable and refractory cells, which can and cannot participate in waves, respectively. Recent evidence suggests that cholinergic waves may be modulated by the extracellular concentration of ACh. Here, we construct a simplified, biophysically consistent, reaction-diffusion model of cholinergic retinal waves capable of recapitulating wave dynamics observed in mice retina recordings. The dense, recurrent connectivity of SACs is modeled through local, excitatory coupling occurring via the volume release and diffusion of ACh. In addition to simulation, we are thus able to use non-linear wave theory to connect wave features to underlying physiological parameters, making the model useful in determining appropriate pharmacological manipulations to experimentally produce waves of a prescribed spatiotemporal character. The model is used to determine how ACh mediated connectivity may modulate wave activity, and how parameters such as the spontaneous activation rate and sAHP refractory period contribute to critical wave size variability. PMID:25474327

  11. Magnetic field contribution to the Lorentz model.

    PubMed

    Oughstun, Kurt E; Albanese, Richard A

    2006-07-01

    The classical Lorentz model of dielectric dispersion is based on the microscopic Lorentz force relation and Newton's second law of motion for an ensemble of harmonically bound electrons. The magnetic field contribution in the Lorentz force relation is neglected because it is typically small in comparison with the electric field contribution. Inclusion of this term leads to a microscopic polarization density that contains both perpendicular and parallel components relative to the plane wave propagation vector. The modified parallel and perpendicular polarizabilities are both nonlinear in the local electric field strength.

  12. Dust-Acoustic Waves: Visible Sound Waves

    SciTech Connect

    Merlino, Robert L.

    2009-11-10

    A historical overview of some of the early theoretical and experimental work on dust acoustic waves is given. The basic physics of the dust acoustic wave and some of the theoretical refinements that have been made, including the effects of collisions, plasma absorption, dust charge fluctuations, particle drifts and strong coupling effects are discussed. Some recent experimental findings and outstanding problems are also presented.

  13. Are there waves in elastic wave turbulence?

    PubMed

    Mordant, Nicolas

    2008-06-13

    An thin elastic steel plate is excited with a vibrator and its local velocity displays a turbulentlike Fourier spectrum. This system is believed to develop elastic wave turbulence. We analyze here the motion of the plate with a two-point measurement in order to check, in our real system, a few hypotheses required for the Zakharov theory of weak turbulence to apply. We show that the motion of the plate is indeed a superposition of bending waves following the theoretical dispersion relation of the linear wave equation. The nonlinearities seem to efficiently break the coherence of the waves so that no modal structure is observed. Several hypotheses of the weak turbulence theory seem to be verified, but nevertheless the theoretical predictions for the wave spectrum are not verified experimentally.

  14. Mechanical waves during tissue expansion

    NASA Astrophysics Data System (ADS)

    Serra-Picamal, Xavier; Conte, Vito; Vincent, Romaric; Anon, Ester; Tambe, Dhananjay T.; Bazellieres, Elsa; Butler, James P.; Fredberg, Jeffrey J.; Trepat, Xavier

    2012-08-01

    The processes by which an organism develops its shape and heals wounds involve expansion of a monolayer sheet of cells. The mechanism underpinning this epithelial expansion remains obscure, despite the fact that its failure is known to contribute to several diseases, including carcinomas, which account for about 90% of all human cancers. Here, using the micropatterned epithelial monolayer as a model system, we report the discovery of a mechanical wave that propagates slowly to span the monolayer, traverses intercellular junctions in a cooperative manner and builds up differentials of mechanical stress. Essential features of this wave generation and propagation are captured by a minimal model based on sequential fronts of cytoskeletal reinforcement and fluidization. These findings establish a mechanism of long-range cell guidance, symmetry breaking and pattern formation during monolayer expansion.

  15. Ocean Wave Separation Using CEEMD-Wavelet in GPS Wave Measurement

    PubMed Central

    Wang, Junjie; He, Xiufeng; Ferreira, Vagner G.

    2015-01-01

    Monitoring ocean waves plays a crucial role in, for example, coastal environmental and protection studies. Traditional methods for measuring ocean waves are based on ultrasonic sensors and accelerometers. However, the Global Positioning System (GPS) has been introduced recently and has the advantage of being smaller, less expensive, and not requiring calibration in comparison with the traditional methods. Therefore, for accurately measuring ocean waves using GPS, further research on the separation of the wave signals from the vertical GPS-mounted carrier displacements is still necessary. In order to contribute to this topic, we present a novel method that combines complementary ensemble empirical mode decomposition (CEEMD) with a wavelet threshold denoising model (i.e., CEEMD-Wavelet). This method seeks to extract wave signals with less residual noise and without losing useful information. Compared with the wave parameters derived from the moving average skill, high pass filter and wave gauge, the results show that the accuracy of the wave parameters for the proposed method was improved with errors of about 2 cm and 0.2 s for mean wave height and mean period, respectively, verifying the validity of the proposed method. PMID:26262620

  16. Wave Meteorology and Soaring

    NASA Technical Reports Server (NTRS)

    Wiley, Scott

    2008-01-01

    This viewgraph document reviews some mountain wave turbulence and operational hazards while soaring. Maps, photographs, and satellite images of the meteorological phenomena are included. Additionally, photographs of aircraft that sustained mountain wave damage are provided.

  17. Detonation Wave Profile

    SciTech Connect

    Menikoff, Ralph

    2015-12-14

    The Zel’dovich-von Neumann-Doering (ZND) profile of a detonation wave is derived. Two basic assumptions are required: i. An equation of state (EOS) for a partly burned explosive; P(V, e, λ). ii. A burn rate for the reaction progress variable; d/dt λ = R(V, e, λ). For a steady planar detonation wave the reactive flow PDEs can be reduced to ODEs. The detonation wave profile can be determined from an ODE plus algebraic equations for points on the partly burned detonation loci with a specified wave speed. Furthermore, for the CJ detonation speed the end of the reaction zone is sonic. A solution to the reactive flow equations can be constructed with a rarefaction wave following the detonation wave profile. This corresponds to an underdriven detonation wave, and the rarefaction is know as a Taylor wave.

  18. Wave-Current Interaction in Coastal Inlets and River Mouths

    DTIC Science & Technology

    2013-09-30

    STATEMENT A. Approved for public release; distribution is unlimited. Wave-Current Interaction in Coastal Inlets and River Mouths ...study wave-current interaction, and contribute to a comprehensive community data set of coastal inlet and river mouth processes, 2) better understand...Wave-Current Interaction in Coastal Inlets and River Mouths 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d

  19. Explosive Line Wave Generators

    DTIC Science & Technology

    2013-12-01

    curvature produced by each line wave generator. Piezoelectric pins were used for an additional assessment of the explosive lens design...to a visual assessment of the wave curvature from the high speed camera images, the explosive lens design was also evaluated using piezoelectric pins...High Explosive Firing Complex (HEFC). The various explosive line wave generators were taped vertically on a supporting board and the detonation wave

  20. Oceanic wave measurement system

    NASA Technical Reports Server (NTRS)

    Holmes, J. F.; Miles, R. T. (Inventor)

    1980-01-01

    An oceanic wave measured system is disclosed wherein wave height is sensed by a barometer mounted on a buoy. The distance between the trough and crest of a wave is monitored by sequentially detecting positive and negative peaks of the output of the barometer and by combining (adding) each set of two successive half cycle peaks. The timing of this measurement is achieved by detecting the period of a half cycle of wave motion.

  1. The Iowa wave machines

    NASA Astrophysics Data System (ADS)

    Daffron, John D.; Greenslade, Thomas B.; Stille, Dale

    2010-03-01

    Wave machines are a staple of demonstration lectures, and a good pair of wave machines can make the idea of transverse and longitudinal waves clearly evident to students. The demonstration apparatus collection of the University of Iowa contains examples of transverse and longitudinal wave machines that will be of interest to readers of The Physics Teacher. These machines probably date from about 1925 and may have been locally produced. You too can build them.

  2. Intermediate-statistics spin waves

    NASA Astrophysics Data System (ADS)

    Dai, Wu-Sheng; Xie, Mi

    2009-04-01

    In this paper, we show that spin waves, the elementary excitation of the Heisenberg magnetic system, obey a kind of intermediate statistics with a finite maximum occupation number n. We construct an operator realization for the intermediate statistics obeyed by magnons, the quantized spin waves, and then construct a corresponding intermediate-statistics realization for the angular momentum algebra in terms of the creation and annihilation operators of the magnons. In other words, instead of the Holstein-Primakoff representation, a bosonic representation subject to a constraint on the occupation number, we present an intermediate-statistics representation with no constraints. In this realization, the maximum occupation number is naturally embodied in the commutation relation of creation and annihilation operators, while the Holstein-Primakoff representation is a bosonic operator relation with an additional putting-in-by-hand restriction on the occupation number. We deduce the intermediate-statistics distribution function for magnons from the intermediate-statistics commutation relation of the creation and annihilation operators directly, which is a modified Bose-Einstein distribution. On the basis of these results, we calculate the dispersion relations for ferromagnetic and antiferromagnetic spin waves. The relations between the intermediate statistics that magnons obey and the other two important kinds of intermediate statistics, Haldane-Wu statistics and the fractional statistics of anyons, are discussed. We also compare the spectrum of the intermediate-statistics spin wave with the exact solution of the one-dimensional s = 1/2 Heisenberg model, which is obtained by the Bethe ansatz method. For ferromagnets, we take the contributions from the interaction between magnons (the quartic contribution), the next-to-nearest-neighbor interaction, and the dipolar interaction into account for comparison with the experiment.

  3. Appendix: Additional Contributions

    NASA Astrophysics Data System (ADS)

    2011-12-01

    The number of contributions to the Symposium was so high that only the review and invited talks have found place, in the form of articles, in this volume. This Appendix lists all these additional contributions (oral and posters) which are not present as articles. The abstracts of all contributions were published in a booklet produced by the Local Organizing Committee and are available at the SAO/NASA Astrophysics Data System (ADS). More information on these contributions (PowerPoint presentations and/or articles) have been made public in the Internet web site of the conference (http://cab.inta-csic.es/molecular_universe/).

  4. Coronal heating by waves

    NASA Technical Reports Server (NTRS)

    Hollweg, J. V.

    1983-01-01

    Alfven waves or Alfvenic surface waves carry enough energy into the corona to provide the coronal energy requirements. Coronal loop resonances are an appealing means by which large energy fluxes enter active region loops. The wave dissipation mechanism still needs to be elucidated, but a Kolmogoroff turbulent cascade is fully consistent with the heating requirements in coronal holes and active region loops.

  5. Waves of Hanta

    NASA Astrophysics Data System (ADS)

    Abramson, Guillermo

    2003-03-01

    A spatially extended model of the hantavirus infection in deer mice is analyzed. Traveling waves solutions of the infected and susceptible populations are studied in different regimes, controlled by an environmental parameter. The wave of infection is shown to lag behind the wave of susceptible population, and the delay between the two is analyzed numerically and through a piecewise linearization.

  6. Surface wave tomography

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.

    1984-01-01

    Vertically polarized shear wave velocity (VSV), determined primarily from fundamental mode Rayleigh waves, and the difference between the velocity of horizontally polarized shear waves (VSH) and VSV, therefore a measure of anisotropy, are shown. Previously announced in STAR as N84-17728

  7. The road to the discovery of gravitational waves

    NASA Astrophysics Data System (ADS)

    Braginsky, V. B.; Bilenko, I. A.; Vyatchanin, S. P.; Gorodetsky, M. L.; Mitrofanov, V. P.; Prokhorov, L. G.; Strigin, S. E.; Khalili, F. Ya

    2016-09-01

    On 14 September 2015, the two detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO) in the US recorded the first direct detection of gravitational waves. This paper reviews the contributions to this discovery by V B Braginsky's group at the Physics Department of Lomonosov Moscow State University.

  8. The estimate and measurement of longitudinal wave intensity

    NASA Astrophysics Data System (ADS)

    Ruisen, Ming

    1996-08-01

    Quasi-longitudinal waves are one type of structural waves, which are important at high frequencies. This paper studies the estimate theory and measurement technique of quasi-longitudinal waves, analyzes the bias error due to the effect of bending waves. In a two-dimensional quasi-longitudinal wave field, the intensity vector is the sum of the effective intensity vector and the intensity variation vector. Its axial component is proportional to two imaginary parts of cross spectral densities and in the measurement, it is measured by a pair of two-transducer arrays. In a onedimensional quasi-longitudinal wave field, the intensity variation is zero, the intensity is proportional to only one imaginary part of a cross spectral density and it can be measured using a two-transducer array. If bending and quasi-longitudinal waves coexist and the contribution from bending waves cannot be eliminated or reduced to a certain extent, the measured quasi-longitudinal wave intensity will contain a large error. The results measured on the three-beam structure show that quasi-longitudinal wave intensity can be accurately measured using the intensity technique when bending waves are negligible in comparison with quasi-longitudinal waves.

  9. Response of wave excited offshore platforms

    SciTech Connect

    Chang, Shih-Jung; Hahn, G.D.

    1995-09-01

    A study of the resultants of inertia and drag force components induced by waves on offshore structures is made, and the relations between these resultants and the corresponding modal forces that govern the structural response are examined. The information and concepts reported elucidate the main factors that control such forces. Using the deep-water approximation of linear wave theory and the Morison equation, it is shown that the inertia and drag components of the modal forces can be expressed in terms of the sea surface kinematics. This treatment of the wave excitations advances the understanding of their characteristics and contributes to forming a basis for efficient, reliable evaluations of the response of wave- excited offshore platforms.

  10. 25 years of dust acoustic waves

    NASA Astrophysics Data System (ADS)

    Merlino, Robert L.; Merlino

    2014-12-01

    The dust acoustic wave (DAW) was first discussed by P. K. Shukla in May of 1989 at the First Capri Workshop on Dusty Plasmas. In the past 25 years, the subsequent publication of the linear and nonlinear properties of the DAW (Rao, N. N., Shukla, P. K. and Yu, M. Y. 1990 Planet. Space Sci. 38, 543) has generated and sustained a large body of theoretical and experimental research that has clarified the physics of collective effects in dusty plasmas. A unique feature of the DAW is that it can be observed (literally) using laser illumination and high-speed videography, revealing details of wave-particle interactions at an unprecedented single particle level. This paper attempts to review some of the contributions and extensions of dust acoustic wave physics, as well as identify recent findings that illustrate the potential importance of this dust wave in the agglomeration of dust particles.

  11. Gravitational Waves from Oscillons after Inflation.

    PubMed

    Antusch, Stefan; Cefalà, Francesco; Orani, Stefano

    2017-01-06

    We investigate the production of gravitational waves during preheating after inflation in the common case of field potentials that are asymmetric around the minimum. In particular, we study the impact of oscillons, comparatively long lived and spatially localized regions where a scalar field (e.g., the inflaton) oscillates with large amplitude. Contrary to a previous study, which considered a symmetric potential, we find that oscillons in asymmetric potentials associated with a phase transition can generate a pronounced peak in the spectrum of gravitational waves that largely exceeds the linear preheating spectrum. We discuss the possible implications of this enhanced amplitude of gravitational waves. For instance, for low scale inflation models, the contribution from the oscillons can strongly enhance the observation prospects at current and future gravitational wave detectors.

  12. Holocaust survivors: three waves of resilience research.

    PubMed

    Greene, Roberta R; Hantman, Shira; Sharabi, Adi; Cohen, Harriet

    2012-01-01

    Three waves of resilience research have resulted in resilience-enhancing educational and therapeutic interventions. In the first wave of inquiry, researchers explored the traits and environmental characteristics that enabled people to overcome adversity. In the second wave, researchers investigated the processes related to stress and coping. In the third wave, studies examined how people grow and are transformed following adverse events, often leading to self-actualize, client creativity and spirituality. In this article the authors examined data from a study, "Forgiveness, Resiliency, and Survivorship among Holocaust Survivors" funded by the John Templeton Foundation ( Greene, Armour, Hantman, Graham, & Sharabi, 2010 ). About 65% of the survivors scored on the high side for resilience traits. Of the survivors, 78% engaged in processes considered resilient and felt they were transcendent or had engaged in behaviors that help them grow and change over the years since the Holocaust, including leaving a legacy and contributing to the community.

  13. Gravitational Waves from Oscillons after Inflation

    NASA Astrophysics Data System (ADS)

    Antusch, Stefan; Cefalà, Francesco; Orani, Stefano

    2017-01-01

    We investigate the production of gravitational waves during preheating after inflation in the common case of field potentials that are asymmetric around the minimum. In particular, we study the impact of oscillons, comparatively long lived and spatially localized regions where a scalar field (e.g., the inflaton) oscillates with large amplitude. Contrary to a previous study, which considered a symmetric potential, we find that oscillons in asymmetric potentials associated with a phase transition can generate a pronounced peak in the spectrum of gravitational waves that largely exceeds the linear preheating spectrum. We discuss the possible implications of this enhanced amplitude of gravitational waves. For instance, for low scale inflation models, the contribution from the oscillons can strongly enhance the observation prospects at current and future gravitational wave detectors.

  14. Propagating wave correlations in complex systems

    NASA Astrophysics Data System (ADS)

    Creagh, Stephen C.; Gradoni, Gabriele; Hartmann, Timo; Tanner, Gregor

    2017-01-01

    We describe a novel approach for computing wave correlation functions inside finite spatial domains driven by complex and statistical sources. By exploiting semiclassical approximations, we provide explicit algorithms to calculate the local mean of these correlation functions in terms of the underlying classical dynamics. By defining appropriate ensemble averages, we show that fluctuations about the mean can be characterised in terms of classical correlations. We give in particular an explicit expression relating fluctuations of diagonal contributions to those of the full wave correlation function. The methods have a wide range of applications both in quantum mechanics and for classical wave problems such as in vibro-acoustics and electromagnetism. We apply the methods here to simple quantum systems, so-called quantum maps, which model the behaviour of generic problems on Poincaré sections. Although low-dimensional, these models exhibit a chaotic classical limit and share common characteristics with wave propagation in complex structures.

  15. Including wave interference in radiative transfer theory for P-SV waves

    NASA Astrophysics Data System (ADS)

    Haney, M. M.; van Wijk, K.; Snieder, R.

    2010-12-01

    The theory of radiative transfer (RT) has successfully been applied to model the envelopes of high frequency (> 1 Hz) seismic waves in the Earth, attesting to the importance of multiple scattering in this frequency range. An advantage of RT over traditional techniques lies in its ability to separately estimate the mechanisms of intrinsic and scattering attenuation. In addition, RT satisfies energy conservation. However, it is well known that RT ignores the contribution of wave interference; it is for this reason that phenomena such as coherent backscattering are not described within RT. Therefore, RT must be considered an incomplete theory and a more general description of multiple wave scattering must be sought in order to describe the full range of possible wave phenomena in the Earth. By deriving RT from a fundamental level for a one-dimensional layered acoustic medium, we have formulated a new theory, similar to RT, which includes wave interference (Haney and van Wijk, 2007; PRE). The inclusion of wave interference allows localization to be accurately represented in an updated RT theory. The derivation of the new theory also provides insight into the connections between multiple scattering theory and interferometry. Building on this result, we extend the acoustic theory to P-SV waves in a layered elastic medium. The extension highlights the difficulty in accounting for wave interference in the presence of more than one stream of energy (e.g., P- and SV-waves). The new theory enables the issue of equipartitioning of localized elastic energy to be addressed, a topic that has received little attention previously. Predictions of the theory are tested against finite-difference numerical simulations of P-SV waves for an ensemble of randomly layered media. Finally, we comment on the type of seismic data sets suited to observe such interference contributions in practice.

  16. Acoustic-gravity waves, theory and application

    NASA Astrophysics Data System (ADS)

    Kadri, Usama; Farrell, William E.; Munk, Walter

    2015-04-01

    Acoustic-gravity waves (AGW) propagate in the ocean under the influence of both the compressibility of sea water and the restoring force of gravity. The gravity dependence vanishes if the wave vector is normal to the ocean surface, but becomes increasingly important as the wave vector acquires a horizontal tilt. They are excited by many sources, including non-linear surface wave interactions, disturbances of the ocean bottom (submarine earthquakes and landslides) and underwater explosions. In this introductory lecture on acoustic-gravity waves, we describe their properties, and their relation to organ pipe modes, to microseisms, and to deep ocean signatures by short surface waves. We discuss the generation of AGW by underwater earthquakes; knowledge of their behaviour with water depth can be applied for the early detection of tsunamis. We also discuss their generation by the non-linear interaction of surface gravity waves, which explains the major role they play in transforming energy from the ocean surface to the crust, as part of the microseisms phenomenon. Finally, they contribute to horizontal water transport at depth, which might affect benthic life.

  17. Wave turbulence in annular wave tank

    NASA Astrophysics Data System (ADS)

    Onorato, Miguel; Stramignoni, Ettore

    2014-05-01

    We perform experiments in an annular wind wave tank at the Dipartimento di Fisica, Universita' di Torino. The external diameter of the tank is 5 meters while the internal one is 1 meter. The tank is equipped by two air fans which can lead to a wind of maximum 5 m/s. The present set up is capable of studying the generation of waves and the development of wind wave spectra for large duration. We have performed different tests including different wind speeds. For large wind speed we observe the formation of spectra consistent with Kolmogorv-Zakharov predictions.

  18. Fast wave current drive

    SciTech Connect

    Goree, J.; Ono, M.; Colestock, P.; Horton, R.; McNeill, D.; Park, H.

    1985-07-01

    Fast wave current drive is demonstrated in the Princeton ACT-I toroidal device. The fast Alfven wave, in the range of high ion-cyclotron harmonics, produced 40 A of current from 1 kW of rf power coupled into the plasma by fast wave loop antenna. This wave excites a steady current by damping on the energetic tail of the electron distribution function in the same way as lower-hybrid current drive, except that fast wave current drive is appropriate for higher plasma densities.

  19. Spectra of Surface Waves

    DTIC Science & Technology

    1989-03-22

    with a wave follower during Marsen. J. Gophysical Res. 88, 9844-9849. 11. Hughes, B.A., 1978. The effects on internal waves on surface waves : 2...Spectra of Surface Waves K. Watson March 1989 JSR-88-130 Approved for public release; distribution unlimited. DTIC SELECTE JUN0 11989 0 JASONE The...Arlington, VA 22209 8503Z 11. TITLE (hlde Secvfty Cof.kaftn) SPECTRA OF SURFACE WAVES (U) 12. PERSONAL AUTHOfRS) K. Watson 13a. TYPE OF REPORT 13b. TIME

  20. Waves of energy

    NASA Astrophysics Data System (ADS)

    Smith, F. G. W.; Charlier, R. H.

    1981-06-01

    Possible means for harnessing the energy contained in ocean waves are considered. Problems associated with the low-grade nature of wave energy and the rate at which wave crests approach are pointed out, and simple devices already in use for the supply of energy to bell buoys, whistle buoys and lighted buoys are noted. Attention is then given to wave energy conversion systems based on the focusing of waves onto a narrow ramp leading to a reservoir from which water is released to power a turbine generator; a slightly submerged circular shell which directs waves into its center cavity where waves act to turn a turbine (the Dam-Atoll); a long vertical pipe with an internal valve allowing water to move in an upward direction (the Isaacs wave-energy pump); a turbine located at the bottom of an open-topped pipe (the Masuda buoy); a completely submerged closed air chamber from which runs a large pipe open to the sea; a wave piston which acts by the compression of air to drive a turbine; a massive structure with upper and lower reservoirs (the Russel rectifier); and devices which consist of floating or submerged objects which transfer wave energy to pumps (the Salter duck and Cockerell raft.) It is concluded that although wave-powered generators are not likely to become competitive in the near future or provide more than a small portion of world demand, they may be found useful under special conditions.

  1. Martian atmospheric lee waves

    NASA Technical Reports Server (NTRS)

    Pirraglia, J. A.

    1975-01-01

    Mariner 9 television pictures of Mars extensive mountain lee wave phenomenon in the northern mid-latitudes during winter were evaluated. The characteristic wave length of the lee waves is readily observable, and in a few cases the boundaries of the wave patterns, as well as the wave length, are observed. The cloud patterns resulting from the waves generated by the flow across a mountain or crater are shown to be dependent upon the velocity profile of the air stream and the vertical stability of the atmosphere. Using the stability as inferred by the temperature structure obtained from the infrared spectrometer data, a two layer velocity model of the air stream is used in calculations based on the theory of mountain lee waves. Results yield magnitudes generally in agreement with various other circulation models.

  2. [F-waves].

    PubMed

    Wang, F C; Massart, N; Kaux, J-F; Bouquiaux, O

    2011-12-01

    F-waves result from the discharge of the motoneurons following their antidromic activation. The F-wave appears, as an indirect (the F-wave latency decreases when the stimulation site moves away from the muscular detection) and late response (occurring after the M response). In practice, the most useful parameter is the F-wave minimal latency, provided that at least seven distinct F-waves are evoked. When the analysis is relative either to the controlateral side, or to a former examination, this parameter is one of most sensitive in electroneuromyography. F-wave evocation implies conduction along the entire peripheral nervous system, and particularly its proximal part, which is not investigated by nervous trunks conduction velocity studies. Thus, F wave study is the most useful in plexopathies and polyradiculonevritis. In the early phase of Guillain-Barré syndrome, their absence may be the unique sign indicative of proximal conduction blocks.

  3. Wavelet-based group and phase velocity measurements: application to ambient noise cross correlation observations from OBS survey offshore Taiwan

    NASA Astrophysics Data System (ADS)

    Wang, W. W.; Yang, H. Y.; Hung, S. H.; Kuo, B. Y.

    2016-12-01

    In recent years, empirical Green's functions (EGFs) reconstructed from ambient noise cross-correlation functions (NCFs) between paired stations provide the unprecedented interstation path coverage within highly instrumented regions for high-resolution tomographic imaging. Dispersion analysis of the retrieved signals including multimode surface waves and body waves often excited by highly nonstationary noise sources becomes a routine but essential task. Since 2008, a number of broadband OBS experiments from the Institute of Earth Sciences (IES), Academia Sinica of Taiwan and TAIGER, a US-Taiwan cooperative research project, have been conducted in deep sea east of Taiwan. In this study, we use continuous recordings of vertical displacements and differential pressure gauges in 36 broadband OBSs deployed offshore eastern Taiwan to investigate the subseafloor structures from extracted Rayleigh waves and the source origin contributing to the generation of very long-period infragravity waves. We apply a wavelet-based method to characterize the time-varying spectral properties and measure the frequency-dependent group and phase velocities of these waves. The results show fundamental mode Rayleigh waves in both the displacement and DPG derived NCFs with a dominant period of 3-5 s and relatively slow speed of 0.5-1.0 km/s, while the other group of earlier dispersive arrivals predominant at 1-3 s, likely associated with higher mode surface waves or body waves, only emerges in the DPG derived NCFs propagates at a much faster speed of 1.5-3 km/s. The infragravity waves at periods ranging from 50 to 160 s found in DPGs records show the speed of 0.05-0.1 km/s. With these robust dispersion measurements, we will conduct the Bayesian inversion to constrain the radial velocity structures beneath the seafloor.

  4. Indian – American contributions to psychiatric research

    PubMed Central

    Pandurangi, Anand K.

    2010-01-01

    The Indian Diaspora, especially in North America, is a visible force in the field of psychiatric medicine. An estimated 5000 persons of Indian origin practice psychiatry in the USA and Canada, and an estimated 10% of these are in academic psychiatry. Wide ranging contributions, from molecular biology of psychiatric disorders to community and cultural psychiatry, are being made by this vibrant group of researchers. This article is a brief summary and work-in-progress report of the contributions by Indian – American psychiatric researchers. Although not exhaustive in coverage, it is meant to give the reader an overview of the contributions made by three waves of researchers over a span of 50 years. PMID:21836715

  5. Experimental and Numerical Studies on Wave Breaking Characteristics over a Fringing Reef under Monochromatic Wave Conditions

    PubMed Central

    2014-01-01

    Fringing reefs play an important role in protecting the coastal area by inducing wave breaking and wave energy dissipation. However, modeling of wave transformation and energy dissipation on this topography is still difficult due to the unique structure. In the present study, two-dimensional laboratory experiments were conducted to investigate the cross-shore variations of wave transformation, setup, and breaking phenomena over an idealized fringing reef with the 1/40 reef slope and to verify the Boussinesq model under monochromatic wave conditions. One-layer and two-layer model configurations of the Boussinesq model were used to figure out the model capability. Both models predicted well (r 2 > 0.8) the cross-shore variation of the wave heights, crests, troughs, and setups when the nonlinearity is not too high (A 0/h 0 < 0.07 in this study). However, as the wave nonlinearity and steepness increase, the one-layer model showed problems in prediction and stability due to the error on the vertical profile of fluid velocity. The results in this study revealed that one-layer model is not suitable in the highly nonlinear wave condition over a fringing reef bathymetry. This data set can contribute to the numerical model verification. PMID:25276853

  6. Quantifying Wave Attenuation due to Salt Marshes with a Phase-Averaged Wave Model

    NASA Astrophysics Data System (ADS)

    Marsooli, R.; Orton, P. M.; Blumberg, A. F.; Georgas, N.

    2016-12-01

    This study uses a mixture of laboratory validation, real-world site/scenario modeling, and data on seasonal variation in salt marsh characteristics to quantify their capacity to mitigate storm waves. We assess the accuracy of four existing empirical formulas to determine the vegetation drag coefficient and, in turn, vegetation-induced wave attenuation. We adopt these formulas in the phase-averaged wave model of Mellor et al. (2008), MDO hereafter, which is improved in the present study to simulate wave energy dissipation due to vegetation drag force. One attribute of MDO is speed, due to parameterized energy in frequency space, and as a result the model may be preferable for hazard assessments and ensemble forecasting. We evaluate the performance of the improved MDO wave model and the empirical drag formulas using existing laboratory data. Comparisons between the model results and measurements show that the model based on the drag formula of Kobayashi et al. (1993) performs better than other models. We further apply MDO based on this formula to Jamaica Bay, the largest natural open space left in New York City, to quantify the influence of estuarine-scale salt marshes on storm waves. The model results show that the vegetation in summer season, when Spartina alterniflora is at its maximum height, is more effective to reduce wave height than in fall season. Moreover, the influence of the Spartina on wave height is more pronounced during a severe storm than a moderate storm. This is because the smaller water depth during a moderate storm causes intense depth-induced wave breaking over shallow marsh islands and thus the contribution of vegetation drag to wave attenuation becomes negligible. On the other hand, during a severe storm with high water elevation, the depth-induced breaking is small and vegetation-induced drag becomes the primary source of wave attenuation.

  7. Cycloidal Wave Energy Converter

    SciTech Connect

    Stefan G. Siegel, Ph.D.

    2012-11-30

    This program allowed further advancing the development of a novel type of wave energy converter, a Cycloidal Wave Energy Converter or CycWEC. A CycWEC consists of one or more hydrofoils rotating around a central shaft, and operates fully submerged beneath the water surface. It operates under feedback control sensing the incoming waves, and converts wave power to shaft power directly without any intermediate power take off system. Previous research consisting of numerical simulations and two dimensional small 1:300 scale wave flume experiments had indicated wave cancellation efficiencies beyond 95%. The present work was centered on construction and testing of a 1:10 scale model and conducting two testing campaigns in a three dimensional wave basin. These experiments allowed for the first time for direct measurement of electrical power generated as well as the interaction of the CycWEC in a three dimensional environment. The Atargis team successfully conducted two testing campaigns at the Texas A&M Offshore Technology Research Center and was able to demonstrate electricity generation. In addition, three dimensional wave diffraction results show the ability to achieve wave focusing, thus increasing the amount of wave power that can be extracted beyond what was expected from earlier two dimensional investigations. Numerical results showed wave cancellation efficiencies for irregular waves to be on par with results for regular waves over a wide range of wave lengths. Using the results from previous simulations and experiments a full scale prototype was designed and its performance in a North Atlantic wave climate of average 30kW/m of wave crest was estimated. A full scale WEC with a blade span of 150m will deliver a design power of 5MW at an estimated levelized cost of energy (LCOE) in the range of 10-17 US cents per kWh. Based on the new results achieved in the 1:10 scale experiments these estimates appear conservative and the likely performance at full scale will

  8. Unusually Large Runup Events

    NASA Astrophysics Data System (ADS)

    Garcia-Medina, G.; Ozkan-Haller, H. T.; Holman, R. A.; Ruggiero, P.

    2016-02-01

    Understanding the primary hydrodynamic processes that cause extreme runup events is important for the prediction of dune erosion and coastal flooding. Large runups may be caused by a superposition of physical and environmental conditions, bore-bore capture, infragravity-short wave interaction, and/or swash-backwash interaction. To investigate the conditions leading to these events we combine optical remote sensing observations (Argus) and state-of-the-art phase resolving numerical modeling (primarily NHWAVE). We evaluate runup time series derived from across-shore transects of pixel intensities in two very different beaches: Agate (Oregon, USA) and Duck (North Carolina, USA). The former is a dissipative beach where the runup is dominated by infragravity energy, whereas the latter is a reflective beach where the runup is dominated by short surface gravity waves. Phase resolving numerical models are implemented to explore an expanded parameter set and identify the mechanisms that control these large runups. Model results are in good qualitative agreement with observations. We also distinguish unexpected runups, which are defined by having an unexpectedly large excursion distance in comparison to the hourly-to-daily local runup conditions and do not necessarily represent a statistical extrema. These events pose significant safety hazards. We evaluate the relative contribution of the dominating physics to extreme and unexpected runup events.

  9. Mathematics: Contributions by Women.

    ERIC Educational Resources Information Center

    Dewar, Jacqueline M.

    1991-01-01

    Describes a core course in a women's-studies program at Loyola Marymount University. Provides information, resources, and an annotated bibliography useful for making students more aware of women's contributions to mathematics. Contains 38 references. (ASK)

  10. EUV Coronal Waves: Atmospheric and Heliospheric Connections and Energetics

    NASA Astrophysics Data System (ADS)

    Patsourakos, S.

    2015-12-01

    Since their discovery in late 90's by EIT on SOHO, the study EUV coronal waves has been a fascinating andfrequently strongly debated research area. While it seems as ifan overall consensus has been reached about the nurture and nature of this phenomenon,there are still several important questions regarding EUV waves. By focusing on the most recentobservations, we will hereby present our current understanding about the nurture and nature of EUV waves,discuss their connections with other atmospheric and heliospheric phenomena (e.g.,flares and CMEs, Moreton waves, coronal shocks, coronal oscillations, SEP events) and finallyassess their possible energetic contribution to the overall budget of relatederuptive phenomena.

  11. Wave-modified mean exothermic heating in the mesopause region

    NASA Technical Reports Server (NTRS)

    Hickey, Michael P.; Walterscheid, Richard L.

    1994-01-01

    We employ a model of wave-driven OH nightglow fluctuations to calculate the effects of gravity waves on the chemical exothermic heating due to reactions involving odd hydrogen and odd oxygen species in the mesopause region. Using a model based on time means and deviations from those means, it is demonstrated that gravity waves contribute to the time-average exothermic heating. The effect can be significant because the fractional fluctuations in minor species density can be substantially greater than the fractional fluctuation of the major gas density. Our calculations reveal that the waves mitigate the exothermic heating, demonstrating their potential importance in the heat budget of the mesopause region.

  12. Wave-packet dynamics of Bogoliubov quasiparticles: Quantum metric effects

    NASA Astrophysics Data System (ADS)

    Liang, Long; Peotta, Sebastiano; Harju, Ari; Törmä, Päivi

    2017-08-01

    We study the dynamics of the Bogoliubov wave packet in superconductors and calculate the supercurrent carried by the wave packet. We discover an anomalous contribution to the supercurrent, related to the quantum metric of the Bloch wave function. This anomalous contribution is most important for flat or quasiflat bands, as exemplified by the attractive Hubbard models on the Creutz ladder and sawtooth lattice. Our theoretical framework is general and can be used to study a wide variety of phenomena, such as spin transport and exciton transport.

  13. Hydrodynamic balance of solitary waves on falling liquid films

    NASA Astrophysics Data System (ADS)

    van Wachem, Berend; Denner, Fabian; Charogiannis, Alexandros; Pradas, Marc; Markides, Christos N.; Kalliadasis, Serafim

    2016-11-01

    Falling liquid films at sufficiently high Reynolds numbers are unstable to long-wave perturbations which at low frequencies evolve into fast moving solitary waves. These solitary waves are strongly nonlinear structures characterised by a dominant elevation with a long tail and steep front, typically with capillary ripples preceding the main wave hump. The objective of our work is to identify the key physical mechanisms governing these solitary waves through direct numerical simulations and experiments. Our results demonstrate that the height and shape of solitary waves is governed by a subtle balance between inertia and surface tension. This leads, for instance, to a stabilisation of the wave height after the onset of flow recirculation in the solitary waves in the moving frame of reference, since the flow rate and, consequently, the effective inertia acting on the waves, are reduced as a result of the recirculation. In addition, the capillary ripples in front of the main solitary humps are strongly contributing to the hydrodynamic balance of solitary waves and we establish a connection between the creation of capillary ripples and the height, stability and speed of the solitary wave. We acknowledge financial support from the Engineering and Physical Sciences Research Council through Grants No. EP/K008595/1 and No. EP/M021556/1.

  14. A Novel Route to Reach a p-Wave Superfluid Fermi Gas

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Tokitake; Inotani, Daisuke; Ohashi, Yoji

    2017-01-01

    We theoretically propose an idea to realize a p-wave superfluid Fermi gas. To overcome the experimental difficulty that a p-wave pairing interaction to form p-wave Cooper pairs damages the system before the condensation growth, we first prepare a p-wave pair amplitude (Φp) in a spin-orbit coupled s-wave superfluid Fermi gas, without any p-wave interaction. Then, by suddenly changing the s-wave interaction with a p-wave one (Up) by using a Feshbach resonance, we reach the p-wave superfluid phase with the p-wave superfluid order parameter being symbolically written as Δp ˜ UpΦp. In this letter, we assess this scenario within the framework of a time-dependent Bogoliubov-de Gennes theory. Our results would contribute to the study toward the realization of unconventional pairing states in an ultracold Fermi gas.

  15. Irregular wave functions of a hydrogen atom in a uniform magnetic field

    NASA Technical Reports Server (NTRS)

    Wintgen, D.; Hoenig, A.

    1989-01-01

    The highly excited irregular wave functions of a hydrogen atom in a uniform magnetic field are investigated analytically, with wave function scarring by periodic orbits considered quantitatively. The results obtained confirm that the contributions of closed classical orbits to the spatial wave functions vanish in the semiclassical limit. Their disappearance, however, is slow. This discussion is illustrated by numerical examples.

  16. Surface waves in three-dimensional electromagnetic composites and their effect on homogenization.

    PubMed

    Xiong, Xiaoyan Y Z; Jiang, Li Jun; Markel, Vadim A; Tsukerman, Igor

    2013-05-06

    Reflection and transmission of electromagnetic waves at the boundaries of periodic composites (electromagnetic/optical metamaterials) depends in general on both bulk and surface waves. We investigate the interplay of these two contributions using three-dimensional full-wave numerical simulations and a recently developed non-asymptotic homogenization theory.

  17. Symmetry structure of a wave equation on some classes of Bianchi cosmological models

    NASA Astrophysics Data System (ADS)

    Jamal, S.; Kara, A. H.; Narain, R.; Shabbir, G.

    2015-04-01

    Nonlinear wave equations are constructed on certain Bianchi models and a symmetry analysis of these equations are performed to construct some exact solutions. Conservation laws of the respective wave equations are also obtained by the application of Noether's theorem. We show how a knowledge of these contributes to the reduction of the wave equation on this manifold.

  18. Linear Elastic Waves

    NASA Astrophysics Data System (ADS)

    Revenough, Justin

    Elastic waves propagating in simple media manifest a surprisingly rich collection of phenomena. Although some can't withstand the complexities of Earth's structure, the majority only grow more interesting and more important as remote sensing probes for seismologists studying the planet's interior. To fully mine the information carried to the surface by seismic waves, seismologists must produce accurate models of the waves. Great strides have been made in this regard. Problems that were entirely intractable a decade ago are now routinely solved on inexpensive workstations. The mathematical representations of waves coded into algorithms have grown vastly more sophisticated and are troubled by many fewer approximations, enforced symmetries, and limitations. They are far from straightforward, and seismologists using them need a firm grasp on wave propagation in simple media. Linear Elastic Waves, by applied mathematician John G. Harris, responds to this need.

  19. RADIATION WAVE DETECTION

    DOEpatents

    Wouters, L.F.

    1960-08-30

    Radiation waves can be detected by simultaneously measuring radiation- wave intensities at a plurality of space-distributed points and producing therefrom a plot of the wave intensity as a function of time. To this end. a detector system is provided which includes a plurality of nuclear radiation intensity detectors spaced at equal radial increments of distance from a source of nuclear radiation. Means are provided to simultaneously sensitize the detectors at the instant a wave of radiation traverses their positions. the detectors producing electrical pulses indicative of wave intensity. The system further includes means for delaying the pulses from the detectors by amounts proportional to the distance of the detectors from the source to provide an indication of radiation-wave intensity as a function of time.

  20. Hysteresis of ionization waves

    SciTech Connect

    Dinklage, A.; Bruhn, B.; Testrich, H.; Wilke, C.

    2008-06-15

    A quasi-logistic, nonlinear model for ionization wave modes is introduced. Modes are due to finite size of the discharge and current feedback. The model consists of competing coupled modes and it incorporates spatial wave amplitude saturation. The hysteresis of wave mode transitions under current variation is reproduced. Sidebands are predicted by the model and found in experimental data. The ad hoc model is equivalent to a general--so-called universal--approach from bifurcation theory.

  1. Millimeter Wave Ocular Effects

    DTIC Science & Technology

    1987-02-20

    illustrates the rabbit head in holder by photography (a), thermography (b) and thermographic profile (c). The temperature of the cornea was measured using an...and graphs of profiles of the 40 temperatures difference (final-initial) of the rabbit cornea heated by the focused beam of millimeter waves from the...antenna. 5. Cooling of the cornea by air flow. 43 6. Temperature as a function of power applied using 45 continuous wave millimeter waves of

  2. Kinesthetic Transverse Wave Demonstration

    NASA Astrophysics Data System (ADS)

    Pantidos, Panagiotis; Patapis, Stamatis

    2005-09-01

    This is a variation on the String and Sticky Tape demonstration "The Wave Game," suggested by Ron Edge. A group of students stand side by side, each one holding a card chest high with both hands. The teacher cues the first student to begin raising and lowering his card. When he starts lowering his card, the next student begins to raise his. As succeeding students move their cards up and down, a wave such as that shown in the figure is produced. To facilitate the process, students' motions were synchronized with the ticks of a metronome (without such synchronization it was nearly impossible to generate a satisfactory wave). Our waves typically had a frequency of about 1 Hz and a wavelength of around 3 m. We videotaped the activity so that the students could analyze the motions. The (17-year-old) students had not received any prior instruction regarding wave motion and did not know beforehand the nature of the exercise they were about to carry out. During the activity they were asked what a transverse wave is. Most of them quickly realized, without teacher input, that while the wave propagated horizontally, the only motion of the transmitting medium (them) was vertical. They located the equilibrium points of the oscillations, the crests and troughs of the waves, and identified the wavelength. The teacher defined for them the period of the oscillations of the motion of a card to be the total time for one cycle. The students measured this time and then several asserted that it was the same as the wave period. Knowing the length of the waves and the number of waves per second, the next step can easily be to find the wave speed.

  3. WaveNet

    DTIC Science & Technology

    2015-10-30

    Coastal Inlets Research Program WaveNet WaveNet is a web-based, Graphical-User- Interface (GUI) data management tool developed for Corps coastal...data from different sources, and employs a combination of Fortran , Python and Matlab codes to process and analyze data for USACE applications...Grays Harbor, WA; Cape Canaveral, FL. WaveNet is employs a Google Map interface to query, select, and display data for a given geographic region

  4. A statistical survey of electrostatic electron cyclotron harmonic waves based on THEMIS FFF wave data

    NASA Astrophysics Data System (ADS)

    Ni, Binbin; Gu, Xudong; Fu, Song; Xiang, Zheng; Lou, Yuequn

    2017-03-01

    -driven pitch angle scattering and to determine the precise contributions of ECH waves to the plasma sheet electron dynamics and diffuse auroral electron precipitation.

  5. Thermal-Wave Microscope

    NASA Technical Reports Server (NTRS)

    Jones, Robert E.; Kramarchuk, Ihor; Williams, Wallace D.; Pouch, John J.; Gilbert, Percy

    1989-01-01

    Computer-controlled thermal-wave microscope developed to investigate III-V compound semiconductor devices and materials. Is nondestructive technique providing information on subsurface thermal features of solid samples. Furthermore, because this is subsurface technique, three-dimensional imaging also possible. Microscope uses intensity-modulated electron beam of modified scanning electron microscope to generate thermal waves in sample. Acoustic waves generated by thermal waves received by transducer and processed in computer to form images displayed on video display of microscope or recorded on magnetic disk.

  6. Optical rogue waves.

    PubMed

    Solli, D R; Ropers, C; Koonath, P; Jalali, B

    2007-12-13

    Recent observations show that the probability of encountering an extremely large rogue wave in the open ocean is much larger than expected from ordinary wave-amplitude statistics. Although considerable effort has been directed towards understanding the physics behind these mysterious and potentially destructive events, the complete picture remains uncertain. Furthermore, rogue waves have not yet been observed in other physical systems. Here, we introduce the concept of optical rogue waves, a counterpart of the infamous rare water waves. Using a new real-time detection technique, we study a system that exposes extremely steep, large waves as rare outcomes from an almost identically prepared initial population of waves. Specifically, we report the observation of rogue waves in an optical system, based on a microstructured optical fibre, near the threshold of soliton-fission supercontinuum generation--a noise-sensitive nonlinear process in which extremely broadband radiation is generated from a narrowband input. We model the generation of these rogue waves using the generalized nonlinear Schrödinger equation and demonstrate that they arise infrequently from initially smooth pulses owing to power transfer seeded by a small noise perturbation.

  7. Internal waves, Andaman Sea

    NASA Image and Video Library

    1994-09-30

    STS068-236-044 (30 September-11 October 1994) --- These internal waves in the Andaman Sea, west of Burma, were photographed from 115 nautical miles above Earth by the crew of the Space Shuttle Endeavour during the Space Radar Laboratory 2 (SRL-2) mission. The internal waves smooth out some of the capillary waves at the surface in bands and travel along the density discontinuity at the bottom of the mixed layer depth. There is little evidence of the internal waves at the surface. They are visible in the Space Shuttle photography because of sunglint, which reflects off the water.

  8. Photonics surface waves on metamaterials interfaces.

    PubMed

    Takayama, Osamu; Bogdanov, Andrey; Lavrinenko, Andrei V

    2017-09-12

    A surface wave (SW) in optics is a light wave, which is supported at an interface of two dissimilar media and propagates along the interface with its field amplitude exponentially decaying away from the boundary. The research on surface waves has been flourishing in last few decades thanks to their unique properties of surface sensitivity and field localization. These features have resulted in applications in nano-guiding, sensing, light-trapping and imaging based on the near-field techniques, contributing to the establishment of the nanophotonics as a field of research. Up to present, a wide variety of surface waves has been investigated in numerous material and structure settings. This paper reviews the recent progress and development in the physics of SWs localized at metamaterial interfaces, as well as bulk media in order to provide broader perspectives on optical surface waves in general. For each type of the surface waves, we discuss material and structural platforms. We mainly focus on experimental realizations in the visible and near-infrared wavelength ranges. We also address existing and potential application of SWs in chemical and biological sensing, and experimental excitation and characterization methods. © 2017 IOP Publishing Ltd.

  9. Gravitational waves induced by spinor fields

    NASA Astrophysics Data System (ADS)

    Feng, Kaixi; Piao, Yun-Song

    2015-07-01

    In realistic model building, spinor fields with various masses are present. During inflation, a spinor field may induce gravitational waves as a second order effect. In this paper, we calculate the contribution of a single massive spinor field to the power spectrum of primordial gravitational wave by using a retarded Green propagator. We find that the correction is scale invariant and of order H4/MP4 for arbitrary spinor mass mψ. Additionally, we also observe that when mψ≳H , the dependence of correction on mψ/H is nontrivial.

  10. Satellite observations of gravity wave activity and dissipation during sudden stratospheric warmings

    NASA Astrophysics Data System (ADS)

    Ern, Manfred; Preusse, Peter; Riese, Martin

    2015-04-01

    Sudden stratospheric warmings (SSWs) are a circulation anomaly that occurs mainly at high northern latitudes in boreal winter. During major SSWs the eastward directed polar jet reverses, and, for a certain period, the stratosphere is governed by anomalous westward winds. It is known that both planetary waves and gravity waves contribute to the formation and evolution of SSWs. However, the small horizontal scales of gravity waves (tens to a few thousand km) challenge both observations and modeling of gravity waves. Therefore, the role of gravity waves during SSWs is still not fully understood. In particular, gravity waves should play an important role during the recovery of the stratopause and of the eastward directed polar jet after major SSWs. This is indicated by several modeling efforts. However, validation by global observations of gravity waves is still an open issue. Gravity wave momentum fluxes and potential gravity wave drag were derived from HIRDLS and SABER satellite observations, and the role of gravity waves during recent SSWs in the boreal winters 2001/2002-2013/2014 is investigated. We find that gravity waves with slow horizontal phase speeds, likely mountain waves, play an important role during SSWs. Both gravity wave momentum fluxes and gravity wave drag are enhanced before the central date of major SSWs. After the central date, gravity wave momentum fluxes and gravity wave drag in the stratosphere are strongly reduced. Still, gravity wave drag contributes to the wind reversals related to the anomalous westward winds. Another finding is that, after major SSWs, the contribution of gravity wave drag at the bottom of re-established eastward directed polar jets is small. At the top of those jets, however, strong gravity wave drag is found, which indicates that gravity waves contribute to the downward propagation of newly formed polar jets and of elevated stratopauses to their "climatological" altitude. This confirms recent modeling work by, for example

  11. Wave optics in black hole spacetimes: the Schwarzschild case

    NASA Astrophysics Data System (ADS)

    Nambu, Yasusada; Noda, Sousuke

    2016-04-01

    We investigate the wave optics in the Schwarzschild spacetime. Applying the standard formalism of wave-scattering problems, the Green function represented by the sum over the partial waves is evaluated using the Poisson sum formula. The effect of orbiting scattering due to the unstable circular orbit for null rays is taken into account as the contribution of the Regge poles of the scattering matrix and the asymptotic form of the scattering wave is obtained in the eikonal limit. Using this wave function, images of the black hole illuminated by a point source are reconstructed. We also discuss the wave effect in the frequency domain caused by the interference between the direct and the winding rays.

  12. Cellular and network mechanisms of spike-wave seizures.

    PubMed

    Blumenfeld, Hal

    2005-01-01

    Spike-wave seizures are often considered a relatively "pure" form of epilepsy, with a uniform defect present in all patients and involvement of the whole brain homogeneously. Here, we present evidence against these common misconceptions. Rather than a uniform disorder, spike-wave rhythms arise from the normal inherent network properties of brain excitatory and inhibitory circuits, where they can be provoked by many different insults in several different brain networks. Here we discuss several different cellular and molecular mechanisms that may contribute to the generation of spike-wave seizures, particularly in idiopathic generalized epilepsy. In addition, we discuss growing evidence that electrical, neuroimaging, and molecular changes in spike-wave seizures do not involve the entire brain homogeneously. Rather, spike-wave discharges occur selectively in some thalamocortical networks, while sparing others. It is hoped that improved understanding of the heterogeneous defects and selective brain regions involved will ultimately lead to more effective treatments for spike-wave seizures.

  13. Microstrip disk antennas. I - Efficiency of space wave launching.

    NASA Astrophysics Data System (ADS)

    de Assis Fonseca, S. B.; Giarola, A. J.

    1984-06-01

    The behavior of space, surface and leaky waves in microstrip antennas and the effects on the efficiency of space wave launching are studied theoretically, along with the effects of the physical characteristics of the dielectric layer over the antenna ground plane. Since the waves are excited in an antenna substrate, the radiated fields are expressed in terms of the cavity model with magnetic sidewalls and dyadic Green's function in stratified media. The contributions of space and surface waves are quantified and efficiency and directivity values are determined as functions of the antenna dimensions. Truncations in the dielectric are shown to cause undulations in the antenna radiation patterns, arising from the interference of space wave fields with fields produced when the surface wave is incident in the truncation region. Truncating the dielectric as far as possible from the antenna elements and implementing lower dielectric values in the disk radius ratios and the dielectric relative to the permittivities could reduce the interference problem.

  14. Alfvén waves in the structured solar corona

    NASA Astrophysics Data System (ADS)

    Cally, Paul S.

    2017-04-01

    A simple model of a periodic ensemble of closely packed flux tubes, sitting atop a vertically stratified layer, reveals that an incident fast wave from below preferentially converts almost immediately to Alfvén waves in the flux tubes, with kink waves restricted to at most a very few Fourier modes. This suggests that observations of coronal kink modes in such structured systems may greatly underestimate the net wave-energy flux being transported into and through the corona, much of which may reside in harder-to-observe Alfvén waves. The processes of mode conversion/resonant absorption and Alfvén phase mixing are implicated. It is suggested that the Sun's internal p-mode field - the 5-min oscillations - may contribute substantially to the process by supplying incident fast waves in the chromosphere that scatter and mode-convert in the tube ensemble.

  15. Raman three-wave interaction in partially spin polarized plasma

    NASA Astrophysics Data System (ADS)

    Shahid, M.; Iqbal, Z.; Jamil, M.; Murtaza, G.

    2017-10-01

    By employing the separate spin evolution-quantum hydrodynamic model (SSE-QHD), the nonlinear growth rate of the parametric decay instability is studied via the Raman scattering process of three-wave coupling. SSE-QHD equations are solved for the pump wave (O-mode), sideband Shear Alfvén wave, and the electron plasma perturbations. It is observed that the spectrum of the electron plasma waves is modified due to newly generated spin dependent waves which contribute in the coupling process. The nonlinear growth rate as a result of three wave coupling is plotted for different sets of parameters and conditions. It is also observed that the growth rate is suppressed due to the spin effects. Shifting of diamagnetic behavior of plasma to paramagnetic behavior is noticed.

  16. Excitation of Electron Cyclotron Harmonic Waves in Earth's Magnetotail

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaojia

    This dissertation investigates the generation mechanism, spatial distribution and characteristics of electrostatic electron cyclotron harmonic (ECH) waves under different plasma sheet conditions, and quantifies the role of these waves in producing the diffuse aurora. THEMIS observations from five magnetotail seasons, along with ray-tracing, and electron diffusion codes have been utilized towards that goal. By modeling the wave growth and quasi-linear pitch-angle diffusion of electrons with realistic parameters for the magnetic field, loss-cone distribution and wave intensity (obtained from observations as a function of magnetotail location), we estimate the loss-cone fill ratio and the contribution of auroral energy flux from wave-induced electron precipitation. We conclude that ECH waves are the dominant driver of electron precipitation in the middle to outer magnetotail.

  17. Propagation and Dissipation of MHD Waves in Coronal Holes

    NASA Astrophysics Data System (ADS)

    Dwivedi, B. N.

    2006-11-01

    bholadwivedi@gmail.com In view of the landmark result on the solar wind outflow, starting between 5 Mm and 20 Mm above the photosphere in magnetic funnels, we investigate the propagation and dissipation of MHD waves in coronal holes. We underline the importance of Alfvén wave dissipation in the magnetic funnels through the viscous and resistive plasma. Our results show that Alfvén waves are one of the primary energy sources in the innermost part of coronal holes where the solar wind outflow starts. We also consider compressive viscosity and thermal conductivity to study the propagation and dissipation of long period slow longitudinal MHD waves in polar coronal holes. We discuss their likely role in the line profile narrowing, and in the energy budget for coronal holes and the solar wind. We compare the contribution of longitudinal MHD waves with high frequency Alfvén waves.

  18. Broadband high-frequency waves detected at dipolarization fronts

    NASA Astrophysics Data System (ADS)

    Yang, J.; Cao, J. B.; Fu, H. S.; Wang, T. Y.; Liu, W. L.; Yao, Z. H.

    2017-04-01

    Dipolarization front (DF) is a sharp boundary most probably separating the reconnection jet from the background plasma sheet. So far at this boundary, the observed waves are mainly in low-frequency range (e.g., magnetosonic waves and lower hybrid waves). Few high-frequency waves are observed in this region. In this paper, we report the broadband high-frequency wave emissions at the DF. These waves, having frequencies extending from the electron cyclotron frequency fce, up to the electron plasma frequency fpe, could contribute 10% to the in situ measurement of intermittent energy conversion at the DF layer. Their generation may be attributed to electron beams, which are simultaneously observed at the DF as well.

  19. Opportunities for shear energy scaling in bulk acoustic wave resonators.

    PubMed

    Jose, Sumy; Hueting, Raymond J E

    2014-10-01

    An important energy loss contribution in bulk acoustic wave resonators is formed by so-called shear waves, which are transversal waves that propagate vertically through the devices with a horizontal motion. In this work, we report for the first time scaling of the shear-confined spots, i.e., spots containing a high concentration of shear wave displacement, controlled by the frame region width at the edge of the resonator. We also demonstrate a novel methodology to arrive at an optimum frame region width for spurious mode suppression and shear wave confinement. This methodology makes use of dispersion curves obtained from finite-element method (FEM) eigenfrequency simulations for arriving at an optimum frame region width. The frame region optimization is demonstrated for solidly mounted resonators employing several shear wave optimized reflector stacks. Finally, the FEM simulation results are compared with measurements for resonators with Ta2O5/ SiO2 stacks showing suppression of the spurious modes.

  20. Observational indications of downward-propagating gravity waves in middle atmosphere lidar data

    NASA Astrophysics Data System (ADS)

    Kaifler, N.; Kaifler, B.; Ehard, B.; Gisinger, S.; Dörnbrack, A.; Rapp, M.; Kivi, R.; Kozlovsky, A.; Lester, M.; Liley, B.

    2017-09-01

    Two Rayleigh lidars were employed at a southern-hemisphere mid-latitude site in New Zealand (45°S) and a northern-hemisphere high-latitude site in Finland (67°N) in order to observe gravity waves between 30 and 85 km altitude under wintertime conditions. Two-dimensional wavelet analysis is used to analyze temperature perturbations caused by gravity waves and to determine their vertical wavelengths and phase progression. In both datasets, upward phase progression waves occur frequently between 30 and 85 km altitude. Six cases of large-amplitude wave packets are selected which exhibit upward phase progression in the stratosphere and/or mesosphere. We argue that these wave packets propagate downward and we discuss possible wave generation mechanisms. Spectral analysis reveals that superpositions of two or three wave packets are common. Furthermore, their characteristics often match those of upward-propagating waves which are observed at the same time or earlier. In the dataset means, the contribution of upward phase progression waves to the potential energy density Ep is largest in the lower stratosphere above Finland. There, Ep of upward and downward phase progression waves is comparable. At 85 km one third of the potential energy carried by propagating waves is attributed to upward phase progression waves. In some cases Ep of upward phase progression waves far exceeds Ep of downward phase progression waves. The downward-propagating waves might be generated in situ in the middle atmosphere or arise from reflection of upward-propagating waves.

  1. Advances in enzyme technology--UK contributions.

    PubMed

    Woodley, J M

    2000-01-01

    Enzyme technology has been a recognised part of bioprocess engineering since its inception in the 1950s and 1960s. In this article the early history of enzyme technology is discussed and the subsequent developments in enzyme isolation, enzyme modification and process technology are described. These creative developments have put enzyme technology in a position of huge potential to contribute to environmentally compatible and cost effective means of industrial chemical synthesis. Recent developments in protein modification to produce designer enzymes are leading a new wave of enzyme application.

  2. Oceanic-wave-measurement system

    NASA Technical Reports Server (NTRS)

    Holmes, J. F.; Miles, R. T.

    1980-01-01

    Barometer mounted on bouy senses wave heights. As wave motion raises and lowers barometer, pressure differential is proportional to wave height. Monitoring circuit samples barometer output every half cycle of wave motion and adds magnitudes of adjacent positive and negative peaks. Resulting output signals, proportional to wave height, are transmitted to central monitoring station.

  3. Oceanic-wave-measurement system

    NASA Technical Reports Server (NTRS)

    Holmes, J. F.; Miles, R. T.

    1980-01-01

    Barometer mounted on bouy senses wave heights. As wave motion raises and lowers barometer, pressure differential is proportional to wave height. Monitoring circuit samples barometer output every half cycle of wave motion and adds magnitudes of adjacent positive and negative peaks. Resulting output signals, proportional to wave height, are transmitted to central monitoring station.

  4. Realization of the cooperation between traveling wave component and standing wave component in thermoacoustic regenerator

    NASA Astrophysics Data System (ADS)

    Gang, Zhou; Qing, Li

    2014-01-01

    The regenerator is the core of a thermoacoustic engine or refrigerator, which consists of smooth or tortuous porous media, such as parallel plates or stainless stacked-screen. Due to regenerator presence, the real acoustic field is neither a pure standing wave nor a pure travelling wave and the thermoacoustic effect is the hybrid effect of the traveling wave component (TWC) and the standing wave component (SWC). To achieve both high efficiency and gain for a given temperature ratio, one has to choose an optimum phase lead Φm of the oscillating pressure relative to velocity in the middle of the regenerator to give the best combination of TWC and SWC. In this paper, based on linear thermoacoustic theory, the phase lead Φm which can make both the traveling wave and the standing wave contribute to the thermoacoustic conversions, are analyzed and optimized. To realize cooperation between TWC and SWC in thermoacoustic regenerator, a mathematical model of a 1/2 wavelength duct with a regenerator driven by double speakers was built, which can provide an appropriate traveling-wave field in the regenerator by changing the driving conditions including amplitude and the phase difference of the driving voltages. According to this, the influence of the acoustic field and the regenerator's structure on the thermoacoustic conversion is analyzed, and the optimum condition for the thermoacoustic conversion is discussed. This work is significant to understand thermoacoustic conversion mechanisms of regenerators in the real acoustic field.

  5. Physical measurements of breaking wave impact on a floating wave energy converter

    NASA Astrophysics Data System (ADS)

    Hann, Martyn R.; Greaves, Deborah M.; Raby, Alison

    2013-04-01

    Marine energy converter must both efficiently extract energy in small to moderate seas and also successfully survive storms and potential collisions. Extreme loads on devices are therefore an important consideration in their design process. X-MED is a SuperGen UKCMER project and is a collaboration between the Universities of Manchester, Edinburgh and Plymouth and the Scottish Association for Marine Sciences. Its objective is to extend the knowledge of extreme loads due to waves, currents, flotsam and mammal impacts. Plymouth Universities contribution to the X-MED project involves measuring the loading and response of a taut moored floating body due to steep and breaking wave impacts, in both long crested and directional sea states. These measurements are then to be reproduced in STAR-CCM+, a commercial volume of fluid CFD solver, so as to develop techniques to predict the wave loading on wave energy converters. The measurements presented here were conducted in Plymouth Universities newly opened COAST laboratories 35m long, 15.5m wide and 3m deep ocean basin. A 0.5m diameter taut moored hemispherical buoy was used to represent a floating wave energy device or support structure. The changes in the buoys 6 degree of freedom motion and mooring loads are presented due to focused breaking wave impacts, with the breaking point of the wave changed relative to the buoy.

  6. Power from Ocean Waves.

    ERIC Educational Resources Information Center

    Newman, J. N.

    1979-01-01

    Discussed is the utilization of surface ocean waves as a potential source of power. Simple and large-scale wave power devices and conversion systems are described. Alternative utilizations, environmental impacts, and future prospects of this alternative energy source are detailed. (BT)

  7. Power from Ocean Waves.

    ERIC Educational Resources Information Center

    Newman, J. N.

    1979-01-01

    Discussed is the utilization of surface ocean waves as a potential source of power. Simple and large-scale wave power devices and conversion systems are described. Alternative utilizations, environmental impacts, and future prospects of this alternative energy source are detailed. (BT)

  8. Thermal-Wave Imaging.

    ERIC Educational Resources Information Center

    Rosencwaig, Allan

    1982-01-01

    Thermal features of and beneath the surface of a sample can be detected and imaged with a thermal-wave microscope. Various methodologies for the excitation and detection of thermal waves are discussed, and several applications, primarily in microelectronics, are presented. (Author)

  9. Waves at Navigation Structures

    DTIC Science & Technology

    2015-10-30

    channels, ports and harbors, and coastal beaches . It conducts basic research on the coupling of wave and flow models to calculate waves and...TX; Matagorda Bay, TX; Hilo Harbor, HI; Kikiaola Harbor, HI; Dana Point Harbor, CA; Pillar Point Harbor, CA (Figure 3); Ocean Beach , CA; Noyo

  10. The Relativistic Wave Vector

    ERIC Educational Resources Information Center

    Houlrik, Jens Madsen

    2009-01-01

    The Lorentz transformation applies directly to the kinematics of moving particles viewed as geometric points. Wave propagation, on the other hand, involves moving planes which are extended objects defined by simultaneity. By treating a plane wave as a geometric object moving at the phase velocity, novel results are obtained that illustrate the…

  11. Waves in polar lows

    NASA Astrophysics Data System (ADS)

    Orimolade, A. P.; Furevik, B. R.; Noer, G.; Gudmestad, O. T.; Samelson, R. M.

    2016-08-01

    In a rather stationary fetch, one would not expect large waves in polar low situations. However, the picture changes when one considers a moving fetch. The significant wave heights that may be associated with the recorded polar lows on the Norwegian continental shelf from December 1999 to October 2015 are estimated using a one-dimensional parametric wave model. A comparison of the measured and the forecasted significant wave heights in two recent polar low cases in the Barents Sea is presented. The estimated significant wave heights show that the values could have been up to and above 9 m. The forecasted significant wave heights considerably underestimated the measured significant wave heights in the two recent polar low cases that are considered. Furthermore, a generalization of the fetch-limited wave equation in polar lows is proposed, which allows the wind field to vary in space and time, and is shown to give results that are consistent with the one-dimensional parametric model.

  12. The Relativistic Wave Vector

    ERIC Educational Resources Information Center

    Houlrik, Jens Madsen

    2009-01-01

    The Lorentz transformation applies directly to the kinematics of moving particles viewed as geometric points. Wave propagation, on the other hand, involves moving planes which are extended objects defined by simultaneity. By treating a plane wave as a geometric object moving at the phase velocity, novel results are obtained that illustrate the…

  13. Those Elusive Gravitational Waves

    ERIC Educational Resources Information Center

    MOSAIC, 1976

    1976-01-01

    The presence of gravitational waves was predicted by Einstein in his theory of General Relativity. Since then, scientists have been attempting to develop a detector sensitive enough to measure these cosmic signals. Once the presence of gravitational waves is confirmed, scientists can directly study star interiors, galaxy cores, or quasars. (MA)

  14. Gravitational waves from inflation

    NASA Astrophysics Data System (ADS)

    Guzzetti, M. C.; Bartolo, N.; Liguori, M.; Matarrese, S.

    2016-09-01

    The production of a stochastic background of gravitational waves is a fundamental prediction of any cosmological inflationary model. The features of such a signal encode unique information about the physics of the Early Universe and beyond, thus representing an exciting, powerful window on the origin and evolution of the Universe. We review the main mechanisms of gravitational-wave production, ranging from quantum fluctuations of the gravitational field to other mechanisms that can take place during or after inflation. These include e.g. gravitational waves generated as a consequence of extra particle production during inflation, or during the (p)reheating phase. Gravitational waves produced in inflation scenarios based on modified gravity theories and second-order gravitational waves are also considered. For each analyzed case, the expected power spectrum is given. We discuss the discriminating power among different models, associated with the validity/violation of the standard consistency relation between tensor-to-scalar ratio r and tensor spectral index nT. In light of the prospects for (directly/indirectly) detecting primordial gravitational waves, we give the expected present-day gravitational radiation spectral energy-density, highlighting the main characteristics imprinted by the cosmic thermal history, and we outline the signatures left by gravitational waves on the Cosmic Microwave Background and some imprints in the Large-Scale Structure of the Universe. Finally, current bounds and prospects of detection for inflationary gravitational waves are summarized.

  15. Supergranular waves revisited

    NASA Astrophysics Data System (ADS)

    Langfellner, Jan; Birch, Aaron; Gizon, Laurent

    2017-08-01

    Solar supergranules remain a mysterious phenomenon, half a century after their discovery. One particularly interesting aspect of supergranulation is its wave-like nature detected in Fourier space. Using SDO/HMI local helioseismology and granulation tracking, we provide new evidence for supergranular waves. We also discuss their influence on the evolution of the network magnetic field using cork simulations.

  16. Slow frictional waves

    NASA Astrophysics Data System (ADS)

    Viswanathan, Koushik; Sundaram, Narayan; Chandrasekar, Srinivasan

    Stick-slip, manifest as intermittent tangential motion between two dry solid surfaces, is a friction instability that governs diverse phenomena from automobile brake squeals to earthquakes. We show, using high-speed in situ imaging of an adhesive polymer interface, that low velocity stick-slip is fundamentally of three kinds, corresponding to passage of three different surface waves -- separation pulses, slip pulses and the well-known Schallamach waves. These waves, traveling much slower than elastic waves, have clear distinguishing properties. Separation pulses and Schallamach waves involve local interface separation, and propagate in opposite directions while slip pulses are characterized by a sharp stress front and do not display any interface detachment. A change in the stick-slip mode from separation to slip pulse is effected simply by increasing the normal force. Together, these three waves constitute all possible stick-slip modes in adhesive friction and are shown to have direct analogues in muscular locomotory waves in soft bodied invertebrates. A theory for slow wave propagation is also presented which is capable of explaining the attendant interface displacements, velocities and stresses.

  17. Those Elusive Gravitational Waves

    ERIC Educational Resources Information Center

    MOSAIC, 1976

    1976-01-01

    The presence of gravitational waves was predicted by Einstein in his theory of General Relativity. Since then, scientists have been attempting to develop a detector sensitive enough to measure these cosmic signals. Once the presence of gravitational waves is confirmed, scientists can directly study star interiors, galaxy cores, or quasars. (MA)

  18. Search for Gravitational Waves

    NASA Astrophysics Data System (ADS)

    Tsubono, K.

    The current status of the experimental search for gravitational waves is reviewed here. The emphasis is on the Japanese TAMA project. We started operation of the TAMA300 laser interferometric detector in 1999, and are now collecting and analyzing observational data to search for gravitational wave signals.

  19. Advanced Gravitational Wave Detectors

    NASA Astrophysics Data System (ADS)

    Blair, D. G.; Howell, E. J.; Ju, L.; Zhao, C.

    2012-02-01

    Part I. An Introduction to Gravitational Wave Astronomy and Detectors: 1. Gravitational waves D. G. Blair, L. Ju, C. Zhao and E. J. Howell; 2. Sources of gravitational waves D. G. Blair and E. J. Howell; 3. Gravitational wave detectors D. G. Blair, L. Ju, C. Zhao, H. Miao, E. J. Howell, and P. Barriga; 4. Gravitational wave data analysis B. S. Sathyaprakash and B. F. Schutz; 5. Network analysis L. Wen and B. F. Schutz; Part II. Current Laser Interferometer Detectors: Three Case Studies: 6. The Laser Interferometer Gravitational-Wave Observatory P. Fritschel; 7. The VIRGO detector S. Braccini; 8. GEO 600 H. Lück and H. Grote; Part III. Technology for Advanced Gravitational Wave Detectors: 9. Lasers for high optical power interferometers B. Willke and M. Frede; 10. Thermal noise, suspensions and test masses L. Ju, G. Harry and B. Lee; 11. Vibration isolation: Part 1. Seismic isolation for advanced LIGO B. Lantz; Part 2. Passive isolation J-C. Dumas; 12. Interferometer sensing and control P. Barriga; 13. Stabilizing interferometers against high optical power effects C. Zhao, L. Ju, S. Gras and D. G. Blair; Part IV. Technology for Third Generation Gravitational Wave Detectors: 14. Cryogenic interferometers J. Degallaix; 15. Quantum theory of laser-interferometer GW detectors H. Miao and Y. Chen; 16. ET. A third generation observatory M. Punturo and H. Lück; Index.

  20. Contribution Margin Budgeting.

    ERIC Educational Resources Information Center

    Tambrino, Paul A.

    2001-01-01

    Describes Iowa Valley Community College District's Contribution Margin Budgeting (CMB) program, successfully implemented to stave off bankruptcy. In this program, each responsibility center receives credit for all income generated and is charged for all expenditures, and each must build its own reserve against revenue shortfalls and unanticipated…

  1. Contributed Papers, 1967.

    ERIC Educational Resources Information Center

    Special Libraries Association, New York, NY. Documentation Div.

    Included are six papers from the Special Libraries Association Documentation Division's Contributed Papers Session at the National Conference in New York, May 28 - June 1, 1967, which were not included in the November, 1967 issue of Special Libraries. The papers are: (1) "The Bibliographical Control of Aerospace Industry Conference Literature…

  2. Spectra of Baroclinic Inertia-Gravity Wave Turbulence

    NASA Technical Reports Server (NTRS)

    Glazman, Roman E.

    1996-01-01

    Baroclinic inertia-gravity (IG) waves form a persistent background of thermocline depth and sea surface height oscillations. They also contribute to the kinetic energy of horizontal motions in the subsurface layer. Measured by the ratio of water particle velocity to wave phase speed, the wave nonlinearity may be rather high. Given a continuous supply of energy from external sources, nonlinear wave-wave interactions among IG waves would result in inertial cascades of energy, momentum, and wave action. Based on a recently developed theory of wave turbulence in scale-dependent systems, these cascades are investigated and IG wave spectra are derived for an arbitrary degree of wave nonlinearity. Comparisons with satellite-altimetry-based spectra of surface height variations and with energy spectra of horizontal velocity fluctuations show good agreement. The well-known spectral peak at the inertial frequency is thus explained as a result of the inverse cascade. Finally, we discuss a possibility of inferring the internal Rossby radius of deformation and other dynamical properties of the upper thermocline from the spectra of SSH (sea surface height) variations based on altimeter measurements.

  3. Spectra of Baroclinic Inertia-Gravity Wave Turbulence

    NASA Technical Reports Server (NTRS)

    Glazman, Roman E.

    1996-01-01

    Baroclinic inertia-gravity (IG) waves form a persistent background of thermocline depth and sea surface height oscillations. They also contribute to the kinetic energy of horizontal motions in the subsurface layer. Measured by the ratio of water particle velocity to wave phase speed, the wave nonlinearity may be rather high. Given a continuous supply of energy from external sources, nonlinear wave-wave interactions among IG waves would result in inertial cascades of energy, momentum, and wave action. Based on a recently developed theory of wave turbulence in scale-dependent systems, these cascades are investigated and IG wave spectra are derived for an arbitrary degree of wave nonlinearity. Comparisons with satellite-altimetry-based spectra of surface height variations and with energy spectra of horizontal velocity fluctuations show good agreement. The well-known spectral peak at the inertial frequency is thus explained as a result of the inverse cascade. Finally, we discuss a possibility of inferring the internal Rossby radius of deformation and other dynamical properties of the upper thermocline from the spectra of SSH (sea surface height) variations based on altimeter measurements.

  4. Vector financial rogue waves

    NASA Astrophysics Data System (ADS)

    Yan, Zhenya

    2011-11-01

    The coupled nonlinear volatility and option pricing model presented recently by Ivancevic is investigated, which generates a leverage effect, i.e., stock volatility is (negatively) correlated to stock returns, and can be regarded as a coupled nonlinear wave alternative of the Black-Scholes option pricing model. In this Letter, we analytically propose vector financial rogue waves of the coupled nonlinear volatility and option pricing model without an embedded w-learning. Moreover, we exhibit their dynamical behaviors for chosen different parameters. The vector financial rogue wave (rogon) solutions may be used to describe the possible physical mechanisms for the rogue wave phenomena and to further excite the possibility of relative researches and potential applications of vector rogue waves in the financial markets and other related fields.

  5. Electromagnetic wave energy converter

    NASA Technical Reports Server (NTRS)

    Bailey, R. L. (Inventor)

    1973-01-01

    Electromagnetic wave energy is converted into electric power with an array of mutually insulated electromagnetic wave absorber elements each responsive to an electric field component of the wave as it impinges thereon. Each element includes a portion tapered in the direction of wave propagation to provide a relatively wideband response spectrum. Each element includes an output for deriving a voltage replica of the electric field variations intercepted by it. Adjacent elements are positioned relative to each other so that an electric field subsists between adjacent elements in response to the impinging wave. The electric field results in a voltage difference between adjacent elements that is fed to a rectifier to derive dc output power.

  6. SQUARE WAVE AMPLIFIER

    DOEpatents

    Leavitt, M.A.; Lutz, I.C.

    1958-08-01

    An amplifier circuit is described for amplifying sigmals having an alternating current component superimposed upon a direct current component, without loss of any segnnent of the alternating current component. The general circuit arrangement includes a vibrator, two square wave amplifiers, and recombination means. The amplifier input is connected to the vibrating element of the vibrator and is thereby alternately applied to the input of each square wave amplifier. The detailed circuitry of the recombination means constitutes the novelty of the annplifier and consists of a separate, dual triode amplifier coupled to the output of each square wave amplifier with a recombination connection from the plate of one amplifier section to a grid of one section of the other amplifier. The recombination circuit has provisions for correcting distortion caused by overlapping of the two square wave voltages from the square wave amplifiers.

  7. Sculpting Waves (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Engheta, Nader

    2015-09-01

    In electronics controlling and manipulating flow of charged carriers has led to design of numerous functional devices. In photonics, by analogy, this is done through controlling photons and optical waves. However, the challenges and opportunities are different in these two fields. Materials control waves, and as such they can tailor, manipulate, redirect, and scatter electromagnetic waves and photons at will. Recent development in condensed matter physics, nanoscience, and nanotechnology has made it possible to tailor materials with unusual parameters and extreme characteristics and with atomic precision and thickness. One can now construct structures much smaller than the wavelengths of visible light, thus ushering in unprecedented possibilities and novel opportunities for molding fields and waves at the nanoscale with desired functionalities. At such subwavelength scales, sculpting optical fields and waves provides a fertile ground for innovation and discovery. I will discuss some of the exciting opportunities in this area, and forecast some future directions and possibilities.

  8. Experiments on excitation waves

    NASA Astrophysics Data System (ADS)

    Müller, S. C.

    Recent trends in the experimentation on chemical and biochemical excitation waves are presented. In the Belousov-Zhabotinsky reaction, which is the most suitable chemical laboratory system for the study of wave propagation in excitable medium, the efficient control of wave dynamics by electrical fields and by light illumination is illustrated. In particular, the effects of a feedback control are shown. Further new experiments in this system are concerned with three-dimensional topologies and boundary effects. Important biological applications are found in the aggregation of slime mould amoebae, in proton waves during oscillatory glycolysis, and in waves of spreading depression in neuronal tissue as studied by experiments in chicken retina. Numerical simulations with appropriate reaction-diffusion models complement a large number of these experimental findings.

  9. Gravity-Wave astronomy

    NASA Astrophysics Data System (ADS)

    Grishchuk, Leonid Petrovich

    The article concerns astronomical phenomena , related with discovery of gravitational waves of various nature: 1) primordial (relic) gravitational waves, analogous to MWBR 2) gravitational waves due to giant collisions in the Universe between 2a) Macroscopic black Holes in the centers of Galaxies 2b) Tidal disruption of neutron stars by Black holes 2c) deformations of the space-time by stellar mass Black Holes moving near giant Black Holes in the centers of Galaxies 2d) Supernovae phenomena 2e) accretion phenomena on Black Holes and Neutron stars. The Earth based interferometric technics (LIGO Project) to detect gravitational waves is described as well as the perspectiva for a space Laser Interferometric Antena (LISA)is discussed. The article represents a modified text of the Plenary talk "Gravity-Wave astronomy" given at the XI International gravitational Conference (July 1986, Stockholm, Sweden).

  10. Theory of Gravitational Waves

    NASA Astrophysics Data System (ADS)

    Le Tiec, Alexandre; Novak, Jérôme

    The existence of gravitational radiation is a natural prediction of any relativistic description of the gravitational interaction. In this chapter, we focus on gravitational waves, as predicted by Einstein's general theory of relativity. First, we introduce those mathematical concepts that are necessary to properly formulate the physical theory, such as the notions of manifold, vector, tensor, metric, connection and curvature. Second, we motivate, formulate and then discuss Einstein's equation, which relates the geometry of spacetime to its matter content. Gravitational waves are later introduced as solutions of the linearized Einstein equation around flat spacetime. These waves are shown to propagate at the speed of light and to possess two polarization states. Gravitational waves can interact with matter, allowing for their direct detection by means of laser interferometers. Finally, Einstein's quadrupole formulas are derived and used to show that nonspherical compact objects moving at relativistic speeds are powerful gravitational wave sources.

  11. Holographic tunneling wave function

    NASA Astrophysics Data System (ADS)

    Conti, Gabriele; Hertog, Thomas; van der Woerd, Ellen

    2015-12-01

    The Hartle-Hawking wave function in cosmology can be viewed as a decaying wave function with anti-de Sitter (AdS) boundary conditions. We show that the growing wave function in AdS familiar from Euclidean AdS/CFT is equivalent, semiclassically and up to surface terms, to the tunneling wave function in cosmology. The cosmological measure in the tunneling state is given by the partition function of certain relevant deformations of CFTs on a locally AdS boundary. We compute the partition function of finite constant mass deformations of the O( N ) vector model on the round three sphere and show this qualitatively reproduces the behaviour of the tunneling wave function in Einstein gravity coupled to a positive cosmological constant and a massive scalar. We find the amplitudes of inhomogeneities are not damped in the holographic tunneling state.

  12. Project GlobWave

    NASA Astrophysics Data System (ADS)

    Busswell, Geoff; Ash, Ellis; Piolle, Jean-Francois; Poulter, David J. S.; Snaith, Helen; Collard, Fabrice; Sheera, Harjit; Pinnock, Simon

    2010-12-01

    The ESA GlobWave project is a three year initiative, funded by ESA and CNES, to service the needs of satellite wave product users across the globe. Led by Logica UK, with support from CLS, IFREMER, SatOC and NOCS, the project will provide free access to satellite wave data and products in a common format, both historical and in near real time, from various European and American SAR and altimeter missions. Building on the successes of similar projects for Sea Surface Temperature and ocean colour, the project aims to stimulate increased use and analysis of satellite wave products. In addition to common-format satellite data the project will provide comparisons with in situ measurements, interactive data analysis tools and a pilot spatial wave forecast verification scheme for operational forecast production centres. The project will begin operations in January 2010, with direction from regular structured user consultation.

  13. Removing Wave Artifacts from Eddy Correlation Data

    NASA Astrophysics Data System (ADS)

    Neumann, Andreas; Brand, Andreas

    2017-04-01

    The German Wadden Sea is an extensive system of back-barrier tidal basins along the margin of the southern North Sea. Due to their high productivity and the strong retention potential of labile organic carbon high mineralization rates are expected in this system. Since the sediment bed is sandy, the oxygen fluxes across the sediment-water interface (SWI) may be enhanced by strong tidal currents as well as by wind-induced surface waves. In order to measure oxygen fluxes in-situ without disturbance of the sediment, the Eddy Correlation method (ECM) was introduced to aquatic geoscience by Berg et al. (2003). The method is based on correlating turbulent fluctuations of oxygen concentration and vertical velocity measured at high frequency above the SWI. The method integrates over spatial heterogeneities and allows the observation of total benthic oxygen fluxes in complex systems where other methods like flux chamber deployments and oxygen profile measurements in the sediment fail. Therefore, the method should also reflect effects like the enhancement of oxygen fluxes by porewater advection driven by waves and currents over sandy sediments. Unfortunately the ECM suffers from wave contamination due to stirring sensitivity of the electrodes, spatial separation between the oxygen electrode and the location of velocity measurement as well as by a tilt of the measurement setup at the deployment side. In order to correct for this wave contamination we tested the method of spectral reconstruction initially introduced by Bricker and Monismith (2007) for the determination of Reynolds-stresses in wave-affected environments. In short, this method attempts to remove the wave signal from the Power spectral densities of oxygen concentration and vertical velocity fluctuations by cutting off the wave peak in these spectra. The wave contribution to the co-spectrum between both quantities is then reconstructed by assuming that the phasing in the wave band is dominated by the waves. Based

  14. Extra-pair paternity in waved albatrosses.

    PubMed

    Huyvaert, K P; Anderson, D J; Jones, T C; Duan, W; Parker, P G

    2000-09-01

    We estimated the rate of extra-pair fertilizations (EPFs) in waved albatrosses (Phoebastria irrorata) on Isla Española, Galápagos, Ecuador, using multilocus minisatellite DNA fingerprinting. Waved albatrosses are socially monogamous, long-lived seabirds whose main population is on Española. Aggressive extra-pair copulation (EPC) attempts have been observed in the breeding colony during the days preceding egg-laying. Our genetic analyses of 16 families (single chicks and their attending parents) revealed evidence of EPFs in four families. In all cases males were the excluded parent. These data suggest that waved albatrosses have an unusually high rate of EPF relative to taxa with similar life histories. Future behavioural observations will determine the extent to which forced vs. unforced EPCs contribute to this high EPF rate.

  15. Stress Generation and Adolescent Depression: Contribution of Interpersonal Stress Responses

    ERIC Educational Resources Information Center

    Flynn, Megan; Rudolph, Karen D.

    2011-01-01

    This research examined the proposal that ineffective responses to common interpersonal problems disrupt youths' relationships, which, in turn, contributes to depression during adolescence. Youth (86 girls, 81 boys; M age = 12.41, SD = 1.19) and their primary female caregivers participated in a three-wave longitudinal study. Youth completed a…

  16. Standing Waves on a Shoestring.

    ERIC Educational Resources Information Center

    Hendrix, Laura

    1992-01-01

    Describes the construction of a wave generator used to review the algebraic relationships of wave motion. Students calculate and measure the weight needed to create tension to generate standing waves at the first eight harmonics. (MDH)

  17. Spatial equation for water waves

    NASA Astrophysics Data System (ADS)

    Dyachenko, A. I.; Zakharov, V. E.

    2016-02-01

    A compact spatial Hamiltonian equation for gravity waves on deep water has been derived. The equation is dynamical and can describe extreme waves. The equation for the envelope of a wave train has also been obtained.

  18. Dynamics of baroclinic wave systems

    NASA Technical Reports Server (NTRS)

    Barcilon, Albert; Weng, Hengyi

    1989-01-01

    The research carried out in the past year dealt with nonlinear baroclinic wave dynamics. The model consisted of an Eady baroclinic basic state and uneven Elkman dissipation at the top and bottom boundaries with/without slopes. The method of solution used a truncated spectral expansion with three zonal waves and one or two meridional modes. Numerical experiments were performed on synoptic scale waves or planetary scale waves with/without wave-wave interaction.

  19. Avicenna's contribution to cardiology.

    PubMed

    Chamsi-Pasha, Mohammed A R; Chamsi-Pasha, Hassan

    2014-01-01

    Ibn Sina, known in the West as Avicenna, was the most famous and influential of all the Islamic philosopher-scientists. His most important medical works are the Canon of Medicine medical encyclopedia and a treatise on cardiac drugs. His Canon of Medicine remained the standard text in both the East and West until the 16(th) century. Avicenna's description of cardiac diseases was logically presented perhaps for the first time in the history of medicine. Avicenna was the first to describe carotid sinus hypersensitivity, which presents with vasovagal syncope. He was a pioneer in pulsology and the first correct explanation of pulsation was given by Avicenna, after he refined Galen's theory of the pulse. Besides, he discussed the action of available drugs on the heart in details and mentioned their indications and contraindications. In conclusion, Avicenna made important contributions to cardiology. This article describes some of his contributions in this field.

  20. Abstracts of contributed papers

    SciTech Connect

    Not Available

    1994-08-01

    This volume contains 571 abstracts of contributed papers to be presented during the Twelfth US National Congress of Applied Mechanics. Abstracts are arranged in the order in which they fall in the program -- the main sessions are listed chronologically in the Table of Contents. The Author Index is in alphabetical order and lists each paper number (matching the schedule in the Final Program) with its corresponding page number in the book.

  1. Wave phenomena in sunspots

    NASA Astrophysics Data System (ADS)

    Löhner-Böttcher, Johannes

    2016-03-01

    Context: The dynamic atmosphere of the Sun exhibits a wealth of magnetohydrodynamic (MHD) waves. In the presence of strong magnetic fields, most spectacular and powerful waves evolve in the sunspot atmosphere. Allover the sunspot area, continuously propagating waves generate strong oscillations in spectral intensity and velocity. The most prominent and fascinating phenomena are the 'umbral flashes' and 'running penumbral waves' as seen in the sunspot chromosphere. Their nature and relation have been under intense discussion in the last decades. Aims: Waves are suggested to propagate upward along the magnetic field lines of sunspots. An observational study is performed to prove or disprove the field-guided nature and coupling of the prevalent umbral and penumbral waves. Comprehensive spectroscopic observations at high resolution shall provide new insights into the wave characteristics and distribution across the sunspot atmosphere. Methods: Two prime sunspot observations were carried out with the Dunn Solar Telescope at the National Solar Observatory in New Mexico and with the Vacuum Tower Telescope at the Teide Observatory on Tenerife. The two-dimensional spectroscopic observations were performed with the interferometric spectrometers IBIS and TESOS. Multiple spectral lines are scanned co-temporally to sample the dynamics at the photospheric and chromospheric layers. The time series (1 - 2.5 h) taken at high spatial and temporal resolution are analyzed according to their evolution in spectral intensities and Doppler velocities. A wavelet analysis was used to obtain the wave power and dominating wave periods. A reconstruction of the magnetic field inclination based on sunspot oscillations was developed. Results and conclusions: Sunspot oscillations occur continuously in spectral intensity and velocity. The obtained wave characteristics of umbral flashes and running penumbral waves strongly support the scenario of slow-mode magnetoacoustic wave propagation along the

  2. Global Coronal Waves

    NASA Astrophysics Data System (ADS)

    Chen, P. F.

    2016-02-01

    After the Solar and Heliospheric Observatory (SOHO) was launched in 1996, the aboard Extreme Ultraviolet Imaging Telescope (EIT) observed a global coronal wave phenomenon, which was initially named ``EIT wave" after the telescope. The bright fronts are immediately followed by expanding dimmings. It has been shown that the brightenings and dimmings are mainly due to plasma density increase and depletion, respectively. Such a spectacular phenomenon sparked long-lasting interest and debates. The debates were concentrated on two topics, one is about the driving source, and the other is about the nature of this wavelike phenomenon. The controversies are most probably because there may exist two types of large-scale coronal waves that were not well resolved before the Solar Dynamics Observatory (SDO) was launched: one is a piston-driven shock wave straddling over the erupting coronal mass ejection (CME), and the other is an apparently propagating front, which may correspond to the CME frontal loop. Such a two-wave paradigm was proposed more than 13 years ago, and now is being recognized by more and more colleagues. In this paper, we review how various controversies can be resolved in the two-wave framework and how important it is to have two different names for the two types of coronal waves.

  3. Undamped electrostatic plasma waves

    SciTech Connect

    Valentini, F.; Perrone, D.; Veltri, P.; Califano, F.; Pegoraro, F.; Morrison, P. J.; O'Neil, T. M.

    2012-09-15

    Electrostatic waves in a collision-free unmagnetized plasma of electrons with fixed ions are investigated for electron equilibrium velocity distribution functions that deviate slightly from Maxwellian. Of interest are undamped waves that are the small amplitude limit of nonlinear excitations, such as electron acoustic waves (EAWs). A deviation consisting of a small plateau, a region with zero velocity derivative over a width that is a very small fraction of the electron thermal speed, is shown to give rise to new undamped modes, which here are named corner modes. The presence of the plateau turns off Landau damping and allows oscillations with phase speeds within the plateau. These undamped waves are obtained in a wide region of the (k,{omega}{sub R}) plane ({omega}{sub R} being the real part of the wave frequency and k the wavenumber), away from the well-known 'thumb curve' for Langmuir waves and EAWs based on the Maxwellian. Results of nonlinear Vlasov-Poisson simulations that corroborate the existence of these modes are described. It is also shown that deviations caused by fattening the tail of the distribution shift roots off of the thumb curve toward lower k-values and chopping the tail shifts them toward higher k-values. In addition, a rule of thumb is obtained for assessing how the existence of a plateau shifts roots off of the thumb curve. Suggestions are made for interpreting experimental observations of electrostatic waves, such as recent ones in nonneutral plasmas.

  4. On wave radar measurement

    NASA Astrophysics Data System (ADS)

    Ewans, Kevin; Feld, Graham; Jonathan, Philip

    2014-09-01

    The SAAB REX WaveRadar sensor is widely used for platform-based wave measurement systems by the offshore oil and gas industry. It offers in situ surface elevation wave measurements at relatively low operational costs. Furthermore, there is adequate flexibility in sampling rates, allowing in principle sampling frequencies from 1 to 10 Hz, but with an angular microwave beam width of 10° and an implied ocean surface footprint in the order of metres, significant limitations on the spatial and temporal resolution might be expected. Indeed there are reports that the accuracy of the measurements from wave radars may not be as good as expected. We review the functionality of a WaveRadar using numerical simulations to better understand how WaveRadar estimates compare with known surface elevations. In addition, we review recent field measurements made with a WaveRadar set at the maximum sampling frequency, in the light of the expected functionality and the numerical simulations, and we include inter-comparisons between SAAB radars and buoy measurements for locations in the North Sea.

  5. Shoaling internal solitary waves

    NASA Astrophysics Data System (ADS)

    Sutherland, B. R.; Barrett, K. J.; Ivey, G. N.

    2013-09-01

    The evolution and breaking of internal solitary waves in a shallow upper layer as they approach a constant bottom slope is examined through laboratory experiments. The waves are launched in a two-layer fluid through the standard lock-release method. In most experiments, the wave amplitude is significantly larger than the depth of the shallow upper layer so that they are not well described by Korteweg-de Vries theory. The dynamics of the shoaling waves are characterized by the Iribarren number, Ir, which measures the ratio of the topographic slope to the square root of the characteristic wave slope. This is used to classify breaking regimes as collapsing, plunging, surging, and nonbreaking for increasing values of Ir. For breaking waves, the maximum interface descent, Hi⋆, is predicted to depend upon the topographic slope, s, and the incident wave's amplitude and width, Asw and Lsw, respectively, as Hi⋆≃4sAswLsw. This prediction is corroborated by our experiments. Likewise, we apply simple heuristics to estimate the speed of interface descent, and we characterize the speed and range of the consequent upslope flow of the lower layer after breaking has occurred.

  6. Wave action power plant

    SciTech Connect

    Lucia, L.V.

    1982-03-16

    A wave action power plant powered by the action of water waves has a drive shaft rotated by a plurality of drive units, each having a lever pivotally mounted on and extending from said shaft and carrying a weight, in the form of a float, which floats on the waves and rocks the lever up and down on the shaft. A ratchet mechanism causes said shaft to be rotated in one direction by the weight of said float after it has been raised by wave and the wave has passed, leaving said float free to move downwardly by gravity and apply its full weight to pull down on the lever and rotate the drive shaft. There being a large number of said drive units so that there are always some of the weights pulling down on their respective levers while other weights are being lifted by waves and thereby causing continuous rotation of the drive shaft in one direction. The said levers are so mounted that they may be easily raised to bring the weights into a position wherein they are readily accessible for cleaning the bottoms thereof to remove any accumulation of barnacles, mollusks and the like. There is also provided means for preventing the weights from colliding with each other as they independently move up and down on the waves.

  7. Multiscale Climate Emulator of Multimodal Wave Spectra: MUSCLE-spectra

    NASA Astrophysics Data System (ADS)

    Rueda, A.; Hegermiller, C.; Alvarez Antolinez, J. A.; Camus, P.; Vitousek, S.; Ruggiero, P.; Barnard, P.; Erikson, L. H.; Tomas, A.; Mendez, F. J.

    2016-12-01

    Characterization of multimodal directional wave spectra is important for many offshore and coastal applications, such as marine forecasting, coastal hazard assessment, and design of offshore wave energy farms and coastal structures. However, the multivariate and multiscale nature of wave climate variability makes this problem complex yet tractable using computationally-expensive numerical models. So far, the skill of statistical-downscaling models based parametric (unimodal) wave conditions is limited in large ocean basins such as the Pacific. The recent availability of long-term directional spectral data from buoys and wave hindcast models allows for development of stochastic models that include multimodal sea-state parameters. This work introduces a statistical-downscaling framework based on weather types to predict multimodal wave spectra (e.g., significant wave height, mean wave period, and mean wave direction from different storm systems, including sea and swells) from large-scale atmospheric pressure fields. For each weather type, variables of interest are modeled using the categorical distribution for the sea-state type, the Generalized Extreme Value (GEV) distribution for wave height and wave period, a multivariate Gaussian copula for the interdependence between variables, and a Markov chain model for the chronology of daily weather types. We apply the model to the Southern California coast, where local seas and swells from both the Northern and Southern Hemispheres contribute to the multimodal wave spectrum. This work allows attribution of particular extreme multimodal wave events to specific atmospheric conditions, expanding knowledge of time-dependent, climate-driven offshore and coastal sea-state conditions that have a significant influence on local nearshore processes, coastal morphology, and flood hazards.

  8. Impact of gravity waves on long-range infrasound propagation

    NASA Astrophysics Data System (ADS)

    Millet, Christophe; Lott, François; De La Camara, Alvaro

    2016-04-01

    In this work we study infrasound propagation in acoustic waveguides that support a finite number of propagating modes. We analyze the effects of gravity waves on these acoustic waveguides. Testing sound propagation in such perturbed fields can potentially be used to improve the gravity wave models. A linear solution modeling the interaction between an incoming acoustic wave and a randomly perturbed atmosphere is developed, using the forward-scattering approximation. The wave mode structure is determined by the effective sound speed profile which is strongly affected by gravity wave breaking. The random perturbations are described by a stochastic field predicted by a multiwave stochastic parameterization of gravity waves, which is operational in the LMDz climate model. The justification for this approach is two fold. On the one hand, the use of a few monochromatic waves mimics the observations of rather narrow-banded gravity wave packets in the lower stratosphere. On the other hand, the stochastic sampling of the gravity wave field and the random choice of wave properties deals with the inherent unpredictability of mesoscale dynamics from large scale conditions provided by the meteorological reanalysis. The transmitted acoustic signals contain a stable front and a small-amplitude incoherent coda. A general expression for the stable front is derived in terms of saddle-point contributions. The saddle-points are obtained from a WKB approximation of the vertical eigenvalue problem. This approach extract the dominant effects in the acoustic - gravity wave interaction. We present results that show how statistics of the transmitted signal are related to a few saddle-points and how the GW field can trigger large deviations in the acoustic signals. While some of the characteristics of the stable front can be directly related to that of a few individual gravity waves, it is shown that the amount of the launched gravity waves included in climate models can be estimated using

  9. Retinal Wave Behavior through Activity-Dependent Refractory Periods

    PubMed Central

    Godfrey, Keith B; Swindale, Nicholas V

    2007-01-01

    In the developing mammalian visual system, spontaneous retinal ganglion cell (RGC) activity contributes to and drives several aspects of visual system organization. This spontaneous activity takes the form of spreading patches of synchronized bursting that slowly advance across portions of the retina. These patches are non-repeating and tile the retina in minutes. Several transmitter systems are known to be involved, but the basic mechanism underlying wave production is still not well-understood. We present a model for retinal waves that focuses on acetylcholine mediated waves but whose principles are adaptable to other developmental stages. Its assumptions are that a) spontaneous depolarizations of amacrine cells drive wave activity; b) amacrine cells are locally connected, and c) cells receiving more input during their depolarization are subsequently less responsive and have longer periods between spontaneous depolarizations. The resulting model produces waves with non-repeating borders and randomly distributed initiation points. The wave generation mechanism appears to be chaotic and does not require neural noise to produce this wave behavior. Variations in parameter settings allow the model to produce waves that are similar in size, frequency, and velocity to those observed in several species. Our results suggest that retinal wave behavior results from activity-dependent refractory periods and that the average velocity of retinal waves depends on the duration a cell is excitatory: longer periods of excitation result in slower waves. In contrast to previous studies, we find that a single layer of cells is sufficient for wave generation. The principles described here are very general and may be adaptable to the description of spontaneous wave activity in other areas of the nervous system. PMID:18052546

  10. The radiation of surface wave energy: Implications for volcanic tremor

    NASA Astrophysics Data System (ADS)

    Haney, M. M.; Denolle, M.; Lyons, J. J.; Nakahara, H.

    2015-12-01

    The seismic energy radiated by active volcanism is one common measurement of eruption size. For example, the magnitudes of individual earthquakes in volcano-tectonic (VT) swarms can be summed and expressed in terms of cumulative magnitude, energy, or moment release. However, discrepancies exist in current practice when treating the radiated energy of volcano seismicity dominated by surface waves. This has implications for volcanic tremor, since eruption tremor typically originates at shallow depth and is made up of surface waves. In the absence of a method to compute surface wave energy, estimates of eruption energy partitioning between acoustic and seismic waves typically assume seismic energy is composed of body waves. Furthermore, without the proper treatment of surface wave energy, it is unclear how much volcanic tremor contributes to the overall seismic energy budget during volcanic unrest. To address this issue, we derive, from first principles, the expression of surface wave radiated energy. In contrast with body waves, the surface wave energy equation is naturally expressed in the frequency domain instead of the time domain. We validate our result by reproducing an analytical solution for the radiated power of a vertical force source acting on a free surface. We further show that the surface wave energy equation leads to an explicit relationship between energy and the imaginary part of the surface wave Green's tensor at the source location, a fundamental property recognized within the field of seismic interferometry. With the new surface wave energy equation, we make clear connections to reduced displacement and propose an improved formula for the calculation of surface wave reduced displacement involving integration over the frequency band of tremor. As an alternative to reduced displacement, we show that reduced particle velocity squared is also a valid physical measure of tremor size, one based on seismic energy rate instead of seismic moment rate. These

  11. Multiscale climate emulator of multimodal wave spectra: MUSCLE-spectra

    NASA Astrophysics Data System (ADS)

    Rueda, Ana; Hegermiller, Christie A.; Antolinez, Jose A. A.; Camus, Paula; Vitousek, Sean; Ruggiero, Peter; Barnard, Patrick L.; Erikson, Li H.; Tomás, Antonio; Mendez, Fernando J.

    2017-02-01

    Characterization of multimodal directional wave spectra is important for many offshore and coastal applications, such as marine forecasting, coastal hazard assessment, and design of offshore wave energy farms and coastal structures. However, the multivariate and multiscale nature of wave climate variability makes this complex problem tractable using computationally expensive numerical models. So far, the skill of statistical-downscaling model-based parametric (unimodal) wave conditions is limited in large ocean basins such as the Pacific. The recent availability of long-term directional spectral data from buoys and wave hindcast models allows for development of stochastic models that include multimodal sea-state parameters. This work introduces a statistical downscaling framework based on weather types to predict multimodal wave spectra (e.g., significant wave height, mean wave period, and mean wave direction from different storm systems, including sea and swells) from large-scale atmospheric pressure fields. For each weather type, variables of interest are modeled using the categorical distribution for the sea-state type, the Generalized Extreme Value (GEV) distribution for wave height and wave period, a multivariate Gaussian copula for the interdependence between variables, and a Markov chain model for the chronology of daily weather types. We apply the model to the southern California coast, where local seas and swells from both the Northern and Southern Hemispheres contribute to the multimodal wave spectrum. This work allows attribution of particular extreme multimodal wave events to specific atmospheric conditions, expanding knowledge of time-dependent, climate-driven offshore and coastal sea-state conditions that have a significant influence on local nearshore processes, coastal morphology, and flood hazards.

  12. Rossby wave energy dispersion from tropical cyclone in zonal basic flows

    NASA Astrophysics Data System (ADS)

    Shi, Wenli; Fei, Jianfang; Huang, Xiaogang; Liu, Yudi; Ma, Zhanhong; Yang, Lu

    2016-04-01

    This study investigates tropical cyclone energy dispersion under horizontally sheared flows using a nonlinear barotropic model. In addition to common patterns, unusual features of Rossby wave trains are also found in flows with constant vorticity and vorticity gradients. In terms of the direction of the energy dispersion, the wave train can rotate clockwise and elongate southwestward under anticyclonic circulation (ASH), which contributes to the reenhancement of the tropical cyclone (TC). The wave train even splits into two obvious wavelike trains in flows with a southward vorticity gradient (WSH). Energy dispersed from TCs varies over time, and variations in the intensity of the wave train components typically occur in two stages. Wave-activity flux diagnosis and ray tracing calculations are extended to the frame that moves along with the TC to reveal the concrete progress of wave propagation. The direction of the wave-activity flux is primarily determined by the combination of the basic flow and the TC velocity. Along the flux, the distribution of pseudomomentum effectively illustrates the development of wave trains, particularly the rotation and split of wave propagation. Ray tracing involves the quantitative tracing of wave features along rays, which effectively coincide with the wave train regimes. Flows of a constant shear (parabolic meridional variation) produce linear (nonlinear) wave number variations. For the split wave trains, the real and complex wave number waves move along divergent trajectories and are responsible for different energy dispersion ducts.

  13. Wave-wave interactions in solar type III radio bursts

    SciTech Connect

    Thejappa, G.; MacDowall, R. J.

    2014-02-11

    The high time resolution observations from the STEREO/WAVES experiment show that in type III radio bursts, the Langmuir waves often occur as localized magnetic field aligned coherent wave packets with durations of a few ms and with peak intensities well exceeding the strong turbulence thresholds. Some of these wave packets show spectral signatures of beam-resonant Langmuir waves, down- and up-shifted sidebands, and ion sound waves, with frequencies, wave numbers, and tricoherences satisfying the resonance conditions of the oscillating two stream instability (four wave interaction). The spectra of a few of these wave packets also contain peaks at f{sub pe}, 2f{sub pe} and 3 f{sub pe} (f{sub pe} is the electron plasma frequency), with frequencies, wave numbers and bicoherences (computed using the wavelet based bispectral analysis techniques) satisfying the resonance conditions of three wave interactions: (1) excitation of second harmonic electromagnetic waves as a result of coalescence of two oppositely propagating Langmuir waves, and (2) excitation of third harmonic electromagnetic waves as a result of coalescence of Langmuir waves with second harmonic electromagnetic waves. The implication of these findings is that the strong turbulence processes play major roles in beam stabilization as well as conversion of Langmuir waves into escaping radiation in type III radio bursts.

  14. Modified shock waves for extracorporeal shock wave lithotripsy: a simulation based on the Gilmore formulation.

    PubMed

    Canseco, Guillermo; de Icaza-Herrera, Miguel; Fernández, Francisco; Loske, Achim M

    2011-10-01

    Extracorporeal shock wave lithotripsy (SWL) is a reliable therapy for the treatment of urolithiasis. Nevertheless, improvements to enhance stone fragmentation and reduce tissue damage are still needed. During SWL, cavitation is one of the most important stone fragmentation mechanisms. Bubbles with a diameter between about 7 and 55μm have been reported to expand and collapse after shock wave passage, forming liquid microjets at velocities of up to 400m/s that contribute to the pulverization of renal calculi. Several authors have reported that the fragmentation efficiency may be improved by using tandem shock waves. Tandem SWL is based on the fact that the collapse of a bubble can be intensified if a second shock wave arrives tenths or even a few hundredths of microseconds before its collapse. The object of this study is to determine if tandem pulses consisting of a conventional shock wave (estimated rise time between 1 and 20ns), followed by a slower second pressure profile (0.8μs rise time), have advantages over conventional tandem SWL. The Gilmore equation was used to simulate the influence of the modified pressure field on the dynamics of a single bubble immersed in water and compare the results with the behavior of the same bubble subjected to tandem shock waves. The influence of the delay between pulses on the dynamics of the collapsing bubble was also studied for both conventional and modified tandem waves. For a bubble of 0.07mm, our results indicate that the modified pressure profile enhances cavitation compared to conventional tandem waves at a wide range of delays (10-280μs). According to this, the proposed pressure profile could be more efficient for SWL than conventional tandem shock waves. Similar results were obtained for a ten times smaller bubble.

  15. Stress wave focusing transducers

    SciTech Connect

    Visuri, S.R., LLNL

    1998-05-15

    Conversion of laser radiation to mechanical energy is the fundamental process behind many medical laser procedures, particularly those involving tissue destruction and removal. Stress waves can be generated with laser radiation in several ways: creation of a plasma and subsequent launch of a shock wave, thermoelastic expansion of the target tissue, vapor bubble collapse, and ablation recoil. Thermoelastic generation of stress waves generally requires short laser pulse durations and high energy density. Thermoelastic stress waves can be formed when the laser pulse duration is shorter than the acoustic transit time of the material: {tau}{sub c} = d/c{sub s} where d = absorption depth or spot diameter, whichever is smaller, and c{sub s} = sound speed in the material. The stress wave due to thermoelastic expansion travels at the sound speed (approximately 1500 m/s in tissue) and leaves the site of irradiation well before subsequent thermal events can be initiated. These stress waves, often evolving into shock waves, can be used to disrupt tissue. Shock waves are used in ophthalmology to perform intraocular microsurgery and photodisruptive procedures as well as in lithotripsy to fragment stones. We have explored a variety of transducers that can efficiently convert optical to mechanical energy. One such class of transducers allows a shock wave to be focused within a material such that the stress magnitude can be greatly increased compared to conventional geometries. Some transducer tips could be made to operate regardless of the absorption properties of the ambient media. The size and nature of the devices enable easy delivery, potentially minimally-invasive procedures, and precise tissue- targeting while limiting thermal loading. The transducer tips may have applications in lithotripsy, ophthalmology, drug delivery, and cardiology.

  16. Propagation of Moreton Waves

    NASA Astrophysics Data System (ADS)

    Zhang, Yuzong; Kitai, Reizaburo; Narukage, Noriyuki; Matsumoto, Takuma; Ueno, Satoru; Shibata, Kazunari; Wang, Jingxiu

    2011-06-01

    With the Flare-Monitoring Telescope (FMT) and Solar Magnetic Activity Research Telescope (SMART) at Hida observatory of Kyoto University, 13 events of Moreton waves were captured at Hα center, Hα ±0.5 Å, and Hα ±0.8 Å wavebands since 1997. With such samples, we have studied the statistical properties of the propagation of Moreton waves. Moreton waves were all restricted in sectorial zones with a mean value of 92°. However, their accompanying EIT waves, observed simultaneously with SOHO/EIT at extreme-ultraviolet wavelength, were very isotropic with a quite extended scope of 193°. The average propagation speeds of the Moreton waves and the corresponding EIT waves were 664 km s-1 and 205 km s-1, respectively. Moreton waves propagated either under large-scale close magnetic flux loops, or firstly in the sectorial region where two sets of magnetic loops separated from each other and diverged, and then stopped before the open magnetic flux region. The location swept by Moreton waves had a relatively weak magnetic field as compared to the magnetic fields at their sidewalls. The ratio of the magnetic flux density between the sidewall and the path falls in the range of 1.4 to 3.7 at a height of 0.01 solar radii. Additionally, we roughly estimated the distribution of the fast magnetosonic speed between the propagating path and sidewalls in an event on 1997 November 3, and found a relatively low-fast magnetosonic speed in the path. We also found that the propagating direction of Moreton waves coincided with the direction of filament eruption in a few well-observed events. This favors an interpretation of the ``Piston'' model, although further studies are necessary for any definitive conclusion.

  17. Demonstration of Shear Waves, Lamb Waves, and Rayleigh Waves by Mode Conversion.

    ERIC Educational Resources Information Center

    Leung, W. P.

    1980-01-01

    Introduces an experiment that can be demonstrated in the classroom to show that shear waves, Rayleigh waves, and Lamb waves can be easily generated and observed by means of mode conversion. (Author/CS)

  18. Circular rogue wave clusters.

    PubMed

    Kedziora, David J; Ankiewicz, Adrian; Akhmediev, Nail

    2011-11-01

    Using the Darboux transformation technique and numerical simulations, we study the hierarchy of rational solutions of the nonlinear Schrödinger equation that can be considered as higher order rogue waves in this model. This analysis reveals the existence of rogue wave clusters with a high level of symmetry in the (x,t) plane. These structures arise naturally when the shifts in the Darboux scheme are taken to be eigenvalue dependent. We have found single-shell structures where a central higher order rogue wave is surrounded by a ring of first order peaks on the (x,t) plane.

  19. Towards Gravitational Wave Astronomy

    NASA Astrophysics Data System (ADS)

    Losurdo, Giovanni

    This chapter is meant to introduce the reader to the forthcoming network of second-generation interferometric detectors of gravitational waves, at a time when their construction is close to completion and there is the ambition to detect gravitational waves for the first time in the next few years and open the way to gravitational wave astronomy. The legacy of first-generation detectors is discussed before giving an overview of the technology challenges that have been faced to make advanced detectors possible. The various aspects outlined here are then discussed in more detail in the subsequent chapters of the book.

  20. Dangerous Electric Waves,

    DTIC Science & Technology

    1982-01-06

    AD-All 283 FOREIGN TECHNOLOGY DIV WRIGHT-PATTERSON AFR OH F/6 19/5 DANGEROUS ELECTRIC WAVES,(U) JAN 82 F X IANCHENG UNCLASS IFI ED FTO-ID(RS)T-O 891...TECHNOLOGY DIVISION DANGEROUS ELECTRIC WAVES by Feng Xiancheng FEB 2 1982 A Approved for public release; distribution unlimited. 82 02 01 070 AlH...FTD -ID(H ST-0891-81 EDITED TANSLATION FTD-ID(RS)T-0891-81 6 January 1982 MICROFICHE NR: FTD-81-C-002058 DANGEROUS ELECTRIC WAVES

  1. Internal Wave Observations in Drake Passage

    NASA Astrophysics Data System (ADS)

    Firing, Y. L.; Chereskin, T. K.

    2012-12-01

    Internal wave energy in Drake Passage is investigated using an ongoing time series (>8 years) of shipboard acoustic Doppler current profiler (SADCP) data collected on transits of the U.S. Antarctic supply vessel as well as 287 full-depth lowered ADCP and CTD profiles made on five process cruises that were part of the cDrake experiment (cdrake.org). The lateral and vertical distributions of upward- and downward-propgating internal wave energy are examined in the context of local bathymetry and background currents. Downward-propagating energy predominates in the surface layer, but over steep topography in some parts of Drake Passage upward-propagating energy is elevated even 1000 m above topography. The generation of internal wave energy by geostrophic flow over topography in the area is estimated and compared to the total observed internal wave energy during the cruises, while the time variability of this contribution to the internal wave energy is investigated using a 4-year time series of bottom currents from the cDrake project. Shear spectra and the shear-strain relationship are compared with the Garrett and Munk model (Garrett and Munk, 1975) and with the spectral shapes and variance ratios found in other regions by other authors.

  2. Analysis of critically refracted longitudinal waves

    NASA Astrophysics Data System (ADS)

    Pei, Ning; Bond, Leonard J.

    2015-03-01

    Fabrication processes, such as, welding, forging, and rolling can induce residual stresses in metals that will impact product performance and phenomena such as cracking and corrosion. To better manage residual stress tools are needed to map their distribution. The critically refracted ultrasonic longitudinal (LCR) wave is one such approach that has been used for residual stress characterization. It has been shown to be sensitive to stress and less sensitive to the effects of the texture of the material. Although the LCR wave is increasingly widely applied, the factors that influence the formation of the LCR beam are seldom discussed. This paper reports a numerical model used to investigate the transducers' parameters that can contribute to the directionality of the LCR wave and hence enable performance optimization when used for industrial applications. An orthogonal test method is used to study the transducer parameters which influence the LCR wave beams. This method provides a design tool that can be used to study and optimize multiple parameter experiments and it can identify which parameter or parameters are of most significance. The simulation of the sound field in a 2-D "water-steel" model is obtained using a Spatial Fourier Analysis method. The effects of incident angle, standoff, the aperture and the center frequency of the transducer were studied. Results show that the aperture of the transducer, the center frequency and the incident angle are the most important factors in controlling the directivity of the resulting LCR wave fields.

  3. Analysis of critically refracted longitudinal waves

    SciTech Connect

    Pei, Ning Bond, Leonard J.

    2015-03-31

    Fabrication processes, such as, welding, forging, and rolling can induce residual stresses in metals that will impact product performance and phenomena such as cracking and corrosion. To better manage residual stress tools are needed to map their distribution. The critically refracted ultrasonic longitudinal (LCR) wave is one such approach that has been used for residual stress characterization. It has been shown to be sensitive to stress and less sensitive to the effects of the texture of the material. Although the LCR wave is increasingly widely applied, the factors that influence the formation of the LCR beam are seldom discussed. This paper reports a numerical model used to investigate the transducers' parameters that can contribute to the directionality of the LCR wave and hence enable performance optimization when used for industrial applications. An orthogonal test method is used to study the transducer parameters which influence the LCR wave beams. This method provides a design tool that can be used to study and optimize multiple parameter experiments and it can identify which parameter or parameters are of most significance. The simulation of the sound field in a 2-D 'water-steel' model is obtained using a Spatial Fourier Analysis method. The effects of incident angle, standoff, the aperture and the center frequency of the transducer were studied. Results show that the aperture of the transducer, the center frequency and the incident angle are the most important factors in controlling the directivity of the resulting LCR wave fields.

  4. Bubbles attenuate elastic waves at seismic frequencies

    NASA Astrophysics Data System (ADS)

    Tisato, Nicola; Quintal, Beatriz; Chapman, Samuel; Podladchikov, Yury; Burg, Jean-Pierre

    2016-04-01

    The vertical migration of multiphase fluids in the crust can cause hazardous events such as eruptions, explosions, pollution and earthquakes. Although seismic tomography could potentially provide a detailed image of such fluid-saturated regions, the interpretation of the tomographic signals is often controversial and fails in providing a conclusive map of the subsurface saturation. Seismic tomography should be improved considering seismic wave attenuation (1/Q) and the dispersive elastic moduli which allow accounting for the energy lost by the propagating elastic wave. In particular, in saturated media a significant portion of the energy carried by the propagating wave is dissipated by the wave-induced-fluid-flow and the wave-induced-gas-exsolution-dissolution (WIGED) mechanisms. The WIGED mechanism describes how a propagating wave modifies the thermodynamic equillibrium between different fluid phases causing the exsolution and the dissolution of the gas in the liquid, which in turn causes a significant frequency dependent 1/Q and moduli dispersion. The WIGED theory was initially postulated for bubbly magmas but only recently was extended to bubbly water and experimentally demonstrated. Here we report these theory and laboratory experiments. Specifically, we present i) attenuation measurements performed by means of the Broad Band Attenuation Vessel on porous media saturated with water and different gases, and ii) numerical experiments validating the laboratory observations. Finally, we will extend the theory to fluids and to pressure-temperature conditions which are typical of phreatomagmatic and hydrocarbon domains and we will compare the propagation of seismic waves in bubble-free and bubble-bearing subsurface domains. With the present contribution we extend the knowledge about attenuation in rocks which are saturated with multiphase fluid demonstrating that the WIGED mechanism could be extremely important to image subsurface gas plumes.

  5. Rogue waves in baroclinic flows

    NASA Astrophysics Data System (ADS)

    Zuo, Da-Wei; Gao, Yi-Tian; Feng, Yu-Jie; Xue, Long; Sun, Yu-Hao

    2017-05-01

    We investigate an AB system, which can be used to describe marginally unstable baroclinic wave packets in a geophysical fluid. Using the generalized Darboux transformation, we obtain higher-order rogue wave solutions and analyze rogue wave propagation and interaction. We obtain bright rogue waves with one and two peaks. For the wave packet amplitude and the mean-flow correction resulting from the self-rectification of the nonlinear wave, the positions and values of the wave crests and troughs are expressed in terms of a parameter describing the state of the basic flow, in terms of a parameter responsible for the interaction of the wave packet and the mean flow, and in terms of the group velocity. We show that the interaction of the wave packet and mean flow and also the group velocity affect the propagation and interaction of the amplitude of the wave packet and the self-rectification of the nonlinear wave.

  6. Lattice Waves, Spin Waves, and Neutron Scattering

    DOE R&D Accomplishments Database

    Brockhouse, Bertram N.

    1962-03-01

    Use of neutron inelastic scattering to study the forces between atoms in solids is treated. One-phonon processes and lattice vibrations are discussed, and experiments that verified the existence of the quantum of lattice vibrations, the phonon, are reviewed. Dispersion curves, phonon frequencies and absorption, and models for dispersion calculations are discussed. Experiments on the crystal dynamics of metals are examined. Dispersion curves are presented and analyzed; theory of lattice dynamics is considered; effects of Fermi surfaces on dispersion curves; electron-phonon interactions, electronic structure influence on lattice vibrations, and phonon lifetimes are explored. The dispersion relation of spin waves in crystals and experiments in which dispersion curves for spin waves in Co-Fe alloy and magnons in magnetite were obtained and the reality of the magnon was demonstrated are discussed. (D.C.W)

  7. Spin Waves in Quasiequilibrium Spin Systems

    SciTech Connect

    Bedell, Kevin S.; Dahal, Hari P.

    2006-07-28

    Using the Landau Fermi liquid theory we discovered a new propagating transverse spin wave in a paramagnetic system which is driven slightly out of equilibrium without applying an external magnetic field. We find a gapless mode which describes the uniform precession of the magnetization in the absence of a magnetic field. We also find a gapped mode associated with the precession of the spin current around the internal field. The gapless mode has a quadratic dispersion leading to a T{sup 3/2} contribution to the specific heat. These modes significantly contribute to the dynamic structure function.

  8. Dark- and bright-rogue-wave solutions for media with long-wave-short-wave resonance.

    PubMed

    Chen, Shihua; Grelu, Philippe; Soto-Crespo, J M

    2014-01-01

    Exact explicit rogue-wave solutions of intricate structures are presented for the long-wave-short-wave resonance equation. These vector parametric solutions feature coupled dark- and bright-field counterparts of the Peregrine soliton. Numerical simulations show the robustness of dark and bright rogue waves in spite of the onset of modulational instability. Dark fields originate from the complex interplay between anomalous dispersion and the nonlinearity driven by the coupled long wave. This unusual mechanism, not available in scalar nonlinear wave equation models, can provide a route to the experimental realization of dark rogue waves in, for instance, negative index media or with capillary-gravity waves.

  9. Wave Dissipation and Balance - NOPP Wave Project

    DTIC Science & Technology

    2011-09-01

    with a common structure , and now estimating the “cumulative term” with the breaking probabilities used for the main dissipation term. This has led to a...captured by the new parameterizations, but that will require the analysis of more detailed measurement campaigns Ardhuin et al. (2011b). These result have...much more flat bias as a function of wave height (figure 1). A detailed case study of the February 2011 storm Quirin, in the North Atlantic, has shown

  10. Measurement of high frequency waves using a wave follower

    NASA Technical Reports Server (NTRS)

    Tang, S.; Shemdin, O. H.

    1983-01-01

    High frequency waves were measured using a laser-optical sensor mounted on a wave follower. Measured down-wind wave slope spectra are shown to be wind speed dependent; the mean square wave-slopes are generally larger than those measured by Cox and Munk (1954) using the sun glitter method.

  11. Electromagnetic transduction of ultrasonic waves

    NASA Astrophysics Data System (ADS)

    Passarelli, Frank; Alers, George; Alers, Ron

    2012-05-01

    Excitation and detection of ultrasonic vibrations without physical contact has proven to be of great commercial value. First used to excite the resonant vibration of bar shaped laboratory specimens in the 1930's, it was Bruce Thompson's contributions in 1973-5 that launched their practical application to a wide range of difficult NDE problems. As a fresh PhD, he championed the use of mathematical models for the electromagnetic transduction process in order to guide the design and construction of practical transducers. His early papers presented both theoretical and experimental results that exposed the wide range of wave types that could be generated along with the environmental conditions that could be overcome. Several laboratories around the world established research programs to apply the electromagnetic transducer (EMAT) to specific NDE problems. This paper will summarize those applications made by the authors.

  12. Resonance wave pumping with surface waves

    NASA Astrophysics Data System (ADS)

    Carmigniani, Remi; Gharib, Morteza; Violeau, Damien; Caltech-ENPC Collaboration

    2015-11-01

    The valveless impedance pump enables the production or amplification of a flow without the use of integrated mobile parts, thus delaying possible failures. It is usually composed of fluid-filled flexible tubing, closed by solid tubes. The flexible tube is pinched at an off-centered position relative to the tube ends. This generates a complex wave dynamic that results in a pumping phenomenon. It has been previously reported that pinching at intrinsic resonance frequencies of the system results in a strong pulsating flow. A case of a free surface wave pump is investigated. The resonance wave pump is composed of a rectangular tank with a submerged plate separating the water into a free surface and a recirculation rectangular section connected through two openings at each end of the tank. A paddle placed at an off-center position above the submerged plate is controlled in a heaving motion with different frequencies and amplitudes. Similar to the case of valveless impedance pump, we observed that near resonance frequencies strong pulsating flow is generated with almost no oscillations. A linear theory is developed to pseudo-analytically evaluate these frequencies. In addition, larger scale applications were simulated using Smoothed Particle Hydrodynamic codes.

  13. Wave Separation, Wave Intensity, the Reservoir-Wave Concept, and the Instantaneous Wave-Free Ratio: Presumptions and Principles.

    PubMed

    Westerhof, Nico; Segers, Patrick; Westerhof, Berend E

    2015-07-01

    Wave separation analysis and wave intensity analysis (WIA) use (aortic) pressure and flow to separate them in their forward and backward (reflected) waves. While wave separation analysis uses measured pressure and flow, WIA uses their derivatives. Because differentiation emphasizes rapid changes, WIA suppresses slow (diastolic) fluctuations of the waves and renders diastole a seemingly wave-free period. However, integration of the WIA-obtained forward and backward waves is equal to the wave separation analysis-obtained waves. Both the methods thus give similar results including backward waves spanning systole and diastole. Nevertheless, this seemingly wave-free period in diastole formed the basis of both the reservoir-wave concept and the Instantaneous wave-Free Ratio of (iFR) pressure and flow. The reservoir-wave concept introduces a reservoir pressure, Pres, (Frank Windkessel) as a wave-less phenomenon. Because this Windkessel model falls short in systole an excess pressure, Pexc, is introduced, which is assumed to have wave properties. The reservoir-wave concept, however, is internally inconsistent. The presumed wave-less Pres equals twice the backward pressure wave and travels, arriving later in the distal aorta. Hence, in contrast, Pexc is minimally affected by wave reflections. Taken together, Pres seems to behave as a wave, rather than Pexc. The iFR is also not without flaws, as easily demonstrated when applied to the aorta. The ratio of diastolic aortic pressure and flow implies division by zero giving nonsensical results. In conclusion, presumptions based on WIA have led to misconceptions that violate physical principles, and reservoir-wave concept and iFR should be abandoned. © 2015 American Heart Association, Inc.

  14. Gravitational-wave joy

    NASA Astrophysics Data System (ADS)

    seyithocuk; jjeherrera; eltodesukane; GrahamRounce; rloldershaw; Beaker, Dr; Sandhu, G. S.; Ophiuchi

    2016-03-01

    In reply to the news article on the LIGO collaboration's groundbreaking detection of gravitational waves, first predicted by Einstein 100 years ago, from two black holes colliding (pp5, 6-7 and http://ow.ly/Ylsyt).

  15. Inventing the Wave Catchers.

    ERIC Educational Resources Information Center

    Fisher, Arthur

    1983-01-01

    Physicists and engineers advance the state of several arts in the design of gravitational-wave detection equipment. Provides background information and discusses the equipment (including laser interferometer), its use, and results of several experimental studies. (JN)

  16. Magnetoresistive waves in plasmas

    NASA Astrophysics Data System (ADS)

    Felber, F. S.; Hunter, R. O., Jr.; Pereira, N. R.; Tajima, T.

    1982-10-01

    The self-generated magnetic field of a current diffusing into a plasma between conductors can magnetically insulate the plasma. Propagation of magnetoresistive waves in plasmas is analyzed. Applications to plasma opening switches are discussed.

  17. Sound wave transmission (image)

    MedlinePlus

    When sounds waves reach the ear, they are translated into nerve impulses. These impulses then travel to the brain where they are interpreted by the brain as sound. The hearing mechanisms within the inner ear, can ...

  18. Nonspreading Wave Packets.

    ERIC Educational Resources Information Center

    Berry, M. V.; Balazs, N. L.

    1979-01-01

    Explains properties of the Airy packet that show that quantum wave functions correspond to a family of orbits and not to a single particle. Introducing the Airy packet into elementary quantum mechanics courses is recommended. (HM)

  19. Traveling-wave photodetector

    SciTech Connect

    Hietala, V.M.; Vawter, G.A.

    1992-12-31

    The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size.

  20. Gravitational waves: Stellar palaeontology

    NASA Astrophysics Data System (ADS)

    Mandel, Ilya; Farmer, Alison

    2017-07-01

    A third gravitational-wave signal has been detected with confidence, produced again by the merger of two black holes. The combined data from these detections help to reveal the histories of the stars that left these black holes behind.

  1. Traveling-wave photodetector

    DOEpatents

    Hietala, V.M.; Vawter, G.A.

    1993-12-14

    The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size. 4 figures.

  2. Traveling-wave photodetector

    DOEpatents

    Hietala, Vincent M.; Vawter, Gregory A.

    1993-01-01

    The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size.

  3. WindWaveFloat

    SciTech Connect

    Weinstein, Alla

    2011-11-01

    Presentation from the 2011 Water Peer Review includes in which principal investigator Alla Weinstein discusses project progress in development of a floating offshore wind structure - the WindFloat - and incorporation therin of a Spherical Wave Energy Device.

  4. Nonlinear thermal surface waves

    NASA Astrophysics Data System (ADS)

    Gradov, O. M.; Stenflo, L.

    1984-09-01

    It is shown that density profile modifications near a plasma surface can survive at moving localized spots because of the radiation pressure of leaking wave field fluctuations. The properties of these luminous surface cavitons are studied.

  5. Heat Wave Safety Checklist

    MedlinePlus

    ... heat has caused more deaths than all other weather events, including floods. A heat wave is a ... care for heat- related emergencies … ❏ Listen to local weather forecasts and stay aware of upcoming temperature changes. ❏ ...

  6. Internal Ocean Waves

    NASA Image and Video Library

    2006-07-17

    The false-color VNIR image from NASA Terra spacecraft was acquired off the island of Tsushima in the Korea Strait shows the signatures of several internal wave packets, indicating a northern propagation direction.

  7. Pan and Waves

    NASA Image and Video Library

    2013-07-08

    The shepherd moon Pan orbits Saturn in the Encke gap while the A ring surrounding the gap displays wave features created by interactions between the ring particles and Saturnian moons in this image from NASA Cassini spacecraft.

  8. Saturn's quasiperiodic magnetohydrodynamic waves

    NASA Astrophysics Data System (ADS)

    Yates, J. N.; Southwood, D. J.; Dougherty, M. K.; Sulaiman, A. H.; Masters, A.; Cowley, S. W. H.; Kivelson, M. G.; Chen, C. H. K.; Provan, G.; Mitchell, D. G.; Hospodarsky, G. B.; Achilleos, N.; Sorba, A. M.; Coates, A. J.

    2016-11-01

    Quasiperiodic ˜1 h fluctuations have been recently reported by numerous instruments on board the Cassini spacecraft. The interpretation of the sources of these fluctuations has remained elusive to date. Here we provide an explanation for the origin of these fluctuations using magnetometer observations. We find that magnetic field fluctuations at high northern latitudes are Alfvénic, with small amplitudes (˜0.4nT), and are concentrated in wave packets similar to those observed in Kleindienst et al. (2009). The wave packets recur periodically at the northern magnetic oscillation period. We use a magnetospheric box model to provide an interpretation of the wave periods. Our model results suggest that the observed magnetic fluctuations are second harmonic Alfvén waves standing between the northern and southern ionospheres in Saturn's outer magnetosphere.

  9. Inventing the Wave Catchers.

    ERIC Educational Resources Information Center

    Fisher, Arthur

    1983-01-01

    Physicists and engineers advance the state of several arts in the design of gravitational-wave detection equipment. Provides background information and discusses the equipment (including laser interferometer), its use, and results of several experimental studies. (JN)

  10. Turbulence generation by waves

    SciTech Connect

    Kaftori, D.; Nan, X.S.; Banerjee, S.

    1995-12-31

    The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased. Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.

  11. Comparison of wave propagation through ice covers in calm and storm conditions

    NASA Astrophysics Data System (ADS)

    Li, Jingkai; Kohout, Alison L.; Shen, Hayley H.

    2015-07-01

    Motivated by a dramatic reduction in Arctic sea ice cover, interest in the field of wave-ice interaction has accelerated over the past few years. Recent observations have identified that large waves (>3 m) have a linear attenuation rate, rather than the previously assumed exponential rate that is found for small waves. This suggests that waves penetrate further into the ice cover than previously expected. To explore this further we tested two exponentially decaying wave models. Contributions from nonlinear and wind generation source terms enabled both models to reproduce the observed regime shift. Essentially, the accumulation of nonlinear and wind energy contributions to long (and thus higher amplitude) waves can offset the ice damping, thus reducing the apparent attenuation. This study highlights the relevance of considering frequency dependence when analyzing wave attenuation in sea ice field data.

  12. Behavioral science space contributions.

    PubMed

    Harris, P R

    1989-07-01

    In anticipation of longer missions on the space stations, Mir and Freedom, as well as a potential return to the Moon and the exploration of Mars, human survival and the quality of life aloft will be increasingly dependent upon research in the behavioral and biological sciences. This article reviews the possible contributions to space habitation of the behavioral sciences--especially anthropology, psychology, and sociology. Before space settlements become a reality, the author makes a case for the broadening of the engineering approach to human factor studies, and consideration of the integrative living systems theory in space planning and management.

  13. Examining suicide: imaging's contributions.

    PubMed

    Church, Elizabeth J

    2015-01-01

    For many people, the death of hope leads inexorably to the conclusion that the only viable solution, the only way to put an end to unendurable pain, is suicide. What leads a person to commit this final, desperate act, and how might we predict, intervene, and prevent suicide? Health care workers, including radiologic technologists, can play an important role in detecting warning signs in patients and in better understanding what factors may lead to suicide. Although certain forms of suicide such as suicide bombings and assisted suicide are beyond its scope, this article explores medical imaging's contributions to the study of this phenomenon.

  14. Wind Wave Behavior in Fetch and Depth Limited Estuaries

    PubMed Central

    Karimpour, Arash; Chen, Qin; Twilley, Robert R.

    2017-01-01

    Wetland dominated estuaries serve as one of the most productive natural ecosystems through their ecological, economic and cultural services, such as nursery grounds for fisheries, nutrient sequestration, and ecotourism. The ongoing deterioration of wetland ecosystems in many shallow estuaries raises concerns about the contributing erosive processes and their roles in restraining coastal restoration efforts. Given the combination of wetlands and shallow bays as landscape components that determine the function of estuaries, successful restoration strategies require knowledge of wind wave behavior in fetch and depth limited water as a critical design feature. We experimentally evaluate physics of wind wave growth in fetch and depth limited estuaries. We demonstrate that wave growth rate in shallow estuaries is a function of wind fetch to water depth ratio, which helps to develop a new set of parametric wave growth equations. We find that the final stage of wave growth in shallow estuaries can be presented by a product of water depth and wave number, whereby their product approaches 1.363 as either depth or wave energy increases. Suggested wave growth equations and their asymptotic constraints establish the magnitude of wave forces acting on wetland erosion that must be included in ecosystem restoration design. PMID:28098236

  15. Diurnal Variability and Kelvin Wave Propagation Through Maritime Continent

    NASA Astrophysics Data System (ADS)

    Flatau, M. K.; Baranowski, D. B.; Flatau, P. J.; Matthews, A. J.

    2014-12-01

    The 10 year series of the equatorial Kelvin waves obtained from the analysis of TRMM precipitation were examined to evaluate the impact of the diurnal variability of convection on the wave propagation through Maritime Continent. The convection in the Kelvin waves appears to be strongly phase locked in the area of the Maritime continent with the pronounced afternoon maximum. The diurnal phase locking is also evident as Kelvin waves propagate trough the Indian Ocean basin, suggesting that at least some Kelvin waves in this area are forced by the diurnally varying heat source related either to the convection over the land such as Eastern Africa or Madagascar, or over ocean areas with the high SST variability. We examine the hypothesis that the "matching" of the convective phase of the waves with the afternoon maximum of convection over Sumatra influences the wave strength after it crosses the Maritime Continent and can contribute to MJO propagation. The observational results based on observed Kelvin waves are supported by the results of the shallow water model of the interaction of the dry Kelvin wave with the diurnally oscillating heat source.

  16. Wind Wave Behavior in Fetch and Depth Limited Estuaries.

    PubMed

    Karimpour, Arash; Chen, Qin; Twilley, Robert R

    2017-01-18

    Wetland dominated estuaries serve as one of the most productive natural ecosystems through their ecological, economic and cultural services, such as nursery grounds for fisheries, nutrient sequestration, and ecotourism. The ongoing deterioration of wetland ecosystems in many shallow estuaries raises concerns about the contributing erosive processes and their roles in restraining coastal restoration efforts. Given the combination of wetlands and shallow bays as landscape components that determine the function of estuaries, successful restoration strategies require knowledge of wind wave behavior in fetch and depth limited water as a critical design feature. We experimentally evaluate physics of wind wave growth in fetch and depth limited estuaries. We demonstrate that wave growth rate in shallow estuaries is a function of wind fetch to water depth ratio, which helps to develop a new set of parametric wave growth equations. We find that the final stage of wave growth in shallow estuaries can be presented by a product of water depth and wave number, whereby their product approaches 1.363 as either depth or wave energy increases. Suggested wave growth equations and their asymptotic constraints establish the magnitude of wave forces acting on wetland erosion that must be included in ecosystem restoration design.

  17. Wind Wave Behavior in Fetch and Depth Limited Estuaries

    NASA Astrophysics Data System (ADS)

    Karimpour, Arash; Chen, Qin; Twilley, Robert R.

    2017-01-01

    Wetland dominated estuaries serve as one of the most productive natural ecosystems through their ecological, economic and cultural services, such as nursery grounds for fisheries, nutrient sequestration, and ecotourism. The ongoing deterioration of wetland ecosystems in many shallow estuaries raises concerns about the contributing erosive processes and their roles in restraining coastal restoration efforts. Given the combination of wetlands and shallow bays as landscape components that determine the function of estuaries, successful restoration strategies require knowledge of wind wave behavior in fetch and depth limited water as a critical design feature. We experimentally evaluate physics of wind wave growth in fetch and depth limited estuaries. We demonstrate that wave growth rate in shallow estuaries is a function of wind fetch to water depth ratio, which helps to develop a new set of parametric wave growth equations. We find that the final stage of wave growth in shallow estuaries can be presented by a product of water depth and wave number, whereby their product approaches 1.363 as either depth or wave energy increases. Suggested wave growth equations and their asymptotic constraints establish the magnitude of wave forces acting on wetland erosion that must be included in ecosystem restoration design.

  18. New contributions to transit-time damping in multidimensional systems

    NASA Technical Reports Server (NTRS)

    Robinson, P. A.

    1989-01-01

    The existence of two previously unrecognized contributions to transit-time damping in systems of more than one dimension is demonstrated and discussed. It is shown that these contributions cannot be treated by one-dimensional analyses unless it is assumed that the gradient of the field perpendicular to itself always vanishes. Such an assumption is unjustified in general and the new contributions can dominate damping by fast particles in more general situations. Analytic expressions obtained using a Born approximation are found to be in excellent agreement with numerical test-particle calculations of transit-time damping for a variety of field configurations. These configurations include those of a resonance layer and of a spherical wave packet, which approximates a collapsing wave packet in a strongly turbulent plasma. It is found that the fractional power absorption can be strongly enhanced in non-slablike field configurations.

  19. The wave of the future - Searching for gravity waves

    NASA Astrophysics Data System (ADS)

    Goldsmith, Donald

    1991-04-01

    Research on gravity waves conducted by such scientists as Gamov, Wheeler, Weber and Zel'dovich is discussed. Particular attention is given to current trends in the theoretical analysis of gravity waves carried out by theorists Kip Thorne and Leonid Grishchuk. The problems discussed include the search for gravity waves; calculation of the types of gravity waves; the possibility of detecting gravity waves from localized sources, e.g., from the collision of two black holes in a distant galaxy or the collapse of a star, through the Laser Interferometer Gravitational Wave Observatory; and detection primordial gravity waves from the big bang.

  20. Transport of parallel momentum by collisionless drift wave turbulence

    SciTech Connect

    Diamond, P. H.; McDevitt, C. J.; Guercan, Oe. D.; Hahm, T. S.; Naulin, V.

    2008-01-15

    This paper presents a novel, unified approach to the theory of turbulent transport of parallel momentum by collisionless drift waves. The physics of resonant and nonresonant off-diagonal contributions to the momentum flux is emphasized, and collisionless momentum exchange between waves and particles is accounted for. Two related momentum conservation theorems are derived. These relate the resonant particle momentum flux, the wave momentum flux, and the refractive force. A perturbative calculation, in the spirit of Chapman-Enskog theory, is used to obtain the wave momentum flux, which contributes significantly to the residual stress. A general equation for mean k{sub parallel} () is derived and used to develop a generalized theory of symmetry breaking. The resonant particle momentum flux is calculated, and pinch and residual stress effects are identified. The implications of the theory for intrinsic rotation and momentum transport bifurcations are discussed.

  1. Vorticity equation for MHD fast waves in geospace environment

    NASA Technical Reports Server (NTRS)

    Yamauchi, M.; Lundin, R.; Lui, A. T. Y.

    1993-01-01

    The MHD vorticity equation is modified in order to apply it to nonlinear MHD fast waves or shocks when their extent along the magnetic field is limited. Field-aligned current (FAC) generation is also discussed on the basis of this modified vorticity equation. When the wave normal is not aligned to the finite velocity convection and the source region is spatially limited, a longitudinal polarization causes a pair of plus and minus charges inside the compressional plane waves or shocks, generating a pair of FACs. This polarization is not related to the separation between the electrons and ions caused by their difference in mass, a separation which is inherent to compressional waves. The resultant double field-aligned current structure exists both with and without the contributions from curvature drift, which is questionable in terms of its contribution to vorticity change from the viewpoint of single-particle motion.

  2. Shock wave initiated by an ion passing through liquid water

    NASA Astrophysics Data System (ADS)

    Surdutovich, Eugene; Solov'Yov, Andrey V.

    2010-11-01

    We investigate the shock wave produced by an energetic ion in liquid water. This wave is initiated by a rapid energy loss when the ion moves through the Bragg peak. The energy is transferred from the ion to secondary electrons, which then transfer it to the water molecules. The pressure in the overheated water increases by several orders of magnitude and drives a cylindrical shock wave on a nanometer scale. This wave eventually weakens as the front expands further; but before that, it may contribute to DNA damage due to large pressure gradients developed within a few nanometers from the ion’s trajectory. This mechanism of DNA damage may be a very important contribution to the direct chemical effects of low-energy electrons and holes.

  3. Vorticity equation for MHD fast waves in geospace environment

    NASA Technical Reports Server (NTRS)

    Yamauchi, M.; Lundin, R.; Lui, A. T. Y.

    1993-01-01

    The MHD vorticity equation is modified in order to apply it to nonlinear MHD fast waves or shocks when their extent along the magnetic field is limited. Field-aligned current (FAC) generation is also discussed on the basis of this modified vorticity equation. When the wave normal is not aligned to the finite velocity convection and the source region is spatially limited, a longitudinal polarization causes a pair of plus and minus charges inside the compressional plane waves or shocks, generating a pair of FACs. This polarization is not related to the separation between the electrons and ions caused by their difference in mass, a separation which is inherent to compressional waves. The resultant double field-aligned current structure exists both with and without the contributions from curvature drift, which is questionable in terms of its contribution to vorticity change from the viewpoint of single-particle motion.

  4. Comparative observations of plasma waves at the outer planets

    NASA Technical Reports Server (NTRS)

    Kurth, W. S.

    1992-01-01

    Observations of the plasma-wave spectra from the four major outer planets are examined with particular attention given to the instabilities related to the precipitation of energetic particles. Wave-particle interactions involving hiss, chorus, and electron-cyclotron harmonic emissions are studied. These interactions contribute about 10 exp 13 W into the Jovian atmosphere, and the electron-cyclotron emissions on Saturn are shown to contribute significantly to the precipitation of energetic electrons. Whistler-mode waves are shown to exist at Uranus with intensities that could put 3-40 keV electrons on strong diffusion, but the amplitudes of the emissions are not sufficient to make them a significant part of precipitation. Weak electron-cyclotron harmonic emissions and whistler modes are detected at Neptune, suggesting that the present dataset is based on regions of low wave intensities.

  5. Wave Propagation Program

    SciTech Connect

    McCandless, Kathleen; Petersson, Anders; Nilsson, Stefan; Sjogreen, Bjorn

    2007-01-08

    WPP is a massively parallel, 3D, C++, finite-difference elastodynamic wave propagation code. Typical applications for wave propagation with WPP include: evaluation of seismic event scenarios and damage from earthquakes, non-destructive evaluation of materials, underground facility detection, oil and gas exploration, predicting the electro-magnetic fields in accelerators, and acoustic noise generation. For more information, see User’s Manual [1].

  6. Kinematics Under Wind Waves

    DTIC Science & Technology

    1989-09-01

    components of the total velocity field, negligible measurement noise, and a completely linear wave field. Yefimov and Khristoforov (1971) have investigated...The directional spreading of the real wave field must also be considered ([82] and [3]). Yefimov and Khristoforov concluded that the spectrum of the...different. As observed by Yefimov and Khristoforov the upper linit of high coherence decreased with increasing depth (Figure 9). The horizontal

  7. Near Shore Wave Processes

    DTIC Science & Technology

    2016-06-07

    given the offshore wave conditions . OBJECTIVES We hypothesize that the wave-induced kinematic, sediment and morphologic processes are nonlinearly... WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Naval Postgraduate School,Department of Oceanography,Monterey,CA,93943 8...basis of our process modeling and analysis work . In addition, the comprehensive Delft3D morphology model was acquired from the Dutch and is being assessed

  8. Sound Waves Levitate Substrates

    NASA Technical Reports Server (NTRS)

    Lee, M. C.; Wang, T. G.

    1982-01-01

    System recently tested uses acoustic waves to levitate liquid drops, millimeter-sized glass microballoons, and other objects for coating by vapor deposition or capillary attraction. Cylindrical contactless coating/handling facility employs a cylindrical acoustic focusing radiator and a tapered reflector to generate a specially-shaped standing wave pattern. Article to be processed is captured by the acoustic force field under the reflector and moves as reflector is moved to different work stations.

  9. Vortex waves in sunspots

    NASA Astrophysics Data System (ADS)

    López Ariste, A.; Centeno, R.; Khomenko, E.

    2016-06-01

    Context. Waves in the magnetized solar atmosphere are one of the favourite means of transferring and depositing energy into the solar corona. The study of waves brings information not just on the dynamics of the magnetized plasma, but also on the possible ways in which the corona is heated. Aims: The identification and analysis of the phase singularities or dislocations provide us with a complementary approach to the magnetoacoustic and Aflvén waves propagating in the solar atmosphere. They allow us to identify individual wave modes, shedding light on the probability of excitation or the nature of the triggering mechanism. Methods: We use a time series of Doppler shifts measured in two spectral lines, filtered around the three-minute period region. The data show a propagating magnetoacoustic slow mode with several dislocations and, in particular, a vortex line. We study under what conditions the different wave modes propagating in the umbra can generate the observed dislocations. Results: The observed dislocations can be fully interpreted as a sequence of sausage and kink modes excited sequentially on average during 15 min. Kink and sausage modes appear to be excited independently and sequentially. The transition from one to the other lasts less than three minutes. During the transition we observe and model the appearance of superoscillations inducing large phase gradients and phase mixing. Conclusions: The analysis of the observed wave dislocations leads us to the identification of the propagating wave modes in umbrae. The identification in the data of superoscillatory regions during the transition from one mode to the other may be an important indicator of the location of wave dissipation.

  10. Edge wave visualization

    NASA Technical Reports Server (NTRS)

    Dominek, Allen K.; Nguyen, Truong X.

    1991-01-01

    Scattering mechanisms that involve edge waves are addressed. The behavior of edge waves and their interaction with flat, perfectly conducting plates are depicted in the time domain through a visualization of surface currents that flow on the surface, as an incident Gaussian pulse of energy washes over the surface. Viewing these surface currents allows a very clear physical interpretation and appreciation of the scattering process.

  11. Millimeter Wave Nonreciprocal Devices.

    DTIC Science & Technology

    1983-01-03

    gradients of the dc bias field saturation magnetization , or magnetic anisotrophy can control mode properties of magnetostatic waves (MSW) propagating in...measures microwave magnetic field patterns of magnetostatic waves in LPE- YIG thin films has been developed. The probe’s sensing element is either a... magnetic resonance mode of a YIG sphere. Theoretical analyses show that there is a critical ratio between the -4-Ai p. , , . , l!~ mj radius of the

  12. Hysteretic Faraday waves.

    PubMed

    Périnet, Nicolas; Falcón, Claudio; Chergui, Jalel; Juric, Damir; Shin, Seungwon

    2016-06-01

    We report on the numerical and theoretical study of the subcritical bifurcation of parametrically amplified waves appearing at the interface between two immiscible incompressible fluids when the layer of the lower fluid is very shallow. As a critical control parameter is surpassed, small amplitude surface waves bifurcate subcritically toward highly nonlinear ones with twice their amplitude. We relate this hysteresis with the change of shear stress using a simple stress balance, in agreement with numerical results.

  13. WaveNet

    DTIC Science & Technology

    2014-10-27

    interface to display data from different sources, and employs a combination of Fortran , Python and Matlab codes to process and analyze data for...Coastal Inlets Research Program WaveNet WaveNet is a web-based, Graphical-User- Interface (GUI) data management tool developed for the Corps’ coastal...Report Documentation Page Form ApprovedOMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per

  14. J Wave Syndromes

    PubMed Central

    Antzelevitch, Charles; Yan, Gan-Xin

    2009-01-01

    The J wave, also referred to as an Osborn wave, is a deflection immediately following the QRS complex of the surface ECG. When partially buried in the R wave, the J wave appears as a J point elevation or ST segment elevation. Several lines of evidence have been advanced suggesting that arrhythmias associated with early repolarization (ER) pattern in the inferior leads or mid- to lateral precordial leads, Brugada syndrome (BrS) as well arrhythmias associated with hypothermia and the acute phase of ST segment elevation myocardial infarction (STEMI), are mechanistically linked to abnormalities in the manifestation of the transient outward current (Ito)-mediated J wave. Although BrS and early repolarization syndrome (ERS) differ with respect to the magnitude and lead location of abnormal J wave manifestation, they can be considered to represent a continuous spectrum of phenotypic expression that we propose be termed J wave syndromes. This review attempts to summarize our current state of knowledge concerning J-wave syndromes, bridging basic and clinical aspects. We propose to divide ERS into three subtypes: Type 1, displaying an ER pattern predominantly in the lateral precordial leads, is prevalent among healthy male athletes and rarely seen in VF survivors; Type 2, displaying an ER pattern predominantly in the inferior or infero-lateral leads, is associated with a higher level of risk; whereas Type 3, displaying an ER pattern globally in the inferior, lateral and right precordial leads, is associated with the highest level of risk for development of malignant arrhythmias and is often associated with VF storms. PMID:20153265

  15. Wind Generated Rogue Waves in an Annular Wave Flume.

    PubMed

    Toffoli, A; Proment, D; Salman, H; Monbaliu, J; Frascoli, F; Dafilis, M; Stramignoni, E; Forza, R; Manfrin, M; Onorato, M

    2017-04-07

    We investigate experimentally the statistical properties of a wind-generated wave field and the spontaneous formation of rogue waves in an annular flume. Unlike many experiments on rogue waves where waves are mechanically generated, here the wave field is forced naturally by wind as it is in the ocean. What is unique about the present experiment is that the annular geometry of the tank makes waves propagating circularly in an unlimited-fetch condition. Within this peculiar framework, we discuss the temporal evolution of the statistical properties of the surface elevation. We show that rogue waves and heavy-tail statistics may develop naturally during the growth of the waves just before the wave height reaches a stationary condition. Our results shed new light on the formation of rogue waves in a natural environment.

  16. Observed Seismic Solitary Waves

    NASA Astrophysics Data System (ADS)

    Bataille, K.

    2008-05-01

    A feature that has been observed for many decades in a variety of instruments, without a solid explanation, is a signal with a shape of a "bump" in velocity records, especially near small earthquakes. This signal arrives at times close to the S wave and has commonly being argued by some to be a nonlinear effect of the instrument (Aki and Richards, 1980), while by others as to be a real earth motion due to an unknown wave propagation phenomena. Here we propose that these observations are seismic solitary waves. The seismic solitary wave arises from an equation that describes the propagation of Love waves within a general nonlinear media. For a specific "bump-like" solution, the dispersive and nonlinear effects balance each other, allowing its propagation without distortion for long distances. Solitary waves have been observed in a variety of physical systems, including the ocean, but so far it has not been recognized in the seismological literature. The theory and modelling of several observations from different instruments will be presented.

  17. A simple wave driver

    NASA Astrophysics Data System (ADS)

    Kağan Temiz, Burak; Yavuz, Ahmet

    2015-08-01

    This study was done to develop a simple and inexpensive wave driver that can be used in experiments on string waves. The wave driver was made using a battery-operated toy car, and the apparatus can be used to produce string waves at a fixed frequency. The working principle of the apparatus is as follows: shortly after the car is turned on, the wheel starts to turn at a constant angular speed. A rod that is fixed on the wheel turns at the same constant angular speed, too. A tight string that the wave will be created on is placed at a distance where the rod can touch the string. During each rotation of the wheel, the rod vibrates the string up and down. The vibration frequency of this rod equals the wheel’s rotation frequency, and this frequency value can be measured easily with a small magnet and a bicycle speedometer. In this way, the frequency of the waves formed in the rope can also be measured.

  18. Ocean wave electric generators

    SciTech Connect

    Rosenberg, H.R.

    1986-02-04

    This patent describes an apparatus for generating electricity from ocean waves. It consists of: 1.) a hollow buoyant duck positioned in the path of waves including a core about the center axis of which the duck rotates, a lower chamber portion having liquid therein and an upper chamber portion having air therein. The air is alternately compressed and expanded by the liquid in the chamber during the rotational motion of the duck caused by waves. A turbine mounted in the upper portion of the duck is driven by the compressed and expanded air. A generator is coupled to the turbine and operated to produce electrical energy and an air bulb; 2.) a spine having a transverse axial shaft anchoring the spine to the ocean floor. The upper portion of the spine engages the duck to maintain the duck in position. The spine has a curved configuration to concentrate and direct wave energy. The spine configuration acts as a scoop to increase the height of wave peaks and as a foil to increase the depth of wave troughs.

  19. Surfing a magnetic wave

    NASA Astrophysics Data System (ADS)

    Dehandschoewercker, Eline; Quere, David; Clanet, Christophe

    2014-11-01

    Surfing is a free surface sport in which the athlete rides a wave standing on a board. However, any object plunged into the water or put on its surface is not always captured by an approaching wave, just like the classic example of a fisching float. So, a particle can be captured or not by a wave. Two regimes are defined: surf (captured) and drift (not captured). We focus on the question of the transition between these two regimes. Here we address the question with a magnetic wave. We have developed an experimental setup which allows the control of all relevant physical parameters. Liquid oxygen, which is paramagnetic and undergoes Leidenfrost effect, can be used to ensure magnetic and frictionless particles. A permanent magnet in translatory movement allows us to create a definite magnetic wave. We discuss the motion of oxygen drops deposited on an smooth and horizontal surface above an approaching magnet. First we show the existence of a critical speed below which drops are captured and determine how it depends on the velocity and intensity of the magnetic wave. Then we experimentally investigate the parameters that would affect the movement of drops in each regime. Finally, models have been developed to interpret magnetic drops motion and guarantee an efficient control.

  20. Ultrasonic Lamb wave tomography

    NASA Astrophysics Data System (ADS)

    Leonard, Kevin R.; Malyarenko, Eugene V.; Hinders, Mark K.

    2002-12-01

    Nondestructive evaluation (NDE) of aerospace structures using traditional methods is a complex, time-consuming process critical to maintaining mission readiness and flight safety. Limited access to corrosion-prone structure and the restricted applicability of available NDE techniques for the detection of hidden corrosion or other damage often compound the challenge. In this paper we discuss our recent work using ultrasonic Lamb wave tomography to address this pressing NDE technology need. Lamb waves are ultrasonic guided waves, which allow large sections of aircraft structures to be rapidly inspected for structural flaws such as disbonds, corrosion and delaminations. Because the velocity of Lamb waves depends on thickness, for example, the travel times of the fundamental Lamb modes can be converted into a thickness map of the inspection region. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. Our work focuses on tomographic reconstruction to produce quantitative maps that can be easily interpreted by technicians or fed directly into structural integrity and lifetime prediction codes. Laboratory measurements discussed here demonstrate that Lamb wave tomography using a square perimeter array of transducers with algebraic reconstruction tomography is appropriate for detecting flaws in aircraft materials. The speed and fidelity of the reconstruction algorithms as well as practical considerations for person-portable array-based systems are discussed in this paper.

  1. Traveling-Wave Tubes

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.

    1998-01-01

    The traveling-wave tube (TWT) is a vacuum device invented in the early 1940's used for amplification at microwave frequencies. Amplification is attained by surrendering kinetic energy from an electron beam to a radio frequency (RF) electromagnetic wave. The demand for vacuum devices has been decreased largely by the advent of solid-state devices. However, although solid state devices have replaced vacuum devices in many areas, there are still many applications such as radar, electronic countermeasures and satellite communications, that require operating characteristics such as high power (Watts to Megawatts), high frequency (below 1 GHz to over 100 GHz) and large bandwidth that only vacuum devices can provide. Vacuum devices are also deemed irreplaceable in the music industry where musicians treasure their tube-based amplifiers claiming that the solid-state and digital counterparts could never provide the same "warmth" (3). The term traveling-wave tube includes both fast-wave and slow-wave devices. This article will concentrate on slow-wave devices as the vast majority of TWTs in operation fall into this category.

  2. Full wave simulation of lower hybrid waves in Maxwellian plasma based on the finite element method

    SciTech Connect

    Meneghini, O.; Shiraiwa, S.; Parker, R.

    2009-09-15

    A full wave simulation of the lower-hybrid (LH) wave based on the finite element method is presented. For the LH wave, the most important terms of the dielectric tensor are the cold plasma contribution and the electron Landau damping (ELD) term, which depends only on the component of the wave vector parallel to the background magnetic field. The nonlocal hot plasma ELD effect was expressed as a convolution integral along the magnetic field lines and the resultant integro-differential Helmholtz equation was solved iteratively. The LH wave propagation in a Maxwellian tokamak plasma based on the Alcator C experiment was simulated for electron temperatures in the range of 2.5-10 keV. Comparison with ray tracing simulations showed good agreement when the single pass damping is strong. The advantages of the new approach include a significant reduction of computational requirements compared to full wave spectral methods and seamless treatment of the core, the scrape off layer and the launcher regions.

  3. Horizontal and Vertical Wave Parameters of Thermospheric Gravity Waves, and Relationship to Neutral Winds

    NASA Astrophysics Data System (ADS)

    Nicolls, M. J.; Vadas, S.; Sulzer, M. P.; Aponte, N.

    2013-12-01

    We report on experimental techniques and results for extracting horizontal and vertical wave parameters of thermospheric gravity waves using incoherent scatter radar (ISR) measurements of the three-dimensional properties of traveling ionospheric disturbances (TIDs). We use results from the Poker Flat Incoherent Scatter Radar (PFISR) and the Arecibo Observatory (AO) to extract the three-dimensional properties of waves, including horizontal and vertical wavelengths, phase speeds, and propagation directions. Comparison to theoretical ray tracing results sheds light on the dissipative and wind filtering mechanisms that drive the measurements. High-resolution vertical wavelength measurements reveal maxima at the altitudes near where the TID amplitude is maximum, consistent with gravity wave packet theory. Simultaneous measurements of lower thermospheric neutral winds reveal the effects of strong winds (often greater that 150 m/s) on determining the wave spectra at higher altitudes. We discuss how these measurements can shed light on the lower atmospheric sources that contribute to thermospheric gravity waves and drive ionospheric variability.

  4. Wave-particle interactions in the radiation belts: effect of wave spectra

    NASA Astrophysics Data System (ADS)

    Vassiliadis, Dimitris; Tornquist, Mattias; Koepke, Mark

    2014-10-01

    Particle acceleration in Earth's radiation belts is often explain in terms of radial diffusion theory. Some of the most important contributions to diffusive transport are stochastic as well as resonant interactions with low-frequency (Alfven/magnetosonic) waves. While spectra of such waves are traditionally assumed to be broadband and spectrally white, a number of recent studies [Rae et al., 2012; Ozeke et al., 2012] indicate that the spectra of ground geomagnetic pulsations are significantly more complex. We examine power-law spectra in particle simulations in a realistic magnetospheric field configuration and report on their effect on the transport and energization of the pre-storm electron population.

  5. Rain waves-wind waves interaction application to scatterometry

    NASA Technical Reports Server (NTRS)

    Kharif, C.; Giovanangeli, J. P.; Bliven, L.

    1989-01-01

    Modulation of a rain wave pattern by longer waves has been studied. An analytical model taking into account capillarity effects and obliquity of short waves has been developed. Modulation rates in wave number and amplitude have been computed. Experiments were carried out in a wave tank. First results agree with theoretical models, but higher values of modulation rates are measured. These results could be taken into account for understanding the radar response from the sea surface during rain.

  6. Wave Momentum Flux Parameter: A Descriptor for Nearshore Waves

    DTIC Science & Technology

    2004-07-16

    characterizing the wave nonlinearity. D 2004 Elsevier B.V. All rights reserved. Keywords: Coastal structures; Iribarren number; Nonlinear waves; Solitary...Local Iribarren number, n tanaffiffiffiffiffiffi H=L p Deepwater Iribarren number, no tanaffiffiffiffiffiffiffiffiffi Ho=Lo p or...solitary waves, although there are some definitions for solitary wave length which would allow use of the other wave parameters.2. The Iribarren number One

  7. Genesis of the characteristic pulmonary venous pressure waveform as described by the reservoir-wave model.

    PubMed

    Bouwmeester, J Christopher; Belenkie, Israel; Shrive, Nigel G; Tyberg, John V

    2014-09-01

    Conventional haemodynamic analysis of pulmonary venous and left atrial (LA) pressure waveforms yields substantial forward and backward waves throughout the cardiac cycle; the reservoir wave model provides an alternative analysis with minimal waves during diastole. Pressure and flow in a single pulmonary vein (PV) and the main pulmonary artery (PA) were measured in anaesthetized dogs and the effects of hypoxia and nitric oxide, volume loading, and positive-end expiratory pressure (PEEP) were observed. The reservoir wave model was used to determine the reservoir contribution to PV pressure and flow. Subtracting reservoir pressure and flow resulted in 'excess' quantities which were treated as wave-related.Wave intensity analysis of excess pressure and flow quantified the contributions of waves originating upstream (from the PA) and downstream (from the LA and/or left ventricle (LV)).Major features of the characteristic PV waveform are caused by sequential LA and LV contraction and relaxation creating backward compression (i.e.pressure-increasing) waves followed by decompression (i.e. pressure-decreasing) waves. Mitral valve opening is linked to a backwards decompression wave (i.e. diastolic suction). During late systole and early diastole, forward waves originating in the PA are significant. These waves were attenuated less with volume loading and delayed with PEEP. The reservoir wave model shows that the forward and backward waves are negligible during LV diastasis and that the changes in pressure and flow can be accounted for by the discharge of upstream reservoirs. In sharp contrast, conventional analysis posits forward and backward waves such that much of the energy of the forward wave is opposed by the backward wave.

  8. Genesis of the characteristic pulmonary venous pressure waveform as described by the reservoir-wave model

    PubMed Central

    Bouwmeester, J Christopher; Belenkie, Israel; Shrive, Nigel G; Tyberg, John V

    2014-01-01

    Conventional haemodynamic analysis of pulmonary venous and left atrial (LA) pressure waveforms yields substantial forward and backward waves throughout the cardiac cycle; the reservoir wave model provides an alternative analysis with minimal waves during diastole. Pressure and flow in a single pulmonary vein (PV) and the main pulmonary artery (PA) were measured in anaesthetized dogs and the effects of hypoxia and nitric oxide, volume loading, and positive-end expiratory pressure (PEEP) were observed. The reservoir wave model was used to determine the reservoir contribution to PV pressure and flow. Subtracting reservoir pressure and flow resulted in ‘excess’ quantities which were treated as wave-related. Wave intensity analysis of excess pressure and flow quantified the contributions of waves originating upstream (from the PA) and downstream (from the LA and/or left ventricle (LV)). Major features of the characteristic PV waveform are caused by sequential LA and LV contraction and relaxation creating backward compression (i.e. pressure-increasing) waves followed by decompression (i.e. pressure-decreasing) waves. Mitral valve opening is linked to a backwards decompression wave (i.e. diastolic suction). During late systole and early diastole, forward waves originating in the PA are significant. These waves were attenuated less with volume loading and delayed with PEEP. The reservoir wave model shows that the forward and backward waves are negligible during LV diastasis and that the changes in pressure and flow can be accounted for by the discharge of upstream reservoirs. In sharp contrast, conventional analysis posits forward and backward waves such that much of the energy of the forward wave is opposed by the backward wave. PMID:25015922

  9. SNR degradation in square-wave subcarrier downconversion

    NASA Technical Reports Server (NTRS)

    Feria, Y.; Statman, J.

    1992-01-01

    This article presents a study of signal-to-noise ratio (SNR) degradation in the process of square-wave subcarrier downconversion. The study shows three factors that contribute to the SNR degradation: the cutoff of the higher frequency components in the data, the approximation of a square wave with a finite number of harmonics, and nonideal filtering. Both analytical and simulation results are presented.

  10. Nonlinear Generalized Hydrodynamic Wave Equations in Strongly Coupled Dusty Plasmas

    SciTech Connect

    Veeresha, B. M.; Sen, A.; Kaw, P. K.

    2008-09-07

    A set of nonlinear equations for the study of low frequency waves in a strongly coupled dusty plasma medium is derived using the phenomenological generalized hydrodynamic (GH) model and is used to study the modulational stability of dust acoustic waves to parallel perturbations. Dust compressibility contributions arising from strong Coulomb coupling effects are found to introduce significant modifications in the threshold and range of the instability domain.

  11. Ion-Acoustic Waves in Self-Gravitaing Dusty Plasma

    SciTech Connect

    Kumar, Nagendra; Kumar, Vinod; Kumar, Anil

    2008-09-07

    The propagation and damping of low frequency ion-acoustic waves in steady state, unmagnetised, self-gravitating dusty plasma are studied taking into account two important damping mechanisms creation damping and Tromso damping. It is found that imaginary part of wave number is independent of frequency in case of creation damping. But when we consider the case of creation and Tromso damping together, an additional contribution to damping appears with the increase in frequency attributed to Tromso effect.

  12. Seasonal mean temperature changes control future heat waves

    NASA Astrophysics Data System (ADS)

    Argüeso, Daniel; Di Luca, Alejandro; Perkins-Kirkpatrick, Sarah E.; Evans, Jason P.

    2016-07-01

    Increased temperature will result in longer, more frequent, and more intense heat waves. Changes in temperature variability have been deemed necessary to account for future heat wave characteristics. However, this has been quantified only in Europe and North America, while the rest of the globe remains unexplored. Using late century global climate projections, we show that annual mean temperature increases is the key factor defining heat wave changes in most regions. We find that commonly studied areas are an exception rather than the standard and the mean climate change signal generally outweighs any influence from variability changes. More importantly, differences in warming across seasons are responsible for most of the heat wave changes and their consideration relegates the contribution of variability to a marginal role. This reveals that accurately capturing mean seasonal changes is crucial to estimate future heat waves and reframes our interpretation of future temperature extremes.

  13. Inherently unstable internal gravity waves due to resonant harmonic generation

    NASA Astrophysics Data System (ADS)

    Liang, Yong; Zareei, Ahmad; Alam, Mohammad-Reza

    2017-01-01

    Here we show that there exist internal gravity waves that are inherently unstable, that is, they cannot exist in nature for a long time. The instability mechanism is a one-way (irreversible) harmonic-generation resonance that permanently transfers the energy of an internal wave to its higher harmonics. We show that, in fact, there are countably infinite number of such unstable waves. For the harmonic-generation resonance to take place, nonlinear terms in the free surface boundary condition play a pivotal role, and the instability does not obtain for a linearly-stratified fluid if a simplified boundary condition such as rigid lid or linear form is employed. Harmonic-generation resonance presented here also provides a mechanism for the transfer of the energy of the internal waves to the higher-frequency part of the spectrum where internal waves are more prone to breaking, hence losing energy to turbulence and heat and contributing to oceanic mixing.

  14. Projection of wave conditions in response to climate change: A community approach to global and regional wave downscaling

    USGS Publications Warehouse

    Erikson, Li H.; Hemer, M.; Lionello, Piero; Mendez, Fernando J.; Mori, Nobuhito; Semedo, Alvaro; Wang, Xiaolan; Wolf, Judith

    2015-01-01

    Future changes in wind-wave climate have broad implications for coastal geomorphology and management. General circulation models (GCM) are now routinely used for assessing climatological parameters, but generally do not provide parameterizations of ocean wind-waves. To fill this information gap, a growing number of studies use GCM outputs to independently downscale wave conditions to global and regional levels. To consolidate these efforts and provide a robust picture of projected changes, we present strategies from the community-derived multi-model ensemble of wave climate projections (COWCLIP) and an overview of regional contributions. Results and strategies from one contributing regional study concerning changes along the eastern North Pacific coast are presented.

  15. Flow generated by surfaces waves

    NASA Astrophysics Data System (ADS)

    Punzmann, Horst; Francois, Nicolas; Xia, Hua; Shats, Michael

    2017-04-01

    Trajectories of fluid parcels on the surface have been described analytically for progressing irrotational waves, where particles move in the direction of wave propagation. Waves in the laboratory and in nature are more complex due to the development of instabilities that render ideal planar 2D propagating waves into complex 3D waves. The motion of particles in such waves is not well understood. In this talk I will present experiments in the short wavelength gravity-capillary range that demonstrate the generation of surface flows by propagating waves driven by a vertically oscillating plunger. At low amplitude, in a quasi-linear wave regime, buoyant particle tracers move in the direction of the wave propagation. At high wave amplitude, modulation instability (or Benjamin-Feir instability) renders the planer wave front into wave packets. This affects the macroscopic flow such that floaters drift against the direction of the wave, towards the plunger wave source [1]. The role of surface vorticity generation by waves will be discussed. Reference: Punzmann H., Francois N., Xia H., Falkovich G. and Shats M.; Generation and reversal of surface flows by propagating waves, Nature Physics 10, 658-663 (2014).

  16. Ring Current-Electromagnetic Ion Cyclotron Waves Coupling

    NASA Technical Reports Server (NTRS)

    Khazanov, G. V.

    2005-01-01

    The effect of Electromagnetic Ion Cyclotron (EMIC) waves, generated by ion temperature anisotropy in Earth s ring current (RC), is the best known example of wave- particle interaction in the magnetosphere. Also, there is much controversy over the importance of EMIC waves on RC depletion. Under certain conditions, relativistic electrons, with energies 21 MeV, can be removed from the outer radiation belt (RB) by EMIC wave scattering during a magnetic storm. That is why the calculation of EMIC waves must be a very critical part of the space weather studies. The new RC model that we have developed and present for the first time has several new features that we have combine together in a one single model: (a) several lower frequency cold plasma wave modes are taken into account; (b) wave tracing of these wave has been incorporated in the energy EMIC wave equation; (c) no assumptions regarding wave shape spectra have been made; (d) no assumptions regarding the shape of particle distribution have been made to calculate the growth rate; (e) pitch-angle, energy, and mix diffusions are taken into account together for the first time; (f) the exact loss-cone RC analytical solution has been found and coupled with bounce-averaged numerical solution of kinetic equation; (g) the EMIC waves saturation due to their modulation instability and LHW generation are included as an additional factor that contributes to this process; and (h) the hot ions were included in the real part of dielectric permittivity tensor. We compare our theoretical results with the different EMIC waves models as well as RC experimental data.

  17. Ring Current-Electromagnetic Ion Cyclotron Waves Coupling

    NASA Technical Reports Server (NTRS)

    Khazanov, G. V.

    2005-01-01

    The effect of Electromagnetic Ion Cyclotron (EMIC) waves, generated by ion temperature anisotropy in Earth s ring current (RC), is the best known example of wave- particle interaction in the magnetosphere. Also, there is much controversy over the importance of EMIC waves on RC depletion. Under certain conditions, relativistic electrons, with energies 21 MeV, can be removed from the outer radiation belt (RB) by EMIC wave scattering during a magnetic storm. That is why the calculation of EMIC waves must be a very critical part of the space weather studies. The new RC model that we have developed and present for the first time has several new features that we have combine together in a one single model: (a) several lower frequency cold plasma wave modes are taken into account; (b) wave tracing of these wave has been incorporated in the energy EMIC wave equation; (c) no assumptions regarding wave shape spectra have been made; (d) no assumptions regarding the shape of particle distribution have been made to calculate the growth rate; (e) pitch-angle, energy, and mix diffusions are taken into account together for the first time; (f) the exact loss-cone RC analytical solution has been found and coupled with bounce-averaged numerical solution of kinetic equation; (g) the EMIC waves saturation due to their modulation instability and LHW generation are included as an additional factor that contributes to this process; and (h) the hot ions were included in the real part of dielectric permittivity tensor. We compare our theoretical results with the different EMIC waves models as well as RC experimental data.

  18. Surface-wave potential for triggering tectonic (nonvolcanic) tremor

    USGS Publications Warehouse

    Hill, D.P.

    2010-01-01

    Source processes commonly posed to explain instances of remote dynamic triggering of tectonic (nonvolcanic) tremor by surface waves include frictional failure and various modes of fluid activation. The relative potential for Love- and Rayleigh-wave dynamic stresses to trigger tectonic tremor through failure on critically stressed thrust and vertical strike-slip faults under the Coulomb-Griffith failure criteria as a function of incidence angle is anticorrelated over the 15- to 30-km-depth range that hosts tectonic tremor. Love-wave potential is high for strike-parallel incidence on low-angle reverse faults and null for strike-normal incidence; the opposite holds for Rayleigh waves. Love-wave potential is high for both strike-parallel and strike-normal incidence on vertical, strike-slip faults and minimal for ~45?? incidence angles. The opposite holds for Rayleigh waves. This pattern is consistent with documented instances of tremor triggered by Love waves incident on the Cascadia mega-thrust and the San Andreas fault (SAF) in central California resulting from shear failure on weak faults (apparent friction, ????? 0.2). However, documented instances of tremor triggered by surface waves with strike-parallel incidence along the Nankai megathrust beneath Shikoku, Japan, is associated primarily with Rayleigh waves. This is consistent with the tremor bursts resulting from mixed-mode failure (crack opening and shear failure) facilitated by near-lithostatic ambient pore pressure, low differential stress, with a moderate friction coefficient (?? ~ 0.6) on the Nankai subduction interface. Rayleigh-wave dilatational stress is relatively weak at tectonic tremor source depths and seems unlikely to contribute significantly to the triggering process, except perhaps for an indirect role on the SAF in sustaining tremor into the Rayleigh-wave coda that was initially triggered by Love waves.

  19. Shear-wave Velocity Structure and Inter-Seismic Strain Accumulation in the Up-Dip Region of the Cascadia Subduction Zone: Similarities to Tohoku?

    NASA Astrophysics Data System (ADS)

    Collins, J. A.; McGuire, J. J.; Wei, M.

    2013-12-01

    The up-dip region of subduction zone thrusts is difficult to study using land-based seismic and geodetic networks, yet documenting its ability to store and release elastic strain is critical for understanding the mechanics of great subduction earthquakes and tsunami generation. The 2011 Tohoku earthquake produced extremely large slip in the shallowest portion of the subduction zone beneath a region of the fore-arc that is comprised of extremely low-velocity, unconsolidated sediments [Tsuru et al. JGR 2012]. The influence of the sediment material properties on the co-seismic slip distribution and tsunami generation can be considerable through both the effects on the dynamic wavefield during the rupture [Kozdon and Dunham, BSSA 2012] and potentially the build up of strain during the inter-seismic period. As part of the 2010-2011 SeaJade experiment [Scherwath et al, EOS 2011], we deployed 10 ocean bottom seismographs (OBS) on the continental slope offshore of Vancouver Island in the region of the NEPTUNE Canada observatory. One goal of the experiment is to measure the shear modulus of the sediments lying above the subducting plate using the seafloor compliance technique. Using seafloor acceleration measured by broadband seismometer and seafloor pressure measured by Differential Pressure Gauge (DPG), we estimate the compliance spectrum in the infra-gravity wave band (~0.002-0.04 Hz) at 9 sites following the methodology of Crawford et al. [JGR, 1991]. We calibrated DPG sensitivities using laboratory measurements and by comparing teleseismic Rayleigh arrivals recorded on the seismometer and DPG channels [Webb, pers. comm]. We correct the vertical-component seismometer data for tilt using the procedure of Crawford and Webb [BSSA, 2000], Corrections for the gravitational attraction of the surface gravity waves [Crawford et al., JGR, 1998] are important at frequencies of 0.003-0.006 Hz only. Typically, the coherences are high (>0.7) in the 0.006 to 0.03 Hz range. We invert

  20. Ferromagnetic transition in harmonically trapped Fermi gas with higher partial-wave interactions

    NASA Astrophysics Data System (ADS)

    Sun, Zongli; Gu, Qiang

    2017-01-01

    Spontaneous ferromagnetic transition in trapped Fermi gas is studied in the presence of a higher partial-wave interaction. At the mean-field level, the ground-state energy contribution from an arbitrary partial wave is derived, with which the equilibrium density profile of each spin component can be calculated. Our results show that, in the spin-\\tfrac{1}{2} Fermi gas, the individual repulsive d-wave interaction can induce ferromagnetic transition; while the individual repulsive or attractive p- and f-wave interactions fail. In addition, the higher partial waves can have a remarkable influence on the ferromagnetic phase induced by the s-wave interaction. The repulsive d-wave interaction and attractive p- or f-wave interactions lower the s-wave Stoner point and critical particle number, while the attractive d-wave interaction and repulsive p- or f-wave interactions increase them. In addition, our results also show that both repulsive d-wave interaction and attractive p- or f-wave interactions can enhance the ferromagnetic state induced by s-wave interaction.

  1. Lamb wave diffraction tomography

    NASA Astrophysics Data System (ADS)

    Malyarenko, Eugene Valentinovich

    As the worldwide aviation fleet continues to age, methods for accurately predicting the presence of structural flaws, such as hidden corrosion and disbonds, that compromise air worthiness become increasingly necessary. Ultrasonic guided waves, Lamb waves, allow large sections of aircraft structures to be rapidly inspected. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. In addition, human inspection process tends to be highly subjective, slow and prone to errors. The only practical alternative to traditional inspection routine is a software expert system capable of interpreting data with minimum error and maximum speed and reliability. Such a system would use the laws of guided wave propagation and material parameters to help signal processing algorithms automatically extract information from digitized waveforms. This work discusses several practical approaches to building such an expert system. The next step in the inspection process is data interpretation, and imaging is the most natural way to represent two-dimensional structures. Unlike conventional ultrasonic C-scan imaging that requires access to the whole inspected area, tomographic algorithms work with data collected over the perimeter of the sample. Combined with the ability of Lamb waves to travel over large distances, tomography becomes the method of choice for solving NDE problems. This work explores different tomographic reconstruction techniques to graphically represent the Lamb wave data in quantitative maps that can be easily interpreted by technicians. Because the velocity of Lamb waves depends on the thickness, the traveltimes of the fundamental modes can be converted into a thickness map of the inspected region. Lamb waves cannot penetrate through holes and other strongly scattering defects and the assumption of straight wave paths, essential for many tomographic algorithms

  2. Invariants of 4-wave interactions

    NASA Astrophysics Data System (ADS)

    Balk, A.; Ferapontov, E.

    1993-05-01

    We give a complete description of one-dimensional 4-wave resonance interactions in which some extra quantities (besides momentum, energy, number of quasiparticles) are conserved. In this way we obtain new consideration laws for the kinetic equations for waves. In particular, we consider waves in optical fibers, the system of four resonantly interacting wave packets, long wave interactions of annihilation-creation type, various wave systems with quadratic dispersion laws. The results can be important for various problems concerning nonlinear wave dynamics, e.g. for nonlinear optics of waveguides.

  3. Defined contribution health benefits.

    PubMed

    Fronstin, P

    2001-03-01

    This Issue Brief discusses the emerging issue of "defined contribution" (DC) health benefits. The term "defined contribution" is used to describe a wide variety of approaches to the provision of health benefits, all of which have in common a shift in the responsibility for payment and selection of health care services from employers to employees. DC health benefits often are mentioned in the context of enabling employers to control their outlay for health benefits by avoiding increases in health care costs. DC health benefits may also shift responsibility for choosing a health plan and the associated risks of choosing a plan from employers to employees. There are three primary reasons why some employers currently are considering some sort of DC approach. First, they are once again looking for ways to keep their health care cost increases in line with overall inflation. Second, some employers are concerned that the public "backlash" against managed care will result in new legislation, regulations, and litigation that will further increase their health care costs if they do not distance themselves from health care decisions. Third, employers have modified not only most employee benefit plans, but labor market practices in general, by giving workers more choice, control, and flexibility. DC-type health benefits have existed as cafeteria plans since the 1980s. A cafeteria plan gives each employee the opportunity to determine the allocation of his or her total compensation (within employer-defined limits) among various employee benefits (primarily retirement or health). Most types of DC health benefits currently being discussed could be provided within the existing employment-based health insurance system, with or without the use of cafeteria plans. They could also allow employees to purchase health insurance directly from insurers, or they could drive new technologies and new forms of risk pooling through which health care services are provided and financed. DC health

  4. Slow strain waves in the Earth: observational evidence and models

    NASA Astrophysics Data System (ADS)

    Bykov, Victor

    2014-05-01

    Recent remarkable progress in theoretical studies of the solitary strain waves, that have contributed greatly to the solution of the fundamental problem of strain waves in the Earth, is overviewed. The concept of strain waves generated in the Earth is based on the results of the study of earthquake distribution and slow tectonic deformation processes and the transfer of geophysical field anomalies. Propagation of strain waves is represented quantitatively by the rates of earthquake migration and geophysical responses to active faulting. These processes, and possibly the related strain waves, are either of global (global tectonic waves) or local (strain waves in faults) scales (Bykov, 2005). Global tectonic waves propagating at velocities from 10 to 100 km/yr are detected from migration of large earthquakes (Stein et al., 1997), seismic velocity anomalies (Nevsky et al., 1987), offsets of water level in wells along faults (Barabanov et al. 1988), or from transient displacement of seismic reflectors (Bazavluk and Yudakhin, 1993). Strain waves along crustal faults at velocities of 1-10 km/day are inferred from radon, electrokinetic and hydrogeodynamic signals, such as solitary waves (Nikolaevskiy, 1998). Migration of episodic tremor and slow slip events along plate boundaries in subduction zones and transform fault zones at a rate of 10 km/day, on an average (Schwartz and Rokosky, 2007), may be new evidence and indication of strain waves in the Earth. The detected mechanisms of strain wave exciting are caused by the block and microplate rotation, relative block displacement in crustal fault zones, transform faults, zones of the lithospheric plate collision and subduction and irregularity of the Earth's rotation (Bykov, 2005). These waves in the shape of kinks or solitons moving at velocities a great number of orders less than those of the ordinary seismic waves provide the possibility to explain slow stress redistribution in the crust. During a recent decade the sine

  5. Various Boussinesq solitary wave solutions

    SciTech Connect

    Yates, G.T.

    1995-12-31

    The generalized Boussinesq (gB) equations have been used to model nonlinear wave evolution over variable topography and wave interactions with structures. Like the KdV equation, the gB equations support a solitary wave solution which propagates without changing shape, and this solitary wave is often used as a primary test case for numerical studies of nonlinear waves using either the gB or other model equations. Nine different approximate solutions of the generalized Boussinesq equations are presented with simple closed form expressions for the wave elevation and wave speed. Each approximates the free propagation of a single solitary wave, and eight of these solutions are newly obtained. The author compares these solutions with the well known KdV solution, Rayleigh`s solution, Laitone`s higher order solution, and ``exact`` numerical integration of the gB equations. Existing experimental data on solitary wave shape and wave speed are compared with these models.

  6. Effects of D region ionization on radio wave propagation

    NASA Technical Reports Server (NTRS)

    Larsen, T. R.

    1979-01-01

    The effects of anomalous D region ionization upon radio wave propagation are described for the main types of disturbances: sudden ionospheric disturbances, relativistic electron events, magnetic storms, auroral disturbances, polar cap events, and stratospheric warmings. Examples of radio wave characteristics for such conditions are given for the frequencies between the extremely low (3-3000 Hz) and high (3-30 MHz) frequency domains. Statistics on the disturbance effects and radio wave data are given in order to contribute towards the evaluation of possibilities for predicting the radio effects.

  7. Partial Wave Dispersion Relations: Application to Electron-Atom Scattering

    NASA Technical Reports Server (NTRS)

    Temkin, A.; Drachman, Richard J.

    1999-01-01

    In this Letter we propose the use of partial wave dispersion relations (DR's) as the way of solving the long-standing problem of correctly incorporating exchange in a valid DR for electron-atom scattering. In particular a method is given for effectively calculating the contribution of the discontinuity and/or poles of the partial wave amplitude which occur in the negative E plane. The method is successfully tested in three cases: (i) the analytically solvable exponential potential, (ii) the Hartree potential, and (iii) the S-wave exchange approximation for electron-hydrogen scattering.

  8. Satellite Spots Turbulence Producing Mountain Waves in the Stratosphere

    NASA Technical Reports Server (NTRS)

    Britt, Robert Roy

    2002-01-01

    When masses of air flow over massive mountains, invisible waves often roil high into the stratosphere, affecting weather and mixing the chemicals that contribute to ozone depletion. The waves also create turbulence that can be a danger to high-altitude research missions by NASA's lightweight ER-2 aircraft, as well as shuttle flights upon reentry. In Friday's issue of the journal Science, researchers report for the first time a technique that allows them to see temperature signatures from these invisible mountain waves. The method, involving high-resolution, satellite-based measurement of adjacent pockets of the atmosphere, is expected to aid in spotting turbulence and, one day, improve weather forecasts.

  9. Effects of D region ionization on radio wave propagation

    NASA Technical Reports Server (NTRS)

    Larsen, T. R.

    1979-01-01

    The effects of anomalous D region ionization upon radio wave propagation are described for the main types of disturbances: sudden ionospheric disturbances, relativistic electron events, magnetic storms, auroral disturbances, polar cap events, and stratospheric warmings. Examples of radio wave characteristics for such conditions are given for the frequencies between the extremely low (3-3000 Hz) and high (3-30 MHz) frequency domains. Statistics on the disturbance effects and radio wave data are given in order to contribute towards the evaluation of possibilities for predicting the radio effects.

  10. A Profile of Corporate Contributions.

    ERIC Educational Resources Information Center

    Smith, Hayden W.

    The extent and distribution of charitable contributions by corporations were studied. In addition to a history of giving from 1936 to 1981, information is presented on corporate contributions in 1977 in terms of the distribution of companies (1) by size of contributions, (2) by contributions as percentage of net income, (3) by industry, and (4) by…

  11. Slow Magnetoacoustic Wave Oscillation of an Expanding Coronal Loop

    NASA Astrophysics Data System (ADS)

    Schmidt, J. M.; Ofman, L.

    2011-10-01

    We simulated an expanding loop or slow coronal mass ejection (CME) in the solar corona dimensioned with size parameters taken from real coronal expanding loops observed with the STEREO spacecraft. We find that the loop expands to Sun's size within about one hour, consistent with slow CME observations. At the top of the loop, plasma is being blown off the loop, enabled with the reconnection between the loop's flux rope magnetic field and the radial magnetic field of the Sun, thus yielding feeding material for the formation of the slow solar wind. This mechanism is in accordance with the observed blob formation of the slow solar wind. We find wave packets traveling with local sound speed downward toward the footpoints of the loop, already seen in coronal seismology observations and simulations of stationary coronal loops. Here, we generalize these results for an expanding medium. We also find a reflection of the wave packets, identified as slow magnetoacoustic waves, at the footpoints of the loop. This confirms the formation of standing waves within the coronal loop. In particular, the reflected waves can partly escape the loop top and contribute to the heating of the solar wind. The present study improves our understanding on how loop material can emerge to form blobs, major ingredients of slow CMEs, and how the release of the wave energy stored in slow magnetoacoustic waves, and transported away from the Sun within expanding loops, contributes to the acceleration and formation of the slow solar wind.

  12. Continuation of spiral waves

    NASA Astrophysics Data System (ADS)

    Bordyugov, Grigory; Engel, Harald

    2007-04-01

    We describe a new numerical method of computing rigidly rotating spiral waves, which is based on solving the Neumann boundary-value problem for the radius-dependent angular Fourier modes. Utilizing the established continuation engine AUTO, our method is simple in implementation and can be easily modified to suit a particular reaction-diffusion system. Since the method does not involve direct simulations of the reaction-diffusion system, unstable branches of rigidly rotating spiral waves can be computed as well. We illustrate our method by computing single- and multi-armed spirals in the Barkley model. Continuation of single-armed spirals displays nearly identical results with the Barkley’s continuation code STEADY. The dependence of spiral waves on the geometry of the medium reproduces the results of numerical simulations reported before in [A.M. Pertsov, E.A. Ermakova, A.V. Panfilov, Rotating spiral waves in a modified Fitz-Hugh-Nagumo model, Physica D 14 (1) (1984) 117-124], revealing, however, some subtle details like non-monotonous dependence of the rotation frequency on the disc radius and the existence of an unstable rotating solution that separates coexisting free and pinned spirals. We demonstrate that on bounded discs, spiral waves are accompanied by boundary spots - slowly rotating solutions which are localized near the outer boundary of the disc. Boundary spots are shown to be closely related to one- and two-dimensional unstable critical solutions, such as unstable pulses in one dimension and critical fingers in two dimensions, which separate spiral waves from shrinking wave segments.

  13. Competition between outer zone electron scattering by plasmaspheric hiss and magnetosonic waves

    NASA Astrophysics Data System (ADS)

    Ni, Binbin; Hua, Man; Zhou, Ruoxian; Yi, Juan; Fu, Song

    2017-04-01

    We quantify the electron scattering effects of simultaneous plasmaspheric hiss and magnetosonic waves that occurred in two neighboring time intervals but with distinct wave intensity profiles on 21 August 2013. Their combined scattering is found capable of causing electron distribution variations largely distinguishable from the consequences of individual waves. The net effect of electron diffusion relies strongly on the relative dominance of the two wave intensities, which also controls the relative contribution of each wave mode. In combination, MS waves slow down the hiss-induced loss of 100 keV electrons, and hiss efficiently inhibits the electron butterfly distribution caused by MS waves to produce a gradual acceleration process. Our results strongly suggest that comprehensive simulations of the radiation belt electron dynamics should carefully incorporate the combined scattering and complex competition resulting from simultaneous occurrences of various magnetospheric emissions, including, but not limited to, plamaspheric hiss and magnetosonic waves.

  14. Tsunami focusing and leading wave height

    NASA Astrophysics Data System (ADS)

    Kanoglu, Utku

    2016-04-01

    Field observations from tsunami events show that sometimes the maximum tsunami amplitude might not occur for the first wave, such as the maximum wave from the 2011 Japan tsunami reaching to Papeete, Tahiti as a fourth wave 72 min later after the first wave. This might mislead local authorities and give a wrong sense of security to the public. Recently, Okal and Synolakis (2016, Geophys. J. Int. 204, 719-735) discussed "the factors contributing to the sequencing of tsunami waves in the far field." They consider two different generation mechanisms through an axial symmetric source -circular plug; one, Le Mehaute and Wang's (1995, World Scientific, 367 pp.) formalism where irritational wave propagation is formulated in the framework of investigating tsunamis generated by underwater explosions and two, Hammack's formulation (1972, Ph.D. Dissertation, Calif. Inst. Tech., 261 pp., Pasadena) which introduces deformation at the ocean bottom and does not represent an immediate deformation of the ocean surface, i.e. time dependent ocean surface deformation. They identify the critical distance for transition from the first wave being largest to the second wave being largest. To verify sequencing for a finite length source, Okal and Synolakis (2016) is then used NOAA's validated and verified real time forecasting numerical model MOST (Titov and Synolakis, 1998, J. Waterw. Port Coast. Ocean Eng., 124, 157-171) through Synolakis et al. (2008, Pure Appl. Geophys. 165, 2197-2228). As a reference, they used the parameters of the 1 April 2014 Iquique, Chile earthquake over real bathymetry, variants of this source (small, big, wide, thin, and long) over a flat bathymetry, and 2010 Chile and 211 Japan tsunamis over both real and flat bathymetries to explore the influence of the fault parameters on sequencing. They identified that sequencing more influenced by the source width rather than the length. We extend Okal and Synolakis (2016)'s analysis to an initial N-wave form (Tadepalli

  15. Modelling Ocean Surface Waves in Polar Regions

    NASA Astrophysics Data System (ADS)

    Hosekova, Lucia; Aksenov, Yevgeny; Coward, Andrew; Bertino, Laurent; Williams, Timothy; Nurser, George A. J.

    2015-04-01

    agreement with observations. In addition to our global implementation, the method is currently also tested in the TOPAZ framework (Towards an Operational Prediction system for the North Atlantic European Coastal Zones). We will discuss the two modeling strategies (global 35 km resolution and pan-Arctic 3 km resolution) and analyse model biases. The study contributes to the EU FP7 project 'Ships and Waves Reaching Polar Regions (SWARP)', aimed at developing techniques for sea ice and waves modelling and forecasting in the MIZ in the Arctic. The method will be implemented as part of the EU Global Monitoring and Environmental Security system GMES.

  16. Nonstationary distributions of wave intensities in wave turbulence

    NASA Astrophysics Data System (ADS)

    Choi, Yeontaek; Jo, Sanggyu; Kwon, Young-Sam; Nazarenko, Sergey

    2017-09-01

    We obtain a general solution for the probability density function (PDF) of wave intensities in non-stationary wave turbulence. The solution is expressed in terms of the initial PDF and the wave action spectrum satisfying the wave-kinetic equation. We establish that, in the absence of wave breaking, the wave statistics converge to a Gaussian distribution in forced-dissipated wave systems while approaching a steady state. Also, we find that in non-stationary systems, if the statistic is Gaussian initially, it will remain Gaussian for all time. Generally, if the statistic is not initially Gaussian, it will remain non-Gaussian over the characteristic nonlinear evolution time of the wave spectrum. In freely decaying wave turbulence, substantial deviations from Gaussianity may persist infinitely long.

  17. Longitudinal shear wave and transverse dilatational wave in solids.

    PubMed

    Catheline, S; Benech, N

    2015-02-01

    Dilatation wave involves compression and extension and is known as the curl-free solution of the elastodynamic equation. Shear wave on the contrary does not involve any change in volume and is the divergence-free solution. This letter seeks to examine the elastodynamic Green's function through this definition. By separating the Green's function in divergence-free and curl-free terms, it appears first that, strictly speaking, the longitudinal wave is not a pure dilatation wave and the transverse wave is neither a pure shear wave. Second, not only a longitudinal shear wave but also a transverse dilatational wave exists. These waves are shown to be a part of the solution known as coupling terms. Their special motion is carefully described and illustrated.

  18. Potential changes of wave steepness and occurrence of rogue waves

    NASA Astrophysics Data System (ADS)

    Bitner-Gregersen, Elzbieta M.; Toffoli, Alessandro

    2015-04-01

    Wave steepness is an important characteristic of a sea state. It is also well established that wave steepness is one of the parameter responsible for generation of abnormal waves called also freak or rogue waves. The study investigates changes of wave steepness in the past and future wave climate in the North Atlantic. The fifth assessment report IPCC (2013) uses four scenarios for future greenhouse gas concentrations in the atmosphere called Representative Concentration Pathways (RCP). Two of these scenarios RCP 4.5 and RCP 8.5 have been selected to project future wave conditions in the North Atlantic. RCP 4.5 is believed to achieve the political target of a maximum global mean temperature increase of 2° C while RPC 8.5 is close to 'business as usual' and expected to give a temperature increase of 4° C or more. The analysis includes total sea, wind sea and swell. Potential changes of wave steepness for these wave systems are shown and compared with wave steepness derived from historical data. Three historical data sets with different wave model resolutions are used. The investigations show also changes in the mean wind direction as well as in the relative direction between wind sea and swell. Consequences of wave steepness changes for statistics of surface elevation and generation of rogue waves are demonstrated. Uncertainties associated with wave steepness projections are discussed.

  19. Reflection and Refraction of Acoustic Waves by a Shock Wave

    NASA Technical Reports Server (NTRS)

    Brillouin, J.

    1957-01-01

    The presence of sound waves in one or the other of the fluid regions on either side of a shock wave is made apparent, in the region under superpressure, by acoustic waves (reflected or refracted according to whether the incident waves lie in the region of superpressure or of subpressure) and by thermal waves. The characteristics of these waves are calculated for a plane, progressive, and uniform incident wave. In the case of refraction, the refracted acoustic wave can, according to the incidence, be plane, progressive, and uniform or take the form of an 'accompanying wave' which remains attached to the front of the shock while sliding parallel to it. In all cases, geometrical constructions permit determination of the kinematic characteristics of the reflected or refractive acoustic waves. The dynamic relationships show that the amplitude of the reflected wave is always less than that of the incident wave. The amplitude of the refracted wave, whatever its type, may in certain cases be greater than that of the incident wave.

  20. Gravitational Wave Astronomy

    NASA Astrophysics Data System (ADS)

    Finn, Lee Samuel

    2012-03-01

    If two black holes collide in a vacuum, can they be observed? Until recently, the answer would have to be "no." After all, how would we observe them? Black holes are "naked" mass: pure mass, simple mass, mass devoid of any matter whose interactions might lead to the emission of photons or neutrinos, or any electromagnetic fields that might accelerate cosmic rays or leave some other signature that we could observe in our most sensitive astronomical instruments. Still, black holes do have mass. As such, they interact—like all mass—gravitationally. And the influence of gravity, like all influences, propagates no faster than that universal speed we first came to know as the speed of light. The effort to detect that propagating influence, which we term as gravitational radiation or gravitational waves, was initiated just over 50 years ago with the pioneering work of Joe Weber [1] and has been the object of increasingly intense experimental effort ever since. Have we, as yet, detected gravitational waves? The answer is still "no." Nevertheless, the accumulation of the experimental efforts begun fifty years ago has brought us to the point where we can confidently say that gravitational waves will soon be detected and, with that first detection, the era of gravitational wave astronomy—the observational use of gravitational waves, emitted by heavenly bodies—will begin. Data analysis for gravitational wave astronomy is, today, in its infancy and its practitioners have much to learn from allied fields, including machine learning. Machine learning tools and techniques have not yet been applied in any extensive or substantial way to the study or analysis of gravitational wave data. It is fair to say that this owes principally to the fields relative youth and not to any intrinsic unsuitability of machine learning tools to the analysis problems the field faces. Indeed, the nature of many of the analysis problems faced by the field today cry-out for the application of